Effect of Co2+ ions on structural, morphological and optical properties of ZnO nanoparticles synthesized by sol–gel auto combustion method

Undoped and Co2+ doped ZnO nanoparticles have been successfully synthesized by sol–gel auto combustion method. The ratio of metal nitrates to citric acid was taken at 1:1.11. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared and Uv–visible spectroscopy techniques. The X-ray powder diffraction analysis revealed the formation of single phase having hexagonal wurtzite structure. The lattice constant ‘a’ increases while ‘c’ decreases as Co2+ concentration ‘x’ increases. The average crystallite size obtained from XRD data is in the range of 19–15 nm. The X-ray density, atomic packing factor, strain, surface area to volume ratio, etc was obtained using XRD data. SEM analysis showed that the prepared nanoparticles are in nano regime, nearly spherical and loosely agglomerates. EDAX analysis showed that composition obtained is near stoichiometries. In order to understand functional group and vibrational frequency band position of synthesized nanoparticles FTIR technique was used. FTIR analysis results observed that vibrational frequency band position of Zn–O shifted to higher frequency band with Co2+ ion increasing host semiconductor nanoparticles. Uv–visible absorption spectra showed that absorption edge shifted to higher wavelength with increasing Co2+ concentration while corresponding energy band gap of semiconductor nanoparticles decreases with increasing Co2+ concentration.