OPTICAL-ABSORPTION OF GLASSES IN THE SYSTEM (AS2SE3)(1-XTL)

The optical absorption coefficient (a)has been measured at the absorpt ion edge for three glasses of composition (As2Se3)(1-x)Tl-x (x is in t he range 0.0-0.7). The values of alpha were in the range 10(5)-10(7) c m(-1). For the glasses in the system (As2Se3)(1-x)Tl-x with the larges t values of x there is distinct evidence of an additional absorption m echanism near the lower energy. In attempting to explain the origin of this feature we have suggested that for these glasses a sub-band, ass ociated with the presence of thallium, projects into the pseudogap at the edge of the valence band; this sub-band may have a tail of states due to compositianl disorder. The gamma irradiatin (up to 10 Mrad) has no detectable effect on the optical energy gap.