The optical absorption spectra of the Tl0 centre induced in thallium borate glasses

The optical absorption spectra of binary thallium borate glasses irradiated by x-rays and high energy electrons were obtained. On irradiation, the Tl0 centre, i.e. on electron trapped on the thallous ion, was generated in glasses with a Tl2O content of less than 20 mol%. On the other hand, such a centre was observed only at the early stage after irradiation in the high thallium glasses. These characteristic phenomena are a reflection of the change in the effective positive charge on the thallium ion in the glasses. The Tl0 centre diminished with increasing temperature, the partner in the recombination reaction being the hole centre generated on the oxide ion in the borate network. In samples doped with Cd2+ and Cl- ions, the Cd2+ ion reduced the formation of Tl0 centres, whereas the Cl- ion did not show any marked effect. However, the Cl2 centre was formed only in those glasses with low thallium ion contents. This finding is the same as that observed in alkali borate glasses. The thermal stability of the Cl2- centre is greater than that of the other centres generated in the parent glass. (author)