Morphological, microstructural, and photoluminescence characterization of heterogeneous/homogeneous TeO₂nanostructures based on effect of different N₂gas flow rates

TeO₂nanowires 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-TeO₂nanoparticles on the surface of pre-formed thick TeO₂nanowires were heterogeneously formed. Subsequently, uniform thin TeO₂nanowires without the γ-TeO₂phase were homogeneously synthesized by changing only the inlet N₂gas 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 N₂gas showed a synergetic effect between (1) bead-like orthorhombic γ-TeO₂nanoparticles that show two specific emission bands at 388 nm and 590 nm; and (2) uniform tetragonal TeO₂nanowires that show a characteristic emission band at 440 nm. In contrast, the pure tetragonal TeO₂nanostructures synthesized under a N₂gas 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 TeO₂structures are also discussed.