Laser characteristics of 2-µm microchip Tm,Ho:Lu<Subscript>2</Subscript>SiO<Subscript>5</Subscript> laser

Cryogenic temperature operation of a 〈010〉-cut microchip Tm,Ho:Lu₂SiO₅ laser end-pumping by a fiber-coupled laser-diode is presented. A 2.73 W absorbed pump power is used to generate a maximum laser output of 470 mW, representing a 17.2% optical-to-optical conversion efficiency and a 61.7% slope efficiency corresponding to absorbed power. In the experiment, the oscillating wavelength shifting from 2.03 to 2.08 μm has been observed and a single 2.03 μm wavelength oscillation has obtained. To our knowledge, this work is the first time to investigate the Cryogenic temperature operation of microchip Tm,Ho:Lu₂SiO₅.     

Review of AdS/CFT Integrability,Chapter II.2: Quantum Strings in AdS<Subscript>5</Subscript> × S<Superscript>5</Superscript>

We review the semiclassical analysis of strings in AdS₅ × S⁵ with a focus on the relationship to the underlying integrable structures. We discuss the perturbative calculation of energies for strings with large charges, using the folded string spinning in AdS₃ ? AdS₅ as our main example. Furthermore, we review the perturbative light-cone quantisation of the string theory and the calculation of the worldsheet S-matrix.     

KF-doped BaTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ferroelectric ceramics by solid-state reaction of KF and sol–gel-derived BaTi<Subscript>2</Subscript>O<Subscript>5</Subscript> powders

We report KF-doping work on the recently found ferroelectric material BaTi₂O₅. The ceramic samples, Ba_1-xK_xTi₂O_5-xF_x, were synthesized by solid-state reaction of mixed KF and sol–gel-derived BaTi₂O₅ powders at 1150 °C. An almost pure phase was obtained for nominal composition x≤0.097, while electron probe microanalysis indicated that the real incorporated K and F contents were less than half of the nominal values. It was observed that KF-doping is beneficial in enhancing the ceramic density to some extent, which is a key issue in sol–gel-derived BaTi₂O₅ ceramics, due to a possible liquid-phase sintering mechanism through the presence of melted KF at the sintering temperature. Scanning electron microscopy images showed that these porous ceramic samples are composed of sub-micron-sized powder aggregates which, with increasing KF-doping, undergo further agglomeration. Dielectric measurement from room temperature to ∼ 560 °C showed a broad ferroelectric phase transition, with T_C ∼ 430 °C for the undoped sample. As KF-doping increases, T_C decreases, and the magnitude of the dielectric constant maximum also displays a decreasing trend. The strongly reduced dielectric response can be partly understood by regarding the porous ceramic sample as a composite material composed of bulk BaTi₂O₅ and air, where the porosity has a significant influence on the effective dielectric constant. PACS 77.84.-s; 77.84.Dy; 81.20.Fw     

Characterization and transport properties of 10BaO–xAg<Subscript>2</Subscript>O–(85-x)V<Subscript>2</Subscript>O<Subscript>5</Subscript>–5TeO<Subscript>2</Subscript> glass system

Silver-based quaternary glasses were prepared by splat quenching technique. X-ray diffraction and differential scanning calorimetry were done for confirming their amorphous nature. The conductivity of the glasses was measured in the frequency range from 1 Hz to 32 MHz from room temperature to 373 K. Conductivity data, which obeys the Arrhenius type behavior, shows minimum at 30 mol% Ag₂O, suggesting that the conductivity mechanisms are different above and below these two regions. The minimum in conductivity is accompanied by an inverse behavior of activation energy. Experimental data suggests that a polaron hopping mechanism operates in the electronically conducting domain of 20 ≤ × ≤ 30, and an interstitial pair mechanism operates in the ionically conducting domain of 35 ≤ × ≤ 55.     

Microwave dielectric properties of the 5.5Li<Subscript>2</Subscript>O–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–7TiO<Subscript>2</Subscript> ceramics

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 5.5:1:7 was prepared by solid state reaction route. The phase and structure of the ceramic were characterized by X-ray diffraction and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The microwave dielectric ceramic has low sintering temperature (∼1075°C) and good microwave dielectric properties of ε _r=42, Q×f=16900 GHz (5.75 GHz), and τ _f =63.7 ppm/°C. The addition of B₂O₃ can effectively lower the sintering temperature from 1075 to 875°C and does not induce degradation of the microwave dielectric properties. Obviously, the LNT ceramics can be applied to microwave low temperature-cofired ceramics (LTCC) devices.     

μSR study of Eu<Subscript>0.8</Subscript>Ce<Subscript>0.2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>5</Subscript> and EuMn<Subscript>2</Subscript>O<Subscript>5</Subscript> multiferroics

A comparative μSR study of ceramic samples of the EuMn₂O₅ and Eu_0.8Ce_0.2Mn₂O₅ multiferroics is performed in the temperature range from 15 to 300 K. It is found that the Ce doping of the EuMn₂O₅ sample slightly reduces the temperature of the magnetic phase transition from T _N = 45 K for the EuMn₂O₅ sample to T _N = 42.5 K for the Eu_0.8Ce_0.2Mn₂O₅ sample. Below the temperature T _N for both samples, there are two types of localization of a thermalized muon with different temperature dependences of the precession frequency of the magnetic moment of the muon in an internal magnetic field. The higher frequency in both samples refers to the initial antiferromagnetic matrix. The behavior of this frequency in Eu_0.8Ce_0.2Mn₂O₅ follows the Curie–Weiss law with the exponent β = 0.29 ± 0.02, which differs from the value β = 0.39 standard for 3D Heisenberg magnetics and is observed in EuMn₂O₅, because of the strong frustration of the doped sample. The temperature-independent low frequency is due to the presence of Mn³⁺–Mn⁴⁺ ferromagnetic pairs located along the b axis of the antiferromagnetic matrix and in the regions of phase separation, which contain such ion pairs and e _g electrons recharging them. In both samples, polarization losses are the same (about 20%) and are associated with the formation of Mn⁴⁺–Mn⁴⁺ + Mu complexes near Mn³⁺–Mn⁴⁺ ferromagnetic pairs. In the temperature interval from 25 to 45 K, the separation of the Eu_0.8Ce_0.2Mn₂O₅ structure into two fractions where the relaxation rates of polarization of muons differ by an order of magnitude is revealed. This effect is due to a change in the state of regions of phase separation (1D superlattices) at the indicated temperatures. Such effect in EuMn₂O₅ is significantly weaker.     

Dynamic magnetic susceptibility of compounds in Gd<Subscript>5</Subscript>Si<Subscript>2−x</Subscript>Ge<Subscript>2−x</Subscript>Sn<Subscript>2x</Subscript> (2x = 0 − 0.1) system

The dynamic magnetic susceptibility (χ_ac) of magnetically ordered Gd₅Si_2?xGe_2?xSn_2x compounds with the partial substitution for silicon and germanium atoms by isovalent tin atoms (2x = 0 ? 0.1) has been investigated experimentally. From the temperature dependence of χ_ac the Curie temperatures of these alloys are determined. It is established that tin-doped alloys have higher Curie temperatures as compared to Gd₅Si₂Ge₂ (ΔT _C ≈ 15 K).     

GaSb-based mid-infrared 2–5 μm laser diodes

Laser diodes emitting at room temperature in continuous wave regime (CW) in the mid-infrared (2–5 μm spectral domain) are needed for applications such as high sensitivity gas analysis by tunable diode laser absorption spectroscopy (TDLAS) and environmental monitoring. Such semiconductor devices do not exist today, with the exception of type-I GaInAsSb/AlGaAsSb quantum well laser diodes which show excellent room temperature performance, but only in the 2.0–2.6 μm wavelength range. Beyond 2.6 μm, type-II GaInAsSb/GaSb QW lasers, type-III ‘W’ InAs/GaInSb lasers, and interband quantum cascade lasers employing the InAs/Ga(In)Sb/AlSb system, all based on GaSb substrate, are competitive technologies to reach the goal of room temperature CW operation. These different technologies are discussed in this paper. To cite this article: A. Joullié, P. Christol, C. R. Physique 4 (2003).     

{H[Cu（trans-Hcydta）]&#183;2Bzim&#183;1．5H2O&#183;0．5MeOH&#183;HClO4}的合成、结构和量子化学研究

反式．1，2-环已二胺四乙酸与铜离子合成标题配合物，经X射线衍射测定配合物的晶体分子结构，并用量子化学方法研究配合物的电子结构及分子轨道组成、该晶体属于单斜晶系，空间群为P2(1)／c，晶胞参数：a=1．6360(6)，b=1．3814(5)，c=1．5503(5)nm，β=90．885(7)&#176;，V=3．503(2)nm^3，Z=4，Dx=1．495g／cm^3，u(MoKa)=7、74cm^-1，F(000)=1640，R1=0．0750，wR=0.1526；配合物中Cu-O键长为0．193～0．22nm，中心铜与配基原子形成畸型四棱锥。     

Magnetic and crystal structures of iron-ion-doped TbBaCo<Subscript>2</Subscript>O<Subscript>5 + γ</Subscript>

Neutron diffraction and magnetic studies of a TbBaCo₂O_{5 + γ} polycrystalline sample with a perovskite-like layered structure have revealed that spontaneous magnetization appears at 305 K and decreases sharply below 200 K. It has been shown that the crystal structure is described by space group Pmmm with a 2a _p · a _tp · 2a _p unit cell. The magnetic structure in the high-temperature magnetic phase consists of the G-type antiferromagnetic and ferromagnetic components, whereas the magnetic structure in the low-temperature phase is a G-type antiferromagnetic. The ferromagnetic component appears due to the noncollinearity of the magnetic moments of Co³⁺ ions, which are in the high-spin state in pyramids and in the low-spin state in octahedrons. The antiferromagnetic component is present in the octahedral sublattice, because oxygen vacancies are partially ordered.     

Ga-induced restructuring of Si(5 5 12) − 2 × 1 reconstructed surface at room temperature

Motivated by the need to form 1D-nanostructured dopants on silicon surfaces, we have attempted to grow Ga on the high index Si(5 5 12) surface which has a highly trenched (1D) morphology. The evolution of the interface with Ga adsorption in the monolayer regime has been probed by in situ AES, LEED and EELS. Controlling the kinetics by changing the Ga flux rates shows an interesting difference in the 1.0 to 1.5 ML region. The low flux rate (0.03 ML/minute) results in a Frank van der Merwe (layer by layer) growth mode up to 2 ML, while the higher flux rate (0.1 ML/minute) shows a transient island formation after the completion of 1 ML. The low rate shows the formation of 2 × (3 3 7) and (2 2 5) superstructures, while only the 2 × (3 3 7) is observed in a wide coverage range for the higher rate. The results demonstrate the ability to kinetically control the surface phases with different electronic properties of this technologically important interface.     

Cu–CeO<Subscript>2</Subscript> nanocomposites: mechanochemical synthesis,physico-chemical properties,CO-PROX activity

Catalytic systems designated for preferential oxidation of CO in the presence of H₂ are prepared by ball milling of Cu and CeO₂, a simple and cheap one-step process to synthesize such catalysts. It is found that after 60 min of milling, a mixture of 8 wt.% Cu–CeO₂ powders exhibits CO conversion of 96% and CO selectivity of about 65% at 438 K. Two active oxygen states, which are not observed in case of pure CeO2, were detected in the nanocomposite lattice and attributed to the presence of Cu in surface sites as well as in subsurface bulk sites. Correspondingly, oxidation of CO to CO₂ was found to occur in a two-stage process with T _max ≈ 395/460 K, and oxidation of H₂ to H₂O likewise in a two-stage process with T _max ≈ 465/490 K. The milled powder consists of CeO₂ crystallites sized 8–10 nm agglomerated to somewhat larger aggregates, with Cu dispersed on the surface of the CeO₂ crystallites, and to a lesser extent present as Cu₂O.

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Graphical abstract ?

     

Structure,stability, and thermomechanical properties of Ca-substituted Pr<Subscript>2</Subscript>NiO<Subscript>4 + δ</Subscript>

Ca-substituted layered nickelates with a general Pr_2–x Ca _x NiO_{4 + δ} composition (x = 0–0.7, Δx = 0.1) were prepared in the present work and their structural and physic-chemical properties were investigated in order to select the most optimal materials, which can be used as cathodes for solid oxide fuel cells. With an increase in Ca content in Pr_2–x Ca _x NiO_{4 + δ} the following tendencies were observed: (i) a decrease in the concentration of nonstoichiometric oxygen (δ), (ii) a decrease in the unit cell parameters and volume, (iii) stabilization of the tetragonal structure, (iv) a decrease of the thermal expansion coefficients, and (v) enchancement of thermodynamic stability and compatibility with selected oxygen- and proton-conducting electrolytes. The Pr_1.9Ca_0.1NiO_{4 + δ} material, having highest δ value, departs from the general “properties–composition” dependences ascertained. This indicates that oxygen non-stoichiometry has determining influence on the functional properties of layered nickelates.     

Hydrothermal synthesis,characterization, and luminescence of Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>:RE (RE = Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>) nanofibers

Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca₂B₂O₅:Eu³⁺ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca₂B₂O₅:Tb³⁺ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy³⁺-doped Ca₂B₂O₅ nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu³⁺-, Tb³⁺-, Dy³⁺-doped Ca₂B₂O₅ nanofibers, respectively. It is suggested that Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers could be an efficient phosphor for lighting and display.     

Conductance studies of NaCl,KCl, NaBr,KBr, NaI,Bu<Subscript>4</Subscript>NI,and NaBPh<Subscript>4</Subscript> in water + 2-propoxyethanol mixtures at 298.15 K

The molar conductances of sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium iodide (NaI), tetrabutylammonium iodide (Bu₄NI), and sodium tetraphenylborate (NaBPh₄) in water?+?2-propoxyethanol binary mixtures at T?=?298.15 K were determined. Conductance values were analyzed using a low-concentration chemical model (lcCM). The ionic conductivities of Na⁺, K⁺, Bu₄N⁺, Cl^?, I^?, Br^?, and BPh₄ ^? ions were determined using Fuoss–Hirsch’s assumption. The dependencies of the values of limiting molar conductance (Λ _o), limiting ionic conductance of the individual anions (λ _o ^± ), and Walden products (Λ _o???η and λ _o ^± ???η) as a function of the composition of water?+?2-propoxyethanol binary mixtures were discussed.

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Graphical abstract Limiting molar conductances Λ _o [S·cm²·mol^?1] of NaCl, NaBr, NaI, KCl, NaBPh₄, and NBu₄I as a function of the mole fraction, x ₂, in water (1)?+?2-propoxyethanol (2) mixtures at 298.15 K: empty diamonds NaCl, empty squares NaBr, empty triangles NaI, filled triangles KCl, filled squares NaBPh₄, and filled diamonds NBu₄I

     

Electrical switching in the MoO<Subscript>3</Subscript>–WO<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> and MoO<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

High field electrical switching on blown films of MoO₃(60%)–P₂O₅(40%), MoO₃(50%)–WO₃(10%)–P₂O₅(40%), and MoO₃(45%)–WO₃(15%)–P₂O₅(40%) having different thicknesses was studied and compared. Switching was observed using two terminal samples. S-type current–voltage characteristic (current-controlled negative resistance—CCNR) with memory was observed in molybdenum–phosphate glasses, but N-type characteristic (voltage-controlled negative resistance—VCNR) with threshold in tungsten–molybdenum–phosphate glasses was observed. The important observation was that with the addition of WO₃ to binary MoO₃–P₂O5 led to a change of I–V characteristic from CCNR with memory to VCNR with threshold. The measurements of density and molar volume showed linear relation between MoO₃ content and density which decreased with the increase of MoO₃ content. The samples’ thickness had no significant effect on threshold voltage. The attained results also indicated that the electrode material had no effect on switching property of devices. The switching behavior of the devices did not show any dependence on the polarity of the applied voltage. In terms of the effect of heat on the switching behavior of molybdenum–phosphate glasses, it was found that threshold voltage decreases with increasing of temperature. Finally, the switching phenomenon was explained by thermal (formation of crystalline filaments) and electronic models.     

White,green, and yellow photoluminescence in the (CaO · Al<Subscript>2</Subscript>O<Subscript>3</Subscript> · SiO<Subscript>2</Subscript>): Eu system

It is shown that nitrogen-laser excited (2CaO · m(Al₂O₃) · SiO₂): Eu photoluminescent phosphors obtained by direct solid-state synthesis at 1350°C emit white, green, and yellow lights when Al₂O₃ content m in the system decreases from 0.40 to 0.05. The coordinates of these colors correspond to the coordinates of light warning systems according to International Commission on Illumination (CIE) and are close to the coordinates of primary colors in the EBU and NTSC TV standards.     

Odd autoionizing 2p<Subscript>1/2</Subscript><Superscript>5</Superscript>n(s<Superscript>′</Superscript>/d<Superscript>′</Superscript>) resonances of Ne excited from the 2p<Superscript>5</Superscript>3p[K]<Subscript>J</Subscript> states

Absolute photoionization cross sections for Ne atoms in the excited levels (Paschen notation ) were calculated at near threshold energies within the configuration interaction Pauli-Fock approach including core polarization. The computed spectra and the lineshape parameters of the odd parity 2p_1/2 ⁵ns^′/d^′ autoionizing resonances are found to be in good agreement with high resolution laser spectroscopic results. Guided by the theoretical results, improved analyses of the measured spectra by superimposed Fano-type profiles were achieved. Theoretical predictions are presented for resonances which have not yet been studied experimentally. In addition, we report the absolute partial photoionization cross sections for the ²P_3/2 and ²P_1/2 channel at photoelectron energies up to 7 eV. Except for the highest lying 2p₁(¹S₀) level, these cross sections monotonically decrease with energy (as reported earlier in single-electron calculations for the Ne(2p⁵3p) configuration) with branching ratios which essentially reflect the core composition of the 2p_x levels. For the 2p₁ level the resonance structure and the partial cross sections are strongly influenced by a Cooper-Seaton minimum in the d_3/2 ^′ channel,located just above the ²P_1/2 ionization limit.     

Protonic conduction and diffusion in the hydrous oxides V2O5·nH2O,Nb2O5·nH2O,Ta2O5·nH2O and CeO2·nH2O

Conductivity (ac and dc) measurements are reported for hydrous V₂O₅, Nb₂O₅, Ta₂O₅ and CeO₅ in the range 250<T/K<320. Ambient temperature conductivities increase with water content and (SEM) agglomerate size, the most highly conductive material being Ta₂O₅·3.92 H₂O (α₂₉₈=3×10⁻⁴S cm⁻¹). There is no simple composition dependence of conductivity activation energy. ¹H NMR relaxation time measurements in the range 170<t/K<330 are also reported. The data consistent with chemical exchange between a range of interparticle protonic environments, but there is no simple link with conductivities.