Optical properties in cadmium borogermanate glasses

Photochromism and photoconduction were investigated for glasses in the system CdO-B2O3-GeO2. The optimum photoresponse was determined for various systematic substitutions. Photochromic density plotted as a function of CdO content at constant GeO2/B2O3 ratio showed a maximum around CdO=45mol % and decreased with further addition of CdO. Photoconductivity increased with increasing CdO content as well as with GeO2/B2O3 ratio. Too high CdO concentration caused a decrease in photoconductivity because of breakdown of a continuous glass network. On this basis, it is concluded that oxygen hole centers in the vicinity of four-coordinated boron atoms are responsible for the photochromism, whereas cadmium ions associated with GeO6 groups are responsible for photoconduction.