Thermochromism and temperature dependence of the energy gap in cadmium aluminum bismuthate glasses

Reversible thermochromic coloration was detected in Bi0(1.5)-CdO-AlO1.5 system glasses. The relevant parameters were strongly dependent on the BiO1.5 content. It was suggested that the weakened and more polarized Bi-O bond due to increased BiO1.5 content enhanced the thermochromism of the glasses. The redshift of absorption edges at room temperature and the increase in the temperature coefficient of the shift with increasing BiO1.5 content were analyzed. The thermochromic mechanism was explained in terms of the temperature dependence of the optical energy gap caused mainly by electron-phonon interaction.