Optical properties of sol–gel fabricated Co/SiO2 nanocomposites

Cobalt nanoparticles were grown in silica glass and silica film on silicon substrate by annealing of the sol–gel prepared porous silicate matrices doped with cobalt nitrate. Annealing of doped porous silicate matrices was performed at various conditions that allowed to obtain the nanocomposite glasses with various content of metallic Co. The absorption and photoluminescence spectra of Co/SiO2 glasses were measured. In the absorption spectra at 285 nm (4.34 eV) we observed the band corresponding to the surface plasmon resonance in Co nanoparticles. The spectra proved the creation of Co2+ ions in tetrahedral and octahedral coordinations in silica glass as well. The formation of nanoparticles of cobalt oxides at annealing in air was revealed by XRD and absorption measurements. The measured reflection spectra of Co/SiO2 film also demonstrate the surface plasmon resonance in Co nanoparticles.