Enhancement of the emission from TeO2 nanorods by encapsulation with ZnO

TeO2-core/ZnO-shell nanorods were synthesized by a two-step process comprising thermal evaporation of Te powders and atomic layer deposition of ZnO. Scanning electron microscopy images exhibit that the core-shell nanorods are 50 - 150 nm in diameter and up to a few tens of micrometers in length, respectively. Transmission electron microscopy and X-ray diffraction analysis revealed that the cores and shells of the core-shell nanorods were polycrystalline simple tetragonal TeO2 and amorphous ZnO with ZnO nanocrystallites locally, respectively. Photoluminescence measurement revealed that the TeO2 nanorods had a weak broad violet band at approximately 430 nm. The emission band was shifted to a yellowish green region (similar to 540 nm) by encapsulation of the nanorods with a ZnO thin film and the yellowish green emission from the TeO2-core/ZnO-shell nanorods was enhanced significantly in intensity by increasing the shell layer thickness. The highest emission was obtained for 125 ALD cycles (ZnO coating layer thickness: similar to 15 nm) and its intensity was much higher than that of the emission from the uncapsulated TeO2 nanorods. The origin of the enhancement of the emission by the encapsulation is discussed in detail. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim