The collisional stabilization of excited β-naphthylamine molecules by the paraffin hydrocarbons in the gas phase

The transfer of vibrational energy from molecules of β-naphthylamine excited by the mercury lines at 2804 Å and 2652 Å to the homologous series of paraffin hydrocarbons up to n-hexane has been investigated in the gas phase at 180°C. Although the average amount of energy transferred collisionally increases with the complexity of the added gas by a factor of 5, the transfer efficiency expressed as an accommodation coefficient remains virtually unchanged.

A transfer mechanism based on the internal redistribution of vibrational energy within the collision complex is examined, in terms of which it is unnecessary to invoke vibration-vibration transfer except for pentane and hexane. The collision duration estimated on the basis of this model is well within an order of magnitude of that expected from collision diameters and relative velocities of the molecules concerned.     

LaOBr:Er3+,Tm3+红外跃迁的研究

对在基质LaOBr中分别加入Er3+和Tm3+稀土离子时的红外光谱强度随Er3+和Tm3+离子浓度的变化规律进行了研究.通过对在基质LaOBr中同时加入Er3+和Tm3+稀土离子对它们的发光强度随着浓度的变化呈现不同规律的研究,证实了发生于Er3+和Tm3+稀土离子之间的能量转移是影响Er3+和Tm3+红外发光的重要因素.并且,这种能量转移过程是以共振传递的方式进行的.另外,通过对Er3+的4S3/2能级寿命的测量,给出这种能量转移的直接证据.     

Power limitations of the cw He-Hg laser

The variation of output power with discharge current in the hollow-cathode cw He-Hg laser has been investigated. In strong contrast to the comparable data for the positive-column discharge, the 6150 Å transition shows no turnover in output power with increasing current. Laser powers approaching 100 mW (cw) have been achieved at 6150 Å using a 3mm-bore, 50cm-long tube. Investigation of the excitation mechanisms for the 6150 and 7945 Å transitions confirms both are excited by thermal energy charge transfer reactions.     

Influence of the radiationless transitions on an intensity of the optical radiation emitted by excited atoms ejected from solids by an ion beam

The excited atoms of the target material are ejected during an ion bombardment of solids. These atoms belong to one of two velocity groups — fast or slow. The fast atoms arise in binary collisions of bombarding ions with target atoms and the slow ones are knocked out as a result of a sputtering process. Excited atoms flying off the surface intersect the solid-vacuum boundary and can transfer their excitation energy in the radiationless transitions mainly of the resonance ionization type. The probability of this process depends strongly on the electronic energy level structure of solids and a velocity of ejected atoms. On this statement our method of the electronic energy level structure of solids study is based by means of investigation of excited atoms velocity spectrum. On the results of paper [4] we remark that in their experimental conditions the surface of the lithium target was apparently strongly oxidized. Using our method and results of paper [4] we can estimate the energy width of the conduction band of Li₂O to 0.4 eV. In general the cascade corrections to the mean life times of excited atoms may be important and one can take them into account. The detailed analysis of the influence of the cascade corrections to the mean life times of upper excited states of some TiI lines (λλ 5210 Å, 5064 Å, 4682 Å, 3981 Å, 4533 Å, 4856 Å) was carried out. It was found that in the case when our method was applied to determination of the work function of metallic titanium the cascade corrections either are negligible or not necessary.     

Fluorescence spectroscopic studies on the multicomponent system coumarin 1/fluorescein/rhodamine B in ethanol

The steady-state fluorescence spectra of the three-component system coumarin 1/fluorescein/rhodamine B in 95% ethanol were studied at room temperature. In the appropriate concentration ranges, upon the excitation of coumarin 1 at 377 nm, the ternary dye mixture solution emitted simultaneously with three bands centered at 443, 528, and 575 nm, respectively. The analysis of the data seems to indicate that there is significant energy transfer between these three dyes and that the main contribution corresponds to the Förster nonradiative mechanism. The critical transfer distances between each two of the three components were calculated to be 48.4 Å for the coumarin 1/fluorescein pair, 42.2 Å for the coumarin 1/rhodamine B pair, and 65.5 Å between fluorescein and rhodamine B dyes. The system can potentially be used to obtain three primary outputs at different wavelengths in a dye laser system.     

Elastic scattering cross section of photons by water: limits for the free atom approximation

Several papers can be found in the literature in which elastic and inelastic experimental scattering cross sections of photons by water with energies in the keV range are measured. Usually, the authors use some kind of normalization with theoretical values, because of the difficulties in obtaining some parameters necessary to obtain absolute cross sections from the measurements. A reasonable range of momentum transfer has been covered, but nevertheless, inconsistencies and gaps still remain. In this work, we address the problem performing absolute cross section measurements in the high momentum transfer region (0.33 Å^?1 ≤ x ≤ 4.5 Å^?1), where no structure effects can be observed. We compare the results with theory to validate it in an intermediary region (0.33 Å^?1 ≤ x ≤ 1.72 Å^?1) and then use the experimental values to normalize data in the low‐energy region (0.078 Å^?1 ≤ x ≤ 1.72 Å^?1) to obtain the experimental cross section in that region. From the comparison, we concluded that for momentum transfers, x between 0.7 and 4.5 Å^?1 the scattering can be considered as being due to free atoms in free molecules. Therefore, the scattering cross sections may be considered as a sum of those from free atoms. Theoretically, the scattering cross sections can be obtained from the form factors as well as from the second‐order perturbation theory (S‐matrix) because there is no significant difference between both. On the other hand, for x ≤ 0.7 Å^?1, interference between the photon‐scattered amplitudes due to liquid structure generates oscillations in the cross section values. Copyright © 2014 John Wiley & Sons, Ltd.     

Energy transfer in amorphous anthracene-tetracene films

Sensitized fluorescence in amorphous anthracene-tetracene layers formed by vacuum-sublimation onto 77 K substrates is investigated as a function of tetracene concentration, sample temperature and annealing conditions. It is found that in the temperature range 77 to 130 K host-guest energy transfer in unannealed samples occurs by Förster long range coupling between anthracene excimers and single tetracene molecules. The experimental transfer distance R₀ = 28.7 ± 2.3 Å is in fair agreement with the calculated value R_{0, theor} = 25.8 ± 1.6 Å. Population of the excimer-forming sites must involve singlet exciton motion through the host matrix.     

Excitonic excitation spectra in ZnS: Cl crystal under pressure

The 3363 Å peak in the excitation spectrum of the S-A luminescence in the ZnS:Mn Cl cubic crystal at R.T. is ascribed to the A exciton. Its pressure coefficient is found as 6.4±0.2 meV/kbar, close to ρ = 6.3±0.2 meV/kbar reported for the gap in ZnS cubic crystal from the reflectivity measurements. This peak decreases by cooling and has not been observed at 85 K. The uv-excitation of the Mn-luminescence at R.T. is due to the energy transfer from the S-A to the Mn²⁺ centers, whereas the excitation peak at the exciton energy at 85 K comes from the excitation of the Mn²⁺ centers by the recombination energy of the Mn²⁺ bound excitons.     

Energy transfer in I2-HD mixtures

Collisional energy transfer from the vibrational level ν=43 of the B state of I₂ in I₂-HD mixtures was investigated by exciting with the 5145 Å line of an Ar⁺ laser. Relaxation rates were measured for different vibrational quantum changes in state B. Analysis of the energy transfer data indicated the possibility of a resonant energy transfer mechanism taking place between the excited I₂ molecules and the ground state HD molecules (vibrational to rotational relaxation).     

Effect of electric field on the electronic properties of functionalized germanane by organic molecular adsorption

Modulating the doping effect and charge transfer in germanane is very important for germanane-based electronic or optoelectronic devices with reproducible electrical characteristics. In this letter, we investigate the effect of electric field on the electronic properties of functionalized germanane by tetrathiafulvalene (TTF) molecular adsorption through first-principles calculations. It is found that the nondestructive n-type doping effect induced by tetrathiafulvalene (TTF) molecular adsorption could be linearly tuned by external electric field ranged from −0.3 V/Å to 0.3 V/Å. Especially under the electric field of −0.3 V/Å, an excellent n-type doping in germanane can be realized where the energy difference between the filled band maximum of dopant and the conduction band minimum of germanane for electron excitation is only 0.085 eV. More interestingly, once the external electric field exceeds 0.15 V/Å, the typical electron donor molecule TTF would even overturn to accept the electrons from germanane substrate.     

Eu3+在Y2O3-Bi2O3体系中发光性能的研究

Y2O3:Eu3+磷光体中的Eu3+在6100Å附近呈现很强的尖峰发射.这个磷光体虽然在阴极射线和短波紫外光(约2500Å激发下是十分有效的,但是对于长波紫外光激发却很不灵敏.Datta[2]於1967年报导在Y2O3:Eu3+磷光体中加入少量Bi3+,在3650Å长波紫外光激发下可增强Eu3+在6100Å的尖峰发射强度.     

Structure and electrophysical properties of ferrocobaltites <Emphasis Type="Italic">Ln</Emphasis>BaFeCoO<Subscript>5 + δ</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = Tb,Dy, Ho,Y)

The ferrocobaltites LnBaFeCoO^{5 + δ} (Ln = Tb, Dy, Ho, Y) have been synthesized, and the parameters of their crystal structure have been determined. The thermal expansion, electrical resistivity ρ, and thermopower S of the synthesized compounds have been investigated in air at temperatures in the range from 300 to 1100 K. The compounds have a tetragonal structure (symmetry space group P4/mmm) with the unit cell parameters a = 3.9000 Å and c = 7.5922 Å (Ln = Tb, δ = 0.31), a = 3.8973 Å and c = 7.5679 Å (Ln = Dy, δ = 0.34), a = 3.8970 Å and c = 7.5507 Å (Ln = Ho, δ = 0.28), and a = 3.9029 Å and c = 7.5538 Å (Ln = Y, δ = 0.25). The ferrocobaltites under investigation are p-type semiconductors, and their electrical resistivity ρ and thermopower S decrease in the sequence Tb → Ho → Y → Dy (at room temperature). The linear thermal expansion coefficient of the LnBaFeCoO^{5 + δ} phases in the vicinity of the temperatures ranging from 465 to 535 K increases from (1.15?1.23) × 10^?5 to (1.73?1.93) × 10^?5 K^?1. The parameters of charge transfer in these ferrocobaltites have been determined. It has been found that an increase in the temperature leads to an increase in the excitation energy of charge carriers and a decrease in the activation energy of charge carrier transfer.     

高掺杂Ce3+,Tb3+在正硼酸盐中的发光特性及能量传递

本文利用纳秒技术和一般光谱学技术系统地研究了Ce3+,Tb3+离子在LnBO3(Ln=La,Gd和Y)中的发光特性和能量传递机制.发现在La1-xCexBO3中Ce3+离子的浓度在0.1mol以上才出现明显的浓度猝灭.故对敏化剂Ce3+可以高浓度掺杂.本文对高掺杂下材料的发光特性,Ce3+到Tb3+能量传递的规律和机制进行了系统研究.给出了在正硼酸盐中绿色发光材料的最佳配比.     

Dispersion relation of low-energy excitations in Zr<Subscript>50</Subscript>Be<Subscript>50</Subscript> metallic glass

A high-resolution (1.5 meV) inelastic neutron scattering experiment is carried out to investigate in detail the low momentum (0.6–1.5 Å^?1) dynamic response in Zr₅₀Be₅₀ metallic glass. The results are obtained on the hot neutron three-axis spectrometer IN1 in the Laue-Langevin Institute (Grenoble, France). A comparison with recent neutron scattering results for the momentum transfer region above 1.4 Å^?1 shows a minimum in the dispersion relation of low energy excitations near the prepeak of the static structure factor. These excitations appear to be due to the short-range order in this amorphous system.     

Messung der quasi-elastischen Neutronenstreuung in Glyzerin mit einem hochauflösenden Kristallspektrometer

A new neutron crystal spectrometer with an energy resolution of 6 · 10^?7 eV was installed at the Munich reactor. The high energy resolution is based on the backscattering of neutrons on silicon single crystals. The energy of the neutrons striking the glycerol sample is varied by Doppler shifting. With this spectrometer the quasielastic line broadening in glycerol was investigated at constant momentum transfer (κ=1.4 ± 0.25) Å^?1 as a function of temperature. The diffusion constants deduced from the experiment are in the order of 10^?7 cm²/s to 5 · 10^?9 cm²/s.     

Open Channel Structure of MscL: A Patch-Clamp and Spectroscopic Study

MscL, the bacterial mechanosensitive (MS) channel of large conductance, has become a prototype channel to study structure–function relationship of the MS class of ion channels. Within a few years of cloning the mscL gene, the three-dimensional structure of the MscL protein was determined by X-ray crystallography, which allowed for detailed molecular studies of its structure and function. A combination of the (1) patch-clamp recording examining the function of MscL channels reconstituted into artificial liposomes, and (2) electron paramagnetic resonance (EPR) and fluorescence resonance energy transfer (FRET) spectroscopy examining structural changes occurring during gating of the reconstituted channels, provided a plausible molecular mechanism of gating of MS channels. This experimental approach helped to establish two physical mechanisms as triggers of the MscL channel gating by lipid bilayer deformation forces: (1) the energetic cost of protein-bilayer hydrophobic mismatch and (2) the geometric consequences of bilayer intrinsic curvature. The results of the EPR and FRET spectroscopic studies showed that the open state of MscL is highly dynamic, supporting a water-filled pore of at least 25 Å in diameter corresponding to an overall change in diameter of the channel protein of about 15 Å.     

Intramolecular energy transfer in naphthalene-containing polyesters: Experiment and simulation for model compounds derived from five aliphatic dicarboxylic acids and 2-hydroxynaphthalene

Steady-state fluorescence depolarization measurements and molecular dynamics simulations have been used to study the efficiency of nonradiative intramolecular singlet energy transfer between 2-naphthoxy groups, denoted N, in model compounds for polyesters derived from 2,6-dihydroxy-naphthalene and aliphatic dicarboxylic acids. The five bichromophoric compounds studied are the diesters abbreviated as N-OOC-(CH₂)_n-COO-N;n = 2–6, which are condensation products obtained from 2-naphthol and aliphatic dicarboxylic acids. The anisotropy of the fluorescence of these compounds dispersed in a solid matrix of glassy poly(methyl methacrylate) indicates that there is nonradiative singlet energy transfer between naphthoxy groups. The efficiency of this transfer depends onn. A theoretical treatment using molecular dynamics simulations for the conformations of the five model compounds has been performed in order to evaluate the parameters related to the efficiency of the transfer. The experimental and theoretical variation of such parameters withn is consistent with the estimated Förster radius of 9–10 Å for this system.     

Photoluminescence properties of Ca9Lu(PO4)7:Ce3+, Mn2+ prepared by conventional solid-state reaction

A new red-emitting phosphor Ca₉Lu(PO₄)₇:Ce³⁺, Mn²⁺ has been synthesized by solid-state reaction, and its luminescence properties have been investigated. The broad red emission peaked at 645 nm of Mn²⁺ is greatly enhanced by the sensitizer Ce³⁺ due to efficient energy transfer from Ce³⁺ to Mn²⁺. The energy transfer was demonstrated to belong to a resonant type via a dipole–quadrupole mechanism. The critical distance for Ce³⁺→Mn²⁺ energy transfer was calculated to be 15.04 Å by concentration quenching method. Preliminary results indicate that the phosphor might be a promising red phosphor for UV-based white LEDs.     

Isotactic poly(p-fluorostyrene): X-ray structure determination

Using as a starting point the atomic positions determined by potential energy calculations, the crystal structure of isotactic poly(p-fluorostyrene) has been determined from X-ray diffraction data. It is found that two chains having 4, helical conformations pack into a metrically orthorhombic unit cell with a = 17.6 Å, b = 12.1 Å, and c = 8.25 Å (chain axis). Satisfactory agreement between the calculated and observed structure factors was obtained only when statistical variation of left- and right-handed parallel helices was considered.     

碳纳米管阀门的分子动力学研究

以Lennard-Jones位能式与Brenner-Tersoff位能式为基础,经由分子动力学模拟,探讨流体分子与碳管间质、能传递的关系.首先在一(5,5)armchair碳管侧面,分别移除不同数目的碳原子,形成阀口(A_av=17.3~116.9Å2),进行模拟.结果显示,常用的自扩散行为在该环境下不足以完全说明物性,即在相同系统温度下,阀口的大小也会改变氢原子逸出速度V_b(Breakthrough velocity).为此,必须考虑麦克斯韦-波尔兹曼能量分布方程(Maxwell-Boltzmann energy distribution)修正,此外,原子释放率与阀口尺寸有明显的相依性.同时研究中亦发现,阀门不同几何尺寸引起位能障(Potential energy barrier)、功函数(Work function)以及能隙(Energy gap)的改变,进而影响粒子通过时流率、流速等动力行为.可利用该特性,作为控制原子、分子流动的纳米阀门、粒子分离或化学反应器等基础设计依据.