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Sample records for baf2 caf2 laf3

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Deadmore, Daniel L.; Sliney, Harold E.

    1987-01-01

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

  3. CaF2, BaF2 and SrF2 crystals’ optical anisotropy parameters

    NASA Astrophysics Data System (ADS)

    Snetkov, I. L.; Yakovlev, A. I.; Palashov, O. V.

    2015-09-01

    Using the original method, based on measurements of thermally induced depolarization, the optical anisotropy parameters of CaF2, BaF2 and SrF2 cubic crystals were measured and compared with what is known from the literature. Euler angles of crystallographic axis orientation [C], in which the thermally induced depolarization is minimal, were determined using experimental results for studied fluorides.

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

    SciTech Connect

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  6. Photoluminescence properties of Eu 3+:ZrF 4-BaF 2-LaF 3-YF 3-AlF 3-NaF glasses

    NASA Astrophysics Data System (ADS)

    Kam, C. H.; Buddhudu, S.

    2004-02-01

    This paper presents the results concerning the photoluminescence spectra of 53ZrF 4-20BaF 2-2LaF 3-2YF 3-3AlF 3-(20- x)NaF- xEuF 3 multi-component heavy metal fluoride glasses with the Eu 3+=0.2, 0.4, 0.8, 1.0, 1.2 and 1.4 mol% in order to evaluate the threshold of concentration quenching ( Cq=1 mol%) which corresponds to the concentration limit clearly revealing an intense red emission ( 5D 0→ 7F 2 at 614 nm) from such a luminescent glass. A bright red emission was observed by the naked eye from these materials under an UV source. The dopant ion concentration quenching on the emission behaviour has been ascribed to cross-relaxation and dipole-dipole interactions in the glass matrices. Influence of changes in active ions content (N Eu3+×10 22 cm -3) on the values of inter-ionic distance ( ri Å) and polaron radius ( rp Å) has been verified. The photoluminescence spectra are constituted essentially by six emission transitions of ( 5D 0→ 7F J=0,1,2,3,4,5 ) between the wavelengths of 575 and 720 nm. We have also investigated the dependence of emission intensities and lifetimes on various pump wavelengths and identified a more suitable excitation line at 394 nm, which belongs to the transition 7F 0→ 5L 6 of Eu 3+ ion.

  7. Absolute refractive indices and thermal coefficients of CaF2, SrF2, BaF2, and LiF near 157 nm.

    PubMed

    Burnett, John H; Gupta, Rajeev; Griesmann, Ulf

    2002-05-01

    We present high-accuracy measurements for wavelengths near 157 nm of the absolute index of refraction, the index dispersion, and the temperature dependence of the index for the ultraviolet optical materials with cubic symmetry: CaF2, SrF2, BaF2, and LiF. Accurate values of these quantities for these materials are needed for designs of the lens systems for F2 excimer-laser-based exposure tools for 157-nm photolithography. These tools are expected to use CaF2 as the primary optical material and possibly one of the others to correct for chromatic aberrations. These optical properties were measured by the minimum deviation method. Absolute refractive indices were obtained with an absolute accuracy of 5 x 10(-6) to 6 x 10(-6). PMID:12009162

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    Phase transitions and equations of state of the alkaline earth fluorides CaF2 , SrF2 , and BaF2 were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm3¯m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF2 and SrF2 : these materials were observed to transform to a hexagonal (P63/mmc) Ni2In -type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF2 , the Ni2In -type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF2 and SrF2 , the fluorite-cotunnite transition results in a volume decrease of 8-10% , while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni2In -type phase is ˜5% . The percentage increase in the bulk modulus (ΔK) across the transition is greater when the cation is smaller. While for BaF2 , ΔK is 10-30% , ΔK values for SrF2 and CaF2 are 45-65% and 20-40% . Although shock data for CaF2 have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.

  9. Near infrared ultrafast pump-probe spectroscopy with ZrF4-BaF2-LaF3-AlF3-NaF fiber supercontinuum

    NASA Astrophysics Data System (ADS)

    Fischbach, Stefan; Gorbach, Andrey V.; Di Nuzzo, Daniele; Da Como, Enrico

    2015-07-01

    We report on the performance of a setup designed for femtosecond pump-probe spectroscopy in the near infrared (NIR) spectral region. We generate a supercontinuum (SC) probe by coupling 140 fs light pulses at 1550 nm into a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. The combined high nonlinearity and transparency of the ZBLAN fluoride glass allows us to obtain a SC probe from 1 to 2.6 ?m. The NIR pulses are used to demonstrate a proof of principle experiment probing the relaxation of photo induced excitations in a conjugated polymer:fullerene blend film. The results show the possibility to perform fibre based NIR SC femtosecond spectroscopy at >100 KHz repetition rate and using lasers with pulse energy just above 300 nJ.

  10. Ionic, electronic and ion-diffusion controlled relaxation processes in CaF2, BaF2 and LiBaF3 crystals

    NASA Astrophysics Data System (ADS)

    Ziraps, V.; Kulis, P.; Tale, I.; Veispals, A.

    The ionic, electronic and anion-diffusion controlled thermally stimulated relaxation (TSR) processes at 80-700 K in CaF2 BaF2 and LiBaF3 crystals (X-ray irradiated or non-irradiated) have been investigated by means of ionic conductivity, ionic thermally stimulated (TS) depolarization current (TSDC); as well as current (TSC), luminescence (TSL) and bleaching (TSB) techniques. Above 250-290 K broad and overlapping anion TSDC peaks and correlated TSB stages are detected. The TSB kinetics is initiated and controlled by anion detrapping and interaction with the localized charges, i.e., the anion-diffusion controlled TSR processes take place in fluorides. The TSL and TSC data for LiBaF3 indicate that the lifetime and drift of electrons at 80-250 K is very small because of deep retrapping. The main TSL peaks at 132K, 170K and 220 K are caused by Vk center detrapping and hole-diffusion controlled tunnel recombination within pairs like .

  11. Luminescence and decay behaviour of Tb 3+:ZrF 4-BaF 2-LaF 3-YF 3-AlF 3-NaF optical glasses

    NASA Astrophysics Data System (ADS)

    Kam, C. H.; Buddhudu, S.

    2003-09-01

    The present investigation aims at elucidating the photoluminescence behaviour of Tb 3+ doped 53ZrF 4-20BaF 2-2LaF 3-2YF 3-3AlF 3-(20- x)-NaF- xTbF 3 (where x=0.2,0.4,0.6,0.8,1.0,1.5 and 2.0 mol%) optical glasses. We have measured two prominently intense emission blue group bands ( 5D 3→ 7F j=6,5,4,3 at 382, 415, 436 and 461 nm) and green group bands ( 5D 4→ 7F j=6,5,4,3 at 488, 544, 584 and 623 nm) with an excitation at λexc=229 nm (4f 8→4f 75d 1) from these ZBLYAN glasses. Under a UV source (15 W), more prominent and rich green luminescent colour (544 nm) has been noticed from these terbium glasses. In particular, glass with low Tb 3+ (0.2 mol%) content has displayed the emission transitions of 5D 3→ 7F j=6,5,4,3 and at still higher concentrations these emission bands have disappeared completely because of resonant energy transfer phenomenon or cross-relaxation process. The mechanism behind such a process has been explained in terms of an energy level diagram. Among the seven-terbium glasses, one glass with 1.0 mol% of Tb 3+ (as the optimum content) has revealed an intense green emission.

  12. 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)

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

    1982-12-01

    Thin films (? 5000 ) 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 ). Deposition of BaF 2 and CaF 2 onto cleaned, well-ordered (001) InP held at temperatures above 200C 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.

  13. High-temperature tribological properties of NiCoCrAlY-WSe2-BaF2CaF2 solid lubricant coatings prepared by plasma spraying

    NASA Astrophysics Data System (ADS)

    Chen, X. H.; Yuan, X. J.; Xia, J.; Yu, Z. H.

    2015-12-01

    In this paper, NiCoCrAlY-WSe2-BaF2CaF2 solid lubricant coatings were produced on a substrate by plasma spray and investigated at the high temperature, such as 500 C and 800 C. The structure of the coatings was characterized using XRD pattern and scanning electron microscopy. The TC1 (83wt% NiCoCrAlY) coating has a low friction coefficient at 500C, where the WSe2 is a good solid lubricant. The TC2 (65wt% NiCoCrAlY) coating has the low friction coefficient (0.279) at 800C, due to the formation of BaCrO4 on the surfaces. As a result, the TC2 coating has the optimal tribological property in the wide temperature.

  14. 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)

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

    2012-03-01

    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.

  15. Infrared thermooptic coefficient measurement of polycrystalline ZnSe, ZnS, CdTe, CaF(2), and BaF(2), single crystal KCI, and TI-20 glass.

    PubMed

    Harris, R J; Johnston, G T; Kepple, G A; Krok, P C; Mukai, H

    1977-02-01

    An interferometric technique has been used to determine the thermooptic coefficient (dn/dT) of polycrystalline ZnSe and ZnS at 0.6328 microm, 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CdTe and TI-20 glass at 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CaF(2) and BaF(2) at 0.6328 microm, 1.15 microm, and 3.39 microm, and pure and europium-doped single crystal KCl at 0.6328 microm, 1.15microm, 3.39 microm, and 10.6 microm. The values were obtained over the temperature range of 25-65 degrees C and were calculated using the observed change in optical path of the samples as they were heated. Some difficulties in thermometry were encountered in the standard configuration of sample and thermocouple probe, so measurements were made in an oil bath at the shortest wavelength at which the sample was transparent to provide temperature correction factors for each sample. An empirical dispersion relation for dn/dT has also been found for the semiconductor materials. This dispersion relation is of the form dn/dT = aR(b), where R is defined as lambda(2)/(lambda(2) - lambda(g)(2)), lambda(g) is the short wavelength cutoff associated with the energy gap, and a and b are constants which are different for each material. PMID:20168506

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

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Stanford, Malcolm K.

    2008-01-01

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

  17. Light scattering and computer simulation studies of superionic pure and La-doped BaF2

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    A combination of both Raman and Brillouin scattering experiments as well as Molecular Dynamics (MD) was used to study the superionic behaviour of BaF2 doped with a wide range of LaF3 concentrations (0 ⩽ x ⩽ 50 mol%). Raman spectroscopy reveals that for undoped BaF2 and those doped with 5% and 10% LaF3, the room temperature spectra show the usual T2g symmetry mode at 241 cm-1 whereas for those doped with 20%, 30% and 50% LaF3, the dominant Raman mode is of the Eg symmetry situated at ∼263, 275 and 286 cm-1, respectively. The Raman linewidths show near linear increases with temperature followed by rapid increases above the characteristic transition temperatures (Tc), being at 1200, 850, 800, 975, 950 and 920 K for LaF3 concentrations of 0, 5, 10, 20, 30 and 50; respectively. The temperature dependence of the squares of the Brillouin frequencies (ΔωB)2 of the LA and TA acoustic modes respectively related to elastic constants C11 and C44 showed linear decreases followed by significant deviations around the same temperatures (Tc), at which the Raman linewidths start to show substantial increases. The complementary studies using MD simulations show that the diffusion coefficients increase markedly above the same temperatures observed experimentally. The extrinsic fluorine ion trajectories were also determined from the MD simulations to better understand the mechanisms of diffusion.

  18. BaF 2 scintillators with wire chamber readout for positron emission tomography

    NASA Astrophysics Data System (ADS)

    Bruyndonckx, P.; Debruyne, J.; Etienne, L.; Gruwé, M.; Guerard, B.; Tavernier, S.; Shuping, Zhang

    1991-12-01

    This work is part of the design study for a medical positron emission tomography (PET) system based on the use of BaF 2 scintillator and photosensitive wire chambers with TMAE. The number of photoelectrons per MEV (phe/MeV) is measured in the wire chamber and on a photomultiplier for crystals from five different suppliers. For the best crystals 26.7±2.0 phe/MeV in TMAE are observed, corresponding to an average quantum efficiency of TMAE for the fast component of BaF 2 of (7.6±0.7)%. The performance of a PET scanner based on this principle was evaluated with a detailed Monte Carlo simulation. It is shown that the reduced energy resolution with wire chambers has only a marginal effect on the scatter rejection in the scanner. Finally LaF 3:Nd 3+ as an alternative to BaF 2 was tested and found to give a disappointing photoelectron yield.

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

  20. An insight into the local Oh →Td instability in BaF2:Mn2+

    NASA Astrophysics Data System (ADS)

    Garcia-Fernandez, P.; Aramburu, J. A.; Barriuso, M. T.; Moreno, M.

    2010-11-01

    While most complexes in fluorite-type lattices (CaF2, SrF2, CdF2) containing Mn2+ impurities remain cubic at all temperatures, electron paramagnetic resonance (EPR) measurements have shown that the one in BaF2 is tetrahedral below 50K. This surprising behaviour is intrinsic to the centre and not associated to any close defect or pure lattice phase-transition. Through the use of density functional (DFT) calculations we show that the distortion is linked to the unexpected low force constant along the tetrahedral distortion mode with a2u symmetry in these complexes and the large metal-ligand distance existing in BaF2:Mn2+. Ultimately, these facts reflect that, for substitutional impurities in fluorite-type crystals, the ligand-ligand interaction is dominant over the metal-ligand one.

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

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Lu, Meihua

    2007-07-01

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

  2. Dielectric, modulus and impedance analysis of LaF 3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Arun Kumar, D.; Selvasekarapandian, S.; Nithya, H.; Sakunthala, A.; Hema, M.

    2010-09-01

    Lanthanum fluoride nanoparticles have been synthesized by the simple method of direct precipitation from an aqueous solution. TG/DTA analysis confirms the sample formation at low temperature (300 C). Structure of LaF 3 nanoparticles has been analyzed by XRD and LaF 3 is found to be in tysonite structure. From the XRD spectra the average particle size is found to be 15 nm using the Scherrer formula. The impedance, modulus and dielectric spectra analysis of the prepared LaF 3 nanoparticles has been studied using AC impedance spectroscopy. The ionic conductivity of LaF 3 nanoparticles is significantly increased by an order from 10 -6 to 10 -5 S cm -1. The modulus and dielectric spectra analysis confirms the non-Debye type behavior in the material.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  4. Properties of AlF3 and LaF3 films at 193nm

    NASA Astrophysics Data System (ADS)

    Xue, Chunrong; Shao, Jianda

    2010-10-01

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

  5. Systematic study of sensitized LaF3:Eu3+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Janssens, S.; Williams, G. V. M.; Clarke, D.

    2011-01-01

    We have performed a systematic structural, vibrational, and optical study of LaF3:Eu3+ nanoparticles capped with oleic acid (OA) or OA and sensitized with thenoyltrifluoroacetone (TTA). The average nanoparticle size was around 11 nm for all Eu3+ concentrations. A shift in the energy of the Raman active modes is observed with increasing Eu3+ concentration that can be accounted for by a decrease in the unit cell volume. Sensitization by TTA was observed and resulted in an 18 000% increase in the photoluminescence (PL) intensity for TTA/OA capped LaF3:Eu3+ nanoparticles when compared with OA capped LaF3:Eu3+ nanoparticles. There is also a large increase in the D50?F72 PL intensity, when normalized to the D50?F71 PL magnetic dipole transition intensity, for TTA/OA capped nanoparticles. The changes in the PL intensities, PL lifetimes, Judd-Ofelt parameters, stimulated emission cross sections, and quantum efficiencies, for OA and TTA/OA capped LaF3:Eu3+ nanoparticles with increasing Eu3+ concentration can be accounted for by a model that separates the Eu3+ sites into sites near the surface and Eu3+ sites in the core as well as nonradiative recombination sites near the surface. The large increase in PL intensity due to TTA sensitization means that TTA capped LaF3:Eu3+ can potentially be used for applications that include optical amplification.

  6. Ice nucleation on BaF2(111)

    NASA Astrophysics Data System (ADS)

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

    2005-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

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

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

    SciTech Connect

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

    2010-11-15

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

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

    SciTech Connect

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

    2008-03-15

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

  10. Investigation of luminescent properties of LaF3:Nd3+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Wyrwas, Marek; Miluski, Piotr; Zmojda, Jacek; Kochanowicz, Marcin; Jelen, Piotr; Sitarz, Maciej; Dorosz, Dominik

    2015-09-01

    Lanthanum fluoride nanoparticles doped with Nd3+ ions obtained via solvothermal method have been presented. Doped nanoparticles were prepared in two-step method. Firstly rare-earth chlorides were synthesized from oxides and then they were used to prepare LaF3 particles. The luminescence spectra shows typical for crystalline materials Stark splitting at 880 nm corresponding 4F3/2 to 4I9/2 level transition and 1060 nm matching 4F3/2 to 4I11/2 level transition. The highest luminescence intensity was achieved for sample doped with 0.75% wt. of Nd3+, and the longest decay time for sample doped with 0.5% wt. which reached 328 μs. The XRD pattern analysis confirmed that obtained material consists of crystalline LaF3, the grain size was estimated from Sherrer's formula and equaled about 25nm.

  11. Test of a BaF2 scintillation crystal

    NASA Astrophysics Data System (ADS)

    Schippers, J. M.; Devries, J.

    1983-04-01

    Gamma energy response and temporal resolution of a BaF2 crystal were compared with those of a Pilot-U plastic. Using a photomultiplier, the possibility to use the fast ultraviolet component of the gamma ray excited emission spectrum for positron lifetime measurements was investigated. For the gamma energy response, the BaF2 crystal (height 2.5 cm, diameter 2.5 cm) was coupled to the multiplier with and without an optical coupling compound. In an existing spectrometer, temporal resolution of Pilot-U detectors with 0.5 and 2.5 cm thickness and the BaF2 crystal was measured. As positron emitters, NA22, Co60, Cs137, Am241, Co57, and Bi2O7 were used. To obtain a temporal resolution comparable to the 0.5 Pilot-U plastic, a 1 mm thick crystal should be used. An improvement is obtained by omitting the (ultraviolet absorbing) coupling compound. For tomographic time of flight purposes, the use of positron emitters with a maximum gamma energy of 300 keV is recommended.

  12. Synthesis of LaF3 nanosheets with high fluorine mobility investigated by NMR relaxometry and diffusometry

    NASA Astrophysics Data System (ADS)

    Gulina, L. B.; Schfer, M.; Privalov, A. F.; Tolstoy, V. P.; Murin, I. V.

    2015-12-01

    Ionically conducting lanthanum fluoride (LaF3), displaying a nanoscopic lamellar structure, has been synthesized at the surface of an aqueous solution of LaCl3 and HF. The structure and the chemical composition of the conductor have been analyzed by SEM, electron probe microanalysis, X-ray powder diffraction, FTIR, and 19F magic angle spinning nuclear magnetic resonance (NMR) spectroscopy. The fluorine dynamics have been studied by NMR diffusometry and relaxometry in a temperature range from room temperature up to 875 K. The fluorine self-diffusion coefficient of the nanostructured LaF3 is about two orders of magnitude larger than that of bulk LaF3. This novel material is highly promising for many typical applications of fluorine ionic systems.

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

    PubMed

    Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

    2011-08-01

    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/SiO(2) (400 nm) substrate. A deposited LaF(3) film was applied as solid electrolyte and sputtered Pt film was used as the sensing electrode. The patterns of the Pt and LaF(3) were realized by the micromachining processes. The LaF(3) 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. PMID:21895252

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

    PubMed

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

    2015-02-01

    Chitosan functionalized luminescent rare earth doped terbium nanoparticles (LaF3:Tb(3+)/chi NPs) as a drug carrier for methotrexate (MTX) was designed using a simple chemical precipitation method. The synthesized chitosan functionalized nanoparticles were found to be spherical in shape with an average diameter of 10-12nm. They are water soluble and biocompatible, in which the hydroxyl and amino functional groups on its surface are utilized for the bioconjugation of the anticancer drug, the methotrexate. The nature of MTX binding with LaF3:Tb(3+)/chi nanoparticles were examined using X-ray diffraction, zeta potential analyzer and transmission electron microscopy. The other interactions due to complex formation between MTX and LaF3:Tb(3+)/chi NPs were carried out by UV-Visible, steady and excited state fluorescence spectroscopy. The photo-physical characterization revealed that the adsorption and release of MTX from LaF3:Tb(3+)/chi NPs is faster than gold nanoparticles and also confirms that this may be due to weak interaction i.e. the Vander Waals force of attraction between the carboxyl and amino group of drug and nanoparticles. The maximum percentage yield and entrapment efficiency of 85.910.71 and 83.82 0.14 were achieved at a stochiometric ratio of 4:5 of MTX and LaF3:Tb(3+)/chi nanoparticles respectively. In addition, antitumoral activity study reveals that MTX conjugated LaF3:Tb(3+)/chi nanoparticles show higher cytotoxic effect on MCF-7 breast cancer cell lines than that of free MTX. PMID:25661354

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

    PubMed

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

    2014-05-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    SciTech Connect

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

    2011-12-31

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

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

    PubMed

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

    2014-06-01

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

  19. Trigonal LaF3: a novel SRS-active crystal

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. A solvent extraction route for CaF2 hollow spheres.

    PubMed

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

    2010-11-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    PubMed Central

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

    2013-01-01

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

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

    SciTech Connect

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

    2012-01-01

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

  4. Molecular Dynamics Simulations for Melting Temperatures of SrF2 and BaF2

    NASA Astrophysics Data System (ADS)

    Huang, Xiao-yu; Cheng, Xin-lu; Fan, Chao-lei; Chen, Qiong; Yuan, Xiao-li

    2009-06-01

    The shell-model molecular dynamics method was applied to simulate the melting temperatures of SrF2 and BaF2 at elevated temperatures and high pressures. The same method was used to calculate the equations of state for SrF2 and BaF2 over the pressure range of 0.1 MPa-3 GPa and 0.1 MPa-7 GPa. Compared with previous results for equations of state, the maximum errors are 0.3% and 2.2%, respectively. Considering the pre-melting in the fluorite-type crystals, we made the necessary corrections for the simulated melting temperatures of SrF2 and BaF2. Consequently, the melting temperatures of SrF2 and BaF2 were obtained for high pressures. The melting temperatures of SrF2 and BaF2 that were obtained by the simulation are in good agreement with available experimental data.

  5. Development of CaF 2 special refractory components

    NASA Astrophysics Data System (ADS)

    Ghosh, Abhijit; Upadhyaya, D. D.; Prasad, Ram; Suri, A. K.

    2001-12-01

    Among the non-oxide refractories, the fluorides of Ca and Mg are of considerable importance in the processing of reactive metals and alloys in nuclear industry. This work deals with the development of specific CaF 2 shapes for casting of uranium metal ingots. Studies were carried out in optimizing the slip properties to fabricate dense green components which on sintering at 850 C attain a theoretical density of approximately 85%. An important feature of this work is in providing a synergistic approach in waste recycling and, as well, in maintaining the assured high purity of the metal produced.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    PubMed

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

    2008-06-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  10. The importance of surface treatment on the amount of light detected from BaF 2

    NASA Astrophysics Data System (ADS)

    Anderson, D. F.; Lamb, D. C.

    1987-10-01

    The effect of the exposure to room air on the light output in the "short" component at 220 nm of BaF 2 crystals is presented. We also show that the light output in this component can be predicted from the measurement of the transmission at two wavelengths.

  11. Relaxation of electronic excitations in CaF2 nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  12. Enhanced emission of ultra-small-sized LaF3:RE3+ (RE = Eu, Tb) nanoparticles through 1,2,4,5-benzenetetracarboxylic acid sensitization.

    PubMed

    Li, Suwen; Zhang, Xiao; Hou, Zhiyao; Cheng, Ziyong; Ma, Pingan; Lin, Jun

    2012-09-21

    Uniform, ultra-small-sized and well-water-dispersible LaF(3) nanoparticles doped with trivalent rare earth (RE) ions (Eu(3+) or Tb(3+)) have been synthesized by a simple, low temperature synthesis route. The nanoparticles, with sizes of about 3.2 nm (for those doped with Eu(3+)) and 3.0 nm (for those doped with Tb(3+)), are roughly spherical and monodisperse. 1,2,4,5-Benzenetetracarboxylic acid (labeled as BA) as sensitizer has been bonded to the surface of the nanoparticles, which can sensitize the emission of RE(3+) in the LaF(3) nanoparticles. The BA-LaF(3):RE(3+) (RE = Eu or Tb) nanoparticles have a broad absorption band in the UV domain, and show enhanced luminescence of RE(3+) based on an energy transfer from BA ligands to RE(3+) ions (i.e. the so-called "antenna effect"). Due to the dual protection of organic ligands (BA) and inorganic matrices (LaF(3)), BA-LaF(3):RE(3+) (RE = Eu or Tb) nanoparticles have longer excited state lifetimes than LaF(3):RE(3+) (RE = Eu or Tb) nanoparticles as well as lanthanide coordination polymers of BA. PMID:22864859

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

    PubMed

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

    2015-06-10

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

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

    NASA Astrophysics Data System (ADS)

    Tan, Yan; Nakamura, Atsushi; Kubono, Atsushi

    2016-03-01

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

  15. Interconnection of defect entropies and enthalpies in BaF2 revisited

    NASA Astrophysics Data System (ADS)

    Skordas, Efthimios S.

    2016-02-01

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

  16. Study of response of scintillation detector based on BaF2 crystals and nanoceramics

    NASA Astrophysics Data System (ADS)

    Batenkov, O. I.; Yurevich, V. I.; Garibin, E. A.; Reyterov, V. M.; Gusev, P. E.; Krutov, M. A.; Fedorov, P. P.; Veshchikov, A. S.

    2016-01-01

    Fast and slow components of responses of scintillation detectors based on BaF2 crystals and nanoceramics with various activators are studied by the registration of annihilation gamma-quanta with an energy of 511 keV. A comparative analysis of the obtained results for the determination of promising scintillators for the development of detectors with high time and pulse height resolution is carried out.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    PubMed Central

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

    2014-01-01

    Optical read-out and manipulation of the nuclear spin state of single rare-earth ions doped in a crystal enable the large-scale storage and the transport of quantum information. Here, we report the photo-luminescence excitation spectroscopy results of single Pr3+ ions in a bulk crystal of LaF3 at 1.5?K. In a bulk sample, the signal from a single ion at the focus is often hidden under the background signal originating from numerous out-of-focus ions in the entire sample. To combine with a homemade cryogenic confocal microscope, we developed a reflecting objective that works in superfluid helium with a numerical aperture of 0.99, which increases the signal by increasing the solid angle of collection to 1.16? and reduces the background by decreasing the focal volume. The photo-luminescence excitation spectrum of single Pr3+ was measured at a wing of the spectral line of the 3H4 ? 3P0 transition at 627.33?THz (477.89?nm). The spectrum of individual Pr3+ ions appears on top of the background of 60?cps as isolated peaks with intensities of 2030?cps and full-width at half-maximum widths of approximately 3?MHz at an excitation intensity of 80?W cm?2. PMID:25482137

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  1. 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)

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

    2012-11-01

    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.

  2. Growth of a smooth CaF2 layer on NdFeAsO thin film

    NASA Astrophysics Data System (ADS)

    Sumiya, N.; Kawaguchi, T.; Chihara, M.; Tabuchi, M.; Ujihara, T.; Ichinose, A.; Tsukada, I.; Ikuta, H.

    2014-05-01

    We studied the method to grow a smooth and flat CaF2 layer on NdFeAsO thin films since CaF2 is a promising candidate material for the barrier layer of a superconducting junction. When the CaF2 layer was grown at 800°C, the surface was very rough because {111} facets had grown preferentially. However, when CaF2 was grown at lower temperatures and post-annealed in situ at 800°C for 30 min the facets were eliminated and a CaF2 layer with a smooth surface was obtained. Fluorine diffusing from CaF2 into NdFeAsO was observed when CaF2 was grown at high temperatures, but the diffusion was suppressed by lowering the growth temperature to 400°C.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    PubMed

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

    2015-11-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

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

    PubMed

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

    2015-02-15

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

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

    NASA Astrophysics Data System (ADS)

    Moszy?ski, M.; Allemand, R.; Cormoreche, E.; Laval, M.; Odru, R.; Vacher, J.

    1984-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  10. Ultra-precision process of CaF2 single crystal

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    This paper proposes a new chemical mechanical polishing (CMP) process method for CaF2 single crystal to get ultraprecision surface. The CMP processes are improving polishing pad and using alkaline SiO2 polishing slurry with PH=8, PH=11 two phases to polish, respectively, and the roughness can be 0.181nm Rq (10?m10?m). The CMP process can't get high surface figure, so we use ion beam figuring (IBF) technology to obtain high surface figure. However, IBF is difficult to improve the CaF2 surface roughness. We optimize IBF process to improve surface figure and keep good surface roughness too. Different IBF incident ion energy from 400ev to 800ev does not affect on the surface roughness obviously but the depth of material removal is reverse. CaF2 single crystal can get high precision surface figure (RMS=2.251nm) and still keep ultra-smooth surface (Rq=0.207nm) by IBF when removal depth is less than 200nm. The researches above provide important information for CaF2 single crystal to realize ultra-precision manufacture.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  13. Study of BaF2 with 511 KeV Gamma Rays

    NASA Astrophysics Data System (ADS)

    Miller, Jon

    1996-05-01

    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..

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

    PubMed

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

    2014-01-31

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

  15. Time- and energy-resolution measurements of BaF2, BC-418, LYSO and CeBr3 scintillators

    NASA Astrophysics Data System (ADS)

    Ackermann, Ulrich; Egger, Werner; Sperr, Peter; Dollinger, Gnther

    2015-06-01

    We have investigated the time and energy resolution (TTiming, ?E/E) of four different scintillator materials BaF2, BC-418, LYSO and CeBr3 at a gamma energy of 511 keV in views of their possible usage for time, energy and position resolution for positron annihilation experiments. The shape of each scintillator was a cylinder with a diameter of 25 mm and a height of 10 mm readout by a Photonis XP2020/URQ photomultiplier tube. The best single time resolution was determined for each photomultiplier-scintillator setup in a three step optimization process. The optimized single time resolutions (FWHM) for BaF2, BC-418, LYSO and CeBr3 were 119 ps, 117 ps, 269 ps and 127 ps, respectively. We measured the energy resolution of the photomultiplier-scintillator setups which show a photopeak in the energy spectrum. The energy resolutions ?E/E of BaF2, LYSO and CeBr3 were 9.8%, 9.7% and 5.4%, respectively. The overall most promising material for measuring simultaneously time, energy and position resolution for positron annihilation experiments seems to be CeBr3 due to its very good time and energy resolution characteristics.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  20. High-performance metal-semiconductor-metal InGaN photodetectors using CaF2 as the insulator

    NASA Astrophysics Data System (ADS)

    Sang, Liwen; Liao, Meiyong; Koide, Yasuo; Sumiya, Masatomo

    2011-03-01

    The authors report on the high-performance metal-semiconductor-metal (MSM) photodetectors (PDs) fabricated on high-quality InGaN film by introducing a superwide bandgap calcium fluoride (CaF2) as the insulator. The dark current of the PDs with CaF2 is drastically reduced by six orders of magnitude compared with those without CaF2, resulting in an extremely high discrimination ratio larger than 106 between ultraviolet and visible light. The responsivity at 338 nm is as high as 10.4 A/W biased at 2 V, corresponding to a photocurrent gain around 40. The CaF2 layer behaves as an excellent insulator for the InGaN-based MSM-PDs in dark condition, while it allows the electron injection through the metal/semiconductor interface under ultraviolet illumination, contributing to the photocurrent gain without sacrificing the response time (˜ms).

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

    PubMed

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

    2015-11-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2002-06-01

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

  4. Paramagnetic hyperfine splitting in the Eu Mssbauer spectra of CaF(2):Eu.

    PubMed

    Selling, J; Bielemeier, B; Wortmann, G; Johnson, J A; Alp, E E; Chen, T; Brown, D E; Johnson, C E; Schweizer, S

    2008-06-30

    (151)Eu Mssbauer spectra in zero magnetic field of highly dilute (0.1 mol%) Eu(2+) ions in CaF(2) showed an almost temperature-independent asymmetrically split pattern, arising from the paramagnetic hyperfine interaction AS. I in a cubic crystal field with slow electron spin relaxation; in a small external magnetic field B of 0.2 T such that g?(B)B>A an almost symmetrical pattern was observed. Both the spectra with and without external field are well described using the spin Hamiltonian and previous electron paramagnetic resonance data. A more concentrated (2 mol% Eu(2+)) sample exhibited a strongly broadened symmetrical resonance line due to an increased Eu-Eu spin relaxation rate; in an external magnetic field of 0.2 T the Mssbauer spectra exhibited further broadening and additional magnetic structures due to the reduced relaxation rate. When a large field of 6 T was applied such that g?(B)B is much larger than the crystal field splitting, a fully resolved hyperfine pattern was observed at 2.5 K, with an effective field at the Eu nuclei of -33.7 T; at higher temperatures superimposed patterns originating from excited electronic states were observed in the spectra. The present results on the highly dilute CaF(2) : 0.1%Eu(2+) sample deliver a straightforward explanation for previous observations of a seemingly large dependence of the Eu(2+) isomer shift on europium concentration. PMID:19816547

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    PubMed

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

    2015-01-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. Hyperfine splittings and Zeeman infrared absorption of Tb3+ -doped CaF2 and SrF2

    NASA Astrophysics Data System (ADS)

    Wells, Jon-Paul R.; Jones, Glynn D.

    2009-09-01

    We report on the observation of pseudoquadrupole splittings of sharp infrared-absorption lines of CaF2:Tb3+ . These splittings are large enough to be directly observed because the Tb3+ electronic ground levels consists of two singlets separated by only 0.18cm-1 for the F- C4v center. Both the hyperfine splittings and measured Zeeman splittings for F- C4v centers in CaF2:Tb3+ and SrF2:Tb3+ can be accounted for using wave functions derived from a previously published crystal-field analysis of experimental energy levels.

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

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  12. Laser damage and ablation of differently prepared CaF2(111) surfaces

    NASA Astrophysics Data System (ADS)

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

    1999-12-01

    Ablation thresholds and damage behavior of cleaved and polished CaF2(111) surfaces produced by single shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. The standard polishing yields an ablation threshold of typically 20 J/cm2. When surfaces are polished chemo-mechanically the threshold is raised to 43 J/cm2. Polishing by diamond turning leads to intermediate values around 30 J/cm2. Cleaved surfaces possess no well-defined damage threshold. The damage topography of conventionally polished surfaces shows ablation of flakes across the laser heated area with cracks along the cleavage planes. In the case of chemo-mechanical polishing only a few cracks appear. Diamond turned surfaces show small optical absorption, but cracks and ablation of tiles. The origin of such different damage behavior is discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    PubMed

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

    2014-03-14

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

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

    NASA Astrophysics Data System (ADS)

    Lorenz, Pierre; Ehrhardt, Martin; Zimmer, Klaus

    2013-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

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

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

    EPA Science Inventory

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

  19. Specific spectroscopic and laser properties of Tm3+ ions in hot-formed CaF2 laser ceramics

    NASA Astrophysics Data System (ADS)

    Doroshenko, M. E.; Papashvili, A. G.; Alimov, O. K.; Martynova, K. A.; Konyushkin, V. A.; Nakladov, A. N.; Osiko, V. V.; Jelinkova, H.; Sulc, J.; Nemec, M.

    2016-01-01

    The formation of new Tm3+ tetragonal optical centers with spectroscopic properties different from those for regular ones in hot-formed CaF2 ceramics is observed. The influence of the new centers formation on the fluorescence and laser properties of the 2 ?m 3F43H6 transition under ~795?nm laser diode excitation is studied.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    PubMed

    Moyers, M F; Nelson, G A

    2009-08-01

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

  2. Fractal and multifractal characteristics of swift heavy ion induced self-affine nanostructured BaF2 thin film surfaces.

    PubMed

    Yadav, R P; Kumar, Manvendra; Mittal, A K; Pandey, A C

    2015-08-01

    Fractal and multifractal characteristics of self-affine surfaces of BaF2 thin films, deposited on crystalline Si ⟨1 1 1⟩ substrate at room temperature, were studied. Self-affine surfaces were prepared by irradiation of 120 MeV Ag(9+) ions which modified the surface morphology at nanometer scale. The surface morphology of virgin thin film and those irradiated with different ion fluences are characterized by atomic force microscopy technique. The surface roughness (interface width) shows monotonic decrease with ion fluences, while the other parameters, such as lateral correlation length, roughness exponent, and fractal dimension, did not show either monotonic decrease or increase in nature. The self-affine nature of the films is further confirmed by autocorrelation function. The power spectral density of thin films surfaces exhibits inverse power law variation with spatial frequency, suggesting the existence of fractal component in surface morphology. The multifractal detrended fluctuation analysis based on the partition function approach is also performed on virgin and irradiated thin films. It is found that the partition function exhibits the power law behavior with the segment size. Moreover, it is also seen that the scaling exponents vary nonlinearly with the moment, thereby exhibiting the multifractal nature. PMID:26328566

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

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Vogt, Jochen

    2007-06-01

    The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (11) translational symmetry already after an exposure of 3L (1L =10-6Torrs) at temperatures below 150K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 462kJmol-1, corresponding to a desorption temperature of 165K. The desorption of multilayers was observed at 150K, consistent with a binding energy of 422kJmol-1. Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (?3 ?3 )R30 lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200K, consistent with an unexpectedly strong bonding of the molecules to the substrate.

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

    NASA Astrophysics Data System (ADS)

    Matsutani, Akihiro; Ohtsuki, Hideo; Koyama, Fumio

    2008-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  10. Actinide burner fuel: Potential compositions based on the thermodynamic evaluation of MF-PuF 3 (M = Li, Na, K, Rb, Cs) and LaF 3-PuF 3 systems

    NASA Astrophysics Data System (ADS)

    Beneš, O.; Konings, R. J. M.

    2008-07-01

    In previous studies a thermodynamic description of the LiF-NaF-KF-RbF-CsF-LaF 3 system was presented. In order to add PuF 3 to this system the assessments of LiF-PuF 3, NaF-PuF 3, KF-PuF 3, RbF-PuF 3, CsF-PuF 3 and LaF 3-PuF 3 binary phase diagrams have been made. In case of the LiF-PuF 3 and NaF-PuF 3 the assessments have been based on known experimental data. The other binary systems have not been measured yet and the thermodynamic description has been made using the excess parameters from the previously assessed binaries containing LaF 3, which is considered as a proxy compound for PuF 3. The main aim of this study is to analyze potential compositions for a molten salt fast burner fuel.

  11. Studies of EPR spectra and defect structure for Er3+ ions in BaF2 and SrF2 crystals

    NASA Astrophysics Data System (ADS)

    Li, Hui; Kuang, Xiao-Yu; Mao, Ai-Jie; Li, Cheng-Gang

    2013-02-01

    The local lattice structure and electron paramagnetic resonance (EPR) spectra have been studied systematically by diagonalizing 364 × 364 complete energy matrices for a f11 ion in a trigonal ligand-field. By simulating the calculated Stark levels and EPR parameters to the experimental results, the shift parameters are determined for Er3+ ions in BaF2 and SrF2. The results show that the trigonal center is attributed to an interstitial F- ion located at the [1 1 1] axis of the cube, and the nearest ligand close to the charge compensator has a displacement towards central ion by 0.042 Å for L center in BaF2:Er3+ and 0.026 Å for J center in SrF2:Er3+, respectively. Moreover, the relationships between g-factors and shift parameter ΔZ as well as orbit reduction factor k' are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  13. The role of graphite boat design in liquid phase epitaxial growth of PbSe 0.78Te 0.22 on BaF 2

    NASA Astrophysics Data System (ADS)

    McCann, Patrick J.; Aanegola, Srinath K.

    1994-08-01

    Two different sliding substrate graphite boats were designed and fabricated for liquid phase epitaxial (LPE) growth of PbSe 0.78Te 0.22 on BaF 2 substrates. Layer morphologies were observed using optical and scanning electron microscopy. The first boat did not yield smooth and continuous epitaxial layers even though a number of growth variations were tried. The second boat, however, consistently produced high quality epitaxial layers of PbSe 0.78Te 0.22 on {100} BaF 2 substrates. Differences in the way the graphite boat traps growth solution vapors over the substrate prior to growth are believed to be responsible for the dramatic differences in these LPE growth morphologies. We suspect that formation of a barium-chalcogenide reaction product on the BaF 2 substrate surface prior to growth is essential for obtaining good epitaxial layers and that trapping of growth solution vapors over the substrate prior to growth allows better control of this epitaxy-enabling substrate surface reaction.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1997-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  17. Transmission and reflection studies of thin films in the vacuum ultraviolet

    NASA Technical Reports Server (NTRS)

    Peterson, Lennart R.

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

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

    SciTech Connect

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

    2005-05-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    SciTech Connect

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    A kinetic study for isothermal melt crystallization of CaO-SiO2-CaF2-based mold fluxes with different basicity of 0.94 and 1.34 has been carried out systematically by DSC measurements. The kinetic parameters were determined by Johnson-Mehl-Avrami equation. The average Avrami exponent of cuspidine (3CaO2SiO2CaF2) crystallization for mold flux of lower basicity (0.94) is calculated to be 3.1, implying that the crystallization mode is instantaneous nucleation followed by 3-dimensional growth. For the mold flux of higher basicity (1.34), the average Avrami exponent of cuspidine equals to 3.4, strongly suggesting that the growth is still 3 dimensional but the nucleation should be continuous. It was found that the effective crystallization rate constant for both mold fluxes increases as the crystallization temperature decreases, showing that the crystallization rate could be governed by nucleation rate. The negative effective activation energy indicates an anti-Arrhenius behavior for crystallization of the mold fluxes studied. Therefore, it is concluded that the melt crystallization for the commercial mold fluxes will be determined by thermodynamics of nucleation which is relevant to degree of undercooling. The morphology of cuspidine crystals observed by SEM agreeds well with the isothermal crystallization kinetics results.

  4. Paramagnetic hyperfine splitting in the E151u Mssbauer spectra of CaF2:Eu2+

    NASA Astrophysics Data System (ADS)

    Selling, J.; Bielemeier, B.; Wortmann, G.; Johnson, J. A.; Alp, E. E.; Chen, T.; Brown, D. E.; Johnson, C. E.; Schweizer, S.

    2008-06-01

    E151u Mssbauer spectra in zero magnetic field of highly dilute (0.1 mol%) Eu2+ ions in CaF2 showed an almost temperature-independent asymmetrically split pattern, arising from the paramagnetic hyperfine interaction AS.I in a cubic crystal field with slow electron spin relaxation; in a small external magnetic field B of 0.2 T such that g?BB>A an almost symmetrical pattern was observed. Both the spectra with and without external field are well described using the spin Hamiltonian and previous electron paramagnetic resonance data. A more concentrated (2 mol% Eu2+ ) sample exhibited a strongly broadened symmetrical resonance line due to an increased Eu-Eu spin relaxation rate; in an external magnetic field of 0.2 T the Mssbauer spectra exhibited further broadening and additional magnetic structures due to the reduced relaxation rate. When a large field of 6 T was applied such that g?BB is much larger than the crystal field splitting, a fully resolved hyperfine pattern was observed at 2.5 K, with an effective field at the Eu nuclei of -33.7T ; at higher temperatures superimposed patterns originating from excited electronic states were observed in the spectra. The present results on the highly dilute CaF2:0.1%Eu2+ sample deliver a straightforward explanation for previous observations of a seemingly large dependence of the Eu2+ isomer shift on europium concentration.

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

    NASA Astrophysics Data System (ADS)

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

    1989-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    PubMed

    Yu, Shenglei; Yang, Zhongmin; Xu, Shanhui

    2010-05-01

    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

  10. A Study of the Superfluid Transition in Helium Films Adsorbed to a Rough CaF2 Surface Over a Large Temperature Range

    NASA Astrophysics Data System (ADS)

    Schwarz, Marty; Wadleigh, Laura; Luhman, Dwight

    2013-03-01

    Rough two-dimensional substrates, such as thermally deposited CaF2, 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 use a single rough CaF2 substrate and study the superfluid transition in adsorbed helium films over a wide range of temperatures. Our results show that as the transition temperature increases the abrupt jump in superfluid density at the transition become less distinct. The changing characteristics of the transition on a single CaF2 substrate with temperature suggest that the reduced observability of the transition on rough substrates cannot be explained entirely by simple surface geometry effects, such as tortuosity.

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

    NASA Astrophysics Data System (ADS)

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

    1994-01-01

    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 (770C) 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.

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2016-04-01

    This study evaluated if Carbon dioxide (CO2) (λ 10.6 μm) laser irradiation combined with acidulated phosphate fluoride gel application (APF gel) enhances "CaF2" uptake by demineralized enamel specimens (DES) and inhibits enamel lesion progression. Thus, two studies were conducted and DES were subjected to APF gel combined or not with CO2 laser irradiation (11.3 or 20.0 J/cm(2), 0.4 or 0.7 W) performed before, during, or after APF gel application. In study 1, 165 DES were allocated to 11 groups. Fluoride as "CaF2 like material" formed on enamel was determined in 100 DES (n = 10/group), and the surface morphologies of 50 specimens were evaluated by scanning electron microscopy (SEM) before and after "CaF2" extraction. In study 2, 165 DES (11 groups, n = 15), subjected to the same treatments as in study 1, were further subjected to a pH-cycling model to simulate a high cariogenic challenge. The progression of demineralization in DES was evaluated by cross-sectional microhardness and polarized light microscopy analyses. Laser at 11.3 J/cm(2) applied during APF gel application increased "CaF2" uptake on enamel surface. Laser irradiation and APF gel alone arrested the lesion progression compared with the control (p < 0.05). Areas of melting, fusion, and cracks were observed. CO2 laser irradiation, combined with a single APF application enhanced "CaF2" uptake on enamel surface and a synergistic effect was found. However, regarding the inhibition of caries lesion progression, no synergistic effect could be demonstrated. In conclusion, the results have shown that irradiation with specific laser parameters significantly enhanced CaF2 uptake by demineralized enamel and inhibited lesion progression. PMID:26873502

  14. Spectroscopic properties of Yb-doped CaF2-YF3 solid-solution laser crystal

    NASA Astrophysics Data System (ADS)

    Wu, Yeqing; Su, Liangbi; Wang, Qingguo; Li, Hongjun; Zhan, Yaoyu; Jang, Dapeng; Qian, Xiaobo; Wang, Chuanyong; Zheng, Lihe; Chen, Hongbing; Xu, Jun; Ryba-Romanowski, Witold; Solarz, Piotr; Lisiecki, Radoslaw

    2013-10-01

    The spectroscopic properties of Yb:CaF2-YF3 disordered crystals obtained by the vertical Bridgman method were studied. The 3 at.% Yb, 3 at.% Y:CaF2 crystal absorption cross section ?abs centered at 974 nm reached 7.2 10-21 cm2 and the fluorescence lifetime was 3.54 ms at room temperature. Experimental results show that co-doping Y3+ ions at different Y:Yb ratios can modulate the spectroscopy and lengthen the luminescence lifetime of Yb3+ ions in the CaF2 lattice. There are three main kinds of lattice in the 3 at.% Yb, 3 at.% Y:CaF2 crystal, as concluded from the low-temperature spectra.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-01-01

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

  19. Nonlinear Luminescence Response of CaF2:Eu and YAlO3:Ce to Single-Ion Excitation

    SciTech Connect

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

    2014-01-21

    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-flightscintillatorphotoelectric 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

    The interaction of water with freshly cleaved BaF2(111) surfaces at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes. The images strongly suggest a high surface diffusion of water molecules on the surface indicated by the accumulation of water at step edges forming two-dimensional bilayered structures. Steps running along the ?110? crystallographic directions show a high degree of hydrophilicity, as evidenced by small step-film contact angles, while steps running along other directions exhibiting a higher degree of kinks surprisingly behave in a quite opposite way. Our results prove that morphological defects such as steps can be crucial in improving two-dimensional monolayer wetting and stabilization of multilayer grown on surfaces that show good lattice mismatch with hexagonal ice.

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

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

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

  2. Impurity-trapped excitons and electron traps in CaF2:Yb2+ and SrF2:Yb2+ probed by transient photoluminescence enhancement

    NASA Astrophysics Data System (ADS)

    Senanayake, P. S.; Wells, J. P. R.; Reid, M. F.; Berden, G.; Meijerink, A.; Reeves, R. J.

    2013-01-01

    CaF$_2$:Yb$^{2+}$ and SrF$_2$:Yb$^{2+}$ crystals have been investigated by a two-color UV + IR transient photoluminescence enhancement technique. The enhancement gives information about both changes in internal energy levels of the excitons and liberation of electrons from traps in the crystals.

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

    PubMed

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  7. Growth of CsLiB6O10 thin films on Si substrate by pulsed laser deposition using SiO2 and CaF2 as buffer layers

    NASA Astrophysics Data System (ADS)

    Yeo, J. S.; Akella, A.; Huang, T. F.; Hesselink, L.

    1998-03-01

    CsLiB6O10 (CLBO) thin films are grown on Si (100) and (111) substrates using lower index SiO2 and CaF2 as buffer layers by pulsed KrF (248 nm) excimer laser ablation of stoichiometric CLBO targets over a temperature range of 425 to 725°C. A CaF2 buffer layer is grown on Si by laser ablation while SiO2 is prepared by standard thermal oxidation. From extended x-ray analysis, it is determined that CaF2 is growth with preferred orientation on Si (100) at temperatures lower than 525°C while on Si (111) substrate, CaF2 is grown epitaxially over the temperature range; this agrees well with observed reflection high energy electron diffraction patterns. X-ray 2θ-scans indicate that crystalline CLBO are grown on SiO2/Si and CaF2/Si (100). Analysis of reflectance spectra from CLBO/SiO2/Si yields the absorption edge at 182 nm. Surface roughness of the CaF2 and CLBO/CaF2/Si film are 19 and 15 nm, respectively. This relatively rough surface caused by the ablation of wide bandgap CaF2 and CLBO limits the application of CLBO for waveguiding measurement.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  9. Initial CaF2 reactions on Si(1 1 4)-2 1: Isolated silicides, faceting and partial CaF adsorption

    NASA Astrophysics Data System (ADS)

    Kim, Hidong; Duvjir, Ganbat; Dugerjav, Otgonbayar; Li, Huiting; Seo, Jae M.

    2015-12-01

    When CaF2 molecules are deposited on Si(1 1 4)-2 1 held at 500 C, two kinds of isolated and symmetric Ca-silicide units are initially formed. With increasing CaF2 deposition to 0.4 ML, instead of the terrace being filled with them, a trench composed of (1 1 3) and (1 1 7) facets appears on the surface as a result of substrate etching induced by dissociated F atoms. Selectively on this (1 1 3) facet, a 2 2 CaF overlayer is formed uniformly. In the present studies, using scanning tunneling microscopy and synchrotron photoemission spectroscopy, the origins of such isolation of Ca-silicide units on the (1 1 4) terrace as well as selective adsorption of CaF on the (1 1 3) facet have been disclosed.

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

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  11. CaF2-Based Near-Infrared Photocatalyst Using the Multifunctional CaTiO3 Precursors as the Calcium Source.

    PubMed

    Huang, Shouqiang; Guo, Shengjuan; Wang, Qingji; Zhu, Nanwen; Lou, Ziyang; Li, Liang; Shan, Aidang; Yuan, Haiping

    2015-09-16

    Multistage formation of fluoride upconversion agents from the related-semiconductor precursors provides a promising route for the fabrication of near-infrared (NIR) photocatalysts with high photocatalytic activities. Herein, the cotton templated CaTiO3 "semiconduction" precursors (C-CaTiO3) were used to synthesize the NIR photocatalyst of Er3+/Tm3+/Yb3+-(CaTiO3/CaF2/TiO2) (C-ETYCCT), and the functions of the Ca2+ source for CaF2 and the heterostructure formations were displayed by C-CaTiO3. The generated CaF2 acted as the host material for the lanthanide ions, and the heterostructures were constructed among anatase, rutile, and the remaining CaTiO3. The induced oxygen vacancies and Ti3+ ions enabled the samples to utilize most of the upconversion luminescence for photocatalysis. The NIR driven degradation rate of methyl orange (MO) over C-ETYCCT reached 52.34%, which was 1.6 and 2.5 times higher than those of Er3+/Tm3+/Yb3+-(CaTiO3/TiO2) (C-ETYCT) and Er3+/Tm3+/Yb3+-(CaTiO3/CaF2) (C-ETYCC), respectively. The degradation rates of MO and salicylic acid over C-ETYCCT with UV-vis-NIR light irradiation were also much higher than those of other samples, which were mainly results of the contributions of its high upconversion luminescence and the efficient electron-hole pair separation. PMID:26305907

  12. Influence of Fe and Cu seed layers on the magnetoresistance in Fe/Cu superlattices grown on Si(111) and CaF 2(111) /Si(111)

    NASA Astrophysics Data System (ADS)

    Mosca, D. H.; Mattoso, N.; Kakuno, E. M.; Schreiner, W. H.; Mazzaro, I.; Teixeira, S. R.

    1996-04-01

    The structural characterization of superlattices was carried out by X-ray diffraction, reflectivity measurements and TEM. Our results indicate that the superlattices are very different from the structural point of view, whereas the magnetoresistance values are rather similar with respect to the magnitude and field dependence at room temperature, independently of the Cu and Fe 50 seed layers grown on Si(111) or Si(111)/CaF 2(111).

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    The crystallization characteristics of CaF2-CaO-Al2O3 slags with varying amounts of SiO2 were experimentally studied. The effects of slag crystallization behaviors on the horizontal heat transfer and lubrication performance in drawing-ingot-type electroslag remelting (ESR) were also evaluated in terms of as-cast ingots surface quality and drawing-ingot operation. The results show that increasing SiO2 addition from 0 to 6.8 mass pct strongly suppresses the crystallization of ESR type CaF2-CaO-Al2O3 slags. The crystallization temperature of the studied slags decreases with the increase in SiO2 addition. The liquidus temperatures of the slags also show a decreasing trend with increasing SiO2 content. In CaF2-CaO-Al2O3-(SiO2) slags, faceted 11CaO7Al2O3CaF2 crystals precipitate first during continuous cooling of the slag melts, followed by the formation of CaF2 at lower temperatures. 11CaO7Al2O3CaF2 was confirmed to be the dominant crystalline phase in the studied slags. CaF2-CaO-Al2O3 slags with a small amount of SiO2 addition are favorable for providing sound lubrication and horizontal heat transfer in mold for drawing-ingot-type ESR, which consequently bring the improvement in the surface quality of ESR ingot and drawing-ingot operating practice as demonstrated by plant trials.

  16. Radiation Damage Effects in Far Ultraviolet Filters and Substrates

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  2. Ab initio calculations on the O2 3--Y3+ center in CaF2 and SrF2: its electronic structure and hyperfine constants

    NASA Astrophysics Data System (ADS)

    Botis, Sanda M.; Adriaens, Davy A.; Pan, Yuanming

    2009-01-01

    The O2 3--Y3+ center in fluorite-type structures (CaF2 and SrF2) has been investigated at the density functional theory (DFT) level using the CRYSTAL06 code. Our calculations were performed by means of the hybrid B3PW method in which the Hartree-Fock exchange is mixed with the DFT exchange functional, using Becke’s three parameter method, combined with the non-local correlation functionals by Perdew and Wang. Our calculations confirm the stability and the molecular character of the O2 3--Y3+ center. The unpaired electron is shown to be almost exclusively localized on and equally distributed between the two oxygen atoms that are separated by a bond distance of 2.47 Å in CaF2 and 2.57 Å in SrF2. The calculated 17O and 19F hyperfine constants for of the O2 3--Y3+ center are in good agreement with their corresponding experimental values reported by previous electron paramagnetic resonance and electron nuclear double resonance studies, while discrepancies are notable for the 89Y hyperfine constants.

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

    NASA Astrophysics Data System (ADS)

    Robelin, Christian; Chartrand, Patrice

    2007-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  5. Influence of substituting B2O3 for CaF2 on the bonding behaviour to bone of glass-ceramics containing apatite and wollastonite.

    PubMed

    Kitsugi, T; Yamamuro, T; Nakamura, T; Yoshii, S; Kokubo, T; Takagi, M; Shibuya, T

    1992-01-01

    Glass-ceramics containing crystalline oxy-fluoroapatite (Ca10(PO4)6(O,F2)) and wollastonite (CaSiO3) (designated AWGC) are reported to have a fairly high mechanical strength as well as the capability of forming a chemical bond with bone tissue. The chemical composition is MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, and CaF2 0.5 in weight ratio. In this study the influence of substituting B2O3 for CaF2 on the bonding behaviour of glass-ceramics containing apatite and wollastonite to bone tissue was investigated. Two kinds of glass-ceramics containing apatite and wollastonite were prepared. CaF2 0.5 was replaced with B2O3 at 0.5 and 2.0 in weight ratio (designated AWGC-0.5B and AWGC-2.0B). Rectangular ceramic plates (15 x 10 x 2 mm, abraded with No. 2000 alumina powder) were implanted into a rabbit tibia. The failure load, when an implant detached from the bone, or the bone itself broke, was measured. The failure load of AWGC-0.5B was 8.00 +/- 1.82 kg at 10 weeks after implantation and 8.16 +/- 1.36 kg at 25 weeks after implantation. The failure load of AWGC-2B was 8.08 +/- 1.70 kg at 10 weeks after implantation and 9.92 +/- 2.46 kg at 25 weeks after implantation. None of the loads for the two kinds of glass-ceramics decreased as time passed. Giemsa surface staining and contact microradiography revealed direct bonding between glass-ceramics and bone. SEM-EPMA showed a calcium-phosphorus rich layer (reaction zone) at the interface of ceramics and bone tissue. The thickness of the reaction zone was 10 to -15 microns and did not increase as time passed.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1610964

  6. Surface-enhanced resonance Raman scattering of trivalent metal tetraphenylporphine complexes in a layered structure of a CaF 2-roughened substrate/sample/Ag

    NASA Astrophysics Data System (ADS)

    Takenaka, A.; Takeuchi, S.; Kobayashi, Y.; Itoh, K.

    1985-07-01

    Surface-enhanced resonance Raman scattering spectra were measured for trivalent metal tetraphenylporphine complexes, such as Fe(III)TPPCl, Mn(III)TPPCl and Cr(III)TPPCl, in a layered structure having a CaF 2-roughened substrate/sample/Ag configuration. Each surface spectrum is appreciably different from the resonance Raman scattering spectrum of the corresponding metalloporthine but similar to the RRS spectrum of the corresponding ?-oxo dimer ([Fe(III)TPP] 2O or [Mn(III)TPP] 2) or a monohydroxy complex Cr(III)TPPOH. This result indicates that, when the above-mentioned metalloporphines interact with Ag vapor during its deposition process, the complexes are converted to the ?-oxo dimers and the monohydroxy complex, respectively.

  7. Direct comparison of Yb3+:CaF2 and heavily doped Yb3+:YLF as laser media at room temperature.

    PubMed

    Pirri, Angela; Alderighi, Daniele; Toci, Guido; Vannini, Matteo; Nikl, Martin; Sato, Hiroki

    2009-09-28

    We report an extensive comparison of the laser performances of diode-pumped Yb(3+):YLF (30% at.) and Yb(3+):CaF(2) (5% at.) crystals, lasing at room-temperature and operating in two different operation mode, i.e. Continuous Wave (CW) and quasi-CW. An in-depth investigation of the crystals behavior by changing the pump power, clearly shows the crystal absorption depends on the lasing conditions. Therefore, we report an unambiguous definition of the slope efficiency calculated taken into account the real measured crystal absorption under laser action. Finally, we present a study of problems related to thermally induced losses which are expected influencing the laser performance. PMID:19907622

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  10. Spin-Hamiltonian parameters for the tetragonal GdM3+-Fi- centers in CaF2 and SrF2 crystals

    NASA Astrophysics Data System (ADS)

    Yang, Wei-Qing; Zhang, Ying; Lin, Yuan; Zheng, Wen-Chen

    2013-02-01

    The spin-Hamiltonian parameters (g factors g//, g⊥ and zero-field splittings b20, b40, b44, b60, b64) of the tetragonal GdM3+-Fi- centers in CaF2 and SrF2 crystals at T ≈ 1.8 K are calculated from the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters used are estimated from the superposition model with the reported defect structural data obtained from the analyses of superhyperfire interaction constants at the same temperature. The calculated results are in reasonable agreement with the experimental values. It appears that the above defect structural data reported in the previous paper are suitable and the diagonalization (of energy matrix) method is effective to the studies of spin-Hamiltonian parameters for 4f7 ions in crystals.

  11. Thermodynamic evaluation and optimization of the LiF-NaF-KF-MgF2-CaF2 system using the modified quasi-chemical model

    NASA Astrophysics Data System (ADS)

    Chartrand, Patrice; Pelton, Arthur D.

    2001-06-01

    A complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the LiF-NaF-KF-MgF2-CaF2 system and optimized model parameters have been found. The model parameters obtained for binary and ternary subsystems can be used to predict thermodynamic properties and phase equilibria for the multicomponent system. The modified quasi-chemical model for short-range ordering (SRO) was used for the molten salt phase. For solutions with NaF or KF together with MgCl2 or CaCl2, the calculations indicate a large degree of ordering on the cationic sublattice, with Mg-alkali and Ca-alkali second-nearest-neighbor (SNN) pairs being favored.

  12. Characterization of epitaxial EuS(111) thin films on BaF2(111) and SrF2(111) substrates grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Senba, Shinya; Matsumoto, Naoki; Jomura, Mitsuhiro; Asada, Hironori; Koyanagi, Tsuyoshi; Kishimoto, Kengo; Fukuma, Yasuhiro

    2013-06-01

    We have successfully grown EuS (111) epitaxial films on BaF2 (111) and SrF2 (111) substrates by using molecular beam epitaxy at substrate temperatures ( T S 's) between 100 and 500 °C. Pole figures of X-ray diffraction indicate a high degree of in-plane orientation, and all of the samplesshow very high resistivity. The surface roughness for 10-nm-thick EuS films on BaF2 (111) and SrF2 (111) substrates measured by using atomic force microscopy (AFM) are 0.122 and 0.092 nm, respectively. The Curie temperature of the EuS films increases up to ˜16 K with increasing T S . We also try to manipulate the coercive force, which is an important magnetic property, by Te-doping to achieve an anti-parallel magnetization state between two ferromagnetic layers in spin devices. The obtained coercive force for the Te-doped film (110 Oe) is large compared with that for the undoped one (20 Oe).

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    The new ternary compound Al15Ge4Ni3 (?2 in the system Al-Ge-Ni) was synthesized in single crystalline form by a special annealing procedure from samples located in the three phase fields [L+Al+?2] and [L+Ge+?2]. The crystal structure of Al15Ge4Ni3 was determined by single-crystal X-ray diffraction. The compound crystallizes in a new structure type in space group I43m, Pearson Symbol cI88, cubic lattice parameter a=11.405(1) . Phase diagram investigations indicate stoichiometric composition without considerable homogeneity range; ?2 melts peritectically at T=444 C. The crystal structure of Al15Ge4Ni3 shows a unique combination of simple Cu3Au- and CaF2-type building blocks: a three dimensional network of CaF2-type units, formed by Ni and Al atoms, is interspaced by clusters (Al6Ge8) resembling unit cells of the Cu3Au-type. Both structural motifs are connected by Al-Ge bonds. The ground state energy of the compound was obtained by DFT calculations and the densities of states were analyzed in detail. In addition, electron density maps were calculated in four different sections through the unit cell using the full potential linearized augmented plane-wave (FLAPW) method. The bonding situation in Al15Ge4Ni3 was discussed combining results from electronic calculations with the analysis of the coordination of atoms.

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

    NASA Astrophysics Data System (ADS)

    Barandiarán, Zoila; Seijo, Luis

    2015-10-01

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

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

    PubMed

    Barandiarán, Zoila; Seijo, Luis

    2015-10-14

    Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF2 and Yb/Sr pairs in SrF2 crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4f(N-1)5d excited states of Y b(2+): these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b(2+) + Ca(2+) (Sr(2+)) → Y b(3+) + Ca(+) (Sr(+)) electron phototransfer. This mechanism applies to all the observed Y b(2+) 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b(2+) because the Y b(3+)-Ca(+) states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b(2+) at the wavelengths of the first 4f-5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b(2+) active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF2 host, associated with the lowest 4f-5d band. PMID:26472390

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

    SciTech Connect

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

    2001-01-12

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

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

    NASA Astrophysics Data System (ADS)

    Ochoa, Franklyn E. Colmenares

    2006-12-01

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

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

    PubMed Central

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

    2014-01-01

    Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, Tc, of the material. In this paper we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density (Fp = Jc 0H) by more than 60% compared to a single layer film, reaching a maximum of 84?GN/m3 at 22.5?T and 4.2?K, the highest value ever reported in any 122 phase. PMID:25467177

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

    DOE PAGESBeta

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

    2014-12-03

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

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

    SciTech Connect

    Ochoa, Franklyn E. Colmenares

    2006-12-04

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

  1. Angular-dependent vortex pinning mechanism and magneto-optical characterizations of FeSe0.5Te0.5 thin films grown on CaF2 substrates

    NASA Astrophysics Data System (ADS)

    Yuan, Pusheng; Xu, Zhongtang; Ma, Yanwei; Sun, Yue; Tamegai, Tsuyoshi

    2016-03-01

    Magneto-optical (MO) characterizations and the angular-dependent critical current density (J c(Θ)) of epitaxial FeSe0.5Te0.5 (FST) thin films grown on CaF2 single-crystalline substrates were performed. The MO images show typical rooftop patterns in the remanent state from which a large, homogeneous, and almost isotropic self-field J c over 2 × 106 A cm‑2 at 8 K was obtained. The vortex pinning mechanism is investigated measuring the magnetic field and angular-dependent critical current density J c. The FST films exhibit small anisotropy of J c in the whole applied magnetic field range below 15 K. The Dew-Hughes model and angular scaling analyses prove that pointlike normal cores, which are distributed randomly in the FST film, dominate the pinning in the FST films on CaF2 substrates.

  2. SPECIAL ISSUE DEVOTED TO THE 25th ANNIVERSARY OF THE A.M. PROKHOROV GENERAL PHYSICS INSTITUTE: Efficient lasing in diode-pumped Yb3+:CaF2-SrF2 solid-solution single crystals

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

    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 was 83%.

  3. SPECIAL ISSUE DEVOTED TO THE 90TH ANNIVERSARY OF A.M. PROKHOROV: Continuously tunable cw lasing near 2.75 ?m in diode-pumped Er3+ : SrF2 and Er3+ : CaF2 crystals

    NASA Astrophysics Data System (ADS)

    Basiev, Tasoltan T.; Orlovskii, Yu V.; Polyachenkova, M. V.; Fedorov, Pavel P.; Kuznetsov, S. V.; Konyushkin, V. A.; Osiko, Vyacheslav V.; Alimov, Olimkhon K.; Dergachev, Alexey Yu

    2006-07-01

    CW lasing is obtained in Er3+(5%) : CaF2 and Er3+(5%) : SrF2 crystals near 2.75 ?m with 0.4 and 2 W of output powers, respectively, upon transverse diode laser pumping into the upper 4I11/2 laser level of erbium ions at 980 nm. Continuous tuning of the laser wavelength between 2720 and 2760 nm is realised in the Er3+ : SrF2 crystal.

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

    PubMed Central

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

    2015-01-01

    Summary There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.51 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 34 nm above the surface when the formation of a capillary neck dominates the tipsample interaction. PMID:25977852

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

    PubMed

    Napast, Viktor; Mokon, Joe; Homak, Marko; Petek, Aljana; Gaber?ek, Miran

    2015-01-01

    The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: Pb, Bi and Sn. Two types of electrolytes were selected: Na3AlF6 -AlF3 - BaCl2 - NaCl and Li3AlF3 - BaF2. We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of Al-Pb system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode. PMID:26680707

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

    PubMed Central

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

    2012-01-01

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

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

    PubMed

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

    2015-05-01

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

  8. 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)

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

    2014-05-01

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

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

    PubMed

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

    2014-09-01

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

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

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1992-01-01

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

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

    SciTech Connect

    Whittenberger, J.D. )

    1992-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    PubMed

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

    2016-01-15

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

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

    PubMed

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

    2014-06-01

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

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

    PubMed

    Malherbe, Cedric; Eppe, Gauthier; Gilbert, Bernard

    2014-08-19

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

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

    PubMed

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    SciTech Connect

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

    2011-11-01

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

  19. Structural and functional characterisation of slab waveguides written in Er3+ - doped tellurite glass, CaF2, Bi4(GeO4)3 and Bi12GeO20 crystals via implantation of MeV N+ ions

    NASA Astrophysics Data System (ADS)

    Bnysz, I.; Berneschi, S.; Khanh, N. Q.; Lohner, T.; Fried, M.; Petrik, P.; Zolnai, Z.; Lengyel, K.; Pter, .; Watterich, A.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.

    2010-11-01

    Ion implantation proved to be a universal technique for producing waveguides in most optical materials. Tellurite glasses are used as hosts of rare-earth elements for the development of fibre and integrated optic amplifiers and lasers covering all the main telecommunication bands. Er3+- doped tellurite glasses are very attractive materials for the fabrication of broadband amplifiers in wavelength division multiplexing (WDM) around 1.55 ?m, as they exhibit large stimulated cross sections and broad emission bandwidth. First objective of the present research was to optimise parameters of waveguide fabrication in the Er: tellurite glass via implantation of MeV energy N+ ions in a wide range of implanted doses. Besides of glasses, slab optical waveguides were designed and fabricated in CaF2, Bi4Ge3O12 and Bi12GeO20 crystals, also using MeV energy N+ ions. Waveguides were characterised using UV/VIS and NIR absorption spectroscopy, spectroscopic ellipsometry and m-line spectroscopy. Part of the implanted samples was annealed to improve waveguide properties. We report on first working slab waveguides fabricated in CaF2 crystals using implantation of MeV-energy medium-mass ions.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    DOE Data Explorer

    Kristin Persson

    2014-11-02

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

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

    SciTech Connect

    Kristin Persson

    2014-11-02

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

  4. Crystallization of heavy metal fluoride glasses

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

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

    PubMed

    Ode, Aiko

    2014-02-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1993-03-01

    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.

  10. Flame synthesis of calcium-, strontium-, barium fluoride nanoparticles and sodium chloride.

    PubMed

    Grass, Robert N; Stark, Wendelin J

    2005-04-01

    Non-oxidic salts such as NaCl, CaF2, SrF2 and BaF2 were synthesised using a flame spray method; optional doping of such fluorides with rare earth elements suggests possible applications in optics. PMID:15791326

  11. 5 d-4 f luminescence of Nd3+, Gd3+, Er3+, Tm3+, and Ho3+ ions in crystals of alkaline earth fluorides

    NASA Astrophysics Data System (ADS)

    Radzhabov, E. A.; Prosekina, E. A.

    2011-09-01

    The vacuum ultraviolet emission spectra of alkaline-earth fluoride (CaF2, SrF2, BaF2) crystals with rare earth impurity ions (Nd, Gd, Er, Tm, Ho) have been investigated. The main luminescence bands are described well by the transitions from the lowest excited 5 d state to different 4 f levels of rare earth ions.

  12. Versatile fluoride substrates for Fe-based superconducting thin films

    NASA Astrophysics Data System (ADS)

    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

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  14. Note: response characteristics of the sensor based on LaF3 thin film to different humidified gases.

    PubMed

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

    2012-05-01

    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 N(2), 5% O(2), and 50% O(2) 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 O(2) 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. PMID:22667667

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

    SciTech Connect

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

    2001-06-24

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

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

    SciTech Connect

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

    2001-07-12

    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.

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

    SciTech Connect

    Kristin Persson

    2014-11-02

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

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  19. Communication: Growing room temperature ice with graphene

    NASA Astrophysics Data System (ADS)

    Verdaguer, Albert; Segura, Juan Jos; Lpez-Mir, Laura; Sauthier, Guillaume; Fraxedas, Jordi

    2013-03-01

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

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

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; DellaCorte, Christopher

    2003-01-01

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

  1. limination du bore du silicium par plasma inductif sous champ lectrique

    NASA Astrophysics Data System (ADS)

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

    1993-05-01

    We analyzed purification mechanisms of silicon by inductive plasma with a fluoride slag. The aim is to study boron elimination from doped electronic grade silicon in function of the nature of the slag to obtain a photovoltaic grade silicon. The steady began with the calculation and the comparison of the stability diagram of boron compounds in presence of CaF2, BaF2 and MgF2. This study led us to conclude that BaF2 is the better slag for silicon purification. This has been confirmed by experience. In a second time, we made purifications under electric bias to enhance slag efficiency. We noticed that BaF2 is more sensitive to electric bias than other slags. Nous avons analys le mcanisme de purification du silicium sous plasma inductif en prsence d'un laitier fluor. L'objectif principal est d'tudier l'limination du bore du silicium lectronique dop en fonction de la nature du fluorure pour obtenir un silicium de qualit photovoltaque. L'tude a commenc par l'tablissement et la comparaison de diagrammes des composs du bore en prsence de CaF2, de MgF2 et de BaF2. Nous avons dduit de cette premire tude que BaF2 est le meilleur laitier pour la purification du silicium. Ceci a t corrobor par l'exprience. Nous avons ensuite opr en prsence d'un champ lectrique dans le but d'amliorer encore l'efficacit des laitiers. Nous avons constat que BaF2 est plus sensible au champ lectrique que les deux autres laitiers utiliss.

  2. A Study of the Superfluid Transition in $(4) {He} 4 He Films Adsorbed to Rough {CaF}_2$ CaF 2 Over a Large Temperature Range

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    Rough two-dimensional substrates, such as thermally deposited , 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 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 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.

  3. Excitation of Pr3+ ions in alkaline-earth fluorides

    NASA Astrophysics Data System (ADS)

    Radzhabov, E.; Nagirnyi, V.

    2010-11-01

    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 SrF2 is assumed to be caused by the closeness of a local vibronic frequency to the lattice phonon one. Excitation spectra of 4f-4f and 5d-4f transitions are substantially different pointing on to the different excitation mechanisms of both groups of lines. The 4f-4f lines show an intense excitation peak adjacent to the exciton peak. This infers that excitons created near to Pr3+ ions can feed the 4f-4f transitions. The efficiency of excitation of the 4f-4f and 5d-4f emission bands is quite low in the region of band-to-band transitions. An apparent peak at 19 eV in the excitation spectrum of the BaF2-Pr 5d-4f emission (230 nm) coincides well with that of the crossluminescence. No similar peaks were observed in CaF2 or SrF2 excitation spectra. We conclude that the main channel of energy transfer from the host to Pr3+ ions is realized resonantly through crossluminescence in BaF2-Pr.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  6. Brillouin lasing with a CaF2 whispering gallery mode resonator.

    PubMed

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

    2009-01-30

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    The laser quality transparent СаF2:Tm fluoride ceramics has been prepared by hot forming. Comparative study of absorption and emission spectra of СаF2:Tm (4 mol.% TmF3) ceramic and single crystal samples demonstrated that these materials possess almost identical spectroscopic properties. Laser oscillations of СаF2:Tm ceramics were obtained at 1898 nm under diode pumping, with the slope efficiency of 5.5%. Also, the continuous-wave (CW) laser have been obtained for СаF2:Tm single crystal at 1890 nm pumped by a diode laser was demonstrated.

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

    SciTech Connect

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

    1999-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  10. Absolute Light Yield Measurements on SrF_2 and BaF_2 Doped With Rare Earth Ions

    NASA Astrophysics Data System (ADS)

    Shendrik, Roman; Radzhabov, Evgeny

    2014-02-01

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

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

    SciTech Connect

    Ullmann, J. L.

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

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

    PubMed

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

    2008-05-29

    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

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

    PubMed

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

    2012-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    PubMed

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

    2012-10-15

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

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

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

  19. Spatial inhomogeneity in crystalline materials and saddle-type congruent melting points in ternary systems

    NASA Astrophysics Data System (ADS)

    Fedorov, P. P.; Buchinskaya, Irina I.

    2012-01-01

    Solidification of multicomponent melts to solid solutions is considered in terms of thermodynamic topological analysis. The use of phase portraits of systems for finding congruent melting points (invariant points) is discussed. Methods for predicting the existence of invariant points in ternary systems are considered. An example analysis is presented for two series of fluoride systems (CaF2-SrF2-RF3 and SrF2-BaF2-RF3, where R are rare-earth elements). The stability of melt crystallization in the vicinity of congruent melting singular points of solid solutions is discussed. The bibliography includes 104 references.

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1997-04-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    PubMed Central

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

    2012-01-01

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

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

    SciTech Connect

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

    2012-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Nicoara, Irina; Stef, Marius; Pruna, Andreea

    2008-04-01

    Calcium fluoride crystals doped with YbF 3 and PbF 2-, NaF- and LiF-codoped were grown using the vertical Bridgman method. Transparent, high quality, with various high Yb 2+ 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 Pb 2+, Li + and Na + ions on the absorption spectra and on the Yb 2+ ions content has been studied. High-intensity emission bands in the near-UV spectral region, not reported before, have been observed for excitation by 230 nm. A comparison of our results with those obtained by other authors is also given.

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

    NASA Astrophysics Data System (ADS)

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

    2006-10-01

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

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

    SciTech Connect

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

    2006-03-13

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

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

    NASA Technical Reports Server (NTRS)

    Ward, LaNita D.

    2004-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Frey, Bradley J.; Leviton, Douglas B.

    2004-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  17. Generation of high-fidelity few-cycle pulses at 2.1 ?m via cross-polarized wave generation.

    PubMed

    Ricci, Aurlien; Silva, Francisco; Jullien, Aurlie; Cousin, Seth L; Austin, Dane R; Biegert, Jens; Lopez-Martens, Rodrigo

    2013-04-22

    We demonstrate the generation of temporally clean few-cycle pulses at 2.1 ?m by shortening of 6-optical-cycle pulses via cross-polarized wave (XPW) generation in BaF(2), CaF(2) and CVD-Diamond crystals. By combining spectra and single-shot third-order intensity cross-correlation traces in a novel Bayesian pulse retrieval technique, we measured pulse durations of 20 fs, corresponding to 2.8 optical cycles. Our results show that XPW generation in the infrared could provide a high-fidelity source of few-cycle pulses for strong-field physics applications. It could also serve as an injector for high-peak power ultrafast mid-IR wavelength parametric amplifiers. PMID:23609680

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

    NASA Technical Reports Server (NTRS)

    Dellacorte, C.; Edmonds, B. J.

    1995-01-01

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

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

    NASA Technical Reports Server (NTRS)

    DellaCorte, Chris

    1998-01-01

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

  20. Ionic charge transport, thermoactivated delocalization and interaction with radiation-induced defects in LiBaF3 crystals

    NASA Astrophysics Data System (ADS)

    Ziraps, V.; Kulis, P.; Tale, I.; Veispals, A.

    The ionic and ion-diffusion controlled thermally stimulated relaxation (TSR) processes in CaF2, BaF2 and LiBaF3 crystals have been investigated at 290-650 K by means of the ionic conductivity, ionic thermally stimulated depolarization current (TSDC) and X-ray induced optical absorption spectra TS bleaching (TSB) techniques. In the region of the extrinsic ionic conductivity a number of the ionic TSDC peaks (anion vacancy and interstitial detrapping) and correlated TSB stages have been detected for the first time. The TSR and TSB kinetics above RT in fluoride crystals (X-ray irradiated at RT) are initiated and controlled by the anion interaction with the radiation-induced defects, i.e., the anion diffusion controlled processes take place.

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

    NASA Technical Reports Server (NTRS)

    Stanford, Malcolm K.; DellaCorte, Christopher

    2002-01-01

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

  2. Some electronic and magnetic properties of Fluoride ion in Fluoride structure nanocrystals

    NASA Astrophysics Data System (ADS)

    Imtani, Ali Nasir

    2012-01-01

    We have investigated the effects of the environment potential around Fluoride ion on some important electronic and magnetic properties such as dipole polarisability, moment of oscillator strengths S(k) and magnetic susceptibility. The theoretical procedure is based on the variational-perturbation theory with two parameter trial functions incorporated in an ionic model. We estimate these properties in four cases for Fluoride ion; free ion, ion under different potentials, ion in the crystals and ion in nanocrystal, CdF2, CaF2, PbF2, SrF2 and BaF2. Our results indicate that these properties vary with ion environments and the free state of Fluoride ion has higher values and there is linearity behaviour of these properties with lattice constant. For Fluoride ion in nanocrystal, we have found that there is an extra parameter that can also affect the dipole polarisability, the number of ions in the structure.

  3. Patterning of insulating surfaces by electronic excitation

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

    The interaction of swift heavy ions with any material is governed by a strong electronic excitation. In insulators this often leads to permanent modifications. We have irradiated various insulating materials (SrTiO3,TiO2,Al2O3,CaF2,SrF2,BaF2,andLiF) with swift heavy ions and have studied the irradiated surfaces by means of scanning force microscopy. For all materials used in this study we find one nanosized hillock per incident ion if the beam is oriented perpendicular with respect to the surface. Under oblique angles we find elongated chains of discontinuous nanodots on all crystalline materials investigated here.

  4. Ceramic planar waveguide structures for amplifiers and lasers

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  5. Electronic structure of fluorides: general trends for ground and excited state properties

    NASA Astrophysics Data System (ADS)

    Cadelano, E.; Cappellini, G.

    2011-05-01

    The electronic structure of fluorite crystals are studied by means of density functional theory within the local density approximation for the exchange correlation energy. The ground-state electronic properties, which have been calculated for the cubic structures CaF2, SrF2, BaF2, CdF2, HgF2, β-PbF2, using a plane waves expansion of the wave functions, show good comparison with existing experimental data and previous theoretical results. The electronic density of states at the gap region for all the compounds and their energy-band structure have been calculated and compared with the existing data in the literature. General trends for the ground-state parameters, the electronic energy-bands and transition energies for all the fluorides considered are given and discussed in details. Moreover, for the first time results for HgF2 have been presented.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Barandiarán, Zoila; Seijo, Luis

    2014-12-01

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

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

    PubMed

    Barandiarán, Zoila; Seijo, Luis

    2014-12-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The dynamics of Tm3+ optical center formation with increasing thulium concentration and the influence of different optical centers on the fluorescence and laser properties of the 2 ?m 3F43H6 transition under ~795?nm laser diode excitation is studied.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  15. ZBLAN Microgravity Study

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    Ablation thresholds and damage behavior of cleaved and polished surfaces of CaF2, BaF2, LiF and MgF2 subjected to single-shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. For CaF2, standard polishing yields an ablation threshold of typically 20 J/cm2. When the surface is polished chemo-mechanically, the threshold can be raised to 43 J/cm2, while polishing by diamond turning leads to intermediate values around 30 J/cm2. Cleaved surfaces possess no well-defined damage threshold. When comparing different fluoride surfaces prepared by diamond turning it is found that the damage resistivity roughly scales with the band gap. We find an ablation threshold of 40 J/cm2 for diamond turned LiF while the MgF2 surface can withstand a fluence of more than 60 J/cm2 without damage. The damage topography of conventionally polished surfaces shows flaky ablation across the laser-heated area with cracks along the cleavage planes. No ablation is observed in the case of chemo- mechanical polishing; only a few cracks appear. Diamond turned surfaces show small optical absorption but mostly cracks and ablation of flakes and, in some cases, severe damage in the form of craters larger than the irradiated area. The origin of such different damage behavior is discussed.

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

    NASA Technical Reports Server (NTRS)

    Bhushan, B.; Gray, S.

    1978-01-01

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

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

    SciTech Connect

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

    2012-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  2. 4.5 W mid-infrared supercontinuum generation in a ZBLAN fiber pumped by a Q-switched mode-locked Tm3+- doped fiber laser

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    SciTech Connect

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

    2011-08-18

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    SciTech Connect

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

    2014-01-01

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

  7. Designing a 1.7-5.3 ?m athermalized lens

    NASA Astrophysics Data System (ADS)

    Bardazzi, R.

    2008-10-01

    In the framework of a research program a broad band lens (1.75.3 ?m) has been designed to be inserted in an optoelectronic system of the Italian Navy. The optoelectronic system operates over full spectral band or over one of the seven sub-bands that are selected inserting spectral filters mounted on a wheel. The optoelectronic system FOV is 20x15, aperture F/# 2.4 and it is optically athermalized in the range -30+70 C. Color aberrations correction and athermalization was obtained by means an appropriate choice of optical materials (Cleartran, Sapphire, BaF2 and CaF2). The optical athermalization has been achieved for an all aluminum mechanical mounting. The lens mechanical mounting is quite cheap as no moving parts are present while focusing is obtained regardless the objective temperature. The optical layout is composed by five lenses. The design was driven to have a low sensitive manufacturing and mounting tolerances. A diffractive lens free solution was selected because of the unacceptable radiation losses in the higher diffractive orders due to the wide spectral band. Dedicated BBAR coatings for Sapphire and Cleartran have been developed.

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

    PubMed

    Weil, Matthias

    2015-06-01

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

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

    NASA Technical Reports Server (NTRS)

    Stanford, M. K.; DellaCorte, C.

    2004-01-01

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

  10. Self-lubricating coatings for high-temperature applications

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E.

    1987-01-01

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

  11. Thermal lensing compensation optics for high power lasers

    NASA Astrophysics Data System (ADS)

    Scaggs, Michael; Haas, Gil

    2011-03-01

    Athermalization of focusing objectives is a common technique for optimizing imaging systems in the infrared where thermal effects are a major concern. The athermalization is generally done within the spectrum of interest and not generally applied to a single wavelength. The predominate glass used with high power infrared lasers in the near infrared of one micron, such as Nd:YAG and fiber lasers, is fused silica which has excellent thermal properties. All glasses, however, have a temperature coefficient of index of refraction (dn/dT) where as the glass heats up its index of refraction changes. Most glasses, fused silica included, have a positive dn/dT. A positive dn/dT will cause the focal length of the lens to decrease with a temperature rise. Many of the fluoride glasses, like CaF2, BaF2, LiF2, etc. have a negative dn/dT. By applying athermalization techniques of glass selection and optical design, the thermal lensing in a laser objective of a high power laser system can be substantially mitigated. We describe a passive method for minimizing thermal lensing of high power laser optics.

  12. Tribological and mechanical comparison of sintered and HIPped PM212 - High temperature self-lubricating composites

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    1988-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    1987-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Valco, Mark J.

    1999-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Moses, Lance M.; Farnsworth, Paul B.

    2015-11-01

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

  18. 2.7 μm emission of high thermally and chemically durable glasses based on AlF3

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    AlF3-based glasses (AlF3-YF3-CaF2-BaF2-SrF2-MgF2) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 μm 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 (ΔT, 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 μm) 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 μm 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 μm.

  19. The influence of TeO2 on thermal stability and 1.53 μm spectroscopic properties in Er(3+) doped oxyfluorite glasses.

    PubMed

    Wang, Fengchao; Cai, Muzhi; Chen, Rong; Jing, Xufeng; Li, Bingpeng; Tian, Ying; Zhang, Junjie; Xu, Shiqing

    2015-11-01

    In this work, the thermal and spectroscopic properties of Er(3+)-doped oxyfluorite glass based on AMCSBYT (AlF3-MgF2-CaF2-SrF2-BaF2-YF3-TeO2) system for different TeO2 concentrations from 6 to 21 mol% is reported. After adding a suitable content of TeO2, the thermal ability of glass improves significantly whose ΔT and S can reach to 118 °C and 4.47, respectively. The stimulated emission cross-section reaches to 7.80×10(-21) cm(2) and the fluorescence lifetime is 12.18 ms. At the same time, the bandwidth characteristics reach to 46.41×10(-21) cm(2) nm and the gain performance is 63.73×10(-21) cm(2) ms. These results show that the optical performances of this oxyfluorite glass are very well. Hence, AMCSBYT glass with superior performances might be a useful material for applications in optical amplifier around 1.53 μm. PMID:26037501

  20. Thermal conductivity of single crystals with a fluorite structure: Cadmium fluoride

    NASA Astrophysics Data System (ADS)

    Popov, P. A.; Fedorov, P. P.; Osiko, V. V.

    2010-03-01

    The thermal conductivity of Ca, Sr, Ba, and Cd difluoride single crystals and the CdF2 samples doped by 3 mol % NdF3, 15 mol % HoF3, and 10 mol % ErF3 has been studied using the method of steady longitudinal heat flow in the temperature range 50-300 K. The thermal conductivity of the matrices of these compounds decreases in the order CaF2-SrF2-BaF2-CdF2. The temperature dependences of the phonon mean free path for these crystals have been calculated from experimental data and exhibit different behaviors. It has been assumed that the intense phonon scattering observed in the undoped CdF2 sample is caused by the specific features of the processes of phonon-phonon scattering. The formation of heterovalent solid solutions of cadmium difluoride and rare-earth trifluorides is accompanied by a drastic decrease in the thermal conductivity and a change in its character from that typical of dielectric single crystals to that typical of glassy materials.

  1. X-Ray Absorption Spectroscopy and Computer Modelling Study of Nanocrystalline Binary Alkaline Earth Fluorides

    NASA Astrophysics Data System (ADS)

    Chadwick, A. V.; Düvel, A.; Heitjans, P.; Pickup, D. M.; Ramos, S.; Sayle, D. C.; Sayle, T. X. T.

    2015-04-01

    Nanocrystalline samples of Ba1-xCaxF2 prepared by high-energy milling show an unusually high F- ion conductivity, which exhibit a maximum in the magnitude and a minimum in the activation energy at x = 0.5. Here, we report an X-ray absorption spectroscopy (XAS) at the Ca and Sr K edges and the Ba L3 edge and a molecular dynamics (MD) simulation study of the pure and mixed fluorides. The XAS measurements on the pure binary fluorides, CaF2, SrF2 and BaF2 show that high-energy ball-milling produces very little amorphous material, in contrast to the results for ball milled oxides. XAS measurements of Ba1-xCaxF2 reveal that for 0 < x <1 there is considerable disorder in the local environments of the cations which is highest for x = 0.5. Hence the maximum in the conductivity corresponds to the composition with the maximum level of local disorder. The MD calculations also show a highly disordered structure consistent with the XAS results and similarly showing maximum disorder at x = 0.5.

  2. 2.7 μm emission of high thermally and chemically durable glasses based on AlF3.

    PubMed

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Kumar, Malay

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

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

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Smith, Guy A.

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Torres, Anthony Samuel

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

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

    NASA Astrophysics Data System (ADS)

    Kulkarni, Ojas P.

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

  8. Mechanisms for the Crystallization of ZBLAN

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  10. A fluorocarbon plastic scintillator for neutron detection: Proof of concept

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The fast neutron nuclear reactions, such as 19F(n, ?)16N and 19F(n, p)19O, can be used to detect highly energetic neutrons due to their energy thresholds above which these activation reactions can occur. This was recently shown (Gozani et al., 2011 [2]) as a means to detect concealed nuclear materials via the detection of the high energy (?3 MeV) prompt neutrons emitted during the photofission process. Fluorine-loaded scintillation detectors, such as inorganic BaF2 and CaF2, and non-hydrogenous fluorocarbon (FC) liquid scintillators, such as Saint-Gobain BC-509 and Eljen Technology EJ-313, are possible candidates. The latter was selected and implemented in the above mentioned reference. In our paper, we propose a new pentafluorostyrene-based plastic scintillator (F-plastic) which can be a good alternative to the abovementioned scintillators. The fluorine content of F-plastic is equal to 3.731022 atoms/cm3, and the F/H ratio is 1.66. The fluorescence and radioluminescence spectra of the F-plastic display an emission maximum centered approximately at 420 nm. The light output measured for gamma rays is 3100300 photons/MeV, which is approximately 30% of the light output of the standard EJ-200 plastic scintillator and is similar to EJ-313. The response of the F-plastic to neutrons and gamma rays is presented and compared to the EJ-200 scintillator. Additionally, the n/? pulse shape discrimination (PSD) was measured and showed improvement of the discrimination at neutron energies as high as 3 MeV.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  12. Cryogenic engineering for OMEGA2000: design and performance

    NASA Astrophysics Data System (ADS)

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

    2003-03-01

    Omega2000 is a prime focus near infrared (NIR) wide-field camera for the 3.5 meter telescope at Calar Alto/Spain. Having a large field of view and an excellent optical quality, the instrument is particularly designed for survey observations. A cryogenic four lens focal reducer delivers a 15.4 x 15.4 arcminute field of view (FOV) with a pixel scale of 0.45"/pixel. The lenses are made of various optical materials, including CaF2 and BaF2 with diameters of up to 150 mm. They must be specially mounted to survive cooling and to follow the tight tolerances (+/- 0.05 mm for lens centricity and +/- 30 arcsec for lens tilt) required by the optical design. For a wide range of observing applications, a filter mechanism can hold up to 17 filters of 3 inch diameter in 3 filter wheels. For exact and reproducible filter positions, a mechanical locking mechanism has been developed which also improves the cool-down performance of the filter wheels and filters. This mechanism allows a minimum distance of about 3 mm between the filter wheels. A Rockwell HAWAII-2 FPA is used to cover the wavelength range from 0.85 ?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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  14. New infrared detectors and solar cells

    NASA Technical Reports Server (NTRS)

    Sher, A.

    1979-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Tsuo, Y. H.; Sher, A.

    1981-01-01

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

  16. Broadband reflectance coatings for vacuum ultraviolet application

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Striebing, Donald R.; DellaCorte, Christopher

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  20. Sum frequency generation spectroscopy study of an ionic liquid at a graphene-BaF2 (111) interface.

    PubMed

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

    2014-05-15

    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

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

    PubMed

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

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  5. Microstructural characterization in nanocrystalline ceramic thin films

    NASA Astrophysics Data System (ADS)

    Kim, Hakkwan

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

  6. Fabrication and Properties of a Metal-Insulator - Type Oxygen Sensor Using Lanthanum Trifluoride as the Sole Dielectric.

    NASA Astrophysics Data System (ADS)

    Mattingly, William Brashear, III

    1995-01-01

    Oxygen sensors were fabricated using a metal-insulator -semiconductor construction where the sole 'insulator' is a thin film of LaF_3, an ionic conductor. The typical oxide or nitride layers were eliminated producing a simple Pt/LaF_3/Si design. LaF_3 films, 200-300nm thick, were directly deposited on n-type Si(111) using a high temperature effusion cell in an ultra high vacuum MBE chamber. The film morphology could be controlled from polycrystalline to near single crystal epitaxy. Epitaxial films exhibited a single relaxed variant with the LaF _3 c-axis normal to the silicon surface and the in-plane LaF_3(10^ -10) parallel to Si(110). Polycrystalline films also showed a high degree of LaF_3 c-axis normal texture. Films doped with strontium were also produced. Polycrystalline films were more robust and fabricated into MIS (metal-insulator-semiconductor) capacitors. Capacitance voltage tests of the devices demonstrate nearly ideal MIS capacitor behavior. The flatband voltages were typically within 300mV of the calculated value. Bias challenge tests developed in the lab showed less than 70mV flatband voltage shift. The dielectric constant of undoped LaF_3 films measured close to 14. Doped films, rm Sr_{x}La_ {1-x}F_3 x =.06, showed a dielectric constant of 275, at 100kHz. Oxygen partial pressure tests were performed with mixtures of dry nitrogen and dry oxygen. Oxygen partial pressures were varied between 2.5 times 10^{-4} and 1.0 atmosphere. The steady state data are consistent with a Pt/LaF _3 interface adsorption mechanism, where the work function of the platinum gate metal is modulated. The mechanism is not a half-cell Nernst-type response. Langmiur isotherm fitted data indicate the response range for undoped devices is 0.3 V. Signal drift was less than 5 mV/day. The metal free-surface reactions and the dipole species at the Pt/LaF_3 interface are yet to be determined. Device kinetic studies show the time required for full equilibration after a step in oxygen partial pressure is 24 hours at 90^circC. Initial response kinetics to downward steps in oxygen show the activation energy of the process is 0.54 eV.

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

    NASA Technical Reports Server (NTRS)

    Bill, R. C.

    1974-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Yao, Mingzhen

    2011-12-01

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

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

    SciTech Connect

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

    2008-01-28

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

  10. Exterior surface damage of calcium fluoride outcoupling mirrors for DUV lasers.

    PubMed

    Bauer, Michael; Bischoff, Martin; Jukresch, Sigrid; Hlsenbusch, Thomas; Matern, Ansgar; Grtler, Andreas; Stark, Robert W; Chuvilin, Andrey; Kaiser, Ute

    2009-05-11

    Damage of optical components due to laser irradiation reduces reliability and limits durability. Calcium fluoride (CaF(2)) is commonly used for deep UV laser optics because it shows a very low tendency of color center formation as, compared to other UV-X optical materials. Here, we report on the exterior damage of CaF(2) UV-X optics due to radiation with high pulse-energy densities (80 mJ/cm(2)) from an ArF laser. At such high energy densities, damage occurs on the external resonator side. The damage is generated by a partial alteration of the CaF(2) substrate to crystalline CaCO(3) (calcite). The decomposition of CaF(2) is mainly driven by photochemical processes in the presence of water vapor, which are induced by the UV-laser light and the elevated temperature within the beam profile. PMID:19434158

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

    PubMed

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

    2010-10-01

    The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 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

  12. Raman scattering efficiency of graphene

    NASA Astrophysics Data System (ADS)

    Klar, P.; Lidorikis, E.; Eckmann, A.; Verzhbitskiy, I. A.; Ferrari, A. C.; Casiraghi, C.

    2013-05-01

    We determine the Raman scattering efficiency of the G and 2D peaks in graphene. Three substrates are used: silicon covered with 300 or 90 nm oxide, and calcium fluoride (CaF2). On Si/SiOx, the areas of the G and 2D peak show a strong dependence on the substrate due to interference effects, while on CaF2 no significant dependence is detected. Unintentional doping is reduced by placing graphene on CaF2. We determine the Raman scattering efficiency by comparison with the 322 cm-1 peak area of CaF2. At 2.41 eV, the Raman efficiency of the G peak is 20010-5 m-1Sr-1, and changes with the excitation energy to the power of 4. The 2D Raman efficiency is at least one order of magnitude higher than that of the G peak, with a different excitation energy dependence.

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

    PubMed

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

    2014-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    PubMed

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

    2015-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Fujihara, Shinobu; Schneller, Theodor; Waser, Rainer

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    We report the observation of stimulated Brillouin scattering and lasing at 1550 nm in barium fluoride (BaF2) crystal. Brillouin lasing was achieved with ultra-high quality (Q) factor monolithic whispering gallery mode mm-size disk resonators. Overmoded resonators were specifically used to provide cavity resonances for both the pump and all Brillouin Stokes waves. Single and multiple Brillouin Stokes radiations with frequency shift ranging from 8.2 GHz up to 49 GHz have been generated through cascaded Brillouin lasing. BaF2 resonator-based Brillouin lasing can find potential applications for high-coherence lasers and microwave photonics.

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

    PubMed

    Feng, Li; Wu, Yinsu

    2015-05-01

    Optical properties of Ho(3+)-doped SiO2-BaF2-ZnF2 glasses have been investigated on the basis of the Judd-Ofelt theory. Judd-Ofelt intensity parameters, radiative transition probabilities, fluorescence branching ratios and radiative lifetimes have been calculated for different glass compositions. Upconversion emissions were observed in Ho(3+)/Yb(3+)-codoped SiO2-BaF2-ZnF2 glasses under 980nm excitation. The effects of composition, concentration of the doping ions, and excitation pump power on the upconversion emissions were also systematically studied. PMID:25703369

  20. Time-resolved spectroscopy of 5d-4f transitions in Pr3+ doped alkali-earth fluorides

    NASA Astrophysics Data System (ADS)

    Shendrik, R.; Radzhabov, E.; Nagirnyi, V.

    2010-11-01

    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 and 8 ns depended on concentration of Pr3+. Thus, the presence of aggregates might be the cause of such faster components.

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

    NASA Astrophysics Data System (ADS)

    Kondo, Takahiro; Ito, Tsuyohito

    2013-09-01

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

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

    SciTech Connect

    GIARE, C; Palazzo, J; Goyal, Amit; WANG, G; LU, T

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ullmann, J. L.

    2014-09-01

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

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

    SciTech Connect

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

    2007-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  6. Photon absorption graphs: 1 keV to 10 MeV

    NASA Astrophysics Data System (ADS)

    Bom, V. R.; Hollander, R. W.

    1983-01-01

    Photon absorption graphs for H2 (liquid), He (liquid), Be, C, Al, Ar (gas), Fe, Cn, Ge, Kr (gas), Mo, Sn, Xe (gas), Dy, An, Pb, U, NaI, NE102A, Kapton, Mylar, Hostaphan, polyethylene, and BaF2 are presented.

  7. The improved scintillation crystal lead tungstate scintillation for PET

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  8. A computerized glow curve analysis (GCA) method for WinREMS thermoluminescent dosimeter data using MATLAB.

    PubMed

    Harvey, John A; Rodrigues, Miesher L; Kearfott, Kimberlee J

    2011-09-01

    A computerized glow curve analysis (GCA) program for handling of thermoluminescence data originating from WinREMS is presented. The MATLAB program fits the glow peaks using the first-order kinetics model. Tested materials are LiF:Mg,Ti, CaF(2):Dy, CaF(2):Tm, CaF(2):Mn, LiF:Mg,Cu,P, and CaSO(4):Dy, with most having an average figure of merit (FOM) of 1.3% or less, with CaSO(4):Dy 2.2% or less. Output is a list of fit parameters, peak areas, and graphs for each fit, evaluating each glow curve in 1.5 s or less. PMID:21561783

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  10. Standardized cell samples for midIR technology development

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    PubMed

    Liu, Wei-Ting; Li, Kung-Cheh

    2011-01-01

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

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

    SciTech Connect

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

    2010-11-01

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

  13. Dynamics of 23 (1/CM) Phonons in Lanthanum-Fluoride and the Effects of Resonant Raman Scattering.

    NASA Astrophysics Data System (ADS)

    Yom, Sang Seop

    The dynamics of 23 cm('-1) phonons in LaF(,3) doubly doped with Pr('3+) and Dy('3+) have been studied at low temperatures with magnetic fields up to 30 kG. The two crystal field states, ('1)D(,2)(I) and (II), of Pr('3+) ion are chosen as the source and detector of the phonons while the ground state manifolds, ('6)H(,15/2)(I) and (II), of Dy('3+) ion are tuned to the 23 cm('-1) phonons. We discuss the resonant Raman scattering of the 23 cm('-1) phonons by Dy('3+) ions. In singly doped LaF(,3):0.05% Pr('3+), the anharmonic phonon lifetime (600 ns) is obtained from the decay of the phonon-induced ('1)D(,2)(II) hot luminescence after selective optical excitation with a Nd:YAG pumped dye laser (bandwidth (TURN)0.3 cm('-1)). The long-time tail of the time-resolved spectrum shows an effect of thermal phonons which are generated by the upconversion process involving the ('3)P(,0) state. The phonon lifetime is reduced to 50 ns in more concentrated samples (0.5% Pr('3+)). In a doubly-doped sample (0.05% Pr('3+) and 0.01% Dy('3+)), the lifetime is reduced by up to a factor of 6 when the transitions within the ('6)H(,15/2) ground manifold of Dy('3+) are tuned with a magnetic field into resonance with the 23 cm('-1) phonons. Our model calculation shows that the 23 cm('-1) phonons downshift their energy by Raman processes resulting in a shorter 23 cm('-1) phonon decay time when the Zeeman components of the ('6)H(,15/2)(I and II) states of Dy('3+) are resonant with the phonon energy. Resonances are observed at 15.9 and 22.7 kG, consistent with the observed Dy('3+) splittings. Finally, we report the potential usefulness of systems such as LaF(,3):Er('3+), LaF(,3):Dy('3+), and YAlO(,3):Er('3+) for further phonon studies. We confirm that two magnetically inequivalent sites exist in the YAlO(,3):Er('3+) system. Some experiments are suggested to investigate the large wavevector phonon dynamics further.

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

    USGS Publications Warehouse

    Greenland, L.P.

    1968-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  16. Response of TL materials to diagnostic radiology X radiation beams.

    PubMed

    Maia, Ana F; Caldas, Linda V E

    2010-01-01

    The main objective of this study was to carry out a direct performance comparison among some known types of TLDs-three types of CaSO(4):Dy pellets, sintered Al(2)O(3) pellets, LiF:Mg,Ti (Harshaw TLD-100), CaF(2):Dy (Harshaw TLD-200) and CaF(2):Mn (Harshaw TLD-400)-in the energy and dose ranges of diagnostic radiology beams. Several dosimetric characteristics were evaluated, such as reproducibility, sensitivity, calibration curves, lower dose limits and energy dependence. PMID:20097569

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

    PubMed

    Hashimoto, Y; Hiraga, F; Kiyanagi, Y

    2015-12-01

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

  18. Skylab ultraviolet stellar astronomy experiment S019

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

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

    PubMed

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

    2009-07-30

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

  20. Effect of VUV F2 laser irradiation on fluoride crystal

    NASA Astrophysics Data System (ADS)

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

    2003-07-01

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

  1. Characteristics of thin calcium fluoride barrier layers for field-effect transistors and functional electronic devices

    NASA Astrophysics Data System (ADS)

    Illarionov, Yu. Yu.; Vexler, M. I.; Suturin, S. M.; Fedorov, V. V.; Sokolov, N. S.

    2010-05-01

    Thin (2-7 monolayer thick) layers of calcium fluoride (CaF2) of device quality have been obtained using molecular beam epitaxy on Si(111) substrates. The current-voltage characteristics of metal-insulator-semiconductor (MIS) structures with these films well correspond to theoretical results obtained with correctly taking into account the conserved transverse wave vector component of tunneling carriers. According to calculations, the tunneling currents in CaF2 based MIS structures are smaller than those in the standard structures with oxides used in field-effect transistors.

  2. Relationship between the defect structure and fluorine-ion conductivity of La1 - y Sr y F3 - y (0 ? y ? 0.15) crystals according to X-ray and neutron diffraction data

    NASA Astrophysics Data System (ADS)

    Bolotina, N. B.; Chernaya, T. S.; Kalyukanov, A. I.; Verin, I. A.; Sorokin, N. I.; Fykin, L. E.; Isakova, N. N.; Sobolev, B. P.

    2015-05-01

    The defect structure of crystals of as-grown nonstoichiometric tysonite (LaF3 type) La1 - y Sr y F3 - y phase ( y = 0, 0.05, 0.07, and 0.15) has been investigated by X-ray diffraction and neutron diffraction. A concentration-driven structural transition from the ?-La1 - y Sr y F3 - y modification to the ?-La1 - y Sr y F3 - y modification in the range y = 0.05-0.10 has been observed for the first time. This transition correlates with the maximum of fluorine-ion conductivity ( y = 0.05 0.02) and the maximum in the melting curve ( y = 0.07 0.03). ?-LaF3 and ?-La0.95Sr0.05F2.95 crystals belong to the trigonal system (sp. gr. , Z = 6) and are twinned according to the merohedral twin law. Fine changes in the fluorine sublattice of ?-La0.95Sr0.05F2.95 increase conductivity ?293K to 3 10-4 S/cm; hence, these crystals can be used as fluorine-conducting solid electrolytes (FCSEs) in solid-state ionics devices. Additional possibilities of ion transport over twin joints are discussed. In ?-La0.85Sr0.15F2.85 crystal the symmetry group changes to P63/ mmc, Z = 2; it is not twinned and its fluorine-ion conductivity is reduced.

  3. Multiple-magnetic field 139La NMR and density functional theory investigation of the solid lanthanum(III) halides.

    PubMed

    Ooms, Kristopher J; Feindel, Kirk W; Willans, Mathew J; Wasylishen, Roderick E; Hanna, John V; Pike, Kevin J; Smith, Mark E

    2005-09-01

    Results from a solid-state 139La NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX3; X=F, Cl, Br, I) at applied magnetic fields of 7.0, 9.4, 11.7, 14.1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The 139La quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl3 and LaI3, respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from -135 ppm for LaF3 to 700 ppm for LaI3, which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF3 through LaI3. DFT calculations of the 139La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally. PMID:16125375

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

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

    2013-11-21

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

  6. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2002-01-01

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

  7. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2003-01-01

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

  8. Fluorspar

    USGS Publications Warehouse

    Miller, M.

    2012-01-01

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

  9. Applications of quantum cascade lasers in chemical sensing

    NASA Astrophysics Data System (ADS)

    Wu, Sheng; Deev, Andrei; Tang, Yongchun

    2010-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

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

    PubMed

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  15. Low background techniques in CANDLES

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  16. EPR studies of the mechanochemically Er3+-activated fluorite nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    In the present work we show with EPR spectroscopy that the simultaneous grinding of the crystalline CaF2 and ErF3 salts leads to the mechanochemical doping of the single Er3+ ions in the CaF2 host. Dependence of the EPR spectra intensity on the grain size indicates clearly that the Er3+ centers are created at the surface of the particles. Dominant part of the observed paramagnetic centers represent the Er3+ ions substituting the regular quasicubic Ca2+ lattice site (g = 6.7) perturbed by the vicinity of the surface. Fine particles of CaF2 reveal also the nearly-isotropic EPR signal at g ~ 1.97 that originates from the surface defects and can be used for characterization of the obtained samples with respect of the average grain size. Grinding of the of the CaF2 and ErF3 mixture in the ratio of 100:1 during 12 hours gives the surface density of the Er3+ ions of ~ 0.1 nm-2, or ~ 104 Er3- ions per the 190-nm size particle.

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

    PubMed

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

    2003-08-01

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

  18. Lattice dynamics and thermal conductivity of calcium fluoride via first-principles investigation

    NASA Astrophysics Data System (ADS)

    Qi, Yuan-Yuan; Zhang, Tian; Cheng, Yan; Chen, Xiang-Rong; Wei, Dong-Qing; Cai, Ling-Cang

    2016-03-01

    The lattice thermal conductivity of CaF2 is accurately computed from a first-principles theoretical approach based on an iterative solution of the Boltzmann transport equation. The second- and third-order interatomic force constants are generated from a real-space finite-difference supercell approach. Then, the force constants for both the second- and third-order potential interactions are used to calculate the lattice thermal conductivity and related physical quantities of CaF2 at temperatures ranging from 30 K to 1500 K. The obtained lattice thermal conductivity 8.6 W/(m.K) for CaF2 at room temperature agrees better with the experimental value than other theoretical data, demonstrating the promise of this parameter-free approach in providing precise descriptions of the lattice thermal conductivity of materials. The obtained dielectric parameters and phonon spectrum of CaF2 accord well with available data. Meanwhile, the temperature dependence curves of the lattice thermal conductivity, heat capacity, and phonon mean free path are presented.

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

    PubMed

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

    2016-02-01

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

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

    PubMed Central

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

    2012-01-01

    Objectives Previous studies have developed calcium phosphate and fluoride releasing composites. Other studies have incorporated chlorhexidine (CHX) particles into dental composites. However, CHX has not been incorporated in calcium phosphate and fluoride composites. The objectives of this study were to develop nanocomposites containing amorphous calcium phosphate (ACP) or calcium fluoride (CaF2) nanoparticles and CHX particles, and investigate S. mutans biofilm formation and lactic acid production for the first time. Methods Chlorhexidine was frozen via liquid nitrogen and ground to obtain a particle size of 0.62 m. 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 1020 folds and reduced the acid production, compared to the controls. CFU on nanocomposites with CHX were three orders of magnitude less than that on commercial composite. Mechanical properties of nanocomposites with CHX matched a commercial composite without fluoride. Significance The novel calcium phosphate and fluoride nanocomposites could be rendered antibacterial with CHX to greatly reduce biofilm formation, acid production, CFU and metabolic activity. The antimicrobial and remineralizing nanocomposites with good mechanical properties may be promising for a wide range of tooth restorations with anti-caries capabilities. PMID:22317794

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

  4. Superconducting Films On Microwave Dielectric Substrates

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Miller, M. D.

    1981-01-01

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

  6. Optical properties of Ce3+ doped fluorophosphates scintillation glasses

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  8. Variation of photoluminescence features in Pr3+ doped lithium-fluoro-borate glass by changing different modifier oxides (MgO, CaO, CdO and PbO)-Judd-Ofelt theory application

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Pr3+ (1.0 mol%) doped different modifier oxide based six lithium-fluoro-borate glasses with chemical composition of 49Li2B4O7-20BaF2-10NaF-20MO (where M= Mg, Ca, Cd and Pb), 49Li2B4O7-20BaF2-10NaF-10MgO-10CaO and 49Li2B4O7-20BaF2-10NaF-10CdO-10PbO were prepared by conventional melt quenching technique. Judd-Ofelt theory has been applied for evaluating the Judd-Ofelt intensity parameters for Pr3+ ion in these glass compositions and are in turn to used to predict radiative properties such as radiative transition probabilities (AT), branching ratios (β) and stimulated emission cross-section (σP). Stimulated emission cross-section (σp) of prominent emission transitions, 3P0→3H4 and 1D2→3H4 of Pr3+ ion in all lithium-fluoro-borate glasses were calculated. Among all the emission transitions, 3P0→3H4 posseses higher branching ratio and stimulated emission cross-section in Mg-Ca glass, which leads to the best laser excitation at 487 nm wavelength.

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

    NASA Astrophysics Data System (ADS)

    Iwamoto, Hiromi; Ebata, Keiji; Nanba, Hirokuni

    2003-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Sibczynski, P.; Kownacki, J.; Moszyński, M.; Iwanowska-Hanke, J.; Syntfeld-Każuch, A.; Gójska, A.; Gierlik, M.; Kaźmierczak, Ł.; Jakubowska, E.; Kędzierski, G.; Kujawiński, Ł.; Wojnarowicz, J.; Carrel, F.; Ledieu, M.; Lainé, F.

    2015-09-01

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

  11. Mixedness determination of rare earth-doped ceramics

    NASA Astrophysics Data System (ADS)

    Czerepinski, Jennifer H.

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

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

    NASA Astrophysics Data System (ADS)

    Ogawa, Izumi

    2009-10-01

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

  13. Damage precursor measurements on UV optical coatings

    NASA Astrophysics Data System (ADS)

    Ettrich, K.; Blaschke, Holger; Welsch, Eberhard

    1995-07-01

    For application in UV thin film optics the thermal contribution to the laser-induced optical breakdown was investigated utilizing time-resolved photothermal probe beam deflection (MIRAGE) technique. The potentiality of this method for the determination of both the subdamage range and the onset of single-shot-damage of Al2O3/SiO2 and LaF3/MgF2 high-reflective coatings by using the thermal branch of the MIRAGE technique could be demonstrated. Examining the dielectric mirrors by 248 nm KrF laser irradiation, distinct damage precursor features were found. Thus, the physical origin of the UV-pulsed radiation breakdown in HR coatings can be elucidated.

  14. Nanocomposite materials for radiation detection

    NASA Astrophysics Data System (ADS)

    Sahi, Sunil

    2013-03-01

    Colloidal quantum dots (CdTe, CdSe, and ZnO) have attracted tremendous interest in wide range of application from biological imaging, biosensing, solar cells to optoelectronic devices. However very few published reports on the radiation detection based on colloidal quantum dots. Quantum dots based nanocomposite materials could be a promising material for radiation detection because of their short luminescence life time and high quantum efficiencies as a consequence of quantum size confinement. However stopping power of most quantum dots is low and their scintillation luminescence is very weak. The combination of high stopping power of inorganic scintillator (CeF3LaF3: Ce, YAG:Ce) and high efficiency of quantum dot could potentially lead to a new class of scintillator. We have studied the nanocomposite of inorganic scintillator and quantum dot based on energy transfer principle and investigate the scintillation properties of nanocomposite scintillator.

  15. Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials.

    PubMed

    Kaczmarek, Anna M; Van Hecke, Kristof; Van Deun, Rik

    2015-04-21

    This review focuses on rare-earth carbonate materials of nano- and micro-size. It discusses in depth the different types of rare-earth carbonate compounds, diverse synthetic approaches and possibilities for chemical tuning of the size, shape and morphology. The interesting luminescence properties of lanthanide doped rare-earth carbonates and their potential applications for example as efficient white light sources and biolabels are reviewed. Additionally the use of these materials as precursors for the synthesis of nano-/micro-sized oxides, and their application as sacrificial templates for morphology-controlled synthesis of other materials such as YVO4, LaF3, NaYF4 and others is overviewed. PMID:25714401

  16. A new imaging device based on UV scintillators and a large area gas photomultiplier

    NASA Astrophysics Data System (ADS)

    Sekiya, H.; Ida, C.; Kubo, H.; Kurosawa, S.; Miuchi, K.; Tanimori, T.; Taniue, K.; Yoshikawa, A.; Yanagida, T.; Yokota, Y.; Fukuda, K.; Ishizu, S.; Kawaguchi, N.; Suyama, T.

    2011-05-01

    A new type high spatial resolution radiation detector based on a UV scintillator+a UV imaging gas photomultiplier is presented. The prototype UV detector consists of a 10 cm10 cm ?PIC, 2 GEMs and a semitransparent CsI photocathode deposited on a MgF2 window. The effective photo-sensitive area is ?34 mm and the readouts are 400 ?m pitch strips. A newly developed 20 mm size LaF3(Nd) crystal which emits 172 nm photons is coupled to the detector for the first step. The detector was tested in pulse mode operation with 5.5 MeV ? particles from 241Am. The single photoelectrons were successfully detected and the images of the crystal shape were clearly obtained.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  18. Improved characterization of Si-SiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Su, P.

    Silicon is the heart of modern semiconductor devices. The dominance of Si in semiconductor technology depends on the superior quality and properties of thermally grown SiO2 compared with the oxide that can be placed on any other semiconductor. The well established quasistatic and conductance methods used in the study of the Si-SiO2 interface are improved by using an effectively thin composite insulator, low carrier concentration substrates, and most importantly, low level illumination at a wavelength that creates electron hole pairs. The samples investigated had a thermally grown oxide prepared in dry oxygen. They were never exposed to H2 or H2O at an elevated temperature. The composite gate insulator was completed by having an e-gun deposited 250 A layer on LaF3. The resulting interface, subjected to the improved experimental method, yields a wealth of distinctive structure rather than the often reported featureless U-shaped interface-state density.

  19. Dimorphism of RF3 ( R = La-Nd) crystals based on the data of X-ray diffraction studies

    NASA Astrophysics Data System (ADS)

    Bolotina, N. B.; Chernaya, T. S.; Verin, I. A.; Khrykina, O. N.; Sobolev, B. P.

    2016-01-01

    The ratio of two forms of tysonite in nominally pure single crystals of RF3 ( R = La-Nd) obtained from melts under identical conditions (the as-grown state) is studied for the first time by X-ray diffraction. Crystals of RF3 with R = La-Nd belong to the ?-LaF3 structural type (space group Pbar 3c1, Z = 6) and form twins. Samples 0.2-0.4 in diameter contain inclusions of the high-temperature a form (space group P63/ mmc, Z = 2). It is shown that twinning and dimorphism of the RF3 crystals ( R = La-Nd) have a common structural basis.

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

    PubMed Central

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  2. Nanoscintillators for radiation detection

    NASA Astrophysics Data System (ADS)

    Hall, Ryan Gregory

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

  3. Atomic scale control of hexaphenyl molecules manipulation along functionalized ultra-thin insulating layer on the Si(1 0 0) surface at low temperature (9 K).

    PubMed

    Chiaravalloti, Franco; Dujardin, Gérald; Riedel, Damien

    2015-02-11

    Ultra-thin CaF2 layers are grown on the Si(1 0 0) surface by using a Knudsen cell evaporator. These epitaxial structures are studied with a low temperature (9 K) scanning tunneling microscope and used to electronically decouple hexaphenyl molecules from the Si surface. We show that the ultra-thin CaF2 layers exhibit stripe structures oriented perpendicularly to the silicon dimer rows and have a surface gap of 3.8 eV. The ultra-thin semi-insulating layers are also shown to be functionalized, since 80% of the hexaphenyl molecules adsorbed on these structures self-orients along the stripes. Numerical simulations using time-dependent density functional theory allow comparison of computed orbitals of the hexaphenyl molecule with experimental data. Finally, we show that the hexaphenyl molecules can be manipulated along or across the stripes, enabling the molecules to be arranged precisely on the insulating surface. PMID:25414151

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  5. Metalorganic vapor phase epitaxy of GaAs on Si using II a-flouride buffer layers

    NASA Astrophysics Data System (ADS)

    Tiwari, A. N.; Freundlich, A.; Beaumont, B.; Blunier, S.; Zogg, H.; Teodoropol, S.; Vri, C.

    1992-11-01

    Metalorganic vapor phase epitaxy has been used for the first time to grow epitaxial GaAs layers on (111) and (100) oriented Si either using CaF 2 or stacked (Ca,Sr)F 2/CaF 2 as a buffer. The GaAs layers show sharp and well resolved electron channeling patterns. The Rutherford backscattering (RBS) ion channeling minimum yield is 5% for (111) orientation and 6% for (100) orientation. The GaAs(111) layers are untwinned. The strain in the GaAs layer has been measured with RBS and X-ray diffraction and it is found that the thermal mismatch-induced strain in the GaAs layer is considerably lower than in similar GaAs films grown without flouride buffer.

  6. Upconversion use for viewing and recording infrared images

    NASA Astrophysics Data System (ADS)

    Pollack, S. A.; Chang, D. B.; Shih, I.-Fu; Tzeng, R.

    1987-10-01

    The upconversion of 1.54 micron radiation to shorter wavelengths has been studied in CaF2 crystals doped with Er (3+) ions. Experimental measurements of the intensity dependence and temporal behavior of the upconverted radiation give results in good qualitative agreement with a simple model of a cooperative luminescence process. Measurements with a silicon diode matrix array (DMA) of the spatial distribution of the luminescence from screens of CaF2 doped with ER (3+), which were irradiated with an Er laser, showed that the resolution is not limited by the cooperative luminescent process but is determined by the granularity and/or thickness of the screens. Good results on 1.54 micron beam profiles were obtained with a computer-based image recording system incorporating the screen-DMA combination. A linear dependence on intensity without saturation of the DMA was achieved by interposing neutral density filters between the screen and the DMA.

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-08-01

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

  9. Low Radioactivity in CANDLES

    SciTech Connect

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

    2005-09-08

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

  10. Detection and Manipulation of the Statistical Fluctuations in Nuclear Spin Ensembles Using Magnetic Resonance Force Microscopy

    NASA Astrophysics Data System (ADS)

    Mamin, H. J.

    2005-03-01

    We have detected and manipulated the naturally occurring ?N statistical polarization in nuclear spin ensembles using MRFM. We have studied fluorine nuclei in CaF2, as well as protons in the polymer PMMA and the protein collagen. The ensembles studied contained of order 10^8 nuclear spins, corresponding to volumes of order (200nm)^3, which resulted in statistical polarizations of order 10^4 net spins. We have also implemented a scheme similar to one proposed by Weitekamp et al, in which we suppressed the effect of the statistical uncertainty so as to extract meaningful information from time-averaged measurements. In this way, we have successfully made nutation and transverse spin relaxation measurements in a nominally unpolarized sample of CaF2 at low temperatures.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  12. Control of magnetic anisotropy in (111)SmAl2 films

    NASA Astrophysics Data System (ADS)

    Avisou, A.; Dufour, C.; Dumesnil, K.

    2008-04-01

    This study enlightens how the magnetic anisotropy might be tailored in magnetic films by the proper choice of the substrate. Single crystalline (111)SmAl2 films have been grown by molecular beam epitaxy on two substrates: (1120)Al2O3 and (111)CaF2. Hysteresis loops measured along the different crystallographic directions are the signature of the following: (i) a uniaxial anisotropy with an easy direction perpendicular to the (111) growth plane when the film is grown on Al2O3; (ii) a [111] hard magnetic direction when the film is grown on CaF2. This effect can be understood if we consider the influence of the thermal strains on the various energy terms which govern the easy magnetization direction. The relevant parameters to determine the easy magnetization direction are the relative sign and absolute values of the strains and of the magnetoelastic constants.

  13. VUV-spectroscopy of Ce3+ -doped crystals with fluorite-type structure

    NASA Astrophysics Data System (ADS)

    Bezhanov, V.; Chernov, S.; Kolobanov, V.; Kirkin, R.; Mikhailin, V.; Karimov, D.

    2010-11-01

    The spectral properties of two-component Ca1-xSrxF2:Ce3+(0.05 mol%) (x = 0.75, 0.41, 0.25, 0.14) crystals in UV spectral region were investigated. It was shown that spectral properties of Ca1-xSrxF2:Ce3+(0.05 mol%) in UV spectral region have intermediate position between those for pure CaF2 and SrF2 crystals. The optical constants were calculated from reflectance spectrum for CaF2, SrF2, Ca1-xSrxF2:Ce3+(0.05 mol%) (x = 0.75, 0.25) crystals by use of Kramers-Kronig relations for complex reflection coefficient and Fresnel formulas.

  14. Controlling energy transfer between multiple dopants within a single nanoparticle

    PubMed Central

    DiMaio, Jeffrey R.; Sabatier, Clment; Kokuoz, Baris; Ballato, John

    2008-01-01

    Complex core-shell architectures are implemented within LaF3 nanoparticles to allow for a tailored degree of energy transfer (ET) between different rare earth dopants. By constraining specific dopants to individual shells, their relative distance to one another can be carefully controlled. Core-shell LaF3 nanoparticles doped with Tb3+ and Eu3+ and consisting of up to four layers were synthesized with an outer diameter of ?10 nm. It is found that by varying the thicknesses of an undoped layer between a Tb3+-doped layer and a Eu3+-doped layer, the degree of ET can be engineered to allow for zero, partial, or total ET from a donor ion to an acceptor ion. More specifically, the ratio of the intensities of the 541-nm Tb3+ and 590 nm Eu3+ peaks was tailored from <0.2 to ?2.4 without changing the overall composition of the particles but only by changing the internal structure. Further, the emission spectrum of a blend of singly doped nanoparticles is shown to be equivalent to the spectra of co-doped particles when a core-shell configuration that restricts ET is used. Beyond simply controlling ET, which can be limiting when designing materials for optical applications, this approach can be used to obtain truly engineered spectral features from nanoparticles and composites made from them. Further, it allows for a single excitation source to yield multiple discrete emissions from numerous lanthanide dopants that heretofore would have been quenched in a more conventional active optical material. PMID:18250307

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

    PubMed Central

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

    2009-01-01

    We have studied the luminescence decay and trace biomaterials detection potential of two surface-functionalized nanoparticles, poly(ethylene glycol) bis(carboxymethyl) ether-coated LaF3:Ce,Tb (~20 nm) and thioglycolic acid-coated ZnS/Mn (~5 nm). Upon UV excitation, these nanoparticles emitted fluorescence peaking at 540 and 597 nm, respectively, in solution. Fluorescence imaging revealed that these nanoparticles targeted the trace biomaterials from fingerprints that were deposited on various nonporous solid substrates. Highly ordered, microscopic sweat pores within the friction ridges of the fingerprints were labeled with good spatial resolutions by the nanoparticles on aluminum and polymethylpentene substrates, but not on glass or quartz. In solution, these nanoparticles exhibited multicomponent fluorescence decays of resolved lifetimes ranging from nano-to microseconds and of average lifetimes of ~24 and 130 µs for the coated LaF3:Ce,Tb and ZnS:Mn, respectively. The long microsecond-decay components are associated with the emitters at or near the nanocrystal core surface that are sensitive to the size, surface-functionalization, and solvent exposure of the nanoparticles. When the nanoparticles were bound to the surface of a solid substrate and in the dried state, a decrease in the microsecond decay lifetimes was observed, indicative of a change in the coating environment of the nanocrystal surface upon binding and solvent removal. The average decay lifetimes for the surface-bound ZnS:Mn in the dried state were ~60, 30, and 11 µs on quartz, aluminum, and polymethylpentene, respectively. These values were still 2 orders of magnitude longer than the typical fluorescence decay background of most substrates (e.g., ~0.36 µs for polymethylpentene) in trace forensic evidence detections. We conclude that coated ZnS: Mn nanoparticles hold great promise as a nontoxic labeling agent for ultrasensitive, time-gated, trace evidence detections in nanoforensic applications. PMID:20072713

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  17. Optical whispering gallery mode resonances in asymmetric morphologies

    NASA Astrophysics Data System (ADS)

    Mohageg, Makan

    This dissertation describes the experimental realization of optical whispering-gallery-mode resonators constructed from crystalline material with various symmetries. Nonlinear optical scattering in disk-shaped resonators constructed from CaF 2 and LiNbO3 is discussed, as is the nonlinear optics of LN resonators with ferroelectric poling structures. Optical whispering-gallery-mode resonators with extended axes and highly elliptical geometries are presented. Experimentally observed effects of internal anisotropy on mode structure is also covered.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  19. Separation of High Order Harmonics with Fluoride Windows

    SciTech Connect

    Allison, Tom; van Tilborg, Jeroen; Wright, Travis; Hertlein, Marcus; Falcone, Roger; Belkacem, Ali

    2010-08-02

    The lower orders produced in high order harmonic generation can be effciently temporally separated into monochromatic pulses by propagation in a Fluoride window while still preserving their femtosecond pulse duration. We present calculations for MgF2, CaF2, and LiF windows for the third, fifth, and seventh harmonics of 800 nm. We demonstrate the use of this simple and inexpensive technique in a femtosecond pump/probe experiment using the fifth harmonic.

  20. The epitaxial growth of evaporated Cu/CaF2 bilayers on Si(111)

    NASA Astrophysics Data System (ADS)

    Mattoso, N.; Mosca, D. H.; Mazzaro, I.; Teixeira, S. R.; Schreiner, W. H.

    1995-03-01

    Successful and unexpected epitaxial growth of Cu/CaF2 bilayers on hydrogen terminated Si(111) wafers by thermal evaporation is reported. The bilayers were characterized with conventional x-ray diffraction experiments, grazing angle incidence x-ray diffraction experiments, rocking curves, and ? scans. The growth mode of Cu films on CaF2 epitaxially grown on Si(111) is completely different from that of the Cu film grown directly on Si(111).

  1. Status report on dark matter search with low activity scintillators

    NASA Astrophysics Data System (ADS)

    Bacci, C.; Belli, P.; Bernabei, R.; Dai, C.; Di Nicolantonio, W.; Ding, L. K.; Gaillard-Lecanu, E.; Giraud-Heraud, Y.; Kuang, H. H.; Incicchitti, A.; Mallet, J.; Mosca, L.; Prosperi, D.; Tao, C.; Chambon, B.; Chazal, V.; De Jsus, M.; Drain, D.; Messous, Y.; Pastor, C.; BPRS (Beijing, Paris, Roma, Saclay) Collaboration

    1994-05-01

    The BPRS experiment is dedicated to particle Dark Matter search with low activity scintillators. Preliminary results on Weakly Interacting Massive Particles (WIMPs) have been already obtained with NaI(Tl) and CaF 2(Eu) target-detectors. New detector developments are in progress. A new search for Strongly Interacting Massive Particles (SIMPs) with NaI(Tl) scintillators have been also performed.

  2. Lubricating Properties of Some Bonded Fluoride and Oxide Coatings for Temperature to 1500 F

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E.

    1960-01-01

    The lubricating properties of some experimental ceramic coatings, diffusion-bonded fluoride coatings, and ceramic-bonded fluoride coatings were determined. The experiments were conducted in an air atmosphere at a sliding velocity of 430 feet per minute and at temperatures from 75 to 1500 F. Several ceramic coatings provided substantial reductions in friction coefficient and rider wear (compared with the unlubricated metals). For example, a cobaltous oxide (CoO) base coating gave friction coefficients of 0.24 to 0.36 within the temperature range of 75 to 1400 F; serious galling and welding of the metal surfaces were prevented. The friction coefficients were higher than the arbitrary maximum (0.2) usually considered for effective boundary lubrication. However, when a moderately high friction coefficient can be tolerated, this type of coating may be a useful antiwear composition. Diffusion-bonded calcium fluoride (CaF2) on Haynes Stellite 21 and on Inconel X gave friction coefficients of 0.1 to 0.2 at 1500 F. Endurance life was dependent on the thermal history of the coating; life improved with increased exposure time at elevated temperatures prior to running. Promising results were obtained with ceramic-bonded CaF2 on Inconel X. Effective lubrication and good adherence were obtained with a 3 to 1 ratio of CaF2 to ceramic. A very thin sintered and burnished film of CaF2 applied to the surface of this coating further improved lubrication, particularly above 1350 F. The friction coefficient was 0.2 at 500 F and decreased with increasing temperature to 0.06-at 1500 F. It was 0.25 at 75 F and 0.22 at 250 F.

  3. Application of different TL detectors for the photon dosimetry in mixed radiation fields used for BNCT.

    PubMed

    Burgkhardt, B; Bilski, P; Budzanowski, M; Bttger, R; Eberhardt, K; Hampel, G; Olko, P; Straubing, A

    2006-01-01

    Different approaches for the measurement of a relatively small gamma dose in strong fields of thermal and epithermal neutrons as used for Boron Neutron Capture Therapy (BNCT) have been studied with various thermoluminescence detectors (TLDs). CaF(2):Tm detectors are insensitive to thermal neutrons but not tissue-equivalent. A disadvantage of applying tissue-equivalent (7)LiF detectors is a strong neutron signal resulting from the unavoidable presence of (6)Li traces. To overcome this problem it is usual to apply pairs of LiF detectors with different (6)Li content. The experimental determination of the thermal neutron response ratio of such a pair at the Geesthacht Neutron Facility (GeNF) operated by PTB enables measurement of the photon dose. In the experimental mixed field of thermal neutrons and photons of the TRIGA reactor at Mainz the photon dose measured with different types of (7)LiF/(nat)LiF TLD pairs agree within a standard uncertainty of 6% whereas the CaF(2):Tm detectors exhibit a photon dose by more than a factor of 2 higher. It is proposed to determine suitable photon energy correction factors for CaF(2):Tm detectors with the help of the (7)LiF/(nat)LiF TLD pairs in the radiation field of interest. PMID:16644976

  4. Ultra-high resistive and anisotropic CoPd-CaF2 nanogranular soft magnetic films prepared by tandem-sputtering deposition

    NASA Astrophysics Data System (ADS)

    Naoe, Masayuki; Kobayashi, Nobukiyo; Ohnuma, Shigehiro; Iwasa, Tadayoshi; Arai, Ken-Ichi; Masumoto, Hiroshi

    2015-10-01

    Ultra-high resistive and anisotropic soft magnetic films for gigahertz applications are desirable to demonstrate the really practical films. Here we present a study of novel nanogranular films fabricated by tandem-sputtering deposition. Their electromagnetic properties and nanostructure have also been discussed. These films consisted of nanocrystallized CoPd alloy-granules and CaF2 matrix, and a specimen having a composition of (Co0.69Pd0.31)52-(Ca0.31F0.69)48 exhibited distinct in-plane uniaxial anisotropy after uniaxial field annealing with granule growth. Its complex permeability spectra have a ferromagnetic resonance frequency extending to the Super-High-Frequency band due to its higher anisotropy field, and its frequency response was quite well reproduced by a numerical calculation based on the Landau-Lifshitz-Gilbert equation. Furthermore, it was clarified that the CaF2-based nanogranular film exhibits a hundredfold higher electrical resistivity than conventional oxide or nitride-based films. Higher resistivity enables the film thickness to achieve a margin exceeding threefold against eddy current loss. The greater resistivity of nanogranular films is attributed to the wide energy bandgap and superior crystallinity of CaF2 matrix.

  5. Effect of Fluorine on the Structure of High Al2O3-Bearing System by Molecular Dynamics Simulation

    NASA Astrophysics Data System (ADS)

    Fan, Guozheng; He, Shengping; Wu, Ting; Wang, Qian

    2015-08-01

    Calcium aluminosilicate is the most important slag system in continuous casting, while CaF2 is commonly used as a fluxing agent in mold fluxes. In this study, the structural properties of the CaO-Al2O3-SiO2-CaF2 system with varying fluorine content have been investigated by molecular dynamics simulation using the pairwise potential model. The results showed that with the substitution of oxygen ions by fluorine ions, the average bond length of Si-O remained unchanged, while the average bond length of Al-O increased from 1.74 to 1.75 . The addition of fluorine contributed to the increase in the bridging oxygen proportion and the network connectivity ( Q n ) degree, suggesting that the polymerization of melts was enhanced. Meanwhile, the threefold-coordinated Al was found when mass fraction of fluorine was increased, and it was due to that the fluorine ions substituted the oxygen ions and formed the [AlO3F] tetrahedron. The Al avoidance principle is not applicable in the CaO-Al2O3-SiO2-CaF2 system with a high content of Al2O3.

  6. A method for the production of composite scintillators for dosimetry in diagnostic radiology.

    PubMed

    Nowotny, R; Taubeck, A

    2009-03-21

    Plastic scintillators are used in the dosimetry of photons in radiotherapy. Their use in diagnostic radiology is affected by the drop in response at lower photon energies due to inadequate composition (effective atomic number) and chemical quenching. To compensate for this deficiency, a method for the production of composite polystyrene-based plastic scintillators was devised allowing the incorporation of inorganic scintillation powder. Disks of 10 mm diameter and 1 mm thickness optimized for a flat energy response referred to kerma in air were produced using CaWO(4), ZnS:Ag and CaF(2):Eu as additives. In an HVL range of 2.26-13.69 mmAl, the response was within an interval of +/-2.8% for CaF(2):Eu as additive, +/-3.2% for CaWO(4) and +/-10.9% for ZnS:Ag, respectively. The response of a commercial plastic scintillator (BC470) stays within +/-13.6%. The temperature dependence of the composite scintillator using CaF(2):Eu is lowest with a variation of +3.7% to -3.6% in an interval from 5 degrees C to 45 degrees C. The deficiency in photon absorption at lower energies due to the effective atomic number is reduced but not fully compensated by the additive scintillators. The optimized concentrations were established for the scintillator dimensions used. PMID:19218738

  7. Effect of aluminum phosphate additions on composition of three-component plasma-sprayed solid lubricant

    NASA Technical Reports Server (NTRS)

    Jacobson, T. P.; Young, S. G.

    1982-01-01

    Image analysis (IA) and electron microprobe X-ray analysis (EMXA) were used to characterize a plasma-sprayed, self-lubricating coating, NASA LUBE PS106, specified by weight percent as 35NiCr-35Ag-30CaF2. To minimize segregation of the powder mixture during the plasma-spraying procedure, monoaluminum phosphate was added to form agglomerate particles. Three concentrations of AlPO4 were added to the mixtures: 1.25, 2.5, and 6.25 percent by weight. Analysis showed that 1.25 wt% AlPO4 yielded a CaF2 deficiency, 2.5 wt% kept the coating closest to specification, and 6.25 wt% yielded excess CaF2 as well as more impurities and voids and a deficiency in silver. Photomicrographs and X-ray maps are presented. The methods of IA and EMXA complement each other, and the reasonable agreement in the results increases the confidence in determining the coating composition.

  8. Effects of fluoride on in vitro enamel demineralization analyzed by ?F MAS-NMR.

    PubMed

    Mohammed, N R; Kent, N W; Lynch, R J M; Karpukhina, N; Hill, R; Anderson, P

    2013-01-01

    The mechanistic action of fluoride on inhibition of enamel demineralization was investigated using (19)F magic angle spinning nuclear magnetic resonance (MAS-NMR). The aim of this study was to monitor the fluoride-mineral phase formed on the enamel as a function of the concentration of fluoride ions [F(-)] in the demineralizing medium. The secondary aim was to investigate fluorapatite formation on enamel in the mechanism of fluoride anti-caries efficacy. Enamel blocks were immersed into demineralization solutions of 0.1 M acetic acid (pH 4) with increasing concentrations of fluoride up to 2,262 ppm. At and below 45 ppm [F(-)] in the solution, (19)F MAS-NMR showed fluoride-substituted apatite formation, and above 45 ppm, calcium fluoride (CaF2) formed in increasing proportions. Further increases in [F(-)] caused no further reduction in demineralization, but increased the proportion of CaF2 formed. Additionally, the combined effect of strontium and fluoride on enamel demineralization was also investigated using (19)F MAS-NMR. The presence of 43 ppm [Sr(2+)] in addition to 45 ppm [F(-)] increases the fraction of fluoride-substituted apatite, but delays formation of CaF2 when compared to the demineralization of enamel in fluoride-only solution. PMID:23712030

  9. Study of the presence of fluorine in the recycled fractions during carbothermal treatment of EAF dust.

    PubMed

    Menad, N; Ayala, J N; Garcia-Carcedo, Fernando; Ruiz-Aycar, E; Hernndez, A

    2003-01-01

    Carbothermal treatment tests of electric arc furnace dusts (EAFD) using the Waelz kiln process were carried out in pilot-scale for the production of zinc oxide. The association of halides in the EAFD, and the recycled products, such as zinc oxide fumes and high-grade iron contents fractions were examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. XRD reveals the presence of chlorine and fluorine in the dusts in the form of KCl, NaCl and CaF2. An ultra-pure fraction of zinc was obtained after the Double Leaching Waelz Oxide (DLWO) process was performed on the zinc oxide fumes. The halide contents were reduced to approximately 100 ppm Cl and 700 ppm F. The rest of these elements are in the form of CaF2. About 65% F is volatilised as lead and zinc fluorides, 15% is expected in the magnetic fractions and 20% in non-magnetic fractions as CaF2 and MnF2, respectively. PMID:12909089

  10. Spectroscopic analysis of Ho3+ transitions in different modifier oxide based lithium-fluoro-borate glasses

    NASA Astrophysics Data System (ADS)

    Balakrishna, A.; Rajesh, D.; Ratnakaram, Y. C.

    2014-10-01

    In recent investigations it was observed that the presence of different structural groups in borate glasses was favorable for spectroscopic investigations of rare earth doped borate glasses. Consequent to these observations, the heavy metal fluoride glasses doped with Ho3+ ions received much attention due to their wide transparency in the ultraviolet to infrared region. Keeping these observations in view, the present paper makes an attempt to present spectral investigations of Ho3+ doped lithium-fluoro-borate glasses of the compositions Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. These rare earth doped glasses were synthesized by melt quenching technique and an investigation was carried out to observe the structural (SEM and FT-IR) and optical (absorption and luminescence) properties. The paper also aims at the determination of three phenomenological Judd-Ofelt intensity parameters and special attention was paid to study the emission properties by employing the J-O intensity parameters. The visible emission spectra of Ho3+ ion in different lithium-fluoro-borate glasses were recorded by exciting the samples at 409 nm. The results revealed that among all the glass matrices, cadmium glass matrix have shown higher stimulated emission cross-section, which indicates that this is a good lasing material at this wavelength and highly useful for laser excitation.

  11. Effect of modifier oxides on absorption and emission properties of Eu3+ doped different lithium fluoroborate glass matrices

    NASA Astrophysics Data System (ADS)

    Ratnakaram, Y. C.; Balakrishna, A.; Rajesh, D.

    2012-11-01

    Eu3+ doped lithium fluoroborate glass with different modifier oxides (Li2B4O7-BaF2-NaF-MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li2B4O7-BaF2-NaF-MgO+CaO, Li2B4O7-BaF2-NaF-CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state (7F0) of different absorption bands of Eu3+ are calculated. From the optical absorption measurements and using the Judd-Ofelt (J-O) theory, J-O parameters (Ωλλ=2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities (A), radiative life-times (τR), and branching ratios (βr) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections (σP) are obtained for the emission transitions, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 of Eu3+ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the 5D0→7F2 transition have been measured and analyzed for all the glass matrices.

  12. Measurement of the Gd157(n,?) reaction with the DANCE ? calorimeter array

    NASA Astrophysics Data System (ADS)

    Chyzh, A.; Baramsai, B.; Becker, J. A.; Be?v?, F.; Bredeweg, T. A.; Couture, A.; Dashdorj, D.; Haight, R. C.; Jandel, M.; Kroll, J.; Krti?ka, M.; Mitchell, G. E.; O'Donnell, J. M.; Parker, W.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Walker, C. L.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2011-07-01

    The Gd157(n,?) reaction was measured with the DANCE ? calorimeter (consisting of 160 BaF2 scintillation detectors) at the Los Alamos Neutron Science Center. The multiplicity distributions of the ? decay were used to determine the resonance spins up to En=300 eV. The ?-ray energy spectra for different multiplicities were measured for the s-wave resonances. The shapes of these spectra were compared with simulations based on the use of the DICEBOX statistical model code. Simulations showed that the scissors mode is required not only for the ground-state transitions but also for transitions between excited states.

  13. 25Na and 25Mg fragmentation on 12C at 9.23 MeV per nucleon at TRIUMF

    NASA Astrophysics Data System (ADS)

    St-Onge, Patrick; Boisjoli, Mark; Frgeau, Marc-Olivier; Gauthier, Jrme; Wallace, Barton; Roy, Ren

    2012-10-01

    HERACLES is a multidetector that is used to study heavy-ion collisions, with ion beams with an energy range between 8 to 15 MeV per nucleon. It has 78 detectors axially distributed around the beam axis in 6 rings allowing detection of multiple charged fragments from nuclear reactions. HERACLES has 4 different types of detectors, BC408/BaF2 phoswich, Si/CsI(Tl) telescope, BC408/BC444 phoswich and CsI(Tl) detectors. The multidetector has been run with a radioactive 25Na beam and a stable 25Mg beam at 9.23 MeV per nucleon on a carbon target.

  14. Measurement of Liquid Surface Temperature by a Infrared Radiation Thermometer

    NASA Astrophysics Data System (ADS)

    Hihara, Eiji; Fujita, Isamu; Saito, Takamoto

    A method for measuring liquid. surface temperature by a infrared radiation thermometer is described. When the temperature is measured through a glass plate, following corrections are required: (1) transmissivity of the glass plate, (2) Thermal radiation from the glass plate, and (3) thermal radiation from the room walls which reflects at the glass plate. In this study, a correction method of the above effects is presented, and is confirmed by the experiment. The surface temperature of water was measured through a BaF2 plate in the range of 40?90°C. The accuracy of the measurements was within 0.5C.

  15. Prompt ?-rays from the Fast Neutron Induced Fission on 235,238U and 232Th

    NASA Astrophysics Data System (ADS)

    Lebois, M.; Wilson, J. N.; Halipr, P.; Leniau, B.; Matea, I.; Oberstedt, A.; Oberstedt, S.; Verney, D.

    Preliminary results from the first experiment using the LICORNE neutron source at the IPN Orsay are presented. Prompt fission gamma rays from fast-neutron induced fission of 238U, 232Th and 235U were detected. Thick samples of around 50 g of 238U and 232Th are used for the first part of the experiment. An ionisation chamber containing ? 10 mg samples of 238U and 235U to provide a fission trigger is used for the second part of the experiment. Gamma rays have been detected using 17 high efficiency BaF2 detectors and 6 LaBr3 scintillator detectors.

  16. On-line ion chemistry for the AMS analysis of 90Sr and 135,137Cs

    NASA Astrophysics Data System (ADS)

    Eliades, J.; Zhao, X.-L.; Litherland, A. E.; Kieser, W. E.

    2013-01-01

    The analysis of 90Sr by AMS has so far required the use of very large tandem accelerators in order to separate the isobar 90Zr by the rate-of-energy-loss method. The analysis of 135,137Cs by AMS has never been attempted as the separation of the isobars 135,137Ba by the traditional method requires even higher energies, so that this approach would become prohibitively expensive for routine analysis. Following the successful demonstration of Cl--S- separation by the Isobar Separator, the same apparatus was used to test the separation of other pairs of isobars. Surprisingly effective results were obtained with NO2 gas in the cases of SrF3--ZrF3- and CsF2--BaF2- separations. Reduction factors of ∼4 × 10-6 for ZrF3-/SrF3- and ∼2 × 10-5 for BaF2-/CsF2- were measured. SrF3- and CsF2- are both super-halogen anions and are preferentially produced in the ion source rather than ZrF3- and BaF2- when using the PbF2 matrix-assisted method. Reduction factors for ion source production with such targets of ∼3 × 10-5 for ZrF3--SrF3- and ∼5 × 10-4 for BaF2--CsF2- were found. The combined methods would suggest a theoretical detection sensitivity for 90Sr/Sr ∼6 × 10-16, 135Cs/Cs ∼7 × 10-15 and 137Cs/Cs ∼1 × 10-14, assuming 10 ppm Zr and Ba contamination in the AMS targets. In addition to the earlier Cl--S- separation work, these measurements further illustrate the potential of on-line ion chemical methods for broadening the analytical scope of small AMS systems.

  17. Spin Measurements of n +87Sr for Level Density Studies

    NASA Astrophysics Data System (ADS)

    Gunsing, F.; Fraval, K.; Mathelie, M.; Valenta, S.; Bečvář, F.; Rusev, G.; Tonchev, A. P.; Mitchell, G.; Baramsai, B.; Altstadt, S.; Andrzejewski, J.; Audouin, L.; Barbagallo, M.; Bécares, V.; Belloni, F.; Berthoumieux, E.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calviani, M.; Calviño, F.; Cano-Ott, D.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Duran, I.; Dressler, R.; Eleftheriadis, C.; Ferrari, A.; Ganesan, S.; García, A. R.; Giubrone, G.; Gonçalves, I. F.; González-Romero, E.; Griesmayer, E.; Guerrero, C.; Hernández-Prieto, A.; Jenkins, D. G.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Koehler, P.; Kokkoris, M.; Krtička, M.; Kroll, J.; Lampoudis, C.; Langer, C.; Leal-Cidoncha, E.; Lederer, C.; Leeb, H.; Leong, L. S.; Losito, R.; Manousos, A.; Marganiec, J.; Martínez, T.; Massimi, C.; Mastinu, P. F.; Mastromarco, M.; Mendoza, E.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Mondalaers, W.; Paradela, C.; Pavlik, A.; Perkowski, J.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifarth, R.; Riego, A.; Robles, M. S.; Rubbia, C.; Sabaté-Gilarte, M.; Sarmento, R.; Saxena, A.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Tagliente, G.; Tain, J. L.; Tarrío, D.; Tassan-Got, L.; Tsinganis, A.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T.; Žugec, P.

    2014-05-01

    We have used the 4π BaF2 gamma-ray detector array at the n_TOF neutron time-of-flight facility at CERN for an experiment in order to determine the spins of resonances of n +87Sr by measuring the gamma-ray spectra and multiplicity distributions. The first results are presented here. We have assigned the orbital momentum ℓ to all evaluated resonances on the basis of their neutron widths. Further we have assigned the spin J to 16 s-wave resonances on based the population of low-lying levels.

  18. Spectroscopy of divalent rare earth ions in fluoride crystals

    NASA Astrophysics Data System (ADS)

    Shendrik, R.; Myasnikova, A. S.; Radzhabov, E. A.; Nepomnyashchikh, A. I.

    2016-01-01

    We have studied the absorption spectra of x-ray irradiation-induced Ce2+ and Pr2+ ions in crystals of alkaline-earth fluorides. We have calculated absorption spectra of divalent praseodymium ions in SrF2 crystals doped with Pr2+ for the first time. The calculated spectra agree rather well with the experimental data. In crystals containing induced Ce2+ ions we have found strong electron-phonon coupling. In BaF2, we do not observe bands corresponded to divalent Ce or Pr ions.

  19. Triple coincidence PALS setup based on fast pulse digitizers

    NASA Astrophysics Data System (ADS)

    Bosnar, D.; ?ur?evi?, B.; Paveli?, L.; Bosnar, S.

    2015-06-01

    We have assembled positron annihilation lifetime spectroscopy system that consists of three BaF2 detectors with XP2020URQ PMTs which are directly coupled to DRS4 evaluation board. Both time and energy information of the detected gamma rays are reconstructed. In the off-line analysis, by using selected cuts on energies of gamma rays, double, as well as triple coincidence events can be extracted. The setup is very suitable for the determination of contributions of positronium three gamma annihilations which can be of interest in the investigations of various porous materials.

  20. Conversion of Oxyfluoride Based Coated Conductors

    SciTech Connect

    Dan Wesolowski

    2006-11-01

    Direct measurements of HF pressure in equilibrium with the film during the BaF2 process are sorely needed. It is the HF partial pressure that governs the rate at which the film composition is changing and is, therefore, an important factor in controlling the composition/time trajectory of the film. Establishing the composition/time trajectory of both MOD-derived and e-beam derived films for a given set of conditions is another goal for the project. These studies will provide a fundamental understanding of the ex situ process for producing coated conductors.

  1. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  2. Understanding Low Energy Gamma Emission from Fission and Capture with DANCE

    NASA Astrophysics Data System (ADS)

    Wilburn, Grey; Couture, Aaron; Mosby, Shea

    2012-10-01

    Los Alamos National Laboratory's Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 barium fluoride (BaF2) detectors in a 4? array used to study cross-section measurements from neutron capture reactions. Further, recent studies have taken advantage of DANCE to study the gamma emission from fission, which is not well characterized. Neutron capture is studied because of its relevance to nuclear astrophysics (almost all elements heavier than iron are formed via neutron capture) and nuclear energy, where neutron capture is a poison in the reactor. Gamma ray cascades following neutron capture and fission include photons with energies between 100 keV and 10 MeV. DANCE uses a ^6LiH sphere to attenuate scattered neutrons, the primary background in DANCE. Unfortunately, it also attenuates low energy gamma rays. In order to quantify this effect and validate simulations, direct measurements of low energy gammas were made with a high purity germanium (HPGe) crystal. HPGe's allow for high resolution measurements of low energy gamma rays that are not possible using the BaF2 crystals. The results and their agreement with simulations will be discussed.

  3. Measurement of prompt fission neutron spectrum using a gamma tag double time-of-flight setup

    NASA Astrophysics Data System (ADS)

    Blain, Ezekiel

    Current uncertainties in the prompt fission neutron spectrum have a significant effect of up to 4% on keff for reactor criticality and safety calculations. Therefore, a method was developed at RPI to improve the accuracy of the measurement of the prompt fission neutron spectrum. This method involves using an array of BaF2 gamma detectors to tag that a fission event has occurred, and a double time-of-flight setup to obtain the prompt fission neutron spectrum as a function of incident neutron energy. The gamma tagging method improves upon conventional fission chambers by allowing for much larger sample sizes to be utilized while not suffering from effects of discriminator level on the shape of the prompt fission neutron spectrum. A coincidence requirement on an array of 4 BaF2 gamma detectors is used to determine the timing of the fission event. Furthermore, a method is under development for the use of thin plastic scintillators for measurement of the prompt fission neutron spectrum with low energies. Measurements with spontaneous fission of . {252} Cf show good agreement with previous datasets and current evaluations as well as providing accurate data down to 50 keV with the plastic scintillator detector. Preliminary incident neutron beam analysis was performed with 238U and shows good agreement with the current evaluations demonstrating the feasibility of the gamma tagging method for in beam prompt fission neutron spectrum measurements of various isotopes.

  4. Precipitation of barium flouride microcrystals from electrolytic solutions: The influence of the composition of the precipitating solutions

    NASA Astrophysics Data System (ADS)

    Kolar, Z.; Binsma, J. J. M.; Suboti?, B.

    1984-02-01

    The composition, shape and size of the particles obtained by precipitation in aqueous solutions of various barium salts (chloride, nitrate and acetate) with various fluorides (ammonium, sodium and hydrogen) have been studied by X-ray powder diffraction analysis and scanning electron microscopy. From Ba(NO 3) 2 in combination with NH 4F or NaF and from Ba(C 2H 3O 2) 2 in combination with NH 4F, NaF or HF, precipitates of pure cubic-BaF 2 (?-BaF 2) are obtained. The shape and size of ?-BaF 2 particles depend on the combination of the compounds used for the precipitation and their concentrations. It appears that only when (equal volumes of) solutions of Ba(NO 3) 2 (0.125 mol dm -3) or Ba(C 2H 3O 2) 2 (0.125 and 0.150 mol dm -3) and NH 4F (0.250 or 0.300 mol dm -3) are mixed particles are formed as more or less regular cubes with smooth faces. These crystals are suitable to be used in studies of the transport of ions from crystals to the solution and vice versa with the aid of radioactive tracers ("heterogeneous isotopic exchange" studies).

  5. Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET.

    PubMed

    Mondal, Nagendra Nath

    2009-10-01

    This study presents Monte Carlo Simulation (MCS) results of detection efficiencies, spatial resolutions and resolving powers of a time-of-flight (TOF) PET detector systems. Cerium activated Lutetium Oxyorthosilicate (Lu(2)SiO(5): Ce in short LSO), Barium Fluoride (BaF(2)) and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr(3)) scintillation crystals are studied in view of their good time and energy resolutions and shorter decay times. The results of MCS based on GEANT show that spatial resolution, detection efficiency and resolving power of LSO are better than those of BaF(2) and LaBr(3), although it possesses inferior time and energy resolutions. Instead of the conventional position reconstruction method, newly established image reconstruction (talked about in the previous work) method is applied to produce high-tech images. Validation is a momentous step to ensure that this imaging method fulfills all purposes of motivation discussed by reconstructing images of two tumors in a brain phantom. PMID:20098551

  6. HERACLES : a multidetector for heavy-ion collisions at TRIUMF

    NASA Astrophysics Data System (ADS)

    St-Onge, Patrick; Gauthier, Jrme; Wallace, Barton; Roy, Ren

    2014-01-01

    HERACLES is a multidetector that has been modified to study heavy-ion collisions, using an ion beam with an energy range between 8 to 15 MeV per nucleon. It has 78 detectors axially distributed around the beam axis in 6 rings allowing detection of multiple charged fragments from nuclear reactions. HERACLES has 4 different types of detectors, BC408/BaF2 phoswich, Si/CsI(Tl) telescope, BC408/BC444 phoswich and CsI(Tl) detectors. 25 Na + 12 C, 25 Na + 27 Al, 25 Mg + 12 C and 25 Mg + 27 Al reactions have been used to characterize the multidetector. Element identification up to Z = 12 is achieved with the BC408/BaF2 phoswich detectors, up to Z = 15 with the Si/CsI(Tl) telescopes and up to Z = 12 with the BC408/BC444 phoswich detectors. Isotopic identification is reached with the CsI(Tl) detector up to Z = 2.

  7. Low-dimensional [110]-orientated lead chalcogenides for mid-infrared lasers

    NASA Astrophysics Data System (ADS)

    Shi, Zhisheng; Lu, Xiaoling; Zhao, Fanghai; Majumdar, Amitava; Ray, Dewali; Singh, Roopa; Bondili, Swathi; Li, Donghui; Jain, Shikha

    2004-12-01

    Low dimensional lead salt structure such as quantum-well (QW) structure is proposed for the fabrication of opto-electronic devices. Among [100], [111], and [110] orientations, [110]-orientated QW structure offers the highest gain. Theoretical simulations of [110] QW Pb-salt edge-emitting lasers show a 70-degree temperature increase in continuous-wave (CW) operation compared to the conventional [100]-orientated lasers. With modestly reduced Auger recombination of low dimensional material and with improved heat dissipation for laser structure, CW operation with about 10 mW output powers at room temperature for PbSe QW laser is predicted. PbSe epitaxial layer and PbSe/PbSrSe QW structures were, for the first time, successfully grown on [110]-orientated BaF2 substrate by molecular-beam-epitaxy (MBE). The linewidth of the rocking curve from high-resolution x-ray diffraction (HRXRD) measurement for PbSe thin film is 60 arcsec, which indicates high crystalline quality. The dislocation density estimated by the rocking curve is 1.18x107 cm-2. Photoluminescence intensity of [110]-orientated samples was twice as high as that on [111]-orientated BaF2 substrates from the same MBE run.

  8. Chemical Transformation of Crystalline Hafnium Tetrafluoride Studied by Perturbed Angular Correlation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dey, Chandi Charan C.

    2009-11-01

    The chemical transformation of the trihydrate hafnium tetrafluoride crystal has been studied with varying temperature using the time-differential perturbed angular correlation technique. The 133 - 482 keV ? -? cascade of 181Ta after the ? --decay of 181Hf has been selected and a four detector BaF2-BaF2 coincidence set up has been used for measurements. The crystal was produced by evaporating a solution of HfF62-complex in HF at room temperature. Contrary to the earlier report, it has been found that the trihydrate hafnium tetrafluoride compound dehydrates directly to HfF4 without producing any intermediate monohydrate and present results do not support the earlier idea that two water molecules of HfF43H2O are loosely bound. Present investigations exhibit a superheated state for the hafnium tetrafluoride crystal. In dehydrated HfF4, two different Hf sites have been observed which suggests two different structures for the anhydrous HfF4.

  9. The effect of water pressure on the texture and morphology of MOD-YBCO films on buffered metal substrates

    NASA Astrophysics Data System (ADS)

    Chung, K. C.; Yoo, J. M.; Kim, Y. K.; Wang, X. L.; Dou, S. X.

    2009-02-01

    The influence of water pressure in the metal-organic deposition (MOD) method on the texture and morphology of YBa2Cu3O7-X (YBCO) films grown on buffered metal substrates was investigated. The water pressure was varied from 4.2% to 10.0%, with the other process parameters, such as annealing temperature and oxygen pressure, kept constant. In this work, a YBCO precursor solution was prepared using a fluorine-free Y and Cu precursor solution with the addition of Sm. MOD-YBCO films were fabricated by continuous slot-die coating and calcination, followed by high temperature annealing. Using x-ray diffraction analysis, unreacted phase peaks, such as BaF2 peaks, were found in the samples made at a water pressure of 4.2%; however, the BaF2 peak intensity was much reduced as the water pressure was increased. The higher water pressure of about 10.0% in this experiment led to the poor crystallinity of MOD-YBCO films, possibly due to the fast reaction with the supplied water vapor. Meanwhile, the morphologies of the YBCO films were not much different from each other in the range of water pressure of this work. The maximum critical current density of 3.8 MA cm-2 was obtained when the sample was made at the water pressure of 6.2% and the annealing temperature of 780 C.

  10. Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET

    PubMed Central

    Mondal, Nagendra Nath

    2009-01-01

    This study presents Monte Carlo Simulation (MCS) results of detection efficiencies, spatial resolutions and resolving powers of a time-of-flight (TOF) PET detector systems. Cerium activated Lutetium Oxyorthosilicate (Lu2SiO5: Ce in short LSO), Barium Fluoride (BaF2) and BriLanCe 380 (Cerium doped Lanthanum tri-Bromide, in short LaBr3) scintillation crystals are studied in view of their good time and energy resolutions and shorter decay times. The results of MCS based on GEANT show that spatial resolution, detection efficiency and resolving power of LSO are better than those of BaF2 and LaBr3, although it possesses inferior time and energy resolutions. Instead of the conventional position reconstruction method, newly established image reconstruction (talked about in the previous work) method is applied to produce high-tech images. Validation is a momentous step to ensure that this imaging method fulfills all purposes of motivation discussed by reconstructing images of two tumors in a brain phantom. PMID:20098551

  11. Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses

    NASA Astrophysics Data System (ADS)

    Taira, Y.; Toyokawa, H.; Kuroda, R.; Yamamoto, N.; Adachi, M.; Tanaka, S.; Katoh, M.

    2013-05-01

    High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90 collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

  12. Correlated fluorine diffusion and ionic conduction in the nanocrystalline F(-) solid electrolyte Ba(0.6)La(0.4)F(2.4)-(19)F T1(ρ) NMR relaxation vs. conductivity measurements.

    PubMed

    Preishuber-Pflügl, F; Bottke, P; Pregartner, V; Bitschnau, B; Wilkening, M

    2014-05-28

    Chemical reactions induced by mechanical treatment may give access to new compounds whose properties are governed by chemical metastability, defects introduced and the size effects present. Their interplay may lead to nanocrystalline ceramics with enhanced transport properties being useful to act as solid electrolytes. Here, the introduction of large amounts of La into the cubic structure of BaF2 served as such an example. The ion transport properties in terms of dc-conductivity values of the F(-) anion conductor Ba1-xLaxF2+x (here with x = 0.4) considerably exceed those of pure, nanocrystalline BaF2. So far, there is only little knowledge about activation energies and jump rates of the elementary hopping processes. Here, we took advantage of both impedance spectroscopy and (19)F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. While macroscopic transport is governed by an activation energy of 0.55 to 0.59 eV, the elementary steps of hopping seen by NMR are characterised by much smaller activation energies. Fortunately, we were able to deduce an F(-) self-diffusion coefficient by the application of spin-locking NMR relaxometry. PMID:24728404

  13. UV/blue upconversion in Nd3+:TeO2 glass, effect of modifiers and heat treatment on the fluorescence bands.

    PubMed

    Verma, R K; Kumar, K; Rai, S B

    2009-10-15

    Upconversion (UC) emissions in UV/blue region have been observed in Nd(3+) doped tellurite glass on 532 nm excitation. The UC bands have been observed at 360, 387, 417 and 452 nm due to the (4)D(3/2)-->(4)I(9/2), (4)D(3/2)-->(4)I(11/2), (4)D(3/2)-->(4)I(13/2) and (4)D(3/2)-->(4)I(15/2) transitions, respectively and they show two photon character. The effect of BaCO(3), BaF(2) and BaCl(2) glass modifiers on the UC efficiency has been studied and Judd-Ofelt intensity parameters have been calculated and compared. The BaCl(2) modified glass showed maximum UC intensity among the three modifiers and this enhancement in UC intensity has been related to the reduction in average phonon frequency of the glass sample. Heat treatments of the BaF(2) and BaCl(2) modified samples also show enhancement in UC intensity while the BaCO(3) modified sample has no such effect. Lifetime of the (4)D(3/2) level has been measured to understand the mechanism responsible for UC emission. Temperature dependent fluorescence studies have been done on the (4)F(3/2), (4)F(5/2) and (2)S(3/2) emitting levels and results show that Nd(3+) doped tellurite glass can be used as a temperature sensor. PMID:19747875

  14. a Study of Epitaxial Growth of Calcium Fluoride on Silicon

    NASA Astrophysics Data System (ADS)

    Howard, L. K.

    Available from UMI in association with The British Library. The alkaline earth fluorides are good insulators at room temperature and have received significant attention as epitaxial dielectrics on semiconductors, their crystal structure and lattice parameters resembling those of common semiconductors. Such dielectrics enable passivation of semiconductors lacking stable oxides, isolation of devices on one substrate, and fabrication of 3-dimensional epitaxial heterostructures. The CaF_2/Si system was the structure investigated since the room temperature lattice mismatch is only 0.6%. A vacuum system was therefore developed for the deposition of CaF_2 onto silicon, and an RBS system, incorporating detector cooling, developed to establish the dependence of epitaxy on substrate temperature using channeling of 340 keV protons (giving an enhanced depth resolution and improved sensitivity to light elements compared to 2 MeV He^{+ } analysis). Epitaxial growth was obtained on n-type Si(111) and Si(100) substrates at 400-750 ^circC and 575-675^ circC respectively. A reaction between the CaF_2 and silicon occurred at higher temperatures producing non-uniform films. The epitaxy was also dependent on film thickness, the optimum de-channelled fractions obtained in the film of 8.25% and 15.2% for Si(111) and Si(100) substrates respectively were unobtainable for films under 1200 A. The insulator surface morphology was examined using Scanning Electron Microscopy. Epitaxial films on Si(111) were generally smooth, while preferential growth along <110> directions was observed for epitaxial insulators on Si(100), possibly due to slip along the (111) fluorite cleavage planes resulting from differences in the thermal expansion coefficients of CaF_2 and silicon and an increase in lattice mismatch with substrate temperature, although no cracking of the insulator was observed. The insulation and electrical properties of the films were investigated. Film resistivities upto 5E8 Omegacm and breakdown voltages of approximately 1E5 V/cm were obtained from I-V characteristics. The C-V characteristics of several films exhibited large flat -band voltage shifts and significant hysteresis consistent with poor insulator-semiconductor interfaces and contaminated insulators, possibly caused by a comparatively poor deposition vacuum (1E-7 torr rather than 1E-10 torr or better for MBE-grown films), insufficient control over deposition rate, and/or inadequate substrate preparation. Thus good epitaxy of CaF_2 was readily obtainable on Si(111) substrates, but proved more difficult on Si(100). The CaF_2 insulation properties were poor, however, suggesting modifications to the deposition technique and use of higher quality (better than 99%) source material may be necessary to produce satisfactory insulators.

  15. Evolution of the CaF?:Tm (TLD-300) glow curve as an indicator of beam quality for low-energy photon beams.

    PubMed

    Muoz, I D; Avila, O; Gamboa-deBuen, I; Brandan, M E

    2015-03-21

    We study the high- to low- temperature signal ratio (HLTR) of the CaF2:Tm glow curve as a function of beam quality for low-energy photon beams with effective energy between 15.2 and 33.6?keV, generated with W, Mo and Rh anodes. CaF2:Tm dosemeters (TLD-300) were exposed to x-rays and (60)Co gamma-rays. Glow curves were deconvoluted into 7 peaks, using computerized glow curve deconvolution and HLTR was evaluated. Air kerma and dose in water were between 2.1-15.0?mGy and 49.8-373.8?mGy, respectively. All peaks in the glow curve showed a linear response with respect to air kerma and dose in water. HLTR values decreased monotonically between 1.029? ?0.010 (at 15.2?keV) and 0.821? ?0.011 (33.6?keV), and no effects due to the use of different anode/filter combinations were observed. The results indicate a relatively high value of HLTR (about 1 for 17?keV effective energy, or 3?keV??m(-1) track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique. PMID:25683355

  16. Measuring 19F(?,n) with VANDLE for Nuclear Safeguards

    NASA Astrophysics Data System (ADS)

    Peters, William; Clement, R. C. C.; Smith, M. S.; Pain, S. D.; Thompson, S.; Cizewski, J. A.; Reingold, C.; Manning, B.; Burcher, S.; Bardayan, D. W.; Tan, W.-P.; Stech, E.; Smith, M. K.; Smith, K.; Avetisyan, R.; Long, A.; Battaglia, A.; Marley, S.; Gyurjinyan, A.; Ilyushkin, S.; O'Malley, P. D.; Madurga, M.; Paulauskas, S. V.; Taylor, S.; Febbraro, M.

    2014-09-01

    UF6 is used in many parts of the Uranium Fuel Cycle, and various techniques are used by nonproliferation agencies to monitor and account for the material. One of the most promising non-destructive assay (NDA) methods consists of measuring gross neutron rates induced by uranium-decay alpha particles reacting with the fluorine and emitting a neutron. This method, however, currently lacks reliable nuclear data on the 19F(?,n) reaction cross section to determine an accurate neutron yield rate for a given sample of UF6. We have used the Versatile Array of Neutron Detectors at Low Energy (VANDLE) to measure the cross section and coincident neutron spectrum over an energy range pertinent to NDA in a two part experiment: First at Notre Dame with a LaF3 target and a pulsed alpha-particle beam, and second at ORNL with a windowless He-gas target and a 19F beam. The motivation for this measurement and preliminary results will be presented. UF6 is used in many parts of the Uranium Fuel Cycle, and various techniques are used by nonproliferation agencies to monitor and account for the material. One of the most promising non-destructive assay (NDA) methods consists of measuring gross neutron rates induced by uranium-decay alpha particles reacting with the fluorine and emitting a neutron. This method, however, currently lacks reliable nuclear data on the 19F(?,n) reaction cross section to determine an accurate neutron yield rate for a given sample of UF6. We have used the Versatile Array of Neutron Detectors at Low Energy (VANDLE) to measure the cross section and coincident neutron spectrum over an energy range pertinent to NDA in a two part experiment: First at Notre Dame with a LaF3 target and a pulsed alpha-particle beam, and second at ORNL with a windowless He-gas target and a 19F beam. The motivation for this measurement and preliminary results will be presented. This work is funded in part by NSF Grant 1068192, DOE Office of Science, and the NNSA Office of Defense Nuclear Nonproliferation R&D.

  17. Light-emitting nanocomposites and novel amorphous polymers for optical applications

    NASA Astrophysics Data System (ADS)

    Gipson, Kyle Garrod

    Polymeric optical materials generally are comprised of amorphous polymers that are transparent in at visible wavelengths but exhibit strong absorption bands in the near-infrared making them less useful for many optical applications. Attenuation, which is the absorption per unit length, largely results from the high vibrational energy associated with carbon-hydrogen bonds contained in the polymer backbone. Attenuation can be mitigated by optical amplification utilizing light emitting additives. Investigated in this dissertation are synthesis techniques for the fabrication of light-emitting polymer nanocomposites and their resultant thermal and rheological characteristics for potential use as polymer optical fibers or films. Inorganic nanocrystals doped with optically active rare-earth ions (Tb 3+:LaF3) treated with organic ligands were synthesized in water and methanol in order to produce polymethyl methacrylate (PMMA) light-emitting nanocomposites. Two different aromatic ligands (acetylsalicylic acid, ASA and 2-picolinic acid, PA) were employed to functionalize the surface of Tb 3+:LaF3 nanocrystals. We have used infrared spectroscopy, thermal analysis, elemental analysis, dynamic light scattering, rheological measurements and optical spectroscopy to investigate the nanoparticle structure and composition response of ligand-capped nanocrystals under various synthesis parameters. A theoretical interpretation of particle-to-particle interactions also was conducted which supported our study of the potential of agglomeration within the nanoparticle suspensions. Novel amorphous polymers (e.g. perfluorocyclobutyl aryl ethers, PFCB), which do not exhibit strong C-H vibrations, have been reported to possess excellent optical properties. Little is known of the intrinsic properties of PFCBs (e.g. biphenylvinyl ether, BPVE and hexafluoroisopropylidene vinyl ether, 6F) as well as the behavior of the polymer melt during extrusion. We preformed empirical and experimental thermal and rheological evaluations of BPVE, 6F and polymer nanocomposites of varying loading levels. These studies provide greater understanding of the melt performance of BPVE, 6F and for optically active nanoparticles within PMMA. The data and the use of a fiber melt extrusion modeling package allowed for the construction of viable initial melt fiber extrusion parameters. Many researchers have focused on the development of polymer light-emitting nanocomposites and novel amorphous polymers for optical applications. I, however, have focused particularly on developing a fundamental understanding of the nanoparticle synthesis. My work concentrates on the surface chemistry of the nanoparticle with an emphasis on the interaction between the surface attached ligand and the polymer matrix. This research will aide in the development of a more optimized and compliant polymeric nanocomposites for optical applications.

  18. Determination of the irradiation field at the research reactor TRIGA Mainz for BNCT.

    PubMed

    Nagels, S; Hampel, G; Kratz, J V; Aguilar, A L; Minouchehr, S; Otto, G; Schmidberger, H; Schtz, C; Vogtlnder, L; Wortmann, B

    2009-07-01

    For the application of the BNCT for the excorporal treatment of organs at the TRIGA Mainz, the basic characteristics of the radiation field in the thermal column as beam geometry, neutron and gamma ray energies, angular distributions, neutron flux, as well as absorbed gamma and neutron doses must be determined in a reproducible way. To determine the mixed irradiation field thermoluminescence detectors (TLD) made of CaF(2):Tm with a newly developed energy-compensation filter system and LiF:Mg,Ti materials with different (6)Li concentrations and different thicknesses as well as thin gold foils were used. PMID:19380234

  19. Atomic force microscope studies of fullerene films - Highly stable C60 fcc (311) free surfaces

    NASA Technical Reports Server (NTRS)

    Snyder, Eric J.; Tong, William M.; Williams, R. S.; Anz, Samir J.; Anderson, Mark S.

    1991-01-01

    Atomic force microscopy and X-ray diffractometry were used to study 1500 A-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 (111) substrte. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.

  20. Ionic liquid synthesis of luminescent nano-cubes and their microstructure characterization

    NASA Astrophysics Data System (ADS)

    Ma, Qianmin; Ping, Lulu; Zhang, Helen Meihua; Yang, Jinglian; Wang, Qianming

    2015-07-01

    Regular CaF2:Eu3+ nano-cubes undergo ionic liquid (diallyldimethylammonium tetrafluoroborate, abbreviated as DTB)-mediated synthesis reactions in the presence of Eu(NO3)3?6H2O. The formation of uniform and mono-dispersed particles relies primarily on a one-pot hydrothermal method. The correlations between reaction temperature, doping concentration and crystalline structures have been clarified. In addition, the photoluminescence features and their influencing factors were extensively studied. In the case of Eu3+ containing phosphors, the application of new structure directing reagents will be convenient for the design of functional nanomaterials.

  1. Ultra-trace analysis of 41Ca in urine by accelerator mass spectrometry: An inter-laboratory comparison

    NASA Astrophysics Data System (ADS)

    Jackson, George S.; Hillegonds, Darren J.; Muzikar, Paul; Goehring, Brent

    2013-10-01

    A 41Ca interlaboratory comparison between Lawrence Livermore National Laboratory (LLNL) and the Purdue Rare Isotope Laboratory (PRIME Lab) has been completed. Analysis of the ratios assayed by accelerator mass spectrometry (AMS) shows that there is no statistically significant difference in the ratios. Further, Bayesian analysis shows that the uncertainties reported by both facilities are correct with the possibility of a slight under-estimation by one laboratory. Finally, the chemistry procedures used by the two facilities to produce CaF2 for the cesium sputter ion source are robust and do not yield any significant differences in the final result.

  2. Ultra-trace analysis of 41Ca in urine by accelerator mass spectrometry: an inter-laboratory comparison

    PubMed Central

    Jackson, George S.; Hillegonds, Darren J.; Muzikar, Paul; Goehring, Brent

    2013-01-01

    A 41Ca interlaboratory comparison between Lawrence Livermore National Laboratory (LLNL) and the Purdue Rare Isotope Laboratory (PRIME Lab) has been completed. Analysis of the ratios assayed by accelerator mass spectrometry (AMS) shows that there is no statistically significant difference in the ratios. Further, Bayesian analysis shows that the uncertainties reported by both facilities are correct with the possibility of a slight under-estimation by one laboratory. Finally, the chemistry procedures used by the two facilities to produce CaF2 for the cesium sputter ion source are robust and don't yield any significant differences in the final result. PMID:24179312

  3. Generation of Kerr combs centered at 4.5 ?m in crystalline microresonators pumped with quantum-cascade lasers.

    PubMed

    Savchenkov, Anatoliy A; Ilchenko, Vladimir S; Di Teodoro, Fabio; Belden, Paul M; Lotshaw, William T; Matsko, Andrey B; Maleki, Lute

    2015-08-01

    We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 ?m, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8). PMID:26258334

  4. Furnaces: Improving low cement castables by non-wetting additives

    NASA Astrophysics Data System (ADS)

    Afshar, Saied; Allaire, Claude

    2001-08-01

    Aluminosilicate castables, which are widely used in aluminum transformation furnaces, are susceptible to chemical reactions between molten aluminum and the furnace refractory lining. To prevent those reactions, commercial additives such as BaSO4, CaF2, and AlF3 are generally added in castables. This article presents and analyzes the effect of various amounts of the above additives as well as the influence of pre-firing temperatures on the corrosion behavior of an aluminosilicate low cement castable matrix in contact with liquid Al-5%Mg alloy.

  5. Technology for Solar Array Production on the Moon

    NASA Technical Reports Server (NTRS)

    Landis, Geoffrey A.

    2002-01-01

    Silicon, aluminum, and glass are the primary raw materials that will be required for production of solar arrays on the moon. A process sequence is proposed for producing these materials from lunar regolith is proposed, consisting of separating the required materials from lunar rock with fluorine. Fluorosilane produced by this process is reduced to silicon; the fluorine salts are reduced to metals by reaction with metallic potassium. Fluorine is recovered from residual MgF and CaF2 by reaction with K2O. Aluminum, calcium oxide, and magnesium oxide are recovered to manufacture structural materials and glass.

  6. Laser-Induced Damage of Calcium Fluoride

    SciTech Connect

    Espana, A.; Joly, A.G.; Hess, W.P.; Dickinson, J.T.

    2004-01-01

    As advances continue to be made in laser technology there is an increasing demand for materials that have high thresholds for laser-induced damage. Laser damage occurs when light is absorbed, creating defects in the crystal lattice. These defects can lead to the emission of atoms, ions and molecules from the sample. One specific field where laser damage is of serious concern is semiconductor lithography, which is beginning to use light at a wavelength of 157 nm. CaF2 is a candidate material for use in this new generation of lithography. In order to prevent unnecessary damage of optical components, it is necessary to understand the mechanisms for laser damage and the factors that serve to enhance it. In this research, we study various aspects of laser interactions with CaF2, including impurity absorbance and various forms of damage caused by incident laser light. Ultraviolet (UV) laser light at 266 nm with both femtosecond (fs) and nanosecond (ns) pulse widths is used to induce ion and neutral particle emission from cleaved samples of CaF2. The resulting mass spectra show significant differences suggesting that different mechanisms for desorption occur following excitation using the different pulse durations. Following irradiation by ns pulses at 266 nm, multiple single-photon absorption from defect states is likely responsible for ion emission whereas the fs case is driven by a multi-photon absorption process. This idea is further supported by the measurements made of the transmission and reflection of fs laser pulses at 266 nm, the results of which reveal a non-linear absorption process in effect at high incident intensities. In addition, the kinetic energy profiles of desorbed Ca and K contaminant atoms are different indicating that a different mechanism is responsible for their emission as well. Overall, these results show that purity plays a key role in the desorption of atoms from CaF2 when using ns pulses. On the other hand, once the irradiance reaches high levels, like that of the fs case, significant desorption is possible due to multi-photon absorption by the intrinsic material.

  7. Analysis of multiple pulse NMR in solids

    NASA Technical Reports Server (NTRS)

    Rhim, W.-K.; Elleman, D. D.; Vaughan, R. W.

    1973-01-01

    The general problems associated with the removal of the effects of dipolar broadening from solid-state NMR spectra are analyzed. The effects of finite pulse width and H sub 1 inhomogeneity are shown to have limited the resolution of previous pulse cycles, and a new eight-pulse cycle designed to minimize these problems is discussed. Spectra for F-19 in CaF2 taken with this cycle are presented which show residual linewidth near 10 Hz. The feasibility of measuring proton chemical shift tensors is discussed.

  8. a Theory of the Electronic Properties of Calcium FLUORIDE(111) and SILICON(111) Surfaces and the Calcium FLUORIDE/SILICON(111) Interface.

    NASA Astrophysics Data System (ADS)

    Engle, William Paul

    1992-05-01

    In this work we have used an empirical tight binding --Green's function (ETB-GF) method to investigate the surface and interface properties of crystalline solids. Our ETB -GF method allows the study of a truly semi-infinite sample and calculation of the positions of the localized states, their strengths, and how they decay into the bulk. This ETB-GF method can also be used to calculate densities of the bulk states at each layer along with the individual contributions of the various orbitals and how they are modified by the presence of the surface. We have used this technique to calculate the bulk and surface properties of silicon (111) and calcium fluoride (CaF_2 ) (111) as well as the interface properties of these two materials. For silicon, we have extended the existing empirical tight binding Hamiltonian of Chadi and Cohen (CC) by incorporating two additional second nearest neighbor (2nn) terms. This resulted in a much better agreement in the conduction band with the empirical pseudopotential method (EPM) calculation of Chelikowsky and Cohen including more accurate band gaps at Gamma, X, and L, with a slightly less accurate valence band structure. Our calculation of the As-passivated Si (111) system shows that it produces an unoccupied surface state in the band gap and two resonance states inside the valence band in close agreement with those found in previous experimental studies. Furthermore, this calculation predicts the existence of another localized state in the conduction band which has so far remained experimentally undetected. We then proceeded to determine the material parameters for CaF_2 and calculated the local density of states (LDOS) bulk CaF_2 and the ideal, unrelaxed, unreconstructed surface layer. The results show surface states at both the fluorine and calcium layers due to cleaving of the bonds at the surface. Finally we studied the interface properties of CaF_2/Si (111) and calculated the LDOS at each side of the interface. The results show an interface state in the gap in agreement with both theoretical and experimental results. The results are also in agreement with previous Ca-Si interface bond length calculations and small F-Si bonding at the interface.

  9. Parameterization of interatomic potential by genetic algorithms: A case study

    NASA Astrophysics Data System (ADS)

    Ghosh, Partha S.; Ranawat, Y. S.; Arya, A.; Dey, G. K.

    2015-06-01

    A framework for Genetic Algorithm based methodology is developed to systematically obtain and optimize parameters for interatomic force field functions for MD simulations by fitting to a reference data base. This methodology is applied to the fitting of ThO2 (CaF2 prototype) - a representative of ceramic based potential fuel for nuclear applications. The resulting GA optimized parameterization of ThO2 is able to capture basic structural, mechanical, thermo-physical properties and also describes defect structures within the permissible range.

  10. Initial stage of laser ablation of LiCaAlF6 single crystal under F2 laser irradiation

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Y.; Narazaki, A.; Sato, T.; Kurosaki, R.; Niino, H.; Sato, H.; Fukuda, T.

    Initial stage of F2 laser ablation of LiCaAlF6 single crystal was investigated for clarifying the possibility of applying this wide bandgap fluoride crystal to vacuum ultraviolet (VUV) optical components. The ablation threshold, determined by the appearance of line emission from ablated species, was approximately 2 Jcm-2pulse-1, similar to that of VUV grade CaF2 single crystal. The laser-induced damage on the front surface of LiCaAlF6 was faint, though adhesion of aggregated particulates of several microns was observed.

  11. NMR spin-lattice relaxation time T(1) of thin films obtained by magnetic resonance force microscopy.

    PubMed

    Saun, Seung-Bo; Won, Soonho; Kwon, Sungmin; Lee, Soonchil

    2015-05-01

    We obtained the NMR spectrum and the spin-lattice relaxation time (T1) for thin film samples by magnetic resonance force microscopy (MRFM). The samples were CaF2 thin films which were 50 nm and 150 nm thick. T1 was measured at 18 K using a cyclic adiabatic inversion method at a fixed frequency. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental environment. PMID:25828244

  12. Detection of thin film NMR spectrum by Magnetic Resonance Force Microscopy

    NASA Astrophysics Data System (ADS)

    Saun, Seung-Bo; Kwon, Sungmin; Lee, Soonchil; Won, Soonho

    2014-03-01

    NMR is widely used in many fields due to its powerful advantages such as nondestructive, chemically selective detection, and local probing. However, because of its low sensitivity, it is difficult to investigate thin film samples by conventional NMR. MRFM is the combined technic of NMR and Scanning Probe Microscopy (SPM), and it enabled exceptional sensitivity increasement of NMR detection. We succeeded in detecting general thin film NMR spectrum for the first time by modifying the MRFM. CaF2 34nm thin film NMR was detected and we observed 20 Gauss spectrum in proximity to bulk spectrum which is about 10 Gauss.

  13. NMR spin-lattice relaxation time T1 of thin films obtained by magnetic resonance force microscopy

    NASA Astrophysics Data System (ADS)

    Saun, Seung-Bo; Won, Soonho; Kwon, Sungmin; Lee, Soonchil

    2015-05-01

    We obtained the NMR spectrum and the spin-lattice relaxation time (T1) for thin film samples by magnetic resonance force microscopy (MRFM). The samples were CaF2 thin films which were 50 nm and 150 nm thick. T1 was measured at 18 K using a cyclic adiabatic inversion method at a fixed frequency. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental environment.

  14. Potential energy - induced nanostructuring of insulator surfaces by impact of slow, very highly charged ions

    NASA Astrophysics Data System (ADS)

    Meissl, W.; Ginzel, R.; Heller, R.; El-Said, A. S.; Kowarik, G.; Vasko, C.; Gsselsberger, C.; Ritter, R.; Solleder, B.; Simon, M.; Facsko, S.; Crespo Lpez-Urrutia, J. R.; Lemell, C.; Papalo, R. M.; Mller, W.; Ullrich, J.; Burgdrfer, J.; Aumayr, F.

    2009-11-01

    We have recently shown that the impact of individual slow highly charged ions is able to induce permanent nano-sized hillocks on the surface of a CaF2 single crystal. The experimentally observed threshold of the projectile ion potential energy necessary for hillock formation could be linked to a solid-liquid phase transition (nano-melting). In this contribution we report on similar nano-sized surface modifications as a result of the potential energy of impacting highly charged ions for other surfaces.

  15. Modelling surface restructuring by slow highly charged ions

    NASA Astrophysics Data System (ADS)

    Wachter, G.; T?ksi, K.; Betz, G.; Lemell, C.; Burgdrfer, J.

    2013-12-01

    We theoretically investigate surface modifications on alkaline earth halides due to highly charged ion impact, focusing on recent experimental evidence for both etch pit and nano-hillock formation on CaF2 (A.S. El-Said et al., Phys. Rev. Lett. 109, (2012) 117602 [1]). We discuss mechanisms for converting the projectile potential and kinetic energies into thermal energy capable of changing the surface structure. A proof-of-principle classical molecular dynamics simulation suggests the existence of two thresholds which we associate with etch pit and nano-hillock formation in qualitative agreement with experiment.

  16. Phonon confinement effect in calcium fluoride nanoparticles

    NASA Astrophysics Data System (ADS)

    Ricci, Pier Carlo; Casu, Alberto; Giudici, Giovanni De; Scardi, Paolo; Anedda, Alberto

    2007-08-01

    Nanocrystalline CaF 2 were obtained by ball-milled synthetic fluorite powders. Raman spectra of nanocrystals with average sizes of 10-25 nm are reported and the correlation between the band shape of the only allowed Raman mode at 322 cm -1 and the crystals dimensions is discussed. While in such systems local temperature and pressure effects play a minor role, variations in the shape of the Raman band can be correctly reproduced by a model based on the phonon confinement that effectively takes into account the anisotropy of the phonon dispersion curve.

  17. Target-ion-source system for RNB facility at KEK Tanashi

    NASA Astrophysics Data System (ADS)

    Jeong, S. C.; Ishiyama, H.; Kawakami, H.; Miyatake, H.; Ishida, Y.; Tojyo, E.; Oyaizu, M.; Mizutani, S.; Yoshikawa, N.; Tanaka, M. H.; Kawashima, H.; Fuchi, Y.; Wada, M.; Katayama, I.; Nomura, T.

    2002-04-01

    For the radioactive nuclear beam facility at KEK Tanashi based on an isotope separator on-line (ISOL), two different types of ion sources are currently employed: a single stage 6.4 GHz ECR and a surface ionization-type ion sources. Several proton-rich radioactive nuclear beams were developed for astrophysical interests. LiF powder target in a water-cooled Cu container is used for the production of Ne isotopes and CaF 2 mixed with fine graphite powder for Na isotopes. The ion beams are bunched at the exit of the ion source in order to reduce the beam loss in post acceleration.

  18. Generation of ultrashort 90 J deep-ultraviolet pulses by dual broadband frequency doubling with ?-BaB2O4 crystals at 1 kHz

    NASA Astrophysics Data System (ADS)

    Zhou, Chun; Kanai, Teruto; Watanabe, Shuntaro

    2015-01-01

    Fourth-harmonic pulses of a 1 kHz chirped-pulse amplification (CPA) Ti:sapphire laser have been generated by a scheme of dual broadband frequency doubling with two ?-BaB2O4 (BBO) crystals. The pulse energy was 90 J with a bandwidth of 2.7 nm (full width at half maximum, FWHM) at a central wavelength of 220 nm. The pulse width was measured to be 45 fs by autocorrelation with the two-photon fluorescence of CaF2, which was much smaller than that (120 fs) obtained by conventional frequency conversion.

  19. In the search of new electrocaloric materials: Fast ion conductors

    NASA Astrophysics Data System (ADS)

    Cazorla, Claudio

    We analyse the effects of applying an electric field on the critical temperature at which superionicity appears in archetypal fast ion conductor CaF2, by means of molecular dynamics simulations. We find that the onset of superionicity can be reduced by about 100 K when relatively small electric fields of ?50 KV cm-1 are applied. Under large enough electric fields, however, ionic conductivity is depleted. The normal to superionic phase transition is characterised by a large increase of entropy, thereby sizeable electrocaloric effects can be realised in fast ion conductors that are promising for solid-state cooling applications.

  20. Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

    SciTech Connect

    David H Hurley; Marat Khafizov; Zilong Hua; Rory Kennedy; Heng Ban

    2012-05-01

    A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k=(e2/D)1/2. To generalize this approach, sensitivity analysis was conducted for materials having a range of thermal conductivities. Experimental validation was sought using two substrate materials, SiO2 and CaF2, both coated with thin titanium films. The measured conductivities compare favorably with literature values.

  1. Scintillation properties of SrF2 and SrF2-Ce3+ crystals

    NASA Astrophysics Data System (ADS)

    Shendrik, R. Yu.; Radzhabov, E. A.; Nepomnyashchikh, A. I.

    2013-07-01

    This Letter presents the results of measuring scintillation properties of pure SrF2 crystals and crystals activated by various concentrations of Ce3+ ions. The light yield of these materials is compared to that of the known scintillators NaI-Tl and CaF2-Eu2+. Strontium fluoride crystals activated with Ce3+ ions are found to be characterized by high light yield and to be promising materials for use in scintillation detectors employed for γ-ray well logging.

  2. Analysis of the electroluminescence features of silicon metal-insulator-semiconductor structures as a tool for diagnostics of the injection properties of a dielectric layer

    NASA Astrophysics Data System (ADS)

    Illarionov, Yu. Yu.; Vexler, M. I.; Isakov, D.; Fedorov, V. V.; Sing, Yew Kwang

    2013-10-01

    A technique for diagnostics of the injection properties of thin dielectric layers based on analysis of the data on silicon electroluminescence in a metal-insulator-semiconductor structure is proposed. The possibility of applying this technique to control the electron injection energy (in particular, when the barrier parameters are poorly known) is demonstrated by the example of samples with CaF2 and HfO2/SiO2. The results obtained are important for application of the insulators under study in microelectronic devices.

  3. Intergranular fracture of lithium fluoride-22 percent calcium fluoride hypereutectic salt at 800 K

    NASA Technical Reports Server (NTRS)

    Raj, Subramanium V.; Whittenberger, J. Daniel

    1990-01-01

    Substantial strain-hardening was noted during the initial stages of deformation in constant-velocity compression tests conducted on as-cast samples of the LiF-22 mol pct CaF2 hypereutectic salt at 800 K. The deformed specimens exhibited extensive grain-boundary cracking and cavitation, suggesting that such cracking, in conjunction with interfacial sliding, is important for cavity nucleation at grain boundaries and at the LiF-CaF2 interfaces. Cavity growth and interlinkage occur through the preferential failure of the weaker LiF phase.

  4. Liquidus Temperatures of Cryolite Melts With Low Cryolite Ratio

    NASA Astrophysics Data System (ADS)

    Apisarov, Alexei; Dedyukhin, Alexander; Nikolaeva, Elena; Tinghaev, Pavel; Tkacheva, Olga; Redkin, Alexander; Zaikov, Yurii

    2011-02-01

    The effect of calcium fluoride on liquidus temperatures of the cryolite melts with a low cryolite ratio (CR) was studied. The systems KF-NaF-AlF3 and KF-LiF-AlF3 with CRs of 1.3, 1.5, and 1.7 have been investigated. The liquidus curves of systems containing CaF2 are different and depend on the K/(K + Na) and K/(K + Li) ratios. In potassium cryolite with CRs of 1.3 and 1.5, the calcium fluoride solubility is low and increases with NaF (LiF) concentration.

  5. Thermal transformation of quaternary compounds in NaF-CaF 2-AlF 3 system

    NASA Astrophysics Data System (ADS)

    Zaitseva, Julia N.; Yakimov, Igor S.; Kirik, Sergei D.

    2009-08-01

    Details of quaternary compounds formation in the system NaF-CaF 2-AlF 3 are specified. To achieve this aim, the samples of phases NaCaAlF 6 and Na 2Ca 3Al 2F 14 have been obtained by high-temperature solid-phase synthesis. Their thermal behavior when heated up to 800 °C has been studied using the methods of high-temperature X-ray diffraction (XRD) and thermal analysis (TA). The system under consideration can be regarded as a quasibinary section CaF 2-NaAlF 4, where at T=745-750 °C invariant equilibrium is implemented with the phases CaF 2-NaCaAlF 6-Na 2Ca 3Al 2F 14-(liquid melt)-(NaAlF 4). The peculiarity of the equilibrium is NaAlF 4 metastability at normal pressure. Below the equilibrium temperature the quaternary phase Na 2Ca 3Al 2F 14 is stable and NaCaAlF 6 above this temperature. The phase NaCaAlF 6 fixed by rapid quenching from high temperatures and when heated up to 640 °C decomposes, yielding Na 2Ca 3Al 2F 14. Further heating in vacuum at temperature up to 740 °C results in decomposition of Na 2Ca 3Al 2F 14 into CaF 2 and Na 3AlF 6. The expected reverse transformation of Na 2Ca 3Al 2F 14 into NaCaAlF 6 has not been observed under experimental conditions. Transformations in bulk samples reveal direct and reverse transformation of quaternary phases. SynopsisThermal transformation of the quaternary compounds in system (NaF-CaF 2-AlF 3) was investigated using high-temperature X-ray diffraction (XRD) and thermal analysis (TA). In the system the invariant equilibrium is implemented with the phases CaF 2-NaCaAlF 6-Na 2Ca 3Al 2F 14-(liquid melt)-(NaAlF 4) at T=745-750 °C.

  6. Lead Tungstate and Silicon Photomultipliers for Transmission Z-spectroscopy in Cargo Inspection Systems

    NASA Astrophysics Data System (ADS)

    Langeveld, Willem G. J.; Janecek, Martin

    The bremsstrahlung X-ray spectrum in high-energy, high-intensity X-ray cargo inspection systems is attenuated and modified by cargo materials depending on the cargo atomic number (Z). Spectroscopy of transmitted x rays is thus useful to measure the approximate Z of the cargo. Due to the broad features of the energy spectrum, excellent energy resolution is not required. Such "Z-Spectroscopy" (Z-SPEC) is possible at low enough count rates. A statistical approach, Z-SCAN (Z-determination by Statistical Count-rate ANalysis), can also be used, complementing Z-SPEC at high count rates. Both approaches require fast X-ray detectors and fast digitizers. Z-SPEC, in particular, benefits from very fast scintillators, in order to avoid signal pile-up.Preferentially, Z-SPEC, Z-SCAN and cargo imaging are implemented in a single detector array to reduce system cost, weight, and complexity. To preserve good spatial resolution of the imaging subsystem, dense scintillators are required. Previously, we studied ZnO, BaF2 and PbWO4, as well as suitable photo-detectors, read-out electronics and digitizers. ZnO is not suitable because it self-absorbs its scintillation light. BaF2 emits in the UV, either requiring fast wavelength shifters or UV-sensitive solid state read-out devices, and it also has a long decay time component. PbWO4 is currently the most attractive choice because it does not have these problems, but it is significantly slower and has low light output. There is thus a need for alternative fast high-density scintillators that emit visible light. Alternatively, there is a need for a fast solid-state read-out device that is sensitive to UV light for use with BaF2, or other UV-emitting scintillators. Here, we present results of tests performed with PbWO4 crystals, reflector materials and silicon photomultipliers.

  7. Influence of modifier oxides on spectroscopic properties of Sm3+ doped lithium fluoroborate glass

    NASA Astrophysics Data System (ADS)

    Ratnakaram, Y. C.; Balakrishna, A.; Rajesh, D.; Seshadri, M.

    2012-11-01

    Sm3+ doped lithium fluoro-borate glasses with different modifier oxides (Li2B4O7-BaF2-NaF-MO where M = Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li2B4O7-BaF2-NaF-MgO+CaO, Li2B4O7-BaF2-NaF-CdO+PbO) were prepared by means of melt quenching method. These samples were characterized by XRD, FTIR, optical absorption and fluorescence techniques at room temperature. The XRD profiles of all the glasses confirm their amorphous nature and the FTIR spectra reveal the presence of BO3 and BO4 units along with the strong OH- groups in the glass matrices. The influence of modifier oxides on Judd-Ofelt (J-O) intensity parameters and intensity of the emission lines are reported. Judd-Ofelt theory is used to study the spectral properties and to calculate the radiative transition probabilities (AT), branching ratios (βR), integrated absorption cross sections (Σ) and radiative lifetimes (τR) for certain spectral transitions. From the emission spectral analysis, emission cross-sections (σP) are calculated for the four emission transitions, 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 of Sm3+ ion in different lithium fluoro-borate glasses. Among the four transitions, it is observed that the transition 4G5/2 → 6H7/2 has higher emission cross-section (σP) in all the glass matrices, except in Mg, Cd and Mg-Ca glass matrices. The non-exponential nature of the luminescence decay curves of 4G5/2 level of Sm3+ doped glass matrices are also reported.

  8. Investigation into nanostructured lanthanum halides and CeBr3 for nuclear radiation detection

    NASA Astrophysics Data System (ADS)

    Guss, Paul; Guise, Ronald; Mukhopadhyay, Sanjoy; Yuan, Ding

    2011-09-01

    Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and cerium bromide (CeBr3) without requiring the growth of large crystals. Nanostructured detectors may allow us to engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have been seen in photoluminescence from silicon nanocrystals in a densely packed ensemble. We have fabricated nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr3. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.

  9. Investigation into Nanostructured Lanthanum Halides and CeBr3 for Nuclear Radiation Detection

    SciTech Connect

    Guss, P. P., Guise, R., Mukhopadhyay, S., Yuan, D.

    2011-07-06

    Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and cerium bromide (CeBr3) without requiring the growth of large crystals [1]. Nanostructured detectors may allow us to engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have been seen in photoluminescence from silicon nanocrystals in a densely-packed ensemble [2]. We have fabricated nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr3. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.

  10. Laser deposition and structuring of laser active planar waveguides of Er:ZBLAN, Nd:YAG and Nd:GGG for integrated waveguide lasers

    NASA Astrophysics Data System (ADS)

    Gottmann, Jens; Moiseev, Leonid; Wortmann, Dirk; Vasilief, Ion; Starovoytova, Larisa; Ganser, Dimitri; Wagner, Ralph

    2007-02-01

    Laser radiation is used both for the deposition of the laser active thin films and for the micro structuring to define wave guiding structures for the fabrication of waveguide lasers. Thin films of Er:ZBLAN (a glass consisting of ZrF 4, BaF II, LaF 3, AlF 3, NaF, ErF 3) for green upconversion lasers (545 nm), Nd:YAG (Y 3Al 5O 12) and Nd:GGG (Gd 3Ga 5O 12) for infrared lasers (1064 nm) are produced. Manufacturing of the laser active waveguides by micro-structuring is done using fs laser ablation of the deposited films. The structural and optical properties of the films and the damping losses of the structured waveguides are determined in view of the design and the fabrication of compact and efficient diode pumped waveguide lasers. The resulting waveguides are polished, provided with resonator mirrors, pumped using diode lasers and characterized. Laser operation of a ridge waveguide structure grown by pulsed laser deposition and structured by fs laser ablation is demonstrated. A 1 ?m thick, 100 ?m wide and 3 mm long structured waveguide consisting of amorphous neodymium doped Gd 3Ga 5O 12 has shown laser activity at 1.068 ?m when pumped by a diode laser at 808 nm.

  11. Improving Tribological Properties of Multialkylated Cyclopentanes under Simulated Space Environment: Two Feasible Approaches.

    PubMed

    Fan, Xiaoqiang; Wang, Liping; Li, Wen; Wan, Shanhong

    2015-07-01

    Space mechanisms require multialkylated cyclopentanes (MACs) more lubricious, more reliable, more durable, and better adaptive to harsh space environments. In this study, two kinds of additives were added into MACs for improving the tribological properties under simulated space environments: (a) solid nanoparticles (tungsten disulfide (WS2), tungsten trioxide (WO3), lanthanum oxide (La2O3), and lanthanum trifluoride (LaF3)) for steel/steel contacts; (b) liquid additives like zinc dialkyldithiophosphate (ZDDP) and molybdenum dialkyldithiocarbamate (MoDTC) for steel/steel and steel/diamond-like carbon (DLC) contacts. The results show that, under harsh simulated space environments, addition of the solid nanoparticles into MACs allows the wear to be reduced by up to one order magnitude, while liquid additives simultaneously reduce friction and wear by 80% and 93%, respectively. Friction mechanisms were proposed according to surface/interface analysis techniques, such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The role of solid nanoparticles in reducing friction and wear mainly depends on their surface enhancement effect, and the liquid additives are attributed to the formation of tribochemical reaction film derived from ZDDP and MoDTC on the sliding surfaces. PMID:26067481

  12. Evidence of energy transfer in nanoparticle-porphyrins conjugates for radiation therapy enhancement

    NASA Astrophysics Data System (ADS)

    Kudinov, Konstantin; Cooper, Daniel; Tyagi, Pooja; Bekah, Devesh; Bhattacharyya, Dhrittiman; Hill, Colin; Ha, Jonathan Kin; Nadeau, Jay; Bradforth, Stephen

    2015-03-01

    We report progress towards combining radiation therapy (RT) and photodynamic therapy (PDT) using scintillating nanoparticle (NP)-photosensitizer conjugates. In this approach, scintillating NPs are excited by clinically relevant ionizing radiation sources and subsequently transfer energy to conjugated photosensitizers via FRET, acting as an energy mediator between ionizing radiation and photosensitizer molecules. The excited photosensitizers generate reactive oxygen species that can induce local damage and immune response. Advantages of the scheme include: 1) Compared with traditional radiation therapy, a possible decrease of the total radiation dose needed to eliminate the lesion; 2) Compared with traditional PDT, the ability to target deeper and more highly pigmented lesions; 3) The possibility of additional photosensitizing effects due to the scintillation of the nanoparticles. In this work, the photosensitizer molecule chlorin e6 was covalently bound to the surface of LaF3:Ce NPs. After conjugation, the photoluminescence intensity of NPs decreased, and fluorescence lifetime of conjugated chlorin e6 became sensitive to excitation wavelength, suggesting rapid FRET. In addition, scintillation spectra of nanoparticles were measured. Preliminary calculations suggest that the observed scintillation efficiencies are sufficient to enhance RT. In vitro cancer cell studies suggest conjugates are taken up by cells. Survival curves with radiation exposure suggest that the particles alone cause radiosensitization comparable to that seen with gold nanoparticles.

  13. NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations.

    PubMed

    Sadoc, Aymeric; Body, Monique; Legein, Christophe; Biswal, Mamata; Fayon, Franck; Rocquefelte, Xavier; Boucher, Florent

    2011-11-01

    (19)F isotropic chemical shifts for alkali, alkaline earth and rare earth of column 3 basic fluorides are measured and the corresponding isotropic chemical shieldings are calculated using the GIPAW method. When using the PBE exchange-correlation functional for the treatment of the cationic localized empty orbitals of Ca(2+), Sc(3+) (3d) and La(3+) (4f), a correction is needed to accurately calculate (19)F chemical shieldings. We show that the correlation between experimental isotropic chemical shifts and calculated isotropic chemical shieldings established for the studied compounds allows us to predict (19)F NMR spectra of crystalline compounds with a relatively good accuracy. In addition, we experimentally determine the quadrupolar parameters of (25)Mg in MgF(2) and calculate the electric field gradients of (25)Mg in MgF(2) and (139)La in LaF(3) using both PAW and LAPW methods. The orientation of the EFG components in the crystallographic frame, provided by DFT calculations, is analysed in terms of electron densities. It is shown that consideration of the quadrupolar charge deformation is essential for the analysis of slightly distorted environments or highly irregular polyhedra. PMID:21947333

  14. Excimer mirror thin film laser damage competition

    NASA Astrophysics Data System (ADS)

    Stolz, Christopher J.; Blaschke, Holger; Jensen, Lars; Mdebach, Heinrich; Ristau, Detlev

    2011-12-01

    Excimer lasers are a critical technology for the $400 billion annual market of manufactured integrated circuits. Other uses of excimer lasers include medical applications such as laser eye surgery and micro-machining industrial applications. Ultraviolet laser mirrors are used for beam steering, therefore high reliability is desired for such commercial industrial applications. A laser damage competition of excimer mirror coatings creates the opportunity to survey private industry, governmental institutions, and university labs allowing a direct laser resistance comparison of samples tested under identical conditions. The major requirement of the submitted coatings was a minimum reflectance of 97% at 193 nm at normal incidence. The choice of coating materials, design, and deposition method were left to the participant. Damage testing was performed with a 193 nm excimer laser at a pulse length of 13 ns. A double blind test assured sample and submitter anonymity so only a summary of the deposition process, coating materials, layer count and spectral results are presented. In summary, a 70 difference was seen in the twelve submitted mirror samples, with the highest laser resistant sample being deposited by resistive heating and composed of three materials (LaF3, AlF3, & MgF2). Laser resistance was strongly affected by substrate cleaning, coating deposition method, and coating material selection whereas layer count had a minimal impact.

  15. Luminescence and scintillation properties of rare-earth-doped LuF3 scintillation crystals

    NASA Astrophysics Data System (ADS)

    Pejchal, Jan; Fukuda, Kentaro; Kurosawa, Shunsuke; Yokota, Yuui; Yoshikawa, Akira

    2015-03-01

    The Nd-doped and Er-doped LuF3 single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd-Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er3+ to Nd3+ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF3:Nd 8% standard. The leading Nd3+ 5d-4f emission was situated at 176 nm, while the Er3+ 5d-4f emission for Er-doped samples was observed at 163 nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1-3 mol%. No Er3+ 5d-4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er3+ to Nd3+ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one.

  16. Atomic origin of 3d(9)4?f(1) configuration in La(3+) solids.

    PubMed

    Yu, S-W; Carpenter, M H; Ponce, F; Friedrich, S; Lee, J-S

    2015-10-14

    We have studied the excited electronic structure of LaBr3(Ce) scintillator by soft x-ray spectroscopy such as x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES). The La 3d XAS and XES spectra of LaBr3(Ce) are compared with those of other La(3+)?solids (LaF3, La2O3, and La metal). From this comparison, it turns out that the La 3d XAS and XES spectra from all the La(3+) solids considered here appear at almost the same energy, even though the corresponding binding energies of the 3d core holes determined by XPS (x-ray photoelectron spectroscopy) are very different. As a result, we argue that the atomic nature of the 3d?4f configuration created by 3d?4f? ? 3d?4f x-ray absorption process in La(3+) solids is maintained via the localized 4?f?(1) state, which screens the 3d core holes differently from one La(3+) solid to another. PMID:26401640

  17. Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

    PubMed

    Masai, Hirokazu; Yanagida, Takayuki; Mizoguchi, Teruyasu; Ina, Toshiaki; Miyazaki, Takamichi; Kawaguti, Noriaki; Fukuda, Kentaro

    2015-01-01

    Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors. PMID:26292726

  18. Response of thermoluminescent dosimeters to photons simulated with the Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Moralles, M.; Guimarães, C. C.; Okuno, E.

    2005-06-01

    Personal monitors composed of thermoluminescent dosimeters (TLDs) made of natural fluorite (CaF 2:NaCl) and lithium fluoride (Harshaw TLD-100) were exposed to gamma and X rays of different qualities. The GEANT4 radiation transport Monte Carlo toolkit was employed to calculate the energy depth deposition profile in the TLDs. X-ray spectra of the ISO/4037-1 narrow-spectrum series, with peak voltage (kVp) values in the range 20-300 kV, were obtained by simulating a X-ray Philips MG-450 tube associated with the recommended filters. A realistic photon distribution of a 60Co radiotherapy source was taken from results of Monte Carlo simulations found in the literature. Comparison between simulated and experimental results revealed that the attenuation of emitted light in the readout process of the fluorite dosimeter must be taken into account, while this effect is negligible for lithium fluoride. Differences between results obtained by heating the dosimeter from the irradiated side and from the opposite side allowed the determination of the light attenuation coefficient for CaF 2:NaCl (mass proportion 60:40) as 2.2 mm -1.

  19. Theoretical and Practical Implications of the Effects of Temperature during Irradiation and during Pre - and Post-Irradiation Storage on the Response of Thermoluminescence Dosimeters.

    NASA Astrophysics Data System (ADS)

    de Planque, E. Gail

    Experiments have been conducted to determine the applicability of the Randall-Wilson theory for describing the behavior of CaF(,2):Mn thermoluminescence dosimeters (Harshaw TLD-400 chips). Results were obtained for four different conditions: irradiation followed by storage, irradiation after storage, irradiation both preceded and followed by storage, and continuous simultaneous irradiation and storage. The experiments were performed for storage intervals of approximately 1, 2, 3, 5, 6 and 7 days at five different storage temperatures: -25, +20, +65, +150 and +175(DEGREES)C. The results indicate fading that is described not by the Randall-Wilkins theory but rather as a function of the logarithm of the storage time. While the results suggest that the trapping efficiency is independent of temperature, they do demonstrate a small decrease in TL response with storage time prior to irradiation which is independent of temperature and time (> 17 hours) and hence probably not dosimetric in origin but perhaps optically related. Glow curve analyses support the concept of a band of traps rather than a single trap. The overall results are compared to other data available in the literature most of which is for room-temperature storage. These data, show remarkably good agreement when uniformly normalized. Although peripheral experiments revealed problems associated with self-irradiation as well as a decline in sensitivity with use, the stability experiment results verify the highly favorable stability properties of CaF(,2):Mn for common widespread application.

  20. The Solubility of Aluminum in Cryolite-Based Electrolyte-Containing KF

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Yu, Jiangyu; Gao, Bingliang; Liu, Yibai; Hu, Xianwei; Shi, Zhongning; Wang, Zhaowen

    2016-04-01

    The solubility of aluminum in NaF-AlF3-CaF2-KF-A12O3 electrolyte system at 1253 K (980 °C) has been measured by the analysis of quenched samples saturated with aluminum. The content of the dissolved metal in the quenched melt was determined by collecting the volume of hydrogen gas when a finely crushed sample is treated with HCl. Addition of 0 to 5 pct KF has no obvious effect on the solubility of aluminum in cryolite-based melts with molar ratio of NaF/AlF3 (cryolite ratio) ranging from 2.2 to 3.0. The solubility of aluminum increases from 0.015 to 0.026 wt pct with cryolite ratio increases from 2.2 to 4.0 in the NaF-AlF3-5 wt pct CaF2-3 wt pct A12O3 electrolyte at 1253 K (980 °C). Aluminum solubility was affected by both chemical replacement reaction of Al + 3NaF = AlF3 + 3Na and physical dissolution.