We report the third-order nonlinear optical (NLO) properties and optical limiting (OL) thresholds of pure CdS and Ni-doped CdS thin films have been investigated with the Z-scan technique under continuous wave laser excitation. Nanocrystalline CdS thin films with various doping concentrations of Ni (0%, 1%, 3%, 5% and 10 at.%) are prepared by spray-pyrolysis technique. XRD patterns reveal that all the prepared films are polycrystalline and the incorporation of Ni does not lead to major changes in the crystalline phase of Cd1−xNixS thin films. The surface morphology of the prepared films is impacted by the Ni-doping and is indicated by Field Emission Scanning Electron Microscopy (FESEM) images. With an increase in Ni-doping concentration, the energy band-gap value decreased from 2.48 eV to 2.23 eV. From the Z-scan data, it is observed that the material show strong two-photon absorption (2PA) and with an increase in Ni-doping concentrations from 0 to 10 at.%, the nonlinear absorption coefficient (β) are enhanced from 0.92 × 10−5 to 4.46 × 10−5 (cm W−1), nonlinear refractive index (n2) from 0.2967 × 10−9 to 0.1297 × 10−8 (cm2 W−1) and thereby the third-order NLO susceptibility (χ(3)) values also increased from 1.7075 × 10−6 to 7.4743 × 10−6 (esu). OL characteristics of the prepared films are studied at the experimental wavelength. The results propose that the Cd1−xNixS film is a capable material for nonlinear optical devices at 532 nm and optical power limiting applications.
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