Radiation induced defects in Sr2B5O9Br:Ce3+ storage phosphor

Radiation induced defects in polycrystalline pure and Ce3+ doped Sr2B5O9Br storage phosphors have been investigated using EPR and optical absorption methods. The EPR of irradiated pure Sr2B5O9Br represents two overlapping spectra in the 335-340 mT range from paramagnetic electron and hole trapping centres, which are stable at room temperature. These centres are attributed to F(Br-) and OBr- centres, i.e. an electron trapped in a bromine vacancy and a hole trapped on an oxygen ion at a bromine site. The 1s → 2p transitions of F(Br-) centres cause the optical absorption band at 560 nm. Another observed absorption band at 365 nm was attributed to the transitions of O- centres. Thus electron and hole trapping in pure Sr2B5O9Br occurs in VBr and OBr2- aggregates, which are created during the synthesis. EPR and optical absorption measurements on Ce3+ doped Sr2B5O9Br reveal similar defects as in pure material. It is very likely that the same defects take part in the processes of thermally and photo-stimulated luminescence