Intensity and composition-dependent sign reversal of non-linearity in TiO₂/CeO₂ nanocomposites

CeO₂/TiO₂ composite nanoparticles with different Ce/Ti molar ratios have been successfully synthesized via sol–gel method. It was found that the band gap of the nanocomposite is tunable by varying Ce/Ti content. The nonlinear response of the sample was studied by using the nanosecond laser pulses from a Q switched Nd:Yag laser employing the Z-scan method. Open aperture Z-scan experiment revealed that with the increase in the CeO₂ amount in the nanocomposite, the non-linearity of the composite increases, and it was assumed that this could be due to the modification of TiO₂ dipole symmetry by the addition of CeO₂. Closed aperture Z-scan experiment showed that when the CeO₂ amount increases, positive nonlinear refraction decreases, and this could be attributed to the increase in the two photon absorption which subsequently suppresses the nonlinear refraction.