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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)

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.

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

1990-01-01

2

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

NASA Astrophysics Data System (ADS)

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.

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

3

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

4

Surface modifications of BaF2 and CaF2 single crystals by slow highly charged ions  

NASA Astrophysics Data System (ADS)

Ion-irradiation of solid surfaces is considered as one of the promising and powerful techniques for material nanostructuring. Recently, slow highly charged ions (HCI) have shown their potential in creating surface nanostructures in various solids. Here, we focus on the surface modifications of BaF2 and CaF2 single crystals by HCI. Despite the fact that both materials belong to alkaline-earth fluorides with the same crystalline structure, they exhibit different sensitivity for HCI-induced nanostructure. We discuss similarities and differences for the creation of HCI-induced nanohillocks and etch pits in both materials and their dependence on potential and kinetic energy deposition. Furthermore, we compare the results with modifications induced by swift heavy ions (SHI), in order to reach a better understanding of the mechanisms responsible for the creation of nanostructures in ionic fluoride single crystals.

El-Said, A. S.; Heller, R.; Wilhelm, R. A.; Facsko, S.; Aumayr, F.

2014-08-01

5

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

6

Numerical results on two-body and (two + three)-body lattice dynamics of CaF2, SrF2, and BaF2  

Microsoft Academic Search

Utilizing semiempirical two-body and (two + three)-body force fields, respectively, two distinct sets of shell-model calculations are reported on the crystal dynamics of CaF2, SrF2, and BaF2. The central force computations cover longwave properties, dispersion curves, specific heat, and thermal expansion. Also included are numerical results for mean square amplitudes as calculated conventionally and, in addition, by a new computational

1973-01-01

7

Structures of BaF2-CaF2 heterolayers and their influences on ionic conductivity.  

PubMed

Recently, artificial ion conductors have been prepared by growing epitaxial heterolayers consisting of BaF2-CaF2 using molecular beam epitaxy. The ionic conductivity of these heterolayers shows a strong dependence on the layer thickness [N. Sata, S. Eberman, K. Eberl, and J. Maier, Nature 408, 996 (2000)]. In this paper three such heterolayers with different spacings (sample A: 80 nm, sample B: 10 nm, sample C: 1 nm) are investigated by conventional transmission electron microscopy and high-resolution transmission electron microscopy. The spacings are chosen such that they fall into the three conductivity regimes observed in N. Sata et al. (l > 50 nm; 8 < l < 50 nm; l < 8 nm). In accordance with conductivity studies, the samples with spacings of 10 nm or greater (A,B) are epitaxial and continuous, whereas in the case of extremely small spacing (C) the continuity of the layers is destroyed by formation of a column-like structure. Analytical electron microscopy reveals that, instead of forming multilayers, Ca and Ba separate in different columns in sample C. The structure properties of sample A (large l) are quite ideal: Planar interfaces with regular arrays of misfit dislocations with their Burgers vectors on the interface are observed. In the case of sample B (medium l) the lattice misfit is accommodated, in addition, by wavy interfaces associated with dislocations characterized by a Burgers vector that makes a large angle to the interfaces. The (111) lattice spacing very close to the interfaces is markedly changed due to this novel relaxation mechanism in the multilayer. The influences of the crystallographic defects on the ionic conductivity are also discussed. PMID:15268377

Jin-Phillipp, N Y; Sata, N; Maier, J; Scheu, C; Hahn, K; Kelsch, M; Ruhle, M

2004-02-01

8

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

NASA Astrophysics Data System (ADS)

Phase transitions and equations of state of the alkaline earth fluorides CaF2 , SrF2 , and BaF2 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¯m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF2 and SrF2 : these materials were observed to transform to a hexagonal (P63/mmc) Ni2In -type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF2 , the Ni2In -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 CaF2 and SrF2 , 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 Ni2In -type phase is ˜5% . The percentage increase in the bulk modulus (?K) across the transition is greater when the cation is smaller. While for BaF2 , ?K is 10-30% , ?K values for SrF2 and CaF2 are 45-65% and 20-40% . Although shock data for CaF2 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.

Dorfman, Susannah M.; Jiang, Fuming; Mao, Zhu; Kubo, Atsushi; Meng, Yue; Prakapenka, Vitali B.; Duffy, Thomas S.

2010-05-01

9

Molecular beam epitaxial growth of Eu-doped CaF2 and BaF2 on Si X. M. Fang, T. Chatterjee, and P. J. McCann  

E-print Network

and BaF2 on Si was carried out in an Intevac Modular GEN II MBE system with a back- ground pressure of 10-based technol- ogy. Nd- and Er-doped CaF2 films grown on Si substrates by molecular beam epitaxy MBE have that Eu can be incorporated into epitaxial CaF2 films grown on Si 100 by MBE and that Eu doping as high

McCann, Patrick

10

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

PubMed

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

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

2014-05-01

11

Ionic conductivity of the phases of five types formed in the BaF2-GdF3 system  

NASA Astrophysics Data System (ADS)

The ionic conductivity has been measured in ceramic phases of five structure types found in the BaF2-GdF3 system: the fluorite type (CaF2), its trigonal and tetragonal distortions, the tysonite type (LaF3), and the orthorhombic ?-YF3 modification. The phases have been obtained by solid-phase synthesis from BaF2 and GdF3 mixtures in hermetic nickel containers at 925, 964, and 1067°C for 108-360 h in a fluorine atmosphere. Their conductivity ? is compared in correlation with the composition and structure type. The highest conductivity values are found for the tysonite Gd1 - y Ba y F3 - y phase (0.10 ? y ? 0.25): (1-2) × 10-3 S/cm at 683 K. The ordered Ba0.60Gd0.40F2.40 and Ba0.57Gd0.43F2.43 phases with fluorite-derived structures and different degrees of order are characterized by the lowest conductivities: i(1.5-3.5 × 10-5) S/cm.

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

2012-07-01

12

LaF3 insulators for MIS structures  

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

13

Labelling of silica microspheres with fluorescent lanthanide-doped LaF3 nanocrystals  

NASA Astrophysics Data System (ADS)

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

Zhang, Yong; Lu, Meihua

2007-07-01

14

Formation of LaF 3 microcrystals in sol–gel silica  

Microsoft Academic Search

A novel sol–gel process for silica\\/fluoride composites is described. Crystallization of LaF3 in the sol–gel silica has been investigated. Dry silica gels containing La3+ and trifluoroacetate ions (CF3COO?) were produced from tetramethylorthosilicate (TMOS), methanol, dimethylformamide, lanthanum acetate, trifluoroacetic acid, water and nitric acid. By heating the gels at temperatures above 300°C, LaF3 microcrystals with a size of 10–30 nm were

Shinobu Fujihara; Chizuko Mochizuki; Toshio Kimura

1999-01-01

15

Nd3+ doped LaF3 nanoparticles as self-monitored photo-thermal agents  

NASA Astrophysics Data System (ADS)

In this work, we demonstrate how LaF3 nanoparticles activated with large concentrations (up to 25%) of Nd3+ ions can simultaneously operate as biologically compatible efficient nanoheaters and fluorescent nanothermometers under single beam (808 nm) infrared laser excitation. Nd3+:LaF3 nanoparticles emerge as unique multifunctional agents that could constitute the first step towards the future development of advanced platforms capable of simultaneous deep tissue fluorescence bio-imaging and controlled photo-thermal therapies.

Rocha, Uéslen; Upendra Kumar, K.; Jacinto, Carlos; Ramiro, Julio; Caamaño, Antonio J.; García Solé, José; Jaque, Daniel

2014-02-01

16

Spectroscopic properties of LaF3:Tm3+ nanoparticle-doped  

E-print Network

fibres containing aluminium by the solution-doping method", Ceramics 4, 363-366 (1991) [5] B. Faure et al-prepared fibers using LaF3:Tm3+ (1 mol %) nanoparticles as the RE carrier during the fabrication process. The 10-20 nm diameter nanoparticles were produced by precipitation methods [3], suspended in ethanol and were

Paris-Sud XI, Université de

17

Bioconjugations of polyethylenimine-capped LaF3:Ce, Tb nanoparticles with bovine serum albumin and photoluminescent properties.  

PubMed

Water-soluble Ce3+ and Tb3+ co-doped LaF3 nanoparticles with surfaces functionalized by a layer of polyethylenimine (PEI) were synthesized via a facile one-step hydrothermal method. Bovine serum albumin (BSA) protein was conjugated with LaF3:Ce, Tb nanoparticles via free amino groups on the surfaces of the nanocrystals. The final products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet (UV) spectrophotometry, and photoluminescence (PL) spectroscopy. XRD results showed that pure hexagonal phase LaF3:Ce, Tb nanoparticles could be obtained via a PEI assisted hydrothermal process at 180 degrees C for 24 h. The FE-SEM results showed that the morphology of pure LaF3:Ce, Tb nanoparticles was spherical with an average diameter of -20 nm. The UV spectra showed that BSA had been conjugated with LaF3:Ce, Tb nanoparticles. The photoluminescent (PL) properties of LaF3:Ce, Tb nanoparticles were also studied. The strong green emission of Tb3+ in LaF3:Ce, Tb nanoparticles suggests that these nanoparticles may have potential applications for labels in biological imaging and immunoassays. PMID:24734615

Zhang, Wei; Hua, Ruinian; Shao, Wanyue; Zhao, Jun; Na, Liyan

2014-05-01

18

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

SciTech Connect

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.

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

2008-03-15

19

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

20

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

NASA Astrophysics Data System (ADS)

In this paper, fluorescent-magnetic Fe 3O 4@LaF 3:Ce,Tb nanocomposites were synthesized by combining fluorescent LaF 3:Ce,Tb and magnetic Fe 3O 4 nanoparticles into new 'two-in-one' entities. The obtained Fe 3O 4@LaF 3:Ce,Tb nanocomposites were small (about 30 nm in diameter) and well dispersed in water. Under ultraviolet light irradiation, the Fe 3O 4@LaF 3:Ce,Tb nanocomposites emitted bright green fluorescence, and they could be easily manipulated by an external magnetic field. Such bifunctional nanocomposites may find many biomedical applications, such as cancer detection and drug delivery. And the method we used can be extended to the synthesis of other nanocomposites based on lanthanide-doped materials and metal oxides.

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

2009-02-01

21

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

PubMed

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 structural properties were assessed with atomic-force microscopy, x-ray diffraction, TEM techniques that involved conventional thinning methods for the layers. For measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed. The dispersion behavior of both deposition materials, which was determined on the basis of various independent photometric measurements and data reduction techniques, is in good agreement with that published in the literature and with the bulk properties of the materials. The refractive indices of the MgF2 coatings ranged from 1.415 to 1.440 for the wavelength of the ArF excimer laser (193 nm) and from 1.435 to 1.465 for the wavelength of the F2 excimer laser (157 nm). For single layers of LaF3 the refractive indices extended from 1.67 to 1.70 at 193 nm to approximately 1.80 at 157 nm. The IBS process achieves the best homogeneity and the lowest surface roughness values (close to 1 nm(rms)) of the processes compared in the joint experiment. In contrast to MgF2 boat and e-beam evaporated coatings, which exhibit tensile mechanical stress ranging from 300 to 400 MPa, IBS coatings exhibit high compressive stress of as much as 910 MPa. A similar tendency was found for coating stress in LaF3 single layers. Experimental results are discussed with respect to the microstructural and compositional properties as well as to the surface topography of the coatings. PMID:12064402

Ristau, Detlev; Günster, Stefan; Bosch, Salvador; Duparré, Angela; Masetti, Enrico; Ferré-Borrull, Josep; Kiriakidis, George; Peiró, Francesca; Quesnel, Etienne; Tikhonravov, Alexander

2002-06-01

22

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

23

Trigonal LaF3: a novel SRS-active crystal  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

24

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

SciTech Connect

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.

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

2011-12-31

25

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

E-print Network

­10 %, while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase to the Ni2In-type phase is 5%. The percentage increase in the bulk modulus K across the transition all crys- tallize in the cubic fluorite structure Fm3¯m, Z=4 , which consists of a cubic close-packed

Duffy, Thomas S.

26

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

PubMed

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

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

2015-02-01

27

A solvent extraction route for CaF2 hollow spheres.  

PubMed

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

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

2010-11-21

28

Gamma irradiation effect on photoluminescence from functionalized LaF3:Ce nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

29

Sensitized luminescence of LaF3:Eu3+ nanoparticles through pyromellitic acid.  

PubMed

The LaF3 nanoparticles doped with different concentration Eu3+ ions are prepared by a simple and low temperature synthetic route. The nanoparticles with the size of about 3.5 nm are roughly spherical and monodisperse. The emission of Eu3+ ions is sensitized through pyromellitic acid bonded onto the surface of nanoparticles. The structure, morphology, photoluminescence properties and fluorescence dynamics are studied systemically. The results show that the sensitized nanoparticles have a broad absorption band in the UV domain and high asymmetry radio, and enhanced Eu3+ luminescence by "antenna effect" of ligands. The excited state lifetimes of sensitized nanoparticles are longer than those of un-sensitized nanoparticles and corresponding europium complexes. PMID:24734612

Li, S Wen; Ren, H Juan; Ju, S Guang

2014-05-01

30

Ion beam induced damage in CaF2  

Microsoft Academic Search

The change in lattice parameter and the induced damage are studied in single crystal CaF2 bombarded by a 15 MeV Cl ion beam. The lattice parameter change (strain) and the damage for increasing ion beam dose (5 × 1012\\/cm2 to 7 × 1015\\/cm2) is observed via X-ray rocking curve analysis using a double-crystal diffractometer and X-ray reflection topography. The ion

C. R. Wie; T. Vreeland; T. A. Tombrello

1985-01-01

31

Elastic Constants of CaF2 at Different Temperature  

NASA Astrophysics Data System (ADS)

A simple and straightforward method for evaluating and predicting elastic constants as a function of temperature is presented on the basis of Murnaghan and Tallon models with first approximation. This theoretical method is used to predict successfully the values of elastic constants C11, C12 and C44 in GPa for CaF2 that are in reasonably good agreement with experimental data.

Sharma, Sheetal; Verma, Ajay Singh; Jindal, V. K.

2011-07-01

32

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

PubMed

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

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

2014-06-01

33

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

SciTech Connect

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.

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

2010-01-21

34

Synchrotron x-ray diffraction studies of the lattice and magnetic structure of epitaxial Dy films in LaF3\\/Dy\\/LaF3 sandwiches (abstract)  

Microsoft Academic Search

Lattice and magnetic x-ray diffraction from a 2000 A? thick film of Dy, sandwiched by LaF3 films on a GaAs(111) substrate, are reported. The structure was grown by molecular beam epitaxy with the c axis of the Dy parallel to the LaF3c axis and GaAs [111] axis. We find that the c-axis lattice constant of the Dy has a similar

R. F. C. Farrow; M. F. Toney; B. D. Hermsmeier; S. S. P. Parkin; D. G. Wiesler

1991-01-01

35

Synchrotron x-ray diffraction studies of the lattice and magnetic structure of epitaxial Dy films in LaF3\\/Dy\\/LaF3 sandwiches  

Microsoft Academic Search

Lattice and magnetic x-ray diffraction from a 2000 A? thick film of Dy, sandwiched by LaF3 films on a GaAs(111) substrate, are reported. The structure was grown by molecular beam epitaxy with the c axis of the Dy parallel to the LaF3c axis and GaAs [111] axis. We find that the c-axis lattice constant of the Dy has a similar

R. F. C. Farrow; M. F. Toney; B. D. Hermsmeier; S. S. P. Parkin; D. G. Wiesler

1991-01-01

36

Toxicity Assessments of Near-infrared Upconversion Luminescent LaF3:Yb,Er in Early Development of Zebrafish Embryos  

PubMed Central

This study reports the effects of upconversion nanoparticles (UCNPs) LaF3:Yb,Er on zebrafish, with the aim of investigating UCNPs toxicity. LaF3:Yb,Er were prepared by an oleic acid/ionic liquid two-phase system, and characterized by transmission electron microscope and X-ray powder diffraction. 140 zebrafish embryos were divided into six test groups and one control group, and respectively were injected into 5, 25, 50, 100, 200, 400 ?g/mL LaF3:Yb,Er@SiO2 solution, and respectively were raised for 5 days. Each experiment was repeated ten times. Results showed that water-soluble LaF3:Yb,Er were successfully prepared, and did not exhibit obvious toxicity to zebrafish embryos under 100 ?g/mL, but exhibited chronic toxicities 200 ?g/mL in vivo, resulting in malformations and delayed hatching rate and embryonic and larval development. The excretion channels of LaF3:Yb,Er in adult zebrafish were mainly found in the intestine after being injected evenly for 24 h. In conclusion, the exploration of LaF3:Yb,Er for in vivo applications in animals and humans must consider UCNPs biocompatibility. PMID:23606912

Wang, Kan; Ma, Jiebing; He, Meng; Gao, Guo; Xu, Hao; Sang, Jie; Wang, Yuxia; Zhao, Baoquan; Cui, Daxiang

2013-01-01

37

Toxicity assessments of near-infrared upconversion luminescent LaF3:Yb,Er in early development of zebrafish embryos.  

PubMed

This study reports the effects of upconversion nanoparticles (UCNPs) LaF3:Yb,Er on zebrafish, with the aim of investigating UCNPs toxicity. LaF3:Yb,Er were prepared by an oleic acid/ionic liquid two-phase system, and characterized by transmission electron microscope and X-ray powder diffraction. 140 zebrafish embryos were divided into six test groups and one control group, and respectively were injected into 5, 25, 50, 100, 200, 400 ?g/mL LaF3:Yb,Er@SiO2 solution, and respectively were raised for 5 days. Each experiment was repeated ten times. Results showed that water-soluble LaF3:Yb,Er were successfully prepared, and did not exhibit obvious toxicity to zebrafish embryos under 100 ?g/mL, but exhibited chronic toxicities 200 ?g/mL in vivo, resulting in malformations and delayed hatching rate and embryonic and larval development. The excretion channels of LaF3:Yb,Er in adult zebrafish were mainly found in the intestine after being injected evenly for 24 h. In conclusion, the exploration of LaF3:Yb,Er for in vivo applications in animals and humans must consider UCNPs biocompatibility. PMID:23606912

Wang, Kan; Ma, Jiebing; He, Meng; Gao, Guo; Xu, Hao; Sang, Jie; Wang, Yuxia; Zhao, Baoquan; Cui, Daxiang

2013-01-01

38

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

39

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

PubMed

In this report, uniform LaF(3):Ln mesoporous spheres have been synthesized by a facile and mild in situ ion-exchange method using yolk-like La(OH)3:Ln mesoporous spheres as templates, which were prepared through a self-produced bubble-template route. It was found that the structures of the final LaF(3):Ln can simply be tuned by adding a polyetherimide (PEI) reagent. LaF(3):Ln hollow mesoporous spheres (HMSs) and LaF(3):Ln flower-like mesoporous spheres (FMSs) were obtained when assisted by PEI and in the absence of PEI. The up-conversion (UC) luminescence results reveal that the doping of Nd(3+) ions in LaF(3):Ln can markedly influence the UC emissions of the products. It is interesting that an obvious thermal effect is achieved due to the energy back-transfer from Tm(3+) to Nd(3+) ions under 980 nm near-infrared (NIR) irradiation. The LaF(3):Yb/Er/Tm/Nd HMSs show good biocompatibility and sustained doxorubicin (DOX) release properties. In particular, upon 980 nm NIR irradiation, the photothermal effect arising from the Nd(3+) doping induces a faster DOX release from the drug release system. Moreover, UC luminescence images of LaF(3):Yb/Er/Tm/Nd HMSs uptaken by MCF-7 cells exhibit apparent green emission under 980 nm NIR irradiation. Such a multifunctional carrier combining UC luminescence and hyperthermia with the chemotherapeutic drugs should be of high potential for the simultaneous anti-cancer therapy and cell imaging. PMID:25359551

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

2014-12-21

40

Storage and phase conjugation of multiple images using backward-stimulated echoes in Pr(3+):LaF3  

NASA Astrophysics Data System (ADS)

Long-term storage and phase conjugation of multiple images have been observed by using a backward-stimulated echo scheme in the 3H4-3P0 transition of Pr(3+):LaF3 crystal. The temporal order of the multiple-echo images is the reverse of that of the input images. Each of the echo images is a phase-conjugate replica of the input images and lasts as long as 15 sec. This constitutes, in principle, the first reported demonstration of an ultrafast holographic movie using a stimulated photon echo.

Kim, M. K.; Kachru, R.

1987-08-01

41

Glycine-assisted hydrothermal synthesis of single-crystalline LaF 3:Eu 3+ hexagonal nanoplates  

Microsoft Academic Search

In this paper, large-scale LaF3:Eu3+ hexagonal nanoplates with uniform diameter were controllably synthesized by a glycine-assisted hydrothermal method at 150°C using La(NO3)3, Eu(NO3)3 and NH4F as the reactants. During the synthetic procedure, different amino acids (glycine, lysine and glutamic acid) were first used as the complexing and surface-functionalizing agents for the preparation of rare earth luminescent nanomaterials. Different amino acids

Xiaofeng Yang; Xiangting Dong; Jinxian Wang; Guixia Liu

2009-01-01

42

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

PubMed

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

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

2014-02-14

43

Study of the oxygen incorporation during growth of large CaF 2-crystals  

NASA Astrophysics Data System (ADS)

Single crystalline calcium fluoride (CaF 2) is designated as optical material in systems for photolithographic processing of silicon ICs at wavelengths in the deep ultraviolet. The prerequisites for this application are a high transmission and a high resistance with respect to radiation damage under high-intensity laser irradiation. Pure CaF 2 has excellent transmission properties without absorption bands over a wide wavelength range from UV to IR. Selective absorption bands exist in CaF 2 only if the crystal contains impurities. Oxygen is considered as a major impurity in CaF 2. In the present contribution incorporation of oxygen during crystal growth and its influence on the optical properties of CaF 2 is investigated systematically by a specially designed crystal growth facility and processing. A special gas supply system is used to introduce oxygen directly into the CaF 2-melt during crystal growth by a Bridgman-type technique. The concentration of the oxygen in the growth atmosphere and therewith in the crystal was varied over a wide range during growth. The oxygen concentration in the as-grown CaF 2-crystal was determined quantitatively by a special characterization technique called elastic recoil detection (ERD). Concentrations between 5 and 144 ppm were detected. Investigations of the optical properties of the oxygen-doped CaF 2-crystal revealed that the oxygen causes an increase of the absorption in the UV range with a maximum at 197 nm. The relation between the oxygen concentration in the crystal and the absorption coefficient at 197 nm was found to be linear. This calibration relation can now be used in general for the quantitative determination of the oxygen concentration in CaF 2-crystals by absorption measurements at 197 nm. Furthermore, the influence of oxygen on the radiation hardness was examined for X-ray and excimer F 2-laser (157 nm) irradiation.

Molchanov, A.; Friedrich, J.; Wehrhan, G.; Müller, G.

2005-01-01

44

Atomistic simulations of the pressure-induced phase transitions in BaF2 crystals  

Microsoft Academic Search

The pressure-induced sequence of phase transitions of the BaF2 fluorite was studied within the shell-model approach. This fluorite crystal presents two pressure-induced phase transitions at approximately 3 and 15 GPa. The interatomic potentials were calculated by using relevant physical properties measured at ambient conditions. These potentials were used to minimize the lattice enthalpy at high hydrostatic pressures. By comparing the

A. P. Ayala

2001-01-01

45

PROPRITS OPTIQUES ET MISSION PHOTOLECTRIQUE DES MONOCRISTAUX ET DES COUCHES MINCES DE BaF 2  

E-print Network

, the reflecting power, and the photoelectric emission of single crystals and thin layers of BaF2. The position of the reflecting power and the photoelectric emission at 10-11. eV. tE JOURNAL DE PHYSIQUE TOME 26, FEVRIER 1965'absorption est situe vers 1350 A (9,1 eV), c'est-à-dire a des longueurs d'onde nettement plus courtes que celles

Paris-Sud XI, Université de

46

Technique of CeF3 impurity concentration control in LaF3 crystals by means of the UV absorption spectra  

NASA Astrophysics Data System (ADS)

The presence of impurities in the crystals has an important influence on their properties. A sensitive method of the impurity control in the crystals without their destruction is the investigation of their absorption spectra. In this work we have studied the LaF3 tysonite crystals widely used as the laser matrices. The LaF3 crystals were grown from the melt by Bridgman-Stockbarger method using the reagents with trade mark high pure and chemical pure. The crystal absorption spectra were recorded in the range of 200-300 nm and the obtained results have shown that the crystals grown from the high pure reagents had no absorption bands in the UV region and the crystals grown from the chemical pure reagents had well defined characteristic absorption bands at (lambda) = 205, 218, 235, 248 nm. Spectral experiments have confirmed the assumption that the UV-absorption bands in the latter crystal samples were caused by the presence of CeF3 impurity in the chemical pure reagents. A technique was developed for evaluation of CeF3 content in LaF3 crystals and in chemical pure mixture of LaF3 with the accuracy +/- 0.0005 mol.%.

Krivandina, Elena A.; Zhmurova, Zinaida I.; Glushkova, Tatiana M.; Kiselev, Dmitrii F.; Firsova, Marina M.; Shtyrkova, Antonina P.

2001-03-01

47

Vacuum Ultraviolet Fluorescence Spectroscopy of Nd3+:LaF3 Using Femtosecond Extreme Ultraviolet Free Electron Laser  

NASA Astrophysics Data System (ADS)

Time-resolved vacuum ultraviolet (VUV) fluorescence was observed from a Czochralski method-grown Nd3+:LaF3 crystal excited by 61 nm femtosecond pulses from the extreme ultraviolet free-electron laser (EUV-FEL). The 172 nm fluorescence peak exhibited double exponential fluorescence decay with slow and fast decay components of 6.7 and 1.9 ns, respectively. The spectral profile is similar to those previously reported, but the double exponential nature has never been attained using conventional short-wavelength pulsed lasers. Our results demonstrate the importance of the EUV-FEL for short-wavelength spectroscopy, not just for rare-earth-doped fluorides but also for wide-band-gap semiconductors such as AlGaN.

Shinzato, Yuki; Yamanoi, Kohei; Nishi, Ryosuke; Takeda, Kohei; Nakazato, Tomoharu; Shimizu, Toshihiko; Sarukura, Nobuhiko; Cadatal-Raduban, Marilou; Fukuda, Kentaro; Kurosawa, Shunsuke; Yokota, Yuui; Yoshikawa, Akira; Togashi, Tadashi; Nagasono, Mitsuru; Ishikawa, Tetsuya

2013-02-01

48

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

PubMed

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

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

2014-01-21

49

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

50

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

PubMed

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

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

2015-02-15

51

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

52

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

53

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

PubMed Central

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

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

2014-01-01

54

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)

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.

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

2014-10-01

55

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)

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.

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

2014-12-01

56

Ultra-precision process of CaF2 single crystal  

NASA Astrophysics Data System (ADS)

This paper proposes a new chemical mechanical polishing (CMP) process method for CaF2 single crystal to get ultraprecision surface. The CMP processes are improving polishing pad and using alkaline SiO2 polishing slurry with PH=8, PH=11 two phases to polish, respectively, and the roughness can be 0.181nm Rq (10?m×10?m). The CMP process can't get high surface figure, so we use ion beam figuring (IBF) technology to obtain high surface figure. However, IBF is difficult to improve the CaF2 surface roughness. We optimize IBF process to improve surface figure and keep good surface roughness too. Different IBF incident ion energy from 400ev to 800ev does not affect on the surface roughness obviously but the depth of material removal is reverse. CaF2 single crystal can get high precision surface figure (RMS=2.251nm) and still keep ultra-smooth surface (Rq=0.207nm) by IBF when removal depth is less than 200nm. The researches above provide important information for CaF2 single crystal to realize ultra-precision manufacture.

Yin, Guoju; Li, Shengyi; Xie, Xuhui; Zhou, Lin

2014-08-01

57

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

58

Nanostructuring CaF2 surfaces with slow highly charged ions  

NASA Astrophysics Data System (ADS)

In recent years the potential of slow highly charged ions (HCI) as tools for nanostructuring purposes has received considerable attention and a wide range of material classes, from insulating ionic crystals, polymers and ultrathin films, to semiconducting and conducting substrates have been investigated regarding their response to individual HCI impact. For the majority of investigated materials, however, consistent theoretical modeling to supplement with experimental evidence and to satisfactorily explain the complete physical process from ion approach and impact to the formation of an individual nanostructure is still lacking. CaF2, from both an experimental and theoretical point of view, might be considered the most thoroughly investigated material. Combining results from numerous studies has allowed for the generation of a "phase diagram" for nanostructuring of CaF2 in dependence of ion beam parameters. This paves the way for a first unified picture, as implications from this phase diagram should be applicable to similar materials as well.

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

2014-04-01

59

Ultralow-threshold Raman lasing with CaF2 resonators.  

PubMed

We demonstrate efficient Raman lasing with CaF2 whispering-gallery-mode resonators. Continuous-wave emission threshold is shown to be possible below 1 microW with a 5mm cavity, which is to our knowledge orders of magnitude lower than in any other Raman source. Low-threshold lasing is made possible by the ultrahigh optical quality factor of the cavity, of the order of Q=5x10(10). Stokes components of up to the fifth order were observed at a pump power of 160 microW, and up to the eighth order at 1 mW. A lasing threshold of 15 microW was also observed in a 100 microm CaF2 microcavity. Potential applications are discussed. PMID:17186052

Grudinin, Ivan S; Maleki, Lute

2007-01-15

60

Metal( CoSi2)/Insulator( CaF2) Resonant Tunneling Diode  

NASA Astrophysics Data System (ADS)

Negative differential resistance (NDR) of nanometer-thick triple-barrier metal( CoSi2)/insulator( CaF2) resonant tunneling diode (RTD) and the structure dependence of its characteristics are demonstrated. The device consists of metal-insulator (M-I) heterostructures with two metallic ( CoSi2) quantum wells and three insulator ( CaF2) barriers grown on an n-Si(111) substrate. A typical peak-to-valley current ratio (P/V ratio) obtained at 77 K was 2 3 and the largest P/V ratio was 25. A P/V ratio as high as 2 was obtained at 300 K. M-I RTDs with two quantum wells of various thicknesses were fabricated in order to investigate the dependence of resonance voltage on the thickness of the two quantum wells. Reasonable agreement was obtained between theory and experiment for this dependence.

Suemasu, Takashi; Watanabe, Masahiro; Suzuki, Jun; Kohno, Yoshifumi; Asada, Masahiro; Suzuki, Nobuhiro

1994-01-01

61

Magnetic manifestations of thermoluminescence excitation in CaF 2 :Mn (TLD400)  

Microsoft Academic Search

Magnetic susceptibility as a function of temperature (4–250K) and EPR spectra at room temperature were studied for thermoluminescence detectors (TLD) CaF2:Mn with either stored dose information or cleaned dose by annealing. No essential variations of Mn2+ number in detectors were found due to dose storage; however, the exchange interactions between manganese ions are observed as deviations from Curie–Weiss law. These

Mikhail Danilkin; Aleksei Kirillov; Sergei Klimonsky; Vyacheslav Kuznetsov; Aime Lust; Hugo Mändar; Vladimir Nikiforov; Arno Ratas; Aleksandr Ruchkin; Viktor Seeman

2007-01-01

62

High-power tunable diode-pumped Yb3+:CaF2 laser  

Microsoft Academic Search

Results of diode-pumped cw laser operation of an Yb3+:CaF2 single crystal are reported for what is to our knowledge the first time. With a 5-at.% Yb3+-doped sample we obtained 5.8-W output power at 1053 nm for 15 W of incident power at 980 nm. The laser wavelength could be tuned from 1018 to 1072 nm, and a small-signal gain as

A. Lucca; M. Jacquemet; F. Druon; F. Balembois; P. Georges; P. Camy; J. L. Doualan; R. Moncorgé

2004-01-01

63

High-power diode-pumped Yb3+:CaF2 femtosecond laser  

Microsoft Academic Search

We report what is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb3+:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at.% Yb3+-doped sample and prisms for dispersion compensation we obtained pulses as short as 150 fs, with 880 mW of average power and up to 1.4-W

A. Lucca; G. Debourg; M. Jacquemet; F. Druon; F. Balembois; P. Georges; P. Camy; J. L. Doualan; R. Moncorgé

2004-01-01

64

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

E-print Network

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

Krems, Roman

65

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

66

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

E-print Network

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

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

2014-01-01

67

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

E-print Network

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

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

2014-07-22

68

Intense photoluminescence at 2.7 ?m in transparent Er 3+:CaF2-fluorophosphate glass microcomposite.  

PubMed

Er3+ doped CaF2-fluorophosphate (FP) glass microcomposites were produced by heat-treating the mixture of Er3+:CaF2 precipitate and FP glass powder above the melting temperature of the FP glass. The appearance of CaF2 crystallites in the resulting composites was confirmed by x ray diffraction. Despite the fact that the average diameter of the crystallites was around 10 ?m as revealed by the micromorphology study, a transparent composite was obtained by matching the refractive index of FP glass to that of CaF2. Intense IR fluorescence at around 2.7 ?m was observed in the composite, implying the composite would be a promising candidate for IR lasers and amplifiers. PMID:22089559

Fan, Jintai; Yuan, Xinqiang; Li, Rihong; Dong, Hongxing; Wang, Jun; Zhang, Long

2011-11-15

69

Effect of CaF 2 on densification and properties of hydroxyapatite–zirconia composites for biomedical applications  

Microsoft Academic Search

Hydroxyapatite (HA) composites with zirconia (ZrO2) up to 40vol% were fabricated with the addition of CaF2. The sinterability of the composites was found to be enhanced markedly by the addition of small amounts of CaF2 (<5vol%). Decomposition of HA to ?-TCP was suppressed due to the substitution of F? for OH?, consequently forming fluor-hydroxyapatite (FHA) solid solution. This suppression of

Hae-Won Kim; Yoon-Jung Noha; Young-Hag Koh; Hyoun-Ee Kim; Hyun-Man Kim

2002-01-01

70

Dark matter search experiment with CaF2(Eu) scintillator at Kamioka Observatory  

E-print Network

We report recent results of a WIMP dark matter search experiment using 310g of CaF2(Eu) scintillator at Kamioka Observatory. We chose a highly radio-pure crystal, PMTs and radiation shields, so that the background rate decreased considerably. We derived limits on the spin dependent WIMP-proton and WIMP-neutron coupling coefficients, a_p and a_n. The limits excluded a part of the parameter space allowed by the annual modulation observation of the DAMA NaI experiment.

Y. Shimizu; M. Minowa; W. Suganuma; Y. Inoue

2005-10-13

71

Microstructure and tribological properties of laser clad CaF 2\\/Al 2O 3 self-lubrication wear-resistant ceramic matrix composite coatings  

Microsoft Academic Search

Self-lubrication wear-resistant CaF2\\/Al2O3 ceramic matrix composite coatings were fabricated on substrates of Al2O3 by laser cladding CaF2–Al2O3 mixed powder blends. Compared with laser clad monolithic Al2O3 coatings, the CaF2\\/Al2O3 coating has much superior wear resistance and noticeably lower friction coefficient under dry sliding wear test conditions.

H. M. Wang; Y. L. Yu; S. Q. Li

2002-01-01

72

Facile fabrication and upconversion luminescence enhancement of LaF3:Yb3+/Ln3+@SiO2 (Ln = Er, Tm) nanostructures decorated with Ag nanoparticles.  

PubMed

A novel hybrid nanostructure, that is a Ag nanoparticle decorated LaF(3):Yb(3+)/Ln(3+)@SiO(2) nanosphere (Ln=Er, Tm), was constructed by a facile strategy, and characterized by XRD, TEM, FTIR, XPS and UV-vis-NIR absorption. Obvious spectral broadening and red-shift on the surface plasmon resonance were obtained by adjusting the size and configuration of Ag nanoparticles. Effective upconversion luminescence enhancements for Er(3+) and Tm(3+) containing samples were obtained. It is suggested that the luminescence enhancement results from both the excitation and emission processes, and the configuration of the studied hybrid nanostructure is an efficient system to enhance the luminescence emission of rare earth doped nanomaterials. It is believed that the enhancement from the hybrid nanostructure will find great potential in the development of photovoltaic solar cells. PMID:24398901

He, Enjie; Zheng, Hairong; Dong, Jun; Gao, Wei; Han, Qingyan; Li, Junna; Hui, Le; Lu, Ying; Tian, Huani

2014-01-31

73

Facile fabrication and upconversion luminescence enhancement of LaF3:Yb3+/Ln3+@SiO2 (Ln=Er, Tm) nanostructures decorated with Ag nanoparticles  

NASA Astrophysics Data System (ADS)

A novel hybrid nanostructure, that is a Ag nanoparticle decorated LaF3:Yb3+/Ln3+@SiO2 nanosphere (Ln=Er, Tm), was constructed by a facile strategy, and characterized by XRD, TEM, FTIR, XPS and UV-vis-NIR absorption. Obvious spectral broadening and red-shift on the surface plasmon resonance were obtained by adjusting the size and configuration of Ag nanoparticles. Effective upconversion luminescence enhancements for Er3+ and Tm3+ containing samples were obtained. It is suggested that the luminescence enhancement results from both the excitation and emission processes, and the configuration of the studied hybrid nanostructure is an efficient system to enhance the luminescence emission of rare earth doped nanomaterials. It is believed that the enhancement from the hybrid nanostructure will find great potential in the development of photovoltaic solar cells.

He, Enjie; Zheng, Hairong; Dong, Jun; Gao, Wei; Han, Qingyan; Li, Junna; Hui, Le; Lu, Ying; Tian, Huani

2014-01-01

74

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

PubMed

Highly uniform and well-dispersed CaF(2) hollow spheres with tunable particle size (300-930 nm) have been synthesized by a facile hydrothermal process. Their shells are composed of numerous nanocrystals (about 40 nm in diameter). The morphology and size of the CaF(2) products are strongly dependent on experimental parameters such as reaction time, pH value, and organic additives. The size of the CaF(2) hollow spheres can be controlled from 300 to 930 nm by adjusting the pH value. Nitrogen adsorption-desorption measurements suggest that mesopores (av 24.6 nm) exist in these hollow spheres. In addition, Ce(3+)/Tb(3+)-codoped CaF(2) hollow spheres can be prepared similarly, and show efficient energy transfer from Ce(3+) to Tb(3+) and strong green photoluminescence of Tb(3+) (541 nm, (5)D(4)-->(7)F(5) transition of Tb(3+), the highest quantum efficiency reaches 77%). The monodisperse CaF(2):Ce(3+)/Tb(3+) hollow spheres also have desirable properties as drug carriers. Ibuprofen-loaded CaF(2):Ce(3+)/Tb(3+) samples still show green luminescence of Tb(3+) under UV irradiation, and the emission intensity of Tb(3+) in the drug-carrier system varies with the released amount of ibuprofen, so that drug release can be easily tracked and monitored by means of the change in luminescence intensity. The formation mechanism and luminescent and drug-release properties were studied in detail. PMID:20391571

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

2010-05-17

75

Optical gain in Y2+:CaF2 crystal: potential medium for near-infrared tunable lasers  

NASA Astrophysics Data System (ADS)

Y2+ (4d1 configuration) ion is proposed to be a new laser active optical center. As an example Y2+ in CaF2 crystals demonstrates broad luminescence band with peak at 1146 nm and halfwidth of 2155 cm-1 at room temperature when excited with 532 nm light. It was observed that Y2+ centers in CaF2 are stable under excitation with 532 nm radiation with pumping power density of 233 MW/cm2 from flash-lamp pumped Q-switched Nd3+:YAG laser. Optical gain has been measured in CaF2:Y2+ amplifier at 1150 nm wavelength. It is concluded that Y2+ doped crystals seems to be promising materials for tunable solid-state lasers.

Ter-Mikirtychev, Valerii V.

1998-05-01

76

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

PubMed

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

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

2015-01-14

77

Characterization of infrared optical properties of transparent materials  

Microsoft Academic Search

The spectral, distribution of the absorption in the spectral region from 2.5-12 micrometer was measured by infrared wavelength modulation technique on: CaF2; LiF; NaCl; NaF; LaF3; BaF2; MgF2, SrF2; MgO. Both surface and volume contaminants were identified. Rayleigh-Brillouin scattering was measured on single and polycrystalline KCl. In addition, Rayleigh-Brillouin and Raman measurements were performed on fluoride glasses. Infrared optical derivative

R. Braunstein

1981-01-01

78

Characterization of infrared optical properties of transparent materials  

NASA Astrophysics Data System (ADS)

Chemical and structural imperfections which occur in highly transparent insulators and semiconductors were studied by a range of electromagnetic and electronic techniques. These utilized infrared wavelength modulation, high contrast Raman and Brillouin scattering and photoinduced transients spectroscopy techniques. The spectoral distribution of the absorption in the spectral region from 2.5-12 gamma was measured by infrared wavelength modulation techniques on: CaF2, LiF, NaCl, NaF, LaF3, BaF2, MgF2, SrF2, MgO, KCl, and KBr.

Braunstein, R.

1983-03-01

79

Formation of the CRS2-CAF2 group II intron splicing complex is mediated by a 22-amino acid motif in the COOH-terminal region of CAF2.  

PubMed

CRS2-associated factors 1 and 2 (CAF1 and CAF2) are closely related proteins that function in concert with chloroplast RNA splicing 2 (CRS2) to promote the splicing of specific sets of group II introns in maize chloroplasts. The CRS2-CAF complexes bind tightly to their cognate group II introns in vivo, with the CAF subunit determining the intron specificity of the complex. In this work we show that the CRS2-CAF complexes are stable in the absence of their intron targets and that CRS2 binds a 22 amino acid motif in the COOH-terminal region of CAF2 that is conserved in CAF1. Yeast two-hybrid assays and co-fractionation studies using recombinant proteins show that this motif is both necessary and sufficient to bind CRS2. The 22-amino acid motif is predicted to form an amphipathic helix whose hydrophobic surface is conserved between CAF1 and CAF2. We propose that this surface binds the hydrophobic patch on the surface of CRS2 previously shown to be necessary for the interaction between CRS2 and CAF2. PMID:16379013

Ostheimer, Gerard J; Rojas, Margarita; Hadjivassiliou, Haralambos; Barkan, Alice

2006-02-24

80

On the thermoluminescence emission spectra of CaF 2: Tm  

NASA Astrophysics Data System (ADS)

Thermoluminescence (TL) emission spectra in the visible and near infrared region of TLD-300 (CaF 2: Tm) commonly used for TL dosimetry were studied at exposures 286 and 7300 R. The TL emission spectra from 300 to 900 nm are observed every 2°C from 50°C to 320°C. Glow peaks appear at 110°C, 145°C, 235°C and 265°C. Emission bands in the spectra were measured at 357, 460, 655 and 805 nm. Discussion is given about a possibility of using the infrared emission band 805 nm as well as the visible emission bands in the routine work of radiation detector dosimetry at a temperature of around 145°C. Further we discuss the change of the integral glow curve for each of these emission bands for the exposure radiation at 286 and 7300 R.

Rasheedy, Mahmoud Said; Nishimura, Fumio; Ichimori, Toshihiro

1991-07-01

81

Magnetic circular dichroism of colour centres in CaF2 : Na J. L. Doualan, J. Margerie, F. Martin-Brunetire,  

E-print Network

L-375 Magnetic circular dichroism of colour centres in CaF2 : Na J. L. Doualan, J. Margerie, F. Abstract. - The magnetic circular dichroism (M.C.D.) of several centres in additively coloured CaF2 : Na understood : several centres have been reliably identified by their absorption and fluorescence bands

Boyer, Edmond

82

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

E-print Network

of this deposition procedure have been described elsewhere [5]. Germanium films were simultaneously deposited by thermal evaporation on unbuffered (bare glass) and CaF2 buffered glass substrates with substrate carried out in a high vacuum chamber with a base pressure of 5 Ã? 10Ã?8 Torr. The substrate to source

Wang, Gwo-Ching

83

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

E-print Network

incidence. The details of this deposition procedure have been described elsewhere [5]. Germanium films were simultaneously deposited by thermal evaporation on unbuffered (bare glass) and CaF2 buffered glass substrates carried out in a high vacuum chamber with a base pressure of 5 Ã? 10Ã?8 Torr. The substrate to source

Wang, Gwo-Ching

84

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...

85

Location of the Energy Levels of the Rare-Earth Ion in BaF2 and CdF2  

E-print Network

The location of the energy levels of rare-earth (RE) elements in the energy band diagram of BaF2 and CdF2 crystals is determined. The role of RE3+ and RE2+ ions in the capture of charge carriers, luminescence, and the formation of radiation defects is evaluated. It is shown that the substantial difference in the luminescence properties of BaF2:RE and CdF2:RE is associated with the location of the excited energy levels in the band diagram of the crystals.

P. A. Rodnyi; I. V. Khodyuk; G. B. Stryganyuk

2010-09-07

86

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

87

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

in an Intevac GEN II modular MBE system. The Si 111 substrates were cleaned using the modified Shiraki method- lar beam epitaxy MBE on both Si 111 and BaF2 111 sub- strates are described and results from diode­VI semiconductor thin films due to optical pumping. II. EXPERIMENTS A. MBE growth procedures PbSe/PbSrSe MQW

McCann, Patrick

88

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

89

Investigation of the spin-Hamiltonian parameters for the trigonal U5+ center in CaF2 crystal.  

PubMed

The spin-Hamiltonian parameters (g factor g(//), g(perpendicular) and hyperfine structure constants A(//), A(perpendicular)) of the trigonal U(5+) center in CaF(2) crystal have been calculated from the complete diagonalization (of energy matrix) method (CDM) for 5f(1) ions in trigonal crystal field and under an external magnetic field. In the calculation, the crystal-field parameters are estimated from the superposition model. From the calculations, these spin-Hamiltonian parameters are reasonably explained, and the defect model (i.e., the trigonal U(5+) center is attributed to U(5+) substituting for Ca(2+) in CaF(2) with six F(-) ions replaced by O(2-) and the other two F(-) sites vacant because of charge compensation) given in the previous paper is confirmed. The results are discussed. PMID:20308011

Zheng, Wen-Chen; Liu, Hong-Gang; Yang, Wei-Qing; Su, Ping

2010-06-01

90

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

PubMed

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 Ca(2+)-binding ability in the C-terminal lobe suggest that the EF-hand Ca(2+)-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. PMID:25367003

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

2014-12-21

91

Nano-structuring of CaF2 surfaces by slow highly charged ions: simulation and experiment  

NASA Astrophysics Data System (ADS)

The impact of individual slow highly charged ions (HCI) on insulators can create nano-scale surface modifications. We present recent experimental results on nano-hillock and etch pit formation on CaF2, where the appearance of surface modifications is observed only above a threshold projectile potential and kinetic energy depending on the type of damage. A proof-of-principle molecular dynamics simulation offers insights into the early stages of damage formation.

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

2014-04-01

92

Radial Diffraction Strength and Elastic Behavior of CaF2 in Low- and High-Pressure Phases  

SciTech Connect

The radial-diffraction lattice behavior of CaF2 was analyzed in its low-pressure (fluorite) and high-pressure phase up to 11.5 GPa using radial x-ray diffraction techniques in the diamond anvil cell. Between 3.5 and 7.1 GPa, fluorite develops a radial-diffraction strength of {approx}0.8 GPa. The corresponding lattice anisotropy of the fluorite phase was measured to be equal to 0.73, in good agreement with previous Brillouin spectroscopy measurements. By 8.8 GPa, CaF2 has undergone a phase transformation to its high-pressure (orthorhombic) phase, with a corresponding volume decrease of 10.4%. By 11.5 GPa, the volume drop between the low-pressure and high-pressure phase has increased to 11.5%. In addition, the high-pressure phase is found to withstand a significantly larger differential stress than the low-pressure fluorite phase, with a large degree of lattice anisotropy. In the maximum stress direction at 8.8 GPa, we observe a time-dependent evolution of the lattice parameters of CaF2, indicating that the high-pressure structure is still undergoing deformation on time scales of hours after the phase boundary has been crossed.

Kavner,A.

2008-01-01

93

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

NASA Astrophysics Data System (ADS)

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

Klein, Claude A.

2005-05-01

94

New optical transitions of colour centres in CaF2 : Na+ J. L. Doualan, A. Hamadia, J. Margerie and F. Martin-Brunetire  

E-print Network

a study of their magnetic circular dichroism. We have recently discovered in CaF2 : Na' several other C, or their vibrational satellites, while others are still uni- dentified J. Physique 45 (1984) 1779-1787 NOVEMBRE 1984

Paris-Sud XI, Université de

95

Transmission and reflection studies of thin films in the vacuum ultraviolet  

NASA Technical Reports Server (NTRS)

Both the transmittance and reflectance of 2 mm thick MgF2 substrates and of thin films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on these substrates were measured for the wavelength range 120 nm to 230 nm. Results for BaF2, LaF2 and MgF2 show promise as being good materials from which interference filters can be made. The software and related hardware needed to take large amounts of data automatically in future measurements of the transmittance and reflectance was developed.

Peterson, Lennart R.

1989-01-01

96

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

E-print Network

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

Boyer, Edmond

97

The influence of TiC, CaF 2 and MnS additives on friction and lubrication of sintered high speed steels at elevated temperature  

Microsoft Academic Search

Friction behaviours of sintered high speed steels containing TiC, CaF2 and MnS additives and lubrication mechanisms of these additives have been investigated at sliding conditions at 600°C. Results shown that these additives strongly affected friction behaviours of the sintered high speed steels. Ceramic carbide TiC, as a bonding agent and enhancement phase, bonded the solid lubricant CaF2 and MnS surrounding

Zuomin Liu; T. H. C. Childs

1996-01-01

98

The study of wear characteristics of sintered high speed steels containing CaF 2, MnS and TiC additives at elevated temperature  

Microsoft Academic Search

The wear characteristics of five kinds of sintered high speed steels, which contain MnS, TiC and CaF2 additives, have been investigated at 600°C. The results show that the MnS, TiC and CaF2 additives greatly affect the wear of the steels, and that TiC can improve the wear resistance of the steels. There is also evidence that, at elevated temperature, a

Liu Zuomin; T. H. C Childs

2004-01-01

99

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

PubMed

Visible light excitable and color tunable ?5% Eu(3+)-doped LaF3 nanocrystals (NCs), containing 9-oxidophenalenone ligands bound to the surface as visible light sensitizers for Eu(3+) dopants, have been synthesized by a facile solution-based method. The crystalline phase structure, size, composition, morphology and luminescence properties of the NCs are characterized using X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and steady-state and time-resolved emission spectroscopy. The results show that these NCs are very small in size (<10 nm), display high degree of crystallinity and have pure tysonite structure of LaF3 with P3[combining macron]c1 space group. The visible light excitation of the capping ligands triggers an alternate display of steady-state, short-lived blue emission (? < 1 ns) and time-delayed, long-lived sensitized red Eu(3+) emission (? = 0.41 ms), allowing photoluminescence chromacity tuning as a function of delay time within a specific inorganic composition. The visible light sensitization of the dopant Eu(3+) sites proves more efficient than direct excitation of 5% Eu(3+)-doped LaF3 NCs capped by citrate ligands. The dopant Eu(3+) ions are well protected from non-radiative deactivation through high-energy vibrations of the organic capping ligands which is proved by the long lifetime of the sensitized Eu(3+) emission. The time-resolved emission spectra collected over a period of several milliseconds reveal that the dopant Eu(3+) ions occupy at least three different sites in the NC host. It is further inferred that the sensitized Eu(3+) emission primarily comes from surface dopant sites and sites just underneath the surface of the NCs. We propose that some of the interior Eu(3+) sites also display sensitized emission, which are indirectly populated via Eu(3+) ? Eu(3+) energy migration from surface-sensitized Eu(3+) sites of the NCs. PMID:25567779

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

2015-02-21

100

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

PubMed

Europium doped glass-ceramics containing BaF(2) nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF(2) nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm(-1) has been demonstrated from the emission spectra of Eu(3+) ions showing the transitions from upper excitation states (5)D(J) (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu(3+)) ions to divalent (Eu(2+)) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu(2+) to Eu(3+) ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu(3+) to Eu(2+) under normal air atmospheric condition has been observed in a BaF(2) containing oxyfluoride glass-ceramics system. PMID:22048984

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

2012-03-01

101

Electron paramagnetic resonance and optical spectroscopy of Yb3+ ions in SrF2 and BaF2; an analysis of distortions of the crystal lattice near Yb3+  

Microsoft Academic Search

SrF2 and BaF2 crystals, doped with the Yb3+ ions, have been investigated by electron paramagnetic resonance and optical spectroscopy. As-grown crystals of SrF2 and BaF2 show the two paramagnetic centres for the cubic (Tc) and trigonal (T4) symmetries of the Yb3+ ions. Empirical diagrams of the energy levels were established and the potentials of the crystal field were determined. Information

M L Falin; K I Gerasimov; V A Latypov; A M Leushin

2003-01-01

102

Energy transfer from benzoic acid to lanthanide ions in benzoic acid-functionalized lanthanide-doped CaF 2 nanoparticles  

NASA Astrophysics Data System (ADS)

The preparation of benzoic acid-functionalized CaF 2:Ln 3+ (Ln = Eu or Tb) nanoparticles and their sensitized luminescence are described in this report. First, to achieve sufficient proof for energy transfer from benzoic acid (BA) to lanthanide ions doped in nanoparticles, we employ Eu 3+ as the microscopic probe and investigate the luminescent spectra of benzoic acid-functionalized CaF 2:Eu 3+ (BA-CaF 2:Eu 3+) nanoparticles. Next, to further reveal the difference between sensitized luminescence and common luminescence for Eu 3+ doped in CaF 2 nanoparticles, we study the emission spectra of BA-CaF 2:Eu 3+ nanoparticles excited at 286 nm and 397 nm, respectively. Finally, we analyze and compare the luminescent spectra of BA-CaF 2:Tb 3+ and CaF 2:Ce 3+, Tb 3+ nanoparticles in detail. Our results indicate that both Eu 3+ and Tb 3+ doped in CaF 2 nanoparticles can be efficiently sensitized through benzoic acid.

Wang, Jianshe; Wang, Zongwu; Li, Xia; Wang, Si; Mao, Huadan; Li, Zhongjun

2011-06-01

103

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

104

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

NASA Astrophysics Data System (ADS)

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.

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

1989-12-01

105

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

NASA Astrophysics Data System (ADS)

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.

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

2012-11-01

106

Folic acid-conjugated LaF3:Yb,Tm@SiO2 nanoprobes for targeting dual-modality imaging of upconversion luminescence and X-ray computed tomography.  

PubMed

Development of multimodal contrast agents for in vivo simultaneous multimodality imaging is an emerging interdiscipline that is paving the avenue toward the goal of personalized medicine. Herein, folic acid-conjugated silica-modified LaF(3):Yb,Tm upconversion nanoparticles (UCNPs@SiO(2)-FA) with high La content in a single particle were strategically designed and prepared for simultaneously targeting dual-modality imaging of upconversion luminescence (UCL) and X-ray computed tomography (CT). LaF(3) UCNPs were synthesized by a novel oleic acid (OA)/ionic liquid (IL) two-phase system. Afterward, a folic acid molecule was covalently anchored on the surface of UCNPs with a silane coupling agent. The UCNPs@SiO(2)-FA exhibits good stability, water dispersibility and solubility, low cytotoxicity, good biocompatibility, highly selective targeting, excellent X-ray attenuation, and UCL emission under excitation at 980 nm. In vivo UCL and CT images of mice show the UCNPs@SiO(2)-FA can be used in targeting dual-modality imaging. These results suggest that the as-prepared nanoprobe is a good candidate with excellent imaging and targeting ability for targeting dual-modality imaging of UCL and CT. PMID:23134318

Ma, Jiebing; Huang, Peng; He, Meng; Pan, Liyuan; Zhou, Zhijun; Feng, Lili; Gao, Guo; Cui, Daxiang

2012-12-01

107

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

SciTech Connect

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

Liu, Peng [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK); Zhang, Yanwen [ORNL] [ORNL; Xiao, Haiyan [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK); Xiang, Xia [University of Electronic Science and Technology of China (UESTC)] [University of Electronic Science and Technology of China (UESTC); Wang, Xuelin [Shandong University, Jinan, China] [Shandong University, Jinan, China; Weber, William J [ORNL] [ORNL

2014-01-01

108

Optical absorption properties and valence states of uranium in CaF 2 crystals grown by TGT  

NASA Astrophysics Data System (ADS)

Calcium fluoride single crystals doped with uranyl nitrate were grown by an improved temperature gradient technique under different conditions. Absorption spectra, energy levels and unit cell parameters were studied to analyze the possible color centers and valence states of uranium ions in as-grown U:CaF 2 crystals. Uranium in U:CaF 2 crystals grown in the presence of PbF 2 as an oxygen scavenger is trivalent. F-centers and other defects related to oxygen, with respective absorption lines at 604 and 526 nm, and impure valence states of uranium ions exist in U 3+:CaF 2 when the molar ratio of PbF 2 to U is less than 25. In the absence of PbF 2, U:CaF 2 crystals are multicolor, consisting of red, cerise, yellow and green volumes from inside to outside where the red part in the core is still U 3+:CaF 2. Mixed valence states of uranium ions exist in the crystal. The valences of uranium ions are inferred to gradually increase from +3 to +6 according to the graded changes of the absorption spectra and unit cell parameters.

Su, Liangbi; Yang, Weiqiao; Xu, Jun; Dong, Yongjun; Zhou, Guoqing

2004-09-01

109

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

PubMed Central

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

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

2014-01-01

110

Quantum Interference of Electron Wave in Metal (CoSi2)/Insulator (CaF2) Resonant Tunneling Hot Electron Transistor Structure  

NASA Astrophysics Data System (ADS)

We report the observation of multiple negative differential resistance (NDR) in nanometer-thick metal (CoSi2)/insulatro (CaF2) resonant tunneling hot electron transistor (RHET) grown on a silicon substrate. In this transistor, electrons from a resonant tunneling emitter with a 2.2-nm-thick CoSi2 quantum well are transferred to the conduction band of a 4.0-nm-thick CaF2 collector barrier region. Multiple NDR observed here may be attributed to the modulation of the transmission probability of electron waves due to quantum interference in the conduction band of the insulator (CaF2) collector barrier layer between two metal (CoSi2) layers, which is a different mechanism from the resonance in quantum wells previously reported.

Suemasu, Takashi; Kohno, Yoshifumi; Saitoh, Wataru; Suzuki, Nobuhiro; Watanabe, Masahiro; Asada, Masahiro

1994-12-01

111

Negative Differential Resistance of CaF 2/CdF 2 Triple-Barrier Resonant-Tunneling Diode on Si(111) Grown by Partially Ionized Beam Epitaxy  

NASA Astrophysics Data System (ADS)

Room-temperature negative differential resistance (NDR) of triple-barrier cadmium di-fluoride (CdF2)/calcium di-fluoride (CaF2) heterostructure resonant-tunneling diode (RTD) on a Si(111) substrate has been demonstrated. CdF2/CaF2 multilayered heterostructures were grown on a Si(111) substrate using partially ionized beam epitaxy to obtain atomically flat interfaces. The RTD structures, which consist of triple CaF2 energy barriers and double CdF2 quantum wells, were fabricated by electron beam (EB) lithography and dry etching to avoid thermal and chemical damage to the CdF2 layers. In the current-voltage characteristics of the RTD, NDR was clearly observed even at room temperature and the maximum peak-to-valley (P/V) ratio was about 6.

Watanabe, Masahiro; Aoki, Yuichi; Saito, Wataru; Tsuganezawa, Mika

1999-02-01

112

Room temperature negative differential resistance of CdF2/CaF2 double-barrier resonant tunneling diode structures grown on Si(100) substrates  

NASA Astrophysics Data System (ADS)

The authors have demonstrated the crystal growth of CaF2/CdF2/CaF2 multilayered heterostructures on Si(100) substrates as double-barrier resonant tunneling diode structures by a low-temperature growth technique. Current-voltage characteristics were investigated and the authors observed negative differential resistance (NDR) characteristics at room temperature. The peak-to-valley current ratio was 2-8, and 13 at maximum, and peak current density was 80-90A /cm2. The quantum-well layer thickness dependence of NDR peak voltages is also discussed on the basis of qualitative analytical model using the Esaki-Tsu formula.

Kanazawa, Tohru; Fujii, Ryo; Wada, Takafumi; Suzuki, Yusuke; Watanabe, Masahiro; Asada, Masahiro

2007-02-01

113

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

SciTech Connect

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

Ullmann, J.L.; Esch, E.-I.; Haight, R.C.; Hunt, L.; O'Donnell, J.M.; Reifarth, R. [LANSCE Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Agvaanluvsan, U. [Physics Dept., North Carolina State University, Raleigh, NC 27695C (United States); Alpizar, A.; Hatarik, R. [LANSCE Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Physics Department, Colorado School of Mines, Golden, Colorado 80401 (United States); Bond, E.M.; Bredeweg, T.A.; Kronenberg, A.; Rundberg, R.S.; Vieira, D.J.; Wilhelmy, J.B. [Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Folden, C.M.; Hoffman, D.C. [Nuclear Science Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (United States); Greife, U. [Physics Department, Colorado School of Mines, Golden, Colorado 80401 (United States); Schwantes, J.M. [Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Nuclear Science Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (United States); Strottman, D.D. [Theory Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)] [and others

2005-05-24

114

Spatially selective Er/Yb-doped CaF2 crystal formation by CO2 laser exposure  

NASA Astrophysics Data System (ADS)

We report the glass-ceramic precipitation on the oxyfluoride glass surface by spatially selective annealing with a CO2 laser and a heat gun exposure. X-ray diffraction analysis showed the formation of major CaF2 and miner Ca2SiO4 nanoparticles. We observed ?100 nm nanoparticle aggregation by tunneling electron microscopy and element distribution in glass and crystal phases. Spatial distribution of glass ceramics near the glass surface was probed by confocal fluorescence microscope by using much enhanced emission from the Er ions in the laser-treated area. Strong emissions at 365 nm excitation and visible up-conversion emissions at 980 nm excitation also indicated well incorporation of Er and Yb ions into a crystalline environment.

Kim, Dong-Seon; Lee, Jin-Ho; Lim, Ki-Soo

2014-10-01

115

Nd3+:CaF2 crystal with controlled photoluminescence spectroscopic properties by codoping Y3+ ions  

NASA Astrophysics Data System (ADS)

High optical quality Nd,Y-codoped CaF2 crystals with diameter 3-inch were obtained by TGT method. Absorption and emission spectra were recorded at 5 K, 12 K, and 300 K respectively. Judd-Ofelt theory was applied to obtain standard parameter ?t (t = 2, 4, 6) and the fitting result of experimental lifetime of Nd3+4F3/2 ? 4I11/2 transition. Broad and flat 1.06 ?m emission spectra of Nd3+ ions were obtained with Y3+-codoping. The largest emission bandwidth of Nd3+4F3/2 ? 4I11/2 transition is up to 28 nm. The results revealed that codoping Y3+ ions in Nd:CaF2 crystal can effectively modulate the spectra properties of Nd3+ ions, in addition to the reduction of fluorescence concentration-quenching.

Wang, Qingguo; Su, Liangbi; Ma, Fengkai; Zhan, Yaoyu; Jiang, Dapeng; Qian, Xiaobo; Wang, Jingya; Zheng, Lihe; Xu, Jun; Ryba-Romanowski, Witold; Solarz, Piotr; Lisiecki, Radoslaw

2013-12-01

116

Analysis of single- and double-barrier tunneling diode structures using ultrathin CaF2/CdF2/Si multilayered heterostructures grown on Si  

NASA Astrophysics Data System (ADS)

The current–voltage (I–V) characteristics of single-barrier and double-barrier tunneling diode structures using CaF2/CdF2/Si ultrathin multilayered heterostructures grown on Si substrates have been theoretically analyzed and their material parameters, such as the conduction band discontinuity (?EC) at the heterointerface and effective mass (m*), have been evaluated by fitting simulation with the measured I–V characteristics. ?EC between the ultrathin (1–3 nm) CaF2 and Si layers and m* for CaF2 were found to be 1.5–2.3 eV and 0.3–1.0m0, respectively. A clear thickness dependence of these parameters was observed, and the deviations of m* and ?EC were approximately 30–50%, which probably originated from the thin layer thicknesses in atomic order. Using the estimated values derived from the single-barrier tunneling diodes, m* for CdF2 was also estimated to be 0.36m0 by fitting simulation of double-barrier diodes. These results will contribute to clarifying the design principle of tunneling devices with CaF2 and enhancing quantitative studies on electron transport in atomically thin multilayered heterostructures.

Suda, Keita; Kuwata, Yuya; Watanabe, Masahiro

2015-04-01

117

Reflection high-energy electron diffraction study of the molecular beam epitaxial growth of CaF2 on Si(110)  

E-print Network

was carried out in an Intevac modular GEN-II MBE system equipped with a Varian electron gun operated at 9.5 ke electron microscopy SEM data on the mo- lecular beam epitaxial MBE growth of CaF2 on Si 110 . We also

McCann, Patrick

118

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

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

119

pH-responsive drug delivery system based on luminescent CaF(2):Ce(3+)/Tb(3+)-poly(acrylic acid) hybrid microspheres.  

PubMed

In this study, we design a controlled release system based on CaF(2):Ce(3+)/Tb(3+)-poly(acrylic acid) (PAA) composite microspheres, which were fabricated by filling the pH-responsive PAA inside CaF(2):Ce(3+)/Tb(3+) hollow spheres via photopolymerization route. The CaF(2):Ce(3+)/Tb(3+) hollow spheres prepared by hydrothermal route possess mesoporous structure and show strong green fluorescence from Tb(3+) under UV excitation. Doxorubicin hydrochloride (DOX), a widely used anti-cancer drug, was used as a model drug to evaluate the loading and controlled release behaviors of the composite microspheres due to the good biocompatibility of the samples using MTT assay. The composite carriers provide a strongly pH-dependent drug release behavior owing to the intrinsic property of PAA and its interactions with DOX. The endocytosis process of drug-loaded microspheres was observed using confocal laser scanning microscopy (CLSM) and the in vitro cytotoxic effect against SKOV3 ovarian cancer cells of the DOX-loaded carriers was investigated. In addition, the extent of drug release could be monitored by the altering of photoluminescence (PL) intensity of CaF(2):Ce(3+)/Tb(3+). Considering the good biocompatibility, high drug loading content and pH-dependent drug release of the materials, these hybrid luminescent microspheres have potential applications in drug controlled release and disease therapy. PMID:22196902

Dai, Yunlu; Zhang, Cuimiao; Cheng, Ziyong; Ma, Ping'an; Li, Chunxia; Kang, Xiaojiao; Yang, Dongmei; Lin, Jun

2012-03-01

120

Planar stress relaxation in solid phase epitaxial CaF2 films grown on (111)Si by in situ rapid isothermal processing  

NASA Astrophysics Data System (ADS)

Planar strain in CaF2 films on (111) Si substrate has been measured by an x-ray double-crystal diffraction technique using rocking curves. The films grown by a solid phase epitaxial approach using in situ rapid isothermal processing are almost free of tensile planar strain, and free from defects as observed by the transmission electron microscope diffraction pattern.

Singh, R.; Kumar, A.; Thakur, R. P. S.; Chou, P.; Chaudhuri, J.; Gondhalekar, V.; Narayan, J.

1990-04-01

121

CaF2/CdF2 Double-Barrier Resonant Tunneling Diode with High Room-Temperature Peak-to-Valley Ratio  

NASA Astrophysics Data System (ADS)

We have demonstrated room-temperature negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) on the order of 105 using CaF2/CdF2 double-barrier resonant tunneling diode (DBRTD) structures grown on Si(111) substrates. A CdF2 quantum-well layer was grown by molecular-beam epitaxy (MBE) and CaF2 barrier layers were formed by MBE combined with the partially ionized beam technique on an n^+-Si(111) substrate with 0.07^\\circ miscut, in order to reduce the pinhole density of CaF2 barrier layers. The dispersion of the peak current density and bias voltage of the NDR implies that the layer thickness fluctuation of each CaF2 barrier and CdF2 quantum-well layer is suppressed below ±1 unit layer of the (111) atomic plane for DBRTDs with an 18 ?m diameter electrode. The peak and valley currents agreed reasonably with those obtained by theoretical estimation.

Watanabe, Masahiro; Funayama, Toshiyuki; Teraji, Taishi; Sakamaki, Naoto

2000-07-01

122

Readout concepts for the suppression of the slow component of BaF2 for the upgrade of the TAPS spectrometer at ELSA  

NASA Astrophysics Data System (ADS)

For the measurement at extremely high interaction rates with fast scintillators, pile-up of consecutive events is a limiting factor. With a decay time of 600 ps of the fast crossluminescence component, Barium Fluoride (BaF2) is one of the fastest inorganic scintillators known today. However, the dominating slow component with a 3 orders of magnitude longer decay time of 630 ns limits the rate capability. To circumvent this limit, different approaches have been made in the past. The slow component can be suppressed for example by doping the crystals with rare earth ions like La3+. The paper will give an overview over the various concepts investigated in the past and present the suppression via optical band pass filters. This method has been chosen for the upgrade of the BaF2 crystals in the most forward region of the TAPS-spectrometer at ELSA in Bonn. It allows to reuse the existing crystals and to achieve a high degree of suppression of the slow component. The focus of the paper will be on the selection of the filters, the achievable rate capability and the energy resolution of the fast component.

Diehl, Stefan; Novotny, Rainer W.; Wohlfahrt, Benjamin; Beck, Reinhard

2015-02-01

123

Raman and interband optical spectra of epitaxial layers of the topological insulators Bi2Te3 and Bi2Se3 on BaF2 substrates  

NASA Astrophysics Data System (ADS)

We report results of Raman and ellipsometric spectroscopy of the topological insulators Bi2Te3 and Bi2Se3 grown by molecular beam epitaxy on BaF2 (111) substrates. Surfaces and interfaces of the films are probed by Raman scattering from the front and back sides of the samples, which is possible owing to the transparent substrate. Surface modifications induced by intense illumination with exciting laser light have been detected, with excess tellurium at the surface during and after exposure. We also report data for thin epilayers containing a fractional number of unit cells and/or incomplete Bi2Te3 and Bi2Se3 quintuples. We have used spectroellipsometric measurements to obtain response functions and have derived the penetration depth of light in the 1.0–6.5 eV range.

Humlí?ek, J.; Hemzal, D.; Dubroka, A.; Caha, O.; Steiner, H.; Bauer, G.; Springholz, G.

2014-09-01

124

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

PubMed Central

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 (Xe22+ to Xe30+) 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

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

125

CaF2/Si/CaF2 double-barrier resonant-tunnelling diodes on Si substrates  

NASA Astrophysics Data System (ADS)

CaF2/Si/CaF2 double-barrier resonant-tunnelling diodes have been fabricated by various processes with molecular beam epitaxy in SiO2 windows patterned on Si(111) substrates. Two types of I-V characteristics with negative differential resistance (NDR) were observed in the temperature range from 75 K up to about 200 K. The one is very stable in forward and backward voltage sweeps, and, in contrast to earlier reports, it does not show any hysteresis or trapping effects. Typical diode parameters were: peak voltage Vp = 0.7 V, peak-to-valley current ratio P/V = 1.7 and peak current density Ip = 2 mA cm-2 at 105 K. The second is less stable and the NDR appeared only during forward bias sweeps, possibly due to local trapping effects. But it has larger P/V ratios, the typical parameters being: Vp = 1.2 V,P/V = 5 and Ip = 11 mA cm-2 at 77 K. The observed peak current densities of both NDR types are about five orders of magnitude higher than those reported previously for diodes with the similar structure. We assume that an inhomogeneous Si quantum-well thickness with the current flow localized in small regions of the diode area causes the observed variations in peak voltages, multiple NDR regions, peak spreading and exponentially rising background currents.

Wang, C. R.; Müller, B. H.; Hofmann, K. R.

2003-11-01

126

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)

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.

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

127

Suppression of Leakage Current of CdF2/CaF2 Resonant Tunneling Diode Structures Grown on Si(100) Substrates by Nanoarea Local Epitaxy  

NASA Astrophysics Data System (ADS)

CdF2/CaF2 resonant tunneling diode (RTD) structures of 100 nm diameter were fabricated in SiO2 hole arrays formed on Si(100) substrates. RTD structures were grown by molecular beam epitaxy (MBE) in SiO2 hole arrays. After the growth of the initial CaF2 layer at a substrate temperature of 120 °C, in situ annealing at 500 °C was carried out to reduce the density of defects or pinholes in the barrier layer. In the measurement of current-voltage (I-V) characteristics, negative differential resistance (NDR) was clearly demonstrated at room temperature. The peak-to-valley current ratio (PVCR) was 106. The valley current was significantly suppressed. Results obtained here strongly indicates that the RTD structures proposed in this study are promising for high-quality NDR elements compatible with Si LSI technology based on Si(100) substrates.

Kanazawa, Tohru; Morosawa, Atsushi; Fujii, Ryo; Wada, Takafumi; Suzuki, Yusuke; Watanabe, Masahiro; Asada, Masahiro

2007-06-01

128

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

Microsoft Academic Search

The analytical figures of merit for ultraviolet laser ablation-inductively coupled plasma mass spectrometry (UV-LA-ICP-MS) at 266 nm with respect to the trace element analysis of high-purity, UV-transmitting alkaline earth halides are investigated and discussed. Ablation threshold energy density values and ablation rates for mono- and poly-crystalline CaF2 samples were determined. Furthermore, Pb-, Rb-, Sr-, Ba- and Yb-specific analysis was performed.

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

2002-01-01

129

Stem Cell Labeling using Polyethylenimine Conjugated (?-NaYbF4:Tm3+)/CaF2 Upconversion Nanoparticles  

PubMed Central

We report on a polyethylenimine (PEI) covalently conjugated (?-NaYbF4:Tm3+)/CaF2 upconversion nanoparticle (PEI-UCNP) and its use for labeling rat mesenchymal stem cells (rMSCs). The PEI-UCNPs absorb and emit near-infrared light, allowing for improved in vivo imaging depth over conventional probes. We found that such covalent surface conjugation by PEI results in a much more stable PEI-UCNP suspension in PBS compared to conventional electrostatic layer by layer (LbL) self-assembling coating approach. We systematically examined the effects of nanoparticle dose and exposure time on rat mesenchymal stem cell (rMSC) cytotoxicity. The exocytosis of PEI-UCNPs from labeled rMSCs and the impact of PEI-UCNP uptake on rMSC differentiation was also investigated. Our data show that incubation of 100-µg/mL PEI-UCNPs with rMSCs for 4 h led to efficient labeling of the MSCs, and such a level of PEI-UCNP exposure imposed little cytotoxicity to rMSCs (95% viability). However, extended incubation of PEI-UCNPs at the 100 µg/mL dose for 24 hour resulted in some cytotoxicity to rMSCs (60% viability). PEI-UCNP labeled rMSCs also exhibited normal early proliferation, and the internalized PEI-UCNPs did not leak out to cause unintended labeling of adjacent cells during a 14-day transwell culture experiment. Finally, PEI-UCNP labeled rMSCs were able to undergo osteogenic and adipogenic differentiation upon in vitro induction, although the osteogenesis of labeled rMSCs appeared to be less potent than that of the unlabeled rMSCs. Taken together, PEI-UCNPs are promising agents for stem cell labeling and tracking. PMID:23606911

Zhao, Liang; Kutikov, Artem; Shen, Jie; Duan, Chunying; Song, Jie; Han, Gang

2013-01-01

130

Accelerated damage to blank and antireflectance-coated CaF2 surfaces under 157-nm laser irradiation  

NASA Astrophysics Data System (ADS)

Successful insertion of 157-nm lithography into production requires that materials comprising the optical train meet the lifetime requirements of the industry. At present, no degradation of bulk fluoride materials has been observed for at least up to 109 pulses. However, last year we reported on the surface damage to fluoride materials that appeared after 3-4x109 pulses at moderate fluences of 3-4 mJ/cm2/pulse2. This damage manifested itself as a precipitous transmission drop of up to 50% at 157 nm and was accompanied by the formation of a porous rough surface layer about 0.20 ?m thick. Understanding this surface damage is important for the durability of laser windows and beam delivery optics, and it may also help elucidate fundamental 157-nm photophysics of fluoride surfaces. To understand the underlying phenomena, we have designed and constructed a new accelerated damage test chamber. The chamber utilizes 157-nm light from a lithography-grade laser operating at 1000 Hz. Inside the chamber, light is focused onto the sample to a submillimeter spot size. The chamber allows us to test in-situ transmission of multiple spots on a given sample over a range of fluences up to 140 mJ/cm2/pulse without breaking purge. We have used this chamber to understand the scaling of the damage mechanism for both uncoated and antireflectance (AR) -coated CaF2 samples as a function of laser repetition rate and fluence. Substrate damage appears to be governed by a complex set of mechanisms, both thermal and non-thermal in origin. Preliminary damage studies of AR-coated substrates show that AR-coating related degradation occurs well before the onset of the substrate surface damage.

Liberman, Vladimir; Rothschild, Mordechai; Palmacci, Stephen T.; Efremow, Nikolay N.; Sedlacek, Jan H. C.; Grenville, Andrew

2003-06-01

131

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

132

Characterization of infrared optical properties of transparent materials  

NASA Astrophysics Data System (ADS)

The spectral, distribution of the absorption in the spectral region from 2.5-12 micrometer was measured by infrared wavelength modulation technique on: CaF2; LiF; NaCl; NaF; LaF3; BaF2; MgF2, SrF2; MgO. Both surface and volume contaminants were identified. Rayleigh-Brillouin scattering was measured on single and polycrystalline KCl. In addition, Rayleigh-Brillouin and Raman measurements were performed on fluoride glasses. Infrared optical derivative spectroscopy was employed to determine: Stress in Si on sapphire, strain in ion implanted GaAs, free carrier screening of hyperbolic excitons in GaAs, deep levels in Si and GaAs and vibrational modes in oxides of Si, GaAs and HgCdTe.

Braunstein, R.

1981-05-01

133

Radiation Damage Effects in Far Ultraviolet Filters and Substrates  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

134

The growth of YBCO films with high critical current at reduced pressures using the BaF2 ex situ process  

NASA Astrophysics Data System (ADS)

The growth of 0.9-1.0 µm thick Y Ba2Cu3O7-dgr (YBCO) films on biaxially textured Ni-3 at.% W (NiW) substrates using the BaF2 ex situ process was investigated at reduced pressures. By varying the water vapour pressure (PH2O), Y-BaF2-Cu-O (YBFCO) precursor films deposited by e-beam co-evaporation were converted at a reduced total pressure (Ptotal) of 50-55 Torr and conversion temperature (TS) of 740 °C for a wet conversion time (tW) of 60 min. Critical current density (JC) values greater than 1 MA cm-2 for the thick YBCO films were obtained under the condition of varying PH2O from low pressure to 10 Torr. The transition temperatures (TC) of the samples were over 90 K with DgrTC = 1.8-2.5 K. Pre-heat treatment of the precursor films on CeO2/Y SZ/Y2O3/Ni/NiW substrates under an O2 atmosphere condition before the conversion resulted in smooth surfaces without large secondary phase particles embedded in the films.

Yoo, J.; Leonard, K. J.; Hsu, H. S.; Heatherly, L.; List, F. A.; Lee, D. F.; Gapud, A. A.; Martin, P. M.; Cook, S.; Paranthaman, M.; Goyal, A.; Kroeger, D. M.

2004-10-01

135

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

NASA Astrophysics Data System (ADS)

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.

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

2009-03-01

136

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

PubMed

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

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

2015-03-21

137

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)

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.

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

2015-03-01

138

Investigation of change of the composition and structure of the CaF2/Si films surface at the low-energy bombardment  

NASA Astrophysics Data System (ADS)

The influence of the bombardment by the Ar+, Ba+ and Na+ ions and the subsequent annealing on composition and electron structure of a surface of the CaF2/Si (1 1 1) films is studied. The energy band diagram of the epitaxial nanofilm systems of the Ca-CaF2-Si type is constructed. Optimum regimes of ion implantation and annealing for the production of three-componental nanodimensional structures of the Ca1-XCOXF2 type are determined and parameters of their energy bands are estimated.

Umirzakov, B. E.; Tashmukhamedova, D. A.; Ruzibaeva, M. K.; Djurabekova, F. G.; Danaev, S. B.

2014-05-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

140

Effects of CaF2 vis-a-vis TiO2 as nucleating agent in SiO2-Al2O3-CaO glass-ceramics  

NASA Astrophysics Data System (ADS)

The independent effects of CaF2 and TiO2 on the glass-ceramics based on SiO2-Al2O3-CaO system have been investigated. The crystallization behavior, microstructure, mechanical properties and chemical resistance of the glass-ceramics were studied by Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), FTIR, mechanical and chemical resistance measurements. The CaF2 containing glass ceramics are found to be much superior to that of TiO2 containing glass ceramics on the basis of sintering strength, mechanical and chemical properties.

Mukherjee, Debasis Pradip; Datta, Tanmoy; Das, Sudip Kumar

2013-06-01

141

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)

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.

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

142

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

143

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

144

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

145

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

146

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

NASA Astrophysics Data System (ADS)

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

Ochoa, Franklyn E. Colmenares

2006-12-01

147

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

PubMed Central

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

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

148

Surface assessment of CaF2 deep-ultraviolet and vacuum-ultraviolet optical components by the quasi-Brewster angle technique.  

PubMed

The requirements for optical components have drastically increased for the deep-ultraviolet and vacuum-ultraviolet spectral regions. Low optical loss, high laser damage threshold, and long lifetime fluoride optics are required for microlithographic applications. A nondestructive quasi-Brewster angle technique (qBAT) has been developed for evaluating the quality of optical surfaces including both top surface and subsurface information. By using effective medium approximation, the negative quasi-Brewster angle shift at wavelengths longer than 200 nm has been used to model the distribution of subsurface damage, whereas the positive quasi-Brewster angle shift for wavelengths shorter than 200 nm has been explained by subsurface contamination. The top surface roughness depicted by the qBAT is consistent with atomic force microscopy measurements. The depth and the microporous structure of the subsurface damage measured by the qBAT has been confirmed by magnetorheological finishing. The technique has been extended to evaluate both polished and antireflection-coated CaF(2) components. PMID:16855659

Wang, Jue; Maier, Robert L

2006-08-01

149

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

SciTech Connect

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

Ochoa, Franklyn E. Colmenares [Undergraduate Mechanical Engineering, Polytechnic University of Puerto Rico (Puerto Rico)

2006-12-04

150

Multiple Negative Differential Resistance due to Quantum Interference of Hot Electron Waves in Metal (CoSi 2)/Insulator (CaF 2) Heterostructures and Influence of Parasitic Circuit Elements  

NASA Astrophysics Data System (ADS)

We report the observation of multiple negative differential resistance (NDR) in a metal (CoSi2)/insulator (CaF2) resonant tunneling hot electron transistor structure. Multiple NDR observed here can be attributed to the modulation of the transmission probability of hot electron waves due to quantum interference in the conduction band of the insulator (CaF2) collector barrier layer between two metal (CoSi2) layers. By reducing the influence of the Schottky diode at the CoSi2/Si interface, relatively clear and low-voltage NDR is observed. It is found, by a simulation including parasitic elements, that the collector resistance and leakage current greatly influence the current voltage characteristics.

Saitoh, Wataru; Suemasu, Takashi; Kohno, Yoshifumi; Watanabe, Masahiro; Asada, Masahiro

1995-08-01

151

Molecular beam epitaxial growth of Bi2Se3-and Tl2Se-doped PbSe and PbEuSe on CaF2 /Si,,111...  

E-print Network

The growth of PbSe and PbEuSe on CaF2 /Si 111 was carried out in an Intevac Modular GEN II MBE system. ThreeEuSe as an midinfrared material has recently been grown on PbSe substrates by molecular beam epitaxy MBE .1 The smallTe and PbSe under MBE growth conditions.1,8 In this work, we report results on the incorpo- ration of Bi2Se3

McCann, Patrick

152

Optical study of hyperfine coupling in the 7F0 and 5D0 states of two Eu3+ centers in CaF2 and CdF2  

Microsoft Academic Search

The hyperfine interaction in the 7F0 and 5D0 states in oxygen-compensated Eu3+ centers of C3v symmetry in CaF2 and CdF2 is reported. Optically detected nuclear-magnetic-resonance measurements determine (i) the hyperfine structure in the two states and (ii) their nuclear Zeeman splittings. In addition, optical hole burning is used to measure (iii) the quadratic electronic Zeeman effect on the 7F0--> 5D0

A. J. Silversmith; A. P. Radlinski; N. B. Manson

1986-01-01

153

Magnetic anisotropy of cobalt nanoparticle 2D arrays grown on corrugated MnF2(1 1 0) and CaF2(1 1 0) surfaces  

NASA Astrophysics Data System (ADS)

Cobalt nanoparticle 2D arrays with different effective thicknesses of cobalt layer (2 nm < deff < 10 nm) were grown by molecular beam epitaxy on CaF2(1 1 0)/Si(0 0 1) and MnF2(1 1 0)/CaF2(1 1 0)/Si(0 0 1) substrates with corrugated morphology of the surface. Surface morphology analysis showed that for effective thickness of cobalt layer deff = 5 nm the lateral dimensions of cobalt islands are about 5-10 nm and the distances between the islands differs in a half along and across the grooves. In both types of the heterostructures the shape of hysteresis loops measured by LMOKE depend on orientation of in-plane magnetic field relative to the direction of the grooves. The azimuthal dependence of coercive field Hc in Co/CaF2(1 1 0)/Si(0 0 1) structures corresponds to Stoner-Wohlfarth model's predictions, which takes into account the anisotropy of individual particles. In contrast to that, in Co/MnF2(1 1 0)/CaF2(1 1 0)/Si(0 0 1) structures these dependences are analogous to those predicted by the model based on account of magnetic-dipole interaction between particles which are placed in chains (chain-of-spheres-model). Possible explanations of the difference in magnetic anisotropy are suggested.

Baranov, D. A.; Krichevtsov, B. B.; Gastev, S. V.; Banschikov, A. G.; Fedorov, V. V.; Koshmak, K. V.; Suturin, S. M.; Sokolov, N. S.

2013-02-01

154

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

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

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

2015-04-01

155

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

NASA Astrophysics Data System (ADS)

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

Schwab, B. E.

2004-12-01

156

Formation of hydroxyapatite onto glasses of the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives.  

PubMed

New bioactive glasses with compositions based on the CaO-MgO-SiO(2) system and additives of B(2)O(3), P(2)O(5), Na(2)O, and CaF(2) were prepared. The in vitro mineralization behaviour was tested by immersion of powders or bulk glasses in simulated body fluid (SBF). Monitoring of ionic concentrations in SBF and scanning electron microscopy (SEM) observations at the surface of the glasses were conducted over immersion time. Raman and infrared (IR) spectroscopy shed light on the structural evolution occurring at the surface of the glasses that leads to formation of hydroxyapatite. PMID:16309741

Agathopoulos, S; Tulyaganov, D U; Ventura, J M G; Kannan, S; Karakassides, M A; Ferreira, J M F

2006-03-01

157

Improved Reproducibility in CaF2/Fe3Si/CaF2 Ferromagnetic Resonant Tunneling Diodes on Si(111) Substrates by Selected-Area Molecular Beam Epitaxy  

NASA Astrophysics Data System (ADS)

CaF2 (3 nm)/Fe3Si (5 nm)/CaF2 (3 nm) ferromagnetic resonant tunneling diodes (RTDs) approximately 200 nm in diameter were grown on an n+-Si(111) substrate through SiO2 hole arrays by selected-area molecular beam epitaxy (MBE). Selected-area MBE improved the yield of negative differential resistance (NDR) observed in the current-voltage (J-V) characteristics. Approximately 40% of the RTDs showed clear NDR in the room temperature J-V characteristics, where the forward bias was applied to the Fe3Si upper layers with respect to the n+-Si substrate.

Sadakuni-Makabe, Kenji; Suzuno, Mitsushi; Harada, Kazunori; Akinaga, Hiro; Suemasu, Takashi

2010-06-01

158

Multi-phonon-assisted relaxation and Yb3+ sensitized bright red-dominant upconversion luminescence of Ho3+ in YF3-BaF2-Ba(PO3)2 glass  

NASA Astrophysics Data System (ADS)

Unusual bright red-dominant upconversion light was observed in Ho3+/Yb3+ co-doped YF3-BaF2-Ba(PO3)2 glasses excited by the 980-nm laser diode at room temperature. The integral intensity ratios of the red upconversion emission to the green one reached about 10:1 in optimized 0.125Ho3+-15Yb3+ co-doped sample. In order to find out its behind-the-scene mechanism, the optical properties and the phonon-assisted relaxations on the excited levels of Ho3+ in our samples were investigated. Additionally, the effects of the concentrations of the doping ions, excitation pump power, and temperature on the upconversion emissions were also systematically studied. These results revealed that the proper phonon frequency of fluorophosphate glasses, the efficient phonon-assisted relaxations from 5I6 to 5I7 levels (4,960 s-1), and the long lifetime of the 5I7 (about 2.8 ms) levels should be responsible for bright red upconversion emission at a much greater concentration ratio of C{Yb/3+}/C{Ho/3+}.

Lai, Boyuan; Feng, Li; Zhang, Jianhui; Wang, Jing; Su, Qiang

2013-01-01

159

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

PubMed

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

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

2015-05-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

161

Restricted open-shell configuration interaction cluster calculations of the L-edge X-ray absorption study of TiO(2) and CaF(2) solids.  

PubMed

X-ray metal L-edge spectroscopy has proven to be a powerful technique for investigating the electronic structure of transition-metal centers in coordination compounds and extended solid systems. We have recently proposed the Restricted Open-Shell Configuration Interaction Singles (ROCIS) method and its density functional theory variant (DFT/ROCIS) as methods of general applicability for interpreting such spectra. In this work, we apply the ROCIS and DFT/ROCIS methods for the investigation of cluster systems in order to interpret the Ca and Ti L-edge spectra of CaF2 and TiO2 (rutile and anatase), respectively. Cluster models with up to 23 metallic centers are considered together with the hydrogen saturation and embedding techniques to represent the extended ionic and covalent bulk environments of CaF2 and TiO2. The experimentally probed metal coordination environment is discussed in detail. The influence of local as well as nonlocal effects on the intensity mechanism is investigated. In addition, the physical origin of the observed spectral features is qualitatively and quantitatively discussed through decomposition of the dominant relativistic states in terms of leading individual 2p-3d excitations. This contribution serves as an important reference for future applications of ROCIS and DFT/ROCIS methods in the field of metal L-edge spectroscopy in solid-state chemistry. PMID:24871209

Maganas, Dimitrios; DeBeer, Serena; Neese, Frank

2014-07-01

162

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)

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.

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

1976-01-01

163

SHELL MODEL CALCULATIONS OF POINT DEFECT FORMATION ENERGIES IN FLUORITE CRYSTALS  

Microsoft Academic Search

RCsumC. - Les energies de formation des defauts de Frenkel dans CaF2, SrF2, BaF2 et U02, sont calculees theoriquement. Ces valeurs sont comparees aux determinations experimentales. L'accord est bon dans le cas de CaF2 et BaF2. Le mauvais accord dans le cas de U02 conduit a suggerer le reexamen de I'interpretation des resultats experimentaux. Abstract. - Shell model potentials are

C. R. A. CATLOW; M. J. NORGETT

1973-01-01

164

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

PubMed

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

Malherbe, Cedric; Eppe, Gauthier; Gilbert, Bernard

2014-08-19

165

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

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

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

2014-06-01

166

Effect of the parameters of dynamic hot pressing on the structure and properties of the powder material ZhGrO, 8D2N3G3CaF 2 14 I. Initial porosity, work of compaction, sintering temperature and time, technological gap  

Microsoft Academic Search

The powdered antifriction iron base material ZhGrO,SD2N3G3CaF214 [I] is obtained from a multicomponent charge with the following composition, (wt.) %: 0.8 C; 2 Cu; 3 Mn; 3 Ni; 14 CaF2, the remainder Fe, by the method of dynamic hot pressing (DHP) of porous compacts. In the present work we investigate the effect of the parameters of DHP on the structure

Yu. G. Dorofeev; G. Sh. Musaélov; A. T. Mamedov

1990-01-01

167

Fiber and Integrated Optics, 19, 211-217 (2000) A Review of IR Transmitting, Hollow Waveguides  

E-print Network

from plastic, metal, or glass tubes that have highly reflective coatings deposited on the inside Examples Glass Heavy metal fluoride-HMFG Germanate Chalcogenide ZBLAN - (ZrF4-BaF2-LaF3-AlF3-NaF) GeO2-Pb

168

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

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

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

169

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

SciTech Connect

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

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

2011-11-01

170

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

171

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

172

Dielectric characterisation of Barium Fluoride at cryogenic temperatures using TE 011 and quasi TE 0mn mode dielectric resonators  

Microsoft Academic Search

Barium Fluoride (BaF2), mainly used in optical applications, has similar properties to those of CaF2 but better stability under environmental conditions. In this paper, we report measurements of loss tangent and the real part of the relative permittivity ?r of single crystal BaF2 in the temperature range from 14 to 290K at frequencies of 8, 10.4, 12.1, 17.6, 21.1 and

M. V. Jacob; J. G. Hartnett; J. Mazierska; J. Krupka; M. E. Tobar

2006-01-01

173

Nanosecond UV laser damage and ablation from fluoride crystals polished by different techniques  

Microsoft Academic Search

Ablation thresholds and damage behavior of cleaved and polished surfaces of CaF2, BaF2, LiF and MgF2 subjected to single-shot irradiation with 248 nm\\/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. For CaF2, standard polishing yields an ablation threshold of typically 20 J\\/cm2. When the surface is polished chemo-mechanically, the threshold can be

M. Reichling; J. Sils; H. Johansen; E. Matthias

1999-01-01

174

Crystallization of heavy metal fluoride glasses  

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

175

Enhanced refractive index without absorption in optical fibers via an indirect incoherent pump field  

NASA Astrophysics Data System (ADS)

We demonstrate a scheme for realizing the refractive index with zero absorption in an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF optical fiber. It is found that the refraction index of the probe laser can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optical-fiber communication.

Ge, Qiang

2014-12-01

176

19F nuclear relaxation in an ionic conductor : TlSn2F5 Laboratoire de Chimie des Matriaux (*), E.N.S.C.M., 8, rue de l'Ecole-Normale, 34075 Montpellier, France  

E-print Network

which make this compound one of the best ionic conductors via the F- ions. J. Physique - LETTRES 42 on compounds with the fluo- rite structure : CaF2 [1], PbF2 [2], BaF2 [3] or on com- pounds with a derived the fluorine conductivity in ionic conductors : , - weak coordination of the fluorine ion, - structures

Paris-Sud XI, Université de

177

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

178

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)

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.

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

1994-01-01

179

Lithium self-diffusion in some heavy metal fluoride glasses  

Microsoft Academic Search

Li self-diffusion has been studied below Tg in a series of ZrF4–BaF2–LaF3–LiF glasses with LiF contents of 10, 20, and 30mol%, respectively. The DLi? values range between about 10?12 and 10?15cm2\\/s and increase with increasing LiF content from 10 to 20% by two orders of magnitude. The stable isotopes 6Li (enriched) and 7Li and an SNMS depth profiling were used.

Anna Buksak; Günther H. Frischat; Gerhard Heide

2007-01-01

180

Transport processes in heavy metal fluoride glasses  

Microsoft Academic Search

Na self-diffusion, Li self-diffusion, Na+–Li+ ion exchange, electrical conductivity, and mechanical relaxation have been studied below Tg on glasses of the system ZrF4–BaF2–LaF3–AF (A=Na, Li), with A=10, 20, 30mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of

G. H. Frischat; A. Buksak; G. Heide; B. Roling

2007-01-01

181

Sodium self-diffusion in some heavy metal fluoride glasses  

Microsoft Academic Search

Na self-diffusion has been studied below Tg in a series of ZrF4–BaF2–LaF3–NaF glasses with NaF contents of 10, 20, and 30 mol%, respectively. The DNa? values range between about 10?12 and 10?14 cm2\\/s and drop exponentially with increasing NaF content. For the precision of the diffusion data an anhydrous deposition of the radioactive tracer 22Na on the highly reactive glass

Anna Buksak; Günther H Frischat

2003-01-01

182

JOURNAL DE PHYSIQUE Colloque C9, suppl6ment au n012, Tome 48, d6cembre ,1987  

E-print Network

, La1 and L 2,3 P2,15 l i n e s of neodymium, a s well a s on the L emission band 3 o f lanthanum and L the doped crystals i n comparison with the reference samples: BaF2 LaF3 and a metallic neodymium allowed us t o describe the role o f the 4f electrons of neodymium and of the 4f s h e l l of lan- thanum i n t h

Boyer, Edmond

183

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

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

184

COMMUNICATIONS Midinfrared photoluminescence from IVVI semiconductors  

E-print Network

substrates in an Intevac GEN II modular MBE system. Typical structures consisted of a 20-Ã?-thick CaF2 layer by molecular beam epitaxy MBE .2 In spite of a more than 12% lattice parameter mis- match and a 700% thermalSe/ PbSrSe multiple quantum well MQW materials grown by MBE on BaF2 substrates was reported.5 Similar MQW

McCann, Patrick

185

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

NASA Technical Reports Server (NTRS)

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.

Stanford, Malcolm K.; DellaCorte, Christopher

2003-01-01

186

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

NASA Technical Reports Server (NTRS)

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).

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

1994-01-01

187

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

SciTech Connect

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

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

2001-06-24

188

Identification of hydrogen isotopes with the BaF 2 electromagnetic calorimeter TAPS  

Microsoft Academic Search

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

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

1996-01-01

189

BAF(2) POST-DEPOSITION REACTION PROCESS FOR THICK YBCO FILMS.  

SciTech Connect

The basic processes of the so-called BaF{sub 2} process for the formation of YBa{sub 2}Cu{sub 3}O{sub 7}, YBCO, films as well as its advantages over the in situ formation processes are discussed in the previous chapter. The process and the properties of YBCO films by this process were also nicely described in earlier articles by R. Feenstra, et al. Here, we will discuss two pertinent subjects related to fabrication of technologically viable YBCO conductors using this process. These are (1) the growth of thick (>> 1 {micro}m) c-axis-oriented YBCO films and (2) their growth rates. Before the detail discussions of these subjects are given, we first briefly discuss what geometrical structure a YBCO-coated conductor should be. Then, we will provide examples of simple arguments for how thick the YBCO films and how fast their growth rates need to be. Then, the discussions in the following two sections are devoted to: (1) the present understanding of the nucleation and the growth process for YBCO, and why it is so difficult to grow thick c-axis-oriented films (> 3 {micro}m), and (2) our present understanding of the YBCO growth-limiting mechanism and methods to increase the growth rates. The values of critical-current densities J{sub c} in these films are of primary importance for the applications,. and the above two subjects are intimately related to the control of J{sub c} of the films. In general, the lower the temperatures of the YBCO formation are the higher the values of J{sub c} of the films. Thus, the present discussion is limited to those films which are reacted at {approx}735 C. This is the lowest temperature at which c-axis-oriented YBCO films (1-3 {micro}m thick) are comfortably grown. It is also well known that the non-c-axis oriented YBCO platelets are extremely detrimental to the values of J{sub c} such that their effects on J{sub c} dwarf essentially all of other microstructural effects which control J{sub c}. Hence, the discussion given below is mainly focused on how to avoid the growth of these crystallites when the films are thick and/or the growth rates are high.

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

2001-07-12

190

Phase Diagram for Nanostructuring CaF2 Surfaces by Slow Highly Charged Ions  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

191

Brillouin lasing with a CaF2 whispering gallery mode resonator.  

PubMed

Stimulated Brillouin scattering with both pump and Stokes beams in resonance with whispering gallery modes of an ultrahigh Q calcium fluoride resonator is demonstrated for the first time. The resonator is pumped with 1064 nm light and has 3 muW Brillouin lasing threshold. The scattering is observed due to the unique morphology of the resonator reducing the phase mismatch between the optical modes and the hypersound wave. PMID:19257418

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

2009-01-30

192

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

E-print Network

a lasing threshold of the order of 100 W, owing mostly to a high intracavity intensity buildup factor possible by the ultrahigh optical quality factor of the cavity, of the order of Q=5 1010 . Stokes. However, the Q factor of fused-silica cavities is subject to deg- radation due to atmospheric water

193

Efficient Raman laser based on a CaF2 resonator Ivan S. Grudinin1,  

E-print Network

for higher Q factors and the associated in- tracavity optical power buildup, which along with a higher Raman threshold is made pos- sible by the ultrahigh optical quality factor of the cavity, which is on the order as they are compact and fiber-compatible. Their high optical Q factors make it possible to easily achieve high

194

Slag Metal Reactions in Binary CaF2-Metal Oxide Welding Fluxes  

E-print Network

submerged arc welds on carbon steel plate. Supplementary argon shielding was used to prevent atmospheric fluxes may decompose into suboxides in the presence of welding arcs, thereby providing higher levels of 0 chemically, may decompose into suboxides in the presence of the welding arc plasma. Such oxides produce

Eagar, Thomas W.

195

Design and characterization of achromatic 132° retarders in CaF2 and fused silica  

Microsoft Academic Search

Mueller matrix ellipsometers (MMEs) are known to be less affected by noise if the compensators have a 132° phase shift between the slow and fast axis. This paper reports on the design and characterization of two custom-made achromatic compensators with minimal deviation from 132° retardation as a function of wavelength. The compensators are based on the dual Fresnel rhomb geometry.

F. Stabo-Eeg; M. Kildemo; E. Garcia-Caurel; M. Lindgren

2008-01-01

196

Transformation of color centers during hologram recording in an additively colored CaF2 crystal  

NASA Astrophysics Data System (ADS)

When holograms are recorded on color centers in calcium fluoride crystals, these centers undergo spatial redistribution in the crystal bulk, which is accompanied by their transformation. The nature of this transformation has been investigated by optical spectroscopy and confocal scanning microscopy. It is shown that, under the recording conditions we used, the degree of center aggregation increases in both minima and maxima of the interference field in which the recording performed. The enhanced aggregation in field minima is caused by the increase in the concentration color centers, while the additional aggregation in maxima is determined by the specific conditions of hologram recording: the wavelength and power density of recording radiation and the crystal temperature.

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

2014-03-01

197

Generation of Kerr combs in MgF2 and CaF2 microresonators  

Microsoft Academic Search

We report on a study of hyper-parametric oscilla- tion in high-Q calcium fluoride and magnesium fluoride optical microresonators, and show that, magnesium fluoride microres- onators generate wider Raman-free Kerr frequency combs at telecom wavelengths, in contrast with calcium fluoride ones. We observed 30 nm wide frequency combs in magnesium fluoride microresonators pumped with only 2 mW of continuous wave 1543

W. Liang; A. B. Matsko; A. A. Savchenkov; V. S. Ilchenko; D. Seidel; L. Maleki

2011-01-01

198

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

PubMed

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

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

199

Structural, electronic and elastic properties of some fluoride crystals: an ab initio study  

NASA Astrophysics Data System (ADS)

The structural, electronic and elastic properties, as well as the IR and Raman central zone phonon frequencies of CaF 2, SrF 2 and BaF 2, have been evaluated by using the periodic ab initio linear combination of atomic orbitals method implemented in the CRYSTAL package. The Hartree-Fock and different density functionals, namely the local density (LDA) and the generalized gradient (GGA), as well as the hybrid B3LYP, Hamiltonians, have been used. The binding energy, equilibrium lattice parameter, elastic constants ( Cij) and central zone phonon frequencies exhibit a regular and consistent trend in the series, in good agreement with experimental data.

Mérawa, Mohammadou; Llunell, Miquel; Orlando, Roberto; Gelize-Duvignau, Michel; Dovesi, Roberto

2003-01-01

200

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

NASA Technical Reports Server (NTRS)

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.

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

1978-01-01

201

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

E-print Network

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.

Roman Shendrik; Evgeny Radzhabov

2013-08-19

202

PHYSICS LETTERS 3 December 1973Volume 46A, number 2 PHOTON ECHOES IN LaF3 :Nd3+ AND YAG:Nd3+*  

E-print Network

+ in the three crystalline hosts. The photon echo amplitude in each crystal de- pended upon both magnetic field, Columbia University, New York, N. Y. 10027, USA Received 1 October 1973 Magnetic field and temperature on sample tempera- ture and applied magnetic field. In all three crystals, the ground state 419,2 is split

203

Optical properties of Er3+-doped fluoride glass channel waveguides  

NASA Astrophysics Data System (ADS)

The latest results on the preparation and characterization of Er3+-doped fluoride glass channel waveguides are presented. The waveguides are prepared by means of ion exchange between fluoride and chloride ions, through a silica mask, on ZBLA (ZrF4-BaF2-LaF3-AlF3) fluoride glass substrate. Single mode propagation is demonstrated at 1.55 ?m for a 10-mm long, 5-?m wide waveguide. Propagation losses are found to be not greater than 0.28 dB/cm. An "on/off' gain of 3.9 dB is measured at the output of a 1% Er3+-4% Ce3+-doped fluoride waveguide, with about 240 mW incident pump power at 980 nm. Modelisation studies show that net gain could be achieved in (Er3+, Ce3+) doubly-doped and (Er3+, Ce3+, Yb3+) triply doped fluoride waveguides.

Haquin, Herve; Vasilief, Ion; Fonteneau, Gilles; Nazabal, Virginie; Adam, Jean-Luc; Guy, Stephan; Jacquier, Bernard; Couchaud, Maurice; Rabarot, Maurice; Fulbert, Laurent

2004-06-01

204

Fluoride glass starting materials - Characterization and effects of thermal treatment  

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

205

Electronic Structure of Alkaline-Earth Fluorides Studied by Model Clusters. I. Ground State  

NASA Astrophysics Data System (ADS)

We present the results of molecular-orbital calculations for alkaline-earth fluorides, i.e., CaF2, SrF2 and BaF2.The discrete variational (DV) X? method is applied to two types of model clusters, i.e., one centered at the cation site and the other at the anion site. Electrostatic potential due to the ions outside the cluster has been calculated with direct summation of the Coulomb potential of point charges by the Coker's method.The electronic structures obtained by the present models agree well with those obtained by photoelectron spectroscopy.The outer-most Ba2+ 5 p core band is found to have a width of less than 2 eV which is much smaller than the proposed value in interpreting the excitation spectrum of Auger free luminescence and the total photoelectric yield spectrum.The ionic radii of alkaline-earth and fluorine ions in CaF2, SrF2 and BaF2 are determined by investigating the charge distribution. The ionic radii thus obtained are in good agreement with the crystal values of Shannon and Prewitt.

Ikeda, Takashi; Kobayashi, Hideyuki; Ohmura, Yoshihiro; Nakamatsu, Hirohide; Mukoyama, Takeshi

1997-04-01

206

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

207

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

208

Microwave-assisted rapid synthesis and characterization of CaF2 particles-filled cellulose nanocomposites in ionic liquid.  

PubMed

In this article, we try to compound cellulose/alkali earth metal fluorides (MF2, M=Ca, Mg, Sr, Ba) nanocomposites via microwave-assisted ionic liquid method, wherein cellulose/CaF2 and cellulose/MgF2 were successfully synthesized through this method while cellulose/SrF2 and cellulose/BaF2 could not be synthesized. We focused on the synthesis of cellulose/CaF2 and investigated the influences of the different time and different temperature for the synthesis of cellulose/CaF2 nanocomposites. The influence of different heating methods such as oil-bath heating method was also studied. Ionic liquid ([Bmim][BF4]) was used for dissolving microcrystalline cellulose and providing the source of fluoride ionic and the alkali earth metal nitrate (Ca(NO3)2, Mg(NO3)2, Sr(NO3)2, and Ba(NO3)2) was used as the reaction initiator. They were investigated by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TG), derivative thermogravimetric (DTG), and energy-dispersive X-ray spectra (EDS). The different heating modes have influence on the morphology and property. The different temperature and heating time also have a certain influence on the morphology and crystallinity of calcium fluoride. PMID:25659685

Deng, Fu; Fu, Lian-Hua; Ma, Ming-Guo

2015-05-01

209

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

PubMed Central

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

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

2012-01-01

210

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

SciTech Connect

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

Bredeweg, T. A.; Fowler, M. M.; Bond, E. M.; Chadwick, M. B.; Hunt, L. F.; O'Donnell, J. M.; Rundberg, R. S.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M. [Los Alamos National Laboratory, Los Alamos, NM, 87545 (United States); Becker, J. A.; Clement, R. R. C.; Esch, E.-I.; Macri, R. A.; Wu, C.-Y. [Lawrence Livermore National Laboratory, Livermore, CA, 94550 (United States); Ethvignot, T.; Granier, T. [CEA-DAM, BP 12, Bruyeres-le-Chatel, 91680 (France); Yurkon, J. E. [National Superconducting Cyclotron Laboratory, East Lansing, MI, 48824 (United States)

2006-03-13

211

Graphitic carbon grown on fluorides by molecular beam epitaxy.  

PubMed

We study the growth mechanism of carbon molecules supplied by molecular beam epitaxy on fluoride substrates (MgF2, CaF2, and BaF2). All the carbon layers form graphitic carbon with different crystallinities depending on the cation. Especially, the growth on MgF2 results in the formation of nanocrystalline graphite (NCG). Such dependence on the cation is a new observation and calls for further systematic studies with other series of substrates. At the same growth temperature, the NCG on MgF2 has larger clusters than those on oxides. This is contrary to the general expectation because the bond strength of the carbon-fluorine bond is larger than that of the carbon-oxygen bond. Our results show that the growth of graphitic carbon does not simply depend on the chemical bonding between the carbon and the anion in the substrate. PMID:23286607

Jerng, Sahng-Kyoon; Lee, Jae Hong; Kim, Yong Seung; Chun, Seung-Hyun

2013-01-01

212

Tribological Performance of PM300 Solid Lubricant Bushings for High Temperature Applications  

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

213

Graphitic carbon grown on fluorides by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

We study the growth mechanism of carbon molecules supplied by molecular beam epitaxy on fluoride substrates (MgF2, CaF2, and BaF2). All the carbon layers form graphitic carbon with different crystallinities depending on the cation. Especially, the growth on MgF2 results in the formation of nanocrystalline graphite (NCG). Such dependence on the cation is a new observation and calls for further systematic studies with other series of substrates. At the same growth temperature, the NCG on MgF2 has larger clusters than those on oxides. This is contrary to the general expectation because the bond strength of the carbon-fluorine bond is larger than that of the carbon-oxygen bond. Our results show that the growth of graphitic carbon does not simply depend on the chemical bonding between the carbon and the anion in the substrate.

Jerng, Sahng-Kyoon; Lee, Jae Hong; Kim, Yong Seung; Chun, Seung-Hyun

2013-01-01

214

Fluorescence and phosphorescence of photomultiplier window materials under electron irradiation  

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

215

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

NASA Technical Reports Server (NTRS)

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

Stanford, Malcolm K.; DellaCorte, Christopher

2002-01-01

216

Ceramic planar waveguide structures for amplifiers and lasers  

NASA Astrophysics Data System (ADS)

Ceramic and crystalline weakly guiding optical fibres with the core - cladding refractive index difference of 10-2 - 10-4 are fabricated by a hot pressing method. The waveguides with one or several cores for operation in the spectral range 0.2 - 5 ?m are produced. The waveguides are based on CaF2, SrF2, and BaF2 ceramics and crystals and their solid solutions doped with trivalent Pr, Nd, Tb, Dy, Yb, Ho, Er, and Tm ions, as well as on LiF ceramics and crystals with colour centres. The first results of investigation of the lasing properties of ceramic SrF2 : NdF waveguides under diode pumping are presented, and the prospects of further investigation are discussed.

Konyushkin, V. A.; Nakladov, A. N.; Konyushkin, D. V.; Doroshenko, Maxim E.; Osiko, Vyacheslav V.; Karasik, Aleksandr Ya

2013-01-01

217

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

218

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

NASA Technical Reports Server (NTRS)

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.

Dellacorte, C.; Edmonds, B. J.

1995-01-01

219

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

NASA Astrophysics Data System (ADS)

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

Stanford, Malcolm K.; Dellacorte, Christopher

2006-03-01

220

Graphitic carbon grown on fluorides by molecular beam epitaxy  

PubMed Central

We study the growth mechanism of carbon molecules supplied by molecular beam epitaxy on fluoride substrates (MgF2, CaF2, and BaF2). All the carbon layers form graphitic carbon with different crystallinities depending on the cation. Especially, the growth on MgF2 results in the formation of nanocrystalline graphite (NCG). Such dependence on the cation is a new observation and calls for further systematic studies with other series of substrates. At the same growth temperature, the NCG on MgF2 has larger clusters than those on oxides. This is contrary to the general expectation because the bond strength of the carbon-fluorine bond is larger than that of the carbon-oxygen bond. Our results show that the growth of graphitic carbon does not simply depend on the chemical bonding between the carbon and the anion in the substrate. PMID:23286607

2013-01-01

221

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

NASA Technical Reports Server (NTRS)

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

Frey, Bradley J.; Leviton, Douglas B.

2004-01-01

222

Bright white light through up-conversion of a single NIR source from sol-gel-derived thin film made with Ln3+-doped LaF3 nanoparticles.  

PubMed

White light was generated from a single silica thin film made with Yb0.75La0.2Eu0.05F3, La0.45Yb0.5Er0.05F3, and La0.75Yb0.2Tm0.05F3 nanoparticles by exciting with a single source near-infrared light (980 nm CW diode laser). Eu3+ and Tm3+ ions are responsible for red and blue emission, respectively. Er3+ ion is responsible for green as well as red emission. The Commission Internationale de l'Eclairage (CIE) coordinates of the resulting light were easily adjusted by controlling the concentration of Ln3+ (Eu3+, Er3+, Tm3+) ions in the nanoparticles as well as the concentration of Ln3+-doped nanoparticles in the sol-gel thin layer. PMID:16144374

Sivakumar, Sri; van Veggel, Frank C J M; Raudsepp, Mati

2005-09-14

223

Effect of group velocity dispersion on supercontinuum generation and filamentation in transparent solids  

NASA Astrophysics Data System (ADS)

We experimentally investigate the spectral extent and spectral profile of the supercontinuum (SC) generated in transparent solids: barium fluoride, calcium fluoride, and fused silica upon irradiation by intense femtosecond-long pulses of 800, 1,380, and 2,200 nm light. These wavelengths correspond to the normal and anomalous group velocity dispersion (GVD) regimes in fused silica calcium fluoride and barium fluoride. We observe an isolated (anti-Stokes) wing on the blue side most prominently in fused silica but also in CaF2. The SC conversion efficiency is measured for the long wavelengths used in our experiments. We also present results on filamentation in BaF2 in the anomalous GVD regime, including visualization of focusing-refocusing events within the crystal; the size of a single filament is also determined. The 15-photon absorption cross section in BaF2 is deduced to be 6.5 × 10-190 cm30 W-15 s-1.

Dharmadhikari, Jayashree A.; Deshpande, Rucha A.; Nath, Arpita; Dota, Krithika; Mathur, Deepak; Dharmadhikari, Aditya K.

2014-10-01

224

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

NASA Technical Reports Server (NTRS)

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).

Bhushan, B.; Gray, S.

1978-01-01

225

Epitaxial Semiconductor/fluoride Composites by MBE.  

NASA Astrophysics Data System (ADS)

Composites consisting of nanocrystallites of Si and Ge embedded in epitaxial CaF_2 on Si(111) substrates have been fabricated by MBE and characterized. The volume fraction of Si in the composites ranged from less than 1% to 57% and the smallest Si particle sizes observed by TEM had linear dimensions of 20 nm with an average linear dimension of 40 nm. The Si nanocrystallites observed by TEM have oblate (pancake) shapes in the plane of the CaF _2 host. Ion channeling results yield Ca chi minima of less than 5% near the surface indicating that the CaF_2 host is of high crystalline quality. No photoluminescence was observed from these Si nanocrystallites at room temperature from 380 nm to 1000 nm using 351 nm excitation and from 440 nm to 800 nm using 442 nm excitation. The majority of both Si and Ge, deposited in small amounts at elevated temperatures on the surface of epitaxial CaF_2 on Si(111) substrates, does not stick. Experiments suggest that chemical reactions between a Si flux and a CaF_2 surface are minimal at 850^circC, implying that thermal desorption is the loss mechanism. A cluster growth model was developed that indicates the amount of either Si or Ge that will stick to a CaF_2 (111) surface has a linear dependence on growth rate and time and an exponential dependence on inverse temperature in the limit of low Si or Ge coverage. An exponential 1/kT fit to the re-evaporation data yields activation energies of 2.0 +/- 0.2 eV and 0.60 +/- 0.05 eV for Si and Ge respectively. Within the model, these activation energies represent the difference between the activation energies for thermal desorption and surface diffusion. To obtain Si nanocrystallites of dimension less than 10 nm, an order of magnitude prediction of cluster size as a function growth parameters suggests typical Si growth rate of 0.1 nm/s and growth times less than 5 s are required at 850^circC. Both CaF_2 and BaF _2 as well as fluoride alloys were grown epitaxially on Si(111) and Si(001) substrates using Knudsen cells designed and constructed for this purpose. The cells use a graphite heating element. The design criteria that were met include cell crucible temperatures up to 1600 ^circC at a power consumption of about 1 KW, thin film thickness uniformities within +/-2% over a 4^{ ''} wafer, and mass 28(primarily N_2 and CO) partial pressures in the low 10^{-9} mb range during CaF_2 evaporation.

Taylor, Anthony Park

226

Commercial Production of Heavy Metal Fluoride Glass Fiber in Space  

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

227

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

NASA Astrophysics Data System (ADS)

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

Xie, Ping; Gosnell, T. R.

1995-05-01

228

ZBLAN Microgravity Study  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

229

High Purity Zirconium Tetrafluoride For Fluoride Glass Applications  

NASA Astrophysics Data System (ADS)

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

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

1989-06-01

230

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

PubMed

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

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

2014-04-01

231

Transport processes in heavy metal fluoride glasses  

NASA Astrophysics Data System (ADS)

Na self-diffusion, Li self-diffusion, Na+ Li+ ion exchange, electrical conductivity, and mechanical relaxation have been studied below Tg on glasses of the system ZrF4 BaF2 LaF3 AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na+ Li+ ion exchange reach a minimum at ? 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F- and Li+ ions to the transport. Moreover, the presence of the three partially interacting mobile species F-, Na+, Li+ obviously leads to an anionic cationic mixed ion effect. Applying the Nernst Einstein equation to the Li+ transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li+ movement via energetically suitable sites near F- ions. Likewise the Nernst Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.

Frischat, G. H.; Buksak, A.; Heide, G.; Roling, B.

2007-05-01

232

A novel 2-?m pulsed fiber laser based on a supercontinuum source and its application to mid-infrared supercontinuum generation  

NASA Astrophysics Data System (ADS)

A new method to achieve 2-?m pulsed fiber lasers based on a supercontinuum (SC) is demonstrated. The incident pump light is a pulsed SC which contains a pump light and a signal light at the same time. The initial signal of the seed laser is provided by the incident pump light and amplified in the cavity. Based on this, we obtain a 2-?m pulsed laser with pulse repetition rate of 50 kHz and pulse width of 2 ns from the Tm-doped fiber laser. This 2-?m pulsed laser is amplified by two stages of fiber amplifiers, then the amplified laser is used for mid-infrared (mid-IR) SC generation in a 10-m length of ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. An all-fiber-integrated mid-IR SC with spectrum ranging from 1.8 ?m to 4.3 ?m is achieved. The maximal average output power of the mid-IR SC from the ZBLAN fiber is 1.24 W (average output power beyond 2.5 ?m is 340 mW), corresponding to an output efficiency of 6.6% with respect to the 790-nm pump power.

Yang, Wei-Qiang; Zhang, Bin; Hou, Jing; Yin, Ke; Liu, Ze-Jin

2014-05-01

233

A method for compensating the polarization aberration of projection optics in immersion lithography  

NASA Astrophysics Data System (ADS)

As the numerical aperture (NA) of 193nm immersion lithography projection optics (PO) increasing, polarization aberration (PA) leads to image quality degradation seriously. PA induced by large incident angle of light, film coatings and intrinsic birefringence of lens materials cannot be ignored. An effective method for PA compensation is to adjust lens position in PO. However, this method is complicated. Therefore, in this paper, an easy and feasible PA compensation method is proposed: for ArF lithographic PO with hyper NA (NA=1.2), which is designed by our laboratory, the PA-induced critical dimension error (CDE) can be effectively reduced by optimizing illumination source partial coherent factor ?out. In addition, the basic idea of our method to suppress pattern placement error (PE) is to adopt anti-reflection (AR) multi-layers MgF2/LaF3/MgF2 and calcium fluoride CaF2 of [111] crystal axes. Our simulation results reveal that the proposed method can effectively and quantificationally compensate large PA in the optics. In particular, our method suppresses the dynamic range of CDE from -12.7nm ~ +4.3nm to -1.1nm ~ +1.2nm, while keeping PE at an acceptable level.

Jia, Yue; Li, Yanqiu; Liu, Lihui; Han, Chunying; Liu, Xiaolin

2014-08-01

234

A method for estimating the local lattice distortions near a magnetic ion from ligand hyperfine parameters: Yb 3+ trigonal centers in SrF 2 and BaF 2  

Microsoft Academic Search

An empirical relationship describing the radial dependence of the nondipole part of the anisotropic constant for the ligand\\u000a hyperfine interaction in alkaline-earth fluorides is proposed. This relationship is used for calculating the distances between\\u000a the magnetic ion and the fluorine ions involved in its nearest environment. The results of the calculations are in good agreement\\u000a with the values obtained by

Ts. A. Gavasheli; D. M. Daraseliya; D. L. Dzhaparidze; R. I. Mirianashvili; O. V. Romelashvili; T. I. Sanadze

2006-01-01

235

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)

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.

El-Said, A. S.

2012-07-01

236

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

NASA Technical Reports Server (NTRS)

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

Stanford, M. K.; DellaCorte, C.

2004-01-01

237

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

NASA Technical Reports Server (NTRS)

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

Dellacorte, Christopher

1987-01-01

238

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

PubMed

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

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

2014-01-01

239

Photomultiplier window materials under electron irradiation - Fluorescence and phosphorescence  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

240

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

PubMed

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

Gallais, Laurent; Commandré, Mireille

2014-02-01

241

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

NASA Technical Reports Server (NTRS)

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

Dellacorte, Christopher

1988-01-01

242

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

243

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

244

Self-lubricating coatings for high-temperature applications  

NASA Technical Reports Server (NTRS)

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

Sliney, Harold E.

1987-01-01

245

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

NASA Astrophysics Data System (ADS)

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.

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

246

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

247

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

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.

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

248

Interfacial tension and contact angle variations of SUS304 melt in contact with solid oxides and CaO-SiO 2 Al 2 O 3 (CaF 2 ) slags at 1470°C  

Microsoft Academic Search

Study on the interfacial properties of SUS304 melt in contact with pedestal oxides and also liquid slags of varying chemistry\\u000a was carried out by using a combination of the sessile drop method and a X-ray fluoroscopic technique at 1470°C. Interfacial\\u000a tension and contact angle were obtained directly from a numerical solution of the Young-laplace equation. Surface tension\\u000a of SUS304 was

Sung-Mo Seo; Young-Hyun Paik; Dong-Sik Kim; Won-Pyo Lee

1996-01-01

249

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

SciTech Connect

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

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

2011-08-18

250

Spin-Lattice Relaxation Times of Cu2+ in CuSO4.5H2O and Yb3+ in CaF2 by Nuclear Dynamic Polarization  

Microsoft Academic Search

Dynamic polarization of protons in CuSO4.5H2O-doped ZnSO4.7H2O and F19 nuclei in Yb3+-doped calcium fluoride (trigonal sites) has been observed in the range 1.6-4.2°K. Concentration, temperature, and microwave-power dependencies of the polarization and relaxation times of the nuclei are measured, and these dependencies are deduced for the Cu2+ and Yb3+ electron relaxation times. Copper electrons are found to relax mainly by

J. S. Karra; Harvey Waldman

1969-01-01

251

2-D electron spin transient nutation spectroscopy of Lanthanoid ion Eu 2+ ( 8 S 7\\/2 ) in a CaF 2 single crystal on the basis of FT-pulsed electron spin resonance spectroscopy: Transition moment spectroscopy  

Microsoft Academic Search

This work demonstrates the usefulness of pulsed electron spin resonance (ESR)-based two-dimensional electron spin transient\\u000a nutation (2-D ESN) spectroscopy for complete assignments of complicated fine-structure hyperfine ESR spectra including hyperfine\\u000a forbidden transitions from electronic and nuclear high-spin systems. The 2-D ESN spectroscopy is termed transition moment\\u000a spectroscopy as spectra are acquired as a function of transition moment instead of transition

H. Matsuoka; K. Sato; D. Shiomi; T. Takui

2003-01-01

252

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

253

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

NASA Technical Reports Server (NTRS)

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.

Tucker, Dennis S.; Smith, Guy A.

2004-01-01

254

Picosecond passively mode-locked mid-infrared fiber laser  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

255

Mechanisms for the Crystallization of ZBLAN  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

256

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

NASA Astrophysics Data System (ADS)

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

Kumar, Malay

257

Sol-Gel Synthesis of Fluoride Glasses and Thin Films: the Effects of Processing on the Chemical, Physical, Optical, and Rare Earth Fluorescence Properties of Sol - Zbla Glasses.  

NASA Astrophysics Data System (ADS)

Fluoride glasses have the potential to be ultra -low loss optical fiber and active optical devices due to their intrinsic clarity, wide transmission window, and low phonon energy. Unfortunately, conventional processing methods have failed to produce defect free glasses, fibers, or thin films. However, sol-gel techniques offer high purity, low temperature processing routes conducive to high quality optics. Thus, a modified sol-gel technique was investigated as an alternative approach for fluoride glass production. Hydrous oxide gels and thin films were prepared by hydrolyzing an alcoholic solution of alkoxides and hydroxides. Subsequent fluorination of the gels in gaseous hydrogen fluoride led to the successful formation of ZBLA (rm 57ZrF _4-36BaF_2-4LaF _3-3AlF_3, in mol%) fluoride glasses. However, the resulting glasses had inferior optical properties. The thermal processing and analysis of these materials was then studied to determine the cause of the poor transparency and to find a remedy. The poor transparency of the sol-gel fluoride glasses was due to residual organics that led to carbon and reduced zirconium species that were strongly absorbing. However, optical quality glasses could be produced by removing these contaminants via treatment with a high temperature oxidizing atmosphere such as NF_3 or SF _6 without introducing other contaminants such as oxygen. The resulting glasses had chemical, electrical, mechanical, and optical properties commensurate with conventionally prepared glasses. It was also found that hydrocarbon contamination could be avoided altogether by using an inorganic sol-gel process involving the polymerization of zirconium hydroxychloride salts. To study the gel structure and local environment of rare earth dopants during thermal processing and conversion of the gel, Eu^{3+} fluorescence spectroscopy was employed. The Eu^{3+ } fluorescence revealed a change in site symmetry and decrease in host phonon energy upon fluorination. In addition to the well known red Eu^{3+ } luminescence, ultraviolet, blue, and green emissions were also observed in fluoride glasses and discovered to be concentration dependent. The Eu^ {3+} fluorescence was concluded to be a good probe for evaluating sol-gel fluoride materials and that the concentration dependence of the high energy emissions of Eu^{3+} was due to electric dipole-dipole and dipole-quadrupole cross relaxations.

Dejneka, Matthew J.

1995-01-01

258

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

259

A fluorocarbon plastic scintillator for neutron detection: Proof of concept  

NASA Astrophysics Data System (ADS)

The fast neutron nuclear reactions, such as 19F(n, ?)16N and 19F(n, p)19O, can be used to detect highly energetic neutrons due to their energy thresholds above which these activation reactions can occur. This was recently shown (Gozani et al., 2011 [2]) as a means to detect concealed nuclear materials via the detection of the high energy (?3 MeV) prompt neutrons emitted during the photofission process. Fluorine-loaded scintillation detectors, such as inorganic BaF2 and CaF2, and non-hydrogenous fluorocarbon (FC) liquid scintillators, such as Saint-Gobain BC-509 and Eljen Technology EJ-313, are possible candidates. The latter was selected and implemented in the above mentioned reference. In our paper, we propose a new pentafluorostyrene-based plastic scintillator (F-plastic) which can be a good alternative to the abovementioned scintillators. The fluorine content of F-plastic is equal to 3.73×1022 atoms/cm3, and the F/H ratio is 1.66. The fluorescence and radioluminescence spectra of the F-plastic display an emission maximum centered approximately at 420 nm. The light output measured for gamma rays is 3100±300 photons/MeV, which is approximately 30% of the light output of the standard EJ-200 plastic scintillator and is similar to EJ-313. The response of the F-plastic to neutrons and gamma rays is presented and compared to the EJ-200 scintillator. Additionally, the n/? pulse shape discrimination (PSD) was measured and showed improvement of the discrimination at neutron energies as high as 3 MeV.

Hamel, Matthieu; Sibczynski, Pawel; Blanc, Pauline; Iwanowska, Joanna; Carrel, Frédérick; Syntfeld-Ka?uch, Agnieszka; Normand, Stéphane

2014-12-01

260

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

E-print Network

layer of the n-Si/SiO2/Si3N4/LaF3/Pt field effect structure was used as the gate electrode experiments was an n-Si/SiO2/Si3N4/LaF3/Pt layer system (Fig. 1). The freshly prepared sensors showed a fast: 1 - Pt layer; 2 - LaF3 layer; 3 - SiO2/Si3N4 layer; 4 - n-Si; 5 - ohmic contact (Al); 6 ­ photo

Moritz, Werner

261

COMPARATIVE MEDICINE LABORATORY ANIMAL FACILITIES  

E-print Network

3.E.10 COMPARATIVE MEDICINE LABORATORY ANIMAL FACILITIES STANDARD OPERATING PROCEDURE for DISPOSAL applies to all Research staff and LAF staff disposing of glass waste in the LAF. 3. PROCEDURE: a. Glass

Krovi, Venkat

262

Insulators for Pb(1-x)Sn(x)Te  

NASA Technical Reports Server (NTRS)

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.

Tsuo, Y. H.; Sher, A.

1981-01-01

263

New infrared detectors and solar cells  

NASA Technical Reports Server (NTRS)

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

Sher, A.

1979-01-01

264

Broadband reflectance coatings for vacuum ultraviolet application  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

265

Fluoride thin film formation with low optical absorption by gas cluster ion beam assisted deposition  

NASA Astrophysics Data System (ADS)

Gas cluster ion beam (GCIB) shows characteristics of low-energy irradiation effect and dense energy deposition. GCIB-assisted deposition is expected to be used for high-quality fluoride film formation, although these films are sensitive to damage by ion irradiation. In this study, LaF 3 and MgF 2 films were deposited by SF 6-GCIB-assisted deposition. When the acceleration voltage was 3-7 kV, the deposited LaF 3 film had a high packing density, small columnar structure, and very flat surface. The average roughness of the LaF 3 film surface was 0.25 nm by the surface smoothing effect of the GCIB. The LaF 3 film density showed 5.90 g/cm 3, which was very close to the theoretical density of crystalline LaF 3. The refractive index ( n) of the LaF 3 film increased from 1.62 to 1.72 with an increase in the ion current density. The extinction coefficient ( k) was 1 × 10 -3 at a wavelength of 193 nm. By the deposition of a thin layer of Al 2O 3(extinction coefficient: 5 × 10 -3) on the quartz substrate as an interfacial film, a strong adhesive fluoride film was obtained.

Nakazawa, S.; Toyoda, N.; Mochiji, K.; Mitamura, T.; Yamada, I.

2007-08-01

266

Evaluation of Gamma-Ray Response of Tm: Single Crystals  

Microsoft Academic Search

Tm3+ doped BaF2 single crystal scintillator has been investigated. Undoped, 0.1, 0.5, and 1% Tm -doped BaF2 are compared in terms of their decay time, light yield, non-proportionality and energy resolution. The fast component of Tm doped BaF2 is characterized by a 5 ~ 6 ns decay time and it can be related to the Tm3+ 5d - 4f VUV

Naoto Abe; Yuui Yokota; Takayuki Yanagida; Noriaki Kawaguchi; Jan Pejchal; Akira Yoshikawa

2010-01-01

267

PS300 Tribomaterials Evaluated at 6500C by Bushing Test Rig  

NASA Technical Reports Server (NTRS)

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.

Striebing, Donald R.; DellaCorte, Christopher

2004-01-01

268

Reaction Sintering and Mechanical Properties of Hydroxyapatite-Zirconia Composites with Calcium Fluoride Additions  

Microsoft Academic Search

The effects of calcium fluoride (CaF2) additions on the densi- fication and mechanical properties of hydroxyapatite-zirconia composites (HA-ZrO2) were investigated. When small amount of CaF2 was added, the density of the composites was markedly enhanced. The reactions of HA with CaF2, which led to the formation of fluorapatite (FA), were attributed to the observed improvements in densification. When HA-20-vol%-ZrO2 com-

Hae-Won Kim; Young-Hag Koh; Byung-Ho Yoon; Hyoun-Ee Kim

2002-01-01

269

Chitosan conjugation: a facile approach to enhance the cell viability of LaF?:Yb,Er upconverting nanotransducers in human breast cancer cells.  

PubMed

In this study, chitosan functionalized LaF3:Yb,Er upconverting nanotransducers (UCNTs) with controlled size and shape have been successfully synthesized by a facile one pot precipitation method. The chitosan encapsulated UCNTs show bright upconversion fluorescence upon excitation with 974 nm NIR region. The average crystallite size of UCNTs about 7.6 nm was achieved using chitosan mediated synthesis. The FTIR result confirms the chitosan coating over the LaF3:Yb,Er nanoparticles. Due to the surface modification using natural biopolymer chitosan, the as-prepared nanocrystals show excellent biocompatibility even at high dose at 200 ?g/ml. To the best of our knowledge the presented work is the first report on in vitro analysis of chitosan conjugated LaF3:Yb,Er upconverting nanocrystals in human breast (MCF-7) cancer cells. These nanotransducers can be used as luminescent probes for bioimaging and deep tissue cancer therapeutic applications. PMID:25659702

Gayathri, Sethuraman; Ghosh, Oriparambil Sivaraman Nirmal; Sudhakara, P; Viswanath, Annamraju Kasi

2015-05-01

270

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films.  

PubMed

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

Lee, Hye Jin; Kim, Seuk Buom; Park, Yong Joon

2012-01-01

271

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

Microsoft Academic Search

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.

Hiroki Naito; Shinobu Fujihara; Toshio Kimura

2003-01-01

272

Titanium dioxide/calcium fluoride nanocrystallite for efficient dye-sensitized solar cell. A strategy of enhancing light harvest  

NASA Astrophysics Data System (ADS)

Enhancement of light harvest for dye excitation is a persistent objective in dye-sensitized solar cell (DSSC). We present here the fabrication of titanium dioxide/calcium fluoride (TiO2/CaF2) photoanodes for efficient DSSC applications. Owing to the interference effect of incident light beams reflected from TiO2/CaF2 and CaF2/electrolyte interfaces, the light intensity and therefore dye excitation have been markedly enhanced. The crystal structure and therefore photovoltaic performance are optimized by adjusting CaF2 dosage. A maximum power conversion efficiency of 7.66% is measured from the DSSC employing TiO2/0.5 wt% CaF2 nanocrystallite in comparison with 6.02% for the solar cell with pristine TiO2 anode.

Wang, Zubin; Tang, Qunwei; He, Benlin; Chen, Xiaoxu; Chen, Haiyan; Yu, Liangmin

2015-02-01

273

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

E-print Network

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

Moritz, Werner

274

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

PubMed

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

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

2015-01-14

275

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

276

Above-room-temperature continuous-wave mid-infrared photoluminescence from PbSe/PbSrSe quantum wells  

E-print Network

in an Intevac GEN II Modular MBE system. Before transfer to the growth chamber, freshly cleaved 1 cm 1 cm BaF2 grown by molecular-beam epitaxy MBE . IV­VI semiconductors have several unique properties that make them In this work, IV­VI quantum-well structures were grown on BaF2 111 substrates by MBE. Growth was car- ried out

McCann, Patrick

277

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

278

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)

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.

Yuan, Haojie

1992-09-01

279

Fluorite solubility in hydrous haplogranitic melts at 100 MPa David Dolejs *, Don R. Baker  

E-print Network

of fluorine enrichment in peralkaline rhyolites and calc-alkaline batholiths. On the other hand, high Ca; Granite; Rhyolite; Melt; Thermodynamics 1. Introduction Fluorite, CaF2, is the most common fluoride

Long, Bernard

280

Charge carrier trapping and thermoluminescence in calcium fluoride based phosphors  

NASA Astrophysics Data System (ADS)

This paper reviews recent progress in the understanding and applications of the phenomenon of thermoluminescence (TL) in calcium fluoride based phosphors. The formation of charge carrier traps in rare earth and Mn doped CaF 2 and the effects of dose and the LET of radiation on the glow curve are discussed. The dosimetric properties and applications of the popular materials like CaF 2:Tm, CaF 2:Mn and CaF 2:Dy are also described. The various explanations for the TL phenomenon in these materials are given to highlight the complications and difficulties in completely understanding the mechanisms involved. Optical absorption, ESR, electrical relaxation studies and detailed analysis of the TL emission spectrum lead to the identification of some charge carrier traps and luminescent centres, but one-to-one trap/luminescent centre correlation is very difficult.

Jain, V. K.

281

Physical and Chemical Considerations of the Role of Firmly and Loosely Bound Fluoride in Caries Prevention  

Microsoft Academic Search

Historically, there has been considerable debate concerning the roles of loosely bound (calcium fluoride) and firmly bound (fluorapatite) fluoride for caries prevention. Research now shows that fluorapatite (FAP) is a finite reaction product of enamel\\/apatite fluoridation with or without CaF2 formation, suggesting that CaF 2 always be considered as a supplement to, rather than a substitute for, FAP formation. In

D. J. White; G. H. Nancollas

1990-01-01

282

Application of Reutilization Technology to Calcium Fluoride Sludge from Semiconductor Manufacturers  

Microsoft Academic Search

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.

Wei-Ting Liu; Kung-Cheh Li

2011-01-01

283

PROPRITS MAGNTO-OPTIQUES DE MATRIAUX PARA-, FERRO-ET ANTIFERROMAGNTIQUES CONTENANT L'ION EUROPIUM DIVALENT  

E-print Network

'ION EUROPIUM DIVALENT J. FERRÉ (*) Laboratoire d'Optique Physique, EPCI (**) 10, rue Vauquelin, 75231 Paris matrices cristallines d'une part (CaF2, KCl), des chalcogénures d'europium EuX, d'autre part (X = O, S, Se) of isolated Eu2+ ions (in CaF2 and KCl) and of europium chalcogenides EuX (X = O, S, Se, Te) are compared

Paris-Sud XI, Université de

284

Positron production using a 1.7 MV pelletron accelerator  

NASA Astrophysics Data System (ADS)

We report the foremost phase of a fourth generation positron source, being constructed at the Federal University of Rio de Janeiro. Positron yields are reported by making use of the 19F(p,?e+e-)16O reaction, where the fluorine target is in the form of a CaF2 pellet. Positron production has been observed by detecting 511 keV annihilation gamma rays emerging from the irradiated CaF2 target.

Alcantara, K. F.; Crivelli, P.; Santos, A. C. F.

2013-04-01

285

Formation and luminescence of lower symmetrical tellurite anti-glass phases  

NASA Astrophysics Data System (ADS)

Two series of nonstoichiometric lanthanoid tellurite phases have been identified which are similar to cubic ( Ln,Te)O n anti-glass phases with CaF 2 defect structure. Their X-ray diagrams indicate low-symmetrical CaF 2 superstructures. Monoclinic (or pseudotetragonal) subcells were determined. Anti-glass disorder is consistent with the Eu 2+ and Te 4+ luminescence of one series, but can be excluded for the other one.

Trömel, M.; Münch, E.; Blasse, G.; Dirksen, G. J.

1988-10-01

286

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

PubMed

This paper presents a "one-pot" procedure to synthesize polystyrene/(rare-earth-doped nanoparticles) (PS/REDNPs) hybrid hollow spheres via the in situ diffusion of organic core into inorganic shell under strong capillary force. In this approach, when carboxyl-capped PS colloids were deposited by different REDNPs in aqueous medium, such as LaF3:Eu3+, LaF3:Ce3+-Tb3+, and YVO4:Dy3+, PS/REDNPs inorganic-organic hybrid hollow spheres could be directly obtained via the in situ diffusion of core PS chains into the voids between rare-earth-doped nanoparticles through the strong capillary force. Not only is the synthetic procedure versatile and very simple, but also the obtained hybrid hollow spheres are hydrophilic and luminescent and could be directly used in chemical and biological fields. PMID:20828167

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

2010-10-01

287

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)

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.

Whittaker, Edward Anthony

288

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

NASA Technical Reports Server (NTRS)

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.

Bill, R. C.

1974-01-01

289

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

SciTech Connect

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.

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

2008-01-28

290

Investigation into nanostructured lanthanum halides and CeBr3 for nuclear radiation detection  

Microsoft Academic Search

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. 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

Paul Guss; Ronald Guise; Sanjoy Mukhopadhyay; Ding Yuan

2011-01-01

291

The scintillation properties of cerium-doped lanthanum fluoride  

Microsoft Academic Search

We report on the scintillation properties of cerium-doped lanthanum fluoride (LaF3), a newly discovered dense (5.9 g\\/cm3) heavy-atom scintillator. We have investigated four dopant concentrations (0.01%, 1%, 10% and 50% mole fraction of CeF3) and measured the emission spectrum, light output and decay time distribution. The light output increases with increasing cerium concentration until a maximum is reached at 2200

W. W. Moses; S. E. Derenzo

1990-01-01

292

Development of biosensors based on an electrolyte isolator semiconductor (EIS) capacitor structure and their application for process monitoring. Part I. Development of the biosensors and their characterization  

Microsoft Academic Search

Simple non-structured fluoride sensitive electrolyte isolator semiconductor (EIS) chips consisting of SiSiO2Si3N4LaF3 layers were used as transducers for measuring the H2O2 concentration by peroxidasej (POD) and combined this H2O2 sensor with various oxidases, which form H2O2 in stoichiometric amount. The concentrations of the following analytes were measured with this system: glucose with glucose oxidase (GOD) and POD, maltose with amyloglucosidase

C. Menzel; T. Lerch; T. Scheper; K. Schügerl

1995-01-01

293

Interaction strength of weakly coupled pairs measured by a two laser spectroscopy technique  

E-print Network

(2) of Pr . Grossly, the shift of a satellite from the main line is an indication of the spatial distance between the two ions of the pair : the larger this shift, the nearer the ions. With weakly doped crystals-conversion fluorescence from 3Po. On the right, energy levels of interest for Pr3 + : LaF3. The method used for the direct

Paris-Sud XI, Université de

294

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

SciTech Connect

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.

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

2001-01-01

295

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

296

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

NASA Astrophysics Data System (ADS)

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

Fujihara, Shinobu; Schneller, Theodor; Waser, Rainer

2004-01-01

297

Optical transitions of Ho(3+) in oxyfluoride glasses and upconversion luminescence of Ho(3+)/Yb(3+)-codoped oxyfluoride glasses.  

PubMed

Optical properties of Ho(3+)-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 Ho(3+)/Yb(3+)-codoped SiO2-BaF2-ZnF2 glasses under 980nm excitation. The effects of composition, concentration of the doping ions, and excitation pump power on the upconversion emissions were also systematically studied. PMID:25703369

Feng, Li; Wu, Yinsu

2015-05-01

298

Cascaded Brillouin lasing in monolithic barium fluoride whispering gallery mode resonators  

E-print Network

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.

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

2015-01-01

299

Optical transitions of Tm3+ in oxyfluoride glasses and compositional and thermal effect on upconversion luminescence of Tm3+/Yb3+-codoped oxyfluoride glasses.  

PubMed

Optical properties of Tm(3+)-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 Tm(3+)/Yb(3+)-codoped SiO2-BaF2-ZnF2 glasses under 980 nm excitation. The effects of composition, concentration of the doping ions, temperature, and excitation pump power on the upconversion emissions were also systematically studied. PMID:24051289

Feng, Li; Wu, Yinsu; Liu, Zhuo; Guo, Tao

2014-01-24

300

Optical transitions of Tm3+ in oxyfluoride glasses and compositional and thermal effect on upconversion luminescence of Tm3+/Yb3+-codoped oxyfluoride glasses  

NASA Astrophysics Data System (ADS)

Optical properties of Tm3+-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 Tm3+/Yb3+-codoped SiO2-BaF2-ZnF2 glasses under 980 nm excitation. The effects of composition, concentration of the doping ions, temperature, and excitation pump power on the upconversion emissions were also systematically studied.

Feng, Li; Wu, Yinsu; Liu, Zhuo; Guo, Tao

2014-01-01

301

Electronic and Nuclear Magnetic Relaxation in Crystals with Fluorite Structure Containing Eu2+ or Mn2+  

Microsoft Academic Search

The spin-lattice relaxation time T1 was measured for Eu2+ in BaF2 and for Mn2+ in BaF2 and SrF2 at about 9 GHz. The nuclear relaxation time of the F19 nucleus was also measured at 29 MHz at temperatures below 77°K. Each impurity ion shows a one-phonon relaxation with T1~T-1 in the liquid-helium region, and a Raman relaxation with T1~T-5 at

Joseph B. Horak; A. W. Nolle

1967-01-01

302

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

PubMed

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

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

2013-01-01

303

Low temperature epitaxial growth of Ge on cube- textured Ni  

SciTech Connect

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.

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

304

Burst Reaction of Thin Films Excited by High-Flux Soft X-Rays  

NASA Astrophysics Data System (ADS)

High-flux soft-X-ray irradiation effects were investigated for the thick a-Si:H and ?c-Si:H films, glass, MgF2 and CaF2 plates. The a-Si:H film of 7500 nm thickness has been burst, and its broken fragments flew off within several seconds. From the changes of Raman spectra before and after the irradiation and the film thickness dependence, it is thought that this is caused by rapid crystallization. SR-induced etching of glass, MgF2 and CaF2 plates has been observed. Photon energy dependence of the etching depth has been found. Exciting the Si K-shell is effective for etching the glass substrate. On the other hand, photon flux is important in the case of fluoride, and the maximum etching rate of CaF2 is more than 1 ?m/min.

Kanashima, Takeshi; Okuyama, Masanori; Okamoto, Hiroaki; Hattori, Kiminori; Ohashi, Haruhiko; Ishiguro, Eiji

305

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

NASA Astrophysics Data System (ADS)

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

Ullmann, J. L.

2014-09-01

306

Three-Compartment Photoreactor for Laser Isotope Separation off Tritium  

Microsoft Academic Search

A new photoreactor has been designed and tested for laser isotope separation of tritium using trifluoromethane as a working substance. The reactor consists of three compartments in series which are stirred efficiently with recirculation pumps independently. The CO2 laser beam is sequentially focused with BaF2 lenses serving as the beam entrance windows of the compartments. In this reactor the reaction

Kazuo Takeuchi; Mitsushi Motoyama; Ichiro Inoue

1987-01-01

307

OAK RIDGE NATIONAL LABORATORY U. S. DEPARTMENT OF ENERGY  

E-print Network

.Y. Zhai Metals and Ceramics Division A. Goyal, L. Heatherly, S. Kang, D. M. Kroeger, D. F. Lee, P a viable high rate process to fabricate high quality buffer layers · Collaborate with LANL and ANL Methods: ·YBCO: ex-situ BaF2 process ·YSZ and CeO2 : rf sputtering ·Y2O3: e-beam ·Ni: dc sputtering

308

Measurement of the 241Am and the 243Am Neutron Capture Cross Sections at the n_TOF Facility at CERN  

NASA Astrophysics Data System (ADS)

The capture cross sections of 241Am and 243Am were measured at the n_TOF facility at CERN in the epithermal energy range with a BaF2 Total Absorption Calorimeter. A preliminary analysis of the 241Am and a complete analysis of the 243Am measurement, including the data reduction and the resonance analysis, have been performed.

Mendoza, E.; Cano-Ott, D.; Guerrero, C.; Altstadt, S.; Andrzejewski, J.; Audouin, L.; Barbagallo, M.; Bécares, V.; Be?vá?, F.; Belloni, F.; Berthoumieux, E.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Duran, I.; Dressler, R.; Dzysiuk, N.; Eleftheriadis, C.; Ferrari, A.; Fraval, K.; Ganesan, S.; García, A. R.; Giubrone, G.; Gómez-Hornillos, M. B.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Gunsing, F.; Gurusamy, P.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Kivel, N.; Koehler, P.; Kokkoris, M.; Korschinek, G.; Krti?ka, M.; Kroll, J.; Langer, C.; Lederer, C.; Leeb, H.; Leong, L. S.; Losito, R.; Manousos, A.; Marganiec, J.; Martínez, T.; Mastinu, P. F.; Mastromarco, M.; Massimi, C.; Meaze, M.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondelaers, W.; Paradela, C.; Pavlik, A.; Perkowski, J.; Pignatari, M.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Roman, F.; Rubbia, C.; Sarmento, R.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Tagliente, G.; Tain, J. L.; Tarrío, D.; Tassan-Got, L.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Versaci, R.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T. J.; Žugec, P.

2014-05-01

309

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.)

310

s-Process branchings in He-shell flash convection The production of half of all elements heavier than iron takes place through  

E-print Network

as a diagnostic tool. Temperatures in the stellar interior are often related to the physics of mixing has started in fall 2005. (n,) measurements of radioactive samples with the DANCE 4 BaF2 array have been updated and integrated. With these tools we will be able to translate the nuclear physics

Herwig, Falk

311

Simulation of point defects in high-density luminescent crystals: Oxygen in barium fluoride J. M. Vail, E. Emberly, and T. Lu  

E-print Network

Simulation of point defects in high-density luminescent crystals: Oxygen in barium fluoride J. M June 1997; revised manuscript received 25 August 1997 Barium fluoride is an example of a high. INTRODUCTION Barium fluoride, BaF2, is an important representative of a class of high-density luminescent

Pandey, Ravi

312

Rare earths in lead-free oxyfluoride germanate glasses  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

313

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

E-print Network

SR-FTIR Study of Bacteria-Water Interactions: Acid-base Titration and Silification Experiments/base titration and Si precipitation experiments. The objectives of this research are to identify the reactive through fluid cell with BaF2 and ZnSe windows separated by a 6 um mylar spacer. Acid-base titration and Si

314

Spectroscopy and lasing of cryogenically cooled Yb,?Na:CaF 2  

Microsoft Academic Search

Absorption, photoluminescence and cw-lasing properties of a novel Na+-codoped Yb3+:CaF2 laser crystal are investigated in the temperature range from 10 K to 290 K. Cryogenic cooling leads to the disappearance\\u000a of the ground-state absorption in the spectral region above 1000 nm and a substantial increase of emission and absorption\\u000a cross-sections. A particular advantage of the Yb3+, Na+-codoped CaF2 crystal lies in the possibility

A. Pugzlys; G. Andriukaitis; D. Sidorov; A. Irshad; A. Baltuska; W. J. Lai; P. B. Phua; L. Su; J. Xu; H. Li; R. Li; S. Alisauskas; A. Marcinkevicius; M. E. Fermann; L. Giniunas; R. Danielius

2009-01-01

315

Growth and characterization of single crystal insulators on silicon  

NASA Technical Reports Server (NTRS)

An overview of the growth and characterization of epitaxial insulators on semiconductors is presented. The potential applications include semiconductor-on-insulator structures, three-dimensional and/or high-density integrated circuits, optoelectronic applications such as integrated waveguides and improved gate insulators. The growth and physical characterization of epitaxial fluorides on semiconductors are discussed. Consideration is also given to the epitaxial overgrowth of epitaxial metal layers with CaF2 as well as to the formation of a novel superlattice of Ca particles in epitaxial CaF2.

Schowalter, Leo J.; Fathauer, Robert W.

1989-01-01

316

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

317

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

SciTech Connect

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

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

2010-11-01

318

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

USGS Publications Warehouse

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.

Greenland, L.P.

1968-01-01

319

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

NASA Astrophysics Data System (ADS)

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.

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

320

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

E-print Network

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

Gao, Chi

321

Commerce Control List Supplement No. 1 to Part 774 Category 2--page 1 Export Administration Regulations September 28, 2001  

E-print Network

. Calcium fluoride (CaF2); a.2. Calcium zirconate (metazirconate) (Ca2ZrO3); a.3. Cerium sulphide (Ce2S3); a. Nitridedniobium-titanium-tungstenalloy (approximately 50% Nb, 30% Ti, 20% W); a.8. Yttrium oxide (yttria) (Y2O3

Bernstein, Daniel

322

Smithsonian Widefield Infrared Camera Warren R. Browna, Brian A. McLeoda, John C. Gearya, and Emily C. Bowsherb  

E-print Network

the thermal design and the detector mount, all of which have been incorporated into the upcoming MMT element, the second lens, as the pressure window. Our CaF2 / IR Fused Quartz doublet provides excellent calculations predict a 10% spot size change for a 2 lens tilt or a 0.25 mm lens de-center from the optical axis

323

Simultaneous measurement of thermal lens and temperature map in ytterbium-doped fluoride crystals  

E-print Network

Simultaneous measurement of thermal lens and temperature map in ytterbium-doped fluoride crystals J assessment of both the temperature map and the thermal lens (TL) properties of Yb3+ :CaF2 and Yb3+ :SrF2 with or without laser operation. We notice that all TL dioptric powers (Dth) are negative. Since the thermal lens

Paris-Sud XI, Université de

324

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

Microsoft Academic Search

Detectors based on optically stimulated luminescence are useful for fast neutron dosimetry. For this one needs the neutron sensitivity of these detectors. We describe a procedure for the calculation of the neutron sensitivity. For CaF2:Mn embedded in polyethylene the calculated values are compared with experimentally determined neutron sensitivities. There is good agreement.

Jürgen Fellinger; Jürgen Henniger; Klaus Hübner

1984-01-01

325

Strength and fluoride release characteristics of a calcium fluoride based dental nanocomposite  

PubMed Central

Secondary caries and restoration fracture remain the two most common problems in restorative dentistry. Release of fluoride ions (F) could be a substantial benefit because F could enrich neighboring enamel or dentin to combat caries. The objective of this study was to incorporate novel CaF2 nanoparticles into dental resin to develop stress-bearing, F-releasing nanocomposite. CaF2 nanoparticles, prepared in our laboratories for the first time, were combined with reinforcing whisker fillers in a resin. Flexural strength (mean ± sd; n = 6) was 110 ± 11 MPa for the composite containing 30% of CaF2 and 35% whiskers by mass. It matched the 108 ± 19 MPa of a stress-bearing, non-releasing commercial composite (Tukey’s at 0.05). The composite containing 20% CaF2 had a cumulative F release of 2.34 ± 0.26 mmol/L at 10 weeks. The initial F release rate was 2 µg/(h·cm2), and the sustained release rate after 10 weeks was 0.29 µg/(h·cm2). These values exceeded the reported releases of traditional and resin-modified glass ionomer materials. In summary, nanocomposites were developed with relatively high strength as well as sustained release of fluoride ions, a combination not available in current materials. These strong and F releasing composites may yield restorations that can reduce the occurrence of both secondary caries and restoration fracture. PMID:18708252

Xu, Hockin H. K.; Moreau, Jennifer; Sun, Limin; Chow, Laurence C.

2008-01-01

326

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

E-print Network

with an Ar plasma transparent conducting indium­tin­oxide ITO contacts either on the bare CaF2 surface, with higher doped samples showing a more pronounced long wavelength tail. Although both metal and indium­tin­oxide evaporated aluminum. Following metallization, the samples were annealed in forming gas 80% N2, 20% H2 for 20

McCann, Patrick

327

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

E-print Network

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

Zens, Timothy

328

Accepted for publication in the Journal of Applied Physics. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of  

E-print Network

phases Mg3MnH7, Mg2FeH6, and Mg2CoH5. Following the discovery of the switchable mirror phenomenon to that of the high-temperature, cubic form of Mg2NiH4, with a CaF2-type metal atom arrangement. Cubic Mg2FeH6

329

Supplementary Material (ESI) For Analyst This journal is (C) The Royal Society of Chemistry 2010 www.rsc.org/analyst | Analyst  

E-print Network

/min flow rate. The mid-IR laser beam was focused with a 150 mm focal length CaF2 lens (Infrared Optical due to the losses of trimethylamine (TMA), HPO4(CH2)2N(CH3)3, LiPO4(CH2)2N(CH3)3, oleic acid (18

Vertes, Akos

330

Synthesis and solubility of calcium fluoride\\/hydroxyfluorapatite nanocrystals for dental applications  

Microsoft Academic Search

As the mineral phase of tooth enamel consists of apatite containing fluoride, the “CaF2-like” salts are of significant interest in dentistry for their roles as labile fluoride reservoirs in caries prevention. Fluoride ion is required for normal dental development because of its therapeutic ability of osteoporosis healing and stimulating osteoblast activity both in vitro and in vivo. In this research,

Mahmoud Azami; Sasan Jalilifiroozinezhad; Masoud Mozafari; Mohammad Rabiee

2011-01-01

331

Development of a high resolution beta camera for a direct measurement of positron distribution on brain surface  

Microsoft Academic Search

We have developed and tested a high resolution beta camera for a direct measurement of positron distribution on the brain surface of animals. The beta camera consists of a thin CaF2(Eu) scintillator, a tapered fiber optic plate (tapered fiber) and a position sensitive photomultiplier tube (PSPMT). The tapered fiber is the key component of the camera. We have developed two

S. Yamamoto; C. Seki; K. Kashikura; H. Fujita; T. Matsuda; R. Ban; I. Kanno

1997-01-01

332

Georae M. Bodner I The Introductionof Crystallographic Thomas Greenbowe  

E-print Network

and physical properties of in the lecture. For manv vears. we at Purdue Universitv have solids, we need to tell, the structural similaritiesbetween apparently unre- lated compounds such as CsCl and CaF2,and the regularity of extended structures in ionic solids in general. Indeed we often deliberately neglected the structure

Bodner, George M.

333

JOURNAL.DE PHYSIQUE IV Colloque C5,supplCment au Journal de Physique I, Vol. 1,dCcembre 1991  

E-print Network

center) is the first and best studied electronic defect species in solid state physics and chemistry. I state chemistry - see e.g. Kroger /S/ - . But in many cases the experimental verification in solids) I CaFz(s) I K, KCaFg(s) - K, KCI(1) (1) This technique using CaF2 a s a solid electrolyte was first

Boyer, Edmond

334

MATERIALS AND MOLECULAR RESEARCH DIVISION Annual Report 1977.  

E-print Network

to study with solid state electrolytes such as stabilizedSolid State Electrochemical Studies of Group III-V Alloys Employing A CaF2 Solid Electrolyte . . . . . . . . . . . . . . . . . .Solid State Electrochemical Studies of the Standard Gibbs Energy of Formation of B-Gallium Sesquioxide Using a Calcia-Stabilized Zirconia Electrolyte,

Authors, Various

2011-01-01

335

Effect of various additives on microstructure, mechanical properties, and in vitro bioactivity of sodium oxide-calcium oxide-silica-phosphorus pentoxide glass-ceramics.  

PubMed

The partial substitution of MgO, TiO2, or CaF2 for CaO in the Na2O-CaO-SiO2-P2O5 (45S5) system was conducted by the sol-gel method and a comparative study on structural, mechanical properties, and bioactivity of the glasses was reported. Based on thermogravimetric and differential thermal analysis, the gels were sintered with a suitable heat treatment procedure. The glass-ceramic properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and so on, and the bioactivity of the glass-ceramic was evaluated by in vitro assays in simulated body fluid (SBF). Results indicate that with the partial substitution of MgO, TiO2, CaF2 for CaO in glass composition, the mechanical properties of the glass-ceramics have been significantly improved. Furthermore, CaF2 promotes glass crystallization and the crystallization does not inhibit the glass-ceramic bioactivity. All samples possess bioactivity; however, the bioactivity of these glass-ceramics is quite different. Compared with 45S5, the introduction of MgO decreases the ability of apatite induction. The addition of TiO2 does not significantly improve the bioactivity, and the replacement of CaO by CaF2 shows a higher bioactivity. PMID:23777867

Li, H C; Wang, D G; Hu, J H; Chen, C Z

2013-09-01

336

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

PubMed Central

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

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

2003-01-01

337

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

PubMed

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

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

2003-08-01

338

JOURNALDE PHYSIQUE IV Colloque C5, suppldment au Journal de Physique III, Volume 6, septembre 1996  

E-print Network

or semiconductor emissive tip covered by dielectric epitaxial layers containing dopant ions or defects. Such dopant ions or defects can possess a number of excited states lying in the forbidden zone of a dielectric silicon tips covered by thin dielectric CaF2 layers containing Sm dopant ions. Some indications

Boyer, Edmond

339

header for SPIE use Fluoropolymers for 157nm Lithography: Optical Properties from VUV  

E-print Network

header for SPIE use Fluoropolymers for 157nm Lithography: Optical Properties from VUV Absorbance materials. Here we focus on ultratransparent fluoropolymers for 157 nm pellicle applications where the pellicle's etalon design. Comparison of VUV absorbance measurements of fluoropolymer thin films on CaF2

Rollins, Andrew M.

340

On Yb:CaF2 and Yb:SrF2 : Review of spectroscopic and thermal properties and their  

E-print Network

). 5. A. Lucca, M. Jacquemet, F. Druon, F. Balembois, P. Georges, P. Camy, J.L. Doualan and R. Moncorgé, High power tunable diode-pumped Yb3+ :CaF2 laser, Opt. Lett. 29 1879-1881 (2004) 6. A.Lucca, G. Debourg

Paris-Sud XI, Université de

341

Images of phonons transmitted across twist-bonded (1 1 1) -oriented cubic crystals: symmetry doubling in the ballistic intensity  

NASA Astrophysics Data System (ADS)

The geometry of the ballistic focusing patterns of phonons transmitted through identical (1 1 1) cubic crystals twist bonded at a 60° angle exhibits six-fold symmetry. We consider the conditions under which those phonon intensities possess the exact six-fold symmetry. The results are illustrated for phonons transmitted though (1 1 1)-oriented CaF2 slabs.

Obata, Hiroshi; Tanaka, Yukihiro; Tamura, Shin-ichiro

2002-05-01

342

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

PubMed Central

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

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

2012-01-01

343

Physical and chemical considerations of the role of firmly and loosely bound fluoride in caries prevention.  

PubMed

Historically, there has been considerable debate concerning the roles of loosely bound (calcium fluoride) and firmly bound (fluorapatite) fluoride for caries prevention. Research now shows that fluorapatite (FAP) is a finite reaction product of enamel/apatite fluoridation with or without CaF2 formation, suggesting that CaF2 always be considered as a supplement to, rather than a substitute for, FAP formation. In the presence of low levels of fluoride in the solution phase, the crystallization of hydroxyapatite is enhanced, while the corresponding dissolution is retarded. Fluoride in the bulk FAP or CaF2 solid phase, in contrast, has limited impact on crystal growth or dissolution kinetics. Both FAP and CaF2 can provide F to the solution phase to enhance remineralization and retard demineralization of enamel HAP crystallites. The FAP provides most of this F under low pH conditions, while CaF2 provides F at neutral or lower pH. The reactivity of fluoride on sound and carious enamel differs significantly. Carious enamel acquires more fluoride, acquires it more quickly, and itself acts as a source of retained fluoride in comparison with the more limited reactivity of sound enamel. Overall, the most important question concerning fluoride reactivity relates to its efficiency in enhancing remineralization or retarding demineralization processes. This is influenced not only by the reaction products, e.g., loosely or firmly bound fluoride, but also by the nature of the enamel substrate and frequency of application of the topical fluoridating agent. Inasmuch as the reactivity of bulk HAP is dominated by surface layers of FAP material, the debate over usefulness of various fluoride reaction products solely on a chemical level is no longer critical. Instead, all factors influencing the efficiency of a fluoridating regimen must be considered in the development of improved systems for caries prevention. PMID:2179318

White, D J; Nancollas, G H

1990-02-01

344

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

NASA Astrophysics Data System (ADS)

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.

Otto, Frederick William

345

Microstructural and ionic transport studies of hydrothermally synthesized lanthanum fluoride nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

346

PAC studies with LSO scintillation crystals  

NASA Astrophysics Data System (ADS)

The LSO (lutetium oxyorthosilicate, Lu 2SiO 5) scintillation crystal has been shown to improve the efficiency of positron emission tomographs considerably due to its large average atomic number. This makes LSO also interesting for perturbed angular correlation since today's solid state studies require appropriate probes for specific purposes, like 77Br, 187W or 172Lu, with more complex energy spectra. We investigated the applicability of this new scintillator for perturbed angular correlation studies especially in experiments where the improvement of energy resolution as compared to BaF 2 is important without loosing time resolution. From these improvements we expect a larger effective anisotropy. Further, due to the high average atomic number of LSO its photopeak efficiency is considerably higher. We present here test measurements with 172Lu in thulium and a comparison with measurements on a BaF 2 setup.

Valentini, Riccardo; Vianden, Reiner

2010-11-01

347

Spectroscopic properties of Yb3+-doped TeO2—BaO—BaF2—Nb2O5-based oxyfluoride tellurite glasses  

NASA Astrophysics Data System (ADS)

A series of oxyfluoride glasses with the compositions of 75 mol% TeO2, 10 mol% Nb2O5, (15 mol%-x) BaO, x BaF2 (x = 0 mol%, 5 mol%, 10 mol%, 15 mol%) doped with Yb2O3 were prepared by the melt-quenching method. Their emission cross-sections, fluorescence lifetimes, and gain properties were investigated by using the absorption spectra and the fluorescence decay curves. The results show that by substituting BaF2 for BaO, the emission cross-section decreases from 1.37 pm2 to 1.21 pm2, and the fluorescence lifetime increases from 0.71 ms to 0.96 ms. These properties indicate that this oxyfluoride tellurite glass may have potential uses as the Yb2O3-doped gain medium in a solid laser.

Lin, She-Bao; Wang, Peng-Fei; She, Jiang-Bo; Guo, Hai-Tao; Xu, Shen-Nuo; Yu, Cheng-Long; Liu, Chun-Xiao; Peng, Bo

2014-09-01

348

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

NASA Astrophysics Data System (ADS)

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

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

1991-01-01

349

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

NASA Astrophysics Data System (ADS)

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

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

1990-04-01

350

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

351

Development and Performance Test of Picosecond Pulse X-ray Excited Streak Camera System for Scintillator Characterization  

NASA Astrophysics Data System (ADS)

To observe time and wavelength-resolved scintillation events, picosecond pulse X-ray excited streak camera system is developed. The wavelength range spreads from vacuum ultraviolet (VUV) to near infrared region (110-900 nm) and the instrumental response function is around 80 ps. This work describes the principle of the newly developed instrument and the first performance test using BaF2 single crystal scintillator. Core valence luminescence of BaF2 peaking around 190 and 220 nm is clearly detected by our system, and the decay time turned out to be of 0.7 ns. These results are consistent with literature and confirm that our system properly works.

Yanagida, Takayuki; Fujimoto, Yutaka; Yoshikawa, Akira; Yokota, Yuui; Kamada, Kei; Pejchal, Jan; Chani, Varely; Kawaguchi, Noriaki; Fukuda, Kentaro; Uchiyama, Koro; Mori, Kuniyoshi; Kitano, Ken; Nikl, Martin

2010-05-01

352

Synthesis and crystal structures of Ba 6Mg 11F 34 and the solid solutions Ba 6Mg 11? x M (II) x F 34 (M (II) = Mn, Fe) and luminescence of Ba 6Mg 11F 34: Eu 2+  

Microsoft Academic Search

Ba6Mg11F34, a new compound of the pseudobinary BaF2–MgF2 system, has been synthesized by solid state techniques from stoichiometric amounts of BaF2 and MgF2 and its crystal structure determined by single crystal X-ray diffraction (space group P1?, a=7.5084(6), b=9.9192(8), c=10.0354(8)Å, ?=81.563(2), ?=72.402(2), ?=71.198(1)°, 3899 structure factors, 233 parameters, R(F2>2?(F2))=0.018, wR(F2 all) = 0.046). It is isotypic with the copper(II) analogue, Ba6Cu11F34.

W. Kerbe; M. Weil; F. Kubel; H. Hagemann

2004-01-01

353

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

E-print Network

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.

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

2015-01-01

354

Analysis of additives in polymers by thin-layer chromatography coupled with Fourier transform-infrared microscopy  

Microsoft Academic Search

A new, fast and convenient method based on coupled thin-layer chromatography (TLC) and Fourier transform-infrared (FT-IR) microscopy is developed to separate, detect and identify the additives in polymers. After the TLC development, the analytes were transferred on to a barium fluoride (BaF2) salt plate via a special capillary technique and analysed by FT-IR microscopy. The additives used for stabilization of

Wenxuan He; Robert Shanks; Gandara Amarasinghe

2002-01-01

355

Current limiting defects in Ba(Fe 1-x Cox)2As2 and YBa2Cu3O 7-x films.  

E-print Network

Magnetic Field Laboratory, Tallahassee, FL 32310, USA Ron Feenstra Oak Ridge National Laboratory, Oak Ridge;YBa2Cu3O 7-x Tc = 89.7 ­ 90.0 K Coated conductors grown with e-beam BaF2 ex situ (350 nm thick), PLD thick YBCO LTLSM vs. MO responses on YBCO test sample 0 V 0.54 V T=10.4 K Hext=40 mT A B ),(),( yx

Weston, Ken

356

Molecular beam epitaxy of PbSrSe and PbSePbSrSe multiple quantum well structures for use in midinfrared light emitting devices  

E-print Network

) substrates in a GEN II MBE system. BaF2 substrates were freshly cleaved from a 111 -oriented 1 cm 1 cm ingot Vacuum Society. S0734-211X 00 04903-9 I. INTRODUCTION Molecular beam epitaxy MBE of the IV­VI binary to grow PbSrSe with a high Sr solu- bility and a wide tunable energy band gap. Recently, MBE grown Pb

McCann, Patrick

357

Thermoelectric property features of PbTe monocrystalline and polycrystalline films  

Microsoft Academic Search

The equations of a regression were obtained by methods of mathematical planning of many- factors experiments. These equations determine a dependence of thermoelectric parameters of PbTe thin films prepared by hot wall the method from technological factors: temperatures of evaporation, walls of the chamber and deposition. PbTe thin films were layed sieged on pins (111) of BaF2 monocrystals and on

D. M. Freik; R. I. Zapukhlyak; M. A. Lopjanka; G. D. Mateik; R. Ya. Mikhajlonka

358

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

NASA Technical Reports Server (NTRS)

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

Miller, M. D.

1981-01-01

359

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

Microsoft Academic Search

In this strategy of depositing the basic building blocks of superconductors, semiconductors, and dielectrics having common elements, researchers deposited superconducting films of Y-Ba-Cu-O, semiconductor films of Cu2O, and dielectric films of BaF2 and Y2O3 by metal oxide chemical vapor deposition (MOCVD). By switching source materials entering the chamber, and by using direct writing capability, complex device structures like three terminal

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

1991-01-01

360

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

Microsoft Academic Search

In this strategy of depositing the basic building blocks of superconductors, semiconductors, and dielectric having common elements, researchers deposited superconducting films of Y-Ba-Cu-O, semiconductor films of Cu2O, and dielectric films of BaF2 and Y2O3 by metal oxide chemical vapor deposition (MOCVD). By switching source materials entering the chamber, and by using direct writting capability, complex device structures like three-terminal hybrid

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

1990-01-01

361

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

362

Microstructure of YBa2Cu3O(7-x) thin films grown on single-crystal SrTiO3  

Microsoft Academic Search

The microstructure of the YBa2Cu3O(7-x) thin films grown on (001) and (014) single-crystal SrTiO3 was studied using TEM. The films were prepared by coevaporation of Y, BaF2 and Cu, and annealing in oxygen at 850 C. Three types of YBa2Cu3O(7-x) grains, misoriented from each other by 90 deg, were observed to grow epitaxially on both (001) and (014) surface orientations,

Siu-Wai Chan; D. M. Hwang; L. Nazar

1989-01-01

363

JOURNAL DE PHYSIQUE Colloque C5, supplment au n12, Tome 42, dcembre 1982 page C5-405  

E-print Network

with high mobility and low carrier concentration. Thin films of CdS and CdTe deposited on BaF2, SrF2 couches minces épi taxiées de CdS, CdTe, de sels de plomb, de matériau semimagnëtique Pb, Mn Te et de Ga%) ayant une grande mobilité et une faible concentration de porteurs. Les couches minces de CdS et Cd

Paris-Sud XI, Université de

364

Reflective UV photocathodes with gas-phase electron extraction: solid, liquid, and adsorbed thin films  

Microsoft Academic Search

The photoemission quantum efficiency of reflective photocathodes in methane gas has been investigated in the spectral range between 140 and 250 nm. The spectral response of solid metals and CsI, as well as of liquid and solid TMAE film, have been measured. The high quantum efficiency of CsI (35% at 170 nm) makes it attractive for BaF2 or xenon scintillation

Jacques Séguinot; Georges Charpak; Y. Giomataris; Vladimir Peskov; Johann Tischhauser; Thomas Ypsilantis

1990-01-01

365

Superconducting Films On Microwave Dielectric Substrates  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

366

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

Microsoft Academic Search

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,

P Capek; V Sasinková; N Wellner; A Ebringerová

2000-01-01

367

Development of low-absorption AR coatings for CO2 laser by ion assisted deposition  

NASA Astrophysics Data System (ADS)

We have developed an anti-reflection (AR) coating technique designed for high power carbon dioxide (CO2) lasers that has low absorption and high resistance to humidity. This was achieved by performing ion-assisted deposition (IAD) using a Xe ion beam to apply BaF2 and ZnSe used as coating materials with extremely low bulk absorption coefficients. It was found that to achieve highly compact BaF2 thin films with low absorption on polycrystalline ZnSe substrates, both a surface flatness treatment using Xe ion bombardment and an optimized IAD condition of relatively low ion energy up to 200 eV are required. The absorption of the new (BaF2/ZnSe) AR coated ZnSe lens is 0.10 to 0.12%, approximately half that of conventional (ThF4/ZnSe) AR coated lenses. The new lens has both excellent anti-aging performance and a high resistance to humidity.

Iwamoto, Hiromi; Ebata, Keiji; Nanba, Hirokuni

2003-02-01

368

High-temperature thermodynamic properties of the vanadium carbides V2C and VC0.73 determined using a galvanic cell technique  

NASA Astrophysics Data System (ADS)

The standard free energies of formation of V2C and VC0.73 have been obtained from electromotive force (emf) measurements on the following galvanic cells with BaF2-BaC2 solid solutions as the electrolyte: Ta, Ta2CBaF2-BaC2V, V2 (850 to 1200K) (D) VC0.73, V2C BaF2-BaC2 Cr, Cr23C6 (850 to HOOK) (E) VC0.73, V2C BaF2-BaC2 Mo, Mo2C (890 to 1247 K) (F) Combining the results of this study with previous work1151 and those of Kukarni et al., [19.25] the following equations for ?Gf° of V2C and VC0.73 have been determined: From cell (D), ?Gv2c°(±1263) = -152,824(±9200) + 5.45(±0.27)7 Joule for the reaction 2V + C = V2C. From cell (E), ?Gvc 0.73°(±662) = -96,790.8(±6511.7) + 7.0(±0.3)r Joule/g * atom V From cell (F), ?Gvc 0.73°(±665) = -97,000(±4606) + 6.79(±0.78)J Joule/g * atom V for the reaction V + 0.73C = VC0.73.

Coltters, R. G.; Nava, Z.

1991-10-01

369

CANDLES for the study of ^48Ca double beta decay  

NASA Astrophysics Data System (ADS)

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

Ogawa, Izumi

2009-10-01

370

A theoretical study of fluorides scintillating crystals: Methodology and application  

NASA Astrophysics Data System (ADS)

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

Jiang, Huitian

371

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

NASA Astrophysics Data System (ADS)

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.

Wald, Lawrence Leroy

372

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

NASA Astrophysics Data System (ADS)

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.

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

1989-08-01

373

Crossover from hole- to electron-dominant regions in iron-chalcogenide superconductors induced by Te/Se substitution  

NASA Astrophysics Data System (ADS)

We have investigated a Te/Se substitution effect on the field dependence of Hall resistivity in FeSe1?xTex (x = 0.5–0.7) thin films grown on LaAlO3 and CaF2 substrates. By observing the magnetic field dependence of Hall resistivity, the crossover from hole- to electron-dominant regions is observed to occur between x = 0.5 and 0.6 in the films on LaAlO3, while no such crossover is observed in those on CaF2. The results indicate that the substitution of Te for Se effectively acts as electron doping, while the lattice strain also has an additional effect on the balance of hole and electron densities. These two factors can be independently used to optimize superconducting transition temperature so as to tune the doping level near the boundary where the hole density becomes equal to the electron density.

Tsukada, Ichiro; Nabeshima, Fuyuki; Ichinose, Ataru; Komiya, Seiki; Hanawa, Masafumi; Imai, Yoshinori; Maeda, Atsutaka

2015-04-01

374

Observation of fluorapatite formation under hydrolysis of tetracalcium phosphate in the presence of KF by means of soft X-ray emission and absorption spectroscopy.  

PubMed

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) in 0.1 mol/l KH2PO4 containing 62-83 mmol/l KF was studied with the help of X-ray fluorescence measurements. Fluorine X-ray emission and absorption spectra of the final product of hydrolysis and reference samples (CaF2 and Ca5(PO4)3F) were measured at Beamline BL-2C of Photon Factory (PF, Tsukuba). Based on these measurements we concluded that hydrolysis of TTCP in the presence of KF converts it into fluorapatite. Formation of CaF2, which is often found in the hydrolysis of hydroxyapatite at high fluoride concentration, was not observed. PMID:15348202

Kurmaev, E Z; Matsuya, S; Shin, S; Watanabe, M; Eguchi, R; Ishiwata, Y; Takeuchi, T; Iwami, M

2002-01-01

375

Low Radioactivity in CANDLES  

SciTech Connect

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

Kishimoto, T.; Ogawa, I.; Hazama, R.; Yoshida, S.; Umehara, S.; Matsuoka, K.; Sakai, H.; Yokoyama, D.; Mukaida, K.; Ichihara, K.; Tatewaki, Y.; Kishimoto, K.; Hirano, Y.; Yanagisawa, A.; Ajimura, S. [Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043 (Japan)

2005-09-08

376

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

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

377

Atomic scale control of hexaphenyl molecules manipulation along functionalized ultra-thin insulating layer on the Si(1?0?0) surface at low temperature (9 K)  

NASA Astrophysics Data System (ADS)

Ultra-thin CaF2 layers are grown on the Si(1?0?0) surface by using a Knudsen cell evaporator. These epitaxial structures are studied with a low temperature (9 K) scanning tunneling microscope and used to electronically decouple hexaphenyl molecules from the Si surface. We show that the ultra-thin CaF2 layers exhibit stripe structures oriented perpendicularly to the silicon dimer rows and have a surface gap of 3.8 eV. The ultra-thin semi-insulating layers are also shown to be functionalized, since 80% of the hexaphenyl molecules adsorbed on these structures self-orients along the stripes. Numerical simulations using time-dependent density functional theory allow comparison of computed orbitals of the hexaphenyl molecule with experimental data. Finally, we show that the hexaphenyl molecules can be manipulated along or across the stripes, enabling the molecules to be arranged precisely on the insulating surface.

Chiaravalloti, Franco; Dujardin, Gérald; Riedel, Damien

2015-02-01

378

Neutron beam dosimetry at the NRL cyclotron  

Microsoft Academic Search

A 35 MeV deuteron beam impinging upon a thick Be target is being employed to generate a neutron beam for radiobiological experiments of relevance to later possible fast neutron therapy trials. The primary calibration of the beam has been based upon tissue-equivalent plastic ionization chambers, calibrated in turn with 60Co gamma -rays. CaF2:Mn and 7LiF (TLD-700) thermoluminescent dosemeters have been

F. H. Attix; R. B. Theus; P. Shapiro; R. E. Surratt; A. E. Nash; S. G. Gorbics

1973-01-01

379

Characterization of a two-dimensional, thermoluminescent, dose-mapping system: Uniformity, reproducibility, and calibrations  

Microsoft Academic Search

Initial testing of a new, commercially available, thermoluminescent dosimetry system is reported. The radiation detectors consist of two-dimensional arrays of 104 CaF2:Mn dosimeters, deposited on flexible polyimide sheets. The spatial resolution is 3 mm, and the combined thickness of the dosimeters and the substrate is 185 ?m. Exposed sheets are processed by laser heating. This system is compatible with intense,

D. L. Fehl; D. J. Muron; B. R. Sujka; D. W. Vehar; L. J. Lorence; R. L. Westfall; S. C. Jones; J. A. Sweet; P. Braunlich

1994-01-01

380

Fabrication of diffractive phase elements by F2-laser ablation of fused silica  

Microsoft Academic Search

F2-laser ablation at 157 nm was used for generating sub-micron surface relief structures on fused silica to define binary diffractive phase elements (DPE). A pattern array of 128 x 128 pixels was excised using the F2 laser in combination with a high resolution processing system comprising of CaF2 beam-homogenization optics and a high-resolution Schwarzschild reflective objective. A square projection mask

Malte Schulz-Ruthenberg; Juergen Ihlemann; Gerd Marowsky; Amir H. Nejadmalayeri; Mi L. Ng; Jianzhao Li; Peter R. Herman

2003-01-01

381

Effect of Yb3+ concentration on optical properties of Yb:CaF2 transparent ceramics  

E-print Network

Effect of Yb3+ concentration on optical properties of Yb:CaF2 transparent ceramics Andréas Lyberis Keywords: CaF2 Ytterbium Transparent ceramics Spectroscopy a b s t r a c t In Yb:CaF2, the coordination, and fluorescence lifetime of 0.1, 1, 5, and 10 at% Yb:CaF2 ceramics to determine whether Yb3+ substitutes

382

200-fs, 2mJ pulses from 1kHz Yb3+,Na+:CaF2 cryogenic amplifier  

Microsoft Academic Search

By merging Yb fiber oscillator and cryogenically cooled DPSS Yb3+,Na+: CaF2 RA we have generated 195-fs 2-mJ pulses at a 1-kHz repetition rate. Amplification substantially beyond 2 mJ is feasible by improving the quality of surface polishing and AR coatings, as well as by optimizing the RA cavity. Spectral shaping of the seed is crucial for amplification of broad spectra

G. Andriukaitis; A. Pugzlys; L. Su; J. Xu; R. Li; W. J. Lai; P. B. Phua; A. Marcinkevicius; M. E. Fermann; L. Giniunas; R. Danielius; A. Baltuska

2009-01-01

383

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

NASA Technical Reports Server (NTRS)

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

Sliney, Harold E.

1960-01-01

384

Effect of post-thaw dilution with caffeine, pentoxifylline, 2’-deoxyadenosine and prostatic fluid on motility of frozen-thawed dog semen  

Microsoft Academic Search

The aim of the experiment was to evaluate the motility pattern of frozen-thawed canine semen to which pentoxifyilline (PTX), caffeine (CAF), 2’-deoxyadenosine (DX), and prostatic fluid (PROST) were added after thawing. Semen evaluations were performed using computer-assisted sperm analysis (CASA) at thawing and during 120min of incubation at 37°C. Three experiments were conducted: 1) to establish which concentrations of stimulants

C. Milani; A. Fontbonne; E. Sellem; C. Stelletta; O. Gérard; S. Romagnoli

2010-01-01

385

Polarization-sensitive optical response of plasmonic metasurfaces  

Microsoft Academic Search

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

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

2011-01-01

386

Separation of high order harmonics with fluoride windows.  

PubMed

The ensemble of lower orders produced in high order harmonic generation can be efficiently temporally separated 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 use this simple and inexpensive technique in a pump/probe experiment to resolve femtosecond dynamics in the ethylene molecule. PMID:19466143

Allison, T K; van Tilborg, J; Wright, T W; Hertlein, M P; Falcone, R W; Belkacem, A

2009-05-25

387

Sol-gel Preparation of Fluoridated Hydroxyapatite in Ca(NO 3 ) 2 PO(OH) 3? x (OEt) x HPF 6 System  

Microsoft Academic Search

Fluoridated hydroxyapatite (FHA) has been successfully synthesized via sol-gel method with HPF6 as the fluorine containing reagent. The chemical reactions induced by HPF6 addition and the formation process of fluoridated hydroxyapatite (FHA) are investigated. The hydrolysis and alcoholysis of\\u000a HPF6 release F ion into the solution which, in turn, reacts with Ca ion to form nanocrystalline CaF2 (nc-CaF2). These nc-CaF2

Kui Cheng; Sam Zhang; Wengjian Weng

2006-01-01

388

Fluoride-containing bioactive glasses: Effect of glass design and structure on degradation, pH and apatite formation in simulated body fluid  

Microsoft Academic Search

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in particular, dental applications for caries inhibition. Melt-derived glasses in the system SiO2–P2O5–CaO–Na2O with increasing amounts of CaF2 were prepared by keeping network connectivity and the ratio of all other components constant. pH

Delia S. Brauer; Natalia Karpukhina; Matthew D. O’Donnell; Robert V. Law; Robert G. Hill

2010-01-01

389

The Mechanism of Fluoride-Induced Hypocalcaemia  

Microsoft Academic Search

1 Fluoride intoxication leads to sudden cardiac death which has been assumed to result from the accompanying severe hypocalcaemia. The aim of this study has been to investigate the suggestion that fluorapatite formation rather than CaF2 precipitation is responsible for this low calcium.2 Measurements of free Ca2+ and F- ion concentrations in HEPES buffered solutions containing F-, Ca2+, and phosphate

A. B. T. J. Boink; J. Wemer; J. Meulenbelt; H. A. M. G. Vaessen; D. J. de Wildt

1994-01-01

390

Global aspects of the energy landscape of metastable crystal structures in ionic compounds  

Microsoft Academic Search

Understanding the properties of complex systems requires the analysis of their energy landscape. Using simple models for the crystalline compounds MgF2 and CaF2 as example landscapes, we show that, in addition to the construction of tree-graph approximations of the landscape, the threshold algorithm can be employed to calculate local densities of states for regions of the landscape around local minima,

M. A. C. Wevers; J. C. Schön; M. Jansen

1999-01-01

391

Separation of High Order Harmonics with Fluoride Windows  

SciTech Connect

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.

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

2010-08-02

392

Optical whispering gallery mode resonances in asymmetric morphologies  

NASA Astrophysics Data System (ADS)

This dissertation describes the experimental realization of optical whispering-gallery-mode resonators constructed from crystalline material with various symmetries. Nonlinear optical scattering in disk-shaped resonators constructed from CaF 2 and LiNbO3 is discussed, as is the nonlinear optics of LN resonators with ferroelectric poling structures. Optical whispering-gallery-mode resonators with extended axes and highly elliptical geometries are presented. Experimentally observed effects of internal anisotropy on mode structure is also covered.

Mohageg, Makan

393

A comparative study of confined organic monolayers by Raman scattering and sum-frequency spectroscopy  

Microsoft Academic Search

The structure of a Langmuir–Blodgett (LB) monolayer of Zn arachidate at the solid–solid interface has been studied by Raman scattering and sum-frequency (SF) spectroscopy. The monolayer was confined in the contact between a CaF2 prism and a MgF2 lens at an average pressure of 60 MPa. This is the first report of an unenhanced Raman spectrum of an organic monolayer

David A Beattie; Sarah Haydock; Colin D Bain

2000-01-01

394

Burst Reaction of Thin Films Excited by High-Flux Soft X-Rays  

Microsoft Academic Search

High-flux soft-X-ray irradiation effects were investigated for the thick a-Si:H and muc-Si:H films, glass, MgF2 and CaF2 plates. The a-Si:H film of 7500 nm thickness has been burst, and its broken fragments flew off within several seconds. From the changes of Raman spectra before and after the irradiation and the film thickness dependence, it is thought that this is caused

Takeshi Kanashima; Masanori Okuyama; Hiroaki Okamoto; Kiminori Hattori; Haruhiko Ohashi; Eiji Ishiguro

2002-01-01

395

Characterization of infrared optical properties of transparent materials  

Microsoft Academic Search

Chemical and structural imperfections which occur in highly transparent insulators and semiconductors were studied by a range of electromagnetic and electronic techniques. These utilized infrared wavelength modulation, high contrast Raman and Brillouin scattering and photoinduced transients spectroscopy techniques. The spectoral distribution of the absorption in the spectral region from 2.5-12 gamma was measured by infrared wavelength modulation techniques on: CaF2,

R. Braunstein

1983-01-01

396

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

Microsoft Academic Search

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

J. Kirton; A. M. White

1969-01-01

397

Effects of fluoride on in vitro enamel demineralization analyzed by ¹?F MAS-NMR.  

PubMed

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

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

2013-01-01

398

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

NASA Technical Reports Server (NTRS)

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.

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

1982-01-01

399

Two CRM protein subfamilies cooperate in the splicing of group IIB introns in chloroplasts  

PubMed Central

Chloroplast genomes in angiosperms encode ?20 group II introns, approximately half of which are classified as subgroup IIB. The splicing of all but one of the subgroup IIB introns requires a heterodimer containing the peptidyl-tRNA hydrolase homolog CRS2 and one of two closely related proteins, CAF1 or CAF2, that harbor a recently recognized RNA binding domain called the CRM domain. Two CRS2/CAF-dependent introns require, in addition, a CRM domain protein called CFM2 that is only distantly related to CAF1 and CAF2. Here, we show that CFM3, a close relative of CFM2, associates in vivo with those CRS2/CAF-dependent introns that are not CFM2 ligands. Mutant phenotypes in rice and Arabidopsis support a role for CFM3 in the splicing of most of the introns with which it associates. These results show that either CAF1 or CAF2 and either CFM2 or CFM3 simultaneously bind most chloroplast subgroup IIB introns in vivo, and that the CAF and CFM subunits play nonredundant roles in splicing. These results suggest that the expansion of the CRM protein family in plants resulted in two subfamilies that play different roles in group II intron splicing, with further diversification within a subfamily to accommodate multiple intron ligands. PMID:18799595

Asakura, Yukari; Bayraktar, Omer Ali; Barkan, Alice

2008-01-01

400

Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials.  

PubMed

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

Kaczmarek, Anna M; Van Hecke, Kristof; Van Deun, Rik

2015-04-10

401

Spectroscopic and Relaxation Study of the Tritium -LABELLED-6 State in PRASEODYMIUM(3+):LANTHANUM-FLUORIDE.  

NASA Astrophysics Data System (ADS)

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.

Kichinski, Robert Thomas

1988-12-01

402

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

PubMed Central

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

Mi, Cong-Cong; Tian, Zhen-huang; Han, Bao-fu; Mao, Chuan-bin; Xu, Shu-kun

2012-01-01

403

Upconversion luminescence of Yb 3+/Tb 3+ co-doped tellurite glasses  

NASA Astrophysics Data System (ADS)

In the article the upconversion luminescence ofTeO2- GeO2 - PbO - PbF2- BaO - Nb2O5 - LaF3 glass system co-doped withYb 3+ /Tb 3+ under 976 nm laser diode excitation was investigated. The influence of Tb2O3concentration on the luminescent properties was determined. Measured strong luminescence at492, 547, 588, 622 nm correspond to 5D4?7FJ (J=6, 4, 3) transitions. Energy transfer (ET) mechanism involved in observed emission was discussed. The highest upconversion emission intensity was obtained in the tellurite glass co-doped with 0.5 Yb2O3/0.5 Tb2O3 (mol%).

Kochanowicz, Marcin; Zmojda, Jacek; Dorosz, Dominik; Miluski, Piotr; Dorosz, Jan

2014-05-01

404

Plasma-assisted deposition of metal fluoride coatings and modeling the extinction coefficient of as-deposited single layers.  

PubMed

We realized metal fluoride coatings with a high packing density and a low extinction coefficient by plasma (ion)-assisted deposition. The densification can be performed by different types of plasma sources, e.g., by a Leybold LION source and a Leybold APSpro, respectively. But the as-deposited coatings show a characteristic absorption behavior, whereas the absorption losses can be reduced in a postdeposition UV treatment step. We show experimental results of the plasma-assisted metal fluorides before and after the UV treatment and present a new model that allows us to describe and calculate the characteristic absorption losses of LaF3, MgF2, and AlF3. PMID:21460944

Bischoff, Martin; Stenzel, Olaf; Friedrich, Karen; Wilbrandt, Steffen; Gäbler, Dieter; Mewes, Stefan; Kaiser, Norbert

2011-03-20

405

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

PubMed Central

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

2013-01-01

406

Nanoscintillators for radiation detection  

NASA Astrophysics Data System (ADS)

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

Hall, Ryan Gregory

407

Measurement of nuclear and electronic Zeeman effects using optical hole-burning spectroscopy.  

PubMed

The excited-state nuclear Zeeman effect and quadratic-electronic Zeeman effect were studied in Pr(3+):LaF(3) using laser-induced hole burning. Hole burning in an external magnetic field gave values for the excited-state enhanced nuclear g tensor of g(x)beta/h = 2.2, g(y)beta/h = 1.9, and g(z)beta/h = 3.6 kHz/G. By applying the field after hole burning, quadratic-electronic Zeeman coefficients as small as 0.1 Hz/G(2) were measured. The hyperfine coupling constant in the excited (1)D(2) level was found to be A(J) = 600 MHz. PMID:19701339

Macfarlane, R M; Shelby, R M

1981-02-01

408

Evaluation of outgassing from a fluorinated resist for 157-nm lithography  

NASA Astrophysics Data System (ADS)

We have evaluated the outgassing products and the in-situ transmittance of a contaminated CaF2 substrate for monocyclic fluoropolymers with four protecting groups: methoxymethyl (MOM), tert-butoxycarbonyl (t-BOC), menthoxymethyl (MM), and 2-cyclohexylcyclohexyloxymethyl (CCOM). We have also evaluated the same type of fluoropolymer with seven kinds of photo-acid generators (PAGs) added to a base fluoropolymer solution. We found little correlation between the total amount of outgassing from the polymer and the decreasing rate of the CaF2 substrate transmittance caused by outgassing adhesion. Although the MOM protecting group generated the largest amount of outgassing products, the most substantial decrease in the transmittance was observed for the t-BOC protecting group. Also, the outgassing products due to use of a PAG did not greatly reduce the absorption coefficient of a CaF2 substrate regardless of the kind of PAG. Therefore, the absorption coefficient of the outgassing-contaminated CaF2 substrate appears to be more sensitive to the type of protecting group, especially the t-BOC protecting group including a t-butyl unit, rather than the type of fluoropolymer or PAG. We analyzed the substrate surface contaminant due to the t-butyl unit by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS), and found that increasing amounts of organic compounds, containing mainly C- and H-atoms, were adhered to and deposited on the substrate surface with an increasing irradiation dose. We speculate that the contaminants on a CaF2 surface with or without an anti-reflective coating were formed not only through mere physical adsorption, but also through certain chemical combinations. We conclude that in terms of material design of the fluoropolymer resist for 157-nm lithography, we need to pay attention to the protecting group of polymers, especially the t-BOC or t-butyl protecting group, which generates isobutene product during 157-nm irradiation.

Irie, Shigeo; Fujii, Kiyoshi; Itakura, Yasuo; Kawasa, Youichi; Egawa, Keiji; Uchino, Ikuo; Sumitani, Akira; Itani, Toshiro

2004-05-01

409

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

NASA Astrophysics Data System (ADS)

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

Kim, Dong-Geun

410

Spectroscopic analysis of Ho3+ transitions in different modifier oxide based lithium-fluoro-borate glasses  

NASA Astrophysics Data System (ADS)

In recent investigations it was observed that the presence of different structural groups in borate glasses was favorable for spectroscopic investigations of rare earth doped borate glasses. Consequent to these observations, the heavy metal fluoride glasses doped with Ho3+ ions received much attention due to their wide transparency in the ultraviolet to infrared region. Keeping these observations in view, the present paper makes an attempt to present spectral investigations of Ho3+ doped lithium-fluoro-borate glasses of the compositions Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. These rare earth doped glasses were synthesized by melt quenching technique and an investigation was carried out to observe the structural (SEM and FT-IR) and optical (absorption and luminescence) properties. The paper also aims at the determination of three phenomenological Judd-Ofelt intensity parameters and special attention was paid to study the emission properties by employing the J-O intensity parameters. The visible emission spectra of Ho3+ ion in different lithium-fluoro-borate glasses were recorded by exciting the samples at 409 nm. The results revealed that among all the glass matrices, cadmium glass matrix have shown higher stimulated emission cross-section, which indicates that this is a good lasing material at this wavelength and highly useful for laser excitation.

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

2014-10-01

411

Thin films of Y1Ba2Cu3Ox deposited using three target CO-sputtering and their applications to microbridge junctions and single-element IR detectors  

Microsoft Academic Search

We have produced superconducting thin films of Y1Ba2Cu3Ox (YBCO) on SrTiO3, ZrO2(Y2 O3), and Al2O3 having Tc's of 90 K and sharp DeltaTc's (0.3 K for 90% to 10% on SrTiO3 and 3.3×105 A\\/cm2 at 78 K). Samples were fabricated in a three target magnetron co-sputtering, computer controlled system using separate BaF2, Y, and Cu targets. Rutherford backscatterng (RBS) and

J. Y. Josefowicz; D. B. Rensch; A. T. Hunter; H. Kumura; B. M. Clemens; J. Spargo; E. Wiener-Avnir; G. Kerber; J. A. Wilson; W. D. Jack; J. M. Myroszynyk; R. E. Kvaas

1989-01-01

412

Study of a high resolution 3D PET scanner  

NASA Astrophysics Data System (ADS)

Some results of a study of the properties of a low pressure multistep avalanche chamber with BaF 2 scintillators and with TMAE as the photosensitive gas for a 3D PET scanner are presented. Absolute gas amplification was carefully measured by two independent methods, giving rise to a maximum attainable total gain of the order of 10 7. A typical electron transmission efficiency of 20-30% was obtained. The time resolution of the detector can be optimized to be ˜ 6 ns FWHM.

Shuping, Zhang; Bruyndonckx, P.; Goldberg, M. B.; Tavernier, S.

1994-09-01

413

Diluted magnetic semiconductor Ge 1? x Mn x Te films prepared by molecular beam epitaxy  

Microsoft Academic Search

We report the growth of IV–VI diluted magnetic semiconductor Ge1?xMnxTe thin films on BaF2 (111) substrates with high Mn ion concentration (x=0.98) by solid-source molecular-beam epitaxy. The film structure and orientation were characterized by in-situ reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD). The chemical concentration was determined by X-ray Photoelectron Spectroscopy (XPS). The thin film shows ferromagnetic ordering

W. Q. Chen; K. L. Teo; M. B. A. Jalil; Y. F. Liew; T. C. Chong

2006-01-01

414

Measurement of the Neutron Capture Cross Section of the Fissile Isotope 235U with the CERN n_TOF Total Absorption Calorimeter and a Fission Tagging Based on Micromegas Detectors  

NASA Astrophysics Data System (ADS)

Current and future nuclear technologies require more accurate nuclear data on (n,?) cross sections and the ?-ratios of fissile isotopes. Their measurement presents several difficulties, mainly related to the strong fission ?-ray background competing with the weaker ?-ray cascades used as the experimental signature of the (n,?) process. A specific setup was used at the CERN n_TOF facility in 2012 for the measurement of the (n,?) cross section and ?-ratios of fissile isotopes and used for the case of the 235U isotope. The setup consists of a set of micromegas fission detectors surrounding the 235U samples all placed inside a segmented BaF2 Total Absorption Calorimeter.

Balibrea, J.; Mendoza, E.; Cano-Ott, D.; Guerrero, C.; Berthoumieux, E.; Altstadt, S.; Andrzejewski, J.; Audouin, L.; Barbagallo, M.; Bécares, V.; Be?vá?, F.; Belloni, F.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Duran, I.; Dressler, R.; Dzysiuk, N.; Eleftheriadis, C.; Ferrari, A.; Fraval, K.; Ganesan, S.; García, A. R.; Giubrone, G.; Gómez-Hornillos, M. B.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Gunsing, F.; Gurusamy, P.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Kawano, T.; Kivel, N.; Koehler, P.; Kokkoris, M.; Korschinek, G.; Krti?ka, M.; Kroll, J.; Langer, C.; Lampoudis, C.; Lederer, C.; Leeb, H.; Leong, L. S.; Losito, R.; Manousos, A.; Marganiec, J.; Martínez, T.; Mastinu, P. F.; Mastromarco, M.; Massimi, C.; Meaze, M.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondelaers, W.; Paradela, C.; Pavlik, A.; Perkowski, J.; Pignatari, M.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Roman, F.; Rubbia, C.; Sarmento, R.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Stetcu, I.; Sabaté, M.; Tagliente, G.; Tain, J. L.; Tarrío, D.; Tassan-Got, L.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Versaci, R.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T. J.; Žugec, P.

2014-05-01

415

Spin Measurements of n +87Sr for Level Density Studies  

NASA Astrophysics Data System (ADS)

We have used the 4? BaF2 gamma-ray detector array at the n_TOF neutron time-of-flight facility at CERN for an experiment in order to determine the spins of resonances of n +87Sr by measuring the gamma-ray spectra and multiplicity distributions. The first results are presented here. We have assigned the orbital momentum ? to all evaluated resonances on the basis of their neutron widths. Further we have assigned the spin J to 16 s-wave resonances on based the population of low-lying levels.

Gunsing, F.; Fraval, K.; Mathelie, M.; Valenta, S.; Be?vá?, F.; Rusev, G.; Tonchev, A. P.; Mitchell, G.; Baramsai, B.; Altstadt, S.; Andrzejewski, J.; Audouin, L.; Barbagallo, M.; Bécares, V.; Belloni, F.; Berthoumieux, E.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Cano-Ott, D.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Duran, I.; Dressler, R.; Eleftheriadis, C.; Ferrari, A.; Ganesan, S.; García, A. R.; Giubrone, G.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Guerrero, C.; Hernández-Prieto, A.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Koehler, P.; Kokkoris, M.; Krti?ka, M.; Kroll, J.; Lampoudis, C.; Langer, C.; Leal-Cidoncha, E.; Lederer, C.; Leeb, H.; Leong, L. S.; Losito, R.; Manousos, A.; Marganiec, J.; Martínez, T.; Massimi, C.; Mastinu, P. F.; Mastromarco, M.; Mendoza, E.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondalaers, W.; Paradela, C.; Pavlik, A.; Perkowski, J.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Robles, M. S.; Rubbia, C.; Sabaté-Gilarte, M.; Sarmento, R.; Saxena, A.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Tagliente, G.; Tain, J. L.; Tarrío, D.; Tassan-Got, L.; Tsinganis, A.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T.; Žugec, P.

2014-05-01

416

Gamma-ray cascade transitions in ^112Cd and ^114Cd following capture of epithermal neutrons  

NASA Astrophysics Data System (ADS)

Investigation of the properties of the ?-ray transitions in the cadmium isotopes are of importance for nuclear structure and applied physics due to the high cross section for capture of thermal neutrons by ^111Cd and ^113Cd. We report results from a neutron-capture experiment on ^natCd carried out at LANL's LANSCE using the 4? BaF2 DANCE array. Isolated resonances with known spins were selected to study the ?-ray cascade transitions in ^112Cd and ^114Cd. Experimental results are compared with predictions from the code DICEBOX to determine the optimal ?-ray strength function that reproduces these cascade transitions.

Rusev, G.; Jandel, M.; Bredeweg, T. A.; Taddeucci, T. N.; Ullmann, J. L.; Krticka, M.

2012-10-01

417

Data Acquisition System for the Detector for Advanced Neutron Capture Experiments (DANCE)  

NASA Astrophysics Data System (ADS)

Nuclear and high energy physics experiments continue to grow in complexity. This increase in "experimental" complexity requires a matching increase in the complexity of the system used to acquire the data from the experimental apparatus. The Detector for Advanced Neutron Capture Experiments (DANCE), a 4? BaF2 array located at the Manuel J. Lujan Jr. Neutron Scattering Center at Los Alamos National Laboratory is a prime example of this increasing experimental complexity. We will describe several of the important issues that arose during the development of a data acquisition system based on MIDAS/ROOT, and the methods used to overcome these issues.

Bredeweg, T. A.; Reifarth, R.; Ullmann, J. L.; Haight, R. C.; O'Donnell, J. M.; Wouters, J. M.; Wilhelmy, J. B.; Rundberg, R. S.; Vieira, D. J.

2003-04-01

418

25Na and 25Mg fragmentation on 12C at 9.23 MeV per nucleon at TRIUMF  

NASA Astrophysics Data System (ADS)

HERACLES is a multidetector that is used to study heavy-ion collisions, with ion beams with an energy range between 8 to 15 MeV per nucleon. It has 78 detectors axially distributed around the beam axis in 6 rings allowing detection of multiple charged fragments from nuclear reactions. HERACLES has 4 different types of detectors, BC408/BaF2 phoswich, Si/CsI(Tl) telescope, BC408/BC444 phoswich and CsI(Tl) detectors. The multidetector has been run with a radioactive 25Na beam and a stable 25Mg beam at 9.23 MeV per nucleon on a carbon target.

St-Onge, Patrick; Boisjoli, Mark; Frégeau, Marc-Olivier; Gauthier, Jérôme; Wallace, Barton; Roy, René

2012-10-01

419

10(-10) temporal contrast for femtosecond ultraintense lasers by cross-polarized wave generation.  

PubMed

We take advantage of nonlinear properties associated with chi(3) tensor elements in BaF2 cubic crystal to improve the temporal contrast of femtosecond laser pulses. The technique presented is based on cross-polarized wave (XPW) generation. We have obtained a transmission efficiency of 10% and 10(-10) contrast with an input pulse in the millijoule range. This filter does not affect the spectral shape or the phase of the cleaned pulse. It also acts as an efficient spatial filter. In this method the contrast enhancement is limited only by the extinction ratio of the polarization discrimination device. PMID:15865399

Jullien, Aurélie; Albert, Olivier; Burgy, Frédéric; Hamoniaux, Guy; Rousseau, Jean-Philippe; Chambaret, Jean-Paul; Augé-Rochereau, Frédérika; Chériaux, Gilles; Etchepare, Jean; Minkovski, Nikolay; Saltiel, Solomon M

2005-04-15

420

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

421

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

PubMed

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. PMID:25638066

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

2015-01-01

422

Raman spectra and structure of fluoroaluminophosphate glasses  

Microsoft Academic Search

Fluoroaluminophosphate glasses are promising materials for rare earth doping, but their structure is not yet well known. The structural changes which take place in the 39AlF3–11NaF–10LiF–(40?x)(CaF2–MgF2–SrF2–BaF2)–xNaPO3 system, with increasing NaPO3 content (0–15 mol%), have been studied by polarised Raman and also infrared reflectance spectroscopies. The Raman spectra of the glasses, at low-phosphate content, presented a polarised band peaking near 520cm?1,

Lu??s F Santos; Rui M Almeida; Victor K Tikhomirov; Animesh Jha

2001-01-01

423

Growth and magnetic properties of IV-VI diluted magnetic semiconductor Ge1-xCrxTe  

NASA Astrophysics Data System (ADS)

IV-VI diluted magnetic semiconductor Ge1-xCrxTe films were grown on BaF2 substrates by molecular-beam epitaxy. The Ge1-xCrxTe film up to x=0.103 is single phase as determined by reflection high-energy electron diffraction and x-ray diffraction measurements. The optical band gap decreases with increasing Cr composition. Ferromagnetic order of the Ge1-xCrxTe films is characterized by direct magnetization and anomalous Hall effect measurements.

Fukuma, Y.; Taya, T.; Miyawaki, S.; Irisa, T.; Asada, H.; Koyanagi, T.

2006-04-01

424

Carrier-induced ferromagnetism in Ge0.92Mn0.08Te epilayers with a Curie temperature up to 190 K  

NASA Astrophysics Data System (ADS)

IV-VI diluted magnetic semiconductor Ge0.92Mn0.08Te epilayers are grown on BaF2 substrates by molecular beam epitaxy. The ferromagnetic behaviors, such as the spontaneous magnetization, the coercive field, and the Curie temperature TC, are altered by the hole concentration p. In the Ge0.92Mn0.08Te layer with high p, strong magnetic anisotropy and the temperature dependence of the magnetization expected for homogeneous ferromagnets are observed, implying that long-range ordering is induced by the holes. The maximum TC reaches 190 K for 1.57×1021 cm-3.

Fukuma, Y.; Asada, H.; Miyawaki, S.; Koyanagi, T.; Senba, S.; Goto, K.; Sato, H.

2008-12-01

425

TiF(4) varnish-A (19)F-NMR stability study and enamel reactivity evaluation.  

PubMed

The aim of this study was to develop a titanium tetrafluoride (TiF(4)) varnish and evaluate the stability of the formulation and its reactivity with dental enamel. The varnish was prepared in a resinous matrix using ethanol 96% as solvent. Samples (n=45) were aged at 65 degrees C and 30% of relativity humidity (RE n degrees 01/05-ANVISA) and after 3, 6, 9 and 12 months, nine samples were removed for evaluation and compared with fresh samples. Chemical stability of TiF(4) varnish was determinate by (19)F-NMR and the reactivity of the formulation was quantified by formation of fluoride loosely (CaF(2)) and firmly bound (fluorapatite; FA) to enamel. For reactivity comparisons, a varnish without TiF(4) was used as control. The loss of soluble fluoride was about 0.9% after one year of storage. The values of the reactivity (mean+/-S.D.) of fresh, aged at 3, 6, 9 and 12 months and control samples were: CaF(2) (microg F/mm(2)): 89.3+/-27.5(a); 54.5+/-14.3(b); 51.2+/-29.8(b); 69.3+/-21.3(a); 48.0+/-27.4(b); 0.10+/-0.07(c), FA (microg F/g): 2477.5+/-1044.0(a); 2484.8+/-992.0(a); 2580.0+/-1383.9(a); 2517.2+/-929.9(a); 2121.0+/-1059.2(a); 330.0+/-180.0(b), respectively. Means followed by distinct letters were statistically different (p<0.05). After one year of storage, the formulation was chemically stable and the levels of FA were maintained. However there was an initial decrease in the ability to form CaF(2). PMID:18175996

Nóbrega, Carolina Bezerra Cavalcanti; Fujiwara, Fred Yukio; Cury, Jaime Aparecido; Rosalen, Pedro Luiz

2008-01-01

426

Arabidopsis Orthologs of Maize Chloroplast Splicing Factors Promote Splicing of Orthologous and Species-Specific Group II Introns1[W  

PubMed Central

Chloroplast genomes in plants and green algae contain numerous group II introns, large ribozymes that splice via the same chemical steps as spliceosome-mediated splicing in the nucleus. Most chloroplast group II introns are degenerate, requiring interaction with nucleus-encoded proteins to splice in vivo. Genetic approaches in maize (Zea mays) and Chlamydomonas reinhardtii have elucidated distinct sets of proteins that assemble with chloroplast group II introns and facilitate splicing. Little information is available, however, concerning these processes in Arabidopsis (Arabidopsis thaliana). To determine whether the paucity of data concerning chloroplast splicing factors in Arabidopsis reflects a fundamental difference between protein-facilitated group II splicing in monocot and dicot plants, we examined the mutant phenotypes associated with T-DNA insertions in Arabidopsis genes encoding orthologs of the maize chloroplast splicing factors CRS1, CAF1, and CAF2 (AtCRS1, AtCAF1, and AtCAF2). We show that the splicing functions and intron specificities of these proteins are largely conserved between maize and Arabidopsis, indicating that these proteins were recruited to promote the splicing of plastid group II introns prior to the divergence of monocot and dicot plants. We show further that AtCAF1 promotes the splicing of two group II introns, rpoC1 and clpP-intron 1, that are found in Arabidopsis but not in maize; AtCAF1 is the first splicing factor described for these introns. Finally, we show that a strong AtCAF2 allele conditions an embryo-lethal phenotype, adding to the body of data suggesting that cell viability is more sensitive to the loss of plastid translation in Arabidopsis than in maize. PMID:17071648

Asakura, Yukari; Barkan, Alice

2006-01-01

427

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

428

Nanostructure morphology and atomically resolved images of chains and planes of YBCO single crystals grown with different additives  

NASA Astrophysics Data System (ADS)

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.

Narlikar, A. V.; Samanta, S. B.; Changkang, Chen; Yongle, Hu; Hodby, J. W.; Wanklyn, B. M.

1996-01-01

429

Identification and rejection of scattered neutrons in AGATA  

NASA Astrophysics Data System (ADS)

? 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 ? rays with the ?-ray tracking technique. The BaF2 detectors were used for a time-of-flight measurement, which gave an independent discrimination of neutrons and ? rays and which was used to optimise the ?-ray tracking-based neutron rejection methods. It was found that standard ?-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 ? ray, and figure-of-merit value. The experimental results of tracking with neutron rejection agree rather well with GEANT4 simulations.

?enyi?it, M.; Ataç, A.; Akkoyun, S.; Ka?ka?, A.; Bazzacco, D.; Nyberg, J.; Recchia, F.; Brambilla, S.; Camera, F.; Crespi, F. C. L.; Farnea, E.; Giaz, A.; Gottardo, A.; Kempley, R.; Ljungvall, J.; Mengoni, D.; Michelagnoli, C.; Million, B.; Palacz, M.; Pellegri, L.; Riboldi, S.; ?ahin, E.; Söderström, P. A.; Valiente Dobon, J. J.

2014-01-01

430

Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses  

NASA Astrophysics Data System (ADS)

High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.

2013-05-01

431

UV/blue upconversion in Nd3+:TeO2 glass, effect of modifiers and heat treatment on the fluorescence bands.  

PubMed

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

Verma, R K; Kumar, K; Rai, S B

2009-10-15

432

X-ray excited optical luminescence studies on the system BaXY(X,Y=F, Cl, Br, I)  

NASA Astrophysics Data System (ADS)

The present paper reports the experimental observations on the x-ray excited optical luminescence (XEOL) along with the afterglow and colour center features found for the barium salts, represented by the formula, BaXY, where X and Y are the halides. The system thus consists of four dihalides (BaF_{2},ldots,BaI_{2}) and six mixed halides (BaFCl,{ldots},BaBrI). To start with, it was found that on two of the binary halides of barium, BaClI and BaBrI, no literature exists, and so these were prepared for the first time and their crystal structures were determined. An x-ray generator of 3-kW rating was next coupled to a spectrometer via a high throughput fiberoptic sensor for recording the luminescence spectra under x-irradiation. Also presented in this paper are the observations on the BaXY compounds in which about 0.1 mole% of Eu^{2+} was doped, in order to study the efficiency between the prompt luminescence and the photostimulated luminescence in these compounds. The crystal structure varies from fluorite (BaF_{2}), to matlockite (BaFX) and finally to orthorhombic (BaCl_{2}, ldots,BaBrI) for these compounds. Hence searching for systematics and empirical relations in the observed XEOL behaviour of these compounds is still a challenging problem.

Rajan, K. Govinda; Jestin Lenus, A.

2005-08-01

433

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

PubMed

Chemical reactions induced by mechanical treatment may give access to new compounds whose properties are governed by chemical metastability, defects introduced and the size effects present. Their interplay may lead to nanocrystalline ceramics with enhanced transport properties being useful to act as solid electrolytes. Here, the introduction of large amounts of La into the cubic structure of BaF2 served as such an example. The ion transport properties in terms of dc-conductivity values of the F(-) anion conductor Ba1-xLaxF2+x (here with x = 0.4) considerably exceed those of pure, nanocrystalline BaF2. So far, there is only little knowledge about activation energies and jump rates of the elementary hopping processes. Here, we took advantage of both impedance spectroscopy and (19)F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. While macroscopic transport is governed by an activation energy of 0.55 to 0.59 eV, the elementary steps of hopping seen by NMR are characterised by much smaller activation energies. Fortunately, we were able to deduce an F(-) self-diffusion coefficient by the application of spin-locking NMR relaxometry. PMID:24728404

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

2014-05-28

434

HERACLES : a multidetector for heavy-ion collisions at TRIUMF  

NASA Astrophysics Data System (ADS)

HERACLES is a multidetector that has been modified to study heavy-ion collisions, using an ion beam with an energy range between 8 to 15 MeV per nucleon. It has 78 detectors axially distributed around the beam axis in 6 rings allowing detection of multiple charged fragments from nuclear reactions. HERACLES has 4 different types of detectors, BC408/BaF2 phoswich, Si/CsI(Tl) telescope, BC408/BC444 phoswich and CsI(Tl) detectors. 25 Na + 12 C, 25 Na + 27 Al, 25 Mg + 12 C and 25 Mg + 27 Al reactions have been used to characterize the multidetector. Element identification up to Z = 12 is achieved with the BC408/BaF2 phoswich detectors, up to Z = 15 with the Si/CsI(Tl) telescopes and up to Z = 12 with the BC408/BC444 phoswich detectors. Isotopic identification is reached with the CsI(Tl) detector up to Z = 2.

St-Onge, Patrick; Gauthier, Jérôme; Wallace, Barton; Roy, René

2014-01-01

435

Pressure-induced phase transition and structural properties of CrO2  

Microsoft Academic Search

The structural properties and pressure-induced phase transitions of CrO2 have been investigated using the pseudopotential plane-wave method based on the density functional theory (DFT). The rutile-type (P42\\/mnm), CaCl2-type (Pnnm), pyrite-type (P?3), and CaF2-type (Fm-3m) phases of CrO2 have been considered. The structural properties such as lattice parameters, bulk moduli and its pressure derivative are consistent with the available experimental data.

H. Y. Wu; Y. H. Chen; C. R. Deng; X. F. Su

2012-01-01

436

Anti-washout carboxymethyl chitosan modified tricalcium silicate bone cement: preparation, mechanical properties and in vitro bioactivity  

Microsoft Academic Search

Anti-washout CaF2 stabilized C3S (F-C3S) bone cement was prepared by adding water-soluble carboxymethyl chitosan (CMCS) to the hydration liquid. The setting time,\\u000a compressive strength and in vitro bioactivity of the CMCS modified F-C3S (CMCS–C3S) pastes were evaluated. The results indicate that CMCS–C3S pastes could be stable in the shaking simulated body fluid (SBF) after immediately mixed. The addition of CMCS

Qing LinXianghui LanYanbao Li; Xianghui Lan; Yanbao Li; Yinhui Yu; Yaru Ni; Chunhua Lu; Zhongzi Xu

2010-01-01

437

Influence of electrolyte impurities on current efficiency in aluminium electrolysis cells  

Microsoft Academic Search

The influence of electrolyte impurity species on current efficiency with respect to aluminium (CE) was studied in a specially designed laboratory cell at 980°C, with a graphite anode and a cathodic current density of 0.85Acm-2. The electrowinning was performed in a base melt of Na3AlF6 with a NaF\\/AlF3 molar ratio of 2.5 and with 4–6wt% Al2O3 and 5wt% CaF2. Impurity

Å. Sterten; P. A. Solli; E. Skybakmoen

1998-01-01

438

Passively Q-switched microchip laser R. Haring, R. Paschotta, R. Fluck,* E. Gini, H. Melchior, and U. Keller  

E-print Network

crystal (e.g., Co2 :LaMgAl11O19,4,5 Er:Ca5(PO4)3F,6 U4 :CaF2,7,8 U4 :SrF2,9 Co2 :ZnSe,10 Cr2 :ZnSe11. Melchior, and U. Keller Institute of Quantum Electronics, Swiss Federal Institute of Technology (ETH), ETH thresholds and high efficiencies can be designed with SESAMs because the losses can be kept well below 1

Keller, Ursula

439

Laser-Induced Damage of Calcium Fluoride  

SciTech Connect

As advances continue to be made in laser technology there is an increasing demand for materials that have high thresholds for laser-induced damage. Laser damage occurs when light is absorbed, creating defects in the crystal lattice. These defects can lead to the emission of atoms, ions and molecules from the sample. One specific field where laser damage is of serious concern is semiconductor lithography, which is beginning to use light at a wavelength of 157 nm. CaF2 is a candidate material for use in this new generation of lithography. In order to prevent unnecessary damage of optical components, it is necessary to understand the mechanisms for laser damage and the factors that serve to enhance it. In this research, we study various aspects of laser interactions with CaF2, including impurity absorbance and various forms of damage caused by incident laser light. Ultraviolet (UV) laser light at 266 nm with both femtosecond (fs) and nanosecond (ns) pulse widths is used to induce ion and neutral particle emission from cleaved samples of CaF2. The resulting mass spectra show significant differences suggesting that different mechanisms for desorption occur following excitation using the different pulse durations. Following irradiation by ns pulses at 266 nm, multiple single-photon absorption from defect states is likely responsible for ion emission whereas the fs case is driven by a multi-photon absorption process. This idea is further supported by the measurements made of the transmission and reflection of fs laser pulses at 266 nm, the results of which reveal a non-linear absorption process in effect at high incident intensities. In addition, the kinetic energy profiles of desorbed Ca and K contaminant atoms are different indicating that a different mechanism is responsible for their emission as well. Overall, these results show that purity plays a key role in the desorption of atoms from CaF2 when using ns pulses. On the other hand, once the irradiance reaches high levels, like that of the fs case, significant desorption is possible due to multi-photon absorption by the intrinsic material.

Espana, A.; Joly, A.G.; Hess, W.P.; Dickinson, J.T.

2004-01-01

440

Characteristics of 355 nm Laser Damage in Bulk Materials  

NASA Astrophysics Data System (ADS)

The laser damage resistances of four crystals (CaF2, MgF2, Al2O3, and SiO2) and fused silica (JGS1) irradiated at 355 nm (8 ns, 300-on-1) are reported. The laser-induced damage threshold is measured using a tripled Nd:YAG laser system. The results obtained from the pure crystals are in accordance with their specific optical, mechanical, and thermal properties. An empirical law based on the Franz—Keldysh effect can interpret the experimental results.

Yu, Zhen-Kun; He, Hong-Bo; Qi, Hong-Ji; Fang, Zhou; Li, Da-Wei

2013-06-01

441

Ultra-trace analysis of 41Ca in urine by accelerator mass spectrometry: an inter-laboratory comparison  

PubMed Central

A 41Ca 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

Jackson, George S.; Hillegonds, Darren J.; Muzikar, Paul; Goehring, Brent

2013-01-01

442

Observation of fluorapatite formation under hydrolysis of tetracalcium phosphate in the presence of KF by means of soft X-ray emission and absorption spectroscopy  

Microsoft Academic Search

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) in 0.1 mol\\/l KH2PO4 containing 62–83 mmol\\/l KF was studied with the help of X-ray fluorescence measurements. Fluorine X-ray emission and absorption spectra of the final product of hydrolysis and reference samples (CaF2 and Ca5(PO4)3F) were measured at Beamline BL-2C of Photon Factory (PF, Tsukuba). Based on these

E. Z. Kurmaev; S. Matsuya; S. Shin; M. Watanabe; R. Eguchi; Y. Ishiwata; T. Takeuchi; M. Iwami

2002-01-01

443

High-gain amplification in Yb:CaF2 crystals pumped by a high-brightness Yb-doped 976 nm fiber laser  

NASA Astrophysics Data System (ADS)

We report on high single-pass gain in Yb:CaF2 crystal longitudinally pumped with a 40 W high-brightness fiber laser source based on an ytterbium-doped ultra-large core photonic crystal rod-type fiber operating at 976 nm. A single-pass small-signal gain of 3.2 has been achieved in a 6 % Yb-doped 10-mm-long CaF2 crystal at room temperature, outperforming any CW-diode-pumped scheme and paving the way towards very promising innovative lasers and amplifiers schemes merging the Yb-doped solid-state and fiber technologies.

Machinet, G.; Andriukaitis, G.; Sévillano, P.; Lhermite, J.; Descamps, D.; Pugžlys, A.; Baltuška, A.; Cormier, E.

2013-05-01

444

Analysis of multiple pulse NMR in solids  

NASA Technical Reports Server (NTRS)

The general problems associated with the removal of the effects of dipolar broadening from solid-state NMR spectra are analyzed. The effects of finite pulse width and H sub 1 inhomogeneity are shown to have limited the resolution of previous pulse cycles, and a new eight-pulse cycle designed to minimize these problems is discussed. Spectra for F-19 in CaF2 taken with this cycle are presented which show residual linewidth near 10 Hz. The feasibility of measuring proton chemical shift tensors is discussed.

Rhim, W.-K.; Elleman, D. D.; Vaughan, R. W.

1973-01-01

445

Determination of candidate structures for simple ionic compounds through cell optimisation  

Microsoft Academic Search

We show at the example of several simple ionic compounds (NaCl, CsCl, LiF, NaF, KF, RbF, CsF, CaO, MgO, K2O, Li2O, MgF2, CaF2, Al2O) that the global minimisation of the energy through variation of both the basis vectors of the simulation cell and the relative positions of the atoms within the cell leads to structures that are good candidates for

J. C. Schön; M. Jansen

1995-01-01

446

Preparation and Organized Assembly of Nanoparticulate TiO 2–Stearate Alternating Langmuir–Blodgett Films  

Microsoft Academic Search

Nanoparticulate TiO2–stearate Langmuir–Blodgett-type monolayers and multilayers were directly obtained by using TiO2hydrosol as the subphase. The surface pressure-versus-surface area isotherms showed that the monolayer could be compressed to a mean molecular area of 0.25 nm2. The monolayer was transferred onto a CaF2or Si substrate at a dipping speed of 18 cm\\/min and surface pressure of 25 mN\\/m. It exhibited Y-type

Lin Song Li; Zheng Hui; Yongmei Chen; Xin Tong Zhang; Xiaogang Peng; Zhongfan Liu; Tie Jin Li

1997-01-01

447

Note: Broadband cavity ring-down spectroscopy of an intra-cavity bulk sample  

NASA Astrophysics Data System (ADS)

A cavity ring-down (CRD) setup equipped with a pulsed broadband light source (480 nm ? ?? 650 nm) and a multichannel detection system (temporal gate width ?? = 20 ns) is used to simultaneously record the optical loss spectrum of an intra-cavity CaF2 sample and its changes upon transverse ArF laser irradiation at 193 nm. The CRD setup with mirrors of high reflectivity (R > 99.93%) allows to register loss changes of 5 × 10-5 with a spectral resolution of 0.3 nm in less than 2 min.

Zeuner, T.; Paa, W.; Mühlig, C.; Stafast, H.

2013-03-01

448

Nonmetallic substrates for growth of silicene: an ab initio prediction.  

PubMed

By means of first-principles calculations we predict the stability of silicene layers as buckled honeycomb lattices on Cl-passivated Si(1?1?1) and clean CaF2(1?1?1) surfaces. The van der Waals interaction between silicene and the inert substrate stabilizes the adsorbate system while not destroying the Si pz-derived linear bands forming Dirac cones at the Brillouin zone corners. Only small gaps of about 3 and 52 meV are opened. PMID:24728001

Kokott, S; Pflugradt, P; Matthes, L; Bechstedt, F

2014-05-01

449

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

PubMed

Attenuated total reflectance infrared spectroscopy and complementary scanning electron microscopy were applied to analyze the surface structure of enamel apatite exposed to citric acid and to investigate the protective potential of fluorine-containing reagents against citric acid-induced erosion. Enamel and, for comparison, geological hydroxylapatite samples were treated with aqueous solutions of citric acid and sodium fluoride of different concentrations, ranging from 0.01 to 0.5 mol/L for citric acid solutions and from 0.5 to 2.0% for fluoride solutions. The two solutions were applied either simultaneously or consecutively. The citric acid-induced structural modification of apatite increases with the increase in the citric acid concentration and the number of treatments. The application of sodium fluoride alone does not suppress the atomic level changes in apatite exposed to acidic agents. The addition of sodium fluoride to citric acid solutions leads to formation of surface CaF2 and considerably reduces the changes in the apatite P-O-Ca framework. However, the CaF2 globules deposited on the enamel surface seem to be insufficient to prevent the alteration of the apatite structure upon further exposure to acidic agents. No evidence for fluorine-induced recovery of the apatite structure was found. PMID:18588337

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

2008-07-24

450

Identification of salt-alloy combinations for thermal energy storage applications in advanced solar dynamic power systems  

NASA Technical Reports Server (NTRS)

Thermodynamic calculations based on the available data for flouride salt systems reveal that a number of congruently melting compositions and eutectics exist which have the potential to meet the lightweight, high energy storage requirements imposed for advanced solar dynamic systems operating between about 1000 and 1400 K. Compatibility studies to determine suitable containment alloys to be used with NaF-22CaF2-13MgF2, NaF-32CaF2, and NaF-23MgF2 have been conducted at the eutectic temperature + 25 K for each system. For these three NaF-based eutectics, none of the common, commercially available high temperature alloys appear to offer adequate corrosion resistance for a long lifetime; however mild steel, pure nickel and Nb-1Zr could prove useful. These latter materials suggest the possibility that a strong, corrosion resistant, nonrefractory, elevated temperature alloy based on the Ni-Ni3Nb system could be developed.

Whittenberger, J. D.; Misra, A. K.

1987-01-01

451

Syntheses, structural characterization, and DPPH radical scavenging activity of cocrystals of caffeine with 1- and 2-naphthoxyacetic acids  

NASA Astrophysics Data System (ADS)

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.

Suresh Kumar, G. S.; Seethalakshmi, P. G.; Sumathi, D.; Bhuvanesh, N.; Kumaresan, S.

2013-03-01

452

A Ribonuclease III Domain Protein Functions in Group II Intron Splicing in Maize Chloroplasts[W  

PubMed Central

Chloroplast genomes in land plants harbor ?20 group II introns. Genetic approaches have identified proteins involved in the splicing of many of these introns, but the proteins identified to date cannot account for the large size of intron ribonucleoprotein complexes and are not sufficient to reconstitute splicing in vitro. Here, we describe an additional protein that promotes chloroplast group II intron splicing in vivo. This protein, RNC1, was identified by mass spectrometry analysis of maize (Zea mays) proteins that coimmunoprecipitate with two previously identified chloroplast splicing factors, CAF1 and CAF2. RNC1 is a plant-specific protein that contains two ribonuclease III (RNase III) domains, the domain that harbors the active site of RNase III and Dicer enzymes. However, several amino acids that are essential for catalysis by RNase III and Dicer are missing from the RNase III domains in RNC1. RNC1 is found in complexes with a subset of chloroplast group II introns that includes but is not limited to CAF1- and CAF2-dependent introns. The splicing of many of the introns with which it associates is disrupted in maize rnc1 insertion mutants, indicating that RNC1 facilitates splicing in vivo. Recombinant RNC1 binds both single-stranded and double-stranded RNA with no discernible sequence specificity and lacks endonuclease activity. These results suggest that RNC1 is recruited to specific introns via protein–protein interactions and that its role in splicing involves RNA binding but not RNA cleavage activity. PMID:17693527

Watkins, Kenneth P.; Kroeger, Tiffany S.; Cooke, Amy M.; Williams-Carrier, Rosalind E.; Friso, Giulia; Belcher, Susan E.; van Wijk, Klaas J.; Barkan, Alice

2007-01-01

453

Liquidus Temperature Depression in Cryolitic Melts  

NASA Astrophysics Data System (ADS)

The electrolyte in Hall-Héroult cells for the manufacture of primary aluminum nominally contains only cryolite (Na3AlF6) with additions of AlF3, CaF2, and Al2O3. However, impurities are present, entering the process with the feedstock. The effect on the liquidus temperature by the impurities cannot be calculated correctly by the well-known equation for freezing-point depression in binary systems simply because the electrolyte cannot be regarded as a binary system. By extending the equation for freezing-point depression to the ternary system NaF-AlF3-B, it appeared that the acidity of the impurity B plays a major role. Some calculations were made using an ideal Temkin model, and for most types of impurities, the effect on the liquidus temperature will be larger in an industrial electrolyte than what can be estimated from the equation for freezing-point depression in cryolite. Experimental data on the liquidus temperature in the system Na3AlF6-AlF3-Al2O3-CaF2-MgF2 show that the effect of MgF2 on the liquidus temperature increases strongly with decreasing NaF/AlF3 molar ratio, and it is suggested that MgF2 forms an anion complex, probably MgF{4/2-}.

Solheim, Asbjørn

2012-08-01

454

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.  

PubMed

In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright ?111? streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles. PMID:24046491

Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

2013-08-01

455

Ellipsometric and optical study of some uncommon insulator films on 3-5 semiconductors  

NASA Technical Reports Server (NTRS)

Optical properties of three types of insulating films that show promise in potential applications in the 3-4 semiconductor technology were evaluated, namely a-C:H, BN and CaF2. The plasma deposited a-C:H shows an amorphous behavior with optical energy gaps of approximately 2 to 2.4 eV. These a-C:H films have higher density and/or hardness, higher refractive index and lower optical energy gaps with increasing energy of the particles in the plasma, while the density of states remains unchanged. These results are in agreement, and give a fine-tuned positive confirmation to an existing conjecture on the nature of a-C:H films (1). Ion beam deposited BN films show amorphous behavior with energy gap of 5 eV. These films are nonstoichiometric (B/N approximately 2) and have refractive index, density and/or hardness which are dependent on the deposition conditions. The epitaxially grown CaF2 on GaAs films have optical parameters equal to bulk, but evidence of damage was found in the GaAs at the interface.

Alterovitz, S. A.; Warner, J. D.; Liu, D. C.; Pouch, J. J.

1985-01-01

456

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

NASA Technical Reports Server (NTRS)

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.

Dellacorte, Christopher

1989-01-01

457

Beam tests of a Fast-RICH prototype with VLSI readout electronics  

NASA Astrophysics Data System (ADS)

In this report we discuss the Fast Ring Imaging Cherenkov technique that we have developed for application to proximity-focused LiF (or CaF 2) solid radiator and multiwire chamber photon detector with cathode-pad readout using TEA in CH 4 as photosensor. We describe the full-scale Prototype of 12 000 pads (5.334 × 6.604 mm 2) we have built, and briefly the dedicated VLSI readout electronics we have developed. We report in detail the investigations we have performed in a hadron test beam at the CERN PS, and compare the results obtained to the expected performances. The maximum momentum for ?/K separation at 3? achieved in these tests is 2.86 GeV/ c for LiF (2.39 GeV/ c for CaF 2). The experimentally achieved Cherenkov merit factors, after correction for azimuthal angle acceptance, are N0 = 65.5 cm -1 (57.7 cm -1), to be compared with 53.8 cm -1 (50.2 cm -1) from Monte Carlo calculations. Operation of the detector over several months has proven the technique reliable and robust, and suitable for application in high-luminosity hadron colliders like LHC, as well as e +e - B-Factories like KEK (Japan), SLAC (USA), and Cornell (USA).

Séguinot, J.; Ypsilantis, T.; Jobez, J. P.; Arnold, R.; Guyonnet, J. L.; Chesi, E.; Tischhauser, J.; Adachi, I.; Sumiyoshi, T.; Mountain, R. J.

1994-11-01

458

Carbon Solubility in the CaO-SiO2-3MgO-CaF2 Slag System  

NASA Astrophysics Data System (ADS)

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.

Park, Jun-Yong; Jung, Sung-Mo; Sohn, Il

2014-04-01

459

Electrokinetic Behavior of Fluoride Salts as Explained from Water Structure Considerations  

PubMed

Unlike the other silver halides, silver fluoride is positively charged in its saturated solution as determined by nonequilibrium electrophoresis measurements. In the absence of surface hydrolysis reactions, other fluoride salts (LiF, CaF2 , and MgF2 ) also are positively charged in their saturated solutions. Furthermore, the electrokinetic behavior of these fluoride salts is rather insensitive to the fluoride ion activity in neutral or acidic solutions, and reversal of the sign of the surface charge by fluoride addition is not possible. Based on FTIR transmission spectra to describe the water structure of ionic solutions, in situ FTIR/internal reflection spectroscopy (FTIR/IRS) has been used to spectroscopically characterize interfacial water at fluoride salt surfaces. The experimental spectra were examined by consideration of the O-H stretching region (3000-3800 cm-1 ) associated with the vibrational spectra of interfacial water. These results reveal a unique hydration state for fluorides and explain the anomalous electrokinetic behavior of fluoride salts such as LiF, CaF2 , and MgF2 , which show an unexpected insensitivity to the fluoride ion concentration in solution. It appears that this insensitivity is due to the formation of strong hydrogen bonding of the fluoride ions with water molecules. This hydration state prevents the accommodation of excess fluoride ions at surface lattice sites and accounts for the observed electrokinetic behavior. PMID:9241159

Hu; Lu; Veeramasuneni; Miller

1997-06-01

460

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.  

PubMed

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. PMID:25085153

Chiarello, Gian Luca; Nachtegaal, Maarten; Marchionni, Valentina; Quaroni, Luca; Ferri, Davide

2014-07-01

461

Fluoride-containing bioactive glasses: effect of glass design and structure on degradation, pH and apatite formation in simulated body fluid.  

PubMed

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in particular, dental applications for caries inhibition. Melt-derived glasses in the system SiO(2)-P(2)O(5)-CaO-Na(2)O with increasing amounts of CaF(2) were prepared by keeping network connectivity and the ratio of all other components constant. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid at 37 degrees C over up to 2 weeks were investigated. Crystal phases formed in SBF were characterized using infrared spectroscopy, X-ray diffraction with Rietveld analysis and solid-state nuclear magnetic resonance spectroscopy ((19)F and (31)P MAS-NMR). Results show that incorporation of fluoride resulted in a reduced pH rise in aqueous solutions compared to fluoride-free glasses and in formation of fluorapatite (FAp), which is more chemically stable than hydroxyapatite or carbonated hydroxyapatite and therefore is of interest for dental applications. However, for increasing fluoride content in the glass, fluorite (CaF(2)) was formed at the expense of FAp. Apatite formation could be favoured by increasing the phosphate content in the glass, as the release of additional phosphate into the SBF would affect supersaturation in the solution and possibly favour formation of apatite. PMID:20132911

Brauer, Delia S; Karpukhina, Natalia; O'Donnell, Matthew D; Law, Robert V; Hill, Robert G

2010-08-01

462

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 to 1400 K  

NASA Technical Reports Server (NTRS)

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.

Misra, Ajay K.; Whittenberger, J. Daniel

1987-01-01

463

Synthesis of High-Temperature Self-lubricating Wear Resistant Composite Coating on Ti6Al4V Alloy by Laser Deposition  

NASA Astrophysics Data System (ADS)

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.

Luo, Jian; Liu, Xiu-Bo; Xiang, Zhan-Feng; Shi, Shi-Hong; Chen, Yao; Shi, Gao-Lian; Wu, Shao-Hua; Wu, Yu-Nan

2015-03-01

464

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 - 1400 K  

NASA Astrophysics Data System (ADS)

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.

Misra, Ajay K.; Whittenberger, J. Daniel

465

[Studies on the hygiene of arc-welding. (Part 8). Effects of atmospheric conditions on the chemical composition of fumes from low hydrogen welding].  

PubMed

Welding fumes were generated from several kinds of low hydrogen type electrodes which changed the atmosphere with use of various gases, such air, Ar, CO2 and N2, and were collected in water with an impinger. These fumes were analyzed by X-ray refractometry and chemical analysis, and pH of their collecting water was measured. Based on these results, this paper discusses the mechanism of scattering K and Na in fumes from low hydrogen welding which are considered to be the sources of respiratory tract irritation. All sample fumes from low hydrogen welding in several atmospheric conditions contained fluorite (CaF2). The pH of water in which all sample fumes were collected remarkably elevated. Chemical composition ratios of both K2O and Na2O in all sample fumes were larger than those in coating materials. The sample fumes from welding in each of both N2 and CO2 atmosphere showed higher ratios of K2O and Na2O than those in Ar. The conclusions obtained from the discussion are as follows: The potential gradient of the arc becomes larger during welding in the atmosphere with use of N2 or CO2 because the dissociation voltage of N2 and CO2 is very low. Furthermore, fluorite (CaF2) makes the slag more fluid. Then, K and Na become easily dispersed from the arc column of low hydrogen welding. PMID:3773298

Mori, T; Akashi, S; Takeoka, K; Yoshinaka, M

1986-05-01

466

Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 - 1400 K  

NASA Technical Reports Server (NTRS)

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.

Misra, Ajay K.; Whittenberger, J. Daniel

1987-01-01

467

Comparison of the pinning energy in Fe(Se1-xTex) compound between single crystals and thin films  

NASA Astrophysics Data System (ADS)

Among the families of iron-based superconductors, we investigate flux pinning mechanisms in the Fe(Se1-xTex) compound. We perform magneto-resistance and current-voltage measurements on single-crystals, as well as on several epitaxial thin films grown on different substrates (CaF2, LaAlO3). The activation energy is derived as a function of magnetic field, U(H). The influence of magnetic field orientation on the pinning energy activation mechanism is also studied, leading to the anisotropy analysis which reveals low anisotropy in thin films grown on CaF2 substrate with respect to single crystals and films grown on LaAlO3. Concerning the dominant pinning regime, the exponents of the power law dependence U0(H) ~ H-? have been evaluated, confirm that weak pinning is a general characteristic of this compound. The single exponent feature, generally noticed on thin films grown on SrTiO3 substrate and associated to a strong single vortex regime, has been observed in thin films grown on LaAlO3, only in the parallel configuration. At the end, this overall comparison can be useful to develop a technological material able to compete with high temperature superconductors.

Leo, A.; Guarino, A.; Grimaldi, G.; Nigro, A.; Pace, S.; Bellingeri, E.; Kawale, S.; Ferdeghini, C.; Giannini, E.

2014-05-01

468

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

NASA Technical Reports Server (NTRS)

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.

Dellacorte, Christopher

1988-01-01

469

Effect of nitrogen alloying and the electroslag refining process on the properties of AISI M41 steel  

NASA Astrophysics Data System (ADS)

Nitrogen produces very beneficial effects in high-speed steel and can therefore be regarded as a significant alloying element in ferrous materials. In order to attain the goal of this study, to investigate the effect of nitrogen alloying and the electroslag refining (ESR) process on the properties of AISI M41 steel, two high-speed steels were melted in an air induction furnace (IF). The first one is a standard AISI M41 high-speed steel. The second one is nitrogen-alloyed M41. The produced ingots were used as consumable electrodes in ESR under three different CaF2-based fluxes. The steel produced from the IF and ESR was heat treated. Hardness, secondary hardness, and microstructure were also studied. It was concluded that both ESR and nitrogen alloying improve the hardness profile of the quenched-tempered high-speed steels. The highest secondary hardness and highest softening resistance were attained by ESR of high-nitrogen high-speed steel (M41N) under CaF2/CaO/Al2O3: 55/30/15 slag. The ESR improves the shape, size, and distribution of precipitates in the produced ingot. Quenching and tempering treatment conditions the retained austenite that is present in the as-cast steel by precipitation of carbide and forming martensite on cooling to room temperature.

Mattar, Taha; El Fawakhry, Kamal; Halfa, Hossam; El Demerdash, Mahmoud

2006-12-01

470

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

PubMed Central

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

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

2012-01-01

471

Investigation into nanostructured lanthanum halides and CeBr3 for nuclear radiation detection  

NASA Astrophysics Data System (ADS)

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. 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. 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.

Guss, Paul; Guise, Ronald; Mukhopadhyay, Sanjoy; Yuan, Ding

2011-09-01

472

Investigation into Nanostructured Lanthanum Halides and CeBr3 for Nuclear Radiation Detection  

SciTech Connect

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.

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

2011-07-06

473

Excimer mirror thin film laser damage competition  

NASA Astrophysics Data System (ADS)

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.

Stolz, Christopher J.; Blaschke, Holger; Jensen, Lars; Mädebach, Heinrich; Ristau, Detlev

2011-12-01

474

Vacuum deposited optical coatings experiment (AO 138-4)  

NASA Technical Reports Server (NTRS)

The aim of this experiment was to test the optical behavior of 20 components and coatings subjected to space exposure. Most of them are commonly used for their reflective or transmittive properties in spaceborne optics. They consist in several kind of metallic and dielectric mirrors designed for the 0.12 to 10 microns spectrum, UV, and NIR bandpass filters, visible, and IR antireflecting coatings, visible/IR dichroic beam splitters, and visible beam splitter. The coatings were deposited on various substrates such as glasses, germanium, magnesium fluoride, quartz, zinc selenide, and kanigened aluminum. Several coating materials were used such as Al, Ag, Au, MgF2, LaF3, ThF3, ThF4, SiO2, TiO2, ZrO2, Al2O3, MgO, Ge, and ZnSe. Five samples of each component were manufactured. Two flight samples were mounted in such a way that one was directly exposed to space and the other looking backwards. The same arrangement was used for the spare samples stored on ground in a box identical to the flight one and they were kept under vacuum during the LDEF mission. Finally, one set of reference components was stocked in a sealed box under a dry nitrogen atmosphere. By comparing the preflight and postflight optical performances of the five samples of each component, it is possible to detect the degradations due to the space exposure.

Charlier, Jean

1991-01-01

475

Near-infrared emission and energy transfer in tellurite glasses co-doped with erbium and thulium ions  

NASA Astrophysics Data System (ADS)

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.

Zmojda, Jacek; Kochanowicz, Marcin; Ragin, Tomasz; Dorosz, Dominik; Sitarz, Maciej

2014-05-01

476

High performance fluoride optical coatings for DUV optics  

NASA Astrophysics Data System (ADS)

In deep ultraviolet region that typical applications are used on the ArF wavelength, coated optics should meet stringent requirements of optical systems. To meet these requirements, systematical researches are carried out on fabrication and characterization methods of fluoride coatings. First, by optimizing of deposition processes, dense coatings with the refractive index of ~1.7 for LaF3 and ~1.4 for MgF2, together with extinction coefficients of ~2×10-4 on 193nm were realized. The transmission of AR coating for 193nm achieved by using optimized deposition techniques is 99.8%. Second, a method of designing shadowing masks was developed to solve the problem of correcting coating thickness distributions for complex DUV systems. By using the method, the thickness distribution error specification of 3% PV has been achieved on substrates with ~300mm diameters and large curvatures. Finally, the laser calorimetry method is used to evaluate the laser radiation stability of fluoride coatings. It is turned out that the damage coefficients of fluoride coatings, which are defined as the values of unrecoverable increase of the absorption during the laser irradiation process, are much lower than that of fused silica substrates. The above progresses could further support the realization of high performance DUV optical systems.

Zhang, Lichao; Cai, Xikun

2014-08-01

477

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)

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.

Bolotina, N. B.; Chernaya, T. S.; Verin, I. A.; Sorokin, N. I.; Sobolev, B. P.

2015-01-01

478

Optoacoustic measurements of water vapor absorption at selected CO laser wavelengths in the 5-micron region  

NASA Technical Reports Server (NTRS)

Measurements of water vapor absorption were taken with a resonant optoacoustical detector (cylindrical pyrex detector, two BaF2 windows fitted into end plates at slight tilt to suppress Fabry-Perot resonances), for lack of confidence in existing spectral tabular data for the 5-7 micron region, as line shapes in the wing regions of water vapor lines are difficult to characterize. The measurements are required for air pollution studies using a CO laser, to find the differential absorption at the wavelengths in question due to atmospheric constituents other than water vapor. The design and performance of the optoacoustical detector are presented. Effects of absorption by ambient NO are considered, and the fixed-frequency discretely tunable CO laser is found suitable for monitoring urban NO concentrations in a fairly dry climate, using the water vapor absorption data obtained in the study.

Menzies, R. T.; Shumate, M. S.

1976-01-01

479

A Phase Relation Study of Ba-Y-Cu-O Coated-Conductor Films Using the Combinatorial Approach  

SciTech Connect

Phase relationships in bulk and thin film Ba-Y-Cu-O high-Tc superconductor system were determined at processing conditions relevant for industrial production of coated conductors. Our results demonstrated that the absence of BaY2CuO5 (which has a critical effect on flux pinning) at 735 C--a typical temperature employed in production of coated conductors--in thin films processed in situ from the BaF2 precursor is caused by the sluggish reaction kinetics rather than by the presence of fluorine in the system. Thermodynamic calculations combined with annealing experiments confirmed that BaY2CuO5 is thermodynamically stable but forms at temperatures higher than 735 C.

Wong-Ng, W. [National Institute of Standards and Technology (NIST); Otani, M. [National Institute of Standards and Technology (NIST); Levin, I. [National Institute of Standards and Technology (NIST); Schenck, P. [National Institute of Standards and Technology (NIST); Yang, Z. [National Institute of Standards and Technology (NIST); Liu, G. [National Institute of Standards and Technology (NIST); Cook, L. P. [National Institute of Standards and Technology (NIST); Feenstra, Roeland [ORNL; Zhang, W. [American Superconductor Corporation, Westborough, MA; Rupich, Marty [American Superconductor Corporation, Westborough, MA

2009-01-01

480

In-beam spectroscopic studies of the 44S nucleus  

NASA Astrophysics Data System (ADS)

The structure of the 44S nucleus has been studied at GANIL through the one proton knock-out reaction from a 45Cl secondary beam at 42 A·MeV. The ? rays following the de-excitation of 44S were detected in flight using the 70 BaF2 detectors of the Château de Cristal array. An exhaustive ??-coincidence analysis allowed an unambiguous construction of the level scheme up to an excitation energy of 3301 keV. The existence of the spherical 22+ state is confirmed and three new ?-ray transitions connecting the prolate deformed 21+ level were observed. Comparison of the experimental results to shell model calculations further supports a prolate and spherical shape coexistence with a large mixing of states built on the ground state band in 44S.

Cáceres, L.; Sohler, D.; Grévy, S.; Sorlin, O.; Dombrádi, Zs.; Bastin, B.; Achouri, N. L.; Angélique, J. C.; Azaiez, F.; Baiborodin, D.; Borcea, R.; Bourgeois, C.; Buta, A.; Bürger, A.; Chapman, R.; Dalouzy, J. C.; Dlouhy, Z.; Drouard, A.; Elekes, Z.; Franchoo, S.; Gaudefroy, L.; Iacob, S.; Laurent, B.; Lazar, M.; Liang, X.; Liénard, E.; Mrazek, J.; Nalpas, L.; Negoita, F.; Nowacki, F.; Orr, N. A.; Penionzhkevich, Y.; Podolyák, Zs.; Pougheon, F.; Poves, A.; Roussel-Chomaz, P.; Saint-Laurent, M. G.; Stanoiu, M.; Stefan, I.

2012-02-01