Abstract
Glasses in the system Na2O–GeO2 were prepared via melt quenching technique. The optical absorption spectra were measured in the wavelength range from 190 to 1000nm. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. The position of the absorption edge and hence the value of the optical band gap were found to show anomalous behavior depending on the glass composition. The absorption in these glasses is believed to be associated with indirect transitions. The origin of the Urbach energy is associated with phonon-assisted indirect transitions. The temperature-dependence of DC conductivity for these glasses has been examined in the temperature range 463–623K. It reveals that the obtained activation energy (0.04–0.54eV) of these glasses was glass composition dependent.