Influence of Annealing Temperatures on Raman and Optical Absorption Spectra of TiO2 Nanorod Thin Film Coatings

Titanium dioxide (TiO2) is an important semiconductor material widely used in both fundamental studies and technological applications. Herein, TiO2 nanorod thin film coatings were fabricated on transparent conductive fluorine-doped tin oxide (FTO) substrates using a hydrothermal synthesis approach, followed by annealing at various temperatures. The effects of annealing temperatures on the Raman and optical absorption spectra were systematically investigated to elucidate the behavior of Raman-active lattice vibrations and optical transitions. As the annealing temperatures increased, both the full width at half maximum of the Raman vibrational modes and the band gap of the TiO2 nanorod thin films decreased. These trends indicate enhanced crystallinity and phonon lifetimes at higher annealing temperatures. The longer phonon lifetimes contribute to reduced electron–hole recombination, while the narrower band gap extends the optical absorption range into the visible region. This study provides valuable insights into the relationship between annealing temperatures and the structural, vibrational and optical properties of rutile TiO2 nanorod thin film coatings, highlighting their potential for improved performance in photoelectrocatalytic and optoelectronic applications.