ea. The first bandgap reflects
the effect of N-doping on the main band edges of the oxide. The second
gap, which is narrower than the original value, suggests that
nitrogen doping contributed to the redshift of the bandgap. This
narrower bandgap will facilitate excitation of electrons from the
valence band to the conduction band in the doped oxide semiconductor
under visible light illumination, which can result in higher
photocatalytic activities.