Electronic structure of layered tantalates photocatalysts, RbLnTa(2)O(7) (Ln=La, Pr, Nd, and Sm)

The correlation of electronic structure with photocatalytic properties of l ayered perovskite tantalates, RbLnTa(2)O(7) (Ln=La, Pr, Nd, and Sm), contai ning the partly-occupied Ln4f shell is studied by means of valence band pho toemission (XPS) measurement and first-principles calculations of the band structure based on the all-electron full-potential linear augmented plane-w ave (FLAPW) method. The unoccupied La4f level is located on the bottom of t he conduction band, whereas the partially occupied 4f levels become lowered with an increase of 4f electrons down to the position above the valence ba nd 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 oc cupied 4f orbitals are not completely localized but partly contribute to th e hybridization with O2p and Ta5d orbitals. The different photocatalytic ac tivity of the present system for the overall water splitting is closely rel ated 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 dens ity of states (DOS) distribution in both bands. (C) 2001 Elsevier Science L td. All rights reserved.