First-principles Study Of Optical Properties Of TiO₂ Doped With Nonmetals

Because TiO₂ have some particular physical chemistry properties such as nontoxic, good chemical stability and recycle, it is deemed to good materials for photocatalytic. But as band gap of TiO₂ is big, TiO₂ only can absorb ultraviolet part of sun's rays. It is greatly restricted development of TiO₂. Doping is primary approach of improving photocatalytic ability. The paper base on the first principles, study electronic structure and optical properties of intrinsic TiO₂ and TiO₂ doped with nonmetals by using computer calculated. The reason of causing the absorption band of optical catalysis to red-shift was explained, and these results of TiO₂ doped with nonmetals were sumed up and compared. For gained these important results, the paper does the following works.Firstly, electronic structure and optical properties of intrinsic TiO₂ were calculated. By analysing band structure,density of states, Valence band of pure TiO₂ mainly due to 2p density of oxygen and conductor band mainly due to 3d density of titanium was educed. Then optical properties were analysed. By studying the peak value of absorption coefficient, refractive index and dielectric function, optical response area of intrinsic TiO₂ mainly be in the UV area was educed. These are fullly prepared for the following studies of nonmetals doped TiO₂.Secondly, N-doped TiO₂ was analysed in detailed in the paper. Results show that N-doped TiO₂ made energy band gap reduced, the imaginary part of dielectric function and absorption spectra are moving to low-energy area, that is, it can cause the absorption band of optical catalysis to red-shift. The main reason is the outer 2p electron states of O and N were strongly mixed, it cause the top of the valence band shift upwards, and 2p density of O and 3d density of Ti were associated intensively, it cause the bottom of conductor band shift downwords. Similarly these are fullly prepared for the following studies of familiar nonmetals doped TiO₂.Finally C, P, N, S doped anatase TiO₂ were compared and analysed in the paper. The results show that C, P, N, S doped anatase TiO₂ all can cause the absorption band of optical catalysis to red-shift, the absorpotion coefficient in the visible light region is increased. The doping of P not only causes the absorption band to red-shift, and also gives rise to extremely big absorption coefficient in the visible region.