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

BaFBr is usually contaminated with oxygen which influences the performance of this well known x-ray storage phosphor material. Oxygen is incorporated as a diamagnetic O2- ion on F- sites with a nearby charge-compensating vacancy in the Br- sublattice, as is known from the paramagnetic O-F(-) and F(Br-) centres created by room-temperature x-irradiation and studied in detail with electron paramagnetic resonance (EPR) techniques. It is shown that BaFBr:O-F(2-) has a luminescence band excited 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. optically detected magnetic resonance (ODMR)), it is shown that the luminescence is due to an excited tripler state of an O-F(2-)-Br- vacancy pair. Time-resolved ODMR measurements reveal the same radiative lifetimes as seen in luminescence. No singlet emission was observed. The zero-field splitting can be explained assuming a F(Br-)-O-F(-) pair defect as the excited tripler state.