ULTRAVIOLET OPTICAL ABSORPTIONS OF SEMICONDUCTING COPPER PHOSPHATE-GLASSES

Ultraviolet optical absorptions of semiconducting copper phosphate glasses with batch compositions of 40%, 50%, and 55% CuO have been examined as a function of [Cu2+]/[Cu(total)] in the glasses. The optical energy gap, E(opt), obtained from the fundamental absorption edge depends upon both glass composition and the ratio [Cu2+]/[Cu(total)] in the glass. E(opt) increases as CuO content and [Cu2+]/[Cu(total)] in the glass are raised. This trend is explained by speculating upon the energy band structure of copper phosphate glass. However, the Urbach energy, DELTAE, obtained from the tail of the optical absorption edge is affected solely by [Cu2+]/[Cu(total)] in the glass. An absorption band of Cu1+ (in its crystal field) occurs in the vicinity of the absorption tail and is responsible for the increase of DELTAE with reducing [Cu2+]/[Cu(total)] in the glass.