Preparation of Co2+:MAl2O4/SiO2 (M=Zn, Mg) nanocomposites by sol–gel method

Co2+:MAl2O4/SiO2 (M=Zn and Mg) nanocomposites, containing nanocrystalline Co2+-doped MAl2O4 dispersed in silica glass matrix, were obtained by sol–gel method, and the corresponding precursor gels were prepared by using two different aluminum salts as starting materials. Co2+:ZnAl2O4 nanocrystals were precipitated when the gels were heated up to 900 °C, and the crystallite size is in the range of 9–20 nm, depending on the heat-treatment temperature and the aluminum salt grades. When using aluminum-iso-propoxide (Al(OPri)3) as starting material, Co2+:MgAl2O4 nanocrystals were formed by heating the gels above 1000 °C. Co2+ ions were located in tetrahedral sites in ZnAl2O4 (or MgAl2O4) nanocrystals replacing Zn2+ (or Mg2+) ions.