Defect controlled tuning of the ratio of ultraviolet to visible light emission in TiO2 thin films

The photoluminescence (PL) of sol-gel TiO2 thin film has been found to be largely dependent on the post-deposition processing such as annealing at 500 degrees C in air, vacuum and ultraviolet (UV) light curing at room temperature. A detailed analysis of room temperature PL spectra shows that the UV/VIS PL peak intensity ratio is maximum for the film which has been annealed at 500 degrees C in air. X-ray photoelectron spectroscopy confirms the presence of Ti3+ type of point defects. The visible emission is deconvoluted to green and orange emissions. Analyses of the present experimental results indicate that V-o and/or Ti3+ causes the green emission and OH and/or excess O-2 adsorption on TiO2 surface probably causes the orange emission. The time correlated single photon counting spectroscopy data of the UV PL indicates higher number defects in vacuum annealed and UV cured films as compared to the air annealed film. Correlation of the results altogether allows us to conclude that the surface defects those causing the visible emission are smaller in number in the air annealed film. The present results may be useful for tuning the relative PL intensities of UV, green and orange emissions. (C) 2016 Elsevier B.V. All rights reserved.