Fast self-bleaching Nb2O5-based photochromics for high security dynamic anti-counterfeiting and optical storage applications

Inorganic photochromic (PC) materials have been increasingly recognised as potential candidates for anti-counterfeiting and optical storage applications. However, static and single displays of PC materials in bright and dark fields poses a security threat to the stored information. In this study, a novel PC material, Nb2O5, exhibiting rapid self-bleaching behaviour over time at room temperature, was developed. The colouring-bleaching reversible dynamic processes of this PC material can be demonstrated by visually readable up-conversion (UC) luminescence. The maximum self-recovery level of the PC and UC luminescence was approximately 97.4% and 91.3%, respectively. Inspired by this self-bleaching feature, a new encryption or optical storage method was designed by constructing two-phase composites displaying completely different PC behaviours. The encoded or stored information was recorded using two commercial laser diodes (LEDs) (365 nm and 405 nm). The results suggest that the security level of the composite anti-counterfeiting design improved significantly, and it was superior than that of a traditional single PC material. The discovery of self-bleaching PC materials may promote more innovative designs for future high-security dynamic anti-counterfeiting and optical storage applications.