Ultraviolet (UV) and orange emissions have been observed from vapor-liquid-solid grown SnO2 nanowires. From the luminescence, the donor and acceptor binding energies have been estimated. The dependence of the orange luminescence on the diameters of tin oxide nanowires has been observed and the wavelength of the UV luminescence is found to depend on the laser power. Both the shift in the UV and the intensity of the orange luminescence is found to be dependent on the surface states of the tin oxide nanowires.

Luminescence data obtained in the visible region from the SnO 2 nanowires are used to determine the defect levels within the bandgap responsible for the strong orange emission, and a shift in the orange luminescence is seen at low temperatures. Temperature-dependent photoluminescence (PL) in the UV region shows the merging of the various emission lines at low temperature into a single broad UV peak with increasing temperatures. Investigations of PL and transmission electron microscope-energy dispersive x-ray spectroscopy (TEM-XEDS) from wires of different diameters show that the luminescence in the gap originates from surface states and thinner wires have more oxygen vacancies compared to thicker ones. Nanowires post rapid thermal annealing in two different ambients viz. oxygen and nitrogen are compared, using Raman, photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS) as characterization tools. Our data demonstrate that annealing in oxygen improves the crystalline quality of the nanowires due to the decrease in the oxygen vacancies.

Tin oxide nanowires have been grown on p-type silicon substrates using a gold-catalyst-assisted vapor-liquid-solid growth process. The nanowires were annealed in the presence of oxygen at 700 degrees C for different time intervals. The changes in material properties of the nanowires after annealing were investigated using various characterization techniques. Annealing improves the crystal quality of the nanowires as seen from Raman spectroscopy analysis. Photoluminescence (PL) data indicates a decrease in the oxygen vacancies and defects after annealing, affecting the luminescence from the nanowires. In addition, x-ray photoelectron spectroscopy (XPS) was used to obtain the changes in the tin and oxygen atomic concentrations before and after annealing, from which the stoichiometry was calculated.

Nanocrystalline titanium dioxide (TiO 2 ) photoanodes with four different film thicknesses from 5.57µm to 20.65µm were prepared by doctor-blade technique. Performance of dye sensitized solar cells (DSSCs) fabricated with these photoanodes were studied using current-voltage characteristics and incident photon-to-current conversion efficiency (IPCE) measurements. Electrochemical impedance spectroscopy (EIS) was used to analyze the effect of TiO 2 film thickness on the charge transfer resistance and electron life time in the solar cells. Voltage decay measurements were used to study the recombination process of photo generated charge carriers. These studies revealed that the photovoltaic properties of DSSCs largely depend on the film thickness of TiO 2 photoanode. Further, the DSSCs fabricated using a TiO 2 film of 12.73 µm thickness exhibited the best photovoltaic performance with highest incident photon-to-current conversion efficiency, highest short-circuit photocurrent, lowest charge transfer resistance, highest electron life time and lowest recombination life time.