The role of defects on linear and nonlinear optical properties of pristine and nickel doped zinc oxide nanoparticles

We herein report the marked influence of defects on the optical and nonlinear optical properties of nanoparticles, revealed from our investigations on pristine and nickel doped zinc oxide nanoparticles (Zn(1 _ x)NixO). These nanoparticles have been prepared via a simple and cost-effective hydrothermal technique, and their structure has been confirmed by X-ray diffraction analysis. Field emission scanning electron microscopy shows the rod-like structure of Zn(1 _ x)NixOnanoparticles, and X-ray Photoelectron Spectra confirm the existence of divalent oxidation states of zinc (Zn) and nickel. The presence of defect states due oxygen (O2) vacancies along with Zn interstitials have been identified from the Raman spectra. An indirect relation between the band gap energy and Urbach energy has been manifested from the linear optical studies using ultraviolet-visible (UV-Vis) absorption spectra. Photoluminescence emission peaks have been noted in the visible region for an excitation wavelength (lambda ex) of 325 nm. The suppression of peaks in the UV region is attributed to the presence of defects in the syn-thesized samples. Third order nonlinear optical studies reveal an increment in the nonlinear parameters on doping, which can be correlated with the influence of defects like Zn interstitials and O2 vacancies developed in the materials.