Morphological, microstructural, and photoluminescence characterization of heterogeneous/homogeneous TeO2 nanostructures based on effect of different N2 gas flow rates

TeO 2 nanowires with diameters ranging from a few tens to hundreds of nanometers and lengths of a few tens of micrometers were prepared by thermal evaporation of Te powder with a Co catalyst. Initially, bead-like γ-TeO 2 nanoparticles on the surface of pre-formed thick TeO 2 nanowires were heterogeneously formed. Subsequently, uniform thin TeO 2 nanowires without the γ-TeO 2 phase were homogeneously synthesized by changing only the inlet N 2 gas flow rates and keeping other process parameters constant. The morphological and microstructural evolution of the two different nanomaterials was examined by X-ray diffraction, energy-dispersive X-ray spectrometry, and scanning and transmission electron microscopy. The optical properties of the nanomaterials were also investigated using photoluminescence spectroscopy. The emission peaks in the PL measurement without the supply of N 2 gas showed a synergetic effect between (1) bead-like orthorhombic γ-TeO 2 nanoparticles that show two specific emission bands at 388 nm and 590 nm; and (2) uniform tetragonal TeO 2 nanowires that show a characteristic emission band at 440 nm. In contrast, the pure tetragonal TeO 2 nanostructures synthesized under a N 2 gas flow rate of 2 standard liters per minute flow rate revealed a red-shifted emission band at 450 nm compared to heterogeneous structures of the same composition. The origins of the growth and emission mechanisms in the different TeO 2 structures are also discussed.