The mechanism of photocatalyst and the effects of co-doping CeO2 on refractive index and reflectivity from DFT calculation

Abstract

In this paper, the structural, electronic and optical properties of (N, P), (N, S), (C, P) and (C, S) co-doped CeO2 are studied by using the method of density functional theory (DFT) + U method. The calculated lattice constant, the charge, the bond order, the cell volume and the bond length of CeO2 are consistent with previous experimental and theoretical results. For co-doped CeO2 systems, the calculated results show that the lattice constants, the bond order of CeO as well as the cell volume increase, while the charge of Ce decrease. Due to co-doping, the energy gap (Eg) between valence band and conduction band becomes narrower than that of pure CeO2. Meanwhile, the electron structures of the co-doped CeO2 are changed, which may lead to transformation of optical properties. Nonmetallic atomic orbital (C 2p, N 2p, P 3p, S 3p) and metal atomic orbital (Ce 4f and 5d) are hybridized, except for the hybridization between Ce (4f and 5d) and O (2p). Compared with CeO2, Eg between Ce 4f and Ce 5d becomes smaller. Further, the optical absorption, refractive index and reflectivity of them are investigated. The calculated results reveal that their absorption edges have a red shift. Co-doping enhances visible light photocatalytic activity, which is related to the transition of valence band → conduction band, and Ce 4f → Ce 5d. The co-doped CeO2 has high refractive index and reflectivity. Therefore they may be becoming an important materials in single (or multilayered) optical coatings and optical reflective pigments.