G.F. de Sá

Fluorescence enhancement induced by the presence of small silver particles in Eu3+ doped materials

Abstract We study the effect of small silver particles on the emission spectrum of Eu3+ doped materials. Depending on the excitation frequency and the concentration of silver particles embedded in the host material, a significant enhancement of the fluorescence from the Eu3+ ions is observed. This experimental observation corroborates the importance of the long-range electromagnetic interaction between the plasmons on the silver particles and the host medium. A theoretical analysis based on the electromagnetic model is made and satisfactory agreement with experiment is obtained.

White light simulation by up-conversion in fluoride glass host

Abstract We have produced white light using infrared excitation by addictive synthesis of red, green and blue (RGB) upconverted radiation, in a lanthanide-doped fluoride-based glass, named full-color glass, FCG-III. This glass generates simultaneously RGB emissions from 980 nm excitation by up-conversion process, with high precision of color coordinates and high efficiency. The ions Er 3+ and Tm 3+ were used as simultaneous narrow line emitters of the three primary light colors. The Tm 3+ and Er 3+ concentrations in the glass host were adjusted, favoring light color tuning and generation of a wide color gamut in the visible spectrum, and white light simulation under single infrared excitation.

Eu(III) and Gd(III) complexes with pirazyne-2-carboxylic acid: luminescence and modelling of the structure and energy transfer process

Abstract The synthesis and spectroscopic study of the complexes of Eu(III) and Gd(III) with pyrazine-2-carboxylic acid (pya) are described. The number of water molecules (n) in the first coordination sphere of the Eu(III) ion has been determined through comparison between the experimental and theoretical Stark levels, giving n=3, where the geometry of Eu(III) complex has been previously optimised using the Sparkle model. Based on this number of water molecules it has been predicted that the excited states for the complex Eu(pya)3·3H2O and the results have been used to carry out an experimental and theoretical analysis of the intensities of the 4f–4f transitions and intramolecular energy transfer processes. Structural data were used to perform theoretical predictions of the Judd–Ofelt intensity parameters (Ωλ, λ=2,4). The satisfactory results obtained are an indication that the models used can lead to reliable predictions of the structure and 4f–4f intensities. A complete theoretical model to calculate the luminescent properties of lanthanide compounds has been used to analyze the emission quantum yield of the Eu(pya)3·3H2O compound. This approach has provided an optimum emission quantum yield of 9.2%.

Doped polymers with Ln(III) complexes: simulation and control of light colors

Complexes of Eu(III) and Tb(III) were dispersed in polystyrene for the purpose of generating the primary red and green light colors, and simulating of the secondary yellow color. The polymer was doped with one or both complexes. Under ultraviolet excitation, the Eu(III) and Tb(III) complex-doped polymers, both solid state light emitters, generate the red and green colors, respectively. The Eu(III) and Tb(III) mixed complexes in the polymer present the characteristic emissions of the lanthanide ions, simulating the secondary yellow light color.

Lanthanide complexes dispersed in enamel: a promising new material for photonic devices

Abstract A lanthanide-thin-film based dosimeter with high sensitivity and selectivity to UV cumulative measurements was developed. The dosimeter is based on nitrocellulose–enamel and has been designed in order to present useful responses covering the three main UV regions related to skin damage effects: UV-A (365 nm), UV-B (315 nm), UV-C (290 nm).The active part of the system is a thin layer of commercial nitrocellulose enamel ultrasound-mixed with lanthanide complex powder. We have monitored the Eu (III) emission ( 5 D 0 → 7 F 2 ) and the Tb (III) emission ( 5 D 4 → 7 F 5 ) as a function of UV exposure time and a luminescence decrease of the Eu (III) emission was observed. Since this effect is irreversible, a memory effect is associated to the system allowing dosimetry measurements. For the red (600 nm), green (540 nm) and blue (430 nm) excitation the luminescence remained the same, which reinforces the UV selectivity of the dosimeter proposed. We may also adjust the dosimeter sensitivity by controlling the amount of powder mixed with the enamel.

Synthesis, spectroscopic studies and structure prediction of the new Tb(3-NH2PIC)3·3H2O complex

Abstract The synthesis, spectroscopic properties and structure prediction of the complex of Tb(III) with 3-aminopyridine-2-carboxylic acid (3-NH2PIC) are described. The complex was characterized by elemental analysis and IR, absorption and emission spectra. The C, H and N elemental analysis consistent with the formulation of the compound as Tb(3-NH2PIC)3·3H2O. This complex exhibits a luminescence intensity that is attenuated to that of its Eu+3 congener. The Sparkle model, used for structural computations of lanthanide complexes (SMLC), was applied to the new complex. The calculation used an INDO/S-CI model for determination of the electronic spectrum.

Typification and quality control of the Andiroba (Carapa guianensis) oil via mass spectrometry fingerprinting

The oil from the seeds of the “Andiroba” tree, which is found throughout most tropical America, contains high levels of unsaturated triacylglycerols (TAG), which makes it attractive to the cosmetics industry. A significant amount of limonoids also confers to this Amazonian oil several pharmaceutical and medical properties. In addition, the oil is also a potential feedstock for biodiesel production, and its many uses have intensified its extractive exploitation in recent years. Herein we report on the characterization of the TAG, free fatty acids (FFA) and limonoid profiles of the Andiroba oil via mass spectrometry (MS) fingerprinting using direct electrospray ionization mass spectrometry (ESI-MS). An ambient desorption/ionization technique known as easy ambient sonic-spray ionization (EASI-MS) was also evaluated with similar results. ESI-MS was performed either for a methanolic solution of a few microliters of the fresh oil or from a simple aqueous extract whereas EASI-MS was applied directly to a droplet of the oil resting on a paper surface. The efficacy of these MS fingerprinting techniques requiring no pre-separation and no or very simple sample preparation protocols was investigated and compared for the typification and quality of this valuable Amazonian oil.

An example of concentration sensitive electron-phonon coupling in {(C4H9)4N}3 EuxY1−x(NCS)6 and a new hypothesis for self-quenching

The strong vibronic one-phonon side-bands of the 5D0 → 7F0 emission of Eu3+ in {(C4H9)4N}3 EuxY1−x(NCS)6 are used to compute the Huang-Rhys electron-phonon coupling factor (S0) of Eu3+ with the mode at 35 cm-1. Increasing concentration from 1 to 100 is found to lead to a doubling of the electron-phonon coupling strength. Generalization of such an effect is proposed as a new hypothesis for part of the self-quenching process of rare-earth ions.

Spectroscopy and crystallization behavior of Eu3+-doped La2O3:B2O3 binary glasses

Abstract xLa2O3:(1 − x)B2O3 (x = 0.19−0.28) and 19La2O3:1Eu2O3:80B2O3 glasses were synthesized and investigated by X-ray diffraction, differential thermal analysis, transmittance spectroscopy in the ultraviolet-infrared region, infrared vibrational spectroscopy and luminescence spectroscopy. Eu3+ doped glass has also been investigated by fluorescence line narrowing techniques. Single-phase polycrystalline LaB3O6:5%Eu, LaBO3:5%Eu and La3BO6:5%Eu samples were synthesized for comparison. Devitrification was observed to yield single-phase LaB3O6 glass ceramics. Nucleation begins at the surface and is heterogeneous. There is no indication of Eu3+ partitioning into the crystal phase. The results indicate that in the glass as annealed there are already domains in which the Eu3+ ions experience a ligand field close to that experienced in LaB3O6 crystals.

Optical studies and microstructure of Eu3+-doped fluoroborate glasses containing silver particles☆

Abstract We have investigated the fluorescence enhancement for Eu 3+ ions in fluoroborate glasses containing a highly inhomogeneous size distribution of silver particles. Electron microscopy investigations and energy dispersive analysis of X-ray revealed two main features: 1. (1) heterogeneity in the concentration of silver particles and 2. (2) a highly inhomogeneous size distribution of particles, with particle sizes peaking around 15 and 60 A.