Stimulation of the photoluminescent properties of electrospinning TiO₂ nanofibres induced by structural modifications resulting from annealing at high temperatures

Electrospinning technique has been used to prepare TiO₂ nanofibres. The crystalline phase transformation occurred due to thermal treatments in the temperature range of 100–1000 °C, from anatase to rutile through the anatase-rutile mixed, which was verified by X-ray diffraction, high-resolution transmission electronic microscopy and Raman scattering. The effects of the annealing temperature on the surface morphology and the chemical stoichiometry of titanium dioxide nanofibres were determined by scanning electron microscopy and energy dispersion spectrometry. The nanofibres diameter was in the range of 115–137 nm in the investigated temperature range. Clear evidence of structural phase transformation from pure anatase to pure rutile structures including the anatase-rutile mixed phase have been obtained by ultraviolet–visible and photoluminescence spectroscopy. TiO₂ nanofibres band gap energy could be tuned from 3.59 to 2.42 eV by varying the annealing temperature estimated by room temperature absorbance. The photoluminescent emission ranged in the 2.36–1.47 eV region as a function of the thermal treatment temperature, which is a consequence of the TiO₂ nanofibres crystalline phase transformation and reduction of the band gap energy.