Preparation and characterization of nanocrystalline ZnO particles from a hydrothermal process

Rod-like ZnO nanoparticles were prepared by the hydrolysis of zinc acetate under heating in diethylene glycol (DEG). Structural characterization of the synthesized powders was investigated by XRD, FT-IR, electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM). The size of the particles increased as the amount of H2O added increased in the nano size range. The average crystallite size calculated from the XRD patterns varied from 6 to 64 nm corresponding to the amount of H2O added. The ZnO nanopartilces possess the wurtzite type crystallographic structure. It was found that these ZnO nanoparticles had singly ionized oxygen vacancy defect (V-O(+)) and O-2(-) superoxide ions from the EPR investigations. A strong near UV emission of the ZnO nanoparticles at about 380 nm was observed and its intensity decreased as the amount of H2O increased. This emission of ZnO nanoparticles is found to be particles size dependent due to the confinement effect. A green emission at about 540 nm due to the recombination of electrons trapped at singly ionized oxygen vacancies defect (V-O(+)) appeared when the amount of H2O increased. The intensity of the green emission increases as the concentration of V-O(+) increases.