Radiative lifetimes for ultraviolet transitions in C,N and O ions by the pulse decay method

The pulse-decay method has been used to measure radiative lifetimes of several low-lying states of CI, CII, OI, NI and NII giving spectral lines between 916 and 1657 Å. Measured lifetimes of these states ranged. from 1.2 to 8.2 nsec. Agreement with the results of others using different methods is reasonably good. In particular, comparison with lifetimes measured by Hutchison using the phase-shift method with the same basic experimental apparatus shows no systematic differences between the two methods.     

Fourier transform emission lifetime spectrometer

We report a rapid and low cost Fourier transform spectrometer that uses a path length modulated Michelson interferometer to simultaneously measure excitation spectra and excitation wavelength-dependent emission lifetimes. Excitation spectra and lifetimes of excited tris(2,2'-bipyridyl) ruthenium(II) measured using this technique corresponded to values known in the literature. Excitation-dependent lifetimes of porous silicon measured with this technique suggest the influence of quantum confinement effects. This method may be useful for measuring mixtures of emitting species with closely spaced lifetimes as well as studying excitation wavelength-dependent emission phenomena.     

LnxRE1-xP5O14(LRPP)晶体的光谱研究

研究了50多种LnxRE1-xP5O14(Ln3+:Pr3+,Nd3+,Er3+,RE:La3+→Lu3+,Y3+,Sc3+)晶体的紫外可见吸收光谱,荧光光谱和红外吸收光谱.计算了室温下Pr3+,Er3+离子的振子强度.讨论了晶体的荧光寿命.     

Lifetimes of excited levels of Kr I and Kr II

The lifetimes of eight levels belonging to the 6p configuration of KrI and thirteen levels belonging to different configurations of KrII have been measured. The levels were excited by short electron pulses of appropriate energy and the lifetimes determined by a delayed coincidence method using single photon counting techniques. All measurements were carried out at different gas pressures. The measured lifetimes of the KrII levels are compared with other experimental results obtained by a different method (beam-foil spectroscopy) and with calculations made in the intermediate coupling scheme.     

Testing Fluorescence Lifetime Standards using Two-Photon Excitation and Time-Domain Instrumentation: Rhodamine B,Coumarin 6 and Lucifer Yellow

Having good information about fluorescence lifetime standards is essential for anyone performing lifetime experiments. Using lifetime standards in fluorescence spectroscopy is often regarded as a straightforward process, however, many earlier reports are limited in terms of lifetime concentration dependency, solvents and other technical aspects. We have investigated the suitability of the fluorescent dyes rhodamine B, coumarin 6, and lucifer yellow as lifetime standards, especially to be used with two-photon excitation measurements in the time-domain. We measured absorption and emission spectra for the fluorophores to determine which wavelengths we should use for the excitation and an appropriate detector range. We also measured lifetimes for different concentrations, ranging from 10^?2– 10^?6 M, in both water, ethanol and methanol solutions. We observed that rhodamine B lifetimes depend strongly on concentration. Coumarin 6 provided the most stable lifetimes, with a negligible dependency on concentration and solvent. Lucifer yellow lifetimes were also found to depend little with concentration. Finally, we found that a mix of two fluorophores (rhodamine B/coumarin 6, rhodamine B/lucifer yellow, and coumarin 6/lucifer yellow) all yielded very similar lifetimes from a double-exponential decay as the separate lifetimes measured from a single-exponential decay. All lifetime measurements were made using two-photon excitation and obtaining lifetime data in the time-domain using time-correlated single-photon counting.     

Optical study of erbium-doped La3Ga5.5Ta0.5O14 single crystal

Single crystals of erbium-doped La₃Ga_5.5 Ta_0.5O₁₄, grown by the Czochralski method, have been investigated using methods of optical spectroscopy. Room-temperature absorption spectra were analysed in the framework of the Judd-Ofelt theory. Radiative transition rates, radiative lifetimes and luminescence branching ratios for luminescent levels of Er³⁺ have been evaluated and compared to measured luminescence intensities and lifetimes. The laser potential associated with the ⁴I_13/2-⁴I_15/2 transition near 1.55 μm has been assessed. It has been concluded that La₃Ga_5.5 Ta_0.5,O₁₄:Er crystal is an intermediate gain laser material exhibiting strong inhomogeneous broadening of absorption bands, advantageous for optical pumping with laser diodes.     

Y3Ga5O12:Cr3+激光晶体的发光特性

在10K—300K温度范围内测量了Cr3+:Y3Ga5O12晶体对应于2E→4A2与4T2→4A2跃迁谱峰的荧光寿命。得出2E、2T1与4T2态的辐射寿命分别为965.8μs、130.7μs与88.6μs。理论拟合的标准相对误差为2.85%。分析了荧光的热猝灭机理,导出了荧光寿命和辐射量子效率的温度依赖关系。     

SmxLa1-xP5O14和DyxY1-xP5O14晶体的荧光寿命研究

本文用脉冲衰减法和时间分辨荧光光谱法测量了六种不同稀土离子浓度的SmxLa1-xP5O4晶体的4G5/2→6HJ(J=5/2,7/2,9/2,11/2)四个能级和七种不同稀土离子浓度的DyxY1-xP5O14晶体的4F9/2→6HJ(J=15/2,13/2,11/2,9/2)四个能级的荧光寿命和荧光强度。结果指出,在这类晶体中,Sm3+和Dy3+的荧光寿命随着离子的浓度增加而变短,存在着严重的荧光浓度猝灭现象。最后还讨论了浓度与寿命,寿命与荧光强度的关系。     

Measurement of the lifetime of the first excited state in17O and17F

A new version of the “recoil distance method”, making use of a gas target, has been used to determine the lifetime of the 871 keV level in¹⁷O and of the 495 keV level in¹⁷F. The measured values of the lifetimes are (2.32±0.08) · 10^?10 sec and (3.96±0.10) · 10^?10 sec for¹⁷O and¹⁷F, respectively.     

Radiative lifetimes of Rydberg 6pnd J=2 states of Pb I by multichannel quantum defect theory

Energy levels of the odd-parity 6pnd J=2 Rydberg states of Pb I are analysed by the multichannel quantum defect theory (MQDT) in the frame of a five-channel three-limit calculation model. With optimal MQDT parameters, channel admixture coefficients are obtained and used to calculate the theoretical lifetimes of the levels by comparing to the previously measured lifetimes. The predicted lifetimes for higher-lying Rydberg states are given and discussed. These predicted lifetimes are very different from those obtained by the four-channel two-limit model pl:eviously used, which means that introduction of the additional interacting channel is important for studying the 6pnd J=2 Rydberg states of Pb I.     

Inelastic quasiparticle lifetimes of the Shockley surface state band on Ni(111)

We present a study of the low-energy quasiparticle lifetimes of the Shockley surface state on the Ni(111) surface with scanning tunnelling spectroscopy. By measuring the coherence length of the decaying standing wave pattern at straight step edges electron and hole lifetimes have been determined. The values of the lifetime measured on this ferromagnetic surface show to be considerable smaller than the values obtained from noble metal surfaces. This is explained by differences in the electron density of states at the Fermi energy but has to include substantial spin-flip scattering. Furthermore hole lifetimes appear to be larger than electron lifetimes with the same excitation energy. Although only results for the majority spin component are presented, a spin-dependent selfenergy is expected.     

Lifetime-measurements of alkali-molecules excited by different laserlines

Absorbing different lines of acw-argon ion laser or a He-Ne-laser the alkali molecules Na₂, K₂, Rb₂ and Cs₂ can be pumped into different rotational-vibrational levels of an excited electronic state. The lifetimes of these states have been measured using the phase shift technique at a modulation frequency of 18 Mc/sec. Because of collisions with the always present alkali atoms the excited molecules may undergo collision-induced transitions to other states and their lifetimes are dependent on the atomic pressure. This dependence was measured and the spontaneous lifetimes were obtained by extrapolation against zero pressure. Different collision processes are discussed which compete with the unperturbed fluorescence.     

Anharmonic phonon lifetimes in carbon nanotubes: evidence for a one-dimensional phonon decay bottleneck

High-resolution Raman spectroscopy is applied to suspended single-walled carbon nanotubes (SWNTs) to elucidate the puzzling differences in the lifetime of the radial breathing mode (RBM) obtained from different experimental techniques. Whereas recent tunneling experiments suggest a room temperature RBM lifetime as long as 10 ns, previous Raman experiments yield lifetimes shorter than 2 ps. The lifetimes obtained in this study are longer than 5 ps-a significant step in the direction of the tunneling results. We argue that the remaining discrepancy is due to the existence of phonon decay bottlenecks caused by the one-dimensional nature of nanotubes. Numerical simulations of the RBM decay show that it is possible to reconcile the short lifetimes measured spectroscopically with the long lifetimes obtained in tunneling experiments.     

Sub-Structures Formed in the Excited State are Responsible for Tryptophan Residues Fluorescence in β-Lactoglobulin

Origin of tryptophan residues fluorescence in β-lactoglobulin is analyzed. Fluorescence lifetimes and spectra of β-lactoglobulin solution are measured at pH going from 2 to 12 and in 6 M guanidine. Tryptophan residues emit with three lifetimes at all conditions. Two lifetimes (0.4–0.5 ns and 2–4 ns) are in the same range of those measured for tryptophan free in solution. Lifetimes in the denatured states are lower than those measured in the native state. Pre-exponential values are modified with the protein structure. Data are identical to those already obtained for other proteins. Fluorescence lifetimes characterize internal states of the tryptophan residues (Tryptophan sub-structures) independently of the tryptophan environments, the third lifetime results from the interaction that is occurring between the Trp residues and its environment. Pre-exponential values characterize substructures populations. In conclusion, tryptophan mission occurs from substates generated in the excited state. This is in good agreement with the theory we described in recent works.     

Some lifetimes and transition probabilities in Cu(I)

Radiative lifetimes of 7 levels in the Cu(I) 3d⁹ 4s4p configuration have been measured using a delayed coincidence technique; copper vapor was excited in an argon buffer gas and cross sections for collisional destruction of copper levels by argon were also obtained. Transition probabilities of the lines originating from these levels have been determined using the measured lifetimes and branching ratios.     

Measurements of radiative lifetime of high-lying odd parity energy levels of U I

We have measured the radiative lifetimes of nine odd-parity high-lying energy levels of atomic uranium (U I) using pump probe techniques. These measurements were carried out by employing a resonance ionisation mass spectrometry (RIMS) setup consisting of three dye lasers and a Time-of-Flight Mass Spectrometer (TOF-MS). In most of the cases, our measurement values match reasonably well with those reported in the literature; however, large deviations were also observed in two long-lived cases, which we have tried to explain. The lifetimes of three odd parity energy levels of U I were measured for the first time.     

环境辐射对原子高激发能级Stark态寿命的影响

在外电场中用激光两步激发使Na原子在待测Stark态（n=17，m=0）上实现布居．用延迟脉冲场电离方法测量了部分Stark态的寿命及环境黑体辐射对其实际寿命的影响，并与理论计算值作了比较．实验和计算表明：对n=17的Stark簇各能态，室温下环境黑体辐射引起的受激跃迁对其寿命的影响与自发辐射跃迁已达同一数量级．寿命越长的Stark态，黑体辐射的影响程度越大，这一因素连同Stark混合效应均使同一Stark簇内各能态实际寿命的差异变小． 关键词：     

Pressure dependence of positron lifetimes in V3Si

We have measured positron lifetimes in V₃Si at hydrostatic pressures of 0 to 20 kb, at room temperature. The lifetimes were independent of pressure, within the experimental uncertainty of ± 2 ps; the results of eight measurements all were between 129 and 133 ps.     

Positron lifetime measurement in NaNO2

Positron lifetimes in NaNO₂ were measured as a function of temperature. The lifetime spectra consisted of one component, and could not be resolved into two component. The positron trapping model is not applicable in this case. Observed changes of lifetimes around the transition temperature could not be understood only by the volume dilatation, but they must be affected by the ferro-para electric phase transition