INVESTIGATIONS ON PHOTOLUMINESCENCE PROPERTIES OF NANOCRYSTALLINE ZNO PARTICLES SYNTHESIZED BY SOL-GEL ROUTE.

ZnO nanoparticles (ZnO–NPs) were synthesized using sol–gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). In this study, the effects of annealing temperature on photoluminescence (PL) of ZnO-NPs were studied. ZnO was annealed at various temperatures between 500 and 800 °C. The X-ray diffraction (XRD) results demonstrated that grain size increased with increase of annealing temperature. The average size of the nanoparticles was determined by SEM as well as XRD data and found to be 50 nm after annealing at 800 °C. As the annealing temperature increased from 500 to 800 °C, the intensities of both UV peak and that of green luminescence (GL) enhanced monotonously. The enhancement in the UV peak intensity is attributed to the decrease of grain boundaries and surface states; whereas, the remarkable improvement in the GL is assigned to the out-diffusion of oxygen from the sample up to 800 °C. It supports that GL is induced by the singly ionized oxygen vacancies. These oxygen vacancies are saturated due to the finiteness of the defects at 800 °C.