172 resultados para BaFCl : Eu2
Resumo:
SrMgF4xEuyTbEu3+Eu2+TbEu3+Eu2+Eu2+ESREu3+Tb3+Eu3+Tb3+Eu2+Tb4+.
Resumo:
A valence change from RE3+ to RE2+ (RE=Eu, Sm, Yb) was observed in samples of SrB4O7: RE prepared by solid state reaction at high temperature in air. The phosphors SrB4O7: RE2+ show efficient luminescence at room temperature. The broad band d-f emissions of Eu2+ and Yb2+ are at 367 and 360 nm respectively. The sharp line f-f emissions of the Sm2+ ion (5D0-F-7(J)) are in the range 680-780 nm. The probable reasons for the valence change of Eu, Sm and Yb in this host are discussed.
Resumo:
The spectrochemistry of Eu2+-doped perovskite KMgF3 was examined and discussed. Eu2+ can replace some of the K+ in the KMgF3 crystal, and simultaneously the corresponding cation hole can be compensated with the F- or O2- in the matrix. The emission intensity of Eu2+ due to the f --> f transition increased when Na+, Rb+ or F- was doped in KMgF3:Eu2+. Two mechanisms of charge compensation were proposed. No obvious valence change of Eu2+ occurred in KMgF3:Eu2+ after calcinating at high temperature, e.g. 900-degrees-C. It was found that the valence stability of Eu2+ improved after incorporation into the matrix.
Resumo:
The synthesis and photophysical evaluation of two enatiomerially pure dimetallic lanthanide luminescent triple-stranded helicates is described. The two systems, formed from the chiral (R,R) ligand 1 and (S,S) ligand 2, were produced as single species in solution, where the excitation of either the naphthalene antennae or the pyridiyl units gave rise to Eu(III) emission in a variety of solvents. Excitation of the antennae also gave rise to circularly polarized Eu(III) luminescence emissions for Eu2:13 and Eu2:23 that were of equal intensity and opposite sign, confirming their enantiomeric nature in solution providing a basis upon which we were able to assign the absolute configurations of Eu2:13 and Eu2:23.
Resumo:
The synthesis of the C2-symmetrical ligand 1 consisting of two naphthalene units connected to two pyridine-2,6-dicarboxamide moieties linked by a xylene spacer and the formation of LnIII-based (Ln1/4 Sm, Eu, Tb, and Lu) dimetallic helicates [Ln2 13] in MeCN by means of a metal-directed synthesis is described. By analyzing the metal-induced changes in the absorption and the fluorescence of 1, the formation of the helicates, and the presence of a second species [Ln2 12] was confirmed by nonlinear- regression analysis. While significant changes were observed in the photophysical properties of 1, the most dramatic changes were observed in the metal-centred lanthanide emissions, upon excitation of the naphthalene antennae. From the changes in the lanthanide emission, we were able to demonstrate that these helicates were formed in high yields (ca. 90% after the addition of 0.6 equiv. of LnIII), with high binding constants, which matched well with that determined from the changes in the absorption spectra. The formation of the LuIII helicate, [ Lu2 13 ] , was also investigated for comparison purposes, as we were unable to obtain accurate binding constants from the changes in the fluorescence emission upon formation of [Sm2 13], [Eu2 13], and [Tb2 13].
Resumo:
Este estudo transversal est focado na propriedade de luminescncia persistente do aluminato de estrncio co-dopado com crio (III), disprsio (III) e eurpio (II), SrAl2O4:Ce3+, Dy3+, Eu2+, em sistemas de sinalizao de reas de risco e emergncias para pessoas com deficincias. Na rea da cincia e engenharia dos materiais, foram desenvolvidos novos materiais com caractersticas nanomtricas, nanotubos, nanoarames e nanobastes luminescentes de SrAl2O4:Ce3+, Dy3+, Eu2+ para aplicaes na rea da reabilitao e acessibilidade de pessoas com deficincias. Os nanotubos foram obtidos a partir de micro- e nano-partculas precursoras sintetizadas por reaco do estado-slido e tratamento trmico de recozedura (1273-1473 K). Os nanoarames e nanobastes foram preparados por moagem, sonificao e recozedura (373 K). Novas nanocpsulas de aluminatos luminescentes dopados com crio (III) e encapsulados com TiO2 foram criadas de modo a obter-se materiais multifuncionais, designadamente com aco fotocataltica antimicrobiana, antibacteriana e resistncia gua. Tais aluminatos podem ser amplamente aplicados como superfcies higinicas, auto-limpantes, em biomateriais, no domnio de medicamentos antibiticos, na formulao de vacinas, e com nfase aplicao em cermicas fotoluminescentes. As metodologias de obteno de tais nanoestruturas de aluminato de estrncio dopado com crio (III) e do seu encapsulamento, desenvolvidas no mbito desta tese, so aplicveis a diversos aluminatos dopados com outros ies lantandeos (Ln consiste em La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Tm ou Lu) com a frmula M(1-x-y)N2O4:Cex, Lny, onde M Be, Mg, Ca, Sr ou Ba. Na rea da oftalmologia, foi desenvolvido um equipamento mdico para o diagnstico de biofuncionalidade das clulas retinais fotoreceptoras, e como suporte telemedicina oftalmolgica. Este equipamento foi utilizado para realizar testes de viso cromtica FM100HUE em fundo branco/preto para a personalizao de materiais luminescentes. Os resultados demonstraram uma biofuncionalidade celular visibilidade fotpica das cores em fundo preto superior no grupo de tratamento, composto por pessoas com retinopatia diabtica (n=38), em comparao ao grupo de referncia (n=38). Estes resultados sugerem a recomendao de materiais com fotoluminescncia persistente (em=485-555 nm), incluindo SrAl2O4:Ce3+, Dy3+, Eu2+, para o referido grupo de tratamento, em sinalizao de emergncia e em ambientes de baixa iluminao. Na rea da arquitectura, foi proposta uma nova aplicao dos referidos nanomateriais luminescentes base de SrAl2O4:Ce3+, Dy3+, Eu2+ em cermica de revestimento, tendo em vista a sua boa visibilidade e uso por pessoas com deficincias. Novos pavimentos, cermicos, fotoluminescentes, foram desenhados com propriedades multisensoriais (contraste tctil, sonoro e visual) e antimicrobianas, para pessoas portadoras de deficincias utilizarem, no escuro, com a prioridade de salvar vidas em emergncias. Tais pisos, com relevos, podem ser combinados de modo a compor um sistema exclusivo de sinalizao fotoluminescente multisensorial que possibilita a rpida evacuao mediante o uso de auxlios de mobilidade (e.g. bengala, cadeira de rodas, andadores, muletas). A soluo integrada de tais inovaes que potencializa a propriedade de luminescncia persistente de SrAl2O4:Ce3+, Dy3+, Eu2+ de modo acessvel para as pessoas com deficincias, pode contribuir para salvar vidas, no escuro, em emergncias.
Resumo:
An efficient reddish orange emission MgSrAl(10)O(17):Sm(3+) phosphor was prepared by the combustion method. The phosphor has been characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis measurements. Photoluminescence spectrum revealed that samarium ions are present in trivalent oxidation states. The phosphor exhibits two thermally stimulated luminescence (TSL) peaks at 210 degrees C and 450 degrees C. Electron spin resonance studies were carried out to identify the defect centres responsible for the TSL process in MgSrAl(10)O(17):Sm(3+) phosphor. Three defect centres have been identified in irradiated phosphor and these centres are tentatively assigned to an O(-) ion and F(+) centres. O(-) ion (hole centre) correlates with the 210 degrees C TSL peak while one of the F+ centres (electron centre) appears to relate to the 450 degrees C TSL peak. (C) 2010 Elsevier B.V. All rights reserved.
Resumo:
The persistent luminescence materials, barium aluminates doped with Eu(2+) and Dy(3+) (BaAl(2)O(4): Eu(2+),Dy(3+)), were prepared with the combustion synthesis at temperatures between 400 and 600 degrees C as well as with the solid state reaction at 1500 degrees C. The concentrations of Eu(2+)/Dy(3+) (in mol% of the Ba amount) ranged from 0.1/0.1 to 1.0/3.0. The electronic and defect energy level structures were studied with thermoluminescence (TL) and synchrotron radiation (SR) spectroscopies: UV-VUV excitation and emission, as well as with X-ray absorption near-edge structure (XANES) methods. Theoretical calculations using the density functional theory (DFT) were carried out in order to compare with the experimental data. (C) 2010 Elsevier Inc. All rights reserved.
Optical energy storage properties of Sr(2)MgSi(2)O(7):Eu(2+),R(3+) persistent luminescence materials
Resumo:
The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr(2)MgSi(2)O(7):Eu(2+),R(3+) materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr(2)MgSi(2)O(7):Eu(2+),R(3+) material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 A degrees C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr(2)MgSi(2)O(7):Eu(2+),R(3+) materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R(3+) co-dopants.
Resumo:
MgAl(2)O(4):Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at 600, 700, 800 and 900 degrees C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800 degrees C. Infrared spectra of the phosphors showed bands around 700 and 520 cm(-1) corresponding to the AlO(6) groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900 degrees C indicating the MgAl(2)O(4) spinel phase. Grain size in the range 20-30 nm were observed by measurement of transmission electron microscopy (TEM). The emission spectra of the phosphors show a broadened band at 480 nm assigned to the 4f(G)5d -> 4f(7) ((8)S(7/2)) transition of Eu(2+) ion overlapped to the (4)F(9/2) -> (6)H(15/2) transition of the Dy(3+) ion. Besides, the (4)F(9/2) -> (6)H(13/2) transition (579 nm) of Dy(3+) ion is overlapped with the (5)D(0) -> (7)F(0) (578 nm) and (5)D(0) -> (7)F(1) (595 nm) transitions from the Eu(3+) ion. Excitation spectra of the sample heated at 900 degrees C monitoring the excitation at 615 nm of (5)D(0) -> (7)F(2) transition of Eu(3+) ion exhibit a broad band assigned to the O -> Eu(3+) ligand-to-metal charge-transfer states (LMCT) around 280 nm. The samples present green persistent luminescence after exposure to UV radiation. The chromaticity coordinates were obtained from the luminescence emission spectrum. (C) 2008 Elsevier B.V. All rights reserved.
Resumo:
This is a work involving fundamental studies of chemistry where the synthesis and structural characterization, as well as a possible future application of these new compounds as luminescent sensors or sunscreen agents, complexes with 4,4 diaminostilbene-2,2-disulfonic (DSD) and trivalent lanthanide ions La3+, Nd3+, Eu3+, Gd3+ and Yb3+, were synthesized in the ratio of 3 mmol: 1 mmol (DSD: lanthanides). The complexes obtained with these ions were present in powder form and were characterized by complexometric titration with EDTA CHN Elemental analysis, molecular absorption spectroscopy in the ultraviolet region, the absorption spectroscopy in the infrared, thermal analysis (TG / DTG), Nuclear Magnetic Resonance - NMR 1H and Luminescence Spectroscopy. The complexometric titration and CHN analysis, confirmed the TG / DTG which suggest that these complexes have the following general chemical formulas: [La2(C14H12S2O6N2)2(H2O)2Cl2].7H2O,[Nd2(C14H12S2O6N2)2(H2O)2Cl2].6H2O,[Eu2(C14 H12S2O6N2)2(H2O)2Cl2].7H2O,[Gd2(C14H12S2O6N2)2(H2O)2Cl2].4H2O e [Yb2(C14H12S2O6N2)2(H2O)2].6H2O. The disappearance of the bands in the infrared spectrum at 2921 cm-1 and 2623 cm-1 and the displacement of the bands in the spectra of the amine complex indicate that the lanthanide ion is coordinated to the oxygen atoms and the sulfonate groups of the nitrogens amines, suggesting the formation of the dimer. The disappearance of the signal and the displacement signal SO3H amines in the 1H NMR spectrum of this complex are also indicative coordination and dimer formation. The Thermogravimetry indicates that the DSD is thermally stable in the range of 40 to 385C and their complexes with lanthanide ions exhibit weight loss between 4 and 5 stages. The Uv-visible spectra indicated that the DSD and complexes exhibit cis isomers. The analysis of luminescence indicates that the complexes do not exhibit emission in the region of the lanthanides but an intense emission part of the binder. This is related to the triplet states of the ligand, which are in the lowest energy state emitting lanthanide ions, and also the formation of the dimer that suppress the luminescence of ion Eu3+. The formation of dimer was also confirmed by calculating the europium complex structure using the model Hamiltonian PM6 and Sparkle
Resumo:
The new europium binuclear complex [Eu2(dcpz) 2(suc)(H2O)8](H2O) 1.5 (dcpz = 3,5-dicarboxypyrazolate and suc = succinate) has been synthesized and structurally characterized by single crystal X-ray diffraction methods. The binuclear complex crystallizes in the triclinic space group P1 and consists of two lanthanide ions linked by two different bridging organic ligands. 3D supramolecular framework is constructed by hydrogen bonds. The compound shows strong red emission under UV excitation at room temperature associated to IL transitions indicating a ligand to metal energy transfer mechanism since the triplet energy level lies higher than that of europium 5D0 level. Magnetic susceptibility studies showed weak temperature dependence characteristic of the Van Vleck paramagnetism. 2013 Elsevier Ltd. All rights reserved.
Resumo:
Ps-graduao em Qumica - IQ
Resumo:
Coordenao de Aperfeioamento de Pessoal de Nvel Superior (CAPES)
