Lanthanum Fluoride Research Articles

Rapid fusion method for determination of actinides in fecal samples

A new rapid fusion method for the determination of actinides in fecal samples has been developed at the Savannah River National Laboratory that can be used for emergency response or routine bioassay analyses. If a radiological dispersive device, improvised nuclear device or nuclear accident occur, there will be an urgent need for rapid analyses of environmental, food and bioassay matrices. If an inhalation event occurs and there is confirmed radionuclide activity present via urine analyses of individuals, fecal analyses will typically be required to determine the soluble/insoluble fraction of actinides present as a result of the event to allow a more reliable estimate of radiological dose. The new method for actinides in fecal samples uses accelerated furnace heating, a rapid sodium hydroxide fusion method, a lanthanum fluoride matrix removal step, and a column separation process with stacked TEVA, TRU and DGA resin cartridges. The rapid fusion method provides rugged digestion of any refractory particles present, essential for reliable analysis of actinides in fecal samples. Alpha spectrometry was used to determine the actinide isotopes, but this method can be adapted for assay by inductively-coupled plasma mass spectrometry for actinide isotopes with longer half-lives that have sufficient mass to allow measurement. The method showed high chemical recoveries and effective removal of interferences. The determination of actinides in fecal samples can be performed in less than 12 h in an emergency with excellent quality for emergency samples. The new method, which is much less tedious and time-consuming than other reported methods, can be used for emergency or routine fecal sample analyses. This enables more timely estimates of radiological dose to be performed that utilize soluble/insoluble actinide ratios.

Rapid fusion method for determination of plutonium isotopes in large rice samples

A new rapid fusion method for the determination of plutonium in large rice samples has been developed at the Savannah River National Laboratory (Aiken, SC, USA) that can be used to determine very low levels of plutonium isotopes in rice. The recent accident at Fukushima Nuclear Power Plant in March, 2011 reinforces the need to have rapid, reliable radiochemical analyses for radionuclides in environmental and food samples. Public concern regarding foods, particularly foods such as rice in Japan, highlights the need for analytical techniques that will allow very large sample aliquots of rice to be used for analysis so that very low levels of plutonium isotopes may be detected. The new method to determine plutonium isotopes in large rice samples utilizes a furnace ashing step, a rapid sodium hydroxide fusion method, a lanthanum fluoride matrix removal step, and a column separation process with TEVA Resin™ cartridges. The method can be applied to rice sample aliquots as large as 5 kg. Plutonium isotopes can be determined using alpha spectrometry or inductively-coupled plasma mass spectrometry (ICP-MS). The method showed high chemical recoveries and effective removal of interferences. The rapid fusion technique is a rugged sample digestion method that ensures that any refractory plutonium particles are effectively digested. The MDA for a 5 kg rice sample using alpha spectrometry is 7 × 10−5 mBq g−1. The method can easily be adapted for use by ICP-MS to allow detection of plutonium isotopic ratios.

Lanthanum halide nanoparticle scintillators for nuclear radiation detection

Nanoparticles with sizes <10 nm were fabricated and characterized for their nanocomposite radiation detector properties. This work investigated the properties of several nanostructured radiation scintillators, in order to determine the viability of using scintillators employing nanostructured lanthanum trifluoride. Preliminary results of this investigation are consistent with the idea that these materials have an intrinsic response to nuclear radiation that may be correlated to the energy of the incident radiation.

Investigation on LaF 3 -Impregnated Porous Silicon Heterostructur as Potentionmetric Sensor for Fluoride Ion in Aqueous Medium

Impregnation of pores of porous silicon (PS) by Lanthanum Fluoride (LaF3) using a novel one-step chemical bath technique, and application of the LaF3-impregnated porous silicon (PS) structure (LaF3/PS) as a potentiometric fluoride ion sensor have been investigated in this article. The impregnation of LaF3 inside the pores of porous silicon was achieved using a chemical bath technique developed by this group. The Scanning Electron Microscopy (SEM) and EDX on the cross-section of LaF3/PS/Si structure confirmed the LaF3 film deposition inside the pores of PS. The heterostructure of LaF3/PS/Si was investigated as fluoride ion (F - ) sensor in aqueous medium. The high specific area of PS was taken as the key subject to investigate the high fluoride sensitivity of the LaF3/PS structure in aqueous medium. When experimented with home made fluoride solution having various concentrations the annealed LaF3/PS/Si structure was found to detect the fluoride ion in aqueous solution. Its response was found linear in the fluoride concentration range of 2.28~4.28 pF. As capacitive sensor the overall fluoride sensitivity was found to be over-Nernstian (400 mV/pF). The experimental results indicate that LaF3-impregnated porous silicon structure (LaF3/PS) can be used as a high-sensitive fluoride-ion sensor in aqueous medium.

Measurements of Natural Radioactivity in Some Granite Samples Using Alpha Spectrometric Analysis

Alpha spectrometry using pulse height analysis has been used for the determination of uranium concentrations in different environmental samples. The concentration of 238U was measured by both destructive and non-destructive techniques with a detection limit of less than 1.8 mBq/kg. However, because of the extremely low 234U concentrations in environmental samples, it was necessary to use a destructive technique to separate U from the sample matrices as well as remove interfering elements from the sample solution to determine 238U/234U ratio. In this study, the uranium was separated from the environmental samples using anion exchangers in (Dowex 1 × 8 Cl? form) and purified via co-precipitation with Lanthanum fluorides (LaF3) and the alpha source prepared by electrodeposition. The results obtained were validated using some certified reference samples.

Measurements of Natural Radioactivity in Some Granite Samples Using Alpha Spectrometric Analysis

Alpha spectrometry using pulse height analysis has been used for the determination of uranium concentrations in different environmental samples. The concentration of 238U was measured by both destructive and non-destructive techniques with a detection limit of less than 1.8 mBq/kg. However, because of the extremely low 234U concentrations in environmental samples, it was necessary to use a destructive technique to separate U from the sample matrices as well as remove interfering elements from the sample solution to determine 238U/234U ratio. In this study, the uranium was separated from the environmental samples using anion exchangers in (Dowex 1 × 8 Cl? form) and purified via co-precipitation with Lanthanum fluorides (LaF3) and the alpha source prepared by electrodeposition. The results obtained were validated using some certified reference samples.

Self-organization of particles in the superionic phase of lanthanum trifluoride

When a laser beam (λ = 396.3 nm) propagates through a nonuniformly heated superionic LaF3 crystal in the direction of lattice constant c, alternating bright and dark fringes arise on the screen. The fringes run from the warmer face to the colder one. The number and width of the fringes are found to depend on the temperature gradient in the crystal: the smaller (greater) the temperature difference between the faces, the smaller (greater) the number of moving fringes. It is the author’s opinion that this effect is due to the wave transfer of applied heat and reflects the self-organization and collective displacements of the ions of the “quasi-liquid” sublattice in a nonuniform temperature field. A qualitative model of heat wave transfer in the LaF3 superionic phase is suggested.

氟化镧掺钕纳米激光材料的制备及光学性能

氟化镧掺钕纳米激光材料的制备及光学性能

Synthesis and characterization of rhombohedral- and tetragonal-lanthanum oxyfluoride powders

Rhombohedral- and tetragonal-lanthanum oxyfluoride (LaOF) powders were prepared by thermal decomposition of lanthanum(III) carbonate fluoride (LaFCO3) powders that had been obtained from boiling an aqueous solution containing lanthanum(III) salt, fluoride ion (F−), and urea. The conversion process of LaFCO3 to LaOF was monitored by thermogravimetry, powder X-ray diffraction, and 19F magic-angle spinning nuclear magnetic resonance spectroscopy. The crystal structure (rhombohedral, tetragonal) of LaOF depended on the mole ratio of F− to La3+ ions in the preparation of LaFCO3, and tetragonal-LaOF was completely transformed into rhombohedral-LaOF at 1000°C. The difference in crystal structures was reflected in the intensity of the 5D0→7F0 transition peak in the luminescence spectra of Eu3+-doped LaOF powders.

Thermal conductivity of LaF3-based single crystals and ceramics

The thermal conductivity of lanthanum fluoride based single crystals and ceramics (LaF3, La0.975Nd0.025F3, and La0.95Sr0.05F2.95) has been measured at temperatures from 50 to 693 K by an absolute steady-state axial flow technique. We have not detected any anomalies indicative of “two-level systems.” The heat capacity of LaF3 single crystals has been measured in the temperature range 56–300 K. The results are used to evaluate the c-axis phonon mean free path as a function of temperature for single-crystal LaF3.

Mid-Infrared Grating Couplers for Silicon-on-Sapphire Waveguides

Theoretical and experimental results of mid-infrared (mid-IR) gratings for coupling between transverse-electric (TE)/transverse-magnetic (TM) mode silicon-on-sapphire (SOS) waveguides and zirconium, barium, lanthanum, aluminum, and sodium fluoride (ZBLAN) fibers are presented. The shallow-etched uniform grating, full-etched subwavelength grating, and apodized grating are analyzed theoretically. TE mode shallow-etched apodized gratings with coupling efficiency of 80.6% and TM mode full-etched apodized subwavelength gratings with coupling efficiency of 39.6% are predicted at the wavelength of 2.75 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex> </formula> by finite-difference time-domain (FDTD) simulation. An <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Er}^{3+} \ndash \hbox{Pr}^{3+}$</tex></formula> co-doped ZBLAN fiber laser is set up to be used as a mid-IR light source at 2.75 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> . Coupling efficiencies of 32.6% and 11.6% to TE mode and TM mode SOS waveguides, respectively, were obtained experimentally with uniform grating couplers. The dependence of coupling efficiency on etch depth, grating period, fill factor, and incident angle are also studied.

Optical Characteristic Improvement of Neodymium-Doped Lanthanum Fluoride Thin Films Grown by Pulsed Laser Deposition for Vacuum Ultraviolet Application

Neodymium-doped lanthanum fluoride (Nd3+:LaF3) thin films were successfully grown on MgF2(001) substrates by pulsed laser deposition. Photoluminescence spectra revealed a dominant peak at 173 nm with a decay time of 7.8 ns, which is similar to the results obtained from a bulk Nd3+:LaF3 crystal. Improvements in crystalline quality and vacuum ultraviolet (VUV) luminescence quantum efficiency were achieved by substrate heating, with optimum results being obtained at 400 °C. These results would open up possibilities in the development of a light-emitting device operating in the VUV region.

Optical Characteristic Improvement of Neodymium-Doped Lanthanum Fluoride Thin Films Grown by Pulsed Laser Deposition for Vacuum Ultraviolet Application

Neodymium-doped lanthanum fluoride (Nd3+:LaF3) thin films were successfully grown on MgF2(001) substrates by pulsed laser deposition. Photoluminescence spectra revealed a dominant peak at 173 nm with a decay time of 7.8 ns, which is similar to the results obtained from a bulk Nd3+:LaF3 crystal. Improvements in crystalline quality and vacuum ultraviolet (VUV) luminescence quantum efficiency were achieved by substrate heating, with optimum results being obtained at 400 °C. These results would open up possibilities in the development of a light-emitting device operating in the VUV region.

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films

The electrochemical properties of fluoride-coated lithium cobalt oxide [LiCoO2] thin films were characterized. Aluminum fluoride [AlF3] and lanthanum fluoride [LaF3] coating layers were fabricated on a pristine LiCoO2 thin film by using a spin-coating process. The AlF3- and LaF3-coated films exhibited a higher rate capability, cyclic performance, and stability at high temperature than the pristine film. This indicates that the AlF3 and LaF3 layers effectively protected the surface of the pristine LiCoO2 film from the reactive electrolyte.

Non-stabilized europium-doped lanthanum oxyfluoride and fluoride nanoparticles well dispersed in thin silica films

Well dispersed non-stabilized lanthanum oxyfluoride and fluoride nanoparticles were prepared in situ in thin silica films from rapid thermal decomposition of lanthanum tris-trifluoroacetate under nitrogen atmosphere. The thin silica films were obtained from sol–gel method and spin-coating. The spectroscopic properties of the non-stabilized nanoparticles as well the nanoparticles dispersed into thin silica films were studied in order to apply the system in future photonic applications such as erbium(III)-doped waveguide amplifiers. The non-stabilized nanoparticles were characterized by XRD, FT-IR, Transmission Electron Microscopy, Confocal Raman Spectroscopy and steady-state and time-resolved Luminescence Spectroscopy and these characterizations were used as a starting point to characterize the nanoparticles dispersed into the films. According to the temperature of the thermal treatments, the non-stabilized nanoparticles may present Eu(III)-doped LaOF in tetragonal and rhombohedral phases as well as a mixed phase of Eu(III)-doped LaF3 and LaOF. The tetragonal LaOF phase has C4v La(III) point symmetry and is more symmetric than the rhombohedral LaOF phase, where the La(III) ion has C3v symmetry, consequently tetragonal LaOF presented lower Ω2 values than rhombohedral LaOF. Theoretical calculations of Judd–Ofelt intensity parameters were also performed and were in good agreement with the experimental values. The samples containing the mixed phase of LaF3 and LaOF presented lower values of intensity parameters than pure LaOF phases. The samples containing the mixed phase presented higher values of emission lifetimes and quantum efficiencies. Confocal Raman spectroscopy of these samples complements the luminescence studies and indicates which LaOF phase is present in the mixed phase of LaF3 and LaOF. The rapid thermal decomposition of the precursor tris-trifluoroacetate on thin silica films results in well-dispersed 10 nm nanoparticles. The mixed phase of LaF3 and LaOF phases is also present in thin films. The luminescence of the Eu(III) and Er(III)/Yb(III)-doped LaF3/LaOF nanoparticles containing thin silica films presented broad emission bands suggesting that in the future the systems may be applied as erbium(III)-doped waveguide amplifiers.

Synthesis, micro-structural, and electrical analysis on lanthanum fluoride

Lanthanum fluoride nanorod and nanoparticles have been synthesized by a simple method with and without sonication, respectively. Thermogravimetric/differential thermal analysis confirms the sample formation at low temperature for the sonication-assisted sample than the directly prepared sample. The structure of the prepared lanthanum fluoride nanorods and nanoparticles has been analyzed by X-ray diffraction studies and the micro-structural properties have been studied using transmission electron microscopy. The transmission electron microscopic image reveals a capsule-like shape for the sample prepared under sonication. Ion conduction and conductivity analysis of the prepared nanorods and nanoparticles has been studied using AC impedance spectroscopy, and the ionic conductivity was found to increase by an order for the sample prepared with sonication.

Rapid determination of actinides in emergency food samples

A new rapid method for the determination of actinides in food samples has been developed at the Savannah River Site Environmental Lab (Aiken, SC, USA) that can be used for emergency response or routine food samples. If a radiological dispersive device or improvised nuclear device event occurs, there will be a urgent need for rapid analyzes of many different environmental matrices, as well as food samples, to support dose mitigation and protect general populations from radioactivity that may enter the food chain. The recent accident at Fukushima nuclear power plant in March, 2011 reinforces the need to have rapid analyzes for radionuclides in environmental and food samples. The new method to determine actinides in food samples utilizes a furnace ashing step, a rapid sodium hydroxide fusion method, a lanthanum fluoride matrix removal step, and a column separation process with stacked TEVA, TRU, and DGA resin cartridges. The furnace ashing and rapid fusion steps are performed in relatively inexpensive, reusable zirconium crucibles. Alpha emitters are prepared using rare earth micro precipitation for counting by alpha spectrometry. The method showed high chemical recoveries and effective removal of interferences. The determination of actinides in food samples can be performed in less than 8 h for 10 g samples with excellent quality for emergency samples using short count times. Larger food samples (100 g) may be processed in 24 h or less. The rapid fusion technique is a rugged sample digestion method that ensures that any refractory actinide particles are effectively digested. This method can be used to meet the derived intervention level guidelines recommended by the U.S. Food and Drug Administrations.

Lanthanum trifluoride nanoparticles prepared using ionic liquids

Lanthanum fluorides are important materials for their optical properties especially in the form of thin film or nanoparticles. In this paper we describe preparation of LaF3 nanoparticles by simple one-step synthesis. Ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) was used both as fluorination agent and solvent in the first preparation method and KPF6 (fluorination agent) dissolved in ionic liquid 1-butyl-3-methylimidazolium chloride (bmimCl) in the second synthesis procedure. In both cases liquid La(NO3)3 was used as the source of lanthanum. Reaction was performed at 200°C for 90min. Obtained white powders were washed by distilled water and methanol, dried on air and analyzed by Nanophox (particle size distribution), X-ray diffraction and by SEM and HRTEM. Nanoparticles of pure LaF3 were prepared and their size was estimated from X-ray pattern to be 11.0 and 11.6nm in the first and second case, respectively. Sizes of nanocrystals were conformed by HRTEM. It was observed by SEM that nanoparticles tend to form irregular aggregates and their average size was estimated by Nanophox. Although nanocrystals prepared by both ways are of very similar size, the sizes of their aggregates differ significantly (730nm from bmimPF6 vs. 3600nm from KPF6 in bmimCl).

The Preparation Method of Solid Electrolyte Lanthanum Fluoride Powder

LaF3 powder is prepared by means of three methods . The traditional precipitation of LaC13 with HF action, sol-gel of La (CH3COO) 3 with NH4F action then gel is handled by infrared furnace and microwave method of La (CO3)3 as La source with NH4F action to become LaF3 Ultra-fine powder under the action of microwave. Through the SEM photographs, it can be revealed that the powder particles are different. Precipitation particles diameter is 10 μm; sol-gel method of particle is 1 um and there are a lot of needle-like particles; microwave particles is 100nm.

Surface complexation onto nanosized lanthanum fluoride

The surface chemical modification of LaF3 nanocrystals with 4-(2-pyridylazo)resorcinol and Xylenol orange was investigated. The study of the complexes of these ligands with lanthanum ions in aqueous solution and on the LaF3 surface revealed significant differences in their properties. The surface complexes are characterized by the slower kinetics of the formation and higher stability.