## 3 Results and Discussion
This indicates the occurrence of the yellow phase (\(\delta\)) for the OAm-CsPbI\({}_{3}\) PeQDs, which is also evidenced by the yellow-colored OAm-CsPbI\({}_{3}\) PeQD film (inset in Figure 5a). In contrast, as expected, the XRD pattern of the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs remains completely unchanged with high and sharp peaks (\(\alpha\)-phase CsPbI\({}_{3}\)), as can also be seen from the dark red SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQD film (inset in Figure 5a). This verifies that the storage stability of CsPbI\({}_{3}\) PeQDs is improved by a SiO\({}_{2}\) coating. Figure 5b,c show the evolutional PL spectra of OAm- and SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQD solutions under continuous heating at 100 \({}^{\circ}\)C in air, respectively. For the OAm-CsPbI\({}_{3}\) PeQDs, it can be seen that when the temperature is raised to 100 \({}^{\circ}\)C, the PL intensity decreases immediately and continues to do so as time goes on, with a red shift of 4 nm. After 60 min heating, the PL intensity decreases to 36% of the initial value (Figure 5d). This can be also be observed visually, since the color of the OAm-CsPbI\({}_{3}\) PeQD solution changes from bright red at room temperature to dark brown at 100 \({}^{\circ}\)C (insets in Figure 5b), which can be attributed to the detachment of dynamic capping ligands which introduces more defect-relative nonradiative recombination and leads to the growth of PeQDs [54]. As \begin{table}
\begin{tabular}{c c c c c c c} \hline
**CsPbI\({}_{3}\) PeQDs** & \(\tau_{1}\) **(ns)** & **A\({}_{1}\) (\%)** & \(\tau_{2}\) **(ns)** & **A\({}_{2}\) (\%)** & **\(k_{\text{r}}\) (\(s^{-1}\))** & \(k_{\text{nr}}\) (\(s^{-1}\))** & \(\tau_{\text{avg}}\) **(ns)** \\ \hline
**OAm** & 21.64 & 87.86 & 48.27 & 12.14 & 0.0312 & 0.0047 & 27.91 \\
**SiO\({}_{2}\)** & 22.32 & 81.19 & 41.12 & 18.81 & 0.0348 & 0.0011 & 27.94 \\ \hline \end{tabular}
\end{table} 
Table 1: Fitting and calculated results for the CsPbI\({}_{3}\) PeQDs based on the TRPL in Figure 4c and PLQY. expected, the PL intensity of the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs was almost unchanged in the first 30 min heating at 100 \({}^{\circ}\)C and remained at approximately 87% of the initial intensity after 60 min heating (Figure 5c,d). Furthermore, there was no visible shift in PL spectra. This is also evidenced by the unchanged color of the PeQD solution during the heating (insets in Figure 5c). These results indicate that the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs exhibit a significantly enhanced stability against heating due to the protection of the SiO\({}_{2}\) coating. To evaluate the effect of the SiO\({}_{2}\) coating on the stability of the CsPbI\({}_{3}\) PeQDs against polar solvents, the CsPbI\({}_{3}\) PeQD solutions in hexane were diluted by ethanol (with hexane:ethanol = 10:1). The corresponding evolutional PL spectra were obtained and are shown in Figure 6. It can be shown that after the addition of ethanol, the OAm-CsPbI\({}_{3}\) PeQDs show a significant drop in PL intensity within the initial 5 min and become almost completely quenched at 20 min (Figure 6a,c). At the same time, the corresponding photographs of the OAm-CsPbI\({}_{3}\) PeQD solutions were taken and are shown in Figure 6d. These images show that the OAm-CsPbI\({}_{3}\) PeQDs gradually become light in color and turbid as time increases, and finally turn from a dark red color into a yellow color that does not emit PL any longer (Figure 6e), indicating the occurrence of a non-fluorescent yellow phase, which is consistent with the PL results and previous studies [17]. In great contrast, the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs only show a marginal decrease in PL intensity within the first 5 min and gradually decrease (Figure 6b,c) thereafter. At 40 min, the PL intensity still maintains 79% of the initial value. During the whole process, for the SiO\({}_{2}\)-CsPbI\({}_{3}\) PeQDs, the daylight photographs show no visible change, and the UV photographs indicate a slight decrease in emission (Figure 6d,e), in line with the PL results.