A comparison of the optical properties of glass and of evaporated amorphous thin films of BaO-TeO2

Two series of glass and thin film specimens of BaO-TeO₂ were prepared. The optical absorption edges and infrared absorption spectra were investigated. It was found that the fundamental absorption edge is a function of BaO content in both kinds of films and that the absorption is due to indirect electronic transitions. The values of optical gap for blown films were greater than those of thin evaporated films, but the widths of the band tails were greater for the evaporated thin films, which were expected to be more disordered than the thin blown glass films.