## 3 Results and Discussion
Both the red shift in UV-vis and PL spectra signify the increase in particle size caused by the SiO\({}_{2}\) coating, which agrees with the TEM results. Importantly, the full width at half maximum of the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs considerably reduces from 40 nm to 28 nm for the OAm-CsPbI\({}_{3}\) PeQDs, which could be ascribed to the more uniform size distribution of the CsPbI\({}_{3}\) PeQDs due to the SiO\({}_{2}\) coating. Expectedly, the PLQY increases from 89.6% for the OAm-CsPbI\({}_{3}\) PeQDs to 97.5% for the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, as is clear from the improved PL from the UV light photographs (insets in Figure 4b). Together, these results verify that SiO\({}_{2}\) is more effective in passivating surface defects and thus enhancing radiative emission. Figure 4: (**a**) UV-vis absorption spectra; (**b**) PL spectra; and (**c**) the PL decay curves of the OAm-CsPbI\({}_{3}\) and SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs. The insets show the (left) day and (right) UV light photographs of both CsPbI\({}_{3}\) PeQDs. Figure 3: Characterizations for the OAm\(-\) and SiO\({}_{2}\)–CsPbI\({}_{3}\) PeQDs: (**a**) XRD patterns; (**b**) FTIR spectra; (**c**) high-resolution XPS spectra of Si 2p; and (**d**) atomic ratios of I, N, and Si to Pb. To further uncover the origin of the PL enhancement, time-resolved PL (TRPL) spectra were obtained, as displayed in Figure 4c. It can be well described by a biexponential fitting Equation (1). The average lifetimes (\(\tau_{\text{avg}}\)) were calculated using Equation (2) and the fitting data as shown in Table 1. Short-lived \(\tau_{1}\) is related to the recombination by defects and traps, and long-lived \(\tau_{2}\) is related to the radiative recombination, while A\({}_{1}\) and A\({}_{2}\) are the fractional contributions of the decay components [50]. Comparing with OAm-CsPbI\({}_{3}\) PeQDs, the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs have a lower A\({}_{1}\) and a higher A\({}_{2}\), which proves that nonradiative decay is suppressed by the SiO\({}_{2}\) coating, which is beneficial for the recombination of the generated excitons and results in a high PLQY [51]. The radiative and nonradiative components of the total PL decay were further determined using Equations (3) and (4) [52]. The nonradiative decay rate (\(k_{\text{nr}}\)) decreases by 76.6% from 0.0047 s\({}^{-1}\) for OAm-CsPbI\({}_{3}\) PeQDs to 0.0011 s\({}^{-1}\) for SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, while the decay rate (\(k_{\text{r}}\)) increases by 11.5%, from 0.0312 s\({}^{-1}\) for OAm-CsPbI\({}_{3}\) PeQDs to 0.0348 s\({}^{-1}\) for SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs. This result (increase in \(k_{\text{r}}\) and decrease in \(k_{\text{nr}}\)) clearly confirms that the SiO\({}_{2}\) coating on CsPbI\({}_{3}\) PeQDs enables the effective passivation of surface defects and thus enhances the PLQY [51]. \[\text{I(t)}=\text{A}_{1}\exp(-t/\tau_{1})+\text{A}_{2}\exp(-t/\tau_{2}) \tag{1}\]  
\[\tau_{\text{avg}}=\frac{\text{A}_{1}\tau_{1}^{2}+\text{A}_{2}\tau_{2}^{2}}{ \text{A}_{1}\tau_{1}+\text{A}_{2}\tau_{1}} \tag{2}\]  
\[\frac{1}{k_{\text{r}}}=\frac{\tau_{\text{avg}}}{\text{PLQY}} \tag{3}\]  
\[\frac{1}{k_{\text{nr}}}=\frac{\tau_{\text{avg}}}{1-\text{PLQY}} \tag{4}\]  
Subsequently, we investigated the stability of CsPbI\({}_{3}\) PeQDs with 0 and 4 mmol APTES precursor against air, heat, and polar solvent. Figure 5a shows the XRD patterns of the OAm- and SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQD films on glass substrates before and after 7-day storage under ambient air atmosphere. From the XRD pattern of OAm-CsPbI\({}_{3}\) PeQDs, it can be seen that, after 7-day storage under ambient atmosphere, the symmetry is reduced, with the profiles becoming broader, and, importantly, extra diffraction peaks at 22.8, 26.5, and 37.7\({}^{\circ}\), which are marked with a green star (\(\star\)) and are assigned to yellow phase (\(\delta\)) CsPbI\({}_{3}\)[44,53].