Enabling Multicolor Information Encryption: Oleylammonium-Halide-Assisted Reversible Phase Conversion between Cs₄PbX₆ and CsPbX₃ Nanocrystals

Recently, halide perovskites have been recognized for their thermochromic characteristics, showing significant potential in information encryption applications. However, the limited luminescence color gamut hinders the encryption of complex multicolor information. Herein, for the first time, multicolor thermochromic perovskites with luminescence covering the entire visible spectrum have been designed. Oleylammonium halide salts facilitate a reversible phase transformation between nonluminescent Cs₄PbX₆ nanocrystals (NCs) and luminescent CsPbX₃ NCs upon heating or cooling. This process occurs without the need for external addition or removal of ligands or metal salts, enabling efficient and intelligent information encryption. A proof-of-concept demonstration successfully encrypts and decrypts multicolor digital information. This work not only advances the understanding of phase transformations in perovskites but also highlights their significant potential for information encryption applications.