VS2/MoS2 nanocomposite with reverse saturable absorption for optical limiting and nonlinear optical applications

Transition metal dichalcogenides (TMDs) have been widely used as nonlinear optical materials. In the current study, hydrothermally prepared VS2/MoS2 nanocomposite was investigated for the non-linear study through the Z-scan technique. Z-scan is a straightforward method for determining how much a laser beam's phase changes when it passes through a nonlinear substance. This phase change, Delta Phi, is simply connected to the change in index of refraction, Delta n, and yields both its sign and magnitude. Furthermore, the change in transmission due to nonlinear absorption that is associated with the change in the absorption coefficient, Delta alpha, can also be independently determined using a Z-scan. X-ray diffraction (XRD) resembles the development of the hexagonal phase of VS2 as well as composite. The crystallite size decreased with the increased amount of Mo precursors. The morphological study confirms the formation of a nano-sheet-like structure for VS2 and a flower-like structure of the VS2/MoS2 composite. The high-resolution transmission electron microscopy(HRTEM) images contain both crystallographic planes, confirming the formation of the composite. The prepared material also shows tunable bandgap properties. The direct bandgap value lies in the range from 3.65 to 3.4 eV. The open aperture transmittance data provide information about the nonlinear absorption phenomenon, and the closed aperture transmittance data provide information about the phase shift of the light, that leads to a nonlinear refractive index (n(2)). The composite shows both self-focusing and self-defocusing nature. From the Z-scan experimental result, it is found that the saturable absorption (SA) properties of the pristine VS2 changed to reverse saturable absorption (RSA) after the formation of the composite with MoS2. The nonlinear absorption coefficient for VS2, VS2/MoS2-1, VS2/MoS2-2, and VS2/MoS2-3 are -(24.15 +/- 0.25), 0.183 +/- 127 x 10(-4), 0.115 +/- 3.96 x 10(-4), and 0.139 +/- 3.084 x 10(-5) cm/W, respectively. The composite shows significant optical limiting properties for 100 mW laser source. The increase in nonlinear susceptibility, nonlinear refractive index, and nonlinear absorption coefficient are useful for optical limiting and nonlinear optical device applications.a