Influence of Heat-Treatment Conditions on the Optical Properties of Bismuth-Containing Composites Based on High-Silica Porous Glass

— Bismuth-containing composite materials are synthesized by the impregnation of matrices of thermally modified porous glass (PG) in 0.5 M aqueous solutions of bismuth nitrate followed by heat treatment. The optical density spectra of the obtained materials are studied depending on the heat treatment temperature (400–870°C). When the temperature of the heat treatment is increased, the distribution of bismuth in the samples becomes more homogeneous. The heat treatment in the range of 650 to 870°C leads to the degree of bismuth oxidation changing from Bi 3+ to Bi 2+ ions with the formation of dimers and clusters of bismuth.