Optical Properties Of Anatase TiO2 Research Articles

Effect of Ag doping concentration on the electronic and optical properties of anatase TiO2: a DFT-based theoretical study

The electronic and optical properties of pure and Ag-doped anatase TiO2 have been calculated by spin-polarized density functional theory. Ag-doped TiO2 with different Ag doping concentrations ranging from 2.08 to 8.33 % was investigated, and the electronic and optical properties evaluated. Substitutional Ag doped at Ti sites introduced Ag 4d states just above the valence-band maximum, which may help in shifting visible-light excited electrons to the conduction band. Our results show that increasing the doping concentration will enhance visible-light absorption up to Ag doping concentration of 6.25 %; however, further increase of the doping concentration leads to a decrease in visible-light absorption. These results indicate the possibility of tailoring the band gap and optical absorption of TiO2 doped with Ag by varying the doping concentration. The enhanced visible-light absorption for Ag-doped TiO2 with doping concentration of 6.25 % may be due to the existence of widely distributed Ag 4d states above the valence-band maximum and the optimal doping concentration. Ag doping shifted the absorption edge of TiO2 towards visible light, consistent with recent experimental results. Our calculation results provide a reasonable explanation for the experimental findings.

Ab initio calculations for the electronic and optical properties of Y‐doped anatase TiO2

AbstractThe yttrium (Y)‐doping effects on the electronic and optical properties of anatase TiO2 have been studied based on density functional theory calculations. Y substitution at Ti sites induces effective reduction in the band gap of anatase TiO2 and the Fermi level is shifted up in the band gap, this will be helpful in enhancing visible light absorption and electron‐hole pair separation, respectively. Optical properties show that Y doping shifts absorption edge of the TiO2 towards visible region and Y doping concentration of 4.16% have best visible light absorption among all models attributed to the optimal doping concentration. Our results may provide reasonable explanation for the experimental result. magnified imageOptical absorption spectra of pure TiO2 and Y‐doped TiO2 with different Yttrium (Y) doping concentration.

Calculations show improved photoelectrochemical performance for N, Ce, and Ce + N doped anatase TiO2

The effect of substitutional N, Ce, and Ce + N doping on the electronic structure and optical properties of anatase TiO2 have been investigated by using first-principles calculations and considering the strong correlation effect. It is found that Ce + N doping results in bandgap narrowing and also leads to a red-shift of the absorption edge of TiO2, which could meet the demand for water splitting. The decreases in the bandgap are 0.47 eV, 0.21 eV, and 1.05 eV by N, Ce, and Ce + N doping, respectively. Magnetism appears in N and Ce + N doped TiO2, which is attributed to the mismatch between the spin up and spin down states of O-2p, N-2p, and Ce-4f (for Ce + N doped). We predict that Ce + N doping is one of the best choices for enhancing the photoelectrochemical activity of TiO2.

Effects of Zr doping on electronic structures and optical properties of anatase TiO<sub>2</sub>

The systematic trends, and effect introduced by Zr-doped to TiO2, of electronic structure and optical properties of anatase TiO2 have been calculated by the plane-wave ultra-soft pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. Through the current calculations, the density of state (DOS), energy band structure and optical absorption coefficients have been obtained for TiO2 and compared with the doped TiO2, the influence of the electronic structure and optical properties caused by Zr doping has been presented qualitatively together. The results revealed that the energy band gap has been decreased owing to the doped Zr, whereas the optical absorption coefficients has been increased in the region of 360~400 nm and a red shift of absorption band can be found. Accordingly, photo catalytic activity of TiO2 has been enhanced. The current calculations show good agreement with experimental data.

First-principles study on electronic structure and optical properties of anatase TiO2 codoped with nitrogen and iron

The crystal structure, electronic structure and optical properties of nitrogen and iron codoped anatase TiO2 were studied by using the plane-wave ultrasoft pesudopotentials method based on density functional theory. The calculated results show that the octahedral dipole moments in nitrogen and iron codoped TiO2 increase due to the changes in lattice parameters, bond length and charge of atoms, which is very effective for the separation of photoexcited electron-hole pairs and the improvement of the photocatalytic activity of TiO2. Some impurity energy levels of codoped TiO2 are below the conduction band minimum, and others are above the valence band maximum. The distance between them is narrowed, which results in the redshift of the optical absorption edges to visible-light region. These impurity energy levels can reduce the recombination rate of photoexcited carriers and improve the photocatalytic efficiency of TiO2. Compared with that of Fe doped TiO2, for the codoped TiO2, the density of states peak of impurity energy levels above the valence band maximum increase apparently, which increases the electronic transition probability from the impurity energy levels to the conduction band, and improves the solar energy utilization. If the impurity level is not taken into account, compared with that of pure TiO2, the CB edge position and the VB edge position of codoped TiO2 is only slightly changed, it means that the strong redox capacity of codoping photocatalysts is still excellent.

Effects of lanthanide doping on electronic structures and optical properties of anatase TiO2 from density functional theory calculations

The supercells of pure anatase TiO2 and lanthanide-doped anatase TiO2 were calculated by density functional theory with the plane-wave ultrasoft pesudopotentials method. The effects of lanthanide doping on the crystal structure, electronic structure, optical properties and photocatalytic activity were investigated according to the calculation data. The results indicate that lanthanide doping could remarkably improve the photocatalytic activity of TiO2, and the effect of improvement was sensitive to the atomic electronic configuration and ionic radius. Most lanthanide-doped TiO2 simultaneously realized visible-light response and maintained strong redox potentials. The conclusions would have important significance for understanding and further developing TiO2 photocatalysts that are active under visible-light irradiation.

Effects of S doping on electronic structures and photocatalytic properties of anatase TiO2

The crystal structure, impurity formation energy, electronic structure and optical properties of anatase TiO2 doped with sulfur in different valence states were studied by using the plane-wave ultrasoft pseudopotential method based on first_principles. The calculations shown that the existence form of sulfur element in anatase TiO2 was related to the experimental conditions; the octahedral dipole moments were increased due to the changes of lattice parameters, bond length and charges on atoms; the band gap narrowed and the curves of light absorption red-shifted to visible-light region due to the position of conduction band downward shifting, the position of valence band upper shifting and the width of valence band broadening result from hybridizing S 3p states with O 2p states and Ti 3d states. All of these results can explain the better photocatalytic properties of S-doped anatase TiO2 in visible-light region. According to these results, the effects on electronic structures and photocatalytic properties of anatase TiO2 doping with different valence states of sulfur were compared and analyzed.

First-principles study the optical properties of anatase TiO2 by N-doping

We have calculated the optical properties of anatase TiO2 and anatase TiO2 by N-doping by plane-wave pseudo-potential method (PWP), namely the imaginary part of dielectric function ε2(ω),the optical absorption coefficient I(ω) and the reflectivity R(ω). We have given an explanation in terms of band structures why the optical spectrum has three main peaks around 2.93 eV,3.56 eV and 3.97 eV after N-doping. Our studies of the optical spectra show that the Red-shift will happen after N-doping, and experimental phenomena also approve the result.