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

Abstract

The photoluminescence (PL) of sol–gel TiO2thin film has been found to be largely dependent on the post-deposition processing such as annealing at 500°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°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 VO and/or Ti3+causes the green emission and OH and/or excess O2 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.