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1

Water adsorption on (111) surfaces of BaF2 and CaF2  

NASA Astrophysics Data System (ADS)

Water adsorption on polished (111) surfaces of BaF2 and CaF2 was studied at room temperature under ultrahigh vacuum conditions by optical second-harmonic generation. Above 104 langmuirs, the total second-harmonic yield decreases with increasing exposure. The azimuthal anisotropy is influenced differently on each substrate. Below 104 langmuirs the 3m symmetry of the crystal surface is preserved in both cases, but more pronounced for CaF2. At high doses the symmetry remains for BaF2, but vanishes for CaF2. The results point to pseudomorphous epitaxial growth of water on BaF2 but not on CaF2.

Zink, J. C.; Reif, J.; Matthias, E.

1992-06-01

2

Synthesis, structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers.  

PubMed

Atomistic simulations have shown that the calculated conductivity of nano-polycrystalline BaF2/CaF2 heterolayers is considerably higher than the component bulk materials and we predict that grain-boundary diffusion is the key to fast ionic conductivity in these systems. PMID:12931976

Sayle, Dean C; Doig, James A; Parker, Stephen C; Watson, Graeme W

2003-08-01

3

Thermal-mismatch-strain relaxation in epitaxial CaF2, BaF2\\/CaF2, and PbSe\\/BaF2\\/CaF2 layers on Si(111) after many temperature cycles  

Microsoft Academic Search

The thermal mismatch strain in stacks containing PbSe, BaF2, and\\/or CaF2 on Si(111) substrates is relieved by the glide of dislocations in the principal \\\\{100\\\\} glide system. The strain in the BaF2(111) and CaF2(111) buffer layers is relaxed at room temperature regardless of whether they form the top layer in the stack or are overgrown by other layers. PbSe (as

H. Zogg; S. Blunier; A. Fach; C. Maissen; P. Müller; S. Teodoropol; V. Meyer; G. Kostorz; A. Dommann; T. Richmond

1994-01-01

4

Lattice and thermal misfit dislocations in epitaxial CaF2\\/Si(111) and BaF2CaF2\\/Si(111) structures  

Microsoft Academic Search

Atomic force microscopy reveals straight slip steps resulting from dislocation glide in the primary \\\\{100\\\\} glide system in ``low mismatch'' CaF2\\/Si(111) structures. From the height and spacing of the steps, the strain relieved by these misfit dislocations is compatible with the relief of the tensile thermal strain change on cooldown. In ``high mismatch'' BaF2\\/CaF2\\/Si(111) structures, dislocations which relieve the thermal

S. Blunier; H. Zogg; C. Maissen; A. N. Tiwari; R. M. Overney; H. Haefke; P. A. Buffat; G. Kostorz

1992-01-01

5

Absorption and Fluorescence of Sm2+ in CaF2, SrF2, and BaF2  

Microsoft Academic Search

The absorption and fluorescence of the Sm2+ ion have been studied for three host lattices, CaF2, SrF2, and BaF2. Measurements of intensity, linewidth, quantum efficiency, and Zeeman splitting are reported. Energy levels belonging to the 4f shell have been identified, and a preliminary analysis of the 4f-->5d transitions is presented.

D. L. Wood; W. Kaiser

1962-01-01

6

Enhanced processability of ZrF4-BaF2-LaF3-AlF3-NaF glass in microgravity  

NASA Astrophysics Data System (ADS)

Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 ?m in the UV to 7 ?m in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx - Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subject to a heating and quenching test apparatus on the parabolic aircraft, under a controlled 0-g and hyper-g environment and compared with 1-g ground tests. The microgravity duration on board Zero-G Corporation parabolic aircraft is approximately 20 seconds and the hyper-g intervals are approximately 56 seconds. Optical microscopy examination elucidates crystal growth in ZBLAN is suppressed when processed in a microgravity environment. The crystallization temperature, Tx, at which crystals form increased, therefore, significantly broadening the working temperature range for ZBLAN.

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

2013-06-01

7

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

2012-04-04

8

Preparation and characterization of atmospheric plasma-sprayed NiCr\\/Cr 3C 2–BaF 2·CaF 2 composite coating  

Microsoft Academic Search

NiCr alloy-coated BaF2•CaF2 eutectic and Cr3C2 powders were respectively prepared by both pressurized hydrogen reduction and solid state alloying technology. Using this NiCr\\/Cr3C2–BaF2•CaF2 composite powder, a derived coating was produced by atmospheric plasma spray (APS) technology. Microstructures and phase compositions of the powders, as well as the deposited coating, were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Chuanbing Huang; Lingzhong Du; Weigang Zhang

2009-01-01

9

Thermal Coefficient of Refractive Index of Polycrystalline ZnSe, BaF2 and CaF2 in the Visible and Near Infrared.  

National Technical Information Service (NTIS)

An interferometric technique has been used to measure the thermal coefficient of the refractive index of polycrystalline ZnSe, BaF2, and CaF2 at the HeNe laser wavelengths, 0.6328, 1.15, and 3.39 micrometers, in the range 25 -65C. The values obtained were...

H. Mukai

1975-01-01

10

Mechanochemical synthesis of nonstoichiometric nanocrystals La 1 ? y Ca y F 3 ? y with a tysonite structure and nanoceramic materials from CaF 2 and LaF 3 crystals  

Microsoft Academic Search

The nonstoichiometric phases La1 ? y\\u000a Ca\\u000a y\\u000a F3 ? y\\u000a (y = 0.15, 0.20) with a tysonite (LaF3) structure have been prepared for the first time by the mechanochemical synthesis from CaF2 and LaF3 crystals. The average size of coherent scattering regions is approximately equal to 10–30 nm. It has been shown that the\\u000a compositions of the phases prepared

B. P. Sobolev; I. A. Sviridov; V. I. Fadeeva; S. N. Sul’yanov; N. I. Sorokin; Z. I. Zhmurova; I. I. Khodos; A. S. Avilov; M. A. Zaporozhets

2008-01-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

12

High anion conductivity in a ternary non-equilibrium phase of BaF(2) and CaF(2) with mixed cations.  

PubMed

A highly conductive ternary fluoride with mixed cations is prepared by joint high-energy ball milling of cubic BaF(2) and CaF(2) in the ratio 0.4 : 0.6. The sample produced at room temperature consists of a nanocrystalline, defect-rich mixed (Ba,Ca)F(2) phase with retained cubic symmetry as well as of single-phase CaF(2) particles. The anion conductivity of the mixed phase, which decomposes at higher temperature (770 K) into BaF(2) and CaF(2), exceeds that of single-phase nanocrystalline BaF(2) by two and that of CaF(2) by four orders of magnitude. In turn, these conductivities are each greater by about two orders than those of the respective microcrystalline counterparts. Structural features of the samples are characterized by X-ray diffraction, TEM and (19)F MAS NMR spectroscopy. Static (19)F NMR spectra confirm the unexpectedly high anion conductivity probed by impedance spectroscopy. PMID:19370201

Ruprecht, B; Wilkening, M; Feldhoff, A; Steuernagel, S; Heitjans, P

2009-03-19

13

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

Microsoft Academic Search

We present high-accuracy measurements for wavelengths near 157 nm of the absolute index of refraction, the index dispersion, and the temperature dependence of the index for the ultraviolet optical materials with cubic symmetry: CaF2, SrF2, BaF2, and LiF. Accurate values of these quantities for these materials are needed for designs of the lens systems for F2 excimer-laser-based exposure tools for

John H. Burnett; Rajeev Gupta; Ulf Griesmann

2002-01-01

14

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

PubMed

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

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

2004-02-01

15

Microstructure and Tribological Properties of Plasma Sprayed NiCr\\/Cr 3 C 2 and NiCr\\/Cr 3 C 2 BaF 2 CaF 2 Composite Coatings  

Microsoft Academic Search

\\u000a NiCr alloy coated BaF2-CaF2 eutectic and Cr3C2 powders (NiCr\\/Cr3C2 and NiCr\\/BaF2-CaF2) are prepared by pressurized hydrogen reduction and solid state alloying process. NiCr\\/Cr3C2 and NiCr\\/Cr3C2-BaF2-CaF2 coatings are fabricated by atmospheric plasma spray technology. Both the coatings exhibit low porosity, high micro-hardness\\u000a and high cohesive strength. Compared with NiCr\\/Cr3C2 coating, the NiCr\\/Cr3C2-BaF2-CaF2 coating shows much more superior wear resistance and noticeably

Chuanbing Huang; Lingzhong Du; Weigang Zhang

16

Effect of NiCr Clad BaF 2 ·CaF 2 Addition on Wear Performance of Plasma Sprayed Chromium Carbide-Nichrome Coating  

Microsoft Academic Search

NiCr clad BaF2·CaF2 fluoride eutectic powders were added into chromium carbide-nichrome feedstock to improve the tribological properties of NiCr-Cr3C2 coating, and the structures, mechanical, and ball-on-disk sliding wear performance of the coating were characterized. The\\u000a results show that NiCr cladding can effectively decrease the density and thermophysical difference between the feedstock components,\\u000a while alleviate the decarburization and oxidization of the

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

2010-01-01

17

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

PubMed

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

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

2002-05-01

18

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

PubMed

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

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

2011-11-01

19

The atomic and electronic structure of CaF2 and BaF2 crystals with H centers: a hybrid DFT calculation study.  

PubMed

Using the B3PW method we simulate the ground state of H center systems for CaF(2) and BaF(2) crystals. The energy difference between H centers with different orientations shows that the H center oriented in the [111] direction in alkaline earth fluorides is the most stable. We present the geometric relaxations of the neighboring atoms surrounding the H center. The combination energy of an H center and the formation energy of the related F-H pair in both alkaline earth fluorides are discussed. We also report the electronic structure of the H center systems. The effective charges and spins of the substitutional and interstitial fluorine atoms show that the hole is located at the interstitial fluorine. The band structures are presented. By studying the DOS sketches the constituents of the defect bands are clarified. PMID:21386345

Jia, Ran; Shi, Hongting; Borstel, Gunnar

2010-01-15

20

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

NASA Astrophysics Data System (ADS)

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

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

21

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

22

Temperature dependence of the dielectric permittivity of CaF(2), BaF(2) and Al(2)O(3): application to the prediction of a temperature-dependent van der Waals surface interaction exerted onto a neighbouring Cs(8P(3/2)) atom.  

PubMed

The temperature behaviour in the range 22-500?°C of the dielectric permittivity in the infrared range is investigated for CaF(2), BaF(2) and Al(2)O(3) through reflectivity measurements. The dielectric permittivity is retrieved by fitting reflectivity spectra with a model taking into account multiphonon contributions. The results extrapolated from the measurements are applied to predict a temperature-dependent atom-surface van der Waals interaction. We specifically consider as the atom of interest Cs(8P(3/2)), the most relevant virtual couplings of which fall in the range of thermal radiation and are located in the vicinity of the reststrahlen band of fluoride materials. PMID:21828444

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

2009-05-27

23

Irradiation Damage in SrF2 and BaF2.  

National Technical Information Service (NTIS)

The thermoluminescence of rare-earth-doped SrF2 and BaF2 irradiated with x rays at 77K is interpreted in terms of the appearance and disappearance of three paramagnetic hole centers. The V(K) center is similar to one previously reported in CaF2. The V(K')...

A. Tzalmona P. S. Pershan

1969-01-01

24

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

Microsoft Academic Search

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

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

2002-01-01

25

Galvanostatic investigation of electrochemical processes at the LaF 3 \\/M (M: Ag, Bi) interface  

Microsoft Academic Search

The electrochemical processes at the interface between solid fluorine-conducting electrolyte LaF3(Eu2+ 0.8 mol %) and silver or bismuth electrodes in the two-electrode cell with nonpolarizable reference electrode are studied\\u000a using the galvanostatic method. The anodic galvanostatic transients of LaF3: Eu2+\\/Ag and LaF3: Eu2+\\/Bi interfaces are linearized on the log(? ? ?max), vs. t coordinates, i.e. the rate of LaF3|MF\\u000a n

M. S. Turaeva; S. A. Kot

2009-01-01

26

Local symmetry change in BaF2:Mn2+ at approximately 50 K: microscopic insight.  

PubMed

The microscopic origin of the abrupt cubic-tetrahedral symmetry change associated with the local a(2u) vibrational mode observed by electron paramagnetic resonance in BaF(2):Mn(2+) at approximately 50 K is explored by means of density functional theory calculations. It is found that while the a(2u) vibrational frequencies calculated for MnF(8) (6-) in CaF(2) (168 cm(-1)) and SrF(2) (132 cm(-1)) are real, in the case of BaF(2):Mn(2+), the adiabatic potential curve along this mode exhibits a double well with a small barrier of 50 cm(-1). Although the ground and first excited vibrational states are localized around the energy minima, the rest of the excited states resemble those of a harmonic oscillator centered at Q(a(2u))=0. Moreover, only the inclusion of the anharmonic coupling between a(2u) and t(1u) modes allows one to understand the T(d)-O(h) transition temperature. It is shown that both the unusually high Mn(2+)-F(-) distance in BaF(2):Mn(2+) and the pseudo-Jahn-Teller interaction of the t(2g)(xy;xz;yz) antibonding orbital with filled t(1u) orbitals favor the a(2u) instability. The calculated a(2u) force constant for different electronic states supports this conclusion. PMID:18376949

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

2008-03-28

27

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

28

Influence of Water Treatment of LaF3 Crystal on LaF3Based Oxygen Sensor Workable at Room Temperature  

Microsoft Academic Search

The effects of a water treatment of the LaF3 single crystal on an LaF3-based oxygen sensor were investigated. It was found that the oxygen-sensing properties were significantly affected by the water treatment depending on the perovskite-type oxides (LaCrO3, LaCoO3, La0.8Ca0.2MnO3) used as the sensing electrode material and the duration of the treatment. As revealed by XPS, the treatment induced the

Jerzy P. Lukaszewicz; Norio Miura; Noboru Yamazoe

1991-01-01

29

Properties of AlF3 and LaF3 films at 193nm  

NASA Astrophysics Data System (ADS)

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

Xue, Chunrong; Shao, Jianda

2010-05-01

30

Luminescence behavior of Eu3+ doped LaF3 nanoparticles  

Microsoft Academic Search

Europium-doped LaF3 nanoparticles have been prepared by the ionic\\u000a reaction in the ethanol at 60 degrees C. From the XRD pattern of\\u000a nanoparticles and the emission spectra of Eu3+ ions, it has been\\u000a concluded that the Eu3+ ions could easily substitute the La3+ sites and\\u000a the solid solution La1-xEuxF3 can be synthesized. Due to very low phonon\\u000a energies of LaF3

Daibo Pi; Feng Wang; Xianping Fan; Minquan Wang; Y. Zhang

2005-01-01

31

Solid-State Glucose Sensor Using LaF3Based Transducer  

Microsoft Academic Search

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

Norio Miura; Naoko Matayoshi; Noboru Yamazoe

1989-01-01

32

Controlled synthesis of uniform LaF3 polyhedrons, nanorods and nanoplates using NaOH and ligands  

NASA Astrophysics Data System (ADS)

A facile and productive method has been developed to synthesize uniform LaF3 nanocrystals with controllable shapes, including polyhedrons, nanorods and nanoplates. By tuning the amount of NaOH and ligands (oleic acid and octadecylamine), we can finely tailor the shapes and sizes of LaF3 nanocrystals. Three prepared LaF3 nanostructures were well characterized, followed by a series of control experiments to propose a mechanism for the shape control. Based on the success in materials synthesis, controlled patterning of LaF3 nanoplates on substrates has also been achieved. After Yb/Er or Yb/Tm was co-doped in these LaF3 nanostructures, they could serve as nanoparticulate host matrices to give strong upconversion luminescence, showing great potential in biomedical applications considering their small sizes and well-defined shapes.

Bao, Longyi; Li, Zhengquan; Tao, Qingling; Xie, Jianjian; Mei, Yuanyuan; Xiong, Yujie

2013-04-01

33

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

34

Fabrication of BaF2 Infrared Windows.  

National Technical Information Service (NTIS)

The feasibility was investigated of the fabrication of polycrystalline BaF2 windows for infrared lasers by the hot isostatic pressing process (HIP). A method of treatment with HF gas for the preparation and surface cleanup of the BaF2 powder was developed...

A. E. Austin J. J. Mueller J. F. Miller K. C. Brog

1974-01-01

35

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

36

Solid-State Glucose Sensor Using LaF3-Based Transducer  

NASA Astrophysics Data System (ADS)

A new-type glucose sensor using a LaF3-based transducer was investigated as the first example of a solid-electrolytecoupled biosensor. The sensor element was composed of the following electrochemical cell: (reference electrode) Sn+SnF2|LaF3|Pt-glucose oxidase (sensing electrode). The e.m.f. of the sensor cell was found to vary logarithmically with a change in glucose concentration in the range from 2× 10-5 to 1× 10-2 M in a phosphate buffer solution of pH 6.9. The 90% response time to 3× 10-2 M glucose was about 15 s at 30°C. The sensitivity of the sensor to glucose was fairly stable for the test period of about 30 days.

Miura, Norio; Matayoshi, Naoko; Yamazoe, Noboru

1989-08-01

37

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

38

Hardness of CaF2 and BaF2 Solid Lubricants at 25 to 670 Deg C.  

National Technical Information Service (NTIS)

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 fluor...

D. L. Deadmore H. E. Sliney

1987-01-01

39

Ice nucleation on BaF2(111).  

PubMed

The mechanism of heterogeneous ice nucleation on inorganic substrates is not well understood despite work on AgI and other materials over the past 50 years. We have selected BaF(2) as a model substrate for study since its (111) surface makes a near perfect match with the lattice of the basal face of I(h) ice and would appear to be an ideal nucleating agent. Two series of experiments were undertaken. In one, nucleation of thin film water formed from deposition of vapor on BaF(2)(111) faces was explored with the finding that supercooling to -30 degrees C was required before freezing occurred. In the other series, nucleation of liquid water on submerged BaF(2) crystals was studied. Here supercooling to -15 degrees C was needed before ice formed. The reason why BaF(2) is such a poor nucleating agent contains clues to realistic mechanisms of heterogeneous nucleation. Our explanation of these results follows the model of Fletcher [J. Chem. Phys. 29, 572 (1958)] who showed that heterogeneous ice nucleating ability depends on how well ice wets a substrate. In this view, a smooth BaF(2)(111) face is poor at nucleation because ice only partially wets its surface. In an extension of Fletcher's model, our calculations, consistent with the experimental results demonstrate that the pitting of a submerged BaF(2) crystal dramatically improves its ice nucleating ability. PMID:15740398

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

2005-02-01

40

Influence of structural evolution on fluorescence properties of transparent glass ceramics containing LaF 3 nanocrystals  

Microsoft Academic Search

The structural evolution and the fluorescence properties of Er3+-doped oxyfluoride glass ceramics were investigated for samples at different stages of LaF3 crystallization. TEM observation revealed the homogeneous precipitation of spherical LaF3 crystals sized in the range of 10–15nm among the glassy matrix for a sample heated to 690°C. The crystallization induced the splitting of Er3+ emission peaks and the appearance

E. Ma; Zhongjian Hu; Yuansheng Wang; Feng Bao

2006-01-01

41

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

Microsoft Academic Search

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

Bing Yan; Jianhua Wu

2009-01-01

42

Polarization of CAF2:SM(3+) Fluorescence.  

National Technical Information Service (NTIS)

The particular environments which produce two different types of CaF2:Sm(3+) fluorescence were deduced from study of the polarization of each spectrum. Either trigonal or tetragonal symmetry was observed and attributed to the local charge compensator asso...

T. F. Ewanizky P. J. Caplan J. R. Pastore

1965-01-01

43

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

NASA Astrophysics Data System (ADS)

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

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

2011-08-01

44

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

Thermoluminescence and Paramagnetic Hole Centers in BaF2.  

National Technical Information Service (NTIS)

Thermoluminescence of rare-earth doped BaF2, irradiated with X rays at 77K, is interpreted in terms of the appearance and disappearance of three paramagnetic hole centers. One of the centers is associated with an interstitial fluorine. (Author)

A. Tzalmona P. S. Pershan

1968-01-01

46

Test van een BaF2 Scintillatiekristal (Test of a BaF2 Scintillation Crystal).  

National Technical Information Service (NTIS)

Gamma energy response and temporal resolution of a BaF2 crystal were compared with those of a Pilot-U plastic. Using a photomultiplier, the possibility to use the fast ultraviolet component of the gamma ray excited emission spectrum for positron lifetime ...

J. M. Schippers J. Devries

1983-01-01

47

Diode pumped laser operation and spectroscopy of Pr3+:LaF3.  

PubMed

We report on the first results of diode pumped laser operation of Pr3+:LaF3 in a quasi continuous wave (qcw) mode with average output powers of up to 80.0 mW (? 161.3 mW qcw) and a maximum slope efficiency of 37% at 719.8 nm. Furthermore it was possible to operate the laser at 537.1 nm and 635.4 nm and to tune the emission wavelength from 609 nm to 623 nm. The pump source was an InGaN laser diode with a maximum output power of 1 W at a central emission wavelength of 442 nm. PMID:23037089

Reichert, F; Moglia, F; Marzahl, D-T; Metz, P; Fechner, M; Hansen, N-O; Huber, G

2012-08-27

48

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

PubMed

Single layers of MgF2 and LaF3 were deposited upon superpolished fused-silica and CaF2 substrates by ion-beam sputtering (IBS) as well as by boat and electron beam (e-beam) evaporation and were characterized by a variety of complementary analytical techniques. Besides undergoing photometric and ellipsometric inspection, the samples were investigated at 193 and 633 nm by an optical scatter measurement facility. The structural properties were assessed with atomic-force microscopy, x-ray diffraction, TEM techniques that involved conventional thinning methods for the layers. For measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed. The dispersion behavior of both deposition materials, which was determined on the basis of various independent photometric measurements and data reduction techniques, is in good agreement with that published in the literature and with the bulk properties of the materials. The refractive indices of the MgF2 coatings ranged from 1.415 to 1.440 for the wavelength of the ArF excimer laser (193 nm) and from 1.435 to 1.465 for the wavelength of the F2 excimer laser (157 nm). For single layers of LaF3 the refractive indices extended from 1.67 to 1.70 at 193 nm to approximately 1.80 at 157 nm. The IBS process achieves the best homogeneity and the lowest surface roughness values (close to 1 nm(rms)) of the processes compared in the joint experiment. In contrast to MgF2 boat and e-beam evaporated coatings, which exhibit tensile mechanical stress ranging from 300 to 400 MPa, IBS coatings exhibit high compressive stress of as much as 910 MPa. A similar tendency was found for coating stress in LaF3 single layers. Experimental results are discussed with respect to the microstructural and compositional properties as well as to the surface topography of the coatings. PMID:12064402

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

2002-06-01

49

Defect entropies and enthalpies in BaF2  

NASA Astrophysics Data System (ADS)

Various experimental techniques have revealed that the predominant intrinsic point defects in BaF2 are anion Frenkel defects. Their formation, enthalpy and entropy, as well as the corresponding parameters for the fluorine vacancy and fluorine interstitial motion have been determined. In addition, low temperature dielectric relaxation measurements in BaF2doped with uranium leads to the parameters ?0, E in the Arrhenius relation ? = ?0 exp( E/ k B T) for the relaxation time ?. For the relaxation peak associated with a single tetravalent uranium, the migration entropy deduced from the pre-exponential factor ?0 is smaller than the anion Frenkel defect formation entropy by almost two orders of magnitude. We show that, despite their great variation, the defect entropies and enthalpies are interconnected through a model based on anharmonic properties of the bulk material which have been recently studied by employing density-functional theory and density-functional perturbation theory.

Katsika-Tsigourakou, Vassiliki; Skordas, Efthimios S.

2010-12-01

50

Properties of optical greases for BaF2 scintillators  

Microsoft Academic Search

Properties of different optical oils and greases in the UV light region were studied using transmission and photoelectron measurements. The results show that not all of the greases commonly used for scintillators are applicable to the BaF2 detector, which have a fast component in the UV region. Results obtained for a spectrometer consisting of a cylindrical well-polished 48 mm diam.

W. Klamra; Th. Lindblad; M. Moszynski; L. O. Norlin

1987-01-01

51

Test of a BaF2 scintillation crystal  

NASA Astrophysics Data System (ADS)

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

Schippers, J. M.; Devries, J.

1983-04-01

52

Fluoride Release from CaF2 and Enamel Demineralization  

Microsoft Academic Search

The anticaries effect of professional fluoride (F) application has been attributed to calcium-fluoride-like deposits (CaF2) formed on enamel, but this has not been clearly demonstrated. We hypothesized that CaF2 formed on plaque-free enamel by F application would reduce enamel demineralization due to the increase of F availability in fluid of subsequently formed plaque. We created distinct levels of CaF2 on

L. M. A. Tenuta; R. V. Cerezetti; A. A. Del Bel Cury; C. P. M. Tabchoury; J. A. Cury

2008-01-01

53

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

54

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

55

Process for Forming Epitaxial BaF2 on GaAs.  

National Technical Information Service (NTIS)

A process for growing single crystal epitaxial BaF2 layers on gallium arsenide substrates by slowly reacting Ba, BaCl2, BaI2, BaBr2, BaF2.BaCl2, BaF2.BaBr2, BaF2.BaI2, BaC12.BaBr2 , Ba3(GaF6)2, BaH2, or BaO2 vapor with a clean, hot GaAs substrate at 500 t...

T. K. Chu F. Santiago M. Stumborg

1995-01-01

56

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

PubMed Central

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

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

2013-01-01

57

Process for Forming Epitaxial BaF2 on GaAs.  

National Technical Information Service (NTIS)

A process for growing single crystal epitaxial BaF2 layers on gallium arsenide substrates by slowly reacting BaF2 vapor with the clean, hot GaAs substrate at 500 to 700 deg C in high vacuum until a uniform, thin (approx. 12A) layer of reaction product is ...

F. Santiago T. K. Chy M. F. Stumberg

1994-01-01

58

Ytterbium Clusters in Fluorite CaF2  

NASA Astrophysics Data System (ADS)

The crystal structure of the ytterbium hexameric cluster in CaF2 has been calculated in the framework of the embedded-cluster method within the shell model, in pair potential approximation. The crystal field parameters and scheme of the energy levels for Yb6F36 hexameric cluster were calculated in the exchange charges model. Also, the optical spectra of Yb3+ single center in CaF2 (cubic and tetragonal symmetry) was calculated and discussed.

Nikiforov, Anatoliy E.; Chernyshev, Vladimir A.; Volodin, Vasiliy P.; Avram, Nicolae M.; Avram, Calin N.

2009-05-01

59

Sensitivity of CaF2 Thermoluminescent Materials to Fast Neutrons,  

National Technical Information Service (NTIS)

The object of the present study is to determine the relative sensitivities of three types of solid CaF2, TL-materials of commercial grade - TLD-200 (CaF2:Dy), TLD-300 (CaF2:TM) and TLD-400 (CaF2:Mn) - under well defined experimental conditions. The TL-res...

J. B. Dielhof A. J. Bos J. Zoetelief J. J. Broerse

1987-01-01

60

CaF2 Formation: Cariostatic Properties and Factors of Enhancing the Effect  

Microsoft Academic Search

CaF2 or a CaF2-like material\\/phosphate-contaminated CaF2 is a major reaction product during topical treatment of dental hard tissues. Recently, evidence has suggested that CaF2 is formed not only on surfaces but also to some extent in the enamel. The minimum concentration of fluoride required for CaF2 formation is not well known and may depend on whether calcium is available from

Bjørn Øgaard

2001-01-01

61

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

PubMed

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

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

2008-04-23

62

Fluoride release from CaF2 and enamel demineralization.  

PubMed

The anticaries effect of professional fluoride (F) application has been attributed to calcium-fluoride-like deposits (CaF(2)) formed on enamel, but this has not been clearly demonstrated. We hypothesized that CaF(2) formed on plaque-free enamel by F application would reduce enamel demineralization due to the increase of F availability in fluid of subsequently formed plaque. We created distinct levels of CaF(2) on enamel to evaluate a dose-response effect. Enamel blocks were mounted in contact with a S. mutans test plaque and used in situ by 10 volunteers. F released to the fluid phase of this substrate ("plaque fluid") was measured before a cariogenic challenge. "Plaque fluid" F concentration was highly correlated to the enamel CaF(2) concentration (r = 0.96, p < 0.001) and to consequent enamel demineralization (r = -0.75, p < 0.001). The results suggest that F released to plaque fluid from CaF(2) formed on enamel may play a significant role in the anticaries effect of professionally applied F agents. PMID:18946010

Tenuta, L M A; Cerezetti, R V; Del Bel Cury, A A; Tabchoury, C P M; Cury, J A

2008-11-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

64

Structural transition of BaF2 nanocrystals under high pressure  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

65

Photon avalanche upconversion and pump power studies in LaF3:Er3+/Yb3+ phosphor  

NASA Astrophysics Data System (ADS)

Hexagonal LaF3:Er3+/Yb3+ phosphor material has been synthesized by chemical precipitation method to obtain high near-infrared to green upconversion (UC) efficiency. Its thermal, structural and fluorescence properties have been studied. UC emission bands have been observed up to 315 nm in UV region. The effect of input pump power on the intensities of various emission bands has been studied in detail and photon avalanche UC mechanism has been identified. On increasing the excitation power, some bands have shown saturation in intensity. Also, at higher pump intensities two new UC bands were observed and their origin has been discussed. The phosphor has also been tested for possible UC-based fingerprint detection.

Singh, A. K.; Kumar, K.; Pandey, A. C.; Parkash, O.; Rai, S. B.; Kumar, D.

2011-09-01

66

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

NASA Astrophysics Data System (ADS)

Uniform, ultra-small-sized and well-water-dispersible LaF3 nanoparticles doped with trivalent rare earth (RE) ions (Eu3+ or Tb3+) have been synthesized by a simple, low temperature synthesis route. The nanoparticles, with sizes of about 3.2 nm (for those doped with Eu3+) and 3.0 nm (for those doped with Tb3+), are roughly spherical and monodisperse. 1,2,4,5-Benzenetetracarboxylic acid (labeled as BA) as sensitizer has been bonded to the surface of the nanoparticles, which can sensitize the emission of RE3+ in the LaF3 nanoparticles. The BA-LaF3:RE3+ (RE = Eu or Tb) nanoparticles have a broad absorption band in the UV domain, and show enhanced luminescence of RE3+ based on an energy transfer from BA ligands to RE3+ ions (i.e. the so-called ``antenna effect''). Due to the dual protection of organic ligands (BA) and inorganic matrices (LaF3), BA-LaF3:RE3+ (RE = Eu or Tb) nanoparticles have longer excited state lifetimes than LaF3:RE3+ (RE = Eu or Tb) nanoparticles as well as lanthanide coordination polymers of BA.

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

2012-08-01

67

Slip Systems and plastic anisotropy in CaF2  

Microsoft Academic Search

An examination was made of the slip planes activated in high-purity CaF2 single crystals with various orientations deformed by compression between 20 °C and 600 °C. It was found that 110 was the most difficult and 100 the easiest to activate. These results are compared to results for UO2 and zirconia.

A. Muñoz; A. Domínguez-Rodríguez; J. Castaing

1994-01-01

68

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

2010-09-28

69

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

70

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

71

Spontaneous ring-like self-assembly of BaF2 nanoparticles.  

PubMed

Self-assembly of BaF2 nanoparticles was described. BaF2 nanoparticles were prepared by microemulsion technology. The self-assembly of the particles is spontaneous without coating reagent on the surface or external force being applied during the procedure of sample preparation. XRD examination and ICP data showed the phase purity of the final product; FTIR spectroscopy confirmed that there was no organic species leaved in the product. By depositing one drop of colloid solution containing BaF2 particles on the TEM grid directly, we can get the ring-like self-assembly with larger particles dispersing peripherally to form a ring and smaller particles inside this ring forming circles. PMID:15913244

Lian, Hongzhou; Liu, Jie; Ye, Zeren; Shi, Chunshan

2005-03-01

72

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

73

A model of CaF2 indentation  

NASA Astrophysics Data System (ADS)

A finite element model (FEM) of calcium fluoride (CaF2) with a rate-dependent mesoplastic constitutive formulation was developed and compared with nanoindentation tests. Indentations on the three main crystallographic planes (100), (110), and (111) of (CaF2) were analyzed. Appropriate material parameters were obtained by correlating the FEM results and the corresponding experimental load-displacement curves. The simulations show a value in the range of 74-110 MPa for the initial shear yield strength and a value in the range of 100-180 MPa for the self-hardening modulus. Such estimates can be used to examine the detailed stress distribution induced by the indentation.

Zhang, Q.; Lambropoulos, J. C.

2007-02-01

74

Optical properties of a CaF2 crystal  

NASA Astrophysics Data System (ADS)

The electronic structure, the charge-density distribution, and the optical-absorption spectrum of a CaF2 crystal are studied by means of a first-principles local-density calculation. The calculated imaginary part of the dielectric function is in good agreement with experimental measurement up to 27.0 eV. We have also used a simplified self-interaction-correction (SIC) model to address the problem of band-gap underestimation in the local-density calculation. Although some marginal improvement in the optical result has been achieved, there is no strong evidence of unequivocal rectification other than an increment in the band gap. This study shows additional (non-SIC) correction to the conduction-band states of CaF2 may also be necessary.

Gan, Fanqi; Xu, Yong-Nian; Huang, Ming-Zhu; Ching, W. Y.; Harrison, Joseph G.

1992-04-01

75

Multi-phonon assisted upconversion emission and power dependence studies in LaF3:Er3+ phosphor.  

PubMed

LaF3:Er3+ phosphor is synthesized through chemical precipitation method and its upconversion (UC) emission studies have carried out using 532-nm excitation. Phosphor has shown two-photon absorption UV bands at the 325 nm, 342 nm, 383 nm, 403 nm and 411 nm wavelengths. At relatively higher excitation powers multi-phonon assisted energy migration from 2H11/2 (4S3/2) level to the upper 4F3/2, 4F5/2 and 4F7/2 levels has observed and this energy migration opened new channel of emission at 440 nm, 453 nm and 488 nm due to the 4F3/2?4I15/2, 4F5/2?4I15/2 and 4F7/2?4I15/2 transitions, respectively. Temperature dependent UC measurement is also done and observed emission pattern is correlated with the power dependence studies. Upconversion bands at 411 and 488 nm wavelengths have shown reversal in intensity as either excitation power or sample temperature is increased and hence these two bands are found to act as optical switch. Planck blackbody like continuum emission has also observed at higher excitation powers. PMID:23399910

Singh, A K; Kumar, K; Pandey, A C; Rai, S B; Kumar, D

2013-01-19

76

Molecular Dynamics Studies of Superionic Conductor CaF2  

Microsoft Academic Search

In the molecular dynamics study of the superionic conductor CaF2, the ionic soft-core system, of which the pair potential consists of the Coulombic and soft-core potentials, is investigated. The influence of the potential, especially of the softness of the soft-core repulsion, on the distribution of anions and diffusion paths is studied. We also study the dynamics of the diffusion in

Yutaka Kaneko; Akira Ueda

1988-01-01

77

Synthesis and characterization of CaF 2 nanocrystals  

Microsoft Academic Search

Calcium fluoride nanocrystals (CaF2) were synthesized by two different techniques namely co-precipitation and hydrothermal. The synthesized nanocrystals were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared red spectroscopy (FTIR), scanning electron microscopy (SEM), optical absorption and photoluminescence (PL). The crystallite size estimated using Scherer's formula was found to be in the range 30–35nm for nanocrystals synthesized by co-precipitation method

C. Pandurangappa; B. N. Lakshminarasappa; B. M. Nagabhushana

2010-01-01

78

One-step synthesis and enhanced luminescence of Eu-doped BaF2 nanocubes.  

PubMed

Europium (Eu3+) doped BaF2 nanocubes were synthesized successfully by a simple method, using oleic acid (OA) as a capping agent. The structure properties were characterized by XRD, FE-SEM, and FTIR. FE-SEM analysis indicates that the prepared nanomaterials have nanocubic morphology with a side length about 150 nm and can be controlled well by adjusting OA concentration. Moreover, the photoluminescence spectra of the samples were investigated. The emission intensity of the BaF2:Eu3+ nanocubes have been enhanced greatly after modified with proper amount of OA, which is promising for new applications and optical devices. PMID:22413237

Liu, Ning; Zhao, Dan; Zhang, Daisheng; Wang, Lili; Qin, Weiping

2011-11-01

79

Bi-doped BaF2 crystal for broadband near-infrared light source.  

PubMed

Bi-doped BaF(2) crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF(2) crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi(2+) or Bi(+) centers adjacent to F vacancy defects are the origins of the observed NIR emissions. PMID:19333280

Ruan, Jian; Su, Liangbi; Qiu, Jianrong; Chen, Danping; Xu, Jun

2009-03-30

80

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

81

Thermoluminescence Response of CaF2:Mn, CaF2:Dy and CaSO4:Tm to Protons and Alpha-Particles,  

National Technical Information Service (NTIS)

Proton/gamma and alpha/gamma response ratios have been measured for very fine powders of the thermoluminescent phosphors CaF2:Mn, CaF2:Dy and CaSO4:Tm. This has been done as part of an evaluation of these phosphors for use in a combined neutron/gamma ther...

S. McGowan R. A. Gravelle

1987-01-01

82

Thermoluminescence Response of CaF2:Mn, CaF2:Dy and CaSO4:Tm to Protons and Alpha-Particles,  

National Technical Information Service (NTIS)

Proton/gamma and alpha/gamma response ratios have been measured for very fine powders of the thermoluminescent phosphors CaF2:Mn, CaF2:Dy and CaSO4:Tm. This has been done as Part of an evaluation of these phosphors for use in a combined neutron/gamma ther...

S. McGowan R. A. Gravelle

1987-01-01

83

Response of MEDEA BaF2 detectors to 20-280 MeV photons  

NASA Astrophysics Data System (ADS)

The response function of MEDEA BaF2 crystals to high energy photons, up to 280 MeV, has been studied using monochromatic ?-rays from the in flight annihilation of positron beams. The experimental response functions are compared to the results of Monte Carlo simulations based on the EGS3 code and parametrized over the whole investigated energy range.

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

1993-05-01

84

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

Microsoft Academic Search

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

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

1992-01-01

85

Photoluminescence of ZnO nanocrystals embedded in BaF2 matrices by magnetron sputtering.  

PubMed

This paper describes ZnO nanocrystals embedded in BaF2 matrices by the magnetron sputtering method in an attempt to use fluoride as a shell layer to embed ZnO nanocrystals core. BaF2 is a wide-band gap material, and can confine carriers in the ZnO films. As a result, the exciton emission intensity should be enhanced. The sample was annealed at 773 K, and X-ray diffraction (XRD) results showed that ZnO nanocrystals with wurtzite structure were embedded in BaF2 matrices. Raman-scattering spectra also confirmed the formation of ZnO nanoparticles. Abnormal longitudinal-optical (LO) phonon-dominant multiphonon Raman scattering was observed in the sample. Room-temperature photoluminescence (PL) spectra showed an ultraviolet emission peak at 374 nm. The origin of the ultraviolet emission is discussed here with the help of temperature-dependent PL spectra. The ultraviolet emission band was a mixture of free exciton and bound exciton recombination observed in the low temperature PL spectra (at 77 K). Abnormal temperature dependence of ultraviolet near-band-edge emission-integrated intensity of the sample was observed. The band tail state was observed in the absorption spectra, illustrating that the impurity-related defects were caused by the shell of the BaF2 grain layer. For comparison, ZnO films on BaF2 substrates were also fabricated by the magnetron sputtering method, and the same measurement methods were used. PMID:18468116

Zang, C H; Liu, Y C; Mu, R; Zhao, D X; Zhang, J Y; Ma, J G; Lu, Y M; Yao, B; Shen, D Z; Fan, X W

2008-03-01

86

Tribological investigation of CaF 2 nanocrystals as grease additives  

Microsoft Academic Search

Calcium fluoride (CaF2) nanocrystals with average grain size of 60nm were synthesized via a precipitation method. The morphology and structure of nanocrystals were characterized by means of transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). TEM and XRD showed that CaF2 nanocrystals are cubic particles in submicron scale. The tribological properties of the prepared CaF2 nanocrystals as an additive

Libo Wang; Bo Wang; Xiaobo Wang; Weimin Liu

2007-01-01

87

Upconversion luminescence of monodisperse CaF2:Yb(3+)/Er(3+) nanocrystals.  

PubMed

Monodispersed CaF(2):Yb(3+)/Er(3+) nanocrystals have been prepared via a facile wet chemical technology. The upconversion luminescence properties of CaF(2):Yb(3+)/Er(3+) nanocrystals were compared with those of NaYF(4):Yb(3+)/Er(3+) nanocrystals with different phases and particle sizes. The results indicated that CaF(2) is a promising host material for producing desirable upconversion luminescence. PMID:19775118

Wang, Guofeng; Peng, Qing; Li, Yadong

2009-10-14

88

A BaF2 crystal array for high energy g-ray measurements  

NASA Astrophysics Data System (ADS)

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

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

2001-07-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

90

Visualization of focusing-refocusing cycles during filamentation in BaF2  

NASA Astrophysics Data System (ADS)

Filamentation occurs within a 1.5 cm-long crystal of BaF2 during the propagation of intense, ultrashort (40 fs) pulses of 800 nm light; a systematic study as a function of incident power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density and the six-photon absorption cross section. At low incident power, a single filament is formed within the crystal; two or more filaments are observed along the direction transverse to laser propagation at higher incident powers. Further, due to fluorescence from six-photon absorption (6PA), we are able to map the intensity variation in the focusing-refocusing cycles along the direction of laser propagation. At still higher incident powers, we observe splitting of multiple filaments. By measuring the radius ( L min ) of single filament inside BaF2, we obtain estimates of peak intensities ( I max ) and electron densities ( ? max ) to be 3.26×1013 W cm-2 and 2.81×1019 cm-3, respectively. Use of these values enables us to deduce that the 6PA cross-section in BaF2 is 0.33×10-70 cm12 W-6 s-1.

Dharmadhikari, A. K.; Dharmadhikari, J. A.; Mathur, D.

2009-02-01

91

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

92

Nuclear Magnetic Resonance Studies of Pure and Samarium-Doped CAF2 Crystals.  

National Technical Information Service (NTIS)

The spin-lattice relaxation time T1 of Fluorine-19 was measured over a temperature range of 77 to 1300K in natural and synthetic CaF2 crystals and in CaF2 crystals doped with 0.05% Sm, 0.16% Sm, and 1.20% Sm. Most of the data was taken with the magnetic f...

R. J. Lysiak P. P. Mahendroo

1965-01-01

93

MBE Grown Ge Nanostructures on CaF(2)/Si(111).  

National Technical Information Service (NTIS)

Germanium nanocrystals were grown on CaF(2)/Si( 111) by molecular beam epitaxy. Specific features of Ge and CaF(2) growth have been analyzed in this work using electron diffraction and atomic force microscopy Well-pronounced Ge quantum dots were observed ...

L. V. Sokolov M. M. Moisseeva N. S. Sokolov O. P. Pchelyakov

2000-01-01

94

Surface Depletion of InSb by SiO and CaF2.  

National Technical Information Service (NTIS)

Increase in resistance of thin films of InSb with thickness of vacuum-deposited overlays of SiO and CaF2 indicates surface depletion in the semiconductor. Also, the equivalent depletion depth and the net trapped charge are evaluated for the case of a CaF2...

F. C. Luo M. Epstein

1972-01-01

95

The first fluoride one-dimensional nanostructures: microemulsion-mediated hydrothermal synthesis of BaF2 whiskers.  

PubMed

A convenient microemulsion-mediated hydrothermal process was employed for the first synthesis of BaF2 whiskers with lengths up to 50 mum and aspects ratios as high as 1000, each of which is a single crystal with a growth direction of (111). A directed aggregation growth process mediated by the microemulsion droplet building blocks is proposed for the formation of BaF2 whiskers. PMID:16220931

Cao, Minhua; Hu, Changwen; Wang, Enbo

2003-09-17

96

Characterization of CaF2 surfaces using Adsorption-Desorption Isotherms and Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

We are interested in using rough CaF2 films to study the superfluid transition in two-dimensional helium systems. These experiments require quantitative information regarding the topography of the CaF2 surfaces. The surface roughness of CaF2 films is known to increase with film thickness as has been shown with previous atomic force microscopy (AFM) measurements [1]. We have fabricated a series of CaF2 samples of different film thicknesses and thus different surface roughnesses. These surfaces were studied using AFM and adsorption-desorption isotherm measurements with liquid nitrogen at T=77 K. The isotherm measurements allow us to determine the pore size distribution of each CaF2 film thickness. We find the emergence of hysteretic capillary condensation due to deep pores in the CaF2 as the film thickness increases. The development of these deep pores is also seen in our AFM measurements. Our combined results provide a detailed description of CaF2 surface roughness which can be utilized in the planned superfluid experiment. [1] D.R. Luhman and R.B. Hallock, Phys Rev. E 70, 051606 (2004).

Wadleigh, L. R.; Luhman, D. R.; Bumcrot, P. G.

2012-02-01

97

A 4? BaF2 detector for measuring neutron capture on unstable nuclei.  

NASA Astrophysics Data System (ADS)

Measurements of neutron capture on unstable nuclei are important for studies of s-process nucleosynthesis, nuclear waste transmutation, and stewardship science. A 160-element, 4? BaF2 detector array and neutron flight path has been designed to make capture measurements at the moderated spallation neutron source at LANSCE. Measurements can be made on as little as 1 mg of sample material over energies from thermal to near 100 keV. We will describe the design and construction status of the DANCE array and present flux measurements from the flight path commissioning experiment.

Ullmann, J. L.; Haight, R. C.; Hunt, L.; Seabury, E. H.; Rundberg, R. S.; Dragowsky, M. R.; Fowler, M. M.; Miller, G. G.; Wilhelmy, J. B.; Strottman, D. D.; Chamberlin, E. P.; Heil, M.; Reifarth, R.; Kaeppeler, F.

2002-04-01

98

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.

2013-03-01

99

Eu 2+ ions and CaF 2-containing transparent glass-ceramics  

Microsoft Academic Search

Transparent glass-ceramics have been prepared by heat-treating 45SiO2–20Al2O3–10CaO–25CaF2 glasses doped with Eu2+ ions (in mol%). The precipitated crystalline phase in the glass-ceramics was CaF2. TEM observation showed the precipitated crystalline phase had a size of 11–18nm and dispersed in the amorphous phase without clustering. Fluorescence measurements showed that Eu2+ ions entered into the CaF2 crystalline phase and gave a much

J Fu; J. M Parker; P. S Flower; R. M Brown

2002-01-01

100

Tm3+:CaF2 planar waveguides grown by liquid phase epitaxy on CaF2 substrates showing signal enhancement at 1.92 ?m  

NASA Astrophysics Data System (ADS)

We report on relative gain measurements at 1.92 ?m in Tm:CaF2 films grown on pure CaF2 substrates by using Liquid Phase Epitaxy with CaCl2 as a solvent. Electron microscopy and X-ray diffraction measurements show that the Tm3+:CaF2 films are about 5 ?m thick and have a small lattice mismatch with the CaF2 substrate. Room temperature emission spectra of the Tm3+ ions around 1.9 ?m exhibit the same structure as in the bulk crystals and the lifetime of the 3F4 metastable level is found equal to about 12.8 ms. The Tm:CaF2 films are guiding optical waves and exhibit a relative gain of 7% at 1.92 ?m when pumped at 0.765 ?m.

Renard, S.; Camy, P.; Doualan, J. L.; Moncorgé, R.; Couchaud, M.; Ferrand, B.

2006-08-01

101

[Upconversion properties of sodium and aluminum fluorides coated BaF2 material].  

PubMed

Sodium and aluminum fluorides coated BaF2 was synthesized by hydrothermal method. It was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and fluorescence spectrophotometer, respectively. The analysis results indicated that sodium and aluminum fluorides existed in the form of sodium fluoride and sodium fluoroaluminate, which combined with BaF2 surface via chemical bonds, and exhibited coated structure. Fluorescence spectroscopy testing showed that there were two wide upconversion emission peaks with maxima at 304 and 324 nm under the excitation at 583 and 863 nm, respectively. Its phosphorescence life time was greater than 18.4 ms, and the emission intensity exhibited a rising process from the beginning and a decaying process after 15 ms. The luminescence mechanism was proposed according to the energy conversion process of the upconversion emission, the results showed that the upconversion emission belonged to the quantum confinement effect-interface light emission center radiative recombination. PMID:22497128

Liu, En-zhou; Fan, Jun; Hu, Xiao-yun; Ye, Yan-xi; Hou, Wen-qian

2012-01-01

102

Swift heavy-ions induced sputtering in BaF2 thin films  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

104

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

SciTech Connect

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

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

1986-02-15

105

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

NASA Astrophysics Data System (ADS)

Single-crystal calcium fluoride (CaF2) is an indispensable optical material for the deep ultraviolet radiation lithography system. The requirement for extremely high performance using in lithography system can be not satisfied by using conventional polishing because the polishing powder are easy to embed to surface due to its relative softness. In the process of rough finishing of CaF2, ductile cutting of CaF2 is considered as a suitable technology instead of tradition polishing to efficiently achieve super-smooth surface without impurity. In this paper, a theoretical and experimental study on the ductile cutting of CaF2 is presented. An energy model for ductile mode cutting of CaF2 is developed, in which the critical undeformed chip thickness can be predicted from the workpiece material characteristics and cutting parameters. The model is verified with experimental results from the micro-grooving of CaF2 on an ultra-precision lathe using a circle diamond crystals tool. The pattern of micro-grooving is inspected using optical microscope, the critical cutting depth of ductile-to-brittle is measured using white-light interferometer. It is shown that the predicted results for the critical undeformed chip thickness corresponding to ductile cutting agree well with the experimental results. Finally, ductile cutting of CaF2 is carried out under the cutting conditions as the maximum undeformed thickness less than the critical undeformed thickness of 233nm obtained above, ductile mode cutting of CaF2 has been achieved a super smooth surface with roughness of 3.50nm (Ra) measured by AFM is obtained.

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

2010-05-01

106

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

Microsoft Academic Search

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

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

2009-01-01

107

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

Microsoft Academic Search

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

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

2009-01-01

108

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

Microsoft Academic Search

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

G C Jain; L C Jain; T S Murty

1981-01-01

109

The apatite formation ability of CaF2 doping tricalcium silicates in simulated body fluid.  

PubMed

The purpose of this study was to investigate the effects of CaF(2) on the apatite formation ability of tricalcium silicates (Ca(3)SiO(5), C(3)S) and the mechanism of apatite formation on C(3)S pastes. Different amounts of CaF(2) (0, 1, 2 and 3 wt%) were mixed in the raw materials during the synthesis process of C(3)S. The apatite formation ability of the CaF(2) doping C(3)S was examined by soaking the one-day setting pastes in simulated body fluid (SBF). The fluoride concentrations, pH values, structural and morphological variations of the pastes were examined during soaking in SBF. With the addition of CaF(2), the initial crystalline apatite formation time of the pastes was decreased from three days to one day. After soaking for seven days, the thicknesses of apatite layers depositing on the surface of C(3)S doped with 0, 1, 2 and 3 wt% CaF(2) were about 88, 102, 168 and 136 microm, respectively. C(3)S doped with 2 wt% CaF(2) showed the better ability to induce the formation of apatite. Furthermore, the mechanism of the apatite formation of the CaF(2) doping C(3)S pastes may be attributed to the formation and stability of F-substituted apatite determined by x-ray photoelectron spectroscopy (XPS) at the early age. The results indicated that CaF(2) doping C(3)S has better in vitro bioactivity, and may be used to prepare novel bone cement. PMID:19567937

Lin, Qing; Li, Yanbao; Lan, Xianghui; Lu, Chunhua; Chen, Yixin; Xu, Zhongzi

2009-06-30

110

Use of a rapid anneal to improve CaF2:Si (100) epitaxy  

Microsoft Academic Search

Post-anneals of short duration at high temperature are shown to improve significantly the quality of CaF2 films on Si (100). An anneal at 1100 °C for 20 s in an Ar ambient reduced ?min, the ratio of backscattered 1.8-MeV 4He+ ions in the aligned to random direction, from 0.26 for an as-grown CaF2 film to 0.03 following the post-anneal. This

Loren Pfeiffer; Julia M. Phillips; T. P. Smith; W. M. Augustyniak; K. W. West

1985-01-01

111

Zero-phonon lines in CaF2 and SrF2  

Microsoft Academic Search

A number of prominent zero-phonon lines have been investigated in additively coloured CaF2 and SrF2 using uniaxial stress. Stark effect and magneto-optical techniques. It is tentatively suggested that a line at 598.8 nm in CaF2 may be a transition of a square planar F4 complex. There is a corresponding centre in SrF2. Other lines investigated appear to be associated with

J. H. Beaumont; A. L. Harmer; W. Hayes; A. R. L. Spray

1972-01-01

112

Synthesis and optical studies of gamma irradiated Eu doped nanocrystalline CaF 2  

Microsoft Academic Search

Europium (Eu) doped Calcium fluoride (CaF2) nanoparticles are synthesized by co-precipitation method and characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Also, optical absorption and photoluminescence (PL) results on gamma irradiated Eu doped CaF2 nanoparticles are presented. The PXRD patterns confirmed the cubic crystallinity of the samples and the particle size is

C. Pandurangappa; B. N. Lakshminarasappa; B. M. Nagabhushana

2011-01-01

113

Single-point diamond turning of CaF 2 for nanometric surface  

Microsoft Academic Search

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

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

2004-01-01

114

[FT-IR study on the solid-state reaction of bilirubin on BaF2].  

PubMed

Bilirubinate complexes are the main component of pigment gallstones and the recent researches suggested that bilirubin free radical plays a role in some biological processes. In this paper the solid-state reaction of bilirubin on BaF2 was examined by FT-IR. The solid-state reaction was produced by grinding the crystalline bilirubin and single crystals BaF2 together in an agate mortar. From the results the free radical mechanism is suggested in the solid-state reaction of bilirubin on BaF2. The replacement of H on NH of pyrrole by Ba2+ was prior to that of H on COOH. The structure of the resultant complex from the solid-state reaction is different compared with that from the liquid-state reaction. PMID:15810303

Yang, Z; Weng, S; Wu, J

1998-04-01

115

EPR spectra of the Mn2+ ion in the oxyfluoride glass ceramics containing BaF2 nanocrystalline phase  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) spectroscopy has been used to investigate structure of the oxyfluoride glass ceramics containing BaF2 fluoride component. Mn2+ ion has been used as a paramagnetic probe. After successful material synthesis and thermal treatment at temperatures above first crystallization temperature transparent glass ceramics samples were obtained. For these samples superhyperfine (SHF) structure in the X-band EPR spectra taken at 77 K has been observed. Such SHF structure is characteristic to fluorine hyperfine interaction observed in the fluoride crystals. Obtained data allow analyzing the structure of the BaF2 crystallites and possible location of the Mn2+ ion in the BaF2 crystalline lattice.

Berzins, Dz; Fedotovs, A.; Kiselova, O.; Sarakovskis, A.

2012-08-01

116

Phase transition and thermodynamic properties of CaF2 via first principles  

NASA Astrophysics Data System (ADS)

The structural stabilities, phase transitions and thermodynamic properties of CaF2 under high pressure and temperature are investigated by first-principles calculations based on the plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of CaF2 under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. Our results demonstrate that the sequence of the pressure-induced phase transition of CaF2 is the fluorite structure (Fm3m), PbCl2-type structure (Pnma) and Ni2In-type structure (P63/mmc), and the transition pressures are obtained. The temperature-dependent volume and thermodynamic properties of Fm3m phase CaF2 at 0 GPa are presented. The thermodynamic properties of CaF2 in Fm3m, Pnma and P63/mmc phases at 300 K are predicted using the corrected and uncorrected quasi-harmonic approximation model. The variations of the thermal expansion ? and heat capacity CV with pressure P and temperature T of CaF2 in the three phases are systematically obtained.

Qi, Yuan-Yuan; Cheng, Yan; Liu, Min; Chen, Xiang-Rong; Cai, Ling-Cang

2013-10-01

117

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

NASA Astrophysics Data System (ADS)

The emission spectrum, the time dependence of the luminescence, the excitation spectrum and the reflectance spectrum have been measured for the pure BaF2 crystal, the BaF2:Sr crystals with Sr++ concentrations of 2 and 5 mol%, the BaF2:MgF2 crystal with a mole mixing ratio of 1:2, and the pure CsBr crystal and the CsBr:LiBr crystal with a mole mixing ratio of 1:1. The measurements have been made by using synchrotron orbital radiation and high-energy electrons produced by gamma-rays. It is shown that the BaF2, the BaF2:Sr and the BaF2:MgF2 crystals have the Auger-free luminescence having decay times around 0.90 ns. The slow and fast luminescence components of the BaF2 crystal are suppressed by introduction Sr++ and Mg++ ions. It is, however, clearly seen that the suppression of the slow component is more effectively occurring than that of the fast component, especially in the BaF2:MgF2 crystal. By analyzing the Auger-free luminescence spectrum, it is shown that the valence band widths are 2.7 +/- 0.3 eV, 2.7 +/- 0.3 eV and 4.2 +/- 0.3 eV and the band-gap energies are 11.1 +/- 0.3 eV, 11.1 +/- 0.4 eV and 11.9 +/- 0.4 eV for BaF2, BaF2:Sr and BaF2:MgF2 crystals, respectively. The introduction of LiBr into CsBr has resulted in a significant enhancement in the luminescence intensity, attaining 40 times larger intensity than that of CsBr crystal at room temperature, due to the suppression of the non-radiative relaxation of the outer-most core holes due to the absorption induced by the Urbach effect. The observations of the increases in the band gap-energy, the exciton energy and the decay time of the CsBr:LiBr crystal compared with those of the CsBr crystal support the argument given in the present study regarding the suppression of the Urbach effect in the CsBr:LiBr crystal. The decay times observed are 0.20 +/- 0.05 ns and 0.90 +/- 0.06 ns for CsBr and CsBr:LiBr crystals, respectively. On leave from Instituto de Pesquisas Energéticas e Nucleares, IPEN/CNEN-SP, Trav. R no. 400, Cidade Universitária, Sa~o Paulo, Brazil.

Hamada, Margarida Mizue

1994-03-01

118

Visible single-shot autocorrelator in BaF2 for subpicosecond KrF laser pulses  

NASA Astrophysics Data System (ADS)

A single-shot autocorrelator based on the two-photon excited fluorescence of BaF2 in the visible region at 400 nm has been developed for ultrashort KrF laser pulses at 248 nm. Operation in the visible region offers simplification in the required optical components as compared with previously reported systems, which used ultraviolet fluorescence emission. The fluorescence intensity is also used to measure the two-photon absorption coefficient of BaF2, yielding a value of beta = 1.3 +/- 0.4 \\times 10-10 cm/W.

Li, Y. M.; Fedosejevs, R.

1996-05-01

119

Visible single-shot autocorrelator in BaF(2) for subpicosecond KrF laser pulses.  

PubMed

A single-shot autocorrelator based on the two-photon excited fluorescence of BaF(2) in the visible region at 400 nm has been developed for ultrashort KrF laser pulses at 248 nm. Operation in the visible region offers simplification in the required optical components as compared with previously reported systems, which used ultraviolet fluorescence emission. The fluorescence intensity is also used to measure the two-photon absorption coefficient of BaF(2), yielding a value of ? = 1.3 ± 0.4 × 10(-10) cm/W. PMID:21085400

Li, Y M; Fedosejevs, R

1996-05-20

120

Remarkable differences in photoluminescence properties between BaF2:Eu3+ microrods and nanorods.  

PubMed

The preparation process and photoluminescent properties of one-dimensional BaF2:Eu3+ nanorods (NRs) and microrods (MRs) were investigated. The results indicate that the samples were NRs with uniform diameters in the range of 30-50 nm, and lengths in the range of 1.2-3 microm when cooled to room temperature naturally. However, the samples were MRs with length of 1.5-3.0 microm and outer diameters of 200-250 nm when cooled to room temperature immediately. Furthermore, the relative intensity of 5D0 --> 7F2 depended on the two structures obtained under different temperatures. This work demonstrates that a MRs may be more favorable than NRs for photoluminescence. PMID:20355665

De, Gejihu; Gui, Bao; Wang, Weihua

2010-03-01

121

Microscopic analysis of the chemical reaction between Fe(Te, Se) thin films and underlying CaF2  

NASA Astrophysics Data System (ADS)

To understand the chemical reaction at the interface of Fe(Te, Se) and CaF2 materials, we used transmission electron microscopy to analyze five types of Fe(Te, Se) superconducting thin films prepared on different types of substrate: two on a CaF2 substrate, one on a CaF2 substrate with a CaF2 buffer layer, one on a CaF2 substrate with an FeSe buffer layer, and one on a LaAlO3 substrate with a CaF2 buffer layer. Energy-dispersive x-ray spectroscopy analysis revealed a potential interdiffusion between fluorine and selenium that plays a significant role in the variation of the lattice parameters. We conclude that the lattice parameters of the Fe(Te, Se) thin films are primarily determined by the chemical substitution of anions, while the lattice mismatch plays a secondary role.

Ichinose, A.; Nabeshima, F.; Tsukada, I.; Hanawa, M.; Komiya, Seiki; Akiike, T.; Imai, Y.; Maeda, A.

2013-07-01

122

Effect of Bi ion on Eu 2+  ? Eu 3+ conversion in CaF 2 :Eu phosphors for RPL dosimetry  

Microsoft Academic Search

UV photo-excited Eu2+ and Eu3+ luminescence from CaF2:Eu and CaF2:Eu, Bi phosphors were investigated. The effect of gamma exposure followed by temperature effect shows conversion mechanism\\u000a between Eu2+ ? Eu3+ ion in CaF2:Eu and CaF2:Eu, Bi phosphors which were studied for RPL dosimetry. The photoluminescence and X-ray diffraction characterization are reported\\u000a in this article.

S. J. DhobleI; I. M. Nagpure; N. S. Dhoble; Pablo Molina

123

RHEED intensity oscillations observed during the growth of CaF2 on Si(111)  

NASA Astrophysics Data System (ADS)

Analyses of reflection high-energy electron diffraction (RHEED) intensity changes observed during initial stages of heteroepitaxial growth of calcium fluoride (CaF2) on Si(111) are presented. Layers obtained by deposition of CaF2 on a hot (550 °C) substrate demonstrate a high-quality crystallographic structure. The state of the surfaces of growing layers is studied with the in situ combination of RHEED azimuthal plots and rocking curve. The intensity of the reflected beam is calculated by solving the one-dimensional Schrödinger equation.

Daniluk, Andrzej; Mazurek, Piotr; Paprocki, Krzysztof; Miko?ajczak, Pawe?

1998-05-01

124

Synthesis and upconversion luminescence properties of CaF2:Yb3+/Tm3+ microspheres.  

PubMed

CaF2:Yb3+/Tm3+ microspheres were synthesized by using a simple hydrothermal method. Their structures and morphologies were characterized by X-ray diffraction (XRD) and field-effective scanning electron microscopy (FESEM). The microspheres were formed from a large number of nanospheres with almost the same diameter after annealing. The growth mechanism of the microspheres was discussed. Strong ultraviolet (UV) and blue upconversion (UC) emission from the CaF2 microspheres was observed under 980 nm excitation. The enhancement of the UV UC emission was attributed to the size effect of the nanoscale particles. PMID:22413321

Jiang, Tao; Zhao, Dan; Qin, Weiping

2011-11-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

126

Double beta decay study of 48Ca by CaF2 scintillator  

NASA Astrophysics Data System (ADS)

A CaF2 scintillation detector system (ELEGANT VI) is developed to search for neutrinoless double beta decay (0?DBD) of 48Ca. No events were observed around the Q-value energy region after the analysis of 4.23 kg yr data. To derive the lower limit for the half-life, the expected number of background events was estimated by a Monte Carlo simulation using the measured activities of 214Bi and 220Rn inside CaF2 crystals. A new lower limit is obtained to be 1.8 × 1022 yr at the 90% C.L.

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

2003-06-01

127

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

128

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

129

Properties of ultra-large CaF2 crystals for the high NA optics  

NASA Astrophysics Data System (ADS)

CaF2(Calcium fluoride) lens materials are required for the most important component of the ArF laser lithography stepper for the reason of its excellent transparency in DUV region and excellent laser durability as compared with quartz. Last year we reported to succeed in growing both <111> and <100> crystals, which had 210m diameter and 150mm length by the Czochralski (CZ) method with high productivity1). The obtained CaF2 crystal had low stress birefringence by way of the optimized annealing process. Although, for the higher NA system, larger CaF2 single crystals are required for the lens materials having the high quality and high productivity. To meet the above mentioned demands, we made efforts to produce and succeeded the first in the world ultra-large (?300mm over) and high quality CaF2 single crystal by the CZ method with high productivity. The crystal had very low stress birefringence, good transparency in DUV region and good homogeneity. It was also easy to control the orientation of the crystal by the selection of seed crystal.

Hatanaka, Y.; Yanagi, H.; Nawata, T.; Inui, Y.; Mabuchi, T.; Yasumura, K.; Nishijima, E.; Fukuda, T.

2005-05-01

130

Analysis of thermoluminescence kinetics of CaF2(Tm) peaks with glow curve deconvolution  

Microsoft Academic Search

The purpose of this study is to achieve detailed information on kinetic parameters of the peaks of a dosimetric material. First and general order kinetic formulas are applied with a computerized deconvolution technique to CaF2(Tm) thermoluminescence glow curves. A comparison is presented between deconvolution kinetic parameters and parameters obtained applying Chen's method.

C. Bacci; P. Bernardini; A. di Domenico; C. Furetta; B. Rispoli

1990-01-01

131

Scanning Force Imaging of Atomic Size Defects on the CaF2\\\\(111\\\\) Surface  

Microsoft Academic Search

Cleaved (111) surfaces on CaF2 were imaged with scanning force microscopy operated in the dynamic mode in ultrahigh vacuum. Imaging the pristine surface reveals an atomic scale contrast with the structure expected for the fluorine terminated surface. We always reproduced the perfect surface periodicity never observing stable defects. However, after exposing the surface to 280 L of oxygen while constantly

M. Reichling; C. Barth

1999-01-01

132

Electronic shielding by closed shells in CaF2:Yb3+  

Microsoft Academic Search

ENDOR measurements on tetragonal 173Yb3+ sites in CaF2 give a value of (1-gamma?)\\/(1-sigma2) = 75 +\\/- 18, much smaller than theoretical estimates, or previous experimental values. This may indicate sizeable, previously neglected, effects of covalency.

J. M. Baker; W. B. J. Blake

1969-01-01

133

Hardness anisotropy of SrF 2 , BaF 2 , NaCl and AgCl crystals  

Microsoft Academic Search

The value of Knoop microhardness was obtained for crystals of SrF2, BaF2, NaCl and AgCl by indentation in various directions on several crystallographic planes. In all cases, the hardness is essentially dependent on the crystallographic direction along the long axis of the indentor and independent of the plane of indentation, as first reported by Garfinkle and Garlick for other cubic

G. Y. Chin; M. L. Green; L. G. Uitert; W. A. Hargreaves

1973-01-01

134

Variation of luminescence decay in BaF2 crystal excited by electrons, alpha particles and fission fragments  

Microsoft Academic Search

The time dependence of the luminescence from BaF2 crystal excited by electrons, alpha particles and fission fragments has been studied for wavelengths of 180-400 nm by a single-photon counting technique. A (220 +\\/- 10) nm component with a lifetime of 0.88 ns is observed for electron and fission fragment excitation. No 220 nm component is observed for alpha particle excitation.

S. Kubota; M. Suzuki; F. Shiraishi; Y. Takami

1986-01-01

135

RAPID COMMUNICATION: A new method of HF control for synthesizing YBCO using the BaF2 ex situ process  

NASA Astrophysics Data System (ADS)

The removal of hydrogen fluoride gas (HF) is a significant problem for the ex situ processing of large area YBCO precursor coated conductors employed in the BaF2 process. We propose a new solution based on the in situ chemical absorption of HF. This approach allows the design of a simple ex situ reactor, which, in theory, has an extremely large capacity to uniformly absorb HF and permit the uniform growth of crystalline YBCO.

Solovyov, Vyacheslav F.; Wiesmann, Harold J.; Suenaga, Masaki

2003-11-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

137

Onset of the optical damage in CaF(2) optics caused by deep-UV lasers.  

PubMed

The exterior sides of calcium fluoride (CaF(2)) outcoupling mirrors are damaged by ArF laser light irradiation with high pulse-energy densities (80 mJ/cm(2)). The damage is generated by a partial alteration of the CaF(2) substrate to calcite. The CaF(2) decomposition is driven by photochemical processes due to the UV light and the presence of water vapor and is supported by elevated temperatures within the laser beam transmitting area. Small filaments act as starting points for the decomposition process, where kerogenous carbon and calcite can occur. PMID:20016623

Bauer, Michael; Bischoff, Martin; Hülsenbusch, Thomas; Matern, Ansgar; Stark, Robert W; Kaiser, Norbert

2009-12-15

138

Ultralow-threshold Raman lasing with CaF2 resonators.  

PubMed

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

Grudinin, Ivan S; Maleki, Lute

2007-01-15

139

Study of haze in 193nm high dose irradiated CaF2 crystals  

NASA Astrophysics Data System (ADS)

Crystalline calcium fluoride is one of the key materials for 193 nm lithography and is used for laser optics, beam delivery system optics and stepper/scanner optics. Laser damage occurs, when light is absorbed, creating defects in the crystal. Haze is known as a characteristic optical defect after high dose irradiation of CaF2 - an agglomeration of small scattering and absorbing centers. In order to prevent unnecessary damage of optical components, it is necessary to understand the mechanism of laser damage, the origin of haze and the factors that serve to prevent it. Stabilized M centers were described as reversible absorbing defects in CaF2, which can be annealed by lamp or laser irradiation. In this study the irreversible defects created by 193 nm laser irradiation were investigated.

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

2009-10-01

140

Shock Hugoniot and high pressure melting curve for CaF2  

NASA Astrophysics Data System (ADS)

CaF2 is an important class of super ionic crystals whose structural properties are of much theoretical and experimental interest at high pressure and temperature. In the present study high pressure melting curve and equations of states (static and dynamics) of B1 phase of CaF2 were investigated. Total energy was calculated by using the DFT based plane-wave pseudopotential (PW-DFT) within the generalized gradient approximation. Nearest-neighbor second-moment tight-binding energy model (TB-SMA) was used for calculating both static and dynamic equations of states. Parameters of the TB-SMA model were determined by the present ab initio pseudopotential calculations. While volume dependence of Grüneisen parameter was used within the Lindemann's criterion to calculate high pressure melting curve. It is found that the present simple TB-SMA scheme is able to mimic shock Hugoniot for such fluorides correctly.

Joshi, R. H.; Patel, A. B.; Bhatt, N. K.; Thakore, B. Y.; Jani, A. R.

2013-06-01

141

Windows for HF\\/DF chemical lasers - CaF2 or ZnSe  

Microsoft Academic Search

An investigation of laser-driven phenomena occurring in CaF2 and ZnSe window materials which affect the performance of high energy laser systems at chemical wavelengths is reported. The systems studied comprised an optical cavity, relay tube, beam expander, and output window to the focus. An analysis of the cumulative phaseshifts due to beam defocusing and distortion caused by thermally generated aberrations

C. A. Klein

1981-01-01

142

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

Microsoft Academic Search

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

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

2004-01-01

143

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

Microsoft Academic Search

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

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

1997-01-01

144

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

Microsoft Academic Search

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

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

2004-01-01

145

CaF2 in Enamel Biopsies 6 Weeks and 18 Months after Fluoride Treatment  

Microsoft Academic Search

Fluoride concentrations were studied in enamel biopsies from maxillary central incisors 6 weeks and 18 months after fluoride treatment. In the short-term study biopsies were obtained prior to and after treatment with acidic sodium or ammonium fluoride. The findings showed that large amounts of fluoride were deposited in enamel from NH4F treatment (mean concentration 84,723 ppm), indicating substantial CaF2 formation.

V. Caslavska; P. Gron; R. L. Kent; K. Joshipura; P. F. De Paola

1991-01-01

146

Free-inducation-decay measurements and determination of moments in CaF2  

Microsoft Academic Search

The results of measurements of F19 free-induction-decay (fid) signals in CaF2 are presented. The measurements were performed at 4.2 and 77 K using conventional pulsed-nuclear-magnetic-resonance and zero-time-resolution techniques. The recorded signals spanned four orders of magnitudes and permitted a direct comparison with various theoretical predictions for the asymptotic behavior of the fid signals for long times. A function was constructed,

M. Engelsberg; I. J. Lowe

1974-01-01

147

Effect of CaF2 Content on Rate of Fluoride Release from Filled Resins  

Microsoft Academic Search

Information on the time-dependent release of fluoride from filled resins containing fluoride particles as a function of particle content and solution pH is limited. This study characterized the fluoride ion release from filled resins containing CaF2 particles as a function of filler content and pH. Urethane dimethacrylate and triethylene glycol dimethacrylate resins were used to make filled-resin disks containing 9.09,

K. J. Anusavice; N.-Z. Zhang; C. Shen

2005-01-01

148

Spectroscopy of Yb3+:CaF2 : From isolated centers to clusters  

Microsoft Academic Search

A detailed spectroscopic study of Yb3+:CaF2 is made by using laser selective excitation, low-temperature time-resolved fluorescence, and Raman techniques. Three dominant types of Yb3+ isolated ion centers are identified at very low (0.03at.%) dopant concentration: two of them with cubic and tetragonal symmetries and the third one not clearly identified but likely of trigonal symmetry. Fluorescence decays strongly differ from

V. Petit; P. Camy; J.-L. Doualan; X. Portier; R. Moncorgé

2008-01-01

149

Nuclear Spin-Lattice Relaxation in CaF2 Crystals via Paramagnetic Centers  

Microsoft Academic Search

The results of nuclear spin-lattice relaxation-time measurements in the laboratory reference frame (T1) and the rotating reference frame (T1r), made on F19 nuclei in CaF2 crystals doped either with Eu3+, Ce3+, or Mn2+ paramagnetic centers, are reported. From 0.25 to 0.36 of the Debye temperature, values of the correlation time tauc are found from T1r minima for Mn2+ ions. Over

D. Tse; I. J. Lowe

1968-01-01

150

Lattice relaxation of highly excited self-trapped excitons in CaF2  

Microsoft Academic Search

We have investigated relaxation in the lattice of CaF2 at 80 K, caused by the electronic excitation of self-trapped excitons. We employed sequential excitation: first an electron pulse to create self-trapped excitons, and second a laser pulse addressed to the electron or the hole. Hole excitation gives rise to stable F centers; these are not generated in significant numbers by

Katsumi Tanimura; Takanori Katoh; Noriaki Itoh

1989-01-01

151

Optical study of Yb(3+)/Yb(2+) conversion in CaF(2) crystals.  

PubMed

Yb(3+) ions with various site symmetries have been observed in the absorption and emission spectra of Yb(3+):CaF(2) crystals, both ?-irradiated and annealed in hydrogen. The absorption intensity value is found to be much higher for the ?-irradiated crystal and strongly dependent on the gamma dose. The UV absorption spectra of ?-irradiated and H(2)-annealed CaF(2):5 at.% Yb(3+) crystals are quite similar. Yb(2+) absorption bands are observed at 360, 315, 271, 260, 227 and 214 nm, which are called A, B, C, D, F and G bands, respectively. For ?-irradiated CaF(2):30 at.% Yb(3+), an additional band at 234 nm can be seen. It is suggested that only a negligible amount of Yb(3+) ions are converted into Yb(2+) under the ?-irradiation. The presence of Yb(2+) is confirmed by the 565 and 540 nm luminescence under 357 nm excitation. It is also suggested that the excitation in the A, C, D and F absorption bands of Yb(2+) gives rise to photo-ionization of Yb(2+) ions and electrons in the conduction band to form the excited Yb(3+) ions which emit IR Yb(3+) luminescence.The UV absorption and emission spectra obtained for ?-irradiated and H(2)-annealed crystals have different structures. This suggests that different mechanisms are responsible for the creation of Yb(2+) ions. ?-irradiation favours Yb(2+) isolated centres by reduction of Yb(3+) ions located at Ca(2+) lattice sites, whereas annealing in hydrogen favours Yb(2+) centres neighbouring Yb(3+) ions when a Yb(3+) ion pair captures a Compton electron. Also, ?-irradiation does not change the position of Yb(3+) ions converted into Yb(2+) in the CaF(2) lattice. In the case of H(2) annealing, a Yb(3+) ion converted to Yb(2+) is shifted to the Ca(2+) position in the lattice. PMID:21690695

Kaczmarek, S?awomir M; Tsuboi, Taiju; Ito, Masahiko; Boulon, Georges; Leniec, Grzegorz

2005-06-10

152

Spectroscopic properties of CaF2:U4+ as a saturable absorber  

Microsoft Academic Search

The spectroscopic properties of crystals of CaF2:U4+ have been examined in light of recent interest expressed for this material as a saturable absorber in the passive Q switching of near infrared solid state lasers. The detailed crystal-field splitting of the energy levels of U4+(5f2 ) is analyzed for the ion in different charge-compensated sites. Identification of the site is based

John B. Gruber; Dhiraj K. Sardar; Larry D. Merkle; Bahram Zandi; Richard Jarman; J. Andrew Hutchinson

2001-01-01

153

Onset of laser ablation in CaF2 crystal under excimer laser irradiation  

Microsoft Academic Search

With the widespread application of excimer lasers for micro- processing, optically transparent materials in the UV region have become more important as optical components. The transparent materials currently available commercially are silica glass and fluoride crystals, CaF2 and MgF2. The resistance of these materials against cumulative irradiation of excimer lasers is required from the viewpoint of application, and it is

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

2002-01-01

154

Growth and hydrogenation of epitaxial yttrium switchable mirrors on CaF 2  

Microsoft Academic Search

Rutherford backscattering (RBS) ion channeling measurements and X-ray diffraction experiments are performed to study the epitaxial nature of as-deposited yttrium on CaF2?111? substrates and the effect of hydrogenation on the crystalline quality. The RBS and X-ray results clearly demonstrate the unique epitaxial relation between as-deposited films and the substrate, which is preserved upon loading with hydrogen. X-Ray diffraction reveals: (i)

E. S. Kooij; J. H. Rector; D. G. Nagengast; J. W. J. Kerssemakers; B. Dam; R. Griessen; A. Remhof; H. Zabel

2002-01-01

155

The Zeeman Spectra of Gd3+ in CaF2 at Cubic Sites.  

National Technical Information Service (NTIS)

The octet S7/2 ground state Gd3+ is split only 0.149/cm by the cubic crystal field in CaF2 and is described at 11.3 kG by the projection quantum number J sub Z referred to the magnetic field axis and behaves like a spin 7/2 system with an isotropic g valu...

J. A. Detrio

1969-01-01

156

Temperature-dependent refractive index of CaF2 and Infrasil 301  

NASA Astrophysics Data System (ADS)

In order to enable high quality lens designs using calcium fluoride (CaF2) and Heraeus Infrasil 301 (Infrasil) for cryogenic operating temperatures, we have measured the absolute refractive index of these two materials as a function of both wavelength and temperature using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center. 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 ?m, while for Infrasil, we cover temperatures ranging from 35 to 300 K and wavelengths from 0.4 to 3.6 ?m. For CaF2, we compare our index measurements to measurements of other investigators. For Infrasil, we compare our measurements to the material manufacturer's data at room temperature and to cryogenic measurements for fused silica from previous investigations including one of our own. Finally, we provide temperature-dependent Sellmeier coefficients based on our measured data to allow accurate interpolation of index to other wavelengths and temperatures.

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

2007-10-01

157

The Detector for Advanced Neutron Capture Experiments: A 4? BaF2 Detector for Neutron Capture Measurements at LANSCE  

NASA Astrophysics Data System (ADS)

The Detector for Advanced Neutron Capture Experiments (DANCE) is a 162-element 4? 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.; Agvaanluvsan, U.; Alpizar, A.; Bond, E. M.; Bredeweg, T. A.; Esch, E.-I.; Folden, C. M.; Greife, U.; Hatarik, R.; Haight, R. C.; Hoffman, D. C.; Hunt, L.; Kronenberg, A.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Schwantes, J. M.; Strottman, D. D.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.

2005-05-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

159

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

PubMed

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

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

2011-11-15

160

Spectroscopic properties of Er3+ ions in transparent oxyfluoride glass ceramics containing CaF2 nano-crystals  

Microsoft Academic Search

In this paper, the spectroscopic properties of Er3+-doped oxyfluoride glass ceramics containing CaF2 nano-crystals are systematically investigated. X-ray diffraction (XRD) and transmission electron microscope (TEM) experiments confirmed the formation of CaF2 nano-crystals in the glassy matrix. Based on the Judd-Ofelt theory, the intensity parameters Omega2,4,6, spontaneous emission probability, radiative life, radiative quantum efficiency, width of the emission line, stimulated emission

Daqin Chen; Yuansheng Wang; Yunlong Yu; En Ma; Zhongjian Hu

2005-01-01

161

A GaAsMISFET using an MBE-grown CaF2 gate insulator layer  

Microsoft Academic Search

The CaF2 layer and an undoped GaAs channel layer grown by molecular beam epitaxy (MBE) on a semi-insulating GaAs (100) substrate. The two layers are grown sequentially inside the same MBE chamber to form a clean CaF2-GaAs interface. A self-aligned process using a WSix gate metal is used to fabricate the MISFET. A 1- ?m gate-length FET exhibiting a transconductance

T. Waho; F. Yanagawa

1988-01-01

162

Aqueous solution synthesis of CaF2 hollow microspheres via the ostwald ripening process at room temperature.  

PubMed

Nearly monodispersive CaF2 hollow microspheres were synthesized by a facile aqueous solution route from the mixed aqueous solutions of CaCl2, Na2WO4, and NaF at room temperature. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and N2 adsorption-desorption techniques. The CaF2 hollow microspheres have an average diameter of about 1.5 microm and a hollow interior of 0.5 microm. The shell is composed of numerous single-crystalline nanoparticles with diameter of about 20 nm. The morphologies and diameters of the CaF2 products are strongly dependent on the experimental parameters, such as the concentration of the aqueous NaF solution and the reaction temperature. The synthetic experiments indicate that the growth process of CaF2 hollow microspheres involves first the formation of CaWO4 solid microspheres and then the formation of CaF2 solid microspheres through the reaction between CaWO4 and F(-) ions controlled by the difference of the solubility product for CaWO4 and CaF2. Phenomenological elucidation based on TEM observations and XRD patterns of intermediate products at different precipitation stages indicates that the formation mechanism for the CaF2 hollow microspheres is related to the Ostwald ripening mechanism. N2 adsorption-desorption measurement shows that the CaF2 hollow microspheres possess a high Brunauer-Emmett-Teller surface area and porosity properties. The synthetic procedure is straightforward and represents a new example of the Ostwald ripening mechanism for the formation of inorganic hollow structures in an aqueous solution at room temperature. PMID:20356002

Wang, Wen-Shou; Zhen, Liang; Xu, Cheng-Yan; Chen, Jun-Zhou; Shao, Wen-Zhu

2009-04-01

163

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

Microsoft Academic Search

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

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

2002-01-01

164

Structural and mechanical properties of evaporated pure and mixed MgF2-BaF2 thin films  

NASA Astrophysics Data System (ADS)

To grow dense and hard MgF2 films substrate temperatures of about 300 degrees C are required, which unfortunately leads to high tensile film stress and the ability of crack formation. Lowering tensile stress in MgF2 films can be achieved by admixture a second fluoride material of higher cation radius than Mg2+. While former investigation were performed with non-heated films the purpose of the present work was to verify the behavior of mixed films when deposited at elevated substrate temperatures. One of the promising add material is BaF2 which enables evaporation of appropriate pre-mixed materials from a single source. The BaF2 content in the mixed films was varied from 3 to 55 mol percent in the MgF2 host. Optical, mechanical, and structural properties of samples deposited at different substrate temperatures have been studied by spectral photometry, IR spectroscopy, ex situ measurement of mechanical stress, x-ray diffraction, and -reflectometry, RBS, as well as investigation of surface morphology.

Thielsch, Roland; Pommies, Matthieu; Heber, Joerg; Kaiser, Norbert; Ullmann, Jens

1999-09-01

165

Optimising the design of a large-area positron camera based on BaF2-TMAE/MWPC technology  

NASA Astrophysics Data System (ADS)

A prototype annihilation photon detector has been constructed by the RMH/ICR/RAL collaboration based on the coupling of a 50 × 50 × 8 mm3 BaF2 scintillator to a low pressure TMAE filled multiwire proportional chamber. Its design is undergoing optimisation and currently achieved performance is 8 mm FWHM spatial resolution, 12 ns time resolution and 19% efficiency. The problems associated with scaling up this technology for a clinical PET system were investigated using Monte Carlo techniques. The size of the required detectors (600 × 400 mm2) will result in the use of tiles of BaF2. A comparison between a single slab and a 6 × 4 array of 16 mm thick crystals was made and the errors introduced were studied. Spatial resolution was degraded 40% axially and 27% radially/tangentially by multiple crystals. However, the imaging of distributed sources demonstrates that in any practical situation quality degradation comes primarily from scattering. Further studies to determine the distribution of scatter expected from the proposed detector are outlined.

Suckling, J.; Ott, R. J.; Marsden, P. K.; Bateman, J. E.; Connolly, J. F.; Stephenson, R.

1991-12-01

166

CaF_2 whispering-gallery-mode-resonator stabilized-narrow-linewidth laser  

NASA Astrophysics Data System (ADS)

A fiber laser is stabilized using a Calcium Fluoride (CaF2) whispering-gallery-mode resonator. It is set up using a semiconductor optical amplifier as a gain medium. The resonator is critically coupled through prisms, and used as a filtering element to suppress the laser linewidth. Using the self-heterodyne beat technique the linewidth is determined to be 13 kHz. This implies an enhancement factor of 10^3 with respect to the passive cavity linewidth. The three-cornered hat method shows a stability of 10^(-11) after 10 \\mu s.

Sprenger, B.; Schwefel, H. G. L.; Lu, Z. H.; Svitlov, S.; Wang, L. J.

2010-08-01

167

CaF2 whispering-gallery-mode-resonator stabilized-narrow-linewidth laser.  

PubMed

A fiber laser is stabilized by introducing a calcium fluoride (CaF(2)) whispering-gallery-mode resonator as a filtering element in a ring cavity. It is set up using a semiconductor optical amplifier as a gain medium. The resonator is critically coupled through prisms, and used as a filtering element to suppress the laser linewidth. A three-cornered-hat method is used and shows a stability of 10(-11) after 10 micros. Using the self-heterodyne beat technique, the linewidth is determined to be 13 kHz. This implies an enhancement factor of 10(3) with respect to the passive cavity linewidth. PMID:20808352

Sprenger, B; Schwefel, H G L; Lu, Z H; Svitlov, S; Wang, L J

2010-09-01

168

Effect of porosity on impedance of CaF2 ceramic  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

169

Neutrino-less double-? decay of Ca48 studied by CaF2(Eu) scintillators  

NASA Astrophysics Data System (ADS)

We searched for the neutrino-less double-? decay(0???) of Ca48 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 · day. It gives a lower limit (90% confidence level) of T1/20???>2.7×1022 year for the half-life of 0??? of Ca48. Combined with our previous data for 1553 kg · day [I. Ogawa , Nucl. Phys. A730, 215 (2004)], we obtained a more stringent limit of T1/20???>5.8×1022 year.

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

2008-11-01

170

Paramagnetic Resonance Spectrum of Manganese in Cubic MgO and CaF2  

Microsoft Academic Search

The paramagnetic resonance spectrum of manganese in cubic MgO and CaF2 has been analyzed at wavelengths of one and three cm. The cubic field splitting in MgO is given by 3a=(+55.9+\\/-0.9)×10-4 cm-1. The twofold degenerate level lies lower than the fourfold degenerate level. The hyperfine structure constant is A=(-81.0+\\/-0.2)×10-4 cm-1; g=2.0014+\\/-0.0005. The large cubic field splitting and the reduced hyperfine

W. Low

1957-01-01

171

Formation and partial recovery of optically induced local dislocations inside CaF2 single crystal.  

PubMed

We reported on the formation of a microstructure (skew cross-shaped pattern) in bulk CaF(2) single crystal, which originates from local dislocations and microcracks around the focal point of a single infrared femtosecond laser beam. Relations between morphology of the microstructure and the laser power as well as the number of laser pulses were discussed. Furthermore, it was observed that the optically induced microstructure could be partially erased by additional irradiation of its neighboring area with femtosecond laser pulses. High-resolution transmission electron microscope (HRTEM) observations confirmed the disappearance of some local dislocations after the additional femtosecond laser irradiation. PMID:19434189

Qian, Bin; Song, Juan; Dong, Guoping; Su, Liangbi; Zhu, Bin; Liu, Xiaofeng; Sun, Shengzhi; Zhang, Qiang; Qiu, Jianrong

2009-05-11

172

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

Microsoft Academic Search

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

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

2002-01-01

173

Fabrication and spectroscopic broadening properties for 1.5 microm amplification of Er(3+)-doped BaF2 nanoparticles.  

PubMed

We show the potential application of Er(3+)-doped BaF2 nanoparticles prepared from microemulsion technology for 1.5 microm amplification in telecommunication. Nanoparticles with different sizes of about 8, 10, and 20.5 nm were prepared. The XRD patterns showed the excursion of diffraction peaks. When the particle size is smaller or the diffraction angle is larger, this kind of excursion will be more serious. The emission bands of Er3+ at 1.54 microm for the three particle sizes at were as follows: 8 nm particles--145 nm, 10 nm particles--124 nm, and 20.5 nm particles--82 nm (full width at half maximum, FWHM), or 173, 153, 97 nm (deltalambda(eff)), respectively. In all the three cases, the emission spectra were flat from 1.53 to 1.56 microm. PMID:18468158

Lian, Hongzhou; Liu, Jie; Ye, Zeren; Shi, Chunshan

2008-03-01

174

The ordered hydrocerussite-type structure of (PbCO3)2.BaF2.  

PubMed

Single crystals of synthetic (PbCO(3))(2).BaF(2), bis[lead(II) carbonate] barium difluoride, have been grown under hydrothermal conditions. The compound crystallizes in the ordered hydrocerussite [(PbCO(3))(2).Pb(OH)(2)] structure and can be derived from a close packing of the metal atoms with a stacking sequence of [c(h)(2)](3) along the c axis. O and F atoms are situated approximately in the tetrahedral voids, resulting in the formation of a slightly distorted [BaF(6)O(6)] icosahedron and a [1+6+3]-coordinate Pb atom, with one short bond to F, six bonds to O and three longer bonds to additional O atoms. The carbonate group deviates only slightly from the geometry of an equilateral triangle. PMID:12205369

Weil, Matthias

2002-08-31

175

Test of the statistical model in Mo96 with the BaF2? calorimeter DANCE array  

NASA Astrophysics Data System (ADS)

The ?-ray cascades following the Mo95(n,?)Mo96 reaction were studied with the ? calorimeter DANCE (Detector for Advanced Neutron Capture Experiments) consisting of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center. The ?-ray energy spectra for different multiplicities were measured for s- and p-wave resonances below 2 keV. The shapes of these spectra were found to be in very good agreement with simulations using the DICEBOX statistical model code. The relevant model parameters used for the level density and photon strength functions were identical with those that provided the best fit of the data from a recent measurement of the thermal Mo95(n,?)Mo96 reaction with the two-step-cascade method. The reported results strongly suggest that the extreme statistical model works very well in the mass region near A=100.

Sheets, S. A.; Agvaanluvsan, U.; Becker, J. A.; Be?vá?, F.; Bredeweg, T. A.; Haight, R. C.; Jandel, M.; Krti?ka, M.; Mitchell, G. E.; O'Donnell, J. M.; Parker, W.; Reifarth, R.; Rundberg, R. S.; Sharapov, E. I.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

2009-02-01

176

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

NASA Astrophysics Data System (ADS)

CaF2:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF2 phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO3, HF acid and MnCl2 as raw materials following co-precipitation method. TL sensitivity of the prepared phosphor was compared with other well established phosphors used for radiation dosimetry. It was found that the TL sensitivity is higher by a factor of 10 with respect to LiF:Mg, Ti, TLD-100 and half to that of CaSO4:Dy (0.05 mol%) phosphor. X-ray diffraction, TL emission spectrum and ESR spectrum taken of the prepared phosphor confirms the crystal structure, Mn2+ emission and incorporation Mn in the crystal, respectively. No significant fading of the dosimetric peak was observed of the prepared phosphor for a storage period of 45 days. The dose linearity of the phosphor was found to be in the range of 50 Gy-3 kGy within an uncertainty of about 10%. An attempt was made to determine the kinetic parameters of TL glow curve and the parameters related to optically stimulated luminescence. In view of its long range of dose linearity, it can be used for the dosimetry of commercial irradiator generally used for the irradiation of food and grains in our country.

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

2009-02-01

177

Electronic and elastic properties of CaF2 under high pressure from ab initio calculations  

NASA Astrophysics Data System (ADS)

Calcium fluoride CaF2 has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF2 is the fluorite structure (Fm\\bar {3}m ), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni2In-type structure (P63/mmc). The two transitions occur at pressures of 8 GPa and 105 GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the Fm\\bar {3}m and the forepart of Pnma phases. However, on increasing the pressure beyond 60 GPa, the gap decreases, which is due to the fluorine pz-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the ch (or ao) direction for the orthorhombic phase is stronger than that in the hexagonal crystal.

Shi, H.; Luo, W.; Johansson, B.; Ahujia, R.

2009-10-01

178

Specific ion effects of salt solutions at the CaF2/water interface.  

PubMed

Calcium fluoride is a slightly soluble compound commonly extracted from ores via flotation at elevated pH, where surfactant molecules bind with hydroxylated surface sites. The addition of F-(aq) suppresses surfactant adsorption by replacing these sites. In this paper, we look at the effects of aqueous Cl-, Br-, F-, and SO4(2-) on the water structure at the CaF2/H2O interface at a pH where surface hydroxylation has not yet occurred. Using static and time-resolved vibrational sum-frequency spectroscopy (VSFS), we find that aqueous Cl- and Br- have only electrostatic screening effects on the interface and do not perturb the interfacial water or surface structure. Sulfate, which we find to be strongly attracted to the interface, affects the interfacial water more than Cl- or Br-. This is in contrast to F- ions that directly interact with the surface and alter the water structure and bonding at the CaF2 surface in addition to screening the surface charge. PMID:20423063

Hopkins, Adam J; Schrödle, Simon; Richmond, Geraldine L

2010-07-01

179

Novel CaF(2) nanocomposite with high strength and fluoride ion release.  

PubMed

Secondary caries and restoration fracture remain common problems in dentistry. This study tested the hypothesis that combining nano-CaF(2) and glass fillers would yield nanocomposites with high mechanical properties and F release. Novel CaF(2) nanoparticles (56-nm) were synthesized via spray-drying and incorporated into resin. F release increased with increasing the nano-CaF(2) content, or with decreasing pH (p < 0.05). F-release rates at 70-84 days were 1.13 microg/(cm(2) x day) and 0.50 microg/(cm(2) x day) for nanocomposites containing 30% and 20% nano-CaF(2), respectively. They matched the 0.65 microg/(cm(2) x 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 CaF(2) 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

2010-05-03

180

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

PubMed

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

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

2008-06-30

181

Onset of laser ablation in CaF2 crystal under excimer laser irradiation  

NASA Astrophysics Data System (ADS)

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

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

2002-06-01

182

Femtosecond laser-induced subwavelength ripples on Al, Si, CaF2 and CR-39  

NASA Astrophysics Data System (ADS)

The formation of self-organized subwavelength ripples on Al, Si, CaF2 and CR-39 induced by 25 fs laser pulses at central wavelength of 800 nm has been observed under certain experimental conditions. In case of Al subwavelength gratings with periodicities ranging from 20 to 220 nm are reported. For CaF2 the periodicity goes up to 625 nm. In case of Si, nano-gratings have the periodicity of 10-100 nm. The interspacing of these gratings is 60 nm in case of CR-39. These features which are significantly shorter than incident laser wavelength are observed at the irradiation fluence slightly higher than the ablation threshold regardless of the target material. In addition to these nanoripples, classical or microripples with an average spacing of 1-2 ?m have also been registered on irradiated surfaces of Al and Si. These microripples have appeared at fluence higher than that is required for nanoripple-formation. It has been found that the formation of the laser-induced ripples is strongly dependent and quite sensitive to the incident laser fluence and the selection of material.

Bashir, Shazia; Shahid Rafique, M.; Husinsky, Wolfgang

2012-03-01

183

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

184

Temperature dependence of the hyperfine coupling constant of 151Eu2+ in SrF2 and BaF2  

Microsoft Academic Search

The theory for the temperature dependence of the hyperfine constant of rare earth S state ions in cubic crystals is applied to measurements taken on 151Eu2+ in SrF2 and BaF2. Satisfactory qualitative agreement is obtained.

S. Lee; D. P. Ames; T. J. Menne

1968-01-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

186

Electronic transitions at the CaF2\\/Si(111) interface probed by resonant three-wave mixing spectroscopy  

Microsoft Academic Search

Resonant optical second-harmonic and sum-frequency generation are applied to probe electronic transitions at the Ca-terminated epi- taxial CaF2\\/Si(111) interface. A band gap of 2.4 eV is established for the interface states, a value twice as large as that in bulk Si, but only (1\\/5 of the band gap in CaF2. The experimental three-wave-mixing spectra can be modeled by a two-dimensional

T. F. Heinz; F. J. Himpsel; E. Palange; E. Burstein

1989-01-01

187

THERMOLUMINESCENCE DOSIMETRY PROPERTIES OF NEW Cu DOPED CaF2 NANOPARTICLES.  

PubMed

Nanoparticles of Cu-doped calcium fluoride were synthesised by using the hydrothermal method. The structure of the prepared nanomaterial was characterised by the X-ray diffraction (XRD) pattern and energy dispersive spectrometer. The particle size of 36 nm was calculated from the XRD data. Its shape and size were also observed by scanning electron microscope. Thermoluminescence (TL) and photoluminescence of the produced phosphor were also considered. The computerised glow curve deconvolution procedure was used to identify the number of glow peaks included in the TL glow curve of the CaF2:Cu nanoparticles. The TL glow curve contains two overlapping glow peaks at ?413 and 451 K. The TL response of this phosphor was studied for different Cu concentrations and the maximum sensitivity was found at 1 mol% of Cu impurity. Other dosimetric characteristics of the synthesised nanophosphor are also presented and discussed. PMID:23765071

Zahedifar, M; Sadeghi, E

2013-06-13

188

Dynamic dimer formation between superionic fluorines in CaF2  

NASA Astrophysics Data System (ADS)

Recently we have elucidated the formation of the dynamic dimers in the conductor ?-CuI through the analyses of the correlation peaks of the partial pair-distribution functions and the partial angle distribution functions with the first principles molecular dynamics (MD) method.(J. Phys. Soc. Jpn. 81,055603(2012).) The present study investigate the formation of the dynamic dimers and the migration paths of the dimers in the conductor CaF2 with the MD method. The fluorines form the dynamic 32f-8c dimers with the coordinate (x,x,x) x=0.300. These incommensurate dimers allow to decrease the migration barriers of the fluorines.

Saito, Masashi; Tasaka, Tomofumi; Tsumuraya, Kazuo

2013-03-01

189

Convertible holograms in CaF2 crystals with color centers  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

190

Intercomparison of dosimetry systems based on CaF2:Mn TL detectors.  

PubMed

The responses of readings by the TL dosimetry system MR200 TL developed in-house and used at JSI and the TOLEDO TL system used at RBI are compared. Ten measurements at different doses ranging from 0.01 mSv to 5 Sv were carried out. A set of 36 dosemeters with three pellets of CaF2:Mn were irradiated in radiation fields of 137Cs and 60Co. Analysis of the measured results shows that at doses below 0.1 Sv, readers' outputs do not differ >5% from each other. At doses >1 Sv, the results obtained by the MR200 reader must be corrected with a known factor. Finally, the reproducibility of the results from the MR200 was tested. PMID:16735564

Zorko, B; Miljani?, S; Veki?, B; Stuhec, M; Gobec, S; Ranogajec-Komor, M

2006-05-30

191

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

192

Effect of surface orientation on dissolution rates and topography of CaF2  

NASA Astrophysics Data System (ADS)

This paper reports how during dissolution differences in surface chemistry affect the evolution of topography of CaF2 pellets with a microstructure similar to UO2 spent nuclear fuel. 3D confocal profilometry and atomic force microscopy were used to quantify retreat rates and analyze topography changes on surfaces with different orientations as dissolution proceeds up to 468 h. A NaClO4 (0.05 M) solution with pH 3.6 which was far from equilibrium relative to CaF2 was used.Measured dissolution rates depend directly on the orientation of the exposed planes. The {1 1 1} is the most stable plane with a dissolution rate of (1.2 ± 0.8) × 10-9 mol m-2 s-1, and {1 1 2} the least stable plane with a dissolution rate 33 times faster that {1 1 1}. Surfaces that expose both Ca and F atoms in the same plane dissolve faster. Dissolution rates were found to be correlated to surface orientation which is characterized by a specific surface chemistry and therefore related to surface energy. It is proposed that every surface is characterized by the relative proportions of the three reference planes {1 1 1}, {1 0 0} and {1 1 0}, and by the high energy sites at their interceptions.Based on the different dissolution rates observed we propose a dissolution model to explain changes of topography during dissolution. Surfaces with slower dissolution rate, and inferred lower surface energy, tend to form while dissolution proceeds leading to an increase of roughness and surface area. This adjustment of the surface suggests that dissolution rates during early stages of dissolution are different from the later stages. The time-dependency of this dynamic system needs to be taken into consideration when predicting long-term dissolution rates.

Godinho, J. R. A.; Piazolo, S.; Evins, L. Z.

2012-06-01

193

Dependence of infrared-to-ultraviolet emission enhancement on Yb3+, Er3+:CaF2 nanoparticle dimension.  

PubMed

In the nanocomplexes with Yb3+, Er(3+)-codoped calcium fluoride (CaF2:Yb3+, Er3+) nanoparticles, the infrared (IR)-to-ultraviolet (UV) upconversion (UC) properties were explored under 980 nm laser diode (LD) excitation. The strong enhancement of UV emission at 407 nm was observed. An UP mechanism of the materials was discussed. PMID:20355611

Zhang, Jisen; Zhang, Liguo; Lv, Shaozhe; Qin, Weiping

2010-03-01

194

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

Microsoft Academic Search

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

Ali Eftekhari-Bafrooei; Satoshi Nihonyanagi; Eric Borguet

2009-01-01

195

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

NASA Astrophysics Data System (ADS)

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

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

196

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

PubMed

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

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

2010-10-05

197

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

NASA Astrophysics Data System (ADS)

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

Lorenz, Pierre; Ehrhardt, Martin; Zimmer, Klaus

2013-01-01

198

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

PubMed

The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (1 x 1) translational symmetry already after an exposure of 3 L (1 L=10(-6) Torr s) at temperatures below 150 K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 46+/-2 kJ mol(-1), corresponding to a desorption temperature of 165 K. The desorption of multilayers was observed at 150 K, consistent with a binding energy of 42+/-2 kJ mol(-1). Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (square root of 3 x square root of 3)R30 degrees lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200 K, consistent with an unexpectedly strong bonding of the molecules to the substrate. PMID:17614580

Vogt, Jochen

2007-06-28

199

Fluorine dynamics in BaF2 crystal lattice as an example of complex motion in a simple system.  

PubMed

Fluorine relaxation profiles for a BaF(2) single crystal collected at several temperatures have been analyzed in terms of essentially different motional models: free rotational and free translational diffusion. The analysis has been performed to critically review the sensitivity of field dependent relaxation studies to mechanisms of molecular motions. The tested motional models do not realistically describe the fluorine dynamics within the crystal lattice. They have been chosen to attempt to answer quite fundamental questions regarding the feasibility of the field dependent nuclear spin relaxation studies to provide unique information on dynamic processes: 1. Is it possible to get information about the motional mechanisms by analyzing relaxation profiles collected in a broad frequency range? 2. To what extent is it possible to reasonably reproduce relaxation profiles in terms of unrealistic motional models? It has been concluded from the analysis that the rotational model leading to a single exponential correlation function explains the experimental data much better than the translational one. Validity regimes of the second order perturbation theory have been discussed in the context of the investigated system and the applied models. PMID:19269796

Kruk, D; Privalov, A F; Gumann, P; Fujara, F

2009-01-22

200

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

Microsoft Academic Search

The Detector for Advanced Neutron Capture Experiments (DANCE) is a 162-element 4pi 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

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

2005-01-01

201

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

PubMed

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

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

2009-11-01

202

Excitons emissions and Raman scattering of ZnO nanoparticles embedded in BaF2 matrices by reactive magnetron sputtering.  

PubMed

ZnO nanoparticles embedded in BaF2 matrix were fabricated by rf magnetic sputtering technology. The optical properties of high quality ZnO nanoparticles, thermally post treated in a N2 atmosphere, were investigated by temperature-dependence photoluminescence measurement. Free exciton and localized exciton were observed at the low temperature. Free exciton peak was at 3.374 eV and localized exciton peak was at 3.420 eV, dominating the PL spectrum at 77 K. Free exciton transition was observed at 3.310 eV at room temperature, whereas the localized exciton transition was at 3.378 eV. The multiple-phonon Raman scattering spectrum showed that ZnO nanoparticles embedded in BaF2 matrix had a large deformation energy originated from lattice mismatch between ZnO and BaF2 matrix. Analysis of the fitting results from the temperature dependence of FWHM of ZnO exciton illustrated that the large value of gamma(ph) was good qualitative agreement with the large deformation potential. PMID:22413302

Zang, C H; Su, J F; Liu, Y C; Tang, C J; Fang, S J; Zhang, D M; Zhang, Y S

2011-11-01

203

Low-pressure plasma-sprayed ZrO 2–CaF 2 composite coating for high temperature tribological applications  

Microsoft Academic Search

The microstructure and tribological behavior of low-pressure plasma-sprayed (LPPS) ZrO2–CaF2 composite coatings were studied. Optimum spray parameters were obtained to produce a less porous and strongly adherent ZrO2–CaF2 composite through carefully selecting the powder feed rate, primary gas pressure and spraying distance. The as-sprayed composite coating exhibited a typical lamellar structure of ZrO2 and CaF2 constituents, with a lot of

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

2001-01-01

204

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

2013-05-02

205

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

PubMed

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

Moyers, M F; Nelson, G A

2009-08-01

206

Scintillation Response of CaF2 to H and He over a Continuous Energy Range  

SciTech Connect

Recent demands for new radiation detector materials with improved ?-ray detection performance at room temperature have prompted research efforts on both accelerated material discovery and efficient techniques that can be used to identify material properties relevant to detector performance. New material discovery has been limited due to the difficulties of large crystal growth to completely absorb ??energies; whereas high-quality thin films or small crystals of candidate materials can be readily produced by various modern growth techniques. In this work, an ion-scintillator technique is demonstrated that can be applied to study scintillation properties of thin films and small crystals. The scintillation response of a benchmark scintillator, europium-doped calcium fluoride (CaF2:Eu), to energetic proton and helium ions is studied using the ion-scintillator approach based on a time of flight (TOF) telescope. Excellent energy resolution and fast response of the TOF telescope allow quantitative measurement of light yield, nonlinearity and energy resolution over an energy range from a few tens to a few thousands of keV.

Zhang, Yanwen; Xiang, Xia; Weber, William J.

2008-06-07

207

EPR study of Ni+ and Ni3+ in x-irradiated CaF2  

NASA Astrophysics Data System (ADS)

EPR measurements of CaF2:Ni crystals before and after room-temperature (RT) x irradiation are reported. Depending on the rare-earth impurity content a small concentration of Ni+ centers is observed in "as-grown" crystals. During RT x irradiation the Ni+ concentration increases. At least two different kinds of Ni+ centers are observed in the EPR spectra. One of them has tetragonal symmetry with g?=2.569 and g?=2.089 and gives a superhyperfine (SHF) structure, due to the interaction with four equivalent flouride ions, which can be resolved at liquid-nitrogen temperature (LNT). The other one has an almost tetragonal symmetry with g factors and SHF structure very close to the former one but the (SHF) structure is resolved at RT. The first Ni+ center is associated with a (NiF4)3- molecular ion with the Ni+ at a distance of about 0.37 Å from the plane of the fluorine atoms. The other EPR signal is assigned to a similar center with some kind of perturbation. An isotropic EPR signal (g=2.003) with a well-resolved superhyperfine structure due to the interaction with eight equivalent fluorines has been detected in some of the samples after RT x irradiation. The tentative model proposed for the center responsible for this signal is a Ni3+ ion at a Ca2+ substitutional position.

Gonzalez, J. Casas; den Hartog, H. W.; Alcala, R.

1980-05-01

208

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

PubMed

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

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

2010-03-06

209

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

PubMed

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

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

2011-01-31

210

Progressive changes in surface structure and electronic properties on Si(001) surface by CaF2 adsorption  

NASA Astrophysics Data System (ADS)

Ab initio calculations, based on pseudopotentials and density functional theory, have been performed to investigate the atomic geometry and electronic structures of calcium fluoride (CaF2) on the Si(001) surface. We have considered the experimentally observed (2×1) and (3×1) reconstructions with different bonding configurations of the CaF2 molecule on the Si(001) surface. Our total energy calculations suggest that the (3×1) structure is slightly more preferable than the (2×1). The key structural parameters and electronic surface properties of their most stable structures have been discussed. In contrast to the experimental results, the most stable structures contain an appreciable bonding nature between the surface Si and F atoms, however, no real bonding between Si and Ca atoms is indicated.

Alzahrani, A. Z.; Usanmaz, D.

2011-06-01

211

Novel Synthesis of CaF2 Nanocrystals and the Effect of Pyridine Addition on Their Crystal Size  

NASA Astrophysics Data System (ADS)

Various types of calcium fluoride nanocrystals were prepared by the reactions between calcium metal and ammonium fluoride in liquid ammonia. The obtained nanocrystals were observed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), absorption spectroscopy, and fluorescent spectroscopy. The particle size of pure CaF2 nanocrystals was about 14 nm. The addition of pyridine and the selection of the period of pyridine removal gave two particle size ranges, which were 8--10 and 13--15 nm. The nanocrystals were successfully doped with Mn2+ and Eu2+. The optical properties of the nanocrystals were investigated. The results implied that Eu2+ was stable in the CaF2 nanocrystals.

Rungrodnimitchai, Supitcha

2011-01-01

212

Search for neutrino-less double beta decay of 48Ca by CaF2 scintillator  

NASA Astrophysics Data System (ADS)

A CaF2 scintillation detector system (ELEGANT VI) has been operating at Oto Cosmo Observatory to study double beta decays of 48Ca. No events were observed around the Q-value energy region after the analysis of 4.23 kgyr data. To derive the lower limit for the half-life of the neutrino-less double beta decay of 48Ca, the expected number of background events in that energy region was estimated by a Monte Carlo simulation using the measured activities of 214Bi and 220Rn inside CaF2 crystals. A new lower limit is obtained to be 1.4×1022 yr at the 90% C.L. An experimental sensitivity is 5.9×1021 yr at the 90% C.L.

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

2004-01-01

213

Laser-induced damage in SiO 2 and CaF 2 with picosecond and femtosecond laser pulses  

Microsoft Academic Search

Single- and multiple-shot damage thresholds and plasma-emission thresholds for fused silica and CaF2 are reported for 790 nm photons as a function of laser pulse width (190 fs – 4.5 ps). The results are compared with single-shot plasma-emission measurements [1] and with multiple-shot damage measurements [2]. Both the damage threshold and the plasma-emission threshold are shown to decrease with decreasing

H. Varel; D. Ashkenasi; A. Rosenfeld; R. Herrmann; F. Noack; E. E. B. Campbell

1996-01-01

214

Temperature dependence of the elastic moduli and damping for polycrystalline LiF22% CaF 2 eutectic salt  

Microsoft Academic Search

The Young's and shear moduli and damping were measured for as-cast polycrystalline LiF-22 (mol%) CaF2 eutectic specimens as a function of temperature using the piezoelectric ultrasonic composite oscillator technique (PUCOT). The shear modulus decreased with increasing temperature from about 40 GPa at 295 K to about 30 GPa at 1000 K, while the Young's modulus decreased from about 115 GPa

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

1991-01-01

215

Symmetry of spatial-dispersion-induced birefringence and its implications for CaF2 ultraviolet optics  

Microsoft Academic Search

The discovery of a significant spatial-dispersion-induced bire- fringence (intrinsic birefringence) in CaF2 at ultraviolet wavelengths has had a major impact on the design of 157 nm lithography systems, requir- ing complete redesign of the optics to take account of the imaging aber- rations resulting from the birefringence and the accompanying index an- isotropy. This intrinsic birefringence phenomena results from a

John H. Burnett; Zachary H. Levine; Eric L. Shirley; John H. Bruning

2002-01-01

216

Codoping Na+ to modulate the spectroscopy and photoluminescence properties of Yb3+ in CaF2 laser crystal  

Microsoft Academic Search

Three kinds of Yb3+- and Na+-codoped CaF2 laser crystal with different Na:Yb ratios of 0, 1.5, and 10 are grown by the temperature gradient technique. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes belonging to the transitions between ground state ?F_7\\/2 and excited state ?F_5\\/2 of Yb3+ ions in the three crystals are measured to study the effect of Na+. Experimental

Liangbi Su; Jun Xu; Hongjun Li; Weiqiao Yang; Zhiwei Zhao; Jiliang Si; Yongjun Dong; Guoqing Zhou

2005-01-01

217

Lowest 4f-->5d Transition of Trivalent Rare-Earth Ions in CaF2 Crystals  

Microsoft Academic Search

The lowest 4f-->5d ultraviolet absorption band of eleven (Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) of the fourteen trivalent rare-earth (RE) ions in host CaF2 crystals has been measured. The room temperature absorption cross section [cm2] and half-width [cm-1] of these bands for the first-half series of RE3+ are larger than that of the second-half

Eugene Loh

1966-01-01

218

Femtosecond time-resolved spectroscopy of the formation of self-trapped excitons in CaF2  

Microsoft Academic Search

Self-trapped excitons (STE's) in CaF2 are formed via two distinct processes after band-gap excitation by femtosecond light pulses at low temperatures; the fast process terminates within a few ps after excitation, and the slow process that follows the former lasts over 20 ps. The fast formation of STE's is associated with the decay of the precursor, which shows a broad

Katsumi Tanimura

2001-01-01

219

Influence of Na-related defects on DUV nonlinear absorption in CaF2: nanosecond versus femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

The influence of Na stabilized F and M centers on the DUV absorption behavior of CaF2 is comparatively studied for nanosecond and femtosecond laser pulses by in-situ transmission and laser induced fluorescence measurements. For 193 nm nanosecond pulses the steady state transmission of ArF laser pulses through CaF2 is measured in dependence on the incident fluence H <= 10 mJ cm-2 pulse-1. The related absorption coefficients ?st(H) are proportional to H and rationalized by effective 1- and 2-photon absorption coefficients ?eff and ?eff, respectively. The ?eff and ?eff values increase with the Na content of the CaF2 samples as identified by the fluorescence of Na related MNa centers at 740 nm. This relation is simulated by a complex rate equation model describing the ArF laser induced MNa generation and annealing. MNa generation starts with intrinsic 2-photon absorption in CaF2 yielding self-trapped excitons (STE). These pairs of F and H centers can separate upon thermal activation and the F centers combine with FNa to form MNa centers. MNa annealing occurs by its photo dissociation into a pair of F and FNa centers. Comparative transmission measurements with DUV femtosecond pulses are done using the fourth harmonic of a Ti:Safs- laser at 197 nm. The resulting ?eff values virtually show no dependence on the MNa center concentration. Furthermore, the absolute ?eff values are lower by a factor of three compared to those obtained for nanosecond pulses. This is explained by additional two-step absorption for nanosecond pulses after formation of self-trapped excitons (STE).

Mühlig, Ch.; Stafast, H.; Triebel, W.; Zeuner, Th.; Karras, Ch.; Letz, M.

2009-10-01

220

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

221

Formation of Eu 2+ and Eu 3+ centers in synthesis of CaF 2 :Eu luminophores  

Microsoft Academic Search

We have studied the effect of CaF2:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu3+ predominates over Eu2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu3+\\/Eu2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the\\u000a samples, due to

M. I. Danilkin; A. P. Belousov; S. O. Klimonskii; V. D. Kuznetsov; A. L. Lust; V. N. Nikiforov; L. N. Paama; I. Kh. Pammo; V. O. Seeman

2007-01-01

222

Novel Synthesis of CaF2 Nanocrystals and the Effect of Pyridine Addition on Their Crystal Size  

Microsoft Academic Search

Various types of calcium fluoride nanocrystals were prepared by the reactions between calcium metal and ammonium fluoride in liquid ammonia. The obtained nanocrystals were observed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), absorption spectroscopy, and fluorescent spectroscopy. The particle size of pure CaF2 nanocrystals was about 14 nm. The addition of pyridine and the selection of the period

Supitcha Rungrodnimitchai

2011-01-01

223

Formation of Eu2+ and Eu3+ centers in synthesis of CaF2:Eu luminophores  

Microsoft Academic Search

We have studied the effect of CaF2:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu3+ predominates over Eu2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu3+\\/Eu2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the samples, due to

M. I. Danilkin; A. P. Belousov; S. O. Klimonskii; V. D. Kuznetsov; A. L. Lust; V. N. Nikiforov; L. N. Paama; I. Kh. Pammo; V. O. Seeman

2007-01-01

224

Influence of Na-related defects on ArF laser absorption in CaF2  

NASA Astrophysics Data System (ADS)

ArF laser pulse transmission through commercial high purity CaF2 is determined by measuring the energy of each pulse before and behind the sample up to an incident fluence H of 10 mJ/cm2. The steady state transmission of ArF laser pulses decreases with increasing fluence. The related absorption coefficients ? st( H) are proportional to H and rationalized by effective 1- and 2-photon absorption coefficients 2.4×10-4 cm-1? ? eff?16.8×10-4 cm-1 and 1.7×10-9 cm W-1? ? eff?9.3×10-9 cm W-1, respectively. The ? eff and ? eff values increase with the Na content of the CaF2 samples as identified by the fluorescence of Na-related M Na centers at 740 nm. This relation is simulated by a rate equation model describing the ArF laser induced M Na generation in the dark periods between the laser pulses and their annealing during laser irradiation. M Na generation starts with intrinsic 2-photon absorption in CaF2, yielding self-trapped excitons (STE). These pairs of F and H centers move upon thermal activation and the F centers combine with F Na to form M Na centers. M Na annealing occurs by its photo dissociation into a pair of F and F Na centers.

Mühlig, C.; Triebel, W.; Stafast, H.; Letz, M.

2010-05-01

225

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

SciTech Connect

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

Kavner,A.

2008-01-01

226

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

227

Laser-excited nonlinear properties of BaF2 and its application in a single-shot spatially insensitive autocorrelator  

NASA Astrophysics Data System (ADS)

A detailed investigation of laser-generated nonlinear processes of undoped barium fluoride is presented including two-photon-excited exciton fluorescence, color-center formation and damage-threshold measurements. A single-shot autocorrelator based on two-photon fluorescence of BaF2 was constructed to measure the phase and amplitude of pulses provided by large apeture excimer lasers. The capabilities of the autocorrelator are demonstrated at 248 nm and 268 nm with pulses in the regime of 100 fs to 10 ps.

Osvay, K.; Ross, I. N.; Hooker, C. J.; Lister, J. M. D.

1994-09-01

228

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

PubMed

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

Mitachi, S; Miyashita, T

1983-08-15

229

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

PubMed

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

Yu, Shenglei; Yang, Zhongmin; Xu, Shanhui

2010-03-04

230

Liquid phase epitaxy of crystalline REBa2Cu3O6+? films on reactive substrates using the BaF2-BaO-CuO flux  

NASA Astrophysics Data System (ADS)

Phase relations concerning the crystal formation of YBa2Cu3O6 +? and NdBa2Cu3O6+? phases from the BaF2-BaO-CuO flux have been investigated by the liquid phase epitaxial technique on various substrates. As the amount of BaF2 in the solution increases, the temperature of REBa2Cu3O6+? (RE = Y, Nd) formation decreases down to about 920°C not only in the Y system but also in the Nd system. The decrease of the growth temperature allows us to form liquid phase epitaxial thick films on the reactive substrates such as yttria-stabilized zirconia and SrTiO3, which rapidly react with REBa2Cu3O6+? and the melt of barium cuprate flux at high temperatures. Our studies have also revealed that the seed layer pre-deposited on the substrates plays an important role in epitaxial growth of REBa2Cu3O6+? to form thick films on these substrates.

Niiori, Y.; Yamada, Y.; Hirabayashi, I.; Tanaka, S.

1997-02-01

231

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

232

Influence of sodium impurities on arf excimer-laser-induced absorption in CaF2 crystals.  

PubMed

The formation of color centers induced by irradiation with ArF excimer lasers in CaF(2) crystals was found to depend strongly on the sodium impurity concentration. Sodium-related color centers were generated by two-photon absorption because the slope of the induced absorption coefficient just after irradiation started was proportional to the square of the laser fluence. The saturation absorption also depended on laser fluence, and a photobleaching induced absorption phenomenon was observed. We concluded that the saturation absorption level was determined by the equilibrium between two-photon excitation and one-photon reverse reaction. PMID:18349970

Komine, N; Sakuma, S; Shiozawa, M; Mizugaki, T; Sato, E

2000-08-01

233

Passively Q-switched Yb(3+) laser with Yb(3+)-doped CaF(2) crystal as saturable absorber.  

PubMed

Passive Q-switching of a diode-pumped Yb:LYSO laser at 1060 nm with a Yb(3+) ions-doped CaF(2) crystal without the excited-state absorption (ESA) was demonstrated. An average output power of 174 mW with pulse duration of 5.6 mus and repetition rate of 27 kHz have been obtained under the unoptimized conditions. And the Q-switching conversion efficiency was as high as 51.7%. PMID:19532474

Su, Liangbi; Zhang, Dan; Li, Hongjun; Du, Juan; Xu, Yi; Liang, Xiaoyan; Zhao, Guangjun; Xu, Jun

2007-03-01

234

CaF2:Tm (TLD300) thermoluminescent response and glow curve induced by gamma-rays and ions  

Microsoft Academic Search

The thermoluminescent response of CaF2:Tm after exposure to 60Co gamma-rays at doses from 0.44 Gy to 8.75 kGy and to low fluences (105 ˜ 108 cm-2) of 25 and 40 MeV 1H, 75 and 120 MeV 3He, 180, 300 and 480 MeV 12C, 400 MeV 16O and 800 MeV 20Ne ion beams, spanning a LET interval up to about 500

G. Massillon-Jl; I. Gamboa-Debuen; A. E. Buenfil; M. A. Monroy-Rodríguez; M. E. Brandan

2008-01-01

235

CaF 2:Tm (TLD300) thermoluminescent response and glow curve induced by ?-rays and ions  

Microsoft Academic Search

The thermoluminescent response of CaF2:Tm after exposure to 60Co ?-rays at doses from 0.44Gy to 8.75kGy and to low fluences (105?108cm?2) of 25 and 40MeV 1H, 75 and 120MeV 3He, 180, 300 and 480MeV 12C, 400MeV 16O and 800MeV 20Ne ion beams, spanning a LET interval up to about 500keV\\/?m, has been investigated. A careful deconvolution analysis of the glow

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

2008-01-01

236

Defect Characterization of High Thermal Conductivity CaF2 Doped AlN Ceramics by Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

Calcium fluoride additive was used to produce high thermal conductivity AlN ceramics which has no grain boundary phase. Thermal conductivity of AlN is determined by the point defect, represented as oxygen related defect, within the AlN grain. The defect density characterization of high thermal conductivity CaF2 doped AlN ceramics after heat treatment was conducted by Raman spectroscopy. As measure Raman linewidth broadening, the point defect density variation after heat treatment and corresponding thermal conductivity change was investigated.

Lee, Hyeon-Keun; Kim, Do Kyung

237

Electrical conductivity of NaF-AlF3-CaF2-Al2O3 melts  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

238

Growth of polar axis oriented tetragonal Pb(Zr,Ti)O 3 films on CaF 2 substrates with transparent (La 0.07Sr 0.93)SnO 3  

Microsoft Academic Search

Epitaxial (La0.07Sr0.93)SnO3 [LSSO] films were deposited on CaF2 substrates by pulse laser deposition. The (100)c orientation of LSSO films was observed only on (110)CaF2, whereas (110)c orientation was found on (111)CaF2 and (100)CaF2. (001) polar axis oriented tetragonal Pb(Zr0.35Ti0.65)O3 films were grown on the fabricated (100)cLSSO?(110)CaF2 by pulsed metal organic chemical vapor deposition. The (001)Pb(Zr0.35Ti0.65)O3?(100)cLSSO?(110)CaF2 stack structure exhibited about 70%

Satoru Utsugi; Yoshitaka Ehara; Hidenori Tanaka; Tomoaki Yamada; Hiroshi Funakubo; Hiroshi Uchida

2010-01-01

239

Modification of mechanical properties of e-gun evaporated MgF 2 and CaF 2 thin films under ion beam bombardment  

NASA Astrophysics Data System (ADS)

The effect of ion beam assistance on mechanical properties (hardness and adhesion) of MgF 2 and CaF 2 thin films has been investigated. These films have been deposited by e-gun evaporation and bombarded during growth with an ion beam produced by a Kaufman source. The Knoop hardness has been calculated after having performed on the samples some indentation by an ultra-microindenter and measured the impression size by an eyepiece mounted on an optical microscope. The film adhesion has been measured by the scratch test technique. To investigate the influence of the ion source parameters on the mechanical properties, different ion beam energies (200-800 eV) have been used. Bombarded samples are harder (610 and 750 kg/mm 2 for CaF 2 and MgF 2 samples, respectively) than unbombarded samples (380 and 300 kg/mm 2 for CaF 2 and MgF 2, respectively). Critical loads (load where the delamination of the coating begins) of 12 and 3 N for bombarded MgF 2 and CaF 2 respectively and 4 and 1 N for unbombarded MgF 2 and CaF 2 samples have been found.

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

1989-12-01

240

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

241

Paramagnetic hyperfine splitting in the 151Eu M?ssbauer 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.

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

242

Optical absorption properties and valence states of uranium in CaF2 crystals grown by TGT  

NASA Astrophysics Data System (ADS)

Calcium fluoride single crystals doped with uranyl nitrate were grown by an improved temperature gradient technique under different conditions. Absorption spectra, energy levels and unit cell parameters were studied to analyze the possible color centers and valence states of uranium ions in as-grown U:CaF2 crystals. Uranium in U:CaF2 crystals grown in the presence of PbF2 as an oxygen scavenger is trivalent. F-centers and other defects related to oxygen, with respective absorption lines at 604 and 526 nm, and impure valence states of uranium ions exist in U3+:CaF2 when the molar ratio of PbF2 to U is less than 25. In the absence of PbF2, U:CaF2 crystals are multicolor, consisting of red, cerise, yellow and green volumes from inside to outside where the red part in the core is still U3+:CaF2. Mixed valence states of uranium ions exist in the crystal. The valences of uranium ions are inferred to gradually increase from +3 to +6 according to the graded changes of the absorption spectra and unit cell parameters.

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

2004-09-01

243

Electronic and elastic properties of CaF(2) under high pressure from ab initio calculations.  

PubMed

Calcium fluoride CaF(2) has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). Our results demonstrate that the sequence of the pressure-induced structural transition of CaF(2) is the fluorite structure ([Formula: see text]), the orthorhombic cotunnite-type structure (Pnma), and the hexagonal Ni(2)In-type structure (P6(3)/mmc). The two transitions occur at pressures of 8 GPa and 105 GPa, accompanied by volume collapses of 8.4% and 1.2%, respectively. The energy band gap increases with pressure in the [Formula: see text] and the forepart of Pnma phases. However, on increasing the pressure beyond 60 GPa, the gap decreases, which is due to the fluorine p(z)-states shifting toward the Fermi energy. In addition, the elastic properties versus pressure are also discussed. Our calculated elastic constants for the cubic phase at ambient pressure are in agreement with the experimental values. The stress-strain coefficient calculations show that shear transformations in the Pnma phase are more difficult than in the cubic phase and the compressibility along the c(h) (or a(o)) direction for the orthorhombic phase is stronger than that in the hexagonal crystal. PMID:21693988

Shi, H; Luo, W; Johansson, B; Ahujia, R

2009-09-23

244

Novel SiO2-deposited CaF2 substrate for vibrational sum-frequency generation (SFG) measurements of chemisorbed monolayers in an aqueous environment.  

PubMed

A novel SiO(2)-deposited CaF(2) (SiO(2)/CaF(2)) substrate for measuring vibrational sum-frequency generation (SFG) spectra of silane-based chemisorbed monolayers in aqueous media has been developed. The substrate is suitable for silanization and transparent over a broad range of the infrared (IR) probe. The present work demonstrates the practical application of the SiO(2)/CaF(2) substrate and, to our knowledge, the first SFG spectrum at the solid/water interface of a silanized monolayer observed over the IR fingerprint region (1780-1400 cm(-1)) using a back-side probing geometry. This new substrate can be very useful for SFG studies of various chemisorbed organic molecules, particularly biological compounds, in aqueous environments. PMID:22732544

Padermshoke, Adchara; Konishi, Shouta; Ara, Masato; Tada, Hirokazu; Ishibashi, Taka-Aki

2012-06-01

245

NIR-to-NIR two-photon excited CaF2:Tm3+,Yb3+ nanoparticles: multifunctional nanoprobes for highly penetrating fluorescence bio-imaging.  

PubMed

In this study, we report on the remarkable two-photon excited fluorescence efficiency in the "biological window" of CaF(2):Tm(3+),Yb(3+) nanoparticles. On the basis of the strong Tm(3+) ion emission (at around 800 nm), tissue penetration depths as large as 2 mm have been demonstrated, which are more than 4 times those achievable based on the visible emissions in comparable CaF(2):Er(3+),Yb(3+) nanoparticles. The outstanding penetration depth, together with the fluorescence thermal sensitivity demonstrated here, makes CaF(2):Tm(3+),Yb(3+) nanoparticles ideal candidates as multifunctional nanoprobes for high contrast and highly penetrating in vivo fluorescence imaging applications. PMID:21957870

Dong, Ning-Ning; Pedroni, Marco; Piccinelli, Fabio; Conti, Giamaica; Sbarbati, Andrea; Ramírez-Hernández, Juan Enrique; Maestro, Laura Martínez; Iglesias-de la Cruz, Maria Carmen; Sanz-Rodriguez, Francisco; Juarranz, Angeles; Chen, Feng; Vetrone, Fiorenzo; Capobianco, John A; Solé, José García; Bettinelli, Marco; Jaque, Daniel; Speghini, Adolfo

2011-10-06

246

Initial stages of high-temperature CaF2/Si(001) epitaxial growth studied by surface X-ray diffraction.  

PubMed

Surface X-ray diffraction was applied to study structure of the fluorite-silicon interface forming upon epitaxial growth of CaF2 on Si(001) surface kept at 750 degrees C. Samples with CaF2 coverage of 1.5-4 (110)-monolayers were grown and in-situ characterized using synchrotron radiation. The 3 x 1-like surface reconstruction was observed in agreement with the previous studies by electron diffraction. Interestingly, a well pronounced splitting of the fractional x 1/3 reflections was revealed. This splitting was ascribed to the effect of antiphase domain boundaries in the row-like structure of the interface layer. The in-plane integrated intensities were used to reconstruct two-dimensional atomic structure of the high-temperature CaF2/Si(001) interface. PMID:21776666

Suturin, Sergey M; Sokolov, Nikolai S; Banshchikov, Aleksander G; Kyutt, Reginald N; Sakata, Osami; Shimura, Takayoshi; Harada, Jimpei; Tabuchi, Masao; Takeda, Yoshikazu

2011-04-01

247

Metal (CoSi 2)/Insulator (CaF 2) Hot Electron Transistor Fabricated by Electron-Beam Lithography on a Si Substrate  

NASA Astrophysics Data System (ADS)

We fabricated a small-area metal (CoSi2)/insulator (CaF2) hot electron transistor using electron-beam lithography. The transistor is composed of a CoSi2/CaF2 (1.9 nm)/CoSi2 (1.9 nm) tunnel emitter and a CaF2 (5 nm) collector barrier on an n-Si(111) substrate. The emitter mesa area is 0.9 × 0.9 µm2. Although the measured characteristics show, for the first time, clear transistor action with a curve similar to those of semiconductor HETs, the collector current increases without saturation due to leakage current through the SiO2 film under the external electrode pads. The intrinsic device characteristics (zero leakage current) exhibited saturation, and a current gain ? ? 36 was obtained at 77 K.

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

1995-10-01

248

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

Microsoft Academic Search

We have demonstrated room-temperature negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) on the order of 105 using CaF2\\/CdF2 double-barrier resonant tunneling diode (DBRTD) structures grown on Si(111) substrates. A CdF2 quantum-well layer was grown by molecular-beam epitaxy (MBE) and CaF2 barrier layers were formed by MBE combined with the partially ionized beam technique on an n^+-Si(111) substrate

Masahiro Watanabe; Toshiyuki Funayama; Taishi Teraji; Naoto Sakamaki

2000-01-01

249

Epitaxial Growth and Electrical Characteristics of CaF2\\/Si\\/CaF2 Resonant Tunneling Diode Structures Grown on Si(111) 1^\\\\circ-off Substrate  

Microsoft Academic Search

CaF2\\/Si\\/CaF2 double-barrier resonant tunneling diode (RTD) structures have been epitaxially grown on a Si(111) substrate using molecular beam epitaxy (MBE) with the partially ionized beam method. A 3.4-nm-thick Si quantum-well layer was epitaxially formed on a 1-nm-thick CaF2 barrier layer grown on the Si(111) substrate tilted 1^\\\\circ toward the azimuth, of which the terrace width was uniformly controlled by thermal

Masahiro Watanabe; Yoshifumi Iketani; Masahiro Asada

2000-01-01

250

Microstructure and tribological properties of low-pressure plasma-sprayed ZrO 2–CaF 2–Ag 2O composite coating at elevated temperature  

Microsoft Academic Search

Microstructure and tribological properties of low-pressure plasma-sprayed (LPPS) ZrO2–CaF2–Ag2O (ZFA) composite coating were studied by means of optical microscope, scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDXA), electron probe microanalyzer (EPMA) and high-temperature reciprocating wear tester. Coating selected for this investigation was 8wt.% Y2O3 partially stabilized zirconia coating doped with CaF2 and Ag2O as the solid lubricants. The

J. H Ouyang; S Sasaki; K Umeda

2001-01-01

251

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

PubMed

The interaction of water with freshly cleaved BaF(2)(111) surfaces at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes. The images strongly suggest a high surface diffusion of water molecules on the surface indicated by the accumulation of water at step edges forming two-dimensional bilayered structures. Steps running along the 110 crystallographic directions show a high degree of hydrophilicity, as evidenced by small step-film contact angles, while steps running along other directions exhibiting a higher degree of kinks surprisingly behave in a quite opposite way. Our results prove that morphological defects such as steps can be crucial in improving two-dimensional monolayer wetting and stabilization of multilayer grown on surfaces that show good lattice mismatch with hexagonal ice. PMID:20572735

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

2010-06-21

252

Growth and characterization of high purity epitaxial yttrium iron garnet films grown from BaO-B2O3-BaF2 flux  

NASA Astrophysics Data System (ADS)

The growth of yttrium iron garnet (YIG) epitaxial films of excellent purity from a lead-free BaO-B2O3-BaF2 flux and their characterization by the magnetic resonance methods are reported. The films were prepared by the standard dipping liquid-phase epitaxy onto gadolinium gallium garnet substrates of three crystallographic orientations (111), (110), and (100). The objective of utilization of a lead-free flux was to reduce the content of impurities and intrinsic defects in the garnet films and to obtain samples with minimum microwave losses. The samples exhibited very narrow NMR and spin wave linewidths. The diamagnetic and paramagnetic doping of YIG with ions of different valency and segregation of these ions between the garnet layer and the barium melt were also studied and the relevant distribution coefficients for doping into the tetrahedral (Ga, Al, Si Ge), octahedral (In) and dodecahedral (La, Ca) sites were determined.

Kuera, M.; Nitsch, K.; Tpánková, H.; Maryko, M.; Reiche, P.

2003-08-01

253

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

254

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

255

Magnetic properties of arrays of cobalt nanoparticles on the CaF2(110)/Si(001) surface  

NASA Astrophysics Data System (ADS)

The Co/CaF2/Si(001) heterostructures with the corrugated (110) surface of the CaF2 buffer layer have been grown by molecular beam epitaxy. The structures are nanoparticle arrays of single-crystal Co, mostly of the cubic fcc modification. The behavior of the magnetic hysteresis loops as a function of the density of coverage of the substrate by cobalt islands, the island size, and the temperature is studied using the magnetooptical technique. At low coverage densities, where the effective cobalt film thickness d eff is less than the critical value d {eff/ c }, the magnetic structure of the films at T = 294 K can be visualized as an ensemble of superparamagnetic, weakly interacting nanoparticles and is characterized by small values of the coercive field H c and the remanent magnetization M rem. A decrease in the temperature leads to a strong increase in H c and M rem, which is associated with the transition of the islands to the blocked state. The blocking temperature of the structures is T b ˜ 280 K. The magnetic anisotropy parameter K and the saturation magnetization M s of the islands depend on the growth temperature of cobalt T Co. An increase in the coverage density above the critical thickness d {iff/ c } at T = 294 K brings about a strong increase in H c and M rem and the appearance of a hysteresis loop anisotropy originating from the corrugated structure of the CaF2 buffer layer. The experimental results are compared with the model of an ensemble of noninteracting superparamagnetic particles.

Krichevtsov, B. B.; Gastev, S. V.; Il'Yushchenkov, D. S.; Kaveev, A. K.; Sokolov, N. S.

2009-01-01

256

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

2011-12-21

257

Electron spectroscopy of the nanostructures created in Si, GaAs, and CaF2 surface layers using low-energy ion implantation  

NASA Astrophysics Data System (ADS)

A review of the experimental results on the study of the Si, GaAs, and CaF2 surface layers that are created using the low-energy ion implantation is presented. Optical and electron spectroscopy and microscopy are employed in the experiments.

Umirzakov, B. E.; Tashmukhamedova, D. A.; Muradkabilov, D. M.; Boltaev, Kh. Kh.

2013-06-01

258

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

NASA Astrophysics Data System (ADS)

Tm3+ and Ho3+ codoped transparent glass ceramic (GC) containing CaF2 nanocrystals were fabricated by melt-quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of CaF2 nanocrystals among the glass matrix. Energy-dispersive x-ray spectroscopy results evidenced the incorporation of Tm3+ and Ho3+ into the CaF2 nanocrystals. Judd-Ofelt parameters were calculated based on the absorption spectra, the smaller ?2 and larger ?6 imply that Tm3+ and Ho3+ ions has entered into a symmetrical ionic crystal field. 2.02 ?m emission spectral of the GC samples were recorded at room temperature with an excitation of 808 nm laser diode. The enhancement of the emission at 2.02 ?m in the GC samples could be attributed to more efficient cross relaxation process of Tm3+:3H4+Tm3+:3H6-->2Tm3+:3H4, and energy transfer from Tm3+ to Ho3+ benefited from the incorporation of rare earth ions into CaF2 nanocrystals.

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

2010-05-01

259

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

260

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

261

The use of the green emission in Er(3+)-doped CaF(2) crystals for thermometry application.  

PubMed

We report here the use of the green upconversion emissions originating from the thermally coupled levels (2)H(11/2) and (4)S(3/2) of the Er(3+) ion in CaF(2):Er (0.01 at.%) for thermometry application in the range 303-423 K. The mechanism responsible for excitation of the green emitting levels is a sequential two-photon absorption process. The fluorescence intensity ratio (FIR) of the green upconversion emissions at wavelengths of about 519 and 551 nm is studied as a function of temperature in the range 303-423 K using a 634 nm tunable dye laser as an excitation source. It is found that the logarithm of the FIR varies linearly with the inverse of temperature. The gap between the two thermally coupled levels (4)S(3/2) and (2)H(11/2) was determined to be about 721 cm(-1). This value is in good agreement with that found by spectroscopic investigations. The calibration curve is established, and the temperature is calculated. PMID:21693950

Chouahda, Z; Jouart, J P; Duvaut, T; Diaf, M

2009-05-26

262

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

263

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

264

High quantum fluorescence yield of Er3+ at 1.5 ?m in an Yb3+, Ce3+-codoped CaF2 crystal  

NASA Astrophysics Data System (ADS)

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 ?m region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 ? 4I13/2 transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+4I11/2 level. The quaternary-doped CaF2 system shows great potential to achieve high laser performance in the 1.5 ?m region.

Xu, Jun; Su, Liangbi; Li, Hongjun; Zhang, Dan; Wen, Lei; Lin, Hui; Zhao, Guangjun

2007-04-01

265

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

Microsoft Academic Search

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

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

1990-01-01

266

Thermodynamics of mixing of liquids in the system Ca 3 (PO 4 ) 2 CaCl 2 CaF 2 Ca(OH) 2  

Microsoft Academic Search

Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatite exchange equilibria and solid solution behavior. New experimental data and published phase equilibria are used to determine a thermodynamic model of melts and solids along the binary joins of the anhydrous apatite system Ca 3 (PO 4 ) 2 ---CaCl 2 ---CaF 2 ---Ca(OH)

R. C. Tacker; J. C. Stormer Jr.

1993-01-01

267

A performance study on a phoswich detector consisting of an inner NE213 scintillator and an outer CaF 2(Eu) crystal wall  

Microsoft Academic Search

We developed a new phoswich detector. The detector consists of an inner NE213 organic liquid scintillator and an outer thin CaF2(Eu) crystal which are coupled to a photomultiplier. The charged particles produced in the NE213 scintillator by the interaction of radiation with the detector either stop in the NE213 scintillator or pass through both the NE213 scintillator and the outer

Masashi Takada; Tokushi Shibata; Yoshitomo Uwamino; Takashi Nakamura

1996-01-01

268

Formation of CaF2 on Sound Enamel and in Caries-Like Enamel Lesions after Different Forms of Fluoride Applications in vitro  

Microsoft Academic Search

The formation of calcium fluoride (CaF2) was measured on sound enamel (SE) and in caries-like enamel lesions (CL) after treatment in vitro with 2% neutral NaF or Duraphat®. The caries-like lesions were created by exposure to acidified gel at pH 4.5 within a 0.07-cm2 window punched in water-repellant tape. The same window area was used in series (n = 10)

C. Bruun; H. Givskov

1991-01-01

269

Electron-Nuclear-Double-Resonance and Electron-Paramagnetic-Resonance Analysis of the Ytterbium-Fluorine Superhyperfine Interaction in CaF2: Yb3+  

Microsoft Academic Search

Superhyperfine structure in the EPR spectrum of Yb3+ in cubic sites of CaF2 has been investigated with EPR at both 9 Gc\\/sec and 35 Gc\\/sec and with ENDOR at 9 Gc\\/sec. The EPR measurements showed that the superhyperfine splitting is anisotropic and that the number of observable lines (17 at 9 Gc\\/sec along ) and the splitting of the lines

U. Ranon; James S. Hyde

1966-01-01

270

Tribological behaviors of hot-pressed Al 2O 3\\/TiC ceramic composites with the additions of CaF 2 solid lubricants  

Microsoft Academic Search

Al2O3\\/TiC ceramic composites with the additions of CaF2 solid lubricants were produced by hot pressing. The effect of the solid lubricant on the microstructure and mechanical properties of the ceramic composite has been studied. The friction coefficient and wear rates were measured using the ring-block method, and the tribological behaviors were discussed in relation to its mechanical properties and microstructure.

Deng Jianxin; Cao Tongkun; Ding Zeliang; Liu Jianhua; Sun Junlong; Zhao Jinlong

2006-01-01

271

Intrinsic luminescence excitation spectrum and extended x-ray absorption fine structure above the K edge in CaF2  

Microsoft Academic Search

Excitation spectra of the 4.44-eV intrinsic luminescence in a single crystal of CaF2 at liquid-nitrogen temperature was measured using synchrotron radiation in the x-ray region. The intrinsic luminescence at 4.44 eV is due to self-trapped exciton recombination. The intensity of the emitted uv light was measured as a function of the x-ray photon energy from below the calcium K edge

A. Bianconi; D. Jackson; K. Monahan

1978-01-01

272

Spin-Lattice Coefficients for Gd3+ and Eu2+ in CaF2 and for Gd3+ in CaO  

Microsoft Academic Search

We have measured the spin-lattice coefficients of Eu2+ and Gd3+ in CaF2 and Gd3+ in CaO by studying the effect of uniaxial stress on the EPR spectra of these ions. The experimental data show that fourth-order terms in the spin-lattice Hamiltonian give significant contributions. The values of the second-order spin-lattice coefficients are given, and the fourth-order contribution is tentatively identified

R. Calvo; R. A. Isaacson; Z. Sroubek

1969-01-01

273

Composite (CaF 2 + ?-Al 2O 3) solid electrolytes: Preparation, properties and application to the solid oxide galvanic cells  

Microsoft Academic Search

Calcium fluoride based composites containing up to 25 mol. % ?-Al2O3 disperse phase were prepared. Electrical conductivities of the samples were measured in the temperature range 400–700 °C by the d.c. four-probe method. Dispersions of ?-Al2O3 up to 5 m\\/o were found to enhance the conductivity of pure CaF2. The conductivity values were increased two orders of magnitude higher than

G. Róg; A. Kielski; A. Koz?owska-Róg; M. Bu?ko

1998-01-01

274

Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF 2(1 1 1) surface  

Microsoft Academic Search

We investigate the formation of nano-sized hillocks on the (111) surface of CaF2 single crystals by impact of slow highly charged ions. Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about 14keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solid–liquid

A. S. El-Said; W. Meissl; M. C. Simon; J. R. Crespo López-Urrutia; C. Lemell; J. Burgdörfer; I. C. Gebeshuber; Hp. Winter; J. Ullrich; C. Trautmann; M. Toulemonde; F. Aumayr

2007-01-01

275

Low-dimensional sublattice melting by pressure: Superionic conduction in the phase interfaces of the fluorite-to-cotunnite transition of CaF2  

Microsoft Academic Search

The pressure-induced phase transformation of calcium fluoride (CaF2) from the cubic-fluorite-type structure (Fm3¯m) to the orthorhombic cotunnite (PbCl2) type structure (Pnma) is investigated from transition path sampling molecular dynamics simulations. Starting from an artificially prepared transformation route connecting fluorite to cotunnite, subsequent trajectory rectification evolved to a distinct picture of the favored mechanism. The latter is characterized by nucleation and

Salah Eddine Boulfelfel; Dirk Zahn; Oliver Hochrein; Yuri Grin; Stefano Leoni

2006-01-01

276

Synthesis and luminescent properties of rare-earth-doped CeO 2–CaF 2 solid solutions via chemical solution routes  

Microsoft Academic Search

CeO2–CaF2 solid solutions were synthesized by a chemical solution method starting from metal acetates, trifluoroacetic acid as a fluorine source, and anhydrous ethanol as a solvent. Precursor gels, which were obtained by drying the resultant ethanolic solution at 110°C, were heat-treated at a temperature in the range 400–1000°C in air to obtain powdery products. Elemental analysis by energy dispersive X-ray

Shinobu Fujihara; Hiroki Sato

2011-01-01

277

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

278

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

PubMed

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

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

2011-02-18

279

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

Microsoft Academic Search

As part of a program to provide reassurance that the cobalt- base superalloy Haynes? Alloy 188 can adequately contain a LiF-\\u000a CaF2 eutectic thermal energy storage salt, 4900- and 10,000- hr exposures of Haynes? Alloy 188 to LiF- 22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized\\u000a and the

J. D. Whittenberger

1992-01-01

280

Mechanical properties of haynes® alloy 188 after exposure to LiF22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours  

Microsoft Academic Search

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

J. D. Whittenberger

1992-01-01

281

Stem cell labeling using polyethylenimine conjugated (?-NaYbF4:Tm3+)/CaF2 upconversion nanoparticles.  

PubMed

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

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

2013-03-20

282

Reel-to-reel ex situ conversion of high critical current density electron-beam co-evaporated BaF2 precursor on RABiTS  

NASA Astrophysics Data System (ADS)

A reel-to-reel furnace equipped with seven transverse flow modules has been developed to continuously process ex situ BaF2 precursor coated conductors. Experimental results have revealed that as the precursor thickness increases, the processing parameters need to be adjusted in order to obtain high quality YBCO films with Jc' s greater than 1 MA cm-2 at 77 K and self-field. For thin precursors, a relatively aggressive conversion environment of high P(H2O) can be used to obtain epitaxial YBCO with an extremely small amount of undesirable random or a-axis grains. Thin 0.3 µm YBCO was converted on a 2.3 m long by 1 cm wide Ni RABiTS substrate, yielding an end-to-end Ic of 18.9 A (Jc = 0.63 MA cm-2). 16 cm sectional measurements showed that the tape performance is uniform, with a mean Ic of 19.1 A (0.64 MA cm-2) and a 5.4% SD. In thick precursors, however, a less aggressive environment in the form of low P(H2O) is better suited for epitaxial YBCO nucleation during the incubation period. By using a low initial P(H2O) with progressively higher values during later stages of conversion, an end-to-end Ic of 92 A (1.02 MA cm-2) was obtained in 1.1 m long by 1 cm wide 0.9 µm YBCO on better-textured Ni-W RABiTS. This conductor possesses uniform Ic according to 1 cm sectional measurements with a mean Ic of 94.4 A (1.05 MA cm-2) and only 4.3% SD. Further adjustment in the P(H2O) schedule resulted in a 45 cm long sample with end-to-end Ic of 111.8 A (1.24 MA cm-2), a mean Ic of 114.8 A (1.28 MA cm-2) and 4.8% SD. The highest Ic of 138 A (1.53 MA cm-2) was obtained in a short 0.9 µm YBCO sample on a pre-treated Ni-W RABiTS substrate.

Lee, D. F.; Leonard, K. J.; Heatherly, L., Jr.; Yoo, J.; List, F. A.; Rutter, N.; Cook, S. W.; Sathyamurthy, S.; Paranthaman, M.; Martin, P. M.; Goyal, A.; Kroeger, D. M.

2004-03-01

283

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

Microsoft Academic Search

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

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

2005-01-01

284

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

NASA Astrophysics Data System (ADS)

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

Jiang, Nan

2011-07-01

285

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

NASA Astrophysics Data System (ADS)

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

Nassaralla, C.; Fruehan, R. J.

1992-03-01

286

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

NASA Astrophysics Data System (ADS)

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

Robelin, Christian; Chartrand, Patrice

2007-12-01

287

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

Microsoft Academic Search

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

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

1995-01-01

288

Electroslag remelting with all-fluoride low conductivity slags  

Microsoft Academic Search

The electrical conductivity of liquids in the composition ranges CaF2 + 0 to 12 wt pct AIF3; CaF2 + 0 to 20 wt pct LaF3; and CaF2 + 0 to 30 wt pct YF3 has been determined at 1500? and 1600?C. It is deduced from the conductivities and the form of the phase diagrams of these\\u000a systems that CaF2 +

G. Bacon; A. Mitchell; R. M. Nishizaki

1972-01-01

289

Investigation of the spin-lattice coupling coefficients G11 and G44 for CaF2:V3+ crystal  

NASA Astrophysics Data System (ADS)

In this Letter a uniform and simple method is established to calculate the spin-lattice coupling coefficients G11 and G44 for all dn ions in fourfold or eightfold cubic coordination from the formulas of zero-field splitting in tetragonal and trigonal symmetries. Based on this, the analytic expressions of G11 and G44 for d2 ions in eightfold cubic coordination are given, and as an example, the coefficients G11 and G44 for CaF2:V3+ crystal are calculated by applying the same parameters as those in the calculation within the framework of the exchange-charge model. The calculated results are closer to the experimental values than those calculated from the exchange-charge model.

Zheng, Wen-Chen

1990-05-01

290

Sorption and desorption properties of a CaH2/MgB2/CaF2 reactive hydride composite as potential hydrogen storage material  

NASA Astrophysics Data System (ADS)

The hydrogenation behavior of 3CaH2+4MgB2+CaF2 composite was studied by manometric measurements, powder X-ray diffraction, differential scanning calorimetry and attenuated total reflection infrared spectroscopy. The maximum observed quantity of hydrogen loaded in the composite was 7.0 wt%. X-ray diffraction showed the formation of Ca(BH4)2 and MgH2 after hydrogenation. The activation energy for the dehydrogenation reaction was evaluated by DSC measurements and turns out to be 162±15 kJ mol-1 H2. This value decreases due to cycling to 116±5 kJ mol-1 H2 for the third dehydrogenation step. A decrease of ca. 25-50 °C in dehydrogenation temperature was observed with cycling. Due to its high capacity and reversibility, this composite is a promising candidate as a potential hydrogen storage material.

Suarez Alcantara, K.; Boesenberg, U.; Zavorotynska, O.; Bellosta von Colbe, J.; Taube, K.; Baricco, M.; Klassen, T.; Dornheim, M.

2011-11-01

291

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

PubMed

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

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

2010-10-26

292

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

PubMed

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

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

2009-09-28

293

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

SciTech Connect

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

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

1986-06-01

294

Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF2(1 1 1) surface  

NASA Astrophysics Data System (ADS)

We investigate the formation of nano-sized hillocks on the (1 1 1) surface of CaF2 single crystals by impact of slow highly charged ions. Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about 14 keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solid liquid phase transition (“melting”) on the nanoscale. With increasing potential energy, both the basal diameter and the height of the hillocks increase. The present results reveal a remarkable similarity between the present predominantly potential energy driven process and track formation by the thermal spike of swift (˜GeV) heavy ions.

El-Said, A. S.; Meissl, W.; Simon, M. C.; Crespo López-Urrutia, J. R.; Lemell, C.; Burgdörfer, J.; Gebeshuber, I. C.; Winter, Hp.; Ullrich, J.; Trautmann, C.; Toulemonde, M.; Aumayr, F.

2007-05-01

295

EPR and magnetic properties of MgO-CaO-SiO2-P2O5-CaF2-Fe2O3 glass-ceramics  

NASA Astrophysics Data System (ADS)

Glass-ceramics have been derived from 4.5MgO(45-x)CaO34SiO216P2O50.5CaF2xFe2O3 (x=5, 10, 15, 20 wt%) glasses by heat treatment. Room temperature electron paramagnetic resonance (EPR) spectra and temperature-dependent magnetic susceptibility (?) of the glass-ceramics have been obtained. The EPR absorption line centered at g?4.3 disappeared at higher concentrations of iron oxide. The intensity and line width of the EPR absorption line centered at g?2.1 increased as the iron oxide concentration was increased. Temperature-dependent magnetization of samples with low iron oxide content revealed ferrimagnetic as well as paramagnetic contributions. Information about the structural changes involving iron ions, their valence state and the type of magnetic interactions between the Fe ions as a function of composition was obtained using EPR and ? studies.

Singh, Rajendra Kumar; Srinivasan, A.

2009-09-01

296

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

297

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

298

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

National Technical Information Service (NTIS)

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 incrementa...

M. K. Stanford C. DellaCorte D. Eylon

2002-01-01

299

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

National Technical Information Service (NTIS)

The effects of BaF2-CaF2 particle size and size distribution on PS304 feedstock powder flowability have been investigated. Angular BaF2-CaF2 eutectic powders were produced by comminution and classified by screening to obtain 38 to 45 microns 45 to 106 mic...

C. DellaCorte D. Eylon M. K. Stanford

2002-01-01

300

The Effects of CaF2, Basicity, and Atmospheric Conditions on the Solubility of Carbon and Nitrogen in the CaO-SiO2-Al2O3-Based Slag System  

NASA Astrophysics Data System (ADS)

The solubility of carbon and nitrogen in the CaF2-CaO-SiO2-Al2O3 slag system was studied. The effects of the CaF2, extended basicity (CaO/(SiO2 + Al2O3)), and atmospheric conditions on the dissolution behavior of the carbon and nitrogen, as well as the correlations of the behaviors with the slag structure observed at 1773 K (1500 °C), are presented. Increases in the extended basicity and the CaF2 increased the solubility of carbon in the slag. In the case of nitrogen dissolution, a characteristic parabolic curve with an identifiable minimum was observed for the slag. This curve shape correlated with a change in the dominant mechanism of dissolution from an incorporated to a free nitride. The solubility of carbon in the mixture of CO with N2 was significantly higher than that of carbon in the mixture of CO with Ar and is likely due to the formation of cyanide. Thus, when carbon is present in significant quantities in the slag, the solubility of nitrogen in the slag increases. The degree of depolymerization of the slag with increased content of CaO/(SiO2 + Al2O3) and CaF2 was verified using Fourier transform infrared and Raman spectroscopy.

Park, Jun-Yong; Sohn, Il

2013-02-01

301

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

302

Preparation of YBa2Cu3O7-x films on cap-layer-buffered MgO substrates using precursor films deposited from Y, BaF2 and Cu  

NASA Astrophysics Data System (ADS)

YBa2Cu3O7-x (YBCO) is prepared by low-oxygen-pressure annealing of precursor films which are deposited from Y, BaF2 and Cu sources at room temperature. In the annealing process, pure oxygen gas is introduced into the reaction chamber. The other gases, for example, water vapor or nitrogen gas, are not intentionally introduced. We previously reported that it is difficult to control the in-plane alignment YBCO films on MgO substrates. Therefore, a single cap layer (BaSnO3) or double cap layers (CeO2/BaSnO3) are deposited on the MgO substrate. Subsequently, the YBCO films are prepared on the cap-layer-buffered MgO substrates. We evaluated the crystallinity and the film growth of the YBCO films on single-cap-layer-buffered and double-cap-layer-buffered MgO substrates.

Ichinose, A.; Yamamoto, Y.; Mukaida, M.; Kikuchi, A.; Tachikawa, K.; Akita, S.; Inoue, K.; Matsumoto, K.; Yoshida, Y.; Horii, S.

2004-10-01

303

Thermodynamics of mixing of liquids in the system Ca 3(PO 4) 2?CaCl 2?CaF 2?Ca(OH) 2  

NASA Astrophysics Data System (ADS)

Molten calcium halide and hydroxide salts may be used as flux and reactants in determining apatite exchange equilibria and solid solution behavior. New experimental data and published phase equilibria are used to determine a thermodynamic model of melts and solids along the binary joins of the anhydrous apatite system Ca 3(PO 4) 2?CaCl 2?CaF 2?Ca(OH) 2. In this model, melt components are expressed as Ca0.5X, where X is hydroxide or a halogen, or as Ca 1.5PO 4. The derived binary interaction parameters ( WG' s) are sufficient to describe deviations from Raoultian behavior for the data. Standard state data are derived for molten Ca(OH) 2 and Ca 3(PO 4) 2, and for the intermediate compounds CaClF, CaClOH, and Ca 2PO 4Cl. Melts in the CaCl 2?CaF 2 system show ideal mixing behavior, while the calcium hydroxide-bearing molten salts form asymmetric regular solutions. The hydroxide-bearing melts show the small positive enthalpies of mixing typical for mixed-anion salts. Similar behavior is measured in simpler molten salt mixtures. The positive deviations from Raoultian behavior are not a mathematical artifact of the model. Data are less extensive for the salt-phosphate systems but cover the essential portions of the systems where salt to phosphate ratios are high. The mixtures of the molten salts and phosphates salts show large negative enthalpy interaction parameters ( WH), as is expected in eutectic systems which mix a high-melting-point crystal with a low-melting-point flux. Adequate reproduction of the data requires that some entropy interaction parameters be negative, although small. This implies the presence of ordering in the melt, which is manifested in more polymerized phosphate liquids and glasses as halogenated and hydroxylated orthophosphate and pyrophosphate species. Results of the model indicate that the quaternary system is a good choice for determination of activity-composition relations for the apatites. Comparison of common sources of standard state thermodynamic data ( ROBIE et al., 1979; JANAF, CHASE et al., 1985; CODATA, GARVIN et al., 1987) shows that the data for the salts are very similar where they are not identical. At temperatures below 900°C in the ternary systems, liquid compositions will be on or near the apatite-crystalline salt cotectics, and dissolve less than 1 mol% Ca 3(PO 4) 2. This makes CaCl 2?CaF 2 mixtures excellent candidates for determination of unambiguous apatite activity-compositional relations. Only the Ca(OH) 2 liquidus is strongly affected by the addition of phosphate, but this effect is closely described by a regular solution model.

Tacker, R. C.; Stormer, J. C., Jr.

1993-10-01

304

Spin-Hamiltonian parameters for the tetragonal Gd(M)3+-F(i)- centers in CaF(2) and SrF(2) crystals.  

PubMed

The spin-Hamiltonian parameters (g factors g(//), g(?) and zero-field splittings b(2)(0), b(4)(0), b(4)(4), b(6)(0), b(6)(4)) of the tetragonal Gd(M)(3+)-F(i)(-) centers in CaF(2) and SrF(2) crystals at T?1.8K are calculated from the diagonalization (of energy matrix) method based on the one-electron crystal field mechanism. In the calculations, the crystal field parameters used are estimated from the superposition model with the reported defect structural data obtained from the analyses of superhyperfire interaction constants at the same temperature. The calculated results are in reasonable agreement with the experimental values. It appears that the above defect structural data reported in the previous paper are suitable and the diagonalization (of energy matrix) method is effective to the studies of spin-Hamiltonian parameters for 4f(7) ions in crystals. PMID:23298858

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

2012-12-20

305

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

306

High-resolution digital dosimetric system for spatial characterization of radiation fields using a thermoluminescent CaF2:Dy crystal  

SciTech Connect

A high-resolution digital dosimetric system has been developed for the spatial characterization of radiation fields. The system comprises the following: 0.5-mm-thick, 25-mm-diam CaF2:Dy thermoluminescent crystal; intensified charge coupled device video camera; video cassette recorder; and a computerized image processing subsystem. The optically flat single crystal is used as a radiation imaging device and the subsequent thermally stimulated phosphorescence is viewed by the intensified camera for further processing and analysis. Parameters governing the performance characteristics of the system were measured. A spatial resolution limit of 31 +/- 2 microns (1 sigma) corresponding to 16 +/- 1 line pairs/mm measured at the 4% level of the modulation transfer function has been achieved. The full width at half maximum of the line spread function measured independently by the slit method or derived from the edge response function was found to be 69 +/- 4 microns (1 sigma). The high resolving power, speed of readout, good precision, wide dynamic range, and the large image storage capacity make the system suitable for the digital mapping of the relative distribution of absorbed doses for various small radiation fields and the edges of larger fields.

Atari, N.A.; Svensson, G.K.

1986-05-01

307

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

PubMed

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

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

2013-02-05

308

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

SciTech Connect

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

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

2006-12-04

309

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

Microsoft Academic Search

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

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

2001-01-01

310

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

311

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

312

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

NASA Astrophysics Data System (ADS)

DANCE (Detector for Advanced Neutron Capture Experiments) is a 4? array of BaF2 crystals installed at LANSCE, Lujan Center. Neutron capture measurements on ^157Gd and ^89Y nuclei were conducted using this facility. The absolute cross sections of the ^89Y(n,?) reaction was measured for the first time ever in the neutron energy range of 10 eV -- 10 keV and improvements were made in the 10 -- 300 keV range. The error bars were significantly reduced and number of cross section points was increased since the past ^89Y(n,?) experiments. The ^157Gd(n,?) cross section was determined at En = 20 eV -- 300 keV by normalizing the experimental DANCE data to a well known resonance taken from the ENDF/B-VII library. Computer simulations of the ^157Gd(n,?) cascades and DANCE pulse height function were made using DICEBOX and GEANT4 codes and simulated Esum and E? spectra are compared to the experimental DANCE data. Values of spin and photon strength function (PSF) of the ^157Gd(n,?) resonances are provided in the range of En = 2 -- 300 eV using spin dependence upon a ?-ray multiplicity.

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

2009-10-01

313

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

314

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: A study of resistance of absorbing centres in a Pr2+:CaF2 crystal to high-power laser radiation  

NASA Astrophysics Data System (ADS)

A change in the absorption coefficient of Pr2+:CaF2 crystal in the spectral region from 530 to 1000 nm is found after irradiation by 30-mJ, 20-ns pulses from a repetitively pulsed 1.064-?m neodymium laser with a radiation power density of 500 MW cm-2. After irradiation by 105 pulses, the spectrum of the absorption coefficient variation ?? represents a broad band (~3000 cm-1) centred at 710 nm with the maximum value of ??=1.1 cm-1.

Il'ichev, Nikolai N.; Pashinin, Pavel P.; Gulyamova, E. S.

2001-07-01

315

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

Microsoft Academic Search

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

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

1967-01-01

316

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

PubMed Central

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

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

2012-01-01

317

(?-NaYbF4:Tm(3+))/CaF2 core/shell nanoparticles with efficient near-infrared to near-infrared upconversion for high-contrast deep tissue bioimaging.  

PubMed

We describe the development of novel and biocompatible core/shell (?-NaYbF(4):Tm(3+))/CaF(2) nanoparticles that exhibit highly efficient NIR(in)-NIR(out) upconversion (UC) for high contrast and deep bioimaging. When excited at ~980 nm, these nanoparticles emit photoluminescence (PL) peaked at ~800 nm. The quantum yield of this UC PL under low power density excitation (~0.3 W/cm(2)) is 0.6 ± 0.1%. This high UC PL efficiency is realized by suppressing surface quenching effects via heteroepitaxial growth of a biocompatible CaF(2) shell, which results in a 35-fold increase in the intensity of UC PL from the core. Small-animal whole-body UC PL imaging with exceptional contrast (signal-to-background ratio of 310) is shown using BALB/c mice intravenously injected with aqueously dispersed nanoparticles (700 pmol/kg). High-contrast UC PL imaging of deep tissues is also demonstrated, using a nanoparticle-loaded synthetic fibrous mesh wrapped around rat femoral bone and a cuvette with nanoparticle aqueous dispersion covered with a 3.2 cm thick animal tissue (pork). PMID:22928629

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

2012-09-04

318

Computer aided design of nano-structured materials with tailored ionic conductivities.  

PubMed

We show, using simulation techniques, that the high ionic conductivity in BaF2/CaF2 heterolayers is because the interfaces reduce the activation energy barriers to mobility and increase the number of charge carriers. PMID:19785169

Sayle, Dean C; Doig, James A; Parker, Stephen C; Watson, Graeme W; Sayle, Thi X T

2005-01-01

319

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

320

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

PubMed

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

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

2010-12-29

321

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

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

322

ZBLAN Microgravity Study.  

National Technical Information Service (NTIS)

One of the greatest obstacles with the fluorozirconate ZBLAN (ZrF4-BaF2-LaF3-AIF3-NaF) is the problem of devitrification. Fluoride glasses have a narrow working range and the viscosity is a strong function of temperature. Rates of nucleation and growth of...

G. L. Workman G. A. Smith S. OBrien L. Adcock

1995-01-01

323

Effect of Microgravity on Crystallization of ZBLAN Fibers.  

National Technical Information Service (NTIS)

ZrF4-BaF2-LaF3-AlF3-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 ...

D. S. Tucker

1994-01-01

324

Purification of Metal Fluorides for the Ultra Low Loss Program.  

National Technical Information Service (NTIS)

By using radiotracer techniques the practical limits for the preparation of high purity ZrF4, HfF4, and LaF3 via NRL current technology have been determined. The required concentration of impurities in BaF2, AiF3, and NaF for a 0.01 dB/km loss are calcula...

K. J. Ewing

1990-01-01

325

[Comparison of embryotoxic effects of inorganic fluorides].  

PubMed

A comparison of the toxicity of SnF2, BaF2, KF, CaF2, and MgF2 shows that the hard-to-dissolve fluorides CaF2 and MgF2 are absolutely safe. The other fluorides tested showed no toxic effects in dosages relevant for caries prophylaxis and with oral application. PMID:289491

Stratmann, K R

1979-06-01

326

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

PubMed Central

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

Baniahmad, A; Thormeyer, D; Renkawitz, R

1997-01-01

327

Direct Determination of the NaF/AlF3 Molar Ratio by Raman Spectroscopy in NaF-AlF3-CaF2 Melts at 1000 °C.  

PubMed

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

Malherbe, Cedric; Gilbert, Bernard

2013-08-29

328

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

SciTech Connect

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

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

1992-08-01

329

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

SciTech Connect

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

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

2011-11-01

330

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

PubMed

The present study investigates the influence of SrO on structure, apatite-forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with the composition (mol.%): (36.07 - x) CaO-xSrO-19.24MgO-5.61P(2)O(5)-38.49SiO(2)-0.59CaF(2), where x varies between 0 and 10. The detailed structural analysis of the glasses is made by infrared spectroscopy and magic angle spinning-nuclear magnetic resonance spectroscopy. Silicon is predominantly present as Q(2) (Si) species, while phosphorus is found as orthophosphate in all the investigated glasses. The apatite-forming ability of glasses is investigated by immersion of glass powders in simulated body fluid for time durations varying between 1 h and 7 days. While increasing the Sr(2+)/Ca(2+) ratio in the glasses does not affect their structure significantly, their apatite-forming ability is decreased considerably. Further, physico-chemical degradation of glasses is studied in accordance with ISO 10993-14 "Biological evaluation of medical devices - Part 14: Identification and quantification of degradation products from ceramics" in Tris-HCl and citric acid buffer, and the possible implications of the ion release profiles from the glasses in different solutions are discussed. The addition of strontium to the glasses leads to a sevenfold decrease in chemical degradation of glasses in Tris-HCl. The sintering of glass powders renders glass ceramics (GCs) with varying degrees of crystallinity and good flexural strength (98-131 MPa), where the mechanical properties depend on the nature and amount of crystalline phases present in the GCs. PMID:21763793

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

2011-07-02

331

Effect of particle morphology on flow characteristics of a composite plasma spray powder  

NASA Astrophysics Data System (ADS)

The effects of BaF2-CaF2 particle morphology on National Aeronautics and Space Administration (NASA) PS304 feedstock powder flowability were investigated, BaF2-CaF2 eutectic powders were fabricated by comminution (producing an angular morphology) and by gas atomization (producing a spherical morphology). The fluoride powders were added incrementally to the other powder constituents of the NASA PS304 feedstock, (Ni-Cr, Cr2O3, and Ag powders). A linear relationship between flow time and concentration of the BaF2-CaF2 powder was found. The flow of the powder blend with spherical BaF2-CaF2 was better than that with angular BaF2-CaF2. The flowability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. However, the flow of the powder blend with spherical fluorides was independent of fluoride concentration. The results suggest that for this material blend, particle morphology plays a significant role in flow behavior, offering potential methods to improve powder flowability and enhance the commercial potential. These findings may be applicable to other difficult-to-flow powders such as cohesive ceramics.

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

2004-12-01

332

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

333

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

2013-10-01

334

BaF2/GaAs Electronic Components.  

National Technical Information Service (NTIS)

Metal insulator semiconductor field effect transistors (MISFETs), charge coupled devices (CCDs), and capacitors based on an epitaxial barium fluoride (BF2) insulator layer deposited directly onto a single crystal gallium arsenide (GaAs) substrate.

F. Santiago T. K. Chu

1994-01-01

335

Radiation damage in BaF2 crystals.  

National Technical Information Service (NTIS)

The effects of radiation damage and recovery have been studied in BaF(sub 2) crystals exposed to (sup 60)Co radiation. The change in optical transmission and scintillation light output have been measured as a function of dose up to 4.7 (times) 10(sup 6) r...

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

1991-01-01

336

Performance of the BaF2calorimeter TAPS  

Microsoft Academic Search

The electromagnetic calorimeter TAPS (Two\\/Three Arm Photon Spectrometer) - comprising in its present set-up 384 individual plastic-BaF2 scintillator telescopes - has been constructed to identify and measure hard photons and neutral mesons via the reconstruction of the invariant mass from their two or three photon decay modes. Photons can be detected up to an energy of 15GeV with high resolution

R. Novotny

1997-01-01

337

Room-temperature photon avalanche up-conversion in Er-doped fluoride glass and fibre pumped at 700 nm  

Microsoft Academic Search

A strong emission at 550 nm as well as a series of other wavelengths have been observed in Er-doped ZrF4-BaF2-LaF3-AlF3-NaF fibres and bulk glass at room temperature when the excitation wavelength is about 700 nm, which is far away from the absorptions from the ground state of Er3+ ions. Measurements of excitation, time delay and intensity dependence versus pump power

Yihong Chen; D. Meichenin; F. Auzel

1995-01-01

338

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

339

Photoluminescence and radiationless processes in Mn2+-doped Ca1-xSrxF2 fluorites as a function of pressure and temperature. A structural correlation study  

Microsoft Academic Search

This work investigates the photoluminescence (PL) properties of Mn2+-doped fluorites in CaF2, BaF2, SrF2, and in solid solutions Ca1-xSrxF2. In particular, we focus on the radiationless processes leading to the surprising disappearance of the Mn2+ PL on passing from CaF2: Mn2+ to SrF2: Mn2+ or BaF2: Mn2+. For this purpose emission, excitation, lifetime, and time-resolved spectroscopy as a function of

F. Rodríguez; I. Hernández; M. Moreno; R. Alcalá

2003-01-01

340

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

Microsoft Academic Search

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

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

1999-01-01

341

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

SciTech Connect

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

Hamilton, D.S.

1986-01-01

342

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

343

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

PubMed

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

Grass, Robert N; Stark, Wendelin J

2005-02-03

344

Growth of YBa2Cu3O7-? on alkaline earth flouride substrates and thin films  

NASA Astrophysics Data System (ADS)

The growth and characterization of YBa2Cu3O7-? (YBCO) thin films grown by laser ablation on MgF2 (100), CaF2 (100), SrF2 (100), and BaF2 (100) substrates, and on CaF2 and BaF2 thin films on LaAlO3 (100) substrates, are described. High quality superconducting YBCO films could be grown directly only on the BaF2 substrates and thin films. YBCO films grown directly on MgF2 or CaF2 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 SrF2 and CaF2 substrates and thin films only with an yttria-stabilized zirconia buffer layer and/or with a low YBCO growth temperature, while YBCO grown on MgF2 yielded insulating films for all growth conditions investigated. The highest quality YBCO films were obtained on BaF2 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

345

Tribological and Microstructural Comparison of Hipped PM212 and PM212/au Self-Lubricating Composites.  

National Technical Information Service (NTIS)

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 follo...

M. S. Bogdanski H. E. Sliney C. Dellacorte

1992-01-01

346

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

347

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

348

Determination of gross alpha activity in urine by microprecipitation with LaF3 and alpha spectrometry.  

National Technical Information Service (NTIS)

This paper describes a method for the determination of gross alpha activity (actinides) in urine. The method presents the advantage of being a relatively cheap, simple multipurpose analytical procedure. It consists of the coprecipitation of actinides as F...

G. G. Jia S. Bazzarri F. Micci C. Testa

1990-01-01

349

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

NASA Astrophysics Data System (ADS)

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.

1994-09-01

350

Additive coloring of CaF2:Sm crystals  

NASA Astrophysics Data System (ADS)

The study of the mechanism of additive coloring of calcium fluoride crystals, both pure and samarium-doped, demonstrates dynamical nature of processes that, in the course of coloring, tend to maintain equilibrium between Sm3+ and Sm2+ ions.

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

2010-06-01

351

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

Microsoft Academic Search

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

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

2006-01-01

352

Strong red-light scattering from colloidal copper in ZBLAN fluoride glass  

Microsoft Academic Search

Following extended thermal processing under reducing conditions, fluoride glasses with a composition close to the standard 53% ZrF4-20% BaF2-4% LaF3-3% AlF3-20% NaF (ZBLAN) formulation scatter red light in a band centred at around 600 nm, together with an associated extinction band centred at around 570 nm. Some samples show a dichroic effect of appearing red in back-scattered light but blue

Andrew Edgar

1997-01-01

353

High-Q microresonators for mid-IR light sources and molecular sensors.  

PubMed

We propose and demonstrate a simple and reliable method for fabricating high-quality whispering-gallery mode (WGM) optical microresonators in "mid-IR relevant" low-loss ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) glasses. Intrinsic quality factors of 10(7) have been demonstrated, providing great promise for WGM-based mid-IR (MIR) devices. Absorption-limited Q-factors of over 3×10(8) are anticipated over the 2.0 to 3.2 ?m MIR wavelength range in ZBLAN microcavities in the foreseeable future. PMID:23114305

Way, Brandyn; Jain, Ravinder K; Hossein-Zadeh, Mani

2012-11-01

354

Effects of Gravity on ZBLAN Glass Crystallization.  

PubMed

The effects of gravity on the crystallization of ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF glasses have been studied using the NASA KC-135 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. PMID:15644351

Tucker, Dennis S; Ethridge, Edwin C; Smith, Guy A; Workman, Gary

2004-11-01

355

Influence of fluorescence reabsorption and trapping on solid-state optical cooling.  

PubMed

We analyze the random process of fluorescence reabsorption and trapping in solid-state optical materials in general and its influence on the efficiency of optical cooling of solids by anti-Stokes fluorescence in particular. Using the absorption and fluorescence spectra of Yb3+:ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) as input data, we employ a random-walk model to test analytical approximations of the fluorescence escape efficiency and cooling efficiency, including reflections at the boundary. PMID:15929307

Heeg, Bauke; DeBarber, Peter A; Rumbles, Garry

2005-05-20

356

Stark level analysis for Er 3+-doped ZBLAN glass  

Microsoft Academic Search

From the absorption and emission spectra recorded in a conventional way at 13 K, the Stark levels in manifolds from 4I15\\/2 to 2H9\\/2 for Er3+-doped ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) glass have been investigated by means of the effective crystal field model previously proposed to describe the average of local symmetries occupied by rare earth ions in oxide glasses [1]. This model, based

Y. D. Huang; M. Mortier; F. Auzel

2001-01-01

357

Manufacturing of Er:ZBLAN ridge waveguides by pulsed laser deposition and ultrafast laser micromachining for green integrated lasers  

Microsoft Academic Search

Laser radiation is used both for the deposition of the laser active thin films and for the microstructuring to define wave guiding structures for the fabrication of waveguide lasers. Thin films of Er:ZBLAN (a fluoride glass consisting of ZrF4, BaF2, LaF3, AlF3, NaF, ErF3) for green up-conversion lasers (545nm) are produced by pulsed laser deposition using ArF excimer laser radiation

Jens Gottmann; Leonid Moiseev; Ion Vasilief; Dirk Wortmann

2008-01-01

358

Pressure and temperature-dependence of elastic properties of a ZBLAN glass  

Microsoft Academic Search

The hydrostatic and uni-axial pressures, and the temperature-dependence of elastic properties of a 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF (ZBLAN) glass were determined by ultrasonic pulse-echo techniques. The experimental results are used to obtain elastic constants of the glass. The normal behavior of negative temperature-dependence and positive pressure-dependence of the ultrasonic velocities were observed for this glass. The pressure-derivative of shear modulus and bulk modulus,

L. G. Hwa; Y. J. Wu; W. C. Chao; C. H. Chen

2002-01-01

359

Power scalable mid-infrared supercontinuum generation in ZBLAN fluoride fibers with up to 1.3 watts time-averaged power  

Microsoft Academic Search

Mid-infrared supercontinuum (SC) extending to ~4.0 mum is generated with 1.3 W time-averaged power, the highest power to our knowledge, in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fiber by using cladding-pumped fiber amplifiers and modulated laser diode pulses. We demonstrate the scalability of the SC average power by varying the pump pulse repetition rate while maintaining the similar peak power. Simulation results obtained

Chenan Xia; Malay Kumar; Ming-Yuan Cheng; Ravi S. Hegde; Mohammed N. Islam; Almantas Galvanauskas; Herbert G. Winful; Fred L. Terry Jr.; Mike J. Freeman; Marcel Poulain; Gwenael Mazé

2007-01-01

360

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

361

New Process for Fluoride Glass Preform Fabrication Using Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

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 ?-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 is applicable to the preparation of fluoride glass preforms. It is promising for the realization of ultra-low loss and long-length optical fibers.

Fujiura, Kazuo; Ohishi, Yasutake; Takahashi, Shiro

1989-12-01

362

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

Microsoft Academic Search

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

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

2009-01-01

363

784-nm amplified spontaneous emission from Tm3+-doped fluoride glass fiber pumped by an 1120-nm fiber laser.  

PubMed

We report 784-nm (1G4 --> 3H5 transition) amplified spontaneous emission (ASE) from Tm3+-doped fluoride (ZrF4-BaF2-LaF3-AlF3-NaF) glass fiber pumped by an 1120-nm fiber laser. To our best knowledge, this is the first report of 784-nm (1G4 --> 3H5 transition) ASE in a Tm3+-doped fluoride fiber laser. Its effects on a 480-nm (1G4 --> 3H6 transition) blue laser were also discussed. PMID:15751881

Qin, Guanshi; Huang, Shenghong; Feng, Yan; Shirakawa, A; Ueda, Ken-ichi

2005-02-01

364

Exposure of high-reflecting fluoride coatings under high fluence conditions at 193nm  

NASA Astrophysics Data System (ADS)

The paper presents results of investigations in evaporated LaF3-MgF2 and LaF3-AlF3 classical high-reflecting multilayers deposited on super-polished CaF2 substrates. In addition to typical spectroscopic inspections up to the band edge of fluoride substances in the VUV spectral range, the work is dedicated to the determination of laser-induced damage threshold at moderate pulse numbers for the wavelength 193 nm. Further on, dose dependent irradiation tests are performed well below the fluence level of damage onset indicating changes for the spectral transfer functions. These experimental observations are discussed in order to find a correlation to the characteristic damage behavior of both material combinations. In contrast to the standard evaporation process, partial-reflecting fluoride coatings have been deposited under ion-assisted conditions with fluorine gas. Results of damage tests will show excellent performance to high fluence levels.

Blaschke, H.; Riggers, W.; Ristau, D.

2010-10-01

365

Optical materials characterization final technical report february 1, 1978-september 30, 1978. Technical note  

SciTech Connect

Data obtained as part of the Optical Materials Characterization Program are summarized in this report. Room temperature values of refractive index as a function of wavelength are presented for the following materials: commercially grown KCl, reactive atmosphere processed (RAP) KCl, KCl nominally doped with 1.5% KI, hot forged CaF2, fusion cast CaF2, CaF2 doped with Er (0.001% to 3% Er), SrF2, chemical vapor deposited (CVD) ZnSe (2 specimens), and ZnS (CVD, 2 specimens). Data for the thermo-optic constant (dn/dT) and the linear thermal expansion coefficient are given for the following materials over the temperature range -180 degrees C to 200 degrees C: Al2O3, BaF2, CaF2, CdF2, KBr, KCl, LiF, MgF2, NaCl, NaF, SrF2, ZnS (CVD), and ZnSe (CVD). The piezo-optic constants of the following materials are presented: As2S3 glass, CaF2, BaF2, Ge, KCl, fused SiO2, SrF2, a chalcogenide glass (Ge 33%, As 12%, Se 55%) and ZnSe (CVD).

Feldman, A.; Horowitz, D.; Waxter, R.M.; Dodge, M.J.

1979-02-01

366

Spectral hole burning in the trivalent thulium ion.  

PubMed

Spectral hole burning is reported for the trivalent thulium ion with measurements on the (3)H(6)(1) ? (3)H(4)(1) transition of LaF(3):Tm(3+) and two sites (A and B) of CaF(2):Tm(3+) at 1.5 K. Hole burning occurs by population storage in the metastable (3)F(4) level. The holes were scanned by an electric-field ramp applied directly to the sample, the frequency being calibrated by burning multiple holes with a frequency-modulated laser. This yielded the hole widths as well as the Stark coefficients for the transition studied, which are 8.3 kHz/V cm(-1) parallel to the C(2) axis (LaF(3):Tm(3+)) and for CaF(2):Tm(3+) are 25 kHz/V cm(-1) (site A), and 4.6 kHz/V cm(-1) (site B) for fields along the (001) direction. From the polarization behavior of the holes, the sites in CaF(2) are assigned to the F(-)-compensated C(4nu) and C(3nu) sites, respectively. PMID:19802287

Macfarlane, R M

1993-05-15

367

Communication: Growing room temperature ice with graphene  

NASA Astrophysics Data System (ADS)

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

Verdaguer, Albert; Segura, Juan José; López-Mir, Laura; Sauthier, Guillaume; Fraxedas, Jordi

2013-03-01

368

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

Microsoft Academic Search

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

Wenchao Wang

2004-01-01

369

Nanostructures created in SiO 2 surface: A comparison between the impingement by slow highly charged ions and by swift heavy ions  

Microsoft Academic Search

Swift heavy ions (SHI) of MeV–GeV energy lead to the creation of nanometric surface structures as well as modifications in the bulk along the ion penetration depth. Recently, similar surface modifications have been observed for the impact of individual slow highly charged ions (HCI). Non-amorphizable ionic-halide single crystals, like KBr, CaF2 and BaF2, are considered as the most intensively studied

A. S. El-Said

370

Thermal mismatch strain relaxation of epitaxial IV–VI\\/Si(111) structures on multiple temperature cycling to cryogenic temperatures  

Microsoft Academic Search

Epitaxial narrow gap PbSe is grown by MBE (molecular beam epitaxy) onto Si(111) substrates with the aid of a BaF2\\/CaF2 buffer layer. The tensile strain which builds up on cool-down after growth due to the thermal expansion mismatch is relaxed by creation and movement of misfit dislocations in the main glide system. The thermal mismatch strain relaxes even at liquid-nitrogen

H. Zogg; S. Teodoropol

1995-01-01

371

Elastic properties of several amorphous solids and disordered crystals below 100 K  

Microsoft Academic Search

We have measured the internal friction and speed of sound variation at temperatures between 60 mK and room temperature for amorphous CdGeAs2, Polystyrene, and Stycast 2850FT epoxy, and the disordered crystals (ZrO2)0.89(CaO)0.11 and (CaF2)0.74(LaF3)0.26. A comparison of our results with an extensive review of previously published data shows a remarkable similarity in the internal friction of disordered solids below ~5rK.

K. A. Topp; David G. Cahill

1996-01-01

372

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

SciTech Connect

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

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

2001-06-24

373

Slow Component Suppression and Radiation Damage in Doped BaF2 Crystals.  

National Technical Information Service (NTIS)

The scintillation and radiation damage properties of barium fluoride crystals doped with various rare earths have been studied in an attempt to develop a fast, radiation hard scintillating crystal with a suppressed slow component for use at high counting ...

C. L. Woody P. W. Levy J. A. Kierstead

1988-01-01

374

Optical materials characterization  

NASA Astrophysics Data System (ADS)

The refractive indices of three prisms of chemical vapor deposited ZnS were measured at room temperature over the wavelength range 540 nm to 1.083 micrometers. The refractive indices of eight specimens of CaF2 doped with Er were measured from 404.7 nm to 1.083 micrometers. The doping range was 0.001% to 3% Er. Interferometric measurements of dn/dT were made over the temperature range -180 to 200 C at the wavelengths 632.8 nm and 3.39 micrometers on single crystal specimens of BaF2, CaF2, reactive atmosphere processed (RAP) KBr, RAP KCl, KCl, doped with KI, LiF, NaF and SrF2, and on chemical vapor deposited (CVD) ZnSe and hot forged CaF2.

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

1977-03-01

375

Ionic conduction mechanisms in CaF2 and CaF 2-Al2O3 nanocomposite films on Al2O 3 substrates.  

National Technical Information Service (NTIS)

Thin films of pure CaF(sub 2) and nanocomposite mixtures of Al(sub 2)O(sub 3) with CaF(sub 2) were sublimated on Al(sub 2)O(sub 3) substrates. Interdigital electrodes allowed in situ measurements of the electrical conduction vs thickness, deposition rate,...

F. A. Modine D. Lubben J. B. Bates

1993-01-01

376

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

PubMed

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

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

2008-04-30

377

Determination of intrinsic mid-infrared absorption of a fluoride glass.  

PubMed

The intrinsic mid-infrared optical absorption of a ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) glass has been determined by combining laser calorimetry and spark-source mass spectrographic analysis. The total optical absorption of four samples of varying purity was measured at 3.9 microm with laser calorimetry. The extrinsic contribution to the total absorption for each glass was calculated from the measured concentration of rare-earth impurity ions and known extinction coefficients. The intrinsic absorption of this glass at 3.9 microm determined from the difference between the total measured absorption and the calculated extrinsic absorption is 6.11 (+/-0.61) x 10(-4) cm(-1). PMID:19777029

Jewell, J M; Aggarwal, I D

1991-10-15

378

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

PubMed

A mid-infrared supercontinuum (SC) is generated in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fibers from amplified nanosecond laser diode pulses with a continuous spectrum from approximately 0.8 microm to beyond 4.5 microm. The SC has an average power of approximately 23 mW, a pump-to-SC power conversion efficiency exceeding 50%, and a spectral power density of approximately -20 dBm/nm over a large fraction of the spectrum. The SC generation is initiated by the breakup of nanosecond laser diode pulses into femtosecond pulses through modulation instability, and the spectrum is then broadened primarily through fiber nonlinearities in approximately 2-7 m lengths of ZBLAN fiber. The SC long-wavelength edge is consistent with the intrinsic ZBLAN material absorption. PMID:16902616

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

2006-09-01

379

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

PubMed

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

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

2012-10-15

380

Passively continuous-wave mode-locked Er(3+)-doped ZBLAN fiber laser at 2.8 ?m.  

PubMed

An Er(3+)-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) fiber laser was passively mode-locked by inserting a Fe(2+):ZnSe crystal into the free space part of the cavity. Continuous-wave mode-locked pulses at 2.8 ?m with a pulse duration of 19 ps estimated from the spectral bandwidth and an average power of 51 mW were generated when a collimated beam traversed the Fe(2+):ZnSe crystal, while Q-switched mode-locked pulses were obtained when the Fe(2+):ZnSe crystal was illuminated by the focused beam. PMID:23041880

Wei, Chen; Zhu, Xiushan; Norwood, R A; Peyghambarian, N

2012-09-15

381

Power scalable mid-infrared supercontinuum generation in ZBLAN fluoride fibers with up to 1.3 watts time-averaged power.  

PubMed

Mid-infrared supercontinuum (SC) extending to ~4.0 mum is generated with 1.3 W time-averaged power, the highest power to our knowledge, in ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF...) fluoride fiber by using cladding-pumped fiber amplifiers and modulated laser diode pulses. We demonstrate the scalability of the SC average power by varying the pump pulse repetition rate while maintaining the similar peak power. Simulation results obtained by solving the generalized nonlinear Schrödinger equation show that the long wavelength edge of the SC is primarily determined by the peak pump power in the ZBLAN fiber. PMID:19532312

Xia, Chenan; Kumar, Malay; Cheng, Ming-Yuan; Hegde, Ravi S; Islam, Mohammed N; Galvanauskas, Almantas; Winful, Herbert G; Terry, Fred L; Freeman, Mike J; Poulain, Marcel; Mazé, Gwenael

2007-02-01

382

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

383

Observation of anti-stokes fluorescence cooling in thulium-doped glass  

PubMed

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

Hoyt; Sheik-Bahae; Epstein; Edwards; Anderson

2000-10-23

384

On the cosmic-ray induced background in neutral pion production measurements with a BaF2 multidetector  

NASA Astrophysics Data System (ADS)

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

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

1995-02-01

385

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

386

Development studies for a high-rate positron camera based on a BaF2/TMAE system  

NASA Astrophysics Data System (ADS)

Clinical experience with our existing (Mark-II) positron camera has shown that the modest sensitivity and low maximum data rate of the device limit its clinical application. The latter problem is caused by the high singles rates encountered by the detectors and the sensitivity is limited by the conversion efficiency of the 511 keV gamma rays. We report the progress of our studies into a new positron camera system based on barium fluoride scintillators coupled to a low-pressure TMAE-filled MWPC which is read out by fast delay lines. According to our estimates this system will yield a sensitivity and a maximum data rate more than an order of magnitude higher than our existing system with comparable spatial resolution.

Bateman, J. E.; Connolly, J. F.; Stephenson, R.; Marsden, P. K.; Ott, R. J.; Suckling, J.

1989-11-01

387

Brillouin Lasing with a CaF2 Whispering Gallery Mode Resonator  

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

388

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

389

Colour centres formation in CaF2 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 106 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

390

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

NASA Astrophysics Data System (ADS)

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

Zahedifar, M.; Sadeghi, E.

2012-12-01

391

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

392

Low Threshold Optical Oscillations in a Whispering Gallery Mode CaF2 Resonator  

Microsoft Academic Search

We have observed low-threshold optical hyperparametric oscillations in a high-Q fluorite whispering gallery mode resonator. The oscillations result from the resonantly enhanced four-wave mixing occurring due to Kerr nonlinearity of the material. We demonstrate that, because of the narrow bandwidth of the resonator modes as well as the high efficiency of the resonant frequency conversion, the oscillations produce stable narrow-band

Anatoliy A. Savchenkov; Andrey B. Matsko; Dmitry Strekalov; Makan Mohageg; Vladimir S. Ilchenko; Lute Maleki

2004-01-01

393

Electronic energy bands in the fluorite structure: CaF2 and CdF2  

Microsoft Academic Search

The electronic band structures of calcium and cadmium fluoride are calculated by a combined tight-binding and pseudopotential method. The overall shape of the valence bands is found to be the same in these two compounds and agrees quite well with a \\

J. P. Albert; C. Jouanin; C. Gout

1977-01-01

394

Generation of optical frequency combs with a CaF2 resonator.  

PubMed

We demonstrate optical frequency combs using the fluorite whispering gallery mode resonator as a nonlinear Kerr medium. Two regimes of generation are observed, giving the record low repetition rate of 13 GHz, equal to the cavity's free spectral range (FSR) or high repetition rates of multiples of cavity FSR. An intermediate regime was also observed. Raman lasing spectrum similar to modulation instability in fibers was observed for the first time to the best of our knowledge. PMID:19340157

Grudinin, Ivan S; Yu, Nan; Maleki, Lute

2009-04-01

395

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

SciTech Connect

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

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

1999-09-01

396

Lateral manipulation of atomic size defects on the CaF(2)(111) surface.  

PubMed

Atomic scale manipulation on insulating surfaces is one of the great challenges of non-contact atomic force microscopy. Here we demonstrate lateral manipulation of defects occupying single ionic sites on a calcium fluoride (111)-surface. Defects stem from the interaction of the residual gas with the surface. The process of surface degradation is briefly discussed. Manipulation is performed over a wide range of path lengths ranging from tens of nanometres down to a few lattice constants. We introduce a simple manipulation protocol based on line-by-line scanning of a surface region containing defects to be manipulated, and record tip-surface distance and cantilever resonance frequency detuning as a function of the manipulation pathway in real time. We suggest a hopping model to describe manipulation where the tip-defect interaction is governed by repulsive forces. PMID:21727406

Hirth, S; Ostendorf, F; Reichling, M

2006-03-10

397

Phase diagram for nanostructuring CaF(2) surfaces by slow highly charged ions.  

PubMed

The impact of individual slow highly charged ions (HCI) on alkaline earth halide and alkali halide surfaces creates nano-scale surface modifications. For different materials and impact energies a wide variety of topographic alterations have been observed, ranging from regularly shaped pits to nanohillocks. We present experimental evidence for the creation of thermodynamically stable defect agglomerations initially hidden after irradiation but becoming visible as pits upon subsequent etching. A well defined threshold separating regions with and without etch-pit formation is found as a function of potential and kinetic energies of the projectile. Combining this novel type of surface defects with the previously identified hillock formation, a phase diagram for HCI induced surface restructuring emerges. The simulation of the energy deposition by the HCI in the crystal provides insight into the early stages of the dynamics of the surface modification and its dependence on the kinetic and potential energies. PMID:23005676

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

2012-09-14

398

Trigonal Crystal-Field Energy Levels of Sm(+3) IN CaF2 (Type I).  

National Technical Information Service (NTIS)

Approximate first-order trigonal crystal-field-split energy levels are derived and fitted theoretically for the Sm(3+)-in-CaF2 (Type I) sextet H(7/2), (9/2), (11/2) states of the ground multiplet involved in fluorescence. Crystal-field theory and the Stev...

N. Rabbiner

1968-01-01

399

Synthesis and optical characterizations of Yb-doped CaF 2 ceramics  

Microsoft Academic Search

Nanopowders of Yb-doped calcium fluoride were obtained by three different ways: mechanical alloying, reverse micelle method and co-precipitation. Transmission electron microscopy showed that the particle sizes were monodispersed for the powders obtained from soft chemistry with an average size around 20nm and polydispersed for the powder from the chemical alloying. An annealing step at 400°C is needed to remove impurities

P. Aubry; A. Bensalah; P. Gredin; G. Patriarche; D. Vivien; M. Mortier

2009-01-01

400

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.

2012-05-01

401

Microstructure and tribological properties of ZrO 2(Y 2O 3) matrix composites doped with different solid lubricants from room temperature to 800 °C  

Microsoft Academic Search

In this paper, spark plasma sintering is employed to synthesize a variety of self-lubricating ZrO2(Y2O3) matrix composites by tailoring the chemical compositions. The additives of BaF2, CaF2, Ag, Ag2O, Cu2O, BaCrO4, BaSO4, SrSO4 and CaSiO3 were incorporated into the ceramic matrix to evaluate their potentials as effective high-temperature solid lubricants from room temperature to 800°C by using a ball-on-block friction

J. H. Ouyang; Y. F. Li; Y. M. Wang; Y. Zhou; T. Murakami; S. Sasaki

2009-01-01

402

Multiwavelength laser rate calorimetry on various infrared window materials  

Microsoft Academic Search

The effective optical absorption coefficient obtained by the slope method of laser calorimetry is presented for a number of materials at a variety of laser wavelengths. The materials studied include MgF2, NaCl, KCl, LiYF4, CaF2, LiF, YAG, Al2O3 (sapphire), SiO2, BaF2,SrF2, CORTRAN 9753 and 9754 glass, ZBT glass, GGG, MgO-Al2O3 (spinel), ZnSe, MgO, Si, As2S3, ZnS, and calcium aluminate glasses.

N. C. Fernelius; G. S. Coble; D. V. Dempsey; J. A. Detrio; J. A. Fox; P. R. Greason; G. T. Johnston; D. B. Oquinn

1982-01-01

403

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

404

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

NASA Astrophysics Data System (ADS)

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

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

1997-04-01

405

Infrared properties of highly transparent solids  

NASA Astrophysics Data System (ADS)

The optical properties of highly transparent single crystals of KBr, KCl, CaF2 and BaF2 have been measured using laser calorimetric techniques and wavelength modulation spectroscopy techniques in the spectral range for 2.5 to 12 microns in cooperation with the University of California at Los Angeles (UCLA). Rich and varied absorption structures in the spectra were observed in all of the crystals enabling an identification of volume and surface absorption. Similar dominant bands are observed in many of the crystals indicating the presence of common impurities regardless of the crystal and origin of its growth. However, varied fine structure was observed in different crystals which are indicative of the individual characteristics of the chemistry of the crystal preparation. The measurements were performed in laboratory and dry nitrogen ambients and the physical absorption and desorption of surface contaminants was readily observed. Ellipsometric techniques were developed to evaluate and measure the strain and anisotropy in infrared optical films. Improved Reactive Atmosphere Processing (RAP) techniques were developed and studied using a two zone RAP furnace for single crystal growth of BaF2 and CaF2 which resulted in improved infrared transmission in the 3 to 5 micron wavelength region for the first time.

Braunstein, M.

1980-07-01

406

Optical materials characterization  

NASA Astrophysics Data System (ADS)

The refractive index of fusion cast CaF2 was measured at room temperature over the wavelength range 0.2144 micrometers to 8.662 micrometers and the data were fitted to a Selmeier type equation. Measurements of refractive index of hot forged CaF2 were extended to the wavelength range 0.2024 micrometers to 0.2483 micrometers. Data are presented for dn/dT of single crystal specimens of CaF2, BaF2, reactive atmosphere processed (RAP) KC1 and KBr, LiF, NaF, and 2SrF2, and polycrystalline chemical vapor deposited (CVD) ZnSe and ZnS. The measurements were done by the method of Fizeau interferometry over the temperature range -180 deg to 200 C at the wavelengths 0.6328 micrometers, 1.15 micrometers, 3.39 micrometers and 10.6 micrometers. Data are presented for the refractive indices, the linear thermal expansion and dn/dT of Lexan and Plexiglas 55.

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

1977-08-01

407

Achromatic lens systems for near infrared instruments. II. Performances and limitations of standard Flint glasses  

NASA Astrophysics Data System (ADS)

This paper investigates which normal Flint glasses are best suited for the design of lens systems working in the infrared up to about 1.7 mu m, and possibly up to 2.5 mu m. Between 0.9 and 2.5 mu m the best known achromatic pairs are BaF_2-IRG2 and SrF_2-IRG3 and, to a lesser extent, CaF_2-IRG7 (Oliva & Gennari 1995). Unfortunately, Schott will most probably stop the production of these very little used and commercially uninteresting IRG glasses. Here we show that equally good performances can be obtained coupling BaF_2 or SrF_2 with standard SF glasses. The pairs we analyze in details are BaF_2-SF6 and BaF_2-SF56A, and we also present new measurements of transmission for several SF glasses which are quite transparent up to 1.65 mu m and can be therefore readily employed in fiber-fed spectrographs and other instruments which do not extend beyond the H atmospheric window. At longer wavelengths the use of SF glasses is limited by strong water absorption features, but these could be eliminated by preparing the glass in vacuum environment. Although this production is expensive and commercially unattractive, we hope however that a large enough group of astronomers will support glass manufacturers in the production of ``IR-grade SF glasses''. As a practical application we present representative results of the design of F/2 (4 lenses) and F/1.4 (5 lenses) cameras for near infrared (0.95-2.5 mu m) spectrometers.

Oliva, E.; Gennari, S.

1998-03-01

408

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

2011-06-21

409

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

410

Study of CaF2 samples using DUV birefringence measurement and x-ray diffraction techniques  

NASA Astrophysics Data System (ADS)

In this paper we report measurement results of optical lithography grade calcium fluoride samples using deep ultraviolet (DUV) birefringence and X-ray diffraction methods. Linear birefringence maps of a variety of calcium fluoride samples were generated from measurements at both optical lithography wavelengths (157 nm, 193 nm and 248 nm) and at 632.8 nm. Comparing the respective wavelength results for birefringence in certain samples showed significant differences in birefringence patterns observed at 157 nm and 633 nm for a light beam propagating along the [111] crystal axis. Such differences cannot be explained from the dispersion of stress birefringence at those wavelengths. Our interpretation is that the discrepancy in the birefringence patterns observed at 157 nm and 633 nm is due to crystal defects in those calcium fluoride samples. The crystal quality of those calcium fluoride samples was subsequently determined by X-ray diffraction techniques. The results obtained from both birefringence and X-ray data substantiate each other qualitatively for judging the crystal quality of calcium fluoride samples.

Wang, Baoliang; Rosch, William

2007-09-01

411

Correlation of Electron Paramagnetic Resonance and Optical-Absorption Spectra of CaF2:Yb3+  

Microsoft Academic Search

An account is given of a combined optical and paramagnetic resonance investigation of trivalent ytterbium ions in ten different sites in calcium fluoride. Correlation between site geometry and optical absorption has been obtained for six of these by examining crystals prepared by different methods. A single optical-absorption line was observed for all but one of these sites, so that it

J. Kirton; S. D. McLaughlan

1967-01-01

412

Point defects in CaF2 and CeO2 investigated by the periodic electrostatic embedded cluster method.  

PubMed

A periodic electrostatic embedding scheme is presented that uses the periodic fast multipole method. The convergence of properties with increasing cluster size is examined for cluster models of calcium fluoride. Properties investigated are the electron density, the density of states, the electronic excitation of color centers, and energies of defect formation. The embedded cluster method is applied to CeO(2) and oxygen vacancies in bulk CeO(2) as well as on its (111) surface. Employing the PBE0 functional, vacancy formation energies of 3.0 and 3.3 eV have been obtained for the bulk and the (111) surface, respectively. Formation of subsurface defects requires 3.33 eV (singlet open shell). The localization of the electrons left behind on defect formation in Ce 4f states is discussed. Occupied Ce 4f states are well localized on nearest Ce atoms for surface and subsurface vacancies. Localization apart from the vacancy was obtained for bulk. The total CPU time spent on the embedding part did not exceed 30 s on a single CPU even if 8000 basis functions of the cluster are involved. PMID:19425801

Burow, Asbjörn M; Sierka, Marek; Döbler, Jens; Sauer, Joachim

2009-05-01

413

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

414

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

SciTech Connect

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

DePriest, Kendall Russell; Griffin, Patrick Joseph

2003-07-01

415

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

SciTech Connect

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

DEPRIEST, KENDALL R.

2002-11-01

416

Point defects in CaF2 and CeO2 investigated by the periodic electrostatic embedded cluster method  

Microsoft Academic Search

A periodic electrostatic embedding scheme is presented that uses the periodic fast multipole method. The convergence of properties with increasing cluster size is examined for cluster models of calcium fluoride. Properties investigated are the electron density, the density of states, the electronic excitation of color centers, and energies of defect formation. The embedded cluster method is applied to CeO2 and

Marek Sierka; Joachim Sauer

2009-01-01

417

Point defects in CaF2 and CeO2 investigated by the periodic electrostatic embedded cluster method  

NASA Astrophysics Data System (ADS)

A periodic electrostatic embedding scheme is presented that uses the periodic fast multipole method. The convergence of properties with increasing cluster size is examined for cluster models of calcium fluoride. Properties investigated are the electron density, the density of states, the electronic excitation of color centers, and energies of defect formation. The embedded cluster method is applied to CeO2 and oxygen vacancies in bulk CeO2 as well as on its (111) surface. Employing the PBE0 functional, vacancy formation energies of 3.0 and 3.3 eV have been obtained for the bulk and the (111) surface, respectively. Formation of subsurface defects requires 3.33 eV (singlet open shell). The localization of the electrons left behind on defect formation in Ce 4f states is discussed. Occupied Ce 4f states are well localized on nearest Ce atoms for surface and subsurface vacancies. Localization apart from the vacancy was obtained for bulk. The total CPU time spent on the embedding part did not exceed 30 s on a single CPU even if 8000 basis functions of the cluster are involved.

Burow, Asbjörn M.; Sierka, Marek; Döbler, Jens; Sauer, Joachim

2009-05-01

418

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

419

Thermal expansion measurements on four optical materials from room temperature to 10 k.  

PubMed

In a continuing study of the physical properties of optical materials, measurements are reported of the linear thermal expansion coefficients for four ir-transmitting materials in the temperature range 10-300 K. A new glass and three polycrystalline materials were investigated by use of a three-terminal capacitance- type dilatometer incorporated into a cryostat. The glass, designated No. 20 by Texas Instruments, Inc., is a nonoxide chalcogenide glass with the composition Ge(33)Se(55)As(l2). One of the po]ycrystalline materials studied, T-12 (Harshaw Chemical Co.), is an optically integral two-phase material composed of equal molar proportions of CaF(2) and BaF(2). The other two materials are microcrystalline, hot-pressed forms of CdS and CdTe (Irtran 6), manufactured by the Eastman Kodak Co. PMID:20119054

Browder, J S; Ballard, S S

1972-04-01

420

Graphitic carbon grown on fluorides by molecular beam epitaxy.  

PubMed

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

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

2013-01-03

421

Brewster angle prism retroreflectors for cavity enhanced spectroscopy.  

PubMed

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

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

2009-06-01

422

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

NASA Astrophysics Data System (ADS)

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

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

423

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

NASA Astrophysics Data System (ADS)

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

Stanford, Malcolm K.; Dellacorte, Christopher

2006-03-01

424

Graphitic carbon grown on fluorides by molecular beam epitaxy  

PubMed Central

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

2013-01-01

425

Total losses analysis and calculations for PbSe/PbSrSe multiple quantum well structures  

NASA Astrophysics Data System (ADS)

In order for laser oscillation to occur, the modal gain at the lasing photon energy must equal the total losses. In this work, we analyze and calculate the total losses due to the free carrier absorption, optical waveguide scattering and the laser cavity end losses for PbSe/Pb0.934Sr0.066 Se quantum well laser structures. The small confinement factor value causes the free carrier absorption loss to be negligible. The calculated scattering loss values showed a decreasing order for the MQW, MMQW and SCH-SQW structures, for a surface roughness amplitude of 10nm. Increasing the surface roughness amplitude increases these scattering losses even further. However, the calculated cavity loss calculations showed that its values are in an increasing order for the MQW (or MMQW) and SCH-SQW structures. These cavity losses are lowest for uncoated cavity ends. Coating these ends with a quarter wavelength BaF2 layer increases the total cavity loss. In addition, coating the cavity ends with alternating quarter wavelength layers of BaF2 and CaF2 also results in an increase in the cavity loss. The increase in cavity loss due to coating is caused by the decrease in the mirrors' reflectivity values. These results show that coating with fluoride layers can best be utilized in applications where high transitivity values are needed.

Khodr, M.

2010-08-01

426

Alternative technique for laser cooling with superradiance  

NASA Astrophysics Data System (ADS)

We present a theoretical scheme for laser cooling of rare-earth-doped solids with optical superradiance (SR), which is the coherent, sharply directed spontaneous emission of photons by a system of laser-excited rare-earth ions in the solid-state host (glass or crystal). We consider an Yb+-doped ZnF4-BaF2-LaF3-AlF3-NaF (ZBLAN) sample pumped at a wavelength 1015 nm, with a rectangular pulsed source with a power of ˜433 W and a duration of 10 ns. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR permits an increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare-earth-doped solids with anti-Stokes spontaneous incoherent radiation (fluorescence). This scheme overcomes the limitation of using only low phonon energy glasses for laser cooling.

Nemova, Galina; Kashyap, Raman

2011-01-01

427

Synthesis and evaluation of ultra-pure rare-earth-doped glass for laser refrigeration  

NASA Astrophysics Data System (ADS)

Significant progress has been made in synthesizing and characterizing ultra-pure, rare-earth-doped ZIBLAN (ZrF4-InF3- BaF2-LaF3-AlF3-NaF) glass capable of laser refrigeration. Yb3+-doped ZIBLAN glass was produced from fluoride precursors which were individually purified by solvent extraction and subsequently treated with hydrofluoric gas at elevated temperatures to remove oxygen impurities. We have developed two-band differential luminescence thermometry (TBDLT) as a new non-invasive, spectroscopic technique to evaluate the intrinsic quality of Yb3+ doped laser-cooling samples. TBDLT measures changes in the local temperature upon laser excitation via the small changes in the 2F5/2-->2F7/2 fluorescence spectrum. Two commercial band pass filters in combination with a balanced dual InGaAs photodetector are used to select and integrate regions of interest in the fluorescence spectrum with sub-millisecond resolution. The TBDLT technique successfully finds the zero-crossing temperature (ZCT), which is the minimum temperature to which a Yb3+ doped sample can cool, independent of surface heating. ZCT is a useful measure for the presence of impurities and the overall quality of the laser-cooling material. Favorable laser cooling results were obtained for several 1% Yb3+-doped glasses with varying degrees of purity.

Patterson, Wendy M.; Hehlen, Markus P.; Sheik-Bahae, Mansoor; Epstein, Richard I.

2009-02-01

428

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

429

Ion and electron trapping: release and relaxation processes in fluoride crystals  

NASA Astrophysics Data System (ADS)

The thermally stimulated relaxation (TSR) processes in CaF2, BaF2 and LiBaF3 crystals (X-ray irradiated at LNT or RT) have been investigated by means of the ionic conductivity, thermally stimulated (TS) ionic depolarization current (TSDC), TS current (TSC), TS luminescence (TSL) and thermal bleaching techniques. The ionic TSDC measurements evidence that under DC field fluorides accumulate large ionic space-charge (thermoelectric state is formed) as a result of the migrating anion interstitial and/or vacancy capture on defects. In the ionic conductivity region (290 - 650 K) the thermoelectric state anneals, and several wide and overlapping anionic TSDC peaks are detected. The ionic TSDC stages correlate with the X-ray induced absorption band (F-type and other) thermal bleaching stages. These data evidence that the TSR processes are initiated and controlled by the anion defect thermal detrapping and interaction with the color centers and other localized charges. The anion diffusion-controlled TSR processes take place in fluorides. The TSL, TSC and TSL efficiency (TSL/TSC) data evidence that holes and, probably, the interstitials are detrapped: in CaF2 -- at 125 - 190 K, 260 - 320 K; in LiBaF3 -- at 132 K, 170 K and 220 K. The hole or interstitial diffusion-controlled radiative recombination (TSL) takes place above LNT.

Ziraps, Valters; Kulis, Peteris; Tale, Ivars

2001-04-01

430

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

NASA Astrophysics Data System (ADS)

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

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

431

Absorption measurement of HR coated mirrors at 193nm with a Shack-Hartmann wavefront sensor  

NASA Astrophysics Data System (ADS)

All dielectric HR mirror coatings consisting of AlF3/LaF3/Oxide layers were deposited on DUV grade fused silica and CaF2. A novel technique was employed to measure the absorption of these mirrors during irradiation by a 193nm ArF excimer laser source. The method involves the application of a photothermal measurement technique. The setup uses a Shack-Hartmann wavefront sensor to measure wavefront deformation caused by the heating of the coating by the ArF beam. Laser calorimetric measurements of absorption were used to calibrate the wavefront sensor. Gage R&R (Repeatability & Reproducibility) measurements were done to show that this is a practical test technique for use in production. The new test setup was used to investigate HR mirror coatings both before and after exposure to high average power ArF laser beams. HR mirror samples were irradiated by a 193 nm kilohertz laser source for either 500 million or 18.6 billion pulses. The spatial resolution is sufficient to make wavefront distortion measurements both inside and outside of the laser beam footprint. The differences between wavefront distortion measured inside the beam footprint compared to measured outside the beam footprint can be explained by compaction of the coating in the area heated by the ArF laser. Interesting wavefront distortion results from testing mirrors with either fused silica or CaF2 substrates can be explained by considering the figure of merit of these materials for excimer laser mirror substrates.

Cho, Byungil; Danielewicz, Edward; Rudisill, J. Earl

2011-10-01

432

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

NASA Astrophysics Data System (ADS)

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

Sobolev, B. P.

2012-05-01

433

Optical absorption and fluorescence properties of Dy3+: SFB glasses  

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

434

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

435

Mechanical properties of haynes alloy 188 after 22,500 hours of exposure to LiF22CaF 2 and vacuum at 1093 K  

Microsoft Academic Search

As a continuation of a study of a space-based thermal energy storage system centered on a LiF-CaF2 eutectic salt contained\\u000a by Haynes alloy 188, this Co-base superalloy was subjected to molten salt, its vapor, and vacuum for 22,500 h at 1093 K. Samples\\u000a from all three exposure conditions were tensile tested between 77 to 1200 K; in addition, vacuum and

J. D. Whittenberger

1994-01-01

436

Mechanical properties of haynes alloy 188 after 22,500 hours of exposure to LiF22CaF2 and vacuum at 1093 K  

Microsoft Academic Search

As a continuation of a study of a space-based thermal energy storage system centered on a LiF-CaF2 eutectic salt contained by Haynes alloy 188, this Co-base superalloy was subjected to molten salt, its vapor, and vacuum for 22,500 h at 1093 K. Samples from all three exposure conditions were tensile tested between 77 to 1200 K; in addition, vacuum and

J. D. Whittenberger

1994-01-01

437

Ab initio calculation of ?2(omega) including the electron-hole interaction: Application to GaN and CaF2  

Microsoft Academic Search

We present a computationally efficient first-principles scheme to calculate ?2(omega) for crystalline insulators, including the electron-hole interaction. The effective Hamiltonian for electron-hole pairs contains both the exchange and direct parts of this interaction. An iterative scheme is used in which the omega moments of ?2(omega) are computed by repeated action of the Hamiltonian on electron-hole pair states. The scheme is

Lorin X. Benedict; Eric L. Shirley

1999-01-01

438

The Influence of Different Fluoride Compounds and Treatment Conditions on Dental Enamel: A Descriptive in vitro Study of the CaF2 Precipitation and Microstructure  

Microsoft Academic Search

Electron and atomic force microscopy techniques have been applied to characterize both the in vitro deposition intensity and the microstructure of the KOH-soluble fluoride precipitates on human dental enamel. The study was focused on the effects of amine fluoride, sodium fluoride and sodium monofluorophosphate having a fluoride concentration of 0.1% F in acidulated and aqueous solutions. Under certain conditions, fluoride

Matthias Petzold

2001-01-01

439

Energy resolution and nonlinearity of NaI(Tl), CaF2(Eu), and plastic scintillators measured with the wide-angle Compton-coincidence technique  

Microsoft Academic Search

Compton cameras are of general interest in various fields of operation. Because of the ability to locate and identify remote sources, homeland security supports the development of such devices in a rugged and reliable form. The decisions upon appropriate materials for the scatter- and absorber plane depend on performance and economical trade-offs. In order to estimate the expected performance of

Katja Roemer; Guntram Pausch; Claus-Michael Herbach; Maciej Kapusta; Yong Kong; Ralf Lentering; Cristina Plettner; Juergen Stein; Marek Moszynski; Lukasz Swiderski; Tomasz Szczesnik

2010-01-01

440

Nature of the Transient BaF2-Related Phases in the "BaF2" Processing of Ba2YCu3O7-x Superconductors  

SciTech Connect

Transient BaF{sub 2}-based oxyfluoride phases are thought to play a critical role in the formation of the c-textured Ba{sub 2}YCu{sub 3}O{sub 7-x} layers of coated conductors. In situ high-temperature x-ray diffraction from the precursor films containing pure BaF{sub 2} as well as pseudobinary BaF{sub 2-Y}, BaF{sub 2-}Cu, and Y-Cu mixtures and heat treated in water vapor under reduced conditions revealed that the transient BaF{sub 2}-based superstructures, similar to those observed during formation of Ba{sub 2}Cu{sub 3}O{sub 7-x}, develop even from the pure BaF{sub 2} precursor. These superstructures results from the dissolution of oxygen in BaF{sub 2} leading to formation of the oxyfluoride phase, Ba(F{sub 2-2x}{open_square}{sub x})O{sub x}, with an ordered arrangement of O, F, and F vacancies.

Wong-Ng, W. [National Institute of Standards and Technology (NIST); Levin, I. [National Institute of Standards and Technology (NIST); Cook, L. P. [National Institute of Standards and Technology (NIST); Feenstra, Roeland [ORNL

2006-01-01

441

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

442

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

443

Mid-infrared supercontinuum laser system and its biomedical applications  

NASA Astrophysics Data System (ADS)

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

Xia, Chenan

444

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

445

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

SciTech Connect

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

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

2012-07-01

446

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

447

Light-addressable potentiometric fluoride (F ?) sensor  

Microsoft Academic Search

In this work, light-addressable potentiometric sensor (LAPS) has been investigated for fluoride (F?) sensing in aqueous medium. Vacuum-evaporated LaF3 has been studied as the fluoride-sensing layer in the LAPS heterostructure. Instead of using the conventional structure of Si\\/SiO2\\/LaF3 or Si\\/SiO2\\/Si3N4\\/LaF3, a simple structure of Si\\/LaF3 has been prepared as the LAP fluoride-sensor. The sensor was prepared with 50nm LaF3 layer

Koji Furuichi; Tatsuo Yoshinobu; Hiroshi Iwasaki

2002-01-01

448

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

449

Vacuum tribological behaviour of self lubricant quasicrystalline composite coatings  

NASA Astrophysics Data System (ADS)

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

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

2003-09-01

450

Thermo-stress analysis of actively cooled diagnostic windows for quasi-continuous operation of the W7-X stellarator  

NASA Astrophysics Data System (ADS)

Finite element method calculations have been performed in order to develop and demonstrate the design of actively cooled windows for the W7-X stellarator which are adequate for diagnostics in the UV, VIS and IR spectral regions at quasi-stationary thermal loads of 50 kW m-2, mainly originating from short-wavelength radiation. The results have shown that sapphire which is suitable for the spectral range from 150 nm to 4.5 ?m is the only material for large window diameters (about 13 cm) which could cope with the expected maximum power loads for W7-X of 50 kW m-2 for more than 20 min. Other materials like fused silica, MgF2, ZnSe and ZnS can only be used for smaller diameter windows (<5 cm) or lower thermal loads. CaF2 and BaF2 are unacceptable as W7-X window materials because of strong in-plane distortions during long pulses. The investigations show in which operating regimes the different materials are suitable with regard to pulse duration and power load for windows of different diameters and thicknesses.

Ogorodnikova, O. V.; König, R.; Pospieszczyk, A.; Schweer, B.; Linke, J.

2005-05-01

451

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

NASA Astrophysics Data System (ADS)

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

El-Said, A. S.

2012-07-01

452

Self-lubricating coatings for high-temperature applications  

SciTech Connect

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

Sliney, H.E.

1987-11-01

453

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

SciTech Connect

Selected tribological, mechanical and thermophysical properties of two versions of PM212 (sintered and hot isostatically pressed, HIPped) are compared. PM212, a high temperature self-lubricating composite, contains 70 wt percent metal bonded chromium carbide, 15 wt percent CaF2/BaF2 eutectic and 15 wt percent silver. PM212 in the sintered form is about 80 percent dense and has previously been shown to have good tribological properties from room temperature to 850 C. Tribological results of a fully densified, HIPped version of PM212 are given. They are compared to sintered PM212. In addition, selected mechanical and thermophysical properties of both types of PM212 are discussed and related to the tribological similarities and differences between the two PM212 composites. In general, both composites display similar friction and wear properties. However, the fully dense PM212 HIPped composite exhibits slight lower friction and wear than sintered PM212. This may be attributed to its generally higher strength properties. The sintered version displays stable wear properties over a wide load range indicating its promise for use in a variety of applications. Based upon their properties, both the sintered and HIPped PM212 have potential as bearing and seal materials for advanced high temperature applications. 12 refs.

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

1992-11-01

454

Interfacial tension between aluminum and NaCl-KCl-based salt systems  

NASA Astrophysics Data System (ADS)

Aluminum scrap is frequently remelted under a NaCl-KCl based salt flux cover to prevent oxidation, to aid in the stripping of oxide films, and to improve drop coalescence. In this process, the interfacial tension between the aluminum metal and the salt flux plays an important role. However, the measurement of interfacial tensions at high temperature is difficult and prone to errors. Therefore, an interfacial tension model, presented in this article, has been developed. The interfacial tension between aluminum and NaCl-KCl based melts does not change with the addition of chlorides or with variations in the composition of the NaCl-KCl melt. On the other hand, the addition of fluorides decreases the interfacial tension to various extents due to the adsorption of sodium and/or potassium at the interface. Addition of AlF3 is the least effective; additions of LiF, MgF2, CaF2, BaF2, or SrF2 are moderately effective; and additions of NaF or KF are the most effective in lowering the interfacial tension.

Roy, Raja R.; Utigard, Torstein A.

1998-08-01

455

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

456

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

SciTech Connect

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

Dellacorte, C.

1987-07-01

457

Spectroscopic investigations of Nd3+-, Er3+-, Er3+/Yb3+-, and Tm3+-ions doped SiO2-Al2O3-CaF2-GdF3 glasses  

NASA Astrophysics Data System (ADS)

This paper reports on the absorption, visible and near-infrared luminescence properties of Nd3+, Er3+, Er3+/2Yb3+, and Tm3+ doped oxyfluoride aluminosilicate glasses. From the measured absorption spectra, Judd-Ofelt (J-O) intensity parameters (?2, ?4 and ?6) have been calculated for all the studied ions. Decay lifetime curves were measured for the visible emissions of Er3+ (558 nm, green), and Tm3+ (650 and 795 nm), respectively. The near infrared emission spectrum of Nd3+ doped glass has shown full width at half maximum (FWHM) around 45 nm (for the 4F3/2?4I9/2 transition), 45 nm (for the 4F3/2?4I11/2 transition), and 60 nm (for the 4F3/2?4I13/2 transition), respectively, with 800 nm laser diode (LD) excitation. For Er3+, and Er3+/2Yb3+ co-doped glasses, the characteristic near infrared emission bands were spectrally centered at 1532 and 1544 nm, respectively, with 980 nm laser diode excitation, exhibiting full width at half maximum around 50 and 90 nm for the erbium 4I13/2?4I15/2 transition. The measured maximum decay times of 4I13/2?4I15/2 transition (at wavelength 1532 and 1544 nm) are about 5.280 and 5.719 ms for 1Er3+ and 1Er3+/2Yb3+ (mol%) co-doped glasses, respectively. The maximum stimulated emission cross sections for 4I13/2?4I15/2 transition of Er3+ and Er3+/Yb3+ are 10.81×10-21 and 5.723×10-21 cm2. These glasses with better thermal stability, bright visible emissions and broad near-infrared emissions should have potential applications in broadly tunable laser sources, interesting optical luminescent materials and broadband optical amplification at low-loss telecommunication windows.

Lakshminarayana, G.; Mao, Mengfei; Yang, Rong; Qiu, J. R.; Brik, M. G.

2009-11-01

458

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

459

The study of devitrification processes in heavy-metal fluoride glasses.  

PubMed

Heavy-metal fluoride glasses are very promising optical fiber materials because of their predicted ultralow loss and long transparency range. Although conventional silica fibers have attained their theoretical minimum loss of 0.15 dB/km, fluoride glasses have the potential to yield losses of only 0.001 dB/km. Fluoride glasses also exhibit transparency into mid-IR frequencies, a region inaccessible to silica fibers. However, this group of glasses is very unstable to devitrification during both bulk glass synthesis and fiber-drawing. This instability has limited their commercial exploitation to a small niche market in the laser industry. The ZBLAN glass (53ZrF(4)-20BaF(2)-4LaF(3)-3AlF(3)-20NaF) is the most promising of these materials since its fiber-drawing region lies on the edge, or possibly just outside its crystallization region. It is believed that additional research into understanding the nucleation mechanics involved in the devitrification of fluoride glasses will lead to the development of technology to suppress such nucleation, or at least minimize the associated crystallization temperature region, allowing high optical quality fibers to be produced. It has recently been demonstrated that a microgravity environment can suppress devitrification in ZBLAN glass preform preparation, and that devitrification may be reduced when preparing ZBLAN terrestrially in a containerless facility. It is believed that the role of viscosity is critical in the devitrification mechanism of ZBLAN glass and in determining the optimum fiber-drawing temperature. Unfortunately, viscosity data for fluoride glasses are only available above the melting point and around the glass transition. A piezoelectric viscometer has been developed and is being used to determine the missing viscosity data in the fiber-drawing and crystallization temperature regions. Shear thinning of the glasses and/or the application of hydrostatic pressure on the glasses have been recently proposed to be responsible for devitrification during fiber-drawing at 1 g and in reduced gravity. The study we report here is to explore the extent to which such a proposal is realistic. PMID:15644353

Dunkley, Ian R; Smith, Reginald W; Varma, Sudhanshu

2004-11-01

460

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

461

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.

462

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

463

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

464

Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films  

PubMed Central

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

2012-01-01

465

Optical Measurements of Electron Paramagnetic Spin-Spin Interactions in Crystals.  

NASA Astrophysics Data System (ADS)

The paramagnetic spin-spin interaction is investigated by means of optical probing. The Zeeman sublevel population difference in the ground state of divalent thulium ions doped in alkali-earth fluoride crystals (CaF(,2), SrF(,2) and BaF(,2)) is monitored by making use of magnetooptical activities (magnetic circular dichroism (MCD) and Faraday rotation) of the ions. Neighboring thulium spins are coupled via cross-relaxation (CR) at certain magnetic fields, and the CR signal appears as a change in population difference as the magnetic field is swept when the system is optically pumped. Several CR peaks are explained by Tm-Tm two particle process, Tm-Tm-Tm three particle process and Tm-Tm (excited state) two particle process. Cross-relaxations between different species are investigated using CaF(,2) crystals containing divalent thulium and divalent holmium ions. For the crystal of .02% Tm and .00001% Ho, only the lowest order CR is observed. For the sample of .02% Tm and .001% Ho, a great many CR resonances are observed and they can be well interpreted by Tm-Tm -Ho three particle process and Ho (forbidden transition) -Tm two particle process. This strongly coupled system also shows a transient relaxation anomaly and an EPR quenching effect. They are thermodynamically explained by the energy flow from Tm to Ho via the CR. An anomalous heating of holium spins is also observed and this may be explained by a phonon bottleneck effect in the Orbach process. The other aspect of the spin-spin interaction appears as a spin diffusion. The spin spatial diffusion is studied by the Bragg scattering signal from an optically induced grating in the crystal. Theoretical suggestion of the Bragg scattering experiment is made, and the numerical estimate of the signal intensity is given. The Bragg scattering signal will contain two parts. One stems from the optical population grating and the other from the Zeeman sublevel population grating. The spin diffusion constant might be obtained from the Zeeman grating. Finally the diffusion theory for a spin-phonon coupled system is given. Simultaneous diffusion equations of spins and phonons are solved for various cases. If the bottleneck factor connecting spins and phonons is big, the phonon diffusion plays an important role. If the coupling is small, the system can be solved using a perturbation method.

Mitsunaga, Masaharu

466

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

NASA Astrophysics Data System (ADS)

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

Stultz, Robert Dale

467

Phosphate base laser glasses  

SciTech Connect

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

Izumitani, T.; Tsuru, M.

1980-12-16

468

Cryogenic engineering for OMEGA2000: design and performance  

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

469

Electrical conductivity of low melting baths for aluminium electrolysis: the system Na 3 AlF 6 Li 3 AlF 6 - AlF 3 and the influence of additions of Al 2 O 3 , CaF 2 , and MgF 2  

Microsoft Academic Search

The electrical conductivity was investigated for a section of the molten ternary mixture Na3AlF6-Li3AlF6-AlF3 with molar ratio n(Li3AlF6):n(AlF3) = 1 : 2. The conductivity of this system can be described by the following equation: \\u000a$$\\\\begin{gathered} k\\/S cm^{ - 1} {\\\\text{ }} = {\\\\text{ }}7.22{\\\\text{ }}exp \\\\left( { - 1204.3\\/T\\\\left( K \\\\right)} \\\\right){\\\\text{ }} + {\\\\text{ }}0.97{\\\\text{ }}\\\\chi \\\\left( {Li_3 AlF_6

P. Fellner; S. Midtlyng; A. Sterten; J. Thonstad

1993-01-01

470

Photon Stimulated Desorption Investigations of Positive Ions of MgO, TiO2, Yb2O3, Nd2O3, H2OSi(100), CaF2/Si and of H2O, CO and NO on Yb and Nd in the Energy Range 14 eV Up to 800 eV.  

National Technical Information Service (NTIS)

Photon-stimulated desorption of positive ions from surfaces has been studied with synchrotron radiation in the photon energy range 14 -800 eV of the 'FLIPPER'-monochromator using a time-of-flight mass spectrometer. TiO/sub 2/, as a prototype of a maximal ...

F. Senf

1987-01-01

471

Determination of the thermo-optic coefficient dn\\/ dT of ytterbium doped ceramics (Sc 2O 3, Y 2O 3, Lu 2O 3, YAG), crystals (YAG, CaF 2) and neodymium doped phosphate glass at cryogenic temperature  

Microsoft Academic Search

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

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

472

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

2012-01-05

473

Nanosecond image processing using stimulated photon echoes  

NASA Astrophysics Data System (ADS)

Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimulated photon echoes in a rare-earth-doped crystal of 0.1 at. pct Pr(3+):LaF3. Two spatially encoded laser pulses (pictures) resonant with the 3P0-3H4 transition of Pr(3+) were stored by focusing the image pulses sequentially into the Pe(3+):LaF3 crystal. The stored information is retrieved and processed by a third read pulse, generating the echo that is the spatial convolution or correlation of the input images. Application of this scheme to high-speed pattern recognition is discussed.

Xu, E. Y.; Kroll, S.; Huestis, D. L.; Kachru, R.; Kim, M. K.

1990-05-01

474

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

475

Crystallization and fluorescence properties of Nd 3+-doped transparent oxyfluoride glass ceramics  

Microsoft Academic Search

Nd3+-doped transparent oxyfluoride glass ceramics containing CaF2 were prepared through controlled crystallization of melt-quenched glass. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) observation revealed the precipitation of CaF2 crystallites with about 13nm in size among the glass matrix after heat-treatment at 650°C for 2h. Non-isothermal investigation on CaF2 crystallization kinetics showed that the apparent activation energy Ea and

Daqin Chen; Yuansheng Wang; Yunlong Yu; Zhongjian Hu

2005-01-01

476

Optical materials characterization final technical report february 1, 1978-september 30, 1978. Technical note  

Microsoft Academic Search

Data obtained as part of the Optical Materials Characterization Program are summarized in this report. Room temperature values of refractive index as a function of wavelength are presented for the following materials: commercially grown KCl, reactive atmosphere processed (RAP) KCl, KCl nominally doped with 1.5% KI, hot forged CaF2, fusion cast CaF2, CaF2 doped with Er (0.001% to 3% Er),

A. Feldman; D. Horowitz; R. M. Waxter; M. J. Dodge

1979-01-01

477

The Effect of Calcium Fluoride on Slag Viscosity  

NASA Astrophysics Data System (ADS)

The effect of CaF2 on the viscosity of high-basicity Al2O3-CaO-MgO-SiO2 (-CaF2) slags for secondary steelmaking was studied using a Brookfield digital viscometer. The addition of approximately 3 mass pct CaF2 could decrease the liquidus temperature substantially in the case of high CaO containing slags, leading to good flowability of the slag at the temperature of the ladle treatment. The addition of CaF2 had the strongest effect on the viscosity of liquid slag with high SiO2 content.

Wu, Liushun; Gran, Jimmy; Sichen, Du

2011-10-01

478

Thermodynamic study of some solid solutions in the CaO-ZrO2 system by emf method  

Microsoft Academic Search

The thermodynamic properties of some solid solutions in the CaO-ZrO2 system have been investigated by using solid electrolyte galvanic cells of the type: O2, PtCaO, CaF2CaF2 (tF = 1) deltaCaO(1 - delta)ZrO2, CaF2Pt, O2. The influence of CaF2 added in electrodes on the thermodynamic equilibrium was investigated. It was shown that the heterogeneous field with cubic solid solution reaches the

V. A. Levitski; P. B. Narchuk; Ju. Hekimov; Ja. I. Gerassimov

1977-01-01

479

Utilization of Rare Earth Ions in Single Crystals in Infrared Quantum Counter-Amplifier Device Application.  

National Technical Information Service (NTIS)

The report describes laser induced infrared quantum counter (optical double resonance) upconversion experiments. Highly efficient infrared upconversion (at 2.03 micrometers) in LaCl3:Pr(3+), LaF3:Pr(3+), and SrCl2:Pr(3+) has been achieved by means of a tu...

F. K. Fong

1972-01-01

480

Thermoluminescent Dosimetry and Its Use at the US Army Nuclear Defense Laboratory.  

National Technical Information Service (NTIS)

The report discusses CaF2:Mn and LiF thermoluminescent dosimeters (TLD). CaF2:Mn vacuum tube TLD and 1/2 mini TLD provide reliable gamma-exposure measurements from 5,000 to 50,000 R. Used with energy discrimination and 6LiF thermal neutron shields, the TL...

N. N. Gibson T. W. Crimmins K. D. Conley J. R. Jacobson

1968-01-01

481

Observation of the Orientational Transition in Hexa(hexylthio)Triphenylene using Polarized FTIR Study  

Microsoft Academic Search

The results of polarised FTIR study of hexa-(hexylthio)-triphenylene (HHTT), contained between ZnSe and CaF2 windows, are being presented. This gives some supplementary information on orientation of molecules in different phases. An orientational transition of HHTT contained between two CaF2 windows in Dhd phase is being reported.

T. Perova; S. Tsvetkov; J. Vij; S. Kumar

2000-01-01

482

The Emission Spectra of Various Thermoluminescent Materials.  

National Technical Information Service (NTIS)

The thermoluminescence emission spectra of various materials were determined using a quartz-prism spectrograph. The materials studied include: CaF2:Mn, CaSO4:Mn, Li2B4O7:Mn, LiF(TLD-100), CaF2(MBLE), and a terbium-activated lithium-aluminosilicate thermol...

S. G. Gorbics

1966-01-01

483

Study of Non-Oxide Materials with Defect Structures.  

National Technical Information Service (NTIS)

Three types of defects were described and found to exist in high concentration. These defects were exemplified by: (a) The system 3NaF.5YF3-CaF2 (The Half-Breed Defect Type); (b) The system CaF2-YF3 (The Interstitial Anion Defect Type); (c) The system LaF...

D. A. Buckner P. C. Velasquez

1964-01-01

484

Submerged Arc Welding of Titanium.  

National Technical Information Service (NTIS)

Studies of flux shielded welding of titanium indicate that acceptable submerged arc weld bead shape may not be attained with pure CaF2 flux. Addition of chlorides to the CaF2 flux improves the weld bead shape but reduces the deoxidizing potential of the f...

G. Hunter G. B. Kenney M. Ring B. A. Russell T. W. Eagar

1978-01-01

485

Thermodynamics of the YAl–YAl 2 system  

Microsoft Academic Search

The emf method using solid-state galvanic cells based on a CaF2 single crystal as electrolyte has been used to investigate the thermodynamics of the intermetallic couple YAl–YAl2. These represent two out of the five intermetallic compounds shown in the Y–Al phase diagram. Two kinds of cells were studied:?Pt\\/Y,YF3\\/CaF2s.c.\\/YAl,YAl2,YF3\\/Pt+and?Pt\\/YAl,YAl2,CaAlF5,CaF2\\/CaF2s.c.\\/FeAl,a+,CaAlF5;CaF2\\/Pt+The cell reactions expected are, respectively, 2YAl (s)=YAl2 (s)+Y (s) and YAl (s)+Al

G. Borzone; A. Ciccioli; P. L. Cignini; M. Ferrini; D. Gozzi

2000-01-01

486

Optimization of the Scintillator Size for Positron Lifetime Measurements  

NASA Astrophysics Data System (ADS)

Optimization of the measurement condition for positron annihilation lifetime spectroscopy (PALS) is discussed from the viewpoint of non-destructive "on-site" material inspection. Numerical analysis based on a least-squares estimation and experiments with various sizes of BaF2 scintillators by conventional PALS suggested that the use of relatively large BaF2 scintillators enables on-site material inspection by PALS with reasonable accumulation time and time resolution.

Yamawaki, M.; Kobayashi, Y.; Hattori, K.; Watanabe, Y.

2013-06-01

487

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

488

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

NASA Astrophysics Data System (ADS)

Prompt fission neutrons are one of the strongest signatures of the fission process. Depending on the fission inducing radiation, their average number ranges from 2.5 to 4 neutrons per fission. They are more energetic and abundant, by about 2 orders of magnitude, than the delayed neutrons (?3 vs. ?0.01) that are commonly used as indicators for the presence of fissionable materials.The detection of fission prompt neutrons, however, has to be done in the presence of extremely intense probing radiation that stimulated them. During irradiation, the fission stimulation radiation, X-rays or neutrons, overwhelms the neutron detectors and temporarily incapacitate them. Consequently, by the time the detectors recover from the source radiation, fission prompt neutrons are no longer emitted. In order to measure the prompt fission signatures under these circumstances, special measures are usually taken with the detectors such as heavy shielding with collimation, use of inefficient geometries, high pulse height bias and gamma-neutron separation via pulse-shape discrimination with an appropriate organic scintillator. These attempts to shield the detector from the flash of radiation result in a major loss of sensitivity. It can lead to a complete inability to detect the fission prompt neutrons.In order to overcome the blinding induced background from the source radiation, the detection of prompt fission neutrons needs to occur long after the fission event and after the detector has fully recovered from the source overload. A new approach to achieve this is to detect the delayed activation induced by the fission neutrons. The approach demonstrates a good sensitivity in adverse overload situations (gamma and neutron "flash") where fission prompt neutrons could normally not be detected.The new approach achieves the required temporal separation between the detection of prompt neutrons and the detector overload by the neutron activation of the detector material. The technique, called Threshold Activation Detection (TAD), is to utilize appropriate substances that can be selectively activated by the fission neutrons and not by the source radiation and then measure the radioactively decaying activation products (typically beta and gamma rays) well after the source pulse. The activation material should possess certain properties: a suitable half-life of the order of seconds; an energy threshold below which the numerous source neutrons will not activate it (e.g., 3 MeV); easily detectable activation products (typically >1 MeV beta and gamma rays) and have a usable cross-section for the selected reaction. Ideally the substance would be a part of the scintillator.There are several good material candidates for the TAD, including fluorine, which is a major constituent of available scintillators such as BaF2, CaF2 and hydrogen free liquid fluorocarbon. Thus the fluorine activation products, in particular the beta particles, can be measured with a very high efficiency in the detector.The principles, applications and experimental results obtained with the fluorine based TAD are discussed.

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

2011-10-01

489