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W. Ryba-Romanowski G. Dominiak-Dzik S. Golab W. A. Pisarski I. Pracka 《Journal of Applied Spectroscopy》1995,62(5):903-909
Conclusions Nonradiative energy transfer between similar and different rare-earth ions in LiNbO3 has been evidenced for the first time. The contribution of nonradiative energy transfer to the decay of the1G4 and3H4 levels of thulium and the4S3/2 and4I13/2 levels of erbium is significant for activator concentrations of the order of several thousand ppm in LiNbO3. The excitation of higher-lying levels of both activators is transferred faster in codoped crystal to the lowest luminescent
levels, from which the luminescence in the 1–2-μm spectral region occurs. This accelerated relaxation is advantageous for
broadband optical pumping since the contribution of radiative transitions competing with the3F4−3H6 laser transition of thulium is reduced. On the other hand, it appears that erbium ions will influence adversely the efficiency
of a laser-diode-pumped LiNbO3∶Er, Tm laser operating near 1.8 μm since the part of the3H4 excitation transferred to erbium ions is emitted from the long-lived4I11/2 level of Er3+. Furthermore, the4I13/2 excitation is not transferred fully to thulium ions and is lost in4I13/2−4I15/2 emission. Lithium niobate singly doped with thulium is more promising since the cross-relaxation process that transfers the
excitation from the3H4 level to the3F4 level appears to be efficient in this host.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 5, pp. 125–133, September–October, 1995. 相似文献
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Diana Gonzalez Joseph T. Golab Andrew J. Cigler James A. Kaduk 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(7):706-715
The crystal structures of a new polymorph of dipotassium hydrogen citrate, 2K+·HC6H5O72?, and potassium rubidium hydrogen citrate, K+·Rb+·HC6H5O72?, have been solved and refined using laboratory powder X‐ray diffraction and optimized using density functional techniques. In the new polymorph of the dipotassium salt, KO7 and KO8 coordination polyhedra share corners and edges to form a three‐dimensional framework with channels parallel to the a axis and [111]. The hydrophobic methylene groups face each other in the channels. The un‐ionized carboxylic acid group forms a strong charge‐assisted hydrogen bond to the central ionized carboxylate group. The hydroxy group forms an intermolecular hydrogen bond to a different central carboxylate group. In the potassium rubidium salt, the K+ and Rb+ cations are disordered over two sites, in approximately 0.72:0.28 and 0.28:0.72 ratios. KO8 and RbO9 coordination polyhedra share corners and edges to form a three‐dimensional framework with channels parallel to the a axis. The un‐ionized carboxylic acid group forms a strong charge‐assisted hydrogen bond to an ionized carboxylate group. The hydroxy group forms an intermolecular hydrogen bond to the central carboxylate group. Density functional theory (DFT) calculations on the ordered cation structures suggest that interchange of K+ and Rb+ at the two cation sites changes the energy insignificantly. 相似文献
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Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude. 相似文献
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Martin W. Feyereisen Rick A. Kendall Jeff Nichols David Dame Joseph T. Golab 《Journal of computational chemistry》1993,14(7):818-830
The use of a cluster of workstations as an alternative supercomputer resource is demonstrated using the ab initio direct SCF and RPA code DISCO. DISCO was implemented using several different mechanisms to achieve the requisite parallelization. The various parallel software mechanisms are characterized based upon several different criteria, including portability, ease of use, and relative efficiency. The application of direct SCF and RPA techniques to study the static polarizability of paranitroaniline is described. © 1993 John Wiley & Sons, Inc. 相似文献
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Dodi Heryadi Danny L. Yeager Joseph T. Golab Jeffrey A. Nichols 《Theoretical chemistry accounts》1995,90(5-6):273-290
Summary We applied the multiconfigurational spin tensor electron propagator method (MCSTEP) for determining the lowest few (in energy) vertical ionization potentials (IPs) of HF, H2O, NH3, CH4, N2, CO, HNC, HCN, C2H2, H2CO, and B2H6. We chose these molecules so that we could compare MCSTEP IPs with recently reported extended Koopmans' theorem (EKT) IPs on the same molecules. Using standard Dunning core-valence basis sets with relatively small complete active spaces, MCSTEP results are in very good to excellent agreement with experiment. These MCSTEP IPs are obtained using matrices no larger than 400 × 400. EKT matrices are even smaller; however, to obtain similar but generally slightly worse agreement with experiment, fairly large active spaces are required with EKT. 相似文献
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在一系列H模放电条件下,建立了一个旨在研究等离子体温度分布剖面不变性的数据库。介绍了数据库建立过程中要解决的关键问题和所用软件,对等离子体温度分布剖面不变性及芯部约束与边缘参数的关系进行了研究。 相似文献