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 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.