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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. 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.

  3. Investigation of the superionic behaviour of BaF2 (x mol% LaF3) by Raman and Brillouin scattering and molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Rammutla, K. E.; Comins, J. D.; Erasmus, R. M.; Netshisaulu, T. T.; Ngoepe, P. E.; Chadwick, A. V.

    High temperature Raman and Brillouin light scattering experiments have been combined with molecular dynamics simulations to provide a comprehensive study of the superionic state of BaF2 (x mol% LaF3) over a particularly wide range of LaF3 dopant concentrations from x =0 to 50. Room temperature Raman spectra for x =0, 5 and 10 show the usual T-2g symmetry mode at 241 cm(-1) , but for samples with x =20, 30 and 50 the dominant Raman mode is at higher frequencies and of E-g symmetry. The temperature dependence of the Raman line-widths show initial near linear increases followed by substantial increases above temperatures (T-c) at 1200, 850, 800, 975, 950 and 920 K for x =0, 5, 10, 20, 30 and 50. In the Brillouin scattering experiments, the acoustic modes respectively related to elastic constants C-11 and C-44 initially showed a quasi-linear decrease in frequency with increasing temperature. Above the same characteristic values of T-c , where the Raman line-widths show marked increases, there are substantial decreases in the elastic constant C-11 for all samples with x =0 to 50. Only the doped samples showed significant decreases in C-44 at corresponding values of T-c . Molecular dynamics (MD) simulations have been carried out on the same systems. From the calculated mean square displacements, the diffusion coefficients (D) of the mobile fluorine ions were calculated as a function of temperature for each of the samples. Substantial increases in the values of D occur above the respective values of T-c determined in the light scattering experiments. The MD simulations also provide details of the mechanisms of diffusion of the mobile fluorine ions. The results emphasize the role of motional effects as an explanation of the mechanisms responsible and provide a self-consistent explanation of the dominant processes in the superionic phase of doped fluorites.

  4. Enhanced processability of ZrF4-BaF2-LaF3-AlF3-NaF glass in microgravity

    NASA Astrophysics Data System (ADS)

    Torres, Anthony; Ganley, Jeff; Maji, Arup; Tucker, Dennis; Starodubov, Dmitry

    2013-06-01

    Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the UV to 7 μm in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx - Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subject to a heating and quenching test apparatus on the parabolic aircraft, under a controlled 0-g and hyper-g environment and compared with 1-g ground tests. The microgravity duration on board Zero-G Corporation parabolic aircraft is approximately 20 seconds and the hyper-g intervals are approximately 56 seconds. Optical microscopy examination elucidates crystal growth in ZBLAN is suppressed when processed in a microgravity environment. The crystallization temperature, Tx, at which crystals form increased, therefore, significantly broadening the working temperature range for ZBLAN.

  5. 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.

  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. Experimental study of Raman-active two-level systems and the boson peak in LaF3-doped fluorite mixed crystals

    NASA Astrophysics Data System (ADS)

    Tu, J. J.; Sievers, A. J.

    2002-09-01

    A broad spectral distribution of two-level systems (TLS) displaying only A1g symmetry, not Eg or T2g, is observed in the low-frequency, low-temperature Raman spectra of fluorite single crystal hosts doped with large amounts of LaF3. The observed range of each TLS spectrum is found to be independent of the dopant concentration although each of the three crystalline hosts, CaF2, SrF2, and BaF2, displays a slightly different cutoff frequency. In a somewhat higher frequency range but still far below the Brillouin Zone TA phonon mode frequency, a boson peak, showing Eg symmetry, is also observed and its strength is proportional to the defect-induced vibrational Raman activity for the three crystal lattices. A surprising property is that for all three host crystals the boson peak center frequency increases with increasing lattice disorder. The strengths of the TLS spectra show distinctively different La3+ concentration dependencies in each host, which is also different from that observed for the boson peaks. By comparing the density of state of TLS derived from the Raman scattering to the P¯ density of states value determined from the earlier specific heat measurements, the number density of Raman-active TLS is separated from the coupling coefficient. When the total number density of Raman-active TLS is examined versus different physical properties it is found that lattice disorder, not the LaF3 concentration per se, is the important variable. The experimental results are consistent with a model where the TLS number density is controlled by the law of mass action with the ``effective'' temperature associated with the production of TLS determined by the frozen-in lattice disorder. Good agreement is found for the number density of TLS versus concentration as determined from the present Raman scattering data and the previous far infrared measurements when the far infrared dipole moment is used as a single fitting parameter. However, in contrast with the far infrared studies, no TLS excited state transitions are observed in Raman scattering. The overall findings from this study suggest that the Raman and infrared active TLS distributions, which extends up to about 2 meV, are associated with extended entities.

  8. Luminescent LaF3:Ce-doped organically modified nanoporous silica xerogels

    NASA Astrophysics Data System (ADS)

    Yao, Mingzhen; Hall, Ryan; Chen, Wei; Mohite, Dhairyashil P.; Leventis, Nicholas; Lu, Ning; Wang, Jinguo; Kim, Moon J.; Luo, Huiyang; Lu, Hongbing

    2013-01-01

    Organically modified silica compounds (ORMOSILs) were synthesized by a sol-gel method from amine-functionalized 3-aminopropyl triethoxylsilane and tetramethylorthosilicate and were doped in situ with LaF3:Ce nanoparticles, which in turn were prepared either in water or in ethanol. Doped ORMOSILs display strong photoluminescence either by UV or X-ray excitation and maintain good transparency up to a loading level of 15.66% w/w. The TEM observations demonstrate that ORMOSILs remain nanoporous with pore diameters in the 5-10 nm range. LaF3:Ce nanoparticles doped into the ORMOSILs are rod-like, 5 nm in diameter and 10-15 nm in length. Compression testing indicates that the nanocomposites have very good strength, without significant lateral dilatation and buckling under quasi-static compression. LaF3:Ce nanoparticle-doped ORMOSILs have potential for applications in radiation detection and solid state lighting.

  9. Neodymium-doped LaF(3) nanoparticles for fluorescence bioimaging in the second biological window.

    PubMed

    Rocha, Ueslen; Kumar, Kagola Upendra; Jacinto, Carlos; Villa, Irene; Sanz-Rodríguez, Francisco; Iglesias de la Cruz, María del Carmen; Juarranz, Angeles; Carrasco, Elisa; van Veggel, Frank C J M; Bovero, Enrico; Solé, José García; Jaque, Daniel

    2014-03-26

    The future perspective of fluorescence imaging for real in vivo application are based on novel efficient nanoparticles which is able to emit in the second biological window (1000-1400 nm). In this work, the potential application of Nd(3+) -doped LaF(3) (Nd(3+) :LaF(3) ) nanoparticles is reported for fluorescence bioimaging in both the first and second biological windows based on their three main emission channels of Nd(3+) ions: (4) F(3/2) →(4) I(9/2) , (4) F(3/2) →(4) I(11/2) and (4) F(3/2) →(4) I(13/2) that lead to emissions at around 910, 1050, and 1330 nm, respectively. By systematically comparing the relative emission intensities, penetration depths and subtissue optical dispersion of each transition we propose that optimum subtissue images based on Nd(3+) :LaF(3) nanoparticles are obtained by using the (4) F3/2 →(4) I11/2 (1050 nm) emission band (lying in the second biological window) instead of the traditionally used (4) F(3/2) →(4) I(9/2) (910 nm, in the first biological window). After determining the optimum emission channel, it is used to obtain both in vitro and in vivo images by the controlled incorporation of Nd(3+) :LaF(3) nanoparticles in cancer cells and mice. Nd(3+) :LaF(3)nanoparticles thus emerge as very promising fluorescent nanoprobes for bioimaging in the second biological window. PMID:24123958

  10. Neodymium-doped LaF(3) nanoparticles for fluorescence bioimaging in the second biological window.

    PubMed

    Rocha, Ueslen; Kumar, Kagola Upendra; Jacinto, Carlos; Villa, Irene; Sanz-Rodríguez, Francisco; Iglesias de la Cruz, María del Carmen; Juarranz, Angeles; Carrasco, Elisa; van Veggel, Frank C J M; Bovero, Enrico; Solé, José García; Jaque, Daniel

    2014-03-26

    The future perspective of fluorescence imaging for real in vivo application are based on novel efficient nanoparticles which is able to emit in the second biological window (1000-1400 nm). In this work, the potential application of Nd(3+) -doped LaF(3) (Nd(3+) :LaF(3) ) nanoparticles is reported for fluorescence bioimaging in both the first and second biological windows based on their three main emission channels of Nd(3+) ions: (4) F(3/2) →(4) I(9/2) , (4) F(3/2) →(4) I(11/2) and (4) F(3/2) →(4) I(13/2) that lead to emissions at around 910, 1050, and 1330 nm, respectively. By systematically comparing the relative emission intensities, penetration depths and subtissue optical dispersion of each transition we propose that optimum subtissue images based on Nd(3+) :LaF(3) nanoparticles are obtained by using the (4) F3/2 →(4) I11/2 (1050 nm) emission band (lying in the second biological window) instead of the traditionally used (4) F(3/2) →(4) I(9/2) (910 nm, in the first biological window). After determining the optimum emission channel, it is used to obtain both in vitro and in vivo images by the controlled incorporation of Nd(3+) :LaF(3) nanoparticles in cancer cells and mice. Nd(3+) :LaF(3)nanoparticles thus emerge as very promising fluorescent nanoprobes for bioimaging in the second biological window.

  11. X-Ray Luminescence of LaF3:Tb3+ and LaF3:Ce3+, Tb3+ Water Soluble Nanoparticles

    SciTech Connect

    Liu, Y.; Chen, Wei; Wang, Shaopeng; Joly, Alan G.; Westcott, Sarah L.; Woo, Boon K.

    2008-03-15

    Utilizing scintillation nanoparticles as agents for photodynamic therapy for cancer treatment necessitates the use of biocompatible and water soluble nanoparticles. In this article, we report the synthesis and X-ray luminescence of water soluble Ce and Tb doped LaF3 nanoparticles. The nanoparticles are conjugated with folic acid and meso-tetra (o-carboxyphenyl) porphyrin. X-ray luminescence is observed from the nanoparticles in both powder and solution samples. More importantly, singlet oxygen has been detected from the conjugated system following X-ray excitation. These preliminary observations indicate that water-soluble scintillation nanoparticles can be potentially used in photodynamic therapy for deep-tissue cancer treatment.

  12. 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 Сa0.95Yb0.05F2.05 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 Сa0.97Yb0.03F2.03 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 Н = 3.2 GPa and fracture toughness К1С = 0.65 МPа 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.

  13. Pressure dependence of the emission in CaF2 : Yb2+

    NASA Astrophysics Data System (ADS)

    Mahlik, S.; Lazarowska, A.; Grinberg, M.; Wells, J.-P. R.; Reid, M. F.

    2015-08-01

    We present a detailed spectroscopic investigation of CaF2 doped with Yb2+ performed at high hydrostatic pressure which is applied in a diamond anvil cell. At ambient pressure and at temperatures lower than 175 K, the luminescence consists of a single broad band peaked at 18 500 cm-1, attributed to the recombination of impurity-trapped excitons. Increasing pressure causes the luminescence to be observable at higher temperature. At a pressure of 72 kbar luminescence can be observed up to 275 K. The emission lineshape does not strongly depend on pressure below 85 kbar. However, at 85 kbar it is blue shifted to 21 630 cm-1. This is attributed to the known phase transition of the CaF2 crystal from cubic to the orthorhombic phase. The absolute energy of the ground and 4f135d states of Yb2+ as well as the energy of the impurity-trapped exciton with respect to valence and conduction bands have been estimated. The results, are discussed in comparison with the pressure dependences observed for the luminescence of BaF2 : Eu2+ and CaF2 : Eu2+. The difference between the spectral properties of Eu2+ and Yb2+ is attributable to the fact that the ground and 4f65d states of Eu2+ are placed deeper in the CaF2 bandgap than the ground and excited 4f135d states of Yb2+, whereas the energies of the impurity-trapped exciton states for Yb2+ and Eu2+ with respect to the conduction band are approximately the same.

  14. Improved luminescence in water-soluble hollow LaF3:Eu3+ nanoparticles by introducing Li+ ions

    NASA Astrophysics Data System (ADS)

    Fan, Ting; Lü, Jiantao; Lin, Futian; Zhou, Zifan

    2016-04-01

    Improved red emission in polyvinylpyrrolidone (PVP)-coated hollow LaF3:Eu3+ nanoparticles by introducing Li+ ions was found for the first time via a one-step template-free hydrothermal method. The hollow formation can be attributed to self-recrystallization and a local Ostwald ripening thermodynamic process. Pores were clearly seen and widely distributed in all LaF3 nanoparticles. The introduction of Li+ ions did not introduce new crystalline phases and resulted in little change in size and morphology of the LaF3 nanoparticles. The main diffraction peaks were found to shift slightly with the Li+ doping concentrations, which indicates that Li+ changes the crystal field environment of Eu3+. The excitation and red emission intensity both doubled when codoped with 7 mol% Li+ ions. The widely distributed pores and improved luminescence properties of our nanoparticles facilitated the construction of new nanocomposites for novel biological applications.

  15. Ag@SiO2/LaF3:Eu3+ Composite Nanostructure and Its Surface Enhanced Luminescence Effect.

    PubMed

    Han, Qingyan; Zhang, Yaqiong; Ren, Zebin; Wang, Zhaojin; Gao, Wei; He, Enjie; Zheng, Hairong

    2016-04-01

    Ag@SiO2/LaF3:Eu3+ core-shell nanostructure was synthesized with a wet chemical method in which the SiO2 layer functioned as a separation layer between Ag-core and LaF3:Eu3+ luminescence material. With this system, surface enhanced luminescene of LaF3:Eu3+ with Ag substrate was investigated, and an obvious enhancement effect was observed. The dependence of the luminescence enhancement on the distance between the luminescence shell and the metallic core was studied too. It is believed that the enhancement effect presented by the current hybrid nanostructure system has great potential in the development of photovoltaic cells. PMID:27451704

  16. Solubility of uranium oxide in molten salt electrolysis bath of LiF-BaF2 with LaF3 additive

    NASA Astrophysics Data System (ADS)

    Alangi, Nagaraj; Mukherjee, Jaya; Gantayet, L. M.

    2016-03-01

    The solubility of UO2 in the molten mixtures of equimolar LiF-BaF2(1:1) with LaF3 as additive was studied in the range of 1423 K-1523 K. The molten fluoride salt mixture LiF-BaF2 LaF3 was equilibrated with a sintered uranium oxide pellet at 1423 K, 1473 K, 1523 K and the salt samples were collected after equilibration. Studies were conducted in the range of 10%-50% by weight additions of LaF3 in the equimolar LiF-BaF2(1:1) base fluoride salt bath. Solubility of UO2 increased with rise in LaF3 concentration in the molten fluoride in the temperature range of 1423 K-1523 K. At a given concentration of LaF3, the UO2 solubility increased monotonously with temperature. With mixed solvent, when UF4 was added as a replacement of part of LaF3 in LiF-BaF2(1:1)-10 wt% LaF3 and LiF-BaF2(1:1)-30 wt% LaF3, there was an enhancement of solubility of UO2.

  17. [Study on the Hydrothermal Synthesis and Fluorescence of LaF3 : Tb3+, Ce3+ Nanocrystals].

    PubMed

    Xu, Shi-hua; Huang, Zhong-jing; Liu, Guo-cong; Wei, Qing-min

    2016-03-01

    LaF3 : Tba3+, Ce3+ nanocrystals were prepared with hydrothermal method with the help of cetyltrimethyl ammonium bromide (CTAB). The effects of pH values of the solution, Ce3+/Tb+ ratio value and reaction time on the luminescent properties were investigated. XRD analysis shows that the as-prepared samples possess hexagonal phase and their main diffraction peaks of samples are similar to the standard card (JCPDS 32-0483). Compared with pure LaF3, the main diffraction peaks of the doped samples have a slight shift, showing existing isomorphous substitution between La3+ and the doped rare earth ions in parent lattice of LaF3. It is found from TEM results that the as-prepared samples have good crystallinity and their average grain sizes change in the range of 20-50 nm. The excitation spectra indicate that the stronger excitation spectrum peaks exist at 250 nm, which is assigned to the transition of 4f --> 5d from Ce3+. When activated at 250 nm, all LaF3 : Tb3+, Ce3+ nanocrystals possess weak blue emission at 490 nm (electric dipole transition, 5D4 --> 7F6) and good green emission at 543 nm (magnetic dipole transition, 5D4 -->7F5). As the Ce3+/Tb+ ratio increases, the fluorescence intensities increase at first and then weaken, and reach the strongest green emission at n(Ce)3+ /n(Tb)3+ = 4. The pH values have some influence on the colors and intensities of the LaF3 : Tb3+, Ce3+ nanocrystals. The sample prepared at pH 9 presents the best color, while the one at pH 7 exhibits the strongest green emission. Besides, increasing reaction time is helpful to improve color purity of sample and enhance its green emission. PMID:27400520

  18. 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 χ(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 exсitation at room temperature. Sesqui-octave-spanning Stokes and anti-Stokes frequency comb generation as well as many-step cascaded and cross-cascaded up-conversion χ(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.

  19. Luminescence and scintillation properties of BaF2sbnd Ce transparent ceramic

    NASA Astrophysics Data System (ADS)

    Luo, Junming; Sahi, Sunil; Groza, Michael; Wang, Zhiqiang; Ma, Lun; Chen, Wei; Burger, Arnold; Kenarangui, Rasool; Sham, Tsun-Kong; Selim, Farida A.

    2016-08-01

    Cerium doped Barium Fluoride (BaF2sbnd Ce) transparent ceramic was fabricated and its luminescence and scintillation properties were studied. The photoluminescence shows the emission peaks at 310 nm and 323 nm and is related to the 5d-4f transitions in Ce3+ ion. Photo peak at 511 keV and 1274 keV were obtained with BaF2sbnd Ce transparent ceramic for Na-22 radioisotopes. Energy resolution of 13.5% at 662 keV is calculated for the BaF2sbnd Ce transparent ceramic. Light yield of 5100 photons/MeV was recorded for BaF2sbnd Ce(0.2%) ceramic and is comparable to its single crystal counterpart. Scintillation decay time measurements shows fast component of 58 ns and a relatively slow component of 434 ns under 662 keV gamma excitation. The slower component in BaF2sbnd Ce(0.2%) ceramic is about 200 ns faster than the STE emission in BaF2 host and is associated with the dipole-dipole energy transfer from the host matrix to Ce3+ luminescence center.

  20. LaF3 core/shell nanoparticles for subcutaneous heating and thermal sensing in the second biological-window

    NASA Astrophysics Data System (ADS)

    Ximendes, Erving Clayton; Rocha, Uéslen; Kumar, Kagola Upendra; Jacinto, Carlos; Jaque, Daniel

    2016-06-01

    We report on Ytterbium and Neodymium codoped LaF3 core/shell nanoparticles capable of simultaneous heating and thermal sensing under single beam infrared laser excitation. Efficient light-to-heat conversion is produced at the Neodymium highly doped shell due to non-radiative de-excitations. Thermal sensing is provided by the temperature dependent Nd3+ → Yb3+ energy transfer processes taking place at the core/shell interface. The potential application of these core/shell multifunctional nanoparticles for controlled photothermal subcutaneous treatments is also demonstrated.

  1. 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.

  2. Paclitaxel conjugated Fe3O4@LaF3:Ce3+,Tb3+ nanoparticles as bifunctional targeting carriers for Cancer theranostics application

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    The bi-functional Chitosan functionalized magnetite doped luminescent rare earth nanoparticles (Fe3O4@LaF3: Ce3+,Tb3+/chi NPs) as a carrier of paclitaxel (PTX) drug was designed using a co-precipitation and facile direct precipitation method. The synthesized nanoparticles are spherical in shape with a typical diameter of 19-37 nm respectively. They are water soluble, super paramagnetic and biocompatible, in which the amino groups on the nanoparticles surface are used for the conjugation with an anticancer drug, paclitaxel. The nature of PTX binding with Fe3O4@LaF3: Ce3+,Tb3+/chi nanoparticles were studied using X-ray diffraction, vibrating sample magnetometer and scanning electron micrograph. The nature of interactions between PTX and Fe3O4@LaF3: Ce3+,Tb3+/chi NPs due to complex formation were conceded out by various spectroscopic methods viz., UV-visible, steady state and excited state fluorescence spectroscopy. The photo-physical characterization reveals that the adsorption and release of PTX from Fe3O4@LaF3:Tb3+/chi nanoparticles is quicker when compared with other nanoparticles and also confirms that this may be due to the hydrogen bond formation between the hydroxyl group of drug and amino group of nanoparticles respectively. The maximum loading capacity and entrapment efficiency of 83.69% and 80.51% were attained at a ratio of 5:8 of PTX and Fe3O4@LaF3: Ce3+,Tb3+/chi NPs respectively. In addition with that, antitumoral activity study of PTX conjugated Fe3O4@LaF3:Tb3+/chi nanoparticles exhibits increased cytotoxic effects on A549 lung cancer cell lines than that of unconjugated PTX.

  3. Phase formation in the BaB2O4-BaF2 system

    NASA Astrophysics Data System (ADS)

    Bekker, T. B.; Fedorov, P. P.; Kokh, A. E.

    2012-07-01

    It is shown that the BaB2O4-BaF2 system is quasi-binary with the following eutectics coordinates: 760°C, 59 mol % BaF2, 41 mol % BaB2O4. Due to the intense pyrohydrolysis during the growth of β-BaB2O4 crystals from the 55.6 mol % BaB2O4-44.4 mol % BaF2 composition, the Ba5B4O11 compound is formed in the system. This process leads to the cocrystallization of the β-BaB2O4 and Ba5B4O11 phases and impedes the formation of high-quality crystals.

  4. Luminescent and kinetic properties of the polystyrene composites based on BaF2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Demkiv, T. M.; Halyatkin, O. O.; Vistovskyy, V. V.; Gektin, A. V.; Voloshinovskii, A. S.

    2016-02-01

    Luminescence-kinetic properties of polystyrene composites based on BaF2 nanoparticles were studied. The electron emission from the nanoparticles due to the photoelectric effect is the main luminescence excitation mechanism in the case of polystyrene composites loaded with small BaF2 nanoparticles (~20 nm). Scintillation pulse of polystyrene composites possesses only fast decay component with the time constant τ~2 ns, and its emission intensity considerably exceeds the one for pure polystyrene scintillator upon the X-ray excitations.

  5. Simultaneous effects of relaxation and polarization transfer in LaF3-type crystals as sources of dynamic information.

    PubMed

    Lips, O; Kruk, D; Privalov, A; Fujara, F

    2007-05-01

    Fluorine nuclear magnetic resonance (NMR) spin-lattice relaxation dispersion has been measured for pure LaF(3) and La(1-x)Sr(x)F(3-x) for admixture concentrations x ranging from 0.01% up to 16%. The relaxation dispersion experiments have been carried out in a wide frequency range (20 kHz-40 MHz) at temperatures between 300 and 1400 K. The data have been analyzed using the recently published [J. Magn. Res. 179 (2006) 250] relaxation model for multispin systems of mutually interacting quadrupolar and dipolar nuclei. Rate constants of the fluorine ionic jumps within and among distinct fluorine sublattices have been extracted. Characteristic effects of the polarization transfer between fluorine and lanthanum spins have been observed and attributed to slow dynamics within one of the fluorine sublattices.

  6. [Stability of CaF2 at high temperature].

    PubMed

    Qi, Qingjie; Liu, Jianzhong; Cao, Xinyu; Zhou, Junhu; Zhang, Shuxin; Kefa, Cen

    2002-05-01

    In this paper, the stabilities of CaF2 in atmosphere, dry and moist air at elevated temperatures were studied by gaseous fluorides direct absorption and fluoride ion-selective electrode (ISE) measurements technique supplemented by differential thermal analysis (DTA), chemical analysis (pyrohydrolysis-ISE method) and X-ray diffraction (XRD) analysis. The principal reaction was shown to be hydrolysis of CaF2 at high temperature and CaF2 were actually hydrolyzed appreciably at about 830 +/- 10 degrees C in moist atmospheres. Kinetics calculation showed that hydrolysis reaction was first order and the activation energy for the hydrolysis was 115 +/- 2 kJ/mol, applicable over the range 850 degrees C-1350 degrees C. The research results will be of significance for fluoride pollution control during coal combustion and clay-brickmaking. PMID:12145925

  7. [Stability of CaF2 at high temperature].

    PubMed

    Qi, Qingjie; Liu, Jianzhong; Cao, Xinyu; Zhou, Junhu; Zhang, Shuxin; Kefa, Cen

    2002-05-01

    In this paper, the stabilities of CaF2 in atmosphere, dry and moist air at elevated temperatures were studied by gaseous fluorides direct absorption and fluoride ion-selective electrode (ISE) measurements technique supplemented by differential thermal analysis (DTA), chemical analysis (pyrohydrolysis-ISE method) and X-ray diffraction (XRD) analysis. The principal reaction was shown to be hydrolysis of CaF2 at high temperature and CaF2 were actually hydrolyzed appreciably at about 830 +/- 10 degrees C in moist atmospheres. Kinetics calculation showed that hydrolysis reaction was first order and the activation energy for the hydrolysis was 115 +/- 2 kJ/mol, applicable over the range 850 degrees C-1350 degrees C. The research results will be of significance for fluoride pollution control during coal combustion and clay-brickmaking.

  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. On structural and lattice dynamic stability of LaF3 under high pressure: A first principle study

    NASA Astrophysics Data System (ADS)

    Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

    2015-06-01

    Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ˜19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.

  10. 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.

  11. 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 1.16π 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

  12. Multi-phonon assisted upconversion emission and power dependence studies in LaF3:Er3+ phosphor.

    PubMed

    Singh, A K; Kumar, K; Pandey, A C; Rai, S B; Kumar, D

    2013-04-01

    LaF3:Er3+ phosphor is synthesized through chemical precipitation method and its upconversion (UC) emission studies have carried out using 532-nm excitation. Phosphor has shown two-photon absorption UV bands at the 325 nm, 342 nm, 383 nm, 403 nm and 411 nm wavelengths. At relatively higher excitation powers multi-phonon assisted energy migration from 2H11/2 (4S3/2) level to the upper 4F3/2, 4F5/2 and 4F7/2 levels has observed and this energy migration opened new channel of emission at 440 nm, 453 nm and 488 nm due to the 4F3/2→4I15/2, 4F5/2→4I15/2 and 4F7/2→4I15/2 transitions, respectively. Temperature dependent UC measurement is also done and observed emission pattern is correlated with the power dependence studies. Upconversion bands at 411 and 488 nm wavelengths have shown reversal in intensity as either excitation power or sample temperature is increased and hence these two bands are found to act as optical switch. Planck blackbody like continuum emission has also observed at higher excitation powers.

  13. Direct growth of nanocrystalline graphitic carbon films on BaF2 by alcohol CVD

    NASA Astrophysics Data System (ADS)

    Tan, Yan; Nakamura, Atsushi; Kubono, Atsushi

    2016-03-01

    Multilayered nanocrystalline graphitic carbon films were directly formed on BaF2 substrates by the alcohol chemical vapor deposition method using ethanol. Domain size was typically 46 nm as estimated from the peak intensity ratios of G- and D-band of the Raman spectra, which were higher than currently reported values for various dielectric substrates. Sheet resistance measured by the four-probe method was 900 Ω/sq. A possible formation mechanism of the graphitic carbon layer was discussed referring to the results of X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) for a composition analysis. It was found that the graphitic carbon layers were formed on the BaO surface, which was produced by the oxidization of the BaF2 substrate by the ethanol source.

  14. Improved Upconversion Luminescence in Water-Soluble Yb3+/Er3+ Codoped LaF3 Nanoparticles Through Ca2+ Doping.

    PubMed

    Liu, Shihu; Zhang, Peng; Li, Daguang; Lan, Min; Wang, Zhe; Qin, Weiping; Zha, Dan; Wang, Lili

    2016-04-01

    Monodisperse water-soluble LaF3: Yb3+/Er3+ nanocrystals (NCs) have been successfully fabricated via a fast, facile, and environmentally-friendly polyol process with polyvinylpyrrolidone (PVP) as an amphiphilic surfactant. The obtained NCs with a small size of 18 nm can be well dispersed in hydrophilic solutions. Meanwhile, their upconversion (UC) luminescence intensity was increased through Ca2+ doping due to the decrease of symmetry around rare earth ions. PMID:27451730

  15. Preparation of LaF3:Eu3+ Based Inorganic-Organic Hybrid Nanostructures via an Ion Exchange Method and Their Strong Luminescence.

    PubMed

    Wang, Xiaojing; Yang, Yi; Chen, Nan; Liu, Bingfa; Liu, Guihua

    2016-04-01

    Lanthanide doped inorganic-organic hybrid nanostructures have received much attention in recent years due to their strong luminescence sensitized by organic ligands via an energy transfer route. In this work, an ion exchange method was used to prepare Eu3+ doped LaF3 based inorganic-organic hybrid nanostructures with organic ligands. The undoped LaF3 nanoparticles were first synthesized by a hydrothermal method, and Eu3+ ions were then ion exchanged into these LaF. nanoparticles to form the Eu3+ doped LaF3 nanoparticles, which were then used to prepare the inorganic-organic hybrid nanostructures with benzoic acid and 2-thenoyltrifluoroacetone. As a result of the luminescence sensitization, strong luminescence was observed in these inorganic-organic hybrid nanostructures, and the luminescence enhancement was over 40 times. Dependence of the luminescence of the hybrid nanostructures on the doping concentration and amount of organic ligands was studied in detail, and optimization was conducted to obtain the maximum luminescence for the hybrid nanostructures. PMID:27451698

  16. Spectral engineering of LaF3:Ce3+ nanoparticles: The role of Ce3+ in surface sites

    NASA Astrophysics Data System (ADS)

    Jacobsohn, L. G.; Toncelli, A.; Sprinkle, K. B.; Kucera, C. J.; Ballato, J.

    2012-04-01

    Due to the high surface-to-volume ratio, luminescence centers on the surface have relative dominance in the overall spectral response of nanoparticles. The luminescence of LaF3:Ce3+ nanoparticles was investigated in the spectral and temporal domains with a particular focus on the role of Ce3+ on the surface. These nanoparticles present two luminescence bands at 4.10 eV and 4.37 eV attributed to Ce3+ transitions from the 5d level to the spin-orbit split 4f ground levels 2F5/2 and 2F7/2, in addition to a low-energy band at 3.62 eV that has been attributed to Ce3+ ions residing in perturbed sites. The growth of up to three undoped shells, ca. 0.9 nm thick each, around the core promoted a progressive enhancement of luminescence output, concomitant with an increase in the fluorescence lifetime due to the weakening of energy transfer through multipolar interaction between Ce3+ in the core and quenching defects on the surface. Also, the growth of the first shell led to a decrease in the relative intensity of the low-energy band and a 0.23 eV shift to higher energies. These results were interpreted as being due to the existence of two types of perturbed sites, one on the surface that is eliminated by the growth of the first shell, and another within the volume of the nanoparticle, similar to observations in bulk single crystals. This work demonstrates how surface engineering can affect and control the luminescence behavior of this nanomaterial.

  17. Sensitized luminescence from water-soluble LaF3:Eu nanocrystals via partially-capped 1,10-phenanthroline: time-gated emission and multiple lifetimes.

    PubMed

    Irfanullah, Mir; Bhardwaj, Navneet; Chowdhury, Arindam

    2016-08-01

    Water dispersible citrate-capped LaF3:Eu(5%) nanocrystals (NCs) have been partially surface-functionalized by 1,10-phenanthroline (phen) via a ligand exchange method to produce novel water dispersed citrate/phen-capped LaF3:Eu(5%) NCs in which citrate ligands preserve the water dispersibility of the NCs and phen ligands act as sensitizers of surface Eu(3+)-dopant sites. The partial ligand exchange and the formation of water dispersed NCs have been monitored by (1)H NMR spectroscopy, as well as luminescence measurements at different time intervals during the reaction. These NCs display a distinct phen-sensitized Eu(3+)-emission profile with enhanced intensity in water as compared to the emission profile and intensity obtained upon direct excitation. Time-resolved (or time-gated) emission spectroscopy (TRES) has been used to probe PL dynamics of Eu(3+)-sites of LaF3:Eu(5%) NCs by taking advantage of selectively sensitizing surface Eu(3+)-dopant sites by phen ligands as well as by exciting all the Eu(3+)-sites in the NCs upon direct excitation. TRES upon direct excitation of the citrate-capped LaF3:Eu(5%) NCs reveals that Eu(3+)-dopants occupy at least three different sites, each with a different emission profile and lifetime, and emission from purely interior Eu(3+)-sites has been resolved due to their long lifetime as compared to the lifetime of purely surface and near surface Eu(3+)-sites. In contrast, the phen-sensitized emission from citrate/phen-capped LaF3:Eu(5%) NCs displays similar emission profiles and lifetimes in TRES measurements, which reveal that phen truly sensitizes purely surface dopant sites of the NCs in water, all of which have nearly the same local environment. The phen-sensitized Eu(3+)-emission of the NCs in water remains stable even upon addition of various buffer solutions at physiological pH, as well as upon addition of water-miscible organic solvents. Furthermore, the two-photon excitation (λex. = 720 nm) of these water-soluble phen-capped NCs produces bright red Eu(3+) emission, which reveals that these NCs are promising for potential applications in biological imaging. PMID:27435878

  18. Influence of surface coating on structural, morphological and optical properties of upconversion-luminescent LaF3:Yb/Er nanoparticles

    NASA Astrophysics Data System (ADS)

    Ansari, Anees A.; Yadav, Ranvijay; Rai, S. B.

    2016-07-01

    LaF3:Yb/Er (core), LaF3:Yb/Er@LaF3 (core/shell) and LaF3:Yb/Er@LaF3@SiO2 (core/shell/SiO2) nanoparticles were synthesized using citric-acid-based complexation process. X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, optical absorption, band-gap energy ( E g), Fourier transform infrared and upconversion emission spectroscopy were employed to investigate the structural, morphological and optical properties of the synthesized core and core/shell/SiO2 nanoparticles. These core/shell/SiO2 nanoparticles can be well dispersed in aqueous solvents to form clear colloidal solution. The optical band-gap energy was decreased after shell formation due to increase in the crystalline size. The growth of an inactive and porous silica layers simultaneously on the surface of luminescent core-nanoparticles resulting an increase in average crystalline size of the nanoparticles. As-prepared inert shell-coated core/shell nanoparticles show intensive upconversion-luminescence as compared to the seed-core and silica-surface-modified core/shell/SiO2 nanoparticles because luminescent ions (Yb3+ and Er3+) ions located at the particle surface were protected from the non-radiative decay arising from surface dangling bonds and capping agent. However, our study revealed that there was only a slight reduction in upconversion efficiency for the silica-modified core/shell nanoparticles, indicating that upconversion properties of the upconversion nanoparticles are largely preserved in the core/shell/SiO2 nanoparticles. Absorption and upconversion-luminescence properties were examined for future application in the development of optical devices as well as optical bioprobes.

  19. Optical properties of CaF2 and Yb3+:CaF2 for laser applications

    NASA Astrophysics Data System (ADS)

    Stäblein, Jörg; Pöhl, Karin; Weisleder, Andreas; v. d. Gönna, Gordon; Töpfer, Thomas; Hein, Joachim; Siebold, Mathias

    2011-06-01

    Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authorś process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

  20. 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.

  1. Ultrafast Electronic Excitation in CaF2 Crystals

    NASA Astrophysics Data System (ADS)

    Xu, Shizhen; Jia, Tianqing; Li, Xiaoxi; Feng, Donghai; Sun, Haiyi; Li, Chengbin; Wang, Xiaofeng; Kuroda, Hirao; Li, Ruxin; Xu, Zhizhan

    2005-11-01

    A new pump and probe experimental system was developed, the pump pulse duration of which is stretched and is much longer than that of the probe pulse. Using this system, time-resolved electronic excitation processes and damage mechanisms in CaF2 crystals were studied. The measured reflectivity of the probe pulse begins to increase at the peak of the pump pulse and increases rapidly in the latter half of the pump pulse, when the pump pulse duration is stretched to 580 fs. Our experimental results indicate that both multiphoton ionization and impact ionization play important roles in the generation of conduction band electrons, at least they do so when the pump pulse durations are equal to or longer than 580 fs.

  2. Down-shifting in Ce3+-Tb3+ co-doped SiO2-LaF3 nano-glass-ceramics for photon conversion in solar cells

    NASA Astrophysics Data System (ADS)

    Velázquez, J. J.; Rodríguez, V. D.; Yanes, A. C.; del-Castillo, J.; Méndez-Ramos, J.

    2012-10-01

    95SiO2-5LaF3 sol-gel derived nano-glass-ceramics single doped with Ce3+ or Tb3+ and co-doped with Ce3+-Tb3+ were synthesized by thermal treatment of precursor glasses. Precipitation of LaF3 nanocrystals during ceramming process was confirmed by X-ray diffraction with mean size ranging from 12 to 15 nm. An exhaustive spectroscopic analysis has been carried out. As a result, it was found that the green emission of Tb3+ ions was greatly enhanced through down shifting process, due to efficient energy transfer from Ce3+ to Tb3+ ions in the glass-ceramics, which is favored by the reduction of the interionic distances when the dopant ions are partitioned into LaF3 nanocrystals. These results suggest the use of these materials to improve the efficiency of solar cells.

  3. Further study of scintillation counters with BaF 2 crystals for time-of-flight positron tomography in medicine

    NASA Astrophysics Data System (ADS)

    Moszyński, M.; Allemand, R.; Cormoreche, E.; Laval, M.; Odru, R.; Vacher, J.

    1984-10-01

    The study and the optimalisation of scintillation counters consisting of R1668 (R1398 with quartz window) photomultipliers and BaF 2 crystals were carried-out in order to construct a 96 counter ring for time-of-flight positron tomography. The photoelectron yield measured for CsF and BaF 2 crystals permitted us to estimate the photoelectron collection efficiency at different light wavelengths for R1668 photomultiplier in relation to the XP2020Q. This experiment, and the time resolution study, showed that at present the ability of R1668 photomultiplier for timing with BaF 2 crystals is limited by a poor collection of photoelectrons produced by UV light. It was shown that a certain modification of the voltage between D 1 and D 2 dynodes improves the time resolution by 10%. A comparison of BaF 2 crystals of different shapes showed that pyramidal cut crystal with a small opening angle equal to 1° ensures both a high detection efficiency and a good time resolution for 511 keV γ-rays. The best time resolution equal to 330 ps and the typical one equal to 350 ps were achieved with two counters for time-of-flight positron tomography.

  4. Preparation and Properties of Ce3+:BaF2 Transparent Ceramics by Vacuum Sintering.

    PubMed

    Luo, Junming; Ye, Lifang; Xu, Jilin

    2016-04-01

    Ce0.001Ba0.999F2.001 powders were prepared by a chemical coprecipitation method using Ba(N03)2, KF.2H2O and Ce(NO3)3 6H20 as raw materials. Ce0.001Ba0.999F2.001 transparent ceramics were prepared by vacuum sintering. The results show that the Ce0.001Ba0.999F2.001 powders were blocky, and both powdered and sintered transparent ceramics were composed of BaF2 phases without the secondary phase. The maximum light transmittance of the Ce0.001Ba0.999F2.001 transparent ceramics reached 55%. The fracture morphology shows a cleavage fracture with a few micropores. The fluorescence spectra show that the Ce0.1Ba0.999F2.001 powders displayed emissions at 410 nm, 480 nm and 620 nm under 275 nm excitation. The Ce0.1Ba0.9F2.1 transparent ceramics displayed0emissions at 450 nm and 620 nm under 294 nm excitation. PMID:27451752

  5. Phosphate Capacities of CaF2-MgO and CaF2-CaO-MgO Slags

    NASA Astrophysics Data System (ADS)

    Akbari, F.; Pickles, C. A.

    2015-02-01

    Previously published sulphide capacity data and thermodynamic arguments have been employed to calculate the phosphate capacities and the phosphorus partition ratios between a molten carbon saturated iron alloy and binary CaF2-MgO slags and also ternary CaF2 -CaO-MgO slags at 1450 °C. For the CaF2-MgO binary system, a linear relationship was found between the phosphate and the sulphide capacities as follows: log ? = 1.2 log Cs + 25.2. For the ternary CaF2-CaO-MgO system at 1450 °C, the logarithm of the calculated phosphate capacities ranged from 19.47 to 20.15. With the addition of CaO, the phosphate capacities initially increased, reached a maximum and then decreased slightly. The addition of MgO to the CaF2-CaO system resulted in a decrease in the phosphate capacity. The calculated phosphorus partition ratios increased slightly with increasing mole fraction of CaO in the ternary system.

  6. EXAFS measurements on Mn doped CaF2 phosphor with different Mn concentrations

    NASA Astrophysics Data System (ADS)

    Patra, N.; Bakshi, A. K.; Bhattacharyya, D.

    2016-05-01

    Extended X-ray Absorption Fine Structure (EXAFS) measurements have been carried out on Mn doped CaF2 phosphors with synchrotron radiation at the Mn K edge. Measurements have been carried out on samples prepared with different concentrations of Mn dopants. The data have been analyzed to find out the Mn-F bond lengths and % of Mn doped CaF2 phase in the samples. The change in thermoluminescence glow peak temperature in CaF2:Mn phosphor with variation in Mn concentration has been correlated to the parameters obtained from EXAFS measurements.

  7. Studies on decay time of fluorescence from a series of Ce-doped BaF 2 crystals

    NASA Astrophysics Data System (ADS)

    Zizong, Xu; Zhufang, Gong; Jin, Chang; Caoshy, Shi; Dingzhong, Sheng; Xianglong, Yuan; Zhiwen, Yin

    1992-11-01

    Time distribution curves of fluorescence from BaF 2 crytals doped with various concentrations Ce have been measured using a time spectrometer with time resolution of 680 ps FWHM. Fitting the experimental data to a multi-exponential function, the decay times and relative yields of fluorescence components are determined. Comparing these with the results of the emission spectrum excited by X-rays, some conclusions are drawn.

  8. A neutron scintillator based on transparent nanocrystalline CaF2:Eu glass ceramic

    NASA Astrophysics Data System (ADS)

    Struebing, Christian; Chong, JooYun; Lee, Gyuhyon; Zavala, Martin; Erickson, Anna; Ding, Yong; Wang, Cai-Lin; Diawara, Yacouba; Engels, Ralf; Wagner, Brent; Kang, Zhitao

    2016-04-01

    There are no efficient Eu2+ doped glass neutron scintillators reported due to low doping concentrations of Eu2+ and the amorphous nature of the glass matrix. In this work, an efficient CaF2:Eu glass ceramic neutron scintillator was prepared by forming CaF2:Eu nanocrystals in a 6Li-containing glass matrix. Through appropriate thermal treatments, the scintillation light yield of the transparent glass ceramic was increased by a factor of at least 46 compared to the as-cast amorphous glass. This improvement was attributed to more efficient energy transfer from the CaF2 crystals to the Eu2+ emitting centers. Further light yield improvement is expected if the refractive index of the glass matrix can be matched to the CaF2 crystal.

  9. Numerical modeling of radiative heat transfer in Bridgman solidification of semi-transparent BaF 2 crystals

    NASA Astrophysics Data System (ADS)

    Stelian, C.

    2007-08-01

    The radiative heat transfer during Bridgman solidification of semi-transparent barium fluoride (BaF 2) crystals is numerically investigated by using the commercial software FIDAP. This code uses the P-1 approximation for the participating media modeling. The thermal field and the solid-liquid interface shape are computed for an opaque melt-crystal sample, a semi-transparent grey sample and a semi-transparent non-grey sample. The transient numerical analysis of the latent heat influence on the interface deflection shows a significant effect on the interface shape. In the case of an opaque sample, this effect is huge because of the small thermal conductivity of the BaF 2 melt. The interface curvature is drastically reduced when the latent heat is taken into account, and the growth front, which has a convex shape, becomes flat when the growth rate increases. The latent heat effect is reduced in the case of the participating BaF 2 sample because the effective thermal conductivity of the melt is augmented by the internal radiative heat transfer. The internal radiative effect is small at low solidified fractions but becomes significant when the crystal length increases, leading to a more curved interface. When the growth rates are greater than a critical value, the interface becomes concave and a destabilization of the growth process can occur. These results are in agreement with previous experimental measurements of the interface curvature and analytical investigations of the factors affecting the interface deflection.

  10. Pulse pile-up and dead time corrections for digitized signals from a BaF2 calorimeter

    NASA Astrophysics Data System (ADS)

    Mendoza, E.; Cano-Ott, D.; Guerrero, C.; Berthoumieux, E.

    2014-12-01

    The pulse pile-up and associated dead time effects in an 243Am(n,γ) cross section measurement with a BaF2 Total Absorption Calorimeter at the CERN n_TOF facility have been characterized. In this case, reliable corrections of these effects are crucial because of the complex detector configuration and of the high count rate induced by the sample activity of 50 MBq. The techniques, which have been developed for offline processing of the present data, may be of general interest for the analysis of other experiments using digital acquisition systems.

  11. Effect of CaF2 addition on optical properties of barium phosphate glasses

    NASA Astrophysics Data System (ADS)

    Kumar, N. Manoj; Rao, G. Venkateswara; Akhila, B. E.; Shashikala, H. D.

    2014-04-01

    Ternary barium phosphate glasses, (50-X)BaO-XCaF2-50P2O5 have been prepared by adding 0-10 mol% of CaF2 to binary barium phosphate glasses. The amorphous nature of the prepared glasses was confirmed by X-ray diffraction technique. The UV-Visible absorption spectra have been recorded, optical band gap energy Eopt and Urbach energy Etail were determined. Shift in Eopt and Etail with increase in concentration of CaF2 is noted. FTIR analysis was carried out to investigate the short and intermediate-range orders in glasses. Shift of (P-O-P) band to higher wave number with the substitution of BaO with CaF2 shows the shortening of the phosphate chains. Hardness and density of glass samples were measured and correlated with the composition of glasses.

  12. Modification of luminescence spectra of CaF2:Eu2+.

    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.

  13. Thermoluminescent dosimetric properties of CaF2:Tm produced by combustion synthesis

    NASA Astrophysics Data System (ADS)

    de Vasconcelos, D. A. A.; Barros, V. S. M.; Khoury, H. J.; Asfora, V. K.; Oliveira, R. A. P.

    2016-04-01

    Calcium Fluoride is one of the oldest known thermoluminescent materials and is considered to be one of the most sensitive. This work presents the dosimetric properties results of CaF2:Tm produced by combustion synthesis. The X-ray diffraction confirmed that CaF2 was successfully produced. TL emission spectra, obtained using a Hammamatsu optical spectrometer, have the same lines of commercial CaF2:Tm, although transitions 3P0→3F4 (455 nm) and 1G4→3H6 (482 nm) are shown to be proportionally more intense. The deconvolution technique was employed and seven glow peaks were found similar to the commercial CaF2:Tm. A linear dose response curve was obtained for the range 0.1 mGy to 100 Gy, with the onset of a supralinear behavior at 50 Gy up to 100 Gy. The minimum measurable dose for gamma was around 100 μGy for a 6.0 mm diameter by 1.0 mm in thickness pellet. No significant fading was observed in 60 days of storage, within experimental uncertainties, showing that the main dosimetric peak is stable.

  14. 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

  15. Test of the statistical model in Mo96 with the BaF2γ calorimeter DANCE array

    NASA Astrophysics Data System (ADS)

    Sheets, S. A.; Agvaanluvsan, U.; Becker, J. A.; Bečvář, F.; Bredeweg, T. A.; Haight, R. C.; Jandel, M.; Krtička, 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 γ-ray cascades following the Mo95(n,γ)Mo96 reaction were studied with the γ calorimeter DANCE (Detector for Advanced Neutron Capture Experiments) consisting of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center. The γ-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,γ)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.

  16. Response of a BaF 2 scintillation detector to quasi-monoenergetic fast neutrons in the range of 45 to 198 MeV

    NASA Astrophysics Data System (ADS)

    Gunzert-Marx, K.; Schardt, D.; Simon, R. S.; Gutermuth, F.; Radon, T.; Dangendorf, V.; Nolte, R.

    2005-01-01

    We have studied the neutron response of a scintillation detector consisting of a 14 cm long, hexagonal-shaped BaF 2-crystal with an inner diameter of 8.75 cm coupled to an EMI9821QB photomultiplier tube. The detector was exposed to calibrated quasi-monoenergetic neutron fields obtained from 7Li(p,n) 7Be reactions. The measurements were performed at neutron energies of 45, 60, 96, 147 and 198 MeV as given by the energies of the incident protons. The experimental pulse-height spectra of the BaF 2-detector are compared with Monte Carlo simulations using the FLUKA code. The detection efficiency of the BaF 2-detector in the energy range of 45-198 MeV was determined as a function of the discriminator threshold and compared to the literature data. At neutron energies above 100 MeV the detection efficiency of the BaF 2-detector was found to be a factor of two higher than that of an NE213-detector of comparable size.

  17. Investigation on nanoscale processes on the BaF2(111) surface in various solutions by frequency modulation atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kobayashi, Naritaka; Kawamura, Ryuzo; Yoshikawa, Hiroshi Y.; Nakabayashi, Seiichiro

    2016-06-01

    In this study, we have directly observed nanoscale processes that occur on BaF2(111) surfaces in various solutions using liquid-environment frequency modulation atomic force microscopy (FM-AFM) with a true atomic resolution. In addition, to investigate atomic-scale mechanisms of crystal growth process of BaF2, we determined a suitable solution for atomic-resolution FM-AFM imaging of the BaF2(111) surface. For undersaturated solutions, the surface is roughened by barium hydroxo complexes in the case of high pH, whereas by dissolution and proton or water molecule adsorption throughout the surface in the case of low pH. On the other hand, for supersaturated solutions, the surface shows two-dimensional nucleation and growth (σ = 0.1) and three-dimensional crystal growth with tetrahedral structures (σ = 1), where σ is the degree of supersaturation. The atomic-resolution imaging of the BaF2(111) surface has been demonstrated in potassium fluoride (KF) and the supersaturated (σ = 0.1 and 1) solutions, wherein atomically flat terraces are shown at least for about 30 min.

  18. Epitaxial Growth of CaF2 Films on Si(111) Studied by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Kametani, Keisuke; Sudoh, Koichi; Iwasaki, Hiroshi

    2002-01-01

    Using ultrahigh vacuum scanning tunneling microscopy, we have studied the early stages of the epitaxial growth of CaF2 films on Si(111) at 630°C at a slow deposition rate of 0.2 monolayer (ML) per minute. After formation of CaF interface layer, we observe the film grows in the sequence of step edge decoration, one-dimensional islands growth on the terrace, formation of clusters of the islands, coalescence of the island cluster and filling of gaps between the one-dimensional islands in the cluster and between the island clusters to complete a layer. By such a sequence, epitaxial CaF2 films with atomically flat surface could be grown in layer-by-layer fashion up to 3 ML. The growth mode is discussed in relation to kinetic phase diagram [M. A. Olmstead: Thin Films: Heteroepitaxial Systems, eds. W. K. Liu and M. B. Santos (World Scientific, Singapore, 1999) Chap. 5].

  19. 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.

  20. Studies of the facetting of the polished (100) face of CaF 2

    NASA Astrophysics Data System (ADS)

    Deuster, V.; Schick, M.; Kayser, Th.; Dabringhaus, H.; Klapper, H.; Wandelt, K.

    2003-04-01

    The present paper deals with studies of the facetting of the polished (1 0 0) surface of CaF 2 during annealing and growth in UHV using low energy electron diffraction (LEED), atomic force microscopy (AFM), and transmission electron microscopy (TEM). First morphological modifications of the polished surfaces become visible at temperatures of T=874 K. Surfaces annealed at T=974 K exhibit a micro-roughening with pyramidal protrusions and corresponding depressions. LEED studies indicate the evolution of {1 1 1} facets. Reflexes from the (1 0 0) surface are not seen. After growth of about 660 monolayers of CaF 2 at T=1093 K and a saturation ratio S=33 from the vapor phase, larger pyramid-like or hip roof-like crystallites are developed. The results of AFM height profiles as well as of the LEED investigations indicate again the formation of {1 1 1} facets as proved by their angles of 54.7 o with the base (1 0 0) surface. This shows that the crystallites are homoepitaxially grown on the underlying CaF 2 substrate.

  1. Studies of the Facetting of the Polished (100) Face of CaF2

    NASA Astrophysics Data System (ADS)

    Dabringhaus, H.; Schick, M.; Wandelt, K.; Deuster, V.; Kayser, Th.; Klapper, H.

    2003-12-01

    The present paper deals with studies of the facetting of the polished (100) surface of CaF2 during annealing and growth in UHV using low energy electron diffraction (LEED), atomic force microscopy (AFM), and transmission electron microscopy (TEM). First morphological modifications of the polished surfaces become visible at temperatures of T = 874 K. Surfaces annealed at T = 974 K exhibit a micro-roughening with pyramidal protrusions and corresponding depressions. LEED studies indicate the evolution of {111} facets. Reflexes from the (100) surface are not seen. After growth of about 660 monolayers of CaF2 at T = 1093 K and a saturation ratio S = 33 from the vapor phase, larger pyramid-like or hip roof-like crystallites are developed. The results of AFM height profiles as well as of the LEED investigations indicate again the formation of {111} facets as proved by their angles of 54.7° with the base (100) surface. This shows that the crystallites are homoepitaxially grown on the underlying CaF2 substrate.

  2. 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.

  3. Effect of NiCr Clad BaF2·CaF2 Addition on Wear Performance of Plasma Sprayed Chromium Carbide-Nichrome Coating

    NASA Astrophysics Data System (ADS)

    Du, Lingzhong; Huang, Chuanbing; Zhang, Weigang; Zhang, Jingmin; Liu, Wei

    2010-03-01

    NiCr clad BaF2·CaF2 fluoride eutectic powders were added into chromium carbide-nichrome feedstock to improve the tribological properties of NiCr-Cr3C2 coating, and the structures, mechanical, and ball-on-disk sliding wear performance of the coating were characterized. The results show that NiCr cladding can effectively decrease the density and thermophysical difference between the feedstock components, while alleviate the decarburization and oxidization of the constituent phases, and form the coating with a uniform and dense microstructure. However, the addition of BaF2·CaF2 has a negative effect on mechanical properties of the coating. When the temperature reaches 500 °C, the BaF2·CaF2 eutectic is soften by the heat and smeared by the counterpart, thus the low shear stress lubricating film forms between the contact surface, that improves the tribological properties dramatically. At this temperature, the dominant wear mechanisms also change from splats spallation and abrasive wear at room temperature to plastic deformation and plawing by the counterpart. Within the temperature range from 600 to 800 °C, the friction coefficient, the wear rates of NiCr/Cr3C2-10% BaF2·CaF2 coating and its coupled Si3N4 ball are 20%, 40%, and 75% lower than those of the NiCr/Cr3C2 coating, respectively. The NiCr/Cr3C2-BaF2·CaF2 coating shows superior wear performance to the NiCr/Cr3C2 coating without lubricant additive.

  4. 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

    2015-11-21

    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

  5. Europium-doped LaF3 nanocrystals with organic 9-oxidophenalenone capping ligands that display visible light excitable steady-state blue and time-delayed red emission.

    PubMed

    Irfanullah, Mir; Sharma, Dharmendar Kumar; Chulliyil, Ramya; Chowdhury, Arindam

    2015-02-21

    Visible light excitable and color tunable ∼5% Eu(3+)-doped LaF3 nanocrystals (NCs), containing 9-oxidophenalenone ligands bound to the surface as visible light sensitizers for Eu(3+) dopants, have been synthesized by a facile solution-based method. The crystalline phase structure, size, composition, morphology and luminescence properties of the NCs are characterized using X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and steady-state and time-resolved emission spectroscopy. The results show that these NCs are very small in size (<10 nm), display high degree of crystallinity and have pure tysonite structure of LaF3 with P3[combining macron]c1 space group. The visible light excitation of the capping ligands triggers an alternate display of steady-state, short-lived blue emission (τ < 1 ns) and time-delayed, long-lived sensitized red Eu(3+) emission (τ = 0.41 ms), allowing photoluminescence chromacity tuning as a function of delay time within a specific inorganic composition. The visible light sensitization of the dopant Eu(3+) sites proves more efficient than direct excitation of 5% Eu(3+)-doped LaF3 NCs capped by citrate ligands. The dopant Eu(3+) ions are well protected from non-radiative deactivation through high-energy vibrations of the organic capping ligands which is proved by the long lifetime of the sensitized Eu(3+) emission. The time-resolved emission spectra collected over a period of several milliseconds reveal that the dopant Eu(3+) ions occupy at least three different sites in the NC host. It is further inferred that the sensitized Eu(3+) emission primarily comes from surface dopant sites and sites just underneath the surface of the NCs. We propose that some of the interior Eu(3+) sites also display sensitized emission, which are indirectly populated via Eu(3+) → Eu(3+) energy migration from surface-sensitized Eu(3+) sites of the NCs.

  6. Simultaneous measurement of (n, γ) and (n, fission) cross sections with the DANCE 4π 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 4π 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 γ-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 γ-ray calorimetry (i.e. total γ-ray energy versus γ-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 (σγ/σf) 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.

  7. Excitation of the 4d shell in Sb, Te, and BaF2 with inelastic electron scattering: Collective or single particle?

    NASA Astrophysics Data System (ADS)

    Franck, Carl; Schnatterly, S. E.

    1982-06-01

    Simple models suggest that the momentum-transfer (q) dependence of inelastic electron scattering is sensitive to the difference between collective and single-particle behavior in atomic dynamics. We measured the energy centroid of the 4d continuum peak for 0

  8. Luminescence properties of dual valence Eu doped nano-crystalline BaF2 embedded glass-ceramics and observation of Eu2+ → Eu3+ energy transfer.

    PubMed

    Biswas, Kaushik; Sontakke, Atul D; Sen, R; Annapurna, K

    2012-03-01

    Europium doped glass-ceramics containing BaF(2) nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF(2) nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm(-1) has been demonstrated from the emission spectra of Eu(3+) ions showing the transitions from upper excitation states (5)D(J) (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu(3+)) ions to divalent (Eu(2+)) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu(2+) to Eu(3+) ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu(3+) to Eu(2+) under normal air atmospheric condition has been observed in a BaF(2) containing oxyfluoride glass-ceramics system.

  9. Optical characterization of Tm3+ doped Bi2O3-GeO2-Ga2O3 glasses in absence and presence of BaF2

    NASA Astrophysics Data System (ADS)

    Han, Kexuan; Zhang, Peng; Wang, Shunbin; Guo, Yanyan; Zhou, Dechun; Yu, Fengxia

    2016-08-01

    In this paper, Two new Bi2O3-GeO2-Ga2O3 glasses (one presence of BaF2) doped with 1mol% Tm2O3 were prepared by melt-quenching technique. Differential thermal analysis (DTA), the absorption, Raman, IR spectra and fluorescence spectra were measured. The Judd–Ofelt intensity parameters, emission cross section, absorption cross section, and gain coefficient of Tm3+ ions were comparatively investigated. After the BaF2 introduced, the glass showed a better thermal stability, lower phonon energy and weaker OH‑ absorption coefficient, meanwhile, a larger ~1.8 μm emission cross section σem (7.56 × 10‑21 cm2) and a longer fluorescence lifetime τmea (2.25 ms) corresponding to the Tm3+: 4F3 → 3H6 transition were obtained, which is due to the addition of fluoride in glass could reduce the quenching rate of hydroxyls and raise the cross-relaxation (3H6 + 3H4 → 3F4 + 3F4) rate. Our results suggest that the Tm3+ doped Bi2O3-GeO2-Ga2O3 glass with BaF2 might be potential to the application in efficient ~1.8 μm lasers system.

  10. Optical characterization of Tm3+ doped Bi2O3-GeO2-Ga2O3 glasses in absence and presence of BaF2

    PubMed Central

    Han, Kexuan; Zhang, Peng; Wang, Shunbin; Guo, Yanyan; Zhou, Dechun; Yu, Fengxia

    2016-01-01

    In this paper, Two new Bi2O3-GeO2-Ga2O3 glasses (one presence of BaF2) doped with 1mol% Tm2O3 were prepared by melt-quenching technique. Differential thermal analysis (DTA), the absorption, Raman, IR spectra and fluorescence spectra were measured. The Judd–Ofelt intensity parameters, emission cross section, absorption cross section, and gain coefficient of Tm3+ ions were comparatively investigated. After the BaF2 introduced, the glass showed a better thermal stability, lower phonon energy and weaker OH− absorption coefficient, meanwhile, a larger ~1.8 μm emission cross section σem (7.56 × 10−21 cm2) and a longer fluorescence lifetime τmea (2.25 ms) corresponding to the Tm3+: 4F3 → 3H6 transition were obtained, which is due to the addition of fluoride in glass could reduce the quenching rate of hydroxyls and raise the cross-relaxation (3H6 + 3H4 → 3F4 + 3F4) rate. Our results suggest that the Tm3+ doped Bi2O3-GeO2-Ga2O3 glass with BaF2 might be potential to the application in efficient ~1.8 μm lasers system. PMID:27506152

  11. Fluorine-ion conductivity of different technological forms of solid electrolytes R 1- y M y F3- y (LaF3 Type ) ( M = Ca, Sr, Ba; R Are Rare Earth Elements)

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    We have investigated the conductivity of some representatives of different technological forms of fluoride-conducting solid electrolytes R 1- y M y F3- y ( M = Ca, Sr, Ba; R are rare earth elements) with an LaF3 structure: single crystals, cold- and hot-pressing ceramics based on a charge prepared in different ways (mechanochemical synthesis, solid-phase synthesis, and fragmentation of single crystals), polycrystalline alloys, etc. It is shown (by impedance spectroscopy), that different technological forms of identical chemical composition ( R, M, y) exhibit different electrical characteristics. The maximum conductivity is observed for the single-crystal form of R 1- y M y F3- y tysonite phases, which provides (in contrast to other technological forms) the formation of true volume ion-conducting characteristics.

  12. Laser induced nanoparticle formation in single crystal CaF2

    NASA Astrophysics Data System (ADS)

    Cramer, L.; Langford, S. C.; Dickinson, J. T.

    2004-03-01

    Single crystal calcium fluoride (CaF2) is a material currently being used for vacuum ultra-violet optical components. However, all metal halides have a strong tendency to form point defects under energetic particle and optical irradiation which can degrade performance. Here we examine the consequences of exposing CaF2 to 157 nm excimer laser light. This exposure causes absorption in the visible region due to formations of nanoclusters (colloids) of Ca metal in the bulk. The formation mechanism involves exciton production via two photon absorption. Heating can affect the colloid growth; we have examined the change of transmission at 532 nm vs. temperature during coloring with 157 nm excimer laser light. We find maximum coloration to occur at 50 C. The colloids can also be easily made with exposure to low-energy electrons. The absorption due to colloids can be bleached with subsequent exposure to appropriate laser light. We compare bleaching rates at various wavelengths from 157-1064 nm and find that absorption due to plasmon excitation in the colloids and accompanying heating is the likely bleaching mechanism.

  13. Study on TL and OSL characteristics of indigenously developed CaF 2:Mn phosphor

    NASA Astrophysics Data System (ADS)

    Bakshi, A. K.; Dhabekar, Bhushan; Rawat, N. S.; Singh, S. G.; Joshi, V. J.; Kumar, Vijay

    2009-02-01

    CaF 2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF 2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO 3, HF acid and MnCl 2 as raw materials following co-precipitation method. TL sensitivity of the prepared phosphor was compared with other well established phosphors used for radiation dosimetry. It was found that the TL sensitivity is higher by a factor of 10 with respect to LiF:Mg, Ti, TLD-100 and half to that of CaSO 4:Dy (0.05 mol%) phosphor. X-ray diffraction, TL emission spectrum and ESR spectrum taken of the prepared phosphor confirms the crystal structure, Mn 2+ emission and incorporation Mn in the crystal, respectively. No significant fading of the dosimetric peak was observed of the prepared phosphor for a storage period of 45 days. The dose linearity of the phosphor was found to be in the range of 50 Gy-3 kGy within an uncertainty of about 10%. An attempt was made to determine the kinetic parameters of TL glow curve and the parameters related to optically stimulated luminescence. In view of its long range of dose linearity, it can be used for the dosimetry of commercial irradiator generally used for the irradiation of food and grains in our country.

  14. Facile and controllable synthesis of monodisperse CaF2 and CaF2:Ce3+/Tb3+ hollow spheres as efficient luminescent materials and smart drug carriers.

    PubMed

    Zhang, Cuimiao; Li, Chunxia; Peng, Chong; Chai, Ruitao; Huang, Shanshan; Yang, Dongmei; Cheng, Ziyong; Lin, Jun

    2010-05-17

    Highly uniform and well-dispersed CaF(2) hollow spheres with tunable particle size (300-930 nm) have been synthesized by a facile hydrothermal process. Their shells are composed of numerous nanocrystals (about 40 nm in diameter). The morphology and size of the CaF(2) products are strongly dependent on experimental parameters such as reaction time, pH value, and organic additives. The size of the CaF(2) hollow spheres can be controlled from 300 to 930 nm by adjusting the pH value. Nitrogen adsorption-desorption measurements suggest that mesopores (av 24.6 nm) exist in these hollow spheres. In addition, Ce(3+)/Tb(3+)-codoped CaF(2) hollow spheres can be prepared similarly, and show efficient energy transfer from Ce(3+) to Tb(3+) and strong green photoluminescence of Tb(3+) (541 nm, (5)D(4)-->(7)F(5) transition of Tb(3+), the highest quantum efficiency reaches 77%). The monodisperse CaF(2):Ce(3+)/Tb(3+) hollow spheres also have desirable properties as drug carriers. Ibuprofen-loaded CaF(2):Ce(3+)/Tb(3+) samples still show green luminescence of Tb(3+) under UV irradiation, and the emission intensity of Tb(3+) in the drug-carrier system varies with the released amount of ibuprofen, so that drug release can be easily tracked and monitored by means of the change in luminescence intensity. The formation mechanism and luminescent and drug-release properties were studied in detail.

  15. Fluoride rinse effect on retention of CaF2 formed on enamel/dentine by fluoride application.

    PubMed

    Falcão, Amanda; Masson, Nadia; Leitão, Tarcísio Jorge; Botelho, Juliana Nunes; Ferreira-Nóbilo, Naiara de Paula; Tabchoury, Cínthia Pereira Machado; Tenuta, Livia Maria Andaló; Cury, Jaime Aparecido

    2016-01-01

    Calcium fluoride-like materials ("CaF2") formed on dental surfaces after professional fluoride application are unstable in the oral environment but can be retained longer with a daily NaF mouthrinse. We tested the effect of twice daily 0.05% NaF rinses on the retention of "CaF2" formed on enamel and dentine after applying acidulated phosphate fluoride (APF). "CaF2" formed on enamel/dentine by APF application significantly decreased after exposure to artificial saliva and the 0.05% NaF rinse was ineffective to avoid this reduction. These findings suggest that the combination of APF and 0.05% NaF is not clinically relevant, either for caries or dental hypersensitivity. PMID:27050937

  16. Estimation Model for Electrical Conductivity of CaF2-CaO-Al2O3 Slags

    NASA Astrophysics Data System (ADS)

    Shi, Guan-yong; Zhang, Ting-an; Dou, Zhi-he; Niu, Li-ping

    2016-09-01

    Electrical conductivity is one of the most important properties of molten slags. It has an important influence on process parameter selection of the electroslag remelting process. In the present work, a new model for estimating electrical conductivity of high-temperature slags has been proposed via calculating the conductivity by electrical conductivity of pure substances and interaction parameters between the different components in the slag has been proposed. In this model, the Arrhenius law is used to describe the relationship between electrical conductivity and temperature of slags. This model has been successfully applied to the CaF2-Al2O3, CaF2-CaO, and CaO-Al2O3, as well as CaF2-CaO-Al2O3 systems, and the calculated results are in good agreement with the measured values.

  17. Luminescence emission of natural fluorite and synthetic CaF2:Mn (TLD-400)

    NASA Astrophysics Data System (ADS)

    Topaksu, Mustafa; Correcher, Virgilio; Garcia-Guinea, Javier

    2016-02-01

    The luminescence properties of natural white fluorite indicate that it could be employed as radiation dosimeter similarly to synthetic CaF2:Mn (TLD-400). The cathodoluminescence emission of the natural sample (two maxima) meanwhile TLD-400 (one peak) exhibits a different behaviour associated with the chemical composition. The mineral sample displays (i) a significant UV-blue emission associated with different structural defects (negligible in the synthetic sample) and (ii) a shift of the green emission to higher wavelengths respect to the TLD-400. The green induced TL emission also shows significant differences in intensity (higher in TLD-400) and sensitivity. Both samples display a complex induced green TL glow curve that could not be analysed assuming the model based on the discrete trap distribution. The Tm-Tstop method indicates the presence of close overlapping groups of components linked probably to a continuum in the trap distribution rather than a single trapping level.

  18. Thermoluminescence dosimetry properties of new Cu doped CaF(2) nanoparticles.

    PubMed

    Zahedifar, M; Sadeghi, E

    2013-12-01

    Nanoparticles of Cu-doped calcium fluoride were synthesised by using the hydrothermal method. The structure of the prepared nanomaterial was characterised by the X-ray diffraction (XRD) pattern and energy dispersive spectrometer. The particle size of 36 nm was calculated from the XRD data. Its shape and size were also observed by scanning electron microscope. Thermoluminescence (TL) and photoluminescence of the produced phosphor were also considered. The computerised glow curve deconvolution procedure was used to identify the number of glow peaks included in the TL glow curve of the CaF2:Cu nanoparticles. The TL glow curve contains two overlapping glow peaks at ∼413 and 451 K. The TL response of this phosphor was studied for different Cu concentrations and the maximum sensitivity was found at 1 mol% of Cu impurity. Other dosimetric characteristics of the synthesised nanophosphor are also presented and discussed.

  19. Commissioning the DANTE array of BaF2 detectors at TRIUMF-ISAC using a fast-timing lifetime measurement

    NASA Astrophysics Data System (ADS)

    Cross, D. S.; Ball, G. C.; Garrett, P. E.; Triambak, S.; Williams, S. J.; Andreoiu, C.; Churchman, R.; Garnsworthy, A. B.; Hackman, G.; Leslie, J. R.; Orce, J. N.; Sumithrarachchi, C. S.; Svensson, C. E.

    2011-08-01

    The Di-pentagonal Array for Nuclear Timing Experiments (DANTE) is an array of ten BaF2 detectors used in conjunction with the 8π gamma-ray spectrometer at the TRIUMF-ISAC radioactive-ion beam facility. DANTE is used to conduct direct lifetime measurements of nuclear excited states in the picosecond - nanosecond range. This, in turn, will aid in probing the collective structures of deformed nuclei. The capability of DANTE to measure nanosecond-scale lifetimes is demonstrated by using a 152Eu source. The half-life of the Iπ = 21+ state of 152Sm is measured to be 1.426 ± 0.018 ns.

  20. 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.

  1. Orientation epitaxy of Ge1–xSnx films grown on single crystal CaF2 substrates

    DOE PAGES

    A. J. Littlejohn; Zhang, L. H.; Lu, T. -M.; Kisslinger, K.; and Wang, G. -C.

    2016-03-15

    Ge1–xSnx films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal (111) and (100) CaF2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 °C to 400 °C we report temperature-dependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (θ/2θ) scans indicate single orientation Ge1–xSnx(111) films are grown on CaF2(111) substrates at each temperature, while a temperature-dependent superposition of (111) and (100) orientations are exhibited in films grown on CaF2(100) above 250 °C. This is the firstmore » report of (111) oriented Ge1–xSnx grown on a (100) oriented CaF2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. θ/2θ results indicate substitutional Sn alloying in each film of about 5%, corroborated by energy dispersive spectroscopy. In addition, morphological and electrical properties are measured by scanning electron microscopy, atomic force microscopy and Hall mobility measurements and are also shown to be dependent upon growth temperature.« less

  2. Ab-initio Calculations of Electronic Properties of Calcium Fluoride (CaF2)

    NASA Astrophysics Data System (ADS)

    Bohara, Bir; Franklin, Lashounda; Malozovsky, Yuriy; Bagayoko, Diola

    We have performed first principle, local density approximation (LDA) calculations of electronic and related properties of cubic calcium fluorite (CaF2) . Our non-relativistic computations employed the Ceperley and Alder LDA potential and the linear combination of atomic orbitals (LCAO) formalism. The implementation of the LCAO formalism followed the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). We discuss the electronic energy bands, including the large band gap, total and partial density of states, electron and hole effective masses, and the bulk modulus. Our calculated, indirect (X- Γ) band gap is 12.98 eV; it is 1 eV above an experimental value of 11.8 eV. The calculated bulk modulus (82.89 GPA) is excellent agreement with the experimental result of 82.0 +/-0.7. Our predicted equilibrium lattice constant is 5.42Å. Acknowledgments: This work is funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR], and NSF HRD-1002541, the US Department of Energy, National, Nuclear Security Administration (NNSA) (Award No. DE-NA-0002630), LaSPACE, and LONI-SUBR.

  3. Dose response of CaF2:Tm to charged particles of different LET.

    PubMed

    Moyers, M F; Nelson, G A

    2009-08-01

    Thermoluminescent dosimeters are well established for performing calibrations in radiotherapy and for monitoring dose to personnel exposed to low linear energy transfer (LET) ionizing radiation. Patients undergoing light ion therapy and astronauts engaged in space flight are, however, exposed to radiation fields consisting of a mix of low- and high-LET charged particles. In this study, glow curves from CaF2:Tm chips were examined after exposure to various electron and ion beams. The annealing and readout procedures for these chips were optimized for these beams. After a 10 min prereadout annealing at 100 degrees C, the optimized glow curve samples the light output between 95 and 335 degrees C with a heating rate of 2 degrees C/s. The ratio of the integral of the glow curve under peaks 4-6 to the integral under peak 3 was approximately 0.9 for electrons, 1.0 for entrance protons, 1.6 for peak protons, and 2.2 for entrance carbon, silicon, and iron ions. The integral light output per unit dose in water for the iron exposures was about half as much as for the electron exposures. The peak-area-ratio can be used to determine a dose response factor for different LET radiations. PMID:19746804

  4. 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 μm, 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.

  5. Interferometric measurements of thermo-optic coefficients of ZnS, CaF2, and Ge in the infrared

    NASA Astrophysics Data System (ADS)

    Mangin, Jacques; Strimer, Pierre; Schillinger, Marc; Meyzonnette, Jean-Louis P.; Thebault, Jacques; Aymonier, C.

    1996-08-01

    The thermo-optic coefficient (delta) n divided by (delta) T of CaF2, ZnS and Ge single crystals have been measured in the infrared from 20 degrees C to 100 degrees C. The laser interferometric method employed allows a determination of (delta) n divided by (delta) T with an accuracy close to 10-6K-1 in the case of nonabsorbing materials. For Ge the uncertainty is increased by a factor of 3 and is mainly due to its increasing absorption coefficient with temperature. The behavior of ZnS was examined at 1.06 micrometers and 10.6 micrometers laser radiations; CaF2 and Ge were investigated respectively at 1.06 micrometers and 10.6 micrometers.

  6. 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

  7. Structural and optical study of CaF2 nanoparticles produced by a microwave-assisted hydrothermal method

    NASA Astrophysics Data System (ADS)

    Bezerra, Claudiane dos S.; Valerio, Mário E. G.

    2016-11-01

    CaF2 nanoparticles were synthesized by the microwave-assisted hydrothermal method. With the addition of the ethylenediamine (EDA) as chelating agent, the size of the particles was reduced. The CaF2 exhibit single phase identified for X-ray diffraction (XRD) and confirmed by Rietveld refinement. Scanning electron microscopy (SEM) images showed nanoparticles with non-uniform morphology and statistical analysis of collections of particles reviewed that the EDA decreases both the average particle size and average aspect ratio of the particles. The chemical composition of the surface of the particles was investigated by X-ray Photoelectron Spectroscopy (XPS) and the results indicated the presence of reasonable amounts of hydroxyl groups and oxygen ions in the samples produced with EDA. Radioluminescence (RL) measurements showed that both types of nanoparticles presented intrinsic scintillation emission formed by two main bands and that the CaF2 samples produced without EDA presented higher emission intensity. The broad RL band centered at approximately 293 nm is related to self-trapped exciton (STE) emission of calcium fluoride, while the band at 428 nm can be due to the presence of F centers. The STE excitation and optical band gap were measured through photoluminescent excitation spectra in the VUV range.

  8. Swift heavy ion irradiation of CaF2 - from grooves to hillocks in a single ion track

    NASA Astrophysics Data System (ADS)

    Gruber, Elisabeth; Salou, Pierre; Bergen, Lorenz; El Kharrazi, Mourad; Lattouf, Elie; Grygiel, Clara; Wang, Yuyu; Benyagoub, Abdenacer; Levavasseur, Delphine; Rangama, Jimmy; Lebius, Henning; Ban-d'Etat, Brigitte; Schleberger, Marika; Aumayr, Friedrich

    2016-10-01

    A novel form of ion-tracks, namely nanogrooves and hillocks, are observed on CaF2 after irradiation with xenon and lead ions of about 100 MeV kinetic energy. The irradiation is performed under grazing incidence (0.3°-3°) which forces the track to a region in close vicinity to the surface. Atomic force microscopy imaging of the impact sites with high spatial resolution reveals that the surface track consists in fact of three distinct parts: each swift heavy ion impacting on the CaF2 surface first opens a several 100 nm long groove bordered by a series of nanohillocks on both sides. The end of the groove is marked by a huge single hillock and the further penetration of the swift projectile into deeper layers of the target is accompanied by a single protrusion of several 100 nm in length slowly fading until the track vanishes. By comparing experimental data for various impact angles with results of a simulation, based on a three-dimensional version of the two-temperature-model (TTM), we are able to link the crater and hillock formation to sublimation and melting processes of CaF2 due to the local energy deposition by swift heavy ions.

  9. Swift heavy ion irradiation of CaF2 - from grooves to hillocks in a single ion track.

    PubMed

    Gruber, Elisabeth; Salou, Pierre; Bergen, Lorenz; El Kharrazi, Mourad; Lattouf, Elie; Grygiel, Clara; Wang, Yuyu; Benyagoub, Abdenacer; Levavasseur, Delphine; Rangama, Jimmy; Lebius, Henning; Ban-d'Etat, Brigitte; Schleberger, Marika; Aumayr, Friedrich

    2016-10-12

    A novel form of ion-tracks, namely nanogrooves and hillocks, are observed on CaF2 after irradiation with xenon and lead ions of about 100 MeV kinetic energy. The irradiation is performed under grazing incidence (0.3°-3°) which forces the track to a region in close vicinity to the surface. Atomic force microscopy imaging of the impact sites with high spatial resolution reveals that the surface track consists in fact of three distinct parts: each swift heavy ion impacting on the CaF2 surface first opens a several 100 nm long groove bordered by a series of nanohillocks on both sides. The end of the groove is marked by a huge single hillock and the further penetration of the swift projectile into deeper layers of the target is accompanied by a single protrusion of several 100 nm in length slowly fading until the track vanishes. By comparing experimental data for various impact angles with results of a simulation, based on a three-dimensional version of the two-temperature-model (TTM), we are able to link the crater and hillock formation to sublimation and melting processes of CaF2 due to the local energy deposition by swift heavy ions. PMID:27518588

  10. The evaluation of CaF 2:Mn-polyethylene detectors with the aid of the optically stimulated luminescence (OSL)

    NASA Astrophysics Data System (ADS)

    Henniger, Jürgen; Horlbeck, Bernd; Hübner, Klaus; Prokert, Konrad

    1982-12-01

    A serious problem in using TL detectors for neutron dosimetry is their low sensitivity to fast neutrons. Therefore, radiator-detector combinations are employed. But in this case the restricted temperature stability of the radiator material is disadvantageous. This difficulty can be overcome by using the optically stimulated luminescence (OSL). The production of suitable detectors for OSL dosimetry and a convenient evaluation equipment are described. The results given for CaF 2:Mn-polyethylene detectors show that OSL evaluation is useful for dosimetry in mixed neutron gamma fields.

  11. 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.

  12. Influence of some impurities on the emission properties of CaF2:YbF3 crystals

    NASA Astrophysics Data System (ADS)

    Stef, Marius; Nicoara, Irina; Cirlan, Florina; Para, Irina; Velazquez, Matias; Buse, Gabriel

    2015-12-01

    Various concentrations of YbF3 -doped and NaF or PbF2 co-doped CaF2 crystals were grown using the conventional Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum using a shaped graphite furnace. The crystals have been cooled to room temperature using an established procedure. Room temperature absorption spectra have been obtained using a Shimadzu 1650PC spectrophotometer. Photoluminescent properties in IR spectral range were analyzed using a spectrofluorimeter Horiba Fluorolog 3. An IR laser diode at 932 nm was also used an directly injected in the equipment. The emission spectra are influenced by the concentration of co-dopant added to the melt, and the excitation wavelength. The high emission peak at 979 nm overlaps with the absorption peak. The highest intensity in the IR emission (around 1029 nm) is obtained for CaF2:0.72 mol% YbF3 crystal by excitation at 932 nm (diode lamp).

  13. 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.

    2014-01-21

    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.

  14. Deformation of as-cast LiF-22 mol pct CaF2 hypereutectic salt between 500 and 1015 K

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    Results are presented on compression tests conducted on as-cast LiF-22 mol pct CaF2 hypereutectic specimens at nominal strain rates between 1.8 x 10 to the -6th/sec and 0.25/sec over the temperature range 500-1015 K. In all instances, the stress-strain curves showed broad maxima, with negative strain-hardening rates after the peak stress sigma(max). It was found that, at low temperatures and high stresses, the CaF2 lamellae are rigid while the LiF matrix exhibits extensive transgranular cavitation, while at high temperatures and low stresses the CaF2 lamellae break down and spheroidize while the LiF matrix does not cavitate. It was concluded that the mechanical properties of the as-cast hypereutectic LiF-22 mol pct CaF2 are governed by the rate of deformation of the CaF2 phase. It is suggested that, for thermal energy storage applications, a spheroidal microstructure is more desirable than a lamellar structure.

  15. 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 α-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.

  16. Resistance switching memory characteristics of CaF2/Si/CaF2 resonant-tunneling quantum-well heterostructures sandwiched by nanocrystalline Si secondary barrier layers

    NASA Astrophysics Data System (ADS)

    Kuwata, Yuya; Suda, Keita; Watanabe, Masahiro

    2016-07-01

    A novel resistance switching memory using CaF2/Si/CaF2 resonant-tunneling quantum well heterostructures sandwiched by nanocrystalline Si (nc-Si) as secondary barrier layers has been proposed and the room temperature current–voltage characteristics of the basic resistance switching memory operation have been demonstrated. A resistance switching voltage of 1.0 V, a peak current density of approximately 42 kA/cm2, and an ON/OFF ratio of 2.8 were observed. In particular, more than 28000 write-read-erase cyclic memory operations have been demonstrated by applying pulsed input voltage sequences, which suggests better endurance than the device using a CaF2/CdF2/CaF2 heterostructure.

  17. Resistance switching memory characteristics of CaF2/Si/CaF2 resonant-tunneling quantum-well heterostructures sandwiched by nanocrystalline Si secondary barrier layers

    NASA Astrophysics Data System (ADS)

    Kuwata, Yuya; Suda, Keita; Watanabe, Masahiro

    2016-07-01

    A novel resistance switching memory using CaF2/Si/CaF2 resonant-tunneling quantum well heterostructures sandwiched by nanocrystalline Si (nc-Si) as secondary barrier layers has been proposed and the room temperature current-voltage characteristics of the basic resistance switching memory operation have been demonstrated. A resistance switching voltage of 1.0 V, a peak current density of approximately 42 kA/cm2, and an ON/OFF ratio of 2.8 were observed. In particular, more than 28000 write-read-erase cyclic memory operations have been demonstrated by applying pulsed input voltage sequences, which suggests better endurance than the device using a CaF2/CdF2/CaF2 heterostructure.

  18. CO2 laser irradiation enhances CaF2 formation and inhibits lesion progression on demineralized dental enamel-in vitro study.

    PubMed

    Zancopé, Bruna R; Rodrigues, Lívia P; Parisotto, Thais M; Steiner-Oliveira, Carolina; Rodrigues, Lidiany K A; Nobre-dos-Santos, Marinês

    2016-04-01

    This study evaluated if Carbon dioxide (CO2) (λ 10.6 μm) laser irradiation combined with acidulated phosphate fluoride gel application (APF gel) enhances "CaF2" uptake by demineralized enamel specimens (DES) and inhibits enamel lesion progression. Thus, two studies were conducted and DES were subjected to APF gel combined or not with CO2 laser irradiation (11.3 or 20.0 J/cm(2), 0.4 or 0.7 W) performed before, during, or after APF gel application. In study 1, 165 DES were allocated to 11 groups. Fluoride as "CaF2 like material" formed on enamel was determined in 100 DES (n = 10/group), and the surface morphologies of 50 specimens were evaluated by scanning electron microscopy (SEM) before and after "CaF2" extraction. In study 2, 165 DES (11 groups, n = 15), subjected to the same treatments as in study 1, were further subjected to a pH-cycling model to simulate a high cariogenic challenge. The progression of demineralization in DES was evaluated by cross-sectional microhardness and polarized light microscopy analyses. Laser at 11.3 J/cm(2) applied during APF gel application increased "CaF2" uptake on enamel surface. Laser irradiation and APF gel alone arrested the lesion progression compared with the control (p < 0.05). Areas of melting, fusion, and cracks were observed. CO2 laser irradiation, combined with a single APF application enhanced "CaF2" uptake on enamel surface and a synergistic effect was found. However, regarding the inhibition of caries lesion progression, no synergistic effect could be demonstrated. In conclusion, the results have shown that irradiation with specific laser parameters significantly enhanced CaF2 uptake by demineralized enamel and inhibited lesion progression.

  19. In vitro degradation, cytocompatibility and hemolysis tests of CaF2 doped TiO2-SiO2 composite coating on AZ31 alloy

    NASA Astrophysics Data System (ADS)

    Li, Bing; Chen, Yun; Huang, Wei; Yang, Wenzhong; Yin, Xiaoshuang; Liu, Ying

    2016-09-01

    In this study, a CaF2 doped TiO2-SiO2 composite coating was successfully coated onto AZ31 alloy by sol-gel method. Electrochemical tests, in vitro degradation, direct cellular experiment and hemolysis tests were conducted and the results showed that the CaF2 doped TiO2-SiO2 composite coating can not only improve the corrosion resistance, but also enhance the biocompatibility of AZ31 alloy. XRD, SEM and EDX were also performed to characterize the crystalline structures, morphologies and chemical compositions of the coatings.

  20. The role of two-step excitation processes in laser cooling experiments: CaF2:Eu2+

    NASA Astrophysics Data System (ADS)

    Feofilov, S. P.; Kulinkin, A. B.; Konyushkin, V. A.; Nakladov, A. N.

    2016-10-01

    The fluorescence of CaF2 single-crystals containing Eu2+ ions was studied under the excitation in the long-wavelength tail of the absorption spectrum which is due to electric dipole allowed transitions ("laser cooling regime"). Though no actual cooling was detected, spectra with a dominant anti-Stokes component were observed which demonstrate the possibility to employ electron-phonon bands of Eu2+ f-d transitions for optical refrigeration. The absence of observable optical refrigeration is ascribed to Eu2+ two-step photoionization processes that are responsible for the excited state absorption. The role of two-step excitation of impurity centers (excited state absorption) in laser cooling experiments is discussed.

  1. 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.

  2. Effect of cryogenic temperature on spectroscopic and laser properties of Er,La:SrF2-CaF2 crystal

    NASA Astrophysics Data System (ADS)

    Švejkar, Richard; Šulc, Jan; Němec, Michal; Jelínková, Helena; Doroshenko, Maxim E.; Nakladov, Andrei N.; Osiko, Vjatcheslav V.

    2016-03-01

    The laser and spectroscopic properties of crystal Er,La:SrF2-CaF2 at temperature range 80 - 300 K, which is appropriate for generation of radiation around 2.7 um is presented. The sample of Er,La:SrF2-CaF2 (concentration Er(0.04), La(0.12):Ca(0.77)Sr(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:SrF2-CaF2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:SrF2-CaF2 together with the fluorescence decay time were measured in dependence on temperature. The excitation of Er,La:SrF2-CaF2 was carried out by a laser diode radiation (pulse duration 5 ms, repetition rate 20 Hz, pump wavelength 973 nm). Laser resonator was hemispherical, 140 mm in length with at pumping mirror (HR @ 2.7 µm) and spherical output coupler (r = 150 mm, R = 95 % @ 2.5 - 2.8 µm). Tunability of laser at 80 K in range 2690 - 2765 nm was obtained using MgF2 birefringent filter. With decreasing temperature of sample the fluorescence lifetime of manifold 4I11/2 (upper laser level) became shorter and intensity of up-conversion radiation was increasing. The highest slope efficiency with respect to absorbed power was 2.3 % at 80 K. The maximum output of peak amplitude power was 0.3 W at 80 K, i.e. 1.5 times higher than measured this value at 300 K. The wavelength generated by Er,La:SrF2-CaF2 laser (2.7 µm) is relatively close to absorption peak of water (3 µm) and so, one of the possible usage should be in medicine and spectroscopy.

  3. 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

    2014-07-18

    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.

  4. 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.

  5. A viscoplastic model with application to LiF-22 percent CaF2 hypereutectic salt

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Walker, K. P.

    1990-01-01

    A viscoplastic model for class M (metal-like behavior) materials is presented. One novel feature is its use of internal variables to change the stress exponent of creep (where n is approximately = 5) to that of natural creep (where n = 3), in accordance with experimental observations. Another feature is the introduction of a coupling in the evolution equations of the kinematic and isotropic internal variables, making thermal recovery of the kinematic variable implicit. These features enable the viscoplastic model to reduce to that of steady-state creep in closed form. In addition, the hardening parameters associated with the two internal state variables (one scalar-valued, the other tensor-valued) are considered to be functions of state, instead of being taken as constant-valued. This feature enables each internal variable to represent a much wider spectrum of internal states for the material. The model is applied to a LiF-22 percent CaF2 hypereutectic salt, which is being considered as a thermal energy storage material for space-based solar dynamic power systems.

  6. Laser performance of diode-pumped Nd, Y-codoped CaF 2-SrF 2 mixed crystal

    NASA Astrophysics Data System (ADS)

    Liu, J.; Fan, M. W.; Su, L. B.; Jiang, D. P.; Ma, F. K.; Zhang, Q.; Xu, J.

    2014-03-01

    A disordered Nd, Y-codoped CaF2-SrF2 mixed crystal was obtained by the temperature gradient technique (TGT). The absorption and fluorescence spectra of the crystal were measured at room temperature. Diode-pumped continuous-wave (CW) and Q-switched laser operations were demonstrated at 1056 nm with a 0.65 at.% Nd, 10 at.% Y-codoped crystal, for the first time to our knowledge. The CW output power of 724 mW was obtained in a compact linear cavity. Also the Q-switched pulse characteristics of Nd, Y:CaF2-SrF2 laser crystal were reported based on Cr4+:YAG saturable absorbers in a folded cavity. The shortest pulse width of 110 ns and the highest peak power of 383 W were obtained when the initial transmission of the Cr4+:YAG crystals was 90%. The dependence of the operational parameters on the pump power was also investigated experimentally.

  7. Void lattice formation in electron irradiated CaF2: Statistical analysis of experimental data and cellular automata simulations

    NASA Astrophysics Data System (ADS)

    Zvejnieks, G.; Merzlyakov, P.; Kuzovkov, V. N.; Kotomin, E. A.

    2016-02-01

    Calcium fluoride (CaF2) is an important optical material widely used in both microlithography and deep UV windows. It is known that under certain conditions electron beam irradiation can create therein a superlattice consisting of vacancy clusters (called a void lattice). The goal of this paper is twofold. Firstly, to perform a quantitative analysis of experimental TEM images demonstrating void lattice formation, we developed two distinct image filters. As a result, we can easily calculate vacancy concentration, vacancy cluster distribution function as well as average distances between defect clusters. The results for two suggested filters are similar and demonstrate that experimental void cluster growth is accompanied by a slight increase of the void lattice constant. Secondly, we proposed a microscopic model that allows us to reproduce a macroscopic void ordering, in agreement with experimental data, and to resolve existing theoretical and experimental contradictions. Our computer simulations demonstrate that macroscopic void lattice self-organization can occur only in a narrow parameter range. Moreover, we studied the kinetics of a void lattice ordering, starting from an initial disordered stage, in a good agreement with the TEM experimental data.

  8. 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

  9. The effect of CaF2 on thermodynamics of CaO-CaF2-SiO2(-MgO) slags

    NASA Astrophysics Data System (ADS)

    Choi, Chul-Hwan; Jo, Sung-Koo; Kim, Seon-Hyo; Lee, Kwang-Ro; Kim, Jeong-Tae

    2004-02-01

    To address the role of CaF2 in the CaO-CaF2-SiO2(-MgO) slag system employed for the production of low-pressure rotor steels, the thermodynamic aspects of the slag were investigated by equilibrating it with liquid iron at 1873 K in CaO or MgO crucibles. Presaturation of slag with an oxide block piece of CaO or MgO in a Pt crucible and application of a carbon paste to the outside of an oxide crucible were designed to prevent crucible failure during the slag-metal experiments. The liquidus isotherm and phase boundary of the preceding slag system were investigated using the slag-metal equilibria. Also, the effect of CaF2 on the sulfide capacity and the activity coefficient of Fe t O were of particular interest in controlling the sulfur level and cleanliness of low-pressure rotor steels.

  10. Enhanced upconversion emission in crystallization-controllable glass-ceramic fiber containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals.

    PubMed

    Peng, Wencai; Fang, Zaijin; Ma, Zhijun; Qiu, Jianrong

    2016-10-01

    Functional nanocrystal-containing materials have been a hot topic in recent years. However, few researches have focused on functional nanocrystals contained in optical glass fibers. In this research, transparent CaF2 glass-ceramic was prepared by a melt-quenching method. Greatly enhanced upconversion luminescence was observed after heat treatment. By applying a novel method called melt-in-tube, precursor fiber free of crystals was fabricated at the drawing temperature where the clad was softened while the core was melted. Glass-ceramic fiber with fiber core containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals was obtained after heat treatment at a relatively low temperature. Electron probe micro-analyzer measurement shows no obvious element diffusion between the core and clad. Greatly enhanced upconversion emission was detected in the glass-ceramic fiber excited by a 980 nm laser, suggesting the developed glass-ceramic fiber is a promising material for upconversion laser. PMID:27576586

  11. Fast and thermal neutron response of BeO and Li 2B 4O 7: Mn in comparison with LiF and CaF 2

    NASA Astrophysics Data System (ADS)

    Henaish, B. A.; Sayed, A. M.; Morsy, S. M.

    1980-12-01

    The thermal and fast neutron response of BeO (four types) and Li 2B 4O 7: Mn, in comparison with that of LiF (TLD 100 and TLD-700) and CaF 2: Mn, has been investigated. For fast neutrons, the response of all the investigated phosphors was found to be negligible compared with their γ-response. For thermal neutrons, the four types of BeO as well as CaF 2: Mn showed a very poor response, below that of TLD-700, while Li 2B 4O 7: Mn gave a resp onse similar to that of TLD-100 and was nearly 1500 times that of BeO.

  12. Enhanced upconversion emission in crystallization-controllable glass-ceramic fiber containing Yb3+-Er3+ codoped CaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Peng, Wencai; Fang, Zaijin; Ma, Zhijun; Qiu, Jianrong

    2016-10-01

    Functional nanocrystal-containing materials have been a hot topic in recent years. However, few researches have focused on functional nanocrystals contained in optical glass fibers. In this research, transparent CaF2 glass-ceramic was prepared by a melt-quenching method. Greatly enhanced upconversion luminescence was observed after heat treatment. By applying a novel method called melt-in-tube, precursor fiber free of crystals was fabricated at the drawing temperature where the clad was softened while the core was melted. Glass-ceramic fiber with fiber core containing Yb3+-Er3+ codoped CaF2 nanocrystals was obtained after heat treatment at a relatively low temperature. Electron probe micro-analyzer measurement shows no obvious element diffusion between the core and clad. Greatly enhanced upconversion emission was detected in the glass-ceramic fiber excited by a 980 nm laser, suggesting the developed glass-ceramic fiber is a promising material for upconversion laser.

  13. Enhanced upconversion emission in crystallization-controllable glass-ceramic fiber containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals.

    PubMed

    Peng, Wencai; Fang, Zaijin; Ma, Zhijun; Qiu, Jianrong

    2016-10-01

    Functional nanocrystal-containing materials have been a hot topic in recent years. However, few researches have focused on functional nanocrystals contained in optical glass fibers. In this research, transparent CaF2 glass-ceramic was prepared by a melt-quenching method. Greatly enhanced upconversion luminescence was observed after heat treatment. By applying a novel method called melt-in-tube, precursor fiber free of crystals was fabricated at the drawing temperature where the clad was softened while the core was melted. Glass-ceramic fiber with fiber core containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals was obtained after heat treatment at a relatively low temperature. Electron probe micro-analyzer measurement shows no obvious element diffusion between the core and clad. Greatly enhanced upconversion emission was detected in the glass-ceramic fiber excited by a 980 nm laser, suggesting the developed glass-ceramic fiber is a promising material for upconversion laser.

  14. 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 μm-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.

  15. Formation and investigation of ultrathin layers of Co2FeSi ferromagnetic alloy synthesized on silicon covered with a CaF2 barrier layer

    NASA Astrophysics Data System (ADS)

    Grebenyuk, G. S.; Gomoyunova, M. V.; Pronin, I. I.; Vyalikh, D. V.; Molodtsov, S. L.

    2016-03-01

    Ultrathin (∼2 nm) films of Co2FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ. Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3p and Co 3p electrons. The study shows that the synthesis of the Co2FeSi ferromagnetic alloy occurs in the temperature range of 200-400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

  16. 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.

  17. 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.

  18. DANCE (Detector for Advanced Neutron Capture Experiments) is a 4π 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 4π 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,γ) 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,γ) experiments. The ^157Gd(n,γ) 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,γ) cascades and DANCE pulse height function were made using DICEBOX and GEANT4 codes and simulated Esum and Eγ spectra are compared to the experimental DANCE data. Values of spin and photon strength function (PSF) of the ^157Gd(n,γ) resonances are provided in the range of En = 2 -- 300 eV using spin dependence upon a γ-ray multiplicity.

  19. Preparation and Electrochemical Characterization of Aluminium Liquid Battery Cells With Two Different Electrolytes (NaCl-BaCl2-AlF3-NaF and LiF-AlF3-BaF2).

    PubMed

    Napast, Viktor; Moškon, Jože; Homšak, Marko; Petek, Aljana; Gaberšček, Miran

    2015-01-01

    The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: Pb, Bi and Sn. Two types of electrolytes were selected: Na(3)AlF(6) -AlF(3) - BaCl(2) - NaCl and Li(3)AlF(3) - BaF(2). We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of Al-Pb system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode. PMID:26680707

  20. Preparation and Electrochemical Characterization of Aluminium Liquid Battery Cells With Two Different Electrolytes (NaCl-BaCl2-AlF3-NaF and LiF-AlF3-BaF2).

    PubMed

    Napast, Viktor; Moškon, Jože; Homšak, Marko; Petek, Aljana; Gaberšček, Miran

    2015-01-01

    The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: Pb, Bi and Sn. Two types of electrolytes were selected: Na(3)AlF(6) -AlF(3) - BaCl(2) - NaCl and Li(3)AlF(3) - BaF(2). We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of Al-Pb system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode.

  1. 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.

  2. 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.

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

    PubMed

    Barandiarán, Zoila; Seijo, Luis

    2015-10-14

    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 4f(N-1)5d excited states of Y b(2+): these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b(2+) + Ca(2+) (Sr(2+)) → Y b(3+) + Ca(+) (Sr(+)) electron phototransfer. This mechanism applies to all the observed Y b(2+) 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b(2+) because the Y b(3+)-Ca(+) states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b(2+) 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 b(2+) 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. PMID:26472390

  4. Al15Ge4Ni3: A new intergrowth structure with Cu3Au- and CaF2-type building blocks

    NASA Astrophysics Data System (ADS)

    Reichmann, Thomas L.; Jandl, Isabella; Effenberger, Herta S.; Herzig, Peter; Richter, Klaus W.

    2015-05-01

    The new ternary compound Al15Ge4Ni3 (τ2 in the system Al-Ge-Ni) was synthesized in single crystalline form by a special annealing procedure from samples located in the three phase fields [L+Al+τ2] and [L+Ge+τ2]. The crystal structure of Al15Ge4Ni3 was determined by single-crystal X-ray diffraction. The compound crystallizes in a new structure type in space group I4¯3m, Pearson Symbol cI88, cubic lattice parameter a=11.405(1) Å. Phase diagram investigations indicate stoichiometric composition without considerable homogeneity range; τ2 melts peritectically at T=444 °C. The crystal structure of Al15Ge4Ni3 shows a unique combination of simple Cu3Au- and CaF2-type building blocks: a three dimensional network of CaF2-type units, formed by Ni and Al atoms, is interspaced by clusters (Al6Ge8) resembling unit cells of the Cu3Au-type. Both structural motifs are connected by Al-Ge bonds. The ground state energy of the compound was obtained by DFT calculations and the densities of states were analyzed in detail. In addition, electron density maps were calculated in four different sections through the unit cell using the full potential linearized augmented plane-wave (FLAPW) method. The bonding situation in Al15Ge4Ni3 was discussed combining results from electronic calculations with the analysis of the coordination of atoms.

  5. 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

  6. The effects of pre-irradiation heat treatment and heating rate on the thermoluminescence glow peaks of natural CaF2

    NASA Astrophysics Data System (ADS)

    Yüksel, Mehmet; Topaksu, Mustafa; Necmeddin Yazici, A.; Yeǧingil, Zehra; Doǧan, Tamer

    2010-05-01

    In this article, we have investigated the effects of pre-irradiation heat treatments on the thermoluminescence (TL) glow peaks of natural fluorite (CaF2) collected from the central Anatolia region of Turkey. A typical TL glow curve of phosphor consists of four clear glow peaks with maximum intensities occurring at temperatures around 100 °C, 120 °C, 190 °C and 290 °C for a sample irradiated to a dose of 48 Gy and readout at a heating rate of 1 °C/s. It was observed that the intensities of all the TL glow peaks are strongly sensitive to annealing temperatures and durations. Annealing at 450 °C for 15 min was found to be the best for reproducibility of experimental results. The dose-responses of individual TL peaks of this material were also examined after annealing at 450 °C for 15 min by β-irradiation to doses between 0.04 Gy and ≈10.4 kGy. It was observed that the total area and peak heights of all glow peaks showed similar trends with increasing radiation dose; first, they increased linearly up to ≈50 Gy and then saturation effects began above this dose value. The effect of heating rate on the TL glow peaks of the mineral was also studied and it was observed that the intensities of glow peaks are differently affected with variation in heating rate.

  7. Trace element analysis of synthetic mono- and poly-crystalline CaF 2 by ultraviolet laser ablation inductively coupled plasma mass spectrometry at 266 and 193 nm

    NASA Astrophysics Data System (ADS)

    Koch, J.; Feldmann, I.; Hattendorf, B.; Günther, D.; Engel, U.; Jakubowski, N.; Bolshov, M.; Niemax, K.; Hergenröder, R.

    2002-06-01

    The analytical figures of merit for ultraviolet laser ablation-inductively coupled plasma mass spectrometry (UV-LA-ICP-MS) at 266 nm with respect to the trace element analysis of high-purity, UV-transmitting alkaline earth halides are investigated and discussed. Ablation threshold energy density values and ablation rates for mono- and poly-crystalline CaF 2 samples were determined. Furthermore, Pb-, Rb-, Sr-, Ba- and Yb-specific analysis was performed. For these purposes, a pulsed Nd:YAG laser operated at the fourth harmonic of the fundamental wavelength (λ=266 nm) and a double-focusing sector field ICP-MS detector were employed. Depending on the background noise and isotope-specific sensitivity, the detection limits typically varied from 0.7 ng/g for Sr to 7 ng/g in the case of Pb. The concentrations were determined using a glass standard reference material (SRM NIST612). In order to demonstrate the sensitivity of the arrangement described, comparative measurements by means of a commercial ablation system consisting of an ArF excimer laser (λ=193 nm) and a quadrupole-type ICP-MS (ICP-QMS) instrument were carried out. The accuracy of both analyses was in good agreement, whereas ablation at 266 nm and detection using sector-field ICP-MS led to a sensitivity that was one order of magnitude above that obtained at 193 nm with ICP-QMS.

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

    DOE PAGES

    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 » 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.« less

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

    SciTech Connect

    Ochoa, Franklyn E. Colmenares

    2006-12-04

    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.

  10. Ab initio multiconfiguration self-consistent-field calculations of the excited states of a Mn impurity in CaF2

    NASA Astrophysics Data System (ADS)

    Lewandowski, A. C.; Wilson, T. M.

    1994-08-01

    We analyze Mn absorption in CaF2:Mn by the employment of ab inito quantum-mechanical cluster calculations and ligand-field methods. The [MnF8]6- Oh cluster is chosen to represent the isolated Mn2+ substitutional impurity in an otherwise perfect crystal. The methods of unrestricted open-shell Hartree-Fock self-consistent field (SCF), Mo/ller-Plesset perturbation theory to second- and fourth-order, and singles and doubles configuration interaction are used to calculate the spin sextet and quartet ground states. With the active space consisting of the Mn 3d molecular orbitals, the spin quartet excited states are calculated by the method of multiconfiguration SCF. It was found that the presence of an external field designed to reproduce the Madelung potential difference within the cluster did not significantly affect the Mn d-to-d transitions. The crystal-field term splitting diagrams for the eight-coordinated Mn2+ impurity in Oh symmetry are calculated. The results showed a narrowing of the multiplet terms in energy with respect to the six-coordinated Oh result. This increases the crystal-field parameter Dq from the previously published value of 420-570 cm-1.

  11. Capillary and van der Waals interactions on CaF2 crystals from amplitude modulation AFM force reconstruction profiles under ambient conditions.

    PubMed

    Calò, Annalisa; Robles, Oriol Vidal; Santos, Sergio; Verdaguer, Albert

    2015-01-01

    There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.5-1 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 3-4 nm above the surface when the formation of a capillary neck dominates the tip-sample interaction.

  12. Fluoride evaporation and crystallization behavior of CaF2-CaO-Al2O3-(TiO2) slag for electroslag remelting of Ti-containing steels

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-bin; Cho, Jung-wook; Zheng, Ding-li; Li, Jing

    2016-06-01

    To elucidate the behavior of slag films in an electroslag remelting process, the fluoride evaporation and crystallization of CaF2-CaO-Al2O3-(TiO2) slags were studied using the single hot thermocouple technique. The crystallization mechanism of TiO2-bearing slag was identified based on kinetic analysis. The fluoride evaporation and incubation time of crystallization in TiO2-free slag are found to considerably decrease with decreasing isothermal temperature down to 1503 K. Fish-bone and flower-like CaO crystals precipitate in TiO2-free slag melt, which is accompanied by CaF2 evaporation from slag melt above 1503 K. Below 1503 K, only near-spherical CaF2 crystals form with an incubation time of less than 1 s, and the crystallization is completed within 1 s. The addition of 8.1wt% TiO2 largely prevents the fluoride evaporation from slag melt and promotes the slag crystallization. TiO2 addition leads to the precipitation of needle-like perovskite (CaTiO3) crystals instead of CaO crystals in the slag. The crystallization of perovskite (CaTiO3) occurs by bulk nucleation and diffusion-controlled one-dimensional growth.

  13. Capillary and van der Waals interactions on CaF2 crystals from amplitude modulation AFM force reconstruction profiles under ambient conditions

    PubMed Central

    Calò, Annalisa; Robles, Oriol Vidal; Santos, Sergio

    2015-01-01

    Summary There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.5–1 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 3–4 nm above the surface when the formation of a capillary neck dominates the tip–sample interaction. PMID:25977852

  14. Preliminary Experiments and Determination of the Thermal Gradient in a 12.7 mm CaF2 Furnace Assembly, Humboldt State University Piston-Cylinder Laboratory

    NASA Astrophysics Data System (ADS)

    Schwab, B. E.

    2004-12-01

    A 12.7 mm piston-cylinder laboratory has been established at Humboldt State University. A series of double-thermocouple (DTC) experiments were performed to measure the thermal profile of the furnace assembly following the procedures of Pickering et al. (1998, Amer. Min.). Furnace assemblies consist of a 304 stainless base plug, CaF&_{2} sleeve, straight-walled graphite heater tube, crushable MgO inner parts, and lower graphite plug and ring which allow for extrusion of the graphite heater tube during shortening of the sleeve and MgO pieces. Careful measurement of pre- and post-run assembly parts indicate an average 30-35% shortening of the assembly. DTC results show a thermal peak that is displaced \\sim2.0 mm above the center of the effective furnace, defined as the length of inner MgO pieces post-run. This offset is in the same direction (upward, toward base plug), but slightly less than the offset described by Pickering et al. (1998). A secondary measure of the thermal profile using spinel growth via reaction between MgO and Al_{2}O_{3} assembly parts (e.g., Watson et al., 2002, CMP) is underway. A single partial melting experiment was performed at 1.0 GPa and 1330\\degC for 72 hours using intermediate peridotite starting material INT-A in a graphite-lined Pt capsule with vitreous carbon spheres as a melt sink. Phase compositions were determined by electron microprobe and mass balance calculations were made to determine melt fraction and mineral mode. Initial calculations yield glass:olivine:cpx:opx:spinel proportions of: 5.0:54.2:15.9:23.9:1.1. These preliminary results correspond well with previous work performed at the University of Oregon on the same starting material (Schwab and Johnston, 2001). The best match is with a 1315\\degC experiment (INT-A13) in terms of mode (6.9:53.7:13.4:25.0:1.0) and glass composition, indicating that the temperature of this initial experiment may be slightly cooler than the target temperature, however the results of this interlaboratory comparison are still within the \\pm10-15\\deg$C temperature uncertainty of the piston cylinder apparatus. Additional calibration experiments are ongoing.

  15. The optically stimulated luminescence (OSL) properties of LiF:Mg,TI, Li2B4O7:CU, CaSO4:Tm, and CaF2:MN thermoluminescent (TL) materials.

    PubMed

    Kearfott, Kimberlee J; Geoffrey West, William; Rafique, Muhammad

    2015-05-01

    This paper reports on an investigation into the optically stimulated luminescence (OSL) properties of several known thermoluminescent materials, namely LiF:Mg,Ti, Li2B4O7:Cu, CaSO4:Tm, and CaF2:Mn. Samples were irradiated to air doses of 15mGy, 150mGy and 1.5Gy and analyzed using a commercially available OSL reader system to determine their luminescence response to continuous blue and infrared light (IR) excitation, centered at 470nm and 830nm wavelengths, respectively. CaF2:Mn did not show an OSL response with either IR or blue light stimulation. Li2B4O7:Cu and LiF:Mg,Ti demonstrated relatively weak OSL signals only under blue light excitation. CaSO4:Tm exhibited OSL under both IR and blue light stimulation at sensitivities roughly one order of magnitude less than the OSL response of α-Al2O3:C under the same conditions. PMID:25769010

  16. 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 μm, 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 μm 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.

  17. Cross sections for He and Ne isotopes in natural Mg, Al, and Si, He isotopes in CaF2, Ar isotopes in natural Ca, and radionuclides in natural Al, Si, Ti, Cr, and stainless steel induced by 12- to 45-MeV protons

    NASA Technical Reports Server (NTRS)

    Walton, J. R.; Heymann, D.; Yaniv, A.; Edgerley, D.; Rowe, M. W.

    1976-01-01

    Stacks of thin Mg, Al, Si, Ca, CaF2, Ti, and stainless steel foils were bombarded in twelve irradiations by a variable energy cyclotron. Cross sections are reported for He and Ne in natural Mg, Al, and Si, and for He in CaF2, and for Ar in natural Ca, as determined from mass spectrometer analysis of the inert gases. In addition, cross sections of Na-22 in natural Al and Si, of V-48 in natural Ti, and of Cr-51, Mn-52, and Co-57 in stainless steel are reported. From these were deduced Cr-51 and Mn-52 cross sections in natural Cr.

  18. Annealing of electron damage in mid-IR transmitting fluoride glass

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Doremus, Robert H.

    1986-01-01

    Damage in ZrF4-BaF2-LaF3 glass induced by high-energy electrons was studied by ESR and optical spectroscopy. An optical absorption band at 314 nm in the irradiated glass annealed rapidly above about 50 C, probably by a second-order reaction at room temperature; the ESR lines annealed very slowly at room temperature.

  19. SiO2 and CaF2 Behavior During Shielded Metal Arc Welding and Their Effect on Slag Detachability of the CaO-CaF2-SiO2 Type ENiCrFe-7-Covered Electrode

    NASA Astrophysics Data System (ADS)

    Wang, Huang; Qin, Renyao; He, Guo

    2016-09-01

    The metallurgical behavior during shielded metal arc welding (SMAW) and the slag detachability of the CaO-CaF2-SiO2 type ENiCrFe-7-covered electrodes was investigated. The results indicated that the slag detachability could be improved as the SiO2 in the flux coatings decreased. When the SiO2 in the flux coating was 10.9 pct, about 28.3 pct CaF2 resulted in the best slag detachability. The CaF2 and SiO2 in the flux coating interacted during SMAW to form gaseous SiF4 to be evacuated. In the reactions, one SiO2 consumed two CaF2, leading to the reduction of the ratio of CaF2/SiO2. After comparing the slag compositions, the best slag detachability was obtained at CaO:CaF2:SiO2 = 1.7:1.8:1, but the worst slag detachability appeared at CaO:CaF2:SiO2 = 1.3:0.9:1. The XRD analysis revealed that the oxides and fluorides in the slags preferred to gather together to form cuspidine and other complex phases. If the CaF2 was dominant in the slags, they intended to form homogenous porous microstructures that were relatively strong and would most likely detach from the weld metal in blocks, exhibiting good slag detachability. If the cuspidine phase was dominant, the slags exhibited a `rock strata'-like microstructure in the intergranular area. Such microstructure was very fragile and could be broken into fine powders that were easily embedded in the weld ripples, leading to slag adhesions. This work provides the researcher with a wealth of information and data, which will also be beneficial to the welding material producers and users.

  20. The impact of shell host (NaYF4/CaF2) and shell deposition methods on the up-conversion enhancement in Tb3+, Yb3+ codoped colloidal α-NaYF4 core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Prorok, Katarzyna; Bednarkiewicz, Artur; Cichy, Bartlomiej; Gnach, Anna; Misiak, Malgorzata; Sobczyk, Marcin; Strek, Wieslaw

    2014-01-01

    Lanthanide doped, up-converting nanoparticles have found considerable interest as luminescent probes in the field of bio-detection. Although the nanoparticles (NPs) have already been successfully applied for fluorescent bio-imaging and bio-assays, the efficiency of the up-conversion process seems to be the bottle-neck in rigorous applications. In this work, we have shown enhancement of the up-conversion in colloidal α-NaYF4:Yb3+, Tb3+ doped nanocrystals owing to passivation of their surface. We have studied quantitatively the influence of the shell type (NaYF4 and CaF2), its thickness, as well as the shell deposition method (i.e. single thick shell vs. multi-layer shell) on the luminescent properties of the nanoparticles. The results showed that up to 40-fold up-conversion intensity enhancement may be obtained for the core-shell nanoparticles in comparison with the bare core nanoparticles, irrespective of the shell type and deposition method. Moreover, the suitability of the NaYF4:Yb3+, Tb3+ core-shell NPs for multi-color emission and spectral multiplexing has been presented.Lanthanide doped, up-converting nanoparticles have found considerable interest as luminescent probes in the field of bio-detection. Although the nanoparticles (NPs) have already been successfully applied for fluorescent bio-imaging and bio-assays, the efficiency of the up-conversion process seems to be the bottle-neck in rigorous applications. In this work, we have shown enhancement of the up-conversion in colloidal α-NaYF4:Yb3+, Tb3+ doped nanocrystals owing to passivation of their surface. We have studied quantitatively the influence of the shell type (NaYF4 and CaF2), its thickness, as well as the shell deposition method (i.e. single thick shell vs. multi-layer shell) on the luminescent properties of the nanoparticles. The results showed that up to 40-fold up-conversion intensity enhancement may be obtained for the core-shell nanoparticles in comparison with the bare core nanoparticles, irrespective of the shell type and deposition method. Moreover, the suitability of the NaYF4:Yb3+, Tb3+ core-shell NPs for multi-color emission and spectral multiplexing has been presented. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05412h

  1. 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.

  2. Scattering Effect of Iron Metallic Particles on the Extinction Coefficient of CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 Glasses

    NASA Astrophysics Data System (ADS)

    Yoon, Dae-Woo; Cho, Jung-Wook; Kim, Seon-Hyo

    2016-08-01

    The extinction coefficient of the CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 glasses has been studied using a FT-IR and a UV-visible spectrometer in the range of 0.5-5 μm to investigate thermal radiation through glassy flux film during continuous casting of steels. In present investigations, iron oxide has been reduced to metallic iron droplets by reaction with graphite crucible during melting, which brings considerable increase of the extinction coefficient due to the scattering. To analyze the scattering effect of these droplets on the extinction coefficient, the number density and size parameter of metallic particles have been measured using an automated scanning electron microscope. The number of metallic particles is intensively proportional to boron contents due to the transition of molar structure, BO4 to BO3, with increasing boron oxide. It is found that calculated scattering coefficients based on Mie scattering theory are in good agreement with measured ones. As the increased scattering coefficient of glassy film would not cause any serious side effects on casting operations, utilization of scattering effects is believed to be significantly essential for the future design of commercial mold fluxes.

  3. Scattering Effect of Iron Metallic Particles on the Extinction Coefficient of CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 Glasses

    NASA Astrophysics Data System (ADS)

    Yoon, Dae-Woo; Cho, Jung-Wook; Kim, Seon-Hyo

    2016-10-01

    The extinction coefficient of the CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 glasses has been studied using a FT-IR and a UV-visible spectrometer in the range of 0.5-5 μm to investigate thermal radiation through glassy flux film during continuous casting of steels. In present investigations, iron oxide has been reduced to metallic iron droplets by reaction with graphite crucible during melting, which brings considerable increase of the extinction coefficient due to the scattering. To analyze the scattering effect of these droplets on the extinction coefficient, the number density and size parameter of metallic particles have been measured using an automated scanning electron microscope. The number of metallic particles is intensively proportional to boron contents due to the transition of molar structure, BO4 to BO3, with increasing boron oxide. It is found that calculated scattering coefficients based on Mie scattering theory are in good agreement with measured ones. As the increased scattering coefficient of glassy film would not cause any serious side effects on casting operations, utilization of scattering effects is believed to be significantly essential for the future design of commercial mold fluxes.

  4. Role of nickel ion coordination on spectroscopic properties of multi-component CaF2-Bi2O3-P2O5-B2O3 glass-ceramics

    NASA Astrophysics Data System (ADS)

    Suresh, S.; Narendrudu, T.; Kumar, A. Suneel; Rao, M. V. Sambasiva; Ram, G. Chinna; Rao, D. Krishna

    2016-10-01

    Multi-component CaF2-Bi2O3-P2O5-B2O3 glasses doped with different concentrations of NiO 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), differential thermal analysis (DTA) as well as conventional spectroscopic studies viz., optical absorption, Fourier transform infrared (FTIR) and Raman. The XRD and SEM studies have indicated that the samples contain well defined and randomly distributed grains of different crystalline phases. The optical absorption studies together with FTIR and Raman measurements indicated the gradual transformation of nickel ions from tetrahedral sites to octahedral sites (lasing sites) as the concentration of NiO is increased beyond 1.5 mol%. All these investigations have indicated that the growing degree of disorder in the glass ceramic network at higher concentrations of NiO. Glass ceramics doped with NiO beyond 1.5 mol% appear to be suitable for getting laser emission due to 3T2(F) → 3A2(F) transition in NIR region. These glass-ceramics can be expected as an amplification medium for tunable lasers and broadband optical amplifiers for wavelength division multiplexing transmission system.

  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 β-CaSiO(3). (β-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 β-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.

  6. 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 β-CaSiO3 (β-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.

  7. 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.

  8. 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-filling the PAMA interiorly through photo-initiated polymerization. The UCHNs showed orange fluorescence 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.

  9. 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.

  10. 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-filling the PAMA interiorly through photo-initiated polymerization. The UCHNs showed orange fluorescence 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

  11. Materials Data on LaF3 (SG:139) 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

  12. Pulsed periodic laser excitation of upconversion luminescence for deep biotissue visualization

    NASA Astrophysics Data System (ADS)

    Pominova, D. V.; Ryabova, A. V.; Linkov, K. G.; Romanishkin, I. D.; Kuznetsov, S. V.; Rozhnova, J. A.; Konov, V. I.; Loschenov, V. B.

    2016-08-01

    Emission spectral properties and quantum efficiency of upconversion particles NaYF4, SrF2, LaF3, BaF2 и CaF2, doped with rare earth ions pair Yb3+–Er3+ were studied using continuous wave (CW) and pulsed periodic excitation modes in the near infrared (NIR) spectral range. Analysis of the obtained results showed that the intensity ratio of upconversion luminescence in green and red spectral ranges depends on excitation pulse duration. Thus, by changing the pulse duration the spectral properties of upconversion luminescence can be controlled. Crystals with higher phonon energy are more sensitive to the change of pumping mode. Interpretation of results was performed on the rate equation model basis. Using numerical methods for all energy levels involved in the upconversion process the population and depopulation dynamics were obtained with respect to the duration of the excitation pulses. It was shown that about 30 ms was required for the complete population of 4F9/2 state, from which the luminescence in the red spectral range occurs. When the pulse duration was less than 30 ms, the 4F9/2 population did not reach a steady state and the intensity of the luminescence in the red part of the spectrum was reduced. The theoretical dependence of the upconversion luminescence intensity in the green and red ranges of the excitation pulse duration for NaYF4:Yb0.2–Er0.02 composition was obtained and demonstrates good agreement with the experimental results.

  13. Pulsed periodic laser excitation of upconversion luminescence for deep biotissue visualization

    NASA Astrophysics Data System (ADS)

    Pominova, D. V.; Ryabova, A. V.; Linkov, K. G.; Romanishkin, I. D.; Kuznetsov, S. V.; Rozhnova, J. A.; Konov, V. I.; Loschenov, V. B.

    2016-08-01

    Emission spectral properties and quantum efficiency of upconversion particles NaYF4, SrF2, LaF3, BaF2 i CaF2, doped with rare earth ions pair Yb3+-Er3+ were studied using continuous wave (CW) and pulsed periodic excitation modes in the near infrared (NIR) spectral range. Analysis of the obtained results showed that the intensity ratio of upconversion luminescence in green and red spectral ranges depends on excitation pulse duration. Thus, by changing the pulse duration the spectral properties of upconversion luminescence can be controlled. Crystals with higher phonon energy are more sensitive to the change of pumping mode. Interpretation of results was performed on the rate equation model basis. Using numerical methods for all energy levels involved in the upconversion process the population and depopulation dynamics were obtained with respect to the duration of the excitation pulses. It was shown that about 30 ms was required for the complete population of 4F9/2 state, from which the luminescence in the red spectral range occurs. When the pulse duration was less than 30 ms, the 4F9/2 population did not reach a steady state and the intensity of the luminescence in the red part of the spectrum was reduced. The theoretical dependence of the upconversion luminescence intensity in the green and red ranges of the excitation pulse duration for NaYF4:Yb0.2-Er0.02 composition was obtained and demonstrates good agreement with the experimental results.

  14. Effect of particle morphology on flow characteristics of a composite plasma spray powder

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    The effects of BaF2-CaF2 particle morphology on National Aeronautics and Space Administration (NASA) PS304 feedstock powder flowability were investigated, BaF2-CaF2 eutectic powders were fabricated by comminution (producing an angular morphology) and by gas atomization (producing a spherical morphology). The fluoride powders were added incrementally to the other powder constituents of the NASA PS304 feedstock, (Ni-Cr, Cr2O3, and Ag powders). A linear relationship between flow time and concentration of the BaF2-CaF2 powder was found. The flow of the powder blend with spherical BaF2-CaF2 was better than that with angular BaF2-CaF2. The flowability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. However, the flow of the powder blend with spherical fluorides was independent of fluoride concentration. The results suggest that for this material blend, particle morphology plays a significant role in flow behavior, offering potential methods to improve powder flowability and enhance the commercial potential. These findings may be applicable to other difficult-to-flow powders such as cohesive ceramics.

  15. 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.

  16. 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.

  17. 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.

  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. 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).

  20. 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.

  1. 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

  2. An APD for the efficient detection of the fast scintillation component of BaF2

    NASA Astrophysics Data System (ADS)

    Hitlin, D. G.; Kim, J. H.; Trevor, J.; Hoenk, M.; Hennessy, J.; Jewell, A.; Farrell, R.; McClish, M.

    2016-07-01

    Barium fluoride crystals are the baseline choice for the calorimeter of the Mu2e experiment at Fermilab. By the fast (decay time 0.9 ns) 220 nm scintillation component and discriminating against the larger slow (decay time 630 ns) 300 nm component, it is possible to build a radiation-hard calorimeter with good energy and time resolution and high rate capability. This requires a solid state photosensor with high quantum efficiency at 220 nm, discrimination against the 300 nm component and good rise and decay times. Progress on the development of such a sensor is presented.

  3. 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.

  4. 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.

  5. 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.

  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. 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.

  8. Crystallization of BaF2-ZnF2-YbF3-ThF4 glass

    NASA Technical Reports Server (NTRS)

    Garcia, Roberto; Doremus, Robert H.; Ko, Sen-Hou; Margraf, Tracey; Bansal, Narottam P.

    1988-01-01

    The phases and the rates of crystallization in a Ba-Zn-Yb-Th fluoride glass were studied using differential scanning calorimetry, XRD, and observational and chemical SEM analyses. The crystallizing phases that were identified included a BaYbTh fluoride, ZnF2, and YbF3. The BaYbTh fluoride crystallized first at about 450 C, and ZnF2, which was excluded from this phase, crystallized at its surfaces. At higher temperatures, the BaYbTh fluoride phase decomposed partially to BaThF6 and YbF3 phases.

  9. Achromatic lens systems for near infrared instruments.

    NASA Astrophysics Data System (ADS)

    Oliva, E.; Gennari, S.

    1995-11-01

    The chromatic characteristics of glasses transmitting in the near infrared (λ<=2.5μm) are analyzed. Achromatic systems with superb characteristics can be obtained by coupling the crystals BaF_2_, SrF_2_ and CaF_2_ with the IR Schott glasses irg2, irg3 and irg7, respectively. The best performances are obtained using BaF_2_-irg2 and SrF_2_- irg3 while CaF_2_-irg7 is worse (due to the lower Abbe number of CaF_2_) but significantly better than other pairs normally used in IR astronomical instrumentation. Use of these combinations could much simplify the design of astronomical focal plane instruments. Measurements of the refraction index of the IR glasses at cryogenic temperatures are however necessary. As a practical application we present the preliminary design of a F/11-F/4.3 focal reducer for the Italian 3.5 m Galileo telescope. The system employs 6 spherical lenses and its image quality matches the requirements of a 1024^2^ array with 18.5μm pixels in both the imaging and spectroscopic (with grism) modes.

  10. Characterization of optical thin films for applications at 10.6 μm

    NASA Astrophysics Data System (ADS)

    Kaspar, Martin; Pfefferkorn, R.; Ramm, Juergen

    1990-08-01

    Electron beam evaporation and ion assisted deposition have been used to prepare BaF2, LaF3 and HoF3 single layers. These fluorides were chosen as low index materials for laser applications at 10.6 Lm. The films were characterized by Rutherford backscattering (RBS), x-ray diffraction, scanning electron microscopy (SEM), stress measurement, laser calorimetry, and spectrophotometry. The influence of substrate temperature, deposition rate, ion energy, and ion to molecule arrival ratio on film growth was analysed and related to the optical properties. Although each material reacts differently to the deposition parameters, ion assisted deposition leads to an increase of the absorption loss at the laser wavelength for all three materials.

  11. 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.

  12. Efficient lasing at near 3 μm by a Dy-doped ZBLAN fiber laser pumped at ~ 1.1 μm by an Yb fiber laser

    NASA Astrophysics Data System (ADS)

    Tsang, Y. H.; El-Taher, A. E.

    2011-11-01

    Operation of a single-clad Dy3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser operating at mid-infrared near 3 μm is presented. The laser is pumped by an Yb3+-doped silica fiber laser centered at 1088 nm. An output of near 0.1 W with a slope efficiency of up to 23% with respect to absorbed pump power was measured. The laser performance, theoretical modeling and laser spectrum of Dy fiber laser system with respect to various cavity losses are studied. The experimental slope efficiency is more than 4.5 times higher than the previous demonstration, and is 64% of the Stokes efficiency limit. The efficiency was improved by using cavity mirrors of reflectivities of 99 and 50%. The emission central wavelength and spectral width are found to be dependent on the pump power and output coupler, reflectivity.

  13. 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.

  14. Synthesis and Characterization of Nd(3+)-Doped CaF2 Nanoparticles.

    PubMed

    Yuan, Dan; Li, Weiwei; Mei, Bingchu; Song, Jinghong

    2015-12-01

    The Ca(1-x)F(2+x):Nd(x) nanoparticles were synthesized by chemical direct precipitation method. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Image analyzer, absorption spectrum and transmittance were taken to characterization the phases, morphologies, sizes, size distribution and optical properties of the samples. The results indicate that the Ca(1-x)F(2+x):Nd(x) samples can be rationally modified in size and morphology by altering the Nd3+ ions doping concentration. With increasing concentration of Nd3+ ions, the particle size decreased from 24 to 14 nm, the intensity of the diffraction peaks decreased, the Ca(1-x)F(2+x):Nd(x) particles aggregated ion of the formed clusters which should have an effect on both speed and orientation of the particles growth. The transmittance of ceramics with a thickness of 2 mm showed that the transmittance can reach 90% when the doping concentration was 5%, which should be profitable for LD pumping. PMID:26682406

  15. 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.

  16. 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 СаF2:Tm fluoride ceramics has been prepared by hot forming. Comparative study of absorption and emission spectra of СаF2:Tm (4 mol.% TmF3) ceramic and single crystal samples demonstrated that these materials possess almost identical spectroscopic properties. Laser oscillations of СаF2: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 СаF2:Tm single crystal at 1890 nm pumped by a diode laser was demonstrated.

  17. Zeeman effect in CaF(2Pi(3/2)).

    PubMed

    Krems, R V; Egorov, D; Helton, J S; Maussang, K; Nguyen, S V; Doyle, J M

    2004-12-15

    The Zeeman effect in the excited A 2Pi(3/2) state of CaF is measured and analyzed over a wide range of magnetic fields. It is found that the splitting of the Zeeman levels is largely determined by the coupling between different rotational states and there are no low-field seeking states in the J=3/2 manifold of Zeeman levels at high magnetic fields. A model of the Zeeman spectrum based on the ligand-field theory of CaF is shown to be accurate in the interval of magnetic fields 0-5 Tesla. This demonstrates that the magnetic moment of the CaF(A 2Pi(3/2)) molecule is effectively determined by the spin angular momentum of a single electron and the orbital motion of the valence electron around the Ca2+ core. An analysis of the Zeeman spectrum as a function of the molecular rotational constant indicates that 2Pi(3/2) molecules should have significant rotational constants (at least as large as twice the rotational constant of CaF) to be amenable to magnetic trapping in high fields.

  18. 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 μm, 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 μm). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 - 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ~ 98% @ 1.01 - 1.09 μm. 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%.

  19. 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.

  20. Catalog of infrared and cryo-optical properties for selected materials

    NASA Technical Reports Server (NTRS)

    Heaney, James B.; Alley, Phillip W.; Bradley, Scott E.

    1991-01-01

    This report will describe the status of an effort to catalog the refractive index, absorption, reflectance and transmittance of selected IR transmitting materials over the wavelength range from 1 to 1000 microns, and at temperatures from 300 to about 2 K. Data are presented for LiF, CaF2, BaF2, KBr, and TlBr, as well as for KRS-5 (TlBr-I) and KRS-6 (TlBr-Cl). A cryooptical measurements facility at NASA-Goddard, which has been used to generate some of the cataloged data, is also described.

  1. Dynamical simulations of superionicity in alkaline-earth halides

    NASA Astrophysics Data System (ADS)

    Zhou, L. X.; Hardy, J. R.; Cao, H. Z.

    1996-04-01

    Superionicity in alkaline-earth halides CaF 2, SrF 2 and BaF 2 has been studied by molecular dynamical simulations using Gordon-Kim potentials. These dynamical simulations employ a novel technique to monitor the motion of ions which clearly demonstrates the nature of the superionic phases in these crystals. While in the superionic phase, the Ca 2+, Ba 2+, and Sr 2+ ions maintain ideal lattice positions, the F - ions flow between them in a correlated linear manner closely related to that proposed previously by Boyer.

  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. Élimination du bore du silicium par plasma inductif sous champ électrique

    NASA Astrophysics Data System (ADS)

    Combes, R.; Morvan, D.; Picard, G.; Amouroux, J.

    1993-05-01

    We analyzed purification mechanisms of silicon by inductive plasma with a fluoride slag. The aim is to study boron elimination from doped electronic grade silicon in function of the nature of the slag to obtain a photovoltaic grade silicon. The steady began with the calculation and the comparison of the stability diagram of boron compounds in presence of CaF2, BaF2 and MgF2. This study led us to conclude that BaF2 is the better slag for silicon purification. This has been confirmed by experience. In a second time, we made purifications under electric bias to enhance slag efficiency. We noticed that BaF2 is more sensitive to electric bias than other slags. Nous avons analysé le mécanisme de purification du silicium sous plasma inductif en présence d'un laitier fluoré. L'objectif principal est d'étudier l'élimination du bore du silicium électronique dopé en fonction de la nature du fluorure pour obtenir un silicium de qualité photovoltaïque. L'étude a commencé par l'établissement et la comparaison de diagrammes des composés du bore en présence de CaF2, de MgF2 et de BaF2. Nous avons déduit de cette première étude que BaF2 est le meilleur laitier pour la purification du silicium. Ceci a été corroboré par l'expérience. Nous avons ensuite opéré en présence d'un champ électrique dans le but d'améliorer encore l'efficacité des laitiers. Nous avons constaté que BaF2 est plus sensible au champ électrique que les deux autres laitiers utilisés.

  4. Simultaneous measurement of (n,γ) and (n,fission) cross sections with the DANCE 4π 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 γ-ray energy and γ-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,γ)/(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.

  5. 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.

  6. 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. Frictions 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 PM212/Au was not determined, it may be due to practice morphology differences between the gold and silver and their effect on powder metallurgy processing.

  7. 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.

  8. 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.

  9. Epitaxy versus oriented heterogeneous nucleation of organic crystals on ionic substrates

    NASA Astrophysics Data System (ADS)

    Sarma, K. R.; Shlichta, P. J.; Wilcox, W. R.; Lefever, R. A.

    1997-04-01

    It is plausible to assume that epitaxy is a special case of heterogeneous nucleation in which a restrictive crystallographic relationship exists between substrate and deposit orientations. This would mean that epitaxial substrates should always induce a perceptible reduction in the critical supercooling for nucleation of the deposit. To test this hypothesis, the critical supercoolings of six organic compounds were measured on glass and 11 single-crystal cleaved substrates including (0001) graphite, (001) mica, (111) BaF 2, SrF 2, and CaF 2, and (100) KCl, KBr, KI, NaCl, NaF, and LiF. Reductions in supercooling (with reference to glass substrates) were checked many times for repeatability and reproducibility and shown in almost all cases to have a standard deviation of 1 C or less. Acetanilide, benzoic acid, and p-bromochlorobenzene showed a wide range of supercooling reductions and were oriented on all crystalline substrates. Naphthalene and p-dibromobenzene showed only slight supercooling reductions but were oriented on all substrates, including glass. Benzil showed strong supercooling reductions only for mica and KI but was oriented not only in these cases but also with KI, BaF 2, CaF 2, and graphite. There was little correlation between degree of lattice match and either supercooling reduction or degree of preferred orientation. These results suggest that, for the systems and geometry studied, forces such as molecular dipole binding and growth anisotropy had a stronger effect than lattice match.

  10. Neutron contribution to CaF2:Mn thermoluminescent dosimeter response in mixed (n/y) field environments.

    SciTech Connect

    DePriest, Kendall Russell; Griffin, Patrick Joseph

    2003-07-01

    Thermoluminescent dosimeters (TLDs), particularly CaF{sub 2}:Mn, are often used as photon dosimeters in mixed (n/{gamma}) field environments. In these mixed field environments, it is desirable to separate the photon response of a dosimeter from the neutron response. For passive dosimeters that measure an integral response, such as TLDs, the separation of the two components must be performed by postexperiment analysis because the TLD reading system cannot distinguish between photon- and neutron-produced response. Using a model of an aluminum-equilibrated TLD-400 (CaF{sub 2}:Mn) chip, a systematic effort has been made to analytically determine the various components that contribute to the neutron response of a TLD reading. The calculations were performed for five measured reactor neutron spectra and one theoretical thermal neutron spectrum. The five measured reactor spectra all have experimental values for aluminum-equilibrated TLD-400 chips. Calculations were used to determine the percentage of the total TLD response produced by neutron interactions in the TLD and aluminum equilibrator. These calculations will aid the Sandia National Laboratories-Radiation Metrology Laboratory (SNL-RML) in the interpretation of the uncertainty for TLD dosimetry measurements in the mixed field environments produced by SNL reactor facilities.

  11. Neutron Contribution to CaF2:Mn Thermoluminescent Dosimeter Response in Mixed (n/y) Field Environments

    SciTech Connect

    DEPRIEST, KENDALL R.

    2002-11-01

    Thermoluminescent dosimeters (TLDs), particularly CaF{sub 2}:Mn, are often used as photon dosimeters in mixed (n/{gamma}) field environments. In these mixed field environments, it is desirable to separate the photon response of a dosimeter from the neutron response. For passive dosimeters that measure an integral response, such as TLDs, the separation of the two components must be performed by post-experiment analysis because the TLD reading system cannot distinguish between photon and neutron produced response. Using a model of an aluminum-equilibrated TLD-400 chip, a systematic effort has been made to analytically determine the various components that contribute to the neutron response of a TLD reading. The calculations were performed for five measured reactor neutron spectra and one theoretical thermal neutron spectrum. The five measured reactor spectra all have dosimetry quality experimental values for aluminum-equilibrated TLD-400 chips. Calculations were used to determined the percentage of the total TLD response produced by neutron interactions in the TLD and aluminum equilibrator. These calculations will aid the Sandia National Laboratories-Radiation Metrology Laboratory (SNL-RML) in the interpretation of the uncertainty for TLD dosimetry measurements in the mixed field environments produced by SNL reactor facilities.

  12. 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 μm. 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

  13. A new approach to prepare well-dispersed CaF(2) nanoparticles by spray drying technique.

    PubMed

    Sun, Limin; Chow, Laurence C; Bonevich, John E; Wang, Tongxin; Mitchell, James W

    2011-08-01

    Previously, nano-sized calcium fluoride (CaF₂) particles were prepared using a spray drying method by simultaneously feeding Ca(OH)₂ and NH₄F solutions to a two-liquid nozzle. The aim of the present study was to prepare better-dispersed nano-CaF₂ particles by co-forming a soluble salt, sodium chloride (NaCl). NaCl of various concentrations were added to the NH(4) F solution, leading to formation of (CaF₂ +NaCl) composites with CaF₂ /NaCl molar ratios of 4/1, 4/4, and 4/16. Pure nano-CaF₂ was also prepared as the control. Powder X-ray diffraction analysis showed that the products contained crystalline CaF₂ and NaCl. Scanning electron microscopy examinations showed that both the CaF₂ /NaCl composite and pure CaF₂ particles were about (50-800) nm in size and consisted of primary CaF₂ particles of < 50 nm in size. BET surface area measurements showed similar primary particle sizes for all samples. Dynamic light scattering measurements showed that the washed (CaF₂+NaCl) particles were much smaller than the pure CaF₂ as the dissolution of NaCl "freed" most of the primary CaF₂ particles, leading to a greater degree of particle dispersion. The well-dispersed nano-CaF₂ may be expected to be a more effective anticaries agent than NaF by providing longer lasting elevations of fluoride concentrations in oral fluids.

  14. 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.

  15. 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.

  16. 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.

  17. Fluorescence and phosphorescence of photomultiplier window materials under electron irradiation

    NASA Technical Reports Server (NTRS)

    Viehmann, W.; Eubanks, A. G.; Bredekamp, J. H.

    1974-01-01

    The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation were investigated using a Sr-90/Y-90 beta emitter as the electron source. Spectral emission curves of UV grade, optical grade, and electron-irradiated samples of MGF2 and LiF, CaF2, BaF2, sapphire, fused silica, and UV transmitting glasses were obtained over the spectral range of 200 nm to 650 nm. Fluorescence yields, expressed as the number of counts in a solid angle of 2 pi steradian per 1MeV of incident electron energy deposited, were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively.

  18. Effects of humidity on the flow characteristics of a composite plasma spray powder

    NASA Astrophysics Data System (ADS)

    Stanford, Malcolm K.; Dellacorte, Christopher

    2006-03-01

    The effects of environmental humidity on the flow characteristics of a multicomponent (composite) plasma spray powder have been investigated. Angular and spherical BaF2-CaF2 powder was fabricated by comminution and by atomization, respectively. The fluorides were blended with nichrome, chromia, and silver powders to produce a composite plasma spray feedstock. The tap density, apparent density, and angle of repose were measured at 50% relative humidity (RH). The flow of the powder was studied from 2 to 100% RH. The results suggest that the feedstock flow is only slightly degraded with increasing humidity below 66% RH and is more affected above 66% RH. There was no flow above 90% RH except with narrower particle size distributions of the angular fluorides, which allowed flow up to 95% RH. These results offer guidance that enhances the commercial potential for this material system.

  19. Giantically blue-shifted visible light in femtosecond mid-IR filament in fluorides.

    PubMed

    Dormidonov, A E; Kompanets, V O; Chekalin, S V; Kandidov, V P

    2015-11-01

    A giant blue shift (more than 3000 nm) of an isolated visible band of supercontinuum was discovered and studied in the single filament regime of Mid-IR femtosecond laser pulse at powers slightly exceeding critical power for self-focusing in fluorides. At the pulse central wavelength increasing from 3000 nm to 3800 nm the spectral maximum of the visible band is shifted from 570 nm and 520 nm up to 400 nm and 330 nm for BaF(2) and CaF(2), respectively, its spectral width (FWHM) being reduced from 50 - 70 nm to 14 nm. It is shown that the formation of this narrow visible wing is a result of the interference of the supercontinuum components in the anomalous group velocity dispersion regime. PMID:26561190

  20. Preliminary Evaluation of PS300: A New Self-Lubricating High Temperature Composite Coating for Use to 800 C

    NASA Technical Reports Server (NTRS)

    Dellacorte, C.; Edmonds, B. J.

    1995-01-01

    This paper introduces PS300, a plasma sprayed, self-lubricating composite coating for use in sliding contacts at temperatures to 800 C. PS300 is a metal bonded chrome oxide coating with silver and BaF2/CaF2 eutectic solid lubricant additives. PS300 is similar to PS200, a chromium carbide based coating, which is currently being investigated for a variety of tribological applications. In pin-on-disk testing up to 650 C, PS300 exhibited comparable friction and wear properties to PS200. The PS300 matrix, which is predominantly chromium oxide rather than chromium carbide, does not require diamond grinding and polishes readily with silicon carbide abrasives greatly reducing manufacturing costs compared to PS200. It is anticipated that PS300 has potential for sliding bearing and seal applications in both aerospace and general industry.

  1. 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.

  2. 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.

  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. Room-temperature upconversion fiber laser tunable in the red, orange, green, and blue spectral regions

    NASA Astrophysics Data System (ADS)

    Xie, Ping; Gosnell, T. R.

    1995-05-01

    We report continuous-wave tunable laser operation over the 635-637-, 605-622-, 517-540-, and 491- 493-nm wavelength bands in Pr3+/Yb3+ -doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) optical fiber. A single Ti:sapphire laser is used as the pump source. With as little as 60 mW of pump power launched into the fiber, laser output is obtained over the entire pump-wavelength tuning range of 780 to 880 nm. At a pump wavelength of 860 nm, we have produced output powers of 300 mW at 635 nm (760 mW of launched pump power), 45 mW at 615 nm (430 mW of launched power), 20 mW at 520 nm (200 mW of launched power), and 4 mW at 493 nm (200 mW of launched power).

  5. 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.

  6. 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.

  7. Wavelength-tunable mid-infrared femtosecond Raman soliton generation in birefringent ZBLAN photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Sharma, Sneha; Kumar, Jitendra

    2016-03-01

    A solid core high birefringent ZrF4-BaF2-LaF3-AlF3-NaF photonic crystal fiber (PCF) with low confinement loss is proposed for the generation of Raman soliton source in the mid-infrared region. The birefringence value of the PCF reaches the magnitude of 10- 3 and confinement loss is 0.05 dB/m at 3000 nm wavelength. Numerical simulation of femtosecond Raman soliton generation based on soliton self-frequency shift in the birefringent PCF is analyzed using the coupled nonlinear Schrodinger equation and split-step Fourier method. We investigate the dependence of output pulse width, wavelength shift, and conversion efficiency of Raman soliton formation on several input parameters. A femtosecond Raman soliton source with its wavelength tunable from 1500 to 3600 nm can be obtained. It is found that the maximum conversion efficiency is 93% when the wavelength is tuned by varying the initial input chirp.

  8. High Purity Zirconium Tetrafluoride For Fluoride Glass Applications

    NASA Astrophysics Data System (ADS)

    Withers, Howard P.; Monk, V. A.; Cooper, G. A.

    1989-06-01

    A totally anhydrous process has been developed for the preparation of high purity zirconium tetrafluoride for use in low loss fluoride glass applications. The ZrF4 purityis 99.99997% with respect to all transition elements (excluding HO based on analysis by spark source mass spectrometry (SSMS) and graphite furnace/atomic absorption spectroscopy (GF/AA). The only transition elements detected by these techniques were Fe, Ni and Cr, while Co and Cu were consistently below the detection limits. The anhydrous nature of the process, which is strictly maintained by the choice of reactants, affords product with very low oxide and hydroxide content. Total oxygen concentrations of less than 10 ppm have been measured by the inert gas fusion technique. A ZBLAN glass composition prepared using this ZrF4 showed extremely low UV absorption having an absorption constant of 1 cm-1 at 198 nm. ZrF4 from this process was also used in a ZBLAN glass fiber whose minimum optical loss was measured at 6.3 dB/km over 150 meters of fiber. The process is straightforward to scale up and has also been demonstrated to be useful for the preparation of HfF4, BaF2, A1F3 and LaF3.

  9. 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.

  10. Thirteen watt all-fiber mid-infrared supercontinuum generation in a single mode ZBLAN fiber pumped by a 2 μm MOPA system.

    PubMed

    Yang, Weiqiang; Zhang, Bin; Xue, Guanghui; Yin, Ke; Hou, Jing

    2014-04-01

    All-fiber-integrated mid-infrared (mid-IR) supercontinuum (SC) generation in a single mode ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber with 13 W average output power and a spectrum extending from ∼1.9 to 4.3 μm is reported, which we believe is the highest output power for mid-IR SC generation in ZBLAN fibers. The overall optical conversion efficiency from the 790 nm pump light of the last stage Tm-doped fiber (TDF) amplifier to the total SC output was 20%, and the SC power for wavelengths longer than 2.5 μm was 6.85 W with a power ratio of 52.69% with respect to the total SC power. The mid-IR SC generation in ZBLAN fiber was pumped by a 2 μm master oscillator power amplifier (MOPA) system, which is also very appropriate for high power 2-2.5 μm region SC generation. We also demonstrate high efficiency SC generation in the TDF amplifier with 62.1 W average power, 39.8% optical efficiency, and a spectrum extending from 1.9 to 2.7 μm. PMID:24686621

  11. Increasing the working temperature range of ZrF-BaF-LaF-AlF-NaF glass through microgravity processing

    NASA Astrophysics Data System (ADS)

    Torres, Anthony; Ganley, Jeff; Maji, Arup; Tucker, Dennis; Starodubov, Dmitry

    2014-03-01

    Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the ultraviolet to 7 μm in the infrared regions. However, crystallites formed during the fiber-drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx-Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subjected to a heating and quenching test apparatus on the parabolic aircraft under a controlled μ-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy examination elucidates that crystal growth in ZBLAN is suppressed and initiates at a later temperature when processed in a microgravity environment. Thus, the crystallization temperature, Tx, at which the crystals form has increased. The glass transition temperature, Tg, remains constant, as crystallization does not occur until approximately 360°C for this composition of ZBLAN. Therefore, the working temperature range for ZBLAN has been broadened.

  12. 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.

  13. 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.

  14. Cold shock induces apoptosis of dorsal root ganglion neurons plated on infrared windows.

    PubMed

    Aboualizadeh, Ebrahim; Mattson, Eric C; O'Hara, Crystal L; Smith, Amanda K; Stucky, Cheryl L; Hirschmugl, Carol J

    2015-06-21

    The chemical status of live sensory neurons is accessible with infrared microspectroscopy of appropriately prepared cells. In this paper, individual dorsal root ganglion (DRG) neurons have been prepared with two different protocols, and plated on glass cover slips, BaF2 and CaF2 substrates. The first protocol exposes the intact DRGs to 4 °C for between 20-30 minutes before dissociating individual neurons and plating 2 hours later. The second protocol maintains the neurons at 23 °C for the entire duration of the sample preparation. The visual appearance of the neurons is similar. The viability was assessed by means of trypan blue exclusion method to determine the viability of the neurons. The neurons prepared under the first protocol (cold exposure) and plated on BaF2 reveal a distinct chemical signature and chemical distribution that is different from the other sample preparations described in the paper. Importantly, results for other sample preparation methods, using various substrates and temperature protocols, when compared across the overlapping spectral bandwidth, present normal chemical distribution within the neurons. The unusual chemically specific spatial variation is dominated by a lack of protein and carbohydrates in the center of the neurons and signatures of unraveling DNA are detected. We suggest that cold shock leads to apoptosis of DRGs, followed by osmotic stress originating from ion gradients across the cell membrane leading to cell lysis. PMID:26000346

  15. 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.

  16. 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).

  17. Measurement of the Np237(n,γ) cross section from 20 meV to 500 keV with a high efficiency, highly segmented 4π BaF2 detector

    NASA Astrophysics Data System (ADS)

    Esch, E.-I.; Reifarth, R.; Bond, E. M.; Bredeweg, T. A.; Couture, A.; Glover, S. E.; Greife, U.; Haight, R. C.; Hatarik, A. M.; Hatarik, R.; Jandel, M.; Kawano, T.; Mertz, A.; O'Donnell, J. M.; Rundberg, R. S.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.

    2008-03-01

    The Np237(n,γ)Np238 cross section has been measured in the neutron energy range from 20 meV to 500 keV using the DANCE array at the Los Alamos National Laboratory. This new facility allows experiments with submilligram samples and is therefore well suited to investigate isotopes with half-lives as low as a few hundred days. In this benchmark measurement, only 0.42 mg of Np237 was sufficient to determine differential cross sections relative to the well-known resonance at 0.5 eV. The thermal cross section was measured to σ2200m/s=177±5 barn, σkT=25.3meV=167±4 barn and the resonance integral to RI=693±6 barn.

  18. New measurements of (n,γ) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4π 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 γ detector arrays such as the DANCE array (Detector for Advanced Neutron Capture Experiments), which cannot clearly differentiate γ-rays resulting from the two exit channels. With the addition of a high efficiency, 4π fission-tagging detector it is possible to deconvolve the two contributions to the total γ-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.

  19. New measurements of (n,γ) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4π 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 γ detector arrays such as DANCE. Additional instrumentation is required to deconvolve the two contributions to the total observed γ-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.

  20. 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

  1. 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 μm 3F4-3H6 transition under ~795 nm laser diode excitation is studied.

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

    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 μm 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 μm 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.

  3. Highly stable, monolithic, single-mode mid-infrared supercontinuum source based on low-loss fusion spliced silica and fluoride fibers.

    PubMed

    Yin, Ke; Zhang, Bin; Yao, Jinmei; Yang, Linyong; Chen, Shengping; Hou, Jing

    2016-03-01

    A 0.8 to 4.5 μm highly stable all-fiber spliced mid-infrared supercontinuum (SC) source was presented. The joint between the single-mode (SM) pump silica fiber and the ZBLAN fiber (ZrF4 - BaF2 - LaF3 - AlF3 - NaF, a type of fluoride fiber) was fusion spliced, which greatly improved the SC's stability. The low-loss splicing was guaranteed by the similar mode field areas of the fundamental mode LP(01) of the silica and ZBLAN fibers. At the splicing joint the ZBLAN fiber enveloped the silica fiber, thus increasing the robustness of the splice. A low splicing loss of less than 0.1 dB was calculated, which ensured that the whole SC source was very reliable. The SC had a maximal average power of 550.8 mW with a 1.5 dB spectral bandwidth ranging from 2642 to 4065 nm. In particular, the SC power for λ>3.8  μm was measured to be 116.1 mW with a power ratio of ∼21.1% of the total SC power. Perfect Gaussian beam profiles of the SC source demonstrated its SM operation. Over 12 h of continuous operation of this SC source showed its outstanding power stability with a root mean square variation of 0.59%, which also demonstrated the high quality of the fusion spliced joint. PMID:26974087

  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 μm, 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 μm/ 2.65 μm/ 3.1 μm/ 3.5 μm.

  5. 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.

  6. 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.

  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.

  8. 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.

  9. Vacuum tribological behaviour of self lubricant quasicrystalline composite coatings

    NASA Astrophysics Data System (ADS)

    Garcí de Blas, F. J.; Román, A.; de Miguel, C.; Longo, F.; Muelas, R.; Agüero, A.

    2003-09-01

    High temperature resistant self-lubricant coatings are needed in space vehicles for components that operate at high temperatures and/or under vacuum. Thick composite lubricant coatings containing quasicrystalline alloys (QC) as the hard phase for wear resistance, have been deposited by thermal spray. The coatings also comprise lubricating materials (silver and BaF2-CaF2 eutectic) and NiCr as the tough component. This paper describes the vacuum tribological properties of TH103, a coating belonging to this family, with excellent microstructural quality. The coating was deposited by HVOF and tested under vacuum on a pin-on-disc tribometer. Different loads, linear speeds and pin materials were studied. The pin scars and disc wear tracks were characterized by EDS-SEM. A minimum mean steady friction coefficient of 0.32 was obtained employing a X-750 Ni superalloy pin in vacuum conditions under 10 N load and 15 cm/s linear speed, showing moderate wear of the disc and low wear of the pin.

  10. Photomultiplier window materials under electron irradiation - Fluorescence and phosphorescence

    NASA Technical Reports Server (NTRS)

    Viehmann, W.; Eubanks, A. G.; Pieper, G. F.; Bredekamp, J. H.

    1975-01-01

    The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation have been investigated using a Sr-90/Y-90 beta emitter as the electron source. Spectral emission curves of UV-grade, optical-grade, and electron-irradiated samples of MgF2 and LiF, and of CaF2, BaF2, sapphire, fused silica, and UV-transmitting glasses were obtained over the 200-650-nm spectral range. Fluorescence yields were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively. Optical-grade MgF2 and LiF, as well as electron-irradiated UV-grade samples of these two materials, show enhanced fluorescence due to color-center formation and associated emission bands in the blue and red wavelength regions. Large variations in fluorescence intensities were found in UV-grade sapphire samples of different origins, particularly in the red end of the spectrum, presumably due to various amounts of chromium-ion content. Phosphorescence decay with time is best described by a sum of exponential terms, with time constants ranging from a few minutes to several days.

  11. 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.

  12. Designing a 1.7-5.3 μm athermalized lens

    NASA Astrophysics Data System (ADS)

    Bardazzi, R.

    2008-10-01

    In the framework of a research program a broad band lens (1.7÷5.3 μm) has been designed to be inserted in an optoelectronic system of the Italian Navy. The optoelectronic system operates over full spectral band or over one of the seven sub-bands that are selected inserting spectral filters mounted on a wheel. The optoelectronic system FOV is 20°x15°, aperture F/# 2.4 and it is optically athermalized in the range -30°÷+70° C. Color aberrations correction and athermalization was obtained by means an appropriate choice of optical materials (Cleartran, Sapphire, BaF2 and CaF2). The optical athermalization has been achieved for an all aluminum mechanical mounting. The lens mechanical mounting is quite cheap as no moving parts are present while focusing is obtained regardless the objective temperature. The optical layout is composed by five lenses. The design was driven to have a low sensitive manufacturing and mounting tolerances. A diffractive lens free solution was selected because of the unacceptable radiation losses in the higher diffractive orders due to the wide spectral band. Dedicated BBAR coatings for Sapphire and Cleartran have been developed.

  13. 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.

  14. Self-lubricating coatings for high-temperature applications

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E.

    1987-01-01

    Some present-day aeropropulsion systems impose severe demands on the thermal and oxidative stability of lubricant, bearing, and seal materials. These demands will be much more severe for operational systems around the turn of the century. Solid lubricants with maximum temperature capabilities of about 1100 C are known. Unfortunately, none of the solid lubricants with the highest temperature capabilities are effective below approximately 400 C. However, research shows that silver and stable fluorides, such as calcium and barium fluoride act synergistically to provide lubrication from below room temperature to approximately 900 C. Plasma-sprayed, self-lubricating composite coatings that were developed at Lewis are described. Background information is given on coatings, designed as PS100 and PS101, that contain the solid lubricants in a Nichrome matrix. These coatings have low friction coefficients over a wide temperature range, but they have inadequate wear resistance for some long-duration applications. Wear resistance was dramatically improved in a recently developed coating PS200, by replacing the Nichrome matrix material with metal-bonded chromium carbide containing dispersed silver and calcium fluoride/barium fluoride eutectic (CaF2/BaF2). The lubricants control friction and the carbide matrix provides excellent wear resistance. Successful tests of these coatings are discussed.

  15. 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.

  16. 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 μm 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.

  17. 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

  18. Core-shell-shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) with remarkably enhanced upconversion luminescence.

    PubMed

    Su, Yue; Liu, Xiuling; Lei, Pengpeng; Xu, Xia; Dong, Lile; Guo, Xianmin; Yan, Xingxu; Wang, Peng; Song, Shuyan; Feng, Jing; Zhang, Hongjie

    2016-07-01

    Core-shell-shell heterostructures of α-NaLuF4:Yb/Er@NaLuF4:Yb@MF2 (M = Ca, Sr, Ba) have been successfully fabricated via the thermal decomposition method. Upconversion nanoparticles (UCNPs) were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), upconversion luminescence (UCL) spectroscopy, etc. Under 980 nm excitation, the emission intensities of the UCNPs are remarkably enhanced after coating the MF2 (M = Ca, Sr, and Ba) shell. Among these samples, CaF2 coated UCNPs show the strongest overall emission, while BaF2 coated UCNPs exhibit the longest lifetime. These results demonstrate that alkaline earth metal fluorides are ideal materials to improve the UCL properties. Meanwhile, although the lattice mismatch between the ternary NaREF4 core and the binary MF2 (M = Sr and Ba) shell is relatively large, the successfully synthesized NaLuF4:Yb/Er@NaLuF4:Yb@MF2 indicates a new outlook on the fabrication of heterostructural core-shell UCNPs. PMID:27327414

  19. Solvothermal synthesis of well-dispersed MF(2) (M = Ca,Sr,Ba) nanocrystals and their optical properties.

    PubMed

    Zhang, Xiaoming; Quan, Zewei; Yang, Jun; Yang, Piaoping; Lian, Hongzhou; Lin, Jun

    2008-02-20

    MF(2) (M = Ca,Sr,Ba) nanocrystals (NCs) were synthesized via a solvothermal process in the presence of oleic acid and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, UV/vis absorption spectra, photoluminescence (PL) excitation and emission spectra, and lifetimes, respectively. In the synthetic process, oleic acid as a surfactant played a crucial role in confining the growth and solubility of the MF(2) NCs. The as-prepared CaF(2), SrF(2) and BaF(2) NCs present morphologies of truncated octahedron, cube and sheet in a narrow distribution, respectively. Possible growth mechanisms were proposed to explain these results. The as-prepared NCs are highly crystalline and can be well dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrate strong emission bands centred at 400 nm in photoluminescence (PL) spectra compared with the cyclohexane solvent. The PL properties of the colloidal solutions of the as-prepared NCs can be ascribed to the trap states of surface defects.

  20. 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.

  1. Investigation of Thermal Processing on the Properties of PS304: A Solid Lubricant Coating

    NASA Technical Reports Server (NTRS)

    Benoy, Patricia A.; Williams, Syreeta (Technical Monitor)

    2002-01-01

    The effect of thermal processing on PS304, a solid lubricant coating, was investigated. PS304 is a plasma sprayed solid lubricant consisting of 10% Ag and 10% BaF2 and CaF2 in a eutectic mixture for low and high temperature lubricity respectively. In addition, PS304 contains 20% Cr2O3 for increased hardness and 60% NiCr which acts as a binder. All percents are in terms of weight not volume. Previous research on thermal processing (NAG3-2245) of PS304 revealed that substrate affected both the pre- and post-anneal hardness of the plasma spray coating. The objective of this grant was to both quantify this effect and determine whether the root cause was an artifact of the substrate or an actual difference in hardness due to interaction between the substrate and the coating. In addition to clarifying past research developments new data was sought in terms of coating growth due to annealing.

  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. 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.

  4. Single-frequency, single-polarization holmium-doped ZBLAN fiber laser

    NASA Astrophysics Data System (ADS)

    Zhu, X.; Zong, J.; Miller, A.; Wiersma, K.; Norwood, R. A.; Prasad, N. S.; Chavez-Pirson, A.; Peyghambarian, N.

    2013-02-01

    We present the performance of a single frequency, single-polarization holmium (Ho3+)-doped ZBLAN (ZrF4-BaF2-LaF3- AlF3-NaF) fiber laser at 1200 nm. This distributed Bragg reflector (DBR) fiber laser was developed by splicing a 22 mm long highly Ho3+-doped ZBLAN fiber to a pair of silica fiber Bragg gratings (FBG). The successful fusion splicing of silica fiber to ZBLAN fiber, with their very different melting temperatures, was accomplished by using NP Photonics proprietary splicing technique. The 3 mol% Ho3+-doped ZBLAN fiber had a core diameter of 6.5 μm and a cladding diameter of 125 μm. The threshold of this laser was seen to be about 260 mW, and when the pump power was 520 mW, the output power was about 10 mW. The efficiency of the 1200 nm single-frequency fiber laser, i.e. the ratio of the output power to the launched pump power, was about 3.8%. The linewidth of the 1200 nm single-frequency fiber laser was estimated to be about 100 kHz by comparing the measured frequency noise of the 1200 nm single-frequency fiber laser with that of 1 μm NP Photonics single-frequency fiber lasers whose linewidths have been measured to be in the 1- 10 kHz range. The relative intensity noise of this DBR all-fiber laser was measured to be < 110 dB/Hz at the relaxation oscillation peak and the polarization extinction ratio was measured to be > 19 dB. Due to its low phonon energy and long radiative lifetimes, rare-earth-doped ZBLAN allows various transitions that are typically terminated in silica glass, resulting in ultraviolet, visible, and infrared rare-earth doped ZBLAN lasers. Therefore, our results highlight the exciting prospect that the accessible wavelength range of single-frequency DBR fiber lasers can be expanded significantly by using rare-earth-doped ZBLAN fibers.

  5. Effects of Li+ ions on the enhancement of up-conversion emission in Ho3+-Yb3+ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Zhencai; Zhou, Dacheng; Yang, Yong; Gao, Yuan; Ren, Peng; Qiu, Jianbei

    2016-10-01

    The up-conversion (UC) emission of Ho3+-Yb3+ and Li+ co-doped transparent glass ceramics 45SiO2-15Al2O3-12Na2CO3-21BaF2-7LaF3-0.2HoF3-1YbF3-xLi2CO3 (x = 0, 0.5, 1, 2, 4 and 6 mol%) containing Ba2LaF7 nanocrystals were investigated. These glass ceramics samples were prepared using the conventional quenching techniques. The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). Compared with the glass ceramics sample without Li+, the UC emission intensity of glass ceramics samples with Li+ were enhanced. It can be proved that the Li+ can affect the enhancement up-conversion (UC) emission. Particularly, the green UC emission intensity band centered at 546 nm was strongly increased twice with the concentration of Li+ increasing up to 4 mol%. Through the comparison and analysis of the energy graph, it was shown that the 5F4/5S2→5I8 transition of Ho3+ ion obtained the green (546 nm) light. There are two weak fluorescences in the red (657 nm) region and near infrared (753 nm) region of spectrum, which is the 5F4/5S2→5I7 and 5F5→5I8 transition of Ho3+. Therefore, the emission results showed that the incorporation of Li+ ions into the Ba2LaF7:Eu3+ lattice could induce a remarkable change of the emission intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that the symmetry of the lattice was destroyed by Li+ in glass ceramics. The possible mechanism responsible for the enhancement of UC emission in Ho-Yb co-doped was discussed.

  6. 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.

  7. 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.

  8. Understanding the role of gravity in the crystallization suppression of ZBLAN glass

    NASA Astrophysics Data System (ADS)

    Torres, Anthony Samuel

    Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the UV to 7 μm in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its low loss-capability. Other researchers have shown that microgravity processing leads to suppressed crystal growth in ZBLAN glass, which can lead to lower transmission loss in the desired mid-IR range. However, the mechanism governing crystal growth suppression has not been thoroughly investigated. In the present research multiple ZBLAN samples were subjected to a heating and quenching test apparatus on a parabolic aircraft under controlled μ-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy (transmission and polarized) along with SEM examination elucidates that crystal growth in ZBLAN is suppressed when processed in a microgravity environment. Hence crystallization occurs at a higher temperature in μ-g and the working temperature range at which the fiber can be manufactured has been extended. We postulate that the fundamental process of nano-scale mass transfer (lack of buoyancy driven convection) in the viscous glass is the mechanism responsible for crystal growth suppression in microgravity. Suppressing molecular mobility within the semi-molten glass starves nucleating crystallites and prevents any further growth. A COMSOL Multi-Physics model was developed to show the velocity contours due to convection processes in a 1-g, μ-g, and hyper-g environment. Analytical models show that while suppressing convection is relevant at fiber drawing temperatures (360°C), mass transfer due to diffusion dominates at higher temperatures leading to crystal growth at temperatures ≥400°C. ZBLAN fibers are also known for their poor handling ability. Therefore an analysis of the thermal degradation of ZBLAN optical fibers based on fracture mechanics was also conducted. Conditions of crack initiation and stable versus unstable crack growth leading to fiber fracture were analyzed to explain behavior observed from controlled flexure tests of ZBLAN optical fibers exposed to various temperatures.

  9. Generation of broadband mid-infrared supercontinuum radiation in cascaded soft-glass fibers

    NASA Astrophysics Data System (ADS)

    Kneis, C.; Robin, T.; Cadier, B.; Brilland, Laurent; Caillaud, Celine; Troles, Johann; Manek-Hönninger, I.; Eichhorn, M.; Kieleck, C.

    2016-03-01

    The generation of mid-infrared (mid-IR) radiation, ranging from 2 - 5 μm, is getting much attention in recent years thanks to many applications it can be used for, e.g. in free space optical communication, range finding, counter measures and remote chemical sensing systems. It also plays an increasing role in medicine, for instance in optical tissue ablation or optical coherence tomography, owing to the high water absorption in that wavelength range. In this research study, a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride fiber is pumped by a Q-switched mode-locked (QML) thulium (Tm3+)- doped double-clad silica fiber laser, emitting at around 2 μm, to generate mid-IR supercontinuum (SC). Further spectral broadening of this SC radiation is achieved by coupling it into a chalcogenide arsenide-selenide (AsSe) photonic crystal fiber (PCF). An output power of 24 W at 2 μm has been achieved in QML operation for the Tm3+-doped fiber laser. The SC output power from the ZBLAN fiber has been 7.8 W with a spectrum extending to approximately 4.1 μm. For further wavelength broadening experiments, a long-wave-pass filter with a 3 dB edge around 3.6 μm has been implemented between the ZBLAN and the AsSe fiber to cut out the residual pump light at 2 μm and the radiation between 2 μm and 3.5 μm. The pump power was approximately 120 mW with a spectrum from 3.5 μm to 3.9 μm. First proof of principal experiments has been performed with 20 mW of averaged output power and a spectrum extending to 4.9 μm. The coupling efficiency of the SC radiation from the ZBLAN fiber into the AsSe fiber has been around 30%.

  10. 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.

  11. The Thermal Conductivity of Lanthanum TRI-FLURIDE:0.1% Erbium from 1.8 K to 100 K.

    NASA Astrophysics Data System (ADS)

    Vinson, Wayne Wright

    1987-12-01

    Scope of Study. The purpose of this study was to obtain and analyse the principal thermal conductivities of crystalline lanthanum tri-fluoride (doped with 0.1% erbium), and calcuim fluoride. The conductivity for LaF _3 was measured parallel and perpendicular to the high-symmentry axis; and for face-centered cubic CaF_2, along one of the (100) directions. The measurements were taken from 1.8 K to 100 K using a ^4He cryostat of standard design, where the lowest temperatures were obtained by pumping ^4 He vapor. The data were analyzed for each sample by using a Gaussian numerical integration routine to calculate appropriate Debye integrals to model the curves obtained. A scattering rate of the form tau^{-1} = v/L + Aomega^4 + (B_1 + B_2exp (-Theta/aT) omega^4 T + Domega where each of the coefficients A, B_1, B _2, and D were initially estimated from theoretical considerations, was adjusted to obtain the best fit to the data. The form of the normal phonon-phonon term, B omega^4T, was obtained by thermalizing the anharmonic decay rates, tau ^{-11} = C_{ rm m}omega^5, as predicted by precious theories and verified for each of the samples in studies in the literature. Findings and Conclusions. Practically all the features of the thermal conductivities obtained which can be accounted for by the model employed have met with satisfactory agreement, certainly qualitatively, and no significant inconsistencies arose from the quantitative treatment. Because of the satisfactory comparison of the results of this study with those of phonon spectroscopy, we suggest that the form of the phonon-phonon interaction term might behave as omega^4T rather than the omega^2T and omega ^2T^3 forms extensively employed in the literature. Prediction of the anharmonic decay rates for various other technologically important crystals were done by applying the methods of this study to their thermal conductivities obtained from the literature, thus suggesting directions for further investigation.

  12. Broadband reflectance coatings for vacuum ultraviolet application

    NASA Technical Reports Server (NTRS)

    Herzig, Howard; Fleetwood, C. M., Jr.; Flint, B. K.

    1987-01-01

    An experimental investigation has obtained results indicating that neither LaF3 nor LiYF4 are acceptable alternatives to MgF2 as coatings for vacuum-deposited aluminum mirrors from which high UV reflectance down to 1150 A is required. Nevertheless, LaF3 may prove useful in those specialized applications in which the suppression of lower wavelength emissions, such as the 1216-A hydrogen line, is desirable.

  13. Investigations on spectroscopic properties of Dy3+ doped zinc telluro-fluoroborate glasses for laser and white LED applications

    NASA Astrophysics Data System (ADS)

    Suthanthirakumar, P.; Marimuthu, K.

    2016-12-01

    A new series of Zinc telluro-fluoroborate glasses (ZTFB) doped with Dy3+ ions with the chemical composition (30-x) B2O3 + 30TeO2 + 16ZnO + 10ZnF2 + 7CaF2 + 7BaF2 + xDy2O3 (where x = 0.05, 0.1, 0.25, 0.5, 1 and 2 in wt%) have been synthesized by the conventional melt quenching technique and the prepared glass samples were characterized through XRD, FTIR, UV-Vis-NIR optical absorption, photoluminescence and decay spectral measurements. The XRD patterns have been recorded to confirm the amorphous nature. The FTIR spectral measurements were carried out to identify the functional groups present in the title glasses. From the energy band positions of the absorption spectra, bonding parameters (βbar and δ) have been calculated to identify the covalent/ionic nature of the metal-ligand bond present in the prepared glasses. The Judd-Ofelt (JO) intensity parameters Ωλ (λ = 2, 4 and 6) have been calculated from the oscillator strengths of the different absorption bands to understand the nature of the ligand environment around the Dy3+ ions. The radiative parameters such as transition probability (A), stimulated emission cross-section (σPE), radiative lifetime (τR) and branching ratios (βR) corresponding to the 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, and 4F9/2 → 6H11/2 emission transitions have been determined using JO parameters and the refractive index values. The CIE chromaticity coordinates were calculated from the luminescence spectra to explore the dominant emission colour of the title glasses and the obtained results were discussed in detail and reported.

  14. 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.

  15. Cryogenic engineering for OMEGA2000: design and performance

    NASA Astrophysics Data System (ADS)

    Baumeister, Harald; Bizenberger, Peter; Bayler-Jones, Coryn A. L.; Kovács, Zoltan; Röser, Hermann-Josef; Rohloff, Ralf-Rainer

    2003-03-01

    Omega2000 is a prime focus near infrared (NIR) wide-field camera for the 3.5 meter telescope at Calar Alto/Spain. Having a large field of view and an excellent optical quality, the instrument is particularly designed for survey observations. A cryogenic four lens focal reducer delivers a 15.4 x 15.4 arcminute field of view (FOV) with a pixel scale of 0.45"/pixel. The lenses are made of various optical materials, including CaF2 and BaF2 with diameters of up to 150 mm. They must be specially mounted to survive cooling and to follow the tight tolerances (+/- 0.05 mm for lens centricity and +/- 30 arcsec for lens tilt) required by the optical design. For a wide range of observing applications, a filter mechanism can hold up to 17 filters of 3 inch diameter in 3 filter wheels. For exact and reproducible filter positions, a mechanical locking mechanism has been developed which also improves the cool-down performance of the filter wheels and filters. This mechanism allows a minimum distance of about 3 mm between the filter wheels. A Rockwell HAWAII-2 FPA is used to cover the wavelength range from 0.85 μm to 2.4 μm. Special care has been taken with regard to the thermal coupling of the detector. The thermal connection is made by gold layers on the fanout board and an additional spring-loaded mechanism. A warm mirror baffle system has been developed, in order to minimize the thermal background for K band observations. The camera is a focal reducer only and has no cold pupil stop.

  16. Structural and luminescence behaviour of Er3+ doped telluro-fluoroborate glasses

    NASA Astrophysics Data System (ADS)

    Karthikeyan, P.; Suthanthirakumar, P.; Vijayakumar, R.; Marimuthu, K.

    2015-03-01

    The Er3+ doped telluro-fluoroborate glasses with the chemical composition (30 - x)B2O3 + 30TeO2 + 16ZnO + 10ZnF2 + 7CaF2 + 7BaF2 + xEr2O3 (x = 0.05, 0.1, 0.5, 0.75, 1.0 and 3 in wt%) have been prepared by melt quenching technique and characterized through XRD, SEM, FTIR, Raman, absorption and luminescence spectral analysis. The XRD and SEM measurements were made to examine the amorphous nature. The presence of various stretching and bending vibration modes of functional groups have been investigated through FTIR and Raman spectra. The bonding parameters (β bar and δ) were calculated from the absorption spectra to claim the covalent/ionic nature of the metal-ligand bond in the prepared glasses. From the absorption spectra, optical band gap energies (Eopt) corresponding to the direct and indirect allowed transitions were calculated to analyze the electronic band structure. The Urbach energy values have also been estimated and discussed. The Judd-Ofelt (JO) intensity parameters (Ωλ (λ = 2, 4, 6)) were determined from the absorption spectra in order to study the symmetry around the RE ion site and used to compute the radiative properties such as transition probability (AR), stimulated emission cross-section ( σPE) and branching ratios (βR) for the different emission transitions. The emission intensities of the prepared glasses were characterized through CIE 1931 chromaticity diagram and the results were discussed and compared with the reported literature.

  17. 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 μm to 1.7 μm) 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 μm. 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.

  18. Surface assessment and mitigation of DUV optics

    NASA Astrophysics Data System (ADS)

    Wang, Jue

    2015-09-01

    CaF2 is one of the foremost optical materials used in ArF excimer laser optics. Surface quality of optically finished CaF2 plays an important role in the component's lifetime. Several techniques were employed to assess surface quality of optically finished CaF2 in terms of top surface and subsurface damage, resulting in subsurface-damagefree CaF2. UV light and plasma interaction with CaF2 surfaces were investigated. The results were discussed in terms of surface roughness and cleanness associated with surface finishing and optical coatings.

  19. [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

  20. Hydrothermally synthesized barium fluoride nanocubes for thermoluminescence dosimetry

    NASA Astrophysics Data System (ADS)

    Bhadane, Mahesh S.; Dahiwale, S. S.; Bhoraskar, V. N.; Dhole, S. D.

    2016-05-01

    In this work, we report a hydrothermally synthesized Dy doped BaF2 (BaF2:Dy) nanocubes and its Thermoluminescence studies. The synthesized BaF2:Dy samples was found to posses FCC structure and having average size ~ 60-70 nm, as revealed through X-Ray Diffraction. Cubical morphology having size ~90 nm was observed from TEM analysis. The 60Co γ- ray irradiated BaF2:Dy TL dosimetric experiments shows a pre-dominant single glow peak at 153 °C, indicating a single level trap present as a metastable state. Furthermore, BaF2:Dy nanophosphor shows a sharp linear response from 10 Gy to 3 kGy, thus it can be applicable as a gamma dosimeter.

  1. Cluster models and ab initio calculations of (19)F NMR isotropic chemical shifts for inorganic fluorides.

    PubMed

    Body, Monique; Silly, Gilles; Legein, Christophe; Buzaré, Jean-Yves

    2005-05-26

    (19)F NMR isotropic chemical shift (delta(iso)) calculations are performed in crystallized compounds using the GIAO method with the B3LYP hybrid functional at DFT level. Clusters centered on the studied fluorine atoms mimic the crystalline structures. The 6-311+G(d) basis set is chosen for the central fluorine atom, and the LanL2DZ basis set for the others. The metal atoms are described by the 3-21G(2d) basis set or, when not available, by the CRENBL basis set with the corresponding ECP, and augmented with 2d polarization functions when existing. First, for high-symmetry systems (MF, MF(2), and MF(3) compounds), a systematization of the cluster building up from coordination spheres is proposed, generalized to fluoroperovskites and fluoroaluminates KAlF(4) and RbAlF(4). When applied to rather low symmetry systems such as barium fluorometalates BaMgF(4), BaZnF(4), and Ba(2)ZnF(6), the definition of the coordination spheres is far from easy. Then, for structures built up from a MF(6) octahedron network, we may define different "starting clusters": [FM(2)F(8)] for the shared fluorine atoms, [FMF(4)] for the unshared ones, and [FBa(4)](7+) for the "free" ones. Analogous "starting clusters" are then tested on compounds from the NaF-AlF(3), BaF(2)-AlF(3), and CaF(2)-AlF(3) binary systems and for alpha-BaCaAlF(7) that are also built up from a MF(6) octahedron network. For each of these corresponding fluorine sites, delta(iso) values are calculated with the "starting clusters" and several larger clusters and compared to the experimental delta(iso) values. For the barium-containing clusters, the RMS deviation is equal to 51 ppm. It is suggested that this result may be related to the poor quality of the barium basis sets for which no polarization functions are available for the moment. In total, chemical shifts were calculated for 122 fluorine sites, in a various range of compounds. For the clusters without barium, the ab initio method leads to a RMS equal to 22 ppm, which is a quite nice result keeping in mind that the (19)F chemical shift range is larger than 200 ppm. PMID:16852244

  2. PS300 Tribomaterials Evaluated at 6500C by Bushing Test Rig

    NASA Technical Reports Server (NTRS)

    Striebing, Donald R.; DellaCorte, Christopher

    2004-01-01

    A new facility has been developed to test the tribological behavior (friction and wear) of PS300 solid lubricant bushings at high temperatures. PS300 is a commercially available solid lubricant invented at the NASA Glenn Research Center. It can be prepared as a plasma spray coating or as a free-standing powder metallurgy component, designated PM300. PS300 and PM300 composites are designed to lubricate sliding components at temperatures above the capability of today's best oils, greases, and solid lubricants. One of the primary applications being pursued for PM300 is the development of bushings for use in high-temperature machinery. Examples include inlet guide vane bushings for gas turbines and conveyors, and bearings for industrial furnaces and ovens. Encouraging preliminary field trials indicate that PS300 and PM300 lubricant materials have been commercialized successfully in several industrial applications. However, the lack of laboratory performance data has hindered further commercialization especially for new applications that differ significantly from the established experience base. The purpose of the newly developed bushing test rig will be to determine the performance characteristics of PM300, and other materials, under conditions closely matching intended applications. The data will be used to determine engineering friction and wear rates and to estimate the life expectancy of bushings for new applications. In the new rig, the bushing is loaded against a rotating shaft inside a furnace enclosure (see the preceding photograph). Loads can vary from 5 to 200 N, speeds from 1 to 400 rpm, and temperatures from 25 to 800 C. Furnace temperature, bushing temperature, shaft speed, and torque are monitored during the test, and wear of both the bushing and the shaft is measured after testing is completed. Initially, PM300 bushings will be evaluated and compared with lower temperature, traditional bushing materials like graphite and porous bronze. The baseline PM304 composition is 60 wt% NiCr (a binder), 20 wt% Cr2O3 (a hardener), 10 wt% BaF2/CaF2 (a high-temperature lubricant), and 10 wt% Ag (a low-temperature lubricant). Future research efforts will include determining the effects of load, sliding speed, and temperature on tribological performance and, possibly, tailoring composition for specific applications. We expect that the availability of measured performance data will enhance the market penetration of PM300 technology.

  3. Epitaxial growth of rare-earth trifluorides on III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Ritchie, Sayuri

    Epitaxial growths of rare-earth trifluorides on III--V semiconductors have been investigated. Synchrotron photoemission spectroscopy showed a complete coverage of III--V substrates by LaF3 and ErF3 films and interfacial chemical reactions at the interface. In the LaF 3 films on GaAs(111) substrates, residual tensile strains were detected by high-resolution X-ray diffraction (HRXRD) contrary to the expected compressive strains in the case of a pseudomorphic growth. The tensile strains are interpreted as being due to the differential thermal contractions of the fluorides and the semiconductors during cooling. The correlations between the bulk structure and the surface structure of the LaF3 films on GaAs and InP substrates have been studied by X-ray rocking curve measurements, grazing incidence X-ray scattering and atomic force microscopy. The lateral coherence lengths in the LaF3 films from the X-ray rocking curves and the height-height surface correlation lengths from the X-ray scattering and the atomic force microscopy were comparable to each other and were associated with the lattice mismatch of the system at the growth temperature. The results are interpreted in terms of strain relieving defects surrounding the columns of coherent crystals. The kinetics of LaF3 film growths on III--V semiconductors were investigated using the self-affine surface structure analysis for the X-ray specular/diffuse scattering and the atomic force microscopy. The scaling exponents for the film growth obtained from the analysis were closest to the exponents predicted by the Villain-Lai-Das Sarma model in which the surface diffusion of deposited particles is the most important process in the film growth. InP single crystal islands have been grown on LaF3/InP(111) heterostructures. The InP islands are observed to be faceted with three-fold symmetry as expected for (111) orientation. A small broadening of the InP substrate diffraction peak is interpreted as being due to inhomogeneous strains associated with the InP islands and differential thermal contraction of the LaF3films during cooling.

  4. 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.

  5. Neutron beam test of barium fluoride crystal for dark matter direct detection

    NASA Astrophysics Data System (ADS)

    Guo, C.; Ma, X. H.; Wang, Z. M.; Bao, J.; Dai, C. J.; Guan, M. Y.; Liu, J. C.; Li, Z. H.; Ren, J.; Ruan, X. C.; Yang, C. G.; Yu, Z. Y.; Zhong, W. L.

    2016-10-01

    In order to test the capabilities of Barium Fluoride (BaF2) crystal for dark matter direct detection, nuclear recoils are studied with mono-energetic neutron beam. The energy spectra of nuclear recoils, quenching factors for elastic scattering neutrons and discrimination capability between neutron inelastic scattering events and γ events are obtained for various recoil energies of the F content in BaF2.

  6. 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.

  7. Capillary-force-induced formation of luminescent polystyrene/(rare-earth-doped nanoparticle) hybrid hollow spheres.

    PubMed

    Chen, Min; Xie, Lin; Li, Fuyou; Zhou, Shuxue; Wu, Limin

    2010-10-01

    This paper presents a "one-pot" procedure to synthesize polystyrene/(rare-earth-doped nanoparticles) (PS/REDNPs) hybrid hollow spheres via the in situ diffusion of organic core into inorganic shell under strong capillary force. In this approach, when carboxyl-capped PS colloids were deposited by different REDNPs in aqueous medium, such as LaF3:Eu3+, LaF3:Ce3+-Tb3+, and YVO4:Dy3+, PS/REDNPs inorganic-organic hybrid hollow spheres could be directly obtained via the in situ diffusion of core PS chains into the voids between rare-earth-doped nanoparticles through the strong capillary force. Not only is the synthetic procedure versatile and very simple, but also the obtained hybrid hollow spheres are hydrophilic and luminescent and could be directly used in chemical and biological fields.

  8. Investigation of Water-Soluble X-ray Luminescence Nanoparticles for Photodynamic Activation

    SciTech Connect

    Liu, Yuanfang; Chen, Wei; Wang, Shaopeng; Joly, Alan G.

    2008-01-28

    In this letter, we report the synthesis of LaF3:Tb3+-MTCP (meso-Tetra(4-carboxyphenyl) porphine) nanoparticle conjugates and investigate the energy transfer as well as singlet oxygen generation following X-ray irradiation. Our observations indicate that LaF3:Tb3+-MTCP nanoparticle conjugates are efficient photodynamic agents that can be initiated by X-rays at a reasonably low dose. The addition of folic acid to facilitate targeting to folate receptors on tumor cells has no effect on the quantum yield of singlet oxygen in the nanoparticle-MTCP conjugates. Our pilot studies indicate that water-soluble scintillation nanoparticles can be potentially used to activate photodynamic therapy as a promising deep cancer treatment.

  9. 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.

  10. The Growth and Characterization of Germanium-Carbon Alloy Thin Films and Solid Phase Equilibria for Metal-Silicon - Ternary Systems: Magnesium, Calcium, Strontium, Barium, Scandium, Yttrium, Lanthanum, Titanium, Zirconium and Hafnium

    NASA Astrophysics Data System (ADS)

    Yuan, Haojie

    1992-09-01

    Thin films of pure germanium-carbon alloys (Ge _{rm x}C _{rm 1-x} with 0 <=q x <=q 1) have been grown on Si and Al_2O_3 substrates by pulsed laser ablation in a high vacuum chamber. The films were analyzed by x-ray 0-20 diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), conductivity measurements and optical absorption spectroscopy. The analyses of these new materials showed that films of all compositions were amorphous, free of contamination and uniform in composition. By changing the film composition, the optical band gap of these semiconducting films was varied from 0.00 eV to 0.85 eV for x = 0.0 to 1.0 respectively. According to the AES results, the carbon atoms in the Ge-C alloy thin film samples have a bonding structure that is a mixture of sp^2 and sp^3 hybridizations. The presence of the sp^2 C is apparently what causes the bandgap of amorphous Ge-C alloys to decrease with increasing carbon concentration. The solidus portion of the ternary phase diagrams of the type M-Si-O, where M = Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr and Hf have been derived at 298K and 1 atm oxygen partial pressure by investigating the bulk reactions possible in these systems. These phase diagrams, which have been determined by experiments and by calculations using thermodynamic data available, can be used to predict the occurrence of the reaction products or the stability of the phases present at the interfaces between different solid materials. Hence, they provide guides in designing thin film structures and in selecting candidate materials to form chemically stable interfaces. A research effort has been made on the investigation of the growth of diamond thin films from a carbon containing solid-CI_4, using laser ablation technique. The film grown by laser ablation from CI _4 is mainly composed of carbon with very small amount of oxygen and iodine as indicated by x-ray photoelectron spectroscopy data. The Auger electron spectroscopy result shows that the film grown contains a mixture of sp^2 and sp^3 hybridized carbon. By using x-ray powder diffraction and magnetic susceptibility measurements methods, we studied the chemical stability of candidate interlayer materials between YBa _2Cu_3O _7-delta and Si. The results show that CaF_2 reacts with YBCO while BaF_2 is chemically stable with YBCO. LaGaO_3 and Ca _2SiO_4 are chemically stable with Si and more investigations need to be made on the reactivity between Ca_2SiO _4 and YBCO.

  11. Preparation of lanthanum trifluoride nanoparticles surface-capped by tributyl phosphate and evaluation of their tribological properties as lubricant additive in liquid paraffin

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    LaF3 nanoparticles surface-capped by tributyl phosphate (denoted as TBP-LaF3) were prepared by in situ surface modification route. The size, morphology and phase structure of as-prepared TBP-LaF3 nanoparticles were analyzed by means of X-ray diffraction and transmission electron microscopy. The thermal stability of as-synthesized TBP-LaF3 nanoparticles was evaluated based on thermogravimetric analysis, and their tribological properties as additive in liquid paraffin were evaluated with a four-ball friction and wear tester. Moreover, the morphology of worn steel surfaces was analyzed with a scanning electron microscope, and the composition and chemical state of typical elements on worn steel surfaces were examined with an X-ray photoelectron spectroscope. Results show that as-synthesized TBP-LaF3 nanoparticles possess good thermal stability and excellent anti-wear and load-carrying capacities as well as good friction-reducing ability. This is because, on the one hand, TBP as the surface-modifier is able to improve the dispersibility of LaF3 nanoparticles in liquid paraffin and allows good adsorption of LaF3 nanoparticles on sliding steel surfaces. On the other hand, active P element of TBP can form tribochemical reaction film on sliding steel surfaces. As a result, the boundary lubricating film consisting of adsorbed LaF3 nanoparticles and tribochemical reaction film results in greatly improved friction-reducing and anti-wear abilities as well as load-carrying capacity of the lubricant base stock and gives rise to significantly reduced friction and wear of the steel-steel sliding pair.

  12. 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.

  13. Thermal quenching of thermoluminescence in TLD-200, TLD-300 and TLD-400 after β-irradiation

    NASA Astrophysics Data System (ADS)

    Kafadar, Vural E.

    2011-02-01

    The dosimetric characteristics of many TL materials are influenced by changes in location, size and shape of the glow curves due to changes in the heating rate. In this study, the effect of heating rate on the integrated peak areas of CaF 2:Dy (TLD-200), CaF 2:Tm (TLD-300) and CaF 2:Mn (TLD-400) crystals have been investigated after β-irradiation. It was observed that the peak temperatures of all peaks shifted to the high temperature sides and the integrated peak areas decrease as the heating rate increases due to thermal quenching, whose efficiency increases as temperature increases.

  14. The effects of heating rate on the dose response characteristics of TLD-200, TLD-300 and TLD-400

    NASA Astrophysics Data System (ADS)

    Kafadar, V. Emir; Necmeddin Yazici, A.; Güler Yildirim, R.

    2009-10-01

    In the given study; the effects of heating rates on the dose response characteristics of CaF 2:Dy (TLD-200), CaF 2:Tm (TLD-300) and CaF 2:Mn (TLD-400) crystals have been investigated using the dose dependence curve and dose response function f( D). It was observed from the dose response functions that the linearity and behaviour of the TL glow peaks of TLD-200 and TLD-400 are affected, but the TLD-300 is not affected from the heating rate.

  15. Nanocrystallization in Fluorochlorozirconate Glass-Ceramics.

    PubMed

    Alvarez, Carlos J; Liu, Yuzi; Leonard, Russell L; Johnson, Jacqueline A; Petford-Long, Amanda K

    2013-11-01

    Heat treating fluorochlorozirconate (FCZ) glasses nucleates nanocrystals in the glass matrix, resulting in a nanocomposite glass-ceramic that has optical properties suitable for use as a medical imaging plate. Understanding the way in which the nanocrystal nucleation proceeds is critical to controlling the optical behavior. The nucleation and growth of nanocrystals in FCZ glass-ceramics was investigated with in situ transmission electron microscopy heating experiments. The experiments showed the nucleation and growth of previously unreported BaF2 nanocrystals in addition to the expected BaCl2 nanocrystals. Chemical analysis of the BaF2 nanocrystals shows an association with the optically active dopant previously thought only to interact with BaCl2 nanocrystals. The association of the dopant with BaF2 crystals suggests that it plays a role in the photoluminescent (PL) properties of FCZ glass-ceramics.

  16. Interfacial reactions and microstructure of BaTiO 3 films prepared using fluoride precursor method

    NASA Astrophysics Data System (ADS)

    Fujihara, Shinobu; Schneller, Theodor; Waser, Rainer

    2004-01-01

    Interfacial reactions of BaF 2 and TiO 2 were investigated in preparing BaTiO 3 thin films using a fluoride precursor method. Trifluoroacetate solutions were prepared from barium acetate, titanium tetraisopropoxide (TTIP), and trifluoroacetic acid (TFA, CF 3COOH) with additives such as water and acetylacetone. The solutions were deposited on platinized Si wafers by spin-coating, were pyrolysed at 400 °C in air and were finally heated typically at 700 °C in a water vapor atmosphere. The perovskite BaTiO 3 phase was obtained although a small portion of BaF 2 remained unreacted. Thus, the films were characterized as the mixture of BaTiO 3, BaF 2, and amorphous TiO 2. Influence of the solution chemistry on the phase evolution and microstructure was examined in order to discuss the reaction pathway of the perovskite phase.

  17. Nanocrystallization in Fluorochlorozirconate Glass-Ceramics

    PubMed Central

    Alvarez, Carlos J.; Liu, Yuzi; Leonard, Russell L.; Johnson, Jacqueline A.; Petford-Long, Amanda K.

    2014-01-01

    Heat treating fluorochlorozirconate (FCZ) glasses nucleates nanocrystals in the glass matrix, resulting in a nanocomposite glass-ceramic that has optical properties suitable for use as a medical imaging plate. Understanding the way in which the nanocrystal nucleation proceeds is critical to controlling the optical behavior. The nucleation and growth of nanocrystals in FCZ glass-ceramics was investigated with in situ transmission electron microscopy heating experiments. The experiments showed the nucleation and growth of previously unreported BaF2 nanocrystals in addition to the expected BaCl2 nanocrystals. Chemical analysis of the BaF2 nanocrystals shows an association with the optically active dopant previously thought only to interact with BaCl2 nanocrystals. The association of the dopant with BaF2 crystals suggests that it plays a role in the photoluminescent (PL) properties of FCZ glass-ceramics. PMID:24707056

  18. AES analysis of barium fluoride thin films

    NASA Astrophysics Data System (ADS)

    Kashin, G. N.; Makhnjuk, V. I.; Rumjantseva, S. M.; Shchekochihin, Ju. M.

    1993-06-01

    AES analysis of thin films of metal fluorides is a difficult problem due to charging and decomposition of such films under electron bombardment. We have developed a simple algorithm for a reliable quantitative AES analysis of metal fluoride thin films (BaF 2 in our work). The relative AES sensitivity factors for barium and fluorine were determined from BaF 2 single-crystal samples. We have investigated the dependence of composition and stability of barium fluoride films on the substrate temperature during film growth. We found that the instability of BaF 2 films grown on GaAs substrates at high temperatures (> 525°C) is due to a loss of fluorine. Our results show that, under the optimal electron exposure conditions, AES can be used for a quantitative analysis of metal fluoride thin films.

  19. Friction and Wear Characteristics of Plasma-Sprayed Self-Lubrication Coating with Clad Powder at Elevated Temperatures up to 800 °C

    NASA Astrophysics Data System (ADS)

    Huang, Chuanbing; Du, Lingzhong; Zhang, Weigang

    2014-02-01

    NiCr/(Cr3C2-BaF2·CaF2) coating was fabricated by atmospheric plasma spray technology using clad powder. The coating shows low porosity, high microhardness and bonding strength, and it also exhibits good friction reduction and wear resistance at elevated temperatures up to 800 °C which is due to the formation of a kind of continuous BaF2·CaF2 eutectic lubricating film. The excellent mechanical and tribological properties of the coating are partially attributed to the protection of NiCr layer of the composite powders which can decrease oxidation, decarburization of Cr3C2, and ablation of BaF2·CaF2 eutectic during spray and deposition process.

  20. Preparation and optimization of calcium fluoride particles for dental applications.

    PubMed

    Koeser, Joachim; Carvalho, Thiago Saads; Pieles, Uwe; Lussi, Adrian

    2014-07-01

    Fluorides are used in dental care due to their beneficial effect in tooth enamel de-/remineralization cycles. To achieve a desired constant supply of soluble fluorides in the oral cavity, different approaches have been followed. Here we present results on the preparation of CaF2 particles and their characterization with respect to a potential application as enamel associated fluoride releasing reservoirs. CaF2 particles were synthesized by precipitation from soluble NaF and CaCl2 salt solutions of defined concentrations and their morphology analyzed by scanning electron microscopy. CaF2 particles with defined sizes and shapes could be synthesized by adjusting the concentrations of the precursor salt solutions. Such particles interacted with enamel surfaces when applied at fluoride concentrations correlating to typical dental care products. Fluoride release from the synthesized CaF2 particles was observed to be largely influenced by the concentration of phosphate in the solution. Physiological solutions with phosphate concentration similar to saliva (3.5 mM) reduced the fluoride release from pure CaF2 particles by a factor of 10-20 × as compared to phosphate free buffer solutions. Fluoride release was even lower in human saliva. The fluoride release could be increased by the addition of phosphate in substoichiometric amounts during CaF2 particle synthesis. The presented results demonstrate that the morphology and fluoride release characteristics of CaF2 particles can be tuned and provide evidence of the suitability of synthetic CaF2 particles as enamel associated fluoride reservoirs.

  1. Experimental evidence of self-limited growth of nanocrystals in glass.

    PubMed

    Bhattacharyya, Somnath; Bocker, Christian; Heil, Tobias; Jinschek, Jörg R; Höche, Thomas; Rüssel, Christian; Kohl, Helmut

    2009-06-01

    Growth of nanocrystals precipitated in glasses with specific compositions can be effectively limited by diffusion barriers forming around crystallites. For the first time, we do experimentally prove this concept of self-limited growth on the nanoscale for a SiO(2)/Al(2)O(3)/Na(2)O/K(2)O/BaF(2) glass in which BaF(2) nanocrystals are formed. As shown by advanced analytical transmission electron microscopy techniques, the growth of these BaF(2) crystals, having great potential for photonic applications, is inherently limited by the formation of a ca. 1 nm wide SiO(2) shell.

  2. Lead-barium fluoroborate glass ceramics doped with Nd3+ or Er3+

    NASA Astrophysics Data System (ADS)

    Petrova, O. B.; Sevostjanova, T. S.; Anurova, M. O.; Khomyakov, A. V.

    2016-02-01

    Lead-barium fluoroborate glasses in the PbF2-BaF2-B2O3, PbF2-BaO-B2O3, and PbO- BaF2-B2O3 systems doped with rare-earth ions (Nd3+ or Er3+) are synthesized and studied. It is shown that, based on these glasses, it is possible to produce transparent glass ceramics with fluoride crystalline phases, including ceramics with one crystalline phase of the fluorite structure. The spectral and luminescent properties of the doped glasses, glass ceramics, and polycrystalline complex fluorides containing Pb, Ba, and rare ions are studied.

  3. 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.

  4. Effect of Halide Flux on Physicochemical Properties of MgCl2-Based Molten Salts for Accelerating Zirconium Production: Thermodynamic Assessment

    NASA Astrophysics Data System (ADS)

    Shin, Jae Hong; Park, Joo Hyun

    2016-07-01

    The effective halide flux additive for increasing the density of MgCl2 mixture and for decreasing the activity of MgCl2 was investigated in order to improve the reaction efficiency between gaseous ZrCl4 and fresh Mg melt to produce zirconium sponge. Thermochemical computation using FactSageTM software was primarily carried out, followed by the experimental confirmation. The addition of CaCl2, BaCl2, MgF2, and CaF2 to the molten MgCl2 increases the density of the melts, indicating that these halide additives can be a candidate to increase the density of the MgCl2-based molten salts. Among them, BaCl2, MgF2, and CaF2 are the useful additives. The activity of MgCl2 can be reduced by the addition of BaCl2, KCl, NaCl, MgF2, and CaF2, among which the CaF2 is the most effective additive to reduce the activity of MgCl2 with the strongest negative deviation from an ideality. Thus, the addition of CaF2 to the MgCl2, forming the MgCl2-CaF2 binary melt, is the most effective way not only to increase the density of the melt but also to decrease the activity of MgCl2, which was experimentally confirmed. Consequently, the production rate of zirconium sponge by magnesiothermic reduction process can be accelerated by the addition of CaF2.

  5. Effect of Halide Flux on Physicochemical Properties of MgCl2-Based Molten Salts for Accelerating Zirconium Production: Thermodynamic Assessment

    NASA Astrophysics Data System (ADS)

    Shin, Jae Hong; Park, Joo Hyun

    2016-09-01

    The effective halide flux additive for increasing the density of MgCl2 mixture and for decreasing the activity of MgCl2 was investigated in order to improve the reaction efficiency between gaseous ZrCl4 and fresh Mg melt to produce zirconium sponge. Thermochemical computation using FactSageTM software was primarily carried out, followed by the experimental confirmation. The addition of CaCl2, BaCl2, MgF2, and CaF2 to the molten MgCl2 increases the density of the melts, indicating that these halide additives can be a candidate to increase the density of the MgCl2-based molten salts. Among them, BaCl2, MgF2, and CaF2 are the useful additives. The activity of MgCl2 can be reduced by the addition of BaCl2, KCl, NaCl, MgF2, and CaF2, among which the CaF2 is the most effective additive to reduce the activity of MgCl2 with the strongest negative deviation from an ideality. Thus, the addition of CaF2 to the MgCl2, forming the MgCl2-CaF2 binary melt, is the most effective way not only to increase the density of the melt but also to decrease the activity of MgCl2, which was experimentally confirmed. Consequently, the production rate of zirconium sponge by magnesiothermic reduction process can be accelerated by the addition of CaF2.

  6. The improved scintillation crystal lead tungstate scintillation for PET

    NASA Astrophysics Data System (ADS)

    Wan, Youbao; WU, Rurong; Xiao, Linrong; Zhang, Jianxin; Yang, Peizhi; Yan, Hui

    2009-07-01

    As a valuable material for the detecting of γ-ray, PbWO4 and BaF2:PbWO4 crystals were grown by a novel multi-crucible temperature gradient system developed by ourselves. Utilizing a topical partial heating method, this system can form a topical partial high temperature in its hearth. Thus this system could melt raw materials in step by step as requirement. The advantage of this method is that there would be solid obstruct left on the melt in the procedure of the crystal growing up. The left obstruct could prevent the volatilization of the component in the melt. Hence it is helpful for the composition homogenization in the crystal. The system also offers a sustaining device for multi-crucibles and thus it can grow many crystals simultaneity. The optical properties and scintillation properties of the crystals were studied. The results reveal that the ions doping improves the scintillation properties of the crystal. The transmittance spectra show that the transmittance of BaF2:PbWO4 crystals are better than that of PbWO4 crystals. For the PbWO4 crystals, their absorption edge is at 325nm, and their maximum transmittance is 68%. For the BaF2:PbWO4 crystals, their absorption edge is at 325nm and their maximum transmittance is upto76%. The X-ray excited luminescence spectra shows that the luminescence peak is at 420nm for the samples of PbWO4 crystal while the peak is at 430nm for the samples of BaF2:PbWO4 crystal respectively. The luminescence intensity of the samples of BaF2:PbWO4 crystal is about two times than that of PbWO4 crystal. And their peak shape is different for the two kind of crystal. The light yield of BaF2:PbWO4 crystals is about 2.9 times than that of PbWO4 crystal Analyzing these scintillation properties, we find that the VPb 3+ and VO- defects do harm for the optical properties of the crystal. Ions doping method could reduce the defect concentration and improving its illumination performance of the crystal. Specially, the doped F- ions in O2- site can induce the aberrance of the [WO4]2- tetrahedron and form [WO3F]- tetrahedron which has more active blue light yield, thus improve the light yield of the crystal. The improved light yield of BaF2:PbWO4 crystals is valuable for the medical diagnosing instrument PET and CT with high resolving power

  7. [Using barium fluoride fine particles as stationary phase for TLC/FTIR analysis].

    PubMed

    Liu, Xi; Pan, Qing-hua; Ding, Jie; Zhu, Qing; He, An-qi; Yue, Shi-juan; Li, Xiao-pei; Hu, Li-ping; Xia, Jin-ming; Liu, Cui-ge; Wei, Yong-ju; Yu, Jiang; Yang, Zhan-lan; Zhu, Xi; Xu, Yi-zhuang; Wu, Jin-guang

    2011-07-01

    In situ TLC/FTIR technique has tremendous potential in the analysis of complex mixtures. However, the progress in this technique was quite slow. The reason is that conventional stationary phase such as silica gel etc. has strong absorption in FTIR spectrum and thus brings about severe interference in the detection of samples. To solve the problem, the authors propose to use barium fluoride fine particles as stationary phase of TLC plate. The reasons are as follows: Barium fluoride wafer has been extensively used as infrared window in FTIR experiments and it has no absorbance in an IR region between 4 000 and 800 cm'. As a matter of fact, the atomic mass of barium and fluoride is quite large, thus the normal vibration of BaF2 lattice is limited in far-IR region and low frequency part of mid-IR region. Therefore, the interference caused by IR absorption of stationary phase can be resolved if BaF2 is used as stationary phase of TLC plate. Moreover, BaF2 is quite stable and insolvable in water and most organic solvents and it will not be dissolved by mobile phase or react with samples in TLC separation. Additionally, decreasing the particle size of BaF2 is very important in TLC/FTIR analysis technique. The reason is two-fold: First, decreasing the particle size of stationary phase is helpful to improving the efficiency of separation by TLC plate; second, decreasing the size of BaFz particle can improve the quality of FTIR spectra by alleviating the problem of light scattering. By optimizing the synthetic conditions, fine particles of barium fluoride were obtained. SEM results indicate that the size of the BaF2 particles is around 500 nm. FTIR spectrum of the BaF2 particles shows that no absorption of impurity was observed. Moreover, the elevation of baseline caused by light scattering is insignificant. The authors have developed a new technique named "settlement volatilization method" to prepare TLC plate without polymeric adhesive that may bring about significant interference in FTIR analysis. Preliminary TLC experiments proved that the TLC plate using BaF2 fine particles as stationary phase can separate rhodamine B from methylene blue successfully. Applications of barium fluoride fine particles as stationary phase have bright perspective in the development of new in-situ TLC/FTIR analysis techniques. PMID:21942020

  8. Construction of prototypes of a new class of infrared detectors

    NASA Technical Reports Server (NTRS)

    Sher, A.

    1976-01-01

    A class of infrared detectors is proposed and experimental results are presented for a prototype device. The material used is LaF3, an ionic conductor with a capacitance that varies exponentially with temperature. The detectivity of a prototype detector is estimated from measured signal voltages and incident power, and a Johnson noise voltage calculated from the measured resistance. For the parameters characterizing this device the estimated detectivity is consistent with a theoretical prediction. The theory further predicts an optimum detectivity for much thinner devices than the prototypes.

  9. 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.

  10. 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.

  11. 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.

  12. Fluoride coatings on orthodontic wire for controlled release of fluorine ion.

    PubMed

    Lee, Su-Hee; Kim, Hae-Won; Kong, Young-Min; Kim, Hyoun-Ee; Lee, Sung-Ho; Chang, Young-Il

    2005-10-01

    The purpose of this study was to develop a new method of releasing fluorine in a controlled manner for applications in the field of orthodontic Ti-based wire, namely the coating of fluorides on Ti. Thin films of two fluoride compounds, CaF(2) and MgF(2), were coated on Ti via the electron-beam evaporation method. The fluorine was released rapidly from the as-deposited MgF(2) coating within a short period(,) and then the release rate slowed down. When the MgF(2) coating was heat treated, this initial burst effect was decreased, but a significant amount of cracks were generated. On the other hand, in the case of the as-deposited CaF(2) coating, fluorine was released linearly for the entire period, without an initial burst. In the heat-treated CaF(2) coatings the trend was similarly observed. The linear fluorine release from the CaF(2) coatings, even in the as-deposited state, was attributed to the high degree of crystallinity of the coatings. A preliminary cell test showed favorable cell viability on both the fluoride coatings. Given their sustained and controlled fluorine release, these fluoride coatings, particularly CaF(2), are suggested to be potentially useful in the field of orthodontic Ti-based wire.

  13. A calcium prerinse required to form calcium fluoride in plaque from a sodium fluoride rinse.

    PubMed

    Vogel, G L; Tenuta, L M A; Schumacher, G E; Chow, L C

    2014-01-01

    The purpose of this study is to determine whether a calcium (Ca) prerinse used before a 228 µg/g (ppm) fluoride (F) rinse would induce the formation of 'calcium fluoride-like' (CaF2-like) deposits in human dental plaque. Sixty minutes after the use of the Ca prerinse/F rinse, plaque samples were collected from 10 volunteers, homogenized, and split into 2 aliquots. The plaque mass from one aliquot was then extracted with a 'plaque-like' solution that extracted all the CaF2-like deposits. The total F in both aliquots was then determined and compared. The results demonstrated that, as in previous studies, the Ca prerinse induced large increases in plaque fluid and total plaque F. However, unlike previous results without the Ca prerinse, 30% of the plaque F deposits were CaF2 or CaF2-like. Given that maintaining an elevated F concentration in the vicinity of a developing lesion may play an important role in the cariostatic effect of this ion, and the potential advantages of CaF2-like deposits as an F source, these results suggest that a Ca prerinse may increase the cariostatic effect of topical agents.

  14. Pilot-scale fluoride-containing wastewater treatment by the ballasted flocculation process.

    PubMed

    Wang, Bin-Yuan; Chen, Zhong-Lin; Zhu, Jia; Shen, Ji-Min; Han, Ying

    2013-01-01

    A pilot-scale ballasted flocculation system was used to remove fluoride from one type of industrial wastewater. The system included the formation of calcium fluoride (CaF2) using calcium hydroxide followed by coagulation sedimentation. Calcium fluoride was recycled as nuclei for enhancing CaF2 precipitation and as a ballasting agent for improving fluoride removal and flocculation efficiency. Factors affecting fluoride and turbidity removal efficiencies, including pH in the CaF2-reacting tank and coagulation-mixing tank, sludge recycling ratio, and dosages of FeCl3 and polyacrylamide (PAM), were investigated in the pilot-scale system. The recycled CaF2 precipitates improved CaF2 formation kinetics, enhanced fluoride removal and flocculation performance. Under the optimized condition, the ballast flocculation process reduced fluoride concentration from 288.9 to 10.67 mg/L and the turbidity from 129.6 NTU to below 2.5 NTU. PMID:23823549

  15. Spin Hamiltonian Spectroscopy in PRASEODYMIUM(3):LANTHANUM Trifluoride.

    NASA Astrophysics Data System (ADS)

    Otto, Frederick William

    An optically detected anticrossing in solid state laser spectroscopy produced by cross-relaxation is reported. Spin -spin cross-relaxation between the ^{141 }Pr and ^{19}F spin reservoirs in Pr^{+3}:LaF _3 and its influence on the ^{141}Pr NMR spectrum is observed. The detection technique employed combines optical pumping and hole burning with either an external magnetic field sweep or rf resonance saturation producing slow transient changes in resonant laser transmission. At a certain value of the external magnetic field, where the energy level splittings of Pr and F spins match, a level repulsion and discontinuity of the Pr^{+3} NMR lines is observed. This effect is interpreted as the "anticrossing" of the combined Pr-F spin-spin reservoir energy states. The Zeeman - Quadrupole Hamiltonian spectrum of the lowest hyperfine optical ground state manifold of Pr^ {+3}:LaF_3 is mapped out over a wide range of Zeeman magnetic fields. A new method is proposed for dynamically polarizing nuclei by means of optical pumping, using resonant cross-relaxation between rare spins and spin reservoirs.

  16. Spectroscopic properties of Nd3+ doped transparent oxyfluoride glass ceramics.

    PubMed

    Yu, Yunlong; Chen, Daqin; Ma, En; Wang, Yuansheng; Hu, Zhongjian

    2007-07-01

    In this paper, the spectroscopic properties of Nd(3+) doped transparent oxyfluoride glass ceramics containing LaF(3) nano-crystals were systematically studied. The formation and distribution of LaF(3) nano-crystals in the glass matrix were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on Judd-Ofelt theory, the intensity parameters Omega(t) (t=2, 4, 6), spontaneous emission probability, radiative lifetime, radiative quantum efficiency, width of the emission line and stimulated emission cross-section of Nd(3+) were evaluated. Particularly, the effect of Nd(3+) doping level on them was discussed. With the increase of Nd(3+) concentration in the glass ceramic, the experimental luminescence lifetime, radiative quantum efficiency and stimulated emission cross-section vary from 353.4 micros, 78.3% and 1.86 x 10(-20)cm(2) to 214.7 micros, 39.9% and 1.52 x 10(-20)cm(2), respectively. The comparative study of Nd(3+) spectroscopic parameters in different hosts suggests that the investigated glass ceramic system is potentially applicable as laser materials for 1.06 microm emission.

  17. 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.

  18. Bi-material crystalline whispering gallery mode microcavity structure for thermo-opto-mechanical stabilization

    NASA Astrophysics Data System (ADS)

    Itobe, Hiroki; Nakagawa, Yosuke; Mizumoto, Yuta; Kangawa, Hiroi; Kakinuma, Yasuhiro; Tanabe, Takasumi

    2016-05-01

    We fabricated a calcium fluoride (CaF2) whispering gallery mode (WGM) microcavity with a computer controlled ultra-precision cutting process. We observed a thermo-opto-mechanical (TOM) oscillation in the CaF2 WGM microcavity, which may influence the stability of the optical output when the cavity is employed for Kerr comb generation. We studied experimentally and numerically the mechanism of the TOM oscillation and showed that it is strongly dependent on cavity diameter. In addition, our numerical study suggests that a microcavity structure fabricated with a hybrid material (i.e. CaF2 and silicon), which is compatible with an ultra-high Q and high thermal conductivity, will allow us to reduce the TOM oscillation and stabilize the optical output.

  19. Application of reutilization technology to calcium fluoride sludge from semiconductor manufacturers.

    PubMed

    Liu, Wei-Ting; Li, Kung-Cheh

    2011-01-01

    Glass ceramics were prepared from mixtures of wastes generated from refining of waste glass and semiconductor industrial wastewater sludge. The aim is then indeed to study the possible use and effects of integrating calcium fluoride (CaF2) as present in semiconductor wastewater sludge in the silica (glass) melts. CaF2 sludge was blended with a conditioner according to characteristics of the target. Calcium oxide-silicon dioxide-aluminum oxide system glass ceramics have relatively high melting points. Addition of CaF2 sludge to fluxes can significantly reduce the melting point and hence improve the kinetics of the reactions. CaF2 sludge and waste glass were co-melted in various ratios to elucidate their interactions at various heating temperatures. The results indicate that the lowest melting temperature was 1163 degrees C, obtained for the CaF2 sludge-waste glass mixture at a ratio 6:4 (wt:wt), which is significantly lower than that of CaF2 sludge (1378 degrees C). The benefits of using melting to dispose of sludge are the reduction of waste and the fixation of heavy metals. Heat treatment was used to convert the obtained glass into glass ceramics. Heavy metal leaching tests revealed that melting conditions lowered the heavy metal concentrations in the leachate to an order of magnitude lower than that in the sludge. Consequently, industrial sludge can be safely used as a fine aggregate material for a potentially wide range of construction applications. PMID:21305892

  20. 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.

  1. Optimal moderator materials at various proton energies considering photon dose rate after irradiation for an accelerator-driven ⁹Be(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 8 MeV to 30 MeV. The optimal moderator materials were found to be MgF2 for proton energies less than 10 MeV 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

  2. Optimal moderator materials at various proton energies considering photon dose rate after irradiation for an accelerator-driven ⁹Be(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 8 MeV to 30 MeV. The optimal moderator materials were found to be MgF2 for proton energies less than 10 MeV 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.

  3. 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.

  4. On the fundamental limits of Q factor of crystalline dielectric resonators.

    PubMed

    Grudinin, Ivan S; Matsko, Andrey B; Maleki, Lute

    2007-03-19

    The temperature dependence of the processes which fundamentally limit optical quality factor of ideal crystalline whispering gallery mode resonators is investigated. The example of CaF(2) is used to show that spontaneous Raman scattering is the main limitation of the quality factor at low temperatures. Stimulated Raman scattering is also shown to be important at any temperature. We experimentally demonstrate nonlinear absorption due to stimulated Raman scattering in a real cavity at room temperature and theoretically derive Raman gain of CaF(2). We conclude that optical storage times in excess of one second could be achieved in millimeter sized cavities.

  5. 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.

  6. Skylab ultraviolet stellar astronomy experiment S019.

    PubMed

    O'Callaghan, F G; Henize, K G; Wray, J D

    1977-04-01

    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 CaF(2) objective prism, and an achromatized field corrector lens system of CaF(2) and LiF. Observations of 188 star fields, each covering 4.0 degrees 5.0 degrees , were conducted at the Skylab antisolar airlock with the aid of an articulated mirror system (AMS) which allowed acquisition within 30 degrees degrees 360 degrees band of the sky.

  7. In-situ integrated processing and characterization of thin films of high temperature superconductors, dielectrics and semiconductors by MOCVD

    NASA Technical Reports Server (NTRS)

    Singh, R.; Sinha, S.; Hsu, N. J.; Thakur, R. P. S.; Chou, P.; Kumar, A.; Narayan, J.

    1991-01-01

    In this strategy of depositing the basic building blocks of superconductors, semiconductors, and dielectrics having common elements, researchers deposited superconducting films of Y-Ba-Cu-O, semiconductor films of Cu2O, and dielectric films of BaF2 and Y2O3 by metal oxide chemical vapor deposition (MOCVD). By switching source materials entering the chamber, and by using direct writing capability, complex device structures like three terminal hybrid semiconductor/superconductor transistors can be fabricated. The Y-Ba-Cu-O superconducting thin films on BaF2/YSZ substrates show a T(sub c) of 80 K and are textured with most of the grains having their c-axis or a-axis perpendicular to the substrate. Electrical characteristics as well as structural characteristics of superconductors and related materials obtained by x-ray deffraction, electron microscopy, and energy dispersive x-ray analysis are discussed.

  8. A simple phoswich system

    NASA Astrophysics Data System (ADS)

    Ramsden, D.; Zhang, S. N.

    1988-06-01

    Normal phoswich detector systems use a combination of NaI(Tl) and CsI(Na) scintillators and require the application of careful pulse-shape discriminator techniques to resolve the two components in the scintillation light output which have decay constants of 250 and 630 ns respectively. These techniques provide a good anticoincidence veto efficiency for a relatively narrow range in the ratio of energy deposits in the two crytals and for a detector system whose temperature is carefully controlled. This paper describes the performance of a simple phoswich which makes use of the fast UV signal from a BaF 2 crystal to provide a prompt veto signal. The performance to be expected from various combinations of a BaF 2 anticoincidence crystal with other primary detectors is presented. These simulations have been verified by simple experimental tests.

  9. 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.

  10. Solubility of BaS in BaO-BaF2 slag and the Influence of FeOx, SiO2, Cr2O3, BaCI2, CaO, and MgO on the sulfide capacity of this system

    NASA Astrophysics Data System (ADS)

    Rachev, Ivan P.; Tsukihashi, Fumitaka; Sano, Nobuo

    1992-03-01

    The influence of SiO2, FeOx, Cr2O3, BaCl2, CaO, and MgO on the sulfide capacity of the BaO-BaF2 system was measured at 1473 K, using a gas-slag-metal equilibration technique. It was found that the substitution of BaF2 by SiO2, FeOx, Cr2O3, and BaCl2 decreases the sulfide capacity of the BaO-BaF2 system. Similar results were obtained for the carbonate capacity. The CaO-saturated BaO-BaF2 flux, however, was found to have slightly higher sulfide and carbonate capacities than the pure BaO-BaF2 flux. The solubility of CaO increased with increasing BaF2 content and was 18 mol pet in BaF2 at 1473 K. The solubility of MgO in the BaO-BaF2 system at the same temperature is very low, and it has no effect on the sulfide and carbonate capacities. The solubility of BaS in the BaO-BaF2 system was also measured at 1473 K and had its maximum for the slag containing 40 mass pet BaO. The activity of BaO in the system was calculated from those data.

  11. Optical properties of Ce3+ doped fluorophosphates scintillation glasses

    NASA Astrophysics Data System (ADS)

    Yao, Yongxin; Liu, Liwan; Zhang, Yu; Chen, Danping; Fang, Yongzheng; Zhao, Guoying

    2016-01-01

    Fluorophosphates (P2O5-BaO-BaF2-Al2O3-Gd2O3-Ce2O3) glasses with different Gd2O3 and BaF2 concentrations have been prepared by a melt quenching method. The effect of Gd2O3 and BaF2 on the glass performance including the density, absorption as well as luminescence properties under both ultraviolet (UV) and X-ray excitation was studied systematically. Energy transfer from Gd3+ to Ce3+ plays an important role in the scintillation mechanism of these glasses and the optimum concentration of Gd2O3 is found to be approximately 3 mol%. The highest integrated light emission intensity of these glass samples excited by X-ray is 25% of BGO and the decay time constants are in the range of 25-35 ns, much shorter than the 300 ns decay time of BGO. Meanwhile, replacing lighter compound BaO with the BaF2 can increase the density of the glasses and also improve the light yield.

  12. 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.

  13. 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.

  14. 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.

  15. Calcium fluoride nanoparticles induced suppression of Streptococcus mutans biofilm: an in vitro and in vivo approach.

    PubMed

    Kulshrestha, Shatavari; Khan, Shakir; Hasan, Sadaf; Khan, M Ehtisham; Misba, Lama; Khan, Asad U

    2016-02-01

    Biofilm formation on the tooth surface is the root cause of dental caries and periodontal diseases. Streptococcus mutans is known to produce biofilm which is one of the primary causes of dental caries. Acid production and acid tolerance along with exopolysaccharide (EPS) formation are major virulence factors of S. mutans biofilm. In the current study, calcium fluoride nanoparticles (CaF2-NPs) were evaluated for their effect on the biofilm forming ability of S. mutans in vivo and in vitro. The in vitro studies revealed 89 % and 90 % reduction in biofilm formation and EPS production, respectively. Moreover, acid production and acid tolerance abilities of S. mutans were also reduced considerably in the presence of CaF2-NPs. Confocal laser scanning microscopy and transmission electron microscopy images were in accordance with the other results indicating inhibition of biofilm without affecting bacterial viability. The qRT-PCR gene expression analysis showed significant downregulation of various virulence genes (vicR, gtfC, ftf, spaP, comDE) associated with biofilm formation. Furthermore, CaF2-NPs were found to substantially decrease the caries in treated rat groups as compared to the untreated groups in in vivo studies. Scanning electron micrographs of rat's teeth further validated our results. These findings suggest that the CaF2-NPs may be used as a potential antibiofilm applicant against S. mutans and may be applied as a topical agent to reduce dental caries.

  16. 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.

  17. Low background techniques in CANDLES

    NASA Astrophysics Data System (ADS)

    Nakajima, K.; Iida, T.; Kishimoto, T.; Matsuoka, K.; Nomachi, M.; Umehara, S.; Chan, W. M.; Kakubata, H.; Li, X.; Maeda, T.; Ohata, T.; Temuge, B.; Tetsuno, K.; Trang, V. T. T.; Uehara, T.; Yoshida, S.; Morishita, K.; Ogawa, I.; Sakamoto, K.; Tamagawa, Y.; Yoshizawa, M.; Fushimi, K.; Hazama, R.; Naktani, N.; Suzuki, K.

    2015-08-01

    CANDLES is a double beta decay experiment using 48Ca in CaF2 crystals. The measurement is being performed with prototype detector (CANDLES III) for high sensitive measurement in the future. Recent status of detector improvements and background reduction techniques are described in this paper.

  18. 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.

  19. Film Thickness Dependence of Crystal Structure in 100-Oriented Epitaxial Pb(Zr0.65Ti0.35)O3 Films Grown on Single-Crystal Substrates with Different Thermal Expansion Coefficients

    NASA Astrophysics Data System (ADS)

    Ehara, Yoshitaka; Yasui, Shintaro; Ishii, Koji; Funakubo, Hiroshi

    2012-09-01

    100-oriented epitaxial Pb(Zr0.65Ti0.35)O3 films with various film thicknesses from 0.1 to 3 µm were grown on (100)cSrRuO3 ∥ (100)SrTiO3 and (100)cSrRuO3 ∥ (100)LaNiO3 ∥ (001)CaF2 substrates. The out-of-plane/in-plane lattice parameter ratio of the films on the CaF2 substrates was larger than that on the SrTiO3 substrates up to 1.1 µm film thickness, while (90°-α) (α was defined as the internal tilt angle) was almost 0°. Results of analysis of Raman spectra and piezoresponse images suggest that the 1.1-µm-thick film grown on the (100)cSrRuO3 ∥ (100)LaNiO3 ∥ (001)CaF2 substrate had tetragonal symmetry with a polar-axis orientation. Moreover, the saturation polarization values of the films measured from P-E hysteresis loops correspond to the two Ps values estimated from the thermodynamic theory, assuming the change in the polar direction due to the symmetry change to tetragonal, and from the crystal distortion in tetragonal symmetry. This can be explained by the large compressive stress from the CaF2 substrate having a large thermal expansion coefficient.

  20. Calcium fluoride nanoparticles induced suppression of Streptococcus mutans biofilm: an in vitro and in vivo approach.

    PubMed

    Kulshrestha, Shatavari; Khan, Shakir; Hasan, Sadaf; Khan, M Ehtisham; Misba, Lama; Khan, Asad U

    2016-02-01

    Biofilm formation on the tooth surface is the root cause of dental caries and periodontal diseases. Streptococcus mutans is known to produce biofilm which is one of the primary causes of dental caries. Acid production and acid tolerance along with exopolysaccharide (EPS) formation are major virulence factors of S. mutans biofilm. In the current study, calcium fluoride nanoparticles (CaF2-NPs) were evaluated for their effect on the biofilm forming ability of S. mutans in vivo and in vitro. The in vitro studies revealed 89 % and 90 % reduction in biofilm formation and EPS production, respectively. Moreover, acid production and acid tolerance abilities of S. mutans were also reduced considerably in the presence of CaF2-NPs. Confocal laser scanning microscopy and transmission electron microscopy images were in accordance with the other results indicating inhibition of biofilm without affecting bacterial viability. The qRT-PCR gene expression analysis showed significant downregulation of various virulence genes (vicR, gtfC, ftf, spaP, comDE) associated with biofilm formation. Furthermore, CaF2-NPs were found to substantially decrease the caries in treated rat groups as compared to the untreated groups in in vivo studies. Scanning electron micrographs of rat's teeth further validated our results. These findings suggest that the CaF2-NPs may be used as a potential antibiofilm applicant against S. mutans and may be applied as a topical agent to reduce dental caries. PMID:26610805

  1. Calculation and experimental determination of the fast neutron sensitivity of OSL detectors with hydrogen containing radiators

    NASA Astrophysics Data System (ADS)

    Fellinger, Jürgen; Henniger, Jürgen; Hübner, Klaus

    1984-11-01

    Detectors based on optically stimulated luminescence are useful for fast neutron dosimetry. For this one needs the neutron sensitivity of these detectors. We describe a procedure for the calculation of the neutron sensitivity. For CaF 2:Mn embedded in polyethylene the calculated values are compared with experimentally determined neutron sensitivities. There is good agreement.

  2. Microstructure and wear behavior of γ/Al 4C 3/TiC/CaF 2 composite coating on γ-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 ( γ) 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 ( γ) matrix during the laser cladding process.

  3. All-optical Photonic Oscillator with High-Q Whispering Gallery Mode Resonators

    NASA Technical Reports Server (NTRS)

    Savchenkov, Anatoliy A.; Matsko, Andrey B.; Strekalov, Dmitry; Mohageg, Makan; Iltchenko, Vladimir S.; Maleki, Lute

    2004-01-01

    We demonstrated low threshold optical photonic hyper-parametric oscillator in a high-Q 10(exp 10) CaF2 whispering gallery mode resonator which generates stable 8.5 GHz signal. The oscillations result from the resonantly enhanced four wave mixing occurring due to Kerr nonlinearity of the material.

  4. 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 μm 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

  5. Calcium fluoride windows for high-energy chemical lasers

    NASA Astrophysics Data System (ADS)

    Klein, Claude A.

    2006-10-01

    The development of high-energy lasers requires optical windows capable of handling megajoule beam energies without compromising the system's performance. Calcium fluoride (CaF2) has been identified as a prime candidate for windows operating at chemical laser wavelengths due to very low bulk absorption and exceptionally small thermal lensing coefficients; it is, however, vulnerable to structural failure owing to poor mechanical strength characteristics and a large thermal stress factor. It is, therefore, essential to properly assess the ultimate potential of this material, which we attempt to do here in the following manner: (a) We assemble reliable numbers for all pertinent properties of (111)-oriented CaF2 single crystals and polycrystalline isotropic aggregates (PIAs), such as fusion-cast CaF2, which requires addressing issues relating to the elastic properties, the stress-optic coefficients, and the flexural strength. (b) We provide correct analytical expressions for evaluating the impact of pressure- and beam-induced effects on wave-front phase distortions and mechanical failure modes, taking advantage of a previous investigation [J. Appl. Phys. 98, 043103 (2005)]. (c) We perform detailed calculations on "model" windows made of either (111)CaF2 or (PIA )CaF2 that transmit optimally truncated Gaussian beams at wavelengths of 1.15 and 3.39μm, for run times such that lateral heat conduction and surface cooling can be ignored. Our main conlusions are as follows: (a) With CaF2 windows thermal lensing, as measured in terms of the Strehl ratio and on assuming coating absorptances of no more than 3×10-5, is of no consequence in the sense that catastrophic failure may occur at fluence levels way below the threshold for optical distortion. (b) Evidence of a poor Weibull shape factor (m ≃3.5) degrades the design safety margins, which requires operating at peak intensities of no more than 100kW/cm2 to achieve optimum on-target fluences. (c) Regarding the issue of (111)CaF2 vs (PIA)CaF2, we note that fusion-cast material outperforms single crystals based on the figure of merit for distortion, as well as fracture and yield strengths, but contrary to (111)-oriented material, it exhibits birefringence that may rule out its use if depolarization is of concern.

  6. Antibacterial and physical properties of calcium-phosphate and calcium-fluoride nanocomposites with chlorhexidine

    PubMed Central

    Cheng, Lei; Weir, Michael D.; Xu, Hockin H. K.; Kraigsley, Alison M.; Lin, Nancy J.; Lin-Gibson, Sheng; Zhou, Xuedong

    2012-01-01

    Objectives Previous studies have developed calcium phosphate and fluoride releasing composites. Other studies have incorporated chlorhexidine (CHX) particles into dental composites. However, CHX has not been incorporated in calcium phosphate and fluoride composites. The objectives of this study were to develop nanocomposites containing amorphous calcium phosphate (ACP) or calcium fluoride (CaF2) nanoparticles and CHX particles, and investigate S. mutans biofilm formation and lactic acid production for the first time. Methods Chlorhexidine was frozen via liquid nitrogen and ground to obtain a particle size of 0.62 µm. Four nanocomposites were fabricated with fillers of: Nano ACP; nano ACP+10% CHX; nano CaF2; nano CaF2+10% CHX. Three commercial materials were tested as controls: A resin-modified glass ionomer, and two composites. S. mutans live/dead assay, colony-forming unit (CFU) counts, biofilm metabolic activity, and lactic acid were measured. Results Adding CHX fillers to ACP and CaF2 nanocomposites greatly increased their antimicrobial capability. ACP and CaF2 nanocomposites with CHX that were inoculated with S. mutans had a growth medium pH > 6.5 after 3 d, while the control commercial composites had a cariogenic pH of 4.2. Nanocomposites with CHX reduced the biofilm metabolic activity by 10–20 folds and reduced the acid production, compared to the controls. CFU on nanocomposites with CHX were three orders of magnitude less than that on commercial composite. Mechanical properties of nanocomposites with CHX matched a commercial composite without fluoride. Significance The novel calcium phosphate and fluoride nanocomposites could be rendered antibacterial with CHX to greatly reduce biofilm formation, acid production, CFU and metabolic activity. The antimicrobial and remineralizing nanocomposites with good mechanical properties may be promising for a wide range of tooth restorations with anti-caries capabilities. PMID:22317794

  7. [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

  8. 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.; Moszyński, M.; Iwanowska-Hanke, J.; Syntfeld-Każuch, A.; Gójska, A.; Gierlik, M.; Kaźmierczak, Ł.; Jakubowska, E.; Kędzierski, G.; Kujawiński, Ł.; 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 β- 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 β- 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.

  9. A theoretical study of fluorides scintillating crystals: Methodology and application

    NASA Astrophysics Data System (ADS)

    Jiang, Huitian

    Theoretical computation and simulation study has been performed on important scintillating fluorides crystal BaF2 and PbF2. The structural, electronic, transport and defects properties are investigated under different methodology schemes. The thesis provide accurate and detailed understandings of fundamental electronic structures of them in different phases for the very first time. A new expanded module for which provide the CRYSTAL program package with full capability in ECP (effective pseudo-potential) method calculation is developed and successfully applied into the this study. We present the results of an all-electron first principles study on BaF 2 in its stable (cubic) and high-pressure phases. A LCAO (linear combination of atomic orbitals) approach in the framework of DFT is employed for total energy calculations in cubic, orthorhombic and hexagonal phases of BaF 2. A fitting of the energy surface to the equation of state yields the lattice constant and the bulk modulus of these phases at zero pressure which are in good agreement with the corresponding experimental values. Analysis of band structure determines the high-pressure phases to be direct-gap materials and no metallization of BaF2 is predicted to occur for pressures up to 50 GPa. Furthermore, several peaks observed in the spectroscopic experiments have been identified with interband transitions in the cubic BaF2. We also performed the small-core ECP first principles calculation on Pb2 in its cubic, orthorhombic and hexagonal phases. For cubic phase, the accurate theoretical band data now are available with the structural properties were very well generated. It is predicted with direct band gap at X. The band structures of orthorhombic and hexagonal phases are first time calculated. We predict the orthorhombic and hexagonal phase PbF2 has indirect band gap. These results may help to clarify some doubts and controversies in the experiments and promote the application studies. At last, a discussion on the results from this study is held. Special attention is paid to the methodology level questions on theoretical computations and simulations. The main limitations of methods used in this work are summarized and analyzed with future method developments and application studies suggested. The thesis finally concludes with some fundamental perspectives in theoretical computation and simulation work. (Abstract shortened by UMI.)

  10. Spectroscopic, thermal and cw dual-wavelength laser characteristics of Nd:LaF3 single crystal

    NASA Astrophysics Data System (ADS)

    Hong, Jiaqi; Zhang, Lianhan; Li, Jing; Wang, Zhaowei; He, Jingliang; Zhang, Peixiong; Wang, Yaqi; Hang, Yin

    2016-03-01

    A Nd-doped LaF3 crystal was grown by Czochralski method, and the rocking curves of (0 0 2) and (1 1 0) diffraction planes show good crystallinity quality of the as-grown crystal. Room-temperature fluorescence spectrum and transmittance spectrum of Nd:LaF3 crystal were investigated, both indicating probable dual-wavelength emissions at ∼1.04 μm and ∼1.06 μm. The thermal diffusivity and thermal conductivity of Nd:LaF3 crystal were detailed studied. Cw dual-wavelength laser operation of Nd:LaF3 single crystal at 1040 nm and around 1065 nm with LD pumping was demonstrated. A maximum output power of 302 mW was obtained with a slope efficiency of about 18.5% with respect to the pump power. The results of our study indicate the Nd:LaF3 crystal a promising laser crystal.

  11. 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.

  12. 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

  13. Fluorescence decay dynamics of surface-functionalized nanoparticles

    NASA Astrophysics Data System (ADS)

    Ajimo, Jacob; Ma, Lun; Yao, Mingzhen; Zhang, Xing; Como, John; Hope-Weeks, Louisa; Huang, Juyang; Chen, Wei; Cheng, Kwan

    2008-10-01

    We report the fluorescence decay dynamics of surface-functionalized nanoparticles (NPs), poly(ethylene glycol) bis(carboxymethyl) ether coated LaF3: Ce,Tb and thioglycolic acid coated ZnS:Mn, in solution and also in the surface-bound phase. The NPs exhibited high quantum yield and multi-component decays, and of average lifetime of 20-130 microseconds in solution, but 10-60 microseconds in the bound phase depending on the solid substrates. Our results suggest that the coated ZnS:Mn nanoparticles hold great promise as a non-toxic labeling agent for ultra-sensitive, time-gated, trace biomaterials detections in nano-forensic applications.

  14. Rare earth doped glass-ceramics containing NaLaF4 nanocrystals

    NASA Astrophysics Data System (ADS)

    Elsts, E.; Krieke, G.; Rogulis, U.; Smits, K.; Zolotarjovs, A.; Jansons, J.; Sarakovskis, A.; Kundzins, K.

    2016-09-01

    Oxyfluoride glasses 16Na2O-9NaF-5LaF3-7Al2O3-63SiO2 (mol%) activated with 3% terbium, dysprosium, praseodymium and neodymium fluorides have been prepared and studied by differential thermal analysis, cathodoluminescence, X-ray induced luminescence, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. We found out that the presence of crystalline phase enhances the X-ray induced luminescence intensity. X-ray induced luminescence is the most intense for the sample activated with terbium and treated at 700 °C, whereas the praseodymium and neodymium activated samples have the fastest decay times.

  15. Nanoscintillators for radiation detection

    NASA Astrophysics Data System (ADS)

    Hall, Ryan Gregory

    In the search for faster, more effective methods for detection of and protection against radiological weapons, advances in materials for radiation detection are a critical component of any successful strategy. This work focuses on producing inexpensive, but highly sensitive, nanoparticle alternatives to existing single-crystal installations. Attention is given to particular types of promising inorganic scintillators: LaF3, yttrium-aluminum-garnet (YAG), and SrF2, each one an inorganic host doped with additional elements that encourage luminescent decay and increase effective Z-value. I examine the possible routes to synthesize these compounds, and the difficulties and benefits of each method. After synthesizing these materials, testing was performed to determine comparative performance against each other and commercial solutions, identify structural and compositional characteristics, and explore routes for fixing the scintillators into a detector assembly. The unifying goal is to develop a scintillating material suitable for consistent dosimetry and radio-isotope identification applications.

  16. Luminescent and scintillating properties of lanthanum fluoride nanocrystals in response to gamma/neutron irradiation: codoping with Ce activator, Yb wavelength shifter, and Gd neutron captor

    NASA Astrophysics Data System (ADS)

    Vargas, J. M.; Blostein, J. J.; Sidelnik, I.; Rondón Brito, D.; Rodríguez Palomino, L. A.; Mayer, R. E.

    2016-09-01

    A novel concept for gamma radiation detection and spectroscopy, and detection of thermal neutrons based on co-doped lanthanum fluoride nanocrystals containing gadolinium is presented. The trends of colloidal synthesis of the mentioned material, LaF3 co-doped with Ce3+ as the activator, Yb3+ as the wavelength-shifter and Gd3+ as the neutron captor, is reported. Nanocrystals of the mentioned material were characterized by transmission electron microscopy, X ray diffraction, energy dispersive X ray spectroscopy, optical absorption, and photoluminescence spectroscopy. Gamma detection and its potential spectroscopy feature have been confirmed. The neutron detection capability has been confirmed by experiments performed using a 252Cf neutron source.

  17. Spectroscopic and thermal characterizations of Yb:LaF3 single crystal

    NASA Astrophysics Data System (ADS)

    Hong, Jiaqi; Zhang, Lianhan; Hang, Yin; Xu, Min

    2016-10-01

    A Yb3+ doped LaF3 laser crystal was detailed investigated by both spectroscopic and thermal measurements. A peak absorption at 974 nm with FWHM broader than 60 nm makes the crystal suitable to InGaAs LDs. Fluorescence spectrum and calculated spectroscopic parameters show potential of Yb:LaF3 crystal to laser operations around 1009 nm. A relatively long fluorescence lifetime of 2.92 ms was detected for Yb3+:2F5/2 manifold. The thermal diffusivity and specific heat capacity in the range of 300-575 K were studied to calculate the thermal conductivity of Yb:LaF3. The results indicate that the Yb:LaF3 crystal is a good candidate for diode-pumped ∼1 μm solid-state laser applications.

  18. Luminescence Decay Dynamics and Trace Biomaterials Detection Potential of Surface-Functionalized Nanoparticles.

    PubMed

    Cheng, Kwan H; Aijmo, Jacob; Ma, Lun; Yao, Mingzhen; Zhang, Xing; Como, John; Hope-Weeks, Louisa J; Huang, Juyang; Chen, Wei

    2008-10-22

    We have studied the luminescence decay and trace biomaterials detection potential of two surface-functionalized nanoparticles, poly(ethylene glycol) bis(carboxymethyl) ether-coated LaF(3):Ce,Tb (~20 nm) and thioglycolic acid-coated ZnS/Mn (~5 nm). Upon UV excitation, these nanoparticles emitted fluorescence peaking at 540 and 597 nm, respectively, in solution. Fluorescence imaging revealed that these nanoparticles targeted the trace biomaterials from fingerprints that were deposited on various nonporous solid substrates. Highly ordered, microscopic sweat pores within the friction ridges of the fingerprints were labeled with good spatial resolutions by the nanoparticles on aluminum and polymethylpentene substrates, but not on glass or quartz. In solution, these nanoparticles exhibited multicomponent fluorescence decays of resolved lifetimes ranging from nano-to microseconds and of average lifetimes of ~24 and 130 micros for the coated LaF(3):Ce,Tb and ZnS:Mn, respectively. The long microsecond-decay components are associated with the emitters at or near the nanocrystal core surface that are sensitive to the size, surface-functionalization, and solvent exposure of the nanoparticles. When the nanoparticles were bound to the surface of a solid substrate and in the dried state, a decrease in the microsecond decay lifetimes was observed, indicative of a change in the coating environment of the nanocrystal surface upon binding and solvent removal. The average decay lifetimes for the surface-bound ZnS:Mn in the dried state were ~60, 30, and 11 micros on quartz, aluminum, and polymethylpentene, respectively. These values were still 2 orders of magnitude longer than the typical fluorescence decay background of most substrates (e.g., ~0.36 micros for polymethylpentene) in trace forensic evidence detections. We conclude that coated ZnS: Mn nanoparticles hold great promise as a nontoxic labeling agent for ultrasensitive, time-gated, trace evidence detections in nanoforensic applications.

  19. Sulfide capacities of CaO-CaF2-CaCl2 melts

    NASA Astrophysics Data System (ADS)

    Simeonov, Simeon; Sakai, Toshihiko; Maeda, Masafumi

    1992-06-01

    The sulfide capacityC_{s^{2 - } } = ({text{pct S}}^{{text{2 - }}} )(p_{{text{O}}_{text{2}} } /p_{{text{S}}_{text{2}} } )^{1/2} ) of CaO-CaF2-CaCl2 slag was determined at temperatures from 1000 °C to 1300 °C by equilibrating molten slag, molten silver, and CO-CO2-Ar gas mixture. The sulfide capacity increases with replacing CaCl2 by CaF2 in slags of constant CaO contents. The sulfide capacity also increases with increasing temperature as well as with increasing CaO content at a constant ratio of CaF2/CaCl2 of unity. A linear relationship between the sulfide capacity and carbonate capacity in literature was observed on a logarithmic scale.

  20. In-situ growth of superconducting SmO1−xFxFeAs thin films by pulsed laser deposition

    PubMed Central

    Haindl, Silvia; Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Hosono, Hideo

    2016-01-01

    Oxypnictide thin film growth by pulsed laser deposition (PLD) is one of many insufficiently resolved issues in the research of iron-based superconductors. Here we report on the successful realization of superconducting SmO1−xFxFeAs oxypnictide thin film growth by in-situ PLD on CaF2 (fluorite) substrates. CaF2 acts as fluorine supplier by diffusion and thus enables superconducting oxypnictide thin film growth by PLD. Films are grown heteroepitaxially and characteristically have a broad resistive normal-to-superconducting transition. Best films have onset transition temperatures around 40 K. The proposed in-situ PLD film growth offers an alternative and cheap route for the fabrication of iron oxypnictides. PLD becomes now an additional option for iron oxypnictide synthesis. PMID:27767066

  1. 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.

  2. Low Radioactivity in CANDLES

    SciTech Connect

    Kishimoto, T.; Ogawa, I.; Hazama, R.; Yoshida, S.; Umehara, S.; Matsuoka, K.; Sakai, H.; Yokoyama, D.; Mukaida, K.; Ichihara, K.; Tatewaki, Y.; Kishimoto, K.; Hirano, Y.; Yanagisawa, A.; Ajimura, S.

    2005-09-08

    CANDLES is the project to search for double beta decay of 48Ca by using CaF2 crystals. Double beta decay of 48Ca has the highest Q value among all nuclei whose double beta decay is energetically allowed. This feature makes the study almost background free and becomes important once the study is limited by the backgrounds. We studied double beta decays of 48Ca by using ELEGANTS VI detector system which features CaF2(Eu) crystals. We gave the best limit on the lifetime of neutrino-less double beta decay of 48Ca although further development is vital to reach the neutrino mass of current interest for which CANDLES is designed. In this article we present how CANDLES can achieve low radioactivity, which is the key for the future double beta decay experiment.

  3. Theory of noncontact friction for atom-surface interactions

    NASA Astrophysics Data System (ADS)

    Jentschura, U. D.; Janke, M.; DeKieviet, M.

    2016-08-01

    The noncontact (van der Waals) friction is an interesting physical effect, which has been the subject of controversial scientific discussion. The direct friction term due to the thermal fluctuations of the electromagnetic field leads to a friction force proportional to 1 /Z5 (where Z is the atom-wall distance). The backaction friction term takes into account the feedback of thermal fluctuations of the atomic dipole moment onto the motion of the atom and scales as 1 /Z8 . We investigate noncontact friction effects for the interactions of hydrogen, ground-state helium, and metastable helium atoms with α -quartz (SiO2), gold (Au), and calcium difluorite (CaF2). We find that the backaction term dominates over the direct term induced by the thermal electromagnetic fluctuations inside the material, over wide distance ranges. The friction coefficients obtained for gold are smaller than those for SiO2 and CaF2 by several orders of magnitude.

  4. Microstructure refinement and enhanced critical current density in binary doped SmFeAsO superconductor

    NASA Astrophysics Data System (ADS)

    Anooja, J. B.; Aswathy, P. M.; Varghese, Neson; Aloysius, R. P.; Syamaprasad, U.

    2014-04-01

    The iron-pnictide Sm1-xCaxFeAsO1-2xF2x superconductor was prepared and the combined effect of electron and hole doping was studied in detail. It is observed that the binary doping using CaF2 improves the microstructure tremendously with a preferred orientation of the (00l) planes. Moreover, a maximum TC of 53.8 K and a transport JC of 880 A/cm2 (12 K), which is double to that of the F-doped sample, are achieved. The dopant CaF2 seems to be a potential candidate for solving the grain-connectivity concerns in iron-pnictides paving the way towards conductor development.

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

    PubMed

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

    2015-06-28

    We report on heterogeneous core/shell CaF2:Yb(3+)/Ho(3+)@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:Yb(3+)/Ho(3+) 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. PMID:26035440

  6. Measurement of U-235 Fission Neutron Spectra Using a Multiple Gamma Coincidence Technique

    SciTech Connect

    Ji Chuncheng; Kegel, G.H.R.; Egan, J.J.; DeSimone, D.J.; Alimeti, A.; Roldan, C.F.; McKittrick, T.M.; Kim, D.-S.; Chen, X.; Tremblay, S.E.

    2005-05-24

    The Los Alamos Model of Madland and Nix predicts the shape of the fission neutron energy spectrum for incident primary neutrons of different energies. Verifications of the model normally are limited to measurements of the fission neutron spectra for energies higher than that of the primary neutrons because the low-energy spectrum is distorted by the admixture of elastically and inelastically scattered neutrons. This situation can be remedied by using a measuring technique that separates fission from scattering events. One solution consists of using a fissile sample so thin that fission fragments can be observed indicating the occurrence of a fission event. A different approach is considered in this paper. It has been established that a fission event is accompanied by the emission of between seven and eight gamma rays, while in a scattering interaction, between zero and two gammas are emitted, so that a gamma multiplicity detector should supply a datum to distinguish a fission event from a scattering event. We proceed as follows: A subnanosecond pulsed and bunched proton beam from the UML Van de Graaff generates nearly mono-energetic neutrons by irradiating a thin metallic lithium target. The neutrons irradiate a 235U sample. Emerging neutron energies are measured with a time-of-flight spectrometer. A set of four BaF2 detectors is located close to the 235U sample. These detectors together with their electronic components identify five different events for each neutron detected, i.e., whether four, three, two, one, or none of the BaF2 detectors received one (or more) gamma rays. We present work, preliminary to the final measurements, involving feasibility considerations based on gamma-ray coincidence measurements with four BaF2 detectors, and the design of a Fission-Scattering Discriminator under construction.

  7. Glass transition and composite formation in InF3-containing oxyfluoroniobate system

    NASA Astrophysics Data System (ADS)

    Savchenko, N. N.; Ignatieva, L. N.; Marchenko, Yu. V.; Bouznik, V. M.

    2016-05-01

    The glasses in the system MnNbOF5-BaF2-InF3 have been firstly synthesized and studied. The thermal parameters of these glasses are analyzed. It was stated that glass of the composition 40MnNbOF5-40BaF2-20InF3 is the most thermal stable in the system under study. By X-ray analysis the compositions of the crystalline phases obtained at the glass thermal treatment were determined: the main phases are Ba3In2F12 and BaNbOF5. By Raman and IR spectra analysis it was stated that the networks of glasses in the system are built by the structural type of the glasses in NbO2F-BaF2 system: (NbOnFm) polyhedra joined oxygen bridges. Indium trifluoride forms InF6 polyhedra, which are embeded between oxyfluoroniobate ions, forming a common networks or forms its own layers from InF6 polyhedra. IR-spectroscopy method showed that at devitrification of the sample 30MnNbOF5-50BaF2-20InF3 the band position and shape change in going from glass state to crystalline. The bands in the range 900-700 cm-1 shift into the low-frequency range and transformed into narrow peaks characteristic for the crystalline state. It was determined that for this sample the IR-spectroscopy method fixes the presence of the crystalline phases at 340°C without time of exposure, despite the fact that X-ray analysis shows an amorphous state for this sample at the same temperature. It was suggested, that controlling the composition and conditions of annealing of the glasses it can be obtain the transparent glass-ceramics of definite composition.

  8. 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.

  9. 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.

  10. Compositional and crystallographic changes on enamel when irradiated by Nd:YAG or Er,Cr:YSGG lasers and its resistance to demineralization when associated with fluoride

    NASA Astrophysics Data System (ADS)

    Zezell, D. M.; Ana, P. A.; Benetti, C.; Goulart, V. P.; Bachmann, L.; Tabchoury, C. P. M.; Cury, J. A.

    2010-02-01

    This study investigated the compositional and crystallographic changes on enamel when irradiated by Er,Cr:YSGG (λ=2.7μm, 8.5J/cm2) or Nd:YAG (λ=1064nm, 84.9J/cm2 associated with black coating), its resistance to demineralization when irradiation is associated with fluoride (APF-gel), and CaF2-like material formation and retention. Sample surfaces were analyzed by ATR-FTIR (4000-650cm-1, 4cm-1) resolution. Irradiation with Er,Cr:YSGG laser promoted a significant decrease on carbonate content of enamel. After Nd:YAG irradiation, it was observed a significant decrease of carbonate and amides I and II. X-ray diffraction showed that both laser irradiations promoted formation of α-tricalcium phosphate and tetracalcium phosphate, and a significant increase on the crystal growth of the enamel apatite (ANOVA, p<0.05 was used for all analysis). These changes can explain the improved resistance of enamel to demineralization observed in the second part of the study, in which 240 enamel slices were divided in 8 groups, received 4 min of professional fluoride gel (APF-gel 1.23%F-) applied before or after irradiation. After treatments, the formation of calcium fluoride (CaF2) was determined. The remaining slabs of each group were submitted to a 10-day pH-cycling model and, subsequently, enamel demineralization was evaluated by cross-sectional microhardness. Both lasers significantly reduced enamel demineralization (ANOVA, p<0.05), and the previous APF-gel application followed by laser showed the higher reduction of enamel demineralization. CaF2 formed before pH-cycling was significantly higher in groups were APF was associated with laser irradiation. After demineralization, these groups also presented higher CaF2 retention in respect to isolated treatments (only APF or only laser), suggesting its anticaries potential.

  11. 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.

  12. Selection and use of TLDS for high precision NERVA shielding measurements

    NASA Technical Reports Server (NTRS)

    Woodsum, H. C.

    1972-01-01

    An experimental evaluation of thermoluminescent dosimeters was performed in order to select high precision dosimeters for a study whose purpose is to measure gamma streaming through the coolant passages of a simulated flight type internal NERVA reactor shield. Based on this study, the CaF2 chip TLDs are the most reproducible dosimeters with reproducibility generally within a few percent, but none of the TLDs tested met the reproducibility criterion of plus or minus 2%.

  13. Phenotypic Consequences of a Spontaneous Loss of Heterozygosity in a Common Laboratory Strain of Candida albicans.

    PubMed

    Ciudad, Toni; Hickman, Meleah; Bellido, Alberto; Berman, Judith; Larriba, Germán

    2016-07-01

    By testing the susceptibility to DNA damaging agents of several Candida albicans mutant strains derived from the commonly used laboratory strain, CAI4, we uncovered sensitivity to methyl methanesulfonate (MMS) in CAI4 and its derivatives, but not in CAF2-1. This sensitivity is not a result of URA3 disruption because the phenotype was not restored after URA3 reintroduction. Rather, we found that homozygosis of a short region of chromosome 3R (Chr3R), which is naturally heterozygous in the MMS-resistant-related strains CAF4-2 and CAF2-1, confers MMS sensitivity and modulates growth polarization in response to MMS. Furthermore, induction of homozygosity in this region in CAF2-1 or CAF4-2 resulted in MMS sensitivity. We identified 11 genes by SNP/comparative genomic hybridization containing only the a alleles in all the MMS-sensitive strains. Four candidate genes, SNF5, POL1, orf19.5854.1, and MBP1, were analyzed by generating hemizygous configurations in CAF2-1 and CAF4-2 for each allele of all four genes. Only hemizygous MBP1a/mbp1b::SAT1-FLIP strains became MMS sensitive, indicating that MBP1a in the homo- or hemizygosis state was sufficient to account for the MMS-sensitive phenotype. In yeast, Mbp1 regulates G1/S genes involved in DNA repair. A second region of homozygosis on Chr2L increased MMS sensitivity in CAI4 (Chr3R homozygous) but not CAF4-2 (Chr3R heterozygous). This is the first example of sign epistasis in C. albicans.

  14. Hyper-Parametric Oscillations in a Whispering Gallery Mode Fluorite Resonator

    NASA Technical Reports Server (NTRS)

    Savchenkov, Anatoliy; Strekalov, Dmitry; Mohageg, Makan; Ilchenko, Vladimir; Matsko, Andrey; Maleki, Lute

    2004-01-01

    This viewgraph presentation summarizes the hyper-parametric oscillations observations of the fluorite resonator. The reporters have observed various nonlinear effects in ultra-high Q crystalline whispering gallery mode (WGM) resonators. In particular, it was demonstrated a low threshold optical hyper-parametric oscillations in a high-Q (Q=1010) CaF2 WGM resonator. The oscillations result from the resonantly enhanced four-wave-mixing occurring due to Kerr nonlinearity of the material.

  15. 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.

  16. (n, γ) 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 4π 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.

  17. Measurement of the Gd157(n,γ) reaction with the DANCE γ calorimeter array

    NASA Astrophysics Data System (ADS)

    Chyzh, A.; Baramsai, B.; Becker, J. A.; Bečvář, F.; Bredeweg, T. A.; Couture, A.; Dashdorj, D.; Haight, R. C.; Jandel, M.; Kroll, J.; Krtička, 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,γ) reaction was measured with the DANCE γ calorimeter (consisting of 160 BaF2 scintillation detectors) at the Los Alamos Neutron Science Center. The multiplicity distributions of the γ decay were used to determine the resonance spins up to En=300 eV. The γ-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.

  18. System for measuring temporal profiles of scintillation at high and different linear energy transfers by using pulsed ion beams.

    PubMed

    Koshimizu, Masanori; Kurashima, Satoshi; Taguchi, Mitsumasa; Iwamatsu, Kazuhiro; Kimura, Atsushi; Asai, Keisuke

    2015-01-01

    We have developed a system for measuring the temporal profiles of scintillation at high linear energy transfer (LET) by using pulsed ion beams from a cyclotron. The half width at half maximum time resolution was estimated to be 1.5-2.2 ns, which we attributed mainly to the duration of the pulsed ion beam and timing jitter between the trigger signal and the arrival of the ion pulse. The temporal profiles of scintillation of BaF2 at different LETs were successfully observed. These results indicate that the proposed system is a powerful tool for analyzing the LET effects in temporal profiles of scintillation.

  19. Prompt γ-rays from the Fast Neutron Induced Fission on 235,238U and 232Th

    NASA Astrophysics Data System (ADS)

    Lebois, M.; Wilson, J. N.; Halipré, P.; Leniau, B.; Matea, I.; Oberstedt, A.; Oberstedt, S.; Verney, D.

    Preliminary results from the first experiment using the LICORNE neutron source at the IPN Orsay are presented. Prompt fission gamma rays from fast-neutron induced fission of 238U, 232Th and 235U were detected. Thick samples of around 50 g of 238U and 232Th are used for the first part of the experiment. An ionisation chamber containing ∼ 10 mg samples of 238U and 235U to provide a fission trigger is used for the second part of the experiment. Gamma rays have been detected using 17 high efficiency BaF2 detectors and 6 LaBr3 scintillator detectors.

  20. Study of the presence of fluorine in the recycled fractions during carbothermal treatment of EAF dust.

    PubMed

    Menad, N; Ayala, J N; Garcia-Carcedo, Fernando; Ruiz-Ayúcar, E; Hernández, A

    2003-01-01

    Carbothermal treatment tests of electric arc furnace dusts (EAFD) using the Waelz kiln process were carried out in pilot-scale for the production of zinc oxide. The association of halides in the EAFD, and the recycled products, such as zinc oxide fumes and high-grade iron contents fractions were examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. XRD reveals the presence of chlorine and fluorine in the dusts in the form of KCl, NaCl and CaF2. An ultra-pure fraction of zinc was obtained after the Double Leaching Waelz Oxide (DLWO) process was performed on the zinc oxide fumes. The halide contents were reduced to approximately 100 ppm Cl and 700 ppm F. The rest of these elements are in the form of CaF2. About 65% F is volatilised as lead and zinc fluorides, 15% is expected in the magnetic fractions and 20% in non-magnetic fractions as CaF2 and MnF2, respectively.

  1. Thermochemistry of calcium oxide and calcium hydroxide in fluoride slags

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, S.; Mitchell, A.

    1990-08-01

    Calcium oxide activity in binary CaF2-CaO and ternary CaF2-CaO-Al2O3 and CaF2-CaO-SiO2 slags has been determined by CO2-slag equilibrium experiments at 1400 °C. The carbonate ca-pacity of these slags has also been computed and compared with sulfide capacity data available in the literature. The similarity in trends suggests the possibility of characterizing carbonate capacity as an alternative basicity index for fluoride-base slags. Slag-D2O equilibrium experi-ments are performed at 1400°C with different fluoride-base slags to determine water solubility at two different partial pressures of D2O, employing a new slag sampling technique. A novel isotope tracer detection technique is employed to analyze water in the slags. The water solubility data found show higher values than the previous literature data by an order of magnitude but show a linear relationship with the square root of water vapor partial pressure. The activity of hydroxide computed from the data is shown to be helpful in estimating water solubility in in-dustrial electroslag remelting (ESR) slags.

  2. Effects of fluoride on in vitro enamel demineralization analyzed by ¹⁹F MAS-NMR.

    PubMed

    Mohammed, N R; Kent, N W; Lynch, R J M; Karpukhina, N; Hill, R; Anderson, P

    2013-01-01

    The mechanistic action of fluoride on inhibition of enamel demineralization was investigated using (19)F magic angle spinning nuclear magnetic resonance (MAS-NMR). The aim of this study was to monitor the fluoride-mineral phase formed on the enamel as a function of the concentration of fluoride ions [F(-)] in the demineralizing medium. The secondary aim was to investigate fluorapatite formation on enamel in the mechanism of fluoride anti-caries efficacy. Enamel blocks were immersed into demineralization solutions of 0.1 M acetic acid (pH 4) with increasing concentrations of fluoride up to 2,262 ppm. At and below 45 ppm [F(-)] in the solution, (19)F MAS-NMR showed fluoride-substituted apatite formation, and above 45 ppm, calcium fluoride (CaF2) formed in increasing proportions. Further increases in [F(-)] caused no further reduction in demineralization, but increased the proportion of CaF2 formed. Additionally, the combined effect of strontium and fluoride on enamel demineralization was also investigated using (19)F MAS-NMR. The presence of 43 ppm [Sr(2+)] in addition to 45 ppm [F(-)] increases the fraction of fluoride-substituted apatite, but delays formation of CaF2 when compared to the demineralization of enamel in fluoride-only solution. PMID:23712030

  3. Patternless light outcoupling enhancement method for top-emission organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Kim, Doo-Hoon; Lee, Ho-Nyeon

    2016-11-01

    An increase of 65% in the luminous flux of a top-emission organic light-emitting diode (TE-OLED) was obtained by fabricating a stacked N,N‧-bis(naphthalen-1-yl)-N,N‧-bis(phenyl)benzidine (NPB) (0.2 µm)/CaF2 (2.5 µm) light outcoupling layer on the TE-OLED. The high-refractive-index NPB layer extracted the trapped light energy in the TE-OLED for input into the light outcoupling layer and protected the top cathode of the TE-OLED from damage due to the CaF2 layer. The surface morphology of the CaF2 layer had an irregular shape consisting of randomly dispersed pyramids; the irregular structure scattered the waveguide mode energy into air. By combining the effects of the NPB and CaF2 layers, the external quantum efficiency of the TE-OLED was increased significantly. The light outcoupling layer can be fabricated using a thermal evaporation process without patterning and, hence, provides a practical solution for the enhancement of TE-OLED light outcoupling using a patternless fabrication process.

  4. Study of 48Ca double beta decay with CANDLES

    NASA Astrophysics Data System (ADS)

    Ogawa, Izumi; CANDLES Collaboration

    2008-11-01

    CANDLES is the project to search for double beta decay of 48Ca by using CaF2 scintillators. If neutrinos have Majorana mass they violate lepton number conservation and neutrino-less double beta decay (OvDBD) can then take place. Therefore the study of the 0 vDBD is one of the most fundamental researches to be carried out in a coming decade. We have been studying the DBD of 48Ca using CaF2 scintillators. The Q value of 48Ca is the highest (4.27 MeV) among potential DBD nuclei. It is far above energies of γ-rays from natural radio-activities (maximum 2.615 MeV from 208TI decay), therefore we can naturally expect small backgrounds in the energy region we are interested in. Required performances for the detector are radio-purity, good background rejection efficiency and good energy resolution. We have constructed CANDLES III detector in our laboratory at sea level, which consists of 60 CaF2 crystals with the total mass of 191 kg. We are studying the basic performances of the system, including the light collection, position reconstruction and background rejection. On the bases of experiences in CANDLES III, the CANDLES project will be scaled up to several tons of calcium to have the sensitivity to the mass region of interest.

  5. Impact of mechanical stress on ferroelectricity in (Hf0.5Zr0.5)O2 thin films

    NASA Astrophysics Data System (ADS)

    Shiraishi, Takahisa; Katayama, Kiliha; Yokouchi, Tatsuhiko; Shimizu, Takao; Oikawa, Takahiro; Sakata, Osami; Uchida, Hiroshi; Imai, Yasuhiko; Kiguchi, Takanori; Konno, Toyohiko J.; Funakubo, Hiroshi

    2016-06-01

    To investigate the impact of mechanical stress on their ferroelectric properties, polycrystalline (Hf0.5Zr0.5)O2 thin films were deposited on (111)Pt-coated SiO2, Si, and CaF2 substrates with thermal expansion coefficients of 0.47, 4.5, and 22 × 10-6/ °C, respectively. In-plane X-ray diffraction measurements revealed that the (Hf0.5Zr0.5)O2 thin films deposited on SiO2 and Si substrates were under in-plane tensile strain and that their volume fraction of monoclinic phase decreased as this strain increased. In contrast, films deposited on CaF2 substrates were under in-plane compressive strain, and their volume fraction of monoclinic phase was the largest among the three kinds of substrates. The maximum remanent polarization of 9.3 μC/cm2 was observed for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2, while ferroelectricity was barely observable for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2/CaF2. This result suggests that the in-plane tensile strain effectively enhanced the ferroelectricity of the (Hf0.5Zr0.5)O2 thin films.

  6. 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.

  7. 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.

  8. Status and future prospect of 48Ca double beta decay search in CANDLES

    NASA Astrophysics Data System (ADS)

    Iida, T.; Nakajima, K.; Ajimura, S.; Batpurev, T.; Chan, W. M.; Fushimi, K.; Hazama, R.; Kakubata, H.; Khai, B. T.; Kishimoto, T.; Li, X.; Maeda, T.; Masuda, A.; Matsuoka, K.; Morishita, K.; Nakatani, N.; Nomachi, M.; Noshiro, S.; Ogawa, I.; Ohata, T.; Osumi, H.; Suzuki, K.; Tamagawa, Y.; Tesuno, K.; Trang, V. T. T.; Uehara, T.; Umehara, S.; Yoshida, S.

    2016-05-01

    The observation of neutrino-less double beta decay (0vßß) would be the most practical way to prove the Majorana nature of the neutrino and lepton number violation. CANDLES studies 48Ca double beta decay using CaF2 scintillator. The main advantage of 48Ca is that it has the highest Q-value (4.27 MeV) among all the isotope candidates for 0vßß. The CANDLES III detector is currently operating with 300kg CaF2 crystals in the Kamioka underground observatory, Japan. In 2014, a detector cooling system and a magnetic cancellation coil was installed with the aim to increase light emission of CaF2 scintillator and photo-electron collection efficiency of the photo-multipliers. After this upgrade, light yield was increased to 1000 p.e./MeV which is 1.6 times larger than before. According to data analysis and simulation, main background source in CANDLES is turned out to be high energy external gamma-ray originating neutron capture on the surrounding materials, so called (n,γ). Upgrading the detector by installing neutron and gamma-ray shield can reduce the remaining main backgrounds by two order magnitude. In this report, we discuss the detail of (n,γ) and background reduction by additional shielding.

  9. Experimental study and thermodynamic modelling of the calcium oxide-silicon oxide-aluminum oxide-calcium fluoride system

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Geun

    Mould flux for the continuous casting process is a major concern for the steelmaking industry. Nowadays, more than 90 % of steel is being produced by the continuous casting process, which requires mould flux as an essential additive. The development of mould flux has been achieved by the conventional trial and error approach since it was first introduced in industry in the 1960s. Recently, the interest on the properties of fluorine has increased a lot since it is reported that fluorine has important functions such as playing a critical role on the crystallization behavior, and decreasing the melting point and viscosity of slag. However, the conventional way to find a suitable mould flux is not efficient to face the increasingly stringent requirements of the continuous casting process such as thin slab casting and higher casting speed. Therefore, fundamental phase diagram study on mould flux systems is clearly necessary, and thermodynamic modeling is the most effective way to design new mould flux in terms of time and money saving. The major components of mould flux, the CaO-SiO2-Al2O 3-CaF2 system, are investigated in this study as these four constituents will mostly affect the largest numbers of properties. Unfortunately, fluorine has high volatility at high temperature and high reactivity with other materials. Therefore, the results of previous experiments on F-containing systems are characterized by large discrepancies due to composition alteration and unexpected reactions during the experiment. As literature data show inconsistent results between each other, key phase diagram experiments were performed in this study. The phase diagram experiments were conducted with the quenching method in sealed Pt capsules to prevent fluorine loss during the experiment. The analyses were performed using a FE-SEM equipped with an EDS system, and a newly developed technique which produces more precise quantitative results for the equilibrium phase composition. The CaO liquidus of the CaO-CaF 2 binary system, which the literature data differ from each other by up to 50 mol %, was confirmed. The CaO solubility in solid CaF2 was found for the first time and reaches about 5 mol % at the eutectic temperature. The liquidus of the CaO-Al2O3-CaF2 and CaO-SiO 2-CaF2 systems were carefully studied and the miscibility gap in the CaO-Al2O3-CaF2 system was proved to be much smaller than that reported in literature. Also, thermal analysis was performed using DSC in a Pt crucible. The eutectic temperatures of the CaO-CaF2 and CaAl2O4-CaF2 systems were successfully measured and the alpha to beta-CaF2 polymorphic transition was confirmed. Based on the new experimental data and reliable literature data, thermodynamic modeling of the CaO-SiO2-Al 2O3-CaF2 system was also carried out. The results of thermodynamic calculation can be very beneficial for new mould flux design.

  10. 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 4π geometry allows for highly efficient detection of prompt γ-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 γ-ray energy and total γ-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 γ-ray energy was established for mono-energetic γ-rays.

  11. 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 4π 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.

  12. Thin film growth of a topological crystal insulator SnTe on the CdTe (111) surface by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ishikawa, Ryo; Yamaguchi, Tomonari; Ohtaki, Yusuke; Akiyama, Ryota; Kuroda, Shinji

    2016-11-01

    We report molecular beam epitaxial growth of a SnTe (111) layer on a CdTe template, fabricated by depositing it on a GaAs (111)A substrate, instead of BaF2 which has been conventionally used as a substrate. By optimizing temperatures for the growth of both SnTe and CdTe layers and the SnTe growth rate, we could obtain SnTe layers of the single phase grown only in the (111) orientation and of much improved surface morphology from the viewpoint of the extension and the flatness of flat regions, compared to the layers grown on BaF2. In this optimal growth condition, we have also achieved a low hole density of the order of 1017 cm-3 at 4 K, the lowest value ever reported for SnTe thin films without additional doping. In the magnetoresistance measurement on this optimized SnTe layer, we observe characteristic negative magneto-conductance which is attributed to the weak antilocalization effect of the two-dimensional transport in the topological surface state.

  13. Resonant nature of intrinsic defect energy levels in PbTe revealed by infrared photoreflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Bingpo; Cai, Chunfeng; Jin, Shuqiang; Ye, Zhenyu; Wu, Huizhen; Qi, Zhen

    2014-07-01

    Step-scan Fourier-transform infrared photoreflectance and modulated photoluminescence spectroscopy were used to characterize the optical transitions of the epitaxial PbTe thin film grown by molecular beam epitaxy on BaF2 (111) substrate in the vicinity of energy gap of lead telluride at 77 K. It is found that the intrinsic defect energy levels in the electronic structure are of resonant nature. The Te-vacancy energy level is located above the conduction band minimum by 29.1 meV. Another defect (VX) energy level situated below valance band maximum by 18.1 meV is also revealed. Whether it is associated with the Pb vacancy is still not clear. It might also be related to the misfit dislocations stemming from the lattice mismatch between PbTe and BaF2 substrate. The experimental results support the theory prediction (N. J. Parada and G. W. Pratt, Jr., Phys. Rev. Lett. 22, 180 (1969), N. J. Parada, Phys. Rev. B 3, 2042 (1971)) and are consistent with the reported Hall experimental results (G. Bauer, H. Burkhard, H. Heinrich, and A. Lopez-Otero, J. Appl. Phys. 47, 1721 (1976)).

  14. Depolarization properties of the femtosecond supercontinuum generated in condensed media

    NASA Astrophysics Data System (ADS)

    Kumar, R. Sai Santosh; Deepak, K. L. N.; Rao, D. Narayana

    2008-10-01

    In this paper, we present a study of depolarization of a supercontinuum across its spectral range as a function of the femtosecond laser pump intensity for an anisotropic crystalline condensed medium, potassium-dihydrogen-phosphate (KDP) crystal, and compare our results with commonly used supercontinuum generation (SCG) materials, namely borosilicate glass Schott (BK-7) glass (representing isotropic amorphous condensed media) and BaF2 (isotropic crystalline condensed media). Our results show that at higher input powers, depolarization in the continuum increases for BK-7, BaF2 , and along the direction of the optic axis of the KDP crystal. However, in the case of KDP crystal, we observe that the depolarization properties are strongly dependent on (i) the plane of polarization of incident light and (ii) the orientation of the crystal with respect to the incident light. Our studies also confirm that one can achieve SCG in a KDP crystal that maintains the same state of input polarization even at high input intensities when proper orientation of the crystal is used.

  15. Correlated fluorine diffusion and ionic conduction in the nanocrystalline F(-) solid electrolyte Ba(0.6)La(0.4)F(2.4)-(19)F T1(ρ) NMR relaxation vs. conductivity measurements.

    PubMed

    Preishuber-Pflügl, F; Bottke, P; Pregartner, V; Bitschnau, B; Wilkening, M

    2014-05-28

    Chemical reactions induced by mechanical treatment may give access to new compounds whose properties are governed by chemical metastability, defects introduced and the size effects present. Their interplay may lead to nanocrystalline ceramics with enhanced transport properties being useful to act as solid electrolytes. Here, the introduction of large amounts of La into the cubic structure of BaF2 served as such an example. The ion transport properties in terms of dc-conductivity values of the F(-) anion conductor Ba1-xLaxF2+x (here with x = 0.4) considerably exceed those of pure, nanocrystalline BaF2. So far, there is only little knowledge about activation energies and jump rates of the elementary hopping processes. Here, we took advantage of both impedance spectroscopy and (19)F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. While macroscopic transport is governed by an activation energy of 0.55 to 0.59 eV, the elementary steps of hopping seen by NMR are characterised by much smaller activation energies. Fortunately, we were able to deduce an F(-) self-diffusion coefficient by the application of spin-locking NMR relaxometry.

  16. 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

  17. 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.

  18. 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.

  19. On structural and lattice dynamic stability of LaF{sub 3} under high pressure: A first principle study

    SciTech Connect

    Sahoo, B. D. Joshi, K. D.; Gupta, Satish C.

    2015-06-24

    Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ∼19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.

  20. Evidence of energy transfer in nanoparticle-porphyrins conjugates for radiation therapy enhancement

    NASA Astrophysics Data System (ADS)

    Kudinov, Konstantin; Cooper, Daniel; Tyagi, Pooja; Bekah, Devesh; Bhattacharyya, Dhrittiman; Hill, Colin; Ha, Jonathan Kin; Nadeau, Jay; Bradforth, Stephen

    2015-03-01

    We report progress towards combining radiation therapy (RT) and photodynamic therapy (PDT) using scintillating nanoparticle (NP)-photosensitizer conjugates. In this approach, scintillating NPs are excited by clinically relevant ionizing radiation sources and subsequently transfer energy to conjugated photosensitizers via FRET, acting as an energy mediator between ionizing radiation and photosensitizer molecules. The excited photosensitizers generate reactive oxygen species that can induce local damage and immune response. Advantages of the scheme include: 1) Compared with traditional radiation therapy, a possible decrease of the total radiation dose needed to eliminate the lesion; 2) Compared with traditional PDT, the ability to target deeper and more highly pigmented lesions; 3) The possibility of additional photosensitizing effects due to the scintillation of the nanoparticles. In this work, the photosensitizer molecule chlorin e6 was covalently bound to the surface of LaF3:Ce NPs. After conjugation, the photoluminescence intensity of NPs decreased, and fluorescence lifetime of conjugated chlorin e6 became sensitive to excitation wavelength, suggesting rapid FRET. In addition, scintillation spectra of nanoparticles were measured. Preliminary calculations suggest that the observed scintillation efficiencies are sufficient to enhance RT. In vitro cancer cell studies suggest conjugates are taken up by cells. Survival curves with radiation exposure suggest that the particles alone cause radiosensitization comparable to that seen with gold nanoparticles.

  1. 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

  2. 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 3d⁹4f¹ configuration created by 3d¹⁰4f⁰ → 3d⁹4f¹ 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.

  3. Phase transformation and fluorescent enhancement of ErF3 at high pressure

    NASA Astrophysics Data System (ADS)

    Li, Wentao; Ren, Xiangting; Huang, Yanwei; Yu, Zhenhai; Mi, Zhongying; Tamura, Nobumichi; Li, Xiaodong; Peng, Fang; Wang, Lin

    2016-09-01

    Pressure-induced phase transformation and fluorescent properties of ErF3 were investigated here using in-situ synchrotron X-ray diffraction and photoluminescence up to 32.1 GPa at room temperature. Results showed that ErF3 underwent a reversible pressure-induced phase transition from the β-YF3-type to the fluocerite LaF3-type at 9.8 GPa. The bulk moduli B0 for low- and high-pressure phases were determined to be 130 and 208 GPa, respectively. Photoluminescencent studies showed that new emission lines belonging to the transition of 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 appeared during phase transition, suggesting pressure-induced electronic band splitting. Remarkably, significant pressure-induced enhancement of photoluminescence was observed, which was attributed to lattice distortion of the material under high pressure.

  4. The stable and water-soluble neodymium-doped lanthanide fluoride nanoparticles for near infrared probing of copper ion.

    PubMed

    Xue, Fang-Min; Wang, He-Fang

    2012-09-15

    Neodymium (Nd(3+)) doped nanomaterials exhibited the unique near infrared (NIR) luminescence properties. However, the application of Nd-doped nanomaterials to chemosensors was rarely explored. Herein, the water-soluble 2-aminoethyl dihydrogen phosphate stabilized Nd-doped LaF(3) (ADP-Nd-LaF(3)) nanoparticles were explored as the NIR probe for chemosensors. The NIR emission intensity at 1061 nm of ADP-Nd-LaF(3) nanoparticles kept stable in the aqueous solution of various pH and coexisting of most common metal ions except copper ion, consequently, the ADP-Nd-LaF(3) nanoparticles were developed as a high selective NIR probe for Cu(II). The NIR emission of ADP-Nd-LaF(3) exhibits a linear quenching response to Cu(II) in the range 5-100 μM, with a detection limit of 0.8 μM. The precision of eleven replicate detections of 5 μM Cu(II) was 0.5% (RSD). The recovery of spiked Cu(II) in human urine and waste water samples ranged from 102 to 109%. The possible mechanism of Cu(II)-induced fluorescence quenching of ADP-Nd-LaF(3) nanoparticles was also discussed.

  5. Solid electrolytes for fluoride ion batteries: ionic conductivity in polycrystalline tysonite-type fluorides.

    PubMed

    Rongeat, Carine; Reddy, M Anji; Witter, Raiker; Fichtner, Maximilian

    2014-02-12

    Batteries based on a fluoride shuttle (fluoride ion battery, FIB) can theoretically provide high energy densities and can thus be considered as an interesting alternative to Li-ion batteries. Large improvements are still needed regarding their actual performance, in particular for the ionic conductivity of the solid electrolyte. At the current state of the art, two types of fluoride families can be considered for electrolyte applications: alkaline-earth fluorides having a fluorite-type structure and rare-earth fluorides having a tysonite-type structure. As regard to the latter, high ionic conductivities have been reported for doped LaF3 single crystals. However, polycrystalline materials would be easier to implement in a FIB due to practical reasons in the cell manufacturing. Hence, we have analyzed in detail the ionic conductivity of La(1-y)Ba(y)F(3-y) (0 ≤ y ≤ 0.15) solid solutions prepared by ball milling. The combination of DC and AC conductivity analyses provides a better understanding of the conduction mechanism in tysonite-type fluorides with a blocking effect of the grain boundaries. Heat treatment of the electrolyte material was performed and leads to an improvement of the ionic conductivity. This confirms the detrimental effect of grain boundaries and opens new route for the development of solid electrolytes for FIB with high ionic conductivities. PMID:24444763

  6. Quasi-Elastic Light Scattering and Dynamic Parameters of the Internal Motion in Superionic Crystals of LNF3 (Ln = La, Ce)

    NASA Astrophysics Data System (ADS)

    Krivorotov, V. F.; Mirzaev, S. Z.; Nuzhdov, G. S.

    2016-07-01

    Low-frequency light scattering in superionic crystals of the LaF3 structural type was studied. The laser light scattering spectra of LnF3 single crystals at 90o scattering geometry were obtained over a wide temperature range. The scattering intensity increased sharply in the temperature range in which the mobility of the fl uoride ions increased. The experimental scattering curves were represented as the sum of three central Lorentz contours. The "narrow" Lorentzian had width Γ1 = 0.8-4.2 cm-1; the "medium" Lorentzian, Γ2 = 4.2-27 cm-1; and the "wide" Lorentzian, Γ3 = 42-96 cm-1. These corresponded to relaxation times τ1 ≈ (0.13-0.67) × 10-11 s, τ2 ≈ (0.20-1.27) × 10-12 s, and τ3 ≈ (0.56-1.27) × 10-13 s that were associated with different types of displacement of fl uoride ions into interstices. The activation energy ΔEd obtained from the temperature dependence of the Lorentz contour width was found to be many times less than the energy Ed determining the dynamic parameters of ion motion in the LnF3 lattice.

  7. Gene expression patterns in granulosa cells and oocytes at various stages of follicle development as well as in in vitro grown oocyte-and-granulosa cell complexes.

    PubMed

    Munakata, Yasuhisa; Kawahara-Miki, Ryoka; Shiratsuki, Shogo; Tasaki, Hidetaka; Itami, Nobuhiko; Shirasuna, Koumei; Kuwayama, Takehito; Iwata, Hisataka

    2016-08-25

    Follicle development is accompanied by proliferation of granulosa cells and increasing oocyte size. To obtain high-quality oocytes in vitro, it is important to understand the processes that occur in oocytes and granulosa cells during follicle development and the differences between in vivo and in vitro follicle development. In the present study, oocytes and granulosa cells were collected from early antral follicles (EAFs, 0.5-0.7 mm in diameter), small antral follicles (SAFs, 1-3 mm in diameter), large antral follicles (LAFs, 3-7 mm in diameter), and in vitro grown oocyte-and-granulosa cell complexes (OGCs), which were cultured for 14 days after collection from EAFs. Gene expression was analyzed comprehensively using the next-generation sequencing technology. We found top upstream regulators during the in vivo follicle development and compared them with those in in vitro developed OGCs. The comparison revealed that HIF1 is among the top regulators during both in vivo and in vitro development of OGCs. In addition, we found that HIF1-mediated upregulation of glycolysis in granulosa cells is important for the growth of OGCs, but the cellular metabolism differs between in vitro and in vivo grown OGCs. Furthermore, on the basis of comparison of upstream regulators between in vivo and in vitro development of OGCs, we believe that low expression levels of FLT1 (VEGFA receptor), SPP1, and PCSK6 can be considered causal factors of the suboptimal development under in vitro culture conditions.

  8. 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.

  9. Gene expression patterns in granulosa cells and oocytes at various stages of follicle development as well as in in vitro grown oocyte-and-granulosa cell complexes

    PubMed Central

    MUNAKATA, Yasuhisa; KAWAHARA-MIKI, Ryoka; SHIRATSUKI, Shogo; TASAKI, Hidetaka; ITAMI, Nobuhiko; SHIRASUNA, Koumei; KUWAYAMA, Takehito; IWATA, Hisataka

    2016-01-01

    Follicle development is accompanied by proliferation of granulosa cells and increasing oocyte size. To obtain high-quality oocytes in vitro, it is important to understand the processes that occur in oocytes and granulosa cells during follicle development and the differences between in vivo and in vitro follicle development. In the present study, oocytes and granulosa cells were collected from early antral follicles (EAFs, 0.5–0.7 mm in diameter), small antral follicles (SAFs, 1–3 mm in diameter), large antral follicles (LAFs, 3–7 mm in diameter), and in vitro grown oocyte-and-granulosa cell complexes (OGCs), which were cultured for 14 days after collection from EAFs. Gene expression was analyzed comprehensively using the next-generation sequencing technology. We found top upstream regulators during the in vivo follicle development and compared them with those in in vitro developed OGCs. The comparison revealed that HIF1 is among the top regulators during both in vivo and in vitro development of OGCs. In addition, we found that HIF1-mediated upregulation of glycolysis in granulosa cells is important for the growth of OGCs, but the cellular metabolism differs between in vitro and in vivo grown OGCs. Furthermore, on the basis of comparison of upstream regulators between in vivo and in vitro development of OGCs, we believe that low expression levels of FLT1 (VEGFA receptor), SPP1, and PCSK6 can be considered causal factors of the suboptimal development under in vitro culture conditions. PMID:27108636

  10. Crystal field splitting of the 4f 5d electronic configuration of Pr 3+ ions in wide band gap fluoride dielectric crystals

    NASA Astrophysics Data System (ADS)

    Sarantopoulou, E.; Kollia, Z.; Cefalas, A. C.; Semashko, V. V.; Yu. Abdulsabirov, R.; Naumov, A. K.; Korableva, S. L.; Szczurek, T.; Kobe, S.; McGuiness, P. J.

    2002-07-01

    The absorption and the laser-induced fluorescence spectra of Pr 3+ ion in YF 3, LaF 3, KY 3 F 10 and LiLuF 4, single crystal hosts were obtained in the vacuum ultraviolet region of the spectrum. The energy position and the spacing of the levels of the 4f 5d electronic configuration depend on the host matrix. In addition, strong vacuum ultraviolet emission bands were observed, following crystal excitation at 157 nm with the molecular fluorine laser. The emission bands were due to the interconfigurational 4 f 5 d→4 f2 dipole-allowed transitions in Pr 3+ ions, and they were assigned to the transitions between the edge of the lowest Stark component of the 4f 5d electronic configuration and the levels of the 4f 2 electronic configuration. The VUV spectra can be interpreted by applying the crystal field model, and taking into consideration that lanthanide contraction of the 4f n-1 5d electronic configurations of the rare earth ions, and shielding of the positive ion charge from the electrons in the 4f n electronic configuration is taking place. Finally, a new method for monitoring the concentration of the rare earth ions in wide band gap fluoride dielectric crystals in a non-destructive way, by measuring magnetic dipole moments with the vibrating sample magnetometer (VSM) method, is presented for the first time to our knowledge for this type of crystals.

  11. Energies of 4f^N and 4f^N-15d States Relative to Host Bands in Rare-earth-doped Fluorides

    NASA Astrophysics Data System (ADS)

    Thiel, C. W.; Joubert, M.-F.; Tkachuk, A.

    2005-03-01

    Energies of 4f^N states relative to crystal band states were measured for rare-earth ions in the optical host materials LiYF4, Na0.4Y0.6F2.2, and LaF3 using x-ray photoemission spectroscopy. Spectra were modeled to determine the valence band maximum and 4f^ electron binding energies in each material. These results were combined with 4f^N to 4f^N-15d transition energies to determine 5d binding energies for the lowest levels of excited 4f^N-15d configurations. While 4f^N ground-state energies vary within several eV of the valence band maximum for different rare-earth ions in each host, the lowest 4f^N-15d states have similar energies and are several eV below the bottom of the conduction band. A simple model accurately described 4f^N and 4f^N-15d binding energies across the entire series of rare-earth ions. These results improve the understanding of optical materials for lasers, phosphors, and spectral hole burning applications for optical signal processing and data storage.

  12. Upconversion in erbium-doped transparent glass ceramics

    NASA Astrophysics Data System (ADS)

    Jones, Gina Christine

    2005-11-01

    Transparent glass ceramics (TGCs) are a class of materials that are composed of a robust glass matrix which is densely embedded with nanometer-sized fluoride crystals: In bulk, fluoride materials tend to have poor handling and mechanical properties, and can be expensive to produce. In contrast, the forming and handling properties of the TGC are similar to those of the precursor, glass, and are engineered to be robust and mechanically stable. Rare earth ions can be incorporated into the TGC during manufacture and can become partially segregated into the crystalline phase. There they experience the low-phonon energy environment of the fluoride nanocrystallite, which induces long energy level lifetimes and enhanced frequency upconversion. Therefore, rare earth doped TGCs can have the spectroscopic properties of a crystal with the durability of an aluminosilicate glass. Upconversion fluorescence is studied for an aluminosilicate TGC containing LaF3 nanocrystallites and doped with an erbium density of 1.7 x 1020 CM-3. Time gated fluorescence and excitation spectra as well as photoluminescence decays are used to find the nature and origin of this fluorescence. It is determined that energy transfer upconversion occurs only in the nanocrystallite phase and sequential two-photon absorption upconversion occurs in both glass and crystal phases.

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

    PubMed

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

    2015-03-21

    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 (60)Co 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 μm(-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. PMID:25683355

  14. Gamma Ray Emission Tomography and Angular Correlation Measurements to Study the Distribution and Binding Site of Selenium.

    NASA Astrophysics Data System (ADS)

    Dahni, Anwar

    Available from UMI in association with The British Library. The distribution of ^ {75}Se in tissue equivalent materials was investigated employing Gamma ray Emission Topography with a rectilinear scanner utilizing NaI(Tl) and BGO detectors. The reconstructed images, using Filtered Back Projection and Iterative techniques were presented in 2D colour and 3D representations. Using a lead collimator of aperture 1.5 x 20 mm and 70 length, the distribution of selenium with variation of volume and concentration was examined and clearly seen. Several corrections such as background, scattering, attenuation compensation and X-ray characteristic suppression, were performed to improve the quality of the images which was evaluated in terms of the fidelity factor. The possibility of quantifying an image was considered with regard to spatial resolution and least detectable concentration. The spatial resolution was measured using two small vials containing the same concentration of selenium, the value obtained was the same as the width of the collimator aperture. The value of the least detectable concentration of selenium however, was difficult to find, due to the many ambiguous factors involved. The binding site of selenium which is based on quadrupole interaction with the surrounding electric field, was investigated employing Perturbed Angular Correlation (PAC) experiments using NaI(Tl) and BaF_2 detectors. Using NaI(Tl) detectors, it was difficult to observe the perturbation, due to the poor time resolution. The BaF_2 detector according to the literature has a shorter light emission decay time constant (0.6 ns), suggested that a better time resolution than that found with the NaI(Tl) detectors could be obtained. A Perturbed Angular Correlation experiment employing BaF _2 detectors and a fast-slow coincidence system was set up. The time differential PAC of selenium in solution showed an unperturbed angular correlation pattern. The main problem is the very short half life of the intermediate state of ^{75}Se (0.3 ns), making it difficult to observe the perturbation effect. The time resolution of the system (5.4 ns) will need to be improved by an order of magnitude or more for the investigations to continue.

  15. 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.

  16. Optical properties and spectroscopic study of different modifier based Pr(3+):LiFB glasses as optical amplifiers.

    PubMed

    Balakrishna, A; Babu, S; Kumar, Vinod; Ntwaeaborwa, O M; Ratnakaram, Y C

    2017-01-01

    In this paper, we report the preparation and optical characterization of Pr(3+) doped lithium fluoro borate (LiFB) glasses for six different chemical compositions of Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. The structural and optical properties of these glasses were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), optical absorption and photoluminescence techniques. The optical absorption spectra of Pr(3+) ions in LiFB glasses have been recorded in the UV-VIS-NIR region. The optical absorption data are used to calculate various spectroscopic parameters such as Racah (E(1), E(2), E(3)) and spin-orbit interaction (ξ4f) parameters. Judd-Ofelt (J-O) (Ωλ where λ=2, 4 and 6) intensity parameters were determined by applying J-O theory, which in turn used to calculate the radiative properties such as radiative transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βr) for all emission levels of Pr(3+) ion in different LiFB glass matrices. By using the J-O theory and luminescence parameters, stimulated emission cross sections (σp) of prominent transitions, (3)P0→(3)H4 and (1)D2→(3)H4 of Pr(3+) ion in all LiFB glasses were calculated. (3)P0→(3)H4 possesses higher branching ratios and stimulated emission cross-sections for the Pr(3+):LiFB(Mg-Ca) glass, which can be used as a best laser excitation. The optical gain parameter (σpxτR) was noticed higher in Pr(3+):LiFB(Mg-Ca) and Pr(3+):LiFB(Cd-Pb) glasses for the transition (3)P0→(3)H4 transition, and these glasses have potential for optical amplification at 488 nm wavelength. PMID:27434876

  17. Optical properties and spectroscopic study of different modifier based Pr(3+):LiFB glasses as optical amplifiers.

    PubMed

    Balakrishna, A; Babu, S; Kumar, Vinod; Ntwaeaborwa, O M; Ratnakaram, Y C

    2017-01-01

    In this paper, we report the preparation and optical characterization of Pr(3+) doped lithium fluoro borate (LiFB) glasses for six different chemical compositions of Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. The structural and optical properties of these glasses were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), optical absorption and photoluminescence techniques. The optical absorption spectra of Pr(3+) ions in LiFB glasses have been recorded in the UV-VIS-NIR region. The optical absorption data are used to calculate various spectroscopic parameters such as Racah (E(1), E(2), E(3)) and spin-orbit interaction (ξ4f) parameters. Judd-Ofelt (J-O) (Ωλ where λ=2, 4 and 6) intensity parameters were determined by applying J-O theory, which in turn used to calculate the radiative properties such as radiative transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βr) for all emission levels of Pr(3+) ion in different LiFB glass matrices. By using the J-O theory and luminescence parameters, stimulated emission cross sections (σp) of prominent transitions, (3)P0→(3)H4 and (1)D2→(3)H4 of Pr(3+) ion in all LiFB glasses were calculated. (3)P0→(3)H4 possesses higher branching ratios and stimulated emission cross-sections for the Pr(3+):LiFB(Mg-Ca) glass, which can be used as a best laser excitation. The optical gain parameter (σpxτR) was noticed higher in Pr(3+):LiFB(Mg-Ca) and Pr(3+):LiFB(Cd-Pb) glasses for the transition (3)P0→(3)H4 transition, and these glasses have potential for optical amplification at 488 nm wavelength.

  18. Dynamics recording of holographic gratings in a photochromic crystal of calcium fluoride

    NASA Astrophysics Data System (ADS)

    Borisov, Vladimir N.; Barausova, Ekaterina V.; Veniaminov, Andrey V.; Andervaks, Alexandr E.; Shcheulin, Alexandr S.; Ryskin, Alexandr I.

    2016-08-01

    Dynamics of diffraction efficiency was monitored during recording a holographic grating in additively coloured CaF2 photochromic crystal at 180-200°C. Reciprocity failure revealed in the study was attributed to diffusion playing the crucial role in grating formation: recording at larger laser power goes faster but requires more energy. The efficiency of a recorded hologram is found to depend on the temperature; maximum diffraction is measured at the temperature far below that of recording, supposedly because of dramatic distortions suffered by the crystal along with exposure.

  19. 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.

  20. Determination of the irradiation field at the research reactor TRIGA Mainz for BNCT.

    PubMed

    Nagels, S; Hampel, G; Kratz, J V; Aguilar, A L; Minouchehr, S; Otto, G; Schmidberger, H; Schütz, C; Vogtländer, L; Wortmann, B

    2009-07-01

    For the application of the BNCT for the excorporal treatment of organs at the TRIGA Mainz, the basic characteristics of the radiation field in the thermal column as beam geometry, neutron and gamma ray energies, angular distributions, neutron flux, as well as absorbed gamma and neutron doses must be determined in a reproducible way. To determine the mixed irradiation field thermoluminescence detectors (TLD) made of CaF(2):Tm with a newly developed energy-compensation filter system and LiF:Mg,Ti materials with different (6)Li concentrations and different thicknesses as well as thin gold foils were used.

  1. Generation of Kerr combs centered at 4.5 μm 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 μm, 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).

  2. Generation of Kerr combs centered at 45 μm in crystalline microresonators pumped with quantum-cascade lasers

    NASA Astrophysics Data System (ADS)

    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 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$^8$.

  3. 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.

  4. 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.

  5. Characterization of Vc-Vb Particles Reinforced Fe-Based Composite Coatings Produced by Laser Cladding

    NASA Astrophysics Data System (ADS)

    Qu, K. L.; Wang, X. H.; Wang, Z. K.

    2016-03-01

    In situ synthesized VC-VB particles reinforced Fe-based composite coatings were produced by laser beam melting mixture of ferrovanadium (Fe-V) alloy, boron carbide (B4C), CaF2 and Fe-based self-melting powders. The results showed that VB particles with black regular and irregular blocky shape and VC with black flower-like shape were uniformly distributed in the coatings. The type, amount, and size of the reinforcements were influenced by the content of FeV40 and B4C powders. Compared to the substrate, the hardness and wear resistance of the composite coatings were greatly improved.

  6. Space environmental effects on coated optics

    NASA Technical Reports Server (NTRS)

    Donovan, T. M.; Bennett, J. M.; Gyetvay, S. R.

    1991-01-01

    Several multilayer coated mirror designs developed for potential space applications were tested on the Long Duration Exposure Facility (LDEF) along with single layer witness coatings deposited on fused silica and a coated CaF2 window. Performance requirements included high mirror reflectivity, low absorption, low scatter, environmental durability, and radiation hardness. The designs were selected in screening tests using combined electron, proton, and simulated solar UV radiation. The purpose of the space test was to validate the above test results and determine the effects of atomic oxygen and contamination on mirror performance.

  7. Generation of Kerr combs centered at 4.5 μm 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 μm, 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

  8. Design and fabrication of a multi-purpose soft x-ray array diagnostic system for KSTAR.

    PubMed

    Lee, Seung Hun; Chai, Kil Byoung; Jang, Siwon; Ko, Won-Ha; Kim, Junghee; Seo, Dongcheol; Lee, Jongha; Bogatu, I N; Kim, Jin-Soo; Choe, Wonho

    2012-10-01

    A multi-purpose soft x-ray array diagnostic system was developed for measuring two-dimensional x-ray emissivity profile, electron temperature, Ar impurity transport, and total radiation power. A remotely controlled filter wheel was designed with three different choices of filters. The electron temperature profile can be determined from the ratio of two channels having different thickness of Be layer, and the Ar impurity concentration transport can be determined from a pair of Ar Ross filters (CaF(2) and NaCl thin films). Without any filters, this diagnostic system can also be used as a bolometer.

  9. Low and moderate doses of caffeine late in exercise improve performance in trained cyclists.

    PubMed

    Talanian, Jason L; Spriet, Lawrence L

    2016-08-01

    The aim of the present study was to assess if low and moderate doses of caffeine delivered in a carbohydrate-electrolyte solution (CES) late in exercise improved time-trial (TT) performance. Fifteen (11 male, 4 female) cyclists (age, 22.5 ± 0.9 years; body mass, 69.3 ± 2.6 kg; peak oxygen consumption, 64.6 ± 1.9 mL·min(-1)·kg(-1)) completed 4 double-blinded randomized trials. Subjects completed 120 min of cycling at ∼60% peak oxygen consumption with 5 interspersed 120-s intervals at ∼82% peak oxygen consumption, immediately followed by 40-s intervals at 50 W. Following 80 min of cycling, subjects either ingested a 6% CES (PL), a CES with 100 mg (low dose, 1.5 ± 0.1 mg·kg body mass(-1)) of caffeine (CAF1), or a CES with 200 mg (moderate dose, 2.9 ± 0.1 mg·kg body mass(-1)) of caffeine (CAF2). Following the 120-min cycling challenge, cyclists completed a 6-kJ·kg body mass(-1) TT. There was no difference between respiratory, heart rate, glucose, free fatty acid, body mass, hematocrit, or urine specific gravity measurements between treatments. The CAF2 (26:36 ± 0:22 min:s) TT was completed faster than CAF1 (27:36 ± 0:32 min:s, p < 0.05) and both CAF1 and CAF2 TTs were completed faster than PL (28:41 ± 0:38 min:s, p < 0.05). Blood lactate was similar between trials and rose to a greater extent during the TT (p < 0.05). In summary, both doses of caffeine delivered late in exercise improved TT performance over the PL trial and the moderate dose (CAF2) improved performance to a greater extent than the low dose (CAF1).

  10. Low and moderate doses of caffeine late in exercise improve performance in trained cyclists.

    PubMed

    Talanian, Jason L; Spriet, Lawrence L

    2016-08-01

    The aim of the present study was to assess if low and moderate doses of caffeine delivered in a carbohydrate-electrolyte solution (CES) late in exercise improved time-trial (TT) performance. Fifteen (11 male, 4 female) cyclists (age, 22.5 ± 0.9 years; body mass, 69.3 ± 2.6 kg; peak oxygen consumption, 64.6 ± 1.9 mL·min(-1)·kg(-1)) completed 4 double-blinded randomized trials. Subjects completed 120 min of cycling at ∼60% peak oxygen consumption with 5 interspersed 120-s intervals at ∼82% peak oxygen consumption, immediately followed by 40-s intervals at 50 W. Following 80 min of cycling, subjects either ingested a 6% CES (PL), a CES with 100 mg (low dose, 1.5 ± 0.1 mg·kg body mass(-1)) of caffeine (CAF1), or a CES with 200 mg (moderate dose, 2.9 ± 0.1 mg·kg body mass(-1)) of caffeine (CAF2). Following the 120-min cycling challenge, cyclists completed a 6-kJ·kg body mass(-1) TT. There was no difference between respiratory, heart rate, glucose, free fatty acid, body mass, hematocrit, or urine specific gravity measurements between treatments. The CAF2 (26:36 ± 0:22 min:s) TT was completed faster than CAF1 (27:36 ± 0:32 min:s, p < 0.05) and both CAF1 and CAF2 TTs were completed faster than PL (28:41 ± 0:38 min:s, p < 0.05). Blood lactate was similar between trials and rose to a greater extent during the TT (p < 0.05). In summary, both doses of caffeine delivered late in exercise improved TT performance over the PL trial and the moderate dose (CAF2) improved performance to a greater extent than the low dose (CAF1). PMID:27426699

  11. Scissors Mode in Gd Nuclei

    NASA Astrophysics Data System (ADS)

    Kroll, J.; Baramsai, B.; Becker, J. A.; Bečvář, F.; Bredeweg, T. A.; Couture, A.; Chyzh, A.; Dashdorj, D.; Haight, R. C.; Jandel, M.; Krtička, M.; Mitchell, G. E.; O'Donnell, J. M.; Parker, W.; Rundberg, R. S.; Ullmann, J. L.; Vieira, G. J.; Walker, C. L.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2012-02-01

    Spectra of γ rays following neutron capture at isolated resonances of 6 stable Gd isotopes were measured with highly segmented BaF2 detector DANCE at the Los Alamos LANSCE spallation neutron source. The main emphasis was put on studying the γ-cascade decay of neutron resonances to get unique information on photon strength. An analysis of the accumulated γ-ray spectra within the extreme statistical model leads to an inescapable conclusion that scissors mode resonances are built not only on the ground-state, but also on excited levels in all product nuclei studied. The results on summed B(M1)↑ strength and energy of the scissors mode are compared with systematics of scissors mode parameters for the ground-state transitions deduced from nuclear resonance fluorescence measurements. A specific feature of our experiments is the investigation of scissors mode of odd nuclei, for which the nuclear resonance fluorescence provides only limited information.

  12. Measurement of Neutron Capture Cross Section of 62Ni in the keV-Region

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

    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 4π 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 μm thick Mylar foil.

  13. Energetic photons through water: an undergraduate experiment with correlated γ-rays from 22Na

    NASA Astrophysics Data System (ADS)

    La Rocca, P.; Riggi, F.

    2016-07-01

    Measurements of the speed of light have been carried out in the past by the correlation between gamma rays detected in two scintillation detectors. To demonstrate that the speed of gamma rays in a transparent medium is very close to that observed in the vacuum, a time-of-flight experiment was organized in an educational context with undergraduate students, making use of two BaF2 detectors and a small intensity 22Na source. Measurements of time-of-flight spectra were carried out for several values of the distance between the two detectors, allowing us to extract the speed of photons in air. A measurement was also done with an amount of water along the photon path and the result compared with that obtained in air. Various experimental aspects of the interaction of gammas with the detectors were finally addressed through GEANT simulations of the setup to interpret the results.

  14. Low temperature processing of single domain YBa 2Cu 3O y thick films from Y 2O 3 fabrics on Ag-Pd alloy substrates

    NASA Astrophysics Data System (ADS)

    Reddy, E. S.; Goodilin, E. A.; Tarka, M.; Zeisberger, M.; Schmitz, G. J.

    2002-08-01

    Single domain YBa 2Cu 3O y (Y123) thick films (∼100 μm) were fabricated on untextured Ag12 wt.%Pd alloy substrates from Y 2O 3 cloths by an infiltration and growth process. The process involves the infiltration of Y 2O 3 cloths placed on metallic substrates by barium cuprates and copper oxide liquids at 970 °C. The infiltrated Y 2O 3 cloth is subsequently transformed into single domain Y123 during a slow cooling schedule in the presence of a c-axis oriented Nd123 seed crystal placed at the top center of the fabric. The solidification window for single domain growth is lowered to 970-950 °C using liquid phases containing up 10 wt.% Ag and small amounts of BaF 2.

  15. 63Ni (n ,γ ) 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.; Krtička, 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 π BaF2 array DANCE. The (n ,γ ) 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.

  16. Spin and parity assignments for Mo94,95 neutron resonances

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    The γ rays following the Mo94,95(n,γ) reactions were measured as a function of incident neutron energy by the time-of-flight method with the DANCE (Detector for Advanced Neutron Capture Experiments) array of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center. The targets were enriched samples: 91.59% Mo94 and 96.47% Mo95. The γ-ray multiplicities and energy spectra for different multiplicities were measured in s- and p-wave resonances up to En=10 keV for Mo94 and up to En=2 keV for Mo95. Definite spins and parities were assigned in Mo96 for about 60% of the resonances, and tentative spins and parities were assigned for the remaining resonances. In Mo95 the parities were determined for the observed resonances, confirming previously known assignments.

  17. 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.; Krtička, M.; Bečvář, 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.

  18. Photon strength functions of 156Gd from radiative capture of resonance neutrons

    NASA Astrophysics Data System (ADS)

    Baramsai, B.; Kroll, J.; Mitchell, G. E.; Agvaanluvsan, U.; Bečvář, F.; Bredeweg, T. A.; Chyzh, A.; Couture, A.; Dashdorj, D.; Haight, R. C.; Jandel, M.; Keksis, A. L.; Krtička, M.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Walker, C. L.

    2013-04-01

    The 155Gd(n,γ) reaction was measured with the DANCE γ-ray calorimeter (consisting of 160 BaF2 scintillation detectors) at the Los Alamos Neutron Science Center. The γ-ray energy spectra for different multiplicities were obtained 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 photon strength functions (PSFs) successfully describing the decay of 156Gd are very similar to the PSFs describing the decay of previously published 158Gd results. It was demonstrated that the scissors mode is required not only for the ground-state transitions, but also for transitions between excited states.

  19. Measurement of the 97Mo(n ,γ ) reaction with the DANCE γ calorimeter array

    NASA Astrophysics Data System (ADS)

    Walker, C. L.; Krtička, M.; Baramsai, B.; Bečvář, 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 γ rays following the 97Mo(n ,γ ) 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 γ decay following slow neutron capture in 95Mo. On the other hand, the spectra are inconsistent with PSFs describing some other experimental data in 98Mo.

  20. 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.

  1. Proton Radiography With Timepix Based Time Projection Chambers.

    PubMed

    Biegun, Aleksandra K; Visser, Jan; Klaver, Tom; Ghazanfari, Nafiseh; van Goethem, Marc-Jan; Koffeman, Els; van Beuzekom, Martin; Brandenburg, Sytze

    2016-04-01

    The development of a proton radiography system to improve the imaging of patients in proton beam therapy is described. The system comprises gridpix based time projection chambers, which are based on the Timepix chip designed by the Medipix collaboration, for tracking the protons. This type of detector was chosen to have minimal impact on the actual determination of the proton tracks by the tracking detectors. To determine the residual energy of the protons, a BaF 2 crystal with a photomultiplier tube is used. We present data taken in a feasibility experiment with phantoms that represent tissue equivalent materials found in the human body. The obtained experimental results show a good agreement with the performed simulations. PMID:26701179

  2. Hot Wall Epitaxy And Characterization Of Bismuth And Antimony Thin Films On Barium Fluoride Substrates

    NASA Astrophysics Data System (ADS)

    Collazo, Ramon; Dalmau, Rafael; Martinez, Antonio

    1998-03-01

    We have grown thin films of bismuth and antimony using hot wall epitaxy. The epitaxial films were grown on (111)-BaF2 substrates. The chemical integrity of the films was established using Auger electron spectroscopy and X ray Photoelectron Spectroscopy. The thickness of the films was measured using an atomic force microscope to establish their growth rate. The crystallographic properties of the films were assessed using x-ray diffraction techniques. Both bismuth and antimony thin films were found to be oriented with the [003] direction perpendicular to the plane of the films. Pole figures of both types of films indicate the epitaxial nature of the films. Bi/Sb multilayer structures were grown using the same growth technique. We will report on the results of the characterization of these films as well as on the growth apparatus and process. Work supported in part by EPSCoR-NSF Grant EHR-9108775 and NCRADA-NSWCDD-92-01.

  3. Holmium-doped fluorotellurite microstructured fibers for 2.1 μm lasing.

    PubMed

    Yao, Chuanfei; He, Chunfeng; Jia, Zhixu; Wang, Shunbin; Qin, Guanshi; Ohishi, Yasutake; Qin, Weiping

    2015-10-15

    Holmium (Ho3+)-doped fluorotellurite microstructured fibers based on TeO2-BaF2-Y2O3 glasses are fabricated by using a rod-in-tube method. By using a 1.992 μm fiber laser as the pump source, lasing at 2.077 μm is obtained from a 27 cm long Ho3+-doped fluorotellurite microstructured fiber. The maximum unsaturated power is about 161 mW and the corresponding slope efficiency is up to 67.4%. The influence of fiber length on lasing at 2.1 μm is also investigated. Our results show that Ho3+-doped fluorotellurite microstructured fibers are promising gain media for 2.1 μm laser applications.

  4. Mechanochemical preparation of nanocrystalline BaFCl doped with samarium in the 2+ oxidation state.

    PubMed

    Wang, Xiang-lei; Liu, Zhi-qiang; Stevens-Kalceff, Marion A; Riesen, Hans

    2014-09-01

    We report a facile mechanochemical preparation method for nanocrystalline BaFCl doped with samarium in the 2+ oxidation state by ball milling BaCl2, BaF2, and SmI2 under a nitrogen atmosphere. The resulting phosphors were characterized by powder X-ray diffraction; electron microscopy, X-ray photoelectron spectroscopy; and photoluminescence, photoexcitation, cathodoluminescence, and diffuse reflectance spectroscopy. This is the first report of a direct preparation method of Sm(2+) doped alkaline earth fluorohalides at room temperature and points to a significant potential for the preparation of a wide range of related X-ray storage phosphors containing rare earth ions in divalent and trivalent cationic states by mechanochemical methods.

  5. Tapered fluorotellurite microstructured fibers for broadband supercontinuum generation.

    PubMed

    Wang, Fang; Wang, Kangkang; Yao, Chuanfei; Jia, Zhixu; Wang, Shunbin; Wu, Changfeng; Qin, Guanshi; Ohishi, Yasutake; Qin, Weiping

    2016-02-01

    Fluorotellurite microstructured fibers (MFs) based on TeO2-BaF2-Y2O3 glasses are fabricated by using a rod-in-tube method. Tapered fluorotellurite MFs with varied transition region lengths are prepared by employing an elongation machine. By using a tapered fluorotellurite MF with a transition region length of ∼3.3  cm as the nonlinear medium and a 1560 nm femtosecond fiber laser as the pump source, broadband supercontinuum generation covering from 470 to 2770 nm is obtained. The effects of the transition region length of the tapered fluorotellurite MF on supercontinuum generation are also investigated. Our results show that tapered fluorotellurite MFs are promising nonlinear media for generating broadband supercontinuum light expanding from visible to mid-infrared spectral region. PMID:26907442

  6. Thin films of barium fluoride scintillator deposited by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kirlin, P. S.; Binder, R.; Winn, D. R.; O'Hare, J.; LaPierre, C.; Whitmore, M.

    1990-04-01

    We have used metal-organic chemical vapor deposition (MOCVD) technology to coat optical substrates with thin (˜1-10 μm thick) films of inorganic BaF 2 scintillator. Scanning electron microscope (SEM) photographs indicate that high-quality epitaxial crystalline film growth was achieved, with surface defects typically smaller than optical wavelengths. The scintillation light created by the deposition of ionizing radiation in the scintillating films was measured with a photomultiplier and shown to be similar to bulk melt-grown crystals. The results demonstrate the potential of these composite optical materials for planar and fiber scintillation radiation detectors in high energy and nuclear physics, synchrotron radiation research, and in radiation and X-ray imaging and monitoring.

  7. 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.

  8. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    DOE PAGES

    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

  9. 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.

  10. Lead-gallium glasses and glass-ceramics doped with SiO2 for near infrared transmittance

    NASA Astrophysics Data System (ADS)

    Marczewska, Agnieszka; Środa, Marcin; Nocuń, 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 μm. 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 μm due to the presence of hydroxyl groups and simultaneously reduces transmittance in the range of 5-6.5 μm 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.

  11. The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

    NASA Technical Reports Server (NTRS)

    Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

    1990-01-01

    The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding.

  12. Interfacial tension of aluminum in cryolite melts

    NASA Astrophysics Data System (ADS)

    Utigard, T.; Toguri, J. M.

    1985-06-01

    The interfacial tension between aluminum and cryolite melts containing different salt additions has been measured based on a combination of the sessile drop and X-ray radiographie technique. A computer program was used to calculate the interfacial tension from approximately twenty randomly measured coordinate points of the drop profile. Aluminum and salt mixtures containing different amounts of Na3AlF6, A1F3, NaF, A12O3, CaF2, KF, LiF, and NaCl were melted in a graphite or alumina crucible in a graphite resistor furnace under an argon atmosphere. The interfacial tension was found to be strongly dependent on the NaF/AlF3 ratio. At the cryolite composition the interfacial tension was 481 mN/m at 1304 K, while it was 650 mN/m when the NaF/AlF3 ratio was equal to 1.5. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. Additions of A12O3 increased the interfacial tension for a given NaF/AlF3 ratio. KF was found to be surface active, while CaF2, LiF, and NaCl slightly increased the interfacial tension by decreasing the sodium activity.

  13. Optimized readout system for cooled optically stimulated luminescence

    NASA Astrophysics Data System (ADS)

    Miller, S. D.; Eschbach, P. A.

    1990-09-01

    Cooled Optically Stimulated Luminescence (COSL) in CaF2:Mn is an ionizing radiation dosimetry method recently developed at the Pacific Northwest Laboratory (PNL). In this method CaF2:Mn crystals irradiated by gamma radiation at room temperature are cooled to liquid nitrogen temperature (77 K), stimulated by ultraviolet laser light at 326 nm, and allowed to warm to room temperature. Light emission proportional to the gamma exposure occurs as the TLD warms from liquid nitrogen temperature to room temperature. The new method is an example of a highly sensitive phototransfer technique which could form the basis for future radiation dosimetry applications. Measurements to date have shown high potential for measuring gamma exposures in the range of 10 microR. The high sensitivity of the COSL technique is due in part to the larger quantum efficiency of radiative recombination at low temperatures and to the complete absence of the incandescent background associated with conventional thermoluminescent readout methods. Along with the potential for a system which is more sensitive than thermoluminescent readers, multiple COSL readouts can be performed with minimal reduction in the COSL intensity. The multiple readout capability can serve as a possible permanent dosimetry record, thus allowing the reanalysis of a questionable reading. In an attempt to optimize the sensitivity of the COSL method, a new readout system is being developed.

  14. Tribological properties of alumina-boria-silicate fabric from 25 C to 850 C

    SciTech Connect

    Dellacorte, C. )

    1989-07-01

    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. 8 refs.

  15. Effects of additives on the phase transformation, occurrence state, and the interface of the Ti component in Ti-bearing blast furnace slag

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Zhang, Wu; Zhang, Ju-hua; Li, Guang-qiang

    2016-09-01

    The influences of additives on the phase transformation, occurrence state, and the interface of the Ti component in Ti-bearing blast furnace slag were investigated. After oxidation, most of the Ti component in the slag was enriched into the perovskite phase, which served as the Ti-rich phase during the crystallization process. The phase transformation, occurrence state, and the interface of the Ti component were observed to be affected by the addition of different types of agents. During the oxidation process, titanaugite and Ti-rich diopside phases gradually transformed into non-Ti phases (anorthite: CaMgSi2O6 and CaAl2Si2O8) in the form of dendrites or columns, which were observed to be distributed at the surface of the perovskite phase. Several more cracks appeared along the grain boundaries of the perovskite phase after the addition of P2O5, facilitating the liberation of the perovskite phase. Composite additives combining both an acid and a base, such as CaO + CaF2 or P2O5 + CaF2, were used. We observed that the disadvantages of using single additives were successfully overcome.

  16. 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-}.

  17. Development of Low-Fluoride Slag for Electroslag Remelting: Role of Li2O on the Viscosity and Structure of the Slag

    NASA Astrophysics Data System (ADS)

    Shi, Cheng-Bin; Shin, Seung-Ho; Zheng, Ding-Li; Cho, Jung-Wook; Li, Jing

    2016-10-01

    The effect of the substitution of CaF2 with Li2O on the viscosity and structure of low-fluoride CaF2-CaO-Al2O3-MgO slag was studied with an aim to develop low-fluoride slag for electroslag remelting. Increasing Li2O addition up to 4.5 mass pct was observed to significantly reduce the slag viscosity monotonically. Increasing temperature significantly lowered the viscosity of slag, whereas this influence is less effective with increasing Li2O content especially above 3.5 mass pct. The activation energy for viscous flow decreases with increasing Li2O content. The polymerization degree of aluminate networks decreased with increasing Li2O content, as demonstrated by Raman analysis. The dominant structural unit in [AlO4]5--tetrahedral network is Q_{Al}4 . The amount of symmetric Al-O0 stretching vibrations significantly decreased with increasing Li2O content. The relative fraction of Q_{Al}4 in the [AlO4]5--tetrahedral units shows a decreasing trend, whereas Q_{Al}2 increases with the increase in Li2O content accordingly. The change in slag viscosity with chemistry variation agrees well with the changes in slag structural units.

  18. 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 α = γ = 90°, whereas β = 111.4244(18)° for [(caf)(1-naa)] and β = 109.281(6)° for [(caf)(2-naa)]. The crystal packing is predominantly stabilized by hydrogen bonding and π-π 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.

  19. The Solubility of Aluminum in Cryolite-Based Electrolyte-Containing KF

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Yu, Jiangyu; Gao, Bingliang; Liu, Yibai; Hu, Xianwei; Shi, Zhongning; Wang, Zhaowen

    2016-04-01

    The solubility of aluminum in NaF-AlF3-CaF2-KF-A12O3 electrolyte system at 1253 K (980 °C) has been measured by the analysis of quenched samples saturated with aluminum. The content of the dissolved metal in the quenched melt was determined by collecting the volume of hydrogen gas when a finely crushed sample is treated with HCl. Addition of 0 to 5 pct KF has no obvious effect on the solubility of aluminum in cryolite-based melts with molar ratio of NaF/AlF3 (cryolite ratio) ranging from 2.2 to 3.0. The solubility of aluminum increases from 0.015 to 0.026 wt pct with cryolite ratio increases from 2.2 to 4.0 in the NaF-AlF3-5 wt pct CaF2-3 wt pct A12O3 electrolyte at 1253 K (980 °C). Aluminum solubility was affected by both chemical replacement reaction of Al + 3NaF = AlF3 + 3Na and physical dissolution.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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 (τ) and higher quantum efficiency (η) 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.

  5. Water orientation and hydrogen-bond structure at the fluorite/water interface.

    PubMed

    Khatib, Rémi; Backus, Ellen H G; Bonn, Mischa; Perez-Haro, María-José; Gaigeot, Marie-Pierre; Sulpizi, Marialore

    2016-01-01

    Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF2/water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the "free OH" signature in the VSFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of CaF2/water interfaces and state-of-the-art ab initio molecular dynamics simulations which include electronic structure effects. PMID:27068326

  6. Mode-locking operation of quasi-continuous diode pumped TGT-grown Nd,Y-codoped:SrF2 crystal

    NASA Astrophysics Data System (ADS)

    Jelínek, Michal; Kubeček, 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. TL detectors for gamma ray dose measurements in criticality accidents.

    PubMed

    Miljanić, Saveta; Zorko, Benjamin; Gregori, Beatriz; Knezević, Zeljka

    2007-01-01

    Determination of gamma ray dose in mixed neutron+gamma ray fields is still a demanding task. Dosemeters used for gamma ray dosimetry are usually in some extent sensitive to neutrons and their response variations depend on neutron energy i.e., on neutron spectra. Besides, it is necessary to take into account the energy dependence of dosemeter responses to gamma rays. In this work, several types of thermoluminescent detectors (TLD) placed in different holders used for gamma ray dose determination in the mixed fields were examined. Dosemeters were from three different institutions: Ruder Bosković Institute (RBI), Croatia, JoZef Stefan Institute (JSI), Slovenia and Autoridad Regulatoria Nuclear (ARN), Argentina. All dosemeters were irradiated during the International Intercomparison of Criticality Accident Dosimetry Systems at the SILENE Reactor, Valduc, June 2002. Three accidental scenarios were reproduced and in each irradiation the dosemeters were exposed placed on the front of phantom and 'free in air'. Following types of TLDs were used: 7LiF (TLD-700), CaF2:Mn and Al2O3:Mg,Y-all from RBI; CaF2:Mn from JSI and 7LiF (TLD-700) from ARN. Reported doses were compared with the reference values as well as with the values obtained from the results of all participants. The results show satisfactory agreement with other dosimetry systems used in the Intercomparison. The influence of different types of holders and applied corrections of dosemeters' readings are discussed. PMID:17369267

  8. Near-infrared diode-pumped white-light emission from erbium-doped calcium fluoride crystal

    NASA Astrophysics Data System (ADS)

    Culp, Mical; Edwards, Vernessa M.; Reddi, B. Rami

    2016-02-01

    CaF2 is a cubic material and Erbium enters the lattice in triply ionized state. Erbium occupies Ca sites in the material. Defects occur in the material because a trivalent dopant ion replaces a divalent host ion. Er3+ occupies several different sites. Absorption spectrum of Er3+-doped CaF2 revealed absorption peaks at 255, 365, 379, 407, 441, 449, 487, 522, 539, 652 and 798 nm. When the sample was excited with an 800 nm near-infrared laser it revealed emissions at 390, 415, 462, 555, 665 and 790 nm. The absorption and emission peaks are identified with Er3+ spectral transitions. The sample color appears to be either white or green under near-infrared laser excitation. Emission color was found to be dependent on the pump laser wavelength used and laser power. Excitation spectral recordings were made by tuning the pump laser wavelength. The sample emission appears to be white under near-infrared excitation as well as violet laser excitation. Excited state lifetimes are measured to analyze the data. Our studies indicate that this sample is useful in solid state lighting applications.

  9. 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

    2016-02-01

    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.

  10. New insights into structural alteration of enamel apatite induced by citric acid and sodium fluoride solutions.

    PubMed

    Wang, Xiaojie; Klocke, Arndt; Mihailova, Boriana; Tosheva, Lubomira; Bismayer, Ulrich

    2008-07-24

    Attenuated total reflectance infrared spectroscopy and complementary scanning electron microscopy were applied to analyze the surface structure of enamel apatite exposed to citric acid and to investigate the protective potential of fluorine-containing reagents against citric acid-induced erosion. Enamel and, for comparison, geological hydroxylapatite samples were treated with aqueous solutions of citric acid and sodium fluoride of different concentrations, ranging from 0.01 to 0.5 mol/L for citric acid solutions and from 0.5 to 2.0% for fluoride solutions. The two solutions were applied either simultaneously or consecutively. The citric acid-induced structural modification of apatite increases with the increase in the citric acid concentration and the number of treatments. The application of sodium fluoride alone does not suppress the atomic level changes in apatite exposed to acidic agents. The addition of sodium fluoride to citric acid solutions leads to formation of surface CaF2 and considerably reduces the changes in the apatite P-O-Ca framework. However, the CaF2 globules deposited on the enamel surface seem to be insufficient to prevent the alteration of the apatite structure upon further exposure to acidic agents. No evidence for fluorine-induced recovery of the apatite structure was found.

  11. 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.

  12. 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.

  13. Water orientation and hydrogen-bond structure at the fluorite/water interface

    PubMed Central

    Khatib, Rémi; Backus, Ellen H. G.; Bonn, Mischa; Perez-Haro, María-José; Gaigeot, Marie-Pierre; Sulpizi, Marialore

    2016-01-01

    Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF2/water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the “free OH” signature in the VSFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of CaF2/water interfaces and state-of-the-art ab initio molecular dynamics simulations which include electronic structure effects. PMID:27068326

  14. 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.

  15. Spectroscopy and lasing of cryogenically cooled Yb, Na:CaF2

    NASA Astrophysics Data System (ADS)

    Pugžlys, A.; Andriukaitis, G.; Sidorov, D.; Irshad, A.; Baltuška, A.; Lai, W. J.; Phua, P. B.; Su, L.; Xu, J.; Li, H.; Li, R.; Ališauskas, S.; Marcinkevičius, A.; Fermann, M. E.; Giniūnas, L.; Danielius, R.

    2009-10-01

    Absorption, photoluminescence and cw-lasing properties of a novel Na+-codoped Yb3+:CaF2 laser crystal are investigated in the temperature range from 10 K to 290 K. Cryogenic cooling leads to the disappearance of the ground-state absorption in the spectral region above 1000 nm and a substantial increase of emission and absorption cross-sections. A particular advantage of the Yb3+, Na+-codoped CaF2 crystal lies in the possibility of a direct pumping in the vicinity of the zero phonon line while nearly perfectly avoiding an overlap with the stimulated emission. Further advantages of the low-temperature operation are demonstrated by achieving a close to the theoretical limit slope efficiency of 92% in a cw-laser operation with an output coupler of 28%. By seeding stretched pulses from a femtosecond Yb fiber oscillator into a cryogenically cooled DPSS Yb3+, Na+:CaF2 regenerative amplifier, we obtain >3-mJ pulses at a 1-kHz repetition rate with a spectral bandwidth exceeding 12 nm. The pulses are compressed with a single grating compressor to 173 fs as verified by SHG FROG. Shaping of the spectral amplitude of the seed and active control of the higher-order phase is shown to be crucial for obtaining sub-200-fs pulses at multi-mJ energies.

  16. Mechanism of Calcium Fluoride Acceleration for Vacuum Carbothermic Reduction of Magnesia

    NASA Astrophysics Data System (ADS)

    Jiang, Yun; Liu, Yu-qin; Ma, Hong-wen; Zhou, Wei-gong

    2016-04-01

    The use of a small amount of calcium fluoride as an additive greatly accelerated the reduction of magnesia during the preparation of magnesium from magnesia using the vacuum carbothermic reduction method. At 1573 K (1300 °C), the magnesia reaction rates of the samples with 1, 3, and 5 pct CaF2 were all approximately 26 pct, three times that of free CaF2, and they were arranged in order of the calcium fluoride weight percentages at 1673 K (1400 °C). The residues were analyzed using chemical analysis, XRD, SEM, EDS, and XRF. The possible acceleration mechanism was discussed. Calcium fluoride combined with magnesia and silicon dioxide to form a eutectic that melted as a channel to aid the solid-solid reaction between carbon and magnesia at approximately 1573 K (1300 °C). Calcium fluoride in the molten state offered free calcium ions and fluorine ions. Fluorine ions entered and distorted the magnesia crystal lattice. The structural strength and chemical stability of the magnesia crystal lattice decreased, which facilitated the magnesia reduction by carbon. Calcium ions were employed to generate the calcium and magnesium silicate. The easyly evaporating fluorides, including magnesium fluoride and silicon tetrafluoride, were regarded as the main reason for the loss of fluorine.

  17. Water orientation and hydrogen-bond structure at the fluorite/water interface

    NASA Astrophysics Data System (ADS)

    Khatib, Rémi; Backus, Ellen H. G.; Bonn, Mischa; Perez-Haro, María-José; Gaigeot, Marie-Pierre; Sulpizi, Marialore

    2016-04-01

    Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF2/water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the “free OH” signature in the VSFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of CaF2/water interfaces and state-of-the-art ab initio molecular dynamics simulations which include electronic structure effects.

  18. Effect of substrate choice and tissue type on tissue preparation for spectral histopathology by Raman microspectroscopy.

    PubMed

    Fullwood, Leanne M; Griffiths, Dave; Ashton, Katherine; Dawson, Timothy; Lea, Robert W; Davis, Charles; Bonnier, Franck; Byrne, Hugh J; Baker, Matthew J

    2014-01-21

    Raman spectroscopy is a non-destructive, non-invasive, rapid and economical technique which has the potential to be an excellent method for the diagnosis of cancer and understanding disease progression through retrospective studies of archived tissue samples. Historically, biobanks are generally comprised of formalin fixed paraffin preserved tissue and as a result these specimens are often used in spectroscopic research. Tissue in this state has to be dewaxed prior to Raman analysis to reduce paraffin contributions in the spectra. However, although the procedures are derived from histopathological clinical practice, the efficacy of the dewaxing procedures that are currently employed is questionable. Ineffective removal of paraffin results in corruption of the spectra and previous experiments have shown that the efficacy can depend on the dewaxing medium and processing time. The aim of this study was to investigate the influence of commonly used spectroscopic substrates (CaF2, Spectrosil quartz and low-E slides) and the influence of different histological tissue types (normal, cancerous and metastatic) on tissue preparation and to assess their use for spectral histopathology. Results show that CaF2 followed by Spectrosil contribute the least to the spectral background. However, both substrates retain paraffin after dewaxing. Low-E substrates, which exhibit the most intense spectral background, do not retain wax and resulting spectra are not affected by paraffin peaks. We also show a disparity in paraffin retention depending upon the histological identity of the tissue with abnormal tissue retaining more paraffin than normal.

  19. Rational design and optimization of plasmonic nanoarrays for surface enhanced infrared spectroscopy

    PubMed Central

    Liberman, Vladimir; Adato, Ronen; Jeys, Thomas H.; Saar, Brian G.; Erramilli, Shyamsunder; Altug, Hatice

    2012-01-01

    We present an approach for rational design and optimization of plasmonic arrays for ultrasensitive surface enhanced infrared absorption (SEIRA) spectroscopy of specific protein analytes. Motivated by our previous work that demonstrated sub-attomole detection of surface-bound silk fibroin [Proc. Natl. Acad. Sci. U.S.A. 106, 19227 (2009)], we introduce here a general framework that allows for the numerical optimization of metamaterial sensor designs in order to maximize the absorbance signal. A critical feature of our method is the explicit compensation for the perturbative effects of the analyte's refractive index which alters the resonance frequency and line-shape of the metamaterial response, thereby leading to spectral distortion in SEIRA signatures. As an example, we leverage our method to optimize the geometry of periodic arrays of plasmonic nanoparticles on both Si and CaF2 substrates. The optimal geometries result in a three-order of magnitude absorbance enhancement compared to an unstructured Au layer, with the CaF2 substrate offering an additional factor of three enhancement in absorbance over a traditional Si substrate. The latter improvement arises from increase of near-field intensity over the Au nanobar surface for the lower index substrate. Finally, we perform sensitivity analysis for our optimized arrays to predict the effects of fabrication imperfections. We find that <20% deviation from the optimized absorbance response is readily achievable over large areas with modern nanofabrication techniques. PMID:22714181

  20. 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.

  1. 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

  2. Creation of trapped electrons and holes in alkaline-earth fluoride crystals doped by rare-earth ions

    NASA Astrophysics Data System (ADS)

    Radzhabov, E.

    2002-06-01

    Defects in Ce 3+- and Eu 2+-doped alkaline-earth fluorides, created by vacuum ultraviolet (VUV) photons with energy lower than that of the band gap, were investigated by various methods: thermostimulated luminescence, photostimulated luminescence and optical absorption. The CaF 2:Eu 2+ thermoluminescence curves in the range of 60-330 K due to various types of trapped holes were the same after VUV illumination as after X-ray irradiation. Thermoluminescence curves of Ce 3+-doped alkaline-earth fluorides created by VUV illumination or X-ray irradiation were generally similar. However, Vk thermoluminescence peaks were absent in VUV-illuminated CaF 2:Ce 3+ and SrF 2:Ce 3+ crystals. Creation of Ce 2+ characteristic bands was observed in photostimulated luminescence spectra as well as in optical absorption spectra of vacuum ultraviolet-illuminated or X-ray-irradiated Ce 3+-doped crystals. The proposed mechanism of creation of trapped hole and trapped electron defects by vacuum ultraviolet illumination involves charge transfer-type transitions, in which the electron transfers from valence band to an impurity level, lying in the band gap. Comparison of all involved energies of transitions in the crystals investigated shows that the sum of all transition energies is less than that of the band gap by 1-3 eV. This energy difference can be considered as the energy of lattice relaxation around created Ce 2+ or Eu + ions.

  3. VUV spectroscopy of nominally pure and rare-earth ions doped LiCaAIF6 single crystals as promising materials for 157 nm photolithography

    NASA Astrophysics Data System (ADS)

    Cefalas, Alkiviadis C.; Sarantopoulou, Evangelia; Kollia, Z.; Abdulsabirov, R. Y.; Korableva, S. L.; Naumov, A. K.; Semashko, V. V.; Kobe, S.; McGuiness, P. J.

    2002-07-01

    Recently it was found that birefringence is induced in CaF2 crystals when they are illuminated with laser light at 157 nm. Taking into consideration that CaF2 is the only optical material used in 157 nm photolithography today, the possibility to use new wide band gap fluoride crystals as optical elements for 157 nm photolithography, even those of non-cubic symmetry, should be considered. Additionally fluoride dielectric crystals with wide band gaps doped with trivalent rare-earth (RE) ions can be used as passive or active optical elements int eh VUV. For doped crystals, applications depend on the structure of the energy level pattern of the 4fn-15d electronic configuration and RE ion concentration. In this work we are exploiting the use of wide band gap fluoride dielectric crystals doped with RE ions. The laser induced fluorescence spectrum at 157 nm, and the absorption spectra of the LiCaAlF6 crystals, pure and doped with RE ions, were investigated in the VUV region of the spectrum. A new m4tehod for monitoring RE concentration in wide band gap fluoride crystals, that is based on vibrating sample magnetometer measurement is presented as well.

  4. Atomistic interpretation of solid solution hardening from spectral analysis.

    PubMed

    Plendl, J N

    1971-05-01

    From analysis of a series of vibrational spectra of ir energy absorption and laser Raman, an attempt is made to interpret solid solution hardening from an atomistic point of view for the system CaF(2)/SrF(2). It is shown to be caused by the combined action of three atomic characteristics, i.e., their changes as a function of composition. They are deformation of the atomic coordination polyhedrons, overlap of the outer electron shells of the atom pairs, and the ratio of the ionic to covalent share of binding. A striking nonlinear behavior of the three characteristics, as a function of composition, gives maximum atomic bond strength to the 55/45 position of the system CaF(2)/SrF(2), in agreement with the measured data of the solid solution hardening. The curve for atomic bond strength, derived from the three characteristics, is almost identical to the curve for measured microhardness data. This result suggests that the atomistic interpretation, put forward in this paper, is correct.

  5. Efficient burst mode amplifier for ultra-short pulses based on cryogenically cooled Yb³⁺:CaF₂.

    PubMed

    Körner, Jörg; Hein, Joachim; Liebetrau, Hartmut; Seifert, Reinhard; Klöpfel, Diethard; Kahle, Martin; Loeser, Markus; Siebold, Mathias; Schramm, Ulrich; Kaluza, Malte C

    2013-11-18

    We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms are be generated and amplified. They contain 50 to 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps prior to amplification. The amplifier stage is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled up to 915 mJ using a longer pump duration. This corresponds to an efficiency as high as 25% of extracted energy from absorbed pump energy. This is the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier.

  6. Fluoride-selective optical sensor based on aluminum(III)-octaethylporphyrin in thin polymeric film: further characterization and practical application.

    PubMed

    Badr, Ibrahim H A; Meyerhoff, Mark E

    2005-10-15

    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-visible 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 lambda(max) of the porphyrin and 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 microM-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

  7. Phase- and size-controllable synthesis of hexagonal upconversion rare-earth fluoride nanocrystals through an oleic acid/ionic liquid two-phase system.

    PubMed

    He, Meng; Huang, Peng; Zhang, Chunlei; Ma, Jiebing; He, Rong; Cui, Daxiang

    2012-05-01

    Herein, we introduce a facile, user- and environmentally friendly (n-octanol-induced) oleic acid (OA)/ionic liquid (IL) two-phase system for the phase- and size-controllable synthesis of water-soluble hexagonal rare earth (RE = La, Gd, and Y) fluoride nanocrystals with uniform morphologies (mainly spheres and elongated particles) and small sizes (<50 nm). The unique role of the IL 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) and n-octanol in modulating the phase structure and particle size are discussed in detail. More importantly, the mechanism of the (n-octanol-induced) OA/IL two-phase system, the formation of the RE fluoride nanocrystals, and the distinctive size- and morphology-controlling capacity of the system are presented. BmimPF(6) is versatile in term of crystal-phase manipulation, size and shape maintenance, and providing water solubility in a one-step reaction. The luminescent properties of Er(3+)-, Ho(3+)-, and Tm(3+)-doped LaF(3), NaGdF(4), and NaYF(4) nanocrystals were also studied. It is worth noting that the as-prepared products can be directly dispersed in water due to the hydrophilic property of Bmim(+) (cationic part of the IL) as a capping agent. This advantageous feature has made the IL-capped products favorable in facile surface modifications, such as the classic Stober method. Finally, the cytotoxicity evaluation of NaYF(4):Yb,Er nanocrystals before and after silica coating was conducted for further biological applications.

  8. Lasing properties of new Nd 3+-doped tungstate, molybdate, and fluoride materials under selective optical pumping

    NASA Astrophysics Data System (ADS)

    Šulc, Jan; Jelínkova, Helena; Basiev, Tolstoban T.; Doroschenko, Maxim E.; Ivleva, Ludmila I.; Osiko, Vyacheslav V.; Zverev, Peter G.

    2006-02-01

    The purpose of this work was to determine the relative efficiencies of new Nd 3+-doped laser active/Raman - tungstate, molybdate, and fluoride - materials (SrWO 4, PbWO 4, BaWO 4, SrMoO 4, PbMoO 4, SrF II, and LaF 3) under selective longitudinal optical pumping by the alexandrite (~750nm), or diode (~800nm) laser. Crystals with various length, orientations and active ions concentrations were tested. To optimize the output of the tested lasers a set of input dichroic and output dielectric mirrors with different reflectivities were used. For realized lasers operating at pulsed free-running regime, threshold energy, slope efficiency, emission wavelength, and radiation polarization were determined. For each crystal, fluorescence lifetime and absorption coefficient under given pumping were established. The slope efficiency in case of Nd 3+:PbMoO 4 laser at wavelength 1054nm was measured to be 54.3% with total efficiency of 46% which is the best result obtained for all new tested crystals. For Nd 3+ doped SrWO 4, PbWO 4, and BaWO 4 crystals simultaneous laser and self-Raman emission were demonstrated in Q-switched regime. Thus newly proposed laser Raman crystals demonstrate high efficiency for Nd 3+ laser oscillations comparable with well known and widely used Nd:KGW crystal. Further improvement in the quality of tungstate and molybdate type crystals should result in further increase in lasing efficiency at 1.06μm wavelength. Self Raman frequency conversion of Nd 3+-laser oscillations in these crystals should result in high efficient pulse shortening, high peak power and new wavelengths in 1.2-1.5μm wavelength region.

  9. In vitro remineralizing effect of fluoride varnishes containing sodium trimetaphosphate.

    PubMed

    Manarelli, M M; Delbem, A C B; Lima, T M T; Castilho, F C N; Pessan, J P

    2014-01-01

    This study analyzed the effects of fluoride varnishes supplemented with sodium trimetaphosphate (TMP) on the remineralization of caries-like lesions in vitro. Bovine enamel discs were selected through surface hardness (SH) and caries-like lesions were induced. SH was again determined and the blocks were divided into 7 experimental groups (n = 24/group): placebo (no fluoride or TMP), 5% TMP, 2.5% NaF, 2.5% NaF/5% TMP, 5% NaF, 5% NaF/5% TMP and commercial formulation (Duraphat™, 5% NaF), following a blind protocol. Discs were treated with the varnishes and kept in a remineralizing solution for 4 h and a demineralizing solution for 2 h. Varnishes were then removed and half of the discs were used for analysis of loosely (CaF2) and firmly bound fluoride. The remaining discs were submitted to a pH-cycling regimen for 6 days. The percentage of surface hardness recovery (%SHR), cross-sectional hardness (ΔKHN) and enamel CaF2 and fluoride were determined. Data were analyzed by ANOVA and by Student-Newman-Keuls' test (p < 0.05). A dose-response relationship was observed between fluoride concentrations in the varnishes and %SHR. The 5% TMP varnish led to %SHR similar to that obtained for the placebo. When TMP was used in association with fluoride, however, significantly higher %SHR were observed in comparison with their counterparts without TMP. Moreover, ΔKHN obtained for the 5% NaF/5% TMP was significantly lower among all groups tested. Higher concentrations of CaF2 and fluoride were observed for Duraphat and 5% NaF, followed by 5% NaF/5% TMP, 2.5% NaF and 2.5% NaF/5% TMP (p < 0.05). It was concluded that the supplementation of fluoride varnishes with TMP leads to enhanced remineralizing effect of artificial caries lesions in vitro.

  10. 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 1.2μm. 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.

  11. 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 μm 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 μm. 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

  12. In vitro remineralizing effect of fluoride varnishes containing sodium trimetaphosphate.

    PubMed

    Manarelli, M M; Delbem, A C B; Lima, T M T; Castilho, F C N; Pessan, J P

    2014-01-01

    This study analyzed the effects of fluoride varnishes supplemented with sodium trimetaphosphate (TMP) on the remineralization of caries-like lesions in vitro. Bovine enamel discs were selected through surface hardness (SH) and caries-like lesions were induced. SH was again determined and the blocks were divided into 7 experimental groups (n = 24/group): placebo (no fluoride or TMP), 5% TMP, 2.5% NaF, 2.5% NaF/5% TMP, 5% NaF, 5% NaF/5% TMP and commercial formulation (Duraphat™, 5% NaF), following a blind protocol. Discs were treated with the varnishes and kept in a remineralizing solution for 4 h and a demineralizing solution for 2 h. Varnishes were then removed and half of the discs were used for analysis of loosely (CaF2) and firmly bound fluoride. The remaining discs were submitted to a pH-cycling regimen for 6 days. The percentage of surface hardness recovery (%SHR), cross-sectional hardness (ΔKHN) and enamel CaF2 and fluoride were determined. Data were analyzed by ANOVA and by Student-Newman-Keuls' test (p < 0.05). A dose-response relationship was observed between fluoride concentrations in the varnishes and %SHR. The 5% TMP varnish led to %SHR similar to that obtained for the placebo. When TMP was used in association with fluoride, however, significantly higher %SHR were observed in comparison with their counterparts without TMP. Moreover, ΔKHN obtained for the 5% NaF/5% TMP was significantly lower among all groups tested. Higher concentrations of CaF2 and fluoride were observed for Duraphat and 5% NaF, followed by 5% NaF/5% TMP, 2.5% NaF and 2.5% NaF/5% TMP (p < 0.05). It was concluded that the supplementation of fluoride varnishes with TMP leads to enhanced remineralizing effect of artificial caries lesions in vitro. PMID:24526110

  13. [Study on Spectral Characteristics of Two Kinds of Home-Made Novel Yb-Doped Fluoride Laser Crystals].

    PubMed

    Xu, Wen-bin; Chai, Lu; Shi, Jun-kai; Song, You-jian; Hu, Ming-lie; Wang, Qing-yue; Su, Liang-bi; Jiang, Da-peng; Xu, Jun

    2015-09-01

    Yb-doped fluoride crystals are of important another Yb-doped laser materials besides Yb-doped oxide, which are becoming one of interests for developing tunable lasers and ultrafast lasers. In this paper, the systematic and contrastive experiments of the optical spectral characteristics are presented for two types of home-made novel Yb-doped fluoride laser crystals, namely, Yb-doped CaF2-SrF2 mixed crystal and co-doped Yb, Y:CaF2 single crystal. The fluorescent features of Yb-doped CaF2-SrF2 mixed crystal and co-doped Yb, Y:CaF2 single crystal are apparently different by the fluorescence experiment. The physical mechanism of these fluorescence spectra were analyzed and proposed. The influence of doping concentrations of active Yb(3+) ions or co-doping Y ions on the absorption of Yb-doped CaF2-SrF2 mixed crystal and co-doped Yb, Y:CaF2 single crystal was experimentally investigated, and the optimal values of doping concentrations of active Yb(3+) ions or co-doping Y ions in the two types of fluoride laser crystals were obtained. Continuous-wave laser operation for the two novel fluoride laser crystals has been achieved in three-mirror-folded resonator using a laser diode as the pump source. Therein, the laser operation for the co-doped Yb, Y:CaF2 crystal is demonstrated for the first time. For the two types of fluoride laser crystals (four samples), the input-output power relational curves, the optical slope efficiencies and the laser spectra were demonstrated by the laser experiments. By comparisons between the two types of fluoride laser crystals in the absorbability, fluorescence and laser spectra, laser threshold and slope efficiency of the continuous-wave laser operation, the results show that the best one of the four samples in spectral and laser characteristics is co-doped 3at%Yb, 6at% Y:CaF2 single crystal, which has an expected potential in the application. The research results provide available references for improving further laser performance of Yb-doped fluoride crystals.

  14. Application of 252Cf plasma desorption mass spectrometry in dental research

    NASA Astrophysics Data System (ADS)

    Fritsch, Hans-Walter; Schmidt, Lothar; Köhl, Peter; Jungclas, Hartmut; Duschner, Heins

    1993-07-01

    Topically applied fluorides introduced in dental hygiene products elevate the concentration levels of fluoride in oral fluids and thus also affect chemical reactions of enamel de- and remineralisation. The chemical reactions on the surface of tooth enamel still are a subject of controversy. Here 252Cf-plasma desorption mass spectrometry and argon ion etching are used to analyse the molecular structure of the upper layes of enamel. The mass spectrum of untreated enamel is characterised by a series of cluster ions containing phosphate. It is evident that under certain conditions the molecular structure of the surface enamel is completely transformed by treatment with fluorides. The result of the degradation and precipitation processes is reflected by a total replacement of the phosphate by fluoride in the measured cluster ion distribution. Stepwise etching of the upper layers by Ar+ ions reveals the transition from a nearly pure CaF2 structure to the unchanged composition of the enamel mineral.

  15. 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.

  16. Monolayer-to-bilayer transformation of silicenes and their structural analysis

    NASA Astrophysics Data System (ADS)

    Yaokawa, Ritsuko; Ohsuna, Tetsu; Morishita, Tetsuya; Hayasaka, Yuichiro; Spencer, Michelle J. S.; Nakano, Hideyuki

    2016-02-01

    Silicene, a two-dimensional honeycomb network of silicon atoms like graphene, holds great potential as a key material in the next generation of electronics; however, its use in more demanding applications is prevented because of its instability under ambient conditions. Here we report three types of bilayer silicenes that form after treating calcium-intercalated monolayer silicene (CaSi2) with a BF4- -based ionic liquid. The bilayer silicenes that are obtained are sandwiched between planar crystals of CaF2 and/or CaSi2, with one of the bilayer silicenes being a new allotrope of silicon, containing four-, five- and six-membered sp3 silicon rings. The number of unsaturated silicon bonds in the structure is reduced compared with monolayer silicene. Additionally, the bandgap opens to 1.08 eV and is indirect; this is in contrast to monolayer silicene which is a zero-gap semiconductor.

  17. Maskless fabrication of broadband antireflection nanostructures on glass surfaces

    NASA Astrophysics Data System (ADS)

    Tamayo R, E. E.; Hoshii, T.; Tamaki, R.; Watanabe, K.; Sugiyama, M.; Okada, Y.; Miyano, K.

    2016-06-01

    In order to reduce reflection losses at the surface of glass optical components, we have developed a plasma-etching fabrication method in which a CaF2 mask is self-assembled on the glass surface, generating nanostructures of around 100 nm in size, fabricated with an approximate etching rate of 10 nm per minute, and with controllable height, depending on the process time. By treating glasses with different compositions, it was found that the nanostructures can be successfully fabricated in a glass composed mainly of SiO2, but with 10% CaO content. In addition to the high aspect ratio and tapered geometry of the nanostructures, through cross-section composition analysis, graded Si and O compositions were also found within the nanostructures. The combined contribution of the geometrical and graded composition effects resulted in broadband 96% and over 99% transmittance on one-side and both-side treated glass substrates, respectively.

  18. Vitroceramic interface deposited on titanium substrate by pulsed laser deposition method.

    PubMed

    Voicu, Georgeta; Miu, Dana; Dogaru, Ionut; Jinga, Sorin Ion; Busuioc, Cristina

    2016-08-30

    Pulsed laser deposition (PLD) method was used to obtain biovitroceramic thin film coatings on titanium substrates. The composition of the targets was selected from SiO2-CaO-P2O5-(CaF2) systems and the corresponding masses were prepared using the sol-gel method. The depositions were performed in oxygen atmosphere (100mTorr), while the substrates were heated at 400°C. The PLD deposited films were analysed through different experimental techniques: X-ray diffraction, scanning (SEM, EDX) and transmission (HRTEM, SAED) electron microscopy and infra-red spectroscopy coupled with optical microscopy. They were also biologically tested by in vitro cell culture and the contact angle was determined. The bioevaluation results indicate a high biocompatibilty of the obtained materials, demonstrating their potential use for biomedical applications. PMID:26546909

  19. 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.

  20. Evaluate Scintillation Response Over a Continuous Energy Region

    SciTech Connect

    Zhang, Yanwen; Elfman, Mikael; Milbrath, Brian D.; Weber, William J.

    2008-06-26

    A recently developed fast analysis technique utilizing a time of flight (TOF) telescope is demonstrated to obtain relevant quantitative data on material scintillation response to energetic He particles. With superior energy resolution and fast response of the TOF telescope, energy of individual particle before impinging on a scintillating crystal can be determined with a high counting rate, which allows quantitative study of material performance over a continuous energy range in a relatively short time. Scintillation performances in terms of light output, nonlinearity and energy resolution in bismuth germinate (BGO) and europium-doped calcium fluoride (CaF2:Eu) Crystals are demonstrated, and the corresponding energy resolution is compared with gamma-ray tests on the same crystals.

  1. Samarium-neodymium direct dating of fluorite mineralization.

    PubMed

    Chesley, J T; Halliday, A N; Scrivener, R C

    1991-05-17

    The direct dating of many styles of hydrothermal mineralization has proved difficult, limiting understanding of the geological processes that lead to crustal fluid flow and the formation of major ore deposits. The hydrothermal mineral fluorite (CaF(2)) displays large variations in rare earth element (REE) abundance and samarium/neodymium ratios within a single vein. Samarium-neodymium dating of fluorite from the classic granite-hosted tin deposits of southwest England demonstrates its use as a precise chronometer of mineralization. The concentrations of light rare earth elements (LREEs) in the fluorites are highly variable and suggest the coeval precipitation of an LREE-rich phase as the most likely cause of the extreme variation in samarium/neodymium ratios.

  2. 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.

  3. Luminescent properties of lithium-phosphate-borate glasses doped with Tb3+/ Eu3+ ions

    NASA Astrophysics Data System (ADS)

    Valiev, D. T.; Stepanov, S. A.; Cong, Liu

    2016-02-01

    The luminescence of Li2O-B2O3-P2O5-CaF2 scintillation glass doped Tb3+, Eu3+ under different types of excitation sources are investigated. Changing the europium concentration of 0.5 to 1 wt% leads changes in luminescence intensity of Tb3+ ions. The luminescence spectrum of the Tb3+ ions are depend on the concentration of Eu3+. It was found, that the luminescence decay kinetics of terbium ion in the band 543 nm depending on the concentration of europium and from type of excitation. The difference in the nature of the luminescence decay kinetics of glasses under pulsed photo- and electronic excitation discussed.

  4. The Long Forgotten Compound: CoTe, and its Epitaxial Film Growth and Properties

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiwei; Zhu, Zhihai; Hines, William A.; Budnick, Joseph I.; Wells, Barrett O.

    As part of our investigation of Co-doped, Fe-chalcogenide superconductors, we have synthesized films of CoTe; a long forgotten binary compound. Using pulsed laser deposition, we have grown epitaxial films on MgO, CaF2, and SrTiO3 and have found that careful control of growth conditions allows for the synthesis of either (001) or (101) oriented films. X-ray diffraction shows the structure of the films is hexagonal. However, we also find the surprising presence of the nominally disallowed (001) peak. We also report temperature dependent transport and magnetic properties. This material may be of interest as a magnetic semiconductor and for its relationship to chemically doping Fe-based superconductors. DOE/BES Contract DE-FG02-00ER45801.

  5. 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.

  6. Infrared bulk and surface absorption by nearly transparent crystals.

    PubMed

    Rosenstock, H B; Gregory, D A; Harrington, J A

    1976-09-01

    We present an analysis of laser calorimetric data that deduces both the bulk and the surface absorption in a single run. The method involves use of long rod geometry combined with an analytical solution of the heat equation for the temperature distribution in a sample that is heated both internally and on the surfaces. Bulk and surface absorption coefficients, heat transfer coefficient, and thermal diffusivity appear as parameters; the last is treated as known, and the thermal rise curve is fitted to the three others. The solution obtained is valid at all points and times, and measurement of the temperature during and after laser heating at different points therefore narrows the possible fit considerably. Examples illustrating the method are presented for ZnSe, CaF(2) NaF:Li, NaCl, KBr, and KC1 at 2.7 microm, 3.8 microm, and 10.6 microm. Surface absorption is found to be dominant in all cases.

  7. 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.

  8. Thermodynamic modeling of REE behavior in oxidized hydrothermal fluids of high sulfate sulfur concentrations

    NASA Astrophysics Data System (ADS)

    Shironosova, G. P.; Kolonin, G. R.; Borovikov, A. A.; Borisenko, A. S.

    2016-08-01

    Thermodynamic calculations using the HCh software were made for mineral equilibriums including REEs in the fluoride-sulfide-chloride-carbonate-sulfate-system in the presence of Na, Ca, and P with fluids of various acidities-alkalinities [11]. The obtained thermodynamic characteristics of thenardite allowed us to carry out the calculations for this phase under complicated hydrothermal conditions simulating the presence of oxidized fluids at 500-100°C and 2000-125 bar. Among other solid phases, REEs-fluorite, monazite, and REE-F-apatite were formed as CaF2-(Ln,Y)F3, LnPO4, and Ca5(PO4)3F-(Ln,Y)3(PO4)3 ideal solid solutions, respectively, where Ln is La, Ce, Pr, Nd, Sm, Eu, and Gd. Xenotime, anhydrite, elemental sulfur, and calcite were found as well.

  9. 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

  10. Cross sections for proton induced high energy γ -ray emission (PIGE) in reaction 19 F(p, αγ)16 O at incident proton energies between 1.5 and 4 MeV

    NASA Astrophysics Data System (ADS)

    Cabanelas, P.; Cruz, J.; Fonseca, M.; Henriques, A.; Lourenço, F.; Luís, H.; Machado, J.; Pires Ribeiro, J.; Sánchez-Benítez, A. M.; Teubig, P.; Velho, P.; Zarza-Moreno, M.; Galaviz, D.; Jesus, A. P.

    2016-08-01

    We have studied the high energy gamma-rays produced in the reaction 19 F(p, αγ)16 O for incident proton energies from 1.5 to 4.0 MeV over NaF/Ag and CaF2/Ag thin targets in two different sets of data. Gamma-rays were detected with a High Purity Ge detector with an angle of 130° with respect to the beam axis. The cross-sections for the high energy gamma-rays of 6.129, 6.915 and 7.115 MeV have been measured for the whole group between 5 and 7.2 MeV with accuracy better than 10%. A new energy range was covered and more points are included in the cross-sections data base expanding the existing set of data. Results are in agreement with previous measurements in similar conditions.

  11. 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.

  12. A TL/OSL emission spectrometer extension of the Risø reader.

    PubMed

    Bos, A J J; Winkelman, A J M; Le Masson, N J M; Sidorenko, A V; van Eijk, C W E

    2002-01-01

    The integration of a low cost, compact sized spectrometer with the Risø reader is described. The luminescence light emitted by the sample is transmitted by an optical fibre onto a fixed entrance slit of a spectrograph. The light is measured with a high sensitivity 2048-element CCD-linear array detector (Avantes PC2000) sensitive in the UV-VIS region. The CCD array has a low readout noise and a photon sensitivity of 86 photons per count. Examples are given of both thermally and optically stimulated 3-D spectra showing the luminescence spectra as a function of temperature and time respectively. Spectra from CaF2:Tm (TLD-300) chips could be distinguished from the background (2 SD) at a 0.7 Gy dose level. PMID:12382717

  13. Advanced titanium processing

    SciTech Connect

    Hartman, Alan D.; Gerdemann, Stephen J.; Schrems, Karol K.; Holcomb, Gordon R.; Argetsinger, Edward R.; Hansen, Jeffrey S.; Paige, Jack I.; Turner, Paul C.

    2001-01-01

    The Albany Research Center of the U.S. Department of Energy has been investigating a means to form useful wrought products by direct and continuous casting of titanium bars using cold-wall induction melting rather than current batch practices such as vacuum arc remelting. Continuous ingots produced by cold-wall induction melting, utilizing a bottomless water-cooled copper crucible, without slag (CaF2) additions had minor defects in the surface such as ''hot tears''. Slag additions as low as 0.5 weight percent were used to improve the surface finish. Therefore, a slag melted experimental Ti-6Al-4V alloy ingot was compared to a commercial Ti-6Al-4V alloy ingot in the areas of physical, chemical, mechanical, and corrosion attributes to address the question, ''Are any detrimental effects caused by slag addition''?

  14. Surface Tension Drives the Orientation of Crystals at the Air-Water Interface.

    PubMed

    Chevalier, Nicolas R; Guenoun, Patrick

    2016-07-21

    The fabrication of oriented crystalline thin films is essential for a range of applications ranging from semiconductors to optical components, sensors, and catalysis. Here we show by depositing micrometric crystal particles on a liquid interface from an aerosol phase that the surface tension of the liquid alone can drive the crystallographic orientation of initially randomly oriented particles. The X-ray diffraction patterns of the particles at the interface are identical to those of a monocrystalline sample cleaved along the {104} (CaCO3) or {111} (CaF2) face. We show how this orientation effect can be used to produce thin coatings of oriented crystals on a solid substrate. These results also have important implications for our understanding of heterogeneous crystal growth beneath amphiphile monolayers and for 2D self-assembly processes at the air-liquid interface. PMID:27389283

  15. 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.

  16. The influence of dicarboxylic acids: Oxalic acid and tartaric acid on the compressive strength of glass ionomer cements

    NASA Astrophysics Data System (ADS)

    Permana, Ahmadi Jaya; Setyawati, Harsasi; Hamami, Murwani, Irmina Kris

    2016-03-01

    Glass ionomer cement (GIC) has limitation on the mechanical properties especially compressive strength. The change of compressive strength of GIC by adding oxalic acid and tartaric acid has been investigated. Oxalic acid and tartaric acid was added to the liquid components at concentrations of 0 - 15% (w/w). Powder component of GIC was made from optimum experimental powder glass SiO2-Al2O3-CaF2. GIC was characterized by compressive strength test, SEM-EDX and FTIR. The addition of tartaric acid to GIC has greater improvement than addition of oxalic acid. The addition of tartaric acid at 10 % (w/w) to GIC has greatest value of compressive strength.

  17. 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.

  18. A synchrotron-radiation-based variable angle ellipsometer for the visible to vacuum ultraviolet spectral range

    NASA Astrophysics Data System (ADS)

    Neumann, M. D.; Cobet, C.; Kaser, H.; Kolbe, M.; Gottwald, A.; Richter, M.; Esser, N.

    2014-05-01

    A rotating analyzer spectroscopic polarimeter and ellipsometer with a wide-range θ-2θ goniometer installed at the Insertion Device Beamline of the Metrology Light Source in Berlin is presented. With a combination of transmission- and reflection-based polarizing elements and the inherent degree of polarization of the undulator radiation, this ellipsometer is able to cover photon energies from about 2 eV up to 40 eV. Additionally, a new compensator design based on a CaF2 Fresnel rhomb is presented. This compensator allows ellipsometric measurements with circular polarization in the vacuum ultraviolet spectral range and thus, for example, the characterization of depolarizing samples. The new instrument was initially used for the characterization of the polarization of the beamline. The technical capabilities of the ellipsometer are demonstrated by a cohesive wide-range measurement of the dielectric function of epitaxially grown ZnO.

  19. Effect of Physicochemical Properties of Slag and Flux on the Removal Rate of Oxide Inclusion from Molten Steel

    NASA Astrophysics Data System (ADS)

    Park, Jun Seok; Park, Joo Hyun

    2016-08-01

    The slag-metal reaction experiments were carried out using a high-frequency induction furnace to confirm the effect of slag composition on the removal rate of inclusions in molten steel through the CaO-based slags. The apparent rate constant of oxygen removal (k O) was obtained as a function of slag composition. It increased with increasing basicity, and the content of MgO and CaF2, whereas it decreased by increasing the content of Al2O3 in the slag. The removal rate of inclusions was strongly affected not only by the driving force of the chemical dissolution but also by the viscosity of the slags and fluxes.

  20. 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.