EPR studies of Gd3+-doped Ce2(SO4)3.8H2O and La2(SO4)3.9H2O single crystals

EPR spectra of Gd³⁺-doped Ce₂(SO₄)₃.8H₂O and La₂(SO₄)₃.9H₂O single crystals have been measured with an X-band spectrometer at room and low temperatures. The absolute signs of spin Hamiltonian parameters have been determined for the La₂(SO₄)₃.9H₂O host from intensities of lines at liquid helium temperature; for the Ce₂(SO₄).8H₂O host the lines broaden considerably below 60 K, not permitting the determination of absolute signs of spin Hamiltonian parameters. The data are analysed using a rigourous least-squares procedure, fitting simultaneously all lines obtained for several orientations of the external magnetic field. The zero-field splittings have been computed for both the hosts. The characteristics of EPR spectra of Gd³⁺ in these hosts are compared with those obtained in other rare-earth trisulphate octahydrate hosts.     

Optical and electrical characterization of cadmium selenide doped with cobalt

The optical and electrical properties of Co²⁺ ions in CdSe have been investigated. Absorption, photoluminescence, electron paramagnetic resonance, and Hall measurements were used to characterize a cobalt-doped (1×10¹⁹ cm⁻³) single crystal. Infrared absorption and emission spectra associated with transitions between the ⁴A₂(F) ground state and the ⁴T₁(F) and ⁴T₂(F) excited states are described. At 10 K, spin-orbit splittings result in three structured absorption bands associated with the ⁴A₂(F) to ⁴T₁(F) transition having zero-phonon lines at 4926, 5101, and 5724 cm⁻¹. The ⁴A₂(F) to ⁴T₂(F) transition shows two zero-phonon lines at 2874 and 3286 cm⁻¹, also accompanied by vibronic structure. Intrinsic lattice modes explain most of the sharp-line structure observed at low temperature, except for a subset of peaks where local modes (25-30 cm⁻¹) are invoked. Using below-band-gap light, selective excitation allows detection of the ⁴T₁(F) to ⁴A₂(F) recombination at liquid-helium temperatures. The activation of free carriers in our n-type material containing shallow donors is affected by the presence of cobalt, and we find the Co^+/++ level to be about 34 meV below the conduction band of CdSe.     

Spectre d'absorption et effet Zeeman de l'ion Mn2+ dans un sulfate acide de manganese et de potassium MnK4H2(SO4)4, 2H2O a basse temperature

We present aborption spectra of an oriented single crystal of MnK₄H₂(SO₄)₄, 2H₂O at temperatures between 20 and 1.6 K. This salt has orthorhombic symmetry and gives, both in the visible and ultraviolet regions, an absorption spectrum which changes considerably when the temperature decreases from 20 to 4.2 K. The spectrum has sharp lines at 1.6 K in the two absorption regions corresponding to teh excited levels ⁴A₁⁴E(⁴G) and ⁴T₂(⁴D). A study has been made of the Zeeman splitting of these sharp lines; a discontinuity has been observed in the Zeeman splitting as a function of magnetic field at 1.6 K. This discontinuity is a consequence of a magnetically-ordered phase.     

The detection of trinitrotoluene by pure nuclear quadrupole resonance

The data of the observation of the nuclear quadrupole resonance signal in trinitrotoluene C₆H₂(NO₂)₃CH₃ are reported. The measurements are carried out on a crude industrial sample of the Chinese manufacturing at 293 K. It is shown that the lines of the monoclinic form and probably orthorhombic forms are present in our spectra, but the most suitable lines for the detection of trinitrotoluene belong to the monoclinic form. The results of our experiments specify an opportunity of application of the pulse method of nuclear quadrupole resonance for the detection of trinitrotoluene in crude industrial samples.     

Analyses of the thermal shifts of spectral lines in Nd3+-doped LiYF4 laser crystal

The red-shift of spectral line E ₁(R ₁????Y ₂) and blue-shift of line E ₂(R ₁????X ₅) with temperature in Nd³⁺-doped LiYF₄ laser crystal are studied by considering both the static contribution due to lattice thermal expansion and vibrational contribution due to electron?Cphonon interaction. The study is based on the analyses of pressure and temperature dependences of these spectral lines. It is found that for both lines, the static and vibrational contributions result in the blue- and red-shift, respectively. So, the observed red-shift of line E ₁ and blue-shift of line E ₂ are due respectively to the static contribution being smaller and larger than the vibrational one. Also, we infer that the thermal shifts of lines E ₃(R ₁????Y ₅) and E ₄(R ₂????Y ₅) are very small because both contributions may be approximately canceled. When both the contributions are contained, whether the red-shift or blue-shift of a spectral line can be fitted with the almost same theoretical expression as that by including only the vibrational contribution used in red-shift in the previous papers if we change the expression concerning electron?Cphonon interaction coefficient.     

Modified multipulse technique for the effective detection of pure nuclear quadrupole resonance

Modification of the steady-state free precession (SSFP) multipulse technique for the effective detection of nuclear quadrupole resonance (NQR) signals was studied. This modification is based on the use of the preparatory pulse in the SSFP pulse sequences. It was shown that under certain conditions the total intensity of accumulated NQR signal can be increased. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of sodium nitrite (NaNO₂) are presented and convincingly demonstrate the technique’s effectiveness.     

Chemical shifts of Cr Kα and Kβ1, 3 lines by WDXRF spectrometry

Chemical shift and full widths at half maximum (FWHM) intensity of chromium Kα and Kβ_{1, 3} lines were examined for 12 kinds of materials containing chromium (CH₃CO₂)₇Cr₃(OH)₂, CrK(SO₄)₂.12H₂O, Cr(NO3)₃.9H₂O, Cr₂O₃, CrF₂, CrF₃.4H₂O, CrCl₂, CrCl₃, CrCl₃.6H₂O, [CrCl₂(H₂O)₄]Cl.2H₂O, Cr₂(SO₄)₃.15H₂O, CrO and Cr metal by wavelength‐dispersive X‐ray fluorescence (WDXRF) spectrometry. The chemical shifts, asymmetry index and the half‐widths of both the X‐ray emission lines show interesting trends with the oxidation state of chromium. It was observed that the chemical shifts for F compounds are higher than Cl compounds. It was also found larger chemical shifts and FWHM for Kβ_{1, 3} lines than Kα ones. It should be noted that the magnitude of chemical shifts increases with increase in the number of ligand atoms. Copyright © 2009 John Wiley & Sons, Ltd.     

N2 and O2 pressure broadening and pressure shift in the 4ν2 band of OCS

To measure accurately OCS concentrations in planetary atmospheres, it is important to know precisely nitrogen and oxygen pressure broadening and pressure-induced shift coefficients for the lines used in the retrievals. We present in this study the corresponding coefficients for lines of the P and R branches of the 4ν₂ band of the primary isotopologue of carbonyl sulfide (¹⁶O¹²C³²S).For this purpose, infrared absorption spectra of a natural carbonyl sulfide (OCS) gas sample were recorded at an unapodized resolution of 0.004 cm⁻¹, at room temperature for different pressures of N₂ and O₂, using a Bruker IFS125HR spectrometer at the LISA Laboratory in France. The line parameters were derived using the multispectrum fitting method applied to the measured shapes of the lines, including the interference effects caused by the line overlaps.The results are compared with earlier measurements and with values calculated using a semi-classical model based upon the Robert and Bonamy formalism that reproduces rather well the experimental m (m=−J for P(J) lines and m=J+1 for R(J) lines) quantum number dependence of the N₂ and O₂ broadening coefficients. On the other hand most of the lines studied here have positive shift coefficients, which do not show any systematic dependence on m. However, in previous studies of the ν₃, 2ν₃ and ν₂ bands, these coefficients were negative for all lines.     

Optogalvanic detection of velocity-selective optical pumping in an open, cascade atomic medium

We performed two-color spectroscopy of the (4s²) ¹S₀ → (4s4p) ¹P₁ → (4p²) ¹D₂ calcium atomic transition and observed velocity-selective optical pumping in a calcium hollow cathode lamp by means of optogalvanic detection. The optical pumping signature in optogalvanic detection is compared to that of fluorescence and transmission detections. The optogalvanic technique is found to be a very sensitive method of detecting optical pumping and could be used in distinguishing optical pumping from electromagnetically induced transparency.     

A Mössbauer effect study of the electronic and structural properties of Fe9(PO4)O8

Fe₉(PO₄)O₈ is a mixed valence compound with both layers of (FeO)₆, which are similar to those in stoichiometric wüstite, FeO, and layers of Fe₃PO₆, which are similar to those found in anhydrous iron(III) phosphate, FePO₄. A detailed Mössbauer effect study between 232 and 850 K of the electronic and structural properties of Fe₉(PO₄)O₈ has been undertaken for comparison purposes and to study any valence averaging electron delocalization or exchange that may be present. An earlier single crystal X-ray study has revealed that Fe₉(PO₄)O₈ crystallizes with five distinct iron sites in the ratio of 1∶1∶2∶4∶1. The differently distorted octahedral Fe(1), Fe(3), and Fe(4) sites contain divalent iron, the tetrahedral Fe(5) site contains divalent iron, and the octahedral Fe(2) site contains trivalent iron. Because of the variety of iron sites, the paramagnetic Mössbauer spectra of Fe₉(PO₄)O₈ are complex and exhibit many partially resolved lines. The logarithm of the Mössbauer spectral absorption area and the median isomer shift vary linearly with temperature and yield an effective Mössbauer temperature of 300 K for Fe₉(PO₄)O₈. The temperature dependence of the median isomer shift indicates electron delocalization into an unspecified conduction band above 630 K. The differing site degeneracies, site symmetries, and site valencies make it possible to fit the Mössbauer spectra of Fe₉(PO₄)O₈ with two different models, both of which yield a realistic temperature dependence of the hyperfine parameters, but which lead to different conclusions about the presence of valence averaging electron exchange. Hence, the Mössbauer spectra can not, unequivocally, demonstrate the presence of valence averaging in Fe₉(PO₄)O₈. However, the spectra do indicate the presence of structural changes, both above and below 295 K, which are consistent with a monoclinic space group as suggested by the presence of the weak superlattice reflections reported earlier. The relative component spectral areas indicate, in agreement with the relative Wigner-Seitz cell volumes, that the iron(III) on the Fe(2) site has a relatively low recoil-free fraction, whereas the six-coordinate iron(II) on the Fe(1) site has a relatively high recoil-free fraction.     

Refinement of the (NH4)3H(SO4)2 crystal structure: II. X-ray and neutron single-crystal diffraction from phase II at room temperature

The crystal of (NH₄)₃H(SO₄)₂ is of special interest due to the possible influence of ammonium ion on the series of phase transitions: I↔II↔ III↔IV↔V↔VII. Earlier, the x-ray single-crystal diffraction study of phase II of the (NH₄)₃H(SO₄)₂ crystal showed that the crystal structure of this compound had two crystallographically independent groups of the ammonium ions NH₄(1) and NH₄(2) but orientational positions of these ammonium ions were not determined exactly. The refinement of the NH₄(1) and NH₄(2) orientational positions in phase II was carried out by the x-ray and neutron single-crystal diffraction study. The analysis of difference Fourier maps of electron charge density and nuclear density suggested the possibility of disordering of NH₄(2) ammonium ions. The text was submitted by the authors in English.     

Spectroscopic characteristics of Pr<Superscript>3+</Superscript> in biaxial La<Subscript>2</Subscript>(WO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

A Pr³⁺-doped La₂(WO₄)₃ crystal grown by the Czochralski method has been investigated as a promising laser material. The principal axes of the optical indicatrix and Pr³⁺ concentration of the crystal were determined. The polarized absorption, fluorescence spectra and fluorescence decay curves of the main emission multiplets of the crystal were measured at room temperature. The spectroscopic parameters were obtained by the modified Judd–Ofelt theory combined with the normalized method. The peak stimulated emission cross-sections of the major emission lines were estimated. The good spectroscopic properties imply that the Pr³⁺:La₂(WO₄)₃ crystal is a potential laser gain medium for solid-state laser and self-stimulated Raman laser applications. PACS 78.20.-e; 42.70.Hj     

Absorption spectrum of the Mn2+ ions in crystals of lanthanum manganese double nitrate and praseodymium manganese double nitrate

The optical absorption spectrum of the Mn²⁺ ions in the two double nitrates La₂Mn₃(NO₃)₁₂ ? 24H₂O and Pr₂Mn₃(NO₃)₁₂ ? 24H₂O were measured up to 30000 cm^?1. Uniaxial stress was applied to the crystals to determine the multiplicity of the observed zero phonon lines belonging to the transitions from the groundstate⁶ A ₁ (⁶ S) to the excited states⁴ E(⁴ G) and⁴ T ₂(⁴ D). The Zeeman effect of the states⁴ A ₁(⁴ G) and⁴ E(⁴ G) was measured with magnetic fields up to 6.4T. The effect of covalency and trigonal field, especially to the states⁴ A ₁ (⁴ G) and⁴ E(⁴ G), is briefly discussed.     

EPR and optical properties of KYb(WO4)2 and KTb0.2Yb0.8(WO4)2 single crystals

Well oriented KYb(WO₄)₂ and KTb_0.2Yb_0.8(WO₄)₂ single crystals have been investigated for their magnetic and optical properties using the Raman and EPR techniques. The registered EPR signal is dominated by three lines ascribed to ytterbium ions: one main and two satellites. Tb ions, although non-paramagnetic, distinctly modify magnetic properties of the KYb(WO₄)₂ single crystal. Basic parameters of the spin Hamiltonian, including Zeeman and hyperfine terms (g and A matrices) as well the spatial orientation between principal and crystallographic axes systems were determined for both crystals.     

Structure and proton conductivity of mechanochemically treated 50CsHSO4·50CsH2PO4

Mixtures of CsHSO₄ and CsH₂PO₄ were mechanochemically treated using a planetary type of ball mill. The changes in structure and proton conductivity of the solid acid compounds with the treatment have been investigated. Cs₃(HSO₄)₂(H₂PO₄) and Cs₅(HSO₄)₃(H₂PO₄)₂ were formed during milling. The mechanochemically treated composite consisting of Cs₃(HSO₄)₂(H₂PO₄) and Cs₅(HSO₄)₃(H₂PO₄)₂ showed higher conductivity than the untreated mixture. In addition, a high temperature phase of Cs₂(HSO₄)(H₂PO₄) was generated from the composite at around 100 °C on heating. Conductivity of the mechanochemically treated composite significantly increased at temperatures around 90 °C on heating. The value becomes 2 × 10^− 3 S cm^− 1 at around 180 °C. On the other hand, no steep decrease is observed on cooling. The activation energies of the mechanically milled sample with high conductivities were estimated to be about 0.3 eV for both heating and cooling processes. The relatively high proton conductivity and a low activation energy for the proton conduction should be ascribed to the presence of the high temperature phase of Cs₂(HSO₄)(H₂PO₄).     

Unique crystal growth with crystal axis rotation in multi-ferroic β′-(Sm,Gd)2(MoO4)3 narrow lines patterned by lasers in glass

The morphology and orientation of multi-ferroic β′-(Sm,Gd)₂(MoO₄)₃ crystals in the lines patterned by laser irradiations in 3Sm₂O₃–18.25Gd₂O₃–63.75MoO₃–15B₂O₃ (mol%) glass were examined using transmission electron microscope (TEM) observations in order to clarify the origin of the appearance of periodic birefringence in an atomic-scale level. The crystallographic direction of crystals in the lines was determined from selected area electron diffraction (SAED) patterns in TEM observations, and it was demonstrated that a gradual rotation of crystallographic axes takes place along the crystal growth direction (laser scanning direction). The unique crystal growth with a spiral-like rotation of the crystallographic axes is due to the gradual rotation of (MoO₄)²⁻ tetrahedral units in β′-(Sm,Gd)₂(MoO₄)₃ crystals. The laser-induced crystallization, in which the region and direction of crystal growth are restricted artificially to a narrow space, provides a new crystal growth engineering.     

Role of metastable atoms and molecules of helium in excitation transfer to hydrogen atoms

The afterglow of a discharge in helium with a small admixture of hydrogen is studied spectroscopically (p=40 Torr, [e]≤10¹¹ cm^?3). The time-resolved measurements of intensities of the first four lines of the Balmer series are performed. The concentrations of metastable helium atoms and molecules are evaluated from the relative intensity of the absorption lines. The ratios of excitation transfer rates from atoms He(2 ³ S ₁) k ₁(n) and molecules of helium He₂(a 2sσ ³Σ _u ⁺ ) k ₂(n) to atomic hydrogen H*(n) are measured to be k ₁(n=3)/k ₂(n=3)=0.04±0.02 and k ₁(n=4)/k ₂(n=4)=0.01±0.02. The ratios of excitation rate constants k ₂(n) corresponding to different states H(n) are measured to be k ₁(n=4)/k ₂(n=3)=0.023±0.01; k ₁(n=5)/k ₂(n=3)≤0.013; and k ₁(n=6)/k ₂(n=3)≤0.007.     

Er3+，Tm3+共掺的NaY(WO4)2晶体的光谱分析和上转换发光

在室温下，测量了Er:Tm:NaY(WO₄)₂晶体的吸收光谱、激发光谱、发射光谱以及上转换发光，并运用J-O理论对测量的结果进行了计算，得出了Er:Tm:NaY(WO₄)₂晶体的强度参数.报道了Tm，Er离子间特殊的能量传递和相关上转换，解释了离子间的能级跃迁过程.同时，对于Er增强Tm离子近红外发光的特性也作了充分研究. 关键词： 4)₂晶体')" href="#">Er:Tm:NaY(WO₄)₂晶体 吸收光谱 发射光谱 激发光谱 上转换     

Flower-like Ni3(NO3)2(OH)4@Zr-metal organic framework (UiO-66) composites as electrode materials for high performance pseudocapacitors

Zr-metal organic frameworks (Zr-MOFs, UIO-66) as a kind of crystalline porous material possess controllable porous structure and strong thermal stability up to 753 K. In this paper, we synthesized Ni₃(NO₃)₂(OH)₄, Zr-MOF with high specific surface area (1073 m² g⁻¹) and Ni₃(NO₃)₂(OH)₄@Zr-MOF composite for pseudocapacitor material. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were taken to characterize the structure and morphology of Ni₃(NO₃)₂(OH)₄, Zr-MOF, and Ni₃(NO₃)₂(OH)₄@Zr-MOF. The porous structure of Zr-MOF favors the utilization of the active material Ni₃(NO₃)₂(OH)₄ and interfacial charge transport and provides short diffusion paths for ions, which results in a high specific capacitance. Electrochemical properties are evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge measurement. A maximum specific capacitance (SC) of 992 F/g was obtained from CV at a scan rate of 5 mVs⁻¹, which is higher than Zr-MOF (∼134 F g⁻¹) and Ni₃(NO₃)₂(OH)₄ (∼753 F g⁻¹). Meanwhile, the Ni₃(NO₃)₂(OH)₄@Zr-MOF composite electrode exhibits a good cycling stability over 3000 cycles.

     

Facile fabrication of pomponlike microarchitectures of lanthanum molybdate via an ultrasound route

Pomponlike La₂(MoO₄)₃ microstructures assembled with single-crystalline nanoflakes have been facilely fabricated via a surfactant-assisted ultrasound route for the first time. Various synthesis conditions were examined, such as the surfactant concentration, the molecular structure of surfactants, and the pH value. The obtained pomponlike microstructures were characterized by X-ray diffraction (XRD), (field-emission) scanning electron microscopy [(FE)SEM], transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. It has been revealed that a minimum concentration of sodium dodecylsulfate (SDS) was required for the formation of pomponlike La₂(MoO₄)₃ microstructures. When the SDS concentration is above 0.02 mol L⁻¹, the pomponlike microstructures become more perfect, and the size is also increased with the increasing SDS concentration. Under the same sonication, similar pomponlike microstructures were obtained when a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used instead of the anionic surfactant SDS, indicating that the hydrophobic alkyl chains are an important factor for the formation of the pomponlike La₂(MoO₄)₃ microstructures. It is also found that the pomponlike La₂(MoO₄)₃ microstructures can only be obtained within an optimal pH range of 8.0–9.0 under sonication. Based on TEM, Fourier transform infrared spectroscopy (FT-IR) and solubilization experiment, a formation mechanism of pomponlike La₂(MoO₄)₃ microstructures was proposed, in which the collaborative action of surfactants and sonication plays a key role. Furthermore, the porosity of the pomponlike La₂(MoO₄)₃ microstructures were discussed.