Optical Spectra of Thallium in Glasses as Related to Crystals and Solutions

Abstract

The absorption and emission spectra of thallium in fused silica, aluminoborate, and phosphate glasses are similar to those of thallium‐doped alkali halides and solutions. The absorption and emission bands in the different systems can be attributed to transitions within the central Tl⁺ ion in a center with a (TlX_n)^(n−1)— configuration, where X stands for the anions neighboring the Tl⁺ ion. There is a shift in the absorption bands with the nature of the anions and cations neighboring the Tl⁺ ion. This shift may be related to the chemical shift observed in NMR studies. The thallium centers in glass are possibly present in ordered regions in the glass structure. The minimum size of such an ordered region is estimated to be about 15 Å. There are indications of dimers being formed in thallium‐doped fused silica.