Syntheses and electroluminescent properties of two europium ternary complexes Eu(DBM)3(PBO) and Eu(DBM)3(PBT)

Two europium complexes, Eu(DBM)₃(PBO) and Eu(DBM)₃(PBT) (DBM=dibenzoylmethanato, PBO=2-(2-pyridyl)benzoxazole, PBT=2-(2-pyridyl)benzothiazole), were prepared and used as emitting materials in organic electroluminescent (EL) devices. The devices with the structures ITO/TPD/Eu(DBM)₃(PBO) (or Eu(DBM)₃(PBT)/BCP/Alq₃/Mg:Ag/Ag emit red light originating from the europium complexes.     

Fluorescence enhancement of samarium complex co-doped with terbium complex in a poly(methyl methacrylate) matrix

The fluorescence property of Sm(DBM)₃phen- (DBM—dibenzoylmethide, phen—1,10-phenanthroline) and Tb(DBM)₃phen-co-doped poly(methyl methacrylate) (PMMA) was investigated. The excitation, emission spectra and fluorescence lifetime of the co-doped samples were examined. In the co-doped samples, the luminescence intensities of Sm³⁺ enhance with an increase of the Tb(DBM)₃phen content and with a decrease of the Sm(DBM)₃phen content. The reason for the fluorescence enhancement effect in the co-doped polymer is the intermolecular energy transfer. To give a vivid picture for this co-doped system, a model for the fluorescence enhancement of Sm(DBM)₃phen- and Tb(DBM)₃phen-co-doped PMMA is presented.     

Synthesis and electroluminescent properties of a carbozole-functionalized europium(III) complex

A novel europium(III) complex, tris(dibenzoylmethanate){1-[9-hexyl-9H-carbazole]-2-(2-pyridyl)-benzimidazole}europium(III) [Eu(DBM)₃(CAR-PyBM)] functionalized by a carbozole fragment, was synthesized and used as emitting material in organic electroluminescent (EL) devices. Compared with the device based on an unfunctional Eu(III) complex, [Eu(DBM)₃HPyBM] (HPyBM=2-(2-pyridyl)benzimidazole), the EL performances of the device using [Eu(DBM)₃(CAR-PyBM)] as an emitter was significantly enhanced due to the improvement of hole-transporting ability. The maximum efficiency and luminance of red emission achieved from the device with the configuration of ITO/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′diamine (TPD, 50 nm)/ [Eu(DBM)₃(CAR-PyBM)] (30 nm)/1,3,5-tirs-(N-phenylbenzimidazol-2-yl)benzene (TPBI, 20 nm)/LiF (1.5 nm)/Al were 4.2 cd/A and 200 cd/m², respectively.     

Columinescence of dye molecules in nanostructures of metal ion complexes

The mechanism of columinescence (fluorescence sensitization) of dyes incorporated in nanostructures of metal complexes is studied. It is shown for the first time that the columinescence of dyes is due to the transfer of excitation energy from ligands and metal ions of complexes that form nanostructures. It is proven that the dye columinescence of rhodamine 6G (R6G) molecules incorporated into nanostructures of Al(DBM)₃phen, Al(DBM) _n (OH)_{6 ? 2n} , and Eu(DBM)₃phen (DBM is dibenzoylmethane) nanostructures is completely determined by the singlet excitation energy migration from ligands to R6G molecules. It is shown that, at small concentrations of R6G, the R6G columinescence intensity is lower in nanostructures of metal complexes with a high probability of S-T conversion and that this difference disappears at large concentrations of R6G. In the case of Nile blue (whose S ₁ level lies below the ⁵ D ₀ level of Eu(III)) incorporated in nanostructures of Eu(DBM)₃phen complexes, as well as in nanostructures of Al(DBM)₃phen and Gd(DBM)₃phen complexes with admixture of Eu complexes, we observed the S-S energy transfer from DBM to NB in addition to the delayed sensitized fluorescence of NB previously observed in nanostructures of Eu complexes, which was caused by the energy transfer from the ⁵ D ₀ level of Eu(III) to NB. At dye concentrations below 100 nM, the efficiency of NB sensitization due to the migration of singlet excitation energy from DBM is lower than in the case of the energy transfer from Eu(III) ions, while, at large concentrations of the dye, the S-S energy transfer successfully competes with the sensitization of NB by Eu(III) ions. The use of dye columinescence makes it possible to easily determine dye concentrations of 2–100 nM in solutions with standard spectrofluorimeters.     

Experimental natural lifetime determination of the Ar(II) lower laser levels

The natural lifetimes of the (³P)4s²P_3/2,1/2 levels of the Ar(II) spectrum have been determined from the natural broadening of argon lines, measured with a Fabry—Pérot interferometer. The natural broadening was determined from the lines with wavelengths of 4880 and 4965 Å by comparing them with the lines at 4806 and 5009 Å having negligible natural broadening. The natural lifetime of the 4s²P_3/2 level appeared to be τ = 0.19 (±6%) ns and of the 4s²P_1/2 level τ = 0.18 (±15%) ns. These values are about 1.5 to 2 times as small as those determined by other authors either experimentally by using a Fabry—Pérot interferometer by the method of Ballik, or calculated using intermediate coupling.The differences between the two experimental methods are discussed.     

A spectroscopic study of uranium(VI) interaction with magnetite

The uranium sorbed onto commercial magnetite has been characterized by using two different spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). Magnetite samples have been put in contact with uranium(VI) solutions in conditions in which a high uranium uptake is expected. After several days, the magnetite surface has been analysed by XPS and EXAFS. The XPS results obtained are not conclusive regarding the uranium oxidation state in the magnetite surface. On the other hand, the results obtained with the EXAFS technique show that the uranium-magnetite sample spectrum has characteristics from both the UO₂ and schoepite spectra, e.g. a relatively high coordination number of equatorial oxygens and two axial oxygens, respectively. These results would indicate that the uranium sorbed onto magnetite would be a mixture of uranium(IV) and uranium(VI).     

The adsorption of methyl iodide on uranium and uranium dioxide: Surface characterization using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES)

The adsorption of methyl iodide on uranium and on uranium dioxide has been studied at 25 °C. Surfaces of the substrates were characterized before and after adsorption by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The XPS binding energy results indicate that CH₃I adsorption on uranium yields a carbide-type carbon, UC, and uranium iodide, UI₃. On uranium dioxide the carbon electron binding energy measurements are consistent with the formation of a hydrocarbon, —CH₃-type moiety. The interpretation of XPS and AES spectral features for CH₃I adsorption on uranium suggest that a complex dissociative adsorption reaction takes place. Adsorption of CH₃I on UO₂ occurs via a dissociative process. Saturation coverage occurs on uranium at approximately two langmuir (1 L = 10^?6 Torr s) exposure whereas saturation coverage on uranium dioxide is found at about five langmuir.     

An EDXRF method for determination of uranium and thorium in AHWR fuel after dissolution

A fast energy dispersive x‐ray fluorescence (EDXRF) method requiring only microgram amounts of analytes, i.e. uranium (U) and thorium (Th), in their mixtures in solution form is described. Calibration solutions and samples covering the fuel composition range (0–5% of U in U + Th) of advanced heavy water reactor (AHWR) were prepared by mixing uranium and thorium solutions. A known fixed amount of internal standard yttrium (Y) was added to these solutions. EDXRF spectra of calibration solutions and samples were measured by taking 20 µl aliquots on 30 mm diameter filter papers, after drying, using a Rh target tube operated at 40 kV and 500 µA. Calibration plots were made by plotting U/Y, U/Th and Th/Y amount ratios against the respective intensity ratios of Th Lα, U Lα and Y Kα. In the first set, U was determined using Y as an internal standard, and for Th determination, U, thus determined, was used as an internal standard since the amounts of Th and Y were kept constant in the calibration solutions and samples. In the second set, both U and Th were varied and determined using Y as internal standard. The results of U and Th determinations showed a precision of about 3% (1s) and the results deviated from the expected values by <3% in most of the cases. This approach has an advantage that it requires only microgram amounts of sample, thus mitigating radiation hazards associated with radioactive samples as well as the amount of radioactive analytical waste generated is quite less. Copyright © 2009 John Wiley & Sons, Ltd.     

Determinations of Uranium(VI) Binding Properties with some Metalloproteins (Transferrin,Albumin, Metallothionein and Ferritin) by Fluorescence Quenching

The interactions between uranium and four metalloproteins (Apo-HTf, HSA, MT and Apo-EqSF) were investigated using fluorescence quenching measurements. The combined use of a microplate spectrofluorometer and logarithmic additions of uranium into protein solutions allowed us to define the fluorescence quenching over a wide range of [U]/[Pi] ratios (from 0.05 to 1150) at physiologically relevant conditions of pH. Results showed that fluorescence from the four metalloproteins was quenched by UO₂²⁺. Stoichiometry reactions, fluorescence quenching mechanisms and complexing properties of metalloproteins, i.e. binding constants and binding sites densities, were determined using classic fluorescence quenching methods and curve-fitting software (PROSECE). It was demonstrated that in our test conditions, the metalloprotein complexation by uranium could be simulated by two specific sites (L₁ and L₂). Results showed that the U(VI)–Apo-HTf complexation constant values (log K₁ = 7.7, log K₂ = 4.6) were slightly higher than those observed for U(VI)–HSA complex (log K₁ = 6.1, log K₂ = 4.8), U(VI)–MT complex (log K₁ = 6.5, log K₂ = 5.6) and U(VI)–Apo-EqsF complex (log K₁ = 5.3, log K₂ = 3.9). PROSECE fitting studies also showed that the complexing capacities of each protein were different: 550 moles of U(VI) are complexed by Apo-EqSF while only 28, 10 and 5 moles of U(VI) are complexed by Apo-HTf, HSA and MT, respectively.     

Volatile metal β-diketonates — new precursors for the sonochemical synthesis of nanosized materials — sonolysis of thorium(IV) β-diketonates

Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(IV) β-diketonates Th(HFAA)₄ and Th(DBM)₄, where HFAA and DBM are hexafluoroacetylacetone and dibenzoylmethane respectively, causes them to decompose in hexadecane solutions, forming solid thorium compounds. The first-order rate constants for Th(IV) β-diketonate degradation were found to be (9.3±0.8)×10⁻³ for Th(HFAA)₄ and (3.8±0.4)×10⁻³ min⁻¹ for Th(DBM)₄, (T=92°C, I=3 W cm⁻²). The rate of the sonochemical reaction increased with the rising β-diketonate volatility and decreased with the rising hydrocarbon solvent vapor pressure. Solid sonication products consisted of a mixture of thorium carbide ThC₂ and Th(IV) β-diketonate partial degradation products. The average ThC₂ particle size was estimated to be about 2 nm. ThC₂ formation was attributed to the high-temperature reaction occurring within the cavitating bubble. The thorium β-diketonate partial degradation products formed in the liquid reaction zones surrounding the cavitating bubbles.     

1.53 μm photoluminescence from ErYb(DBM)<Subscript>3</Subscript>MA containing polymer

We investigated the optical properties of the ErYb(DBM)₃MA complexes and the ErYb(DBM)₃MA containing polymer. Absorption and photoluminescence spectra confirm that the presence of Yb³⁺ ions enhances luminescence efficiency of Er³⁺ ions. The full width at half maximum bandwidth (FWHM) is ∼80 nm wide around 1.53 μm wavelength. We also fabricated ErYb containing polymeric channel waveguides using reactive ion etching technique. As an input pump of 120 mW was used, a ∼1.53 μm spontaneous emission was obtained in a 4-mm-long waveguide. PACS 42.00.00; 42.70.Jk; 42.82.Et     

Band Displacement Process with Redox Reactions for Uranium Isotope Separation by Chemical Exchange between U(IV)-Resin and U(VI)-Solution

The extreme limits for ²³⁵U/²³⁸U % at ambiant temperature were determined experimentally with a long time band displacement process (almost 1 year) using the isotope exchange reaction between U(IV)_resin and U(VI)_solution. These limits are 0.738 and 0.712, considering ²³⁵U/²³⁸ = 0.725% for natural uranium. The redox reactions, allowing the band displacement were: 1) in front of the band is the reduction of U(VI) in solution by a cathionic resin in Ti(III)-form; 2) in the tail of the band is the oxydation of U(IV) in resin by a solution containing Fe(III) ions.     

Synthesis, photoluminescence and bioconjugation of rare-earth (Eu) complexes-embedded silica nanoparticles

Eu(DBM)₃Phen-embedded silica nanoparticles were synthesized in water-in-oil (W/O) microemulsion containing aqueous phase of Eu(DBM)₃Phen, surfactant Triton X-100, cosurfactant octanol and oil-phase cyclohexane. The size and morphology of the nanoparticles were characterized by transmission electron microscopy (TEM). The low-temperature time-resolved emission spectra indicate that the Eu complex in the silica nanoparticles have longer lifetime than that of the pure complex. Under 355 nm continuous excitation, the nanoparticles show high resistance to photobleaching. The free amino groups were attached to silica surfaces by copolymerization of 3-aminopropyl(triethoxy)silane. Preliminary results demonstrated that the silica-coated Eu complex nanoparticles can be a probe in the detection of biomolecular interactions.     

Betterment in EDXRF analytical results for compositional characterization of mixed uranium thorium oxide samples with bead specimens compared with pressed pellet specimens

A comparative study on the energy dispersive X‐ray fluorescence analytical results of uranium determinations, in uranium and uranium–thorium mixed oxides, using specimens in the form of fused beads and pressed pellets, has been made. It was observed that in case of fusion bead specimens, the intensity of the analyte lines was approximately 1.6 times of that observed in pellet specimens under identical instrumental conditions. In case of uranium oxide samples, the analytical results with bead specimens were slightly better compared with the pellet specimens. However, in case of the uranium–thorium oxide mixtures, the average precision obtained with bead specimen was significantly better (1%, 1 s) in comparison with that achieved using pellet specimens (7%, 1 s). This difference may be due to the hardness of thorium oxide compared with uranium oxide, which affects the homogeneity of the pellet specimens prepared. In fusion bead method of sample preparation, even highly refractory material like ThO₂ forms uniform glass beads. Addition of internal standard further improves the analytical results, with reduction in the percent deviation of energy dispersive X‐ray fluorescence results from the expected values to 3% from 7% compared with that obtained using without internal standard. The fusion bead method of sample preparation will be very useful for characterization of sintered (U,Th)O₂ pellets, which are highly refractory and difficult to dissolve. Copyright © 2016 John Wiley & Sons, Ltd.     

Optical transition properties of Eu in Eu(DBM)3phen mono-dispersed microspheres for microcavity laser application

Mono-dispersed microspheres of ternary complex Eu(DBM)₃phen (DBM=dibenzoylmethide; phen=1,10-phenanthroline) were prepared through a facile process. The obtained sample was characterized by means of X-ray powder diffraction (XRD) and scanning electron microscope (SEM). And the luminescence properties of the Eu(DBM)₃phen were investigated by the fluorescence spectra and the fluorescence decay. According to Judd-Ofelt theory, the optical transition intensity parameters Ω_λ (λ=2, 4 and 6) were obtained to be 20.99×10⁻²⁰, 0.98×10⁻²⁰ and 1.79×10⁻²⁰ cm², respectively. The radiative transition properties of ⁵D₀ level, including transition rates, branch ratios and radiative transition lifetime were calculated. As a potential material for microsphere lasers, the optical gain performance for ⁵D₀→⁷F₂ transition was also evaluated.     

Luminescence of Nile red as indicator of composition of nanoparticles from diketonate complexes of trivalent metals

We study the sensitization of fluorescence of Nile red in nanoparticles formed in aqueous solutions of complexes of Al, In, Sc, and Lu with DBM, DBM, and phen and of complexes of In with MBTA and phen. We show that, at concentrations of Nile red of 2–50 nM and complexes of 10–30 μM, the fluorescence intensity of Nile red in aqueous solutions increases by 1.5–2 orders of magnitude compared to its fluorescence in H₂O. We find that, at these concentrations of Nile red in solutions of complexes Al, the dye is completely contained in nanoparticles from these complexes. We show that Nile red molecules are inhomogeneously distributed in nanoparticles from complexes and, upon the completion of the formation of nanoparticles, dye molecules tend to be localized in regions of nanoparticles formed from diketonate complexes M(diketone)₃phen (M is Lu or In) and Al(DBM)₃. Upon the localization of Nile red in these regions, the maximum of its fluorescence spectrum shifts toward ∼600 nm and, upon the penetration of Nile red into nanoparticles from Sc complexes, the shift of the maximum of its fluorescence spectrum compared to the spectrum in water does not exceed 10 nm. The shifts of the spectra are collated with the ability of ions to form diketonate and hydroxy diketonate complexes. We demonstrate that the fluorescence of Nile red is efficiently sensitized, not only upon its penetration into nanoparticles formed from complexes, but also upon its adsorption on the nanoparticle surface when Nile red molecules are introduced in solutions of already formed nanoparticles.     

Application of a cw quantum cascade laser CO2 analyser to catalytic oxidation reaction monitoring

Catalytic oxidation reaction monitoring has been performed for the first time with a trace gas carbon dioxide analyser based on a continuous wave (cw), thermoelectrically cooled (TEC), distributed feedback (DFB) quantum cascade laser (QCL) operating at around 2307 cm^?1. The reaction kinetics for carbon monoxide oxidation over a platinum catalyst supported on yttria-stabilised zirconia were followed by the QCL CO₂ analyser and showed that it is a powerful new tool for measuring low reaction rates associated with low surface area model catalysts operating at atmospheric pressures. A detection limit was determined of 40 ppb (1 standard deviation) for a 0.1 s average and a residual absorption standard deviation of 1.9×10^?4.     

Fabrication and amplified spontaneous emission of Eu(DBM) <Subscript>3</Subscript>Phen doped step-index polymer optical fiber

A step-index polymer optical fiber (SI POF) with a core of poly(methyl methacrylate) (PMMA) containing Eu(DBM)₃Phen has been fabricated by a preform technique. Fluorescence analysis showed that there is not obvious change in the local environment around Eu³⁺with the increase of Eu(DBM)₃Phen doping concentration. Amplified spontaneous emission (ASE) phenomenon of the doped SI POF by end-pumping with an Ar⁺-laser of 457.9 nm at ambient temperature was observed. The threshold of the pump power for the onset of ASE is found to be 120 mW for the doped SI POF with a length of 50 cm, the length is also found to be the optimal length for maximum ASE power under the input power of 200 mW. The maximum quantum conversion efficiency of the fiber is about 40%.     

Non-destructive assay and computational model for enrichment verification of UF6 cylinders

Verification of ²³⁵U enrichment in uranium hexafluoride (UF₆) cylinders is often achieved by destructive (DA) and non-destructive assay (NDA) techniques. These techniques are time consuming and need suitable and similar standard. This is in addition to the loss of nuclear material in the case of destructive analysis.This paper introduces an innovative approach for verifying of ²³⁵U enrichment in UF₆ cylinder. The approach is based on measuring dose rate (μSv/h) due to the emitted gamma rays of ²³⁵U at the surface of the cylinder and then calculating the activity of uranium and enrichment percentage inside the cylinder by a developed three dimensional model. Attenuation of the main ²³⁵U gamma transitions due to the cylinder wall (5B type of Ni alloy) was also calculated and corrected for. The method was applied on UF₆ cylinders enriched with 19.75% of ²³⁵U. The calculated enrichment was found to be 18% with 9% uncertainty. By the suggested method, the calculated total uranium activity inside one of the investigated UF₆ cylinder was found close to the target (certified) value (5.6 GBq) with 9% uncertainty. The method is currently developed by taking into consideration other parameters.