Preparation and optical characterization of transparent, microporous TiO2 xerogel monoliths

This paper focuses on the sol–gel preparation and spectroscopic characterization of transparent and rare earth-doped TiO2 monoliths, for further applications in luminescence. The preparation method was based on a sol–gel technique applied to titanium isopropoxide as the precursor. By controlling the hydrolysis of this precursor by the intermediate of an esterification reaction, and by also controlling the rate of drying, transparent TiO2 xerogel monoliths were obtained at room temperature. The monoliths prepared in this manner were transparent to wavelengths between 400 and 1400 nm. They had a microporous texture, a specific surface area of ≈330 m2 g−1 and they were partly X-ray amorphous. After heat treatment at 823 K for 6 h in air, the N2 adsorption isotherm analysis indicated that a densification process occurred altogether with a phase transition from partly amorphous to anatase. The X-ray diffraction spectra indicated that the anatase crystals had a size in the range of the nm, while the UV transmission spectra kept the same characteristics as at room temperature.