Structural and optical properties of unannealed and annealed ZnO nanoparticles prepared by a chemical precipitation technique

In this paper we report the structural, electronic and optical properties of ZnO nanocrystals synthesized by a facile chemical method. ZnO nanoparticles prepared by this method were investigated employing X-ray diffraction (XRD), Transmission electron microscope (TEM), Atomic force microscope (AFM), Fourier transform infrared (FTIR), UV–Visible and Fluorescence (FL) spectroscopy. In order to study the effect of annealing on ZnO nanoparticles, we have analyzed pre- and post-annealed nanoparticles. It was observed that annealing treatment removes the impurities and consequently enhances the purity of ZnO nanoparticles without influencing their wurtzite phase. The absorption and excitation transitions occurring in annealed ZnO nanoparticles are similar to those in unannealed ZnO; however, some fluorescence emissions are altered. On the one hand, annealing assists in obtaining the pure ZnO nanoparticles without affecting their size and crystal structure; on the other hand channels of radiative combination are affected by the annealing process.