Large single-ion anisotropy and ferromagnetic intrachain interaction in four Ni-compounds of formula NiX2L2 with X = Cl,Br; L = N2C3H4, NC5H5

The specific heat has been measured of powdered samples of NiX₂L₂ (X = Cl, Br; L = pyrazole, pyridine), compounds which can be considered as weakly antiferromagnetically coupled ferromagnetic chains with large uniaxial single-ion anisotropy. The intrachain exchange constants and the zero-field splitting parameters for the four compounds have been deduced from the specific heat data, using accurate numerical calculations for the isotropic Heisenberg spin S = 1 linear chain model with uniaxial single-ion anisotropy.     

Luminescent properties of nanoparticles YPXV1−XO4:Dy phosphors

Phosphors of nanoparticles YP_XV_1−XO₄:Dy³⁺ (0?X?1) have been prepared by a citrate sol-gel method. X-ray diffraction, transmission electron microscope (TEM), scanning electron microscope (SEM) and photoluminescence excitation and emission spectra were utilized to characterize the phosphors. The results of XRD showed that a solid solution formed in YP_XV_1−XO₄:Dy³⁺ phosphor series from X=0 to X=1 with zircon structure. TEM and SEM studies revealed that the obtained YP_XV_1−XO₄:Dy³⁺ nanocrystals appeared to be spherical with some agglomeration and their sizes ranged from 30 to 80 nm. Upon short ultraviolet excitation, the optical properties of all the powder presented that the characteristic transitions of Dy³⁺ due to ⁴F_9/2-⁶H_15/2 (blue) and ⁴F_9/2-⁶H_13/2 (yellow) were detected. Besides this, in the system of YP_XV_1−XO₄:Dy³⁺, the yellow-to-blue intensity ratio (Y/B) depended on the value of P/V greatly, with the increasing of X value and the decreased Y/B value. The phosphor found to yield white light when the value of X in the range of X=0.775-0.85, the optimum concentration for Dy³⁺ is 1 mol% of Y in the host, and the emission intensity increased with the annealing temperature.     

Specific heat and crystalline electric field parameters in TmxY1−xAl2

Specific heat measurements on Tm_xY_1?xAl₂ have been performed to determine the crystalline electric field parameters in Tm_xY_1?xAl₂. We find for the ground state the Γ⁽¹⁾₅ triplet and for the Lea, Leask and Wolf parameters X = (0.47 ± 0.03) and W = (0.034 ± 0.013) meV.     

Rotational analysis of the A2Πi → X2Πr band system of the sulfur monoxide cation,SO+

Six bands in the 0-v″ progression and three bands in the 1-v″ progression of the A²Π_i → X²Π_r visible system of SO⁺ have been recorded photoelectrically and rotationally assigned. Molecular constants for v′ = 0 and 1 in the A state and for v″ = 4–9 in the X state have been obtained using direct fitting and merging techniques.     

Nuclear ferromagnetic resonance on Co2B and on some dilute alloys

The NMR of Co⁵⁹ at 4.2 K in the compound Co₂ B and in the series (Co_0.99X_0.01)₂B where X = Ti, V, Cr, Mn, Fe and Ni is developed in this paper. The NMR spectrum of Co₂B shows a single narrow line which indicates that the easy magnetization direction is parallel to the tetragonal axis. In a static external field the shift of the line indicates that the hyperfine field is negative.Spin-lattice relaxation time T₁ measurements show that the density of states at the Fermi level reaches a maximum in the vicinity of X = V, Cr, in agreement with previous magnetic, resistivity and specific heat investigations. These results are interpreted by the virtual bound state concept.     

The rotational spectrum of BiO radical in its X1Π1/2 and X2Π3/2 states

Rotational spectra have been observed for BiO produced in a DC discharge through a low pressure mixture of O₂, Ar, and Bi vapor. Because of the highly non-thermal distribution of states, it has been possible to observe spectra arising from the X₁²Π_1/2 level up to v = 9 and for the X₂²Π_3/2 level up to v = 5 near 10 538 cm⁻¹. Precise rotational and hyperfine parameters have been determined for the observed states. By using available near infrared (NIR) data in a merged fit, the 0-0 and 1-1 fine structure intervals have been more precisely determined. Although the quality of the fit is very good, the interpretation of the hyperfine constants is complicated by relativistic effects and the interaction of the X₂ state with A₁⁴Π_3/2 state. The magnetic and quadrupole coupling constants will be compared with those of the Bi atom and related molecules.     

Analysis of the Comet-Tail (AΠi-XΣ) Bands of CO

In the electronic emission spectrum of the isotopic carbon monoxide ion ¹³C¹⁶O⁺ molecule, seven bands of the comet-tail (A²Π_i-X²Σ⁺) system have been recorded and analyzed. The spin splitting in most observed lines of the bands 1-0, 2-0, 3-0, 4-0, 5-0, 2-1, and 7-1 comprising over 1900 lines has been recorded under high resolution by using conventional spectroscopy. The rotational analysis of bands has been performed by nonlinear least-squares procedures and by means of effective Hamiltonians of Brown et al., the rovibronic structure parameters have been obtained. As a result of multistaged and merged analysis of the currently obtained bands of the A-X system and of the bands of the B-X system obtained earlier the state of information about the energy structure has been significantly enlarged for the A state and enlarged and improved for the X state. Also RKR potential curves have been calculated for both states and Franck-Condon factors as well as r-centroids of the comet-tail system of ¹³C¹⁶O⁺.     

Determination of the B1Π-X1Σ and C1Σ-X1Σ electronic transitions strengths of CaO

The strengths S_e of the B¹Π-X¹∑ and C¹∑-X¹∑ electronic transitions of the CaO molecule have been determined by absorption measurements in a shock tube. Powdered calcium oxide and a gaseous mixture of oxygen and argon in the ratio of 1:5 or 1:9 were introduced into the shock channel. The CaO gas-phase concentration was determined by using the equilibrium constant for CaO?Ca+O; atomic oxygen concentration was calculated and that of calcium was measured spectroscopically. The values of S_e (in atomic units) are for B¹Π-X¹∑, 2.32±0.49; for C¹∑-X¹∑, 2.88±0.67.     

Solid solution formation in the systems CuMIIIX2-AgMIIIX2 where MIII=Al,Ga, In and X2=S,Se

A study of solid solution formation in the systems CuAlX₂-AgAlX₂, CuGaX₂-AgGaX₂ and CuInX₂-AgInX₂, where X=S, Se, has shown that when M^III=Al and Ga, CuM^IIIX₂ and AgM^IIIX₂ were not completely miscible. The CuInX₂-AgInX₂ system, however, showed complete solid solubility. The limits of solid solubility are explained in terms of the c/a ratio, and the internal atomic coordinate u. The lattice constant a is a linear function of composition, while c bows upwards. This behavior is also discussed in terms of trends in 2-c/a.     

The properties of five highly conducting salts: (TMTSF)2X, X = PF6-, AsF6-, SbF6-, BF4- and NO3-, derived from tetramethyltetraselenafulvalene (TMTSF)

The properties of five new highly conducting salts of TMTSF, (TMTSF)₂X, X = PF₆^-, AsF₆^-, SbF₆^-, BF₄^- and NO₃^- are reported. The measurements include d.c. and m.w. conductivity, thermopower, optical reflectivity, magnetic susceptibility and ¹⁹F-NMR. Preliminary structural data indicate uniform donor stacks. Metal to insulator transitions in four materials occur below 20 K, where specific conductivities higher than 10⁵ (Ω-cm)^?1 are observed for two salts (X = PF₆^- and NO₃^-).     

Determination of the B1II-X1Σ and C1Σ-X1Σ electronic transitions strengths of CaO

The strengths S_e of the B¹II-X¹Σ electronic transitions of the CaO molecule have been determined by absorption measurements in a shock tube. Powdered calcium oxide and a gaseous mixture of oxygen and argon in the ratio of 1:5 or 1:9 were introduced into the shock channel. The CaO gas-phase concentration was determined by using the equilibrium constant for CaO?Ca + O; atomic oxygen concentration was calculated and that of calcium was measured spectroscopically. The values of S_e (in atomic units) are for B¹II-X¹Σ, 1.7 ± 0.5; for C¹Σ-X¹Σ, 2.1 ± 0.6.     

Preparation and properties of disordered NaBi(XO4)2, X=W or Mo, crystals doped with rare earths

NaBi_1−xRE_x(XO₄)₂, X=W or Mo and RE=Pr, Nd, Ho, Er and Yb single crystals have been grown by the Czochralski technique. Rare earth concentrations about 3.5×10²⁰ cm⁻³ have been achieved in crystals with good optical quality. Melt stability is obtained by synthesising NaBi(XO₄)₂ from the precursor Na₂X₄O₁₃ phase and minimising Mo volatility. The strength of W and Mo compounds to chemical attack and thermal annealing in several atmospheres is reported. Mo compound is etched by inorganic acids and becomes coloured after vacuum annealing. The optical absorption, photoluminescence and refractive indices of the hosts are characterised and show a dichroic character. The lattice disorder induces broadening of the 10 K optical absorption of the rare earth impurities.     

The aΔg→XΣg magnetic dipole transition of S2

Emission spectra of the 0-0 band of the a¹Δ_g→X³Σ⁻_g magnetic dipole transition of S₂ have been observed in the near-infrared spectral region near 4400 cm⁻¹. The S₂ molecules were generated in a fast-flow system by passing S_x or S₂Cl₂ vapor in Ar carrier gas through a microwave discharge and were excited by electronic-to-electronic energy transfer from metastable singlet oxygen O₂(a¹Δ_g). Medium-resolution spectra of the b¹Σ⁺_g→X³Σ⁻_g and a¹Δ_g→X³Σ⁻_g transitions of S₂ were measured with a Fourier-transform spectrometer. By comparing the bandshape of the 0-0 band of the a→X system with a computer simulation calculated with literature data of the rotational constants of the X and a states, the origin of the 0-0 band was determined to be ν₀=4394.25±0.2 cm⁻¹.     

Laser spectroscopy of the B[21.68]8-X8, B′[21.65]8-X8 and C[22.3]7-X27 transitions of holmium monofluoride

The spectrum of holmium monofluoride (HoF) in the blue (420-480 nm) region has been studied using laser-induced fluorescence. Previous work [J. Phys. B 7 (1974) L234] had assigned several bands in this region to the B8-X8 transition. By obtaining wavelength selected laser excitation spectra at high resolution and rotationally analyzing seven bands in this region, we have shown that not all the bands previously assigned to the B8-X8 system belong to the same electronic transition and have identified three separate transitions which we have labelled B8-X8, B′8-X8, and C7-X₂7. Preliminary low resolution dispersed fluorescence spectra have shown several excited states at energies greater than 4000 cm⁻¹ above the ground state and, though not all could be assigned, ligand field theory calculations are consistent with assigning them to the first excited spin-orbit component of the Ho⁺(4f¹⁰6s²)F⁻ ground state configuration or to the first excited configuration, Ho⁺(4f¹¹6s)F⁻. The results of the dispersed fluorescence experiments also tentatively place the X₂7 state at ∼70 cm⁻¹ above the ground X7 state.     

The bΣ(b0) → XΣ(X10,X21) and aΔ(a2) → X21 transitions of AsBr

Emission spectra of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺,X₂1) and a¹Δ(a2) → X₂1 transitions of AsBr have been measured in the near-infrared spectral region with a Fourier-transform spectrometer. The arsenic bromide radicals were generated in fast-flow systems by reaction of arsenic vapor (As_x) with bromine and were excited by microwave-discharged oxygen. The most prominent features in the spectrum are the Δv = +1,0,−1, and −2 band sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺) transition in the range 11 700-12 700 cm⁻¹. With lower intensities, the Δv = 0 and −1 sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₂1) sub-system show up in the same range. Further to the red, between 6000 and 6700 cm⁻¹, the Δv = 0, +1, and −1 sequences of the hitherto unknown a¹Δ(a2) → X₂1 transition are observed. Analyses of medium- and high-resolution spectra have yielded improved molecular constants for the X₁0⁺, X₂1, and b0⁺ states and first values of the electronic energy and the vibrational constants of the a2 state.     

High-resolution study of the bΣ(b0)→XΣ(X10) transition of PI

Emission spectra of the b¹Σ⁺(b0⁺)→X³Σ⁻(X₁0⁺) transition of phosphorus iodide have been measured with a high-resolution Fourier-transform spectrometer. The PI radicals were generated and excited in a fast-flow system by reaction of phosphorus vapor (P_x) with iodine and microwave-discharged oxygen. Four sequences, Δv=0,+1,−1,−2, of the b¹Σ⁺(b0⁺)→X³Σ⁻(X₁0⁺) transition of PI comprising 28 bands were observed. Six bands were measured at high spectral resolution. Vibrational and rotational analyses have yielded accurate spectroscopic constants of the X₁0⁺ and b0⁺ states (in cm⁻¹): X₁0⁺: ω_e=371.296(4), ω_ex_e=1.3302(9), B_e=0.1194117(2), α_B=−0.0005676(7), D_e=4.56(2) ×10⁻⁸; b0⁺: T_e=11136.921(4), ω_e=400.165(6), ω_ex_e=1.345(2), B_e=0.1239237(2), α_B=−0.0005540(2), D_e=4.84(5) × 10⁻⁸, where the numbers in parentheses are the standard deviations of the parameters. No emissions of the b0⁺→X₂1 sub-system nor of the a¹Δ(a2)→X³Σ⁻(X₂1) transition have been observed leaving PI the only group Va halide for which the spin splitting in the X³Σ⁻ ground state is still unknown.     

Scattering parameters from an analysis of the hall electron mobility in Ga1−xAlxAs alloys

Hall mobilities in high purity epitaxial layers of n-type Ga_1?xA_xAs alloys with room-temperature electron concentrations in the range (5–10) × 10¹⁵ cm^?3 have been measured at 300 K for alloy compositions in the range 0? x ? 0.78. Models for the variation of various material parameters with composition are developed. The acoustic deformation potentials for the Π and X conduction band minima, the intervalley coupling constants for electron scattering among the X-X and L-X minima and the longitudinal optical phonon temperature for these scatterings and the polar optical scattering in the X minima have been determined from a theoretical fit to the experimental data. The electron mobilities in the Π, L and X minima are found to decrease with the composition in the range 0≦ x ? 0.45, show a minimum at x ? 0.50 and then increase again with composition. These mobility variations are reflected in the minimum in the Hall mobility at x ? 0.5 due to intense non-equivalent electron scattering involving the L and x minima. The minimum in the electron mobilities in the Π and X minima have been identified to occur mainly due to the space charge and intervalley scattering among the L and X minima, respectively. The number of equivalent x minima in Ga_1?x Al_x As alloys are estimated to be three and are, thus, situated at the zone edge.     

Tetragonal distortion for AIBIIICVI2 chalcopyrite compounds

Pauli-force constants and Simons-Bloch radii for the atoms of groups IB, III and VI are reported. The latter have been used to define a dimensionless quantity ΔX_ch which is found to be correlated in an analytical way with the observed tetragonal distortion δ of A^IB^IIIC^VI₂ type chalcopyrite compounds.     

NMR relaxation of 7Li in concentrated lithium-ammonia solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li in lithium-ammonia solutions have been measured at -57°C over the concentration range X_Li = 0.01–0.20 (X_Li: mole fraction of Li). The Knight shift increases with increasing metal concentration, while the relaxation rate, 1/T₁, shows a broad minimum around X_Li = 0.07.     

Vibrational analysis of the a3Σ+-X1Σ+ and b3Π-X1Σ+ band systems of GeS

Spectra of GeS have been obtained in a chemiluminescent flame produced by the reaction Ge + OCS → GeS + CO. Neither of the known band systems, D¹Π-X¹Σ⁺ and E¹Σ⁺-X¹Σ⁺, was observed, but two new band systems in the regions 350–400 and 420–650 nm were obtained. By comparison with similar systems in isovalent molecules, these were assigned as b³Π₁-X¹Σ⁺ and a³Σ⁺-X¹Σ⁺, respectively. Vibrational assignments were made with the help of the germanium isotope effect and vibrational constants were obtained for the states involved. Approximate Morse potential Franck-Condon factors were computed and were shown to fit the general trend of the intensity distribution for both systems. Addition of active nitrogen to the flame was shown to increase the intensity of the b-X system by an order of magnitude while hardly affecting the a-X system. Constants (in cm^?1) obtained for the two new states are: a³Σ⁺: T_e = 21986.3 ± 2.3, ω_e = 388.9 ± 1.0, ω_ex_e = 1.35 ± 0.11; b³Π₁: T_e = 27192.0 ± 1.8, ω_e = 435.4 ± 1.1, ω_ex_e = 1.68 ± 0.20.