Absorption and photoluminescence characteristics of Co2+:MgAl2O4 nanocrystals embedded in sol–gel derived SiO2-based glass

Abstract Co 2+ :MgAl 2 O 4 nanocrystals embedded in SiO 2 -based glass have been prepared by heating the gels of composition 5MgO–6Al 2 O 3 –89SiO 2 – x CoO ( x =0.2, 0.4, 0.6, 1.0) (mol%). When the gel samples were heated up to 1000 °C, MgAl 2 O 4 nanocrystals were precipitated and Co 2+ ions were located in the tetrahedral sites in MgAl 2 O 4 nanocrystals. X-ray diffraction analysis shows that the diameter of MgAl 2 O 4 crystal is ∼5–15 nm. Absorption and emission bands in the visible and near infrared regions have been observed from transparent Co 2+ :MgAl 2 O 4 /SiO 2 nanocomposites. The observed absorption and emission spectra are characteristic of tetrahedral Co 2+ in crystals. The intensity of absorption bands increases with the increasing of heat-treatment temperature and Co 2+ concentration, while with the increasing of Co 2+ concentration, the fluorescence intensity decreases and the fluorescence spectra in the visible range show a red shift. The crystal field parameter D q of 405 cm −1 and the Racah parameters B of 752 m −1 and C of 3388 cm −1 were calculated for tetrahedral Co 2+ ions.