Fast and Reversible Quasi-Solid-State Anion Exchange in Highly Luminescent CsPbX Perovskite Nanocrystals for Dual-Mode Encryption-Decryption.

Solid-state anion exchange method is easy to handle and beneficial to improve stability of CsPbX (X = Cl, Br, I) perovskites nanocrystals (NCs) with respect to anion exchange in liquid phase. However, the corresponding exchange rate is rather slow due to the limited diffusion rate of anions from solid phases, resulting in mixed-halide perovskite NCs. Herein,  a fast and reversible post-synthetic quasi-solid-state anion exchange method in CsPbX NCs with inorganic potassium halide KX salts/polyvinylpyrrolidone (PVP) thin film is firstly reported.