Wurtzite ZnO nanoparticles have been coated by anatase phase TiO2 layers using a chemical co-precipitation technique to synthesize heterogeneous ZnO-TiO2 core-shell nanostructures. The structural characterizations of as-prepared core-shell nanoparticles have been studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray photoelectron spectroscopy (EDX). Linear optical studies have been performed using photoluminescence (PL) emission spectra at an excitation wavelength of 300 nm. A blue shift towards shorter wavelengths has been observed in the NBE-related energies of core-shell samples as compared to blank ZnO core. Nonlinear optical parameters have been examined using the Z-scan technique under a 532 nm Gaussian laser beam with 10 ns short pulse width and 200 Hz repetition rate as an excitation source. All samples have exhibited a negative value of nonlinear refraction index and also reverse saturable absorption due to two-photon absorption phenomenon. The results of Z-scan analysis have revealed the stronger third-order nonlinearities for core-shell nanoheterojunctions compared to blank ZnO nanoparticles. The estimated values of the third-order susceptibility have exhibited measures up to the highest magnitude of 8.10 × 10 4esu belonging to ZnO-TiO2-1 sample, which shows an enhancement about four times higher than that of blank ZnO.
