STUDY OF OPTICAL-ABSORPTION EDGES IN MGO-P2O5 GLASSES

A series of glass specimens were prepared from the binary glasses (MgO-P2O5) and their densities and optical absorption edges in the ultraviolet-visible ranges were measured. It was found that the fundamental absorption edge is a function of glass composition and at lower values of the absorption coefficients-alpha(omega) it follows the so-called Urbach edge. From this edge the value of E(e), the width of the tail of localized states in the bandgap, did not vary significantly with glass composition. In the higher energy region, the behaviour of alpha(omega) suggests that there are two different transition energies for electrons, namely direct allowed transitions and non-direct transitions in k space. From these results some information about the band structure of MgO-P2O5 glass is presented.