Tungstate Multifunctional Photochromic Material for Unlimited Optical Information Storage: Using Alkaline Earth Metal Ions to Regulate Photochromic Effect

ABSTRACT Photochromic (PC) materials have attracted considerable interest due to their promising applications in erasable optical storage, where long‐term stability is a critical requirement. In this work, a series of (Ca,Sr)WO 4 :0.5%Bi 3+ PC solid solutions were synthesized at different temperatures, and their PC behavior was systematically investigated. The PC performance can be tuned by adjusting the ratio of Sr 2+ and Ca 2+ in the (Ca,Sr)WO 4 :0.5%Bi 3+ materials. The introduction of Sr 2+ can significantly enhance the PC effect of the CaWO 4 :0.5%Bi 3+ material until its concentration reaches 75%, and it has a reverse effect when the concentration reaches 90%. Furthermore, flexible PC films were fabricated to demonstrate practical optical information storage, exhibiting stable data retention without external stimuli. On the basis of the reversible PC behavior, an encrypted disk architecture was further designed to realize unlimited optical information storage by selectively encoding and reading information from different concentric rings. This work provides a feasible strategy for regulating photochromism through alkaline earth metal ion engineering and offers a new platform for high‐security optical storage and encryption applications.