Photoluminescence study of Eu+3 doped ZnO nanocolumns prepared by electrodeposition method

Europium doped ZnO (ZnO:Eu) nanocolumns were grown on indium tin oxide substrates (ITO) by electrodeposition method in zinc nitrate aqueous solution with different concentration of Eu. According to XRD results electrodeposited ZnO:Eu films exhibit thigh crystalline quality with a preferential orientation parallel to c-axis. Moreover, the (002) peak position shifts toward to lower angles confirming the incorporation of Eu+3 ions into the ZnO lattice. The crystallite size of a pure ZnO decreases when increasing the Eu doping. SEM images reveal a well dense nanocolumns arrays perpendicular to the surface. Furthermore, doping with Eu+3 ions leads to a change in the top of nanocolumns from hexagonal to conic-hexagonal shape. The average diameters of nanocolumns are found to be around 200 nm and 180 nm for undoped ZnO and Eu doped ZnO, respectively. Photoluminescence (PL) emission from ZnO:Eu thin films reveals the typical peaks related to excitons and intrinsic defects in ZnO and four narrow peaks in the red region attributed to 4f-shell transition in Eu+3 ions. As Eu doping increased, PL peaks related to Eu+3 emission showed an increase in intensity and a shift in its wavelength position. A schematic drawing of the excitation mechanism and related emission process is proposed.