abstract
Much is known about the photoluminescence of lanthanide-containing systems, particularly amorphous silicates or organic-inorganic hybrids and crystalline metal-organic frameworks. Comparatively, stoichiometric microporous Ln-silicates are poorly studied. Here, we report the exceptional photoluminescence of microporous AV-24, K-7[Ln(3)Si(12)O(32))center dot xH(2)O (Ln(3+) = Sm3+, Eu3+, Gd3+, Tb3+), the first silicate possessing Ln(3+)-O-Ln(3+) dimers (inter-Ln distance ca. 3.9 angstrom), i.e., two edge-sharing {LnO(6)} octahedra embedded in a crystalline matrix. It is totally unprecedented that in AV-24 Eu3+-O-Eu3+ dimers behave like discrete entities, i.e., molecules: they (i) have a unique emission signature, with pseudopoint group symmetry (C-i), different from the symmetry (C-1) of each individual constituent Eu3+ ion, and (ii) exhibit the unusually long D-5(0) lifetime of 10.29 ms (12 K). In accord with the experimental evidence, a molecular orbital model shows that the Eu3+-O-Eu3+ dimers are energetically more stable than the individual metal ions.
keywords
MICROPOROUS LANTHANIDE SILICATES; RARE-EARTH IONS; ENERGY-TRANSFER; TRANSITIONS; SPECTRA; LIGHT; CONDUCTIVITY; LUMINESCENCE; INTENSITIES; FIELD
subject category
Chemistry
authors
Ananias, D; Kostova, M; Paz, FAA; Neto, ANC; De Moura, RT; Malta, OL; Carlos, LD; Rocha, J
our authors
Albano Neto Carneiro Neto
Junior Researcher
Duarte Ananias
Assistant Researcher
Filipe Alexandre Almeida Paz
Principal Researcher
João Rocha
Full Professor
Luís Carlos
Full professoracknowledgements
We acknowledge the Portuguese Foundation for Science and Technology (FCT), PTDC and FEDER, EMMI for financial support of this work. We thank Prof. Sidney Ribeiro (UNESP Araraquara, Brazil) for useful discussions.