Generation of F centres and hole centres in the nonstoichiometric x-ray storage phosphor BaFBr

After x-irradiation of nonstoichiometric , besides the centre a new intrinsic hole centre was found by electron paramagnetic resonance (EPR). The powder EPR line of this new centre can be simulated assuming an molecule on a fluoride site. The new hole centre is stable at room temperature and is the anti-centre of the centre in the F centre generation process. Magic angle spinning nuclear magnetic resonance (MAS-NMR) experiments on nonstoichiometric show not only resonances of on regular lattice sites, but also resonances which are due to on bromine sites (`fluorine antisites'). There are about 10% fluorine antisites in the nonstoichiometric powder which corresponds to the excess fluorine determined by chemical analysis. The generation of electron trap-hole trap pairs upon x-irradiation originates at the fluorine antisites.