Luminescence of Eu3+ and Pr3+ in the weberite, Ca2La3Sb3O14

Abstract The spectroscopic properties of the Eu 3+ and Pr 3+ ions in the weberite, Ca 2 La 3 Sb 3 O 14 are examined in this paper. The Eu 3+ is used as a structural probe ion to elucidate the local site symmetry of the La 3+ ion in Ca 2 La 3 Sb 3 O 14 . The interpretation of the Eu 3+ emission spectrum is not consistent with the C 2h and S 2 (C i ) point symmetry that are prescribed for the La 3+ sites by the I 2/ m 11 space group of Ca 2 La 3 Sb 3 O 14 . The emission spectrum of Ca 2 La 3 Sb 3 O 14 :Pr 3+ is dominated by emission transitions emanating from the 1 D 2 state. The low energy of the Pr 3+ 4f 2  → 4f 1 5d 1 interconfiguration excitation transition in Ca 2 La 3 Sb 3 O 14 (3.83 eV or 32 258 cm −1 ) is attributed to the high covalence which is induced by short Pr 3+ O 2− bond distances within the coordination polyhedral units in the lattice. The high covalence of chemical bonding appears to be the hallmark of the weberite structure. A study that compares the optical properties of Eu 3+ and Pr 3+ in the weberites, Ca 2 La 3 Sb 3 O 14 and NaGdSb 2 O 7 is presented.