Study on the reduction of Eu3+ -> Eu2+ in Sr4Al14O25: Eu prepared in air atmosphere

Compounds of Sr4Al14O15: Eu were prepared in air atmosphere by high temperature solid state reaction. The reduction of Eu3+--> Eu2+ was firstly observed in the aluminate phosphor of Sr4Al14O25: Eu synthesized in air condition. This made aluminate a new family and Sr4Al14O25 a new member of compounds in which Eu3+ ion could be reduced to Eu2+ form when fired in air atmosphere. The reduction of Eu3+ --> Eu2+ in Sr4Al14O25: Eu was explained by means of a charge compensation model. Experiments based on the model were designed and carried out, and the results supported this model.

Tuning the Eu luminescence in glass materials synthesized in air by adjusting glass compositions

The doped Eu3+ ions can be partly reduced to Eu2+ in a series of MO-B2O3: Eu (M=Ba, Sr, Ca) glasses synthesized in air atmosphere, but not in the 12CaO-7Al(2)O(3): Eu glass. The different redox-behavior of Eu ions in these two glass systems is attributed to the different host optical basicity. It is found that a lower valence state of Eu2+ is more favorable in acidic glasses, which have lower optical basicities. A notion of the critical value of optical basicity is introduced empirically, which can be used as a guide for the selection of glass composition suitable to incorporate Eu2+ for luminescence. (C) 2006 Elsevier B.V. All rights reserved.

Reduction of Eu3+ to Eu2+ in MAl2Si2O8 (M = Ca, Sr, Ba) in air condition

In general, the reduction of Eu3+ to Eu2+ in solids needs an annealing Process in a reducing atmosphere. in this paper, it is of great interest and importance to find that the reduction of Eu3+ to Eu2+ can be realized in a series of alkaline-earth metal aluminum silicates MAl2Si2O8 (M = Ca, Sr, Ba) just in air condition. The Eu2+-doped MAl2Si2O8 (M = Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong hand emissions of 4f(6)5d(1)-4f(7) from Eu2+ were observed at 417, 404 and 373 nm in air-annealed CaAl2Si2O8, SrAl2Si2O8 and BaAl2Si2O8, respectively, under ultraviolet excitation although the Eu3+ precursors were employed. In addition, under low-voltage electron beam excitation, Eu2+-doped MAl2Si2O8 also shows strong blue or ultraviolet emission corresponding to 4f(6)5d(1)-4f(7) transition.

Synthesis and characterization of (phenolphthalein/4,4 '-thiodiphenol) PES copolymers

Copolymers based on monomers phenolphthalein (PP)/4,4'-thiodiphenol (Bis-T)/4,4'-dichlorodiphenylsulfone (DCDPS) were prepared by a route involving the toluene, N-methyl-2-pyrrolidone and anhydrous potassium carbonate synthesis. The range of optimum reaction temperature was between 185 and 195 degrees C. The copolymers were characterized by C-13 NMR, differential scanning calorimetry (DSC) and torsion braid analysis. It was found that all of the copolymers were random and homogeneous and their glass transition temperatures (T-g) decreased linearly with an increase of Bis-T contents in the copolymers. The thermal stability determined by thermogravimetry analysis in air atmosphere indicated that the copolymer had better resistance to thermo-oxidative degradation. Dynamic mechanical measurement showed that (PP/Bis-T) PES copolymers containing 0-50 mol% of Bis-T components had two secondary relaxations. (C) 1998 Elsevier Science Ltd. All rights reserved.

菱铁矿热转变过程中岩石磁学性质基本特征

利用吉林大栗子铁矿纯菱铁矿样品，系统测量了菱铁矿在空气环境的的磁化特征，揭示出其饱和曙剩磁（ＳＩＲＭ）、剩磁矫顽力（ＨＣＲ）和居里温度（ＴＣ）随加热温度升高而秘珠系列变化，菱放氧化中准稳定态性矿物磁赤铁矿是中间产物之一，并且具有较高的热稳定性，Ｘ射线衍射和穆斯堡尔效应等分析结果证实了岩石磁学研究所揭示的菱铁矿氧化中磁性矿物转变过程，菱铁矿氧化过程中结晶结构的转变可能会影响其氧化产物的磁性特性。

Hydrogen sensors based on AlGaN/AIN/GaN Schottky diodes

Pt/AlGaN/AIN/GaN Schottky diodes are fabricated and characterized for hydrogen sensing. The Pt Schottky contact and the Ti/Al/Ni/Au ohmic contact are formed by evaporation. Both the forward and reverse currents of the device increase greatly when exposed to hydrogen gas. A shift of 0.3 V at 300K is obtained at a fixed forward current after switching from N-2 to 10%H-2+N-2. The sensor responses under different concentrations from 50ppm H-2 to 10%H-2+N-2 at 373K are investigated. Time dependences of the device forward current at 0.5 V forward bias in N-2 and air atmosphere at 300 and 373K are compared. Oxygen in air accelerates the desorption of the hydrogen and the recovery of the sensor. Finally, the decrease of the Schottky barrier height and sensitivity of the sensor are calculated.

Characterization of FeNi3 alloy in Fe-Ni-O system synthesized by citric acid combustion method

Fe-Ni-O samples, with Fe/Ni ratio ranging from 2 to 1/3, were synthesized. Samples synthesized with and without citric acid in the precursor were compared and it was found that the addition of citric acid is the necessary condition for FeNi3 formation; it was found that FeNi3 alloys were formed in these samples even when calcined in an air atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy measurements were used to characterize the samples. Because of the existence of FeNi3 alloys, Fe-Ni-O samples showed strong reactivity to NO and NO + O-2 but were inert to O-2 alone.

A new oxide ion conductor: La3GaMo2O12

A new oxide ion conductor, La3GaMo2O12, with a bulk conductivity of 2.7 X 10(-2) S.cm(-1) at 800 degrees C in air atmosphere was prepared by the traditional solid-state reaction. The room temperature X-ray diffraction data could be indexed on a monoclinic cell with lattice parameters of a=0.5602(2) nm, b=0.3224(1) nm, c= 1.5741(1) nm, beta= 102.555(0)degrees, V=0.2775(2) nm(3) and space group Pc(7). Ac impedance measurements in various atmospheres further support that it is an oxide ion conductor. This material was stable in various atmospheres with oxygen partial pressure P(O-2) ranging from 1.0 X 10(5) to 1.0 X 10(-7) Pa at 800 degrees C. A reversible polymorphic phase transition occurred at elevated temperatures as confirmed by the differential thermal analysis and dilatometric measurement.

Polyimides from isomeric biphenyltetracarboxylic dianhydrides and the effects of chemical structure on solubility

A series of homopolyimides and copolyimides was synthesized by the solution condensation of biphenyltetracarboxylic dianhydride (BPDA) isomers and various diamines followed by chemical imidization. These polyimides had intermediate to high molecular weights with inherent viscosities of 0.34-1.01 dL/g for homopolyimides and 0.48-1.02 dL/g for copolyimides. Thermogravimetric analysis indicated that the aromatic polyimides were stable up to 500degreesC, and the 5% weight loss temperatures were recorded in the range of 506-597degreesC in an air atmosphere and in the range of 517-601degreesC in a nitrogen atmosphere, depending on the diamines used. The glass transition temperatures of aromatic homopolyimides were above 271degreesC, while the glass transition temperatures of the copolyimides increased with an increase in the 2, 2', 3, 3'-BPDA-component. The effects of the chemical structure of the polymer chain on the solubility were investigated. It was found that the solubility of BPDA-based polyimides could be improved by the introduction of flexible units, nonlinear and non-coplanar units, and copolymerization. The polyimides with nonlinear and non-coplanar units derived from 2, 2', 3, 3'-BPDA appeared to have prominently enhanced solubility in polar aprotic solvents and polychlorocarbons when compared with the homopolyimide derived from 3, 3', 4, 4'-BPDA.

Synthesis and properties of aromatic polyimides derived from 2,2,' 3,3 '-biphenyltetracarboxylic dianhydride

2,2,'3,3' -Biphenyltetracarboxylic dianhydride (2,2,'3,3'-BPDA) was prepared by a coupling reaction of dimethyl 3-iodophthalate. The X-ray single-crystal structure determination showed that this dianhydride had a bent and noncopolanar structure, presenting a striking contrast to its isomer, 3,3,'4,4'-BPDA. This dianhydride was reacted with aromatic diamines in a polar aprotic solvent such as N,N-dimethylacetamide (DMAc) to form polyamic acid intermediates, which imidized chemically to polyimides with inherent viscosities of 0.34-0.55 dL/g, depending on the diamine used. The polyimides from 2,2,'3,3'-BPDA exhibited a good solubility and were dissolved in polar aprotic solvents and polychlorocarbons. These polyimides have high glass transition temperatures above 283 degrees C. Thermogravimetric analyses indicated that these polyimides were fairly stable up to 500 degrees C, and the 5% weight loss temperatures were recorded in the range of 534-583 degrees C in nitrogen atmosphere and 537-561 degrees C in air atmosphere. All polyimides were amorphous according to X-ray determination. (C) 1999 John Wiley & Sons, Inc.

Luminescent properties of Ba-3(PO4)(2):Eu, Tb phosphors

Luminescence of europium (III), europium(II) and terbium(III) has been observed in Ba-3(PO4)(2):Eu, Tb phosphors which are synthesized in air atmosphere. The valence state of europium is influenced by amount of terbium. It is notable that the relative intensity of the emission spectra peaks corresponding to Eu2+ is increased if the amount of Tb3+ is increased. These phenomena can be explained by an electron transfer mechanism. We predict a new kind of two-rare-earth codoped trichromatic phosphors in Ba-3(PO4)(2) matrix.

The spectral properties of BaB8O13:Eu,Tb phosphors

The luminescence properties of BaB8O13:xEu,yTb phosphors which were synthesized in air atmosphere have been studied. The emissions of europium(III), terbium(III) and europium(II) have been observed in BaB8O13:xEu, yTb phosphors. Electron paramagnetic resonance (EPR) studies were carried out. The intensities of EPR peaks of europium(II) are increased if terbium(III) is increased in BaB8O13:Eu3+,yTb(3+) phosphors. So the valence state of europium is influenced by terbium(III). These phenomena can be explained by an electron transfer mechanism. We found a new kind of method to prepare trichromatic phosphor that two rare earth ions activated in a BaB8O13 matrix.

Luminescence properties of SrB4O7: Eu, Tb phosphors

In this paper, the luminescence properties of SrB4O7: xEu, yTb phosphors were investigated. The SrB4O7: xEu, yTb phosphors were first synthesized in air atmosphere, and the emission spectra of Eu2+, Eu3+ and Tb3+ ions have been observed in phosphors. We found that the relative intensity of the emission of Eu2+ ion in the same matrix are increased when Tb3+ is incorporated in SrB4O7:Eu phosphor. So the valence state of europium is influenced by terbium. These phenomena can be explained using an electron transfer theory.