A Structural and Spectroscopic Investigation of Rhombohedral Pyrochlores M2La3Sb3O14 (M = Mg or Ca) Doped with Eu3+

Mg 2 La 3 Sb 3 O 14 and Ca 2 La 3 Sb 3 O 14 are rhombohedral pyrochlores. A detailed structural investigation shows that, as a consequence of the larger difference in the ionic radii of La 3+ and Mg 2+ with respect to La 3+ and Ca 2+ , in the former compound there is an ordered distribution of the cations and a local inversion symmetry for La 3+ sites. On the contrary, because of the cationic disorder observed in Ca 2 La 3 Sb 3 O 14 , breaking of the local inversion symmetry at La 3+ is observed. This very peculiar structural behavior has a big impact on the Eu 3+ luminescence spectroscopy of the doped materials Mg 2 La 3 Sb 3 O 14 :1% Eu 3+ and Ca 2 La 3 Sb 3 O 14 :1% Eu 3+ . Moreover, first-principles calculations confirm the structural evidence, and elucidate the structure-spectroscopy relationships of these Eu 3+ -doped materials.