XUltraviolet-visible emission from three-dimensional WO3-x nanowire networks

The photoluminescence spectra of WO3-x nanowire networks, WO3 nanowires networks, and the bulk phase WO3 powder have been investigated under the continuous wave excitation light at 320 nm. Two broad band emissions in spectrum of WO3-x nanowire networks are observed including the ultraviolet-visible (UV-vis) emission centered at 395 nm and the blue emission centered at 467 nm. The authors demonstrate that the blue emission in WO3-x nanowire networks is due to band-band transition of the bulk phase WO3 and the UV-vis emission is attributed to the state of oxygen vacancies, which are characterized by using scanning electron microscopy and x-ray photoelectron spectroscopy. The UV-vis emission exhibits a strong dependence on the excitation wavelength, while the blue emission is independent of the excitation wavelength. The UV-vis emission is discussed in configuration-coordinate diagram of a localized state of oxygen vacancies. In particular, this state of defect is a high-lying resonant state in the conduction band of WO3.