APPLICATION OF THE CORRELATION-CRYSTAL-FIELD DELTA-FUNCTION MODEL IN ANALYSES OF PR3-LEVEL STRUCTURES IN CRYSTALLINE HOSTS((4F(2)) ENERGY)

The 4f(2) electronic energy-level structures observed for Pr3+ in seve n different crystalline host materials are analyzed and compared. The analyses are based on a model Hamiltonian that includes consideration of both one-electron crystal-field (CF) and two-electron correlation-c rystal-field (CCF) interactions. Special attention is given to the imp ortance of CCF interactions in determining the crystal-field energy-le vel structures observed within particular anomalous multiplet manifold s of Pr3+ such as the D-1(2) and (1)G(4) multiplets, which typically e xhibit crystal-field energy-level structures that cannot be explained in terms of 'standard' one-electron CF interaction models. It is shown in the present study that the apparently anomalous behavior of these multiplets can be explained in terms of two-electron CCF effects. It i s further shown that the relevant CCF effects can be satisfactorily mo deled by use of a highly restricted 'delta-function' form of the gener al two-electron CCF model Hamiltonian, where the dominant two-electron correlation effects are assumed to arise from spin-paired electrons o ccupying the same angular orbital. Incorporation of this restricted CC F model Hamiltonian into the modeling calculations requires the introd uction of only one or two additional parameters beyond those required for the standard one-electron CF modeling calculations, and satisfacto rily resolves the major discrepancies between observed and calculated crystal-field splittings for the anomalous D-1(2) and (1)G(4) multiple t manifolds in the energy-level structures of LaCl3:Pr3+, GdCl3:Pr3+ C s2NaPrCl6, Cs2NaYCl6:Pr3+, LiYF4:Pr3+, LiBiF4:Pr3+, and CsCdBr3:Pr3+. (C) 1998 Elsevier Science B.V.