| dc.description.abstract | The optical band gaps, crystal structure, and anatase-to-rutile phase transformation were studied on Nb-doped TiO; (concentration range 0.02-0.06 at. % Nb5+) films prepared by high temperature diffusion method. The Nb-doped TiO;films displayed a slight yellow colour attributed to O-Nb=O centres and an enhanced visible light absorption with a red shift of 18.2 nm of the optical absorption edge from 394 nm for pure Ti02film to 412.2 nm for 0.04 at. % Nb-doped TiO;film. This represents a band gap lowering of 0.181 e V due to the donor-type behavior of niobium.
As the niobium concentration increased, the enhancement in light absorption at the investigated concentration range goes through a maximum at 0.04 at. % Nb5+ with minimum band gap of 3.017 eV and starts to decrease again at 0.06 at. % Nb5+ with a band gap of 3.036 ev' The fabricated films exhibited rather low transmittance and reflectance. Despite higher rutilization, at the doping temperature of 850ﾰC used, crystal sizes (39-43 nm) obtained from X-ray diffraction spectra depicted a significant increase in surface areas which is attributed to retardation of exaggerated anatase-rutile phase transformation caused by Nb-doping into the Ti02 matrix. | en_US |
