Color change of glass and glass-ceramics in Bi₂O₃-CdO-Al₂O₃ system

Color change and its mechanisms for glasses and glass-ceramics in the Bi₂O₃-CdO-Al₂O₃ system prepared under various melting and annealing conditions were investigated. It was suggested that brown color of the glasses with comparatively low Bi content which were obtained by melting at high temperatures was caused by metallic Bi while deep green color of the glasses with comparatively high Bi content resulted from Bi²⁺ and defects. The deep color of the glasses markedly faded after annealing treatments for long time. Formation of the transparent glass-ceramics was assumed to be related to the oxygen defects. Color of the glass-ceramics was explained in term of oxygen defects and crystalline phases formed by annealing treatments.