Luminescence properties of Ce3+ in KMF3(M=Mg, Ca, Sr, Ba) hosts with perovskite structure

KMF3(M = Mg, Ca, Sr, Ba) compounds were synthesized by solid state reaction under argon atmosphere. Their structures were determined by X-ray diffraction. It belongs to cubic system with perovskite structure. The excitation and emission spectra of KMF3:Ce3+ were measured. According to the characteristics of spectral structures, the occupation site of Ce3+ is discussed.

层状La-Ba-Cu复合氧化物在CO还原NO反应中活性的研究

氮氧化物是严重的空气污染物,催化消除氮氧化物是环保催化研究的热点问题,在已有报道的催化剂体系中复合氧化物和含铜分子筛受到人们的普遍关注,文献中已有报道ABO_3(A=Ln;B=Cr,Mn,Fe,Co,Ni)型复合氧化物作为CO还原NO反应的催化剂.但迄今尚未见有合成LaCuO_3的报道,有关含铜复合氧化物作催化剂的大多是A_2BO_4型的.呈ABO_3结构的含铜复合氧化物只有成层状的超导体如YBa_2Cu_3O_7,本文为了探讨复合氧化物晶体结构对催化活性的影响,首次研究了3种层状ABO_3结构的La-Ba-Cu复合氧化物对CO还原NO反应的活性,发现它们均具有较高的活性,并首次提出了Ba离子在此反应中的作用.1 实验方法催化剂的制备和Cu价态分析见文献[4,5]CO还原NO反应在固定床流动反应体系中进行,反应管为内径6mm石英管,催化剂粒度为40～80目,用量0.2g,空速为7000h~(-1),原料气为NO7.5×10~(-3),CO8.0×10~(-3),He平衡.采用英国产的Pyc Pan气相色谱分析检测N_2O,CO_2,0.5nm分子筛色谱柱检测NO,CO转化率. H_2-TPR在自制装置上...

离子型晶体的点电荷电量的确定和晶体的化学键性质MX(M=Mg,Ca,Sr,Ba,X=O,S,Se,Te;不含MgTe)

离子型晶体的点电荷电量的确定和晶体的化学键性质ＭＸ（Ｍ＝Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｘ＝Ｏ，Ｓ，Ｓｅ，Ｔｅ；不含ＭｇＴｅ）孟庆波武志坚张思远（中国科学院长春应用化学研究所稀土无机材料实验室，长春１３００２２）ＮｅｔＣｈａｒｇｅａｎｄＣｈｅｍｉｃａｌＢｏｎ...

Y-Ba-Cu-O mixed oxides for production of diphenols in liquid-solid phase

Superconductor mixed oxides were often used as catalysts at higher temperature in gas phase oxidations, and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of YBa2Cu3O7+/-x and Y2BaCuO5+/-x in the phenol hydroxylation at lower temperature with H2O2 as oxygen donor was studied, and found that the superconductor YBa2Cu3O7+/-x, has no catalytic activity for phenol hydroxylation, but Y2BaCuO5+/-x does, even has better catalytic activity and stability than most previously reported ones. With the studies of catalysis of other simple metal oxides and perovskite-like mixed oxides, a radical substitution mechanism is proposed and the experimental facts are explained clearly, and draw a conclusion that the perovskite-like mixed oxides with (AO)(ABO(3)) and (AO)2(ABO(3)) structure have better catalytic activity than the simple perovskite oxides with (ABO(3))(3) structure alone, and (AO) structure unit is the key for the mixed oxides to have the phenol hydroxylation activity. No pollution of this process is very important for its further industrial application.

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.

Investigation of Catalysis of Y-Ba-Cu-O Mixed Oxides in Phenol Hydroxylation

Superconductor Y-Ba-Cu-O mixed oxides were synthesized and their catalysis in phenol hydroxylation was studied too. Results show that, Y2BaCuO5 has better activity than that of YBa2Cu3O7-x, With the catalysis study of another mixed oxide La2CuO4 a conclusion that AO structure unit is the key for mixed oxides to have high activity in phyenol hydroxylation was drawn. Meanwhile, the effects of reaction temperature, medium and medium (water) pH on phenol hydroxylation catalyzed by Y2BaCuO5 and the stability of the mixed oxides were also studied.

MMgF_4(M=Ca,Sr,Ba)体系中Eu和Tb的电荷迁移

于不同气流中,合成了MMgF_4:xEU,yTb复合氟化物燐光体.该体系中Eu~(3+)和Eu~(2+)共存.Tb的存在影响Eu的价态存在形式.ESR测试表明,随Tb的掺入浓度增加,Eu~(2+)的浓度呈规律性变化.随Eu的掺入,样品的XPS谱中出现了四价铽的Tb_3d(5/2)特征伴峰.认为Eu~(3+)和Tb~(3+)之间存在电荷迁移平衡.即Eu~(3+)+Tb~(3+)(?)Eu~(2+)+Tb~(4+).通过半定量手段研究了SrMgF_4中这一平衡的平衡常数.

Ce~（3＋）在钙钛矿型KMF_3（M＝Mg、Ca、Sr、Ba）基质中的发光特性

采用高温固相反应法，在Ａｒ气氛中合成了ＫＭＦ３（Ｍ＝Ｍｇ、Ｃａ、Ｓｒ、Ｂａ）基质化合物和掺杂Ｃｅ３＋的磷光体。经Ｘ射线衍射分析确定，ＫＭｇＦ３和ＫＣａＦ３属于立方晶系、钙钛矿型结构，ＫＳｒＦ３和ＫＢａＦ３具有类似的结构。测定了ＫＭＦ３∶Ｃｅ３＋的发光光谱，观察到与其结构对应的分为二种不同的光谱结构，讨论了Ｃｅ３＋的取代格位

Studies on the synthetic, structural, electrical and magnetic properties of Ln(n)MCo(n)O(3n+1) (Ln=Sm, Gd; M=Sr, Ba; n=1,2)

Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been synthesized successfully by solid state reaction mathod. The X-Ray diffraction spectra show that they are all isostructural with Sr3Ti2O7, and Ln(2)SrCo(2)O(7)(Ln=Sm,Gd) crystallized in tetragonal system, Sm2BaCo2O7 in orthrhombic system. The Co-O bonds in CoO2 planes of Ln(2)SrCo(2)O(7) are shorter than those of LnSrCoO(4)(Ln=Sm, Gd), and so their delectrons are more delocalized and their electrical resistivities are smaller. The electrical resistivities versus temperature in the range 300 similar to 1100K showed that the five brides show the characters of weakly localized systems. In the lower temperature range, the magnetic behaviors of Gd2SrCo2O7 and GdSrCoO4 fit Curie-Weiss law well, and the magnetic exchange reaction in CoO2 sublattices of Gd2SrCo2O7 is ferromagnetic, but that of GdSrCoO4 is antiferromagnetic. The other three oxides with Sm3+ showed complex magnetic behaviors which is perhaps related with the complexity of Sm3+.

THE EFFECT ON PHYSICAL-PROPERTIES OF THE SUBSTITUTION OF CA OR BA FOR SR IN NDSRNIO4

A new solid solution series, NdSr(1-x)M(x)NiO(4) (M = Ca: 0.0 less than or equal to x less than or equal to 1.0; M = Ba: 0.0 less than or equal to x less than or equal to 0.6), was synthesized by solid state reaction, and the structures, magnetic and electrical properties and optical spectra of this series have been studied. All the samples crystalized in tetragonal systems, with the exception of NdCaNiO4, which crystallized in the orthohombic system. IR spectra of NdSr1-xCaxNiO4 indicated that the lengths of two Ni-O bonds decrease with increasing Ca content. The electrical conduction changed from metallic-type to semiconductive-type when x greater than or equal to 0.4 (M = Ca, Ba), and the room temperature resistivities of NdSr1-xCaxNiO4 increased with the increase of Ca content. Magnetic susceptibility measurements revealed that Ni+3 ions in all the samplies were in low-spin state over the temperature range 77-300 K.

A STUDY OF SURFACE OXYGEN SPECIES FROM LA-ME-O (ME=MG, CA, SR, BA) CATALYSTS FOR METHANE OXIDATIVE COUPLING

CO2-TPD was used to study the surface basicity of La-Me-O mixed oxides and O-2-TPD, CH4-TPD were employed to study the surface active oxygen species. Comparing the CO2-TPD with O-2-TPD, we can see that the basicity of catalyst is in parallel with the catalystic activity. The stronger basicity is more profitable for the catalyst to adsorb oxygen to form active oxygen species and to activate CH4 by breaking a C-H bond, By comparing the catalytic activity, the results showed that La-Ba-O(La/Ba=7/3) catalyst had the strongest basicity, and it gave the highest CH4 conversion and C-2 selectivity, The results from the pulse reaction showed that the lattice oxygen participated in the OCM reaction without gas oxygen, and it was the selective oxygen species.

STUDIES ON THE SYNTHETIC, STRUCTURAL, ELECTRICAL, AND MAGNETIC-PROPERTIES OF THE NEW LAYERED OXIDES LN(2)MCO(2)O(7) (LN=SM, GD, M=SR, BA)

Three new oxides Ln(2)MCo(2)O(7) (Ln = Sm, Gd; M = Sr, Ba) have been synthesized in solid state reaction method. The powder X-ray diffraction spectra show that they are all isostructural with Sr3Ti2O7. The electrical resistivities in the temperature range 300-1100 K show that they are all semiconductors, and a transition to metals is observed at 1053, 1053, and 573 K for Sm2SrCo2O7, Gd2SrCo2O7, and Sm2BaCo2O7, respectively. The magnetic suspectivities of Gd2SrCo2O7 in the temperature range 300-673 K fit the Curie-Weiss law well. A plateau is observed in the curves of Sm(2)MCo(2)O(7) (M = Sr, Ba) which is attributed to the configuration state change of Co(III) from low spin to high spin. (C) 1995 Academic Press, Inc.

MMgF_4：Eu（M＝Ca，Sr，Ba）体系中铕离子的发光中心及价态

合成了铕离子激活的ＭＭｇＦ４．磷光体，研究了Ｅｕ３＋离子的光谱特征与基质化合物的关系，存在三类发光中心，讨论了基质组成对铕离子价态的影响。