Optical Spectra and Magnetic Behavior of a Wide Range of Europium(III) Oxo-Compounds: Analysis of the Ligand-Field Effects.

The europium-oxygen interaction in nine different europium(III) oxo-compounds (including C-type Eu2O3) was investigated on the basis of powder reflectance spectra (near-IR/vis/UV) and temperature-dependent magnetic measurements. Computation of the transition energies and of the effective Bohr magneton numbers for Eu3+ in the different ligand fields were performed within the framework of the angular overlap model (AOM) using the computer program BonnMag. These calculations show that all electronic transition energies in the optical spectra, the magnetic susceptibilities as well as their temperature dependence, are very well-accounted for by AOM. BonnMag provides a facile way to perform these calculations. Analysis of the obtained "best fit" AOM parameters eσ(EuIII-O) shows that these are significantly influenced by the further bonding partners of oxygen ("second-sphere ligand-field effect"). An increase of eσ, max(EuIII-O) from 404 cm-1 (EuPO4) to 687 cm-1 (EuSbO4), both normalized to d(EuIII-O) = 2.38 Å, is found. Correlation of this variation to oxide polarizability and optical basicity of the oxo-compounds is discussed.