Reversible Photochromism and Multicolor Luminescence Modulation for X‐Ray Detection and Secure Information Encryption

Abstract Conventional X‐ray‐responsive materials face significant limitations including instability, complex processing, low resolution, or single‐mode signaling, which hinder advanced X‐ray detection, imaging, and anti‐counteferting. Addressing these challenges, a comprehensive investigation is conducted on multifunctional Eu ³⁺ ‐doped Gd ₂ SiO ₅ , a material that combines photochromism with radioluminescence and photoluminescence. Through experimental and theoretical analyses, the reversible X‐ray‐induced photochromism (arising from oxygen vacancy‐related color centers) and tunable multicolor emission (from self‐trapped exciton states and Eu ³⁺ transitions) are revealed. These mechanisms enable dual‐mode, linear optical responses to X‐ray dose via dynamic absorption and emission modulation. The optimized phosphor achieves high light yield (47041 photons MeV ⁻¹ ), high spatial resolution, and stability under harsh conditions. Integration into flexible PDMS films facilitates high‐resolution X‐ray imaging devices. Critically, by leveraging intrinsic multicolor luminescence, a prototype of selective information encryption using optical filters and decryption via RGB color channel separation is demonstrated. These findings highlight the versatility of Gd ₂ SiO ₅ :Eu ³⁺ phosphors and their potential to drive innovations in next‐generation X‐ray imaging, sensing, and security technologies.