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161.
采用常规固相反应于1200℃下制备了具有褐钇铌矿结构的Y2O3·Nb2O5·B2O3(Y(0.93)Eu(0.07))2O3·Nb2O5·B2O3和(Y(0.91)Eu(0.07)Bi0.02))2O3·Nb2O5·B2O3等光体,研究了它们的发光性质:结果表明,在268nm紫外光激发下,由于NbO4基团于410nm处发生1T→1A1跃迁,致使Y2O5·Nb2O5·B2O3呈现更亮的紫外发射。体系中的B2O3可降低反应温度,增强NbO4和Eu(3+)的发光强度。(Y(0.091)Eu(0.07)Bi(0.02))2O3·Nb2O5·B2O3燐光体系中所观察到的NbO4→Eu(3+)和Bi(3+)→Eu(3+)的能量传递使红光发射明显增强。 相似文献
162.
Summary The fluoroescence quenching of 1,4-dimethoxynaphthalene (1) and 1,8-dimethoxynaphthalene (2) by tetraphenylporpyrin (3), 9,10-diphenylanthracene (4), and 3-cyano-4-phenyl-6-(p-tolyl)-pyridin-2-one (5) has been studied in chloroform solution. The quenching occursvia a resonance energy transfer mechanism. The rate constant for the energy transfer (k
ET) of donor2 is slower than that of1 by the same acceptors, indicating that the steric effect dominates the ionization potential effect in all systems. The calculated critical transfer distances (R
0) are 17–72 Å. In contrast, charge transfer is the predominant pathway of electronic deexcitation in the fluorescence quenching of donors1 and2 by 7,7,8,8-tetracyanoquinone-dimethane (6) in chloroform. The roles of temperature and geometrical structure of the donors on the efficiency of fluorescence quenching of1 and2 by acceptor6 have also been studied.
Wechselwirkung des angeregten Singlett-Zustands von 1,4- und 1,8-Dimethoxynaphthalin mit einigen organischen Verbindungen: eine Untersuchung zur Fluoreszenzlöschung
Zusammenfassung Die Löschung der Fluoreszenz von 1,4-Dimethoxynaphthalin (1) und 1,8-Dimethoxynaphthalin (2) durch Tetraphenylporphyrin (3), 9,10-Diphenylanthracen (4) und 3-Cyano-4-phenyl-6-(p-tolyl)-pyridin-2-on (5) in Chloroform wurde untersucht. Die Löschung verläuft über einen Resonanzenergietransfermechanismus. Die Geschwindigkeitskonstante für den Energietransfer (k ET) ist bei gleichem Akzeptor für den Donor2 niedriger als für1. Daraus läßt sich schließen, daß in allen untersuchten Systemen der sterische Effekt über den Effekt des Ionisierungspotentials dominiert. Die berechneten kritischen Transferdistanzen betragen 17–72 Å. Im Gegensatz zu diesen Beobachtungen verläuft der vorherrschende Relaxationsmechanismus bei der Fluoreszenzlöschung von1 und2 durch 7,7,8,8-Tetracyanochinon-dimethan (6) über einencharge-transfer-Prozeß. Die Einflüsse von Temperatur und Geometrie der Verbindungen auf die Effizienz der Fluoreszenzlöschung von1 und2 durch den Akzeptor6 wurden ebenfalls untersucht.相似文献
163.
Nonisothermal kinetics of the solid‐solid phase transition in (n‐C10H21NH3)2ZnCl4(C10Zn), (n‐C16H33NH3)2ZnCl4(C16Zn) and their binary system were determined by Kissinger and Ozawa methods from DSC measurements. The activation energy Ea of the binary system shows a waving dependence on WC10Zn%, which is caused by not only an intermediate (C10H21NH3)(n‐C16H33NH3)ZnCl4 but also three solid solution ranges (α, β, γ) in the phase diagram of C10Zn‐C16Zn. The variations of the layer d‐spacing are also convenient for the above result. 相似文献
164.
对于NO分子轨道的能级次序现有两种不同的说法,不少人根据NO与O_2~+是等电子体,由O_2~+分子的能级次序确定NO分子组态。本文用NO和O_2~(+)从头计算结果以及NO的紫外光电子能谱相结合的方法说明NO的5σ轨道是弱成键轨道,5σ的轨道能稍高于1π轨道能,也就是说NO的能级次序是与N_2分子相同的;NO与O_2~+虽是等电子体,但是能级次序并不相同,因此由O_2~+的能级次序确定NO分子的电子组态是不妥的。 相似文献
165.
Summary A simple gas chromatographic method has been developed for analysis of hydrogen sulfide in hydrogen at the 0.5 to 100 ppm level. After enriching the traces of hydrogen sulfide by absorption in a gas loop packed with the chosen column support at 77 K it was determined by using a Chromosorb G column with silicone 550 and phthalic anhydride as liquid phases, hydrogen as carrier gas and a thermal conductivity detector. The detection limit was found to be about 0.5 ppm of hydrogen sulfide. 相似文献
166.
167.
The effect of vibrational excitation of HBr on the H+HBrH2+Br and H+HBrH+HBr reactions has been investigated on the extended LEPS surface (ELEPS) constructed on the basis of quantum chemically calculated points of PES. Together with this surface the LEPS surface of Sudhakaran and Raff [1] was used for comparison at two relative translational energies. A quasiclassical trajectory method was used to study the abstraction and exchange reaction dynamics. The reactive cross section was calculated as a function of the relative collision energy and the vibrational state of HBr. The following conclusions can be drawn from the results of the study: (i) vibrational excitation v=0 v=2 more than doubles the reaction cross section, (ii) the increase in the collision energy is most effectively channelled into the product translational energy.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday 相似文献
168.
R. I. Damper Y. Marchand J.-D. S. Marsters A. I. Bazin 《Journal of Sol-Gel Science and Technology》1997,8(2):147-160
A common requirement in speech technology is to align two different symbolic representations of the same linguistic ‘message’.
For instance, we often need to align letters of words listed in a dictionary with the corresponding phonemes specifying their
pronunciation. As dictionaries become ever bigger, manual alignment becomes less and less tenable yet automatic alignment
is a hard problem for a language like English. In this paper, we describe the use of a form of the expectation-maximization
(EM) algorithm to learn alignments of English text and phonemes, starting from a variety of initializations. We use the British
English Example Pronunciation (BEEP) dictionary of almost 200,000 words in this work. The quality of alignment is difficult
to determine quantitatively since no ‘gold standard’ correct alignment exists. We evaluate the success of our algorithm indirectly
from the performance of a pronunciation by analogy system using the aligned dictionary data as a knowledge base for inferring
pronunciations. We find excellent performance—the best so far reported in the literature. There is very little dependence
on the start point for alignment, indicating that the EM search space is strongly convex. Since the aligned BEEP dictionary
is a potentially valuable resource, it is made freely available for research use. 相似文献
169.
通过3-氨基-4-羟基苯甲酸盐酸盐(AHBAH),2,5-二氨基-1,4-苯硫醇盐酸盐(DABDT)和2,5-噻吩二羧酸(TDA)在多聚磷酸中缩聚,合成了一系列不同组成的高、低带隙无规共聚物聚(2,5-苯并噁唑)-co-聚(2,5-噻吩基苯并二噻唑)(ABPBO-co-PBZTT),并制备了一系列由ABPBO和PBZTT组成的共混物.通过紫外-可见吸收光谱、光致荧光光谱研究了聚合物不同组成和结构变化对光物理性能的影响.随着共聚物中PBZTT含量的增加,共聚物的发射波长红移,并发生了明显的ABPBO结构吸收能量向PBZTT转移的现象,共聚物膜的量子效率比纯PBZTT膜的量子效率有明显提高.共混物虽然也发生了能量转移现象,但其更易于形成集聚体,量子效率与纯的PBZTT聚合物相比,并没有明显提高. 相似文献
170.
Karen L. Frindell Matthew R. Robinson Alois Popitsch 《Journal of solid state chemistry》2003,172(1):81-88
Selected photoluminescence in the wavelength range of 600-1540 nm is generated by energy transfer from a light-gathering mesostructured host lattice to an appropriate rare earth ion. The mesoporous titania thin films, which have a well-ordered pore structure and two-phase walls made of amorphous titania and TiO2 nanocrystallites, were doped with up to 8 mol% lanthanide ions, and the ordered structure of the material was preserved. Exciting the titania in its band gap results in energy transfer and it is possible to observe photoluminescence from the crystal field states of the rare earth ions. This process is successful for certain rare earth ions (Sm3+, Eu3+, Yb3+, Nd3+, Er3+) and not for others (Tb3+, Tm3+). A mechanism has been proposed to explain this phenomenon, which involves energy transfer through surface states on titania nanocrystals to matching electronic states on the rare earth ions. 相似文献