Reduction of Eu3 + to Eu2 + in Al-Codoped Silica Glasses Fabricated by the Sol-Gel Technique and CO2-Laser Processing

The spectroscopic properties of europium in aluminium codoped silica glasses produced by the sol-gel technique have been studied with respect to the dopant concentrations and the thermal processing applied to the samples. After thermal annealing at temperatures up to 950_°C the bright red fluorescence around 613 nm characteristic for the trivalent europium ions (Eu^{3 +}) has been observed. The lifetime was measured to be 0.1–2.4 ms depending on dopant concentrations and thermal treatment. Subsequent CO₂-laser processing in air (short time remelting) gave rise to a bright blue fluorescence consisting of two broad bands, lying around 450 and 490 nm, with their peak position depending on the ratio between the aluminium and europium concentrations. The fluorescence lifetimes were found to be shorter than 1 s. This blue fluorescence is attributed to the divalent europium ion (Eu^{2 +}), leading to the conclusion that the CO₂-laser processing of europium doped alumina-silica glasses resulted in the reduction of the trivalent to the divalent europium ion. Laser processing could therefore be a valid alternative to conventional thermal annealing for the generation of Eu^{2 +} in alumina-silica glasses.     

Comparison of synchronous and laser-induced fluorescence spectroscopy applied to the Eu(III)-fulvate complexation

The complexation of europium ion (Eu(III)) with a soil fulvic acid (FA) has been studied at pH 5 in 0.01 M NaClO₄ by different experimental methods, i.e. synchronous fluorescence spectroscopy (SyFS) and time resolved laser-induced fluorescence spectroscopy (TRLFS). A series of SyFS quenching spectra was obtained by increasing the Eu(III) concentration and keeping the FA concentration constant. The emission spectra and fluorescence lifetimes of the Eu(III) bound to the FA were also measured by a TRLFS system using the same solution used in the SyFS spectral measurement. From the analysis of the fluorescence data obtained by the SyFS and the TRLFS using a non-linear least-squares method, the concentration of the binding sites (C_L) of the FA accessible for the Eu(III) and the corresponding conditional stability constants (log K) were estimated. The two different methods gave rise to constants being comparable with one another. The log K and C_L values (mean ± standard deviation of three determinations) determined by the SyFS were 6.4 ± 0.2 (6.7 ± 0.1 μmol L⁻¹: by the TRLFS) and 10 ± 1 μmol L⁻¹ (7 ± 1 μmol L⁻¹: by the TRLFS), respectively. The applicability of the FA fluorescence quenching techniques for estimating the europium binding parameters was proved by the direct monitoring of the Eu(III) bound to the FA using the TRLFS system.     

Europium speciation by time-resolved laser-induced fluorescence

Time-resolved laser-induced fluorescence has been used to investigate Eu complexes formed with a few main ligands encountered in natural waters: hydroxide, carbonate and humic substances. By varying pH and concentrations of ligands at fixed europium concentration and ionic strength, it was possible, together with free europium Eu³⁺, to identify spectrally and temporally carbonate complexes, namely Eu(CO₃)⁺, Eu(CO₃)₂⁻ and Eu(CO₃)₃³⁻ and humate complexes EuHA. For hydroxide complexes, no differences were found in terms of fluorescence spectra and lifetimes. A spectral interpretation is described by using deconvolution for all systems.     

Cathodic europium(III) electroluminescence at an oxide-coated aluminum electrode

Electroluminescence is produced at an oxide-coated aluminum electrode during cathodic polarization of the electrode in an acetate solution containing nitrate and traces of europium(III). The europium(III) ion in the ⁵D₀ state is the emitter. Linear log-log calibration plots are obtained for the range 1 × 10^?8?1 × 10^?5 M europium(III). A mechanism for the cathodic luminescence is proposed.     

Preparation and Luminescence Properties of the Ternary Europium Complex Incorporated into an Inorganic/Polymer Matrix by a Sol-Gel Method

Ternary europium complexes with thenoyltrifluoroacetone (TTA) and phenanthroline (phen) were incorporated into SiO₂/polymer matrix by a sol-gel method. The gels exhibit the characteristic emission bands of europium ion. In addition, Eu³⁺ presents a longer fluorescence lifetime in gel than in the corresponding pure complex powder. Concentration effects on the luminescence intensity were investigated. The reasons that are responsible for above results are also discussed in the context.     

A New Fluorimetric Reagent for Determination of Trace Amounts of Europium

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｃｈｅｍｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆｒａｒｅ ｅａｒｔｈｅｌｅｍｅｎｔｓａｒｅｖｅｒｙｓｉｍｉｌａｒ ,ｃｏｎｓｅｑｕｅｎｔｌｙ ,ｉｔｉｓｄｉｆｆｉｃｕｌｔｔｏｄｅｔｅｃｔａｎｉｎ ｄｉｖｉｄｕａｌｉｏｎｉｎｔｈｅｉｒｍｉｘｔｕｒｅｓｏｗｉｎｇｔｏｔｈｅｉｎｔｅｒｆｅｒｅｎｃｅｏｆｏｔｈｅｒｒａｒｅ ｅａｒｔｈｅｌｅｍｅｎｔｓ .Ｄｕｅｔｏａｈｉｇｈｅｒｓｅｎｓｉｔｉｖｉｔｙａｎｄｓｅｌｅｃｔｉｖｉｔｙ ,ｆｌｕｏｒｉｍｅｔｒｉｃｍｅｔｈｏｄｓｏｆｒａｒｅ ｅａｒｔｈｅｌ…     

In‐situ Synthesis and Photoluminescence of a Europium Porphyrin Complex Incorporated in the Silica Matrix

A practicable synthesis method is explored to synthesize a europium porphyrin complex in which a water‐soluble positively charged 5,10,15,20‐tetrakis(4‐trimethylammoniophenyl)porphyrin iodide, H₂TMePPI, is immobilized into the sol‐gel silica matrix and then in‐situ metallized with the Eu³⁺ ion. The product is characterized by means of the solid UV diffusion reflection spectra, fluorescence spectra, and thermal gravimetric analysis (TG). The solid UV diffusion reflection spectra show that the number of Q bands in the product is less than that of the H₂TMePPI ligand, which is one of the important characteristics of porphyrin metallization. The fluorescence spectra of the product are different from that of the silica doped with free Eu³⁺ ions, implying the different function of Eu³⁺ ions in the product. The TG curves show that the thermal stability of the Eu(III)TMePPI entrapped into silica is higher than that of the H₂TMePPI. The effect of a heat treatment and an UV‐light irradiation on the photoluminescence properties of the composite is investigated in details. The stronger interaction between Eu(III)TMePPI and SiO₂ in the composite is responsible for the different spectra.     

Fluorescence properties of mixed-ligand europium carboxylates

Mixed-ligand binuclear and mononuclear europium carboxylate complexes with nitrogen-and phosphorus-containing neutral ligands have been studied by luminescence and X-ray photoelectron spectroscopy. The coordination of neutral ligands through the nitrogen donor atom leads to an increase in electron density at the Eu³⁺ atom. In groups of carboxylates of the same type, the coordination of neutral donor ligands leads to an increase in the relative intensity of the ⁵ D ₀-⁷ F ₄ electric dipole transition. Analysis of the luminescence excitation spectra points to the presence of two excitation energy transfer channels for mixed-ligand europium trifluoroacetate and toluate complexes and of one channel for europium cinnamate complexes with neutral ligands.     

Synthesis and characterization thesulphides type ZnS(1-x)MSx

ZnS_(1-x)MS_x(x=0.01 and M=Mn²⁺, Cu²⁺ and Eu²⁺) compounds have been obtained by precipitation from homogeneous solutions of zinc, copper, manganese and europium salts, with S^2- as the precipitating anion, formed by the decomposition of thioacetamide. The thermal study of the milled zinc acetate, thioacetamide, copper acetate, manganese acetate and europium nitrate, respectively, was studied for thermal analyis TG/DSC. XRD respect exhibits a zinc blend crystal structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fluorescence of the 5Do state of the europium ion in the gas phase

The fluorescence of vapors of europium dipivaloylmethanate (EuL₃), excited by pulsed UV radiation, has been investigated. The fluorescence was observed in the transition ⁵D_o ⁷F₂ of the europium ion (Eu³⁺) (wavelength 6120 Å). An increase of the fluorescence signal by a factor of 3 was established when the cell with the EuL₃ vapors was placed in the optical resonator.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 367–370, May–June, 1985.     

Assembly of novel Tb3+/Eu3+ sensitized cellulose gels and their emission behaviors

In this paper, a novel luminescent hydrogel was successfully prepared by incorporating Tb-HSA (HSA = Human Serum Albumin) complex into cellulose host. The green luminescence intensities of Tb(III) exhibited on–off changes in terms of pH variation. At the same time, europium activated phosphor (GdVO₄:Eu³⁺) was immobilized into the cellulose hydrogels through two approaches. The photophysical properties of luminescent gels with the temperature variation were investigated by fluorescence. The new group of soft materials will display task-specific usages in sensing fields.     

Spectral and optical properties of high-optical-quality organic glasses under prolonged ultraviolet irradiation

The effect of prolonged UV irradiation on optical and spectral luminescent properties of two types of high-quality optical organic glasses are studied by electronic absorption spectroscopy, spectrofluorimetry, IR spectroscopy, and atomic force microscopy. Glasses 2.3 mm in thickness are obtained through the layer-by-layer photopolymerization of an oligo(epoxy diacrylate) mixture with benzyl methacrylate and oligo(carbonate dimethacrylate). After the addition of europium tris(benzoyltrifluoroacetonate) to the photopolymerizing compositions, glasses that luminesce in the red spectral region are produced. The action of light gives rise to a slow photodecomposition of the luminescent component and causes a decline in the intensity of the band due to ⁵ D ₀ → ⁷ F ₂ transition of the europium cation. The growth of absorption in the yellow-green spectral region favors formation of an internal light filter; as a result, the photodecomposition of the europium complex in deep layers proceeds at a smaller rate than that in surface layers. IR-spectroscopy measurements demonstrate the accumulation of hydroxyl groups in oligo(carbonate dimethacrylate) films during irradiation in air. In an inert atmosphere, practically no photodegradation products are evolved from the matrix material.     

Evaluation of electrochemical charge-transfer rates by using (real) laplace space analysis: Single potential-step chronoamperometry of hexacyanoferrate(III)/(II) and Europium(III)/(II) couples

The one-electron hexacyanoferrate(III)/(II) and europium(III)/(II) redox couples were evaluated by using single-pulse chronoamperometry at a planar glassy carbon electrode (and also a mercury-pool electrode for europium) to test Wijnen's method for calculating heterogeneous electron-transfer rate constants by using (real-axis) Laplace space analysis. The k⁰ values obtained for the former couple in potassium or lithium chloride supporting electrolytes agreed well with published constants obtained by diverse real-time techniques. Transfer coefficients (α⁰) obtained from (? in k^a/?η)_η=0 for LiCl electrolyte were 0.4–0.5, rather than 0.22 previously reported. The cathodic rate values calculated for europium(III) reduciton (in NaClO₄/HClO₄) on both glassy carbon and mercury agreed very well with each other and with published values obtained by d.c. polarography and faradaic impedance measurements. Owing to several factors, including its ability to utilize virtually any set of recorded i(t) data points, Wijnen's Laplace technique offers an attractive alternative to conventional single-pulse analysis in real-time.     

Application de la radiopolarographie a l'étude dequelques éléments à l'échelle des indicateurs

Basic equations of classical polarography are transposed and tested withmanganese and europium at tracer scale. Using the previously presented automatic system, standard dispersion for experimental points is about 3% and residual activity before the wave 3±2% compared with diffusion activity A_d. Results with manganese in 10^?3M ≤[LiCl]≤10^?1M and 2≤pH≤4 solutions, give an experimental yield about 100%, E_1/2=?1.47 V/SCE and α?0.85. The last values agree with results achieved at a weighable scale. For potentials <?2.00 V/SCE a screening effect with supporting electrolyte ions is observed. The screening effect influence on the diffusion coefficient is taken into consideration and results for europium (R?100%, E_1/2??1.95 V/ECS, α=1 at pH 2.7) are in good agreement with the literature. Radiopolarograms for Mn and Eu and mixtures of both are similar. Thus the range of polarographic analysis is enlarged.     

Temperature dependence of fluorescence for EuCl3 in LiCl-KCl eutectic melt

The fluorescence of EuCl₃ in LiCl-KCl eutectic melt according to temperature changes was investigated, and the spontaneous partial reduction of Eu³⁺ to Eu²⁺ at high temperature was confirmed by the fluorescence results. The fluorescence decreases when the temperature increases, and this was examined in detail. The studies of fluorescence provided information regarding the chemical and physical behavior of europium ions in the molten salt according to the temperature changes. It is applicable for monitoring species and concentrations and estimating the approximate chemical structure of the ions in molten salts.     

Rare earth tungsten bronzes: a new method of synthesis. Perspectives for their application as inert matrices for transmutation of long-life actinide elements

A new method of synthesis of oxide tungsten bronzes containing lanthanide (Ln) Nd and Eu, based on thermal degradation of polyoxotungstate compounds, is proposed. The simplicity of the method allows to consider this class of compounds with chemical formula, Ln_xWO₃, as potential inert target for incineration or transmutation of minor actinides, Am and Cm, in neutron reactors. Nd and Eu were used as analogues of transplutonium elements. Powder X-ray diffraction patterns of compounds synthesized reveal a cubic perovskite structure. The lanthanide content in bronzes was determined by optical spectroscopy analysis. The experimental density of the pressed bronze samples was estimated at 6.58 g cm⁻³, i.e., 89% of the crystallographic value. The thermal stability of the bronzes synthesized was checked up to 900°C in an inert atmosphere. Leaching tests were performed for europium bronzes in nitric acid solutions using luminescence technique.     

Spectroscopic properties of lanthanoid benzene carboxylates in the solid state: Part 2. Polar substituted benzoates

Europium and terbium complexes of ortho, meta and para substituted benzoate ligands including nitrobenzoate (NBA), aminobenzoate (ABA), hydroxybenzoate (OHBA) and methoxybenzoate (MeOBA) have been synthesised by metathesis reactions, carried out in aqueous media. The complexes were characterised by elemental, compositional and structural investigations, including microanalysis, EDTA titrations, differential thermal analysis, infra red spectroscopy, X-ray powder diffraction and single crystal structural analyses. Besides this, strong emphasis was on the determination of the optoelectronic properties of the compounds in the solid state. In this regard, reflectance, excitation and emission spectra were recorded. From these, the emission and excitation efficiencies were determined. The relative intensities as well as the splitting patterns of the ⁵D₀ → ⁷F_J transitions in the europium emission spectra are discussed.     

Determination for Enterobacter cloacae based on a europium ternary complex labeled DNA probe

The fast detection and accurate diagnosis of the prevalent pathogenic bacteria is very important for the treatment of disease. Nowadays, fluorescence techniques are important tools for diagnosis. A two-probe tandem DNA hybridization assay was designed for the detection of Enterobacter cloacae based on time-resolved fluorescence. In this work, the authors synthesized a novel europium ternary complex Eu(TTA)₃(5-NH₂-phen) with intense luminescence, high fluorescence quantum yield and long lifetime before. We developed a method based on this europium complex for the specific detection of original extracted DNA from E. cloacae. In the hybridization assay format, the reporter probe was labeled with Eu(TTA)₃(5-NH₂-phen) on the 5′-terminus, and the capture probe capture probe was covalent immobilized on the surface of the glutaraldehyde treated glass slides. The original extracted DNA of samples was directly used without any DNA purification and amplification. The detection was conducted by monitoring the fluorescence intensity from the glass surface after DNA hybridization. The detection limit of the DNA was 5 × 10⁻¹⁰ mol L⁻¹. The results of the present work proved that this new approach was easy to operate with high sensitivity and specificity. It could be conducted as a powerful tool for the detection of pathogen microorganisms in the environment.     

Fluorescence spectra of laser-excited YO molecules in a H2O2Ar flame

CW dye laser induced fluorescence emission and thermal emission spectra of YO-molecules in a 1 atm H₂O₂Ar flame of 2430 K were recorded simultaneously. Narrow band laser excitation was applied to four rotational lines in the (1, 1) Q-branch of the A²Π_{$\text{3}\text{2}$}→X²Σ⁺ transition and broadband excitation was applied to several separate Q-branches of the A²Π_{$\text{1}\text{2}$,$\text{3}\text{2}$}→X²Σ⁺ transitions. From the differences between the fluorescence emission spectra and thermal emission spectra, we conclude that collisional de-excitation of an excited vibronic level takes place by vibrational relaxation, decay to the electronic ground state and by intermultiplet transfer in order of increasing probability.     

Formation and dissociation kinetics of Eu(III) complexes with H5do3ap and similar dota-like ligands

Complexation kinetics of the europium(III)-H₅do3ap complex (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-(methylphosphonic acid)) was studied at 25 °C and I = 0.1 M KCl and compared with the analogous H₄dota-like ligands. The mechanism of the formation reactions between the europium(III) ion and H₃do3a, H₄dota and H₄dota analogs having one methylphosphonic (H₅do3ap) or phosphinic acid pendant arms with a propionate side chain (H₅do3ap^PrA) was proposed on the basis of TRLIFS measurements. The experimental data of the dissociation kinetics of the europium(III) complexes with H₅do3ap and H₅do3ap^PrA ligands show that there is no change in reactivity of the complexes due to the side chain of the phosphinic acid bifunctional chelate. The TRLIFS study of the proton-assisted decomplexation reaction of the europium(III) complexes with H₃do3a, H₄dota, H₅do3ap and H₅do3ap^PrA demonstrates different behaviour influenced by a change in the number of water molecules during the reaction. The advantages and disadvantages of the TRLIFS methodology as a new experimental technique for simultaneous evaluation of kinetics and reaction mechanisms are discussed.