Intermediate Ce~(3+) defect level induced photoluminescence and third-order nonlinear optical effects in TiO_2-CeO_2 nanocomposites

摘要

We report on the linear and nonlinear optical studies of TiO_2-CeO_2 nanocomposites. It was found that the band gap of the nanocomposite can be tuned by varying Ce/ Ti content. Nonlinear absorption characteristics of these samples were studied by employing open aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). It has been observed that as the CeO_2 amount increases, band gap of the nanocomposites decreases and the reason proposed for the change in band gap is the smudging of localised states of Ce~(3+) into the forbidden energy gap, thus acting as the intermediate state. Fluorescence studies confirmed the above argument. Nonlinear investigation revealed that with increase in the CeO_2 amount, the two-photon absorption coefficient increased due to the modification of TiO_2 dipole symmetry. Suitable candidature of the nanocomposites for the fabrication of nonlinear optical devices was proved by determining the optical limiting threshold.