Optical properties of polydisperse submicrometer aggregates of sulfur-containing zinc oxide consisting of spherical nanocrystallites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Spherical microparticles formed by agglomerated spherical nanocrystals of sulfur-containing ZnO were prepared by homogeneous precipitation of ZnS followed by thermal treatment under an air atmosphere. The samples were characterized by thermogravimetry (TG), X-ray diffraction (XRD) and Raman, UV-Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopies. The particle morphologies were observed by transmission and scanning electron microscopies (TEM and SEM), showing that spherical microparticles of sulfur-containing ZnO are formed by aggregates of 25 nm spherical nanocrystallites. XRD and TEM results show the presence of ZnO and ZnS phases for short time thermal treatments and only the ZnO wurtzite phase for longer thermal treatments. The presence of Zn-S bonds in sulfur-containing zinc oxide decreases the ZnO band gap energy as verified by DRS, probably due to a valence band offset.354902908Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Structural Investigation and Photoluminescent Properties of Gadolinium(III), Europium(III) and Terbium(III) 3-Mercaptopropionate Complexes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This work reports on the synthesis, crystallographic determination and spectroscopic characterization of gadolinium(III), terbium(III) and europium(III) 3-mercapto propionate complexes, aqua-tris(3-mercaptopropionate) lanthanide(III) - [Ln(mpa)(3)(H2O)]. The Judd-Ofelt intensity parameters were experimentally determined from emission spectrum of the [Eu(mpa)(3)(H2O)] complex and they were also calculated from crystallographic data. The complexes are coordination polymers, where the units of each complex are linked together by carboxylate groups leading to an unidimensional and parallel chains that by chemical interactions form a tridimensional framework. The emission spectrum profile of the [Eu(mpa)(3)(H2O)] complex is discussed based on point symmetry of the europium(III) ion, that explains the bands splitting observed in its emission spectrum. Photoluminescent analysis of the [Gd(mpa)(3)(H2O)] complex show no efficient ligand excitation but an intense charge transfer band. The excitation spectra of the [Eu(mpa)(3)(H2O)] and [Tb(mpa)(3)(H2O)] complexes do not show evidence of energy transfer from the ligand to the excited levels of these trivalent ions. Therefore the emission bands are originated only by direct f-f intraconfigurational excitation of the lantanide(III) ions.241203211Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2009/54066-7

Determination of Judd-Ofelt Intensity Parameters of Pure Samarium(III) Complexes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This work reports an alternative aproach to obtain the Judd-Ofelt intensity parameters of Sm(III) complexes with the general formula: [Sm(tta)(3)(L)(n)], with L = H2O, triphenylphosphine oxide (tppo), 2,2'-bipyridine (bipy) and 1,10-phenantroline (phen); n = 2 for H2O and tppo and n = 1 for phen and bipy, using the absorption spectra of rare earth complexes where the powders are dispersed in KBr pellets. This approach can be applied to other complexes of rare earth ions that have spin allowed transitions and it is validated by comparing the emission spectra of the complexes with those dispersed in KBr pellets.21622372243Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver nanoparticles substrate

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Active surface-enhanced Raman scattering (SERS) silver nanoparticles substrate was prepared by multiple depositions of Ag nanoparticles on glass slides. The substrate is based on five depositions of Ag nanoparticles on 3-aminopropyl-trimetoxisilane (APTMS) modified glass slides, using APTMS sol-gel as linker molecules between silver layers. The SERS performance of the substrate was investigated using 4-aminobenzenethiol (4-ABT) as Raman probe molecule. The spectral analyses reveal a 4-ABT Raman signal enhancement of band intensities, which allow the detection of this compound in different solutions. The average SERS intensity decreases significantly in 4-ABT diluted solutions (from 10(-4) to 10(-6) mol L-1), but the compound may still be detected with high signal/noise ratio. The obtained results demonstrate that the Ag nanoparticles sensor has a great potential as SERS substrate. (C) 2013 Elsevier B.V. All rights reserved.68246250Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Particle size tailoring and luminescence of europium(III)-doped gadolinium oxide obtained by the modified homogeneous precipitation method: Dielectric constant and counter anion effects

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This work reports on controlling the particle size distribution of europium(III)-doped gadolinium oxide samples prepared through a topochemical reaction carried out by thermal treatment of europium(III)-doped gadolinium hydroxycarbonate. Hydroxycarbonate samples were obtained by a modified homogeneous precipitation method using different solvent mixtures, such as water:ethanol, water:ethylene glycol, water:tert-butanol, and different counter ions such as nitrate and chloride. The luminescent properties of the oxide samples, are characteristics of europium(III) ions, with the hypersensitive transition ((5)D(0) --> (7)F(2)) being the most intense emission peak and the emission lifetime values are typical for this system. The spherical particle size distribution of europium(III)-doped gadolinium oxide can be tailored by selecting the counter anion types, the chemical nature of the alcohol and the dielectric constant of the reaction media. The appropriate control of these parameters allows the preparation of rare-earth doped gadolinium samples having monomodal particle size distributions with mean sizes between 30 and 90 nanometers. (C) 2010 Elsevier B.V. All rights reserved.36741699155160Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Erbium and ytterbium co-doped SiO2 : GeO2 planar waveguide prepared by the sol-gel route using an alternative precursor

The sol-gel method combined with a spin-coating technique has been successfully applied for the preparation of rare-earth doped silica:germania films used for the fabrication of erbium-doped waveguide amplifiers (EDWA), presenting several advantages over other methods for the preparation of thin films. As with other methods, the sol-gel route also shows some drawbacks, such as cracks related to the thickness of silica films and high hydrolysis rate of certain precursors such as germanium alkoxides. This article describes the preparation and optical characterization of erbium and ytterbium co-doped SiO2:GeO2 crack-free thick films prepared by the sol-gel route combined with a spin-coating technique using a chemically stable non-aqueous germanium oxide solution as an alternative precursor. The non-crystalline films obtained are planar waveguides exhibiting a single mode at 1,550 nm with an average thickness of 3.9 mu m presenting low percentages of porosity evaluated by the Lorentz-Lorenz Effective Medium Approximation, and low stress, according to the refractive index values measured in both transversal electric and magnetic polarizations. Weakly confining core layers (0.3% < Delta n < 0.75%) were obtained according to the refractive index difference between the core and buffer layers, suggesting that low-loss coupling EDWA may be obtained. The life time of the erbium I-4(13/2) metastable state was measured as a function of erbium concentration in different systems and based on these values it is possible to infer that the hydroxyl group was reduced and the formation of rare-earth clusters was avoided.45217918

Crystalline SnO2 Nanoparticles Size Probed by Eu3+ Luminescence

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Size-controlled europium(III)-doped SnO2 nanoparticles dispersed inside of porous Vycor glass (PVG) were synthesized using the impregnation and decomposition cycle (IDC) method. XRD, DRS, and TEM analyses proved that the observed cumulative mass gain after each IDC is associated to a controlled growing of the SnO2 nanoparticles. Europium(III) emission spectra Were acquired for all samples and clear differences on the relative intensity of the D-5(0)-> F-7(2)/D-5(0)-> F-7(1) transitions were observed for different SnO2 nanoparticle sizes. The changes in the europium(III) emission spectra could be correlated with the increase of nanoparticle: sizes. The smaller superficial nanoparticle area decreases the amount of europium(III) at the surface, where it can be located in different environments over distorted symmetry sites, compared to the crystal lattice sites, where the ions probably are located, when the particles become bigger with no changes in their crystallinity degree. The linear plot between the asymmetric intensity ration of the D-5(0)-> F-7(2)/D-5(0)-> F-7(1) transitions and the particles area/volume ratio calculated from the XRD Scherrer data and particle size frequency counts (similar to 1/d) confirmed this behavior.111045114516Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Luminescent properties of passivated europium(III)-doped rare earth oxide sub-10 nm nanoparticles

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Passivated nanoparticles of europium(III)-doped yttrium, lanthanum and gadolinium oxides were synthesized by a modified sol-gel method and their luminescent properties were studied. The passivation of the nanoparticles surface is confirmed by infrared spectroscopy. Gadolinium and yttrium oxides crystalize as cubic phases while the lanthanum oxide has hexagonal phase. The emission spectra of the samples show broad transitions attributed to europium(III) ions probably due to structure disorder caused by the size and also by the high surface/volume ratio of the nanoparticles. The Judd-Ofelt intensity parameters were obtained from the emission spectra. The passivation of the nanoparticles surface, with trioctylphosphine oxide, does not significantly alter the values of Omega(2) and Omega(4) parameters and slightly increases the emission quantum efficiency of the nanoparticles that possesses lower values of Omega(2) parameter than bulk samples.3827942801Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Synthesis and Photoluminescent Properties of Lanthanides Acetoacetanilide Complexes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This work reports on the photoluminescent properties of three new lanthanide complexes with acetoacetanilide (aaa), a beta-diketonate ligand. The complexes have the general molecular formulae [RE(aaa)(3)(H2O)], they are soluble in organic solvents such as ethanol and chloroform and insoluble in water. The energy of the triplet state was determined at about 4,700 cm(-1) higher than the D-5(4) emitting level of the Tb(III) ion, leading to an absolute quantum yield of 22 % for the [Tb(aaa)(3)(H2O)] complex. The photoluminescent properties were studied and the luminescence parameters of the [Eu(aaa)(3)(H2O)] complex were experimentally determined. The photostabilities of the complexes under continuous UV irradiation were measured and the data indicate low stability of the [Tb(aaa)(3)(H2O)] complex when the system is excited at the band attributed to energy transfer from the ligand to terbium(III) ion. However, its photostability is significantly improved under inert atmosphere.235939946Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Spontaneous formation of highly dispersed spheroidal metallic silver nanoparticles in surfactant-free N,N-dimethylacetamide

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The present work describes a simple method for preparing highly dispersed spheroidal metallic silver nanoparticles in surfactant-free N,N-dimethylacetamide solution. The optical properties, shape and size of the metallic silver nanoparticles obtained in N,N-dimethylacetamide after different times of reaction were characterized using UV-vis absorption spectroscopy and transmission electron microscopy. The average size of the metallic silver nanoparticles is smaller than that obtained by the well established procedure using N,N-dimethyformamide. Using optimized geometries for N,N-dimethylacetamide and N,N-dimethyformamide, vertical ionization energies and electron affinities were calculated by means of the UHF/DFT calculations of cations and anions, respectively. The difference between ionization energies and electron affinities is higher for N,N-dimethyformamide indicating that it is a harder base than N,N-dimethylacetamide. Therefore, N,N-dimethyformamide probably interacts more weakly with Ag(I) ions than does N,N-dimethylacetamide. The strength of this chemical interaction has implications on the stabilization and dispersion of silver nanoparticles obtained in N,N-dimethylacetamide. The low cost, simple methodology may be used as a platform for further studies in surface-enhanced Raman spectroscopy as well as with other optical properties that depend on the surface plasmon resonance of metallic silver nanoparticles. (C) 2011 Elsevier B.V. All rights reserved.16115-1615171521Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP