Molecule-Like Eu³⁺-Dimers Embedded in an Extended System Exhibit Unique Photoluminescence Properties

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)] x xH(2)O (Ln(3+) = Sm(3+), Eu(3+), Gd(3+), Tb(3+)), the first silicate possessing Ln(3+)-O-Ln(3+) dimers (inter-Ln distance ca. 3.9 A), i.e., two edge-sharing {LnO(6)} octahedra embedded in a crystalline matrix. It is totally unprecedented that in AV-24 Eu(3+)-O-Eu(3+) 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 Eu(3+) ion, and (ii) exhibit the unusually long (5)D(0) lifetime of 10.29 ms (12 K). In accord with the experimental evidence, a molecular orbital model shows that the Eu(3+)-O-Eu(3+) dimers are energetically more stable than the individual metal ions.

The luminescence of NaxEu3+(2−x)/3MoO4scheelites depends on the number of Eu-clusters occurring in their incommensurately modulated structure

“…7), which mainly contribute to quantum yields. At lower temperature, luminescence intensity from the diatomic Eu1-clusters increases faster, 20 and the lower-percent component, 6-14%, corresponding to Eu2 becomes undetectable. Hence, the behavior of the decays directly correlates with the Eu 3+ crystallographic characteristics, which are different for 3-and (3 + 1)-dimension structural symmetry.…”

New RE microporous heteropolyhedral silicates containing 41516182tetrahedral sheets

“…K 7 Ln 3 [Si 12 O 32 ]ÁxH 2 O; Ananias et al, 2009); finally, quaternary tetrahedra require T/O > 2/5 and, more importantly, the sheet must be either branched (e.g. If only tertiary tetrahedra occur T/O = 2/5, as in micas and in the compounds described in this article; the presence of non-tertiary tetrahedra implies T/O < 2/5 (e.g.…”

Crystal structures of new potassium silicates and aluminosilicates of Sm, Tb, Gd, and Yb and their relation to the armstrongite (CaZr(Si6O15)·3H2O) structure

“…Only water and very little K were identified in the center of the channels of the KTb-silicate. 6 A very similar structure was described in reference [12] Differences are restricted to the occupation of the structural channels.…”