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

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 LiNbO₃: 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. Sm³⁺ 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.