CaF_2:Ce~(3+)中的电荷补偿问题的探讨

在不同的反应条件下,运用固相反应的方法合成了CaF_2∶Ce~(3+)多种粉末磷光体,测定了它们的荧光光谱,发现了3种不同的发光中心,并探讨了3种发光中心的转化规律;研究了不同阳离子电荷补偿剂对CaF_2∶Ce~(3+)光谱性质的影响;指出了不同发光中心的产生是电荷补偿途径不同所致。

CaF_2:Ce~(3+)晶体的光谱性质及γ线辐照效应

Ce~(3+)只有一个4f电子,基态能级为~2F_(5/2)和~2F(7/2),两能级差约为2200cm~(-1),Ce~(3+)不同于其它三价稀土离子,一般是d→f跃迁,特征发射为d→~2F_(5/2)和d→~2F_(7/2)跃迁引起的两宽带。CaF_2∶Ce~(3+)晶体中,当Ce~(3+)取代Ca~(2+)时,存在电荷补偿问题。Manthey讨论了CaF_2∶Ce~(3+)中间隙F~-充当电荷剂问题,Feofilov探讨了CaF_2∶Ce~(3+)的氧补偿问题,指出当有氧存在时,它

KMgF_3中Ce~(3+)的发射中心及取代格位的研究

本文用高温固相扩散反应方法及坩埚下降法制备了KMgF_(3~-)Ce~(3+)及KMg_(1-x)M_xF_(3~-)Ce~(3+)(M=Be~(2+),Ca~(2+))的粉末样品及KMgF_(3~-)Ce~(3+)单晶,测定了它们的激发光谱和发射光谱,发现KMgF_(3~-)Ce~(3+)中存在两种不同的发射中心,且证明了这是不同的电荷补偿途径所致,而不是Ge~(3+)占据了不同的阳离子格位所致.通过X射线四圆衍射仪的检测及Be~(2+)和Ca~(2+)对KMgF_(3~-)Ce~(3+)中Mg~(2+)取代后的光谱变化,推断Ce~(3+)占据KMgF_3中K~+的格位.

THE CATALYTIC BEHAVIOR AND REACTION-MECHANISM OF THE BI-CE-O SYSTEM CATALYSTS IN THE OXIDATIVE DEHYDROAROMATIZATION OF PROPYLENE

Oxidative dehydroaromatization of propylene was investigated by the pulse technique over two kinds of single oxide catalysts. With the Bi2O3 catalyst, the main dimer product was 1,5-hexadiene, and the dimerization activity was stable to pulse number even if the catalyst was partly reduced to the bulk. With the CeO2 catalyst, benzene was mainly formed instead of 1,5-hexadiene, but the activity decreased rapidly with increasing pulse number, indicating that only the lattice oxygen near the catalyst surface could be used for oxidative dimerization and the further aromatization. The Bi-Ce-O system catalyst was found in this study to give higher aromatization activity and showed better stability, compared to the Bi-Sn-O catalyst. Although the Bi-Ce-O catalyst was only a mixture of the two component oxides from X-ray diffraction analysis, there was a significant combination effect on the selectivity to benzene. The highest and the most stable selectivity of benzene was obtained at Bi/Ce = 1. In the TPD spectrum of Bi-Ce-O catalyst, there are not only the lattice oxygen (beta-oxygen) over 620-degrees-C due to the reduction of Bi2O3, but also a great deal of the alpha-oxygen desorbed about 400-degrees-C, which is considered the absorbed oxygen in the bulk. This absorbed oxygen could probably be a compensation of the lattice oxygen through the route of gaseous --> absorbed --> lattice oxygen in the binary catalyst system. By the kinetic study on the Bi-Ce-O catalyst, the dimer formation rate was the first-order with respect to the partial pressure of propylene and zero-order of oxygen. Although detail investigation would be made further, it was considered that the complete oxidation of propylene would mainly take place parallelly on some different sites, and the rate-determining step of propylene dimerization occurred probably between an adosrbed propylene and a gaseous one by an Eley-Rideal type mechanism.

氨氧化La-Ce-Co氧化物催化剂氧的性能研究

用X射线衍射和程序升温脱附方法研究了八个La-Ce-Co氧化物催化剂的结构及其氧的性能,试验了不同催化剂氨氧化反应前后氧的程脱并比较了其脱出氧的变化。测定了催化剂活性、组成及元素价态。发现催化剂的活性与三价钴离子的浓度成正比。催化剂中晶格氧的再生能力强,即氧化还原性能好,催化活性就高。结果表明,氨在La-Ce-Co氧化物体系催化剂上的氧化可能遵循Redox机理。Co~(3+)是活性中心。在催化剂中以少量Ce~(4+)取代La~(3+),可在催化剂中产生阳离子空位La_(1-x)CoO_(3+λ),有利于Co~(3+)的稳定加速体相中氧和电子的传递,促进催化剂的再氧化速度。从而提高催化剂的活性。

K_2NaAlF_6:Ce~(3+)和KAlF_4:Ce~(3+)磷光体的光谱特性

采用高温固相反应法,在Ar气氛中,合成了K_2NaAlF_6和KAlF_4基质化合物.分别测定了它们的结构,并计算了晶胞参数.测定了K_2NaAlF_6:Ce~(3+)和KAlF_4:Ce~(3+)磷光体的激发光谱和荧光光谱,根据Ce~(3+)的光谱结构的特点,讨论了Ce~(3+)的取代格位.

Ce~(3+)-Gd~(3+)在某些稀土硼酸盐体系中的能量传递

Ce~(3+)离子有一个宽而强的4f-5d吸收带,它能有效地吸收能量。Ce~(3+)离子的荧光寿命非常短,能将能量有效地传递给其它离子起敏化作用。对于Ce~(3+)→Tb~3+),Ce~(3+)→EU~(3+)和Ce~(2+)→Mn~(3+)的敏化作用已有许多报导,并在灯用发光材料上获得应用。Blasse等提出在Ce~(3+)敏化Tb~(3+)时。用Gd~(3+)作中间体能获得高效发光材料。由于Ce~(3+)的5d能级强烈地依赖于基质,其发射波长可以从紫外到红区,而Gd~(3+)的4f-4f跃迁的激发和发射峰值随基质的变化改变不大,因此将有可能呈现不同的Ce~(3+)-Gd~(3+)的能量转移过程。

CaS:Ce~(3+)磷光体的合成及发光性质

本文研究了不同合成条件对CaS:Ce~(3+)磷光体发光性质的影响。CaS:Ce~(3+)的发光强度随Ce~(3+)离子的浓度发生变化,最佳浓度为1.001×10~(-3)mol。对应于新的单一热释发光峰(426K)的陷阱参数为,陷阱深度E=1.01eV,逃逸频率因素S=1.2×10~(11)s~(-1),磷光体的热释发光满足二级动力学过程。

GENERAL ALPHA-N INDEX AND ITS APPLICATION .1. GENERAL ALPHA-N INDEX AND ITS APPLICATION IN THE EXTRACTION OF Y, CE, U, AND TH BY NEUTRAL PHOSPHORUS EXTRACTANCTS

The general a(N) index is established for molecules containing heteroatoms, rings, and multiple bonds. The general a(N) index is able to describe molecules with minute differences in structure and can also reveal the properties of molecules. This theory is successfully applied to the case of neutral phosphorus extractants. Both the molecular polarity and steric effect are characterized by the general a(N) index. The relationships between these properties and the distribution ratios for extracting Y, Ce, U, and Th are also shown by the general a(N) index.

碱金属碱土金属磷酸盐中Ce~(3+)的发光

磷酸盐是一类极好的发光和激光基质。稀土的多聚磷酸盐晶体、磷酸盐玻璃均可用于激光材料,掺稀土的碱金属磷酸盐已用于X射线或阴极射线发光材料。Ce~(3+)在某些磷酸盐中的发光与敏化作用已有综述,Ce~(3+)敏化的某些磷光体已做成光致发光材料。碱金属碱土金属磷酸盐中Ce~(3+)的发光研究报道甚少,仅见到对KCaCe(PO_4)_2和

LnAlO_3中Ce~(3+),Tb~(3+),Dy~(3+)的发光及Ce-Tb,Ce-Dy的敏化发光(Ln=La,Gd,Y)

本文采用BaF_2作为助熔剂和抑制剂经固相反应合成了一系列以LnAlO_3(Ln=La,Gd,Y)为基质的磷光体,系统地研究了LnAlO_3中Ce~(3+),Tb~(3+),Dy~(3+)的发光及Ce-Tb,Ce-Dy的敏化发光,发现随Ln的不同,LnAlO_3作为基质对激活剂的发光性质的影响也不同,本文得到一些规律性结果,并作了讨论。

ZrO_2-Y_2O_3:Ce,Fe,Co晶体的发光光谱和电子顺磁共振

本文详细解释先前测量的(YSZ)ZrO_2-Y_2O_3(88:12):CeO_2(0.01,0.3,0.5wt%),Fe:O:0.03wt%+CeO_20.01wt%,CoO(0.1,0.3wt%)晶体γ辐照前后的吸收光谱。以250—310nm激发,测量这些晶体的发光光谱,定性研究不同浓度铈、钻杂质对YSZ色心发光的影响。YSZ在400—600nm色心发光因受到铈、钴杂质再吸收,使它的发光强度减弱。这种现象在γ辐照后变得更为明显。为了证实掺杂YSZ缺陷结构存在和杂质离子价态,测量了这些晶体辐照前后的电子顺磁共振。由单电荷(Y_((zr),V_n)′自由自旋和Fe~(3+)离子的ESR信号变化,反推铈、钻杂质在YSZ晶体中的价态变化。并和吸收光谱加以比较。

Eu~(2+)和Ce~(3+)在钙钛矿型氟化物中的光谱特征和能量传递

对具d-f和f-f两种跃迁形式的Eu~(2+)和具d-f跃迁特征的Ce~(3+),讨论了它们在ABF_3(A=K~(+),Ba~(2+);B=Li~(+),Mg~(2+),Ca~(2+))中的光谱特征。根据Eu~(2+)、Ce~(3+)在KCaF_3基质中的能级关系,实现了在复合氟化物中Ce~(3+)对Eu~(2+)能量传递,探讨了能量传递机理,并计算了传递量子效率。

Ce_(0.9)RE_(0.1)P_5O_(14)晶体中Ce~(3+)的发光寿命研究

利用时间相关单光子计数方法系统地测定了Ce_(0.9)RE_(0.1)P_5O_(14)晶体中Ce~(3+)的发光寿命。发现荧光寿命数值能够较好地说明双掺晶体中除Ce而外的其它稀土离子对Ce~(3+)的发光强度的增强或猝灭现象。

RE_(1-x)B_xF_(3-y)(RE=Y、La、Ce、Gd;B=Ca、Ba)的敏感性质的研究

LaF_3作为离子选择性电极和对气体的敏感性质已进行了一定的研究,但其他稀土氟化物的敏感性质却未见报道。本文合成了RE_(1-x)B_xF_(3-y),研究了它们的结构、电学性质及敏感性质,得到有可能在150℃使用的固体电解质氧敏材料。 (一) RE_(1-x)B_xF_(3-y)的结构分析 结构分析表明,Ca、Ba置换RE的含量少时,如La_(0.95)Ba_(0.05)F_(3-y)、Ce_(0.95)Ca_(0.05)F_(3-y)的X射线衍射分析结果与LaF_3、CeF_3相似,说明它们是固溶体。而Ca置换RE含量较多时,如Y_(0.71)Ca_(0.29)F_(3-y)、Gd_(0.85)Ca_(0.15)F_(3-主)的X射线衍射分析结果却与相应的YF_3和GdF_3完全不