Polarized Optical Spectra, Transition Line Strengths, and the Electronic Energy-Level Structure of Eu(dpa)33- Complexes in Single Crystals of Hexagonal Na3[Yb0.95Eu0.05(dpa)3]·NaClO4·10H2O

Abstract

Polarized optical absorption and emission measurements are used to locate and assign 52 crystal-field energy levels split out of the 4f6 electronic configuration of Eu3+ in single crystals of Na3[Yb0.95Eu0.05(dpa)3]·NaClO4·10H2O (where dpa ≡ dipicolinate dianion ≡ 2,6-pyridinedicarboxylate). In these crystals, each Eu3+ is coordinated to three dipicolinate (dpa) ligands, and the tris-terdentate Eu(dpa)33- chelate structures have trigonal-dihedral (D3) symmetry. The combined optical absorption and emission measurements provide access to the energy-level structures of 27 different 4f6[SL]J multiplet manifolds of Eu3+, and 21 of these multiplet manifolds are represented among the 52 crystal-field levels that are characterized with respect to both location (energy) and symmetry properties. The energy-level data obtained from experiment are analyzed in terms of a model Hamiltonian that includes consideration of both isotropic and nonisotropic 4f-electron/crystal-field interactions. A parametrized form of this Hamiltonian is used to perform parametric fits of calculated-to-experimental energy-level data, and the results obtained from these data fits show a root mean square (rms) deviation of 9.8 cm-1 between calculated and observed energies. The Hamiltonian parameters evaluated from the energy-level analyses provide information about both the anisotropies and the overall strength of the 4f-electron/crystal-field interactions that contribute to the energy-level structure of Eu(dpa)33- complexes. In addition to energy-level data, the absorption measurements performed in this study permit the quantitative determination of relative optical line strengths for 22 different Stark-level-to-Stark-level transitions observed in the low-temperature axial absorption spectra of Eu(dpa)33- in Na3[Yb0.95Eu0.05(dpa)3]·NaClO4·10H2O.