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. Investigation of the superionic behaviour of BaF 2 ( x ?mol% LaF 3 ) by raman and brillouin scattering and molecular dynamics simulations

    Microsoft Academic Search

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

    2002-01-01

    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 BaF 2 ( x v mol% LaF 3 ) over a particularly wide range of LaF 3 dopant concentrations from x =0 to 50. Room temperature Raman spectra for x =0, 5 and 10 show

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

    Microsoft Academic Search

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

    2002-01-01

    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

  4. Luminescence and photoionization processes of Yb2+ in CaF2, SrF2 and BaF2

    E-print Network

    Paris-Sud XI, Université de

    2105 Luminescence and photoionization processes of Yb2+ in CaF2, SrF2 and BaF2 B. Moine, B les propriétés de fluorescence et de photoconductivité de Yb2+ dans CaF2, SrF2 et BaF2. On présente In this paper, we analyze the fluorescence and the photoconductivity properties of Yb2+ in CaF2, SrF2 and BaF2

  5. 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.

  6. Monte Carlo simulation of gamma-ray response of BaF2 and CaF2

    NASA Astrophysics Data System (ADS)

    Gao, F.; Xie, Y. L.; Wang, Z. G.; Kerisit, S.; Wu, D. X.; Campbell, L. W.; Van Ginhoven, R. M.; Prange, M.

    2013-11-01

    We have employed a Monte Carlo (MC) method to study intrinsic properties of two alkaline-earth halides, namely, BaF2 and CaF2, relevant to their use as radiation detector materials. The MC method follows the fate of individual electron-hole (e-h) pairs and thus allows for a detailed description of the microscopic structure of ionization tracks created by incident ?-ray radiation. The properties of interest include the mean energy required to create an e-h pair, W, Fano factor, F, the maximum theoretical light yield, and the spatial distribution of e-h pairs resulting from ?-ray excitation. Although W and F vary with incident photon energy at low energies, they tend to constant values at energies higher than 1 keV. W is determined to be 18.9 and 19.8 eV for BaF2 and CaF2, respectively, in agreement with published data. The e-h pair spatial distributions exhibit a linear distribution along the fast electron tracks with high e-h pair densities at the end of the tracks. Most e-h pairs are created by interband transition and plasmon excitation in both scintillators, but the e-h pairs along fast electron tracks in BaF2 are slightly clustered, forming nanoscale domains and resulting in the higher e-h pair densities than in CaF2. Combining the maximum theoretical light yields calculated for BaF2 and CaF2 with those obtained for CsI and NaI shows that the theoretical light yield decreases linearly with increasing band gap energy.

  7. Monte Carlo Simulation of Gamma-Ray Response of BaF2 and CaF2

    SciTech Connect

    Gao, Fei; Xie, YuLong; Wang, Zhiguo; Kerisit, Sebastien N.; Wu, Dangxin; Campbell, Luke W.; Van Ginhoven, Renee M.; Prange, Micah P.

    2013-12-01

    We have employed a Monte Carlo (MC) method to study intrinsic properties of two alkaline-earth halides, namely BaF2 and CaF2, relevant to their use as radiation detector materials. The MC method follows the fate of individual electron-hole (e-h) pairs and thus allows for a detailed description of the microscopic structure of ionization tracks created by incident ?-ray radiation. The properties of interest include the mean energy required to create an e-h pair, W, Fano factor, F, the maximum theoretical light yield, and the spatial distribution of e-h pairs resulting from ?-ray excitation. Although W and F vary with incident photon energy at low energies, they tend to constant values at energies higher than 1 keV. W is determined to be 18.9 and 19.8 eV for BaF2 and CaF2, respectively, in agreement with published data. The e-h pair spatial distributions exhibit a linear distribution along the fast electron tracks with high e-h pair densities at the end of the tracks. Most e-h pairs are created by interband transition and plasmon excitation in both scintillators, but the e-h pairs along fast electron tracks in BaF2 are slightly clustered, forming nanoscale domains and resulting in the higher e-h pair densities than in CaF2. Combining the maximum theoretical light yields calculated for BaF2 and CaF2 with those obtained for CsI and NaI shows that the theoretical light yield decreases linearly with increasing band gap energy.

  8. Phase transitions and equations of state of alkaline earth fluorides CaF2, SrF2, and BaF2 to Mbar pressures

    E-print Network

    Duffy, Thomas S.

    Phase transitions and equations of state of alkaline earth fluorides CaF2, SrF2, and BaF2 to Mbar received 28 April 2010; published 27 May 2010 Phase transitions and equations of state of the alkaline at ambient conditions for the alkaline earth fluorides CaF2, SrF2, and BaF2. Fluorides are widely used

  9. Spatially selected synthesis of LaF 3 and Er 3+-doped CaF 2 crystals in oxyfluoride glasses by laser-induced crystallization

    NASA Astrophysics Data System (ADS)

    Kusatsugu, M.; Kanno, M.; Honma, T.; Komatsu, T.

    2008-05-01

    Oxyfluoride glasses with a small amount of NiO are prepared using a conventional melt quenching technique, and the spatially selected crystallization of LaF 3 and CaF 2 crystals is induced on the glass surface by irradiations of continuous wave lasers with a wavelength of ?=1064 or 1080 nm. Dots and lines including LaF 3 crystals are patterned by heat-assisted (300 °C) laser irradiations ( ?=1064 nm) with a power of P=1 W and an irradiation time of 10 s for dots and a scanning speed of S=5 ?m/s for lines. Lines consisting of CaF 2 crystals are also patterned in an ErF 3-doped oxyfluoride glass by laser irradiations ( ?=1080 nm) with a power of P=1.7 W and a scanning speed of S=2 ?m/s, and the incorporation of Er 3+ ions into CaF 2 crystals is confirmed from micro-photoluminescence spectrum measurements. It is proposed that the lines patterned by laser irradiations in this study are consisted of the composite of LaF 3 or CaF 2 nanocrystals and SiO 2-based oxide glassy phase. It is demonstrated that a combination of Ni 2+-dopings and laser irradiations is effective in spatially selected local crystallizations of fluorides in oxyfluoride glasses.

  10. 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.

  11. Comparative spectroscopic and laser properties of Yb 3+ -doped CaF 2 , SrF 2 and BaF 2 single crystals

    Microsoft Academic Search

    P. Camy; J. L. Doualan; A. Benayad; M. von Edlinger; V. Ménard; R. Moncorgé

    2007-01-01

    We present the spectroscopic properties and room-temperature cw tunable laser operation of Yb3+-doped CaF2, SrF2 and BaF2 single crystals grown and studied in the same conditions. Emission cross sections, lifetimes, laser thresholds, laser slope\\u000a efficiencies and laser wavelength tuning ranges are compared. It appears that Yb3+-doped BaF2 might be more promising for diode-pumped high power laser operation.

  12. 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.

  13. 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 ?m in the UV to 7 ?m 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.

  14. Upconversion luminescence properties of Yb3+ and Tm3+ codoped amorphous fluoride ZrF4-BaF2-LaF3-AlF3-NaF thin film prepared by pulsed laser deposition.

    PubMed

    He, Chunfeng; Qin, Guanshi; Zhao, Dan; Chuai, Xiaohong; Wang, Lili; Zheng, Kezhi; Qin, Weiping

    2014-05-01

    The Yb3+ and Tm3+ co-doped 55.98ZrF4-28BaF2-2.5LaF3-4AlF3-7NaF-2.5YbF3-0.02TmF3 amorphous fluoride film was prepared by pulsed laser deposition. The spectroscopic properties and energy transfer analysis of this film were studies in detail. Ultraviolet and visible upconversion emissions were observed under the infrared excitation at 980 nm. In comparison with that of its target, the upconversion emissions of the film in the visible and ultraviolet range were greatly enhanced. The possible energy transfer mechanism of the emissions was given to understand the upconversion process. This kind of thin films has potential applications for the integrated optical waveguide amplifier and ultraviolet laser. PMID:24734646

  15. Enhanced ultraviolet upconversion luminescence of Tm and Yb codoped ZrF4-BaF2-LaF3-AlF3-NaF glass.

    PubMed

    He, Chunfeng; Zhao, Dan; Qin, Guanshi; Zheng, Kezhi; Qin, Weiping

    2011-11-01

    Ultraviolet (UV) upconversion (UC) luminescence properties of Tm3+ ions sensitized by Yb3+ ions in ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass were studied in detail. Under the excitation from a 980 nm continuous wave (CW) diode laser, red, blue, and even UV emissions were observed in the fluorozirconate glass. Several fluorescence bands appeared in the UC emission spectrum from 292.8 nm to 805.8 nm. The UC emission peaks at 291 nm, 347 nm, 363 nm, 454 nm, 475 nm, 647 nm, 687 nm, and 804 nm correspond to the transitions of 1I6 --> 3H6, 1I6 --> 3F4, 1D2 --> 3H6, 1D2 --> 3F4, 1G4 --> 3H6, 1G4 --> 3F4, 3F3 --> 3H6, and 3H4 --> 3H6, respectively. Experimental results of intensity dependence of the up-converted fluorescence on the pump power indicate a five-photon excitation scheme of 1I6 energy level. PMID:22413235

  16. Low-frequency inelastic light scattering in a ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass.

    PubMed

    Adichtchev, S V; Malinovsky, V K; Ignatieva, L N; Merkulov, E B; Surovtsev, N V

    2014-05-14

    Low-frequency (down to 30 GHz) inelastic light scattering is studied in a multicomponent glass ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) in a wide temperature range. The contributions of the THz vibrational spectrum (boson peak) and of the fast relaxation are extracted and analyzed. It is shown that the fast relaxation spectrum is described by a distribution of relaxation times leading to a power-law ?(?) dependence in the frequency range 30-300 GHz. Temperature dependence of ?(T) is well described by the Gilroy-Phillips model, while the integrated intensity of the fast relaxation increases significantly with the temperature. This feature distinguishes the fast relaxation in ZBLAN from the case of most single-component glasses. Thermodynamic and kinetic fragility indexes are significantly different for the ZBLAN glass. The correlations between the boson peak intensity, elastic moduli, and fragility index, found earlier for single-component glasses, are fulfilled for the thermodynamic fragility index of ZBLAN. In contrast, the correlation between the fast relaxation intensity at Tg and the fragility holds better for the kinetic fragility index of ZBLAN. We propose that thermodynamic and kinetic fragilities reflect different aspects of glassy dynamics in the case of glass formers with the complex chemical composition and structure topology: the former correlates with the elastic properties and the boson peak, the latter with the relaxation. PMID:24832289

  17. Low-frequency inelastic light scattering in a ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass

    NASA Astrophysics Data System (ADS)

    Adichtchev, S. V.; Malinovsky, V. K.; Ignatieva, L. N.; Merkulov, E. B.; Surovtsev, N. V.

    2014-05-01

    Low-frequency (down to 30 GHz) inelastic light scattering is studied in a multicomponent glass ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) in a wide temperature range. The contributions of the THz vibrational spectrum (boson peak) and of the fast relaxation are extracted and analyzed. It is shown that the fast relaxation spectrum is described by a distribution of relaxation times leading to a power-law ?? dependence in the frequency range 30-300 GHz. Temperature dependence of ?(T) is well described by the Gilroy-Phillips model, while the integrated intensity of the fast relaxation increases significantly with the temperature. This feature distinguishes the fast relaxation in ZBLAN from the case of most single-component glasses. Thermodynamic and kinetic fragility indexes are significantly different for the ZBLAN glass. The correlations between the boson peak intensity, elastic moduli, and fragility index, found earlier for single-component glasses, are fulfilled for the thermodynamic fragility index of ZBLAN. In contrast, the correlation between the fast relaxation intensity at Tg and the fragility holds better for the kinetic fragility index of ZBLAN. We propose that thermodynamic and kinetic fragilities reflect different aspects of glassy dynamics in the case of glass formers with the complex chemical composition and structure topology: the former correlates with the elastic properties and the boson peak, the latter with the relaxation.

  18. Optical and structural properties of LaF3 thin films.

    PubMed

    Bischoff, Martin; Gäbler, Dieter; Kaiser, Norbert; Chuvilin, Andrey; Kaiser, Ute; Tünnermann, Andreas

    2008-05-01

    LaF(3) thin films of different thicknesses were deposited on CaF(2) (111) and silicon substrates at a relatively low substrate temperature of 150 degrees C. Optical (transmittance, reflectance, refractive index, and extinction coefficient) and mechanical (morphology and crystalline structure) properties have been investigated and are discussed. It is shown that LaF(3) thin films deposited on CaF(2) (111) substrates are monocrystalline and have a bulklike dense structure. Furthermore, it is presented that low-loss LaF(3) thin films can be deposited not only by boat evaporation but also by electron beam evaporation. PMID:18449239

  19. 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.

  20. Ultraviolet optical and microstructural properties of MgF2 and LaF3 coatings deposited by ion-beam sputtering and boat and electron-beam evaporation

    Microsoft Academic Search

    Detlev Ristau; Stefan Gunster; Salvador Bosch; Angela Duparre; Enrico Masetti; Josep Ferre-Borrull; George Kiriakidis; Francesca Peiro; Etienne Quesnel; Alexander Tikhonravov

    2002-01-01

    Single layers of MgF2 and LaF3 were deposited upon superpolished fused-silica and CaF2 substrates by ion-beam sputtering (IBS) as well as by boat and electron beam (e-beam) evaporation and were characterized by a variety of complementary analytical techniques. Besides undergoing photometric and ellipsometric inspection, the samples were investigated at 193 and 633 nm by an optical scatter measurement facility. The

  1. Ultralow threshold green lasing and optical bistability in ZBNA (ZrF4-BaF2-NaF-AlF3) microspheres

    NASA Astrophysics Data System (ADS)

    Wu, Yuqiang; Ward, Jonathan M.; Nic Chormaic, Síle

    2010-02-01

    Upconversion lasing and fluorescence from active microspheres fabricated from a novel fluorozirconate, Er3+ doped glass, ZBNA (ZrF4-BaF2-NaF-AlF3), when pumped at 978 nm via a tapered optical fiber is demonstrated. An ultralow, green lasing threshold of ˜3 ?W for 550 nm emissions is measured. This is one order of magnitude lower than that previously reported for ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) microspheres. Optical bistability effects in ZBNA microspheres are reported and the bistable mechanism is discussed and attributed to shifts of the whispering gallery modes due to thermal expansion of the sphere, where heating is achieved by optical pumping around 978 nm. The effect of the bistability on the upconversion lasing is examined and we report multiple bistability loops within the microspheres.

  2. LaF3 insulators for MIS structures

    NASA Technical Reports Server (NTRS)

    Sher, A.; Tsuo, Y. H.; Moriarty, J. A.; Miller, W. E.; Crouch, R. K.; Seiber, B. A.

    1979-01-01

    Thin films of LaF3 deposited on Si or GaAs substrates have been observed to form blocking contacts with very high capacitances. This results in comparatively hysteresis-free and sharp C-V (capacitance-voltage) characteristics for MIS structures. Such structures have been used to study the interface states of GaAs with increased resolution and to construct improved photocapacitive infrared detectors.

  3. Transfer of PbSe\\/PbEuSe epilayers grown by MBE on BaF 2-coated Si(111)

    Microsoft Academic Search

    H. Z Wu; X. M Fang; R Salas; D McAlister; P. J McCann

    1999-01-01

    Epitaxial growth of PbSe\\/PbEuSe\\/BaF2\\/CaF2 heterostructures was carried out by a molecular beam epitaxy on Si(111) wafers. Successful transfer of 3-?m thick PbSe\\/PbEuSe epilayers was accomplished by bonding the MBE-grown samples face down to polished copper plates followed by the removal of the silicon substrate by dissolving the BaF2 buffer layer in water. Nomarski microscopy and surface profile characterization showed that

  4. Pressure dependence of the emission in CaF2?:?Yb(2.).

    PubMed

    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 Yb(2+) 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 4f(13)5d states of Yb(2+) 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?:?Eu(2+) and CaF2?:?Eu(2+). The difference between the spectral properties of Eu(2+) and Yb(2+) is attributable to the fact that the ground and 4f(6)5d states of Eu(2+) are placed deeper in the CaF2 bandgap than the ground and excited 4f(13)5d states of Yb(2+), whereas the energies of the impurity-trapped exciton states for Yb(2+) and Eu(2+) with respect to the conduction band are approximately the same. PMID:26171576

  5. Properties of AlF3 and LaF3 films at 193nm

    NASA Astrophysics Data System (ADS)

    Xue, Chunrong; Shao, Jianda

    2010-10-01

    In order to develop low loss, high-performance 193nm Fluoride HR mirrors and anti-reflection coatings, LaF3 and AlF3 materials, used for a single-layer coating, were deposited by a molybdenum boat evaporation process. Various microstructures that formed under different substrate temperatures and with deposition rates were investigated. The relation between these microstructures (including cross section morphology, surface roughness and crystalline structure), the optical properties (including refractive index and optical loss) and mechanical properties (stress) were investigated. Furthermore, AlF3 used as a low-index material and LaF3 used as a high-index material were designed and deposited for multilayer coatings. Transmittance, reflectance, stress, and the laser-induced damage threshold (LIDT) were studied. It is shown that AlF3 and LaF3 thin films, deposited on the substrate at a temperature of 300 °C, obtained good quality thin films with high transmittance and little optical loss at 193 nm. For multilayer coatings, the absorption mainly comes from LaF3. Based on these studies, The thickness of 193nm films was controled by a 1/3 baffle with pre-coating technology. the LaF3/AlF3 AR coantings and HR mirrors at 193nm were designed and deposited. Under the present experimental conditions, the reflectance of LaF3/AlF3 HR mirror is up to 96%, and its transmittance is 1.5%. the LaF3/AlF3 AR coanting's residual reflectance is less than 0.14%, and single-sided transmittance is 93.85%. To get a high-performance 193nm AR coating, super-polished substrate is the best choice.

  6. Synthesis of Fe 3O 4@LaF 3:Ce,Tb nanocomposites with bright fluorescence and strong magnetism

    Microsoft Academic Search

    H. He; M. Y. Xie; Y. Ding; X. F. Yu

    2009-01-01

    In this paper, fluorescent-magnetic Fe3O4@LaF3:Ce,Tb nanocomposites were synthesized by combining fluorescent LaF3:Ce,Tb and magnetic Fe3O4 nanoparticles into new ‘two-in-one’ entities. The obtained Fe3O4@LaF3:Ce,Tb nanocomposites were small (about 30nm in diameter) and well dispersed in water. Under ultraviolet light irradiation, the Fe3O4@LaF3:Ce,Tb nanocomposites emitted bright green fluorescence, and they could be easily manipulated by an external magnetic field. Such bifunctional nanocomposites

  7. 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

  8. Solid-State Glucose Sensor Using LaF3Based Transducer

    Microsoft Academic Search

    Norio Miura; Naoko Matayoshi; Noboru Yamazoe

    1989-01-01

    A new-type glucose sensor using a LaF3-based transducer was investigated as the first example of a solid-electrolytecoupled biosensor. The sensor element was composed of the following electrochemical cell: (reference electrode) Sn+SnF2|LaF3|Pt-glucose oxidase (sensing electrode). The e.m.f. of the sensor cell was found to vary logarithmically with a change in glucose concentration in the range from 2× 10-5 to 1× 10-2

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

    SciTech Connect

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

    2010-11-15

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

  10. 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.

  11. Radiation characteristics of epitaxial CaF2 on silicon

    Microsoft Academic Search

    Yasushiro Nishioka; Chih-Chen Cho; Scott R. Summerfelt; Bruce E. Gnade; George A. Brown

    1991-01-01

    The radiation characteristics of a Al\\/CaF2\\/Si capacitor have been investigated. The single-crystal CaF2 film has been grown on Si(111) at a temperature as low as 300°C by molecular beam epitaxy (MBE). Previous studies showed that CaF2 films grown on Si(111) above 500°C exhibited flat C-V curves, suggesting a pinned CaF2\\/Si(111) interface. However, the authors have been able to obtain unpinned

  12. A study of the LaF3\\/Si(111) interface using UPS and XPS

    Microsoft Academic Search

    C L Griffiths; R H Williams

    1990-01-01

    LaF3 layers ranging in thickness from submonolayer to several monolayers were deposited onto room temperature Si(111)-7 7 clean surfaces, and subsequently annealed at temperatures from 400C to 750C to promote ordering. The overlayers and the detailed interface reactions were probed with high resolution XPS in our home laboratory, and by soft XPS using the synchrotron source SRS at Daresbury laboratory,

  13. A study of the LaF3\\/Si(111) interface using UPS and XPS

    Microsoft Academic Search

    C. L. Griffiths; R. H. Williams

    1990-01-01

    LaF3 layers ranging in thickness from submonolayer to several monolayers were deposited onto room temperature Si(111)-7 × 7 clean surfaces, and subsequently annealed at temperatures from 400°C to 750°C to promote ordering. The overlayers and the detailed interface reactions were probed with high resolution XPS in our home laboratory, and by soft XPS using the synchrotron source SRS at Daresbury

  14. Crystal field of rare earth impurities in LaF3

    NASA Astrophysics Data System (ADS)

    Novák, P.; Kuneš, J.; Knížek, K.

    2014-11-01

    The crystal field parameters of 13 trivalent lanthanide ions substituted for La in LaF3 were calculated using the combination of the band structure and Wannier function calculations. Performing an atomic exact diagonalization with thus obtained crystal-field parameters we compute the crystal-field splitting of atomic multiplets. The calculation is compared with the available experimental results and a good agreement is found.

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

    Microsoft Academic Search

    M. Lukac; E. L. Hahn

    1989-01-01

    A Stark modulated optical pumping spectroscopic technique is applied to study Pr+3 ion pair absorption satellites of a 3H4(Gamma1)-1D2(Gamma1) (gamma=592.5 nm) transition in Pr+3:LaF3. In addition to sigma polarized absorption satellites, bulk crystal symmetry forbidden pi polarized absorption satellites are observed. We attribute these pi polarized absorptions to crystal symmetry breaking lattice distortions in the vicinity of a Pr+3 ion

  16. Inter-atomic force constants of BaF2 by diffuse neutron scattering measurement

    NASA Astrophysics Data System (ADS)

    Sakuma, Takashi; Makhsun, Sakai, Ryutaro; Xianglian, Takahashi, Haruyuki; Basar, Khairul; Igawa, Naoki; Danilkin, Sergey A.

    2015-04-01

    Diffuse neutron scattering measurement on BaF2 crystals was performed at 10 K and 295 K. Oscillatory form in the diffuse scattering intensity of BaF2 was observed at 295 K. The correlation effects among thermal displacements of F-F atoms were obtained from the analysis of oscillatory diffuse scattering intensity. The force constants among neighboring atoms in BaF2 were determined and compared to those in ionic crystals and semiconductors.

  17. Phase transitions and equations of state of alkaline earth fluorides CaF2 and SrF2 to 95 GPa

    NASA Astrophysics Data System (ADS)

    Dorfman, S. M.; Jiang, F.; Mao, Z.; Kubo, A.; Prakapenka, V.; Duffy, T. S.

    2007-12-01

    AX2 compounds include a wide range of oxides and salts of broad interest in geoscience, materials science and chemistry, such as SiO2 and CaF2, and have in common a sequence of phase transitions dependent on ionic size ratio and electronic properties (Leger and Haines, 1997). Shock compression studies have shown that CaF2 transforms to a highly incompressible phase above 1 Mbar along the Hugoniot (Nellis, 2007). In this study we examine phase transitions and equations of state of the alkaline earth fluorides CaF2 and SrF2 to 95 GPa. Angle-dispersive x-ray diffraction experiments were performed on CaF2 and SrF2 samples in laser-heated diamond anvil cells at beamlines X17B3 of the National Synchrotron Light Source and 13-ID-D of the GSECARS sector at the Advanced Photon Source. We confirmed that both materials undergo a phase transition from the cubic fluorite structure to the orthorhombic cotunnite-type structure at pressures less than 10 GPa. Both materials further transform to a hexagonal Ni2In-type structure at 84 and 36 GPa, respectively, following laser heating. This finding is consistent with theoretical calculations and the behavior of the analog compound BaF2 (Leger et al., 1995). For SrF2, the Ni2In-type phase was confirmed by Rietveld refinement. On decompression with heating, we found that Ni2In-type SrF2 passes through an intermediate orthorhombic phase at 28 GPa before returning to cotunnite structure at 22 GPa. This transition appears analogous to the isosymmetric phase transition to the Co2Si-type structure reported in PbF2 by Haines et al. (1998). Unit cell parameters and volumes were determined as a function of pressure for the new phases. We also constrained the equation of state of the cotunnite phase of CaF2 to 82 GPa. Fitting the data to a Birch-Murnaghan equation of state yields a zero-pressure bulk modulus of 97.9 GPa with a pressure derivative of 5.6 for cotunnite-type CaF2. This work represents the first synthesis and characterization of the Ni2In-type phase for these compositions and the first report of Co2Si structure in an alkaline earth fluoride.

  18. Phase Transitions and Equations of State of Alkaline Earth Fluorides CaF2 SrF2 and BaF2 to Mbar Pressures

    SciTech Connect

    S Dorfman; F Jiang; Z Mao; A Kubo; Y Meng; V Prakapenda; T Duffy

    2011-12-31

    Phase transitions and equations of state of the alkaline earth fluorides CaF{sub 2}, SrF{sub 2}, and BaF{sub 2} were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm3{sup -}m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF{sub 2} and SrF{sub 2}: these materials were observed to transform to a hexagonal (P6{sub 3}/mmc) Ni{sub 2}In-type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF{sub 2}, the Ni{sub 2}In-type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF{sub 2} and SrF{sub 2}, the fluorite-cotunnite transition results in a volume decrease of 8-10%, while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni{sub 2}In-type phase is {approx}5%. The percentage increase in the bulk modulus ({Delta}K) across the transition is greater when the cation is smaller. While for BaF{sub 2}, {Delta}K is 10-30%, {Delta}K values for SrF{sub 2} and CaF{sub 2} are 45-65% and 20-40%. Although shock data for CaF{sub 2} have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.

  19. Raman and Infrared spectra of (BaF2)n (n=1-6) clusters

    E-print Network

    Pandey, Ratnesh K; Nigam, Sandeep; Pandey, Ravindra; Pandey, Avinash C

    2015-01-01

    The vibrational properties of alkaline-earth metal fluoride clusters (BaF2)n (n=1-6) are investigated in the framework of density functional theory. The calculated Raman and Infrared (IR) spectra reveals shift in Raman and IR peak position towards lower frequency region with the increase in the cluster size. Further the calculated spectra have been compared with the experimental vibrational spectra of bulk BaF2 crystal. Even though the smaller size cluster lacks translational symmetry, the structural and vibrational characteristic of (BaF2)5-6 are nearer to bulk counterpart.

  20. A solvent extraction route for CaF2 hollow spheres.

    PubMed

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

    2010-11-21

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

  1. Refluxing synthesis, photoluminescence and binding ability to deoxyribonucleic acid of water-soluble rare earth ion-doped LaF3 nanoparticles.

    PubMed

    Wang, Zhenling; Zhang, Yi; Li, Chunyang; Zhang, Xinlei; Chang, Jiazhong; Xie, Jianping; Li, Chengwei

    2014-06-01

    Water-soluble rare earth ion (Ce3+, Tb3+)-doped LaF3 nanoparticles with the ability to bind to deoxyribonucleic acid (DNA) were prepared by the refluxing method in a glycerol/water mixture and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and so on. The obtained LaF3:Ce3+, LaF3:Tb3+ and LaF3:Ce3+, Tb3+ nanoparticles are well crystallized with a hexagonal structure and composed of spherical particles with an average size from 11 to 19 nm. The as-prepared samples can be dispersed into water to form a colloidal solution. Under ultraviolet (UV) light irradiation, the emission lines of Tb3+ in the co-doped LaF3:Ce3+, Tb3+ are evidently strengthened compared to those in the single-doped LaF3:Tb3+ nanoparticles, which is due to the energy transfer from Ce3+ to Tb3+ ions in the LaF3:Ce3+, Tb3+ samples. The biological experiment confirms that the water-soluble LaF3:Ce3+, Tb3+ nanoparticles can be bonded to the DNA molecules and emit visible light under UV irradiation. These luminescent nanoparticles could be used similarly to ethidium bromide (EtBr), which has been used extensively as a DNA staining reagent. The advantage that LaF3:Ce3+, Tb3+ nanoparticles have lower toxicity than EtBr makes them a potential reagent instead of EtBr in the DNA staining in biological experiments. PMID:24738421

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

    E-print Network

    Rodríguez, Fernando

    Pressure-induced photoluminescence in Mn2¿ -doped BaF2 and SrF2 fluorites Ignacio Herna -doped BaF2 and SrF2 using high-pressure techniques. The aim is to understand the surprising PL behavior temperature (SrF2) or at any temperature (BaF2) at ambient pressure. We associate the loss of Mn2 PL

  3. Formation and Luminescence Phenomena of LaF3:Ce3+ Nanoparticles and Lanthanide-Organic Compounds in Dimethyl Sulfoxide

    SciTech Connect

    Yao, Mingzhen; Joly, Alan G.; Chen, Wei

    2010-01-21

    LaF3:Ce3+ doped nanoparticles were synthesized at different temperatures in dimethyl sulfoxide by the chemical reaction of lanthanum nitrate hydrate and cerium nitrate hexahydrate with ammonium fluoride. The formation of Ce3+ doped LaF3 nanoparticles is confirmed by X-ray diffraction and high resolution transmission electron microscopy. An intense emission at around 310 nm from the d - f transition of Ce3+ was observed from the LaF3:Ce3+ powder samples. However, in solution samples, the ultraviolet emission from Ce3+ is mostly absent, but intense luminescence is observed in the visible range from blue to red. The emission wavelength of the solution samples is dependent on the reaction time and temperature. More interestingly, the emission wavelength varies with the excitation wavelength. Most likely, this emission is from the metalorganic compounds of Ce3+ or La3+ and DMSO as similar phenomena are also observed when lanthanum nitrate hydrate or cerium nitrate hexahydrate are heated in DMSO.

  4. Response of MEDEA BaF 2 detectors to 20-280 MeV photons

    NASA Astrophysics Data System (ADS)

    Bellia, G.; Alba, R.; Coniglione, R.; Del Zoppo, A.; Finocchiaro, P.; Maiolino, C.; Migneco, E.; Piattelli, P.; Sapienza, P.; Frascaria, N.; Lhenry, I.; Roynette, J. C.; Suomijärvi, T.; Alamanos, N.; Auger, F.; Gillibert, A.; Pierroutsakou, D.; Sida, J. L.; Silveira Gomes, P. R.

    1993-05-01

    The response function of MEDEA BaF 2 crystals to high energy photons, up to 280 MeV, has been studied using monochromatic ?-rays from the in flight annihilation of positron beams. The experimental response functions are compared to the results of Monte Carlo simulations based on the EGS3 code and parametrized over the whole investigated energy range.

  5. CaF2(Eu): an ``old'' scintillator revisited

    NASA Astrophysics Data System (ADS)

    Plettner, C.; Pausch, G.; Scherwinski, F.; Herbach, C. M.; Lentering, R.; Kong, Y.; Römer, K.; Grodzicka, M.; Szcze?niak, T.; Iwanowska, J.; Moszy?ski, M.

    2013-06-01

    Homeland security applications demand performant two-plane Compton-camera systems, with high detector efficiency, good nuclide identification and able to perform in-field conditions. A low-Z scintillator has been proposed and studied as a promising candidate for use in the scattering plane of a scintillator-based Compton camera: CaF2(Eu) [1]. All the relevant properties for the application of this scintillator in a mobile Compton camera system, have been addressed: the energy resolution and the non-proportionality at room temperature and in the temperature range of -20°C to +55°C, the photoelectron yield and the relative light yield in the relevant temperature range. A new method of inferring the relative light output of scintillators has been proposed.

  6. Preparation of CaF 2 based phosphors by solid state metathesis

    NASA Astrophysics Data System (ADS)

    Ugemuge, N. S.; Tajne, D. S.; Dhopte, S. M.; Muthal, P. L.; Moharil, S. V.

    2011-01-01

    Synthesis of CaF 2:Eu and CaF 2:Ce phosphors by solid state metathesis is reported for the first time. CaF 2 could be prepared in few minutes using domestic microwave oven. Though CaF 2 is formed by metathesis, luminescence centres were not formed in one step; as-prepared samples did not show any luminescence. Samples reduced at 1000 °C for 1 h exhibited very intense, characteristic emission. Activator concentration, and in turn, the intensity of luminescence depends on the partition coefficient of the activator in the host and the washable reaction products (KCl in the present case). In case of Europium, most of the activator is retained by CaF 2 while for Cerium a significant fraction of the added activator is washed away with KCl.

  7. High-reflectivity mirrors by Al2O3, LaF3 and AlF3 for 193 nm application

    NASA Astrophysics Data System (ADS)

    Sun, Jian; Li, Xu; Zhang, Weili; Yi, Kui; Shao, Jianda

    2014-03-01

    As important components in deep-ultraviolet (DUV) optics, especially 193 nm lithographic systems, high-reflectivity (HR) mirrors with excellent optical properties and long lifetimes are needed urgently. In this study, we designed and produced three HR coatings for 193 nm on fused quartz substrates: Al2O3/AlF3 coating, LaF3/AlF3 coating and a double stack mirror with combined Al2O3/AlF3 and LaF3/AlF3. The reflectance of the Al2O3/AlF3 coating with 14 layer pairs reached 98.0% at 193 nm. However, the absorption of Al2O3 prevented the reflectance to increase further. The maximum reflectance of the LaF3/AlF3 coating with 15 layer pairs reached 98.1%, with initial micro-cracks formation. The reflectance decreased as the number of layer pairs increased to 16 because of numerous micro-cracks. The mirror with combined Al2O3/AlF3 and LaF3/AlF3 coatings which combined their advantages obtained a reflectance of 98.8% at 193 nm after deposition. This value could still reach 98.5% at 4 months after deposition and remain stable thereafter. Therefore, the combined coating of Al2O3/AlF3 and LaF3/AlF3 is an excellent candidate for practical application.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  9. 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.

  10. Monodispersed LaF3 nanocrystals: shape-controllable synthesis, excitation-power-dependent multi-color tuning and intense near-infrared upconversion emission.

    PubMed

    Rao, Ling; Lu, Wei; Ren, Guozhong; Wang, Haibo; Yi, Zhigao; Liu, Hongrong; Zeng, Songjun

    2014-02-14

    In this study, monodispersed and high-quality hexagonal phase LaF3 nanocrystals with different shapes and sizes were synthesized by a solvothermal method using oleic acid as the stabilizing agent. The as-prepared LaF3 nanocrystals were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), and analysis of the upconversion spectra. The TEM results reveal that the samples present high uniformity and monodispersity and are self-assembled into a two-dimensional ordered array. Moreover, the shape, size and structure of the nanocrystals can be readily tuned by adjusting the NaF content. With increasing content of NaF, the shape of the LaF3 nanocrystals changed from particle to rod and the size gradually increased. More importantly, high NaF content favors the formation of one-dimensional nanorods. High Y b(3+) and Er(3+) content is beneficial to synthesizing the hexagonal phase of NaLaF4 nanocrystals. Furthermore, the TEM results show that the shape and size of the LaF3 nanocrystals can also be tuned by doping lanthanide ions, which provides a new route for size and shape control of nanocrystals. In addition, LaF3 nanocrystals co-doped with Y b(3+)/Tm(3+) present efficient near-infrared (NIR)-NIR upconversion luminescence. More importantly, the upconversion luminescent colors can be readily tuned from blue-white to blue by adjusting the excitation power. Therefore, it is expected that these LaF3 nanocrystals with well-controlled shape, size and NIR-NIR upconversion emission have potential applications in biomedical imaging fields. PMID:24434274

  11. Direct Search for Spin-Dependent WIMPS with CaF2 Detector

    NASA Astrophysics Data System (ADS)

    Hazama, R.; Ogawa, I.; Mukaida, K.; Ajimura, S.; Hirano, Y.; Ichihara, K.; Ishikawa, Y.; Itamura, M.; Katsuki, A.; Kishimoto, K.; Matsuoka, K.; Miyawaki, H.; Nitta, T.; Sakai, H.; Shiomi, S.; Suzuki, N.; Tanaka, Y.; Tatewaki, Y.; Tomii, S.; Umehara, S.; Yokoyama, D.; Yoshida, S.; Kishimoto, T.

    2008-04-01

    A CaF2 scintillator complex system (ELEGANT VI) is developed to search for the axial-vector coupled dark matter (WIMPs) and study the neutrino-less double beta decay of 48Ca. Active light guides of pure CaF2 crystals which are on both sides of the central CaF2(Eu) crystal act as a 4? active shield, combined with surrounding CsI(Tl) scintillators. The whole system is in operation at the underground laboratory (Oto Cosmo Observatory) located in Nara. In this article recent several improvements and our current status of the investigation are described, especially putting emphasis on the radioactive impurities of CaF2 crystal and development of flash scaler/trigger system with FPGA (Field Programmable Gate Array) to do a single photon counting and a noise-cut via photon time distribution.

  12. Highly Efficient FRET System Capable of Deep Photodynamic Therapy Established on X-ray Excited Mesoporous LaF3:Tb Scintillating Nanoparticles.

    PubMed

    Tang, Yong'an; Hu, Jun; Elmenoufy, Ahmed H; Yang, Xiangliang

    2015-06-10

    Photodynamic therapy (PDT) for deep-seated tumor is largely impeded by the limited penetration depth of excitation light in tissue. X-ray is considered as an ideal energy source to activate photosensitizers (PSs) located deep within the body with the assistance of scintillating nanoparticles (ScNPs). However, the efficacy under this concept is not satisfying due to the low scintillating luminescence and weak energy transfer from ScNPs to PSs. Here, mesoporous LaF3:Tb ScNPs were successfully synthesized by a facile hydrothermal process to act as PS carriers and X-ray energy transducers, owing to their good ionizing radiation stopping power and high luminescence efficiency. The formation mechanism of porous structure was elucidated in detail with classical crystallization theory. After a systematic investigation, LaF3:Tb ScNPs with optimized scintillating luminescence were obtained for loading Rose Bengal (RB) to establish an efficient FRET system, owing to their excellent spectral match. The FRET efficiency between ScNPs and RB was calculated to be as high as 85%. Under irradiation, enhanced (1)O2 generation induced by LaF3:Tb-RB nanocomposites via FRET process was detected. This LaF3:Tb-RB FRET system shows great potential to be applied in X-ray stimulated PDT for deep-seated tumors in the future. PMID:25974980

  13. Etch pit shapes on {110} surfaces of CaF 2 crystals

    Microsoft Academic Search

    G C Jain; L C Jain; T S Murty

    1981-01-01

    {110} surfaces of CaF2 crystals are etched with different concentrations of HCl. It is found that concentrated HCl produces characteristic rectangular\\u000a pyramidal etch pits and 2 volume percent HCl produces boat shaped etch pits. Such variations in the etch pit shapes on {110}\\u000a surfaces of CaF2 crystals with different concentrations of HCl have been explained. Concentrated H2SO4 is found to

  14. Single-point diamond turning of CaF 2 for nanometric surface

    Microsoft Academic Search

    Jiwang Yan; Jun’ichi Tamaki; Katsuo Syoji; Tsunemoto Kuriyagawa

    2004-01-01

    Single-crystal CaF 2 is an important optical material. In this work, single-point diamond turning experiments were performed to investigate the nanometric machining characteristics of CaF 2. The effects of tool feed, tool rake angle, workpiece crystal orientation and cutting fluid were examined. It was found that two major types of microfracturing differing in mechanism limited the possibility of ductile regime

  15. Evaluation of high-quality CaF2 single crystals for ultraviolet laser applications

    Microsoft Academic Search

    Shiro Sakuragi; Yutaka Taguchi; Hiroyuki Sato; Akinari Kasai; Hirokuni Nanba; Taketoshi Kawai; Satoshi Hashimoto

    2005-01-01

    High quality window\\/plate shaped CaF2 single crystals have developed by vertical Bridgman method of with diameters of 50, 100, and 200 mm and 210 mm width, 200mm length. The CaF2 windows of 30mm diameter obtained from big crystals have evaluated the transmission spectra from 120 nm to 220nm by single beam VUV spectrometer. We could obtain bulk transmission spectra by

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

    Microsoft Academic Search

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

    2009-01-01

    CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared

  17. Study on TL and OSL characteristics of indigenously developed CaF2:Mn phosphor

    Microsoft Academic Search

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

    2009-01-01

    CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared

  18. Surfactant-free synthesis, luminescent properties, and drug-release properties of LaF3 and LaCO3F hollow microspheres.

    PubMed

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

    2014-01-21

    Uniform LaF3 and LaCO3F hollow microspheres were successfully synthesized through a surfactant-free route by employing La(OH)CO3 colloidal microspheres as a sacrificial template and NaBF4 as the fluorine source. The synthetic process consists of two steps: the preparation of a La(OH)CO3 precursor via a facile urea-based precipitation and the following formation of lanthanide fluoride hollow microspheres under aqueous conditions at low temperature (50 °C) and short reaction time (3 h), without using any surfactant and catalyst. The formation of hollow spheres with controlled size can be assigned to the Kirkendall effect. It is found that the phase and structure of the products can be simply tuned by changing the pH values of the solution. Time-dependent experiments were employed to study the possible formation process. N2 adsorption/desorption results indicate the mesoporous nature of LaF3 hollow spheres. Yb(3+)/Er(3+) (Ho(3+)) and Yb(3+)/Tm(3+)-doped LaF3 hollow spheres exhibit characteristic up-conversion (UC) emissions of Er(3+) (Ho(3+)) and Tm(3+) under 980 nm laser-diode excitation, and Ce(3+)/Tb(3+)-doped LaF3 and LaCO3F emit bright yellow-green and near-white light under UV irradiation, respectively. In particular, LaF3:Yb/Er and LaCO3F:Ce/Tb hollow microspheres exhibit obvious sustained and pH-dependent doxorubicin release properties. The luminescent properties of the carriers allow them to be tracked or monitored during the release or therapy process, suggesting their high potential in the biomedical field. PMID:24364762

  19. Influence of CaF2 on the Viscosity and Structure of Manganese Ferroalloys Smelting Slags

    NASA Astrophysics Data System (ADS)

    Park, Joo Hyun; Ko, Kyu Yeol; Kim, Tae Sung

    2015-04-01

    Addition of CaF2 to the CaO-SiO2-MnO (CaO/SiO2 = 0.5) system, which corresponds qualitatively to a silicomanganese ferroalloy smelting slag, affected not only the critical (crystallization) temperature ( T CR) but also the viscosity at high temperatures, and its influence on slag properties was strongly dependent on the content of MnO in the slag. The viscosity of CaF2-free 10 mass pct MnO slag was relatively high, i.e., about 10 dPa s at 1773 K (1500 °C), but decreased continuously upon addition of CaF2 to the system. In contrast, the viscosity of the 40 pct MnO system was very low, i.e., 1 dPa s at 1773 K (1500 °C), and CaF2 did not have a large effect. This indicates that Mn2+ is a strong network modifier in manganese ferroalloy smelting slags. Nevertheless, CaF2 addition was very effective at decreasing the viscosity of low MnO slags at low temperatures. The activation energy for the viscous flow of silicate melts decreased linearly in response to CaF2 addition, but this tendency was less pronounced in the more basic composition of the slag. The effect of CaF2 on the viscosity and activation energy for viscous flow of melts was analyzed quantitatively using micro-Raman spectra of quenched glass samples and the silicate polymerization index, i.e., Q3/Q2 ratio. The polymerization index decreased continuously with increasing CaF2 content in less basic (10 pct MnO or C/S = 0.5) slags, whereas it was not affected by CaF2 content in highly basic (40 pct MnO and C/S = 1.0) slags. Bulk thermophysical properties of the CaO-SiO2-MnO-CaF2 slags were quantitatively correlated with the structural information of the slags.

  20. Growth of CdTe Films on Amorphous Substrates Using CaF2 Nanorods as a Buffer Layer

    E-print Network

    Wang, Gwo-Ching

    Growth of CdTe Films on Amorphous Substrates Using CaF2 Nanorods as a Buffer Layer NICHOLAS LICAUSI biaxially textured CdTe films were grown on biaxial CaF2 buffer layers. The CaF2 nanorods were grown by oblique angle vapor deposition and possessed a {111}h121i biaxial texture. The CdTe film was deposited

  1. Altered photoemission satellites at CaF2-and SrF2-on-Si,,111... interfaces Eli Rotenberg*

    E-print Network

    Olmstead, Marjorie

    Altered photoemission satellites at CaF2- and SrF2-on-Si,,111... interfaces Eli Rotenberg diffraction, are compared for thick, thin, and monolayer films of CaF2 and SrF2 on Si 111 . Intrinsic. The most likely explanation for the new cation satellites at the CaF2/Si 111 SrF2/Si 111 interface

  2. Microstructure and IR transmittance of spark plasma sintering translucent AlN ceramics with CaF 2 additive

    Microsoft Academic Search

    Y. Xiong; Z. Y. Fu; H. Wang; Y. C. Wang; Q. J. Zhang

    2005-01-01

    Translucent AlN ceramics were fabricated by spark plasma sintering (SPS) with and without CaF2 as sintering additive. An increase in the amount of CaF2 up to 3% in mass did not further increase the density, however improved the IR transmittance. The sample doped with 3% in mass CaF2 yielded the maximum transmittance of 54.7% in medium IR region. The microstructures

  3. Note: Characterization of CaF2/acetone bandpass photon detector with Kr filter gas

    NASA Astrophysics Data System (ADS)

    Maniraj, M.; Sekhar, B. N. Raja; Barman, S. R.

    2012-04-01

    A modified design of a CaF2/acetone bandpass photon detector that uses Kr as a filter gas to tune the energy resolution is presented. Our design combines two standard single window detector tubes to build the Kr filter gas chamber. Synchrotron radiation has been used to determine the energy resolution of the detector, as a function of Kr pressure. The improvement in the detector energy resolution by 250 meV compared to the CaF2/acetone detector is better than that reported earlier. Substantial variation in the shape of the CaF2/acetone detector response functions is observed for different acetone pressure (?3 mbar), and anode voltage (?800 V). Our analysis reveals that the changes in the shape of the detector response function are associated to different regions of the detector operation.

  4. Growth and optical properties of partially transparent Eu doped CaF2 ceramic

    NASA Astrophysics Data System (ADS)

    Ghosh, Manoranjan; Sen, Shashwati; Pitale, S. S.; Goutam, U. K.; Shinde, Seema; Patra, G. D.; Gadkari, S. C.

    2014-04-01

    Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size˜12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu3+ as the dominant substituting ions at the Ca2+ sites of CaF2 lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu3+ sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites.

  5. Dark matter search with CaF2 scintillator at Osaka

    NASA Astrophysics Data System (ADS)

    Ogawa, I.; Hazama, R.; Mukaida, K.; Kishimoto, K.; Sakai, H.; Katsuki, A.; Itamura, T.; Umehara, S.; Yoshida, S.; Kishimoto, T.

    2008-07-01

    A CaF2 scintillator complex system (ELEGANT VI) is developed to search for the axial-vector coupled dark matter (WIMPs) and study the neutrino-less double beta decay of 48 Ca. Active light guides of pure CaF2 crystals which are on both sides of the central CaF2(Eu) crystal act as a 4? active shield, combined with surrounding CsI(T1) scintillators. The whole system is at the underground laboratory (Oto Cosmo Observatory) located in Nara. In this article our current status of the investigation are described, especially putting emphasis on the development of flash scaler to do a single photon counting.

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

    PubMed Central

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  8. > Upconversion Nanophosphors (UCNPs) areYb, Ln (Er, Tm, and Ho) doped into hosts of NaYF4, LaF3, Y2O3,

    E-print Network

    Petta, Jason

    > Upconversion Nanophosphors (UCNPs) areYb, Ln (Er, Tm, and Ho) doped into hosts of NaYF4, LaF3, Y2 by multi excitation. > Prof. Ju'sgroup hasdeveloped NaYF4 based UCNPs. Optimizing BlueEmission Up of 20% Yband 2% Er isdoped into the NaYF4 structure. (authorized) (e.g.2) For blue emissions, an ion

  9. The Analysis of Main Dosimetric Glow Peaks in CaF2:Tm (TLD-300)

    NASA Astrophysics Data System (ADS)

    Vural, E. Kafadar; Metin, Bedir; A. Necmeddin, Yaz?c?; Tülin, Günal

    2013-05-01

    The thermoluminescence properties of CaF2:Tm (TLD-300) are examined in detail after ?-irradiation at room temperature. The glow curve of the sample shows two main dosimetric glow peaks: P3 (at ~150°C) and P5 (at ~250°C). The additive dose, variable heating rate, computer glow curve deconvolution, peak shape and three points methods are used to evaluate the trapping parameters, namely the order of kinetics (b), activation energy (E) and frequency factor (s) associated with the dosimetric thermoluminescent glow peaks (P3 and P5) of CaF2:Tm (TLD-300) after different dose levels with ?-irradiation.

  10. Small angle grain boundary Ge films on biaxial CaF 2/glass substrate

    NASA Astrophysics Data System (ADS)

    Gaire, C.; Clemmer, P. C.; Li, H.-F.; Parker, T. C.; Snow, P.; Bhat, I.; Lee, S.; Wang, G.-C.; Lu, T.-M.

    2010-02-01

    We demonstrated that it is possible to grow single crystal-like Ge films on a glass substrate using a biaxially textured CaF 2 buffer layer at a low temperature of ˜400 °C. The CaF 2 buffer layer with the (1 1 1)<1 2 1> biaxial orientation was grown by the oblique angle deposition technique and characterized by X-ray pole figure analysis. Transmission electron microscopy revealed that the Ge(1 1 1) heteroepitaxial films possess a single crystal-like structure with small angle grain boundaries of ?2° misorientation.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  13. Molecular beam epitaxy growth of PbSe on BaF2-coated Si,,111... and observation of the PbSe growth interface

    E-print Network

    McCann, Patrick

    Se epilayer to copper plates has been successfully accomplished by bonding followed by removal of the BaF2 /Ca-thick PbSe epilayers was accomplished by bonding the MBE-grown samples face down to polished copper plates followed by the removal of the silicon substrate by dissolving the BaF2 buffer layer in water. High

  14. Dark Matter Search with CaF2 Scintillators in Osaka

    NASA Astrophysics Data System (ADS)

    Ogawa, I.; Kishimoto, T.; Hazama, R.; Ajimura, S.; Matsuoka, K.; Suzuki, N.; Nitta, T.; Miyawaki, H.; Shiomi, S.; Tanaka, Y.; Ejiri, H.; Kudomi, N.; Kume, K.; Ohsumi, H.; Fushimi, K.

    2000-01-01

    A detector system which consists of CaF2 scintillators surrounded by active and passive shields, is developed to search for spin coupled dark matter. The whole system is in operation at the underground laboratory located in Nara (Oto Cosmo Observatory) which has effectively 1.2 km water equivalent shield. In this article our current status of the investigation is described.

  15. Neutron response of the LAMBDA spectrometer and neutron interaction length in BaF2

    E-print Network

    Balaram Dey; Debasish Mondal; Deepak Pandit; S. Mukhopadhyay; Surajit Pal; K. Banerjee; Srijit Bhattacharya; A. De; S. R. Banerjee

    2013-06-17

    We report on the neutron response of the LAMBDA spectrometer developed earlier for high-energy gamma-ray measurement. The energy dependent neutron detection efficiency of the spectrometer has been measured using the time-of-flight (TOF) technique and compared with that of an organic liquid scintillator based neutron detector (BC501A). The extracted efficiencies have also been compared with those obtained from Monte Carlo GEANT4 simulation. We have also measured the average interaction length of neutrons in the BaF2 crystal in a separate experiment, in order to determine the TOF energy resolution. Finally, the LAMBDA spectrometer has been tested in an in-beam-experiment by measuring neutron energy spectra in the 4He + 93Nb reaction to extract nuclear level density parameters. Nuclear level density parameters obtained by the LAMBDA spectrometer were found to be consistent with those obtained by the BC501A neutron detector, indicating that the spectrometer can be efficiently used as a neutron detector to measure the nuclear level density parameter.

  16. Neutron response of the LAMBDA spectrometer and neutron interaction length in BaF2

    NASA Astrophysics Data System (ADS)

    Dey, Balaram; Mondal, Debasish; Pandit, Deepak; Mukhopadhyay, S.; Pal, Surajit; Banerjee, K.; Bhattacharya, Srijit; De, A.; Banerjee, S. R.

    2013-11-01

    We report on the neutron response of the LAMBDA spectrometer developed earlier for high-energy ?-ray measurement. The energy dependent neutron detection efficiency of the spectrometer has been measured using the time-of-flight (TOF) technique and compared with that of an organic liquid scintillator based neutron detector (BC501A). The extracted efficiencies have also been compared with those obtained from Monte Carlo GEANT4 simulation. We have also measured the average interaction length of neutrons in the BaF2 crystal in a separate experiment, in order to determine the TOF energy resolution. Finally, the LAMBDA spectrometer has been tested in an in-beam-experiment by measuring neutron energy spectra in the 4He+93Nb reaction to extract nuclear level density parameters. Nuclear level density parameters obtained by the LAMBDA spectrometer were found to be consistent with those obtained by the BC501A neutron detector, indicating that the spectrometer can be efficiently used as a neutron detector to measure the nuclear level density parameter.

  17. Optical free induction decay of the 4G {5}/{2} ? 6H {5}/{2} transition of LaF 3:Sm 3+

    NASA Astrophysics Data System (ADS)

    Macfarlane, R. M.; Shelby, R. M.

    1986-06-01

    The population decay time ( T1) and optical dephasing time ( T2) of the 4G {5}/{2} ? 6H {5}/{2} transition LaF 3:Sm 3+ at 5598 Å has been measured. At 1.6 K, T1 = 7.7 ms and T2 = 110 ns. The oscillator strength of this transition is 6 × 10 -9. The dephasing time was measured by observing the optical free induction decay following intracavity laser frequency switching or intracavity phase switching.

  18. Influence of SiO2 undercoat on the laser-induced damage threshold of 355 nm LaF3/AlF3 multilayer reflectors

    NASA Astrophysics Data System (ADS)

    Li, Xu; Zhang, Weili; Sun, Jian; Hou, Yongqiang; Liu, Wenwen; He, Kai; Wei, Chaoyang; Yi, Kui

    2013-07-01

    In the pursuit for 355 nm high laser resistant dielectric coatings, layer-pair number of 10 and 15 LaF3/AlF3 high reflectors with and without SiO2 undercoat were prepared on BK7 substrates. The results indicate considerable increase in 355 nm laser-induced damage threshold (LIDT) for samples with undercoat. The samples were analyzed in Normalized Electric Field Intensity distribution, total stress, damage depth and damage morphology, revealing that SiO2 undercoat benefits fluoride coatings by shielding substrate defects and reducing coating defects.

  19. Effect of heat treatment in HF atmosphere on the optical and electrical properties of BaF 2 ceramics

    Microsoft Academic Search

    N. I. Sorokin; D. N. Karimov; O. N. Komar’kova; E. A. Krivandina; A. N. Smirnov; S. P. Chernov; B. P. Sobolev

    2009-01-01

    Using optical spectroscopy and complex impedance measurements, we have studied the transmission spectra and electrical conductivity\\u000a of different BaF2 samples: ceramic prepared by vacuum hot pressing (200 MPa, 870°C, 20 min), the same ceramic after heat treatment in a reactive\\u000a HF atmosphere (1200°C, 120 min), and a single crystal grown from the melt in vacuum. Heat treatment of the as-prepared

  20. 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.

  1. Nonradiative relaxation rates in CaF 2:Sm 2+ measured by photoionization spectral holeburning

    NASA Astrophysics Data System (ADS)

    Macfarlane, R. M.; Brocklesby, W. S.; Bloch, P. D.; Harley, R. T.

    1986-05-01

    The temperature dependence of the width of spectral holes burned in the 4f 6A 1g?4f 55d A 1u absorption line (6958 Å) of CaF 2:Sm 2+ has been measured and used to determine the phonon coupling which controls nonradiative relaxation between the A 1u and E u levels. We confirm an assertion made by Akimov and Kaplyanskii that the phonon coupling among the lowest three 4f 55d levels of CaF 2:Sm 2+ exhibits strong selection rules. In particular, the "deformational" E g phonons are two orders of magnitude more effective than "rotational" T 1g phonons in inducing nonradiative relaxation.

  2. The measured electron response nonproportionalities of CaF2 , BGO, and LSO

    Microsoft Academic Search

    T. D. Taulbee; B. D. Rooney; W. Mengesha; J. D. Valentine

    1997-01-01

    To study the light yield nonproportionality and intrinsic energy resolution of inorganic scintillators, a Compton coincidence technique was previously designed, implemented and benchmarked. This technique provides the ability to accurately measure the electron response of scintillation materials and thus provides an accurate means of studying these characteristics. In this study, the electron responses of two “classic” scintillators (CaF2(Eu) and Bi4

  3. Electronic structure of metal CoSi2\\/insulator CaF2 superlattice

    Microsoft Academic Search

    Koji Akai; Mitsuru Matsuura

    1999-01-01

    Electronic structure of metal CoSi2\\/insulator CaF2 superlattice is studied by the full-potential linearized augmented plane-wave method, based on the density-functional theory. From the comparison of calculated total energies for some atomic configurations in the superlattice interface, it is concluded that the Si layer is in contact with a F layer at the interface. Using this atomic configuration, the band structure

  4. Zeeman effect in CaF,,2 R. V. Krems,a)

    E-print Network

    Krems, Roman

    Zeeman effect in CaF,,2 3Õ2... R. V. Krems,a) D. Egorov, J. S. Helton, K. Maussang, S. V. Nguyen August 2004; accepted 16 September 2004 The Zeeman effect in the excited A 2 3/2 state of CaF is measured to interactions with an external mag- netic field can be controlled; measurements of the Zeeman effect may reveal

  5. Dosimetry properties of Tm-doped single CaF 2 crystals

    Microsoft Academic Search

    B Marczewska; P Bilski; M Budzanowski; P Olko; V Chernov

    2001-01-01

    The dosimetry properties of thermoluminescence CaF2:Tm detectors with thulium concentrations of 0.1%, 0.3%, 0.5%, 0.6% and 0.7%, developed from single crystals grown by the Stockbarger method at the Institute of Geochemistry, Irkutsk, Russia, were investigated. The relative TL efficiency, ?, after 5.3MeV Am-241 ?-particle irradiation and the Cs-137 ?-ray dose response after doses up to 10Gy, of interest for radiation

  6. Structural transitions and relaxation processes during the epitaxial growth of ultrathin CaF2 films on Si(111)

    E-print Network

    Deiter, Carsten

    The structure and morphology of ultrathin lattice matched CaF2 films of very few monolayers thickness, which were deposited on Si(111) substrates by molecular-beam epitaxy, have been studied in situ by synchrotron based ...

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

    PubMed

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

    2013-08-15

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

  8. Electron-paramagnetic-resonance investigations of divalent einsteinium-253 in SrCl2 and BaF2

    Microsoft Academic Search

    L. A. Boatner; R. W. Reynolds; C. B. Finch; M. M. Abraham

    1976-01-01

    The electron-paramagnetic-resonance (EPR) spectrum of 253Es2+ (5f11 electronic configuration) has been observed in the cubic single-crystal hosts BaF2 and SrCl2. The spectrum obtained at ~24 GHz and a temperature of 4.2 K exhibited a well-resolved eight-line hyperfine pattern (I=72) for 253Es2+ in both host crystals. The magnetic field positions of the observed transitions were independent of the magnetic field orientation,

  9. Photothermal transformation of color centers in CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Shcheulin, A. S.; Angervaks, A. E.; Aksenova, K. A.; Gainutdinov, R. V.; Ryskin, A. I.

    2015-04-01

    Photothermal transformations of color centers in additively colored calcium fluoride crystals and in a colored crystal with a recorded hologram have been investigated. It is shown that the absorption spectrum of a colored crystal can be reconstructed within the entire transparency range of the matrix crystal by varying both factors affecting the sample—actinic radiation wavelength and temperature—as well as the duration of their effect. This possibility is important for the application of additively colored CaF2 crystals as a holographic medium.

  10. CONTROL OF LASER RADIATION PARAMETER: Temporal evolution of a coherent stimulated radiation pulse in the three-level system in a Pr3+ : LaF3 crystal

    NASA Astrophysics Data System (ADS)

    Agafonov, Aleksandr I.; Grigoryan, Grigorii G.; Znamenskiy, Nikolay V.; Manykin, Eduard A.; Orlov, Yurii V.; Petrenko, Evgenii A.; Shashkov, Andrei Yu

    2004-09-01

    The temporal characteristics of coherent stimulated radiation at the 3P0— 3H6 transition in the Pr3+ ion in a LaF3 matrix are studied by tuning the pump frequency in the vicinity of the 3H4— 3P0 transition. It is found that in the case of the exact tuning to the resonance, a laser pulse, consisting of a train of picosecond spikes of total duration about 10 ns, was delayed by 3-4 ns with respect to the pump pulse onset. As the pump pulse detuning was increased, the shape of the coherent laser pulse changes and its delay increased up to 10 ns. The experimental results are interpreted theoretically.

  11. Crystallization kinetics and spectroscopic investigations on Tb3+ and Yb3+ codoped glass ceramics containing CaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Huang, Lihui; Qin, Guanshi; Arai, Yusuke; Jose, Rajan; Suzuki, Takenobu; Ohishi, Yasutake; Yamashita, Tatsuya; Akimoto, Yusuke

    2007-11-01

    Transparent Tb3+ and Yb3+ codoped oxyfluoride glass ceramics containing CaF2 nanocrystals were prepared by melt quenching and subsequent heat treatment. Crystallization kinetics of CaF2 nanocrystals was investigated by differential scanning calorimetric method. The average apparent activation energy Ea of the crystallization was ˜498kJ /mol. Moreover, the value of the Avrami exponent n was 1.01. These results suggest that the crystallization mechanism of CaF2 is a diffusion controlled growth process of needles and plates of finite long dimensions. X-ray diffraction patterns and transmission electron microscopy image confirmed the CaF2 nanocrystals in the glass ceramic. Ultraviolet (UV) and visible emission spectra of the as-made glass and the glass ceramic with an excitation of a 974nm laser diode were recorded at room temperature. An intense UV emission at 381nm was observed in the glass ceramic. The origin of the enhancement of the emission at 381nm was investigated using spectroscopic technique and Judd-Ofelt analysis. The enhancement of the emission at 381nm could be attributed to the change of the ligand field of Tb3+ ions due to the incorporation of some Tb3+ and Yb3+ ions into CaF2 nanocrystals in the glass ceramic.

  12. New fast scintillators on the base of BaF2 crystals with increased light yield of 0.9 ns luminescence for TOF PET

    NASA Astrophysics Data System (ADS)

    Seliverstov, D. M.; Demidenko, A. A.; Garibin, E. A.; Gain, S. D.; Gusev, Yu. I.; Fedorov, P. P.; Kosyanenko, S. V.; Mironov, I. A.; Osiko, V. V.; Rodnyi, P. A.; Smirnov, A. N.; Suvorov, V. M.

    2012-12-01

    Presently a growing interest to time-of-flight PET is observed in a number of experimental works using LSO as scintillation crystals. We propose to use as scintillators BaF2 crystals and ceramics produced from identical material but with essentially more high light yield in the fast component of emission spectra. A light yield amplification of BaF2 single crystal fast component of 2 to 2.5 times is achieved in crystals annealed in CF4 and doped by scandium at concentration of 0.5 to 2.0 mol%. Ceramics from BaF2 doped by Sc have amplification factor order of 1.7 to 2.5. One can consider to produce scintillator of size 10×10×20 mm3with an improved light transmission of ceramics in the range (200-250) nm up to single crystal level and with a light yield of 0.9 ns component at the level of 3000 to 4000 ph/MeV. Another promising scintillator obtained in our collaboration is BaF2:Tm3+. In this case one can have a scintillator in UV range with a time decay 0.9 ns and a strongly decreased yield of BaF2 slow component.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  15. Effective segregation coefficient of Er3+ ions in ErF3-doped CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Munteanu, M.; Stef, M.; Bunoiu, O.; Nicoara, I.

    2010-03-01

    ErF3-doped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the characteristic peaks of the Er3+ ions. The dopant distribution along two crystals has been investigated using the optical absorption method. The effective segregation coefficient of the Er3+ ions has been calculated using the classical Scheil relationship between the impurity concentration and the crystal growth conditions. The effective segregation coefficient of the Er3+ions in the CaF2 host depends slightly on the doping concentration, and varies between 0.99 and 1.03, for 0.8 mol % ErF3 and 2 mol % ErF3-doped CaF2 crystals, respectively.

  16. Accelerated Fabrication and Upconversion Luminescence of Yb3+/Er3+-Codoped CaF2 Nanocrystal by Microwave Heating

    NASA Astrophysics Data System (ADS)

    Li, Yuanyao; Liu, Tiegen; Du, Yang

    2012-08-01

    Because of the drastic reduction in processing time and energy cost, the microwave radiation applied as an alternative method to synthesize solids has been recently investigated. Yb3+/Er3+-codoped CaF2 (CaF2:Yb3+/Er3+) nanocrystals are fabricated using this approach, and the phenomenon of microwave-enhanced mass transport is observed in this process. The upconversion mechanisms and properties of such nanocrystal have also been studied. Charge compensation and microwave ponderomotive effect are considered as the cause of the specific up-conversion spectrum. This synthesis method and the as-prepared CaF2:Yb3+/Er3+ nanocrystal may be potentially useful for advanced phosphor, imaging, anti-counterfeiting labeling, etc.

  17. Influence of the Er3+ Ions Concentration on the Structural Deformation in Doped CaF2 Crystals

    NASA Astrophysics Data System (ADS)

    Nicoara, I.; Munteanu, M.; Stef, M.; Preda, E.; Buse, G.

    2010-08-01

    Calcium fluoride crystals doped with ErF3 were grown using the Bridgman technique. The dissolved Er ions in CaF2 are trivalent and this leads to the formation of charge-compensating defects. The local compensation, by an interstitial or substitutional F- ion, creates the isolated centers, with various crystal field symmetries of the trivalent erbium ions in the CaF2 host. To study the charge-compensating defects in these crystals we used two methods: the optical absorption spectra and the dielectric spectra.

  18. Convertible holograms in CaF2 crystals with color centers

    NASA Astrophysics Data System (ADS)

    Angervaks, Alexandr E.; Shcheulin, Aleksandr S.; Ryskin, Aleksandr I.

    2013-05-01

    When recording hologram in ionic CaF2 crystal with color centers, the center conversion is accompanied with their spatial redistribution. The peculiar diffusion-drift mechanism of the recording is responsible for the extremely high hologram stability to both heating and illumination of the sample with a hologram by non-coherent radiation. However such photo-thermal treatment of the sample results in partial or total transformation of the center type and modification in their space distribution. Thus, keeping the hologram, such treatment influences its character of diffraction response, diffraction efficiency and profile. This work describes the mechanism and the character of these changes. It is shown that photo-thermal treatment can be used for fabrication of thick (up to 10 mm thickness) high stable holograms when reading out both in visible and infrared ranges of the spectrum.

  19. Fabrication, properties and thermo-luminescent dosimetric application of CaF2:Mn transparent ceramic

    NASA Astrophysics Data System (ADS)

    Singh, S. G.; Sen, Shashwati; Patra, G. D.; Bhattacharya, S.; Singh, A. K.; Shinde, Seema; Gadkari, S. C.

    2012-09-01

    An optically transparent ceramic of CaF2:Mn has been prepared by hot pressing of nano-phase powders under vacuum conditions. The transmission recorded for a 1 mm thick sample at 800 nm was about 50%. A scanning electron micrograph exhibited a pore-free structure without any secondary phases at the grain boundaries. The doping concentration of Mn and its oxidation state as determined using secondary ion mass spectrometry and X-ray photoemission spectroscopy were 1.5 at.% and Mn2+, respectively. The photo-luminescence properties of these ceramics were studied and their application as a thermo-luminescent dosimeter has been established. These ceramics were able to measure low level doses down to about 3 mGy and exhibited a linear output up to 100 mGy.

  20. A Unique TAS Setup for high multiplicity events at VECC, Kolkata using BaF2 detectors

    NASA Astrophysics Data System (ADS)

    Mukherjee, G.; Dey, Balaram; Mukhopadhyay, S.; Pandit, Deepak; Pal, Surajit; Pai, H.; Banerjee, S. R.

    2014-03-01

    A granular total absorption spectrometer (TAS) has been developed at the Variable Energy Cyclotron Centre, Kolkata, India using 50 elements of BaF2 detectors and covering 4?. The advantage with such a granular setup is that one can get sum spectrum with the condition of different multiplicity hits in an event. It has been shown that one can get clean sum-peaks devoid of individual peaks with the choice of two or higher fold of multiplicity. The large granularity makes it a unique TAS setup particularly for the high multiplicity events. The set up has been tested using different radioactive sources with one, two or multiple ? rays in cascade. The set up is ready to be used online.

  1. Morphology and texture evolution of nanostructured CaF2 films on amorphous substrates under oblique incidence flux.

    PubMed

    Gaire, C; Snow, P; Chan, T-L; Yuan, W; Riley, M; Liu, Y; Zhang, S B; Wang, G-C; Lu, T-M

    2010-11-01

    The morphology and biaxial texture of vacuum evaporated CaF(2) films on amorphous substrates as a function of vapour incident angle, substrate temperature and film thickness were investigated by scanning electron microscopy, x-ray pole figure and reflection high energy electron diffraction surface pole figure analyses. Results show that an anomalous [220] out-of-plane texture was preferred in CaF(2) films deposited on Si substrates at < 200?°C with normal vapour incidence. With an increase of the vapour incident angle, the out-of-plane orientation changed from [220] to [111] at a substrate temperature of 100?°C. In films deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at 100?°C to [111] at 400?°C. In films deposited with an oblique vapour incidence at 100?°C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness (20 nm or more). Using first principles density functional theory calculation, it was shown that [220] texture formation is a consequence of energetically favourable adsorption of CaF(2) molecules onto the CaF(2)(110) facet. PMID:20921590

  2. Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n

    E-print Network

    Wang, Gwo-Ching

    Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n , P.C. Clemmer of semiconductor on an amorphous substrate such as glass results in either polycrystalline or fiber textured film report a heteroepitaxial growth of biaxially textured Ge film on glass substrate with biaxially textured

  3. Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n

    E-print Network

    Wang, Gwo-Ching

    Small angle grain boundary Ge films on biaxial CaF2/glass substrate C. Gaire a,n , P.C. Clemmer demonstrated that it is possible to grow single crystal-like Ge films on a glass substrate using a biaxially such as glass results in either polycrystalline or fiber textured film, biaxially textured films of insulating

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

    EPA Science Inventory

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

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

    PubMed

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

    2011-01-31

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

  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. Comprehensive structural and optical characterization of MBE grown MoSe2 on graphite, CaF2 and graphene

    NASA Astrophysics Data System (ADS)

    Vishwanath, Suresh; Liu, Xinyu; Rouvimov, Sergei; Mende, Patrick C.; Azcatl, Angelica; McDonnell, Stephen; Wallace, Robert M.; Feenstra, Randall M.; Furdyna, Jacek K.; Jena, Debdeep; Xing, Huili Grace

    2015-06-01

    We report the structural and optical properties of a molecular beam epitaxy (MBE) grown 2-dimensional (2D) material molybdenum diselenide (MoSe2) on graphite, CaF2 and epitaxial graphene. Extensive characterizations reveal that 2H–MoSe2 grows by van-der-Waals epitaxy on all three substrates with a preferred crystallographic orientation and a Mo:Se ratio of 1:2. Photoluminescence at room temperature (?1.56 eV) is observed in monolayer MoSe2 on both CaF2 and epitaxial graphene. The band edge absorption is very sharp, <60 meV over three decades. Overcoming the observed small grains by promoting mobility of Mo adatoms would make MBE a powerful technique to achieve high quality 2D materials and heterostructures.

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

    E-print Network

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

    2007-10-11

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

    A large BaF 2 detector array along with its dedicated CAMAC electronics and VME based data acquisition system has been designed, constructed and installed successfully at VECC, Kolkata for studying high energy ? rays ( >8 MeV). The array consists of 162 detector elements. The detectors were fabricated from bare barium fluoride crystals (each measuring 35 cm in length and having cross-sectional area of 3.5×3.5 cm2). The basic properties of the detectors (energy resolution, time resolution, efficiency, uniformity, fast to slow ratio, etc.) were studied exhaustively. Complete GEANT3 Monte Carlo simulations were performed to optimize the detector design and also to generate the response function. The detector system has been used successfully to measure high energy photons from 113Sb, formed by bombarding 145 and 160 MeV 20Ne beams on a 93Nb target. The measured experimental spectra are in good agreement with those from a modified version of the statistical model code CASCADE. In this paper, we present the complete description of this detector array along with its in-beam performance.

  10. Materials for high-energy laser windows: oxyfluoride glass vs. fusion-cast CaF2

    NASA Astrophysics Data System (ADS)

    Klein, Claude A.

    2005-05-01

    The process of selecting suitable materials for high-energy laser windows involves considerations realting to (a) the flexural strength, (b) the thermal stresses, and (c) the optical distortion. Optical distortion ocnsiderations strongly favor low-absorbtion materials ythat exhibit a negitive thermo-optic coefficient (dn/dT) in conjunction with minimal stress-birefringence (qd\\overline -q? ~=0). For this reason, calcium floride has been the primary candidate for many years, but the efforts to strengthen this material have not been successful. Recently, a new glass compostion-oxyfloride glass (OFG)-has been promoted as an ideal solution in the sense that it will allow fabricating large "athermal" windows for operation at the chemical oxygen-iodine laser wavelength. It is, therefore, of interest to properly assess the merits of OFG in comparison to CaF2, which we do here on the basis of available (Dec '04) property data for fusion-cast CaF2 and OFG. Oxyfloride glass was found to be deficient in regard to thermal diffusivity, which may lead to excessive coating-induced compressive stresses, and stress- birefringence, which rules out creating a distortion-free window. It is suggested that future efforts should be directed at strengthening CaF2 in view of this material's exceptionally low absorbtion and almost no stress-birefringence

  11. August 15, 2004 / Vol. 29, No. 16 / OPTICS LETTERS 1879 High-power tunable diode-pumped Yb3+:CaF2 laser

    E-print Network

    Paris-Sud XI, Université de

    will permit exploitation of these favorable characteristics, hosts with high thermal conductivities structure that leads to broad absorption and emission bands, comparable to those of glasses,5 which CaF2 potentially suitable as a ceramic l

  12. Soft X-ray emission spectroscopy study of CaF 2(film)/Si(111): non-destructive buried interface analysis

    NASA Astrophysics Data System (ADS)

    Iwami, M.; Kusaka, M.; Hirai, M.; Tagami, R.; Nakamura, H.; Watabe, H.

    1997-06-01

    A soft X-ray emission spectroscopy (SXES) study under an energetic electron irradiation is first applied to a non-destructive buried interface analysis of a CaF 2(film ˜ 40 nm)/Si(111) contact system, where the energy of primary electrons, Ep, is ? 5 keV. The present work has explored the usefulness of the application of the SXES method to the interface study to give rise to the following findings: the CaF 2/Si(111) interface shows rather sharp transition from the top CaF 2 to the substrate Si, there certainly is a Ca-silicide layer at the CaF 2/Si(111) interface, the thickness of the silicide layer is estimated to be less than several nm, and the e-beam excited SXES non-destructive study is very powerful to analyze a specimen with rather thick top film (> 40 nm) and thin interface layer (< several nm).

  13. Characterization of thin epitaxial CaF2 layers on Si(111) using impurity luminescent probes, X-ray standing waves and X-ray diffractometry

    Microsoft Academic Search

    J. C. Alvarez; K. Hirano; A. Yu Kazimirov; M. V. Kovalchuk; A. Ya Kreines; N. S. Sokolov; N. L. Yakovlev

    1992-01-01

    The structure crystalline quality and elastic strain of CaF2 epitaxial layers on Si(111) substrates have been studied using an impurity photoluminescent probe, X-ray standing waves and X-ray rocking curves. Molecular beam epitaxy was used to grow 10 nm thick films. The CaF2\\/Si(111) interface was formed at 770 degrees C and the films were grown at temperatures of 100, 550, 660

  14. December 1, 2004 / Vol. 29, No. 23 / OPTICS LETTERS 2767 High-power diode-pumped Yb3+:CaF2 femtosecond laser

    E-print Network

    Boyer, Edmond

    December 1, 2004 / Vol. 29, No. 23 / OPTICS LETTERS 2767 High-power diode-pumped Yb3+:CaF2 is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb31:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at

  15. Phase transitions and equations of state of alkaline earth fluorides CaF2 and SrF2 to 95 GPa

    Microsoft Academic Search

    S. M. Dorfman; F. Jiang; Z. Mao; A. Kubo; V. Prakapenka; T. S. Duffy

    2007-01-01

    AX2 compounds include a wide range of oxides and salts of broad interest in geoscience, materials science and chemistry, such as SiO2 and CaF2, and have in common a sequence of phase transitions dependent on ionic size ratio and electronic properties (Leger and Haines, 1997). Shock compression studies have shown that CaF2 transforms to a highly incompressible phase above 1

  16. Mid-infrared Verdet coefficient studies in GaAs, BaF2, and LaSrGaO4, and ZnSe

    Microsoft Academic Search

    Myoung-Hwan Kim; Volker Kurz; Gheorghe Acbas; Chase Ellis; John Cerne

    2009-01-01

    We measure the mid-infrared (wavelength lambda=11 - 0.8 mum; 0.1 - 1.5 eV) Faraday rotation and ellipticity in GaAs, BaF2, LaSrGaO4, and ZnSe. Since these materials are commonly used as substrates and windows in the mid-infrared, it is important to measure the Faraday signals for background subtraction and to test the accuracy of our measurement techniques. The light sources are

  17. Hyperfine and quadrupole interactions of trigonal 157 Gd 3+ centers in SrF 2 and BaF 2 . Analysis of distortions in the nearest atomic environment

    Microsoft Academic Search

    A. D. Gorlov; A. P. Potapov

    2000-01-01

    Trigonal 157Gd3+ impurity centers in SrF2 and BaF2 were experimentally studied by EPR and double electron-nuclear resonance (DENR) techniques. Parameters of the hyperfine and\\u000a quadrupole interactions between these centers were determined. Possible distortions of the nearest atomic environment of the\\u000a impurity centers are estimated within the framework of a superposition model using the EPR and DENR data for the centers

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  19. Enhanced 2.0 microm emission and gain coefficient of transparent glass ceramic containing BaF2: Ho3+,Tm3+ nanocrystals.

    PubMed

    Zhang, W J; Zhang, Q Y; Chen, Q J; Qian, Q; Yang, Z M; Qiu, J R; Huang, P; Wang, Y S

    2009-11-01

    Transparent glass ceramic containing BaF(2):Ho(3+),Tm(3+) nanocrystals has been prepared by melt quenching and subsequent thermal treatment. The precipitation of BaF(2) nanocrystals was confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Intense 2.0 microm fluorescence originating from Ho(3+): (5)I(7) --> (5)I(8) transition was achieved upon excitation with 808 nm laser diode. A large ratio of forward Tm(3+) --> Ho(3+) energy transfer constant to that of backward process indicated high efficient energy transfer from Tm(3+)((3)F(4)) to Ho(3+)((5)I(7)), benefited from the reduced ionic distances of Tm(3+)-Tm(3+) and Tm(3+)-Ho(3+) pairs and low phonon energy environment with the incorporation of rare-earth ions into the precipitated BaF(2) nanocrystals. The results indicate that glass ceramic is a promising candidate material for 2.0 microm laser. PMID:19997333

  20. NUCLEAR PHYSICS: Phonon Dispersion and Thermodynamics Properties of CaF2 via Shell Model Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Hu, Cui-E; Zeng, Zhao-Yi; Gong, Min; Gou, Qing-Quan

    2009-05-01

    The phonon and thermodynamics properties of face-centered cubic CaF2 at high pressure and high temperature are investigated by using the shell model interatomic pair potential within General Utility Lattice Program (GULP). The phonon dispersion curves and the corresponding density of state (PDOS) in this work are consistent with the experimental data and other theoretical results. The transverse optical (TO) and longitudinal optical (LO) mode splitting as well as heat capacity at constant volume CV and entropy S versus pressure and temperature are also obtained.

  1. Concentration dependence of the Judd-Ofelt parameters of Er3 + ions in CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Preda, E.; Stef, M.; Buse, G.; Pruna, A.; Nicoara, I.

    2009-03-01

    In the present study, various concentrations of ErF3-doped CaF2 crystals were grown using the vertical Bridgman method. The Judd-Ofelt intensity parameters ? t (t= 2, 4, 6) for f-f transitions of Er3 + ions were determined from optical absorption spectra. The concentration dependence of the intensity parameters radiative transition probability, oscillator strength, branching ratio and radiative lifetime was also investigated. The predicted radiative lifetimes were compared with those of the Er3 + transitions reported in various hosts. Apart from the green and red emissions, reported by other researchers, a UV (314 nm) emission band was observed, not reported previously.

  2. Electrical conductivity of NaF-AlF3-CaF2-Al2O3 melts

    NASA Astrophysics Data System (ADS)

    Bakin, K. B.; Simakova, O. N.; Polyakov, P. V.; Mikhalev, Yu. G.; Simakov, D. A.; Gusev, A. O.

    2010-08-01

    The electrical conductivity of NaF-AlF3-Al2O3 melts with a CaF2 concentration of 5 wt % is measured at a continuously varying cell constant when the molar cryolitic ratio CR = [NaF]/[AlF3] changes from 1.2 to 2.0 [1, 2]. The experimental data are used to obtain a regression equation to describe the dependence of the electrical conductivity of the melts under study on CR, the alumina content, and temperature { ?] = f(CR, [Al2O3], T)}.

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

    NASA Astrophysics Data System (ADS)

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

    1989-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  5. Cobalt epitaxial nanoparticles on CaF2/Si(111): Growth process, morphology, crystal structure, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Sokolov, N. S.; Suturin, S. M.; Krichevtsov, B. B.; Dubrovskii, V. G.; Gastev, S. V.; Sibirev, N. V.; Baranov, D. A.; Fedorov, V. V.; Sitnikova, A. A.; Nashchekin, A. V.; Sakharov, V. I.; Serenkov, I. T.; Shimada, T.; Yanase, T.; Tabuchi, M.

    2013-03-01

    We study molecular beam epitaxy growth, morphology, crystal structure, and magnetic properties of Co nanoislands on CaF2/Si(111) surface. In order to have a full appreciation of complex growth kinetics at different stages, a comprehensive study of Co growth on CaF2 is carried out by atomic force, scanning electron, and transmission electron microscopies in the direct space, as well as by x-ray and electron diffraction in the reciprocal space. These experimental data are complemented by theoretical modeling. Magnetic properties are characterized by magneto-optical Kerr effect and superconducting quantum interference device magnetometries. Key effects influencing the Co growth on fluorite are addressed, including the sticking probability, the preferential nucleation sites, the size and shape time evolution, the dependence of Co morphology on temperature and Co exposure, and the coalescence mechanism. The two-stage deposition technique is developed, whereby the low-temperature seeding stage is used to facilitate Co nucleation, and the follow-up high-temperature deposition yields Co particles with high crystalline quality. Our results enable precise control over the resulting morphology, spatial ordering, and crystal structure affecting the magnetic properties. In particular, it is demonstrated that the transformation from dense to isolated Co nanoparticles leads to the change of the in-plane and out-of-plane magnetic anisotropy and also the sign of polar and longitudinal magneto-optical Kerr effects.

  6. 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

    2015-04-01

    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.

  7. Refractive-index dispersion for BaF2-GdF3-ZrF4-AlF3 glasses.

    PubMed

    Mitachi, S; Miyashita, T

    1983-08-15

    Refractive-index dispersion measurements were performed on bulk specimens of 2-, 4-, or 6-mol % AlF(3) doped 33BaF(2)-4GdF(3)-63ZrF(4) (mol %) glass and 4-mol % LiF, CsF, YF(3), CdF(2), SnF(2), or PbF(2) doped 31.68BaF(2)-3.84GdF(3)-60.48ZrF(4)-4AIF(3) (mol %) glass in the wavelength region from 0.4047 to 5.3036 microm. The material dispersion curve and zero material dispersion wavelength were estimated on the basis of refractive- index dispersion measurements. The slope of the material dispersion curve for these fluoride glasses was less steep than that for SiO2 glass in the wavelength range estimated. The zero material wavelength lambda(0) shifted to a shorter wavelength with increasing AlF3 concentration. The lambda(0) is 1.675 microm for 31.68BaF(2)- 3.84GdF(3)-60.48ZrF(4)-4AlF(3) (mol %) glass. When 4-mol % LiF, CsF, YF(3), CdF(2), SnF(2), or PbF(2) were doped into these glasses, each lambda(0) shifted from 1.675 to 1.670, 1.668, 1.673, 1.681, 1.683, or 1.704 microm, respectively. The temperature dependence values of the refractive-index dispersion and material dispersion for 31.68BaF(2)-3.84GdF(3) -60.48ZrF(4)-4AIF(3) (mol %) glass were also obtained. The temperature coefficients of the refractive index were negative values (dn/dT(relative) = -1.0 X 10(-5)/degrees C) and the wavelength dependence of dn/dT was small. The wavelength lambda(0) shifted from 1.675 to 1.605 microm, due to the rise in the measurement temperature from 25 degrees C to 250 degrees C. PMID:18196149

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

    PubMed Central

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

    2014-01-01

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

  9. The Exicor DUV birefringence measurement system and its application to measuring lithography-grade CaF2 lens blanks

    NASA Astrophysics Data System (ADS)

    Wang, Baoliang; Griffiths, C. O.; Rockwell, Rick R.; List, Jennifer; Mark, Doug

    2003-11-01

    Optical lithography continues its transition to shorter wavelengths to support the semiconductor industry"s production of faster microchips to meet evolving market demands. The next step for optical lithography is likely to use the F2 excimer laser at 157.63 nm (157 nm,according to the industry" s naming convention).At 157 nm, among the limited number of fluoride crystals with acceptable optical properties calcium fluoride is the only practical lens material for step and scan systems due to its readiness for mass production. Since the discovery of intrinsic birefringence in CaF2 at deep ultraviolet (DUV)wavelengths,the optical lithography industry has developed a critical interest in measuring birefringence at 157 nm. In response to this need, we have developed a DUV birefringence measurement system. In this article,we describe the working principle, system construction, technical performance and selected applications for measuring lithography grade calcium fluoride lens blanks at DUV wavelengths.

  10. Spectroscopic investigation of 2.02 ?m emission in Ho3+/Tm3+ codoped transparent glass ceramic containing CaF2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Chen, Q. J.; Zhang, W. J.; Qian, Q.; Yang, Z. M.; Zhang, Q. Y.

    2010-05-01

    Tm3+ and Ho3+ codoped transparent glass ceramic (GC) containing CaF2 nanocrystals were fabricated by melt-quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of CaF2 nanocrystals among the glass matrix. Energy-dispersive x-ray spectroscopy results evidenced the incorporation of Tm3+ and Ho3+ into the CaF2 nanocrystals. Judd-Ofelt parameters were calculated based on the absorption spectra, the smaller ?2 and larger ?6 imply that Tm3+ and Ho3+ ions has entered into a symmetrical ionic crystal field. 2.02 ?m emission spectral of the GC samples were recorded at room temperature with an excitation of 808 nm laser diode. The enhancement of the emission at 2.02 ?m in the GC samples could be attributed to more efficient cross relaxation process of Tm3+:H34+Tm3+:H36?2Tm3+:H34, and energy transfer from Tm3+ to Ho3+ benefited from the incorporation of rare earth ions into CaF2 nanocrystals.

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

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

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

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

    E-print Network

    Chen, Long-Qing

    2013-01-01

    In particular, CaF2 (Refs. 2,3) is a typical superionic conductor.1 CeO2 has been used in catalytic converters,16 Computationally, the advantage of the linear response method is that it directly evaluates the dynamical matrix- teractions. According to the reduced dynamical matrix from Wallace,22 the reduced dynamical matrix

  13. High quantum yield and low concentration quenching of Eu3+ emission in oxyfluoride glass with high BaF2 and Al2O3 contents

    NASA Astrophysics Data System (ADS)

    Shinozaki, Kenji; Honma, Tsuyoshi; Komatsu, Takayuki

    2014-06-01

    New oxyfluoride glasses of 1Eu2O3-50BaF2-xAl2O3-(50-x)B2O3 (x = 0-25), yEu2O3-50BaF2-25Al2O3-25B2O3 (y = 0-10) (mol), and zEu2O3-1Tb4O7-50BaF2-25Al2O3-25B2O3 (z = 0, 0.5) (mol) with a high fluorine content (F/(F + O) = 0.4) were synthesized by using a conventional melt-quenching method, and photoluminescence properties such as quantum yield (?), lifetime (?), and concentration quenching effect of Eu3+ ions were clarified. The glass with 25Al2O3 showed an excellent red luminescence with extremely high quantum yield (?) of 97% in the visible region at the excitation of the wavelength ? = 396 nm and a long lifetime of ? = 3.29 ms for the emission (? = 612 nm) of Eu3+ ions at the 5D0 level. The effect of concentration quenching in these glasses was also very small, e.g., ? = 72% even for the glass with 10Eu2O3. The values of ? = 52% for the green emission of Tb3+ ions and of ? = 81% for the yellow emission of Eu3+-Tb3+ co-doped ions were also achieved in the glasses. The present study indicates that rare-earth ions of Eu3+ and Tb3+ are dispersed homogeneously in these oxyfluriode glasses and the degree of their its asymmetry (i.e., the electric field gradient) is also widely distributed due to the coordination of both F- and O2- ions. The new oxyfluoride glasses with high BaO and Al2O3 contents have a high potential as hosts for new phosphors with rare-earth ions.

  14. 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

  15. 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.

  16. Up-conversion luminescence properties and energy transfer of Er3+/Yb3+ co-doped oxyfluoride glass ceramic containing CaF2 nano-crystals

    NASA Astrophysics Data System (ADS)

    Ma, Chen-Shuo; Jiao, Qing; Li, Long-Ji; Zhou, Da-Cheng; Yang, Zheng-Wen; Song, Zhi-Guo; Qiu, Jian-Bei

    2014-05-01

    The Er3+/Yb3+ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy (TEM) images showed that CaF2 nano-crystals of 20-30 nm in diameter precipitated uniformly in the glass matrix. Comparing with the host glass, high efficiency upconversion luminescence of Er3+ at 540 nm and 658 nm was observed in the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er3+ and Yb3+ was convinced and the possible mechanism of Er3+ up-conversion was discussed.

  17. To PLAnetary Transit or not? An extremely large field of view camera with a CaF2 component tested in thermo-vacuum

    NASA Astrophysics Data System (ADS)

    Bergomi, M.; Magrin, D.; Farinato, J.; Viotto, V.; Ragazzoni, R.; Brunelli, A.; Dima, M.; Christiansen, P.; Ghigo, M.; Laubier, D.; Pasquier, H.; Piazza, D.; Pagano, I.; Piotto, G.; Basile, G.; Catala, C.

    2012-09-01

    Because of its nicely chromatic behavior, Calcium Fluoride (CaF2) is a nice choice for an optical designer as it can easily solve a number of issues, giving the right extra degree of freedom in the optical design tuning. However, switching from tablet screens to real life, the scarcity of information -and sometimes the bad reputation in term of fragility- about this material makes an overall test much more than a "display determination" experiment. We describe the extensive tests performed in ambient temperature and in thermo-vacuum of a prototype, consistent with flight CTEs, of a 200mm class camera envisaged for the PLATO (PLAnetary Transit and Oscillations of Stars) mission. We show how the CaF2 lens uneventfully succeeded to all the tests and handling procedures, and discuss the main results of the very intensive test campaign of the PLATO Telescope Optical Unit prototype.

  18. Phosphorus distribution between carbon-saturated iron at 1350 °C and lime-based slags containing Na 2 O and CaF 2

    Microsoft Academic Search

    W. H. Van Niekerk; R. J. Dippenaar

    1998-01-01

    The Corex process is capable of consistently producing hot metal with very low silicon contents (<0.1 pct), and as a consequence,\\u000a its hot metal is ideally suited for the external removal of phosphorus. Various studies have shown that small additions of\\u000a Na2O significantly enhance the ability of lime-based slags to dephosphorize liquid iron. Additions of fluxes (such as CaF2) may

  19. Particle size effect in CaF2:Mn\\/Teflon TLD response at photon energies from 5-1250 keV

    Microsoft Academic Search

    G. A. Carlson; L. Lorence; D. W. Vehar; R. S. Klingler

    1990-01-01

    Thermoluminescent dosimeters (TDLs) fabricated by embedding CaF 2:Mn powder in a Teflon matrix (TTLDs) are sometimes used to monitor dose in silicon-device radiation effects experiments. A potential advantage of TTLDs over other types of TLDs for this application is that their weighted-average mass energy-absorption coefficient is near that of Si. Experimental results are presented which demonstrate that for moderate-energy X-rays,

  20. Influence of CaF2 and Li2O on the Viscous Behavior of Calcium Silicate Melts Containing 12 wt pct Na2O

    NASA Astrophysics Data System (ADS)

    Park, Hyun Shik; Kim, Hyuk; Sohn, Il

    2011-04-01

    Understanding the viscous behavior of silica-based molten fluxes is essential in maintaining the reliability of steel casting operations and in preventing breakouts. In particular, high concentrations of aluminum in recently developed transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) steels tend to promote reduction of silica in the mold fluxes that result in the formation of alumina, which in turn increases the viscosity. To counteract this effect, significant amounts of fluidizers such as CaF2 and Li2O are required to ensure that mold fluxes have acceptable lubrication and heat transfer characteristics. The viscous behavior of the slag system based on CaO-SiO2-12 wt pct Na2O with various concentrations of CaF2 and Li2O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives. CaF2 additions up to 8 wt pct were effective in decreasing the viscosity by breaking the network structure of molten fluxes, but CaF2 concentrations above this level had a negligible effect on viscosity. Li2O additions up to 2 wt pct were also effective in decreasing the viscosity, but the effect was comparatively negligible above 2 wt pct. Using Fourier transform infrared (FTIR) analysis of as-quenched slag samples, it was concluded that the viscosity was controlled more effectively by changing the larger complex silicate structures of rings and chains than by changing the amounts of simpler dimers and monomers.

  1. Electrodeposition and characterization of Al 2O 3–Cu(Sn), CaF 2–Cu(Sn) and talc–Cu(Sn) electrocomposite coatings

    Microsoft Academic Search

    Y. L Wang; Y. Z Wan; Sh. M Zhao; H. M Tao; X. H Dong

    1998-01-01

    Electrocomposite coatings consisting of Al2O3, CaF2, talc particles and copper–tin alloy were prepared by means of the conventional electrodeposition technique. The effects of cathode current density, particle concentration in the bath and stir rate on the volume percentage of particles Vp in the composite coatings were investigated. It was shown that current density, effective particle concentration in the plating solution

  2. Spectral hole burning of Eu 2+ in MBE-grown superlattices of CaF 2: Eu 2+ CdF 2

    Microsoft Academic Search

    D. M. Boye; Y. Sun; R. S. Meltzer; S. P. Feofilov; N. S. Sokolov; A. Khilko; J. C. Alvarez

    1997-01-01

    Persistent spectral hole burning is observed for the 413 nm 4f7(8S72) ? 4f65d(?8) zero-phonon transition of Eu2+ in MBE-grown superlattices of CaF2:Eu2+CdF2 on Si(111). Possible mechanisms for the trapping of the photoionized electron are discussed in terms of the band offsets of the superlattice layers.

  3. X-ray scattering from surfaces and interfaces and its application to the characterization of {CaF2}/{Si(111) } interfaces

    NASA Astrophysics Data System (ADS)

    Harada, J.; Takahashi, I.; Itoh, Y.; Sokolov, N. S.; Yakovlev, N. L.; Shusterman, Y.; Alvarez, J. C.

    1996-05-01

    A survey of X-ray scattering techniques developed so far is presented keeping in mind that the appearance of the next generation of synchrotron radiation sources makes such techniques one of the promising probes for ex situ and in situ characterization of the surface and the interface of an epitaxially grown crystal. On the basis of the intensity formula given by one of the present authors [J. Harada, Ultramicroscopy 52 (1993) 233], it is shown that diffuse scattering associated with the crystal truncation rod is closely related to the local atomic arrangement on a surface. Our current X-ray scattering studies on {CaF2}/{Si(111) } films grown by the MBE method are presented and the growth condition of the four types of interface structure found in {CaF2}/{Si(111) } is discussed. A hydrogen-terminated Si(111) surface was found to be a promising substrate for the low-temperature growth of CaF 2 films.

  4. Lanthanide doped upconverting colloidal CaF2 nanoparticles prepared by a single-step hydrothermal method: toward efficient materials with near infrared-to-near infrared upconversion emission.

    PubMed

    Pedroni, Marco; Piccinelli, Fabio; Passuello, Tiziana; Giarola, Marco; Mariotto, Gino; Polizzi, Stefano; Bettinelli, Marco; Speghini, Adolfo

    2011-04-01

    Colloidal Er(3+)/Yb(3+), Tm(3+)/Yb(3+) and Ho(3+)/Yb(3+) doped CaF(2) nanoparticles have been prepared by a one-pot hydrothermal procedure and their upconversion properties have been investigated. PMID:21336370

  5. Mechanical properties of haynes® alloy 188 after exposure to LiF22CaF 2 , air, and vacuum at 1093 K for periods up to 10,000 hours

    Microsoft Academic Search

    J. D. Whittenberger

    1992-01-01

    As part of a program to provide reassurance that the cobalt- base superalloy Haynes? Alloy 188 can adequately contain a LiF-\\u000a 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\\u000a and the

  6. 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.

  7. Mid-infrared Verdet coefficient studies in GaAs, BaF2, and LaSrGaO4, and ZnSe

    NASA Astrophysics Data System (ADS)

    Kim, Myoung-Hwan; Kurz, Volker; Acbas, Gheorghe; Ellis, Chase; Cerne, John

    2009-03-01

    We measure the mid-infrared (wavelength ?=11 - 0.8 ?m; 0.1 - 1.5 eV) Faraday rotation and ellipticity in GaAs, BaF2, LaSrGaO4, and ZnSe. Since these materials are commonly used as substrates and windows in the mid-infrared, it is important to measure the Faraday signals for background subtraction and to test the accuracy of our measurement techniques. The light sources are lasers and a new custom-modified double-pass prism monochromator with a Xe lamp, which allowed continuous broadband measurements in the 0.31-1.5 eV energy range. Surprisingly, we find reproducible ellipticity signals, even though the radiation is well below the absorption edge of these materials and therefore no circular dichroism is expected. We suggest that the Faraday ellipticity is produced by the static retardance (Rs) of the ZnSe photoelastic modulator (PEM), which converts rotation signals into ellipticity. We determine Rs experimentally from the Faraday rotation and ellipticity ratio, produced by either applying a magnetic field or rotating the polarization of light incident on the PEM. Work supported by the Research Corp. Cottrell Scholar Award, NSF-CAREER-DMR0449899, and an instrumentation award from the CAS.

  8. Molecular structure and dynamics of off-center Cu2+ ions and strongly coupled Cu2+Cu2+ pairs in BaF2 crystals: Electron paramagnetic resonance and electron spin relaxation studies

    Microsoft Academic Search

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

    2007-01-01

    X-band and Q-band electron paramagnetic resonance (EPR) spectra of Cu2+ in BaF2 crystal were recorded in the temperature range of 4.2-200 K. Spin-Hamiltonian parameters of single Cu2+ complexes and of Cu2+-Cu2+ pairs were derived and discussed. A special attention was paid to the dimeric species. Their molecular ground state configuration was found as having antiferromagnetic intradimer coupling with the singlet-triplet

  9. Molecular structure and dynamics of off-center Cu2+ ions and strongly coupled Cu2+–Cu2+ pairs in BaF2 crystals: Electron paramagnetic resonance and electron spin relaxation studies

    Microsoft Academic Search

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

    2007-01-01

    X-band and Q-band electron paramagnetic resonance (EPR) spectra of Cu2+ in BaF2 crystal were recorded in the temperature range of 4.2–200 K. Spin-Hamiltonian parameters of single Cu2+ complexes and of Cu2+–Cu2+ pairs were derived and discussed. A special attention was paid to the dimeric species. Their molecular ground state configuration was found as having antiferromagnetic intradimer coupling with the singlet-triplet

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  11. Tribological properties of spark-plasma-sintered ZrO 2(Y 2O 3)–CaF 2–Ag composites at elevated temperatures

    Microsoft Academic Search

    J. H. Ouyang; S. Sasaki; T. Murakami; K. Umeda

    2005-01-01

    Spark-plasma sintering is employed to synthesize self-lubricating ZrO2(Y2O3) matrix composites with different additives of CaF2 and Ag as solid lubricants by tailoring the composition and by adjusting the sintering temperature. The friction and wear behavior of ZrO2(Y2O3) matrix composites have been investigated in dry sliding against an alumina ball from room temperature to 800°C. The effective self-lubrication at different temperatures

  12. A Density Model Based on the Modified Quasichemical Model and Applied to the NaF-AlF3-CaF2-Al2O3 Electrolyte

    NASA Astrophysics Data System (ADS)

    Robelin, Christian; Chartrand, Patrice

    2007-12-01

    A theoretical model for the density of multicomponent inorganic liquids based on the modified quasichemical model has been presented in a previous article. In the present article, this model is applied to the NaF-AlF3-CaF2-Al2O3 electrolyte. By introducing in the Gibbs energy of the liquid phase, temperature-dependent molar volume expressions for the pure fluorides and oxides, and pressure-dependent excess parameters for the binary (and sometimes higher-order) interactions, it is possible to reproduce, and eventually predict, the molar volume and the density of the multicomponent liquid phase using standard interpolation methods. All available density data for the NaF-AlF3-CaF2-Al2O3 liquid were collected and critically evaluated, and optimized pressure-dependent model parameters have been found. This new volumetric model can be used with Gibbs energy minimization software, to calculate the molar volume and the density of cryolite-based melts used for the electroreduction of alumina in Hall-Héroult cells.

  13. Solubility of niobium in the system CaCO3 CaF2 NaNbO3 at 0.1 GPa pressure: implications for the crystallization of pyrochlore from carbonatite magma

    Microsoft Academic Search

    Roger H. Mitchell; Bruce A. Kjarsgaard

    2004-01-01

    Experimental data are presented for the solubility of NaNbO3 in the ternary system CaCO3 CaF2 NaNbO3 (or calcite fluorite lueshite) over the temperature range 500 1,000°C at 0.1 GPa pressure. Liquidus to solidus phase relationships are given for the pseudo-binary join ([CaCO3]60[CaF2]40)100-x (NaNbO3)x (0

  14. Solubility of niobium in the system CaCO 3 –CaF 2 –NaNbO 3 at 0.1 GPa pressure: implications for the crystallization of pyrochlore from carbonatite magma

    Microsoft Academic Search

    Roger H. Mitchell; Bruce A. Kjarsgaard

    2004-01-01

    Experimental data are presented for the solubility of NaNbO 3 in the ternary system CaCO 3–CaF 2–NaNbO 3 (or calcite–fluorite–lueshite) over the temperature range 500–1,000°C at 0.1 GPa pressure. Liquidus to solidus phase relationships are given for the pseudo-binary join ([CaCO 3] 60[CaF 2] 40) 100- x–(NaNbO 3) x (0x3 in these liquids is about 17 wt% (or 13.8 wt% Nb 2O 5)

  15. The effects of water vapor, heating, and chemical and mechanical polishing on MOS capacitors passivated with BaF 2–B 2O 3–GeO 2–SiO 2 glasses

    Microsoft Academic Search

    Keiji Kobayashi

    1999-01-01

    The capacitance and voltage (C–V) characteristics of metal oxide semiconductor (MOS) capacitors passivated with BaF2–B2O3–GeO2–SiO2 and BaO–B2O3–GeO2–SiO2 glasses with various OH– radicals and the effects of water vapor, heat, and chemical and mechanical polishing on these MOS capacitors were investigated. As the OH– absorption coefficients of the glasses increased, an adverse effect on the recovery of hysteresis loops of C–V

  16. A comparison of CaF2:Mn thermoluminescent dosimeter chips to aluminum and silicon x-ray calorimeters in the pulsed Hermes III environment

    NASA Astrophysics Data System (ADS)

    Fehl, D. L.; Sujka, B. R.; Vehar, D. W.; Westfall, R. L.; Lorence, L. J., Jr.; Rice, D. A.; Gilbert, D. W.

    1995-01-01

    Hermes III is a pulsed power, Bremsstrahlung simulator used for radiation-hardness testing of electronics components [19-MeV spectrum, 20-ns pulse duration, and typical doses (silicon) ?100 krad (1 kGy)]. CaF2:Mn thermoluminescent dosimeter chips (TLDs) have been compared to a set of x-ray calorimeters in the Hermes III environment for doses between 10-75 krad. Similar to a design reported by Murray and Attix, this set of detectors included different dosimetric materials (silicon and aluminum) and two independent temperature sensors (thermistors and thermocouples). The electronic recording system was also updated. The average disagreement between TLDs and calorimeters was 1%-3%. Radiation transport calculations, however, suggest a possible bias of 4%-6% (source unknown). With the silicon calorimeter the ac bridge, which measured the resistance of thermistor temperature sensors, was extremely sensitive to EMP.

  17. Biaxially textured Al film growth on CaF2 nanostructures toward a method of preparing single-crystalline Si film on glass substrates.

    PubMed

    Li, Huafang; Snow, Patrick; He, Ming; Wang, Pei-I; Wang, Gwo-Ching; Lu, Toh-Ming

    2010-10-26

    We report the room temperature growth of biaxially textured Al films and further demonstrate the use of these Al films in preparing single-crystalline Si layers on glass substrates. The formation of the biaxial texture in Al film relies on the existence of the CaF(2) buffer layer prepared using oblique angle physical vapor deposition, which consists of single-crystalline nanorods with caps that are in the form of inverted nanopyramids. The single-crystalline Si film was obtained upon crystallization of the amorphous Si film deposited through physical evaporation on the biaxially textured Al film. This method of preparing single-crystalline Si film on glass substrate is potentially attractive for being employed in silicon technology and in fabrication of low-cost electronic devices. PMID:20839785

  18. Estimation Model for Electrical Conductivity of Molten CaF2-Al2O3-CaO Slags Based on Optical Basicity

    NASA Astrophysics Data System (ADS)

    Birol, Burak; Polat, Gökhan; Saridede, Muhlis Nezihi

    2015-02-01

    Slag properties, such as electrical conductivity, thermal conductivity, density, viscosity, and surface tension, and the prediction of these properties play an important role in melting and metal refining. Optical basicity depends on the electronegativity of the ions of an individual oxide. This feature represents the bonding characteristics, ionization ability, ion size, and consequently the mobility of free ions inside the slag. These properties affect the electrical conductivity of slags. Therefore, in the current study, various slags containing mainly CaF2 and various oxides were prepared. The optical basicity value of each slag was calculated and their electrical conductivities were measured between 1450°C and 1600°C. The relationship between the optical basicity and the measured properties were discussed. It was observed that increasing optical basicity increases the electrical conductivity as well as the temperature. Thus, a new model for predicting electrical conductivity of slags was built between 1450°C and 1600°C depending on optical basicity and temperature.

  19. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  1. Investigation of ion induced damage in KBr, YAG:Ce, CaF2:Eu and CsI:Tl irradiated by various-energy protons

    NASA Astrophysics Data System (ADS)

    Lin, L. Y.; Leitner, D.; Benatti, C.; Perdikakis, G.; Krause, S. W.; Rencsok, R.; Nash, S.; Wittmer, W.

    2015-03-01

    New experimental results on the scintillation processes for KBr, YAG:Ce, CaF2:Eu and CsI:Tl crystals under H2+ irradiation for the energy range of 600-2150 keV/u are systematically reported. The scintillation light yield was measured as a function of accumulated particle fluence at the rare isotope ReAccelerator (ReA) facility of the National Superconducting Cyclotron Laboratory (NSCL). The data indicates that YAG:Ce and CsI:Tl can maintain stable luminescence under continuous ion bombardment for at least a total fluence of 1.8×1012 ions/mm2 in the energy range used for this experiment. On the other hand, the luminescence of CaF2:Eu shows a rapid initial decay but then maintains a nearly constant luminescence yield. The extraordinary scintillation response of KBr is initially enhanced under ion bombardment, approaches a maximum, and then eventually decays. The scintillation efficiency of the CsI:Tl scintillator is superior to the other materials. The stability of the measured beam profile width deducted from the different scintillator materials in static beam conditions was also investigated as a function of irradiation time. We observed that the low-energy H2+ bombardment (25 keV/u) on the YAG:Ce scintillator can lead to the significant degradation of the scintillation yields. Different scintillation degradation responses for the low- and high-energy bombardments can be attributed to the transmission loss of the emitted light inside the crystal caused by displacement damages.

  2. Dependence of the profile of a hologram recorded on color centers in a CaF2 crystal on the type of hologram-forming centers

    NASA Astrophysics Data System (ADS)

    Shcheulin, A. S.; Angervaks, A. E.; Veniaminov, A. V.; Zakharov, V. V.; Ryskin, A. I.

    2012-12-01

    A hologram recorded in a CaF2 crystal by modulating the concentration of simple centers ( F, M, R, and N) and highly aggregated (mainly colloidal) color centers has been exposed to incoherent 365-nm light to a dose of about 4000 J/cm2 at a temperature of 80°C. As a result of this exposure, the color centers were almost completely transformed into quasi-colloidal centers. The hologram was retained, and its diffraction efficiency increased; the intensity and number of observed diffraction orders increased as well. Analysis of the angular dependences of the diffraction response made it possible to construct a spatial profile of the hologram, which turned out to be much narrower in comparison with the initial-hologram profile; both profiles differ from a sinusoidal one. The hologram's stability to such a large exposure to incoherent light at an elevated temperature is related to the peculiar diffusion-drift mechanism of hologram recording on color centers in ionic crystals.

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

    PubMed

    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(Fe(1-x)Co(x))(2)As(2) 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, J(c). Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, T(c), of the material. In this paper we demonstrate that strain induced by the substrate can further improve J(c) of both single and multilayer films by more than that expected simply due to the increase in T(c). The multilayer deposition of Ba(Fe(1-x)Co(x))(2)As(2) on CaF2 increases the pinning force density (F(p) = J(c) × µ0H) by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m(3) at 22.5 T and 4.2 K, the highest value ever reported in any 122 phase. PMID:25467177

  4. Switchable yttrium-hydride mirrors grown on CaF2(111): A x-ray photoelectron spectroscopy and diffraction study

    NASA Astrophysics Data System (ADS)

    Hayoz, J.; Schoenes, J.; Schlapbach, L.; Aebi, P.

    2001-10-01

    The epitaxial growth of Y (hydride) films on CaF2(111) has been investigated using x-ray photoelectron spectroscopy, x-ray photoelectron diffraction, and low energy electron diffraction (LEED). For Y deposition at 700 °C the formation of high-quality epitaxial hcp(0001) oriented Y films is observed. Whenever the Y films showed good surface quality, the surface is rich in F. Only when the deposition temperature was chosen so low that the LEED reflexes were very broad was no fluorine detected. This is a strong indication that F acts as a surfactant. For Y deposition at room temperature under a H2 partial pressure of 5×10-6 mbar we observe the formation of a F-free, transparent YH2.3 film of a red/yellow color and poor crystallinity. Hydrogen unloading is accomplished by annealing to 600 °C. The film loses its transparency, the poorly ordered fcc(111) lattice converts to a well-ordered hcp(0001) lattice, and F contamination is restored.

  5. Long range order in 2-D arrays of nanometer-sized Fe islands on CaF2/Si(111) (invited) (abstract)

    NASA Astrophysics Data System (ADS)

    Scheinfein, M. R.; Schmidt, K. E.; Heim, K. R.; Hembree, G. G.

    1996-04-01

    The effective magnetic moment was measured as a function of Fe island size during the initial stages of Fe growth on CaF2/Si(111) in an ultrahigh vacuum scanning electron microscope equipped with an in situ SMOKE analysis chamber. This substrate was selected for its wide bandgap, chemical inertness, viability of integration into an Si based technology and the availability of nanopatterning using electron beams for producing devices. Fe grown at room temperature initially nucleates into a monodisperse distribution of 3-D islands at very high nucleation densities (8×1012/cm2). Increased Fe coverages lead to 2-D island growth. A room temperature superparamagnetic to ferromagnetic phase transition occurs as a function of Fe island radius. Mean field and Monte Carlo calculations illustrate that three distinct magnetic phases exist as a function of island diameter. Ferromagnetic order is present at room temperature when r?3 nm, superparamagnetism is favored when 2 nm < r <3 nm, and a frustrated random antiferromagnetic phase exists when r<2 nm. Further depositions of Ag on superparamagnetic Fe island arrays produce Ag islands which couple the covered Fe island moments in-plane, implying that the Ag mediates the magnetic exchange between individual Fe islands within an Ag island. Implications for 2-D giant magnetoresistance devices will be discussed.

  6. 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.

  7. Alkali-doped heavy metal fluoride glasses studied by positron annihilation lifetime spectroscopy

    Microsoft Academic Search

    A. J. Hill; P. J. Newman; J. Javorniczky; D. R. MacFarlane

    1995-01-01

    Heavy metal fluoride glasses of varying alkali metal fluoride have been studied by positron annihilation lifetime spectroscopy. The alkali series 53ZrF4 · (40 - x)BaF2 · 4LaF3 · 3AlF3 · xLiF and 53ZrF4 · (40 - x)BaF2 · 4LaF3 · 3AlF3 · xCsF are compared with the mixed alkali series 53ZrF4 · 20BaF2 · 4LaF3 · 4LaF3 · 3AlF3 ·

  8. Extraction of pure spectral signatures and corresponding chemical maps from EPR imaging data sets: identifying defects on a CaF2 surface due to a laser beam exposure.

    PubMed

    Abou Fadel, Maya; Zhang, Xin; de Juan, Anna; Tauler, Roma; Vezin, Hervé; Duponchel, Ludovic

    2015-04-01

    A calcium fluoride (CaF2) plate was exposed to pulsed laser irradiations inducing surface morphological and ionization changes on its surface. More precisely surface damages mainly correspond to intrinsic defects. Electron paramagnetic resonance (EPR) hyperspectral imaging is a powerful technique able to characterize the defects formed on the CaF2 surface. Indeed, EPR hyperspectral images provide spatial and spectral information about the sample studied. In fact, these images possess a great potential to obtain accurate and reliable knowledge about the chemical composition and the distribution of the component due to the presence of the spatial aspect. However, the complexity of such hyperspectral data sets imposes the use of advanced chemometric tools to extract valuable information on the considered physicochemical system. Therefore, Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) is proposed to identify and locate the different constituents in the images. The originality of this work is that it reports on the application of MCR-ALS, for the first time, on electron paramagnetic resonance (EPR) imaging data sets that will furnish the distribution maps and the spectral signatures of all components present in the sample. The results show the identification of different intrinsic defects on a CaF2 sample from the sole information in the raw image measurements and, therefore, confirm the potential of this methodology and the important role of spatial information contained in the image. PMID:25730682

  9. 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

  10. 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. PMID:25977852

  11. Molecular structure and dynamics of off-center Cu2+ ions and strongly coupled Cu2+-Cu2+ pairs in BaF2 crystals: Electron paramagnetic resonance and electron spin relaxation studies

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

    X-band and Q-band electron paramagnetic resonance (EPR) spectra of Cu2+ in BaF2 crystal were recorded in the temperature range of 4.2-200K. Spin-Hamiltonian parameters of single Cu2+ complexes and of Cu2+-Cu2+ pairs were derived and discussed. A special attention was paid to the dimeric species. Their molecular ground state configuration was found as having antiferromagnetic intradimer coupling with the singlet-triplet splitting J =-35cm-1. The zero-field splitting being D =0.0365cm-1 at 4.2K increases with temperature as an effect of thermal population of excited dimer configurations. Electron spin echo (ESE) method was used for measurements of electron spin lattice and phase relaxation. The spin-lattice relaxation data show that except for coupling to the host lattice phonons the Cu2+ ions are involved in local mode motions with energy of 82cm-1. Phase relaxation (ESE dephasing) of single Cu2+ ions is due to spin diffusion at low temperatures. This relaxation is hampered for temperatures higher than 30K due to the triplet state population of neighboring Cu2+-Cu2+ dimers, which disturb dipolar coupling between Cu2+ ions. For higher temperatures the relaxation is dominated by Raman T1 processes. Fourier transform ESE spectrum displays dipolar Cu-F splitting which allowed determination of the off-center shift of Cu2+ as ?s=0.132nm. The dynamical effects observed in EPR spectra and in electron spin relaxation both for single Cu2+ ions and Cu2+-Cu2+ pairs are discussed as due to jumps between six off-center positions in the crystal unit cell and jumps between various dimer configurations.

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

    PubMed Central

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

    2012-01-01

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

  13. 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.

  14. Influence of aluminum ions on fluorescent spectra and upconversion in codoped CaF2-Al2O3-P2O5-SiO2:Ho3+ and Er3+ glass system

    NASA Astrophysics Data System (ADS)

    Gandhi, Y.; Rao, M. V. Ramachandra; Rao, Ch. Srinvasa; Srikumar, T.; Kityk, I. V.; Veeraiah, N.

    2010-07-01

    The glasses of the composition 20CaF2-xAl2O3-(59-x)P2O5-20SiO2:1.0Ho2O3/1.0Er2O3 and 20CaF2-xAl2O3-(59-x)P2O5-20SiO2:(0.6Ho2O3+0.4Er2O3) with x varying from 2 to 10 mol % have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350-2100 nm were studied at ambient temperature. The Judd-Ofelt theory was applied to characterize the absorption and luminescence spectra of Ho3+ and Er3+ ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio ?, and the radiative life time ? for blue (B), green (G), and red (R) emission levels of these glasses have been evaluated. The radiative life times for these transitions of Ho3+ and Er3+ have also been measured. The variations observed in these parameters were discussed in the light of varying coordinations (tetrahedral and octahedral positions) of Al3+ ions in the glass network. The energy transfer between the two rare earth ions (Ho3+ and Er3+) in codoped CaF2-Al2O3-P2O5-SiO2 glass system in the visible and near infrared (NIR) regions has also been investigated as a function of varying concentration of Al2O3. A significant enhancement in the intensities of B, G, and R lines has been observed due to codoping. The quantitative analysis of these results (with the aid of the data on IR and Raman spectral studies) has indicated that the glasses mixed with around 6.0 mol % of Al2O3 is the optimum concentration for yielding the highest quantum efficiency and for maximum energy transfer with low phonon losses.

  15. Characterisation of slab waveguides, fabricated in CaF2 and Er-doped tungsten-tellurite glass by MeV energy N+ ion implantation, using spectroscopic ellipsometry and m-line spectroscopy

    NASA Astrophysics Data System (ADS)

    Bányász, I.; Berneschi, S.; Lohner, T.; Fried, M.; Petrik, P.; Khanh, N. Q.; Zolnai, Z.; Watterich, A.; Bettinelli, M.; Brenci, M.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.; Speghini, A.

    2010-05-01

    Slab waveguides were fabricated in Er-doped tungsten-tellurite glass and CaF2 crystal samples via ion implantation. Waveguides were fabricated by implantation of MeV energy N+ ions at the Van de Graaff accelerator of the Research Institute for Particle and Nuclear Physics, Budapest, Hungary. Part of the samples was annealed. Implantations were carried out at energies of 1.5 MeV (tungsten-tellurite glass) and 3.5 MeV (CaF2). The implanted doses were between 5 x 1012 and 8 x 1016 ions/cm2. Refractive index profile of the waveguides was measured using SOPRA ES4G and Woollam M-2000DI spectroscopic ellipsometers at the Research Institute for Technical Physics and Materials Science, Budapest. Functionality of the waveguides was tested using a home-made instrument (COMPASSO), based on m-line spectroscopy and prism coupling technique, which was developed at the Materials and Photonics Devices Laboratory (MDF Lab.) of the Institute of Applied Physics in Sesto Fiorentino, Italy. Results of both types of measurements were compared to depth distributions of nuclear damage in the samples, calculated by SRIM 2007 code. Thicknesses of the guiding layer and of the implanted barrier obtained by spectroscopic ellipsometry correspond well to SRIM simulations. Irradiationinduced refractive index modulation saturated around a dose of 8 x 1016 ions/cm2 in tungsten-tellurite glass. Annealing of the implanted waveguides resulted in a reduction of the propagation loss, but also reduced the number of supported guiding modes at the lower doses. We report on the first working waveguides fabricated in an alkali earth halide crystal implanted by MeV energy medium-mass ions.

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

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

    SciTech Connect

    Whittenberger, J.D. (NASA, Lewis Research Center, Cleveland, OH (United States))

    1992-08-01

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

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

    PubMed

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

    2014-09-01

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

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

    PubMed

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

    2014-06-01

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

  20. Direct determination of the NaF/AlF3 molar ratio by Raman spectroscopy in NaF-AlF3-CaF2 melts at 1000 °C.

    PubMed

    Malherbe, Cedric; Gilbert, Bernard

    2013-09-17

    For the last 40 years, Raman spectroscopy has been very useful in investigating the structure of corrosive molten salts, such as the cryolite-based melts widely used as electrolyte in the Hall-Heroult process. Even if this process remains the most economically efficient for metallic aluminum electro-production, it suffers from a high energy loss, which is dependent on the melt composition. Therefore, controlling the chemical composition of the electrolyte is essential. The present paper proposes to apply Raman spectroscopy for the direct determination of the NaF-AlF3 molar ratio in NaF-AlF3-CaF2-based melts. Despite the experimental difficulties, a calibration curve based on equilibria taking place in the melt has been developed and the procedure has been successfully compared to industrial samples of known compositions. The possible exportation of the laboratory scale procedure to an industrial environment application for the control of the Hall-Heroult process is finally discussed. PMID:23988269

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

    PubMed

    Malherbe, Cedric; Eppe, Gauthier; Gilbert, Bernard

    2014-08-19

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

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

    PubMed

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

    2015-05-01

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

  3. 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.

  4. 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.

  5. Incorporation of OH species in fluorozirconate glasses: nature and influence on physical properties

    Microsoft Academic Search

    M. Clara Gonçalves; Rui M. Almeida

    1996-01-01

    The main purpose of the present study is to correlate the presence of controlled amounts of residual OH groups with the values of several physical properties, namely, the characteristic temperatures, linear thermal expansion coefficient, density, refractive index, microhardness, ultrasonic velocities, elastic constants and infrared transmission of ZrF4-based fluoride glasses. A series of glass samples were prepared in the ZrF4?BaF2?LaF3?AlF3?NaF system,

  6. 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.

  7. Characterization of the defects in a ZBLAN glass

    NASA Astrophysics Data System (ADS)

    Li, Ruihua; Wang, Huirong; Deng, Peizhen; Gan, Fuxi

    1990-10-01

    Theoretically light transmission losses as low as lO3dB/Km are possible in optical fibers made from heavy metal fluoride glasses. One reason for this has not yet been achieved is scattering due to defects in the glass. A study of defects in ZrF4BaF2LaF3A1F3NaF (ZBLAN) glass has been carried out by laser light scattering tomography Leitz optical microscopy scanning electron microscopy energy dispersive spectroscopy and wavelength dispersive spectroscopy. Defects as light scattering centers were exhibited and their appearance dimensions and distribution were observed throughout the samples. The commonly found crystallites in this glass were identified to be LaF3 in different shapes and sizes. The formation mechanism and contribution of the defects to extrinsic scattering loss are discussed. 1 .

  8. Propriétés tribologiques de revêtements et couches minces anti-frottement à haute température

    Microsoft Academic Search

    Yves Pauleau

    1997-01-01

    Low friction coatings of tenth ?m in thickness operating at high temperatures are composed of either metal oxides (PbO, CdO) or alkaline earth metal fluorides (CaF2, BaF2). These oxides and fluorides can be associated with other solid lubricant materials such as graphite or silver to extend the service temperature range from room temperature to about 800°C. Sliding contacts can also

  9. Fabrication of thin-film cleaved cavities using a bonding and cleaving fixture

    Microsoft Academic Search

    D. W. McAlister; P. J. McCann; H. Z. Wu; X. M. Fang

    2000-01-01

    A novel method for the fabrication of cleaved-cavities has been developed that uses a copper plate assembly to support semiconductor layers after substrate removal. PbSe layers were grown through a combination of molecular beam epitaxy and liquid phase epitaxy on Si (100) substrates using CaF2 and BaF2 buffer layers. After growth the sample was bonded to the edges of a

  10. Self-Lubricating Composites of Porous Nickel and Nickel-Chromium Alloy Impregnated with Barium Fluoride-Calcium Fluoride Eutectic

    Microsoft Academic Search

    Harold E. Sliney

    1966-01-01

    Porous nickel and nickel chromium were filled with BaF2-CaF2 eutectic composition by vacuum impregnation at 2000 F. The friction and wear properties of the resulting composites were determined in air and in hydrogen from 80 to 1500 F. Higher friction coefficients were obtained compared with coatings of the same fluoride composition on dense metals, however low wear and excellent wear

  11. 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.

  12. 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.

  13. Analysis of soliton self-frequency shift in ZBLAN fiber as a broadband supercontinuum medium

    NASA Astrophysics Data System (ADS)

    Yan, Xin; Liao, Meisong; Suzuki, Takenobu; Ohishi, Yasutake

    2013-03-01

    In this paper, Soliton self-frequency shift (SSFS) in ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is investigated based on Raman gain coefficients and generalized nonlinear SchrÖdinger equation. We have measured the Raman gain coefficient spectrum of a fluoride ZBLAN glass. The Raman response function and Raman fraction of ZBLAN fibers are obtained from the actual Raman gain spectrum. The enhanced SSFS in the ZBLAN fiber under investigation as compared to the silica fiber is mainly due to the combination of nonlinear coefficient and Raman response function enhancement. Therefore, ZBLAN fiber is promising materials for SSFS.

  14. Self-fabricated single mode waveguide in fluoride glass excited by self-channeled plasma filaments

    Microsoft Academic Search

    Sung-Hak Cho; Won-Seok Chang; Jae-Goo Kim; Kyoung-Hyun Whang

    2007-01-01

    Self-fabricated permanent structure of single mode waveguide in optical fluoride glasses was demonstrated using the self-channeled plasma filament excited by a femtosecond (130 fs) Ti:sapphire laser (lambdap=790 nm). The photoinduced refractive index modification in ZrF4-BaF2-LaF3-AlF3-NaF glasses reached a length of approximately 10-15 mm from the input surface of the optical glass with the diameters ranging from 5 to 8 mum

  15. Mid-infrared supercontinuum generation to 4.5 mum in ZBLAN fluoride fibers by nanosecond diode pumping

    Microsoft Academic Search

    Chenan Xia; Malay Kumar; Ojas P. Kulkarni; Mohammed N. Islam; Fred L. Terry Jr.; Mike J. Freeman; Marcel Poulain; Gwenael Mazé

    2006-01-01

    A mid-infrared supercontinuum (SC) is generated in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fibers from amplified nanosecond laser diode pulses with a continuous spectrum from ˜0.8 mum to beyond 4.5 mum. The SC has an average power of ˜23 mW, a pump-to-SC power conversion efficiency exceeding 50%, and a spectral power density of ˜-20 dBm\\/nm over a large fraction of the spectrum. The

  16. 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.

  17. Volume 58A, number 3 PHYSICS LEUERS 23 August 1976 PHOTON ECHO MODULATION EFFECTS IN LaF3

    E-print Network

    - the ground multiplet with three substates in the cx- tion, however in the presence of an external field nuclear magnetic moments. Photon echoes arising from these ~ 0.5 coherently excited multilevel systems pulses are therefore able to connect every substate in moment would eliminate the F--Pr 3~magneticinterac

  18. 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).

  19. Optical absorption and fluorescence properties of Dy3+: SFB glasses

    Microsoft Academic Search

    D. Uma Maheswari; J. Suresh Kumar; T. Sasikala; A. Mohan Babu; K. Pavani; Kiwan Jang; L. Rama Moorthy

    2009-01-01

    This paper presents the preparation and spectroscopic characterization of Dy3+-doped sodium fluoroborate (SFB) glasses of the type (50-x) B2O3 + 25 Na2O + 10 CaF2 + 10 AlF3 + 5 LaF3 + x DyF3 (x = 0.01, 0.1, 0.5,1.0, 2.0 and 4.0 mol%). By measuring the area under absorption bands, the experimental oscillator strengths are determined. The Judd-Ofelt (J-O) intensity

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

    DOE Data Explorer

    Kristin Persson

    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

  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. Identification of hydrogen isotopes with the BaF 2 electromagnetic calorimeter TAPS

    Microsoft Academic Search

    T. Matulewicz; L. Aphecetche; Y. Charbonnier; H. Delagrange; F. M. Marqués; G. Martínez; Y. Schutz

    1996-01-01

    The mass spectrum of hydrogen isotope was deduced from the kinetic energy and time-of-flight (TOF) measured with the segmented electromagnetic calorimeter TAPS. The reactions studied were Kr + Ni at 60A MeV and Ar + Ca at 180A MeV. Proper corrections for the energy lost by charged particles in passive absorbers between the target and the scintillator are essential to

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

    PubMed

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

    2012-01-01

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

  4. Persistent spectral holeburning in CaF_2:Tm^3+:D^-

    NASA Astrophysics Data System (ADS)

    Strickland, N. M.; Cone, R. L.; Macfarlane, R. M.

    1998-03-01

    We report the observation of persistent spectral holeburning on the ^3H6 arrow ^3H4 transition of the trivalent thulium ion at 800 nm, with the goal of obtaining long-term persistence for optical storage, frequency references and signal processing. Deuteration treatment of rare-earth doped calcium fluoride gives rise to a number of new spectroscopic centers in which a rare-earth ion is adjacent to one or more negative deuteride ions. Laser-induced migration of the deuteride ions associated with such centers gives rise to bleaching of the rare-earth absorption profile. In the case of Tm^3+, hole widths of 18 MHz have been measured, and the holes show no measurable degradation 6 hours after burning. The strong ^3H_6(1)arrow ^3H_4(1) transitions of these Tm^3+ centers are favorable for application as frequency references as they have no hyperfine structure, and diode lasers are available in this spectral region.

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

    DOE Data Explorer

    Kristin Persson

    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

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

    SciTech Connect

    Kristin Persson

    2014-11-02

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

  7. Some dielectric and optical properties of ErF 3-doped CaF 2 crystals

    NASA Astrophysics Data System (ADS)

    Nicoara, Irina; Munteanu, Mihai; Preda, Eleonora; Stef, Marius

    2008-04-01

    Calcium fluoride crystals doped with ErF 3 and PbF 2 have been grown using the vertical Bridgman method. Temperature and frequency dependence of the complex dielectric constant have been measured at seven audio frequencies (1-100 kHz) over the temperature range of 150-300 K. The activation energy for dipole reorientation and the relaxation time constant, ?0, has been determined from the observed relaxation processes. The effect of Er 3+, Pb 2+ ions and the X-ray irradiation on the optical and dielectric spectra was studied. A comparison of our results with those obtained by other authors is also given.

  8. Biaxially Textured Al Film Growth on CaF2 Nanostructures toward a Method of

    E-print Network

    Wang, Gwo-Ching

    -Crystalline Si Film on Glass Substrates Huafang Li,* Patrick Snow, Ming He, Pei-I Wang,* Gwo-Ching Wang, and Toh consider- able interest in the growth of biaxi- ally crystallographic textured films on glass and flexible textured films can have comparable properties to their single- crystalline counterparts, and (b) the glass

  9. Last advances in Yb3+ doped CaF2 ceramics synthesis

    NASA Astrophysics Data System (ADS)

    Mortier, Michel; Lyberis, Andréas; Saganuma, Akiko; Stevenson, Adam; Vivien, Daniel; Gredin, Patrick; Patriarche, Gilles

    2011-02-01

    One at% Yb:CaF2 transparent ceramics for high power lasers are obtained by vacuum sintering and hot pressing nanoparticles synthesized through a soft chemistry route. The residual optical losses of these ceramics are as low as 0.09 cm-1 (corresponding to an in-line transmittance of 96.7%) at 1200 nm. Densification during sintering is limited by large voids, but pressure assisted densification after sintering results in high optical quality transparent ceramics. Absorption spectra are similar to Yb:CaF2 single crystal, and the fluorescence lifetime was measured to be 2 ms in the wavelength 1010 to 1050 nm range. The 1 at% Yb:CaF2 transparent ceramics successfully produced laser oscillation at 1031 nm when placed in an Omega-type laser cavity under 970 nm diode laser pumping.

  10. Ultralow-threshold Raman lasing with CaF2 Ivan S. Grudinin and Lute Maleki

    E-print Network

    possible by the ultrahigh optical quality factor of the cavity, of the order of Q=5 1010 . Stokes radiation at vir- tually any wavelength within a material's spectral transparency window. Generation in a WGM cavity is given by the following equation6 : Pth = 2 n2 gcQSQP Vm P S . 1 Here, n

  11. Pressure-induced Structrual Transitino in CaF2 Nanocrystals

    SciTech Connect

    J Wang; J Hao; Q Wang; Y Jin; F Li; B Liu; Q Li; B Liu; Q Cui

    2011-12-31

    The structural transition of CaF{sub 2} nanocrystals was studied by in situ high pressure synchrotron radiation X-ray diffraction measurements up to about 46.5?GPa at ambient temperature. A pressure-induced fluorite structure (Fm3m) to orthorhombic PbCl{sub 2}-type structure (Pnma) transition starts at 14.0?GPa, and phase transition is sluggish. The orthorhombic phase of nanocrystalline CaF{sub 2} is stable up to 46.5?GPa. The enhancement of transition pressure in CaF{sub 2} nanocrystals as compared with the corresponding bulk material is mainly caused by the surface energy difference between the phases involved.

  12. Last advances in Yb3+ doped CaF2 ceramics synthesis

    Microsoft Academic Search

    Michel Mortier; Andréas Lyberis; Akiko Suganuma; Adam Stevenson; Daniel Vivien; Patrick Gredin; Gilles Patriarche

    2011-01-01

    One at% Yb:CaF2 transparent ceramics for high power lasers are obtained by vacuum sintering and hot pressing nanoparticles synthesized through a soft chemistry route. The residual optical losses of these ceramics are as low as 0.09 cm-1 (corresponding to an in-line transmittance of 96.7%) at 1200 nm. Densification during sintering is limited by large voids, but pressure assisted densification after

  13. Laser interactions with embedded Ca metal nanoparticles in single crystal CaF2

    E-print Network

    Dickinson, J. Thomas

    the wavelength dependence of the bleaching process to the wavelength dependence associated with Mie absorption- tals produced by rapid growth for the National Ignition Facility.3,4 When damage is caused called colloids, are readily produced by relatively low energy electrons 2 keV at modest doses 5 mC/cm2

  14. Structural, electronic and optical properties of fluorite-type compounds

    NASA Astrophysics Data System (ADS)

    Khenata, R.; Daoudi, B.; Sahnoun, M.; Baltache, H.; Rérat, M.; Reshak, A. H.; Bouhafs, B.; Abid, H.; Driz, M.

    2005-09-01

    A theoretical study of structural, elastic, electronic and optical properties of CaF2, SrF2 and BaF2 is presented, using the full-potential linearized augmented plane-wave (FPLAPW) method as implemented in the Wien97 code. In this approach the generalized gradient approximation (GGA) was used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus, its pressure derivative and elastic constants. Band structure, density of states, pressure coefficients of energy gaps and refractive indices are also given. The results are compared with previous calculations and experimental data.

  15. 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.

  16. Effect of Ca and buffer layers on the performance of organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum

    Microsoft Academic Search

    Shengwei Shi; Dongge Ma

    2010-01-01

    The effects of buffer layers, including LiF, LiCl, NaF, NaCl, NaI, KI, RbF, RbCl, CsF, CsCl, MgF2, CaF2, BaF2, and BaCl2 on electron injection and device performance in organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum, were investigated systematically. The insertion of the buffer layers at the organic\\/cathode interface not only reduced the operating voltage, but also enhanced the luminance and

  17. 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.

  18. On the cosmic-ray induced background in neutral pion production measurements with a BaF 2 multidetector

    NASA Astrophysics Data System (ADS)

    Badalà, A.; Barbera, R.; Palmeri, A.; Pappalardo, G. S.; Riggi, F.; Russo, A. C.; Russo, G.; Turrisi, R.

    1995-02-01

    The problem of the cosmic-ray induced background in neutral pion production measurements with barium fluoride multidetectors is discussed. As a reference example, the response to cosmic rays of the MEDEA photon spectrometer is studied. The interaction of the cosmic radiation with the experimental filter has been treated by means of full Monte Carlo computer simulations with the GEANT3 code. The results of the simulations are compared with experimental data and general criteria to minimize the cosmic background are discussed.

  19. Absolute light yield measurements on SrF$_{2}$ and BaF$_{2}$ doped with rare earth ions

    E-print Network

    Shendrik, Roman

    2013-01-01

    Results of absolute light output measurements on strontium and barium fluoride doped with PrF$_3$ and CeF$_3$ are presented and compared with scintillators having well-known light output (NaI-Tl, CsI-Tl, BGO). For pure SrF$_2$ crystal we obtain a value of about 28600 photons/MeV.

  20. Absolute light yield measurements on SrF$_{2}$ and BaF$_{2}$ doped with rare earth ions

    E-print Network

    Roman Shendrik; Evgeny Radzhabov

    2013-08-19

    Results of absolute light output measurements on strontium and barium fluoride doped with PrF$_3$ and CeF$_3$ are presented and compared with scintillators having well-known light output (NaI-Tl, CsI-Tl, BGO). For pure SrF$_2$ crystal we obtain a value of about 28600 photons/MeV.

  1. Single-frequency Ho(3+)-doped ZBLAN fiber laser at 1200 nm.

    PubMed

    Zhu, Xiushan; Zong, Jie; Miller, Andy; Wiersma, Kort; Norwood, R A; Prasad, Narasimha S; Chavez-Pirson, Arturo; Peyghambarian, N

    2012-10-15

    A single-frequency (SF) fiber laser at 1200 nm was developed with a distributed Bragg reflector (DBR) configuration by splicing a 22 mm long highly holmium-doped ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF) fiber with a pair of silica fiber Bragg gratings. The linewidth was estimated to be less than 100 kHz based on the measured frequency noise. The relative intensity noise was measured to be <110 dB/Hz at the relaxation oscillation peak and the polarization extinction ratio was measured to be >19 dB. Our results highlight the exciting prospect that wavelength coverage of SF DBR fiber lasers can be expanded significantly by using rare-earth-doped ZBLAN fibers. PMID:23073405

  2. White emission from Tm3+/Tb3+/Eu3+ co-doped fluoride zirconate under ultraviolet excitation

    NASA Astrophysics Data System (ADS)

    Sun, Jian; Zhang, Xiao-Song; Yuan, Lin-Lin; Feng, Zhi-Jun; Ling, Zhi; Li, Lan

    2014-11-01

    We synthesize Tm3+/Tb3+/Eu3+ triply-doped ZrF4—BaF2—LaF3—AlF3—NaF (ZBLAN) transparent glass by using a melt-quenching method. Under excitation of 365 nm, the white emission with Commission internationale deL'Eclairage (CIE) coordinates of (0.33, 0.33) is achieved at the Eu3+ concentration of 1.1 mol%. The mechanisms for white emission and the energy transfer process of Tb3+ ? Eu3+ are discussed in terms of the photoluminescence, photoluminescence excitation spectra, and the light emission decay curves. The nature for the Tb3+ ? Eu3+ energy transfer is described with the aid of an energy level diagram.

  3. 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.

  4. 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.

  5. 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.

  6. Pressure induced structural and magnetic phase transition in magnesium nitrides MgNx (x = 1, 2, 3): A first principles study

    NASA Astrophysics Data System (ADS)

    Rajeswarapalanichamy, R.; Sudhapriyanga, G.; Cinthia, A. Jemmy; Santhosh, M.; Murugan, A.

    2014-04-01

    The structural and magnetic properties of magnesium nitrides are investigated by the first principles calculations based on density functional theory using Vienna ab-initio simulation package. The calculated lattice parameters are in good agreement with the available results. A pressure-induced structural phase transition from NaCl to CsCl in MgN, CaF2 to AlB2 in MgN2 and LaF3 to BiF3 phase in MgN3 is observed. At ambient condition MgN and MgN3 are stable in the ferromagnetic state. On further increasing the pressure, a ferromagnetic to non magnetic transition is observed in MgN.

  7. 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.

  8. 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.

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

    PubMed Central

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

    2012-01-01

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

  10. 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.

  11. Giant resonance studies with the ORNL-TAMU-MSU BaF2 detector array (Managed by Lockheed Martin Energy Research Corp. for the U.S. DOE)

    Microsoft Academic Search

    R. L. Varner; J. R. Beene; N. Gan; D. H. Olive; D. W. Stracener

    1996-01-01

    The inelastic excitation and photon decay of giant resonances is a powerful tool for the study of the nuclear continuum. Photon decay can be used to isolate the giant dipole resonance (GDR) under conditions in which it is weakly excited, and embedded in in a large background. Excitation of this collective isovector mode by the hadronic interaction in the scattering

  12. Molecular beam epitaxial growth of IVVI multiple quantum well structures on Si,,111... and BaF2,,111... and optical studies of epilayer heating

    E-print Network

    McCann, Patrick

    transmission, and midinfrared photoluminescence PL . Numerous satellite diffraction peaks and narrow linewidths heating in the MQW samples due to optical pumping. For a typical laser pumping power of 9.1 W/cm2 temperatures and allow light emission using low inten- sity pump sources such as unfocused diode lasers. PL

  13. 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.

  14. 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.

  15. 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.

  16. Strain and strain relaxation analysis of superconducting Ba(Fe0.92Co0.08)2As2 films on various substrates

    NASA Astrophysics Data System (ADS)

    Rafti, Artemis; Lei, Q. Y.; Golalikhani, M.; Withanage, W. K.; Qiu, J.; Hambe, M.; Williams, F.; Yang, Q.; Temple, D.; Bauer, E. D.; Ronning, F.; Jia, Q. X.; Wang, X. F.; Chen, X. H.; Weiss, J. D.; Hellstrom, E. E.; Xi, X. X.

    2014-03-01

    We have grown high quality, optimally doped superconducting Ba(Fe0.92Co0.08)2 As2 films on SrTiO3, (La, Sr)(Al, Ta)O3, LaAlO3, CaF2 and BaF2 substrates. The variation in lattice mismatch allows the study of epitaxial strain effects on the structural and transport properties of the films. Reciprocal space mapping has been employed for detailed strain and strain relaxation analysis of the Ba(Fe0.92Co0.08)2As2 films on the different substrates. We observed large substrate dependant changes in both in plane and out of plane lattice parameters. Furthermore, the crystallinity of the grown films, the lattice constant and lattice volume evolution with strain and strain relaxation were investigated, revealing an epitaxial strain and strain relaxation dependence on the superconducting transition temperature.

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

    PubMed

    Barandiarán, Zoila; Seijo, Luis

    2014-12-21

    In this paper, we report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorite-type crystals associated with Yb(2+)-Yb(3+) mixed valence pairs. By means of embedded cluster, wave function theory ab initio calculations, we show that the widely studied, very broad band, anomalous emission of Yb(2+)-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb(2+)-Yb(3+) mixed valence pairs. The IVCT luminescence is very efficiently excited by a two-photon upconversion mechanism where each photon provokes the same strong 4f(14)-1A1g? 4f(13)((2)F7/2)5deg-1T1u absorption in the Yb(2+) part of the pair: the first one, from the pair ground state; the second one, from an excited state of the pair whose Yb(3+) moiety is in the higher 4f(13)((2)F5/2) multiplet. The Yb(2+)-Yb(3+) ? Yb(3+)-Yb(2+) IVCT emission consists of an Yb(2+) 5deg ? Yb(3+) 4f7/2 charge transfer accompanied by a 4f7/2 ? 4f5/2 deexcitation within the Yb(2+) 4f(13) subshell: [(2)F5/25deg,(2)F7/2] ? [(2)F7/2,4f(14)]. The IVCT vertical transition leaves the oxidized and reduced moieties of the pair after electron transfer very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are subtracted from the normal emission. The IVCT energy diagrams resulting from the quantum mechanical calculations explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4f emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2; and the presence of additional 5d-4f emissions in SrCl2 which are absent in SrF2. They also allow to interpret and reproduce recent experiments on transient photoluminescence enhancement in Yb(2+)-doped CaF2 and SrF2, the appearance of Yb(2+) 4f-5d absorption bands in the excitation spectra of the IR Yb(3+) emission in partly reduced CaF2:Yb(3+) samples, and to identify the broadband observed in the excitation spectrum of the so far called anomalous emission of SrF2:Yb(2+) as an IVCT absorption, which corresponds to an Yb(2+) 4f5/2 ? Yb(3+) 4f7/2 electron transfer. PMID:25527954

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

    NASA Astrophysics Data System (ADS)

    Barandiarán, Zoila; Seijo, Luis

    2014-12-01

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

  19. 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

  20. 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).

  1. 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 ?m in the ultraviolet to 7 ?m 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 ?-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.

  2. 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.

  3. 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.

  4. 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.

  5. Optical absorption and fluorescence properties of Dy3+: SFB glasses

    NASA Astrophysics Data System (ADS)

    Maheswari, D. Uma; Kumar, J. Suresh; Sasikala, T.; Mohan Babu, A.; Pavani, K.; Jang, Kiwan; Rama Moorthy, L.

    2009-07-01

    This paper presents the preparation and spectroscopic characterization of Dy3+-doped sodium fluoroborate (SFB) glasses of the type (50-x) B2O3 + 25 Na2O + 10 CaF2 + 10 AlF3 + 5 LaF3 + x DyF3 (x = 0.01, 0.1, 0.5,1.0, 2.0 and 4.0 mol%). By measuring the area under absorption bands, the experimental oscillator strengths are determined. The Judd-Ofelt (J-O) intensity parameters ?? (? = 2, 4, 6) are evaluated by the least square fit method. These phenomenological parameters are used to predict luminescence properties of the lanthanide ions in SFB glasses. Photoluminescence spectra and lifetimes of 4F9/2 level of Dy3+ ions in these glasses have been measured by exciting with 348 nm line of xenon flash lamp. The measured decay curves exhibit single exponential at lower concentrations of 0.01, 0.1, 0.5 and 1.0 mol% and non-exponential at higher concentrations of 2.0 and 4.0 mol%. The predicted ?R and (?R values of 4F9/2 transition are compared with the experimentally measured values. From the magnitude of stimulated emission cross sections (?e), branching ratios (?m), multiphonon relaxation rates (WMP), the most potential laser transitions are identified and the utility of these glasses as laser active material is discussed.

  6. Dependences of the density of M 1- x R x F2 + x and R 1- y M y F3- y single crystals ( M = Ca, Sr, Ba, Cd, Pb; R means rare earth elements) on composition

    NASA Astrophysics Data System (ADS)

    Sorokin, N. I.; Krivandina, E. A.; Zhmurova, Z. I.

    2013-11-01

    The density of single crystals of nonstoichiometric phases Ba1 - x La x F2 + x (0 ? x ? 0.5) and Sr0.8La0.2 - x Lu x F2.2 (0 ? x ? 0.2) with the fluorite (CaF2) structure type and R 1 - y Sr y F3 - y ( R = Pr, Nd; 0 ? y ? 0.15) with the tysonite (LaF3) structure type has been measured. Single crystals were grown from a melt by the Bridgman method. The measured concentration dependences of single crystal density are linear. The interstitial and vacancy models of defect formation in the fluorite and tysonite phases, respectively, are confirmed. To implement the composition control of single crystals of superionic conductors M 1 - x R x F2 + x and R 1 - y M y F3 - y in practice, calibration graphs of X-ray density in the MF2- RF3 systems ( M = Ca, Sr, Ba, Cd, Pb; R = La-Lu, Y) are plotted.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    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 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 ?-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.

  9. Three-and four-m-thick YBa2Cu3O7 layers with high critical-current densities on flexible metallic substrates by the BaF2 process

    E-print Network

    Johnson, Peter D.

    -current density Jc for these films was 3.8 103 A/mm2 at 77 K and in 1 T external magnetic field perpendicular to the film plane. Also, estimated critical-current densities per width of tape Jcw at zero magnetic field making multilayers of YBCO 1 m and CeO2 50 nm films by PLD.5 This is, in essence, replacing a thick film

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  11. Excitation of the S-1(0) State of Trivalent Praseodymium in Insulating Crystals

    NASA Astrophysics Data System (ADS)

    Levey, Christopher Gerrit

    In this dissertation we present an investigation of the fluorescence and two-photon absorption properties of the ('1)S(,0) state of Pr('3+) in LaF(,3) and several other crystal hosts. The high-lying (4f('2)) ('1)S(,0) state of Pr('3+) is of particular interest because it is the closest of the meta-stable rare earth levels to the next configuration of opposite parity (the 4f5d band), and this proximity varies from host to host. However, the ('1)S(,0) state has received relatively little attention because its energy is beyond the range of dye lasers and frequency doubling crystals. We excite the ('1)S(,0) state directly, through a two-photon excited state absorption process, and indirectly, through pumping the 4f5d band. In most host materials the ('1)S(,0) level of Pr('3+) lies above the lowest 4f5d band component, and consequently only 4f5d band emission is observed. In LaF(,3), however, the ('1)S(,0) state lies below the band, and only the ('1)S(,0) emission is observed. In Pr('3+):CaF(,2) there are sites with each of these properties, and both ('1)S(,0) and 4f5d emission are observed, with a relative strength that is concentration dependent. Two-photon absorption from the ('3)H(,4) ground state into the ('1)S(,0) state is doubly forbidden by the two-photon spin and J selection rules ((DELTA)S = 0 and (DELTA)J <= 2), and we have not observed this transition. However, we do observe a two-photon absorption into the ('1)S(,0) state from each of the lowest two Stark components of the meta-stable ('1)D(,2) state. These transitions are allowed by all two-photon selection rules, though not for all polarizations, and we observe a strong polarization dependence. We also observe line narrowing of this transition as a smaller subset of the ('1)D(,2) population is excited, and we see homogeneous broadening of the transition as the temperature is raised to 77K. The ('1)S(,0) lifetime is much shorter than that predicted by the Judd-Ofelt theory, and is only weakly concentration dependent. We account for the short lifetime with a modification of the theory to make it more appropriate for transitions involving one state which is very close to the next opposite parity configuration.

  12. TV-VI semiconductor quantum well lasers, physics and engineering

    NASA Astrophysics Data System (ADS)

    Khodr, Majed Fouad

    1994-05-01

    In this work, a theoretical model that calculates the gain-current density relationship for IV-VI semiconductor quantum well lasers was developed. The model, based on Kane's two band model, solves for the anisotropy in the constant energy surfaces and for the strong nonparabolicity of the bands. The system investigated was the EuSePbSe(0.78)Te(0.22) quantum well structure at 77 K. The nonparabolicity of the bands in the growth direction was found to shift the energy levels in the PbSe(0.78)Te(0.22) quantum well to lower energies as compared to a quantum well with parabolic bands. Nonparabolicity of the bands also resulted in an energy dependent density of states in the junction plane of the structure. These two effects cause the gain-current density relation for the parabolic system to be altered. The single quantum well (SQW) design was optimized by investigating three quantum well structures: the multiple quantum well (MQW), the modified multiple quantum well (MMQW) and the separate confinement heterostructure-single quantum well (SCH-SQW) structures. The effects of nonparabolicity on the confinement factor and threshold current values were also calculated. Nonparabolicity lowers the confinement factor values and thus, the modal gain. Also, it increases the threshold current values for short cavity lasers. For moderate and long cavity lasers, these effects are negligible. Studies were performed on BaF2 films because of their importance as intermediate layers that lattice match the IV-VI semiconductor devices to silicon. BaF2 films were grown in a vacuum system with a base pressure of 10(exp -6) Torr on Si(111) substrates at four substrate temperatures: room temperature, 250 C, 450 C and 650 C. The fluoride films were characterized using ellipsometry, X-ray diffraction, scanning electron microscopy (SEM) and capacitance versus voltage techniques. At a growth temperature of 650 C, the BaF2 films were epitaxial with a (111) preferred growth direction. At this temperature, the surface was partially smooth with some cracking apparent. Prolonged heating of a chemically uncleaned substrate before deposition resulted in smooth and crack-free CaF2 films. The electrical properties of the films correlated with the thermal history of the sample rather than with the crystalline quality.

  13. Iv-Vi Semiconductor Quantum Well Lasers, Physics and Engineering

    NASA Astrophysics Data System (ADS)

    Khodr, Majed Fouad

    In this work, a theoretical model that calculates the gain-current density relationship for IV-VI semiconductor quantum well lasers was developed. The model, based on Kane's two band model, solves for the anisotropy in the constant energy surfaces and for the strong nonparabolicity of the bands. The system investigated was the EuSe-PbSe _{0.78}Te_{0.22} quantum well structure at 77 K. The nonparabolicity of the bands in the growth direction was found to shift the energy levels in the PbSe_{0.78}Te _{0.22} quantum well to lower energies as compared to a quantum well with parabolic bands. Nonparabolicity of the bands also resulted in an energy dependent density of states in the junction plane of the structure. These two effects cause the gain-current density relation for the parabolic system to be altered. The single quantum well (SQW) design was optimized by investigating three quantum well structures: the multiple quantum well (MQW), the modified multiple quantum well (MMQW) and the separate confinement heterostructure-single quantum well (SCH-SQW) structures. The effects of nonparabolicity on the confinement factor and threshold current values were also calculated. Nonparabolicity lowers the confinement factor values and thus, the modal gain. Also, it increases the threshold current values for short cavity lasers. For moderate and long cavity lasers, these effects are negligible. Studies were performed on BaF_2 films because of their importance as intermediate layers that lattice match the IV-VI semiconductor devices to silicon. BaF_2 films were grown in a vacuum system with a base pressure of 10^ {-6} Torr on Si(111) substrates at four substrate temperatures: room temperature, 250^ circC, 450^circC and 650^circC. The fluoride films were characterized using ellipsometry, X-ray diffraction, scanning electron microscopy (SEM) and capacitance versus voltage techniques. At a growth temperature of 650 ^circC, the BaF_2 films were epitaxial with a (111) preferred growth direction. At this temperature, the surface was partially smooth with some cracking apparent. Prolonged heating of a chemically uncleaned substrate before deposition resulted in smooth and crack-free CaF_2 films. The electrical properties of the films correlated with the thermal history of the sample rather than with the crystalline quality.

  14. 4.5 W mid-infrared supercontinuum generation in a ZBLAN fiber pumped by a Q-switched mode-locked Tm3+- doped fiber laser

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  16. Mid-infrared supercontinuum laser system and its biomedical applications

    NASA Astrophysics Data System (ADS)

    Xia, Chenan

    A mid-infrared supercontinuum (SC) laser system is developed, which provides a continuous spectrum from ˜0.8 to ˜4.5 microm and is pumped by amplified nanosecond laser diode pulses. The SC laser uses ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fluoride fibers. The SC light source is all-fiber-integrated with no moving parts, operates at room temperature, and eliminates the need of mode-locked lasers. The time-averaged power of the SC is scalable up to 10.5 W by amplifying the pump pulses using cladding-pumped erbium/ytterbium co-doped fiber power amplifiers. SC has also been generated in silica fibers with spectrum extending to ˜3 microm and an average power up to 5.3 W. The SC laser system comprises an all-fiber-spliced high power pump laser system followed by nonlinear optical generation fibers, i.e. ZBLAN and silica fibers. The SC generation is initiated by breaking up the nanosecond diode pulses into femtosecond pulses through modulation instability, and the spectrum is then broadened through the interplay of self-phase modulation, parametric four-wave mixing, and stimulated Raman scattering. Theoretical simulations have been carried out to study the SC generation mechanism by numerically solving the generalized nonlinear Schrodinger equation. The SC long wavelength edge is limited by the intrinsic fiber material absorption, i.e. ˜3 microm in silica fibers and ˜4.5 microm in ZBLAN fibers, respectively. Mid-infrared absorption spectroscopy of the constituents of normal artery, e.g. endothelial cells and smooth muscle cells, and atherosclerotic plaques, e.g. adipose tissue, macrophages and foam cells, and selective ablation of lipid-rich tissues have also been demonstrated using the SC laser system.

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

    PubMed

    Weil, Matthias

    2015-06-01

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

  18. Nanostructures created in SiO2 surface: A comparison between the impingement by slow highly charged ions and by swift heavy ions

    NASA Astrophysics Data System (ADS)

    El-Said, A. S.

    2012-07-01

    Swift heavy ions (SHI) of MeV-GeV energy lead to the creation of nanometric surface structures as well as modifications in the bulk along the ion penetration depth. Recently, similar surface modifications have been observed for the impact of individual slow highly charged ions (HCI). Non-amorphizable ionic-halide single crystals, like KBr, CaF2 and BaF2, are considered as the most intensively studied materials after irradiation with HCI. In this contribution we study the creation of surface nanostructures in an amorphizable material, namely SiO2 quartz after irradiation with slow highly charged Xe ions from the Electron Beam Ion Trap at Helmholtz Zentrum Dresden-Rossendorf and swift xenon ions from Universal Linear Accelerator at GSI in Darmstadt. After irradiation at room temperature, the crystals were investigated by scanning force microscopy. For both SHI and HCI, the created nanostructures exhibit the shape of hillocks. Moreover UV-VIS spectroscopy was performed to identify the defects created by ion irradiation at high fluence. The results are discussed in terms of the creation mechanisms driven by the dependence on both potential and kinetic energies of the ions.

  19. 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)].

  20. 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.

  1. 2.7 ?m emission of high thermally and chemically durable glasses based on AlF3.

    PubMed

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

    2014-01-01

    AlF3-based glasses (AlF3-YF3-CaF2-BaF2-SrF2-MgF2) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 ?m mid-infrared emission in the AlF3-based glasses was also investigated through the absorption and emission spectra. Both the temperature of glass transition and the characteristic temperatures (?T, Hr, k(gl)) of the fluoroaluminate glasses were much larger than those of the ZBLAN glasses. The corrosion phenomenon can be observed by naked-eye, and the transmittance dropped dramatically (0% at 3 ?m) when the ZBLAN glass was placed into distilled water. However, the AlF3-based glass was relatively stable. The fluoroaluminate glasses possessed large branching ratio (20%) along with the emission cross section (9.4×10(-21) cm(-2)) of the Er(3+):(4)I(11/2)?(4)I(13/2) transition. Meanwhile, the enhanced 2.7 ?m emission in highly Er(3+)-doped AYF glass was obtained. Therefore, these results showed that this kind of fluoride glass has a promising application for solid state lasers at 3 ?m. PMID:24402172

  2. 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.

  3. Structural and transport properties of epitaxial Ba(Fe1?xCox)2As2 thin films on various substrates

    NASA Astrophysics Data System (ADS)

    Lei, Q. Y.; Golalikhani, M.; Yang, D. Y.; Withanage, W. K.; Rafti, A.; Qiu, J.; Hambe, M.; Bauer, E. D.; Ronning, F.; Jia, Q. X.; Weiss, J. D.; Hellstrom, E. E.; Wang, X. F.; Chen, X. H.; Williams, F.; Yang, Q.; Temple, D.; Xi, X. X.

    2014-11-01

    A comprehensive microstructural study was conducted on optimally-doped epitaxial Ba(Fe1?xCox)2As2 thin films grown by pulsed laser deposition on various substrates of a wide range of lattice constants: SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, MgO, CaF2, and BaF2. We found that epitaxial strain directly affects the superconductivity in the film, with the transition temperature decreasing linearly with increasing in-plane lattice constant of the film. However, the strain is not determined by the lattice mismatch between the film and substrate. Instead, the mosaic spread of the grain orientation in the film and the thermal expansion coefficient of the substrate were found to correlate well with the in-plane lattice constant of the film. The result confirms the importance of structural distortions to the superconductivity in the Ba(Fe1?xCox)2As2 films.

  4. 2.7 ?m emission of high thermally and chemically durable glasses based on AlF3

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  5. 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 [Ruhr-Universitat Bochum; Behrends, F [Westfalische Wilhelsm-Universitat Munster; Cybinska, J [Ruhr Universitat Bochum; Eckert, H [Westfalische Wilhelsm-Universitat Munster; Mudring, Anja -V [Ames Laboratory

    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.

  6. Fission products behavior in molten fluoride salts: Speciation of La3+ and Cs+ in melts containing oxide ions

    NASA Astrophysics Data System (ADS)

    Rollet, Anne-Laure; Veron, Emmanuel; Bessada, Catherine

    2012-10-01

    In this paper we address the effects of fission products on the speciation in molten fluoride salts. Numerous systems with cross-connections have been investigated in order to better identify the influence of CsF in a fluoride melt containing rare earth and oxides : LaF3-AF (A = Li, Na, K, Rb and Cs), LaF3-LiF-CsF, LaF3-LiF-CaF2, LaF3-LiF-CaO, LaF3-LiF-CaO-CsF. In this goal, we performed high temperature NMR experiments and followed in situ the evolution of 19F, 23Na, 85Rb, 133Cs and 139La NMR chemical shifts. In LaF3-AF-CsF and LaF3-AF-CaF2 systems, the coordination number of lanthanum cation ranges from 6 to 8 depending on the LaF3 concentration and on the polarizability of the other cations. The addition of oxide (CaO) in the latter mixtures leads to the formation of lanthanum oxyfluoride species that precipitate in LaOF when CaO concentration is increased. The addition of CsF to LaF3-LiF-CaO yields to a displacement of the dissolved versus precipitated LaOF proportion.

  7. Microwave study of photoconductivity induced by laser pulses in rare-earth-doped dielectric crystals

    NASA Astrophysics Data System (ADS)

    Joubert, M.-F.; Kazanskii, S. A.; Guyot, Y.; Gâcon, J.-C.; Pédrini, C.

    2004-04-01

    Transient responses of the dielectric permittivity ?=?1-i?2 of rare-earth-doped dielectric crystals under pulsed laser excitation were studied by the 8-mm microwave resonator technique at room temperature. The fluorite-type crystals (CaF2, SrF2, and BaF2) which contained divalent ions of Sm, Eu, and Tm, as well as Lu2(SiO4)O and Y3Al5O12 doped with trivalent Ce ions were investigated. The dielectric response to a laser pulse contains two different types of signals: electronic and heating ones. The electronic peak, which is quite fast (from 40 to 100 ns or more), is the signature of electrons released into the conduction band following an impurity photoionization. The prolonged heating signal has a sawtooth form on which oscillations are imposed. It is due to modulation of the dielectric constant by a sudden temperature rise and subsequent elastic vibrations of the sample caused by the energy absorbed from the laser pulse. In different crystals the electronic peak was caused by the transient response of either ?1, ?2, or a mixture of the two. The modulation of the dielectric loss factor ?2 corresponds to conventional photoconductivity, i.e., the photoexcitation of mobile electrons. The modulation of the dielectric constant ?1 corresponds to the photoexcitation of “bound” electrons, probably captured by traps. The threshold energies of photons at which the photoionization of rare-earth ions may occur, were determined for CaF2:Sm2+ (3.3 eV) and Lu2(SiO4)O:Ce3+ (3.1 eV). In fluorite-type crystals doped with Sm2+ or Tm2+ ions, the significant reduction of a lifetime of electrons in a conduction band was revealed with an increase in energy of laser pulses. In SrF2:Eu crystal the record-high signals of “photoconductivity” were observed upon excitation by VIS light in the optical region of “transparency” of this crystal. The microwave resonant technique may be used for detail studying the photoionization dynamics of rare-earth ions and finding the location of their energy levels with respect to the host conduction band in doped insulators.

  8. Phosphate base laser glasses

    SciTech Connect

    Izumitani, T.; Tsuru, M.

    1980-12-16

    A phosphate base laser glass comprising 55-70% P2O5, 1-15% Al2O3, 0-25% Li2O, 0-25% Na2O, 0-8% K2O, the total proportion of Li2O, Na2O, and K2O being 10-25%, 0-15% BaO, 0-15% ZnO, 0-15% CaO , 0-15%, sro, 0-15% MgO, the total proportion of BaO, ZnO, CaO, SrO, and MgO being 5-15%, 0-5% Y2O3, 0-5% La2O3, 0-5% GeO2, 0-5% CeO2, 0-3% Nb2O5, 0-3% MnO2, 0-2% Ta2O5, 0-1% Sb2O3, and 0.01-5% Nd2O3, all % being mole %. The phosphate base laser glass of this invention has a high induced emission cross section, a low non-linear refractive index coefficient, and excellent acid resistance and divitrification resistance. By replacing partially or wholely one or more of LiO2, Na2O, K2O, BaO, ZnO, CaO, SrO, MgO or Al2O3 by LiF, NaF, KF , BaF2ZnF2, CaF2, SrF2, MgF2 or AlF3, respectively, the above properties of the laser glass are further improved.

  9. 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 ?m and a cladding diameter of 125 ?m. 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 ?m 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.

  10. 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 ?m in the UV to 7 ?m 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 ?-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 ?-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, ?-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.

  11. 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.

  12. 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.

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

    NASA Technical Reports Server (NTRS)

    Tsuo, Y. H.; Sher, A.

    1981-01-01

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

  14. 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.

  15. A Wide-Field Camera for 1-2.5mu M Imaging at the 2.3 and 6.5m Telescopes

    NASA Astrophysics Data System (ADS)

    McCarthy, D. W.; Ge, J.; Hinz, J. L.; Finn, R. A.; Low, F. J.; Cheselka, M.; Salvestrini, K.

    1998-12-01

    The advent of large format focal plane arrays permits efficient wide-field imaging at near-infrared wavelengths. We have commissioned a new camera (PISCES) to provide circular fields of 8.5 and 3.0 arcmin diameter at the f/9 foci of the 2.3m Bok telescope and 6.5m MMT. The design uses refractive optics with spherical lenses made from conventional materials (CaF_2, BaF_2, IR-SiO_2). The dewar window is an achromatic doublet which produces a high quality pupil image. A cold pupil stop yields low emissivity by baffling the telescope's central obscuration, primary edge, and spider vanes. Pupil-viewing optics provide precise alignment of the telescope pupil. Four additional lenses then reimage the telescope focal plane at f/3.3, leading to scales of 0.5 and 0.18 arcsec/pixel, respectively. These scales are well matched to the seeing at the two sites. The focal plane array is a 1024x1024 pixel HgCdTe (HAWAII readout) detector from Rockwell. PISCES utilizes an SDSU array controller based on fiber-optic communication with a PCI-bus computer. Performance measurements have been conducted at the 2.3m telescope. Image quality is FWHM <2 pixels across the full array from 1-2.5mu m. Overall instrument transmission is 50-55%, including the detector quantum efficiency. Emissivity is measured to be 5-7%. On the 2.3m telescope, point source detection limits of J=17.5, H=17.0, K_s=16.5 (10-sigma/min) are achieved routinely. At the 6.5m MMT we anticipate an improvement of ~ 2 magnitudes. PISCES is currently being used for scientific studies of quasar environments (Finn et al., this conference), searches for brown dwarfs as common proper motion companions, and imaging of star formation regions. PISCES and its successor (ARIES) on the 6.5m MMT are supported by the NSF through grant AST-9623788.

  16. [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

  17. Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films

    PubMed Central

    2012-01-01

    The electrochemical properties of fluoride-coated lithium cobalt oxide [LiCoO2] thin films were characterized. Aluminum fluoride [AlF3] and lanthanum fluoride [LaF3] coating layers were fabricated on a pristine LiCoO2 thin film by using a spin-coating process. The AlF3- and LaF3-coated films exhibited a higher rate capability, cyclic performance, and stability at high temperature than the pristine film. This indicates that the AlF3 and LaF3 layers effectively protected the surface of the pristine LiCoO2 film from the reactive electrolyte. PMID:22221488

  18. Blue Emission of ZnGa 2 O 4 Nanoparticles Dispersed in Fluoride Thin Films via Sol-Gel Process

    Microsoft Academic Search

    Hiroki Naito; Shinobu Fujihara; Toshio Kimura

    2003-01-01

    Nanocomposite thin films where ZnGa2O4 nanoparticles were dispersed in fluorides, MgF2 or LaF3, were prepared by a sol-gel method using metal acetates and nitrates as starting reagents and trifluoroacetatic acid as a fluorine source. ZnGa2O4 and the fluorides such as MgF2 and LaF3 were formed simultaneously after the heat treatment of the spin-coated gel films as evidenced by X-ray diffraction.

  19. OAK RIDGE NATIONAL LABORATORY U.S. DEPARTMENT OF ENERGY

    E-print Network

    Solution Based Buffer Layers Deposition Methods: ·YBCO: ex-situ BaF2 (or TFA) ·YSZ and CeO2 : rf sputtering · Compatible with ex-situ BaF2 (or TFA) Materials under consideration La2Zr2O7 (LZO) and CeO2 NiW YBCO Y2O3 YSZ CeO2 NiW Solution Buffers YBCO #12;OAK RIDGE NATIONAL LABORATORY U.S. DEPARTMENT OF ENERGY 26 28 30

  20. Radiation damage and recovery in the light emittance efficiency and the attenuation length of barium fluoride scintillator

    Microsoft Academic Search

    Akira Murakami; Hiromitsu Asakura; Hideki Yoshinaka

    1991-01-01

    Radiation damage and its recovery in the light emittance efficiency and the attenuation length of barium fluoride (BaF2) scintillator have been investigated. The light yield and transmittance of small samples of BaF2 scintillator were measured after gamma-irradiation from 0.5×104 to 1.1×105 Gy for deterioration, and after sunlight exposure for recovery. Suspension of deterioration was observed both in light yield and

  1. An in situ spectroscopic study of the local structure of oxyfluoride melts: NMR insights into the speciation in molten LiF-LaF3-Li2O systems.

    PubMed

    Rollet, Anne-Laure; Matsuura, Haruaki; Bessada, Catherine

    2015-01-14

    The local structure of molten LaF3-LiF-Li2O has been investigated by high temperature NMR spectroscopy. The (139)La and (19)F chemical shifts have been measured as a function of temperature and composition. The NMR spectra show that Li2O reacts completely with LaF3 to form a LaOF compound in the solid state below the melting temperature of the sample. LaOF is not completely dissolved in the fluoride melt and solid LaOF is observed in the (19)F spectra for Li2O concentrations above 10 mol%. We discuss the local environment of lanthanum ions in molten LaF3-LiF-Li2O and compare the results to those with the LaF3-LiF-CaO system. The analysis of the temperature and Li2O concentration dependences of the (139)La and (19)F chemical shifts suggests that several kinds of lanthanum oxyfluoride long-lived LaOxFy(3-x-y) units are present in the melt. PMID:24851926

  2. 1250 IEEE SENSORS JOURNAL VOL. 6, NO. 5, OCTOBER 2006 Room-Temperature Hydrogen Sensitivity

    E-print Network

    Moritz, Werner

    layer at the metal/oxide interface lead to a change of the threshold voltage in field-effect transistors, and Jan Szeponik Abstract--An LaF3 layer was shown to improve the character- istics of field-effect gas and a detection limit of 10-ppm hydrogen in atmospheric air. The response time was shown to be about 110

  3. Pion dosimetry with thermoluminescent materials.

    PubMed

    Hoffmann, W; Möller, G; Blattmann, H; Salzmann, M

    1980-09-01

    Various thermoluminescent materials (6LiF, 7LiF, Li2B4O7:Mn, CaSO4:Dy, CaF2:Mn, CaF2-Dy, CaF2:Tm) were irradiated with pi- mesons throughout the depth dose distribution of a beam with central momentum of 176 MeV/c. Doses from 0.05 to 2 Gy were used and linearity and reproducibility were investigated. For LiF, CaF2:Dy and CaF2:Tm, low- and high-temperature peaks were analysed separately. CaF2:Tm was found to be the most suitable for pi- dosimetry since the total dose and the high LET component could be determined using the integral TL signal and the peak height ratio of the 150 degrees C and 240 degrees C peaks. In the dose range used, both peak responses are linear with dose and the sensitivity of the materials is 10 times that of LiF. The reproducibility was +/- 3%. The high temperature peak of 7LiF is too small to be determined accurately and the high temperature peak of CaF2:Dy decreases with increasing LET in the same way was the low temperature peak does, so that no LET information can be extracted. PMID:7454772

  4. 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.

  5. Microstructural characterization in nanocrystalline ceramic thin films

    NASA Astrophysics Data System (ADS)

    Kim, Hakkwan

    The primary objective of this research is to investigate the effects of process variables on microstructure in several fluoride and oxide thin films prepared by vapor deposition, in order to predict the properties and behaviors of nanocrystalline thin film materials. There are three distinct stages of this research. The first stage focuses on measuring of the porosity in polycrystalline thin films of a variety of fluorides as a function of the substrate temperature during deposition, and discussing the mechanism by which the porosity varies as a function of the process variables. We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF 2) and calcium fluoride (CaF2) using an atomic force microscope (AFM) and a quartz crystal thickness monitor. The porosity is very sensitive to the substrate temperature and decreases as the substrate temperature increases. Consistent behavior is observed among all of the materials in this study. The second stage is to understand the film microstructure including grain growth and texture development, because these factors are known to influence the behavior and stability of polycrystalline thin films. This study focuses on grain growth and texture development in polycrystalline lithium fluoride thin films using dark field (DF) transmission electron microscopy (TEM). It is demonstrated that we can isolate the size distribution of <111> surface normal grains from the overall size distribution, based on simple and plausible assumptions about the texture. The {111} texture formation and surface morphology were also observed by x-ray diffraction (XRD) and AFM, respectively. The grain size distributions become clearly bimodal as the annealing time increases, and we deduce that the short-time size distributions are also a sum of two overlapping peaks. The smaller grain-size peak in the distribution corresponds to the {111}-oriented grains which do not grow significantly, while all other grains increase in size with annealing time. A novel feature of the LiF films is that the {111} texture component strengthens with annealing, despite the absence of growth for these grains, through the continued nucleation of new grains. The third stage focuses on the evaluation of triple junction energy in nanocrystalline ZrO2 thin films. Grain boundaries and triple junctions are important aspects of the microstructure of most crystalline materials, and it is necessary to understand them to be able to predict the behavior of bulk polycrystals and polycrystalline thin films. Triple junctions, where three grains or grain boundaries meet, become increasingly important in nanocrystalline materials where they occupy an increasing fraction of the total volume of the material. It would therefore be of great significance to know whether, and if so how triple junction energy varies. In this study we evaluate triple junction energies in nanocrystalline ZrO2 thin films using thickness mapping images produced by energy filtered transmission electron microscopy (EFTEM), which enable us to measure the surface topography associated with grain boundaries and triple junctions. In our films, the triple junction energy is deduced to be either zero (within the accuracy of the measurement) for most, but significantly positive for a few of the junctions.

  6. Characterization of the glow-peak fading properties of six common thermoluminescent materials

    Microsoft Academic Search

    John A. Harvey; Nathan P. Haverland; Kimberlee J. Kearfott

    2010-01-01

    The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 30d are examined. Glow peaks were fit to the first-order kinetics model using a computerized glow curve deconvolution program. Dosimeters studied were LiF:Mg,Ti, CaF2:Dy, CaF2:Tm, CaF2:Mn, LiF:Mg,Cu,P, and CaSO4:Dy. LiF:Mg,Ti and LiF:Mg,Cu,P experienced significant pre-irradiation fading. All

  7. JOURNAL DE PHYSIQUE Colloque C6, suppltment au no 11-12, Tome 33, Novembre-Dtcembre 1972,page 87 ACOUSTIC INTERFEROMETRY IN LIQUID HELIUM FILMS

    E-print Network

    Paris-Sud XI, Université de

    pour cent de thulium divalent cornrne ions paramagnktiques, est l'une des applicationsde cette on cleaved surfaces of CaF2 containingdivaient thulium as the paramagnetic ion. In effect this has allowed

  8. Luminescence of rare-earth ions in epitaxial fluoride layers

    NASA Astrophysics Data System (ADS)

    Sokolov, Nikolai S.; Yakovlev, Nikolai L.

    1996-01-01

    Epitaxial fluoride layers (CaF2, SrF2 and CdF2) were grown and doped with rare- earth ions by means of molecular beam epitaxy. This technique allows creation of new fluoride heterostructures (including superlattices) with high level and controlled profile of doping. Photoluminescence spectra of divalent ions (Eu2+ and Sm2+) were used to study strains and stress relaxation in the films. In the structures grown by MBE one can observe effects which are not actual in bulk crystals. They are crossing of 4f6 and 4f55d levels of Sm2+ ions in CaF2 layers with tensile strain as high as 2%, new shape of inhomogeneously broadened Sm2+ zero phonon emission line in very thin CaF2 layers arising from modification of strain fields of defects near the surface, bleaching of photoluminescence of RE ions in thin CaF2:Sm2+ layers on Si(111) and in CdF2-CaF2:Eu2+ superlattices. Luminescence of trivalent ions (Nd3+ and Er3+) in CaF2 films is quenched at much higher concentration of the dopants than in bulk crystals. It makes these films very attractive for potential optoelectronic applications.

  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. Investigation of water-soluble x-ray luminescence nanoparticles for photodynamic activation

    NASA Astrophysics Data System (ADS)

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

    2008-01-01

    In this letter, we report the synthesis of LaF3:Tb3+-meso-tetra(4-carboxyphenyl) porphine (MTCP) 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 production in the nanoparticle-MTCP conjugates. Our pilot studies indicate that water-soluble scintillation nanoparticles can potentially be used to activate photodynamic therapy as a promising deep cancer treatment modality.

  11. 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.

  12. Hyperfine Structure of the Singlet DEUTERIUM(2) - Triplet HYDROGEN(4) Transition in PRASEODYMIUM:LANTHANUM - Measured Using Photon Echo Modulation Spectroscopy.

    NASA Astrophysics Data System (ADS)

    Whittaker, Edward Anthony

    After a brief description of the relevant physical properties of the Pr('3+);LaF(,3) system, the method of photon echo modulation spectroscopy is explained. The results of an experiment to measure the hyperfine structure of the ('1)D(,2)((GAMMA)(,1))-('3)H(,4)((GAMMA)(,1)) transition in Pr('3+):LaF(,3) using the echo modulation method are presented. The hyperfine transition frequencies and linewidths for the ('1)D(,2) level were found to be 3.72 MHz (70 kHz), 4.79 MHz (60 kHz) and 8.51 MHz (30 kHz). A separate result gives new information concerning the relative orientation of the principle axes systems of the effective hyperfine Hamiltonians of the ('1)D(,2)-('3)H(,4) levels. This information is displayed using a new graphical method and suggests that there is intrinsically a great deal of symmetry in the relative orientation parameter.

  13. Photoluminescence properties of Ho3+ ion in lithium-fluoroborate glass containing different modifier oxides

    NASA Astrophysics Data System (ADS)

    Balakrishna, A.; Rajesh, D.; Ratnakaram, Y. C.

    2014-04-01

    Trivalent holmium (0.5 mol%) doped lithium fluoro-borate glasses with the chemical compositions 49.5Li2B4O7-20BaF2-10NaF-20MO (where M=Mg, Ca, Cd and Pb), 49.5Li2B4O7-20BaF2-10NaF-10MgO-10CaO and 49.5Li2B4O7-20BaF2-10NaF-10CdO-10PbO were synthesized and investigated their photoluminescence properties. The variation in chemical composition by varying modifier oxides causes changes in the structural spectroscopic behavior of Ho3+ ions. These changes are examined by UV-VIS- NIR and luminescence spectroscopic techniques. The visible luminescence spectra were obtained by exciting samples at 409 nm radiation.

  14. 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. PMID:24707056

  15. 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

  16. Measurement of the 19F(?,n) Cross Section for Nuclear Safeguards Science

    NASA Astrophysics Data System (ADS)

    Reingold, C. S.; Cizewski, J. A.; Burcher, S.; Manning, B.; Peters, W. A.; Clement, R. R. C.; Smith, M. S.; Bardayan, D. W.; Stech, E.; Tan, W. P.; Madurga, M.; Ilyushkin, S.; Thompson, S.; Vandle Collaboration

    2014-09-01

    A precise measurement of the 19F(?,n) cross section will improve Non Destructive Assays (NDA) of UF6 and other actinide-fluoride samples via neutron detection techniques. The cross section will be determined with two complementary approaches. We have already bombarded a LaF3 target with a pulsed 4He beam from the Notre Dame FN tandem accelerator; next, we will send a fluorine beam from the ORNL tandem through a pure helium gas target. The neutron spectra from both of these reactions will be measured using the Versatile Array of Neutron Detectors at Low Energy (VANDLE), and coincident ? rays with a HPGe detector. We report here on data taken with VANDLE and a HPGe detector on a LaF3 target. This poster outlines the motivation for this experiment, explains the stages of this experiment, and presents both of our experimental setups and preliminary data. A precise measurement of the 19F(?,n) cross section will improve Non Destructive Assays (NDA) of UF6 and other actinide-fluoride samples via neutron detection techniques. The cross section will be determined with two complementary approaches. We have already bombarded a LaF3 target with a pulsed 4He beam from the Notre Dame FN tandem accelerator; next, we will send a fluorine beam from the ORNL tandem through a pure helium gas target. The neutron spectra from both of these reactions will be measured using the Versatile Array of Neutron Detectors at Low Energy (VANDLE), and coincident ? rays with a HPGe detector. We report here on data taken with VANDLE and a HPGe detector on a LaF3 target. This poster outlines the motivation for this experiment, explains the stages of this experiment, and presents both of our experimental setups and preliminary data. This work is supported by the NNSA, NSF, and DOE.

  17. JOURNAL DEPHYSIQUE ColloqueC7, suppl6rnentau nO1O,Tome 46,octobre 1985 page C7-247

    E-print Network

    Paris-Sud XI, Université de

    of Dy3+ are tuned with a magnetic field Into resonance with the 23 cm-l phonons. Our analysis suggests to the energy difference between the two lowest Dy3+ levels. I. EXPERIMENTAL RESULTS The lifetime of 23 cn-I-phonons in LaF3, doubly doped with Pr3+ (-05%)and Dy3+ (0.01%) is measured in the presence of an external

  18. Three-micron laser action in Dy3+

    Microsoft Academic Search

    B. M. Antipenko; A. L. Ashkalunin; Artur A. Mak; B. V. Sinitsyn; Yu V. Tomashevich; G. S. Shakhkalamyan

    1980-01-01

    An experimental investigation was made of laser action in Dy3+ ions in an LaF3 crystal excited by neodymium laser radiation. It is shown by calculation that neodymium laser radiation may be converted to the three-micron range with an efficiency of the order of 10% using Y3Al5O12:Yb3+:Dy3+ and BaY2F8:Dy3+ media. Bibtex entry for this abstract Preferred format for this abstract (see

  19. Spectral and Temporal Dynamics of Far Infrared Generated Phonons in Lanthanum Fluoride

    Microsoft Academic Search

    William Alden Blossom Tolbert

    1990-01-01

    This thesis is concerned with the far infrared (FIR) generation of nonequilibrium acoustic phonons in LaF_3:Pr^{3+ } (0.5%), and the subsequent spectral and temporal dynamics that occur as the system relaxes toward equilibrium. Monochromatic, high occupation number ( ~1) populations of acoustic phonons are generated at frequencies throughout the acoustic spectrum via FIR pumping. This direct generation of phonons at

  20. Enhanced spectroscopic properties in Er 3+/Yb 3+-activated fluoride glass-ceramics planar waveguides

    NASA Astrophysics Data System (ADS)

    Péron, O.; Duverger-Arfuso, C.; Jestin, Y.; Boulard, B.; Ferrari, M.

    2009-07-01

    Bulk and planar waveguides fluoride glass-ceramics activated by erbium and ytterbium ions were prepared in the ZrF 4-LaF 3-ErF 3 system. Waveguides were obtained by use of physical vapor deposition process. All samples were characterized by luminescence spectroscopy. The results are discussed with the aim of assessing the role of ytterbium on the optical and spectroscopic properties of erbium doped glass-ceramics bulk and waveguides.

  1. An investigation of the thermal sensitivity and stability of the -NaYF4:Yb,Er upconversion nanophosphors

    E-print Network

    Ju, Yiguang

    An investigation of the thermal sensitivity and stability of the -NaYF4:Yb,Er upconversion of the hexagonal -phase NaYF4:Yb,Er nanophosphors as a function of temperature 300­450 K was examined under 978 nm The lanthanide ions Ln3+ Ln=Yb, Er, Tm, and Ho doped into either fluorides, e.g., NaYF4 and LaF3, or oxides, e

  2. A novel deep photodynamic therapy modality combined with CT imaging established via X-ray stimulated silica-modified lanthanide scintillating nanoparticles.

    PubMed

    Elmenoufy, Ahmed H; Tang, Yong'an; Hu, Jun; Xu, Huibi; Yang, Xiangliang

    2015-07-16

    Multifunctional LaF3:Tb scintillating nanoparticles (ScNPs) coated with homogenous layers of silica and subsequently tethered with RB covalently were elaborated. The nanoconjugates with a high colloidal stability and biocompatibility could generate a reasonable amount of (1)O2 through efficient energy transfer upon external illumination, which enables them to be potentially applied in diagnosis and photodynamic therapy for deep seated tumour. PMID:26136105

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

    SciTech Connect

    Mukundan, R. (Rangachary); Brown, D. R. (David R.); Garzon, F. H. (Fernando H.); Brosha, E. L. (Eric L.)

    2001-01-01

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

  4. Optical transitions of Ho3+ in oxyfluoride glasses and upconversion luminescence of Ho3+/Yb3+-codoped oxyfluoride glasses

    NASA Astrophysics Data System (ADS)

    Feng, Li; Wu, Yinsu

    2015-05-01

    Optical properties of Ho3+-doped SiO2-BaF2-ZnF2 glasses have been investigated on the basis of the Judd-Ofelt theory. Judd-Ofelt intensity parameters, radiative transition probabilities, fluorescence branching ratios and radiative lifetimes have been calculated for different glass compositions. Upconversion emissions were observed in Ho3+/Yb3+-codoped SiO2-BaF2-ZnF2 glasses under 980 nm excitation. The effects of composition, concentration of the doping ions, and excitation pump power on the upconversion emissions were also systematically studied.

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

    E-print Network

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

    2015-01-01

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

  6. Low temperature epitaxial growth of Ge on cube- textured Ni

    SciTech Connect

    GIARE, C [Rensselaer Polytechnic Institute (RPI); Palazzo, J [Rensselaer Polytechnic Institute (RPI); Goyal, Amit [ORNL; WANG, G [Rensselaer Polytechnic Institute (RPI); LU, T [Rensselaer Polytechnic Institute (RPI)

    2012-01-01

    Quasi- single crystal Ge films were grown on [001]<010> textured Ni substrate at a temperature of 350 oC using an insulating buffer layer of CaF2. A direct deposition of Ge on Ni at 350 oC was shown to alloy with Ni. From x- ray pole figure analysis, it was shown that Ge grew epitaxially with the same orientation as CaF2 and the dispersions in the out- of- plane and in- plane directions were found to be 1.7 0.1o and 6 1o, respectively. In the out- of- plane direction, Ge[111]||CaF2[111]||Ni[001]. In addition, the Ge consisted of four equivalent in- plane oriented domains such that two mutually orthogonal directions: Ge 211 and Ge 011 are parallel to mutually orthogonal directions: Ni 110 and Ni 110 , respectively of the Ni(001) surface. This was shown to be originated from the four equivalent in- plane oriented domains of CaF2 created to minimize the mismatch strain between CaF2 and Ni in those directions.

  7. High energy photon emission 

    E-print Network

    Jabs, Harry

    1997-01-01

    The primary goal of this work was to initiate the use of BaF2 arrays for detection of high energy photon emission from nuclear reactions. A beam from the Texas A&M University K-500 Superconducting Cyclotron, and a variety of detectors for hard...

  8. Development of a fast radiation detector based on barium fluoride scintillation crystal.

    PubMed

    Han, Hetong; Zhang, Zichuan; Weng, Xiufeng; Liu, Junhong; Guan, Xingyin; Zhang, Kan; Li, Gang

    2013-07-01

    Barium fluoride (BaF2) is an inorganic scintillation material used for the detection of X?gamma radiation due to its relatively high density, equivalent atomic number, radiation hardness, and high luminescence. BaF2 has a potential capacity to be used in gamma ray timing experiments due to the prompt decay emission components. It is known that the light output from BaF2 has three decay components: two prompt of those at approximately 195 nm and 220 nm with a decay constant around 600-800 ps and a more intense, slow component at approximately 310 nm with a decay constant around 630 ns which hinders fast timing experiments. We report here the development of a fast radiation detector based on a BaF2 scintillation crystal employing a special optical filter device, a multiple reflection multi-path ultraviolet region short-wavelength pass light guides (MRMP-short pass filter) by using selective reflection technique, for which the intensity of the slow component is reduced to less than 1%. The methods used for this study provide a novel way to design radiation detector by utilizing scintillation crystal with several emission bands. PMID:23902059

  9. LLIINNAACC rreeppoorrtt 11--22000022 Internal Report

    E-print Network

    Shyamasundar, R.K.

    the Faraday Cup (LIN1). In order to phase match this pulsed beam into the LINAC, the bunch is further using a 2" BaF2 detector near the Faraday cup LIN3. As different resonators (R1-R4) in three modules (M1

  10. Glasses containing lutetium fluoride

    Microsoft Academic Search

    Petr Melnikov; Gisele de Carvalho; Marcelo Nalin; Younes Messaddeq; Sydney J. Ribeiro

    1998-01-01

    Glasses containing lutetium fluoride have been prepare in the system BaF2 - SrF2 - ZnF2 - LuF3 - InF3. The composition of the phases crystallizing out of these glasses suggests octahedral pre-arrangement comprising (LuF6) and [Sr(Ba)F2] structural fragments.

  11. Effect of growth temperature on composition control for vapor deposition of YBa2Cu3O7-? precursor films

    NASA Astrophysics Data System (ADS)

    Liu, Chong; Wang, Lianhong; Shu, Yonghua; Fan, Jing

    2014-12-01

    This work aims at exploiting the role of growth temperature on the dynamic behavior of deposition atoms as well as its resultant impact on the composition control during the synthesis of YBa2Cu3O7-? precursor films by vapor codeposition. The codeposition of Yt, BaF2 and Cu is performed in vacuum chamber under a wide range of growth temperature from 25°C to 600°C, the mass of each element deposited on LaAlO3 substrate and thus the film composition is examined by the inductively coupled plasma atomic emission spectroscopy. It is shown that the deposition amount of Cu decreases obviously with the increase of growth temperature; however, the mass of Yt and BaF2 deposited on the substrate appears to be insensitive to growth temperature. Moreover, high temperature may also trigger the influence of adsorbates composition on Cu desorption, and therefore the deposition amount of Cu decreases almost linearly as the mol fraction of BaF2 in the adlayers increases. Nevertheless, when the deposition is conducted at room temperature, the influence of mol fraction of BaF2 on Cu desorption vanishes. The detailed mechanisms associated with above phenomena are unveiled by molecular dynamics analysis, additionally the physical picture about adsorption behaviors on the growing interface under different deposition conditions is summarized, which is valuable for handling the composition control during the vapor codeposition of different functional films.

  12. Equilibrium : ConcFromKsp (8 Variations)

    NSDL National Science Digital Library

    The K sp of BaF 2 is 1.7 x 10 -6 mol/L in water at 25 o C. What is the concentration of barium ions in equilibrium with solid barium fluoride? (Assume that the only relevant reaction is the solubility-product equilibrium.)

  13. Bleaching effects in photoluminescence of rare-earth ions in fluoride heterostructures

    NASA Astrophysics Data System (ADS)

    Gastev, S. V.; Alvarez, J. C.; Vitvinsky, V. V.; Sokolov, Nikolai S.; Khilko, A. Y.

    1996-01-01

    Bleaching effects in photoluminescence (PL) of rare earth Sm2+ ions in CaF2:Sm/Si(111) heterostructures and Eu2+ ions in [CdF2/CaF2:EU]n/Si(111) superlattices have been observed for the first time. The PL was excited by He-Ne ((lambda) equals 633 nm) and N2 ((lambda) $equals 337 nm) lasers respectively. It was found that illumination of wavelength (lambda)

  14. Spectroscopic, dielectric properties and local structure observation by EXAFS for Nd,Y:CaF2 crystal

    NASA Astrophysics Data System (ADS)

    Ma, F. K.; Zhang, Q.; Jiang, D. P.; Su, L. B.; Shao, Y. J.; Wang, J. Y.; Tang, F.; Xu, J.; Solarz, P.; Ryba-Romanowski, W.; Lisiecki, R.; Macalik, B.

    2014-10-01

    Trivalent impurity ions are clustered easily in fluoride crystals. With the addition of Y3+ spectral properties are greatly enhanced. Low temperature absorption and emission spectra are performed to unfold the optical centers in Nd3+,Y3+:CaF2 crystals. The strongest absorption line at around 790?nm belongs to M luminescence quenched centers in 1%Nd3+:CaF2; and at 797?nm to L? centers for a codoped one. For emission spectra 1049.3?nm and 1068.7?nm are attributed to M? and N? non quenched centers; 1054.6?nm to an L? site in a 1%Nd3+,5%Y3+:CaF2 sample. EXAFS spectra, an intuitive approach, are applied to reveal that the first coordination number of Nd3+ increased from 9.2 to 10.7 with the addition of Y3+ ions, and the local lattice expanded.

  15. Double Beta Decay of ^48Ca Studied by ELEGANTS VI

    NASA Astrophysics Data System (ADS)

    Ogawa, Izumi; Kishimoto, Kohji; Umehara, Saori; Katuski, Atsunari; Sakai, Hitoshi; Yokoyama, Daisuke; Mukaida, Kentaro; Tomii, Satoshi; Ajimura, Shuhei; Matsuoka, Kenji; Kishimoto, Tadafumi

    2001-10-01

    A CaF2 scintillation detector system (ELEGANT VI) is developed to search for neutrino-less double beta decay (0???) of ^48Ca and spin coupled dark matter. ^48Ca is the most factorable isotope among other potential ?? decay nuclei because it has the largest Q-value (4.27 MeV) of the decay ^48Ca arrow ^48Tl then the possibility of the occurrence is highest and little background is expected. CsI(Tl) scintillators and active lightguides (pure CaF2 crystals) which are on both sides of the central CaF_2(Eu) crystal act as 4? active shields. The whole system is in operation at the underground laboratory located in Nara (Oto Cosmo Observatory) which has effectively 1.4 km water equivalent shield. We will report our current status of the investigation.

  16. 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

  17. 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.

  18. A comparison of thermal neutron and gamma ray sensitivities of common TLD materials

    Microsoft Academic Search

    K. Ayyangar; A. R. Lakshmanan; B. Chandra; K. Ramadas

    1974-01-01

    The thermal neutron responses in the range 1010 to 2*1012 n cm-2 and the gamma -ray sensitivities of common thermoluminescent materials (CaSO4:Dy, CaSO4:Tm, CaF2:Dy, CaF2:Mn, Li2B4O7:Mn, LiF (TLD-700, TLD-100, TLD-600), Mg2SiO4:Tb and BeO) have been studied in detail and the results compared with those published elsewhere.

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

    Microsoft Academic Search

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

    2005-01-01

    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

  20. 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.

  1. 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.

  2. On the role of the 4fLu level in the scintillation mechanisms of cerium-doped lutetium-based fluoride crystals

    Microsoft Academic Search

    W. Blanc; C. Dujardin; J. C. Gâcon; C. Pedrini; B. Moine; A. N. Belsky; I. Kamenskikh; M. Kirm; G. Zimmerer

    1999-01-01

    Optical properties of two pairs of Ce3+-doped scintillating materials, (LiLuF4, LiYF4) and LuF3, LaF3), are presented. 4f14-->4f13-5d transitions of Lu3+ are shown to occur between 8-10 eV in the transmission spectra of the Lu-based compounds. in this domain, the transfer of electronic excitation from lutetium to crerium is inefficient, the transmission spectra and the corresponding Ce3+ excitation spectra being anticorrelated.

  3. Optical properties of some fluoride compounds and their application to dosimetry N. Kristianpoller a,*, W. Chen b

    E-print Network

    Chen, Reuven

    to that of the classic dosimeter TLD-100 (LiF:Mg,Ti). For example, the sensitivity of SrF2:Pr3þ has been found used as optical materials. Some doped fluoride crystals like LiF:Mg,Ti (TLD-100) or CaF2: Dy (TLD-200

  4. A scintillating bolometer for experiments on double beta decay

    Microsoft Academic Search

    A. Alessandrello; V. Bashkirov; C. Brofferio; C. Bucci; D. V. Camin; O. Cremonesi; E. Fiorini; G. Gervasio; A. Giuliani; A. Nucciotti; M. Pavan; G. Pessina; E. Previtali; L. Zanotti

    1998-01-01

    The scintillation yields of CaF2 crystals with different doping concentration of Europium have been measured at low temperatures and their bolometric behavior has been investigated. After these studies we have constructed the first “scintillating bolometer” where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from ?-particles in

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. The phostron: A phoswich counter for neutron and charged particle detection

    Microsoft Academic Search

    C. Pastor; F. Benrachi; B. Chambon; B. Cheynis; D. Drain; A. Dauchy; A. Giorni; C. Morand

    1984-01-01

    A phoswich detector able to detect and identify gammas, neutrons and charged particles (p, d, t, alpha) of 10-100 MeV is described. It consists of a CaF2(Eu) scintillator optically coupled with a NE213 liquid scintillator.

  10. The Canadian Mineralogist Vol. 46, pp. 737-740 (2008)

    E-print Network

    Chakhmouradian, Anton

    2008-01-01

    Tuttle, who was then one of world's leading experimental petrologists and inventor of the Tuttle cold, carbonatites were not believed to be igneous rocks, and it was experiments at Penn State by Wyllie & Tuttle of the ternary system CaF2­Ca(OH)2­CaCO3 (Gittins & Tuttle 1964). Simultaneously, John coedited with Tuttle

  11. Shocked H2O ice: Thermal emission measurements and the criteria for phase changes during impact events

    E-print Network

    Stewart, Sarah T.

    plate and enclosed in an 1 Â 10À4 Pa ($1 microtorr) vacuum chamber with a downrange CaF2 windowShocked H2O ice: Thermal emission measurements and the criteria for phase changes during impact bodies may produce transient liquid water and vapor. We present the first thermal emission measurements

  12. Biaxial CdTe/CaF2 films growth on amorphous surface , F. Tang a

    E-print Network

    Wang, Gwo-Ching

    Biaxial CdTe/CaF2 films growth on amorphous surface W. Yuan a, , F. Tang a , H.-F. Li a , T. Parker electron microscopy Metal organic chemical vapor deposition A continuous and highly biaxially textured CdTe nanorods as a buffer layer. The interface between the CdTe film and CaF2 nanorods and the morphology

  13. J Biol Phys (2009) 35:57 DOI 10.1007/s10867-009-9132-5

    E-print Network

    2009-01-01

    warmed the tube on the outside. A few micrograms of the material sublimated and got deposited's law from first principles. I had struggled mightily, butchering the expression for the drift velocity expensive CaF2 windows. So, Ohm's law or not, I got the job. A clumsy experimentalist with indifferent

  14. Observation of whispering gallery modes in the mid-Infrared with a Quantum Cascade Laser: possible applications to nanoliter chemical

    E-print Network

    Jensen, Grant J.

    Observation of whispering gallery modes in the mid-Infrared with a Quantum Cascade Laser: possible coupling scheme for mid-infrared is described. Future applications of WGM resonators as hyphenated inline chromatography sensors are discussed. KEY WORD LIST Mid Infrared CaF2 Whispering Gallery Mode, Quantum Cascade

  15. COMMUNICATIONS Midinfrared photoluminescence from IVVI semiconductors

    E-print Network

    McCann, Patrick

    interconnect technologies. PbSe/Pb1 xSrxSe MQW structures were grown on 3 in. diameter 111 -oriented silicon operation currents. This is a fundamental problem to be solved since direct band gap semiconductor materials1 xSrxSe layers was 3%. Detailed procedures for CaF2 and IV­VI semiconductor growth on 111 -oriented

  16. 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.

  17. Influence of alkali content and alkali mixing on the chemical durability of fluorozirconate glasses

    Microsoft Academic Search

    Xiujian Zhao; Sumio Sakka

    1993-01-01

    The corrosion of alkali-containing fluorozirconate glasses in water and acidic and alkaline solutions was studied with glasses of the compositions (100-x) (0.6ZrF4·0.1AlF3·0.3BaF2)· xLiF and 48ZrF4·8AlF3·24BaF2·xLiF·(20-x)NaF. The corrosion of the glasses in deionized water and 0.1 n HCl solution is mainly controlled by diffusion with an inductive period due to the passage from reaction-controlled to diffusion-controlled mechanisms, and the weight loss

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

    E-print Network

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

    2015-01-01

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

  19. An educational tool for demonstrating the TOF-PET technique

    Microsoft Academic Search

    T. Bäck; J. Cederkäll; B. Cederwall; A. Johnson; A. Kerek; W. Klamra; J van der Marel; J. Molnár; D. Novák; D. Sohler; M. Steèn; P. Uhlèn

    2001-01-01

    A detector system for positron emission tomography with time-of-flight capability has been built to serve as an educational tool for undergraduate students. The set-up consists of 48 BaF2 scintillator crystals, each coupled to a fast photo-multiplier tube, mounted in a circular geometry. The analogue detector pulses are handled by fast constant fraction discriminators. A dedicated unit reduces the 48 channels

  20. Picosecond lifetime measurements in147Pm

    NASA Astrophysics Data System (ADS)

    Seo, T.

    1991-12-01

    Half-lives of excited levels in147Pm have been measured using BaF2 scintillators. New values of t1/2 are 2420(10), 43(5), 22(9), 17(10) and 17(10) ps for the 91.1, 410.5, 489.2, 531.0 and 685.9 keV level, respectively. E2 enhancement factors of ?-transitions have been deduced.

  1. FT-IR study of plant cell wall model compounds: pectic polysaccharides and hemicelluloses

    Microsoft Academic Search

    P Capek; V Sasinková; N Wellner; A Ebringerová

    2000-01-01

    Pectic polysaccharides and hemicelluloses extracted from plants were studied in highly hydrated films on BaF2 discs. Distinctive absorption band maxima in the mid-infrared region at 1200–800cm?1 were shown to be useful for the identification of polysaccharides with different structure and composition. Two series of the hexopyranose and pentopyranose monosaccharides, which are the structural units of the plant cell wall polysaccharides,

  2. Impurity Absorption Loss due to Rare Earth Elements in a Fluoride Glass

    Microsoft Academic Search

    Yasutake Ohishi; Seiko Mitachi; Shuichi Shibata; Toyotaka Manabe

    1981-01-01

    Optical spectra for each of the rare earth element doped BaF2-GdF3-ZrF4 glasses were measured. It was found that, in the 2-5 mum wavelength region, Ce, Pr, Nd, Sm, Tb and Dy contribute to the absorption loss and the loss magnitude due to each rare earth element of lppmw is several tens of dB per kilometer at the absorption peaks. It

  3. Molecular beam epitaxial growth of high quality Pb 1? x Sn x Te layers with 0? x?1

    Microsoft Academic Search

    P. H. O. Rappl; H. Closs; S. O. Ferreira; E. Abramof; C. Boschetti; P. Motisuke; A. Y. Ueta; I. N. Bandeira

    1998-01-01

    Lead tin telluride epitaxial layers with tin concentrations covering the whole compositional range have been grown by molecular beam epitaxy on cleaved BaF2 (111) substrates, using PbTe and SnTe solid sources. The full width at half maximum of the (222) rocking curve of these samples, measured by a four crystal high resolution X-ray diffraction apparatus, was about 400arcsec for the

  4. Rare ISotopes INvestigation at GSI (RISING) using gamma-ray spectroscopy at relativistic energies

    Microsoft Academic Search

    H. J. Wollersheim; D. E. Appelbe; A. Banu; R. Bassini; T. Beck; F. Becker; P. Bednarczyk; K.-H. Behr; M. A. Bentley; G. Benzoni; C. Boiano; U. Bonnes; A. Bracco; S. Brambilla; A. Brunle; A. Burger; K. Burkard; P. A. Butler; F. Camera; D. Curien; J. Devin; P. Doornenbal; C. Fahlander; K. Fayz; H. Geissel; J. Gerl; M. Gorska; H. Grawe; R. Griffiths; G. Hammond; M. Hellstrom; J. Hoffmann; H. Hubel; J. Jolie; J. V. Kalben; M. Kmiecik; I. Kojouharov; R. Kulessa; N. Kurz; I. Lazarus; J. Li; J. Leske; R. Lozeva; A. Maj; S. Mandal; B. Million; G. Munzenberg; S. Muralithar; M. Mutterer; P. J. Nolan; G. Neyens; J. Nyberg; W. Prokopowicz; V. F. E. Pucknell; P. Reiter; D. Rudolph; N. Saito; T. R. Saito; D. Seddon; H. Schaffner; J. Simpson; K.-H. Speidel; J. Styczen; K. Summerer; N. Warr; H. Weick; C. Wheldon; O. Wieland; M. Winkler

    2005-01-01

    The Rare ISotopes INvestigation at GSI project combines the former EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, BaF2-HECTOR detectors, and the fragment separator at GSI for high-resolution in-beam ?-ray spectroscopy measurements with radioactive beams. These secondary beams produced at relativistic energies are used for Coulomb excitation or secondary fragmentation experiments in order to explore the nuclear structure of the projectiles

  5. The improved scintillation crystal lead tungstate scintillation for PET

    Microsoft Academic Search

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

    2009-01-01

    As a valuable material for the detecting of gamma-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

  6. Study of VUV emission and ?-ray responses of Nd:BaF 2 scintillaotor

    Microsoft Academic Search

    Takayuki Yanagida; Noriaki Kawaguchi; Yuui Yokota; Sumito Ishidu; Kentaro Fukuda; Akira Yoshikawa; Jan Pejchal; Martin Nikl; Vladimir Babin; Hiroyuki Sekiya; Kei Kamada

    2010-01-01

    Nd3+ 1%, 5% and 10% doped BaF2 single crystals were grown by the micro-pulling down method. Photoluminescence properties, including excitation and emission spectra and luminescence decay were measured under synchrotron radiation excitation at the Superlumi station in HASYLAB at DESY (Hamburg, Germany). The Nd3+ related 5d-4f emission lines peaking around 180 nm, 230 nm, and 260 nm, identified as the 5d–4Ij, 5d–4Fj, and

  7. Plastic-strain localization in barium fluoride single crystals at elevated temperatures

    Microsoft Academic Search

    N. P. Skvortsova

    2006-01-01

    The strain distribution is studied in BaF2 crystals subjected to compression tests along [110] and [112] at a constant strain rate in the temperature range T = (0.22–0.77)T\\u000a m. At T > 0.5T\\u000a m, the plastic strain in deformed samples is found to be strongly localized in narrow bands, where the shear strain reaches\\u000a several hundred percent. The degree of

  8. Dependence of the conductivity on the concentration and the hopping frequency of charge carriers in fluoride glasses

    Microsoft Academic Search

    M. Sural; A. Ghosh

    2000-01-01

    The conductivity spectra of fluoride glasses in the system ZrF4-BaF2-YF2-LiF with varying LiF content has been reported at different temperatures in the frequency range 10 Hz-2 MHz. The experimental data have been analyzed in the framework of the Almond-West formalism. The concentration and hopping frequency of the charge carriers, the dc conductivity, and the activation energy have been determined from

  9. Evaluation of buffer materials for fluorine contained solid phase epitaxy of 123 films on MgO substrates

    Microsoft Academic Search

    Y. Yamamoto; M. Mukaida; A. Ichinose; K. Matsumoto; Y. Yoshida; S. Horii; A. Saito; S. Ohshima

    2004-01-01

    Recently solid phase epitaxial YBa2Cu3O7?? films such as metal organic deposition using trifluoroacetate (TFA-MOD) technique, chemical solution-based coating pyrolysis, and BaF2 ex situ post reaction process have been improving their crystalline quality. In order to grow thick films, larger thermal expansion coefficient substrates than that of YBCO are preferable. From the viewpoint of thermal expansion coefficient, MgO is a promising

  10. Monte Carlo simulation of Nal(TI) gamma-spectra in sea water

    Microsoft Academic Search

    D. S. Vlachos; C. Tsabaris

    2003-01-01

    In the field of gamma spectroscopy, detection systems such as NaI(Tl), HPGe, CdZnTe, Csl, BaF2, BGO, GaAs are widely known. In a marine environment only the NaI(Tl) and HPGe detectors have been used for in situ monitoring of radioactivity due to their high efficiency and to their capability of detecting in a wide energy range. HPGe detectors have been used

  11. Si and GaAs photocapacitive MIS infrared detectors

    NASA Technical Reports Server (NTRS)

    Sher, A.; Tsuo, Y. H.; Moriarty, J. A.; Miller, W. E.; Crouch, R. K.

    1980-01-01

    Improvement of the previously reported photocapacitive MIS infrared detectors has led to the development of exceptional room-temperature devices. Unoptimized peak detectivities on the order of 10 to the 13th cm sq rt Hz/W, a value which exceeds the best obtainable from existing solid-state detectors, have now been consistently obtained in Si and GaAs devices using high-capacitance LaF3 or composite LaF3/native-oxide insulating layers. The measured spectral response of representative samples is presented and discussed in detail together with a simple theory which accounts for the observed behavior. The response of an ideal MIS photocapacitor is also contrasted with that of both a conventional photoconductor and a p-i-n photodiode, and reasons for the superior performance of the MIS detectors are given. Finally, fundamental studies on the electrical, optical, and noise characteristics of the MIS structures are analyzed and discussed in the context of infrared-detector applications.

  12. 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.

  13. Differentiation of molecules in a mixed self-assembled monolayer of H-and Cl-terminated bicyclo[2.2.2]octane derivatives

    NASA Astrophysics Data System (ADS)

    Fujii, Shintaro; Fujihira, Masamichi

    2006-04-01

    H- and Cl-terminal groups of bicyclo[2.2.2]octane (BCO) derivatives in a mixed self-assembled monolayer (SAM) on Au(111) were imaged using a modified Si tip with a CaF2 nanocluster to differentiate the two terminals, which have different electronegativities. In order to achieve this we fabricated a new sample holder, on which a CaF2 single crystal and the mixed SAM on Au(111) could be mounted side by side. We transferred the holder with the two samples into a ultrahigh vacuum (UHV) atomic force microscopy (AFM) chamber. Upon cleaving the CaF2 single crystal under UHV, a fresh and clean CaF2(111) surface parallel with the SAM surface appeared within 2 mm of the separation. The modified Si tip was prepared by repeatedly making contact between a Si tip and the CaF2(111) surface. The resulting modified tip could image the atomic periodicity of a Ca2+ and an F- sublattice on the CaF2(111) surface depending on the sign of the tip-terminating ion, i.e. an F- and a Ca2+ ion, respectively, as reported previously (Foster et al 2002 Phys. Rev. B 66 235417). Using the modified Si tip with the known tip-terminating ion, we observed the Cl-terminal in the surrounding H-terminals in the mixed SAM by noncontact (NC) AFM. Here, the Cl-terminal is negatively charged due to its electronegativity and thus the BCO moiety with the Cl-terminal is terminated by a C?+-Cl?- permanent dipole, while the H-terminal is almost neutral. The Cl-terminal appeared brighter (more attractive) and darker (more repulsive) than the surrounding H-terminals in NC-AFM images depending on the sign of the tip-terminating ion, i.e. a Ca2+ and an F- on the modified tip, respectively, although the relationship between the image contrast and the sign of the tip-terminating ion was not always perfect because of the instability of the tip-terminating ion on the nanocluster. The present method can be used to distinguish terminal groups with different electronegativities.

  14. 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.

  15. Phase Transition and Melting Curves of Calcium Fluoride via Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Zeng, Zhao-Yi; Chen, Xiang-Rong; Zhu, Jun; Hu, Cui-E.

    2008-01-01

    The phase transition and melting curves of CaF2 are investigated by using the general utility lattice programme (GULP) via the shell model with molecular dynamics method. By calculating the entropy H (at 0K) and Gibbs free energy G* (at 300K), we find that the phase transition pressure from the face-centred cubic (fcc) structure to the orthorhombic structure is 11.40 GPa and 9.33 GPa at 0K and 300K, respectively. The modified melting point of the fcc CaF2 is in the range of 1650-1733 K at 0GPa. All these results are well consistent with the available experimental data and other theoretical results. We also obtain that the melting temperature of high pressure phase is 990-1073K at 10 GPa. Moreover, the temperature dependences of the elastic constants Cij, bulk module B and shear module G are also predicted.

  16. Generation and amplification of ultraviolet light pulses by means of parametric four-wave interactions in transparent solid-state media

    NASA Astrophysics Data System (ADS)

    Darginavi?ius, J.; Tamošauskas, G.; Valiulis, G.; Dubietis, A.

    2010-04-01

    We experimentally demonstrate efficient generation of the ultrashort ultraviolet light pulses by means of phase-matched four-wave optical parametric amplification and four-wave difference frequency mixing in wide bandgap solids with cubic nonlinearity. Broadband four-wave optical parametric amplification around 330 nm is achieved in optically isotropic fused silica and CaF2 crystals, suggesting amplification bandwidth of ˜20 nm that is able supporting ultraviolet light pulses as short as 7.5 fs (in the transform limit). Efficient generation of 3-rd (351 nm), 5-th (211 nm), and 6-th (176 nm) harmonics with 1-ps pulses of the Nd:glass laser is experimentally demonstrated through non-collinearly phase-matched four-wave difference-frequency mixing in fused silica, CaF2 and MgF2 crystals.

  17. Coupling of phonon-polariton modes at dielectric-dielectric interfaces by the ATR technique

    NASA Astrophysics Data System (ADS)

    Cocoletzi, G. H.; Olvera Hernández, J.; Martínez Montes, G.

    1989-08-01

    We report the calculated ATR dispersion relation of the interface phonon-polariton modes in the prism-dielectric-dielectric configuration. Comparison of electromagnetic dispersion relations (EMDR) with the ATR dispersion relations are presented for three different interfaces: I) GaAs/GaP, II) CdF2/CaF2 and III) CaF2/GaP in two propagation windows, using the Otto and Kretschmann geometries for p-polarized light. We have studied the three cases using angle and frequency scans for each window and geometry. The results indicate that it is possible to excite and detect phonon-polariton modes at the dielectric-dielectric interface.

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  20. Mixedness determination of rare earth-doped ceramics

    NASA Astrophysics Data System (ADS)

    Czerepinski, Jennifer H.

    The lack of chemical uniformity in a powder mixture, such as clustering of a minor component, can lead to deterioration of materials properties. A method to determine powder mixture quality is to correlate the chemical homogeneity of a multi-component mixture with its particle size distribution and mixing method. This is applicable to rare earth-doped ceramics, which require at least 1-2 nm dopant ion spacing to optimize optical properties. Mixedness simulations were conducted for random heterogeneous mixtures of Nd-doped LaF3 mixtures using the Concentric Shell Model of Mixedness (CSMM). Results indicate that when the host to dopant particle size ratio is 100, multi-scale concentration variance is optimized. In order to verify results from the model, experimental methods that probe a mixture at the micro, meso, and macro scales are needed. To directly compare CSMM results experimentally, an image processing method was developed to calculate variance profiles from electron images. An in-lens (IL) secondary electron image is subtracted from the corresponding Everhart-Thornley (ET) secondary electron image in a Field-Emission Scanning Electron Microscope (FESEM) to produce two phases and pores that can be quantified with 50 nm spatial resolution. A macro was developed to quickly analyze multi-scale compositional variance from these images. Results for a 50:50 mixture of NdF3 and LaF3 agree with the computational model. The method has proven to be applicable only for mixtures with major components and specific particle morphologies, but the macro is useful for any type of imaging that produces excellent phase contrast, such as confocal microscopy. Fluorescence spectroscopy was used as an indirect method to confirm computational results for Nd-doped LaF3 mixtures. Fluorescence lifetime can be used as a quantitative method to indirectly measure chemical homogeneity when the limits of electron microscopy have been reached. Fluorescence lifetime represents the compositional fluctuations of a dopant on the nanoscale while accounting for billions of particles in a fast, non-destructive manner. The significance of this study will show how small-scale fluctuations in homogeneity limit the optimization of optical properties, which can be improved by the proper selection of particle size and mixing method.

  1. Optical and Nuclear Spin Spectroscopy in PRASEODYMIUM(3+):LANTHANUM Fluoride by Optical Pumping

    NASA Astrophysics Data System (ADS)

    Wald, Lawrence Leroy

    A Stark Modulated Optical Pumping (SMOP) technique was used as a sensitive probe of optical hole-burning to study the effects of nuclear spin interactions in Pr ^{3+}:LaF_3. The results of two experiments are reported. In the first experiment, the SMOP technique is applied for optical detection of the NQR spectrum of the Pr^{3+} optical ground state. Frequency and linewidth variations of the Pr ^{3+} ground state hyperfine levels for different positions within the main ^3 H_4(Gamma1) -^1D_2(Gamma 1) inhomogeneous optical line and satellite transitions of Pr^{3+}:LaF _3 are observed. A linear increase in the broadening of the Pr^{3+} hyperfine transitions, without a shift of central frequency, is measured as the laser is tuned toward the wings of the inhomogeneous optical transition. The linear variation is attributed to electric quadrupole broadening caused by changes in local density of point defects across the Stark broadened optical transition. The optically detected NQR spectra of the satellite transitions associated with Pr ion pairs are shifted in frequency, and for most satellites are narrower in width than the NQR spectra found in the wings of the main inhomogeneous optical line. In the second experiment, direct evidence for the presence of a spin diffusion barrier or "frozen core" in Pr^{3+}:LaF _3 is observed by examining the cross relaxation between the Pr and F nuclei in a magnetic field chosen so that a pair of the optical ground state Pr^ {3+} hyperfine energy levels matches the F splitting or a multiple of the F splitting. This level crossing condition allows resonant flip-flop interactions with the nearest neighbor frozen core fluorine spins to re-populate Pr^{3+} hyperfine levels emptied by laser hole-burning, and is detected as enhanced absorption of the laser beam. The coupling of core fluorine spins to bulk fluorine spins during Pr-F cross-relaxation is measured by NMR of the bulk fluorine spin magnetization. The rate of cross relaxation between the Pr spins and the bulk F spins measured in this way is at least three to four orders of magnitude slower than that expected in the absence of a spin diffusion barrier. This reduction of coupling indicates nearly complete de-tuning of the frozen core F spins immediately surrounding the Pr^{3+} ion, cutting off resonant coupling with the bulk F spins.

  2. Effect of fluorspar and other fluxes on slag-metal equilibria involving phosphorus and sulfur

    Microsoft Academic Search

    G. J. W. Kor

    1977-01-01

    The effect of additions of fluorspar-and potential substitutes such as borate, manganese ore, and ilmenite---to basic steelmaking slags on the equilibrium phosphorus and sulfur distribution ratio has been studied at 1550deltaC. From laboratory slag-metal equilibrium studies it was found that the presence of CaF2 in concentrations between 1.5 and 5 wt pct in the slag (equivalent to 2 and 6

  3. Quantitative evaluation for effective removal of phosphorus for SoG-Si

    Microsoft Academic Search

    Eun Jin Jung; Byung Moon Moon; Dong Joon Min

    2011-01-01

    Production of solar cells has increased rapidly in recent years, and metallurgical production of solar grade silicon (SoG-Si), has increased compared with more expensive processes such as Siemens process and Cz processes. It is important to understand the thermodynamic behavior of phosphorus in slag for optimized refinement of SoG-Si. In this study, the thermodynamic behavior of phosphorus in the CaO–SiO2–CaF2

  4. Energy of secondary ions desorbed from insulating films by MeV heavy ions as a function of projectile velocity

    Microsoft Academic Search

    O. Becker; K. Wien

    1986-01-01

    The influence of projectile velocity on the axial energy distribution and mean axial energy of secondary ions was measured with a double-field time-of-flight method at the GSI accelerator-system. The secondary ions were ejected from thin layers ( ~ 150 nm) of CsI, MgO, CaF2, valine and phenylalanine irradiated with Sn and U projectiles. The mean energy of ions like Cs+

  5. Deletion of the SSK1 Response Regulator Gene in Candida albicans Contributes to Enhanced Killing by Human Polymorphonuclear Neutrophils

    Microsoft Academic Search

    Chen Du; Richard Calderone; John Richert; Dongmei Li

    2005-01-01

    The isolation and partial functional characterization of the two-component response regulator SSK1 gene of Candida albicans was previously reported. Compared to wild-type (CAF2-1) and gene-reconstituted (SSK23) strains, the ssk1 null strain (SSK21) was avirulent in a murine model of hematogenously disseminated candidiasis and less able to adhere to human esophageal cells. More recent data indicate that SSK21 is sensitive to

  6. Development of a thermal scintillating detector for double beta decay of 48Ca

    Microsoft Academic Search

    A. Alessandrello; V. Bashkirov; C. Brofferio; D. V. Camin; O. Cremonesi; E. Fiorini; G. Gervasio; A. Giuliani; M. Pavan; G. L. Pessina; E. Previtali; L. Zanotti

    1992-01-01

    Among double beta candidates 48Ca stands out for its 4.271 MeV transition energy, well above most of the contribution of natural gamma and beta radioactivity, but extremely near to the energy released in the alpha decay of 238U (4.274 MeV including nucleus recoil). A CaF2(Eu) detector with both thermal pulse and scintillation light readout would give very good discrimination against

  7. 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%.

  8. Experiments with phase change thermal energy storage canisters for Space Station Freedom

    Microsoft Academic Search

    Thomas W. Kerslake

    1991-01-01

    The solar dynamic power module proposed for the Space Station Freedom (SSF) uses the heat of fusion of a phase change material (PCM) to efficiently store thermal energy for use during eclipse periods. The PCM, a LiF-20CaF2 salt, is contained in annular, metal canisters located in a heat receiver at the focus of a solar concentrator. PCM canister ground-based experiments

  9. WIMP Search by DAMA at Gran Sasso

    E-print Network

    Bernabei, R; Belli, P; Cappella, F; Cerulli, R; Dai Chang Jiang; He, H L; Ignesti, G; Incicchitti, A; Kuang Hao Huai; Ma, J M; Montecchia, F; Nozzoli, F; Prosperi, D

    2002-01-01

    DAMA is searching for rare processes by developing and using several kinds of radiopure scintillators: in particular, NaI(Tl), liquid Xenon and CaF$_2$(Eu). Here only the results released so far on the WIMP annual modulation signature are summarized and compared with results from other experiments, including the recent re-analysis of CDMS-I data. Next perspectives are also shortly addressed.

  10. In vivo effects of fluoride on enamel permeability

    Microsoft Academic Search

    Stefano Chersoni; Angelica Bertacci; David H. Pashley; Franklin R. Tay; Lucio Montebugnoli; Carlo Prati

    2011-01-01

    This in vivo study evaluated the effects of topical fluoride application on enamel by repeated scanning electron microscopy\\u000a analysis of replicas. Baseline fluid droplets were employed as qualitative indication of enamel permeability. CaF2-like globules were detected in vivo after fluoride application and were not found after professional brushing, ultrasound\\u000a action, or chemical extraction. Absence of water permeability of enamel was

  11. Lyman-alpha imagery of comet Kohoutek, and far-UV magnitudes of stars

    Microsoft Academic Search

    T. Page

    1974-01-01

    The Apollo-16 S201 electronographic camera backup model was modified for use on the Skylab AMS-SAL, which reduced its 20 deg FOV to about 7 deg unvignetted. Over 500 frames were exposed by automatic sequencer through LiF and CaF2. The Lyman-alpha halo of comet Kohoutek has been analyzed for nine occasions, and its long, pointed tail was imaged in 1250-1600 A

  12. 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.

  13. 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.

  14. Optical materials characterization. Semi-annual technical report 1 Feb31 Jul 77

    Microsoft Academic Search

    A. Feldman; D. Horowitz; R. M. Waxler; M. J. Dodge; W. K. Gladden

    1977-01-01

    The refractive index of fusion cast CaFâ was measured at room temperature over the wavelength range 0.2144 to 8.662 mm and the data were fitted to a Selmeier type equation. Measurements of refractive index of hot forged CaF2 were extended to the wavelength range 0.2024 to 0.2483 mm. Data are presented for dn\\/dT of single crystal specimens of CaFâ, BaFâ,

  15. Polarization-sensitive optical response of plasmonic metasurfaces

    Microsoft Academic Search

    Paul G. Thompson; Claudiu G. Biris; Edward J. Osley; Richard M. Osgood Jr.; Nicolae C. Panoiu; Paul A. Warburton

    2011-01-01

    We have fabricated arrays of nanoscale asymmetric cruciform apertures that support localized surface-plasmon polaritons (LSPPs) in the lower mid-infrared. The cruciform apertures were created by focussed ion beam milling into a gold film on a CaF2 substrate. The measured transmission spectra of these arrays show two distinct maxima that correspond to the excitation of LSPPs, the magnitude of which can

  16. Charged-Particle Emission upon Ruby Laser Irradiation of Transparent Dielectric Materials

    Microsoft Academic Search

    D. L. Rousseau; G. E. Leroi; W. E. Falconer

    1968-01-01

    Positive and negative charged particle currents induced in vacuo by high-power laser irradiation of transparent dielectric materials below the threshold for physical damage have been investigated. Soft glass, Pyrex, fused quartz, Supracil quartz, CaF2, LiF, and sapphire all show similar behavior. Currents as large as 1010 charged particles per pulse are obtained using ruby laser radiation with normal mode power

  17. Removal of uranium from aqueous HF solutions

    Microsoft Academic Search

    H. Pulley; S. F. Seltzer

    1980-01-01

    This invention is a simple and effective method for removing uranium from aqueous HF solutions containing trace quantities of the same. The method comprises contacting the solution with particulate calcium fluoride to form uranium-bearing particulates, permitting the particulates to settle, and separating the solution from the settled particulates. The CaF2 is selected to have a nitrogen surface area in a

  18. Nanocrystalline materials for the dosimetry of heavy charged particles: A review

    Microsoft Academic Search

    Numan Salah

    2011-01-01

    Thermally stimulated luminescence or better known as thermoluminescence (TL) is a powerful technique extensively used for dosimetry of ionizing radiations. TL dosimeter (TLD) materials presently in use are inorganic crystalline materials. They are in the form of chips, single crystals or microcrystalline size powder. The most popular are LiF:Mg,Ti, LiF:Mg,Cu,P, CaSO4:Dy, CaF2:Dy and Al2O3:C. However, these TLD materials are not

  19. Study of reliability of TLDs for the photon dose mapping in reactor neutron fields for BNCT

    Microsoft Academic Search

    G. Gambarini; F. Gallivanone; M. Carrara; S. Nagels; L. Vogtlander; G. Hampel; L. Pirola

    2008-01-01

    Photon dose measurements in radiation fields having the proper characteristics for boron neutron capture therapy (BNCT) present several troubles. The thermal neutron flux is very high and produces a significant contribution to the response of most dosimeters. The consistency of photon dose measurements with CaF2:Tm and LiF:Mg, Ti thermoluminescent dosimeters has been studied. A method is described for obtaining the

  20. High-efficiency frequency conversion in deep ultraviolet with a KBe2BO3F2 prism-coupled device

    Microsoft Academic Search

    Guiling Wang; Xiaoyang Wang; Yong Zhou; Chengming Li; Yong Zhu; Zuyan Xu; Chuangtian Chen

    2008-01-01

    Using a 2.3 mm thick KBe2BO3F2 crystal optically contacted with CaF2 in a prism-coupled device, fourth-harmonic generation of a femtosecond (150 fs) Ti:sapphire laser system at wavelength 200 nm with a high conversion efficiency of 26.1% has been recently obtained. The maximum output at 200 nm is 10.7 mW.

  1. High-efficiency frequency conversion in deep ultraviolet with a KBe(2)BO(3)F(2) prism-coupled device.

    PubMed

    Wang, Guiling; Wang, Xiaoyang; Zhou, Yong; Li, Chengming; Zhu, Yong; Xu, Zuyan; Chen, Chuangtian

    2008-01-20

    Using a 2.3 mm thick KBe(2)BO(3)F(2) crystal optically contacted with CaF(2) in a prism-coupled device, fourth-harmonic generation of a femtosecond (150 fs) Ti:sapphire laser system at wavelength 200 nm with a high conversion efficiency of 26.1% has been recently obtained. The maximum output at 200 nm is 10.7 mW. PMID:18204738

  2. 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.

  3. The PRIME Lab biomedical program

    Microsoft Academic Search

    George S Jackson; David Elmore; Frank A Rickey; Sharif M Musameh; Pankaj Sharma; Darren Hillegonds; Louis Coury; Peter Kissinger

    2000-01-01

    The biomedical accelerator mass spectrometry (AMS) initiative at PRIME Lab including the status of equipment and sample preparation is described. Several biomedical projects are underway involving one or more of the nuclides: 14C, 26Al and 41Ca. Routine production of CaF2 and graphite is taking place. Finally, the future direction and plans for improvement of the biomedical program at PRIME Lab

  4. Zeeman Effect in the Absorption Spectra of Trivalent Ytterbium Ions in Different Site Symmetries in Calcium Fluoride

    Microsoft Academic Search

    J. Kirton; A. M. White

    1969-01-01

    The Zeeman effect has been observed in the optical spectra of Yb3+ ions in different sites in CaF2. All but one of the correlations between ESR and optical spectra, reported by Kirton and McLaughlan, have been checked and confirmed, and the upper-state g values have been determined. Ambiguity in the interpretation of the rhombic spectra has been eliminated, and we

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  6. Influence of radionuclide adsorption on detection efficiency and energy resolution for flow-cell radiation detectors

    Microsoft Academic Search

    T. A. DeVol; M. E. Keillor; L. W. Burggraf

    1996-01-01

    Flow-cell and batch test experiments were performed to determine the uranyl ion adsorption onto and\\/or complexation with CaF2:Eu scintillator as a function of pH. The flow-cell experiments were modeled with an energy dispersive Monte Carlo algorithm. At pH 2, the flow-cell and batch tests gave consistent results, detection efficiency ~60% and distribution coefficient (Kd ) ~0.3-0.7 mL\\/g, with the model.

  7. Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

    Microsoft Academic Search

    Etsuro Shibata; Haiping Sun; Katsumi Mori

    1999-01-01

    The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction\\u000a rate of MnO from slag were examined at 1450 C to 1550 C by using high carbon iron alloys and CaO-SiO2-CaF2 slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between\\u000a the slag

  8. Microstructural effects on the transmittance of translucent AlN ceramics by SPS

    Microsoft Academic Search

    Y. Xiong; Z. Y. Fu; H. Wang

    2006-01-01

    Two kinds of translucent aluminum nitride (AlN) ceramics with CaF2 and Y2O3 as sintering additives, respectively, are fabricated by spark plasma sintering (SPS) at 1800°C for 10min under the same sintering conditions and the microstructures are characterized using X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) attached with an energy dispersive X-ray microanalyzer (EDX). The content

  9. Response of thermoluminescent dosimeters to photons simulated with the Monte Carlo method

    Microsoft Academic Search

    M. Moralles; C. C. Guimarães; E. Okuno

    2005-01-01

    Personal monitors composed of thermoluminescent dosimeters (TLDs) made of natural fluorite (CaF2:NaCl) and lithium fluoride (Harshaw TLD-100) were exposed to gamma and X rays of different qualities. The GEANT4 radiation transport Monte Carlo toolkit was employed to calculate the energy depth deposition profile in the TLDs. X-ray spectra of the ISO\\/4037-1 narrow-spectrum series, with peak voltage (kVp) values in the

  10. Electron emission yield from thin Al and insulating layers induced by 3 MeV He 2+ and 3 keV electron impact

    Microsoft Academic Search

    M. Steinbatz; A. Schinner; E. Steinbauer; O. Benka

    2002-01-01

    The kinetic electron yield was measured for the impact of 3 MeV He2+ ions and 3 keV electrons on thin layers of Al on Cu, of Al2O3 on Al, and of CeO2 and CaF2 on Si backings. The dependence of the yield on the layer thickness was determined. For Al on Cu a decreasing yield was observed for increasing Al

  11. 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.

  12. Morphologic defects in Cr3+:LiCaAlF6 crystals grown by the Czochralski method

    NASA Astrophysics Data System (ADS)

    Klimm, D.; Seiranian, K.; Reiche, Peter; Polity, A.; Krause-Rehberg, R.

    1997-07-01

    The paper reports on the growth of Cr3+:LiCaAlF6 single crystals by the Czochralski method from a stoichiometric melt of LiF, CaF2, and AlF3. (Cr3+ doping was obtained by the replacement of about 3 Mol-% AlF3 by the corresponding quantity CrF3.) Only the peripheric region and the neck of the crystals have high optical quality, whereas scattering 'needles' of typically 5 multiplied by 5 multiplied by 35 micrometers cubed can be observed in the top region and very small particles very much less than 1 micrometer ('dust') can be observed in the bottom part of the crystals. By EDX element analysis performed after ion beam thinning of the samples the needles were determined to have an excess Ca content in comparison to the LiCaAlF6 matrix. The binary compound LiAlF4 has the highest vapor pressure in the ternary system LiF - CaF2 - AlF3. It can be concluded, that LiAlF4 evaporates continuously during crystal growth, leaving in the melt CaF2 in excess. The incongruently melting compound Ca2AlF7 is considered to be the most probable candidate for the observed scattering centers.

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

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  14. Microwave-assisted one-pot synthesis of water-soluble rare-earth doped fluoride luminescent nanoparticles with tunable colors

    PubMed Central

    Mi, Cong-Cong; Tian, Zhen-huang; Han, Bao-fu; Mao, Chuan-bin; Xu, Shu-kun

    2012-01-01

    Polyethyleneimine (PEI) functionalized multicolor luminescent LaF3 nanoparticles were synthesized via a novel microwave-assisted method, which can achieve fast and uniform heating under eco-friendly and energy efficient conditions. The as-prepared nanoparticles possess a pure hexagonal structure with an average size of about 12 nm. When doped with different ions (Tb3+ and Eu3+), the morphology and structure of the nanoparticles were not changed, whereas the optical properties varied with doped ions and their molar ratio, and as a result emission of four different colors (green, yellow, orange and red) were achieved by simply switching the types of doping ions (Eu3+ versus Tb3 +) and the molar ratio of the two doping ions. PMID:22879690

  15. Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials.

    PubMed

    Kaczmarek, Anna M; Van Hecke, Kristof; Van Deun, Rik

    2015-04-21

    This review focuses on rare-earth carbonate materials of nano- and micro-size. It discusses in depth the different types of rare-earth carbonate compounds, diverse synthetic approaches and possibilities for chemical tuning of the size, shape and morphology. The interesting luminescence properties of lanthanide doped rare-earth carbonates and their potential applications for example as efficient white light sources and biolabels are reviewed. Additionally the use of these materials as precursors for the synthesis of nano-/micro-sized oxides, and their application as sacrificial templates for morphology-controlled synthesis of other materials such as YVO4, LaF3, NaYF4 and others is overviewed. PMID:25714401

  16. Spectroscopic and Relaxation Study of the Tritium -LABELLED-6 State in PRASEODYMIUM(3+):LANTHANUM-FLUORIDE.

    NASA Astrophysics Data System (ADS)

    Kichinski, Robert Thomas

    1988-12-01

    The relaxation behavior and hyperfine structure of the terminal ^3H_6 <=vel of the ^3P _0 - ^3H_6 transition (5985 A) in Pr^{3+ }:LaF_3 were studied using the excited state photon echo technique. The echo intensity was recorded as a function of pulse separation over nine decades of intensity. The echo signal decays exponentially with a T_2 of 250 nsec and Fourier analysis of the echo modulation yields the nuclear hyperfine splittings of the ^3 H_6<=vel. The fast decay is anomalous and remains so after examination of several possible explanations of this rate. We present stimulated echo data taken on the same transition which confirms the presence of a fast relaxation and indicates that it is due to a population decay out of the ^3 H_6 level. Temperature relaxation data is also presented.

  17. Effect of modifier oxides on absorption and emission properties of Eu3+ doped different lithium fluoroborate glass matrices

    NASA Astrophysics Data System (ADS)

    Ratnakaram, Y. C.; Balakrishna, A.; Rajesh, D.

    2012-11-01

    Eu3+ doped lithium fluoroborate glass with different modifier oxides (Li2B4O7-BaF2-NaF-MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li2B4O7-BaF2-NaF-MgO+CaO, Li2B4O7-BaF2-NaF-CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state (7F0) of different absorption bands of Eu3+ are calculated. From the optical absorption measurements and using the Judd-Ofelt (J-O) theory, J-O parameters (???=2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities (A), radiative life-times (?R), and branching ratios (?r) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections (?P) are obtained for the emission transitions, 5D0?7F1, 5D0?7F2, 5D0?7F3 and 5D0?7F4 of Eu3+ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the 5D0?7F2 transition have been measured and analyzed for all the glass matrices.

  18. Influence of modifier oxides on spectroscopic properties of Sm3+ doped lithium fluoroborate glass

    NASA Astrophysics Data System (ADS)

    Ratnakaram, Y. C.; Balakrishna, A.; Rajesh, D.; Seshadri, M.

    2012-11-01

    Sm3+ doped lithium fluoro-borate glasses with different modifier oxides (Li2B4O7-BaF2-NaF-MO where M = Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li2B4O7-BaF2-NaF-MgO+CaO, Li2B4O7-BaF2-NaF-CdO+PbO) were prepared by means of melt quenching method. These samples were characterized by XRD, FTIR, optical absorption and fluorescence techniques at room temperature. The XRD profiles of all the glasses confirm their amorphous nature and the FTIR spectra reveal the presence of BO3 and BO4 units along with the strong OH- groups in the glass matrices. The influence of modifier oxides on Judd-Ofelt (J-O) intensity parameters and intensity of the emission lines are reported. Judd-Ofelt theory is used to study the spectral properties and to calculate the radiative transition probabilities (AT), branching ratios (?R), integrated absorption cross sections (?) and radiative lifetimes (?R) for certain spectral transitions. From the emission spectral analysis, emission cross-sections (?P) are calculated for the four emission transitions, 4G5/2 ? 6H5/2, 4G5/2 ? 6H7/2, 4G5/2 ? 6H9/2 and 4G5/2 ? 6H11/2 of Sm3+ ion in different lithium fluoro-borate glasses. Among the four transitions, it is observed that the transition 4G5/2 ? 6H7/2 has higher emission cross-section (?P) in all the glass matrices, except in Mg, Cd and Mg-Ca glass matrices. The non-exponential nature of the luminescence decay curves of 4G5/2 level of Sm3+ doped glass matrices are also reported.

  19. A low-fluorine solution with a 2:1 F/Ba mole ratio for the fabrication of YBCO films

    NASA Astrophysics Data System (ADS)

    Wu, Wei; Feng, Feng; Zhao, Yue; Tang, Xiao; Xue, Yunran; Shi, Kai; Huang, Rongxia; Qu, Timing; Wang, Xiaohao; Han, Zhenghe; Grivel, Jean-Claude

    2014-03-01

    In previously reported low-fluorine MOD-YBCO studies, the lowest F/Ba mole ratio of the precursor solution was 4.5. Further lowering the F/Ba ratio would bring benefits for the environment, thick film deposition, and an understanding of the heat treatment process. On the other hand, the F/Ba ratio must be at least 2 for full conversion of the Ba-precursor to BaF2 to avoid the formation of BaCO3, which is detrimental to the superconducting performance of YBCO films. In this study, a solution with a 2:1 F/Ba mole ratio was developed, and the fluorine content of this solution was approximately only 10.3% of that used in the conventional TFA-MOD method. Attenuated total reflectance-Fourier transform-infrared spectra (ATR-FT-IR) revealed that BaCO3 was remarkably suppressed in the as-pyrolyzed film—and eliminated at 700?°C. Thus, YBCO films with a critical current density (Jc) of over 5 MA cm-2 (77 K, 0 T, 200 nm thickness) could be obtained on lanthanum aluminate single-crystal substrates. In situ FT-IR spectra showed that no obvious fluorinated gaseous by-products were detected in the pyrolysis step, which indicated that all F atoms might remain in the film as fluorides. X-ray diffraction ?/2? scans showed the presence of BaF2—but not of Y F3 or CuF2—in films quenched at 400-800?°C. The formation priority of BaF2 over Y F3 and CuF2 was interpreted by examining the chemical equilibrium of the potential reactions. Our study could enlarge the synthesis window of precursor solutions for MOD-YBCO fabrication, and serve as a foundation for continuously and systematically studying the influence of fluorine content in the precursor solutions.

  20. 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. [Department of Physics and Applied Physics, University of Massachusetts Lowell, One University Avenue, Lowell, MA 01854 (United States)

    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.

  1. 4.8 mum vertical emitting PbTe quantum-well lasers based on high-finesse EuTe\\/Pb1-xEuxTe microcavities

    Microsoft Academic Search

    G. Springholz; T. Schwarzl; M. Aigle; H. Pascher; W. Heiss

    2000-01-01

    Vertical laser emission at 4.8 mum from PbTe quantum wells in high-finesse Pb0.95Eu0.05Te\\/EuTe microcavity structures at temperatures between 35 and 85 K is reported. The vertical-cavity laser structure was grown by molecular-beam epitaxy on BaF2(111) substrates, and consisted of a 2lambda cavity with four 20 nm quantum wells at the cavity antinodes. Laser emission was excited by optical pumping with

  2. Dependence of thermo-mechanical and mechanical properties of novel fluorophosphate glass on various rare earth dopants

    Microsoft Academic Search

    Ju H. Choi; Alfred Margaryan; Ashot Margaryan; Frank G. Shi

    2008-01-01

    The dependence of thermo-mechanical, and mechanical properties on various rare earth dopants (RE) including Nd2O3, Er2O3, and Yb2O3 in 0.4MgF2-0.4BaF2-0.1Ba(PO3)2-0.1Al(PO3)3 glasses (MBBA system) is systematically investigated. MBBA system doped with RE dopants presented the potential application\\u000a in the field of communication and high power layer system in the previous reports. In this work, it is found that the density\\u000a of

  3. OAK RIDGE NATIONAL LABORATORY U. S. DEPARTMENT OF ENERGY

    E-print Network

    YBCO FY2005FY2002 Ni-W (50µm) Ni (1.5 µm) Y2O3 (~ 50 nm) YSZ (~ 200 nm) CeO2 (~20 nm) YBCO (~ 0.3-1 µm) Ni-W (50µm) Ni (1.5 µm) Y2O3 (~ 50 nm) YSZ (~ 200 nm) CeO2 (~20 nm) YBCO (~ 0.3-1 µm) Deposition Methods: ·YBCO: ex-situ BaF2 process ·YSZ and CeO2 : rf sputtering ·Y2O3: e-beam ·Ni: dc sputtering

  4. The effect of Er 3+ and Sm 3+ on phase separation and crystallization in Na 2O\\/K 2O\\/BaF 2\\/BaO\\/Al 2O 3\\/SiO 2 glasses

    Microsoft Academic Search

    Jordana Rocha Barros; Christian Bocker; Christian Rüssel

    2010-01-01

    Thermal annealing of Sm+3 or Er+3 doped Na2O\\/K2O\\/BaF2\\/BaO\\/Al2O3\\/SiO2 glasses led to the precipitation of nanocrystalline BaF2. The mean crystallite sizes were in the range from 9 to 15 nm as shown by XRD line broadening. Whereas glasses without rare earth oxides showed crystallites homogenously dispersed in the amorphous matrix, those doped with 0.05 mol% ErF3 or SmF3 showed highly agglomerated crystals. The

  5. Quantum well structures based on PbTe\\/Pb(1-x)Sn(x)Te

    Microsoft Academic Search

    F. F. Sizov; Iu. G. Troian; V. V. Teterkin; M. V. Apatskaia; Zh. V. Gumeniuk-Sychevskaia

    1989-01-01

    A study is made of the optical transmission spectra and electrophysical properties of quantum well structures and superlattices based on PbTe\\/Pb0.8Sn0.2Te deposited by the 'hot wall' method on the (111) planes of BaF2 substrates over 1-5-micron-thick PbTe and Pb0.8Sn0.2Te buffer layers. The optical absorption spectra associated with the quantization of the energy spectrum are identified, and the two-dimensional nature of

  6. [Development of X-ray excited fluorescence spectrometer].

    PubMed

    Ni, Chen; Gu, Mu; Di, Wang; Cao, Dun-Hua; Liu, Xiao-Lin; Huang, Shi-Ming

    2009-08-01

    An X-ray excited fluorescence spectrometer was developed with an X-ray tube and a spectrometer. The X-ray tube, spectrometer, autocontrol method and data processing selected were roundly evaluated. The wavelength and detecting efficiency of the apparatus were calibrated with the mercury and tungsten bromine standard lamps, and the X-ray excited emission spectra of BaF2, Cs I (Tl) crystals were measured. The results indicate that the apparatus has advantages of good wavelength resolution, high stability, easy to operation and good radioprotection. It is a wery effective tool for exploration of new scintillation materials. PMID:19839360

  7. Rare ISotopes INvestigation at GSI (RISING) using gamma-ray spectroscopy at relativistic energies

    NASA Astrophysics Data System (ADS)

    Wollersheim, H. J.; Appelbe, D. E.; Banu, A.; Bassini, R.; Beck, T.; Becker, F.; Bednarczyk, P.; Behr, K.-H.; Bentley, M. A.; Benzoni, G.; Boiano, C.; Bonnes, U.; Bracco, A.; Brambilla, S.; Brünle, A.; Bürger, A.; Burkard, K.; Butler, P. A.; Camera, F.; Curien, D.; Devin, J.; Doornenbal, P.; Fahlander, C.; Fayz, K.; Geissel, H.; Gerl, J.; Górska, M.; Grawe, H.; Grebosz, J.; Griffiths, R.; Hammond, G.; Hellström, M.; Hoffmann, J.; Hübel, H.; Jolie, J.; Kalben, J. V.; Kmiecik, M.; Kojouharov, I.; Kulessa, R.; Kurz, N.; Lazarus, I.; Li, J.; Leske, J.; Lozeva, R.; Maj, A.; Mandal, S.; Meçzy?ski, W.; Million, B.; Münzenberg, G.; Muralithar, S.; Mutterer, M.; Nolan, P. J.; Neyens, G.; Nyberg, J.; Prokopowicz, W.; Pucknell, V. F. E.; Reiter, P.; Rudolph, D.; Saito, N.; Saito, T. R.; Seddon, D.; Schaffner, H.; Simpson, J.; Speidel, K.-H.; Stycze?, J.; Sümmerer, K.; Warr, N.; Weick, H.; Wheldon, C.; Wieland, O.; Winkler, M.; Ziebli?ski, M.

    2005-02-01

    The Rare ISotopes INvestigation at GSI project combines the former EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, BaF 2-HECTOR detectors, and the fragment separator at GSI for high-resolution in-beam ?-ray spectroscopy measurements with radioactive beams. These secondary beams produced at relativistic energies are used for Coulomb excitation or secondary fragmentation experiments in order to explore the nuclear structure of the projectiles or projectile like nuclei by measuring de-excitation photons. The newly designed detector array is described and the performance characteristics are given. Moreover, particularities of the experimental technique are discussed.

  8. Physical characteristics of TTV03, a new high spatial resolution time-of-flight positron tomograph

    Microsoft Academic Search

    B. Mazoyer; R. Trebossen; C. Schoukroun; B. Verrey; A. Syrota; J. Vacher; P. Lemasson; O. Monnet; A. Bouvier; J. L. Lecomte

    1990-01-01

    TTV03, a novel high-spatial-resolution TOF-PET (time-of-flight positron emission tomography) system, is presented. The machine consists of four 89-cm-diameter rings made of 7-mm-wide, 18-mm-high, 45-mm-deep BaF2 crystals (324 per ring) individually coupled to 11-mm-diameter phototubes. The transaxial resolution (full width at half maximum or FWHM) in the reconstructed image is 5.7 mm at center, 5.7 mm (tangential), and 6.5 mm (radial)

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Study on the initial stages of water corrosion of fluorozirconate glasses

    Microsoft Academic Search

    A. P. Rizzato; C. V. Santilli; S. H. Pulcinelli; Y. Messaddeq; A. F. Craievich; P. Hammer

    2004-01-01

    The surface corrosion process associated with the hydrolysis of fluorozirconate glass, ZBLAN (53ZrF4, 20BaF2, 20NaF, 4LaF2, 3AlF3) was investigated using X-ray photoelectron spectroscopy (XPS), grazing-incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). After a short exposure period (25min) of the glass surface to deionized water the XPS data indicate an increase of the oxygen

  11. Detection of ? mesons in heavy-ion collisions at 100 MeV/nucleon

    NASA Astrophysics Data System (ADS)

    Badalà, A.; Barbera, R.; Palmeri, A.; Pappalardo, G. S.; Riggi, F.; Russo, A. C.; Turrisi, R.

    1997-02-01

    A study of the detection of ? mesons in heavy-ion collisions at 100 MeV/nucleon by a large array of BaF 2 modules has been carried out using full GEANT3 simulations. The most probable decay modes of the ? mesons have been considered. Invariant mass spectra from the detection of two or more electromagnetic showers are discussed. The different sources of contamination are evaluated. The detection limits in terms of production cross section are discussed. An analysis of experimental data taken at 95 MeV/nucleon with the MEDEA array showed a few events which are compatible with the ? ? ?? decay.

  12. Synthesis and Characterization of (1-x)BaTiO3-xBaF2-xLiF Ceramics

    Microsoft Academic Search

    D. Talantikite-Touati; L. Benziada

    2012-01-01

    Oxyfluoride phases have been synthesized in free atmosphere at 950°C during 4 hours, using the BaTiO3 perovskite and the fluorides BaF2 and LiF. The XRD study at room temperature on powder, for various compositions has shown the formation of a new solid solution (1-x)BaTiO3-xBaF2-xLiF in the range 0

  13. Influence of network modifiers on conductivity and relaxation parameters in some series of fluoride glasses containing LiF

    Microsoft Academic Search

    J. M. Réau; Xu Yong Jun; J. Senegas; Ch. Le Deit; M. Poulain

    1997-01-01

    A new series of fluoride glasses of formulation ZrF4(0.25)-ZnF2(0.15)-YF3(0.05)-AlF3(0.10)-CdF2 (0.17 ? 2x5)-BaF2(0.28 ? 3x5)-LiF(x) and containing a wide LiF concentration range (0 ? xLiF ? 0.35) has been investigated by impedance spectroscopy: the variation of various electrical parameters has been determined as a function of composition. The results obtained with two other series of fluoride glasses covering the (0 ?

  14. Triple coincidence PALS setup based on fast pulse digitizers

    NASA Astrophysics Data System (ADS)

    Bosnar, D.; ?ur?evi?, B.; Paveli?, L.; Bosnar, S.

    2015-06-01

    We have assembled positron annihilation lifetime spectroscopy system that consists of three BaF2 detectors with XP2020URQ PMTs which are directly coupled to DRS4 evaluation board. Both time and energy information of the detected gamma rays are reconstructed. In the off-line analysis, by using selected cuts on energies of gamma rays, double, as well as triple coincidence events can be extracted. The setup is very suitable for the determination of contributions of positronium three gamma annihilations which can be of interest in the investigations of various porous materials.

  15. Study on luminescent property of Tb(3+)-doped silicate nano-scintillating glass.

    PubMed

    Jingwen, Lv; Xu, Yang; Shengchun, Xiao; Tao, Zheng

    2010-03-01

    By optimizing a Tb(3+)-doped silicate nano-scintillating glass matrix, sensitizer and brightening agent components, the processing conditions such as the melting temperature, holding time, atmosphere, and heat treatment were improved, and the temperature of the heat treatment was changed to generate BaF2 nano-crystal in the glass. The resulting nanocrystals have a better rare earth solubility and a lower phonon energy; therefore the luminescent property of Tb(3+)-doped silicate nano-scintillating glass has been noticeably improved. PMID:20355612

  16. Spectroscopy of divalent rare earth ions in fluoride crystals

    E-print Network

    Shendrik, R; Radzhabov, E A; Nepomnyashchikh, A I

    2015-01-01

    We have studied the absorption spectra of x-ray irradiation-induced Ce2+ and Pr2+ ions in crystals of alkaline-earth fluorides. We have calculated absorption spectra of divalent praseodymium ions in SrF2 crystals doped with Pr2+ for the first time. The calculated spectra agree rather well with the experimental data. In crystals containing induced Ce2+ ions we have found strong electron-phonon coupling. In BaF2, we do not observe bands corresponded to divalent Ce or Pr ions.

  17. UV/blue upconversion in Nd3+:TeO2 glass, effect of modifiers and heat treatment on the fluorescence bands.

    PubMed

    Verma, R K; Kumar, K; Rai, S B

    2009-10-15

    Upconversion (UC) emissions in UV/blue region have been observed in Nd(3+) doped tellurite glass on 532 nm excitation. The UC bands have been observed at 360, 387, 417 and 452 nm due to the (4)D(3/2)-->(4)I(9/2), (4)D(3/2)-->(4)I(11/2), (4)D(3/2)-->(4)I(13/2) and (4)D(3/2)-->(4)I(15/2) transitions, respectively and they show two photon character. The effect of BaCO(3), BaF(2) and BaCl(2) glass modifiers on the UC efficiency has been studied and Judd-Ofelt intensity parameters have been calculated and compared. The BaCl(2) modified glass showed maximum UC intensity among the three modifiers and this enhancement in UC intensity has been related to the reduction in average phonon frequency of the glass sample. Heat treatments of the BaF(2) and BaCl(2) modified samples also show enhancement in UC intensity while the BaCO(3) modified sample has no such effect. Lifetime of the (4)D(3/2) level has been measured to understand the mechanism responsible for UC emission. Temperature dependent fluorescence studies have been done on the (4)F(3/2), (4)F(5/2) and (2)S(3/2) emitting levels and results show that Nd(3+) doped tellurite glass can be used as a temperature sensor. PMID:19747875

  18. Nanostructure morphology and atomically resolved images of chains and planes of YBCO single crystals grown with different additives

    NASA Astrophysics Data System (ADS)

    Narlikar, A. V.; Samanta, S. B.; Changkang, Chen; Yongle, Hu; Hodby, J. W.; Wanklyn, B. M.

    1996-01-01

    Bulk single crystals of superconducting YBCO (YBa 2Cu 3O 7), grown with incorporation of different additives like BaF 2, B 2O 3 and Bi 2O 3, have been investigated to gain an insight into the problem of combating Tc degradation due to aluminium contamination from the crucible material. Electron probe microanalysis (EPMA) along with Tc values of the above crystals, shows that, with BaF 2 introduced as additive, the contamination due to aluminium is significantly reduced, which improves crystal growth and superconductivity. The crystals have been subjected to high resolution imaging of planes and chains using STM, while the ensuing changes in the conductance spectra of chains due to Al contamination were studied by scanning tunnelling spectroscopy (STS). The contamination of Cu?O chains is corroborated by chains becoming quasi-insulating on account of substitutional disorder, and also by the increase in their surface roughness at the atomic level. The effect of additives is discussed and the observed Tc variation is linked with the relative changes in the adulteration and disordering of Cu?O chains. The results are in general accord with the role of interlayer coupling between CuO 2 planes and other effects that are known to control the Tc of layered cuprates.

  19. The effect of water pressure on the texture and morphology of MOD-YBCO films on buffered metal substrates

    NASA Astrophysics Data System (ADS)

    Chung, K. C.; Yoo, J. M.; Kim, Y. K.; Wang, X. L.; Dou, S. X.

    2009-02-01

    The influence of water pressure in the metal-organic deposition (MOD) method on the texture and morphology of YBa2Cu3O7-X (YBCO) films grown on buffered metal substrates was investigated. The water pressure was varied from 4.2% to 10.0%, with the other process parameters, such as annealing temperature and oxygen pressure, kept constant. In this work, a YBCO precursor solution was prepared using a fluorine-free Y and Cu precursor solution with the addition of Sm. MOD-YBCO films were fabricated by continuous slot-die coating and calcination, followed by high temperature annealing. Using x-ray diffraction analysis, unreacted phase peaks, such as BaF2 peaks, were found in the samples made at a water pressure of 4.2%; however, the BaF2 peak intensity was much reduced as the water pressure was increased. The higher water pressure of about 10.0% in this experiment led to the poor crystallinity of MOD-YBCO films, possibly due to the fast reaction with the supplied water vapor. Meanwhile, the morphologies of the YBCO films were not much different from each other in the range of water pressure of this work. The maximum critical current density of 3.8 MA cm-2 was obtained when the sample was made at the water pressure of 6.2% and the annealing temperature of 780 °C.

  20. Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET.

    PubMed

    Mondal, Nagendra Nath

    2009-10-01

    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 (Lu(2)SiO(5): Ce in short LSO), Barium Fluoride (BaF(2)) and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr(3)) 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 BaF(2) and LaBr(3), 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

  1. Laser-Induced Damage of Calcium Fluoride

    SciTech Connect

    Espana, Aubrey L.; Joly, Alan G.; Hess, Wayne P.; Dickinson, J T.

    2004-12-01

    Radiation damage of materials has long been of fundamental interest, especially since the growth of laser technology. One such source of damage comes from UV laser light. Laser systems continue to move into shorter wavelength ranges, but unfortunately are limited by the damage threshold of their optical components. For example, semiconductor lithography is making its way into the 157nm range and requires a material that can not only transmit this light (air cannot), but also withstand the highly energetic photons present at this shorter wavelength. CaF2, an alkaline earth halide, is the chosen material for vacuum UV 157 nm excimer radiation. It can transmit light down to 120 nm and is relatively inexpensive. Although it is readily available through natural and synthetic sources, it is often times difficult to find in high purity. Impurities in the crystal can result in occupied states in the band gap that induce photon absorption [2] and ultimately lead to the degradation of the material. In order to predict how well CaF2 will perform under irradiation of short wavelength laser light, one must understand the mechanisms for laser-induced damage. Laser damage is often a two-step process: initial photons create new defects in the lattice and subsequent photons excite these defects. When laser light is incident on a solid surface there is an initial production of electron-hole (e-h) pairs, a heating of free electrons and a generation of local heating around optically absorbing centers [3]. Once this initial excitation converts to the driving energy for nuclear motion, the result is an ejection of atoms, ions and molecules from the surface, known as desorption or ablation [3]. Secondary processes further driving desorption are photoabsorption, successive excitations of self-trapped excitons (STE's) and defects, and ionization of neutrals by incident laser light [3]. The combination of laser-induced desorption and the alterations to the electronic and geometrical structure of the lattice result in defect formation. In the material CaF2 some of these defects take the form of F-centers, an electron trapped at a halogen vacancy [4], and H-centers, a F2- molecular ion at a single lattice site [5]. While the F-centers are stable, the H-centers are transient but can form into aggregates that are stable. There are many different configurations the defects can take based on the relative position of F and H centers in the lattice and this is extensively discussed in literature [1,4,5]. Once these defects have formed they cause further absorption of light, which ultimately induces particle emission and the production of even more defects. Various forms of laser-induced damage of CaF2 have been studied. For example, the mechanism for photon-stimulated desorption (PSD) of F+ from CaF2 (111) is discussed in ref. 6 and the energy threshold, distribution and kinetics governing electron-stimulated desorption (ESD) is investigated in ref. 7. The desorption of neutral Ca and F atoms has also been explored [1]. In this paper I focus on the emission of ions and neutrals from CaF2 under the irradiation of pulsed laser light at 266 nm, in addition to a brief study of its purity and transmittance.

  2. Evolution of the CaF?: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??m(-1) track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique. PMID:25683355

  3. Evaluation of flow cell detector configurations combining simultaneous preconcentration and scintillation detection for monitoring of pertechnetate in aqueous media.

    PubMed

    Hughes, Lara D; DeVol, Timothy A

    2006-04-01

    Flow cell detectors were developed for simultaneous concentration and scintillation detection of technetium-99 in water. Evaluated flow cell geometries consisted of a coil and a fountain flow cell design; the latter is based on radial solution flow through a resin bed interfaced with a photomultiplier tube through a polycarbonate window. The sorptive scintillating media investigated were (1) an extractive scintillator combining a porous polystyrene resin with the extractant Aliquat-336 and fluor 2-(1-naphthyl)-5-phenyloxazole, (2) a mixed bed of organic scintillator (BC-400) and Tc-selective resin (TEVA), and (3) a mixed bed of inorganic scintillator particles (CaF2-Eu) with either TEVA resin or strong base anion-exchange resin (Dowex 1 x 8-400(Cl)). Depending on flow cell geometry and medium, the detection efficiencies for 99Tc ranged from 7.26 (BC-400/TEVA in coil geometry) to 50.20% (CaF2(Eu)/Dowex 1 x 8-400(Cl) in fountain flow cell geometry). The configuration with the highest sensitivity, CaF2(Eu)/Dowex 1 x 8-400(Cl) in coil geometry, can detect 99Tc as low as 3.78 Bq L(-1) for a 100-s count interval and a 200-mL sample, which is below the current regulatory level of 33 Bq L(-1). The issue of sensor reusability was addressed in this research, and its potential application at near neutral pH was demonstrated. The optimal sensor design was evaluated with a 99Tc-spiked synthetic groundwater matrix. PMID:16579605

  4. Structure of hydrides based on V-Cr alloys

    NASA Astrophysics Data System (ADS)

    Lushnikov, S. A.; Verbetskii, V. N.; Somenkov, V. A.; Glazkov, V. P.

    2014-11-01

    The structure of deuterides based on V0.9Cr0.1 and V0.5Cr0.5 alloys has been investigated by neutron diffraction at room and low (77 K) temperatures. It is found that V0.9Cr0.1D2.0 deuteride has a CaF2 ( Fm3 m) crystal structure, which corresponds to vanadium dihydride. V0.5Cr0.5D0.7 deuteride has a NiAs ( P6/3 mmc) structure type, similar to chromium hydride.

  5. Effect of fluorspar and other fluxes on slag-metal equilibria involving phosphorus and sulfur

    Microsoft Academic Search

    G. J. W. Kor

    1977-01-01

    The effect of additions of fluorspar-and potential substitutes such as borate, manganese ore, and ilmenite—to basic steelmaking\\u000a slags on the equilibrium phosphorus and sulfur distribution ratio has been studied at 1550?C. From laboratory slag-metal equilibrium\\u000a studies it was found that the presence of CaF2 in concentrations between 1.5 and 5 wt pct in the slag (equivalent to 2 and\\u000a 6

  6. Development of glass-ceramics by sintering and crystallization of fine powders of calcium-magnesium-aluminosilicate glass

    Microsoft Academic Search

    D. U. Tulyaganov; M. J. Ribeiro; J. A. Labrincha

    2002-01-01

    Natural raw materials normally used in the ceramic and glass industry were studied for the production of calcium–magnesium–aluminosilicate glass or glass-ceramic materials. Sintering and crystallization processes of fine powders of parent glass with chemical composition (wt.%) 46.00 SiO2, 15.90 Al2O3, 1.20 Fe2O3, 0.42 TiO2, 23.50 CaO, 9.37 MgO, 0.04 Na2O, 0.98 K2O, 1.95 P2O5 and 0.35 CaF2 were studied. Crystallization

  7. Experimental search for the low-energy nuclear transition in 229Th with undulator radiation

    NASA Astrophysics Data System (ADS)

    Yamaguchi, A.; Kolbe, M.; Kaser, H.; Reichel, T.; Gottwald, A.; Peik, E.

    2015-05-01

    To search for the lowest energy nuclear isomeric transition in 229Th in solid samples, a novel adsorption technique which prepares 229Th atoms on a surface of CaF2 is developed. Adsorbed 229Th is exposed to highly intensive undulator radiation in the wavelength range between 130 and 320 nm, which includes the indirectly measured nuclear resonance wavelength 160(10) nm. After the excitation, fluorescence from the sample is detected with a VUV sensitive photomultiplier tube. No clear signal relating to the nuclear transition is observed and possible reasons are discussed.

  8. Improvement in the quality of LiCaAlF 6 single crystal as window material

    NASA Astrophysics Data System (ADS)

    Sato, H.; Bensalah, A.; Yoshikawa, A.; Nikl, M.; Machida, H.; Fukuda, T.

    2003-10-01

    Three-in. size LiCaAlF 6 (LiCAF) single crystals were successfully grown by the Czochralski method. Both measurements of the transmission spectra in the VUV regions and the X-ray rocking curve analysis showed that the crystallinity of LiCAF single crystal was improved by the annealing. Optical absorption measurements in the UV/VIS spectral regions following X-ray irradiation were performed in order to compare the radiation damage with a lithography-grade CaF 2 crystal.

  9. Initial stage of laser ablation of LiCaAlF6 single crystal under F2 laser irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Y.; Narazaki, A.; Sato, T.; Kurosaki, R.; Niino, H.; Sato, H.; Fukuda, T.

    Initial stage of F2 laser ablation of LiCaAlF6 single crystal was investigated for clarifying the possibility of applying this wide bandgap fluoride crystal to vacuum ultraviolet (VUV) optical components. The ablation threshold, determined by the appearance of line emission from ablated species, was approximately 2 Jcm-2pulse-1, similar to that of VUV grade CaF2 single crystal. The laser-induced damage on the front surface of LiCaAlF6 was faint, though adhesion of aggregated particulates of several microns was observed.

  10. Transport and structural properties of Bi-Sr-Ca-Cu-oxide thin films prepared by reactive magnetron sputtering

    Microsoft Academic Search

    D. W. Face; J. T. Kucera; J. Crain; M. M. Matthiesen; D. Steel; D. A. Rudman; T. P. Orlando; G. Somer

    1989-01-01

    Highly oriented superconducting thin films of Bi-Sr-Ca-Cu-oxides have been reproducibly prepared by reactive magnetically-enhanced triode sputtering using three separate metal targets (Sr, Ca, and Cu-Bi). The as-deposited films had composition ratios of Bi:Sr:Ca:Cu that were very close to either 2:2:1:2 or 2:2:2:3. The films were deposited on SrTiO3, MgO, CaF2, Al2O3, and yttria stabilized zirconia (YSZ) substrates and had thicknesses

  11. Ionic liquid synthesis of luminescent nano-cubes and their microstructure characterization

    NASA Astrophysics Data System (ADS)

    Ma, Qianmin; Ping, Lulu; Zhang, Helen Meihua; Yang, Jinglian; Wang, Qianming

    2015-07-01

    Regular CaF2:Eu3+ nano-cubes undergo ionic liquid (diallyldimethylammonium tetrafluoroborate, abbreviated as DTB)-mediated synthesis reactions in the presence of Eu(NO3)3?6H2O. The formation of uniform and mono-dispersed particles relies primarily on a one-pot hydrothermal method. The correlations between reaction temperature, doping concentration and crystalline structures have been clarified. In addition, the photoluminescence features and their influencing factors were extensively studied. In the case of Eu3+ containing phosphors, the application of new structure directing reagents will be convenient for the design of functional nanomaterials.

  12. Preparation and characterization of lithium hexafluorophosphate for lithium-ion battery electrolyte

    Microsoft Academic Search

    Jian-wen LIU; Xin-hai LI; Zhi-xing WANG; Hua-jun GUO; Wen-jie PENG; Yun-he ZHANG; Qi-yang HU

    2010-01-01

    A promising preparation method for lithium hexafluorophosphate (LiPF6) was introduced. Phosphorus pentafluoride (PF5) was first prepared using CaF2 and P2O5 at 280°C for 3 h. LiPF6 was synthesized in acetonitrile solvent by LiF and PF5 at room temperature (20?30) for 4 h°C. The synthesized LiPF6 was characterized by infrared spectrometry and X-ray diffraction(XRD). Atomic absorption and ion chromatography results show

  13. Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

    SciTech Connect

    David H Hurley; Marat Khafizov; Zilong Hua; Rory Kennedy; Heng Ban

    2012-05-01

    A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k=(e2/D)1/2. To generalize this approach, sensitivity analysis was conducted for materials having a range of thermal conductivities. Experimental validation was sought using two substrate materials, SiO2 and CaF2, both coated with thin titanium films. The measured conductivities compare favorably with literature values.

  14. 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. PMID:19380234

  15. Nonaqueous sol–gel synthesis, characterization and catalytic properties of metal fluoride supported palladium nanoparticles

    Microsoft Academic Search

    Pratap T. Patil; Anton Dimitrov; Holm Kirmse; Wolfgang Neumann; Erhard Kemnitz

    2008-01-01

    High surface area (HS) metal fluoride supported palladium catalysts (Pd0\\/MFx) (MFx=AlF3, MgF2, CaF2 and KMgF3) together with the respective Pd-free HS-MFx catalysts have been prepared via a novel sol–gel synthesis. In a first step, the reaction of anhydrous hydrogen fluoride (aHF) with the respective solutions of the metal alkoxides containing up to 10% Pd(acac)2 yielded the catalyst precursors as HS-gels.

  16. Epitaxial switchable yttrium-hydride mirrors

    NASA Astrophysics Data System (ADS)

    Nagengast, D. G.; Kerssemakers, J. W. J.; van Gogh, A. T. M.; Dam, B.; Griessen, R.

    1999-09-01

    By means of x-ray scattering and scanning probe microscopy it is shown that high-quality epitaxial Y films can be deposited on (111)-CaF2 substrates. The films can reversibly be switched from metallic YH2 to transparent insulating YH3-?. Although hydrogen absorption involves an expansion of the lattice and a symmetry change from hcp to fcc, the epitaxiality of the film remains intact during the switching process. The transparency and the insulating nature of the substrate opens unique possibilities to investigate electrically and optically these switchable mirror films in the single crystalline state.

  17. Generation of ultrashort 25-?J pulses at 200 nm by dual broadband frequency doubling with a thin KBe2BO3F2 crystal.

    PubMed

    Zhou, Chun; Kanai, Teruto; Wang, Xiaoyang; Zhu, Yong; Chen, Chuangtian; Watanabe, Shuntaro

    2012-06-18

    Ultrashort pulses with a 25-?J output energy were generated at 200 nm by dual broadband frequency doubling with a thin KBe(2)BO(3)F(2) (KBBF) crystal at 1 kHz as the fourth harmonic of a high power Ti:sapphire laser. The spectrum was broadened to a spectral width of 2.25 nm. The pulse duration of 56 fs was measured by single-shot autocorrelation with two-photon fluorescence from self-trapped excitons in a CaF(2) crystal. PMID:22714434

  18. Effect of substitution on F.C.C. and B.C.C. hydridephase formation in the TiCr 2–H 2 system

    Microsoft Academic Search

    S. N Klyamkin; A. Yu Kovriga; V. N Verbetsky

    1999-01-01

    Phase transformations of TiCr1.8, ZrCr2, Ti0.9Zr0.1Cr1.8, Ti0.7Zr0.3Cr1.8 and TiCr1.7Fe0.1 intermetallic compounds during their interaction with hydrogen at pressuresfrom 1 to 200 MPa and temperatures of 195 and 295 K are studied. Formation of three types ofhydride phases are stated by X-ray diffraction method: (I) hexagonal Laves phase preserving theMgZn2 structure of the initial intermetallic, (II) F.C.C. phase of CaF2structure type

  19. Generation of Kerr combs centered at 4.5{\\mu}m in crystalline microresonators pumped by quantum cascade lasers

    E-print Network

    Savchenkov, Anatoliy A; Di Teodoro, Fabio; Belden, Paul M; Lotshaw, William T; Matsko, Andrey B; Maleki, Lute

    2015-01-01

    We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF$_2$ and MgF$_2$ whispering-gallery mode resonators pumped with continuous wave room temperature quantum cascade lasers. The combs were centered at 4.5$\\mu$m, the longest wavelength to date. A frequency comb wider than a half of an octave was demonstrated when approximately 20mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10$^8$.

  20. Metastable He deexcitation at semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Pasquali, L.; Nannarone, S.

    2005-04-01

    A review is given of the application of metastable deexcitation spectroscopy (MDS) to the study of the interface formation between semiconductors and different materials. In particular we present an overview of the results obtained on nanostructured interfaces, where strain and reaction between the substrate and the overlayer atoms drive the growth mode and the morphology of the system. As prototypical examples we discuss the growth of CaF 2 on silicon and rare earths (Yb, Er) on silicon and gallium arsenide. The mechanisms and chemical reactions which bring to interface formation are examined on the basis of MDS results and their comparison with photoemission.

  1. Parameterization of interatomic potential by genetic algorithms: A case study

    NASA Astrophysics Data System (ADS)

    Ghosh, Partha S.; Ranawat, Y. S.; Arya, A.; Dey, G. K.

    2015-06-01

    A framework for Genetic Algorithm based methodology is developed to systematically obtain and optimize parameters for interatomic force field functions for MD simulations by fitting to a reference data base. This methodology is applied to the fitting of ThO2 (CaF2 prototype) - a representative of ceramic based potential fuel for nuclear applications. The resulting GA optimized parameterization of ThO2 is able to capture basic structural, mechanical, thermo-physical properties and also describes defect structures within the permissible range.

  2. Preparation, Thermal Behaviour, and Structure of Calcium Trifluoroacetate Monohydrate

    Microsoft Academic Search

    Mitko Khristov; Pavel Peshev; Olyana Angelova; Rosica Petrova; Josef Macicek

    1998-01-01

    Summary.  ?Calcium trifluoroacetate was prepared as its monohydrate Ca(CF3COO)2?H2O by reaction of CaCO3 with an aqueous solution of CF3COOH. It has been established by thermogravimetry and differential thermal analysis that this salt possesses a low thermal\\u000a stability. When heated in air, decomposition starts already at 106°C, yielding the final product CaF2. Single crystals of Ca(CF3COO)2?H2O were obtained and found to be

  3. Kerr effect-assisted self-compression in dielectric to single-cycle pulse width and to terawatt power level in mid-IR

    NASA Astrophysics Data System (ADS)

    Bravy, B. G.; Gordienko, V. M.; Platonenko, V. T.

    2015-06-01

    The self-compression of sub-TW mid-IR (?=4-5 ?m) femtosecond laser pulse in a non-linear dielectric medium was numerically modeled. Combination of the Kerr non-linearity and negative group velocity dispersion in CaF2 crystal was found to result in compression of the incident laser pulse to a 1-2-cycle pulse width. The possibility for suppression of small-scale self-focusing in conditions when the pulse power was several orders of magnitude above the critical self-focusing power was analyzed. Intrinsic concentration of free carriers was found to play important role in pulse evolution during its propagation.

  4. Ultra-trace analysis of (41)Ca in urine by accelerator mass spectrometry: an inter-laboratory comparison.

    PubMed

    Jackson, George S; Hillegonds, Darren J; Muzikar, Paul; Goehring, Brent

    2013-10-15

    A (41)Ca interlaboratory comparison between Lawrence Livermore National Laboratory (LLNL) and the Purdue Rare Isotope Laboratory (PRIME Lab) has been completed. Analysis of the ratios assayed by accelerator mass spectrometry (AMS) shows that there is no statistically significant difference in the ratios. Further, Bayesian analysis shows that the uncertainties reported by both facilities are correct with the possibility of a slight under-estimation by one laboratory. Finally, the chemistry procedures used by the two facilities to produce CaF2 for the cesium sputter ion source are robust and don't yield any significant differences in the final result. PMID:24179312

  5. Distribution of niobium or tantalum between fluorine-containing slag and iron in blast furnace smelting

    NASA Astrophysics Data System (ADS)

    Han, Qiyong; Deng, Jian; Huang, Shiliang; Fang, Ying

    1990-10-01

    The distribution of Nb or Ta between iron and slag in blast furnace smelting is closely related to Si-Nb or Si-Ta equilibrium. Most of the Nb or Ta enters the iron when the equilibrium distribution of Nb or Ta is reached. The equilibrium distribution ratios of Nb and Ta are substantially independent of both the basicity and the CaF2 content of the slag but are markedly affected by the reaction temperature. The Ta contents in slag and iron were measured by the radioactive isotope182Ta.

  6. Technological possibilities of processing the sublimates of electron-beam remelting of niobium to form ferroniobium

    NASA Astrophysics Data System (ADS)

    Chumarev, V. M.; Leont'ev, L. I.; Potapov, V. I.; Udoeva, L. Yu.; Upolovnikova, A. G.

    2012-01-01

    The possibility of melting of ferroniobium from the sublimates of electron-beam remelting of niobium ingots is studied using thermodynamic analysis and a "hot" simulation. The basic requirements for the conditions of processing of sublimates with various (Nb/Al)met ratios are evaluated and determined. A ferroalloy the contents of controlled impurities in which correspond to certain ferroniobium grades of Russian and foreign standards is produced by melting of charges containing the sublimates, a deoxidizer (Fe2O3), and a flux (CaO, CaF2) in an electroslag furnace.

  7. 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.

  8. 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.

  9. Growth of congruently melting Ca0.59Sr0.41F2 crystals and study of their properties

    NASA Astrophysics Data System (ADS)

    Karimov, D. N.; Komar'kova, O. N.; Sorokin, N. I.; Bezhanov, V. A.; Chernov, S. P.; Popov, P. A.; Sobolev, B. P.

    2010-05-01

    Homogeneous crystals of Ca0.59Sr0.41F2 alloy (sp. gr., Fm bar 3 m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF2-SrF2 phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties of Ca0.59Sr0.41F2 and MF2 crystals ( M = Ca, Sr) have been studied and comparatively analyzed. Ca0.59Sr0.41F2 crystals are transparent in the range of 0.133-11.5 ?m, have refractive index n D = 1.436, microhardness H ? = 2.63 ± 0.10 GPa, ion conductivity ? = 5 × 10-5 S/cm at 825 K, and thermal conductivity k = 4.0 W m-1 K-1 at 300 K. It is shown that the optical properties of Ca0.59Sr0.41F2 crystals are intermediate between those of CaF2 and SrF2, whereas their mechanical and electrical characteristics are better than the latter compounds.

  10. On-Chip Electrolytic Chemistry for the Tuning of Graphene Devices

    NASA Astrophysics Data System (ADS)

    Schmucker, Scott; Ruppalt, Laura; Culbertson, James; Do, Jae Won; Lyding, Joseph; Robinson, Jeremy; Cress, Cory

    2015-03-01

    The inherent interfacial nature of two-dimensional materials has motivated the tuning of these films by choice of substrate or chemical functionalization. Such parameters are generally selected during fabrication, and therefore remain static during device operation. However, the possibility of dynamic chemistry in a tunable solid-state system will enable the development of new devices which fully leverage the rich chemistry of graphenic materials. Here, we fabricate a novel device for localized, dynamic doping and functionalization of graphene that is compatible with CMOS processing. The device is enabled by a top-gated, solid electrochemical cell designed with calcium fluoride (CaF2) substituting the oxide of a traditional MOSFET. When the CaF2 is gated, F flows from cathode to anode, segregating Ca and F. In this work, one electrode is graphene. When saturated with fluorine, graphene undergoes covalent modification, becoming a wide-bandgap semiconductor. In contrast, when functionalized with calcium or dilute fluorine, graphene is electron or hole doped, respectively. With transport, Raman, and XPS, we demonstrate this lithographically localized and reversible modulation of graphene's electronic and chemical character.

  11. 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.

  12. Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 to 1400 K

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.; Whittenberger, J. Daniel

    1987-01-01

    Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.

  13. 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.

  14. Quantum mechanical cluster calculations of critical scintillationprocesses

    SciTech Connect

    Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.

    2000-02-22

    This paper describes the use of commercial quantum chemistrycodes to simu-late several critical scintillation processes. The crystalis modeled as a cluster of typically 50 atoms embedded in an array oftypically 5,000 point charges designed to reproduce the electrostaticfield of the infinite crystal. The Schrodinger equation is solved for theground, ionized, and excited states of the system to determine the energyand electron wavefunction. Computational methods for the followingcritical processes are described: (1) the formation and diffusion ofrelaxed holes, (2) the formation of excitons, (3) the trapping ofelectrons and holes by activator atoms, (4) the excitation of activatoratoms, and (5) thermal quenching. Examples include hole diffusion in CsI,the exciton in CsI, the excited state of CsI:Tl, the energy barrier forthe diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trappingby activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation risetime.

  15. Adding diffuse reflectance infrared Fourier transform spectroscopy capability to extended x-ray-absorption fine structure in a new cell to study solid catalysts in combination with a modulation approach

    NASA Astrophysics Data System (ADS)

    Chiarello, Gian Luca; Nachtegaal, Maarten; Marchionni, Valentina; Quaroni, Luca; Ferri, Davide

    2014-07-01

    We describe a novel cell used to combine in situ transmission X-ray absorption spectroscopy (XAS) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in a single experiment. The novelty of the cell design compared to current examples is that both radiations are passed through an X-ray and IR transparent window in direct contact with the sample. This innovative geometry also offers a wide surface for IR collection. In order to avoid interference from the crystalline IR transparent materials (e.g., CaF2, MgF2, diamond) a 500 ?m carbon filled hole is laser drilled in the center of a CaF2 window. The cell is designed to represent a plug flow reactor, has reduced dead volume in order to allow for fast exchange of gases and is therefore suitable for experiments under fast transients, e.g., according to the concentration modulation approach. High quality time-resolved XAS and DRIFTS data of a 2 wt.% Pt/Al2O3 catalyst are obtained in concentration modulation experiments where CO (or H2) pulses are alternated to O2 pulses at 150 °C. We show that additional information can be obtained on the Pt redox dynamic under working conditions thanks to the improved sensitivity given by the modulation approach followed by Phase Sensitive Detection (PSD) analysis. It is anticipated that the design of the novel cell is likely suitable for a number of other in situ spectroscopic and diffraction methods.

  16. Synthesis of High-Temperature Self-lubricating Wear Resistant Composite Coating on Ti6Al4V Alloy by Laser Deposition

    NASA Astrophysics Data System (ADS)

    Luo, Jian; Liu, Xiu-Bo; Xiang, Zhan-Feng; Shi, Shi-Hong; Chen, Yao; Shi, Gao-Lian; Wu, Shao-Hua; Wu, Yu-Nan

    2015-05-01

    Laser deposition was adopted to prepare novel Ni-based solid solution (?-NiCrAlTi)/ TiC/?-Ti/CaF2 high-temperature self-lubricating wear resistant composite coating on Ti6Al4V alloy. Microstructure, micro-hardness, wear behavior, and counter-body effect of the coating were investigated systematically. It can be seen that the coating mainly consists of ?-NiCrAlTi, TiC, ?-Ti, and small fine CaF2 particles. Average micro-hardness of the coating is 1023 HV0.3, which is about three-factor higher than that of Ti6Al4V substrate (380 HV0.3). The friction coefficient and wear rate of the coating decrease at all test temperatures to different extents with respect to the substrate. The improvement in wear resistance is believed to be the combined effects of the ?-NiCrAlTi solid solution, the dominating anti-wear capabilities of the reinforced TiC carbides, and the self-lubricating property of CaF2.

  17. Influence of substrate type on transport properties of superconducting FeSe0.5Te0.5 thin films

    NASA Astrophysics Data System (ADS)

    Yuan, Feifei; Iida, Kazumasa; Langer, Marco; Hänisch, Jens; Ichinose, Ataru; Tsukada, Ichiro; Sala, Alberto; Putti, Marina; Hühne, Ruben; Schultz, Ludwig; Shi, Zhixiang

    2015-06-01

    FeSe0.5Te0.5 thin films were grown by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrate shows no influence on the lattice parameters of the films, whereas the type of substrate affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density Jc(?) at ? = 180° (H||c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no Jc(?) peaks for H||c were observed in films on CaF2 and LaAlO3. Jc(?) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg–Landau approach with appropriate anisotropy ratio ?J. The scaling parameter ?J is decreasing with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 films on Fe-buffered MgO substrates.

  18. Response of thermoluminescent dosimeters to photons simulated with the Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Moralles, M.; Guimarães, C. C.; Okuno, E.

    2005-06-01

    Personal monitors composed of thermoluminescent dosimeters (TLDs) made of natural fluorite (CaF 2:NaCl) and lithium fluoride (Harshaw TLD-100) were exposed to gamma and X rays of different qualities. The GEANT4 radiation transport Monte Carlo toolkit was employed to calculate the energy depth deposition profile in the TLDs. X-ray spectra of the ISO/4037-1 narrow-spectrum series, with peak voltage (kVp) values in the range 20-300 kV, were obtained by simulating a X-ray Philips MG-450 tube associated with the recommended filters. A realistic photon distribution of a 60Co radiotherapy source was taken from results of Monte Carlo simulations found in the literature. Comparison between simulated and experimental results revealed that the attenuation of emitted light in the readout process of the fluorite dosimeter must be taken into account, while this effect is negligible for lithium fluoride. Differences between results obtained by heating the dosimeter from the irradiated side and from the opposite side allowed the determination of the light attenuation coefficient for CaF 2:NaCl (mass proportion 60:40) as 2.2 mm -1.

  19. Carbon Solubility in the CaO-SiO2-3MgO-CaF2 Slag System

    NASA Astrophysics Data System (ADS)

    Park, Jun-Yong; Jung, Sung-Mo; Sohn, Il

    2014-04-01

    The carbon solubility in the CaO-SiO2-3MgO-CaF2 slag system at 1773 K (1500 °C) was investigated under CO/Ar and CO/N2 gases. Higher extended basicity [(CaO + MgO)/SiO2) increased the carbon solubility in the slag as the activity of free oxygen ions (] promoted the reaction of the free carbide mechanism. Higher CaF2 also resulted in higher carbon dissolution into the slag as fluorine ions interact with the bridged oxygen (O0) in the melt structure to increase the activity of the free oxygen ions in the melt. Structural information obtained from the Fourier transformed infra-red (FT-IR) and Raman revealed a depolymerization of the network structure as the simpler structural units of NBO/Si = 4 increased and the Si-O-Si bending vibrations decreased with higher basicity and CaF2 content. This correlated well with higher free oxygen ions (O2-) in the slag system and subsequently higher carbon dissolution. A correlation of the theoretical optical basicity (?th) with the logarithm of the carbon content in slag showed a relatively similar trend and an increase of carbon was observed with higher optical basicity.

  20. Resistance Switching Memory Characteristics of Si/CaF2/CdF2 Quantum-Well Structures Grown on Metal (CoSi2) Layer

    NASA Astrophysics Data System (ADS)

    Denda, Junya; Uryu, Kazuya; Watanabe, Masahiro

    2013-04-01

    A novel scheme of resistance switching random access memory (ReRAM) devices fabricated using Si/CaF2/CdF2/CaF2/Si quantum-well structures grown on metal CoSi2 layer formed on a Si substrate has been proposed, and embryonic write/erase memory operation has been demonstrated at room temperature. It has been found that the oxide-mediated epitaxy (OME) technique for forming the CoSi2 layer on Si dramatically improves the stability and reproducibility of the current-voltage (I-V) curve. This technology involves 10-nm-thick Co layer deposition on a protective oxide prepared by boiling in a peroxide-based solution followed by annealing at 550 °C for 30 min for silicidation in ultrahigh vacuum. A switching voltage of lower than 1 V, a peak current density of 32 kA/cm2, and an ON/OFF ratio of 10 have been observed for the sample with the thickness sequence of 0.9/0.9/2.5/0.9/5.0 nm for the respective layers in the Si/CaF2/CdF2/CaF2/Si structure. Results of surface morphology analysis suggest that the grain size of crystal islands with flat surfaces strongly affects the quality of device characteristics.

  1. 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.

  2. Syntheses, structural characterization, and DPPH radical scavenging activity of cocrystals of caffeine with 1- and 2-naphthoxyacetic acids

    NASA Astrophysics Data System (ADS)

    Suresh Kumar, G. S.; Seethalakshmi, P. G.; Sumathi, D.; Bhuvanesh, N.; Kumaresan, S.

    2013-03-01

    Caffeine:1-naphthoxyacetic acid [(caf)(1-naa)] and caffeine:2-naphthoxyacetic acid [(caf)(2-naa)] cocrystals have been synthesized and single crystals were grown by slow evaporation technique. The structures of the grown crystals were elucidated using single crystal X-ray diffraction analysis. Both the cocrystals belong to the monoclinic crystallographic system with space group P21/c, Z = 4, and ? = ? = 90°, whereas ? = 111.4244(18)° for [(caf)(1-naa)] and ? = 109.281(6)° for [(caf)(2-naa)]. The crystal packing is predominantly stabilized by hydrogen bonding and ?-? stacking interactions. The presence of unionized -COOH functional group in both the cocrystals was identified by FTIR spectral analysis. Thermal behavior and stability of both the cocrystals were studied by TGA/DTA analyses. Solvent-free formation of these cocrystals was confirmed by powder X-ray diffraction analyses. The theoretical energy of cocrystals showed that the formers have higher energy than cocrystals 1 and 2. DPPH radical scavenging activity of cocrystals 1 and 2 is slightly greater than the formers.

  3. Fluorine substitution in YBa 2Cu 3O 7-x

    NASA Astrophysics Data System (ADS)

    Kim, J. S.; Swinnea, J. S.; Manthiram, A.; Steinfink, H.

    1988-04-01

    Superconducting YBa 2Cu 3O 6.94 is sealed with ZnF 2 in 2:1 and 1:1 mole ratios in evacuated Vycor tubes, care being taken to keep the powdered materials physically separate. The ampules are heated at 280-290°C for several days. The ZnF 2 is converted to ZnO and F - is introduced to produce YBa 2Cu 3O xF y. The composition of one preparation appears to be YBa 2Cu 3O 6.6F 0.4. The fluorinated phases are semiconductors. When they are heated to 600 °C BaF 2 and CuO is produced as the lattice F - reacts. At 900 °C Y 2BaCuO 5 is also observed in an x-ray diffraction diagram in addition to a remaining superconducting oxide component that had T c ? 85K.

  4. Photoemission study of amorphous and crystalline GeTe and (Ge,Mn)Te semiconductors

    NASA Astrophysics Data System (ADS)

    Knoff, W.; Pietrzyk, M. A.; Reszka, A.; Kowalski, B. J.; Taliashvili, B.; Story, T.; Johnson, R. L.; Or?owski, B. A.

    2013-12-01

    Resonant photoemission spectroscopy was applied to compare the valence band structure of Ge0.9Mn0.1Te and GeTe semiconductor layers deposited on BaF2 substrate in monocrystalline and amorphous forms. In (Ge,Mn)Te the contribution of Mn 3d5 electronic orbitals to density of states was found in three binding energy regions: below the top of the valence band (Eb<4.2 eV), at the binding energy range 4.2-4.4 eV, and in many-body satellite at 9-13 eV. The comparative analysis of the photoemission spectra based on configuration interaction model showed that p-d hybridization effects, important for magnetic and optical properties of (Ge,Mn)Te, are stronger in monocrystalline than in amorphous (Ge,Mn)Te layers.

  5. Gigahertz (GHz) hard x-ray imaging using fast scintillators

    NASA Astrophysics Data System (ADS)

    Wang, Zhehui; Guardincerri, Elena; Rathman, D. D.; Azzouz, M. E.; Barnes, Cris W.; Berger, R.; Bond, E. M.; Craig, D. M.; Holtkamp, David; Kapustinsky, J. S.; Klimenko, Alexei V.; Kwiatkowski, K.; Merl, R. B.; Morris, C. L.; Perry, J. O.; Ramberg, E.; Reich, R. K.; Ronzhin, A.; Warner, K.; Williams, R. T.; Zhu, Ren-Yuan

    2013-09-01

    Gigahertz (GHz) imaging technology will be needed at high-luminosity X-ray and charged particle sources. It is plausible to combine fast scintillators with the latest picosecond detectors and GHz electronics for multi-frame hard Xray imaging and achieve an inter-frame time of less than 10 ns. The time responses and light yield of LYSO, LaBr3, BaF2 and ZnO are measured using an MCP-PMT detector. Zinc Oxide (ZnO) is an attractive material for fast hard X-ray imaging based on GEANT4 simulations and previous studies, but the measured light yield from the samples is much lower than expected.

  6. Magnetotransport properties of flux melt grown single crystals of Co-substituted manganites with perovskite structure

    NASA Astrophysics Data System (ADS)

    Khalyavin, D. D.; Pekala, M.; Bychkov, G. L.; Shiryaev, S. V.; Barilo, S. N.; Troyanchuk, I. O.; Mucha, J.; Misiorek, H.; Szymczak, R.; Baran, M.; Szymczak, H.

    2003-02-01

    Single crystals of La1-xBaxMn1-yCoyO3 (0.26 leq x leq 0.37; 0 leq y leq 0.31) perovskites were grown by the flux melt technique using the BaO-B2O3-BaF2 ternary system as a solvent. It was found that the cobalt content in the crystals is determined by the average oxidized state of the manganese ions and depends nonlinearly on the molar ratio of Co/Mn in the initial mixture. All the crystals exhibit ferromagnetic behaviour at low temperatures as well as a jump of resistivity and a magnetoresistance peak around the Curie temperature, gradually decreasing as the cobalt content increases. The low-temperature ferromagnetic phase transforms from the metallic to the semiconducting state with increase in cobalt content.

  7. YBa2Cu3O7-? superconducting films prepared by low pressure post-annealing

    NASA Astrophysics Data System (ADS)

    Wang, Lianhong; Liu, Chong; Fan, Jing

    2014-12-01

    YBa2Cu3O7-? precursor films are deposited on 2? LaAlO3 wafer by the co-evaporation technique using Y, BaF2 and Cu as evaporation sources. After deposition, the films are annealed at low-pressure atmosphere with the composition of oxygen and water vapour. Compared with the normal pressure annealing, it is shown that low pressure can greatly improve the superconducting properties of 2? YBCO films with thickness larger than 500 nm, as the microcrack on films surface becomes unobservable the microwave surface resistance is greatly reduced. Furthermore, it is also revealed that the optimal processing window for making high quality superconducting YBCO films through ex-situ process is relatively small, therefore the ambient in annealing furnace is crucial important and should be precisely controlled.

  8. Crystal Identification In Modular Array Detectors For High Spatial Resolution PET

    NASA Astrophysics Data System (ADS)

    Weinberg, Irving N.; Dahlbom, Magnus; Ricci, Anthony; Hoffman, Edward J.

    1986-01-01

    The use of detector arrays in PET has been proposed and studied as a economical means of obtaining very high resolution images. The properties of detector arrays for use in high resolution PET scanners were investigated. Analytical approximations and Monte Carlo simulations were used to design detector arrays consisting of six to eight crystals coupled to two photomultipliers to allow identification of the individual crystals. Arrays of 2.85 mm thick crystals of Bismuth Germanate (BGO), Gadolinium Orthosilicate (GSO), and Barium Fluoride (BaF2) were examined. The effect of interdetector materials such as lead, and plastic on positioning accuracy was tested. Assembled arrays of six 2.85 mm thick BG0 crystals yielded line spread function FWHMs of 2.4 to 3.2 millimeters. The limiting resolution of detector arrays was found to be defined by the scintillation light yield of the crystals, the light gathering efficiency of the detector arrays, and the fraction of interdetector scatter.

  9. Color centers in LiCaAlF6 single crystals and their suppression by doping

    NASA Astrophysics Data System (ADS)

    Sato, Hiroki; Machida, Hiroshi; Shimamura, Kiyoshi; Bensalah, Amina; Satonaga, Tomohiko; Fukuda, Tsuguo; Mihokova, Eva; Dusek, Michal; Nikl, Martin; Vedda, Anna

    2002-05-01

    LiCaAlF6 (LiCAF) single crystals pure and doped with MgF2 and BaF2 were successfully grown by the Czochralski technique. Optical absorption measurements in the UV/Visible spectral regions following x-ray irradiation (radiation induced absorption) were performed in order to investigate the radiation damage of the crystals. The F-center absorption band at 262 nm is the dominating induced absorption feature. The amplitude of the F-absorption band is suppressed by more than a factor of 3 in Mg-doped LiCAF compared to undoped, while for Ba-doped LiCAF, almost no variation is obtained. In Mg-doped crystals the optimum doping concentration is of about 0.2 mol % of MgF2 in the melt.

  10. Development of thermal sensor based on PbTe thin films in MEMS design

    NASA Astrophysics Data System (ADS)

    Dashevsky, Zinovi; Rabih, Eli; Dariel, Moshe

    2005-08-01

    The work of a MEMS-technology compatible thin-film thermoelectric IR radiation sensor with multiple PbTe thermocouples is simulated. The sensitivity up to 350 V/W is predicted. PbTe thin films are grown on the BaF2(111) buffered Si(111) substrates, using the hot-wall-beam epitaxy technique. Indium and zinc ion implantation is applied to transform the as-grown p-PbTe films into the n-type thermocouple counterpart films. With a dose of 10l6 cm-2 and exposition time of 3-4 h, a 4-pm-thick film is homogeneously reversed, retaining the high epitaxial quality.

  11. Thermal-wave-modulated superconducting quantum interference device susceptometry for thin magnetic layers

    NASA Astrophysics Data System (ADS)

    Enichlmair, H.; Krenn, H.

    1994-04-01

    Thermal waves are excited by a chopped nonresonant light wave in a 3.2 ?m EuTe layer on a crystalline BaF2 substrate. The glass fiber optic sample holder is at rest within the pickup coil of a superconducting quantum interference device susceptometer. The thermal wave amplitude (simulated by a two-dimensional heat conduction model) is a function of temperature and chop rate of illumination and modulates only the magnetic properties of the epitaxial layer. Therefore, the novel method has an enhanced dynamic range and sensitivity (resolution of magnetic moment ?2×10-9 emu) and resolves the antiferromagnetic phase transition of the EuTe layers at TN=9.8 K even for small magnetic fields of 10 G.

  12. [A study on the concentration quenching of Tm3+ upconversion luminescence].

    PubMed

    Chen, B; Wang, H; Huang, S

    2001-06-01

    In this work, we have a designation and preparation of MFT glasses for upconversion, the glasses consisted of TeO2 and fluoride: PbF2, AlF3, BaF2, NaF and the impurity Tm2O3. In this glass system the oxide improve forming ability, the fluorides improve the microscopic environment around RE ions in glasses. In this glass host the content of Tm2O3 achieves to 4% mol and crystallization no occurred. A detail study on the concentration quenching of upconversion luminescence for 1G4-->3H6 and 1D2-->3H4 transitions was completed. The experimental results directed that the quenching concentration was 0.6 mol.% and higher 3 times than in other glasses materials. The cross relaxation and mechanism of concentration quenching were discussed. PMID:12947647

  13. Investigation of the properties of a 1?×1? LaBr 3:Ce scintillator

    NASA Astrophysics Data System (ADS)

    Nicolini, R.; Camera, F.; Blasi, N.; Brambilla, S.; Bassini, R.; Boiano, C.; Bracco, A.; Crespi, F. C. L.; Wieland, O.; Benzoni, G.; Leoni, S.; Million, B.; Montanari, D.; Zalite, A.

    2007-11-01

    The properties of a cylindrical 1?×1? LaBr 3:Ce scintillator (Brillance 380) were investigated. The energy resolution at ?-ray energy of 662 keV was measured to be smaller than 3% and the intrinsic time resolution was found to be ?230 ps. Two different aspects were investigated. The first is the detailed study of the crystal self-activity, emitting ? and ? particles and ?-rays, by measuring coincidences with ?-rays in HPGe, BGO and BaF 2 detectors. In particular, the coincidence with an HPGe detector allowed to isolate clearly the different contributions from 227Ac (chemical homologue of lanthanum) and its daughter nuclei down to the stable 207Pb. The second aspect is the determination of the efficiency for ?-ray detection, measured at 1 MeV and simulated using GEANT4 up to 15 MeV as a function of the detector size.

  14. Surface hardening of optic materials by deposition of diamond like carbon coatings from separated plasma of arc discharge

    NASA Astrophysics Data System (ADS)

    Osipkov, A. S.; Bashkov, V. M.; Belyaeva, A. O.; Stepanov, R.; Mironov, Y. M.; Galinovsky, A. L.

    2015-02-01

    This article considers the issue of strengthening of optic materials used in the IR spectrum by deposition of diamond like carbon coatings from separated plasma arc discharge. The report shows results of tests of bare and strengthened optical materials such as BaF2, MgF2, Si, Ge, including the testing of their strength and spectral characteristics. Results for the determination of optical constants for the DLC coatings deposited on substrates of Ge and Si, by using separated plasma, are also presented. Investigations showed that surface hardening of optical materials operable in the IR range, by the deposition of diamond like carbon coating onto their surface, according to this technology, considerably improves operational properties and preserves or improves their optic properties.

  15. High critical currents and flux creep effects in e-gun deposited epitaxially 00L oriented superconducting YBa2Cu3O7-? films

    NASA Astrophysics Data System (ADS)

    Dam, B.; Stollman, G. M.; Berghuis, P.; Guo, S. Q.; Flipse, C. F. J.; Lensink, J. G.; Griessen, R. P.

    1989-02-01

    Thin films of YBa2Cu3O7-? have been made by codeposition of Cu, Y and BaF2 in a UHV system. Annealing in humid oxygen at 835 °C produces high quality single phase preferentially c oriented films. In 1000 Å thin films the transport current density is larger than 106 A/cm2 at 86 K. Even 500 Å films prove to be superconducting above 77 K. Extrapolation to zero field of the magnetization data obtained from torque experiments are consistent with the current transport data. This indicates that the sample is homogeneous and the critical state model can be applied. Both magnetic relaxation measurements and flux creep resistivity in a magnetic field indicate the importance of thermally activated processes.

  16. Gamma-Ray Spectroscopy at TRIUMF-ISAC

    SciTech Connect

    Garrett, P. E.; Svensson, C. E.; Andreoiu, C.; Bandyopadhyay, D.; Finlay, P.; Grinyer, G. F.; Hyland, B.; Illes, E.; Phillips, A. A.; Schumaker, M. A.; Valiente-Dobon, J. J.; Wong, J. [Department of Physics, University of Guelph, Guelph, Ontario, N1G2W1 (Canada); Ball, G. C.; Hackman, G.; Andreyev, A.; Chan, S.; Coombes, H.; Churchman, R.; Morton, A. C.; Pearson, C. J. [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T 2A3 (Canada)] (and others)

    2006-03-13

    The 8{pi} spectrometer at TRIUMF-ISAC consists of 20 Compton-suppressed germanium detectors and various auxiliary devices. The Ge array, once used for studies of nuclei at high angular momentum, has been transformed into the world's most powerful device dedicated to radioactive-decay studies. Many improvements in the spectrometer have been made, including a high-throughput data acquisition system, installation of a moving tape collector, incorporation of an array of 20 plastic scintillators for {beta}-particle tagging, 5 Si(Li) detectors for conversion electrons, and 10 BaF2 detectors for fast-lifetime measurements. Experiments can be performed where data from all detectors are collected simultaneously, resulting in a very detailed view of the nucleus through radioactive decay. A number of experimental programmes have been launched that take advantage of the versatility of the spectrometer, and the intense beams available at TRIUMF-ISAC.

  17. Photon intensity interferometry with multidetectors

    NASA Astrophysics Data System (ADS)

    Badalà, A.; Barbera, R.; Palmeri, A.; Pappalardo, G. S.; Riggi, F.; Russo, A. C.; Russo, G.; Turrisi, R.

    1994-12-01

    The technique of two-photon interferometry in heavy ion collisions at the intermediate energies is discussed and the importance of a new methodology, used in the treatment of the experimental data, is evidenced. For the first time, both the relative momentum, qrel, and the relative energy, q0, of the two correlated photons have been simultaneously used to extract the source size and lifetime of the emitting source. As an application, the performances of the BaF 2 ball of the MEDEA multidetector as a photon intensity interferometer have been evaluated. The response of such a detector to correlated pairs of photons has been studied through full GEANT3 simulations. The effects of the experimental filter on the photon correlation function have been investigated, and the noise, induced in the correlation signal by cosmic radiation, neutral pion decay, and ?-conversion, has also been estimated.

  18. The effect of Er 3+ and Sm 3+ on phase separation and crystallization in Na 2O/K 2O/BaF 2/BaO/Al 2O 3/SiO 2 glasses

    NASA Astrophysics Data System (ADS)

    Barros, Jordana Rocha; Bocker, Christian; Rüssel, Christian

    2010-12-01

    Thermal annealing of Sm +3 or Er +3 doped Na 2O/K 2O/BaF 2/BaO/Al 2O 3/SiO 2 glasses led to the precipitation of nanocrystalline BaF 2. The mean crystallite sizes were in the range from 9 to 15 nm as shown by XRD line broadening. Whereas glasses without rare earth oxides showed crystallites homogenously dispersed in the amorphous matrix, those doped with 0.05 mol% ErF 3 or SmF 3 showed highly agglomerated crystals. The latter was due to droplet phase separation in the rare earth doped glasses as proved by transmission electron microscopy while in the undoped glasses phase separation did not occur. Furthermore, the size of the droplets depended on the BaO-concentration. Fluorescence emission spectra of a samarium doped sample showed higher intensities than in the glasses they were prepared from.

  19. Multiphase monitoring by annihilation radiation coincidence mode

    NASA Astrophysics Data System (ADS)

    Vidal, A.; Viesti, G.; Osorio, C.; Pino, F.; Horvath, A.; Barros, H.; Caldogno, M.; Greaves, E. D.; Sajo-Bohus, L.

    2012-02-01

    A multiphase monitoring system employing nuclear techniques is reported, which is aimed to provide a rapid - decision tool in oilfield applications. Liquid phase time variation is monitored employing two large volume BaF2 detectors. The radioisotope source of 22Na is a positron emitter, therefore two antiparallel gammas are produced per decay, and phase flow in pipes is related to the count rate of gamma pulses in coincidence providing information on transient liquid phase during transport. Oil, gas, water fraction measurements were performed at a specialized test station assembled in our laboratory to model a wide range of field operating conditions. The time dependence of the mixed substances is monitored with the two most relevant hydrodynamic parameters, the density (type of the fluid) and the flow rate, in a LabView® environment. Performance of the monitoring system; its limitations and the possibility for further improvements are also provided.

  20. 80mBr/80Br A New Electron-Gamma PAC Probe

    NASA Astrophysics Data System (ADS)

    Correia, J. G.; Haas, H.; Araujo, J. P.; Marques, J. G.; Soares, J. C.; Melo, A. A.; ISOLDE Collaboration

    2001-11-01

    Conversion electron-gamma PAC measurements of the 49 37 keV cascade in 80Br through the intermediate 2- state with T 1/2=7.4 ns were performed with a system of two magnetic lens spectrometers and two BaF2 scintillation detectors. The parent 80mBr activity with a halflife of 4.4 hrs was implanted into Ni, Zn and graphite at the ISOLDE separator at CERN. The observed interaction frequency in the nickel matrix is in good agreement with the known value of the hyperfine field for Br in Ni and the magnetic moment of the 2- state. From the measured quadrupole interaction in Zn and graphite the electric field gradients at Br were obtained.

  1. Investigation of the Time Performance of a LYSO Array for TOF-PET

    E-print Network

    Jun-Hui, Liu; Feng-Feng, Cheng; Dao-Wu, Li; Zhi-Ming, Zhang; Bao-Yi, Wang; Long, Wei

    2015-01-01

    Positron Emission Tomography (PET) using time-of-flight information, which can greatly improve the quality of the reconstructed image, has recently become an exciting topic. In this work, 3.2mm*3.2mm*25mm finger-like LYSO crystals were used to make a 5*5 array, coupled to the Hamamatsu H8500 photomultiplier tube (PMT) as a detector. A fast leading-edge discriminator was designed for the LYSO-H8500 detector. Average coincidence time resolution FWHM of 330 ps was obtained for the LYSO detector with a reference BaF2 detector, whose time resolution for 511 keV {\\gamma}-rays was FWHM 150 ps. Time resolution FWHM of 294 ps was calculated for the LYSO detector, and coincidence time resolution of FHWM 415 ps can be expected for two identical LYSO detectors.

  2. Crystallization and spectroscopic properties in Er3+ doped oxyfluorogermanate glass ceramics containing Na

    NASA Astrophysics Data System (ADS)

    Hu, Yuebo; Qiu, Sawei; Gao, Yuan; Qiu, Jianbei

    2015-07-01

    The Er3+ doped oxyfluorogermanate glasses, with a composition containing Na element, were synthesized by the conventional melting-quenching technique. When Na element was introduced into the composition of oxyfluorogermanate glass, the crystals behavior was investigated in details. Depending on the annealing procedure supplied, thermal annealing of precursor glasses in the system GeO2/BaF2/AlF3/Na2O/NaF/ZnO/GdF3/ErF3 led to the precipitation of different crystal phase nanocrystals. It was confirmed the nanocrystals in GC600 is orthorhombic NaBaAlF6 which led to enhance obviously in the UC luminescence of Er3+. However, the nanocrystals in G585 led to decrease in the UC luminescence, which indicated few Er ions enter into the lattice of this nanocrystal phase. The reason of the decrease in UC emission intensity of GC585 was analyzed.

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

    NASA Astrophysics Data System (ADS)

    Marczewska, Agnieszka; ?roda, Marcin; Nocu?, Marek; Sulikowski, Bogdan

    2015-07-01

    Lead-gallium glasses, due to the absence of typical glass-forming components, are characterized by an increased tendency to crystallization. Despite this, they are interesting materials due to a shift of IR absorption edge up to 6-7 ?m. The paper considers how the SiO2 dopant affects thermal stability and the UV-VIS and IR transmittance of lead-gallium glasses. The base lead-gallium glass (0.75PbO·0.25Ga2O3) was modified by the addition of 5, 10 and 15 mol% SiO2, respectively. DTA/DSC data showed that the glasses are characterized by the multi-stage crystallization, which is changed with the amount of silica doped. The XRD analysis confirmed that: (i) different forms of lead oxide crystallize after heat treatment of the glass, and (ii) the Ga2PbO4 phase is formed at higher temperatures. The silica admixture allowed inserting a few percent of BaF2 into the lead-gallium glass structure. It was found that a transparent glass-ceramic based on the lead-gallium glass with a low phonon barium fluoride phase can be obtained during the thermal treatment. The study of UV-VIS-IR transmittance shows that 10-15 mol% SiO2 in the lead-gallium glasses diminishes the absorption band in the range of 2.6-4 ?m due to the presence of hydroxyl groups and simultaneously reduces transmittance in the range of 5-6.5 ?m from 10 to 20%. Introduction of SiO2 to the glass results in the increase of transmittance in the shorter wavelength region and the UV-edge shift is observed. It was also confirmed that the BaF2 nanocrystallites exert no effect on the transmittance of the spectrum analyzed.

  4. 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.

  5. Identification and rejection of scattered neutrons in AGATA

    E-print Network

    M. ?enyi?it; A. Ataç; S. Akkoyun; A. Ka?ka?; D. Bazzacco; J. Nyberg; F. Recchia; S. Brambilla; F. Camera; F. C. L. Crespi; E. Farnea; A. Giaz; A. Gottardo; R. Kempley; J. Ljungvall; D. Mengoni; C. Michelagnoli; B. Million; M. Palacz; L. Pellegri; S. Riboldi; E. ?ahin; P. A. Söderström; J. J. Valiente Dobon; the AGATA collaboration

    2013-06-12

    Gamma rays and neutrons, emitted following spontaneous fission of 252Cf, were measured in an AGATA experiment performed at INFN Laboratori Nazionali di Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors (12 36-fold segmented high-purity germanium crystals), placed at a distance of 50 cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment was to study the interaction of neutrons in the segmented high-purity germanium detectors of AGATA and to investigate the possibility to discriminate neutrons and gamma rays with the gamma-ray tracking technique. The BaF2 detectors were used for a time-of-flight measurement, which gave an independent discrimination of neutrons and gamma rays and which was used to optimise the gamma-ray tracking-based neutron rejection methods. It was found that standard gamma-ray tracking, without any additional neutron rejection features, eliminates effectively most of the interaction points due to recoiling Ge nuclei after elastic scattering of neutrons. Standard tracking rejects also a significant amount of the events due to inelastic scattering of neutrons in the germanium crystals. Further enhancements of the neutron rejection was obtained by setting conditions on the following quantities, which were evaluated for each event by the tracking algorithm: energy of the first and second interaction point, difference in the calculated incoming direction of the gamma ray, figure-of-merit value. The experimental results of tracking with neutron rejection agree rather well with Geant4 simulations.

  6. Excimer mirror thin film laser damage competition

    NASA Astrophysics Data System (ADS)

    Stolz, Christopher J.; Blaschke, Holger; Jensen, Lars; Mädebach, Heinrich; Ristau, Detlev

    2011-12-01

    Excimer lasers are a critical technology for the $400 billion annual market of manufactured integrated circuits. Other uses of excimer lasers include medical applications such as laser eye surgery and micro-machining industrial applications. Ultraviolet laser mirrors are used for beam steering, therefore high reliability is desired for such commercial industrial applications. A laser damage competition of excimer mirror coatings creates the opportunity to survey private industry, governmental institutions, and university labs allowing a direct laser resistance comparison of samples tested under identical conditions. The major requirement of the submitted coatings was a minimum reflectance of 97% at 193 nm at normal incidence. The choice of coating materials, design, and deposition method were left to the participant. Damage testing was performed with a 193 nm excimer laser at a pulse length of 13 ns. A double blind test assured sample and submitter anonymity so only a summary of the deposition process, coating materials, layer count and spectral results are presented. In summary, a 70× difference was seen in the twelve submitted mirror samples, with the highest laser resistant sample being deposited by resistive heating and composed of three materials (LaF3, AlF3, & MgF2). Laser resistance was strongly affected by substrate cleaning, coating deposition method, and coating material selection whereas layer count had a minimal impact.

  7. Near-infrared emission and energy transfer in tellurite glasses co-doped with erbium and thulium ions

    NASA Astrophysics Data System (ADS)

    Zmojda, Jacek; Kochanowicz, Marcin; Ragin, Tomasz; Dorosz, Dominik; Sitarz, Maciej

    2014-05-01

    In the paper optical properties of 40TeO2 - 20GeO2 - 30(PbO - PbF2)- 10(BaO - Nb2O5 - LaF3) glass system co-doped with Er3+/Tm3+ ions were investigated. The maximum of phonon energy at 790cm-1 in fabricated tellurite glass which was determined by FTIR measurements. Optimisation of glass composition led to the emission at 1820 nm which was observed in results of energy transfer (ET) between Er3+and Tm3+ions under the optical exciting at 976 nm. In order to determine the optimal conditions of ET between exited energy levels of co-doped RE ionsthe dependence of the near-infrared emission upon the thulium ions concentration was studied. In result of that broadband emission in the range from1500 to 1900 nm was achieved owing to the superposition of electronic transition in Er3+ (4I13/2 ? 4I15/2) and Tm3+ (3F4 ? 3H6) ions.The highest efficiency of energy transfer was obtained in glass co-doped with 0.2Er2O3/0.3 Tm2O3.

  8. 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.

  9. 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

  10. Effect of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped in transparent glass-ceramics

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The glass and glass-ceramics samples with composition of 50SiO2-10AlF3-(30-x)BaF2-5TiO2-3.95LaF3- xMnCO3-0.05ErF3-1YbF3 (in mol%, x=0, 0.5, 0.8, 1.0, and 1.2) were prepared using the conventional quenching techniques. The effects of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped transparent glass-ceramics under the changing of heat treatment temperatures and concentrations of Mn2+ ions were investigated. The structural investigation carried out by X-ray diffraction (XRD), and transmission electron microscopy evidenced the formation of cubic Ba2LaF7 nanocrystals. The efficiency upconversion emission of Mn2+/Er3+/Yb3+ tri-doped was observed in the glass-ceramics. The upconversion mechanism and energy transfer between Mn2+-Yb3+ dimer and Er3+ ions were investigated.

  11. [Spectroscopic study on the interaction of glass matrixes and nanoparticles in Tm3+ doped oxyfluoride glass ceramics].

    PubMed

    Zhang, Xiang-Yu; Li, Lin; Gao, Dang-Li; Zheng, Hai-Rong

    2009-10-01

    Fluorescence emission spectra from Tm3+ in crystal phase and glass phase were separated under selective excitation of 1D2 level in Tm3+ doped transparent oxyfluoride glass ceramics containing LaF3 nanocrystals. Emissions from the crystal phase and from the glass phase were detected. The influence of the interaction between glass matrix and nanocrystals on the optical characteristics of Tm3+ ions in the two different local environments was investigated. The results indicate that the increase in nanocrystal size results in a decrease in the impact of oxides glass on Tm3+ in the crystal phase, and an enhancement of the impact of nanocrystals on Tm3+ in the glass phase. For smaller nanoparticles, the emission efficiency of Tm3+ ions in the crystal phase was reduced, and the influence of nanocrystals on the ions in the glass phase was reduced too. The larger the nanocrystal size, the weaker the influence of oxide glass on the Tm3+ ions in the crystal phase, and the better performance of fluorescence emission. It was also found that the content of SiO2 in glass matrix could affect the emission efficiency of Tm3+ in both environments. PMID:20038050

  12. Role of Ca2+ in the change in the structure type and the fluoride-ion conductivity in crystals upon transition from ?-ErF3 to Er0.715Ca0.285F2.715

    NASA Astrophysics Data System (ADS)

    Bolotina, N. B.; Chernaya, T. S.; Verin, I. A.; Sorokin, N. I.; Sobolev, B. P.

    2015-01-01

    The symmetry-dependent structural differences and the fluoride-ion conductivity of the ?-ErF3 crystal (the orthorhombic ?-YF3 type) and the phase Er0.715Ca0.285F2.715 (the hexagonal tysonite modification ?-LaF3) are revealed. A change in the ?-YF3 structure type is caused by the partial replacement of Er3+ by Ca2+. It was shown that the contribution of Ca2+ to the conductivity of the phases R 1 - y Ca y F3 - y is not limited to the creation of V {F/+} anion vacancies. The crystals of Er0.715Ca0.285F2.715 characterized by cation-composition heterogeneity have structural features (different from the vacancies in the anionic sublattice), which can exert a positive effect on the mobility of fluoride anions. This factor may play a more important role in ion transport than the concentration of anion vacancies.

  13. Binary and ternary superlattices self-assembled from colloidal nanodisks and nanorods.

    PubMed

    Paik, Taejong; Diroll, Benjamin T; Kagan, Cherie R; Murray, Christopher B

    2015-05-27

    Self-assembly of multicomponent anisotropic nanocrystals with controlled orientation and spatial distribution allows the design of novel metamaterials with unique shape- and orientation-dependent collective properties. Although many phases of binary structures are theoretically proposed, the examples of multicomponent assemblies, which are experimentally realized with colloidal anisotropic nanocrystals, are still limited. In this report, we demonstrate the formation of binary and ternary superlattices from colloidal two-dimensional LaF3 nanodisks and one-dimensional CdSe/CdS nanorods via liquid interfacial assembly. The colloidal nanodisks and nanorods are coassembled into AB-, AB2-, and AB6-type binary arrays determined by their relative size ratio and concentration to maximize their packing density. The position and orientation of anisotropic nanocrystal building blocks are tightly controlled in the self-assembled binary and ternary lattices. The macroscopic orientation of the superlattices is further tuned by changing the liquid subphase used for self-assembly, resulting in the formation of lamellar-type binary liquid crystalline superlattices. In addition, we demonstrate a novel ternary superlattice self-assembled from two different sizes of nanodisks and a nanorod, which offers the unique opportunity to design multifunctional metamaterials. PMID:25927895

  14. Luminescence and scintillation properties of rare-earth-doped LuF3 scintillation crystals

    NASA Astrophysics Data System (ADS)

    Pejchal, Jan; Fukuda, Kentaro; Kurosawa, Shunsuke; Yokota, Yuui; Yoshikawa, Akira

    2015-03-01

    The Nd-doped and Er-doped LuF3 single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd-Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er3+ to Nd3+ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF3:Nd 8% standard. The leading Nd3+ 5d-4f emission was situated at 176 nm, while the Er3+ 5d-4f emission for Er-doped samples was observed at 163 nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1-3 mol%. No Er3+ 5d-4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er3+ to Nd3+ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one.

  15. Investigation into Nanostructured Lanthanum Halides and CeBr3 for Nuclear Radiation Detection

    SciTech Connect

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

    2011-07-06

    Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and cerium bromide (CeBr3) without requiring the growth of large crystals [1]. Nanostructured detectors may allow us to engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have been seen in photoluminescence from silicon nanocrystals in a densely-packed ensemble [2]. We have fabricated nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr3. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.

  16. Energy Transfer in Rare Earth Ion Clusters and Fluorescence from Rare Earth Doped LANTHANUM(1.85)STRONTIUM(0.15)COPPER -OXYGEN(4) Superconductors.

    NASA Astrophysics Data System (ADS)

    Tissue, Brian Max

    1988-12-01

    Laser spectroscopy of rare earth ions in solids was used to study mechanisms of non-resonant energy transfer within rare earth clusters, and to detect insulating, impurity phases in rare earth doped La_{1.85 }Sr_{0.15}CuO _4 superconductors. The mechanisms of phonon-assisted, non-resonant energy transfer were studied in well-defined dimer sites in Er^{3+ }:SrF_2 and Pr ^{3+}:CaF_2. Application of a magnetic field to Er^{3+} :SrF_2 greatly increased the energy transfer rate. The magnetic field dependence in Er^{3+}:SrF _2 indicates that the mechanism of non-resonant energy transfer is a two-phonon, resonant process (Orbach process). Application of a magnetic field to Pr ^{3+}:CaF_2 had no effect on the energy transfer rate because no significant Zeeman splittings occurred. The temperature dependence of the energy transfer rate in Pr^{3+ }:CaF_2 showed the mechanism to be a one-phonon-assisted process at low temperatures and predominantly an Orbach process above 10 K. In the second part of this thesis, laser spectroscopy of a Eu ^{3+} probe ion is developed to detect impurity phases in La_{1.85 }Sr_{0.15}CuO _4 superconductors. Two impurity phases were found in polycrystalline La_ {1.85}Sr_{0.15} CuO_4: unreacted La _2O_3 starting material, and a La-silicate phase, which formed from contamination during sintering. The spectroscopic technique was found to be more than 100 times more sensitive than powder x -ray diffraction to detect minor impurity phases. In preparing the superconductors, several studies were made on the effect of Pr^{3+}, Eu ^{3+}, Bi^{3+ }, and fluorine dopants on the superconducting properties of La_{1.85}Sr _{0.15}CuO_4 and La_2Cuo_4 . Pr^{3+}, Eu ^{3+}, Bi^ {3+}, and F_2 doping all decreased the superconductivity in La_ {1.85}Sr^{0.15} CuO_4. Treating semi-conducting La_2CuO_4 in F_2 gas converted it to a superconductor with an onset T_{rm c} of 30-35 K.

  17. In-situ Crystallization of Highly Volatile Commercial Mold Flux Using an Isolated Observation System in the Confocal Laser Scanning Microscope

    NASA Astrophysics Data System (ADS)

    Park, Jun-Yong; Ryu, Jae Wook; Sohn, Il

    2014-08-01

    The in situ crystallization behavior of highly volatile commercial mold fluxes for medium carbon steels was investigated using the confocal laser scanning microscope (CLSM) equipped with an optimized isolated observation system. The highly volatile compounds of the mold flux were suppressed during heating allowing direct observation in the CLSM. Cooling rates of 25, 50, 100, 400, and 800 K/min were incorporated and continuous cooling transformation (CCT) diagrams of 4 different commercial mold fluxes for medium carbon steels were developed. Identification of the crystalline phase was conducted with XRD and SEM-EDS analysis. A cuspidine crystalline was observed in all samples at various cooling rates. With higher basicity, CaF2, and NaF, the crystallization of the fluxes was enhanced according to the CCT diagram. As the slag structure becomes depolymerized, the diffusion rate of the cathodic ions seems to increase.

  18. Flux entrapment and Titanium Nitride defects during electroslag remelting

    NASA Astrophysics Data System (ADS)

    Busch, Jonathan D.

    Electroslag remelted (ESR) ingots of INCOLOY alloys 800 and 825 are particularly prone to macroscale slag inclusions and microscale cleanliness issues. Formation of these structures near the ingot surface can cause significant production yield losses (˜10%) due to the necessity of extensive surface grinding. Slag inclusions from near the outer radius of the toe end of alloy 800 and 825 ingots were found to be approximately 1 to 3 mm in size and have a multiphase microstructure consisting of CaF2, CaTiO3, MgAl 2O4, MgO and some combination of Ca12Al14 O32F2 and/or Ca12Al14O 33. These inclusions were often surrounded by fields of 1 to 10 ?m cuboidal TiN particles. A large number of TiN cuboids were observed in the ESR electrode with similar size and morphology to those observed surrounding slag inclusions in the ESR ingots, suggesting that the TiN particles are relics from ESR electrode production process. Samples taken sequentially throughout the EAF-AOD processes showed that the TiN cuboidals that are found in ESR ingots form between tapping the AOD vessel into the AOD ladle and the casting of ESR electrodes. Analysis of slag skin at various heights of alloy 825 ingots revealed that the phase fraction of CaF2 decreased, whereas TiCaO 3 and Ca12Al14O32F2 increased, from toe to head. The observed increase in TiO2 content suggests that at most a two-fold increase in viscosity of the slag would be expected. Similar analysis of alloy 800 ingots did not reveal significant trends in slag skin composition, possibly due to differences in ingot geometry or the presence of Al toe additions during the remelting of alloy 800. Directional solidification experiments were conducted to determine the solidification sequences of two common ESR slags: Code 316 (33% CaF2, 33% CaO, and 33% Al2O3) and Code 59 (50% CaF2, 20% CaO, 22% Al2O3, 5% MgO, and 3% TiO2). In both cases the changes in slag phase fraction as a function of solidification time were not as significant as predicted. This suggests substantial solute concentrations within each phase, significant gas phase reactions or insufficient imposed temperature gradient for directional planer solidification. Optical microscopy and SEM analysis revealed a dendritic structure with Ca12 Al14O32F2 as the primary phase and significant interdendritic porosity. EDS analysis showed that Al segregates to the primary phase while F segregates to the interdendritic regions. Parametric studies using a numerical model of ESR suggests that the ESR process is quite sensitive to changes in slag electrical conductivity and not very sensitive to changes in slag viscosity.

  19. Effects of additives on the selectivity of byproducts and dry removal of fluorine for abating tetrafluoromethane in a discharge reactor.

    PubMed

    Tsai, Cheng-Hsien; Kuo, Zhao-Zhi

    2009-01-30

    The removal efficiency of tetrafluoromethane (CF(4)) was significantly enhanced by adding additives (H(2), O(2), H(2)+O(2), H(2)O) in an atmospheric-pressure microwave plasma reactor. However, large amounts of fluorine (F(2)) were produced in this study. Moreover, the selectivity of F(2) was apparently greater than that of HF (in H(2)-based condition) or COF(2) (in O(2)-based abatement). Notably, in an O(2)-rich environment, more F(2) and a larger amount of CO(2) were produced. Subsequently, F(2) can be effectively removed by reacting with CaO to form CaF(2) at 200 degrees C via an in situ dry, chemical absorption process in the low-temperature afterglow discharge zone within the same plasma reactor. PMID:18550278

  20. Evolution of local atomic structure during solidification of Al2Au liquid: An ab initio study

    SciTech Connect

    Xiong, L.H.; Lou, H.B.; Wang, X.D.; Debela, T.T.; Cao, Q.P.; Zhang, D.X.; Wang, S.Y.; Wang, C.Z.; Jiang, J.Z.

    2014-04-01

    The local atomic structure evolution in Al2Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt-Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al2Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of < 0,4,4,0 >, < 0,3, 6,0 > and < 0,4,4,2 > with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF2-type Al2Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al2Au alloy. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.