The effects of Sc doping and O vacancy on the electronic states and optical properties of m-BiVO4

Abstract

Based on density functional theory (DFT), the effects of scandium (Sc) doping and oxygen vacancy (VO) on the electronic states and optical properties of monoclinic BiVO4 (m-BiVO4) are investigated. The generalized gradient approximation plus U (GGA+U) method is adopted during the calculation of the electronic properties to compensate for the limitations of the DFT method. The ideal m-BiVO4 has a direct band gap of 2.400 eV, and if Bi in m-BiVO4 is substituted by Sc (subSc-Bi), the direct band gap will be reduced to 2.393 eV. However, if V is replaced by Sc (subSc-V) as well as oxygen vacancy induced (subSc–V+VO), the band gap will become indirect with values of 1.913 and 2.198 eV, respectively. The reduction capability is in the sequence of subSc–Bi > ideal > subSc–V+VO > subSc–V, while the oxidation capability is in the order of ideal > subSc–Bi > subSc–V+VO > subSc–V. The ε1(0) of the ideal, subSc–Bi, subSc–V, and subSc–V+VO defective m-BiVO4 are 8.290, 8.293, 12.791, and 8.285, respectively. The optical absorptions of ideal and subSc–Bi m-BiVO4 show anisotropy and they are nearly independent of the defect concentration. SubSc–V m-BiVO4 exhibits stronger absorption than the other three semiconductors. The absorptions of subSc–V+VO m-BiVO4 vary widely with the defect concentrations, where 3.906% defect concentration of m-BiVO4 has the strongest absorption. The estimated optical band gaps [Formula: see text] are smaller than Eg for ideal and defective m-BiVO4.