The dependence of 10 Dq crystal field parameter for Mn4+ (3d3 configuration) and the magnitude of 7F1 level splitting for Eu3+ (4f6 configuration) on pyrochlore compositions

The excitation spectra of the six-coordinated Mn4+ ion in the pyrochlores Ln(2)Sn(2)O(7) (Ln = Lu3+, Y3+, and Gd3+) have been determined to examine the variation in the crystal field splitting parameter (10 Dq) on the Mn4+ -O-48f(2-) distance. The results obtained are entirely consistent with the expectation of the electrostatic point charge model since 10 Dq progressively increase with decreasing Mn4+ -O-48f(2-) distance. A comparative study pertaining to the behavior of the Eu3+ (4f(6)) and Mn4+ (3d(3)) ions in the pyrochlores, Ln(2)(Ti,Sn)(2)O-7 (Ln = Lu3+, Y3+, and Gd3+) is presented. The results show that the crystal-field strength that are experienced by the Mn4+ and Eu3+ ions in the Ln(2)Sn(2)O(7) (Ln = Lu3+, Y3+, and Gd3+) family of materials, are anti-correlated. Thus, for the Mn4+ ion with 3d3 configuration, the crystal-field strength increases with decreasing ionic radii of the Ln(3+) cation, while for the Eu3+ ion with 4f6 configuration, an increase with increasing ionic radii of the Ln(3+) cation is observed. However, when the Sn4+ ion of the Y2Sn2O7 lattice are replaced by the Ti4+ ion, the crystal-field strength is reduced to the extent that the exposed Mn4+ 3d(3) electrons and the screened Eu(3+)4f(6) electrons start to behave similarly. These results are explained by the variations in the covalent mixing between the ligand (O-48f(2-)) and the activator (Mn4+ and Eu3+) cations, which is driven by the competition for the O-48f(2-) electron density by the Ln(3+), Sn4+, and Ti4+ ions of the Ln(2)(Ti,Sn)(2)O-7 lattice. (C) 2012 Published by Elsevier B.V.