The identification of intra-configurational states of lanthanides and actinides

Abstract

Criteria for identifying the electronic excited states of lanthanide (III) ions are reviewed. The common practice of using an empirical Hamiltonian for this purpose may sometimes be unreliable by virtue of the neglect of the correlation crystal field (CCF). Cubic sites are virtually essential in identifying the CCF contribution. In such high symmetry two-photon absorption spectroscopy is the only practical technique with which to locate and characterise a large set of excited states. Some examples of the power of this technique are described, and the outcome of a comparison of data from fluoride, chloride and bromide elpasolites is discussed. This indicates that configurations that incorporate covalency and/or ligand polarisation need to be taken into account in explaining deviations from a one-body crystal-field model.