It was noted that O in this material was incorporated as a diamagnetic O2- ion on F- sites, with a nearby charge-compensating vacancy in the Br- sub-lattice. This was revealed by the paramagnetic OF- and F(Br-) centers which were created by room-temperature X-irradiation, and had been studied in detail by using electron paramagnetic resonance techniques. It was shown that OF2--doped BaFBr exhibited a luminescence band that was excited at 4.95eV, and peaked at 2.43eV; with radiative lifetimes of 0.2 and 1ms. By using luminescence-detected electron paramagnetic resonance (optically detected magnetic resonance) techniques, it was shown here that the luminescence was due to an excited triplet state of an OF2--Br- vacancy pair. Time-resolved optically detected magnetic resonance measurements revealed the same radiative lifetimes which were detected in luminescence. No singlet emission was observed. The zero-field splitting was explained by assuming that a F(Br-)-OF- pair defect was the excited triplet state.

F.K.Koschnick, T.Hangleiter, K.S.Song, J.M.Spaeth: Journal of Physics - Condensed Matter, 1995, 7[34], 6925-37