Structure, Optical and Electric Properties of Opal-Bismuth Silicate Nanocomposites

Synthetic opals composed of 300 nm silica spheres are impregnated with a Bi₁₂SiO₂₀ melt at 1190 K. Structure and properties of the as-prepared samples are studied by employing the scanning electron microscopy, X-ray diffraction, and optical spectroscopy and direct current conductivity techniques. The nanocomposites are found to be multi-phase systems composed of Bi₁₂SiO₂₀, Bi₄Si₃O₁₂ and SiO₂ crystallites with an average linear size not less than 20 nm. Formation of Bi₄Si₃O₁₂ crystallites becomes possible as a result of changing in the Bi₂O₃-SiO₂ molar ratio due to the melting of silica spheres. The Raman intensity redistribution observed by surface scanning may be caused by both composition inhomogeneity and concentration of the exciting radiation field at composite defects. The "red" shift of photoluminescence band is observed. Activation energy of direct current conductivity is estimated as 1.1 eV.