OPTICAL-ABSORPTION OF COPPER PHOSPHATE-GLASSES IN THE VISIBLE SPECTRUM

Optical absorption of copper phosphate glasses with batch compositions of 40, 50 and 55 mol% CuO have been examined in the visible and near-infrared range as a function of [Cu2+]/[Cu(total)] in the glasses. An absorption band centered at about 11000 cm-1 is produced due to an octahedral coordination of Cu2+ in the glass with strong tetragonal distortion. This absorption band is resolved into three-component Gaussian bands around 8500, 12000 and 13 250 cm-1. These bands are assigned to the energy transitions 2A1g --> B-2(1g), B-2(2g) --> B-2(1g) and 2E(g)--> B-2(1g), respectively. The degree of tetragonal distortion of Cu2+ coordination is slightly enhanced with increases in the [Cu2+] ratio and CuO content. A minimum absorption in the visible spectrum is produced by overlapping of the absorption bands Of Cu2+ and Cu1+. The position of the minimum absorption shifts to higher wavenumber with increasing [Cu2+] ratio in the glass regardless of glass composition and is responsible for color changes.