Generation of F centres and hole centres in nonstoichiometric BaFBr X-ray storage phosphors

In the nonstoichiometric X-ray storage phosphor BaF1.1Br0.9 a new intrinsic hole centre was found by electron paramagnetic resonance (EPR). It is the anticentre of the F(Br-) centre with which it is generated simultaneously b y X-irradiation. Bleaching into the F(Br-) band destroys it. From the simul ation of the powder EPR spectrum and the generation mechanism the hole cent re is thought to be an H(F-2,F(-)) centre. Magic angle spinning nuclear mag netic resonance (MAS-NMR) revealed that the F excess in nonstoichiometric B aF1.1Br0.9 is due to F- on Br- sites, i.e. F- antisites. The generation of F(Br-) electron trap-hole trap pairs upon X-irradiation originates at the F - antisites.