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 (SiO2) is one of the strategies to protect them from polar solvents and other external factors. Here, we demonstrate the overcoating of CsPbBr3 perovskite nanocrystals with silica by exploiting the anhydride-induced transformation of Cs4PbBr6 nanocrystals. CsPbBr3@SiO2 core–shell nanocrystals are obtained after (i) a reaction between colloidal Cs4PbBr6 nanocrystals and maleic anhydride in toluene that yields CsPbBr3 nanocrystals and maleamic acid and (ii) a silica-shell growth around CsPbBr3 nanocrystals via hydrolysis of added alkoxysilanes. The reaction between Cs4PbBr6 nanocrystals and maleic anhydride is necessary to promote shell formation from alkoxysilanes, as demonstrated in control experiments. The best samples of as-prepared CsPbBr3@SiO2 nanocrystals consist of ∼10 nm single-crystal CsPbBr3 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 PbBr2 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 CsPbBr3@SiO2 nanocrystal formation.