Analysis of Ligand Field Effects in Europium(III) Phosphates

Optical spectra (powder reflectance, UV/Vis/NIR region), and temperature dependent magnetic behavior (chi, mu/mu(B)) were recorded for the series of anhydrous europium(III) phosphates (Eu3O3)-O-III(PO4), (EuPO4)-P-III, (Eu2P4O13)-P-III, lt- and ht-Eu-III(PO3)(3), and (EuP5O14)-P-III. By modeling within the AOM framework, the experimental data can be related to the ligand-field splitting experienced by the Eu3+ ions in the various mainly low-symmetry coordination environments. Our study confirms the well-established relation e(sigma)(Eu3+-O2-) ~ d(Eu3+-O2-)(-7.0) between the AOM parameter and the interatomic distance. In addition it is shown that e(sigma)(Eu3+-O2-) depends strongly on the highly variable polarizability of the oxygen ligator atoms. This polarizability can be related to the optical basicity ? of the various phosphates.