The influence of oxide impurity on the generation by X-irradiation of F centres in BaFBr

Using magneto-optical and optically detected electron paramagnetic resonance methods, it is shown that in BaFBr single crystals grown using standard procedures the ubiquitous oxide impurity is primarily responsible for the X-irradiation-induced formation of F(Br - ) centres. The bromide vacancy formed to charge compensate O 2- is implicated in the direct trapping of electrons. F(F - ) centres are also produced by irradiation, probably by an exciton collapse process requiring thermal activation. Cross relaxation measurements show that many of the F(F - ) and F(Br - ) centres are spatially correlated, more than expected on statistical grounds. The relevance of these results to the use of rare earth-activated BaFBr materials as storage phosphors is discussed.