Two-photon spectra of single-crystal gadolinium diglycolate.

Studies on parity-allowed two-photon transitions within the f n configuration of Gd 3+ ion in a trigonal crystal, gadolinium diglycolate, are presented. The assignment of components of each J manifold is supported by a 13-parameter energy-level calculation. The relative two-photon integrated intensities for J manifolds, as well as relative line strengths for its Stark components, are calculated by second- and third-order perturbation theory, including spin-orbit interaction within intermediate f n d configurations. Although many of the spectral features are explained by comparison of observed and calculated values, certain gross anomalies, inherent in the crystal-field model, still remain. The exercise points out the need to develop a workable theory for two-photon intensities taking into account the important role played by ligands.