Refluxed sol–gel synthesized ZnO nanopowder with variable zinc precursor concentrations
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ZnO nanoparticles were synthesized using refluxed sol–gel method with variable zinc precursor concentration ranging from 0.1 to 0.2 M. The structural, morphology and optical properties of ZnO nanostructures were investigated using different characterization techniques. Concentration of zinc precursor significantly affects the morphology, structural and optical properties. All ZnO samples prepared are pure hexagonal wurtzite in structure and the crystallite sizes increases from 24 to 35 nm. The average lattice parameters were calculated as a = 0.3267 nm and c = 0.5232 nm. The average bond length of ZnO nanocrystalline was calculated to be around 0.1988 nm. The photoluminescence measurement result shows that both UV (at 380 nm) and visible (between 428 and 636 nm centered at 540 nm) emissions are displayed with the excitation wavelength of 248.6 nm from NeCu laser source. The room temperature photoluminescence measurement shows that the emission wavelength shifted towards the higher wavelength as zinc precursor concentration increases. The intensity ratio of the near-band-edge emission to deep-level emission increases as zinc precursor concentration increases. With low temperature photoluminescence (from 84 to 300 K) measurement, the emission energy increases from 3.28 to 3.35 eV. The deep-level emission of the ZnO was displayed in the green and yellow regions of the visible spectrum. The reflectance spectra from UV–Vis spectroscopy show that the concentration of zinc precursor has a significant effect on the band gaps of the material which decreased from 3.26 to 3.24 eV as the zinc precursor concentration increased from 0.1 to 0.2 M.
The authors would like to acknowledge the Directorate of research of the Free State University for the funding of this research.
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