Cr和C共掺TiO_2的电子结构和光学性质的研究

利用第一性原理计算,研究了Cr与C共掺锐钛矿型TiO_2的能带的结构,态密度和光学性质.我们构建了两种不等价的Cr与C紧邻共掺体系:CrC_1-TiO_2和CrC_2-TiO_2.CrC_1-TiO_2体系在价带上方出现了主要由C-2p轨道和Cr-3d轨道耦合成的子带.同时,由于姜-泰勒变形效应,Cr-3d轨道的t_(2g)轨道进一步分裂的成Cr-3d_(yz)轨道在导带底形成附加带,有效带隙较纯TiO_2相比变窄了0.84eV.CrC_2-TiO_2体系带隙中有深带隙态存在,由于深间隙态的存在,价带顶到深带隙的能量宽度为0.84eV,电子从价带顶转移到导带底的所需要的能量将大大减小.最后,我们对纯TiO_2和Cr与C紧邻共掺TiO_2的光学特性进行了计算.结果显示Cr与C共掺TiO_2的光学吸收谱都有很好的可见光区域分布,大大提高了太阳光的利用率.

Study on the electronic structure and optical properties of Cr and C doped TiO2

Using the first-principle calculations, the band structure, density of states and optical properties of Cr and C doped anatase TiO2 were studied . We have constructed two kinds of Cr and C co-doping systems: CrC1-TiO2 and CrC2-TiO2 . For the CrC1-TiO2 system, there are subbands which are mainly composed of C-2p orbit and Cr-3d orbit. At the same time, due to the Jahn-Teller effect, the t2g orbit of Cr-3d orbit further splits into Cr-3dyz orbit and forms an additional band at the bottom of the conduction band. The effective band gap is narrowed ~0.84 eV than that of pure TiO2. For the CrC2-TiO2 system, there is a deep band gap state in the band gap. Because of the deep gap state, the energy width from the valence band top to the deep band gap is ~0.84 eV, and the energy required for electron transfer from the valence band top to the conduction band bottom will be greatly reduced. Finally, we calculated the optical properties of pure TiO2 and Cr and C co-doped TiO2. The results show that the optical absorption spectra of Cr and C co-doped TiO2 have a good distribution of visible light region, which greatly improves the utilization of sunlight.