Submicrowatt-driven near-infrared luminescence from perovskite-fluoride quantum-cutting heterostructures for gas sensing

Domain: chemistry
Published: 2026-03-17
Editorial outcome: major_revision

Abstract
The pursuit of wideband tunable near-infrared (NIR) light sources has reached fever pitch due to advances in photonic chips, optical communications, and molecular trace detection. Lanthanide ions (Ln3+), renowned for their characteristic NIR luminescence, have nevertheless been stymied by the challenges of an extremely low molar extinction coefficient and linear absorption. Herein, a sensitisation methodology is presented that capitalises on the quantum cutting-engineered heterostructure nanoparticles (CsPbX : Yb3+-NaYF : Yb3+, Ln3+), to achieve multi-wavelength 3 4 NIR luminescence spanning the 900-2200 nm spectrum. The designed heterostructure exhibits an unprecedented absorption bandwidth (200–690 nm) across the UV-visible spectrum, with an exceptionally low stimulation threshold at the sub-microwatt level (50 µW cm-2). The NIR luminescent wavelengths can be precisely modulate by meticulously adjusting the dopant Ln3+ ions leveraging Yb3+-mediated quantum cutting processes. Spectroscopic analysis reveals a directed energy transfer pathway at the perovskite-fluoride heterogeneous interface: perovskite host→Yb3+ (perovskite) →Yb3+ (NaYF4) →Ln3+. This architecture demonstrates multiplexed gas detection capabilities under AI-assisted analysis, facilitating the simultaneous identification and monitoring of multiple marker gases in complex environments. Our work provides a scalable strategy for constructing ultra-broadband NIR light sources, with implications for high-throughput spectroscopic sensing.

Introduction
Near-infrared (NIR) spectroscopy holds a great promise as a sensing technique because it provides rich fingerprint information that accurately identifies numerous gases through their specific absorption wavelengths1-7. Nevertheless, most current near-infrared gas sensing systems rely on on-chip techniques that employ costly single-wavelength infrared lasers. The operational wavelength range of on-chip sensors is inherently defined by the single-mode and optical guiding conditions of the waveguides. This consequently restricts the detection to specific gases, significantly limiting sensor selectivity8-10. Consequently, developing broadband near-infrared light sources with wide wavelength coverage and scalable manufacturing capabilities is crucial for overcoming this technological bottleneck. In contrast to costly and complex-to-prepare traditional infrared-emitting semiconductors like GaAs11, 12, InP13, 14, and PbS15, 16, lanthanide ions (Ln3+) doped nanomaterials offer numerous advantages, including abundant infrared emitting energy levels, diverse spectral emission bands, large Stokes shifts, and stable photochemistry17-22. This makes them a promising choice for constructing high-quality NIR light sources.

Considerable progress has been made in recent years in research on rare-earth-activated NIR luminescence. However, two critical challenges impede its application in infrared gas detection: (1) The emission of existing NIR luminescent materials is predominantly limited to narrow, isolated bands, such as Er3+ at 1530 nm23, Tm3+ at 808 nm24, Nd3+ at 1064 nm25, Tm3+ at 1460 nm26, and Ho3+ at 2000 nm27. This constraint substantially restricts the variety and range of detectable gases and hinders the selective development of infrared gas detection technologies for multiple marker gases. (2) The intrinsic parity-forbidden nature of 4f–4f electronic transitions in Ln3+ ions results in an extremely low molar extinction coefficient (typically <10 cm-1·M-1) and linear absorption behavior confined to discrete laser wavelengths (e.g., 808 nm, 980 nm, and 1540 nm)18-20, 28. Consequently, exciting rare-earth ions for NIR emission requires the use of multiple lasers with specific wavelengths that match the energy levels of different ions. To advance the development of multiplexed and selective NIR gas sensors, both issues must be addressed at the level of light source design. Recent efforts have explored various strategies to mitigate these limitations, such as employing Cr3+ sensitization to reduce the excitation threshold for NIR emission29, and utilizing symmetric core–shell nanostructures to achieve broadband excitation via co-sensitization of Ho3+ and Nd3+ 30. Although these strategies have yielded notable advancements, they have not yet addressed the fundamental limitations of rare-earth-based NIR luminescence, namely its narrow emission spectrum and dependence on discrete excitation wavelengths. Therefore, it is challenging to build the efficient multi-wavelength NIR light sources with low excitation thresholds and broad excitation bands.

Lead halide perovskite quantum dots (PeQDs) possess a significant absorption cross-section, provide broad and adjustable UV-visible absorption, and can be excited within an extensive range from 200 to 700 nm31-33. Their perfect octahedral coordination makes them a promising host material for lanthanide ions34. Particularly, Yb3+ ion doped PeQDs demonstrated the efficient quantum cutting behavior, extending the emission wavelength to the NIR range35, 36. However, a valence mismatch between Ln3+ and Pb 2+ ions imposes restrictions on the Ln3+ doping concentration in PeQDs, significantly hindering the achievement of efficient multi-wavelength NIR luminescence. As reported by Zhang and colleagues, PeQDs can effectively unite with NaYF , 4 which serves as an exceptional host for Ln3+ ions37, 38. Consequently, we formulated a bold hypothesis: could we develop a low-power excitation source for efficient NIR light emission by employing Yb3+ ion doped PeQDs to enhance the absorption cross-section, doping a high concentration of Ln3+ ions into the NaYF host, and effectively merging them through a core-shell 4 heterostructure structure? Importantly, the well-established nanocrystal core-shell coating technique using NaYF can seamlessly incorporate various Ln3+ ions into a cohesive system30, 39, 4 40, thus establishing a promising foundation for implementing NIR spectrum gas detection technology with comprehensive wavelength coverage.

Building upon the considerations above, we present an innovative sensitization approach to achieve ultra-wideband excitation and finely tuned NIR luminescence using heterostructure nanoparticles denoted as CsPbX : Yb3+-NaYF : Yb3+, Ln3+ (Fig.1). Our sensitization strategy 3 4 employed PeQDs as the optical absorption antennae, Yb3+ ions doped in both PeQDs and NaYF 4 as the collaborative energy transfer medium, and Ln3+ ions as the activators responsible for generating NIR luminescence. This approach involves creating a energy transfer pathway from the perovskite host to Yb3+ ions in the perovskite host, then to Yb3+ ions in NaYF shell and finally to 4 the Ln3+ ions, referred to as PeQD-Yb3+ (PeQD)-Yb3+ (NaYF ) -Ln3+. The process begins with the 4 absorption of incident photons by the PeQD. Electrons on the conduction band of the PeQD are then transferred to Yb3+ ions via a quantum cutting process. Subsequently, energy is transferred to the luminescent Ln3+ through interfacial energy transfer between Yb3+ ions in the PeQDs and Yb3+ ions in the NaYF : Yb3+, Ln3+, ultimately leading to multi-wavelength near-infrared luminescence. 4 The PeQDs provide NaYF : Yb3+, Ln3+ with ultra-wideband absorption capabilities, while the joint 4 medium Yb3+ ion facilitates excitation energy transfer to each luminescent Ln3+ ion. Unlike prior nanoparticles doped with Ln3+ ion that achieved NIR emission, the heterostructure, sensitized by PeQDs, exhibits a wide excitation band spanning from 200 to 690 nm. Therefore, this proposed sensitization strategy enables the efficient acquisition of NIR fluorescence with a broad response across the UV-visible spectrum compliance to various excitation requirements, including low-power white light and multi-wavelength excitation, as opposed to a limited selection of single wavelength lasers. Furthermore, we have successfully integrated NaYF : Yb3+, Ln3+, and PeQDs 4 doped with diverse luminescence centers into a unified multilayer core–shell nanoparticles. This multilayer core–shell nanoparticles can dedicate multi-wavelength fluorescence within the 900-2200 nm range under low-power white-light excitation conditions, demonstrating significant potential for multiplexed gas detection applications.

Results
Fig.1 illustrates the mechanism underlying the high-efficiency generation of NIR emissions. Upon the combination of CsPbX : Yb3+ and NaYF : Yb3+, Ln3+ (Ln=Ho, Er, Tm, Ce), the CsPbX 3 4 3 PeQDs demonstrate broad excitation coverage in the UV-visible spectrum, and NaYF provides 4 an ample supply of sites for doping Ln3+ ions. Directly energy transfer through the joint mediator Yb3+ ions significantly enhances the electron population within the E energy level of Ln3+ ions. 2 This enhancement leads to a substantial improvement in the NIR emission. The outermost layer of NaYF effectively mitigates energy losses caused by surface defects41. Notably, the efficient 4 quantum cutting process, exhibiting a photoluminescence quantum yield (PLQY) of ~148.4%, amplifies the energy transfer mechanism, continuously enhancing NIR fluorescence emissions (Supplementary Note 1 and Supplementary Fig. 1). During the initial phase of the experiment, we adjusted the NIR fluorescence characteristics of Ln3+ ions doped NaYF by precisely changing the 4 concentration of dopant ions. It is well known that Ln3+ ions like Ho3+, Er3+, Tm3+ have the ability to emit at NIR region. Four kinds of nanoparticles (NPs) (NaYF : Yb3+, Tm3+@ NaYF , NaYF : 4 4 4 Yb3+, Er3+, Ce3+@ NaYF , NaYF : Yb3+, Ho3+@ NaYF , NaYF : Yb3+, Ho3+, Ce3+@ NaYF ) were 4 4 4 4 4 synthesized using a standard solvothermal method42. Transmission electron microscopy (TEM) image analysis displays uniform spherical NPs with an average diameter of approximately 35 nm (Supplementary Fig. 2). The presence of well-defined lattice stripes with a spacing of 0.52 nm indicates the high crystallinity of the as-prepared NPs. The hexagonal phase structure of the NPs was confirmed by X-ray powder diffraction (XRD) measurement (Supplementary Fig. 3). Elemental mapping images (Supplementary Fig. 4) further elucidate the spatial distribution of elements within the core-shell structure. The emission spectra of Tm/Yb, Er/Yb/Ce, Ho/Yb, and Ho/Yb/Ce doped NaYF are shown in Fig. 2a, pumped by a 980 nm light source. Tm3+, Er3+, and 4 Ho3+ ions contribute to NIR emission at wavelengths of 1460 nm (3H -3F ), 1527 nm (4I -4I ), 4 4 13/2 15/2 1180 nm (5I -5I ), and 1952 nm (5I -5I ), with their respective energy level transitions outlined in 6 8 7 8 Fig. 2d. Particularly, the introduction of Ce3+ ions produces an effective cross-relaxation pathway for Ce3+-Er3+ (4I +2F →4I +2F ) and Ce3+-Ho3+ (5I +2F →5I +2F ) ion pairs, hence 11/2 5/2 13/2 7/2 6 5/2 7 7/2 generating the NIR strong emissions of Er3+ ions at 1527 nm and Ho3+ ions at 1952 nm43, 44. Fig. 2b-2c and Supplementary Fig. 5-8 show the strong correlations between NIR fluorescence intensity and dopant ion concentrations. The ideal doping concentration for Tm3+ ions is only 0.6% due to significant concentration quenching effect, whereas Er3+ and Ho3+ ions have optimal concentrations of 5% and 6%, respectively. Doping with 6% Ho3+ ions is necessary to obtain the maximum luminescence at both 1180 nm and 1952 nm. Interestingly, doping with Ce3+ ions enhances the 1952 nm emission of Ho3+ ions, but at the expense of the 1180 nm emission intensity (Fig. 2b and Fig. 2d). This phenomenon can be attributed to the cross-relaxation process 5I +2F →5I +2F , which accelerates the transition of electrons from the 5I energy level to the 6 5/2 7 7/2 6 5I energy level, leading to a significant increase in the electron population at the 5I energy level 7 7 (Fig. 2d). As a result, the emission at 1180 nm decreases while the emission at 1952 nm increases. Following rigorous modulation of dopant ion concentrations, the optimal NIR nanoparticles were ultimately synthesized: NaYF : 0.6% Tm3+, 25% Yb3+@ NaYF ; NaYF : 5% Er3+, 35% Yb3+, 4% 4 4 4 Ce3+@ NaYF ; NaYF : 6% Ho3+, 20% Yb3+@ NaYF ; and NaYF : 6% Ho3+, 20% Yb3+, 6% Ce3+@ 4 4 4 4 NaYF , respectively. 4

In order to produce the previous mentioned multi-band emissions in a single NP, it is feasible to create a multilayer core-shell NPs with several emitting centers. Based on the penetration depth of NIR light, the multilayer core-shell structure was constructed. The core, NaYF : 6% Ho3+, 20% 4 Yb3+, 6% Ce3+, exhibited emissions centered at 1180 nm and 1952 nm. Multilayer core-shell nanoparticles (NaYF : 6%Ho3+, 20%Yb3+, 6%Ce3+@NaYF : 5%Er3+, 35%Yb3+, 4%Ce3+@NaYF : 4 4 4 0.6%Tm3+, 25%Yb3+@NaYF ), short for CSSS, were created by a sequential coating technique. 4 Morphological and structural analysis of CSSS, illustration in Supplementary Fig. 9-11, confirmed a homogeneous hexagonal-phase multilayered core-shell structure. Notably, the multi-band NIR emission spectra of CSSS is depicted in Fig. 2e and achieves 1180 nm, 1460 nm, 1527 nm and 1952 nm emissions within a single NP. The core-shell design enables the multi-band NIR emissions, but the absorption and excitation problems remain to be solved before practical applications, and we are all well-aware of the narrow-band absorption problem caused by the 4f forbidden transition of rare-earth ions.

For an advanced NIR light source, a wide range of absorption and excitation is needed to adapt to a variety of operating conditions, such as the uncertain excitation wavelength and power. To overcome the inherent constraint posed by the limited absorption cross-section of Ln3+ ions and obtain a highly efficient NIR light source, we create a heterostructure through combining the PeQDs with NaYF : Yb3+, Ln3+ NPs, specifically Yb3+ doped PeQDs embedded in a matrix of 4 NaYF : Yb3+, Ln3+ NPs with a NaYF passivation shell, denoted as PeQD -NPs (CsPbX : Yb3+- 4 4 Yb Ln 3 NaYF : Yb3+, Ln3+@NaYF (X=Cl, Br, I; Ln = Ho, Er, Tm, Ce)), as shown in Fig. 3a. In this 4 4 structure, PeQDs with a wide absorption band ranging serves as the light absorber, which can sensitize the emitters in the NaYF matrix through energy transfer process. Notably, a distinctive 4 aspect of our methodology involves the use of oleylamine bromide (OAmBr) as a stabilizing agent for the PeQDs structure, as detailed in the Supplementary Information.45, 46 Since the inert NaYF 4 coating can obscure the resolution of the PeQD, characterization was performed on uncoated CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ heterostructure (Supplementary Fig. 12-13). The 1.5 1.5 4 addition of an outer undoped NaYF shell was a subsequent optimization step to enhance material 4 stability and luminescence efficiency. The high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image measurement of CsPbCl Br : Yb3+-NaYF : Yb3+, 1.5 1.5 4 Er3+, Ce3+ heterostructure was performed in order to clearly distinguish the creation of the heterostructure (Fig. 3b-d). Based on their bright and dark fluctuations, it is evident that the PeQDs (dark area) are uniformly distributed in NaYF : Yb3+, Er3+, Ce3+. The heterostructure NPs 4 (CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+) have an average total size of about 27.3 nm 1.5 1.5 4 (Supplementary Fig. 12). After coating with an inert NaYF shell (3.91 nm thick), the final size of 4 the NPs increases to about 35.1 nm (Supplementary Fig. 13). The magnified image of Fig. 3c shows that the PeQDs have different shapes and variable sizes, which can be attributed to the dissolution phenomenon during the formation of the heterostructure37, 47. The high-resolution energy dispersive X-ray spectrometer (EDS) mapping images clearly illustrate the spatial distribution of Er and Yb, revealing that Er is predominantly localized at the outer region of the heterostructure, whereas Yb exhibits a homogeneous distribution throughout the entire heterostructure matrix (Fig. 3d), which indicates that the CsPbCl Br : Yb3+ PeQDs are 1.5 1.5 successfully ensembled in NaYF :Ln matrix. Furthermore, high-resolution transmission electron 4 microscopy (HRTEM) imaging, performed with a spherical aberration corrector, directly reveals the lattice fringes of the CsPbCl Br : Yb3+ and NaYF : Yb3+, Er3+, Ce3+, allowing for the 1.5 1.5 4 determination of their relative orientations (Fig. 3e). The heterogeneous interface of CsPbCl Br : 1.5 1.5 Yb3+ and NaYF : Yb3+, Er3+, Ce3+ can be clearly distinguished. The in-situ mapping results further 4 reveal the distribution of Yb in the two different lattice environments (Fig. 3f). Moreover, the general level EDS also clearly shows the distribution of the elements, providing evidence for the formation of the heterostructure (Fig. 3g). Line scan analyses at the atomic level consistently reveal the distribution of elements (especially Pb, which are clustered only in the core) as well as the heterostructure boundaries, which provide sufficient evidence for the formation of CsPbCl Br : 1.5 1.5 Yb3+-NaYF : Yb3+, Ln3+ heterostructure (Fig. 3h). Similarly, PeQD -NPs , PeQD -NPs , 4 Yb Yb/Tm Yb Yb/Ho and PeQD -NPs have also been characterised and all exhibit well-defined heterostructure Yb Yb/Ho/Ce (Supplementary Fig. 12-16). The XRD results jointly confirm the superior crystalline quality of the heterostructure nanoparticles, showing only the PeQD and NaYF : Yb3+, Ln3+ phases with 4 no additional phases detected (Supplementary Fig. 17). Furthermore, X-ray photoelectron spectroscopy (XPS) was employed for compositional analysis of the films consisting of CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce 3+, at varying etching depths (Supplementary Fig. 18). 1.5 1.5 4 When etching depth up to 3 nm, there is a rapid reduction in the elemental content of Y, Yb, Er, and Ce. Conversely, the proportions of Pb and Cl slightly increased (Fig. 3i). The evidence presented above conclusively affirms the successful synthesis of the heterostructure in PeQD - Yb NPs Ln .

Spectroscopic characterisation was carried out to characterise the optical properties of the PeQD -NPs heterostructure. The PeQD -NPs , CsPbX : Yb3+-NaYF : 35%Yb3+, 5%Er3+, Yb Ln Yb Yb/Er/Ce 3 4 4%Ce3+@NaYF (X=Cl, Br, I), typically exhibits tunable broadband absorption, as illustrated in 4 Supplementary Fig. 19. The excitation spectra monitored at 1527 nm can be effectively modulated by adjusting the composition of the PeQDs, enabling optimal coverage of the ultra-wide range from 200-690 nm (Supplementary Fig. 20). As shown in Fig. 4a, PeQD -NPs exhibits a Yb Yb/Er/Ce remarkable excitation advantage compared to the narrow excitation linewidth of Ln3+ ions in NaYF : Yb3+, Er3+, Ce3+@NaYF . This advantage is characterised by a significant broaden of the 4 4 excitation wavelength and a remarkable increase in the intensity of the excitation spectra. A consistent agreement is observed across datasets PeQD -NPs , PeQD -NPs , and Yb Yb/Tm Yb Yb/Ho PeQD -NPs (Supplementary Fig. 21). These findings suggest that the heterostructure of Yb Yb/Ho/Ce PeQD -NPs plays a crucial role in reducing the excitation threshold for the NIR emission of Yb Ln NaYF : Yb3+, Ln3+, and indicate that the PeQD -NPs system holds significant potential for 4 Yb Ln achieving efficient NIR luminescence with broadband, low-threshold excitation. Amazingly, PeQD -NPs can be independently pumped by multiple wavelengths, enabling the Yb Yb/Er/Ce collection of robust NIR luminescence under white-light irradiation, as shown in Fig. 4b. This marks a significant achievement in producing NIR emission under white light illumination.

Importantly, according to the power-dependent spectrum, the excitation power threshold for PeQD -NPs at 1527 nm is approximately 50 µW cm⁻², which is 306 times lower than that Yb Yb/Er/Ce of NaYF : Yb3+, Er3+, Ce3+@NaYF (Fig. 4c and Supplementary Fig. 22). At the excitation power 4 4 threshold (15.3 mW cm-2) of NaYF : Yb3+, Er3+, Ce3+@NaYF , the emission intensity of PeQD - 4 4 Yb NPs is nearly 80 times higher than that of NaYF : Yb3+, Er3+, Ce3+@NaYF (Fig. 4c). Fig. Yb/Er/Ce 4 4 4d and Supplementary Fig. 23 show the intensity of the NIR spectrum as the halide composition of PeQDs changes. Notably, the CsPbCl Br : Yb3+-NPs exhibit the highest NIR luminescence 1.5 1.5 Ln intensity. CsPbCl Br : Yb3+-NPs displayed an intensity 96.1 times greater than that of 1.5 1.5 Yb/Er/Ce NaYF : Yb3+, Er3+, Ce3+@NaYF . A significant reduction in NIR luminescence is observed as the 4 4 halogen ions transform to Br and I. This phenomenon is attributed to the alteration of PeQDs bandgap, disrupting the requisite conditions for Yb3+ ions to achieve quantum cutting. To further evaluate the NIR emission performance of PeQD -NPs , the PLQY of CsPbCl Br : Yb3+- Yb Ln 1.5 1.5 NPs was measured at 1527 nm, reaching approximately 23.45%. This value significantly Er/Yb/Ce surpasses that of the infrared-emitting fluorescent materials currently reported (see Supplementary Table 2). Similarly, PeQD -NPs , PeQD -NPs , and PeQD -NPs can also Yb Yb/Tm Yb Yb/Ho Yb Yb/Ho/Ce generate NIR emission through the same mechanism as PeQD -NPs , producing NIR Yb Yb/Er/Ce fluorescence at multiple distinct wavelengths (Fig. 4e). Furthermore, we designed and synthesized the heterostructure NPs with four coating shells, CsPbCl Br : Yb3+-NaYF : 6% Ho3+, 20% Yb3+, 1.5 1.5 4 6% Ce3+@NaYF : 5% Er3+, 35% Yb3+, 4% Ce3+@NaYF : 0.6% Tm3+, 25% Yb3+@NaYF , short 4 4 4 for PeQD -CSSS. The morphological evolution at each stage of the preparation process is Yb illustrated in Supplementary Fig. 24, revealing that the final composite structure exhibits a NP size of approximately 47.8 nm. Under white light excitation, the PeQD -CSSS emits multiple NIR Yb wavelengths spanning from 900 to 2200 nm, as demonstrated in Fig. 4f. The PLQY measured for the photoluminescence in the 900–1700 nm range is approximately 37.1%. The ultra-wide NIR emission, broad absorption band and low excitation threshold enable the NIR light source to perform a range of infrared spectroscopy applications.

Subsequently, we take CsPbCl Br : Yb3+-NPs as an example to investigate the 1.5 1.5 Yb/Er/Ce mechanism underlying NIR luminescence in PeQD -NPs heterostructures. As illustrated in Fig. Yb Ln 5a and Supplementary Fig. 25, ➀-➄ elucidates the impact of Yb3+ ions occupying distinct doping sites in the heterostructure nanoparticles on NIR luminescence excited with 365 nm light. Initially, NaYF : Er3+, Ce3+@NaYF displays feeble NIR emission when excited by 365 nm light (), and 4 4 the luminescence of PeQD- NPs essentially stays the same after the incorporation of PeQDs Er/Ce (). This observation implies that the energy transfer from PeQDs to Er3+ ions (process Ⅰ in Fig. 5f) does not occur readily. Further introducing an appropriate amount of Yb3+ ions into the shell layer of PeQD-NPs , the NIR emission intensity of the resulting PeQD-NPs Er/Ce Yb/Er/Ce did not exhibit a significant enhancement and remained comparable to that of NaYF : Er3+, Ce3+@NaYF 4 4 (). This rules out the possibility that the energy transfer process Ⅱ in Fig. 5f, involving energy transfer from PeQDs to Yb3+ (in NaYF shell) and then to Ln3+, is the root cause of the 4 enhancement in the NIR luminescence of the Ln3+ ions. With the introduction of Yb3+ ions into PeQDs, as PeQD -NPs nanoparticles display exceptional 980 nm luminescence (Fig. 5a). Yb Er/Ce This luminescence results from the highly efficient quantum cutting process facilitated by CsPbCl Br : Yb3+ PeQDs with PLQY of 148.35% (Supplementary Note 1). However, the 1.5 1.5 emission from Ln3+ ions remains relatively unchanged, concluding that PeQDs doped with Yb3+ cannot directly transfer energy to Ln3+ ions in the outer shell, thereby precluding the energy transfer process Ⅲ (Fig. 5f). Remarkably, by dispersing Yb3+ ions within both the PeQDs and the NaYF : 4 Er3+, Ce3+, there is an unexpected increase in the emission of Er3+ ions near 1540 nm, as evident in Fig. 5a . In contrast to the spectrum in Fig. 5a , PeQD - NPs exhibit a substantial Yb Yb/Er/Ce reduction in fluorescence around 980 nm. Therefore, we can hypothesize that the sudden increase in the NIR emission of Er3+ ions is due to the quantum cutting emission of Yb3+ ions and followed by an effective energy transfer from Yb3+ ion (2F level) in PeQDs to Yb3+ ion (2F level) in 7/2 7/2 NaYF , then to Er3+ ions (4I level), corresponding to the energy transition process Ⅳ shown in 4 11/2 Fig. 5f. Due to the energy transfer process from the perovskite host to the Yb3+ ion (perovskite host), then to Yb3+ ion (NaYF ) and to Ln3+ ion, the NIR luminescence of PeQD -NPs , 4 Yb Yb/Er/Ce PeQD -NPs , PeQD -NPs , and PeQD -NPs was significantly enhanced, with Yb Yb/Tm Yb Yb/Ho/Ce Yb Yb/Ho enhancements of 96.1, 10.5, 8.8, and 8.5 times, respectively (Supplementary Fig. 26).

Notably, the highest improved NIR luminescence of CsPbCl Br : Yb3+-NPs can be 1.5 1.5 Yb/Er/Ce attributed to the precise energy level matching between the 4I energy level of the Er3+ ion and 11/2 the 2F energy level of the Yb3+ ion. The findings depicted in Fig. 5b reveal a marginal reduction 7/2 in exciton lifetimes upon the incorporation of Er3+ ions and Yb3+ ions into the NaYF layer. Notably, 4 the introduction of Er3+ ions has no discernible impact on the fluorescence lifetimes of Yb3+ ions within the PeQDs (right image of Fig. 5b). Conversely, the fluorescence lifetime of Yb3+ ions in the PeQDs experiences a substantial decrease following the incorporation of Yb3+ ions into the NaYF 4 shell layer (Fig. 5b). This observed phenomenon further substantiates the existence of the energy transfer process Ⅳ (Fig. 5f). Similarly, we observe comparable lifetime of Yb3+ ions in samples PeQD -NPs , PeQD -NPs , and PeQD -NPs (Fig. 5c), which further Yb Yb/Tm Yb Yb/Ho/Ce Yb Yb/Ho supports the universality of the energy transfer process from the perovskite host to the Yb3+ ion (perovskite host), then to Yb3+ ion (NaYF ) and to Ln3+ ion. The energy transfer efficiency in 4 PeQD -NPs can be calculated using the following equation: Yb Yb/Er/Ce

𝜏
1
𝜂 = 1− (1)
𝜏
0

where τ represents the exciton lifetime or Yb3+ ion lifetime when NaYF is not doped with Er3+ 0 4 ions or Yb3+ ions. 𝜏 represents the exciton lifetime or Yb3+ ion lifetime when NaYF is doped 1 4 with varying concentrations of Er3+ ions or Yb3+ ions. The energy transfer efficiencies for processes Ⅰ-Ⅲ in Fig. 5f are consistently below 10% (Fig. 5d). In contrast, the calculated energy transfer efficiency for process Ⅳ is notably high at 73.6% (Fig. 5d), signifying the dominance of Yb3+ joint medium energy transfer in system PeQD -NPs . In Fig. 5e, the emission peak position of Yb Yb/Er/Ce Yb3+ ions in PeQDs is situated at 990 nm, while it is found at 976 nm in NaYF , which is attributed 4 to variations in the crystal field environment. When excited by 365 nm light, the heterostructure PeQD -NaYF : Yb exhibits two distinct emission peaks of Yb3+ ions in the spectrum: 976 nm and Yb 4 990 nm. These peaks correspond to the distinct lattice fields of NaYF and PeQDs, respectively. 4 Notably, it is imperative to acknowledge that NaYF : Yb3+ cannot be directly excited by the 365 4 nm light source. Consequently, the luminescence observed at 976 nm arises from energy transfer originating from Yb3+ ions in PeQDs to Yb3+ ions in NaYF . The above results indiate the energy 4 transfer route Ⅳ is the main source of NIR emission, which has been summarized in Fig. 5f. Also the same energy transfer process was monitored in PeQD -NPs , PeQD -NPs , and Yb Yb/Tm Yb Yb/Ho/Ce PeQD -NPs , being depicted in Supplementary Fig. 27.

This tunable multi-wavelength light source, when integrated with NIR spectroscopy for gas detection applications, such as replacing existing chromatograph light sources, will play a pivotal role in deciphering gas molecules within enigmatic environments, holding potential for remote detection of exoplanetary atmospheres. This technological synergy facilitates not only the meticulous analysis of atmospheric gas compositions but also the identification of latent biosignatures, thereby paving the way for a comprehensive investigation into environmental conditions.

Based on the above findings, we employed PeQD -CSSS as a NIR light source for the Yb unknown multiplexed gas detection, investigating technological approaches for analyzing the gas compositions (Fig. 6a-b). Fig. 6c shows the experimental optical setup, where gas molecules are positioned at the front of the spectrometer to provide absorption fingerprints about the gases. As depicted in Fig. 6d, the detection results encompass the typical marker gases such as hydrogen sulfide, ethylene, ammonia gas, ethanol, formaldehyde, and toluene. The highlighted circle markers indicate deviations in the NIR emission spectra of PeQD -CSSS attributable to gas Yb molecule absorption48. Notably, absorption peaks are observed at 1575, 1517, 973 and 1418 nm for hydrogen sulfide, ethylene, toluene and formaldehyde, respectively. The ethanol gas exhibits characteristic detection peaks at 1184 and 1459 nm. For ammonia gas, distinct peaks appear at 1165, 1531, 1544 and 2000 nm, offering enhanced detection specificity. This gas sensing system overcomes the drawbacks of poor selectivity for the gas sensors, such as semiconductor and electrochemical sensors, by allowing the simultaneous detection of several gas mixes since the emission spectra of PeQD -CSSS covers a wide NIR range (Supplementary Fig. 28). According Yb to the Beer-Lambert law, gas molecules absorb light energy as the beam traverses through the gas, as described by the equation:

𝐼 = 𝐼 𝑒−𝑘𝑏𝑐 (2)
0

where I and I represent the outgoing and incident light intensities, respectively, k is the gas 0 absorption coefficient, b is the thickness of the absorbing layer, and c denotes the concentration of the gas under measurement. The spectral evolution of the NIR source PeQD -CSSS with Yb increasing gas concentration is depicted in Supplementary Fig. 29-34, revealing the NIR characteristics associated with different gases. Notably, the NIR spectra intensity gradually diminishes as gas concentration increases, aligning perfectly with the principles of Beer-Lambert's law. The fitted equation is as follows tables:

Table 1: Fitted equations for each gas concentration tested.
Gas Characteristic wavelength Fitted equation
ammonia gas 1165 nm 𝑦 = −34.41𝑒 −𝑥 ⁄25.56 +34.9
1531 nm 𝑦 = −12.48𝑒 −𝑥 ⁄15.1 +12.52
1544 nm 𝑦 = −22.08𝑒 −𝑥 ⁄29.68 +22.11
2000 nm 𝑦 = −19.88𝑒 −𝑥 ⁄14.24 +19.92
hydrogen sulfide 1575 nm 𝑦 = −30.98𝑒 −𝑥 ⁄10.7 +30.95
ethanol 1184 nm 𝑦 = −46.92𝑒 −𝑥 ⁄4.67 +46.88
1459 nm 𝑦 = −28.78𝑒 −𝑥 ⁄16.75 +28.73
ethene 1517 nm 𝑦 = −14.83𝑒 −𝑥 ⁄13.58 +14.87
toluene 973 nm 𝑦 = −31.64𝑒 −𝑥 ⁄8.64 +31.76
formaldehyde 1418 nm 𝑦 = −42.86𝑒 −𝑥 ⁄11.04 +43.1

In these equations, y signifies the percentage relative reduction in the NIR spectral integral intensity and x denotes the gas concentration. The results of the testing and fitting curves are presented in Fig. 6e. This demonstrates that effective gas detection can be accomplished by harnessing the extensive NIR spectrum of PeQD -CSSS. The detection limits of the developed Yb NIR gas detection system for all six tested gases were calculated. The results indicated that all detection limits were below 20.7 ppm (Supplementary Table 3 and Note 2).

Furthermore, machine learning (ML)-assisted mixed gas detection at different concentrations from 100 to 700 ppm were conducted for better identification and monitoring of different gases (Supplementary Table 4, Note 3 and Supplementary Fig. 35). Random forest is a type of supervised learning algorithm that constructs multiple decision trees by randomly selecting samples and features, and achieves more accurate classification or regression results by integrating the predictions of these decision trees (Fig. 6f)4 9. The feature variables consist of “gas spectral lines” and “measurement results” in our work. Among them, “gas spectral lines” refer to the characteristic wavelength positions. “Measurement results” are the relative changes in the number of emitted photons within the absorption band of the target gas before and after gas introduction, calculated from the integral area of the spectrum. Together, these two types of features serve as the model independent variables, providing discriminative information from intrinsic gas properties and gas–spectrum interaction intensity. The prediction results are presented in Fig. 6g, demonstrating that gas detection with our NIR spectroscopy is highly effective in accurately distinguishing the components and concentration of gas mixtures, achieving 98.4% accuracy on the independent test set. This is further corroborated by the linear regression analysis of the mixed gas concentration shown in Fig. 6h. The fitted curve exhibits R2 of 0.996, indicating a high degree of consistency between the predicted and actual gas concentrations. Furthermore, when compared with the baseline models and other AI-based gas sensing studies in the IR domain, our approach exhibits notably superior accuracy performance for mixed gas detection (Supplementary Table 5 and 6). These findings fully demonstrate the significant potential of ML-assisted NIR spectroscopy induced by PeQD -CSSS heterostructure nanoparticles in accurately distinguishing the Yb composition and concentration of gas mixtures. To validate the high applicability of PeQD -CSSS Yb heterostructure nanoparticles in gas detection, we designed experiments to simulate the gas compositions of Planet 1, Planet 2, Planet 3, Planet 4, and Planet 5. The simulated gas compositions and their corresponding concentrations are presented in Supplementary Fig. 36. The test results, shown in Fig. 6i, demonstrate the accurate detection of gas types and concentrations for each simulated planetary environment. This approach offers a promising approach for exploring the atmospheric conditions and potential hazards of unknown environments in the future.

Methods
Chemicals
HoCl •6H O (99.99%), YbCl •6H O (99.99%), ErCl •6H O (99.9%), YCl •6H O (99.9%), 3 2 3 2 3 2 3 2 TmCl •6H O (99.9%), Sodium hydroxide (NaOH; >98 %), ammonium fluoride (NH F; >98 %), 3 2 4 Cs CO (99.9%), PbCl (99.9%), PbBr (99.9%), PbI (99.9%), oleic acid (OA, technical grade 2 3 2 2 2 90%, Aldrich), 1-octadecene (ODE, technical grade 90%, Aldrich), oleylamine (OAm, technical grade 95%), cyclohexane (>98%), methanol (>95%), Hydrobromic acid (48%), were all purchased from Sigma‐Aldrich and used as starting materials without further purification.

Synthesis of Cs-oleate
Cs CO (0.8 g), ODE (25 mL), and OA (1.5 mL) were added to a 50-mL 3-neck round-bottom 2 3 flask and heated the solution to 100 °C for 1 hour until the powder was completely dissolved. To avoid sample oxidation, the flask was filled with continuous N .
2

Synthesis of CsPbCl : Yb3+ PeQDs
3 For the synthesis of CsPbCl : Yb3+ PeQDs, PbCl (0.3 mmol) and YbCl ·6H O (0.3 mmol) were 3 2 3 2 loaded into a 50 mL three-neck round-bottom flask along with OAm (1 mL), OA (1 mL), and ODE (10 mL). The flask was purged with N for three minutes to remove residual oxygen. Subsequently, 2 the reaction mixture was heated to 160 °C under a nitrogen atmosphere and maintained for one hour to ensure complete dissolution. After the solution became transparent, the temperature was raised to 240 °C and maintained for 20 minutes. Then, 0.8 mL of the pre-prepared Cs-oleate solution (0.09 mol/L) was rapidly injected. Following exactly 30 seconds of reaction, the flask was immersed in an ice-water bath to quench the reaction. The product was isolated by washing with cyclohexane, centrifuged at 8000 g for 10 minutes, and the precipitate was redispersed in 5 mL cyclohexane for storage.

Anion exchange synthesis of CsPbCl Br : Yb3+ and CsPbBr I : Yb3+ PeQDs
x 3-x x 3-x
PbBr (0.1 mmol) or PbI (0.1 mmol) were mixed with 5 mL ODE in a 25 mL three-neck round- 2 2 bottom flask and degassed under vacuum at 120 °C for 10 minutes. Subsequently, dried OA (0.2 mL) and OAm (0.2 mL) were injected at 120 °C under a continuous nitrogen flow. Following complete dissolution, the solution prepared as described above was added dropwise to a CsPbCl : 3 Yb3+ PeQDs (typically at 10 mg/mL) solution to initiate anion exchange. Upon completion of the reaction, the emission peaks of the resulting solution were measured using a fluorescence spectrometer. The PeQDs were isolated by centrifugation (8,000 g, 10 minutes), and the supernatant was carefully removed. The resulting precipitate was then redispersed in hexane for subsequent characterization.

Synthesis of NaYF : Ln3+@NaYF (Ln=Yb, Ho, Er, Tm, Ce) NPs
4 4
The designed NaYF : Ln3+@NaYF (Ln = Yb, Ho, Er, Tm, Ce) NPs were synthesized via a 4 4 modified solvothermal method. In a typical synthesis, a 100 mL three-neck round-bottom flask was charged with 6 mL OA, 15 mL ODE, and lanthanide chloride precursors (YCl ·6H O and 3 2 LnCl ·6H O, Ln = Yb, Ho, Er, Tm, Ce) with a total lanthanide content of 1 mmol. The specific 3 2 dopant compositions were as follows:
• NaYF 4 : 0.6 % Tm3+, 25 % Yb3+
• NaYF 4 : 5% Er3+, 35% Yb3+, 4% Ce3+
• NaYF 4 : 6% Ho3+, 20% Yb3+
• NaYF 4 : 6% Ho3+, 20% Yb3+, 6% Ce3+
Under continuous nitrogen flow, the mixture was heated to 160 °C with vigorous stirring for 1 hour to form lanthanide-oleate complexes, then cooled to room temperature. Subsequently, a methanolic solution (6 mL) containing NaOH (2.5 mmol) and NH F (4 mmol) was added dropwise, 4 followed by stirring for 1 hour at room temperature. The methanol was then removed by heating to 80 °C. Following the complete removal of methanol, the reaction mixture was subsequently heated to 300 °C and held at this temperature for 1.5 hours. The reactants were then cooled to room temperature, the resulting NPs were purified by repeated centrifugation (6000 g, 10 min) using an ethanol-cyclohexane (1:1 v/v) solvent system. The purified NPs were finally redispersed in 5 mL of cyclohexane for subsequent shell growth procedures. The solution concentration after dispersion was determined to be approximately 0.14 mol/L.

For the synthesis of NaYF : Ln3+@NaYF core-shell NPs, a shell precursor solution was prepared 4 4 following the aforementioned procedure, containing 1 mmol of YCl ·6H O. The reaction mixture 3 2 was cooled to room temperature (25 °C), after which a methanolic solution (6 mL) containing NaOH (2.5 mmol) and NH F (4 mmol) was added. The mixture was first stirred at 30 °C for 1 4 hour, then heated to 80 °C and maintained at this temperature for 1 hour to ensure complete methanol evaporation, before finally being cooled gradually to room temperature.

Next, 5 mL of the pre-synthesized NPs solution (0.14 mol/L) was added dropwise to the three-neck round-bottom flask under continuous stirring and maintained for 30 minutes to ensure uniform mixing of the core NPs with the shell-forming precursor solution. The temperature was then systematically increased to 110 °C to remove residual cyclohexane. Upon complete solvent evaporation, the reaction mixture was heated to 300 °C under a nitrogen atmosphere and maintained at this temperature for 1.5 hours to promote controlled shell growth. After this period, the mixture was cooled to room temperature, and the core-shell NPs were collected by centrifugation (8,000 g, 10 minutes) for subsequent characterization.

Synthesis of CSSS NPs
The multi-layer core-shell structured NPs (CSSS) were synthesized via a solvothermal approach. The synthetic procedure followed a similar protocol to that described for NaYF : Ln3+@NaYF in 4 4 the previous section. In a typical synthesis, a 100 mL three-neck round-bottom flask was charged with oleic acid (6 mL), 1-octadecene (15 mL), and lanthanide chloride precursors with a total lanthanide content of 1 mmol.

The addition ratios of rare earth ions in the core layer are as follows: NaYF : 6% Ho3+, 20% Yb3+, 4 6% Ce3+. Under continuous nitrogen flow, the mixture was heated to 160 °C with vigorous stirring for 1 hour to form lanthanide-oleate complexes, then cooled to room temperature. Subsequently, a methanolic solution (6 mL) containing NaOH (2.5 mmol) and NH F (4 mmol) was added 4 dropwise, followed by stirring for 1 hour at room temperature. The methanol was then removed by heating to 80 °C. Following the complete removal of methanol, the reaction mixture was subsequently heated to 300 °C and held at this temperature for 1.5 hours.

After cooling to room temperature, the resulting NPs were purified by repeated centrifugation (6000 g, 10 min) using an ethanol-cyclohexane (1:1 v/v) solvent system. The purified NPs were finally redispersed in 5 mL of cyclohexane for subsequent shell growth procedures.

For the synthesis of core-shell (CS) NPs, a shell precursor solution was prepared following the aforementioned procedure, containing 1 mmol of LnCl ·6H O (The types and concentrations of 3 2 rare earth ions can be found in the synthesis process of NaYF : 5% Er3+, 35% Yb3+, 4% Ce3+ NPs). 4 The reaction mixture was cooled to room temperature (25 °C), after which a methanolic solution (6 mL) containing NaOH (2.5 mmol) and NH F (4 mmol) was added. The mixture was first stirred 4 at 30 °C for 30 minutes, then heated to 80 °C and maintained at this temperature for 1 hour to ensure complete methanol evaporation, before finally being cooled gradually to room temperature.

Next, 5 mL of the pre-synthesized NPs solution was added dropwise to the three-neck round-bottom flask under continuous stirring and maintained for 30 minutes to ensure uniform mixing of the core NPs with the shell-forming precursor solution. The temperature was then systematically increased to 110 °C to remove residual cyclohexane. Upon complete solvent evaporation, the reaction mixture was heated to 300 °C under a nitrogen atmosphere and maintained at this temperature for 1.5 hours to promote controlled shell growth. After this period, the mixture was cooled to room temperature. The resulting NPs were purified by repeated centrifugation (6000 g, 10 min) using an ethanol-cyclohexane (1:1 v/v) solvent system. The purified NPs were finally redispersed in 5 mL of cyclohexane for subsequent shell growth procedures.

The synthesis procedures for the core-shell-shell (CSS) and core-shell-shell-shell (CSSS) NPs are consistent with that of the core-shell (CS) structure. The distinction among these architectures resides in the composition of the outermost shell layers. Specifically, the CSS NPs are coated with a NaYF shell doped with 0.6% Tm3+ and 25% Yb3+, whereas the CSSS NPs are epitaxially grown 4 with an undoped NaYF shell. 4

Synthesis of oleylammonium bromide (OAmBr)
First, 10 mL of OAm and 1 mL of HBr were charged into a 25 mL three-neck round-bottom flask. The mixture was heated to 80 °C under vacuum and maintained at this temperature for 1 hour under continuous nitrogen flow. Subsequently, the temperature was raised to 120 °C and the reaction was allowed to proceed for an additional 2 hours under nitrogen atmosphere. The resulting solution was then collected at 120 °C in a nitrogen-purged vial and immediately sealed with a septum. This procedure yielded a clear yellow OAmBr solution, which was subsequently used without further purification.

Synthesis of PeQD -NaYF : Ln3+@NaYF (Ln=Yb, Ho, Er, Tm, Ce) and PeQD -CSSS NPs
Yb 4 4 Yb
A 5 mL of the as-synthesized CsPbX : Yb3+ PeQDs was thoroughly mixed with 1 mL of OAmBr, 3 ultrasonicated for 5 min, centrifuged to remove the supernatant, and the collected precipitate was redispersed in 5 mL of cyclohexane to form the core material for subsequent processing. For the NaYF : Ln3+ shell synthesis, a reaction mixture comprising 15 mL of ODE, 6 mL of OA, and a 4 stoichiometrically controlled mixture of rare earth chlorides (total 1 mmol, with molar ratios precisely matching the target NaYF : Ln3+ composition) was loaded into a 100 mL three-necked 4 round-bottom flask under continuous nitrogen flow. The mixture was gradually heated to 160°C and maintained at this temperature for 1 h until complete dissolution was achieved, as evidenced by the formation of a homogeneous transparent solution. Upon cooling to ambient temperature, 6 mL of a methanolic solution containing NaOH (2.5 mmol) and NH F (4 mmol) was introduced 4 dropwise under vigorous magnetic stirring. The mixture was first stirred at 30 °C for 30 minutes, then heated to 80 °C and maintained at this temperature for 1 hour to ensure complete methanol evaporation, before finally being cooled gradually to room temperature. For the core-shell heterostructure assembly, 5 mL of the pretreat CsPbX : Yb3+ PeQDs solution was introduced 3 into the cooled NaYF : Ln3+ precursor solution under constant stirring. After uniform mixing at 4 room temperature for 30 min, the temperature was ramped to 110 °C to ensure complete removal of cyclohexane. Subsequent thermal treatment involved a controlled temperature increase to 270 °C to promote the epitaxial growth of cubic-phase NaYF : Ln3+ while preserving the structural 4 integrity of the cubic-phase CsPbX : Yb3+ core. Following a 30 min stabilization period at 270 °C 3 to ensure complete phase formation, the temperature was further elevated to 300 °C for 1.5 h to finalize the PeQD -NaYF : Ln3+ heterostructure nanoparticles. The outermost NaYF shell layer 4 4 was subsequently deposited following an identical protocol to the NaYF : Ln3+ coating process 4 described above.

For the synthesis of PeQD -CSSS NPs, the same methodology was employed with systematic Yb variations in the identity and stoichiometric ratios of the shell-layer rare earth ions, as predetermined by the experimental design matrix.

Gas Detection Process
The flow diagram of the gas detection system is illustrated in Fig. 6c. During spectral testing, the gas sample is introduced into a simple gas channel positioned between the NIR-emitting sample and the spectral acquisition detector. This configuration ensures full interaction between the gas and the incident infrared light, allowing the gas to absorb photons at its characteristic wavelengths. Consequently, the collected spectrum exhibits attenuation at these specific wavelengths, which serves as the basis for gas detection and quantification. The type of target gas can be determined based on its characteristic attenuation wavelength, while the gas concentration can be quantified by analyzing the intensity attenuation percentage at this wavelength. Together, these measurements enable a complete gas detection process. Throughout the procedure, a 365 nm ultraviolet laser was used as the excitation source, operating at a power density of 50 mW·cm-2.

Characterization
UV/vis-NIR absorption spectra were obtained by using a Shimadzu UV-3101PC UV-Vis scanning spectrophotometer in the range of 200–1100 nm. The morphology and size of the products were analyzed using field emission transmission electron microscopy (FE-TEM) on a JEOL JEM-2100F microscope fitted with an energy dispersive X-ray spectrometer (EDS) for elemental mapping. The spherical aberration of the (specify sample, e.g., nanoparticles) was analyzed using an FEI Themis Z transmission electron microscope (TEM) operated at 300 kV, which was corrected for spherical aberration (Cs-corrected). The instrument achieves a resolution of <0.5 Å following spherical aberration correction. A X‐ray diffraction (XRD) patterns were recorded by using a Rigaku D/Max-Ra X-ray diffractometer with a monochromated Cu Kα radiation (λ = 1.54178 Å). X-ray photoelectron spectroscopy (XPS) was performed using a Kratos Axis Ultra DLD spectrometer. The measurements were conducted using a monochromatic Al Kα X-ray source (hν = 1486.6 eV) operated at 150 W. The spectrometer is equipped with a multichannel plate and a delay line detector. All data were acquired under an ultra-high vacuum of 1.0 × 10-9 Torr. The samples were pumped using a laser system comprising an Nd: YAG laser (1064 nm), a third-harmonic generator (355 nm), and a tunable optical parametric oscillator (OPO, Continuum Precision II 8000). This system, which served as the light source for collecting spectra and lifetimes, provided pulses with a duration of 10 ns, a repetition rate of 10 Hz, and a line width of 4-7 cm-1. A photomultiplier combined with a double-grating monochromator was used for spectral collection. In the measurements of luminescent dynamics, the samples were pumped using the Tektronix AFG1022 with a pulse duration of 10 ns, and a repetition frequency of 100 Hz. PLQY measurements were conducted on an Edinburgh Instruments FLS-1000 fluorescence spectrometer. The system was configured with an SM4 integrating sphere for light collection and employed a 150 W continuous-wave xenon lamp as the excitation source. The test samples were prepared by dispersion in cyclohexane, and the baseline was established using a blank reference cuvette filled with an equivalent volume of pure cyclohexane. This methodology ensures accurate photon counting for PLQY calculation by accounting for solvent scattering and absorption. Fianium WhiteLASE was employed as a white light excitation source in conjunction with a long-pass filter featuring a cutoff wavelength of 800 nm. The gas cylinders holding various target gases are connected to DGL-III gas and liquid distribution system (ELITE TECH). The system is capable of achieving high-precision control of the gas flow rate to obtain testing gases of different components and concentrations. Subsequently, the gases from this system are carried to the chamber for the measurement.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, the authors proposed a novel sensitization mechanism (perovskite host→Yb3+ (perovskite) →Yb3+ (NaYF4) →Ln3+) in a perovskite@NaYF4 core-shell nanoparticles. This innovative approach addresses two critical challenges simultaneously: it overcomes the inherently small absorption cross-section of lanthanide ions while maintaining sufficient doping capacity. Particularly noteworthy is the mechanism's ability to achieve efficient broadband near-infrared (NIR) fluorescence emission under low-power white light excitation, a rare and significant advancement in the field. Furthermore, the authors employed this NIR light source to achieve precise classification of gas mixtures and simulate extraterrestrial gas exploration—an approach that holds significant scientific relevance. This multi-wavelength NIR luminescent composite structure holds significant potential for applications in diverse fields, including quantum communication and photonic chip development. Given its scientific merit and broad relevance, the manuscript appears suitable for publication in Nature Communications. However, I have several minor questions that I would like to address with the authors.\n1. The excitation spectrum in Fig. 3a appears to be limited to approximately 660 nm. Could the authors clarify whether this range is constrained by the instrumentation's light source? Additionally, it would be valuable to understand if the material exhibits excitation responses at longer wavelengths. Please also specify the characteristic emission wavelengths corresponding to this excitation spectrum.\n2. Figure 3f presents the emission spectrum under low-power white light excitation. For better characterization of the material's photophysical properties, could the authors please provide the power density of the excitation source used in these measurements? This quantitative information would significantly enhance the reproducibility and comparative analysis of the results.\n3. Currently, non-toxic lanthanide-based halides (e.g., Cs2NaLnX6 and Cs3LnCl6) have attracted considerable research attention in this field. Could the composite structure proposed in this manuscript potentially employ these lanthanide-based halides as sensitizers, which would significantly mitigate material biotoxicity while maintaining comparable performance?\n4. Could the authors include in the Supporting Information the experimental conditions used for spherical aberration-corrected electron microscopy in Figure 2? This would enhance the reproducibility of the work and provide valuable technical details for readers.", "reviewer_2": "General considerations\nThe authors presented a very detailed and scientifically sound investigation for the development of core-shell nanoparticles perfectly engineered to guarantee a broadband absorption in the visible range, together with a broad near-infrared photoluminescence emission. The limitations of some previous approaches from the literature were clearly discussed, and a novel technical solution was developed. Moreover, the material’s composition was optimized and tested on a specific application: the detection of gas molecules. The use of AI was also employed to verify the simultaneous identification and monitoring of multiple marker gases relevant to extraterrestrial exploration.\nStrengths\nMy overall opinion on this research is very positive. The authors overcame several critical points, which were addressed by a well-planned scientific approach. They were able to understand the Physics beneath the energy transfer process and to optimize the materials composition to maximize absorption and emission. The idea of separating the absorption part from the emission part was excellent. Absorption was mediated by a PeQD, highly absorbing in the visible, while emission was obtained by a rare-earth-doped (RE3+) NaYF4 matrix, a well-known low phonon material with high RE3+ solubility.\nAn example of application for multiplexing gas sensing was also proposed and tested, considering several gases and compositions and obtaining a clear validation of the approach by the support of artificial intelligence.\nWeaknesses\nA key point for optical phosphors is the total quantum yield (QY = emitted photons / absorbed photons). The QY of the optimized nanoparticles should be reported and compared with other systems. Could the increased absorbance allow to overcome possible QY limitations in practical applications?\nMy main concern is about the proposed field of application: to be used, this technology needs to be brought in the place of analysis. This is highly limiting or impossible for planets far from Earth. Additionally, the possibility of sending other common equipment would probably be a preferred choice. This aspect requires better justification.\nFinally, what is the detection limit for the different gases? Is it comparable to other approaches?", "reviewer_3": "Y. Wang and co-workers report a novel hybrid material based on Yb3+-doped perovskite quantum dots (PeQDs) and Ln3+-doped NaYF4, leveraging the NIR emission of the Ln3+, while using the PeQDs as a novel antenna for efficient UV excitation. The optical data indicate strong enhancement of the NIR emission from the Ln-doped PeQD/NaYF4 core/shell/shell hybrids compared to pure Ln-doped NaYF4. This is potentially very interesting, with potential impact on the field. However, the paper does not provide the necessary experimental information and data to fully support the claims made. The authors stay vague when it comes to experimental details, and there is a lack of in-depth characterization. Some claims are not supported by the findings. Therefore, I cannot recommend publication of the manuscript.\nDetailed comments are provided in the following.\n1. The authors claim that the underlaying mechanism is a quantum cutting process. However, there are no data provided to confirm that. In-depth analysis of the quantum yield (QY) would be required, unveiling QY values of close to 200% (or at least larger than 100%). Conversely, the authors only briefly mention a QY value of 23%. No details are provided how this value was obtained.\n2. The Experimental Details section is very poor, lacking information. It would not be possible to repeat the described experiments. For instance:\na. Dopant concentrations in mol% and their respective amounts (mg, mol) should be added.\nb. There is no procedure provided that explains the growth of the NaYF4 shells on the PeQDs. The section Synthesis of QDYb@NaYF4: Ln3+@NaYF4 (Ln=Yb, Ho, Er, Tm, Ce) NCs does not mention how the QDs are introduced into the reaction.\nc. Figure 1: CSSS NC? This NP architecture is not described in the Experimental details.\nd. Why was a Nd laser (and the third harmonic) used for excitation? Why not a simple UV excitation source? This would be particularly relevant to demonstrate the possible use of low-P excitation.\ne. Excitation power density information is missing.\nf. It is not clear whether the PL data are obtained in solid state or on dispersions (Concentration of NPs in the dispersion? Solvent used?).\ng. Experimental details about the gas sensing are not sufficient to allow for reproduction of the experiment.\n3. Data provided in the ESI are poorly described in the figure captions and/or are not sufficient to support the claims made. For instance:\na. A too small number of NPs is shown in TEM images. Larger areas with more NPs need to be shown to confirm the homogeneity of the samples. TEM images and size distribution plots including average sizes and standard deviation should be provided for all core-only, core/shell, core/shell/shell, and core/shell/shell/shell NPs. Information about shell thickness should be provided for all shells in all samples.\nb. Dopant concentration should be included in the figure captions.\nc. EDX mapping: TEM images of the region of interest should be added; scale bars are missing. E.g. Fig S2: What are the data series in a, b, c, and d? “elemental line scan analysis curves” – what is meant by this caption?\nd. All photoluminescence spectra should be labeled with f-f transitions.\ne. All photoluminescence spectra should show numbers on the y-axis to allow for comparison of the intensities (ESI and main text). Without numbers, the claimed enhancement is not visible.\nf. It is not clear what is meant by “NaYF4, monitoring wavelength of 1180nm.” (Fig S6 and elsewhere). Such wording indicates that the shown data are an excitation spectrum. On the other hand, excitation spectra shown in the manuscript and ESI lack information about the monitored wavelength.\ng. XPS spectra should be labeled (and deconvoluted is necessary).\nh. Information about I, Br, Cl amounts is missing in Figures S12 and S13 (meaning of the shades of green and rainbow, respectively).\ni. Figure S15: It is not clear what the y-axis means. The z-axis should show values to allow for the comparison of the emission intensities obtained for the different compositions.\nj. Information about excitation wavelength, laser power density, and solvent and NP concentration in the dispersion (or solid state?) are missing.\n4. Confirmation that the set concentration for Ce in mol% was indeed incorporated should be provided (e.g., ICP).\n5. Confirmation of the PeQD/NaYF4 structure (Figure 2): Elemental mapping of the core elements is missing. EDX in Fig 2d is not convincing for the QD elements. Could error bars be added to Figure 2f to demonstrate homogeneity of the samples. Fig 2f: Which element does the half-filled blue hexagon symbol represent?\n6. Power-dependent spectra should be shown to support statements about the power threshold.\n7. “Furthermore, we combine 257 CsPbCl1.5Br1.5: Yb3+ PeQDs with CSSS…” – how was this done? What is the resulting structure?\n8. Fig 4a: it is not clear from which spectral range is cut from the x-axis by the axis cut (and why it is cut).\n9. What are the 4 bars per mechanism in Fig 4d? What is x in the legend?\n10. Gas sensing: What is the LOD for the gas sensor? A comparison of the sensing performance with established sensors and other sensors reported in the literature should be provided.\nAdditional comments:\n- English language needs major revision. Some sentences are difficult to follow (especially in the experimental details section). For instance (there are many more errors or unclear wording):\no What is meant by „highly doped Ln3+ ions within“ (a host can be highly doped but not an ion)?\no All the processes must be refilled with N2. – It is not clear what this means.\no It was continued heated at 160 °C for 1 h and refilled with N2. Then the solution was then increased to 240 °C and maintained for 20 minutes. Then Cs-oleate (0.8 mL) was quickly injected into the bottle… - It is not clear what this means.\no The anion source after complete solubilization…\no XRD curves\no Notably, our distinctive technical involves…\no Further to incorporate Yb3+ ion in the outer NaYF4 shell, the spectral obtained from the PeQD@NaYF4: Yb3+, Er3+, Ce3+ …\no Yb3+ lifetime decay - either lifetime or decay\n- Figure 4b and c: The x-axis label is not correct - should be time, not lifetime.\n- The authors introduce Ln3+ ions as lanthanum ions. This is not correct. Lanthanum has the elemental symbol La, and La3+ ions do not undergo any f-f transitions, hence, no luminescence.\n- Introduction: Examples given for NIR emitting Ln-based phosphors is very limited. It is not clear how they were chosen. Additional context and description of state-of-the-art NIR Ln-based emitters should be included. Likewise, the Introduction lacks discussion of the state-of- the-art of NIR-based gas sensors.\n- The abbreviation for the system and the energy pathway introduced at line 86, page 4, is difficult to understand.\n- The authors claim that high energy lasers are a drawback of conventional Ln-based phosphors. Direct Ln excitation does not require high-energy lasers. Such statement is mis-leading (and incorrect).\n- Building on the previous study,… - a reference should be provided.", "reviewer_4": "The scope of this review is only on the machine learning (ML) aspects of the gas sensing reported in the manuscript.\nThe manuscript presents the application of a ML method, namely random forest (RF), in utilizing the extensive near infrared spectrum of Cl1.5Br1.5-PeQDYb@CSSS, to predict labels and concentrations of several gas molecules (ammonia, hydrogen sulfide, ethanol, ethene, toluene, and formaldehyde).\nMy overall recommendation is to accept with major revisions only on the ML aspect of the gas sensing reported in the manuscript. Please note my recommendations do not go beyond the machine learning (ML) aspects of the gas sensing reported in the manuscript.\nThe paragraph (lines 403-425) describing the ML aspects is too short and lacks key details regarding the methodology and its soundness for the AI-driven gas sensing analysis.\nSpecifically, the following points should be addressed, and relevant details should be provided.\n1. Please clarify the training-testing splits or folds. Please also provide the total number of samples in the train and test set as well. Without that contextual information the accuracy metric of 98.4% is difficult to assess. Since for larger train split and smaller test split the accuracy metric may simply reflect repeatability. Furthermore, was the metric calculated based on a k-fold cross-validation average? Please also specify the number of trees used, tree depth, splitting criteria, class weighting, hyper parameter search strategy, and the cross validation scheme (k fold? Leave-one-out? stratified?) as well.\n2. In lines 408-409, it is stated that “characteristic wavelength and peak intensity change” are utilized for speciation and quantification, however Fig. 5b–c suggests the full spectrum is available for the model to learn. Was the RF model built on raw intensities, hand‑picked peaks, or engineered features? Was the model fed with individual signals or signals converted to images? A schematic (similar to Fig. 5d) and complete feature (independent variables) list would help clarify the inputs and outputs to the RF model greatly benefit the sensor community in pursuing AI-sensor integration for gas-phase species detection in the future.\n3. Narayanan and Kappor stated in a recently published comment (Nature 640, 312-314 (2025) doi: https://doi.org/10.1038/d41586-025-01067-2),\n“Our concern is mainly about these modelling-based approaches, in which AI is used to make predictions or test hypotheses about how a system functions. One common source of error is ‘leakage’, an issue that arises when information from a model’s evaluation data improperly influences its training process. When this happens, a machine-learning model might simply memorize patterns in the evaluation data instead of capturing the meaningful patterns behind the phenomenon of interest. This limits the real-world applicability of such models and produces little in terms of scientific knowledge.”\nWith that context and the effects of leakage in mind, ensemble models, such as RF, requires fine tuning or pruning techniques to work well. The authors should state and briefly discuss if such techniques were implemented to address the issues of overfitting and leakage?\n4. The manuscript lacks benchmarks against recent AI based gas sensing studies in the IR domain, where these same molecules have been classified and quantified in both pure and mixed samples, using several deep learning models as well as classical ML models and ensemble models, from experiments as well as simulated data. I recommend including at least one baseline model for speciation and concentration prediction comparison for each molecule, and report uncertainty (e.g., confidence intervals, fold wise SDs, or precision–recall curves) to strengthen methodological rigor. Because this work’s main departures from prior studies are the simulated planetary conditions and the new sensor platform, providing those comparisons will let readers determine the true performance gains.\n5. In Figure 5d, the numbering of the decision trees in the random forest model appears to be incorrect. Each tree is numbered as 1.\n6. Recent work has shown AI assisted gas sensing for both trace and mixed gas environments. This manuscript’s strength lies in its quantum engineered nanocrystals, yet lines 33 34 of the abstract imply a broader advance in AI sensor integration. The AI/ML section is too brief to assess such novelty since only simulated mixtures in assumed planetary environments, pressure/temperature variations, are provided, and the results Fig. 5g is a proof of concept simulation. This should be clearly stated so as not to expand the claim presented in this study."}, "author_response": "The details of a point-by-point response to the editor and reviewers were listed below:\nThe reviewer #1\nComment 1: The excitation spectrum in Fig. 3a appears to be limited to approximately 660 nm. Could the authors clarify whether this range is constrained by the instrumentation's light source? Additionally, it would be valuable to understand if the material exhibits excitation responses at longer wavelengths. Please also specify the characteristic emission wavelengths corresponding to this excitation spectrum.\nResponse: Thank you for your valuable comments. The broadband excitation spectrum observed for sample PeQD @NPs in Figure 3a can be primarily ascribed to the Yb Er/Yb/Ce band-edge transition of perovskite quantum dots constituting the core material. In the present study, CsPbI was employed as the core material, which typically exhibits an 3 emission peak at approximately 670 nm. The material exhibits a broad excitation band spanning from 200 nm to 660 nm. Accordingly, the excitation spectrum was measured only up to 660 nm. Nevertheless, it was observed that the excitation signal does not fully decay by this wavelength, indicating residual excitation activity beyond the measured range. To address this limitation, we subsequently performed additional excitation spectrum measurements, monitoring the emission at 1527 nm. Additionally, the excitation spectrum in Supplementary Information has been revised, as depicted in the updated figure below. The revised versions of the images appear as Figure 3a in the main text (page 13) and Figure S20 in the Supplementary Information. We kindly invite the reviewers to evaluate these modifications.\nFigure a. Comparative excitation spectra of PeQD @NPs (CsPbCl Br : Yb Er/Yb/Ce 1.5 1.5 Yb@NaYF : Yb, Er, Ce@NaYF ) and NPs (NaYF : Yb, Er, Ce@NaYF ). The 4 4 Er/Yb/Ce 4 4 halide ion in PeQDs is I⁻. Figure b. Excitation spectra of NPs , NPs , and Yb/Tm Yb/Ho NPs before and after their coating on PeQD cores. The chemical composition Yb/Ho/Ce Yb of PeQD @NPs is CsPbCl Br : Yb@NaYF : Yb, Ln@NaYF (Ln=Tm, Ho, Yb Yb/Ln 1.5 1.5 4 4 Ce).\nComment 2: Figure 3f presents the emission spectrum under low-power white light excitation. For better characterization of the material's photophysical properties, could the authors please provide the power density of the excitation source used in these measurements? This quantitative information would significantly enhance the reproducibility and comparative analysis of the results.\nResponse: Thank you for your valuable comments. The emission spectrum measurements in Figure 3f were conducted using an ultra-broadband white-light laser (240–2400 nm) as the excitation source. To minimize interference from infrared wavelengths, a long-pass filter (cutoff wavelength: 800 nm) was employed during testing. The excitation power density was maintained at 20 mW cm-2. These experimental details are explicitly documented in the caption of Figure 3f (page 14) of the manuscript (highlighted in yellow for emphasis).\nComment 3: Currently, non-toxic lanthanide-based halides (e.g., Cs2NaLnX6 and Cs3LnCl6) have attracted considerable research attention in this field. Could the composite structure proposed in this manuscript potentially employ these lanthanide-based halides as sensitizers, which would significantly mitigate material biotoxicity while maintaining comparable performance?\nResponse: Thank you for your valuable comments. As noted by the reviewers, the synthesis of lead-free perovskites has become well-established, with their fluorescence quantum yields being comparable to those of CsPbX perovskite quantum dots. 3 Moreover, lead-free perovskite systems such as Cs NaLnX and Cs LnCl demonstrate 2 6 3 6 exceptional stability, rendering them highly suitable as sensitizers for the composite nanocrystals proposed in this study. Importantly, the remarkably low biotoxicity of Cs NaLnX and Cs LnCl significantly enhances the potential biomedical applications 2 6 3 6 of these composite nanocrystals, particularly in NIR-II bioimaging. Nevertheless, a critical challenge remains in the substantial lattice mismatch between Cs NaLnX /Cs LnCl and NaYF , which hinders the formation of composite structures. 2 6 3 6 4 This issue warrants further investigation to develop effective solutions.\nComment 4: Could the authors include in the Supporting Information the experimental conditions used for spherical aberration-corrected electron microscopy in Figure 2? This would enhance the reproducibility of the work and provide valuable technical details for readers.\nResponse: Thank you for your valuable comments. Spherical aberration analysis was conducted using a FEI Themis Z transmission electron microscope (TEM) operated at an acceleration voltage of 300 kV. The instrument achieves a resolution of <0.5 Å following spherical aberration correction. To ensure experimental reproducibility, detailed operating conditions have been included in the Supplementary Information (page 7), with key parameters highlighted for clarity.\nThe reviewer #2:\nThank you for the valuable comments on our work. Below are the replies to your review comments.\nComment 1: A key point for optical phosphors is the total quantum yield (QY = emitted photons / absorbed photons). The QY of the optimized nanoparticles should be reported and compared with other systems. Could the increased absorbance allow to overcome possible QY limitations in practical applications?\nResponse: Thank you for your valuable comments. Quantum yield (QY) serves as a critical performance metric for luminescent materials. In this study, to address the inherent limitation of rare earth ions' small absorption cross-section, we incorporated perovskite quantum dots as sensitizers due to their high absorption coefficients in the ultraviolet-visible spectral range. This strategic approach substantially improved the material's absorption capacity, leading to highly efficient multi-wavelength infrared luminescence. The relationship between absorption and luminescence is nuanced; enhanced infrared emission, while linked to absorption, does not guarantee a proportional increase in QY. Consequently, overcoming practical QY limitations requires a reasonable design of energy transfer to increase the radiative transitions and reduce non-radiative transitions. Nevertheless, comparative analysis with previously reported systems demonstrates that our perovskite nanocrystal-sensitized multi-wavelength infrared emission exhibits three significant advantages: (1) the broadest emission wavelength range, (2) the highest fluorescence QY among nanomaterial-based systems, and (3) the practical benefits of facile nanomaterial preparation and processing. A detailed comparison with existing systems is presented in Table 1.\nTable 1. Compilation of the characteristics of luminescent materials exhibiting infrared emission. This table corresponds to Supplementary Table 2 (SI page 29) of the revised manuscript. Please consult it for verification.\nHost luminescence center NIR emission PLQY\nband\nCs AgInCl : Bi Phosphor Nd3+/Yb3+/Er3+/Tm3+ 900-2000 nm 13%\n2 6\nCs K Rb (In Sb )Cl Sm3+/Nd3+/Er3+ 850-1650 nm 20.3%\n2 0.5 0.5 0.95 0.05 6\nNanoparticles\nCs AgInCl Nanoparticles Bi3+/Er3+ 994 nm, 1540 ----\n2 6\nnm\nGGO/BASO Glass Ni2+ 1100-1800 nm ----\nCuInSe @ZnS Quantum Dots ---- 920-1224 nm 21.8%\n3 4\n(\nλem=900-\n)\n1700 nm\nComment 2: My main concern is about the proposed field of application: to be used, this technology needs to be brought in the place of analysis. This is highly limiting or impossible for planets far from Earth. Additionally, the possibility of sending other common equipment would probably be a preferred choice. This aspect requires better justification. Finally, what is the detection limit for the different gases? Is it comparable to other approaches?\nResponse: Thank you for your valuable comments. This study presents an infrared spectral absorption-based method for detecting mixed gases in unknown environments. The selected luminescent materials exhibit multiple distinct emission peaks within the 900–2200 nm spectral range, enabling precise discrimination between different gaseous species and accurate concentration quantification. To realize the extraterrestrial detection concept, we need to mount the detection system on a spacecraft. Atmospheric composition can be analyzed remotely without the need for direct sampling or planetary landing. This significantly mitigates the risks associated with conventional in situ detection methods. However, at present, we lack sufficient funding to support this endeavor.\nWe agree with reviewer that the detection system can be loaded into equipment such as a chromatograph based on its ultra-wide tunable near-infrared emission. We have revised the descriptions of extraterrestrial detection in order to avoid overstating the case. The relevant modifications have been marked in yellow on page 18 of the manuscript (lines 4-7) for your review.\nThe concern regarding the limits of detection (LOD) our infrared gas sensing technique has been addressed in the revised manuscript. The detailed methodology is elaborated in Supplementary Note 1 (SI page 8), and the corresponding LOD values are summarized in Supplementary Table 3 (SI page 29). Although this value does not represent the highest level of gas concentration detection performance, the core advantage of this method is its dual capability for the accurate identification of gas mixture components and their simultaneous quantification driven by designed AI method. This dual functionality represents an improvement over commercial gas sensors—such as semiconductor and electrochemical sensors—which often struggle to discriminate between multiple gas species in mixtures.\nSupplementary Table 3. A list of the measured LODs was compiled for the different gases evaluated using the near-infrared spectroscopy gas sensing system.\nGas Ammonia Hydrogen\nEthylene Ethanol Toluene Formaldehyde\nclass gas Sulfide\nLOD\n20.7 10.4 15.9 14.6 18.2 13.7\n(ppm)\nThe reviewer #3:\nThank you for the valuable comments on our work. Below are the replies to your review comments.\nComment 1: That the authors claim that the underlaying mechanism is a quantum cutting process. However, there are no data provided to confirm that. In-depth analysis of the quantum yield (QY) would be required, unveiling QY values of close to 200% (or at least larger than 100%). Conversely, the authors only briefly mention a QY value of 23%. No details are provided how this value was obtained.\nResponse: Thank you for your valuable comments. This study employs CsPbCl Br : 1.5 1.5 Yb3+ as the core of the composite material. This quantum cutting material has been widely recognized in the literature as a highly efficient luminescent system, exhibiting a remarkable photoluminescence quantum yield (PLQY) approaching 200% (Adv. Mater., 2017, 13,1704149; Nano Lett., 2019, 19, 6904-6913; Energy Environ. Sci., 2019, 12, 2486; Nano Lett., 2019, 19, 338-341). To ensure the reliability of our measurements, we conducted multiple independent verifications of the core material's PLQY throughout the experimental process. The corresponding PLQY result is 148.35% (presented in Figure a), representing a typical quantum cutting process.\nBuilding upon this foundation, we have successfully implemented a directed energy transfer process that utilizes the efficient quantum cutting emission of Yb3+ ions and their collaborative energy transfer to generate rare-earth ion infrared emission. The 23% PLQY value corresponds to the PLQY of the CsPbCl Br : Yb3+@NaYF :Er3+, 1.5 1.5 4 Yb3+, Ce3+@NaYF nanocrystals, measured at an emission of 1527 nm under 365 nm 4 excitation. This PLQY value is lower than the quantum cutting result as the energy transfer from the quantum cutting core (CsPbCl Br : Yb3+) to shell (NaYF :Er3+, 1.5 1.5 4 Yb3+, Ce3+) lead to partial photon losses. Furthermore, during the revision of the manuscript, the PLQY of the NIR (900-1700 nm) emission from CsPbCl Br : 1.5 1.5 Yb3+@CSSS nanocrystals was evaluated under 365 nm excitation and was determined to be approximately 37.1%. The PLQY was measured using an Edinburgh Instruments FLS1000 spectrometer equipped with an integrating sphere. The sample, prepared as a diluted low-concentration solution, exhibited a PLQY. The description of the PLQY in the main text has been revised accordingly (page 13, lines 3–7 and 17-18). Please refer to the updated version for review.\nFigure a. PLQY of the CsPbCl Br : Yb core material. A quantum yield of 148.35% 1.5 1.5 under 365 nm excitation provides experimental validation of the quantum cutting mechanism.\nComment 2: The Experimental Details section is very poor, lacking information. It would not be possible to repeat the described experiments.\nResponse: Thank you for your valuable comments. We have made detailed additions to improve the reproducibility and credibility of the research.\na. Dopant concentrations in mol% and their respective amounts (mg, mol) should be added.\nResponse: We have supplemented the Experimental Section in the Supporting Information with: (i) precise doping concentrations of all rare earth ions, and (ii) exact quantities of chemical reagents employed. For the reviewer's convenience, these additions have been highlighted with a yellow background on pages 2–7 of the Supplementary Information.\nb. There is no procedure provided that explains the growth of the NaYF shells on the PeQDs. The section Synthesis of QD @NaYF : Ln3+@NaYF (Ln=Yb, Ho, Er, Tm, Yb 4 4 Ce) NCs does not mention how the QDs are introduced into the reaction.\nResponse: In response to the issue of material synthesis, we have provided comprehensive synthetic details for the QD @NaYF : Ln3+@NaYF (Ln = Yb, Ho, Yb 4 4 Er, Tm, Ce) nanocrystals in the Supporting Information. For the reviewer's convenience, these critical methodological additions have been highlighted with a yellow background on pages 5–7 of the Supplementary Information.\nc. Figure 1: CSSS NC? This NP architecture is not described in the Experimental details.\nResponse: Multilayer core-shell nanocrystals (NaYF : 6%Ho3+, 20%Yb3+, 4 6%Ce3+@NaYF : 5%Er3+, 35%Yb3+, 4%Ce3+@NaYF : 0.6%Tm3+, 4 4 25%Yb3+@NaYF ), short for CSSS, were created by a sequential coating technique. 4 The preparation of CSSS nanocrystals follows a protocol analogous to that of NaYF : 4 Ln3+@NaYF , with the key modification being two additional iterations of the shell- 4 coating procedure. Detailed synthetic protocols for CSSS-structured nanocrystals have now been incorporated into the Supporting Information (page 4-5) (highlighted in yellow for ease of reference).\nd. Why was a Nd laser (and the third harmonic) used for excitation? Why not a simple UV excitation source? This would be particularly relevant to demonstrate the possible use of low-P excitation.\nResponse: Our initial experimental design employed laser excitation due to two primary considerations. (1) Given the inherently small absorption cross-section of rare-earth ions, the emission of NaYF :Ln3+ NPs is relatively weak under excitation of UV 4 light sources. Consequently, a higher-power laser was employed as the excitation source. (2) To achieve accurate comparison of luminous intensity, we employ a uniform pump source to ensure consistent excitation conditions, which is critical for the accurate comparison of emission spectra between different nanoparticle systems (e.g., QD@NaYF :Ln3+ NPs and NaYF :Ln3+ NPs). Moreover, the laser source can also be 4 4 adjusted to the required very low intensity. Subsequent investigations revealed that the QD@UCNPs system exhibited dramatically reduced excitation thresholds. We also performed the emission spectra under low-power-density UV lamps and white light sources (Figure 3e and 3f). Remarkably, detectable infrared emission persisted even at ultralow excitation power densities, with a minimum threshold of 0.05 mW cm-2 being achieved.\ne. Excitation power density information is missing.\nResponse: We have added experimentally determined excitation power density values to the manuscript, with these additions highlighted for easy reference. In all experiments utilizing a 980 nm laser source, the excitation power density was consistently maintained at 100 W·cm-2. For measurements conducted with a 365 nm laser, a uniform power density of 15 mW·cm-2 was applied. The power density of the white light excitation source is 20 mW cm-2. Any deviations from these conditions are explicitly indicated in the corresponding figure captions. Please see the figure captions on pages 8, 14, and 17 of the manuscript for details of the relevant modifications.\nf. It is not clear whether the PL data are obtained in solid state or on dispersions (Concentration of NPs in the dispersion? Solvent used?).\nResponse: All the experimental investigations were conducted using powder sample. The as-synthesized nanocrystals (1 mmol) in the form of a powder precipitate were retained for comprehensive characterization, including spectroscopic analysis and lifetime measurements. This information is provided in the figure captions on pages 9, 14, and 18 of the manuscript and has been marked in yellow for easy identification.\ng. Experimental details about the gas sensing are not sufficient to allow for reproduction of the experiment.\nResponse: We have added the methodological details of the gas detection experiments in the Supporting Information. These comprehensive additions, which have been highlighted (yellow background) for easy reference, were implemented to ensure the highest possible experimental reproducibility (SI page 7 “Gas Detection Process”).\nComment 3: Data provided in the ESI are poorly described in the figure captions and/or are not sufficient to support the claims made.\nResponse: Thank you for your valuable comments. We have made detailed revisions and additions to improve the credibility of the research.\na. A too small number of NPs is shown in TEM images. Larger areas with more NPs need to be shown to confirm the homogeneity of the samples. TEM images and size distribution plots including average sizes and standard deviation should be provided for all core-only, core/shell, core/shell/shell, and core/shell/shell/shell NPs. Information about shell thickness should be provided for all shells in all samples.\nResponse: We have revised the original Figures S1 and S9 to include TEM images with broader field-of-view representations. Additionally, we have provided comprehensive TEM characterization of the multilayer core-shell architecture, including: core, core-shell, core-shell-shell and core-shell-shell-shell structures. Each image is accompanied by corresponding size distribution histograms with statistical analysis (mean ± standard deviation), clearly labeled scale bars, and explicit shell thickness measurements. Accordingly, the revised TEM image has been updated in the Supplementary Information. Please see the updated version for your review.\nFigure S1. TEM and HRTEM images of NaYF : Yb3+, Ln3+@NaYF (Ln = Ho, Er, Tm, 4 4 Ce), with an enlarged TEM view for enhanced visualization of nanoparticle uniformity. A size distribution histogram including statistical data (standard deviation) and scale markers is also provided (SI page 10).\nFigure S11. Enlarged TEM images of CsPbCl Br : Yb3+@NaYF : 0.6%Tm3+, 1.5 1.5 4 25%Yb3+, CsPbCl Br : Yb3+@NaYF : 6%Ho3+, 20%Yb3+, CsPbCl Br : 1.5 1.5 4 1.5 1.5 Yb3+@NaYF : 6%Ho3+, 20%Yb3+, 6%Ce3+, and CsPbCl Br : Yb3+@NaYF : 5%Er3+, 4 1.5 1.5 4 35%Yb3+, 4%Ce3+ nanoparticles, highlighting their uniformity. Corresponding size distribution histograms and quantitative metrics (standard deviation and scale) are also presented (SI page 14).\nFigure S12. Enlarged TEM images of CsPbCl₁.₅Br₁.₅:Yb3+@ NaYF : 0.6%Tm3+, 4 25%Yb3+@NaYF , CsPbCl Br : Yb3+@ NaYF : 6%Ho3+, 20%Yb3+@NaYF , 4 1.5 1.5 4 4 CsPbCl Br : Yb3+@ NaYF : 6%Ho3+, 20%Yb3+, 6%Ce3+@NaYF , and 1.5 1.5 4 4 CsPbCl Br : Yb3+@ NaYF : 5%Er3+, 35%Yb3+, 4%Ce3+@NaYF nanoparticles, 1.5 1.5 4 4 highlighting their uniformity. Corresponding size distribution histograms and quantitative metrics (standard deviation and scale) are also presented (SI page 15).\nFigures S23. TEM characterization of each layer in the QD@CSSS (CsPbCl Br : 1.5 1.5 Yb3+@NaYF : 6% Ho3+, 20% Yb3+, 6% Ce3+@NaYF : 5% Er3+, 35% Yb3+, 4% 4 4 Ce3+@NaYF : 0.6% Tm3+, 25% Yb3+@ NaYF ). Corresponding schematics and 4 4 quantitative data (thickness, size distribution, and standard deviation) are included (SI page 21).\nb. Dopant concentration should be included in the figure captions.\nResponse: We fully acknowledge the importance of specifying dopant concentrations in figure captions for complete material characterization. Accordingly, we have systematically incorporated the exact dopant ion concentrations in all relevant figure captions. These critical additions have been highlighted (yellow background) to facilitate the reviewer's evaluation.\nc. EDX mapping: TEM images of the region of interest should be added; scale bars are missing. E.g. Fig S2: What are the data series in a, b, c, and d? “elemental line scan analysis curves” – what is meant by this caption?\nResponse: We have carefully restructured all EDS mapping results following the reviewer's suggestions. Specifically, the revised figures now incorporate the following essential elements: corresponding TEM images, properly calibrated scale bars, and detailed compositional data for the regions of interest. We gratefully acknowledge the reviewer's identification of the inaccurate term \"elemental line scan analysis curves.\" This terminology has been uniformly replaced with the technically correct \"EDS elemental mapping\" throughout the manuscript. The corrections have been implemented in all affected sections, and we will implement more rigorous terminology verification procedures in our future manuscript preparations. The modified results are presented in Figures S3 (page 11), S9 (page 14), and 13–15 (page 16-17) of the Supplementary Information.\nd. All photoluminescence spectra should be labeled with f-f transitions.\nResponse: All photoluminescence spectra have been reinterpreted in terms of f-f transitions, providing clearer assignment of emission peaks in both the main text and supplementary materials. This revision offers more precise characterization of the optical transitions.\ne. All photoluminescence spectra should show numbers on the y-axis to allow for comparison of the intensities (ESI and main text). Without numbers, the claimed enhancement is not visible.\nResponse: The inclusion of vertical axis values in the emission spectra enables a more intuitive comparison of spectral intensities. Accordingly, the vertical axes of all photoluminescence spectra have been provided for reference.\nf. It is not clear what is meant by “NaYF4, monitoring wavelength of 1180nm.” (Fig S6 and elsewhere). Such wording indicates that the shown data are an excitation spectrum. On the other hand, excitation spectra shown in the manuscript and ESI lack information about the monitored wavelength.\nResponse: We acknowledge that the initial characterization of \"monitoring wavelength of 1180 nm and 2000 nm\" in original Figures S5 and S6 lacked sufficient precision, potentially causing misinterpretation as excitation spectra. The experimental objective was to systematically investigate the effect of varying rare-earth ion concentrations on emission intensities at the specific wavelengths of 1180 nm and 1952 nm, in order to identify the optimal doping levels. To clarify this methodology, we have both revised the relevant figure captions (see yellow highlights in Figures S6 and S7, pages 12–13 of the SI) and consistently incorporated monitoring wavelength specifications throughout all excitation spectra in both the main text and Supplementary Information.\ng. XPS spectra should be labeled (and deconvoluted is necessary).\nResponse: We have systematically reanalyzed the XPS data, including spectral deconvolution and peak assignment, to clarify the chemical states of the target elements. The processed results, accompanied by detailed annotations, are presented in Figure S17 (SI page 17). For further verification, please refer to the Supplementary Information in the corresponding section.\nh. Information about I, Br, Cl amounts is missing in Figures S12 and S13 (meaning of the shades of green and rainbow, respectively).\nResponse: According to reviewer’s suggestion, we have incorporated the meaning of each line for Cl, Br, and I along the periphery of the corresponding spectrum (see the figure below). These modifications are now available for review (See Figures S18–S19 on pages 18 of the SI.).\nFigures a and b present the absorption and excitation spectra of CsPbX : Yb@NaYF : 3 4 Yb, Er, Ce, respectively. In this notation, X denotes halide species including Cl, Br, I, or their mixed compositions (Cl Br and Br I ). To facilitate visual identification of x 3-x x 3-x the halide composition in each sample, corresponding captions were implemented. The excitation spectrum shown in Figure b was acquired with a monitoring wavelength of 1527 nm.\ni. Figure S15: It is not clear what the y-axis means. The z-axis should show values to allow for the comparison of the emission intensities obtained for the different compositions.\nResponse: Figure S15 displays the NIR emission spectra of the composite structures obtained through systematic variation of halide ion composition in perovskite quantum dots. While the y-axis currently denotes the halide composition for each corresponding spectrum, we recognize that this representation may not provide optimal clarity. To enhance interpretability, we have (1) revised the figure caption to provide a detailed explanation of the compositional variations, and (2) explicitly annotated the z-axis values to enable direct comparison of spectral intensities. These modifications are presented in the revised Figure S22 for your evaluation (SI page 20). Furthermore, the modified results have been incorporated into the figure below for reference.\nFigures (a-c) NIR fluorescence spectra of PeQD @NPs , PeQD @NPs , and Yb Yb/Tm Yb Yb/Ho PeQD @NPs with changing the halide composition of PeQDs. The y-axis Yb Yb/Ho/Ce represents the gradual transition in halogen composition from chlorine to iodine (Cl,Br,I), with the specific mixed-halogen stoichiometries ordered as: Cl, Cl Br , 2 1 Cl Br , Cl Br , Br, Br I , Br I , Br I , and I (from right to left).\n1.5 1.5 1 2 2 1 1.5 1.5 1 2\nj. Information about excitation wavelength, laser power density, and solvent and NP concentration in the dispersion (or solid state?) are missing.\nResponse: All photoluminescence spectra of the composite structures were acquired under 365 nm excitation, except for those obtained under white light excitation. Certain studies on the optical properties of NaYF : Ln@ NaYF employ 980 nm laser excitation, 4 4 as illustrated in Figure 1. In all experiments utilizing a 980 nm laser source, the excitation power density was consistently maintained at 100 W·cm-2. For measurements conducted with a 365 nm laser, a uniform power density of 15 mW·cm-2 was applied. The power density of the white light excitation source is 20 mW cm-2. Any deviations from these conditions are explicitly indicated in the corresponding figure captions. Please see the figure captions on pages 8, 14, and 17 of the manuscript for details of the relevant modifications\nAll experimental investigations were conducted using powder sample. The as-synthesized nanocrystals (1 mmol) in the form of a powder precipitate were retained for comprehensive characterization, including spectroscopic analysis and lifetime measurements. This information is provided in the figure captions on pages 9, 14, and 18 of the manuscript and has been marked in yellow for easy identification.\nComment 4: Confirmation that the set concentration for Ce in mol% was indeed incorporated should be provided (e.g., ICP).\nResponse: Thank you for your valuable comments. The elemental composition of the QD@UCNPs was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). The results for selected elements, presented in the Table 2, demonstrate good agreement with the nominal feed ratios.\nTable 2. A comparison between the nominal feed concentrations and the experimentally measured concentrations of Y, Yb, Er, and Ce in QD@UCNPs is presented. The standard doping concentrations for Y, Yb, Er, and Ce were established based on the molar ratios used during synthesis, while the actual molar percentages were quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES). See Supplementary Table 1 on page 28 of the SI for the relevant data.\nElement Y: Yb: Er: Ce Nominal (mol%) Actual (mol%)\nY 56: 35: 5: 4 56 54.2\nYb 56: 35: 5: 4 35 30.7\nEr 56: 35: 5: 4 5 4.6\nCe 56: 35: 5: 4 4 3.2\nComment 5: Confirmation of the PeQD/NaYF4 structure (Figure 2): Elemental mapping of the core elements is missing. EDX in Fig 2d is not convincing for the QD elements. Could error bars be added to Figure 2f to demonstrate homogeneity of the samples. Fig 2f: Which element does the half-filled blue hexagon symbol represent?\nResponse: Thank you for your valuable comments. In the original manuscript, the elemental mapping of Cs, Pb, Cl, and Br in Figure 2d appears unclear due to their relatively low concentrations and the dark color scheme used for representation. Additionally, downscaling the original high-resolution image further reduced the visibility of these low-content elements. To improve clarity, we have enhanced the brightness of the images and marked the nanocrystals with dotted outlines. The revised figure now includes enlarged elemental maps, which relatively clearly demonstrate the distribution of Cs, Pb, Cl, and Br within the perovskite quantum dots (See the Figure a below).\nAdditionally, the nanocrystals corresponding to Figure 2d were re-prepared and subjected to EDX mapping analysis, as presented in Figure b below. The results confirm the presence of Cs, Pb, Cl, and Br at detectable concentrations. Although the signal intensities of these elements are relatively low and less visually prominent compared to other elements, they remain clearly identifiable. This finding is further supported by elemental line scan analysis (See the Figure c below), which also verifies the existence of Cs, Pb, Cl, and Br.\nTo better illustrate sample uniformity, error bars have been incorporated into Figure 2f. The half-filled blue hexagon in Figure 2f resulted from a drafting error. We have now corrected this representation. Please review the updated figure (See the Figure d below).\nThank you for your comment. The corresponding revision has been incorporated into Figure 2 on page 11 of the manuscript for your review.\nFigure a. Enlarged view of the Cs, Pb, Cl, and Br elemental distribution in the PeQDs from Fig. 2d.\nFigure b．Repeated analysis of elemental distribution. EDS mapping was repeated to verify the presence and distribution of Cs, Pb, Cl, and Br.\nFigure c．Elemental line scan analysis results for the sample in Figure 2d of the manuscript.\nFigure d. Modified results derived from the original Figure 2f. To enhance the demonstration of sample uniformity, error bars were incorporated and minor inaccuracies were rectified.\nComment 6: Power-dependent spectra should be shown to support statements about the power threshold.\nResponse: Thank you for your valuable comments. To validate the excitation threshold reported in this study, we systematically measured emission spectra under progressively reduced excitation power densities (20 → 0.03 mW cm-2), as presented in the accompanying figure below. The research sample is CsPbCl Br : Yb@NaYF : Er, 1.5 1.5 4 Yb, Ce. The 1527 nm emission signal became undetectable at less than 0.05 mW cm-2, with no observable signal below this threshold power density. These experimental results have been included in Figure S21 (SI page 19) in the revised manuscript to substantiate our threshold determination. At an excitation power density of 0.05 mW cm-2, Yb3+ ions demonstrate intense 980 nm emission, whereas Er3+ ions exhibit minimal emission at 1527 nm.\nFigure. Quantitative determination of the excitation threshold for CsPbCl Br : 1.5 1.5 Yb3+@NaYF : Er3+, Yb3+, Ce3+ nanocomposite (denoted as PeQD @NPs ) via 4 Yb Er/Yb/Ce power-dependent PL spectroscopy. The pink region highlights the minimum detectable emission signal from PeQD @NPs at 1527 nm, corresponding to an excitation Yb Er/Yb/Ce power density of 0.05 mW cm-2.\nComment 7: “Furthermore, we combine CsPbCl1.5Br1.5: Yb3+ PeQDs with CSSS…” – how was this done? What is the resulting structure?\nResponse: Thank you for your valuable comments. The multilayer core-shell structure was fabricated by integrating CsPbCl Br : Yb3+ PeQDs with CSSS, exhibiting the 1.5 1.5 following layer-by-layer composition: CsPbCl Br : Yb3+@NaYF : 6%Ho3+, 1.5 1.5 4 20%Yb3+, 6%Ce3+@NaYF : 5%Er3+, 35%Yb3+, 4%Ce3+@NaYF : 1%Tm3+, 4 4 20%Yb3+@NaYF . As illustrated in the inset of Figure 3f, each constituent layer is 4 explicitly annotated. For comprehensive characterization, the corresponding TEM image and schematic representation of this hierarchical architecture are provided below.\nFigure (a) presents a schematic illustration of the multilayer core-shell architecture fabricated through the integration of CsPbCl Br :Yb3+ PeQDs with CSSS, 1.5 1.5 accompanied by a corresponding layer-specific elemental distribution profile. Figures (b) and (c) display TEM images and the associated size distribution analysis of the core-shell nanostructures, respectively.\nComment 8: Fig 4a: it is not clear from which spectral range is cut from the x-axis by the axis cut (and why it is cut).\nResponse: Thank you for your valuable comments. The horizontal axis in Figure 4a is truncated to emphasize the two distinct emission peaks at 980 nm and 1540 nm, which constitute the only spectral features within this range. It should be noted that the use of axis breakpoints does not affect the interpretation of the data. For completeness, the x-axis in Figure 4a (Manuscript Page 17) has been restored to present the entire dataset in the manuscript.\nComment 9: What are the 4 bars per mechanism in Fig 4d? What is x in the legend?\nResponse: Thank you for your valuable comments. Figure 4d presents the energy transfer efficiency for four distinct energy transfer pathways (I-IV) illustrated in Figure 4f, corresponding to different material compositions. The labels I-IV in both figures represent four specific energy transfer pathways. In response to your inquiry, we have revised the plotting method, and the updated version is presented below as Figure a. The figure comprises four separate bar charts in which the horizontal axis denotes variations in ion concentration across different material systems, while the vertical axis represents the corresponding calculated energy transfer efficiency. As you correctly noted, each bar reflects the energy transfer efficiency value associated with specific changes in material composition and dopant ion concentration. We have now supplemented the x-axis to explicitly indicate the doping concentrations of the relevant ions, such as Er and Yb, as referenced in your query. The relevant revisions are located on page 17 of the manuscript for your review at your convenience.\nFigures (a-b). Correspond to Figures 4d and 4f in the manuscript, respectively. Figure 4d quantitatively presents the calculated energy transfer efficiencies for the four possible pathways in the QD@UCNP composite structure, while Figure 4f schematically illustrates these energy transfer mechanisms. The figures maintain direct correspondence, with computational analysis revealing that Process IV predominantly governs the NIR emission in the QD@UCNP system.\nComment 10: Gas sensing: What is the LOD for the gas sensor? A comparison of the sensing performance with established sensors and other sensors reported in the literature should be provided.\nResponse: Thank you for your valuable comments. The concern regarding the limits of detection (LOD) of our NIR gas sensing technique has been addressed in the revised manuscript. The detailed methodology is elaborated in Supplementary Note 1 (SI page 8), and the corresponding LOD values are summarized in Supplementary Table 3 (SI page 29) for your review. Although this value does not represent the highest level of gas concentration detection performance, the core advantage of this method is its dual capability for the accurate identification of gas mixture components and their simultaneous quantification driven by designed AI method. This dual functionality represents an improvement over commercial gas sensors—such as semiconductor and electrochemical sensors—which often struggle to discriminate between multiple gas species in mixtures. Therefore, we compared the accuracy performance of gas type discrimination and gas concentration prediction using different models. The results show that our approach integrating ultra-broadband NIR light sources with machine learning, demonstrates superior accuracy performance of 98.4% for mix gas detection (see Supplementary Table 5).\nSupplementary Table 3. A list of the measured LODs was compiled for the different gases evaluated using the near-infrared spectroscopy gas sensing system.\nGas Ammonia Hydrogen\nEthylene Ethanol Toluene Formaldehyde\nclass gas Sulfide\nLOD\n20.7 10.4 15.9 14.6 18.2 13.7\n(ppm)\nSupplementary Table 5. Performance comparison of different models in gas type discrimination or gas concentration prediction.\nSimultaneous\nRelevant gas Accuracy F1\nModel Detection of Ref.\ntype (%) (%)\nMultiple Gases\nSVN No 92.6 /\nDecision tree No 73 /\nLinear discriminant\nEthanol No 57.1 / 6\nanalysis\nK-NN No 87.3 /\nSVN Yes 96 /\nDA-ResNet12 99.88 /\nAmmonia;\nRF 93.94 /\nEthanol; No 7\nSVN 88.56 /\nEthylene\nXGBoost 97.82 /\nCNN Ammonia Yes 82-97 67-95 8\nSVM Ammonia No 98.4 / 9\nSVN Ethylene Yes 97.7 / 10\nCatboost Ammonia Yes 95 0.94\nHydrogen 11\nCatboost Yes 97 0.97\nsulfide\nCNN Aromatic No 89 / 12\nAmmonia,\nHydrogen\nsulfide,\nThis\nRandom forest Ethanol, Yes 98.4% 0.98\nwork\nEthene,\nToluene,\nFormaldehyde\nAdditional comments:\n- English language needs major revision. Some sentences are difficult to follow (especially in the experimental details section).\nResponse: Thank you for your valuable comments. Based on the valuable feedback received, we have meticulously revised the entire manuscript and SI to ensure linguistic accuracy and adherence to academic writing standards. Specifically, we have enhanced the clarity and completeness of the experimental methodology section and made concerted efforts to improve the overall readability of the manuscript for a broad scientific audience. Below is a point-by-point response to each additional comment for your review.\no What is meant by „highly doped Ln3+ ions within“ (a host can be highly doped but not an ion)?\nResponse: We have revised it to “Consequently, we formulated a bold hypothesis: could we develop a low-power excitation source for efficient NIR light emission by employing Yb3+ ion-doped PeQDs to enhance the absorption cross-section, doping a high concentration of Ln3+ ions in the NaYF host, and effectively merging them 4 through a core-shell structure”(See manuscript page 4, lines 19-23.).\no All the processes must be refilled with N2. – It is not clear what this means.\nResponse: During the synthesis of nanocrystals, the entire preparation apparatus must be purged with nitrogen gas to eliminate oxygen and prevent oxidation of the samples. We have provided a more detailed and clear revision. These modifications are highlighted in yellow in the SI (\"Synthesis of Cs-oleate,\" page 2).\no It was continued heated at 160 °C for 1 h and refilled with N2. Then the solution was then increased to 240 °C and maintained for 20 minutes. Then Cs-oleate (0.8 mL) was quickly injected into the bottle… - It is not clear what this means.\nResponse: We have revised the description of the CsPbX nanocrystal synthesis 3 process in the Experimental Section in response to your question regarding the methodological details. The modifications are outlined below:\nSynthesis of CsPbCl : Yb3+ PeQDs\no The anion source after complete solubilization…\nResponse: The term “anion source after complete solubilization” refers to PbBr or 2 PbI that has been fully dissolved in solvents such as oleic acid, oleylamine, or 2 octadecene. During the synthesis process, these solutions are added dropwise to the CsPbCl :Yb3+ quantum dot suspension, leading to the partial replacement of Cl⁻ ions 3 by Br⁻ or I⁻ ions through an anion exchange process. Accordingly, these compounds are appropriately described as anion sources. In response to your comment, we have revised the relevant part of the Experimental Section as follows:\nAnion exchange synthesis of CsPbCl Br : Yb3+ and CsPbBr I : Yb3+ PeQDs\nx 3-x x 3-x\nPbBr (0.1 mmol) or PbI (0.1 mmol) were mixed with 1-octadecene (ODE, 5 mL) 2 2 in a 25 mL three-neck round-bottom flask and degassed under vacuum at 120 °C for 10 minutes. Subsequently, dried oleic acid (OA) and oleylamine (OAm, 0.2 mL each) were injected at 120 °C under a continuous nitrogen flow. Following complete dissolution, the solution prepared as described above was added dropwise to a CsPbCl : Yb3+ PeQD (typically at 10 mg/mL) solution to initiate anion exchange. 3 Upon completion of the reaction, the emission peaks of the resulting solution were measured using a fluorescence spectrometer. The PeQDs were isolated by centrifugation (8,000 rpm, 10 minutes), and the supernatant was carefully removed. The resulting precipitate was then redispersed in hexane for subsequent characterization.\no XRD curves\nResponse: We have replaced all instances of “XRD curves” in the manuscript with “XRD patterns” and highlighted them in yellow for your review. Please see the captions for Figures S2 (page 10), S14 (page 10), and S16 (page 17) in the Supplementary Information.\no Notably, our distinctive technical involves…\nResponse: The corresponding revision has been incorporated into the main text and are highlighted in yellow for your convenience. The detailed modifications are as follows:\nNotably, a distinctive aspect of our methodology involves the use of oleylamine bromide (OAmBr) as a stabilizing agent for the PeQDs structure, as detailed in the Supplementary Information (Manuscript, Page 9, Lines 19–21).\no Further to incorporate Yb3+ ion in the outer NaYF4 shell, the spectral obtained from the PeQD@NaYF4: Yb3+, Er3+, Ce3+ …\nResponse: We have revised the statement in the manuscript as follows: Further introducing an appropriate amount of Yb3+ ions into the shell layer of Cl Br – 1.5 1.5 PeQD@NaYF : Er3+, Ce3+, the NIR emission intensity of the resulting Cl Br – 4 1.5 1.5 PeQD@NaYF : Yb3+, Er3+, Ce3+ did not exhibit a significant enhancement and 4 remained comparable to that of NaYF : Er3+, Ce3+ (Manuscript, Page 15, Lines 1-3).\n4\no Yb3+ lifetime decay - either lifetime or decay\nResponse: Thank you for the suggestion. We have updated the term to \"lifetime of Yb3+ ion\" in the manuscript (Manuscript, Page 16, Lines 8).\n- Figure 4b and c: The x-axis label is not correct - should be time, not lifetime.\nResponse: We have modified the x-axis labels in Figures 4b and c to “Time,” as shown in the figure below. The relevant revisions in the manuscript are on page 17.\nFigure (b-c). Lifetime properties of the core–shell structured materials with optimized x-axis labeling for improved clarity.\n- The authors introduce Ln3+ ions as lanthanum ions. This is not correct. Lanthanum has the elemental symbol La, and La3+ ions do not undergo any f-f transitions, hence, no luminescence.\nResponse: Thank you for your suggestion. We have updated \"lanthanum ions\" to \"lanthanide ions\" throughout the manuscript. In the original manuscript, we inadvertently used the term \"Lanthanum ions\" as a general representation for rare earth ions. We sincerely appreciate your meticulous review, which brought this inaccuracy to our attention. Upon further consideration, we recognize that \"Lanthanum ions\" (La3+) specifically denotes the ionic form of lanthanum, whereas the broader class of lanthanide ions (Ln3+) should be employed when referring to the collective trivalent ions of lanthanide elements. To address this, we have systematically revised all relevant instances throughout the manuscript to ensure terminological precision. We kindly invite your review of these modifications (Manuscript, Page 4, Line 13).\n- Introduction: Examples given for NIR emitting Ln-based phosphors is very limited. It is not clear how they were chosen. Additional context and description of state-of-the-art NIR Ln-based emitters should be included. Likewise, the Introduction lacks discussion of the state-of- the-art of NIR-based gas sensors.\nResponse: Thank you for these insightful suggestions. In response, we have revised Section [Introduction] to incorporate an analysis of Ln-based near-infrared luminescence, along with an expanded discussion on near-infrared gas sensing technologies. Additionally, examples of Ln-based luminescent materials have been updated throughout the manuscript. All modifications have been highlighted in yellow for ease of review (Manuscript, Page 3, Lines 4–11 and 18–29; Page 4, Lines 1–7).\n- The abbreviation for the system and the energy pathway introduced at line 86, page 4, is difficult to understand.\nResponse: Thank you for your valuable suggestion. To improve the clarity and precision of the manuscript, we have replaced the general term “system” with the more specific “multilayer core–shell nanocrystals” in the revised version. The energy transfer mechanism proposed in this work involves a core–shell heterostructure composed of PeQD and NaYF . The process begins with the absorption of incident photons by the 4 PeQD. Electrons in the conduction band of the PeQD are then transferred to Yb3+ ions via a quantum cutting process. Subsequently, energy is transferred to the luminescent lanthanide ions (Ln3+) through interfacial energy transfer between Yb3+ ions located in the core and those in the shell, ultimately leading to multi-wavelength near-infrared luminescence. Accordingly, the energy transfer pathway is described in the manuscript as “PeQD → Yb3+ (PeQD) → Yb3+ (NaYF ) → Ln3+”, where the notations in 4 parentheses indicate the doping sites of the Yb3+ ions. A comprehensive illustration of this mechanism is provided in Scheme 1. All of the aforementioned revisions have been carefully incorporated into the manuscript and are highlighted in yellow on page 5 of the main text for your convenience. Please kindly review these changes.\nScheme 1. Enhanced mechanism of NIR luminescence based on perovskite quantum dots sensitized Ln3+ doped NaYF and the proposal of a novel energy 4 transfer pathway across the substrate of PeQD-Yb3+ (PeQD)-Yb3+ (NaYF )-Ln3+.\n4\n- The authors claim that high energy lasers are a drawback of conventional Ln-based phosphors. Direct Ln excitation does not require high-energy lasers. Such statement is mis-leading (and incorrect).\nResponse: Thank you for your valuable comment. We fully acknowledged this issue during the revision process. The original term \"high-energy lasers\" was inaccurate and has therefore been revised to \"single wavelength laser\" in the amended version of the manuscript. The revised sentence is provided below and has been highlighted in yellow in the main text to facilitate review.\n“Therefore, this proposed sensitization strategy enables the efficient acquisition of NIR fluorescence with a broad response across the UV-visible spectrum compliance to various excitation requirements, including low-power white light and multi-wavelength excitation, as opposed to a limited selection of single wavelength lasers.” (Page 5, Line 20 of the manuscript)\n- Building on the previous study,… - a reference should be provided.\nResponse: The gas sensing applications presented in the latter section of this work are fundamentally derived from our prior investigation into the optical characteristics of the QD@UCNP nanocomposites. The term \"Based on previous research...\" refers specifically to our own findings on the material's photophysical properties detailed in Figures 1-4, and therefore does not necessitate an additional citation. To preempt any confusion, we have amended the text to read \"Based on the above findings...\" with the modification highlighted in yellow (Manuscript, Page 18, Line 11).\nThe reviewer #4:\nThank you for the valuable comments on our work. Below are the replies to your review comments.\nComment 1: Please clarify the training-testing splits or folds. Please also provide the total number of samples in the train and test set as well. Without that contextual information the accuracy metric of 98.4% is difficult to assess. Since for larger train split and smaller test split the accuracy metric may simply reflect repeatability. Furthermore, was the metric calculated based on a k-fold cross-validation average? Please also specify the number of trees used, tree depth, splitting criteria, class weighting, hyper parameter search strategy, and the cross validation scheme (k fold? Leave-one-out? stratified?) as well.\nResponse: We appreciate the valuable comments from the reviewers. In response to your concerns regarding training-testing splits, accuracy, model parameters, we have provided the detailed supplementary explanations for each issue as follows:\nThe experimental dataset constructed in this study contains a total of 9,485 samples. For the gas identification task, a random forest classification model was constructed. Stratified sampling strategy was adopted to divide the data into training and test sets at an 8:2 ratio. This partitioning method ensures the consistency of gas type and concentration distributions between the training and test sets, thereby avoiding the impact of data distribution bias on the evaluation of the model generalization ability. Meanwhile, StandardScaler was used for the standardization of input features to eliminate dimensional differences, further ensuring the stability of the training process.\nThe 98.4% accuracy is not calculated as the average of k-fold cross-validation results, but rather represents the classification result on the aforementioned independent test set. After training and parameter optimization, the prediction accuracy of the model on the test set data that was not involved in the training can objectively reflect the actual generalization performance of the model. For the model optimization, the grid search strategy was employed for hyperparameter search. The optimal parameter combination was screened by iterating through the key parameter grid of the random forest and combining with 5-fold stratified cross-validation. The \"stratified\" design ensures that the class distribution of data in each fold during cross-validation is consistent with that of the original dataset, effectively avoiding evaluation bias caused by data distribution imbalance and thus guaranteeing the objectivity of the model generalization ability evaluation.\nAdditionally, regarding the details of the random forest model (including key hyperparameters such as n_estimators and max_depth), we have completely provided the optimal parameter configurations for both classification and regression tasks in “Database and method in Supplementary Note 2” part (SI page 9) and Supplementary Table 4 (SI page 29) of the Supporting Information. Thank you very much for your insightful and valuable advice.\nIn conclusion, we have provided the relevant descriptions including training-testing splits, accuracy and model parameters and Supplementary Table 4 in Supporting Information. In the main text, we provided a description of the accuracy. Please see achieving 98.4% accuracy on the independent test set. (Manuscript, page 19, lines 27–30; page 20, lines 12–18)\nComment 2: In lines 408-409, it is stated that “characteristic wavelength and peak intensity change” are utilized for speciation and quantification, however Fig. 5b–c suggests the full spectrum is available for the model to learn. Was the RF model built on raw intensities, hand-picked peaks, or engineered features? Was the model fed with individual signals or signals converted to images? A schematic (similar to Fig. 5d) and complete feature (independent variables) list would help clarify the inputs and outputs to the RF model greatly benefit the sensor community in pursuing AI-sensor integration for gas-phase species detection in the future.\nResponse: We sincerely thank the reviewer for the valuable comments and apologize for the insufficient explanation of the model input features and the related schematic in our previous study. Firstly, Fig. 5b depicts the relative change in the number of emitted photons within the absorption band before and after introducing the target gas. The primary purpose is to verify the discriminative value of the characteristic wavelengths for gas species identification of our designed new light source from a physical perspective. Fig. 5c illustrates the spectral attenuation trend as a function of concentration for a single target gas, explaining the scientific rationale for quantifying concentration based on changes in emitted photons. These two figures focus on extracting the physical significance of key features, aiming to justify the design of the model inputs rather than directly presenting the full spectral input dimensions of the model. We emphasize this distinction to avoid any potential misunderstanding.\nSecondly, the model inputs are neither raw spectral intensities nor simply manually selected peaks. Instead, the feature variables consist of “gas spectral lines” and “measurement results.” “Gas spectral lines” refer to the characteristic wavelength positions automatically output by the spectrometer through spectral analysis. “Measurement results” are the relative changes in the number of emitted photons within the absorption band of the target gas before and after gas introduction, calculated from the integral area of the spectrum. Together, these two types of features serve as the model independent variables, providing discriminative information from two dimensions: “intrinsic gas properties” and “gas–spectrum interaction intensity.”\nThe model inputs are provided as structured numerical feature vectors rather than converted into image signals. This ensures the model focuses on key discriminative information and avoids the impact of redundant full-spectrum data on training efficiency.\nFinally, we acknowledge the importance of the model schematic for explaining the mechanism. Therefore, we have redrawn the random forest model schematic (Fig. 5d) to more clearly present the design concept. Thanks for the worthy comments.\nWe have provided the relevant descriptions of model input features (Please see the sections highlighted in yellow in the manuscript: page 19, lines 27–30; page 20, lines 1–15) and updated Figure 5 in the manuscript.\nComment 3: Narayanan and Kappor stated in a recently published comment (Nature 640, 312-314 (2025) doi: https://doi.org/10.1038/d41586-025-01067-2), “Our concern is mainly about these modelling-based approaches, in which AI is used to make predictions or test hypotheses about how a system functions. One common source of error is ‘leakage’, an issue that arises when information from a model’s evaluation data improperly influences its training process. When this happens, a machine-learning model might simply memorize patterns in the evaluation data instead of capturing the meaningful patterns behind the phenomenon of interest. This limits the real-world applicability of such models and produces little in terms of scientific knowledge.” With that context and the effects of leakage in mind, ensemble models, such as RF, requires fine tuning or pruning techniques to work well. The authors should state and briefly discuss if such techniques were implemented to address the issues of overfitting and leakage?\nResponse: Thank you for your valuable comments. We highly agree with the concerns raised by Narayan and Kapoor regarding \"data leakage\" and model generalization in their literature, which is also a core issue that our study has focused on preventing and controlling in model design and data processing.\nTo prevent overfitting risks, a combined strategy of \"parameter grid search + model complexity constraint\" is adopted to achieve effective prevention. This essentially equates to the \"fine-tuning and pruning optimization\" of the integrated model. Through GridSearchCV combined with 5-fold stratified cross-validation, multi-dimensional parameter grids are designed for the classification and regression tasks to fine-tune core parameters such as n_estimators and max_depth. Among them, the optimization of max_depth can directly control the complexity of a single decision tree to avoid overfitting caused by excessive tree depth, which is equivalent to the \"pruning\" operation of the base learners in the integrated model. The optimization of n_estimators balances the model variance and bias, ensuring a balance between \"fitting sufficiency\" and \"generalization stability\". For the classification task, \"stratified sampling\" is used to divide the training/test sets in an 8:2 ratio to ensure the consistency of sample distribution.\nIn terms of data leakage prevention, StandardScaler is used to standardize the input features to eliminate differences in scale. All operations involving random processes are fixed with random_state = 42. This setting not only ensures that the sample division results and the initial state of the model in different experiments are completely consistent to achieve result reproducibility, but also fundamentally avoids the implicit data leakage risk introduced by the uncertainty of the random process.\nWe have provided the relevant descriptions of model in “Database and method in Supplementary Note 2” part in in Supporting Information.\nComment 4: The manuscript lacks benchmarks against recent AI based gas sensing studies in the IR domain, where these same molecules have been classified and quantified in both pure and mixed samples, using several deep learning models as well as classical ML models and ensemble models, from experiments as well as simulated data. I recommend including at least one baseline model for speciation and concentration prediction comparison for each molecule, and report uncertainty (e.g., confidence intervals, fold wise SDs, or precision–recall curves) to strengthen methodological rigor. Because this work’s main departures from prior studies are the simulated planetary conditions and the new sensor platform, providing those comparisons will let readers determine the true performance gains.\nResponse: Thank you for your valuable suggestions. In fact, during the initial design phase of the study, we had already carried out relevant work on the establishment of comparative baseline model. First, separate baseline models were constructed for each target gas. Logistic regression and linear regression were used as classical machine learning baselines, while random forest served as the ensemble model baseline. These baselines were applied to complete the tasks of gas type identification and concentration prediction, respectively. The key uncertainty metrics have been supplemented and reported in Supplementary Table 5 to further enhance the rigor of the proposed method.\nIn addition, according to your suggestion, we have reviewed the research literature on recent AI based gas sensing studies in the IR domain. However, there are relatively few relevant reports, especially the several types of gases that are relevant to our work and detected using actual light sources. We have added a comparative table (Supplementary Table 6) in the supplementary materials, which covers various deep learning models, classic machine learning models, and ensemble models for each target molecule. Our approach developed here, integrating ultra-broadband NIR light sources with machine learning, demonstrates superior performance with respect to accuracy for mix gas detection.\nWe have updated the Supplementary Table 5 and 6 and descriptions in the Supplementary Information (“Database and method in Supplementary Note 2”part) and main text (Manuscript, Page 20, Lines 15–18).\nComment 5: In Figure 5d, the numbering of the decision trees in the random forest model appears to be incorrect. Each tree is numbered as 1.\nResponse: Thank you for your valuable feedback. We sincerely apologize for the errors present in the initial manuscript. In response, we have expanded the section on machine learning and have redesigned the schematic diagram of the random forest model, which is provided below for your review.\nFigure. Model diagram of random forest algorithm. The revised figure has now been incorporated as Figure 5d in the main text.\nComment 6: Recent work has shown AI assisted gas sensing for both trace and mixed gas environments. This manuscript’s strength lies in its quantum engineered nanocrystals, yet lines 33 34 of the abstract imply a broader advance in AI sensor integration. The AI/ML section is too brief to assess such novelty since only simulated mixtures in assumed planetary environments, pressure/temperature variations, are provided, and the results Fig. 5g is a proof of concept simulation. This should be clearly stated so as not to expand the claim presented in this study.\nResponse: Thank you for your feedback.\nWe believe that the integration of AI with our novel light source-based detection technology is a complementary improvement. For emerging detection technologies—especially those relying on newly developed light sources (such as our quantum cutting-based broadband source)—the lack of mature, standardized calibration protocols and the intrinsic variability of novel optical components often introduce unique error sources that cannot be fully addressed by traditional hardware optimization alone. The AI-driven error reduction strategy proposed herein directly targets these technology-specific challenges, thereby enhancing the reliability and practical applicability of our mixed gas detection system. In addition, this work holds the potential to bolster the analysis of gas compositions on unknown environments in the future and provides a proof of concept for analyzing the unknown extraterrestrial gas environment.\nIn response to your valuable perspective, we have carefully revised the description of the integration between AI and the detection system in the revised manuscript, so as not to expand the claim presented in this study. We revised the description of the potential application of exoplanetary atmospheres in order to avoid overstating the case. We have revised the abstract to moderate our claims, with changes highlighted in yellow. The AI/ML section has also been expanded in the main text (page 19, lines 27–30; page 20, lines 1–17, highlighted for easy reference). Please review these specific updates.\nReviewer #4 (Remarks on code availability):\nI did not find any supporting code in the supplementary material with the paper and thus I did not review any code. I strongly encourage the authors to host their code, and relevant data in GitHub or similar repository if possible.\nResponse: Special thanks to the reviewer for your comments. We have uploaded code to GitHub. You and readers can find the source code at https://github.com/554632107/gas_task_analysis.git.\nWe sincerely thank the editor and reviewers for their recognition of our revised manuscript. Addressing the insightful comment from Reviewer 3, we have thoroughly revised the manuscript and provided a detailed response accordingly.\nThe details of a point-by-point response to the editor and reviewers were listed below:\nThe reviewer #3\nI thank the authors for the detailed revisions and replies provided. While this has significantly improved the clarity of the manuscript, some aspects remain unclear and require further revision prior to consideration of the manuscript for publication.\nComment 1: Discrepancy and contradiction between NP architecture schemes and data\nThe manuscript introduces the NP architecture as PeQD:Yb core / NaYF4:Ln shell / NaYF4 shell, which is in agreement with the schematic in Figure S23. However, this is not in agreement with the left scheme in Scheme 1, which shows PeQDs embedded in a matrix of NaYF4:Ln with an undoped NaYF4 shell. HRTEM images in Fig. 2 indeed support the schematic of Scheme 1, yet not that of the general description nor the schematic in Fig. S23.\nScheme 1 further shows an unclear schematic for the zoom-in: it appears as a hollow NaYF4:Ln shell with multiple PeQDs inside.\nThe schematic in Fig 2a shows something different again: a core with multiple PeQDs in an unlabelled matric, an inner NaYF4:Ln shell and an outer undoped NaYF4 shell.\nThe schematics in Fig 2a and 2f are not in agreement with the data shown in Fig.2: The schematics show core/shell/shell architecture. The data were obtained on core/shell (based on the figure caption).\nAlso, with respect to the discussion of that figure at Page 10, line 242: The addition of an outer undoped shell is described. Subsequently, the description of data shown in Fig 2 seem to revolve around samples prior such addition of the undoped shell. This is confusing.\nScheme in Fig 4f is miss-leading as it depicts a clear core/shell boarder between PeQDs and NaYF4:Ln (based on discussion and data, the PeQDs rather seem to be embedded into a NaYF4:Ln matrix.\nAnother example for confusion between description, schemes, and data: Page 10, Line 224: Why is Er primarily located in the shell? Based on the description provided above, the shell is supposed to be undoped.\nOverall, this is very confusing, and the authors are encouraged to check and revise schematics and descriptions for better clarity.\nIn addition, it is not clear how multiple PeQDs can fit within the given core matrix. For instance, Fig S23: The PeQDs are shown to be ca. 11 nm in size. After first “shelling”, the size is 21 nm. How many PeQDs are embedded in the NaYF4:Ln matrix? What is the size of the PeQDs after possible shelling-induced dissolution?\nEDS maps are not showing clear localized elemental distributions that would support QD elements in the core of the overall architecture.\nResponse: Thank you for your valuable suggestions. We have addressed the various points raised in Question 1 and provided detailed responses below:\n(a) The manuscript introduces the NP architecture as PeQD:Yb core / NaYF4:Ln shell / NaYF4 shell, which is in agreement with the schematic in Figure S23. However, this is not in agreement with the left scheme in Scheme 1, which shows PeQDs embedded in a matrix of NaYF4:Ln with an undoped NaYF4 shell. HRTEM images in Fig. 2 indeed support the schematic of Scheme 1, yet not that of the general description nor the schematic in Fig. S23.\nResponse (a):\nThank you for your meticulous observation and critical comment regarding the consistency of the nanostructure architecture across the manuscript, schematics (Scheme 1 and Figure S23), and HRTEM characterization. The designed heterostructure is precisely defined as multiple small PeQD:Yb nanocrystals as the core → NaYF :Ln shell (functional shell) → outermost undoped NaYF 4 4 shell (passivation shell). This architecture is the core design throughout our study, and the HRTEM images in Figure 2 directly support this structure. To eliminate potential ambiguity, we have revised the structural description from the original “core-shell” to “multi-PeQDs embedded in NaYF :Ln”. We revised this structure 4 designation to PeQDs- NaYF :Ln heterostructure, which more intuitively reflects 4 the spatial distribution of multiple PeQD core within the NaYF :Ln shell, avoiding 4 misinterpretation of a single-core configuration.\nWe recognized that the original Figure S23 was overly simplified and failed to reflect the \" PeQDs- NaYF :Ln heterostructure + undoped NaYF shell\" structure. 4 4 To address this, we have redrawn Figure S23, with the updated model shown in Figure R1.\nFigure R1 (Figure S23). (a-e) TEM characterization images of each layer in the PeQD -CSSS structure (CsPbCl Br : Yb3+-NaYF : 6% Ho3+, 20% Yb3+, 6% Yb 1.5 1.5 4 Ce3+@NaYF : 5% Er3+, 35% Yb3+, 4% Ce3+@NaYF : 0.6% Tm3+, 25% Yb3+@ NaYF ). 4 4 4 Corresponding structural schematics are provided, along with quantitative data including layer thickness, size distribution, and standard deviation. Notably, Figure b does not specify shell layer thickness due to the disordered nature of the PeQD -C Yb composite formation process. In this system, PeQDs are randomly distributed throughout the NaYF matrix, analogous to watermelon seeds in a fruit, without 4 forming a well-defined interfacial boundary. Consequently, a distinct shell thickness cannot be determined.\n(b) Scheme 1 further shows an unclear schematic for the zoom-in: it appears as a hollow NaYF4:Ln shell with multiple PeQDs inside. The schematic in Fig 2a shows something different again: a core with multiple PeQDs in an unlabelled matric, an inner NaYF4:Ln shell and an outer undoped NaYF4 shell.\nResponse (b):\nWe sincerely appreciate the reviewers for pointing out the inaccuracies in our manuscript and deeply regret these oversights. We have revised the zoom-in section to explicitly show multiple PeQD:Yb nanocrystals embedded in a continuous NaYF :Ln 4 functional shell (not a hollow shell). The “unlabeled matrix” was intended to represent the NaYF :Ln functional shell but lacked explicit labeling, leading to ambiguity. We 4 have now clearly labeled this region as “NaYF :Yb3+, Ln3+” to eliminate confusion. 4 Following your helpful suggestion, we have revised the figure, and the updated version (Figure R2) is submitted for your kind review.\nFigure R2. Figure 2 in the manuscript.\n(c) The schematics in Fig 2a and 2f are not in agreement with the data shown in Fig.2: The schematics show core/shell/shell architecture. The data were obtained on core/shell (based on the figure caption). Also, with respect to the discussion of that figure at Page 10, line 242: The addition of an outer undoped shell is described. Subsequently, the description of data shown in Fig 2 seem to revolve around samples prior such addition of the undoped shell. This is confusing.\nResponse (c):\nWe acknowledge the reviewer's attention to detail regarding the XPS sample. The data presented in Figure 2 (including XPS, TEM, and optical characterizations) were acquired from the intermediate CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ 1.5 1.5 4 heterostructure (without the outer undoped NaYF shell). This decision was based 4 on two key reasons: first, the outermost undoped NaYF passivation shell (≈4 nm) 4 would significantly obscure the spatial distribution of PeQDs and Er/Yb/Ce in electron microscopy characterizations (e.g., EDS mapping resolution would be compromised, making it impossible to distinguish Er signals from the NaYF :Yb3+, 4 Ln3+ functional shell vs. background). Comparative TEM images (Figure R3) demonstrate that the intermediate structure avoids this shielding effect, enabling clear visualization of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ interface and 1.5 1.5 4 element distribution. Second, this approach ensures analytical consistency across all techniques. Characterizing the intermediate structure is sufficient to verify the core objective—successful formation of the CsPbX : Yb3+-NaYF : Yb3+, 3 4 Ln3+@NaYF NPs. The outermost passivation shell is a subsequent optimization 4 step (for stability/luminescence efficiency) that does not alter the elemental distribution or interface properties.\nThe original schematics in Figure 2a and 2f were intended to illustrate the complete synthetic route of our final optimized sample (CsPbCl Br : Yb3+-NaYF : Yb3+, 1.5 1.5 4 Er3+, Ce3+@NaYF ), but we failed to clearly distinguish it from the actual tested 4 sample (CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+) in the initial version. 1.5 1.5 4 We have updated the schematics in Figure 2a and 2f to accurately represent the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ structure of the samples used for the 1.5 1.5 4 tests in Figure 2. On Page 9, Line 22-26, we have clarified the timeline of sample preparation and testing: “Since the inert NaYF coating can obscure the resolution 4 of the PeQD, characterization was performed on uncoated CsPbCl Br : Yb3+- 1.5 1.5 NaYF : Yb3+, Er3+, Ce3+ NPs (Figure S11-12). The addition of an outer undoped 4 NaYF shell was a subsequent optimization step to enhance material stability and 4 luminescence efficiency. The data presented in Figure 2 were obtained from the intermediate heterostructure samples prior to this outer shell modification, aiming to validate the successful formation of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, 1.5 1.5 4 Ce3+ heterostructure.”\nFigure R3. TEM morphology comparison between PeQD -NaYF : Er, Yb, Ce@ Yb 4 NaYF and PeQD -NaYF : Er, Yb, Ce.\n(d) Scheme in Fig 4f is miss-leading as it depicts a clear core/shell boarder between PeQDs and NaYF4:Ln (based on discussion and data, the PeQDs rather seem to be embedded into a NaYF4:Ln matrix.\nResponse (d):\nThank you for your perceptive observation and valuable feedback. To clarify, the actual structure of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ component is 1.5 1.5 4 multiple discrete CsPbCl Br : Yb3+ PeQDs uniformly dispersed and embedded 1.5 1.5 within a continuous NaYF :Ln matrix, rather than a separate core-shell 4 configuration with a clear interface. This embedded design is critical to our work, as it enables intimate contact between CsPbCl Br : Yb3+ and the NaYF : Ln 1.5 1.5 4 host—facilitating efficient energy transfer across the heterointerfaces, which is robustly supported by our optical characterization data.\nThe revised Figure 4f removes the “core/shell boundary” and instead uses distinct colors/textures to depict PeQDs as discrete nanodomains embedded within a continuous NaYF :Ln matrix. 4\n(e) Another example for confusion between description, schemes, and data: Page 10, Line 224: Why is Er primarily located in the shell? Based on the description provided above, the shell is supposed to be undoped. Overall, this is very confusing, and the authors are encouraged to check and revise schematics and descriptions for better clarity.\nResponse (e):\nThank you for your perceptive observation and valuable feedback. To clearly demonstrate the formation of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ 1.5 1.5 4 heterostructure, we deliberately used the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, 1.5 1.5 4 Ce3+ intermediate structure (rather than the final CsPbCl Br : Yb3+-NaYF : Yb3+, 1.5 1.5 4 Er3+, Ce3+@ NaYF architecture) for the characterization in Figure 2 (including 4 TEM, HRTEM, line scanning, EDS mapping, and XPS) as was explained in Response (c).\nThe EDS mapping and line scanning data in Figure 2f clearly confirm that Er is concentrated in the NaYF :Er,Yb,Ce layer for CsPbCl Br : Yb3+-NaYF : Yb3+, 4 1.5 1.5 4 Er3+, Ce3+ heterostructure, which also indicated that the CsPbCl Br : Yb3+ PeQDs 1.5 1.5 were successfully ensembled in NaYF :Ln matrix. The original contradiction arose 4 from failing to state the measured sample is CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, 1.5 1.5 4 Ce3+ heterostructure.\nThe updated Figure 2a has placed particular emphasis on the measured sample (CsPbCl Br :Yb-NaYF₄: Er,Yb,Ce heterostructure). Please refer to the updated 1.5 1.5 Figure 2.\n(f) In addition, it is not clear how multiple PeQDs can fit within the given core matrix. For instance, Fig S23: The PeQDs are shown to be ca. 11 nm in size. After first “shelling”, the size is 21 nm. How many PeQDs are embedded in the NaYF4:Ln matrix? What is the size of the PeQDs after possible shelling-induced dissolution?\nEDS maps are not showing clear localized elemental distributions that would support QD elements in the core of the overall architecture.\nResponse (f):\nThank you for your valuable suggestions. Our experimental results reveal that during the formation of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ structure, 1.5 1.5 4 significant dissolution of CsPbCl Br : Yb3+ PeQDs occurs, accompanied by a 1.5 1.5 clear morphological evolution from well-defined quadrilateral shapes to various irregular forms, as shown in Figures 2b1–b3. This morphological alteration precludes accurate size assessment of the PeQDs. Measurements indicate that the PeQDs embedded within the NaYF : Ln matrix have sizes ranging from 1.9 to 5.2 4 nm. Moreover, during electron microscopy characterization, we observed that not all PeQDs could be fully visualized, as illustrated in Figure R3. As a result, it is not feasible to quantitatively determine the number of PeQDs encapsulated within the NaYF : Ln matrix. 4\nThe spatial resolution of EDS mapping is compromised in the CsPbCl Br : Yb3+- 1.5 1.5 NaYF : Yb3+, Er3+, Ce3+ structure due to the extremely small inter-particle spacing 4 and high density of the PeQDs. Under these conditions, the electron beam interaction volume and secondary fluorescence effects generate extensive false signals and artifacts. These phenomena introduce pronounced false signals and artifacts around the actual elemental locations, thereby obscuring the local elemental distribution in the EDS maps.\nComment 2: Experimental details still lack information required to reproduce the experiments. For instance: “Then 0.8 mL of cesium oleate solution was rapidly injected.” - What is the concentration of the Cs oleate solution? Providing the volume alone will not allow the reader to reproduce the synthesis. “5 mL of the pre-synthesized NPs supernatant” - What is meant by NPs supernatant? What is the mg/mL concentration of NPs in that supernatant? Experimental details about the QY measurements are missing (instrumentation, setting, power density, choice of blank, standard deviation / error etc).\nResponse：\nWe are grateful for your valuable comment. To address this, we wish to clarify that the \"cesium oleate solution\" indeed corresponds to the Cs-oleate solution synthesized in the preceding step. Based on our stoichiometric calculations, its concentration is approximately 0.09 mol/L. We have integrated this important detail into the synthesis procedure to enhance reproducibility. The updated sentence is: \"Then, 0.8 mL of the pre-prepared Cs-oleate solution (0.09 mol/L) was rapidly injected.\"\nThe term \"5 mL of the pre-synthesized NPs supernatant\" in the synthesis step refers to the supernatant collected after the NPs were redispersed in 5 mL of cyclohexane, subjected to ultrasonic dispersion, and allowed to settle. This corresponds to the material state described in the preceding step: \"The purified NPs were finally redispersed in 5 mL of cyclohexane for subsequent shell growth.\" The supernatant concentration after dispersion was determined to be approximately 0.14 mol/L. This value has been added to the Supporting Information (page 4, line 1) and is marked in yellow for your review. To guarantee batch-to-batch comparability, all syntheses are conducted under rigorously identical conditions.\nPLQY measurements were conducted on an Edinburgh Instruments FLS-1000 fluorescence spectrometer. The system was configured with an SM4 integrating sphere for light collection and employed a 150 W continuous-wave xenon lamp as the excitation source. The test samples were prepared by dispersion in cyclohexane, and the baseline was established using a blank reference cuvette filled with an equivalent volume of pure cyclohexane. This methodology ensures accurate photon counting for PLQY calculation by accounting for solvent scattering and absorption. A comprehensive description of this procedure can be found on Page 8 of the Supplementary Information, with the relevant text highlighted for easy identification.\nComment 3: Quantum cutting is represented in Scheme 1 (right) as taking place for the PeQD host to Yb energy transfer. If that was the case, a more than 100% QY would be expected for the Yb3+ emission in a control sample that consists of PeQDs:Yb. The author mention this in their response letter and Figure a therein. This data and discussion should be provided in the manuscript (or SI).\nResponse：\nThank you for your insightful feedback. As recommended, we have added a discussion on the Yb-doped PeQDs that exhibit a PLQY exceeding 100% to the Supplementary Information (Supplementary Note 1 in page 9), and provide clear explain in the yellow-highlighted section on page 6 of the manuscript. The added text has been highlighted for your convenience.\nComment 4: Counts axis in all size distribution plots should include values to indicate how many NPs were subjected to size analysis (Fig S1 and elsewhere).\nThe size distribution for the PeQDs in Fig S23 seems to have a too small standard deviation. Looking at the obvious size variations in the TEM image and the broadness of the histogram (from 8 to 15 nm), a standard deviation of 0.17 nm seems not to be realistic. Is this indeed the standard deviation or rather the error of the fit? Same for the other histograms in Fig. S23 (and elsewhere across the manuscript / SI): standard deviations seem to be too small for the histograms given.\nScale bars are missing in the HRTEM plots in Fig S1 and elsewhere.\nResponse: Thank you for your keen observation and valuable suggestions. The error value in the previous size distribution histogram represented the Gaussian fitting deviation. We apologize for any confusion this may have caused. The graph has now been updated to indicate the actual size deviation, and following your suggestion, the vertical axis has been revised to display the number of nanoparticles measured. Furthermore, scale bars have been added to the HRTEM images. We welcome your review of these revisions.\nComment 5: Reference numbers for XRD patterns are provided in Fig S2 and S16 but the chemical composition and phase of these references are missing. Fig S10 mentions a reference card but not reference data are added to the plot.\nResponse: Thank you for your suggestion. The sample characterized in Figure S2 and S16 has the composition NaYF : Yb3+, Ln3+@NaYF (Ln = Ho, Er, Tm, Ce) and 4 4 PeQD -NaYF : Yb3+, Ln3+@NaYF (Ln=Ho, Er, Tm, Ce) heterostructure, respectively. Yb 4 4 Due to the length of the formula, an abbreviation is used in the figure for clarity. The full chemical details are provided in the accompanying notes. The samples in Figure S2 all exhibit a hexagonal crystal structure. Please also note that the heterostructure in Figure S16 is composed of cubic-phase CsPbCl Br : Yb3+ and hexagonal-phase 1.5 1.5 NaYF : Yb3+, Ln3+@NaYF (Ln=Ho, Er, Tm, Ce). These details are now provided in 4 4 the updated annotations.\nFurthermore, we have included the standard reference card in Figure S10, as shown below (Figure R4). Please see the revised manuscript.\nFigure R4 (Figure S10). X-ray powder diffraction patterns (XRD) for CSSS (NaYF : 4 6% Ho3+, 20% Yb3+, 6% Ce3+@NaYF : 5% Er3+, 35% Yb3+, 4% Ce3+@NaYF : 0.6% 4 4 Tm3+, 25% Yb3+@ NaYF ). 4\nComment 6: It is suggested to tone down the wording in the abstract:\nWhat is meant by quantum-engineering? “unprecedented absorption bandwidth (200–690 nm) across the UV-visible spectrum, 27 enabling efficient excitation at sub-microwatt levels (50 μW cm-2).”: At 50uW cm-2, the emission cannot be called efficient. It is barely visible in the provided PL spectrum. Indeed, most spectra shown were obtained at power densities that are orders of magnitudes higher, including the gas sensing. At what power density were the reported QY values obtained? This statement in the abstract is miss-leading.\nResponse:\nThank you for this insightful feedback. In this study, \"quantum-engineering\" denotes the mechanism we proposed that facilitates efficient energy transfer within the heterostructure via a quantum cutting process. To prevent any potential confusion, we have replaced the term with \"quantum cutting-engineering\" for greater precision. The revision is highlighted on page 2, line 7 of the revised manuscript.\nWe agree with the comment that the emission at 50 µW cm-2 could not be described as efficient and have therefore revised the abstract accordingly. The updated text now states: \"The designed heterostructure exhibits an unprecedented absorption bandwidth (200–690 nm) across the UV-visible spectrum, with an exceptionally low stimulation threshold at the sub-microwatt level (50 µW cm-2).\" This revision can be found in the abstract on page 2, lines 9–11.\nAs noted in our response to Question 2, the PLQY was measured under a 365 nm power density of ~200 mW cm-2. This differs from the lower power spectral tests due to the use of different, specialized instruments. The PLQY system's light source operates at this fixed power. Crucially, the linear nature of the luminescence ensures that the reported PLQY is independent of this excitation power.\nComment 7: The introduction should not ignore previous work on Ln-NPs that demonstrated Tm and Ho emission at 1400 and 2000 nm, respectively.\nResponse: Thank you for this valuable suggestion. We agree that prior studies on Ln-doped nanoparticles (Ln-NPs) featuring emissions at ~1400 nm and ~2000 nm are important to contextualize our work. Accordingly, in the Introduction (page 3, line 21), we have integrated a discussion on the ~1460 nm emission of Tm³⁺ and the ~2000 nm emission of Ho³⁺, supported by appropriate citations, to provide a more comprehensive research background. These additions are now available for your review.\nThe Reviewer #4\nI did notice that the README includes non-English text and does not provide a detailed explanation of the workflow.\nResponse: Thank you for your thorough review of the code. We have updated all non-English text to English to enhance accessibility for international readers. The code remains accessible via the original link.\nThe details of a point-by-point response to the editor and reviewers were listed below:\nThe reviewer #3\nComment 1: The dissolution of the QDs upon enbedding into the Ln:NaYF4 seems not to be mentioned. This might have an affect on ion distribution and consequently energy transfer. Mentioning would make the reader aware of it.\nResponse: Thank you for your valuable suggestions. We agree with your observation that PeQD dissolution alters ion distribution. In our original manuscript, the dissolution of PeQD during heterogeneous structure formation is described (page 8, lines 26-28). The released ions (Cs, Pb, Cl, Br) share similar valence and ionic size with atoms in the NaYF shell, which could result in partial site occupancy (e.g., Cs at Na sites, Cl/Br at 4 F sites, Pb at Ln sites). While such substitution is possible, XRD confirms no significant lattice distortion or new phase formation. Additionally, these ions lack energy levels. Thus, the ion redistribution does not impact energy transfer within the composite. This is explained in the main text (page 9, lines 18–20), as follows: The XRD results jointly confirm the superior crystalline quality of the heterostructure nanoparticles, showing only the PeQD and NaYF : Yb3+, Ln3+ phases with no additional phases detected Yb 4 (Figure S17).\nComment 2: \"Supernatant\" in the SI lines 82 and 91 seems to be the wrong word to me. A supernatant would be the nanomaterial-free solvent after NPs have been precipitated. I believe the authors mean the concentration of the nanomaterial dispersion.\nResponse：\nWe are grateful for your valuable comment. Following your observation, we have revised the three instances of the term “Supernatant” in the Supplementary Information to “solution”, as it refers to the solution used to disperse NPs at a specific concentration. The revisions are made at: Page 3, line 23; Page 4, line 1; and Page 5, line 8. For ease of review, these changes are highlighted in yellow.\nComment 3: Figure S8 misses a scale bar.\nResponse：Thank you for your review. We have incorporated a scale bar into Figure S8, as shown below for your reference."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The article in its present form is much improved with respect to its previous edition. All my concerns have been well addressed or explained. I recommend it for publication without further change.", "reviewer_2": "The authors have addressed my comments clearly and satisfactorily. The revised manuscript is scientifically sound, well-structured, and makes a valuable contribution to the field. I recommend it for publication in this journal.\nBest Regards,\nF. Enrichi", "reviewer_3": "I thank the authors for the detailed revisions and replies provided. While this has significantly improved the clarity of the manuscript, some aspects remain unclear and require further revision prior to consideration of the manuscript for publication.\n1. Discrepancy and contradiction between NP architecture schemes and data\nThe manuscript introduces the NP architecture as PeQD:Yb core / NaYF4:Ln shell / NaYF4 shell, which is in agreement with the schematic in Figure S23. However, this is not in agreement with the left scheme in Scheme 1, which shows PeQDs embedded in a matrix of NaYF4:Ln with an undoped NaYF4 shell. HRTEM images in Fig. 2 indeed support the schematic of Scheme 1, yet not that of the general description nor the schematic in Fig. S23.\nScheme 1 further shows an unclear schematic for the zoom-in: it appears as a hollow NaYF4:Ln shell with multiple PeQDs inside.\nThe schematic in Fig 2a shows something different again: a core with multiple PeQDs in an unlabelled matric, an inner NaYF4:Ln shell and an outer undoped NaYF4 shell.\nThe schematics in Fig 2a and 2f are not in agreement with the data shown in Fig.2: The schematics show core/shell/shell architecture. The data were obtained on core/shell (based on the figure caption). Also, with respect to the discussion of that figure at Page 10, line 242: The addition of an outer undoped shell is described. Subsequently, the description of data shown in Fig 2 seem to revolve around samples prior such addition of the undoped shell. This is confusing.\nScheme in Fig 4f is miss-leading as it depicts a clear core/shell boarder between PeQDs and NaYF4:Ln (based on discussion and data, the PeQDs rather seem to be embedded into a NaYF4:Ln matrix.\nAnother example for confusion between description, schemes, and data: Page 10, Line 224: Why is Er primarily located in the shell? Based on the description provided above, the shell is supposed to be undoped.\nOverall, this is very confusing, and the authors are encouraged to check and revise schematics and descriptions for better clarity.\nIn addition, it is not clear how multiple PeQDs can fit within the given core matrix. For instance, Fig S23: The PeQDs are shown to be ca. 11 nm in size. After first “shelling”, the size is 21 nm. How many PeQDs are embedded in the NaYF4:Ln matrix? What is the size of the PeQDs after possible shelling-induced dissolution?\nEDS maps are not showing clear localized elemental distributions that would support QD elements in the core of the overall architecture.\n2. Experimental details\nExperimental details still lack information required to reproduce the experiments. For instance:\n“Then 0.8 mL of cesium oleate solution was rapidly injected.” - What is the concentration of the Cs oleate solution? Providing the volume alone will not allow the reader to reproduce the synthesis.\n“5 mL of the pre-synthesized NPs supernatant” - What is meant by NPs supernatant? What is the mg/mL concentration of NPs in that supernatant?\nExperimental details about the QY measurements are missing (instrumentation, setting, power density, choice of blank, standard deviation / error etc).\n3. Quantum yield\nQuantum cutting is represented in Scheme 1 (right) as taking place for the PeQD host to Yb energy transfer. If that was the case, a more than 100% QY would be expected for the Yb3+ emission in a control sample that consists of PeQDs:Yb. The author mention this in their response letter and Figure a therein. This data and discussion should be provided in the manuscript (or SI).\n4. Size distribution histograms and HRTEM images\nCounts axis in all size distribution plots should include values to indicate how many NPs were subjected to size analysis (Fig S1 and elsewhere).\nThe size distribution for the PeQDs in Fig S23 seems to have a too small standard deviation. Looking at the obvious size variations in the TEM image and the broadness of the histogram (from 8 to 15 nm), a standard deviation of 0.17 nm seems not to be realistic. Is this indeed the standard deviation or rather the error of the fit? Same for the other histograms in Fig. S23 (and elsewhere across the manuscript / SI): standard deviations seem to be too small for the histograms given.\nScale bars are missing in the HRTEM plots in Fig S1 and elsewhere.\n5. XRD reference patterns\nReference numbers for XRD patterns are provided in Fig S2 and S16 but the chemical composition and phase of these references are missing.\nFig S10 mentions a reference card but not reference data are added to the plot.\n6. Wording in Abstract\nIt is suggested to tone down the wording in the abstract:\nWhat is meant by quantum-engineering?\n“unprecedented absorption bandwidth (200–690 nm) across the UV-visible spectrum, 27 enabling efficient excitation at sub-microwatt levels (50 μW cm-2).”: At 50uW cm-2, the emission cannot be called efficient. It is barely visible in the provided PL spectrum. Indeed, most spectra shown were obtained at power densities that are orders of magnitudes higher, including the gas sensing. At what power density were the reported QY values obtained? This statement in the abstract is miss-leading.\n7. Referencing\nThe introduction should not ignore previous work on Ln-NPs that demonstrated Tm and Ho emission at 1400 and 2000 nm, respectively.", "reviewer_4": "The authors have satisfactorily addressed all AI/ML-related concerns raised in original review. The clarified dataset size, independent test-set accuracy, and detailed description of the random forest hyperparameter with stratification improve the transparency and reproducibility of the analysis.\nThe expanded explanation of feature construction and the updated schematic also made the workflow clearer for the readers. Revisions to moderate the AI claims and the release of code are appreciated. Based strictly on the ML/AI components of the revised manuscript, I find the methodology sound and suitable for publication and recommend as such."}, "author_response": "The details of a point-by-point response to the editor and reviewers were listed below:\nThe reviewer #3\nI thank the authors for the detailed revisions and replies provided. While this has significantly improved the clarity of the manuscript, some aspects remain unclear and require further revision prior to consideration of the manuscript for publication.\nComment 1: Discrepancy and contradiction between NP architecture schemes and data\nThe manuscript introduces the NP architecture as PeQD:Yb core / NaYF4:Ln shell / NaYF4 shell, which is in agreement with the schematic in Figure S23. However, this is not in agreement with the left scheme in Scheme 1, which shows PeQDs embedded in a matrix of NaYF4:Ln with an undoped NaYF4 shell. HRTEM images in Fig. 2 indeed support the schematic of Scheme 1, yet not that of the general description nor the schematic in Fig. S23.\nScheme 1 further shows an unclear schematic for the zoom-in: it appears as a hollow NaYF4:Ln shell with multiple PeQDs inside.\nThe schematic in Fig 2a shows something different again: a core with multiple PeQDs in an unlabelled matric, an inner NaYF4:Ln shell and an outer undoped NaYF4 shell.\nThe schematics in Fig 2a and 2f are not in agreement with the data shown in Fig.2: The schematics show core/shell/shell architecture. The data were obtained on core/shell (based on the figure caption).\nAlso, with respect to the discussion of that figure at Page 10, line 242: The addition of an outer undoped shell is described. Subsequently, the description of data shown in Fig 2 seem to revolve around samples prior such addition of the undoped shell. This is confusing.\nScheme in Fig 4f is miss-leading as it depicts a clear core/shell boarder between PeQDs and NaYF4:Ln (based on discussion and data, the PeQDs rather seem to be embedded into a NaYF4:Ln matrix.\nAnother example for confusion between description, schemes, and data: Page 10, Line 224: Why is Er primarily located in the shell? Based on the description provided above, the shell is supposed to be undoped.\nOverall, this is very confusing, and the authors are encouraged to check and revise schematics and descriptions for better clarity.\nIn addition, it is not clear how multiple PeQDs can fit within the given core matrix. For instance, Fig S23: The PeQDs are shown to be ca. 11 nm in size. After first “shelling”, the size is 21 nm. How many PeQDs are embedded in the NaYF4:Ln matrix? What is the size of the PeQDs after possible shelling-induced dissolution?\nEDS maps are not showing clear localized elemental distributions that would support QD elements in the core of the overall architecture.\nResponse: Thank you for your valuable suggestions. We have addressed the various points raised in Question 1 and provided detailed responses below:\n(a) The manuscript introduces the NP architecture as PeQD:Yb core / NaYF4:Ln shell / NaYF4 shell, which is in agreement with the schematic in Figure S23. However, this is not in agreement with the left scheme in Scheme 1, which shows PeQDs embedded in a matrix of NaYF4:Ln with an undoped NaYF4 shell. HRTEM images in Fig. 2 indeed support the schematic of Scheme 1, yet not that of the general description nor the schematic in Fig. S23.\nResponse (a):\nThank you for your meticulous observation and critical comment regarding the consistency of the nanostructure architecture across the manuscript, schematics (Scheme 1 and Figure S23), and HRTEM characterization. The designed heterostructure is precisely defined as multiple small PeQD:Yb nanocrystals as the core → NaYF :Ln shell (functional shell) → outermost undoped NaYF 4 4 shell (passivation shell). This architecture is the core design throughout our study, and the HRTEM images in Figure 2 directly support this structure. To eliminate potential ambiguity, we have revised the structural description from the original “core-shell” to “multi-PeQDs embedded in NaYF :Ln”. We revised this structure 4 designation to PeQDs- NaYF :Ln heterostructure, which more intuitively reflects 4 the spatial distribution of multiple PeQD core within the NaYF :Ln shell, avoiding 4 misinterpretation of a single-core configuration.\nWe recognized that the original Figure S23 was overly simplified and failed to reflect the \" PeQDs- NaYF :Ln heterostructure + undoped NaYF shell\" structure. 4 4 To address this, we have redrawn Figure S23, with the updated model shown in Figure R1.\nFigure R1 (Figure S23). (a-e) TEM characterization images of each layer in the PeQD -CSSS structure (CsPbCl Br : Yb3+-NaYF : 6% Ho3+, 20% Yb3+, 6% Yb 1.5 1.5 4 Ce3+@NaYF : 5% Er3+, 35% Yb3+, 4% Ce3+@NaYF : 0.6% Tm3+, 25% Yb3+@ NaYF ). 4 4 4 Corresponding structural schematics are provided, along with quantitative data including layer thickness, size distribution, and standard deviation. Notably, Figure b does not specify shell layer thickness due to the disordered nature of the PeQD -C Yb composite formation process. In this system, PeQDs are randomly distributed throughout the NaYF matrix, analogous to watermelon seeds in a fruit, without 4 forming a well-defined interfacial boundary. Consequently, a distinct shell thickness cannot be determined.\n(b) Scheme 1 further shows an unclear schematic for the zoom-in: it appears as a hollow NaYF4:Ln shell with multiple PeQDs inside. The schematic in Fig 2a shows something different again: a core with multiple PeQDs in an unlabelled matric, an inner NaYF4:Ln shell and an outer undoped NaYF4 shell.\nResponse (b):\nWe sincerely appreciate the reviewers for pointing out the inaccuracies in our manuscript and deeply regret these oversights. We have revised the zoom-in section to explicitly show multiple PeQD:Yb nanocrystals embedded in a continuous NaYF :Ln 4 functional shell (not a hollow shell). The “unlabeled matrix” was intended to represent the NaYF :Ln functional shell but lacked explicit labeling, leading to ambiguity. We 4 have now clearly labeled this region as “NaYF :Yb3+, Ln3+” to eliminate confusion. 4 Following your helpful suggestion, we have revised the figure, and the updated version (Figure R2) is submitted for your kind review.\nFigure R2. Figure 2 in the manuscript.\n(c) The schematics in Fig 2a and 2f are not in agreement with the data shown in Fig.2: The schematics show core/shell/shell architecture. The data were obtained on core/shell (based on the figure caption). Also, with respect to the discussion of that figure at Page 10, line 242: The addition of an outer undoped shell is described. Subsequently, the description of data shown in Fig 2 seem to revolve around samples prior such addition of the undoped shell. This is confusing.\nResponse (c):\nWe acknowledge the reviewer's attention to detail regarding the XPS sample. The data presented in Figure 2 (including XPS, TEM, and optical characterizations) were acquired from the intermediate CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ 1.5 1.5 4 heterostructure (without the outer undoped NaYF shell). This decision was based 4 on two key reasons: first, the outermost undoped NaYF passivation shell (≈4 nm) 4 would significantly obscure the spatial distribution of PeQDs and Er/Yb/Ce in electron microscopy characterizations (e.g., EDS mapping resolution would be compromised, making it impossible to distinguish Er signals from the NaYF :Yb3+, 4 Ln3+ functional shell vs. background). Comparative TEM images (Figure R3) demonstrate that the intermediate structure avoids this shielding effect, enabling clear visualization of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ interface and 1.5 1.5 4 element distribution. Second, this approach ensures analytical consistency across all techniques. Characterizing the intermediate structure is sufficient to verify the core objective—successful formation of the CsPbX : Yb3+-NaYF : Yb3+, 3 4 Ln3+@NaYF NPs. The outermost passivation shell is a subsequent optimization 4 step (for stability/luminescence efficiency) that does not alter the elemental distribution or interface properties.\nThe original schematics in Figure 2a and 2f were intended to illustrate the complete synthetic route of our final optimized sample (CsPbCl Br : Yb3+-NaYF : Yb3+, 1.5 1.5 4 Er3+, Ce3+@NaYF ), but we failed to clearly distinguish it from the actual tested 4 sample (CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+) in the initial version. 1.5 1.5 4 We have updated the schematics in Figure 2a and 2f to accurately represent the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ structure of the samples used for the 1.5 1.5 4 tests in Figure 2. On Page 9, Line 22-26, we have clarified the timeline of sample preparation and testing: “Since the inert NaYF coating can obscure the resolution 4 of the PeQD, characterization was performed on uncoated CsPbCl Br : Yb3+- 1.5 1.5 NaYF : Yb3+, Er3+, Ce3+ NPs (Figure S11-12). The addition of an outer undoped 4 NaYF shell was a subsequent optimization step to enhance material stability and 4 luminescence efficiency. The data presented in Figure 2 were obtained from the intermediate heterostructure samples prior to this outer shell modification, aiming to validate the successful formation of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, 1.5 1.5 4 Ce3+ heterostructure.”\nFigure R3. TEM morphology comparison between PeQD -NaYF : Er, Yb, Ce@ Yb 4 NaYF and PeQD -NaYF : Er, Yb, Ce.\n(d) Scheme in Fig 4f is miss-leading as it depicts a clear core/shell boarder between PeQDs and NaYF4:Ln (based on discussion and data, the PeQDs rather seem to be embedded into a NaYF4:Ln matrix.\nResponse (d):\nThank you for your perceptive observation and valuable feedback. To clarify, the actual structure of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ component is 1.5 1.5 4 multiple discrete CsPbCl Br : Yb3+ PeQDs uniformly dispersed and embedded 1.5 1.5 within a continuous NaYF :Ln matrix, rather than a separate core-shell 4 configuration with a clear interface. This embedded design is critical to our work, as it enables intimate contact between CsPbCl Br : Yb3+ and the NaYF : Ln 1.5 1.5 4 host—facilitating efficient energy transfer across the heterointerfaces, which is robustly supported by our optical characterization data.\nThe revised Figure 4f removes the “core/shell boundary” and instead uses distinct colors/textures to depict PeQDs as discrete nanodomains embedded within a continuous NaYF :Ln matrix. 4\n(e) Another example for confusion between description, schemes, and data: Page 10, Line 224: Why is Er primarily located in the shell? Based on the description provided above, the shell is supposed to be undoped. Overall, this is very confusing, and the authors are encouraged to check and revise schematics and descriptions for better clarity.\nResponse (e):\nThank you for your perceptive observation and valuable feedback. To clearly demonstrate the formation of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ 1.5 1.5 4 heterostructure, we deliberately used the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, 1.5 1.5 4 Ce3+ intermediate structure (rather than the final CsPbCl Br : Yb3+-NaYF : Yb3+, 1.5 1.5 4 Er3+, Ce3+@ NaYF architecture) for the characterization in Figure 2 (including 4 TEM, HRTEM, line scanning, EDS mapping, and XPS) as was explained in Response (c).\nThe EDS mapping and line scanning data in Figure 2f clearly confirm that Er is concentrated in the NaYF :Er,Yb,Ce layer for CsPbCl Br : Yb3+-NaYF : Yb3+, 4 1.5 1.5 4 Er3+, Ce3+ heterostructure, which also indicated that the CsPbCl Br : Yb3+ PeQDs 1.5 1.5 were successfully ensembled in NaYF :Ln matrix. The original contradiction arose 4 from failing to state the measured sample is CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, 1.5 1.5 4 Ce3+ heterostructure.\nThe updated Figure 2a has placed particular emphasis on the measured sample (CsPbCl Br :Yb-NaYF₄: Er,Yb,Ce heterostructure). Please refer to the updated 1.5 1.5 Figure 2.\n(f) In addition, it is not clear how multiple PeQDs can fit within the given core matrix. For instance, Fig S23: The PeQDs are shown to be ca. 11 nm in size. After first “shelling”, the size is 21 nm. How many PeQDs are embedded in the NaYF4:Ln matrix? What is the size of the PeQDs after possible shelling-induced dissolution?\nEDS maps are not showing clear localized elemental distributions that would support QD elements in the core of the overall architecture.\nResponse (f):\nThank you for your valuable suggestions. Our experimental results reveal that during the formation of the CsPbCl Br : Yb3+-NaYF : Yb3+, Er3+, Ce3+ structure, 1.5 1.5 4 significant dissolution of CsPbCl Br : Yb3+ PeQDs occurs, accompanied by a 1.5 1.5 clear morphological evolution from well-defined quadrilateral shapes to various irregular forms, as shown in Figures 2b1–b3. This morphological alteration precludes accurate size assessment of the PeQDs. Measurements indicate that the PeQDs embedded within the NaYF : Ln matrix have sizes ranging from 1.9 to 5.2 4 nm. Moreover, during electron microscopy characterization, we observed that not all PeQDs could be fully visualized, as illustrated in Figure R3. As a result, it is not feasible to quantitatively determine the number of PeQDs encapsulated within the NaYF : Ln matrix. 4\nThe spatial resolution of EDS mapping is compromised in the CsPbCl Br : Yb3+- 1.5 1.5 NaYF : Yb3+, Er3+, Ce3+ structure due to the extremely small inter-particle spacing 4 and high density of the PeQDs. Under these conditions, the electron beam interaction volume and secondary fluorescence effects generate extensive false signals and artifacts. These phenomena introduce pronounced false signals and artifacts around the actual elemental locations, thereby obscuring the local elemental distribution in the EDS maps.\nComment 2: Experimental details still lack information required to reproduce the experiments. For instance:\n“Then 0.8 mL of cesium oleate solution was rapidly injected.” - What is the concentration of the Cs oleate solution? Providing the volume alone will not allow the reader to reproduce the synthesis.\n“5 mL of the pre-synthesized NPs supernatant” - What is meant by NPs supernatant? What is the mg/mL concentration of NPs in that supernatant?\nExperimental details about the QY measurements are missing (instrumentation, setting, power density, choice of blank, standard deviation / error etc).\nResponse：\nWe are grateful for your valuable comment. To address this, we wish to clarify that the \"cesium oleate solution\" indeed corresponds to the Cs-oleate solution synthesized in the preceding step. Based on our stoichiometric calculations, its concentration is approximately 0.09 mol/L. We have integrated this important detail into the synthesis procedure to enhance reproducibility. The updated sentence is: \"Then, 0.8 mL of the pre-prepared Cs-oleate solution (0.09 mol/L) was rapidly injected.\"\nThe term \"5 mL of the pre-synthesized NPs supernatant\" in the synthesis step refers to the supernatant collected after the NPs were redispersed in 5 mL of cyclohexane, subjected to ultrasonic dispersion, and allowed to settle. This corresponds to the material state described in the preceding step: \"The purified NPs were finally redispersed in 5 mL of cyclohexane for subsequent shell growth.\" The supernatant concentration after dispersion was determined to be approximately 0.14 mol/L. This value has been added to the Supporting Information (page 4, line 1) and is marked in yellow for your review. To guarantee batch-to-batch comparability, all syntheses are conducted under rigorously identical conditions.\nPLQY measurements were conducted on an Edinburgh Instruments FLS-1000 fluorescence spectrometer. The system was configured with an SM4 integrating sphere for light collection and employed a 150 W continuous-wave xenon lamp as the excitation source. The test samples were prepared by dispersion in cyclohexane, and the baseline was established using a blank reference cuvette filled with an equivalent volume of pure cyclohexane. This methodology ensures accurate photon counting for PLQY calculation by accounting for solvent scattering and absorption. A comprehensive description of this procedure can be found on Page 8 of the Supplementary Information, with the relevant text highlighted for easy identification.\nComment 3: Quantum cutting is represented in Scheme 1 (right) as taking place for the PeQD host to Yb energy transfer. If that was the case, a more than 100% QY would be expected for the Yb3+ emission in a control sample that consists of PeQDs:Yb. The author mention this in their response letter and Figure a therein. This data and discussion should be provided in the manuscript (or SI).\nResponse：\nThank you for your insightful feedback. As recommended, we have added a discussion on the Yb-doped PeQDs that exhibit a PLQY exceeding 100% to the Supplementary Information (Supplementary Note 1 in page 9), and provide clear explain in the yellow-highlighted section on page 6 of the manuscript. The added text has been highlighted for your convenience.\nComment 4: Size distribution histograms and HRTEM images\nCounts axis in all size distribution plots should include values to indicate how many NPs were subjected to size analysis (Fig S1 and elsewhere).\nThe size distribution for the PeQDs in Fig S23 seems to have a too small standard deviation. Looking at the obvious size variations in the TEM image and the broadness of the histogram (from 8 to 15 nm), a standard deviation of 0.17 nm seems not to be realistic. Is this indeed the standard deviation or rather the error of the fit? Same for the other histograms in Fig. S23 (and elsewhere across the manuscript / SI): standard deviations seem to be too small for the histograms given.\nScale bars are missing in the HRTEM plots in Fig S1 and elsewhere.\nResponse: Thank you for your keen observation and valuable suggestions. The error value in the previous size distribution histogram represented the Gaussian fitting deviation. We apologize for any confusion this may have caused. The graph has now been updated to indicate the actual size deviation, and following your suggestion, the vertical axis has been revised to display the number of nanoparticles measured. Furthermore, scale bars have been added to the HRTEM images. We welcome your review of these revisions.\nComment 5: XRD reference patterns\nReference numbers for XRD patterns are provided in Fig S2 and S16 but the chemical composition and phase of these references are missing.\nFig S10 mentions a reference card but not reference data are added to the plot.\nResponse: Thank you for your suggestion. The sample characterized in Figure S2 and S16 has the composition NaYF : Yb3+, Ln3+@NaYF (Ln = Ho, Er, Tm, Ce) and 4 4 PeQD -NaYF : Yb3+, Ln3+@NaYF (Ln=Ho, Er, Tm, Ce) heterostructure, respectively. Yb 4 4 Due to the length of the formula, an abbreviation is used in the figure for clarity. The full chemical details are provided in the accompanying notes. The samples in Figure S2 all exhibit a hexagonal crystal structure. Please also note that the heterostructure in Figure S16 is composed of cubic-phase CsPbCl Br : Yb3+ and hexagonal-phase 1.5 1.5 NaYF : Yb3+, Ln3+@NaYF (Ln=Ho, Er, Tm, Ce). These details are now provided in 4 4 the updated annotations.\nFurthermore, we have included the standard reference card in Figure S10, as shown below (Figure R4). Please see the revised manuscript.\nFigure R4 (Figure S10). X-ray powder diffraction patterns (XRD) for CSSS (NaYF : 4 6% Ho3+, 20% Yb3+, 6% Ce3+@NaYF : 5% Er3+, 35% Yb3+, 4% Ce3+@NaYF : 0.6% 4 4 Tm3+, 25% Yb3+@ NaYF ). 4\nComment 6: Wording in Abstract\nIt is suggested to tone down the wording in the abstract:\nWhat is meant by quantum-engineering?\n“unprecedented absorption bandwidth (200–690 nm) across the UV-visible spectrum, 27 enabling efficient excitation at sub-microwatt levels (50 μW cm-2).”: At 50uW cm-2, the emission cannot be called efficient. It is barely visible in the provided PL spectrum. Indeed, most spectra shown were obtained at power densities that are orders of magnitudes higher, including the gas sensing. At what power density were the reported QY values obtained? This statement in the abstract is miss-leading.\nResponse:\nThank you for this insightful feedback. In this study, \"quantum-engineering\" denotes the mechanism we proposed that facilitates efficient energy transfer within the heterostructure via a quantum cutting process. To prevent any potential confusion, we have replaced the term with \"quantum cutting-engineering\" for greater precision. The revision is highlighted on page 2, line 7 of the revised manuscript.\nWe agree with the comment that the emission at 50 µW cm-2 could not be described as efficient and have therefore revised the abstract accordingly. The updated text now states: \"The designed heterostructure exhibits an unprecedented absorption bandwidth (200–690 nm) across the UV-visible spectrum, with an exceptionally low stimulation threshold at the sub-microwatt level (50 µW cm-2).\" This revision can be found in the abstract on page 2, lines 9–11.\nAs noted in our response to Question 2, the PLQY was measured under a 365 nm power density of ~200 mW cm-2. This differs from the lower power spectral tests due to the use of different, specialized instruments. The PLQY system's light source operates at this fixed power. Crucially, the linear nature of the luminescence ensures that the reported PLQY is independent of this excitation power.\nComment 7: Referencing\nThe introduction should not ignore previous work on Ln-NPs that demonstrated Tm and Ho emission at 1400 and 2000 nm, respectively.\nResponse: Thank you for this valuable suggestion. We agree that prior studies on Ln-doped nanoparticles (Ln-NPs) featuring emissions at ~1400 nm and ~2000 nm are important to contextualize our work. Accordingly, in the Introduction (page 3, line 21), we have integrated a discussion on the ~1460 nm emission of Tm³⁺ and the ~2000 nm emission of Ho³⁺, supported by appropriate citations, to provide a more comprehensive research background. These additions are now available for your review."}, {"round": 3, "reviewer_comments": {"reviewer_3": "The authors have significantly clarified the structure of the materials and the manuscript is ready for publication.\nThere are three minor issues I would leave to the discression of the editorial office (maybe something to adress during proofing):\n1. The dissolution of the QDs upon enbedding into the Ln:NaYF4 seems not to be mentioned. This might have an affect on ion distribution and consequently energy transfer. Mentioning would make the reader aware of it.\n2. \"Supernatant\" in the SI lines 82 and 91 seems to be the wrong word to me. A supernatant would be the nanomaterial-free solvent after NPs have been precipitated. I believe the authors mean the concentration of the nanomaterial dispersion.\n3. Figure S8 misses a scale bar."}, "author_response": "The details of a point-by-point response to the editor and reviewers were listed below:\nThe reviewer #3\nComment 1: The dissolution of the QDs upon enbedding into the Ln:NaYF4 seems not to be mentioned. This might have an affect on ion distribution and consequently energy transfer. Mentioning would make the reader aware of it.\nResponse: Thank you for your valuable suggestions. We agree with your observation that PeQD dissolution alters ion distribution. In our original manuscript, the dissolution of PeQD during heterogeneous structure formation is described (page 8, lines 26-28). The released ions (Cs, Pb, Cl, Br) share similar valence and ionic size with atoms in the NaYF shell, which could result in partial site occupancy (e.g., Cs at Na sites, Cl/Br at 4 F sites, Pb at Ln sites). While such substitution is possible, XRD confirms no significant lattice distortion or new phase formation. Additionally, these ions lack energy levels. Thus, the ion redistribution does not impact energy transfer within the composite. This is explained in the main text (page 9, lines 18–20), as follows: The XRD results jointly confirm the superior crystalline quality of the heterostructure nanoparticles, showing only the PeQD and NaYF : Yb3+, Ln3+ phases with no additional phases detected Yb 4 (Figure S17).\nComment 2: \"Supernatant\" in the SI lines 82 and 91 seems to be the wrong word to me. A supernatant would be the nanomaterial-free solvent after NPs have been precipitated. I believe the authors mean the concentration of the nanomaterial dispersion.\nResponse：\nWe are grateful for your valuable comment. Following your observation, we have revised the three instances of the term “Supernatant” in the Supplementary Information to “solution”, as it refers to the solution used to disperse NPs at a specific concentration. The revisions are made at: Page 3, line 23; Page 4, line 1; and Page 5, line 8. For ease of review, these changes are highlighted in yellow.\nComment 3: Figure S8 misses a scale bar.\nResponse：Thank you for your review. We have incorporated a scale bar into Figure S8, as shown below for your reference."}]

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