Annealing effects on photoluminescence of ZnO nanoparticles

Abstract

In this study, the effects of annealing temperature on photoluminescence (PL) of ZnO nanoparticles were studied. ZnO was annealed at various temperatures between 600 and 900 °C. The X-ray diffraction (XRD) results demonstrated that grain size increased with increase of annealing temperature. As the annealing temperature increased from 600 to 800 °C, the intensities of both UV peak and that of green luminescence (GL) enhanced monotonously but reduced at 900 °C. 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. So, it is speculated that the deterioration of GL intensity at 900 °C is due to the evaporation of Zn which is predominant at temperatures higher than 850 °C.