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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

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

NASA Technical Reports Server (NTRS)

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

Deadmore, Daniel L.; Sliney, Harold E.

1987-01-01

3

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

SciTech Connect

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

2013-12-01

4

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

5

Geometry and Vibrational Spectra of Alkaline-Earth Dihalides, Ii. CaF2, SrF2 and BaF2.  

National Technical Information Service (NTIS)

The infrared spectra of 40CaF2, 44CaF2, 86SrF2, 88SrF2 and BaF2 trapped in solid krypton matrices at 20K are reported. From precise measurements of the shifts of the vibrational modes on isotopic substitution upper and lower limits for the apex angles of ...

V. Calder D. E. Mann K. S. Seshadri M. Allavena D. White

1969-01-01

6

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 BaF 2 and CaF 2 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 BaF 2(111) two-dimensional water layers are formed after accumulation at step edges, CaF 2(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 BaF 2( 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

7

Photon emission from 511 keV gamma rays incident on BaF 2 and LaF 3:Nd 3+ crystals using a cesium iodide photocathode detector  

NASA Astrophysics Data System (ADS)

We have studied the possibility of using BaF 2 and LaF 3 doped with Nd 3+, concentrations ranging from 0.1 to 15 mol% as efficient converters of 511 keV gamma rays. We have measured the number of photoelectrons/MeV for both crystals using a parallel-plate avalanche chamber operating with a CsI photocathode. The photocathode is sensitive to wavelengths in the range 160-220 nm. The fast component of the BaF 2 emission spectrum has peaks at roughly 175, 195 and 200 nm, and the LaF 3:Nd 3+ emission spectrum peaks at 173 nm. We measure 3.71 ± 0.04 ± 1.11 photoelectrons/MeV for the BaF 2 and 4.81 ± 0.04 ± 1.44 photoelectrons/MeV for the LaF 3:Nd 3-. The results for BaF 2 and LaF 3:Nd 3+ are consistent with measured scintillation properties of these crystals and CsI photocathode quantum efficiencies.

Kononenko, W.; Heinrich, J. G.; Lockyer, N. S.; Miller, J. M.; Woody, C.; Kwan, S.

1997-02-01

8

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

9

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

NASA Astrophysics Data System (ADS)

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

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

10

Photon emission from 511 keV gamma rays incident on BaF 2 and LaF 3:Nd 3+ crystals using a cesium iodide photocathode detector  

Microsoft Academic Search

We have studied the possibility of using BaF2 and LaF3 doped with Nd3+, concentrations ranging from 0.1 to 15 mol% as efficient converters of 511 keV gamma rays. We have measured the number of photoelectrons\\/MeV for both crystals using a parallel-plate avalanche chamber operating with a CsI photocathode. The photocathode is sensitive to wavelengths in the range 160–220 nm. The

W. Kononenko; J. G Heinrich; N. S Lockyer; J. M Miller; C. Woody; S. Kwan

1997-01-01

11

Behaviors of metal-oxide impurities in CaF 2 and BaF 2 single-crystals grown with PbF 2 scavenger by Stockbarger’s method  

Microsoft Academic Search

The concentrations and distribution of trace amounts of metal impurities in CaF2 and BaF2 single-crystals grown from high purity CaF2 and BaF2 raw powders and 14 kinds of trace amounts of metal-oxide impurity additives (metal elements=Li, Na, Mg, Ca, Sr, Ba, Al, Cr, Fe, Ni, Cu, Y, La and Ce) under the addition of 3wt% PbF2 scavenger by the Stockbarger

Tetsuo Yonezawa; Kentaro Matsuo; Jun Nakayama; Yoji Kawamoto

2003-01-01

12

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

13

Fluorine K? X-Ray Emission Spectra of MgF2, CaF2, SrF2 and BaF2  

NASA Astrophysics Data System (ADS)

The fluorine K? emission spectra in fluorescence from a series of alkaline-earth fluorides MF2 (M=Mg, Ca, Sr and Ba) are measured with a high-resolution two-crystal vacuum spectrometer. An anomalously low intensity of the K1L1 satellite peak arising from 1s-1(2s2p)-1 initial states is observed for SrF2. The measured emission spectra are presented along with the UPS spectra of the F- 2p valence bands obtained by Poole et al. and the fluorine K absorption-edge spectra by Oizumi et al. By using these spectra, the first peak or shoulder in the fluorine K absorption-edge spectra is identified as being due to a core exciton which is formed below the bottom of the conduction band. The binding energy of the exciton is estimated to be 1.3(± 0.3), 1.1(± 0.2), 1.0(± 0.2) and 1.7(± 0.2) eV for MgF2, CaF2, SrF2 and BaF2, respectively.

Sugiura, Chikara; Konishi, Wataru; Shoji, Shizuko; Kojima, Shinjiro

1990-11-01

14

Optical emission and energy disposal characterization of the laser ablation process of CaF2, BaF2, and NaCl at 1064 nm  

NASA Astrophysics Data System (ADS)

A method to simultaneously measure the fraction of incident energy spent as absorbed, scattered, and consumed energy by the plasma generated in the ablation process is presented. The results obtained allowed to make an energy balance in the ablation process of halogenated earth alkaline metal crystals (NaCl, BaF2, and CaF2) and to relate the nature of the crystal structure to the absorbed energy. The latter could be determined by monitoring the magnitude of the breakdown induced by the discharge between the plates of a capacitor. Simultaneously, time resolved optical emission spectroscopy was used to analyze the ion emission intensity and as a function of the energy absorbed by the sample. This plot shows the usual sigmoid behavior for the ablation process with the three typical regions, corresponding to the vaporization, screening, and ablation regimes. A heuristic equation has been used to analyze this process in terms of the nature of the crystal structure. From this equation the critical absorbed energy for each of the studied samples could also be determined.

Villagran-Muñiz, M.; Sobral, H.; Rinaldi, C. A.; Cabanillas-Vidosa, I.; Ferrero, J. C.

2008-11-01

15

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

PubMed

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

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

2014-05-14

16

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

17

Insulating epitaxial films of BaF 2, CaF 2 and Ba xCa 1- xF 2 grown by MBE on InP substrates  

NASA Astrophysics Data System (ADS)

Thin films (? 5000 Å) of BaF 2, CaF 2, and Ba xCa 1- xF 2 have been grown onto InP (001) substrates in a vacuum locked MBE system. Electron diffraction was used to monitor film nucleation and growth at a variety of substrate temperatures. Subsequent ex-situ analysis included X-ray diffraction, electron microscopy and Auger sputter profiling. In addition, capacitance-voltage and current-voltage analyses were performed on MIS sandwich devices formed by evaporating aluminium onto the semiconductor-flouride samples. Deposition of flourides onto room temperature substrates resulted in the growth of smooth, pinhole free, stoichiometric polycrystalline films with little or no preferred orientation. TEM analysis indicates a grain size of the same order as the film thickness (˜ 1000 Å). Deposition of BaF 2 and CaF 2 onto cleaned, well-ordered (001) InP held at temperatures above 200°C resulted in single-crystal, heteroepitaxial growth. In the case of CaF 2, the increase in lattice mismatch on cooling to room temperature resulted in crazing of the epitaxial layer. Film resistivity values around 10 12-10 13? cm and breakdown strengths of 5x10 5V cm -1 have been achieved for both polycrystalline and single-crystal layers. In initial experiments on the growth of Ba xCa 1- xF 2 alloys onto (001) epitaxial films of a single-phase cubic alloy with x ˜ 0.2 were obtained.

Sullivan, P. W.; Farrow, R. F. C.; Jones, G. R.

1982-12-01

18

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)  

NASA Astrophysics Data System (ADS)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF2, SrF2, and BaF2 is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF2 crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ˜2 × 103 pA/cm2). In BaF2 samples, the transformation of BaO into Ba(OH)2 was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)2 into BaO. In the initial stage of irradiation of all MF2 compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF2 matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF2 destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ˜20 nm in the sample.

Nikolaichik, V. I.; Sobolev, B. P.; Zaporozhets, M. A.; Avilov, A. S.

2012-03-01

19

Temperature dependence of the dielectric permittivity of CaF2, BaF2 and Al2O3: application to the prediction of a temperature-dependent van der Waals surface interaction exerted onto a neighbouring Cs(8P3\\/2) atom  

Microsoft Academic Search

The temperature behaviour in the range 22-500 °C of the dielectric permittivity in the infrared range is investigated for CaF2, BaF2 and Al2O3 through reflectivity measurements. The dielectric permittivity is retrieved by fitting reflectivity spectra with a model taking into account multiphonon contributions. The results extrapolated from the measurements are applied to predict a temperature-dependent atom-surface van der Waals interaction.

Thierry Passerat de Silans; Isabelle Maurin; Pedro Chaves de Souza Segundo; Solomon Saltiel; Marie-Pascale Gorza; Martial Ducloy; Daniel Bloch; Domingos de Sousa Meneses; Patrick Echegut

2009-01-01

20

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

NASA Technical Reports Server (NTRS)

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

DellaCorte, Christopher; Stanford, Malcolm K.

2008-01-01

21

Defect formation in BAF 2 crystals doped with cadmium  

NASA Astrophysics Data System (ADS)

Defect formation in BaF 2 single crystals doped with cadmium is investigated by optical absorption, electron paramagnetic resonance (EPR) and thermoluminescence. An optical absorption band observed in X-irradiated at 295 K crystals CaF 2 (at 3.8 eV), SrF 2 (at 3.95 eV) and BaF 2 (at 4.08 eV) is assigned to absorption of Cd +-ions. In addition, two type hole centers: pure V k and perturbed V k-centers, are observed in BaF 2-1%CdF 2 crystals X-irradiated at 77 K.

Nepomnyashchikh, A. I.; Radzhabov, E. A.; Egranov, A. V.; Ivashechkin, V. F.; Istomin, A. S.; Kurobori, T.

2005-01-01

22

Pressure-induced photoluminescence in Mn2+-doped BaF2 and SrF2 fluorites  

NASA Astrophysics Data System (ADS)

This work reports an effective way for inducing room temperature photoluminescence (PL) in Mn2+-doped BaF2 and SrF2 using high-pressure techniques. The aim is to understand the surprising PL behavior exhibited by Mn2+ at the cubal site of the fluorite structure. While Mn2+-doped CaF2 shows a green PL with quantum yield close to 1 at room temperature, Mn2+-doped MF2 (M=Ba,Sr) is not PL either at room temperature (SrF2) or at any temperature (BaF2) at ambient pressure. We associate the loss of Mn2+ PL on passing from CaF2 to SrF2 or BaF2 with nonradiative multiphonon relaxation whose thermal activation energy decreases along the series CaF2?SrF2?BaF2. A salient feature of this work deals with the increase of activation energy induced by pressure. It leads to a quantum yield enhancement, which favors PL recovery. Furthermore, the activation energy mainly depends on the crystal volume per molecule irrespective of the crystal structure or the local symmetry around the impurity. In this way, the relevance of the fluorite-to-cotunnite phase transition is analyzed in connection with the PL properties of the investigated compounds. The PL spectrum and the corresponding lifetime are reported for both structural phases as a function of pressure.

Hernández, Ignacio; Rodríguez, Fernando

2003-01-01

23

Infrared Dispersion and Lattice Vibrations of LaF3  

Microsoft Academic Search

The infrared spectral emittance of oriented single crystals of LaF3 has been measured in the range 4-125 mum. Eleven transitions have been identified whose net moments are perpendicular to the optic axis (Eu, x, y), and five additional bands were observed having net moments parallel to the optic axis (A2u, z). The data, taken near 4.2, 77, and 373°K, were

H. E. Rast; H. H. Caspers; S. A. Miller; R. A. Buchanan

1968-01-01

24

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

25

Microstructures and tribological properties of plasma sprayed WC-Co-Cu-BaF 2/CaF 2 self-lubricating wear resistant coatings  

NASA Astrophysics Data System (ADS)

A promising WC-Co-Cu-BaF 2/CaF 2 self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC-Co, Cu and BaF 2/CaF 2 eutectic. The as-prepared cermet coatings had better frictional behavior comparing with the WC-Co coating. Moreover, the often-occurred decarburization of WC in APS process was noticeably improved due to the binding of copper and BaF 2/CaF 2 phase, which not only offered effective solid lubrication, but also acted as bind phases to mend the microstructure and protected WC from decomposition. The optimized specimen contained 10 wt.% Cu and 10 wt.% BaF 2/CaF 2 in a WC-Co matrix, which had excellent frictional and wear performance. The wear mechanism of the self-lubricating wear resistant coating was discussed with the microstructures, compositions and mechanical properties of the composite materials in detail.

Yuan, Jianhui; Zhu, Yingchun; Ji, Heng; Zheng, Xuebing; Ruan, Qichao; Niu, Yaran; Liu, Ziwei; Zeng, Yi

2010-06-01

26

CaF2:Yb laser ceramics  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

27

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

28

Properties of AlF3 and LaF3 films at 193nm  

NASA Astrophysics Data System (ADS)

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

Xue, Chunrong; Shao, Jianda

2010-05-01

29

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

PubMed

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

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

2014-03-26

30

Luminescent LaF3:Ce-doped organically modified nanoporous silica xerogels  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

31

Intense near-infrared quantum cutting emissions in LaF3:Sm3+ nanocrystals.  

PubMed

In this letter, visible to near-infrared (NIR) quantum cutting (QC) luminescence of -20 nm LaF3:Sm3+ (0.2-1 mol%) nanocrystals (NCs) was first studied. A number of novel NIR QC emissions (850-2000 nm) were distinguished. The results show that the QC emission lines and populating channels depend strongly on Sm3+ concentration due to the cross relaxation processes. The overall QC efficiency is as high as -193% in LaF3:Sm3+ (0.4 mol%) NCs, which shows that NIR QC of Sm3+ is of great significance for enhancing the efficiency of solar cells. PMID:24734602

Tao, Li; Xu, Wen; Bai, Xue; Xu, Sai; Song, Hongwei

2014-05-01

32

Scintillation light yield of BaF 2:Ce  

NASA Astrophysics Data System (ADS)

BaF 2:Ce scintillator is a well-known, reasonably fast and efficient scintillator characterized by a decent stopping power and availability of large size crystals. In this communication we report scintillation light yield measurements on a number of BaF 2:Ce samples cut from one larger boule. We interpret these measurements in a frame of a simple one-dimensional model developed and first tested on LuAP and LuYAP samples. The model is expected to reproduce the observed strong dependence of the effective scintillation light yield against the height of the sample. The fit to experimental points provides a value of the "intrinsic" light yield LY(0), as well as a value of the "loss" parameter ? (scattering and absorption of scintillation light in the sample). Although the value of the loss parameter ?, at around 0.5 cm -1, found from the fit for BaF 2:Ce is clearly lower than a typical value in LuAP and LuYAP, it is, nevertheless, much higher than the value of about 0.05-0.07 cm -1 measured in Delft for LaBr 3:Ce. We have also measured the absorption spectra of BaF 2:Ce crystals. The corrected spectra have been used to estimate contributions from scattering, self-absorption (by Ce-ions) and parasitic absorption from unidentified centers in order to establish physical limits imposed on the light yield from these crystals.

Janus, Sebastian; Wojtowicz, Andrzej J.

2009-01-01

33

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

34

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

35

Influence of ion assistance on LaF3 films deposited by molybdenum boat evaporation.  

PubMed

LaF3 thin films at 193 nm were deposited by the molybdenum boat evaporation with ion-assisted deposition (IAD). Various optical characteristics, stress, and microstructures that formed under different ion-beam voltages of IAD deposition were investigated. The relation between these properties is also discussed. LaF3 films deposited with IAD exhibited small rough surfaces and large optical loss at 193 nm. The largest value of optical loss for films at 193 nm, which were prepared at an ion-beam voltage of 400 V, was 1.55% and the extinction coefficient was smaller than 0.0015. Microstructures and crystalline structures of films were influenced and changed by the ion-assisted deposition process. Tensile stress value of films increased as the ion-beam voltage rose. Refractive index, related to the packing density and microstructures, also increased as the ion-beam voltage rose. PMID:22614587

Liu, Ming-Chung; Lee, Cheng-Chung; Kaneko, Masaaki; Nakahira, Kazuhide; Takano, Yuuichi

2012-05-20

36

Energy Levels of Ce2+ in CaF2  

Microsoft Academic Search

The absorption spectrum of cerium-doped CaF2 has been observed at several temperatures. When the cerium is reduced to the divalent state at room temperature, the absorption spectrum of Ce2+ is found to be unstable against thermal decay or bleaching by visible light; furthermore, this spectrum is found to comprise one state of a photochromic system. The absorption spectrum of CaF2:

R. C. Alig; Z. J. Kiss; J. P. Brown; D. S. McClure

1969-01-01

37

Facile mixed-solvent-thermal synthesis and characterisation of LaF3 : Eu3+\\/Tb3+ monodisperse nanoparticles  

Microsoft Academic Search

LaF3 : 10% Eu\\/Tb monodisperse nanoparticles have been synthesised by a novel mixed-solvent-thermal technology (N,N-dimethyl-formamide (DMF), diethylene glycol (DEG)). When the volume ratio of mixed-solvents (DMF : DEG) is 6 : 12, LaF3 : 10% Eu\\/Tb nanoparticles show a pure hexagonal phase structure with space group of P63\\/mcm. Both the X-ray diffraction pattern and the transmission electron microscope image present

Bing Yan; Jianhua Wu

2009-01-01

38

Bioconjugation of Ln3+-doped LaF3 nanoparticles to avidin.  

PubMed

The binding of Eu3+-doped LaF3 nanoparticles with biotin moieties at the surface of the stabilizing ligand layer to avidin, immobilized on cross-linked aragose beads, is described. The biotin moieties were attached to the nanoparticles by reaction of an activated ester with the amino groups on the surface of the nanoparticles resulting from the 2-aminoethyl phosphate ligands that were coordinated to the surface through the phosphate end. This strategy of employing the reactions of amines with activated esters provides a general platform to modify the surface of the 2-aminophosphate stabilized Ln3+-doped LaF3 nanoparticles with biologically relevant groups. Significant suppression of nonspecific binding to the avidin modified aragose beads has been realized by the incorporation of poly(ethylene glycol) units via the same reaction of a primary amine with an activated ester. The particle size distribution of the functionalized nanoparticles was within 10-50 nm, with a quantum yield of 19% in H2O for the LaF3 nanoparticles codoped with Ce3+ and Tb3+. A discreet, 4 unit poly(ethylene glycol) spaced heterobifunctional cross-linker, functionalized with biotin and N-hydroxysuccinimide at opposite termini, was covalently linked to the 2-aminoethyl phosphate ligand via the N-hydroxysuccinimide activated ester, making an amide bond, imparting biological activity to the particle. Modification of the remaining unreacted amino groups of the stabilizing ligands was done with Me(OCH2CH2)3CH2CH2(C=O)-NHS (NHS = N-hydroxysuccinimide). PMID:16460106

Diamente, Peter R; Burke, Robert D; van Veggel, Frank C J M

2006-02-14

39

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

40

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

41

Theory of Photochromic Centers in CaF2  

Microsoft Academic Search

On the basis of recent optical and EPR work, it has been suggested that the ionized and thermally stable photochromic centers in CaF2 consist of one and two electrons bound at an anion vacancy adjacent to a trivalent impurity cation. For the ionized center, we have shown that the energy levels and wave functions of the isolated F center are

R. Casanova Alig

1971-01-01

42

LETTERS TO THE EDITOR: New crystal lasers utilizing disordered fluoride crystals activated with Nd3+ ions pumped by semiconductor laser radiation  

NASA Astrophysics Data System (ADS)

Diode laser pumping was used to excite for the first time single-mode cw lasing of Nd3+ ions (4F3/2?4I11/2 transition at 300 K) in disordered fluoride crystals (CaF2-YF3, SrF2-GdF3, BaF2-YF3, and BaF2-LaF3).

Kaminski?, A. A.; Verdún, H. R.

1992-02-01

43

Humidity response properties of a potentiometric sensor using LaF3 thin film as the solid electrolyte  

NASA Astrophysics Data System (ADS)

A thin-film type potentiometric sensor has been prepared by the implementation of electro-beam evaporation, rf magnetron sputtering methods, and micromachining processes. Sn film was deposited on n-Si/SiO2 (400 nm) substrate. A deposited LaF3 film was applied as solid electrolyte and sputtered Pt film was used as the sensing electrode. The patterns of the Pt and LaF3 were realized by the micromachining processes. The LaF3 film was characterized by scanning electron microscopy and energy dispersive x ray. Saturated aqueous solutions were used to achieve controlled humidity environments. When the sensor was exposed to humidity environments, the electromotive force (EMF) of the sensor was examined. It was found that the sensor varies with the relative humidity (RH). The stable response curve was presented and non-Nernst behavior between the average EMF values and RH may be shown.

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

2011-08-01

44

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

45

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

46

LaF3:Ce nanocomposite scintillator for gamma-ray detection  

NASA Astrophysics Data System (ADS)

Nanophosphor LaF3:Ce has been synthesized and incorporated into a matrix to form a nanocomposite scintillator suitable for application to ?-ray detection. Owing to the small nanocrystallite size (sub-10 nm), optical emission from the ? / nanophosphor interaction is only weakly Rayleigh scattered (optical attenuation length exceeds 1 cm for 5-nm crystallites), thus yielding a transparent scintillator. The measured energy resolution is ca. 16% for 137Cs ? rays, which may be improved by utilizing brighter nanophosphors. Synthesis of the nanophosphor is achieved via a solution-precipitation method that is inexpensive, amenable to routine processing, and readily scalable to large volumes. These results demonstrate nanocomposite scintillator proof-of- principle and provide a framework for further research in this nascent field of scintillator research.

McKigney, E. A.; Muenchausen, R. E.; Cooke, D. W.; Del Sesto, R. E.; Gilbertson, R. D.; Bacrania, M. K.; Bennett, B. L.; Jacobsohn, L. G.; McCleskey, T. M.; Ott, K. C.; Sitarz, S. C.; Smith, J. F.; Stange, S.

2007-09-01

47

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

48

Dynamics of fluorine ions in LaF3-type crystals investigated by NMR lineshape analysis  

NASA Astrophysics Data System (ADS)

Fluorine nuclear magnetic resonance (NMR) lineshape data were collected for a pure LaF3 single crystal and La1-xSrxF3-x single crystals, doped with admixtures concentrations x up to 16%, from room temperature up to 775 K. The experimental data are analysed within the framework of a theoretical model linking the shape of the spectrum to parameters describing motional processes in the system. The elaborated model includes various types of the fluorine dynamics: diffusion processes occurring inside two distinct fluorine sublattices and inter-lattice exchange motion. This theoretical approach provides a satisfactory and consistent interpretation of the NMR data, without assuming any distribution of the characteristic time constants. The obtained results are discussed in a context of Arrhenius temperature dependences of the correlation times and effects caused by higher concentrations of the admixtures.

Kruk, D.; Lips, O.; Gumann, P.; Privalov, A.; Fujara, F.

2006-02-01

49

Laser conditioning of LaF 3 MgF 2 dielectric coatings at 248 nm  

NASA Astrophysics Data System (ADS)

Highly reflective LaF3/MgF2 systems for a wavelength of 248 nm on MgF2 and crystalline quartz substrates were investigated. The influence of laser conditioning on damage threshold and absorptance was remarkable in those coatings that had a high initial absorptance. Monitoring with a laser calorimeter revealed the conditioning effect to be a function of the irradiation dose rather than of energy density or pulse rate. Furthermore, x-ray photoelectron spectroscopy and transmission electron microscopy investigations showed that conditioning induces stoichiometric and structural changes in the multilayers, especially in near-surface sublayers, whereas scanning electron microscopy and atomic force microscopy investigations indicated that the surface remains unchanged.

Eva, E.; Mann, K.; Kaiser, N.; Anton, B.; Henking, R.; Ristau, D.; Weissbrodt, P.; Mademann, D.; Raupach, L.; Hacker, E.

1996-10-01

50

Structural transition of BaF2 nanocrystals under high pressure  

NASA Astrophysics Data System (ADS)

The structural transition of BaF2 nanocrystals is studied by in situ high pressure synchrotron radiation X-ray diffraction measurements up to about 21.2 GPa at ambient temperature. Two phase transformations were observed at 5.8 and 14.4 GPa, and the two high pressure phases are identified as orthorhombic (Pnma) phase and hexagonal (P63/mmc) phase by Rietveld refinement. Upon decompression, the ?-PbCl2-type metastable phase is retained when the pressure is released. Two phase transformations of the BaF2 nanocrystals are higher than that in bulk BaF2. It is proposed that the size effects are found to influence the BaF2 nanocrystals high-pressure behaviors and the surface energy plays a significant role in the structural stability.

Wang, Jing-Shu; Ma, Chun-Li; Zhu, Hong-Yang; Wu, Xiao-Xin; Li, Dong-Mei; Cong, Ri-Dong; Liu, Jing; Shi, Rui; Cui, Qi-Liang

2013-08-01

51

Digital Pulse Shape Acquisition From BaF2: Preliminary Results  

Microsoft Academic Search

The use of NE102A-BaF2 phoswich detector drastically improves the particle identification with respect to BaF2 crystals. To better exploit the possibility of light ion discrimination we plan to apply digital signal processing to the signals on-beam collected with NE102A-BaF2 phoswich. In this contribution we present the preliminary results obtained for the natural background of BaF2 and for the heavy ion

F. Amorini; E. De Filippo; P. Guazzoni; E. La Guidara; G. Lanzano; A. Pagano; S. Pirrone; S. Russo; P. Russotto; M. Sassi; L. Zetta

2006-01-01

52

Surprising arching sheet-like dendrites growing from BaF2 nanocubes  

Microsoft Academic Search

BaF2 nanocubes were prepared from quaternary reverse micelles of cetyl trimethyl ammonium bromide (CTAB), n-butanol, n-octane, and water. Interestingly, there are arching sheet-like dendrites growing between two neighbouring sides of these cubes. X-ray powder diffraction (XRD) analysis showed that the products were BaF2 single phase. Scanning electron microscopy (SEM) or transition electron microscopy (TEM) was used to estimate the size

Hongzhou Lian; Zeren Ye; Chunshan Shi

2004-01-01

53

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

54

Behaviors of trace amounts of metal-oxide impurities in CaF 2 crystal grown by Stockbarger's method  

Microsoft Academic Search

The concentrations and distribution of trace amounts of metal impurities in CaF2 crystals grown by the Stockbarger method from CaF2 powder and 14 kinds of metal-oxide additives were examined and compared with CaF2 crystals grown from CaF2 powder and metal-fluoride additives. In the CaF2 crystals grown with metal-oxide additives, the Li, Na, Cr, Fe, Ni, Cu and Pb metal-impurities were

Tetsuo Yonezawa; Jun Nakayama; Kunio Tsukuma; Yoji Kawamoto

2002-01-01

55

Auger-free luminescence of the BaF2:Sr, BaF2:MgF2 and CsBr:LiBr crystals under excitation of VUV photons and high-energy electrons  

Microsoft Academic Search

The emission spectrum, the time dependence of the luminescence, the excitation spectrum and the reflectance spectrum have been measured for the pure BaF2 crystal, the BaF2:Sr crystals with Sr++ concentrations of 2 and 5 mol%, the BaF2:MgF2 crystal with a mole mixing ratio of 1:2, and the pure CsBr crystal and the CsBr:LiBr crystal with a mole mixing ratio of

Margarida Mizue Hamada

1994-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

57

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

SciTech Connect

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

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

2012-01-01

58

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

NASA Astrophysics Data System (ADS)

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

Sathyamurthy, Srivatsan; Tuncer, Enis; More, Karren L.; Gu, Baohua; Sauers, Isidor; Paranthaman, M. Parans

2012-03-01

59

Rare earth doped silicate-oxyfluoride glass ceramics incorporating LaF3 nano-crystals for UV-LED color conversion  

NASA Astrophysics Data System (ADS)

Rare earth doped oxyfluoride glass ceramics with LaF3 nano-crystals formed inside were fabricated for color converter of UV-LED. Among various rare earth ions, Dy3+ and Eu3+ showed practically utilizable visible emissions under UV-LED excitation of 365 nm. The visible emission has been improved by the formation of LaF3 brought by heat treatment. X-ray diffraction and transmission electron microscopy along with its energy dispersive spectra confirmed the formation of LaF3 nano-crystals. Compositional dependence and the effects of heat treatment conditions on the visible emissions have been investigated. The CIE chromaticity coordinates of the glasses were also examined for Dy3+ singly doped and co-doped samples. The effect of LaF3 nano-crystals and co-dopants on the visible emission properties of Dy3+ was discussed.

Bae, Suk-Rok; Choi, Yong Gyu; Im, Won Bin; Lee, Ki Seok; Chung, Woon Jin

2013-09-01

60

Excitonic processes in Li and Na-doped CaF2  

Microsoft Academic Search

The optical properties of nominally pure CaF2 crystals as well as those of pure and Li+ and Na+-doped CaF2 powders are compared. The emission band peaking at 3.85 eV and the excitation band in the region of 10-10.6 eV, observed in CaF2: Li and CaF2: Na powders, are ascribed to the radiative decay of a self-trapped exciton perturbed by an

V. Denks; A. Maaroos; V. Nagirnyi; T. Savikhina; V. Vassiltsenko

1999-01-01

61

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.

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

2013-01-01

62

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

63

U^4+ Ions in CaF2 Crystals  

NASA Astrophysics Data System (ADS)

The structure of U^4+ inclusion sites in CaF2 has been studied for 20 crystals, of dopant concentrations from 0.001 to 0.6 mole%, using electron paramagnetic resonance (EPR), Fourier Transform infra-red (FTIR) Zeeman spectroscopy and optical spectroscopy. These confirm the assignment of green crystals to U^4+ ions footnote R. McLaughlin et al, J Chem Phys. 53, 2031 (1970) rather than the U^2+ assignment of Hargreaves footnote W. A. Hargreaves, Phys Rev. B44, 5293 (1991). Two sites are observed, a trigonal EPR site (consistent with a 1:0:3 arangement) and a tetragonal site with an orbital singlet ground-state. The degree of green coloration depends not only on the concentration of U^4+ ions but also on other factors. Thermal studies and selective spectroscopy are being used to determine which other factors are important.

Choi, J.; Raukas, M.; Happek, U.; Watson, A. M.; Campbell, J. A.

1996-03-01

64

Radiation induced thermoluminescence in CaF 2:Tm detectors  

NASA Astrophysics Data System (ADS)

The fact that in CaF 2:Tm, thermoluminescence (TL) glow peaks occuring at different temperatures have different sensitivities to low and high LET radiations, has been found useful for the simultaneous and separate determination of fast neutron and gamma ray absorbed doses from therapeutically used neutron beams. The gamma ray and fast neutron responses of the individual glow peaks are found to be additive for separate and successive irradiations. A glow peak at 150° C which has a relatively smaller sensitivity to densely ionizing radiations, exhibit reduced sensitivity to high doses of even low LET radiations ( 60Co gamma rays). On heat treatment, the relative TL responses of 110, 150 and 240°C glow peaks are found to reduce in different proportions. In view of the present study, the various explanations for the difference in LET dependences of the glow peaks have been analysed.

Pradhan, A. S.; Rassow, J.

1987-03-01

65

Behavior Analysis of CaF2 in Magnesia Carbothermic Reduction Process in Vacuum  

NASA Astrophysics Data System (ADS)

Magnesium production by carbothermic reduction of magnesia with CaF2 in vacuum was investigated experimentally by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and thermodynamic analysis. Thermodynamic calculations indicate that magnesium was generated by a carbothermic reduction among MgO-C system, which should be above 1500 K (1227 °C) (50 Pa). According to the carbothermic reduction analysis, the CaF2 does not participate in the carbothermic process. The experimental results demonstrated that the mass loss increased along with increasing CaF2. The percentage was up to 92 pct with 5 pct CaF2.The reduction degree increased with CaF2 more than it without CaF2 obviously. Considering the reduction degree and economic benefit, 5 pct CaF2 was the optimal choice. The purity of metal magnesium reached 95.59 wt pct, which has perfect crystallization and lamellar structure. CaF2 did not participate in magnesia carbothermic reduction in vacuum; instead, it played a catalytic role during the process.

Tian, Yang; Qu, Tao; Yang, Bin; Dai, Yong-Nian; Xu, Bao-Qiang; Geng, Sen

2012-06-01

66

Heavy ions detection by using BaF2 crystals coupled to thin plastic scintillator  

Microsoft Academic Search

By coupling a thin fast NE102A plastic scintillator to a BaF2 crystal, we have been able to detect and identify simultaneously light charged particles and heavy ions from Z = 1 to Z = 18. Time-of-flight information is used to separate Z = 1 isotopes and to distinguish fission fragments from other reaction products.

G. Lanzanó; A. Pagano; E. de Filippo; E. Pollacco; R. Barth; B. Berthier; E. Berthoumieux; Y. Cassagnou; Sl. Cavallaro; J. L. Charvet; A. Cunsolo; R. Dayras; A. Foti; S. Harar; R. Legrain; V. Lips; C. Mazur; E. Norbeck; S. Urso; C. Volant

1992-01-01

67

Electron paramagnetic resonance of Gd3+ ions in powders of LaF3:Gd3+ nanocrystals  

NASA Astrophysics Data System (ADS)

The observation of electron paramagnetic resonance of Gd3+ ions in nanosized powders of rare-earth fluorides LaF3:Gd3+ has been reported. The measurements have been performed on a single crystal and micro- and nanosized powders at room temperature. Electron paramagnetic resonance spectra and spin-Hamiltonian parameters of Gd3+ ions have been obtained. A qualitative difference of spectra in nano- and micropowders due to the increase in the spread of the crystal field parameters with the decrease in the particle size has been found. The relationship between the single-crystal domain size and the hydrothermal treatment time has been established.

Gazizulina, A. M.; Alakshin, E. M.; Baibekov, E. I.; Gazizulin, R. R.; Zakharov, M. Yu.; Klochkov, A. V.; Korableva, S. L.; Tagirov, M. S.

2014-04-01

68

Additive colouring of CaF2:Yb crystals: determination of Yb2+ concentration in CaF2:Yb crystals and ceramics  

NASA Astrophysics Data System (ADS)

When growing CaF2 crystal doped with rare-earth ions, most of these ions are present in a trivalent state. However, due to contact with graphite crucible, a small proportion of a number of ions (Eu, Sm, Yb and Tm) are reduced to a bivalent state. A similar situation takes place during fabrication of CaF2 ceramics doped with rare-earth metals. This fact is of particular importance for laser CaF2:Yb crystals (ceramics), a promising material for short-pulse, high-power, high-energy diode-pumped solid state lasers since the presence of bivalent Yb ions can be a source of thermal losses. To date, there has been no technique to determine Yb2+ concentration in as-grown crystals. The proposed technique is based on a total reduction of Yb3+ ions via the heating of as-grown CaF2 crystals with known concentration of Yb in the reducing atmosphere of metal vapour and determining the cross section of absorption bands of Yb2+ ions. The knowledge of these parameters allows estimation of the Yb2+ content in CaF2:Yb crystals or ceramics by analysing their absorption spectra. Examples of using this technique are given. The technology of CdF2 crystals reduction (an "additive colouring") and features of colouring of crystals doped with rare-earth ions are considered.

Shcheulin, A. S.; Angervaks, A. E.; Semenova, T. S.; Koryakina, L. F.; Petrova, M. A.; Fedorov, P. P.; Reiterov, V. M.; Garibin, E. A.; Ryskin, A. I.

2013-06-01

69

Ce decay curves in Ce, Tb co-doped LaF3 and the energy transfer mechanism  

NASA Astrophysics Data System (ADS)

Energy transfer phenomena can play an important role in the development of luminescent materials, and hosts co-doped with Ce3+ and Tb3+ ions continue to be actively studied. Several recent reports on Ce, Tb co-doped phosphors suggest different mechanisms for the energy transfer from Ce3+ to Tb3+ ions and further study is required to reach consensus on the mechanism or to understand why different mechanisms dominate in different hosts. A more direct method of analysis is proposed to distinguish between the different types of multipole energy transfer mechanisms. When applied to Ce, Tb co-doped LaF3, the experimental data shows a poor match to any of these models but is consistent with energy transfer through the exchange mechanism. The decay curves of Ce emission in Ce, Tb co-doped LaF3 were also studied to obtain further insight on the energy transfer mechanism. Although the decrease in lifetime with increasing Tb concentration shows that energy transfer occurs through a non-radiative mechanism, the form of the decay curves does not correspond to what is expected for energy transfer via multipole interactions.

Kroon, R. E.; Swart, H. C.; Ntwaeaborwa, O. M.; Seed Ahmed, H. A. A.

2014-04-01

70

Composition versus friction and wear behavior of plasma sprayed WC-(W,Cr)2C-Ni/Ag/BaF2-CaF2 self-lubricating composite coatings for use up to 600 °C  

NASA Astrophysics Data System (ADS)

This paper reports the composition optimization of self-lubricating composite coatings containing WC-(W,Cr)2C-Ni, silver and fluoride eutectics. Various ingredients obtained by powder blending were studied to determine their optimum content in as-prepared composite coatings. An atmospheric plasma spraying (APS) system was used to deposit promising WC-(W,Cr)2C-Ni/Ag/BaF2-CaF2 self-lubricating composite coatings. The friction and wear behavior of the composite coatings sliding against Si3N4 ball was investigated from room temperature to 600 °C. Results show that silver and fluoride eutectics can effectively reduce the friction coefficient of the coatings and the wear volume loss of counterpart balls over the whole temperature range. Thanks to the highest hardness, WC-(W,Cr)2C-Ni coating without silver and fluoride eutectics has the lowest wear rate at room temperature and 600 °C. However, it has a high friction coefficient and a very high wear rate at 200 and 400 °C, due to severe adhesion wear and fatigue wear thereat. Fortunately, introducing appropriate amount of silver and fluoride eutectics contributes to effectively reduce the wear rate of the composite coatings at 200 and 400 °C. The optimized composite coating consists of 70 wt.% WC-(W,Cr)2C-Ni, 15 wt.% Ag and 15 wt.% BaF2/CaF2, and it has excellent friction and wear performance over a wide range of temperature.

Chen, Jianmin; Hou, Guoliang; Chen, Jie; An, Yulong; Zhou, Huidi; Zhao, Xiaoqin; Yang, Jie

2012-11-01

71

A BaF2 crystal array for high energy g-ray measurements  

NASA Astrophysics Data System (ADS)

We shall discuss about the scientific motivation and construction of a 7 x 7 BaF2 crystal array at Variable Energy Cyclotron Centre, Calcutta. This detector would be used to measure high energy g -ray photons from GDR decay and proton--neutron bremsstrahlung reactions at the present 88'' cyclotron and upcoming superconducting cyclotron at VECC, Calcutta. This detector can also be used to measure photons from quark--gluon plasma at the relativistic heavy ion collider (RHIC) in USA.

Ray, A.; Banerjee, S. R.; Das, P.

2001-07-01

72

Molecular dynamics simulation of the superionic conductor BaF 2  

Microsoft Academic Search

Molecular dynamics simulations of the BaF2 fluoride crystal were carried out over a wide range of temperatures in order to study structural and transport characteristics in the low-temperature, the high-temperature superionic, and the molten state. The experimental temperature dependence of the lattice constant was taken into account. A sharp change in total energy of the system in the vicinity of

A. K. Ivanov-Shitz; A. S. Buchstab; S. K. Aityan; H.-H. Kohler

1992-01-01

73

Layer-dependent laser sputtering of BaF2 (111)  

Microsoft Academic Search

Laser-induced sputtering from the (111) surface of BaF2 was investigated under ultrahigh vacuum conditions, applying fluences well below the macroscopic damage threshold. Measurement of the wavelength-dependent desorption of Ba+ indicates that Ba+ is emitted from two chemically different surroundings at the surface. For a fixed wavelength, the emission rates of Ba+ and F+ as functions of time show a distinct

J. Reif; H. Fallgren; H. B. Nielsen; E. Matthias

1986-01-01

74

The use of BaF2 thermoluminescence in determining radiation quality  

Microsoft Academic Search

The thermoluminescence of high-purity BaF2 crystals was studied. The thermoluminescent light output per roentgen as a function of photon energy was measured over the range 30 keV to 1.25 MeV and agrees reasonably well with a calculation based on the assumption that the light output depends only on the energy absorbed in the crystal. The K-edge of Ba is also

R. L. Dixon; F. C. Watts

1972-01-01

75

Photoionization thresholds of rare-earth impurity ions. EuS :CaF2, CeT :YAG, and SmS :CaF2  

SciTech Connect

The spectral dependence of the photoionization energy of EuS :CaF2, CeT :YAG, and SmS :CaF2 systems have been measured and thresholds experimentally determined and compared with theoretical values calculated from electrostatic models. It is shown that the excited state absorption transitions or the persistent hole burning observed by other authors occur above the threshold energy of photoionization of the impurities and that the states of the crystal which form the bottom of the conduction band may play an important role in the strong probability of these processes. A review of thresholds now known is also given.

Pedrini, C.; Rogemond, F.; McClure, D.S.

1986-02-15

76

Suitability of Glass-Encapsulated CAF2:Mn Thermoluminescent Dosimiters for Environmental Radiation Surviellance.  

National Technical Information Service (NTIS)

The suitability of glass-encapsulated CaF2:Mn thermoluminescent dosimeters for environmental radiation surveillance was investigated. More than two hundred dosimeters were subjected to extensive laboratory and field tests. Various parameters such as accur...

J. E. Partridge S. T. Windham J. L. Lobdell J. A. Oppold

1973-01-01

77

The mechanism for material removal in ductile mode cutting of CaF2 brittle crystals  

Microsoft Academic Search

Single-crystal calcium fluoride (CaF2) is an indispensable optical material for the deep ultraviolet radiation lithography system. The requirement for extremely high performance using in lithography system can be not satisfied by using conventional polishing because the polishing powder are easy to embed to surface due to its relative softness. In the process of rough finishing of CaF2, ductile cutting of

Haofeng Chen; Yifan Dai; Xiaoqiang Peng; Ziwen Zheng; Chaoliang Guan

2010-01-01

78

Single-point diamond turning of CaF 2 for nanometric surface  

Microsoft Academic Search

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

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

2004-01-01

79

Composition and morphology studies of ultrathin CaF 2 epitaxial films on silicon  

Microsoft Academic Search

Thin CaF2 films with thicknesses between 1 and 100nm were grown on Si(111) at UHV conditions by evaporation from a CaF2 source. The correlation of film composition and growth morphology with the deposition parameters was studied by various techniques such as heavy-ion elastic recoil detection analysis (ERDA), RBS\\/channeling, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and auger electron spectroscopy

W. Bohne; J. Rohrich; M. Schmidt; A. Schopke; B. Selle; R. Wurz

2001-01-01

80

High pressure optical studies of rare earth ions in CaF2 and other fluorides  

Microsoft Academic Search

High pressure optical absorption studies have been performed on a series of rare-earth ions Sm2+, Dy2+, Sm2+, and Tm2+ in CaF2, Tm2+ in SrF2, EuF2, and Gd3+ in CaF2. For the first five substances the transitions from the 4fn ground state to the 4fn ? 1 5d configuration shift to lower energy with increasing pressure. This is consistent with the

P. J. Wang; H. G. Drickamer

1973-01-01

81

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

82

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

83

Migration parameters of the bound fluorine in trivalent-cation-doped BaF2  

NASA Astrophysics Data System (ADS)

The ratio of the migration entropy s over the migration enthalpy h of the bound fluorine in trivalent-cation-doped BaF2 is estimated with different experimental methods. A thermodynamical model proposed by Varotsos and Alexopoulos is used in order to correlate the ratio s/h with the macroscopic quantities of the host crystal (bulk modulus and thermal-expansion coefficient). This model seems not to be valid in general. We point out that there are deviations for dopants with large ionic radii. In this case, we speculate that the usual arbitrarily chosen attempt frequency of the bound fluorine which leads to the evaluation of s is incorrect.

Grammatikakis, J.; Papathanassiou, A. N.

1992-01-01

84

Windows for HF/DF chemical lasers - CaF2 or ZnSe  

NASA Astrophysics Data System (ADS)

An investigation of laser-driven phenomena occurring in CaF2 and ZnSe window materials which affect the performance of high energy laser systems at chemical wavelengths is reported. The systems studied comprised an optical cavity, relay tube, beam expander, and output window to the focus. An analysis of the cumulative phaseshifts due to beam defocusing and distortion caused by thermally generated aberrations in the window is performed to determine an expression for the degradation in focal intensity. Optical distortion coefficients are derived for laser beams passing through a solid window, and specifically for polycrystalline CaF2 and ZnSe, along with other elastic, optical, and elastic properties. Performance evaluations are analytically compared for the two materials, and CVD ZnSe windows are found suitable for maximizing peak irradiance, while CaF2 is useful for optimizing energy delivery capabilities of HF/DF lasers.

Klein, C. A.

85

Analysis of laser durability of CaF2 for optical lithography  

NASA Astrophysics Data System (ADS)

Photolithography is a key technolgoy for the production of semiconductor devices. It supports the continuing trend towards higher integration density of microelectronic devices. The material used in the optics of lithography tools has to be of extremely high quality to ensure the high demand of the imaging. Due to its properties CaF2 is a material of choice for the application in lithography systems. Because of the compexity of the lithography tools single lenses or lens system modules cannot be replaced. Therefore the lens material has to last the full lifetime of the tool without major degradation. According to the roadmap for next generation of optical lithography tools, like immersion lithography, the requirements of CaF2 for radiation hardness are increasing considerably. We will present a detailed analysis of the key factors influencing the laser hardness covering the complete production chain. Some aspects of the evaluation methods for testing CaF2 laser durability will be presented.

Grabosch, Guenter; Parthier, Lutz; Natura, Ute; Poehl, Karin; Letz, Martin; Muehlig, Christian; Knapp, Konrad

2005-02-01

86

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

87

Effect of CaF2 addition on optical properties of barium phosphate glasses  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

88

Fabrication of microlens arrays in CaF2 by ion milling  

NASA Astrophysics Data System (ADS)

Calcium Fluoride microlens arrays have been produced with the help of an ion milling transfer of photoresist lenses which have been fabricated by two different techniques (i) by a melting resist technique and (ii) gray scale lithography. Major technical problems connected with the ion milling transfer of the photoresist lenses in the CaF2 material are surface roughness enhancement and variation of the lens shape. We studied the ion-induced decomposition of CaF2 and the surface roughness equatio in dependence on different milling conditions. For the microlens patter transfer the ratio of etching rates of the photoresist and the CaF2 have been adjusted by gas admixture of nitrogen to the Ar sputtering gas. The angle dependence of the etching rates leads also to a changing of the lens profile. The effect of ion beam induced surface roughness and the accuracy of the transfer process is discussed.

Flamm, Dieter; Schindler, Axel; Harzendorf, Torsten; Kley, Ernst-Bernhard

2000-08-01

89

Growth and optical properties of partially transparent Eu doped CaF2 ceramic  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

90

Swift heavy-ions induced sputtering in BaF2 thin films  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

91

Suppression of the slow component of BaF2 crystal by introduction of SrF2 and MgF2 crystals  

Microsoft Academic Search

The emission spectrum, the time dependence of the luminescence, the light output, the excitation and the reflectance spectra have been measured for pure BaF2 crystal, for BaF2:Sr crystals with Sr2+ concentrations of 2 and 5 mol% and for BaF2:MgF2 crystal with a mole mixing ratio of 1:2. The measurements have been made by using synchrotron orbital radiation and high-energy electrons

M. M. Hamada; Y. Nunoya; S. Sakuragui; Shinzou Kubota

1994-01-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

93

Femtosecond laser ablation of CaF2: Plasma characterization and thin films deposition  

NASA Astrophysics Data System (ADS)

Nanostructured thin films of CaF2 have been deposited in vacuum by ultra-short pulse laser ablation. The laser-induced plasma, characterized by optical emission spectroscopy and ICCD fast imaging, shows the presence of Ca and F atomic species, neutral and ionized, together with the CaF molecular species. Although continuous blackbody-like emission has not been detected from the plasma, the deposited films, characterized by Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are apparently formed by the coalescence of a large number of nanoparticles composed by stoichiometric CaF2.

De Bonis, A.; Santagata, A.; Galasso, A.; Sansone, M.; Teghil, R.

2014-05-01

94

First-principles calculations of the elastic constants of the cubic, orthorhombic and hexagonal phases of BaF2  

NASA Astrophysics Data System (ADS)

All the elastic constants of cubic, orthorhombic and hexagonal phases of BaF2 have been calculated using first principles methods. We have employed density-functional theory within generalized gradient approximation (GGA) using a plane-wave pseudopotentials method and a plane-wave basis set. The calculated elastic constant values for a cubic phase compare well with recent theoretical and experimental calculations. The bulk modulus derived from the elastic constant calculations of orthorhombic phase of BaF2 is 94.5 GPa and those of hexagonal phase is 161 GPa. These values are in good agreement with experimental data available. Stability of these phases of BaF2 is also estimated in different crystallographic directions.

Nyawere, P. W. O.; Makau, N. W.; Amolo, G. O.

2014-02-01

95

Optimized strategies for thermal re-activation of LaF3/Pt-sensors based on photothermal characterization  

NASA Astrophysics Data System (ADS)

Gas sensors based on a semiconductor-supported LaF3/Pt-structure require regular re-activation by thermal treatment. A convenient way to accomplish this is by applying an electrical current pulse to the Pt-electrode and controlling re-activation by the amount of Joule heat deposited. Pulse length has to be chosen to balance the requirements of thermal energy needed for re-activation and the constraints in peak thermal power to prevent damage. Prerequisite to optimization is a knowledge of the thermal response of the complicated thin film sensor system consisting of several layers with unknown thermal properties. Modulated photothermal microscopy was used to detect inhomogenities in thin film heating and early stages of failure under thermal load. It was found that the formation of gas bubbles in the film is one of the major sources of failure. These measurements were complemented by measurements of transient heating during the re-activation and calculations of the temperature profile in the sample using a finite-element model.

Hartmann, J.; Roth, U.; Moritz, W.; Voigt, P.; Reichling, M.

1999-03-01

96

Variations of properties of the MoS 2LaF 3 cosputtered and MoS 2-sputtered films after storage in moist air  

Microsoft Academic Search

In this paper, some variations of properties of the composite MoS2?LaF3 cospulicred films and the pure MoS2-sputtcrcd films (as the composite films and the pure films respectively) after storage in moist air (? 100% RH) were investigated. The orientation, surface structure and chemical slate of the films were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and X-ray

De-Yang Yu; Jun-An Wang; Jin-Lin Ou Yang

1997-01-01

97

Fabrication of microlens arrays in CaF2 by ion milling  

Microsoft Academic Search

Calcium Fluoride microlens arrays have been produced with the help of an ion milling transfer of photoresist lenses which have been fabricated by two different techniques (i) by a melting resist technique and (ii) gray scale lithography. Major technical problems connected with the ion milling transfer of the photoresist lenses in the CaF2 material are surface roughness enhancement and variation

Dieter Flamm; Axel Schindler; Torsten Harzendorf; Ernst-Bernhard Kley

2000-01-01

98

Spectroscopie et fonctionnement laser de CaF{2}: Yb3+  

NASA Astrophysics Data System (ADS)

CaF{2 }:Yb3+ est un cristal doté de propriétés optiques et thermiques qui en font un matériau de choix pour divers types de fonctionnement laser. Un fonctionnement laser continu accordable entre 1000 et 1060nm et un rendement de conversion de 25% (par rapport au rayonnement de pompage optique incident) ont été déjà obtenus.

Camy, P.; Doualan, J. L.; Petit, V.; Renard, S.; Thuau, M.; Moncorgé, R.

2004-11-01

99

Effect of CaF2 on Interfacial Phenomena of High Alumina Refractories with Al Alloy  

NASA Astrophysics Data System (ADS)

An experimental study was conducted to investigate the interfacial phenomena between Al-alloy and industrial grade high alumina refractories containing varying contents of CaF2 at 1250 °C. Interfacial reaction products and phases formed in the heat-treated refractory samples were characterized using electron probe microanalysis (EPMA) and X-ray diffraction (XRD), respectively, while interfacial phenomena including dynamic wetting behavior were analyzed using the sessile drop technique. Refractories containing less than 5 wt pct CaF2 showed good resistance to reactions with the molten alloy, due to the dominance of corundum, and the presence of anorthite at the interface. However, with a further increase in the additive content, a glassy matrix of anorthite with CaF2 was formed. Formation of this phase significantly increased the intensity of reactions resulting in the buildup of an interfacial layer. The study thus revealed the strong catalytic effect of CaF2 on reactions of high alumina refractories with Al-alloy.

Koshy, Pramod; Gupta, Sushil; Sahajwalla, Veena; Edwards, Phil

2008-08-01

100

Analysis of digital timing methods with BaF 2 scintillators  

NASA Astrophysics Data System (ADS)

Various digital methods were examined for determining the relative arrival times of pulses from to 5.08×2.54 cm BaF 2 scintillators. In this study, pulses from the photomultiplier tubes were digitized by a 1 Gs/s analog-to-digital converter and post processed with multiple techniques. These techniques include: (1) leading edge discrimination, (2) moment-analysis, (3) constant-fraction discrimination, (4) digital constant-fraction discrimination, (5) triangular pulse shaping with a leading edge linear regression, and (6) pulse-shape fitting. Average timing resolutions of 456±8 ps were obtained with constant-fraction discrimination, which is slightly higher than the analog average resolution of 419±7 ps. This study explores the application of these digital techniques for pulse-timing applications and their potential advantages and limitations.

Nelson, Mark A.; Rooney, Brian D.; Dinwiddie, Derek R.; Brunson, Glen S.

2003-06-01

101

Absolute light yield measurements on BaF2 crystals and the quantum efficiency of several photomultiplier tubes  

Microsoft Academic Search

The quantum efficiency (QE) curves of five Philips XP2020Q photomultiplier tubes (PMTs) and one Hamamatsu R2059 PMT were determined using a calibrated Thorn EMI 9426 PMT as a reference. A study of the absolute light yield of a pure BaF2 crystal as a function of wavelength and time is presented

P. Dorenbos; J. T. M. de Haas; R. Visser; C. W. E. van Eijk; R. W. Hollander

1992-01-01

102

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

103

Nanostructures induced by highly charged ions on CaF2 and KBr  

Microsoft Academic Search

Impact of a highly charged ion upon a solid surface can induce dramatic changes in the morphology only by the release of its potential energy. Hillocks and mono-atomic deep pits have been observed on the surfaces of CaF2 and KBr, respectively. For both processes a threshold in the potential energy exists for the creation of these nanostructures. Above this threshold

S. Facsko; W. Meissl; R. Heller; R. Wilhelm; A. S. El-Said; G. Kowarik; R. Ritter; F. Aumayr

2009-01-01

104

Persistent spectral hole burning in deuterated CaF2:Tm3+  

Microsoft Academic Search

We report spectral hole burning in the deuteride (D-) modified Tm3+ centers in CaF2, where the hole burning mechanism is known to involve localized displacement of the D- ions. Two main families of Tm3+-D- centers are present; the Li centers yield spectral holes that have been measured to be fully persistent for 48 hours at liquid-helium temperatures, while spectral holes

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

1999-01-01

105

Hydrothermal synthesis and upconversion properties of CaF2:Er3+/Yb3+ nanocrystals.  

PubMed

A series of rare-earth ions (Er3+ and Yb3+) Co-doped CaF2 upconversion luminescent nanomaterials have been successfully prepared via a facile hydrothermal method using pluronic p123 (p123), pluronic F127 (F127) and sodium citrate as surfactants at 180 degrees C with different reaction time. The crystallographic phase, size and morphology can be controlled by simply tuning the reaction parameters such as the types of surfactants and the reaction time. It is found that reaction time and surfactant play a key role in forming the nanocrystals with different morphologies. X-ray diffraction, field-emission scanning electron microscopy FE-SEM, and photoluminescence spectra were used to characterize the structure, morphology and upconversion luminescence properties of CaF2:Er3+/Yb3+ upconversion nanomaterials, respectively. The experimental results indicate that three monodispersive and highly uniform CaF2:Er3+/Yb3+ nanocrystals with mean size of 200 nm, 3 um, and 700 nm have cubic and sphere shapes, respectively. While the possible mechanisms of upconversion luminescence are analyzed by the diagram of proposed energy transfer mechanisms, the schematic energy level diagrams showing typical upconversion processes for Er3+ also reveals that the as-synthesized CaF2:Er3+/Yb3 nanomaterials may be in the cubic structure with space group Fm-3m, in which Ln3+ cations occupy crystal lattice positions with lower point symmetry, leading to a high upconversion efficiency under the excitation of a 980 nm diode laser. PMID:24734555

Yu, Shiyong; Zhi, Yunxia; Su, Haiquan

2014-05-01

106

LET dependence of thermoluminescent efficiency and peak height ratio of CaF 2:Tm  

Microsoft Academic Search

First-order thermoluminescence (TL) kinetics computerized glow curve deconvolution (CGCD) and manual analysis of the composite peak structures have been applied to study the behaviour of glow peaks 3 and 5 in CaF2:Tm (TLD-300, Harshaw-Thermo Fisher Scientific) single crystals after heavy charged particle (HCP) irradiation with respect to Co60 gamma rays for a linear energy transfer (LET) interval from 2.3 to

M. Hajek; T. Berger; R. Bergmann; N. Vana; Y. Uchihori; N. Yasuda; H. Kitamura

2008-01-01

107

The kinetics of CaF 2 metallization induced by low-energy electron irradiation  

Microsoft Academic Search

Results of experimental and theoretical studies on metal colloid growth after irradiation and subsequent heating of CaF2 are presented. Samples at a temperature of 200 K were irradiated in UHV for 30 min with 2.5 keV electrons. After irradiation samples were heated at a rate of about 1 K\\/min and colloid formation was investigated by optical extinction spectroscopy. Colloid radii

M. Huisinga; N. Bouchaala; R. Bennewitz; E. A. Kotomin; M. Reichling; V. N. Kuzovkov; W. von Niessen

1998-01-01

108

Surface colloid evolution during low-energy electron irradiation of CaF 2(111)  

Microsoft Academic Search

The effects of 1 keV electron irradiation (current density typically 40 ?A cm?2) on the surface structure of CaF2 (111) are studied by scanning force microscopy (SFM) to investigate the role of diffusion in the process of electron-induced surface metal colloid formation. Systematic variation of beam voltage, irradiation time, intensity and dosage is investigated in regard to metal formation on

M. Reichling; R. M. Wilson; R. Bennewitz; R. T. Williams; S. Gogoll; E. Stenzel; E. Matthias

1996-01-01

109

Conductivity enhancement of caf 2 by grain boundary activation with lewis acids  

Microsoft Academic Search

CaF2 fine powder and films were treated with the Lewis acids SbF5 and BF3 to create a strong driving force to draw F? ions out of the boundary regions according to L (surface) + FF (boundary) ? LF? (surface) + VF (boundary) (L = SbF5 or BF3). The conductivity results of polycrystalline ceramics treated in this way indicate a significant

Yuria Saito; Joachim Maier

1996-01-01

110

High quality ultrathin Bi2Se3 films on CaF2 and CaF2/Si by molecular beam epitaxy with a radio frequency cracker cell  

NASA Astrophysics Data System (ADS)

We report a method to fabricate high quality Bi2Se3 thin films using molecular beam epitaxy with a radio frequency cracker cell as an atomic selenium source. With Se-to-Bi ratios close to exact stoichiometry, optimal layer-by-layer growth of high quality Bi2Se3 thin films with smooth surfaces has been achieved on CaF2(111) substrates and Si(111) substrates with a thin epitaxial CaF2 buffer layer (CaF2/Si). Transport measurements show a characteristic weak-antilocalization magnetoresistance in all the films, with the emergence of a weak-localization contribution in the ultrathin film limit. Quantum oscillations, attributed to the topological surface states have been observed, including in films grown on CaF2/Si.

Zhang, Li; Hammond, Robert; Dolev, Merav; Liu, Min; Palevski, Alexander; Kapitulnik, Aharon

2012-10-01

111

Sintering of CaF 2 pellets as nuclear fuel analog for surface stability experiments  

NASA Astrophysics Data System (ADS)

To enable a detailed study of the influence of microstructure and surface properties on the stability of spent nuclear fuel, it is necessary to produce analogs that closely resemble nuclear fuel in terms of crystallography and microstructure. One such analog can be obtained by sintering CaF 2 powder. This paper reports the microstructures obtained after sintering CaF 2 powders at temperatures up to 1240 °C. Pellets with microstructure, density and pore structure similar to that of UO 2 spent nuclear fuel pellets were obtained in the temperature range between 900 °C and 1000 °C. When CaF 2 was sintered above 1100 °C the formation of CaO at the grain boundaries caused the disintegration of the pellet due to hydration occurring after sintering. First results from a novel set-up of dissolution experiments show that changes in roughness, dissolution rate and etch pit shape of fluorite surfaces are strongly dependent on the crystallographic orientation of the expose surface. Consequently, the differences observed for each orientation will affect the overall dissolution rate and will lead to uncertainties in the estimation of dissolution rates of spent nuclear fuel.

Godinho, José R. A.; Piazolo, Sandra; Stennett, Martin C.; Hyatt, Neil C.

2011-12-01

112

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

113

Study of electronic sputtering of CaF2 thin films  

NASA Astrophysics Data System (ADS)

In the present work thin films of CaF2 deposited on Si substrate by electron beam evaporation have been investigated for swift heavy ions induced sputtering and surface modifications. Glancing angle X-ray Diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was performed to determine the sputter yield of CaF2 and a decrease in sputter yield has been observed with increase in film thickness. Thermal spike model has been applied to explain this. The confinement of energy in the grains having size smaller than the electron mean free path (?) results in a higher sputtering yield. Atomic force microscopy (AFM) studies of irradiated CaF2 thin films show formation of cracks on film surface at a fluence of 5 × 1012 ions/cm2. Also RBS results confirm the removal of film from the surface and more exposure of substrate with increasing dose of ions.

Pandey, Ratnesh K.; Kumar, Manvendra; Khan, Saif A.; Kumar, Tanuj; Tripathi, Ambuj; Avasthi, D. K.; Pandey, Avinash C.

2014-01-01

114

Study of BaF2 with 511 KeV Gamma Rays  

NASA Astrophysics Data System (ADS)

Results will be presented on tests conducted with a 20 Torr ethane 1000 Angstrom cesium-iodide photocathode avalanche chamber [1], with a barium-fluoride scintillator window. Positrons are emitted from a sodium-22 source, which annihilate to produce two 0.511 MeV gamma rays. The barium-fluoride scintillator window converts the 0.511 MeV gamma rays into ultraviolet wavelength photons, which are absorbed in the cesium-iodide photocathode. The detector is sensitive to photon wavelengths between 170 and 220 nanometers, with a peak quantum efficiency of 16% at 170 nanometers. The quantum efficiency falls with increased wavelength [2]. Photoelectrons from the cesium-iodide photocathode are multiplied as they are accelerated through 1.5 mm of ethane at 20 Torr by a potential difference ranging between 450 and 550 Volts. If performance is acceptable, this technique could be used in medical imaging applications, such as in a full-body PET scanner, as a replacement for photomultiplier tubes. A Monte Carlo program has been written to describe the detector and processes and results will be presented. REF. [1] M. Staric, et al., Detection of Fast BaF2 Scintillations With a CsI Photocathode Coupled to a MWPC, IEEE Trans. Nucl. Sci., Vol.41, No.4, p742, August 1994. REF. [2] W. Kononenko and N. S. Lockyer, Substrate Studies of Cesium Iodide Photocathodes, July 1995, to be published in Nucl. Instr. and Meth..

Miller, Jon

1996-05-01

115

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

116

Sites structure and spectroscopic properties of Yb-doped and Yb, Na-codoped CaF 2 laser crystals  

Microsoft Academic Search

For the first time, the effect of Na+ on crystal structure, valence state of Yb ions, spectroscopic properties of YbF3-doped CaF2 system was systematically studied. Na+ can greatly suppress the deoxidization of Yb3+ to Yb2+. Absorption and emission spectra showed codoping Na+ with different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in CaF2 lattice in

Liangbi Su; Jun Xu; Hongjun Li; Lei Wen; Yueqin Zhu; Zhiwei Zhao; Yongjun Dong; Guoqing Zhou; Jiliang Si

2005-01-01

117

Characterization of LiF and CaF 2 surfaces using MIES and UPS (HeI)  

Microsoft Academic Search

Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combination withab initio calculations (CRYSTAL-code) were applied to study surface and bulk defects in LiF and CaF2. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF2. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W

D. Ochs; M. Brause; S. Krischok; P. Stracke; W. Maus-Friedrichs; V. Puchin; A. Popov; V. Kempter

1998-01-01

118

Effect of pressure on the optical absorption of REF centers in Ce and Tb doped CaF2  

Microsoft Academic Search

The effect of pressure to 80 kbar has been measured on the absorption peaks associated with REF centers in Ce and Tb doped CaF2. The results are compared with previous data for Gd doped CaF2. The lowest and highest energy excitations [?(1E) and ?(2E)] are associated with an excited state largely of metal 5d(eg) character. The intermediate peak has predominantly

W. D. Drotning; H. G. Drickamer

1973-01-01

119

F-type centers and transformation in BaF2:Sr crystals irradiated by electron beam  

Microsoft Academic Search

Summary form only given. Optical absorption spectra of BaF2 :Sr crystals were studied before and after electron beam irradiation, and the process of F-type center transformation was also analyzed based on the study of absorption spectra. The results showed that 1.5 and 1.8 MeV electron irradiation at the dose of 1015~1016 cm-2 induced F-H pairs, F centers and other centers

Guangcan Wang; Jin Zhang; Jingjing Yang

2000-01-01

120

First-principles study of structural, electronic and optical properties of BaF2 in its cubic, orthorhombic and hexagonal phases  

Microsoft Academic Search

We present the results of a first-principles study on BaF2 in its stable (cubic) and high-pressure phases. A linear combination of atomic orbitals approach in the framework of density functional theory is employed for total energy calculations in cubic, orthorhombic and hexagonal phases of BaF2. A fitting of the energy surface to the equation of state yields the lattice constant

Huitian Jiang; Ravindra Pandey; Clovis Darrigan; Michel Rérat

2003-01-01

121

Creation of nanohillocks on CaF2 surfaces by single slow highly charged ions.  

PubMed

Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as low as 150 x q eV, we find first unambiguous experimental evidence that potential energy alone is sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF(2) single crystal. Our investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock formation which can be linked to a solid-liquid phase transition. PMID:18643543

El-Said, A S; Heller, R; Meissl, W; Ritter, R; Facsko, S; Lemell, C; Solleder, B; Gebeshuber, I C; Betz, G; Toulemonde, M; Möller, W; Burgdörfer, J; Aumayr, F

2008-06-13

122

Nanostructures induced by highly charged ions on CaF2 and KBr  

NASA Astrophysics Data System (ADS)

Impact of a highly charged ion upon a solid surface can induce dramatic changes in the morphology only by the release of its potential energy. Hillocks and mono-atomic deep pits have been observed on the surfaces of CaF2 and KBr, respectively. For both processes a threshold in the potential energy exists for the creation of these nanostructures. Above this threshold the structure size increases linearly with potential energy. The mechanisms for the formation of hillocks and pits are discussed and a first attempt to present a unified microscopic picture is made.

Facsko, S.; Meissl, W.; Heller, R.; Wilhelm, R.; El-Said, A. S.; Kowarik, G.; Ritter, R.; Aumayr, F.

2009-11-01

123

Effect of porosity on impedance of CaF2 ceramic  

NASA Astrophysics Data System (ADS)

Ceramic samples of CaF2 were characterized using impedance spectroscopy to understand the effect of porosity on electrical conductivity upto 150°C. Pellets of cold pressed nano powder as well as those sintered at high temperature and transparent ceramic were investigated. The room temperature conductivity of porous samples (cold pressed and sintered at 700°C) were found to be more than less porous samples (sintered at 1000°C and transparent ceramic). The conductivity was found to increase as the temperature is increased till 100°C and decreases on further increase in temperature. At 150°C transparent ceramic sample shows the maximum conductivity.

Sen, Shashwati; Mittal, Garima; Deshpande, S. K.; Gadkari, S. C.

2013-02-01

124

Conductive nanodots on the surface of irradiated CaF2  

NASA Astrophysics Data System (ADS)

CaF2(111) single crystal surfaces have been irradiated with swift heavy ions under oblique angles resulting in chains of nanosized hillocks. In order to characterize these nanodots with respect to their conductivity we have applied non-contact atomic force microscopy using a magnetic tip. Measurements in UHV as well as under ambient conditions reveal a clearly enhanced electromagnetic interaction between the magnetic tip and the nanodots. The dissipated energy per cycle is comparable to the value found for metals, indicating that the interaction of the ion with the target material leads to the creation of metallic Ca nanodots on the surface.

Roll, Tino; Meier, Marion; Akcöltekin, Sevilay; Klusmann, Miriam; Lebius, Henning; Schleberger, Marika

2008-10-01

125

Microstructure and properties of the composite magnets fabricated with Nd-Fe-B powders coated with CaF2  

NASA Astrophysics Data System (ADS)

Nd-Fe-B powders were coated with CaF2 by three different chemical synthesis methods, named as A: One-step direct precipitation, B: One-step slow dropping, and C: Two-step process. The CaF2-coated Nd-Fe-B powders were hot-pressed and then hot-deformed to fabricate composite magnets. The microstructures, electrical resistivities, and magnetic properties of the Nd-Fe-B composite magnets obtained with different coating methods and parameters were investigated. The results showed that the thickness and continuity of CaF2 coating depended on the coating methods with different Ca(NO3)2 concentrations and coating time. When the Ca(NO3)2 concentration was 2 mol/l, the CaF2 coating synthesized by one-step direct precipitation was a loose and discontinuous film, while the CaF2 coating synthesized by one-step dropping for 30 min was a continuous and dense film, and its thickness reached to 410-450 nm. If the Ca(NO3)2 concentration was further increased to 5.5 mol/l, the thickness of CaF2 reached to 710-900 nm. The electrical resistivities of the composite magnets prepared by one-step slow dropping for 30 min with the Ca(NO3)2 concentrations of 2 and 5.5 mol/l were approximately 680 and 890 ?? cm, which was a 195% and 287% increase, respectively, compared to that of the corresponding magnet prepared with uncoated Nd-Fe-B powders. The coercivities of the composite magnets decreased with increasing thickness of CaF2, while the remanence had only a slight reduction. The composite magnet fabricated by a two-step process achieved both higher maximum energy product ((BH)m = 47.2 MG Oe) and electrical resistivity (847 ?? cm).

Zheng, Liyun; Xin, Honghui; Bi, Wenchao; Zhu, Minggang; Li, Wei; Zhou, Dong

2014-05-01

126

Laser induced nanoparticle formation in single crystal CaF2  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

127

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

129

Epitaxial Growth of Ferromagnetic Fe3Si Films on CaF2/Si(111) by Molecular Beam Epitaxy  

NASA Astrophysics Data System (ADS)

Ferromagnetic Fe3Si/CaF2 hybrid structures were epitaxially grown on Si(111) by molecular beam epitaxy. When Si and Fe were directly deposited on the Si substrate, it was difficult to prevent inclusion of FeSi in the grown films. This problem was overcome by forming a CaF2 epitaxial film on Si(111) first, followed by codeposition of Si and Fe to form Fe3Si. Fe3Si films were epitaxially grown on the CaF2 at 400°C. A distinct square-like hysteresis loop was observed at room temperature in the magnetic field dependence of Kerr rotation.

Sunohara, Tsuyoshi; Kobayashi, Ken'ichi; Umada, Masakazu; Yanagihara, Hideto; Kita, Eiji; Akinaga, Hiroyuki; Suemasu, Takashi

2005-05-01

130

Dipole-relaxation parameters for Ce3+-Fint- complexes in CaF2:Ce and CaF2:Ce,Mn  

NASA Astrophysics Data System (ADS)

Dipole-relaxation parameters for Ce3+-Fint- centers (C4v symmetry) in CaF2 are calculated using the method of ionic thermocurrents (ITC). The data indicate concentration-dependent effects if analyzed using the traditional ITC equation, assuming a single value for the reorientation activation energy. This analysis is unable to account for an observed broadening of the ITC peak as more Ce is added to the crystals. However, as has been published for other MF2:R3+ systems, we find that the broadening can be successfully accounted for by adopting a modified ITC equation which allows for a Gaussian distribution of activation energies about a mean value E0 and with a distribution width p. The parameter E0 is found to be independent of dipole content while p is found to increase with increasing dipole concentration. The data are consistent with a perturbation of the dipole-relaxation parameters due to interactions with other defects within the system. However, the strength of the observed effects is difficult to explain by invoking electrostatic dipole-dipole interactions only. Other perturbations, due perhaps to monopole-dipole interactions or elastic interactions, must be taking place. The data indicate that dipole concentrations calculated by ITC will be in error in the presence of such interactions due to a reduction in the mean contribution per dipole to the overall polarization density. For samples in which interaction effects are negligible, we calculate a dipole moment of 3.12×10-29 C m. The data further indicate that that the addition of Mn to the system causes a decrease in the interaction effects via a reduction in the Ce C4v center dipole moment. It appears that the broadening of the ITC curve is sensitive to the defect structure surrounding the dipoles.

Jassemnejad, B.; McKeever, S. W. S.

1987-12-01

131

Temperature-dependent Urbach tail measurements of CaF2 single crystals  

NASA Astrophysics Data System (ADS)

In the deep ultraviolet spectral range the transmission of high-purity CaF2 was measured using synchrotron radiation. In the vicinity of the band gap below 11.2 eV or for wavelength longer than 90 nm, a scaling behavior of the absorption as a function of photon energy was observed. Temperature-dependent measurements allow one to distinguish two different absorption mechanisms which differ by their ability to couple to phonon excitations. These two types of Urbach tails were analyzed. The origin of the temperature-independent tail is due to defects in the lattice, whereas the temperature-dependent part originates from short-time localization of exciton mode coupling to lattice distortion.

Letz, M.; Gottwald, A.; Richter, M.; Parthier, L.

2009-05-01

132

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

133

Correlation between TL and OSL properties of CaF 2:N  

NASA Astrophysics Data System (ADS)

Natural CaF 2 is very well known thermoluminescent (TL) material, since it has been extensively used as a dosimeter. Its basic advantage is the exhibited high TL sensitivity. In the present work, the optically stimulated luminescence (OSL) sensitivity of this material was studied by exposing it to environmental radiation for time intervals of few hours up to a few days, and was found to be very high. By analyzing the TL glow curves and the OSL decay curves into their individual glow-peaks and components respectively, a relation between specific glow-peaks and OSL components was established. An intense thermal transfer effect occurring during optical stimulation at high temperature was observed and an explanation is offered according to existing models.

Polymeris, George S.; Kitis, George; Tsirliganis, Nestor C.

2006-09-01

134

Void superlattice formation in electron irradiated CaF 2: Theoretical analysis  

NASA Astrophysics Data System (ADS)

CaF 2 is widely adopted as deep-UV window material and thin film optical coating. The void superlattice was observed experimentally under electron irradiation at room temperature. We performed kinetic Monte Carlo (kMC) simulations of the initial stages of the process when short- and intermediate-range order of defects in small Ca colloids and larger interstitial aggregates (F 2 gas voids) is created. The kMC model includes fluorine interstitial-vacancy pair creation, defect diffusion, similar defect attraction and dissimilar defect recombination. Special attention is paid to the statistical analysis of the defect aggregate distribution functions under different conditions (dose rate, defect migration and recombination rates). These simulations demonstrate that under certain conditions the dissimilar aggregate recombination is strongly suppressed which stimulates growth of mobile interstitial aggregates that is a precondition for further void ordering into a superlattice.

Kuzovkov, V. N.; Kotomin, E. A.; Merzlyakov, P.; Zvejnieks, G.; Li, K. D.; Ding, T. H.; Wang, L. M.

2010-10-01

135

Photoemission Study of CaF2- and SrF2-GaAs(110) Interfaces Formed at Room Temperature.  

National Technical Information Service (NTIS)

Group-II cubic fluorides such as Calcium Fluoride CaF2 and Strontium Fluoride SrF2 are very promising for growing epitaxial insulator-on-semiconductor and semiconductor-on-insulator structures. Interfaces formed by evaporating CaF2 or SrF2 on room-tempera...

A. Kahn

1989-01-01

136

Laser-induced front side etching of CaF2 crystals with KrF excimer laser  

NASA Astrophysics Data System (ADS)

The laser-induced front side etching (LIFE) of amorphous materials like fused silica was manifold studied and the LIFE process was sufficient optimized for the fabrication of well-defined etching trenches with a very low surface roughness. The LIFE process is an indirect laser-induced ablation process, the - for the used laser wavelength - transparent substrate was covered by a highly absorbing material and the absorbing process causes a transfer of the laser energy into the substrate and, finally, to an ablation process of the substrate surface. However, the structuring of crystalline materials like CaF2 is a great challenge for the LIFE process. The properties of CaF2(1 1 1) and CaF2(0 0 1) surfaces etched by KrF excimer laser pulses (pulse duration ?tp = 25 ns, wavelength ? = 248 nm) were analysed by white light interferometry (WLI) as well as scanning electron microscopy (SEM). The surface morphologies of laser etched CaF2 surfaces depend on the laser parameters and on the crystal orientation and are frequently characterized by microcracks and flake spallation. The most probable reasons therefore are laser-induced thermal stress or laser-induced shock waves.

Lorenz, Pierre; Ehrhardt, Martin; Zimmer, Klaus

2013-01-01

137

Recording holograms on color centers in CaF2:Na crystals by light with different wavelengths  

NASA Astrophysics Data System (ADS)

The absorption spectra and holographic characteristics of a CaF2:Na crystal sample are measured at different wavelengths within the absorption band of colloidal centers, along with the same characteristics of the samples with holograms after their irradiation by incoherent UV light. Results of the study confirm the diffusion-and-drift mechanism of recording holograms on color centers in ionic crystals.

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

2009-12-01

138

High and low spin energy states of the Tb 3+ 4f 75d configuration in BaF 2  

NASA Astrophysics Data System (ADS)

In this paper we present results of detailed spectroscopic studies of Tb 3+ luminescence from BaF 2:0.075 mol% Tb performed at Superlumi station of Hasylab, DESY, Hamburg and at Institute of Physics, N. Copernicus University, Torun, Poland (IF UMK Torun). We have measured UV/VUV excitation spectra of the dominant blue Tb 3+ luminescence and emission spectra under excitation into various bands found from the excitation spectra. The excitation spectra are dominated by the two well known broad bands due to the parity and spin-allowed (SA) 4f 8 ? 4f 75d transitions. The higher energy triple t-band and unresolved single e-band at lower energies are widely separated (10 Dq about 16,500 cm -1) reflecting the single d-electron energy in the high symmetry cubic crystal field with a relatively low contribution from the low symmetry component. In addition to these bands we have also detected a number of weaker bands at lower energy sides of both dominant SA bands. While the structured band with components at 252.8, 252.3, 250.4 and 248.4 nm clearly corresponds to the SF (spin-forbidden) band found earlier in LiYF 4:Tb, the bands at 183, 178 and 172 nm have been never, to the best of our knowledge, reported before. We present arguments that these new bands are the SF counterparts of the triple SA t-band at about 158 nm. The d-f exchange energies for d(e) and d(t) electrons are different at 7779 and 8245 cm -1, respectively. Although the energy levels corresponding to the identified high and low spin (HS and LS) states of the 4f 75d configuration are, in BaF 2, well separated, there are no SA nor SF transitions generating d-f emission in BaF 2:Tb. This is because the numerous 4f 8 energy levels intercept the excitation energy from 4f 75d levels leading to the well known blue and green Tb 3+ 4f 8 emissions.

Witkowski, Marcin E.; Wojtowicz, Andrzej J.

2011-08-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

140

Irradiation effects in CaF2: ZnO nanostructed crystals  

NASA Astrophysics Data System (ADS)

Effects of ?, X, and UV radiation were studied in CaF2: ZnO single crystals in which ZnO was embedded as nanoparticles. Absorption measurements of these crystals showed a steep increase below 250nm and a weak absorption peak at about 310nm. After prolonged ? irradiation, additional absorption bands were recorded at 395 and 595nm. The irradiated samples showed during heating several thermoluminescence (TL) peaks. Samples which had been exposed to ?-irradiation at RT and subsequently illuminated at LNT with 390nm light showed during re-heating to RT several TL peaks that are attributed to a process of photo-transferred TL (PTTL). Main photoluminescence (PL) emission bands were recorded at 320 and 340nm with excitation maxima near 250 and 300nm. These emission bands were also observed during X-irradiation as well as additional emission bands near 355 and 400nm. In pre-irradiated samples, a 320nm luminescence band could also be excited by 395nm light and is attributed to a process of photostimulation. The stimulation maxima of the OSL and PTTL in the 390nm region are apparently due to the observed absorption band at 395nm induced by the ?-irradiation. The fact that some of the same emission bands appeared in the XL, PL, TL and OSL of this crystal indicates that the same luminescence centers are involved in these emissions.

Kristianpoller, N.; Chen, Wei; Chen, Reuven; Liu, Yinchu

2010-11-01

141

Influence of Various Impurities on the Optical Properties of YbF3-Doped CaF2 Crystals  

NASA Astrophysics Data System (ADS)

Calcium fluoride crystals doped with YbF3 and co-doped with LiF and NaF were grown using the vertical Bridgman method. Several of rare-earth ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF2. The change of valence was attained by various methods. The optical absorption spectra reveal the characteristic absorption bands of the Yb3+ and Yb2+ ions. This means that the developed crystal growth process achieves a good Yb3+ to Yb2+ conversion in the as-grown crystals. The influence of other impurities, such as Na+ or Li+, on the absorption and emission spectrum of YbF3-doped CaF2 was studied. The Li+ and Na+ ions drastically decrease the absorption coefficient of the Yb2+ ions in the UV band and the emission intensity by excitation in 230 nm.

Stef, M.; Pruna, A.; Pecingina-Garjoaba, N.; Nicoara, I.

2007-11-01

142

The formation of metallic nanoparticles in single crystal CaF2 under 157 nm excimer laser irradiation  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important material for vacuum-ultraviolet optical components. Unfortunately, all metal halides tend to form defects when exposed to energetic particles and laser radiation, and these defects can degrade optical performance. Here we examine the consequences of exposing CaF2 to 157 nm excimer laser radiation and show that several tens of thousands of pulses at fluences near 1 J/cm2 can color the material. Absorption spectra of the exposed material confirm the formation of metallic calcium nanoparticles similar to those produced by other forms of energetic radiation. The rate of nanoparticle formation depends on the bulk temperature and displays a local maximum near 50 °C. Absorption measurements at 157 nm display a transient absorption component that grows during prolonged irradiation and disappears on time scales of several minutes after irradiation ceases. The implications of these effects in optical components are discussed.

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

2006-03-01

143

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

144

Upconversion white light of Tm 3+\\/Er 3+\\/Yb 3+ tri-doped CaF 2 phosphors  

Microsoft Academic Search

Tm3+\\/Er3+\\/Yb3+ tri-doped CaF2 phosphors were synthesized using a hydrothermal method. The phosphors were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and up-conversion (UC) emission spectra. After annealing, the phosphors emitted white light under a 980nm continuous wave diode laser (CW LD 2 W) excitation. As the excitation power density changed in the range of 20–260W\\/cm2, the

Chunyan Cao; Weiping Qin; Jisen Zhang; Yan Wang; Guofeng Wang; Guodong Wei; Peifen Zhu; Lili Wang; Longzhen Jin

2008-01-01

145

Influence of Various Impurities on the Optical Properties of YbF3-Doped CaF2 Crystals  

Microsoft Academic Search

Calcium fluoride crystals doped with YbF3 and co-doped with LiF and NaF were grown using the vertical Bridgman method. Several of rare-earth ions (such as Eu, Sm, Ho, Tm, and Yb) can be stabilized in the divalent state in the CaF2. The change of valence was attained by various methods. The optical absorption spectra reveal the characteristic absorption bands of

M. Stef; A. Pruna; N. Pecingina-Garjoaba; I. Nicoara

2007-01-01

146

Some dielectric and optical properties of PbF2-codoped CaF2:YbF3 crystals  

Microsoft Academic Search

YbF3-doped and PbF2-codoped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions. The Pb2+ ions modify the characteristic absorption peaks of the Yb2+ ions, but do not influence the Yb3+ ion peaks. The dielectric relaxation gives information about the impurity-defect aggregates. The obtained dielectric spectra show that

M. Stef; G. Buse; A. Pruna; I. Nicoara

2009-01-01

147

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

148

The colouration of CaF2 crystals by keV and GeV ions  

Microsoft Academic Search

CaF2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 nm. This includes the vacuum UV region. For 100 keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10(17) ions cm(2) )

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

2002-01-01

149

A Study of the Superfluid Transition in ^4{He} Films Adsorbed to Rough {CaF}_2 Over a Large Temperature Range  

NASA Astrophysics Data System (ADS)

Rough two-dimensional substrates, such as thermally deposited {CaF}_2 , have been shown to modify the experimental signatures of the superfluid transition in adsorbed thin helium films. Previous experiments have investigated a series of increasingly rough surfaces over a limited temperature range and found that the features at the superfluid transition become less defined as substrate roughness is increased. In this work we study the superfluid transition in adsorbed helium films over a wide range of temperatures for a series of {CaF}_2 substrates. Our results show that as the transition temperature increases the abrupt jump in superfluid density at the transition becomes less distinct. The changing characteristics of the transition on a single {CaF}_2 substrate with temperature suggest that the reduced observability of the transition on rough substrates cannot be explained entirely by superfluid drag. We discuss several other possible scenarios which may be relevant to the helium films on {CaF}_2.

Wadleigh, L. R.; Luhman, D. R.

2014-05-01

150

Performance characterisation of large area BaF 2-TMAE detectors for use in a whole body clinical PET camera  

NASA Astrophysics Data System (ADS)

The first of two large area detectors which form part of a new whole body positron scanner has been fully characterised and a performance assessment has been completed. The detector consists of an array of crystals coupled to a large area, low pressure multiwire chamber filled with tetrakis-(dimethylamino)-ethylene (TMAE) gas. A complete optimisation has been carried out in the operation of the chamber in order to establish optimal levels of stability and performance. Under the optimised operational conditions the detector exhibits an efficiency of ˜ 25%, with a time and position resolution of 3.5 ns (FWHM) and 6.5 mm (FWHM) respectively. A Monte Carlo simulation of the complete dual headed PET camera has been used to assess the expected image quality in terms of contrast and signal to noise ratio. The simulation has been also used to establish the effect of utilising crystal slabs and a support frame to cover the active area of each detector in comparison with a single sheet of BaF 2. The results demonstrate that the use of crystal tiles results in a small increase in the background noise, not significantly compromising the image quality.

Visvikis, D.; Ott, R. J.; Wells, K.; Flower, M. A.; Stephenson, R.; Bateman, J. E.; Connolly, J.

1997-02-01

151

Sensitization of Pr3+ ions by Eu2+ ions in CaF2 thin films deposited by evaporation  

NASA Astrophysics Data System (ADS)

In the present article, we analyse the possibility of sensitizing the 3Pj levels of Pr3+ ion with Eu2+ ion in CaF2 thin film deposited by evaporation. Indeed, the forbidden nature of the 4f-4f transition of Pr3+ ion makes its absorption too weak for thin film applications, while materials doped with the Pr3+-Yb3+ couple are promising candidates for the achievement of efficient down-converter systems and could allow strong reduction of thermalization losses in silicon solar cells.

Guille, A.; Pereira, A.; Bensalah-Ledoux, A.; Moine, B.; Novotný, M.; Bulí?, J.; Fitl, P.; Lan?ok, J.

2013-11-01

152

Infrared-to-visible upconversion of rare-earth doped glass ceramics containing CaF 2 crystals  

Microsoft Academic Search

Oxy-fluoride glass ceramics containing CaF2 crystals doped with YbF3–LnF3 (Ln=Er, Tm) were prepared by heat-treatment from SiO2–Al2O3–CaO–CaF2 glasses. The upconversion emission spectra of Er3+ and Tm3+ ions in the visible range were measured by 970nm pumping. In the spectrum of the Er doped sample, 540nm upconversion band due to the 4S3\\/2–4I15\\/2 and 660nm band due to the 4F9\\/2–4I15\\/2 were observed.

Yuki Kishi; Setsuhisa Tanabe

2006-01-01

153

Synthesis of optically transparent ceramic of CaF2 doped with Mn and Ce for thermoluminescent dosimetry  

NASA Astrophysics Data System (ADS)

Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically transparent ceramics were obtained by vacuum hot-pressing at 1000°C under 20 MPa pressure for 2 h. The duration of pressure and dehydration of the initial powder was found important to achieve the transparency. 50% transparency was observed for a polished disc of 1 mm thickness. SEM micrographs revealed the absence of voids in hot pressed samples. These samples were found to be highly sensitive and linear for TLD and can measure doses from mGy to kGy.

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

2012-06-01

154

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

NASA Astrophysics Data System (ADS)

We have investigated morphological changes of freshly cleaved CaF 2(1 1 1) single crystal surfaces before and after ion irradiation. We show that with or without irradiation the surface undergoes serious changes within minutes after the cleavage if the samples are exposed to ambient conditions. This is most likely due to the adsorption of water and could be avoided only if working under clean ultra-high-vacuum conditions. Ion-induced modifications on this surface seem to act as centers for an increased rate of adsorption so that any quantitative numbers obtained by atomic force microscopy in such experiments have to be treated with caution.

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

2009-02-01

155

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

NASA Astrophysics Data System (ADS)

We have recently begun a program of high precision measurements of the key production and destruction reactions of important radiochemical diagnostic isotopes, including several isotopes of uranium, plutonium and americium. The detector for advanced neutron capture experiments (DANCE), a 4? BaF 2 array located at the Los Alamos Neutron Science Center, will be used to measure the neutron capture cross sections for most of the isotopes of interest. However, neutron capture measurements on many of the actinides are complicated by the presence of prompt ?-rays arising from low energy neutron-induced fission, which competes with neutron capture to varying degrees. Previous measurements of 235U using the DANCE array have shown that we can partially resolve capture from fission events based on total ?-ray calorimetry (i.e. total ?-ray energy versus ?-ray multiplicity). The addition of a dedicated fission-tagging detector to the DANCE array has greatly improved our ability to separate these two competing processes. In addition to higher quality neutron capture data, the addition of a fission-tagging detector offers a means to determine the capture-to-fission ratio ( ??/ ?f) in a single measurement, which should reduce the effect of systematic uncertainties. We are currently using a dual parallel-plate avalanche counter (PPAC) with the target material electro-deposited directly on the center cathode foil. This design provides a high efficiency for detecting fission fragments and allows loading of pre-assembled target/detector assemblies into the neutron beam line at DANCE. Results from tests of the fission-tag detector, as well as preliminary results from measurements on 235U and 252Cf that utilized the fission-tag detector will be presented.

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

2007-08-01

156

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

157

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

158

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

159

Femtosecond laser pulse excitation of electrons and excitons in CaF2 and SrF2  

NASA Astrophysics Data System (ADS)

Conduction band electrons, valence holes and subsequently self-trapped excitons (STEs) are created in CaF2 and SrF2 by two-photon absorption of 5.9 eV photons. Transient absorption after femtosecond pulse excitation is measured at probe wavelengths of 3.0 eV and 4.4 eV, respectively. Transient absorption of 3.0 eV photons yields a fast initial response in SrF2 due to absorption by conduction band electrons, while in CaF2 we sample the F centre part of the STE at 3.0 eV and determine its formation time constant to be 690 fs. Excitation at 3.0 eV also yields a reduction in STE luminescence sampled nanoseconds after STE creation that is attributed to a forced recombination of the nearest-neighbour defect pair. Probing with 4.4 eV photons yields much weaker absorption but confirms results for 3.0 eV photons. Additionally we observe stronger absorption due to the formation of long living defects.

Lindner, R.; Reichling, M.; Williams, R. T.; Matthias, E.

2001-03-01

160

Yb3+-doped CaF2 cubic fluoride crystal: spectroscopic properties, concentration quenching analysis, and laser optimization  

NASA Astrophysics Data System (ADS)

The ytterbium-doped crystals emitting around 1 ?m under laser-diode pumping between 900-980 nm have received an increasing interest in recent years as solid-state laser materials for high power or ultra-fast lasers. In this paper, our main objective is to contribute to Yb3+-doped fluorides mainly on CaF2 cubic host which are characterized by a high value of the thermal conductivity (9.5 W m-1 K-1) as high as YAG. Yb3+-doped CaF2, mono-doped and concentration gradient fibres were grown by both, the laser heated pedestal growth (LHPG) method and by the Czochralski method. Concerning Yb3+ excited state dynamics, the concentration dependence of the 2F5/2 decay time shows a competition between self-trapping and self-quenching processes. Main parameters useful for a theoretical approach of laser potentiality will be given and laser emission under InGaAs laser-diode pumping will be shown.

Boulon, G.; Ito, M.; Guyot, Y.; Goutaudier, C.; Brenier, A.; Jouini, A.; Sato, H.; Fukuda, T.

2007-08-01

161

Evaluation of granulated BGO, GSO:Ce, YAG:Ce, CaF 2:Eu and ZnS:Ag for alpha\\/beta pulse shape discrimination in a flow-cell radiation detector  

Microsoft Academic Search

Granulated BGO, GSO:Ce, YAG:Ce, and CaF2:Eu; CaF2:Eu coated with a fluorescent polymer, and combinations of coated and uncoated CaF2:Eu with ZnS:Ag were evaluated for their ability to discriminate between alpha and beta particles in a flow-cell radiation detector. The evaluations were based on the analysis of pulse shape spectra. Various granulated scintillators were packed into flow cell detectors that were

T. A DeVol; S. B Chotoo; R. A Fjeld

1999-01-01

162

X-ray crystal truncation rod scattering from MBE grown (CaF 2-SrF 2)/Si(111) superlattices  

NASA Astrophysics Data System (ADS)

Flouride CaF 2-SrF 2 superlattices (SLs) grown by molecular beam epitaxy have been studied by means of X-ray diffractometry for the first time. The diffraction patterns showed reasonably good crystalline quality of the SLs and a type-B epitaxial relation to the Si(111) substrate. From the analysis of the crystal truncation rod (CTR) profiles, based on the pseudomorphic model, it was obtained that despite the same high temperature (770°C) of formation of the CaF 2/Si(111) interface its structure depended on the growth temperature of the SLs. The shape of the CTR profiles confirmed the existence of the superlattice which consists of one or two monolayer thick SrF 2 layers. Some CaF 2/SrF 2-interface roughness was noticeable.

Harada, J.; Itoh, Y.; Shimura, T.; Takahashi, I.; Alvarez, J. C.; Sokolov, N. S.

1994-01-01

163

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.

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

2014-01-01

164

Site-selective laser spectroscopy of CaF2:Pr3+ and CaF2:Pr3+,R3+ (R3+=Y3+, Gd3+, Nd3+)  

NASA Astrophysics Data System (ADS)

Site-selective laser spectroscopy has been used to investigate the defect structure of a 0.1 mol % Pr3+:CaF2 crystal. Twenty-three distinct sites have been identified from the fluorescence spectra. Only three of the sites were found to be single-ion sites while the rest were assigned to be clusters of two or more ions. The single-ion sites are a C4v site, which dominates the spectrum at 0.1 mol %, a cubic site, and a site of low symmetry. Of the 20 cluster sites identified, two sites undergo intracluster energy transfer at a rate slow enough to be directly observed.

Tissue, Brian M.; Wright, John C.

1987-12-01

165

Judd-Ofelt Analysis of the Er3+ Ions in Double-Doped CaF2:(Er3+,Yb3+) Crystal  

Microsoft Academic Search

The double-doped CaF2:(0.14 mol% ErF3,1.31 mol% YbF3) and CaF2:0.12 mol% ErF3 crystals were grown in our crystal research laboratory using the vertical Bridgman method. The Judd-Ofelt intensity parameters Omega2, Omega4, and Omega6 for f-f transitions of Er3+ ions were determined from the optical absorption spectra using various groups of transitions. Using the J-O parameters the radiative transition probability, oscillator strength,

Gabriel Buse; Eleonora Preda; Marius Stef; Andreea Pruna; Florentina Stef; Irina Nicoara

2009-01-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

167

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

168

Some dielectric and optical properties of PbF2-codoped CaF2:YbF3 crystals  

NASA Astrophysics Data System (ADS)

YbF3-doped and PbF2-codoped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions. The Pb2+ ions modify the characteristic absorption peaks of the Yb2+ ions, but do not influence the Yb3+ ion peaks. The dielectric relaxation gives information about the impurity-defect aggregates. The obtained dielectric spectra show that for our low-YbF3-concentration samples, the main dipole complexes are NN type. The Pb2+ ions do not have an important influence on the dielectric spectra. The activation energy for the dipole reorientation and the relaxation time constant have been determined.

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

2009-07-01

169

Thermoluminescence characteristics of the novel CaF2:Dy nanoparticles prepared by using the hydrothermal method  

NASA Astrophysics Data System (ADS)

Dysprosium doped calcium fluoride (CaF2:Dy) nanoparticles were produced for the first time by using the hydrothermal method. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) patterns were utilized to characterize the synthesized material. The particle size of about 43 nm was evaluated from XRD data and supported by the SEM images. The Tm-Tstop and the computerized glow curve de-convolution (CGCD) methods were employed to determine the number of component glow peaks and kinetic parameters of the synthesized nanoparticles. Thermoluminescence glow curve of this phosphor exhibits six overlapping glow peaks. The optimized concentration of Dy impurity was found at 3 mol%. The prepared nanoparticles exhibit a roughly linear dose response to absorbed dose of 1000 Gy received from 60Co gamma source. This finding recommends this nanomaterial as a good candidate for high dose dosimetry. Other dosimetric features of this novel phosphor are also presented and discussed.

Zahedifar, M.; Sadeghi, E.; Harooni, S.

2012-11-01

170

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

NASA Astrophysics Data System (ADS)

Understanding scintillation physics and nonproportionality is essential to accelerate materials discovery that has been restricted due to the difficulties inherent to large crystal growth and complex nature of gamma-solid interaction. Taking advantage of less restrictive growth and deposition techniques for smaller crystal sizes or thin films and better fundamental understanding of ion-solid interactions, a unique ion approach is demonstrated to effectively screen candidate scintillators with relatively small size and evaluate their nonlinear scintillation response. Response of CaF2:Eu and YAlO3:Ce scintillators to single ions of H+, He+, and O3+ are measured by the corresponding pulse height over a continuous energy range using a time-of-flight-scintillator-photoelectric multiplier tube apparatus. Nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering the energy partitioning process. In a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) can be produced by energetic H+, He+ and O3+ ions, respectively, and significantly different impacts on the response characteristics of these two benchmark scintillators are observed. 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 the scintillators to irradiation.

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

2014-01-01

171

Spectroscopic properties and energy transfer analysis of Tm3+-doped BaF2-Ga2O3-GeO2-La2O3 glass.  

PubMed

This paper reports on the spectroscopic properties and energy transfer analysis of Tm(3+)-doped BaF(2)-Ga(2)O(3)-GeO(2)-La(2)O(3) glasses with different Tm(2)O(3) doping concentrations (0.2, 0.5, 2.0, 2.5, 3.0, 3.5, 3.5, 4.0 wt%). Mid-IR fluorescence intensities in the range of 1,300 nm-2,200 nm have been measured when excited under an 808 nm LD for all the samples with the same pump power. Energy level structure and Judd-Ofelt parameters have been calculated based on the absorption spectra of Tm(3+), cross-relaxation rates and multi-phonon relaxation rates have been estimated with different Tm(2)O(3) doping concentrations. The maximum fluorescence intensity at around 1.8 mum has been obtained in Tm(2)O(3)-3 wt% sample and the maximum value of calculated stimulated emission cross-section of Tm(3+) in this sample is about 0.48 x 10(-20) cm(2) at 1,793 nm, and there is not any crystallization peak in the DSC curve of this sample, which indicate the potential utility of Tm(3+)-doped BaF(2)-Ga(2)O(3)-GeO(2)- La(2)O(3) glass for 2.0-microm optical fiber laser. PMID:20204685

Yu, Shenglei; Yang, Zhongmin; Xu, Shanhui

2010-05-01

172

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+:3H4+Tm3+:3H6-->2Tm3+:3H4, 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

173

Photoemission study of CaF2- and SrF2-GaAs(110) interfaces formed at room temperature  

NASA Astrophysics Data System (ADS)

Interfaces formed by evaporating CaF2 or SrF2 on room-temperature GaAs(110) are studied with synchrotron-radiation photoemission spectroscopy. The fluoride films grow uniformly on the GaAs surface. The deposition of CaF2 and SrF2 induces a large initial band bending on p-type GaAs (~0.9 eV) and a small initial band bending on n-type GaAs (~0.25 eV). The valence band is dominated by the F 2p peak which shifts toward high binding energies by ~1.5 eV after the deposition of >=16 Å fluoride. This shift reflects an increase in the valence-band offset between the two materials as the film forms. The final band offsets are estimated at 7.7 and 8.0 eV for CaF2 and SrF2, respectively, and are in qualitative agreement with those expected from the fluoride-Si data. Core-level measurements indicate that no reaction or decomposition of the MF2 molecule takes place at the interface. The F 2s core-level line shape and the increase in the binding-energy separation of F 2s and Ca 3p with increasing coverage suggest the presence of an interface F component. Contrary to the CaF2/Si case, no measurable Ca-substrate bonding effect is observed. The dissociative effect of uv irradiation on the CaF2 film is also investigated.

Mao, D.; Young, K.; Kahn, A.; Zanoni, R.; McKinley, J.; Margaritondo, G.

1989-06-01

174

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

NASA Astrophysics Data System (ADS)

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

Shinozaki, Kenji; Honma, Tsuyoshi; Komatsu, Takayuki

2014-06-01

175

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.

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

176

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

177

CaF 2:Tm (TLD-300) thermoluminescent response and glow curve induced by ?-rays and ions  

NASA Astrophysics Data System (ADS)

The thermoluminescent response of CaF 2:Tm after exposure to 60Co ?-rays at doses from 0.44 Gy to 8.75 kGy and to low fluences (10 5 ˜ 10 8 cm -2) of 25 and 40 MeV 1H, 75 and 120 MeV 3He, 180, 300 and 480 MeV 12C, 400 MeV 16O and 800 MeV 20Ne ion beams, spanning a LET interval up to about 500 keV/?m, has been investigated. A careful deconvolution analysis of the glow curve has been performed in order to obtain information for individual peaks. The region of linear response to gammas extends up to ?1 Gy, while that for ions includes the complete dose interval covered in the study (up to ?1.3 Gy). The ratio between the high- and low-temperature structures in the glow curve is correlated with radiation quality and dependence on ion identity, besides LET, is strongly suggested by the data. The thermoluminescent efficiency to ion exposure, with respect to irradiation with 60Co ?-rays, shows a different dependence on LET for each of the peaks. In general terms, the efficiency reaches a maximum between 1.2 and 1.4 near 6 keV/?m and decreases for higher LET. Peak 3 displays a unique trend, its relative efficiency is always less than 1.0 and shows a strong monotonic inverse dependence with LET.

Massillon-JL, G.; Gamboa-deBuen, I.; Buenfil, A. E.; Monroy-Rodríguez, M. A.; Brandan, M. E.

2008-03-01

178

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

PubMed

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

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

179

Judd-Ofelt Analysis of the Er3+ Ions in Double-Doped CaF2:(Er3+,Yb3+) Crystal  

NASA Astrophysics Data System (ADS)

The double-doped CaF2:(0.14 mol% ErF3,1.31 mol% YbF3) and CaF2:0.12 mol% ErF3 crystals were grown in our crystal research laboratory using the vertical Bridgman method. The Judd-Ofelt intensity parameters ?2, ?4, and ?6 for f-f transitions of Er3+ ions were determined from the optical absorption spectra using various groups of transitions. Using the J-O parameters the radiative transition probability, oscillator strength, branching ratio and radiative lifetime of Er3+ transitions have been calculated. The radiative transition probability and radiative lifetimes are compared to those of Er3+ transitions in other hosts.

Buse, Gabriel; Preda, Eleonora; Stef, Marius; Pruna, Andreea; Stef, Florentina; Nicoara, Irina

2009-05-01

180

Influence of Pb2+ ions on the morphology of etch pits and dislocation density of CaF2:YbF3 crystals  

NASA Astrophysics Data System (ADS)

Various concentrations YbF3 -doped CaF2 and Pb2+ - codoped crystals were grown using the conventional Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum (~ 10-1 Pa) using a shaped graphite furnace. The crystals have been cooled to room temperature using an established procedure. In order to study the etch pits morphology and the dislocations density we used the chemical etching method. This method consists in immersing the cleaved sample in 4NHCl at 60°C for 5 minutes. Small pits are developed at the emergence points of the dislocations. The etch pits have hexagonal shapes for pure CaF2 crystal and triangular sahpes for doped crystals. The dislocations density depends also on the dopant or on the codopant concentration.

Stef, Marius; Stef, Florica; Buse, Gabriel; Nicoara, Irina

2012-08-01

181

Study of Na+ ions influence on the charge compensating defects in CaF2: YbF3 crystals using dielectric relaxation  

NASA Astrophysics Data System (ADS)

YbF3-doped and NaF co-doped calcium fluoride crystals were grown using the Vertical Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum (?10-1 Pa) using a shaped graphite furnace. Room temperature absorption spectra and dielectric spectra were measured to study the effect of Na+ ions on the varieties of Yb3+ sites in CaF2 host. The experimental results show that by co-doping with Na+ ions in different Na:Yb ratios we can modulate the type of charge compensating defects of Yb3+ ions in CaF2 lattice. Dielectric relaxation in double doped (Yb, Na):CaF2 crystals-related with the study the charge compensating defects-was not reported before.

Nicoara, I.; Stef, M.

2012-06-01

182

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

183

Ca-induced structural transformation of the single-domain Si(001) surface: CaF2/Si(001)-4° off  

NASA Astrophysics Data System (ADS)

By scanning tunneling microscopy and synchrotron photoemission spectroscopy, it has been found that through CaF2 exposure to the single-domain Si(001)-4° off surface held at 750 °C, Si dimers on Si(001) terraces are replaced preferentially by dissociated Ca atoms while F atoms are desorbed. The resulting 2 × 3 reconstruction saturates the (001) terraces at a coverage between 0.1 and 0.3 monolayers. Additional CaF2 exposure triggers a structural transformation to a stable hill-and-valley structure composed of wider (001)-2 × 3 terraces and compensating facets comprised of (11 17) and (11 13) units, both with a 6 × 1 surface reconstruction. This study demonstrates that the periodic width of the single domain Si(001) surface can be modulated through adsorbing Ca atoms while maintaining one-dimensional symmetry along the DB steps and the semiconducting nature of the surface.

Kim, Hidong; Dugerjav, Otgonbayar; Arvisbaatar, Amarmunkh; Motlak, Moaaed; Seo, Jae M.

2014-05-01

184

Dependence of luminescence processes and transmission in vacuum-ultraviolet region on surface condition in CaF 2 single crystals  

Microsoft Academic Search

We investigated the effect of the surface condition on luminescence processes in a surface layer of single CaF2 crystals under the excitation by vacuum-ultraviolet (VUV) light (h??13.5 eV). It has been shown that the intensity of the excitonic emission at 4.4 eV in polished crystals essentially decreases with respect to that in freshly cleaved crystals. The decrease at the interband

V. Denks; T Savikhina; V Nagirnyi

2000-01-01

185

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

Microsoft Academic Search

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

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

2005-01-01

186

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.

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

2013-01-01

187

Electron-surface interaction and metallization of the CaF2 (111)-surface studied by photothermal techniques  

NASA Astrophysics Data System (ADS)

The interaction of low energy electrons with the surface of alkaline-earth halides results in a variety of microscopical physical phenomena commonly described in terms of defect formation and diffusion, surface metallization and desorption of neutral- and charged particles. These processes are accompanied by local changes in the electronic and geometrical structure of bulk and surface and result in a variation of macroscopically measurable parameters like modulated optical reflectance and a deformation of the crystal lattice. In this paper it will be shown that photothermal analysis, that so far has mostly been used for the determination of optical and thermophysical properties of materials, is also capable of measuring defect related nonthermal phenomena apparent during electron irradiation of insulator surfaces. Experiments were performed with an intensity modulated electron beam of typically 1 ?A at 1 keV focused into a spot of 1 mm2 on the (111)-surface of a polished CaF2 single crystal under ultra-high vacuum conditions. Measurements revealed that modulated reflectance is sensitive to changes in optical properties induced by electron irradiation induced defects at low electron dosages. At a dosage level where metallization starts, a dramatic change in the modulated reflectance signal was observed indicating changes in electronic structure due to metal clustering at the surface. The photothermal displacement technique has been utilized to monitor surface deformations induced by electron bombardment. It was found that results cannot be explained by a thermo-elastic expansion model that works well for metal surfaces. Therefore, this technique can be used for the measurement of nonthermal contributions to lattice expansion resulting from volume changes of created defects.

Reichling, Michael

1994-03-01

188

Evaluation of granulated BGO, GSO:Ce, YAG:Ce, CaF 2:Eu and ZnS:Ag for alpha/beta pulse shape discrimination in a flow-cell radiation detector  

NASA Astrophysics Data System (ADS)

Granulated BGO, GSO:Ce, YAG:Ce, and CaF 2:Eu; CaF 2:Eu coated with a fluorescent polymer, and combinations of coated and uncoated CaF 2:Eu with ZnS:Ag were evaluated for their ability to discriminate between alpha and beta particles in a flow-cell radiation detector. The evaluations were based on the analysis of pulse shape spectra. Various granulated scintillators were packed into flow cell detectors that were coils of 3.0 mm OD×1.5 mm ID fluorinated ethylene propylene Teflon ® tubing positioned between dual photomultiplier tubes for analysis. The best pulse shape discrimination was obtained for a combination of equal masses of uncoated CaF 2:Eu (63-90 ?m) and ZnS:Ag (10 ?m), which had a 9% spillover. Additional research is needed to reduce the spillover.

DeVol, T. A.; Chotoo, S. B.; Fjeld, R. A.

1999-04-01

189

White up-conversion emission in Ho 3+/Tm 3+/Yb 3+ tri-doped glass ceramics embedding BaF 2 nanocrystals  

NASA Astrophysics Data System (ADS)

Ho 3+/Tm 3+/Yb 3+ tri-doped glass ceramics with white light emitting have been developed and demonstrated. Pumped by 980 nm laser diode (LD), intensive red, green and blue up-conversions (UC) were obtained. The green emission is assigned to Ho 3+ ion and the blue emission is assigned to Tm 3+ ion, whereas the red emission is the combination contribution of the Ho 3+ and Tm 3+ ions. The RGB intensities could be adjusted by tuning the rare-earth ion concentration and pump power intensity. Thus, multicolor of the luminescence, including perfect white light with CIE- X=0.329 and CIE- Y=0.342 in the 1931 CIE chromaticity diagram can be obtained in 0.15 Ho 3+/0.2Tm 3+/3Yb 3+ tri-doped glass ceramics embedding BaF 2 nanocrystals pumped by a single infrared laser diode source of 980 nm at 500 mW. The up-conversion luminescence mechanism of Yb 3+ sensitize Ho 3+ and Tm 3+ ions and the energy transfer from Ho 3+ to Tm 3+ in oxy-fluoride silicate glass ceramics were analyzed.

Li, Chenxia; Xu, Shiqing; Ye, Rengguang; Deng, Degang; Hua, Youjie; Zhao, Shilong; Zhuang, Songlin

2011-04-01

190

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?X??XF2 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

191

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

Microsoft Academic Search

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

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

2005-01-01

192

Local order of Ca in a CaF2-Al2O3-SiO2 glass by electron energy-loss spectroscopy  

NASA Astrophysics Data System (ADS)

Local order of Ca in a CaF2-Al2O3-SiO2 glass is studied using electron energy loss spectroscopy technique. The energy shift of ionization threshold in the Ca L2,3 and the differences in the near-edge structure of the Ca M2,3 edge between the glasses with and without F suggest the local ordering of F around Ca in the F-containing aluminosilicate glass. The local order phenomenon requires the clustering of Ca-F. Therefore, the transparent fluorinated calcium aluminosilicate glass is not structurally and compositionally homogeneous at nanometer scale.

Jiang, Nan

2011-07-01

193

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

Microsoft Academic Search

DANCE (Detector for Advanced Neutron Capture Experiments) is a 4pi array of BaF2 crystals installed at LANSCE, Lujan Center. Neutron capture measurements on ^157Gd and ^89Y nuclei were conducted using this facility. The absolute cross sections of the ^89Y(n,gamma) reaction was measured for the first time ever in the neutron energy range of 10 eV -- 10 keV and improvements

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

2009-01-01

194

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

195

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

NASA Astrophysics Data System (ADS)

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

Robelin, Christian; Chartrand, Patrice

2007-12-01

196

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

NASA Technical Reports Server (NTRS)

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

Whittenberger, J. Daniel

1990-01-01

197

Phosphate capacity of CaO-AI2O3 slags containing CaF2, BaO, Li2O, or Na2O  

NASA Astrophysics Data System (ADS)

Phosphorus partition ratios between CaO-Al2O3 and CaO-Al2O3-CaF2 fluxes and Fe-Csat-P alloys have been measured as a function of slag composition at 1500 °C. The effects of additions of BaO, Li2O, and Na2O to the CaO-Al2O3-CaF2 system on the phosphorus partition ratios at 1400 °C and 1300 °C have been measured. From the partition ratio, and assuming that the oxygen potential is controlled by C-CO equilibrium, the phosphate capacities of the fluxes were calculated. Also, the activities of Li2O and Na2O were measured as a function of slag composition at 1300 °C by equilibrating the flux and the metal with Pb-Li or Pb-Na alloy and CO in a graphite crucible. The results indicate that phosphorus partition ratios with carbon-saturated iron and the phosphate capacities for additions of more basic oxides decrease in the following order: Na2O?;Li2O?;BaO. The activities of Li2O and Na2O in calcium aluminate fluxes have large negative deviations from ideal behavior; the activity coefficients at infinite dilution are on the order of 0.05 and 10-5, respectively.

Nassaralla, C.; Fruehan, R. J.

1992-03-01

198

Optical properties and electronic structure of CaF2 with the screened-exchange (sX)-LDA-FLAPW approach  

NASA Astrophysics Data System (ADS)

Optical measurements have provided an extremely difficult challenge to existing electronic band structure calculations. Although CaF_2, an important large gap insulator, has been intensively investigated, no parameter-free first-principles calculations have been done due to the well-known failure of LDA in treating excited states. Here, we present results of fully first-principles calculations of the electronic structure and optical properties of CaF2 with the self-consistent screened-exchange LDA (sX-LDA) method(Asahi, Mannstadt and Freeman, PRB 59), 7486 (1999). implemented in the FLAPW approach.(Wimmer, Krakauer, Weinert, Freeman, PRB 24), 864 (1981). The calculated optical energy gap, 11.3 eV, is in very good agreement with experiment (11.8 eV)(Tsujibayashi, Toyoda, Sakuragi, Kamada, Itoh, APL 80), 2883 (2002) and so greatly improves the LDA result (7.3 eV). The optical properties, including the real and imaginary parts of the dielectric function determined ab initio with full matrix elements and no parameters, are in good agreement with experiment. A comparison with the results from LDA calculations (with and without a scissors operator to correct the band gap) is also presented.

Mannstadt, W.; Zhao, Yu-Jun; Kim, Miyoung; Freeman, A. J.

2003-03-01

199

Nanotechnology studies of layered fluoride superionic conductors  

Microsoft Academic Search

A computer simulation by a molecular dynamics method at constant volume has been performed on a model material that is composed\\u000a of accumulating two different fluoride conductors: ?BaF2–CaF2–BaF2–CaF2?. The average value of CaF2 and BaF2 for the lattice constant of the new layered material is prepared to hold its mechanical strength. The CaF2 region is compressed and the BaF2 region

K. Nomura; M. Kobayashi

2008-01-01

200

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

201

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

202

Generation of sub-20-fs deep-ultraviolet pulses by using chirped-pulse four-wave mixing in CaF2 plate.  

PubMed

Sub-20-fs deep ultraviolet (DUV) pulses are generated by using nondegenerate, chirped-pulse four-wave mixing of the fundamental and second-harmonic pulses from a commercial Ti:sapphire amplifier in a CaF(2) plate. The energy of the DUV pulses is 3.8 ?J, with a conversion efficiency from total pump energy to DUV of ~3.8%. The DUV pulse is compressed using a pre-chirp, introduced via a fused silica window in the fundamental beam. The central wavelength of the DUV spectrum can be tuned from 257 to 277 nm by adjusting the cross angle between the two pump beams. The spectrum can reach a width of 16.8 nm, which can support a pulse duration of 8.7 fs. PMID:24104615

He, Jinping; Kobayashi, Takayoshi

2013-08-15

203

Advances in growth of fiber crystal by the LHPG technique. Application to the optimization of Yb 3+-doped CaF 2 laser crystals  

NASA Astrophysics Data System (ADS)

The laser heated pedestal growth (LHPG) technique is suitable to grow crystalline fibers and has been successfully applied for the general study of a lot of optical materials as laser crystals. Our general approach on the research of diode-pumped Yb 3+-doped host crystals is presented through typical example of CaF 2 fluoride, which is considered among the important laser crystals either for basic or applied reasons. Spectroscopic characterizations were carried out. Especially, Yb 3+ ( 2F 5/2) excited level experimental decay time dependence on Yb 3+ ion concentration is analyzed by using our own approach on the synthesis of a concentration gradient fiber grown in the laboratory. Our main objective is to contribute to have a better understanding of concentration quenching mechanisms not only in laser crystals but more generally in luminescent materials.

Boulon, G.; Ito, M.; Goutaudier, C.; Guyot, Y.

2006-07-01

204

Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2 crystal: Evidence for two thresholds of damage creation  

NASA Astrophysics Data System (ADS)

CaF2 crystals as representatives of the class of ionic nonamorphizable insulators were irradiated with many different swift heavy ions of energy above 0.5 MeV/u providing a broad range of electronic energy losses (Se). Beam-induced modifications were characterized by Channeling Rutherford Backscattering Spectrometry (C-RBS) and x-ray diffraction (XRD), complemented by transmission electron microscopy (TEM). Results from C-RBS give evidence of significant damage appearing above a Se threshold of 5 ± 2 keV/nm. A second critical Se appears around 18 ± 3 keV/nm; below this value the damage as function of ion fluence saturates at 20%, while above this the damage saturation level increases with Se, reaching ˜60% for ions of Se = 30 keV/nm. XRD measurements also show effects indicating two threshold values. Above 5 keV/nm, the widths of the XRD reflection peaks increase due to the formation of nanograins, as seen by TEM, while a significant decrease of the peak areas only occurs above 18 keV/nm. The track radii deduced from C-RBS measurements are in agreement with those extracted from the fluence evolution of the widths of the XRD peaks. Moreover, track radii deduced from the peak area analysis are slightly smaller but in agreement with previous track observations by high resolution electron microscopy. Calculations based on the inelastic thermal spike model suggest that the lower threshold at 5 keV/nm is linked to the quenching of the molten phase, whereas the threshold at 18 keV/nm can be interpreted as quenching of the boiling phase. The results of CaF2 are compared with other nonamorphizable materials such as LiF and UO2.

Toulemonde, M.; Benyagoub, A.; Trautmann, C.; Khalfaoui, N.; Boccanfuso, M.; Dufour, C.; Gourbilleau, F.; Grob, J. J.; Stoquert, J. P.; Costantini, J. M.; Haas, F.; Jacquet, E.; Voss, K.-O.; Meftah, A.

2012-02-01

205

Long-range coulomb interaction of electrons of 4 f orbitals in impurity centers Yb3+: KZnF3, CsCaF3, and Sm3+: CaF2  

NASA Astrophysics Data System (ADS)

Expressions for calculating the matrix elements of the Coulomb interaction of f electrons of the isolated ion with an infinite crystal lattice have been obtained. The contribution of this interaction to the parameters of the crystal field in impurity centers Yb3+: KZnF3, CsCaF3, and Sm3+: CaF2 has been calculated.

Anikeenok, O. A.

2013-11-01

206

Abnormal size-dependent upconversion emissions and multi-color tuning in Er3+-doped CaF2-YbF3 disordered solid-solution nanocrystals  

NASA Astrophysics Data System (ADS)

A series of Er3+-doped (1 - x)CaF2-xYbF3 (0 ? x ? 0.6) disordered solid-solution nanocrystals with various mean sizes were successfully prepared by a facile solvothermal route. Interestingly, abnormal size-dependent upconversion emissions were demonstrated in these nanocrystals for the first time. With increasing grain size, an obvious enhancement of red to green emission ratio was observed in the Er3+ (2 mol%): 0.4CaF2-0.6YbF3 nanocrystals, which is the opposite of the routine size-dependent upconversion emission behavior reported previously. Taking Eu3+ ions as a structural probe, we investigated the influence of a disordered solid-solution structure on Ln3+ luminescence, and proposed that Ln3+ clusters formed in the host should play a key role to induce this unusual size-dependent upconversion emission phenomenon. As a consequence, multi-colors such as green, yellow, and red upconversion emissions can be easily realized by appropriately modifying the Yb3+ content in the Er3+-doped (1 - x)CaF2-xYbF3 nanocrystals. The reported results will deepen the understanding of size effects on the lanthanide upconversion in nanocrystals.

Chen, Daqin; Lei, Lei; Xu, Ju; Yang, Anping; Wang, Yuansheng

2013-03-01

207

Abnormal size-dependent upconversion emissions and multi-color tuning in Er3+-doped CaF2-YbF3 disordered solid-solution nanocrystals.  

PubMed

A series of Er(3+)-doped (1 - x)CaF(2)-xYbF(3) (0 ? x ? 0.6) disordered solid-solution nanocrystals with various mean sizes were successfully prepared by a facile solvothermal route. Interestingly, abnormal size-dependent upconversion emissions were demonstrated in these nanocrystals for the first time. With increasing grain size, an obvious enhancement of red to green emission ratio was observed in the Er(3+) (2 mol%): 0.4CaF(2)-0.6YbF(3) nanocrystals, which is the opposite of the routine size-dependent upconversion emission behavior reported previously. Taking Eu(3+) ions as a structural probe, we investigated the influence of a disordered solid-solution structure on Ln(3+) luminescence, and proposed that Ln(3+) clusters formed in the host should play a key role to induce this unusual size-dependent upconversion emission phenomenon. As a consequence, multi-colors such as green, yellow, and red upconversion emissions can be easily realized by appropriately modifying the Yb(3+) content in the Er(3+)-doped (1 - x)CaF(2)-xYbF(3) nanocrystals. The reported results will deepen the understanding of size effects on the lanthanide upconversion in nanocrystals. PMID:23386131

Chen, Daqin; Lei, Lei; Xu, Ju; Yang, Anping; Wang, Yuansheng

2013-03-01

208

Investigation of the structure and luminescence properties of CdF2-CaF2 : Eu superlattices on Si(111)  

NASA Astrophysics Data System (ADS)

A complex investigation of CdF2-CaF2 : Eu superlattices with different bilayer thicknesses (2.0-17.5 nm) grown by molecular beam epitaxy on Si(111) has been carried out. The structural perfection of the layers and interfaces of the superlattices have been estimated from the X-ray diffractometry and reflectometry data. The possibility of producing short-period pseudomorphic superlattices with a period of approximately 2 nm has been established. It has been shown that these superlattices are characterized by a larger root-mean-square roughness amplitude of the interfaces as compared to the long-period superlattices. The specific features of cathodoluminescence spectra have been analyzed as a function of the superlattice period. It has been revealed that, with a decrease in the superlattice period, the intrinsic luminescence intensity of fluorides increases in comparison with the intensity of the luminescence associated with the emission of Eu2+ impurity ions; in this case, several Eu3+ luminescence bands appear in the spectrum. The possibilities of electron probe microanalysis for determining the ratio of thicknesses of individual layers in short-period superlattices have been demonstrated.

Valkovskiy, G. A.; Durnev, M. V.; Zamoryanskaya, M. V.; Konnikov, S. G.; Krupin, A. V.; Moroz, A. V.; Sokolov, N. S.; Trofimov, A. N.; Yagovkina, M. A.

2013-07-01

209

Research on the optical spectra, g factors and defect structures for two tetragonal Y2+ centers in the irradiated CaF2: Y crystal  

NASA Astrophysics Data System (ADS)

Based on the defect models that the tetragonal Y2+ (1) center in the irradiated CaF2: Y crystal is due to Y2+ at Ca2+ site associated with a nearest interstitial F- ion along C4 axis and the tetragonal Y2+ (2) center is Y2+ at Ca2+ site where the tetragonal distortion is caused by the static Jahn-Teller effect, the two optical spectral bands and anisotropic g factors for both tetragonal Y2+ centers are calculated. The calculations are made by using two methods based on the cluster approach, one is the complete diagonalization (of energy matrix) method (CDM) and another is the perturbation theory method (PTM). The calculated results for each Y2+ center from CDM and PTM coincide and show reasonable agreement with the experimental values. The calculated isotropic g factor for Y2+ (2) center at higher temperature owing to the dynamical Jahn-Teller effect is also consistent with the observed value. The defect structures (i.e., tetragonal distortion) of the two Y2+ centers are obtained from the calculation. It appears that both theoretical methods can be applied to explain the optical and EPR data, to study the defect model and to determine the defect structures for d1 ions in crystals.

Zheng, Wen-Chen; Mei, Yang; Yang, Yu-Guang; Liu, Hong-Gang

2012-11-01

210

Investigation of the influence of CaS, CaO and CaF 2 fillers on the transfer and wear of nylon by microscopy and XPS analysis  

Microsoft Academic Search

The effect of CaS, CaO and CaF2 fillers on the transfer, friction and wear behaviors of nylon was studied. Sliding was performed in ambient atmosphere at a speed of 1.0 m s?1 and a load of 19.6 N, and a pin-on-disk configuration was used. The filler content in nylon was fixed at 35% by volume. The counterface disk was made

S. Bahadur; Deli Gong; James Anderegg

1996-01-01

211

Relativistic cluster calculation of ligand-field multiplet effects on cation L2,3 x-ray-absorption edges of SrTiO3, NiO, and CaF2  

Microsoft Academic Search

A totally nonempirical relativistic cluster calculation of transition-metal L2,3-edge x-ray-absorption near-edge structure including configuration interaction has been performed. A remarkable predictive power of this calculation has been demonstrated for three contrasting materials with different d-electron numbers and different coordination numbers (SrTiO3, NiO, and CaF2) by excellent reproduction of both the absolute peak energies and their relative intensities without any empirical

Kazuyoshi Ogasawara; Takahiro Iwata; Yukinori Koyama; Takugo Ishii; Isao Tanaka; Hirohiko Adachi

2001-01-01

212

Influence of Li+ and Na+ Ions on the Dielectric Spectra of YbF3 Doped and LiF, NaF Codoped CaF2 Crystals  

Microsoft Academic Search

Various concentrations YbF3 -doped CaF2 and Li- (Na)- codoped crystals were grown using the conventional Bridgman method. The effect of Na+ and Li+ ions on the dielectric spectra was studied. The activation energy and the reciprocal frequency factor have been calculated in order to characterize the observed relaxations. An anomaly of ?1 behavior (not reported before) has been observed which

Andreea Pruna; Marius Stef; Gabriel Buse; Irina Nicoara

2009-01-01

213

Influence of Li+ and Na+ Ions on the Dielectric Spectra of YbF3 Doped and LiF, NaF Codoped CaF2 Crystals  

NASA Astrophysics Data System (ADS)

Various concentrations YbF3 -doped CaF2 and Li- (Na)- codoped crystals were grown using the conventional Bridgman method. The effect of Na+ and Li+ ions on the dielectric spectra was studied. The activation energy and the reciprocal frequency factor have been calculated in order to characterize the observed relaxations. An anomaly of ?1 behavior (not reported before) has been observed which is assigned with a phase transition of the order-disorder type.

Pruna, Andreea; Stef, Marius; Buse, Gabriel; Nicoara, Irina

2009-05-01

214

SPECIAL ISSUE DEVOTED TO THE 25th ANNIVERSARY OF THE A.M. PROKHOROV GENERAL PHYSICS INSTITUTE: Efficient lasing in diode-pumped Yb3+:CaF2SrF2 solid-solution single crystals  

Microsoft Academic Search

Single crystals of solid solutions of a high optical quality are grown in the concentration vicinity of the saddle point of the ternary CaF2-SrF2-YbF3 system. Efficient lasing with a small Stokes shift (at 1025 nm) was obtained in 980-nm diode-pumped single crystals. The total lasing efficiency (with respect to the absorbed average pump power) was 59% and the slope efficiency

T. T. Basiev; S. V. Vasil'ev; M. E. Doroshenko; V. A. Konyushkin; S. V. Kuznetsov; V. V. Osiko; P. P. Fedorov

2007-01-01

215

Clustering and defect structure of CaF2 crystals doped with YbF3 and ErF3 as determined by 19F nuclear magnetic resonance  

Microsoft Academic Search

19F NMR studies of single crystals of CaF2 doped with 2, 1, and 0.5 mole percent of both ErF3 and YbF3 have been carried out at room temperature. In ErF3-doped crystals, 19F resonances have been identified for lattice fluorides having both one and two Er3+ ions in nearest-neighbor cation sites and for an interstitial fluoride with two Er3+ ions in

R. J. Booth; M. R. Mustafa; B. R. McGarvey

1978-01-01

216

Thresholds measured with 350-nm pulses at 25 to 100 Hz for bare polished crystals of CaF2 and for silica sol-gel AR coatings on silica substrates  

Microsoft Academic Search

An XeF laser-damage experiment was used to measure damage thresholds for bare polished crystals of CaF2 and porous silica antireflection coatings on fused silica substrates. Damage was induced by applying 1000 350-nm, 25-ns pulses at repetition rates of 25 to 100 Hz to small (typically 0.12 x .03 cm) sites on the surfaces of the sample. Eight samples of fluorescence-free

M. C. Staggs; D. Milam; I. M. Thomas; J. G. Wilder

1986-01-01

217

Structural and thermal characterization of CaO-MgO-SiO2-P2O5-CaF2 glasses  

SciTech Connect

The paper presents the influence of varying CaO/MgO ratio on the structure and thermal properties of CaO-MgO-SiO2-P2O5-CaF2 glasses. A series of eight glass compositions in the glass forming region of diopside (CaMgSi2O6) - fluorapatite [Ca5(PO4)3F] - wollastonite (CaSiO3) ternary system have been designed and synthesized by varying diopside/wollastonite ratio in glasses. The as prepared melt-quenched glasses have been characterized for their structure by infrared spectroscopy (FTIR) and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy. Silicon is predominantly present as Q2 (Si) species, while phosphorus tends to coordinate in orthophosphate environment in all the investigated glasses. The change in CaO/MgO ratio had an insignificant affect on the structure of glasses. The thermal sintering and crystallization parameters for the studied glasses have been obtained from differential thermal analysis (DTA) while crystalline phase fractions in the sintered glass-ceramics have been analyzed by X-ray diffraction adjoined with Rietveld refinement. Diopside, fluorapatite, wollastonite and pseudowollastonite have crystallized as the main crystalline phases in all the glass-ceramics with their content varying with respect to variation in CaO/MgO ratio in glasses. Scanning electron microscopy (SEM) has been used to shed light on the microstructure of glass-ceramics. The possible implications of structure and sintering behaviour of glasses on their bioactivity have been discussed.

Kansal, Ishu; Goel, Ashutosh; Tulyaganov, Dilshat U.; Rajagopal, Raghu R.; Ferreira, Jose M.

2012-08-01

218

Temperature and pressure dependence of spectral positions and widths of 5D0 ? 7FJ emission lines from Eu3+ ions in the CaF2 crystal  

NASA Astrophysics Data System (ADS)

The effect of temperature (T) and pressure (P) was studied on the emission zero-phonon lines (ZPLs) corresponding to 5D0 ? 7F0,1,2 electronic transitions in Eu3+ centres of trigonal symmetry in the CaF2 crystal. In the T-range 112-493 K at ambient P, all the lines shift to the blue and broaden. Both effects are explained by the dephasing of electronic transitions due to the Raman scattering of acoustic phonons by impurity ions. The T-shift of the lines is caused not only by the change of the electron-phonon interaction (EPI) in impurity centres, but also by the thermal expansion of the host crystal. In the P-range 0.001-7.3 kbar at room temperature, the width of all lines somewhat decreases, most lines shift to the red, the splitting of 7F1,2 multiplet levels in the crystal field increases, and the energy distance between the 5D0 level and the barycentre of the crystal-field sublevels of 7F0, 7F1 and 7F2 levels decreases. The P-narrowing of the ZPLs can be explained by the P-induced decrease of the EPI coefficient in the framework of the Raman mechanism and also by the decrease in the density of states for acoustic phonons due to the P-induced increase in the Debye T of the crystal. The P-shift of the ZPLs is supposedly caused mainly by changes in the direct interaction of external pressure with impurity centres and not by the P-induced contraction of the host crystal.

Kuznetsov, Anatoli; Laisaar, Arlentin; Kikas, Jaak

2013-11-01

219

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

220

Growth of Doped and Undoped Single Crystal Laser Materials in the System (MF2)x.(YF3)(1-x).  

National Technical Information Service (NTIS)

Laser host materials were grown in the CaF2-YF3 and BaF2-YF3 binaries. Two compositions in the former binary were found to be capable of producing single crystals: 9CaF2.YF3 and CaF2.2.6YF3. The former possessed a fluorite structure and the latter was ind...

J. F. Balascio

1975-01-01

221

Experimental evidence for orientation property of Pb(Zr0.35Ti0.65)O3 by manipulating polar axis angle using CaF2 substrate  

Microsoft Academic Search

Perfectly oriented (001), (101), and (111) Pb(Zr0.35Ti0.65)O3 (PZT) films were grown on identical (111)CaF2 substrates by metal-organic chemical vapor deposition. These films exclude domains parallel to the surface; therefore, all domains are actively switchable under the electric field between top and bottom electrodes. Saturation polarization values, Psat(001), Psat(101), and Psat(111), for these PZT films were 75, 50, and 43 muC\\/cm2,

Satoru Utsugi; Takashi Fujisawa; Yoshitaka Ehara; Tomoaki Yamada; Masaaki Matsushima; Hitoshi Morioka; Hiroshi Funakubo

2010-01-01

222

Experimental evidence for orientation property of Pb(Zr0.35Ti0.65)O3 by manipulating polar axis angle using CaF2 substrate  

NASA Astrophysics Data System (ADS)

Perfectly oriented (001), (101), and (111) Pb(Zr0.35Ti0.65)O3 (PZT) films were grown on identical (111)CaF2 substrates by metal-organic chemical vapor deposition. These films exclude domains parallel to the surface; therefore, all domains are actively switchable under the electric field between top and bottom electrodes. Saturation polarization values, Psat(001), Psat(101), and Psat(111), for these PZT films were 75, 50, and 43 ?C/cm2, respectively. This orientation dependency was in a good agreement with the theoretical relationship for a tetragonal PZT single crystal, where Psat(001)=Psat(101)/2=Psat(111)/3.

Utsugi, Satoru; Fujisawa, Takashi; Ehara, Yoshitaka; Yamada, Tomoaki; Matsushima, Masaaki; Morioka, Hitoshi; Funakubo, Hiroshi

2010-03-01

223

Determination of gibbs energies of formation of CaFe 2 O 4 and Ca 2 Fe 2 O 5 from solid-state EMF measurements using CaF 2 as solid electrolyte  

Microsoft Academic Search

The standard Gibbs energy change for the reactions CaO + Fe2O3 ? CaFe2O4 and 2 CaO + Fe2O3 ? Ca2Fe2O5 has been determined from solid-state electromotive force (emf) measurements, using CaF2 as solid electrolyte. The temperature dependence of the standard Gibbs energies of formation from the elements is represented\\u000a by the equations \\u000a \\u000a \\u000a \\u000a \\u000a $$\\\\begin{gathered} \\\\Delta _f G^0 (CaFe_2 O_4 ) =

Stefan Forsberg; Patrik Wikström; Erik Rosén

2002-01-01

224

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

225

The Fluorescent Response of NaI(Tl), CsI(Tl), CsI(Na) and CaF2(Eu) to X-Rays and Low Energy Gamma Rays  

Microsoft Academic Search

The fluorescent response functions of NaI(Tl), CsI(Tl), CsI(Na) and CaF2(Eu) have been determined with thin crystals over the energy range from 3.3 keV to 840 keV. A pronounced nonlinear dependence on photon energy has been observed in this region for all four types of crystals investigated. Qualitatively the response functions for NaI(Tl), CsI(Tl) and CsI(Na) are similar down to a

D. W. Aitken; B. L. Beron; G. Yenicay; H. R. Zulliger

1967-01-01

226

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

227

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

PubMed Central

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

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

2012-01-01

228

Synthesis, bioactivity and preliminary biocompatibility studies of glasses in the system CaO-MgO-SiO2-Na2O-P2O5-CaF2.  

PubMed

New compositions of bioactive glasses are proposed in the CaO-MgO-SiO(2)-Na(2)O-P(2)O(5)-CaF(2) system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO(4)) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts' cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C). PMID:21188484

Tulyaganov, D U; Agathopoulos, S; Valerio, P; Balamurugan, A; Saranti, A; Karakassides, M A; Ferreira, J M F

2011-02-01

229

Effect of ZnO addition on bioactive CaO-SiO2-P2O5-CaF2 glass-ceramics containing apatite and wollastonite.  

PubMed

Some ceramics show bone-bonding ability, i.e. bioactivity. Apatite formation on ceramics is an essential condition to bring about direct bonding to living bone when implanted into bony defects. A controlled surface reaction of the ceramic is an important factor governing the bioactivity and biodegradation of the implanted ceramic. Among bioactive ceramics, glass-ceramic A-W containing apatite and wollastonite shows high bioactivity, as well as high mechanical strength. In this study, glass-ceramics containing zinc oxide were prepared by modification of the composition of the glass-ceramic A-W. Zinc oxide was selected to control the reactivity of the glass-ceramics since zinc is a trace element that shows stimulatory effects on bone formation. Glass-ceramics were prepared by heat treatment of glasses with the general composition: xZnOx(57.0-x)CaOx35.4SiO(2)x7.2P(2)O(5)x0.4CaF(2) (where x=0-14.2mol.%). Addition of ZnO increased the chemical durability of the glass-ceramics, resulting in a decrease in the rate of apatite formation in a simulated body fluid. On the other hand, the release of zinc from the glass-ceramics increased with increasing ZnO content. Addition of ZnO may provide bioactive CaO-SiO(2)-P(2)O(5)-CaF(2) glass-ceramics with the capacity for appropriate biodegradation, as well as enhancement of bone formation. PMID:16765885

Kamitakahara, M; Ohtsuki, C; Inada, H; Tanihara, M; Miyazaki, T

2006-07-01

230

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

231

Effect of yttria addition on mechanical, physical and biological properties of bioactive MgO-CaO-SiO2-P2O5-CaF2 glass ceramic.  

PubMed

Preparation of the bioactive MgO-CaO-SiO2-P2O5-CaF2 glass was carried out utilizing tap casting and powder metallurgy methods. The original composition was modified with 0.2% Y2O3 and carbon additions. The mother and the modified bioglass were examined, and comparative studies were performed between the mother and modified type to study the compositional modification effects on physical, mechanical and biological properties. The histology of mother type showed that this type has a good biocompatibility with no rejection or inflammation reaction with the host bone, and new bone generation and formation were shown in the region of implant. The modification with 0.2% Y2O3 achieved a good improvement in the mechanical properties when compared with the mother system. The histology of this type showed a normal acceptance with no inflammation reactions. On the other hand, the modification with carbon achieved a superior improvement in the mechanical properties compared to the mother bioglass and showed a good acceptance with no inflammation reactions with the host body as well. PMID:18458492

Al-Haidary, J; Al-Haidari, M; Qrunfuleh, S

2008-03-01

232

tau4/tau c/AF-2 of the thyroid hormone receptor relieves silencing of the retinoic acid receptor silencer core independent of both tau4 activation function and full dissociation of corepressors.  

PubMed

Members of the thyroid hormone (TR)-retinoic acid receptor (RAR) subfamily of nuclear hormone receptors silence gene expression in the absence of hormone. Addition of cognate ligands leads to dissociation of corepressors, association of coactivators, and transcriptional activation. Here, we used the hRAR alpha silencer core, which encompasses the ligand binding domain, including receptor regions D and E of RAR alpha without the activation function called tau4/tau c/AF-2 and without the F region, to analyze the mechanisms by which transcriptional silencing is relieved. Although the RAR silencer core is able to bind ligand, it acts as a constitutive transcriptional silencer. We have fused various small activation domains to the C terminus of the silencer core and analyzed hormone-dependent changes in receptor function. We show that nine amino acids derived from the hTRbeta are sufficient to transform the RAR silencer core into a hormone-dependent activator. Lengthening the linker between the silencer core and these nine amino acids is not critical for mediating ligand-induced relief of silencing and activation. In addition, we show that a transactivation function at the C terminus is not required for relief of silencing by the hormone, but it is required for transcriptional activation. Furthermore, we created functional silencer fusions which lose their repressive function upon addition of hormone, although the corepressors SMRT and N-CoR remain attached to the receptor. PMID:9234683

Baniahmad, A; Thormeyer, D; Renkawitz, R

1997-08-01

233

Induced lattice strain in epitaxial Fe-based superconducting films on CaF2 substrates: A comparative study of the microstructures of SmFeAs(O,F), Ba(Fe,Co)2As2, and FeTe0.5Se0.5  

NASA Astrophysics Data System (ADS)

The microstructures of SmFeAs(O,F), Ba(Fe,Co)2As2, and FeTe0.5Se0.5 prepared on CaF2 substrates were investigated using transmission electron microscopy. The SmFeAs(O,F)/CaF2 interface is steep, without a disordered layer. By contrast, a chemical reaction occurs at the interface in the cases of Ba(Fe,Co)2As2 and FeTe0.5Se0.5. The reaction layers are located on opposite sides of the interface for Ba(Fe,Co)2As2 and FeTe0.5Se0.5. We found that the lattice distortion of the three superconducting films on the CaF2 substrates enhances the TC values compared with films prepared on oxide substrates. The origin of this lattice deformation varies depending on the superconducting material.

Ichinose, Ataru; Tsukada, Ichiro; Nabeshima, Fuyuki; Imai, Yoshinori; Maeda, Atsutaka; Kurth, Fritz; Holzapfel, Bernhard; Iida, Kazumasa; Ueda, Shinya; Naito, Michio

2014-03-01

234

Influence of strontium on structure, sintering and biodegradation behaviour of CaO-MgO-SrO-SiO(2)-P(2)O(5)-CaF(2) glasses.  

PubMed

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 the composition (mol.%): (36.07 - x) CaO-xSrO-19.24MgO-5.61P(2)O(5)-38.49SiO(2)-0.59CaF(2), where x varies between 0 and 10. The detailed structural analysis of the glasses is made by infrared spectroscopy and magic angle spinning-nuclear magnetic resonance spectroscopy. Silicon is predominantly present as Q(2) (Si) species, while phosphorus is found as orthophosphate in all the investigated glasses. The apatite-forming ability of glasses is investigated by immersion of glass powders in simulated body fluid for time durations varying between 1 h and 7 days. While increasing the Sr(2+)/Ca(2+) ratio in the glasses does not affect their structure significantly, their apatite-forming ability is decreased considerably. Further, physico-chemical degradation of glasses is 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 the ion release profiles from the glasses in different solutions are discussed. The addition of strontium to the glasses leads to a sevenfold decrease in chemical degradation of glasses in Tris-HCl. The sintering of glass powders renders glass ceramics (GCs) with varying degrees of crystallinity and good flexural strength (98-131 MPa), where the mechanical properties depend on the nature and amount of crystalline phases present in the GCs. PMID:21763793

Goel, Ashutosh; Rajagopal, Raghu Raman; Ferreira, José M F

2011-11-01

235

Preparation and Characterization of High-Purity Metal Fluorides for Photonic Applications.  

National Technical Information Service (NTIS)

We combine chelate-assisted solvent extraction (CASE) and hot hydrogen fluoride gas treatment to enable a general method for the preparation of high-purity binary metal fluorides. The fluorozirconate glass ZBLANI:Yb3+ (ZrF4-BaF2-LaF3- AlF3-NaF-InF3-YbF3),...

M. Sheik-Bahae M. P. Hehlen P. C. Stark T. M. Yoshida W. M. Patterson

2011-01-01

236

Annealing of electron damage in mid-IR transmitting fluoride glass  

NASA Technical Reports Server (NTRS)

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

Bansal, Narottam P.; Doremus, Robert H.

1986-01-01

237

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

238

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

239

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

NASA Astrophysics Data System (ADS)

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

Huang, Chuanbing; Du, Lingzhong; Zhang, Weigang

2014-02-01

240

Resonant enhancement effect on two-photon absorption due to excitons in alkaline-earth fluorides excited with synchrotron radiation and laser light  

NASA Astrophysics Data System (ADS)

Exciton states in wide-gap materials CaF2 and BaF2 have been studied with the technique of two-photon spectroscopy using synchrotron radiation and laser. The two-photon excitation spectrum of CaF2, and that of BaF2 as well, exhibited a clear peak on the high-energy side of the 1S exciton energy. The peaks are attributed to the 2P states of the valence excitons. According to this assignment, the binding energies of the excitons have been determined to be 0.8 and 0.9 eV for CaF2 and BaF2, respectively. The signal intensities were larger than that in the case of one-beam excitation by a factor of about 500, which is attributed to a resonant effect on two-photon absorption.

Tsujibayashi, Toru; Watanabe, Masayuki; Arimoto, Osamu; Itoh, Minoru; Nakanishi, Shunsuke; Itoh, Hiroshi; Asaka, Shuji; Kamada, Masao

1999-09-01

241

Energy transfer and non-linear optical properties at near ultraviolet wavelengths: rare earth 4f->5d transitions in crystals and glasses. Progress report, June 1, 1985-May 31, 1986. [Ce-doped CaF2 and LiYF4  

SciTech Connect

The project has considered several aspects of how high-fluence, near-ultraviolet laser light modifies the optical properties of cerium-doped crystals. Illumination of CeT :CaF2 at 308 nm leads to a two-photon photoionization and the subsequent creation of photochromic color centers. A one-photon photobleaching of these centers and the finite electron acceptor density leads to a complex but solvable rate equation. The electron acceptors are trivalent cerium ions at quasi-cubic sites, which become divalent following the electron capture. The photo-bleaching involves the photoionization of the divalent cerium ions, with the electron returning to the original tetragonal symmetry site. Thermoluminescence measurements are used to study the thermally activated recombination radiation. Measurements of optical gain and loss in CeT :LiYF4 are presented.

Hamilton, D.S.

1986-01-01

242

Photomultiplier Tubes for BaF2\\/BGO Crystal Scintillators  

Microsoft Academic Search

BGO\\/BaFâ crystals have been widely employed as scintillation detectors for radioactive sources and charged particles. Photomultiplier Tubes (PMT) are conventionally used on the detector with these scintillators. For these applications, the PMT with rectangular and dual photocathode (to be coupled with BGO crystal) was developed in order to reduce the dead space among PMTs in assembling them together as a

Hidehiro Kune; Takashi Watanabe; Masahiro Iida; Teruhiko Matsushita; Seiji Suzuki

1986-01-01

243

Excitation of Pr3+ ions in alkaline-earth fluorides  

Microsoft Academic Search

Emission and excitation spectra of CaF2, SrF2, BaF2 doped by PrF3 were measured in vacuum ultraviolet region at 11 K. Emission spectra of several 5d-4f bands of CaF2 and BaF2 show evident vibronic structure with apparent line separated by 400 cm-1 from the main zero phonon line. No such structure was observed in SrF2-Pr. The absence of vibronic structure in

E. Radzhabov; V. Nagirnyi

2010-01-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

245

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

246

Versatile fluoride substrates for Fe-based superconducting thin films  

NASA Astrophysics Data System (ADS)

We demonstrate the growth of Co-doped BaFe2As2 (Ba-122) thin films on CaF2 (001), SrF2 (001), and BaF2 (001) single crystal substrates using pulsed laser deposition. All films are grown epitaxially despite of a large misfit of -10.6% for BaF2 substrate. For all films, a reaction layer is formed at the interface confirmed by X-ray diffraction and for the films grown on CaF2 and BaF2 additionally by transmission electron microscopy. The superconducting transition temperature of the film on CaF2 is around 27 K, whereas the corresponding values of the films on SrF2 and BaF2 are around 22 K and 21 K, respectively. The Ba-122 on CaF2 shows almost identical crystalline quality and superconducting properties as films on Fe-buffered MgO.

Kurth, F.; Reich, E.; Hänisch, J.; Ichinose, A.; Tsukada, I.; Hühne, R.; Trommler, S.; Engelmann, J.; Schultz, L.; Holzapfel, B.; Iida, K.

2013-04-01

247

Growth of YBa 2Cu 3O 7-? on alkaline earth flouride substrates and thin films  

NASA Astrophysics Data System (ADS)

The growth and characterization of YBa 2Cu 3O 7-? (YBCO) thin films grown by laser ablation on MgF 2 (100), CaF 2 (100), SrF 2 (100), and BaF 2 (100) substrates, and on CaF 2 and BaF 2 thin films on LaAlO 3 (100) substrates, are described. High quality superconducting YBCO films could be grown directly only on the BaF 2 substrates and thin films. YBCO films grown directly on MgF 2 or CaF 2 substrates were insulating and showed clear signs of interdiffusion and reaction, as measured by X-ray photoelectron spectroscopy. Superconducting YBCO films could be grown on SrF 2 and CaF 2 substrates and thin films only with an yttria-stabilized zirconia buffer layer and/or with a low YBCO growth temperature, while YBCO grown on MgF 2 yielded insulating films for all growth conditions investigated. The highest quality YBCO films were obtained on BaF 2 substrates ( Tc=87.6 K, ?Tc=0.3 K). These results are discussed in terms of the thermodynamic stability of possible reaction products and the temperature dependence of the ionic mobilities.

Vasquez, R. P.; Foote, M. C.; Hunt, B. D.; Barner, J. B.

1993-03-01

248

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

249

The Absorption Spectrum of Gd(3+) IN Crystals of Alkaline Earth Fluorides - Hextet D Energy Levels.  

National Technical Information Service (NTIS)

The splitting of the hextet D(7/2) and hextet D(9/2) energy levels of Gd(3+) ions in CaF2, SrF2, and BaF2 hosts was measured through absorption experiments at 77K. For each host, crystals with several doping concentrations from 0.1 to 0.85 mole % were use...

D. M. Ware

1970-01-01

250

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

PubMed

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

Ode, Aiko

2014-02-01

251

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

252

Aspects of photoionization of impurities and electron transfer in ionic crystals  

NASA Astrophysics Data System (ADS)

Spectral evidence was found for photoionization in spectra of Eu(sup 2+) and Sm(sup 3+) in BaF2; Ce(sup 3+) was also studied in BaF2, CaF2, and SrF2. Two-photon spectroscopy of forbidden transitions (zero-phonon lines) was extended from NaF: Cu(sup +) to Mn(sup 4+) in Cs2GeF6 and to MgO:Ni(sup 2+).

McClure, D. S.

1993-02-01

253

Opto-acoustic measurement of the absorption coefficients of IR window materials for a CO2 laser  

Microsoft Academic Search

A laser opto-acoustic technique has been used to measure the absorption coefficients of IR window materials (for example NaCl, KCl, AR-coated Ge, BaF2, CaF2 and ZnS) on the R(20) and the P(20) lines of a CO2 laser. In this paper the above materials under their working conditions have also been assessed.

C.-J. Ming; Z.-X. Li; L.-J. Wang; C.-W. Chen; Y.-T. Liu

1982-01-01

254

Charge-transfer bands in crystals of alkaline earth fluorides with Eu3+ and Yb3 + 1  

Microsoft Academic Search

The absorption, luminescence, and excitation spectra of CaF2, SrF2, and BaF2 crystals with EuF3 or YbF3 impurity have been investigated in the range 1 12 eV. In all cases, strong wide absorption bands (denoted as CT1) were observed at energies below the 4 f n -4 f n - 15 d absorption threshold of impurity ions. Weaker absorption bands (denoted

E. A. Radzhabov; A. I. Nepomnyashchikh; V. Kozlovskii

2008-01-01

255

Optical properties of PbS\\/CdS superlattices grown by pulsed laser evaporation  

Microsoft Academic Search

PbS\\/CdS superlattices have been grown on BaF2, CaF2, Si and glass subtrates. Each specimen contained 10 to 23 pairs of the PbS\\/CdS layers. Absorption spectra of the structures have shown specific steps. The energy distribution of the steps has been analysed using models of Tipe-I and Tipe-II superlattices. Experimental results have been shown to follow the theoretical values of the

Sergey F. Musikhin; Ludmila G. Bakueva; Vladimir I. Il'in; Oleg V. Rabizo; Larissa V. Sharonova

1994-01-01

256

Strain-Induced Splitting and Oscillator-Strength Anisotropy of the Infrared Transverse-Optic Phonon in Calcium Fluoride, Strontium Fluoride, and Barium Fluoride  

Microsoft Academic Search

Strain-induced splittings of the infrared-active TO phonon in CaF2, SrF2, and BaF2 are calculated from a least-squares fit of photoelastic dispersion data by an undamped oscillator model. The strain-induced oscillator-strength anisotropy appears negligible; the Szigeti effective charge remains a scalar. The shear deformation potential for [100] strain is ~170 cm-1 in all the materials; for [111] strain it is -82

Albert Feldman; Roy M. Waxler

1980-01-01

257

Application of a high temperature self-lubricating composite coating on steam turbine components  

Microsoft Academic Search

A high temperature self-lubricating composite coating has been successfully applied on steam turbine governor valve lift rods that are subject to metal-to-metal wear and gall at elevated temperature (540 °C). The coating (NASA designation PS304) is a chrome-oxide based plasma sprayed coating with embedded silver and BaF2\\/CaF2 eutectic compound particles to function as solid lubricants. An inspection of the coated

Wenchao Wang

2004-01-01

258

Microscopic Analysis of 5d States Splitting and Charge Transfer Energies Dependence on Interionic Distance in Alkaline Earth Fluorides Doped with Light Trivalent Lanthanides  

Microsoft Academic Search

A first principles fully relativistic analysis (K. Ogasawara et al., Phys. Rev. B2001, 64, 115413) of the dependence of 5d orbitals splitting (10Dq) and charge transfer (CT) energies on interionic distance has been performed for light lanthanides (Ce, Pr, Nd) in CaF2, SrF2, BaF2 crystals. The salient feature of the method is that four?component molecular orbitals (MO) composed of atomic

Mikhail G. Brik; Kazuyoshi Ogasawara

2007-01-01

259

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

260

Stochastic Theory of Coherent Optical Transients. II. Free Induction Decay in Pr3+ : LaF3  

NASA Astrophysics Data System (ADS)

We study how the phase relaxation of the relevant electronic excitation is modified when the laser intensity increases. Especially the change of the free induction decay rate against the Rabi frequency is analytically derived for the intermediate region between the Bloch and the Redfield regimes, which corresponds to the observations by DeVoe and Brewer. Satisfactory coincidence is shown to be obtained, and we propose new experiments that will provide further tests of the theory.

Hanamura, Eiichi

1983-10-01

261

Note: Response characteristics of the sensor based on LaF3 thin film to different humidified gases  

NASA Astrophysics Data System (ADS)

Electromotive force (EMF) transient curves presented that the sensor showed good repeatable response in the humidity environments using ambient atmosphere as the carrier gas at different temperatures. The 90% response time and recovery time were within 40 s and 50 s, respectively. The sensor also presented stable response characteristics in 75.1% RH and 83.6% RH humidity environments using N2, 5% O2, and 50% O2 as the carrier gases, respectively. The EMF always increased with the partial pressure of oxygen in certain relative humidity. However, the ?EMF was decreased with the increase of O2 content in the carrier gas under the condition of the variation of relative humidity from 75.1% to 83.6%. These phenomena revealed that the sensor was sensitive to water vapor without oxygen in the sample gas and too much water vapor had adverse effect on the response to oxygen. Non-Nernst behavior of the sensor was discussed in detail.

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde; Guan, Cheng; Zhang, Bike

2012-05-01

262

Radiation damage studies on new inorganic optical crystals  

Microsoft Academic Search

Luminescent and radiation properties of a series of heavy-element crystals based on CdF2, BaF2, LaF3, Pb0.67Cd0.33F2, Na0.4Yb0.6F2.2, Y3Al5O12 and a lead glass ?-113 are presented. Our investigation shows that the crystals based on CdF2 containing YbF3 and InF3 have radiation resistance ? 10 Mrad.

S. I. Kuptsov; A. S. Solov'ev; V. G. Vasil'chenko; A. A. Bistrova; I. I. Buchinskaya; E. A. Krivandina; B. P. Sobolev; Z. I. Zhmurova; Yu. A. Krechko; Yu. D. Motin; A. V. Antipov

1995-01-01

263

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

264

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

Microsoft Academic Search

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

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

2006-01-01

265

10.5 W Time-Averaged Power Mid-IR Supercontinuum Generation Extending Beyond 4 m With Direct Pulse Pattern Modulation  

Microsoft Academic Search

A novel, all-fiber-integrated supercontinuum (SC) laser is demonstrated and provides up to 10.5 W time-averaged power with a continuous spectrum from ~0.8 to 4 mum. The SC is generated in a combination of standard single-mode fibers and ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride fibers pumped by a laser-diode-based cladding-pumped fiber amplifier system. The output SC pulse pattern can be modulated by directly modulating

Chenan Xia; Zhao Xu; Mohammed N. Islam; Mike J. Freeman; Andy Zakel; Jeremiah Mauricio

2009-01-01

266

Effect of microgravity on crystallization of ZBLAN fibers  

NASA Technical Reports Server (NTRS)

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

Tucker, Dennis S.

1994-01-01

267

Effects of Gravity on ZBLAN Glass Crystallization  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

268

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

269

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

270

Study of BaF2 with 511 KeV Gamma Rays  

Microsoft Academic Search

Results will be presented on tests conducted with a 20 Torr ethane 1000 Angstrom cesium-iodide photocathode avalanche chamber [1], with a barium-fluoride scintillator window. Positrons are emitted from a sodium-22 source, which annihilate to produce two 0.511 MeV gamma rays. The barium-fluoride scintillator window converts the 0.511 MeV gamma rays into ultraviolet wavelength photons, which are absorbed in the cesium-iodide

Jon Miller

1996-01-01

271

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

272

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

273

Determinazione dei Parametri Cinetici del Cristallo Termoluminescente CAF2 (TM) (Determination of the Kinetic Parameters of the Thermoluminescent CaF2 (TM) Crystal).  

National Technical Information Service (NTIS)

The kinetic parameters are determined following different procedures, based on the thermoluminescent light emission characteristics curve. The methods include the initial gradient method, the numerical fitting of the glow curve, and the peak shape method....

P. Bernardini C. Bini M. Crisafulli D. Moraldi S. Orlando

1988-01-01

274

New observations on the pressure dependence of luminescence from Eu2+-doped MF2 (M = Ca, Sr, Ba) fluorides.  

PubMed

The luminescence from Eu(2+) ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu(2+) comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) --> 4f(7) transition of Eu(2+). Above 5 GPa, the pressure behavior of the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) in BaF2:Eu(2+) is the same as the normal emission of Eu(2+) in CaF2 and SrF2 phosphors. PMID:18444634

Su, Fu Hai; Chen, Wei; Ding, Kun; Li, Guo Hua

2008-05-29

275

Synthesis and dosimetric properties of the novel thermoluminescent CaF2:Tm nanoparticles  

NASA Astrophysics Data System (ADS)

Calcium fluoride nanoparticles doped with thulium were synthesized for the first time by using the hydrothermal method. The synthesized nanostructures were characterized by X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The crystallite size of about 40 nm was estimated by Scherer's formula. The shape and size of the nanoparticles were also observed by scanning electron microscope (SEM). Tm-Tstop method and computerized glow curve deconvolution (CGCD) technique were employed to obtain the number of component glow peaks and kinetic parameters of the produced phosphor. Three overlapped thermoluminescence glow peaks were identified at 402, 426 and 467 K in the complex glow curve of this phosphor. The optimized concentration of Tm impurity was obtained at 0.5 mol%. Other thermoluminescence characteristics of this phosphor such as fading, reusability and dose response, reveals superior dosimetry features compared to its microcrystalline counterpart.

Zahedifar, M.; Sadeghi, E.

2012-12-01

276

Colour centres formation in CaF 2 single crystals by ?-rays and reactor neutrons  

Microsoft Academic Search

The induced colour in single crystals of calcium fluoride irradiated with ?-rays and reactor neutrons have been investigated by optical measurements (absorption and photoluminescence). The optical absorption spectrum increases slightly by increasing ?-rays dose up to 106Gy and absorption bands centred at about 225, 260, 340, 396 and 580nm are observed. At higher doses, in the case of reactor neutrons

M. Izerrouken; L. Guerbous; A. Meftah

2010-01-01

277

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

278

Brillouin Lasing with a CaF2 Whispering Gallery Mode Resonator  

NASA Astrophysics Data System (ADS)

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?W 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.

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

2009-01-01

279

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

280

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

Microsoft Academic Search

We report the observation of persistent spectral holeburning on the ^3H6 arrow ^3H4 transition of the trivalent thulium ion at 800 nm, with the goal of obtaining long-term persistence for optical storage, frequency references and signal processing. Deuteration treatment of rare-earth doped calcium fluoride gives rise to a number of new spectroscopic centers in which a rare-earth ion is adjacent

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

1998-01-01

281

Spatial dispersion in CaF2 caused by the vicinity of an excitonic bound state  

Microsoft Academic Search

The microscopic mechanism beyond the optical anisotropy of an ionic crystal which occurs for short wavelengths is investigated. The electron-hole, two particle propagator and its analytical behaviour close to the band edge of the one particle continuum plays a major role for the mechanism of this optical anisotropy. Especially for an ionic crystal the two particle bound state, the exciton,

M. Letza; E. Morsen

282

Spatial dispersion in CaF2 caused by the vicinity of an excitonic bound state  

Microsoft Academic Search

The microscopic mechanism beyond the optical anisotropy of an ionic crystal which occurs for short wavelengths is investigated. The electron-hole, two particle propagator and its analytical behavior close to the band edge of the one particle continuum plays a major role for the mechanism of this optical anisotropy. Especially for an ionic crystal the two particle bound state, the exciton,

Martin Letz; W. Mannstadt; Matthias Brinkmann; Ewald Moersen

2002-01-01

283

Study of haze in artificially grown single crystal CaF2  

NASA Astrophysics Data System (ADS)

The artificially grown calcium fluoride is used as materials of the optics such as the lenses of the illumination optical system and the projection optical system of the lithography equipment that use the sources of light such as excimer lasers. Such calcium fluoride is required high transmittance. However, there are very small scatterers and absorbers inside the crystal and they cause degradation of transmittance. In this study, we examined these defects and clarified the process how they occur. Haze is characteristic optical defect in the artificially grown calcium fluoride. It is thought that haze is an aggregation of very small scatterers and this scatterer is void or calcium oxide crystal. When we irradiate the light into a crystal with much haze, the path of the light looks white. However, we were not able to clarify neither the structure nor components of haze. First, we examined how the scatterers were distributed by an infrared tomography method. The result pointed out that the scatterers were located along sub-grain boundary and dislocation network. We prepared a surface sample for TEM (Transmission Electron Microscopy) with FIB (Focused Ion Beam) from the point where it seemed that the scatterers were located in the dislocation network, and observed it with TEM and analyzed grain boundary region and the grain inside with EDS (Energy Dispersive X-ray Spectroscopy). From the EDS spectrum of the grain boundary region, a very small amount of oxygen was detected, but no oxygen was detected from the grain inside. This suggests that oxygen is located in the grain boundary. From these results, it is suggested that scatterers of haze are made of oxygen voids or calcium oxides crystals.

Azumi, M.

2008-01-01

284

Lattice location and annealing studies of Hf implanted CaF 2  

Microsoft Academic Search

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the ?110? crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of

Thomas Geruschke; Katharina Lorenz; Eduardo Alves; Reiner Vianden

2009-01-01

285

Charge-transfer bands in crystals of alkaline earth fluorides with Eu 3+ and Yb 3 + 1  

Microsoft Academic Search

The absorption, luminescence, and excitation spectra of CaF2, SrF2, and BaF2 crystals with EuF3 or YbF3 impurity have been investigated in the range 1–12 eV. In all cases, strong wide absorption bands (denoted as CT1) were observed at energies below the 4f\\u000a \\u000a n\\u000a -4f\\u000a \\u000a n ? 15d absorption threshold of impurity ions. Weaker absorption bands (denoted as CT2) with energies

E. A. Radzhabov; A. I. Nepomnyashchikh; V. Kozlovski?

2008-01-01

286

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

287

Melting of some alkaline-earth and transition-metal fluorides and alkali fluoroberyllates at elevated pressures: A search for melting systematics  

Microsoft Academic Search

The melting curves of the fluorides ZnF2 and NiF2 (rutile structure), CaF2, SrF2 and BaF2 (fluorite structure), and of the fluoroberyllates Na2BeF4 and Li2BeF4 have been studied at pressures <= 40 kbar by differential thermal analysis in a piston-cylinder high-pressure device. The initial slopes (dTm\\/dP)0 of these melting curves are respectively 7.2, 5.8, 16.7, 15.2, 15.7, 15.1 and <0°C\\/kbar. A

Ian Jackson

1977-01-01

288

Differential cross-section measurements of the d + 19F reaction channels for NRA purposes  

NASA Astrophysics Data System (ADS)

Differential cross-section measurements of the 19F(d,p0-1)20F and 19F(d,?0-3)17O reactions have been performed in the projectile energy region Ed,lab = 1800-3000 keV in steps of 25 keV and for detection angles 150° and 170° using thin LiF and CaF2 targets. To validate the obtained results, benchmarking measurements were performed, using a CaF2 pellet and a thick, mirror-polished BaF2 target at various beam energies. The results are also compared to data from literature, when available, and all the observed discrepancies are discussed.

Paneta, V.; Kokkoris, M.; Lagoyannis, A.; Rakopoulos, V.

2012-11-01

289

Crystallization of BaF2-ZnF2-YbF3-ThF4 glass  

NASA Astrophysics Data System (ADS)

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

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

1988-10-01

290

Crystallization of BaF2-ZnF2-YbF3-ThF4 glass  

Microsoft Academic Search

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

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

1988-01-01

291

Absolute light yield measurements on BaF2 crystals and the quantum efficiency of several photomultiplier tubes  

Microsoft Academic Search

The quantum efficiency curves of five Philips XP2020Q photomultiplier tubes (PMTs), one Hamamatsu R2059 PMT, and a Na-salicylate coated glass window are determined using a calibrated Thorn EMI 9426 PMT as a reference. The QE of XP2020Q PMTs at wavelengths smaller than 230 nm appears much better than the values specified by the manufacturer. Consequently, the often reported photon yield

P. Dorenbos; J. T. M. de Haas; R. Visser; C. W. E. van Eijk; R. W. Hollander

1993-01-01

292

Crystallization of BaF2-ZnF2-YbF3-ThF4 glass  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

293

Evaluation of absorption and emission properties of Yb3+ doped crystals for laser applications  

Microsoft Academic Search

The emission and absorption properties of numerous host crystals doped with Yb3+ ions have been studied. The hosts which have been selected include LiYF4, LaF3, SrF2, BaF2, KCaF3, KY3F10, Rb2NaYF6, BaY2 F8, Y2SiO5, Y3Al5 O12, YAlO3, LuPO4, Ca5(PO4)3F, LiYO2, and ScBO 3. Spectral determinations have been made of the resonant absorption and emission cross sections between 850 and 1100 nm,

Laura D. DeLoach; Stephen A. Payne; L. L. Chase; L. K. Smith; W. L. Kway; W. F. Krupke

1993-01-01

294

Rayleigh scattering in ZrF4-based glasses  

NASA Astrophysics Data System (ADS)

Rayleigh scattering of fluorides in synthetic fluoride glasses is shown to exhibit an inverse fourth power wavelength dependence which can be reduced to the levels observed in the best synthetic silicas. Light scattering in multi-component glasses containing, in mole percent, 51.53 ZrF4, 20.47 BaF2, 5.27 LaF3, 3.24 AlF3, and 19.49 LiF was investigated as a function of wavelength and of angular distribution. The light scattering experimental setup is shown, as is the measured angular distribution of the relative scattering intensity for both horizontally and vertically polarized incident light. The total scattering loss as a function of wavelength is depicted. The extrapolated loss of 0.0027 dB/km observed at four microns nearly reaches the expected minimum loss, which is theoretically predicted to be 0.0015 dB/km.

Tran, D. C.; Sigel, G. H.; Levin, K. H.; Ginther, R. J.

1982-11-01

295

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

296

Chemical Interaction between High-Tc Superconducting Oxides and Alkaline Earth Fluorides  

NASA Astrophysics Data System (ADS)

Reactions of high-Tc superconductors and MF2 (M: Ca, Sr, Ba) were investigated by means of ac susceptibility, X-ray diffraction, and TG-DTA measurements. The superconducting transition temperature (Tconset) of Ba2YCu3O7-? powder mixed with MF2 powder decreased as a result of heat treatment at 600°C in air, whereas it did not decrease by the heat treatment under carefully dried conditions. In contrast, neither of the heat-treatment conditions decreased the Tconset of Bi2Sr2CaCu2Ox mixed with MF2 powder. Heating with MF2 at temperatures higher than 700°C reduced volume fractions of these superconductors even in dry atmosphere and the reactivity increased in the order of BaF2

Hashimoto, Takuya; Asakawa, Toshiaki; Shiraishi, Tadashi; Yoshida, Tsutomu; Yoshimoto, Mamoru; Koinuma, Hideomi

1989-07-01

297

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

298

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

299

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

300

Spectroscopic properties and energy transfer parameters of Er(3+)- doped fluorozirconate and oxyfluoroaluminate glasses.  

PubMed

Er(3+)- doped fluorozirconate (ZrF4-BaF2-YF3-AlF3) and oxyfluoroaluminate glasses are successfully prepared here. These glasses exhibit significant superiority compared with traditional fluorozirconate glass (ZrF4-BaF2-LaF3-AlF3-NaF) because of their higher temperature of glass transition and better resistance to water corrosion. Judd-Ofelt (J-O) intensity parameters are evaluated and used to compute the radiative properties based on the VIS-NIR absorption spectra. Broad emission bands located at 1535 and 2708?nm are observed, and large calculated emission sections are obtained. The intensity of 2708?nm emission closely relates to the phonon energy of host glass. A lower phonon energy leads to a more intensive 2708?nm emission. The energy transfer processes of Er(3+) ions are discussed and lifetime of Er(3+): (4)I13/2 is measured. It is the first time to observe that a longer lifetime of the (4)I13/2 level leads to a less intensive 1535?nm emission, because the lifetime is long enough to generate excited state absorption (ESA) and energy transfer (ET) processes. These results indicate that the novel glasses possess better chemical and thermal properties as well as excellent optical properties compared with ZBLAN glass. These Er(3+)- doped ZBYA and oxyfluoroaluminate glasses have potential applications as laser materials. PMID:24852112

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

2014-01-01

301

Colour centres formation in CaF2 single crystals by gamma-rays and reactor neutrons  

Microsoft Academic Search

The induced colour in single crystals of calcium fluoride irradiated with gamma-rays and reactor neutrons have been investigated by optical measurements (absorption and photoluminescence). The optical absorption spectrum increases slightly by increasing gamma-rays dose up to 106 Gy and absorption bands centred at about 225, 260, 340, 396 and 580 nm are observed. At higher doses, in the case of

M. Izerrouken; L. Guerbous; A. Meftah

2010-01-01

302

Optical spectroscopy of Yb 2+ ions in YbF 3-doped CaF 2 crystals  

Microsoft Academic Search

Transparent colorless Ca1?xYbx F2+x (x=0.0007–0.016) crystals were grown using the vertical Bridgman technique. In order to obtain efficient Yb3+–Yb2+ conversion in the as-grown crystals, a special procedure has been developed. Room temperature optical absorption spectra reveal the characteristic UV absorption bands of the Yb2+ ions in the as-grown crystals, with intensities more than 10 times higher than those reported by

Irina Nicoara; Liliana Lighezan; Monica Enculescu; Ionut Enculescu

2008-01-01

303

Growth of YbF 3-doped CaF 2 crystals and characterization of Yb 3+\\/Yb 2+ conversion  

Microsoft Academic Search

Calcium fluoride crystals doped with YbF3 and PbF2-, NaF- and LiF-codoped were grown using the vertical Bridgman method. Transparent, high quality, with various high Yb2+ contents in the as-grown crystals has been obtained using a special procedure. The optical absorption spectra reveal the characteristic ultraviolet (UV) absorption bands of the divalent Yb ions. Influence of the codoping with Pb2+, Li+

Irina Nicoara; Marius Stef; Andreea Pruna

2008-01-01

304

Concentration distribution of Yb 2+ and Yb 3+ ions in YbF 3:CaF 2 crystals  

Microsoft Academic Search

Calcium fluoride crystals doped with YbF3 were grown using the Bridgman technique. The optical absorption spectra reveal the characteristic UV-absorption bands of divalent Ytterbium. The absorption coefficient of divalent Yb is more than ten times higher than that of trivalent Ytterbium. This shows that the developed crystal growth process achieves a good Yb3+–Yb2+ conversion. The concentration distribution of the Yb2+

Irina Nicoara; Nicolae Pecingina-Garjoaba; Octavian Bunoiu

2008-01-01

305

Properties of expitaxial Pb 1- xSn xSe on CaF 2 covered Si(111) substrates  

NASA Astrophysics Data System (ADS)

Epitaxial narrow gap Pb 1- xSn xSe layers on Si-substrates are used for infrared focal plane arrays for thermal imaging in the 8-12 ?m wavelength range. The density of threading dislocations in the 3-4 ?m thick layers due to the lattice mismatch is about 3 × 10 7 cm -2, in accordance with the width of X-ray rocking curves (100 arc s range). These narrowest widths are obtained only in layers which exhibit high carrier mobilities. Due to the thermal expansion mismatch, misfit dislocations formed during growth glide on each temperature change along the {100} main glide planes. The interaction probabilities of such crossing dislocations leading to strain hardening is extremely low, a rough estimate leads to a value of 10 -5. This is because the cumulative plastic deformation (applied by repeated temperature cycling) is as high as 500%.

Müller, P.; Fach, A.; John, J.; Masek, J.; Paglino, C.; Zogg, H.

1996-08-01

306

A Comparison of CaF2:Mn and LiF Thermoluminescent Dosimeters for Environmental Radiation Monitoring.  

National Technical Information Service (NTIS)

Two types of Thermoluminescent Dosimeters, commonly used for environmental radiation monitoring, were evaluated and compared. The study consisted of approximately four months of field evaluation as part of a pre-operational survey at a nuclear power plant...

J. E. Partridge S. T. Windham J. Eakins J. Lochamy

1973-01-01

307

Physicochemical Properties of Slags. Part 5. Review of the Electrical Conductivity Data for CaF2-Based Slags.  

National Technical Information Service (NTIS)

The various methods of measuring the electrical conductivity of slags are described; the limitations and shortcomings of the various techniques are discussed. A list of recommended experimental procedures for the measurement of the electrical conductivity...

K. C. Mills J. S. Powell

1979-01-01

308

Radiation defects in CaF2 and SrF2 crystals doped with cadmium or zinc  

NASA Astrophysics Data System (ADS)

The formation of radiation defects in calcium and strontium fluoride single crystals doped with cadmium or zinc has been investigated by luminescence and absorption spectroscopy, as well as by electron spin resonance spectroscopy. It was found that x-irradiation could convert divalent impurity ions located at essentially cubic sites into the univalent state. Three types of Cd+ or Zn+ centers differing by local environment with point symmetries Oh, C3v and C2v are identified in the crystals. The formation of the last two results from the interaction between reduced impurities in the cubic environment and anion vacancies. The latter are intrinsic radiation defects and are not created by x-irradiation in undoped crystals. We also discuss the possible implications of the electric field of the charge impurity defects on separation of the intrinsic radiation defects in these crystals.

Egranov, A. V.; Radzhabov, E. A.; Ivashechkin, V. F.; Semenova, M. A.; Vasil'eva, I. E.

2008-11-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

310

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

SciTech Connect

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

DePriest, Kendall Russell; Griffin, Patrick Joseph

2003-07-01

311

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

SciTech Connect

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

DEPRIEST, KENDALL R.

2002-11-01

312

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

PubMed

Previously, nano-sized calcium fluoride (CaF?) particles were prepared using a spray drying method by simultaneously feeding Ca(OH)? and NH?F solutions to a two-liquid nozzle. The aim of the present study was to prepare better-dispersed nano-CaF? particles by co-forming a soluble salt, sodium chloride (NaCl). NaCl of various concentrations were added to the NH(4) F solution, leading to formation of (CaF? +NaCl) composites with CaF? /NaCl molar ratios of 4/1, 4/4, and 4/16. Pure nano-CaF? was also prepared as the control. Powder X-ray diffraction analysis showed that the products contained crystalline CaF? and NaCl. Scanning electron microscopy examinations showed that both the CaF? /NaCl composite and pure CaF? particles were about (50-800) nm in size and consisted of primary CaF? particles of < 50 nm in size. BET surface area measurements showed similar primary particle sizes for all samples. Dynamic light scattering measurements showed that the washed (CaF?+NaCl) particles were much smaller than the pure CaF? as the dissolution of NaCl "freed" most of the primary CaF? particles, leading to a greater degree of particle dispersion. The well-dispersed nano-CaF? may be expected to be a more effective anticaries agent than NaF by providing longer lasting elevations of fluoride concentrations in oral fluids. PMID:21695777

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

2011-08-01

313

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.

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

2012-01-01

314

Charge-transfer bands in crystals of alkaline earth fluorides with Eu3+ and Yb3 + 1  

NASA Astrophysics Data System (ADS)

The absorption, luminescence, and excitation spectra of CaF2, SrF2, and BaF2 crystals with EuF3 or YbF3 impurity have been investigated in the range 1 12 eV. In all cases, strong wide absorption bands (denoted as CT1) were observed at energies below the 4 f n -4 f n - 15 d absorption threshold of impurity ions. Weaker absorption bands (denoted as CT2) with energies 1.5 2 eV lower than those of the CT1 bands have been found in the spectra of CaF2 and SrF2 crystals with EuF3 or YbF3 impurities. The fine structure of the luminescence spectra of CaF2 crystals with EuF3 impurities has been investigated under excitation in the CT bands. Under excitation in the CT1 band, several Eu centers were observed in the following luminescence spectra: C 4 v , O h , and R aggregates. Excitation in the CT2 bands revealed luminescence of only C 4 v defects.

Radzhabov, E. A.; Nepomnyashchikh, A. I.; Kozlovski?, V.

2008-09-01

315

Nonlinear absorption phenomena in optical materials for the UV-spectral range  

NASA Astrophysics Data System (ADS)

A laser calorimetric technique is employed to measure absorptance and laser-induced changes therein on optical components at 248 nm. In BaF 2, a linear increase of absorptance with intensity is observed, but a pure two-photon absorption mechanism can be ruled out because the slope lessens towards shorter pulse lengths. Fused silica, at moderate energy densities, exhibits a reversible, linear absorption increase with energy density; an AR-coated sample mirrors the behavior of the uncoated substrate but discloses an added offset due to coating imperfections. In a series of measurements at constant irradiation parameters, uncoated substrates of Suprasil and CaF 2 reveal a slight exponential decrease in absorptance which might be attributed to surface cleaning or conditioning effects, and absolute absorptance is virtually independent of the sample thickness.

Eva, E.; Mann, K.

1997-02-01

316

Nonlinear absorption phenomena in optical materials for the UV-spectral range  

NASA Astrophysics Data System (ADS)

A laser calorimetric technique is employed to measure absorptance and laser-induced changes therein on optical components at 248 nm. In BaF2 a linear increase of absorptance with intensity is observed, but a pure two- photon absorption mechanism can be ruled out because the slope lessens towards shorter pulse lengths. Fused silica, at moderate energy densities, exhibits a reversible, linear absorption increase with energy density; an AR-coated sample mirrors the behavior of the uncoated substrate but discloses an added offset due to coating imperfections. In a series of measurements at constant irradiation parameters, uncoated substrates of Suprasil and CaF2 reveal a slight exponential decrease in absorptance which might be attributed to surface cleaning or conditioning effects, and absolute absorptance is virtually independent of the sample thickness.

Eva, Eric; Mann, Klaus R.

1996-11-01

317

Crystallization kinetics of AlF 3-based glasses doped with rare earth ions  

Microsoft Academic Search

Different concentrations of NdF3, PrF3, and PrF3, codoped with YbF3, ranging from 0.25 to 2.0 wt%, have been added to an AlF3-base glass with composition (mol%) 30.2AlF3–10.6BaF2–20.2CaF2–8.3YF3–3.5MgF2–3.8NaF–13.2SrF2–10.2ZrF4. The Avrami exponent, n, and activation energy, E, for the base glass, as well as the doped glasses, have been calculated by analyzing the differential scanning calorimetry curves, according to the amended Ozawa–Chen

Tariq Iqbal; A. N Kayani; M. R Shariari; G. Sigeljr

1997-01-01

318

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

319

Brewster angle prism retroreflectors for cavity enhanced spectroscopy.  

PubMed

The design of a high finesse optical cavity made from two prism retroreflectors is fully described. Optical beam propagation calculations to determine the specification of prism angles and relative dimensions, the size of the astigmatic TEM00 beam as it propagates in the cavity, and the sensitivity of the optic axis to changes in prism alignment and fabrication errors are presented. The effects of material dispersion are also quantified for three different materials: fused silica, calcium fluoride, and barium fluoride. The predictions made are found to be in good agreement with experimental results obtained from prisms we had made from fused silica. Prisms made of CaF2 and BaF2 are predicted to be useful for applications in the UV and mid-IR spectral regions, respectively. PMID:19488107

Lehmann, Kevin K; Johnston, Paul S; Rabinowitz, Paul

2009-06-01

320

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

321

Non-proportionality in the scintillation response and the energy resolution obtainable with scintillation crystals  

Microsoft Academic Search

A review and new data are presented on the absolute photon yield emitted by “classical” (NaI(Tl+), CsI(Tl+ ), CsI(Na+), CaF2(Eu2+), Bi4 Ge3O12, and CdWO4) and “modern” (BaF2, Gd2SiO5(Ce 3+), YAlO3(Ce3+), Lu2SiO5(Ce3+), Lu3Al5 O12(Sc3+), and K2LaCl5(Ce3+)) scintillation crystals after absorption of X-rays and ?-rays of energies ranging from 5 keV to 1 MeV. Factors influencing the energy resolution with which high

P. Dorenbos; J. T. M. de Haas; C. W. E. van Eijk

1995-01-01

322

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

323

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

NASA Technical Reports Server (NTRS)

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

DellaCorte, Chris

1998-01-01

324

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

325

Stability of alkali-metal oxides as a function of pressure: Theoretical calculations  

NASA Astrophysics Data System (ADS)

We investigate the regions of thermodynamic stability of possible modifications of the alkali oxides M2O as a function of pressure and type of alkali metal (M=Li,Na,K,Rb,Cs) . The results are in good agreement with experiment at standard pressure, and we find that at elevated pressures, all systems should exhibit a transition from the experimentally observed modifications ( CaF2 - and CdCl2 -type) to one or more high-pressure modifications exhibiting structures belonging to the extended cotunnite family, e.g., the high-pressure (hp)- BaF2 -, the PbCl2 -, the ?-US2 -, or the ?-Ni2Si -type. Metastable modifications that would be stable at sufficiently large negative pressures exhibit the CaCl2 - or the CdCl2 -structure type.

?an?arevi?, Ž.; Schön, J. C.; Jansen, M.

2006-06-01

326

Correlation satellites in deep metal 3p core x-ray photoemission of tetravalent oxides MO2 (M=Ce,Pr,Tb,Hf) and of LaF3  

NASA Astrophysics Data System (ADS)

We have performed an x-ray photoemission (XPS) experiment using tunable x rays in the photon-energy range between 1500 and 3000 eV. The deep metal 3p core-level spectra of the tetravalent oxides MO2, M=Ce, Pr, Tb, and Hf have been measured. The results show that the configuration interaction between localized 4fn and 4fn+1L configuration in the initial state gives final-state peaks 3p4fn, 3p4fn+1L, and 3p4fn+2L2. The final states of Ce 3p core levels of CeO2 have been calculated by the many-body theory in the frame of the filled-band Anderson model.

Bianconi, A.; Miyahara, T.; Kotani, A.; Kitajima, Y.; Yokoyama, T.; Kuroda, H.; Funabashi, M.; Arai, H.; Ohta, T.

1989-02-01

327

Studies on Photoionization and Electron Trapping Process in Rare Earth Codoped Alkaline Earth Fluoride Crystals.  

NASA Astrophysics Data System (ADS)

In crystals with fluorite structure, such as CaF _2, SrF_2, and BaF_2, the process of photoionization of divalent rare earth ion (RE^{2+ }) impurities along with the trapping of electrons by different trivalent RE^{3+} ions have been investigated. It was found that the direct transition from a localized ground state of a rare earth to the conduction band states of the host has a negligible photoionization rate; and photoionization occurs through a localized excited state of the RE ion by thermal ionization or quantum tunneling, depending on the relative energy between the excited state and conduction band. The low energy of the exciton state of Eu ^{2+} in BaF_2 accounts for the lack of photoionization of Eu ^{2+} from the E_ {rm g} band. The Sm^ {3+} and Tm^{3+} demonstrated much higher trapping ability than Ce^{3+}. Electrons can be trapped not only by uncompensated RE^ {3+} but also by the charge compensated one. Relative trapping efficiency of Sm^ {3+} in both sites was measured in the BaF_2 crystal. Further investigation on the charge compensated Sm^{2+} ion, which is stable at low temperature, reveals that the interstitial fluoride compensator can substantially reduce the photoionization threshold, and quench the luminescence of Sm^ {2+} at lower temperature. It is also confirmed from Sm^{2+} absorption and emission spectra that Sm^ {2+}:F^{-} complex has C_{rm 3v} local symmetry in BaF_2. Ce^{3+} ions in cubic sites were reduced by X-ray irradiation at 77K in both SrF_2 and BaF_2 crystals for the first time ever. Ce^ {2+} will return to trivalent state after warming sample to room temperature. When a Ce:Na:CaF _2 crystal was irradiated with x-ray, the absorption spectra of both Ce^{3+} and Ce^{2+} showed no evidence of trapping of electron by Na^ {+} compensated Ce^{3+ }. In general, this work has shown that the ionization efficiency of RE^{2+} in fluorite lattice is affected by the energy of the self -trapped exciton state relative to the localized excited state of impurity and the proximity of charge compensator. It also demonstrates that the trapping cross section of RE ^{3+} strongly depends on the position of the charge compensator and the lattice size of host as well as the chemistry of the impurity itself.

Mou, Wanfeng

1995-01-01

328

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.

2014-05-01

329

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

330

The Effect of Film Thickness on Friction Coefficients for Solid Lubricants; CaF2, MoS2 and Graphite  

Microsoft Academic Search

An experimental investigation has been conducted to determine the effect of film thickness on the friction coefficient of solid powdered lubricants, applied as thin films on the mild steel specimens.Curves representing the coefficient of friction for various film thicknesses, as well as the tabulated data are given. The results are discussed and compared to those theoretically conceivable using the relationship

G. D. Whitehouse; D. Nandan; C. A. Whitehurst

1970-01-01

331

First principles multiplet calculations of the calcium L2, 3 x-ray absorption spectra of CaO and CaF2  

NASA Astrophysics Data System (ADS)

First principles calculations are performed for the interpretation of the L2, 3 x-ray absorption spectrum of calcium oxide and calcium fluoride. The first principles calculations are based on configuration interaction (CI) calculations using fully relativistic molecular spinors. The first principles results are compared to experimental data and also to calculations based on a semi-empirical crystal field multiplet model and also on a multichannel multiple scattering method. We show that the CI calculations show good agreement with experiment, both for bulk and for surface experiments. The remaining differences with experiment and between the theoretical models are discussed in detail.

Miedema, P. S.; Ikeno, H.; de Groot, F. M. F.

2011-04-01

332

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

333

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

334

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

335

Nonstoichiometric fluorides—Solid electrolytes for electrochemical devices: A review  

NASA Astrophysics Data System (ADS)

The solid electrolytes with fluorine-ion conductivity that were revealed during the analysis of the phase diagrams of the MF m - RF n systems within the program of search for new multicomponent fluoride crystalline materials carried out at the Shubnikov Institute of Crystallography, Russian Academy of Sciences, are described. The most widespread and promising materials are the nonstoichiometric phases with fluorite (CaF2) and tysonite (LaF3) structures, which are formed in the MF2- RF3 systems ( M = Ca, Sr, Ba, Cd, or Pb; R = Sc, Y, or La-Lu). These phases have superionic fluorine conductivity due to the anion sublattice disorder. The ionic conductivity of crystals of both structure types has been studied and the limits of its change with composition and temperature are determined. Nonstoichiometric fluorides are used as solid electrolytes in chemical sensors, fluorine sources, and batteries. The prospects of the use of fluorine-ion conductors in solid-state electrochemical devices, principles of their operation, and the problems of optimization of their composition are discussed.

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

2007-09-01

336

Nonstoichiometry in inorganic fluorides: I. Nonstoichiometry in MF m - RF n ( m < n ? 4) systems  

NASA Astrophysics Data System (ADS)

The manifestation of gross nonstoichiometry in MF m - RF n systems ( m < n ? 4) has been studied. Fluorides of 34 elements, in the systems of which phases of practical interest are formed, are chosen. To search for new phases of complex composition, a program for studying the phase diagrams of the condensed state (˜200 systems) has been carried out at the Institute of Crystallography, Russian Academy of Sciences. The main products of high-temperature interactions of the fluorides of elements with different valences ( m ? n) are grossly nonstoichiometric phases of two structural types: fluorite (CaF2) and tysonite (LaF3). Systems of fluorides of 27 elements ( M 1+ = Na, K; M 2+ = Ca, Sr, Ba, Cd, Pb; R 3+ = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; R 4+ = Zr, Hf, Th, U) are selected; nonstoichiometric M 1 - x R x F m(1 - x) + nx phases, which are of greatest practical interest, are formed in these systems. The gross nonstoichiometry in inorganic fluorides is most pronounced in 80 MF2 - RF3 systems ( M = Ca, Sr, Ba, Cd, Pb; R are rare earth elements). The problems related to the growth of single crystals of nonstoichiometric phases and basic fields of their application as new fluoride multicomponent materials, the properties of which are controlled by the defect structure, are considered.

Sobolev, B. P.

2012-05-01

337

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

338

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

339

Antireflection coatings for calcium fluoride laser windows for 5.3 microns  

NASA Astrophysics Data System (ADS)

Four distinct antireflection (AR) coatings and half-wave coatings of their constituent coating materials were evaluated for 5.3 microns on CaF2 and BaF2 substrates. The coating materials were lead and strontium fluoride, thorium tetrafluoride, and zirconium dioxide. The coatings were evaluated with regard to absorption, peak transmission, bandwidth, residual strain, and adhesion. A PbF2/ThF4 AR design had an absorption per surface less than .05 percent. The absorption of ZrO2 is excessive at 5.3. All AR designs passed the scotch tape adhesion test. The index of SrF2 in thin film form is lower than the bulk value. In half-wave coatings of SrF2 an index as low as 1.22 was observed. Bandwidths of three AR designs were 0.5 microns or greater. Absorptions of half-wave coatings at 1.06 and 3.8 microns indicate that further development will be required for these wavelengths. Absorption measurements for the PbF2/ThF4 design for CaF2 windows coated on both sides are reported for 5.3, 3.8, and 2.8 microns. The windows absorbed 0.04 percent, 0.2 percent, and 0.5 percent, respectively. Some designs were plaqued with stress induced birefringence in the visible which did not adversely affect the transmission in the IR. The PbF2, ThF4, and ZrO2 coatings did not show residual strain. The absorption measurements obtained on three different calorimeters are compared.

Ohmer, M. C.

1976-09-01

340

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

NASA Astrophysics Data System (ADS)

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

Levey, Christopher Gerrit

341

The Possibility of Gain among the 5D-4F Transitions of the Rare Earth Ions  

NASA Astrophysics Data System (ADS)

Although a wealth of information exists on the 4f-4f transitions of rare earth ions doped into solid-state materials, relatively little research exists on the 5d -4f transitions present in the same materials. We have studied the 5d-4f transitions of three rare-earth ions in a variety of materials in an attempt to evaluate the potential of the 5d-4f transition as a laser transition. We have measured the pump-probe spectrum of Sm ^{2+}:CaF_2 over a wide spectral region in order to characterize a material known to lase on a 5d-4f transition. We then measured comparable pump-probe spectra for Sm^ {2+} in SrF_2 and SrCl_2. This provided us with a systematic look at the excited state and its dependence on the host material. In addition to investigating divalent samarium, we have investigated other rare-earth ion doped systems similar in nature to known laser systems. Divalent europium, being a neighbor of samarium on the periodic table, has a very similar electronic configuration. Historically, europium has been recognized as an efficient fluorescent material, but has not demonstrated gain in any solid state host. We measured the pump-probe spectrum of divalent europium over a wide spectral region in CaF_2, SrF_2, SrCl_2, and LiCaAlF_6 in order to better understand the nature of the excited states and to evaluate whether it is possible for Eu^ {2+} to exhibit gain in any host medium. Among the trivalent rare earths, two elements, cerium and neodymium, have been demonstrated to lase. We chose expand upon current knowledge of 5d-4f transitions in the trivalent RE ions by studying trivalent praseodymium in CaF_2, SrF_2, BaF_2, BaY_2 F_8, and LiYF_4. Pr^{3+} seemed to be a reasonable candidate for gain, in part because it lies on the periodic table between the two elements which exhibit gain as trivalent ions in solid state media. The recent availability of non-linear crystals with Pu transparency made it possible to pump the ion using the fifth harmonic of Nd:YAG (213 nm).

Lawson, Janice Kay

342

In-volume waveguides by fs-laser direct writing in rare-earth-doped fluoride glass and phosphate glass  

NASA Astrophysics Data System (ADS)

Refractive index modifications are fabricated in the volume of rare-earth-doped glass materials namely Er- and Pr-doped ZBLAN (a fluoride glass consisting of ZrF4, BaF2, LaF3, AlF3, NaF), an Er-doped nano-crystalline glass-ceramic and Yb- and Er-doped phosphate glass IOG. Femtosecond laser radiation (?=500fs, ?=1045nm, f=0.1-5MHz) from an Ybfiber laser is focused with a microscope objective in the volume of the glass materials and scanned below the surface with different scan velocities and pulse energies. Non-linear absorption processes like multiphoton- and avalanche absorption lead to localized density changes and the formation of color centers. The refractive index change is localized to the focal volume of the laser radiation and therefore, a precise control of the modified volume is possible. The width of the written structures is analyzed by transmission light microscopy and additionally with the quantitative phase microscopy (QPm) software to determine the refractive index distribution perpendicular to a waveguide. Structures larger than 50?m in width are generated at high repetition rates due to heat accumulation effects. In addition, the fabricated waveguides are investigated by far-field measurements of the guided light to determine their numerical apertures. Using interference microscopy the refractive index distribution of waveguide cross-sections in phosphate glass IOG is determined. Several regions with an alternating refractive index change are observed whose size depend on the applied pulse energies and scan velocities.

Esser, D.; Wortmann, D.; Gottmann, J.

2009-02-01

343

Solvothermal synthesis of well-dispersed MF2 (M = Ca,Sr,Ba) nanocrystals and their optical properties  

NASA Astrophysics Data System (ADS)

MF2 (M = Ca,Sr,Ba) nanocrystals (NCs) were synthesized via a solvothermal process in the presence of oleic acid and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, UV/vis absorption spectra, photoluminescence (PL) excitation and emission spectra, and lifetimes, respectively. In the synthetic process, oleic acid as a surfactant played a crucial role in confining the growth and solubility of the MF2 NCs. The as-prepared CaF2, SrF2 and BaF2 NCs present morphologies of truncated octahedron, cube and sheet in a narrow distribution, respectively. Possible growth mechanisms were proposed to explain these results. The as-prepared NCs are highly crystalline and can be well dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrate strong emission bands centred at 400 nm in photoluminescence (PL) spectra compared with the cyclohexane solvent. The PL properties of the colloidal solutions of the as-prepared NCs can be ascribed to the trap states of surface defects.

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

2008-02-01

344

The activity of calcium in calcium-metal-fluoride fluxes  

NASA Astrophysics Data System (ADS)

The standard Gibbs energy of reaction Ca (1) + O (mass pct, in Zr) = CaO (s) has been determined as follows by equilibrating molten calcium with solid zirconium in a CaO crucible: ? G° = -64,300(±700) + 19.8(±3.5) T J/mol (1373 to 1623 K) The activities of calcium in the CaOsatd-Ca- MF2 ( M: Ca, Ba, Mg) and CaOsatd-Ca-NaF systems were measured as a function of calcium composition at high calcium contents at 1473 K on the basis of the standard Gibbs energy. The activities of calcium increase in the order of CaF2, BaF2, and MgF2 at the same calcium fraction of these fluxes. The observed activities are compared with those estimated by using the Temkin model for ionic solutions. Furthermore, the possibility of the removal of tramp elements such as tin, arsenic, antimony, bismuth, and lead from carbon-saturated iron by using calcium-metal-fluoride fluxes is discussed.

Ochifuji, Yuichiro; Tsukihashi, Fumitaka; Sano, Nobuo

1995-08-01

345

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

346

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

NASA Technical Reports Server (NTRS)

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

DellaCorte, Christopher; Valco, Mark J.

1999-01-01

347

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

348

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

349

Effect of powders refinement on the tribological behavior of Ni-based composite coatings by laser cladding  

NASA Astrophysics Data System (ADS)

NiCr + Cr3C2 + Ag + BaF2/CaF2 composite coatings were produced on stainless steel (1Cr18Ni9Ti) substrates by laser cladding. Corresponding powders were prepared by high-energy ball milling technique. The friction and wear behavior at room temperature was investigated through sliding against the Si3N4 ball. The morphologies of the wear debris, worn surfaces of both samples and the Si3N4 ball were analyzed by scanning electron microscopy and three dimensional non-contact surface mapping. Results showed that milling time had a great effect on the size, morphology, uniformity of the powders as well as the microstructure and properties of laser cladding coatings. The wear mechanism of the coatings is dominated by abrasive wear, plastic deformation and slight adhesive wear. The consecutive evolution trend of friction coefficient, wear rate as well as microhardness of the serials of coatings produced with powders of different sizes was presented.

Wang, Lingqian; Zhou, Jiansong; Yu, Youjun; Guo, Chun; Chen, Jianmin

2012-06-01

350

Correlation between 19F environment and isotropic chemical shift in barium and calcium fluoroaluminates.  

PubMed

High-speed MAS (19)F NMR spectra are recorded and reconstructed for 10 compounds from BaF(2)-AlF(3) and CaF(2)-AlF(3) binary systems which leads to the determination of 77 isotropic (19)F chemical shifts in various environments. A first attribution of NMR lines is performed for 8 compounds using a superposition model as initially proposed by B. Bureau et al. The phenomenological parameters of this model are then refined to improve the NMR line assignment. A satisfactory reliability is reached with a root-mean-square (RMS) deviation between calculated and measured values equal to 6 ppm. The refined parameters are then successfully tested on alpha-BaCaAlF(7) whose structure was recently determined. Finally, the isotropic chemical shift ranges are defined for shared, unshared, and "free" fluorine atoms encountered in the investigated binary systems. So, the fluorine surroundings can be deduced from the NMR line positions in compounds whose structure is unknown. Such an approach can also be applied to fluoride glasses. PMID:15074964

Body, M; Silly, G; Legein, C; Buzaré, J-Y

2004-04-19

351

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

352

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

353

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

SciTech Connect

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, C.

1987-07-01

354

Tribological and mechanical comparison of sintered and HIPped PM212 - high temperature self-lubricating composites  

SciTech Connect

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. 12 refs.

Dellacorte, C.; Sliney, H.E.; Bogdanski, M.S. (NASA, Lewis Research Center, Cleveland, OH (United States) Case Western Reserve Univ., Cleveland, OH (United States))

1992-11-01

355

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

356

Fundamentals of dislocation nucleation at nanoindentation  

NASA Astrophysics Data System (ADS)

Microelectronics and micromechanics dominate the development of modern techniques now and in the future. Investigations of the mechanical properties in this field are done favourably by nanoindentation, that means the penetration of the surface to nanometer depths using an indentation device. Indentation of perfect solids at nanometer scale is connected to formation of high local stresses. Using this advantage one can observe besides others the homogenous nucleation of dislocations in locally dislocations-free monocrystals. The mechanical stresses responsible for this process can be estimated in the framework of elastic contact theory from Hertz and Sneddon. Experimental results of the loop nucleation measurements shows a good agreement with the theory of dislocations within the isotropic approach. The Pop-in-effect has been observed in metals (Al, Cu, Ni, W), ionic crystals (CaF2, BaF2) and semiconductors (CdTe, GaAs, GaP, InP, ZnSe). Corresponding dislocations were proved by means of microscopy imaging techniques (transmission electron microscopy TEM, cathodoluminescence imaging CL, and imaging of dislocation-etched surfaces).

Grau, P.; Lorenz, D.; Zeckzer, A.

357

Vacuum tribological behaviour of self lubricant quasicrystalline composite coatings  

NASA Astrophysics Data System (ADS)

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

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

2003-09-01

358

Dynamics of the plume containing nanometric-sized particles ejected into the atmospheric air following laser-induced breakdown on the exit surface of a CaF2 optical window  

NASA Astrophysics Data System (ADS)

Laser induced breakdown on the output surface of calcium fluoride produces distinctive visualization of the gaseous material ejection via time-resolved shadowgraphy microscopy. This characteristic behavior allowed a detailed investigation of the directional expansion of the plume at ambient atmospheric conditions and its spatial separation and influence on the forming shockwave. The results also suggest that the material ejection is prolonged, extending more than 300 ns after the termination of the laser pulse. The dynamics of the backward motion of the gaseous material following its initial expansion is also resolved.

Demos, Stavros G.; Negres, Raluca A.; Rubenchik, Alexander M.

2014-01-01

359

Thermogravimetric Analysis of Hydrofluorides of Alkaline Earth Metals.  

National Technical Information Service (NTIS)

It was found that the most thermically stable hydrofluorides are the polyfluorides of strontium and barium. The thermal stability of BaF2.HF > SrF2.HF. The decomposition of the highest hydrofluorides, SrF2.2.5HF, BaF2.3HF, and BaF2.4.5HF, occurs stepwise ...

A. S. Paramzii D. D. Ikrami

1970-01-01

360

Photomultiplier window materials under electron irradiation: fluorescence and phosphorescence.  

PubMed

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 MgF(2) and LiF, and of CaF(2), BaF(2), sapphire, fused silica, and uv-transmitting glasses were obtained over the 200-650-nm spectral range. Fluorescence yields, expressed as the number of counts in a solid angle of 2pi sr/MeV of incident electron energy deposited [MeV(-1) (2pi sr)(-1)], were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively. Typical yields observed with a uv/visible sensitive bialkali cathode range from 10 MeV(-1) (2pi sr)(-1) for uv-grade MgF(2) to approximately 200 MeV(-1) (2pi sr)(-1) for CaF(2). For comparison, sodium-activated cesium iodide, one of the most efficient scintillator materials, yields about 700 MeV(-1) (2pi sr)(-1). High-purity fused silica has the lowest yield, approximately 6 MeVW(-1) (2pi sr)(-1). Optical-grade MgF(2)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. Phosphorescence intensity expressed as a fraction of the steady-state fluorescence intensity is an extremely sensitive measure of crystalline perfection and purity. This fraction ranges from a high of approximately 10(-2) for some fluoride samples to a low of

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

1975-09-01

361

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

NASA Astrophysics Data System (ADS)

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

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

2004-04-01

362

Spectroscopic and Laser Properties of Erbium, Uranium, and Cobalt-Doped Saturable Absorber Q-Switches at 1.5 Microns.  

NASA Astrophysics Data System (ADS)

This thesis is about the research of new solid -state saturable absorber Q-switches for eyesafe lasers. Spectroscopic and laser properties of several candidate materials were measured and theoretically modeled. Most of the work was directed toward Q-switching of the Er:glass laser at 1.53 mum. However, passive Q-switching of the Er:YAG laser at 1.64 ?m was also demonstrated. Er^{3+}:FAP and rm Er^{3+}{:}CaF _2 were the first materials examined as Q -switches for the Er:glass laser in this project. Saturation fluence measurements of these crystals indicated the need for intracavity focusing in order to achieve passive Q -switching. The absorption relaxation lifetimes were inferred from the fluorescence lifetime measurements of the ^4{rm I}_{13/2} <=vel of Er^{3+}. Problems associated with the long relaxation lifetime of this level are discussed. Saturation fluence measurements of uranium-doped di-fluoride crystals (U^{2+} in CaF_2, SrF_2, and BaF_2) revealed that the Q-switching of Er:glass could be achieved in a simple plane-parallel resonator cavity. The absorption relaxation lifetimes were obtained from measurements of the fluorescence lifetime of the rm U^{2+} ^5I_5 metastable state. Fluorescence measurements were made at several temperatures from 300 to 400 K. The identification of U^{2+ } as the active-ion responsible for 1.5 ?m Q-switching is thoroughly discussed. Uranium Q-switch experimental measurements and predictions from a rate equation model are compared. Two cobalt-doped garnet crystals, Co^ {2+}:YSGG and Co^{2+ }:YAG, were studied as well. These materials exhibit fast relaxation lifetimes, determined from pump -probe experiments. Saturation intensity measurements were made, and fast-relaxing absorber theory was applied in modeling the Q-switched Er:glass laser. A novel, near-1.5 ?m laser system was also investigated in this project. A Cr ^{4+}:YAG crystal simultaneously functioned as a passive Q-switch for a 1.06 mu m Nd:YAG laser, and as a laser at 1.44 mum. This system produced a train of 1.44 ?m pulses at a 30 kHz rate.

Stultz, Robert Dale

363

Organic-inorganic hybrid nanoparticles with enhanced rare-earth emissions  

NASA Astrophysics Data System (ADS)

LaF 3 nanoparticles were grown in aqueous solutions containing different surfactants to realize stronger absorption cross-sections and energy transfer to the optical center. Benzoic acid and phthalic acid were selected as the surfactants attached to the nanoparticles. RE-doped LaF 3 samples prepared with these surfactants showed enhanced emissions due to energy transfer from the organic ligand.

Kokuoz, Baris; Kucera, Courtney; DiMaio, Jeffrey R.; Ballato, John

2009-07-01

364

Cryogenic engineering for OMEGA2000: design and performance  

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

365

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

366

Gibbs energies of formation of intermetallic phases in the systems Pt-Mg, Pt-Ca, and Pt-Ba and some applications  

NASA Astrophysics Data System (ADS)

The standard Gibbs energies of formation of platinum-rich intermetallic compounds in the systems Pt-Mg, Pt-Ca, and Pt-Ba have been measured in the temperature range of 950 to 1200 K using solid-state galvanic cells based on MgF2, CaF2, and BaF2 as solid electrolytes. The results are summarized by the following equations: ? G° (MgPt7) = -256,100 + 16.5 T (±2000) J/mol ? G° (MgPt3) = -217,400 + 10.7 T (±2000) J/mol ? G° (CaPt5) = -297,500 + 13.0 T (±5000) J/mol ? G° (Ca2Pt7) = -551,800 + 22.3 T (±5000) J/mol ? G° (CaPt2) = -245,400 + 9.3 T (±5000) J/mol ? G° (BaPt5) = -238,700 + 8.1 T (±4000) J/mol ? G° (BaPt2) = -197,300 + 4.0 T (±4000) J/mol where solid platinum and liquid alkaline earth metals are selected as the standard states. The relatively large error estimates reflect the uncertainties in the auxiliary thermodynamic data used in the calculation. Because of the strong interaction between platinum and alkaline earth metals, it is possible to reduce oxides of Group ILA metals by hydrogen at high temperature in the presence of platinum. The alkaline earth metals can be recovered from the resulting intermetallic compounds by distillation, regenerating platinum for recycling. The platinum-slag-gas equilibration technique for the study of the activities of FeO, MnO, or Cr2O3 in slags containing MgO, CaO, or BaO is feasible provided oxygen partial pressure in the gas is maintained above that corresponding to the coexistence of Fe and “FeO.”

Jacob, K. T.; Abraham, K. P.; Ramachandran, S.

1990-06-01

367

EPR spectra and crystal field of hexamer rare-earth clusters in fluorites  

NASA Astrophysics Data System (ADS)

Disordered fluorite-related solid solutions (AF2)1-x-y (Ln'F3)x (Ln?F3)y , where A=Ca , Sr, Ba; Ln'=Er , Tm, Yb; Ln?=Lu , Y; and x?y=0.001-0.4 , were studied by both optical detection and conventional electron paramagnetic resonance (EPR) techniques. The EPR spectra of paramagnetic rare-earth ions Er3+ , Tm3+ , and Yb3+ in clusters of diamagnetic Y3+ and Lu3+ ions were recorded. It appears that the crystalline electric field at the sites of Ln ions in the clusters is of “nearly” tetragonal symmetry and provides for high values of factors g? , approaching the theoretical limits, and small values of factors g?˜0 in the ground states of the paramagnetic Ln ions. It was assumed that all the clusters of Ln ions in the solid solutions appear to be similar in structure to the hexameric clusters, which are the basic structural units of the homologous series of fluorite-related superstructures (AF2)1-y(LnF3)y with compositions y=5/m , where m is an integer in the range of 13-19. The structure of “symmetric” hexameric clusters in CaF2 , SrF2 , and BaF2 hosts was established by computer simulation. The crystalline electric field and the spectroscopic ground-state parameters for Er3+ , Tm3+ , and Yb3+ ions in the hexameric clusters were calculated and found to be in agreement with the experimental data, being totally different from those known for the “isolated” simple cubic and tetragonal centers in the fluorite crystals.

Kazanskii, S. A.; Ryskin, A. I.; Nikiforov, A. E.; Zaharov, A. Yu.; Ougrumov, M. Yu.; Shakurov, G. S.

2005-07-01

368

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

369

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

NASA Astrophysics Data System (ADS)

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

Torres, Anthony Samuel

370

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

371

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

372

Laser-excited fluorescence of rare earth elements in fluorite: Initial observations with a laser Raman microprobe  

NASA Astrophysics Data System (ADS)

Fluorescence emission spectra of three samples of fluorite containing 226-867 ppm total rare earth elements (REE) were excited by visible and ultraviolet wavelength lines of an argon ion laser and recorded with a Raman microprobe spectrometer system. Narrow emission lines (< 1 nm) due to 4f-4f electron transitions in individual trivalent REE (Pr, Nd, Sm, Eu?, Tb, Dy, Ho, Er, Tm) were observed in the wavelength range of 400-900 nm. Emission from individual REE occur in bands of overlapping lines in the wavelength intervals of 470-495 nm, 535-560 nm, 565-580 nm, 585-620 nm, 640-643 nm, 671.4 nm, and 758.2 nm. A broad band at 419 nm excited by the 363.8-nm ultraviolet line of the laser is due to a 4f-5 d transition in Eu 2+. Two bands of enigmatic origin are a narrow line at 682.8 nm present at all excitation wavelengths in only one sample and a broad band at 720 nm. We have tentatively assigned individual REE to specific lines in each emission band based on selection rules for strongly and weakly allowed 4f-4f transitions and the position of absorption and emission bands documented in the literature for REE in CaF 2 and LaF 3 host crystals. Working curves of integrated peak intensity of emission from Er 3+ and Eu 2+ vs. ppm measured by ICP-MS give linear log-log fits with R2 > 0.9 for Eu 2+ and 0.99 for Er 3+. Detection limits for three micrometer spots are about 0.01 ppm Eu 2+ and 0.07 ppm Er 3+. These limits are less than chondrite abundance for Eu and Er, demonstrating the potential microprobe analytical applications of laser-excited fluorescence of REE in fluorite. However, application of this technique to common rock-forming minerals may be hampered by competition between fluorescence emission and radiationless energy transfer processes involving lattice phonons.

Burruss, Robert C.; Ging, Tom G.; Eppinger, Robert G.; Samson, ain M.

1992-07-01

373

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films  

PubMed Central

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.

2012-01-01

374

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

375

Anion disorder in LnF 3 (Ln = La, Ce, Pr) crystals  

Microsoft Academic Search

The mechanism of lattice “melting” in tysonite-structure superionic trifluorides is analyzed in relation to the structure\\u000a of LaF3 crystals. The ion displacements within the unit cell are shown to correlate with the dynamics of the Raman scattering parameters\\u000a of the crystals. The frequency and intensity of the lines at 370, 392 (LaF3), 376, and 404 cm?1 (PrF3) show anomalous behavior

V. F. Krivorotov; P. K. Khabibullaev; Kh. T. Sharipov

2010-01-01

376

Erbium partitioning in a heavily doped transparent glass ceramic.  

PubMed

An erbium-doped transparent glass ceramic, consisting of LaF3 nanocrystallites with a characteristic length of approximately 20 nm embedded in an aluminosilicate glass matrix and exhibiting infrared-to-green up-conversion, has been studied. The degree of erbium partitioning into the nanocrystallite phase was found using energy transfer coefficients determined from bulk Er3+:LaF3 samples. This transparent glass ceramic sample was found to have a partitioning fraction of 19 +/- 5%. PMID:16127930

Jones, Gina C; Houde-Walter, S N

2005-08-15

377

Solution NMR structure of the barrier-to-autointegration factor-Emerin complex.  

PubMed

The barrier-to-autointegration factor BAF binds to the LEM domain (Em(LEM)) of the nuclear envelope protein emerin and plays an essential role in the nuclear architecture of metazoan cells. In addition, the BAF(2) dimer bridges and compacts double-stranded DNA nonspecifically via two symmetry-related DNA binding sites. In this article we present biophysical and structural studies on a complex of BAF(2) and Em(LEM). Light scattering, analytical ultracentrifugation, and NMR indicate a stoichiometry of one molecule of Em(LEM) bound per BAF(2) dimer. The equilibrium dissociation constant (K(d)) for the interaction of the BAF(2) dimer and Em(LEM), determined by isothermal titration calorimetry, is 0.59 +/- 0.03 microm. Z-exchange spectroscopy between corresponding cross-peaks of the magnetically non-equivalent subunits of the BAF(2) dimer in the complex yields a dissociation rate constant of 78 +/- 2s(-1). The solution NMR structure of the BAF(2)-Em(LEM) complex reveals that the LEM and DNA binding sites on BAF(2) are non-overlapping and that both subunits of the BAF(2) dimer contribute approximately equally to the Em(LEM) binding site. The relevance of the implications of the structural and biophysical data on the complex in the context of the interaction between the BAF(2) dimer and Em(LEM) at the nuclear envelope is discussed. PMID:17355960

Cai, Mengli; Huang, Ying; Suh, Jeong-Yong; Louis, John M; Ghirlando, Rodolfo; Craigie, Robert; Clore, G Marius

2007-05-11

378

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

PubMed

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

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

2005-05-26

379

Sum Frequency Generation Spectroscopy Study of an Ionic Liquid at a Graphene-BaF2 (111) Interface.  

PubMed

Sum frequency generation (SFG) vibrational spectroscopy and contact angle measurements of an ionic liquid, 1-butyl-3-methylimidazolium dicyanamide [BMIM][DCA], at solid-liquid interfaces are reported. Bare solid single crystal BaF2 (111) surface, a single and few layer graphene-coated BaF2 (111) surface are used as the solid substrates. The SFG results indicate that both [BMIM](+) and [DCA](-) can be detected specifically on the graphene-coated BaF2 (111) surface, without coating only [DCA](-) are observed. [DCA](-) anions are attracted to the positively charged BaF2 (111) surface and occupy the first layer at the solid-liquid interface. The graphene coating shields the charged crystal surface and allows both cations and anions to exist at the interface. Furthermore, increase in the contact angle of BaF2 surface after graphene layers deposition suggests that the graphene coating lowers the surface energy. PMID:24785472

Xu, Siyun; Xing, Sirui; Pei, Shin-Shem; Baldelli, Steven

2014-05-15

380

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

381

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

382

Non-stoichiometric BaFBr : Eu2+: a study on phase compositions and their relationship to F-centre formation  

NASA Astrophysics Data System (ADS)

Even though image plate technology is successfully applied in x-ray detection, many questions concerning its detailed functional mechanisms have still not been answered. In this paper it will be shown that a previously suggested non-stoichiometric monophase of BaF1.12Br0.88 : Eu2+ resulting from the BaF2/NH4Br preparation route cannot be supported. It will be demonstrated by x-ray analysis that depending on the starting ratio of BaF2 to NH4Br during sintering or the already synthesized BaFBr : Eu2+ to BaF2 during annealing, stoichiometric BaFBr : Eu2+ with or without a BaF2 phase will always be obtained. Furthermore, it will be shown that in the case of a molar stoichiometric starting ratio of BaF2/NH4Br, partial sublimation of NH4Br during sintering can be hold responsible for the appearance of BaF2 as a second phase. Rietveld refinement is utilized to derive the quantitative amount of the individual phase compositions of BaFBr : Eu2+ and BaF2. In terms of image plate properties, it will be shown that the composition of BaFBr : Eu2+ and BaF2 after the high temperature treatment determines the type of photostimulable colour centre generated during x-irradiation. Finally, the results obtained will be interpreted in terms of published photostimulated luminescence formation models.

Hesse, Sabine; von Seggern, Heinz

2004-03-01

383

Highly selective studies of high energy gamma-rays in ^164Er  

Microsoft Academic Search

For highly selective studies of the high energy gamma-rays from the GDR in excited nuclei, with sum-energy measurements and residual nucleus tagging, the ORNL\\/MSU\\/TAMU BaF2 array of 148 detectors has been integrated with the BGO spin\\/sum- energy spectrometer and the fragment mass analyzer (FMA) at the Argonne ATLAS facility. The high-energy gamma rays are detected in hexagonal BaF2 detectors, arranged

V. Nanal

2000-01-01

384

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

385

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

386

Neutron threshold activation detectors (TAD) for the detection of fissions  

NASA Astrophysics Data System (ADS)

Prompt fission neutrons are one of the strongest signatures of the fission process. Depending on the fission inducing radiation, their average number ranges from 2.5 to 4 neutrons per fission. They are more energetic and abundant, by about 2 orders of magnitude, than the delayed neutrons (?3 vs. ?0.01) that are commonly used as indicators for the presence of fissionable materials. The detection of fission prompt neutrons, however, has to be done in the presence of extremely intense probing radiation that stimulated them. During irradiation, the fission stimulation radiation, X-rays or neutrons, overwhelms the neutron detectors and temporarily incapacitate them. Consequently, by the time the detectors recover from the source radiation, fission prompt neutrons are no longer emitted. In order to measure the prompt fission signatures under these circumstances, special measures are usually taken with the detectors such as heavy shielding with collimation, use of inefficient geometries, high pulse height bias and gamma-neutron separation via pulse-shape discrimination with an appropriate organic scintillator. These attempts to shield the detector from the flash of radiation result in a major loss of sensitivity. It can lead to a complete inability to detect the fission prompt neutrons. In order to overcome the blinding induced background from the source radiation, the detection of prompt fission neutrons needs to occur long after the fission event and after the detector has fully recovered from the source overload. A new approach to achieve this is to detect the delayed activation induced by the fission neutrons. The approach demonstrates a good sensitivity in adverse overload situations (gamma and neutron "flash") where fission prompt neutrons could normally not be detected. The new approach achieves the required temporal separation between the detection of prompt neutrons and the detector overload by the neutron activation of the detector material. The technique, called Threshold Activation Detection (TAD), is to utilize appropriate substances that can be selectively activated by the fission neutrons and not by the source radiation and then measure the radioactively decaying activation products (typically beta and gamma rays) well after the source pulse. The activation material should possess certain properties: a suitable half-life of the order of seconds; an energy threshold below which the numerous source neutrons will not activate it (e.g., 3 MeV); easily detectable activation products (typically >1 MeV beta and gamma rays) and have a usable cross-section for the selected reaction. Ideally the substance would be a part of the scintillator. There are several good material candidates for the TAD, including fluorine, which is a major constituent of available scintillators such as BaF 2, CaF 2 and hydrogen free liquid fluorocarbon. Thus the fluorine activation products, in particular the beta particles, can be measured with a very high efficiency in the detector. The principles, applications and experimental results obtained with the fluorine based TAD are discussed.

Gozani, Tsahi; Stevenson, John; King, Michael J.

2011-10-01

387

The investigation of fast neutron Threshold Activation Detectors (TAD)  

NASA Astrophysics Data System (ADS)

The detection of fast neutrons is usually done by liquid hydrogenous organic scintillators, where the separation between the ever present gamma rays and neutrons is achieved by the pulse shape discrimination (PSD). In many practical situation the detection of fast neutrons has to be carried out while the intense source (be it neutrons, gamma rays or x-rays) that creates these neutrons, for example by the fission process, is present. This source, or ``flash'', usually blinds the neutron detectors and temporarily incapacitates them. By the time the detectors recover the prompt neutron signature does not exist. Thus to overcome the blinding background, one needs to search for processes whereby the desired signature, such as fission neutrons could in some way be measured long after the fission occurred and when the neutron detector is fully recovered from the overload. A new approach was proposed and demonstrated a good sensitivity for the detection of fast neutrons in adverse overload situations where normally it could not be done. A temporal separation of the fission event from the prompt neutrons detection is achieved via the activation process. The main idea, called Threshold Activation Detection (or detector)-TAD, is to find appropriate substances that can be selectively activated by the fission neutrons and not by the source radiation, and then measure the radioactively decaying activation products (typically beta and ?-rays) well after the source pulse has ended. The activation material should possess certain properties: a suitable half-life; an energy threshold below which the numerous source neutrons will not activate it (e.g. about 3 MeV); easily detectable activation products and has a usable cross section for the selected reaction. Ideally the substance would be part of the scintillator. There are several good candidates for TAD. The first one we have selected is based on fluorine. One of the major advantages of this element is the fact that it is a major constituent of available scintillators (e.g., BaF2, CaF2, hydrogen free liquid fluorocarbon). Thus the activation products of the fast prompt neutrons, in particular, the beta particles, can be measured with a very high efficiency in the detector. Other detectors and substances were investigated, such as 6Li and even common detectors such as NaI. The principles and experimental results obtained with F, NaI and 6Li based TAD are shown. The various contributing activation products are identified. The insensitivity of the fluorine based TAD to (d,D) neutrons is demonstrated. Ways and means to reduce or subtract the various neutron induced activations of NaI detector are elucidated along with its fast neutron detection capabilities. 6Li could also be a useful TAD.

Gozani, T.; King, M. J.; Stevenson, J.

2012-02-01

388

Spectroscopic ellipsometry investigations of Eu-doped oxy-fluoride glass and glass-ceramics  

NASA Astrophysics Data System (ADS)

Oxyfluoride glass-ceramics in the system SiO2-Al2O3-CaF2-EuF3 containing Eu3+-doped CaF2 nanocrystals were produced by using controlled crystallization of melt-quenched glass. X-ray diffraction and scanning electron microscopy data have revealed the formation of CaF2 nanocrystals of about 50 nm size. The Eu3+-dopant ions act as the nucleating agent necessary to initiate the crystallization process. The refractive index is higher in the glass ceramics than in the initial glass and varies as the annealing time increases. Two competitive processes are responsible for this behavior, the crystallization of the CaF2 phase and the decrease of the glass ceramic mass density.

Galca, A. C.; Preda, N.; Secu, C. E.; Luculescu, C. R.; Secu, M.

2012-06-01

389

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

PubMed

The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 30 d are examined. Glow peaks were fit to the first-order kinetics model using a computerized glow curve deconvolution program. Dosimeters studied were LiF:Mg,Ti, CaF(2):Dy, CaF(2):Tm, CaF(2):Mn, LiF:Mg,Cu,P, and CaSO(4):Dy. LiF:Mg,Ti and LiF:Mg,Cu,P experienced significant pre-irradiation fading. All types except CaF(2):Mn experienced post-irradiation fading. Ratios of glow-peak areas were fit to exponential decay functions when possible. PMID:20554212

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

2010-10-01

390

Fe–Te–Se epitaxial thin films with enhanced superconducting properties  

Microsoft Academic Search

Epitaxial Fe–Te–Se thin films were deposited by pulsed laser deposition at 250–600 °C on SrTiO3 (100), MgO (100), LaAlO3 (100) and CaF2 (100) single crystal substrates. The best superconducting film was grown on CaF2: K and K with Tdep = 300 °C and 3 Hz. Critical current density Jc (T = 4.2 K) was 0.41 × 106 A cm?2 at

Paolo Mele; Kaname Matsumoto; Kouhei Fujita; Yutaka Yoshida; Takanobu Kiss; Ataru Ichinose; Masashi Mukaida

2012-01-01

391

Luminescence during Eu-implantation into calcium fluoride  

Microsoft Academic Search

A study has been made of luminescence of Eu-implanted CaF2 as a function of the Eu-dose. The Eu-implantation into (111) oriented CaF2 at a random direction was performed with doses ranging from 1012 to 1016 ions\\/cm2 at an energy of 100 keV at nearly room temperature. We observed luminescence from the substrate during Eu-implantation, which is blue at a dose

Keiko Aono; Masaya Iwaki; Susumu Namba

1988-01-01

392

Preparation and optimization of calcium fluoride particles for dental applications.  

PubMed

Fluorides are used in dental care due to their beneficial effect in tooth enamel de-/remineralization cycles. To achieve a desired constant supply of soluble fluorides in the oral cavity, different approaches have been followed. Here we present results on the preparation of CaF2 particles and their characterization with respect to a potential application as enamel associated fluoride releasing reservoirs. CaF2 particles were synthesized by precipitation from soluble NaF and CaCl2 salt solutions of defined concentrations and their morphology analyzed by scanning electron microscopy. CaF2 particles with defined sizes and shapes could be synthesized by adjusting the concentrations of the precursor salt solutions. Such particles interacted with enamel surfaces when applied at fluoride concentrations correlating to typical dental care products. Fluoride release from the synthesized CaF2 particles was observed to be largely influenced by the concentration of phosphate in the solution. Physiological solutions with phosphate concentration similar to saliva (3.5 mM) reduced the fluoride release from pure CaF2 particles by a factor of 10-20 × as compared to phosphate free buffer solutions. Fluoride release was even lower in human saliva. The fluoride release could be increased by the addition of phosphate in substoichiometric amounts during CaF2 particle synthesis. The presented results demonstrate that the morphology and fluoride release characteristics of CaF2 particles can be tuned and provide evidence of the suitability of synthetic CaF2 particles as enamel associated fluoride reservoirs. PMID:24682907

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

2014-07-01

393

Control of oxygen contamination during the growth of optical calcium fluoride and calcium strontium fluoride crystals  

Microsoft Academic Search

The progress, current state, and prognosis for CaF2 as an optical material with wide applicability are reviewed by outlining the basic issues: technology, demand, supply, and metrology. To achieve perfect quality for all application grades of CaF2 grown using a natural fluorite, investigations of the effect of PbF2 and ZnF2 scavengers for removal of oxygen contaminants from the starting material,

J. T. Mouhovski

2007-01-01

394

Influence of Er,Cr:YSGG laser on CaF? -like products formation because of professional acidulated fluoride or to domestic dentifrice application.  

PubMed

This study evaluated the synergy of professional acidulated fluoride gel (APF) or fluoridated dentifrice application combined with Er,Cr:YSGG laser irradiation on the formation of CaF2 -like products (CaF2 ), in vitro. Thus, 272 bovine enamel slabs were randomly distributed among eight groups: G1: untreated enamel; G2: treated with fluoridated dentifrice (NaF, 1,100 ?gF/g); G3: treated with acidulated phosphate fluoride gel (APF, 1.23% F(-) ); G4: irradiated with Er,Cr:YSGG laser at 8.5 J/cm(2) ; G5 and G6: combination of pre-irradiation with Er,Cr:YSGG followed by dentifrice or APF application, respectively; G7: combination of dentifrice application followed by Er,Cr:YSGG irradiation; G8: combination of APF application followed by Er,Cr:YSGG irradiation. After treatments, samples were evaluated by scanning electron microscopy, and the content of CaF2 was determined by an ion specific electrode. Both APF and dentifrice application promoted the formation of CaF2 on enamel, whereas Er,Cr:YSGG irradiation promoted an increase of roughness of the enamel, increasing the surface area. Laser irradiation before fluoridated products increased the content of CaF2 formed when compared to groups that APF or dentifrice were applied isolated. However, the content of CaF2 formed when irradiation was performed after APF or dentifrice was not statically significant when compared to the control groups. In conclusion, Er,Cr:YSGG laser increases the formation of CaF2 on enamel when the irradiation is performed before the application of APF or dentifrice. The association of laser with APF is most promissory for caries prevention because of the higher concentration of CaF2 formation and also the chemical changes promoted by laser irradiation demonstrated in literature. PMID:23630046

Zamataro, Claudia Bianchi; Ana, Patricia Aparecida; Benetti, Carolina; Zezell, Denise Maria

2013-07-01

395

Identification of salt-alloy combinations for thermal energy storage applications in advanced solar dynamic power systems  

Microsoft Academic Search

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,

J. D. Whittenberger; A. K. Misra

1987-01-01

396

The response of a thermoluminescent dosimeter to low energy protons in the range 30–100 keV  

Microsoft Academic Search

This study demonstrates the thermoluminescence (TL) response of CaF2:Tm (commercial name TLD-300) to 30–100keV protons which were generated by means of a Cockcroft–Walton accelerator. The phenomenon in which the total thermoluminescent output from CaF2:Tm (TLD-300) decreases with proton energy from 30 to 100keV (with increase of LET) can be interpreted by the track structure theory (TST). The analysis of the

Tieh-Chi Chu; Sung-Yen Lin; Chu-Chung Hsu; Jao-Perng Lin

2001-01-01

397

Propagation and nanofocusing of infrared surface plasmons on tapered transmission lines: Influence of the substrate  

NASA Astrophysics Data System (ADS)

We study the propagation of mid-infrared surface plasmons on non-tapered and tapered two-wire transmission lines on Si and CaF2 substrates, the two materials representing substrates with large and small refractive index, respectively. A comparative numerical study predicts a larger effective wavelength and an increased propagation length (i.e. weaker damping) for the CaF2 substrate. By near-field microscopy we image the near-field distribution along the transmission lines and experimentally verify surface plasmon propagation. Amplitude- and phase-resolved near-field images of a non-tapered transmission line on CaF2 reveal a standing wave pattern caused by back-reflection of the surface plasmons at the open-ended transmission line. Calculated and experimental near-field images of tapered transmission lines on Si and CaF2 demonstrate that for both substrates the mid-IR surface plasmons are compressed when propagating along the taper. Importantly, the nanofocus at the taper apex yields a stronger local field enhancement for the low-refractive index substrate CaF2. We assign the more efficient nanofocusing on CaF2 to the weaker damping of the surface plasmons.

Sarriugarte, P.; Schnell, M.; Alonso-González, P.; Arzubiaga, L.; Golmar, F.; Casanova, F.; Hueso, L. E.; Hillenbrand, R.

2012-07-01

398

Substrate Engineering for Microelectronic Devices: Molecular Beam Epitaxial Growth of Gallium Arsenide on Calcium FLUORIDE/SILICON(111) Substrates  

NASA Astrophysics Data System (ADS)

This thesis addresses the issue of residual strain in heteroepitaxial layers due to lattice mismatch and thermal expansion coefficient mismatch. In particular, we have tried to solve this problem in desirable heteroepitaxial layers by introducing a CaF_2 strain relaxation buffer. My research focuses on molecular beam epitaxial (MBE) growth of GaAs on CaF_2 /Si(111) substrates. In the thesis, three topics are chosen to be discussed in detail: (1) strain relaxation behavior in epitaxial group-IIa fluoride films, (2) GaAs nucleation on the (111) CaF_2 surface, and (3) optimization of epitaxial growth conditions for GaAs on CaF_2/Si(111) substrates. Residual tensile strain in SrF_2 films has been measured and plotted versus film thickness. An equilibrium force-balance model with a frictional force was proposed to interpret the experimental data. Stress in the CaF_2/Si(111) and SrF _2/Si(111) systems was also measured during thermal cycling from RT to 650^circ C. Both the residual strain versus film thickness and the stress versus temperature show that CaF _2/Si(111) system behaves very differently in strain relaxation than the SrF_2/Si(111) system. In SrF_2 films, residual strain remains even if the film is thicker than 6000A unlike CaF_2 on Si(111) for which CaF _2 films thicker than 3000A are observed to have no strain. It has been observed that, under certain conditions, a chemical reaction between As adatoms and CaF _2 layers can be induced, by which a stable As layer forms on the CaF_2 surface. This As layer modifies the CaF_2 surface free energy and, if properly controlled, leads to 2D nucleation of GaAs on the CaF_2/Si(111) surface as opposed to the more commonly observed 3D growth. A nucleation mode has been proposed to understand the phenomenon. Two kinds of twins have been observed in GaAs films grown on CaF_2/Si(111) substrates: micro-twins and rotational twins. The methods to suppress the formation of twins have been demonstrated. Three growth regimes have been distinguished for epitaxial growth of GaAs on CaF_2/Si(111) substrates. MBE growth conditions for GaAs on CaF _2/Si(111) were optimized. Under the optimal growth condition, excellent crystal quality of GaAs films was achieved (a minimum ion channeling yield of 3.5% is achieved at the GaAs surface) along with specular surface morphology. These GaAs films also exhibit fairly high Hall mobility (mu_{rm n } = 1640 rm cm^2/V{cdot }sec with doping level equal to 3 times 10^{17} cm^{-3}).

Li, Weidan

399

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

400

Nanocrystallization in Fluorochlorozirconate Glass-Ceramics  

PubMed Central

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

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

2014-01-01

401

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

402

Experimental test of the optical Bloch equations for solids using free-induction decay  

NASA Astrophysics Data System (ADS)

Recent studies by DeVoe and Brewer [Phys. Rev. Lett. 50, 1269 (1983)] have shown that the conventional optical Bloch equations markedly fail to describe the optical saturation behavior of the D1 line in the solid Pr3+:LaF3. In this paper we extend these studies to another solid, ruby, using free-induction-decay observations obtained by pulse excitation of the R1 line at 693.4 nm with an ultranarrow-linewidth dye laser. Comparison of the results with Gauss-Markov and random-telegraph-dephasing theories shows approximate agreement for a fluctuation correlation time ?c=T2, the dephasing time. This result is remarkably similar to that obtained for Pr3+:LaF3. However, for theoretical and experimental reasons, we conclude that the theories do not consistently explain the current as well as other data. A qualitative discussion of another dephasing model is given.

Szabo, A.; Muramoto, T.

1989-04-01

403

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

404

Fluorescence decay dynamics of surface-functionalized nanoparticles  

Microsoft Academic Search

We report the fluorescence decay dynamics of surface-functionalized nanoparticles (NPs), poly(ethylene glycol) bis(carboxymethyl) ether coated LaF3: Ce,Tb and thioglycolic acid coated ZnS:Mn, in solution and also in the surface-bound phase. The NPs exhibited high quantum yield and multi-component decays, and of average lifetime of 20-130 microseconds in solution, but 10-60 microseconds in the bound phase depending on the solid substrates.

Jacob Ajimo; Lun Ma; Mingzhen Yao; Xing Zhang; John Como; Juyang Huang; Wei Chen; Kwan Cheng

2008-01-01

405

UV-laser investigation of dielectric thin films  

Microsoft Academic Search

Utilizing thermal Mirage technique, UV laser damage resistivity studies on LaF3\\/MgF2, Al2O3\\/SiO2, and HfO2\\/SiO2 multilayer stacks have been performed at (lambda) equals 248 nm, (tau) equals 20 ns. Investigating these stacks by changing the number of (HL) pairs and the substrate material, optical and thermal coating properties were shown to be responsible for UV single-shot laser damage. Similarly, the damage

K. Ettrich; H. Blaschke; Eberhard Welsch; Peter Thomsen-Schmidt; Dieter Schaefer

1996-01-01

406

Superionic phase transition of doped fluorites  

Microsoft Academic Search

In this paper we present new results of specific-heat experiments on superionic mixtures of cubic lead fluoride and some rare-earth fluorides. The results depend very strongly on the rare-earth ion; for samples doped with LaF3 we observe a peak in the specific heat as a function of T, which is located at an approximately fixed position. This peak, which is

H. W. den Hartog; J. van der Veen

1988-01-01

407

Scintillation mechanisms in cerium fluoride  

Microsoft Academic Search

Ultraviolet photoelectron spectroscopy, optical transmission, fluorescence excitation spectroscopy, and time-resolved fluorescence spectroscopy are used to investigate the scintillation mechanisms of cerium fluoride (CeF 3) and of lanthanum fluoride doped with cerium in concentration s between 0.01% and 50% mole fraction cerium. In LaF 3:Ce the absorption of either optical or ionizing radiation directly or indirectly results in excitation of the

W. W. Moses; S. E. Derenzo; M. J. Weber; A. K. Ray-Chaudhuri; F. Cerrina

1994-01-01

408

Time-resolved spectroscopy of 5d-4f transitions in Pr3+ doped alkali-earth fluorides  

Microsoft Academic Search

We measured time-resolved spectra and emission decay times under pulsed X-ray and synchrotron excitation in alkali-earth fluorides doped with Pr3+ ions. Two fast decay components were found in the emission spectra of BaF2-Pr3+ and SrF2-Pr3+ . These were 4 ns and 21 ns in BaF2-Pr3+ and 8 and 24 ns in SrF2-Pr3+. The intensity of the faster components 4 ns

R. Shendrik; E. Radzhabov; V. Nagirnyi

2010-01-01

409

Positron annihilation study on ZnO-based scintillating glasses  

Microsoft Academic Search

Positron lifetime of ZnO-based scintillating glasses (55?x)SiO2–45ZnO–xBaF2 (x=5, 10, 15mol%) were measured with a conventional fast–fast spectrometer. Three positron lifetime components ?1, ?2, and ?3 are ?0.23ns, ?0.45ns, and ?1.6ns, respectively. All the three positron lifetime components first increase with increasing BaF2 concentration from 5mol% to 10mol%, then decreases as BaF2 further increases to 15mol%. The result suggests that the

Jiaxiang Nie; Runsheng Yu; Baoyi Wang; Yuwen Ou; Yurong Zhong; Fang Xia; Guorong Chen

2009-01-01

410

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

411

The ion-assisted deposition of optical thin films  

NASA Astrophysics Data System (ADS)

The columnar microstructure of most thermally evaporated thin films detrimentally affects many of their properties through a reduction in packing density. In this work, we have investigated ion-assisted deposition as a means of disrupting this columnar growth for a number of coating materials. A Kaufman hot-cathode ion source bombarded thermally evaporated films with low-energy (less than 1000 eV) positive ions during deposition in a cryopumped box coater. We have investigated MgF2, Na3AIF6, AIF3, LaF3, CeF3, NdF3, Al2O3, and AlN. Argon ion bombardment of the fluoride coatings increased their packing densities dramatically. We achieved packing densities near unity without significant absorption for MgF2, LaF3, and NdF3, while Na3AlF6, AlF3, and CeF3 began to absorb before unity packing density could be achieved. Fluorine was preferentially sputtered by the ion bombardment, creating anion vacancies. The films adsorbed water vapor and hydroxyl radicals from the residual chamber atmosphere. These filled the vacancy sites, eliminating absorption in the visible, but the oxygen complexes caused increased absorption in the ultraviolet. For LaF3 and NdF3, a sufficient amount of oxygen caused a phase transformation from the fluoride phase to an oxyfluoride phase.

Targove, James D.

412

Structural, thermal, and luminescence properties of cerium-fluoride-rich oxyfluoride glasses  

NASA Astrophysics Data System (ADS)

Oxyfluoride aluminosilicate glasses containing a high nominal concentration of 35 mol% LaF3 and CeF3 were synthesized, and their structural, thermal, optical absorption, photoluminescence, radio-luminescence, and excited-state relaxation properties were investigated. The structural analysis confirms the amorphous nature of the glasses and finds up to 21 mol% of retained dissolved LaF3 and CeF3. Tetrahedral Si and Al units as well as Si-O-Si and Al-O functional groups are identified. Fluorine is found to replace bridging oxygens and to form both Si-F and Al-F bonds. Glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm) were determined from the DSC thermograms. The CeF3-doped glasses show spectrally broad 5d ? 4f luminescence in the violet-blue (centered around 402 nm) under both direct optical excitation of Ce3+ at 335 nm and X-ray excitation at 25 keV. The relative quantum yield was found to decrease with increasing CeF3 concentration due to energy transfer to residual Ce4+ ions or to Ce3+ coordinated to hydroxyl (OH) impurities followed by non-radiative relaxation. The studied glasses are promising starting materials for the fabrication of glass-ceramics with a high volume fraction of LaF3:Ce3+ nano-crystals.

Lakshminarayana, G.; Weis, Eric M.; Bennett, Bryan L.; Labouriau, Andrea; Williams, Darrick J.; Duque, Juan G.; Sheik-Bahae, Mansoor; Hehlen, Markus P.

2012-12-01

413

Pulsed D2-F2 chain-laser damage to coated window and mirror components  

NASA Astrophysics Data System (ADS)

Large-spot laser damage thresholds were measured for bowl-feed-polished CaF2 and sapphire windows (bare and antireflection-coated) and for highly polished copper mirrors (bare and carbyne-coated) at DF chain-laser wavelengths (3.58-4.78 micrometers). The chain reaction between F2 and D2 was initiated by a magnetically confined electron beam, producing DF-laser outputs of 10 to 20 J in pulses of 0.6 to 0.9 microseconds (FWHM) duration. Energy extracted from a transmission-coupled unstable resonator was focused by means of a CaF2 lens. A soft-aperture technique was employed to suppress effects of Fresnel diffraction so that uniform (top-hat) intensity profiles were obtained along the focusing beam. With this laser system, commercially available antireflection-coated CaF2 and Al2O3 samples were tested and found to have damage thresholds from 17 to 28 J/sq cm 2. Significantly larger damage thresholds were observed for uncoated, polished samples of Al2O3, but damage resistance of uncoated polished CaF2 was found to equal that of the best antireflection-coated CaF2 samples. A highly polished copper mirror had the highest damage threshold of all the materials tested, i.e., 58 J/sq cm 2.

Amimoto, S. T.; Whittier, J. S.; Whittaker, A.; Chase, A.; Hofland, R., Jr.

1983-12-01

414

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

415

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

416

Teflon FEP-clad fluoride glass fibre  

NASA Astrophysics Data System (ADS)

A mid infra-red optical fiber has been developed employing perfluoronated ethylene propylene (teflon FEP) as the cladding and BaF2-GdF3-ZrF4-AlF3 glass as the core. The minimum transmission loss was 0.37 dB/m, measured at 2.55 microns for a 24 m long fiber.

Mitachi, S.; Shibata, S.; Manabe, T.

1981-02-01

417

A fluoride glass optical fiber operating in the mid-infrared wavelength range  

Microsoft Academic Search

An optical fiber operating in the mid-infrared wavelength range is fabricated using ZrF4-based fluoride glass. Material purification, the fiber fabrication process, and transmission properties are presented. The starting materials, ZrF4, BaF2, GdF3, AlF3, and SbF3are carefully purified by sublimation techniques. The \\

SEIKO MITACHI; YASUTAKE OHISHI; TADASHI MIYASHITA

1983-01-01

418

Mechanisms for Species-Selective Oriented Crystal Growth at Organic Templates  

SciTech Connect

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

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

2007-01-01

419

Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis  

NASA Astrophysics Data System (ADS)

Temperatures for primary crystallization of Na3AlF6 in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na3AlF6 was derived: begin{gathered} t/(^circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - {3.45[CaF_2 ]}/{1 + 0.0173[CaF_2 ]} \\ + 0.124[CaF_2 ] \\cdot [AlF_3 ] - 0.00542([CaF_2 ] \\cdot [AlF_3 ])^{1.5} \\ - {7.93[Al_2 O_3 ]}/{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \\cdot [Al_2 O_3 ]} \\ - {8.90[LiF]}/{1 + 0.0047[LiF] + 0.0010[AlF3]^2 } - 3.95[MgF_2 ] - 3.95 \\ where t is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na3AlF6-AlF3-CaF2-Al2O3-LiF-MgF2-KF. The composition limitations are [AlF3] ? [CaF2] ? [LiF] < 20 wt pct, [MgF2] ? [KF] < 5 wt pct, and [A12O3] up to saturation.

Solheim, Asbjørn; Rolseth, Sverre; Skybakmoen, Egil; Støen, Lisbet; Sterten, Åsmund; Støre, Trond

1996-10-01

420

No Calcium-Fluoride-Like Deposits Detected in Plaque Shortly after a Sodium Fluoride Mouthrinse  

PubMed Central

Plaque ‘calcium-fluoride-like’ (CaF2-like) and fluoride deposits held by biological/bacterial calcium fluoride (Ca-F) bonds appear to be the source of cariostatic concentrations of fluoride in plaque fluid. The aim of this study was to quantify the amounts of plaque fluoride held in these reservoirs after a sodium fluoride rinse. 30 and 60 min after a 228 ?g/g fluoride rinse, plaque samples were collected from 11 volunteers. Each sample was homogenized, split into 2 aliquots (aliquots 1 and 2), centrifuged, and the recovered plaque fluid combined and analyzed using microelectrodes. The plaque mass from aliquot 1 was retained. The plaque mass from aliquot 2 was extracted several times with a solution having the same fluoride, calcium and pH as the plaque fluid in order to extract the plaque CaF2-like deposits. The total fluoride in both aliquots was then determined. In a second experiment, the extraction completeness was examined by applying the above procedure to in vitro precipitates containing known amounts of CaF2-like deposits. Nearly identical fluoride concentrations were found in both plaque aliquots. The extraction of the CaF2-like precipitates formed in vitro removed more than 80% of these deposits. The results suggest that either CaF2-like deposits were not formed in plaque or, if these deposits had been formed, they were rapidly lost. The inability to form persistent amounts of CaF2-like deposits in plaque may account for the relatively rapid loss of plaque fluid fluoride after the use of conventional fluoride dentifrices or rinses.

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

2010-01-01

421

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

PubMed

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

Liu, Wei-Ting; Li, Kung-Cheh

2011-01-01

422

Skylab ultraviolet stellar astronomy experiment S019  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

423

Femtosecond Vibrational Spectroscopy and Dynamics of Amphiphilic Monolayers at the Solid/Gas and Solid/Liquid Interfaces.  

NASA Astrophysics Data System (ADS)

We employ nonlinear optical probes to examine the structure and dynamics of amphiphillic monolayers at the CaF2/Air and CaF2/D2O interfaces. Broadband femtosecond sum frequency generation has been used to obtain frequency domain spectra, polarization dynamics and vibrational lifetimes of the amphiphile vibrational modes. The time-resolved sum frequency response displays coherent nuclear motion. Both the coherence and vibrational excitation decay on time scales determined by the nature of the interface environment, the degree of solvation and level of surface inhomogeneity.

Johannson, Tom; Leach, Gary W.

2003-03-01

424

Identification of salt—Alloy combinations for thermal energy storage applications in advanced solar dynamic power systems  

Microsoft Academic Search

.  Thermodynamic calculations based on the available data for flouride salt systems reveal that a number of congruently melting\\u000a compositions and eutectics exist which have the potential to meet the lightweight, high energy storage requirements imposed\\u000a for advanced solar dynamic systems operating between ?1000 and 1400 K. Compatibility studies to determine suitable containment\\u000a alloys to be used with NaF-22CaF2-13MgF2, NaF-32CaF2, and

J. D. Whittenberger; A. K. Misra

1987-01-01

425

New absorption bands in fluorites by heavy gamma irradiation  

Microsoft Academic Search

At least three new bands have been observed in the near infrared region of the absorption spectra of fluorites of different origin after heavy gamma irradiation in the range 106 to 109 R. Studies were also made with a sample of synthetically pure CaF2 crystal and the results indicate that the rare earth impurities abundantly present in the fluorites play

K. S. V. Nambi; T. Higashimura

1971-01-01

426

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

427

Positron Annihilation and Electronic Lattice Structure in Insulator Crystals  

Microsoft Academic Search

The dimensions of the electronic lattice structure of the hexagonal quartz crystal and the fcc CaF2 crystal have been measured by resolving characteristic markings on the angular-correlation curves as observed for the two gamma quanta emitted in the annihilation of positrons with electrons in these crystals.

Werner Brandt; Gérard Coussot; Robert Paulin

1969-01-01

428

Calcium fluoride formation on sound enamel using fluoride solutions with and without lactate.  

PubMed

The formation of calcium (Ca) fluoride (CaF2) on bovine enamel blocks during clinically relevant treatment times using neutral fluoride (F) solutions (0.26 mol/l F) with and without 0.1 mol/l lactate was investigated. Uncoated and pellicle-coated blocks were evaluated for alkali-soluble (1 mol/l KOH, three consecutive 24-hour treatments) Ca, PO4, and F after treatment by the F solutions for 0, 5, 15, 30, and 60 min. There was an overall time-related increase in F recovery, while Ca tended to remain at baseline levels. Less F was recovered from the pellicle-coated blocks. The addition of lactate to the F treatment solution did not result in an overall increase in alkali-soluble F recovery, but did result in the formation of cuboidal shaped crystals which closely approached the morphology of pure CaF2. A 1:2 stoichiometric ratio Ca:2F (mol:mol) was not established based on chemical analyses. The ultrastructural and elemental composition of surface deposits on the samples, as determined using scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy, established the presence of CaF2 after 24-hour F treatments; however, it was not possible to directly demonstrate the formation of CaF2 after clinically relevant treatment times. PMID:8124691

Harding, A M; Zero, D T; Featherstone, J D; McCormack, S M; Shields, C P; Proskin, H M

1994-01-01

429

Selective reflection spectroscopy at the interface between a calcium fluoride window and Cs vapour  

NASA Astrophysics Data System (ADS)

A special vapour cell has been built, that allows the measurement of the atom-surface van der Waals interaction exerted by a CaF2 window at the interface with Cs vapour. Mechanical and thermal fragility of fluoride windows make common designs of vapour cells impractical, so that we have developed an all-sapphire sealed cell with an internal CaF2 window. Although some impurities have remained when filling up the prototype cell, leading to line broadening and a shift, the selective reflection spectrum of the Cs D1 line (894 nm) makes apparent the weak van der Waals surface interaction. The uncertainties introduced by the effects of these impurities in the van der Waals measurement are nearly eliminated when comparing the selective reflection signal at the CaF2 interface of interest and at a sapphire window of the same cell. The ratio of the interactions respectively exerted by a sapphire interface and a CaF2 interface is found to be 0.55±0.25, in good agreement with the theoretical evaluation of ˜0.67.

Laliotis, A.; Maurin, I.; Fichet, M.; Bloch, D.; Ducloy, M.; Balasanyan, N.; Sarkisyan, A.; Sarkisyan, D.

2008-03-01

430

Calibration-Free Electrical Conductivity Measurements for Highly Conductive Slags;Metallurgical Transactions B.  

National Technical Information Service (NTIS)

This research involves the measurement of the electrical conductivity (k) for the ESR (electroslag remelting) slag (60 wt.% CaF2 - 20 wt.% CaO - 20 wt.% Al2O3) used in the decontamination of radioactive stainless steel. The electrical conductivity is meas...

Macdonald Gao Pal Van Den Avyle Melgaard

2000-01-01

431

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

432

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.

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

2008-01-01

433

In vivo effects of fluoride on enamel permeability.  

PubMed

This in vivo study evaluated the effects of topical fluoride application on enamel by repeated scanning electron microscopy analysis of replicas. Baseline fluid droplets were employed as qualitative indication of enamel permeability. CaF(2)-like globules were detected in vivo after fluoride application and were not found after professional brushing, ultrasound action, or chemical extraction. Absence of water permeability of enamel was demonstrated even after removal of CaF(2)-like globules. Droplets reappeared within 1 h in sodium fluoride-treated teeth, but they did not reappear even after 1 week following topical enamel treatment with acidulated phosphate fluoride. Teeth treated with an acidulate fluoride-free solution showed lack of CaF(2)-like globules and no droplets for at least 1 week as detected in acidulate phosphate fluoride-treated teeth. The caries-preventing action of fluoride may be due to its ability to decrease permeability and diffusion pathways. CaF(2)-like globules seem to be indirectly involved in enamel protection over time maintaining an impermeable barrier, and phosphoric acid seemed to play an unexpected fluoride-independent preventive role. PMID:20372949

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

2011-08-01

434

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

435

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

436

Divalent cerium and praseodymium ions in crystals of alkaline-earth fluorides  

NASA Astrophysics Data System (ADS)

We have studied the absorption spectra of radiation-induced divalent cerium and praseodymium ions in crystals of alkaline-earth fluorides. Using ab initio quantum-mechanical methods, we have calculated absorption spectra of divalent praseodymium ions in CaF2 crystals for the first time. The theoretical spectrum agrees rather well with the experimentally registered spectra.

Shendrik, R. Yu.; Myasnikova, A. S.; Egranov, A. V.; Radzhabov, E. A.

2014-05-01

437

Cavity ring-down spectroscopy in the ultraviolet region using calcium fluoride prism retroreflectors  

NASA Astrophysics Data System (ADS)

Cavity ring-down spectroscopy (CRDS) is a highly sensitive laser absorption technique that is useful for trace species detection of atoms and molecules in a range of applications. High sensitivity CRDS detection requires highly reflective mirrors, typically multilayer dielectrics. Such mirrors are available in many spectral regions, though not in the ultraviolet (UV) where optical absorption in the mirror layers tends to limit reflectivities. In our electric propulsion research, detection of boron nitride (BN) via ground state boron atoms near 250 nm is of particular interest. In order to improve the sensitivity of UV CRDS for BN detection, we are developing the use of prism retroreflectors made from calcium fluoride (CaF2). In addition to higher cavity finesse at 250 nm, total internal reflection allows for broadband CRDS with a single experimental setup. We have obtained super-polished UV grade CaF2 samples in order to make transmission measurements. The measurements are obtained by placing the CaF2 samples as loss elements within a CRDS cavity. In this contribution, we present the measurement setup and results of initial CaF2 material characterizations.

Lee, Brian; Yalin, Azer

2009-10-01

438

Evidence for long-range interactions between rare-earth impurity ions in nanocrystals embedded in amorphous matrices with the two-level systems of the matrix  

NASA Astrophysics Data System (ADS)

The low-temperature homogeneous broadening of the electronic transitions of Eu3+ and Pr3+ rare-earth impurity ions in Y2O3 and LaF3 nanocrystals embedded into amorphous materials (polymer and oxyfluoride glass ceramics) was studied with hole-burning and fluorescence line narrowing techniques. It is shown that the homogeneous linewidth is determined by the interaction of the impurity ions contained in the nanocrystals with the two-level systems (TLS's) of the surrounding glass matrix. A comparison of the experiments with a calculation provides direct evidence for the long-range nature of the interaction with the TLS's.

Meltzer, R. S.; Yen, W. M.; Zheng, Hairong; Feofilov, S. P.; Dejneka, M. J.; Tissue, B. M.; Yuan, H. B.

2001-09-01

439

Optical properties and damage thresholds of dielectric UV\\/VUV coatings deposited by conventional evaporation, IAD, and IBS  

Microsoft Academic Search

Conventional evaporation as well as IAD and IBS processes were used to develop low-loss dielectric mirrors and antireflection coatings for the wavelength range 130 to 250 nm. First, single layers of SiO2, Al2O3, HfO2, AlF3, MgF2, LaF3, NdF3, and GdF3 were deposited. The refractive indices, extinction coefficients and packing densities of the layers were determined by spectrophotometric methods in order

Jurgen Kolbe; H. Kessler; T. Hofmann; F. Meyer; Harald Schink; Detlev Ristau

1992-01-01

440

Phase transition control, melt growth of (Gd,RE)F 3 single crystal and their luminescent properties  

Microsoft Academic Search

Rare-earth sesquifluorides with no absorption in visible spectral region, such as LaF3, GdF3, LuF3, YF3, ScF3, are the topic of intense study as a host for luminescence materials. However, except Nd:LaF3, they are not studied as a host for laser materials. The main obstacle troubling further study of GdF3, LuF3, YF3, ScF3 single crystal is the fact that there is

Akira Yoshikawa; Anis Jouini; Kei Kamada; Georges Boulon; Martin Nikl; Fumio Saito

2009-01-01

441

Terbium-activated lithium–lanthanum–aluminosilicate oxyfluoride scintillating glass and glass-ceramic  

Microsoft Academic Search

Terbium-activated lithium–lanthanum–aluminosilicate oxyfluoride scintillating glasses, 55SiO2·6Al2O3·28Li2O·11LaF3 doped with different TbF3 concentrations, have been fabricated and investigated. By appropriate heat treatment of the as-prepared glasses above, transparent glass-ceramics were obtained. Differential scanning calorimetry, X-ray diffraction, optical absorption, and luminescence under both UV and beta-particle excitation have been investigated on as-prepared glasses and glass-ceramics. It has been found that these terbium-activated lithium–lanthanum–aluminosilicate

Z. Pan; K. James; Y. Cui; A. Burger; N. Cherepy; S. A. Payne; R. Mu; S. H. Morgan

2008-01-01

442

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

443

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

444

On ``anomalous'' free induction decay rate  

NASA Astrophysics Data System (ADS)

Generalized non-markovian master equations, which take into account the nonvanishing bath correlation time ? c, are used to explain the "anomalous" (which cannot be described by the well-known Bloch master equations) behaviour of the optical free induction decay recently observed by DeVoe and Brewer [Phys. Rev. Lett. 50 (1983) 1269] for the Pr 3+: LaF 3 at T ? 1.6 K. We found ? c = 5 ?s to be the best fit of our theory to the above experiment provided that T1 = 100 ?s, T2 = 24 ?s. New experimental tests of the non-markovian relaxation theory are proposed.

Apanasevich, P. A.; Kilin, S. Ya.; Nizovtsev, A. P.; Onishchenko, N. S.

1984-12-01

445

Spectral hole burning in thulium-doped glass ceramics.  

PubMed

We have used spectral hole burning to measure the homogeneous linewidth of the (3)H(6)(1)- (3)F(3)(1) transition of Tm(3+) ions doped into oxyfluoride glass ceramics consisting of nanocrystals of LaF(3) in an aluminosilicate glass matrix. From the magnitude of the hole width in the nanocrystals and its dependence on temperature, we propose that excitation of tunneling modes in the adjacent glassy phase as well as of confined mechanical modes in the nanocrystals is responsible for the broadening. PMID:18040343

Macfarlane, R M; Dejneka, M J

2001-04-01

446

Degenerate photon echoes - Simultaneous storage of multiple optical data  

NASA Astrophysics Data System (ADS)

It is shown that simultaneous and spatially overlapping multiple photon echoes can occur following application of a single optical pulse followed by multiple pairs of couterpropagating pulses in various directions (degenerate photon echoes). This scheme has been experimentally verified in Pr(3+):LaF3 for the doubly degenerate case. In the small-pulse-area regime, the two echoes are observed to be independent with no cross talk between them. From the viewpoint of transient optical memory, this makes it possible to store multiple independent optical data in one sample spot and to retrieve any one of them, thereby multiplying the memory capacity of the crystal.

Mitsunaga, M.; Kim, M. K.; Kachru, R.

1988-06-01

447

Bond-orbital theory of electronic response in the alkaline earth halides  

NASA Astrophysics Data System (ADS)

Materials characterization for optical device purposes relies heavily upon a knowledge of material compliances related to dielectric response. This paper applies the bond orbital theory of dielectric response, developed earlier for high symmetry pretransition metal halides and chalcogenides, to the alkaline earth halides, thereby testing its validity in a wider context embracing systems with both high and low local anionic symmetry. After verifying that the primary finding of the theory remains quantitative for linear response in the more general context, nonlinear response (in the form of nonlinear refractive index n2) is calculated and tabulated for the complete series of alkaline earth halides and for LaF 3.

Lines, M. E.

1990-09-01

448

Application of the Tauc-Lorentz formulation to the interband absorption of optical coating materials  

NASA Astrophysics Data System (ADS)

Recent progress in ellipsometry instrumentation permits precise measurement and characterization of optical coating materials in the deep-UV wavelength range. Dielectric coating materials exhibit their first electronic interband transition in this spectral range. The Tauc-Lorentz model is a powerful tool with which to parameterize interband absorption above the band edge. The application of this model for the parameterization of the optical absorption of TiO2, Ta2O5, HfO2, Al2O3, and LaF3 thin-film materials is described.

von Blanckenhagen, Bernhard; Tonova, Diana; Ullmann, Jens

2002-06-01

449

Surfaces, Interfaces, and Heterostructures of Calcium FLUORIDE/SILICON(111)  

NASA Astrophysics Data System (ADS)

This work is concerned with CaF_2 /Si(111) as a prototypical heteroepitaxial system of an extreme form, one built with layers of electronically dissimilar materials, an ionic insulator and a covalent semiconductor. The thesis presents the growth of CaF _2 on Si(111) from three sequential perspectives: (1) as a hybrid Si-CaF_2 reconstructed surface at submonolayer coverages, (2) as a dynamic system making a transition from a surface to a thin film, and (3) as a fully formed thin film or heterostructure. The governing physics at each stage is quite different. Using surface x-ray scattering, we have studied the (3x1) Si(111) reconstruction induced by chemisorption of CaF_2. This reconstruction consists of a parallel array of zig-zag Si adatom chains oriented along < 1| 10>, The orbitals on the Si chain atoms rehybridize into P _{x} and p_ {y} along the surface to form sigma-bonds, and parallel sp _{z} orbitals perpendicular to the surface to give additional pi -bonding. This basic structure, with no dangling bonds at only 1/3 monolayer adsorbate coverage, may explain the occurrence of (3x1) reconstructions among a diverse range of Si-adsorbate systems. The demands of chemisorption and epitaxy are quite different for electronically dissimilar systems. The transition between these two regimes in CaF_2/Si(111), which occurs at 1-5 monolayers of coverage, is studied with transmission electron microscopy (TEM) and photoemission. Changes in the electronic structure of the evolving growth surface result in a Stranski-Krastanow pathway to layer-by-layer composite growth mode, which begins with CaF_2 coherent island formation on a reacted Si-CaF layer. After this transition, layer-by-layer CaF_2 homoepitaxy can be maintained at room temperature, and the critical thickness can thus be extended. Finally, fully formed CaF_2/Si(111) interfaces and heterostructures are studied using x-ray scattering and TEM. For heterostructures grown at high temperatures, the interface Ca atoms in the first CaF layer are located uniquely at T_4 sites. Further, this interface structure is metastable, and a transition from the as-grown structure to a weakly incommensurate (sqrt{3} x sqrt {3})-R30^circ reconstruction is possible.

Wong, Gerard Chee Lai

450

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.

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

2012-01-01

451

Fluorescence dynamics in some solid-state laser materials emitting in the infrared region: Ho3+ doped LiYF4 single crystals and fluoride glasses  

Microsoft Academic Search

It is reported on the fluorescence mechanisms of Er3+ and Ho3+ impurity ions in LiYF4 single crystals and in fluoride glasses so-called BATY and BIZYT with the following compositions: BATY : 20 BaF2-28.75 AlF3-22.5 ThF4- (28.75-x-y) YF3-xHoF3-yErF3. BIZYT : 30 BaF2-30 InF3-20 ZnF2-10 ThF4-(10-x-y) YF3-xHoF3-yErF3.

J. Rubin; A. Brenier; R. Moncorgé; C. Pédrini; B. Moine; G. Boulon; J. L. Adam; J. Lucas; J. Y. Henry

1988-01-01

452

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

453

Mass Spectrometric Studies at High Temperatures. II. The Sublimation Pressures of Magnesium, Strontium, and Barium Fluorides  

Microsoft Academic Search

A mass spectrometer has been employed to measure the sublimation pressures and heats of sublimation for MgF2 over the range 1241° to 1492°K; for SrF2 over the range 1207° to 1563°K; and for BaF2 from 1232° to 1505°K. For MgF2 the results are represented by logPatm=?[(88.3±0.9)?45.76]104T?1+8.53±0.2; for SrF2 by logPatm=?[(99.3±0.7)?45.76]104T?1+8.716±0.01; and for BaF2 the equation is logPatm=?[(85.1±0.9)?45.76]104T?1+7.659±0.01. The errors quoted

John W. Green; Gary D. Blue; Thomas C. Ehlert; John L. Margrave

1964-01-01

454

Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films  

Microsoft Academic Search

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 108 down to 10-2 Omega cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within

Boris A. Akimov; Vladislav A. Bogoyavlenskiy; Ludmila I. Ryabova; Vyacheslav N. Vasil'kov

2000-01-01

455

Some studies of the applications of CsI photocathodes in gaseous detectors  

Microsoft Academic Search

Cesium-iodide photocathodes have been investigated in combination with gaseous detectors. The quantum efficiency of a semi-transparent CsI photocathode has been measured in the UV range and found to be 10% at 140 nm. We report experimental results obtained with such photocathodes coupled to BaF2 and KMgF3 scintillators and read out by parallel-plate gaseous detectors.

G. Charpak; I. Gaudean; Y. Giomataris; V. Peskov; D. Scigocki; F. Sauli; D. Stuart

1993-01-01

456

Some studies of the applications of CsI photocathodes in gaseous detectors  

NASA Astrophysics Data System (ADS)

Cesium-iodide photocathodes have been investigated in combination with gaseous detectors. The quantum efficiency of a semi-transparent CsI photocathode has been measured in the UV range and found to be 10% at 140 nm. We report experimental results obtained with such photocathodes coupled to BaF 2 and KMgF 3 scintillators and read out by parallel-plate gaseous detectors.

Charpak, G.; Gaudean, I.; Giomataris, Y.; Peskov, V.; Scigocki, D.; Sauli, F.; Stuart, D.

1993-09-01

457

On-Beam Digital Pulse Shape Acquisition From NE102A- Phoswich Detector  

Microsoft Academic Search

The use of NE102A-BaF2 phoswich detector drastically improves the particle identification with respect to BaF2 crystals. To better exploit the possibility of light ion discrimination we have applied digital signal processing to the signals, on-beam collected with NE102A-BaF2 phoswich. We present the results obtained for the heavy ion charge identification (up to Z=50) and light particle mass identification, using digital

Francesca Amorini; Enrico De Filippo; Paolo Guazzoni; Elena La Guidara; Gaetano Lanzanò; Stefano Moser; Angelo Pagano; Sara Pirrone; Filippo Riccio; Paolo Russotto; Luisa Zetta

2009-01-01

458

Multiphonon relaxation and infrared-to-visible conversion of Er(3+) and Yb(3+) ions in barium-thorium fluoride glass  

Microsoft Academic Search

The upconversion of IR radiation into green and red fluorescence has been studied for Er(3+) and Yb(3+) ions in BaF2\\/ThF4 fluoride glass over a wide temperature range and several dopant concentrations. At room temperature an upconversion efficiency of 0.000033 has been obtained for the green emission from the glass with 1 mol pct ErF3 and 19 mol pct YbF3 pumped

D. C. Yeh; W. A. Sibley; M. Suscavage; M. G. Drexhage

1987-01-01

459

Polarized Raman Scattering in Rare-Earth Fluoride Glasses.  

National Technical Information Service (NTIS)

The polarized Raman spectra of rare-earth fluoride glasses based on BaF2 and ThF4, in combination with ZnF2, YF3, YbF3, LuF3, and/or AlF3, are reported and compared with those of other heavy-metal fluoride glasses. The spectra of rate-earth fluoride glass...

B. Bendow P. K. Banerjee J. Lucas G. Fonteneau M. G. Drexhage

1985-01-01

460

Multiphonon relaxation and infrared-to-visible conversion of Er3+ and Yb3+ ions in barium-thorium fluoride glass  

Microsoft Academic Search

The upconversion of infrared radiation into green and red fluorescence has been studied for Er3+ and Yb3+ ions in BaF2\\/ThF4 fluoride glass over a wide temperature range and several dopant concentrations. At room temperature an upconversion efficiency of 3.3×10?5 has been obtained for the green emission from the glass with 1 mol % ErF3 and 19 mol % YbF3 pumped

D. C. Yeh; W. A. Sibley; M. Suscavage; M. G. Drexhage

1987-01-01

461

Photoluminescent properties and Raman spectra of ZnO-based scintillating glasses  

Microsoft Academic Search

Glasses in SiO2–ZnO–BaO system with the different ZnO\\/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO

Gujie Qian; S. Baccaro; M. Falconieri; Jiafang Bei; A. Cecilia; Guorong Chen

2008-01-01

462

Scintillators for Photon Detection at Medium Energies  

Microsoft Academic Search

In a comparative study the performance of sub-arrays consisting of large CeF3 and PbWO4 crystals has been investigated with high energy photons below 1GeV. Energy and time resolutions are determined and compared to the corresponding values for BaF2 based on the experience of operating the electromagnetic calorimeter TAPS. Since clean photon detection relies on the discrimination and identification of charged

R. Novotny

2002-01-01

463

RF sputtering of epitaxial lead chalcogenide films in argon and krypton plasma  

Microsoft Academic Search

The measurements of sputtering etch rates for monocrystalline (1 1 1)-oriented epitaxial films of semiconductor binary compounds PbTe, PbSe, PbS in RF high-density low-pressure inductively coupled argon and krypton plasma were performed. Films with 1-5 µm thickness were grown on Si(1 1 1) and BaF2(1 1 1) substrates using molecular beam epitaxy. Sputtering was carried out with the energy of

S. P. Zimin; I. I. Amirov; E. S. Gorlachev

2011-01-01

464

LPE growth and characterization of magnetic garnets grown in BaO-based solvents  

Microsoft Academic Search

The solution growth of magnetic oxides in BaO-based binary and ternary solvents is reviewed, and results of LPE growth of mixed rare earth magnetic bubble garnets in the BaO-B2O3-BaF2 ternar