The mesoporous silica MCM-41 functionalized with a chelating pyrazolylpyridine ligand (MCM-41-L2) was used as a support for the immobilization of tris(β-diketonate) complexes Ln(NTA) 3 [Ln ) Eu, Gd; NTA ) 1-(2-naphthoyl)-3,3,3-trifluoroacetonate]. The derivatized materials were characterized by powder X-ray diffraction, N 2 adsorption, FTIR and FT Raman spectroscopy, Eu L 3 -edge X-ray absorption fine structure (XAFS), diffuse reflectance, and photoluminescence spectroscopy. The spectroscopic studies, supported by ab initio calculations, provide strong evidence that the immobilized europium(III) complex is 8-coordinate, with a local coordination environment that is similar to that for a model complex containing the ligand ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate (L1). No emission from the pyrazolylpyridine ligands is observed in the room-temperature emission spectrum of MCM-41-L2/Eu, despite the fact that only about one-third are engaged in coordination with Eu 3+ ions. In contrast, the pyrazolylpyridine groups in the precursor ligand-silica exhibit efficient emission. Furthermore, the radiance value measured for MCM-41-L2/ Eu (0.33 µW cm -2 ) is only about one-half of that measured for the complex Eu(NTA) 3 ‚L1 (0.73 µW cm -2 ), even though the concentration of emitting centers in the MCM material is much lower. The results point to the existence of an unusual two-step intermolecular energy transfer between "free" and complexed ligands in MCM-41-L2/Eu, culminating in the observation of enhanced Eu 3+ luminescence.

The synthesis and structural characterization of the first examples of microporous europium(III) and terbium(III) silicates (Na(4)K(2)X(2)Si(16)O(38) x 10H(2)O, X = Eu, Tb) are reported. The structure of these solids was solved by powder X-ray diffraction ab initio (direct) methods and further characterized by chemical analysis (EDS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), (23)Na and (29)Si magic-angle spinning (MAS) NMR, and luminescence spectroscopy. Both materials display interesting photoluminescence properties and present potential for applications in optoelectronics. This work illustrates the possibility of combining in a given silicate microporosity and optical activity.

A fine‐tuning of the emission chromaticity from red to green is reported for organic–inorganic nanostructured hybrids co‐doped with Eu3+, Tb3+, and Tm3+. Raising the temperature from 200 to 300 K changes the color coordinates smoothly from the yellowish–green region of the chromaticity diagram towards the red. This is discussed in terms of thermally activated energy‐transfer mechanisms from Tb3+ energy states to the hybrid’s emitting levels.

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