Solvothermal synthesis of nanocrystalline zinc oxide doped with Mn2+, Ni2+, Co2+ and Cr3+ ions

ZnO nanopowders doped with Mn2+, Ni2+, Co2+ and Cr3+ ions have been synthesised for the first time using a solvothermal reaction with microwave heating. The nanopowders were produced from a solution of zinc acetate and manganese (II), chromium (III), nickel (II) and cobalt (II) acetates, using ethylene glycol as a solvent. The content of Ni2+, Co2+ and Cr3+ ions in the solution and in the solid phase were close to each other up to 5 mol%. The doping level of Mn2+ ions in the solid is about 50% of that in the solution. No phases or compounds other than ZnO were detected by X-ray diffraction with Mn2+, Co2+ and Ni2+ doping. With Cr3+ ions a small amount of chromium oxide was found. None of the powders displayed any luminescence after doping. The Mn2+-doped powder displayed a paramagnetic behaviour. ESR and magnetisation investigations have revealed that no clustering of Mn2+ ions occurred up to a doping level of 3.9 mol%. The average grain size of powders doped with Ni2+, Cr3+, Co2+ and Mn2+ for a 10 mol% ion content in the solution was about 20 nm and the grain size dispersion 30%. With increasing dopant content the grain size decreased. It appears that the solvothermal process employed allows relatively high doping levels of the transition metal ions to be achieved without any dopant clustering or oxide precipitation.