Abstracts 1999

Abstract of Publication No. 321

Stefan R. Lüthi, Hans U. Güdel and Markus P. Hehlen
Influence of the chemical environment on the electronic structure and spectroscopic properties of Er3+ doped Cs3Lu2Cl9, Cs3Lu2Br9, and Cs3Y2I9
J. Chem. Phys. 110, 12033-12043 (1999)      Full Text (PDF)      DOI-Link     

Abstract: Energies and intensities of 114, 101, and 76 f-f absorption transitions of Er3+ are determined by high-resolution spectroscopy in the closely related host lattices Cs3Lu2Cl9, Cs3Lu2Br9, and Cs3Y2I9, respectively. The observed trends in the energy-level structure reflect the increasing covalency and the length of the Er3+X bond. The decreasing Coulomb repulsion of the 4f electrons, spin-orbit coupling, and crystal-field potential reduces the energy splittings of the SL, SLJ, and SLJMJ states by 0.5%, 0.5%, and 25%, respectively, along the series ClBrI. Energy-level calculations that include crystal-field and correlation crystal-field terms in the effective Hamiltonian, reproduce most of the experimentally found trends. Root-mean-square standard deviations of 18.0, 19.2, and 21.9 cm1 are reached in least-squares fits to the experimental crystal-field energies. The f-f transition intensities increase along the series ClBrI as a result of the decreasing energy of the f-d bands. In the iodide compound, where the first f-d bands are as low as 30000 cm1, this influence is especially pronounced for the f-f absorptions at higher energy. The quality of the wavefunctions obtained in the energy-level calculations is not sufficient to reliably calculate the relative absorption intensities of individual crystal-field components within a given multiplet transition. This deficiency is ascribed to small deviations of the actual coordination geometry of Er3+ from the C3v point group symmetry that was assumed in the calculation. Intensities are analyzed on the level of multiplet-to-multiplet transitions using the Judd-Ofelt formalism.

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