Electronic band structure studies of anatase TiO2 thin films modified with Ag, Au, or ZrO2 nanophases

In this work we studied electronic structure of sol–gel grown anatase thin films modified with gold, silver, and zirconia. Surface photovoltage spectroscopy and photoluminescence spectroscopy were employed to obtain band diagrams of TiO2, TiO2/Au, TiO2/Ag, and TiO2/ZrO2 thin films. Our results showed presence of energy levels at ∼2.2, ∼2.3–2.4, and ∼2.7–2.9 eV above the top of the valence band, common in all the films. Most of these states are related to oxygen deficiency. Addition of Ag results in noticeable changes in the electronic structure and, in particular, appearance of an energy level at ∼1.8 eV, apparently associated with Ag doping. Addition of Au did not result in significant changes in electronic states and no Au-related gap states were detected. Zirconia addition resulted in an increased number of the native defect-related states whereas no Zr-related states were observed. These results are discussed in relation to the photocatalytic activity of the studied materials and the role of defect states.