Time-resolved Laser-induced Fluorescence Research Articles

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode.

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages.

Temperature field of non-Oberbeck–Boussinesq Rayleigh–Bénard convection in a low aspect ratio cell

A time-resolved experimental investigation was undertaken on the temperature evolution of Rayleigh–Bénard convection (RBC) in a slender convection cell with aspect ratio of Γ=0.1. Experiments were conducted for Rayleigh numbers of Ra=5.3×107, 7.6×107, and 9.5×107 and Prandtl number of Pr≈6 within the non-Oberbeck–Boussinesq (NOB) condition with a temperature difference variation in the range of 30 °C≤ΔT≤40 °C. Measurement of the temperature was by applying time-resolved two-color planar laser-induced fluorescence over the initial 2400 s. Experimental observations showed that the lateral confinement of the convection cell leads to the development of a single large-scale thermal plume instead of multiple plumes. Results showed that contrary to expectations, lateral confinement was found to be ineffective in suppressing temperature oscillations near thermal boundaries. Results also indicated that for Ra=5.3×107, 7.6×107, the temperature oscillations had a frequency of f≈0.028 Hz similar to the frequency of the oscillations in Oberbeck–Boussinesq (OB) RBC. For Ra=9.5×107, however, it was found that the frequency of the oscillations was much lower than the OB RBC with a relatively wide range of the oscillations in the vicinity of f≈0.006 Hz. It is also found that the lateral confinement and formation of singular high-energy thermal plumes leads to an increase in the nonsymmetrical temperature distribution of NOB RBC with a bimodal distribution of the temperature field, deviating significantly from the Gaussian distribution temperature field found in OB RBC.

Experimental Branching Fractions, Transition Probabilities, and Oscillator Strengths in Sm ii

Branching fractions (BFs) of Sm ii for 71 lines from 12 excited levels ranging from 31,638.79 to 35,463.91 cm−1 were determined for the first time based on the Fourier transform spectra available from the National Solar Observatory database. New transition probabilities and oscillator strengths for these lines were derived by combining the determined BFs with reliable lifetimes measured using a time-resolved laser-induced fluorescence technique. Furthermore, BFs for 38 lines from five levels included in earlier studies were also determined for comparisons. The new results reported in this work will be useful in many fields, especially for astrophysics.

Experimental and computational evidence of U(VI)–OH–Si(OH)4 complexes under alkaline conditions: Implications for cement systems

The complexation of uranyl hydroxides with orthosilicic acid was investigated by experimental and theoretical methods. Spectroluminescence titration was performed in a glovebox under argon atmosphere at pH 9.2, 10.5 and 11.5, with [U(VI)] = 10−6 and 5 × 10−6 mol kgw−1. The polymerization effects of silicic acid were minimized by ruling out samples with less than 90 % monomeric silicic acid present, identified via UV–Vis spectrometry using the molybdate blue method. Linear regression analysis based on time-resolved laser-induced fluorescence spectroscopy (TRLFS) results yielded the conditional stepwise formation constants of U(VI)–OH–Si(OH)4 complexes at 0.05 mol kgw−1 NaNO3. The main spectroscopic features – characteristic peak positions and decay-time – are reported for the first time for the UO2(OH)2SiO(OH)3− species observed at pH 9.2 and 10.5 and UO2(OH)2SiO2(OH)22− predominant at pH 11.5. Quantum chemical calculations successfully computed the theoretical luminescence spectrum of the complex UO2(OH)2SiO(OH)3− species, thus underpinning the proposed chemical model for weakly alkaline systems. The conditional stability constants were extrapolated to infinite dilution using the Davies equation, resulting in log10β°(UO2(OH)2SiO(OH)3−) and log10β°(UO2(OH)2SiO2(OH)22−). Implications for U(VI) speciation in the presence and absence of competing carbonate are discussed for silicate-rich environments expected in certain repository concepts for nuclear waste disposal.

Kinetic study of the vibrational relaxation of CH3Zn by collisions with He

Methyl zinc CH3Zn generated in the photolysis of dimethyl zinc (CH3)2Zn at 223 nm was detected with laser-induced fluorescence (LIF) via the A∼2E-X∼2A1 transition. The time-resolved LIF intensity of the level X∼2A1,00 grew with time, indicating that the nascent CH3Zn was highly vibrationally excited. The He-pressure dependence of the growth rates of the LIF intensity was analyzed by the kinetic scheme with a rate-determining step, giving the rate coefficient for vibrational relaxation to the X∼2A1,00 level to be [8.2±0.9(2σ)]×10-13 cm3 molecule−1 s−1. The probability of vibrational relaxation of CH3Zn per collision with He nicely correlates with those of non- or less-polar diatomic molecules.

Experimental branching fractions, transition probabilities, and oscillator strengths of La I

Abstract Experimental branching fractions of 65 lines in La I were measured based on grating spectroscopy of a lanthanum hollow cathode lamp. Combining these branching fractions with previous energy lifetimes measured using time-resolved laser-induced fluorescence (TR-LIF) spectroscopy, absolute transition probabilities and oscillator strengths were determined for 34 lines belonging to transitions 4f5d6s–5d6s2, 4f5d6s–5d3, 5d26p–5d6s2, 5d27p–5d26s and for 31 lines associated with uncertain configurations due to dramatic configuration interaction mixings. These fundamental atomic data will help make atomic models more realistic and provide useful parameters for future astrophysical spectral analysis.

The ESCAPE system: A combined Raman and time-resolved laser-induced fluorescence instrument to analyze planetary material in a controlled environment

Several sample-return missions such as OSIRIS-REx, Hayabusa2, and Mars 2020 recently have or are currently, collecting the most pristine planetary samples we can analyze on Earth since the Apollo missions. Therefore, it is essential to create instrumentation that will allow preliminary compositional analysis of these materials while preventing oxidation, alteration, or contamination from Earth’s environment. At York University, a small, transportable environmental chamber with temperature, pressure, and atmosphere control has been integrated on an optical table with a combined UV (266 nm) and Green (532 nm) Raman, laser-induced fluorescence, and time-resolved laser-induced fluorescence instrument. This system can collect high-resolution 2D spectroscopic maps, long accumulation point analysis and time-resolved fluorescence ‘fingerprinting’. The sample chamber is capable of pressures <10−4 mbar, temperatures <−20 °C, and different atmospheric compositions such nitrogen, argon, or carbon dioxide via gas hookup. The intended use of the system is to detect and identify minerals and organics within sensitive or fragile planetary samples using minimally destructive laser-based techniques, while maintaining specific environmental conditions to preserve and maintain the pristineness of the material being analyzed, such as samples returned from planetary missions.

Equilibrium Thermodynamics of Macropa Complexes with Selected Metal Isotopes of Radiopharmaceutical Interest.

To pursue the design of in vivo stable chelating systems for radiometals, a concise and straightforward method toolbox was developed combining NMR, isothermal titration calorimetry (ITC), and europium time-resolved laser-induced fluorescence spectroscopy (Eu-TRLFS). For this purpose, the macropa chelator was chosen, and Lu3+, La3+, Pb2+, Ra2+, and Ba2+ were chosen as radiopharmaceutically relevant metal ions. They differ in charge (2+ and 3+) and coordination properties (main group vs lanthanides). 1H NMR was used to determine four pKa values (±0.15; carboxylate functions, 2.40 and 3.13; amino functions, 6.80 and 7.73). Eu-TRLFS was used to validate the exclusive existence of the 1:1 Mn+/ligand complex in the chosen pH range at tracer level concentrations. ITC measurements were accomplished to determine the resulting stability constants of the desired complexes, with log K values ranging from 18.5 for the Pb-mcp complex to 7.3 for the Lu-mcp complex. Density-functional-theory-calculated structures nicely mirror the complexes' order of stabilities by bonding features. Radiolabeling with macropa using ligand concentrations from 10-3 to 10-6 M was accomplished by pointing out the complex formation and stability (212Pb > 133La > 131Ba ≈ 224Ra > 177Lu) by means of normal-phase thin-layer chromatography analyses.

Uranium Speciation in a Chalky Soil.

In this article, the speciation and behavior of anthropogenic metallic uranium deposited on natural soil are approached by combining EXAFS (extended X-ray absorption fine structure) and TRLFS (time-resolved laser-induced fluorescence spectroscopy). First, uranium (uranyl) speciation was determined along the vertical profile of the soil and bedrock by linear combination fitting of the EXAFS spectra. It shows that uranium migration is strongly limited by the sorption reaction onto soil and rock constituents, mainly mineral carbonates and organic matter. Second, uranium sorption isotherms were established for calcite, chalk, and chalky soil materials along with EXAFS and TRLFS analysis. The presence of at least two adsorption complexes of uranyl onto carbonate materials (calcite) could be inferred from TRLFS. The first uranyl tricarbonate complex has a liebigite-type structure and is dominant for low loads on the carbonate surface (<10 mgU/kg(rock)). The second uranyl complex is incorporated into the calcite for intermediate (∼10 to 100 mgU/kg(rock)) to high (high: >100 mgU/kg(rock)) loads. Finally, the presence of a uranium-humic substance complex in subsurface soil materials was underlined in the EXAFS analysis by the occurrence of both monodentate and bidentate carboxylate (or/and carbonate) functions and confirmed by sorption isotherms in the presence of humic acid. This observation is of particular interest since humic substances may be mobilized from soil, potentially enhancing uranium migration under colloidal form.

Dynamics of molecular rotors in bulk superfluid helium.

Molecules immersed in liquid helium are excellent probes of superfluidity. Their electronic, vibrational, and rotational dynamics provide valuable clues about the superfluid at the nanoscale. Here we report on the experimental study of the laser-induced rotation of helium dimers inside the superfluid 4He bath at variable temperature. The coherent rotational dynamics of [Formula: see text] is initiated in a controlled way by ultrashort laser pulses and tracked by means of time-resolved laser-induced fluorescence. We detect the decay of rotational coherence on the nanosecond time scale and investigate the effects of temperature on the decoherence rate. The observed temperature dependence suggests a nonequilibrium evolution of the quantum bath, accompanied by the emission of the wave of second sound. The method offers ways of studying superfluidity with molecular nanoprobes under variable thermodynamic conditions.

Eu(III) and Cm(III) Complexation by the Aminocarboxylates NTA, EDTA, and EGTA Studied with NMR, TRLFS, and ITC-An Improved Approach to More Robust Thermodynamics.

The complex formation of Eu(III) and Cm(III) was studied via tetradentate, hexadentate, and octadentate coordinating ligands of the aminopolycarboxylate family, viz., nitrilotriacetate (NTA3-), ethylenediaminetetraacetate (EDTA4-), and ethylene glycol-bis(2-aminoethyl ether)-N,N,N',N'-tetraacetate (EGTA4-), respectively. Based on the complexones' pKa values obtained from 1H nuclear magnetic resonance (NMR) spectroscopic pH titration, complex formation constants were determined by means of the parallel-factor-analysis-assisted evaluation of Eu(III) and Cm(III) time-resolved laser-induced fluorescence spectroscopy (TRLFS). This was complemented by isothermal titration calorimetry (ITC), providing the enthalpy and entropy of the complex formation. This allowed us to obtain genuine species along with their molecular structures and corresponding reliable thermodynamic data. The three investigated complexones formed 1:1 complexes with both Eu(III) and Cm(III). Besides the established Eu(III)-NTA 1:1 and 1:2 complexes, we observed, for the first time, the existence of a Eu(III)-NTA 2:2 complex of millimolar metal and ligand concentrations. Demonstrated for thermodynamic studies on Eu(III) and Cm(III) interaction with complexones, the utilized approach is commonly applicable to many other metal-ligand systems, even to high-affinity ligands.

Time-resolved laser-induced fluorescence spectroscopy and chemometrics for fast identification of U(VI)-bearing minerals in a mining context

We evaluated the potential of time-resolved laser-induced fluorescence spectroscopy (TRLFS) combined with chemometric methods for fast identification of U(VI)-bearing minerals in a mining context. We analyzed a sample set which was representative of several environmental conditions. The set consisted of 80 uranium-bearing samples related to mining operations, including natural minerals, minerals with uranium sorbed on the surface, and synthetic phases prepared and characterized specifically for this study. The TRLF spectra were processed using the Ward algorithm and the K-nearest neighbors (KNN) method to reveal similarities between samples and to rapidly identify the uranium-bearing phase and the associated mineralogical family. The predictive models were validated on an independent dataset, and then applied to test samples mostly taken from U mill tailings. Identification results were found to be in accordance with the available characterization data from X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX). This work shows that TRLFS can be an effective decision-making tool for environmental investigations or geological prospection, considering the large diversity of uranium-bearing mineral phases and their low concentration in environmental samples.

Hydration states of europium(III) adsorbed on silicas with nano-sized pores

The confinement in small spaces influences the complicated reaction involving water molecules under electrostatic potentials at the solid–liquid interface. It is unclear, in particular, how the hydration state of metal ions adsorbed on the surface changes as a function of the pore size. This study analyzed the adsorption states of europium aqua ions (Eu3+) on mesoporous silicas with different pore distributions in comparison with nonporous silica using time-resolved laser-induced fluorescence spectroscopy. The parallel factor analysis was used to differentiate the contribution of different chemical species of Eu3+ to the fluorescence signal and determine the influence of the pore size on each chemical species. The results show that Eu3+ mainly form outer-sphere complexes with silica below pH 6, where Eu3+ adsorption is low. Within nano-sized pores, distortion of the hydration structure and a decrease in the hydration number were suggested in this pH range. As the concentration of the silicate ions derived from the dissolution of silica increases with increasing pH, Eu3+ form the silica/Eu3+/silicate ternary surface complexes. Within nano-sized pores, the concentration of silicate ions decreases due to the overlap of the electric double layer, which inhibits the formation of the ternary surface complex. Furthermore, at high pH, Eu3+ multinuclear complexes formed only on the mesoporous silica surface. This adsorption behavior specific to nano-sized pores could not be concluded by macroscopic adsorption experiments alone because the amount of Eu3+ adsorbed per unit surface area did not differ between the mesoporous and nonporous silicas. Consideration of the silicate complexes should be indispensable in future studies on the adsorption of lanthanide ions using mesoporous silica.

Novel water-soluble aromatic bisdiglycolamide masking agents for the separation of trivalent americium over lanthanides by NTAamide(n-Oct) extractant

Two novel water-soluble aromatic bisdiglycolamides (BisDGAs) of SO3-TEX(m)-BisDGA (sodium bis((2-(2-(diethylamino)− 2-oxoethoxy)acetamido)methyl)benzenesulfonate) and SO3-TEX(p)-BisDGA (sodium 2,5-bis((2-(2-(diethylamino)− 2-oxoethoxy)acetamido)methyl)benzenesulfonate) were synthesized and used as masking agents for the selective extraction and separation of Am3+ over Eu3+ in HNO3 solutions by N,N,N′,N′,N′′,N′′-hexaoctylnitrilotriacetamide (NTAamide(n-Oct)) in n-dodecane. Their influences on the separation effect of Am3+ over Eu3+ were investigated and compared with that of a water-soluble aliphatic bisdiglycolamide of N,N,N′′′,N′′′-tetraethyl-N′,N′′-ethidene bisdiglycolamide (TEE-BisDGA) reported by our previous work. SO3-TEX(m)-BisDGA and SO3-TEX(p)-BisDGA exhibit significantly better masking effects than TEE-BisDGA. The masking selectivity for Eu3+ over Am3+ follows the order of SO3-TEX(m)-BisDGA > SO3-TEX(p)-BisDGA > TEE-BisDGA. During the extraction process, the three BisDGA masking agents form the 1:2 complexes, while the NTAamide (n-Oct) extractant forms the 1:1 complexes with Am3+ and Eu3+. Meanwhile, the conditional stability constants (log β) for the three masking agents with Eu3+ were calculated using the least squares method, which are also in line with those obtained from fluorescence spectrometry (FS). By means of FS, time-resolved laser-induced fluorescence spectrometry (TRLFS), Fourier Transform infrared spectrometry (FT-IR), conductivity, and electrospray ionization mass spectrometry (ESI-MS) analyses, the composition of the complex of Eu3+ with water-soluble BisDGAs (L) was determined to be [Eu(NO3)2(H2O)∙2L](NO3). Furthermore, a batch simulation of multistage countercurrent extraction with 12-stage extraction, 4-stage scrubbing and 8-stage stripping was carried out and demonstrates a highly efficient separation of Am3+ over Lns3+ with the recovery rates above 99.9 % for all metal ions in the simulated feed solution, and with the decontamination factors more than 500 between Am3+ and most of the lanthanide ions.

Development of a sensitivity-enhanced chlorophyll fluorescence lifetime spectroscopic method for nondestructive monitoring of fruit ripening and postharvest decay

Nondestructive monitoring of the environmental changes around fluorescent molecules in postharvest fruit is highly informative for monitoring their ripening and early decay process. In this study, a time-resolved laser-induced fluorescence (TRLIF) spectroscopic system, including a streak camera, spectrometer, and 403 nm picosecond-pulsed laser, was first developed. Then, representative pigments in photosynthesis (chlorophyll a, chlorophyll b, and carotenoids liquid samples) were initially measured and studied to determine whether the developed TRLIF spectroscopic system could produce the characteristics of chlorophyll fluorescence decay traces. Finally, the same approach was tested to monitor the ripening and early decay processes of each three samples of avocado and strawberry. The overall findings demonstrated that the fluorescence lifetime (FLT) of the fruit samples declined steadily during the shelf-life storage. For the avocados samples, the average FLT loss at the wavelength range of 706–749 nm decreased by approximately 23 % and 31 % at 1 and 2 d under shelf-life storage, respectively. For the strawberry samples, the average FLT loss at the wavelength range of 631–706 nm decreased by approximately 22 %, 46 %, 68 %, and 73 % at 0.5, 1, 1.5, and 2 d under the same shelf-life storage condition. This study indicates that the developed TRLIF spectroscopic method is potentially robust and accurate for assessing the ripening and early decay process of various climacteric and non-climacteric fruit.

Speciation and spatial distribution of Eu(III) in fungal mycelium

Europium, as an easy-to-study analog of the trivalent actinides, is of particular importance for studying the behavior of lanthanides and actinides in the environment. Since different soil organisms can influence the migration behavior of these elements, a detailed knowledge of these interaction mechanisms is important. The aim of this study was to investigate the interaction of mycelia of selected wood-inhabiting (S. commune, P. ostreatus, L. tigrinus) and soil-inhabiting fungi (L. naucinus) with Eu(III). In addition to determining the Eu(III) complexes in the sorption solution, the formed Eu(III) fungal species were characterized using scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, chemical microscopy in combination with the time-resolved laser-induced fluorescence spectroscopy. Our data show that S. commune exhibited significantly higher Eu(III) binding capacity in comparison to the other fungi. Depending on fungal strain, the metal was immobilized on the cell surface, in the cell membranes, and within the membranes of various organelles, or in the cytoplasm in some cases. During the bioassociation process two different Eu(III) fungal species were formed in all investigated fungal strain. The phosphate groups of organic ligands were identified as being important functional groups to bind Eu(III) and thus immobilize the metal in the fungal matrix. The information obtained contributes to a better understanding of the role of fungi in migration, removal or retention mechanisms of rare earth elements and trivalent actinides in the environment.

Rate coefficients for the CH(X2Π) + CHX3 (X = Cl and Br) reactions and the propensity of the reactions of CH with halomethanes

Methylidyne (CH) was generated in the ultraviolet multiphoton photolysis of CHCl3 and CHBr3 and detected with laser-induced fluorescence (LIF) via the A2Δ − X2Π (0,0) transition. The time-resolved LIF intensity recorded at varying pressures of CHCl3 and CHBr3 has given the overall rate coefficients for the reactions of CH with CHCl3 and CHBr3. The near gas kinetic rates indicate that CH inserts into the C − Cl and C − Br bonds. The correlation between the rate coefficients for the CH + CHnX4−n (X = F, Cl, and Br) reactions and the heats of reactions for H-, Cl-, Br-elimination is elucidated by the Evans − Polanyi principle.

Calculation Of The Nusselt Number From Temperature And Velocity Data Obtained From Enhanced 3D Two-Colour LIF And 3D PTV In A Rayleigh-Benard Convection Cell

Experimental study of Rayleigh-Benard convection (RBC) requires 3D measurement of the velocity and temperature due to the complexity of the physics of this system. Using a scanning system, the application of the 3D particle image velocimetry (PTV) and 3D time-resolved two-color laser-induced fluorescence (LIF) is investigated on a slender RBC cell. Calculation of the out-of-plane velocity component by using the planar velocity components and applying the continuity law is discussed. From these observations that calculation of the dimensionless heat transfer coefficient, the Nusselt number from the 3D reconstructed temperature field close to the boundary of the fluid domain is investigated.

Experimental and Theoretical Radiative Parameters of Highly Excited Odd-parity Levels in Ir ii

Using the time-resolved laser-induced fluorescence technique, the radiative lifetimes for 15 odd-parity levels from 47,003 to 61,475 cm−1 in Ir ii were measured. To the best of our knowledge, 11 lifetime results among these levels are reported for the first time, and hence they should be a good complement to the measured lifetime data of 10 levels previously published in the literature. The pseudorelativistic Hartree–Fock including core-polarization corrections method was used to calculate the lifetimes and branching fractions (BFs) of the investigated energy levels. Combining the experimental lifetime with the theoretical BFs, the transition probabilities and oscillator strengths for 124 transitions were determined.

Experimental analysis of a non-isothermal confined impinging single plume using time-resolved particle image velocimetry and planar laser induced fluorescence measurements

In this study, the experimental results of the flow behavior of a non-isothermal confined impinging single plume were analyzed. Experimental measurements were performed in the upper plenum of a high-temperature gas-cooled reactor (HTGR) that was scaled, designed, and assembled at Texas A&M University. The goal was to investigate flow mixing, thermal stratification, and plume impingement in the upper plenum of the HTGR under a loss-of-forced-coolant accident and provide a high-fidelity experimental database for validating computational fluid dynamics (CFD) and system codes. Time-resolved particle image velocimetry (TR-PIV) and planar laser-induced fluorescence (P-LIF) measurements were performed in the central plane of the plume flow in the upper plenum. A total power of 0.4 kW of heat was applied to the system. Convergence was achieved for the statistical results from the TR-PIV and P-LIF snapshots. The TR-PIV velocity vectors presented statistical characteristics of the plume flow, such as the mean velocity, root-mean-square fluctuating velocity, and Reynolds stress. The results revealed that the flow reached the maximum velocity far from the jet inlet at y/Dj=2. Furthermore, two-point velocity cross-correlation was performed on the TR-PIV velocity vector fields. Finally, the statistical results were calculated from the P-LIF temperature snapshots and the mean temperature. Furthermore, the temperature profiles were plotted. It was observed that the flow reached the maximum temperature near the plume inlet and decreased downstream.