Multi-modification of ZnO nanorods to enhance the visible absorption

Undoped and transition metals doped zinc oxide nanorods (ZnO NRs) are prepared onto glass substrates using hydrothermal method. Transition metals (Cu, Ag, Au, Co and Mn) are intended to narrow the optical band gap of ZnO NRs. We have optimised the concentration of metal doping and investigated their structural, morphological and optical properties. The X-ray diffraction (XRD) pattern not only reveals that doped ZnO NRs are well oriented in the (002) plane which corresponds to the hexagonal phase but also confirms that metal ions well replaced ZnO ion in the crystal lattice. The scan electron microscopy (SEM) images show the length, diameter with high density and uniform nanorods. The optical band gap of doped ZnO NRs, calculated from UV-Vis spectra using Tauc's method, exhibits the reduction leading to extension of the optical absorption and shift of the absorption edge toward visible light. More interestingly, the visible absorption is enhanced by decorating metal onto doped ZnO NRs based on the localised surface plasmon resonance (LSPR) effect. Since, multi-modification of ZnO NRs materials could be the foundation for the development of optoelectronic devices using visible light, such as OLED, water splitting, solar cells.