Investigation of third-order nonlinear optical properties of nanostructured Ni-doped CdS thin films under continuous wave laser illumination

Abstract

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 Cd<inf>1-x</inf>Ni<inf>x</inf>S 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 (?) are enhanced from 0.92 x 10-5 to 4.46 x 10-5 (cm W-1), nonlinear refractive index (n<inf>2</inf>) from 0.2967 x 10-9 to 0.1297 x 10-8 (cm2 W-1) and thereby the third-order NLO susceptibility (?(3)) values also increased from 1.7075 x 10-6 to 7.4743 x 10-6 (esu). OL characteristics of the prepared films are studied at the experimental wavelength. The results propose that the Cd<inf>1-x</inf>Ni<inf>x</inf>S film is a capable material for nonlinear optical devices at 532 nm and optical power limiting applications. © Springer Science+Business Media, LLC, part of Springer Nature 2019.