Investigation On Microstructure, Energy Gap, Photoluminescence and Magnetic Studies of Co and Cu in Situ Doped ZnO Nanostructures

Abstract Co (3%) doped ZnO and Co, Cu (Co = 3% and Cu = 2 to 4%) dual doped ZnO nanostructures have been prepared using chemical co-precipitation route. Structural analysis indicated that no alteration in hexagonal structure of ZnO and the absence of secondary / impurity phases were detected by Co/Cu addition into ZnO. The size reduction at Cu = 2% is due to the suppression of growth rate and the dissimilarities between Co2+/Cu2+ and Zn2+ and improved size at Cu = 4% is responsible for the more defect sites in Zn-O lattice. The constant c/a ratio (~ 1.602) signified that absence of structural modification by Co/Cu substitution. The modification in optical absorption, transmittance and energy gap of ZnO by Co/Cu addition was discussed by dopants and the stimulated defect states. The continuous widening of energy gap with Cu substitution is clarified using Burstein-Moss (BM) band filling effect through energy level diagram. The existence of Zn-O and Zn-Co/Cu-O bonding was verified by Fourier transform infra-red analysis. The elevated intensity ratio between green and ultra-violet photoluminescence (IG/IUV) at higher Cu concentrations revealed the occurrence of more defects particularly oxygen related defect states in Zn-Co-Cu-O lattice. The observed room temperature ferromagnetism (RTFM) in Co, Cu doped ZnO nanostructures is discussed based on the oxygen vacancy mediated bound magnetic polarons (BMP) and the exchange coupling among the free electrons and local spin polarized electrons.