PHOTOCHROMIC PROPERTIES IN CADMIUM BISMUTH ALUMINATE GLASSES AND ITS OXIDATION TREATMENT EFFECT

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 eff ectively 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 th e Lewis basicity of oxygen atoms increased and the fraction of covalen tly bonded cadmium decreased. The trap density of holes increased and the photogeneration yield decreased. The darkening degree showed a max imum around BiO1.5=13 cation%. The effect of oxidation treatment on th e darkening degree may be related to production of a large amount of m onovalent O- ions with holes in their 2p valence band, and to formatio n of electron centers in cadmium atoms.