Defect‐Engineered Dual‐Mode Photochromism for Reversible Luminescence Modulation and Multifunctional Optical Applications

Abstract Despite significant advances in photochromic luminescent phosphors, selective and reversible luminescence modulation through dual X‐ray and ultraviolet (UV) stimuli remains largely unexplored. Here, a defect‐engineered LiNbO 3 : Bi, Sm phosphor synthesized via high‐temperature solid‐state reaction is reported, exhibiting four synergistic optical functionalities: UV‐induced photochromism, X‐ray‐induced photochromism, photoluminescence, and radioluminescence. For clarity, X‐ray‐induced photochromism/radioluminescence and UV‐induced photochromism/photoluminescence are hereafter abbreviated as XP/RL and UVP/PL, respectively. The material shows reversible white‐to‐red chromatic transitions under 395 nm UV or X‐ray excitation, driven by oxygen vacancy‐mediated color center dynamics. Sm 3 ⁺ emission is selectively modulated by the photochromic state, with up to 67% suppression and 98% recovery, demonstrating high stability and reproducibility. Real‐time and cumulative radiation sensing is enabled via XP, RL, and XP‐modulated PL. In addition, the phosphors are embedded into a flexible polydimethylsiloxane matrix, enabling multi‐modal use as X‐ray imaging and a reconfigurable storage platform. This multifunctional platform offers new capabilities for radiation detection, anti‐counterfeiting, and optical data storage, while advancing the understanding of dual‐mode photochromism in niobate systems.