Water-induced reversible phase transformation between cesium lead halide perovskite nanocrystals enables fluorescent anti-counterfeiting

Abstract

Luminescent materials have been widely used in the field of information security. However, single-mode anticounterfeiting technology with the aid of UV light excitation to generate visible-light emission is rough and easily decrypted. Herein, we build a novel information encryption and decryption technology based on the reversible ON/OFF luminescence of perovskite nanocrystals (NCs) caused by the phase transformation from luminescence-free Cs₄PbX₆ (X = Cl, Br, I) to visible-light-emitting CsPbX₃ NCs. This phase transformation is easily realized by just controlling the water content, where the Cs₄PbBr₆ NCs can be converted to green-emitting CsPbBr₃ NCs under water vapor treatments, and the latter is quickly changed back to Cs₄PbBr₆ NCs by vacuum drying. The water-induced photoluminescence switch is reproducible, stable, and reliable for information encryption and decryption, as demonstrated by inkjet printing patterned films on a glass substrate using the security ink of Cs₄PbBr₆ NCs in cyclohexane solution. Furthermore, each pixel in the patterned film containing confidential information is quite unique in microscopic morphology, enabling multimode anti-counterfeiting if combined with artificial intelligence.