THE INFLUENCE OF OXIDE IMPURITY ON THE GENERATION BY X-IRRADIATION OF F-CENTERS 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 O2- 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.