Evidence of the participation of electronic excited states in the mechanism of positronium formation in substitutional Tb1-xEux(dpm)(3) solid solutions studied by optical and positron annihilation spectroscopies

Positronium formation in the bimary molecular solid solutions Tb1-xEux (dpm)(3) (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the D-5(4) Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.CNPqCNPqFAPEMIGFAPEMIGFAPESPFAPESPRENAMI (National Project)RENAMI (National Project

Synthesis and properties of complexes between lanthanide trifluoroacetates and 2-picoline-N-oxide (2-picNO)

Os compostos obtidos pela reação entre trifluoroacetatos de lantanídeos e a 2-picolina-N-óxido em 2,2-dimetoxipropano têm fórmula geral Ln(TFA)3.2(2-picNO) (Ln = La-Lu, Y, exceto Ce) e apresentam-se com razoável higroscopicidade, cristalinos, inodoros e com cores um pouco menos pronunciadas do que as dos sais hidratados de lantanídeos trivalentes. São solúveis em água, acetonitrila (exceto La), acetona, etanol e metanol, porém insolúveis em nitrobenzeno. Em nitrometano os compostos das terras raras pesadas apresentam considerável solubilidade, enquanto os das leves são praticamente insolúveis. Os intervalos de fusão variam de 224° a 122°C. Os compostos foram caracterizados por análises elementares, medidas de condutância eletrolítica, diagramas de raios-X, espectros na região do infravermelho, espectros eletrônicos de absorção e de emissão. As medidas de condutância eletrolítica em solução de acetonitrila mostram que os compostos se comportam como não eletrólitos. Os difratogramas de raios-X permitiram a identificação de três séries isomorfas, correspondendo a: a) La-Pr; b) Nd-Sm; c) Eu-Lu, Y. Os espectros na região do infravermelho mostram deslocamentos da banda relativa ao estiramento v N-O, em relação à 2-picNO livre, para regiões de menor frequência. Tal deslocamento sugere a coordenação do ligante ao íon central por meio do oxigênio do grupo aminóxido. As bandas vasCOO do TFA apresentam-se desdobradas para todos os compostos, exceto para La e Pr. O aparecimento destes dubletes sugere dois tipos de coordenação aos lantanídeos. O espectro de absorção na região do visível do composto Nd(TFA)3.2(2-picNO) obtido no estado sólido à temperatura ambiente e do nitrogênio líquido e em solução (P = 28,6 cm-2mol.-1.L) de acetonitrila apresentam diferenças de um para o outro, indicando a ocorrência de interação como solvente. Os parâmetros espectroscópicos β-, δ e b1/2 foram calculados, indicando que a ligação íon lantanídeo-ligante possui muito pouco caráter covalente e que a interação Ln-L é essencialmente eletrostática. O composto de Eu(TFA)3.2(2-picNO) apresenta fluorescência intensa e seu espetro de emissão sugere a simetria C2v ao redor do íon Eu3+. Baseados no grupo pontual, nos modos de coordenação e estruturas conhecidas, sugerimos a geometria de antiprisma quadrado para a espécie complexa na qual os oxigênios do grupo TFA e 2-picNO se agrupam ao redor do íon central, de maneira a formar um dímero.The compounds obtained by reaction between hydrated lanthanide trifluoroacetates and 2-picoline-N-oxide in 2,2-dimethoxypropane present the qeneral formula Ln (TFA)3.2(2-picNO) (Ln 2 La-Lu, Y, except Ce). They are hygroscopic, crystalline, with the trivalent hydrated lanthanides, soluble in water, acetonitrile (except La, acetone, ethanol and methanol) and insoluble in nitrobenzene. The lighter lanthanides adducts are considerably soluble and the heavier practically insoluble in nitromethane. The melting ranges vary between 122 and 224°C. The compounds were characterized by elemental analysis, electrolytic conductance measurements, X-ray powder patterns, infrared emission and absorption spectra. Conductance measurements in acetonitrile indicate a behavior of non-electrolytes. According to X-ray patterns, three isomorphous series were detected: a) La-Pr; b) Nd-Sm and c) Eu-Lu,Y. Infrared data show shift of v NO to lower frequencies, in relation to the free 2-picNO, indicating the bonding is through the oxygen. The vasCOO bands are splitted in all the compounds (except La and Pr) and suggest two types of anion coordination. Absorption spectra of the neodyimium compound were determined in solid state at roam and 77 K temperatures, and also in acetonitrile solution. The shapes of the hypersensitive bands are different, showing solvent interaction. Spectroscopic parameters (β-, b1/2 and δ) calculated from solid state spectrum indicate a essentially electrostatic interaction between Ln-L. Fluorescence spectrum of the Eu compound was interpreted in terms of C2v symmetry around the central ion. The geometry of a square antyprism was proposed, based on four TFA groups acting as bridges between two Ln ions, one as bidentate, and the coordination sphere is completed by the 2-picNO

Spectroscopic study of rare earth complexes containing N,N,N,N -tetramethyurea (TMU) as ligands

As reações entre o ligante N,N,N\',N\'-tetrametiluréia (TMU) e sais de isotiocianatos, nitratos, percloratos, brometos e cloretos de lantanídeos (Ln = Nd3+ e Eu3+) conduziram a compostos de fórmulas gerais: Nd(NCS)3.4TMU; Eu(NCS)3.3,5TMU, Ln(NO3)3.3TMU, Ln(ClO4)3.6TMU, LnBr3.3TMU.6H2O, LnCl3.3TMU (Ln = Nd e Eu). As estequiometrias desses complexos foram propostas com base nos resultados dos teores de lantanídeos, obtidos através de análises complexométricas com EDTA, enquanto que os teores de carbono, nitrogênio e hidrogênio foram determinados por microanálise. As medidas de condutância eletrolítica em solução de acetonitrila mostram que os compostos se comportam como não eletrólitos, exceto os derivados do ânion perclorato (eletrólito 1: 3). Os difratogramas de raios-X permitiram identificar que os compostos de neodímio e európio são isomorfos entre si para os ânions perclorato, brometo e nitrato. Os compostos derivados dos ânions cloreto e isotiocianato não apresentam isomorfismo. Os espectros de absorção na região do infravermelho mostram deslocamentos das bandas vC=O para regiões de frequências mais baixas e vC-N para regiões de frequências mais altas, o que evidencia a coordenação pelo átomo de oxigênio da carbonila. A ausência de bandas fortes indicativas da presença de água mostra que os compostos de nitratos, cloretos e percloratos obtidos são todos anidros. A presença da banda na região 3560-3520 cm-1> e 1630-1600 cm-1> para os complexos de brometos obtidos evidencia os modos de estiramentos característicos da água. Os espectros eletrônicos de fluorescência na região do visível dos compostos de európio, obtidos à temperatura ambiente e a 77 K, permitiram sugerir as seguintes simetrias: Eu(NO3)3.3TMU - D3h Eu(ClO4)3.6TMU - Oh EuCl3.3TMU - D3 EuBr3.3TMU.6H2O - D3h Eu(NCS)3.3,5TMU - C3v Eu(F3C-SO3)3.6TMU - Oh A partir destas simetrias, foram calculados os parâmetros de campo cristalino B20, B40, B44, B43 (método dos operadores tensoriais) e também os parâmetros B02, B04, B44, B34 (método dos operadores equivalentes). Os espectros eletrônicos de absorção na região do visível dos compostos de neodímio à temperatura ambiente e a 77 K foram registrados. Os parâmetros espectroscópicos β, b1/2 e δ indicam que nas ligacões de todos os comoostos predomina o caráter eletrostático. A partir dos espectros dos compostos Nd(ClO4)3.6TMU e Nd(F3C-SO3)3.5TMU com simetria cúbica, foram calculados os parâmetros B04, B06, B44, e B64 (Bqk) e por correlação encontramos os parâmetros B40, B60, B44, e B46 (Bkq). Através dos espectros de absorção em solução dos compostos de neodímio foram calculadas as forças do oscilador (P) e a seguinte ordem relativa ao aumento de intensidade das transições hipersensitivas foi observada: Cl-4 NCS- > Br- > Cl- > ClO-4

Synthesis and properties of complexes between lanthanide trifluoroacetates and 2-picoline-N-oxide (2-picNO)

Os compostos obtidos pela reação entre trifluoroacetatos de lantanídeos e a 2-picolina-N-óxido em 2,2-dimetoxipropano têm fórmula geral Ln(TFA)3.2(2-picNO) (Ln = La-Lu, Y, exceto Ce) e apresentam-se com razoável higroscopicidade, cristalinos, inodoros e com cores um pouco menos pronunciadas do que as dos sais hidratados de lantanídeos trivalentes. São solúveis em água, acetonitrila (exceto La), acetona, etanol e metanol, porém insolúveis em nitrobenzeno. Em nitrometano os compostos das terras raras pesadas apresentam considerável solubilidade, enquanto os das leves são praticamente insolúveis. Os intervalos de fusão variam de 224° a 122°C. Os compostos foram caracterizados por análises elementares, medidas de condutância eletrolítica, diagramas de raios-X, espectros na região do infravermelho, espectros eletrônicos de absorção e de emissão. As medidas de condutância eletrolítica em solução de acetonitrila mostram que os compostos se comportam como não eletrólitos. Os difratogramas de raios-X permitiram a identificação de três séries isomorfas, correspondendo a: a) La-Pr; b) Nd-Sm; c) Eu-Lu, Y. Os espectros na região do infravermelho mostram deslocamentos da banda relativa ao estiramento v N-O, em relação à 2-picNO livre, para regiões de menor frequência. Tal deslocamento sugere a coordenação do ligante ao íon central por meio do oxigênio do grupo aminóxido. As bandas vasCOO do TFA apresentam-se desdobradas para todos os compostos, exceto para La e Pr. O aparecimento destes dubletes sugere dois tipos de coordenação aos lantanídeos. O espectro de absorção na região do visível do composto Nd(TFA)3.2(2-picNO) obtido no estado sólido à temperatura ambiente e do nitrogênio líquido e em solução (P = 28,6 cm-2mol.-1.L) de acetonitrila apresentam diferenças de um para o outro, indicando a ocorrência de interação como solvente. Os parâmetros espectroscópicos β-, δ e b1/2 foram calculados, indicando que a ligação íon lantanídeo-ligante possui muito pouco caráter covalente e que a interação Ln-L é essencialmente eletrostática. O composto de Eu(TFA)3.2(2-picNO) apresenta fluorescência intensa e seu espetro de emissão sugere a simetria C2v ao redor do íon Eu3+. Baseados no grupo pontual, nos modos de coordenação e estruturas conhecidas, sugerimos a geometria de antiprisma quadrado para a espécie complexa na qual os oxigênios do grupo TFA e 2-picNO se agrupam ao redor do íon central, de maneira a formar um dímero.The compounds obtained by reaction between hydrated lanthanide trifluoroacetates and 2-picoline-N-oxide in 2,2-dimethoxypropane present the qeneral formula Ln (TFA)3.2(2-picNO) (Ln 2 La-Lu, Y, except Ce). They are hygroscopic, crystalline, with the trivalent hydrated lanthanides, soluble in water, acetonitrile (except La, acetone, ethanol and methanol) and insoluble in nitrobenzene. The lighter lanthanides adducts are considerably soluble and the heavier practically insoluble in nitromethane. The melting ranges vary between 122 and 224°C. The compounds were characterized by elemental analysis, electrolytic conductance measurements, X-ray powder patterns, infrared emission and absorption spectra. Conductance measurements in acetonitrile indicate a behavior of non-electrolytes. According to X-ray patterns, three isomorphous series were detected: a) La-Pr; b) Nd-Sm and c) Eu-Lu,Y. Infrared data show shift of v NO to lower frequencies, in relation to the free 2-picNO, indicating the bonding is through the oxygen. The vasCOO bands are splitted in all the compounds (except La and Pr) and suggest two types of anion coordination. Absorption spectra of the neodyimium compound were determined in solid state at roam and 77 K temperatures, and also in acetonitrile solution. The shapes of the hypersensitive bands are different, showing solvent interaction. Spectroscopic parameters (β-, b1/2 and δ) calculated from solid state spectrum indicate a essentially electrostatic interaction between Ln-L. Fluorescence spectrum of the Eu compound was interpreted in terms of C2v symmetry around the central ion. The geometry of a square antyprism was proposed, based on four TFA groups acting as bridges between two Ln ions, one as bidentate, and the coordination sphere is completed by the 2-picNO

Luminescence of the films of europium (III) with thenoyltriuoroacetonate and macrocyclics.

We discuss the syntheses, properties and the luminescence of the complexes, Eu(TTA)3 á 2L á H2O, where TTA . thenoyltriuoroacetonate, L.15C5 (1,4,7,10-tetraoxa-13-azacyclopentadecane,13-phenyl) and 18C6 (2,3,11,12-dicyclohexano- 1,4,7,10,13,16-hexaoxacyclooctadecane). The ®lm complexes with 15C5 and 18C6 ligands contain only one water molecule. The Xk experimental intensity parameters (k.2 and 4) and the ratio between the intensities of the 5D0 ® 7F0 and 5D0 ® 7F2 transitions (R02) were obtained for the compounds Eu(TTA)3 á 2(15C5) á H2O (X2 .39.5 ´ 10ÿ20 cm2, X4 .8.9 ´ 10ÿ20 cm2 and R02 .0.0087) and Eu(TTA)3 á 2(18C6) á H2O (X2.39.3 ´ 10ÿ20 cm2, X4 .5.8 ´ 10ÿ20 cm2 and R02 .0.0098). The macrocyclic compounds, powder form, were also measured. The luminescence spectra of the Eu(TTA)3 á 2L á H2O ®lms give the largest X2 intensity parameter, due to the hypersensitive 5D0 ® 7F2 transition and indicating that the rare earth ion is in a polarizable chemical environment. The lifetimes of the macrocyclics complexes in the powder and ®lm were measured

Photoluminescence behavior of Eu(3+) ion doped into gamma- and alpha-alumina systems prepared by combustion, ceramic and Pechini methods

Al(2)O(3):Eu(3+)(1%) samples were prepared by combustion, ceramic, and Pechini methods annealed from 400 to 1400 degrees C. XRD patterns indicate that samples heated up to 1000 degrees C present disordered character of activated alumina (gamma-Al(2)O(3)). However, alpha-Al(2)O(3) phase showed high crystallinity and thermostability at 1200-1400 degrees C. The sample characterizations were also carried out by means of infrared spectroscopy (IR), scanning electron microscopy (SEM) and specific surface areas analysis (BET method). Excitation spectra of Al(2)O(3):Eu(3+) samples present broaden bands attributed to defects of Al(2)O(3) matrices and to LMCT state of O -> Eu(3+), however, the narrow bands are assigned to (7)F(0) -> (5)D(J),(5)H(J) and (5)L(J) transitions of Eu(3+) ion. Emission spectra of samples calcined up to 1000 degrees C show broaden bands for (5)D(0) -> (7)F(J) transitions of Eu(3+) ion suggesting that the rare earth ion is in different symmetry sites showed by inhomogeneous line broadening of bands, confirming the predominance of the gamma-alumina phase. For all samples heated from 1200 to 1400 degrees C the spectra exhibit narrow (5)D(0) -> (7)F(J) transitions of Eu(3+) ion indicating the conversion of gamma to alpha-Al(2)O(3) phases, a high intensity narrow peak around 695 nm assigned to R lines of Cr(3+) ion is shown. Al(2)O(3):Eu(3+) heated up to 1100 degrees C presents an increase in the Omega(2) intensity parameter with the increase of temperatures enhancing the covalent character of metal-donor interaction. The disordered structural systems present the highest values of emission quantum efficiencies (eta). CIE coordinates of Al(2)O(3):Eu(3+) are also discussed. (C) 2007 Elsevier Inc. All rights reserved

Persistent luminescence of Eu2+ and Dy3+ doped barium aluminate (BaAl2O4:Eu2+,Dy3+) materials.

Polycrystalline Eu2+ and Dy3+ doped barium aluminate materials, BaAl2O4:Eu2+,Dy3+, were prepared with solid state reactions at temperatures between 700 and 1500 _C. The influence of the thermal treatments on the stability, homogeneity and structure as well as to the UV-excited and persistent luminescence of the materials was investigated by X-ray powder diffraction, SEM imaging and infrared spectroscopies as well as by steady state luminescence spectroscopy and persistent luminescence decay curves, respectively. The IR spectra of the materials prepared at 250, 700, and 1500 _C follow the formation of BaAl2O4 composition whereas the X-ray powder diffraction of compounds revealed how the hexagonal structure was obtained. The morphology of the materials at high temperatures indicated important aggregation due to sintering. The luminescence decay of the quite narrow Eu2+ band at ca. 500 nm shows the presence of persistent luminescence after UV irradiation. The dopant (Eu2+) and co-dopant (Dy3+) concentrations affect the crystallinity and luminescence properties of the materials

Persistent luminescence of Eu2+ and Dy3+ doped barium aluminate (BaAl2O4:Eu2+,Dy3+) materials.

Polycrystalline Eu2+ and Dy3+ doped barium aluminate materials, BaAl2O4:Eu2+,Dy3+, were prepared with solid state reactions at temperatures between 700 and 1500 _C. The influence of the thermal treatments on the stability, homogeneity and structure as well as to the UV-excited and persistent luminescence of the materials was investigated by X-ray powder diffraction, SEM imaging and infrared spectroscopies as well as by steady state luminescence spectroscopy and persistent luminescence decay curves, respectively. The IR spectra of the materials prepared at 250, 700, and 1500 _C follow the formation of BaAl2O4 composition whereas the X-ray powder diffraction of compounds revealed how the hexagonal structure was obtained. The morphology of the materials at high temperatures indicated important aggregation due to sintering. The luminescence decay of the quite narrow Eu2+ band at ca. 500 nm shows the presence of persistent luminescence after UV irradiation. The dopant (Eu2+) and co-dopant (Dy3+) concentrations affect the crystallinity and luminescence properties of the materials

Intermolecular energy transfer and photostability of luminescence-tuneable multicolour PMMA films doped with lanthanide-beta-diketonate complexes

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)(3)(H(2)O)(2)] and [Tb(acac)(3)(H(2)O)(3)] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln(3+)-beta-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand-Ln(3+) intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the (5)D(4) emitting level of the Tb(3+) ion to the excited triplet state T(1) of the tta ligand coordinated to the Eu(3+) ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)CNPqFAPESPinct-INAMIRENAMIREDE-NANOBIOTEC-BRASI

Positronium formation in lanthanide (III) trifluoroacetate with 3-picoline-N-oxide compounds.

Positron annihilation lifetime and Doppler broadening annihilation radiation line shape on the salts Ln(CF3COO)3•xH2O and the adducts Ln(CF3COO)3(3-picNO)•xH2O (Ln=La–Pr, Sm–Lu and Y, and 3-picNO=3picoline-N-oxide, x in the range 0.75–1.33) were performed. Positroniumformation in the adducts, except for the europium complex, was observed. These results are discussed in terms of the electronic properties of the central metal ions