TiO₂–ZnO nanocomposites: synthesis, linear and nonlinear optical analysis

TiO₂–ZnO binary heterojunctions with different molar ratios of TiO₂ to ZnO have been prepared via a two-step co-precipitation method, including the synthesis of TiO₂ nanoparticles (NPs) and then incorporating them into the ZnO matrix. Structural studies and elemental analysis have been carried out by a series of characterization techniques including X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometer. The linear optical characteristics have been investigated using photoluminescence emission spectra at an excitation wavelength of 300 nm to estimate various energy states formed in crystalline structures. The optical nonlinearities of synthesized NPs have been tested by nanosecond laser pulse-based single-beam Z-scan technique. Closed-aperture and open-aperture Z-scan measurements have shown negative lens effects and reverse saturable absorption behaviours for as-synthesized composite nanostructures, respectively. The third-order susceptibilities of TiO₂–ZnO nanocomposites have been estimated to be higher than that of pristine TiO₂ NPs with a maximum value of 4.8 × 10⁻⁴ esu belonging to the sample with a 1:1 molar ratio of TiO₂ to ZnO.