Microstructure, composition, and luminescent properties of bismuth-doped porous glass and optical fiber preforms

Abstract The microstructure of porous glass has been studied by using electron microscopy and X-ray microanalysis. Porous glass has an average pore size of about 4 nm in its interior, while larger pores and channels, up to 40 nm in size, exist in a surface layer, which is about 200 nm in thickness. Transparent consolidated samples with a bismuth concentration in the range ≤ 0.01–0.8 at. % were prepared by impregnation of porous glass with an aqueous solution of bismuth nitrate followed by thermal treatment. The addition of aluminum nitrates to the soaking solution results in the reduction of the bismuth content in the samples. The composition inhomogeneity of the porous glass and nanocrystalline inclusions were investigated on the nanolevel by means of transmission electron microscopy. The luminescence spectra of the samples were typical for aluminosilicate host glasses. The luminescence bands had the same shape in the entire bismuth concentration range from ≤0.01 to 0.8 at.%. The band intensities depend on the bismuth concentration and reach their maxima at 0.1–0.5 at.%.