Hydrothermal growth of ZnO nanostructures with dopants Co2+, Ni2+ and Cu2+ - Structural and luminous characteristics

Transition metal doped ZnO: (Co/Ni/Cu) nanostructures grown using hydrothermal technique at an optimized growth temperature of 200 °C and a growth time of 3 hours exhibit violet photoluminescence emission. The scanning electron micrographs recorded from the as synthesized samples (ZnO:Co, ZnO:Ni and ZnO:Cu) display nanorods, nanosheet and nanoflower morphology depending upon the dopant/doping percentage. The X-ray diffraction and Raman analysis confirm that hexagonal wurtzite structure of ZnO is retained even after nominal doping of Co, Ni and Cu ions. Optical properties of hydrothermally grown ZnO crystals were analysed with respect to doping concentration (3, 4 and 5 wt%) of Co, Ni and Cu. The optical band gap of ZnO:Co decreases with increasing doping concentration, where as in the case of ZnO:Ni and ZnO:Cu, the band gap increases with increasing the doping concetration. Intense violet deep level emission was observed from ZnO:Co, ZnO:Ni and ZnO:Cu samples at room temperature and the intensity of violet luminescence decreased with increasing the doping concentration of Co2+, Ni2+ and Cu2+ ions into ZnO.