Study of blueshift of optical band gap in zinc oxide (ZnO) nanoparticles prepared by low-temperature wet chemical method

We report synthesis of zinc oxide (ZnO) nanoparticles via wet chemical method using molar solutions of zinc nitrate hexahydrate [Zn(NO3)2·6H2O] and ammonium hydroxide (NH4OH) with polyvinylpyrollidone (PVP) as capping agent. The synthesized ZnO nanoparticles are characterized by X-ray diffraction (XRD) technique and electron microscopy (TEM and SEM with EDX) for compositional analysis and surface morphology. The average crystallite size calculated from XRD pattern has been found to be on the order of 8.5 nm. In this work, the hyperbolic band model (HBM) and UV-vis absorption spectra have been utilized to calculate the band gap and nanoparticle size which was proposed by Meulenkamp. It was Meulenkamp who correlated the particle sizes with the wavelength at which the absorption becomes half of that at the shoulder (λ1/2). The optical band gap value of the prepared ZnO nanoparticle is found to be on the order of 3.63 eV which indicates the presence of blueshift. In order to compare the size and distribution of ZnO nanoparticles, TEM has been utilized.