Site‐Selective Occupancy of Eu²⁺ toward High Luminescence Switching Contrast in BaMgSiO₄‐Based Photochromic Materials

Abstract Luminescent inorganic photochromics have great potential applications in 3D optical memory due to their excellent thermal stability and chemical resistance. Nevertheless, constructing inorganic photochromics with a high luminescence switching contrast remains challenging for optical information storage. Understanding inherent relationships between microenvironment changes, photophysical material properties, and rational control of their luminescence properties are crucial to address these issues. This paper proposes an effective strategy to significantly improve the luminescence switching contrast by more than 300% by site‐selective occupancy engineering on BaMgSiO₄:Eu²⁺ photochromic materials. An effective energy transfer process is established between luminescent and photochromic units, which may provide new insights for designing high‐performance optical storage systems. The fabricated flexible films exhibit excellent waterproof, flexibility, and stretchability characteristics, accompanied by reversible color switching and larger color contrast. Optical data storage can be not only visually encoded and decoded on the flexible films by 405 and 532 nm LED excitation, respectively. Writing, erasing, and reading strategies for flexible films are particularly suitable for complex application environments in optical storage and rewritable flexible devices.