Effect of the Bi/Y Ratio on the Spectral Properties of Bismuth-Containing Composite Materials Based on Silicate Porous Glasses

Abstract—Composite materials (CMs) based on matrices of high-silica nanoporous glasses activated by bismuth and yttrium ions have been synthesized. A study was made of the spectral-optical properties (transmission, optical density) and optical absorption characteristics (Urbach energy) of CMs depending on the ratio of introduced bismuth and yttrium (the mass ratio of nitrates in Bi/Y solution from 1 : 1 to 10 : 1) and CM heat-treatment temperature (from 50 to 870°С). Optical spectroscopy revealed that bismuth is in various forms in composites: spherical colloidal particles of bismuth, Bi³⁺, Bi²⁺, Bi⁺ ions; ${\text{Bi}}_{5}^{{3 + }}$ polycations, bismuth dimers. It has been established that the Urbach energy increases with an increase in the heat-treatment temperature of CMs. It was found that an increase in the content of yttrium in CMs (ceteris paribus) leads to the disappearance or appearance of additional absorption bands in the range of 395–740 nm associated with bismuth, which is in various forms (spherical colloidal particles of bismuth, Bi³⁺, Bi²⁺, Bi⁺ ions; ${\text{Bi}}_{5}^{{3 + }}$ polycations, bismuth dimers). In the composites, near-IR region spectroscopy was used to identify vibrations characteristic of lattice vibrations in Y₂O₃, to absorb Bi⁺ ions, Bi⁰ and bismuth dimers ${\text{Bi}}_{2}^{ + }.$