Structure and luminescence of Eu3+-doped class I siloxane-poly(ethylene glycol) hybrids

Transparent, flexible, and luminescent EU3+-doped siloxane-poly(ethylene glycol) (PEG) nanocomposites have been obtained by the sol-gel process. The inorganic (siloxane) and organic PEG phases are usually linked by weak bonds (hydrogen bonds or van der Waals forces), and small-angle X-ray scattering (SAXS) measurements suggest that the structure of these materials consists of fractal siloxane aggregates embedded in the PEG matrix. For low Eu3+ contents, n = 300 and n = 80, the aggregates are small and isolated and their fractal dimensions are 2.1 and 1.7, respectively. These values are close to those expected for gelation mechanisms consisting of reaction-limited cluster-cluster aggregation (RLCCA) and diffusion-limited cluster-cluster aggregation (DLCCA). For high Eu3+ content, SAYS results are consistent with a two-level structure: a primary level of siloxane aggregates and a second level, much larger, formed by the coalescence of the primary ones. The observed increase in the glass transition temperature for increasing Eu3+ content is consistent with the structural model derived from SAXS measurements. Extended X-ray absorption fine structure (EXAFS) and luminescence spectroscopy measurements indicate that under the experimental conditions utilized here Eu3+ ions do not strongly interact with the polymeric phase.

Eu3+ as a spectroscopic probe in phosphors based on spherical fine particle gadolinium compounds

This work reports on the luminescence spectroscopy sensitivity in the determination of the phase purity in gadolinium compounds using Eu3+ as a probe. Cubic Gd2O3 and hexagonal Gd2O2S doped with Eu3+ spherical fine particles were obtained from doped gadolinium basic carbonates with morphological control and were also characterized by IR and XRD. Doped samples present Eu3+ characteristic transitions, with specific energy positions related to each phase. Emission and excitation spectra patterns were established for oxide and oxysulfide compounds, then oxysulfate and oxide impurities generated during oxysulfide preparation were monitored. From emission spectra some experimental intensity parameters were also calculated. All spectroscopic results reflect the presence or not of impurities in all compounds. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

The effect of EU3+ ion doping concentration in Gd2O3 fine spherical particles

This work reports on the preparation of Gd2O3, cubic system, with spherical particles, narrow size distribution, whether or not doped with 1-5 at.% of Eu3+ and the influence of Eu3+ concentration on optical and morphological properties. Average diameter and size distribution particle analyses were performed for all samples from SEM results. Doped samples were also investigated by luminescence spectroscopy and emission kinetic measurements. All oxide samples present a particle average diameter distribution range from 110 to 150 nm and a decrease of particle average diameter with the presence of Eu3+. The particle size decrease is almost the same for all samples with different doping ion concentration. Therefore, the presence of doping ion may be inhibiting particle growth after the nucleation process. From spectroscopic studies, the doping ion distribution in the surface of oxide samples can be considered homogeneous because concentration quenching is not observed, as well as a significant difference among the calculated lifetime for each sample. (C) 2002 Elsevier B.V. B.V. All rights reserved.

EU-3+ AND GD-3+ SPECTROSCOPY IN FLUOROINDATE GLASSES

Luminescence data for Eu3+ and Gd3+ in fluoroindate glasses are compared to those of a fluorozirconate glass. Emission is observed from Eu3+ 5D(J) (J = 0, 1, 2 and 3) and Gd3+ P-6(7/2) excited-state levels and the results put in evidence Eu-Eu and Gd-Eu energy transfer processes. Vibronic bands related to a 320 cm-1 vibrational mode could be observed for Eu3+ luminescent transitions with DELTAJ = 0, 1 and 2 and also for the P-6(7/2) --> S-8(7/2) transition of Gd3+. Lanthanide ion site symmetry is closer to an inversion center in fluoroindate glasses than it is in fluorozirconate.

The Role of the Eu3+ Concentration on the SrMoO4:Eu Phosphor Properties: Synthesis, Characterization and Photophysical Studies

SrMoO4 doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr1-xEuxMoO4 powders, where x = 0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO4:Eu3+ were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 A degrees C for 2 h, 2 theta = 27.8A degrees (100% peak). The excitation spectra of the SrMoO4:Eu3+ (lambda(Em.) = 614 nm) presented the characteristic band of the Eu3 + 5L6 transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO4 matrix. The emission spectra of the SrMoO4:Eu3+ powders (lambda(Exc.) = 394 and 288 nm) show the group of sharp emission bands among 523-554 nm and 578-699 nm, assigned to the D-5(1)-> F-7(0,1and 2) and D-5(0)-> F-7(0,1,2,3 and 4), respectively. The band related to the D-5(0)-> F-7(0) transition indicates the presence of Eu3+ site without inversion center. This hypothesis is strengthened by the fact that the band referent to the D-5(0)-> F-7(2) transition is the most intense in the emission spectra.

Determination of the local site occupancy of Eu3+ ions in ZnAl2O4 nanocrystalline powders

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Photoluminescence of bulks and thin films of Eu3+-doped organic/inorganic hybrids

Organic-inorganic hybrids formed by polyether-based chains grafted to both ends to a siliceous backbone through urea cross-linkages (-NHC=O)NH-), named di-ureasil, have been used as host for incorporation of Eu3+ in the form of EuCl3. The bulks and the thin films, both optically transparent, were characterized by excitation, absorption and emission spectroscopy. Photoluminescence results point out that the Eu3+ ions occupy, at least, two distinct local environments. Besides, the processing method (thin films or bulks) has influence on the energy levels of the hybrid host probably due to the lower degree of organization of the thin films structure. (c) 2007 Elsevier B.V. All rights reserved.

Synthesis of lanthanide oxysulfides activated by Eu3+. A topochemical reaction

The oxysulfide compounds La2O2S:Eu and Y2O2S were obtained directly from thermodecomposition of the respective oxalate compounds under argon and sulfur vapor, the obtained compounds were analyzed by infrared spectroscopy, X ray diffraction and luminescence spectroscopy. The particle size distribution and crystalline habit of the compounds were observed by scanning electron microscopy. Although the particle size of the oxysulfide was found to be 30%-40% smaller than the precursor oxalates, the initial morphology was completely maintained, which indicates the occurrence of a topochemical reaction from oxalates to oxysulfides. © Gauthier-Villars.

Synthesis, characterization and spectroscopy of the europium doped lanthanum trimetaphosphate

Orthorhombic modification of europium doped lanthanum trimetaphosphate has been prepared. The compound was obtained by precipitation of rare earth chloride solution with trimetaphosphoric acid. The characterizations were made using X-ray diffractometry, chemical analysis and infrared spectroscopy. Excitation and emission spectra were recorded at liquid nitrogen and room temperatures. Assignments of the 5D0→7FJ (J=0, 1, 2, 3, 4, 5) transitions were made and an unusual high 5D0→7F4 transition intensity with six split lines has been observed. Structural distortion of the crystal lattice may be caused by the Eu3+ ion inclusion. The simple overlap model was applied for the calculation of the total splitting of the 5D0→7F1 transition, the 5D0→7F0/5D 0→7F2 transition intensity ratio and the Ωλ (λ=2.4) intensity parameters. Theoretical predictions showed to be in good accordance with the experimental data. © 1988 Elsevier Science S.A.

Preparation, characterization and spectroscopy of the europium diphenylphosphinate complex

The purpose of this work is to study the preparation and spectroscopic behavior of the europium diphenylphosphinate complex -Eu(DPP)3. Elemental and thermogravimetric analysis, powder X-ray diffractometry, and infrared spectroscopy were applied to characterize the formula of the final product and the sixfold coordination of the Eu3+ ion. Excitation and emission spectra have been recorded at liquid nitrogen and room temperatures. The 5D0→7F2 transition intensity decreases when T decreases in comparison to the 5D0→7F1 transition intensity. Molecular mechanic calculations were developed in order to obtain the spatial coordinates of the Eu3+ and ligand ions. The simple overlap model was used to calculate the total splitting of the 5D0→7F1 transition, 5D0→7F0/5D 0→7F2 ntensity ratio and the intensity parameters, Ωλ (λ=2 and 4). Good agreements between theoretical predictions and experimental results have been obtained with g=2/3 as the effective charge and α=0.8×10-24 cm3 as the isotropic polarizability of the oxygen. © 1998 Elsevier Science S.A.

Coordination of Eu3+ ions in siliceous nanohybrids containing short polyether chains and bridging urea cross-links

Infrared and photoluminescence spectroscopies have been used to investigate the local environment of the Eu3+ ions in luminescent sol-gel derived materials-di-ureasils-based on a hybrid framework represented by U(600). This host is composed of a siliceous backbone grafted, through urea cross-links, to both ends of polymer segments incorporating 8.5 oxyethylene repeat units. The active centers have been introduced as europium perchlorate, Eu(ClO4)3. Samples with compositions n = 232, 62, 23, 12, and 6 (where n denotes the ratio of (OCH2CH2) moieties per lanthanide ion) have been examined. The combination of the information retrieved from the analysis of characteristic bands of the FTIR spectra-the perchlorate and the Amide I/Amide II features-with that obtained from the photoluminescence data demonstrates that at compositions n = 232 and 62 the anions are free, whereas the Eu3+ ions are complexed by the heteroatoms of the polyether chains. At higher salt concentration, the cations are bonded, not only to the ClO4 - ions, but also to the ether oxygen atoms of the organic segments and to the carbonyl oxygen atoms of the urea linkages. The dual behavior of U(600) with respect to cation coordination has been attributed to the presence in this nanohybrid of strong hydrogen-bonded urea-urea structures, which, at low salt content, cannot be disrupted, thus inhibiting the formation of Eu3+-O=C(urea) contacts and promoting the interaction between the lanthanide ions and the (OCH2CH2) moieties. The present work substantiates the claim that the activation of the coordinating sites of the di-ureasil framework can be tuned by varying either the guest salt concentration at constant chain length or the length of the.organic segments at constant salt concentration. This relevant property opens challenging new prospects in the fields of application of this class of hybrids. © 2001 American Chemical Society.

Structural and optical properties of Eu3+ and Mg2+ doped LiTaO3 obtained via the polymeric precursor method

This work reports on the pure lithium tantalate (LiTaO3), europium (III)-doped LiTaO3 and magnesium (II)-europium (III)-doped LiTaO3 preparared by the polymeric precursor method, using four different powered samples of Eu3+ ion concentrations 0.1 to 1at %. Structural and optical properties of powders have been studied. The different possible sites occupied by the rare earth were examined. The phase contents and lattice parameters were studied by the Rietveld method and the structural disorder in the LiTaO3 host caused by Eu3+ ions was analyzed. Results indicated LiTaO3 free of secondary phases at 650°C and the photoluminescence (PL) emission spectra showed the characteristic sharp emission bands given by Eu3+ ions when they are excited at a wavelength of 399 nm. An increase of dopants contents caused a non-homogeneous broadening and showed a slightly larger one when Mg was added. A displacement of the transition 5D0-7F0 to shorter wavelengths as function of Eu3+ concentration was also noticed.

Efeito da microestrutura na cintilação de nanopartículas de Y2O3 : EU3+

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Nanopartículas de óxido de ítrio dopado com Eu3+ contendo prata

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Photoluminescence properties of CaTiO3:Eu3+ nanophosphor obtained by the polymeric precursor method

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)