Influence of rhodamine 6G doping on the optical properties of TiO2 sol-gel films

Amorphous titanium dioxide (TiO2) thin films doped with rhodamine 6G (R6G) were deposited on glass substrates by the sol-gel process. The optical properties of the films were characterized by photoacoustic, excitation, and fluorescence spectroscopies. The absorption spectra of the R6G-doped TiO2 films exhibited two well-defined absorption regions: an absorption band over 2.0 eV attributed to rhodamine 6G and a band above 3.0 eV corresponding to TiO2 absorption. While the onset of the R6G absorption band was shifted by 0.06 eV towards lower energies as the R6G doping concentration increased within the interval of 0.01–0.10 mol %, the onset to high absorption (TiO2 band) for the doped films decreased only by 0.01 eV within the same interval. In addition, the optical absorption of undoped rutile-phase bulk TiO2 was calculated and compared to the experimental results. The estimated theoretical value of rutile TiO2 sample was 3.0 eV. This theoretical result shows good agreement when compared with the experimental data of undoped TiO2 sol-gel films, as well as the undoped TiO2 film prepared by sputtering.