Multimodal Optical Response of Bi₂SiO₅:Eu³⁺ Phosphor for Visualized X-ray Detection and Reversible Imaging

The development of advanced X-ray-responsive detection materials is essential for ensuring radiation safety and enabling high-precision imaging. Here, we report a Bi₂SiO₅:Eu³⁺ phosphor that exhibits a synergistic multimodal optical response to X-rays, combining radioluminescence, reversible radiochromism, and tunable luminescence modulation within a single material. Upon irradiation, the phosphor undergoes a distinct and reversible color change from white to brown, which correlates linearly with the X-ray dose through a measurable decrease in reflectance. Simultaneously, both its photoluminescence and radioluminescence intensities vary linearly with radiation dose, enabling quantitative optical dosimetry. Spectroscopic and structural analyses reveal that the reversible behavior arises from oxygen-vacancy-mediated color centers, which form without altering the host lattice. Furthermore, a flexible composite film fabricated from Bi₂SiO₅:Eu³⁺ enables multimodal high-resolution (10.3 lp mm^-1) X-ray imaging and direct visual dose readout. This work introduces a promising class of lead-free, multifunctional phosphors and offers mechanistic insight for next-generation intelligent X-ray detection and visualization technologies.