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Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co2+Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed. 相似文献
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Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems. 相似文献
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Observation of a hot high-current electron beam from a self-modulated laser wakefield accelerator 总被引:1,自引:0,他引:1
Santala MI Najmudin Z Clark EL Tatarakis M Krushelnick K Dangor AE Malka V Faure J Allott R Clarke RJ 《Physical review letters》2001,86(7):1227-1230
A highly relativistic electron beam produced by a 50 TW laser-plasma accelerator has been characterized by photonuclear techniques. The beam has large divergence that increases with plasma density. The electron yield also increases with plasma density and reaches up to 4x10(11) electrons ( >10 MeV), with beam current approaching the Alfvén limit. Effective electron temperatures exceeding 8 MeV are found, leading to an order of magnitude higher photonuclear activation yield than in solid target experiments with the same laser system. 相似文献
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A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
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Carbon‐11 Radiolabelling of Organosulfur Compounds: 11C Synthesis of the Progesterone Receptor Agonist Tanaproget
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Tom Haywood Dr. Steven Kealey Santiago Sánchez‐Cabezas Dr. James J. Hall Dr. Louis Allott Dr. Graham Smith Dr. Christophe Plisson Dr. Philip W. Miller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9034-9038
Herein a new 11C radiolabelling strategy for the fast and efficient synthesis of thioureas and related derivatives using the novel synthon, 11CS2, is reported. This approach has enabled the facile labelling of a potent progesterone receptor (PR) agonist, [11C]Tanaproget, by the intramolecular reaction of the acyclic aminohydroxyl precursor with 11CS2, which has potential applications as a positron emission tomography radioligand for cancer imaging. 相似文献