Exploiting the Transformative Features of Metal Halides for the Synthesis of CsPbBr₃@SiO₂ Core–Shell Nanocrystals

The encapsulation of colloidal lead halide perovskite nanocrystals within silica (SiO 2 ) is one of the strategies to protect them from polar solvents and other external factors. Here, we demonstrate the overcoating of CsPbBr 3 perovskite nanocrystals with silica by exploiting the anhydride-induced transformation of Cs 4 PbBr 6 nanocrystals. CsPbBr 3 @SiO 2 core-shell nanocrystals are obtained after (i) a reaction between colloidal Cs 4 PbBr 6 nanocrystals and maleic anhydride in toluene that yields CsPbBr 3 nanocrystals and maleamic acid and (ii) a silica-shell growth around CsPbBr 3 nanocrystals via hydrolysis of added alkoxysilanes. The reaction between Cs 4 PbBr 6 nanocrystals and maleic anhydride is necessary to promote shell formation from alkoxysilanes, as demonstrated in control experiments. The best samples of asprepared CsPbBr 3 @SiO 2 nanocrystals consist of 10 nm single-crystal CsPbBr 3 cores surrounded by 5-7 nm amorphous silica shell. Despite their core-shell structure, such nanostructures are poor emitters and degrade within minutes of exposure to ethanol. The photoluminescence intensity of the core-shell nanocrystals is improved by the treatment with a solution of PbBr 2 and ligands, and their stability in ethanol is extended to several days after applying an additional silica growth step. Overall, the investigated approach outlines a strategy for making colloidal core-shell nanocrystals utilizing the transformative chemistry of metal halides and reveals interesting insights regarding the conditions required for CsPbBr 3 @SiO 2 nanocrystal formation.