Study of cobalt doping on structural and luminescence properties of nanocrystalline ZnO

We have synthesized the Zn1-xCoxO (x=0.01, 0.02, 0.03 and 0.05) nanoparticles by the sol–gel method. The adopted sol gel method needs no reaction agent to control the formation of precipitation except ammonia that is used to control the pH. These samples are characterized using x-ray diffraction (XRD), Scanning Electron Microscope (SEM), Ultraviolet/Visible(UV/V) spectroscopy, Fluorescence spectroscopy, Raman spectroscopy and Fourier transform infra red (FTIR) spectroscopy. The x-ray diffraction patterns show that all the sample are formed in single phase with a complete solubility of Co ions in the ZnO matrix. SEM micrographs show that the Co doped ZnO nanoparticles are hexagonal with wurtzite structure. We have found slight agglomeration of naoparticles for higher concentration of cobalt. Energy dispersive x-ray spectroscopy (EDS) confirms the presence of Zn, Co and O elements. The particle sizes range between 50 - 60 nm. We have observed a decrease in fluorescence intensity with the increase in Co doping but all the Co doped samples show higher value of intensity as compared to pure ZnO in the visible range of spectrum. Raman spectroscopy reveals that the characteristic intense band of ZnO at 435 cm-1 exhibits a decrease in intensity and slightly red shifts with the Co doping. The overall intensity of the samples shows a decrease with the increase in Co doping. FTIR spectra exhibit that the Zn-O band at ~497 cm-1 for pure ZnO is shifted to lower frequency with the increase in Co doping.