OPTICALLY DETECTED MAGNETIC-RESONANCE STUDY OF AN OXYGEN-VACANCY COMPLEX IN BAFBR

BaFBr is usually contaminated with oxygen which influences the perform ance of this well known x-ray storage phosphor material. Oxygen is inc orporated as a diamagnetic O2- ion on F- sites with a nearby charge-co mpensating vacancy in the Br- sublattice, as is known from the paramag netic O-F(-) and F(Br-) centres created by room-temperature x-irradiat ion and studied in detail with electron paramagnetic resonance (EPR) t echniques. It is shown that BaFBr:O-F(2-) has a luminescence band exci ted at 4.95 eV, peaking at 2.43 eV with two radiative lifetimes of 0.2 ms and 1 ms, respectively. With luminescence-detected EPR (i.e. optic ally detected magnetic resonance (ODMR)), it is shown that the lumines cence is due to an excited tripler state of an O-F(2-)-Br- vacancy pai r. Time-resolved ODMR measurements reveal the same radiative lifetimes as seen in luminescence. No singlet emission was observed. The zero-f ield splitting can be explained assuming a F(Br-)-O-F(-) pair defect a s the excited tripler state.