Based on density functional theory, calculations were performed for geometrically optimized N -doped TiO 2 models. The effect of N dopant and its increasing doping concentration on the band structure are elucidated. N doping narrowed the band gap of TiO 2 and introduced isolated N 2p states within the band gap. The location of N 2p states within the band gap can be optimized by N doping concentration. All N -doped TiO 2 models shifted the absorption edge of TiO 2 toward visible light region and increasing N doping concentration improved the visible light absorption. N -doped TiO 2 model having reduced band gap without any isolated states will improve the photocatalytic response. Our results provide strong theoretical background for existing experiments.
Using first principle calculations, the effect of Ce with different doping concentrations in the network of Zirconium dioxide (ZrO2) is studied. The ZrO2 cell volume linearly increases with the increasing Ce doping concentration. The intrinsic band gap of ZrO2 of 5.70 eV reduces to 4.67 eV with the 2.08% Ce doping. In 4.16% cerium doped ZrO2, the valence band maximum and conduction band minimum come closer to each other, about 1.1 eV, compared to ZrO2. The maximum band gap reduction of ZrO2 is observed at 6.25% Ce doping concentration, having the value of 4.38 eV. No considerable shift in the band structure is found with further increase in the doping level. The photo-response of the ZrO2 is modulated with Ce insertion, and two distinct modifications are observed in the absorption coefficient: an imaginary part of the dielectric function and conductivity. A 2.08% Ce-doped ZrO2 modeled system reduces the intensities of peaks in the optical spectra while keeping the peaks of intrinsic ZrO2. However, the intrinsic peaks related to ZrO2 completely vanish in 4.16%, 6.25%, 8.33%, and 12.5% Ce doped ZrO2, and a new absorption hump is created.
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