Luminescence studies in BaFBr and BaFBr:Eu

Photoluminescence (PL), thermostimulated luminescence (TSL) and X-ray induced luminescence (XIL) studies of BaFBr:Eu, BaFBrI:Eu (Fuji) and BaFBr (undoped) reveal that in these phosphors: (i) oxygen impurity and self-trapped exciton (STE) emissions occur at about 480 and 300 nm, respectively; (ii) TSL peaks below RT display O(F)(2-)emission whereas the TSL peak above RT displays 380-400 nm Eu2+ emission; (iii) in the XIL spectra of oxygen rich BaFBr:Eu, the Eu2+ emission builds-up with increasing temperature above 100 K at the expense of 300 nm STE emission which indicates an energy transfer from STE to Eu2+; (iv) in BaFBr:Eu2+ with excess oxygen content, PSL is quenched; (v) in Fuji BaFBrI:Eu2+ which has a very low oxygen content and high PSL efficiency as revealed in its FL, PSL and TSL spectra, only Eu2+ emission is seen in the XIL spectra between 100 and 300 K which indicates an efficient energy transfer from STE to Eu2+; and (vi) the presence of STE emission in BaFBr (undoped) and 400 nm Eu2+ emission in Fuji IP along with O-F(2-) emission in their low temperature TSL spectra is a proof of the trapping of excitons near the O-F(2-) sites during X-irradiation and their release during thermostimulaton. Possible implications of these results on the PSL process in BaFBr:Eu are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.