Structural investigation of the new Ca3Ln2Ge3O12 (Ln=Pr, Nd, Sm, Gd and Dy) compounds and luminescence spectroscopy of Ca3Gd2Ge3O12 doped with the Eu3+ ion

• The structure of the Ca3Ln2Ge3O12 (Ln=Pr, Nd, Sm, Gd and Dy) was determined.
• Different distribution of Ln3+ ions on the three available crystal sites was observed.
• A detailed structural study focused on the metal coordination polyhedra was performed.
• The instability of the silico-carnotite structure out of the range Pr–Dy was discussed.
• The luminescence of the dopant Eu3+ ion in Ca3Gd2Ge3O12 was presented and analyzed.

The crystal structures of new rare earth-based germanate compounds (Ca3Pr2Ge3O12, Ca3Nd2Ge3O12, Ca3Sm2Ge3O12, Ca3Gd2Ge3O12 and Ca3Dy2Ge3O12) have been determined by Rietveld refinement calculations on the collected synchrotron X-ray diffraction powder patterns. A different distribution of the rare earth ions in the three available crystal sites was observed, as the main structural feature. The reasons of the instability of the silico-carnotite structure for lanthanide ions out of the range Pr–Dy have been proposed. Finally, the luminescence spectroscopy of the Eu3+ dopant ion in Ca3Gd2Ge3O12 was presented and analyzed taking into account the observed structural characteristics. The Eu3+ luminescence spectroscopy was also compared with the one of Eu3+ doped Ca3Gd2Si3O12 and Ca3Lu2Si3O12 isostructural materials.

The structural study on Ca3Ln2Ge3O12 exploiting synchrotron X-ray diffraction, allows us to determine the detailed geometry of the coordination polyhedra of the metals and their distribution in the crystal sites. These features are, in the case of Ca3Gd2Ge3O12 host, closely related to the luminescence spectroscopy of the Eu3+ dopant ion.Figure optionsDownload as PowerPoint slide