Band gap tuning and nonlinear optical characterization of TiO2–SiO2 nanocomposites with respect to composition and phase

We report on the linear and nonlinear optical studies on TiO₂–SiO₂ nanocomposites with varying percentage ratio. It is found that optical band gap of the material varies with respect to the amount of the SiO₂ in the composite. Nonlinear optical characterization of these samples was studied by using open as well as closed aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). The nanocomposites showed enhanced nonlinear optical properties than pure TiO₂ and this can be attributed to the surface states and weak dielectric confinement of TiO₂ nanoparticles by SiO₂ matrix. The nanocomposites were thermally treated and similar studies were performed. The anatase form of TiO₂ in the nanocomposites showed superior properties relative to the amorphous and rutile phase of the composite. The involved mechanism is explained by taking into account the dominant role played by the excitons in the TiO₂ nanoparticles.