Spectral-Transforming Electron-Storage Phosphor Enables Retrospective Dose Visualization and X-ray Memory Dosimetry.

X-ray detection is integral to both medical diagnostics and industrial inspections. Nevertheless, the majority of current systems depend on real-time scintillation readouts, which constrain their application in hazardous environments where immediate on-site operations may pose safety risks. In this study, we present an innovative electron storage phosphor synthesized from trace amounts of europium-doped Sr3MgSi2O8, facilitating flexible, time-lapse X-ray detection through utilization of a radiation memory phenomenon. Upon X-ray irradiation, divalent europium emission centers are generated, leading to a distinct color shift from orange-red (typical of Eu3+) to violet (characteristic of Eu2+). The observed chromatic transition allows a qualitative assessment of radiation exposure, while the ratio of the red to blue intensity (R/B) serves as a quantitative indicator of the absorbed dose. Further investigation reveals that intrinsic traps participate in postirradiation electron transfer and actively promote the valence conversion of europium ions. Using this phosphor, a flexible X-ray memory film is fabricated that is capable of retaining latent images for 10 days and producing clear delayed readouts under UV excitation. The film enables dose-resolved delayed imaging of irregular objects, demonstrating its flexibility, simplicity, and reusability. A valence-conversion-based radiophotoluminescence mechanism is established, offering a promising strategy for developing next-generation X-ray memory dosimetry with visualized and quantitative dose mapping capabilities.