1 and 2, the PL was recorded at 10-min intervals, and the findings are illustrated in Figure . In the dark, the CsPbBr3 NCs decomposed by ~50% in both low and high EtOH concentrations after 30 min. When exposed to light for 30 min, CsPbBr3 underwent significant degradation, reaching 85% and 100% decomposition in Sol. 1 and 2, respectively. Interestingly, Cs4PbBr6 NCs displayed a mere 20% decomposition in darkness across both solutions. Furthermore, when illuminated for 30 min, Cs4PbBr6 decomposed by only 35% and 45% in Sol. 1 and 2, respectively. This observation suggests that Cs4PbBr6 decomposes at a slower rate compared to CsPbBr3 in polar solvents. The decomposition process of the NCs is discussed in detail in the subsequent EPR section. According to the optical absorption, TEM, and XRD, the NCs exhibit similar behavior in Sol. 1 and toluene. Thus, we consider only Sol.1 and 2 (and not toluene) for further discussion.