Fast and Reversible Quasi‐Solid‐State Anion Exchange in Highly Luminescent CsPbX3 Perovskite Nanocrystals for Dual‐Mode Encryption–Decryption

Abstract Solid‐state anion exchange method is easy to handle and beneficial to improve stability of CsPbX 3 (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 3 NCs with inorganic potassium halide KX salts/polyvinylpyrrolidone (PVP) thin film is firstly reported. Original morphology of the exchanged NCs is well‐preserved for all samples. Complete anion exchange from Br − to Cl − or I − is successfully achieved in CsPbX 3 NCs within ≈20 min through possible vacancies‐assisted ion exchange mechanism, under ambient conditions and vice versa. Particularly, Br − ‐exchanged CsPbCl 3 and CsPbI 3 NCs exhibit improved optical properties. Encouraged by the attractive fluorescence and persistent luminescence as well as good stability of the resulted CsPbX 3 NCs, an effective dual‐mode information storage–reading application is demonstrated. It is believed that this method can open a new avenue for the synthesis of other direct‐synthesis challenging quantum‐confined perovskite NCs/nanoplates/nanodisks or CsSnX 3 NCs/thin film and provide an opportunity for advanced information storage compatible for practical applications.