ESR study of samarium doped fluorophosphate glasses for high-dose, high-resolution dosimetry

We have studied the effect of samarium doping concentration and thermal annealing on X-ray induced defect centers, including phosphorus-oxygen hole and electron centers (POHC and POEC), in Sm3+-doped fluorophosphate glasses towards developing a potential high-dose, high-resolution detector for microbeam radiation therapy. ESR measurements show that defect center formation is suppressed by increasing the Sm-dopant concentration with POECs more strongly influenced than POHCs. This can be explained by a model based on the competition between defect center formations and Sm3+ ⇆ Sm2+ interconversion. Thermal annealing at increasing moderate temperatures (TA = 100−300 °C) reduces the POHC related ESR and induced absorbance bands while those of POEC continue to survive. ESR measurements over a wider range show the trace of a very broad ESR signal in samples containing Sm2+ ions including those annealed at temperatures between 350 °C and glass transition temperature (Tg ≈ 460 °C). Finally, thermal annealing at 550 °C (> Tg) totally erases all the ESR signals and restores the sample to its original unirradiated state.