Time-resolved Laser-induced Fluorescence Research Articles

Role of Tf2N− anions in the ionic liquid–water distribution of europium(iii) chelates

The replacement of water molecules of [Eu(tta)3(H2O)3] with Tf2N− was evidenced in water-saturated [Cnmim][Tf2N] by time-resolved laser-induced fluorescence spectroscopy.

Study of the Interaction of Eu3+ with Microbiologically Induced Calcium Carbonate Precipitates using TRLFS.

The microbial induced biomineralization of calcium carbonate using the ureolytic bacterium Sporosarcina pasteurii in the presence of trivalent europium, a substitute for trivalent actinides, was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and a variety of physicochemical techniques. Results showed that the bacterial-driven hydrolysis of urea provides favorable conditions for CaCO3 precipitation and Eu3+ uptake due to subsequent increases in NH4+ and pH in the local environment. Precipitate morphologies were characteristic of biogenically formed CaCO3 and consistent with the respective mineral phase compositions. The formation of vaterite with some calcite was observed after 1 day, calcite with some vaterite after 1 week, and pure calcite after 2 weeks. The presence of organic material associated with the mineral was also identified and quantified. TRLFS was used to track the interaction and speciation of Eu3+ as a molecular probe with the mineral as a function of time. Initially, Eu3+ is incorporated into the vaterite phase, while during CaCO3 phase transformation Eu3+ speciation changes resulting in several species incorporated in the calcite phase either substituting at the Ca2+ site or in a previously unidentified, low-symmetry site. Comparison of the biogenic precipitates to an abiotic sample shows mineral origin can affect Eu3+ speciation within the mineral.

Tracking the evolution of soot particles and precursors in turbulent flames using laser-induced emission

A point-wise, time-resolved optical technique is employed to track simultaneously the evolution of soot particles and soot precursors in a turbulent flame of ethylene/nitrogen (1/1 by vol.). A picosecond laser, 80ps@266nm is used to measure scattering and laser-induced fluorescence (LIF) in selected UV and visible bands while Laser-induced incandescence (LII) is excited using a pulsed laser with 8ns@1064nm. Fast photomultiplier tubes are used to ensure time-resolved measurements and LIF decay times of the order of 3.5ns are detected. The LIF signals are attributed to nanoparticles or condensed phase species made up of PAHs, whereas LII was correlated with soot. Data conditioning based on the noise level was made to delineate the potentially large influence of intermittency on the statistics of the detected signals. It was found that LIF signals with long decay times were detected well before the onset of soot particles, as seen by LII, and these continue well into the maximum soot formation region. The correlation between the LII and LIF signals confirmed the co-presence of small nanoparticles together with high concentrations of mature soot. Analysis of conditioned mean soot concentration suggests that the intermittency occurring at the edge and tip of the flame does not locally decrease the soot concentration since large LII signals were still detected. These simultaneous, time-resolved measurements are extremely useful to provide insights on the evolution of combustion-generated particles in turbulent sooting flames.

A canonical geometry to study wall filming and atomization in pre-filming coaxial swirl injectors

A coaxial twin counter-rotating air swirl prefilming injector with necessary optical access, is developed to visualize and quantify its internal fluid dynamics. This research injector consists of a simplex nozzle arranged at the center of two coaxial counter-rotating radial air flow swirlers, and two transparent coaxial tubes are attached, one each to the primary and secondary air swirl paths. Spray from the simplex nozzle is swirled by the primary air and impinges on the inner tube—the prefilmer, undergoes filming, and convects to the tube tip to form a liquid rim, which is sheared by the counter-rotating swirl into finer droplets. Stage-wise phase Doppler particle analyzer measurements indicate the final spray to be much finer than the simplex nozzle spray after undergoing the above processes. Time resolved laser induced fluorescence (TR-LIF) imaging techniques are applied to visualize the wall filming and primary atomization inside the injector. The simplex nozzle spray velocity under the influence of air swirl flow is measured using stereo-particle image velocimetry. The precessing vortex core from the primary swirl imparts a precessing motion to the simplex spray, which in turn induces a non-uniform filming on the prefilmer. The droplet impingement on the prefilmer leads to splashing and crater formation on the surface. The crater size distribution is obtained and compared to the droplet size of the injector spray before impingement. The film thickness variation on the prefilmer surface and the rim thickness are estimated from planar LIF experiments along with a long distance microscope. The thickness of the liquid rim is identified as a major factor in determining the final droplet size at the injector exit. These are correlated to SMD at the injector exit at different air flow rates.

How Do Radionuclides Accumulate in Marine Organisms? A Case Study of Europium with Aplysina cavernicola.

In the ocean, complex interactions between natural and anthropogenic radionuclides, seawater, and diverse marine biota provide a unique window through which to examine ecosystem and trophic transfer mechanisms in cases of accidental dissemination. The nature of interaction between radionuclides, the marine environment, and marine species is therefore essential for better understanding transfer mechanisms from the hydrosphere to the biosphere. Although data pertaining to the rate of global transfer are often available, little is known regarding the mechanism of environmental transport and uptake of heavy radionuclides by marine species. Among marine species, sponges are immobile active filter feeders and have been identified as hyperaccumulators of several heavy metals. We have selected the Mediterranean sponge Aplysina cavernicola as a model species for this study. Actinide elements are not the only source of radioactive release in cases of civilian nuclear events; however, their physicochemical transfer mechanisms to marine species remain largely unknown. We have targeted europium(III) as a representative of the trivalent actinides such as americium or curium. To unravel biological uptake mechanisms of europium in A. cavernicola, we have combined radiometric (γ) measurements with spectroscopic (time-resolved laser-induced fluorescence spectroscopy, TRLIFS, and X-ray absorption near-edge structure, XANES) and imaging (transmission electron microscopy, TEM, and scanning transmission X-ray microscopy, STXM) techniques. We have observed that the colloids of NaEu(CO3)2·nH2O formed in seawater are taken up by A. cavernicola with no evidence that lethal dose has been reached in our working conditions. Spectroscopic results suggest that there is no change of speciation during uptake. Finally, TEM and STXM images recorded at different locations across a sponge cross section, together with differential cell separation, indicate the presence of europium particles (around 200 nm) mainly located in the skeleton and toward the outer surface of the sponge.

Experimental radiative lifetimes for highly excited states and calculated oscillator strengths for lines of astrophysical interest in singly ionized cobalt (Co ii)

This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions of astrophysical interest in singly ionized cobalt. More precisely, nineteen radiative lifetimes in Co+ have been measured with the time-resolved laser-induced fluorescence technique using one- and two-step excitations. Out of these, seven belonging to the high lying 3d$^7$($^4$F)4d configuration in the energy range 90697 - 93738 cm$^{-1}$ are new, and the other twelve from th3d$^7$($^4$F)F)4p configuration with energies between 45972 and 49328 cm$^{-1}$1 are compared with previous measurements. In addition, a relativistic Hartree-Fock model including core-polarization effects has been employed to compute transition rates. Supported by the good agreement between theory and experiment for the lifetimes, new reliable transition probabilities and oscillator strengths have been deduced for 5080 Co II transitions in the spectral range 114 - 8744 nm.

Quantitative picosecond laser-induced fluorescence measurements of nitric oxide in flames

Quantitative concentrations measurements using time-resolved laser-induced fluorescence have been demonstrated for nitric oxide (NO) in flame. Fluorescence lifetimes measured using a picosecond Nd:YAG laser and optical parametric amplifier system have been used to directly compensate the measured signal for collisional quenching and evaluate NO concentration. The full evaluation also includes the spectral overlap between the ∼15cm−1 broad laser pulse and multiple NO absorption lines as well as the populations of the probed energy levels. Effective fluorescence lifetimes of 1.2 and 1.5ns were measured in prepared NO/N2/O2 mixtures at ambient pressure and temperature and in a premixed NH3-seeded CH4/N2/O2 flame, respectively. Concentrations evaluated from measurements in NO/N2/O2 mixtures with NO concentrations of 100–600ppm were in agreement with set values within 3% at higher concentrations. An accuracy of 13% was estimated by analysis of experimental uncertainties. An NO profile measured in the flame showed concentrations of ∼1000ppm in the post-flame region and is in good agreement with NO concentrations predicted by a chemical mechanism for NH3 combustion. An accuracy of 16% was estimated for the flame measurements. The direct concentration evaluation from time-resolved fluorescence allows for quantitative measurements in flames where the composition of major species and their collisional quenching on the probed species is unknown. In particular, this is valid for non-stationary turbulent combustion and implementation of the presented approach for measurements under such conditions is discussed.

Macroscopic and spectroscopic characterization of uranium(VI) sorption onto orthoclase and muscovite and the influence of competing Ca2+

The uranium(VI) sorption onto orthoclase and muscovite, representing the mineral groups of feldspars and micas as important components of the earth crust, was investigated in the presence and absence of Ca2+ under aerobic conditions. Batch experiments were accompanied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) as well as in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. The results indicate that the U(VI) sorption is reduced by Ca2+ at pH⩾8 up to 30% due to the formation of the neutral aqueous Ca2UO2(CO3)3 (aq) complex. TRLFS measurements on the supernatant confirmed the predominance of this Ca2UO2(CO3)3 (aq) complex in accordance with thermodynamic calculations. Furthermore, TRLFS measurements on the mineral suspension as a function of pH (4–9) and Ca2+ revealed the existence of several species. Parallel factor analysis (PARAFAC) indicated the formation of three surface species totally. In the absence of Ca2+, the XOUO2+ and XOUO2CO3− surface complexes were formed, whereas the presence of Ca2+ leads to the formation of XOUO2+ and XOUO2OH as the formation of the aqueous Ca2UO2(CO3)3 (aq) complex reduces the free UO22+ concentration in the solution. In addition, ATR FT-IR spectroscopy confirmed an outer-sphere surface species in the absence of Ca2+. These experimental results were used for the assessment of surface complexation parameters to improve the basis for a mechanistic modeling of the sorption processes of U(VI) onto orthoclase and muscovite including the influence of Ca2+. Namely, logKXOUO2+=1.69 and logKXOUO2CO3-=8.96 were determined for sorption onto orthoclase, whereas logKXOUO2+=0.41 and logKXOUO2CO3-=8.71 best describe sorption onto muscovite in the absence of Ca2+.

EXPERIMENTALLY MEASURED RADIATIVE LIFETIMES AND OSCILLATOR STRENGTHS IN NEUTRAL VANADIUM

ABSTRACT We report a new study of the V i atom using a combination of time-resolved laser-induced fluorescence and Fourier transform spectroscopy that contains newly measured radiative lifetimes for 25 levels between 24,648 cm−1 and 37,518 cm−1 and oscillator strengths for 208 lines between 3040 and 20000 Å from 39 upper energy levels. Thirteen of these oscillator strengths have not been reported previously. This work was conducted independently of the recent studies of neutral vanadium lifetimes and oscillator strengths carried out by Den Hartog et al. and Lawler et al., and thus serves as a means to verify those measurements. Where our data overlap with their data, we generally find extremely good agreement in both level lifetimes and oscillator strengths. However, we also find evidence that Lawler et al. have systematically underestimated oscillator strengths for lines in the region of 9000 ± 100 Å. We suggest a correction of 0.18 ± 0.03 dex for these values to bring them into agreement with our results and those of Whaling et al. We also report new measurements of hyperfine structure splitting factors for three odd levels of V i lying between 24,700 and 28,400 cm−1.

Oscillator strengths for high-excitation Ti ii from laboratory measurements and calculations

This work reports new experimental radiative lifetimes of six 3d2(3F)5s levels in singly ionized titanium, with an energy around 63 000 cm-1 and four 3d2(3F)4p odd parity levels where we confirm previous investigations. Combining the new 5s lifetimes with branching fractions measured previously by Pickering et al., we report 57 experimental log gf values for transitions from the 5s levels. The lifetime measurements are performed using time-resolved laser-induced fluorescence on ions produced by laser ablation. One- and two-step photon excitation is employed to reach the 4p and 5s levels, respectively. Theoretical calculations of the radiative lifetimes of the measured levels as well as of oscillator strengths for 3336 transitions from these levels are reported. The calculations are carried out by a pseudorelativistic Hartree-Fock method taking into account core-polarization effects. The theoretical results are in a good agreement with the experiments and are needed for accurate abundance determinations in astronomical objects. (Less)

Speciation Studies of Metals in Trace Concentrations: The Mononuclear Uranyl(VI) Hydroxo Complexes.

A direct luminescence spectroscopic experimental setup for the determination of complex stability constants of mononuclear uranyl(VI) hydrolysis species is presented. The occurrence of polynuclear species is prevented by using a low uranyl(VI) concentration of 10–8 M (2.4 ppb). Time-resolved laser-induced fluorescence spectra were recorded in the pH range from 3 to 10.5. Deconvolution with parallel factor analysis (PARAFAC) resulted in three hydrolysis complexes. A tentative assignment was based on thermodynamic calculations: UO22+, UO2(OH)+, UO2(OH)2, UO2(OH)3–. An implementation of a Newton–Raphson algorithm into PARAFAC allowed a direct extraction of complex stability constants during deconvolution yielding log(β1M,1°C)1:1 = −4.6, log(β1M,1°C)1:2 = −12.2, log(β1M,1°C)1:3 = −22.3. Extrapolation to standard conditions gave log(β0)1:1 = −3.9, log(β0)1:2 = −10.9, and log(β0)1:3 = −20.7. Luminescence characteristics (band position, lifetime) of the individual mononuclear hydroxo species were derived to serve as a reference data set for further investigations. A correlation of luminescence spectroscopic features with Raman frequencies was demonstrated for the mononuclear uranyl(VI) hydroxo complexes for the first time. Thereby a signal-to-structure correlation was achieved and the complex assignment validated.

Hyperfine structure and lifetime measurements in the 4s2nd 2D3/2 Rydberg sequence of Ga I by time-resolved laser spectroscopy

The hyperfine structure (HFS) constants of the 4s2nd 2D3/2 (n=6–18) Rydberg sequence and the 4s26p 2P3/2 level for two isotopes of 69Ga and 71Ga atoms were measured by means of the time-resolved laser-induced fluorescence (TR-LIF) technique and the quantum beat method. The observed hyperfine quantum beat spectra were analyzed and the magnetic-dipole HFS constants A as well as the electric-quadrupole HFS constants B of these levels were obtained by Fourier transform and a program for multiple regression analysis. Also using TR-LIF method radiative lifetimes of the above sequence states were determined at room temperature. The measured lifetime values range from 69 to 2279ns with uncertainties no more than 10%. To our knowledge, the HFS constants of this Rydberg sequence and the lifetimes of the 4s2nd 2D3/2 (n=10–18) levels are reported for the first time. Good agreement between our results and the previous is achieved.

Quantum chemical calculations and spectroscopic measurements of spectroscopic and thermodynamic properties of given uranyl complexes in aqueous solutions with possible environmental and industrial applications

A brief introduction into computational methodology and preliminary results for spectroscopic (excitation energies, vibrational frequencies in ground and excited electronic states) and thermodynamic (stability constants, standard enthalpies and entropies of complexation reactions) properties of some 1:1, 1:2 and 1:3 uranyl sulphato- and selenato- complexes in aqueos solutions will be given. The relativistic effects are included via Effective Core Potential (ECP), electron correlation via (TD)DFT/B3LYP (dispersion interaction corrected) and solvation is described via explicit inclusion of one hydration sphere beyond the coordinated water molecules. We acknowledge limits of this approximate description – more accurate calculations (ranging from semi-phenomenological two-component spin-orbit coupling up to four-component Dirac-Coulomb-Breit hamiltonian) and Molecular Dynamics simulations are in preparation. The computational results are compared with the experimental results from Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS) and UV-VIS spectroscopic studies (including our original experimental research on this topic). In case of the TRLFS and UV-VIS speciation studies, the problem of complex solution spectra decomposition into individual components is ill-conditioned and hints from theoretical chemistry could be very important. Qualitative agreement between our quantum chemical calculations of the spectroscopic properties and experimental data was achieved. Possible applications for geochemical modelling (e.g. safety studies of nuclear waste repositories, modelling of a future mining site) and analytical chemical studies (including natural samples) are discussed.

Interfacial Engineering Improved the Selective Extraction of Uranyl from Saline Water by Nano-Mg(OH)2 and the Underlying Mechanism

Abundant salts and complex constituents pose challenges to the enrichment of trace-level uranyl from field water samples. On the basis of the chemical behavior of the uranyl cation in several physical–chemical conditions (in the presence of MgCl2 etc.), we developed a facile and green strategy to improve the uranyl extraction from field water samples, different from the traditional way with organic impregnation. In our systems about nano-Mg(OH)2 treating salt lake brine, when the adsorbent is pretreated with a trace amount of UO22+ ion, the ability to extract uranyl from brine can increase by 2–5 times. The molecular dynamics simulation and time-resolved laser-induced fluorescence spectroscopy analysis show that, in the preadsorption stage, UO22+ ions can steadily bind to the Mg(OH)2 (001) surface because of the interaction with surface hydroxyl groups. When pretreated Mg(OH)2 was exposed to brine, the coordination interaction between the preloaded UO22+ ion and the [UO2(CO3)x(2x–2)–] in solution engender...

Time-resolved laser-induced fluorescence measurement of ion and neutral dynamics in a Hall thruster during ionization oscillations

The paper presents spatially and temporally resolved laser-induced fluorescence (LIF) measurements of the xenon ion and neutral velocity distribution functions in a 400 W Hall thruster during natural ionization oscillations at 23 kHz, the so-called “breathing mode.” Strong fluctuations in measured axial ion velocity throughout the discharge current cycle are observed at five spatial locations and the velocity maxima appear in the low current interval. The spatio-temporal evolution of the ion velocity distribution function suggests a propagating acceleration front undergoing periodic motion between the thruster exit plane and ∼1 cm downstream into the plume. The ion LIF signal intensity oscillates almost in phase with the discharge current, while the neutral fluorescence signal appears out of phase, indicating alternating intervals of strong and weak ionization.

The FERRUM project: Experimental lifetimes and transition probabilities from highly excited even 4d levels in Fe ii

We report lifetime measurements of the 6 levels in the 3d6(5D)4d e6G term in Fe ii at an energy of 10.4 eV, and f -values for 14 transitions from the investigated levels. The lifetimes were measured using time-resolved laser-induced fluorescence on ions in a laser-produced plasma. The high excitation energy, and the fact that the levels have the same parity as the the low-lying states directly populated in the plasma, necessitated the use of a two-photon excitation scheme. The probability for this process is greatly enhanced by the presence of the 3d6(5D)4p z6F levels at roughly half the energy difference. The f -values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode discharge lamp recorded with a Fourier transform spectrometer. The data is important for benchmarking atomic calculations of astrophysically important quantities and useful for spectroscopy of hot stars.

Landé factor and lifetime measurements for odd-parity levels of Cr I by time-resolved laser spectroscopy

The Landé gJ factors of 35 levels, and the radiative lifetimes of 43 levels, of neutral chromium in the energy range 23 305.0026 to 53 782.78 cm−1 were measured by time-resolved laser-induced fluorescence and Zeeman quantum beat methods in laser-ablation plasma. Good agreements between the present results and the previous experimental values were achieved for both gJ factors and lifetimes. The measured gJ values are quite close to those calculated under the pure LS-coupling scheme. The lifetime values obtained are in the range 11.4 to 193 ns. To the best of our knowledge, 15 of the Landé factors and 17 of the lifetimes are reported for the first time.

An experimental investigation of geometric effect of upstream converging slot-hole on end-wall film cooling and secondary vortex characteristics

A row of converging slot-holes is applied upstream of a linear GE-E3 high pressure turbine cascade to enhance film-cooling effect in end-wall leading edge region and weaken secondary vortices. Effects of geometric parameters of the converging hole-slot, including inclination angle and outlet-to-inlet area ratio, on time-mean characteristics of secondary vortices and adiabatic film-cooling effectiveness are respectively investigated with Time-Resolved Particle Image Velocimetry (TRPIV) and Planar Laser Induced Fluorescence (PLIF) techniques, at various coolant-to-mainstream blowing ratios. Three types of converging slot-holes with two different area ratios (ARs=1.38 and 0.69) and inclination angles (α=30° and 65°) are chosen, and a 30° cylindrical hole is compared as a reference. The comparison reveals that, the secondary vortices can be weakened by the coolant injection from the cylindrical hole only at higher blowing ratios; however, the 30° converging slot-holes has a potential to simultaneously improve end-wall cooling effect and weaken the secondary vortices, even at lower blowing ratios. For the two 30° converging slot-holes, the configuration with smaller AR=0.69 is a better structure, because that can provide a better film-coverage performance, a higher film cooling effectiveness, and a stronger ability to weaken secondary vortices, compared to larger AR=1.38. For the 65° converging slot-holes, the coolant lifts easily off the end-wall, and the secondary vortices are enhanced by the coolant injection. Therefore, this configuration is not suitable for weakening the secondary vortices.

Radiative lifetimes of odd-parity levels in Nb I

Radiative lifetimes are reported for 37 odd-parity energy levels of neutral niobium (Nb I), out of which 33 have been measured for the first time. The levels belong to electronic configurations 4d35s5p and 4d45p between 18,790 and 35,730cm−1. The time-resolved laser-induced fluorescence spectroscopy technique was employed. The Nb atoms were generated in a free-jet by laser vaporization of niobium metal. Lifetime values reported in this work fall in the range 12–340ns and are accurate to ±10%.

Radiative lifetimes and transition probabilities of neutral lanthanum

The radiative lifetimes of 72 odd-parity levels of neutral lanthanum are measured to ±5% accuracy using time-resolved laser-induced fluorescence on a slow atomic beam. The levels range in energy from 15031 to 32140 cm−1. Branching fraction measurements using Fourier-transform spectroscopy are attempted and completed for all of the 72 levels. The branching fractions, when combined with the radiative lifetimes, yield new transition probabilities for 315 lines of the first spectrum of lanthanum (La i ). This study is part of a larger body of work on the radiative properties of rare earth neutral atoms, and is motivated by research needs in lighting science and astrophysics.