The concentration quenching and crystallographic sites of Eu²⁺ in Ca₂BO₃Cl

A yellow phosphor, Ca2BO3 Cl:Eu2+ , is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f 6 5d 1 →4f 7 transition of Eu2+ . Eu2+ ions occupy two types of Ca2+ sites in the Ca2BO3 Cl lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2+ in Ca2 BO 3 Cl. The emission intensity of Eu2+ in Ca2BO3 Cl is influenced by the Eu2+ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole–dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.     

The effect of intragranular microstress in Al₂O₃-SiC nanocomposites

A theoretical model is established to investigate the intragranular particle residual stress in Al2O3-SiC nanocomposites.Using this model,we calculate the average compressive stress on the Al2O3 grain boundary(GB) and the average tensile stress within Al2O3 grains caused by SiC nanoparticles.The normal compressive stress strengthens the GB,and the average tensile stress weakens the grains.The model gives a reasonable interpretation of the strength changes of Al2O3-SiC nanocomposites with the number of SiC particles.     

The infrared-induced temperature distributions of solid D2 ices

A specific-wavelength infrared(IR) light(λ = 3140 nm) was irradiated into a solid D2 ice prepared in a cylinder target cell.The temperature in the solid D2 ice oscillated periodically with a high amplitude when irradiated by the IR light.The temperature oscillation has been well explained based on the two-dimensional heat transfer theory plus the IR-irradiation effect.The transmission optical imaging reveals that such a temperature oscillation is favorable to recrystallize the solid D2 ice from multicrystal to quasi single crystal.This suggests an efficient method to layer the solid hydrogen-isotope ice for the inertial-confinement-fusion(ICF) experiments.     

The crystal structure,magnetism,and colossal magnetoresistance of Y₂CrS₄

Ternary yttrium chromium sulfide,Y2CrS4,prepared by the solid-state reaction of Y2S3,Cr,and S,was found to exhibit an antiferromagnetic transition at about 64 K.The X-ray diffraction pattern at 300 K was refined with space group Pca2 1,and the structure parameters were determined to be a = 12.51 ,b = 7.53,and c = 12.49.We investigated the magnetotransport properties,and observed negative colossal magnetoresistance reaching up to 2.5 × 10 4 % in the semiconducting compound of Y2CrS4.     

The optical properties of Yb3+ ions in LiTaO3:Nd,Yb crystals

3+ ions excited by energy transfer from Nd³⁺ ions in LiTaO₃:Nd, Yb crystals are presented. The emission band of Yb³⁺ ions is broad, due to the strong phonon-coupling and to the relative large Stark-splitting of the ground ²F_7/2 multiplet. The emission cross-section was evaluated by the reciprocity method, and a value of 0.53×10^-20 cm² was obtained. The gain coefficients derived for the inversion parameters in the range 0.05 to 0.5 indicate positive gain in the 985–1070 nm range. Received: 17 March 1997/Revised version: 10 June 1997     

南中国海海藻刺状鱼栖苔的化学成分研究(I)

从采自南中国海红藻刺状鱼栖苔的乙醇提取物中分离出一个黄酮类化合物，经ＩＲ，ＵＶ，ＦＡＢＭＳ，１Ｈ－１ＨＣＯＳＹ，１３Ｃ－１ＨＣＯＳＹ，ＨＭＢＣ等现代波谱技术确定其结构为５，７－二羟基－２－对羟基苯基－３－Ｏ－（６－Ｏ－对羟基肉桂酰基－β－Ｄ－吡喃葡萄糖基）－４Ｈ－１－苯并吡喃－４－酮，并对碳信号进行了明确归属．这是首次从红藻中分离出黄酮类化合物．     

新的聚苯乙烯负载锌化合物:高效苯酚氧化催化剂(英文)

The novel recyclable free –ONNO– tetradentate Schiff base ligand N,N′‐bis(2‐hydroxy‐3‐ methox‐ybenzaldehyde)4‐methylbenzene‐1,2‐diamine (3‐MOBdMBn) was synthesized. Complexation of this ligand with zinc(3‐MOBdMBn‐Zn) was performed, and the catalytic activity of the complex was evaluated. The polymer‐supported analog of this complex(P‐3‐MOBdMBn‐Zn) was synthesized, and its catalytic activity was studied. These free and polymer‐anchored zinc complexes were prepared by the reactions of metal solutions with one molar equivalent of unsupported 3‐MOBdMBn or P‐3‐MOBdMBn in methanol under nitrogen. The catalytic activity of 3‐MOBdMBn‐Zn and P‐3‐MOBdMBn‐Zn was evaluated in phenol oxidation. The activity of P‐3‐MOBdMBn‐Zn was signif‐icantly affected by the polymer support, and the rate of phenol conversion was around 50% for polystyrene‐supported 3‐MOBdMBn. The experimental results indicated that the reaction rate was affected by the polymer support, and the rate of phenol conversion was 1.64 μmol/(L·s) in the presence of polystyrene‐supported 3‐MOBdMBn.     

核磁共振波谱研究氟化膦配体及其金属配合物的氟谱化学位移

研究了氟化膦类系列配位体（ＧＰＦ２：Ｇ＝Ｆ，Ｅｔ２Ｎ，Ｍｅ２Ｎ，Ｃ５Ｈ１０Ｎ，ｎＰｒＯ，ＰｈＯ，ｎｅｏＰｎＯ，２，５ｄｉＭｅＰｈ，ｉｓｏＰｒ，ｅｔｃ．）及其与金属镍（０）铜（Ｉ）钼（０）金（Ｉ）形成的配合物的核磁共振氟谱化学位移的定量分子建模，发现了其中的一些有用规律．     

Sur la régularité des espaces métriques généraux

Résumé L'auteur propose une autre définition de la notion de régularité d'un espace métrique général (la définition actuelle est due à M. H. Busemann, 1957). La définition nouvelle dépend du point fixé ainsi que d'une direction fixée dans ce point. Hommage de l'auteur à Monsieur le Professeur BeniaminoSegre à l'occasion de son 70^ème anniversaire. Entrata in Redazione l'8 maggio 1973.     

Complete Bell-state analysis for a single-photon hybrid entangled state

We propose a scheme capable of performing complete Bell-state analysis for a single-photon hybrid entangled state.Our single-photon state is encoded in both polarization and frequency degrees of freedom.The setup of the scheme is composed of polarizing beam splitters,half wave plates,frequency shifters,and independent wavelength division multiplexers,which are feasible using current technology.We also show that with this setup we can perform complete two-photon Bell-state analysis schemes for polarization degrees of freedom.Moreover,it can also be used to perform the teleportation scheme between different degrees of freedom.This setup may allow extensive applications in current quantum communications.