Unraveling the mechanism of 720 nm sub-band-gap optical absorption of a Ta3N5 semiconductor photocatalyst: a hybrid-DFT calculation

The Ta3N5 semiconductor photocatalyst possesses a 720 nm (about 1.72 eV) sub-band-gap optical absorption but the mechanism of this optical absorption is still controversial. In this study, the hybrid density functional theory calculations are performed to unravel the mechanism of 720 nm sub-band-gap optical absorption of Ta3N5. By studying the possible optical absorption initiated by the ON impurity and the V-N defect, we find that the 720 nm sub-band-gap optical absorption of Ta3N5 may be ascribed to the electron transition from V-N(center dot) to V-N(center dot center dot center dot). In addition, we propose that the 720 nm sub-band-gap optical absorption can be used to qualitatively evaluate the photocatalytic water splitting ability of Ta3N5.