NaF Crystal Research Articles

Impact of γ-Irradiation on Separation of Nuclear Spin-Relaxation Mechanisms Under Magnetic Saturation in a NaF Crystal

Impact of γ-Irradiation on Separation of Nuclear Spin-Relaxation Mechanisms Under Magnetic Saturation in a NaF Crystal

Interfacial synthesis of Co-based ultrathin nanosheets with NaF crystal as template and inducer: fluorine doped Co(OH)2, porous fluorine doped Co3O4, and porous Co3O4

NaF crystals were used as the template and inducer, and fluorine doped cobalt hydroxy ultrathin nanosheets (F-Co(OH)2) were synthesized at room temperature. F-Co(OH)2 exhibits a petal-like morphology with a thickness of ∼1.7 nm. Porous fluorine doped Co3O4 ultrathin nanosheets (pF-Co3O4) and porous Co3O4 ultrathin nanosheets (p-Co3O4) were synthesized through the calcinations of F-Co(OH)2 at 230 °C and 330 °C, respectively. They exhibit a petal-like morphology with a thickness of ∼1.6 nm. pF-Co3O4 and p-Co3O4 have been applied for the catalytic oxidation benzyl alcohol. At the identical conditions, pF-Co3O4 achieved 100% benzyl alcohol conversion and 100% yield of benzaldehyde, and p-Co3O4 achieved 100% benzyl alcohol with 69.8% yield of benzaldehyde and 30.2% yield of benzoic acid. For the oxidation benzyl alcohol, both pF-Co3O4 and p-Co3O4 have exhibited much higher catalytic efficiencies than bulk Co3O4.

Ab initio Study on Spectral Properties of Charge-Compensated Ce3+ in NaF

We report an ab initio study of spectral properties of Ce3+ doped at Na+ site of the NaF crystal, with the charge imbalance compensated by two oxygen substitutions for fluoride (OF′) in the first coordination shell or two sodium vacancies (VNa′) in the second coordination sphere. Density functional theory calculations within the supercell model are first performed to optimize the local structures of the charge-compensated Ce3+, based on which Ce-centered embedded clusters are constructed and wave function-based CASSCF/CASPT2/RASSI-SO calculations are carried out to obtain the energies of 4f1 and 5d1 levels. By comparing the calculated 4f→5d transition energies with experimental excitation spectra at low temperatures, the lowest 4f→5d transition band peaked at 390 nm is assigned to the Ce3+ with charge compensation by two coordinating OF′ substitutions, rather than to the Ce3+ with compensation by two VNa′ vacancies, as proposed earlier. The electronic reason for the large redshift (by ∼8000 cm−1) of the lowest 4f→d transition as induced by the two nearby OF′ substitutions is analyzed in terms of the changes in the centroid shift and crystal-field splitting.

Formation of color centers and light scattering structures by femtosecond laser pulses in sodium fluoride

Modification of sodium fluoride crystal lattice by means of femtosecond laser pulses with λmax=800nm, energy 0.5mJ, duration 30fs and repetition rate 1kHz has been considered in the paper. Effective formation of simple and complex aggregate color centers and light scattering nanodefects in the channel of a laser beam in NaF crystal have been shown for the first time. Dependences of color centers concentration on the distance between the channel center and its periphery and along the channel have been presented. Influence of external focusing on color centers creation has been revealed. Explanations of the observed phenomena have been presented on the basis of nonlinear processes taking place under the effect of high-intensity femtosecond pulses.

EPR Investigation of the Structure of a Rhombic Co2+ Center in an NaF Crystal

The local structure of the rhombic Co2+ center in NaF crystal is investigated by using the perturbation formulas of electron paramagnetic resonance (EPR) gfactors gi(i = x,y, z) and hyperfine constants Ai for a 3d7 (Co2+) ion in rhombic octahedral symmetry based on a cluster approach. In these formulas, the contributions from the admixture among different states, covalency effect as well as rhombic crystal field are included. By studying the EPR data of the rhombic Co2+ center, one can reasonably obtain the local structural (or rhombic distortion) parameters ΔRc(≈ 0.268 Å) for the central Co2+ and ΔRp(≈ 0.181 Å) for the two F− ions along [100] and [010] axes closest to the Na+ vacancy VNa. The reasonableness of the results is also discussed.

Wave propagation in transversely isotropic plates in generalized thermoelasticity

In this paper, the boundary value problem in generalized thermoelasticity concerning the propagation of plane harmonic waves in a thin, flat, infinite homogeneous, transversely isotropic plate of finite width is solved. The frequency equations corresponding to the symmetric and antisymmetric modes of vibration of the plate are obtained. The limiting and special cases of the frequency equations have also been discussed. Finally, a numerical solution of the frequency equations for a NaF crystal is carried out, and the dispersion curves for the lowest six modes of the symmetric and antisymmetric vibrations are represented graphically at different values of thermal relaxation time.

Excitation of intrinsic and extrinsic luminescence by synchrotron radiation in a NaF crystal

The reflection spectrum as well as the excitation spectrum of self-trapped exciton emission at 2.6 eV has been measured in a NaF crystal at 5 K. The width of a forbidden band equals approximately 12.3 eV.

CU+ and OH− pairs defects interaction in NaF crystals

The presence of Cu + in OH - doped NaF crystal results in several new infrared absorption bands with ∼ 0.2 cm - halfwidth at 100 K, and their relative intensities are strongly impurity concentration dependent. Their assignments are not evident and are mostly attributed to different vibrational internal modes of the molecular OH - perturbed by neighboring Cu + ions. 1 We report the results of the temperature dependence of several OH- sidebands around the 3737.8 cm -1 'free' OH - stretching mode. The temperature dependence reveals a different behaviour from already known OH - quasi free rotor in several cesium halides. 2 For the temperature range from 100 to 300 K, the free OH - halfwidth shows a T 2 behaviour. While for three chosen absorption sidebands are determined to be T 1.6 , T 1.8 and T 2.5 . The lack of observable thermally stimulated depolarization current and electric field induced dichroism 3 indicates that the OH - is frozen-in, so it is also the same with the OH - -Cu + pairs.

Effect of Strong Electron-Phonon Interactions on an Interface Polaron

The present work deals with an electron interacting strongly with both bulk longitudinal optical (LO) phonons and interface (IF) optical phonons in which we adopt and generalize the Tokuda's variational method for studying the interface polaron properties in polar crystals at zero temperature, In our approach, we can reduce the Hamiltonian equation of the system to a pair of integro-differential equations in two variational parameters of the electron wavefunction from which we can calculate various physical properties of an interface polaron including the ground state energy, average numbers of interacting phonons, the average distance from the interface and the anisotropic effective masses of the interface polaron. Numerical results are obtained explicitly for LiF crystal interfaced with NaF crystal as well as other similar systems with varying physical constants, which show the typical trends of variations for the effects of strong electron-phonon interactions on different physical properties of an interface polaron.

On the calculation of the lattice energy of ionic crystals using the detailed electron-density distribution. I. Treatment of spherical atomic distributions and application to NaF

Ewald's method of accelerated convergence [Ewald (1921). Ann. Phys. (Leipzig), 64, 253–287] is generalized to calculate the electrostatic potential of a crystal in which the atoms have overlapping spherical densities. The algorithm is applied to the cubic NaF crystal. The potentials at the Na and F nuclei are calculated for the free-ion model and for the results from a κ refinement of the experimental data of Howard & Jones [Acta Cryst. (1977), A33, 776–783]. The κ refinement indicates an incomplete charge transfer but gives an electrostatic energy close to that of the point-charge model with full charge transfer and a lattice energy that is in good agreement with the experimental value.

Local geometry and resonant vibrations of Cu+:NaF. Results of ab initio perturbed ion, cluster-in-the-lattice calculations involving clusters of 179 ions

The ground state electronic structure and energy of a CuF92Na5−86 cluster (Cu+ plus 12 shells of neighbors) embedded into a quantum lattice representing the NaF crystal are determined by using the ab initio perturbed ion (aiPI) method, with unrelaxed Coulomb–Hartree–Fock (uCHF) correlation energy corrections. Parallel calculations are performed on the NaF92Na5−86 cluster of the pure crystal in order to identify the changes induced by the impurity and to estimate the systematic errors in our calculations. The geometry of the first four shells (32 ions) is allowed to relax by following symmetric breathing modes. An inwards relaxation of −0.12 Å is predicted for the nearest neighbors (nn) shell, but negligible relaxations are found for the outer shells. The substitution of the Na+ ion by the Cu+ impurity is favored by −1.03 eV. The Cu+ ion is found to occupy an on-center octahedral position. The 138 independent Oh force constants corresponding to the vibration of the Cu+ and its first four shells of neighbors are then numerically computed from the aiPI energy using a Richardson iterated, finite-difference limit formula. These force constants give the vibrational modes of the impurity center. Strong couplings are found among vibrational modes of adjacent shells. Vibration frequencies characteristic of the doped system are obtained at 206 cm−1 (1a1g), 108 cm−1 (1t1u), and 173 cm−1 (1eg) determined mainly by the motions of the CuF6 octahedron.

Phase-sensitive optical detection of ballistic phonon heat pulses using frequency-modulation spectroscopy and persistent spectral holes

With the use of laser frequency-modulation (FM) spectroscopy and persistent spectral holes, time-resolved phase-sensitive probing of ballistic phonon heat pulses is accomplished in the interior of a NaF crystal. The ballistic phonon heat pulses are generated by the absorption of a Nd:YAG (neodymium-doped yttrium aluminum garnet) laser pulse in a Cr film on the sample surface. Local measurement of the propagating stress-strain field is illustrated by detecting the modulation of a spectral hole in the inhomogeneously broadened 607-nm color-center absorption in x-irradiated NaF at liquid-helium temperatures. By examining the dependence of the observed phonon time-of-flight data on the polarization of the probing light, the position within the sample, and the phase of FM detection, an identification of the acoustic polarizations of the propagating phonons may be made. The effects of phonon focusing and mode conversion upon reflection must be taken into account to complete the identification. Along with the ability to determine the sign of the acoustic disturbance, this experiment features a strain detection limit of 4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ at a time resolution of 50 ns.

Inversion of molecular spectra by solid environments

It is demonstrated via full-CI cluster calculations of H 2 in a NaF crystal that it is possible for spectra of molecules embedded substitutionally in ionic crystals to be inverted as compared to those of the free state. Such inversions imply, in principle, the possibility of switching mechanisms for large amounts of molecular energy as a function of crystal distortion.

Rich counter using a solid radiator and a low pressure MWPC

A fast compact RICH counter using a NaF crystal as a radiator has been constructed for the first time. This detector was tested with β = 0.82 and β = 1 particles and the results will be presented. The NaF radiator serves also as a window and allows in this way a very compact and light construction. The use of such a detector for particle identification in medium-energy experiments will be shown.

Full Multiple-Scattering Approach to Na K-Edge XANES of NaCl–KCl Mixed Crystal

In this work we studied the Na K-edge XANES spectra of pure NaCl crystal and NaCl–KCl mixed crystal measured by Murata et al. to clarify the geometric and electronic structure around X-ray absorbing atoms by use of the short-range order full multiple scattering calculation. The changes observed in the experimental XANES for the increase of KCl concentration are qualitatively explained by assuming that in a very small scale Nail and KCl grains are to be in contact with each other. We also found that the Na–Cl distance in the boundary region remains nearly the same as in NaCl crystal. The net charge on Na ion in pure NaCl crystal is also estimated and found to be slightly smaller than that in NaF crystal.

Compact fast rich detector using a solid radiator: Principle and first experimental results

The principle and first experimental results for a compact fast RICH detector using a solid radiator (NaF crystal) are presented. This detector can be very thin (≅ 4 cm) and presents a small percentage of radiation length. First experimental results for β = 0.82 and β = 1 particles at different incident angles indicate a good determination of the ring diameter. This type of particle identifier may be quite useful in compact medium energy experiments.

A study of simple ionic crystals by a cluster-model approach. Application to the NaF.

The NaF crystal has been studied by means of a cluster-model formalism. The crystal energy has been obtained from different cluster calculations under reasonable assumptions. Numerical results reveal that electronic properties such as the equilibrium Na-F distance, cohesive energy, bulk modulus, and elastic constants are well predicted by the present approach.

Interatomic radiative transition rates for the sodium fluoride crystal.

Interatomic electric-dipole radiative transition rates for the NaF crystal are calculated for initial 1s, 2s, and 2p holes in the Na/sup +/ ion. The crystal is simulated by a (NaF/sub 6/)/sup 5 -/ cluster embedded in a large number of point ions, and the one-electron molecular orbitals are obtained from open-shell restricted-Hartree-Fock calculations of the initial state and final states. This allows the transition matrix element to be calculated in the self-consistent-field (..delta..SCF) formalism where both initial- and final-state determinantal wave functions are used, and the nonorthogonality of the two sets of molecular orbitals is taken into account. One interatomic radiative transition, the K..beta../sub 1/ satellite line, has been observed as a high-energy satellite of the Na K..cap alpha../sub 1/..cap alpha../sub 2/ line. The measured intensity ratio ..beta../sub 1/..cap alpha../sub 1/..cap alpha../sub 2/ is 1.2 x 10/sup -2/;our theoretical ratio is 1.13 x 10/sup -2/. This level of agreement between theory and experiment is similar to, but somewhat better than, that recently obtained by us for interatomic Auger transitions in NaF, using molecular orbitals from the same calculations. The other interatomic radiative transitions in NaF have considerably smaller transition energies and unobservably small transition rates. The sensitivity of the ratesmore » to the choice of Hartree-Fock Gaussian basis set is explored. Rates based on a single determinantal wave function are compared with the ..delta..SCF rates. The one-center approximation for the K..beta../sub 1/ rate was found to account for 82% of the rate« less

Determination of the scintillation light yield for NaF

An upper limit of the scintillation light yield for a NaF crystal is determined by means of a separate scintillators measurement in the single-photon method. The upper limit thus found using a 60Co source is equal to 10 −6 of that of NaI(Tl).

Interatomic Auger rates for the sodium fluoride crystal.

Interatomic Auger rates for the NaF crystal are calculated for initial 1s, 2s, and 2p holes in the ${\mathrm{Na}}^{+}$ ion. The crystal is simulated by a (${\mathrm{NaF}}_{6}$${)}^{5\mathrm{\ensuremath{-}}}$ cluster embedded in a large number of point ions, and the one-electron orbitals are obtained from restricted Hartree-Fock calculations of the initial state. The continuum-electron orbital is obtained from the Coulomb potential for a spherically averaged superposition of atomic charge densities for the initial state, and exchange is treated by the method of Riley and Truhlar. The continuum orbital is orthogonalized to the occupied molecular orbitals. The calculated Na(KLL) rate is about 20% greater than the experimental value. The calculated interatomic Auger widths for the transitions Na(1s)Na(2p)F(2p), Na(2s)Na(2p)F(2p), and Na(2p)F(2p)F(2p)' [following the notation of J. A. D. Matthew and Y. Komninos, Surf. Sci. 53, 716 (1975)] are 0.001 73, 0.641, and 0.153 eV, respectively. For comparison, the width of the Na(KLL) Auger transition is close to 0.26 eV. All three interatomic transitions have been identified by Citrin, Rowe, and Christman. Widths for the transitions Na(1s)Na(2p)F(2p) and Na(2p)F(2p)F(2p)' can be inferred from experimental data. Theory and experiment agree to within 50%. This represents a considerable improvement over previous theoretical treatments.