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Sample records for baf2 caf2 laf3

  1. Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters

    NASA Technical Reports Server (NTRS)

    Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

    1990-01-01

    An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

  2. Surface tension of ZrF4-BaF2-LaF3 glass

    NASA Technical Reports Server (NTRS)

    Bansal, N. P.; Doremus, R. H.

    1984-01-01

    A solidified pendant drop technique is presently used in the measurement of surface tension of a 62 mol pct ZrF4, 33 mol pct BaF2, 5 mol pct LaF3 heavy metal-fluoride glass, in keeping with a requirement from a comparison experiment planned for microgravity conditions aboard the Space Shuttle. The surface tension at 550 C is 0.174 + or - 0.005 J/sq m.

  3. Hardness of CaF2 and BaF2 solid lubricants at 25 to 670 deg C

    NASA Technical Reports Server (NTRS)

    Deadmore, Daniel L.; Sliney, Harold E.

    1987-01-01

    Plastic deformation is a prominent factor in determining the lubricating value of solid lubricants. Little information is available and its direct measurement is difficult so hardness, which is an indirect measure of this property was determined for fluoride solid lubricant compositions. The Vickers hardness of BaF2 and CaF2 single crystals was measured up to 670 C in a vacuum. The orientation of the BaF2 was near the (013) plane and the CaF2 was about 16 degrees from the degrees from the (1'11) plane. The BaF2 has a hardness of 83 kg/sq mm at the 25 C and 9 at the 600 C. The CaF2 is 170 at 25 C and 13 at 670 C. The decrease in hardness in the temperature range of 25 to 100 C is very rapid and amounts to 40% for both materials. Melts of BaF2 and CaF2 were made in a platinum crucible in ambient air with compositions of 50 to 100 wt% BaF2. The Vickers hardness of these polycrystalline binary compositions at 25 C increased with increasing CaF2 reaching a maximum of 150 kn/sq mm near the eutectic. The polycrystalline CaF2 was 14% softer than that of the single crystal surface and BsF2 was 30% harder than the single crystal surface. It is estimated that the brittle to ductile transition temperature for CaF2 and BaF2 is less than 100 C for the conditions present in the hardness tester.

  4. Defect-induced wetting on BaF 2(111) and CaF 2(111) at ambient conditions

    NASA Astrophysics Data System (ADS)

    Cardellach, M.; Verdaguer, A.; Fraxedas, J.

    2011-12-01

    The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

  5. Vibrational spectra of superionic crystals (BaF2)1 x (LaF3)x F. Kadleca,b,*, P. Simona

    E-print Network

    Ku?el, Petr

    to hopping of F anions, increases by several orders of magnitude with doping. Around the trivalent R3 cations of the activation enthalpy for hops of F anions. The solid solutions (BaF2)1 x(LaF3)x belong to the most studied

  6. Atomized BaF2-CaF7 for Better-Flowing Plasma-Spray Feedstock

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Stanford, Malcolm K.

    2008-01-01

    Atomization of a molten mixture of BaF2 and CaF2 has been found to be superior to crushing of bulk solid BaF2- CaF2 as a means of producing eutectic BaF2-CaF2 powder for use as an ingredient of the powder feedstock of a high-temperature solid lubricant material known as PS304. Developed to reduce friction and wear in turbomachines that incorporate foil air bearings, PS304 is applied to metal substrates by plasma spraying. The constituents of PS304 are: a) An alloy of 80 weight percent Ni and 20 weight percent Cr, b) Cr2O3, c) Ag, and d) The BaF2-CaF2 eutectic, specifically, 62 weight percent BaF2 and 38 weight percent CaF2. The superiority of atomization as a means of producing the eutectic BaF2-CaF2 powder lies in (1) the shapes of the BaF2-CaF2 particles produced and (2) the resulting flow properties of the PS304 feedstock powder: The particles produced through crushing are angular, whereas those produced through atomization are more rounded. PS304 feedstock powder containing the more rounded BaF2-CaF2 particles flows more freely and more predictably, as is preferable for plasma spraying.

  7. SCINTILLATION PROPERTIES OF BaF2:Cd, BaF2, BaF2:Ce, BaF2:Sc, BaF2:Tm CRYSTALS AND CERAMICS; NEW PHOTOSENSORS FOR THE VACUUM ULTRAVIOLET REGION

    E-print Network

    Titov, Anatoly

    SCINTILLATION PROPERTIES OF BaF2:Cd, BaF2, BaF2:Ce, BaF2:Sc, BaF2:Tm CRYSTALS AND CERAMICS; NEW. Introduction Research and development of new scintillation materials is mainly triggered by the growing needs of modern medical imaging, high energy and nuclear physics. Pure BaF2 crystals are widely applied

  8. Pressure-induced photoluminescence in Mn2 -doped BaF2 and SrF2 fluorites

    E-print Network

    Rodríguez, Fernando

    on passing from CaF2 to SrF2 or BaF2 with nonradiative multiphonon relaxation whose thermal activation energy materials, Mn2 green PL is attractive for studying nonradiative processes in isolated impurities since exhibited by the MnF8 6 complex along the fluorite series is noteworthy for investi- gating nonradiative

  9. Effect of local environment on crossluminescence kinetics in SrF2:Ba and CaF2:Ba solid solutions

    NASA Astrophysics Data System (ADS)

    Terekhin, M. A.; Makhov, V. N.; Lebedev, A. I.; Sluchinskaya, I. A.

    2015-10-01

    Spectral and kinetic properties of extrinsic crossluminescence (CL) in SrF2:Ba(1%) and CaF2:Ba(1%) are compared with those of intrinsic CL in BaF2 and are analyzed taking into account EXAFS data obtained at the Ba LIII edge and results of first-principles calculations. The CL decay time was revealed to be longer in SrF2:Ba and CaF2:Ba compared to BaF2. This fact contradicts the expected acceleration of luminescence decay which could result from an increased overlap of wave functions in solid solutions due to shortening of the Ba-F distance obtained in both EXAFS measurements and first-principles calculations. This discrepancy is explained by the effect of migration and subsequent non-radiative decay of the Ba(5p) core holes in BaF2 and by decreasing of the probability of optical transitions between Ba(5p) states and the valence band in SrF2:Ba and CaF2:Ba predicted by first-principles calculations.

  10. Labelling of silica microspheres with fluorescent lanthanide-doped LaF3 nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Lu, Meihua

    2007-07-01

    Fluorescent microspheres have been demonstrated to be useful in a variety of biological applications. Fluorescent silica or polymer microspheres have been produced by incorporation of chromophores into the microspheres, which usually produces microspheres with nonuniform sizes and reduced fluorescence. Here we present a simple and straightforward method to produce silica microspheres with fluorescent lanthanide-doped LaF3 nanocrystals grown on the surface. LaF3 nanocrystals are in situ grown on silica microspheres of different sizes to form a raspberry-like structure. The microspheres exhibit strong fluorescence and the colour could be altered by changing the lanthanide ions doped in LaF3 nanocrystals.

  11. CaF2:Yb laser ceramics

    NASA Astrophysics Data System (ADS)

    Akchurin, M. Sh.; Basiev, T. T.; Demidenko, A. A.; Doroshenko, M. E.; Fedorov, P. P.; Garibin, E. A.; Gusev, P. E.; Kuznetsov, S. V.; Krutov, M. A.; Mironov, I. A.; Osiko, V. V.; Popov, P. A.

    2013-01-01

    CaF2:Yb fluoride laser ceramics, prepared by hot-forming, exhibit the same optical properties as starting single crystals. Slope efficiency of the ?a0.95Yb0.05F2.05 is equal to 35% in the pulsed mode of laser operation. Decrease of ytterbium concentration in CaF2:Yb samples down to 3 mol.% resulted in the essential improvement of ?a0.97Yb0.03F2.03 thermal conductivity from 3.5 to 4.5 W/m K, but slightly decreased (down to 30%) slope efficiency of the samples under both pulsed and CW mode of operation. Alternative hot-pressing synthesis of CaF2:Yb fluoride laser ceramics provided materials with superior mechanical properties (microhardness ? = 3.2 GPa and fracture toughness ?1? = 0.65 ?P? m1/2) in comparison with hot-formed and/or single crystal CaF2:Yb specimens. For the first time, lasing has been observed for the novel aforementioned hot-pressed CaF2:Yb ceramics.

  12. Ice nucleation on BaF2(111)

    NASA Astrophysics Data System (ADS)

    Conrad, Peter; Ewing, George E.; Karlinsey, Robert L.; Sadtchenko, Vlad

    2005-02-01

    The mechanism of heterogeneous ice nucleation on inorganic substrates is not well understood despite work on AgI and other materials over the past 50years. We have selected BaF2 as a model substrate for study since its (111) surface makes a near perfect match with the lattice of the basal face of Ih ice and would appear to be an ideal nucleating agent. Two series of experiments were undertaken. In one, nucleation of thin film water formed from deposition of vapor on BaF2(111) faces was explored with the finding that supercooling to -30°C was required before freezing occurred. In the other series, nucleation of liquid water on submerged BaF2 crystals was studied. Here supercooling to -15°C was needed before ice formed. The reason why BaF2 is such a poor nucleating agent contains clues to realistic mechanisms of heterogeneous nucleation. Our explanation of these results follows the model of Fletcher [J. Chem. Phys. 29, 572 (1958)] who showed that heterogeneous ice nucleating ability depends on how well ice wets a substrate. In this view, a smooth BaF2(111) face is poor at nucleation because ice only partially wets its surface. In an extension of Fletcher's model, our calculations, consistent with the experimental results demonstrate that the pitting of a submerged BaF2 crystal dramatically improves its ice nucleating ability.

  13. Nature of the transient BaF2-related phases in the ``BaF2'' processing of Ba2YCu3O7-x superconductors

    NASA Astrophysics Data System (ADS)

    Wong-Ng, W.; Levin, I.; Cook, L. P.; Feenstra, R.

    2006-03-01

    Transient BaF2-based oxyfluoride phases are thought to play a critical role in the formation of the c-textured Ba2YCu3O7-x layers of coated conductors. In situ high-temperature x-ray diffraction from the precursor films containing pure BaF2 as well as pseudobinary BaF2-Y, BaF2-Cu, and Y-Cu mixtures and heat treated in water vapor under reduced conditions revealed that the transient BaF2-based superstructures, similar to those observed during formation of Ba2Cu3O7-x, develop even from the pure BaF2 precursor. These superstructures results from the dissolution of oxygen in BaF2 leading to formation of the oxyfluoride phase, Ba(F2-2x?x)Ox, with an ordered arrangement of O, F, and F vacancies.

  14. Luminescence Enhancement of CdTe Nanostructures in LaF3:Ce/CdTe Nanocomposites

    SciTech Connect

    Yao, Mingzhen; Zhang, Xing; Ma, Lun; Chen, Wei; Joly, Alan G.; Huang, Jinsong; Wang, Qingwu

    2010-11-15

    Radiation detection demands new scintillators with high quantum efficiency, high energy resolution and short luminescence lifetimes. Nanocomposites consisting of quantum dots and Ce3+ doped nanophosphors may be able to meet these requirements. Here we report the luminescence of LaF3:Ce/CdTe nanocomposites which were synthesized by a wet chemistry method. In LaF3:Ce/CdTe nanocomposites the CdTe quantum dots are converted into nanowires, while in LaF3/CdTe nanocomposites no such conversion is observed. The CdTe luminescence in LaF3:Ce/CdTe nanocomposites is enhanced about 5 times, while in LaF3/CdTe nanocomposites no enhancement was observed. Energy transfer, light-re-absorption and surface passivation are likely the reasons for the luminescence enhancement.

  15. Proton NMR of water colloidal solutions of nanosized crystalline LaF3 and LaF3:Gd3+ particles

    NASA Astrophysics Data System (ADS)

    Alakshin, E. M.; Gizatullin, B. I.; Zakharov, M. Yu.; Klochkov, A. V.; Salikhov, T. M.; Skirda, V. D.; Tagirov, M. S.

    2015-01-01

    A study of the nuclear magnetic relaxation of water protons in a series of colloidal solutions of nanosized lanthanum trifluoride and lanthanum fluoride particles, doped with gadolinium (0.5%). The proton NMR signal was recorded by a "Proton-20 M (Chromatech)" spectrometer. It is established that the rate of longitudinal relaxation depends on the nanoparticle concentration in the water solution, and on their dimension. It is demonstrated that the proton relaxation rate in the LaF3:Gd3+ solution increases with paramagnet concentration in the nanoparticles, and decreases with increasing particle size.

  16. Trigonal LaF3: a novel SRS-active crystal

    NASA Astrophysics Data System (ADS)

    Kaminskii, A. A.; Lux, O.; Hanuza, J.; Rhee, H.; Eichler, H. J.; Zhang, J.; Tang, D.; Shen, D.; Yoneda, H.; Shirakawa, A.

    2014-12-01

    Trigonal fluoride LaF3, widely known as a host crystal for Ln3+-lasants, was found to be an attractive many-phonon Raman material and a subject for the investigation of different ?(3)-nonlinear optical effects. We present the manifestation of photon-phonon interactions related to stimulated Raman scattering (SRS) and Raman-induced four-wave mixing (RFWM) processes, initiated by picosecond ex?itation at room temperature. Sesqui-octave-spanning Stokes and anti-Stokes frequency comb generation as well as many-step cascaded and cross-cascaded up-conversion ?(3)-nonlinear processes have been observed. The recorded spectral lines originated by SRS and RFWM are identified and attributed to the three observed SRS-promoting phonon modes. The lower limit of the steady-state Raman gain coefficient for near-IR first Stokes generation was estimated. Moreover, a brief review of known Ln3+?:?LaF3 laser crystals and SRS-active fluorides is given.

  17. Synthesis and formulation of methotrexate (MTX) conjugated LaF3:Tb(3+)/chitosan nanoparticles for targeted drug delivery applications.

    PubMed

    Mangaiyarkarasi, Rajendiran; Chinnathambi, Shanmugavel; Aruna, Prakasarao; Ganesan, Singaravelu

    2015-02-01

    Chitosan functionalized luminescent rare earth doped terbium nanoparticles (LaF3:Tb(3+)/chi NPs) as a drug carrier for methotrexate (MTX) was designed using a simple chemical precipitation method. The synthesized chitosan functionalized nanoparticles were found to be spherical in shape with an average diameter of 10-12nm. They are water soluble and biocompatible, in which the hydroxyl and amino functional groups on its surface are utilized for the bioconjugation of the anticancer drug, the methotrexate. The nature of MTX binding with LaF3:Tb(3+)/chi nanoparticles were examined using X-ray diffraction, zeta potential analyzer and transmission electron microscopy. The other interactions due to complex formation between MTX and LaF3:Tb(3+)/chi NPs were carried out by UV-Visible, steady and excited state fluorescence spectroscopy. The photo-physical characterization revealed that the adsorption and release of MTX from LaF3:Tb(3+)/chi NPs is faster than gold nanoparticles and also confirms that this may be due to weak interaction i.e. the Vander Waals force of attraction between the carboxyl and amino group of drug and nanoparticles. The maximum percentage yield and entrapment efficiency of 85.91±0.71 and 83.82± 0.14 were achieved at a stochiometric ratio of 4:5 of MTX and LaF3:Tb(3+)/chi nanoparticles respectively. In addition, antitumoral activity study reveals that MTX conjugated LaF3:Tb(3+)/chi nanoparticles show higher cytotoxic effect on MCF-7 breast cancer cell lines than that of free MTX. PMID:25661354

  18. Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln=Eu3+,Ce3+,Tb3+) spherical particles

    NASA Astrophysics Data System (ADS)

    Wang, Zhen-Ling; Chan, H. L. W.; Li, Hiu-Ling; Hao, J. H.

    2008-10-01

    Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to D50?F71 and D50?F72 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.

  19. Gamma irradiation effect on photoluminescence from functionalized LaF3:Ce nanoparticles

    NASA Astrophysics Data System (ADS)

    Srinivasan, T. K.; Panigrahi, B. S.; Arora, A. K.; Venkatraman, B.; Ponraju, D.

    2014-06-01

    Oleic acid coated and uncoated LaF3:Ce nano-phosphor particles were synthesized by a co-precipitation method. Nanoparticles were characterized for their structure, organic coating and optical behavior using an X-ray diffraction, a Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption and Photoluminescence spectroscopy. Sizes of nanoparticles were measured from TEM images and were also estimated using the Scherer formula. UV-vis absorption, Photoluminescent and FTIR measurements were done with nanoparticles before and after gamma irradiation up to a dose of 6.19 kGy. The uncoated nanoparticles exhibit emission only at 305 nm when exited with 250 nm. The oleic acid coated nanoparticles exhibit emissions at 308 and 361 nm when exited with 252 nm. Dependence of photo luminescent intensity on gamma dose was studied and the changes were attributed to radiation induced defect traps and also to the breach or damage in the capping material.

  20. A solvent extraction route for CaF2 hollow spheres.

    PubMed

    Guo, Fuqiang; Zhang, Zhifeng; Li, Hongfei; Meng, Shulan; Li, Deqian

    2010-11-21

    A solvent extraction route is proposed to synthesize CaF(2) hollow spheres, which are formed by reversed micelles in a solvent extraction system templating the self-assembly of CaF(2) nanoparticles. PMID:20877846

  1. Spectroscopy of symmetry broken optical doublets in Pr+3:LaF3

    NASA Astrophysics Data System (ADS)

    Lukac, M.; Hahn, E. L.

    1989-03-01

    A Stark modulated optical pumping spectroscopic technique is applied to study Pr+3 ion pair absorption satellites of a 3H4(?1)-1D2(?1) (?=592.5 nm) transition in Pr+3:LaF3. In addition to ? polarized absorption satellites, bulk crystal symmetry forbidden ? polarized absorption satellites are observed. We attribute these ? polarized absorptions to crystal symmetry breaking lattice distortions in the vicinity of a Pr+3 ion pair. For any Pr+3 ion pair there are two types of transitions from the ground state resulting in a doublet. A ? polarized transition occurs between the mutually coupled Pr+3 ion pair ground state level and the excited symmetric ion pair state. And a ? polarized transition connecting the coupled ion pair ground and the excited anti-symmetric state also occurs. NQR spectroscopy is carried out in order to assign the sattelite doublets to specific Pr+3 ion pairs. The differences between ? and ? transitions provide a measure of the Pr+3 ion pair coupling strength, and confirm that the strongest ion-ion coupling strength is much larger than that expected from the dipole-dipole interaction alone.

  2. LaF3:Ln mesoporous spheres: controllable synthesis, tunable luminescence and application for dual-modal chemo-/photo-thermal therapy

    NASA Astrophysics Data System (ADS)

    Lv, Ruichan; Yang, Guixin; He, Fei; Dai, Yunlu; Gai, Shili; Yang, Piaoping

    2014-11-01

    In this report, uniform LaF3:Ln mesoporous spheres have been synthesized by a facile and mild in situ ion-exchange method using yolk-like La(OH)3:Ln mesoporous spheres as templates, which were prepared through a self-produced bubble-template route. It was found that the structures of the final LaF3:Ln can simply be tuned by adding a polyetherimide (PEI) reagent. LaF3:Ln hollow mesoporous spheres (HMSs) and LaF3:Ln flower-like mesoporous spheres (FMSs) were obtained when assisted by PEI and in the absence of PEI. The up-conversion (UC) luminescence results reveal that the doping of Nd3+ ions in LaF3:Ln can markedly influence the UC emissions of the products. It is interesting that an obvious thermal effect is achieved due to the energy back-transfer from Tm3+ to Nd3+ ions under 980 nm near-infrared (NIR) irradiation. The LaF3:Yb/Er/Tm/Nd HMSs show good biocompatibility and sustained doxorubicin (DOX) release properties. In particular, upon 980 nm NIR irradiation, the photothermal effect arising from the Nd3+ doping induces a faster DOX release from the drug release system. Moreover, UC luminescence images of LaF3:Yb/Er/Tm/Nd HMSs uptaken by MCF-7 cells exhibit apparent green emission under 980 nm NIR irradiation. Such a multifunctional carrier combining UC luminescence and hyperthermia with the chemotherapeutic drugs should be of high potential for the simultaneous anti-cancer therapy and cell imaging.In this report, uniform LaF3:Ln mesoporous spheres have been synthesized by a facile and mild in situ ion-exchange method using yolk-like La(OH)3:Ln mesoporous spheres as templates, which were prepared through a self-produced bubble-template route. It was found that the structures of the final LaF3:Ln can simply be tuned by adding a polyetherimide (PEI) reagent. LaF3:Ln hollow mesoporous spheres (HMSs) and LaF3:Ln flower-like mesoporous spheres (FMSs) were obtained when assisted by PEI and in the absence of PEI. The up-conversion (UC) luminescence results reveal that the doping of Nd3+ ions in LaF3:Ln can markedly influence the UC emissions of the products. It is interesting that an obvious thermal effect is achieved due to the energy back-transfer from Tm3+ to Nd3+ ions under 980 nm near-infrared (NIR) irradiation. The LaF3:Yb/Er/Tm/Nd HMSs show good biocompatibility and sustained doxorubicin (DOX) release properties. In particular, upon 980 nm NIR irradiation, the photothermal effect arising from the Nd3+ doping induces a faster DOX release from the drug release system. Moreover, UC luminescence images of LaF3:Yb/Er/Tm/Nd HMSs uptaken by MCF-7 cells exhibit apparent green emission under 980 nm NIR irradiation. Such a multifunctional carrier combining UC luminescence and hyperthermia with the chemotherapeutic drugs should be of high potential for the simultaneous anti-cancer therapy and cell imaging. Electronic supplementary information (ESI) available: The SAED pattern of flower-like LaF3:Yb,Er spheres. FT-IR spectra of the La(OH)3:Ln precursor, LaF3:Ln HMSs and LaF3:Ln FMSs. UC emission spectra of the La(OH)3:Yb/Er(Ho/Tm) precursor, LaF3:Yb/Er(Ho/Tm) HMSs, LaF3:Yb/Er(Ho/Tm) FMSs under 980 nm NIR excitation. CIE chromaticity diagram of LaF3:10% Yb/0.5% Tm/x%Nd (x = 0, 1, 2) under 980 nm NIR excitation. CIE chromaticity diagram of LaF3:Yb/Er/Tm/Nd under 980 nm NIR excitation. Infrared thermal images of LaF3:Yb/Er, LaF3:Yb/Er/Tm, and LaF3:Yb/Er/Tm/Nd samples before and after irradiation for 6-8 min under 980 nm laser irradiation with the pump power of 0.6 W cm-2. See DOI: 10.1039/c4nr04336g

  3. Colloidal synthesis of BaF2 nanoparticles and their application as fillers in polymer nanocomposites

    SciTech Connect

    Sathyamurthy, Srivatsan; Tuncer, Enis; More, Karren Leslie; Gu, Baohua; Sauers, Isidor; Paranthaman, Mariappan Parans

    2012-01-01

    Nanoparticles of pure and Eu-doped BaF2 have been prepared through sol-gel colloidal synthesis. In addition, BaF2 filled PMMA polymer nanocomposites were fabricated and dielectric properties were measured. The as-synthesized pure and Eu-doped BaF2 nanoparticles were analyzed by both X-ray diffraction and transmission electron microscopy and consisted of crystalline BaF2 particles with an average diameter of 13.6 nm with a standard deviation of about 2.4 nm. The photoluminescence properties of the pure and Eu-doped (2%, 4% and 8%) nanoparticles showed characteristic emission of Eu3+ (5D0 7FJ (J=1-4) transitions). We also measured significantly enhanced dielectric breakdown strength of up to 30% for BaF2 nanocomposites over the unfilled PMMA polymer. This study thus offers some promise of sol-gel synthesis of nanocomposite dielectrics with great potential for use as electrical insulation materials in cryogenic high voltage applications.

  4. Improved photoluminescence and thermal stabilization of glycine functionalized LaF3: Ce nanoparticles useful in bioimaging and biotagging

    NASA Astrophysics Data System (ADS)

    Singh, Amit T.; Khandpekar, M. M.

    2015-05-01

    LaF3:Ce nanocrystals doped with glycine have been synthesized from water soluble chlorides and subsequent irradiation by microwave. The XRD spectra confirms the hexagonal phase structure with cell parameter a = b = 7.173 Å and c = 7.211 Å with space group P 3 cl and particle size of 15 nm. The value is in confirmation with the density functional calculation of structural properties by LDA and GGA potentials predicting merohedral twinned structure of tysonite like compounds. The SEM and TEM images show narrow distribution of nanoparticles with hexagonal and assorted morphology having particle size of 25 nm. The SAED pattern confirms the formation of crystallinity of nanocrystals and traces of different elements in the nanocrystals have been detected by EDAX pattern. The FTIR spectrum shows peaks due to weak organic attachments indicating the capping on the core LaF3:Ce by the functional groups of the organic ligands. The UV spectrum shows the presence of multiple absorption edges corresponding to band gap energies at 5.17 eV, 4.87 eV,4.28 eV,3.40 eV indicating the quantum dot structure of inorganic nanocrystals. The photoluminescence of the nanocrystals has been observed by excitation and emission spectra. The peak at 616 nm shows emission of red fluorescence, indicating its possible applications in bio imaging and biotagging. The TGA/DTA graph shows the stable phases of the nanocrystals synthesized.

  5. Structural, optical and dielectric properties of Ce3+, Pr3+, Nd3+ doped LaF3 hexagonal nanoparticles

    NASA Astrophysics Data System (ADS)

    Gaurkhede, S. G.; Khandpekar, M. M.

    2015-06-01

    Well dispersed, elongated and hexagonal LaF3: Ce3+, Pr3+, Nd3+ nanocrystals have been synthesized by microwave assisted technique. X-ray diffraction (XRD) studies indicates the formation of nanocrystals with unit cell parameters a = b = 7.144 A0, c = 7.281 A0, (c/a = 1.019) and unit cell volume of 321.86 (A0)3 of average crystallite size 21 nm have been traced by from XRD analysis and it is close agreement with transmission electron microscope (TEM) analysis. Ultra-violet (UV) absorption spectrum shows an edge at 250 nm indicating presence of wide transparency window region between 200 nm-800 nm. Fundamental groups have been observed in the Fourier transformation infrared (FTIR) and FT-Raman spectra. The blue luminescent properties of the nanoparticles were investigated by excitation and emission spectra. Room temperature Electrical and dielectric properties were studied for the synthesized nanocrystals the values of conductivity & resistivity is found to be in the order of 10-6 Scm-1 and resistivity 105 ? cm. Low dielectric constant value was observed in the LaF3: Ce3+, Pr3+, and Nd3+ nanocrystals at high frequency indicating its suitability for electro optics applications.

  6. Relaxation of electronic excitations in CaF2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Vistovskyy, V. V.; Zhyshkovych, A. V.; Mitina, N. E.; Zaichenko, A. S.; Gektin, A. V.; Vasil'ev, A. N.; Voloshinovskii, A. S.

    2012-07-01

    The luminescence properties of CaF2 nanoparticles with various sizes (20-140 nm) are studied upon the excitation by VUV and x-ray quanta in order to reveal the influence of ratio of mean free path and thermalization length of charge carriers and nanoparticle size on the self-trapped exciton luminescence. The luminescence intensity for exciting quantum energies corresponding to optical creation of exciton and to the range of electronic excitation multiplication is not so sensitive to nanoparticle size as for quanta with energy of Eg < h? < 2Eg. The dependences of luminescence intensity on nanoparticle size at the excitation by quanta of various energies are discussed in terms of electron-phonon and electron-electron scattering lengths and energy losses on surface defects.

  7. High temperature NMR study of the local structure of molten LaF3-AF (A = Li, Na, K and Rb) mixtures.

    PubMed

    Rollet, Anne-Laure; Godier, Stéphanie; Bessada, Catherine

    2008-06-14

    The local structures of molten lanthanum alkali fluoride binaries have been studied using HT NMR technique. The chemical shifts of (19)F, (23)Na and (139)La in solid and in liquid have been compared for AF (A = alkali) and LaF(3). In pure molten alkali fluorides, the polarisability of anion-cation pairs appears to be a key parameter to depict the observed evolution of (19)F chemical shifts. The influence of the composition has also been studied by measuring the chemical shifts in molten LaF(3)-AF as a function of LaF(3) concentration. A strong influence of the alkali influence is observed. The coordination number of lanthanum is decreased versus AF amount all the more since the alkali atomic number is high. Moreover, the more polarisable the alkali, the less bridging fluorines between the LaF(x) units. PMID:18500398

  8. Enhanced emissions in Tb3+-doped oxyfluoride scintillating glass ceramics containing BaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Huang, Lihui; Jia, Shijie; Li, Yang; Zhao, Shilong; Deng, Degang; Wang, Huanping; Jia, Guohua; Hua, Youjie; Xu, Shiqing

    2015-07-01

    Transparent Tb3+-doped glass ceramics containing BaF2 nanocrystals were prepared by melt-quenching method with subsequent heat treatment. The XRD and EDS results showed the precipitated crystalline phase in the glass matrix was BaF2. Under 376 nm light, Tb3+ doped oxyfluoride glass ceramics containing BaF2 nanocrystals showed more intense green emission than the as-made glass, and the emission intensity increased with increasing heat treatment temperature and time. The lifetimes of 541 nm emission of Tb3+ doped oxyfluoride glass ceramics were longer than that of as-made glass, which are in the range from 3.00 ms to 3.55 ms. Under X-ray excitation, the green emission was enhanced in the glass ceramics compared to the as-made glass. The results indicate Tb3+ doped oxyfluoride glass ceramics containing BaF2 nanocrystals could be a material candidate for X-ray glass scintillator for slow event detection.

  9. Interconnection of defect entropies and enthalpies in BaF$_2$ revisited

    E-print Network

    Skordas, Efthimios S

    2015-01-01

    Here, we investigate the following key prediction of a thermodynamical model that interrelates the defect parameters with the bulk elastic and expansivity data: for various defect processes in a given matrix material, a proportionality exists between defect entropies and enthalpies. The investigation is focused on BaF2 for which ab-initio calculations within density functional theory and the generalized-gradient approximation have been recently made as far as the formation and migration of intrinsic defects is concerned, as well as for the elastic constants. Four defect processes have been studied in BaF$_2$: Anion Frenkel formation, fluorine vacancy migration, fluorine interstitial motion and electrical relaxation associated with a single tetravalent uranium. For these processes, the entropies and enthalpies vary by almost two orders of magnitude and reveal a proportionality between them. We find that this proportionality is solely governed by the bulk elasticity and expansivity data, which conforms to the a...

  10. Spectroscopy of single Pr3+ ion in LaF3 crystal at 1.5 K

    NASA Astrophysics Data System (ADS)

    Nakamura, Ippei; Yoshihiro, Tatsuya; Inagawa, Hironori; Fujiyoshi, Satoru; Matsushita, Michio

    2014-12-01

    Optical read-out and manipulation of the nuclear spin state of single rare-earth ions doped in a crystal enable the large-scale storage and the transport of quantum information. Here, we report the photo-luminescence excitation spectroscopy results of single Pr3+ ions in a bulk crystal of LaF3 at 1.5 K. In a bulk sample, the signal from a single ion at the focus is often hidden under the background signal originating from numerous out-of-focus ions in the entire sample. To combine with a homemade cryogenic confocal microscope, we developed a reflecting objective that works in superfluid helium with a numerical aperture of 0.99, which increases the signal by increasing the solid angle of collection to 1.16? and reduces the background by decreasing the focal volume. The photo-luminescence excitation spectrum of single Pr3+ was measured at a wing of the spectral line of the 3H4 --> 3P0 transition at 627.33 THz (477.89 nm). The spectrum of individual Pr3+ ions appears on top of the background of 60 cps as isolated peaks with intensities of 20-30 cps and full-width at half-maximum widths of approximately 3 MHz at an excitation intensity of 80 W cm-2.

  11. Optical thermometry based on luminescence behavior of Dy3+-doped transparent LaF3 glass ceramics

    NASA Astrophysics Data System (ADS)

    Bu, Y. Y.; Cheng, S. J.; Wang, X. F.; Yan, X. H.

    2015-11-01

    Dy3+-doped transparent LaF3 glass ceramics were fabricated, and its structures of resulting glass ceramics are studied by the X-ray diffraction and transmission electron microscopy. Optical temperature sensing of the resulting glass ceramics in the temperature range from 298 to 523 K is studied based on the down-conversion luminescence of Dy3+ ion. By using fluorescence intensity ratio method, the 4I15/2 and 4F9/2 of Dy3+ ions are verified as thermally coupled levels. A minimum S R = 1.16 × 10-4 K-1 is obtained at T = 294 K. By doping Eu3+ ion, the overall emission color of Eu3+-Dy3+ co-doped transparent glass ceramics can be tuned from white to yellow with the temperature increase through energy transfer between Eu3+ and Dy3+. Additionally, the thermal stability of the Dy3+ single-doped transparent glass ceramics becomes higher after doping Eu3+ ion.

  12. Spectroscopy of single Pr3+ ion in LaF3 crystal at 1.5 K

    PubMed Central

    Nakamura, Ippei; Yoshihiro, Tatsuya; Inagawa, Hironori; Fujiyoshi, Satoru; Matsushita, Michio

    2014-01-01

    Optical read-out and manipulation of the nuclear spin state of single rare-earth ions doped in a crystal enable the large-scale storage and the transport of quantum information. Here, we report the photo-luminescence excitation spectroscopy results of single Pr3+ ions in a bulk crystal of LaF3 at 1.5?K. In a bulk sample, the signal from a single ion at the focus is often hidden under the background signal originating from numerous out-of-focus ions in the entire sample. To combine with a homemade cryogenic confocal microscope, we developed a reflecting objective that works in superfluid helium with a numerical aperture of 0.99, which increases the signal by increasing the solid angle of collection to 1.16? and reduces the background by decreasing the focal volume. The photo-luminescence excitation spectrum of single Pr3+ was measured at a wing of the spectral line of the 3H4 ? 3P0 transition at 627.33?THz (477.89?nm). The spectrum of individual Pr3+ ions appears on top of the background of 60?cps as isolated peaks with intensities of 20–30?cps and full-width at half-maximum widths of approximately 3?MHz at an excitation intensity of 80?W cm?2. PMID:25482137

  13. Monodispersed Silica Nanospheres Encapsulating Fe3O4 and LaF3:Eu3+ Nanoparticles for MRI Contrast Agent and Luminescent Imaging

    NASA Astrophysics Data System (ADS)

    Tian, Yang; Yu, Binbin; Yang, Hong-Yu; Liao, Ji

    2013-02-01

    Bifunctional nanospheres of silica encapsulating Fe3O4 and LaF3:Eu nanoparticles were synthesized in a reverse microemulsion solution. The nanospheres were perfectly monodispersed with a small diameter of 20 nm. The composition of the bifunctional nanospheres was confirmed by powder X-ray diffraction. Their magnetic and luminescent properties were measured at room temperature. The relaxation efficiency and T2-weighted images showed the high-performance for the product as a resonance imaging contrast agent. In addition, a qualitative cell uptake in human cervical cancer HeLa cells demonstrated that the SFLE nanospheres were efficiently up-taken into cytosol. Taken together, these findings suggest that the SiO2/Fe3O4-LaF3:Eu3+ nanospheres are good luminescence probes for bio-imaging.

  14. Microwave-assisted solvothermal synthesis and upconversion luminescence of CaF2:Yb3+/Er3+ nanocrystals.

    PubMed

    Zhao, Jing; Zhu, Ying-Jie; Wu, Jin; Chen, Feng

    2015-02-15

    Water-dispersible CaF2 and Yb(3+)/Er(3+) codoped CaF2 (CaF2:Yb(3+)/Er(3+)) nanocrystals with different sizes and different Yb(3+) and Er(3+) dopant concentrations were synthesized using ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate as a fluorine source by the rapid microwave-assisted solvothermal method. It was found that the morphology, size and crystallinity of CaF2:Yb(3+)/Er(3+) nanocrystals could be adjusted by using adenosine 5'-triphosphate disodium salt (ATP). Yb(3+) and Er(3+) ions were doped into CaF2 nanocrystals to enable upconversion luminescence emission, and the as-prepared CaF2:Yb(3+)/Er(3+) samples exhibited upconversion luminescence upon excitation at 980 nm. Confocal laser scanning microscopy images showed that the CaF2:Yb(3+)/Er(3+) nanocrystals could be used for efficient labeling of human gastric carcinoma cells. Moreover, in vitro cytotoxicity experiments indicated that the as-prepared CaF2:Yb(3+)/Er(3+) nanocrystals had essentially little cytotoxicity. These results indicate that the as-prepared CaF2:Yb(3+)/Er(3+) nanocrystals are promising for the application as a luminescent label material in biological imaging. PMID:25460687

  15. Characterization of electron-beam induced damage structures in natural fluorite, CaF2, by analytical electron microscopy

    NASA Technical Reports Server (NTRS)

    Blake, D. F.; Freund, Friedemann; Allard, L. F.; Echer, C. J.

    1988-01-01

    This paper describes the damage structure induced in natural CaF2 by the electron beam when using TEM. The observed 10-20 nm periodic features with coherent fringe patterns and the pronounced loss of fluorine found after the TEM exposure of 100-line-oriented and 111-oriented sections of CaF2 provides support for the mechanism of damage by decomposition of CaF2 into 2F and Ca, with the Ca precipitates maintaining a close topotaxial relationship with the parent CaF2.

  16. Modification of luminescence spectra of CaF2 : Eu(2.).

    PubMed

    Singh, Vartika S; Joshi, C P; Moharil, S V; Muthal, P L; Dhopte, S M

    2015-11-01

    CaF2 :Eu(2+) is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid-state lighting (SSL), and down-conversion for solar cells. However, emission of CaF2 :Eu(2+) is around 424?nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue - 450?nm, green - 540?nm or red - 610?nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF2 :Eu(2+) to meet these requirements using co-dopants. A Ca0.49 Sr0.50 Eu0.01 F2 phosphor showing better colour coordinates and having an emission maximum around 440?nm was discovered during these studies. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25736486

  17. Dependency of built-in potential of LaF3/porous-silicon heterostructure prepared by chemical bath deposition technique on the concentration of LaCl3 and annealing temperature

    NASA Astrophysics Data System (ADS)

    Rahman, Md. Hafijur; Ismail, Abu Bakar Md.

    2015-11-01

    Effect of LaCl3 concentration and annealing temperature on the built-in potential of LaF3/PS heterojunction has been investigated in this report. LaF3 layers have been deposited by a novel chemical bath deposition (CBD) technique. With this simple technique LaF3 produced as LaCl3 are made to react with hydrofluoric acid on the porous silicon (PS) substrate. This enables direct deposition of LaF3 on the pore walls of the PS leading to a successful passivation of PS. The compositions of the deposited LaF3 were confirmed by energy dispersive of X-ray analysis. The built-in potential decreases with LaCl3 concentration and increases with annealing temperature. Therefore, by changing the LaCl3 concentration and annealing temperature quality of the LaF3 layer on PS can be optimized. From the experimental results it can be concluded that lanthanum fluorides can be deposited on the PS surface by the CBD technique, which provides the required passivation for PS. This passivation can enable the PS to be considered as an important material for photonics.

  18. Influence of LaCl3 concentration and annealing temperature on the diode ideality factor of LaF3/porous-silicon structure prepared by chemical bath deposition technique

    NASA Astrophysics Data System (ADS)

    Hafijur Rahman, Md.; Ismail, Abu Bakar Md.

    2015-08-01

    Effect of LaCl3 concentration and annealing temperature on the diode ideality factor of LaF3/PS heterojunction has been investigated in this report. LaF3 layers have been deposited by a novel chemical bath deposition (CBD) technique. With this simple technique LaF3 produced as LaCl3 are made to react with hydrofluoric acid on the porous silicon (PS) substrate. This enables direct deposition of LaF3 on the pore walls of the PS leading to a successful passivation of PS. The compositions of the deposited LaF3 were confirmed by energy dispersive of X-ray analysis. The diode ideality factor increases with LaCl3 concentration and decreases with annealing temperature. Therefore, by changing the LaCl3 concentration and annealing temperature quality of the LaF3 layer on PS can be optimized. It was also seen that the Ag/LaF3/PS/Si/Ag structure showed the formation of Schottky diode with a threshold voltage of about 5.5 V. From the experimental results it can be concluded that lanthanum fluorides can be deposited into the pores as well as on the top of PS by the CBD technique, which provides the required passivation for PS. This passivation can enable the PS to be considered as an important material for photonics.

  19. Swift heavy-ions induced sputtering in BaF2 thin films

    NASA Astrophysics Data System (ADS)

    Pandey, Ratnesh K.; Kumar, Manvendra; Singh, Udai B.; Khan, Saif A.; Avasthi, D. K.; Pandey, Avinash C.

    2013-11-01

    In our present experiment a series of barium fluoride thin films of different thicknesses have been deposited by electron beam evaporation technique at room temperature on silicon substrates. The effect of film thickness on the electronic sputter yield of polycrystalline BaF2 thin films has been reported in the present work. Power law for sputtered species collected on catcher grids has also been reported for film of lowest thickness. Sputtering has been performed by 100 MeV Au+28 ions. Atomic force microscopy (AFM) has been done to check the surface morphology of pristine samples. Glancing angle X-ray diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was done to determine the areal concentration of Ba and F atoms in the films. A reduction in the sputter yield of BaF2 films with the increase in film thickness has been observed from RBS results. The thickness dependence sputtering is explained on the basis of thermal spike and the energy confinement of the ions in the smaller grains. Also transmission electron microscopy (TEM) of the catchers shows a size distribution of sputtered species with values of power law exponent 1/2 and 3/2 for two fluences 5 × 1011 and 1 × 1012 ions/cm2, respectively.

  20. Microwave characterisation of CaF2 at cryogenic temperatures using a dielectric resonator technique

    E-print Network

    Jacob, Mohan V; Ledenyov, Dimitri O; Krupka, Jerzy; 10.1016/S0955-2219(03)00183-3

    2012-01-01

    Properties of calcium fluoride (CaF2) have been well researched at UV, visible and IR range of frequencies, but not at ultra high frequencies. In this work we report the loss tangent and the real part of relative permittivity of CaF2, measured in the temperatures range of 15 - 81 K and the frequency of 29.25 GHz. The loss tangent and the real part of relative permittivity were determined by measurements of the resonant frequency and the Qo - factor of a TE011 mode cylindrical copper cavity with superconducting plates containing the sample under test. The measured real part of relative permittivity of CaF2 was found to change from 6.484 to 6.505, and the loss tangent from 3.1x10^(-6) to 22.7x10^(-6), when the temperature was varied from 15 to 81 K. Due to the low losses CaF2 can be useful in construction of high Q-factor microwave circuits and devices, operating at the cryogenic temperatures.

  1. Synthesis and characterization of CaF2:Dy nanophosphor for dosimetric application

    NASA Astrophysics Data System (ADS)

    Bhadane, Mahesh S.; Patil, B. J.; Dahiwale, S. S.; Kulkarni, M. S.; Bhatt, B. C.; Bhoraskar, V. N.; Dhole, S. D.

    2015-06-01

    In this work, nanoparticles (NPs) of dysprosium doped calcium fluoride (CaF2:Dy) 1 mol % has been prepared using simple chemical co-precipitation method and its thermoluminescence (TL) dosimetric properties were studied. The synthesized nanoparticle sample was characterized by X-ray diffraction (XRD) and the particle size of face centered cubic phase NPs was found around 30 nm. The shape, morphology and size were also observed by scanning electron microscopy (SEM). From gamma irradiated CaF2:Dy TL curves, it was observed that the total areas of all the glow peak intensities are dramatically changed with increase in annealing temperature. Further, TL glow curve of the CaF2:Dy at 183 °C annealed at 400 °C, showed very sharp linear response in the dose range from 1 Gy to 750 Gy. This linear response of CaF2:Dy nanophosphor as a function of gamma dose is very useful from radiation dosimetric point of view.

  2. A new one-pot strategy to LaF3:Ce,Tb@SiO2 core-shell nanostructures

    NASA Astrophysics Data System (ADS)

    Liu, Lina; Sun, Ruirui; Zhang, Yongsheng; Qin, Ruifei; Zhang, Dongmei; Tang, Chunjuan; Chen, Linfeng; Liu, Lishuang

    2015-10-01

    LaF3:Ce,Tb@SiO2 core-shell nanostructures were synthesized using a new one-pot reverse microemulsion strategy. One-pot method facilitates the synthetic process of this kind of core-shell nanostructures. The crystalline phase, size, morphology, pore structure and luminescence properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen physisorption isotherm, photoluminescence (PL) excitation and emission spectra. The results revealed that the core-shell nanostructures have an average diameter of about 27 nm and cores of about 3 nm, and that these nanostructures contain micropores with an average pore diameter of 0.43 nm. The characteristic emissions of Tb3+ were observed under the excitation of Ce3+ 4f-5d transition due to the energy transfer from Ce3+ to Tb3+. LaF3:Ce,Tb@SiO2 nanostructures can disperse well in water and the colloid can emit bright green light under ultraviolet (UV) irradiation.

  3. Diode-pumped femtosecond mode-locked Nd, Y-codoped CaF2 laser

    NASA Astrophysics Data System (ADS)

    Zhu, Jiangfeng; Zhang, Lijuan; Gao, Ziye; Wang, Junli; Wang, Zhaohua; Su, Liangbi; Zheng, Lihe; Wang, Jingya; Xu, Jun; Wei, Zhiyi

    2015-03-01

    A passively mode-locked femtosecond laser based on an Nd, Y-codoped CaF2 disordered crystal was demonstrated. The Y3+-codoping in Nd?:?CaF2 markedly suppressed the quenching effect and improved the fluorescence quantum efficiency and emission spectra. With a fiber-coupled laser diode as the pump source, the continuous wave tuning range covering from 1042 to 1076?nm was realized, while the mode-locked operation generated 264?fs pulses with an average output power of 180?mW at a repetition rate of 85?MHz. The experimental results show that the Nd, Y-codoped CaF2 disordered crystal has potential in a new generation diode-pumped high repetition rate chirped pulse amplifier.

  4. Cryogenic Temperature-Dependent Refractive Index Measurements of CaF2 and Infrasil 301

    NASA Technical Reports Server (NTRS)

    Frey, Bradley J.; Leviton, Douglas B.; Madison, TImothy J.

    2007-01-01

    In order to enable high quality lens design using calcium fluoride (CaF2) and Heraeus Infrasil 30 (Infrasil) at cryogenic temperatures, we have measured the absolute refractive index of prisms of these two materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For CaF2, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 25 to 300 K at wavelengths from 0.4 to 5.6 micrometers; for Infrasil we cover temperatures ranging from 35 to 300K and wavelengths from 0.4 to 3.6 micrometers. We investigate the interspecimen variability between measurements of two unrelated samples of CaF2, and we also compare our results for Infrasil to previous measurements fo Corning 7980 fused silica. Finally, we provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures and compare those results to other data found in the literature.

  5. Investigation of rare nuclear decays with BaF$_2$ crystal scintillator contaminated by radium

    E-print Network

    P. Belli; R. Bernabei; F. Cappella; V. Caracciolo; R. Cerulli; F. A. Danevich; A. Di Marco; A. Incicchitti; D. V. Poda; O. G. Polischuk; V. I. Tretyak

    2014-07-22

    The radioactive contamination of a BaF$_2$ scintillation crystal with mass of 1.714 kg was measured over 101 hours in the low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of $^{212}$Po (present in the crystal scintillator due to contamination by radium) was measured as $T_{1/2}(^{212}$Po) = 298.8$\\pm$0.8(stat.)$\\pm$1.4(syst.) ns by analysis of the events' pulse profiles. The $^{222}$Rn nuclide is known as 100% decaying via emission of $\\alpha$ particle with $T_{1/2}$ = 3.82 d; however, its $\\beta$ decay is also energetically allowed with $Q_\\beta = 24\\pm21$ keV. Search for decay chains of events with specific pulse shapes characteristic for $\\alpha$ or for $\\beta/\\gamma$ signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of $^{222}$Rn relatively to $\\beta$ decay as $B_\\beta 8.0$ y). Half-life limits of $^{212}$Pb, $^{222}$Rn and $^{226}$Ra relatively to $2\\beta$ decays are also improved in comparison with the earlier results.

  6. Fabrication of IR-transparent microfluidic devices by anisotropic etching of channels in CaF2.

    PubMed

    Lehmkuhl, Brynson; Noblitt, Scott D; Krummel, Amber T; Henry, Charles S

    2015-10-27

    A simple fabrication method for generating infrared (IR) transparent microfluidic devices using etched CaF2 is demonstrated. To etch microfluidic channels, a poly(dimethylsiloxane) (PDMS) microfluidic device was reversibly sealed on a CaF2 plate and acid was pumped through the channel network to perform anisotropic etching of the underlying CaF2 surface. To complete the CaF2 microfluidic device, another CaF2 plate was sealed over the etched channel using a 700 nm thick layer of PDMS adhesive. The impact of different acids and their concentrations on etching was studied, with HNO3 giving the best results in terms of channel roughness and etch rates. Etch rate was determined at etching times ranging from 4-48 hours and showed a linear correlation with etching time. The IR transparency of the CaF2 device was established using a Fourier Transform IR microscope and showed that the device could be used in the mid-IR region. Finally, utility of the device was demonstrated by following the reaction of N-methylacetamide and D2O, which results in an amide peak shift to 1625 cm(-1) from 1650 cm(-1), using an FTIR microscope. PMID:26450455

  7. 2.7 ?m emission in Er3+:CaF2 nanocrystals embedded oxyfluoride glass ceramics.

    PubMed

    Wu, Guobo; Fan, Shaohua; Zhang, Yuanhao; Chai, Guanqi; Ma, Zhijun; Peng, Mingying; Qiu, Jianrong; Dong, Guoping

    2013-08-15

    Using conventional melt-quenching and subsequent thermal treatment, Er(3+) doped CaF(2) transparent glass ceramic (GC) was prepared. X-ray diffraction and high-resolution transmission electron microscopy confirmed the formation and microstructure of CaF(2) nanocrystals in glass. An energy-dispersive spectrometer was used to investigate the distribution of Er(3+) ions and CaF(2) nanocrystals in glass. It was found that Er(3+) ions prefer to concentrate in the CaF(2) nanocrystals rather than in a glass matrix, and the amount of Er(3+) ions plays a key role in the formation of CaF(2) nanocrystals in a glass matrix with the Er(3+) ions as nucleating agent. An intense 2.7 ?m emission due to Er(3+): I(11/2)4 ? I(13/2)4 was achieved upon excitation at 980 nm with a laser diode, while the 2.7 ?m emission can be neglected in the as-prepared glass counterpart, which confirmed the incorporation of Er(3+) ions into CaF(2) nanocrystals. An obvious enhancement of 2.7 ?m emerged in the GC doped with 3% Er(3+) and heat-treated at 620 °C. PMID:24104651

  8. First principles calculations of structural, electronic and optical properties of BaF2 scintillator crystal at ambient conditions

    NASA Astrophysics Data System (ADS)

    Fooladchang, F.; Majidiyan Sarmazdeh, M.; Benam, M. R.; Arabshahi, H.

    2013-10-01

    In this paper some structural, electronic and optical properties of BaF2 scintillator crystal have been calculated in cubic phase. Calculations were performed in DFT framework using FP-LAPW method and GGA and GGA+U approximations for exchange-correlation potential. In structural calculation part, optimum lattice constant and bulk modulus were calculated and these quantities are in good agreement with experimental and theoretical values. In electronic calculation part, energy band structure has been obtained along high symmetry points in k-space. Electronic and optical results with calculated energy gap by a semi-empirical method show that obtained energy gap of both GGA and GGA+U approximations is in good agreement with experimental values and band gap increases with increasing pressure. Also, in this work some optical properties of BaF2 compound such as dielectric function, energy loss function, optical conductivity and refractive index have been obtained. The peaks of optical conductivity are in good agreement with experimental results from reflectance spectroscopy of BaF2 compound. The obtained refractive index is in very good agreement with experimental values in the wavelength range 0.15-2.3 ?m.

  9. Onset of laser ablation in CaF2 crystal under excimer laser irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Yoshizo; Narazaki, Aiko; Sato, Tadatake; Niino, Hiroyuki; Yabe, Akira

    2002-06-01

    With the widespread application of excimer lasers for micro- processing, optically transparent materials in the UV region have become more important as optical components. The transparent materials currently available commercially are silica glass and fluoride crystals, CaF2 and MgF2. The resistance of these materials against cumulative irradiation of excimer lasers is required from the viewpoint of application, and it is important to clarify the mechanisms of the optical damage on these materials. In this paper, we report the onset of laser ablation, that is, the initiation of optical breakdown and plume formation, in CaF2 crystal under cumulative irradiation of an ArF excimer laser. When the laser fluence is below the ablation threshold, a blue luminescence due to self-trapped exciton is observed from the whole laser-irradiated region. When the fluence ins increased near the threshold, successive irradiation finally cause a bright, localized luminescence due to the initiation of laser ablation. SEM images of the laser-damaged region show two features: (1) a small bump with pits of the order of 0.1 micrometers formed by UV laser absorption and following local heating, (2) small cracks with triangular fragments caused by mechanisms stress under local heating.

  10. Update on the DANCE BaF2 Array with Initial Results for Neutron Capture on ^234, 236U

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Reifarth, R.; Esch, E. I.; Fowler, M. M.; Haight, R. C.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Greife, U.; Alpizar, A.; Hatarik, R.

    2003-10-01

    An update on the Detector for Advanced Neutron Capture Experiments (DANCE) will be presented. A new method, based in hardware, has been developed to synchronize acquisition and readout of the 159 element BaF2 array among 14 DAQ computers operating in parallel. Other improvements affecting energy resolution and treatment of signal pileup will also be discussed. As DANCE can be utilized as a calorimeter to reconstruct the neutron binding energy it provides a unique means to discriminate against spurious background counts. Initial results from measurements of neutron capture on ^234U and ^236U in the resonance region will be presented to illustrate the capabilities of the array.

  11. X-ray excited optical luminescence of CaF2: A candidate for UV water treatment

    NASA Astrophysics Data System (ADS)

    Chen, W.; Ma, L.; Schaeffer, R.; Hoffmeyer, R.; Sham, T.; Belev, G.; Kasap, S.; Sammynaiken, R.

    2015-06-01

    Secondary optical processes are becoming more and more important in health and environmental applications. Ultraviolet produced from secondary emission or scintillation can damage DNA by direct photoexcitation or by the creation of reactive oxygen species. X-ray Excited Optical Luminescence (XEOL) and Time Resolved XEOL (TRXEOL) results for the fast emitter, CaF2:ZnO, that have been treated by heating in air and in vacuum, show that the scintillation from the Self Trapped Exciton (STE) emission of CaF2 at 282 nm is dominated by a slow process (>100 ns). A faster but weaker 10 ns component is also present. The ZnO and CaF2 show independent emission. The ZnO bandgap emission at 390 nm has dominant lifetimes of less than 1 ns.

  12. Room temperature fabrication of dielectric Bragg reflectors composed of a CaF2/ZnS multilayered coating.

    PubMed

    Muallem, Merav; Palatnik, Alex; Nessim, Gilbert D; Tischler, Yaakov R

    2015-01-14

    We describe the design, fabrication, and characterization of mechanically stable, reproducible, and highly reflecting distributed Bragg reflectors (DBR) composed of thermally evaporated thin films of calcium fluoride (CaF2) and zinc sulfide (ZnS). CaF2 and ZnS were chosen as the low and high refractive index components of the multilayer DBR structures, with n = 1.43 and n = 2.38 respectively, because neither material requires substrate heating during the deposition process in order to produce optical quality thin films. DBRs consisting of seven pairs of CaF2 and ZnS layers, were fabricated with thicknesses of 96 and 58 nm, respectively, as characterized by high-resolution scanning electron microscopy (HR-SEM), and exhibited a center wavelength of ?c = 550 nm and peak reflectance exceeding 99%. The layers showed good adhesion to each other and to the glass substrate, resulting in mechanically stable DBR coatings. Complete optical microcavities consisting of two such DBR coatings and a CaF2 spacer layer between them could be fabricated in a single deposition run. Optically, these structures exhibited a resonator quality factor of Q > 160. When a CaF2/ZnS DBR was grown, without heating the substrate during deposition, on top of a thin film containing the fluorescent dye Rhodamine 6G, the fluorescence intensity showed no degradation compared to an uncoated film, in contrast to a MgF2/ZnS DBR coating grown with substrate heating which showed a 92% reduction in signal. The ability to fabricate optical quality CaF2/ZnS DBRs without substrate heating, as introduced here, can therefore enable formation of low-loss high-reflectivity coatings on top of more delicate heat-sensitive materials such as organics and other nanostructured emitters, and hence facilitate the development of nanoemitter-based microcavity device applications. PMID:25510469

  13. Effect of CaF2 Addition on the Silicothermic Reduction of MnO in Ferromanganese Slag

    NASA Astrophysics Data System (ADS)

    Heo, Jung Ho; Chung, Yongsug; Park, Joo Hyun

    2015-04-01

    The effect of temperature and CaF2 (fluorspar) addition on the silicothermic reduction behavior of MnO in the CaO-40 pct MnO-SiO2 (C/S = 1.0) system, which is used to simulate high carbon ferromanganese (HCFeMn) slag, was investigated at 1773 K (1500 °C). The production of SiO2 was stoichiometrically balanced with the consumption of MnO in the slag phase in the CaF2-containing systems based on the reaction "[Si] + 2(MnO) = (SiO2) + 2[Mn]," whereas the SiO2 production was lower than the MnO consumption in the CaO-MnO-SiO2 ternary system, which may have originated from the production of SiO gas in the latter. From the temperature dependence of the mass transfer coefficient of SiO2, the activation energy of the silicothermic reduction process was determined to be about 217.9 kJ/mol, which was very close to the activation energy reported in the literature for mass transfer in the slag phase. The mass transfer coefficient of SiO2 exhibited a maximum value at 5 mass pct CaF2, which originated from an increase in the apparent viscosity of the slag due to the precipitation of solid cuspidine at CaF2 content greater than 5 pct. Consequently, the addition of fluxing additive CaF2 should be carefully determined, because an excess of CaF2 results in the formation of cuspidine during silicothermic reactions.

  14. Melting investigation of the system BaF2 BaO 1/2 Y2O3 CuOx H2O

    NASA Astrophysics Data System (ADS)

    Wong-Ng, W.; Cook, L. P.; Suh, J.; Levin, I.; Feenstra, R.

    2005-04-01

    In order to understand low-temperature melting during the 'BaF2 process', equilibria in the quaternary Ba, Y, Cu//O, F reciprocal system have been investigated using a compositional model which can be represented as a trigonal prism. This prism is comprised of three tetrahedra: BaF2-Y F3-CuF2-CuOx, BaF2-Y F3-\\case {1}{2} {\\mathrm {Y_{2}O_{3}}} -CuOx, and BaF2-BaO-\\case {1}{2} {\\mathrm {Y_{2}O_{3}}} -CuOx. Systematic differential thermal analysis (DTA) studies of compositions spaced along compositional vectors extending from the fluoride end of the prism to the oxide end gave evidence of low-melting liquids (<600 °C) near the fluorine-rich region in the BaF2-Y F3-CuF2-CuOx tetrahedron. In the intermediate BaF2-Y F3-\\case {1}{2}{\\mathrm {Y_{2}O_{3}}} -CuOx tetrahedron, a low-temperature DTA peak (550-570 °C) was also identified; this has been shown to be due to a reversible phase transformation in crystalline YOF. In the oxide-rich BaF2-BaO-\\case {1}{2}{\\mathrm {Y_{2}O_{3}}} -CuOx tetrahedron, where, in the presence of water vapour, the principal defluorination process is generally thought to occur, the lowest melting temperature observed was 815 °C at pO2 = 20 Pa and pH2O = 2.1 kPa. However, published observations on films undergoing the BaF2 process have suggested the presence of an amorphous phase thought to be a liquid at {\\le } 735\\,^{\\circ }{\\mathrm {C}} . Based on our results, the low-melting liquids reported in the literature do not appear to exist as a stable liquid phase in the BaF2-BaO-\\case {1}{2}{\\mathrm {Y_{2}O_{3}}} -CuOx-H2O system under the conditions of our experiments. Rather, the formation of low-melting liquid in Ba-Y-Cu-O-F films at {\\le } 735\\,^{\\circ }{\\mathrm {C}} may require (a) relatively fluorine-rich compositions, (b) metastable melting, (c) formation of hydroxide- or hydroxyfluoride-based liquids, or (d) some combination thereof.

  15. Dynamic dimer formation between superionic fluorines in CaF2

    NASA Astrophysics Data System (ADS)

    Saito, Masashi; Tasaka, Tomofumi; Tsumuraya, Kazuo

    2013-03-01

    Recently we have elucidated the formation of the dynamic dimers in the conductor ?-CuI through the analyses of the correlation peaks of the partial pair-distribution functions and the partial angle distribution functions with the first principles molecular dynamics (MD) method.(J. Phys. Soc. Jpn. 81,055603(2012).) The present study investigate the formation of the dynamic dimers and the migration paths of the dimers in the conductor CaF2 with the MD method. The fluorines form the dynamic 32 f-8 c dimers with the coordinate (x,x,x) x=0.300. These incommensurate dimers allow to decrease the migration barriers of the fluorines.

  16. Formation of dissipative structures at hologram recording in CaF2 crystals with color centers

    NASA Astrophysics Data System (ADS)

    Shcheulin, Aleksandr S.; Angervaks, Aleksandr E.; Veniaminov, Andrey V.; Fedorov, Pavel P.; Kuznetsov, Sergey V.; Ryskin, Aleksandr I.

    2015-05-01

    The structurization of holographic planes in holograms recorded in CaF2 crystal with color centers was found. The structurization is apparent in the formation of spiral bundles, which pierce the holographic planes. It testifies to self-organization of color centers in these planes. This process is believed to be linked with colloidal centers, 2D metal islets in the crystal lattice, whose formation and decay during hologram recording at temperatures of 150-190 °C may be considered as a dynamic phase transition that facilitates the generation of stable spatially inhomogeneous (dissipative) structures in the form of bundles. The bundles arise during hologram recording process and remain frozen on cooling of the crystal after the process is finished.

  17. PHYSICAL REVIEW B 88, 024304 (2013) Accurate calculations of phonon dispersion in CaF2 and CeO2

    E-print Network

    Chen, Long-Qing

    2013-01-01

    PHYSICAL REVIEW B 88, 024304 (2013) Accurate calculations of phonon dispersion in CaF2 and CeO2 Yi July 2013) We report the lattice dynamic properties of CaF2 and CeO2 obtained using a direct method dispersion curves. For CeO2, we adopted the Heyd-Scuseria-Ernzerhof hybrid functional and an elongated

  18. Design of multifunctional alkali ion doped CaF2 upconversion nanoparticles for simultaneous bioimaging and therapy.

    PubMed

    Yin, Wenyan; Tian, Gan; Ren, Wenlu; Yan, Liang; Jin, Shan; Gu, Zhanjun; Zhou, Liangjun; Li, Juan; Zhao, Yuliang

    2014-03-14

    Herein, alkali ion doped CaF2 upconversion nanoparticles (UCNPs) were first reported as a multifunctional theranostic platform for dual-modal imaging and chemotherapy. Interestingly, we found that the alkali ions doping approach could efficiently enhance the upconversion luminescence (UCL) intensity, whereas slightly affect the phase and morphology of the resulting products. In order to further improve the UCL efficacy for bioimaging, a pristine CaF2 shell was grown on the CaF2:Yb, Er core surface to enhance the UCL intensity. After being transferred into hydrophilic UCNPs, these water-soluble UCNPs could be served as contrast agents for in vitro/in vivo UCL imaging and X-ray computed tomography (CT) imaging. Furthermore, the as-prepared UCNPs could also be employed as nano-carriers for drug delivery. Doxorubicin (DOX) can be easily loaded onto the UCNPs and the DOX-loaded UCNPs exhibit a good cell killing ability. Therefore, the multifunctional core-shell CaF2 UCNPs with UCL/CT imaging and drug carrier properties may find extensive applications in simultaneous imaging diagnosis and therapy. PMID:24442070

  19. Ultrafast time and frequency domain vibrational dynamics of the CaF2/H2O interface

    NASA Astrophysics Data System (ADS)

    Eftekhari-Bafrooei, Ali; Nihonyanagi, Satoshi; Borguet, Eric

    The structure of water at the CaF2/KOH interface was studied by vibrational sum-frequency-generation (SFG) spectroscopy and ultrafast SFG-Free Induction Decay, suggesting the presence of weakly hydrogen bonded OH at high pH.

  20. Method for producing large, stable concentrations of Sc2+ in optically clear CaF2 crystals

    E-print Network

    Mirov, Sergey B.

    cm23 without degradation of optical quality. We have converted as much as 5% of the scandium dopant to the divalent state. The concentration of divalent scandium is stable during room temperature storage for periods of at least one year. Divalent scandium (Sc21 ) in crystals such as CaF2 has recently generated

  1. FACTORS AFFECTING THE USE OF CAF2:MN THERMOLUMINESCENT DOSIMETERS FOR LOW-LEVEL ENVIRONMENTAL RADIATION MONITORING

    EPA Science Inventory

    An investigation was made of factors affecting the use of commercially-produced CaF2:Mn thermoluminescent dosimeters for low level environmental radiation monitoring. Calibration factors and self-dosing rates were quantified for 150 thermoluminescent dosimeters. Laboratory studie...

  2. Relaxation and interaction of electronic excitations induced by intense ultra short light pulses in BaF2 scintillator

    NASA Astrophysics Data System (ADS)

    Kirm, M.; Nagirnyi, V.; Vielhauer, S.; Feldbach, E.

    2011-06-01

    Excitation density effects have a pronounced influence on relaxation processes in solids. They come into play in scintillating and dosimetric materials exposed to ionizing radiation or in laser materials operating in intense ultraviolet light fields. The scientific understanding of the underlying process is poor, mainly because most of the studies of light emitting materials under short wavelength excitation have been performed at weak and moderate excitation intensities due to limited availability of powerful light sources. Disembodied data on excitation density effects have been reported for wide-gap dielectrics studied by luminescence spectroscopy, by using such excitation sources as powerful ion beams,1,2pulsed electron beams,2,3 and wide-band hard X-ray synchrotron radiation.4 It is obvious that such non-selective excitation is a good tool for revealing density-related phenomena in these materials in general, but for investigating specific features of relaxation processes in insulators, light sources with well defined parameters are necessary. Since the shortwavelength free electron laser (FEL) technology has been devised by an international consortium at HASYLAB of DESY, resulting in the development of TESLA Test facility (TTF)5 and later in the construction of a dedicated FEL source FLASH in Hamburg,6 more advanced studies became possible. The range of interests towards this light source covers the fields from material science and various other branches of physics to structural biology. The pioneering luminescence study revealed excitation density effects in the decay of Ce3+ 5d-4f luminescence in Y3Al5O12 crystals and luminescence of BaF2 crystals in UV-visible range.7 These results motivated systematic investigations of excitation density effects in wide gap crystals using FEL8,9 and high-harmonic-generated VUV radiation,10 and, at lower energies, femtosecond laser pulses in the UV.11,12 The main goal of the present work is to analyze the same phenomenon in wide-band gap BaF2 crystals, where luminescence centres of different origin (self-trapped excitons and cross-luminescence) are present. Using models developed for explaining the non-linear behaviour of luminescence and exciton-exciton interaction effects causing scintillator non-proportionalities,10,13 simulations of luminescence decay curves are performed. Possible quenching effects in the cross-luminescence decay of BaF2 under XUV excitation have been analyzed by Terekhin et al.14

  3. Thin water films grown at ambient conditions on BaF2(111) studied by scanning polarization force microscopy

    NASA Astrophysics Data System (ADS)

    Verdaguer, A.; Cardellach, M.; Fraxedas, J.

    2008-11-01

    The interaction of water with freshly cleaved BaF2(111) surfaces has been studied using scanning force microscopy operated in different modes at room temperature and under controlled humidity. The Kelvin probe microscopy (KPM) mode has been used to study the evolution of the surface potential differences (SPDs). In the 20%-50% relative humidity (RH) range, adsorbed water forms two-dimensional solidlike bilayers (islands). The SPD between water islands and the bare substrate surface exhibits a sign crossover from negative (˜-30 mV) at low RHs to positive (˜+50 mV) at higher RHs, evidencing a cooperative and irreversible flipping of the preferential orientation of water dipoles, from pointing toward the surface evolving into the opposite direction. The KPM results suggest that the classical hexagonal (Ih) bilayer configuration is not the most favorable structure.

  4. Growth of GdBa2Cu3Oy Films Prepared by BaF2 Process Without Water Vapor

    NASA Astrophysics Data System (ADS)

    Kita, R.; Nakamura, T.; Ichinose, A.; Miura, O.; Matsumoto, K.; Yoshida, Y.; Mukaida, M.; Horii, S.

    We have investigated the influences of the heating rate and film thickness on the growth of GdBa2Cu3Oy (GBCO) thin films prepared by the BaF2 ex-situ process without water vapor. Critical current density (Jc) and surface morphology of the GBCO films were improved by increasing the heating rate during growth from 30 to 50°C/min. The GBCO films prepared by the heating rate of 50°C/min had the maximum Jc of 2.1 MA/cm2. The Jc value of the GBCO films was about 2 MA/cm2 up to 200 nm, and decreased to 0.92 MA/cm2 at 400 nm.

  5. Test of the statistical model in Mo96 with the BaF2? calorimeter DANCE array

    NASA Astrophysics Data System (ADS)

    Sheets, S. A.; Agvaanluvsan, U.; Becker, J. A.; Be?vá?, F.; Bredeweg, T. A.; Haight, R. C.; Jandel, M.; Krti?ka, M.; Mitchell, G. E.; O'Donnell, J. M.; Parker, W.; Reifarth, R.; Rundberg, R. S.; Sharapov, E. I.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2009-02-01

    The ?-ray cascades following the Mo95(n,?)Mo96 reaction were studied with the ? calorimeter DANCE (Detector for Advanced Neutron Capture Experiments) consisting of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center. The ?-ray energy spectra for different multiplicities were measured for s- and p-wave resonances below 2 keV. The shapes of these spectra were found to be in very good agreement with simulations using the DICEBOX statistical model code. The relevant model parameters used for the level density and photon strength functions were identical with those that provided the best fit of the data from a recent measurement of the thermal Mo95(n,?)Mo96 reaction with the two-step-cascade method. The reported results strongly suggest that the extreme statistical model works very well in the mass region near A=100.

  6. Fabrication and spectroscopic broadening properties for 1.5 microm amplification of Er(3+)-doped BaF2 nanoparticles.

    PubMed

    Lian, Hongzhou; Liu, Jie; Ye, Zeren; Shi, Chunshan

    2008-03-01

    We show the potential application of Er(3+)-doped BaF2 nanoparticles prepared from microemulsion technology for 1.5 microm amplification in telecommunication. Nanoparticles with different sizes of about 8, 10, and 20.5 nm were prepared. The XRD patterns showed the excursion of diffraction peaks. When the particle size is smaller or the diffraction angle is larger, this kind of excursion will be more serious. The emission bands of Er3+ at 1.54 microm for the three particle sizes at were as follows: 8 nm particles--145 nm, 10 nm particles--124 nm, and 20.5 nm particles--82 nm (full width at half maximum, FWHM), or 173, 153, 97 nm (deltalambda(eff)), respectively. In all the three cases, the emission spectra were flat from 1.53 to 1.56 microm. PMID:18468158

  7. Spectroscopic properties of Pr3+ and Er3+ ions in lead-free borate glasses modified by BaF2

    NASA Astrophysics Data System (ADS)

    Pisarska, Joanna; Pisarski, Wojciech A.; Dorosz, Dominik; Dorosz, Jan

    2015-09-01

    Lead-free oxyfluoride borate glasses singly doped with Pr3+ and Er3+ were prepared and next investigated using absorption and luminescence spectroscopy. In the studied glass system, barium oxide was substituted by BaF2. Two luminescence bands of Pr3+ located at visible spectral region are observed, which correspond to 3P0-3H4 (blue) and 1D2-3H4 (reddish orange) transitions, respectively. The luminescence bands due to 1D2-3H4 transition of Pr3+ are shifted to shorter wavelengths, when BaO was substituted by BaF2. Near-infrared luminescence spectra of Er3+ ions in lead-free borate glasses modified by BaF2 correspond to 4I13/2-4I15/2 transition. Their spectral linewidths increase with increasing BaF2 concentration. The changes in measured lifetimes of rare earth ions are well correlated with the bonding parameters calculated from the optical absorption spectra.

  8. Growth of ultra-violet grade CaF 2 crystals and their application for excimer laser optics

    NASA Astrophysics Data System (ADS)

    Mouchovski, J. T.; Haltakov, I. V.; Lyutskanov, V. L.

    1996-04-01

    A crystal growth method for growing UV grade CaF 2 crystals from fluorspar has being developed using purified Bulgarian fluorspar mixed with 2% PbF 2. Excimer laser damage characteristics of the grown crystals were performed in a specially designed laboratory system into a high pressure camera. It was found that the fluorine mixture does not change, neither on the outer surface of the crystals nor in the bulk even after 3500 h of contact; no color centers were observed on the windows of the XeCl laser and that there are no remarkable differences between the surface and the bulk damage thresholds. Thus, the grown crystals of CaF 2 are suitable for manufacturing windows for excimer lasers and for other optical elements used in UV and vacuum UV spectra regions.

  9. Structural plasticity of calmodulin on the surface of CaF2 nanoparticles preserves its biological function

    NASA Astrophysics Data System (ADS)

    Astegno, Alessandra; Maresi, Elena; Marino, Valerio; Dominici, Paola; Pedroni, Marco; Piccinelli, Fabio; Dell'Orco, Daniele

    2014-11-01

    Nanoparticles are increasingly used in biomedical applications and are especially attractive as biocompatible and biodegradable protein delivery systems. Herein, the interaction between biocompatible 25 nm CaF2 nanoparticles and the ubiquitous calcium sensor calmodulin has been investigated in order to assess the potential of these particles to serve as suitable surface protein carriers. Calmodulin is a multifunctional messenger protein that activates a wide variety of signaling pathways in eukaryotic cells by changing its conformation in a calcium-dependent manner. Isothermal titration calorimetry and circular dichroism studies have shown that the interaction between calmodulin and CaF2 nanoparticles occurs with physiologically relevant affinity and that the binding process is fully reversible, occurring without significant alterations in protein secondary and tertiary structures. Experiments performed with a mutant form of calmodulin having an impaired Ca2+-binding ability in the C-terminal lobe suggest that the EF-hand Ca2+-binding motifs are directly involved in the binding of calmodulin to the CaF2 matrix. The residual capability of nanoparticle-bound calmodulin to function as a calcium sensor protein, binding to and altering the activity of a target protein, was successfully probed by biochemical assays. Even if efficiently carried by CaF2 nanoparticles, calmodulin may dissociate, thus retaining the ability to bind the peptide encompassing the putative C-terminal calmodulin-binding domain of glutamate decarboxylase and activate the enzyme. We conclude that the high flexibility and structural plasticity of calmodulin are responsible for the preservation of its function when bound in high amounts to a nanoparticle surface.Nanoparticles are increasingly used in biomedical applications and are especially attractive as biocompatible and biodegradable protein delivery systems. Herein, the interaction between biocompatible 25 nm CaF2 nanoparticles and the ubiquitous calcium sensor calmodulin has been investigated in order to assess the potential of these particles to serve as suitable surface protein carriers. Calmodulin is a multifunctional messenger protein that activates a wide variety of signaling pathways in eukaryotic cells by changing its conformation in a calcium-dependent manner. Isothermal titration calorimetry and circular dichroism studies have shown that the interaction between calmodulin and CaF2 nanoparticles occurs with physiologically relevant affinity and that the binding process is fully reversible, occurring without significant alterations in protein secondary and tertiary structures. Experiments performed with a mutant form of calmodulin having an impaired Ca2+-binding ability in the C-terminal lobe suggest that the EF-hand Ca2+-binding motifs are directly involved in the binding of calmodulin to the CaF2 matrix. The residual capability of nanoparticle-bound calmodulin to function as a calcium sensor protein, binding to and altering the activity of a target protein, was successfully probed by biochemical assays. Even if efficiently carried by CaF2 nanoparticles, calmodulin may dissociate, thus retaining the ability to bind the peptide encompassing the putative C-terminal calmodulin-binding domain of glutamate decarboxylase and activate the enzyme. We conclude that the high flexibility and structural plasticity of calmodulin are responsible for the preservation of its function when bound in high amounts to a nanoparticle surface. Electronic supplementary information (ESI) available: Supplementary methods and figures. See DOI: 10.1039/c4nr04368e

  10. Responsivity enhancement of mid-infrared PbSe detectors using CaF2 nano-structured antireflective coatings

    NASA Astrophysics Data System (ADS)

    Weng, Binbin; Qiu, Jijun; Yuan, Zijian; Larson, Preston R.; Strout, Gregory W.; Shi, Zhisheng

    2014-01-01

    The CaF2 nano-structures grown by thermal vapor deposition are presented. Significant responsivity improvement (>200%) of mid-infrared PbSe detectors incorporating a 200 nm nano-structured CaF2 coating was observed. The detector provides a detectivity of 4.2 × 1010 cm . Hz1/2/W at 3.8 ?m, which outperforms all the reported un-cooled PbSe detectors. Structural investigations show that the coating is constructed by tapered-shape nanostructures, which creates a gradient refractive-index profile. Analogy to moth-eye antireflective mechanism, the gradient refractive-index nanostructures play the major roles for this antireflection effect. Some other possible mechanisms that help enhance the device performance are also discussed in the work.

  11. Generation of Solid-Source H2O Plasma and Its Application to Dry Etching of CaF2

    NASA Astrophysics Data System (ADS)

    Matsutani, Akihiro; Ohtsuki, Hideo; Koyama, Fumio

    2008-06-01

    We demonstrate the discharge of H2O plasma generated by solid-source H2O placed in a process chamber. Also, we investigated the dry etching process of CaF2 using solid-source H2O (ice) plasma. The average roughness of the etched surface was about 1 nm for an etching depth of in 2 µm which satisfies the requirements for optical device fabrication. We believe that the proposed CaF2 etching process is suitable for the fabrication of optical devices such as gratings or Fresnel lenses. In addition, we think that the H2O plasma including OH radicals obtained by this proposed method may be useful for sterilization and as a new UV light source.

  12. White light generation in Dy(3+)-doped oxyfluoride glass and transparent glass-ceramics containing CaF2 nanocrystals.

    PubMed

    Babu, P; Jang, Kyoung Hyuk; Rao, Ch Srinivasa; Shi, Liang; Jayasankar, C K; Lavín, Víctor; Seo, Hyo Jin

    2011-01-31

    The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram. PMID:21368998

  13. Hydrothermal synthesis and up-conversion luminescence of Ho3+/Yb3+ co-doped CaF2

    NASA Astrophysics Data System (ADS)

    Yang, Zheng; Guo, Chong-Feng; Chen, Ye-Qing; Li, Lin; Li, Ting; Jeong, Jung-Hyun

    2014-06-01

    CaF2:Ho3+/Yb3+ nano-particles with intense green up-conversion (UC) luminescence are successfully synthesized via a facile hydrothermal approach by using NH4F as the fluoride source and Na2EDTA as a chelating reagent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and UC emission spectra are used to characterize the structures, shapes, and luminescent properties of the samples. The effects from fluoride sources and chelating reagents on the formations of CaF2 nano-particles are investigated, and the formation process is also deduced. Under the excitation of a 980-nm laser diode, the samples each show a green up-conversion emission centered at 540 nm corresponding to the 5S2/5F4?5I8 transitions of Ho3+. Moreover, the UC mechanisms of Ho3+/Yb3+ co-doped CaF2 nano-particles are also discussed.

  14. Photothermal Conversion of Color Centers in {CaF}2 Crystals: A Process Underlying the Use of Crystals as a Holographic Medium

    NASA Astrophysics Data System (ADS)

    Shcheulin, A. S.; Angervaks, A. E.; Ryskin, A. I.

    2015-05-01

    Photothermal effects in a holographic medium of calcium fluoride crystals with color centers ({CaF}2) are discussed. It is shown that photochromism of this crystal makes it possible to record volume holograms within its volume and to change their physical properties by photothermal treatments. The diffusion-drift mechanism of a hologram recording in {CaF}2 includes the conversion of centers and their redistribution over the crystal bulk. Depending on the readout wavelength, it is possible to read out amplitude, amplitude phase, or phase holograms. The opportunity to record thick holograms in {CaF}2 and their high resistance with respect to non-coherent illumination at an elevated temperature allows forming narrow-band angular and spectral holographic filters in {CaF}2.

  15. Helium atom scattering study of the interaction of water with the BaF2(111) surface

    NASA Astrophysics Data System (ADS)

    Vogt, Jochen

    2007-06-01

    The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (1×1) translational symmetry already after an exposure of 3L (1L =10-6Torrs) at temperatures below 150K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 46±2kJmol-1, corresponding to a desorption temperature of 165K. The desorption of multilayers was observed at 150K, consistent with a binding energy of 42±2kJmol-1. Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (?3 ×?3 )R30° lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200K, consistent with an unexpectedly strong bonding of the molecules to the substrate.

  16. LAMBDA: Large Area Modular BaF2 Detector Array for the measurement of high energy gamma rays

    E-print Network

    S. Mukhopadhyay; Srijit Bhattacharya; Deepak Pandit; A. Ray; Surajit Pal; K. Banerjee; S. Kundu; T. K. Rana; S. Bhattacharya; C. Bhattacharya; A. De; S. R. Banerjee

    2007-10-11

    A large BaF2 detector array along with its dedicated CAMAC electronics and VME based data acquisition system has been designed, constructed and installed successfully at VECC, Kolkata for studying high energy gamma rays (E>8 MeV). The array consists of 162 detector elements. The detectors were fabricated from bare barium fluoride crystals (each measuring 35 cm in length and having cross-sectional area of 3.5 cm X 3.5 cm X 35.0 cm). The basic properties of the detectors (energy resolution, time resolution, efficiency, uniformity, fast to slow ratio etc.) were studied exhaustively. Complete GEANT3 monte carlo simulations were performed to optimize the detector design and also to generate the response function. The detector system has been used successfully to measure high energy photons from 113Sb, formed by bombarding 145 and 160 MeV 20Ne beams on a 93Nb target. The measured experimental spectra are in good agreement with those from a modified version of the statistical model code CASCADE. In this paper, we present the complete description of this detector array along with its in-beam performance.

  17. Spectroscopic properties and mechanism of Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Hu, Yue-Bo; Qiu, Jian-Bei; Zhou, Da-Cheng; Song, Zhi-Guo; Yang, Zheng-Wen; Wang, Rong-Fei; Jiao, Qing; Zhou, Da-Li

    2014-02-01

    Transparent Tm3+/Er3+/Yb3+ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode (LD), compared with the glass before heat treatment, the Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark-split peaks; X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm3+, Er3+ and (or) Yb3+ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm3+, Er3+ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed.

  18. Enhanced susceptibility of CaF 2(1 1 1) to adsorption due to ion irradiation

    NASA Astrophysics Data System (ADS)

    Akcöltekin, S.; Roll, T.; Akcöltekin, E.; Klusmann, M.; Lebius, H.; Schleberger, M.

    2009-02-01

    We have investigated morphological changes of freshly cleaved CaF2(1 1 1) single crystal surfaces before and after ion irradiation. We show that with or without irradiation the surface undergoes serious changes within minutes after the cleavage if the samples are exposed to ambient conditions. This is most likely due to the adsorption of water and could be avoided only if working under clean ultra-high-vacuum conditions. Ion-induced modifications on this surface seem to act as centers for an increased rate of adsorption so that any quantitative numbers obtained by atomic force microscopy in such experiments have to be treated with caution.

  19. Simultaneous measurement of (n, ?) and (n, fission) cross sections with the DANCE 4? BaF 2 array

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Fowler, M. M.; Becker, J. A.; Bond, E. M.; Chadwick, M. B.; Clement, R. R. C.; Esch, E.-I.; Ethvignot, T.; Granier, T.; Jandel, M.; Macri, R. A.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2007-08-01

    We have recently begun a program of high precision measurements of the key production and destruction reactions of important radiochemical diagnostic isotopes, including several isotopes of uranium, plutonium and americium. The detector for advanced neutron capture experiments (DANCE), a 4? BaF2 array located at the Los Alamos Neutron Science Center, will be used to measure the neutron capture cross sections for most of the isotopes of interest. However, neutron capture measurements on many of the actinides are complicated by the presence of prompt ?-rays arising from low energy neutron-induced fission, which competes with neutron capture to varying degrees. Previous measurements of 235U using the DANCE array have shown that we can partially resolve capture from fission events based on total ?-ray calorimetry (i.e. total ?-ray energy versus ?-ray multiplicity). The addition of a dedicated fission-tagging detector to the DANCE array has greatly improved our ability to separate these two competing processes. In addition to higher quality neutron capture data, the addition of a fission-tagging detector offers a means to determine the capture-to-fission ratio (??/?f) in a single measurement, which should reduce the effect of systematic uncertainties. We are currently using a dual parallel-plate avalanche counter (PPAC) with the target material electro-deposited directly on the center cathode foil. This design provides a high efficiency for detecting fission fragments and allows loading of pre-assembled target/detector assemblies into the neutron beam line at DANCE. Results from tests of the fission-tag detector, as well as preliminary results from measurements on 235U and 252Cf that utilized the fission-tag detector will be presented.

  20. Glass structure and NIR emission of Er3+ at 1.5 ?m in oxyfluoride BaF2-Al2O3-B2O3 glasses

    NASA Astrophysics Data System (ADS)

    Shinozaki, Kenji; Pisarski, Wojciech; Affatigato, Mario; Honma, Tsuyoshi; Komatsu, Takayuki

    2015-12-01

    The glass structure, photoluminescence properties of Eu3+, Judd-Ofelt analysis, and near infrared emissions of Er3+ at 1.5 ?m in the oxyfluoride glasses and glass-ceramics of 1Eu2O3- or 1Er2O3-doped 50BaF2-xAl2O3-(50 - x)B2O3 (x = 0-25 mol%) were investigated. It was clarified on the ground of Raman scattering spectroscopy and F1s and O1s XPS measurements that the glass with no Al2O3 (1Er2O3-50BaF2-50B2O3) is composed of BO3, BO2F and BO3F units with F-Ba bonds. The glasses with 25Al2O3 (1Er2O3-50BaF2-25Al2O3-25B2O3) is mainly composed of BO3- and Al(O,F)x units. Existence of non-bridging oxygen was not detected by O1s-XPS spectra. It was proposed that these structures are largely affected on crystallization behavior, e.g., the glass with no Al2O3 forms BaF2 and ?-BaB2O4 due to Ba-F bonds and the glass with 25Al2O3 forms BaAlBO3F2 because the glass structure composed of BO3 and Al(O,F) units is similar to the BaAlBO3F2 crystal structure. Judd-Ofelt parameters of Er3+ and Eu3+ in the glasses showed almost the same values in ?4 and ?6 for each glass, on the other hand ?2 decreased with addition of Al2O3. The emission spectra of Er3+ at 1.5 ?m in the glasses and glass-ceramics with BaAlBO3F2 crystals showed broad peaks. It is proposed that oxyfluoride glasses and glass-ceramics based on the BaF2-Al2O3-B2O3 system have a high potential for optical device applications such as broadband optical amplifiers.

  1. Modification of mechanical properties of e-gun evaporated MgF2 and CaF2 thin films under ion beam bombardment

    NASA Astrophysics Data System (ADS)

    Scaglione, S.; Flori, D.; Emiliani, G.

    1989-12-01

    The effect of ion beam assistance on mechanical properties (hardness and adhesion) of MgF2 and CaF2 thin films has been investigated. These films have been deposited by e-gun evaporation and bombarded during growth with an ion beam produced by a Kaufman source. The Knoop hardness has been calculated after having performed on the samples some indentation by an ultra-microindenter and measured the impression size by an eyepiece mounted on an optical microscope. The film adhesion has been measured by the scratch test technique. To investigate the influence of the ion source parameters on the mechanical properties, different ion beam energies (200-800 eV) have been used. Bombarded samples are harder (610 and 750 kg/mm2 for CaF2 and MgF2 samples, respectively) than unbombarded samples (380 and 300 kg/mm2 for CaF2 and MgF2, respectively). Critical loads (load where the delamination of the coating begins) of 12 and 3 N for bombarded MgF2 and CaF2 respectively and 4 and 1 N for unbombarded MgF2 and CaF2 samples have been found.

  2. Effects of CaF2 Coating on the Microstructures and Mechanical Properties of Tungsten Inert Gas Welded AZ31 Magnesium Alloy Joints

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Wang, Linzhi; Peng, Dong; Wang, Dan

    2012-11-01

    The effects of CaF2 coating on the macromorphologies of the welded seams were studied by morphological analysis. Microstructures and mechanical properties of butt joints welded with different amounts of CaF2 coatings were investigated using optical microscopy and tensile tests. The welding defects formed in the welded seams and the fracture surfaces were analyzed by scanning electron microscopy. An increase in the amount of CaF2 coating deteriorated the appearances of the welded seams but it improved the weld penetration depth and the depth/width ( D/ W) ratio of the tungsten inert gas (TIG) welded joints. The ?-Mg grains and Mg17(Al,Zn)12 intermetallic compound (IMC) were coarser in the case of a higher amount of CaF2 coating. The increase in the amount of CaF2 coating reduced the porosities and total length of solidification cracks in the fusion zone (FZ). The ultimate tensile strength (UTS) value and elongation increased at first and then decreased sharply.

  3. Kinetics of Isothermal Melt Crystallization in CaO-SiO2-CaF2-Based Mold Fluxes

    NASA Astrophysics Data System (ADS)

    Seo, Myung-Duk; Shi, Cheng-Bin; Baek, Ji-Yeon; Cho, Jung-Wook; Kim, Seon-Hyo

    2015-10-01

    A kinetic study for isothermal melt crystallization of CaO-SiO2-CaF2-based mold fluxes with different basicity of 0.94 and 1.34 has been carried out systematically by DSC measurements. The kinetic parameters were determined by Johnson-Mehl-Avrami equation. The average Avrami exponent of cuspidine (3CaO·2SiO2·CaF2) crystallization for mold flux of lower basicity (0.94) is calculated to be 3.1, implying that the crystallization mode is instantaneous nucleation followed by 3-dimensional growth. For the mold flux of higher basicity (1.34), the average Avrami exponent of cuspidine equals to 3.4, strongly suggesting that the growth is still 3 dimensional but the nucleation should be continuous. It was found that the effective crystallization rate constant for both mold fluxes increases as the crystallization temperature decreases, showing that the crystallization rate could be governed by nucleation rate. The negative effective activation energy indicates an anti-Arrhenius behavior for crystallization of the mold fluxes studied. Therefore, it is concluded that the melt crystallization for the commercial mold fluxes will be determined by thermodynamics of nucleation which is relevant to degree of undercooling. The morphology of cuspidine crystals observed by SEM agreeds well with the isothermal crystallization kinetics results.

  4. Nonlinear luminescence response of CaF2:Eu and YAlO3:Ce to single-ion excitation

    SciTech Connect

    Liu, Peng; Zhang, Yanwen; Xiao, Haiyan; Xiang, Xia; Wang, Xuelin; Weber, William J

    2014-01-01

    Pulse-height of CaF2:Eu and YAlO3:Ce scintillators to single H+, He+ and O3+ ions are measured over a continuous energy range using a time-of-flight (TOF) - scintillator - photoelectric multiplier tube (PMT) apparatus. A nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering energy partitioning process. The results show that, in a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) produced by H+, He+ and O3+ ions irradiation, respectively, have significantly different impacts on the response characteristics of these two benchmark scintillators. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main origin of the nonlinear response of scintillators to irradiation.

  5. Standard Practice for Application of CaF2(Mn) Thermoluminescence Dosimeters in Mixed Neutron-Photon Environments

    E-print Network

    American Society for Testing and Materials. Philadelphia

    2006-01-01

    1.1 This practice describes a procedure for measuring gamma-ray absorbed dose in CaF2(Mn) thermoluminescence dosimeters (TLDs) exposed to mixed neutron-photon environments during irradiation of materials and devices. The practice has broad application, but is primarily intended for use in the radiation-hardness testing of electronics. The practice is applicable to the measurement of absorbed dose from gamma radiation present in fields used for neutron testing. 1.2 This practice describes a procedure for correcting for the neutron response of a CaF2(Mn) TLD. The neutron response may be subtracted from the total response to give the gamma-ray response. In fields with a large neutron contribution to the total response, this procedure may result in large uncertainties. 1.3 More precise experimental techniques may be applied if the uncertainty derived from this practice is larger than the user can accept. These techniques are not discussed here. The references in Section 8 describe some of these techniques. 1.4...

  6. Exploring the retention properties of CaF2 nanoparticles as possible additives for dental care application with tapping-mode atomic force microscope in liquid

    PubMed Central

    Köser, Joachim; Hess, Sylvia; Gnecco, Enrico; Meyer, Ernst

    2014-01-01

    Summary Amplitude-modulation atomic force microscopy (AM-AFM) is used to determine the retention properties of CaF2 nanoparticles adsorbed on mica and on tooth enamel in liquid. From the phase-lag of the forced cantilever oscillation the local energy dissipation at the detachment point of the nanoparticle was determined. This enabled us to compare different as-synthesized CaF2 nanoparticles that vary in shape, size and surface structure. CaF2 nanoparticles are candidates for additives in dental care products as they could serve as fluorine-releasing containers preventing caries during a cariogenic acid attack on the teeth. We show that the adherence of the nanoparticles is increased on the enamel substrate compared to mica, independently of the substrate roughness, morphology and size of the particles. PMID:24455460

  7. Exploring the retention properties of CaF2 nanoparticles as possible additives for dental care application with tapping-mode atomic force microscope in liquid.

    PubMed

    Wasem, Matthias; Köser, Joachim; Hess, Sylvia; Gnecco, Enrico; Meyer, Ernst

    2014-01-13

    Amplitude-modulation atomic force microscopy (AM-AFM) is used to determine the retention properties of CaF2 nanoparticles adsorbed on mica and on tooth enamel in liquid. From the phase-lag of the forced cantilever oscillation the local energy dissipation at the detachment point of the nanoparticle was determined. This enabled us to compare different as-synthesized CaF2 nanoparticles that vary in shape, size and surface structure. CaF2 nanoparticles are candidates for additives in dental care products as they could serve as fluorine-releasing containers preventing caries during a cariogenic acid attack on the teeth. We show that the adherence of the nanoparticles is increased on the enamel substrate compared to mica, independently of the substrate roughness, morphology and size of the particles. PMID:24455460

  8. The Detector for Advanced Neutron Capture Experiments: A 4{pi} BaF2 Detector for Neutron Capture Measurements at LANSCE

    SciTech Connect

    Ullmann, J.L.; Esch, E.-I.; Haight, R.C.; Hunt, L.; O'Donnell, J.M.; Reifarth, R.; Agvaanluvsan, U.; Alpizar, A.; Hatarik, R.; Bond, E.M.; Bredeweg, T.A.; Kronenberg, A.; Rundberg, R.S.; Vieira, D.J.; Wilhelmy, J.B.; Folden, C.M.; Hoffman, D.C.; Greife, U.; Schwantes, J.M.; Strottman, D.D.

    2005-05-24

    The Detector for Advanced Neutron Capture Experiments (DANCE) is a 162-element 4{pi} BaF2 array designed to make neutron capture cross-section measurements on rare or radioactive targets with masses as little as one milligram. Accurate capture cross sections are needed in many research areas, including stellar nucleosynthesis, advanced nuclear fuel cycles, waste transmutation, and other applied programs. These cross sections are difficult to calculate accurately and must be measured. The design and initial performance results of DANCE is discussed.

  9. Self-organization of color centers in holograms recorded in additively colored CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Shcheulin, Aleksandr S.; Angervaks, Aleksandr E.; Veniaminov, Andrey V.; Zakharov, Viktor V.; Fedorov, Pavel P.; Ryskin, Aleksandr I.

    2015-09-01

    The structurization of holographic planes in holograms recorded in CaF2 crystal with color centers was found. It is apparent in the formation of spiral bundles, which pierce the holographic planes. It testifies to the self-organization process of color centers in these planes. This process is supposed to be linked with colloidal centers, 2D metal islets in the crystal lattice, whose formation and decay on hologram recording at temperatures of 150-190 °C may be considered as a dynamic phase transition that facilitates the generation of stable spatially inhomogeneous (dissipative) structures in the form of bundles. They arise on hologram recording and are frozen on cooling of the crystal after the recording process is finished.

  10. Stroboscopic Picosecond Pulse Radiolysis Using Near-Ultraviolet-Enhanced Femtosecond Continuum Generated by CaF2

    NASA Astrophysics Data System (ADS)

    Saeki, Akinori; Kozawa, Takahiro; Okamoto, Kazumasa; Tagawa, Seiichi

    2007-01-01

    For investigations of ultrafast reactions induced by radiation in the short-wavelength region, a near-ultraviolet-enhanced continuum ranging from ca. 390 to 600 nm was generated by focusing the second-harmonic generation (400 nm) of a femtosecond Ti:sapphire laser into a CaF2 plate and applied to stroboscopic picosecond pulse radiolysis. By utilizing a double-pulse detection scheme, the fluctuation between the signal and reference pulses was improved to 2-12% of the standard deviation. The capability of the system in the wavelength region from 400 to 900 nm is demonstrated by measuring transient photoabsorption spectra in water and in tetrahydrofuran solution of biphenyl, where these spectra are attributed to hydrated electrons and the overlap between biphenyl radical anions and the solvated electrons of tetrahydrofuran, respectively.

  11. The colouration of CaF2 crystals by keV and GeV ions

    NASA Astrophysics Data System (ADS)

    Davidson, A. T.; Kozakiewicz, A. G.; Comins, J. D.; Derry, T. E.; Schwartz, K.; Trautmann, C.

    CaF2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 nm. This includes the vacuum UV region. For 100 keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10(17) ions cm(2) ) but no colour centres (F, F-2 etc). For GeV ions (U, Ni) we observe prominent absorption bands in the visible region at fluences of 10(12) ions cm(-2) attributed to extrinsic calcium colloids. New optical features are discussed including an absorption band near 185 nm in the VUV and bands at 604 nm and 672 nm in the visible region.

  12. Directionally solidified Eu doped CaF2/Li3AlF6 eutectic scintillator for neutron detection

    NASA Astrophysics Data System (ADS)

    Kamada, Kei; Hishinuma, Kousuke; Kurosawa, Shunsuke; Shoji, Yasuhiro; Pejchal, Jan; Ohashi, Yuji; Yokota, Yuui; Yoshikawa, Akira

    2015-12-01

    Eu doped CaF2/Li3AlF6 eutectics were grown by ?-PD method. The directionally solidified eutectic with well-aligned 600 nm diameter Eu:CaF2 scintillator fibers surrounded with Li3AlF6 was prepared. The grown eutectics showed an emission peak at 422 nm ascribed to Eu2+ 4f-5d transition from Eu:CaF2 scintillation fiber. Li concentration in the Eu:CaF2-Li3AlF6 eutectic is around 0.038 mol/cm3,which is two times higher than that of LiCaAlF6 single crystal (0.016 mol/cm3). The light yield of Eu:CaF2-Li3AlF6 eutectic was around 7000 ph/neutron. The decay time was about 550 ns (89%) and 1450 ns (11%).

  13. Transient liquid assisted nucleation mechanism of YBa2Cu3O7-? in coated conductor films derived by BaF2 process

    NASA Astrophysics Data System (ADS)

    Gu, Zhao-Hui; Yang, Wen-Tao; Bai, Chuan-Yi; Guo, Yan-Qun; Lu, Yu-Ming; Liu, Zhi-Yong; Lu, Qi; Shu, Gang-Qiang; Cai, Chuan-Bing

    2015-09-01

    It is significant for low-cost preparation of YBa2Cu3O7-? (YBCO) coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the present work, a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal-organic deposition (MOD) or the physical vapor deposition BaF2 process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result. Project supported by the Science and Technology Commission of Shanghai Municipality, China (Grant Nos. 13111102300 and 11dz1100302), the National Natural Science Foundation of China (Grant Nos. 11174193 and 51202141), the National Basic Research Program of China (Grant Nos. 2011CBA00105), and the Science and Technology Commission of Shanghai Municipality, China (Grant No. 14DZ2260700).

  14. Erase-mode recording characteristics of photochromic CaF2, SrTiO3, and CaTiO3 crystals.

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

    Erase-mode optical recording characteristics of photochromic crystal wafers of CaF2:La,Na; CaF2:Ce,Na; SrTiO3:Ni,Mo,Al; and CaTiO3:Ni,Mo have been measured. An argon laser operating at 5145 A was used for both optical recording and optical readout. Sensitometric curves of optical-density change versus logarithm of exposure are shown for a number of erase-beam intensities between 0.2 mW/sq cm and 2 W/sq cm. In this range, time-intensity reciprocity holds for the CaF2 materials but fails for the titanates, particularly at low intensities. The dependences of sensitivity, gamma, and maximum transmission contrast ratio on wafer thickness and material are discussed. Wafers of SrTiO3, CaTiO3, and CaF2 exhibiting approximately equal maximum contrast ratios have relative sensitivities approximately in the ratio 5:2:1, respectively, at an erase intensity of 1 W/sq cm.

  15. Two-dimensional wetting: The role of atomic steps on the nucleation of thin water films on BaF2(111) at ambient conditions

    NASA Astrophysics Data System (ADS)

    Cardellach, M.; Verdaguer, A.; Santiso, J.; Fraxedas, J.

    2010-06-01

    The interaction of water with freshly cleaved BaF2(111) surfaces at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes. The images strongly suggest a high surface diffusion of water molecules on the surface indicated by the accumulation of water at step edges forming two-dimensional bilayered structures. Steps running along the ?1¯10? crystallographic directions show a high degree of hydrophilicity, as evidenced by small step-film contact angles, while steps running along other directions exhibiting a higher degree of kinks surprisingly behave in a quite opposite way. Our results prove that morphological defects such as steps can be crucial in improving two-dimensional monolayer wetting and stabilization of multilayer grown on surfaces that show good lattice mismatch with hexagonal ice.

  16. Structure of Na2O·MO·SiO2·CaF2 (M=Mg, Ca) oxyfluoride glasses

    NASA Astrophysics Data System (ADS)

    Cheng, Jin-shu; Deng, Wei; Wang, Mi-tang

    2012-07-01

    (9-x)CaO·xMgO·15Na2O·60SiO2·16CaF2(x=0, 2, 4, 6, and 9) oxyfluoride glasses were prepared. Utilizing the Raman scattering technique together with 29Si and 19F MAS NMR, the effect of alkaline metal oxides on the Q species of glass was characterized. Raman results show that as magnesia is added at the expense of calcium oxide, the disproportional reaction Q3?Q4+Q2 (Qn is a SiO4 tetrahedron with n bridging oxygens) prompted due to the high ionic field strength of magnesia, magnesium oxide entered into the silicate network as tetrahedral MgO4, and removed other modifying ions for charge compensation. This reaction was confirmed by 29Si MAS NMR. 19F MAS NMR results show that fluorine exists in the form of mixed calcium sodium fluoride species in all glasses and no Si-F bonds were formed. As CaO is gradually replaced by MgO (x=6, 9), a proportion of the magnesium ions combines with fluorine to form the MgF+ species. Meanwhile, some part of Na+ ions complex F- in the form of F-Na(6).

  17. Energy deposition by heavy ions: additivity of kinetic and potential energy contributions in hillock formation on CaF2.

    PubMed

    Wang, Y Y; Grygiel, C; Dufour, C; Sun, J R; Wang, Z G; Zhao, Y T; Xiao, G Q; Cheng, R; Zhou, X M; Ren, J R; Liu, S D; Lei, Y; Sun, Y B; Ritter, R; Gruber, E; Cassimi, A; Monnet, I; Bouffard, S; Aumayr, F; Toulemonde, M

    2014-01-01

    Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5 MeV) highly charged ions (Xe(22+) to Xe(30+)) as well as swift (kinetic energies between 12 and 58 MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. PMID:25034006

  18. Optimization of single crystals of solid electrolytes with tysonite-type structure (LaF3) for conductivity at 293 K: 2. Nonstoichiometric phases R 1- y M y F3- y ( R = La-Lu, Y; M = Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Sorokin, N. I.; Sobolev, B. P.; Krivandina, E. A.; Zhmurova, Z. I.

    2015-01-01

    Single crystals of fluorine-conducting solid electrolytes R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y ( R = La-Lu, Y) with a tysonite-type structure (LaF3) have been optimized for room-temperature conductivity ?293 K. The optimization is based on high-temperature measurements of ?( T) in two-component nonstoichiometric phases R 1 - y M y F3 - y ( M = Sr, Ba) as a function of the MF2 content. Optimization for thermal stability is based on studying the phase diagrams of MF2- RF3 systems ( M = Sr, Ba) and the behavior of nonstoichiometric crystals upon heating when measuring temperature dependences ?( T). Single crystals of many studied R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y phases have ?293 K values large enough to use these materials in solid-state electrochemical devices (chemical sensors, fluorine-ion batteries, accumulators, etc.) operating at room temperature.

  19. Radiation Damage Effects in Far Ultraviolet Filters and Substrates

    NASA Technical Reports Server (NTRS)

    Keffer, Charles E.; Torr, Marsha R.; Zukic, Muamer; Spann, James F.; Torr, Douglas G.; Kim, Jongmin

    1993-01-01

    New advances in VUV thin film filter technology have been made using filter designs with multilayers of materials such as Al2O3, BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2. Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 X 9 R(sub E) orbit will expose the instrument to approximately 275 krads of radiation. In view of the fact that no previous studies have been made on potential radiation damage of these materials in the thin film format, we report on such an assessment here. Transmittances and reflectances of BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2 thin films on MgF2 substrates, Al2O3 thin films on fused silica substrates, uncoated fused silica and MgF2, and four multilayer filters made from these materials were measured from 120 nm to 180 nm before and after irradiation by 250 krads from a Co-60 gamma radiation source. No radiation-induced losses in transmittance or reflectance occurred in this wavelength range. Additional postradiation measurements from 160 nm to 300 nm indicated a 3 - 5% radiation-induced absorption near 260 nm in some of the samples with MgF2 substrates. From these measurements it is concluded that far ultraviolet filters made from the materials tested should experience less that 5% change from exposure to up to 250 krads of high energy radiation in space applications.

  20. Preparation and microstructures of high-current density YBCO films by no-water post-annealing of precursor films including BaF 2

    NASA Astrophysics Data System (ADS)

    Ichinose, Ataru; Kikuchi, Akihiro; Kiss, Takanobu; Tachikawa, Kyoji; Akita, Shirabe; Inoue, Kiyoshi

    2003-10-01

    Precursor films are deposited on SrTiO 3 single crystals at room temperature by the co-evaporation technique using Y, BaF 2 and Cu as evaporation sources. Then, the precursor films are annealed in a low-pressure oxygen atmosphere without introduction of water vapor. A sample with a reflection high-energy electron diffraction (RHEED) pattern exhibiting some streaks, Kikuchi lines and Kikuchi zone, which resembles that of a single crystal, is successfully prepared. According to the cross-sectional TEM observation results, epitaxial growth of this YBCO film is achieved for the entire film thickness. The transport properties are measured using a small bridge with a width of 0.1 mm and a length of 1 mm by a standard four-probe method. The obtained YBCO film has a high Jc of over 1 MA/cm 2 at 77 K and a self-field. Furthermore, we discuss the relationship between the epitaxial YBCO layer thickness and the annealing conditions. Approximately 300- and 400-nm-thick epitaxial YBCO films are successfully prepared.

  1. Effect of SiO2 on the Crystallization Behaviors and In-Mold Performance of CaF2-CaO-Al2O3 Slags for Drawing-Ingot-Type Electroslag Remelting

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-Bin; Li, Jing; Cho, Jung-Wook; Jiang, Fang; Jung, In-Ho

    2015-10-01

    The crystallization characteristics of CaF2-CaO-Al2O3 slags with varying amounts of SiO2 were experimentally studied. The effects of slag crystallization behaviors on the horizontal heat transfer and lubrication performance in drawing-ingot-type electroslag remelting (ESR) were also evaluated in terms of as-cast ingots surface quality and drawing-ingot operation. The results show that increasing SiO2 addition from 0 to 6.8 mass pct strongly suppresses the crystallization of ESR type CaF2-CaO-Al2O3 slags. The crystallization temperature of the studied slags decreases with the increase in SiO2 addition. The liquidus temperatures of the slags also show a decreasing trend with increasing SiO2 content. In CaF2-CaO-Al2O3-(SiO2) slags, faceted 11CaO·7Al2O3·CaF2 crystals precipitate first during continuous cooling of the slag melts, followed by the formation of CaF2 at lower temperatures. 11CaO·7Al2O3·CaF2 was confirmed to be the dominant crystalline phase in the studied slags. CaF2-CaO-Al2O3 slags with a small amount of SiO2 addition are favorable for providing sound lubrication and horizontal heat transfer in mold for drawing-ingot-type ESR, which consequently bring the improvement in the surface quality of ESR ingot and drawing-ingot operating practice as demonstrated by plant trials.

  2. Evolution of the CaF2:Tm (TLD-300) glow curve as an indicator of beam quality for low-energy photon beams

    NASA Astrophysics Data System (ADS)

    Muñoz, I. D.; Avila, O.; Gamboa-deBuen, I.; Brandan, M. E.

    2015-03-01

    We study the high- to low- temperature signal ratio (HLTR) of the CaF2:Tm glow curve as a function of beam quality for low-energy photon beams with effective energy between 15.2 and 33.6?keV, generated with W, Mo and Rh anodes. CaF2:Tm dosemeters (TLD-300) were exposed to x-rays and 60Co gamma-rays. Glow curves were deconvoluted into 7 peaks, using computerized glow curve deconvolution and HLTR was evaluated. Air kerma and dose in water were between 2.1-15.0?mGy and 49.8-373.8?mGy, respectively. All peaks in the glow curve showed a linear response with respect to air kerma and dose in water. HLTR values decreased monotonically between 1.029? ± ?0.010 (at 15.2?keV) and 0.821? ± ?0.011 (33.6?keV), and no effects due to the use of different anode/filter combinations were observed. The results indicate a relatively high value of HLTR (about 1 for 17?keV effective energy, or 3?keV??m-1 track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique.

  3. Temperature-Dependent Refractive Index Measurements of Caf2, Suprasil 3001, and S-FTM16 for the Euclid Near Infrared Spectrometer and Photometer

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.; Miller, Kevin H.; Quijada, Manuel A.; Grupp, Frank D.

    2015-01-01

    Using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, we measured absolute refractive indices at temperatures from 100 to 310 K at wavelengths from 0.42 to 3.6 microns for CaF2, Suprasil 3001 fused silica, and S-FTM16 glass in support of lens designs for the Near Infrared Spectrometer and Photometer (NISP) for ESA's Euclid dark energy mission. We report absolute refractive index, dispersion (dn/d?), and thermo-optic coefficient (dn/dT) for these materials. In this study, materials from different melts were procured to understand index variability in each material. We provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. For calcium fluoride (CaF2) and S-FTM16, we compare our current measurements with CHARMS measurements of these materials made in the recent past for other programs. We also compare Suprasil 3001's indices to those of other forms of fused silica we have measured in CHARMS.

  4. Tensile properties of HA 230 and HA 188 after 400 and 2500 hour exposures to LiF-22CaF2 and vacuum at 1093 K

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    1990-01-01

    The solid-to-liquid phase transformation of the nominal LiF-20CaF2 eutectic at 1043 K is considered to be an ideal candidate thermal energy storage mechanism for a space based low temperature Brayton cycle solar dynamic system. Although Co, Fe, and Ni superalloys are thought to be suitable containment materials for LiF based salts, long term containment is of concern because molten fluorides are usually corrosive and Cr can be lost into space through evaporation. Two examples of commercially available superalloys in sheet form, the Ni-base material HA 230 and the Co-base material Ha 88, have been exposed to molten LiF-22CaF2, its vapor, and vacuum, at 1093 K, for 400 and 2500 hr. Triplicate tensile testing of specimens subjected to all three environments have been undertaken between 77 to 1200 K. Comparison of the weight gain data, microstructure, and tensile properties indicate that little, if any, difference in behavior can be ascribed to the exposure environment.

  5. Long-term 193-nm laser irradiation of thin-film-coated CaF2 in the presence of H2O

    NASA Astrophysics Data System (ADS)

    Liberman, V.; Switkes, M.; Rothschild, M.; Palmacci, S. T.; Sedlacek, J. H. C.; Hardy, D. E.; Grenville, A.

    2005-05-01

    The final projection lens element in a 193-nm immersion-based lithographic tool will be in direct contact with water during irradiation. Thus, any lifetime considerations for the lens must include durability data of lens materials and thin films in a water ambient. We have previously shown that uncoated CaF2 is attacked by water in a matter of hours, as manifested by a substantial increase in AFM-measured surface roughness.1 Thus, CaF2 lenses must be protected, possibly by a thin film, and the coatings tested for laser durability in water. To address the above lifetime concerns, we have constructed a marathon laser-irradiation system for testing thin film exposure to water under long-term laser irradiation. Coated substrates are loaded into a custom water cell, made of stainless steel and Teflon parts. Ultrapure water is delivered from a water treatment testbed that includes particle filtration, deionization and degassing stages. In-situ metrology includes 193-nm laser ratiometry, UV spectrophotometry and spectroscopic ellipsometry, all with spatial profiling capabilities. In-situ results are coupled with off-line microscopy, AFM measurements and spatial surface mapping with spectroscopic ellipsometry at multiple incidence angles. A variety of laser-induced changes have been observed, from complete adhesion loss of protective coatings to more subtle changes, such as laser-induced index changes of the thin films or surface roughening. Implications of the study on expected lifetimes of the protective coatings in the system will be discussed.

  6. Temperature-dependent refractive index measurements of CaF2, Suprasil 3001, and S-FTM16 for the Euclid near-infrared spectrometer and photometer

    NASA Astrophysics Data System (ADS)

    Leviton, Douglas B.; Miller, Kevin H.; Quijada, Manuel A.; Grupp, Frank U.

    2015-09-01

    Using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, we measured absolute refractive indices at temperatures from 100 to 310 K at wavelengths from 0.42 to 3.6 microns for CaF2, Suprasil 3001 fused silica, and S-FTM16 glass in support of lens designs for the Near Infrared Spectrometer and Photometer (NISP) for ESA's Euclid dark energy mission. We report absolute refractive index, dispersion (dn/d?), and thermo-optic coefficient (dn/dT) for these materials. In this study, materials from different melts were procured to understand index variability in each material. We provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. For calcium fluoride (CaF2) and S-FTM16, we compare our current measurements with CHARMS measurements of these materials made in the recent past for other programs. We also compare Suprasil 3001's indices to those of other forms of fused silica we have measured in CHARMS.

  7. Improvement of superconductivity in Fe1+yTe0.6Se0.4 induced by annealing with CaF2 and SmF3

    NASA Astrophysics Data System (ADS)

    Li, Xiong; Sun, Yue; Zhang, Yufeng; Zhou, Wei; Yuan, Feifei; Shi, Zhixiang

    2015-10-01

    We report detailed studies of the CaF2 and SmF3 annealing effects in Fe1+yTe0.6Se0.4 single crystals. Superconductivity in Fe1+yTe0.6Se0.4 single crystals was improved after annealing, which strongly suggested the effectiveness of the CaF2 and SmF3 annealing. In detail, no matter which annealing material was employed, the largest values of superconducting transition temperature and critical current density reached about 14 K and 1.0 × 105 A/cm2 (5 K, in self-field), respectively. Furthermore, compared with the pervious annealing materials, CaF2 and SmF3 are safe and easy-handing.

  8. Characterization of the tribological coating composition 77 wt % CaF2 - 23 wt % Li F fused to IN-750 alloy

    NASA Technical Reports Server (NTRS)

    Deadmore, D. L.; Sliney, H. E.

    1986-01-01

    A coating composed of 77 wt % CaF2 - 23 wt % LiF fused on IN-750 nickel-based alloy was studied using SEM, XRD, EDX, and optical microscopic methods. The surfaces examined were the as-fused coating with no subsequent treatment, the coating after ultrasonic cleaning in water, and the uncoated polished and etched metal. It was found that the coating reacts during fusion with Ti and Nb rich inclusions in the alloy. Numerous small rectangular crystallites of Ca(Ti,Nb) oxide are formed beneath an overlay of fused fluoride composition. These crystallines are stubby and appear to be embedded in the metal substrate surface. It is known from previous studies that this coating-alloy system has good tribological properties in extreme conditions, such as liquid fluorine. It has been concluded from the present study that the short firmly embedded crystalline protuberances contribute to the coating adherence and thereby to enhanced coating wear life.

  9. Temperature dependence of the elastic moduli and damping for polycrystalline LiF-22 pct CaF2 eutectic salt

    NASA Technical Reports Server (NTRS)

    Wolfenden, A.; Lastrapes, G.; Duggan, M. B.; Raj, S. V.

    1991-01-01

    Young's and shear moduli and damping were measured for as-cast polycrystalline LiF-(22 mol pct)CaF2 eutectic specimens as a function of temperature using the piezoelectric ultrasonic composite oscillator technique. The shear modulus decreased with increasing temperature from about 40 GPa at 295 K to about 30 GPa at 1000 K, while the Young modulus decreased from about 115 GPa at 295 K to about 35 GPa at 900 K. These values are compared with those derived from the rule of mixtures using elastic moduli data for LiF and CaF2 single crystals. It is shown that, while the shear modulus data agree reasonably well with the predicted trend, there is a large discrepancy between the theoretical calculations and the Young modulus values, where this disagreement increases with increasing temperature.

  10. On the application of CaF2:Eu and SrF2:Eu phosphors in LED based phototherapy lamp

    NASA Astrophysics Data System (ADS)

    Belsare, P. D.; Moharil, S. V.; Joshi, C. P.; Omanwar, S. K.

    2013-06-01

    In the last few years the interest of scientific community has been increased towards solid state lighting based on LEDs because of their superior advantages over the conventional fluorescent lamps. As the GaN based LEDs are easily available efforts of the researchers are now on making the new phosphors which are excitable in the near UV region (360-400nm) for solid state lighting. This paper reports the photoluminescence characteristics of CaF2:Eu and SrF2:Eu phosphor prepared by wet chemical method. The violet emission of these phosphors with near UV excitation can be useful in making a phototherapy lamp based on LEDs for treating various skin diseases like acne vulgaris and hyperbilirubinemia.

  11. Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF2 and SrF2 crystals

    NASA Astrophysics Data System (ADS)

    Barandiarán, Zoila; Seijo, Luis

    2015-10-01

    Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF2 and Yb/Sr pairs in SrF2 crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4fN-15d excited states of Y b2+: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b2+ + Ca2+ (Sr2+) ? Y b3+ + Ca+ (Sr+) electron phototransfer. This mechanism applies to all the observed Y b2+ 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b2+ because the Y b3+-Ca+ states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b2+ at the wavelengths of the first 4f-5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b2+ active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF2 host, associated with the lowest 4f-5d band.

  12. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

    DOE PAGESBeta

    Tarantini, C.; Kametani, F.; Lee, S.; Jiang, J.; Weiss, J. D.; Jaroszynski, J.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.

    2014-12-03

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature,Tc, of the material. In this study we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp=Jc xmore »??H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m3 at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase.« less

  13. Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

    PubMed Central

    Tarantini, C.; Kametani, F.; Lee, S.; Jiang, J.; Weiss, J. D.; Jaroszynski, J.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.

    2014-01-01

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, Tc, of the material. In this paper we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp = Jc × µ0H) by more than 60% compared to a single layer film, reaching a maximum of 84?GN/m3 at 22.5?T and 4.2?K, the highest value ever reported in any 122 phase. PMID:25467177

  14. Storing Hydrogen, by Enhancing Diamond Powder Properties under Hydrogen Plasma with CaF2 and KF for Use in Fuel Cells

    NASA Astrophysics Data System (ADS)

    Ochoa, Franklyn E. Colmenares

    2006-12-01

    A fuel cell is like a battery that instead of using electricity to recharge itself, it uses hydrogen. In the fuel cell industry, one of the main problems is storing hydrogen in a safe way and extracting it economically. Gaseous hydrogen requires high pressures which could be very dangerous in case of a collision. The success of hydrogen use depends largely on the development of an efficient storage and release method. In an effort to develop a better hydrogen storage system for fuel cells technology this research investigates the use of 99% pure diamond powder for storing hydrogen. Mixing this powder with a calcium fluoride and potassium fluoride compound in its solid form and treating the surface of the powder with hydrogen plasma, modifies the surface of the diamond. After some filtration through distilled water and drying, the modified diamond is treated with hydrogen. We expect hydrogen to be attracted to the diamond powder surface in higher quantities due to the CaF2 and KF treatment. Due to the large surface area of diamond nanopowder and the electronegative terminal bonds of the fluorine particles on the structure's surface, to the method shows promise in storing high densities of hydrogen.

  15. Microstructural properties of (Ba,Sr)TiO3 films fabricated from BaF2/SrF2/TiO2 amorphous multilayers using the combinatorial precursor method

    SciTech Connect

    Takeuchi, I.; Chang, K.; Sharma, R.P.; Bendersky, L.A.; Chang, H.; Xiang, X.-D.; Stach, E.A.; Song, C.-Y.

    2001-01-12

    We have investigated the microstructure of (Ba,Sr)TiO3 films fabricated from BaF2/SrF2/TiO2 amorphous multilayers. Rutherford backscattering spectroscopy and x-ray diffraction studies show that a controlled thermal treatment can interdiffuse the multilayers so as to create predominantly single-phase epitaxial (Ba,Sr)TiO3 films. High resolution cross-sectional transmission electron microscopy investigation of the processed films shows that they consist of large epitaxial grains of (Ba,Sr)TiO3 with atomically sharp interfaces with the LaAlO3 substrates. In addition, we have identified regions where polycrystalline and amorphous phases exist in small pockets in the film matrix. The results here indicate that the combinatorial thin-film synthesis using precursors can produce (Ba,Sr)TiO3 films in combinatorial libraries which exhibit properties similar to those films made by conventional techniques.

  16. DANCE (Detector for Advanced Neutron Capture Experiments) is a 4? array of BaF2 crystals installed at LANSCE, Lujan Center. Neutron capture measurements on ^157Gd and ^89Y nuclei were conducted using this facility.

    NASA Astrophysics Data System (ADS)

    Chyzh, A.; Mitchell, G.; Vieira, D.; Bredeweg, T.; Ullmann, J.; Jandel, M.; Couture, A.; Keksis, A.; Rundberg, R.; Wilhelmy, J.; O'Donnell, J.; Baramsai, B.; Haight, R.; Wouters, J.; Krticka, M.; Parker, W.; Becker, J.; Agvaanlusan, U.

    2009-10-01

    DANCE (Detector for Advanced Neutron Capture Experiments) is a 4? array of BaF2 crystals installed at LANSCE, Lujan Center. Neutron capture measurements on ^157Gd and ^89Y nuclei were conducted using this facility. The absolute cross sections of the ^89Y(n,?) reaction was measured for the first time ever in the neutron energy range of 10 eV -- 10 keV and improvements were made in the 10 -- 300 keV range. The error bars were significantly reduced and number of cross section points was increased since the past ^89Y(n,?) experiments. The ^157Gd(n,?) cross section was determined at En = 20 eV -- 300 keV by normalizing the experimental DANCE data to a well known resonance taken from the ENDF/B-VII library. Computer simulations of the ^157Gd(n,?) cascades and DANCE pulse height function were made using DICEBOX and GEANT4 codes and simulated Esum and E? spectra are compared to the experimental DANCE data. Values of spin and photon strength function (PSF) of the ^157Gd(n,?) resonances are provided in the range of En = 2 -- 300 eV using spin dependence upon a ?-ray multiplicity.

  17. Leaky mode suppression in planar optical waveguides written in Er:TeO2-WO3 glass and CaF2 crystal via double energy implantation with MeV N+ ions

    NASA Astrophysics Data System (ADS)

    Bányász, I.; Zolnai, Z.; Fried, M.; Berneschi, S.; Pelli, S.; Nunzi-Conti, G.

    2014-05-01

    Ion implantation proved to be an universal technique for producing waveguides in most optical materials. Tellurite glasses are good hosts of rare-earth elements for the development of fibre and integrated optical amplifiers and lasers covering all the main telecommunication bands. Er3+-doped tellurite glasses are good candidates for the fabrication of broadband amplifiers in wavelength division multiplexing around 1.55 ?m, as they exhibit large stimulated cross sections and broad emission bandwidth. Calcium fluoride is an excellent optical material, due to its perfect optical characteristics from UV wavelengths up to near IR. It has become a promising laser host material (doped with rare earth elements). Ion implantation was also applied to optical waveguide fabrication in CaF2 and other halide crystals. In the present work first single-energy implantations at 3.5 MeV at various fluences were applied. Waveguide operation up to 1.5 ?m was observed in Er:Te glass, and up to 980 nm in CaF2. Then double-energy implantations at a fixed upper energy of 3.5 MeV and lower energies between 2.5 and 3.2 MeV were performed to suppress leaky modes by increasing barrier width.

  18. (?-NaYbF4:Tm3+)/CaF2 Core/Shell Nanoparticles with Efficient Near-Infrared to Near-Infrared Upconversion for High-Contrast Deep Tissue Bioimaging

    PubMed Central

    Chen, Guanying; Shen, Jie; Ohulchanskyy, Tymish Y.; Patel, Nayan J.; Kutikov, Artem; Li, Zhipeng; Song, Jie; Pandey, Ravindra K.; Ågren, Hans; Prasad, Paras N.; Han, Gang

    2012-01-01

    We describe the development of novel and biocompatible core/shell (?-NaYbF4:Tm3+)/CaF2 nanoparticles which exhibit highly efficient NIRin-NIRout upconversion (UC) for high contrast and deep bioimaging. When excited at ~980 nm, these nanoparticles emit photoluminescence (PL) peaked at ~800 nm. The quantum yield of this UC PL under low power density excitation (~0.3 W/cm2) is 0.6±0.1%. This high UC PL efficiency is realized by suppressing surface quenching effects via hetero-epitaxial growth of a biocompatible CaF2 shell which results in a 35-fold increase in the intensity of UC PL from the core. Small animal whole-body UC PL imaging with exceptional contrast (signal-to-background ratio of 310) is shown using BALB/c mice intravenously injected with aqueously dispersed nanoparticles (700 pmol/kg). High-contrast UC PL imaging of deep tissues is also demonstrated, using a nanoparticle-loaded synthetic fibrous mesh wrapped around rat femoral bone, and a cuvette with nanoparticle aqueous dispersion - covered with a 3.2-cm thick animal tissue (pork). PMID:22928629

  19. Molecular structure and dynamics of off-center Cu(2+) ions and strongly coupled Cu(2+)-Cu(2+) pairs in BaF(2) crystals: electron paramagnetic resonance and electron spin relaxation studies.

    PubMed

    Hoffmann, S K; Goslar, J; Lijewski, S; Ulanov, V A

    2007-09-28

    X-band and Q-band electron paramagnetic resonance (EPR) spectra of Cu(2+) in BaF(2) crystal were recorded in the temperature range of 4.2-200 K. Spin-Hamiltonian parameters of single Cu(2+) complexes and of Cu(2+)-Cu(2+) pairs were derived and discussed. A special attention was paid to the dimeric species. Their molecular ground state configuration was found as having antiferromagnetic intradimer coupling with the singlet-triplet splitting J=-35 cm(-1). The zero-field splitting being D=0.0365 cm(-1) at 4.2 K increases with temperature as an effect of thermal population of excited dimer configurations. Electron spin echo (ESE) method was used for measurements of electron spin lattice and phase relaxation. The spin-lattice relaxation data show that except for coupling to the host lattice phonons the Cu(2+) ions are involved in local mode motions with energy of 82 cm(-1). Phase relaxation (ESE dephasing) of single Cu(2+) ions is due to spin diffusion at low temperatures. This relaxation is hampered for temperatures higher than 30 K due to the triplet state population of neighboring Cu(2+)-Cu(2+) dimers, which disturb dipolar coupling between Cu(2+) ions. For higher temperatures the relaxation is dominated by Raman T(1) processes. Fourier transform ESE spectrum displays dipolar Cu-F splitting which allowed determination of the off-center shift of Cu(2+) as delta(s)=0.132 nm. The dynamical effects observed in EPR spectra and in electron spin relaxation both for single Cu(2+) ions and Cu(2+)-Cu(2+) pairs are discussed as due to jumps between six off-center positions in the crystal unit cell and jumps between various dimer configurations. PMID:17902929

  20. Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1992-01-01

    As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media.

  1. Influence of heat treatments upon the mechanical properties and in vitro bioactivity of ZrO2-toughened MgO-CaO-SiO2-P2O5-CaF2 glass-ceramics.

    PubMed

    Li, Huan-Cai; Wang, Dian-Gang; Meng, Xiang-Guo; Chen, Chuan-Zhong

    2014-09-01

    Zirconia-toughened MgO-CaO-SiO2-P2O5-CaF2 glass-ceramics are prepared using sintering techniques, and a series of heat treatment procedures are designed to obtain a glass-ceramic with improved properties. The crystallization behavior, phase composition, and morphology of the glass-ceramics are characterized. The bending strength, elastic modulus, fracture toughness, and microhardness of the glass-ceramics are investigated, and the effect mechanism of heat treatments upon the mechanical properties is discussed. The bioactivity of glass-ceramics is then evaluated using the in vitro simulated body fluid (SBF) soaking test, and the mechanism whereby apatite forms on the glass-ceramic surfaces in the SBF solution is discussed. The results indicate that the main crystal phase of the G-24 sample undergoing two heat treatment procedures is Ca5(PO4)3F (fluorapatite), and those of the G-2444 sample undergoing four heat treatment procedures are Ca5(PO4)3F and ?-CaSiO3 (?-wollastonite). The heat treatment procedures are found to greatly influence the mechanical properties of the glass-ceramic, and an apatite layer is induced on the glass-ceramic surface after soaking in the SBF solution. PMID:25280855

  2. Influence of local structural disorders on spectroscopic properties of multi-component CaF2-Bi2O3-P2O5-B2O3 glass ceramics with Cr2O3 as nucleating agent

    NASA Astrophysics Data System (ADS)

    Suresh, S.; Narendrudu, T.; Yusub, S.; Suneel Kumar, A.; Ravi Kumar, V.; Veeraiah, N.; Krishna Rao, D.

    2016-01-01

    Multi-component CaF2-Bi2O3-P2O5-B2O3 glasses doped with different concentrations of Cr2O3 were crystallized through heat treatment. The prepared glass ceramic samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and differential thermal analysis (DTA). Spectroscopic studies viz., optical absorption, Fourier transform infrared (FTIR), Raman and electron paramagnetic resonance (EPR) were carried out. The XRD, SEM and DTA studies indicated that the samples contain different crystalline phases. Results of optical absorption and EPR studies pointed out the gradual conversion of chromium ions from Cr3 + state to Cr6 + state with an increase of Cr2O3 content from 0.1 to 0.5 mol%. The results of FTIR, Raman and EPR studies revealed that Cr6 + ions participate in the glass network in tetrahedral positions and seemed to increase the polymerization of the glass ceramics. The quantitative analysis of results of the spectroscopic studies further indicated that the glasses crystallized with low concentration of Cr2O3 are favourable for solid state laser devices.

  3. Influence of local structural disorders on spectroscopic properties of multi-component CaF2-Bi2O3-P2O5-B2O3 glass ceramics with Cr2O3 as nucleating agent.

    PubMed

    Suresh, S; Narendrudu, T; Yusub, S; Suneel Kumar, A; Ravi Kumar, V; Veeraiah, N; Krishna Rao, D

    2016-01-15

    Multi-component CaF2-Bi2O3-P2O5-B2O3 glasses doped with different concentrations of Cr2O3 were crystallized through heat treatment. The prepared glass ceramic samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and differential thermal analysis (DTA). Spectroscopic studies viz., optical absorption, Fourier transform infrared (FTIR), Raman and electron paramagnetic resonance (EPR) were carried out. The XRD, SEM and DTA studies indicated that the samples contain different crystalline phases. Results of optical absorption and EPR studies pointed out the gradual conversion of chromium ions from Cr(3+) state to Cr(6+) state with an increase of Cr2O3 content from 0.1 to 0.5mol%. The results of FTIR, Raman and EPR studies revealed that Cr(6+) ions participate in the glass network in tetrahedral positions and seemed to increase the polymerization of the glass ceramics. The quantitative analysis of results of the spectroscopic studies further indicated that the glasses crystallized with low concentration of Cr2O3 are favourable for solid state laser devices. PMID:26318703

  4. Determination of the Al2O3 content in NaF-AlF3-CaF2-Al2O3 melts at 950 °C by Raman spectroscopy.

    PubMed

    Malherbe, Cedric; Eppe, Gauthier; Gilbert, Bernard

    2014-08-19

    The in situ control of the chemical composition of industrial aluminum smelter is a challenge mainly for physicochemical reasons: high temperature, high surrounding electromagnetic field, and the highly corrosive molten salt electrolyte to deal with. In previous works, we proposed that Raman spectroscopy is a method of choice that could be adapted to real smelters. The laboratory study presented here relies on reproducible Raman spectra recorded on molten mixtures whose compositions are identical to those used during the production of aluminum. A normalization procedure for the Raman spectra is proposed based on the equilibria taking place in the bath. In addition, we discuss two quantitative models to determine the alumina content from the Raman spectra of the molten NaF-AlF3-CaF2-Al2O3 electrolytes. Univariate and multivariate approaches are applied to determine both the COx (alumina content) and the CR (NaF/AlF3 molar ratio) by Raman spectroscopy without referring to an additional internal reference of intensity. The procedure was successfully tested and validated on industrial samples. PMID:25048521

  5. Effect of ZrO(2) additions on the crystallization, mechanical and biological properties of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) bioactive glass-ceramics.

    PubMed

    Li, H C; Wang, D G; Meng, X G; Chen, C Z

    2014-06-01

    A series of ZrO(2) doped MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) bioactive glass-ceramics were obtained by sintering method. The crystallization behavior, phase composition, morphology and structure of glass-ceramics were characterized. The bending strength, elastic modulus, fracture toughness, micro-hardness and thermal expansion coefficient (TEC) of glass-ceramics were investigated. The in vitro bioactivity and cytotoxicity tests were used to evaluate the bioactivity and biocompatibility of glass-ceramics. The sedimentation mechanism and growth process of apatites on sample surface were discussed. The results showed that the mainly crystalline phases of glass-ceramics were Ca(5)(PO4)3F (fluorapatite) and ?-CaSiO(3). (?-wollastonite). m-ZrO(2) (monoclinic zirconia) declined the crystallization temperatures of glasses. t-ZrO(2) (tetragonal zirconia) increased the crystallization temperature of Ca(5)(PO4)(3)F and declined the crystallization temperature of ?-CaSiO(3). t-ZrO(2) greatly increased the fracture toughness, bending strength and micro-hardness of glass-ceramics. The nanometer apatites were induced on the surface of glass-ceramic after soaking 28 days in SBF (simulated body fluid), indicating the glass-ceramic has good bioactivity. The in vitro cytotoxicity test demonstrated the glass-ceramic has no toxicity to cell. PMID:24780435

  6. Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours

    SciTech Connect

    Whittenberger, J.D. )

    1992-08-01

    As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media. 8 refs.

  7. Influence of strontium on structure, sintering and biodegradation behaviour of CaO-MgO-SrO-SiO2-P2O5-CaF2 glasses

    SciTech Connect

    Goel, Ashutosh; Rajagopal, Raghu R.; Ferreira, Jose M.

    2011-11-01

    The present study investigates the influence of SrO on structure, apatite forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with composition: mol.% (36.07 – x) CaO – x SrO - 19.24 MgO – 5.61 P2O5 – 38.49 SiO2 – 0.59 CaF2, where x varies between 0 – 10. The detailed structural analysis of glasses has been made by infra red spectroscopy (FTIR) and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1 h – 7 days. While increasing Sr2+/Ca2+ ratio in glasses did not affect the structure of glasses significantly, their apatite forming ability was decreased considerably. Further, physico-chemical degradation of glasses has been studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris HCl and citric acid buffer and the possible implications of ion release profile from glasses in different solutions has been discussed. The addition of strontium in glasses led to a 7-fold decrease in chemical degradation of glasses in Tris-HCl. The sintering of glass powders rendered glass-ceramics (GCs) with varying degree of crystallinity and good flexural strength (98-131 MPa) where the mechanical properties depend on the nature and amount of crystalline phases present in GCs.

  8. Structure and Crystallization Kinetics of Glassy CaO-Al2O3-SiO2-CaF2-Na2O Mold Fluxes with Varying Basicity

    NASA Astrophysics Data System (ADS)

    Li, Jiangling; Yan, Baijun; Shu, Qifeng; Chou, Kuochih

    2015-07-01

    The structure and the crystallization kinetics of CaO-Al2O3-SiO2-CaF2-Na2O mold fluxes with varying basicities were investigated by solid-state 29Si nuclear magnetic resonance with magic angular spinning (MAS-NMR) and differential thermal analysis (DTA) technique, respectively. 29Si MAS-NMR study indicated that the increase of basicity decreased the degree of polymerization of mold fluxes. With the increasing basicity, Q 0, Q 2, and Q 3 gradually decreased, while Q 1 gradually increased, and the overall degree of polymerization was reduced. Crystallization analysis showed the cuspidine first crystallized from glass, and wollastonite crystal crystallized at elevated temperature for the samples with basicity (defined as CaO/SiO2 mass ratio) values of 0.9 and 1.0, respectively. Only cuspidine was found to crystallize from glass for the samples with basicity values of 1.1 and 1.2, indicating that the crystallization of wollastonite was suppressed with the increase of basicity. Crystallization kinetics analysis by DTA and field emission scanning electron microscopy equipped with energy dispersive spectroscopy investigation showed that growth mechanism of cuspidine is mainly of the diffusion-controlled three-dimensional growth with the increasing number of nuclei during heating. Activation energies for growth of cuspidine decreased with the increasing basicity of mold flux, which indicated that the crystallization ability was enhanced with the increase of basicity. The relationship between structure and crystallization of mold fluxes was established.

  9. Multifunctional hollow CaF2:Yb(3+)/Er(3+)/Mn(2+)-poly(2-Aminoethyl methacrylate) microspheres for Pt(IV) pro-drug delivery and tri-modal imaging.

    PubMed

    Deng, Xiaoran; Dai, Yunlu; Liu, Jianhua; Zhou, Ying; Ma, Ping'an; Cheng, Ziyong; Chen, Yinyin; Deng, Kerong; Li, Xuejiao; Hou, Zhiyao; Li, Chunxia; Lin, Jun

    2015-05-01

    Combining the multi-modal medical imaging with cancer therapy in one single system has attracted the great interests for theranostic purpose. In this paper, CaF2:Yb(3+)/Er(3+)/Mn(2+)-poly(2-Aminoethyl methacrylate) (UCHNs-PAMA) hybrid microspheres were successfully fabricated. The synthetic route to the nanocomposite based on a facile hydrothermal method for fabrication of hollow upconversion (UC) nanospheres at first and then post-?lling the PAMA interiorly through photo-initiated polymerization. The UCHNs showed orange ?uorescence under 980 nm near infrared (NIR) laser excitation, which provided the upconverting luminescence (UCL) imaging modality. Meanwhile, the presence of functional Mn(2+) and Yb(3+) offered the enhanced T1-weighted magnetic resonance (MR) and computed tomography (CT) imaging, respectively. Thanks to introducing amine groups-containing PAMA inside the hollow nanospheres, the Pt(IV) pro-drug, c,c,t-Pt(NH3)2Cl2(OOCCH2CH2COOH)2 (DSP), can be conveniently bonded on the polymer network to construct a nanoscale anti-cancer drug carrier. The UCHNs-PAMA-Pt(IV) nanocomposite shows effective inhibition for Hela cell line via MTT assay. In contrast, Pt(IV) pro-drug and UCHNs-PAMA microspheres behave little cytotoxicity to Hela cells. This should be attributed the fact that the anti-cancer ability can be recovered only when Pt(IV) pro-drug was reduced to Pt(II)-drug in cellular environment. Furthermore, the in vivo experiments on small mice also confirm that the hybrid microspheres have relatively low toxic side effects and high tumor inhibition rate. These findings show that the multifunctional hybrid microspheres have potential to be used as UCL/MR/CT tri-modal imaging contrast agent and anti-cancer drug carriers. PMID:25736505

  10. Structure and Crystallization Kinetics of Glassy CaO-Al2O3-SiO2-CaF2-Na2O Mold Fluxes with Varying Basicity

    NASA Astrophysics Data System (ADS)

    Li, Jiangling; Yan, Baijun; Shu, Qifeng; Chou, Kuochih

    2015-12-01

    The structure and the crystallization kinetics of CaO-Al2O3-SiO2-CaF2-Na2O mold fluxes with varying basicities were investigated by solid-state 29Si nuclear magnetic resonance with magic angular spinning (MAS-NMR) and differential thermal analysis (DTA) technique, respectively. 29Si MAS-NMR study indicated that the increase of basicity decreased the degree of polymerization of mold fluxes. With the increasing basicity, Q 0, Q 2, and Q 3 gradually decreased, while Q 1 gradually increased, and the overall degree of polymerization was reduced. Crystallization analysis showed the cuspidine first crystallized from glass, and wollastonite crystal crystallized at elevated temperature for the samples with basicity (defined as CaO/SiO2 mass ratio) values of 0.9 and 1.0, respectively. Only cuspidine was found to crystallize from glass for the samples with basicity values of 1.1 and 1.2, indicating that the crystallization of wollastonite was suppressed with the increase of basicity. Crystallization kinetics analysis by DTA and field emission scanning electron microscopy equipped with energy dispersive spectroscopy investigation showed that growth mechanism of cuspidine is mainly of the diffusion-controlled three-dimensional growth with the increasing number of nuclei during heating. Activation energies for growth of cuspidine decreased with the increasing basicity of mold flux, which indicated that the crystallization ability was enhanced with the increase of basicity. The relationship between structure and crystallization of mold fluxes was established.

  11. Particle Morphology Effects on Flow Characteristics of PS304 Plasma Spray Coating Feedstock Powder Blend

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; DellaCorte, Christopher; Eylon, Daniel

    2002-01-01

    The effects of BaF2-CaF 2 particle morphology on PS304 feedstock powder flow ability have been investigated. BaF2-CaF2 eutectic powders were fabricated by comminution (angular) and by gas atomization (spherical). The fluoride powders were added incrementally to the other powder constituents of the PS304 feedstock: nichrome, chromia, and silver powders. A linear relationship between flow time and concentration of BaF2-CaF2 powder was found. Flow of the powder blend with spherical BaF2-CaF2 was better than the angular BaF2-CaF2. Flow ability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. Flow of the powder blend with spherical fluorides was independent of fluoride concentration. Results suggest that for this material blend, particle morphology plays a significant role in powder blend flow behavior, offering potential methods to improve powder flow ability and enhance the commercial potential. These findings may have applicability to other difficult-to-flow powders such as cohesive ceramics.

  12. Particle Size Effects on Flow Properties of PS304 Plasma Spray Feedstock Powder Blend

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; DellaCorte, Christopher; Eylon, Daniel

    2002-01-01

    The effects of BaF2-CaF2 particle size and size distribution on PS304 feedstock powder flowability have been investigated. Angular BaF2-CaF2 eutectic powders were produced by comminution and classified by screening to obtain 38 to 45 microns 45 to 106 microns, 63 to 106 microns, 45 to 53 microns, 63 to 75 microns, and 90 to 106 microns particle size distributions. The fluorides were added incrementally from 0 to 10 wt% to the other powder constituents of the PS304 feedstock: nichrome, chromia, and silver powders. The flow rate of the powder blends decreased linearly with increasing concentration of the fluorides. Flow was degraded with decreasing BaF2-CaF2 particle size and with increasing BaF2-CaF2 particle size distribution. A semiempirical relationship is offered to describe the PS304 powder blend flow behavior. The Hausner Ratio confirmed the funnel flow test results, but was slightly less sensitive to differences in BaF2-CaF2 particle size and size distribution. These findings may have applicability to other powders that do not flow easily, such as ceramic powders.

  13. A Study of Mechanochemical Doping of Fluoride Crystals with a Fluorite Structure by Er3+ Ions via Electron Paramagnetic Resonance Spectra

    NASA Astrophysics Data System (ADS)

    Irisova, I. A.; Rodionov, A. A.; Tayurskii, D. A.; Yusupov, R. V.

    2014-05-01

    Using electron paramagnetic resonance (EPR) spectroscopy, we have shown that, upon mecha- noactivated doping of powders of compounds CaF2, SrF2, and BaF2 with Er3+ ions, impurity centers of single erbium ions with cubic symmetry are formed. Investigations of dependences of EPR spectra intensities on the particle size show that the process of mechanochemical doping with Er3+ ions proceeds differently for CaF2, SrF2, and BaF2 host matrices. In the case of CaF2, impurity centers are localized in a very thin near-surface layer of CaF2 particles, in SrF2, the impurity is distributed over the volume of particles, while, in BaF2, there is a layer of a finite thickness for which the probability of doping in the course of mechanosynthesis is very small and the impurity of the rare-earth element is localized in the core of large particles. These data can be explained assuming that the result of mechanosynthesis of particles of fluorides with a fluorite structure doped with Er3+ ions at room temperature is governed by two processes—mechanoactivated diffusion of rare-earth ions into particles and segregation of impurity ions at grain boundaries. In this case, the typical scales for compounds CaF2, SrF2, and BaF2 considerably differ from each other.

  14. Crystallization of heavy metal fluoride glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Bruce, Allan J.; Doremus, R. H.; Moynihan, C. T.

    1984-01-01

    The kinetics of crystallization of a number of fluorozirconate glasses were studied using isothermal and dynamic differential scanning calorimetry and X-ray diffraction. The addition of the fluorides LiF, NaF, AlF3, LaF3 to a base glass composition of ZrF4-BaF2 reduced the tendency to crystallize, probably by modifying the viscosity-temperature relation. ZrF4-BaF2-LaF3-AlF3-NaF glass was the most stable against devitrification and perhaps is the best composition for optical fibers with low scattering loss. Some glasses first crystallize out into metastable beta-BaZr2F10 and beta-BaZrF6 phases, which transform into the most stable alpha-phases when heated to higher temperatures. The size of the crystallites was estimated to be about 600 A from X-ray diffraction.

  15. Materials Data on LaF3 (SG:185) by Materials Project

    DOE Data Explorer

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  16. Materials Data on LaF3 (SG:139) by Materials Project

    DOE Data Explorer

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  17. Thermal Effects on a Low Cr Modification of PS304 Solid Lubricant Coating

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; Yanke, Anne M.; DellaCorte, Christopher

    2004-01-01

    PS304 is a high temperature composite solid lubricant coating composed of Ni-Cr, Cr2O3, BaF2-CaF2 and Ag. The effect of reducing chromium content on the formation of voids in the Ni-Cr particles after heat treatment in PS304 coating was investigated. Coatings were prepared with Ni-20Cr or Ni-10Cr powder and in various combinations with the other constituents of PS304 (i.e., chromia, silver and eutectic BaF2-CaF2 powders) and deposited on metal substrates by plasma spray. Specimens were exposed to 650 C for 24 hr or 1090 C for 15 hr and then examined for changes in thickness, coating microstructure and adhesion strength. Specimens with Ni-10Cr generally had less thickness increase than specimens with Ni-20Cr, but there was great variance in the data. Reduction of chromium concentration in Ni-Cr powder tended to reduce the appearance of voids in the Ni-Cr phase after heat exposure. The presence of BaF2-CaF2 resulted in a significant increase in coating adhesion strength after heat treatment, while coatings without BaF2-CaF2 had no significant change. Chemical composition analysis suggested that the void formation was due to oxidation of chromium in the Ni-Cr constituent.

  18. Development of infrared sensors using energy transfer/energy upconversion processes: Study of laser excited fluorescence in rare Earth ion doped crystals

    NASA Technical Reports Server (NTRS)

    Nash-Stevenson, S. K.; Reddy, B. R.; Venkateswarlu, P.

    1994-01-01

    A summary is presented of the spectroscopic study of three systems: LaF3:Ho(3+), LaF3:Er(3+) and CaF2:Nd(3+). When the D levels of Ho(3+) in LaF3 were resonantly excited with a laser beam of 640 nm, upconverted emissions were detected from J (416 nm), F (485 nm), and E (546 nm) levels. Energy upconverted emissions were also observed from F and E levels of Ho(3+) when the material was excited with an 800 nm near infrared laser. When the D levels of Er(3+) in LaF3 were resonantly excited with a laser beam of 637 nm, upconverted emissions were detected from the E (540 nm) and P (320, 400, and 468 nm) levels. Energy upconverted emissions were also observed from F, E, and D levels of Er(3+) when the material was resonantly excited with an 804 nm near infrared laser. When the D levels of Nd(3+) in CaF2 were resonantly excited with a laser beam of 577 nm, upconverted emissions were detected from the L (360 and 382 nm), K (418 nm), and I (432 nm) levels. Very weak upconverted emissions were detected when this system was irradiated with a near infrared laser. The numbers in parentheses are the wavelengths of the emissions.

  19. Ion beam sputtering of fluoride thin films for 193 nm applications.

    PubMed

    Ode, Aiko

    2014-02-01

    Ion beam sputtering of AlF3, LaF3, and GdF3 as single layers, AR coatings, and HR coatings for 193 nm is presented. The resulting optical properties, such as reflectance/transmittance and optical constants, and material properties, such as surface roughness and film durability, are discussed. The low temperature of the process allows for both CaF2 and fused silica substrates to be used with the same optical results. PMID:24514235

  20. Effect of microgravity on crystallization of ZBLAN fibers

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.

    1994-01-01

    ZrF4-BaF2-LaF3-AIF3-NaF (ZBLAN) optical fiber was flown on board the NASA's KC-135 microgravity aircraft to determine the effects of microgravity on crystal growth in this material. Fiber samples were placed in evacuated quartz ampoules and heated to the crystallization temperature in 0g, 1g, and 2g. The 1g and 2g samples were observed to slump and crystallize. The 0g samples showed no evidence of crystallization.

  1. Effects of Gravity on ZBLAN Glass Crystallization

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Ethridge, Edwin C.; Smith, Guy A.; Workman, Gary

    2004-01-01

    The effects of gravity on the crystallization of ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF glasses have been studied using the NASA KC-135 and a sounding rocket. Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

  2. Effects of Gravity on ZBLAN Glass Crystallization

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Ethridge, Edwin C.; Smith, G. A.; Workman, G.

    2003-01-01

    The effects of gravity on the crystallization of ZrF4-BaF2-LaF3-AlF3- NaF glasses have been studied utilizing NASA's KC135 and a sounding rocket, Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

  3. The Effects of a Magnetic Field on the Crystallization of a Fluorozirconate Glass

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Lapointe, Michael R.; Jia, Zhiyong

    2006-01-01

    An axial magnetic field of 0.1T was applied to ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results and tested by measuring the magnetic susceptibilities of the glass and crystal.

  4. Red-to-violet and near-infrared-to-green energy upconversion in LaF3:Er(3+)

    NASA Technical Reports Server (NTRS)

    Reddy, B. R.; Nash-Stevenson, S. K.

    1994-01-01

    When the (sup 4)F(sub 9/2) state was resonantly excited, emission was detected from the higher states (sup 4)S(sub 3/2)((sup 2)H(sub 11/2), (sup 4)G(sub 11/2), and (sup 2)P(sub 3/2) in addition to the resonant emission. Two- and three-photon processes were found to be responsible in populating the (sup 4)S(sub 3/2) and the (sup 2)P(sub 3/2) states, respectively. Energy upconversion efficiencies into the (sup 4)S(sub 3/2) and the (sup 2)P(sub 3/2) states were found to be 7.2 x 10(exp -3) and 1.4 x 10(exp -4), respectively. When the (sup 4)I(sub 9/2) state was resonantly excited we detected green emission from the (sup 4)S(sub 3/2)((sup 2)H(sub 11/2)). The energy upconversion efficiency of this process was found to be 1.4 x 10(exp -3).

  5. Communication: Growing room temperature ice with graphene

    NASA Astrophysics Data System (ADS)

    Verdaguer, Albert; Segura, Juan José; López-Mir, Laura; Sauthier, Guillaume; Fraxedas, Jordi

    2013-03-01

    Water becomes ordered in the form of hexagonal ice at room temperature under controlled humidity conditions upon confinement in the nanometer range between protective graphene sheets and crystalline (111) surfaces with hexagonal symmetry of the alkali earth fluoride BaF2. Interfacial water/substrate pseudoepitaxy turns out to be a critical parameter since ice is only formed when the lattice mismatch is small, an observation based on the absence of ice on (111) surfaces of isostructural CaF2

  6. Water Atomization of Barium Fluoride: Calcium Fluoride for Enhanced Flow Characteristics of PS304 Feedstock Powder Blend

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; DellaCorte, Christopher

    2003-01-01

    PS304 is a plasma spray deposited solid lubricant coating with feedstock composed of NiCr, Cr2O3, Ag, and BaF2-CaF2 powders. The effects of rounded BaF2-CaF2 particles on the gravity-fed flow characteristics of PS304 feedstock have been investigated. The BaF2-CaF2 powder was fabricated by water atomization using four sets of process parameters. Each of these powders was then characterized by microscopy and classified by screening to obtain 45 to 106 micron particles and added incrementally from 0 to 10 wt% to the other constituents of the PS304 feedstock, namely nichrome, chromia, and silver powders. The relationship between feedstock flow rate, measured with the Hall flowmeter, and concentration of fluorides was found to be linear in each case. The slopes of the lines were between those of the linear relationships previously reported using angular and spherical fluorides and were closer to the relationship predicted using the rule of mixtures. The results offer a fluoride fabrication technique potentially more cost-effective than gas atomization processes or traditional comminution processes.

  7. Intervalence Charge Transfer Luminescence: Interplay between anomalous and 5d-4f emissions in Yb-doped fluorite-type crystals

    E-print Network

    Barandiaran, Zoila

    2014-01-01

    We report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorites associated with Yb2+-Yb3+ mixed valence pairs. We show that the very broad band, anomalous emission of Yb2+-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb2+-Yb3+ mixed valence pairs. It is very efficiently excited by a two-photon upconversion mechanism. The IVCT vertical transition leaves the pair moieties very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are substracted from the normal emission. The ab initio IVCT energy diagrams explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4f emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2; and the prese...

  8. Materials Data on BaF2 (SG:225) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  9. NUCLEATION OF YBA(2)CU(3)O(7-D) IN THE BAF(2) PROCESS

    SciTech Connect

    WU,L.; SOLOVYOV,V.F.; WIESMANN,H.J.; ZHU,Y.; SUENAGA,M.

    2001-06-24

    The nucleation of the c-axis aligned and non-c-axis YBa{sub 2}Cu{sub 3}O{sub {approximately}6.1} (YBCO) from precursor films on [001]-cut SrTiO{sub 3} was investigated for the so-called BaF{sub 2} process. Specimens with different thickness were quenched from 735 C, then studied by transmission electron microscopy and x-ray diffraction techniques. Preceding the formation of YBCO nuclei, three intermediate phases of (Y,Ba) oxy-fluoride and a transition phase without F were found in the precursor films. These were structurally and chemically related to the nuclei of YBCO which was found to be deficient in Cu relative to its stoichiometric composition.

  10. Synthesis and the luminescent properties of the Nd3+ ions doped three kinds of fluoride nanocrystals in organic solvents

    NASA Astrophysics Data System (ADS)

    Chen, Zhuo; Tian, Changyong; Bo, Shuhui; Liu, Xinhou; Zhen, Zhen

    2015-10-01

    Oleic acid (OA)-modified LaF3:Nd, NaYF4:Nd and CaF2:Nd nanocrystals (NCs) with the different Nd3+ ion concentration (2% and 5%) have been prepared. The structure and morphology of NCs were identified by XRD, TEM, FT-IR and TGA. The size of OA-modified NC is a mean diameter of 5-10 nm and can be dispersed in common organic solvents to form a transparent solution. The optical loss of NCs in organic solvent is the first time to discuss in this work. The luminescence properties of NCs were also characterized and studied by fluorescence spectrometer. The nanoparticles in solid and in the solution all exhibited the strong emission at the 1060 nm when the materials were excited around 800 nm. Compared with the LaF3 and CaF2 matrix, NaYF4 as the host can protect the Nd3+ ions more efficiently away from the nonradiative transitions. The longest luminescent lifetime of the solid NaYF4:2%Nd NCs was up to 136 ?s, and the little difference of the fluorescence lifetime existed between the NCs in solid state and in solution. The low optical loss in organic solvent indicated that the Nd3+ ions-doped fluoride NCs are promising materials for optical amplification fields.

  11. F2-laser-induced damage on transparent fluoride crystals

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Yoshizo; Narazaki, Aiko; Sato, Tadatake; Kurosaki, Ryozo; Niino, Hiroyuki; Sato, Hiroki; Satonaga, Tomohiko; Fukuda, Tsuguo

    2004-10-01

    For the application of F2 lasers to micro-/nano-fabrication including photolithography, one of the important research subjects is to eliminate the chromatic aberration, and combination of lenses made of two optical materials with different refractive indices is the effective way. However, only CaF2 is widely applied to lenses for a vacuum ultraviolet (VUV) beam, and a "second material" to be paired with CaF2 is strongly requested. Here, we examined two fluoride crystals which are transparent in the VUV region, BaF2 and LiCaAlF6 grown by the Czochralski technique, as candidates for VUV optics. We investigated the change of the VUV transmittance and the onset of optical damage of these fluoride crystals against F2 laser irradiation. These crystals showed good optical tolerance against cumulative F2 laser irradiation, and the damage threshold of LiCaAlF6 was similar to that of VUV grade CaF2 while that of BaF2 was about half of the other two fluoride crystals.

  12. Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory

    NASA Astrophysics Data System (ADS)

    Foster, A. S.; Trevethan, T.; Shluger, A. L.

    2009-09-01

    Using periodic density functional theory, we calculate the structure and migration energies of fluorine vacancies and interstitials in the bulk and at the stoichiometric bulk-truncated surface of three alkali-earth fluorides: CaF2 , SrF2 , and BaF2 . We then study the adsorption of water and hydrogen, in both molecular and dissociated form, at the ideal surface, and at neutral and charged vacancies in the surface and subsurface layers. The results demonstrate that in nearly all cases molecular adsorption is strongly favored. For the most probable configurations on the surfaces, we also studied the migration paths and barriers, and found that water is highly mobile on the surface, even when adsorbed at defects. In general, CaF2 and SrF2 show similar behavior with respect to water, while adsorption energies and migration barriers for BaF2 are smaller. Finally, we discuss our results in the context of recent experimental Atomic Force Microscopy studies on CaF2 and compare to calculations on other insulating surfaces.

  13. Materials Data on CaF2 (SG:62) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  14. Materials Data on CaF2 (SG:225) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  15. Tunability of laser based on Yb-doped hot-pressed CaF2 ceramics

    NASA Astrophysics Data System (ADS)

    Sulc, Jan; Doroshenko, Maxim E.; Jelínková, Helena; Basiev, Tasoltan T.; Konyushkin, Vasilii A.; Osiko, Vyacheslav V.

    2012-06-01

    The aim of presented study was an investigation of tunability of diode pumped laser based on hot-pressed Yb:CaF2 ceramics. The tested Yb:CaF2 sample was in the form of 3.5mm thick plane-parallel face-polished plate (without AR coatings). The Yb3+ concentration was 5.5 %. A fiber (core diameter 200 ?m, NA= 0.22) coupled laser diode (LIMO, HLU25F200-980) with emission at wavelength 976 nm, was used for longitudinal Yb:CaF2 pumping. The laser diode was operating in the pulsed regime (4 ms pulse length, 20 Hz repetition rate). The duty-cycle 8% ensured a low thermal load even under the maximum diode pumping power amplitude 10W (crystal sample was only air-cooled). This radiation was focused into the crystal (pumping beam waist diameter ~ 170 ?m). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 - 1.09 ?m, HT @ 0.97 ?m) and curved (r = 150mm) output coupler with a reflectivity of ~ 98% @ 1.01 - 1.09 ?m. Tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and the laser active medium. The extremely broad and smooth tuning was obtained. The laser was continuously tunable over ~ 66nm (from 1015nm to 1081 nm) and the tuning band was mostly limited by free spectral range of used birefringent filter. The tunability FWHM was 40 nm corresponding bandwidth 10 THz results in Fourier limited gaussian pulse width ~ 40 fs (FWHM). The maximum output power amplitude 0.68W was obtained at wavelength 1054nm for absorbed pump power amplitude 6W. The laser slope efficiency was 15%.

  16. Biomedical graphite and CaF2 preparation and measurement at PRIME Lab

    NASA Astrophysics Data System (ADS)

    Jackson, George S.; Einstein, Jane A.; Kubley, Tom; Martin, Berdine; Weaver, Connie M.; Caffee, Marc

    2015-10-01

    The biomedical program at PRIME Lab has prepared radiocarbon and 41Ca as tracers for a variety of applications. Over the last decade several hundred 14C samples and several thousand 41Ca samples have been measured per year. Biomedical samples pose challenges that are relatively rare in the AMS community. We will discuss how to prepare and compensate for samples that have isotope ratios above the dynamic range of AMS, high interference rates, and small samples sizes. In the case of 41Ca, the trade off in the chromatography between yield and sample cleanliness will be analyzed. Secondary standards that have isotope ratios commonly encountered in our applications are routinely prepared. We use material from the Joint Research Centre's Institute for Reference Materials and Measurement: IRMM-3701/4, 3701/5, and 3701/6 and a standard produced by PRIME Lab for 41Ca. We use International Atomic Energy Agency's IAEA C-3, IAEA C-7, IAEA C-8, and a ?12.5× modern oxalic acid secondary standard supplied by Lawrence Livermore National Laboratory for 14C. We will discuss our precision, reproducibility, and the relative agreement between our measured and the reported values for these materials.

  17. Spectroscopic Studies of Pulsed-Laser-Induced Damage Sites in Heated CaF2 Crystals

    SciTech Connect

    Bozlee, Brian J.; Exarhos, Gregory J.; Teel, Randy W.

    1999-09-01

    Proceedings contain all papers presented at the 13th Symposium on Optical Materials for High-Powered Lasers, held at the National Institute of Standards and Technology in Boulder, CO, 28 Sept. - 1 Oct. 1998.

  18. Phase diagram for nanostructuring CaF(2) surfaces by slow highly charged ions.

    PubMed

    El-Said, A S; Wilhelm, R A; Heller, R; Facsko, S; Lemell, C; Wachter, G; Burgdörfer, J; Ritter, R; Aumayr, F

    2012-09-14

    The impact of individual slow highly charged ions (HCI) on alkaline earth halide and alkali halide surfaces creates nano-scale surface modifications. For different materials and impact energies a wide variety of topographic alterations have been observed, ranging from regularly shaped pits to nanohillocks. We present experimental evidence for the creation of thermodynamically stable defect agglomerations initially hidden after irradiation but becoming visible as pits upon subsequent etching. A well defined threshold separating regions with and without etch-pit formation is found as a function of potential and kinetic energies of the projectile. Combining this novel type of surface defects with the previously identified hillock formation, a phase diagram for HCI induced surface restructuring emerges. The simulation of the energy deposition by the HCI in the crystal provides insight into the early stages of the dynamics of the surface modification and its dependence on the kinetic and potential energies. PMID:23005676

  19. Spectroscopic, luminescent and laser properties of nanostructured CaF2:Tm materials

    NASA Astrophysics Data System (ADS)

    Lyapin, A. A.; Fedorov, P. P.; Garibin, E. A.; Malov, A. V.; Osiko, V. V.; Ryabochkina, P. A.; Ushakov, S. N.

    2013-08-01

    The laser quality transparent ??F2:Tm fluoride ceramics has been prepared by hot forming. Comparative study of absorption and emission spectra of ??F2:Tm (4 mol.% TmF3) ceramic and single crystal samples demonstrated that these materials possess almost identical spectroscopic properties. Laser oscillations of ??F2:Tm ceramics were obtained at 1898 nm under diode pumping, with the slope efficiency of 5.5%. Also, the continuous-wave (CW) laser have been obtained for ??F2:Tm single crystal at 1890 nm pumped by a diode laser was demonstrated.

  20. [Effect of bivalent alkaline earth fluorides introduction on thermal stability and spectroscopic properties of Er3+/Tm3+ /Yb3+ co-doped oxyfluorogermanate glasses].

    PubMed

    Hu, Yue-bo; Zhang, Xin-na; Zhou, Da-li; Jiao, Qing; Wang, Rong-fei; Huang, Jin-feng; Long, Xiao-bo; Qiu, Jian-bei

    2012-01-01

    Transparent Er3+/Tm3+ /Yb3+ co-doped oxyfluorogermanate glasses alone containing MgF2, CaF2, SrF2 or BaF2 and nano-glass-ceramics only containing BaF2 were prepared. The thermal stabilities and the up-conversion emission properties of the samples were investigated. Analyses of absorbance spectra reveal that the UV cutoff band moves slightly to shortwave band with the doping bivalent cation mass increasing. The results show that the emission color can be adjusted by changing the alkaline earth cation species in the glass matrixes, especially as Mg2+ is concerned, and the emission intensity can increase notably by heating the glass containing alkaline-earth fluoride into glass ceramic containing alkaline-earth fluoride nanocrystals or increasing the content of bivalent alkaline earth fluorides. PMID:22497127

  1. EPR study of electron bombarded alkali- and alkaline-earth halide crystal surfaces

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Lad, R. A.

    1975-01-01

    An EPR study of electron bombarded LiF, NaCl, KCl, CaF2 and BaF2 polycrystalline surfaces has shown that small metal particles are formed on the surfaces of the crystals. Identification was made from CESR signals. The symmetric line-shape of the signals, even at 77 K, indicated that the particles were less than 0.5 micron in diameter. Signals due to F centers were observed in LiF but not in the other halides. Implications to metal deposition are considered.

  2. A multiple pulse zero crossing NMR technique, and its application to F-19 chemical shift measurements in solids

    NASA Technical Reports Server (NTRS)

    Burum, D. P.; Elleman, D. D.; Rhim, W.-K.

    1978-01-01

    A simple multiple-pulse 'zero crossing technique' for accurately determining the first moment of a solid-state NMR spectrum is introduced. This technique was applied to obtain the F-19 chemical shift versus pressure curves up to 5 kbar for single crystals of CaF2 (0.29 + or - 0.02 ppm/kbar) and BaF2 (0.62 + or - 0.05 ppm/kbar). Results at ambient temperature and pressure are also reported for a number of other fluorine compounds. Because of its high data rate, this technique is potentially several orders of magnitude more sensitive than similar CW methods.

  3. Simultaneous measurement of (n,?) and (n,fission) cross sections with the DANCE 4? BaF2 array

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Fowler, M. M.; Becker, J. A.; Bond, E. M.; Chadwick, M. B.; Clement, R. R. C.; Esch, E.-I.; Ethvignot, T.; Granier, T.; Hunt, L. F.; Macri, R. A.; O'Donnell, J. M.; Rundberg, R. S.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C.-Y.; Yurkon, J. E.

    2006-03-01

    Neutron capture cross section measurements on many of the actinides are complicated by low-energy neutron-induced fission, which competes with neutron capture to varying degrees depending on the nuclide of interest. Measurements of neutron capture on 235U using the Detector for Advanced Neutron Capture Experiments (DANCE) have shown that we can partially resolve capture from fission events based on total photon calorimetry (i.e. total ?-ray energy and ?-ray multiplicity per event). The addition of a fission-tagging detector to the DANCE array will greatly improve our ability to separate these two competing processes so that improved neutron capture and (n,?)/(n,fission) cross section ratio measurements can be obtained. The addition of a fission-tagging detector to the DANCE array will also provide a means to study several important issues associated with neutron-induced fission, including (n,fission) cross sections as a function of incident neutron energy, and total energy and multiplicity of prompt fission photons. We have focused on two detector designs with complementary capabilities, a parallel-plate avalanche counter and an array of solar cells.

  4. An overview of DANCE: a 4II BaF[2] detector for neutron capture measurements at LANSCE.

    SciTech Connect

    Ullmann, J. L.

    2004-01-01

    The Detector for Advanced Neutron Capture experiments (DANCE) is a 162-element, 4{pi} BaF{sub 2} array designed to make neutron capture cross-section measurements on rare or radioactive targets with masses as little as 1 mg. Accurate capture cross sections are needed in many research areas, including stellar nucleosynthesis, advanced nuclear fuel cycles, waste transmutation, and other applied programs. These cross sections are difficult to calculate accurately and must be measured. Up to now, except for a few long-lived nuclides there are essentially no differential capture measurements on radioactive nuclei. The DANCE array is located at the Lujan Neutron Scattering Center at LANSCE, which is a continuous-spectrum neutron source with useable energies from below thermal to about 100 keV. Data acquisition is done with 320 fast waveform digitizers. The design and initial performance results, including background minimization, will be discussed.

  5. Effects of Gravity on Crystallization of Fluorozircante Optical Fibers

    NASA Technical Reports Server (NTRS)

    Tucker, D. S.; Scripa, R. N.; Wang, Bingjie; Rigsbee, J. M.

    1998-01-01

    ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) optical fibers were flown on NASA's reduced gravity KC135 aircraft and Conquest I sub-orbital rocket. The purpose of these experiments was to determine the effects of gravity on the crystallization process of this material. Fiber samples encapsulated in evacuated quartz ampoules were heated to the crystallization temperature during flight in reduced gravity and on the ground in unit gravity. Scanning electron and transmission electron microscopy were utilized to study the crystallization behavior. Samples heated under unit gravity conditions exhibited significant crystallization, while fibers heated to the crystallization temperature in reduced gravity showed no signs of crystallization. A mechanism based on microcellular convection is proposed to explain these observed behaviors.

  6. Fluoride glass starting materials - Characterization and effects of thermal treatment

    NASA Technical Reports Server (NTRS)

    Chen, William; Dunn, Bruce; Shlichta, Paul; Neilson, George F.; Weinberg, Michael C.

    1987-01-01

    The production of heavy metal fluoride (HMF) glasses, and the effects of thermal treatments on the HMF glasses are investigated. ZrF4, BaF2, AlF3, LaF3, and NaF were utilized in the synthesis of zirconium-barium-lanthanum-aluminum-sodium fluoride glass. The purity of these starting materials, in particular ZrF4, is evaluated using XRD analysis. The data reveal that low temperature heating of ZrF4-H2O is effective in removing the water of hydration, but causes the production of ZrF4 and oxyfluorides; however, dehydration followed by sublimation results in the production of monoclinic ZrFe without water or oxyfluoride contaminants.

  7. Graphene Q-switched Ho(3+)-doped ZBLAN fiber laser at 1190??nm.

    PubMed

    Liu, Shujing; Zhu, Xiushan; Zhu, Gongwen; Balakrishnan, Kaushik; Zong, Jie; Wiersma, Kort; Chavez-Pirson, Arturo; Norwood, R A; Peyghambarian, N

    2015-01-15

    We report Q-switched pulse operation of holmium (Ho(3+))-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) at ?1190??nm in an all-fiber ring laser by using a fiber-optic graphene saturable absorber, which was fabricated by depositing graphene onto the flat surface of a side-polished D-shaped fiber. Stable Q-switched operation was established at a pump power of 180 mW with a repetition rate of 24 kHz and pulse width of 5.7 ?s. When the pump power was increased to 1125 mW, 0.44 ?J Q-switched pulses with a repetition rate of 111 kHz and a pulse width of 0.8 ?s were generated. PMID:25679830

  8. Low Gravity Rapid Thermal Analysis of Glass

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Ethridge, Edwin C.; Smith, Guy A.

    2004-01-01

    It has been observed by two research groups that ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass crystallization is suppressed in microgravity. The mechanism for this phenomenon is unknown at the present time. In order to better understand the mechanism, an experiment was performed on NASA's KC135 reduced gravity aircraft to obtain quantitative crystallization data. An apparatus was designed and constructed for performing rapid thermal analysis of milligram quantities of ZBLAN glass. The apparatus employs an ellipsoidal furnace allowing for rapid heating and cooling. Using this apparatus nucleation and crystallization kinetic data was obtained leading to the construction of time-temperature-transformation curves for ZBLAN in microgravity and unit gravity.

  9. Tribological and microstructural comparison of HIPped PM212 and PM212/Au self-lubricating composites

    NASA Technical Reports Server (NTRS)

    Bogdanski, Michael S.; Sliney, Harold E.; Dellacorte, Christopher

    1992-01-01

    The feasibility of replacing the silver with the volumetric equivalent of gold in the chromium carbide-based self-lubricating composite PM212 (70 wt. percent NiCo-Cr3C2, 15 percent BaF2/CaF2 eutectic) was studied. The new composite, PM212/Au has the following composition: 62 wt. percent NiCo-Cr3C2, 25 percent Au, 13 percent BaF2/CaF2 eutectic. The silver was replaced with gold to minimize the potential reactivity of the composite with possible environmental contaminants such as sulfur. The composites were fabricated by hot isostatic pressing (HIPping) and machined into pin specimens. The pins were slid against nickel-based superalloy disks. Sliding velocities ranged from 0.27 to 10.0 m/s and temperatures from 25 to 900 C. Friction coefficients ranged from 0.25 to 0.40 and wear factors for the pin and disk were typically low 10(exp -5) cu mm/N-m. HIPped PM212 measured fully dense, whereas PM212/Au had 15 percent residual porosity. Examination of the microstructures with optical and scanning electron microscopy revealed the presence of pores in PM212/Au that were not present in PM212. Though the exact reason for the residual porosity in PM212/Au was not determined, it may be due to particle morphology differences between the gold and silver and their effect on powder metallurgy processing.

  10. Evaluation of Advanced Solid Lubricant Coatings for Foil Air Bearings Operating at 25 and 500 C

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Fellenstein, James A.; Benoy, Patricia A.

    1998-01-01

    The tribological properties of one chrome oxide and one chrome carbide based solid lubricant coating were evaluated in a partial-arc foil bearing at 25 and 500 C. Start/stop bearing operation up to 20,000 cycles were run under 10 kPa (1.5 psi) static deadweight load. Bearing friction (torque) was measured during the test. Specimen wear and SEM/EDS surface analyses were conducted after testing to understand and elucidate the tribological characteristics observed. The chrome oxide coating which contains both (Ag) and (BaF2/CaF2) for low and high temperature lubrication, exhibited low friction in sliding against Al2O3 coated foils at 25 and 500 C. The chrome carbide coating, which lacked a low temperature lubricant but contained BaF2/CaF2 as a high temperature lubricant, exhibited high friction at 25 C and low friction at 500 C against both bare and Al2O3 coated superalloy foil surfaces. Post test surface analyses suggest that improved tribological performance is exhibited when a lubricant film from the coating transfers to the foil surface.

  11. Spectroscopic properties and energy transfer parameters of Er3+- doped fluorozirconate and oxyfluoroaluminate glasses

    NASA Astrophysics Data System (ADS)

    Huang, Feifei; Liu, Xueqiang; Hu, Lili; Chen, Danping

    2014-05-01

    Er3+- doped fluorozirconate (ZrF4-BaF2-YF3-AlF3) and oxyfluoroaluminate glasses are successfully prepared here. These glasses exhibit significant superiority compared with traditional fluorozirconate glass (ZrF4-BaF2-LaF3-AlF3-NaF) because of their higher temperature of glass transition and better resistance to water corrosion. Judd-Ofelt (J-O) intensity parameters are evaluated and used to compute the radiative properties based on the VIS-NIR absorption spectra. Broad emission bands located at 1535 and 2708 nm are observed, and large calculated emission sections are obtained. The intensity of 2708 nm emission closely relates to the phonon energy of host glass. A lower phonon energy leads to a more intensive 2708 nm emission. The energy transfer processes of Er3+ ions are discussed and lifetime of Er3+: 4I13/2 is measured. It is the first time to observe that a longer lifetime of the 4I13/2 level leads to a less intensive 1535 nm emission, because the lifetime is long enough to generate excited state absorption (ESA) and energy transfer (ET) processes. These results indicate that the novel glasses possess better chemical and thermal properties as well as excellent optical properties compared with ZBLAN glass. These Er3+- doped ZBYA and oxyfluoroaluminate glasses have potential applications as laser materials.

  12. Spectroscopic properties and energy transfer parameters of Er3+-doped fluorozirconate and oxyfluoroaluminate glasses.

    PubMed

    Huang, Feifei; Liu, Xueqiang; Hu, Lili; Chen, Danping

    2014-01-01

    Er3+-doped fluorozirconate (ZrF4-BaF2-YF3-AlF3) and oxyfluoroaluminate glasses are successfully prepared here. These glasses exhibit significant superiority compared with traditional fluorozirconate glass (ZrF4-BaF2-LaF3-AlF3-NaF) because of their higher temperature of glass transition and better resistance to water corrosion. Judd-Ofelt (J-O) intensity parameters are evaluated and used to compute the radiative properties based on the VIS-NIR absorption spectra. Broad emission bands located at 1535 and 2708?nm are observed, and large calculated emission sections are obtained. The intensity of 2708?nm emission closely relates to the phonon energy of host glass. A lower phonon energy leads to a more intensive 2708?nm emission. The energy transfer processes of Er3+ ions are discussed and lifetime of Er3+:4I13/2 is measured. It is the first time to observe that a longer lifetime of the 4I13/2 level leads to a less intensive 1535?nm emission, because the lifetime is long enough to generate excited state absorption (ESA) and energy transfer (ET) processes. These results indicate that the novel glasses possess better chemical and thermal properties as well as excellent optical properties compared with ZBLAN glass. These Er3+-doped ZBYA and oxyfluoroaluminate glasses have potential applications as laser materials. PMID:24852112

  13. In-situ spectroscopic investigations of surfactant adsorption and water structure at the CaF2/aqueous solution interfacey

    E-print Network

    Richmond, Geraldine L.

    of this rela- tively high solubility, these salts show very dynamic behavior in their surface properties when in studying bulk properties such as solubility and macroscopic adsorption of ions onto the salt surface have on the bonding interactions, ion exchange behavior, and electrical properties in the interfacial

  14. Application of a volume holographic grating in a CaF2 crystal for measuring linear displacements with nanoscale accuracy

    NASA Astrophysics Data System (ADS)

    Shcheulin, A. S.; Angervaks, A. E.; Kupchikov, A. K.; Verkhovskii, E. B.; Ryskin, A. I.

    2014-12-01

    A holographic method for measuring linear displacements based on the use of a highly stable volume scale hologram recorded in an additively colored calcium fluoride crystal with photochromic color centers is proposed and experimentally approved. The essence of this method lies in measuring and analyzing harmonic signals formed during linear displacement of crystal with a volume hologram in an external interference field. A physical model of the formation of harmonic signals in photodetectors when measuring displacements is considered, and a mathematical method for calculating linear displacements by plotting a Lissajous figure is substantiated. A laboratory breadboard of a device for measuring linear displacements in a range of 10 mm, limited by the aperture of crystal with a recorded 8.7-mm-thick hologram, is designed. When using a scale hologram with a period of 2.18 ?m and a 632.8-nm He-Ne laser for reading this hologram, the error in measuring displacements by this method is 9 nm at a resolution of 3 nm.

  15. Removal of Sulfur from CaF2 Containing Desulfurization Slag Exhausted from Secondary Steelmaking Process by Oxidation

    NASA Astrophysics Data System (ADS)

    Hiraki, Takehito; Kobayashi, Junichi; Urushibata, Satomi; Matsubae, Kazuyo; Nagasaka, Tetsuya

    2012-08-01

    The oxidation behavior of sulfur in desulfurization slag generated from the secondary steelmaking process with air has been investigated in the temperature range of 973 K to 1373 K (700 °C to 1100 °C). Although a high removal rate of sulfur is not achieved at temperatures lower than 1273 K (1000 °C) because of the formation of CaSO4, most of the sulfur is rapidly removed from slag as SO2 gas in the 1273 K to 1373 K (700 °C to 1100 °C) range. This finding indicates that the desulfurization slag generated from the secondary steelmaking process can be reused as a desulfurized flux through air oxidation, making it possible to reduce significantly the amount of desulfurization slag for disposal.

  16. Nanocomposite containing CaF2 nanoparticles: Thermal cycling, wear and long-term water-aging

    PubMed Central

    Weir, Michael D.; Moreau, Jennifer L.; Levine, Eric D.; Strassler, Howard D.; Chow, Laurence C.; Xu, Hockin H. K.

    2012-01-01

    Objectives Fluoride (F) releasing dental restoratives are promising to promote remineralization and combat caries. The objectives of this study were to develop nanocomposite containing calcium fluoride nanoparticles (nCaF2), and to investigate the long-term mechanical durability including wear, thermal-cycling and long-term water-aging behavior. Methods Two types of fillers were used: nCaF2 with a diameter of 53 nm, and glass particles of 1.4 ?m. Four composites were fabricated with fillers of: (1) 0% nCaF2 + 65% glass; (2) 10% nCaF2 + 55% glass; (3) 20% nCaF2 + 45% glass; (4) 30% nCaF2 + 35% glass. Three commercial materials were also tested. Specimens were subjected to thermal-cycling between 5 °C and 60 °C for 105 cycles, three-body wear for 4×105 cycles, and water-aging for 2 years. Results After thermal-cycling, the nCaF2 nanocomposites had flexural strengths in the range of 100-150 MPa, five times higher than the 20-30 MPa for resin-modified glass ionomer (RMGI). The wear scar depth showed an increasing trend with increasing nCaF2 filler level. Wear of nCaF2 nanocomposites was within the range of wear for commercial controls. Water-aging decreased the strength of all materials. At 2 years, flexural strength was 94 MPa for nanocomposite with 10% nCaF2, 60 MPa with 20% nCaF2, and 48 MPa with 30% nCaF2. They are 3-6 fold higher than the 15 MPa for RMGI (p < 0.05). SEM revealed air bubbles and cracks in a RMGI, while composite control and nCaF2 nanocomposites appeared dense and solid. Significance Combining nCaF2 with glass particles yielded nanocomposites with long-term mechanical properties that were comparable to those of a commercial composite with little F release, and much better than those of RMGI controls. These strong long-term properties, together with their F release being comparable to RMGI as previously reported, indicate that the nCaF2 nanocomposites are promising for load-bearing and caries-inhibiting restorations. PMID:22429937

  17. Biaxially-Textured Photovoltaic Film Crystal Silicon on Ion Beam Assisted Deposition CaF2 Seed Layers on Glass

    SciTech Connect

    Groves, J. R.; Li, J. B.; Clemens, B. M.; LaSalvia, V.; Hasoon, F.; Branz, H. M.; Teplin, C. W.

    2012-05-01

    We grow biaxially textured heteroepitaxial crystal silicon (c-Si) films on display glass as a low-cost photovoltaic material. We first fabricate textured CaF{sub 2} seed layers using ion-beam assisted deposition, then coat the CaF{sub 2} with a thin, evaporated epitaxial Ge buffer and finally deposit heteroepitaxial silicon on the Ge. The silicon is grown by hot-wire chemical vapor deposition, a high-rate, scalable epitaxy technology. Electron and X-ray diffraction confirm the biaxial texture of the CaF{sub 2} and epitaxial growth of the subsequent layers. Transmission electron microscopy reveals columnar silicon grains about 500 nm across. We fabricate a proof-of-concept epitaxial film c-Si solar cell with an open circuit voltage of 375 mV that is limited by minority carrier lifetime.

  18. Investigation of the Environmental Durability of a Powder Metallurgy Material

    NASA Technical Reports Server (NTRS)

    Ward, LaNita D.

    2004-01-01

    PM304 is a NASA-developed composite powder metallurgy material that is being developed for high temperature applications such as bushings in high temperature industrial furnace conveyor systems. My goal this summer was to analyze and evaluate the effects that heat exposure had on the PM304 material at 500 C and 650 C. The material is composed of Ni-Cr, Ag, Cr2O3, and eutectic BaF2-CaF2. PM304 is designed to eliminate the need for oil based lubricants in high temperature applications, while reducing friction and wear. However, further investigation was needed to thoroughly examine the properties of PM304. The effects of heat exposure on PM304 bushings were investigated. This investigation was necessary due to the high temperatures that the material would be exposed to in a typical application. Each bushing was cut into eight sections. The specimens were heated to 500 C or 650 C for time intervals from 1 hr to 5,000 hrs. Control specimens were kept at room temperature. Weight and thickness measurements were taken before and after the bushing sections were exposed to heat. Then the heat treated specimens were mounted and polished side by side with the control specimens. This enabled optical examination of the material's microstructure using a metallograph. The specimens were also examined with a scanning electron microscope (SEM). The microstructures were compared to observe the effects of the heat exposure. Chemical analysis was done to investigate the interactions between Ni-Cr and BaF2-CaF2 and between Cr2O3 and BaF2-CaF2 at high temperature. To observe this, the two compounds that were being analyzed were mixed in a crucible in varied weight percentages and heated to 1100 C in a furnace for approximately two hours. Then the product was allowed to cool and was then analyzed by X-ray diffraction. Interpretation of the results is in progress.

  19. Superconducting properties of REBa 2Cu 3O y (RE = Y and Gd) films prepared by BaF 2 process without water vapor

    NASA Astrophysics Data System (ADS)

    Yokoyama, K.; Kita, R.; Ichinose, A.; Miura, O.; Matsumoto, K.; Yoshida, Y.; Mukaida, M.; Horii, S.

    2006-10-01

    We have successfully fabricated YBa2Cu3Oy (Y123) and GdBa2Cu3Oy (Gd123) films on SrTiO3 substrates by the ex situ heat treatment of co-evaporated Y-BaF2-Cu and Gd-BaF2-Cu precursor films prepared by electron beam deposition technique without water vapor. Tc and Jc of the Y123 film were 91.6 K and 0.95 MA cm-2 at 77 K at self-field, respectively. The Gd123 film showed Tc of 93.4 K and Jc of 1.5 MA cm-2 at 77 K at self-field. It was found that the surface morphology of the Y123 and the Gd123 films depended on the partial oxygen pressure during the heat treatment.

  20. Simultaneous measurement of (n,{gamma}) and (n,fission) cross sections with the DANCE 4{pi} BaF2 array

    SciTech Connect

    Bredeweg, T. A.; Fowler, M. M.; Bond, E. M.; Chadwick, M. B.; Hunt, L. F.; O'Donnell, J. M.; Rundberg, R. S.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Becker, J. A.; Clement, R. R. C.; Esch, E.-I.; Macri, R. A.; Wu, C.-Y.; Ethvignot, T.; Granier, T.; Yurkon, J. E.

    2006-03-13

    Neutron capture cross section measurements on many of the actinides are complicated by low-energy neutron-induced fission, which competes with neutron capture to varying degrees depending on the nuclide of interest. Measurements of neutron capture on 235U using the Detector for Advanced Neutron Capture Experiments (DANCE) have shown that we can partially resolve capture from fission events based on total photon calorimetry (i.e. total {gamma}-ray energy and {gamma}-ray multiplicity per event). The addition of a fission-tagging detector to the DANCE array will greatly improve our ability to separate these two competing processes so that improved neutron capture and (n,{gamma})/(n,fission) cross section ratio measurements can be obtained. The addition of a fission-tagging detector to the DANCE array will also provide a means to study several important issues associated with neutron-induced fission, including (n,fission) cross sections as a function of incident neutron energy, and total energy and multiplicity of prompt fission photons. We have focused on two detector designs with complementary capabilities, a parallel-plate avalanche counter and an array of solar cells.

  1. Far Ultraviolet Refractive Index of Optical Materials for Solar Blind Channel (SBC) Filters for HST Advanced Camera for Surveys

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.; Madison, Timothy J.; Petrone, Peter

    1998-01-01

    Refractive index measurements using the minimum deviation method have been carried out for prisms of a variety of far ultraviolet optical materials used in the manufacture of Solar Blind Channel (SBC) filters for the HST Advanced Camera for Surveys (ACS). Some of the materials measured are gaining popularity in a variety of high technology applications including high power excimer lasers and advanced microlithography optics operating in a wavelength region where high quality knowledge of optical material properties is sparse. Our measurements are of unusually high accuracy and precision for this wavelength region owing to advanced instrumentation in the large vacuum chamber of the Diffraction Grating Evaluation Facility (DGEF) at Goddard Space Flight Center (GSFC). Index values for CaF2, BaF2, LiF, and far ultraviolet grades of synthetic sapphire and synthetic fused silica are reported and compared with values from the literature.

  2. The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings

    NASA Technical Reports Server (NTRS)

    DellaCorte, Chris

    1998-01-01

    This paper describes the friction and wear performance of PS304, a modified chrome oxide based coating, for foil gas bearings. PS304 contains 60 wt% NiCr binder, 20 wt% Cr2O3 hardener, and 10 wt% each Ag, and BaF2/CaF2 lubricants. For evaluation, the coating is plasma spray deposited onto test journals which are slid against a superalloy partial arc foil bearing. The test load was 10 KPa (1.5 psi) and the bearings were run under start/stop cyclic conditions. The data show good wear performance of the bearing, especially at temperatures above 25 deg. C. Bearing friction was moderate (micron approx. or equal to 0.4) over the entire temperature range. Based upon the results obtained, the PS304 coating has promise for high temperature, oil-free turbomachinery applications.

  3. The Cryogenic, High-Accuracy, Refraction Measuring System (CHARMS): A New Facility for Cryogenic Infrared through Vacuum Far-Ultraviolet Refractive Index Measurements

    NASA Technical Reports Server (NTRS)

    Frey, Bradley J.; Leviton, Douglas B.

    2004-01-01

    The optical designs of future NASA infrared (IR) missions and instruments, such as the James Webb Space Telescope's (JWST) Near-Mixed Camera (NIRCam), will rely on accurate knowledge of the index of refraction of various IR optical materials at cryogenic temperatures. To meet this need, we have developed a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS). In this paper we discuss the completion of the design and construction of CHARMS as well as the engineering details that constrained the final design and hardware implementation. In addition, we will present our first light, cryogenic, IR index of refraction data for LiF, BaF2, and CaF2, and compare our results to previously published data for these materials.

  4. Effects of Humidity On the Flow Characteristics of PS304 Plasma Spray Feedstock Powder Blend

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; DellaCorte, Christopher

    2002-01-01

    The effects of environmental humidity on the flow characteristics of PS304 feedstock have been investigated. Angular and spherical BaF2-CaF2 powder was fabricated by comminution and by atomization, respectively. The fluorides were added incrementally to the nichrome, chromia, and silver powders to produce PS304 feedstock. The powders were dried in a vacuum oven and cooled to a Tom temperature under dry nitrogen. The flow of the powder was studied from 2 to 100 percent relative humidity (RH) The results suggest that the feedstock flow is slightly degraded with increasing humidity below 66 percent RH and is more affected above 66 percent RH. There was no flow above 88 percent RH. Narrower particle size distributions of the angular fluorides allowed flow up to 95 percent RH. These results offer guidance that enhances the commercial potential for this material system.

  5. Tribological Performance of PM300 Solid Lubricant Bushings for High Temperature Applications

    NASA Technical Reports Server (NTRS)

    Striebing, Donald R.; Stanford, Malcolm K.; DellaCorte, Christopher; Rossi, Anne M.

    2007-01-01

    PM300 is a high temperature solid lubricant material produced through conventional powder metallurgy processing. PM300 is a combination of metal binder (NiCr), hardener (Cr2O3) and lubricant (Ag and BaF2/CaF2) phases and is in commercial use in high temperature furnace conveyors. In this paper, the tribological characteristics of PM300 are evaluated using a newly developed bushing test rig in which PM300 bushings are loaded against rotating steel shafts at temperatures from 25 to 650 C. The data shows that friction and wear are low to moderate and that the lubrication performance (friction) improves with increasing temperature. Several alternative PM300 compositions are evaluated which do not contain silver and are targeted at aircraft gas turbine applications in which environmental compatibility of silver is a concern. It is expected that the data resulting from this research will further the commercialization of this technology.

  6. Density Measurement of Molten Alkaline-Earth Fluorides Using Archimedean Dual-Sinker Method

    NASA Astrophysics Data System (ADS)

    Takeda, Osamu; Yanagase, Kei-ichi; Anbo, Yusuke; Aono, Masahiro; Hoshino, Yosuke; Sato, Yuzuru

    2015-11-01

    The densities of molten alkaline-earth fluorides ({MgF}2, {CaF}2, {SrF}2 , and {BaF}2 ) were measured over the temperature range from 1526 K to 1873 K at ambient pressure using an Archimedean dual-sinker densitometer designed and set up by the authors. The volume difference between two sinkers was precisely determined by considering the wetting conditions between tungsten sinkers and water; appropriate experimental techniques were developed. The wetting condition became unstable when the sinkers were being moved for immersion in water, because the sinkers were moved in a direction that increased the contact angle. The wetting condition became stable when the sinkers were pulled up from the water, because the sinkers were moved in a direction that decreased the contact angle. The force exerted by the surface tension was efficiently canceled, and the volume difference became constant when the sinkers were pulled up. In this study, the total uncertainty was about 0.3 % at a maximum. The densities measured at high temperatures showed good linearity, with small scatter, over a wide temperature range. The densities and molar volumes increased in the following order: {MgF}2, {CaF}2, {SrF}2 , and {BaF}2 . The thermal-expansion coefficients showed anomalous behavior. The large thermal-expansion coefficient of {MgF}2 is attributed to a decrease in the cohesive force as a result of a partial loss of the coulombic force, because of the high charge density.

  7. Intervalence charge transfer luminescence: Interplay between anomalous and 5d - 4f emissions in Yb-doped fluorite-type crystals

    NASA Astrophysics Data System (ADS)

    Barandiarán, Zoila; Seijo, Luis

    2014-12-01

    In this paper, we report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorite-type crystals associated with Yb2+-Yb3+ mixed valence pairs. By means of embedded cluster, wave function theory ab initio calculations, we show that the widely studied, very broad band, anomalous emission of Yb2+-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb2+-Yb3+ mixed valence pairs. The IVCT luminescence is very efficiently excited by a two-photon upconversion mechanism where each photon provokes the same strong 4f14-1A1g? 4f13(2F7/2)5deg-1T1u absorption in the Yb2+ part of the pair: the first one, from the pair ground state; the second one, from an excited state of the pair whose Yb3+ moiety is in the higher 4f13(2F5/2) multiplet. The Yb2+-Yb3+ ? Yb3+-Yb2+ IVCT emission consists of an Yb2+ 5deg ? Yb3+ 4f7/2 charge transfer accompanied by a 4f7/2 ? 4f5/2 deexcitation within the Yb2+ 4f13 subshell: [2F5/25deg,2F7/2] ? [2F7/2,4f14]. The IVCT vertical transition leaves the oxidized and reduced moieties of the pair after electron transfer very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are subtracted from the normal emission. The IVCT energy diagrams resulting from the quantum mechanical calculations explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4f emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2; and the presence of additional 5d-4f emissions in SrCl2 which are absent in SrF2. They also allow to interpret and reproduce recent experiments on transient photoluminescence enhancement in Yb2+-doped CaF2 and SrF2, the appearance of Yb2+ 4f-5d absorption bands in the excitation spectra of the IR Yb3+ emission in partly reduced CaF2:Yb3+ samples, and to identify the broadband observed in the excitation spectrum of the so far called anomalous emission of SrF2:Yb2+ as an IVCT absorption, which corresponds to an Yb2+ 4f5/2 ? Yb3+ 4f7/2 electron transfer.

  8. Interfacial chemical reaction and multiple gap state formation on three layer cathode in organic light-emitting diode: Ca/BaF2/Alq3

    NASA Astrophysics Data System (ADS)

    Kim, Tae Gun; Lee, Hyunbok; Yi, Yeonjin; Lee, Seung Mi; Kim, Jeong Won

    2015-07-01

    A three layer cathode is a promising stack structure for long lifetime and high efficiency in organic light-emitting diodes. The interfacial chemical reactions and their effects on electronic structures for alkaline-earth metal (Ca, Ba)/Alq3 [tris(8-hydroxyquinolinato)aluminum] and Ca/BaF2/Alq3 are investigated using in-situ X-ray and ultraviolet photoelectron spectroscopy, as well as molecular model calculation. The BaF2 interlayer initially prevents direct contact between Alq3 and the reactive Ca metal, but it is dissociated into Ba and CaF2 by the addition of Ca. As the Ca thickness increases, the Ca penetrates the interlayer to directly participate in the reaction with the underlying Alq3. This series of chemical reactions takes place irrespective of the BaF2 buffer layer thickness as long as the Ca overlayer thickness is sufficient. The interface reaction between the alkaline-earth metal and Alq3 generates two energetically separated gap states in a sequential manner. This phenomenon is explained by step-by-step charge transfer from the alkaline-earth metal to the lowest unoccupied molecular orbital states of Alq3, forming new occupied states below the Fermi level.

  9. Static evaluation of surface coatings for compliant gas bearings in an oxidizing atmosphere to 650 C

    NASA Technical Reports Server (NTRS)

    Bhushan, B.; Gray, S.

    1978-01-01

    Hard wear-resistant coatings and soft low shear strength coatings were developed for an air-lubricated compliant journal bearing for a future automotive gas turbine engine. The coatings were expected to function in either 540 or 650 C ambient. Soft lubricant coatings were generally limited in temperature. Therefore emphasis was on the hard wear-resistant coatings. The coating materials covered were TiC, B4C, Cr3C2, WC, SiC, CrB2, TiB2, Cr2O3, Al2O3, Si3N4, Tribaloy 800, CaF2, CaF2-BaF2 eutectic, Ni-Co, silver, CdO-graphite and proprietary compounds. The coatings on test coupons were subjected to static oven screening tests. The test consisted of exposure of material samples in an oven for 300 h at the maximum temperature (540 or 650 C) and ten temperature cycles from room temperature to the maximum service temperature. On the basis of the specimen examinations the following coatings were recommended for future wear tests: TiC (sputtered), Cr2O3 (sputtered), Si3N4 (sputtered), CdO and graphite (fused), Kaman DES (a proprietary coating), CrB2 (plasma sprayed), Cr3C2 (detonation gun) and NASA PS-106 (plasma sprayed).

  10. Friction of self-lubricating surfaces by ion beam techniques

    NASA Astrophysics Data System (ADS)

    Bhattacharya, R. S.; Rai, A. K.

    1992-05-01

    UES, Inc. conducted a research and development program designed to establish conditions for ion implantation/mixing of suitable additives into the surfaces of bulk ceramics and metals for obtaining self-lubricating low friction and wear characteristics. The substrates considered were ZrO2, Al2O3, Si3N4, steel, and Ni-base superalloy. The lubricant additives chosen were BaF2/CaF2Ag, MoS2, WS2, and B2O3. The initial tasks of the program were to synthesis these lubricant compounds by co-implantation of constituent elements if sufficient beams of desired elements were obtained. The final tasks were to investigate high energy (MeV) ion mixing of deposited coatings as well as to investigate ion beam assisted deposition using low energy ion beams. It was shown that MoS2 can be synthesized by co-implantation of Mo(+) and S(+) in ceramic materials with appropriate choice of energies to obtain nearly overlapping depth profiles. The sliding life of DC magnetron sputtered MoS(2) films of thicknesses approximately 7500 A on ceramic materials such as sapphire, Si3N4 and ZrO3 were improved by ten to thousand fold after 2 Mev Ag(+) ion mixing. Ion beam assisted deposition (IBAD) and ion beam mixing were utilized to fabricate self-lubricating coatings of CaF2/Ag and BaF/CaF2/Ag composites.

  11. Energy transfer and upconversion emission of Er3+/Tb3+/Yb3+ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals under heat treatment

    NASA Astrophysics Data System (ADS)

    Dan, Ho Kim; Zhou, Dacheng; Wang, Rongfei; Yu, Xue; Jiao, Qing; Yang, Zhengwen; Song, Zhiguo; Qiu, Jianbei

    2014-01-01

    Transparent glass-ceramics SiO2-AlF3-BaF2-TiO2-LaF3 (SABTL) containing Ba2LaF7 nanocrystals were successfully prepared by heat treatment process through conventional melting method. The crystal size in the glass-ceramics increased gradually under the changing of heat treatment temperatures and times, which was confirmed by the results of XRD, TEM measurements. The intensity of the blue, green and red upconversion luminescence around 490 nm, 525 nm, 546 nm, 657 nm which originate from the transitions 5D4 ? 7FJ (J = 6 and 5) of Tb3+ ions and (2H11/2, 4S3/2, 4F9/2) ? 4I15/2 transitions of Er3+ ions, respectively, were strongly observed after heat treatment under 980 nm laser diode excitation. The intensity of upconversion luminescence was increased gradually with the increase of Yb3+ concentrations and reaches its maximum at 2.5 mol%. The upconversion luminescence and energy transfer process between Tb3+, Yb3+ and Er3+ ions in the glass-ceramics were discussed.

  12. ZBLAN Microgravity Study

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Smith, Guy A.; OBrien, Sue; Adcock, Leonard

    1995-01-01

    One of the greatest obstacles with the fluorozirconate ZBLAN (ZrF4-BaF2-LaF3-AIF3-NaF) is the problem of devitrification. Fluoride glasses have a narrow working range and the viscosity is a strong function of temperature. Rates of nucleation and growth of crystals in the glass depend on the viscosity, making these glasses unstable and prone to crystallization. The viscosity of ZBLAN at the drawing temperature is low, usually between two to five poise, so it is difficult to obtain fibers from their preform melts without crystallization. The preforms usually contain heterogeneous nuclei which grow into microcrystallites above the glass transition temperature, T(g). Since microcrystallites in an optical fiber cause extrinsic light scattering losses of the optical signal, fiber drawing must be completed in a short time to minimize the generation of light scattering centers. To keep these losses to a minimum and to fabricate low scattering loss fibers and other optical components, this research deals with the possibility of minimizing crystallite formation by removing the gravitational influence of solutal segregation of the ZBLAN elements. This report reviews the early work on the KC-135 aircraft, the development of the ZBLAN Rocket Experiment, preparations at the White Sands Missile Range, analysis of the flight and ground test results, lessons learned and future experimentation.

  13. Commercial Production of Heavy Metal Fluoride Glass Fiber in Space

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Workman, Gary L.; Smith, Guy A.

    1998-01-01

    International Space Station Alpha (ISSA) will provide a platform not only for materials research but also a possible means to produce products in space which cannot be easily produced on the ground. Some products may even be superior to those now produced in unit gravity due to the lack of gravity induced convection effects. Our research with ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN glass) has shown that gravity does indeed play a major role in the crystallization behavior of this material. At the present time ZBLAN is being produced on earth in fiber optic form for use in surgical lasers and fiber optic lasers among other applications. High attenuation coefficients, however, have kept this material from being used in other applications such as long haul data transmission links. The high attenuation coefficients are due to impurities which can be removed through improved processing techniques and crystals which can only be removed or prevented from forming by processing in a reduced gravity environment.

  14. Rare-earth doped colour tuneable up-conversion ZBLAN phosphor for enhancing photocatalysis

    NASA Astrophysics Data System (ADS)

    Méndez-Ramos, J.; Acosta-Mora, P.; Ruiz-Morales, J. C.; Sierra, M.; Redondas, A.; Ruggiero, E.; Salassa, L.; Borges, M. E.; Esparza, P.

    2015-03-01

    Rare-earth doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride glasses have been successfully synthesized showing outstanding UV-VIS up-conversion luminescence of Er3+ and Tm3+, sensitized by Yb3+ ions, under near-infrared excitation at 980 nm. The ratio between blue, green and red up-conversion emission bands can be adjusted by varying the pump power density of the incident infrared radiation, resulting in a controlled tuneability of the overall emitting colour from greenish to yellowish. Additionally, the observed high energy UV intense up-conversion emissions are suitable to enhance photocatalytic activity of main water-splitting semiconductor electrodes (such as TiO2) used in sustainable production of hydrogen. Photocatalysis and photolysis degradation of methylene blue in water under sun-like irradiation using benchmark photocatalyst (TiO2 Degussa P25) have been boosted by 20% and by a factor of 2.5 respectively, due to the enhancement of UV radiation that reaches the TiO2 particles by the addition of ZBLAN powder into a slurry-type photo-reactor. Hence, up-conversion ZBLAN phosphors contribute to demonstrate the possibility of transforming the incoming infrared radiation into the UV region needed to bridge the gap of photocatalytic semiconductors.

  15. Near-infrared photocatalysts of BiVO4/CaF2:Er3+, Tm3+, Yb3+ with enhanced upconversion properties

    NASA Astrophysics Data System (ADS)

    Huang, Shouqiang; Zhu, Nanwen; Lou, Ziyang; Gu, Lin; Miao, Chen; Yuan, Haiping; Shan, Aidang

    2014-01-01

    Upconversion photocatalysts have the potential to absorb the near-infrared (NIR) light in solar energy and improve the photocatalytic performance. A hierarchical upconversion photocatalyst of BiVO4 (BVO)/CaF2:Er3+, Tm3+, Yb3+ (CF) combined with the narrow-band semiconductor of BVO and the luminescence agent of CF to enhance upconversion properties was synthesized via the hydrothermal method. The CF particles were deposited homogeneously on the surface of the BVO/CF composite with regular dendritic structure, which led to efficient upconversion emissions. The upconversion emission intensity of the BVO/CF composite was 8 times higher than that of pure CF, through tailoring the crystal symmetry of lanthanide ions by Bi3+ ions. The upconverted ultraviolet (361 and 379 nm), violet (408 nm), and blue (485 nm) light was able to excite BVO for photocatalysis in BVO/CF under NIR irradiation, which improved the degradation rate of methyl orange (MO).Upconversion photocatalysts have the potential to absorb the near-infrared (NIR) light in solar energy and improve the photocatalytic performance. A hierarchical upconversion photocatalyst of BiVO4 (BVO)/CaF2:Er3+, Tm3+, Yb3+ (CF) combined with the narrow-band semiconductor of BVO and the luminescence agent of CF to enhance upconversion properties was synthesized via the hydrothermal method. The CF particles were deposited homogeneously on the surface of the BVO/CF composite with regular dendritic structure, which led to efficient upconversion emissions. The upconversion emission intensity of the BVO/CF composite was 8 times higher than that of pure CF, through tailoring the crystal symmetry of lanthanide ions by Bi3+ ions. The upconverted ultraviolet (361 and 379 nm), violet (408 nm), and blue (485 nm) light was able to excite BVO for photocatalysis in BVO/CF under NIR irradiation, which improved the degradation rate of methyl orange (MO). Electronic supplementary information (ESI) available: Additional tables and figures. See DOI: 10.1039/c3nr05266d

  16. Synthesis and down-conversion luminescence properties of Er3+/Yb3+ co-doped AlF3-PbF2-CaF2 powders

    NASA Astrophysics Data System (ADS)

    Liu, Fangchao; Han, Qun; Liu, Tiegen; Chen, Yaofei; Du, Yang; Yao, Yunzhi

    2015-08-01

    Er3+/Yb3+ co-doped oxy-fluoride powders with varying Er/Yb concentration were prepared by a melt quenching method at various sintering temperature. The effect of the Er/Yb doped concentration and sintering temperature were analyzed by using optical absorption and emission techniques. The Judd-Ofelt theory has been used to evaluate the three intensity parameters (??, where ? = 2, 4 and 6) and calculate the oscillator strengths (fc). Ultraviolet-to-visible emissions were observed under the excitation of a 325 nm CW laser. It was found that the down-conversion fluorescence intensity changes with the sintering temperature and Er/Yb content ratio, the results were explained with the level transitions in Er3+/Yb3+ co-doped systems. The intensity ratios (intensity of 437 nm as reference) of the luminescence spectra that the samples sintered at various temperature are relevant to ?6 parameter which indicates the vibration amplitude of the Er-O distance. The sintering temperature also has an influence on the intensity ratios via affecting the thermalization of the excited 4I15/2 level.

  17. Spectroscopic and laser properties of Tm3+ optical centers in CaF2 crystal under 795?nm diode laser excitation

    NASA Astrophysics Data System (ADS)

    Doroshenko, M. E.; Alimov, O. K.; Papashvili, A. G.; Martynova, K. A.; Konyushkin, V. A.; Nakladov, A. N.; Osiko, V. V.

    2015-12-01

    The dynamics of Tm3+ optical center formation with increasing thulium concentration and the influence of different optical centers on the fluorescence and laser properties of the 2 ?m 3F4–3H6 transition under ~795?nm laser diode excitation is studied.

  18. Charge Reversal Behavior at the CaF2/H2O/SDS Interface as Studied by Vibrational Sum Frequency Spectroscopy

    E-print Network

    Richmond, Geraldine L.

    important insight into the adsorption mechanism that is central to processes such as mineral ore flotation colloidal stabilization, lubrication, petroleum recovery, waterproofing, waste processing, and mineral ore2O interface, demonstrate the complex nature of the adsorption process which includes monomer

  19. Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators

    SciTech Connect

    Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien N.

    2012-07-01

    A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF2 and BaF2. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 {per_thousand}nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF2, BaF2, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs+ relative to Na+, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

  20. New measurements of (n,?) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4? BaF2 array

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Jandel, M.; Fowler, M. M.; Bond, E. M.; Haight, R. C.; Keksis, A. L.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Slemmons, A. K.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Becker, J. A.; Wu, C. Y.; Baker, J. D.; McGrath, C. A.

    2010-11-01

    Accurate neutron-induced reaction data are important to many issues in stockpile stewardship, nuclear reactor design and re-certification, nuclear non-proliferation and nuclear forensics. Of particular interest are the production and destruction reactions for all of the major and most of the minor actinides, including both neutron-induced capture and fission. The competition between capture and fission presents both an obstacle and an opportunity for large ? detector arrays such as the DANCE array (Detector for Advanced Neutron Capture Experiments), which cannot clearly differentiate ?-rays resulting from the two exit channels. With the addition of a high efficiency, 4? fission-tagging detector it is possible to deconvolve the two contributions to the total ?-ray spectrum. Using these tools we are able to conduct simultaneous fission/capture measurements which can simplify background treatment and other sources of systematic uncertainty. An outline of the current experimental program will be presented along with results from neutron capture measurements on ^233,235U and ^239Pu.

  1. New measurements of (n,?) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4? BaF2 array

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Jandel, M.; Fowler, M. M.; Bond, E. M.; Haight, R. C.; Keksis, A. L.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Becker, J. A.; Parker, W. E.; Wu, C. Y.; Baker, J. D.; McGrath, C. A.

    2009-10-01

    Accurate neutron nuclear data are important to many issues in stockpile stewardship, nuclear reactor design and re-certification, nuclear non-proliferation and nuclear forensics. Of particular interest are the production and destruction reactions for all of the major and most of the minor actinides. The competition between capture and fission in many of the actinides presents both an obstacle and an opportunity for large ? detector arrays such as DANCE. Additional instrumentation is required to deconvolve the two contributions to the total observed ?-ray spectrum. However, conducting a simultaneous measurement can simplify background treatment and other sources of systematic uncertainty. An outline of the current experimental program will be presented along with results from neutron capture measurements on ^233,235U and ^239Pu.

  2. Up-conversion emission tuning in triply-doped Yb3+/Tm3+/Er3+ novel fluoro-phosphate glass and glass-ceramics

    NASA Astrophysics Data System (ADS)

    Ledemi, Yannick; Trudel, Andrée.-Anne; Rivera, Victor A. G.; Messaddeq, Younes

    2014-03-01

    New Yb3+, Er3+ and Tm3+ triply doped fluoro-phosphate glasses belonging to the system NaPO3-YF3-BaF2-CaF2 have been prepared by the classical melt-casting technique. Glasses containing up to 10 wt.% of rare-earth ions fluorides have been obtained and characterized by using differential scanning calorimetry (DSC), UV-visible-near-infrared spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and optically homogeneous glass-ceramics have been reproducibly obtained by appropriate heat treatment in view to manage the red, green and blue emissions upon 975 nm laser excitation. According to the applied thermal heat-treatment, a large enhancement of intensity of the up-conversion emission - from 10 to 160 times higher - has been achieved in the glassceramics compared to that of glasses, suggesting incorporation of the rare-earth ions into the crystalline phase. Furthermore, a large range of color rendering has been observed in these materials by controlling the laser excitation power and material crystallization rate. Time-resolved luminescence experiments as well as X-ray diffractometry and scanning electron microscopy techniques have been employed in order to understand and correlate the multicolor emission changes to the crystallization behavior of this material. A progressive phase transformation of the fluorite-type CaF2-based nanocrystals initially generated was observed along with increasing heat-treatment time, thus modifying the rare earth ions spectroscopic features.

  3. High power mid-infrared supercontinuum generation in a single-mode ZBLAN fiber pumped by amplified picosecond pulses at 2 ?m

    NASA Astrophysics Data System (ADS)

    Liu, Kun; Liu, Jiang; Shi, Hongxing; Tan, Fangzhou; Jiang, Yijian; Wang, Pu

    2015-03-01

    We report high power all fiber mid-infrared (mid-IR) supercontinuum (SC) generation in a single-mode ZBLAN (ZrF4- BaF2-LaF3-AlF3-NaF) fiber with up to 21.8 W average output power from 1.9 to beyond 3.8 ?m pumped by amplified picosecond pulses from a master oscillator power amplifier (MOPA) based on small-core single-mode thulium-doped fiber (TDF) with injected seed pulse width of 24 ps and repetition of 93.6 MHz at 1963 nm. The optical-optical conversion efficiency from the 793 nm pump laser of the last stage thulium-doped fiber amplifier (TDFA) to mid-IR SC output is 17%. It is, to the best of our knowledge, the highest average power mid-IR SC generation in a ZBLAN fiber to date. In addition, a noise-like fiber oscillator based on a nonlinear loop mirror (NOLM) with wavepacket width of ~1.4 ns and repetition rate of 3.36 MHz at 1966 nm is also used as a seed of the MOPA for mid-IR SC generation in the ZBLAN fiber. At last, a mid-IR SC from 1.9 to beyond 3.6 ?m with average output power of 14.3W, which is limited by injected noise-like pulses power, is generated. The optical-optical conversion efficiency from the 793 nm pump laser of the last stage TDFA to mid-IR SC output is 14.9%. This proves the amplified noise-like pulses are also appropriate for high power mid-IR SC generation in the ZBLAN fiber.

  4. 4.5 W mid-infrared supercontinuum generation in a ZBLAN fiber pumped by a Q-switched mode-locked Tm3+- doped fiber laser

    NASA Astrophysics Data System (ADS)

    Kneis, C.; Donelan, B.; Berrou, A.; Manek-Hönninger, I.; Cadier, B.; Robin, T.; Poulain, M.; Joulain, F.; Eichhorn, M.; Kieleck, C.

    2015-02-01

    The generation of mid-infrared (mid-IR) supercontinuum (SC) radiation, ranging from 2 - 5 ?m, is subject of intense research due to its wide range of applications. A very popular host media for mid-IR SC generation are soft glass fibers owing to their low-loss transmission in the mid-IR wavelength regime, particularly fluoride fibers are very attractive for high-power operation. In this research study, a diode-pumped Q-switched mode-locked (QML) thulium (Tm3+)-doped double-clad silica fiber laser is used to pump a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber for mid-IR SC generation. The QML regime of the fiber laser is actively generated by two acousto-optic modulators. The Tm3+-fiber laser provided up to 23.5 W (26 W) of average output power in QML (continuous wave) regime with a slope efficiency of 36 % (32 %). The measured beam quality has been close to the diffraction-limit in QML regime. The system delivered mode-locked pulses with a duration of 7.5 ps, measured with a commercial autocorrelator system, at a repetition rate of 46 MHz. The Q-switched envelopes had a width between 50 and 150 ns depending on the output power level and the adjustable repetition rate. Mid-IR SC with an average output power in all spectral bands of 4.5 W have been achieved with more than 3 W/ 1.7 W/ 1 W/ 0.36 W after a long-wave-pass filter with a 3 dB-edge at 2.15 ?m/ 2.65 ?m/ 3.1 ?m/ 3.5 ?m.

  5. Evaluation of particle size distributions produced during ultra-violet nanosecond laser ablation and their relative contributions to ion densities in the inductively coupled plasma

    NASA Astrophysics Data System (ADS)

    Moses, Lance M.; Farnsworth, Paul B.

    2015-11-01

    Relative contributions to ion densities in the inductively coupled plasma (ICP) of particles of various sizes produced by laser ablation (LA) were investigated. Particles generated by 266 nm, ns LA of BaF2, CaF2, and a scandium aluminum alloy, characterized using SEM, consisted of hard and soft agglomerates, spherical particles, and irregularly-shaped particles. Although soft agglomerates and spherical particles were common to aerosols generated by LA in all cases, hard agglomerates appeared to be unique to the scandium aluminum alloy, while irregularly-shaped exfoliated particles were unique to the calcium and barium fluoride windows. The spatial distributions of Ca, Ba, and Sc ions in the ICP were determined from laser-induced fluorescence images taken with filters of pore sizes from 1-8 ?m added in-line to the transport tube upstream from the ICP. In all cases, a significant fraction of the ions formed in the ICP originated from micron-sized particles. Differences in the penetration depths of nanometer-sized agglomerates and micron-sized particles were about 2 mm for Ca and 1 mm for Ba. Differences in the penetration depths of nanometer and micron-sized agglomerates observed in the case of aluminum scandium were much less significant. This suggests that micron-sized hard-agglomerates and nanometer-sized soft-agglomerates experience very similar vaporization patterns. Additionally, there was evidence that flow patterns in the transport tube affect the trajectories of particles entering the plasma.

  6. Tribological and mechanical comparison of sintered and hipped PM212: High temperature self-lubricating composites

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Sliney, Harold E.; Bogdanski, Michael S.

    1992-01-01

    Selected tribological, mechanical and thermophysical properties of two versions of PM212 (sintered and hot isostatically pressed, HIPped) are compared. PM212, a high temperature self-lubricating composite, contains 70 wt percent metal bonded chromium carbide, 15 wt percent CaF2/BaF2 eutectic and 15 wt percent silver. PM212 in the sintered form is about 80 percent dense and has previously been shown to have good tribological properties from room temperature to 850 C. Tribological results of a fully densified, HIPped version of PM212 are given. They are compared to sintered PM212. In addition, selected mechanical and thermophysical properties of both types of PM212 are discussed and related to the tribological similarities and differences between the two PM212 composites. In general, both composites display similar friction and wear properties. However, the fully dense PM212 HIPped composite exhibits slight lower friction and wear than sintered PM212. This may be attributed to its generally higher strength properties. The sintered version displays stable wear properties over a wide load range indicating its promise for use in a variety of applications. Based upon their properties, both the sintered and HIPped PM212 have potential as bearing and seal materials for advanced high temperature applications.

  7. Laser-induced damage thresholds of bulk and coating optical materials at 1030??nm, 500??fs.

    PubMed

    Gallais, Laurent; Commandré, Mireille

    2014-02-01

    We report on extensive femtosecond laser damage threshold measurements of optical materials in both bulk and thin-film form. This study, which is based on published and new data, involved simple oxide and fluoride films, composite films made from a mixture of two dielectric materials, metallic films, and the surfaces of various bulk materials: oxides, fluorides, semiconductors, and ionic crystals. The samples were tested in comparable conditions at 1030 nm, 375 to 600 fs, under single-pulse irradiation. A large number of different samples prepared by different deposition techniques have been tested, involving classical materials used in the fabrication of optical thin film components (Ag, AlF3, Al2O3, HfO2, MgF2, Nb2O5, Pt, Sc2O3, SiO2, Ta2O5, Y2O3, and ZrO2) and their combination with codeposition processes. Their behaviors are compared with the surfaces of bulk materials (Al2O3, BaF2, CaF2, Ge, KBr, LiF, MgF2, NaCl, Quartz, Si, ZnS, ZnSe, and different silica glasses). Tabulated values of results are presented and discussed. PMID:24514214

  8. High-Temperature Solid Lubricants Developed by NASA Lewis Offer Virtually "Unlimited Life" for Oil-Free Turbomachinery

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Valco, Mark J.

    1999-01-01

    The NASA Lewis Research Center is capitalizing on breakthroughs in foil air bearing performance, tribological coatings, and computer analyses to formulate the Oil-free Turbomachinery Program. The program s long-term goal is to develop an innovative, yet practical, oil-free aeropropulsion gas turbine engine that floats on advanced air bearings. This type of engine would operate at higher speeds and temperatures with lower weight and friction than conventional oil-lubricated engines. During startup and shutdown, solid lubricant coatings are required to prevent wear in such engines before the self-generating air-lubrication film develops. NASA s Tribology Branch has created PS304, a chrome-oxide-based plasma spray coating specifically tailored for shafts run against foil bearings. PS304 contains silver and barium fluoride/calcium fluoride eutectic (BaF2/CaF2) lubricant additives that, together, provide lubrication from cold start temperatures to over 650 C, the maximum use temperature for foil bearings. Recent lab tests show that bearings lubricated with PS304 survive over 100 000 start-stop cycles without experiencing any degradation in performance due to wear. The accompanying photograph shows a test bearing after it was run at 650 C. The rubbing process created a "polished" surface that enhances bearing load capacity.

  9. Tribological composition optimization of chromium-carbide-based solid lubricant coatings for foil gas bearings at temperatures to 650 C

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    1988-01-01

    The determination of the tribilogically optimum composition of chromium-carbide-based solid lubricant coatings using a foil gas bearing test apparatus is described. The coatings contain a wear resistant chromium carbide `base stock' with the lubricant additives silver and BaF2-CaF2 eutectic. The coating composition is optimized for air-lubricated foil gas bearings at temperatures ranging from 25 to 650 C. The various compositions were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized Ni-Cr alloy foils, and the test bearings were subjected to repeated start-stop cycles under a bearing unit of 14 kPa. Sliding contact between the coated journal and the smooth foil occurs during bearing start-up before lift-off or hydrodynamic lubrication by the air film and during bearing coast-down. The bearings were tested for 9000 start-stop cycles or until specimen reached a predetermined failure level.

  10. Composition optimization of chromium carbide based solid lubricant coatings for foil gas bearings at temperatures to 650 C

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    1987-01-01

    A test program to determine the optimum composition of chromium carbide based solid lubricant coatings for compliant gas bearings is described. The friction and wear properties of the coatings are evaluated using a foil gas bearing test apparatus. The various coatings were prepared by powder blending, then plasma sprayed onto Inconel 718 test journals and diamond ground to the desired coating thickness and surface finish. The journals were operated against preoxidized nickel-chromium alloy foils. The test bearings were subjected to repeated start/stop cycles under a 14 kPa (2 psi) bearing unit load. The bearings were tested for 9000 start/stop cycles or until the specimen wear reached a predetermined failure level. In general, the addition of silver and eutectic to the chromium carbide base stock significantly reduced foil wear and increased journal coating wear. The optimum coating composition, PS212 (70 wt% metal bonded Cr3C2, 15 wt% Ag, 15% BaF2/CaF2 eutectic), reduced foil wear by a factor of two and displayed coating wear well within acceptable limits. The load capacity of the bearing using the plasma-sprayed coating prior to and after a run-in period was ascertained and compared to polished Inconel 718 specimens.

  11. Crystal structure of the Fe-member of usovite.

    PubMed

    Weil, Matthias

    2015-06-01

    Crystals of the title compound, with the idealized composition Ba2CaFeAl2F14, dibarium calcium iron(II) dialuminium tetra-deca-fluoride, were obtained serendipitously by reacting a mixture of the binary fluorides BaF2, CaF2 and AlF3 in a leaky steel reactor. The compound crystallizes in the usovite structure type (Ba2CaMgAl2F14), with Fe(2+) cations replacing the Mg(2+) cations. The principal building units are distorted [CaF8] square-anti-prisms (point group symmetry 2), [FeF6] octa-hedra (point group symmetry -1) and [AlF6] octa-hedra that are condensed into undulating (2) ?[CaFeAl2F14](4-) layers parallel (100). The Ba(2+) cations separate the layers and exhibit a coordination number of 12. Two crystal structure models with a different treatment of the disordered Fe site [mixed Fe/Ca occupation, model (I), versus underoccupation of Fe, model (II)], are discussed, leading to different refined formulae Ba2Ca1.310?(15)Fe0.690?(15)Al2F14 [model (I)] and Ba2CaFe0.90?(1)Al2F14 [model (II)]. PMID:26090139

  12. Friction and Wear Characteristics of a Modified Composite Solid Lubricant Plasma Spray Coating

    NASA Technical Reports Server (NTRS)

    Stanford, M. K.; DellaCorte, C.

    2004-01-01

    LCR304 is a solid lubricant coating composed of Ni-10Cr, Cr2O3, BaF2-CaF2 and Ag and developed for dimensional stability in high temperature air. This coating is a modification of PS304, which differs in that the Ni-Cr constituent contains 20wt% Cr. The tribological characteristics of LCR304 were evaluated by pin-on-disk and foil air bearing rig testing from 25 to 650 C and compared to previous test results with PS304. For both tests, the friction coefficient decreased as temperature increased from 25 to 650 C. Wear generally decreased with increasing temperature for all pin-on-disk tests. LCR304 coated components produced the least wear of Inconel X-750 counterface materials at 427 and 650 C. These results indicate that the LCR304 coating has potential as a replacement for PS304 in, for example, low cycle (minimum wear) applications where dimensional stability is imperative.

  13. 2.7 ?m emission of high thermally and chemically durable glasses based on AlF3

    NASA Astrophysics Data System (ADS)

    Huang, Feifei; Ma, Yaoyao; Li, Weiwei; Liu, Xueqiang; Hu, Lili; Chen, Danping

    2014-01-01

    AlF3-based glasses (AlF3-YF3-CaF2-BaF2-SrF2-MgF2) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 ?m mid-infrared emission in the AlF3-based glasses was also investigated through the absorption and emission spectra. Both the temperature of glass transition and the characteristic temperatures (?T, Hr, kgl) of the fluoroaluminate glasses were much larger than those of the ZBLAN glasses. The corrosion phenomenon can be observed by naked-eye, and the transmittance dropped dramatically (0% at 3 ?m) when the ZBLAN glass was placed into distilled water. However, the AlF3-based glass was relatively stable. The fluoroaluminate glasses possessed large branching ratio (20%) along with the emission cross section (9.4×10-21 cm-2) of the Er3+:4I11/2-->4I13/2 transition. Meanwhile, the enhanced 2.7 ?m emission in highly Er3+-doped AYF glass was obtained. Therefore, these results showed that this kind of fluoride glass has a promising application for solid state lasers at 3 ?m.

  14. Crystal structure of the Fe-member of usovite

    PubMed Central

    Weil, Matthias

    2015-01-01

    Crystals of the title compound, with the idealized composition Ba2CaFeAl2F14, dibarium calcium iron(II) dialuminium tetra­deca­fluoride, were obtained serendipitously by reacting a mixture of the binary fluorides BaF2, CaF2 and AlF3 in a leaky steel reactor. The compound crystallizes in the usovite structure type (Ba2CaMgAl2F14), with Fe2+ cations replacing the Mg2+ cations. The principal building units are distorted [CaF8] square-anti­prisms (point group symmetry 2), [FeF6] octa­hedra (point group symmetry -1) and [AlF6] octa­hedra that are condensed into undulating 2 ?[CaFeAl2F14]4? layers parallel (100). The Ba2+ cations separate the layers and exhibit a coordination number of 12. Two crystal structure models with a different treatment of the disordered Fe site [mixed Fe/Ca occupation, model (I), versus underoccupation of Fe, model (II)], are discussed, leading to different refined formulae Ba2Ca1.310?(15)Fe0.690?(15)Al2F14 [model (I)] and Ba2CaFe0.90?(1)Al2F14 [model (II)]. PMID:26090139

  15. Optical glasses with high NIR transmission

    NASA Astrophysics Data System (ADS)

    Xu, Wenli; Seifert, Walter

    2003-02-01

    For dioptic instruments working in the near-infrared (NIR), the choice of materials for lenses is mostly limited to special glasses or crystals. Most commonly used are CaF2, BaF2, infrared fused silica, ZnS and ZnSe. Those materials can in general not provide good chromatic correction for fast systems. Moreover, the high index materials, as well as infrared glass like Schott IRG, are quite limited with regard to availability in larger sizes and thicknesses and/or optical quality. An investigation was made for optical glasses from the Schott and Ohara catalogues with high transmission up to a wavelength of 2.4 ?m. For the most promising materials, the transmission from ?0.35?m to ?3.0?m, was measured in the lab with high spectral resolution. A systematic analysis of combinations of those optical glasses with the infrared materials was performed and the combinations with extremely good chromatic correction in the NIR are presented. There were several combinations found which are well corrected even from ?0.55?m to ?2.5?m, as needed for some designs of adaptive optics systems.

  16. Nonstoichiometry in inorganic fluorides: 2. Ionic conductivity of nonstoichiometric M 1 - x R xF2 + x and R 1 - y M yF3 - y crystals ( M = Ca, Sr, Ba; R are rare earth elements)

    NASA Astrophysics Data System (ADS)

    Sobolev, B. P.; Sorokin, N. I.

    2014-11-01

    The peak manifestation of nonstoichiometry in fluoride systems in the number of phases with valuable properties and wide homogeneity ranges is 45 MF2- RF3 systems, where M = Ca, Sr, Ba and R are 15 rare earth elements from La to Lu and Y (with Pm and Sc excluded). A deviation from stoichiometry in crystals of the M 1 - x R xF2 + x (CaF2 fluorite type) and R 1 - y M yF3 - y (LaF3 tysonite type) phases is responsible for the fluorine superionic conductivity ?. The range of variation in ? with changes in the qualitative ( M, R) and quantitative ( x, y) compositions in both structure types is very wide. The ? value changes by a factor of 108 in the M 1 - x R xF2 + x phases (at 500 K) and by a factor of 106 in the R 1 - y M yF3 - y phases (at 293 K). Changing compositions, one can also obtain crystals with ? values large enough for their use as fluorine-conducting solid electrolytes. Phases promising for solid electrolytes were revealed in the MFm- RFn systems ( m < n ? 4), which were studied within the program of searching for new multicomponent fluoride materials at the Institute of Crystallography, Russian Academy of Sciences (IC RAS). Superionic conductivity is one of the peak manifestations of the influence of defect structure of nonstoichiometric crystals on their properties. The subject of this review is the results of the studies performed at the IC RAS on the ionic conductivity of single crystals of the M 1 - x R xF2 + x and R 1 - y M yF3 - y nonstoichiometric phases.

  17. Charge Compensation in RE3+ (RE = Eu, Gd) and M+ (M = Li, Na, K) Co-Doped Alkaline Earth Nanofluorides Obtained by Microwave Reaction with Reactive Ionic Liquids Leading to Improved Optical Properties

    SciTech Connect

    Lorbeer, C; Behrends, F; Cybinska, J; Eckert, H; Mudring, Anja -V

    2014-01-01

    Alkaline earth fluorides are extraordinarily promising host matrices for phosphor materials with regard to rare earth doping. In particular, quantum cutting materials, which might considerably enhance the efficiency of mercury-free fluorescent lamps or SC solar cells, are often based on rare earth containing crystalline fluorides such as NaGdF4, GdF3 or LaF3. Substituting most of the precious rare earth ions and simultaneously retaining the efficiency of the phosphor is a major goal. Alkaline earth fluoride nanoparticles doped with trivalent lanthanide ions (which are required for the quantum cutting phenomenon) were prepared via a microwave assisted method in ionic liquids. As doping trivalent ions into a host with divalent cations requires charge compensation, this effect was thoroughly studied by powder X-ray and electron diffraction, luminescence spectroscopy and 23Na, 139La and 19F solid state NMR spectroscopy. Monovalent alkali ions were codoped with the trivalent lanthanide ions to relieve stress and achieve a better crystallinity and higher quantum cutting abilities of the prepared material. 19F-magic angle spinning (MAS)-NMR-spectra, assisted by 19F{23Na} rotational echo double resonance (REDOR) studies, reveal distinct local fluoride environments, the populations of which are discussed in relation to spatial distribution and clustering models. In the co-doped samples, fluoride species having both Na+ and La3+ ions within their coordination sphere can be identified and quantified. This interplay of mono- and trivalent ions in the CaF2 lattice appears to be an efficient charge compensation mechanism that allows for improved performance characteristics of such co-doped phosphor materials.

  18. Diopside (CaO-MgO-2SiO2)-fluorapatite (9CaO-3P2O5-CaF2) glass-ceramics: Potential materials for bone tissue engineering

    SciTech Connect

    Kansal, Ishu; Goel, Ashutosh; Tulyaganov, Dilshat U.; Pascual, Maria J.; Lee, Hye-Young; Kim, Hae-Won; Ferreira, Jose M.

    2011-08-18

    Glass-ceramics in the diopside (CaMgSi2O6) - fluorapatite [Ca5(PO4)3F] system are potential candidates for restorative dental and bone implant materials. In the present study, a series of glasses along diopside - fluorapatite binary system have been prepared with varying diopside/fluorapatite ratios for their potential applications in bone tissue engineering. The glasses were obtained from compositions with fluorapatite contents varying between 0-40 wt.%. The sintering ability and crystallization kinetics of as obtained amorphous glasses have been studied through hot-stage microscopy (HSM) and differential thermal analysis (DTA), respectively while crystalline phase evolution in sintered GCs has been followed by X-ray diffraction (XRD) adjoined with Rietveld-R.I.R. technique and scanning electron microscopy (SEM). Further, biodegradation and apatite forming ability of glass-ceramics were investigated by immersion of glass-ceramic discs in simulated body fluid (SBF) solution while chemical degradation and weight loss of glass-ceramics were studied by immersion in Tris-HCl in accordance with standard ISO 10993-14. The addition of fluorapatite (10-25 wt.%) in diopside glass system significantly enhanced the sintering ability of glass-ceramics and improved their apatite forming ability along with their biodegradation behaviour. Moreover, the in vitro cellular responses to glass-ceramics showed good cell viability and significant stimulation of osteoblastic differentiation, suggesting the possible use of the glass-ceramics for bone regeneration.

  19. Preparation and tribological properties of fluorosilane surface-modified lanthanum trifluoride nanoparticles as additive of fluoro silicone oil

    NASA Astrophysics Data System (ADS)

    Hou, Xiao; He, Jie; Yu, Laigui; Li, Zhiwei; Zhang, Zhijun; Zhang, Pingyu

    2014-10-01

    LaF3 nanoparticles surface-modified with fluorosilane were synthesized by surface modification technology. The size, morphology and phase structure of as-prepared surface-modified LaF3 nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The tribological properties of surface-modified LaF3 nanoparticles as additive of fluoro silicone oil were evaluated with a four-ball machine, and the morphology and elemental composition of worn steel surfaces were examined with a scanning electron microscope and an X-ray photoelectron spectroscope. Results show that 3-(heptafluoroisopropoxy)propyltriethoxysilane as the modifier is able to improve the dispersibility of LaF3 nanoparticles in fluoro silicone oil. Moreover, when the optimum concentration, 0.08 wt.% of fluorosilane surface-modified LaF3 is added into fluoro silicone oil, as-synthesized fluorosilane surface-modified LaF3 nanoparticles exhibit excellent anti-wear as additive in fluoro silicone oil. The wear scar diameter under the optimum concentration is always smaller than that under the lubrication of fluoro silicone oil alone. Especially, when the load is 500 N, 600 N and 700 N, the wear scar diameter is reduced by 17%, 43% and 42%, respectively. In addition, during the friction process, LaF3 nanoparticles are deposited on the rubbed steel surface to form LaF3 deposition layer which functions jointly with the boundary lubricating film thereby resulting in improved tribological properties.

  20. Visible and Mid-Infrared Supercontinuum Generation and Their Respective Application to Three-Dimensional Imaging and Stand-off Reflection Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kumar, Malay

    The thesis describes broadband supercontinuum (SC) generation in optical fibers for both the visible and mid-infrared regions of the spectrum, and their respective application to 3D imaging and stand-off reflection spectroscopy. Both SC sources leverage mature telecom technology, and are based on a common all-fiber integrated platform comprising a ˜1.55 mum distributed feedback seed laser diode amplified to high peak powers in two stages of cladding pumped Erbium or Erbium-Ytterbium fiber amplifiers. A visible SC extending from 0.45--1.20 mum with 0.74 W of time-averaged power is demonstrated using a two step process. The output of the Er-Yb power amplifier is frequency doubled to ˜0.78 mum using a periodically poled lithium niobate crystal, followed by non-linear spectral broadening in 2m of high nonlinearity photonic crystal fiber. Numerical simulations based on solving the generalized non-linear Schrodinger equation are also presented to verify the underlying SC generation mechanisms and predict further improvements. The above SC source is used in a Fourier domain line scan interferometer to measure the height and identify shape defects of ˜300 mum high solder balls in a ball grid array. The 3D imaging system has an axial resolution of ˜125 nm, transverse resolution of ˜15 mum, and an angular measurement range between 20 to 60 degrees depending on the sample surface roughness. The mid-infrared SC source is generated by pumping a 9m long ZrE 4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber to obtain a spectrum spanning 0.8--4.3 mum with 3.9 W time-averaged power. The output power is linearly scalable with pump power, but requires optimization of the critical splices and thermal management of the gain fiber and pump diodes to ensure stable high power operation. Finally, an application of the mid-IR SC is demonstrated by measuring the diffuse reflection spectra of solid samples at a stand-off distance of 5 m and 100 ms integration time. The samples can be distinguished using a correlation algorithm based on distinct spectral features in the reflection spectrum. Signal to noise ratio calculations show that the distance is limited by space constraints in our lab and can be extended to ˜150 m.

  1. Mechanisms for the Crystallization of ZBLAN

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin C.; Tucker, Dennis S.; Kaukler, William; Antar, Basil

    2003-01-01

    The objective of this ground based study is to test the hypothesis that shear thinning (the non-Newtonian response of viscosity to shear rate) is a viable mechanism to explain the observation of enhanced glass formation in numerous low-g experiments. In 1-g, fluid motion results from buoyancy forces and surface tension driven convection. This fluid flow will introduce shear in undercooled liquids in 1-g. In low-g it is known that fluid flows are greatly reduced so that the shear rate in fluids can be extremely low. It is believed that some fluids may have weak structure in the absence of flow. Very small shear rates could cause this structure to collapse in response to shear resulting in a lowering of the viscosity of the fluid. The hypothesis of this research is that: Shear thinning in undercooled liquids decreases the viscosity, increasing the rate of nucleation and crystallization of glass forming melts. Shear in the melt can be reduced in low-g, thus enhancing undercooling and glass formation. The viscosity of a model glass (lithium di-silicate, L2S) often used for crystallization studies has been measured at very low shear rates using a dynamic mechanical thermal analyzer. Our results are consistent with increasing viscosity with a lowering of shear rates. The viscosity of L2S may vary as much as an order of magnitude depending on the shear rate in the temperature region of maximum nucleation and crystal growth. Classical equations for nucleation and crystal growth rates, are inversely related to the viscosity and viscosity to the third power respectively. An order of magnitude variation in viscosity (with shear) at a given temperature would have dramatic effects on glass crystallization Crystallization studies with the heavy metal fluoride glass ZBLAN (ZrF2-BaF2-LaF3-AlF3-NaF) to examine the effect of shear on crystallization are being initiated. Samples are to be melted and quenched under quiescent conditions at different shear rates to determine the effect on crystallization. The results from this study are expected to advance the current scientific understanding of glass formation in low-g and glass crystallization under glass molding conditions and will improve the scientific understanding of technological processes such as fiber pulling, bulk amorphous alloys, and glass fabrication processes.

  2. The Effects of Gravity on the Crystallization Behavior of Heavy Metal Fluoride Glasses

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Smith, Guy A.

    2004-01-01

    Heavy metal fluoride glasses are used in such applications as fiber lasers and laser amplifiers. ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is one of the more commonly used heavy metal fluoride glasses. ZBLAN is an infrared transmitter and has a theoretical attenuation coefficient of 0.002 db/km. However, due to impurities and small crystallites this attenuation coefficient has not been achieved to date. ZBLAN is a fragile glass which can lead to rapid crystallization, if the glass is not cooled rapidly to below the glass transition temperature or if the glass is reheated near the crystallization temperature for any period of time. Studies carried on at Marshall Space Flight Center and the University of Alabama in Huntsville since 1993 have shown that heating ZBLAN glass at the crystallization temperature in reduced gravity results in a suppression of crystallization when compared to ZBLAN processed in unit gravity. These studies utilized NASA's KC-135 aircraft and the Conquest sounding rocket. In the first series of experiments, short lengths of ZBLAN fiber were heated to the crystallization temperature in reduced gravity on board the KC- 135 and the Conquest sounding rocket and compared with fibers heated in unit gravity. The fibers processed in reduced gravity showed no evidence of crystallization when studied with x-ray diffraction and scanning electron microscopy. However, the fibers processed in unit gravity were completely crystallized. Subsequent experiments included heating small pieces of ZBLAN glass at the crystallization temperature while viewing with a video camera to follow the crystallization phenomenon. In this experiment crystallization was observed in reduced gravity, however, it was suppressed when compared to heating in unit gravity. In the most recent experiment on board the KC-135, rapid thermal analysis of ZBLAN was performed. A mechanism to explain the observations has been proposed. This mechanism is based on shear thinning whereby, the glass undergoes a reduction in viscosity in the 10(exp 5) - 10(exp 7) poise range, allowing more rapid diffusion and thus crystallization. It is proposed that this mechanism is suppressed in reduced gravity. An experiment is presently being conducted to test this theory. With increased knowledge of ZBLAN behavior in reduced gravity, three low earth orbit tiber drawing facilities have been designed. One would be suitable for use on the International Space Station, another while aboard the Space Shuttle and the third system is a fully automated facility which would operate independently of the ISS or Shuttle in a free float mode. The primary benefits of free floating a facility in LEO includes a higher quality of microgravity and reduced safety concerns since it is not in a manned environment.

  3. Picosecond passively mode-locked mid-infrared fiber laser

    NASA Astrophysics Data System (ADS)

    Wei, C.; Zhu, X.; Norwood, R. A.; Kieu, K.; Peyghambarian, N.

    2013-02-01

    Mode-locked mid-infrared (mid-IR) fiber lasers are of increasing interest due to their many potential applications in spectroscopic sensors, infrared countermeasures, laser surgery, and high-efficiency pump sources for nonlinear wavelength convertors. Er3+-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber lasers, which can emit mid-IR light at 2.65-2.9 ?m through the transition from the upper energy level 4I11/2 to the lower laser level 4I13/2, have attracted much attention because of their broad emission range, high optical efficiency, and the ready availability of diode pump lasers at the two absorption peaks of Er3+ ions (975 nm and 976 nm). In recent years, significant progress on high power Er3+- doped ZBLAN fiber lasers has been achieved and over 20 watt cw output at 2.8 ?m has been demonstrated; however, there has been little progress on ultrafast mid-IR ZBLAN fiber lasers to date. We report a passively mode-locked Er3+- doped ZBLAN fiber laser in which a Fe2+:ZnSe crystal was used as the intracavity saturable absorber. Fe2+:ZnSe is an ideal material for mid-IR laser pulse generation because of its large saturable absorption cross-section and small saturation energy along with the excellent opto-mechanical (damage threshold ~2 J/cm2) and physical characteristics of the crystalline ZnSe host. A 1.6 m double-clad 8 mol% Er3+-doped ZBLAN fiber was used in our experiment. The fiber core has a diameter of 15 ?m and a numerical aperture (NA) of 0.1. The inner circular cladding has a diameter of 125 ?m and an NA of 0.5. Both continuous-wave and Q-switched mode-locking pulses at 2.8 ?m were obtained. Continuous-wave mode locking operation with a pulse duration of 19 ps and an average power of 51 mW were achieved when a collimated beam traversed the Fe2+:ZnSe crystal. When the cavity was modified to provide a focused beam at the Fe2+:ZnSe crystal, Q-switched mode-locked operation with a pulse duration of 60 ps and an average power of 4.6 mW was achieved. More powerful and narrower pulses are expected if the dispersion of the cavity can be properly managed.

  4. Single mode optical fiber based devices and systems for mid-infrared light generation, communication and metrology

    NASA Astrophysics Data System (ADS)

    Kulkarni, Ojas P.

    Fiber-optic systems and devices for broadband mid-infrared light generation, communication and optical metrology are developed in this thesis. Using the nonlinear properties of low mid-infrared loss ZrF4-BaF 2-LaF3-AlF3-NaF (ZBLAN) fiber, a mid-infrared supercontinuum (SC) laser based on a thulium-doped fiber amplifier (TDFA) with spectrum extending from ˜1.9-4.5 microm is demonstrated. A higher efficiency, power-scalable, all-fiber integrated mid-infrared light source is realized capable of generating ˜0.7 W time-average power in wavelengths beyond 3.8 microm. The novelty of the laser lies in its two-step spectral shifting architecture. First, amplified laser diode pulses at 1.55 microm are used to generate a SC extending beyond 2 microm in standard SMF using modulation-instability initiated pulse break-up. A TDFA stage is then used to amplify the ˜2 microm components in the standard SMF continuum. By subsequently coupling the amplified ˜2 microm pulses in to a ZBLAN fiber, an SC with up to ˜2.6 W average power, and ˜9% optical conversion efficiency from the power-amp pump to mid-IR output is demonstrated. The two-step methodology leads to extension in the long wavelength edge of the SC from 4.2 microm to ˜4.5 microm, compared to previously demonstrated systems and ˜2.5 times higher optical efficiency in generating wavelengths beyond 3.8 microm. Numerical simulations are also presented based on solving the generalized non-linear Schrodinger equation to verify and extend experimental results. A broadband surface-normal optical modulator for communication applications with operation demonstrated over 1200--2400 nm is also presented. The modulator uses free-carrier effect in GaAs and mode selectivity of SMF to generate up to ˜43% modulation depth with a maximum operating speed of ˜270 MHz. The broad wavelength range of operation of the modulator can potentially enable higher throughput wavelength-division multiplexed optical network architectures based on broadband light sources. Finally, an optical probe for detection of porosity defects in automotive parts is presented. The probe relies on the spatial coherence properties of SMF output to detect defects as small as ˜50 microm lateral dimensions in bores down to 5 mm diameter. The probe uses a novel two-directional scattering-based non-contact approach to detect and classify defects on surfaces, where human inspection is labor-intensive.

  5. Chromatic correction for a VIS-SWIR zoom lens using optical glasses

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Williams, Daniel J. L.; McCarthy, Peter; Visconti, Anthony J.; Bentley, Julie L.; Moore, Duncan T.

    2015-09-01

    With the advancement in sensors, hyperspectral imaging in short wave infrared (SWIR 0.9 ?m to 1.7 ?m) now has wide applications, including night vision, haze-penetrating imaging, etc. Most conventional optical glasses can be material candidates for designing in the SWIR as they transmit up to 2.2 ?m. However, since SWIR is in the middle of the glasses' major absorption wavebands in UV and IR, the flint glasses in SWIR are less dispersive than in the visible spectrum. As a result, the glass map in the SWIR is highly compressed, with crowns and flints all clustering together. Thus correcting for chromatic aberration is more challenging in the SWIR, since the Abbé number ratio of the same glass combination is reduced. Conventionally, fluorides, such as CaF2 and BaF2, are widely used in designing SWIR system due to their unique dispersion properties, even though they are notorious for poor manufacturability or even high toxicity. For lens elements in a zoom system, the ray bundle samples different sections of the each lens aperture as the lens zooms. This creates extra uncertainty in correcting chromatic aberrations. This paper focuses on using only commercially available optical glasses to color-correct a 3X dual-band zoom lens system in the VIS-SWIR. The design tools and techniques are detailed in terms of material selections to minimize the chromatic aberrations in such a large spectrum band and all zoom positions. Examples are discussed for designs with different aperture stop locations, which considerably affect the material choices.

  6. The effect of prolonged exposure to 750 C air on the tribological performance of PM212

    NASA Technical Reports Server (NTRS)

    Bemis, Kirk; Bogdanski, Michael S.; Dellacorte, Christopher; Sliney, Harold E.

    1994-01-01

    The effect of prolonged exposure to 750 C air on the tribological performance and dimensional stability of PM212, a high temperature, self-lubricating composite, is studied. PM212, by weight, contains 70 percent metal-bonded Cr3C2, 15 percent BaF2/CaF2 eutectic, and 15 percent silver. Rub blocks were fabricated from PM212 by cold isostatic pressing followed by sintering. Prior to tribo-testing, the rub blocks were exposed to 750 C air for periods ranging from 100 to 1000 hours. Then, the rub blocks were slid against nickel-based superalloy disks in a double-rub-block tribometer in air under a 66 N load at temperatures from 25 to 750 C with a sliding velocity of 0.36 m/s. Unexposed rub blocks were tested for baseline comparison. Friction coefficients ranged from 0.24 to 0.37 for the unexposed rub blocks and from 0.32 to 0.56 for the exposed ones. Wear for both the composite blocks and superalloy disks was typically in the moderate to low range of 10(exp -5) to 10(exp -6) mm(exp 3)/N-m. Friction and wear data were similar for the rub blocks exposed for 100, 500, and 1000 hours. Prolonged exposure to 750 C air increased friction and wear of the PM212 rub blocks at room temperature, but their triboperformance remained unaffected at higher temperatures, probably due to the formation of lubricious metal oxides. Dimensional stability of the composite was studied by exposing specimens of varying thicknesses for 500 hours in air at 750 C. Block thicknesses were found to increase with increased exposure time until steady state was reached after 100 hours of exposure, probably due to oxidation.

  7. New infrared detectors and solar cells

    NASA Technical Reports Server (NTRS)

    Sher, A.

    1979-01-01

    The inventions and published papers related to the project are listed. The research with thin films of LaF3 deposited on GaAs substrates is reported along with improvements in photocapacitative MIS infrared detectors.

  8. Insulators for Pb(1-x)Sn(x)Te

    NASA Technical Reports Server (NTRS)

    Tsuo, Y. H.; Sher, A.

    1981-01-01

    Thin films of LaF3 were e-gun and thermally deposited on several substrates. The e-gun deposited films are fluorine deficient, have high ionic conductivities that persist to 77 K, and high effective dielectric constants. The thermally deposited material tends to be closer to stoichiometric, and have higher effective breakdown field strengths. Thermally deposited LaF3 films with resistivities in excess of 10 to the 12th power ohms - cm were deposited on metal coated glass substrates. The LaF3 films were shown to adhere well to PbSnTe, surviving repeated cycles between room temperature and 77 K. The LaF3 films on GaAs were also studied.

  9. Variations of BaSnF4 fast ion conductor with the method of preparation and temperature

    NASA Astrophysics Data System (ADS)

    Dénès, Georges; Hantash, Jamil; Muntasar, Abdualhafeed; Oldfield, Philip; Bartlett, Alan

    2006-06-01

    Ionic conductors are solids that have a large number of defects and easy pathways that make it possible for ions to move over long distances in an electric field. In order to be mobile an ion must be small and have a low charge. The fluoride ion is the most mobile anion. The highest performance fluoride ion conductors contain divalent tin, and have a highly layered crystal structure related to the CaF2 fluorite type. BaSnF4 has the ?-PbSnF4 structure, which is a ?2/2 × ?2/2 × 2 superstructure of the fluorite type, where the tetragonal unit-cell and the value of the a and b parameters being equal to half the diagonals of the (a,b) face of fluorite are due to the loss of the F Bravais lattice, and the Sn Sn Ba Ba order along the c parameter is at the origin of the doubling of the c parameter. The BaSnF4 material was prepared first by Dénès et al. (C. R. Acad. Paris C, 280: 831, 1975), and its superionic properties were characterized by Dénès et al. (Solid State Ion., 13: 213, 1984). It was found to have a conductivity three orders of magnitude higher than that of BaF2, with an ionic conduction rate ? i > 0.99. No BaSnF4 was obtained by the aqueous medium, when aqueous solutions of SnF2 and Ba(NO3)2 are mixed together; BaSn2F6 was obtained instead. In a new development of this work, BaSnF4 has been obtained by the wet method for the first time. X-ray powder diffraction showed that the BaSnF4 phase obtained by the wet method varies substantially from one sample to another: (a) signification variations of the c parameter of the tetragonal unit-cell reveals that the interlayer distance is sensitive to the leaching conditions, possibly because some of the leached ions remain in the interlayer spacing; (b) large variations of the crystallite dimensions and, as a result of the two-dimensionality of the structure, a strong crystallite dimension anisotropy are observed, with d? < d?, where d? and d? are the crystallite dimensions parallel to the four-fold main axis, and perpendicular to it, respectively, showing that the layers are very thin and the interlayer interactions are very weak. Variable temperature Mössbauer spectroscopy showed an unusual large variation of the quadrupole splitting with temperature. A tentative explanation based on unusually large bond angles has been proposed.

  10. Variations of BaSnF4 fast ion conductor with the method of preparation and temperature

    NASA Astrophysics Data System (ADS)

    Dénès, Georges; Hantash, Jamil; Muntasar, Abdualhafeed; Oldfield, Philip; Bartlett, Alan

    Ionic conductors are solids that have a large number of defects and easy pathways that make it possible for ions to move over long distances in an electric field. In order to be mobile an ion must be small and have a low charge. The fluoride ion is the most mobile anion. The highest performance fluoride ion conductors contain divalent tin, and have a highly layered crystal structure related to the CaF2 fluorite type. BaSnF4 has the ?-PbSnF4 structure, which is a ?2?2 × ?2?2 × ?2 superstructure of the fluorite type, where the tetragonal unit-cell and the value of the a and b parameters being equal to half the diagonals of the (a, b) face of fluorite are due to the loss of the F Bravais lattice, and the Sn Sn Ba Ba order along the c parameter is at the origin of the doubling of the c parameter. The BaSnF4 material was prepared first by Dénès et al. (C. R. Acad. Paris C, 280: 831, 1975), and its superionic properties were characterized by Dénès et al. (Solid State Ion., 13: 213, 1984). It was found to have a conductivity three orders of magnitude higher than that of BaF2, with an ionic conduction rate ?i>0.99. No BaSnF4 was obtained by the aqueous medium, when aqueous solutions of SnF2 and Ba(NO3)2 are mixed together; BaSn2F6 was obtained instead. In a new development of this work, BaSnF4 has been obtained by the wet method for the first time. X-ray powder diffraction showed that the BaSnF4 phase obtained by the wet method varies substantially from one sample to another: (a) signification variations of the c parameter of the tetragonal unit-cell reveals that the interlayer distance is sensitive to the leaching conditions, possibly because some of the leached ions remain in the interlayer spacing; (b) large variations of the crystallite dimensions and, as a result of the two-dimensionality of the structure, a strong crystallite dimension anisotropy are observed, with d?d?, where d? and d? are the crystallite dimensions parallel to the four-fold main axis, and perpendicular to it, respectively, showing that the layers are very thin and the interlayer interactions are very weak. Variable temperature Mossbauer spectroscopy showed an unusual large variation of the quadrupole splitting with temperature. A tentative explanation based on unusually large bond angles has been proposed.

  11. [Study on the vacuum ultraviolet transmittance of barium fluoride crystals at different temperature].

    PubMed

    Peng, Ru-Yi; Fu, Li-Ping; Tao, Ye

    2014-03-01

    Two VUV-grade BaF2 windows with 0.5 mm-thick and 1 mm-thick respectively were selected to study the transmittance variety with the temperature. The results show that the cutoff wavelength of BaF2 crystals will shift towards the long wave with the increase in temperature. In a certain temperature range, BaF2 crystals can depress 130.4 nm radiation well, and also has a high transmittance at 135.6 nm. Compared with the reported method in which SrF2 crystals can be applied to suppress 130.4 nm stray light by heating, BaF2 crystal can inhibit the 130. 4 nm emission line completely, and thus reduce the power consumption of the device at the same time. This indicates that BaF2 crystals can play an important role in the ionosphere optical remote sensing detection. PMID:25208398

  12. Studies of radiation defects in cerium, europium and terbium activated oxyfluoride glasses and glass ceramics

    NASA Astrophysics Data System (ADS)

    Elsts, E.; Rogulis, U.; Bulindzs, K.; Smits, K.; Zolotarjovs, A.; Trinkler, L.; Kundzins, K.

    2015-03-01

    Terbium, cerium and europium activated oxyfluoride glasses and glass ceramics have been studied by thermally stimulated luminescence (TSL) and optical absorption techniques after the X-ray irradiation. A creation of colour centres in oxyfluoride glass matrix and TSL peaks depending on the activator type were observed. LaF3 and rare earth activators were analysed by SEM-EDS.

  13. Electrochimica Acta 46 (2000) 271277 Mechanistic investigation on an all solid state fluorine

    E-print Network

    Moritz, Werner

    2000-01-01

    Electrochimica Acta 46 (2000) 271­277 Mechanistic investigation on an all solid state fluorine A semiconductor field effect structure Si/SiO2/Si3N4/LaF3/Pt can be used for the detection of fluorine in air fluorine concentrations, respectively. Combining these sensors concentrations between 0.01 and 1000 ppm can

  14. Nanosecond Range Heating and Temperature Measurement on Thin Layers Experiment and Simulation

    E-print Network

    Moritz, Werner

    Nanosecond Range Heating and Temperature Measurement on Thin Layers Experiment and Simulation W for sensitivity measurements, heating resistance and temperature sensor. Taking advantage of using the gate electrode for heating only the sensitive two layer system LaF3/Pt (thickness only 300 nm) has to be at high

  15. Microstructures and properties of superconducting Y-ErBaCuO thin films obtained from disordered Y-ErBaF2Cu films

    NASA Technical Reports Server (NTRS)

    Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Merlo, V.; Messi, R.; Paoluzi, L.; Scopa, L.

    1991-01-01

    The preparation procedure used to obtain superconducting thin films by radio frequency magnetron sputtering of a single mosaic target is described in detail. The single mosaic target is composed of (Y-Er), BaF2, and Cu.

  16. Microstructures and properties of superconducting Y-Er-BaCu-O thin films obtained from disordered Y-Er-BaF2-Cu films

    NASA Technical Reports Server (NTRS)

    Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Messi, R.; Paoluzi, L.; Scopa, L.; Tripodi, P.

    1990-01-01

    Since the first reports on superconducting thin films obtained by evaporating BaF2, Cu and Y(sup 1), or Yb or Er(sup 2), several others have followed. All these reports describe thin films prepared by means of molecular beam cells or electron guns. Researchers show that films with similar properties can be obtained by radio frequency sputtering of a single mosaic target composed by Y-Er, BaF2 and Cu. Process steps are described.

  17. October 15, 2002 / Vol. 27, No. 20 / OPTICS LETTERS 1845 Fluoride semiconductor saturable-absorber mirror for

    E-print Network

    Keller, Ursula

    and at a growth rate of 0.2 mm h. AlGaAs layers with 77% aluminum concentration and the GaAs absorber layer were of thermal expansion of CaF2 is 19.2 3 1026 K21 , i.e., three times higher than that of GaAs. High thermal the first ultrabroadband monolithically grown AlGaAs CaF2 semi- conductor saturable-absorber mirror (SESAM

  18. Role of ultrathin metal fluoride layer in organic photovoltaic cells: mechanism of efficiency and lifetime enhancement.

    PubMed

    Lim, Kyung-Geun; Choi, Mi-Ri; Kim, Ji-Hoon; Kim, Dong Hun; Jung, Gwan Ho; Park, Yongsup; Lee, Jong-Lam; Lee, Tae-Woo

    2014-04-01

    Although rapid progress has been made recently in bulk heterojunction organic solar cells, systematic studies on an ultrathin interfacial layer at the electron extraction contact have not been conducted in detail, which is important to improve both the device efficiency and the lifetime. We find that an ultrathin BaF2 layer at the electron extraction contact strongly influences the open-circuit voltage (Voc ) as the nanomorphology evolves with increasing BaF2 thickness. A vacuum-deposited ultrathin BaF2 layer grows by island growth, so BaF2 layers with a nominal thickness less than that of single-coverage layer (?3 nm) partially cover the polymeric photoactive layer. As the nominal thickness of the BaF2 layer increased to that of a single-coverage layer, the Voc and power conversion efficiency (PCE) of the organic photovoltaic cells (OPVs) increased but the short-circuit current remained almost constant. The fill factor and the PCE decreased abruptly as the thickness of the BaF2 layer exceeded that of a single-coverage layer, which was ascribed to the insulating nature of BaF2 . We find the major cause of the increased Voc observed in these devices is the lowered work function of the cathode caused by the reaction and release of Ba from thin BaF2 films upon deposition of Al. The OPV device with the BaF2 layer showed a slightly improved maximum PCE (4.0 %) and a greatly (approximately nine times) increased device half-life under continuous simulated solar irradiation at 100 mW cm(-2) as compared with the OPV without an interfacial layer (PCE=2.1 %). We found that the photodegradation of the photoactive layer was not a major cause of the OPV degradation. The hugely improved lifetime with cathode interface modification suggests a significant role of the cathode interfacial layer that can help to prolong device lifetimes. PMID:24616332

  19. Synthesis and characterization of lanthanide based nanomaterials for radiation detection and biomedical applications

    NASA Astrophysics Data System (ADS)

    Yao, Mingzhen

    2011-12-01

    Lanthanide based nanomaterials have shown a great potential in various areas such as luminescence imaging, luminescent labels, and detection of cellular functions. Due to the f-f transitions of the metal ion, luminescence of lanthanide ions is characterized by sharp and narrow emissions. In this dissertation lanthanide based nanoparticles such as Ce3+, Eu3+ and other lanthanide ions doped LaF3 were synthesized, their characterization, encapsulation and embedding into hybrid matrix were investigated and some of their biomedical and radiological applications were studied. DMSO is a common solvent which has been used widely for biological applications. LaF3:Ce nanoparticles were synthesized in DMSO and it was found that their fluorescent emission originates from the metal-to-ligand charge-transfer excited states. After conjugation with PpIX and then encapsulation within PLGA, the particles show efficient uptake by cancer cells and great cytotoxicity, which is promising for applications in cancer treatments. However, the emission of Eu3+ in DMSO is totally different from LaF3:Ce, very strong characteristic luminescence is observed but no emissions from metal-to-ligand charge-transfer excited states as observed in LaF3:Ce in DMSO. Besides, it is very interesting to see that the coupling of Eu 3+ with O-H oscillations after water was introduced has an opposite effect on emission peaks at 617 nm and its shoulder peak at 613 nm. As a result, the intensity ratio of these two emissions has a nearly perfect linear dependence on increasing water concentration in Eu-DMSO, which provides a very convenient and valuable method for water determination in DMSO. Ce3+ has been well known as an emitter for radiation detection due to its very short decay lifetime. However, its emission range limited the environment in which the detection system works. Whereas, Quantum dots have high luminescence quantum efficiency but their low stopping power results in very weak scintillation luminescence. Nanocompounds formed with CdTe quantum dots and LaF3:Ce nanoparticles optimize both stopping power and scintillation efficiency based on energy transfer from LaF3:Ce to CdTe. Hybrid matrix materials such as ORMOSIL have superior mechanical properties and a better processability than pure molecular material which could be used as carrier of radiation material. Moreover, embedding a lanthanide complex in a hybrid matrix enhances its thermal stability and luminescence output. LaF3:Ce doped ORMOSIL was synthesized by using two different LaF3:Ce, the nanoparticle doping concentration can reach up to 15.66% while its transparency and luminescent properties were maintained. These materials are very promising for radiation detection.

  20. Some metal-graphite and metal-ceramic composites for use as high energy brake lining materials

    NASA Technical Reports Server (NTRS)

    Bill, R. C.

    1974-01-01

    Materials were studied as candidates for development as potential new aircraft brake lining materials. These families were (1) copper-graphite composites; (2) nickel-graphite composites; (3) copper - rare-earth-oxide (gadolinium oxide (Gd2O3) or lanthanum oxide (La2O3)) composites and copper - rare-earth-oxide (La2O3) - rare-earth-fluoride (lanthanum fluoride (LaF3)) composites; (4) nickel - rare-earth-oxide composites and nickel - rare-earth-oxide - rare-earth-fluoride composites. For comparison purposes, a currently used metal-ceramic composite was also studied. Results showed that the nickel-Gd2O3 and nickel-La2O3-LaF3 composites were comparable or superior in friction and wear performance to the currently used composite and therefore deserve to be considered for further development.

  1. Demonstrating the possibility of implementing the Toffoli gate in crystals doped by rare-earth metal ions

    NASA Astrophysics Data System (ADS)

    Akhmedzhanov, R. A.; Gushchin, L. A.; Zelensky, I. V.; Malakyan, Yu. P.; Sobgaida, D. A.

    2015-07-01

    A scheme for the implementation of the Toffoli gate in inorganic crystals doped by rare-earth metal ions is proposed. A numerical analysis of the factors affecting the fidelity of the Toffoli gate implementation is carried out, and estimates for the available experimental parameters are obtained. A demonstration experiment is set up in which behavior similar to the Toffoli gate is shown for ensembles of Pr3+ ions doped into a LaF3 crystal.

  2. Growth of La[sub 0.8]Sr[sub 0.2]CrO[sub 3] thin films from a fluoride sputtering process.

    SciTech Connect

    Mukundan, R.; Brown, D. R.; Garzon, F. H.; Brosha, E. L.

    2001-01-01

    Dense, thin films of La0.8Sr0.2CrO3 were prepared on fully stabilized yttria-stabilized zirconia, sapphire, and polycrystalline substrates using 90 off axis magnetron sputtering from a stoichiometric LaF3/SrF2/Cr composite target in an Ar atmosphere. Dense, intimately mixed films of LaF3/SrF2/Cr were grown at both ambient sputter temperature and at 400 C with the films deposited at higher temperature exhibiting better adhesion to the substrate. Sputtering rates were typically in the range of 1500 to 2000 Angstroms/hr. Subsequent anneal at 800 C in a H2O/Ar atmosphere converted the films to single-phase La0.8Sr0.2CrO3. The room-temperature deposition of LaF3/SrF2/Cr composite, precursor film permitted the patterning of electrodes for high-temperature electrochemical HC/CO gas sensors that operate using a mixed potential response mechanism. Thin films grown on polycrystalline Al2O3 were used to obtain four-point electronic conductivity measurements.

  3. Cascaded Brillouin lasing in monolithic barium fluoride whispering gallery mode resonators

    E-print Network

    Lin, Guoping; Saleh, Khaldoun; Martinenghi, Romain; Beugnot, Jean-Charles; Sylvestre, Thibaut; Chembo, Yanne K

    2015-01-01

    We report the observation of stimulated Brillouin scattering and lasing at 1550~nm in barium fluoride (BaF$_2$) crystal. Brillouin lasing was achieved with ultra-high quality ($Q$) factor monolithic whispering gallery mode (WGM) mm-size disk resonators. Overmoded resonators were specifically used to provide cavity resonances for both the pump and all Brillouin Stokes waves. Single and multiple Brillouin Stokes radiations with frequency shift ranging from $8.2$ GHz up to $49$ GHz have been generated through cascaded Brillouin lasing. BaF$_2$ resonator-based Brillouin lasing can find potential applications for high-coherence lasers and microwave photonics.

  4. Structure of interfacial water molecules under externally-applied electric field studied by vibrational sum -frequency generation

    NASA Astrophysics Data System (ADS)

    Kondo, Takahiro; Ito, Tsuyohito

    2013-09-01

    We report effects of electric field on the structure of water molecules in the CaF2/water interfacial region by vibrational sum -frequency generation (VSFG) spectroscopy. VSFG gives molecular level information for several layers of molecules at the interface. At the CaF2/water interface with low pH, the CaF2 surface is known to be positively charged and form an electric double layer (EDL). Without externally applied electric field, the water molecules are aligned along the electric field inside the EDL (EF-EDL), with facing oxygen (oxygen-up) to CaF2 surface. According to SFG peak at ~3150 cm-1 attributed to vibration of highly-ordered water molecules, the orientation of water molecules becomes higher as the external electric field is applied to the same direction of the EF-EDL. In contrast, with the applied field in opposite direction of the EF-EDL, the SFG intensity becomes weak and almost zero. When the applied field is further increased, the SFG intensity becomes stronger with the applied field increasing. This increase suggests that the water molecules can be realigned (oxygen -down to CaF2 surface) by externally-applied electric field. Details on the experimental results and discussions will be presented at the meeting.

  5. SR-FTIR Study of Bacteria-Water Interactions: Acid-base Titration and Silification Experiments

    E-print Network

    SR-FTIR Study of Bacteria-Water Interactions: Acid-base Titration and Silification Experiments, we use synchrotron radiation-based FTIR to investigate the chemistry of bacterial surfaces with acid/base through fluid cell with BaF2 and ZnSe windows separated by a 6 um mylar spacer. Acid-base titration and Si

  6. Reel-to-Reel Characterization of Time-Based Phase Evolution in YBCO Coated Conductors

    E-print Network

    Reel-to-Reel Characterization of Time-Based Phase Evolution in YBCO Coated Conductors: The BaF2 and Technology #12;These activities are in support of the Coated Conductor Development Roadmap · Recommended-length coated conductor (CC) fabrication. Approach · Process a length of YBCO CC that encompasses a wide range

  7. Mechanisms for Species-Selective Oriented Crystal Growth at Organic Templates

    SciTech Connect

    Kewalramani,S.; Kim, K.; Evmenenko, G.; Zschack, P.; Karapetrova, E.; Bai, J.; Dutta, P.

    2007-01-01

    Langmuir monolayers floating on supersaturated aqueous subphases can act as templates for the growth of oriented inorganic films--a 'bioinspired' nucleation process. We have performed in situ grazing incidence x-ray diffraction studies of the selective nucleation of BaClF and BaF2 under fatty acid monolayers. The arrangement of the fatty acid headgroups, the monolayer charge, and ion-specific effects all play important roles in selecting the inorganic species. When the monolayer is in a neutral state, both BaClF and BaF2 nucleate at the interface and are well aligned, but when the monolayer headgroup is deprotonated, only oriented BaF2 grows at the interface. We also observe an enhanced alignment of BaF2 crystals during growth from highly supersaturated solutions, presumably due to reorganization of preformed crystals at the organic template. These results show that a delicate interplay between multiple factors governs the oriented growth of inorganic films at organic templates.

  8. Rare earths in lead-free oxyfluoride germanate glasses

    NASA Astrophysics Data System (ADS)

    Pisarski, Wojciech A.; Pisarska, Joanna; Dorosz, Dominik; Dorosz, Jan

    2015-01-01

    Spectroscopic properties of rare earths in lead-free oxyfluoride germanate glasses were studied. The absorption and luminescence spectra of Eu3+, Pr3+ and Er3+ ions were examined as a function of BaF2 concentration and several spectroscopic parameters for rare earths were determined. The ratio of integrated luminescence intensity of the 5D0 ? 7F2 transition to that of the 5D0 ? 7F1 transition of Eu3+ decrease significantly with increasing BaF2 content. The absorption (Er3+) and emission (Pr3+) 'hypersensitive transitions' of rare earths are shifted in direction to shorter wavelengths with increasing BaF2 content in glass composition. Emission spectra and their decays corresponding to the main 4I13/2 ? 4I15/2 laser transition of Er3+ were also analyzed. Quite long-lived NIR luminescence of Er3+ is observed for lead-free glass samples with low BaF2 concentration.

  9. Recent Research with the Detector for Advanced Neutron Capture Experiments (dance) at the LOS Alamos Neutron Science Center

    NASA Astrophysics Data System (ADS)

    Ullmann, J. L.

    2014-09-01

    The DANCE detector at Los Alamos is a 160 element, nearly 4? BaF2 detector array designed to make measurements of neutron capture on rare or radioactive nuclides. It has also been used to make measurements of gamma-ray multiplicity following capture and gamma-ray output from fission. Several examples of measurements are briefly discussed.

  10. Standardized cell samples for midIR technology development

    NASA Astrophysics Data System (ADS)

    Kastl, Lena; Rommel, Christina E.; Kemper, Björn; Schnekenburger, Jürgen

    2015-03-01

    The application of midIR spectroscopy towards human cell and tissue samples is impaired by the need for technical solutions and lacking sample standards for technology development. We here present the standardization of stable test samples for the continuous development and testing of novel optical system components. We have selected cell lines representing the major cellular skin constituents keratinocytes and fibroblasts (NIH-3T3, HaCaT). In addition, two skin cancer cell types (A-375 and SK-MEL-28 cells) were analyzed. Cells were seeded on CaF2 substrates and measured dried and under aqueous medium as well as fixated and unfixated. Several independent cell preparations were analyzed with an FTIR spectrometer in the wave number range from 1000 - 4000 cm-1. The obtained data demonstrate that fixed and dehydrated cells on CaF2 can be stored in pure ethanol for several weeks without significant losses in quality of the spectral properties. The established protocol of cell seeding on CaF2 substrates, chemical fixation, dehydration, storage under ethanol and air-drying is suitable for the production of reliable midIR standards. The retrieved spectra demonstrate that fixed cells on CaF2 can be prepared reproducibly; with stable midIR spectral properties over several weeks and properties mimicking reliable unfixed cells. Moreover, the fixated samples on CaF2 show clear differences in the cell type specific spectra that can be identified by principle component analysis. In summary, the standardized cell culture samples on CaF2 substrates are suitable for the development of a midIR device and the optimization of the specific midIR spectra.

  11. Effect of VUV F2 laser irradiation on fluoride crystal

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Yoshizo; Narazaki, Aiko; Sato, Tadatake; Niino, Hiroyuki

    2003-07-01

    The early stage of optical damae caused by F2 laser irradiation on the wide bandgap fluoride crystal, CaF2, is investigated and compared with the case of ArF laser irradiation. Besides a blue emission band due to self-trapped exciton, sharp emission lines appear and grow at a fluence of about 2 J cm-2, showing the initiation of the optical damage and growth of plume from the F2-laser-irradiated surface of CaF2. There exist cracks and melted structures on the laser-damaged surface, which are caused by thermal stress and vaporization due to laser absorption and following local heating.

  12. Quantitative structure-property relationships of potentially bioactive fluoro phospho-silicate glasses.

    PubMed

    Lusvardi, G; Malavasi, G; Tarsitano, F; Menabue, L; Menziani, M C; Pedone, A

    2009-07-30

    In this work, the glass transition temperature and chemical durability of bioactive phospho-silicate glasses were experimentally determined and correlated to the structural descriptor Fnet derived from classical molecular dynamics simulations. The replacement of CaF2 for Na2O in the parent glass 45S5 enhances both chemical durability and density, while the replacement of CaF2 for CaO lowers chemical durability. The proposed descriptor, Fnet, provides satisfactorily correlations with glass transition temperature and chemical durability over a wide range of compositions. PMID:19572677

  13. Skylab ultraviolet stellar astronomy experiment S019

    NASA Technical Reports Server (NTRS)

    Ocallaghan, F. G.; Henize, K. G.; Wray, J. D.

    1977-01-01

    An objective-prism stellar spectrograph of 15-cm aperture was flown on all three Skylab missions. The wavelength region from 1300 A to 5000 A was covered by a special optical system containing a combination of reflecting telescope optics, a CaF2 objective prism, and an achromatized field-corrector lens system of CaF2 and LiF. Observations of 188 star fields, each covering 4.0 x 5.0 deg of arc, were conducted at the Skylab antisolar airlock with the aid of an articulated mirror system which allowed acquisition within a 30 by 360 deg band of the sky.

  14. Optimal moderator materials at various proton energies considering photon dose rate after irradiation for an accelerator-driven (9)Be(p, n) boron neutron capture therapy neutron source.

    PubMed

    Hashimoto, Y; Hiraga, F; Kiyanagi, Y

    2015-12-01

    We evaluated the accelerator beam power and the neutron-induced radioactivity of (9)Be(p, n) boron neutron capture therapy (BNCT) neutron sources having a MgF2, CaF2, or AlF3 moderator and driven by protons with energy from 8MeV to 30MeV. The optimal moderator materials were found to be MgF2 for proton energies less than 10MeV because of lower required accelerator beam power and CaF2 for higher proton energies because of lower photon dose rate at the treatment position after neutron irradiation. PMID:26272165

  15. Verification of threshold activation detection (TAD) technique in prompt fission neutron detection using scintillators containing 19F

    NASA Astrophysics Data System (ADS)

    Sibczynski, P.; Kownacki, J.; Moszy?ski, M.; Iwanowska-Hanke, J.; Syntfeld-Ka?uch, A.; Gójska, A.; Gierlik, M.; Ka?mierczak, ?.; Jakubowska, E.; K?dzierski, G.; Kujawi?ski, ?.; Wojnarowicz, J.; Carrel, F.; Ledieu, M.; Lainé, F.

    2015-09-01

    In the present study ? 5''× 3'' and ? 2''× 2'' EJ-313 liquid fluorocarbon as well as ? 2'' × 3'' BaF2 scintillators were exposed to neutrons from a 252Cf neutron source and a Sodern Genie 16GT deuterium-tritium (D+T) neutron generator. The scintillators responses to ?- particles with maximum endpoint energy of 10.4 MeV from the n+19F reactions were studied. Response of a ? 5'' × 3'' BC-408 plastic scintillator was also studied as a reference. The ?- particles are the products of interaction of fast neutrons with 19F which is a component of the EJ-313 and BaF2 scintillators. The method of fast neutron detection via fluorine activation is already known as Threshold Activation Detection (TAD) and was proposed for photofission prompt neutron detection from fissionable and Special Nuclear Materials (SNM) in the field of Homeland Security and Border Monitoring. Measurements of the number of counts between 6.0 and 10.5 MeV with a 252Cf source showed that the relative neutron detection efficiency ratio, defined as epsilonBaF2 / epsilonEJ-313-5'', is 32.0% ± 2.3% and 44.6% ± 3.4% for front-on and side-on orientation of the BaF2, respectively. Moreover, the ? 5'' EJ-313 and side-on oriented BaF2 were also exposed to neutrons from the D+T neutron generator, and the relative efficiency epsilonBaF2 / epsilonEJ-313-5'' was estimated to be 39.3%. Measurements of prompt photofission neutrons with the BaF2 detector by means of data acquisition after irradiation (out-of-beam) of nuclear material and between the beam pulses (beam-off) techniques were also conducted on the 9 MeV LINAC of the SAPHIR facility.

  16. Locally increased mortality of gamma-irradiated cells in presence of lanthanide-halide nanoparticles

    NASA Astrophysics Data System (ADS)

    Withers, Nathan J.; Glazener, Natasha N.; Plumley, John B.; Akins, Brian A.; Rivera, Antonio C.; Cook, Nathaniel C.; Smolyakov, Gennady A.; Timmins, Graham S.; Osi?ski, Marek

    2011-03-01

    Cerium-doped lanthanum fluoride colloidal nanocrystals (NCs) offer a way to improve radiation therapy through the enhanced absorption of high-energy photons. The use of Monte Carlo simulation allows the direct calculation of the macroscopic dose enhancement factor (MDEF), a figure of merit for NC-enhanced radiation therapy. Our simulations of brachytherapy using an Ir-192 source agree with previous work on the subject for gold NCs and show effectiveness of LaF3:10%Ce NCs to be approximately 50% that of gold. Polyethylene-glycol-capped LaF3:10%Ce NCs were synthesized, isolated, suspended in phosphate buffered saline (PBS), and characterized with transmission electron microscopy, dynamic light scattering, photoluminescence spectroscopy, and absorption spectroscopy. LaF3:10%Ce NCs were used in radiation dose enhancement experiments that involved an incoming 662 keV gamma flux from dual Cs-137 sources to test the mortality of Saccharomyces cerevisiae. At a small loading of 1.8 mg NC/g of PBS, the experiment did not produce a measurable increased mortality. To understand the results, additional Monte Carlo simulations revealed that the photon energy of 662 keV gamma rays is far from optimal, providing only a 4% increase in dose for a concentration of 18 mg of NCs / g of PBS. Further simulations showed that the optimal photon energy for this technique is 60 keV, tripling the absorbed dose for a concentration of 18 mg of NCs / g of PBS.

  17. Development of a large area gas photomultiplier with GEM/$?$PIC

    E-print Network

    H. Sekiya

    2008-10-06

    We are developing a new photon detector with micro pattern gaseous detectors. A semitransparent CsI photocathode is combined with 10cm$\\times$10cm GEM/$\\mu$PIC for the first prototype which is aimed for the large liquid Xe detectors. Using Ar+C$_2$H$_6$ (10%) gas, we achieved the gas gain of $10^5$ which is enough to detect single photoelectron. We, then, irradiated UV photons from a newly developed solid scintillator, LaF$_3$(Nd), to the detector and successfully detected single photoelectron.

  18. Nanostructured LaF{sub 3}:Ce Quantum Dot Nuclear Radiation Detector

    SciTech Connect

    Guss, P., Guise, R., Reed, M., Mukhopadhyay, S., Yuan, D.

    2010-11-01

    Many radioactive isotopes have low energy X-rays and high energy gamma rays of interest for detection. The goal of the work presented was to demonstrate the possibility of measuring both low-energy X-rays and relatively high-energy gamma rays simultaneously using the nano-structured lanthanum bromide, lanthanum fluoride, or cerium bromide. The key accomplishments of the project was the building and acquisition of the LaF3:Ce nanocomposite detectors. Nanocomposite detectors are sensitive to {gamma}’s as well as n’s and X-rays.

  19. Simultaneous determination of tantalum and hafnium in silicates by neutron activation analysis

    USGS Publications Warehouse

    Greenland, L.P.

    1968-01-01

    A neutron activation procedure suitable for the routine determination of tantalum and hafnium in silicates is described. The irradiated sample is fused with sodium peroxide and leached, and the insoluble hydroxides are dissolved in dilute hydrofluoric acid-hydrochloric acid. After LaF3 and AgCl scavenges, tantalum and hafnium are separated by anion exchange. Tantalum is obtained radiochemically pure; 233Pa and 95Zr contaminants in the hafnium fraction are resolved by ??-ray spectrometry. The chemical yield of the procedure is detemined after counting by re-irradiation. Values for the 8 U.S. Geological Survey standard rocks are reported. ?? 1968.

  20. The influence of restricted geometry of diamagnetic nanoporous media on 3He relaxation

    NASA Astrophysics Data System (ADS)

    Alakshin, E. M.; Gazizulin, R. R.; Zakharov, M. Yu.; Klochkov, A. V.; Morozov, E. V.; Salikhov, T. M.; Safin, T. R.; Safiullin, K. R.; Tagirov, M. S.; Shabanova, O. B.

    2015-01-01

    This is an experimental study of the spin kinetics of 3He in contact with diamagnetic samples of inverse opals SiO2, and LaF3 nanopowder. It is demonstrated that the nuclear magnetic relaxation of the absorbed 3He occurs due to the modulation of dipole-dipole interaction by the quantum motion in the two-dimensional film. It is found that the relaxation of liquid 3He occurs through a spin diffusion to the absorption layer, and that the restricted geometry of diamagnetic nanoporous media has an influence on the 3He relaxation.

  1. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2003-01-01

    The United States had a small quantity of fluorspar production from one mine in Utah during 2002. Most of the fluorspar consumed in the United States continued to come from imports or material purchased from the National Defense Stockpile (NDS). In addition, a small amount of synthetic fluorspar (CaF2) was produced from industrial waste streams.

  2. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2002-01-01

    In 2001, one mine in Utah produced a small quantity of fluorspar. The majority of fluorspar consumed in the United States continued to come from imports or material purchased from the US National Defense Stockpile (NDS). In addition, a small amount of synthetic fluorspar (CaF2) was produced from industrial waste streams.

  3. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2012-01-01

    World fluorspar demand continued to show signs of recovery from 2008-2009 recession. In 2011, nearly all fluorspar (CaF2) consumed in the United States was imported. Hastie Mining and Trucking Co. produced some fluorspar as a byproduct from its limestone quarry operations in Illinois. In addition, a small amount of usable synthetic fluorspar was produced from industrial waste streams.

  4. Negligible Sample Heating from Synchrotron Infrared Beam Michael C. Martina

    E-print Network

    nitrogen cooled MCT-A detector were used and data was collected in reflection geometry covering the 800 dilution of the hydrated DPPC dispersion was placed on a gold-coated piece of glass, and a CaF2 window window on gold but without the DPPC present. Figure 1 shows the measured infrared spectrum

  5. Visible electroluminescence from Eu:CaF2 layers grown by molecular beam epitaxy on p-Si ,,100...

    E-print Network

    McCann, Patrick

    of the photoluminescence PL from the Eu2 ions. This work showed that high concentrations of rare earth ions can be incorporated into MBE-grown CaF2, most prob- ably because low MBE growth temperatures inhibit rare earth ion, with higher doped samples showing a more pronounced long wavelength tail. Although both metal and indium

  6. Non-local heat transport in Alcator C-Mod ohmic L-mode plasmas

    E-print Network

    Gao, Chi

    Non-local heat transport experiments were performed in Alcator C-Mod ohmic L-mode plasmas by inducing edge cooling with laser blow-off impurity (CaF2) injection. The non-local effect, a cooling of the edge electron temperature ...

  7. The mechanical properties of fluoride salts at elevated temperatures. [candidate thermal energy storage materials for solar dynamic systems

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Whittenberger, J. D.

    1989-01-01

    The deformation behavior of CaF2 and LiF single crystals compressed in the 111 and the 100 line directions, respectively, are compared with the mechanical properties of polycrystalline LiF-22 (mol pct) CaF2 eutectic mixture in the temperature range 300 to 1275 K for strain rates varying between 7 x 10 to the -7th and 0.2/s. The true stress-strain curves for the single crystals were found to exhibit three stages in an intermediate range of temperatures and strain rates, whereas those for the eutectic showed negative work-hardening rates after a maximum stress. The true stress-strain rate data for CaF2 and LiF-22 CaF2 could be represented by a power-law relation with the strain rate sensitivities lying between 0.05 and 0.2 for both materials. A similar relation was found to be unsatisfactory in the case of LiF.

  8. Dissociative Binding of Carboxylic Acid Ligand on Nanoceria Surface in Aqueous Solution: A Joint in Situ Spectroscopic Characterization and First-Principles Study

    SciTech Connect

    Lu, Zhou; Karakoti, Ajay S.; Velarde Ruiz Esparza, Luis A.; Wang, Weina; Yang, Ping; Thevuthasan, Suntharampillai; Wang, Hongfei

    2013-11-21

    Carboxylic acid is a common ligand anchoring group to functionalize nanoparticle surfaces. Its binding structures and mechanisms as a function of the oxidation states of metal oxide nanoparticle surfaces are not well characterized experimentally. We present an in situ sum frequency generation vibrational spectroscopy (SFG-VS) study on the binding of deuterated acetic acid on ceria nanoparticles in the aqueous solution. In the SFG experiment, ceria nanoparticles were deposited on the flat surface of a CaF2 hemisphere in contact with acetic acid solutions. While the ceria nanoparticle deprotonated the acetic acid, the CaF2 surface could not. Thus, the binding of the deprotonated acetic acid on ceria can be selectively probed. SFG spectra revealed that the binding modes of the carboxylate group depend on the oxidation states of the ceria surfaces. SFG polarization analysis suggested that the bidentate chelating and bridging binding modes co-exist on the reduced ceria surfaces, while the oxidized ceria surfaces are dominated by the bidentate bridging mode. The direct spectroscopic evidence helps to clarify the binding structures and mechanisms on the ceria nanoparticles. Furthermore, the middle-infrared (IR) transparent CaF2 and its chemical inertness make CaF2 and similar substrate materials good candidates for direct SFG-VS measurement of nanoparticle surface reactions and binding chem-istry.

  9. Damage Threats and Response of Final Optics for Laser-Fusion Power Plants

    E-print Network

    Tillack, Mark

    - irradiating fused silica samples for a IFE-equivalent dose of several months at several temperatures-induced darkening is a particularly serious concern. Highly pure SiO2 and CaF2 have been irradiated. For the case of irradiations at 105 °C and 179 °C, the spectra nearly overlap (sample path length of 1 cm

  10. IEEE ELECTRON DEVICE LETTERS, VOL. 27, NO. 5, MAY 2006 317 Microwave Performance of GaAs MOSFET With

    E-print Network

    been pursued, including SiO2 [1], SiON [2], Al2O3 [3], CaF2 [4], GaS [5], P3N5 [6], and others [7], [8 TO THE wide array of high-electron mobility alloys of varying bandgaps that can be epitaxially grown on its

  11. Applications of quantum cascade lasers in chemical sensing

    NASA Astrophysics Data System (ADS)

    Wu, Sheng; Deev, Andrei; Tang, Yongchun

    2010-09-01

    We show new results in modulating and modifying Quantum Cascade (QC) lasers to make them more suitable for chemical sensing spectroscopy. Spectroscopy results using QC lasers are demonstrated with whispering gallery mode CaF2 disc/ball, saturated absorption in hollow waveguide and direct chemical analysis in water.

  12. Novel broadband amplifier for mid-infrared semiconductor laser and applications in spectroscopy

    NASA Astrophysics Data System (ADS)

    Wu, Sheng; Deev, Andrei; Tang, Yongchun; Li, Zhenyu; Scherer, Axel

    2010-01-01

    An amplifier design for broadband Mid-IR buried-hetero (BH) structure epitaxial laser is presented, and external cavity design based on this amplifier is described. Spectroscopy results characterizing such single frequency lasers are demonstrated with whispering gallery mode CaF2 disc/ball, saturated absorption in hollow waveguide and direct chemical analysis in water.

  13. Group II intron splicing factors derived by diversification of an ancient RNA-binding domain.

    PubMed

    Ostheimer, Gerard J; Williams-Carrier, Rosalind; Belcher, Susan; Osborne, Erin; Gierke, Jennifer; Barkan, Alice

    2003-08-01

    Group II introns are ribozymes whose catalytic mechanism closely resembles that of the spliceosome. Many group II introns have lost the ability to splice autonomously as the result of an evolutionary process in which the loss of self-splicing activity was compensated by the recruitment of host-encoded protein cofactors. Genetic screens previously identified CRS1 and CRS2 as host-encoded proteins required for the splicing of group II introns in maize chloroplasts. Here, we describe two additional host-encoded group II intron splicing factors, CRS2-associated factors 1 and 2 (CAF1 and CAF2). We show that CRS2 functions in the context of intron ribonucleoprotein particles that include either CAF1 or CAF2, and that CRS2-CAF1 and CRS2-CAF2 complexes have distinct intron specificities. CAF1, CAF2 and the previously described group II intron splicing factor CRS1 are characterized by similar repeated domains, which we name here the CRM (chloroplast RNA splicing and ribosome maturation) domains. We propose that the CRM domain is an ancient RNA-binding module that has diversified to mediate specific interactions with various highly structured RNAs. PMID:12881426

  14. Microstructure and wear behavior of ?/Al 4C 3/TiC/CaF 2 composite coating on ?-TiAl intermetallic alloy prepared by Nd:YAG laser cladding

    NASA Astrophysics Data System (ADS)

    Liu, Xiu-Bo; Shi, Shi-Hong; Guo, Jian; Fu, Ge-Yan; Wang, Ming-Di

    2009-03-01

    As a further step in obtaining high performance elevated temperature self-lubrication anti-wear composite coatings on TiAl alloy, a novel Ni-P electroless plating method was adopted to encapsulate the as-received CaF 2 in the preparation of precursor NiCr-Cr 3C 2-CaF 2 mixed powders with an aim to decrease its mass loss and increase its compatibility with the metal matrix during a Nd:YAG laser cladding. The microstructure of the coating was examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) and the friction and wear behavior of the composite coatings sliding against the hardened 0.45% C steel ring was evaluated using a block-on-ring wear tester at room temperature. It was found that the coating had a unique microstructure consisting of primary dendrites TiC and block Al 4C 3 carbides reinforcement as well as fine isolated spherical CaF 2 solid lubrication particles uniformly dispersed in the NiCrAlTi ( ?) matrix. The good friction-reducing and anti-wear abilities of the laser clad composite coating was suggested to the Ni-P electroless plating and the attendant reduction of mass loss of CaF 2 and the increasing of it's wettability with the NiCrAlTi ( ?) matrix during the laser cladding process.

  15. Amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] for long wavelength infrared detection

    E-print Network

    Zens, Timothy

    The structural, electronic, and optical properties of amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films deposited on Corning glass, Al[subscript 2]O[subscript 3] CdZnTe, SiO[subscript 2]-Si, and CaF2 substrates ...

  16. Prevention of enamel demineralization with a novel fluoride strip: enamel surface composition and depth profile

    PubMed Central

    Lee, Bor-Shiunn; Chou, Po-Hung; Chen, Shu-Yu; Liao, Hua-Yang; Chang, Che-Chen

    2015-01-01

    There is no topically applicable low concentration fluoride delivery device available for caries prevention. This study was aimed to assess the use of a low concentration (1450?ppm) fluoride strip as an effective fluoride delivery system against enamel demineralization. The enamel surface composition and calcium-deficient hydroxyapatite or toothpaste treatments were investigated using X-ray photoelectron spectroscopy. In vitro enamel demineralization was assayed using a pH cycling model and the dissolution of calcium ions from the treated specimens was quantified using ion chromatography. After 24-hr fluoride-strip treatment, the enamel was covered with a CaF2 layer which showed a granular morphology of 1??m in size. Below the CaF2 layer was a region of mixed fluorapatite and CaF2. Fluoride infiltrated extensively in enamel to produce highly fluorinated fluorohydroxyapatite. In comparison, low-fluoride-level fluorinated fluorohydroxyapatite was formed on the enamel specimen exposed to toothpaste. The treatments with the fluoride strip as short as 1?hr significantly inhibited enamel demineralization. The fluoride strip was effective for topical fluoride delivery and inhibited in vitro demineralization of enamel by forming CaF2 and fluoride-containing apatites at the enamel surface. It exhibited the potential as an effective fluoride delivery device for general use in prevention of caries. PMID:26293361

  17. Growth of CoSi2 on Si,,001... by reactive deposition epitaxy C. W. Lim, C.-S. Shin, D. Gall, J. M. Zuo, I. Petrov, and J. E. Greene

    E-print Network

    Gall, Daniel

    Growth of CoSi2 on Si,,001... by reactive deposition epitaxy C. W. Lim, C.-S. Shin, D. Gall, J. M. Zuo, I. Petrov, and J. E. Greene Materials Science Department and the Frederick Seitz Materials November 2003; accepted 27 May 2004; published online 25 January 2005 CaF2-structure CoSi2 layers were

  18. [Study on the Influence of Mineralizer on the Preparation of Calcium Aluminates Based on Infrared Spectroscopy].

    PubMed

    Fan, Wei; Wang, Liang; Zheng, Huai-li; Chen, Wei; Tang, Xiao-min; Shang, Juan-fang; Qian, Li

    2015-05-01

    In this study, effect of mineralizer on the structure and spectraproperties of calcium aluminates formation was extensively studied. Medium or low-grade bauxite and calcium carbonate were used as raw material and mineralizer CaF2 as additive. Calcium aluminates can be obtained after mixing fully, calcination and grinding. The prepared calcium aluminates can be directly used for the production of polyaluminiumchloride (PAC), polymeric aluminum sulfate, sodium aluminate and some other water treatment agents. The calcium aluminates preparation technology was optimized by investigating the mass ratio of raw materials (bauxiteand calcium carbonate) and mineralizer CaF2 dosage. The structure and spectra properties of bauxite and calcium aluminates were characterized by Fourier transform infrared(FTIR) spectroscopy analysis and the mineralization mechanism of the mineralizer was studied. FTIR spectra indicated that the addition of mineralizer promoted the decomposition and transformation of the diaspore, gibbsite and kaolinite, the decomposition of calcium carbonate, and more adequately reaction between bauxite and calcium carbonate. In addition, not only Ca in calcium carbonate and Si in bauxite were more readily reacted, but also Si-O, Si-O-Al and Al-Si bonds in the bauxite were more fractured which contributed to the release of Al in bauxite, and therefore, the dissolution rate of Al2O3 could be improved. The dissolution rate of Al2O3 can be promoted effectively when the mineralizer CaF2 was added in a mass ratio amount of 3%. And the mineralizer CaF2 cannot be fully functioned, when its dosage was in a mass percent of 1. 5%. Low-grade bauxite was easier to sinter for the preparation of calcium aluminates comparing with the highgrade one. The optimum material ratio for the preparation of calcium aluminates calcium at 1 250 °C was the mass ratio between bauxite and calcium carbonate of 1 : 0. 6 and mineralizer CaF2 mass ratio percent of 3%. PMID:26415430

  19. Microstructural and ionic transport studies of hydrothermally synthesized lanthanum fluoride nanoparticles

    NASA Astrophysics Data System (ADS)

    Patro, L. N.; Kamala Bharathi, K.; Ravi Chandra Raju, N.

    2014-12-01

    This article presents the structural and transport characteristics of hydrothermally synthesized LaF3 nanoparticles with an average crystallite size of 35nm. The phase formation of the material is confirmed by both X-ray diffraction and transmission electron microscopy techniques. In addition, phase purity of the LaF3 nanoparticles is corroborated by micro-Raman spectroscopy studies. The complex impedance plots at different temperatures reveal that the conductivity is predominantly due to the intrinsic bulk grains and the conductivity relaxation is non-Debye in nature. The frequency variation of conductivity exhibits dispersion at higher frequencies that can be explained with the frame work of Almond-West formalism. The conduction process is controlled by the mobility of the charge carriers and the charge of transport of mobile fluoride ions occur through hopping mechanism. The scaling behavior of both frequency dependence of conductivity and complex impedance plots at different temperatures confirm that the relaxation mechanism of the mobile fluoride ions is independent of temperature.

  20. Effects of Fluoride Dopants in the Starting Materials for BaAl2S4:Eu Thin-Film Phosphors

    NASA Astrophysics Data System (ADS)

    Guo, Runhong; Miura, Noboru; Matsumoto, Hironaga; Nakano, Ryotaro

    2010-01-01

    BaF2 and AlF3 were used for the preparation of BaAl2S4:Eu thin-film phosphors. The blue emission with a peak at 470 nm was obtained particularly because the process temperature was not sufficient for obtaining a peak at 470 nm in the case of a conventional technique. The intensity of the blue emission from BaAl2S4:Eu phosphors prepared using fluoride compounds was higher than that of phosphors prepared without fluoride compounds, and the appropriate annealing temperature decreased during the preparation process. It is considered that BaF2 and AlF3 enhanced the reaction of starting materials and accelerated the crystallization of BaAl2S4. The crystallinity and mean crystal particle size of BaAl2S4:Eu phosphors prepared using fluoride compounds were improved. This is due to the fluoride compounds effectively acting as flux materials.

  1. Barium fluoride whispering-gallery-mode disk-resonator with one billion quality-factor

    E-print Network

    Lin, Guoping; Henriet, Rémi; Jacquot, Maxime; Chembo, Yanne K

    2015-01-01

    We demonstrate a monolithic optical whispering gallery mode resonator fabricated with barium fluoride (BaF$_2$) with an ultra-high quality ($Q$) factor above $10^9$ at $1550$ nm, and measured with both the linewidth and cavity-ring-down methods. Vertical scanning optical profilometry shows that the root mean square surface roughness of $2$ nm is achieved for our mm-size disk. To the best of our knowledge, we show for the first time that one billion $Q$-factor is achievable by precision polishing in relatively soft crystals with mohs hardness of ~$3$. We show that complex thermo-optical dynamics can take place in these resonators. Beside usual applications in nonlinear optics and microwave photonics, high energy particle scintillation detection utilizing monolithic BaF$_2$ resonators potentially becomes feasible.

  2. GEANT4 simulations of the DANCE array

    NASA Astrophysics Data System (ADS)

    Jandel, M.; Bredeweg, T. A.; Couture, A.; Fowler, M. M.; Bond, E. M.; Chadwick, M. B.; Clement, R. R. C.; Esch, E.-I.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Macri, R. A.; Wu, C. Y.; Becker, J. A.

    2007-08-01

    The detector for advanced neutron capture experiments (DANCE) at Los Alamos National Laboratory (LANL) is used for neutron capture cross sections measurements. Its high granularity of 160 BaF2 detectors in a 4? geometry allows for highly efficient detection of prompt ?-rays following a neutron capture. The performance of the detector was simulated using the GEANT4 Monte Carlo code. The model includes all 160 BaF2 crystals with realistic dimensions and geometry. The 6LiH shell, beam pipe, crystal wrapping material, aluminum holders, photomultiplier material and materials of the calibration sources were included in the simulation. Simulated ?-ray energy and total ?-ray energy spectra gated on cluster and crystal multiplicities were compared to measured data using 88Y, 60Co, 22Na calibration sources. Good agreement was achieved. A total efficiency and peak-to-total ratio as a function of ?-ray energy was established for mono-energetic ?-rays.

  3. Superconducting Films On Microwave Dielectric Substrates

    NASA Technical Reports Server (NTRS)

    Warner, J. D.; Bhasin, K. B.; Valco, G. J.; Rohrer, N. J.

    1992-01-01

    Thin films of superconductor YBa(2)Cu(3)O(7-delta), formed on microwave dielectric substrates of SrTiO3, MgO, Al2O3 coated with ZrO2, and LaAlO3. Films formed by repeated sequential desposition of layers of Cu, BaF2, and Y in electro-beam evaporator, followed by annealing in oxygen. Technique employed gives layers uniformity and reproducibility required for fabrication of microwave circuits.

  4. On-line ion chemistry for the AMS analysis of 90Sr and 135,137Cs

    NASA Astrophysics Data System (ADS)

    Eliades, J.; Zhao, X.-L.; Litherland, A. E.; Kieser, W. E.

    2013-01-01

    The analysis of 90Sr by AMS has so far required the use of very large tandem accelerators in order to separate the isobar 90Zr by the rate-of-energy-loss method. The analysis of 135,137Cs by AMS has never been attempted as the separation of the isobars 135,137Ba by the traditional method requires even higher energies, so that this approach would become prohibitively expensive for routine analysis. Following the successful demonstration of Cl--S- separation by the Isobar Separator, the same apparatus was used to test the separation of other pairs of isobars. Surprisingly effective results were obtained with NO2 gas in the cases of SrF3--ZrF3- and CsF2--BaF2- separations. Reduction factors of ?4 × 10-6 for ZrF3-/SrF3- and ?2 × 10-5 for BaF2-/CsF2- were measured. SrF3- and CsF2- are both super-halogen anions and are preferentially produced in the ion source rather than ZrF3- and BaF2- when using the PbF2 matrix-assisted method. Reduction factors for ion source production with such targets of ?3 × 10-5 for ZrF3--SrF3- and ?5 × 10-4 for BaF2--CsF2- were found. The combined methods would suggest a theoretical detection sensitivity for 90Sr/Sr ?6 × 10-16, 135Cs/Cs ?7 × 10-15 and 137Cs/Cs ?1 × 10-14, assuming 10 ppm Zr and Ba contamination in the AMS targets. In addition to the earlier Cl--S- separation work, these measurements further illustrate the potential of on-line ion chemical methods for broadening the analytical scope of small AMS systems.

  5. Development of MBE grown Pb-salt semiconductor lasers for the 8.0 to 15.0 micrometer spectral region

    NASA Technical Reports Server (NTRS)

    Miller, M. D.

    1981-01-01

    Diodes lasers are fabricated using multiple source molecular beam expitaxial growth of (PbSn)Te on BaF2 substrates. Methods for crystal growth, crystal transfer, and device fabrication by photolithographic techniques were developed. The lasers operate in the spectra range from 10 microns to 14 microns and at temperatures from 12K to 60K continuous wave and to 95 K pulsed.

  6. Highly Compressed Two-Dimensional Form of Water at Ambient Conditions

    NASA Astrophysics Data System (ADS)

    Kaya, Sarp; Schlesinger, Daniel; Yamamoto, Susumu; Newberg, John T.; Bluhm, Hendrik; Ogasawara, Hirohito; Kendelewicz, Tom; Brown, Gordon E.; Pettersson, Lars G. M.; Nilsson, Anders

    2013-01-01

    The structure of thin-film water on a BaF2(111) surface under ambient conditions was studied using x-ray absorption spectroscopy from ambient to supercooled temperatures at relative humidity up to 95%. No hexagonal ice-like structure was observed in spite of the expected templating effect of the lattice-matched (111) surface. The oxygen K-edge x-ray absorption spectrum of liquid thin-film water on BaF2 exhibits, at all temperatures, a strong resemblance to that of high-density phases for which the observed spectroscopic features correlate linearly with the density. Surprisingly, the highly compressed, high-density thin-film liquid water is found to be stable from ambient (300 K) to supercooled (259 K) temperatures, although a lower-density liquid would be expected at supercooled conditions. Molecular dynamics simulations indicate that the first layer water on BaF2(111) is indeed in a unique local structure that resembles high-density water, with a strongly collapsed second coordination shell.

  7. CANDLES for the study of ^48Ca double beta decay

    NASA Astrophysics Data System (ADS)

    Ogawa, Izumi

    2009-10-01

    CANDLES is the project to search for double beta decay (DBD) of ^48Ca by using CaF2 scintillators. The Q-value of ^48Ca, which is the highest (4.27 MeV) among potential DBD nuclei, is far above energies of ?-rays from natural radioactivities (maximum 2.615 MeV from ^208Tl decay), therefore we can naturally expect small backgrounds in the energy region we are interested in. We gave the best lower limit on the half-life of neutrino-less double beta decay of ^48Ca by using CaF2(Eu) detector system, ELEGANT VI though further development is highly desirable to reach the mass region of current interest. We have constructed the prototype detector, CANDLES III in our laboratory (Osaka U.) at sea level and studied the basic performance of the system, including the light collection, position reconstruction and background rejection. We are now moving the detector system to new experimental room (room D) at Kamioka underground laboratory (2700 m.w.e.) to avoid large background originated from cosmic rays. At the same time, we are increasing the total mass of the ^48Ca compared to the one in the prototype detector. 96 (instead of 60 in prototype) CaF2 modules which contains 350 g of ^48Ca are immersed in a liquid scintillator (LS) which acts as an active veto (veto phase). The conversion phase contains wavelength shifter (Bis-MSB) which converts the emission light of CaF2(pure) which has a peak in the UV region to the visible one where the quantum efficiency of the PMTs is high enough (maximum at ˜400 nm) and materials at the optical path have good transparencies. Scintillation lights from both the CaF2 modules and the liquid scintillator in veto phase are viewed by large PMTs (48 x13'' and 14 x17'' tubes). All the detector system described above are contained in a water tank which is 3 m in diameter and 4 m in height. The water tank and a purification system of the LS together with LS storage tanks were installed at room D. The purification system of the LS removes the radioactive impurities especially U and Th using the techniques of water-extraction and N2 purge. Other components including the CaF2 modules, the PMTs, the liquid scintillator vessel and DAQ system will be installed soon.

  8. Some studies on a solid state sulfur probe for coal gasification systems

    NASA Technical Reports Server (NTRS)

    Jacob, K. T.; Rao, D. B.; Nelson, H. G.

    1977-01-01

    Measurements on the solid electrolyte cell (Ar + H(2) + H(2)S/CaS + CaF(2) + (Pt)//CaF(2)//(Pt) + CaF(2) + CaS/H(2) + H(2)+Ar) show that the emf of the cell is directly related to the difference in sulfur potentials established at the Ar + H(2) + H(2)S/electrode interfaces. The electrodes convert the sulfur potential gradient across the calcium fluoride electrolyte into an equivalent fluorine potential gradient. Response time of the probe varies from approximately 9 hr at 990 K to 2.5 hr at 1225 K. The conversion of calcium sulfide and/or calcium fluoride into calcium oxide is not a problem anticipated in commercial coal gasification systems. Suggestions are presented for improving the cell for such commercial applications.

  9. Hybrid metal mesh-dielectric mirrors for optically pumped far infrared lasers.

    PubMed

    Danielewicz, E J; Coleman, P D

    1976-03-01

    A hybrid metal metal-dielectrically coated mirror, highly reflecting in the near ir and partially transmitting in the far ir, for use in optically pumped molecular lasers, is described. Ge and CaF(2) were used for the dielectric films, along with Ni meshes deposited on Si substrates. The dielectric dispersion properties of the CaF(2) thin films were studied in the 2-15-microm range to provide design data. With a four layer dielectric coating and a metal mesh, the specular reflection of the mirror could be maintained greater than 90% over a 2-mum range in the near ir, and by choice of mesh, the transmittance in the 400-600-microm range varied from 0% to greater than 40%. PMID:20165053

  10. Influence of thermal distortion in mirrors on the propagation of high power lasers

    NASA Astrophysics Data System (ADS)

    Lv, Ke; Zheng, Wei; Hua, Wei-hong

    2012-10-01

    The root-mean-square (RMS) phase distortion and the strehl ratio in the far-field influenced by the thermal distortion of mirrors in the propagation of high power lasers were calculated. Calculations with different CO2 laser beam intensity distribution indicate that compare with stable cavity whose output is Gaussian, unstable cavity's beam quality influenced by the thermal deformation depends on the slope of the intensity distribution, that is, contents of H2O, and the obscuration. Among the mirror materials such as SiO2, BeO, CaF2 and Si, CaF2 provides the steadiest thermal character in the high power laser irradiance. When the SiO2 mirror is cooled, the RMS phase aberration brought by the thermal deformation would be less. For a high power mirror, cooled by the water is more efficacious than cooled by the wind.

  11. Fabrication and Current-Voltage Characteristics of Fe3Si/CaF2/Fe3Si Magnetic Tunnel Junction

    NASA Astrophysics Data System (ADS)

    Harianto, Teddy; Sadakuni, Kenji; Akinaga, Hiro; Suemasu, Takashi

    2008-08-01

    The possibility of selective wet chemical etching and the current-voltage characteristics (I-V) of Fe3Si (9 nm)/CaF2 (2 nm)/Fe3Si (13 nm) magnetic-tunnel-junctions structures have been investigated. It was found that the Fe3Si and CaF2 layers were selectively etched using a mixture of hydrofluoric and nitric acids (HF:HNO3:H2O = 1:2:400) and a sulfuric solution (H2SO4:H2O = 1:20), respectively. The etch rates were 120 and 45 nm/min at 0 °C for Fe3Si and CaF2, respectively. The I-V characteristics measured at room temperature were well fitted to Simmons' equation within the bias voltages of ±0.3 V using the barrier height ?= 2.5 eV and barrier thickness d = 2.0 nm.

  12. Recovery Behavior of Separating Britholite (Ca3Ce2[(Si,P)O4]3F) Phase from Rare-Earth-rich Slag by Centrifugal Casting

    NASA Astrophysics Data System (ADS)

    Li, Juncheng; Guo, Zhancheng; Yang, Tao; Yue, Zicheng; Ma, Changhao

    2015-05-01

    A new approach to separate britholite phase from the rare-earth-rich slag by super gravity was investigated. With the parameter of G = 500, t = 5 min, T = 1423 K, almost all britholite phase is enriched in the concentrate, while the tailing is made up of CaF2 phase. Under the hypothesis that the RE exists in the slag in terms of RE2O3, with the gravity coefficient G = 500, t = 5 min and T = 1423 K, the mass fraction of RE2O3 in the concentrate is up to 24.67%, while the mass fraction of CaF2 in the tailing is 50.01%. Considering that the mass fraction of RE2O3 is 12.01% in the parallel sample, the recovery ratio of rare earth in the concentrate is up to 76.47% by centrifugal separation.

  13. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2013-01-01

    World fluorspar demand slowed in 2012 and, according to some sources prices decreased, especially in the latter half of the year. In 2012, nearly all fluorspar (CaF2) consumption in the United States was from imports. Hastie Mining and Trucking Co. produced some fluorspar as a byproduct of its limestone quarry operations in Illinois. In addition, a small amount of usable synthetic fluorspar was produced from industrial waste streams.

  14. Lubricating Properties of Some Bonded Fluoride and Oxide Coatings for Temperature to 1500 F

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E.

    1960-01-01

    The lubricating properties of some experimental ceramic coatings, diffusion-bonded fluoride coatings, and ceramic-bonded fluoride coatings were determined. The experiments were conducted in an air atmosphere at a sliding velocity of 430 feet per minute and at temperatures from 75 to 1500 F. Several ceramic coatings provided substantial reductions in friction coefficient and rider wear (compared with the unlubricated metals). For example, a cobaltous oxide (CoO) base coating gave friction coefficients of 0.24 to 0.36 within the temperature range of 75 to 1400 F; serious galling and welding of the metal surfaces were prevented. The friction coefficients were higher than the arbitrary maximum (0.2) usually considered for effective boundary lubrication. However, when a moderately high friction coefficient can be tolerated, this type of coating may be a useful antiwear composition. Diffusion-bonded calcium fluoride (CaF2) on Haynes Stellite 21 and on Inconel X gave friction coefficients of 0.1 to 0.2 at 1500 F. Endurance life was dependent on the thermal history of the coating; life improved with increased exposure time at elevated temperatures prior to running. Promising results were obtained with ceramic-bonded CaF2 on Inconel X. Effective lubrication and good adherence were obtained with a 3 to 1 ratio of CaF2 to ceramic. A very thin sintered and burnished film of CaF2 applied to the surface of this coating further improved lubrication, particularly above 1350 F. The friction coefficient was 0.2 at 500 F and decreased with increasing temperature to 0.06-at 1500 F. It was 0.25 at 75 F and 0.22 at 250 F.

  15. Licence L1S2 Anglais (21h)

    E-print Network

    Avignon et des Pays de Vaucluse, Université de

    , site octaédrique, site tétraédrique) Structures des cristaux métalliques et des cristaux covalents (diamant). Structures des cristaux ioniques: structures types (NaCl, CsCl, ZnS, CaF2...) cristaux'année) PHYSIQUE (90H - 9 crédits) MECANIQUE DU SOLIDE INDEFORMABLE (30H : 15H CM ET 15H TD) - Enseignante : P

  16. Separation of High Order Harmonics with Fluoride Windows

    SciTech Connect

    Allison, Tom; van Tilborg, Jeroen; Wright, Travis; Hertlein, Marcus; Falcone, Roger; Belkacem, Ali

    2010-08-02

    The lower orders produced in high order harmonic generation can be effciently temporally separated into monochromatic pulses by propagation in a Fluoride window while still preserving their femtosecond pulse duration. We present calculations for MgF2, CaF2, and LiF windows for the third, fifth, and seventh harmonics of 800 nm. We demonstrate the use of this simple and inexpensive technique in a femtosecond pump/probe experiment using the fifth harmonic.

  17. Sulfate Adsorption at the Buried Fluorite-Solution Interface Revealed by Vibrational Sum Frequency Generation Spectroscopy

    E-print Network

    Sulfate Adsorption at the Buried Fluorite-Solution Interface Revealed by Vibrational Sum Frequency the adsorption of sulfate at the buried fluorite (CaF2)/Na2SO4 solution surface at pH 7 and 298 K in the presence surface with an average surface free energy of adsorption of -31 ± 3 kJ/mol for pH 7 solutions at 298 K

  18. Heterogeneous core/shell fluoride nanocrystals with enhanced upconversion photoluminescence for in vivo bioimaging

    NASA Astrophysics Data System (ADS)

    Hao, Shuwei; Yang, Liming; Qiu, Hailong; Fan, Rongwei; Yang, Chunhui; Chen, Guanying

    2015-06-01

    We report on heterogeneous core/shell CaF2:Yb3+/Ho3+@NaGdF4 nanocrystals of 17 nm with efficient upconversion (UC) photoluminescence (PL) for in vivo bioimaging. Monodisperse core/shell nanostructures were synthesized using a seed-mediated growth process involving two quite different approaches of liquid-solid-solution and thermal decomposition. They exhibit green emission with a sharp band around 540 nm when excited at ~980 nm, which is about 39 times brighter than the core CaF2:Yb3+/Ho3+ nanoparticles. PL decays at 540 nm revealed that such an enhancement arises from efficient suppression of surface-related deactivation from the core nanocrystals. In vivo bioimaging employing water-dispersed core/shell nanoparticles displayed high contrast against the background.We report on heterogeneous core/shell CaF2:Yb3+/Ho3+@NaGdF4 nanocrystals of 17 nm with efficient upconversion (UC) photoluminescence (PL) for in vivo bioimaging. Monodisperse core/shell nanostructures were synthesized using a seed-mediated growth process involving two quite different approaches of liquid-solid-solution and thermal decomposition. They exhibit green emission with a sharp band around 540 nm when excited at ~980 nm, which is about 39 times brighter than the core CaF2:Yb3+/Ho3+ nanoparticles. PL decays at 540 nm revealed that such an enhancement arises from efficient suppression of surface-related deactivation from the core nanocrystals. In vivo bioimaging employing water-dispersed core/shell nanoparticles displayed high contrast against the background. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02287h

  19. Vacuum-ultraviolet beam array generation by flat micro-optical structures.

    PubMed

    Grunwald, R; Neumann, U; Kebbel, V; Kühn, H J; Mann, K; Leinhos, U; Mischke, H; Wulff-Molder, D

    2004-05-01

    Micro-optical structures for VUV laser beam shaping and wave-front sensing were manufactured by thin-film deposition onto CaF2 and transfer by etching. Arrays of Bessel-like F2 laser beams at a wavelength of 157 nm with extremely small conical angles were generated by microaxicon lenses. Beam propagation was studied in simulations and experiments. Apodization by absorbing layers is proposed for beam cleaning. PMID:15143646

  20. Status report on dark matter search with low activity scintillators

    NASA Astrophysics Data System (ADS)

    Bacci, C.; Belli, P.; Bernabei, R.; Dai, C.; Di Nicolantonio, W.; Ding, L. K.; Gaillard-Lecanu, E.; Giraud-Heraud, Y.; Kuang, H. H.; Incicchitti, A.; Mallet, J.; Mosca, L.; Prosperi, D.; Tao, C.; Chambon, B.; Chazal, V.; De Jésus, M.; Drain, D.; Messous, Y.; Pastor, C.; BPRS (Beijing, Paris, Roma, Saclay) Collaboration

    1994-05-01

    The BPRS experiment is dedicated to particle Dark Matter search with low activity scintillators. Preliminary results on Weakly Interacting Massive Particles (WIMPs) have been already obtained with NaI(Tl) and CaF 2(Eu) target-detectors. New detector developments are in progress. A new search for Strongly Interacting Massive Particles (SIMPs) with NaI(Tl) scintillators have been also performed.

  1. Effect of Fluorine on the Structure of High Al2O3-Bearing System by Molecular Dynamics Simulation

    NASA Astrophysics Data System (ADS)

    Fan, Guozheng; He, Shengping; Wu, Ting; Wang, Qian

    2015-08-01

    Calcium aluminosilicate is the most important slag system in continuous casting, while CaF2 is commonly used as a fluxing agent in mold fluxes. In this study, the structural properties of the CaO-Al2O3-SiO2-CaF2 system with varying fluorine content have been investigated by molecular dynamics simulation using the pairwise potential model. The results showed that with the substitution of oxygen ions by fluorine ions, the average bond length of Si-O remained unchanged, while the average bond length of Al-O increased from 1.74 to 1.75 Å. The addition of fluorine contributed to the increase in the bridging oxygen proportion and the network connectivity ( Q n ) degree, suggesting that the polymerization of melts was enhanced. Meanwhile, the threefold-coordinated Al was found when mass fraction of fluorine was increased, and it was due to that the fluorine ions substituted the oxygen ions and formed the [AlO3F] tetrahedron. The Al avoidance principle is not applicable in the CaO-Al2O3-SiO2-CaF2 system with a high content of Al2O3.

  2. Nanocrystalline SmCo5 magnets with laminated structure and increased electrical resistivity

    NASA Astrophysics Data System (ADS)

    Gabay, A. M.; Marinescu-Jasinski, M.; Li, W. F.; Liu, J. F.; Hadjipanayis, G. C.

    2011-04-01

    Magnetically isotropic Sm-Co permanent magnets with anisotropic electrical conductivity were produced by hot-pressing SmCo5 ultrathin flakes with or without insulating additions of mica, MoS2, CaF2, and B2O3. The laminated structures of the magnets were assured by the natural packing of the flakes in the die. In the additive-free magnets, the resistivity is increased due to oxidized flake boundaries. Additives with platelet-shaped particles (mica, MoS2) and especially those with low-melting temperature (B2O3) form more continuous insulating layers. On the other hand, the CaF2 additive does not react with the magnetic Sm-Co phase. The characteristic values of the maximum energy product and electrical resistivity, measured in orthogonal directions, were 9.7 MG Oe and 130 ?? cm for the additive-free magnet, 5.7 MG Oe and 640 ?? cm for the magnet made with 2 wt. % B2O3 and 5.7 MG Oe and 330 ?? cm for the magnet made with 10 wt. % CaF2.

  3. Effect of aluminum phosphate additions on composition of three-component plasma-sprayed solid lubricant

    NASA Technical Reports Server (NTRS)

    Jacobson, T. P.; Young, S. G.

    1982-01-01

    Image analysis (IA) and electron microprobe X-ray analysis (EMXA) were used to characterize a plasma-sprayed, self-lubricating coating, NASA LUBE PS106, specified by weight percent as 35NiCr-35Ag-30CaF2. To minimize segregation of the powder mixture during the plasma-spraying procedure, monoaluminum phosphate was added to form agglomerate particles. Three concentrations of AlPO4 were added to the mixtures: 1.25, 2.5, and 6.25 percent by weight. Analysis showed that 1.25 wt% AlPO4 yielded a CaF2 deficiency, 2.5 wt% kept the coating closest to specification, and 6.25 wt% yielded excess CaF2 as well as more impurities and voids and a deficiency in silver. Photomicrographs and X-ray maps are presented. The methods of IA and EMXA complement each other, and the reasonable agreement in the results increases the confidence in determining the coating composition.

  4. Ultra-high resistive and anisotropic CoPd-CaF2 nanogranular soft magnetic films prepared by tandem-sputtering deposition

    NASA Astrophysics Data System (ADS)

    Naoe, Masayuki; Kobayashi, Nobukiyo; Ohnuma, Shigehiro; Iwasa, Tadayoshi; Arai, Ken-Ichi; Masumoto, Hiroshi

    2015-10-01

    Ultra-high resistive and anisotropic soft magnetic films for gigahertz applications are desirable to demonstrate the really practical films. Here we present a study of novel nanogranular films fabricated by tandem-sputtering deposition. Their electromagnetic properties and nanostructure have also been discussed. These films consisted of nanocrystallized CoPd alloy-granules and CaF2 matrix, and a specimen having a composition of (Co0.69Pd0.31)52-(Ca0.31F0.69)48 exhibited distinct in-plane uniaxial anisotropy after uniaxial field annealing with granule growth. Its complex permeability spectra have a ferromagnetic resonance frequency extending to the Super-High-Frequency band due to its higher anisotropy field, and its frequency response was quite well reproduced by a numerical calculation based on the Landau-Lifshitz-Gilbert equation. Furthermore, it was clarified that the CaF2-based nanogranular film exhibits a hundredfold higher electrical resistivity than conventional oxide or nitride-based films. Higher resistivity enables the film thickness to achieve a margin exceeding threefold against eddy current loss. The greater resistivity of nanogranular films is attributed to the wide energy bandgap and superior crystallinity of CaF2 matrix.

  5. Neodymium-doped nanoparticles for infrared fluorescence bioimaging: The role of the host

    NASA Astrophysics Data System (ADS)

    del Rosal, Blanca; Pérez-Delgado, Alberto; Misiak, Ma?gorzata; Bednarkiewicz, Artur; Vanetsev, Alexander S.; Orlovskii, Yurii; Jovanovi?, Dragana J.; Drami?anin, Miroslav D.; Rocha, Ueslen; Upendra Kumar, K.; Jacinto, Carlos; Navarro, Elizabeth; Martín Rodríguez, Emma; Pedroni, Marco; Speghini, Adolfo; Hirata, Gustavo A.; Martín, I. R.; Jaque, Daniel

    2015-10-01

    The spectroscopic properties of different infrared-emitting neodymium-doped nanoparticles (LaF3:Nd3+, SrF2:Nd3+, NaGdF4: Nd3+, NaYF4: Nd3+, KYF4: Nd3+, GdVO4: Nd3+, and Nd:YAG) have been systematically analyzed. A comparison of the spectral shapes of both emission and absorption spectra is presented, from which the relevant role played by the host matrix is evidenced. The lack of a "universal" optimum system for infrared bioimaging is discussed, as the specific bioimaging application and the experimental setup for infrared imaging determine the neodymium-doped nanoparticle to be preferentially used in each case.

  6. Uniformity Masks Design Method Based on the Shadow Matrix for Coating Materials with Different Condensation Characteristics

    PubMed Central

    2013-01-01

    An intuitionistic method is proposed to design shadow masks to achieve thickness profile control for evaporation coating processes. The proposed method is based on the concept of the shadow matrix, which is a matrix that contains coefficients that build quantitive relations between shape parameters of masks and shadow quantities of substrate directly. By using the shadow matrix, shape parameters of shadow masks could be derived simply by solving a matrix equation. Verification experiments were performed on a special case where coating materials have different condensation characteristics. By using the designed mask pair with complementary shapes, thickness uniformities of better than 98% are demonstrated for MgF2 (m = 1) and LaF3 (m = 0.5) simultaneously on a 280?mm diameter spherical substrate with the radius curvature of 200?mm. PMID:24227996

  7. Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials.

    PubMed

    Kaczmarek, Anna M; Van Hecke, Kristof; Van Deun, Rik

    2015-04-21

    This review focuses on rare-earth carbonate materials of nano- and micro-size. It discusses in depth the different types of rare-earth carbonate compounds, diverse synthetic approaches and possibilities for chemical tuning of the size, shape and morphology. The interesting luminescence properties of lanthanide doped rare-earth carbonates and their potential applications for example as efficient white light sources and biolabels are reviewed. Additionally the use of these materials as precursors for the synthesis of nano-/micro-sized oxides, and their application as sacrificial templates for morphology-controlled synthesis of other materials such as YVO4, LaF3, NaYF4 and others is overviewed. PMID:25714401

  8. Improved characterization of Si-SiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Su, P.

    Silicon is the heart of modern semiconductor devices. The dominance of Si in semiconductor technology depends on the superior quality and properties of thermally grown SiO2 compared with the oxide that can be placed on any other semiconductor. The well established quasistatic and conductance methods used in the study of the Si-SiO2 interface are improved by using an effectively thin composite insulator, low carrier concentration substrates, and most importantly, low level illumination at a wavelength that creates electron hole pairs. The samples investigated had a thermally grown oxide prepared in dry oxygen. They were never exposed to H2 or H2O at an elevated temperature. The composite gate insulator was completed by having an e-gun deposited 250 A layer on LaF3. The resulting interface, subjected to the improved experimental method, yields a wealth of distinctive structure rather than the often reported featureless U-shaped interface-state density.

  9. Measurement of Liquid Surface Temperature by a Infrared Radiation Thermometer

    NASA Astrophysics Data System (ADS)

    Hihara, Eiji; Fujita, Isamu; Saito, Takamoto

    A method for measuring liquid. surface temperature by a infrared radiation thermometer is described. When the temperature is measured through a glass plate, following corrections are required: (1) transmissivity of the glass plate, (2) Thermal radiation from the glass plate, and (3) thermal radiation from the room walls which reflects at the glass plate. In this study, a correction method of the above effects is presented, and is confirmed by the experiment. The surface temperature of water was measured through a BaF2 plate in the range of 40?90°C. The accuracy of the measurements was within ±0.5°C.

  10. Triple coincidence PALS setup based on fast pulse digitizers

    NASA Astrophysics Data System (ADS)

    Bosnar, D.; ?ur?evi?, B.; Paveli?, L.; Bosnar, S.

    2015-06-01

    We have assembled positron annihilation lifetime spectroscopy system that consists of three BaF2 detectors with XP2020URQ PMTs which are directly coupled to DRS4 evaluation board. Both time and energy information of the detected gamma rays are reconstructed. In the off-line analysis, by using selected cuts on energies of gamma rays, double, as well as triple coincidence events can be extracted. The setup is very suitable for the determination of contributions of positronium three gamma annihilations which can be of interest in the investigations of various porous materials.

  11. Conversion of Oxyfluoride Based Coated Conductors

    SciTech Connect

    Dan Wesolowski

    2006-11-01

    Direct measurements of HF pressure in equilibrium with the film during the BaF2 process are sorely needed. It is the HF partial pressure that governs the rate at which the film composition is changing and is, therefore, an important factor in controlling the composition/time trajectory of the film. Establishing the composition/time trajectory of both MOD-derived and e-beam derived films for a given set of conditions is another goal for the project. These studies will provide a fundamental understanding of the ex situ process for producing coated conductors.

  12. (n, ?) measurements on radioactive isotopes with DANCE

    NASA Astrophysics Data System (ADS)

    Reifarth, R.; Esch, E.-I.; Alpizar-Vicente, A.; Bond, E. M.; Bredeweg, T. A.; Glover, S. E.; Greife, U.; Hatarik, R.; Haight, R. C.; Kronenberg, A.; O'Donnell, J. M.; Rundberg, R. S.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.

    2005-12-01

    The Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos National Laboratory (LANL) is designed as a high efficiency, highly segmented 4? BaF2 detector for calorimetrically detecting gamma rays following a neutron capture. Coupled with the neutron spallation source at the Los Alamos Neutron Science Center (LANSCE), DANCE measurements on unstable isotopes in the energy range between 10 meV and 500 keV will provide many of the missing key reactions that are needed to understand the nucleosynthesis of the heavy elements and will also provide vital information for the design of future reactor concepts.

  13. First tests of a fission-tagging detector for the DANCE array

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Ethvignot, T.; Wilhelmy, J. B.; Esch, E.-I.; Granier, T.; Haight, R. C.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.

    2004-10-01

    A proof-of-principle experiment has been performed with the DANCE 4? BaF2 array to explore the feasibility of adding a fission-tagging detector. The initial tests utilized a deposit of ^235U on a solar cell, which was used to detect the fission fragments, while ?-rays were measured by the DANCE array. The addition of a fission-tagging detector to the DANCE array will provide a means to study several important issues associated with neutron induced fission, including (n,fission) cross sections as a function of incident neutron energy, and total energy and multiplicity of prompt fission photons.

  14. Measurement of the Gd157(n,?) reaction with the DANCE ? calorimeter array

    NASA Astrophysics Data System (ADS)

    Chyzh, A.; Baramsai, B.; Becker, J. A.; Be?vá?, F.; Bredeweg, T. A.; Couture, A.; Dashdorj, D.; Haight, R. C.; Jandel, M.; Kroll, J.; Krti?ka, M.; Mitchell, G. E.; O'Donnell, J. M.; Parker, W.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Walker, C. L.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2011-07-01

    The Gd157(n,?) reaction was measured with the DANCE ? calorimeter (consisting of 160 BaF2 scintillation detectors) at the Los Alamos Neutron Science Center. The multiplicity distributions of the ? decay were used to determine the resonance spins up to En=300 eV. The ?-ray energy spectra for different multiplicities were measured for the s-wave resonances. The shapes of these spectra were compared with simulations based on the use of the DICEBOX statistical model code. Simulations showed that the scissors mode is required not only for the ground-state transitions but also for transitions between excited states.

  15. Data Acquisition System for the Detector for Advanced Neutron Capture Experiments (DANCE)

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Reifarth, R.; Ullmann, J. L.; Haight, R. C.; O'Donnell, J. M.; Wouters, J. M.; Wilhelmy, J. B.; Rundberg, R. S.; Vieira, D. J.

    2003-04-01

    Nuclear and high energy physics experiments continue to grow in complexity. This increase in "experimental" complexity requires a matching increase in the complexity of the system used to acquire the data from the experimental apparatus. The Detector for Advanced Neutron Capture Experiments (DANCE), a 4? BaF2 array located at the Manuel J. Lujan Jr. Neutron Scattering Center at Los Alamos National Laboratory is a prime example of this increasing experimental complexity. We will describe several of the important issues that arose during the development of a data acquisition system based on MIDAS/ROOT, and the methods used to overcome these issues.

  16. Growth and scintillation properties of Yb doped aluminate, vanadate and silicate single crystals

    NASA Astrophysics Data System (ADS)

    Yoshikawa, A.; Ogino, H.; Shim, J. B.; Kochurikin, V. V.; Nikl, M.; Solovieva, N.; Ono, S.; Sarukura, N.; Kikuchi, M.; Fukuda, T.

    2004-09-01

    For the purpose of quick screening for charge transfer (CT) transitions of Yb 3+ in various hosts, (Lu 1- xYb x) 3Al 5O 12 (Yb:LuAG) with x=0.05, 0.15, 0.30 and (Y 1- xYb x)AlO 3 (Yb:YAP) with x=0.05, 0.10, 0.30 were grown by the micro-pulling-down method. (Y,Yb)VO 4 with strong wetting was grown by edge defined film-fed growth method and materials, which require moderate temperature gradient, such as Ca 8(La,Yb) 2(PO 4) 6O 2 and (Gd,Yb) 2SiO 5 were grown by Czochralski method. Strong dependence of the CT luminescence decay time and intensity on temperature was observed for Yb-doped LuAG and YAP. Super fast decay with 0.85 ns decay time was observed in Yb(30%) doped YAP at room temperature. Though the emission intensity is weak at room temperature, it exceeds several times that of PbWO 4. In addition, CT luminescence of Yb:YAP occurs at longer wavelength than in BaF 2, which enables the usage of glass-based photomultiplier for the detection. In addition, higher stopping power will be expected due to the higher density host compared with BaF 2.

  17. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses

    NASA Astrophysics Data System (ADS)

    Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.

    2013-05-01

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

  18. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  19. Measurement of prompt fission neutron spectrum using a gamma tag double time-of-flight setup

    NASA Astrophysics Data System (ADS)

    Blain, Ezekiel

    Current uncertainties in the prompt fission neutron spectrum have a significant effect of up to 4% on keff for reactor criticality and safety calculations. Therefore, a method was developed at RPI to improve the accuracy of the measurement of the prompt fission neutron spectrum. This method involves using an array of BaF2 gamma detectors to tag that a fission event has occurred, and a double time-of-flight setup to obtain the prompt fission neutron spectrum as a function of incident neutron energy. The gamma tagging method improves upon conventional fission chambers by allowing for much larger sample sizes to be utilized while not suffering from effects of discriminator level on the shape of the prompt fission neutron spectrum. A coincidence requirement on an array of 4 BaF2 gamma detectors is used to determine the timing of the fission event. Furthermore, a method is under development for the use of thin plastic scintillators for measurement of the prompt fission neutron spectrum with low energies. Measurements with spontaneous fission of . {252} Cf show good agreement with previous datasets and current evaluations as well as providing accurate data down to 50 keV with the plastic scintillator detector. Preliminary incident neutron beam analysis was performed with 238U and shows good agreement with the current evaluations demonstrating the feasibility of the gamma tagging method for in beam prompt fission neutron spectrum measurements of various isotopes.

  20. Chemical Transformation of Crystalline Hafnium Tetrafluoride Studied by Perturbed Angular Correlation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dey, Chandi Charan C.

    2009-11-01

    The chemical transformation of the trihydrate hafnium tetrafluoride crystal has been studied with varying temperature using the time-differential perturbed angular correlation technique. The 133 - 482 keV ? -? cascade of 181Ta after the ? --decay of 181Hf has been selected and a four detector BaF2-BaF2 coincidence set up has been used for measurements. The crystal was produced by evaporating a solution of HfF62-complex in HF at room temperature. Contrary to the earlier report, it has been found that the trihydrate hafnium tetrafluoride compound dehydrates directly to HfF4 without producing any intermediate monohydrate and present results do not support the earlier idea that two water molecules of HfF4·3H2O are loosely bound. Present investigations exhibit a superheated state for the hafnium tetrafluoride crystal. In dehydrated HfF4, two different Hf sites have been observed which suggests two different structures for the anhydrous HfF4.

  1. The effect of water pressure on the texture and morphology of MOD-YBCO films on buffered metal substrates

    NASA Astrophysics Data System (ADS)

    Chung, K. C.; Yoo, J. M.; Kim, Y. K.; Wang, X. L.; Dou, S. X.

    2009-02-01

    The influence of water pressure in the metal-organic deposition (MOD) method on the texture and morphology of YBa2Cu3O7-X (YBCO) films grown on buffered metal substrates was investigated. The water pressure was varied from 4.2% to 10.0%, with the other process parameters, such as annealing temperature and oxygen pressure, kept constant. In this work, a YBCO precursor solution was prepared using a fluorine-free Y and Cu precursor solution with the addition of Sm. MOD-YBCO films were fabricated by continuous slot-die coating and calcination, followed by high temperature annealing. Using x-ray diffraction analysis, unreacted phase peaks, such as BaF2 peaks, were found in the samples made at a water pressure of 4.2%; however, the BaF2 peak intensity was much reduced as the water pressure was increased. The higher water pressure of about 10.0% in this experiment led to the poor crystallinity of MOD-YBCO films, possibly due to the fast reaction with the supplied water vapor. Meanwhile, the morphologies of the YBCO films were not much different from each other in the range of water pressure of this work. The maximum critical current density of 3.8 MA cm-2 was obtained when the sample was made at the water pressure of 6.2% and the annealing temperature of 780 °C.

  2. Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET

    PubMed Central

    Mondal, Nagendra Nath

    2009-01-01

    This study presents Monte Carlo Simulation (MCS) results of detection efficiencies, spatial resolutions and resolving powers of a time-of-flight (TOF) PET detector systems. Cerium activated Lutetium Oxyorthosilicate (Lu2SiO5: Ce in short LSO), Barium Fluoride (BaF2) and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr3) scintillation crystals are studied in view of their good time and energy resolutions and shorter decay times. The results of MCS based on GEANT show that spatial resolution, detection efficiency and resolving power of LSO are better than those of BaF2 and LaBr3, although it possesses inferior time and energy resolutions. Instead of the conventional position reconstruction method, newly established image reconstruction (talked about in the previous work) method is applied to produce high-tech images. Validation is a momentous step to ensure that this imaging method fulfills all purposes of motivation discussed by reconstructing images of two tumors in a brain phantom. PMID:20098551

  3. Understanding Low Energy Gamma Emission from Fission and Capture with DANCE

    NASA Astrophysics Data System (ADS)

    Wilburn, Grey; Couture, Aaron; Mosby, Shea

    2012-10-01

    Los Alamos National Laboratory's Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 barium fluoride (BaF2) detectors in a 4? array used to study cross-section measurements from neutron capture reactions. Further, recent studies have taken advantage of DANCE to study the gamma emission from fission, which is not well characterized. Neutron capture is studied because of its relevance to nuclear astrophysics (almost all elements heavier than iron are formed via neutron capture) and nuclear energy, where neutron capture is a poison in the reactor. Gamma ray cascades following neutron capture and fission include photons with energies between 100 keV and 10 MeV. DANCE uses a ^6LiH sphere to attenuate scattered neutrons, the primary background in DANCE. Unfortunately, it also attenuates low energy gamma rays. In order to quantify this effect and validate simulations, direct measurements of low energy gammas were made with a high purity germanium (HPGe) crystal. HPGe's allow for high resolution measurements of low energy gamma rays that are not possible using the BaF2 crystals. The results and their agreement with simulations will be discussed.

  4. Atomic force microscope studies of fullerene films - Highly stable C60 fcc (311) free surfaces

    NASA Technical Reports Server (NTRS)

    Snyder, Eric J.; Tong, William M.; Williams, R. S.; Anz, Samir J.; Anderson, Mark S.

    1991-01-01

    Atomic force microscopy and X-ray diffractometry were used to study 1500 A-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 (111) substrte. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.

  5. Initial stage of laser ablation of LiCaAlF6 single crystal under F2 laser irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Y.; Narazaki, A.; Sato, T.; Kurosaki, R.; Niino, H.; Sato, H.; Fukuda, T.

    Initial stage of F2 laser ablation of LiCaAlF6 single crystal was investigated for clarifying the possibility of applying this wide bandgap fluoride crystal to vacuum ultraviolet (VUV) optical components. The ablation threshold, determined by the appearance of line emission from ablated species, was approximately 2 Jcm-2pulse-1, similar to that of VUV grade CaF2 single crystal. The laser-induced damage on the front surface of LiCaAlF6 was faint, though adhesion of aggregated particulates of several microns was observed.

  6. Generation of Kerr combs centered at 4.5 ?m in crystalline microresonators pumped with quantum-cascade lasers.

    PubMed

    Savchenkov, Anatoliy A; Ilchenko, Vladimir S; Di Teodoro, Fabio; Belden, Paul M; Lotshaw, William T; Matsko, Andrey B; Maleki, Lute

    2015-08-01

    We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 ?m, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8). PMID:26258334

  7. Passively Q-switched microchip laser R. Haring, R. Paschotta, R. Fluck,* E. Gini, H. Melchior, and U. Keller

    E-print Network

    Keller, Ursula

    crystal (e.g., Co2 :LaMgAl11O19,4,5 Er:Ca5(PO4)3F,6 U4 :CaF2,7,8 U4 :SrF2,9 Co2 :ZnSe,10 Cr2 :ZnSe11 of the parameters needed for a specific application. Design guidelines20 for Q-switched microchip lasers with SESAMsPassively Q-switched microchip laser at 1.5 m R. Ha¨ring, R. Paschotta, R. Fluck,* E. Gini, H

  8. Generation of ultrashort 90 µJ deep-ultraviolet pulses by dual broadband frequency doubling with ?-BaB2O4 crystals at 1 kHz

    NASA Astrophysics Data System (ADS)

    Zhou, Chun; Kanai, Teruto; Watanabe, Shuntaro

    2015-01-01

    Fourth-harmonic pulses of a 1 kHz chirped-pulse amplification (CPA) Ti:sapphire laser have been generated by a scheme of dual broadband frequency doubling with two ?-BaB2O4 (BBO) crystals. The pulse energy was 90 µJ with a bandwidth of 2.7 nm (full width at half maximum, FWHM) at a central wavelength of 220 nm. The pulse width was measured to be 45 fs by autocorrelation with the two-photon fluorescence of CaF2, which was much smaller than that (120 fs) obtained by conventional frequency conversion.

  9. Continuous-wave broadly tunable diode laser array-pumped mid-infrared Cr2+:CdSe laser

    NASA Astrophysics Data System (ADS)

    Lazarev, V. A.; Tarabrin, M. K.; Kovtun, A. A.; Karasik, V. E.; Kireev, A. N.; Kozlovsky, V. I.; Korostelin, Yu V.; Podmar’kov, Yu P.; Frolov, M. P.; Gubin, M. A.

    2015-12-01

    We demonstrate the operation of a room-temperature, solid-state, broadly tunable Cr-doped CdSe single-crystal continuous-wave laser. Longitudinal pumping with a continuous-wave diode laser array at 1.94 ?m produced a broadband output of 280 mW at 2.6 ?m with an incident power slope efficiency of 12%. With an intracavity Brewster-cut CaF2 prism, we tuned the Cr2+:CdSe laser from 2.45 to 3.06 ?m with a resolution of 10?nm and an output power up to 55 mW.

  10. Analysis of multiple pulse NMR in solids

    NASA Technical Reports Server (NTRS)

    Rhim, W.-K.; Elleman, D. D.; Vaughan, R. W.

    1973-01-01

    The general problems associated with the removal of the effects of dipolar broadening from solid-state NMR spectra are analyzed. The effects of finite pulse width and H sub 1 inhomogeneity are shown to have limited the resolution of previous pulse cycles, and a new eight-pulse cycle designed to minimize these problems is discussed. Spectra for F-19 in CaF2 taken with this cycle are presented which show residual linewidth near 10 Hz. The feasibility of measuring proton chemical shift tensors is discussed.

  11. Technology for Solar Array Production on the Moon

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.

    2002-01-01

    Silicon, aluminum, and glass are the primary raw materials that will be required for production of solar arrays on the moon. A process sequence is proposed for producing these materials from lunar regolith is proposed, consisting of separating the required materials from lunar rock with fluorine. Fluorosilane produced by this process is reduced to silicon; the fluorine salts are reduced to metals by reaction with metallic potassium. Fluorine is recovered from residual MgF and CaF2 by reaction with K2O. Aluminum, calcium oxide, and magnesium oxide are recovered to manufacture structural materials and glass.

  12. Generation of Kerr combs centered at 4.5{\\mu}m in crystalline microresonators pumped by quantum cascade lasers

    E-print Network

    Savchenkov, Anatoliy A; Di Teodoro, Fabio; Belden, Paul M; Lotshaw, William T; Matsko, Andrey B; Maleki, Lute

    2015-01-01

    We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF$_2$ and MgF$_2$ whispering-gallery mode resonators pumped with continuous wave room temperature quantum cascade lasers. The combs were centered at 4.5$\\mu$m, the longest wavelength to date. A frequency comb wider than a half of an octave was demonstrated when approximately 20mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10$^8$.

  13. Potential energy - induced nanostructuring of insulator surfaces by impact of slow, very highly charged ions

    NASA Astrophysics Data System (ADS)

    Meissl, W.; Ginzel, R.; Heller, R.; El-Said, A. S.; Kowarik, G.; Vasko, C.; Gösselsberger, C.; Ritter, R.; Solleder, B.; Simon, M.; Facsko, S.; Crespo López-Urrutia, J. R.; Lemell, C.; Papaléo, R. M.; Möller, W.; Ullrich, J.; Burgdörfer, J.; Aumayr, F.

    2009-11-01

    We have recently shown that the impact of individual slow highly charged ions is able to induce permanent nano-sized hillocks on the surface of a CaF2 single crystal. The experimentally observed threshold of the projectile ion potential energy necessary for hillock formation could be linked to a solid-liquid phase transition (nano-melting). In this contribution we report on similar nano-sized surface modifications as a result of the potential energy of impacting highly charged ions for other surfaces.

  14. Ionic liquid synthesis of luminescent nano-cubes and their microstructure characterization

    NASA Astrophysics Data System (ADS)

    Ma, Qianmin; Ping, Lulu; Zhang, Helen Meihua; Yang, Jinglian; Wang, Qianming

    2015-07-01

    Regular CaF2:Eu3+ nano-cubes undergo ionic liquid (diallyldimethylammonium tetrafluoroborate, abbreviated as DTB)-mediated synthesis reactions in the presence of Eu(NO3)3?6H2O. The formation of uniform and mono-dispersed particles relies primarily on a one-pot hydrothermal method. The correlations between reaction temperature, doping concentration and crystalline structures have been clarified. In addition, the photoluminescence features and their influencing factors were extensively studied. In the case of Eu3+ containing phosphors, the application of new structure directing reagents will be convenient for the design of functional nanomaterials.

  15. In the search of new electrocaloric materials: Fast ion conductors

    NASA Astrophysics Data System (ADS)

    Cazorla, Claudio

    We analyse the effects of applying an electric field on the critical temperature at which superionicity appears in archetypal fast ion conductor CaF2, by means of molecular dynamics simulations. We find that the onset of superionicity can be reduced by about 100 K when relatively small electric fields of ?50 KV cm-1 are applied. Under large enough electric fields, however, ionic conductivity is depleted. The normal to superionic phase transition is characterised by a large increase of entropy, thereby sizeable electrocaloric effects can be realised in fast ion conductors that are promising for solid-state cooling applications.

  16. Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

    SciTech Connect

    David H Hurley; Marat Khafizov; Zilong Hua; Rory Kennedy; Heng Ban

    2012-05-01

    A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k=(e2/D)1/2. To generalize this approach, sensitivity analysis was conducted for materials having a range of thermal conductivities. Experimental validation was sought using two substrate materials, SiO2 and CaF2, both coated with thin titanium films. The measured conductivities compare favorably with literature values.

  17. Intergranular fracture of lithium fluoride-22 percent calcium fluoride hypereutectic salt at 800 K

    NASA Technical Reports Server (NTRS)

    Raj, Subramanium V.; Whittenberger, J. Daniel

    1990-01-01

    Substantial strain-hardening was noted during the initial stages of deformation in constant-velocity compression tests conducted on as-cast samples of the LiF-22 mol pct CaF2 hypereutectic salt at 800 K. The deformed specimens exhibited extensive grain-boundary cracking and cavitation, suggesting that such cracking, in conjunction with interfacial sliding, is important for cavity nucleation at grain boundaries and at the LiF-CaF2 interfaces. Cavity growth and interlinkage occur through the preferential failure of the weaker LiF phase.

  18. Measuring 19F(?,n) with VANDLE for Nuclear Safeguards

    NASA Astrophysics Data System (ADS)

    Peters, William; Clement, R. C. C.; Smith, M. S.; Pain, S. D.; Thompson, S.; Cizewski, J. A.; Reingold, C.; Manning, B.; Burcher, S.; Bardayan, D. W.; Tan, W.-P.; Stech, E.; Smith, M. K.; Smith, K.; Avetisyan, R.; Long, A.; Battaglia, A.; Marley, S.; Gyurjinyan, A.; Ilyushkin, S.; O'Malley, P. D.; Madurga, M.; Paulauskas, S. V.; Taylor, S.; Febbraro, M.

    2014-09-01

    UF6 is used in many parts of the Uranium Fuel Cycle, and various techniques are used by nonproliferation agencies to monitor and account for the material. One of the most promising non-destructive assay (NDA) methods consists of measuring gross neutron rates induced by uranium-decay alpha particles reacting with the fluorine and emitting a neutron. This method, however, currently lacks reliable nuclear data on the 19F(?,n) reaction cross section to determine an accurate neutron yield rate for a given sample of UF6. We have used the Versatile Array of Neutron Detectors at Low Energy (VANDLE) to measure the cross section and coincident neutron spectrum over an energy range pertinent to NDA in a two part experiment: First at Notre Dame with a LaF3 target and a pulsed alpha-particle beam, and second at ORNL with a windowless He-gas target and a 19F beam. The motivation for this measurement and preliminary results will be presented. UF6 is used in many parts of the Uranium Fuel Cycle, and various techniques are used by nonproliferation agencies to monitor and account for the material. One of the most promising non-destructive assay (NDA) methods consists of measuring gross neutron rates induced by uranium-decay alpha particles reacting with the fluorine and emitting a neutron. This method, however, currently lacks reliable nuclear data on the 19F(?,n) reaction cross section to determine an accurate neutron yield rate for a given sample of UF6. We have used the Versatile Array of Neutron Detectors at Low Energy (VANDLE) to measure the cross section and coincident neutron spectrum over an energy range pertinent to NDA in a two part experiment: First at Notre Dame with a LaF3 target and a pulsed alpha-particle beam, and second at ORNL with a windowless He-gas target and a 19F beam. The motivation for this measurement and preliminary results will be presented. This work is funded in part by NSF Grant 1068192, DOE Office of Science, and the NNSA Office of Defense Nuclear Nonproliferation R&D.

  19. Light-emitting nanocomposites and novel amorphous polymers for optical applications

    NASA Astrophysics Data System (ADS)

    Gipson, Kyle Garrod

    Polymeric optical materials generally are comprised of amorphous polymers that are transparent in at visible wavelengths but exhibit strong absorption bands in the near-infrared making them less useful for many optical applications. Attenuation, which is the absorption per unit length, largely results from the high vibrational energy associated with carbon-hydrogen bonds contained in the polymer backbone. Attenuation can be mitigated by optical amplification utilizing light emitting additives. Investigated in this dissertation are synthesis techniques for the fabrication of light-emitting polymer nanocomposites and their resultant thermal and rheological characteristics for potential use as polymer optical fibers or films. Inorganic nanocrystals doped with optically active rare-earth ions (Tb 3+:LaF3) treated with organic ligands were synthesized in water and methanol in order to produce polymethyl methacrylate (PMMA) light-emitting nanocomposites. Two different aromatic ligands (acetylsalicylic acid, ASA and 2-picolinic acid, PA) were employed to functionalize the surface of Tb 3+:LaF3 nanocrystals. We have used infrared spectroscopy, thermal analysis, elemental analysis, dynamic light scattering, rheological measurements and optical spectroscopy to investigate the nanoparticle structure and composition response of ligand-capped nanocrystals under various synthesis parameters. A theoretical interpretation of particle-to-particle interactions also was conducted which supported our study of the potential of agglomeration within the nanoparticle suspensions. Novel amorphous polymers (e.g. perfluorocyclobutyl aryl ethers, PFCB), which do not exhibit strong C-H vibrations, have been reported to possess excellent optical properties. Little is known of the intrinsic properties of PFCBs (e.g. biphenylvinyl ether, BPVE and hexafluoroisopropylidene vinyl ether, 6F) as well as the behavior of the polymer melt during extrusion. We preformed empirical and experimental thermal and rheological evaluations of BPVE, 6F and polymer nanocomposites of varying loading levels. These studies provide greater understanding of the melt performance of BPVE, 6F and for optically active nanoparticles within PMMA. The data and the use of a fiber melt extrusion modeling package allowed for the construction of viable initial melt fiber extrusion parameters. Many researchers have focused on the development of polymer light-emitting nanocomposites and novel amorphous polymers for optical applications. I, however, have focused particularly on developing a fundamental understanding of the nanoparticle synthesis. My work concentrates on the surface chemistry of the nanoparticle with an emphasis on the interaction between the surface attached ligand and the polymer matrix. This research will aide in the development of a more optimized and compliant polymeric nanocomposites for optical applications.

  20. Fluorspar deposits near Meyers Cove, Lemhi County, Idaho

    USGS Publications Warehouse

    Cox, D.C.

    1954-01-01

    The fluorspar deposits near Meyers Cove, Lemhi County, Idaho, are localized along three groups of shear zones: one group strikes northeast and dips steeply northwestward, another strikes northeast and dips gently northwestward, and the third strikes northwest and dips gently southwestward. The country rocks are tuffs and flows of the Casto volcanics of Permian (?) age and the Challis volcanics of late Oligocene or early Miocene age. The known deposits are in a belt about 3 miles long and 2 miles wide and crop out at altitudes between 5,100 feet and 7,200 feet above sea level. The principal vein minerals are fluorite, chalcedony, and barite. The fluorite occurs as lodes, crusts around fragments of rock, and replacements of fine breccia. The lodes range in size from veinlets to vein zones several hundred feet long and as much as 20 feet wide and contain ore that ranges in grade from 40 percent to 85 percent CaF2; the average grade is about 50 percent CaF2.

  1. Study on laser damage of high transmission single layer optical thin film for fused silica glass induced by inclusion

    NASA Astrophysics Data System (ADS)

    Hao, Ming-ming; Lu, Guo-guang; Zhu, Hong-bo; Wang, Li-na

    2015-08-01

    In order to research the laser damage mechanism of high transmission single layer optical thin film for fused silica glass, finite element method was used to calculate laser induced damage threshold (LIDT) and an optical test system with a nanosecond solid-state lasers was set up to determine the LIDT according to standard of ISO 11254. Firstly, finite element model was created at COMSOL multi-physics software and the temperature of inclusion in the optical thin film was calculated with different physical parameter. It is found that temperature at center of the inclusion firstly decreases and then increase with the increasing of inclusion depth. It is also found that the temperature constantly increase with the radius increasing from 20nm to 100nm. Moreover, the inclusion temperature for MgF2 thin film is higher than that of CaF2 thin film. Lastly, LIDT were measured by the optical test system, and the average value of LIDT is 3.7J/cm2 for MgF2 thin film and 4.6J/cm2 for CaF2 thin film, which is well fit with the value calculated by COMSOL software. The study shows that finite element method is an effective method to calculate LIDT for optical thin film and impurity has significant impact on the LIDT of optical thin film and therefore decreasing the density of the impurity would increase the LIDT of the thin film.

  2. Syntheses, structural characterization, and DPPH radical scavenging activity of cocrystals of caffeine with 1- and 2-naphthoxyacetic acids

    NASA Astrophysics Data System (ADS)

    Suresh Kumar, G. S.; Seethalakshmi, P. G.; Sumathi, D.; Bhuvanesh, N.; Kumaresan, S.

    2013-03-01

    Caffeine:1-naphthoxyacetic acid [(caf)(1-naa)] and caffeine:2-naphthoxyacetic acid [(caf)(2-naa)] cocrystals have been synthesized and single crystals were grown by slow evaporation technique. The structures of the grown crystals were elucidated using single crystal X-ray diffraction analysis. Both the cocrystals belong to the monoclinic crystallographic system with space group P21/c, Z = 4, and ? = ? = 90°, whereas ? = 111.4244(18)° for [(caf)(1-naa)] and ? = 109.281(6)° for [(caf)(2-naa)]. The crystal packing is predominantly stabilized by hydrogen bonding and ?-? stacking interactions. The presence of unionized -COOH functional group in both the cocrystals was identified by FTIR spectral analysis. Thermal behavior and stability of both the cocrystals were studied by TGA/DTA analyses. Solvent-free formation of these cocrystals was confirmed by powder X-ray diffraction analyses. The theoretical energy of cocrystals showed that the formers have higher energy than cocrystals 1 and 2. DPPH radical scavenging activity of cocrystals 1 and 2 is slightly greater than the formers.

  3. Effect of doping of calcium fluoride nanoparticles on the photoluminescence properties of europium complexes with benzoic acid derivatives as secondary ligands and 2-aminopyridine as primary ligand

    NASA Astrophysics Data System (ADS)

    Sharma, Garima; Narula, Anudeep Kumar

    2015-08-01

    The present article reports the synthesis of three Eu(III) complexes [Eu(BA)3(2-ap)] (1), [Eu(HBA)3(2-ap)] (2) and [Eu(ABA)3(2-ap)] (3) (BA = benzoic acid, HBA = 2-hydroxy benzoic acid, ABA = 2-amino benzoic acid and 2-ap = 2-aminopyridine) carried out in ethanol solution. The complexes were further doped with CaF2 nanoparticles and a change in the photoluminescence properties was observed. The compositions and structural investigation of the complexes were determined by elemental analysis and Fourier transform infrared spectroscopy (FTIR) which suggest the coordination of ligands with the central Eu(III) ion. The optical properties of the complexes were studied by Ultraviolet Visible absorption spectroscopy (UV-Vis) and photoluminescence studies (PL). The relative PL intensity was enhanced in the Eu(III) complexes doped with CaF2 nanoparticles as compared to the pure Eu(III) complexes, however the increase in intensity varied in the order of ligands ABA > HBA > BA. The photoluminescence lifetime decay curves also revealed the longer lifetime (?) and higher quantum efficiency (?) for europium complexes with ABA ligands suggesting the efficient energy transfer and better sensitizing ability of the ligand to europium ion. The morphology of the synthesized compounds were studied by Scanning Electron Microscopy (SEM) revealing spherical morphology with agglomeration of the nanoparticles.

  4. Local coordination state of rare earth in eutectic scintillators for neutron detector applications

    PubMed Central

    Masai, Hirokazu; Yanagida, Takayuki; Mizoguchi, Teruyasu; Ina, Toshiaki; Miyazaki, Takamichi; Kawaguti, Noriaki; Fukuda, Kentaro

    2015-01-01

    Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca2+ ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu2+ ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors. PMID:26292726

  5. Phosphorus Migration During Direct Reduction of Coal Composite High-Phosphorus Iron Ore Pellets

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng; Xue, Qingguo; Wang, Guang; Zhang, Yuanyuan; Wang, Jingsong

    2015-10-01

    This study investigated the direct reduction process and phosphorus migration features of high-phosphorus iron ores using simulated experiments. Results show that iron oxide was successfully reduced, and a Fe-Si-Al slag formed in carbon-bearing pellets at 1473 K (1200 °C). Fluorapatite then began to decompose into Ca3(PO4)2 and CaF2. As the reaction continued, Ca3(PO4)2 and Fe-Si-Al slag reacted quickly with each other to generate CaAl2Si2O8 and P2, while CaF2 turned into SiF4 gas in the presence of high SiO2. A small amount remained in the slag phase and formed CaAl2Si2O8. Further analysis detailed the migration process of the phosphorus into iron phases, as well as the relationship between carburization and phosphorus absorption in the iron phases. As carbon content in the iron phase increased, the austenite grain boundary melted and formed a large quantity of liquid iron which quickly absorbed the phosphorus. Based on the results of simulation and analysis, this paper proposed a method which reduced the absorption of P by the metallic iron formed and reduced P content in metallic iron during direct reduction.

  6. Mode-locking operation of quasi-continuous diode pumped TGT-grown Nd,Y-codoped:SrF2 crystal

    NASA Astrophysics Data System (ADS)

    Jelínek, Michal; Kube?ek, Václav; Su, Liangbi; Jiang, Dapeng; Ma, Fengkai; Zhang, Qian; Cao, Yuexin; Xu, Jun

    2015-01-01

    Fluoride-type crystals (CaF2, SrF2) doped with neodymium Nd3+ present interesting alternative as a laser active media for the diode-pumped mode-locked laser systems mainly because of their broad emission spectra as well as longer fluorescence lifetime in comparison with well-known materials as Nd:YAG or Nd:YVO4. In comparison with Nd:glass active material, SrF2 and CaF2 have better thermal conductivity. In spite of the thermal conductivity decreases with doping concentration, these crystal might be interesting alternative for the Nd:glass mode-locked laser systems. In this contribution we present the first results of the Nd,Y:SrF2 mode-locked laser diode-pumped at 796nm. Mode-locking operation using SESAM was successfully achieved in the pulsed pumping regime (pulse-duration 1.5 ms, frequency 10 Hz) with the overall average output power of 2.3 mW (corresponding to the power amplitude of 153 mW) in one output beam at the wavelength of ~1055 nm. The actual pulse-duration was 87 ps.

  7. Some studies on a solid-state sulfur probe for coal gasification systems

    NASA Technical Reports Server (NTRS)

    Jacob, K. T.; Rao, D. B.; Nelson, H. G.

    1978-01-01

    As a part of a program for the development of a sulfur probe for monitoring the sulfur potential in coal gasification reactors, an investigation was conducted regarding the efficiency of the solid electrolyte cell Ar+H2+H2S/CaS+CaF2+(Pt)//CaF2//Pt)+CaF2+CaS/H2S+H2+Ar. A demonstration is provided of the theory, design, and operation of a solid-state sulfur probe based on CaF2 electrolyte. It was found that the cell responds to changes in sulfur potential in a manner predicted by the Nernst equation. The response time of the cell at 1225 K, after a small change in temperature or gas composition, was 2.5 Hr, while at a lower temperature of 990 K the response time was approximately 9 hr. The cell emf was insensitive to a moderate increase in the flow rate of the test gas and/or the reference gas. The exact factors affecting the slow response time of galvanic cells based on a CaF2 electrolyte have not yet been determined. The rate-limiting steps may be either the kinetics of electrode reactions or the rate of transport through the electrolyte.

  8. Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

    PubMed

    Masai, Hirokazu; Yanagida, Takayuki; Mizoguchi, Teruyasu; Ina, Toshiaki; Miyazaki, Takamichi; Kawaguti, Noriaki; Fukuda, Kentaro

    2015-01-01

    Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors. PMID:26292726

  9. Synthesis of High-Temperature Self-lubricating Wear Resistant Composite Coating on Ti6Al4V Alloy by Laser Deposition

    NASA Astrophysics Data System (ADS)

    Luo, Jian; Liu, Xiu-Bo; Xiang, Zhan-Feng; Shi, Shi-Hong; Chen, Yao; Shi, Gao-Lian; Wu, Shao-Hua; Wu, Yu-Nan

    2015-05-01

    Laser deposition was adopted to prepare novel Ni-based solid solution (?-NiCrAlTi)/ TiC/?-Ti/CaF2 high-temperature self-lubricating wear resistant composite coating on Ti6Al4V alloy. Microstructure, micro-hardness, wear behavior, and counter-body effect of the coating were investigated systematically. It can be seen that the coating mainly consists of ?-NiCrAlTi, TiC, ?-Ti, and small fine CaF2 particles. Average micro-hardness of the coating is 1023 HV0.3, which is about three-factor higher than that of Ti6Al4V substrate (380 HV0.3). The friction coefficient and wear rate of the coating decrease at all test temperatures to different extents with respect to the substrate. The improvement in wear resistance is believed to be the combined effects of the ?-NiCrAlTi solid solution, the dominating anti-wear capabilities of the reinforced TiC carbides, and the self-lubricating property of CaF2.

  10. On-Chip Electrolytic Chemistry for the Tuning of Graphene Devices

    NASA Astrophysics Data System (ADS)

    Schmucker, Scott; Ruppalt, Laura; Culbertson, James; Do, Jae Won; Lyding, Joseph; Robinson, Jeremy; Cress, Cory

    2015-03-01

    The inherent interfacial nature of two-dimensional materials has motivated the tuning of these films by choice of substrate or chemical functionalization. Such parameters are generally selected during fabrication, and therefore remain static during device operation. However, the possibility of dynamic chemistry in a tunable solid-state system will enable the development of new devices which fully leverage the rich chemistry of graphenic materials. Here, we fabricate a novel device for localized, dynamic doping and functionalization of graphene that is compatible with CMOS processing. The device is enabled by a top-gated, solid electrochemical cell designed with calcium fluoride (CaF2) substituting the oxide of a traditional MOSFET. When the CaF2 is gated, F flows from cathode to anode, segregating Ca and F. In this work, one electrode is graphene. When saturated with fluorine, graphene undergoes covalent modification, becoming a wide-bandgap semiconductor. In contrast, when functionalized with calcium or dilute fluorine, graphene is electron or hole doped, respectively. With transport, Raman, and XPS, we demonstrate this lithographically localized and reversible modulation of graphene's electronic and chemical character.

  11. Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 - 1400 K

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.; Whittenberger, J. Daniel

    1987-01-01

    Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.

  12. Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 to 1400 K

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.; Whittenberger, J. Daniel

    1987-01-01

    Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.

  13. Measurement of polarization assemblies for the Daniel K. Inouye Solar Telescope

    NASA Astrophysics Data System (ADS)

    Schubert, William H.; Petrak, Erika; Baur, Thomas G.

    2015-03-01

    We present here methodology and instrumentation for the precise measurement of retardance and optic axis orientation of retarder assemblies for the Daniel K. Inouye Solar Telescope. This solar telescope will perform broadband polarimetry of the sun. Each Meadowlark assembly is made up of three compound zero order retarders that must have a retardance variation of less than 6.33 nanometers across the greater than 110 millimeter clear aperture. The retardation of each component was measured using a combination of spectral transmission scans and ellipsometry, with test wavelengths of less than a 0.45 nanometer bandwidths and yielding a standard deviation in measurements of less than 0.001 waves. A technique for the measurement of the near zero window (Infrasil® and CaF2) retardance is shown, in addition to retardance measurements of the component waveplates. An average retardance of 0.63 nm for CaF2 and 0.28 nm for Infrasil® was found. Finally, a technique for determining the optic axis tilt of each crystal waveplate using laser ellipsometry is discussed.

  14. Influence of substrate type on transport properties of superconducting FeSe0.5Te0.5 thin films

    NASA Astrophysics Data System (ADS)

    Yuan, Feifei; Iida, Kazumasa; Langer, Marco; Hänisch, Jens; Ichinose, Ataru; Tsukada, Ichiro; Sala, Alberto; Putti, Marina; Hühne, Ruben; Schultz, Ludwig; Shi, Zhixiang

    2015-06-01

    FeSe0.5Te0.5 thin films were grown by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrate shows no influence on the lattice parameters of the films, whereas the type of substrate affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density Jc(?) at ? = 180° (H||c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no Jc(?) peaks for H||c were observed in films on CaF2 and LaAlO3. Jc(?) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg-Landau approach with appropriate anisotropy ratio ?J. The scaling parameter ?J is decreasing with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 films on Fe-buffered MgO substrates.

  15. Local coordination state of rare earth in eutectic scintillators for neutron detector applications

    NASA Astrophysics Data System (ADS)

    Masai, Hirokazu; Yanagida, Takayuki; Mizoguchi, Teruyasu; Ina, Toshiaki; Miyazaki, Takamichi; Kawaguti, Noriaki; Fukuda, Kentaro

    2015-08-01

    Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca2+ ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu2+ ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

  16. Adding diffuse reflectance infrared Fourier transform spectroscopy capability to extended x-ray-absorption fine structure in a new cell to study solid catalysts in combination with a modulation approach

    NASA Astrophysics Data System (ADS)

    Chiarello, Gian Luca; Nachtegaal, Maarten; Marchionni, Valentina; Quaroni, Luca; Ferri, Davide

    2014-07-01

    We describe a novel cell used to combine in situ transmission X-ray absorption spectroscopy (XAS) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in a single experiment. The novelty of the cell design compared to current examples is that both radiations are passed through an X-ray and IR transparent window in direct contact with the sample. This innovative geometry also offers a wide surface for IR collection. In order to avoid interference from the crystalline IR transparent materials (e.g., CaF2, MgF2, diamond) a 500 ?m carbon filled hole is laser drilled in the center of a CaF2 window. The cell is designed to represent a plug flow reactor, has reduced dead volume in order to allow for fast exchange of gases and is therefore suitable for experiments under fast transients, e.g., according to the concentration modulation approach. High quality time-resolved XAS and DRIFTS data of a 2 wt.% Pt/Al2O3 catalyst are obtained in concentration modulation experiments where CO (or H2) pulses are alternated to O2 pulses at 150 °C. We show that additional information can be obtained on the Pt redox dynamic under working conditions thanks to the improved sensitivity given by the modulation approach followed by Phase Sensitive Detection (PSD) analysis. It is anticipated that the design of the novel cell is likely suitable for a number of other in situ spectroscopic and diffraction methods.

  17. Recovery Behavior of Rare Earth from Bayan Obo Complex Iron Ore

    NASA Astrophysics Data System (ADS)

    Ding, Yingui; Xue, Qingguo; Wang, Guang; Wang, Jingsong

    2013-02-01

    A novel process is presented for recovering rare earth from Bayan Obo complex iron ore. The iron ore was reduced and melting separated to produce iron nugget and rare-earth-rich slag. In order to investigate the influence of cooling rate on mineral components, especially the enrichment behavior of RE-containing mineral, the slag was remelted at 1673 K (1400 °C) and the liquid slags were cooled using three types of cooling conditions, water quenching, air cooling, and furnace cooling. Subsequently, the slags were leached by hydrochloric acid to evaluate the relations between leaching efficiency of rare earth and cooling conditions. The results indicated that the slags under different cooling conditions mainly contained fluorite, cefluosil, and cuspidine. The rare-earth mineral is more fully crystallized when the cooling rate of the liquid slag was decreased. The proportion of Ce (III) to Ce (IV) increases with the increase of heating time and decrease of cooling rate. It has been found that the influence of cooling rate on the leaching rate of the rare earth is slight. From water quenching to furnace cooling, the leaching rate of rare earth increases from 97.00 pct to 99.48 pct. After being filtered, filtrate can be used to produce rare-earth chloride. Leached residue, with CaF2 of 64.45 pct and ThO2 of 0.05 pct, can be used to recover CaF2 and extract nuclear source material.

  18. Measurement of Transmittance Variation Due to the Water Vapor Adsorption on Optical Glass Surfaces

    NASA Astrophysics Data System (ADS)

    Itoh, Nobunari; Katoh, Masahiro; Okano, Nobuaki

    Gas adsorption onto optical surfaces equipped in satellites is one of the causes of signal degradation occurred in orbit and water is one of the most potent ad-molecules. To estimate the degradation caused by water adsorption onto optical glass surface, the transmittance measurements were carried out in UV-VIS (200--800nm) and IR (1.7--20?m) wavelength ranges. Five kinds of glasses, SiO2, BK7, Al2O3, CaF2, and ZnSe, which are typically used for satellite optics, were selected as glass samples. In IR wavelength range, a local absorption feature was appeared at ?=3.1?m when a glass temperature was below 200K. The phase change of adsorbed water from vapor to solid may account for the newly appeared absorption. In UV-VIS region, there was no local absorption feature but broad transmittance decrease. BK7 and ZnSe, which are hydrophobic, showed little transmittance decrease and it was hard to find the wavelength dependence for their transmittance spectra. On the other hand, the transmittance spectra of hydrophilic glasses, SiO2, Al2O3, and CaF2, showed wavelength dependence and had the local minimal value. From our computation, it is found that the growth of ice grains on a glass surface makes it possible to reproduct the spectral transmittance degradation detected for hydrophilic glasses.

  19. Liquidus Temperature Depression in Cryolitic Melts

    NASA Astrophysics Data System (ADS)

    Solheim, Asbjørn

    2012-08-01

    The electrolyte in Hall-Héroult cells for the manufacture of primary aluminum nominally contains only cryolite (Na3AlF6) with additions of AlF3, CaF2, and Al2O3. However, impurities are present, entering the process with the feedstock. The effect on the liquidus temperature by the impurities cannot be calculated correctly by the well-known equation for freezing-point depression in binary systems simply because the electrolyte cannot be regarded as a binary system. By extending the equation for freezing-point depression to the ternary system NaF-AlF3-B, it appeared that the acidity of the impurity B plays a major role. Some calculations were made using an ideal Temkin model, and for most types of impurities, the effect on the liquidus temperature will be larger in an industrial electrolyte than what can be estimated from the equation for freezing-point depression in cryolite. Experimental data on the liquidus temperature in the system Na3AlF6-AlF3-Al2O3-CaF2-MgF2 show that the effect of MgF2 on the liquidus temperature increases strongly with decreasing NaF/AlF3 molar ratio, and it is suggested that MgF2 forms an anion complex, probably MgF{4/2-}.

  20. Fluorite solubility equilibria in selected geothermal waters

    USGS Publications Warehouse

    Nordstrom, D.K.; Jenne, E.A.

    1977-01-01

    Calculation of chemical equilibria in 351 hot springs and surface waters from selected geothermal areas in the western United States indicate that the solubility of the mineral fluorite, CaF2, provides an equilibrium control on dissolved fluoride activity. Waters that are undersaturated have undergone dilution by non-thermal waters as shown by decreased conductivity and temperature values, and only 2% of the samples are supersaturated by more than the expected error. Calculations also demonstrate that simultaneous chemical equilibria between the thermal waters and calcite as well as fluorite minerals exist under a variety of conditions. Testing for fluorite solubility required a critical review of the thermodynamic data for fluorite. By applying multiple regression of a mathematical model to selected published data we have obtained revised estimates of the pK (10,96), ??Gof (-280.08 kcal/mole), ??Hof (-292.59 kcal/mole), S?? (16.39 cal/deg/mole) and CoP (16.16 cal/deg/mole) for CaF2 at 25??C and 1 atm. Association constants and reaction enthalpies for fluoride complexes with boron, calcium and iron are included in this review. The excellent agreement between the computer-based activity products and the revised pK suggests that the chemistry of geothermal waters may also be a guide to evaluating mineral solubility data where major discrepancies are evident. ?? 1977.

  1. A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS

    PubMed Central

    Suturin, S. M.; Fedorov, V. V.; Korovin, A. M.; Valkovskiy, G. A.; Konnikov, S. G.; Tabuchi, M.; Sokolov, N. S.

    2013-01-01

    In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright ?111? streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles. PMID:24046491

  2. Tribological properties of alumina-boria-silicate fabric from 25 to 850 C

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    1988-01-01

    Demanding tribological properties are required of the materials used for the sliding seal between the sidewalls and the lower wall of the variable area hypersonic engine. Temperatures range from room temperature and below to operating temperatures of 1000 C in an environment of air, hydrogen, and water vapor. Candidate sealing materials for this application are an alumina-boria-silicate, ceramic, fabric rope sliding against the engine walls which may be made from copper- or nickel-based alloys. Using a pin-on-disk tribometer, the friction and wear properties of some of these potential materials and possible lubrication methods are evaluated. The ceramic fabric rope displayed unacceptably high friction coefficients (0.6 to 1.3) and, thus, requires lubrication. Sputtered thin films of gold, silver, and CaF2 reduced the friction by a factor of two. Sprayed coatings of boride nitride did not effectively lubricate the fabric. Static heat treatment tests at 950 C indicate that the fabric is chemically attacked by large quantities of silver, CaF2, and boron nitride. Sputtered films or powder impregnation of the fabric with gold may provide adequate lubrication up to 1000 C without showing any chemical attack.

  3. Tribological properties of alumina-boria-silicate fabric from 25 C to 850 C

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    1989-01-01

    Demanding tribological properties are required of the materials used for the sliding seal between the sidewalls and the lower wall of the variable area hypersonic engine. Temperatures range from room temperature and below to operating temperatures of 1000 C in an environment of air, hydrogen, and water vapor. Candidate sealing materials for this application are an alumina-boria-silicate, ceramic, fabric rope sliding against the engine walls which may be made from copper- or nickel-based alloys. Using a pin-on-disk tribometer, the friction and wear properties of some of these potential materials and possible lubrication methods are evaluated. The ceramic fabric rope displayed unacceptably high friction coefficients (0.6 to 1.3) and, thus, requires lubrication. Sputtered thin films of gold, silver, and CaF2 reduced the friction by a factor of two. Sprayed coatings of boride nitride did not effectively lubricate the fabric. Static heat treatment tests at 950 C indicate that the fabric is chemically attacked by large quantities of silver, CaF2, and boron nitride. Sputtered films or powder impregnation of the fabric with gold may provide adequate lubrication up to 1000 C without showing any chemical attack.

  4. Identification of salt-alloy combinations for thermal energy storage applications in advanced solar dynamic power systems

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Misra, A. K.

    1987-01-01

    Thermodynamic calculations based on the available data for flouride salt systems reveal that a number of congruently melting compositions and eutectics exist which have the potential to meet the lightweight, high energy storage requirements imposed for advanced solar dynamic systems operating between about 1000 and 1400 K. Compatibility studies to determine suitable containment alloys to be used with NaF-22CaF2-13MgF2, NaF-32CaF2, and NaF-23MgF2 have been conducted at the eutectic temperature + 25 K for each system. For these three NaF-based eutectics, none of the common, commercially available high temperature alloys appear to offer adequate corrosion resistance for a long lifetime; however mild steel, pure nickel and Nb-1Zr could prove useful. These latter materials suggest the possibility that a strong, corrosion resistant, nonrefractory, elevated temperature alloy based on the Ni-Ni3Nb system could be developed.

  5. Ellipsometric and optical study of some uncommon insulator films on 3-5 semiconductors

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Warner, J. D.; Liu, D. C.; Pouch, J. J.

    1985-01-01

    Optical properties of three types of insulating films that show promise in potential applications in the 3-4 semiconductor technology were evaluated, namely a-C:H, BN and CaF2. The plasma deposited a-C:H shows an amorphous behavior with optical energy gaps of approximately 2 to 2.4 eV. These a-C:H films have higher density and/or hardness, higher refractive index and lower optical energy gaps with increasing energy of the particles in the plasma, while the density of states remains unchanged. These results are in agreement, and give a fine-tuned positive confirmation to an existing conjecture on the nature of a-C:H films (1). Ion beam deposited BN films show amorphous behavior with energy gap of 5 eV. These films are nonstoichiometric (B/N approximately 2) and have refractive index, density and/or hardness which are dependent on the deposition conditions. The epitaxially grown CaF2 on GaAs films have optical parameters equal to bulk, but evidence of damage was found in the GaAs at the interface.

  6. Quantum mechanical cluster calculations of critical scintillationprocesses

    SciTech Connect

    Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.

    2000-02-22

    This paper describes the use of commercial quantum chemistrycodes to simu-late several critical scintillation processes. The crystalis modeled as a cluster of typically 50 atoms embedded in an array oftypically 5,000 point charges designed to reproduce the electrostaticfield of the infinite crystal. The Schrodinger equation is solved for theground, ionized, and excited states of the system to determine the energyand electron wavefunction. Computational methods for the followingcritical processes are described: (1) the formation and diffusion ofrelaxed holes, (2) the formation of excitons, (3) the trapping ofelectrons and holes by activator atoms, (4) the excitation of activatoratoms, and (5) thermal quenching. Examples include hole diffusion in CsI,the exciton in CsI, the excited state of CsI:Tl, the energy barrier forthe diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trappingby activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation risetime.

  7. Ion beam effects of 26.0 MeV Cu7+ ions in thin metallic and insulating films during Heavy Ion ERDA measurements

    NASA Astrophysics Data System (ADS)

    Mavhungu, H.; Msimanga, M.; Hlatshwayo, T.

    2015-04-01

    We report on an investigation carried out to determine effects of the probing beam on the structure of typical metallic and insulating thin films during Elastic Recoil Detection Analysis (ERDA) using a heavy ion beam. Metallic niobium nitride (NbN) and insulating calcium fluoride (CaF2) thin films (used as test samples) were irradiated by 26.0 MeV 63Cu7+ ions to fluences of 1.70 × 1014 ions/cm2 and 2.70 × 1014 ions/cm2, respectively. The effects of irradiation on the structural properties of the films were studied using Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). RBS results showed a significant (18%) reduction in the thickness of the CaF2 film due to electronic sputtering compared to only 1% reduction in the NbN film. XRD results showed no significant peak shifts in both films, but rather formation of unidentified peaks in the insulating film. AFM results indicated a substantial decrease in the average surface roughness of the insulating film and only a nominal increase in that of the metallic film. Results of electronic sputtering yield measurements carried out by ERDA are explained in terms of both the Coulomb explosion and the inelastic thermal spike models.

  8. Lead Tungstate and Silicon Photomultipliers for Transmission Z-spectroscopy in Cargo Inspection Systems

    NASA Astrophysics Data System (ADS)

    Langeveld, Willem G. J.; Janecek, Martin

    The bremsstrahlung X-ray spectrum in high-energy, high-intensity X-ray cargo inspection systems is attenuated and modified by cargo materials depending on the cargo atomic number (Z). Spectroscopy of transmitted x rays is thus useful to measure the approximate Z of the cargo. Due to the broad features of the energy spectrum, excellent energy resolution is not required. Such "Z-Spectroscopy" (Z-SPEC) is possible at low enough count rates. A statistical approach, Z-SCAN (Z-determination by Statistical Count-rate ANalysis), can also be used, complementing Z-SPEC at high count rates. Both approaches require fast X-ray detectors and fast digitizers. Z-SPEC, in particular, benefits from very fast scintillators, in order to avoid signal pile-up.Preferentially, Z-SPEC, Z-SCAN and cargo imaging are implemented in a single detector array to reduce system cost, weight, and complexity. To preserve good spatial resolution of the imaging subsystem, dense scintillators are required. Previously, we studied ZnO, BaF2 and PbWO4, as well as suitable photo-detectors, read-out electronics and digitizers. ZnO is not suitable because it self-absorbs its scintillation light. BaF2 emits in the UV, either requiring fast wavelength shifters or UV-sensitive solid state read-out devices, and it also has a long decay time component. PbWO4 is currently the most attractive choice because it does not have these problems, but it is significantly slower and has low light output. There is thus a need for alternative fast high-density scintillators that emit visible light. Alternatively, there is a need for a fast solid-state read-out device that is sensitive to UV light for use with BaF2, or other UV-emitting scintillators. Here, we present results of tests performed with PbWO4 crystals, reflector materials and silicon photomultipliers.

  9. Ultra-broadband amplification through nanotechnology

    NASA Astrophysics Data System (ADS)

    DiMaio, Jeffrey R.; Kokuoz, Baris; Ballato, John

    2006-10-01

    As demands for bandwidth continue to increase, telecommunication networks would greatly benefit from the development of broader-band amplifiers. The currently erbium doped fiber amplifiers are limited to amplification of approximately 100 nm bandwidth window. One method to increase the bandwidth of the fiber amplifier would be to incorporate multiple rare earths (REs) into a single fiber which exhibit emissions from ~1000-1800 nm. Unfortunately, energy transfer between rare earth ions typically results in quenching all but selected emissions negating this approach to potential ultra-broadband amplification. It would be ideal if one could take the individual spectra of an ion and place that ion into a host with no regard to other lanthanides that also are present in the host. This problem can be solved by using a composite material that utilizes nanoparticles to constrain different REs to individual particles thereby controlling or preventing energy transfer. In order to control energy transfer, RE doped LaF 3 nanocrystals were grown in an aqueous solution using a core/shell technique to constrain different rare earth into separate particles or shells within a single particle. Using these techniques, we show that energy transfer can be controlled.

  10. Luminescence and scintillation properties of rare-earth-doped LuF3 scintillation crystals

    NASA Astrophysics Data System (ADS)

    Pejchal, Jan; Fukuda, Kentaro; Kurosawa, Shunsuke; Yokota, Yuui; Yoshikawa, Akira

    2015-03-01

    The Nd-doped and Er-doped LuF3 single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd-Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er3+ to Nd3+ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF3:Nd 8% standard. The leading Nd3+ 5d-4f emission was situated at 176 nm, while the Er3+ 5d-4f emission for Er-doped samples was observed at 163 nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1-3 mol%. No Er3+ 5d-4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er3+ to Nd3+ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one.

  11. Atomic origin of 3d(9)4?f(1) configuration in La(3+) solids.

    PubMed

    Yu, S-W; Carpenter, M H; Ponce, F; Friedrich, S; Lee, J-S

    2015-10-14

    We have studied the excited electronic structure of LaBr3(Ce) scintillator by soft x-ray spectroscopy such as x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES). The La 3d XAS and XES spectra of LaBr3(Ce) are compared with those of other La(3+)?solids (LaF3, La2O3, and La metal). From this comparison, it turns out that the La 3d XAS and XES spectra from all the La(3+) solids considered here appear at almost the same energy, even though the corresponding binding energies of the 3d core holes determined by XPS (x-ray photoelectron spectroscopy) are very different. As a result, we argue that the atomic nature of the 3d?4f¹ configuration created by 3d¹?4f? ? 3d?4f¹ x-ray absorption process in La(3+) solids is maintained via the localized 4?f?(1) state, which screens the 3d core holes differently from one La(3+) solid to another. PMID:26401640

  12. Improving Tribological Properties of Multialkylated Cyclopentanes under Simulated Space Environment: Two Feasible Approaches.

    PubMed

    Fan, Xiaoqiang; Wang, Liping; Li, Wen; Wan, Shanhong

    2015-07-01

    Space mechanisms require multialkylated cyclopentanes (MACs) more lubricious, more reliable, more durable, and better adaptive to harsh space environments. In this study, two kinds of additives were added into MACs for improving the tribological properties under simulated space environments: (a) solid nanoparticles (tungsten disulfide (WS2), tungsten trioxide (WO3), lanthanum oxide (La2O3), and lanthanum trifluoride (LaF3)) for steel/steel contacts; (b) liquid additives like zinc dialkyldithiophosphate (ZDDP) and molybdenum dialkyldithiocarbamate (MoDTC) for steel/steel and steel/diamond-like carbon (DLC) contacts. The results show that, under harsh simulated space environments, addition of the solid nanoparticles into MACs allows the wear to be reduced by up to one order magnitude, while liquid additives simultaneously reduce friction and wear by 80% and 93%, respectively. Friction mechanisms were proposed according to surface/interface analysis techniques, such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The role of solid nanoparticles in reducing friction and wear mainly depends on their surface enhancement effect, and the liquid additives are attributed to the formation of tribochemical reaction film derived from ZDDP and MoDTC on the sliding surfaces. PMID:26067481

  13. Effect of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped in transparent glass-ceramics

    NASA Astrophysics Data System (ADS)

    Kim Dan, Ho; Zhou, Dacheng; Wang, Rongfei; Jiao, Qing; Yang, Zhengwen; Song, Zhiguo; Yu, Xue; Qiu, Jianbei

    2014-12-01

    The glass and glass-ceramics samples with composition of 50SiO2-10AlF3-(30-x)BaF2-5TiO2-3.95LaF3- xMnCO3-0.05ErF3-1YbF3 (in mol%, x=0, 0.5, 0.8, 1.0, and 1.2) were prepared using the conventional quenching techniques. The effects of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped transparent glass-ceramics under the changing of heat treatment temperatures and concentrations of Mn2+ ions were investigated. The structural investigation carried out by X-ray diffraction (XRD), and transmission electron microscopy evidenced the formation of cubic Ba2LaF7 nanocrystals. The efficiency upconversion emission of Mn2+/Er3+/Yb3+ tri-doped was observed in the glass-ceramics. The upconversion mechanism and energy transfer between Mn2+-Yb3+ dimer and Er3+ ions were investigated.

  14. A method to measure prompt fission neutron spectrum using gamma multiplicity tagging

    NASA Astrophysics Data System (ADS)

    Blain, E.; Daskalakis, A.; Block, R. C.; Barry, D.; Danon, Y.

    2016-01-01

    In order to improve on current prompt fission neutron spectrum measurements, a gamma multiplicity tagging method was developed at the Rensselaer Polytechnic Institute Gearttner Linear Accelerator Center. This method involves using a coincidence requirement on an array of BaF2 gamma detectors to determine the timing of a fission event. This allows for much larger fission samples to be used due to the higher penetrability of gammas compared to fission fragments. Additionally, since the method relies on gammas as opposed to fission fragments, the effects of the low level discriminator, used in fission chambers to eliminate alpha events, are not seen. A 252Cf fission chamber was constructed in order to determine the viability of this method as well as the efficiency when compared to a fission chamber. The implemented multiple gamma tagging method was found to accurately reproduce the prompt fission neutron spectrum for the spontaneous fission of 252Cf and to detect 30% of fission events.

  15. Investigation of the Time Performance of a LYSO Array for TOF-PET

    E-print Network

    Jun-Hui, Liu; Feng-Feng, Cheng; Dao-Wu, Li; Zhi-Ming, Zhang; Bao-Yi, Wang; Long, Wei

    2015-01-01

    Positron Emission Tomography (PET) using time-of-flight information, which can greatly improve the quality of the reconstructed image, has recently become an exciting topic. In this work, 3.2mm*3.2mm*25mm finger-like LYSO crystals were used to make a 5*5 array, coupled to the Hamamatsu H8500 photomultiplier tube (PMT) as a detector. A fast leading-edge discriminator was designed for the LYSO-H8500 detector. Average coincidence time resolution FWHM of 330 ps was obtained for the LYSO detector with a reference BaF2 detector, whose time resolution for 511 keV {\\gamma}-rays was FWHM 150 ps. Time resolution FWHM of 294 ps was calculated for the LYSO detector, and coincidence time resolution of FHWM 415 ps can be expected for two identical LYSO detectors.

  16. High critical currents and flux creep effects in e-gun deposited epitaxially 00L oriented superconducting YBa2Cu3O7-? films

    NASA Astrophysics Data System (ADS)

    Dam, B.; Stollman, G. M.; Berghuis, P.; Guo, S. Q.; Flipse, C. F. J.; Lensink, J. G.; Griessen, R. P.

    1989-02-01

    Thin films of YBa2Cu3O7-? have been made by codeposition of Cu, Y and BaF2 in a UHV system. Annealing in humid oxygen at 835 °C produces high quality single phase preferentially c oriented films. In 1000 Å thin films the transport current density is larger than 106 A/cm2 at 86 K. Even 500 Å films prove to be superconducting above 77 K. Extrapolation to zero field of the magnetization data obtained from torque experiments are consistent with the current transport data. This indicates that the sample is homogeneous and the critical state model can be applied. Both magnetic relaxation measurements and flux creep resistivity in a magnetic field indicate the importance of thermally activated processes.

  17. Optoacoustic measurements of water vapor absorption at selected CO laser wavelengths in the 5-micron region

    NASA Technical Reports Server (NTRS)

    Menzies, R. T.; Shumate, M. S.

    1976-01-01

    Measurements of water vapor absorption were taken with a resonant optoacoustical detector (cylindrical pyrex detector, two BaF2 windows fitted into end plates at slight tilt to suppress Fabry-Perot resonances), for lack of confidence in existing spectral tabular data for the 5-7 micron region, as line shapes in the wing regions of water vapor lines are difficult to characterize. The measurements are required for air pollution studies using a CO laser, to find the differential absorption at the wavelengths in question due to atmospheric constituents other than water vapor. The design and performance of the optoacoustical detector are presented. Effects of absorption by ambient NO are considered, and the fixed-frequency discretely tunable CO laser is found suitable for monitoring urban NO concentrations in a fairly dry climate, using the water vapor absorption data obtained in the study.

  18. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    DOE PAGESBeta

    Si, W.; Zhang, C.; Wu, L.; Ozaki, T.; Gu, G.; Li, Q.

    2015-09-01

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk.more »With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.« less

  19. Stability of Grafted Polymer Nanoscale Films toward Gamma Irradiation.

    PubMed

    Borodinov, Nikolay; Giammarco, James; Patel, Neil; Agarwal, Anuradha; O'Donnell, Katie R; Kucera, Courtney J; Jacobsohn, Luiz G; Luzinov, Igor

    2015-09-01

    The present article focuses on the influence of gamma irradiation on nanoscale polymer grafted films and explores avenues for improvements in their stability toward the ionizing radiation. In terms of applications, we concentrate on enrichment polymer layers (EPLs), which are polymer thin films employed in sensor devices for the detection of chemical and biological substances. Specifically, we have studied the influence of gamma irradiation on nanoscale poly(glycidyl methacrylate) (PGMA) grafted EPL films. First, it was determined that a significant level of cross-linking was caused by irradiation in pure PGMA films. The cross-linking is accompanied by the formation of conjugated ester, carbon double bonds, hydroxyl groups, ketone carbonyls, and the elimination of epoxy groups as determined by FTIR. Polystyrene, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, dimethylphenylsilanol, BaF2, and gold nanoparticles were incorporated into the films and were found to mitigate different aspects of the radiation damage. PMID:26259102

  20. Gigahertz (GHz) hard x-ray imaging using fast scintillators

    NASA Astrophysics Data System (ADS)

    Wang, Zhehui; Guardincerri, Elena; Rathman, D. D.; Azzouz, M. E.; Barnes, Cris W.; Berger, R.; Bond, E. M.; Craig, D. M.; Holtkamp, David; Kapustinsky, J. S.; Klimenko, Alexei V.; Kwiatkowski, K.; Merl, R. B.; Morris, C. L.; Perry, J. O.; Ramberg, E.; Reich, R. K.; Ronzhin, A.; Warner, K.; Williams, R. T.; Zhu, Ren-Yuan

    2013-09-01

    Gigahertz (GHz) imaging technology will be needed at high-luminosity X-ray and charged particle sources. It is plausible to combine fast scintillators with the latest picosecond detectors and GHz electronics for multi-frame hard Xray imaging and achieve an inter-frame time of less than 10 ns. The time responses and light yield of LYSO, LaBr3, BaF2 and ZnO are measured using an MCP-PMT detector. Zinc Oxide (ZnO) is an attractive material for fast hard X-ray imaging based on GEANT4 simulations and previous studies, but the measured light yield from the samples is much lower than expected.

  1. Measurement of the ^238U neutron-capture cross section from 30 eV to 100 keV using the DANCE detector at LANSCE

    NASA Astrophysics Data System (ADS)

    Ullmann, John; Bredeweg, Todd; Couture, Aaron; Haight, Robert; Jandel, Marian; Keksis, August; O'Donnell, John; Rundberg, Robert; Vieira, David; Wouters, Jan; Wu, Ching-Yen; Becker, John; Baramsai, Bayarbadrakh; Chyzh, Andrii

    2009-05-01

    The ^238U neutron-capture cross section was measured using the DANCE detector at LANSCE. DANCE is a 4? array consisting of 160 BaF2 crystals, designed for studying neutron capture on small samples of rare or radioactive nuclides. These measurements were made with a 48 mg/cm^2 ^238U target. The measured cross sections are in substantial agreement with previous work. This measurement made use of a water-moderated neutron beam at the Manuel J. Lujan, Jr. Neutron Scattering Center at the Los Alamos National Laboratory, which is supported by the U.S. D.O.E. under contract DE-AC52-06NA25396.

  2. Multiphase monitoring by annihilation radiation coincidence mode

    NASA Astrophysics Data System (ADS)

    Vidal, A.; Viesti, G.; Osorio, C.; Pino, F.; Horvath, A.; Barros, H.; Caldogno, M.; Greaves, E. D.; Sajo-Bohus, L.

    2012-02-01

    A multiphase monitoring system employing nuclear techniques is reported, which is aimed to provide a rapid - decision tool in oilfield applications. Liquid phase time variation is monitored employing two large volume BaF2 detectors. The radioisotope source of 22Na is a positron emitter, therefore two antiparallel gammas are produced per decay, and phase flow in pipes is related to the count rate of gamma pulses in coincidence providing information on transient liquid phase during transport. Oil, gas, water fraction measurements were performed at a specialized test station assembled in our laboratory to model a wide range of field operating conditions. The time dependence of the mixed substances is monitored with the two most relevant hydrodynamic parameters, the density (type of the fluid) and the flow rate, in a LabView® environment. Performance of the monitoring system; its limitations and the possibility for further improvements are also provided.

  3. YBa2Cu3O7-? superconducting films prepared by low pressure post-annealing

    NASA Astrophysics Data System (ADS)

    Wang, Lianhong; Liu, Chong; Fan, Jing

    2014-12-01

    YBa2Cu3O7-? precursor films are deposited on 2? LaAlO3 wafer by the co-evaporation technique using Y, BaF2 and Cu as evaporation sources. After deposition, the films are annealed at low-pressure atmosphere with the composition of oxygen and water vapour. Compared with the normal pressure annealing, it is shown that low pressure can greatly improve the superconducting properties of 2? YBCO films with thickness larger than 500 nm, as the microcrack on films surface becomes unobservable the microwave surface resistance is greatly reduced. Furthermore, it is also revealed that the optimal processing window for making high quality superconducting YBCO films through ex-situ process is relatively small, therefore the ambient in annealing furnace is crucial important and should be precisely controlled.

  4. Scissors Mode of Excited Nuclei from (n,?) Reaction

    NASA Astrophysics Data System (ADS)

    Krti?ka, Milan; Be?vá?, František

    Measurements of ?-ray cascades originating from radiative neutron capture in several deformed nuclei were performed using different experimental setups. Specifically, two-step ? cascades following the capture of thermal neutrons were measured at the ?ež reactor, while multi-step ? cascades following the neutron capture were measured with 4? BaF2 detectors at isolated resonances in Los Alamos and in unresolved resonance region in Karlsruhe. Experimental data from these experiments were analyzed within the statistical approach using the DICEBOX code. Results of the analysis indicate that the scissors mode of excited nuclei plays an important role in the ? decay of all the deformed nuclei studied. Properties of the mode seen from these experiments are discussed.

  5. Fast timing study of a CeBr3 crystal: Time resolution below 120 ps at 60Co energies

    NASA Astrophysics Data System (ADS)

    Fraile, L. M.; Mach, H.; Vedia, V.; Olaizola, B.; Paziy, V.; Picado, E.; Udías, J. M.

    2013-02-01

    We report on the time response of a novel inorganic scintillator, CeBr3. The measurements were performed using a cylindrical crystal of 1-in. in height and 1-in. in diameter at 22Na and 60Co photon energies. The time response was measured against a fast reference BaF2 detector. Hamamatsu R9779 and Photonis XP20D0 fast photomultipliers (PMTs) were used. The PMT bias voltages and Constant Fraction Discriminator settings were optimized with respect to the timing resolution. The Full Width at Half Maximum (FWHM) time resolution for an individual CeBr3 crystal coupled to Hamamatsu PMT is found here to be as low as 119 ps at 60Co energies, which is comparable to the resolution of 107 ps reported for LaBr3(Ce). For 511 keV photons the measured FWHM time resolution for CeBr3 coupled to the Hamamatsu PMT is 164 ps.

  6. Saturation of the all-optical Kerr effect in solids.

    PubMed

    Borchers, Bastian; Brée, Carsten; Birkholz, Simon; Demircan, Ayhan; Steinmeyer, Günter

    2012-05-01

    We discuss the influence of the higher-order Kerr effect (HOKE) in wide bandgap solids at extreme intensities below the onset of optically induced damage. Using different theoretical models, we employ multiphoton absorption rates to compute the nonlinear refractive index by a Kramers-Kronig transform. Within this theoretical framework we provide an estimate for the appearance of significant deviations from the standard optical Kerr effect predicting a linear index change with intensity. We discuss the role of the observed saturation behavior in practically relevant situations, including Kerr lens mode-locking and supercontinuum generation in photonic crystal fibers. Furthermore, we present experimental data from a multiwave mixing experiment in BaF2, which can be explained by the appearance of the HOKE. PMID:22555731

  7. Neutron Capture Experiments Using the DANCE Array at Los Alamos

    NASA Astrophysics Data System (ADS)

    Dashdorj, D.; Mitchell, G. E.; Baramsai, B.; Chyzh, A.; Walker, C.; Agvaanluvsan, U.; Becker, J. A.; Parker, W.; Sleaford, B.; Wu, C. Y.; Bredeweg, T. A.; Couture, A.; Haight, R. C.; Jandel, M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Krti?ka, M.; Be?vá?, F.

    2009-03-01

    The Detector for Advanced Neutron Capture Experiments (DANCE) is designed for neutron capture measurements on very small and/or radioactive targets. The DANCE array of 160 BaF2 scintillation detectors is located at the Lujan Center at the Los Alamos Neutron Science Center (LANSCE). Accurate measurements of neutron capture data are important for many current applications as well as for basic understanding of neutron capture. The gamma rays following neutron capture reactions have been studied by the time-of-flight technique using the DANCE array. The high granularity of the array allows measurements of the gamma-ray multiplicity. The gamma-ray multiplicities and energy spectra for different multiplicities can be measured and analyzed for spin and parity determination of the resolved resonances.

  8. Crystallization and spectroscopic properties in Er3+ doped oxyfluorogermanate glass ceramics containing Na

    NASA Astrophysics Data System (ADS)

    Hu, Yuebo; Qiu, Sawei; Gao, Yuan; Qiu, Jianbei

    2015-07-01

    The Er3+ doped oxyfluorogermanate glasses, with a composition containing Na element, were synthesized by the conventional melting-quenching technique. When Na element was introduced into the composition of oxyfluorogermanate glass, the crystals behavior was investigated in details. Depending on the annealing procedure supplied, thermal annealing of precursor glasses in the system GeO2/BaF2/AlF3/Na2O/NaF/ZnO/GdF3/ErF3 led to the precipitation of different crystal phase nanocrystals. It was confirmed the nanocrystals in GC600 is orthorhombic NaBaAlF6 which led to enhance obviously in the UC luminescence of Er3+. However, the nanocrystals in G585 led to decrease in the UC luminescence, which indicated few Er ions enter into the lattice of this nanocrystal phase. The reason of the decrease in UC emission intensity of GC585 was analyzed.

  9. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    SciTech Connect

    Si, W.; Zhang, C.; Wu, L.; Ozaki, T.; Gu, G.; Li, Q.

    2015-09-01

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.

  10. Growth and characterization of epitaxial bismuth films

    NASA Astrophysics Data System (ADS)

    Partin, D. L.; Thrush, C. M.; Heremans, J.; Morelli, D. T.; Olk, C. H.

    1989-04-01

    Epitaxial Bi thin films have been grown by MBE. These films were grown on 111 line-oriented single-crystal BaF2. Films grown at low temperatures (below 150 C) had microscopically rough surface morphologies. At higher temperatures, no film would nucleate. This suggested a two-step growth process in which films were nucleated at 100 C followed by growth of a thicker film near the melting point of Bi. Electron-microscope observations show the films to be featureless and defect-free on the scale of 100 nm. The films grow with their trigonal axis parallel to the 111 axis of the substrate, and Laue backscattering pictures show they are epitaxial. Mobilities at room temperature are as high as 2.5 sq m/V sec, and increase to over 10 at 20 K and 100 at liquid-He temperatures.

  11. 63Ni (n ,? ) cross sections measured with DANCE

    NASA Astrophysics Data System (ADS)

    Weigand, M.; Bredeweg, T. A.; Couture, A.; Göbel, K.; Heftrich, T.; Jandel, M.; Käppeler, F.; Lederer, C.; Kivel, N.; Korschinek, G.; Krti?ka, M.; O'Donnell, J. M.; Ostermöller, J.; Plag, R.; Reifarth, R.; Schumann, D.; Ullmann, J. L.; Wallner, A.

    2015-10-01

    The neutron capture cross section of the s -process branch nucleus 63Ni affects the abundances of other nuclei in its region, especially 63Cu and 64Zn. In order to determine the energy-dependent neutron capture cross section in the astrophysical energy region, an experiment at the Los Alamos National Laboratory has been performed using the calorimetric 4 ? BaF2 array DANCE. The (n ,? ) cross section of 63Ni has been determined relative to the well-known 197Au standard with uncertainties below 15%. Various 63Ni resonances have been identified based on the Q value. Furthermore, the s -process sensitivity of the new values was analyzed with the new network calculation tool NETZ.

  12. Measurement of Neutron Capture Cross Section of 62Ni in the keV-Region

    SciTech Connect

    Alpizar-Vicente, A. M.; Hatarik, R.; Bredeweg, T. A.; Esch, E.-I.; Haight, R. C.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Greife, U.

    2006-03-13

    The neutron capture cross section of 62Ni, relative to gold as a standard, was determined in the energy range from 250 eV to 100 keV. This energy range covers the region between 5 keV to 20 keV, which is not available in ENDF. Capture events are detected with the 160-fold 4{pi} BaF2 Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center. One of the challenges was to process the high count rate of 4 MHz, which required an optimization of the data acquisition software. The neutron energy was determined by the time-of-flight technique using a flight path of 20.25 m. The sample mass of the 96% enriched 62Ni target was 210 mg and it was mounted in a 1.5 {mu}m thick Mylar foil.

  13. Measurement of the 97Mo(n ,? ) reaction with the DANCE ? calorimeter array

    NASA Astrophysics Data System (ADS)

    Walker, C. L.; Krti?ka, M.; Baramsai, B.; Be?vá?, F.; Bredeweg, T. A.; Chyzh, A.; Haight, R. C.; Jandel, M.; Kroll, J.; Mitchell, G. E.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Valenta, S.; Wilhelmy, J. B.

    2015-07-01

    Spectra of ? rays following the 97Mo(n ,? ) reaction were measured as a function of incident neutron energy with the DANCE (Detector for Advanced Neutron Capture Experiments) array of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center using an enriched 97Mo target. These spectra were used for the assignment of spins of the 97Mo resonances up to neutron energy En=1.7 keV, as well as in the study of photon strength functions (PSFs) in 98Mo. Analysis of the spectra with the nuclear statistical model showed that they can be well reproduced with the same PSF models which well described the ? decay following slow neutron capture in 95Mo. On the other hand, the spectra are inconsistent with PSFs describing some other experimental data in 98Mo.

  14. Lead-gallium glasses and glass-ceramics doped with SiO2 for near infrared transmittance

    NASA Astrophysics Data System (ADS)

    Marczewska, Agnieszka; ?roda, Marcin; Nocu?, Marek; Sulikowski, Bogdan

    2015-07-01

    Lead-gallium glasses, due to the absence of typical glass-forming components, are characterized by an increased tendency to crystallization. Despite this, they are interesting materials due to a shift of IR absorption edge up to 6-7 ?m. The paper considers how the SiO2 dopant affects thermal stability and the UV-VIS and IR transmittance of lead-gallium glasses. The base lead-gallium glass (0.75PbO·0.25Ga2O3) was modified by the addition of 5, 10 and 15 mol% SiO2, respectively. DTA/DSC data showed that the glasses are characterized by the multi-stage crystallization, which is changed with the amount of silica doped. The XRD analysis confirmed that: (i) different forms of lead oxide crystallize after heat treatment of the glass, and (ii) the Ga2PbO4 phase is formed at higher temperatures. The silica admixture allowed inserting a few percent of BaF2 into the lead-gallium glass structure. It was found that a transparent glass-ceramic based on the lead-gallium glass with a low phonon barium fluoride phase can be obtained during the thermal treatment. The study of UV-VIS-IR transmittance shows that 10-15 mol% SiO2 in the lead-gallium glasses diminishes the absorption band in the range of 2.6-4 ?m due to the presence of hydroxyl groups and simultaneously reduces transmittance in the range of 5-6.5 ?m from 10 to 20%. Introduction of SiO2 to the glass results in the increase of transmittance in the shorter wavelength region and the UV-edge shift is observed. It was also confirmed that the BaF2 nanocrystallites exert no effect on the transmittance of the spectrum analyzed.

  15. Ferromagnetic transition in EuS-PbS multilayers

    NASA Astrophysics Data System (ADS)

    Stachow-Wójcik, A.; Story, T.; Dobrowolski, W.; Arciszewska, M.; Ga?azka, R. R.; Kreijveld, M. W.; Swüste, C. H.; Swagten, H. J.; de Jonge, W. J.; Twardowski, A.; Sipatov, A. Yu.

    1999-12-01

    The magnetic properties of multilayers of ferromagnetic EuS intercalated with diamagnetic PbS were studied as a function of the EuS layer thickness (varying from 2 to 200 ML). The critical temperature TC of the paramagnet-ferromagnet phase transition was determined from magnetization vs temperature measurements and was found to depend on the underlying substrate [KCl (100) vs BaF2 (111)] as well as on the thickness of the EuS layer. For thick layers (dEuS~200 ML), which mimic semibulk EuS, the TC values were found shifted with respect to the bulk EuS (about 1 K up for layers grown on KCl and about 3 K down for layers grown on BaF2). This effect is attributed to stress resulting mainly from the difference of thermal expansion coefficients between the substrate and the structure. For thin layers (dEuS<10 ML), a systematic reduction of TC with decreasing EuS layer thickness was observed. This behavior is discussed from two points of view: (a) the reduction of the average number of magnetic neighbors because of the increasing role of the interface for the thin layers, and (b) the three-dimensional/two-dimensional (3D/2D) crossover from a 3D Heisenberg-type ferromagnet to a 2D XY or Ising-like system. The dependence of the magnetic anisotropy on the EuS layer thickness was studied by ferromagnetic resonance measurements. The energy of magnetic anisotropy can be well described as a sum of a thickness-independent (volume) part and a 1/dEuS (surface) term. We found that EuS layers with dEuS>2 Å magnetize in the plane of the structure.

  16. Scintillating Balloon-Enabled Fiber-Optic System for Radionuclide Imaging of Atherosclerotic Plaques

    PubMed Central

    Zaman, Raiyan T.; Kosuge, Hisanori; Carpenter, Colin; Sun, Conroy; McConnell, Michael V.; Xing, Lei

    2015-01-01

    Atherosclerosis underlies coronary artery disease, the leading cause of death in the United States and worldwide. Detection of coronary plaque inflammation remains challenging. In this study, we developed a scintillating balloon-enabled fiber-optic radio-nuclide imaging (SBRI) system to improve the sensitivity and resolution of plaque imaging using 18F-FDG, a marker of vascular inflammation, and tested it in a murine model. Methods The fiber-optic system uses a Complementary Metal-Oxide Silicon (CMOS) camera with a distal ferrule terminated with a wide-angle lens. The novelty of this system is a scintillating balloon in the front of the wide-angle lens to image light from the decay of 18F-FDG emission signal. To identify the optimal scintillating materials with respect to resolution, we calculated the modulation transfer function of yttrium–aluminum–garnet doped with cerium, anthracene, and calcium fluoride doped with europium (CaF2:Eu) phosphors using an edge pattern and a thin-line optical phantom. The scintillating balloon was then fabricated from 10 mL of silicone RTV catalyst mixed with 1 mL of base and 50 mg of CaF2:Eu per mL. The addition of a lutetium oxyorthosilicate scintillating crystal (500 ?m thick) to the balloon was also investigated. The SBRI system was tested in a murine atherosclerosis model: carotid-ligated mice (n = 5) were injected with 18F-FDG, followed by ex vivo imaging of the macrophage-rich carotid plaques and nonligated controls. Confirmatory imaging of carotid plaques and controls was also performed by an external optical imaging system and autoradiography. Results Analyses of the different phosphors showed that CaF2:Eu enabled the best resolution of 1.2 ?m. The SBRI system detected almost a 4-fold-higher radioluminescence signal from the ligated left carotid artery than the nonligated right carotid: 1.63 × 102 ± 4.01 × 101 vs. 4.21 × 101 ± 2.09 × 100 (photon counts), P = 0.006. We found no significant benefit to adding a scintillating crystal to the balloon: 1.65 × 102 ± 4.07 × 101 vs. 4.44 × 101 ± 2.17 × 100 (photon counts), P = 0.005. Both external optical imaging and autoradiography confirmed the high signal from the 18F-FDG in carotid plaques versus controls. Conclusion This SBRI system provides high-resolution and sensitive detection of 18F-FDG uptake by murine atherosclerotic plaques. PMID:25858046

  17. TU-F-12A-06: BEST IN PHYSICS (IMAGING) - A Novel Catheter-Based Radionuclide Imaging System to Characterize Atherosclerotic Plaque

    SciTech Connect

    Zaman, R; Kosuge, H; Carpenter, C; Pratx, G; Sun, C; McConnell, M; Xing, L

    2014-06-15

    Purpose: Atherosclerosis underlies coronary artery diseases, the leading cause of death in the United States and worldwide. In this study, we developed a novel catheter-based radionuclide imaging (CRI) system to image 18F-fluorodeoxyglucose (18F-FDG), a radionuclide, a marker of vascular inflammation, in murine carotid arteries and characterized the system for spatial resolution from multiple scintillating materials. Methods: The catheter system includes 35 mm and 8 mm fixed focal length lenses, which are subsequently connected to a CMOS camera and fiber holder. The distal ferrule of an image bundle is terminated with a wide-angle lens. The novelty of this system is a scintillating balloon with a crystal tip in the front of the wide angle lens to image light from the decay of 18F-FDG emission signal. The scintillating balloon is fabricated from 1mL of silicone RTV catalyst mixed with 1 mL base and 50 mg/mL calcium fluoride doped with Europium (CaF2:Eu). To identify the optimal scintillating materials with respect to resolution, we calculated modulation transfer function (MTF) of Yttrium Aluminum Garnet doped with Cerium (YAG:Ce), anthracene, and CaF2:Eu phosphors using a thin line optical phantom (Fig. 1a-1b). Macrophage-rich FVB murine atherosclerotic carotid plaque model (n = 4) was used in ex vivo experiments. Confirmatory imaging was also performed by an external optical imaging system (IVIS-200). Results: Analysis of the different phosphors (Fig 1b) showed that CaF2:Eu enabled the best resolution of 1.2?m. The CRI system visualized 18F-FDG in atherosclerotic plaques (Fig. 1d). The ligated left carotid (LR) artery exhibited 4× higher 18F-FDG signal intensity compared to the non-ligated right carotid (negative control) artery (1.65×10{sup 2} ±4.07×10{sup 1} vs. 4.44×10{sup 1}±2.17×10{sup 0}, A.U., p = 0.005) and confirmed with IVIS-200 (Fig. 1d). Conclusion: This CRI system enables high-resolution and sensitive detection of 18F-FDG uptake by murine atherosclerotic plaques.

  18. Fluorspar

    NASA Astrophysics Data System (ADS)

    Pelham, L.

    Fluorspar is the commercial name for the mineral fluorite, which commonly occurs as calcium fluoride (CaF2). Fluorspar is the most important commercial source of fluorine, which is a pale-yellow corrosive gas. Fluorspar is considered a strategic and critical commodity because U.S. import reliance is greater than 85% and fluorspar is necessary in most steel and aluminum production processes. Fluorine compounds are also used in the production of nuclear fuel. The chemical and ceramic industries are also significant users of fluorspar. There are many other diverse uses of fluorspar including water fluoridation. Strategic uses of fluorspar were reviewed and fluorspar-related technologies were assessed. Fluorspar reserves and supply-demand relationships were summarized. Economic factors and problems and the impact of environmental requirements on the fluorspar industry were overviewed.

  19. Modification of steelmaking slag by additions of salts from aluminum production

    NASA Astrophysics Data System (ADS)

    Walker, David C.

    The most common slag fluidizer in steelmaking is fluorspar, a mineral primarily composed of CaF2. Because of increasing consumption and decreasing availability of cheap fluorspar, steelmakers are seeking alternative means of achieving slag fluidity. One possible alternative to fluorspar is spent salt from secondary aluminum production. This salt is obtained from the used flux in remelting aluminum scrap and dross. This material is widely available and considered toxic (meaning that use in steelmaking helps to reduce environmental impacts from disposal). This project is an investigation of spent salt as a replacement for fluorspar in slag-fluidizing applications by viscosity measurements and weight loss measurements at high temperatures (to evaluate the amounts of gases are formed). In addition, characterization of raw materials and melted slags by XRD, chemical analysis, and EPMA have been undertaken. The spent salt addition has a positive effect on slag fluidity, and shows promise for use in slags.

  20. Stress versus temperature dependence of activation energies for creep

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Raj, S. V.; Walker, K. P.

    1992-01-01

    The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.

  1. Surface Plasmon Resonance sensor showing enhanced sensitivity for CO2 detection in the mid-infrared range.

    PubMed

    Herminjard, Sylvain; Sirigu, Lorenzo; Herzig, Hans Peter; Studemann, Eric; Crottini, Andrea; Pellaux, Jean-Paul; Gresch, Tobias; Fischer, Milan; Faist, Jérôme

    2009-01-01

    We present the first optical sensor based on Surface Plasmon Resonance (SPR) operating in the mid-infrared range. The experimental setup is based on a Kretschmann geometry with Ti/Au layers deposited on a CaF(2) prism where light excitation is provided by a Quantum Cascade Laser (QCL) source. Evidence of SPR is presented and the sensing capability of the system is demonstrated by using CO(2) and N(2) mixtures as test samples. Due to the absorption of CO(2) at this wavelength, it is shown that the sensitivity of this configuration is five times higher than a similar SPR sensor operating in the visible range of the spectrum. PMID:19129898

  2. Resistance of LiCaAlF6 Single Crystals against F2 Laser Irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Yoshizo; Narazaki, Aiko; Niino, Hiroyuki; Sato, Hiroki; Fukuda, Tsuguo; Shimamura, Kiyoshi

    2003-08-01

    The resistance of LiCaAlF6 single crystals against F2 laser irradiation was studied to examine the possible use of LiCaAlF6 as optical components for F2 laser lithography. After the initial increase by F2 laser cleaning, transmittance of LiCaAlF6 at 157 nm remains relatively unchanged even after irradiation with an F2 laser beam up to 105 pulses at a fluence of approximately 160 mJ\\cdotcm-2\\cdotpulse-1, indicating good tolerance against the cumulative irradiation. We also discuss the mechanism of the initial increase in transmittance with the results of X-ray photoelectron spectroscopy (XPS). The threshold fluence for the onset of optical damage of LiCaAlF6 is approximately 2 J\\cdotcm-2\\cdotpulse-1, similar to that of vacuum ultraviolet (VUV) grade CaF2.

  3. Gibbs energies of formation of chromium carbides

    NASA Astrophysics Data System (ADS)

    Anthonysamy, S.; Ananthasivan, K.; Kaliappan, I.; Chandramouli, V.; Vasudeva Rao, P. R.; Mathews, C. K.; Jacob, K. T.

    1996-07-01

    The carbon potentials corresponding to the two-phase mixtures Cr + Cr23C6, Cr23C6 + Cr7C3, and Cr7C3 + Cr3C2 in the binary system Cr-C were measured in the temperature range 973 to 1173 K by using the methane-hydrogen gas equilibration technique. Special precautions were taken to prevent oxidation of the samples and to minimize thermal segregation in the gas phase. The standard Gibbs energies of formation of Cr23C6, Cr7C3, and Cr3C2 were derived from the measured carbon potentials. These values are compared with those reported in the literature. The Gibbs energies obtained in this study agree well with those obtained from solid-state cells incorporating CaF2 and ThO 2(Y2O3) as solid electrolytes and sealed capsule isopiestic measurements reported in the literature.

  4. Software for HUBER-5042 diffractometer with Displex DE-202 helium cryostat

    NASA Astrophysics Data System (ADS)

    Dudka, A. P.; Verin, I. A.; Antipin, A. M.

    2015-03-01

    A software for structural studies on a Huber-5042 diffractometer with a point detector and closed-cycle Displex DE-202 helium cryostat has been developed. The software package includes programs for the preliminary stage of experiment, planning, data collection, profile analysis of reflections, etc. The measurement of reflections in the 2? angular range from 0° to 152° is provided, which is unique for Eulerian goniometers. Tools for enhancing data collection are demonstrated. Accurate experimental data are obtained for a test CaF2 crystal (sp. gr. , Z = 4, resolution sin?/?max ? 1.354 Å-1, 121 reflections, 16 parameters in refinement, R/ wR = 0.31/0.34%, ??min/??max = -0.08/+0.07 e/Å3).

  5. Radiation Heat Transfer Modeling Improved for Phase-Change, Thermal Energy Storage Systems

    NASA Technical Reports Server (NTRS)

    Kerslake, Thomas W.; Jacqmin, David A.

    1998-01-01

    Spacecraft solar dynamic power systems typically use high-temperature phase-change materials to efficiently store thermal energy for heat engine operation in orbital eclipse periods. Lithium fluoride salts are particularly well suited for this application because of their high heat of fusion, long-term stability, and appropriate melting point. Considerable attention has been focused on the development of thermal energy storage (TES) canisters that employ either pure lithium fluoride (LiF), with a melting point of 1121 K, or eutectic composition lithium-fluoride/calcium-difluoride (LiF-20CaF2), with a 1040 K melting point, as the phase-change material. Primary goals of TES canister development include maximizing the phase-change material melt fraction, minimizing the canister mass per unit of energy storage, and maximizing the phase-change material thermal charge/discharge rates within the limits posed by the container structure.

  6. Accurate determination of ?¹Ca concentrations in spent resins from the nuclear industry by accelerator mass spectrometry.

    PubMed

    Nottoli, Emmanuelle; Bourlès, Didier; Bienvenu, Philippe; Labet, Alexandre; Arnold, Maurice; Bertaux, Maité

    2013-12-01

    The radiological characterisation of nuclear waste is essential for managing storage sites. Determining the concentration of Long-Lived RadioNuclides (LLRN) is fundamental for their long-term management. This paper focuses on the measurement of low (41)Ca concentrations in ions exchange resins used for primary fluid purification in Pressurised Water Reactors (PWR). (41)Ca concentrations were successfully measured by Accelerator Mass Spectrometry (AMS) after the acid digestion of resin samples, followed by radioactive decontamination and isobaric suppression through successive hydroxide, carbonate, nitrate and final CaF2 precipitations. Measured (41)Ca concentrations ranged from 0.02 to 0.03 ng/g, i.e. from 0.06 to 0.09 Bq/g. The (41)Ca/(60)Co activity ratios obtained were remarkably reproducible and in good agreement with the current ratio used for resins management. PMID:24144617

  7. Fresnel reflectance in refractive index estimation of light scattering solid particles in immersion liquid

    NASA Astrophysics Data System (ADS)

    Räty, J.; Niskanen, I.; Peiponen, K.-E.

    2010-06-01

    The refractive index of homogenous particle population can be determined by the so-called immersion liquid method. The idea is to find a known liquid whose refractive index matches the index of the particles. We report on a method that simultaneously obtains the refractive index of particles and that of the immersion liquid. It is based on a system using internal light reflection and Fresnel's theory. The method includes a series of straightforward reflection measurements and a fitting procedure. The validity of the method was tested with CaF2 particles. The method has applications within scientific studies of microparticles and nanoparticles or micro-organism in suspensions. It can be also be utilized in industry for the detection of the refractive index of products involving particles for the purpose of improvement of product quality.

  8. Optical sensing techniques for temperature measurement.

    PubMed

    Reddy, B Rami; Kamma, Indumathi; Kommidi, Praveena

    2013-02-01

    Temperature is an important parameter that needs accurate measurement. Theoretical descriptions of the fluorescence ratio method, fluorescence lifetime sensing, and interferometric methods for temperature measurement are given. Fluorescence lifetime sensing calibration plots have been developed for temperature measurement from 20°C to 600°C using Er(3+)-doped glass, and from 20°C to 90°C using Sm(3+)-doped CaF(2). Lifetime sensing results of Pr(3+)-doped YAG and Ho(3+)-doped fluoride crystals for temperature measurement are also summarized. Mach-Zehnder interferometer measurements revealed that the passage of a 300 mW laser beam of 915 nm changed the temperature of the Yb(3+)-doped YAG crystal by 7.1°C. The interferometer technique is useful for measuring absolute temperature changes in laser cooling studies. PMID:23385939

  9. ADRF experiments using near n.pi pulse strings. [Adiabatic Demagnetization due to Radio Frequency pulses

    NASA Technical Reports Server (NTRS)

    Rhim, W. K.; Burum, D. P.; Elleman, D. D.

    1977-01-01

    Adiabatic demagnetization (ADRF) can be achieved in a dipolar coupled nuclear spin system in solids by applying a string of short RF pulses and gradually modulating the pulse amplitudes or pulse angles. This letter reports an adiabatic inverse polarization effect in solids and a rotary spin echo phenomenon observed in liquids when the pulse angle is gradually changed across integral multiples of pi during a string of RF pulses. The RF pulse sequence used is illustrated along with the NMR signal from a CaF2 single crystal as observed between the RF pulses and the rotary spin echo signal observed in liquid C6F6 for n = 2. The observed effects are explained qualitatively on the basis of average Hamiltonian theory.

  10. Stress versus temperature dependent activation energies in creep

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Raj, S. V.; Walker, K. P.

    1990-01-01

    The activation energy for creep at low stresses and elevated temperatures is lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from that of dislocation climb to one of obstacle-controlled dislocation glide. Along with this change, there occurs a change in the activation energy. It is shown that a temperature-dependent Gibbs free energy does a good job of correlating steady-state creep data, while a stress-dependent Gibbs free energy does a less desirable job of correlating the same data. Applications are made to copper and a LiF-22 mol. percent CaF2 hypereutectic salt.

  11. Inorganic photochromic and cathodochromic recording materials.

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.; Faughnan, B. W.; Phillips, W.

    1971-01-01

    Discussion of studies at RCA Laboratories of the properties of rare-earth-doped CaF2, transition-metal-doped SrTiO3 and iron- or sulfur-doped sodalite as photochromic materials which change color during light or electron beam exposures. Particular attention is given to their photochromic characteristics in single-crystal and powder forms and to their cathodochromic properties in powder form. Details are given on the photochromic mechanisms, spectra, optical density, thermal decay rates, and coloring and bleaching efficiency of their single crystals and on the diffuse reflectance spectra, saturated photochromic contrast ratio, switching and erase sensitivities, and cathodochromic excitation of their photochromic powders. The many attractive characteristics of these materials when used in display storage systems are indicated.

  12. The effect of Ce3+ ions on the spectral and decay characteristics of luminescence phosphate-borate glasses doped with rare-earth ions

    NASA Astrophysics Data System (ADS)

    Valiev, D. T.; Polisadova, E. F.; Belikov, K. N.; Egorova, N. L.

    2014-05-01

    The luminescent characteristics of Li2O-B2O3-P2O5-CaF2 (LBPC) glasses doped with Gd3+ and Tb3+ ions and codoped with Ce3+ are studied by pulsed optical spectrometry under electron beam excitation. It is found that in glass with Ce3+ and Gd3+ ions a decrease in the decay time of gadolinium luminescence in the 312-nm band (6 P J ? 8 S 7/2) was observed. It is shown that in the glass LBPC: Tb, Ce, an increase in the emission intensity in the main radiative transitions in terbium ion was observed. In the kinetics of luminescence band 545 nm of LBPC: Tb, Ce glasses, is present stage of buildup, the character of which changes with the doped of Ce3+ ions. The mechanism of energy transfer in LBP glasses doped with rare elements is discussed.

  13. Fundamental research on a cerenkov radiation sensor based on optical glass for detecting beta-rays

    NASA Astrophysics Data System (ADS)

    Kim, Jae Seok; Jang, Kyoung Won; Shin, Sang Hun; Jeon, Dayeong; Hong, Seunghan; Sim, Hyeok In; Kim, Seon Geun; Yoo, Wook Jae; Lee, Bongsoo; Moon, Joo Hyun; Park, Byung Gi

    2015-01-01

    In this study, a Cerenkov radiation sensor for detecting low-energy beta-particles was fabricated using various Cerenkov radiators such as an aerogel and CaF2-, SiO2-, and Al2O3-based optical glasses. Because the Cerenkov threshold energy (CTE) is determined by the refractive index of the Cerenkov radiator, the intensity of Cerenkov radiation varies according to the refractive indices of the Cerenkov radiators. Therefore, we measured the intensities of Cerenkov radiation induced by beta-particles generated from a radioactive isotope as a function of the refractive indices of the Cerenkov radiators. Also, the electron fluxes were calculated for various Cerenkov radiators by using a Monte Carlo N-Particle extended transport code (MCNPX) to determine the relationship between the intensities of the Cerenkov radiation and the electron fluxes.

  14. Estimated heats of fusion of fluoride salt mixtures suitable for thermal energy storage applications

    NASA Technical Reports Server (NTRS)

    Misra, A. K.; Whittenberger, J. D.

    1986-01-01

    The heats of fusion of several fluoride salt mixtures with melting points greater than 973 K were estimated from a coupled analysis of the available thermodynamic data and phase diagrams. Simple binary eutectic systems with and without terminal solid solutions, binary eutectics with congruent melting intermediate phases, and ternary eutectic systems were considered. Several combinations of salts were identified, most notable the eutectics LiF-22CaF2 and NaF-60MgF2 which melt at 1039 and 1273 K respectively which posses relatively high heats of fusion/gm (greater than 0.7 kJ/g). Such systems would seemingly be ideal candidates for the light weight, high energy storage media required by the thermal energy storage unit in advanced solar dynamic power systems envisioned for the future space missions.

  15. Study of the interfacial reactions between a bioactive apatite-mullite glass-ceramic coating and titanium substrates using high angle annular dark field transmission electron microscopy.

    PubMed

    Stanton, Kenneth T; O'Flynn, Kevin P; Nakahara, Shohei; Vanhumbeeck, Jean-François; Delucca, John M; Hooghan, Bobby

    2009-04-01

    Glass of generic composition SiO(2) . Al(2)O(3) . P(2)O(5) . CaO . CaF(2) will crystallise predominantly to apatite and mullite upon heat-treatment. Such ceramics are bioactive, osseoconductive, and have a high resistance to fracture. As a result, they are under investigation for use as biomedical device coatings, and in particular for orthopaedic implants. Previous work has shown that the material can be successfully enamelled to titanium with an interfacial reaction zone produced during heat treatment. The present study uses high angle annular dark field transmission electron microscopy (HAADF-TEM) to conduct a detailed examination of this region. Results show evidence of complex interfacial reactions following the diffusion of titanium into an intermediate layer and the production of titanium silicides and titanium phosphides. These results confirm previously hypothesised mechanisms for the bonding of silicate bioceramics with titanium alloys. PMID:19034617

  16. Radioluminescence and photoluminescence of Th:CaF2 crystals.

    PubMed

    Stellmer, Simon; Schreitl, Matthias; Schumm, Thorsten

    2015-01-01

    We study thorium-doped CaF2 crystals as a possible platform for optical spectroscopy of the (229)Th nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of (229)Th and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260?nm, and radioluminescence emission above 220?nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200?nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lasers. PMID:26502749

  17. Light-scattering measurements of optical thin-film components at 157 and 193 nm

    NASA Astrophysics Data System (ADS)

    Gliech, Stefan; Steinert, Jorg; Duparre, Angela

    2002-06-01

    An instrument for total backscattering and forward-scattering measurements of optical coating components at 157 and 193 nm is described. The system is operated in both vacuum and nitrogen purge gas. An excimer laser as well as a deuterium lamp can be used as a radiation source. Suppression of the background signal level to 1 part in 106 permits measurements even of low-scatter samples such as superpolished substrates and antireflection coatings. Results of investigations of antireflective and highly reflective multilayers and CaF2 substrates reveal scattering from surface and interface roughness as well as from the volume of the substrate material. First steps to extend the instrument for angle-resolved scatter, transmittance, and reflectance measurements are described.

  18. Fabrication of three-dimensional microdisk resonators in calcium fluoride by femtosecond laser micromachining

    NASA Astrophysics Data System (ADS)

    Lin, Jintian; Xu, Yingxin; Tang, Jialei; Wang, Nengwen; Song, Jiangxin; He, Fei; Fang, Wei; Cheng, Ya

    2014-09-01

    We report on fabrication of on-chip calcium fluoride (CaF2) microdisk resonators using water-assisted femtosecond laser micromachining. Focused ion beam (FIB) milling is used to create ultra-smooth sidewalls. The quality ( Q) factors of the fabricated microresonators are measured to be 4.2 × 104 at wavelengths near 1,550 nm. The Q factor is mainly limited by the scattering from the bottom surface of the disk whose roughness remains high due to the femtosecond laser micromachining process. This technique facilitates the formation of on-chip microresonators on various kinds of bulk crystalline materials, which can benefit a wide range of applications such as nonlinear optics, quantum optics, and chip-level integration of photonic devices.

  19. Relationship between quality, manufacturing technology and structure of welding fluxes

    NASA Astrophysics Data System (ADS)

    Sokolsky, V. E.; Roik, A. S.; Samsonnikov, A. V.; Galinich, V. I.; Tokarev, V. S.; Goncharov, I. A.; Shevchuk, R. N.; Mishchenko, D. D.

    2008-02-01

    Technology for manufacturing of fused fluxes of the AN-67 grade (preparation of charge, melting of flux in electric arc furnace, granulation (pouring of melt into water), drying, screening and packing) was developed in such a way that the resulting granulated welding flux had a fully amorphous structure. However, production of such fluxes involves enormous power expenditures. Therefore, the trend with flux manufacturers is to reduction in time and decrease in ultimate temperatures of the processes, which makes it impossible to remelt high-temperature components of the flux charge. Some welding fluxes of the AN-67 series were examined by the X-ray diffraction method. It is established that certain fluxes produced in the last years contain crystalline components with a high melting point, such as Al2O3 and CaF2, in addition to the amorphous phase. The paper shows the negative effect by this factor on properties of the fluxes

  20. Evolution of local atomic structure during solidification of Al2Au liquid: An ab initio study

    SciTech Connect

    Xiong, L.H.; Lou, H.B.; Wang, X.D.; Debela, T.T.; Cao, Q.P.; Zhang, D.X.; Wang, S.Y.; Wang, C.Z.; Jiang, J.Z.

    2014-04-01

    The local atomic structure evolution in Al2Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt-Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al2Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of < 0,4,4,0 >, < 0,3, 6,0 > and < 0,4,4,2 > with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF2-type Al2Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al2Au alloy. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  1. Materials Refining for Solar Array Production on the Moon

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.

    2005-01-01

    Silicon, aluminum, and glass are the primary raw materials that will be required for production of solar arrays on the moon. A process sequence is proposed for producing these materials from lunar regolith, consisting of separating the required materials from lunar rock with fluorine. The fluorine is brought to the moon in the form of potassium fluoride, and is liberated from the salt by electrolysis in a eutectic salt melt. Tetrafluorosilane produced by this process is reduced to silicon by a plasma reduction stage; the fluorine salts are reduced to metals by reaction with metallic potassium. Fluorine is recovered from residual MgF and CaF2 by reaction with K2O.

  2. Lunar mining of oxygen using fluorine

    NASA Astrophysics Data System (ADS)

    Burt, Donald M.

    1992-09-01

    An important aspect of lunar mining will be the extraction of volatiles, particularly oxygen, from lunar rocks. Thermodynamic data show that oxygen could readily be recovered by fluorination of abundant lunar anorthite, CaAl2Si2O8. Fluorine is the most reactive element, and the only reagent able to extract 100 percent of the oxygen from any mineral, yet it can safely be stored or reacted in nickel or iron containers. The general fluorination reaction, mineral + 2F2 = mixed fluorides = O2, has been used for more than 30 years at a laboratory scale by stable-isotope geochemists. For anorthite, metallic Al and Si may be recovered from the mixed fluorides by Na-reduction, and CaO via exchange with Na2O; the resulting NaF may be recycled into F2 and Na by electrolysis, using lanthanide-doped CaF2 as the inert anode.

  3. Final Report: Center for Programming Models for Scalable Parallel Computing

    SciTech Connect

    Mellor-Crummey, John

    2011-09-13

    As part of the Center for Programming Models for Scalable Parallel Computing, Rice University collaborated with project partners in the design, development and deployment of language, compiler, and runtime support for parallel programming models to support application development for the “leadership-class” computer systems at DOE national laboratories. Work over the course of this project has focused on the design, implementation, and evaluation of a second-generation version of Coarray Fortran. Research and development efforts of the project have focused on the CAF 2.0 language, compiler, runtime system, and supporting infrastructure. This has involved working with the teams that provide infrastructure for CAF that we rely on, implementing new language and runtime features, producing an open source compiler that enabled us to evaluate our ideas, and evaluating our design and implementation through the use of benchmarks. The report details the research, development, findings, and conclusions from this work.

  4. Radioluminescence and photoluminescence of Th:CaF$_2$ crystals

    E-print Network

    Simon Stellmer; Matthias Schreitl; Thorsten Schumm

    2015-06-05

    We study thorium-doped CaF$_2$ crystals as a possible platform for optical spectroscopy of the Th-229 nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of Th-229 and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260 nm, and radioluminescence emission above 220 nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200 nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lasers.

  5. Radioluminescence and photoluminescence of Th:CaF$_2$ crystals

    E-print Network

    Stellmer, Simon; Schumm, Thorsten

    2015-01-01

    We study thorium-doped CaF$_2$ crystals as a possible platform for optical spectroscopy of the Th-229 nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of Th-229 and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260 nm, and radioluminescence emission above 220 nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200 nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lase...

  6. Radioluminescence and photoluminescence of Th:CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Stellmer, Simon; Schreitl, Matthias; Schumm, Thorsten

    2015-10-01

    We study thorium-doped CaF2 crystals as a possible platform for optical spectroscopy of the 229Th nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of 229Th and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260?nm, and radioluminescence emission above 220?nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200?nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lasers.

  7. Frequency-modulated stimulated Brillouin spectroscopy in crystals

    NASA Astrophysics Data System (ADS)

    Sonehara, Toshiaki; Konno, Yusaku; Kaminaga, Hitomi; Saikan, Seishiro; Ohno, Seigo

    2007-05-01

    We have developed a Brillouin spectrometer based on frequency modulation (FM) spectroscopy in order to enhance the detection sensitivity and to detect separately the real and imaginary parts of the Brillouin spectrum. With this spectrometer, we have measured Brillouin spectra at room temperature in a variety of single crystals including SiO2, CaF2, LiNbO3, deuterated L-arginine phosphate, PbMoO4, TeO2, langatate (La3Ta0.5Ga5.3Al0.2O14), and KRS-5. To determine the Brillouin linewidth and shift from the observed FM spectrum, we have derived a spectral formula for the FM-stimulated Brillouin spectrum by taking into account several contributions from both electrostrictive and absorptive Brillouin scattering and polarization ellipticity of pump or probe waves. This formula reproduces the observed FM Brillouin spectra quite well.

  8. Core-hole effect on XANES and electronic structure of minor actinide dioxides with fluorite structure

    NASA Astrophysics Data System (ADS)

    Suzuki, Chikashi; Nishi, Tsuyoshi; Nakada, Masami; Akabori, Mitsuo; Hirata, Masaru; Kaji, Yoshiyuki

    2012-02-01

    The authors investigated theoretically core-hole effects on X-ray absorption near-edge structures (XANES) of Np and Am LIII in neptunium dioxide (NpO2) and americium dioxide (AmO2) with CaF2-type crystal lattices using the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The peak creation mechanism of XANES was shown by examining the electronic structures of these oxides, which indicated that core-hole screening was more marked for AmO2 than for NpO2 because of the difference in the charge transfer between these oxides. Furthermore, the results of charge density analysis suggested that the white line was assigned to the quasi-bound state composed of the localized Np d or Am d components and O components, and that the tail structure was created as a result of delocalized standing waves between the Np or Am atoms.

  9. DUV/VUV light scattering measurement of optical components for lithography applications

    NASA Astrophysics Data System (ADS)

    Gliech, Stefan; Steinert, Joerg; Flemming, Marcel; Duparre, Angela

    2000-11-01

    This paper reports on an instrument designed to measure the total backward and forward scattering of optical components down to the DUV/VUV spectral region. The system is based on a Coblentz sphere imaging the light scattered into the backward or forward hemispheres within an angular range from 2 degree(s) to 85 degree(s) onto the detector according to ISO/DIS 13696. The equipment divides into two set-ups, one operating in air at several wavelengths from 10.6 micrometers to 193 nm, the other one working in a vacuum/nitrogen at 157 nm and 193 nm. The system is fully automated and capable of scanning large sample areas. Both a deuterium lamp and an excimer laser can be used as radiation sources at 193 nm and 157 nm. Results of measurements on fluoride multilayer coatings and CaF2 substrates are presented.

  10. Near-diffraction-limited laser beam shaping with diamond-turned aspheric optics.

    PubMed

    Kasinski, J J; Burnham, R L

    1997-07-15

    We used a pair of diamond-turned CaF(2) aspheres to convert the pure TEM(00) Gaussian spatial profile output of a diode-pumped Nd:YAG laser oscillator into a super-Gaussian intensity profile with a nearly flat phase front. The resulting super-Gaussian beam was nearly diffraction limited with an M(2) of 1.75; in the near field the 5-mm diameter beam retained a nominally flat-top intensity distribution without significant diffraction peaks for an excellent working distance of more than 50cm. A 10% improvement in amplifier-energy extraction obtained by use of the reshaped beam is demonstrated. PMID:18185751

  11. Mobility propagation and dynamic facilitation in superionic conductors.

    PubMed

    Annamareddy, Ajay; Eapen, Jacob

    2015-11-21

    In an earlier work [V. A. Annamareddy et al., Phys. Rev. E 89, 010301(R) (2014)], we showed the manifestation of dynamical heterogeneity (DH)-the presence of clustered mobile and immobile regions-in UO2, a model type II superionic conductor. In the current work, we demonstrate the mechanism of dynamic facilitation (DF) in two superionic conductors (CaF2 and UO2) using atomistic simulations. Using the mobility transfer function, DF is shown to vary non-monotonically with temperature with the intensity of DF peaking at temperatures close to the superionic transition temperature (T?). Both the metrics quantifying DH and DF show remarkable correspondence implying that DF, in the framework of kinematically constrained models, underpins the heterogeneous dynamics in type II superionic conductors. PMID:26590537

  12. High temperature self-lubricating coatings for air lubricated foil bearings for the automotive gas turbine engine

    NASA Technical Reports Server (NTRS)

    Bhushan, B.

    1980-01-01

    coating combinations were developed for compliant surface bearings and journals to be used in an automotive gas turbine engine. The coatings were able to withstand the sliding start/stops during rotor liftoff and touchdown and occasional short time, high speed rubs under representative loading of the engine. Some dozen coating variations of CdO-graphite, Cr2O3 (by sputtering) and CaF2 (plasma sprayed) were identified. The coatings were optimized and they were examined for stoichiometry, metallurgical condition, and adhesion. Sputtered Cr2O3 was most adherent when optimum parameters were used and it was applied on an annealed (soft) substrate. Metallic binders and interlayers were used to improve the ductility and the adherence.

  13. The cavity heat pipe Stirling receiver for space solar dynamics

    NASA Technical Reports Server (NTRS)

    Kesseli, James B.; Lacy, Dovie E.

    1989-01-01

    The receiver/storage unit for the low-earth-orbiting Stirling system is discussed. The design, referred to as the cavity heat pipe (CHP), has been optimized for minimum specific mass and volume width. A specific version of this design at the 7-kWe level has been compared to the space station Brayton solar dynamic design. The space station design utilizes a eutectic mixture of LiF and CaF2. Using the same phase change material, the CHP has been shown to have a specific mass of 40 percent and a volume of 5 percent of that of the space station Brayton at the same power level. Additionally, it complements the free-piston Stirling engine in that it also maintains a relatively flat specific mass down to at least 1 kWe. The technical requirements, tradeoff studies, critical issues, and critical technology experiments are discussed.

  14. Mobility propagation and dynamic facilitation in superionic conductors

    NASA Astrophysics Data System (ADS)

    Annamareddy, Ajay; Eapen, Jacob

    2015-11-01

    In an earlier work [V. A. Annamareddy et al., Phys. Rev. E 89, 010301(R) (2014)], we showed the manifestation of dynamical heterogeneity (DH)—the presence of clustered mobile and immobile regions—in UO2, a model type II superionic conductor. In the current work, we demonstrate the mechanism of dynamic facilitation (DF) in two superionic conductors (CaF2 and UO2) using atomistic simulations. Using the mobility transfer function, DF is shown to vary non-monotonically with temperature with the intensity of DF peaking at temperatures close to the superionic transition temperature (T?). Both the metrics quantifying DH and DF show remarkable correspondence implying that DF, in the framework of kinematically constrained models, underpins the heterogeneous dynamics in type II superionic conductors.

  15. Lunar mining of oxygen using fluorine

    NASA Technical Reports Server (NTRS)

    Burt, Donald M.

    1992-01-01

    An important aspect of lunar mining will be the extraction of volatiles, particularly oxygen, from lunar rocks. Thermodynamic data show that oxygen could readily be recovered by fluorination of abundant lunar anorthite, CaAl2Si2O8. Fluorine is the most reactive element, and the only reagent able to extract 100 percent of the oxygen from any mineral, yet it can safely be stored or reacted in nickel or iron containers. The general fluorination reaction, mineral + 2F2 = mixed fluorides = O2, has been used for more than 30 years at a laboratory scale by stable-isotope geochemists. For anorthite, metallic Al and Si may be recovered from the mixed fluorides by Na-reduction, and CaO via exchange with Na2O; the resulting NaF may be recycled into F2 and Na by electrolysis, using lanthanide-doped CaF2 as the inert anode.

  16. Radioluminescence and photoluminescence of Th:CaF2 crystals

    PubMed Central

    Stellmer, Simon; Schreitl, Matthias; Schumm, Thorsten

    2015-01-01

    We study thorium-doped CaF2 crystals as a possible platform for optical spectroscopy of the 229Th nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of 229Th and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260?nm, and radioluminescence emission above 220?nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200?nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lasers. PMID:26502749

  17. Sodium Dodecyl Sulfate Adsorption onto Positively Charged Surfaces: Monolayer Formation With Opposing Headgroup Orientations

    PubMed Central

    Song, Sang-Hun; Koelsch, Patrick; Weidner, Tobias; Wagner, Matthew S.; Castner, David G.

    2013-01-01

    The adsorption and structure of sodium dodecyl sulfate (SDS) layers onto positively charged films have been monitored in situ with vibrational sum-frequency-generation (SFG) spectroscopy and surface plasmon resonance (SPR) sensing. Substrates with different charge densities and polarities used in these studies include CaF2 at different pH values as well as allylamine and heptylamine films deposited onto CaF2 and Au substrates by radio frequency glow discharge deposition. The SDS films were adsorbed from aqueous solutions ranging in concentration from 0.067 to 20 mM. In general the SFG spectra exhibited well resolved CH and OH peaks. However, at SDS concentrations between 1–8 mM the SFG CH and OH intensities decreased close to background levels. Combined data sets from molecular conformation, orientation, and order sensitive SFG with mass sensitive SPR suggest that the observed changes in SFG intensities above 0.2 mM are related to structural arrangements in the SDS layer. A model is proposed where the SFG intensity minimum between 1–8 mM is associated with a monolayer containing two head group orientations, one pointing towards the substrate and one pointing towards the solution phase. The SFG peaks observed at concentrations below 0.2 mM are dominated by the presence of adsorbed contaminants such as fatty alcohols (e.g., dodecanol), which are more surface active than SDS. As SDS solution concentration is increased above 1 mM SDS molecules are incorporated in the surface layer, with dodecanol continuing to be present in the surface layer for solution concentrations up to at least critical micelle concentration. PMID:24024777

  18. A cryogenic Herriott cell vacuum-coupled to a Bruker IFS-125HR

    NASA Astrophysics Data System (ADS)

    Mantz, Arlan W.; Sung, Keeyoon; Brown, Linda R.; Crawford, Timothy J.; Smith, Mary Ann H.; Malathy Devi, V.; Chris Benner, D.

    2014-10-01

    A new cryogenic Herriott cell and associated transfer optics have been designed and fabricated at Connecticut College under contract with NASA Langley Research Center to operate for the first time with the broad-band Bruker IFS-125HR Fourier transform spectrometer at the Jet Propulsion Laboratory (JPL). This 0.375 m base-length optical cavity produces an absorption path length, at 293 K, of 20.941 (±0.006) m. The Herriott cell, constructed from oxygen-free high conductivity copper, is placed inside its own vacuum enclosure, which is isolated from the transfer optics chamber by one CaF2 window and separately evacuated. The transfer optics chamber is in turn coupled to the sample compartment of the Bruker IFS-125HR holding another set of transfer optics. The entire spectrometer, including the transfer optics chamber can be evacuated to ?10 mTorr; the cell vacuum enclosure is cryogenically evacuated to pressures below 10-6 Torr. A closed-cycle helium refrigerator cools the Herriott cell. Initially tested at Connecticut College for temperatures between 250 and 50 K, the system has successfully been in operation for over two years at JPL. The cell has been used for recording spectra between 75 and 250 K, achieving excellent temperature uniformity (± 0.15 K) and long term stability (< 0.05 K/day). Configured with a single indium-sealed CaF2 window, it has provided Doppler-limited infrared absorption spectra of a number of molecular species above 2000 cm-1 to investigate detailed spectroscopic properties (e.g. molecular line parameters at temperatures and pressures relevant to planetary atmospheres). The design, performance and detailed characterization of the Herriott cell system are discussed.

  19. Relaxation of quasi-transverse phonons in the Herring mechanism and ultrasound absorption in cubic crystals with positive and negative anisotropies of the second-order elastic moduli

    NASA Astrophysics Data System (ADS)

    Kuleyev, I. G.; Kuleyev, I. I.

    2009-11-01

    The phonon relaxation and quasi-transverse ultrasound absorption in the course of Herring and Landau-Rumer anharmonic scattering processes in cubic crystals with positive (Ge, Si, diamond, InSb, LiF, MgO) and negative (KCl, NaCl, CaF2) anisotropies of the second-order elastic moduli have been investigated. A new mechanism of transverse phonon relaxation, according to which the fusion of a transverse (slow or fast) phonon with a slow phonon generates a fast transverse phonon, has been considered in the long-wave-length approximation. This mechanism is similar to the Herring relaxation mechanism for longitudinal phonons. It has been demonstrated that, for crystals of the first group with a considerable anisotropy of the elastic energy (Ge, Si, InSb, LiF, MgO), “anomalous” relaxation processes in which the fusion of a slow transverse phonon with a fast phonon generates a slow transverse phonon are possible in contrast to the Herring relaxation mechanism for longitudinal phonons. These relaxation processes appear to be impossible for all crystals of the second group (KCl, NaCl, CaF2), as well as for crystals of the first group with a small anisotropy of the elastic energy, such as diamond. The angular dependences of the ultrasound absorption coefficient for the Herring and Landau-Rumer mechanisms have been analyzed using the anisotropic-continuum model. It has been shown that, for the crystals of the first group under consideration, the contribution of the Herring mechanism to the long-wavelength ultrasound absorption is small compared to the contribution of the Landau-Rumer mechanism. However, for the KCl and NaCl crystals of the second group in directions of the [001] type, the contribution of the Herring mechanism can significantly exceed the contribution of the Landau-Rumer mechanism.

  20. Enhancement of luminescence in white emitting strontium fluoride core @ calcium fluoride shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Kumam, Nandini; Singh, Ningthoujam Premananda; Singh, Laishram Priyobarta; Srivastava, Sri Krishna

    2015-09-01

    Synthesis of lanthanide-doped fluoride SrF2:3Dy and SrF2:3Dy@CaF2 nanoparticles with different ratios of core to shell (1:0.5, 1:1 and 1:2) has been carried out by employing ethylene glycol route. X-ray diffraction (XRD) patterns reveal that the structure of the prepared nanoparticles was of cubical shape, which is also evident in TEM images. The size of the nanoparticles for core (SrF2:3Dy) is found to increase when core is covered by shell (CaF2). It is also evident from Fourier transform infrared spectroscopy (FTIR) that ethylene glycol successfully controls the growth and acts as a shape modifier by regulating growth rate. In the photoluminescence investigation, emission spectra of SrF2:3Dy is found to be highly enhanced when SrF2:3Dy is covered by CaF2 due to the decrease of cross relaxation amongst the Dy3+-Dy3+ ions. Such type of enhancement of luminescence in homonanostructure SrF2:3Dy@CaF2 (core@shell) has not been studied so far, to the best of the authors' knowledge. This luminescent material exhibits prominently white light emitting properties as shown by the Commission Internationale d'Eclairage (CIE) chromaticity diagram. The calculated correlate colour temperature (CCT) values for SrF2:3Dy, SrF2:3Dy@CaF2 (1:0.05), SrF2:3Dy@CaF2 (1:1) and SrF2:3Dy@CaF2 (1:2) are 5475, 5476, 5384 and 5525 K, respectively, which lie in the cold white region.

  1. Generic Delivery of Payload of Nanoparticles Intracellularly via Hybrid Polymer Capsules for Bioimaging Applications

    PubMed Central

    Sami, Haider; Maparu, Auhin K.; Kumar, Ashok; Sivakumar, Sri

    2012-01-01

    Towards the goal of development of a generic nanomaterial delivery system and delivery of the ‘as prepared’ nanoparticles without ‘further surface modification’ in a generic way, we have fabricated a hybrid polymer capsule as a delivery vehicle in which nanoparticles are loaded within their cavity. To this end, a generic approach to prepare nanomaterials-loaded polyelectrolyte multilayered (PEM) capsules has been reported, where polystyrene sulfonate (PSS)/polyallylamine hydrochloride (PAH) polymer capsules were employed as nano/microreactors to synthesize variety of nanomaterials (metal nanoparticles; lanthanide doped inorganic nanoparticles; gadolinium based nanoparticles, cadmium based nanoparticles; different shapes of nanoparticles; co-loading of two types of nanoparticles) in their hollow cavity. These nanoparticles-loaded capsules were employed to demonstrate generic delivery of payload of nanoparticles intracellularly (HeLa cells), without the need of individual nanoparticle surface modification. Validation of intracellular internalization of nanoparticles-loaded capsules by HeLa cells was ascertained by confocal laser scanning microscopy. The green emission from Tb3+ was observed after internalization of LaF3:Tb3+(5%) nanoparticles-loaded capsules by HeLa cells, which suggests that nanoparticles in hybrid capsules retain their functionality within the cells. In vitro cytotoxicity studies of these nanoparticles-loaded capsules showed less/no cytotoxicity in comparison to blank capsules or untreated cells, thus offering a way of evading direct contact of nanoparticles with cells because of the presence of biocompatible polymeric shell of capsules. The proposed hybrid delivery system can be potentially developed to avoid a series of biological barriers and deliver multiple cargoes (both simultaneous and individual delivery) without the need of individual cargo design/modification. PMID:22649489

  2. Fluoride Selective Optical Sensor Based on Aluminum(III)-Octaethylporphyrin in Thin Polymeric Film: Further Characterization and Practical Application

    PubMed Central

    Badr, Ibrahim H. A.; Meyerhoff, Mark E.

    2008-01-01

    More detailed analytical studies of a new fluoride selective optical sensor based on the use of aluminum(III)-octaethylporphyrin and a lipophilic pH indicator (4?,5?-dibromofluorescein octadecyl ester; ETH-7075) within a thin plasticized poly(vinyl chloride) film are reported. The sensor exhibits extraordinary optical selectivity for fluoride over a wide range of other anions, including anions with far more positive free energies of hydration (e.g., perchlorate, thiocyanate, nitrate, etc.). UV-VIS spectrophotometric studies of the sensing films indicate that fluoride interacts with the Al(III) center of the porphyrin structure, yielding both a change in the Soret band ?max of the porphyrin as well as a change in the protonation state of the pH indicator within the film. The same change in spectral properties of the metalloporphyrin occurs in the absence of added pH indicator or with added tetraphenylborate derivative anionic sites, but optical responses to fluoride in these cases are shown to be irreversible. The presence of the pH indicator and the simultaneous fluoride/proton coextraction equilibrium chemistry is shown to greatly enhance the reversibility of fluoride binding to the Al(III) porphyrin. Optical response toward fluoride can be observed in the range of 0.1 ?M to 1.6 mM. Optical selectivity coefficients of < 10?6 for common anions (e.g., sulfate, chloride, nitrate etc.) and < 10?4 for perchlorate and thiocyanate are obtained. Measurements of fluoride in drinking water via the new optical sensor are shown to correlate well with values obtained for the same samples using a classical LaF3 based fluoride ion-selective electrode method. PMID:16223262

  3. Diffusion-controlled growth of bimineralic merwinite - diopside reaction rims between wollastonite - monticellite interfaces

    NASA Astrophysics Data System (ADS)

    Joachim, B.; Gardes, E.; Heinrich, W.; Abart, R.

    2009-04-01

    At temperatures of 800 °C to 900 °C and 1.2 GPa, monticellite and wollastonite react to form merwinite and diopside after the reaction: 2 monticellite (CaMgSiO4) + 2 wollastonite (CaSiO3) â?? merwinite (Ca3MgSi2O8) + diopside (CaMgSi2O6) We synthesized bimineralic merwinite - diopside reaction rims along the interfaces of cylindric crystals of monticellite and wollastonite. The samples were loaded in a platinum capsule and annealed at 800 °C to 900 °C and 1.2 GPa in a piston cylinder apparatus for 5 to 65 hours. Natural CaF2 was used as pressure medium and the charges were nominally dry. In all experiments, a single layer consisting of bimineralic aggregates of merwinite and diopside was produced in about equal molar amounts. Time series revealed that rim growth is parabolic, indicating that the reaction kinetics is controlled by component diffusion. SEM analysis of the microstructure showed that the original monticellite-wollastonite interface is located in the centre of the reaction rim. This implies that rim growth primarily occurred by transfer of the mobile component MgO from the rim-monticellite interface to the rim-wollastonite interface. The bulk reaction is thus divided into two half reactions occurring at the two reaction fronts. At the rim-monticellite interface the reaction is: 2 monticellite â?? 0.5 merwinite + 0.5 diopside + MgO, and at the rim-wollastonite interface, it is: 2 wollastonite + MgO â?? 0.5 merwinite + 0.5 diopside Using the model of Abart et al. (2009), the effective diffusion coefficients DMgO at 800 °C are estimated at 1.55×10-16± 2.18×10-17 m2/s, and at 900 °C at 2.46×10-16± 3.45×10-17 m2/s. This yields an activation energy of Ea= 45.6 ± 16.4 kJ/mol and a pre-exponential factor log D0 = -13.59 ± 1.26 for the Arrhenius relations to describe the temperature-dependent effective diffusivity of the MgO component in the bimineralic aggregate. IR-spectra revealed distinctive OH-contents in the nominally dry phases monticellite and wollastonite after the experiments, which had not been present in the reactants. Obviously, some hydrogen released by the natural, water-containing CaF2 pressure medium diffused into the capsule, thus producing traces of water inside. The presence of minute amounts of water may strongly enhance the kinetics of the reaction. In fact, if completely waterfree Al2O3-powder is used as pressure medium, no significant reaction occurred, and accordingly, reactants remain OH-free. An Al2O3-layer of 3 mm thickness between the capsule and the CaF2 surrounding delays the onset of rim growth for about one hour. However, once initiated, the reaction progress is the same in instantaneous and delayed reactions. References: Abart R., Petrishcheva E., Fischer F.D., Svoboda J. (2009), Thermodynamic model for diffusion controlled reaction rim growth in a binary system: application to the forsterite-enstatite-quartz system, American Journal of Science, Vol. 309, pp. 114-131

  4. The effect of water on bimineralic reaction rims

    NASA Astrophysics Data System (ADS)

    Joachim, B.; Gardés, E.; Abart, R.; Heinrich, W.

    2011-12-01

    At 900°C and 1.2 GPa monticellite (CaMgSiO4) and wollastonite (CaSiO3) react to form a bimineralic reaction rim of diopside (CaMgSi2O6) and merwinite (Ca3MgSi2O8) according to the reaction: 1 monticellite + 1 wollastonite = 0.5 merwinite + 0.5 diopside Experiments were performed in a piston cylinder apparatus. Dry Al2O3, and natural, water-containing CaF2 were used as pressure media. After runs using CaF2 as pressure medium, IR-spectra of a periclase crystal, which was also loaded into the Pt-capsule, show peaks that may safely be related to OH-defects in the MgO-structure. This indicates that water, stemming from the natural CaF2 diffused into the capsule during the course of the experiment. The amount of water in the capsule increased with increasing run duration. Absence of reaction products in completely dry charges implies that presence of small amounts of water is required to promote nucleation and growth. In wet charges, time series revealed that overall rim growth is parabolic, indicating diffusion control. Textural arguments indicate that the original interface is always located in the center of the rim. This and mass balance considerations let us conclude that overall rim growth is solely controlled by MgO-diffusion. The effective bulk diffusion DMgO is calculated to 10-16.3 +/- 0.2 m2s-1. Further water uptake during the course of the experiment does not affect MgO-diffusivity. During the first stage of rim growth, the reaction products form a lamellar microstructure with alternating, pallisade shaped merwinite and diopside crystals, whereby the long axes of the grains are oriented normal to the original monticellite-wollastonite interface (lamellar type). At longer run durations, diopside and merwinite start to segregate into monomineralic layers with diopside accumulating in the center and merwinite at both sides of the reaction rim (multilayer type). After a run duration of 65 h segregation is almost complete and a triple layer rim forms showing the sequence mtc | mer | di | mer | wo. Increasing water availability significantly increases the mobility of either CaO or SiO2 or both relative to the mobility of MgO. As a consequence, the availability of water affects the structure and organization of the reaction rim. If only very small amounts are present, CaO- and SiO2-mobilities are small compared to the MgO-mobility (LCaO/LMgO << 1), and a lamellar microstructure develops. If more water is available, either CaO or SiO2 or both become more mobile relative to MgO (LCaO/LMgO > 1), and the product phases segregate into distinct monomineralic layers. Consequently, the availability of water does not only affect overall rim growth kinetics (e.g. Yund 1997), but also relative component mobilities and as a consequence the microstructure of reaction rims. Yund RA (1997), Rates of grain boundary diffusion through enstatite and forsterite reaction rims: Contrib Min and Petrol 126: 224-236.

  5. Modeling and Prediction of Surface Plasmon Resonance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Guske, Joshua Travis

    Surface plasmon resonance (SPR) is a spectroscopy that measures the response of a surface wave at the interface of a conductor and a dielectric, called the surface plasmon polariton (SPP). In the Kretschmann configuration, a thin film of the conductor is illuminated under total internal reflection via a prism. At the appropriate angle and frequency, an absorption is seen in reflected p-polarized light. This excitation is highly sensitive to the properties of the dielectric medium, the conductor itself, and the substrate material. Theoretical modeling is valuable in SPR, because of the high sensitivity and the large number of experimental variables involved. As the technology advances, increasingly sophisticated modeling techniques become necessary. In addition, with the aid of theoretical modeling, SPR may be used as a materials characterization tool, to study the properties of the conductors themselves. In this dissertation, several plasmonic systems were studied. First, in chapters 2 and 3, films of silver sandwiched between two layers of non-conductive aluminum-doped zinc oxide (AZO) on glass were considered. The films were prepared by reactive pulsed DC magnetron sputtering, and the silver thickness was varied. The films' SPR response was measured in the near-IR in air. Theoretical modeling of Rp/Rs was performed by the multilayer transfer-matrix method, with the aid of a modified Nelder-Mead simplex optimization algorithm. The initial modeling results suggested that both the silver and AZO properties were significantly different from the bulk materials. In particular, the silver had a higher plasma frequency and high-frequency dielectric constant than bulk, and it was hypothesized that the AZO was contributing charge carriers into the silver layer. However, upon review it was determined that a miscalibration of the incident angles could also explain the results. Second, in chapter 4, films of silver sandwiched between two layers of AZO were deposited using pulsed laser deposition (PLD) onto both glass and CaF2. The film thicknesses were held nearly constant, and the AZO plasma frequency was varied by changing the Al doping concentration and oxygen pressure during deposition. The films' SPR response was measured in near-IR in two separate instruments, in air for the films on glass and in water for the films on CaF2. In the theoretical modeling, which took place via the multilayer transfer-matrix model, the bulk silver dielectric function was used, and the AZO dielectric function was approximated as a hybrid between a conductive Drude model and the ZnO bulk. Initial results were promising, but indicated that the system was limited by the accuracy of the film thickness measurements and the consistency of the deposition process. Third, in chapter 5, pure AZO films were assessed using SPR spectroscopy. The films were deposited using PLD in an oxygen environment onto CaF 2. The SPR responses of the films were measured in both air, in the near-IR, and in water, in the mid-IR. A modified Nelder-Mead simplex optimization algorithm was used to determine the optical constants of the films in the Drude model. The high-frequency dielectric constant was consistent with literature values. However, the plasma frequency and damping constant suggested that the films had a higher free electron mass than is reported in the literature. In addition, the spectra in water were complex, which was explained as the result of interaction of the water molecular vibrations with the surface plasmon polariton in the mid-IR. This is believed to be the first reported observation of a mid-IR water-plasmon interaction in this fashion.

  6. Progress status for the Mu2e calorimeter system

    NASA Astrophysics Data System (ADS)

    Pezzullo, Gianantonio; Budagov, J.; Carosi, R.; Cervelli, F.; Cheng, C.; Cordelli, M.; Corradi, G.; Davydov, Yu; Echenard, B.; Giovannella, S.; Glagolev, V.; Happacher, F.; Hitlin, D.; Luca, A.; Martini, M.; Miscetti, S.; Murat, P.; Ongmonkolkul, P.; Porter, F.; Saputi, A.; Sarra, I.; Spinella, F.; Stomaci, V.; Tassielli, G.

    2015-02-01

    The Mu2e experiment at FNAL aims to measure the charged-lepton flavor violating neutrinoless conversion of a negative muon into an electron. The conversion results in a monochromatic electron with an energy slightly below the muon rest mass (104.97 MeV). The calorimeter should confirm that the candidates reconstructed by the extremely precise tracker system are indeed conversion electrons while performing a powerful ?/e particle identification. Moreover, it should also provide a high level trigger for the experiment independently from the tracker system. The calorimeter should also be able to keep functionality in an environment where the background delivers a dose of ~ 10 krad/year in the hottest area and to work in the presence of 1 T axial magnetic field. These requirements translate in the design of a calorimeter with large acceptance, good energy resolution O(5%) and a reasonable position (time) resolution of ~ < 1 cm (<0.5ns). The baseline version of the calorimeter is composed by two disks of inner (outer) radius of 351 (660) mm filled by 1860 hexagonal BaF2 crystals of 20 cm length. Each crystal is readout by two large area APD's. In this paper, we summarize the experimental tests done so far as well as the simulation studies in the Mu2e environment.

  7. Sb2Te3 and Bi2Te3 Thin Films Grown by Room-Temperature MBE

    NASA Astrophysics Data System (ADS)

    Aabdin, Z.; Peranio, N.; Winkler, M.; Bessas, D.; König, J.; Hermann, R. P.; Böttner, H.; Eibl, O.

    2012-06-01

    Sb2Te3 and Bi2Te3 thin films were grown on SiO2 and BaF2 substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2 nm were alternately deposited at room temperature, and the films were subsequently annealed at 250°C for 2 h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500 nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb2Te3 films at room temperature, i.e., low charge carrier density (2.6 × 1019 cm-3), large thermopower (130 ?V K-1), large charge carrier mobility (402 cm2 V-1 s-1), and resulting large power factor (29 ?W cm-1 K-2). Bi2Te3 films also showed low charge carrier density (2.7 × 1019 cm-3), moderate thermopower (-153 ?V K-1), but very low charge carrier mobility (80 cm2 V-1 s-1), yielding low power factor (8 ?W cm-1 K-2). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.

  8. A direct route for the investigation of crystalline field effects on the spectral properties of Eu3+ ions in designed nanostructures

    NASA Astrophysics Data System (ADS)

    Yu, Hua; Guo, Hui; Zhang, Xiaoyu; Lao, Aiqing; Gao, Shaohua; Li, Qingxuan; Zhao, Lijuan

    2015-08-01

    The spectral properties of lanthanide ions doped in a solid-state matrix, especially the Stark splitting and emission shifts, are strongly influenced by the local crystalline field. Here, we use a direct approach to quantitatively investigate the crystalline field effect on these spectral properties of Eu3+ ions in our designed ?-PbF2:Eu3+ and BaF2:Eu3+ nanostructures. The extremely similar structures in which the central Eu3+ ions have the same site symmetry allow the local crystalline field to be simplified as the same point charge electrostatic field model. In this model, the direction and intensity of the electrostatic field are related to the distortion and expansion degree of the charge cloud of the luminescent center, respectively, and further determine the Stark splitting and emission shift. The theoretical analysis and charge-cloud stimulations were in good agreement with the experimental results. The direction and intensity of the crystalline field were calculated, and showed that the emission spectra shift to red with the increase in intensity. This work provides a comprehensive understanding of the spectral changes induced by a crystalline field, which is of great significance for the design of materials with the desired spectral properties.

  9. Ellipsometric study of YBa2Cu3O(7-x) laser ablated and co-evaporated films

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Sieg, R. E.; Warner, J. D.; Stan, M. A.; Vitta, S.

    1990-01-01

    High temperature superconducting films of YBa2Cu3O(7-x) (YBCO were grown on SrTiO3, LaA1O3, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R=O)=90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaported films was much lower than the value reported for single crystals, and was sample dependent.

  10. Field dependence of resistance transitions in thin films of YBA 2CU 3O 7 and YBA 2CU 4O 8

    NASA Astrophysics Data System (ADS)

    Berghuis, P.; Guo, S. Q.; Van der Slot, A. L. F.; Dam, B.; Stollman, G. M.; Kes, P. H.

    1989-12-01

    Preferentially oriented thin films of YBa 2Cu 3O 7 (123) and YBa 2Cu 4O 8 (248) with the c-axis perpendicular to the substrate have been prepared by e-gun evaporation from Y, BaF 2 and Cu. Critical current and resistance transition measurements have been carried out in magnetic fields parallel to the c-axis. The results will be analysed in terms of a model for thermally activated flux flow combined with two models for flux pinning, one in which the pinning is predominantly caused by twin boundaries and a second in which pinning by dislocations is considered. The resistance broadening in the 248 is well described by the model with dislocation pinning. The B c2 (T) values obtained from the fits compare well with estimates from the fluxflow resistivity and a kink in the resistance vs field curves. The slope of B c2 at T c is 0.37 T/K, a factor four smaller than in the 123.

  11. Measurement and analysis of the Am-243 neutron capture cross section at the n_TOF facility at CERN

    E-print Network

    n_TOF Collaboration; :; E. Mendoza; D. Cano-Ott; C. Guerrero; E. Berthoumieux; U. Abbondanno; G. Aerts; F. Alvarez-Velarde; S. Andriamonje; J. Andrzejewski; P. Assimakopoulos; L. Audouin; G. Badurek; J. Balibrea; P. Baumann; F. Becvar; F. Belloni; F. Calvino; M. Calviani; R. Capote; C. Carrapico; A. Carrillo de Albornoz; P. Cennini; V. Chepel; E. Chiaveri; N. Colonna; G. Cortes; A. Couture; J. Cox; M. Dahlfors; S. David; I. Dillmann; R. Dolfini; C. Domingo-Pardo; W. Dridi; I. Duran; C. Eleftheriadis; L. Ferrant; A. Ferrari; R. Ferreira-Marques; L. Fitzpatrick; H. Frais-Koelbl; K. Fujii; W. Furman; I. Goncalves; E. Gonzalez-Romero; A. Goverdovski; F. Gramegna; E. Griesmayer; F. Gunsing; B. Haas; R. Haight; M. Heil; A. Herrera-Martinez; M. Igashira; S. Isaev; E. Jericha; F. Kappeler; Y. Kadi; D. Karadimos; D. Karamanis; V. Ketlerov; M. Kerveno; P. Koehler; V. Konovalov; E. Kossionides; M. Krticka; C. Lampoudis; H. Leeb; A. Lindote; I. Lopes; R. Lossito; M. Lozano; S. Lukic; J. Marganiec; L. Marques; S. Marrone; T. Martinez; C. Massimi; P. Mastinu; A. Mengoni; P. M. Milazzo; C. Moreau; M. Mosconi; F. Neves; H. Oberhummer; S. O Brien; M. Oshima; J. Pancin; C. Papachristodoulou; C. Papadopoulos; C. Paradela; N. Patronis; A. Pavlik; P. Pavlopoulos; L. Perrot; M. T. Pigni; R. Plag; A. Plompen; A. Plukis; A. Poch; J. Praena; C. Pretel; J. Quesada; T. Rauscher; R. Reifarth; M. Rosetti; C. Rubbia; G. Rudolf; P. Rullhusen; J. Salgado; C. Santos; L. Sarchiapone; I. Savvidis; C. Stephan; G. Tagliente; J. L. Tain; L. Tassan-Got; L. Tavora; R. Terlizzi; G. Vannini; P. Vaz; A. Ventura; D. Villamarin; M. C. Vicente; V. Vlachoudis; R. Vlastou; F. Voss; S. Walter; H. Wendler; M. Wiescher; K. Wisshak

    2014-12-04

    Background:The design of new nuclear reactors and transmutation devices requires to reduce the present neutron cross section uncertainties of minor actinides. Purpose: Reduce the $^{243}$Am(n,$\\gamma$) cross section uncertainty. Method: The $^{243}$Am(n,$\\gamma$) cross section has been measured at the n_TOF facility at CERN with a BaF$_{2}$ Total Absorption Calorimeter, in the energy range between 0.7 eV and 2.5 keV. Results: The $^{243}$Am(n,$\\gamma$) cross section has been successfully measured in the mentioned energy range. The resolved resonance region has been extended from 250 eV up to 400 eV. In the unresolved resonance region our results are compatible with one of the two incompatible capture data sets available below 2.5 keV. The data available in EXFOR and in the literature has been used to perform a simple analysis above 2.5 keV. Conclusions: The results of this measurement contribute to reduce the $^{243}$Am(n,$\\gamma$) cross section uncertainty and suggest that this cross section is underestimated up to 25% in the neutron energy range between 50 eV and a few keV in the present evaluated data libraries.

  12. Multiphonon relaxation and infrared-to-visible conversion of Er(3+) and Yb(3+) ions in barium-thorium fluoride glass

    NASA Astrophysics Data System (ADS)

    Yeh, D. C.; Sibley, W. A.; Suscavage, M.; Drexhage, M. G.

    1987-07-01

    The upconversion of IR radiation into green and red fluorescence has been studied for Er(3+) and Yb(3+) ions in BaF2/ThF4 fluoride glass over a wide temperature range and several dopant concentrations. At room temperature an upconversion efficiency of 0.000033 has been obtained for the green emission from the glass with 1 mol pct ErF3 and 19 mol pct YbF3 pumped by 973-nm radiation with intensity of 16.5 mW/sq cm. For an absorbed intensity of 10 W/sq cm the efficiency for green upconversion emission is predicted to be 2 percent. Radiative transition rates for the excited states of Er(3+) were calculated using Judd-Ofelt (1962) theory, and intensity parameters obtained from measured integrated absorption coefficients. The calculated values of the multiphonon relaxation and the upconversion fluorescence intensity, obtained from the rate-equation model of Wright (1976), are discussed in light of the experimental results.

  13. Neutron capture reactions at DANCE

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.

    2008-05-01

    The Detector for Advanced Neutron Capture Experiments (DANCE) is a 4? BaF2 array consisting of 160 active detector elements. The primary purpose of the array is to perform neutron capture cross section measurements on small (>~100 ?g) and/or radioactive (<~100 mCi) species. The measurements made possible with this array will be useful in answering outstanding questions in the areas of national security, threat reduction, nuclear astrophysics, advanced reactor design and accelerator transmutation of waste. Since the commissioning of DANCE we have performed neutron capture cross section measurements on a wide array of medium to heavy mass nuclides. Measurements to date include neutron capture cross sections on 241,243Am, neutron capture and neutron-induced fission cross sections and capture-to-fission ratio (? = ??/?f) for 235U using a new fission-tagging detector as well as neutron capture cross sections for several astrophysics branch-point nuclei. Results from several of these measurements will be presented along with a discussion of additional physics information that can be extracted from the DANCE data.

  14. New Opportunities in Decay Spectroscopy with the GRIFFIN and DESCANT Arrays

    NASA Astrophysics Data System (ADS)

    Bildstein, V.; Andreoiu, C.; Ball, G. C.; Ballast, T.; Bartlett, C.; Bender, P. C.; Bernier, N.; Bianco, L.; Bishop, D.; Brennan, D.; Bruhn, T.; Cheeseman, A.; Churchman, R.; Ciccone, S.; Davids, B.; Demand, G.; Dillmann, I.; Garnsworthy, A. B.; Garrett, P. E.; Georges, S.; Hackman, G.; Hadinia, B.; Kokke, R.; Krücken, R.; Linn, Y.; Lim, C.; Martin, J.-P.; Miller, D.; Mills, W. J.; Morrison, L. N.; Ohlmann, C. A.; Park, J.; Pearson, C. J.; Pore, J. L.; Rajabali, M. M.; Rand, E. T.; Rizwan, U.; Sarazin, F.; Shaw, B.; Starosta, K.; Svensson, C. E.; Sumithrarachchi, C.; Unsworth, C.; Voss, P.; Wang, Z. M.; Williams, J.; Wong, J.; Wong, S.

    The GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei) project is a major upgrade of the decay spectroscopy capabilities at TRIUMF-ISAC. GRIFFIN will replace the 8? spectrometer with an array of up to 16 large-volume HPGe clover detectors and use a state-of-the-art digital data acquisition system. The existing ancillary detector systems that had been developed for 8?, such as the SCEPTAR array for ?-tagging, PACES for high-resolution internal conversion electron spectroscopy, and the DANTE array of LaBr3/BaF2 scintillators for fast ?-ray timing, will be used with GRIFFIN. GRIFFIN can also accommodate the new neutron detector array DESCANT (Deuterated Scintillator Array for Neutron Tagging), enabling the study of ?-delayed neutron emitters. DESCANT consists of up to 70 detectors, each filled with approximately 2 liters of deuterated benzene, a liquid scintillator that provides pulse-shape discrimination (PSD) capabilities to distinguish between neutrons and ?-rays interacting with the detector. In addition, the anisotropic nature of n-d scattering as compared to the isotropic n-p scattering allows for the determination of the neutron energy spectrum directly from the pulse-height spectrum, complementing the time-of-flight (TOF) information. The installation of GRIFFIN is under way and first experiments are planned for the fall of 2014. The array will be completed in 2015 with the full complement of 16 clovers. DESCANT will be tested coupled with GRIFFIN in spring of 2015.

  15. DANCEing with the Stars: Measuring Neutron Capture on Unstable Isotopes with DANCE

    NASA Astrophysics Data System (ADS)

    Couture, A.; Agvaanluvsan, U.; Baker, J. D.; Bayarbadrahk, B.; Becker, J. A.; Bond, E.; Bredeweg, T. A.; Chyzh, A.; Dashdorj, D.; Fowler, M.; Haight, R. C.; Jandel, M.; Keksis, A. L.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.

    2009-03-01

    Isotopes heavier than iron are known to be produced in stars through neutron capture processes. Two major processes, the slow (s) and rapid (r) processes are each responsible for 50% of the abundances of the heavy isotopes. The neutron capture cross sections of the isotopes on the s process path reveal information about the expected abundances of the elements as well as stellar conditions and dynamics. Until recently, measurements on unstable isotopes, which are most important for determining stellar temperatures and reaction flow, have not been experimentally feasible. The Detector for Advance Neutron Capture Experiments (DANCE) located at the Los Alamos Neutron Science Center (LANSCE) was designed to perform time-of-flight neutron capture measurements on unstable isotopes for nuclear astrophysics, stockpile stewardship, and reactor development. DANCE is a 4-? BaF2 scintillator array which can perform measurements on sub-milligram samples of isotopes with half-lives as short as a few hundred days. These cross sections are critical for advancing our understanding of the production of the heavy isotopes.

  16. Compact dual-crystal optical parametric amplification for broadband IR pulse generation using a collinear geometry.

    PubMed

    Hong, Zuofei; Zhang, Qingbin; Lu, Peixiang

    2013-04-22

    A novel compact dual-crystal optical parametric amplification (DOPA) scheme, collinearly pumped by a Ti:sapphire laser (0.8 ?m), is theoretically investigated for efficiently generating broadband IR pulses at non-degenerate wavelengths (1.2 ?m~1.4 ?m and 1.8 ?m~2.1 ?m). By inserting a pair of barium fluoride (BaF(2)) wedges between two thin ?-barium borate (BBO) crystals, the group velocity mismatch (GVM) between the three interacting pulses can be compensated simultaneously. In this case, the obtained signal spectrum centered at 1.3 ?m is nearly 20% broader and the conversion efficiency is increased, but also the pulse contrast and beam quality are improved due to the better temporal overlap. Furthermore, sub-two-cycle idler pulses with carrier-envelope phase (CEP) fluctuation of sub-100-mrad root mean square (RMS) can be generated. Because a tunable few-cycle IR pulse with millijoule energy is attainable in this scheme, it will contribute to ultrafast community and be particularly useful as a driving or controlling field for the generation of ultrafast coherent x-ray supercontinuum. PMID:23609660

  17. GAMMA: GAMma Multiplicity Filter Array for the selection of angular momentum in heavy ion collision reactions

    E-print Network

    Deepak Pandit; S. Mukhopadhyay; Srijit Bhattacharya; Surajit Pal; A. De; S. R. Banerjee

    2009-12-23

    A 50 element BaF2 gamma-multiplicity filter has been designed, fabricated and installed successfully at the Variable Energy Cyclotron Centre (VECC), Kolkata for angular momentum selection in heavy ion collision reactions. A thorough GEANT3 Monte Carlo simulation was performed to optimize the individual detector shape and geometrical structure of the array. The detectors have been fabricated in-house from bare barium fluoride crystals (each measuring 5 cm in length and having cross-sectional area of 3.5 x 3.5 cm2). The basic detector properties have been studied using the lab standard -ray sources. The response function of the filter has been studied using GEANT3 for mapping the fold distribution of the filter onto the angular momentum space. The multiplicity filter has been used successfully to measure the high angular momentum of the compound nuclei populated in the reaction 20Ne (E = 145 & 160 MeV) + 93Nb, 27Al as well as low angular momentum events from the fission fragments of 252Cf spontaneous fission source. The filter has also been used successfully for correcting non-statistical events involved in the heavy ion fusion reaction.

  18. Hyperfine field at Mn in the intermetallic compound LaMnSi2 measured by PAC using 111Cd nuclear probe

    NASA Astrophysics Data System (ADS)

    Domienikan, C.; Bosch-Santos, B.; Cabrera Pasca, G. A.; Saxena, R. N.; Carbonari, A. W.

    2015-04-01

    Magnetic hyperfine field at Mn site has been measured in the orthorhombic intermetallic compound LaMnSi2 with PAC spectroscopy using radioactive 111In- 111Cd nuclear probe. Samples of LaMnSi2 were prepared by melting pure metallic components in stoichiometric proportion in an arc furnace under argon atmosphere. The samples were sealed in a quartz tube under helium atmosphere, annealed at 1000 °C for 60 h and quenched in water. Samples were analyzed with X-ray diffraction method. 111In was introduced in the samples by thermal diffusion at 1000 °C for 60 h. PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 50 K and 410 K. Results show well defined quadrupole and magnetic interactions at all temperatures. The magnetic hyperfine field (Bhf) measured at 50 K is 7.1(1) T. The temperature dependence of Bhf follows the normal Brillouin-like behavior expected for a simple ferromagnetic ordering. The ferromagnetic transition temperature (Tc) was determined to be 401(1) K.

  19. Kinetics characterization of YBCO thin films growth on LAO (100) single crystals by the TFA-MOD reaction

    NASA Astrophysics Data System (ADS)

    Piñol, S.; Castaño, O.

    2006-06-01

    We have studied in detail the kinetics parameters of the YBa2Cu3O7-x (YBCO) thin films growth on LaAlO3 (100) single crystals by the TFA-MOD method, using an i.n-situ fluoride selective electrode. We have considered: temperature, flow carrier gas rates and water partial pressure dependences in the reaction. Kinetics curves show that it exist an intermediate step before the YBCO formation. This step, which starts during the heating ramp (~400°C) consists in a partial elimination of F from the BaF2 precursor to forms an oxyfluoride intermediate compound. The total YBCO formation appears at temperatures as higher as 700°C. We have found that at low flow carrier gas rates, the reaction is controlled by diffusion mechanisms and the apparent order of YBCO formation is n = 1 respect to the stirring rate, but at higher flow rates the YBCO formation is controlled chemically, then the apparent order is zero. The apparent reaction order of YBCO formation respect to the water pressure also has been studied.

  20. Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties: Study on reaction mechanism of YBa2Cu3O7-x film by Tfa-Mod process

    NASA Astrophysics Data System (ADS)

    Ding, Fa-Zhu; Lü, Xu-Dong; Gu, Hong-Wei; Li, Tao; Cao, Jiang-Li

    2009-04-01

    This paper systematically investigates the intermediate phases of YBa2Cu3O7-x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40-140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.

  1. Comparison of x-ray absorption spectra between water and ice: New ice data with low pre-edge absorption cross-section

    NASA Astrophysics Data System (ADS)

    Sellberg, Jonas A.; Kaya, Sarp; Segtnan, Vegard H.; Chen, Chen; Tyliszczak, Tolek; Ogasawara, Hirohito; Nordlund, Dennis; Pettersson, Lars G. M.; Nilsson, Anders

    2014-07-01

    The effect of crystal growth conditions on the O K-edge x-ray absorption spectra of ice is investigated through detailed analysis of the spectral features. The amount of ice defects is found to be minimized on hydrophobic surfaces, such as BaF2(111), with low concentration of nucleation centers. This is manifested through a reduction of the absorption cross-section at 535 eV, which is associated with distorted hydrogen bonds. Furthermore, a connection is made between the observed increase in spectral intensity between 544 and 548 eV and high-symmetry points in the electronic band structure, suggesting a more extended hydrogen-bond network as compared to ices prepared differently. The spectral differences for various ice preparations are compared to the temperature dependence of spectra of liquid water upon supercooling. A double-peak feature in the absorption cross-section between 540 and 543 eV is identified as a characteristic of the crystalline phase. The connection to the interpretation of the liquid phase O K-edge x-ray absorption spectrum is extensively discussed.

  2. Measuring the true height of water films on surfaces

    NASA Astrophysics Data System (ADS)

    Santos, Sergio; Verdaguer, Albert; Souier, Tewfic; Thomson, Neil H.; Chiesa, Matteo

    2011-11-01

    Measuring the level of hydrophilicity of heterogeneous surfaces and the true height of water layers that form on them in hydrated conditions has a myriad of applications in a wide range of scientific and technological fields. Here, we describe a true non-contact mode of operation of atomic force microscopy in ambient conditions and a method to establish the source of apparent height. A dependency of the measured water height on operational parameters is identified with water perturbations due to uncontrolled modes of imaging where intermittent contact with the water layer, or even the surface, might occur. In this paper we show how to (1) determine when the water is being perturbed and (2) distinguish between four different interaction regimes. Each of the four types of interaction produces measurements ranging from fractions of the true height in one extreme to values which are as large as four times the real height in the other. We show the dependence of apparent height on the interaction regime both theoretically and empirically. The agreement between theory and experiment on a BaF2(111) sample displaying wet and un-wet regions validates our results.

  3. Secondary beam fragments produced by 200 MeV u-1 12C ions in water and their dose contributions in carbon ion radiotherapy

    NASA Astrophysics Data System (ADS)

    Gunzert-Marx, K.; Iwase, H.; Schardt, D.; Simon, R. S.

    2008-07-01

    For applications in heavy-ion radiotherapy, the emission of secondary fragments from 200 MeV u-1 carbon ions was investigated using a 12.78 cm thick water absorber as a tissue-equivalent beam stopping target. Secondary light particles (n, p, d, t, 3He and 4He) produced by nuclear fragmentation and emerging from the target in forward direction were detected with a ?E-E-telescope consisting of NE102 and BaF2 scintillation detectors. Energy spectra of the fragments at angles of 0°, 5°, 10°, 20° and 30° to the beam axis were obtained from time-of-flight measurements. They show a broad maximum at about half of the projectiles energy per nucleon, the shape at high energies is exponential and extends up to the projectiles initial energy per nucleon—for neutrons and protons to about twice the energy of the projectile per nucleon. Comparison of the experimental data with calculations performed with the Monte-Carlo code (partide and heavy ion transport code system (PHITS)) shows fairly good agreement for neutrons, protons and deuterons, but some deviations for tritons and helium fragments. The neutron dose in patient treatments with carbon ions was estimated to be 8 mGy per treatment-Gy based on the measured neutron yield.

  4. SEMICONDUCTOR MATERIALS: Growth orientation and superconducting properties of YBa2Cu3O7-? films prepared by the low-fluorine sol-gel process

    NASA Astrophysics Data System (ADS)

    Li, Lei; Gaoyang, Zhao; Hui, Xu; Juanjuan, Zhao

    2010-08-01

    YBa2Cu3O7-? (YBCO) films were deposited on (100)-oriented LaAlO3 (LAO) single crystal substrates by the dip-coating process using low-fluorine solution. Their microstructures were characterized with the aid of X-ray diffractometry, scanning electron microscopy and high-resolution transmission electron microscopy. Their superconducting properties were measured by the standard four-probe method. The experiment results show that the film obtained under high enough humidity conditions exhibits better c-axis texture and superconducting properties than the film under a relatively low humidity conditions. Based on the classical nucleation and chemical reaction thermodynamics theory, the underlying crystalline and growth mechanisms of YBCO films under certain humidity conditions are explained in combination with our experimental results. It is suggested that the unreacted intermediate phases such as BaF2 and CuO aggregated in the YBCO grain boundary will cause lattice distortion in the YBCO matrix and further induce the formation of a-axis oriented YBCO grains as crystallization proceeds. Therefore, it is believed that the relative content of water vapor within the heat-treatment atmosphere plays quite an important role in the preparation of c-axis oriented YBCO film with good superconducting properties.

  5. Systematic study of highly efficient white light generation in transparent materials using intense femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Dharmadhikari, A. K.; Rajgara, F. A.; Mathur, D.

    2005-01-01

    We report the results of a systematic study of white light generation in different high band-gap optical media (BaF2, acrylic, water and BK-7 glass) using ultrashort (45 fs) laser pulses. We have investigated the influence of different parameters, such as focal position of the incident laser light within the medium, the polarization state of the incident laser radiation and the pulse duration of the incident laser beam on the white light generation. Our results indicate that for intense, ultrashort pulses, the position of physical focus inside the media is crucial in the generation, with high efficiency, of white light spectra over the wavelength range 400 1100 nm. Linearly polarized incident laser light generates white light with higher intensity in the blue region than circularly polarized light. Ultrashort (45 fs) pulses generate a flatter spectrum with higher white light conversion efficiency than longer (300 fs) pulses of the same laser power. We believe that a flat response over a wide range of wavelengths in the continuum may be efficiently compressed for generation of sub-10 fs pulses.

  6. FT-IR Microscopy Of Biomineralization At 20µ Spatial Resolution

    NASA Astrophysics Data System (ADS)

    Mendelsohn, Richard; Hassankhani, Alborz; Pleshko, Nancy; DiCarlo, Edward; Boskey, Adele

    1989-12-01

    FT-IR microscopy offers certain advantages for the study of normal and pathological biomineralizing tissue samples. These include the identification and quantitation of the mineral phase and the determination of the secondary structure of the protein constituents. A drawback of the method is difficulty in interpretation of spectra from samples containing unknown quantities of unknown constituents. We have circumvented this problem by studying the main components of mineralizing tissue, collagen (95% of the protein phase) and hydroxyapatite (main mineral constituent) whose strongest IR bands absorb in relatively clean spectral regions. Samples were prepared for IR microscopy by surgical removal of tissue, fixation in formalin or ethanol, embedding in PMMA or epoxy, and the microtoming of thin (5-8?) sections. Bulk embedding agent was mostly removed with methyl acetate. The sample was squeezed between BaF2 windows for IR studies. Any remaining PMMA or epoxy was removed by spectral subtraction. To evaluate the utility of FT-IR microscopy for study of biomineralization, two systems were examined:

  7. Pr 3+-doped ZBLA fluoride glasses for visible laser emission

    NASA Astrophysics Data System (ADS)

    Olivier, Melinda; Pirasteh, Parastesh; Doualan, Jean-Louis; Camy, Patrice; Lhermite, Hervé; Adam, Jean-Luc; Nazabal, Virginie

    2011-05-01

    Praseodymium doped Fluoride glasses were studied in order to fabricate compact solid state laser sources emitting in the visible range for lighting application and for quantum information processing. The objective of this study is focused on red, green and orange emissions. ZBLA bulk glasses (57%ZrF 4 - 34%BaF 2 - (5 - x)%LaF 3 - 4%AlF 3 - x%PrF 3) have been synthesized under dry argon atmosphere. Physicochemical and optical properties such as density, glass transition temperature, composition, transmission and refractive index have been investigated. Spectroscopic studies have been performed to optimize the rare earth doping level in order to reach the best compromise respecting a good optical quality, a highest lifetime and efficient emission intensity at 635, 605 and 520 nm. Spectroscopic measurements have been carried out on bulk samples with Pr 3+ concentrations ranging from 0.1 to 3 mol% and first characterizations of ion exchanged Pr: ZBLA waveguides are reported.

  8. Comparison of x-ray absorption spectra between water and ice: new ice data with low pre-edge absorption cross-section.

    PubMed

    Sellberg, Jonas A; Kaya, Sarp; Segtnan, Vegard H; Chen, Chen; Tyliszczak, Tolek; Ogasawara, Hirohito; Nordlund, Dennis; Pettersson, Lars G M; Nilsson, Anders

    2014-07-21

    The effect of crystal growth conditions on the O K-edge x-ray absorption spectra of ice is investigated through detailed analysis of the spectral features. The amount of ice defects is found to be minimized on hydrophobic surfaces, such as BaF2(111), with low concentration of nucleation centers. This is manifested through a reduction of the absorption cross-section at 535 eV, which is associated with distorted hydrogen bonds. Furthermore, a connection is made between the observed increase in spectral intensity between 544 and 548 eV and high-symmetry points in the electronic band structure, suggesting a more extended hydrogen-bond network as compared to ices prepared differently. The spectral differences for various ice preparations are compared to the temperature dependence of spectra of liquid water upon supercooling. A double-peak feature in the absorption cross-section between 540 and 543 eV is identified as a characteristic of the crystalline phase. The connection to the interpretation of the liquid phase O K-edge x-ray absorption spectrum is extensively discussed. PMID:25053326

  9. Study of the hyperfine magnetic field at Ta-181 site in the Heusler Co2ScSn, Co2ScGa, and Co2HfSn alloys

    NASA Astrophysics Data System (ADS)

    Attili, Roberta Nunes

    The hyperfine magnetic fields acting on Ta-181 nuclei at the Sc and Hf sites have been measured in Heusler alloys Co2ScSn, Co2ScGa, and Co2HfSn using the time differential perturbed gamma-gamma angular correlation (TDPAC) technique. The measurements were carried out using an automatic spectrometer consisting of two BaF2 detectors and the conventional electronics. The magnitude of hyperfine magnetic field at Ta-181 was measured for all the alloys. The signs of the field were determined in the cases of Co2ScSn and Co2HfSn alloys by performing the perturbed angular correlation measurements with an external polarizing magnetic field of approximately equal to 5 k Gauss. The hyperfine magnetic fields obtained are -187.6 +/- 3.3 and 90.0 +/- 2.1 kOe measured at 77 K for Co2ScSn and Co2ScGa alloys respectively, and -342.4 +/- 10.1 kOe measured at the room temperature for Co2HfSn alloy. These results are discussed and compared with the hyperfine magnetic field systematics in Co-based Heusler alloy.

  10. Enhanced time response of 1-in. LaBr3(Ce) crystals by leading edge and constant fraction techniques

    NASA Astrophysics Data System (ADS)

    Vedia, V.; Mach, H.; Fraile, L. M.; Udías, J. M.; Lalkovski, S.

    2015-09-01

    We have characterized in depth the time response of three detectors equipped with cylindrical LaBr3(Ce) crystals with dimensions of 1-in. in height and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and 10%. Measurements were performed at 60Co and 22Na ?-ray energies against a fast BaF2 reference detector. The time resolution was optimized by the choice of the photomultiplier bias voltage and the fine tuning of the parameters of the constant fraction discriminator, namely the zero-crossing and the external delay. We report here on the optimal time resolution of the three crystals. It is observed that timing properties are influenced by the amount of Ce doping and the crystal homogeneity. For the crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays in addition to the Hamamatsu R9779 PMT has made it possible to improve the LaBr3(Ce) time resolution from the best literature value at 60Co photon energies to below 100 ps.

  11. Growth, structure and optical properties of nonlinear optical crystal BaZnBO3F

    NASA Astrophysics Data System (ADS)

    Xia, Mingjun; Li, R. K.

    2016-01-01

    Nonlinear optical (NLO) crystal BaZnBO3F (BZBF) with the size of about 20×20×0.5 mm3 is obtained from BaF2-NaF flux, and single crystal X-ray diffraction reveals that it belongs to space group P 6 ? with cell parameters of a=5.1045(6) Å, c=4.3116(10) Å and Z=1. In the structure of BZBF, the BO3 planar triangles are interconnected through O atoms from ZnO3F2 trigonal bipyramid to form (Zn3B3O6F6) twelve-membered rings (12-MRs), then the layers which are built with condensation from 12-MRs at ab plane, are further linked by the apical F from ZnO3F2 to form three dimensional framework along the c direction. The title crystal exhibits high transmittance in the range of 300-3000 nm with a UV transmission cutoff at 223 nm according to transmission spectra. Powder SHG tests indicate that the effective NLO coefficient of BZBF crystal is about 2.8 times that of KH2PO4 (KDP) crystal due to perfect alignment of the BO3 groups.

  12. Time-resolved spectra from millivolt EELS data.

    PubMed

    Li, Chufeng; Subramanian, Ganesh; Spence, John C H

    2014-06-01

    The millivolt energy resolution now obtainable in electron energy-loss spectra (EELS) on the latest monochromated scanning transmission electron microscope corresponds, via the uncertainty principle, to a time range of 414 fs (for 10 meV resolution), and a time resolution of 0.138 fs (for energy range of 30 eV). (Thus, the width of an EELS peak is inversely related to the lifetime of an excitation.) This compares favorably with the latest X-ray free electron lasers. The time evolution of a Drude-Lorentz oscillator may be obtained from an EELS using logarithmic deconvolution followed by Kramers-Kronig analysis to extract the frequency-dependent dielectric function, and a final Fourier transform from frequency to time domain. This time-dependent dielectric function was interpreted as the impulse response of electrons, phonons, or ions based on the Drude-Lorentz theory. The time evolution of electronic oscillators from ice and protein, extracted from low resolution experimental data, were compared. Using higher energy resolution data we have also extracted the time-resolved spectra from excitons in an alkali halide, BaF2. Despite the small scanning transmission electron microscope probe size, delocalization limits the spatial resolution to about 50 nm, which is, nevertheless, better than the millimeter resolution of infrared absorption spectroscopy or Raman spectroscopy. PMID:24878029

  13. Probing Fission Time Scales with Neutrons and GDR Gamma Rays

    SciTech Connect

    Schmitt, R. P.; Botting, Tye; Chubarian, G G; Wolf, K; Hurst, B J; Jabs, H; Hamelin, M; Bacak, A; Oganessian, Yuri Ts.; Itkis, M. G.; Kozulin, E M; Kondratiev, N. A.; Salamatin, V S; Pokrovsky, I V; Hanappe, F; de Goes Brennand, E.; Huck, A; Stuttge, L; Liatard, E; Beene, James R; Varner Jr, Robert L; Halbert, Melvyn L; Gan, Ning

    2003-06-01

    The time scales for nuclear fission have been explored using both pre-and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV 16O + 176Yb and 208Pb and 104-MeV 4He + 188Os and 209Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF2 array. The pre-and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, ?, and fission time scales. The ? values ranged from 7 to 20, while the fission times were (31-105) 10?21 s. From Yadernaya Fizika, Vol. 66, No. 6, 2003, pp. 1199-1203.

  14. Simultaneous measurement of (n,?) and (n,fission) cross sections with the DANCE array

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Jandel, M.; Fowler, M. M.; Bond, E. M.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Macri, R. A.; Wu, C. Y.; Becker, J. A.

    2006-10-01

    We have recently begun a program of high precision measurements of the key production and destruction reactions of important radiochemical diagnostic isotopes, including several isotopes of uranium, plutonium and americium. The Detector for Advanced Neutron Capture Experiments (DANCE), a 4? BaF2 array located at the Los Alamos Neutron Science Center, will be used to measure the neutron capture cross sections for most of the isotopes of interest. Since neutron capture measurements on many of the actinides are complicated by the presence of ?-rays arising from low-energy neutron-induced fission, we are currently using a dual parallel-plate avalanche counter with the target material electro-deposited directly on the center cathode foil. This design provides a high efficiency for detecting fission fragments and allows loading of pre-assembled target/detector assemblies into the neutron beam line at DANCE. An outline of the current experimental program will be presented as well as results from measurements on ^235U and ^252Cf that utilized the fission-tag detector.

  15. Preliminary results on ^241,243Am and ^235U (n,?) cross sections measured at DANCE

    NASA Astrophysics Data System (ADS)

    Jandel, M.; Bredeweg, T. A.; Fowler, M. M.; Bond, E. M.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Macri, R. A.; Wu, C.-Y.; Becker, J. A.

    2006-10-01

    The Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos National Laboratory (LANL) was used for neutron capture cross sections measurements. Its high granularity of 160 BaF2 detectors allows for highly efficient detection of prompt gamma-rays following a neutron capture. DANCE is located on the 20.26 m neutron flight path 14 at the Manuel Lujan Jr. Neutron Scattering Center at the Los Alamos Neutron Science Center (LANSCE). The moderated production target provides neutrons in the 0.02 eV - 500 keV energy range. An analysis of neutron capture measurements on ^241,243Am and ^235U targets will be presented. The experiments were carried out using a customized Parallel-Plate Avalanche Counter (PPAC) detector installed in the center of the DANCE array. The PPAC was used as a fission-tagging detector to separate (n,?) from (n,fission) events. Preliminary results of (n,?) cross sections will be presented and compared with the available evaluated data for neutron energies from 0.02 eV to 1 keV. Additional neutron capture measurements with DANCE will be briefly discussed.

  16. ^241Am(n,?) absolute cross sections measured with DANCE

    NASA Astrophysics Data System (ADS)

    Jandel, M.; Bredeweg, T. A.; Fowler, M. M.; Bond, E. M.; Chadwick, M. B.; Clement, R. R.; Couture, A.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Agvaanluvsan, U.; Macri, R. A.; Sheets, S. A.; Wu, C. Y.; Becker, J. A.

    2007-10-01

    ^241Am is present in plutonium due to the beta decay of ^241Pu (t1/2=14.38 years). As such ^241Am can be used as a detector for nuclear forensics. A precise measurement of ^241Am(n,?) cross section is thus needed for this application. The measurement is also of interest for advanced reactor design as part of the Global Nuclear Energy Partnership (GNEP). The Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos National Laboratory (LANL) was used for neutron capture cross section measurement on ^241Am. The high granularity of DANCE (160 BaF2 detectors in a 4? geometry) enables the efficient detection of prompt gamma-rays following a neutron capture. DANCE is located on the 20.26 m neutron flight path 14(FP14) at the Manuel Lujan Jr. Neutron Scattering Center at the Los Alamos Neutron Science Center (LANSCE). The absolute ^241Am(n,?) cross sections were obtained in the range of neutron energies from 0.02 eV to 320 keV. The results will be compared to existing evaluations in detail.

  17. Detector-Response Correction of Two-Dimensional ? -Ray Spectra from Neutron Capture

    SciTech Connect

    Rusev, G.; Jandel, M.; Arnold, C. W.; Bredeweg, T. A.; Couture, A.; Mosby, S. M.; Ullmann, J. L.

    2015-05-28

    The neutron-capture reaction produces a large variety of ?-ray cascades with different ?-ray multiplicities. A measured spectral distribution of these cascades for each ?-ray multiplicity is of importance to applications and studies of ?-ray statistical properties. The DANCE array, a 4? ball of 160 BaF2 detectors, is an ideal tool for measurement of neutron-capture ?-rays. The high granularity of DANCE enables measurements of high-multiplicity ?-ray cascades. The measured two-dimensional spectra (?-ray energy, ?-ray multiplicity) have to be corrected for the DANCE detector response in order to compare them with predictions of the statistical model or use them in applications. The detector-response correction problem becomes more difficult for a 4? detection system than for a single detector. A trial and error approach and an iterative decomposition of ?-ray multiplets, have been successfully applied to the detector-response correction. Applications of the decomposition methods are discussed for two-dimensional ?-ray spectra measured at DANCE from ?-ray sources and from the 10B(n, ?) and 113Cd(n, ?) reactions.

  18. Detector-Response Correction of Two-Dimensional ? -Ray Spectra from Neutron Capture

    DOE PAGESBeta

    Rusev, G.; Jandel, M.; Arnold, C. W.; Bredeweg, T. A.; Couture, A.; Mosby, S. M.; Ullmann, J. L.

    2015-05-28

    The neutron-capture reaction produces a large variety of ?-ray cascades with different ?-ray multiplicities. A measured spectral distribution of these cascades for each ?-ray multiplicity is of importance to applications and studies of ?-ray statistical properties. The DANCE array, a 4? ball of 160 BaF2 detectors, is an ideal tool for measurement of neutron-capture ?-rays. The high granularity of DANCE enables measurements of high-multiplicity ?-ray cascades. The measured two-dimensional spectra (?-ray energy, ?-ray multiplicity) have to be corrected for the DANCE detector response in order to compare them with predictions of the statistical model or use them in applications. Themore »detector-response correction problem becomes more difficult for a 4? detection system than for a single detector. A trial and error approach and an iterative decomposition of ?-ray multiplets, have been successfully applied to the detector-response correction. Applications of the decomposition methods are discussed for two-dimensional ?-ray spectra measured at DANCE from ?-ray sources and from the 10B(n, ?) and 113Cd(n, ?) reactions.« less

  19. New detecting techniques for a future calorimetry

    NASA Astrophysics Data System (ADS)

    Auffray, E.; Buganov, O.; Fedorov, A.; Korjik, M.; Lecoq, P.; Tamulaitis, G.; Tikhomirov, S.; Vasil'ev, A.

    2015-02-01

    In the last forty years, application of crystalline materials in homogeneous Electromagnetic Calorimeters has played a crucial role in the discovery of matter properties and promoted a continuous progress in the detecting technique. The detection systems progressed from small detectors based on NaI(Tl), CsI(Na), BaF2, PbF2, and Bi4Ge3O12 to giant Electromagnetic Calorimeters of CMS, ALICE Collaborations at LHC and PANDA Collaboration at FAIR, where the systems consisted of thousands lead tungstate PbWO4 scintillation crystals. Lead tungstate (PWO) became the most extensively used scintillation material in high energy physics experiments. PWO possesses a unique combination of scintillation properties including high energy and time resolutions in the detection of high energy particles. Here, we report on the results of the two photon absorption in PWO crystals obtained by pump-probe technique using ultra short laser pulses. The results demonstrate that the relaxation processes in PWO offer capability of this material to be used in detection systems to make a time stamp with precision close to 10-12 s or even better.

  20. NASA Tech Briefs, February 2008

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Topics discussed include: Optical Measurement of Mass Flow of a Two-Phase Fluid; Selectable-Tip Corrosion-Testing Electrochemical Cell; Piezoelectric Bolt Breakers and Bolt Fatigue Testers; Improved Measurement of B(sub 22) of Macromolecules in a Flow Cell; Measurements by a Vector Network Analyzer at 325 to 508 GHz; Using Light to Treat Mucositis and Help Wounds Heal; Increasing Discharge Capacities of Li-(CF)(sub n) Cells; Dot-in-Well Quantum-Dot Infrared Photodetectors; Integrated Microbatteries for Implantable Medical Devices; Oxidation Behavior of Carbon Fiber-Reinforced Composites; GIDEP Batching Tool; Generic Spacecraft Model for Real-Time Simulation; Parallel-Processing Software for Creating Mosaic Images; Software for Verifying Image-Correlation Tie Points; Flexcam Image Capture Viewing and Spot Tracking; Low-Pt-Content Anode Catalyst for Direct Methanol Fuel Cells; Graphite/Cyanate Ester Face Sheets for Adaptive Optics; Atomized BaF2-CaF7 for Better-Flowing Plasma-Spray Feedstock; Nanophase Nickel-Zirconium Alloys for Fuel Cells; Vacuum Packaging of MEMS With Multiple Internal Seal Rings; Compact Two-Dimensional Spectrometer Optics; and Fault-Tolerant Coding for State Machines.

  1. Mid-infrared Hall conductivity in CaxSr1-xRuO3 films

    NASA Astrophysics Data System (ADS)

    Kim, M.-H.; Acbas, G.; Yang, M.-H.; Kurz, V.; Eginligil, M.; Cerne, J.; Khalifah, P.; Ohkubo, I.; Christen, H.; Mandrus, D.; Fang, Z.

    2008-03-01

    We have studied the complex longitudinal (?xx) and transverse (Hall, ?xy) conductivities in a series of CaxSr1-xRuO3 films by measuring the magnetic field induced polarization changes of mid-infrared (100 - 1000 meV) radiation in the 10 K-300 K temperature range. The infrared ?xy shows strong energy dependence and sign changes. We compare the complex magneto-conductivities ?xx and ?xy [M.-H. Kim, PRB 2007] with dc measurements and with calculations [Z. Fang, Science 2003] of the intrinsic anomalous Hall effect. To test the accuracy of these measurements and to remove the background magneto-optical response of windows and substrates, the magnetic field induced changes in the polarization of transmitted light also were measured in GaAs, ZnSe, and BaF2. This work was supported by the Research Corp. Cottrell Scholar Award (UB), NSF-CAREER-DMR0449899 (UB), and an instrumentation award from the CAS(UB). Oak Ridge Nat. Lab.is managed by UT- Battelle, LLC, for the U.S. DOE (contract DE-ACO5-00OR22725).

  2. {sup 241}Am(n,{gamma}) cross section in the neutron energy region between 0.02 eV and 300 keV

    SciTech Connect

    Jandel, M.; Bredeweg, T. A.; Bond, E. M.; Chadwick, M. B.; Clement, R. R.; Couture, A.; O' Donnell, J. M.; Haight, R. C.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Macri, R. A.; Wu, C. Y.; Becker, J. A.

    2008-04-17

    The Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos National Laboratory (LANL) was used for a neutron capture cross section measurement on {sup 241}Am. The high granularity of the DANCE array (160 BaF2 detectors in a 4{pi} geometry) enables an efficient detection of prompt gamma rays following neutron capture. The preliminary results on the {sup 241}Am(n,{gamma}) cross section are presented from 0.02 eV to 300 keV. The cross section at thermal energy E{sub n} = 0.0253 eV was determined to be 665{+-}33 barns. Resonance parameters were obtained using the SAMMY7 fit to the measured cross section in the resonance region. Significant discrepancies were found between our results and data evaluations for the first three lowest lying resonances. The cross section for neutrons with E{sub n}>l keV agrees well with the ENDF/B-VII.0 and JENDL-3.3 evaluations.

  3. Current and Future Research at DANCE

    NASA Astrophysics Data System (ADS)

    Jandel, M.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Hayes, A.; Kawano, T.; Mosby, S.; Rusev, G.; Stetcu, I.; Taddeucci, T. N.; Talou, P.; Ullmann, J. L.; Walker, C. L.; Wilhelmy, J. B.

    2015-05-01

    An overview of the current experimental program on measurements of neutron capture and neutron induced fission at the Detector for Advanced Neutron Capture Experiments (DANCE) is presented. Three major projects are currently under way: 1) high precision measurements of neutron capture cross sections on Uranium isotopes, 2) research aimed at studies of the short-lived actinide isomer production in neutron capture on 235U and 3) measurements of correlated data of fission observables. New projects include developments of auxiliary detectors to improve the capability of DANCE. We are building a compact, segmented NEUtron detector Array at DANCE (NEUANCE), which will be installed in the central cavity of the DANCE array. It will provide experimental information on prompt fission neutrons in coincidence with the prompt fission gamma-rays measured by 160 BaF2 crystals of DANCE. Unique correlated data will be obtained for neutron capture and neutron-induced fission using the DANCE-NEUANCE experimental set up in the future.

  4. Detector-Response Correction of Two-Dimensional ?-Ray Spectra from Neutron Capture

    NASA Astrophysics Data System (ADS)

    Rusev, G.; Jandel, M.; Arnold, C. W.; Bredeweg, T. A.; Couture, A.; Mosby, S. M.; Ullmann, J. L.

    2015-05-01

    The neutron-capture reaction produces a large variety of ?-ray cascades with different ?-ray multiplicities. A measured spectral distribution of these cascades for each ?-ray multiplicity is of importance to applications and studies of ?-ray statistical properties. The DANCE array, a 4? ball of 160 BaF2 detectors, is an ideal tool for measurement of neutron-capture ?-rays. The high granularity of DANCE enables measurements of high-multiplicity ?-ray cascades. The measured two-dimensional spectra (?-ray energy, ?-ray multiplicity) have to be corrected for the DANCE detector response in order to compare them with predictions of the statistical model or use them in applications. The detector-response correction problem becomes more difficult for a 4? detection system than for a single detector. A trial and error approach and an iterative decomposition of ?-ray multiplets, have been successfully applied to the detector-response correction. Applications of the decomposition methods are discussed for two-dimensional ?-ray spectra measured at DANCE from ?-ray sources and from the 10B(n, ?) and 113Cd(n, ?) reactions.

  5. Fluorine Diffusion in Titanite: Preliminary Results from Experiments

    NASA Astrophysics Data System (ADS)

    Berds, M. L.; Price, J. D.; Cherniak, D. J.

    2008-12-01

    Recent experiments have yielded new data on fluorine-hydroxyl diffusion in titanite. Experiments utilized natural low-F titanite crystals, sectioned into wafers, polished to 1 ?m alpha alumina and finished with colloidal silica. Prepared crystals were placed with polished faces in contact with a F-rich diffusion source. Each titanite-source assembly was then sealed in an evacuated Si glass ampoule and heated to temperatures between 600 and 900 °C, or sealed in an Ag envelope and heated in a cold-seal pressure vessel to temperatures between 600 and 906 °C at 50 to 100 kPa. Several F sources were employed: PbF, NaF, CaF2, LiF, and fluoroapatite. PbF and NaF strongly reacted with the titanite crystals and their capsules, particularly at higher temperatures. CaF2 and LiF were less destructive, but reacted with and etched the titanite faces, precluding analysis. Titanite retained a polished and largely unaltered surface only in those runs with an apatite source. We noted only a slight change in color (green to brown, likely due to oxidation of minor amounts of Fe present in the titanite) in these runs. We analyzed the polished faces of crystals from successful experiments using nuclear reaction analysis (NRA), employing the 340 keV resonance for the nuclear reaction 19F(p,??) 16O to measure fluorine. The results show elevated fluorine at the surface and diminishing concentrations with depth. Fitting a simple complementary error function to each concentration profile yields a diffusivity, assuming a model of a semi-infinite material with a surface maintained at constant concentration. For the runs at near atmospheric pressure, diffusion coefficients of 2×10-21m2/s and 6×10-21m2/s are obtained at temperatures of 850°C and 889°C, respectively. A single cold seal experiment at 906°C suggests a diffusivity of 3×10-21 m2/s. While preliminary, these data suggest that fluorine-hydroxyl exchange in titanite is more sluggish than in apatite, biotite, and tremolite.

  6. Effects of Different Calcium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

    NASA Astrophysics Data System (ADS)

    Adabifiroozjaei, Esmaeil; Saidi, Ali; Monshi, Ahmad; Koshy, Pramod

    2011-04-01

    Andalusite containing low-cement castables (LCCs) have been used in aluminum casthouses for several decades. CaF2 is commonly added to the refractory to improve its corrosion resistance mainly because of its role in the formation of anorthite (CaAl2Si2O8); the latter has been reported to decrease the penetration of molten aluminum alloys into refractories. This article investigates the effect of the addition of different calcium containing compounds (CaO, CaCO3, CaSO4, CaF2, Clinker white cement, calcia feldspar, wollastonite, and Ca3(PO4)2) on reactions with the refractory constituents to form anorthite as well as the effect of the additives on both the subsequent physical properties and the corrosion resistance of andalusite LCC refractories. Corrosion tests using the Alcoa cup test at temperatures (1123 K [850 °C] for 150 hours and 1433 K [1160 °C] for 72 hours) were conducted to determine the extent of penetration, whereas immersion tests in boiling water were conducted to determine the extent of open porosity in the material. Scanning electron microscopy coupled with energy dispersive spectrometer, optical microscopy, and X-ray diffraction techniques were employed to characterize the phase formations in the materials after the tests. The study demonstrated that both calcia feldspar and clinker white cement had the potential to be used as new additives for decreasing the penetration of molten Al-alloy into the refractory materials. Anorthite formation (in the refractory matrix), along with the absence of glassy phases, were responsible for the improvement in the corrosion resistance of the castables containing calcia feldspar. However, in the sample containing cement, the presence of calcium silicate phases were observed to resist reactions with molten aluminum. The observed results were validated using thermodynamic calculations, which indicated that tricalcium silicates (3CaO.SiO2) and dicalcium silicate (2CaO.SiO2) phases were more resistant than wollastonite (CaSiO3) for applications involving contact with molten aluminum.

  7. Silicate-natrocarbonatite liquid immiscibility in 1917 eruption combeite-wollastonite nephelinite, Oldoinyo Lengai Volcano, Tanzania: Melt inclusion study

    NASA Astrophysics Data System (ADS)

    Sharygin, Victor V.; Kamenetsky, Vadim S.; Zaitsev, Anatoly N.; Kamenetsky, Maya B.

    2012-11-01

    Primary silicate-melt and carbonate-salt inclusions occur in the phenocrysts (nepheline, fluorapatite, wollastonite, clinopyroxene) in the 1917 eruption combeite-wollastonite nephelinite at Oldoinyo Lengai. Silicate-melt inclusions in nepheline clearly show liquid immiscibility phenomena expressed in the presence of carbonate globules in silicate glass. The coexistence of inclusions with markedly different proportions of silicate glass + vapor-carbonate globule in the core of nepheline phenocrysts, the presence of carbonate-salt inclusions in fluorapatite and our heating experiments strongly suggest that their entrapment began at temperatures higher than 1130 °C in an intermediate chamber when initial carbonated nephelinite melt was heterogeneous and represented a mixture of immiscible liquids. Silicate-natrocarbonatite melt immiscibility took place at high temperature and immiscible nephelinite and carbonatite liquids coexisted over a wide temperature range from ? 1130 °C to 600 °C. Homogenization of a carbonate globule (dissolution of the gas bubble in carbonate melt) at 900-940 °C indicates that after separation from silicate magma the natrocarbonatite represented homogeneous liquid in the 900-1130 °C temperature range, whereas below these temperatures immiscible melts of different composition and fluid phase have separated from it. The bulk composition of homogeneous natrocarbonatite melt may be estimated as ? 20% CaF2, 40-60% (Na,K)2CO3 and 20-40% CaCO3 based on the coexistence of nyerereite, calcite and fluorite and the rapid phase transition (carbonate aggregate ? carbonate liquid) at 550-570 °C observed in vapor-carbonate globules of nepheline-hosted silicate-melt inclusions and on the Na2CO3-CaCO3-CaF2 phase diagram. Silicate glasses of nepheline-hosted immiscible inclusions drastically differ from host nephelinite in the abundance of major and trace elements. They are high peralkaline ((Na + K)/Al — up to 9.5) and virtually free of water (H2O < 0.6 wt.%). Their very high Zr/Hf and Nb/Ta ratios and Li contents indicate that these silicate glasses represent the most evolved compositions at Oldoinyo Lengai. The peralkaline character of nephelinite melt is expressed in the composition of the daughter mineral assemblage within silicate-melt inclusions in nepheline (delhayelite, leucite, mica, clinopyroxene). These minerals show strong deficiency in Al and enrichment in Fe3 + that is also common to the groundmass of the Oldoinyo Lengai combeite-wollastonite nephelinites.

  8. Enhancement of luminescence in white emitting strontium fluoride core @ calcium fluoride shell nanoparticles.

    PubMed

    Kumam, Nandini; Singh, Ningthoujam Premananda; Singh, Laishram Priyobarta; Srivastava, Sri Krishna

    2015-12-01

    Synthesis of lanthanide-doped fluoride SrF2:3Dy and SrF2:3Dy@CaF2 nanoparticles with different ratios of core to shell (1:0.5, 1:1 and 1:2) has been carried out by employing ethylene glycol route. X-ray diffraction (XRD) patterns reveal that the structure of the prepared nanoparticles was of cubical shape, which is also evident in TEM images. The size of the nanoparticles for core (SrF2:3Dy) is found to increase when core is covered by shell (CaF2). It is also evident from Fourier transform infrared spectroscopy (FTIR) that ethylene glycol successfully controls the growth and acts as a shape modifier by regulating growth rate. In the photoluminescence investigation, emission spectra of SrF2:3Dy is found to be highly enhanced when SrF2:3Dy is covered by CaF2 due to the decrease of cross relaxation amongst the Dy(3+)-Dy(3+) ions. Such type of enhancement of luminescence in homonanostructure SrF2:3Dy@CaF2 (core@shell) has not been studied so far, to the best of the authors' knowledge. This luminescent material exhibits prominently white light emitting properties as shown by the Commission Internationale d'Eclairage (CIE) chromaticity diagram. The calculated correlate colour temperature (CCT) values for SrF2:3Dy, SrF2:3Dy@CaF2 (1:0.05), SrF2:3Dy@CaF2 (1:1) and SrF2:3Dy@CaF2 (1:2) are 5475, 5476, 5384 and 5525 K, respectively, which lie in the cold white region. Graphical abstract White light emitting homonanostructure material SrF2:3Dy@CaF2(core@shell). PMID:26323391

  9. Production and Refining of Magnesium Metal from Turkey Originating Dolomite

    NASA Astrophysics Data System (ADS)

    Demiray, Yeliz; Yücel, Onuralp

    2012-06-01

    In this study crown magnesium produced from Turkish calcined dolomite by the Pigeon Process was refined and corrosion tests were applied. By using factsage thermodynamic program metalothermic reduction behavior of magnesium oxide and silicate formation structure during this reaction were investigated. After thermodynamic studies were completed, calcination of dolomite and it's metalothermic reduction at temperatures of 1473 K, 1523 K and within a vacuum (varied from 20 to 200 Pa) and refining of crown magnesium was studied. Different flux compositions consisting of MgCl2, KCl, CaCl2, MgO, CaF2, NaCl, and SiO2 with and without B2O3 additions were selected for the refining process. These tests were carried out at 963 K for 15, 30 and 45 minutes setting time. Considerable amount of iron was transferred into the sludge phase and its amount decreased from 0.08% to 0.027%. This refined magnesium was suitable for the production of various magnesium alloys. As a result of decreasing iron content, minimum corrosion rate of refined magnesium was obtained 2.35 g/m2/day. The results are compared with previous studies.

  10. Uranium content and leachable fraction of fluorspars

    USGS Publications Warehouse

    Landa, E.R.; Councell, T.B.

    2000-01-01

    Much attention in the radiological health community has recently focused on the management and regulation of naturally occurring radioactive materials. Although uranium-bearing minerals are present in a variety of fluorspar deposits, their potential consideration as naturally occurring radioactive materials has received only limited recognition. The uranium content of 28 samples of acid- and cryolite-grade (>97% CaF2) fluorspar from the National Defense Stockpile was found to range from 120 to 24,200 ??g kg-1, with a mean of 2,145 ??g kg-1. As a point of comparison, the average concentration of uranium in the upper crust of the earth is about 2,500 ??g kg-1. Leachability of this uranium was assessed by means of the Toxicity Characteristic Leaching Procedure (TCLP). The TCLP extractable fraction ranged from 1 to 98%, with a mean of 24% of the total uranium. The typically low concentrations of uranium seen in these materials probably reflects the removal of uranium-bearing mineral phases during the beneficiation of the crude fluorspar ore to achieve industrial specifications. Future NORM studies should examine crude fluorspar ores and flotation tailings.

  11. Uranium content and leachable fraction of fluorspars.

    PubMed

    Landa, E R; Councell, T B

    2000-09-01

    Much attention in the radiological health community has recently focused on the management and regulation of naturally occurring radioactive materials. Although uranium-bearing minerals are present in a variety of fluorspar deposits, their potential consideration as naturally occurring radioactive materials has received only limited recognition. The uranium content of 28 samples of acid- and cryolite-grade (>97% CaF2) fluorspar from the National Defense Stockpile was found to range from 120 to 24,200 microg kg(-1), with a mean of 2,145 microg kg(-1). As a point of comparison, the average concentration of uranium in the upper crust of the earth is about 2,500 microg kg(-1). Leachability of this uranium was assessed by means of the Toxicity Characteristic Leaching Procedure (TCLP). The TCLP extractable fraction ranged from 1 to 98%, with a mean of 24% of the total uranium. The typically low concentrations of uranium seen in these materials probably reflects the removal of uranium-bearing mineral phases during the beneficiation of the crude fluorspar ore to achieve industrial specifications. Future NORM studies should examine crude fluorspar ores and flotation tailings. PMID:10949254

  12. Fluoride-containing bioactive glasses: Glass design, structure, bioactivity, cellular interactions, and recent developments.

    PubMed

    Shah, Furqan A

    2016-01-01

    Bioactive glasses (BGs) are known to bond to both hard and soft tissues. Upon exposure to an aqueous environment, BG undergoes ion exchange, hydrolysis, selective dissolution and precipitation of an apatite layer on their surface, which elicits an interfacial biological response resulting in bioactive fixation, inhibiting further dissolution of the glass, and preventing complete resorption of the material. Fluorine is considered one of the most effective in-vivo bone anabolic factors. In low concentrations, fluoride ions (F(-)) increase bone mass and mineral density, improve the resistance of the apatite structure to acid attack, and have well documented antibacterial properties. F(-) ions may be incorporated into the glass in the form of calcium fluoride (CaF2) either by part-substitution of network modifier oxides, or by maintaining the ratios of the other constituents relatively constant. Fluoride-containing bioactive glasses (FBGs) enhance and control osteoblast proliferation, differentiation and mineralisation. And with their ability to release fluoride locally, FBGs make interesting candidates for various clinical applications, dentinal tubule occlusion in the treatment of dentin hypersensitivity. This paper reviews the chemistry of FBGs and the influence of F(-) incorporation on the thermal properties, bioactivity, and cytotoxicity; and novel glass compositions for improved mechanical properties, processing, and bioactive potential. PMID:26478431

  13. Mechanochemical synthesis of MgF2 - MF2 composite systems (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Scholz, G.; Breitfeld, S.; Krahl, T.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2015-12-01

    The capability of mechanochemical synthesis for the formation of MgF2-MF2 (M: Ca, Sr, Ba) composites, solid solutions or well-defined compounds was tested applying a fluorination of different fluorine-free metal sources with NH4F directly at milling. No evidence was found for a substitution of Mg2+ with Ca2+ (Sr2+, Ba2+) ions, or vice versa, in rutile or fluorite structure. However, an equimolar ratio of Mg2+ to the second cation allows the mechanochemical synthesis of tetrafluoromagnesates, MMgF4, which is more and more hampered the smaller the radius of the cation M2+ is. BaMgF4 is formed even phase pure from the acetates, SrMgF4 can only be observed in a mixture accompanied by the binary fluorides. In addition, 19F MAS NMR spectra along with calculations of 19F isotropic chemical shift values according to the superposition model point to the formation of a metastable phase of CaMgF4, which disappears at thermal treatment and decomposes into the binary fluorides CaF2 and MgF2.

  14. Two representations of the simple model and its application to 4f-5d excitation spectra of Dy3+ dopants in crystals

    NASA Astrophysics Data System (ADS)

    Xia, S. D.; Duan, C. K.

    2006-10-01

    The 4f-5d excitation spectra of Dy3+ dopants in crystal YPO4 (in CaF2, LiYF4 as well) reported by van Pieterson et al. [Phys. Rev. B 65, 045114 (2002)] are studied theoretically using both the original and extended simple models without or with the non-diagonal matrix elements taken into account. When the non-diagonal matrix elements are taken into account, the same energy levels are obtained in both cases as expected and successfully interpret the 4f-5d spectra. When the non-diagonal matrix elements are neglected, as in actual applications of the simple models, the results of the original simple model is much closer to the complete-calculated ones than those of the extended simple model for ion Dy3+. This means the original simple model is more suitable for ion Dy3+. The effect of J -mixing of final states on the line strength of transitions due to f-electron crystal field, which was ignored previously, is also discussed.

  15. 4fn-->4fn-15d transitions of the light lanthanides: Experiment and theory

    NASA Astrophysics Data System (ADS)

    van Pieterson, L.; Reid, M. F.; Wegh, R. T.; Soverna, S.; Meijerink, A.

    2002-01-01

    The 4fn-->4fn-15d(fd) excitation spectra of the light lanthanides (Ce3+, Pr3+, Nd3+, Sm3+, and Eu3+) incorporated in LiYF4, CaF2, and YPO4 are investigated in the ultraviolet and vacuum-ultraviolet spectral region (100-250 nm). In these host lattices fine structure (zero-phonon lines and vibronic lines) is observed for fd transitions involving the lowest 5d crystal-field state. The observation of zero-phonon lines makes it possible to analyze the complicated structure in the fd spectra and to compare the experimentally observed spectra with energy-level calculations for the 4fn-15d states. Energy-level and intensity calculations were performed by an extension of the commonly used theory for energy-level calculations of 4fn states. A good agreement between experiment and theory is obtained for the overall structure using the crystal-field splitting (from the spectra of Ce3+), the parameters for the splitting of the 4fn-1 core (from the literature on energy level calculations for 4fn states) and the spin-orbit coupling of the 5d electron and Coulomb interaction between 4f and 5d electrons (from atomic parameters using the computer code of Cowan).

  16. Induction of premature mitosis in S-blocked onion cells.

    PubMed

    Sen, R; Ghosh, S

    1998-11-01

    Onion root-tip cells were blocked at S-phase by treating them with 5-aminouracil (5AU). These cells were then further treated with caffeine/2-aminopurine (Caf/2AP) or a combination of both in the presence of 5AU. These tyrosine kinase inhibitors were able to induce premature mitosis in the S-blocked cells as evident from the breaks and gaps in the metaphase chromosomes and the presence of laggards and fragments in anaphase. Immunofluorescence showed normal spindle formation in these cells. Immunoblotting of cyclin B revealed that the level of cyclin B was slightly higher in the recovered and treated samples than the S-blocked one. The level of p(34)was found to be almost equal in all three samples as expected. We failed to observe any significant difference in the level of p(34)containing phosphorylated tyrosine. Such premature induction of mitosis by the purine derivatives has also been reported in BHK cells. However, those cells failed to progress through mitosis. A comparative analysis indicates that the plant cells and the animal cells, perhaps, follow identical pathway for the initiation of mitosis. The possible causes for differential behaviour in mitotic progression in these cells have been discussed. PMID:10873298

  17. Physico-chemical characterization of metal-doped bone chars and their adsorption behavior for water defluoridation

    NASA Astrophysics Data System (ADS)

    Rojas-Mayorga, C. K.; Bonilla-Petriciolet, A.; Silvestre-Albero, J.; Aguayo-Villarreal, I. A.; Mendoza-Castillo, D. I.

    2015-11-01

    New bone chars for fluoride adsorption from drinking water have been synthetized via metallic doping using aluminum and iron salts. A detailed statistical analysis of the metal doping process using the signal-to-noise ratios from Taguchi's experimental designs and its impact on the fluoride adsorption properties of modified bone chars have been performed. The best conditions, including the proper metallic salt, for metal doping were identified to improve the fluoride uptakes of modified bone chars. Results showed that the fluoride adsorption properties of bone chars can be enhanced up to 600% using aluminum sulfate for the surface modification. This aluminum-based adsorbent showed an adsorption capacity of 31 mg/g, which outperformed the fluoride uptakes reported for several adsorbents. Surface interactions involved in the defluoridation process were established using FTIR, DRX and XPS analysis. Defluoridation using the metal-doped bone chars occurred via an ion exchange process between fluoride ions and the hydroxyl groups on the adsorbent surface, whereas the Al(OH)xFy, FexFy, and CaF2 interactions could play also an important role in the removal process. These metal-doped adsorbents anticipate a promising behavior in water treatment, especially in developing countries where the efficiency - cost tradeoff is crucial for implementing new defluoridation technologies.

  18. Infrared spectroscopy to estimate the gross biochemistry associated with different colorectal pathologies

    NASA Astrophysics Data System (ADS)

    Wood, J. J.; Kendall, C.; LLoyd, G. R.; Shepherd, N. A.; Cook, T. A.; Stone, N.

    2011-07-01

    Histopathology provides the gold standard assessment of colonoscopic biopsies. Infrared spectroscopy can potentially map biochemical changes across a tissue section identifying disease. The purpose of this study was to determine if infrared spectroscopy could classify different colorectal pathologies and to investigate biochemical composition. Colonoscopic tissue biopsies were snap frozen at colonoscopy. 10 micron thick sections were mounted on CaF2 slides. 3- D spectral datasets (2 spatial dimensions and one spectral) were measured from thawed specimens using a Perkin Elmer infrared imaging system in transmission mode. Contiguous tissue sections stained with H&E were reviewed by a specialist gastrointestinal pathologist for comparison. Tissue spectra from epithelial tissues were classified using principal components fed linear discriminant analysis with leave one out cross validation. Reference spectra from purchased biochemicals (Sigma-Aldrich) were measured. Ordinary least squares analysis estimated the relative biochemical signal contribution from epithelial regions. Spectra from tissue epithelia measured from normal tissue, hyperplastic polyps, adenomatous polyps, cancer and ulcerative colitis samples were classified with accuracies in excess of 90%. Ordinary least squares analysis demonstrated a higher DNA to cytoplasm ratio in cancer compared to normal tissue. FTIR spectra from epithelia can be used to classify colorectal pathologies with high accuracy. Ordinary least squares analysis shows promise for extraction of useful biochemical information. These techniques could aid the histopathologist and ultimately lead to automated histopathological processing.

  19. Influence of calcium hydroxide on the fate of perfluorooctanesulfonate under thermal conditions.

    PubMed

    Wang, Fei; Lu, Xingwen; Shih, Kaimin; Liu, Chengshuai

    2011-09-15

    To explore the potential fate and transport of perfluorochemicals in the thermal treatment of sludge, perfluorooctanesulfonate (PFOS), a perfluorochemical species commonly dominant in wastewater sludge, was mixed with hydrated lime (Ca(OH)(2)) to quantitatively observe their interaction under different temperatures. The phase compositions of the mixtures after the reactions were qualitatively identified and quantitatively determined using X-ray diffraction technique. The results of the thermogravimetry and differential scanning calorimetry analyses indicate that PFOS gasified directly during the thermal treatment process when the temperature was increased to around 425 °C. However, the formation of CaF(2) at 350 °C suggests that the presence of Ca(OH)(2) in the mixture can lead to the decomposition of PFOS at 350 °C, which is lower than the decomposition temperature of PFOS alone (425 °C). The increase of temperature promoted a solid state reaction between PFOS and Ca(OH)(2), and also enhanced the interaction between the gaseous products of PFOS and CaO (or Ca(OH)(2)). The preferred Ca/F molar ratio to achieve fluorine stabilization by Ca(OH)(2) was above 1:1 in the experiment involving 400 °C and 600 °C treatment. It also showed that equilibrium efficiency is achieved within 5 min at 400 °C and within 1 min above 600°C. PMID:21719193

  20. Experimental metasomatism of monazite and xenotime: mineral stability, REE mobility and fluid composition

    NASA Astrophysics Data System (ADS)

    Hetherington, Callum J.; Harlov, Daniel E.; Budzy?, Bartosz

    2010-07-01

    In this study a Th-bearing monazite from a Brazil beach sand, a low Th monazite from a Malawi carbonatite, and a xenotime from a pegmatite in northern Pakistan were experimentally metasomatised in a series of common metamorphic and igneous fluids at 600°C/500 MPa and 900°C/1000 MPa. Fluids included H2O, NaCl, and KCl brines, CaF2 + H2O, 1 m and 2 m HCl, 1 m and 2 m H2SO4, 1 m NaOH, and Na2Si2O5 + H2O. The monazite show a variety of responses to the fluids ranging from no reaction (KCl + H2O) to small compositional changes and partial replacement of the monazite grain rim by Th-enriched monazite in the NaOH and (Na2Si2O5 + H2O) experiments respectively. The other acid and brine fluids induced varying degrees of partial dissolution in the monazite and xenotime, but no compositional alteration. Partial replacement of monazite grain rims by Th-enriched monazite occurred only in the alkaline fluids as the result of a coupled dissolution-reprecipitation process.