First-principles analysis method for the multiplet structures of rare-earth ions in solids

A first-principles fully relativistic multielectron method based on molecular orbital (MO) theory is applied to the analysis for the 4f5d configurations of Pr3+-doped LaF3, LiYF4 (YLF), and CaF2 crystals. The formation of MOs between the Pr 5d orbitals and the ligand fluorine 2p orbitals is considered using a (PrF11)(8-) and (PrF8)(5-) molecular models. The energy of the lowest level of 4f5d configuration decreases in the order LaF3, LiYF4, and CaF2 (O-h symmetry). The high energy in Pr3+:LaF3 is ascribed to the smaller ligand-field splitting due to the large coordination number. The analysis of many-electron wave functions shows the mixtures between the spin-orbit splitting of the 4f-level MOs and the ligand-field splitting of the 5d-level MOs. Configuration interaction with one-electron excitations gives transition probability to the originally forbidden two-electron excitations, which produce satellite structures in spectra. (C) 2004 Elsevier B.V All rights reserved.