Stabilized Multicolor CsPbBr_3-x I _x Nanocrystals via Ca-I Scorpionate Capping for Down-Light Converters

Anion exchange has been recognized as one of the most effective approaches for mediating the spontaneous formation of mixed-halide perovskite nanocrystals (MHPs) with tunable optical properties and color quality. However, the difference in the diffusion capability of halides, specifically between bromide and iodide species, into MHPs makes these materials prone to halide deficiency, which deteriorates their structural integrity and stability. In this work, we studied the surface passivation and composition engineering by introducing a dinuclear calcium-iodide scorpionate complex (CaI_SC) dispersed into different organic solvents such as chloroform, dichloromethane, 1,2-dichloroethane, and acetonitrile, which favor or hinder the I-for-Br exchange process between this ligand and native CsPbBr₃ perovskite nanocrystals (PNCs). By analyzing the CaI_SC content and the nature of the solvent, we are able to efficiently promote halide exchange, also generating an intermediate mononuclear Ca²⁺ complex, favoring Ca²⁺ doping and the diffusion of a high density of iodide species for triggering Pb²⁺ and halide defect compensation. From this strategy, suitable CaI_SC-capped CsPbBr_3-x I _x PNCs active layers were prepared for the fabrication of efficient down-light converters, with operational stability up to 480 h. This contribution offers an alternative for the processing of stable multicolor PNCs with facile modulation of their photophysical properties, making them adequate for the fabrication of future LED technologies.