Synthesis And Optical Performance Of Ag Doped Tin Oxide Nanowires

Tin oxide (SnO2), an n-type semiconductor with a wide band gap (Eg=3.62 eV), has attracted intense attention due to its potential applications in transistors, photoelectric conversion devices and gas sensors, etc. The doped SnO2 has a higher visible transmittance, infrared reflectance and ultraviolet absorbance. In this discussion, with excellent surface plasmon properties of silver nanostructures as doping elements, the optical properties of SnO2 nanowires could be further improved thanks to the near-field enhancement induced by silver, and eventually, the Ag-doped SnO2 could be more widely used in the fields of optics, photonics and optoelectronics.In this discussion, Ag nanostructures were prepared at room temperature and ambient pressure by a facile solution method, where polyvinylpyrrolidone (PVP) and diluted sulfuric acid (H2SO4) were employed as protectant and ionic ambient regulator, respectively. The influence of the amounts of PVP and diluted H2SO4 on the morphologies and optical properties of the silver nanostructures was discussed. The results showed that the amount of PVP played a decisive role on the morphologies of the silver nanostructures:when the amount of PVP increased from 0 to 0.3g, the morphologies of silver nanostructures successively evolved from spherical particles into flakes, cubes, and thorn balls. Furthermore, the UV-Vis absorption spectra of the silver nanostructures could be de-convoluted to three sub-peaks, which derived from s-band indirect transition (189 nm), sp-d direct transition (193 nm) and d-band indirect transition (200 nm), respectively. And the addition amount of diluted H2SO4 is the main factor to decide whichever is the dominant process between sp-d direct transition and d band indirect transition:the indirect transition will be the dominant process when the addition amount is less than 2ml; while the direct transition will be the dominant one when the addition amount is more than 2ml.Secondly, tin oxide nanowires were prepared by a solvent thermal method. Three experimental variables (Tin oxalate amount, PVP amount, reaction temperature) affecting the morphologies and optical properties were studied by the orthogonal method. The results showed that the temperature is the main factor for making SnO2 to be the nanowires:the optimum reaction temperature for preparation of SnO2 nanowires with uniform morphology is 160℃. Regarding the optical properties of the SnO2 nanowires, the PVP amount is the key factor:with the increase of the amounts of PVP, the emission peak of SnO2 will red-shift in the range of 345-414nm.Lastly, Ag doped SnO2 nanowires with several micrometers in length and tens of nanometers in diameter were successfully prepared by a water bath-oil bath method. Energy Dispersion Spectrometer (EDS) showed that the distribution of silver in the nanowires was uniform. Due to the doping of silver, apart from the original PL peak (313nm) resulting from the oxygen vacancies, two more PL peaks centered at 348nm and 364nm appeared. The intensities of the two new luminescence peaks increased with the increasing of the relative doping amount of silver, which was consistent with the intensity evolution of the absorption peak at 419nm in the UV-Vis spectra. It can be concluded that the new luminescence peaks of Ag doped SnO2 nanowires at 348nm and 364nm may be due to the surface plasmon radiative decay of Ag and the tin vacancies of SnO2, respectively.