Lifetime Measurements Of Excited States Research Articles

Emission beyond 4 μm and mid-infrared lasing in a dysprosium-doped indium fluoride (InF3) fiber.

Optical emission from rare-earth-doped fluoride fibers has thus far been limited to less than 4μm. We extend emission beyond this limit by employing an indium fluoride (InF3) glass fiber as the host, which exhibits an increased infrared transparency over commonly used zirconium fluoride (ZBLAN). Near-infrared pumping of a dysprosium-doped InF3 fiber results in broad emission centered around 4.3μm, representing the longest emission yet achieved from a fluoride fiber. The first laser emission in an InF3 fiber is also demonstrated from the 3μm dysprosium transition. Finally, a frequency domain excited state lifetime measurement comparison between fluoride hosts suggests that multiphonon effects are significantly reduced in indium fluoride fiber, paving the way to more efficient, longer wavelength lasers compared to ZBLAN fibers.

Photophysics of GaN single-photon emitters in the visible spectral range

In this work, we present a detailed photophysical analysis of recently-discovered optically stable, single photon emitters (SPEs) in Gallium Nitride (GaN). Temperature-resolved photoluminescence measurements reveal that the emission lines at 4 K are three orders of magnitude broader than the transform-limited widths expected from excited state lifetime measurements. The broadening is ascribed to ultra-fast spectral diffusion. Continuing the photophysics study on several emitters at room temperature (RT), a maximum average brightness of ~427 kCounts/s is measured. Furthermore, by determining the decay rates of emitters undergoing three-level optical transitions, radiative and non-radiative lifetimes are calculated at RT. Finally, polarization measurements from 14 emitters are used to determine visibility as well as dipole orientation of defect systems within the GaN crystal. Our results underpin some of the fundamental properties of SPE in GaN both at cryogenic and RT, and define the benchmark for future work in GaN-based single-photon technologies.

Excited-state lifetime measurement of silicon vacancy centers in diamond by single-photon frequency upconversion

We report a method with high time resolution to measure the excited-state lifetime of silicon vacancy centers in bulk diamond avoiding timing jitter from the single-photon detectors. Frequency upconversion of the fluorescence emitted from silicon vacancy centers was achieved from 738 nm to 436 nm via sum frequency generation with a short pump pulse. The excited-state lifetime can be obtained by measuring the intensity of upconverted light while the pump delay changes. As a probe, a pump laser with pulse duration of 11 ps provided a high temporal resolution of the measurement. The lifetime extracted from the pump–probe curve was 0.755 ns, which was comparable to the timing jitter of the single-photon detectors.

The γ-γ fast-timing technique and the EXILL&FATIMA campaign

At the Institut Laue-Langevin in Grenoble, germanium-gated γ-γ fast-timing lifetime measurements of nuclear excited states in neutron-rich nuclei have been performed within a prompt γ-ray spectroscopy experimental campaign. We report on results obtained from the cold-neutron induced fission of 235U. The excited secondary fission products were stopped almost instantaneously within the thick target and the γ rays emitted were collected triggerlessly using the EXILL&FATIMA mixed array of HPGe and LaBr3(Ce) detectors. Precise lifetimes could be determined by analysing the γ-γ time difference spectra using the generalized centroid difference method. This picosecondsensitive method provides many advantages and is briefly explained. Still, the major source of systematic errors is related to the contribution of time-correlated Compton background. The EXILL&FATIMA results are discussed with respect to the typical energy-dependent timing behaviour of the background. According to the time response of the background, appropriate methods and a time correction for the sub-nanosecond regime are proposed.

Luminescence dynamics in Eu3+ doped fluoroborate glasses

Rare earth ions doped transparent glasses are among promising solid-state materials for various optical applications. In this report, Eu3+ ions doped new fluoroborate glasses were prepared by conventional melt-quenching technique and their optical properties were characterized by absorption and luminescence spectroscopy as well as excited state lifetime measurements. The absorption spectra revealed the characteristic transitions between the 7F0 ground state and 7F1 first excited state to the upper-lying electronic states. The variation in the luminescence intensity of the radiative transitions occurring at 590 and 611nm and the bi-exponential behavior of the fluorescence decay of the 5D0 level, with different trend for the amplitude of the decays, are discussed in terms of low and high symmetry sites depending on the EuF3 concentration and the possible energy transfer between ions at these sites.

Development of Far-Red and Ultraviolet Digital Frequency-Domain Flow Cytometry Systems

Flow cytometry is a powerful single cell analysis technique that uses fluorescence and light scatter to characterize differences (i.e., phenotype, genotype, morphology, etc.) in large cell populations. Digital excited state lifetime measurements with flow cytometry have been largely underutilized; the measurement of fluorescence decay rates by molecules in or on the surface of cells is challenging to accurately measure when the samples are moving rapidly through the path of a laser excitation source. In past work, we have shown that time-resolved cytometry can provide accurate measurements of the fluorescence lifetime of organic fluorophores at standard cytometric throughputs (∼1000 cells/s). Herein, we advance our digital laser modulation and signal processing approaches to develop cytometry systems that operate across a broader spectral range. We optimized a far-red and ultraviolet (UV) cytometry instruments and present fluorescence microsphere results to determine detection sensitivity. The expansion of time-resolved systems across a wider color spectrum is important for many new applications including the development of near-infrared fluorescent proteins and the detection of UV-excitable autofluorescence in single cells.

Lifetime measurements of excited states in W162 and W164 and the evolution of collectivity in rare-earth nuclei

Lifetimes of the first excited 2(+) states in the extremely neutron- deficient W-162 and W-164 nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data f ...

Investigation of the anomalously low B(E2;41+→21+)/B(E2;21+→01+) ratio in Ce134 through lifetime measurements

The existing experimental value of the ratio ${B}_{4/2}\ensuremath{\equiv}B(E2;{4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})/B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ in $^{134}\mathrm{Ce}$ is less than unity, which is outside the range allowed by current collective models and is highly anomalous. In the present work, new lifetime measurements of excited states in $^{134}\mathrm{Ce}$ have been performed in order to clarify this discrepancy. Excited states of $^{134}\mathrm{Ce}$ were populated by the fusion-evaporation reaction $^{122}\mathrm{Sn}(^{16}\mathrm{O},4n)^{134}\mathrm{Ce}$. The recoil distance doppler shift method was employed, and reliable lifetimes for the ${2}_{1}^{+}, {4}_{1}^{+}, {10}_{2}^{+}$, and ${12}_{2}^{+}$ states were derived from the differential decay curve method. The resulting ${B}_{4/2}$ value is larger than unity, resolving the disagreement with traditional collective models. The new experimental data is in very good agreement with the calculation in the framework of the interacting boson model. The systematic evolution in collectivity of the Ce isotopes is discussed.

Effect of Bridge Alteration on Ground- and Excited-State Properties of Ruthenium(II) Complexes with Electron-Donor-Substituted Dipyrido[3,2-a:2′,3′-c]phenazine Ligands

A series of Ru(II) 2,2'-bipyridine (bpy) complexes with an electron-accepting dipyrido[3,2-a:2',3'-c]phenazine (dppz) ligand coupled to an electron-donating triarylamine (TAA) group have been investigated. Systematic alteration of a bridging unit between the dppz and TAA allowed exploration into how communication between the donor and acceptor is perturbed by distance, as well as by steric and electronic effects. The effect of the bridging group on the electronic properties of the systems was characterized using a variety of spectroscopic methods, including Fourier transform-Raman (FT-Raman) spectroscopy, resonance Raman spectroscopy, and transient resonance Raman (TR2) spectroscopy. These methods were used in conjunction with ground- and excited-state absorption spectroscopy, electrochemical studies, and DFT calculations. The ground-state electronic absorption spectra show distinct variation with the bridging group, with the wavelength observed for the lowest energy electronic transition ranging from 449 nm to 522 nm, accompanied by large changes in the molar absorptivity. The lowest-energy Franck-Condon state was determined to be intra-ligand charge transfer (ILCT) in nature for most compounds. The presence of higher-energy metal-to-ligand charge transfer (MLCT) Ru(II) → bpy and Ru(II) → dppz transitions was also confirmed via resonance Raman spectroscopy. The TR2 spectra showed characteristic dppz• - and TAA• + vibrations, indicating that the THEXI state formed was also ILCT in nature. Excited-state lifetime measurements reveal that the rate of decay is in accordance with the energy gap law and is not otherwise affected by the nature of the bridging unit.

Evolution of collectivity near mid-shell from excited-state lifetime measurements in rare earth nuclei

The B(E2) excitation strength of the first excited 2(+) state in even-even nuclei should directly correlate with the size of the valence space and maximize at mid-shell. A previously found saturation of B(E2) strengths in well-deformed rotors at mid-shell is tested through high-precision measurements of the lifetimes of the lowest-lying 2(+) states of the Hf-168 and W-174 rare earth isotopes. Measurements were performed using fast LaBr3 scintillation detectors. Combined with the recently remeasured B(E2; 2(1)(+) -> 0(1)(+)) values for Hf and W isotopes the new data remove discrepancies observed in the differentials of B(E2) values for these isotopes.

Nuclear structure studies based on the lifetime measurements of excited states in nuclei at the in-beam γ terminal of HI-13 tandem accelerator

Nuclear structure studies based on the lifetime measurements of excited states in nuclei at the in-beam γ terminal of HI-13 tandem accelerator

Ultrafast Torsional Relaxation of Thioflavin-T in Tris(pentafluoroethyl)trifluorophosphate (FAP) Anion-Based Ionic Liquids

Ultrafast spectroscopy on solutes, whose dynamics is very sensitive to the friction in its local environment, has strong potential to report on the microenvironment existing in complex fluids such as ionic liquids. In this work, the torsional relaxation dynamics of Thioflavin-T (ThT), an ultrafast molecular rotor, is investigated in two fluoroalkylphosphate ([FAP])-based ionic liquids, namely, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM][FAP]) and 1-(2-hydroxyethyl)-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([OHEMIM][FAP]), using ultrafast fluorescence up-conversion spectroscopy. The emission quantum yield and the excited-state fluorescence lifetime measurement suggest that the torsional relaxation of Thioflavin-T, in this class of ionic liquids, is guided by the viscosity of the medium. The temporal profile of the dynamic Stokes' shift of ThT, measured from time-resolved emission spectrum (TRES), displays a multiexponential behavior in both ionic liquids. The long time dynamics of the Stokes' shift is reasonably slower for the hydroxyethyl derivative as compared to the ethyl derivative, which is in accordance with their measured shear viscosity. However, the short time dynamics of Stokes' shift is very similar in both the ionic liquids, and seems to be independent of the measured shear viscosity of the ionic liquid. We rationalize these observations in terms of different locations of ThT in these ionic liquids. These results suggest that despite having a higher bulk viscosity in the ionic liquid, they can provide unique microenvironment in their complex structure, where the reaction can be faster than expected from their measured shear viscosity.

The TRIple PLunger for EXotic beams TRIPLEX for excited-state lifetime measurement studies on rare isotopes

A new device, the TRIple PLunger for EXotic beams (TRIPLEX), has been developed for lifetime measurement studies with rare isotope beams. This plunger device holds up to three metal foils in the beam path and facilitates the recoil distance Doppler-shift technique to measure lifetimes of nuclear excited states in the range of 1ps to 1ns. The unique design allows independent movement of the target and the second degrader with respect to a fixed first degrader in between, enabling advanced experimental approaches, such as the differential recoil distance method and the double recoil distance method. The design and control of the device are presented in this paper, together with simulated performances of the new applications. As an example of actual experiments, results from the lifetime measurement of the neutron-rich 17C isotope performed at the National Superconducting Cyclotron Laboratory are shown.

Lifetime measurement of excited low-spin states via the [formula omitted] reaction

In this paper a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of 96Ru, taking advantage of the coincident detection of scattered protons and de-exciting γ-rays as well as the large number of particle and γ-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where (n,n′γ) or – in case of investigating dipole excitations – (γ,γ′) experiments are not feasible due to the lack of sufficient isotopically enriched target material.

Real-Time Quantification of Time-Gated Autofluorescence Spectrum Shape to Track Mitochondrial Metabolism

Recent studies by various groups report the use of NADH as an intrinsic optical biomarker and metabolic indicator. Using measurements of excited-state lifetime or anisotropy decay, different forms of intracellular NADH were identified and monitored, with the response of NADH to metabolic conditions being more complex than a simple concentration change. Recently, we report an approach for the real-time tracking of UV-excited autofluorescence based on the rapid quantification of spectrum shape. Here, we show that nanosecond-gated spectral acquisition - combined with spectrum-shape quantification (such as with spectral phasor analysis) - can be used to track the physiologic response of a cellular system (Saccharomyces cereviseae) to the addition of mitochondrial functional modifiers (e.g., cyanide) and metabolic substrates (e.g., ethanol and glucose). We demonstrate that time-gated detection allows for the rejection of short excited-state-lifetime emission. We observe that the spectrum shape of long excited-state-lifetime autofluorescence exhibits a different response to chemical additions than that of the time-integrated autofluorescence, even allowing for the discrimination between nominally similar responses. Results are consistent with the existence of multiple NADH forms, as changes in autofluorescence spectrum shape cannot be accounted for by a two spectra model. Time-gated spectroscopy combined with rapid spectrum-shape analysis may lead to new and useful approaches for the real-time tracking of cellular metabolic state.

The Generalized Centroid Difference method for lifetime measurements viaγ-γcoincidences using large fast-timing arrays

A novel method for direct electronic “fast-timing” lifetime measurements of nuclear excited states via γ-γ coincidences using an array equipped with N very fast high-resolution LaBr3(Ce) scintillator detectors is presented. The generalized centroid difference method provides two independent “start” and “stop” time spectra obtained without any correction by a superposition of the N(N – 1)/2 calibrated γ-γ time difference spectra of the N detector fast-timing system. The two fast-timing array time spectra correspond to a forward and reverse gating of a specific γ-γ cascade and the centroid difference as the time shift between the centroids of the two time spectra provides a picosecond-sensitive mirror-symmetric observable of the set-up. The energydependent mean prompt response difference between the start and stop events is calibrated and used as a single correction for lifetime determination. These combined fast-timing array mean γ-γ zero-time responses can be determined for 40 keV < Eγ < 1.4 MeV with a precision better than 10 ps using a 152Eu γ-ray source. The new method is described with examples of (n,γ) and (n,f,γ) experiments performed at the intense cold-neutron beam facility PF1B of the Institut Laue-Langevin in Grenoble, France, using 16 LaBr3(Ce) detectors within the EXILL&FATIMA campaign in 2013. The results are discussed with respect to possible systematic errors induced by background contributions.

硫代多联吡啶铂(II)配合物的合成、性质及在光催化制氢中的应用

Two new ligands 4-(p-thioacetic-S-methylphenyl)-6-phenyl-2,2'-bipyridine[(HCNNPh)-N-boolean AND-N-boolean AND center dot(CH2SCOCH3), L3] and 6- (p-thioacetic-S-methylphenyl) -2,2'-bipyridine [(HCNN)-N-boolean AND-N-boolean AND (CH2SCOCH3), L5] as well as their platinum(II) complexes (ClPtCNN)-N-boolean AND-N-boolean AND(PhCH2SCOCH3) (C3) and (ClPtCNN)-N-boolean AND-N-boolean AND center dot (CH2SCOCH3) (CS) were synthesized and characterized by H-1 nuclear magnetic resonance (H-1 NMR), electrospray ionization mass spectra(ESI-MS) and X-ray diffraction(XRD) analysis. Photophysical and electrochemical properties of the complexes were studied based on the UV-Vis absorption and emission spectra, excited-state lifetime measurements. It was found that photogenerated hydrogen efficiencies of [(ClPtCNN)-N-boolean AND-N-boolean AND(CH3) (PhCH3)] (C1), [(ClPtCNN)-N-boolean AND-N-boolean AND(PhCH3)] (C2), C3, [(ClPtCNN)-N-boolean AND-N-boolean AND(CH3)] (C4) and C5 are in accordance with their emission lifetimes, and are arranged in the order C4>C1>C5>C2>C3.

Size vs surface: tuning the photoluminescence of freestanding silicon nanocrystals across the visible spectrum via surface groups.

The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3-4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromism studies.

Fast-timing lifetime measurements of excited states inCu67

The half-lives of the 9/2 + , 13/2+ , and 15/2+ yrast states in the neutron-rich 67Cu nucleus were determined by using the in-beam fast-timing technique. The experimentally deduced E3 transition strength for the decay of the 9/2+ level to the 3/2- ground state indicates that the wave function of this level might contain a collective component arising from the coupling of the odd proton p3/2 with the 3- state in 66Ni. Theoretical interpretations of the 9/2+ state are presented within the particle-vibration weak-coupling scheme involving the unpaired proton and the 3- state from 66Ni and within shell-model calculations with a 56Ni core using the jj44b residual interaction. The shell model also accounts reasonably well for the other measured electromagnetic transition probabilities.

Single-Molecule Exploration of the Photodynamics of LHCII Complexes in Solution

Plants can safely dissipate excess excitation energy during light harvesting to prevent the formation of triplet chlorophyll, which can generate deleterious singlet oxygen. With this regulation, known as non-photochemical quenching (NPQ), efficient light harvesting and photosynthesis can be balanced under fluctuating sunlight intensity without damage to the photosynthetic machinery. NPQ has been extensively studied and key physiological regulatory factors have been identified. For example, it is known that the change in lumen pH or a pH gradient across thylakoid membrane can trigger an energy-dependent quenching (qE) pathway that activates on a timescale of seconds to minutes. However, understanding the molecular mechanism behind NPQ is still a challenge. One important question is whether, upon activation of qE, the number of quenched complexes increases or the degree of quenching in each complex changes. These two cases cannot be differentiated in ensemble-averaged measurements. Therefore, we use the Anti-Brownian ELectrokinetic (ABEL) trap to investigate single copies of light-harvesting complex II (LHCII), the primary antenna in higher plants. Different from other single-molecule techniques that utilize immobilization, perturbations due to surface attachment or encapsulation are avoided, and therefore the intrinsic dynamics and heterogeneity of individual complexes are revealed. We perform measurements of fluorescence intensity, excited-state lifetime, and emission spectra of single LHCII complexes in the ABEL trap. By analyzing the correlated changes in these properties over time, we observe that individual LHCII complexes are found in distinct forms with different extents of quenching. Comparing the results from different conditions known to correlate with qE activation will give a better understanding of NPQ at the molecular level.