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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

High-accuracy multi-configuration Dirac–Hartree–Fock calculations of the energy levels and transition properties of Ga-like to Br-like gadolinium ions

Highlights: • A complete and accurate data set of excitation energies, lifetimes, wavelengths and E1, M1, E2, M2 and E3 line strengths, transition rates, and oscillator strengths for Ga-like to Br-like Gd ions is reported. • The Multi-configuration Dirac–Hartree–Fock method is employed. • The effects of core–valence electron correlation from the deep subshells 3d and 3p have been investigated. • The computed excitation energies from the present MCDHF calculations of the VV+CV{sub 3d}+CV{sub 3p} model agree well with the experimental values. The differences are less than ±0.1% for most of the levels. - Abstract: Theoretical calculations of Ga-like to Br-like gadolinium ions were performed by using the fully relativistic multi-configuration Dirac–Hartree–Fock (MCDHF) method. Extensive lists of excitation energies, wavelengths, line and oscillator strengths, and E1, M1, E2, M2, and E3 transition rates are presented. The effects of core–valence electron correlation from the deep subshells 3d and 3p are investigated and the accuracy of the results is confirmed by comparing with available theoretical and experimental data sets.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1972

Gadolinium-hydrogen ion exchange of zirconium phosphate

The Gd(+3)/H(+) ion exchange on a commercial zirconium phosphate ion exchanger was investigated in chloride, sulfate, and phosphate solutions of Gd(+3) at gadolinium concentrations of 0.001 to 1 millimole per cc and in the pH range of 0 to 3.5. Relatively low Gd(+3) capacities, in the range of 0.01 to 0.1 millimole per g of ion exchanger were found at room temperature. A significant difference in Gd(+3) sorption was observed, depending on whether the ion exchanger was converted from initial conditions of greater or lesser Gd(+3) sorption than the specific final conditions. Correlations were found between decrease in Gd(+3) capacity and loss of exchanger phosphate groups due to hydrolysis during washing and between increase in capacity and treatment with H3PO4. Fitting of the experimental data to ideal ion exchange equilibrium expressions indicated that each Gd(+3) ion is sorbed on only one site of the ion exchanger. The selectivity quotient was determined to be 2.5 + or - 0.4 at room temperature on gadolinium desorption in chloride solutions.

Liu, D. C.↗
DOE OSTI2018

Electronic Structure of GdCuGe Intermetallic Compound

The electronic structure of GdCuGe intermetallic compound has been studied. Spin-polarized energy spectrum calculations have been performed by the band method with allowance for strong electron correlations in the 4f-shell of gadolinium ions. Antiferromagnetic ordering of GdCuGe at low temperatures has been obtained in a theoretical calculation, with the value of the effective magnetic moment of gadolinium ions reproduced in fair agreement with experimental data. The electronic density of states has been analyzed. An optical conductivity spectrum has been calculated for GdCuGe; it reveals specific features that are analogous to the ones discovered previously in the GdCuSi compound with a similar hexagonal structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Application of High-Frequency Electron Paramagnetic Resonance/Electron Spin Echo for the Identification of the Impurity Composition and Electronic Structure of Ceramics Based Garnets

Electron paramagnetic resonance (EPR) spectra of Ce{sup 3+}, Yb{sup 3+}, Cr{sup 3+}, and Gd{sup 3+} impurity ions in yttrium aluminum garnet Y{sub 3}Al{sub 5}O{sub 12} (YAG) ceramics were detected and identified at frequency of 94 GHz. The advantage of measuring the EPR spectra in the high-frequency range compared to the standard EPR technique is shown, which makes it possible to separate the EPR spectra characterized by different anisotropic g-factors and also to isolate the EPR signals due to the splitting of the fine structure for centers with high-spin states. In ceramics with a high content of magnetic Gd{sup 3+} ions, EPR and electron spin echo (ESE) spectra of multi-ionic gadolinium complexes were observed, and EPR spectra of complexes with the maximum number of exchange-coupled gadolinium ions are seen at low temperatures. The temperature dependences of the EPR spectra indicates ferromagnetic ordering of exchange-coupled complexes of gadolinium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Pressure-Induced Decrease in the Curie Temperature of Gd{sub 2}Fe{sub 17}: LSDA+U Calculations

To explain the magnetic properties of advanced ferromagnetic intermetallic compounds of the R{sub 2}Fe{sub 17} (R is a rare-earth element) class, experimentalists often use the hypothesis of competition between ferromagnetic exchange and antiferromagnetic exchange between four types of the nearest iron atoms in nonequivalent lattice sites. For the rhombohedral Gd{sub 2}Fe{sub 17} ferromagnet, we calculate the magnetic moments of iron and gadolinium ions, the parameters of exchange between Fe atoms, and Curie temperature T{sub C} at a zero pressure and during hydrostatic lattice compression. The magnetic moment of the unit cell of Gd{sub 2}Fe{sub 17} is shown to decrease under pressure, and this decrease is almost completely associated with a decrease in the magnetic moments of Fe rather than Gd ions, the pressure dependence of the magnetic moments of which is weaker by an order of magnitude. In contrast to the hypothesis regarding the competition of exchange interactions between different kinds of Fe atoms, the parameters of exchange between the nearest iron atoms in different crystallographic sites are found to be positive ferromagnetic (at a zero pressure and during compression), and a ferromagnetic character of interaction is shown to remain unchanged under pressure even for Fe atoms in the so-called dumbbell sites with the nearest interatomic distances. The Curie temperature T{sub C} of Gd{sub 2}Fe{sub 17} is shown to decrease with increasing pressure. The changes in the exchange parameters and the magnetic moments of Gd{sub 2}Fe{sub 17} during compression are found to be mainly related to a change in the position of energy spectrum branches with respect to each other and the Fermi level ϵ{sub F} rather than to a change in the overlapping of wavefunctions, which play a minor role.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Influence of gadolinium doping on structural, optical, and electronic properties of polymeric graphitic carbon nitride

Polymeric graphitic carbon nitride (gCN) materials have received great attention in the fields of photo and electrocatalysis due to their distinct properties in metal-free systems with high physicochemical stability. Nevertheless, the activity of undoped gCN is limited due to its relatively low specific surface area, low conductivity, and poor dispersibility. Doping Gd atoms in a gCN matrix is an efficient strategy to fine-tune its catalytic activity and its electronic structure. Herein, the influence of various wt% of gadolinium (Gd) doped in melon-type carbon nitride was systematically investigated. Gadolinium-doped graphitic carbon nitride (GdgCN) was synthesized by adding gadolinium nitrate to dicyandiamide during polymerization. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the crystallinity and the morphological properties are influenced by the % of Gd doping. Furthermore, X-ray photoelectron spectroscopy (XPS) studies revealed that the gadolinium ions bonded with nitrogen atoms. Complementary density functional theory (DFT) calculations illustrate possible bonding configurations of Gd ions both in bulk material and on ultrathin melon layers and provide evidence for the corresponding bandgap modifications induced by gadolinium doping.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural description, luminescent and magnetic properties of novel 2-D coordination polymers containing thiazolo[5,4-d]thiazole rings and trivalent lanthanide ions

Highlights: • Reaction between thiazolo[5,4-d]thiazole-2,5-dicarboxylate and lanthanide ions yielded six novel coordination polymers. • Crystallization in gel improved yields and quality of products. • Dc magnetic susceptibilities (from 5 to 300 K) and luminescence spectra are reported. • Eu(III) luminescence indicated a single emitting center, in disagreement with the existence of the two crystallographically distinct ion sites. - Abstract: In this work, we have synthesized six coordination polymers [Ln{sub 2}(Thz){sub 3}·8H{sub 2}O)]·4H{sub 2}O (Ln = La{sup 3+}, Ce{sup 3+}, Nd{sup 3+}, Sm{sup 3+}, Eu{sup 3+}, Gd{sup 3+}; Thz = thiazolo[5,4-d]thiazole-2,5-dicarboxylate). These are the first structures combining this ligand with lanthanides. All compounds crystallize in the P-1 triclinic system, forming a 2-D coordination network. Luminescence spectra for the Nd{sup 3+}, Sm{sup 3+}, and Eu{sup 3+} structures show the typical transitions of these ions, through the antenna effect promoted by the ligand. The magnetic properties of Ce{sup 3+}, Nd{sup 3+}, Sm{sup 3+}, Eu{sup 3+}, Gd{sup 3+} compounds were analyzed in terms of the free ion approximation. The variable-temperature susceptibility fitted with a Curie-Weiss law shows the existence of weak magnetic interactions at low temperatures for the Ce{sup 3+}, Nd{sup 3+} and Sm{sup 3+} compounds, and paramagnetic behavior for the Gd{sup 3+} compound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Efficiently enhanced photoluminescence in Eu3+-doped Lu2(MoO4)3 by Gd3+ substituting

Highlights: • The Gd{sup 3+} doped samples had been discovered to show much better luminescent properties than Lu{sub 2}(MoO{sub 4}){sub 3}:0.02Eu{sup 3+}. • The influence of Gd{sup 3+} ions on luminescence behavior was discussed. • The DFT calculation indicates that the structure of Gd{sub 2}(MoO{sub 4}){sub 3} is more propitious for luminescence than that of Lu{sub 2}(MoO{sub 4}){sub 3}. - Abstract: A series of Lu{sub 2-x}Gd{sub x}(MoO{sub 4}){sub 3}:0.02Eu{sup 3+} (x = 0–2) red-emitting phosphors have been synthesized by the standard solid-state reaction method. Interestingly, the Gd concentration plays a profound role to influence the luminescence property. A conspicuous monotonic increase could be found in the influence of Gd{sup 3+} concentration to the emission intensity, and finally Gd{sub 2}(MoO{sub 4}){sub 3}:0.02Eu{sup 3+} exhibits the strongest red light emission with the intensifying factor even reaching 3.04-fold compared to Lu{sub 2}(MoO{sub 4}){sub 3}:0.02Eu{sup 3+}. Careful structural analysis suggested that up to about 80% (x = 1.6) Lu can be substituted by Gd with the same crystal structure of Lu{sub 2}(MoO{sub 4}){sub 3} being retained, while a higher Gd concentration would lead to it crystallizing in the Gd{sub 2}(MoO{sub 4}){sub 3} structure. We believe that the variation of crystal structure is responsible for the photoluminescence enhancing process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Photoelectric Fields and Band Gap in Doped Lithium Niobate Crystals

Photoinduced light scattering and optical spectroscopy have been used to study the photorefractive effect and determine the band gap in nominally undoped congruent and stoichiometric lithium niobate crystals, as well as in a series of congruent LiNbO{sub 3} crystals doped with Mg, Zn, B, Gd, Y, and Er cations and LiNbO{sub 3} single crystals codoped with Mg:Gd, Mg:Fe, Mg:Y, and Mg:Ta.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Low-Temperature Schottky Anomalies and the Magnetic State of the p Electrons of Oxygen in Substituted Gd{sub 0.4}Sr{sub 0.6}CoO{sub 3–δ} Cobaltites

The XANES spectra (X-ray absorption near-edge spectra) at the K edge of Co and the L{sub 3} edge of Gd in polycrystalline Gd{sub 0.4}Sr{sub 0.6}CoO{sub 3–δ} rare-earth oxides with an ordered and disordered distribution of Gd{sup 3+} and Sr{sup 2+} cations over the A sites in the crystal lattice are measured. The results of XANES measurements do not reveal a noticeable shift in the absorption edge with increasing Sr concentration as compared to the GdCoO{sub 3} parent composition. The measured temperature dependences of the heat capacity of polycrystalline ordered and disordered samples and a single-crystal ordered Gd{sub 0.4}Sr{sub 0.6}CoO{sub 2.85} sample exhibit two Schottky anomalies. These anomalies are thought to be related to the high-spin state of the Co{sup 3+} ions in the pyramidal environment caused by oxygen deficiency and to the magnetic state of oxygen p electrons induced by the doping-assisted generation of a hole in the 2p state. The absence of a noticeable shift in the absorption edge and the presence of two Schottky anomalies support the fact that the charge state of cobalt remains unchanged in the compounds under study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2001

Dipole potentials indicate restructuring of the membrane interface induced by gadolinium and beryllium ions

The dipole component of the membrane boundary potential, phi(d), is an integral parameter that may report on the conformational state of the lipid headgroups and their hydration. In this work, we describe an experimental approach to measurements of the dipole potential changes, Deltaphi(d), and apply it in studies of Be(2+) and Gd(3+) interactions with membranes composed of phosphatidylserine (PS), phosphatidylcholine (PC), and their mixtures. Deltaphi(d) is determined as the difference between the changes of the total boundary potential, phi(b), measured by the IFC method in planar lipid membranes and the surface potential, phi(s), determined from the electrophoretic mobility of liposomes. The Gouy-Chapman-Stern formalism, combined with the condition of mass balance, well describes the ion equilibria for these high-affinity cations. For the adsorption of Be(2+) and Gd(3+) to PC membranes, and of Mg(2+) to PS membranes, the values of Deltaphi(b) and Deltaphi(s) are the same, indicative of no change of phi(d). Binding of Gd(3+) to PS-containing membranes induces changes of phi(d) of opposite signs depending on the density of ionized PS headgroups in the bilayer. At low density, the induced Deltaphi(d) is negative (-30 mV), consistent with the effect of dehydration of the surface. At maximal density (pure PS, neutral pH), adsorption of Be(2+) or Gd(3+) induces an increase of phi(d) of 35 or 140 mV, respectively. The onset of the strong positive dipole effect on PS membranes with Gd(3+) is observed near the zero charge point and correlates with a six-fold increase of membrane tension. The observed phenomena may reflect concerted reorientation of dipole moments of PS headgroups as a result of ion adsorption and lipid condensation. Their possible implications to in-vivo effects of these high-affinity ions are discussed.

Non-NASA Center↗
DOE OSTI2019

Energy Conversion in Gd{sub 2}O{sub 3} Nanocrystals Doped with Er{sup 3+} Ions

The conversion of the energy absorbed by cubic Gd{sub 2}O{sub 3} nanocrystals doped with Er{sup 3+} and codoped with Yb{sup 3+} and Zn{sup 2+} ions in a temperature range of 95–425 K is studied at various concentrations of dopants. The photoluminescence spectra confirm the ability of excitation energy transfer from the Gd{sup 3+} ions or the matrix towards the Er{sup 3+} ions. The population of upper excited states in the Er{sup 3+} ions depends on the way of excitation, which cause the alterations in the probability of multiphonon relaxation from the excited states to the radiative levels. The kinetics of photoluminescence decay exhibit the possible energy transfer from anionic defects created by extra doping with Zn{sup 2+} ions. The temperature dependences of the upconversion luminescence yield for emission lines of 560 and 660 nm are found to be different.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The GdF3 phosphors with enhanced multicolor luminescence via multi-channel excitation and energy migration procedure

Highlights: • Core-shell structured GdF{sub 3} phosphors were synthesized by hydrothermal method. • SiO{sub 2} coating layers prevent aggregation and sintering during thermal annealing. • The annealed CSS nanophosphors were highly dispersible. • The inserted PMA significantly enhances multicolor luminescence. • The annealed CSS phosphors exhibit enhanced multicolor luminescence properties. - Abstract: A collection of GdF{sub 3} core-shell structured (CSS) phosphors were synthesized by hydrothermal method. The as-prepared (AP) phosphors were coated with SiO{sub 2} layers to avoid aggregation and sintering during thermal annealing at 800 °C, after which the SiO{sub 2} layers were etched off and the annealed phosphors became highly dispersible. The annealed CSS phosphor aGdF{sub 3}:Eu{sup 3+}@GdF{sub 3}:Ce{sup 3+},Dy{sup 3+} shows excellent multicolor luminescence performance with the aid of dual-channel excitation and energy migration (EM) procedure of Gd{sup 3+} ions. By inserting pyromellitic acid (PMA) organic ligands into the interfaces between annealed core and AP shell layer regions, the so-called antenna effect of organic ligands of PMA forms a new excitation channel, which makes the CSS phosphor aGdF{sub 3}:Eu{sup 3+}@PMA@GdF{sub 3}:Ce{sup 3+},Dy{sup 3+} exhibit significantly enhanced multicolor luminescence via multi-channel excitation and EM process. The prepared CSS phosphors in this work are excellent candidates for applications in solid-state lighting.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetoelastic Waves in Submicron Yttrium–Iron Garnet Films Manufactured by Means of Ion-Beam Sputtering onto Gadolinium–Gallium Garnet Substrates

A series of equidistant oscillations have been revealed in the transmission spectrum and dispersion law of Damon–Eshbach surface magnetostatic waves (SMSWs) propagating in submicron (200-nm) yttrium–iron garnet (YIG) films manufactured by means of ion-beam sputtering onto gadolinium–gallium garnet (GGG) substrates. These oscillations correspond to the excitation of magnetoelastic waves in the YIG–GGG structure at frequencies of resonant interaction between the surface magnetostatic waves and the elastic shear modes of the wave-guiding YIG–GGG structure. The obtained results show that the studied YIG films are characterized by an efficient magnetoelastic coupling between their spin and elastic subsystems and the matching of acoustic impedances at the YIG–GGG interface, thus providing the possibility to consider the ion-beam sputtering of YIG films onto GGG substrates as a promising technology for the creation of magnonic and straintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Er3+-Yb3+/Er3+-Yb3+-Li+/Er3+-Yb3+-Zn2+:Gd2O3 nanophosphors for efficient frequency upconverter and temperature sensing applications

Highlights: • The Er{sup 3+}-Yb{sup 3+}:Gd{sub 2}O{sub 3} nanophosphors infer the enhancement in UC emission intensity via incorporation of Li{sup +} and Zn{sup 2+} ions. • The average particles size of the developed nanophosphors is found to be lie in nanometer range by XRD and TEM analysis. • The maximum sensitivity ∼ 0.0116 K{sup −1} has been reported in the Er{sup 3+}-Yb{sup 3+}-Zn{sup 2+}:Gd{sub 2}O{sub 3} nanophosphors. • The colour coordinate for the developed Er{sup 3+}-Yb{sup 3+}-Zn{sup 2+}:Gd{sub 2}O{sub 3} nanophosphors lie in the greenish yellow colour region. - Abstract: Er{sup 3+}/Yb{sup 3+}/Li{sup +}/Zn{sup 2+}:Gd{sub 2}O{sub 3} nanophosphors synthesized via combustion synthesis method have been structurally and optically characterized. The average particles size of the developed nanophosphors has been found to be ∼ 25 nm by Transmission Electron Microscopy (TEM) analysis which is in good agreement with the X-rays Diffraction (XRD) results. The significant enhancement in upconversion (UC) emission intensity for green (∼ 20 and 70 times) and red (∼ 7 and 20 times) band have been observed after codoping with Li{sup +} and Zn{sup 2+} ions respectively in Er{sup 3+}-Yb{sup 3+}:Gd{sub 2}O{sub 3} system. The temperature sensing capability of the optimized nanophosphors has been studied corresponding to two thermally coupled {sup 2}H{sub 11/2} and {sup 4}S{sub 3/2} levels of the Er{sup 3+} ions. The sensitivity ∼ 0.0096 K{sup -1}, 0.00109 K{sup -1} and 0.0116 K{sup -1} have been reported in the Er{sup 3+}-Yb{sup 3+}:Gd{sub 2}O{sub 3}, Er{sup 3+}-Yb{sup 3+}- Li{sup +}:Gd{sub 2}O{sub 3} and Er{sup 3+}-Yb{sup 3+}- Zn{sup 2+}:Gd{sub 2}O{sub 3} nanophosphors respectively. The photometric characterizations of the developed nanophosphors have also been reported.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Eu{sup 2+} and Gd{sup 3+} Distributions in Fluorohafnate Glasses Studied by Electron Paramagnetic Resonance

We have studied electron paramagnetic resonance spectra of europium- and gadolinium-activated ZBLAN-type fluorohafnate glasses, using the composition 58HfF{sub 4} · 20BaF{sub 2} · 2LaF{sub 3} · 3AlF{sub 3} · 17NaF as an example. The ratio of the concentration of free Eu{sup 2+} and Gd{sup 3+} ions to that of ions in clusters has been quantitatively evaluated for the first time. The percentage of free ions has been shown to increase significantly with decreasing activator concentration. At activator concentrations of 1.25 mol % EuF{sub 2} and 1 mol % GdF{sub 3}, the activator ions predominantly form clusters and only a small fraction of Eu{sup 2+} and Gd{sup 3+} are present as individual ions, whereas at 0.1 mol % EuF{sub 2} the concentration of free ions is comparable to that of ions in the clusters.

36 MATERIALS SCIENCE↗