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

Abstract

TeO₂ 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 gamma-TeO₂ nanoparticles on the surface of pre-formed thick TeO₂ nanowires were heterogeneously formed. Subsequently, uniform thin TeO₂ nanowires without the gamma-TeO₂ phase were homogeneously synthesized by changing only the inlet N₂ gas flow rates and keeping other process parameters constant. The morphological and microstructural evolution of the two different nanomaterials was examined by Xray diffraction, energy-dispersive X-ray spectrometry, and scanning and transmission electron micro-scopy. 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 gamma-TeO₂ nanoparticles that show two specific emission bands at 388 nm and 590 nm; and (2) uniform tetragonal TeO₂ nanowires that show a characteristic emission band at 440 nm. In contrast, the pure tetragonal TeO₂ nanostructures synthesized under a N₂ 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 TeO₂ structures are also discussed.