Spectroscopic properties of Co2+: ZnAl2O4 nanocrystals in sol–gel derived glass–ceramics Original Research Article

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 800–950 °C. When the gel samples were heated up to 900 °C, ZnAl2O4 nanocrystals were precipitated. Co2+ ions were located in tetrahedral sites in ZnAl2O4 nanocrystals. X-ray diffraction analysis shows that the crystallite sizes of ZnAl2O4 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 Dq 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.