Site selective luminescence spectroscopy of Eu3+ in the rhombohedral pyrochlores Mg2La3Sb3O14 and Ca2La3Sb3O14: Observation of Eu3+ in a strongly distorted site

Low temperature site selective spectroscopy has been used to probe the distribution of the Eu3+ ion on sites available in the ordered and disordered pyrochlores, Mg2La3Sb3O14 and Ca2La3Sb3O14. While the Mg-pyrochlore shows the presence of a single site with inversion symmetry, the emission spectrum of the Ca-pyrochlore is indicative of the presence of several different non-centrosymmetric sites for the dopant ion. These observations are consistent with the structural model that was proposed earlier. The 5D0 →7F0 emission transition in the Ca-pyrochlore occurs at very high energy (17,550 cm−1) and under a very specific excitation wavelength. Possible explanation for this observation is provided.