Mo-doped SnO2 （MTO） nanowires are synthesized by an in-situ doping chemical vapour deposition method. Raman scattering spectra indicate that the lattice symmetry of MTO nanowires lowers with the increase of Mo doping, which implies that Mo ions do enter into the lattice of SnO2 nanowire. Ultraviolet-visible diffuse reflectance spectra show that the band gap of MTO nanowires decreases with the increase of Mo concentration. The photoluminescence emission of SnO2 nanowires around 580~nm at room temperature can also be controlled accurately by Mo-doping, and it is extremely sensitive to Mo ions and will disappear when the atomic ratio reaches 0.46%.
This paper reports that highly purified hexagonal WO3 nanowires are synthesized by a simple hydrothermal method. The as-synthesized WO3 nanowires are investigated in detail by ultraviolet-visible-near infrared spectroscopy and electrical transport measurements under different conditions. It finds that the optical band gap and the diffuse reflection coefficient in the wavelength region above 450 nm of WO3 nanowires decrease observably upon exposure to ultraviolet light or NH3 gas. It is also found that there are electrons being trapped or released in individual WO3 nanowires when scanning bias voltage in different directions upon exposure to ultraviolet and NH3 gas. The experimental results suggest that the chromic properties might be attributed to the injection/extraction of hydrogen ions induced by ultraviolet light irradiation in air or creation/annihilation of oxygen vacancies induced by NH3 gas exposure, which serve as colour centres and trap electrons as polarons. The experimental results also suggest that the hexagonal WO3 nanowires will be a good candidate for sensing reduced gas such as NH3.
