Parelektrische Resonanz von Li+ in KCl

Parelectric resonance (PER) absorption spectra of Li⁺-centers in KCl crystals are measured at 35 and 9 GHz. Measurements for the microwave fieldE ₁ parallel and perpendicular to the static fieldE ₀ for three different orientations relative to the crystal axes can be explained by using the following offcenter tunneling model for the Li⁺-center: The dipole momentp=6.3±0.3 Debye is in [111] direction. Tunneling transitions are possible parallel to the [100] and [110] axis. The corresponding matrix elements are 11.3±0.5 and 3.2±0.5 GHz. The zero field splittings are 9.8±1.5; 22.6±1 and 35.4±3 GHz. Measurements under application of an uniaxial pressureP ₀ support this analysis.     

Paraelectric pairs in lithium doped KBr

The low lying paraelectric modes observed in Li doped KBr have been identified with Li pairs by a systematic far infrared study of isotopic mixtures of the Li dopant. We conclude that isolated Li⁺ ions do not tunnel in KBr but Li⁺ ion pairs do.     

A decomposition of the paraelectric spectrum of KBr:Li+ using hydrostatic pressure

We report paraelectric resonance absorption measurements on KBr:Li⁺ as a function of hydrostatic pressure for frequencies in the range 50– 220 GHz. The lines of the spectra separate into two distinct groups. In one case the zero field splittings increase rapidly with pressure (approx. 0.2 GHz/bar) while the effective electric dipole moment decreases rapidly. For the other, the zero field splittings increase 3–4 times more slowly and the dipole moments appear to be converging to a non zero value. Suprisingly, one of the effective dipole moments is increasing with pressure.     

Downregulation of calcium-dependent NMDA receptor desensitization by sodium-calcium exchangers: a role of membrane cholesterol

Background

The plasma membrane Na⁺/Ca²⁺-exchanger (NCX) has recently been shown to regulate Ca²⁺-dependent N-methyl-d-aspartate receptor (NMDAR) desensitization, suggesting a tight interaction of NCXs and NMDARs in lipid nanoclasters or “rafts”. To evaluate possible role of this interaction we studied effects of Li⁺ on NMDA-elicited whole-cell currents and Ca²⁺ responses of rat cortical neurons in vitro before and after cholesterol extraction by methyl-β-cyclodextrin (MβCD).

Results

Substitution Li⁺ for Na⁺ in the external solution caused a concentration-dependent decrease of steady-state NMDAR currents from 440?±?71 pA to 111?±?29 pA in 140 mM Na⁺ and 140 mM Li⁺, respectively. The Li⁺ inhibition of NMDAR currents disappeared in the absence of Ca²⁺ in the external solution (Ca²⁺-free), suggesting that Li⁺ enhanced Ca²⁺-dependent NMDAR desensitization. Whereas the cholesterol extraction with MβCD induced a decrease of NMDAR currents to 136?±?32 pA in 140 mM Na⁺ and 46?±?15 pA in 140 mM Li⁺, the IC₅₀ values for the Li⁺ inhibition were similar (about 44 mM Li⁺) before and after this procedure. In the Ca²⁺-free Na⁺ solution the steady-state NMDAR currents after the cholesterol extraction were 47?±?6% of control values. Apparently this amplitude decrease was not Ca²⁺-dependent. In the Na⁺ solution containing 1 mM Ca²⁺ the Ca²⁺-dependent NMDAR desensitization was greater when cholesterol was extracted. Obviously, this procedure promoted its development. In agreement, Li⁺ and KB-R7943, an inhibitor of NCX, both considerably reduced NMDA-activated Ca²⁺ responses. The cholesterol extraction itself caused a decrease of NMDA-activated Ca²⁺ responses and, in addition, abolished the effects of Li⁺ and KB-R7943. The cholesterol loading into the plasma membrane caused a recovery of the KB-R7943 effects.

Conclusions

Taken together our data suggest that NCXs downregulate the Ca²⁺-dependent NMDAR desensitization. Most likely, this is determined by a tight functional interaction of NCX and NMDAR molecules because of their co-localization in membrane lipid rafts. The destruction of these rafts is accompanied by an enhancement of NMDAR desensitization and a loss of NCX-selective agent effects on NMDARs.

     

Bestimmung von Potentialparametern für die Wechselwirkung von Ionen und Atomen aus dem Beugungseffekt

This paper is concerned with the determination of the potential parameters from experimental results. The potential parameters are determined from the amplitudes and the positions of the experimental diffraction pattern by applying the general solution of the diffraction effect in [1]. All existing experimental results up to date are referred and evaluated. For the following scattering systems the potential parameters were determined and are presented in a table:⁷Li⁺-He,⁷Li⁺-Ne,⁷Li⁺-Ar,⁷Li⁺-Kr,⁷Li⁺-Xe,⁶Li⁺-Ar and H⁺- Ar.     

Li7 self diffusion in LiAl—An NMR study

The self diffusion of Li⁷ in near stoichiometric LiAl has been investigated by observing the Li⁷ and Al²⁷ NMR relaxation rates. The diffusivity for a Li⁷ atom is determined to be D = 9 × 10^?6 exp (?0.12 eV/kT) cm²/sec. Both the Li⁷ and Al²⁷ rates show the effects of quadrupole relaxation. The electric field gradients from the moving defects in LiAl are a factor of 37 ± 5 stronger at the Al nuclei suggesting covalent character to the bonding.     

Change of the oxidation state of phosphorus in sputtered Li3±xPO4±y and Li3±xPO4±yNz films

Thin Li_3±xPO_4±yN_zLi⁺- electrolyte films prepared by reactive rf-magnetron sputtering of Li₃PO₄ incorporate a certain amount of nitrogen which is made responsible for increased Li⁺-conductivity as well as at least kinetic stability with lithium metal. A possible change of the oxidation state +5 of phosphorus as a result of the sputter process has not yet been considered for explanation. We have found out that it cannot be generally assumed that reactive low power rf-magnetron sputtering of Li₃PO₄ results in fully oxidized films, even when pure O₂ is employed as sputtering gas. Our films immediately react with H₂O releasing a garlic smelling gas. The reaction area is surrounded by a white crust afterwards. CuSO₄ and AgNO₃ aqueous solutions become reduced. Impedance measurements yield an ionic conductivity of 2·10⁻⁶ S/cm at 25 °C and an activation energy of 0.62 eV.     

Low temperature EPR study of the “impurity” resonances in (TCNQ)- and (TCNQ)-2 salts

The so-called “impurity” resonances in polycrystalline Li⁺ (TCNQ)^-, Cu⁺ (TCNQ)^- and Cu⁺ (TCNQ)^-₂ have been studied at liquid helium-temperatures. The Li⁺ (TCNQ)^- resonance is partially resolved at low microwave powers with g_⊥ = 2.0025 ± 0.0005 and g_∥ = 2.008 ± 0.001. Itis found that the (TCNQ) and (TCNQ)^-₂ complexes give characteristics spectra. The possible origin of these resonances is discussed.     

An efficient pathway for Li<Superscript>6</Superscript> isotope enrichment

Separation of lithium isotopes has been achieved using two-step laser photoionization in conjunction with an atomic beam and in-house built time of flight (TOF) mass spectrometer. We present an efficient pathway for the enrichment of Li⁶ isotope by tuning the exciter laser to the 3p ² P _{1/2, 3/2} excited state of Li⁶. A concentration of up to 60% is demonstrated from a natural isotopic abundant lithium sample. In addition, the first measurement of the absolute photoionization cross-section of the 3p excited state of Li⁶ and Li⁷ are reported as 26.8±4 Mb and 25.5±3.8 Mb, respectively. PACS 32.10.Bi; 32.80.t; 32.80.Fb     

Zur Bildungskinetik der F-Folgezentren in KCl

The process of F-center aggregation under light irradiation, which involves ionic movement at low temperatures (observable down to — 60°C), is not at all understood in its mechanism. It is the aim of this work to evaluate quantitatively the kinetics of this process for different F-aggregate centers. In part I the assoziation of F-centers in KCl crystals with isolated Na⁺ or Li⁺ ions was thoroughly investigated as the clearest model case of F-center-aggregation. The reaction product in these crystals after light irradiation, an F-center associated to a Na⁺ or Li⁺ ion as nearest (100) neighbor (F _A -center), is well established in its model and can be detected by its double peak absorption structure. By optical measurements of the rate of F _A -center formation in dependence on light-intensity, time, Na⁺ or Li⁺-concentration, F→F′ conversion rate and temperature, the kinetics of this reaction could be evaluated in a simple equation of bimolecular type. The analysis leads to the conclusion, that either the anion vacancy or the F′-center must be regarded as a unit of high thermal mobility (activation energy 0·6±0·05 eV, jump frequency about 10² sec^?1 at room temperature) which diffuses randomly in the lattice and can be captured by a Na⁺ or Li⁺ ion.     

Luminescence studies of thallium co-doped KBr:Eu2+ powder phosphors

In this study, photoluminescence (PL) and photostimulated luminescence (PSL) properties in KBr:Eu²⁺, Tl⁺ powder phosphors are reported. PL emission spectra of these Tl⁺ co-doped KBr:Eu²⁺ phosphors show four overlapping bands around 310, 325, 360 and 375 nm in addition to the characteristic of Eu²⁺ ions at 420 nm. These additional short wavelength bands were attributed to centres involving Tl⁺ ions. The decrease in PSL intensity of γ-irradiated KBr:Eu²⁺, Tl⁺ powder phosphors with Tl⁺ concentration and the absence of thallium emission bands in PSL were attributed to the efficient electron trapping by Tl⁺ ions during irradiation.     

Twenty-parameter eigenfunctions and energy values of the 23 S States of He and He-like Ions

Twenty-parameter calculations of the energies and wave functions of the first excited states 2³ S of He, Li⁺, Be⁺⁺, B⁺⁺⁺, O⁶⁺, Ne⁸⁺, Mg¹⁰⁺, have been carried out using Hylleraas' method. The energy values have been corrected for mass polarization. The coefficients of the best wave functions are listed. Similar calculations for the 2³ S state of the H^? ion yield an energy value which cannot be distinguished from the energy of a free H atom. For He and Li⁺, in addition, forty-parameter calculations have been carried out. The results compare well with the recent calculations of Pekeris using a somewhat different method. Even after the inclusion of the relativistic correction, the theoretical energy values deviate slightly from the observed. The differences, ?0·10±0·05 cm^?1 for He and ?1·07±0·10 cm^?1 for Li⁺, represent observed values of the Lamb shifts in the 2³ S states. These values agree within their uncertainties with the values predicted from quantum electrodynamics.     

Determination of the diffusion coefficient of lithium ions in nano-Si

The diffusion coefficients of lithium ions (D_Li⁺) in nano-Si were determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). D_Li⁺ values are estimated to be ~ 10^? 12 cm² s^? 1 and exhibit a “W” type varying with the lithium concentration in silicon. Two minimum regions of D_Li⁺ (at Li_2.1 ± 0.2Si and Li_3.2 ± 0.2Si) are found, which probably result from two amorphous compositions (a-Li₇Si₃ and a-Li₁₃Si₄). Besides the two minimum regions, one maximum D_Li⁺ is observed at Li₁₅Si₄, corresponding to the crystallization of highly lithiated amorphous Li_xSi.     

Microwave spectrum of γ-valerolactone

An Ar⁺ laser at 4579 Å is used to excite the B¹Π_u-X¹Σ_g⁺ fluorescence of the ⁶Li⁷Li molecule in a crossed heat pipe oven. The spectrum in the region 4400–6300 Å is recorded photoelectrically with an emphasis on the observation of higher vibrational levels in the ground state close to the dissociation limit. P and R doublets corresponding to v″ ≤ 26 originating from the (v′ = 13, J′ = 19) level are observed and identified using mass-reduced quantum numbers. Two additional ⁶Li⁷Li series, known from earlier work of Velasco, Ottinger, and Zare, are also analyzed. These data are used to construct effective Rydberg-Klein-Rees (RKR) potentials for specific J″ (=9, 19) quantum numbers of the ground state and from them the true (rotationless) potential energy curve (for X¹Σ_g⁺) is derived. This extends the previously known curve of Li₂ from 4.28 to 5.18 Å (outer turning point); this turning point corresponds to an energy which is approximately 88% of the dissociation energy, which is estimated here to be 8516 ± 18 cm^?1.     

Enhancing up conversion luminescence effect of β-NaYF<Subscript>4</Subscript>: Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> by Li<Superscript>+</Superscript> ion doped approach

Up-conversion (UC) is a photoluminescence process which converts few low energy photons to a higher energy photon. This process has more potential usages in many different fields like bioimaging, solar spectrum tuning, and security encoding. Nowadays, researches about UC mostly focusing on biomedical signory and synthesis of nanoparticles. The synthesis of NaYF₄ nanoparticles executed under series of pH value condition results in different morphology and photoluminescence effect. Samples in low pH value created better consequent and quality than the specimen which had higher pH value. In addition, we observed NaYF₄ samples of doping Li⁺, realizing that the action of distorting in the local symmetry around rare-earth ions is caused by Li⁺ doping. The NaYF₄ microparticles which doped higher concentration of Li⁺ has strong fluorescence properties and intensities compared with their corresponding group of Li⁺-free, the blue emission 479 nm luminescence intensities and 454 nm luminescence intensities in NaYF₄:Yb³⁺, Tm³⁺ microparticles doped 20 mol% Li⁺ are enhanced 3 and 8 times, separately. And violet emission luminescence intensities around 345 and 360 nm are about 10 and 7 times, respectively. The result indicated that the improved UC luminescence of NaYF₄:Yb³⁺. Tm³⁺ microparticles with Li⁺ doping have potentially applications.     

Dye laser saturation spectroscopy of the 23 S 1-23 P transition in6, 7Li+ ions

The metastable 2³ S ₁ state and the short lived 2³ P states of the helium-like^{6, 7}Li⁺ ion spectra have been investigated by dye laser saturation spectroscopy in a low-energy Li⁺ ion-beam and fluorescence light detection. The hyperfine structure splittings of all the levels, the 2³ P fine structure intervals and the isotope shift of the 2³ S ₁-2³ P transitions have been measured. These measurements were made by application of a specially constructed tunable dye laser system capable of single-mode laser scans over more than 60 GHz.     

Messung der Zirkularpolarisation der 478 keV-Gammaquanten aus der Reaktion Li6(d,p)Li7 mit 2 MeV-Deuteronen

The circular polarizationP _γ of 478 keVγ quanta from the reaction Li⁶(d, pγ) Li⁷ with 2 MeV deuterons was measured by forward Compton scattering from magnetized iron. The protons were observed at 25° lab angle. The fast neutron background in theγ detector was suppressed by pulse shape discrimination. The resultP _γ=+ 0.022 ± 0.17 with the Basel sign convention confines the ratio of the reduced widthsΘ _± for the capture of the neutron withj=1±1/2 to the regions ?2.36≦Θ ₊/Θ _?≦?0.74 or ?0.06≦Θ ₊/Θ _?≦+0.61.     

K+3P-core excitons in potassium halides studied at low temperatures with high resolution

Reflection spectra of KF, KCl, KBr and KI single crystals have been measured at photon energies of approximately 20 eV with a bandwidth of 10 meV using synchrotron radiation in order to study fine structure and temperature dependence of the excitonic transitions associated with the K⁺3p core level. The crystals were cleaved under ultrahigh vacuum and cooled down to 20 K. Information on energy positions, halfwidths and line shapes for the K⁺3p-core excitons and their temperature dependence has been obtained. A new exciton predicted by the ligand field model was observed. For KI we evaluate an electron-hole exchange energy of only 30 (± 7) meV.