Effect of annealing temperatures on the structural and optical properties of zinc oxide nanoparticles prepared by chemical precipitation method

Abstract

Zinc Oxide Nanoparticles (ZnO-NPs) were synthesized by chemical precipitation method at low temperature using Zinc nitrate hexa hydrate [Zn (NO3)2·6H2O] and sodium hydroxide (NaOH) as precursors followed by annealing at different temperatures ranging from 200 °C to 600 °Cfor two hours. The structural and optical properties of resulting ZnO products were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), Ultra Violet-Visible ((UV–vis)) Spectroscopy and Photo Luminescence(PL) Spectroscopy respectively. The XRD results reveal that the prepared ZnO-NPs exhibit hexagonal wurtzite structure and the increasing annealing temperatures lead to an increase in the average crystallite size as well as improvement in the crystallinity. SEM images reveal the formation of nearly spherical ZnO nanoparticles with slight agglomeration. The FTIR spectra of all the samples exhibits peak, which corresponds to ZnO stretching band. The UV–Vis absorption spectra show a slight red shift along with decrease in optical band gap from 3.84 eV to 3.56 eV with increase in annealing temperature. The room temperature PL spectra with excitation wavelength 320nm show increase in UV emission intensity with respect to annealing temperature.