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All sources NASA NTRS DOE OSTI

DOE OSTI2023

Electrokinetic comparison of CaF 2 and AgCl from a MDS perspective

CaF 2 has limited electrokinetic sensitivity to fluoride ions in solution and the positive CaF 2 surface charge is not reversed at high fluoride ion concentration. Similar insensitivity of surface charge to high fluoride ion concentration has been observed for other alkali and alkaline earth fluoride salts. On the contrary, chloride ions act as potential determining ions for AgCl and reverse the surface charge, as expected. FTIR-IRS results indicate that the AgCl/water interface has a water structure-breaking tendency, whereas the CaF 2 /water interface has a structure-making tendency. Here, it is speculated that the strong hydrogen bonding between fluoride ions and water prevents the accommodation of excess fluoride ions at surface lattice sites of fluorite, and therefore explains the low sensitivity of the fluorite surface charge sign and magnitude to fluoride ion concentration. However, this speculation has not been examined at the molecular level and is evaluated by molecular dynamics simulations (MDS) in the research presented in this paper. Higher hydrogen bond density at the CaF 2 mineral/water interface confirms that the water structure has stronger hydrogen bonding at both the CaF 2 mineral surface and with the F - ion in solution. In this way, the interaction of the F - ion with the CaF 2 surface is inhibited.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Electron passivation in CaF 2 on calcium metal anodes

Current electrolytes in calcium-ion batteries suffer from a lack of stability and degradation caused by reduction from the anode. The solid-electrolyte interphase (SEI) that forms on the anodes during operation stems the flow of electrons from the anode to the electrolyte. CaF 2 is a common inorganic compound found in the SEI, and is derived from electrolyte salts such as Ca(PF 6 ) 2 . CaF 2 can exist in crystalline, polycrystalline, and amorphous phases in the SEI, and as recent work has shown, different phases of the same compound can have vastly different electronic conductivities. Using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that amorphous phase systems enhance electron tunneling in thin CaF 2 films by 1–2 orders of magnitude when compared to crystalline and polycrystalline CaF 2 systems. Transport through several amorphous structures was considered showing that, despite their random structures, their conductance properties are similar. Finally, through analysis of the decay constant β and the low-bias conductance of each system, we show that crystalline and polycrystalline CaF 2 offer greater protection of the electrolyte than amorphous CaF 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

The Li + CaF → Ca + LiF chemical reaction under cold conditions

The calcium monofluoride (CaF) molecule has emerged as a promising candidate for precision measurements, quantum simulation, and ultracold chemistry experiments. Inelastic and reactive collisions of laser cooled CaF molecules in optical tweezers have recently been reported and collisions of cold Li atoms with CaF are of current experimental interest. In this paper, we report ab initio electronic structure and full-dimensional quantum dynamical calculations of the Li + CaF → LiF + Ca chemical reaction. The electronic structure calculations are performed using the internally contracted multi-reference configuration-interaction method with Davidson correction (MRCI + Q). An analytic fit of the interaction energies is obtained using a many-body expansion method. Furthermore, a coupled-channel quantum reactive scattering approach implemented in hyperspherical coordinates is adopted for the scattering calculations under cold conditions. Results show that the Li + CaF reaction populates several low-lying vibrational levels and many rotational levels of the product LiF molecule and that the reaction is inefficient in the 1–100 mK regime allowing sympathetic cooling of CaF by collisions with cold Li atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2009

Analysis of Mass Averaged Tissue Doses in CAM, CAF, MAX, and FAX

To estimate astronaut health risk due to space radiation, one must have the ability to calculate exposure-related quantities averaged over specific organs and tissue types. In this study, we first examine the anatomical properties of the Computerized Anatomical Man (CAM), Computerized Anatomical Female (CAF), Male Adult voXel (MAX), and Female Adult voXel (FAX) models by comparing the masses of various tissues to the reference values specified by the International Commission on Radiological Protection (ICRP). Major discrepancies are found between the CAM and CAF tissue masses and the ICRP reference data for almost all of the tissues. We next examine the distribution of target points used with the deterministic transport code HZETRN to compute mass averaged exposure quantities. A numerical algorithm is used to generate multiple point distributions for many of the effective dose tissues identified in CAM, CAF, MAX, and FAX. It is concluded that the previously published CAM and CAF point distributions were under-sampled and that the set of point distributions presented here should be adequate for future studies involving CAM, CAF, MAX, or FAX. It is concluded that MAX and FAX are more accurate than CAM and CAF for space radiation analyses.

Slaba, Tony C.↗

NASA NTRS2025

Line List for the A 2 Π−X 2 Σ + and the B 2 Σ + −X 2 Σ + Band Systems of CaF

The spectral analysis of molecule-rich asymptotic giant branch (AGB) stars is challenging. Although other calcium and fluorine bearing molecules are observed in the microwave and in the visible spectrum of AGB stars, CaF has never been detected, despite favorable chemical equilibrium predictions. Yet, measuring the CaF abundance could give more insight into the fluorine budget of AGB stars and allow better simulation of stellar spectra. In this work, we present an analysis of the visible spectrum of CaF obtained with a Fourier transform spectrometer. CaF A 2 Π−X 2 Σ + and the B 2 Σ + −X 2 Σ + band systems were excited with a hollow cathode discharge. Using previous fluorescence spectroscopy measurements, highly accurate ground state constants, and reasonable extrapolation schemes, the strongest features of CaF in the visible spectrum can be accurately modeled for both band systems. Spectroscopic constants are determined for A 2 Π with v ≤ 16 and for B 2 Σ + with v ≤ 20. Ab initio transition dipole moment curves of both transitions were calculated and scaled, and we provide a line list with Einstein A coefficients and oscillator strengths. This line list can be used to simulate spectra of CaF at temperatures and pressures relevant to astrophysical environments.

Léo Lavy↗

DOE OSTI2020

Infrared optically stimulated luminescence of rare earth doped CaF 2 and co-doped with Al or Li produced by combustion synthesis

The aim of this paper is to characterize the IRSL response of rare earth doped CaF 2 and co-doped with Al or Li, produced by the solution combustion synthesis (SCS). The results showed a high intensity of the infrared optically stimulated luminescence (IRSL) response for the samples of CaF 2 doped with Tb and co-doped with Li. For the samples of CaF 2 doped with Ce and co-doped with Li present better IRSL response than the samples co-doped with Al. It was also observed that the samples of CaF 2 :Ce,Li present a high fading with 50% reduction of the IRSL signal in a period of 60 min. In case of the CaF 2 :Tb,Li there is no significant fading during this period. For clinical dosimetry the fast fading of the dosimeter is not adequate. However, this feature can be exploited for other applications such as tamper-proof passive systems that detect and timestamp the movement of undeclared nuclear materials, by the estimation of the OSL response of materials with different fading rates.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Bright Infrared‐to‐Ultraviolet/Visible Upconversion in Small Alkaline Earth‐Based Nanoparticles with Biocompatible CaF 2 Shells

Abstract Upconverting nanoparticles (UCNPs) are promising candidates for photon‐driven reactions, including light‐triggered drug delivery, photodynamic therapy, and photocatalysis. Herein, we investigate the NIR‐to‐UV/visible emission of sub‐15 nm alkaline‐earth rare‐earth fluoride UCNPs (M 1− x Ln x F 2+ x , MLnF) with a CaF 2 shell. We synthesize 8 alkaline‐earth host materials doped with Yb 3+ and Tm 3+ , with alkaline‐earth (M) spanning Ca, Sr, and Ba, MgSr, CaSr, CaBa, SrBa, and CaSrBa. We explore UCNP composition, size, and lanthanide doping‐dependent emission, focusing on upconversion quantum yield (UCQY) and UV emission. UCQY values of 2.46 % at 250 W cm −2 are achieved with 14.5 nm SrLuF@CaF 2 particles, with 7.3 % of total emission in the UV. In 10.9 nm SrYbF:1 %Tm 3+ @CaF 2 particles, UV emission increased to 9.9 % with UCQY at 1.14 %. We demonstrate dye degradation under NIR illumination using SrYbF:1 %Tm 3+ @CaF 2 , highlighting the efficiency of these UCNPs and their ability to trigger photoprocesses.

Fischer, Stefan↗

DOE OSTI2020

Bright Infrared‐to‐Ultraviolet/Visible Upconversion in Small Alkaline Earth‐Based Nanoparticles with Biocompatible CaF 2 Shells

Fischer, Stefan↗

DOE OSTI2020

Size- and concentration-dependent Eu 2+ /Eu 3+ mixed luminescent characteristics of rare-earth-doped CaF 2 nanoparticles and their monolithic epoxy nanocomposites

CaF 2 is a promising luminescent host material for a wide range of applications, due to its high transparency, non-hygroscopy, low refractive index, low density, low backscattering efficiency, and abundance in nature. Here we report the photoluminescence (PL) and cathodoluminescence (CL) characteristics of rare-earth-doped CaF 2 nanoparticles and their composite monoliths with epoxy with visible emissions. The CaF 2 nanoparticles of ca. 36, 108 and 305 nm were prepared by a facile solution-mixing process and subsequent hydrothermal treatment. As the particle size decreases, the luminescence intensity increases for single-doped particles, while oppositely decreases for codoped particles because of energy transfer. Further, Eu 2+ - and Tb 3+ -codoped CaF 2 nanoparticles exhibit red emission, providing an efficient path for red emission through an energy transfer by Tb 3+ bridging without direct Eu 3+ doping. The effects of size and concentration are found to be pronounced in CL than PL, as the charge transfer between Eu 2+ and Eu 3+ reduces the concentration quenching in CL. The luminescence emission characteristics of epoxy/CaF 2 monoliths are different from those of particles due to the interactions with the epoxy molecules, and thus the energy transfer is hindered in PL while not in CL, enabling them for high-energy irradiation applications.

36 MATERIALS SCIENCE↗

DOE OSTI2024

High Pressure–Temperature Study of MgF 2 , CaF 2 , and BaF 2 by Raman Spectroscopy: Phase Transitions and Vibrational Properties of AF 2 Difluorides

The phase transition of AF 2 difluorides strongly depends on pressure, temperature, and cationic radius. Here, we have investigated the phase transition of three difluorides, including MgF 2 , CaF 2 , and BaF 2 , at simultaneously high pressures and temperatures using Raman spectroscopy and X-ray diffraction in externally heated diamond anvil cells up to 55 GPa at 300–700 K. Rutile-type difluoride MgF 2 with a small cationic radius undergoes a transition to the CaCl 2 -type phase at 9.9(1) GPa and 300 K, to the HP-PdF 2 -type phase at 21.0(2) GPa, and to the cotunnite-type phase at 44.2(2) GPa. The phase transition pressure to the HP-PdF 2 and cotunnite structure at 300 K for our single crystal was found to be higher than that in previous studies using polycrystalline samples. Elevating the temperature increases the transition pressure from rutile- to the CaCl 2 -type phase but has a negative influence on the transition pressure when MgF 2 transforms from the HP-PdF 2 - to cotunnite-type phase. Meanwhile, the transition pressure from the CaCl 2 - to HP-PdF 2 -type phase for MgF 2 was identified to be independent of the temperature. Raman peaks suspected to belong to the α-PbO 2 -type phase were observed at 14.6–21.0(1) GPa and 400–700 K. At 300 K, difluorides CaF 2 and BaF 2 in the fluorite structure with larger cationic radii transform to the cotunnite-type phase at 9.6(3) and 3.0(3) GPa at 300 K, respectively, and BaF 2 further undergoes a transition to the Ni 2 In-type phase at 15.5(4) GPa. For both CaF 2 and BaF 2 , elevating the temperature leads to a lower transition pressure from fluorite- to the cotunnite-type phase but has little influence on the transition to the Ni 2 In structure. Raman data provide valuable insights for mode Grüneisen parameters. We note that the mode Grüneisen parameters for both difluorides and dioxides vary linearly with the cation radius. Further calculations for the mode Grüneisen parameters at high pressures for MgF 2 , CaF 2 , and BaF 2 yield a deeper understanding of the thermodynamic properties of the difluorides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Molecular-level Regulation of PEO-Based Electrolytes with CaF 2 Nanoparticles for Advanced Solid-State Lithium Metal Batteries

The poly(ethylene oxide) (PEO)-based electrolyte has caught much attention for its flexibility, interfacial compatibility, and low cost, but the low ionic conductivity and poor mechanical strength severely hinder its further application in solid-state batteries. Herein, a molecular level regulation through adding CaF 2 nanoparticle fillers is proposed to enhance the electrochemical performance of the PEO-based electrolyte. The strong coordination effects of the Ca cation with a Li salt anion and ether-oxygen increase the dissociated Li ion concentration and accelerate Li ion migration, thus enhancing the ionic conductivity of the electrolyte when combined with their physical disruption in the PEO matrix (0.31 mS cm -1 at 55 °C). Moreover, the spontaneous reaction between Li and CaF 2 generates a LiF-rich solid electrolyte interphase, which promotes homogeneous Li deposition. Consequently, the PEO-CaF 2 electrolyte delivers symmetric cells over 6300 h and maintains full batteries over 1000 cycles with 80% capacity retention. In conclusion, the assembled pouch-cell displays robust performance, further demonstrating its potential practical application.

Li, Tao [Lanzhou Univ. (China)] (ORCID:00000003196↗

NASA NTRS1993

CAFS: A Cesium Atomic Frequency Standard for GPS block IIR

Kernco, Inc. was selected to design the Cesium Atomic Frequency Standards (CAFS) for the GPS Block IIR NAVSTAR satellites. These spacecraft are scheduled to be launched in the mid-1990's to replenish and upgrade the existing constellation of Global Positioning System satellites. The Block IIR CAFS output frequency is 13.4003378 MHz, the 686th submultiple of the cesium atomic resonance frequency. Using an integer submultiple simplifies the design of the atomic frequency standard's rf multiplier circuits, eliminating the secondary frequency synthesizer needed in previous designs. The GPS Block IIR CAFS design, particularly the improvements made on our earlier Block II design is described. Test results are included.

Wisnia, Jeffry A.↗

NASA NTRS1994

The millimeter-wave spectrum of the CaF radical (X(sup 2)Sigma(+))

The pure rotational spectrum of the CaF radical has been measured in the laboratory using millimeter/sub-mm direct absorption spectroscopy. Fourteen rotational transitions have been detected originating in the v = 0 mode of the species. Rotational lines of the vibrationally excited v = 1, 2, and 3 states have also been observed. Spin-rotation splittings, as well as hyperfine interactions arising from the nuclear spin of the fluorine atom, were resolved in the CaF spectra. Rotational, fine-structure, and in some cases, hyperfine parameters were determined for the various vibrational modes of the molecule from a nonlinear least-squares fit to the data, using a (sup 2)Sigma Hamiltonian, and are in agreement with past measurements. The newly measured rest frequencies for CaF, which are accurate to at least + or - 100 kHz, will enable astronomical searches to be conducted for the molecule in interstellar and circumstellar gas. Given the recent detection of AlF in IRC + 10216, metal fluoride species may be more abundant than previously thought.

Anderson, M. A.↗

DOE OSTI2026

A conveyor-belt magneto-optical trap of CaF

Achieving high-density samples of laser-cooled molecules is a critical step toward advancing applications in precision measurements, ultracold chemistry and quantum science. We report the experimental realization of a high-density conveyor-belt magneto-optical trap for calcium monofluoride (CaF) molecules. The obtained highly-compressed cloud has a mean radius of 64(5) μm and a peak number density of 3.6(5) × 10 10 cm −3 , a 600-fold increase over the conventional red-detuned MOTs of CaF, and the densest molecular MOT observed to date. Subsequent loading of these molecules into an optical dipole trap yields up to 2.6 × 10 4 trapped molecules at a temperature of 14(2) μK with a peak phase-space density of ~ 2.4 × 10 −6 . This opens new possibilities for a range of applications utilizing high-density, optically trapped ultracold molecules.

Yu, Scarlett S. [Harvard Univ., Cambridge, MA (Uni↗

DOE OSTI2021

AmeriFlux FLUXNET-1F US-CF1 CAF-LTAR Cook East

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-CF1 CAF-LTAR Cook East. This is the FLUXNET version of the carbon flux data for the site US-CF1 CAF-LTAR Cook East produced by applying the standard ONEFlux (1F) software. Site Description - CF1 has operated since May 2017 at the R.J. Cook Agronomy Farm outside of Pullman, Washington, and monitors the no-till side of a paired-catchment study that is part of the Longterm Agroecosystem Research (LTAR) site common experiment. CF1 is located in “Cook East,” a field that has been in no-till management since 1998, and represents the Alternative treatment of the LTAR common experiment. It is paired with the CF2 tower location in “Cook West,” which has been in conventional tillage since prior to 1998 and represents the Prevalent treatments of the common experiment. Cook Agronomy Farm is in the high precipitation agroecological zone of the Columbia Plateau’s dryland cropping region. Crop rotations are wheat-based and include winter wheat, spring wheat, chickpea, spring canola, and winter peas. Wheat is the principal cash crop, with other crops grown in rotation for diversity, nutrient, and pest management. Soils are predominantly silt loam texture Mollisols in the Palouse, Thatuna, Naff soil series. The CF1 tower replaced US-RC1, which operated 2012-2016 in a neighboring field that was also in no-till management since 1998. CF1 and RC1 have distinct footprints, aspects, and soil series compositions.

Phillips, Claire L.↗

DOE OSTI2022

AmeriFlux FLUXNET-1F US-CF2 CAF-LTAR Cook West

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-CF2 CAF-LTAR Cook West. This is the FLUXNET version of the carbon flux data for the site US-CF2 CAF-LTAR Cook West produced by applying the standard ONEFlux (1F) software. Site Description - CF2 has operated since May 2017 at the R.J. Cook Agronomy Farm outside of Pullman, Washington, and monitors the conventionally tilled side of a paired-catchment study that is part of the Longterm Agroecosystem Research (LTAR) site common experiment. CF2 is located in “Cook West,” a field that has been in conventional tillage since prior to 1998 and constitutes the Prevalent treatment of the common experiment. In this case, conventional tillage involves chisel plowing after the winter wheat phase of rotations (approximately every 3-4 years) and occasional harrowing. CF2 is paired with the CF1 tower location in “Cook East,” which has been in no-till since 1998 and represents the Alternative treatment of the common experiment. Both fields are planted in the same crops every year. Cook Agronomy Farm is in the high precipitation agroecological zone of the Columbia Plateau’s dryland cropping region. Crop rotations are wheat-based and include winter wheat, spring wheat, chickpea, spring canola, and winter peas. Wheat is the principal cash crop, with other crops grown in rotation for diversity, nutrient, and pest management. Soils are predominantly silt loam texture Mollisols in the Palouse, Thatuna, Naff soil series. The CF2 tower replaced US-RC2, which operated 2012-2016 in a neighboring field that was also conventionally tilled. CF2 and RC2 have distinct footprints, aspects, and soil series compositions.

Huggins, Dave↗

DOE OSTI2022

AmeriFlux FLUXNET-1F US-CF3 CAF-LTAR Boyd North

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-CF3 CAF-LTAR Boyd North. This is the FLUXNET version of the carbon flux data for the site US-CF3 CAF-LTAR Boyd North produced by applying the standard ONEFlux (1F) software.

Huggins, Dave↗

DOE OSTI2022

AmeriFlux FLUXNET-1F US-CF4 CAF-LTAR Boyd South

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-CF4 CAF-LTAR Boyd South. This is the FLUXNET version of the carbon flux data for the site US-CF4 CAF-LTAR Boyd South produced by applying the standard ONEFlux (1F) software.

Huggins, Dave↗