The influence of calcination temperature on optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have synthesized by sol-gel with different calcination temperatures. Scanning electron microscopy (SEM) shows that the morphology of ZnO NPs has large aggregation. Then, X-ray diffraction (XRD) technique confirmed that the XRD pattern of ZnO NPs has polycrystalline wurtzite structure. The crystallite size in (002) plane at a calcination temperature of 200 °C, 400 °C, 600 °C are 9.28 nm, 12.60 nm, 20.11 nm, respectively. The intensity of observed peaks increases when the calcination temperature is higher. The room temperature UV-Vis absorbance of ZnO NPs indicate that the higher calcination temperature cause absorption peak shifted to longer wavelength and the bandgap energy lower. Optical photoluminescence properties confirmed that the UV emission coincides with the green emissions which correspond to the electron transition from the bottom conduction band to Vo, Vzn, and Ozn level. As a result, all the samples of the ZnO NPs have single broad emission in the range of 330 nm-550 nm with the peak at the UV wavelength of 375 nm. Nevertheless, the PL pattern is not linearly with increasing calcination temperature.