Synthesis of Co-doped ZnO nanoparticles by sol-gel method and its characterization

Cobalt doped ZnO nanoparticles with different Co contents have been synthesized by a sol-gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. The structural, morphological, optical and magnetic properties of the as-prepared nanoparticles were investigated by XRD, transmission electron microscopy, UV measurements, photoluminescence and superconducting quantum interference device. The structural properties showed that the obtained nanoparticles are in wurtzite single crystalline phase and no secondary phases were detected which indicated that Co substituted Zn ions. The energy band gap of the ZnO host matrix decreases gradually by increasing the doping concentration. The photoluminescence spectra exhibit intensive emission in the UV range. This emission presents a small shift to longer wavelengths and remarkable decreases in the intensity with increasing Co content. The Magnetic measurements at room temperature reveal diamagnetic behavior for the samples with lower doping concentrations; however, at higher Co content, we noted the presence of both paramagnetic and ferromagnetic behaviors.