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1

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

NASA Astrophysics Data System (ADS)

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

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

1990-10-01

2

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

3

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

NASA Technical Reports Server (NTRS)

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

Deadmore, Daniel L.; Sliney, Harold E.

1987-01-01

4

Radiation Damage in CaF2 and BaF2 Investigated by the Channeling Technique  

Microsoft Academic Search

The radiation damage in single crystals of CaF2 and BaF2 due to room temperature bombardment with 2.0 MeV helium ions has been studied by the channeling technique. Backscattering spectra for the langle111rangle and langle110rangle axial directions were taken after different doses of random irradiation. A slight increase of the aligned yield with radiation dose has been found for both crystals

R. Hellborg; G. Skog

1974-01-01

5

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

SciTech Connect

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

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

2013-12-01

6

From composites to solid solutions: modeling of ionic conductivity in the CaF2-BaF2 system.  

PubMed

By using calcium fluorite and barium fluorite as test materials, we demonstrated that homovalent "dopants" can greatly affect ionic conductivity through locally changing the defect density. Whilst this doping is a state-of-the-art effect in the case of dopants that replace native ions of different charge (heterovalent dopants), it is a rather surprising effect at a first glance for substitutional dopants of the same charge; here, the phenomenon is not electrostatic, but elastic in nature. As a consequence of size mismatch, the smaller Ca atoms in the BaF(2) lattice favored the formation of interstitial sites that were located close to the Ca atoms, whilst doping larger Ba species into the CaF(2) phase favored vacancy formation. In terms of conductivity, and in agreement with the different mobilities, the first doping effect was favorable, whilst the other decreased conductivity. The concentration effects were formalized by a heterogeneous Frenkel reaction that was distinguished from the mean Frenkel reaction by additional (elastic) trapping that became more pronounced the lower the temperature. It was very revealing to relate this phenomenon to CaF(2)-BaF(2) multilayers and composites. In very general terms, these effects in the solid solutions were understood as being the atomistic limit of the interfacial charge-transfer that occurred at the hetero-interface of the crystallites or films, and reflected the transition from heterogeneous doping (higher-dimensional doping) to homogeneous doping (zero-dimensional doping). PMID:22488848

Zahn, Dirk; Heitjans, Paul; Maier, Joachim

2012-05-14

7

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

NASA Astrophysics Data System (ADS)

The interaction of water with freshly cleaved (111) surfaces of isostructural BaF 2 and CaF 2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF 2(111) two-dimensional water layers are formed after accumulation at step edges, CaF 2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF 2( CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

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

2011-12-01

8

Damage ingrowth and recovery in alpha-irradiated CaF2, SrF2, and BaF2  

Microsoft Academic Search

Single crystals of CaF2, SrF2, and BaF2 were irradiated at room temperature with alpha particles emitted from an effectively semi-infinite PuO2 source to a cumulative dose of 3 × 10 alpha particles\\/m. Although no change in the lattice parameter of CaF2 was observed, the crystals exhibited increasing coloration with dose. The lattice parameters of both SrF2 and BaF2 increased exponentially

W. J. Weber

1983-01-01

9

Infrared-laser-induced upconversion from Nd3+:LaF3 heteroepitaxial layers on CaF2(111) substrates by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

This paper reports a systematic analysis on the upconversion fluorescence from a Nd3+-doped LaF3 planar waveguide grown on (111) oriented CaF2 substrates by molecular beam epitaxy. A spectroscopic study of upconversion emission has been carried out at low temperature. Upon infrared excitation into the 2H9/2, 4F5/2, or 4F3/2 multiplets of Nd3+, strong uv upconversion emissions originating from 4D3/2 to 4IJ (J=92, 112, and 132) transitions by a three-photon process have been observed. In addition, other upconversion emissions in the green and orange regions due to two-photon processes were also obtained and attributed to the 4G7/2-->4I9/2, 2G7/2+4G5/2-->4I9/2, and 4G7/2-->4I11/2 transitions, respectively. In accordance with our experimental results, two kinds of energy-transfer processes are proposed as upconversion mechanisms responsible for the different emissions, and which are supported by a rate-equation analysis. The green and orange upconversions originate from an energy-transfer process involving two Nd3+ ions excited in the 4F3/2 state. For the three-photon upconversion, two successive energy cross-relaxation are suggested to populate the 4D3/2 level. The concentration dependence study has shown that the optimum concentration for a Nd3+ dopant is about 1 at. % for all the upconversion emissions. Owing to a guided configuration, upconversion emissions that are hardly detectable in a nonguided configuration at temperature higher than 100 K have now been recorded at room temperature.

Zhang, X.; Serrano, C.; Daran, E.; Lahoz, F.; Lacoste, G.; Muñoz-Yagüe, A.

2000-08-01

10

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

PubMed

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

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

2014-05-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

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)

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

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

1982-12-01

13

Optical and structural properties of LaF3 thin films.  

PubMed

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

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

2008-05-01

14

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

NASA Technical Reports Server (NTRS)

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

DellaCorte, Christopher; Stanford, Malcolm K.

2008-01-01

15

Hetero- and homoepitaxial Nd3+-doped LaF3 thin films grown by molecular beam epitaxy: A spectroscopic study  

NASA Astrophysics Data System (ADS)

Hetero- and homoepitaxial Nd3+-doped LaF3 thin films have been grown by molecular beam epitaxy. Two different orientations of CaF2 substrates, (111) and (110), have been used for the heteroepitaxial structures. High-resolution emission and excitation spectra as well as the decay time of the emission have been measured. The spectroscopic measurements demonstrate that one Nd3+ site is present in the LaF3 layers grown on CaF2(111) substrates but two slightly different Nd3+ centers are resolved in the films on CaF2(110) substrates. One Nd3+ site has been found in the homoepitaxial sample. Slight differences are observed between the centers found in the LaF3 layers and the one observed in the Nd3+-doped LaF3 bulk crystal. For the homoepitaxial layer, the linewidths are similar to those of the bulk crystals, whereas for the heteroepitaxial layers, a broadening is observed.

Lahoz, F.; Daran, E.; Zhang, X.; Muñoz-Yagüe, A.; Cases, R.; Alcalá, R.

1999-10-01

16

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

Microsoft Academic Search

A promising WC–Co–Cu–BaF2\\/CaF2 self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC–Co, Cu and BaF2\\/CaF2 eutectic. The as-prepared cermet coatings had better frictional behavior comparing with the WC–Co coating. Moreover, the often-occurred decarburization of WC in APS process was noticeably improved due to the binding of copper and BaF2\\/CaF2

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

2010-01-01

17

LaF3 insulators for MIS structures  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

18

Preparation and characterization of amorphous GaF 3 and GaF 3–BaF 2 thin films by ECR microwave plasma-enhanced CVD  

Microsoft Academic Search

Amorphous GaF3 and GaF3–BaF2 thin films were prepared by electron cyclotron resonance microwave plasma-enhanced chemical vapor deposition. Metal ?-diketonates and a NF3 gas were used as starting materials and a fluorinating reagent, respectively. Single crystals of CaF2(111) were employed as substrates. Almost contaminant-free and amorphous GaF3 and GaF3–BaF2 films were obtained on the substrates kept at 300 °C at the

Shuhei Takahashi; Masanori Shojiya; Yoji Kawamoto; Akio Konishi

2003-01-01

19

Radiation effects on BaF2 crystals  

Microsoft Academic Search

Nominally pure BaF2, BaF2: Sm (1 mol%), BaF2: Gd (0.05 mol%) and BaF2: Eu (0.02, 0.1 and 1 mol%) single crystals were investigated at room temperature with optical absorption (OA) and electron paramagnetic resonance (EPR) to understand the mechanism of radiation damage. Irradiation of the samples at room temperature with gamma-rays resulted in the electron capture by trivalent impurity ions,

G. M. Ferraz; M. Matsuoka; S. Watanabe; C. M. Sunta

1998-01-01

20

Radiation effects on BaF2 crystals  

Microsoft Academic Search

Nominally pure BaF2, BaF2: Sm (1 mol%), BaF2: Gd (0.05 mol%) and BaF2: Eu (0.02, 0.1 and 1 mol%) single crystals were investigated at room temperature with optical absorption (OA) and electron paramagnetic resonance (EPR) to understand the mechanism of radiation damage. Irradiation of the samples at room temperature with ?-rays resulted in the electron capture by trivalent impurity ions,

G. M. Ferraz; M. Matsuoka; S. Watanabe; C. M. Sunta

1998-01-01

21

BaF2 for microlithography applications  

NASA Astrophysics Data System (ADS)

Optimization is the ultimate goal of numerical modeling of crystal growth processes. We present the most important physical phenomena to establish a numerical process model for an industrial vertical gradient freeze (VGF) process of barium fluoride (BaF2). After reviewing the governing equations we describe an adaptive finite element approach for a phase change problem with internal radiation. We describe an interface to a commercial software package for industrial crystal growth processes to define a numerical process model in a highly automatized way. In this way we can apply an external optimization algorithm to our process model. We use a modified quasi-Newton method to propose an improvement of an industrial VGF growth process of BaF2.

Backofen, Rainer; Ribalta, Angel; Voigt, Axel; Wulff-Molder, Dirk

2007-06-01

22

Properties of AlF3 and LaF3 films at 193nm  

NASA Astrophysics Data System (ADS)

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

Xue, Chunrong; Shao, Jianda

2010-10-01

23

Defect formation and VUV luminescence in BaF2  

NASA Astrophysics Data System (ADS)

Nominally pure BaF2 single crystals were investigated at 77 K with optical absorption and electron paramagnetic resonance to understand the mechanism of radiation damage. We find that X-irradiation at 77 K of undoped BaF2 produces V-k - and F-centres having absorption bands at 3.4 and 2.3 eV respectively.

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

24

Defect formation and VUV luminescence in BaF2  

Microsoft Academic Search

Nominally pure BaF2 single crystals were investigated at 77 K with optical absorption and electron paramagnetic resonance to understand the mechanism of radiation damage. We find that X-irradiation at 77 K of undoped BaF2 produces V-k - and F-centres having absorption bands at 3.4 and 2.3 eV respectively.

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

2002-01-01

25

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

PubMed

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

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

2014-05-01

26

Radiation effects on BaF2 crystals  

NASA Astrophysics Data System (ADS)

Nominally pure BaF2, BaF2: Sm (1 mol%), BaF2: Gd (0.05 mol%) and BaF2: Eu (0.02, 0.1 and 1 mol%) single crystals were investigated at room temperature with optical absorption (OA) and electron paramagnetic resonance (EPR) to understand the mechanism of radiation damage. Irradiation of the samples at room temperature with ?-rays resulted in the electron capture by trivalent impurity ions, Sm3+ and Eu3+, forming the divalent impurity ions. However, no noticeable change in the valency of Gd ions could be observed. One of the nominally pure BaF2 crystals showed a band at 6.10 eV both before and after irradiation, which is due to Pb2+ ions. On irradiation two additional bands at 4.25 and 5.58 eV are observed. A correlation is found between these bands and the EPR spectrum. These OA bands and EPR spectrum are attributed to Pb3+ ions.

Ferraz, G. M.; Matsuoka, M.; Watanabe, S.; Sunta, C. M.

27

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

SciTech Connect

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.

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

2010-11-15

28

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

NASA Astrophysics Data System (ADS)

Single layers of MgF2 and LaF3 were deposited upon superpolished fused-silica and CaF2 substrates by ion-beam sputtering (IBS) as well as by boat and electron beam (e-beam) evaporation and were characterized by a variety of complementary analytical techniques. Besides undergoing photometric and ellipsometric inspection, the samples were investigated at 193 and 633 nm by an optical scatter measurement facility. The structural properties were assessed with atomic-force microscopy, x-ray diffraction, TEM techniques that involved conventional thinning methods for the layers. For measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed. The dispersion behavior of both deposition materials, which was determined on the basis of various independent photometric measurements and data reduction techniques, is in good agreement with that published in the literature and with the bulk properties of the materials. The refractive indices of the MgF2 coatings ranged from 1.415 to 1.440 for the wavelength of the ArF excimer laser (193 nm) and from 1.435 to 1.465 for the wavelength of the F2 excimer laser (157 nm). For single layers of LaF3 the refractive indices extended from 1.67 to 1.70 at 193 nm to approx1.80 at 157 nm. The IBS process achieves the best homogeneity and the lowest surface roughness values (close to 1 nmrms) of the processes compared in the joint experiment. In contrast to MgF2 boat and e-beam evaporated coatings, which exhibit tensile mechanical stress ranging from 300 to 400 MPa, IBS coatings exhibit high compressive stress of as much as 910 MPa. A similar tendency was found for coating stress in LaF3 single layers. Experimental results are discussed with respect to the microstructural and compositional properties as well as to the surface topography of the coatings.

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

2002-06-01

29

LaF3 nanoparticles surface modified with tryptophan and their optical properties  

NASA Astrophysics Data System (ADS)

LaF3 nanoparticles were synthesized by the double-jet precipitation technique in presence of tryptophan (Trp). The product was investigated by TEM, IR, absorption, and luminescence spectroscopies. Interaction of Trp with the nanoparticles results in formation of complexes between Trp and La3+ ions on the nanoparticle surface. Surface density of Trp was found as 0.7 molecule nm-2. It is shown that the modifier effects on LaF3 nanoparticle growth and stability of the surface modified LaF3 colloids. Luminescent properties of LaF3 nanoparticles modified with Trp (Trp@LaF3) are investigated. It is determined that Trp@LaF3 and Trp have the same profiles of excitation and photoluminescence spectra. Effects of pH, ionic strength, and Trp concentration on luminescence intensity are studied. At the same Trp amounts in the systems, Trp@LaF3 luminescence intensity is about 6 times less than Trp luminescence intensity. Such products can be used as luminescent labels.

Safronikhin, Anatoly; Ehrlich, Heinrich; Lisichkin, Georgy

2014-10-01

30

Spectroscopic properties of LaF3:Tm3+ nanoparticle-doped  

E-print Network

-prepared fibers using LaF3:Tm3+ (1 mol %) nanoparticles as the RE carrier during the fabrication process. The 10, preform collapsing and fiber drawing were performed conventionally. Importantly, no post-process heat treatment was applied on the fiber. 2. Results Through SEM analyses on preform and fiber, nanodomains

Paris-Sud XI, Université de

31

Epitaxial growth of Eu doped CaF2 thin film on CaF2 (111)  

NASA Astrophysics Data System (ADS)

Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low temperature solution growth method. The CaF2: Eu films when grown on Si (111) and glass substrate show random orientation having higher degree of surface roughness. As confirmed by the X-ray diffraction and photoluminescence results, Eu (II) ions substitute the Ca sites of CaF2 lattice. Excitation spectrum shows two broad peaks at 282 and 366 nm, which correspond to the allowed transitions of 4f7 to 4f65d1 (eg) and 4f65d1 (t2g) of Eu2+, respectively. Photoluminescence of Eu (II) doped CaF2 films exhibit intense and sharp peak in the blue region of the spectrum.

Ghosh, Manoranjan; Ningthoujam, R. S.; Patra, G. D.; Shinde, Seema; Sen, S.; Bhattacharya, S.; Gadkari, S. C.

2012-06-01

32

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

PubMed

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

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

2014-05-01

33

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

SciTech Connect

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

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

2008-03-15

34

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

PubMed

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

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

2012-05-20

35

Laser conditioning of LaF3/MgF2 dielectric coatings for excimer lasers  

NASA Astrophysics Data System (ADS)

LaF3/MgF2-dieletric thin film combinations can be applied in optics for wavelengths down to 150 nm. Several such HR systems for a wavelength of 248 nm were investigated. In these coatings, the influence of laser conditioning on damage threshold and absorptivity was found to be remarkable. XPS- and TEM-investigations showed that the conditioning effect is related to structural and stoichiometric changes in the multilayers, especially in the near-surface-sublayers.

Kaiser, Norbert; Anton, Bernhard; Jaenchen, H.; Mann, Klaus R.; Eva, Eric; Fischer, C.; Henking, Rainer; Ristau, Detlev; Weissbrodt, Peter; Mademann, Dirk; Raupach, L.; Hacker, Erich J.

1995-07-01

36

Crystal field of rare earth impurities in LaF3  

NASA Astrophysics Data System (ADS)

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

Novák, P.; Kuneš, J.; Knížek, K.

2014-11-01

37

Synthesis and characterization of surface modified LaF3:Ce nano particles  

Microsoft Academic Search

Oleic acid coated LaF3:Ce nano-crystals were synthesized using the co-precipitation technique. Nano-crystals were characterized for their crystal structure, particle size, organic coating and photoluminescence behavior using X-ray diffraction, SEM, FTIR and Photoluminescence spectroscopy. The crystallite size was calculated from the XRD pattern. The surface modified nano-crystal composite exhibits emissions at 306, 372 and 445 nm. A comparison of PL emission

T. K. Srinivasan; B. Venkatraman; M. Kamarudin; D. Ponraju; A. K. Arora

2011-01-01

38

F center in BaF2: Diffuse excited state  

Microsoft Academic Search

The optical properties of the F center in BaF2 are of importance because the F center is a product of radiation damage when the material is used as a luminescent radiation detector. Its optical excitation energy is 2.03 eV, experimentally. We have applied computational modeling to study this process. Our method is based on a quantum molecular cluster containing the

J. M. Vail; W. A. Coish; H. He; A. Yang

2002-01-01

39

Radiation damage in BaF2 crystals  

Microsoft Academic Search

The change in optical transmission of a number of BaF2 crystals has been measured as a function of exposure to 60Co radiation up to a dose of 4.7×106 rad. Although some crystals exhibited a small change in transmission, a greater change in scintillation light output was observed. Several 25-cm-long crystals which have been irradiated showed large changes in both transmission

C. L. Woody; J. A. Kierstead; P. W. Levy; S. Stoll

1992-01-01

40

Radiation damage in BaF2 crystals  

Microsoft Academic Search

Summary form only given. The effects of radiation damage and recovery have been studied in BaF2 crystals exposed to 60Co radiation. The change in optical transmission and scintillation light output has been measured as a function of dose up to 4.7×106 rad. Although some crystals exhibit a small change in transmission, a greater change in scintillation light output is observed.

C. L. Woody; J. A. Kierstead; P. W. Levy; S. Stoll

1991-01-01

41

Optical and luminescence characteristics of BaF2 and BaF2:Tm in vacuum UV and UV spectral regions  

NASA Astrophysics Data System (ADS)

The spectral characteristics of BaF2 and BaF2:Tm crystals and ceramics are compared. The vacuum UV (VUV) and UV absorption spectra and excitation spectra of core-valence and exciton luminescence are investigated. The main exciton and electron-hole processes responsible for the structure of recorded spectra are considered.

Rodnyi, P. A.; Khanin, V. M.; Voloshinovskii, A. S.; Striganyuk, G. B.; Garibin, E. A.; Gusev, P. E.; Krutov, M. A.; Demidenko, A. A.

2014-09-01

42

Magnetic-fluorescent nanohybrids of carbon nanotubes coated with Eu, Gd Co-doped LaF 3 as a multimodal imaging probe  

Microsoft Academic Search

Multifunctional magnetic-fluorescent nanohybrids were successfully fabricated by a facile layer-by-layer (LBL) self-assembly of in situ generated Eu, Gd co-doped LaF3 nanocrystals (LaF3:Eu:Gd) on the surface of multi-walled carbon nanotubes (MWNTs). Photoluminescence (PL) quenching occurred when LaF3:Eu:Gd nanoparticles were directly coated on the surface of MWNTs. By growth of a SiO2 shell spacer between MWNTs and LaF3:Eu:Gd nanocrystals, we circumvented the

Bingdi Chen; Hui Zhang; Ning Du; Bo Zhang; Yulian Wu; Donglu Shi; Deren Yang

43

Structural and Compositional Analysis of LaF3 Thin Films Suitable for Oxygen Sensor  

NASA Astrophysics Data System (ADS)

The lanthanum fluoride film has been prepared by thermal evaporation method. The XRD pattern shows the polycrystalline nature and hexagonal structure of the LaF3 film. The unit cell parameters are calculated and are found to be in good agreement with standard values. The grain size has been calculated using the Debye scherrers formula and is found to be 53 nm. The XPS spectra recorded in the binding energy range 500-850 eV shows three intense peaks corresponding to lanthanum (La3d5/2), fluorine (F1s1/2) and oxygen (O1s) at binding energies around 836, 684 and 530 eV respectively. The oxygen peak corresponding to the surface of the film is due to the adsorption of oxygen at LaF3 film surface. The inner layers of the film consist of multiple oxygen peaks due to the presence of peroxide (HO2-) and superoxide ions (O2-). This impurities leads to the formation of lanthanum oxyfluoride and F deficiencies, which are favorable for the oxygen sensing mechanisms. The optical spectrum shows the low porosity and high transparent nature of the film.

Selvasekarapandian, S.; Vijayakumar, M.; Fujihara, Shinobu; Koji, Shinnosuke

2007-01-01

44

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

PubMed

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

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

2011-08-01

45

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

NASA Astrophysics Data System (ADS)

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

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

2011-08-01

46

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

SciTech Connect

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

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

2011-12-31

47

Influence of thermal annealing and ultraviolet light irradiation on LaF3 thin films at 193 nm  

NASA Astrophysics Data System (ADS)

Lanthanum fluoride (LaF3) thin films were prepared by resistive heating evaporation and electron-beam gun evaporation under the same deposition rate, deposition substrate temperature, and vacuum pressure. The coated LaF3 films were then treated by heat annealing and UV light irradiation. The optical properties, microstructures, stress, and laser-induced damage threshold (LIDT) at a wavelength of 193 nm were investigated. The surface roughness, optical loss, stress, and LIDT of the films were improved after the annealing. The films had better properties when irradiated by UV light as compared with heat annealing.

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

2005-11-01

48

Influence of thermal annealing and ultraviolet light irradiation on LaF3 thin films at 193 nm.  

PubMed

Lanthanum fluoride (LaF3) thin films were prepared by resistive heating evaporation and electron-beam gun evaporation under the same deposition rate, deposition substrate temperature, and vacuum pressure. The coated LaF3 films were then treated by heat annealing and UV light irradiation. The optical properties, microstructures, stress, and laser-induced damage threshold (LIDT) at a wavelength of 193 nm were investigated. The surface roughness, optical loss, stress, and LIDT of the films were improved after the annealing. The films had better properties when irradiated by UV light as compared with heat annealing. PMID:16294967

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

2005-11-10

49

A solvent extraction route for CaF2 hollow spheres.  

PubMed

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

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

2010-11-21

50

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

NASA Astrophysics Data System (ADS)

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

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

1996-10-01

51

F center in BaF2: Diffuse excited state  

NASA Astrophysics Data System (ADS)

The optical properties of the F center in BaF2 are of importance because the F center is a product of radiation damage when the material is used as a luminescent radiation detector. Its optical excitation energy is 2.03 eV, experimentally. We have applied computational modeling to study this process. Our method is based on a quantum molecular cluster containing the defect, embedded in a shell-model crystal. When the excess electron of the F center is kept localized in the molecular cluster, an excitation energy of 3.33 eV is found. When the F-center electron is allowed to become much more diffuse, the ground state remains within the vacancy, but the excited state delocalizes, and the excitation energy drops to about 2.56 eV, but the model is inaccurate because quantum-mechanical features of distant ions are omitted. A polaronic representation of the single diffuse electron is then carefully incorporated with the embedded quantum cluster treatment of the system. The polaron in BaF2 is found to be beyond the intermediate-coupling regime. Feynman's path-integral results for Fröhlich's polaron model give an effective mass of 3.12, in units of band mass. The resultant estimate of F-center excitation energy is 2.04 eV. The successful combination of a quantum molecular cluster modeling element with bulk crystal modeling elements (band mass and polaron correction) warrants further study along these lines. Quantitative and physical limitations of the method and results are discussed.

Vail, J. M.; Coish, W. A.; He, H.; Yang, A.

2002-07-01

52

Defect diffusion in CaF2 for optical applications  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important lens material for deep-ultraviolet optics and a key material for 193 nm lithography. The exposure to high radiation densities requires extreme laser-stability of the material, which is to a large part ensured by a high purity level. However, for long exposure times the optical quality of CaF2 is affected by radiation-induced point defects, namely F- and H-centers. The migration and agglomeration of these point defects play an important role in understanding laser-damage processes on a microscopic level. We use ab-initio methods to investigate the stabilization of laser-induced point defects. As stabilization processes involve defect migration, we also focus on diffusion properties of defects. We present results for the diffusion barrier and details of the transition state of the migrating F-center, which shows good agreement with experimental results.

Stephan, Rix; Natura, Ute; Letz, Martin; Parthier, Lutz; Felser, Claudia

2010-03-01

53

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

PubMed

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

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

2014-06-01

54

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

55

Core-shell LaF3:Er,Yb nanocrystal doped sol-gel materials as waveguide amplifiers  

NASA Astrophysics Data System (ADS)

The oleic acid (OA)-modified LaF3:Er,Yb and LaF3:Er,Yb-LaF3 core-shell nanocrystals are synthesized. The lifetime values could be further improved by incorporating core-shell nanocrystals. A kind of sol-gel derived organic-inorganic hybrid material (SGHM) allows for 50 wt.% or even more of both the two nanocrystals in the matrix, and we give the explanation from scattering analysis. It’s precisely because we use the erbium nanocrystals rather than erbium organic complexes, and avoid the undesirable luminescence quenching by Er-Er clustering with a high Er3+ concentration. LaF3:Er,Yb-LaF3/SGHM transparent films and optical waveguides are also fabricated. The nanocomposite films show strong 1550 nm luminescence intensity under the excitation of 980 nm after heat treatment below 150 °C and the full-width-at-half-maximum is about 51 nm. The loss and optical gain of the waveguide are measured. A relative gain of about 3.5 dB is measured at 1550 nm in a 1.7 cm long waveguide.

Bo, S. H.; Hu, J.; Chen, Z.; Wang, Q.; Xu, G. M.; Liu, X. H.; Zhen, Z.

2009-11-01

56

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

SciTech Connect

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

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

2010-01-21

57

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

58

Monte Carlo analysis of neutron detection with a BaF2 scintillation detector  

Microsoft Academic Search

This work presents the results of investigations aimed at simulating the response of a barium fluoride (BaF2) detector to neutrons and photons. The simulations are performed with the MCNP-PoliMi code, a modification of MCNP-4C. The simulation results are compared to time-of-flight measurements performed with the nuclear materials identification system (NMIS). In particular, the neutron detection capabilities of the BaF2 scintillator

Sara A. Pozzi; John S. Neal; Richard B. Oberer; John T. Mihalczo

2004-01-01

59

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

PubMed Central

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

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

2013-01-01

60

Behavior Analysis of CaF2 in Magnesia Carbothermic Reduction Process in Vacuum  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

61

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

PubMed

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 Nd(3+) 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 Tm(3+) to Nd(3+) 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 Nd(3+) 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. PMID:25359551

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

2014-12-21

62

Preparation of CaF 2 based phosphors by solid state metathesis  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

63

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

SciTech Connect

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

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

2012-01-01

64

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

65

Molten salt synthesis of LaF 3 :Eu 3+ nanoplates with tunable size and their luminescence properties  

Microsoft Academic Search

A molten salt route to LaF3:Eu3+ nanoplate with tunable size was developed and the products were characterized by the X-ray diffraction (XRD), transmission\\u000a electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM) and high-resolution TEM (HR-TEM). It is found\\u000a that the nanoplates with different sizes (ca. 46, 20, and 12 nm) could be obtained when the molar ratio of the reagents NH4F

Yang Tian; Xiuling Jiao; Juan Zhang; Ning Sui; Dairong Chen; Guangyan Hong

2010-01-01

66

The luminescence of BaF2 nanoparticles upon high-energy excitation  

NASA Astrophysics Data System (ADS)

The dependence of X-ray excited luminescence intensity on BaF2 nanoparticle size was studied. A sharp decrease of self-trapped exciton luminescence intensity was observed when the nanoparticle size is less than 80 nm. The main mechanism of the luminescence quenching is caused by the escape of electrons from the nanoparticles. Escape of electrons from nanoparticles is confirmed by the considerable increase of luminescence intensity of the polystyrene scintillator with embedded BaF2 nanoparticles comparing with pure polystyrene scintillator.

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

2014-08-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

68

Optical characterization of materials desposited by different processes: the LaF3 in the UV-visible region  

NASA Astrophysics Data System (ADS)

The optical characterization of materials in thin film phase is a standard task in the field of coating technology. There are experimental circumstances where the accurate comparison between several deposition processes (for the same material) is important. In these cases, several sets of substrates are coated at the different deposition plants. The samples will be subsequently analyzed using, if the plants are at different locations, different spectrophometers and finally the results of all the optical characterizations will be compared. The aim of this work is to present the results of a global procedure for the optical characterization of LaF3 in the UV-visible region, deposited at three different plants. We have used R and T spectrophotometric data and we have assumed the following model for the optical characterization: n(?)=n0+n1/?2, k(?)=k0 exp(k1/(?). Our method characterizes all the samples from the same deposition process by a single set of parameters (instead of a set for each sample), using all the available measurements to determine them in a single numerical fitting, without a significant loss in the quality of the fittins. This procedure reduces the number of parameters and makes the comparison between different deposition processes more clear. By using similar results obtained for MgF2 the optical characterization of stacks (manufactured using MgF2 and LaF3) is also presented.

Bosch, Salvador; Leinfellner, Norbert; Quesnel, Etienne; Duparre, Angela; Ferre-Borrull, Josep; Guenster, Stefan; Ristau, Detlev

2000-10-01

69

1.5 µm photoluminescence of Er3 + in YF3, LuF3, and LaF3 thin films  

NASA Astrophysics Data System (ADS)

We have studied the photoluminescence at 1.5 ?m of the 4I13/2?4I15/2 transition of the Er3+ ion, incorporated as ErF3 into polycrystalline YF3, LuF3, and LaF3 films, deposited onto SiO2 or Si wafers. We conclude that LaF3 is an exceptionally suitable host for Er3+, since it permits high Er3+ concentrations, long lifetimes of the excited level, and a strong Stark splitting. This results in a spectral shape suitable for broadband optical amplifiers with a usable optical bandwidth exceeding 8000 GHz (???60 nm).

Buchal, Ch.; Siegrist, Th.; Jacobson, D. C.; Poate, J. M.

1996-01-01

70

Analysis of tracks induced by cluster ions in CaF2  

NASA Astrophysics Data System (ADS)

Recent experimental data on latent tracks induced in CaF2 by cluster ions are analyzed applying a thermal spike model. The track evolution can be described by the same equations in radiolysis sensitive CaF2 and in the radiolysis resistant Y3Fe5O12, using similar parameter values. The efficiency of the localized energy deposition g=0.18 for CaF2, which is equal within experimental error to that in Y3Fe5O12 at high ion velocities. This indicates that the damage cross section is not sensitive to the ion velocity in CaF2. The similarities observed in the track evolution in insulating crystals, polymers, semiconductors, and high-Tc superconductors are explained by the Gaussian spatial distribution of the excitation energy with close values of the distribution parameters.

Szenes, G.

2000-06-01

71

Laser induced nanoparticle formation in single crystal CaF2  

Microsoft Academic Search

Single crystal calcium fluoride (CaF2) is a material currently being used for vacuum ultra-violet optical components. However, all metal halides have a strong tendency to form point defects under energetic particle and optical irradiation which can degrade performance. Here we examine the consequences of exposing CaF2 to 157 nm excimer laser light. This exposure causes absorption in the visible region

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

2004-01-01

72

Radiation Damage in Epitaxial CaF2 Films on Si Substrates by Ar+ Ion Implantation  

NASA Astrophysics Data System (ADS)

Radiation damage in epitaxial CaF2 films on Si substrates produced by 150 keV Ar+ ion implantation has been investigated using Rutherford backscattering and channeling techniques. It has been found that CaF2 films are more stable than Si crystals for ion bombardment and are not amorphized at such a high dose as 6× 1016 cm-2. Recovery of the damage by subsequent thermal annealing has also been investigated.

Ishiwara, Hiroshi; Orihara, Kouzo; Asano, Tanemasa

1983-07-01

73

Nanocrystalline CaF 2 particles obtained by high-energy ball milling  

Microsoft Academic Search

Structural changes in mechanically treated CaF2 powders have been studied by X-ray diffraction, transmission electron microscopy, thermal analysis, 19F and 1H MAS Nuclear Magnetic Resonance and Electron Paramagnetic Resonance methods.Applying the same methods, the results could be compared with those of mechanochemically synthesized CaF2 samples, prepared for the first time in this study by high-energy ball milling. The applied methods

G.. Scholz; I. Doerfel; D. Heidemann; M. Feist; R. Stoesser

2006-01-01

74

Photodegradation of luminescence in organic-ligand-capped Eu3+:LaF3 nano-particles  

NASA Astrophysics Data System (ADS)

The luminescence from europium doped lanthanum trifluoride (Eu3+:LaF3) nano-crystals can be greatly enhanced by capping with ?-diketonate organic ligands. Here, we report on photo-stability measurements for the case of nano-crystals capped with thenoyltrifluroacetone (TTA) and compared with those capped with an inactive ligand, oleic acid. With exposure to UV pump light, we observed significant decrease in fluorescence and change in emission spectrum of the TTA-capped nano-particles whilst the fluorescence lifetime remained approximately constant. After a dose of order 70 kJ cm-2, the luminescence level was similar to that of oleic acid capped nano-crystals. We discuss possible mechanisms.

King, Gavin G. G.; Taylor, Luke R.; Clarke, David J.; Quilty, J. W.; Longdell, Jevon J.

2014-01-01

75

Significant Suppression of Spontaneous Emission in SiO2 Photonic Crystals Made with Tb3+-Doped LaF3 Nanoparticles  

E-print Network

made with LaF3:Tb3+ nanoparticles were fabricated. The spontaneous emission lifetime of the 5D4 f 7F4 of photoluminescent guests, such as fluorescent dyes and quantum dots. The emission band of fluorescent dyes is often observed for fluorescent dye molecules, are not observed. The bandwidth of a

Brolo, Alexandre G.

76

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

PubMed

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

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

2014-01-21

77

Pyramidal pits created by single highly charged ions in BaF2 single crystals  

Microsoft Academic Search

In various insulators, the impact of individual slow highly charged ions (eV-keV) creates surface nanostructures, whose size depends on the deposited potential energy. Here we report on the damage created on a cleaved BaF2 (111) surface by irradiation with 4.5×qkeV highly charged xenon ions from a room-temperature electron-beam ion trap. Up to charge states q=36 , no surface topographic changes

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

2010-01-01

78

Pyramidal pits created by single highly charged ions in BaF2 single crystals  

NASA Astrophysics Data System (ADS)

In various insulators, the impact of individual slow highly charged ions (eV-keV) creates surface nanostructures, whose size depends on the deposited potential energy. Here we report on the damage created on a cleaved BaF2 (111) surface by irradiation with 4.5×qkeV highly charged xenon ions from a room-temperature electron-beam ion trap. Up to charge states q=36 , no surface topographic changes on the BaF2 surface are observed by scanning force microscopy. The hidden stored damage, however, can be made visible using the technique of selective chemical etching. Each individual ion impact develops into a pyramidal etch pits, as can be concluded from a comparison of the areal density of observed etch pits with the applied ion fluence (typically 108ions/cm2 ). The dimensional analysis of the measured pits reveals the significance of the deposited potential energy in the creation of lattice distortions/defects in BaF2 .

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

2010-07-01

79

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

80

Effect of CaF2 addition on optical properties of barium phosphate glasses  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

81

Growth and optical properties of partially transparent Eu doped CaF2 ceramic  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

82

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

NASA Astrophysics Data System (ADS)

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

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

1999-03-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

84

Ultra-precision process of CaF2 single crystal  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

85

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

NASA Astrophysics Data System (ADS)

High quality window/plate shaped CaF2 single crystals have developed by vertical Bridgman method of with diameters of 50, 100, and 200 mm and 210 mm width, 200mm length. The CaF2 windows of 30mm diameter obtained from big crystals have evaluated the transmission spectra from 120 nm to 220nm by single beam VUV spectrometer. We could obtain bulk transmission spectra by subtracting surface reflection loss between tow kinds of thickness samples. The results show flat spectra without distinct absorption from 130nm to 220nm. In laser-damage tests with the fourth harmonic (4?) of a Nd:YAG laser below 1NW/cm2 at the CaF2 window, a stable output of 600mW was obtained. ArF laser irradiation of 50mJ/cm2 and 6X104 pulses was tried and the degradation in transmission from 130nm to 220nm not observed. These data show that the radiation hardness of our CaF2 crystals is promising for deep ultra-violet laser applications.

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

2005-02-01

86

Phase evolution of Ba2YCu3O6+x films during the BaF2 process  

NASA Astrophysics Data System (ADS)

High-temperature x-ray diffraction and transmission electron microscopy were used to study the phase evolution and reaction kinetics during the ex situ BaF2 conversion process to form Ba2YCu3O6+x (Y-213). For this study, precursor films with compositions corresponding to Y-213 were deposited on single crystal SrTiO3 substrates using an e-beam co-evaporation technique. Two different precursors, (BaF2+Y +Cu) and (BaF2+Y F3+Cu), were used, and the phase evolution in the resulting series of samples was compared. For the (BaF2+Y +Cu) films, at intermediate stages of the conversion process, the amorphous precursor partially crystallized into a mixture of a BaF2-like oxyfluoride phase (a\\approx a_{\\mathrm {BF}}\\approx 6.1~{\\AA } , where BF denotes BaF2) and CuO. At temperatures close to 700 °C, Y2Cu2O5 and a BaF2-related superstructure (a\\approx a_{\\mathrm {BF}}\\surd {3} , b\\approx a_{\\mathrm {BF}}\\surd {6/2} , c\\approx a_{\\mathrm {BF}}\\surd {2/2} ) were observed. For this series of films, the ex situ process involved several hydration/oxidation reactions which ultimately transformed the precursor into the Y-213 phase. The overall reaction scheme can be represented as: {\\mathrm {Ba}}({\\mathrm {O}}_{x}{\\mathrm {F}}_{y})+{\\mathrm {Y_2Cu_2O_5(s)}}+{\\mathrm {CuO(s)}}+ {\\mathrm {H_2O(g)}}\\allowbreak \\to {\\mathrm {Ba_2YCu_3O}}_{6+x} {\\mathrm {(s)+HF(g)}} , where Ba (OxFy) represents both the BaF2-like oxyfluoride and the BaF2-related superstructure phases. The growth of the Y-213 phase and the consumption of BaF2-like phases were approximately linear in time. The resulting Y-213 films were predominantly c-axis textured, along with smaller volume fractions of a-axis textured and randomly oriented regions. For the (BaF2+Y F3+Cu) films investigated, we observed a similar evolution of the Ba (OxFy) phase and the BaF2-related superstructure, along with crystallization of CuO; however, Y2Cu2O5(s) was not observed. The Y F3 component remained amorphous (from x-ray diffraction results) and reacted with Ba (OxFy), CuO and H2O to form Y-213 and Y2O3. The presence of unreacted Ba (OxFy), Y2O3 and CuO in the film after prolonged (>2 h) annealing at 735 °C indicates incomplete Y-213 conversion. We conclude that the (BaF2+Y F3+Cu) precursor was less suitable relative to (BaF2+Y +Cu) under the present processing conditions.

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

2004-09-01

87

Growth and spectroscopic characterization of Pb2+:CaF2 crystals  

NASA Astrophysics Data System (ADS)

CaF2 crystals doped with various concentrations of PbF2 (0.4, 0.5, 1 and 2 mol%) were grown in vacuum, in a shaped graphite furnace using the vertical Bridgman method. The optical absorption spectra reveal the four characteristic UV absorption bands (labeled A, B, C and D) of the Pb2+ ions. As the PbF2 concentration increases, the structure of the bands become clearly visible, that is characteristic for the ns 2 ions in various hosts. High intensity emission bands in the near UV spectral region have been observed. The dependence on the Pb2+ concentration of the optical absorption and emission of the Pb2+:CaF2 crystals were not reported before.

Nicoara, I.; Paraschiva, M.; Stef, M.; Stef, F.

2012-08-01

88

Mechanism of thermoluminescence in CaF2:Eu and CaSO4:Eu phosphors  

Microsoft Academic Search

CaF2:RE and CaSO4:RE are important phosphors. The phosphors corresponding to RE identical to Dy and Tm find applications in thermoluminescence dosimetry using ionizing radiations. Although these phosphors have been in use for several years, the mechanism of thermoluminescence in these phosphors is not well understood. The role of RE ions in emission has been clearly indicated. Two types of model

S. V. Upadeo; T. K. Gundurao; S. V. Moharil

1994-01-01

89

Self-lubrication of sintered ceramic tools with CaF 2 additions in dry cutting  

Microsoft Academic Search

An Al2O3\\/TiC ceramic cutting tool with the additions of CaF2 solid lubricant was produced by hot pressing. The fundamental properties of this ceramic cutting tool were examined. Dry machining tests were carried out on hardened steel and cast iron. The tool wear, the cutting forces, and the friction coefficient between the tool–chip interface were measured. It was shown that the

Deng Jianxin; Cao Tongkun; Yang Xuefeng; Liu Jianhua

2006-01-01

90

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

91

Spectroscopic studies of pulsed-laser-induced damage sites in heated CaF2 crystals  

NASA Astrophysics Data System (ADS)

Based upon previous studies of temperature dependent defect state formation in high energy alpha particle irradiated CaF2 analogous temperature dependent effects were expected to occur when heated crystals were exposed to Q- switching emission from a pulsed Nd:YAG laser. It was shown in the (alpha) -irradiation work that optimum clustering of calcium atoms to form colloids would occur at a critical temperature. In recent work irradiation of isothermally heated crystals at fluences on the order of 1 J/cm2 produced both catastrophic mechanical damage to the crystal as well as localized defect states within the lattice. Below 200 degrees C the mechanical damage was severe, as evidenced by extensive fractures radiating from the damage center along the crystal cleavage planes. However, above 200 degrees C, these fracture lines revealed the presence of CaF2 lattice forbidden bands associated with calcium colloids in addition to a blue shift of the principal T2g CaF2 mode frequency. The T2g line shift signifies the presence of compressive stress in the CaF2 lattice induced by the presence of the calcium colloids. Forbidden phonon line intensities varied with Raman probe wavelength, and the associated Raman excitation profile followed the wavelength response of the optical absorption band at 580 nm, which is ascribed to colloid resonance absorption. The presence of colloid was detected at all temperatures, and the extent of colloid formation was found to be only weakly dependent upon the crystal temperature. This lack of sensitivity may be ascribed to highly located heating of the crystal surface during the laser pulse, which could supersede the effect of ambient temperature. Pulsed Raman studies of thin CaF2 section sat laser fluences just below the damage thresholds did indeed indicate temperature excursions within the laser footprint. For samples held at temperatures above 200 degrees C, the color centers were found to absorb more strongly in the 400-500 nm and NIR regions, Probably indicating greater aggregation of F centers in the crystal.

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

1999-04-01

92

J. Phys.: Condens. Matter 8 (1996) 24572465. Printed in the UK Luminescence from BaF2 : Mn2+  

E-print Network

J. Phys.: Condens. Matter 8 (1996) 2457­2465. Printed in the UK Luminescence from BaF2 : Mn2 Petersburg, Russia Received 10 November 1995 Abstract. Through this work it is shown that the luminescence is similar to that displayed by BaMnF4 crystals. The absence of luminescence associated with isolated Mn2

Rodríguez, Fernando

93

Spectrophotometric determination of absorption in the DUV/VUV spectral range for MgF2 and LaF3 thin films  

NASA Astrophysics Data System (ADS)

The intrinsic absorption of fluoride coating materials tends to higher values in the DUV/VUV spectral range. In respect to applications of this material class for DUV/VUV multilayer systems, like high reflecting mirrors and anti- reflective coatings, the control of absorption is essential for further improvement of the coating quality. However, the reliable determination of absorption losses by photometric techniques has to overcome various obstacles caused by light absorption in air, scattering effects of the coating, and absorption related to contamination of the employed fluoride material. In this contribution spectrophotometric measurements for the characterization of optical data of MgF2 and LaF3 single layers and multi layer systems are presented. An advanced VUV/DUV-spectrophotometer, which has been developed at the Laser Zentrum Hannover for the optimization of thin film production processes, is described. The subsequent optical data evaluation for fluoride single layer coatings is reported and the optical data, n and k, of MgF2 and LaF3 for the spectral range from 130 to 660 nm are presented. Transmittance and reflectance measurements of multilayer coating systems are compared to theoretical calculations for these systems on the basis of the evaluated optical data of the single layers. Observed deviations are discussed under respect of contaminations of the fluoride layer systems.

Guenster, Stefan; Ristau, Detlev; Bosch, Salvador

2000-11-01

94

Photon down-shifting by energy transfer from Sm3+ to Eu3+ ions in sol-gel SiO2-LaF3 nano-glass-ceramics for photovoltaics  

NASA Astrophysics Data System (ADS)

95SiO2-5LaF3 sol-gel derived nano-glass-ceramics single doped with Eu3+ or Sm3+ and codoped with both of them were successfully obtained. XRD measurements confirm the precipitation of LaF3 nanocrystals after the ceramming process, with mean size ranging from 10 to 20 nm which increases with the thermal treatment temperature. The incorporation of rare-earth ions into precipitated LaF3 nanocrystals was confirmed from luminescence spectra. Intense yellow-red emissions were detected under UV and blue light excitation in single and codoped samples. The effect of codoping with Eu3+ and Sm3+ ions and the energy transfer mechanism between them have been analyzed in order to increase the yellow-red emissions.

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

2012-09-01

95

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

96

12C(?,?)16O studied with the Karlsruhe 4? BaF2 detector  

NASA Astrophysics Data System (ADS)

The 12C(?,?)16O reaction is one of the most important in nuclear astrophysics since it determines the ratio of 12C to 16O during stellar helium burning. Experimental data, however, are still subject to large uncertainties due to the almost vanishing cross section at stellar energies. So far, most measurements have been performed with germanium detectors. To compensate for their low efficiency, the highest beam currents had to be used, resulting in target degradation and beam-induced backgrounds. Instead, the present measurement was performed with high-efficiency detectors and low beam currents, using the Karlsruhe 4? BaF2 detector and the pulsed 3.7-MV Van de Graaff accelerator at Karlsruhe Institute of Technology. The 12C(?,?)16O cross sections have been measured at center-of-mass energies E between 1002 and 1510 keV, and the E1 and E2 components were derived with an accuracy comparable to the previous best data obtained with HPGe detectors.

Plag, R.; Reifarth, R.; Heil, M.; Käppeler, F.; Rupp, G.; Voss, F.; Wisshak, K.

2012-07-01

97

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

E-print Network

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

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

2014-01-01

98

Investigation of rare nuclear decays with BaF2 crystal scintillator contaminated by radium  

NASA Astrophysics Data System (ADS)

The radioactive contamination of a BaF2 scintillation crystal with mass of 1.714 kg was measured over 101 hours in the low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of 212Po (present in the crystal scintillator due to contamination by radium) was measured as = 298.8±0.8( stat.)±1.4( syst.) ns by the analysis of the events' pulse profiles. The 222Rn nuclide is known as 100% decaying via the emission of the particle with T 1/2 = 3.82 d; however, its decay is also energetically allowed with keV. Search for decay chains of events with specific pulse shapes characteristic for or for signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of 222Rn relatively to decay as % at 90% C.L. (equivalent to limit on partial half-life y). The half-life limits of 212Pb, 222Rn and 226Ra relatively to 2 decays are also improved in comparison with the earlier results.

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

2014-09-01

99

Cross luminescence of BaF2 crystal: Ab initio calculation  

NASA Astrophysics Data System (ADS)

Using ab initio methods and taking into account the lattice relaxation and polarization caused by the occurrence of the core hole, we have studied theoretically the cross luminescence in barium fluoride crystals in terms of the embedded-cluster approach. Two schemes of modeling of the core hole have been performed—in the form of an additional point charge and in the form of the 5 p state of the barium ion. Calculations have been done both by the Hartree-Fock method and by the density functional method. We have showed that the deformation of the lattice caused by the occurrence of the core hole leads to states localized on fluorine ions of the nearest environment splitting off from the valence band of the BaF2 crystal. The cross-luminescence bands at 5.7, 6.3, and 7.1 eV are caused by transitions from these localized states. We have also showed that the low-energy edge of the cross luminescence is formed by transitions from states that are localized on ions of the second coordination sphere.

Myasnikova, A. S.; Mysovsky, A. S.; Radzhabov, E. A.

2013-03-01

100

Paramagnetic hyperfine splitting in the 151Eu Mössbauer spectra of CaF2:Eu2+  

PubMed Central

151Eu Mössbauer 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 Mössbauer 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 ?33.7 T; 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. PMID:19816547

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

2009-01-01

101

Novel CaF2 Nanocomposite with High Strength and Fluoride Ion Release  

PubMed Central

Secondary caries and restoration fracture remain common problems in dentistry. This study tested the hypothesis that combining nano-CaF2 and glass fillers would yield nanocomposites with high mechanical properties and F release. Novel CaF2 nanoparticles (56-nm) were synthesized via spray-drying and incorporated into resin. F release increased with increasing the nano-CaF2 content, or with decreasing pH (p < 0.05). F-release rates at 70-84 days were 1.13 µg/(cm2·day) and 0.50 µg/(cm2·day) for nanocomposites containing 30% and 20% nano-CaF2, respectively. They matched the 0.65 µg/(cm2·day) of resin-modified glass ionomer (p > 0.1). The nanocomposites had flexural strengths of 70-120 MPa, after 84-day immersion at pH 4, pH 5.5, and pH 7. These strengths were nearly three-fold that of resin-modified glass ionomer, and matched/exceeded a composite with little F release. In summary, novel CaF2 nanoparticles produced high F release at low filler levels, thereby making room in resin for reinforcement glass. This yielded nanocomposites with high F-release and stress-bearing properties, which may help reduce secondary caries and restoration fracture. PMID:20439933

Xu, H.H.K.; Moreau, J.L.; Sun, L.; Chow, L.C.

2010-01-01

102

Laser induced nanoparticle formation in single crystal CaF2  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

103

Nanocrystalline CaF 2 particles obtained by high-energy ball milling  

NASA Astrophysics Data System (ADS)

Structural changes in mechanically treated CaF 2 powders have been studied by X-ray diffraction, transmission electron microscopy, thermal analysis, 19F and 1H MAS Nuclear Magnetic Resonance and Electron Paramagnetic Resonance methods. Applying the same methods, the results could be compared with those of mechanochemically synthesized CaF 2 samples, prepared for the first time in this study by high-energy ball milling. The applied methods indicate that the mechanically treated samples become, under the applied conditions, nanocrystalline. Unexpectedly, the mechanochemically synthesized samples show the same effects, i.e., nanocrystalline samples were formed. In contrast to many oxide compounds, a weak amorphization takes place only after a strong mechanical impact, and essentially in grain boundaries of spherical particles. Observed effects after the application of mechanical impact like broadening of XRD reflections, broadening of 19F resonances, or the decreasing ability for H rad trapping at ambient temperature, are mainly due to decreasing particle sizes as well as very small structural changes in the bulk of the particles. Surprisingly, the spin relaxation of both nuclear spins ( 19F) and electron spins (H rad ) appears to be the most sensitive tool for the investigation of mechanically and chemically induced changes indicating the increasing surface to bulk ratio with increasing mechanical impact.

Scholz, G.; Dörfel, I.; Heidemann, D.; Feist, M.; Stösser, R.

2006-04-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

105

Thermal lens measurements of fluorescence quantum efficiency in Nd 3+-doped fluoride glasses  

Microsoft Academic Search

In this work we used a thermal lens (TL) method in the dual beam mod-mismatched configuration, to determine the fluorescence quantum efficiency, ?. Three kinds of Nd3+-doped fluoride glasses were studied: fluorozirconate 53ZrF4–29BaF2–4.5LaF3–3.5AlF3–10NaF–XNdF3 (ZBLAN); fluoroaluminate 20YF3–40AlF3–20BaF2–20CaF2–XNdF3 (YABC) and fluoroindate 30PbF2–20GaF3–15InF3–15ZnF2–20CaF2–XNdF3 (PGIZCa); with X=1 or 2 mol%. For all these samples we obtained the quantum efficiency, ?, between 0.80–0.94 and 0.67–0.76

A. A. Andrade; T. Catunda; R. Lebullenger; A. C. Hernandes; M. L. Baesso

2001-01-01

106

A 4p BaF2 detector for (n,g) cross section measurements at a spallation neutron source  

E-print Network

The quest for improved neutron capture cross sections for advanced reactor concepts, transmutation of radioactive wastes as well as for astrophysical scenarios of neutron capture nucleosynthesis has motivated new experimental efforts based on modern techniques. Recent measurements in the keV region have shown that a 4p BaF2 detector represents an accurate and versatile instrument for such studies. The present work deals with the potential of such a 4p BaF2 detector in combination with spallation neutron sources, which offer large neutron fluxes over a wide energy range. Detailed Monte Carlo simulations with the GEANT package have been performed to investigate the critical backgrounds at a spallation facility, to optimize the detector design, and to discuss alternative solutions.

M. Heil; R. Reifarth; M. M. Fowler; R. C. Haight; F. Käppeler; R. S. Rundberg; E. H. Seabury; J. L. Ullmann; J. B. Wilhelmy; K. Wisshak

2013-10-16

107

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

PubMed

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

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

2010-05-17

108

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

PubMed

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

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

2014-01-31

109

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

110

Laser interactions with embedded Ca metal nanoparticles in single crystal CaF2  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important material for vacuum-ultraviolet optics. Nevertheless, prolonged exposure to energetic radiation can color the material by producing calcium metal nanoparticles. We compare the effectiveness of laser conditioning treatments at wavelengths ranging from the near infrared to the deep ultraviolet in removing this coloration. Treatments at 157, 532, and 1064 nm can significantly reduce the visible coloration due to nanoparticles. In contrast, irradiation at 248 nm has little effect at fluences below the damage threshold for the material employed in this work. We present evidence that the effect of laser irradiation on coloration is principally thermal and is largely confined to the first 50 ns after each laser pulse. We attribute the wavelength dependence of the bleaching process to the wavelength dependence associated with Mie absorption by metal nanoparticles. The consequences of these observations with regard to laser conditioning processes in bulk optical materials are discussed.

Cramer, L. P.; Schubert, B. E.; Petite, P. S.; Langford, S. C.; Dickinson, J. T.

2005-04-01

111

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

112

LiF and CaF2: Dy thermoluminescent dosimeters.  

PubMed

A study has been made of the characteristics of the LiF glow curve as a function of annealing temperature and time. Two annealing methods with different annealing time were studied. The annealing by a hot air stream may anneal quickly. The annealing method affects the shape of the glow curve. If the annealing procedure and the measurement time after irradiation are constant, the fading does not affect the results, except over a long time for uses in personnel dosimetry. For LiF, TLD-600 had a higher sensitivity for 60Co gamma rays than TLD-100 and -700 by a factor of 1.23. For CaF2: Dy, glow curves of unusual shape were obtained, and its relative response was several times greater than that of normal phosphors. PMID:7434378

Tsuda, M; Ohizumi, Y; Mori, T

1980-01-01

113

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

PubMed

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

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

2014-03-14

114

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...

115

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

116

Synthesis, characteristics and thermoluminescent dosimetry features of ?-irradiated Ce doped CaF2 nanophosphor.  

PubMed

Nanoparticles of cerium doped calcium fluoride (CaF2:Ce) were synthesized for the first time using the hydrothermal method. The formation of nanostructures was confirmed by X-ray diffraction (XRD) patterns, indicating cubic lattice structure for the particles produced. Their shape and size were observed by scanning electron microscopy (SEM). Thermoluminescence characteristics were studied by having the samples irradiated by gamma rays of (60)Co source. The optimum thermal treatment of 400 °C for 30 min was found for the produced nanoparticles. The Tm-Tstop and computerized glow curve deconvolution (CGCD) methods, used to determine the number of component glow peaks and kinetic parameters, indicated seven overlapping glow peaks on the TL glow curve at approximately 394, 411, 425, 445, 556, 594 and 632 K. A linear dose response of up to 2000 Gy, was observed for the prepared nanoparticles. Maximum TL sensitivity was found at 0.4 mol% of Ce impurity. Other TL dosimetry features, including reusability and fading, were also presented and discussed. PMID:23707947

Zahedifar, M; Sadeghi, E; Mozdianfard, M R; Habibi, E

2013-08-01

117

Intense ultraviolet emission from Tb3+ and Yb3+ codoped glass ceramic containing CaF2 nanocrystals  

NASA Astrophysics Data System (ADS)

A transparent Tb3+ and Yb3+ codoped oxyfluoride glass ceramic containing CaF2 nanocrystals was developed. This glass ceramic showed an intense ultraviolet emission at 381nm due to the G65, D35?F67 transitions of Tb3+ ion when excited with a 974nm laser at room temperature. The observed intense ultraviolet emission could be attributed to the change of ligand field of Tb3+ and Yb3+ ions due to the incorporation of some Tb3+ and Yb3+ ions into CaF2 nanocrystals, and the resulting increased branching ratio of the transitions and longer lifetime of D45 level of Tb3+ in the glass ceramic.

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

2007-03-01

118

CaF 2(Eu 2+):LiF – Structural and spectroscopic properties of a new system for neutron detection  

Microsoft Academic Search

A series of composites of CaF2(Eu2+) and LiF with different Ca\\/Li ratios were fabricated via liquid phase consolidation. Luminescent properties of these samples were investigated. Radioluminescence shows the typical Eu2+ blue emission in all the compositions. The energy spectra measured under ? and neutron irradiation indicates that the most promising composition for neutron detection is the eutectic.

Joanna Trojan-Piegza; Jarek Glodo; Vinod Kumar Sarin

2010-01-01

119

Role of Organic Additives in the Sol-Gel Synthesis of Porous CaF 2 Anti-Reflective Coatings  

Microsoft Academic Search

Porous CaF2 anti-reflective coating films were prepared by the sol-gel method. Effects of organic additives on deposition and optical properties of the films were investigated. Amino alcohols (2-aminoethanol, 2-dimethylaminoethanol, and triethanolamine) and alcohols with larger molecular weights (ethyleneglycol, 2-methoxyethanol, cyclohexanol, and 2-(2-n-butoxyethoxy)ethanol) were chosen as the organic additives. Among these additives, cyclohexanol was the most effective to control the surface

Shinobu Fujihara; Yasuhiro Kadota; Toshio Kimura

2002-01-01

120

Theory of the Frenkel Debye boundary layer at the (111) surface of pure CaF2  

Microsoft Academic Search

The present paper is concerned with a theoretical study of the properties of the Frenkel Debye boundary layer at the (111) surface of pure (undoped) CaF2, a crystal with anti-Frenkel defects, i.e. with anion vacancies and interstitials. The study is based on theoretical determinations of the adsorption energies of the fluorine ion at the terrace, step and kink sites on

Heinz Dabringhaus; Mikhail F. Butman

2003-01-01

121

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

PubMed

Nanoparticles are increasingly used in biomedical applications and are especially attractive as biocompatible and biodegradable protein delivery systems. Herein, the interaction between biocompatible 25 nm CaF2 nanoparticles and the ubiquitous calcium sensor calmodulin has been investigated in order to assess the potential of these particles to serve as suitable surface protein carriers. Calmodulin is a multifunctional messenger protein that activates a wide variety of signaling pathways in eukaryotic cells by changing its conformation in a calcium-dependent manner. Isothermal titration calorimetry and circular dichroism studies have shown that the interaction between calmodulin and CaF2 nanoparticles occurs with physiologically relevant affinity and that the binding process is fully reversible, occurring without significant alterations in protein secondary and tertiary structures. Experiments performed with a mutant form of calmodulin having an impaired Ca(2+)-binding ability in the C-terminal lobe suggest that the EF-hand Ca(2+)-binding motifs are directly involved in the binding of calmodulin to the CaF2 matrix. The residual capability of nanoparticle-bound calmodulin to function as a calcium sensor protein, binding to and altering the activity of a target protein, was successfully probed by biochemical assays. Even if efficiently carried by CaF2 nanoparticles, calmodulin may dissociate, thus retaining the ability to bind the peptide encompassing the putative C-terminal calmodulin-binding domain of glutamate decarboxylase and activate the enzyme. We conclude that the high flexibility and structural plasticity of calmodulin are responsible for the preservation of its function when bound in high amounts to a nanoparticle surface. PMID:25367003

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

2014-12-21

122

Quadrupole coupling and crystal-field shielding in CaF2:Eu3+:O2- under hydrostatic pressure  

Microsoft Academic Search

The nuclear quadrupole interactions in the 7F0 ground electronic state and the 5D0 excited state of the 151Eu3+ and 153Eu3+ ions have been investigated by optical means. The optically detected nuclear quadrupole resonance, excitation, and luminescence of the Eu3+-O2- C3v symmetry center have been studied at 4.2 K in single crystals of CaF2:Eu:O under hydrostatic pressure up to 7.5 kbar.

Andrzej P. Radlinski; A. J. Silversmith

1986-01-01

123

Optical detection of electron transfer through interfaces in CaF 2:Eu-CdF 2 SLs  

NASA Astrophysics Data System (ADS)

We present here a further study of unusual features observed in photoluminescence (PL) of Eu 2+ in CaF 2 layers of CaF 2-CdF 2 SLs (SLs) [N.S. Sokolov, S.V.Gastev, A.Yu. Khilko, S.M. Suturin, I.N. Yassievich, J.M. Langer, A. Kozanezcki, Phys.Rev B 59 (1999) R2525]. PL of Eu 2+ in SLs, in contrast to bulk CaF 2:Eu crystals, fades out considerably under continuous UV excitation. This is mainly due to tunneling-assisted photoionization of Eu 2+. We have measured the PL time dependence in uniformly and selectively doped SLs with different periods and compared the results with the calculations in the tunneling model. A careful analysis of PL in selectively doped SLs revealed an additional ionization process suggested to occur in all SLs independent of the Eu ion position. With the account of this process we find that the experimental results are in good agreement with theoretical calculations. We have estimated the values of the main parameters in the tunneling model, which show the best fit with the experiment.

Suturin, S. M.; Basun, S. A.; Gastev, S. V.; Langer, J. M.; Meltzer, R. S.; Sokolov, N. S.

2000-08-01

124

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

E-print Network

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

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

2010-09-07

125

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

126

Time-resolved thermal lens measurements of thermo-optical properties of fluoride glasses  

Microsoft Academic Search

We present measurements of the temperature coefficient of optical path change, ds\\/dT, thermal diffusivity, D, and conductivity, K, using time-resolved mode-mismatched thermal lens method for fluoride (mol%) 53ZrF4–4.5LaF3–3.5AlF3–29BaF2–10NaF (ZBLAN), fluoroaluminate 20YF3–40AlF3–20CaF2–20BaF2 (YABC) and fluoroindates 20GaF3–15InF3–20CaF2–15ZnF2–30PbF2 (PGIZCa), 6GaF3–34InF3–20SrF2–16BaF2–20ZnF2–4NaF (ISZn), 2GdF3–40InF3–20SrF2–16BaF2–20ZnF2–2%NaF (InSBZnGdN). All the samples were crystal free, as verified by X-ray diffraction (XRD), and were at least 3 mm thick. The

S. M Lima; J. A Sampaio; T Catunda; R Lebullenger; A. C Hernandes; M. L Baesso; A. C Bento; F. C. G Gandra

1999-01-01

127

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

129

Neutrino-less Double Beta Decay of 48Ca studied by CaF2(Eu) Scintillators  

E-print Network

We searched for the neutrino-less double beta decay(0nbb) of 48Ca by using CaF2(Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q-value region for the data of 3394 kg days. It gives a lower limit (90% confidence level) of T > 2.7 x 10^22 year for the half life of 0nbb of 48Ca. Combined with our previous data for 1553 kg days, we obtained more stringent limit of T > 5.8 x 10^22 year.

S. Umehara; T. Kishimoto; I. Ogawa; R. Hazama; H. Miyawaki; S. Yoshida; K. Matsuoka; K. Kishimoto; A. Katsuki; H. Sakai; D. Yokoyama; K. Mukaida; S. Tomii; Y. Tatewaki; T. Kobayashi; A. Yanagisawa

2008-10-27

130

Transmission and reflection studies of thin films in the vacuum ultraviolet  

NASA Astrophysics Data System (ADS)

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

Peterson, Lennart R.

1989-12-01

131

Transmission and reflection studies of thin films in the vacuum ultraviolet  

NASA Technical Reports Server (NTRS)

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

Peterson, Lennart R.

1989-01-01

132

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

133

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

134

Studies of the BaF2-BaC2 solid solution as a carbide electrolyte  

NASA Astrophysics Data System (ADS)

A study has been made of the BaF2-BaC2 system for use as a solid electrolyte applicable to measurements of the chemical potential of carbon. From lattice parameter studies of annealed specimens it is concluded that only a limited solid solubility exists; rising from about 0.8 to 1.0 wt pct BaC2 in the temperature interval 973 to 1173 K. Hydrolysis of the solid solutions produced gases containing two carbon atoms with no evidence of single carbon hydrocarbons. This is taken as evidence that the acetylide ion, C 2- 2, of BaC2 is conserved in the solid solution. Galvanic cell studies with Mo-Mo2C and Cr-Cr23C6 electrodes in the temperature range 890 to. 1105 K with electrolytes of differing composition gave results in excellent accord with the most recent measurements of the stabilities of the carbides. Lack of reversibility to graphite indicates a limited application of the electrolyte.

Coltters, R. G.; Belton, G. R.

1980-09-01

135

Response of BaF2, CsI(Tl) and Pb-glass detectors to neutrons below 22 MeV  

NASA Astrophysics Data System (ADS)

The properties of BaF2, CsI(Tl) and Pb-glass for neutron detection were studied using neutrons of kinetic energies up to 22 MeV produced in deuteron induced reactions on a thick LiF target. The neutron absorption length was extracted from a neutron transmission experiment. The absolute efficiency for neutron detection was determined by comparing neutron energy spectra (obtained from time-of-flight) with that of a calibrated liquid scintillator detector. For BaF2 the detection efficiency as a function of the threshold on the light-output signal was studied as well as the possibility of pulse-shape discrimination between signals induced by ?-rays and neutrons. It is found that with increasing energies a detection mechanism comes into play which is different from the (n,?) mechanism predominant at lower energies, and which might allow a (partial) discrimination of ? and neutron induced events at higher neutron energies.

Matulewicz, T.; Grosse, E.; Emling, H.; Grein, H.; Kulessa, R.; Baumann, F. M.; Domogala, G.; Freiesleben, H.

1989-01-01

136

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

NASA Astrophysics Data System (ADS)

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

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

1994-01-01

137

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

PubMed Central

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

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

2014-01-01

138

Cylindrical wave of reflection and conduction in IR transparent BaF2 single crystal excited by 2.5 s duration pulse of CO2 laser  

Microsoft Academic Search

Experiments on optical damage testing by help of 2.5 microsecond(s) , approximately 0.1 J single pulse of 10.6 (mu) CO2 laser showed the appearance of cylindrical geometry WRC in BaF2 single crystal approximately 50 percent transparent for this radiation. It was measured the reflection variations of the He-Ne beam transmitted through the sample at the 30 degree angle to the

Eugene M. Kudriavtsev; Franck Guignard; G. Inglesacis; Michel L. Autric

1998-01-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

140

Experimental study of the adsorption of lithium fluoride on the (111) surface of CaF 2  

NASA Astrophysics Data System (ADS)

The interaction of molecular beams of the lithium fluoride monomers LiF and dimers Li 2F 2 with the (111) surface of CaF 2 crystals has been studied by the method of desorption transients for crystal temperatures between T=777 and 985 K and for total lithium fluoride fluxes jon=1×10 10-1×10 14 cm -2s -1. The studies show that the monomers are adsorbed at the monatomic steps on the CaF 2 surface. The steps have a limited capacity of the order of 10 12 cm -2 for an adsorption direct at them; further monomers are adsorbed in their immediate neighborhood beside already adsorbed monomers. The adsorption times derived from transient desorption fluxes result as ?0 (s)=1.3 (+9.5, -1.15)×10 -15 exp[(2.70±0.17) eV/ kT] for an adsorption direct at the steps and as ?1 (s)=7.6 (+30, -6.0)×10 -15 exp[(2.44±0.11) eV/ kT] beside them. For the dimers, only a portion ?d, 0.5< ?d( T)<0.85, of the impinging dimer flux reaches the steps, while the remainder desorbs quickly. From ?d( T), the ratio of the mean diffusion length xds on the terrace to the mean step distance, ?, is determined as xds/ ?=(2.9±0.9)×10 -2 exp[(0.5±0.05) eV/2 kT]. With ??8×10 -6 cm as derived from atom force microscopic studies jump distances for the dimers in the order of the lattice constant of CaF 2 are obtained corresponding to a surface diffusion model with jumps between neighboring lattice sites. Dimers at the steps are completely dissociated into monomers. For larger monomer concentrations at the steps also a formation of dimers and their subsequent desorption is observed. By a comparison of experimental desorption transients with a simple theoretical model, the above adsorption times as well as a constant k (cm s -1)=8.0(+42, -6.8) exp[-(1.63±0.16) eV/ kT] describing the formation and desorption of the dimers are determined.

Klumpp, St.; Dabringhaus, H.

1998-11-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

142

Ultraviolet-infrared femtosecond laser-induced damage in fused silica and CaF2 crystals  

NASA Astrophysics Data System (ADS)

The damage in fused silica and CaF2 crystals induced by wavelength tunable femtosecond lasers is studied. The threshold fluence is observed to increase rapidly with laser wavelength ? in the region of 250-800nm , while it is nearly a constant for 800

Jia, T. Q.; Chen, H. X.; Huang, M.; Zhao, F. L.; Li, X. X.; Xu, S. Z.; Sun, H. Y.; Feng, D. H.; Li, C. B.; Wang, X. F.; Li, R. X.; Xu, Z. Z.; He, X. K.; Kuroda, H.

2006-02-01

143

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

145

Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates  

NASA Astrophysics Data System (ADS)

We report on the isotropic pinning obtained in epitaxial Fe(Se,Te) thin films grown on CaF2(001) substrate. High critical current density values - larger than 1 MA/cm2 in self field and liquid helium - are reached together with a very weak dependence on the magnetic field and a complete isotropy. Analysis through transmission electron microscopy evidences the presence of defects looking like lattice disorder at a very small scale, between 5 and 20 nm, which are thought to be responsible for such isotropic behavior in contrast to what was observed on SrTiO3, where defects parallel to the c-axis enhance pinning in that direction.

Braccini, V.; Kawale, S.; Reich, E.; Bellingeri, E.; Pellegrino, L.; Sala, A.; Putti, M.; Higashikawa, K.; Kiss, T.; Holzapfel, B.; Ferdeghini, C.

2013-10-01

146

Picosecond kinetic confirmation of overlapping Ca cluster and MNa absorption bands in UV grade CaF2  

NASA Astrophysics Data System (ADS)

The ArF laser induced absorption feature between 450 and 700 nm observed in the bulk of mono crystalline calcium fluoride (CaF2) upon prolonged 193 nm irradiation is shown to have two origins: The first band at 530 nm is revealed by a transient femtosecond (fs) laser transparency spectrum and attributed to Ca clusters (colloid). The second band at 600 nm originates from MNa centers as identified by their laser induced fluorescence excitation spectrum, emission wavelength, and fluorescence lifetime. The analysis of the absorption feature by fs pump-probe techniques benefits from the different lifetimes of the transient transparency (excited states of the Ca clusters) and the fluorescing MNa centers of about 5 ps and 22 ns, respectively.

Zeuner, T.; Paa, W.; Triebel, W.; Mühlig, C.; Stafast, H.

2011-09-01

147

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

E-print Network

of Materials, University of Oklahoma, Norman, Oklahoma 73019 X. M. Fang and P. J. McCann School of Electrical 110 -oriented epitaxy can be sustained. At the initial growth stage, long strips of CaF2 parallel to result from the combination of favorable energetics in exposing the low-energy 111 facets

McCann, Patrick

148

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

E-print Network

based on an Yb31:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at femtosecond laser A. Lucca, G. Debourg, M. Jacquemet, F. Druon, F. Balembois, and P. Georges Laboratoire. Moncorgé Centre Interdisciplinaire de Recherches sur les Ions et les Lasers, Unité Mixte de Recherche 6637

Boyer, Edmond

149

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

PubMed

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

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

2012-03-01

150

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

SciTech Connect

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

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

2005-05-24

151

Up-conversion white light of Tm 3+/Er 3+/Yb 3+ tri-doped CaF 2 phosphors  

NASA Astrophysics Data System (ADS)

Tm 3+/Er 3+/Yb 3+ tri-doped CaF 2 phosphors were synthesized using a hydrothermal method. The phosphors were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and up-conversion (UC) emission spectra. After annealing, the phosphors emitted white light under a 980 nm continuous wave diode laser (CW LD 2 W) excitation. As the excitation power density changed in the range of 20-260 W/cm 2, the chromaticity coordinates of the UC light of the phosphor Ca 0.885Tm 0.005Er 0.01Yb 0.1F 2 fell well in the white region of the 1931 CIE diagram. For the proportion of red, green and blue (RGB) in white light is strict, key factors for achieving UC white light, such as host materials, rare earth ions doping concentrations, annealing temperatures, as well as the excitation power densities, were investigated and discussed.

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

2008-03-01

152

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

PubMed Central

Modification of surface and bulk properties of solids by irradiation with ion beams is a widely used technique with many applications in material science. In this study, we show that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of medium energy (3 and 5?MeV) highly charged ions (Xe22+ to Xe30+) as well as swift (kinetic energies between 12 and 58?MeV) heavy xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be lowered substantially. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. PMID:25034006

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

2014-01-01

153

The exchange charge model and vibronic interactions for Mn2+ doped in CaF2 crystals  

NASA Astrophysics Data System (ADS)

The aim of this work is to present a crystal field analysis of the [CaF8]6- complex in the static crystal field and vibronic interactions in the dynamic crystal field. The modeling of the crystal field parameters and simulated energy level scheme is presented in the exchange charge model. In this model, the crystal field strength 10?Dq for different impurity-ligand distances near the equilibrium position was obtained. By fitting these values to an exponential law, we found n=7.278, as the exponent power, for the 10?Dq dependence (10?Dq?R-n). The electron-phonon interaction of the bivalent manganese ion doped in CaF2 was studied using the single configuration coordination model. Some physical quantities associated with the normal vibration modes a1g and eg of the [CaF8]6- complex coupled with the electron states of Mn2+ such as the Stokes shift and the Huang-Rhys factors are calculated. The obtained results are discussed and compared with experimental data.

Vaida, M.

2012-05-01

154

Theory of the Frenkel Debye boundary layer at the (111) surface of pure CaF2  

NASA Astrophysics Data System (ADS)

The present paper is concerned with a theoretical study of the properties of the Frenkel Debye boundary layer at the (111) surface of pure (undoped) CaF2, a crystal with anti-Frenkel defects, i.e. with anion vacancies and interstitials. The study is based on theoretical determinations of the adsorption energies of the fluorine ion at the terrace, step and kink sites on the surface, which are, together with the assumption of experimental step distances and theoretical kink concentrations, necessary pre-requisites for a quantitative description of the surface charge compensating that of the space-charge region. The results show that, for realistic surface conditions, the surface and space charges, and with them the potential between surface and bulk, are reduced considerably compared with those for an unlimited number of accessible surface sites. Nevertheless, on approaching the surface a strong increase in the anion vacancy concentration against that of the bulk still exists, which should lead to an increased ion conductivity in near-surface regions and thin fluorite layers.

Dabringhaus, Heinz; Butman, Mikhail F.

2003-09-01

155

Pressure dependence of the impurity-trapped exciton emission in BaF2:Eu and BaxSr1-xF2:Eu  

NASA Astrophysics Data System (ADS)

The normal and anomalous emission of Eu2+ in SrF2 , BaF2 , and BaxSr1-xF2 are studied as a function of x and as a function of pressure for x=0 , 0.3, and 1. The anomalous emission converts to the normal emission at pressures of about 40kbar and 30kbar , for x=0.3 and x=1 , respectively. The anomalous emission becomes redshifted as a function of x . The wavelength dependence of the emission lifetime as a function of x provides evidence for the inhomogeneous nature of the emission. It is suggested that each distinct site, with its distribution of Ba and Sr in the 12 nearest-neighbor cation positions, has its unique emission spectrum and that this becomes redshifted with increasing numbers of Ba. The observed anomalous emission then results from the sum of emission spectra from the distinct sites weighted by their statistical probability. The nature of the emission can be understood with a configurational coordinate model assuming that the localized 4f65d1 states and the impurity-trapped exciton states are in thermal equilibrium. For pure BaF2 , a reversal in the relative energies of the two states occurs at the phases transition. For the mixed crystal, the relative energies depend on the number of Ba neighbors so that some sites exhibit anomalous emission while those with one or no Ba show the normal emission.

Gatch, D. B.; Boye, D. M.; Shen, Y. R.; Grinberg, M.; Yen, Y. M.; Meltzer, R. S.

2006-11-01

156

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

158

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

NASA Astrophysics Data System (ADS)

Systematic experiments on irradiation damage in CaF2 were reported in a recent paper [M. Toulemonde , Phys. Rev. BPRBMDO0163-182910.1103/PhysRevB.85.054112 85, 054112 (2012)]. The measurements were performed in a broad range of ion energies and energy deposition and the inelastic thermal spike model was applied for the analysis. Here we demonstrate that contrary to what is stated in the paper, the experimental results do not prove that there is a velocity effect in CaF2 similar to that observed previously in Y3Fe5O12 and other track-forming insulators. We also show that the authors’ results do not support their hypothesis that tracks are formed by quenching of a boiling phase.

Szenes, G.

2013-02-01

159

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

161

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

NASA Astrophysics Data System (ADS)

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

Nicoara, I.; Stef, M.

2012-06-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

163

Growth structure investigation of MgF 2 and NdF 3 films grown by molecular beam deposition on CaF 2(111) substrates  

Microsoft Academic Search

The growth structure of MgF2 and NdF3 films grown on polished CaF2(111) substrates deposited by molecular beam deposition has been investigated using transmission electron microscopy (TEM) of microfractographical and surface replications as well as cross-sectional TEM, atomic force microscopy, packing density, and absorption measurements. It has been shown that by taking advantage of ultrahigh vacuum environments and a special stratification

U. Kaiser; M. Adamik; G. Sáfrán; P. B. Barna; S. Laux; W. Richter

1996-01-01

164

Studies of the growth kinetics of CaF 2(1 1 1) by molecular beam methods and atomic force microscopy  

Microsoft Academic Search

The growth kinetics of the (111) surface of CaF2 single crystals is studied by molecular beam methods and atomic force microscopy for temperatures between 1015 and 1099K and saturation ratios up to 354. After passing a transition stage with repeated two-dimensional nucleation, island growth and coalescence of the growing islands the surface develops growth hillocks with closed loop steps of

M. Schick; H. Dabringhaus; K. Wandelt

2005-01-01

165

Thermo-optical measurements of ytterbium doped ceramics (Sc2O3, Y203, Lu203, YAG) and crystals (YAG, CaF2) at cryogenic temperatures  

NASA Astrophysics Data System (ADS)

In this paper, we report the measurements of the specific heat, the density and the thermal diffusivity at room and cryogenic temperatures of Ytterbium doped cubic sesquioxides (Sc2O3, Y2O3, Lu2O3) ceramics and of Ytterbium doped crystals (YAG, CaF2). These materials appear to have very interesting properties for setting up high average power laser chains useful for plasma physics and for inertial fusion energy drivers.

Le Garrec, B.; Cardinali, V.; Bourdet, G.

2013-05-01

166

An XPS study of the fluorination of carbon anodes in molten NaF–AlF 3 –CaF 2  

Microsoft Academic Search

In the Hall–Héroult process for aluminum production electrolysis takes place in molten cryolite (NaF–AlF3–CaF2) with carbon electrodes. Dewetting of the anode leads to operational instability. A surface energy change due to surface\\u000a fluorocarbon formation during electrolysis is suggested as a contributing factor to diminishing the wettability of the anode.\\u000a In this work the surface composition of graphite anodes after electrolysis

Richard G. Haverkamp

167

Formation of slab waveguides in eulytine type BGO and CaF2 crystals by implantation of MeV nitrogen ions  

NASA Astrophysics Data System (ADS)

Ion implantation, compared with other waveguide fabrication methods, has some unique advantages. It has proved to be a universal technique for producing waveguides in most optical materials. The authors of the present article reported fabrication of channel and slab waveguides in an Erbium-doped tungsten tellurite glass by implantation of MeV energy N+ ions. The present article reports successful adaptation of the same technique to the fabrication of slab waveguides in eulytine type bismuth germanate (BGO) and CaF2 crystals. This is the first report on successful waveguide fabrication in these materials using 3.5 MeV N+ ions at implanted fluences between 5 × 1015 and 4 × 1016 ions/cm2. Spectroscopic ellipsometric measurements revealed the existence of guiding structures in both materials. M-line spectroscopic measurements indicated guiding effect in the as-implanted BGO up to 1550 nm and up to 980 nm in the as-implanted CaF2. Ion implantation induced the appearance of three peaks in the UV/Vis absorption spectrum of CaF2, that can be attributed to colour centres.

Bányász, I.; Berneschi, S.; Khánh, N. Q.; Lohner, T.; Lengyel, K.; Fried, M.; Péter, Á.; Petrik, P.; Zolnai, Z.; Watterich, A.; Nunzi-Conti, G.; Pelli, S.; Righini, G. C.

2012-09-01

168

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

NASA Astrophysics Data System (ADS)

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

Shinozaki, Kenji; Honma, Tsuyoshi; Komatsu, Takayuki

2014-06-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

170

10BaF2:NaF, Na3AlF6/TiO2 composite as a novel visible-light-driven photocatalyst based on upconversion emission  

NASA Astrophysics Data System (ADS)

A rare-earth free upconversion luminescent material, 10BaF2:NaF, Na3AlF6, is synthesized by a hydrothermal method. The study of fluorescent spectrum indicates that it can convert visible light (550 nm—610 nm) into ultraviolet light (290 nm—350 nm), and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature. Subsequently, 10BaF2:NaF, Na3AlF6/TiO2 composite photocatalyst is prepared and its catalytic activity is evaluated by the photocatalytic reduction of CO2 under visible light irradiation (? > 515 nm). The results show that 10BaF2:NaF, Na3AlF6/TiO2 is a more effective photocatalyst for CO2 reduction than pure TiO2, their corresponding methanol yields are 179 and 0 ?mol/g-cat under the same conditions. Additionally, the mechanism of photocatalytic reduction of CO2 on 10BaF2:NaF, Na3AlF6/TiO2 is proposed.

Liu, En-Zhou; Fan, Jun; Hu, Xiao-Yun; Hou, Wen-Qian; Dai, Hong-Zhe

2012-04-01

171

Radiation damage effects in far-ultraviolet filters and substrates  

NASA Astrophysics Data System (ADS)

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 RE 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 on the thin film format, we report on such an assessment here.

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

1993-12-01

172

Structure and surface morphology of MnF2 epitaxial layers grown on grooved and ridged CaF2 (1 1 0) surface  

NASA Astrophysics Data System (ADS)

Structural and surface morphology studies of MnF2 epitaxial layers have been performed by x-ray diffraction and atomic force microscopy (AFM). MnF2 layers of different thicknesses (0.12-1.25 µm) were grown by MBE on Si(0 0 1) substrates with the deposited CaF2-buffer layer having a lang1 1 0rang orientation and a grooved and ridged surface. X-ray diffraction patterns in the 10°-60° angular range have been measured. Profiles of diffraction peaks in two directions—parallel and normal to the diffraction vector—as well as the intensity distribution around 2 2 0 reciprocal lattice points were obtained. It was found that the metastable orthorhombic phase of ?-PbO2 type with [1 1 0] growth direction dominates in the films; a much smaller portion of the stable rutile type phase was also detected, though it increases with the film thickness. As follows from the x-ray diffraction data, the films have a mosaic block structure. Parameters of the crystallites were determined using the Williamson-Hall analysis of angular width of the diffraction peaks. It was obtained that the crystallites of the orthorhombic phase have an elongated shape oriented along the direction of the CaF2 ridges. The AFM study confirms a regular distribution of the orthorhombic crystallites and shows the appearance of some irregular shaped crystallites on the top of the thick MnF2 films.

Kyutt, R. N.; Banshchikov, A. G.; Kaveev, A. K.; Sokolov, N. S.; Lomov, A. A.; Ohtake, Y.; Tabuchi, M.; Takeda, Y.

2007-08-01

173

Radiation Damage Effects in Far Ultraviolet Filters and Substrates  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

174

White up-conversion emission in Ho3+/Tm3+/Yb3+ tri-doped glass ceramics embedding BaF2 nanocrystals  

NASA Astrophysics Data System (ADS)

Ho3+/Tm3+/Yb3+ tri-doped glass ceramics with white light emitting have been developed and demonstrated. Pumped by 980 nm laser diode (LD), intensive red, green and blue up-conversions (UC) were obtained. The green emission is assigned to Ho3+ ion and the blue emission is assigned to Tm3+ ion, whereas the red emission is the combination contribution of the Ho3+ and Tm3+ ions. The RGB intensities could be adjusted by tuning the rare-earth ion concentration and pump power intensity. Thus, multicolor of the luminescence, including perfect white light with CIE-X=0.329 and CIE-Y=0.342 in the 1931 CIE chromaticity diagram can be obtained in 0.15 Ho3+/0.2Tm3+/3Yb3+ tri-doped glass ceramics embedding BaF2 nanocrystals pumped by a single infrared laser diode source of 980 nm at 500 mW. The up-conversion luminescence mechanism of Yb3+ sensitize Ho3+ and Tm3+ ions and the energy transfer from Ho3+ to Tm3+ in oxy-fluoride silicate glass ceramics were analyzed.

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

2011-04-01

175

Cylindrical wave of reflection and conduction in IR transparent BaF2 single crystal excited by 2.5-?s-duration pulse of CO2 laser  

NASA Astrophysics Data System (ADS)

Experiments on optical damage testing by help of 2.5 microsecond(s) , approximately 0.1 J single pulse of 10.6 (mu) CO2 laser showed the appearance of cylindrical geometry WRC in BaF2 single crystal approximately 50 percent transparent for this radiation. It was measured the reflection variations of the He-Ne beam transmitted through the sample at the 30 degree angle to the IR laser axes and crossing it. The nonequilibrium heating of the sample along IR beam axes produced the heat lens and as a consequence the focusing of the He-Ne beam. The cylindrical WRC cross the focused He-Ne beam area and it gives the well pronounced bell shape peak, additional to the analogous reflection variation records made at conditions where He-Ne beam did not cross IR laser axes. The time of focused He-Ne beam crossing by WRC is 40 ms, which correspond to approximately 0.6 mm diameter of focused a beam. One can make conclusions about local optical constants changing inside of solid sample by help of reflection variations in WRC. This work was sponsored by RFBR.

Kudriavtsev, Eugene M.; Guignard, Franck; Inglesacis, G.; Autric, Michel L.

1998-04-01

176

Effect of tip polarity on Kelvin probe force microscopy images of thin insulator CaF2 films on Si(111)  

NASA Astrophysics Data System (ADS)

We investigate thin insulating CaF2 films on a Si (111) surface using a combination of noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). Atomic-scale NC-AFM and KPFM images are obtained in different imaging modes by employing two different tip polarities. The KPFM image contrast and the distance-dependent variation of the local contact potential difference (LCPD) give rise to a tip-polarity-dependent contrast inversion. Ca2+ cations had a higher LCPD contrast than F- anions for a positively terminated tip, while the LCPD provided by a negatively charged tip gave a higher contrast for F- anions. Thus, this result implies that it is essential to determine the tip apex polarity to correctly interpret LCPD signals acquired by KPFM.

Yurtsever, Ayhan; Sugimoto, Yoshiaki; Fukumoto, Masaki; Abe, Masayuki; Morita, Seizo

2012-08-01

177

Resistance switching memory characteristics of Si/CaF2/CdF2/CaF2/Si resonant-tunneling quantum-well structures  

NASA Astrophysics Data System (ADS)

A novel resistance switching memory scheme using Si/CaF2/CdF2/CaF2/Si resonant-tunneling quantum-well (QW) structures grown on a Si substrate has been proposed, and write-read-erase cyclic memory operation has been demonstrated by applying pulsed input voltage sequences at room temperature. A resistance switching voltage of less than 1.0 V, a peak current density of 30-72 kA/cm2, and an ON/OFF ratio of 1.9-30 were observed. Under an appropriate bias condition, a retention time of more than 315 h and cyclic pulsed operation corresponding to write-read-erase-read for more than 4500 cycles were achieved.

Denda, Junya; Uryu, Kazuya; Suda, Keita; Watanabe, Masahiro

2014-04-01

178

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

179

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

180

Reply to ``Comment on `Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2 crystal: Evidence for two thresholds of damage creation' ''  

NASA Astrophysics Data System (ADS)

Experimental data presented in our earlier paper [Toulemonde , Phys. Rev. B10.1103/PhysRevB.85.054112 85, 054112 (2012)] indicate that there are two thresholds for damage creation by swift heavy ions in CaF2. Moreover, the comparison of the track sizes observed by transmission electron microscopy and generated by different cluster and monoatomic ion beams supports the occurrence of a velocity effect in this material.

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

2013-02-01

181

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

Microsoft Academic Search

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

S. Bahadur; Deli Gong; James Anderegg

1996-01-01

182

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)

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%.

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

183

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)

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.

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

184

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

NASA Astrophysics Data System (ADS)

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).

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

2013-06-01

185

Effect of the post-deposition processing ambient on the preparation of superconducting YBa2Cu3O7 - x coevaporated thin films using a BaF2 source  

NASA Astrophysics Data System (ADS)

We have investigated the effect of the post-deposition processing ambient on the preparation of YBa2Cu3O7-x thin films from a BaF2 source. The role of H2O vapor during the high-temperature anneal is understood through a thermodynamic analysis of the fluorine removal reaction. The role of a HF getter (e.g., SiO2) is understood through the same type of analysis. We have demonstrated that a zero resistance transition temperature at 77 K can be obtained for an annealing temperature as low as 690 °C for films deposited on SrTiO3 substrates by increasing the PH2O and decreasing PHF during the high-temperature soak cycle.

Chan, Siu-Wai; Bagley, B. G.; Greene, L. H.; Giroud, M.; Feldmann, W. L.; Jenkin, K. R., II; Wilkins, B. J.

1988-10-01

186

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

SciTech Connect

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.

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

2001-01-12

187

High-temperature background of internal friction in (Co45Fe45Zr10) x (Al2O3)100 - x , Co x (CaF2)100 - x , and Co x (PZT)100 - x nanocomposites  

NASA Astrophysics Data System (ADS)

The elastic ( G) and inelastic ( Q -1) properties of (Co45Fe45Zr10) x (Al2O3)100 - x , Co x (CaF2)100 - x , and Co x (PZT)100 - x ( x = 23-76 at %) nanocomposites obtained by ion-beam sputtering are studied in the temperature range 300-900 K. A significant rise in the Q Q -1 ( T) curve is observed at temperatures above 650 K, which is attributed to thermally activated migration of point defects under the conditions of confined geometry.

Tarasov, D. P.

2013-02-01

188

Radiation damage effects in far-ultraviolet filters, thin films, and substrates.  

PubMed

Advances in vacuum ultraviolet thin-film filter technology have been made through the use of filter designs with multilayers of materials such as Al(2)O(3), BaF(2), CaF(2), HfO(2), LaF(3), MgF(2), and SiO(2). Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 × 9 R(E) orbit will expose the instrument to approximately 250 krad of radiation. Because to our knowledge no previous studies have been made on the potential radiation damage of these materials in the thin-film format, we report on such an assessment here. Transmittances and reflectances of BaF(2), CaF(2), HfO(2), MgF(2), and SiO(2) thin films on MgF(2) substrates, Al(2)O(3) thin films on fused-silica substrates, uncoated fused silica and MgF(2), and four multilayer filters made from these materials were measured from 120 to 180 nm beforeand after irradiation by 250 krad from a (60)Co gamma radiation source. No radiation-induced losses in transmittance or reflectance occurred in this wavelength range. Additional postradiation measurements from 160 to 300 nm indicates 2-5% radiation-induced absorption near 260 nm in some of the samples with MgF(2) substrates. From these measurements we conclude that far-ultraviolet filters made from the materials tested should experience less than 5% change from exposure to up to 250 krad of high-energy radiation in space applications. PMID:20936017

Keffer, C E; Torr, M R; Zukic, M; Spann, J F; Torr, D G; Kim, J

1994-09-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

190

Abnormal Visible Luminescence Mechanism of Tb3+-Yb3+ Codoped SiO2-Al2O3-CaF2 Glass Studied by Time-Resolved Spectra  

NASA Astrophysics Data System (ADS)

The upconversion energy transfer mechanism in Tb3+-Yb3+ co-doped SiO2-Al2O3-CaF2 glass is investigated by time-resolved spectra. The effect of donor ion Yb3+ is involved in the dynamic decay behavior of acceptor ion Tb3+, which provides direct proof for the energy transfer from Yb3+ to Tb3+. The pump power dependence curves show that the upconversion luminescence is a two-photon process. The measured decay curves of the 5D4 state (Tb3+) contain two parts: a slow decay process corresponding to its radiation, and a fast one with a decay parameter approximately twice the lifetime of the 2F5/2 state (Yb3+). The fast decay process is contradictory to the generally accepted cooperative sensitization upconversion rate equation model. Since the effect of the host environmental is excluded by comparative experiments, we believe that there should be another energy transfer mechanism in Tb3+-Yb3+ co-doped SiO2-Al2O3-CaF2 glass in addition to the cooperative sensitization process.

Duan, Qian-Qian; Zhao, Hua; Zhang, Zhi-Guo; Jian, Ao-Qun; Sang, Sheng-Bo; Zhang, Wen-Dong

2014-08-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

192

Crystal structure and electrical property comparisons of epitaxial Pb(Zr,Ti)O3 thick films grown on (100)CaF2 and (100)SrTiO3 substrates  

NASA Astrophysics Data System (ADS)

Epitaxial Pb(Zr,Ti)O3 (PZT) thick films of 2.0-3.0 ?m thickness were grown at 600 °C on (100)cSrRuO3?(100)SrTiO3 and (100)cSrRuO3?(100)LaNiO3?(100)CaF2 substrates by pulsed-metal organic chemical vapor deposition. All films showed (100) and/or (001) orientations with tetragonal symmetry. It was found that there is an almost linear relationship between the estimated thermal strain from the deposition temperature to the Curie temperature and the volume fraction of (001) orientation in the mixture of (100) and (001) orientations for the films on both substrates. Consequently, the perfectly (001)-oriented, i.e., polar-axis-oriented, PZT thick films were obtained on CaF2 with the Zr/(Zr+Ti) ratio from 0.20 to 0.40. Moreover, the lattice parameter of a- and c-axes and their ratio (c /a) of those polar-axis-oriented films were almost the same as the reported data for the powder, suggesting that the large strain is not remaining in those films. The relative dielectric constant (?r) of the polar-axis-oriented Pb(Zr0.35Ti0.65)O3 thick film on CaF2 was 180 at 1 kHz, which is lower than that of (100)/(001)-oriented thick films on SrTiO3 but almost agrees with the theoretically calculated value for the c-axis of PZT single crystals. Well saturated polarization-electric-field hysteresis loops with a good square shape were observed for the polar-axis-oriented thick films, and the saturation polarization and the coercive field values were 74 ?C/cm2 and 64 kV/cm, respectively. These data clearly show that the electrical properties of the polar-axis-oriented epitaxial thick films are similar to the theoretical predictions for PZT single crystals.

Fujisawa, Takashi; Nakaki, Hiroshi; Ikariyama, Rikyu; Yamada, Tomoaki; Ishikawa, Mutsuo; Morioka, Hitoshi; Funakubo, Hiroshi

2009-03-01

193

Femtosecond relaxation kinetics of highly excited M_{Na}^{**} states in CaF2 at 3.2 eV and 4.7 eV  

NASA Astrophysics Data System (ADS)

Femtosecond (fs) laser pulses at variable delay times allowed us to track the fast non-radiative transitions between the manifold of highly excited M_{Na}^{**} states to the lower lying fluorescent M_{Na}^{*} state in CaF2. Two distinct M_{Na}^{**} states of the manifold at 3.16 eV (M_{Na2}^{**}) and 4.73 eV (M_{Na3}^{**}) were populated using the second (SH) and third harmonics (TH) of fs laser light at 785 nm. The population kinetics of the fluorescent M_{Na}^{*} state in the 2 eV excitation energy range was revealed by depleting its fluorescence centered at 740 nm using fundamental near infrared (NIR) fs laser pulses. The related time constants for M_{Na2,3}^{**}{˜}{>} M_{Na}^{*} relaxation amounted to 1.0±0.14 ps and 3.0±0.3 ps upon SH and TH excitation, respectively.

Karras, C.; Mühlig, C.; Paa, W.; Zeuner, T.; Triebel, W.; Stafast, H.

2011-07-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

195

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)

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.

Whittenberger, J. D.

1992-01-01

196

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

PubMed

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

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

2014-06-01

197

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

198

Annealing of electron damage in mid-IR transmitting fluoride glass  

NASA Technical Reports Server (NTRS)

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

Bansal, Narottam P.; Doremus, Robert H.

1986-01-01

199

Determination of reaction kinetic parameters from variable temperature DSC or DTA  

Microsoft Academic Search

An equation is derived for evaluating the kinetic parameters of a transformation from variable temperature DSC or DTA, taking account of the variation in the reaction rate constant with time and temperature. Kinetic parameters for the crystallization of a ZrF4-BaF2-LaF3 glass are calculated using this equation.

N. P. Bansal; R. H. Doremus

1984-01-01

200

Determination of the thermo-optic coefficient dn/dT of ytterbium doped ceramics (Sc2O3, Y2O3, Lu2O3, YAG), crystals (YAG, CaF2) and neodymium doped phosphate glass at cryogenic temperature  

NASA Astrophysics Data System (ADS)

In this paper, we report the measurements of the thermal expansion coefficient and the thermo-optic coefficient dn/dT for the ytterbium doped cubic sesquioxides (Sc2O3, Y2O3, Lu2O3) at cryogenic temperature. These materials appear to have very interesting properties for setting up high average power laser chains useful for plasma physics and for inertial fusion energy drivers. Measurements have also been done on YAG ceramic and crystal, CaF2 crystal, and neodymium phosphate glass (Hoya, LHG-8).

Cardinali, V.; Marmois, E.; Le Garrec, B.; Bourdet, G.

2012-04-01

201

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

202

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

NASA Astrophysics Data System (ADS)

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

Huang, Chuanbing; Du, Lingzhong; Zhang, Weigang

2014-02-01

203

Crystallization of heavy metal fluoride glasses  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

204

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber  

NASA Astrophysics Data System (ADS)

We investigated the optical bistability and multistability in an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.

Wang, Zhiping; Yu, Benli; Zhen, Shenglai; Wu, Xuqiang; Zhu, Jun; Cao, Zhigang

2012-03-01

205

High refractive index without absorption in a rare-earth-ion-doped optical fiber  

NASA Astrophysics Data System (ADS)

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

Wang, Zhiping; Yu, Benli

2012-11-01

206

New Process for Fluoride Glass Preform Fabrication Using Chemical Vapor Deposition  

Microsoft Academic Search

A new process for ZrF4-based fluoride glass preform fabrication is proposed. For the first time, ZrF4-based fluoride glass soot (ZrF4-BaF2-LaF3-AIF3) has been prepared by CVD using metal beta-diketonates and hydrogen fluoride gas as starting materials and fluorinating reagent, respectively. The fluoride glass soot has been consolidated into a transparent glass layer with residual closed pores. The new process using CVD

Kazuo Fujiura; Yasutake Ohishi; Shiro Takahashi

1989-01-01

207

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

208

Versatile fluoride substrates for Fe-based superconducting thin films  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

209

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

NASA Astrophysics Data System (ADS)

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

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

1993-03-01

210

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

211

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

PubMed

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

Ode, Aiko

2014-02-01

212

Journal of Luminescence 48 & 49 (1991) 251--254 251 North-Holland  

E-print Network

3 Sd level in a series of cerium doped oxide and fluoride crystals (Ce3~:LaF 3,Ce 3~:CaF 2,Ce 3~:YLi been and continues to The 5d --* 4f fluorescence transitions of cerium be an active area of research processes of ions in solids. We extend the scope of this work excited cerium ions, we have measured

Hamilton, Douglas S.

213

Absorption and fluorescence measurements of DUV/VUV coatings  

NASA Astrophysics Data System (ADS)

The performance of optical coatings for high power DUV/VUV laser applications depends amongst others on residual absorption in the thin film layers due to impurities or defects. Using pulsed F2 laser induced fluorescence measurements (LIF), characteristic non-intrinsic emissions of praseodymium, cerium and hydrocarbons are identified for several high reflecting AlF3/LaF3 based mirrors on CaF2 substrates. The separate investigations of single AlF3 and LaF3 layers on silicon wafers indicate that these emissions result from the LaF3 material. The amount of the impurities, however, varies strongly between different LaF3 material grades. The influence of different LaF3 material grades on the absorption properties of high reflecting mirrors is measured for the first time upon ArF laser irradiation using the laser induced deflection technique (LID). Low absorption values of less than 1*10-3 are obtained for all samples. The absorption, however, varies by more than a factor of 2 which is correlated to the appearance of the praseodymium and cerium emissions in the LIF spectra.

Mühlig, Ch.; Triebel, W.; Bernitzki, H.; Klaus, M.; Bergmann, J.; Kufert, S.; Bublitz, S.

2005-09-01

214

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

PubMed

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

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

2012-05-01

215

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

216

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

217

Effects of Gravity on ZBLAN Glass Crystallization  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

218

Effect of microgravity on crystallization of ZBLAN fibers  

NASA Technical Reports Server (NTRS)

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

Tucker, Dennis S.

1994-01-01

219

Radiation damage studies on new inorganic optical crystals  

Microsoft Academic Search

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

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

1995-01-01

220

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

Microsoft Academic Search

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 (tau=500fs, lambda=1045nm, f=0.1-5MHz) from an Ybfiber laser is focused with a microscope objective in the volume of the glass

D. Esser; D. Wortmann; J. Gottmann

2009-01-01

221

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

NASA Technical Reports Server (NTRS)

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

Stanford, Malcolm K.; DellaCorte, Christopher

2003-01-01

222

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)

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.

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

2014-11-01

223

Identification of hydrogen isotopes with the BaF 2 electromagnetic calorimeter TAPS  

Microsoft Academic Search

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

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

1996-01-01

224

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

E-print Network

of Q=1010 . The laser is fiber- compatible and is fabricated with a very simple technique. We also resonator as a Ra- man laser. This laser operates as a fiber-compatible de- vice with a bidirectional of fluorite is smaller than that of fused-silica, making it possible to use common optical fibers to couple

225

Last advances in Yb3+ doped CaF2 ceramics synthesis  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

226

Synthesis and thermoluminescence characteristics of Mn doped CaF2 nanoparticles  

NASA Astrophysics Data System (ADS)

Nanoparticles of Mn-doped calcium fluoride were synthesized by hydrothermal method. The formation of nanostructures was confirmed by X-ray diffraction (XRD) pattern. The particle size of about 39 nm was calculated from XRD data. Its shape and size were also observed by scanning electron microscope (SEM). Its thermoluminescence (TL) glow curve contains three overlapping glow peaks at around 399, 436 and 494 K. TL of this phosphor was studied for different Mn concentrations and the maximum sensitivity was found at 3 mol% of Mn impurity.

Zahedifar, M.; Sadeghi, E.; Mohebbi, Z.

2012-03-01

227

Morphology and optical properties of Mg and Sr doped CaF2 nanocrystals  

NASA Astrophysics Data System (ADS)

Magnesium (Mg) and Strontium (Sr) doped Calcium fluoride nanocrystals were synthesized by co-precipitation method. The cubic structure of the samples was confirmed by Powder X-ray diffraction. The average crystallite size of Mg doped samples was found to be ~ 25 nm whereas in Sr doped one it was ~ 35 nm. The morphological features revealed that the nanocrystals were agglomerated, crispy and porous. The as-prepared samples showed the presence of hydroxyl groups. The optical absorption spectrum of as-prepared Mg doped samples showed a strong absorption band peaked at ~ 233 nm whereas the Sr doped one showed a prominent absorption peak at 248 nm. A strong PL emission was observed at ~ 300 nm in Mg doped samples. However, the Sr doped samples showed two prominent emissions at ~ 345 and 615 nm.

Pandurangappa, C.; Lakshminarasappa, B. N.

2012-05-01

228

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

NASA Astrophysics Data System (ADS)

The induced colour in single crystals of calcium fluoride irradiated with ?-rays and reactor neutrons have been investigated by optical measurements (absorption and photoluminescence). The optical absorption spectrum increases slightly by increasing ?-rays dose up to 10 6 Gy and absorption bands centred at about 225, 260, 340, 396 and 580 nm are observed. At higher doses, in the case of reactor neutrons irradiation, the absorption spectrum shows a large absorption band centred at about 415 nm and shoulders at 340 nm and 550 nm. This indicates that the absorption bands at 225, 260 and 580 nm are probably saturated at higher doses. Whereas, the band at 396 nm presents both saturation and linearly increasing behaviour. On heating a sample after irradiation, the absorption bands at 225, 260 and 580 nm disappear at 140 °C, and the 396 nm absorption band disappears above 250 °C. Photoluminescence excited with 325 nm photon shows an emission band centred at about 420 nm in the non-irradiated sample. The intensity of such band deceases after irradiation.

Izerrouken, M.; Guerbous, L.; Meftah, A.

2010-09-01

229

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

NASA Astrophysics Data System (ADS)

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%.

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

2012-06-01

230

Simultaneous measurement of (n,?) and (n,fission) cross sections with the DANCE 4? BaF2 array  

NASA Astrophysics Data System (ADS)

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 ?-ray energy and ?-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,?)/(n,fission) cross section ratio measurements can be obtained. The addition of a fission-tagging detector to the DANCE array will also provide a means to study several important issues associated with neutron-induced fission, including (n,fission) cross sections as a function of incident neutron energy, and total energy and multiplicity of prompt fission photons. We have focused on two detector designs with complementary capabilities, a parallel-plate avalanche counter and an array of solar cells.

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

2006-03-01

231

Two Kinds of Cavity Geometry for Enhanced Laser Cooling of Solids  

NASA Astrophysics Data System (ADS)

We present a comparison between intracavity cooling and external cavity cooling for optical refrigeration. The results show that the intracavity scheme is preferred at low optical densities (< 0.008), while the external cavity scheme is preferred at higher optical densities (> 0.01). We can choose the proper scheme for different cases in experiments. Moreover, under the same conditions, taking Yb3+-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) film as an example, the cooling processes of the two scheme are obtained. The calculated results show that intracavity cooling will achieve a larger temperature drop for a thin film sample. Finally, the diode laser may become a candidate for the intracavity model briefly discussed.

Jia, You-Hua; Zhong, Biao; Yin, Jian-Ping

2010-07-01

232

Characterization of optical thin films for applications at 10.6 ?m  

NASA Astrophysics Data System (ADS)

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

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

1990-08-01

233

Fluoride glass starting materials - Characterization and effects of thermal treatment  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

234

Observation of Anti-Stokes Fluorescence Cooling in Thulium-Doped Glass  

NASA Astrophysics Data System (ADS)

We report the first observation of anti-Stokes fluorescence cooling in a thulium-doped solid with pump excitation at 1.82 ?m

Hoyt, C. W.; Sheik-Bahae, M.; Epstein, R. I.; Edwards, B. C.; Anderson, J. E.

2000-10-01

235

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

236

Brillouin Lasing with a CaF2 Whispering Gallery Mode Resonator Ivan S. Grudinin,* Andrey B. Matsko,  

E-print Network

, and Lute Maleki Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive to the crystalline axes. The propagation direction of the electromagnetic wave is given by the following vector: k

237

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

SciTech Connect

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.

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

2012-05-01

238

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

PubMed

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

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

2011-08-01

239

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

E-print Network

Institute, 110 8th Street, Troy, NY 12180, USA c US Army Armament Research, Development and Engineering microbalance (QCM) and were verified through cross-section SEM images (Carl Zeiss Supra SEM 1550

Wang, Gwo-Ching

240

In-situ spectroscopic investigations of surfactant adsorption and water structure at the CaF2/aqueous solution interfacey  

E-print Network

/aqueous solution interfacey Kevin A. Becraft,a Fred G. Mooreb and Geraldine L. Richmond*a a Department stabilization, waste processing, and mineral ore separations via froth flota- tion.1­3 In these and other

Richmond, Geraldine L.

241

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

242

Investigation of the Environmental Durability of a Powder Metallurgy Material  

NASA Technical Reports Server (NTRS)

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.

Ward, LaNita D.

2004-01-01

243

Radiative to Non-Radiative Processes for Luminescence of Eu 2+ Ion in SrF 2 -BaF 2 Mixed Crystals  

NASA Astrophysics Data System (ADS)

The optical properties of blue and yellow luminescence have been investigated for Eu 2+ (4f 7 ) ions doped into mixed crystals or solid solutions Sr 1-x Ba x F 2 (0?x ?1.0), focusing on the thermal relaxation mechanism.The intense blue band observed in Sr-rich crystals exchanges for a yellow one in Ba-rich crystals below 100 K.For varying the mixture ratio, the two bands conserve persistently each quantity of luminescence peak, intensity, half-linewidth, and lifetime.First measurements of the precise lifetime and the thermal activation energy were carried out against the variation of mixture ratio as well as temperature. For the yellow luminescence, it was found that there was a large differencein the decreasing rates between the spectral intensity and the lifetime.A mechanism of energy transfer from blue to yellow luminescence is discussed byapplying the configuration coordinate diagrams.

Kawano, Katsuyasu; Katoh, Kazuo; Nakata, Ryouhei

1997-06-01

244

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

SciTech Connect

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

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

2006-03-13

245

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

PubMed

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

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

2005-09-14

246

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

NASA Technical Reports Server (NTRS)

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

Frey, Bradley J.; Leviton, Douglas B.

2004-01-01

247

Tribological Performance of PM300 Solid Lubricant Bushings for High Temperature Applications  

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

248

Fluorescence and phosphorescence of photomultiplier window materials under electron irradiation  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

249

Ceramic planar waveguide structures for amplifiers and lasers  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

250

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

NASA Technical Reports Server (NTRS)

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

DellaCorte, Chris

1998-01-01

251

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

252

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

NASA Technical Reports Server (NTRS)

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

Dellacorte, C.; Edmonds, B. J.

1995-01-01

253

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

254

High T(sub c) thin film superconductors: Preparation, patterning and characterization  

NASA Astrophysics Data System (ADS)

A conventional oil-pumped vacuum system equipped with resistively heated tungsten boat sources was used for evaporation of bismuth- or yttrium-based cuprates for high T(sub c) thin film superconductors. A well-ground mixture with atomic proportions of bismuth, SrF2, CaF2 and copper for bismuth-based material, and of YF3, BaF2 and copper for yttrium-based material, was inserted into the boat and then resistively evaporated onto different substrates such as MgO, ZrO2 and SrTiO3 kept at room temperature. Yttrium-based thin films were found to have a better quality upon reduction of fluorine in the constituents. Thus, films prepared with an yttrium BaF2 and copper mixture show a metallic-like behavior, sharper transition and higher zero-resistance temperature as compared with that of films obtained by using a YF2 constiuent instead of yttrium. Bismuth-based thin films were found to lose bismuth during heat treatment unless the copper constiuent ended the evaporation process and was subsequently fully oxidized at 400 C. Bismuth-based patterned films were easily obtained by using a lift-off photolithographic method. Typical thickness of the films was measured to be about 0.5 micron after heat treatment.

Azoulay, J.

255

High Power Continuous-Wave Operation and Dynamics of Soliton Mode-Locked ${\\\\rm Yb,Na}{:}{\\\\rm CaF}_{2}$ Lasers at Room Temperature  

Microsoft Academic Search

We report high power continuous-wave (CW) and passively mode-locked lasers with Yb,Na:CaF2 crystal as gain material. A maximum CW output power of 14.5 W was achieved at the absorbed pump power of 22.8 W, corresponding to the slope efficiency of 63.6%. Furthermore, by using a semiconductor saturable absorber mirror, the CW mode-locking operation was achieved. A shortest duration of 175

Wenqi Ge; Lu Chai; Jie Yan; Minglie Hu; Chingyue Wang; Liangbi Su; Hongjun Li; Lihe Zheng; Jun Xu

2011-01-01

256

Charge Reversal Behavior at the CaF2/H2O/SDS Interface as Studied by Vibrational Sum Frequency Spectroscopy  

E-print Network

and separation, waste processing, and petroleum recovery. Introduction The adsorption of surfactants from colloidal stabilization, lubrication, petroleum recovery, waterproofing, waste processing, and mineral ore to the adhesion and aggregation of surfactant molecules at the solid surface. The attraction of aqueous

Richmond, Geraldine L.

257

Experimental observations of temperature effects in the near-field regime of the Casimir-Polder interaction  

E-print Network

We investigate the temperature dependence of the Casimir-Polder interaction in the electrostatic limit. This unusual phenomenon relies on the coupling between a virtual atomic transition and a thermal excitation of surface polariton modes. We first focus on the scenario where a Cs(8P3/2) atom is next to a CaF2 or a BaF2 surface. Our theoretical predictions show a strong temperature dependence of the van der Waals coefficient at experimentally accessible conditions. A series of spectroscopic measurements performed in a specially designed Cs vapour cell containing a CaF2 tube is presented. Our results illustrate the sensitivity of atom surface-interaction experiments to the quality and chemical stability of the surface material and emphasize the need of using more durable materials, such as sapphire. We finally discuss selective reflection experiments on Cs(7D3/2) in an all-sapphire cell that clearly demonstrate a temperature dependent van der Waals coefficient.

de Silans, Thierry Passerat; Maurin, Isabelle; Gorza, Marie Pascale; Segundo, Pedro Chaves de Souza; Ducloy, Martial; Bloch, Daniel

2014-01-01

258

Friction of self-lubricating surfaces by ion beam techniques  

NASA Astrophysics Data System (ADS)

UES, Inc. conducted a research and development program designed to establish conditions for ion implantation/mixing of suitable additives into the surfaces of bulk ceramics and metals for obtaining self-lubricating low friction and wear characteristics. The substrates considered were ZrO2, Al2O3, Si3N4, steel, and Ni-base superalloy. The lubricant additives chosen were BaF2/CaF2Ag, MoS2, WS2, and B2O3. The initial tasks of the program were to synthesis these lubricant compounds by co-implantation of constituent elements if sufficient beams of desired elements were obtained. The final tasks were to investigate high energy (MeV) ion mixing of deposited coatings as well as to investigate ion beam assisted deposition using low energy ion beams. It was shown that MoS2 can be synthesized by co-implantation of Mo(+) and S(+) in ceramic materials with appropriate choice of energies to obtain nearly overlapping depth profiles. The sliding life of DC magnetron sputtered MoS(2) films of thicknesses approximately 7500 A on ceramic materials such as sapphire, Si3N4 and ZrO3 were improved by ten to thousand fold after 2 Mev Ag(+) ion mixing. Ion beam assisted deposition (IBAD) and ion beam mixing were utilized to fabricate self-lubricating coatings of CaF2/Ag and BaF/CaF2/Ag composites.

Bhattacharya, R. S.; Rai, A. K.

1992-05-01

259

Radiation hardening of strengthened optical fibers and development of new fluoride glasses  

NASA Astrophysics Data System (ADS)

Two independent studies were conducted under this contract: (1) Radiation hardening of compressively strengthened optical fibers; (2) Development of new fluoride glasses. In the first study two preform fabrication processes based on phase separable, leachable alkali borosilicate glasses were evaluated for producing radiation hardened fibers. The first process, known as partial leaching, was found to yield low numerical aperture fibers with moderately high attenuation. Ultra-clean glass melting facilities and extensive composition studies would be required to correct these faults. This was beyond the resources of the contract. The second process, known as molecular stuffing, was used to produce alkali-modified high silica glasses doped with cerium oxide as a radiation hardening agent. Radiation damage kinetic tests were run on these glasses by irradiating the samples with 4-40 ns pulses of 15 MeV electrons and observing the absorption spectra for the time range 0.0000001 sec to 0.1 sec following the electron pulses. The results of these tests show that cerium is not effective, within the time range studies, in suppressing the radiation induced absorption for the high silica glasses tested. In the second study, under this contract, glasses in the HfF4-BaF2-LaF3 family were studied. The effects on glass forming of additions including PbF2, CsF, GdF3 and AlF3 glass was studied.

Mohr, R. K.; Simmons, J. H.; Moynihan, C. T.; Barkatt, A.; Hojaji, H.; Williams, C.; Boulos, M. S.; Gbogi, E. O.; Chung, K. H.

1982-04-01

260

Energy transfer and upconversion emission of Er3+/Tb3+/Yb3+ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals under heat treatment  

NASA Astrophysics Data System (ADS)

Transparent glass-ceramics SiO2-AlF3-BaF2-TiO2-LaF3 (SABTL) containing Ba2LaF7 nanocrystals were successfully prepared by heat treatment process through conventional melting method. The crystal size in the glass-ceramics increased gradually under the changing of heat treatment temperatures and times, which was confirmed by the results of XRD, TEM measurements. The intensity of the blue, green and red upconversion luminescence around 490 nm, 525 nm, 546 nm, 657 nm which originate from the transitions 5D4 ? 7FJ (J = 6 and 5) of Tb3+ ions and (2H11/2, 4S3/2, 4F9/2) ? 4I15/2 transitions of Er3+ ions, respectively, were strongly observed after heat treatment under 980 nm laser diode excitation. The intensity of upconversion luminescence was increased gradually with the increase of Yb3+ concentrations and reaches its maximum at 2.5 mol%. The upconversion luminescence and energy transfer process between Tb3+, Yb3+ and Er3+ ions in the glass-ceramics were discussed.

Dan, Ho Kim; Zhou, Dacheng; Wang, Rongfei; Yu, Xue; Jiao, Qing; Yang, Zhengwen; Song, Zhiguo; Qiu, Jianbei

2014-01-01

261

Transport processes in heavy metal fluoride glasses  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

262

Commercial Production of Heavy Metal Fluoride Glass Fiber in Space  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

263

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

264

Microroughness analysis of thin film components for VUV applications  

NASA Astrophysics Data System (ADS)

For the roughness characterization of optical surfaces a new procedure based on the analysis of their power spectral density (PSD) functions has been developed. The method consists of the fitting of the PSD obtained from Atomic Force Microscopy measurements at different scan sizes to mathematical models. With this procedure the micro- structural properties of optical surfaces and coatings can be represented by a reduced set of numbers that correspond to the characteristic parameters of the mathematical models. For optical coatings this method allows a separate study of the influence of the substrate and layers on the overall sample roughness. As an example, the method is applied to MgF2 and LaF3 films for VUV applications. We investigated a set of single layers deposited onto superpolished Caf2, fused silica and Si substrates. The samples were deposited by ion beam sputtering, boat and e- beam evaporation. A comparison of the influence of the substrate on the development of the roughnesses and lateral structures has been performed, as well as a study of the dependence of the roughness properties of the coatings on the deposition process. Complementary investigations of roughness-related scattering consisting of measurements of Total Scatter at 193 nm and 633 nm and calculation of expected scattering based on the theory are presented.

Ferre-Borrull, Josep; Duparre, Angela; Steinert, Joerg; Ristau, Detlev; Quesnel, Etienne

2000-11-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

266

New measurements of (n,?) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4? BaF2 array  

NASA Astrophysics Data System (ADS)

Accurate neutron-induced reaction data are important to many issues in stockpile stewardship, nuclear reactor design and re-certification, nuclear non-proliferation and nuclear forensics. Of particular interest are the production and destruction reactions for all of the major and most of the minor actinides, including both neutron-induced capture and fission. The competition between capture and fission presents both an obstacle and an opportunity for large ? detector arrays such as the DANCE array (Detector for Advanced Neutron Capture Experiments), which cannot clearly differentiate ?-rays resulting from the two exit channels. With the addition of a high efficiency, 4? fission-tagging detector it is possible to deconvolve the two contributions to the total ?-ray spectrum. Using these tools we are able to conduct simultaneous fission/capture measurements which can simplify background treatment and other sources of systematic uncertainty. An outline of the current experimental program will be presented along with results from neutron capture measurements on ^233,235U and ^239Pu.

Bredeweg, T. A.; Jandel, M.; Fowler, M. M.; Bond, E. M.; Haight, R. C.; Keksis, A. L.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Slemmons, A. K.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Becker, J. A.; Wu, C. Y.; Baker, J. D.; McGrath, C. A.

2010-11-01

267

New measurements of (n,?) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4? BaF2 array  

NASA Astrophysics Data System (ADS)

Accurate neutron nuclear data are important to many issues in stockpile stewardship, nuclear reactor design and re-certification, nuclear non-proliferation and nuclear forensics. Of particular interest are the production and destruction reactions for all of the major and most of the minor actinides. The competition between capture and fission in many of the actinides presents both an obstacle and an opportunity for large ? detector arrays such as DANCE. Additional instrumentation is required to deconvolve the two contributions to the total observed ?-ray spectrum. However, conducting a simultaneous measurement can simplify background treatment and other sources of systematic uncertainty. An outline of the current experimental program will be presented along with results from neutron capture measurements on ^233,235U and ^239Pu.

Bredeweg, T. A.; Jandel, M.; Fowler, M. M.; Bond, E. M.; Haight, R. C.; Keksis, A. L.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Becker, J. A.; Parker, W. E.; Wu, C. Y.; Baker, J. D.; McGrath, C. A.

2009-10-01

268

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

269

Numerical analysis of back scattered signal in infrared optical fibers  

NASA Astrophysics Data System (ADS)

M. MukUndaraO Indian Institute of Technology Madras-600 036 V. C. RaVihaiidran and P. Mythill Anna University Madras-600 025 With the increasing use of fluoride fibres tor communication in the infrared region OTDR technique (1) has been extended conceptually for fluoride fibres in the wave length range 1. 5urn - 4urn. OH is found to be the rnajQr contributing factor whose possibility to be monitored by means of an OTDR- are discussed. I NTRODUCT I ON The most exciting prospect for optical fibres made from fluoride glasses is the possibility of prvoldlng long distance optical communication systems without the need for repeaters and amplifiers. ZrF4 baed glasses are pi''ominent in particu I ar 2 rF4-BaF2-LaF3-A I F3-NaF (2BLAN) offer good properties. Considering the various loss mechanisms the outcome is that fluoride based optical fibre exhibits a low loss window at 2. 53 urn with a theoritical minimum loss approaching 0. 04 dB/KM. Fluoride fibres can transmit both infrared and visibie light. They have many applications outside the field of telecommunications including opticai fibres sensors in remote infrared Spectroscopy'' iaser s''rgerv and ribre 119 lasers. Fluoride glass fibres have high transition temperature and refractive indices conpared to silica glass fibres. the of fluorides is that they have a high rate of crystallization which complicates the fibre fabrication process. The reported minimum loss has remained unchanged iP the 2. 5 pm windiw region

Rao, Mandavilli M.; Ravichandran, Chenniappan; Mythili, P.

1992-12-01

270

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

E-print Network

the large thermal expansion mismatch between PbSe, PbEuSe, and Si.3,4 Such heteroepitaxial growth offers-type carrier concentrations were controlled by adjusting the crystal stoichiometry.3 Since the resulting va diffusion coefficient but it produces a less deep acceptor level for high-energy bandgap alloys thus

McCann, Patrick

271

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

SciTech Connect

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

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

2011-08-18

272

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

NASA Technical Reports Server (NTRS)

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

Dellacorte, Christopher

1988-01-01

273

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

NASA Technical Reports Server (NTRS)

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

DellaCorte, Christopher; Valco, Mark J.

1999-01-01

274

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

275

Mesoscopic fast ion conduction in nanometre-scale planar heterostructures  

NASA Astrophysics Data System (ADS)

Ion conduction is of prime importance for solid-state reactions in ionic systems, and for devices such as high-temperature batteries and fuel cells, chemical filters and sensors. Ionic conductivity in solid electrolytes can be improved by dissolving appropriate impurities into the structure or by introducing interfaces that cause the redistribution of ions in the space-charge regions. Heterojunctions in two-phase systems should be particularly efficient at improving ionic conduction, and a qualitatively different conductivity behaviour is expected when interface spacing is comparable to or smaller than the width of the space-charge regions in comparatively large crystals. Here we report the preparation, by molecular-beam epitaxy, of defined heterolayered films composed of CaF2 and BaF2 that exhibit ionic conductivity (parallel to the interfaces) increasing proportionally with interface density-for interfacial spacing greater than 50 nanometres. The results are in excellent agreement with semi-infinite space-charge calculations, assuming a redistribution of fluoride ions at the interfaces. If the spacing is reduced further, the boundary zones overlap and the predicted mesoscopic size effect is observed. At this point, the single layers lose their individuality and an artificial ionically conducting material with anomalous transport properties is generated. Our results should lead to fundamental insight into ionic contact processes and to tailored ionic conductors of potential relevance for medium-temperature applications.

Sata, N.; Eberman, K.; Eberl, K.; Maier, J.

2000-12-01

276

Mesoscopic fast ion conduction in nanometre-scale planar heterostructures.  

PubMed

Ion conduction is of prime importance for solid-state reactions in ionic systems, and for devices such as high-temperature batteries and fuel cells, chemical filters and sensors. Ionic conductivity in solid electrolytes can be improved by dissolving appropriate impurities into the structure or by introducing interfaces that cause the redistribution of ions in the space-charge regions. Heterojunctions in two-phase systems should be particularly efficient at improving ionic conduction, and a qualitatively different conductivity behaviour is expected when interface spacing is comparable to or smaller than the width of the space-charge regions in comparatively large crystals. Here we report the preparation, by molecular-beam epitaxy, of defined heterolayered films composed of CaF2 and BaF2 that exhibit ionic conductivity (parallel to the interfaces) increasing proportionally with interface density--for interfacial spacing greater than 50 nanometres. The results are in excellent agreement with semi-infinite space-charge calculations, assuming a redistribution of fluoride ions at the interfaces. If the spacing is reduced further, the boundary zones overlap and the predicted mesoscopic size effect is observed. At this point, the single layers lose their individuality and an artificial ionically conducting material with anomalous transport properties is generated. Our results should lead to fundamental insight into ionic contact processes and to tailored ionic conductors of potential relevance for medium-temperature applications. PMID:11140675

Sata, N; Eberman, K; Eberl, K; Maier, J

277

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

278

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

PubMed

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

Gallais, Laurent; Commandré, Mireille

2014-02-01

279

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

281

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

NASA Technical Reports Server (NTRS)

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

Stanford, M. K.; DellaCorte, C.

2004-01-01

282

Analytica Chimica Acta 437 (2001) 183190 Re-activation of an all solid state oxygen sensor  

E-print Network

Analytica Chimica Acta 437 (2001) 183­190 Re-activation of an all solid state oxygen sensor W/SiO2/Si3N4/LaF3/Pt can be used as a potentiometric oxygen sensor working at room temperature. A thermal. Keywords: Chemical sensor; Thermal treatment; Activation; LaF3; Pt 1. Introduction There are several oxygen

Moritz, Werner

283

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

284

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

285

Picosecond passively mode-locked mid-infrared fiber laser  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

286

Single mode optical fiber based devices and systems for mid-infrared light generation, communication and metrology  

NASA Astrophysics Data System (ADS)

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.

Kulkarni, Ojas P.

287

Synthesis and evaluation of rare-earth doped glasses and crystals for optical refrigeration  

NASA Astrophysics Data System (ADS)

This research focused on developing and characterizing rare-earth doped, solid-state materials for laser cooling. In particular, the work targeted the optimization of the lasercooling efficiency in Yb3+ and Tm3+ doped fluorides. The first instance of laser-induced cooling in a Tm3+-doped crystal, BaY2F8 was reported. Cooling by 3 degrees Kelvin below ambient temperature was obtained in a single-pass pump geometry at lambda = 1855 nm. Protocols were developed for materials synthesis and purification which can be applied to each component of ZBLANI:Yb 3+/Tm3+ (ZrF4 -- BaF2 -- LaF3 -- AlF3 -- NaF -- InF3: YbF3/TmF3) glass to enable a material with significantly reduced transition-metal impurities. A method for OH- impurity removal and ultra-drying of the metal fluorides was also improved upon. Several characterization tools were used to quantitatively and qualitatively verify purity, including inductively-coupled plasma mass spectrometry (ICP-MS). Here we found a more than 600-fold reduction in transition-metal impurities in a ZrCl2O solution. A non-contact spectroscopic technique for the measurement of laser-induced temperature changes in solids was developed. Two-band differential luminescence thermometry (TBDLT) achieved a sensitivity of ˜7 mK and enabled precise measurement of the zero-crossing temperature and net quantum efficiency. Several Yb3+-doped ZBLANI glasses fabricated from precursors of varying purity and by different processes were analyzed in detail by TBDLT. Laser-induced cooling was observed at room temperature for several of the materials. A net quantum efficiency of 97.39+/-0.01% at 238 K was found for the best ZBLANI:1%Yb 3+ laser-cooling sample produced from purified metal-fluoride precursors, and proved competitive with the best commercially procured material. The TBDLT technique enabled rapid and sensitive benchmarking of laser-cooling materials and provided critical feedback to the development and optimization of high-performance optical cryocooler materials. Also presented is an efficient and numerically stable method to calculate time-dependent, laser-induced temperature distributions in solids, including a detailed description of the computational procedure and its implementation. The model accurately predicted the zero-crossing temperature, the net quantum efficiency, and the functional shape of the transients, based on input parameters such as luminescence spectra, dopant concentration, pump properties, and several well-characterized material properties.

Patterson, Wendy

288

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

NASA Astrophysics Data System (ADS)

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

Kumar, Malay

289

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

NASA Technical Reports Server (NTRS)

Heavy metal fluoride glasses are used in such applications as fiber lasers and laser amplifiers. ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is one of the more commonly used heavy metal fluoride glasses. ZBLAN is an infrared transmitter and has a theoretical attenuation coefficient of 0.002 db/km. However, due to impurities and small crystallites this attenuation coefficient has not been achieved to date. ZBLAN is a fragile glass which can lead to rapid crystallization, if the glass is not cooled rapidly to below the glass transition temperature or if the glass is reheated near the crystallization temperature for any period of time. Studies carried on at Marshall Space Flight Center and the University of Alabama in Huntsville since 1993 have shown that heating ZBLAN glass at the crystallization temperature in reduced gravity results in a suppression of crystallization when compared to ZBLAN processed in unit gravity. These studies utilized NASA's KC-135 aircraft and the Conquest sounding rocket. In the first series of experiments, short lengths of ZBLAN fiber were heated to the crystallization temperature in reduced gravity on board the KC- 135 and the Conquest sounding rocket and compared with fibers heated in unit gravity. The fibers processed in reduced gravity showed no evidence of crystallization when studied with x-ray diffraction and scanning electron microscopy. However, the fibers processed in unit gravity were completely crystallized. Subsequent experiments included heating small pieces of ZBLAN glass at the crystallization temperature while viewing with a video camera to follow the crystallization phenomenon. In this experiment crystallization was observed in reduced gravity, however, it was suppressed when compared to heating in unit gravity. In the most recent experiment on board the KC-135, rapid thermal analysis of ZBLAN was performed. A mechanism to explain the observations has been proposed. This mechanism is based on shear thinning whereby, the glass undergoes a reduction in viscosity in the 10(exp 5) - 10(exp 7) poise range, allowing more rapid diffusion and thus crystallization. It is proposed that this mechanism is suppressed in reduced gravity. An experiment is presently being conducted to test this theory. With increased knowledge of ZBLAN behavior in reduced gravity, three low earth orbit tiber drawing facilities have been designed. One would be suitable for use on the International Space Station, another while aboard the Space Shuttle and the third system is a fully automated facility which would operate independently of the ISS or Shuttle in a free float mode. The primary benefits of free floating a facility in LEO includes a higher quality of microgravity and reduced safety concerns since it is not in a manned environment.

Tucker, Dennis S.; Smith, Guy A.

2004-01-01

290

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

NASA Astrophysics Data System (ADS)

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

Dejneka, Matthew J.

1995-01-01

291

A fluorocarbon plastic scintillator for neutron detection: Proof of concept  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

292

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

293

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

294

Insulators for Pb(1-x)Sn(x)Te  

NASA Technical Reports Server (NTRS)

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

Tsuo, Y. H.; Sher, A.

1981-01-01

295

Deep UV laser induced fluorescence in fluoride thin films  

NASA Astrophysics Data System (ADS)

Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF3, AlF3, and MgF2. Spectral- and time-resolved measurements reveal the presence of cerium in LaF3 and the influence of hydrocarbons in MgF2 and LaF3. Virtually no fluorescence response is observable in the case of AlF3. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF3. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra.

Heber, J.; Mühlig, C.; Triebel, W.; Danz, N.; Thielsch, R.; Kaiser, N.

296

New infrared detectors and solar cells  

NASA Technical Reports Server (NTRS)

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

Sher, A.

1979-01-01

297

Broadband reflectance coatings for vacuum ultraviolet application  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

298

Broadband reflectance coatings for vacuum ultraviolet application  

NASA Astrophysics Data System (ADS)

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

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

1987-02-01

299

Sensors and Actuators B 49 (1998) 133138 High temperature semiconductor sensor for the detection of  

E-print Network

of fluorine up to 350°C. The use of the structure SiC/SiO2/LaF3/Pt at room temperature leads to results of a single crystal of LaF3 coated with a platinum film to get an all solid state potentiometric device for the determination of fluorine. Drawbacks of this sensor are the high price of the single crystal and the formation

Moritz, Werner

300

Preparation and Properties of Nano-sized Calcium Fluoride for Dental Applications  

PubMed Central

Objectives The aim of the present study was to prepare nano-sized calcium fluoride (CaF2) that could be used as a labile F reservoir for more effective F regimens and as an agent for use in the reduction of dentin permeability. Methods Nano-sized CaF2 powders were prepared using a spray-drying system with a two-liquid nozzle. The properties of the nano CaF2 were studied and the effectiveness of a fluoride (F) rinse with nano CaF2 as the F source was evaluated. The thermodynamic solubility product of the nano CaF2 solution was determined by equilibrating the nano sample in solutions presaturated with respect to macro CaF2. Reactivity of the nano CaF2 was assessed by its reaction with dicalcium phosphate dehydrate (DCPD). F deposition by 13.2 mmol/L F rinse with the nano CaF2 as the F source was determined using a previously published in vitro model. Results X-ray diffraction (XRD) analysis showed pattern of low crystalline CaF2. BET measurements showed that the nano CaF2 had a surface area of 46.3 m2/g, corresponding to a particle size of 41 nm. Transmission Electron Microscopy (TEM) examinations indicated that the nano CaF2 contained clusters comprising particles of (10 to 15) nm in size. The nano CaF2 displayed much higher solubility and reactivity than its macro counterpart. The CaF2 ion activity product (IAP) of the solution in equilibrium with the nano CaF2 was (1.52 ± 0.05) × 10-10, which was nearly four times greater than the Ksp (3.9 × 10-11) for CaF2. The reaction of DCPD with nano CaF2 resulted in more F-containing apatitic materials compared to the reaction with macro CaF2. The F deposition by the nano CaF2 rinse was (2.2 ± 0.3) ?g/cm2 (n = 5), which was significantly (p < 0.001) greater than that ((0.31 ± 0.06) ?g/cm2) produced by the NaF solution. Significance The nano CaF2 can be used as an effective anticaries agent in increasing the labile F concentration in oral fluid and thus enhance the tooth remineralization. It can also be very useful in the treatment for the reduction of dentin permeability. PMID:17481724

Sun, Limin; Chow, Laurence C.

2008-01-01

301

Light yield and surface treatment of barium fluoride crystals  

Microsoft Academic Search

We report on a study of the light yield and surface treatment of barium fluoride (BaF2) scintillation crystals. Using a bialkali photocathode the photoelectron (p.e.) yield of BaF2 crystals was measured to be 130 p.e.\\/MeV for the fast components and 700 p.e.\\/MeV for the slow component. A somewhat hygroscopic nature for the BaF2 is found. Teflon film was found to

Z. Y. Wei; R. Y. Zhu; H. Newman; Z. W. Yin

1991-01-01

302

Superconductivity for Electric Systems Annual Peer Review Washington, DC July 27-29, 2004 University of Wisconsin-Madison  

E-print Network

presenting at DOE annual review. AFOSR MURINIST-G Phase Relations BaF2 process PVD BaF2 LANL UW AMSC ORNL MOD: 400 A/cm-w (Jc = 3.3 - 2.4 MA/cm2) with film thickness 1.2-1.7 µm on an AMSC RABiTSTM template. #12

303

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films.  

PubMed

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

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

2012-01-01

304

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films  

PubMed Central

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

2012-01-01

305

Optical Characteristic Improvement of Neodymium-Doped Lanthanum Fluoride Thin Films Grown by Pulsed Laser Deposition for Vacuum Ultraviolet Application  

NASA Astrophysics Data System (ADS)

Neodymium-doped lanthanum fluoride (Nd3+:LaF3) thin films were successfully grown on MgF2(001) substrates by pulsed laser deposition. Photoluminescence spectra revealed a dominant peak at 173 nm with a decay time of 7.8 ns, which is similar to the results obtained from a bulk Nd3+:LaF3 crystal. Improvements in crystalline quality and vacuum ultraviolet (VUV) luminescence quantum efficiency were achieved by substrate heating, with optimum results being obtained at 400 °C. These results would open up possibilities in the development of a light-emitting device operating in the VUV region.

Ieda, Mirai; Ishimaru, Tatsuya; Ono, Shingo; Yamanoi, Kohei; Cadatal-Raduban, Marilou; Shimizu, Toshihiko; Sarukura, Nobuhiko; Fukuda, Kentaro; Suyama, Toshihisa; Yokota, Yuui; Yanagida, Takayuki; Yoshikawa, Akira

2012-02-01

306

COMPARATIVE MEDICINE LABORATORY ANIMAL FACILITIES  

E-print Network

OF GLASS 1. PURPOSE: This SOP outlines the proper procedure for disposal of glass waste. 2. SCOPE: This SOP applies to all Research staff and LAF staff disposing of glass waste in the LAF. 3. PROCEDURE: a. Glass waste should be disposed of in Glass Disposal Boxes. Glass Disposal Boxes can be obtained from Fisher

Krovi, Venkat

307

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

308

Optical properties of lead-free oxyfluoride germanate glasses doped with Pr3+  

NASA Astrophysics Data System (ADS)

Optical properties of Pr3+ ions in lead-free germanate glasses modified by BaF2 were investigated. Luminescence bands related to 3P0 ? 3H4, 3P0 ? 3H5, 1D2 ? 3H4, 3P0 ? 3H6, 3P0 ? 3F2 transitions of Pr3+ were registered under 450 nm excitation. The relative integrated luminescence intensities of 3P0 ? 3H4 transition (blue) to the 3P0 ? 3F2 transition (red) of Pr3+ ions strongly depend on fluoride modifier BaF2 in glass composition. The blue-to-red luminescence intensity ratios of Pr3+ are drastically reduced, when BaO is partially substituted by BaF2. The luminescence lines due to 3P0 ? 3F2 hypersensitive transition of Pr3+ are blue shifted with increasing BaF2 concentration.

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

2014-05-01

309

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

310

Radiation damage of a barium fluoride scintillator induced with 1 GeV proton irradiation  

Microsoft Academic Search

Radiation damage effects both in the optical transmission and in the fast luminescence component light output due to 1 GeV proton irradiation in a BaF2 crystal scintillator were measured. It was found that the induced light absorption in a BaF2 crystal due to the proton radiation damage is remarkably dependent on the dose accumulation rate. Also, the obtained results show

D. M. Seliverstov; A. I. Shchetkovsky; V. V. Yanovsky

1993-01-01

311

Third-Order Elastic Moduli of Barium Fluoride  

Microsoft Academic Search

The complete set of the six third-order elastic moduli for BaF2 was determined from the change in the sound velocity under hydrostatic and uniaxial pressure. The third-order elastic moduli for BaF2 were found to be nonisotropic, although the second-order moduli are isotropic. The Grueneisen-mode gamma's and their low- and high-temperature limit were calculated from the third-order elastic moduli, as well

D. Gerlich

1968-01-01

312

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

NASA Astrophysics Data System (ADS)

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

Yuan, Haojie

1992-09-01

313

The investigation of fast neutron Threshold Activation Detectors (TAD)  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

314

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

315

Raman scattering efficiency of graphene  

NASA Astrophysics Data System (ADS)

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 ˜200×10-5 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.

Klar, P.; Lidorikis, E.; Eckmann, A.; Verzhbitskiy, I. A.; Ferrari, A. C.; Casiraghi, C.

2013-05-01

316

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

PubMed

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

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

2013-07-01

317

A First-Passage Time Approach to Diffusion in Liquids and Superionic Conductors  

Microsoft Academic Search

As a new tool to investigate single-particle motion in condensed matter, a first-passage time (FPT) approach to diffusion is developed and applied to the molecular dynamics simulations of simple liquids and superionic conductor CaF2. It is shown that a continuous diffusion model reproduces the observed FPT distribution quite well for both liquids and CaF2, which enables us to evaluate diffusion

Yutaka Kaneko; Toyonori Munakata

1994-01-01

318

Detection and Quantification of Calcium Fluoride Using Micro-Raman Spectroscopy  

Microsoft Academic Search

Investigations on the caries-preventive effect of calcium fluoride have been seriously hampered by the lack of adequate detection techniques. In this paper, the micro-Raman technique is introduced as a suitable method for CaF2 quantification with a spot size typically 5 ?m. Advantages of this measuring technique and associated problems are described for CaF2 determination in the presence of large amounts

H. Tsuda; J. Arends

1993-01-01

319

Role of ultrathin metal fluoride layer in organic photovoltaic cells: mechanism of efficiency and lifetime enhancement.  

PubMed

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

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

320

New approaches to epitaxy of transition metals and rare earths - Heteroepitaxy on lattice-matched buffer films on semiconductors  

NASA Astrophysics Data System (ADS)

Examples of new approaches to epitaxy of magnetic transiton metals and rare earths are described. Epitaxy of bcc Fe on lattice-matched In(x)Ga(1-x)As films is accompanied by an interfacial reaction. This is indicative of a more general problem of instability of interfaces between Ni, Fe, Co, and compound semiconductors. Such reactions can be avoided if an intermediate epitaxial film of Ag is interposed between the semiconductor and the Fe. However, this results in long-range coherency strain and tilted epitaxy of Fe. Epitaxial growth of the rare-earth metal Dy onto epitaxial films of LaF3 on GaAs(-1 -1 -1) is described, and the magnetic properties of epitaxial sandwich structures of LaF3/Dy/LaF3 are summarized.

Farrow, R. F. C.; Parkin, S. S. P.; Speriosu, V. S.

1988-11-01

321

Investigation of the absorption induced damage in ultraviolet dielectric thin films  

NASA Astrophysics Data System (ADS)

The interaction of UV laser radiation with optical coatings is investigated by a pulsed two-probe-beam photothermal technique. UV laser damage resistance studies on LaF3/MgF2, Al2O3/SiO2, HfO2/SiO2 multilayer stacks are performed at (lambda) equals 248 nm and (tau) equals 20 ns. By investigating the relationship of the number of high-low (HL) pairs and the substrate material, optical and thermal coating properties are shown to be responsible for UV single-shot laser damage. The damage threshold of selected samples is influenced by the deposition technique. The influence of the bandgap energy of typical UV thin film oxide materials on the damage is investigated. Furthermore, multishot damage measurements on LaF3/MgF2 high-reflection multilayer coatings reveal the accumulation of laser energy in the predamage range and lead to an increase in absorption.

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

1997-02-01

322

Laser induced fluorescence and absorption measurements for DUV optical thin film characterization  

NASA Astrophysics Data System (ADS)

Residual absorption in optical thin films due to impurities or defects causes thermal lens formation upon high power DUV laser irradiation. Furthermore, it may be one reason for functional degradation during prolonged laser irradiation. Pulsed ArF laser induced fluorescence (LIF) and direct absorption measurements (LID technique) are applied to investigate high reflecting coatings made from LaF3, MgF2 and AlF3 with respect to the influence of different raw materials and deposition temperatures. LIF measurements reveal emission bands that are partially attributed to certain impurities or defects which either origin from the raw material or the coating process. In addition, LIF measurements of single MgF2 and LaF3 layers are performed to investigate different raw material qualities and coating processes. The experimental results show the potential of both techniques for sensitive accompanying of coating process development.

Mühlig, Ch.; Triebel, W.; Kufert, S.; Bublitz, S.

2008-09-01

323

UV-laser investigation of dielectric thin films  

NASA Astrophysics Data System (ADS)

Utilizing thermal Mirage technique, UV laser damage resistivity studies on LaF3/MgF2, Al2O3/SiO2, and HfO2/SiO2 multilayer stacks have been performed at (lambda) equals 248 nm, (tau) equals 20 ns. Investigating these stacks by changing the number of (HL) pairs and the substrate material, optical and thermal coating properties were shown to be responsible for UV single-shot laser damage. Similarly, the damage threshold of selected samples is to be influenced by the deposition technique. Furthermore, multishot damage measurements on LaF3/MgF2 high-reflecting multilayer coatings reveal the accumulation of laser energy in the predamage range.

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

1996-05-01

324

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

PubMed

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

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

2010-10-01

325

The assay of 228Ra in biological material.  

PubMed

Some aspects of possible interference in the assay of 228Ra in biological samples were investigated. 228Ra is determined, after coprecipitation with BaSO4, by counting its daughter 228Ac carried on LaF3, due corrections being made for Ba and La recoveries. Tracer studies with 133Ba, 45Ca, 89Sr, 91Y and 234Th, under assay conditions, showed that (i) the small amount (5 mg) of Ba carrier is recovered nearly quantitatively after complete separation from large amounts of Ca (30-480 mg) which if precipitated with Ba would distort the results by falsely high Ba recoveries, (ii) fall-out Sr and Y, as well as natural Th, would not interfere in the assay and (iii) LaF3, in the amounts involved in the assay, produces negligible self-absorption but would enhance the 228Ac activity by as much as about 18% due to scattering. PMID:6480146

Kshirsagar, S G

1984-09-01

326

Development of mechanical stress in fluoride multilayers for UV applications  

NASA Astrophysics Data System (ADS)

Since excimer laser applications extend to deep and vacuum UV wavelengths at 193 nm and 157 nm, renewed research interest has recently arisen on fluoride thin films due to their unrivaled position as wide-band-gap material for the vacuum UV (VUV). In order to evaluate the development of mechanical stress in all dielectric fluoride mirrors which causes difficulties to grow the layer stacks on fused silica substrates with a sufficient large number of quarter-wave pairs of a low (L) and of a high index (H) fluoride material, a systematic study was performed on evaporated quarter-wave stacks of LaF3/MgF2 and LaF3/AlF3 with a growing number of LH-pairs. The samples deposited onto fused silica and silicon substrates by a low-loss evaporation technology in a BAK 640 coating plant were investigated by means of complex ex - situ mechanical stress analysis including temperature dependence of stress, optical measurements, infrared measurements, evaluation of structural and morphological parameters by AFM and XRD. When deposited at high substrate temperature of about 300°C, the LaF3/MgF2 tends show high tensile stress due to the thermal stress component arise from the large thermal expansion coefficient difference between the substrate and the film materials resulting in micro crack formation already starting after deposition of about 10 layer pairs. LaF3/AlF3 appear to have a larger crack resistance due to lower stress which can be correlated to the higher water content in these kind of stacks. By adjusting the deposition temperature, mirror stacks with high reflectance at 193nm can be grown.

Thielsch, Roland; Heber, Joerg; Uhlig, Hein; Kaiser, Norbert

2004-02-01

327

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

E-print Network

suggested for modifying an oxygen sensor [4] using a MIS structure Si/SiO2/Si3N4/ LaF3/Pt for the detection sensor W. Moritz *, L. Bartholoma¨us Walther-Nernst-Institute, Humboldt Uni6ersity Berlin, Bunsenstra�e 1. Depending on the preparation, two different sensor types were investigated having advantages at low or high

Moritz, Werner

328

Investigation into nanostructured lanthanum halides and CeBr3 for nuclear radiation detection  

Microsoft Academic Search

Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and cerium bromide (CeBr3) without requiring the growth of large crystals. Nanostructured detectors may allow us to engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to

Paul Guss; Ronald Guise; Sanjoy Mukhopadhyay; Ding Yuan

2011-01-01

329

The ion-assisted deposition of optical thin films  

NASA Astrophysics Data System (ADS)

The columnar microstructure of most thermally evaporated thin films detrimentally affects many of their properties through a reduction in packing density. In this work, we have investigated ion-assisted deposition as a means of disrupting this columnar growth for a number of coating materials. A Kaufman hot-cathode ion source bombarded thermally evaporated films with low-energy (less than 1000 eV) positive ions during deposition in a cryopumped box coater. We have investigated MgF2, Na3AIF6, AIF3, LaF3, CeF3, NdF3, Al2O3, and AlN. Argon ion bombardment of the fluoride coatings increased their packing densities dramatically. We achieved packing densities near unity without significant absorption for MgF2, LaF3, and NdF3, while Na3AlF6, AlF3, and CeF3 began to absorb before unity packing density could be achieved. Fluorine was preferentially sputtered by the ion bombardment, creating anion vacancies. The films adsorbed water vapor and hydroxyl radicals from the residual chamber atmosphere. These filled the vacancy sites, eliminating absorption in the visible, but the oxygen complexes caused increased absorption in the ultraviolet. For LaF3 and NdF3, a sufficient amount of oxygen caused a phase transformation from the fluoride phase to an oxyfluoride phase.

Targove, James D.

330

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

SciTech Connect

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

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

2001-01-01

331

Toward an athermal HEL optical window: Is oxyfluoride glass the way to go?  

NASA Astrophysics Data System (ADS)

Recently, a new glass composition - oxyfluoride glass (OFGTM) - has been promoted as an ideal solution of the Airborne Laser (ABL) window problem in the sense that it will allow obtaining large "athermal" windows for high-energy lasers (HEL) operating at the chemical oxygen-iodine laser (COIL) wavelength [K. Billman, et al., Proc. SPIE 5647, 207 (2005)]. In this context, we emphazise that the performance of a laser-window material candidate must be assessed not only in terms of its ability to transmit high-power beams without generating undue optical distortion but also in terms of the constraints imposed by stress-related failure modes. Here, we provide the tools to carry out an analysis of both pressure- and beam-induced stresses, in addition to thermally induced aberrations, and illustrate the procedure through model windows made of (111)-oriented CaF2, fusion-cast CaF2, and OFGTM glass. Regarding OFG, we find that (a) this material will be vulnerable to surface compressive stresses on account of its poor thermal conductivity; (b) the stress-birefringence contribution to optical distortions cannot be ignored, which rules out creating a zero-distortion ABL window; and (c) based on Strehl ratios, and in the absence of stress-driven failure modes, OFG outperforms Si02 but does not match the performance of fusion-cast CaF2. Regarding CaF2, we find that (a) fusion-cast CaF2 exhibits substantial stress-induced birefringence, which prohibits using this material if depolarization is an issue; (b) highly-oriented (111)CaF2 exhibits no stress-birefringence at the COIL wavelength, in accord with previous investigations at HF/DF frequencies; and (c) in principle, (111) CaF2 windows may transmit aberration-free beam fluences in the 1-MJ/cm2 range but will require improvements in strength to achieve reliable designs.

Klein, Claude A.

2005-12-01

332

Nanocrystallization in Fluorochlorozirconate Glass-Ceramics  

PubMed Central

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

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

2014-01-01

333

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

NASA Astrophysics Data System (ADS)

Optical properties of Tm3+-doped SiO2-BaF2-ZnF2 glasses have been investigated on the basis of the Judd-Ofelt theory. Judd-Ofelt intensity parameters, radiative transition probabilities, fluorescence branching ratios and radiative lifetimes have been calculated for different glass compositions. Upconversion emissions were observed in Tm3+/Yb3+-codoped SiO2-BaF2-ZnF2 glasses under 980 nm excitation. The effects of composition, concentration of the doping ions, temperature, and excitation pump power on the upconversion emissions were also systematically studied.

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

2014-01-01

334

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

PubMed

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

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

2013-01-01

335

Low temperature epitaxial growth of Ge on cube- textured Ni  

SciTech Connect

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

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

2012-01-01

336

A microscopic model for long-term laser damage in calcium fluoride  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is an important lens material in deep-ultraviolet optics, where it is exposed to high radiation densities. The known rapid damage process in CaF2 upon ArF laser irradiation cannot account for irreversible damage after long irradiation times. We use density functional methods to calculate the properties of laser-induced point defects and to investigate defect stabilization mechanisms on a microscopic level. The mobility of the point defects plays a major role in the defect stabilization mechanisms. Besides stabilization by impurities, we find that the agglomeration of F-centers plays a significant role in long-term laser damage of CaF2. We present calculations on the stability of defect structures and the diffusion properties of the point defects.

Rix, Stephan; Natura, Ute; Letz, Martin; Felser, Claudia; Parthier, Lutz

2009-10-01

337

Quantification of fluorite mass-content in powdered ores using a Laser-Induced Breakdown Spectroscopy method based on the detection of minor elements and CaF molecular bands  

NASA Astrophysics Data System (ADS)

Laser Induced Breakdown Spectroscopy (LIBS) is investigated as a fast and robust method to determine the fluorite (CaF2) mass-content of powdered ore samples. Calibrating samples covering a wide CaF2 concentration range (from 2.3 to 97.6%) are employed. LIBS operating conditions are optimized for the analysis of elemental emission lines and molecular bands, respectively. In particular, LIBS emission intensities from different CaF molecular bands are evaluated to calibrate the fluorite concentration as an alternative to the use of atomic fluorine F I emission lines. Furthermore, the determination of LIBS emission signals from minor elements (e.g. Si I and Mg I) is studied to further improve the accuracy and precision of pure fluorite sample analyses (e.g. [CaF2] > 75%). The proposed LIBS method avoids the tedious dissolution processes that are required by other analytical methods employed in mining industry for the quantitative analysis of fluorite.

Álvarez, C.; Pisonero, J.; Bordel, N.

2014-10-01

338

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

PubMed

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

Liu, Wei-Ting; Li, Kung-Cheh

2011-01-01

339

Z-scan measurements of the anisotropy of nonlinear refraction and absorption in crystals  

Microsoft Academic Search

We introduce a method for measuring the anisotropy of nonlinear absorption and nonlinear refraction in crystals by incorporating a wave plate into the Z-scan apparatus. We demonstrate this method by measuring the polarization dependence of the nonlinear refractive index or two-photon absorption coefficient in BaF2, KTP, and GaAs at wavelengths of 532 and 1064 nm.

R. Desalvo; Mansoor Sheik-Bahae; A. A. Said; David J. Hagan; Eric W. van Stryland

1993-01-01

340

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

NASA Astrophysics Data System (ADS)

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

Ullmann, J. L.

2014-09-01

341

Characterization of High-OD Ultrathin Infrared Neutral Density Filters Simon G. Kaplan, Leonard M. Hanssen, Alan L. Migdall, and Glenn LefeverButtont  

E-print Network

Characterization of High-OD Ultrathin Infrared Neutral Density Filters Simon G. Kaplan, Leonard M of the uncertainties in the transmittance values in both types of systems. Keywords: neutral-density filter, infrared include doped glass filters for the near infrared, or BaF2 crystalline filters for the 9 j.m to 1 1 j.tm C

Migdall, Alan

342

Hyperfine Interact (2013) 222:103108 DOI 10.1007/s10751-012-0663-y  

E-print Network

In and 181 Hf. Keywords TDPAC · Digital signal processing · Nuclear methods · Linux 1 Introduction Building signals from four BaF2 detectors are digitized by Agilent Acqiris U1071A digitizers [6], which feature distribution amplifier, sent to the external MCX input of each card. Each digitizer is housed in a dedicated PC

Ryan, Dominic

343

JOURNAL DE PHYSIQUE Colloque C9, supplin?ent au no 1 1-12, Tome 34, Nooetnbre-Dkcembre 1973, page C9-507 COLOR CENTERS IN SrCI,  

E-print Network

fairly extensively at the group of alkaline earth fluorides CaF,, SrF, and BaF2. Because some'--content is increased further also radiation damage can be observed at temperatures as high as 140 K crystals are reported. In additively colored crystals F-centers could be obtained only after extremely

Paris-Sud XI, Université de

344

High energy photon emission  

E-print Network

The primary goal of this work was to initiate the use of BaF 2 arrays for detection of high energy photon emission from nuclear reactions. A beam from the Texas A&M University K-500 Superconducting Cyclotron, and a variety of detectors for hard...

Jabs, Harry

2012-06-07

345

Collaboration Recoil Polarisation Observables in  

E-print Network

Glazier, D. Watts University of Edinburgh and the Crystal Ball at MAMI collaboration #12;Beam chambers, PID scintillator barrel) s TAPS 384 BaF2 detectors Forward 21 degrees Crystal Ball 672 Na bremsstrahlung photons up to 1.4GeV Glasgow Tagger Target inside ball #12;OGL section of Crystal BAll, PID

Edinburgh, University of

346

Equilibrium : ConcFromKsp (8 Variations)  

NSDL National Science Digital Library

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

347

Energy transfer and non-linear optical properties at near ultraviolet wavelengths: Rare earth 4f yields 5d transitions in crystals and glasses  

NASA Astrophysics Data System (ADS)

The following topics were studied: two-photon transitions from 4f ground state to 5d excited states in Ce(3+):CaF2; optical absorption and photoionization measurements from excited state of Ce(3+):Y3Al5O12; excited state photoionization of Ce(3+) ions in Ce(3+):CaF2; optical gain and loss studies in Ce(3+):LiYF4; Gd yields Cr energy transfer in Cr(3+):GSGG, Cr(3+):GSAG, and Cr(3+):GGG crystals; nonradiative relaxation in Ce(3+) doped crystals and glasses; and grating formation in impurity doped crystals.

Hamilton, D. S.

1992-08-01

348

Growth and characterization of single crystal insulators on silicon  

NASA Technical Reports Server (NTRS)

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

Schowalter, Leo J.; Fathauer, Robert W.

1989-01-01

349

High Temperature Tribological Characteristics of Fe–Mo-based Self-Lubricating Composites  

Microsoft Academic Search

Fe–Mo-based self-lubricating composites were prepared by a powder metallurgical hot-pressing method. The tribological properties\\u000a of Fe–Mo-based composites with varied CaF2 contents at high temperature were evaluated, and the effect of glaze films on the friction and wear characteristics of composites\\u000a were analyzed. The results show that the introduction of CaF2 into Fe–Mo alloys improved the mechanical properties, and the best

Jiesheng Han; Junhong Jia; Jinjun Lu; Jingbo Wang

2009-01-01

350

Defects in calcium fluoride generated by 157 nm laser and low-energy electrons  

NASA Astrophysics Data System (ADS)

Single crystal calcium fluoride (CaF2) is currently being studied for use as an optical material for vacuum ultra-violet applications. It is also being investigated as a material for lithographic masks. Metal halides have a strong tendency to form point defects under energetic particle and photon irradiation. Defect generation is the basis for mask exposure, but is highly detrimental to optics. Here we examine the consequences of exposing single crystal CaF2 to 2 keV electrons and pulsed 157-nm laser light. Low-energy electrons and 157-nm laser light produce metallic colloids in CaF2, which causes absorption in the visible region. Electron induced colloid growth has been studied by others. We study effect of 157-, 193-, 248-, 532-, and 1064-nm laser radiation and heat on colloids in electron-irradiated CaF2. Transmission measurements were used to probe the bleaching process as a function of treatment. Chemical reactions with hydrochloric acid and/or water are strongly enhanced by many defects and can be used to probe the distribution of defects produced by electron- and laser-irradiation. Imaging the treated surface with atomic force microscopy allows us to compare relative defect densities versus depth into the sample. Samples treated with 2-keV electrons were damaged at depths as deep as 600 nm. Electron irradiation also appeared to produce line defects that intersect the surface. 157-nm laser irradiation produced significant crystal damage only to a depth of about 100 nm; line defects were not observed. The stability of CaF2 at the excimer laser wavelengths of 157 and 193 nm is an important issue primarily due to defects formed by electron-hole recombination. In addition to producing lattice defects, electron-hole recombination can proceed radiatively to yield a luminescence centered at 280 nm. Pre-existing defects produced by electron irradiation, polishing, mechanical indentation, or heating change the luminescence intensities. Single crystal CaF2 optical components have become part of newer optical systems for lithography at 193 nm. Soon the laser community would like to see 157 nm lithography become a reality, where CaF2 optical components are among the few alternatives. The study of the defect generation at 157 nm should allow for a better understanding of the inherent issues with using CaF2 as an optical material at this wavelength.

Cramer, Loren Paul

351

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

PubMed

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

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

2011-07-01

352

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

353

Roughness and scattering measurements on thin films for UV/VIS applications  

NASA Astrophysics Data System (ADS)

An attempt is presented of a systematic experimental approach to the problem of scattering and roughness modification after deposition of an optical thin film. BK 7 substrates with different surface qualities have been coated with evaporated MgF2, LaF3 and magnetron sputtered SiO2 and Nb2O5 films as representatives of low index/high index columnar structured and structureless films, respectively. Investigations by total integrated scattering (TIS) and angle resolved scattering (ARS) at 633 nm and 325 nm as well as atomic forced microscopy (AFM) demonstrate the possibility of quite different effects of scattering and roughness modification to occur.

Duparre, Angela; Kiesel, Axel; Kaiser, Norbert; Truckenbrodt, Horst; Schuhmann, Uwe

1994-09-01

354

Application of the Tauc-Lorentz formulation to the interband absorption of optical coating materials  

NASA Astrophysics Data System (ADS)

Recent progress in ellipsometry instrumentation permits precise measurement and characterization of optical coating materials in the deep-UV wavelength range. Dielectric coating materials exhibit their first electronic interband transition in this spectral range. The Tauc-Lorentz model is a powerful tool with which to parameterize interband absorption above the band edge. The application of this model for the parameterization of the optical absorption of TiO2, Ta2O5, HfO2, Al2O3, and LaF3 thin-film materials is described.

von Blanckenhagen, Bernhard; Tonova, Diana; Ullmann, Jens

2002-06-01

355

Development of a large area gas photomultiplier with GEM/$?$PIC  

E-print Network

We are developing a new photon detector with micro pattern gaseous detectors. A semitransparent CsI photocathode is combined with 10cm$\\times$10cm GEM/$\\mu$PIC for the first prototype which is aimed for the large liquid Xe detectors. Using Ar+C$_2$H$_6$ (10%) gas, we achieved the gas gain of $10^5$ which is enough to detect single photoelectron. We, then, irradiated UV photons from a newly developed solid scintillator, LaF$_3$(Nd), to the detector and successfully detected single photoelectron.

H. Sekiya

2008-09-19

356

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

SciTech Connect

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

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

2010-11-01

357

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

USGS Publications Warehouse

A neutron activation procedure suitable for the routine determination of tantalum and hafnium in silicates is described. The irradiated sample is fused with sodium peroxide and leached, and the insoluble hydroxides are dissolved in dilute hydrofluoric acid-hydrochloric acid. After LaF3 and AgCl scavenges, tantalum and hafnium are separated by anion exchange. Tantalum is obtained radiochemically pure; 233Pa and 95Zr contaminants in the hafnium fraction are resolved by ??-ray spectrometry. The chemical yield of the procedure is detemined after counting by re-irradiation. Values for the 8 U.S. Geological Survey standard rocks are reported. ?? 1968.

Greenland, L.P.

1968-01-01

358

Contrast in scanning probe microscopy images of ultra-thin insulator films Andreas Klust,1,  

E-print Network

either do not show CaF2 islands or image them as depressions (contrast inversion) at high negative bias applications and basic research. For instance, insulator films are used as tunneling barriers in electronic review, see Ref. 1 and references therein. Contrast in STM images of insulator films does not necessarily

Olmstead, Marjorie

359

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

E-print Network

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

Zens, Timothy

360

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

361

Visible to infrared down conversion in rare-earth doped fluorides for luminescent solar converters  

NASA Astrophysics Data System (ADS)

Downconversion is investigated as a promising way to enhance silicon solar cells efficiency. The efficiency of the downconversion process is investigated for the (Pr3+, Yb3+) codoping in two fluoride hosts: KY3F10 and CaF2. Strong near-infrared emission from ytterbium ions after excitation of praseodymium ions at 440 nm is observed in both KY3F10 and CaF2 as a result of the efficient energy transfer from praseodymium to ytterbium. In particular, very high Pr3+ to Yb3+ energy transfer efficiencies (ETE) are achieved for low Yb3+ and Pr3+ concentrations (ETE=97% in CaF2:0.5%Pr3+- 1%Yb3+) in CaF2 in comparison with KY3F10. A low Yb3+ concentration offers the advantage to limit the Yb3+ concentration quenching which is observed in other hosts, where the Yb3+ concentration has to be larger to achieve a high ETE for solar cell applications.

Serrano, D.; Braud, A.; Doualan, J.-L.; Camy, P.; Moncorgé, R.

2011-09-01

362

EPR studies of the mechanochemically Er3+-activated fluorite nanoparticles  

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

363

DEPARTMENT OF PHYSICS & ASTRONOMY College of Science  

E-print Network

-Khalilova Spacetime to spacetime-momentum 11.55 ­ 12.10 David McCarthy Modeling Atomic Diffusion 12.10 ­ 12.25 Mike globular clusters of M31 12.15 ­ 12.30 Scot Choi Laser Spectroscopy of interface Eu3+ center in CaF2:Eu

Hickman, Mark

364

Dissociative Binding of Carboxylic Acid Ligand on Nanoceria Surface in Aqueous Solution: A Joint in Situ Spectroscopic Characterization and First-Principles Study  

SciTech Connect

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.

Lu, Zhou; Karakoti, Ajay S.; Velarde Ruiz Esparza, Luis A.; Wang, Weina; Yang, Ping; Thevuthasan, Suntharampillai; Wang, Hongfei

2013-11-21

365

Crystallographic Shear Relations between the Structure Types Alpha-Uranium Trioxide, Calcium Difluoride, Lanthanum Trioxide and Sodium Chloride and a Correlation of some Lanthianide and Actinide Oxide Structures.  

National Technical Information Service (NTIS)

When the alpha-UO3, La2O3 and NaCl structure types are idealized by a topological distortion involving only an extension or contraction of the hexagonal c axis (cubic (111)) it is clear that they are related to each other, and to the CaF2 type, by crystal...

B. G. Hyde

1971-01-01

366

The mechanical properties of fluoride salts at elevated temperatures. [candidate thermal energy storage materials for solar dynamic systems  

NASA Technical Reports Server (NTRS)

The deformation behavior of CaF2 and LiF single crystals compressed in the 111 and the 100 line directions, respectively, are compared with the mechanical properties of polycrystalline LiF-22 (mol pct) CaF2 eutectic mixture in the temperature range 300 to 1275 K for strain rates varying between 7 x 10 to the -7th and 0.2/s. The true stress-strain curves for the single crystals were found to exhibit three stages in an intermediate range of temperatures and strain rates, whereas those for the eutectic showed negative work-hardening rates after a maximum stress. The true stress-strain rate data for CaF2 and LiF-22 CaF2 could be represented by a power-law relation with the strain rate sensitivities lying between 0.05 and 0.2 for both materials. A similar relation was found to be unsatisfactory in the case of LiF.

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

1989-01-01

367

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

Microsoft Academic Search

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

Mahmoud Azami; Sasan Jalilifiroozinezhad; Masoud Mozafari; Mohammad Rabiee

2011-01-01

368

Calcium fluoride windows for high-energy chemical lasers  

NASA Astrophysics Data System (ADS)

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

Klein, Claude A.

2006-10-01

369

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

PubMed Central

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

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

2012-01-01

370

Metal fluoride coatings prepared by ion-assisted deposition  

NASA Astrophysics Data System (ADS)

ArF lithography technology requires minimization of optical losses due to scattering and absorption. Consequently, it is necessary to optimize the coating process of metal fluorides. The properties of metal fluoride thin films are mainly affected by the deposition methods, their parameters (temperature and deposition rate) and the vacuum conditions. A substrate temperature of more than 300°C is a condition for high density and low water content of metal fluorides. Therefore, a substrate temperature of 150°C results in inhomogeneous films with high water content. Until now, the best results were achieved by boat evaporation. This paper will demonstrate that most of the common metal fluorides like MgF2, AlF3, and even LaF3 can be deposited by electron beam evaporation. In comparison to other deposition methods, the prepared thin films have the lowest absorption in the VUV spectral range. Furthermore, metal fluoride thin films were prepared by ion assistance. It will be demonstrated, that they have less water content, high packing density, and low absorption in the VUV spectral range. In this study, single layers of LaF3 and AlF3 and antireflection coatings were prepared by electron beam evaporation with and without ion-assistance. The mechanical, structural, and optical properties were examined and discussed.

Bischoff, Martin; Sode, Maik; Gäbler, Dieter; Bernitzki, Helmut; Zaczek, Christoph; Kaiser, Norbert; Tünnermann, Andreas

2008-09-01

371

Oxide and fluoride coatings for the excimer wavelength 193nm  

NASA Astrophysics Data System (ADS)

The requirements to produce high performance coatings increase dramatically when moving from 248 nm to 193 nm. The quality of DUV thin film components is mainly determined by the optical properties of the applied layer materials. The reduction of losses due to scattering and absorption of dielectric materials is essential for excellent properties of the coating results. The most common oxide and fluoride materials SiO2, Al2O3, MgF2 and LaF3 have been investigated and optimized. Plasma ion assisted deposition was applied for the deposition of the oxide materials, using improved coating equipment such as the modified APSpro (advanced plasma source). The paper reports the results of DUV coatings using plasma ion assisted deposition for the oxide materials. Single layers of silica and alumina and multilayer systems with both materials were investigated. In addition, MgF2 and LaF3, conventionally coated at very high temperatures, have been performed to demonstrate the improved capabilities of the optimized SYRUSpro DUV for DUV applications with all the new features.

Götzelmann, Rainer; Hagedorn, Harro; Zöller, Alfons; Kobiak, Alexei; Klug, Werner

2005-09-01

372

R&D proposal for a fast and radiation hard crystal calorimeter at LHC  

E-print Network

Homogeneous crystal calorimeters are so far the best in terms of energy resolution and compactness. Large scale detectors have been built for several experiments and the engineering problems are well understood. One of these crystals, BaF2, is already well known as a fast and radiation hard scintillator. From our systematic studies of scintillation properties and radiation damage mechanisms of several scintillators, we believe that a complete family of fluorides crystals or glasses should behave like BaF2, but with a shorter radiation length and no slow component. The purpose of this R&D program is to study these materials in order to design a fast, compact, precise and radiation hard electromagnetic calorimeter for the LHC.

Lecoq, P

1990-01-01

373

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

374

A simple radionuclide-driven single-ion source  

NASA Astrophysics Data System (ADS)

We describe a source capable of producing single barium ions through nuclear recoils in radioactive decay. The source is fabricated by electroplating G148d onto a silicon ?-particle detector and vapor depositing a layer of BaF2 over it. S144m recoils from the alpha decay of G148d are used to dislodge Ba+ ions from the BaF2 layer and emit them in the surrounding environment. The simultaneous detection of an ? particle in the substrate detector allows for tagging of the nuclear decay and of the Ba+ emission. The source is simple, durable, and can be manipulated and used in different environments. We discuss the fabrication process, which can be easily adapted to emit most other chemical species, and the performance of the source.

Montero Díez, M.; Twelker, K.; Fairbank, W.; Gratta, G.; Barbeau, P. S.; Barry, K.; DeVoe, R.; Dolinski, M. J.; Green, M.; LePort, F.; Müller, A. R.; Neilson, R.; O'Sullivan, K.; Ackerman, N.; Aharmin, B.; Auger, M.; Benitez-Medina, C.; Breidenbach, M.; Burenkov, A.; Cook, S.; Daniels, T.; Donato, K.; Farine, J.; Giroux, G.; Gornea, R.; Graham, K.; Hagemann, C.; Hall, C.; Hall, K.; Hallman, D.; Hargrove, C.; Herrin, S.; Karelin, A.; Kaufman, L. J.; Kuchenkov, A.; Kumar, K.; Lacey, J.; Leonard, D. S.; Mackay, D.; MacLellan, R.; Mong, B.; Niner, E.; Odian, A.; Piepke, A.; Pocar, A.; Prescott, C. Y.; Pushkin, K.; Rollin, E.; Rowson, P. C.; Sinclair, D.; Slutsky, S.; Stekhanov, V.; Vuilleumier, J.-L.; Wichoski, U.; Wodin, J.; Yang, L.; Yen, Y.-R.

2010-11-01

375

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

376

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

377

Comparison of Ba2YCu3O7-? films on NdGaO3 and LaAlO  

Microsoft Academic Search

The authors have studied the properties of 100-nm films of Ba2YCu3O7-? (BYCO) grown on LaAlO 3(100) and NdGaO3(100) by coevaporation of Cu, Y, and BaF2 followed by a two-stage anneal ex situ. It is found that the structural properties of the films on both substrates are optimized when the maximum temperature of the anneal is 900°C, while the superconducting properties

J. M. Phillips; M. P. Siegal; C. L. Perry; J. H. Marshall

1991-01-01

378

Ultrasonic Investigation on Nanocrystalline Barium Borate (BBO) Glass Ceramics  

Microsoft Academic Search

Barium Borate (BBO) glasses containing different compositions of BaO and B2O3 with BaF2, Cr2O3 and TiO2 have been prepared by normal melting and annealing technique. The prepared bulk BBO glasses have been subjected to heat?treatment. The heat?treated BBO glasses produce nanophase BBO crystals in its structure. The existence of nanophase structure of the BBO crystals have been studied through XRD

A. V. Gayathri Devi; V. Rajendran; K. Jeyasubramanian; N. Suresh Kumar

2006-01-01

379

Determination of titanium by slurry sampling graphite furnace atomic absorption spectrometry with the use of fluoride modifiers  

Microsoft Academic Search

A method for the determination of titanium in graphite furnace atomic absorption spectrometry with slurry sampling was developed. Titanium forms thermally stable carbides in the graphite tube that leads to decreased sensitivity and severe memory effects. Various fluorinating agents, BaF2, NH4F, and CHF3 (Freon-23) were therefore examined in order to reduce or eliminate these problems. Ti was determined, at various

Torunn Marie Sørlie; Grethe Wibetoe

2003-01-01

380

Dynamical fission times in hot ^240Cf from giant dipole gamma-rays emitted during the saddle-to-scission decay  

Microsoft Academic Search

Dynamics of nuclear fission in the temperature range of 1.3-2.0 MeV has been studied in hot ^240Cf in the case of vanishing fission barrier. High energy gamma-rays from the decay of giant dipole resonances built on excited nuclear states were detected in coincidence with fission fragments. Utilizing the high detection efficiency of a large BaF2 array covering 10% of 4pi,

I. Diószegi; A. Broderick; A. Buda; C. R. Morton; P. Paul; N. P. Shaw; J. Velkovska; V. Ziskin; J. R. Beene; N. Gan; M. L. Halbert; D. W. Stracener; R. L. Varner; M. Thoennessen

1998-01-01

381

On the Problems of Oxygen-related Impurity Induced Radiation Damage in the Barium Fluoride Crystal  

Microsoft Academic Search

This report presents a mechanism of oxygen incorporated by the hydrolysis of OW ion rather than the oxidation. The theoretical model of radiation damage in BaF2 is developed which UV absorption bands are chiefly caused by 0 related impurity centers formed from oxygen-related impurities by the ionization. The explanations for several key observations are given. Finally, based on the mechanism

L. M. Wang; L Y. Chen; M. Gu; K. H. Xiang

382

Gamma radiation induced damage effects in the transmission of barium fluoride and cesium fluoride fast crystal scintillators  

Microsoft Academic Search

Radiation damage effects in the optical transmission of bulk material due to 60Co gamma irradiations were measured in samples of barium fluoride (BaF2) and cesium fluoride (CsF). While confirming the exceptional radiation resistance of barium fluoride in the visible and ultraviolet regions of the transmission spectrum, at least up to a gamma dose of a few times 107 rad, the

Stan Majewski; Margaret Kathleen Bentley

1987-01-01

383

Scintillation characteristics of nonstoichiometric phases formed in MF2-GdF3-CeF3 system Part I. (M=Ba), scintillation of Ba0.9Gd0.1- xCexF2.1 (0<=x<=0.1) fluorite-type crystals  

Microsoft Academic Search

As the Ce concentration (x) was increased from 0 to 0.1 (complete replacement of Gd), the emission peak wavelength shifted from 310 (due to Gd3+ emission) to 350nm (due to Ce3+ emission). The light intensity increased from a few percent to 46% of that in BaF2. The decay constant of the dominant emission approached 30-40ns, which is characteristic of the

M. Kobayashi; M. Ishii; B. P. Sobolev; Z. I. Zhmurova; E. A. Krivandina

1999-01-01

384

Scintillation characteristics of nonstoichiometric phases formed in MF 2–GdF 3–CeF 3 system Part I. (M=Ba), scintillation of Ba 0.9Gd 0.1? x Ce x F 2.1 (0? x?0.1) fluorite-type crystals  

Microsoft Academic Search

As the Ce concentration (x) was increased from 0 to 0.1 (complete replacement of Gd), the emission peak wavelength shifted from 310 (due to Gd3+ emission) to 350nm (due to Ce3+ emission). The light intensity increased from a few percent to 46% of that in BaF2. The decay constant of the dominant emission approached 30–40ns, which is characteristic of the

M Kobayashi; M Ishii; B. P Sobolev; Z. I Zhmurova; E. A Krivandina

1999-01-01

385

Color centers in LiCaAlF6 single crystals and their suppression by doping  

Microsoft Academic Search

LiCaAlF6 (LiCAF) single crystals pure and doped with MgF2 and BaF2 were successfully grown by the Czochralski technique. Optical absorption measurements in the UV\\/Visible spectral regions following x-ray irradiation (radiation induced absorption) were performed in order to investigate the radiation damage of the crystals. The F-center absorption band at 262 nm is the dominating induced absorption feature. The amplitude of

Hiroki Sato; Hiroshi Machida; Kiyoshi Shimamura; Amina Bensalah; Tomohiko Satonaga; Tsuguo Fukuda; Eva Mihokova; Michal Dusek; Martin Nikl; Anna Vedda

2002-01-01

386

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

NASA Technical Reports Server (NTRS)

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

Miller, M. D.

1981-01-01

387

Digital pulse-shape discrimination of fast neutrons and ? rays  

Microsoft Academic Search

Discrimination of the detection of fast neutrons and ? rays in a liquid scintillator detector has been investigated using digital pulse-processing techniques. An experimental setup with a 252Cf source, a BC-501 liquid scintillator detector, and a BaF2 detector was used to collect waveforms with a 100Ms\\/s, 14 bit sampling ADC. Three identical ADCs were combined to increase the sampling frequency

P.-A. Söderström; J. Nyberg; R. Wolters

2008-01-01

388

Digital pulse-shape discrimination of fast neutrons and gamma rays  

Microsoft Academic Search

Discrimination of the detection of fast neutrons and gamma rays in a liquid scintillator detector has been investigated using digital pulse-processing techniques. An experimental setup with a 252Cf source, a BC-501 liquid scintillator detector, and a BaF2 detector was used to collect waveforms with a 100 Ms\\/s, 14 bit sampling ADC. Three identical ADCs were combined to increase the sampling

P.-A. Söderström; J. Nyberg; R. Wolters

2008-01-01

389

Anomalous spectral density and two-level system-phonon coupling in an insulating magnetic glass  

E-print Network

979 Anomalous spectral density and two-level system-phonon coupling in an insulating magnetic glass et les propriétés magné- tiques du verre. Abstract. 2014 Low temperature ultrasonic measurements on the magnetic glass (MnF2)0.65(BaF2)0.2(NaPO3)0.15 in the 0.1-1 GHz range give a value for the spectral density

Boyer, Edmond

390

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

Microsoft Academic Search

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

P Capek; V Sasinková; N Wellner; A Ebringerová

2000-01-01

391

Effects of flux additives on the characteristics of Y2.95Al5O12:0.05Ce3+ phosphor: Particle growth mechanism and luminescence  

NASA Astrophysics Data System (ADS)

The dependence of the amount of the BaF2 flux additive on the luminescence of Y2.95Al5O12:0.05Ce3+ phosphors was investigated. The integrated emission intensity of Y2.95Al5O12:0.05Ce3+ prepared without the flux was enhanced by 29% with the addition of BaF2 flux at the optimum amount of 6 wt. %. Such an enhancement can be attributed to the purer phase of Y3Al5O12 and the morphology change from the irregular shape to spherical shape with the smoother surface due to the flux. The morphology and luminescence of Y2.95Al5O12:0.05Ce3+ prepared with the 6 wt. % BaF2 flux additive (Sample II) were further compared with those of Y2.95Al5O12:0.05Ce3+ prepared with the 7 wt. % H3BO3 flux additive (Sample I). The particle size, particle shape, and integrated emission intensity (?ex = 450 nm) of the former were found to be larger, more regular, and 6% higher than those of the latter. The difference in the morphology of Samples I and II, which led to the difference in the emission intensity and the external quantum efficiency, were well explained by the particle growth mechanism.

Chiang, Chung-Hao; Liu, Te-Hsing; Lin, Han-Yu; Kuo, Hung-Yi; Chu, Sheng-Yuan

2013-12-01

392

Preparation and patterning of YBa2Cu3O(x) thin films  

NASA Astrophysics Data System (ADS)

Superconducting YBa2Cu3O(x) thin films have been prepared by annealing multilayers deposited by sequential RF diode sputtering of Y2O3, BaF2, and CuO targets. Reactive sputtering of BaF2 in an Ar/O2 atmosphere yields films containing primarily Ba and O. The F concentration in the as-deposited multilayers is so low that wet-O2 annealing, which is necessary to remove F from films deposited from a BaF2 source by other techniques, is not required. The superconducting phase is formed by post-annealing in dry O2 for one hour at 850 C and two hours at 500 C. Films about 1 micron thick on yttria-stabilized zirconia substrates have a zero-resistance transition temperature of 90 K. Pattern definition is accomplished by using a photoresist mask followed by ion milling in an Ar(+) beam. Exposure to water is not detrimental to film properties, but some damage due to Ar(+) ions is observed after patterning.

Bhushan, M.; Strauss, A. J.

393

CANDLES for the study of ^48Ca double beta decay  

NASA Astrophysics Data System (ADS)

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

Ogawa, Izumi

2009-10-01

394

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

NASA Astrophysics Data System (ADS)

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

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

1989-08-01

395

Electron response of some low-Z scintillators in wide energy range  

NASA Astrophysics Data System (ADS)

Light yield nonproportionality and the intrinsic resolution of some low atomic number scintillators were studied by means of the Wide Angle Compton Coincidence (WACC) technique. The plastic and liquid scintillator response to Compton electrons was measured in the energy range of 10 keV up to 4 MeV, whereas a CaF2:Eu sample was scanned from 3 keV up to 1 MeV. The nonproportionality of the CaF2:Eu light yield has characteristics typical for inorganic scintillators of the multivalent halides group, whereas tested organic scintillators show steeply increasing nonproportionality without saturation point. This is in contrast to the behavior of all known inorganic scintillators having their nonproportionality curves at saturation above energies between tens and several hundred keV.

Swiderski, L.; Marcinkowski, R.; Moszynski, M.; Czarnacki, W.; Szawlowski, M.; Szczesniak, T.; Pausch, G.; Plettner, C.; Roemer, K.

2012-06-01

396

System at 1523 K (1250 °C)  

NASA Astrophysics Data System (ADS)

CaO-SiO2-Al2O3-CaF2 is a base system of mold flux for high Al steels. Phase equilibrium in CaO-SiO2-Al2O3-15 mass pct CaF2 system at 1523 K (1250 °C) was investigated using quenching method followed by X-ray diffraction and Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Isothermal section in this system at 1523 K (1250 °C) with Al2O3 being less than 25 mass pct and CaO/SiO2 (mass pct) being between 0.43 and 1.25 was experimentally constructed. The liquidus composition and seven solid-liquid coexistence regions at 1523 K (1250 °C) were determined.

Li, Jiangling; Shu, Qifeng; Chou, Kuochih

2014-10-01

397

Possible isotopic fractionation effects in material sputtered from minerals  

NASA Technical Reports Server (NTRS)

A model is presented which predicts isotope fractionation in material sputtered from mineral surfaces. According to the model, the fractionation is a function of the fractional abundances of each isotope, the low-energy collision cross sections and the atomic masses, and the fractionation pattern can be nonlinear. Calculations are illustrated for all sets of isotopes in the minerals perovskite, anorthite, akermanite, enstatite and troilite, and it is found that while O is always positively fractionated, with heavier isotopes sputtered preferentially, heavier elements are generally negatively fractionated. It is noted that the model may be tested by experiments on a system such as CaF2, CaI2, in which the Ca sputtered from CaF2 is predicted to be strongly fractionated in a negative sense and that sputtered from CaI2 is predicted to be strongly fractionated in a positive sense.

Haff, P. K.; Watson, C. C.; Tombrello, T. A.

1981-01-01

398

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

399

Doping concentration dependence on VUV luminescence of Tm:CaF2  

NASA Astrophysics Data System (ADS)

Luminescence and scintillation properties of Tm3+ 0.1-15% doped CaF2 crystals were systematically investigated. The crystals were grown by a simple solidification method which allowed us to obtain single crystals conveniently. In X-ray induced radio luminescence spectra, the luminosity of the self-trapped-exciton (STE) emission of CaF2 at 270 nm decreased with increasing of Tm3+ concentration. The Tm3+ 5d-4f transition based emission lines appeared at 175 nm (4f115d high spin state (HS) ? 3H6) and at 165 nm (low spin state (LS) to 3H6). Pulse height spectra were measured under ?-ray irradiation by using vacuum ultra-violet (VUV) sensitive photomultiplier tube (PMT) R8778 and Tm3+ 0.1% doped specimen exhibited the highest light yield.

Kawaguchi, Noriaki; Yanagida, Takayuki; Futami, Yoshisuke; Fujimoto, Yutaka; Fukuda, Kentaro; Kajimoto, Shinji; Fukumura, Hiroshi; Kurosawa, Shunsuke; Yokota, Yuui; Yoshikawa, Akira

2013-09-01

400

Enhancement of photoluminescence and upconversion in Er-Yb codoped nanocrystalline glass-ceramics  

NASA Astrophysics Data System (ADS)

Oxyfluoride glass ceramics containing CaF2 nanocrystals were prepared with dopants of Er2O3 and Yb2O3 through melt-quenching and proper thermal treatments. Emission spectra, emission decay and energy dispersive X-ray spectroscopy analysis of the glass ceramics indicated the incorporation of rare earth ions into CaF2 nanocrystals. Photoluminescence intensity of the glass-ceramics has been increased more than a hundred times compared with that of the precursor glass. We also obtained enormous enhancement in upconversion emission and relative population increase of the 4F9/2 level by energy transfer process under excitation at 980 nm in resonance with the 2F5/2 of Yb3+ and 4I11/2 of Er3+ ions.

Yoo, Mi-Yeon; Lee, Jin-Ho; Jeong, Hong-Myeong; Lim, Ki-Soo; Babu, P.

2013-09-01

401

New high-pressure phase of MgH2: An ab initio constant-pressure study  

NASA Astrophysics Data System (ADS)

The stability of magnesium hydride (MgH2) at high pressure is studied using a constant-pressure ab initio technique. Two phase transformations are successfully observed through the simulations. The rutile structure undergoes a phase transformation into a CaCl2-type phase. Further increase in pressure results into a first-order phase transition into an orthorhombic state within Pbcm symmetry. This phase can be considered as a distorted CaF2-type crystal and does not correspond to the previously proposed MgH2 phases. The transformation mechanism of the CaCl2-Pbcm phase change at the atomistic level is successfully characterized and it is found that the CaCl2-to-Pbcm phase change proceeds via an ideal CaF2-type intermediate phase. These phase transformations are also analyzed using total energy-volume calculations.

Durandurdu, Murat

2014-02-01

402

Metalorganic vapor phase epitaxy of GaAs on Si using II a-flouride buffer layers  

NASA Astrophysics Data System (ADS)

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.

Tiwari, A. N.; Freundlich, A.; Beaumont, B.; Blunier, S.; Zogg, H.; Teodoropol, S.; Vèrié, C.

1992-11-01

403

Low Radioactivity in CANDLES  

SciTech Connect

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

Kishimoto, T.; Ogawa, I.; Hazama, R.; Yoshida, S.; Umehara, S.; Matsuoka, K.; Sakai, H.; Yokoyama, D.; Mukaida, K.; Ichihara, K.; Tatewaki, Y.; Kishimoto, K.; Hirano, Y.; Yanagisawa, A.; Ajimura, S. [Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043 (Japan)

2005-09-08

404

Influence of thermal distortion in mirrors on the propagation of high power lasers  

NASA Astrophysics Data System (ADS)

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.

Lv, Ke; Zheng, Wei; Hua, Wei-hong

2012-10-01

405

Molecular beam epitaxy of InSb on Si substrates using fluoride buffer layers  

E-print Network

Molecular beam epitaxy of InSb on Si substrates using fluoride buffer layers W. K. Liu,a) J The molecular beam epitaxy of InSb/Si structures was accomplished using group IIa fluoride buffer layers. InSb 300 °C and 400 °C, producing In-terminated InSb 111 -A surfaces on CaF2/Si 111 substrates. Reflection

McCann, Patrick

406

Calcium fluoride windows for high-energy chemical lasers  

Microsoft Academic Search

The development of high-energy lasers requires optical windows capable of handling megajoule beam energies without compromising the system’s performance. Calcium fluoride (CaF2) has been identified as a prime candidate for windows operating at chemical laser wavelengths due to very low bulk absorption and exceptionally small thermal lensing coefficients; it is, however, vulnerable to structural failure owing to poor mechanical strength

Claude A. Klein

2006-01-01

407

Calcium fluoride windows for high-energy chemical lasers  

Microsoft Academic Search

The development of high-energy lasers requires optical windows capable of handling megajoule beam energies without compromising the system's performance. Calcium fluoride (CaF2) has been identified as a prime candidate for windows operating at chemical laser wavelengths due to very low bulk absorption and exceptionally small thermal lensing coefficients; it is, however, vulnerable to structural failure owing to poor mechanical strength

Claude A. Klein

2006-01-01

408

Vacuum-ultraviolet beam array generation by flat micro-optical structures.  

PubMed

Micro-optical structures for VUV laser beam shaping and wave-front sensing were manufactured by thin-film deposition onto CaF2 and transfer by etching. Arrays of Bessel-like F2 laser beams at a wavelength of 157 nm with extremely small conical angles were generated by microaxicon lenses. Beam propagation was studied in simulations and experiments. Apodization by absorbing layers is proposed for beam cleaning. PMID:15143646

Grunwald, R; Neumann, U; Kebbel, V; Kühn, H J; Mann, K; Leinhos, U; Mischke, H; Wulff-Molder, D

2004-05-01

409

Paramagnetic Relaxation of Some Rare-Earth Ions in Diamagnetic Crystals  

Microsoft Academic Search

The pulsed-saturation method at 8.9 kMc\\/sec was used to measure the spin-lattice relaxation rate T1-1 for Eu2+, Ho2+, and Tm2+ in CaF2, for Yb3+ in yttrium gallium garnet, yttrium aluminum garnet, and lutetium gallium garnet; for Nd3+ in yttrium gallium garnet and yttrium aluminum garnet; and for Sm3+ in lanthanum ethyl sulphate at low temperatures. The experimental data in most

Chao-Yuan Huang

1965-01-01

410

Prediction of Mechanical Properties in Submerged Arc Weld Metal of C–Mn Steel  

Microsoft Academic Search

The prediction model has been developed for steel weld metal mechanical properties as a function of flux ingredients such as CaO, MgO, CaF2 and Al2O3 in submerged arc welding carried out at fixed welding parameters. The results of quantitative measurements of mechanical properties on eighteen weld metal samples were utilized for developing the prediction equations of mechanical properties applying statistical

Prasanta Kanjilal; Tapan Kumar Pal; Sujit Kumar Majumdar

2007-01-01

411

Optical properties of Pr 3 + , Sm 3 + and Er 3 + ions in apatite, fluorite and phosphate glasses  

Microsoft Academic Search

The luminescence spectra of naturally occurring apatite Ca5[F?(PO4)3] and fluorite CaF2 crystals, containing traces of rare-earth elements have been compared with phosphate glasses doped with Pr3+, Sm3+ and Er3+ ions. The selected excitation bands for luminescence of samarium and praseodymium ions were indicated. Separate emission of Sm3+ ions besides Pr3+ ions in apatite could be measured for ?exc=335, 359 and

S. Body?; M. Czaja; Z. Mazurak

2009-01-01

412

Appl. Phys. B 67, 347350 (1998) Applied Physics B  

E-print Network

Appl. Phys. B 67, 347­350 (1998) Applied Physics B Lasers and Optics © Springer-Verlag 1998 Compact Isolator 19 mm PPLN =23 µmAPP (3X) CaF2 f=50 mm 832nm Po=100mW 1083nm Po=50mW idler=3.61µm Pidler=1.6 µ optic; HWP, half wave plate; ACL, astigmatism correction lens; DBS, dichroic beam splitter; APP

413

Surface modification of Si substrates by CdF 2 molecular beam for stable growth of fluoride ultra-thin heterostructures  

Microsoft Academic Search

The novel method of modifying Si surfaces by using a CdF2 molecular beam was proposed. Si(111) surfaces exposed to a CdF2 molecular beam at 400°C exhibited very smooth surfaces, and the surfaces were found to have different properties from those obtained by the conventional thermal flush method through reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) observation. CaF2

Motoki Maeda; Joji Omae; So Watanabe; Yohei Toriumi; Kazuo Tsutsui

2005-01-01

414

BRIEF COMMUNICATIONS: Optical breakdown of fluoride crystals by KrF laser radiation with ? = 248 nm  

NASA Astrophysics Data System (ADS)

The thresholds of bulk damage of commercially available ultraviolet-transparent MgF2, CaF2, and LiF crystals were determined for ? = 248 nm KrF laser radiation incident in the form of pulses of 70 ns duration. The dependences of the damage thresholds of these crystals on the focal spot diameter were obtained for this diameter from 8 to 1600 ?m.

Klementov, A. D.; Morozov, Nikolai V.; Re?terov, V. M.; Sergeev, P. B.

1989-06-01

415

Characterization of petroleum using near-infrared spectroscopy: Quantitative modeling for the true boiling point curve and specific gravity  

Microsoft Academic Search

This work describes a new approach to predict the true boiling point (TBP) curve and to estimate the API gravity in order to characterize the petroleum processed in refineries by using the information present in its absorbance spectrum obtained in the near-infrared region (NIR). The absorbance spectra were obtained in the range from 3700 to 10000cm?1 employing a CaF2 transmittance

Celio Pasquini; Aerenton Ferreira Bueno

2007-01-01

416

Metal C ring window seal  

Microsoft Academic Search

We have constructed an optical cell with CaF2 windows which are sealed with metal C rings. We have demonstrated vacuum leak rates for He of less than ?10?9 std atm cc\\/s between 20 and 110 °C, as well as pressure cycling between ?10?4 Pa and ?5 MPa. This seal is useful where outgassing or permeability of elastomeric O rings would

Michael T. Duignan; David J. Gerhardt; W. T. Whitney

1989-01-01

417

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

E-print Network

V high voltage. It sprayed methanol/water (1:1) mixture containing 0.1% (v/v) acetic acid at 200 nl/min flow rate. The mid-IR laser beam was focused with a 150 mm focal length CaF2 lens (Infrared Optical, and used without further purification. This model lipid was used to illustrate the utility of reactive

Vertes, Akos

418

Status report on dark matter search with low activity scintillators  

NASA Astrophysics Data System (ADS)

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.

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 Jésus, M.; Drain, D.; Messous, Y.; Pastor, C.; BPRS (Beijing, Paris, Roma, Saclay) Collaboration

1994-05-01

419

PLASTICIT DU SESQUIOXYDE D'YTTRIUM (Y2O3) PAR MICRO-INDENTATION  

E-print Network

oxydes [2], lui confère une grande stabilité par rapport à la température. C'est un des oxydes les moins contexte de l'étude des propriétés plas- tiques de cet oxyde, que ce travail est effectué. 2. Echantillons d'oxyde d'yttrium. - La structure de Y2O3 peut être obtenue à partir de la structure fluorine (CaF2

Paris-Sud XI, Université de

420

Observation of thermoluminescence induced by fission fragments  

Microsoft Academic Search

Thermoluminescence induced in CaF2 powder by fission fragments emanating from a uranium foil bombarded by fast neutrons has been measured as a function of neutron fluence. A linear relationship between the glow produced and the fast neutron fluence between 5 × 1010 and 6.5 × 1011 n\\/cm2 has been obtained, thus establishing the feasibility of the use of this method

K. V. Ettinger; S. A. Durrant; C. Christodoulides

1970-01-01

421

The microscopic theory of diffusion-controlled defect aggregation  

Microsoft Academic Search

The kinetics of diffusion-controlled aggregation of primary Frenkel defects (F and H centers) in irradiated CaF2 crystals is theoretically studied. Microscopic theory is based on the discrete-lattice formalism for the single defect densities (concentrations) and the coupled joint densities of similar and dissimilar defects treated in terms of the Kirkwood superposition approximation. Conditions and dynamics of the efficient F center

E. A. Kotomin; V. N. Kuzovkov

1998-01-01

422

Mineralization behavior of fluorine in perfluorooctanesulfonate (PFOS) during thermal treatment of lime-conditioned sludge.  

PubMed

The fate and transport of the fluorine in perfluorooctanesulfonate (PFOS) during the thermal treatment of lime-conditioned sludge were observed using both qualitative and quantitative X-ray diffraction techniques. Two main fluorine mineralization mechanisms leading to the substantial formation of CaF2 and Ca5(PO4)3F phases were observed. They had a close relationship with the thermal treatment condition and the PFOS content of the sludge. At low temperatures (300-600 °C), CaF2 dominated in the product and increases in treatment time and temperature generally enhanced the fluorine transformation. However, at higher temperatures (700-900 °C), increases in treatment time and temperature had a negative effect on the overall efficiency of the fluorine crystallization. The results suggest that in the high temperature environment there were greater losses of gaseous products such as HF and SiF4 in the transformation of CaF2 to Ca5(PO4)3F, the hydrolysis of CaF2, and the reaction with SiO2. The quantitative analysis also showed that when treating sludge with low PFOS content at high temperatures, the formation of Ca5(PO4)3F may be the primary mechanism for the mineralization of the fluorine in PFOS. The overall results clearly indicate the variations in the fate and transport of fluorine in PFOS when the sludge is subject to different PFOS contents and treatment types, such as heat drying or incineration. PMID:23360134

Wang, Fei; Shih, Kaimin; Lu, Xingwen; Liu, Chengshuai

2013-03-19

423

Densities and molar volumes of refined sodium oxide-containing slag melts  

Microsoft Academic Search

The refined slag mixtures used in electric-arc furnaces and ladle?furnace units usually contain up to 20? 30% fluorite. It is important to replace fluorite, which is employed as a thinning agent for highly basic refining slags, especially from an ecological viewpoint, since CaF 2 decomposes in the zone of electric arcs to yield anhydrous hydrogen fluoride. To form free-running refining

I. A. Magidson; A. V. Basov; N. A. Smirnov; M. V. Ezova

2007-01-01

424

The thermal characteristics of the electroslag process  

Microsoft Academic Search

The heat balance of a laboratory electroslag furnace working in quasisteady state is considered in detail. Results are presented\\u000a for all possible melting mode combinations of direct and alternating (60Hz) current, with live and insulated molds, in air\\u000a or argon atmospheres. The material studied is AISI 4340 steel, using a slag of CaF2 + 25 wt pct A12O3. The temperature

A. Mitchell; S. Joshi

1973-01-01

425

Behavior of nitrogen in a nitrogen-containing chromium-manganese steel during electroslag remelting  

NASA Astrophysics Data System (ADS)

Electroslag remelting of a high-alloyed steel with high contents of nitrogen, chromium, and manganese in an electroslag furnace has been studied. CaF2-MgO-SiO2 slag developed at TsNIITMASh and allowing remelting process at a temperature of 1520-1560°C is used as a flux. It is found that electroslag remelting of high-alloyed steels with a high nitrogen concentration does not change the nitrogen content.

Linchevskii, B. V.; Rigina, L. G.; Takhirov, A. A.

2013-06-01

426

Lubricating Properties of Some Bonded Fluoride and Oxide Coatings for Temperature to 1500 F  

NASA Technical Reports Server (NTRS)

The lubricating properties of some experimental ceramic coatings, diffusion-bonded fluoride coatings, and ceramic-bonded fluoride coatings were determined. The experiments were conducted in an air atmosphere at a sliding velocity of 430 feet per minute and at temperatures from 75 to 1500 F. Several ceramic coatings provided substantial reductions in friction coefficient and rider wear (compared with the unlubricated metals). For example, a cobaltous oxide (CoO) base coating gave friction coefficients of 0.24 to 0.36 within the temperature range of 75 to 1400 F; serious galling and welding of the metal surfaces were prevented. The friction coefficients were higher than the arbitrary maximum (0.2) usually considered for effective boundary lubrication. However, when a moderately high friction coefficient can be tolerated, this type of coating may be a useful antiwear composition. Diffusion-bonded calcium fluoride (CaF2) on Haynes Stellite 21 and on Inconel X gave friction coefficients of 0.1 to 0.2 at 1500 F. Endurance life was dependent on the thermal history of the coating; life improved with increased exposure time at elevated temperatures prior to running. Promising results were obtained with ceramic-bonded CaF2 on Inconel X. Effective lubrication and good adherence were obtained with a 3 to 1 ratio of CaF2 to ceramic. A very thin sintered and burnished film of CaF2 applied to the surface of this coating further improved lubrication, particularly above 1350 F. The friction coefficient was 0.2 at 500 F and decreased with increasing temperature to 0.06-at 1500 F. It was 0.25 at 75 F and 0.22 at 250 F.

Sliney, Harold E.

1960-01-01

427

Occupational exposure to radon and natural gamma radiation in the La Carolina, a former gold mine in San Luis Province, Argentina  

Microsoft Academic Search

Radon and gamma radiation level measurements were carried out inside the La Carolina mine, one of the oldest gold mining camps of southern South America, which is open for touristic visits nowadays. CR-39 track-etch detectors and thermoluminescent dosimeters of natural CaF2 and LiF TLD-100 were exposed at 14 points along the mine tunnels in order to estimate the mean 222Rn

R. M. Anjos; N. Umisedo; A. A. R. da Silva; L. Estellita; M. Rizzotto; E. M. Yoshimura; H. Velasco; A. M. A. Santos

2010-01-01

428

Epitaxial Growth of Tantalum Carbide  

Microsoft Academic Search

Films of tantalum carbide (TaC) known as a material with high melting point (3877°C) are formed on substrates by electron beam evaporation technique. The substrates are CaF2, MgO and NaCl single crystals cleaved in air. The range of substrate temperature is from 25°C to 1030°C. Pressures in the evaporation chamber are about 10-6 Torr during the deposition. Rates of deposition

Toshio Naiki; Masayuki Ninomiya; Masayoshi Ihara

1972-01-01

429

Effect of aluminum phosphate additions on composition of three-component plasma-sprayed solid lubricant  

NASA Technical Reports Server (NTRS)

Image analysis (IA) and electron microprobe X-ray analysis (EMXA) were used to characterize a plasma-sprayed, self-lubricating coating, NASA LUBE PS106, specified by weight percent as 35NiCr-35Ag-30CaF2. To minimize segregation of the powder mixture during the plasma-spraying procedure, monoaluminum phosphate was added to form agglomerate particles. Three concentrations of AlPO4 were added to the mixtures: 1.25, 2.5, and 6.25 percent by weight. Analysis showed that 1.25 wt% AlPO4 yielded a CaF2 deficiency, 2.5 wt% kept the coating closest to specification, and 6.25 wt% yielded excess CaF2 as well as more impurities and voids and a deficiency in silver. Photomicrographs and X-ray maps are presented. The methods of IA and EMXA complement each other, and the reasonable agreement in the results increases the confidence in determining the coating composition.

Jacobson, T. P.; Young, S. G.

1982-01-01

430

Application of different TL detectors for the photon dosimetry in mixed radiation fields used for BNCT.  

PubMed

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

Burgkhardt, B; Bilski, P; Budzanowski, M; Böttger, R; Eberhardt, K; Hampel, G; Olko, P; Straubing, A

2006-01-01

431

Multilayered core-shell structure of polyol-stabilized calcium fluoride nanoparticles characterized by NMR.  

PubMed

Diethyleneglycol (DEG)-stabilized calcium fluoride (CaF(2)) nanoparticles with a mean diameter of about 20 nm consist of an inorganic crystalline core, covered by a roughly monomolecular layer of organic material according to standard physico-chemical analysis. Multinuclear NMR experiments under magic angle spinning were used to identify the constituent (13)C, (1)H and (19)F atoms. All resonances were assigned (DEG, EtOH, H(2)O, H(3)O(+), OH(-), F(-), CaF(2)), and different populations could be discriminated in terms of their mobilities and correlations with neighboring atoms. We observed several different layers: mobile EtOH on the particle surface, an "interphase" containing immobile DEG molecules and fluoride ions, plus the single-crystalline CaF(2) core. It was thus possible for the first time to characterize by NMR all layered components of such core-shell particles, and the thickness of the newly discovered interphase could be estimated from the NMR intensities. PMID:23073344

Witter, Raiker; Roming, Marcus; Feldmann, Claus; Ulrich, Anne S

2013-01-15

432

Calcium Fluoride: New Properties For An Old Material  

NASA Astrophysics Data System (ADS)

A new process for producing large, single, oriented crystals of calcium fluoride (CaF2) has been developed which overcomes the limitations of current growing methods. This process has been reduced to practice and has yielded oriented crystals 17.5 3 x 17.5 x 5 cm3. Currently nearing completion is a system for producing 35 x 35 x 7.5 cm3 single crystals. A scale up to one-meter-square is considered feasible. This crystal growing process makes possible the fabrication of very large CaF2 windows. Suitability for very high power lasers, however, requires attention to properties beyond mere size. A process to generate higher purity growth stock (starting material) was also developed. The additional purification of the growth stock contributes to lower bulk absorption, the absence of color centers and increased radiation hardness. Also identified were several specific impurities which correlate with radiation hardness. A correlation was found between color centers induced by laser radiation and ionizing radiation. The ability of the new process to produce oriented single crystals permits entire laser windows to be fabricated with the <111> direction parallel to the direction of propagation. This orientation is known to reduce thermo-optic distortion and stress induced birefringence. Other CaF2 crystal properties such as tensile strength, absorption and laser damage thresholds were studied and are discussed.

King, C. W.; Nestor, Ontario H.

1989-07-01

433

Two CRM protein subfamilies cooperate in the splicing of group IIB introns in chloroplasts  

PubMed Central

Chloroplast genomes in angiosperms encode ?20 group II introns, approximately half of which are classified as subgroup IIB. The splicing of all but one of the subgroup IIB introns requires a heterodimer containing the peptidyl-tRNA hydrolase homolog CRS2 and one of two closely related proteins, CAF1 or CAF2, that harbor a recently recognized RNA binding domain called the CRM domain. Two CRS2/CAF-dependent introns require, in addition, a CRM domain protein called CFM2 that is only distantly related to CAF1 and CAF2. Here, we show that CFM3, a close relative of CFM2, associates in vivo with those CRS2/CAF-dependent introns that are not CFM2 ligands. Mutant phenotypes in rice and Arabidopsis support a role for CFM3 in the splicing of most of the introns with which it associates. These results show that either CAF1 or CAF2 and either CFM2 or CFM3 simultaneously bind most chloroplast subgroup IIB introns in vivo, and that the CAF and CFM subunits play nonredundant roles in splicing. These results suggest that the expansion of the CRM protein family in plants resulted in two subfamilies that play different roles in group II intron splicing, with further diversification within a subfamily to accommodate multiple intron ligands. PMID:18799595

Asakura, Yukari; Bayraktar, Omer Ali; Barkan, Alice

2008-01-01

434

Two CRM protein subfamilies cooperate in the splicing of group IIB introns in chloroplasts.  

PubMed

Chloroplast genomes in angiosperms encode approximately 20 group II introns, approximately half of which are classified as subgroup IIB. The splicing of all but one of the subgroup IIB introns requires a heterodimer containing the peptidyl-tRNA hydrolase homolog CRS2 and one of two closely related proteins, CAF1 or CAF2, that harbor a recently recognized RNA binding domain called the CRM domain. Two CRS2/CAF-dependent introns require, in addition, a CRM domain protein called CFM2 that is only distantly related to CAF1 and CAF2. Here, we show that CFM3, a close relative of CFM2, associates in vivo with those CRS2/CAF-dependent introns that are not CFM2 ligands. Mutant phenotypes in rice and Arabidopsis support a role for CFM3 in the splicing of most of the introns with which it associates. These results show that either CAF1 or CAF2 and either CFM2 or CFM3 simultaneously bind most chloroplast subgroup IIB introns in vivo, and that the CAF and CFM subunits play nonredundant roles in splicing. These results suggest that the expansion of the CRM protein family in plants resulted in two subfamilies that play different roles in group II intron splicing, with further diversification within a subfamily to accommodate multiple intron ligands. PMID:18799595

Asakura, Yukari; Bayraktar, Omer Ali; Barkan, Alice

2008-11-01

435

Study of resin-bonded calcia investment: Part 1. Setting time and compressive strength.  

PubMed

This study was carried out to develop a new titanium casting investment consisting of calcia as the refractory material and a cold-curing resin system as the binder. The setting time of the investment was investigated under different N,N-dimethyl-p-toluidine (DMPT) contents in methyl methacrylate monomer (MMA) and benzoyl peroxide (BPO) contents in calcia without any sintering agent. The effects of the sintering agents, which were calcium fluoride (CaF2) and calcium chloride (CaCl2), on the compressive strength of the investments were investigated at room temperature before and after heating to two different temperatures. The shortest setting time (68 minutes) of the investment was obtained at 0.37 DMPT/BPO (1.5 vol% /1.0 mass%) ratio by mass. The highest strength (16.5 MPa) was obtained from the investment which contained 2 mass% CaF2 and was heated to 1,100 degrees C. It was found that the developed calcia investment containing 2 mass% CaF2 has a possibility for use in titanium castings. PMID:11218848

Nakai, A

2000-09-01

436

Thermochemistry of calcium oxide and calcium hydroxide in fluoride slags  

NASA Astrophysics Data System (ADS)

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

Chattopadhyay, S.; Mitchell, A.

1990-08-01

437

Laser-induced backside wet etching of fluoride and sapphire using picosecond laser pulses  

NASA Astrophysics Data System (ADS)

Laser-induced backside wet etching (LIBWE) is a promising process for microstructuring of rigid chemical resistant and inert transparent materials. LIBWE with nanosecond laser pulses has been successfully demonstrated in a number of studies. LIBWE in a time scale of femtosecond and picosecond pulse durations has been investigated only in a few studies and just on fused silica. In the present study LIBWE of fluorides (CaF2, MgF2) and sapphire with a mode-locked picosecond ( t p=10 ps) laser at a UV wavelength of ?=355 nm using toluene as absorbing liquid has been demonstrated. The influence of the laser fluence and the pulse number on the etching rate and the achieved surface morphology was investigated. The etching rate grows linearly with the laser fluence in the low and high-fluence ranges with different slopes. The achieved etching rates for CaF2 and for sapphire were in the same range. Contrary to CaF2 and sapphire the etching rates of MgF2 were one magnitude less. For backside etching on sapphire at high fluences smooth surfaces and at low fluences ripples pattern were found, whereas fluoride surfaces showed a trend towards crack formation.

Ehrhardt, M.; Raciukaitis, G.; Gecys, P.; Zimmer, K.

2010-11-01

438

Nanoscintillators for radiation detection  

NASA Astrophysics Data System (ADS)

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

Hall, Ryan Gregory

439

Photo-induced changes in 157-nm optical coatings  

NASA Astrophysics Data System (ADS)

The photo-induced degradation of 157-nm anti-reflective (AR) coatings, and the role of water vapor in the ambient, have been studied with in-situ spectroscopic ellipsometry, atomic force microscopy (AFM), and x-ray photoelectron spectroscopy. Using ellipsometric techniques, we find that MgF2 thin films develop a surface roughness layer under laser irradiation at an incident dose of ~0.1 MJ/cm2. These thin film changes occur well before any changes in 157-nm transmission are observed. The findings are confirmed by ex-situ post-irradiation AFM measurements. LaF3 does not exhibit this effect. Addition of ppm-levels of moisture suppresses surface roughness formation, suggesting that the surface roughness growth may be a precursor to the transmission degradation of full AR stacks that had been observed earlier.

Liberman, Vladimir; Bloomstein, Theodore M.; Rothschild, Mordechai; Palmacci, Stephen T.; Sedlacek, Jan H. C.; Grenville, Andrew

2004-05-01

440

Uniformity Masks Design Method Based on the Shadow Matrix for Coating Materials with Different Condensation Characteristics  

PubMed Central

An intuitionistic method is proposed to design shadow masks to achieve thickness profile control for evaporation coating processes. The proposed method is based on the concept of the shadow matrix, which is a matrix that contains coefficients that build quantitive relations between shape parameters of masks and shadow quantities of substrate directly. By using the shadow matrix, shape parameters of shadow masks could be derived simply by solving a matrix equation. Verification experiments were performed on a special case where coating materials have different condensation characteristics. By using the designed mask pair with complementary shapes, thickness uniformities of better than 98% are demonstrated for MgF2 (m = 1) and LaF3 (m = 0.5) simultaneously on a 280?mm diameter spherical substrate with the radius curvature of 200?mm. PMID:24227996

2013-01-01

441

Damage precursor measurements on UV optical coatings  

NASA Astrophysics Data System (ADS)

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.

Ettrich, K.; Blaschke, Holger; Welsch, Eberhard

1995-07-01

442

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

PubMed Central

Polyethyleneimine (PEI) functionalized multicolor luminescent LaF3 nanoparticles were synthesized via a novel microwave-assisted method, which can achieve fast and uniform heating under eco-friendly and energy efficient conditions. The as-prepared nanoparticles possess a pure hexagonal structure with an average size of about 12 nm. When doped with different ions (Tb3+ and Eu3+), the morphology and structure of the nanoparticles were not changed, whereas the optical properties varied with doped ions and their molar ratio, and as a result emission of four different colors (green, yellow, orange and red) were achieved by simply switching the types of doping ions (Eu3+ versus Tb3 +) and the molar ratio of the two doping ions. PMID:22879690

Mi, Cong-Cong; Tian, Zhen-huang; Han, Bao-fu; Mao, Chuan-bin; Xu, Shu-kun

2012-01-01

443

Controlling energy transfer between multiple dopants within a single nanoparticle  

PubMed Central

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

DiMaio, Jeffrey R.; Sabatier, Clement; Kokuoz, Baris; Ballato, John

2008-01-01

444

Influence of modifier oxides on spectroscopic properties of Sm3+ doped lithium fluoroborate glass  

NASA Astrophysics Data System (ADS)

Sm3+ doped lithium fluoro-borate glasses with different modifier oxides (Li2B4O7-BaF2-NaF-MO where M = Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li2B4O7-BaF2-NaF-MgO+CaO, Li2B4O7-BaF2-NaF-CdO+PbO) were prepared by means of melt quenching method. These samples were characterized by XRD, FTIR, optical absorption and fluorescence techniques at room temperature. The XRD profiles of all the glasses confirm their amorphous nature and the FTIR spectra reveal the presence of BO3 and BO4 units along with the strong OH- groups in the glass matrices. The influence of modifier oxides on Judd-Ofelt (J-O) intensity parameters and intensity of the emission lines are reported. Judd-Ofelt theory is used to study the spectral properties and to calculate the radiative transition probabilities (AT), branching ratios (?R), integrated absorption cross sections (?) and radiative lifetimes (?R) for certain spectral transitions. From the emission spectral analysis, emission cross-sections (?P) are calculated for the four emission transitions, 4G5/2 ? 6H5/2, 4G5/2 ? 6H7/2, 4G5/2 ? 6H9/2 and 4G5/2 ? 6H11/2 of Sm3+ ion in different lithium fluoro-borate glasses. Among the four transitions, it is observed that the transition 4G5/2 ? 6H7/2 has higher emission cross-section (?P) in all the glass matrices, except in Mg, Cd and Mg-Ca glass matrices. The non-exponential nature of the luminescence decay curves of 4G5/2 level of Sm3+ doped glass matrices are also reported.

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

2012-11-01

445

Effect of modifier oxides on absorption and emission properties of Eu3+ doped different lithium fluoroborate glass matrices  

NASA Astrophysics Data System (ADS)

Eu3+ doped lithium fluoroborate glass with different modifier oxides (Li2B4O7-BaF2-NaF-MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li2B4O7-BaF2-NaF-MgO+CaO, Li2B4O7-BaF2-NaF-CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state (7F0) of different absorption bands of Eu3+ are calculated. From the optical absorption measurements and using the Judd-Ofelt (J-O) theory, J-O parameters (???=2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities (A), radiative life-times (?R), and branching ratios (?r) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections (?P) are obtained for the emission transitions, 5D0?7F1, 5D0?7F2, 5D0?7F3 and 5D0?7F4 of Eu3+ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the 5D0?7F2 transition have been measured and analyzed for all the glass matrices.

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

2012-11-01

446

Spectroscopic analysis of Ho3+ transitions in different modifier oxide based lithium-fluoro-borate glasses  

NASA Astrophysics Data System (ADS)

In recent investigations it was observed that the presence of different structural groups in borate glasses was favorable for spectroscopic investigations of rare earth doped borate glasses. Consequent to these observations, the heavy metal fluoride glasses doped with Ho3+ ions received much attention due to their wide transparency in the ultraviolet to infrared region. Keeping these observations in view, the present paper makes an attempt to present spectral investigations of Ho3+ doped lithium-fluoro-borate glasses of the compositions Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. These rare earth doped glasses were synthesized by melt quenching technique and an investigation was carried out to observe the structural (SEM and FT-IR) and optical (absorption and luminescence) properties. The paper also aims at the determination of three phenomenological Judd-Ofelt intensity parameters and special attention was paid to study the emission properties by employing the J-O intensity parameters. The visible emission spectra of Ho3+ ion in different lithium-fluoro-borate glasses were recorded by exciting the samples at 409 nm. The results revealed that among all the glass matrices, cadmium glass matrix have shown higher stimulated emission cross-section, which indicates that this is a good lasing material at this wavelength and highly useful for laser excitation.

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

2014-10-01

447

Infrared spectra of N2O-(orthoD2)N and N2O-(HD)N clusters trapped in bulk solid parahydrogen  

Microsoft Academic Search

High-resolution infrared spectra of the clusters N2O-(ortho-D2)N and N2O-(HD)N, N=1-4, isolated in bulk solid parahydrogen at liquid helium temperatures are studied in the 2225 cm-1 region of the nu3 antisymmetric stretch of N2O. The clusters form during vapor deposition of separate gas streams of a precooled hydrogen mixture (ortho-D2\\/para-H2 or HD\\/para-H2) and N2O onto a BaF2 optical substrate held at

Britney D. Lorenz; David T. Anderson

2007-01-01

448

Infrared spectra of N2O–(orthoD2)N and N2O–(HD)N clusters trapped in bulk solid parahydrogen  

Microsoft Academic Search

High-resolution infrared spectra of the clusters N2O–(ortho-D2)N and N2O–(HD)N, N=1–4, isolated in bulk solid parahydrogen at liquid helium temperatures are studied in the 2225 cm?1 region of the ?3 antisymmetric stretch of N2O. The clusters form during vapor deposition of separate gas streams of a precooled hydrogen mixture (ortho-D2?para-H2 or HD?para-H2) and N2O onto a BaF2 optical substrate held at

Britney D. Lorenz; David T. Anderson

2007-01-01

449

Conversion of Oxyfluoride Based Coated Conductors  

SciTech Connect

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.

Dan Wesolowski

2006-11-01

450

Gamma-ray cascade transitions in ^112Cd and ^114Cd following capture of epithermal neutrons  

NASA Astrophysics Data System (ADS)

Investigation of the properties of the ?-ray transitions in the cadmium isotopes are of importance for nuclear structure and applied physics due to the high cross section for capture of thermal neutrons by ^111Cd and ^113Cd. We report results from a neutron-capture experiment on ^natCd carried out at LANL's LANSCE using the 4? BaF2 DANCE array. Isolated resonances with known spins were selected to study the ?-ray cascade transitions in ^112Cd and ^114Cd. Experimental results are compared with predictions from the code DICEBOX to determine the optimal ?-ray strength function that reproduces these cascade transitions.

Rusev, G.; Jandel, M.; Bredeweg, T. A.; Taddeucci, T. N.; Ullmann, J. L.; Krticka, M.

2012-10-01

451

Multiple-Quantum NMR Coherence Growth in Single-Crystal and Powdered Calcium Fluoride  

NASA Astrophysics Data System (ADS)

Powdered and oriented single-crystal calcium fluoride (CaF 2) samples were used to determine the orientational dependence of 19F multiple-quantum (MQ) NMR coherence development in the absence of variations in lattice spacing and molecular motion on the experimental time scale. The normalized n-quantum coherence intensities and resultant effective spin-cluster size [ N(?)] of the powdered sample were found to be reproducible and insensitive to the cycle time chosen for the underlying eight-pulse MQ excitation sequence. Oscillations in the time-dependent 0Q and 2Q coherence intensities are seen in the oriented single-crystal samples. However, these oscillations are absent in the powdered CaF 2 sample, indicating damping by its orientational-based dipolar-coupling distribution. However, monotonic growth of the effective number of correlated nuclei, N(?), is still observed. In addition, the applicability of an average product-operator model of coherence growth based on the dimensionality of spin distribution, and previously only applied to powders, is tested for oriented single-crystal CaF 2 samples. The powdered and (100)-oriented single crystal show good agreement with the model, while the growth from the (111) orientation is slightly faster than predicted. This difference most likely arises from the unusual dipole structure of the (111)-oriented crystal, where nearest-neighbor couplings become zero. In addition, the refocused MQ signal intensity ( fMQ) is adversely effected by increasing the number of pulses applied in a fixed MQ preparation time. An empirical prediction of fMQ for samples with a static dipolar field is developed and serves as a basis for predicting the effects of motion on this MQ refocusing fraction. This relationship may also provide some insight into the possibility of extending the MQ technique to study correlations over larger length scales as the relatively rapid decay of fMQ typical limits the present experiment to ˜ 10 Å length scales.

Lathrop, D. A.; Handy, E. S.; Gleason, K. K.

452

Ab initio model potential study of local distortions around Cr + and Cr3 + defects in fluorite  

NASA Astrophysics Data System (ADS)

In this paper we present the results of a theoretical study of the local geometry distortions produced by Cr+ and Cr3+ ions in fluorite, by means of the ab initio environment model potential method [J. Chem. Phys. 89, 5739 (1988)]. The valence energy and wave function of the (CrF8)q-(q=7,5) clusters embedded in the CaF2 lattice represented by 118 ab initio model potential ions plus 750 point-charge ions are calculated using a short CI, which includes all states related to the dn ionic configuration. A geometry optimization is performed for CaF2: (CrF8)7- within the cubic point symmetry and for CaF2: (CrF8)5- within the D3d point symmetry; the conclusions of analyses of the multimode Jahn-Teller coupling T1?(?+?2+?'2) are used to address the geometry optimization, which is completed by a final unrestricted search. In an attempt to study all the structures proposed along previous experimental studies, the D3d structure corresponding to an octahedral cluster plus two axially displaced fluorines (octahedron+2) is investigated. Taking the ground state energy of the perfect cube as a reference, the results show that the most stable D3d distortion corresponds to an elongated cube in a 4A2g ground state, with an energy of about -1700 cm-1, while the compressed cube and the octahedron+2 structure energies are found to be -780 and +40 000 cm-1, respectively. A joint analysis of the available experimental data and the results of our calculations are presented.

Seijo, Luis; Barandiarán, Zoila

1991-06-01

453

Reaction characteristics of a tooth-bleaching agent containing H2O2 and NaF: in vitro study of crystal structure change in treated hydroxyapatite and chemical states of incorporated fluorine.  

PubMed

This in vitro study was performed to elucidate the reaction mechanism of sodium fluoride (NaF), which is added to tooth-bleaching agents to lessen the adverse effect of hydrogen peroxide (H2O2) on teeth. Both hydroxyapatite (HAP) and dihydrated dicalcium phosphate (DCPD), model substances for dental hard tissues, dissolved easily in a simple H2O2 solution. In the H2O2/NaF solutions, however, fluorine compounds that could not be identified by X-ray diffraction (XRD) due to the smallness of the products were formed on the surface of the HAP. X-ray photoelectron spectroscopy (XPS) studies demonstrated that fluoridated hydroxyapatite (FHAP) was formed on HAP, and that calcium fluoride (CaF2) formation was accelerated by increasing the concentrations of fluorine and H2O2 along with the partial dissolution of HAP. In H2O2/NaF solution, DCPD also transformed easily to FHAP and CaF2, which are favorable to the remineralization process on the tooth surface. Thus, the mechanism of NaF was elucidated, and its use together with H2O2 for tooth bleaching was proved to be effective. Methodologically, the XPS two-dimensional plot made it possible for the first time to directly estimate the ratio of FHAP and CaF2 in the reaction products, in contrast to the conventional wet-analytical method, which is simply based on the difference in solubility of the two components. PMID:15868064

Tanizawa, Y

2005-01-01

454

HERACLES : a multidetector for heavy-ion collisions at TRIUMF  

NASA Astrophysics Data System (ADS)

HERACLES is a multidetector that has been modified to study heavy-ion collisions, using an ion beam with an energy range between 8 to 15 MeV per nucleon. It has 78 detectors axially distributed around the beam axis in 6 rings allowing detection of multiple charged fragments from nuclear reactions. HERACLES has 4 different types of detectors, BC408/BaF2 phoswich, Si/CsI(Tl) telescope, BC408/BC444 phoswich and CsI(Tl) detectors. 25 Na + 12 C, 25 Na + 27 Al, 25 Mg + 12 C and 25 Mg + 27 Al reactions have been used to characterize the multidetector. Element identification up to Z = 12 is achieved with the BC408/BaF2 phoswich detectors, up to Z = 15 with the Si/CsI(Tl) telescopes and up to Z = 12 with the BC408/BC444 phoswich detectors. Isotopic identification is reached with the CsI(Tl) detector up to Z = 2.

St-Onge, Patrick; Gauthier, Jérôme; Wallace, Barton; Roy, René

2014-01-01

455

Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses.  

PubMed

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. PMID:23742543

Taira, Y; Toyokawa, H; Kuroda, R; Yamamoto, N; Adachi, M; Tanaka, S; Katoh, M

2013-05-01

456

The Binding Effect Of Metal On The Secondary Structure Of Albumin  

NASA Astrophysics Data System (ADS)

On the basis of vibrational analysis, the deconvolution and derivative procedures of amide bands in IR spectra has stimulated the interests in the study on the secondary structure of protein [1, 2]. The inter-relationships between metal ions and binding substances such as protein are important in the living system. However, the influnce of metal ions on the secondary stucture of protein has not been studied in details by this technique. In this investigation, NaC1, KC1,ZnC12, MgC12, CaC12, AlC13, NaNO3, AI (NO3)3, PrC13,NdC13,EuC13,DyC13, TbBr3, Ce(NO3)3, andGd(NO3)3 were reacted with bovine albumin in aqueons solutions for 4-5 hours respectively. The albumin complexes were formed both in supernatants and precipitates. Their FTIR spectra were measured with BaF2 pellet for the precipitates and cast film on BaF2 windows for the supernatants, utilizing a Nicolet 7199B spectrometer.

Li, Ly; Guo, Hai; Liu, Wentian; Wu, Jin-Guang; Xu, Guang-Xian

1989-12-01

457

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

458

Monte Carlo simulation studies on scintillation detectors and image reconstruction of brain-phantom tumors in TOFPET  

PubMed Central

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

Mondal, Nagendra Nath

2009-01-01

459

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

PubMed

Chemical reactions induced by mechanical treatment may give access to new compounds whose properties are governed by chemical metastability, defects introduced and the size effects present. Their interplay may lead to nanocrystalline ceramics with enhanced transport properties being useful to act as solid electrolytes. Here, the introduction of large amounts of La into the cubic structure of BaF2 served as such an example. The ion transport properties in terms of dc-conductivity values of the F(-) anion conductor Ba1-xLaxF2+x (here with x = 0.4) considerably exceed those of pure, nanocrystalline BaF2. So far, there is only little knowledge about activation energies and jump rates of the elementary hopping processes. Here, we took advantage of both impedance spectroscopy and (19)F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. While macroscopic transport is governed by an activation energy of 0.55 to 0.59 eV, the elementary steps of hopping seen by NMR are characterised by much smaller activation energies. Fortunately, we were able to deduce an F(-) self-diffusion coefficient by the application of spin-locking NMR relaxometry. PMID:24728404

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

2014-05-28

460

First Radioactive Beam Experiment with the Modular Neutron Array MoNA  

NASA Astrophysics Data System (ADS)

The Modular Neutron Array (MoNA) is a neutron detector under construction at the NSCL. MoNA will consist of 144 bars of BC-408 plastic scintillator, each being 2 meters long and 10x10 cm^2 in cross section. ?MoNA, consisting of 8 MoNA bars, was used to study the feasibility of detecting ^7He which decays in flight into ^6He and a neutron. A 150 MeV/u ^36Ar beam was used to produce a secondary beam of ^8Li at ˜85MeV/u. The ^8Li beam bombarded a 5.6 mm carbon target where the single proton stripping reaction populating ^7He took place. The subsequent ^6He fragments were detected at zero degrees with a ?E-E detector arrangement consisting of a 1 cm thick plastic scintillator and 10 cm thick BaF2 detector. The corresponding neutron from the ^7He decay was detected with ?MoNA, which was configured in two rows of four detectors above and below the BaF2 detector. From the energy of the ^6He and the position and time-of-flight of the neutron, it is possible to kinematically reconstruct the populated states of ^7He.

Rajabali, Mustafa; Evanger, Melanie; Turner, Ramsey; Luther, Bryan; Baumann, Thomas; Lu, Yao; Thoennessen, Michael; Tryggestad, Erik

2002-10-01

461

Precipitation of barium flouride microcrystals from electrolytic solutions: The influence of the composition of the precipitating solutions  

NASA Astrophysics Data System (ADS)

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).

Kolar, Z.; Binsma, J. J. M.; Suboti?, B.

1984-02-01

462

Understanding Low Energy Gamma Emission from Fission and Capture with DANCE  

NASA Astrophysics Data System (ADS)

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