Incorporating Nitrogen Atoms at TiO₂ Lattice Sites for Improved Transparency and Visible-Light Photocatalytic Activity

Doping nitrogen into titanium dioxide (N-TiO₂) is vital to extend its photocatalytic activity to the visible-light range. However, this often leads to a significant decrease in film transparency, which hinders its usage in environmental applications. In this study, we report the deposition of N-TiO₂ films with a visible-light activity and improved transparency. Using pulsed magnetron sputtering, we achieve a high concentration (∼7.5%) of nitrogen incorporation into anatase TiO₂ films. This results in a much-reduced band gap (∼1.92 eV) and remarkable photocatalytic performance in the visible-light range. More importantly, the transparency of the films does not decrease significantly even at this high doping concentration, in contrast to the samples prepared using the conventional direct current (DC) sputtering process. First-principles calculations indicate that the improved incorporation of nitrogen at the substitutional lattice sites is responsible for the reduced band gap and improved transparency. This work demonstrates a viable method to achieve transparent N-TiO₂ films with a visible-light activity, which could be useful for various environmental applications such as self-cleaning glass.