Enhancement of the ultraviolet emission of ZnO nanorods by terphenyl liquid-crystalline ligands modification

We have developed a novel method to modifying the surface of ZnO nanorods (ZnO NRs) using p-hexoxyterphenylol (HTph-OH) as liquid crystal ligands. The structure and morphology of the modified ZnO NRs were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and atomic force microscopy (AFM). AFM measurement showed that the dispersion of ZnO NRs could be dramatically improved by the surface modification of HTph-OH and further annealing treatment at its liquid crystal state temperature (150 °C). The remarkable decrease of the annealed composite film roughness is because the HTph-OH chains self-organize into more ordered structure induced by mesogens after annealing treatment, which may push the ZnO NRs to form oriented nano-dispersing structure. The optical properties of the modified ZnO NRs were investigated by UV-vis absorption spectroscopy and photoluminescence spectroscopy (PL). Markedly enhanced band-edge ultraviolet photoluminescence and significantly reduced defect-related emission were observed. We attribute this observation to the nearly perfect surface passivation of the ZnO NRs by the HTph-OH molecules. Meanwhile, UV emission of modified ZnO NRs could be further enhanced by increasing the concentration of HTph-OH and annealing treatment at its liquid crystal state temperature.