To substantiate and better understand the decomposition process, we performed an EPR analysis on CsPbBr3 and Cs4PbBr6 NCs in Sol. 1 and 2 with and without illumination (Figure ). Spin trapping EPR spectroscopy effectively detects reactive oxygen species like • OH and O2 •-in biological and chemical contexts despite their short half-lives. Using a spin trap like BMPO, these short-lived radicals can be detected by forming stable adducts. In this study, BMPO was added to the HP-NCs solution for radical detection. An excess amount of BMPO was maintained in both solutions to ensure all produced radicals were effectively trapped. The measurements were performed in the dark and under illumination (by tungsten lamp) at room temperature. To avoid any misinterpretations, we first conducted a series of reference measurements. Specifically, we assessed the rate of radical production in pure solutions (without NCs), and we examined the solutions with the NCs in the dark to understand the effects of solution polarity versus light on the decomposition of the NCs.