Microstructural evolution of transparent glass-ceramics containing Co2+: MgAl2O4 nanocrystals

Transparent glass-ceramics containing Co2+: MgAl2O4 nanocrystals were obtained by the sol–gel process. The gels with composition of 4.9MgO-5.9Al2O3-89SiO2-0.2CoO (mol%) (MAS) were prepared at room temperature, and heat-treated at different temperatures. The structural evolution of the samples was studied with X-ray diffraction (XRD) and infrared spectra. Co2+: MgAl2O4 nanocrystals were precipitated from the MAS system and dispersed in the SiO2-based glass when the sample was heated at 1000 °C. Optical absorption spectra showed that Co2+ ions were located in tetrahedral sites replacing Mg2+ ions in MgAl2O4 nanocrystals. TEM revealed spherical nanocrystals of the size of about 5–15 nm, depending on the heat-treatment temperature. The Co2+: MgAl2O4 nanocrystals in the amorphous silica matrix proved to be very stable up to 1100 °C without any decomposition.