Photoluminescence of X-Ray-Generated Sm2+ in Co-Precipitated SrF2:Sm3+ Nanocrystals

We report on X-ray-induced Sm3+ → Sm2+ reduction in SrF2:Sm3+ nanocrystals of ~40 nm size synthesized via a co-precipitation method. Non-irradiated samples show characteristic Sm3+ f-f 4G5/2 → 6H5/2, 6H7/2, 6H9/2, and 6H11/2 emissions, while X-irradiation induces intense low-temperature Sm2+ 5D0 → 7F1 emission and other Sm2+ lines. The evolution of Sm3+ and Sm2+ photoluminescence intensities with X-ray dose (0–300 Gy) follows first-order kinetics, consistent with a trapping–detrapping mechanism. Compared to CaF2:Sm3+, SrF2:Sm3+ exhibits faster Sm3+ reduction due to the higher X-ray absorption cross section of strontium compared to calcium for Cu-Kα (8 keV) radiation, highlighting its potential as a nanoscale X-ray storage phosphor.