Transport properties of PbSnI4

PbSnI₄ has been prepared from equimolar amounts of PbI₂ and SnI₂. X-ray and DSC measurements show the material to be uniphase in the temperature range 30 to 400°C; it has a tetragonal structure and melts at 379°C. The electrical conductivity is mainly ionic with an ionic transport number greater than 0.99 at 200°C. Conductivity at room temperature is 2.56 × 10⁻⁸ Ω⁻¹ cm⁻¹ while the value at 200°C is 1.25 × 10⁻⁶ Ω⁻¹ cm⁻¹.     

Spectroscopic study of thulium-activated double sodium yttrium fluoride Na<Subscript>0.4</Subscript>Y<Subscript>0.6</Subscript>F<Subscript>2.2</Subscript>:Tm<Superscript>3+</Superscript> crystals: I. Intensity of spectra and luminescence kinetics

Na_0.4Y_0.6F_2.2:Tm³⁺ crystals with a thulium content from 1 to 100 at % have been grown by the Stockbarger-Bridgman method. The optical spectra of Na_0.4Y_0.6F_2.2:Tm³⁺ crystals were investigated in detail at room and low (10 K) temperatures, and the luminescence kinetics was analyzed using different excitation methods. The structure of the Stark splitting of thulium levels as “quasi-centers,” characterized by inhomogeneous broadening of the Stark components, is determined from analysis of the absorption spectrum at 10 K. The oscillator strengths of the transitions from the ground state to excited multiplets are determined from the absorption cross-section spectra at 300 K for ten transitions in the range 5000–38 500 cm^?1 and seven transitions in the range 5000–28 500 cm^?1. The transition intensity parameters Ω _t , obtained by the Judd-Ofelt method from the spectra due to the transitions to ten and seven excited levels, were found to be, respectively, (i) Ω₂ = 1.89 × 10^?20, Ω₄ = 2.16 × 10^?20, and Ω₆ = 1.40 × 10^?20 cm² and (ii) Ω₂ = 2.04 × 10^?20, Ω₄ = 2.01 × 10^?20, and Ω₆ = 1.44 × 10^?20 cm². These values of the intensity parameters were used to calculate the radiative transition probabilities and branching ratios and to estimate the multiphonon nonradiative transition probabilities for NYF:Tm. The luminescence decay kinetics from thulium radiative levels upon their selective excitation by nanosecond laser pulses has been studied and the lifetimes of thulium radiative levels in NYF crystals have been found.     

Low-temperature structural phase transitions of TbB4 and ErB4 studied by high resolution X-ray diffraction and profile analysis

The isostructural rare earth tetraborides TbB₄ and ErB₄ of tetragonal space group P4/mbm undergo structural phase transitions to orthorhombic symmetry around T = 80 K and T = 15 K, respectively. The lattice distortions have been investigated by individual peak profile analysis performed on high-precision X-ray data. The experimental and analytical processing is outlined. The deviations from a tetragonal cell at 4.2 K are 2 × 10⁻² Å for TbB₄ and 3 × 10⁻³ Å for ErB₄. The relative volume change between 300 and 4.2 K is less than 10⁻³ in the TbB₄ lattice and 2.3 × 10⁻³ in ErB₄.The tetragonal to orthorhombic distortions are discussed in the context of the antiferromagnetic phase transitions of TbB₄ at T_N = 43 K and of ErB₄ at T_N = 13 K. The relationship between the structural and magnetic phase transitions differs for the two compounds. In TbB₄, the structural transition, which occurs at a definitely higher temperature than the magnetic ordering, is assumed to be driven by a strong electron-lattice coupling or by an electronic quadrupole-quadrupole interaction. In ErB₄, the structural distortion is attributed to magnetostrictive effects occurring simultaneously with the magnetic ordering process.     

Complex impedance study of annealing effects on polycrystalline KDP conductivity

Annealing effects on the conductivity of KDP (KH₂PO₄) samples prepared either by melting under slight pressure (5.7 kgf/cm²) or by powder compression (1.3 × 10³kgf/cm²) were studied in air by complex impedance spectroscopy. In both cases, annealing at 423 K reduces the conductivities to constant values: from 6.2 × 10 ⁻⁶ to 1.6 × 10⁻⁷ Ω⁻¹ cm⁻¹ for samples prepared by melting and from 1.9 × 10^∼7 to 6.1 × 10^∼8 Ω⁻¹ cm⁻¹ for samples prepared by compression. Heating KDP at about 500 K significantly modifies its electric properties. Two relaxation processes are observed after this treatment. One of them is associated with a fairly strong dielectric polarizability. A small conductivity jump is observed close to 440 K.     

The high-resolution spectrum of the ν1 (A1) band of 12CD3F

The spectrum of the ν₁ (A₁) band of ¹²CD₃F has been recorded with a resolution of 0.010 cm⁻¹ and deconvolved to 0.005 cm⁻¹. Over 1050 transitions have been assigned with K ≤ 16 and J ≤ 42. The spectrum is highly perturbed, exhibiting avoided crossings in most of the observed sub-bands. The origin of most of the local and global resonances has been determined and the coupling constants estimated. Due to the complexity of the spectrum resulting from the 24 potential interacting states in the region, the assigned frequencies were fitted in a restricted manner (K ≤ 3, J ≤ 15), to obtain the following effective constants for the band: ν₀ = 2090.8118(20) cm⁻¹, α^A = 1.19743 × 10⁻² cm⁻¹, and α^B = −1.8489 × 10⁻³ cm⁻¹. From an unrestricted least-squares analysis, fixing the above parameters the β's (D_v^x = D₀^x − β_v^x) were calculated to be β^J = 1.7776 × 10⁻⁷ cm⁻¹, β^JK = 8.3406 × 10⁻⁷ cm⁻¹, and β^K = −6.3829 × 10⁻⁷ cm⁻¹. These constants serve as good starting parameters for the global analysis necessary to fully analyze the 5-μm region of the ¹²CD₃F spectrum.     

Spectroscopic Study of Neodymium-Doped Sodium–Yttrium Double Fluoride Nd<Superscript>3+</Superscript>:Na<Subscript>0.4</Subscript>Y<Subscript>0.6</Subscript>F<Subscript>2.2</Subscript> crystals

Nd³⁺:Na_0.4Y_0.6F_2.2 (Nd³⁺:NYF) crystals are grown by the Stockbarger–Bridgman method for a stoichiometric mixture prepared by the solid-phase method and containing neodymium up to 20 at. %. The absorption spectrum of Nd³⁺:NYF crystals exhibits bands located in the emission region of laser diodes. The peak absorption cross section of the 796.8-nm band is σ _a = 0.96 × 10^–20 cm² and the bandwidth is Δλ = 17.5 nm. The most intense luminescence band is located at 1.05 μ m and the radiative time of the ⁴F_3/2 level is τ₀ = τ_exp ~ 960 μ s. It is shown that the ²P_3/2 and ⁴D_3/2 levels of Nd³⁺:NYF crystals are also radiative with lifetimes τ exp equal to ~110 and 9.5 μ s, respectively. However, these radiative transitions are partially quenched due to nonradiative relaxation. The intensity parameters Ω t are determined by the Judd–Ofelt method to be Ω₂ = 1.18 × 10^–20, Ω₄ = 1.55 × 10^–20, and Ω 6 = 2.85 × 10–20 cm 2. Using these parameters, the probabilities of radiative transitions and branching ratios are calculated, and the probabilities of nonradiative transitions are estimated. A conclusion is made that Nd³⁺:NYF crystals are promising as active media for diode-pumped tunable lasers, in particular, up-conversion-pumped lasers.     

Observation of charmless B meson decays

Using the ARGUS detector at the e⁺e⁻ storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π^± and pp̄π⁺π⁻. The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10⁻⁴ for the three-body and (6.0±2.0±2.2)×10⁻⁴ for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element V_ub is non-zero.     

Eine PrÄzisionsmessung des VerhÄltnisses der Spinresonanzfrequenz von Protonen zur Zyklotronfrequenz freier Elektronen im gleichen Magnetfeld

A new precision measurement of the ratio of the proton NMR frequency to the cyclotron frequency of free electrons in the same magnetic field, Ω _p /Ω_e=γ _p mc/e, has been performed. A cyclotron resonance linewidth of 5 ppm only and a reduction of the large space charge shifts, amounting up to the order of 50 ppm in earlier published measurements, enabled a high accuracy. The final result is Ω _p /Ω _e =1.5209945×10^?3±0.5 ppm, where the NMR is referred to a long cylindrical sample of H₂O, 0.2 m CuSO₄. Corrected to the free proton, we get Ω _p /Ω _e =1.5210329×10^?3±0.6 ppm. Combination of our result with an EPR-measurement ofLambe yields a free electrong-factor ofg=2(1+(α/2π)?(0.30±0.09) (α/π)²) in good agreement with the theoretical valueg=2(1+(α/2π)?0.328(α/π)²±...).     

Optical spectra and emission characteristics of terbium-doped potassium–lead double chloride crystals (KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript>:Tb<Superscript>3+</Superscript>)

Optical transitions in KPb₂Cl₅:Tb³⁺ crystals are studied experimentally and theoretically. The absorption cross-section spectra are plotted and the oscillator strengths of transitions from the ground terbium state to excited multiplets are determined. Intensity parameters Ω_t for KPC:Tb³⁺ are determined by the Judd–Ofelt method to be Ω₂ = 2.70 × 10^–20 cm², Ω₄ = 7.0 × 10^–20 cm², and Ω₆ = 0.72 × 10^–20 cm². These values were used to calculate such characteristics of spontaneous radiative transitions as oscillator strengths, probabilities of radiative transitions, and radiative lifetimes. The emission spectra of KPb₂Cl₅:Tb³⁺ crystals upon UV excitation and the decay kinetics of luminescence from the excited ⁵ D ₃ and ⁵ D ₄ levels are studied experimentally, the lifetimes of these levels are determined, and the dependences of the rates of nonradiative relaxation from the excited ⁷ F _j (j = 0–5), ⁵ D ₄, and ⁵ D ₃ levels to lower-lying terbium levels are calculated. It is shown that the population of the ⁵ D ₄ level in KPC:Tb³⁺ crystals occurs according to a cascade scheme, which leads to quenching of the ⁵ D ₃ level. The calculated data agree well with the known experimental rates of multiphonon nonradiative transitions for Dy:KPC, Nd:KPC, Er:KPC, Tb:KPB, and Nd:KPB crystals. It is shown that transitions in the near-IR (3–6 μm) region in double halide crystals (MPb₂Hal₅) are almost unquenched and the rates of nonradiative relaxation of excited levels spaced by energy gaps ΔE _ji > 1000 cm^–1 are W _ji ^NR < 10³s^–1. This circumstance suggests that it is possible to obtain stimulated emission in KPb₂Cl₅:RE³⁺ crystals in the IR spectral region up to 6 μm.     

Polarized absorption spectra and spectroscopic parameters of Tm3+ in the TmAl3(BO3)4 single crystal

High-optical-quality single crystals of the TmAl₃(BO₃)₄ compound were synthesized from a solution in the melt. The absorption spectra in the σ and π polarizations for the ³ H ₆ → ³ F ₄, ³ H ₆ → ³ H ₅, ³ H ₆ → ³ H ₄, ³ H ₆ → ³ F ₃, ³ H ₆ → ³ F ₂, ³ H ₆ → ¹ G ₄, and ³ H ₆ → ¹ D ₂ transitions in the Tm³⁺ ion were recorded at room temperature. The transition intensities were analyzed in the framework of the Judd-Ofelt theory generalized to the case of anisotropic crystals, and the following parameters of the theory were obtained: Ω₂ = 6.14 × 10^?20 cm², Ω₄ = 3.09 × 10^?20 cm², and Ω₆ = 2.04 × 10^?20 cm². The lifetimes and the branching ratios were determined for all possible transitions.     

Spectroscopic study of erbium-activated crystals of double calcium yttrium fluoride Ca<Subscript>0.89</Subscript>Y<Subscript>0.11</Subscript>F<Subscript>2.11</Subscript>:Er<Superscript>3+</Superscript>: I. Intensity of spectra and luminescence kinetics

Ca_0.89Y_0.11F_2.11:Er³⁺ (CYF:Er) crystals with an erbium content of 1–15 at % have been grown. The optical spectra and luminescence kinetics of CYF:Er crystals have been investigated at low (～5 K) and room temperatures. Based on an analysis of the absorption spectra at low temperature, the structure of Stark splitting of erbium levels in CYF:Er crystals is determined. Room-temperature absorption spectra are used to calculate the spectra of absorption cross sections and oscillator strengths of transitions from the erbium ground state to excited multiplets. It is shown that the absorption spectrum of CYF:Er crystals contains broad bands in the ranges of 790–815 and 965–980 nm, which correspond to the range of emission of laser diodes. For the band peaking near 967 nm, the peak absorption cross section is σ _abs ^max = 2.7 × 10^?21 cm². The intensity parameters are determined by the Judd-Ofelt method to be Ω₂ = 1.39 × 10^?20, Ω₄ = 1.34 × 10^?20, and Ω₆ = 2.24 × 10^?20 cm². The radiative transition probabilities, radiative lifetimes, and branching ratios are calculated with these values. The luminescence decay kinetics from excited erbium levels upon selective excitation is investigated and the experimental lifetimes of the 4F _9/2, ⁴ S _3/2, and ⁴ G _11/2 radiative erbium levels are determined. The dependences of multiphonon relaxation rates on the energy gap in CYF:Er crystals are obtained. The rates of nonradiative multiphonon relaxation from radiative erbium levels are determined.     

Measurement of the 15N(α, γ)19F resonances at Ec.m. = 536 keV and 542 keV

The E_c.m. = 536 keV and E_c.m. = 542 keV resonances in the ¹⁵N(α, γ)¹⁹F reaction have been studied using a thick Ti¹⁵N target, determining ωγ = (9.7 ± 2.0) × 10⁻⁵ eV and ωγ < 1 × 10⁻⁵ eV for these two resonances, respectively. For the 542 keV resonance this value is substantially smaller than had been assumed in earlier model calculations, and this reduces the rate of the analog ¹⁵O(α, γ)¹⁹Ne reaction (connecting the Hot CNO cycle and the rp-process) by a factor of ≈ 3 for temperatures in the region of T₉ = 1.     

Diode laser spectroscopy of the ν1-ν3 band of CF335Cl at 15.84 μm

The vibration-rotation spectrum of CF₃Cl, with natural isotopic abundance, has been recorded in the 622- to 641-cm⁻¹ region using a tunable diode laser spectrometer. The K structure of many P(J) and R(J) manifolds of the ν₁-ν₃ difference band of CF₃³⁵Cl has been resolved and positively identified. The rotational analysis has been extended in the P and R branches up to J = 39 and 47, respectively, and more than 650 lines have been assigned. A least-squares fit of the observed transitions to the energy expression including the quartic centrifugal distortion terms was performed and molecular constants for the ν₁-ν₃ difference band were determined. From the obtained parameters the ν₃ band center of CF₃³⁵Cl was evaluated as 476.9750(4) cm⁻¹ and the values of α₃^A and α₃^B were derived to be 50(1) × 10⁻⁶ and 82.9(6) × 10⁻⁶ cm⁻¹, respectively.     

Spectroscopic properties and structure of the ErFe3(BO3)4 single crystal

Single crystals of the ErFe₃(BO₃)₄ borate were synthesized and their structure was studied. Absorption spectra of the Er³⁺ ion in σ- and π-polarizations of f-f transitions ⁴ I _15/2 → ⁴ I _13/2, ⁴ I _11/2, ⁴ I _9/2, ⁴ F _9/2, ⁴ S _3/2, ² H _11/2, and ⁴ F _7/2 were measured. The refractive index and birefringence were measured as a function of the wavelength. The transition intensities were analyzed within the Judd-Ofelt theory, and the following parameters of the theory were obtained: Ω₂ = 7.056 × 10^?20 cm², Ω₄ = 1.886 × 10^?20 cm², and Ω₆ = 2.238 × 10^?20 cm². Using these parameters, the radiative transition probabilities, luminescence branching ratios, and radiative lifetimes of multiplets were calculated.     

Enhanced electrical transport in LiBrLiI mixed crystals and LiBrAl2O3 composites

LiBrLiI mixed crystals and LiBrAl₂O₃ composites have been studied by means of complex impedance analysis an conductivity, X-ray diffraction, DTA and SEM techniques. The substitution of wrong size I⁻ ions in LiBr increases the conductivity and decreases the migration energy of Li-ion vacancies. These results are consistent with those of the KBr-KI system and earlier predictions. LiBrAl₂O₃ composites exhibit a sharp increase in the conductivity. The highest conductivity obtained was ≈10⁻³ Ω⁻¹ cm⁻¹ at 302°C for LiBr + 10 m/o Al₂O₃.     

Majoron couplings to neutrinos and SN1987A

We use well established data on SN1987A to restrict the coupling g_ee of the majoron to electronic neutrinos in the Gelmini-Roncadelli model. We exclude values from 10⁻⁴ down to 3×10⁻⁶. This range is complementary to the expected laboratory limits from next-round experiments, g_ee⩽10⁻⁴. If this laboratory bound is reached, we may place the stringent limit g_ee ⩽3 ×10 ⁻⁶ on the majoron coupling.     

Rotational analysis of the ν2 band of NH2D

High-resolution diode laser spectra and medium-resolution F-T spectra of deuterated ammonia have been obtained in the 700- to 1030-cm⁻¹ region. Out of about 800 lines measured by diode laser spectroscopy, approximately 500 lines have been assigned to the ν₂ transitions of NH₂D. The parameters for the ground and ν₂ states of NH₂D have been derived by the simultaneous analysis of the infrared and microwave data. The standard deviation for the IR data is ∼8 × 10⁻⁴ cm⁻¹. It is shown that the energy levels of NH₂D in the ν₂ state are heavily perturbed by inversion-rotation interaction and that it is necessary to include higher order inversion-rotation interaction terms to obtain a satisfactory fit of the observed data.     

High-resolution measurements of the ν2 and 2ν2-ν2 bands of SO2

Infrared measurements have been made on SO₂ between 450 and 602 cm⁻¹ with a resolution of 0.005 cm⁻¹. The B-type bands due to the bending mode transitions 010-000 and 020-010 have been assigned and analyzed for the ³²S¹⁶O₂ molecule. A total of 3007 transitions were measured and fit for ³²S¹⁶O₂ with a standard deviation of 0.0004 cm⁻¹. Ro-vibrational constants are given that fit the current measurements and the pure rotational transitions reported in the literature.     

Determination of A0 for CH3D from perturbation-allowed transitions

Ground state combination differences obtained from normally allowed and perturbation-allowed transition in the 2ν₆ band of ¹²CH₃D have been fitted to obtain the following values for rotational constants: A₀ = 5.2508231 ± 0.0000043 cm⁻¹, and D₀^K = (−7.869 ± 0.23) × 10⁻⁵cm⁻¹.     

Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6‐mm‐thick sulfur specimen at 1500 m

The absolute Raman scattering cross sections (σ_RS) for the 471, 217, and 153 cm⁻¹ modes of sulfur were measured as 6.0 ± 1.2 × 10⁻²⁷, 7.7 ± 1.6 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁶ cm² at 815, 799, and 794 nm, respectively, using a 785‐nm pump laser. The corresponding values of σ_RS at 1120, 1089, and 1081 nm were determined to be 1.5 ± 0.3 × 10⁻²⁷, 1.2 ± 0.24 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁷ cm² using a 1064‐nm laser. A temperature‐controlled, small‐cavity (2.125 mm diameter) blackbody source was used to calibrate the signal output of the Raman spectrometers for these measurements. Standoff Raman detection of a 6‐mm‐thick sulfur specimen located at 1500 m from the pump laser and the Raman spectrometer was made using a 1.4‐W, CW, 785‐nm pump laser. Copyright © 2010 John Wiley & Sons, Ltd.