Lifetime Of Ions Research Articles

Temporal and spatial dynamics of optical emission from laser ablation of the first wall materials of fusion device

Laser-induced breakdown spectroscopy (LIBS) has been developed to in situ diagnose the chemical compositions of the first wall in the EAST tokamak. However, the dynamics of optical emission of the key plasma-facing materials, such as tungsten, molybdenum and graphite have not been investigated in a laser produced plasma (LPP) under vacuum. In this work, the temporal and spatial dynamics of optical emission were investigated using the spectrometer with ICCD. Plasma was produced by an Nd:YAG laser (1064 nm) with pulse duration of 6 ns. The results showed that the typical lifetime of LPP is less than 1.4 μs, and the lifetime of ions is shorter than atoms at ∼10−6 mbar. Temporal features of optical emission showed that the optimized delay times for collecting spectra are from 100 to 400 ns which depended on the corresponding species. For spatial distribution, the maximum LIBS spectral intensity in plasma plume is obtained in the region from 1.5 to 3.0 mm above the sample surface. Moreover, the plasma expansion velocity involving the different species in a multicomponent system was measured for obtaining the proper timing (gate delay time and gate width) of the maximum emission intensity and for understanding the plasma expansion mechanism. The order of expansion velocities for various species is These results could be attributed to the plasma sheath acceleration and mass effect. In addition, an optimum signal-to-background ratio was investigated by varying both delay time and detecting position.

Metastable-state lifetime of erbium ions measured in the fiber propagation direction: Expansion of measurable fiber length

We report the measurement of the metastable-state lifetime of erbium ions doped in a fiber. We apply the pump–probe technique with a wavelength-tunable laser array. This technique allows us to measure the lifetime through delayed absorption in the fiber propagation directions. By tuning the wavelength of the pump–probe pulse pairs to a low absorption wavelength, the lifetime of the metastable state is successfully measured in a 5-m-long fiber. The lifetime is determined to be 10.0 ms, which agrees well with previously reported values.

Determination of the lifetime of D 2 − and HD− ions

A method for determining the lifetime of unstable ions is described. The method is based on measuring the decrease in the ion beam current onto a fixed detector with increasing path length of the ion beam from the ion source to the detector. The measurements performed for D− 2 and HD− molecular ions have shown that their lifetimes are 3.5 ± 0.1 and 4.4 ± 0.1 μs, respectively.

Negative ions, molecular electron affinity and orbital structure of cata-condensed polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons are molecules of ecological, astrochemical significance that find practical applications in organic electronics, photonics and the chemical synthesis of novel materials. The utility of these molecules often implies the occurrence of their ionized forms. Studies in the gas phase of elementary processes of energy-controlled interaction of molecules with low-energy electrons shed light on the mechanisms of transient negative ion formation and evolution. Experiments with the individual compounds representing homologous and/or isomeric series of cata-condensed polyaromatic hydrocarbons were carried out by means of negative ion mass spectrometry in the resonant electron capture mode. Literature data obtained by complementary techniques and theoretical quantum chemical methods (ab initio and density functional theory (DFT)) were invoked to treat the experimental observations. Most polycyclic aromatic hydrocarbon (PAH) molecules form long-lived molecular negative ions when exposed to free electrons of thermal or epi-thermal energy, and no fragmentation is observed up to ca 5eV. The lifetimes of such ions with respect to the spontaneous loss of extra-electron vary from tens of microseconds for angular and branched PAH molecules to milliseconds for linear ones, and correlate with the adiabatic electron affinity (EA) of molecules. Detailed analysis of the electronic (orbital) structure of the molecules made it possible to rationalize the relatively low EAs of angular and branched PAH compared with those of linear ones. The obtained results contribute to the field of electron-molecule interactions and may be of importance for the better comprehension of the functioning of organic electronics, for the synthesis of relevant novel materials, and the development of efficient analytical methods capable of discriminating structural isomers.

Dispersion in the results of measuring the lifetime of negative ions due to their adsorption on ionization-chamber walls

The time of extraction of negative ions from the ionization chamber of a static mass spectrometer has been measured as a value that significantly exceeds the time of their free exit from the chamber. It has been established that anomalously long ion extraction time is due to their adsorption on the ionization-chamber walls; as a result, their arrival at the analyzer tube is delayed. It has been shown that negative ions, which were initially generated as noninfinitely long-lived ones with respect to auto splitting off of an additional electron, are stabilized to everlasting ions due to adsorption, and the subsequent contribution from infinitely long-lived ions to the total ion flux reaching the recording system distorts the results of measuring the ion lifetime. It has been shown that some of the adsorbed ions are annihilated because of neutralization due to the additional electron tunneling to the surface. The probability of tunneling increases with an increase in temperature; thus, the temperature dependence of the ion lifetime is also distorted.

Terbium(III) Luminescent Complexes as Millisecond-Scale Viscosity Probes for Lifetime Imaging.

Fluorescent probes that are able to directly measure viscosity are attractive candidates for the study of intracellular environments. We report a new class of luminescent rotors, based on the sensitized emission of a terbium(III) complex. A 4-fold increase in both quantum yield and luminescence lifetime was observed in viscous media for the studied complexes, with a lifetime ranging from 0.23 to 0.89 ms over a broad range of viscosities (0.6-1200 cP). The presented approach, relying on the millisecond-scale luminescence lifetime of the lanthanide ions, was applied to fixed T24 cancer cells using temporal sampling lifetime imaging microscopy.

Upconversion Modulation through Pulsed Laser Excitation for Anti-counterfeiting

Lanthanide-doped upconversion nanomaterials are emerging as promising candidates in optoelectronics, volumetric display, anti-counterfeiting as well as biological imaging and therapy. Typical modulations of upconversion through chemical methods, such as controlling phase, composition, morphology and size enable us to rationally manipulate emission profiles and lifetimes of lanthanide ions by using continuous-wave laser excitation. Here we demonstrate that under pulsed laser excitation the emission color of NaYF4:Er/Tm (2/0.5%)@NaYF4 core-shell nanoparticles has an obvious transformation from green to red colors. Moreover, both pulse duration and repetition frequency are responsible for manipulating the upconversion emission color. The mechanism of the phenomena may be that the pulsed laser sequence triggers the emission levels to non-steady upconversion states first, and then cuts off the unfinished population process within the pulse duration. This pump source dependent and resultant tunable fluorescence emission enables NaYF4:Er/Tm (2/0.5%)@NaYF4 nanoparticles as a promising fluorophore in the transparent anti-fake printing.

Estimating electron affinity from the lifetime of negative molecular ions: Cycloheptatriene derivatives

Cycloheptatriene derivatives are studied by means of resonance electron capture negative ion mass spectrometry (REC NIMS). The average lifetimes of molecular negative ions (NIs) are measured with respect to electron autodetachment. Using the Arrhenius approach, electron affinity EAa of the molecules under study is estimated, and the effective temperature of the resulting negative molecular ions is determined as a function of the electron energy. It is assumed that the dissociation of negative molecular ions in the ground electronic state is a process similar to that of the thermal degradation of molecules.

Metastable-state lifetime of erbium ions measured through delayed absorption in the fiber propagation direction

We performed lifetime measurements of erbium ions doped in fibers with lengths of 20–160 cm. Using a pump–probe technique, we measured the lifetime of the 4I13/2 state of erbium ions in the fiber propagation direction. The dependence of the measured lifetime on fiber length was compared with the lifetime determined by temporally resolving spontaneous emission in the same direction. The dependence of the 4I13/2 lifetime on input power was also measured. We found that the 4I13/2 lifetime of erbium ions was nearly constant at about 10 ms under all the investigated conditions.

Correlation between the shape of the ion mobility signals and the stepwise folding process of polylactide ions.

In the field of polymer characterization, the use of ion mobility mass spectrometry (IMMS) remains mainly devoted to the temporal separation of cationized oligomers according to their charge states, molecular masses and macromolecular architectures in order to probe the presence of different structures. When analyzing multiply charged polymer ions by IMMS, the most striking feature is the observation of breaking points in the evolution of the average collision cross sections with the number of monomer units. Those breaking points are associated to the folding of the polymer chain around the cationizing agents. Here, we scrutinize the shape of the arrival time distribution (ATD) of polylactide ions and associate the broadening as well as the loss of symmetry of the ATD signals to the coexistence of different populations of ions attributed to the transition from opened to folded stable structures. The observation of distinct distributions reveals the absence of folded/extended structure interconversion on the ion mobility time scale (1-10ms) and then on the lifetime of ions within the mass spectrometer at room temperature. In order to obtain information on the possible interconversion between the different observed populations upon ion activation, we performed IM-IM-MS experiments (tandem ion mobility measurements). To do so, mobility-selected ions were activated by collisions before a second mobility measurement. Interestingly, the conversion by collisional activation from a globular structure into a (partially) extended structure, i.e. the gas phase unfolding of the ions, was not observed in the energetic regime available with the used experimental setup. The absence of folded/extended interconversion, even upon collisional activation, points to the fact that the polylactide ions are 'frozen' in their specific 3D structure during the desolvation/ionization electrospray processes. Copyright © 2017 John Wiley & Sons, Ltd.

Влияние поверхностной адсорбции отрицательных ионов в ионном источнике на результаты измерений их времени жизни

Влияние поверхностной адсорбции отрицательных ионов в ионном источнике на результаты измерений их времени жизни, Лукин В.Г., Хвостенко О.Г.

Vacuum systems of linear accelerators of the NICA injection complex

The NICA project, which includes several accelerators of charged particles, is under construction in the Laboratory of High Energy Physics, Joint Institute for Nuclear Research (JINR), Dubna. Obtaining the required vacuum conditions is one of the key points in implementing the project, because reaching the required ion lifetime at all stages of particle acceleration is what determines the effective luminosity of the experiments in the long run. Currently, modernization of the vacuum system of the injection complex of the LU-20 linear accelerator of light ions, one of oldest accelerators in the JINR, is being carried out and the new HILAC linear accelerator for the acceleration of gold ions in the collider mode of the NICA complex is being installed. At the end parts of the linear accelerators, the residual gas pressure must be approximately 10–5 Pa, which is determined by the maximum amplitude of the RF electric field used for the acceleration of ions.

Optimization of parameters of a surface-electrode ion trap and experimental study of influences of surface on ion lifetime

In this paper we report the optimal design and fabrication of a gold-on-silica linear segmented surface-electrode ion trap. By optimizing the thickness and width of the electrodes, we improved the trapping ability and trap scalability. By using some practical experimental operation methods, we successfully minimized the trap heating rate. Consequently, we could trap a string of up to 38 ions, and a zigzag structure with 24 ions, and transport two trapped ions to different zones. We also studied the influences of the ion chip surface on the ion lifetime. The excellent trapping ability and flexibility of operation of the planar ion trap shows that it has high feasibility for application in the development a practical quantum information processor or quantum simulator.

Ca9La(PO4)5(SiO4)Cl2:Dy3+: A white-emitting apatite-type phosphor pumped for n-UV w-LEDs

The Ca9La(PO4)5(SiO4)Cl2:Dy3+ (CLPSCl:Dy3+) powder phosphor with apatite structure has been successfully synthesized via high-temperature solid state method. Single phase in such phosphor was verified through X-ray diffraction (XRD) technique. The Dy ions concentration dependent luminescence properties including emission, excitation and lifetimes of Dy ions were characterized using photoluminescence (PL) spectroscopy. The results showed that CLPSCl:Dy3+ phosphor could efficiently assimilate the n-UV light and emit blue (~486nm) and yellow light (~578nm), originating from the f-f transitions of Dy3+. The critical Dy3+ quenching concentration (QC) was determined to be about 12mol%. The concentration quenching mechanism was also determined to be dipole–dipole interaction.

Multiparticle losses in a linear quadrupole Paul trap

A linear quadrupole Paul trap is fabricated for capturing magnesium and aluminium ions. An experimental cycle performed has demonstrated ion capture and holding in a trap with an average ion lifetime of . Modelling of ion dynamics in the trap shows that the main mechanism responsible for losses of hot ions is multiparticle interaction, which results in that a kinetic energy of some ions increases and they leave the trapping zone. This mechanism is completely suppressed if ions are cooled. Another mechanism is the charge exchange; however, it is not substantial at a high average energy of ions produced in the result of an electron impact. Parameters of the trap allow one to perform precision spectroscopic measurements and to control ion quantum states.

Radiative lifetimes of the bound excited states ofPt−

The intrinsic radiative lifetimes of the $5d^{10}6s$ $^{2}\text{S}_{1/2}$ and $5d^{9}6s^{2}$ $^{2}\text{D}_{3/2}$ bound excited states in the platinum anion $\text{Pt}^{-}$ have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying $5d^{10}6s$ $^{2}\text{S}_{1/2}$ state was measurement to be 2.54$\pm$0.10 s, while only a lifetime in the range of 50 - 200 ms could be estimated for the $5d^{9}6s^{2}$ $^{2}\text{D}_{3/2}$ fine-structure level. The storage lifetime of the $\text{Pt}^{-}$ ion beam was measured to be a little over 15 minutes at a ring temperature of 13 K. The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.

Spectral Behavior of Bias-Dependent Photocurrent and Photoluminescence in Sputtered ZnO Layers

The bias-dependent behavior of the photocurrent (PC) and photoluminescence (PL) of sputtered ZnO layers has been investigated. Based on PC spectroscopy results, the PC intensity of the observed free exciton increased strongly up to electric field of 60 V/cm, after which its rate of increase slightly reduced due to disturbance of field-assisted dissociation of radical ion pairs, which leads to photocarrier generation. Thus, the energy of excitonic PC peaks showed a tendency to red-shift with increasing electric field, being attributed to the induced Stark effect. Therefore, it is concluded that the strong interaction between free excitons and photogenerated PC carriers leads to displacement or widening of the spectrum. In the PL measurements, near-band-edge (NBE) and violet emissions were observed. With increasing electric field, two PL emissions were progressively quenched. The combined PL/PC results reveal that the PL ions associated with the NBE and violet emissions readily interact with the PC carriers of photogenerated electrons and holes. This behavior reduces the recombination ratio and the lifetime of PL ions. So, the PL intensity quenching originates from a decrease in the number of carriers participating in recombination. Consequently, we find that the quenching mechanism of the NBE and violet emissions is strongly related to low external electric field.

Micellar Effects on Photoinduced Electron Transfer in Aqueous Solutions Revisited: Dramatic Enhancement of Cage Escape Yields in Surfactant Ru(II) Diimine Complex/[Ru(NH3)6](2+) Systems.

The effect of cationic micelle incorporation on light induced electron transfer, charge separation and back electron transfer between an aqueous electron donor, [Ru(NH3)6](2+), and a series of Ru(II) diimine complex chromophores/acceptors, is presented. The chromophores have the general formula [(bpy)2Ru(LL)](2+) (LL = bpy; 4-R-4'-methyl-2,2'-bpy, R = pentyl (MC5), terdecyl (MC13), heptadecyl (MC17); 4,4'-di(heptadecyl)-2,2'-bpy (DC17)). Of the five chromophores, the MC13, MC17, and DC17 complexes associate with the added micelle forming surfactant, cetyltrimethylammonium bromide (CTAB). Quenching of the luminescence of the bpy and MC5 complexes by [Ru(NH3)6](2+) is unaffected by addition of surfactant, while rate constants for quenching of the MC13 and MC17 complexes are decreased. Cage escape yields following photoinduced electron transfer to generate [(bpy)2Ru(LL)](+) and [Ru(NH3)6](3+) are approximately 0.1 for all the water-soluble chromophores (excluding DC17) in the absence of added CTAB. In the presence of surfactant, the cage escape yields dramatically increase for the MC13 (0.4) and MC17 (0.6) complexes, while remaining unchanged for [Ru(bpy)3](2+) and the MC5 complex. Back electron transfer of the solvent separated ions is also strongly influenced by the presence of surfactant. For the MC13 and MC17 complexes, back electron transfer rate constants decrease by factors of 270 and 190, respectively. The MC5 complex exhibits two component back electron transfer, with the fast component having a rate constant close to that in the absence of surfactant and a slow component nearly 200 times smaller. Results are interpreted in terms of the partitioning of the 2+ and 1+ forms of the chromophores between aqueous and micellar phases. The extended lifetimes of the radical ions may prove useful in coupling the strong reductants formed to kinetically facile catalysts for reduction of water to hydrogen.

Dissociation of Molecular Ions During the DC Field Evaporation ZnO in Atom Probe Tomography

In atom probe tomography, a tip-shaped sample is evaporated atom by atom in a high DC field. The atoms are field ionized and accelerated to a two-dimensional detector, and their measured impact position and time-of-flight enable the three-dimensional reconstruction of the evaporated volume [I]. In some materials, a large fraction of the material evaporates as molecular ions, which can dissociate in the high DC electric field [2). The study of such dissociations can give valuable information in the field of field induced chemistry [3], to better understand the effect of the electric field on molecules stability. In addition, such dissociations can have an effect on the quality of atom probe data and may induce composition artifacts. The understanding of the way such dissociations affect the data are necessary to predict and maybe correct these artifacts. In this work, we first study experimentally the field evaporation of a ZnO sample. In the figure I .a, a two-dimensional histogram shows the correlation between the time-of-flight difference and the distance between impacts, for pairs of ZnO+ ions detected at the same evaporation event. Different regions can be identified. The horizontal line (region I) mostly corresponds to correlated evaporation [4). The two ions reach the detector at the same time but with spacing on the detector that reflects their original spacing on the tip surface (Figure l .b.I). The diagonal line in the histogram, however, evidences the presence of dissociation of Zn202 2 + ions into ZnO+ ions, with different molecular orientation with respect to the electric field. Depending on the orientation of the parent ion, the Coulomb repulsion between the dissociation products has an effect either on the time-of-flight difference between the two ions (region II) or on the spacing between their impact on the detector (region UI). We show that this correlati.on plot can be used to extract complex information about the dissociation of molecular ions, like the parent ion lifetime, the molecule orientation when dissociation occurs, and the energy transferred by the dissociation (or kinetic energy release). Ab initio calculations are also performed to predict the stability of molecular ions in high field. For simplicity's sake, calculations are performed for the dissociation of Zn02+ ions (Figure 2). It is found that different dissociation paths can exist, with different barriers, depending on the molecule initial orientation. In particular, one orientation leads to the dissociation into neutral oxygen, which cannot be detected by atom probe and can cause important artifacts. This confirms the importance of a future study of dissociation phenomena in high field, both experimental and theoretical [5].

Dissociation Dynamics of Molecular Ions in High dc Electric Field.

In an atom probe, molecular ions can be field evaporated from the analyzed material and, then, can dissociate under the very intense electric field close to the field emitter. In this work, field evaporation of ZnO reveals the emission of Zn2O2(2+) ions and their dissociation into ZnO(+) ions. It is shown that the repulsion between the produced ZnO(+) ions is large enough to have a measurable effect on both the ion trajectories and times of flight. Comparison with numerical simulations of the ion trajectories gives information on the lifetime of the parent ions, the energy released by the dissociation and repulsion, and also the dissociation direction. This study not only opens the way to a new method to obtain information on the behavior of molecular ions in high electric fields by using an atom probe, but also opens up the interesting perspective to apply this technique to a wide class of materials and molecules.