# Phonon Involved Photoluminescence of Mn 2+ Ions Doped CsPbCl 3 Micro-Size Perovskite Assembled Crystals

Jialiang Gao, Yangyang Guo, Xiuhai Zhang, Lu Liu, Huixin Li, Zeyi Cheng, Peng Liu, Fan Dong, Jiandong Wu, Taihong Liu, et al.

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Jialiang Gao, Yangyang Guo, Xiuhai Zhang, Lu Liu, Huixin Li, et al. Phonon Involved Photoluminescence of Mn 2+ Ions Doped CsPbCl 3 Micro-Size Perovskite Assembled Crystals. Advanced Science, 2025, 12, 10.1002/advs.202413402. hal-05396882

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# Phonon Involved Photoluminescence of Mn²⁺ Ions Doped CsPbCl₃ Micro-Size Perovskite Assembled Crystals

Jialiang Gao, Yangyang Guo, Xiuhai Zhang, Lu Liu, Huixin Li, Zeyi Cheng, Peng Liu, Fan Dong, Jiandong Wu, Taihong Liu, Huaming Sun, Miao Zhang,* Hervé Aubin, Hongyue Wang,* and Hongqiang Wang*

Mn²⁺ ions doped CsPbCl₃ perovskite nanocrystals (NCs) exhibit superiority of spin-associated optical and electrical properties. However, precisely controlling the doping concentration, doping location, and the mono-distribution of Mn²⁺ ions in the large-micro-size CsPbCl₃ perovskite host is a formidable challenge. Here, the micro size CsPbCl₃ perovskite crystals (MCs) are reported with uniform Mn²⁺ ions doping by self-assembly of Mn²⁺ ions doped CsPbCl₃ perovskite NCs. The electron-phonon coupling strength is enhanced in the perovskite self-assembled CsPbCl₃ MCs, which remarkably accelerates the PL decay of Mn²⁺ ions in room temperature. Furthermore, the phonon-involved PL emission splits to two peaks at low temperature of 80 K, due to the phonon emission and absorption-induced energy exchange for exciton recombination in Mn²⁺ ions. These findings not only demonstrate a novel material system but also introduce a new theoretical framework for phonon-modulated PL manipulation in Mn²⁺-doped perovskite materials.

## 1. Introduction

Magnetic-ion-doped perovskite nanocrystals (NCs) have shown potential in application such as spintronic,[1,2] bioimaging,[3] information storage,[4] and anti-counterfeiting,[5] owing to their superior dopant-associated optical and electrical properties.[6] In particular, Mn²⁺ doped perovskite NCs show characteristic PL emission that comes from the electrical d-d transition

of Mn²⁺ ions in the ligand field of host lattice.[7,8] Since the d-d transition of Mn²⁺ is a spin-flip process, the direct exciting in Mn²⁺ ion is spin-forbidden.[9,10] Thus, the excitation of Mn²⁺ dopants (from its states of ⁶A₁ to ⁴T₁) need energy transfer from excited host, then the carrier undergoes spin-flip again to emit feature photon with energy difference between ⁶A₁ and ⁴T₁.[11,12] Since the recombination of the exciton in Mn²⁺ ions needs the spin-flipping, which leads to long PL lifetime in milli-second scale, as well as the phonon involved broadening PL linewidth.[4] Thus, the electron-phonon coupling could affect the carrier kinetic and PL properties of Mn²⁺ dopants and perovskite host. It has been widely demonstrated that perovskites show strong electron-phonon coupling associated PL emission,[13] due to the soft lattice of perovskites, which facilitates strong phonon

vibrations. For instance, strong electron-phonon coupling in perovskite lattice induces the self-trap state that is responsible of the broadening of PL spectrum covering the whole visible window.[1,14] Furthermore, the surface phonon modes dominate the PL linewidth of CsPbBr₃ perovskite NCs, and the size of the perovskite NCs could strongly affect the coupling strength of electron and the surface phonon.[15] Therefore, the strength of electron-phonon coupling is varied in the perovskite NCs in

J. Gao, Y. Guo, X. Zhang, H. Li, Z. Cheng, P. Liu, F. Dong, J. Wu, H. Wang, H. Wang
State Key Laboratory of Solidification Processing
Center for Nano Energy Materials
School of Materials Science and Engineering
Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU)
Xi'an 710072, P. R. China
E-mail: hongyue.wang@nwpu.edu.cn; hongqiang.wang@nwpu.edu.cn

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/advs.202413402

© 2024 The Author(s). Advanced Science published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/advs.202413402

L. Liu, T. Liu, H. Sun
Key Laboratory of Applied Surface and Colloid Chemistry
Ministry of Education
School of Chemistry and Chemical Engineering
Shaanxi Normal University
Xi'an 710119, P. R. China

M. Zhang
Materials Institute of Atomic and Molecular Science
Shaanxi University of Science and Technology
Xi'an 710021, P. R. China
E-mail: zhangmiao@sust.edu.cn

H. Aubin
Department of Nanoelectronics Center for Nanoscience and Nanotechnology (C2N)
CNRS University
Paris-Saclay 91120, France
different dimensions, which also provides a possibility to control the PL emission of Mn²⁺ ions doped perovskite through changing the electron–phonon coupling strength in the perovskite NCs with different size.

Although this size-dependent electron–phonon coupling is of significant interest for developing new method to modulate the carrier kinetic and PL emission of Mn²⁺ ions doped perovskite, the magnetic coupling state of Mn²⁺ ions and the distinct ligand field environment still remarkably affect its PL emission and are hardly distinguished.[7,10] For instance, by increasing the doping concentration, the interaction of two near Mn²⁺ ions are increased to form a magnetic coupling state between Mn²⁺ ions, showing accelerated PL lifetime or even quenched PL emission.[2,16] Moreover, the different locations of Mn²⁺ ions (on the surface or inside of the perovskite NCs) exhibit distinct PL decay due to the different ligand field environment.[4] In the most of cases, the PL emission of Mn²⁺ ions doped perovskite NCs is manipulated by varying the doping concentration or the doping locations.[17,18] However, the competition of substitution between Pb²⁺ and Mn²⁺ ions are fierce during the fast crystallization processes of perovskite NCs, and the self-cleaning of perovskite could squeeze the Mn²⁺ impurity out of the lattice.[2] Therefore, to eliminate the interference from the magnetic coupling state of Mn²⁺ ions and the distinct ligand field environment, studies on the electron–phonon manipulated PL emission of Mn²⁺-doped perovskite NCs need to ensure the exact distribution of Mn²⁺ ions in perovskite NCs of different sizes, particularly across the nano-to-micro scale, which remains a formidable challenge.

Here, we show that the micro-size CsPbCl₃ perovskite crystals (MCs) obtained by self-assembly of Mn²⁺ ions doped CsPbCl₃ perovskite NCs. The MCs exhibit homogeneous distribution of Mn²⁺ dopants same as the CsPbCl₃ perovskite NCs, showing identical PL emission and magnetic coupling state of Mn²⁺ ions with the CsPbCl₃ perovskite NCs at room temperature. We found that the strength of electron–phonon coupling is enhanced in this large size of self-assembled CsPbCl₃ MCs, which remarkably changes the carrier kinetic of Mn²⁺ ions for PL emission, showing accelerated PL decay at room temperature and phonon-involved PL splitting at low temperature of 80 K. These two split PL peaks come from the energy exchange between the free exciton and phonon (phonon absorption and phonon emission) during exciton recombination. This phonon-modulated carrier kinetic pioneers a novel channel to manipulate the PL emission of Mn²⁺ doped perovskite materials.

## 2. Results and Discussion

The Mn²⁺ ions doped CsPbCl₃ perovskite NCs were synthesized through ultrasonication-assisted method,[19,20] See the details in the Experimental Section. Figure S1 (Supporting Information) shows the XPS spectra of CsPbCl₃ NCs with and without Mn²⁺ doping. Figure S1a (Supporting Information) presents the spectrum for Mn²⁺-doped CsPbCl₃ NCs, where a peak at ≈645 eV corresponds to the Mn 2p core levels, confirming Mn²⁺ incorporation. Figure S1b,c (Supporting Information) shows spectra for Pb and Cl, where the peaks for both elements shift slightly in the doped sample compared to the undoped reference. These shifts suggest changes in the local chemical environment due

to Mn²⁺ incorporation and are attributed to the substitution of Pb²⁺ by Mn²⁺ in the crystal lattice. A corresponding schematic illustration of the Mn²⁺-doped CsPbCl₃ is provided in Figure S2 (Supporting Information). Figure S3 (Supporting Information) shows the PL, absorption spectra, and TEM images of the NCs, the characteristic PL emission of Mn²⁺ ions with (photoluminescence quantum yield) PLQY of ≈58.5% can be observed, and the feature band edge of CsPbCl₃ is also shown on the absorption spectrum at wavelength of ≈400 nm.[21,22] The mono-dispersed perovskite NCs show uniform cubic shape with mean size of ≈10 nm, this mono-dispersion of perovskite NCs enables the success of followed self-assembly.[23,24] The NCs contained toluene solution was dropped on a glass substrate, which placed in a petri dish, then immediately encapsulate the petri dish with a plastic bag following with pumping to achieve a vacuum of -0.1 MPa for 120 s, placing the encapsulated petri dish in an oven with a constant temperature of 25 °C to achieve the self-assembled MCs. We carried out the self-assembly processes at room temperature of 25 °C to sustain the same Mn²⁺ ion distribution in the perovskite NCs properly. Because the speed of self-assembly process is not linear to the time batch by batch, and the self-assembly process will be terminated once opening the sample, we thus keep the samples in the oven for over 10 days to make sure the success of self-assembly. (see the details in the Experimental Section). The scheme of the self-assembly process is shown in Figure 1a. Under such condition of low vacuum, a small amount of solvent left on the substrate, forming many small and separated droplets on the glass. In these small droplets, the NCs aggregated and formed perovskite self-assembly gradually under the driven force of increased concentration during the process in oven for over 10 days (Figure S4, Supporting Information).

Figure 1b–e shows the optical, SEM, and TEM images of the self-assembly samples. The sample shows characteristic PL emission of Mn²⁺ ion with orange color (Figure 1b). The assembled MCs are dispersed on glass substrate homogeneously (Figure 1c). The inset in Figure 1c shows that the statistical size distribution of the MCs ranges from 1 to 5 µm. The SEM image of MCs in Figure 1d shows a MCs with cubic size of ≈1.5 µm. From TEM image in Figure 1e, many assembled nanoplates are found in the vicinity of the assembled MCs, owing to the solvent treatment during the TEM sample preparation. The MCs cannot be formed on the copper grid directly, we just wash the self-assembly sample with anti-solvent of toluene or hexene to transfer the MCs from the glass substrate into solution, then followed with typical TEM sample preparation. The perovskite NCs could regrowth or recrystallization during this solvent treatment to generate such nanoplates.[28] To avoid the influence of the regrowth nanoplates, the followed optical characterization is conducted on the MCs samples on glass without any solvent treatments.

Moreover, we measured the Mn²⁺ concentration of NCs and MCs, as shown in Table S1 (Supporting Information), the ratio of Mn²⁺/Pb²⁺ in the NCs and MCs are similar. We highlight here that the superlattice of self-assembled NCs were supposed to be formed in this process based on the references,[23,25] however, we have never observed such superlattice structure from our samples. Thus, in this work, we would like to rigorously define the self-assembly of the NCs as MCs rather than superlattice.[26,27] From Figure 1f–h and Figure S5 (Supporting Information), the PL, XRD, EPR and even PLE data of the NCs are not significantly
<figure><img src="image_3.png" /><figcaption>**Figure 1.** a) Scheme of the self-assembly processes. b–e) The optical image, SEM, and TEM images of self-assembled nanocrystals. Inset: The statistical size distribution of the MCs. f–h) The PL, XRD, and EPR spectra of perovskite NCs and self-assembled MCs.</figcaption></figure>

shifted after assembling to MCs for 10 days, only showing a de-
creased PLQY (≈39%) in self-assembled MCs (Figure S6, Sup-
porting Information) because of the unavoidably increased de-
fects of the perovskite that reduces the energy transfer efficiency
between perovskite host and Mn²⁺ dopants. Therefore, we pro-
pose that the self-assembly processes from NCs to MCs will not
change the component of host perovskite, and the distribution
of Mn²⁺ dopants in such large size of MCs is sustained same
as the perovskite NCs, which is facilitated to study the electron-
phonon coupling involved PL emission of the Mn²⁺ doped MCs.
We need to highlight that the dual PL emission is not related to
the size inhomogeneity, the size distribution of the MCs is a sin-
gle Gaussian distribution in the inset of Figure 1c, if the dual PL
emission is caused by the size inhomogeneity, the corresponding
dual Gaussian distribution for size rather than a single distribu-
tion is needed. The linewidth of XRD signal of self-assembled
MCs at 2θ of ≈32 ° is only slightly narrow by comparing with
that of perovskite NCs, indicating the slight increased grain size
of MCs. To sustain the same Mn²⁺ distribution in MCs, we con-
ducted the self-assembly processes in room temperature, only lo-
cal crystallization could be occurred partially in the MCs during
the 10 days of self-assembly,[29] which might be the reason that
we did not observe the superlattice structure with TEM character-
ization and the linewidth of XRD signal is only slightly narrow.
Notably, we extracted the g factors and hyperfine coupling con-
stants of NCs and MCs, as shown in Figure 1h. NCs exhibit g
factor of 2.004 with hyperfine coupling constant of A<sub>NC</sub> = 8.76

mT, and MCs have g factor of 2.003 with hyperfine coupling con-
stant of A<sub>MC</sub> = 8.87 mT, respectively. Both g factors of NCs and
MCs are closed to 2 and these EPR spectra show typical six hy-
perfine splitting, indicating the Mn<sup>2+</sup> located in the octahedral
environment in perovskite lattice with small g-anisotropy, which
is consistent with literatures.<sup>[30,31]</sup> MCs have slightly larger hy-
perfine coupling constant, which is probably due to the uncoor-
dinated Mn<sup>2+</sup> on the surface of NCs transferring into the inner
of perovskite lattice of MCs after self-assembly, the fully coordi-
nating environment increases the ionicity of Mn<sup>2+</sup> to enlarge the
hyperfine coupling constant.<sup>[32]</sup>

We also conducted the temperature-dependent EPR measure-
ments, as shown in Figure S7 (Supporting Information). NCs
and MCs were measured in hexene solution. NCs show typical
evolution of EPR spectra, only the EPR intensity are decreased
with cooling down the temperature, the g factor and hyperfine
coupling constant are not changed significantly. However, MCs
show ruleless evolution of EPR spectra after the temperature de-
creasing to 270 K, probably because the self-assembled MCs are
disassembled or aggregated in the solution.

To study the electron–phonon coupling involved energy trans-
fer kinetic between host perovskite lattice and Mn²⁺ ions, we
conducted femtosecond transient absorption (TA) experiments.
Since the direct excitation of Mn²⁺ ion is spin-forbidden, only
host perovskite signal can be detected at wavelength of ≈390 nm,
as shown in **Figure 2a,b**. We did not observe the significant dif-
ference on the TA data of NCs and self-assembled MCs, as well
<figure><img src="image_4.png" /><figcaption>**Figure 2.** a,b) TA spectra of perovskite NCs and MCs (probe 380–550 nm). c) TA decay and fitting curves of perovskite NCs and MCs. d) Diagram of excitation, energy transfer, and recombination in Mn²⁺ doped CsPbCl₃. e) TRPL data and fitting curves of Mn²⁺ ions doped perovskite NCs and MCs.</figcaption></figure>

as the decay kinetic spectra (Figure 2c; Table S2, Supporting Information). Therefore, the NCs and self-assembled MCs exhibit almost same carrier kinetic in the host perovskite, the carrier kinetic includes the processes of excitation, recombination in perovskite host and energy transfer from perovskite host to Mn²⁺ dopants, which are corresponded to schematic processes of ①, ②, and ③ in Figure 2d. However, the radiative recombination decay of Mn²⁺ dopants (process of ② in Figure 2d) shows remarkably difference between the self-assembled MCs and NCs, the time-resolved PL (TRPL) data of NCs and self-assembled MCs are shown in Figure 2e. By comparing with NCs, self-assembled MCs show significantly different PL decay that apparently consists of two components of radiative recombination in Mn²⁺ ions, one is faster and the other one is slower than that of NCs.

Since the exciton recombination in Mn²⁺ ions is spin-forbidden, the PL of Mn²⁺ ions typically exhibits mono-exponential decay with lifetime as long as in millisecond when the isolated state Mn²⁺ ions are located in the fully coordinated ligand field of the host lattice.[10] For the as-prepared NCs, some Mn²⁺ ions are located on the surface of NCs, those Mn²⁺ ions are partially coordinated with the perovskite host lattice. Then, in the self-assembled MCs, the NCs are melted and the interfaces are disappeared, which lead to those partially coordinated Mn²⁺ ions becoming fully coordinated inside of the perovskite lattice. Since the specific surface of self-assemble MCs is exponentially decreased by comparing that of perovskite NCs, the concentration of Mn²⁺ ions on the surface of NCs is decreased significantly, and transferring into a completed coordination environ-

ment, leading to the ratio of long lifetime component raises in the PL decay by comparing to the perovskite NCs (Figure 2e). Furthermore, the exciton lifetime of Mn²⁺ ion is independent with the host defect, but more sensitive to the magnetic coupling state of Mn²⁺ ions. As shown in Figure 2e and Table S3 (Supporting Information), the self-assembled MCs also show a fast radiative decay component (0.248 ms) with a heavy weight over 50% by comparing to perovskite NCs. Since we have demonstrated above that the host perovskite lattice and the distribution of Mn²⁺ ions are not changed between NCs and self-assembled MCs, this fast PL decay should not originate from the recombination channel of magnetic coupled Mn²⁺ ions. Super-fluorescence is a characteristic emission with fast radiative decay in self-assembled superlattice, which exhibits coherent photon emission at helium temperature (≈4 K), showing red-shifted emission with narrow linewidth.[23,33,34] Thus, it is also impossible to excite super-fluorescence in the self-assembled MCs in room temperature in this work. Then, excluding the magnetic coupling state of Mn²⁺ ions and the super-fluorescence,[35,36] we propose that the fast decay component of TRPL in Figure 2e might come from the enhanced electron-phonon coupling in the self-assembled MCs, which also induces the accelerated recombination due to the superposed wavefunction between exciton and phonons in the lattice.[35,36]

We need to highlight here that the PL emission of Mn²⁺ ions including peak wavelength, full width at half maximum (FWHM), and intensity are remarkably sensitive to temperature, which hampers the extraction of electron-phonon coupling
<figure><img src="image_5.png" /><figcaption>**Figure 3.** a) CsPbCl₃ phonon band structure. b) CsPbCl₃ phonon density of state. c) The optimized geometry unit for DFT calculation. d) The Boson model fitting curves of host perovskite lattice.</figcaption></figure>

information of the Mn²⁺ ions from the temperature-dependent PL spectra. We thus first studied electron–phonon coupling of the exciton of host perovskite in NCs and self-assembled MCs. We calculated the phonon dispersion and phonon density of state of host CsPbCl₃ perovskite through density functional theory (DFT), as shown in **Figure 3a,b**, and the calculation was conducted based on the geometry optimization from CsPbCl₃ perovskite unit, as shown in **Figure 3c**. The phonon energy of the perovskite lattice is in the range of 0–30 meV, which is consistent with references.[36,37] Then, we conducted temperature-dependent PL measurements of the perovskite NCs and MCs, the PL evolution of host CsPbCl₃ perovskite is shown in **Figure S8** (Supporting Information). Then we extracted the PL FWHM data of the host perovskite from **Figure S8** (Supporting Information), and fitted with Boson model:[14]

$$ \Gamma(T) = \Gamma_0 + \sigma T + \Gamma_{LO} \frac{1}{e^{E_{LO}/k_B T} - 1} \quad (1) $$

where Γ₀represents the phonon emission linewidth of the material at 0K, which is associated with the host lattice scattering properties. σdenotes the exciton-acoustic phonon coupling coefficient. Γₐ is exciton-longitudinal optical phonon coefficient that dominates the linewidth broadening at high temperature. Eₐ is the phonon energy, k<sub>B</sub> represents the Boltzmann constant. T is temperature. The fitting results are shown in **Figure 3d** and **Table 1**. The fitting of PL FWHM data of perovskite NCs contains two regimes of (①: 80–180 K) and (②: 180–300 K). For fitting at low-temperature regime ①, it yields electron–phonon coupling coefficient of Γₐ₁ ≈18.6 meV with phonon energy of Eₐ₁ ≈9.9 meV, while for fitting at high temperature regime ②, it yields electron–

<table><caption>**Table 1.** Boson model fitting data of Mn2⁺ ions doped perovskite NCs and MCs.</caption><thead><tr><th rowspan="2"></th><th colspan="2">NCs</th><th>MCs</th></tr><tr><th>①</th><th>②</th><th>/</th></tr></thead><tbody><tr><td>Γ<sub>0</sub> (meV)</td><td>93.8</td><td>73.5</td><td>73.4</td></tr><tr><td>Γ<sub>LO</sub> (meV)</td><td>18.6</td><td>82.6</td><td>141.8</td></tr><tr><td>E<sub>LO</sub> (meV)</td><td>9.9</td><td>41.0</td><td>16.3</td></tr></tbody></table>

phonon coupling coefficient of Γₐ₂ ≈82.6 meV with phonon energy of Eₐ₂ ≈41.0 meV. In the perovskite NCs, by decreasing temperature, the electron–phonon coupling becomes weak and trends to have coupling to phonons with low energy, which is consistent to the theoretical result from reference,[15] where the size of NCs could significantly affects the electron–phonon coupling. In this work, the size of perovskite MCs is much larger than the size of NCs, the corresponded electron–phonon coupling should be stronger in the MC. For the fitting data of MCs, the fitting yields electron–phonon coupling coefficient of Γₐ₃ ≈141.8 meV with phonon energy of Eₐ₃ ≈16.3 meV. The perovskite MCs exhibits much larger electron–phonon coupling coefficient than that of NCs, even though the evolution of PL FWHM of NCs and MCs are superposed at high-temperature regime (180–300 K). The electron–phonon coupling becomes stronger in the MCs, which might be due to the increased defect density in the MCs or the coherent resonance of the phonons in the MCs.

We also extracted Huang-Rhys factor (S) from the PL FWHM data (Figure S9, Supporting Information). For perovskite NCs, the Huang-Rhys factor of S1 is of ≈0.65, and for self-assembled
<figure><img src="image_6.png" /><figcaption>**Figure 4.** a,b) Temperature-dependent PL of Mn²⁺ ions in perovskite NCs. c,d) Temperature-dependent PL of Mn²⁺ ions in perovskite MCs. Three PL spectra in Figure 4b,d are extracted from Figure 4a,c (indicated by white dash lines) at three measurement temperatures of 275, 155, and 85 K, respectively. e) Scheme of the phonon involved splitting PL emission in Mn²⁺ ions doped perovskite MCs.</figcaption></figure>

MCs, the Huang-Rhys factor of S2 is of ≈1.72, indicating NCs is in the weak electron-phonon coupling regime and self-assembled MCs is in the strong electron-phonon coupling regime,[34] which are consistent with the fitting results from Boson model. Therefore, the observed fast PL decay component in self-assembled MCs in Figure 2e originates from the enhanced electron-phonon coupling.

We further found that the enhanced electron-phonon coupling not only accelerates the recombination rate of exciton of Mn²⁺ dopants, but also remarkably affects its PL emission peak at low temperature. By decreasing the temperature from 300 to 80 K, the PL intensity of Mn²⁺ ion in perovskite NCs is gradually decreased, due to the energy transfer from perovskite host to Mn²⁺ dopant is hindered,[38] as shown in Figure 4b. However, For the self-assembled MCs, the intensity of PL emission at wavelength of ≈600 nm (2.07 eV) is also gradually decreased when the temperature is decreasing from 300 to 180 K, then, two peaks appear at wavelength of ≈520 nm (2.38 eV) and 720 nm (1.72 eV) when the temperature is cooling down below than ≈180 K, as shown in Figure 4c,d. Although CsPbCl₃ NCs has phase transition at 193 K, this phase transition will not affect the emission of Mn²⁺ ion significantly, because the band gap of CsPbCl₃ NCs only changed slightly from 1.969 to 1.973 eV,[40] and the PL emission band of Mn²⁺ ion only depends on its own energy difference of ⁶A₁ to ⁴T₁ rather than the band gap of host lattice. An analogous PL emission splitting is also observed in a different batch of perovskite MCs, as shown in Figure S10 (Supporting Information). Since the defect emission will be suppressed in low temperature due to the activity of electron transition from band to defect is prevented, the defect emission intensity should be decreasing with cooling down temperature.[41] The two splitting PL emission (≈518 and ≈703 nm) intensity are increased with decreasing the temperature, the defect emission could be

excluded. In the perovskite host lattice, Mn²⁺ ions located at the center of octahedral ligand field of Cl. It has been reported that the ligand nuclear distortion occurs in the excited Mn²⁺ ions coordinated ligand field,[8,39] leading to a coordinate shifting on the potential energy minimum between excited state of ⁴T₁ and ground state of ⁶A₁, as shown in Figure 4e. Because the excited state of ⁴T₁ is sensitive to vibronic coupling of perovskite host ligand field, the PL emission from electron transition between ⁴T₁ and ⁶A₁ is remarkably broadening.[1,42] Moreover, Perovskite has been widely demonstrated as a characteristic material with feature of strong electron-phonon coupling, and this electron-phonon coupling can even be enhanced in the self-assembled MCs as we discussed above. Therefore, the phonon energy involved PL emission of Mn²⁺ ions could be observed in the self-assembled MCs. The phonon-coupled PL emission, including both phonon energy emission and absorption-associated electron transitions (green and red arrows, respectively), are depicted in Figure 4e. We found that the two PL peaks (520 and 720 nm) exhibit roughly equal energy difference of ≈0.33 eV relative to free exciton emission of 600 nm, indicating the approximal equal energy exchanging occurs to split the PL emission peak toward high energy and low energy sides simultaneously. Since these two PL peaks are broadening and the electron-phonon coupling is enhanced in the perovskite MCs, we propose that the two PL peaks are originated from strong phonons involved Stokes shift and anti-Stokes shift, respectively, as shown in Figure 4e. Although the typical phonon modes of Mn²⁺ center and the host perovskite lattice are lower than 330 meV, the PL emission could be coupled with many phonons in 80 K in the electron-phonon coupling enhanced MCs, showing extremely broadening linewidth, as well as the large Stokes shift and anti-Stokes shift simultaneously. We also suggest that the further studies should cool down the temperature to lower 4 K, the precise observation of Frank-Condon
effect could give more information referring to the phonon involved PL emission from the perovskite MCs.

**3. Conclusion**

In summary, we presented a method for obtaining large size perovskite crystals with uniform distribution of Mn²⁺ dopants, by manipulating the mono-dispersed perovskite NCs to form self-assembled MCs in micro-size. The self-assembled MCs show same uniform distribution of Mn²⁺ ions in the perovskite host lattice by comparing with the perovskite NCs at room temperature. The results of theoretical calculation and temperature-dependent PL reveal that the MCs exhibits enhanced electron-phonon coupling. We first demonstrated that the enhanced electron-phonon coupling in self-assembled MCs remarkably affects the exciton recombination of Mn²⁺ dopants, showing accelerated PL lifetime in room temperature, as well as the phonon energy involved PL splitting at low temperature of 80 K. This work provides a new approach for manipulating the PL emission of Mn²⁺-doped perovskite NCs and presents a novel finding regarding the phonon-coupled carrier transitions in perovskite NCs

**Supporting Information**

Supporting Information is available from the Wiley Online Library or from the author.

**Acknowledgements**

J.G., Y.G., and X.Z contributed equally to this work. This work was financially supported by the National Natural Science Foundation of China (22372132), the National Key R&D Program of China (2023YFE0206300), the Natural Science Foundation of Shaanxi Province (2023-JC-QN-0153). The authors would like to thank the Analytical & Testing Center of Northwestern Polytechnical University for structure and performance characterizations.

**Conflict of Interest**

The authors declare no conflict of interest.

**Data Availability Statement**

The data that support the findings of this study are available from the corresponding author upon reasonable request.

**Keywords**

electron-phonon coupling, Mn²⁺ ions, perovskite nanocrystals, self-assembly

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