Effects of structural disorder and Urbach's rule in binary lead silicate glasses

The behavior of optical spectra of PbO–SiO 2 glasses with different concentrations of lead near the UV absorption edge was analyzed at temperatures from 80 to 470 K. A generalized formulation of modified Urbach's rule (MUR), which is applicable to glassy materials within a broad temperature interval, was proposed for interpretation of the experimental spectral dependences. The effective energy of phonons responsible for the temperature shift of the Urbach edge was calculated in terms of the approach used. It was shown that spectral and temperature parameters of MUR are structure-sensitive and their concentration behavior reflects the change in the type of short-range order in the glassy matrix.