Electric dipole intensity parameters for lanthanide 4f → 4f transitions

Abstract

A general parametrization scheme for the electric dipole intensities of lanthanide 4f → 4f crystal-field transitions is proposed. This parametrization is sufficiently general to accommodate any 4f → 4f intensity mechanism based on the ‘‘one-electron’’ and ‘‘one-photon’’ approximations for lanthanide-ligand-radiation field interactions. It includes as a subset, the familiar Judd–Ofelt–Axe intensity parameters, AtpΞ(t, λ), but introduces additional parameters which are shown to be essential in cases where the lanthanide-ligand pairwise interactions cannot be assumed to be cylindrically symmetric. Expressions are given for calculating the general intensity parameters in terms of two specific intensity mechanisms. Special consideration is given to the effects of ligand polarizability anisotropy on the intensity parameters. A set of ‘‘intrinsic’’ intensity parameters are also introduced. These parameters are defined within the context of the ‘‘superposition’’ model for lanthanide-ligand interactions, and are independent of coordination geometry and lanthanide site symmetry.