Influence of the TiO2 coating and thermal annealing on the structure and photoluminescence properties of MgO nanowires

초록

Influence of the TiO2 layer thickness and thermal annealing on the photoluminescence properties of MgO-core/ TiO2-shell coaxial nanowires were investigated. MgO nanowires were synthesized by thermal evaporation of Mg3N2 powders and then coated with TiO2 by using the metal organic chemical vapor deposition (MOCVD) technique. We performed scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDXS), and photoluminescence (PL) spectroscopy to characterize the of MgO-core/ TiO2-shell coaxial nanowires. The nanowires have very uniform diameters and nanoparticles at their tips, suggestting that they were grown based on vapor-liquid-solid (VLS) mechanism. TEM and XRD analyses revealed that the MgO cores and the TiO2 shells had crystalline face-centered cubic (fcc) and crystalline anatase structures, respectively. The interplanar spacings corresponding to the {111} planes of the MgO core and the {112} planes of the TiO2 shell are 0.243 and 0.331 nm, respectively. PL measurement at room temperature shows that the PL emission intensity of MgO nanowires can be increased by coating them with a TiO2 layer with an appropriate thickness. The PL emission of MgO/TiO2 coaxial nanorods is centered at around 410 nm in the violet region whereas that of MgO nanorods is centered at around 590 nm in the yellow region. The PL emission of the coaxial nanowires is enhanced by annealing in a reducing atmosphere whereas aggravated by annealing in an oxygen atmosphere. Also the origin of the PL enhancement by annealing in an Ar atmosphere is discussed with the aid of energy-dispersive X-ray spectroscopy analyses.