Structure and photoluminescence properties of TeO2/In2O3 coaxial nanowires

TeO2-core/In2O3-shell coaxial nanowires were synthesized by a two-step process comprising the thermal evaporation of Te powders and the sputter-deposition of In2O3. Transmission electron microscopy and X-ray diffraction analysis results indicate that the cores and shells of the annealed coaxial nanowires are single crystal monoclinic-type TeO2 and single crystal body-centered cubic-type In2O3, respectively, although the In2O3 shells were amorphous before annealing. Photoluminescence measurement shows that the TeO2 nanowires have an ultraviolet emission band centered at approximately 380 nm and a weak broad green emission band at approximately 560 nm. On the other hand, the TeO2/In2O3 coaxial nanowires show an intense violet emission band at approximately 425 nm. In other words, the luminescence was significantly enhanced in intensity and red-shifted by In2O3 coating. The enhancement in the violet emission and the red-shift of the ultraviolet emission by In2O3 coating is attributed to the passivation of the surface states. The violet emission from the coaxial nanowires was, however, degraded by subsequent thermal annealing. Energy-dispersive X-ray spectroscopy analysis results suggest that the degradation of the PL emission is caused by the increase in the indium interstitial concentration in the cores during the annealing process. (C) 2011 Elsevier B.V. All rights reserved.