Novel luminescent materials based on silica doped with an europium(III) complex of 2,6-dihydroxybenzoic acid: the crystal structure of [(nBu4N)2[Eu(2,6-Hdhb)(5)(H2O)(2)]

Novel luminescent materials were prepared by introducing a new Eu3+ complex of 2,6-dihydroxybenzoic acid (2,6-H2dhb) into a silica gel made by the sol–gel method. The crystal structure of the resulting complex [nBu4N]2[Eu(2,6-Hdhb)5(H2O)2] was determined using single-crystal X-ray diffraction. The compound was further characterised using FTIR, FT-Raman and elemental analysis. Photoluminescence measurements were performed for the isolated Eu(III) 2,6-dihydroxybenzoate complex and also for the related silica composite material

Lanthanide compounds containing a benzo-15-crown-5 derivatised [60]fullerene and the related [Tb(H2O)(3)(NO3)(2)(acac)]. C14H20O5 supramolecular adduct

Novel lanthanum(III), europium(III) and terbium(III) compounds of a benzo-15-crown-5 [60]fulleropyrrolidine were isolated in the solid state and characterised using vibrational (infrared and Raman) spectroscopy and by 13C CP MAS NMR for the lanthanum(III) compound. The photoluminescence properties were investigated for the europium(III) and terbium(III) compounds. The related [Tb(H2O)3(NO3)2(acac)] C14H20O5 [where acac ¼ acetylacetonate and C14H20O5 ¼ benzo-15-crown-5] supramolecular adduct was isolated using similar synthetic conditions, in the absence of [60]fullerene, and its crystal structure used as a model for the coordination sphere of the lanthanide [60]fullerene derivatives, with further supporting evidence given by photoluminescence measurements

Full-color phosphors from amine-functionalized crosslinked hybrids lacking metal activator ions

Sol-gel derived hybrids that contain OCH2CH2 (polyethylene glycol, PEG) repeat units grafted onto a siliceous backbone by urea, -NHC(=O)NH-, or urethane, -NHC(=O)O-, bridges have been prepared. It is demonstrated that the white light PL of these materials results from an unusual convolution of a longer lived emission that originates in the NH groups of the urea/urethane bridges with shorter lived electron-hole recombinations occurring in the nanometer-sized siliceous domains. The PL efficiencies reported here (maximum quantum yields at room temperature of ≈ 0.20 ± 0.02 at a 400 nm excitation wavelength) are in the same range as those for tetramethoxysilane-formic acid, and APTES-acetic acid, sol-gel derived phosphors. The high quantum yields combined with the possibility of tuning the emission to colors across the chromaticity diagram present a wide range of potential applications for these hybrid materials

Coordenação local do Eu(III) em híbridos orgânicos/inorgânicos emissores de luz branca Eu(III) local coordination in white light emitters organic-inorganic hybrids

<abstract language="eng">Eu3+ luminescence and EXAFS (Extended X-ray Absorption Fine Structure) results are presented for organic-inorganic hybrid gel hosts composed of a siliceous network to which small chains of oxyethylene units are covalently grafted by means of urea bridges. Coordination numbers for Eu3+ ions range from 12.8 to 9.7 with increasing Eu3+ concentration while the Eu3+-first neighbours mean distance is found to be constant at 2.48-2.49 Å in the same concentration range. Emission spectra display a broad band in the green/blue spectral region superposed to narrow lines appearing in the yellow/red region in such a way that for the eyes emission appears white. The broad band is assigned to intrinsic NH groups emission and also to electron-hole recombination in the nanosised siliceous domains. The narrow lines are assigned to intra-4f6, 5D0->7F0-4 Eu3+ transitions and from the energy position of the 7F0-4 levels a mean distance could be calculated for the Eu3+-first neighbours. The calculated results are in good agreement with the experimental ones obtained from EXAFS analysis

Sol-gel-derived potassium-based di-ureasils for "smart windows"

Sol-gel derived KCF3SO3-doped di-urea cross-linked poly(oxyethylene) (POE)/siloxane (di-ureasil) ormolytes with ∞ > n ≥ 1 (n is the number of oxyethylene units per K+ ion) have been analysed. Samples with n > 40 are thermally stable up to 310 ºC. At n ≥ 100, POE crystallites are present. At n = 5 a crystalline POE/KCF3SO3 complex with stoichiometry 1:1 is formed. In the xerogel with n =1 this complex coexists with free salt. The highest ionic conductivity is reached at n = 20. “Free” anions and weakly coordinated CF3SO3- ions appear to be the main charge carriers. The K+ ions interact with the urea carbonyl oxygen atoms at all salt concentrations. Complexation of the cations by POE occurs at n ≤ 20. In the latter composition range, contact ion pairs and higher ionic aggregates develop. The ormolytes were successfully used in the assembly of electrochromic devices (ECDs) that exhibit good electrochemical stability and demonstrate a memory effect. The ECD incorporating the ormolyte with n = 20 displays an average transmittance in the visible region of ca. 90% in the coloured state and of 85-95% in the bleached atate. The corresponding change in colour, evaluated on the basis of the Commission Internationale d/Eclairage (CIE) colour-coordinate system, is reversible: from yellow (0.38, 0.37) for the bleached state to blue (0.29, 0.29) for the coloured state.Fundação para a Ciência e Tecnologia (FCT

Promoting a significant increase in the photoluminescence quantum yield of terbium(III) complexes by ligand modification

Two discrete mononuclear complexes, [Tb(bbpen)(NO3)] (I) and [Tb(bbppn)(NO3)] (II), for which H 2 bbpen = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and H 2 bbppn = N,N'-bis(2-hydroxylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H 2 bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, I and II exhibit remarkably different ϕ values of 21 ± 2% and 67 ± 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for H 2 bbpen and H 2 bbppn confirmed that both ligands are suitable to work as "antennas" for TbIII. Considering the 5D4 lifetime profiles and the significantly higher absolute quantum yield of II, it appears that thermally active nonradiative pathways present in I are minimized in II due to differences in the conformation of the ethylenediamine bridge