Photostimulated luminescence of halogen molecular ions in alkali borate glasses

Photoluminescence spectra from halogen molecular ions in borate glasses have been observed for the first time. When alkali halide is added to alkali borate glasses, X;(X; halogen) molecular ions are formed. The molecules give rise to one or two absorption bands in the ultraviolet regions. In the case of Br-3(-) in glasses, when the sample was excited with light, an emission band was observed at 1950 nm. In the Cl-3(-), emission showed two bands at 800 and 1970 nm. It was found that these spectra depend weakly on alkaline species. The disappearance temperatures of luminescence were 30 and 150 K for Br-3(-) and Cl-3(-) respectively. Nevertheless, the emission of I; could not detected even at 4 K. (On the other hand, in some alkali halide crystals containing excess halogen, luminescence of V centres resembling that of X-3(-) in glasses also has been observed.) From the experimental results for alkali borate glasses by comparing with luminescence of V centres, it is proposed that X-3(-) in glasses show both absorption and emission spectra caused by Sigma(u)* <----> Sigma(g), Pi(g) transitions, and are located about 6 Angstrom away from host atoms and are not adjacent to alkali ions added to borate glass.