Enhancement of third order nonlinear optical responses via alteration of the density of states of electrons: VS2–NiS2 hybrid nanostructure

Abstract

We successfully synthesized VS₂–NiS₂ hybrid nanostructures via a one-pot hydrothermal technique. Microstructural characterizations were carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-visible spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The optical indexes such as n, k, and ε were assessed based on the reflectance spectra data and Kramers–Kronig method. By adding varying amounts of the NiS₂ phase in the hybrid nanostructure, the morphology of the hybrid nanostructures is altered to produce microflowers, nanoflakes, and nanoflowers. These changes affect the nonlinear optical properties. The third order nonlinear optical parameters (n₂, β) were analyzed via a simple and accurate Z-scan technique using different laser powers. The two-photon absorption phenomenon has a significant enhancement effect on the nonlinear absorption process, but the nonlinear refractive behaviour of the different hybrid nanostructures changes from self-defocusing to self-focusing due to the alteration of the electronic state alignment and morphology. The magnitudes of n₂ and β are in the order of 10⁻⁹ cm² W⁻¹ and 10⁻³ cm W⁻¹, respectively. The increasing of the density of states of electrons leads to the improvement of the nonlinear optical responses of the VS₂–NiS₂ hybrid nanostructures in comparison with the pure VS₂ structure. This study demonstrates the great potential of this hybrid nanostructure for optical limiters and modulators as well as photonic devices.