Structural and optical properties of ZnO and manganese-doped ZnO

The structural, morphological and optical properties of manganese oxides supported on commercial ZnO, prepared by impregnation with manganese nitrate, were investigated. The nominal compositions of Mn in the samples were 5, 10, 15 and 20%w/w.The X-ray diffraction (XRD) experiments revealed the presence of the ZnO wurtzite phase in all the samples, and ZnMnO3 was also found in the samples with 15 wt% and 20 wt% of Mn. X-ray photoelectron spectroscopy (XPS) showed the presence of Mn2+ and Mn4+ in the xMnZnO samples. The results showed that the Mn2+ ions had substituted the Zn2+ ions without changing the wurtzite structure of ZnO, while Mn4+ might be assigned to the ZnMnO3 impurity phase. The optical band gap was found to be 3.3 eV for undoped ZnO samples and 3.10 eV for Mn-doped samples. The lattice defect distribution was investigated using the positron annihilation method. The results revealed that the average lifetime is a function of the Mn concentration and the formation of the ZnMnO3 phase.