Preparation and Optical Properties of Transparent Glass‐Ceramics Containing Cobalt(ll) Ions

Transparent glass-ceramics containing ZnAl2O4:Co2+ and LiGa5O8:Co2+ crystallites have been prepared by heat treatment of glasses in the zinc aluminosilicate and lithium gallate silicate systems, respectively. Crystalline LiGa5O8 was already precipitated in an as-prepared specimen, while ZnAl2O4:Co2+ precipitated from the glass upon heat treatment. The crystallite size varies from about 5 to 20 nm with increasing heat treatment temperature for both systems, and glass-ceramics containing crystallites of less than about 10 nm are transparent. The low-temperature optical absorption and emission spectra are compared with those of single crystals, indicating that almost all of the Co2+ ions replace Zn2+ ions in the ZnAl2O4 system, while some of the Co2+ ions are incorporated into the LiGa3O8 system, although the amount of Co2+ which remains in the glass matrix is rather large in the latter system.