Photochromic properties were investigated for glass in the system CdO-Bi2O3-Al2O3. Optical density increased with increasing BiO1.5 content in the glasses at fixed CdO content. The darkening degree could be effectively enhanced by oxidation treatments. The composition dependence and effect of oxidation treatment were studied by X-ray photoelectron and Raman scattering spectroscopies. With increasing BiO1.5 content the Lewis basicity of oxygen atoms increased and the fraction of covalently bonded cadmium decreased. The trap density of holes increased and the photogeneration yield decreased. The darkening degree showed a maximum around BiO1.5=13 cation%. The effect of oxidation treatment on the darkening degree may be related to production of a large amount of monovalent O- ions with holes in their 2p valence band, and to formation of electron centers in cadmium atoms.
