Ion Beam Radiation Effects in Monazite.

International audienceMonazite is a potential matrix for conditioning minor actinides arising from spent fuel reprocessing. The matrix behavior under irradiation must be investigated to ensure long-term containment performance. Monazite compounds were irradiated by gold and helium ions to simulate the consequences of alpha decay. This article describes the effects of such irradiation on the structural and macroscopic properties (density, hardness) of monazites LaPO4 and La0.73Ce0.27PO4. Irradiation by gold ions results in major changes in the material properties. At a damage level of 6.7 dpa, monazite exhibits volume expansion of about 8.1%, a 59% drop in hardness, and structure amorphization, although Raman spectroscopy analysis shows that the phosphate-oxygen bond is unaffected. Conversely, no change in the properties of these compounds was observed after He ion implantation. These results indicate that ballistic effects predominate in the studied dose range

MESURE DE LA DENSITE, DE LA TENSION SUPERFICIELLE ET DE LA VISCOSITE DE L'ALUMINE LIQUIDE EN FONCTION DE LA TEMPERATURE ET DE L'ENVIRONNEMENT PAR LEVITATION AERODYNAMIQUE ASSOCIEE A L'ANALYSE D'IMAGE

ORLEANS-BU Sciences (452342104) / SudocSudocFranceF

Method for Synthesizing Extremeley High Temperature Melting Materials

The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as borides, carbides and transition-metal, lanthanide and actinide oxides, using an Aerodynamic Levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions

X-ray diffraction, 31P NMR and europium photoluminescence properties of the Na2Ba1−xSrxMg(PO4)2 system related to the glaserite type structure

Different samples of a solid solution of glaserite-type structure with the general formula Na2Ba1−xSrxMg(PO4)2(0 ⩽ x ⩽ 1) were synthesized by the Pechini method and characterized by X-ray powder diffraction (XRD), 31P NMR spectroscopy and photoluminescence of europium doped compounds. The XRD patterns show that Na2Ba1−xSrxMg(PO4)2 system adopts the trigonal symmetry with the space group of PView the MathML source3¯m1 for 0 ⩽ x ⩽ 0.55 while from x = 0.6, it crystallizes in the monoclinic symmetry with the space group P21/a. The four resonances observed in the 31P NMR spectra for each composition of the system Na2Ba1−xSrxMg(PO4)2 (0 ⩽ x ⩽ 1) are interpreted on the basis of four configurations of statistical distribution (Ba2+/Sr2+) in the neighboring cationic sites of a PO4 tetrahedron. The photoluminescence of doped samples with divalent and trivalent europium was analyzed according to their compositions

Laser-driven white light generation by mixing blue (BAM), green (GYAG), and red (nitride) phosphors

International audienceIn the present work, a purple laser diode of 405 nm is employed for the excitation of different types of phosphors for thepurpose of building a white light source. Three different types of phosphor materials were synthesized – a blue phosphor(BAM), a green phosphor (GYAG) and a red phosphor based on nitride. These samples were synthesized in the form ofsilicone pellets, having different thicknesses and different concentrations in the silicone matrix. In this study, two differentapproaches were followed. First, the three different samples were stacked together in various combinations to study thecolorimetric parameters of the emitted converted light, particularly the correlated color temperature (CCT) and the colorrendering index (CRI). In the second approach, the three types of phosphors were merged in the same silicone pellet. Pelletswith different thickness and ratio of the three phosphors were prepared, and their CCT and CRI parameters were measuredunder laser excitation. In the first case, a CCT of 2264 K and a CRI of 74 were achieved while with the second approach, anaverage temperature of 4500 K and a CRI of 85 were reached. While the difference between the CRI values for both cases isnot big, the CCT value of the mixed samples is twice as high as the value of the stacked pellets, something attributed tosimultaneous excitation of phosphors in mixed samples while, when stacked, each material is irradiated in a specific order

Thermal analysis of blue laser diode for solid state lighting application

Solid-state light sources based on laser diode are becoming great alternative for LEDs. Improvement of the thermal characteristics of InGaN LD is very important for realizing reliable devices. In this investigation the influence of the temperature of diode on light parameters was studied. White light was obtained by coupling blue light of diode with yellow phosphors: YAG:Ce3+ and GYAG:Ce3+ with nitride. For three values of the temperature of LD’s stem, regulated by Peltier module, CCT, CRI and chromaticity coordinates were measured by spectroradiometer. The importance of emission characteristics of materials was shown. Subsequently, the influence of temperature on laser diode intensity was investigated for 120 hours. This experiment was repeated for different levels of current and temperature. Finally, the steady state of thermal finite element analysis was performed to reveal the distribution of the temperature. The analysis showed the importance of heat sink and also temperature control

YAG and greenYAG+nitride properties for white-light generation using a blue laser diode

The phosphor excitation by blue laser diode and an influence of its irradiation on the material were investigated. Two types of materials were elaborated to perform these experiments—yellow phosphor (YAG) and green phosphor mixed with nitride phosphor (GYAG). These phosphors were packaged into silicone plates, having different thickness and concentration in silicon resin. The results from exciting the phosphor by blue laser present that emission of converted light increases when concentration and thickness increase. Also, the dependency of these two parameters on optical power shows certain behavior. Subsequently, the concentration and thickness were replaced by particle number in sample. It revealed that the dependency of the particle numbers on the optical power can replace the conventional parameters as thickness or concentration. Results show that correlated color temperature finds it dependency on number of particles also. In addition, it turned out, that for each of the material, there might exist an optimal particle number for the maximum luminous power. Finally, the influence of the irradiation of blue laser diode on the materials was investigated. After intensive irradiation for 30 min, we observed that the efficiency of light conversion decreases. It can be caused by damages made by laser on particles. Results show parts of nitride (650 nm) conversion decrease less than yellow or green phosphor. Less affection of irradiation can be explained by nitride being very covalent material, more resistant to modification. Also, we found that there is no fundamental modification of material structure because of no changing in spectrum shape of converted light

Luminescence properties of tungstates and molybdates phosphors: Illustration on ALn(MO₄)₂ compounds (A = alikaline cation, Ln = lanthanides, M = W, Mo)

The photoluminescence characteristics of compounds ALn(MO4)2, with A = Li, Na, K; Ln = Y, La, Gd, Lu, M = Mo, W, are analyzed as a function of their structure. The influences of cation size and electronegativity are discussed in relation with the Struck and Fonger theory, with a view to developing one or more of those compounds as phosphors in relation with the development of white LEDs. It appears that there are various excited states implied in the absorption process, with partially radiative transfer between them. All the radiative mechanisms are strongly related to temperature. Due to their electronegativity, tungstate compounds are the most promising, compared to molybdate ones, especially those in the monoclinic P2/n structure

Correlation between structure and photoluminescence of the europium doped glaserite-type phosphate Na2SrMg(PO4)2

A new phosphate Na2SrMg(PO4)2 has been synthesized and investigated by X-ray diffraction, DTA, 31P NMR spectroscopy and photoluminescence measurements. This compound crystallizes in the space group P21/a of the monoclinic system with the cell parameters: a = 9.158(1) Å, b = 5.267(1) Å, c = 13.498 (1) Å, β = 90.01(1)° and four formula units per cell. Its structure is closely related to that of the mineral glaserite K3Na(SO4)2 and thus it can be described by the general formula XY2M(TO4)2. The X, Y, M and T sites are fully occupied by Sr2+, Na+, Mg2+ and P5+ cations, respectively. The anionic framework is consisted by the stacking along the [001] direction of two kinds of alternating [MgP2O84−]∞ mixed layers parallel to the (a, b) plane and resulting from a corner-sharing between MgO6 octahedra and PO4 tetrahedra. The Sr2+ cations are located within the interlayer space, while those Na+ are found in large cavities bounded to the layers. The DTA analysis showed a congruent melting of this compound at 1374 K. The 31P NMR spectroscopy confirmed the presence of two distinct phosphors sites in the structure. Optical studies were performed on the Na2SrMg(PO4)2 compound doped with Eu3+ and Eu2+. The trivalent europium was used as a local probe, replacing strontium and sodium, what gives complementary and consistent results to the crystallographic analyses. The divalent europium was used to analyze preliminary the potentiality for this compound to be integrated as phosphor in Light Emitting Diode (LED)