Solid-state gallium NMR characterization of cubic gallium nitride prepared by the reaction of gallium arsenide with ammonia

The reaction of cubic gallium arsenide (GaAs) with ammonia yielded gallium nitride (GaN). Powder X-ray diffraction patterns of the GaN products showed that they are a mixture of c- and w-GaN, while their Ga MAS NMR spectra revealed that they have the other phase of GaN besides c- and w-GaN and the high reaction temperature (≥900 °C) induces nitrogen deficiency in GaN. The peaks at 353 and 347 ppm in the ⁷¹Ga MAS NMR spectra were tentatively assigned to c-GaN and an intermediate of w- and c-GaN in the stacking order, respectively. The observed ⁷¹Ga chemical shifts of GaN, GaP, GaAs and GaSb in cubic phase were well correlated with the reciprocal of their band gaps.     

The Pb–Pb and O–Pb Nuclear Spin Coupling in Ba(Pb,Bi)O3 Oxides

We report the ¹⁷O, ²⁰⁷Pb NMR and ¹⁷O–²⁰⁷Pb SEDOR study of superconducting BaPb_1-x Bi _x O₃ (x 0.35) oxides. Inhomogeneous The results points to the formation of microscopically inhomogeneous distribution of the carrier density in metallic phase. The local spin susceptibility is increased around Bi cation within an area, which is delimited by its two first cation shells.     

Characterization of wurtzite indium nitride synthesized from indium oxide by In-115 MAS NMR spectroscopy

Wurtzite indium nitride (w-InN) powders synthesized from the reaction of indium oxide (In₂O₃) with ammonia were characterized by ¹¹⁵In magic-angle spinning (MAS) NMR spectroscopy and nitrogen analyzer. The powders were not a single phase of w-InN but a mixture of w-InN and In-incorporated w-InN. The incorporation of In metal in InN lattice due to thermal decomposition caused the ¹¹⁵In MAS NMR peak of w-InN to be downfield shifted and might be responsible for the increase in the band gap of w-InN.     

Mechanisms of Yb sensitization to Tm for blue upconversion luminescence in fluorophosphate glass

The sensitization mechanisms of Yb³⁺ to Tm³⁺ for the blue upconversion luminescence in fluorophosphate glass were studied. Two different mechanisms exist in the sensitization. One is the sequential sensitization that Tm³⁺ is excited from ³H₆ to ¹G₄ through absorbing three photons transferred from Yb³⁺ one by one. Another is the cooperative sensitization that two Yb³⁺ ions form a couple cluster firstly, and then the couple cluster Yb³⁺ ions transfer their energy to Tm³⁺ and excite it to ¹G₄. With the increment of the concentration of Yb³⁺ ions, the sequential sensitization becomes weak and the cooperative sensitization becomes intense, and the transformation trend of sensitization mechanism with the increment of Yb³⁺ concentration can be clarified by the introduction of Tb³⁺ ions in the glass.     

11B nuclear magnetic resonance in boron-doped diamond

Abstract

This review summarizes recent results obtained by ¹¹B solid-state nuclear magnetic resonance (NMR) on boron-doped diamond, grown by the high-pressure high-temperature (HPHT) or chemical vapor deposition techniques. Simple single-pulse experiments as well as advanced two-dimensional NMR experiments were applied to the boron sites in diamond. It is shown that magic-angle spinning at magnetic fields above 10 T is suitable for observation of high-resolution ¹¹B spectra of boron-doped diamond. For boron-doped HPHT diamonds, the existence of the excess boron that does not contribute to electrical conductivity was confirmed and its ¹¹B NMR signal was characterized. The point-defect structures (B+H complexes and -B-B-/-B-C-B- clusters), postulated previously for the excess boron, were discarded and graphite-like structures were assigned instead.     

11B nuclear magnetic resonance in boron-doped diamond

This review summarizes recent results obtained by ¹¹B solid-state nuclear magnetic resonance (NMR) on boron-doped diamond, grown by the high-pressure high-temperature (HPHT) or chemical vapor deposition techniques. Simple single-pulse experiments as well as advanced two-dimensional NMR experiments were applied to the boron sites in diamond. It is shown that magic-angle spinning at magnetic fields above 10 T is suitable for observation of high-resolution ¹¹B spectra of boron-doped diamond. For boron-doped HPHT diamonds, the existence of the excess boron that does not contribute to electrical conductivity was confirmed and its ¹¹B NMR signal was characterized. The point-defect structures (B+H complexes and -B-B-/-B-C-B- clusters), postulated previously for the excess boron, were discarded and graphite-like structures were assigned instead.     

Spin-Orbital Dynamics in the B-Phase of Superfluid Helium-3

We report numerical calculations on the spin–orbital dynamics of ³He-B within the formalism of Poisson brackets with the two-fluid model by Leggett and Takagi. We incorporate an additional orbital term in the equations for the spin–orbit dynamics which plays an important role at very low temperatures, when the damping of orbit dynamics is small. We also find that, under the relevant experimental conditions, the Brinkman–Smith mode is strongly modified by the orbital dynamics. The orbital momentum does not relax completely to the direction of magnetic field, but remains significantly deflected, particularly at very low temperatures, and precesses at the dipole–dipole frequency and nutate at the NMR frequency. We report numerical calculations of the spin–orbit dynamics in the spatially inhomogeneous case. We solved for the mode of precession near the walls of the experimental cell, which significantly deviates from that, obtained in theoretical calculations in previous publications. We also identified the mechanism of instability of homogeneous precession at very low temperatures, the exponential growth of textural-spin waves of the longitudinal mode of NMR.     

Luminescence of Yb, Yb co-doped silica glass for white light source

Yb²⁺, Yb³⁺ co-doped silica glasses were prepared by solid state reaction under vacuum condition for the first time. The luminescence properties of Yb²⁺-doped silica glass were investigated. There are four strong absorption bands in the Ultraviolet (UV) light region due to the 4f¹⁴-4f¹³5d¹ transition of the Yb²⁺ ions. The main emission wavelength of the Yb²⁺-doped silica glass was around 530 nm by the excited wavelength of 398 nm. The full width at half maximum (FWHM) of the excitation and emission bands were 137 nm, 165 nm respectively. The results suggest the Yb²⁺-doped silica glasses may be the potential medium for white light sources based on near UV LED chip.     

Temperature dependence of luminescence behavior in Er/Yb co-doped transparent phosphate glass ceramics

The effect of temperature on the luminescence intensity of up-conversion and near infrared in Er³⁺/Yb³⁺ co-doped phosphate glass ceramics has been investigated. Efficient green and red up-conversion luminescence and strong infrared fluorescence at 1.54 μm wavelength are observed under excitation of 975 nm. The fluorescence intensity is changing at different temperature and the results are explained with the level transitions in Er³⁺/Yb³⁺ co-doped system. Meanwhile, the lifetime of Er³⁺:⁴I_13/2 level corresponding to different operating temperature and pump power is also discussed, and the experimental results are fitted using multiphonon relaxation theory.     

Coupling characteristics and kurtosis parameter of partially coherent beams in turbulent atmosphere

Coupling properties and kurtosis parameter (K parameter) of arbitrary beams propagating through atmospheric turbulence are investigated. A correlation factor (C⁴-factor) is introduced to describe the influence of turbulence on coupling characteristics. The general analytical expression for C⁴-factor of arbitrary beams in atmospheric turbulence is derived. It is shown that C⁴-factor of arbitrary beams in the turbulent atmosphere depends on the initial second-order moments and fourth-order moments and turbulence quantities. Taking the partially coherent anomalous elliptical hollow Gaussian (PCAEHG) beam as an example, we can obtain that C⁴-factor decreases as structure constant of the refractive index fluctuations and inner scale increase, and waist width and transverse coherence length decrease when z?>?5?km. Moreover, K parameter of PCAEHG beam in turbulent atmosphere converges to 2 when propagation distance is large enough. It indicates that the profile of PCAEHG beams in turbulent atmosphere finally evolves into fundamental Gaussian distribution.     

NMR Studies of the Dynamic Motion of Encapsulated Ions and Clusters in Fullerene Cages: A Wheel Within a Wheel

Nuclear magnetic resonance (NMR) has provided an important approach to investigate the structure and dynamics of encapsulated metal ions and clusters in endohedral metallofullerenes (EMFs). In this paper, we review NMR studies of the environment and dynamics of dimetallic, trimetallic nitride, metal carbide and metal cyanide clusters encapsulated in EMFs. The NMR chemical shielding parameter is a sensitive probe for monitoring the carbon cage (¹³C) and encapsulated clusters (¹³C, ¹⁴N, ¹³⁹La, ⁴⁵Sc, and ⁸⁹Y). Future NMR EMF studies could be very fruitful and help elucidate coupled motion between the carbon cage and encapsulated cluster or other “wheel within a wheel” motional processes.     

A study on hydration behaviors of interlayer cations in montmorillonite by solid state NMR

Solid state ²³Na NMR spectra of Na-montmorillonite under dry and hydrated conditions have been measured to study hydration structure of Na⁺ in interlayer spaces. The ²³Na triple quantum (3Q) MAS NMR experiments have been performed to determine the quadrupole coupling constants (C_Q) and the isotropic chemical shifts (δ_iso). The C_Q values were found to remarkably depend on water content, i.e. the C_Q values increase with changing from dry condition to hydrated one (at around 12.5 wt% water content) and gradually decrease with an increase in the water content. Since the C_Q value is a sensitive parameter to the local structure of the nucleus measured, the changes in C_Q values with water content should correspond to those in the hydration structure of Na^C in the interlayer spaces. Thus, it is considered that the increment of the C_Q value in the water content of 12.5 wt% is due to the formation of hydrated Na⁺ with planner structure, and that the decrease in C_Q values with the water content is attributed to the formation of hydrated Na⁺ with spherical symmetric structure.     

A study on hydration behaviors of interlayer cations in montmorillonite by solid state NMR

Solid state ²³Na NMR spectra of Na-montmorillonite under dry and hydrated conditions have been measured to study hydration structure of Na⁺ in interlayer spaces. The ²³Na triple quantum (3Q) MAS NMR experiments have been performed to determine the quadrupole coupling constants (C_Q) and the isotropic chemical shifts (δ_iso). The C_Q values were found to remarkably depend on water content, i.e. the C_Q values increase with changing from dry condition to hydrated one (at around 12.5 wt% water content) and gradually decrease with an increase in the water content. Since the C_Q value is a sensitive parameter to the local structure of the nucleus measured, the changes in C_Q values with water content should correspond to those in the hydration structure of Na⁺ in the interlayer spaces. Thus, it is considered that the increment of the C_Q value in the water content of 12.5 wt% is due to the formation of hydrated Na⁺ with planner structure, and that the decrease in C_Q values with the water content is attributed to the formation of hydrated Na⁺ with spherical symmetric structure.     

Experiments on the Twisted Vortex State in Superfluid 3He-B

We have performed measurements and numerical simulations on a bundle of vortex lines which is expanding along a rotating column of initially vortex-free ³He-B. Expanding vortices form a propagating front: Within the front the superfluid is involved in rotation and behind the front the twisted vortex state forms, which eventually relaxes to the equilibrium vortex state. We have measured the magnitude of the twist and its relaxation rate as function of temperature above 0.3T _c. We also demonstrate that the integrity of the propagating vortex front results from axial superfluid flow, induced by the twist.      

Structural investigation of polydiacetylenes: A variable temperature solid state13C CP/MAS NMR study

The spectral features in the solid state¹³C CP/MAS NMR of poly (1,1,6,6-tetraphenylhexadiyn diamine) (poly(THD)) are compared with X-ray diffraction. The NMR data suggests that acetylenic carbons are nonequivalent in the unit cell resulting in two resonances. On the other hand, a single acetylenic carbon resonance was observed for poly (1,6-di-N-carbozolyl-2,4-hexadiyne) (poly(DCH)). The orientation of side groups in the crystal structures of poly(DCH) and poly(THD) are responsible for equivalence and nonequivalence of acetylenic carbons. The structural changes due to thermochromic transitions are monitored by variable temperature solid state NMR. The solid state VT NMR data suggest that the backbone and side chain conformations of blue phase and red phases of poly(bis-n-propyl urethane of 5,7-dodecadin-1,12-diol) (poly(PUDO)) are distinctly different. For the first time, we present a solid state NMR spectrum showing the presence of both the blue and red phases of this polymer at the thermochromic transition temperature (ca. 115–125°C).     

Effect of H+ ion irradiation on surface morphology of Fe40Ni40B20 metallic glass

The effect of irradiation by H⁺ ions on surface modifications of metallic glass Fe₄₀Ni₄₀B₂₀, in the as-quenched, structurally related and crystallized state, has been studied. Swollen regions develop on the surface of the as-quenched and structurally relaxed specimens, whereas blisters form on the surface of the crystallized specimen, under identical conditions of irradiation. The results are explained in terms of the distribution of hydrogen in the amorphous and crystallized conditions.     

White light emission of Dy3+-doped and Dy3+:Yb3+-codoped oxyfluoride glass ceramics under 388-nm excitation

Dy³⁺-doped and Dy³⁺:Yb³⁺-codoped oxyfluoride glass ceramics have been prepared by high-temperature solid phase sintering method. The micrographs of scanning electron microscope show that a lot of nanorods are formed on the surface of Dy³⁺:Yb³⁺-codoped sample. The excitation spectra and emission spectra are measured, respectively, and intense photoluminescence peaks at 482 and 575 nm corresponding to the transitions of Dy³⁺ ions are found in single-doped samples under 388-nm excitation. For Dy³⁺:Yb³⁺-codoped oxyfluoride glass ceramics, the intensities at blue and green bands become weaker whereas the intensity at 695 nm gets stronger. The indirect sensitization is detailedly discussed and Commission Internationale de l′E-clairage chromaticity coordinates exhibit that two kinds of oxyfluoride glass ceramics are available candidates for the solid-state white light emission.     

Optical properties of divalent samarium-doped fluorochlorozirconate glasses and glass ceramics

Glass ceramics comprising Sm²⁺-doped barium chloride in both hexagonal and orthorhombic phases embedded in a fluorochlorozirconate glass matrix have been prepared. Divalent samarium doping was effected with the aid of NaBH₄ to partly reduce Sm³⁺ in the starting materials to Sm²⁺. The optical absorption spectrum in unannealed samples shows a strong, broad 4f → 5d band centred at around 340 nm and attributed to Sm²⁺, but no photoluminescence is observed. Following annealing to induce crystallisation of Sm²⁺-doped barium chloride crystals in the glass, photoluminescence is observed in the form of sharp line 4f → 4f transitions, and two broad 5d → 4f bands, the latter centred at around 680 and 900 nm. The 680 nm band disappears below about 250 K whilst the 900 nm band intensity increases with decreasing temperature. The 4f → 4f transitions for Sm²⁺ ions in the orthorhombic phase of barium chloride show an abrupt change in the relative intensity of transitions originating from the ⁵D₁ and ⁵D₀ levels at around 90 K. The effect is attributed to the role of the 5d level in thermally assisted indirect transitions between the ⁵D₁ and ⁵D₀ levels. In contrast, transitions from only the ⁵D₀ level are observed for the hexagonal phase. The temperature dependence of the photoluminescence intensity, and the observation of a different crystal field splitting pattern for the ⁷F₁ level, can be used to distinguish between the two phases. The splitting pattern for the ⁷F₁ level for the hexagonal phase of barium chloride suggests that both possible crystallographic barium sites are occupied by Sm²⁺ ions.     

Effect of aluminium alkoxide with donor-functionalized group on texture and morphology of the alumina prepared by sol-gel processing

A new aluminium alkoxide, Al(OCH₂CH₂OCH₂CH₂OCH₃)₃, with donor-functionalized group was prepared and characterized by elemental analysis, mass spectrometry, and ¹H, ¹³C and ²⁷Al NMR spectroscopy. The prepared aluminium alkoxide was used as a precursor for the synthesis of alumina by the sol-gel processing. The physiochemical properties of alumina that were obtained from hydrolysis of Al(OCH₂CH₂OCH₂CH₂OCH₃)₃ were investigated and compared with that of alumina synthesized from aluminium 2-butoxide. Utilizing Al(OCH₂CH₂OCH₂CH₂OCH₃)₃ as a precursor in sol-gel processing resulted in formation of alumina with significantly lower surface area, smaller pore volume, and pore size in comparison with alumina obtained from aluminium 2-butoxide. A novel morphology was observed for the alumina prepared from aluminium alkoxide with donor-functionalized group.     

A non-solvent approach for high-stiffness all-cellulose biocomposites based on pure wood cellulose

All-cellulose composites are commonly prepared using cellulose solvents. In this study, moldable all-cellulose I wood fiber materials of high cellulose purity (97%) were successfully compression molded. Water is the only processing aid. The material is interesting as a “green” biocomposite for industrial applications. Dissolving wood fiber pulps (Eucalyptus hardwood and conifer softwood) are used and the influence of pulp origin, beating and pressing temperature (20–180 °C) on supramolecular cellulose nanostructure is studied by solid state CP/MAS ¹³C NMR. Average molar mass is determined by SEC to assess process degradation effects. Mechanical properties are determined in tensile tests. High-density composites were obtained with a Young’s modulus of up to 13 GPa. In addition, nanoscale cellulose fibril aggregation was confirmed due to processing, and resulted in a less moisture sensitive material.