Magnetic Structure and Properties of the Rechargeable Battery Insertion Compound Na2FePO4F

The magnetic structure and properties of sodium iron fluorophosphate Na2FePO4F (space group Pbcn), a cathode material for rechargeable batteries, were studied using magnetometry and neutron powder diffraction. The material, which can be described as a quasi-layered structure with zigzag Fe-octahedral chains, develops a long-range antiferromagnetic order below similar to 3.4 K. The magnetic structure is rationalized as a super-exchange-driven ferromagnetic ordering of chains running along the a-axis, coupled antiferromagnetically by super-super-exchange via phosphate groups along the c-axis, with ordering along the b-axis likely due to the contribution of dipole dipole interactions.

氟磷酸盐玻璃的应用研究进展

氟磷酸盐玻璃系统南于其特殊的光学性能和优良的机做与热学性能一直是特种光学玻璃材料领域的一个研究热点。总结了氟磷酸盐玻璃的分类及玻璃组分与其结构的关系，综述了氟磷玻璃在光学器件、高能高功率激光玻璃、光纤激光器、光纤放大器及上转换发光基质材料等领域上的应用，并对其未来的发展进行了展望。

Structural role of fluoride in aluminophosphate sol-gel glasses: High-resolution double-resonance NMR studies

The local structure of Na-Al-P-O-F glasses, prepared by a novel sol-gel route, was extensively investigated by advanced solid-state NMR techniques. Al-21{F-19} rotational echo double resonance (REDOR) results indicate that the F incorporated into aluminophosphate glass is preferentially bonded to octahedral Al units and results in a significant increase in the concentration of six-coordinated aluminum. The extent of Al-F and Al-O-P connectivities are quantified consistently by analyzing Al-27{P-31} and Al-21{F-19} REDOR NMR data. Two distinct types of fluorine species were identified and characterized by various F-19{Al-27}, F-19{Na-23}, and F-19{P-31} double resonance experiments, which were able to support peak assignments to bridging (Al-F-Al, -140 ppm) and terminal (Al-F, -170 ppm) units. On the basis of the detailed quantitative dipole-dipole coupling information obtained, a comprehensive structural model for these glasses is presented, detailing the structural speciation as a function of composition.

碱金属氟化物对掺Yb~(3+)氟磷酸盐玻璃析晶稳定性和光谱性质的影响

研究了碱金属氟化物对掺Yb3+氟磷玻璃的光谱性质和析晶稳定性能的影响。运用倒易法计算了Yb3+的发射截面。结果显示,LiF的引入对吸收和发射截面的提高作用较大并出现最佳引入量极值,其次为KF。碱金属氟化物的引入可提高二元体系的析晶稳定性能,使玻璃网络结构得到改善;拉曼光谱显示二元体系中引入YbF3后玻璃网络结构得到增强,而在引入碱金属氟化物的三元体系中掺杂YbF3后破坏了网络完整性,降低系统析晶稳定性能。

980 nm 抽运下Yb-Tm-Ho 三掺氟磷酸盐玻璃的2 μm 荧光性质

The thermal stability, 2 μm fluorescence properties and energy transfer mechanism in Ho³⁺ doped fluorophosphate glass sensitized by Yb³⁺ and Tm³⁺ were investigated. The characteristic temperatures, absorption spectrum and fluorescence spectrum of the glass sample were measured. ΔT calculated from the characteristic temperatures shows that the thermal stability of fluorophosphate glass is better than fluoride glass. According to the absorption spectrum, several spectroscopic parameters of the glass sample, such as Judd-Ofelt parameters and spontaneous transition probability were calculated and compared with other glass hosts. The largest spontaneous transition probability for Ho³⁺:⁵ I7&rarr⁵I8 transition in fluorophosphate glass which is 78.48 s^-1 indicates that fluorophosphate glass is an appropriate base glass to achieve 2 m fluorescence. From the fluorescence spectrum of the glass sample, the extremely strong 2.0 μm fluorescence intensity is observed, which is higher than the intensity of 1.8 μm fluorescence, showing that Ho³⁺ ions sensitized by Yb³⁺ and Tm³⁺ is efficient. Meanwhile, the absorption sections and emission sections of Yb³⁺, Tm³⁺ and Ho³⁺ were calculated and the pumping scheme and energy transfer mechanism among Yb³⁺, Tm³⁺ and Ho³⁺ are discussed. The study indicates that Yb-Tm-Ho tri-doped fluorophosphate glass is a significant sensitization glass system under 980 nm excitation for 2 μm applications.

808 nm 抽运的Ho3+，Tm3+及Er3+掺杂的氟磷酸盐 玻璃的2.0 μm 光谱性质研究

2.0 μm spectroscopic properties of Er³⁺/Tm³⁺/Ho³⁺ triply-doped fluorophosphate glasses pumped by 808 nm and the energy transfer mechanisms between the three rare earth ions were investigated. J-O theory was used to calculate the parameters of Ho³⁺ in fluorophosphate glasses. Absorption and emission cross-sections and the gain coefficients were calculated. The obtained lifetime r and spontaneous transition probability Ar of Ho³⁺:⁵I7 level were 10.64 ms and 93.95 s^-1 respectively. The calculated maximum emission cross-section of 2.0 μm was 9.26×10^-21 cm². The energy transfer analysis indicated that the cross-relaxation of Tm³⁺ was important and the resonent energy transfer in Er³⁺&rarrHo³⁺, Tm³⁺&rarrHo³⁺, Er³⁺&rarrTm³⁺&rarrHo³⁺ process was the main channel. The study revealed that the Er³⁺/Tm³⁺/Ho³⁺ triply-doped fluorophosphate glass would be a potential material for 2.0 μm emission because of the efficient sensitization of Er³⁺ and Tm³⁺ to Ho³⁺.

Optical transitions and upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

Er3+-doped halide modified tellurite glasses were synthesized by conventional melting and quenching method. The Judd-Ofelt analysis was performed on the absorption spectra and the transition probabilities, excited state lifetimes, and the branching ratios were calculated and discussed. The intense infrared and visible fluorescence spectra under 980 nm excitation were obtained. Strong upconversion signal was observed at pumping power as low as 30 mW in the glasses with halide ions. The upconversion mechanisms and power dependent intensities were discussed, which showed two-photon process are involved for the green and red emissions. The decay times of the emitting states and the corresponding quantum efficiency were determined and explained. (C) 2004 American Institute of Physics.

UV-blue upconverted emission from Nd3+-doped InF3-based heavy-metal fluoride glasses for blue upconversion fibre laser

We report spectral properties and thermal stability of Nd3+-doped InF3-based heavy-metal fluoride glasses. Fluoroindate glasses in the chemical compositions (in mol%) of (38-x)InF3-16BaF(2)-20ZnF(2)-20SrF(2)-3GdF(3)-1GaF(3-)2NaF-xNdF(3) (x = 0.1, 0.5, 1, 2, 3) have been prepared under a controlled atmosphere in a dry box. Strong UVblue upconversion emission from a green excitation wavelength has been observed and the involved mechanisms have been explained. Near-infrared emission occurs simultaneously upon excitation of the UV-blue upconversion emissions with a cw Ar(+)laser. The upconversion spectra have revealed four dominant emissions at 354, 380, 412 and 449 nm, which belong to the transitions of D-4(3/2) -> I-4(9/2), D-4(3/2) -> I-4(11/2) and P-2(3/2) -> I-4(9/2), D-4(3/2) -> I-4(13/2) and P-2(3/2) -> I-4(11/2), D-4(3/2) -> I-4(15/2) and P-2(3/2) -> I-4(13/2), respectively.

AN ACTIVATOR OF BLOOD-COAGULATION FACTOR-X FROM THE VENOM OF BUNGARUS-FASCIATUS

A specific activator of blood coagulation factor X was purified from the venom of Bungarus fasciatus by gel filtration and by ion-exchange chromatography on a Mono-Q column (FPLC). It consisted of a single polypeptide chain, with a mel. wt of 70,000 in reducing and non-reducing conditions. The enzyme had an amidolytic activity towards the chromogenic substrates S-2266 and S-2302 but it did not hydrolyse S-2238, S2251 or S-2222, which are specific substrates for thrombin, plasmin and factor Xa, respectively. The enzyme activated factor X in vitro and the effect was Ca2+ dependent with a Hill coefficient of 7.9. As with physiological activators, the venom activator cleaves the heavy chain of factor X, producing the activated factor Xa alpha. The purified factor X activator from B. fasciatus venom did not activate prothrombin, nor did it cleave or clot purified fibrinogen. The amidolytic activity and the factor X activation activity of the factor X activator from B. fasciatus venom were readily inhibited by serine protease inhibitors such as diisopropyl fluorophosphate (DFP), phenylmethanesulfonyl fluoride (PMSF), benzamidine and by soybean trypsin inhibitor but not by EDTA. These observations suggest that the factor X activator from B. fasciatus venom is a serine protease. It therefore differs from those of activators obtained from Vipera russelli and Bothrops atrox venoms, which are metalloproteinases.

Characterization of a fibrinogen-clotting enzyme from Trimeresurus stejnegeri venom, and comparative study with other venom proteases

Trimeresurus stejnegeri venom, which contains TSV-PA (a specific plasminogen activator sharing 60-70% sequence homology with venom fibrinogen-clotting enzymes), also possesses fibrinogen-clotting activity in vitro. A fibrinogen-clotting enzyme (stejnobin) has been purified to homogeneity by gel filtration and ion-exchange chromatography on a Mono-Q column. It is a single-chain glycoprotein with a mol. wt of 44,000. The NH2-terminal amino acid sequence of stejnobin shows great homology with venom fibrinogen-clotting enzymes and TSV-PA. Like TSV-PA, stejnobin was able to hydrolyse several chromogenic substrates. Comparative study of substrate specificities of stejnobin and other venom proteases purified in our laboratory was carried out on five chromogenic substrates. Stejnobin clotted human fibrinogen with a specific activity of 122 NIH thrombin-equivalent units/mg protein. However, stejnobin did not act on other blood coagulation factors, such as factor X, prothrombin and plasminogen. Diisopropyl fluorophosphate and phenylmethanesulfonyl fluoride inhibited its activity, whereas ethylenediamine tetracetic acid had no effect on it, indicating that it is a serine protease. Although stejnobin showed strong immunological cross-reaction with polyclonal antibodies raised against TSV-PA, it was interesting to observe that, unlike the case of TSV-PA, these antibodies did not inhibit the amidolytic and fibrinogen-clotting activities of stejnobin. (C) 1998 Elsevier Science Ltd. All rights reserved.

Effects of Pallas' viper (Agkistrodon halys pallas) venom on blood coagulation and characterization of a prothrombin activator

The action of Pallas' viper (Agkistrodon halys pallas) venom on blood coagulation was examined in vitro and a strong anticoagulant effect was observed. This action was abolished after treatment with a specific inhibitor of phospholipase A(2) activity (p-bromophenacyl bromide), revealing a procoagulant action in low concentrations of treated venom (around 1 mu g/ml). The effect of the venom an haemostasis was further characterized by measuring its ability to activate purified blood coagulation factors. It is concluded that A. halys pallas venom contains prothrombin activation activity. A prothrombin activator (aharin) was purified from the venom by Sephadex G-75 gel filtration and ion-exchange chromatography on a Mono-Q column. It consisted of a single polypeptide chain, with a mol. wt of 63,000. Purified aharin possessed no amidolytic activity on chromogenic substrates. It did not act on other blood coagulation factors, such as factor X and plasminogen, nor did it cleave or clot purified fibrinogen. The prothrombin activation activity of aharin was readily inhibited by ethylenediamine tetracetic acid (a metal chelator), but specific serine protease inhibitors such as diisopropyl fluorophosphate and phenylmethanesulfonyl fluoride had no effect on it. These observations suggest that, like those prothrombin activators from Echis carinatus and Bothrops atrox venoms, the prothrombin activator from A. halys pallas venom is a metalloproteinase. (C) 1998 Elsevier Science Ltd. All rights reserved.

Thin films prepared from tungstate glass matrix

Vitreous samples containing high concentrations of WO3 (above 40% M) have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. These films were characterized by X-ray diffraction (XRD), perfilometry, X-ray energy dispersion spectroscopy (EDS), M-Lines and UV-vis absorption spectroscopy. In this work, experimental parameters were established to obtain stable thin films showing a chemical composition close to the glass precursor composition and with a high concentration of WO3. These amorphous thin films of about 4 mu m in thickness exhibit a deep blue coloration but they can be bleached by thermal treatment near the glass transition temperature. Such bleached films show several guided modes in the visible region and have a high refractive index. Controlled crystallization was realized and thus it was possible to obtain WO3 microcrystals in the amorphous phase. (C) 2007 Elsevier B.V. All rights reserved.

New glasses in the system InF3-BaF2-ErPO4

New glasses have been obtained in the system InF3-BaF2-ErPO4. Glass compositions with up to 30% mol Er3+ were shown to exist and characterized by thermal analysis, x-ray: diffraction, IR absorption and electronic spectroscopy. The systems with high Er3+ content were studied recording IR and visible emission spectral characteristics. A specially elaborated technique allowed the preparation of a high purity phosphate precursor ErPO4. X-ray identification of the crystalline phases appearing during thermal treatment have been carried out and parameters of a mixed fluoride Ba4In3-nErnF17 calculated.

Concentração de flúor e solubilidade em esmalte de dentes decíduos permanentes jovens após aplicações tópicas de soluções fluoretadas.

The aim of this article was to compare, through the distillation method, the incorporated amount of fluoride and the reduction of solubility in the enamel of both deciduous and young permanent teeth, following topical application of a 2% neutral sodium fluoride solution, according to the Knutson's technique and a 1.23% of acidulated solution, according to the Wellock & Brudevold's technique. The greatest fluoride incorporation was observed in the deciduous teeth after the usage of the 2% neutral solution. The amount of calcium and phosphorus liberation by the acid solution was greatest in the control group, followed by the group of teeth treated in acidulated solution and, finally, by those treated in 2% sodium fluoride solution.

Inhibition of demineralization in vitro around amalgam restorations

Objective: The purpose of this in vitro study was to evaluate some forms of preventing or avoiding demineralization within enamel cavity walls adjacent to amalgam restorations. Method and materials: Third molar teeth were sectioned to obtain 72 specimens, divided into one control and five experimental groups: amalgam only; varnish plus amalgam; acidulated phosphate fluoride plus amalgam; adhesive amalgam; glass-ionomer cement plus amalgam; control (amalgam only, not subjected to a demineralization challenge). The experimental groups were subjected to pH and thermal cycling and then submitted to enamel hardness determinations. Results: Significant differences between the treatment groups revealed that the bonded amalgam technique offered the best resistance to demineralization. The use of cavity varnish resulted in greater mineral loss than amalgam placed alone. Conclusion: The use of an adhesive system, glass-ionomer cement, or acidulated phosphate fluoride under amalgam restorations may interfere with development of secondary caries.