Luminescent center in Br−-rich BaFBr : O2−

In this work, emission, excitation and absorption spectra of pure and 1mol% O2−-doped BaFxBr2−x (x=0.98, 1.0, 1.02) powders were measured. It was found that the spectra of O2−-doped Br−-rich sample (x=0.98) is different from those of the other O2−-doped samples (x=1.0 and 1.02). Its emission peak shifts from 500 to 550nm, and becomes much wider. Absorption spectra show that F(Br−) centers of the X-rayed Br−-rich sample, unlike those of other X-rayed samples, are not disturbed by doped oxygen. With the EPR, it is shown that O2− ions are on the F− sites in either F−-rich (x=1.02) or Br−-rich sample. We suggested that in the Br−-rich sample (x=0.98) the luminescence is due to an OF′–V⋅F pair, instead of the OF′–V⋅Br pair in other samples (x=1.0 and 1.02).