Temperature and compositional dependence of optical absorption edge in glasses containing PbO and TeO2

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Abstract
The optical absorption edge of the sol-gel derived borosilicate, silica, and phosphosilicate glasses containing heavy-metal oxides PbO and TeO2 exhibits a strong dependence on the temperature and composition. As the temperature is varied, a significant reversible thermochromic effect is observed in these glasses with a temperature coefficient as high as 10−3 eV/°C for most compositions, which is in general one magnitude of order greater than those of conventional semiconductor materials. The absorption edge of the glasses containing 10.24 wt. % PbTeO3 at room temperature was located at 3.76, 3.86, and 4.33 eV for the borosilicate, silica, and phosphosilicate glasses, respectively. With an increase in the heavy-metal concentration from 5.36 up to 18.62 wt. % in the borosilicate glasses, the absorption edge moved from 3.80 to 3.31 eV. On further increasing the concentration, the absorption edge no longer showed obvious red-shift. The observed optical characteristics were explained in view of the bond polarizability and structural coordination.