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

Abstract The spectroscopic properties of the Eu3+ and Pr3+ ions in the weberite, Ca2La3Sb3O14 are examined in this paper. The Eu3+ is used as a structural probe ion to elucidate the local site symmetry of the La3+ ion in Ca2La3Sb3O14. The interpretation of the Eu3+ emission spectrum is not consistent with the C2h and S2 (Ci) point symmetry that are prescribed for the La3+ sites by the I2/m11 space group of Ca2La3Sb3O14. The emission spectrum of Ca2La3Sb3O14:Pr3+ is dominated by emission transitions emanating from the 1D2 state. The low energy of the Pr3+4f2 → 4f15d1 interconfiguration excitation transition in Ca2La3Sb3O14 (3.83 eV or 32 258 cm−1) is attributed to the high covalence which is induced by short Pr3+ O2− 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 Eu3+ and Pr3+ in the weberites, Ca2La3Sb3O14 and NaGdSb2O7 is presented.