Spectroscopic properties of Co2+: ZnAl2O4 nanocrystals in sol-gel derived glass-ceramics

Transparent glass-ceramics containing zinc-aluminum spinel (ZnAl2O4) nanocrystals doped with tetrahedrally coordinated Co2+ ions were obtained by the sol-gel method for the first time. The gels of composition SiO2-Al2O3-ZnO-CoO were prepared at room temperature and heat-treated at temperature ranging 800-950degreesC. When the gel samples were heated up to 900degreesC, ZnAl2O4 nanocrystals were precipitated. Co2+ ions were located in tetrahedral sites in ZnAl2O4 nanocrystals. X-ray diffraction analysis shows that the crystallite sizes of ZnA1204 Crystal become large with the heat-treatment temperature and time, and the crystallite diameter is in the range of 10-15 nm. The dependence of the absorption and emission spectra of the samples on heat-treatment temperature were presented. The difference in the luminescence between Co2+ doped glass-ceramic and Co2+ doped bulk crystal was analysed. The crystal field parameter D-q of 423 cm(-1) and the Racah parameters B of 773 cm(-1) and C of 3478.5 cm(-1) were calculated for tetrahedral Co2+ ions. (C) 2003 Elsevier Science Ltd. All rights reserved.