Cathodoluminescence spectra of Mn or Co doped ZnO single crystals

Single crystals of zinc oxide (ZnO), doped with Mn or Co, were grown by a slow cooling method with PbF2 flux and their optical properties were investigated by measuring optical absorption and cathodoluminescence (CL), Ionic charges of doped Mn and Co ions were determined to be divalent from the result of the absorption measurements. The CL spectra of those crystals were affected by both cationic doping and annealing in O-2 gas. Excitonic luminescence was suppressed by annealing in O-2 gas, while visible light emission became intense by annealing. The intensity of CL spectra of doped crystals were much less than that of non-doped crystals and extra luminescence peak appeared in the Co or Mn doped crystals by annealing. The effect of dopant and annealing to varistor properties are discussed on the basis of luminescence measurements.