Electronic structure of layered tantalates photocatalysts, RbLnTa2O7 (Ln=La, Pr, Nd, and Sm)

The correlation of electronic structure with photocatalytic properties of layered perovskite tantalates, RbLnTa(2)O(7) (Ln=La, Pr, Nd, and Sm), containing the partly-occupied Ln4f shell is studied by means of valence band photoemission (XPS) measurement and first-principles calculations of the band structure based on the all-electron full-potential linear augmented plane-wave (FLAPW) method. The unoccupied La4f level is located on the bottom of the conduction band, whereas the partially occupied 4f levels become lowered with an increase of 4f electrons down to the position above the valence band edge (Ln=Pr) and finally fall into the valence band mainly comprised of O2p orbitals (Ln=Nd and Sm). It was suggested that unoccupied as well as occupied 4f orbitals are not completely localized but partly contribute to the hybridization with O2p and Ta5d orbitals. The different photocatalytic activity of the present system for the overall water splitting is closely related to the degree of the Ln-O-Ta hybridization, which affect not only the positions, of the conduction band and valence band edges, but also the density of states (DOS) distribution in both bands. (C) 2001 Elsevier Science Ltd. All rights reserved.