Abstract. The tendency of Eu³⁺ in a crystal to attract an electron from the surrounding ligands and become Eu²⁺ can be represented by a six-body operator acting within the configuration 4f⁶. The matrix elements of this operator within any configuration 4f^N with N>6 are expressible in terms of those of the unit tensors U^(k) and the double tensor V^(1k). This mechanism of charge transfer generally acts in a sense opposite to that of the spin correlated crystal field. This provides a possible source for the anomalous crystal-field splittings of Ho³⁺ 4f^{10 3}K_J as well as the abrupt decline in the sixth-rank crystal-field parameters in passing from Eu³⁺ to Tb³⁺ in the LaCl₃ lattice.

Print publication: Issue 14 (20 May 1980)