Influence of Annealing Temperature on the Optical Properties of TiO2 Thin Films

The optical band gap of TiO2 films greatly determines its electro-optical and photocatalytic properties. By optimizing the annealing temperature of titania film the above said properties can be tuned. The present study investigates the influence of annealing temperature on optical properties of nanostructured titania films fabricated on quartz substrate by spray technique. The white anatasetitania nanoparticles needed for film fabrication is synthesized by precipitation method using titanium isopropoxide. Further, to have fine dispersion of TiO2 nanoparticles in spay solvent, its surface is modified using (3-Glycidyloxypropyltrimethoxysilane(GPTMS). The fabricated films are air annealed at two different temperatures 150 and 300 degrees C and their optical properties are studied. There is significant reduction in optical bandgap of titania film annealed at 300 degrees C to 1.5 eV. However, the optical band gap of the titania film annealed at 150 degrees C is 2.9 eV. The difference is attributed to surface defects and its presence is analyzed from PL spectra. Both the films exhibited emission attributed to oxygen vacancies. Nevertheless the emission intensity for film annealed at 300 degrees C is very low, which indicates the recombination rate of photogenerated electrons and holes are highly reduced. This is also confirmed from time resolved PL decay recorded for excitation 300 nm. (C) 2019 Elsevier Ltd. All rights reserved.