Optical characterization of Fe- and Cu-doped silicon oxide glasses prepared by the sol-gel method

Thin SiO2 films were obtained by the sol-gel process involving the solidification (gelation) of a specially prepared solution of the necessary components including some catalytic additives. The doping impurity was introduced in the solution. After the subsequent annealing in oxidizing or reducing atmosphere, colored glasses were obtained, the kind and intensity of color depending upon the doping and the kind of the subsequent treatment. The glasses obtained were studied with the use of x-rays diffraction, optical and photoacoustic absorption, atomic force microscopy, and Raman light scattering measurements. It was found that, in the doped and heat-treated samples, the introduced metal exists in the form of separate atoms and colloidal metallic or metal oxide particles, whose amount and distribution depend on the kind and percentage of dopant and subsequent treatment. The optical properties are determined by the light absorption and scattering of these inclusions. The infrared absorption bands are also sensitive to doping and subsequent treatment, which is the result of variation of the glass disorder, in particular of phonon scattering.