Exploiting the Transformative Features of Metal Halides for the Synthesis of CsPbBr<sub>3</sub>@SiO<sub>2</sub> Core–Shell Nanocrystals
Christian Rossi, Riccardo Scarfiello, Rosaria Brescia, Luca Goldoni, Gianvito Caputo, Luigi Carbone, Diego Colombara, Luca De Trizio, Liberato Manna, Dmitry Baranov
Abstract
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.