Site-selective spectroscopy in Eu3+ doped alpha-cordierite / Eur. J. Solid State Inorg. Chem.

The location of Eu3+ in alpha-cordierite, synthesized by a sol-gel route, was investigated by using both site-selective spectroscopy and time-resolved spectroscopy. F-7(0) --> D-5(1,2) excitation and D-5(0) --> F-7(0,1,2) emission spectra were performed at 77 K. The Eu3+ ions are distributed in two families : the A family in the structure channels and the B family at (4c) position of D-2h(16) in substitution for Mg2+. Four B subfamilies were characterized and understood as a difference at the second neighbours, i.e., the four possible occupations of the surrounding tetrahedra by Al and Si. The A family was characterized by anomalous spectra : strong D-5(0) --> F-7(0) transition, high position of the D-5(0), D-5(1) and D-5(2) levels and very targe F-7(1,2) splittings. By comparison with Eu-doped apatites, in which similar features occur, a predominant Eu-O bonding of covalent character with one of the oxygen ions bordering the channel was assumed. When the annealing temperature increases, Eu3+ ions migrate from the channel to the (4c) position. / The location of Eu3+ in alpha-cordierite, synthesized by a sol-gel route, was investigated by using both site-selective spectroscopy and time-resolved spectroscopy. F-7(0) --> D-5(1,2) excitation and D-5(0) --> F-7(0,1,2) emission spectra were performed at 77 K. The Eu3+ ions are distributed in two families : the A family in the structure channels and the B family at (4c) position of D-2h(16) in substitution for Mg2+. Four B subfamilies were characterized and understood as a difference at the second neighbours, i.e., the four possible occupations of the surrounding tetrahedra by Al and Si. The A family was characterized by anomalous spectra : strong D-5(0) --> F-7(0) transition, high position of the D-5(0), D-5(1) and D-5(2) levels and very targe F-7(1,2) splittings. By comparison with Eu-doped apatites, in which similar features occur, a predominant Eu-O bonding of covalent character with one of the oxygen ions bordering the channel was assumed. When the annealing temperature increases, Eu3+ ions migrate from the channel to the (4c) position.