Nanosecond Time Range Research Articles

Fabrication and properties of novel multilayered Y3Al5O12/MgAl2O4 ceramics doped with rare-earth ions

Multilayer Y3Al5O12 (YAG)/MgAl2O4 (MAS) ceramics doped with europium and cerium ions exhibiting functionally graded properties was consolidated by the SPS method using during layer-by-layer formation powders approach. The optimal modes for YAG/MAS ceramics doped with rare earth ions preparation were obtained during the SPS process. It was observed that at the isothermal exposure stage at a temperature of 1450 °C shrinkage process stops. Introduction of CeO2, Eu2O3 into the YAG/MAS ceramics leads to a shift in the range of intense shrinkage to lower temperatures. Morphological, optical and luminescent properties have been studied in detail for fabricated YAG/MAS ceramics with different arrangement of the layers. The luminescent properties using time-resolved cathodoluminescence (CL) and steady state photoluminescence (PL) were investigated in detail. The spectral dynamics in nanosecond and millisecond time range was demonstrated after e-beam excitation. The PL efficiency of YAG/MAS ceramics and nature of luminescence centers were analyzed. The novel kind of YAG/MAS functional ceramics could be promising candidate for efficient luminescent converter.

Perylene-derivative singlet exciton fission in water solution.

We provide direct evidence of singlet fission occurring with water-soluble compounds. We show that perylene-3,4,9,10-tetracarboxylate forms dynamic dimers in aqueous solution, with lifetimes long enough to allow intermolecular processes such as singlet fission. As these are transient dimers rather than stable aggregates, they retain a significant degree of disorder. We performed a comprehensive analysis of such dynamic assemblies using time-resolved absorption and fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, and theoretical modelling, allowing us to observe the characteristic signatures of singlet fission and develop a model to characterize the different species observed. Our findings reveal that structure fluctuations within perylene-3,4,9,10-tetracarboxylate associations are key in favoring either singlet fission or charge separation. The efficiency of triplet formation is higher than 100%, and the disordered system leads to triplets living in the nanosecond time range.

Micellization thermodynamics as a function of the temperature of a cationic zwitterionic dodecyl phosphocholine and anionic sodium dodecyl sulfate mixed micelles with fluorometry

As fluorescence parameters such as lifetime, quantum yield, anisotropy and polarisation quantum are extremely sensitive to fluorophores’ microenvironmental changes, changes in the properties of the fluorescence probe have been widely used to study hydrophobic interactions in protein and membrane biology. The current study determines the critical micelle concentration (CMC) of mixed micelles of sodium dodecyl sulfate (SDS) and cationic surfactant N-dodecyl phosphocholine (DPC) based on fluorescence intensity measurements. biomolecular structure analysis and dynamics revealed through the measure of changes in the nanosecond time range. As the temperature rises, the onset of micellization tends to occur at higher concentrations. It was measured versus micelle concentration over a temperature range of (288–338) K. The obtained results were used to estimate the micellization thermodynamic parameters. Surfactant CMC drops to a minimum (T = 308 K) and then rises with temperature forming a parabolic curve as a function of temperature, according to experimental data. The CMCs are first correlated by a polynomial equation to determine the enthalpy of micellization. Both Delta {H}_{mathrm{mic}} and Delta {S}_{mathrm{mic}} appear to decrease monotonically as temperature rises. ΔGmic is negative, indicating that the micellization process is exothermic and favorable. The compensation temperature (Tc) ranged from (313–318) K by linear regression over the whole temperature range and for DPC, SDS, and mixed micelles together.

Ultrafast dynamics in polymeric carbon nitride thin films probed by time-resolved EUV photoemission and UV-Vis transient absorption spectroscopy.

The ground- and excited-state electronic structures of four polymeric carbon nitride (PCN) materials have been investigated using a combination of photoemission and optical absorption spectroscopy. To establish the driving forces for photocatalytic water-splitting reactions, the ground-state data was used to produce a band diagram of the PCN materials and the triethanolamine electron scavenger, commonly implemented in water-splitting devices. The ultrafast charge-carrier dynamics of the same PCN materials were also investigated using two femtosecond-time-resolved pump-probe techniques: extreme-ultraviolet (EUV) photoemission and ultraviolet-visible (UV-Vis) transient absorption spectroscopy. The complementary combination of these surface- and bulk-sensitive methods facilitated photoinduced kinetic measurements spanning the sub-picosecond to few nanosecond time range. The results show that 400 nm (3.1 eV) excitation sequentially populates a pair of short-lived transient species, which subsequently produce two different long-lived excited states on a sub-picosecond time scale. Based on the spectro-temporal characteristics of the long-lived signals, they are assigned to singlet-exciton and charge-transfer states. The associated charge-separation efficiency was inferred to be between 65% and 78% for the different studied materials. A comparison of results from differently synthesized PCNs revealed that the early-time processes do not differ qualitatively between sample batches, but that materials of more voluminous character tend to have higher charge separation efficiencies, compared to exfoliated colloidal materials. This finding was corroborated via a series of experiments that revealed an absence of any pump-fluence dependence of the initial excited-state decay kinetics and characteristic carrier-concentration effects that emerge beyond few-picosecond timescales. The initial dynamics of the photoinduced charge carriers in the PCNs are correspondingly determined to be spatially localised in the immediate vicinity of the lattice-constituting motif, while the long-time behaviour is dominated by charge-transport and recombination processes. Suppressing the latter by confining excited species within nanoscale volumes should therefore affect the usability of PCN materials in photocatalytic devices.

Models of advanced recording systems: A multi-timescale micromagnetic code for granular thin film magnetic recording systems

Micromagnetic modelling provides the ability to simulate large magnetic systems reliably without the computational cost limitation imposed by atomistic modelling. Through micromagnetic modelling it is possible to simulate systems consisting of thousands of grains over a time range of nanoseconds to years, depending upon the solver used. Here we present the creation and release of an open-source multi-timescale micromagnetic code combining three key solvers: Landau-Lifshitz-Gilbert; Landau-Lifshitz-Bloch; Kinetic Monte Carlo. This code, called MARS (Models of Advanced Recording Systems), is capable of accurately simulating the magnetisation dynamics in large and structurally complex single- and multi-layered granular systems as is shown by comparison to established atomistic simulation results. The short timescale simulations are achieved for systems far from and close to the Curie point via the implemented Landau-Lifshitz-Gilbert and Landau-Lifshitz-Bloch solvers respectively. This enables read/write simulations for general perpendicular magnetic recording and also state of the art heat assisted magnetic recording (HAMR). The long timescale behaviour is simulated via the Kinetic Monte Carlo solver, enabling investigations into signal-to-noise ratio and data longevity. The combination of these solvers opens up the possibility of multi-timescale simulations within a single software package. For example the entire HAMR process from initial data writing and data read back to long term data storage is possible via a single simulation using MARS. The use of atomistic parameterisation for the material input of MARS enables highly accurate material descriptions which provide a bridge between atomistic simulation and real world experimentation. Thus MARS is capable of performing simulations for all aspects of recording media research and development. This ranges from material characterisation and optimisation to system design and implementation. The object orientated nature of MARS is structured to facilitate quick and simple development and easy implementation of user defined custom simulation types which can utilise either timescale or a combination of both timescales. Program summaryProgram title: MARSCPC Library link to program files:https://doi.org/10.17632/8mx7cndcdx.1Developer's repository link:https://bitbucket.org/EwanRannala/mars/Code Ocean capsule:https://codeocean.com/capsule/2549929Licensing provisions: MITProgramming language: C++Supplementary material: MARS testing methodology (PDF), HAMR simulation example video.Nature of problem: A combined model that enables the complete modelling of magnetic recording processes at elevated temperatures covering all time scales from writing (nanoseconds) up to long term data storage (years). The model must also accurately describe the granular nature of the recording media as grain sizes are reduced to a few nanometres.Solution method: Short timescale behaviours are captured via the Landau-Lifshitz-Gilbert and Landau-Lifshitz-Bloch solvers for low and high temperature systems respectively. The long time scale behaviours are captured via a kinetic Monte Carlo solver. To enable complex models which account for mixed timescale behaviours the solvers are implemented as a single class structure which allows for dynamic solver selection. The granular structure is generated via a Laguerre-Voronoi tessellation with a custom implemented packing algorithm to produce highly realistic grain size distributions. Complex thermal dependencies of materials can be incorporated via atomistic parameterisation forming a multi-timescale model of the material.

Electron Transfer Quenching of Rhodamine 6G by N-Methylpyrrole Is an Unproductive Process in the Photocatalytic Heterobiaryl Cross-Coupling Reaction.

In the heterobiaryl cross-coupling reaction between aryl halides (Ar-X) and N-methylpyrrole (N-MP) catalyzed by rhodamine 6G (Rh6G+) under irradiation with visible light, a highly active and long-lived (millisecond time range) rhodamine 6G radical (Rh6G•) is formed upon electron transfer from N,N-diisopropylethylamine (DIPEA) to Rh6G+. In this study, we utilized steady-state and time-resolved spectroscopy techniques to demonstrate the existence of another electron-transfer process occurring from the relatively electron-rich N-MP to photoexcited Rh6G+ that was neglected in the previous reports. In this case, the radical Rh6G• formed is short-lived and undergoes rapid recombination (nanosecond time-range), rendering it ineffective in reducing Ar-X to aryl radicals Ar• that can subsequently be trapped by N-MP. This is further demonstrated via two model reactions involving 4'-bromoacetophenone and 1,3,5-tribromobenzene with insignificant product yields after visible-light irradiation in the absence of DIPEA. The unproductive quenching of photoexcited Rh6G+ by N-MP leads to a lower concentration of photocatalyst available for competitive charge transfer with DIPEA and hence decreases the efficiency of the cross-coupling reaction.

Effect of spin-orbit interaction on recombination luminescence of dye in films of halogen-containing derivative poly-N-epoxypropylcarbazole

A photoluminescence kinetics of a cationic polymethine dye in composite polymer films based on halogen-containing derivatives poly-N-epoxypropylcarbazole (PEPC) has been studied. The observed luminescence kinetics is formed by the fluorescence of the dye and recombination luminescence associated with the formation and recombination of electron-hole pairs (EHP). It was shown, that measuring the external magnetic field effect on the kinetics of dye luminescence in a wide time range made it possible to determine the characteristic times of the recombination processes with the involvement of EHP formed from singlet and triplet excited electronic states of the dye molecules and main channels of electron energy transformation in composite films. An enhancement of the spin-orbit interaction in polymers with different heavy atoms leads to an increase in a value of the magnetic effect (g(B)) in the nanosecond time range and to a decrease in g(B) value in the microsecond time range.

Flow analysis of a shock wave at pulse ionization: Riemann problem implementation

An experimental study of the plasma-gas dynamic fluid formed after pulse ionization of the gas flow with a plane shock wave with Mach number 2.2–4.8 is carried out. Nanosecond volume discharge with UV preionization was switched on when the shock moved in a tube channel test section. Energy input occurs in the low-pressure gas volume separated by the shock surface within a time less than 200–300 ns; a single shock wave breaks into three discontinuities in accordance with the 1D Riemann problem solution. The initial (plasma-dynamic) stage of the flow in the nanosecond time range is visualized by glow recording; the supersonic gas processes in the microsecond time range are recorded using high-speed shadow imaging. Quantitative information about the dynamics of the shocks and contact surface (plots of horizontal distance) was obtained within time up to 25 µs. A region with an increased gas-discharge plasma glow intensity, after the discharge electric current termination, was recorded in the time interval from 0.3 to 1.5 µs; it was explained by a jump in gas temperature and density between the new shock wave and the contact discontinuity.

Synthesis and optical properties of Tb3+ or Dy3+-doped MgAl2O4 transparent ceramics

MgAl2O4 ceramics doped with rare earth ions (Tb3+ and Dy3+ ions) were fabricated by SPS technique. Optical properties and pulse cathodoluminescence (PCL) spectra were studied. The redshift effect of the absorption boundary for rare earth (RE) ions doped ceramics was shown. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63 eV caused by F-type centers. It has been demonstrated that the introduction of terbium and dysprosium ions practically does not change the intensity ratio of the bands at 2.72, 3.01, 3.37 eV, but leads to an increase in the band at 3.63 eV in nanosecond time range. There are emission bands related to intrinsic host defects, RE ions dopants (Dy3+, Tb3+), and trace elements (Cr3+ ions) in PCL spectra measured in millisecond time range. The dependences of kinetic characteristics of spinel ceramics were studied. In nanosecond time range, decay kinetics of the MAS ceramics is described by the sum of two exponentials with luminescence decay times are 30 ± 5 ns and 0.8 ± 0.1 μs In the millisecond time interval, the luminescence decay time depends on the dopant ions.

Time-resolved fluorescence measurements on leaves: principles and recent developments

Photosynthesis starts when a pigment in the photosynthetic antennae absorbs a photon. The electronic excitation energy is then transferred through the network of light-harvesting pigments to special chlorophyll (Chl) molecules in the reaction centres, where electron transfer is initiated. Energy transfer and primary electron transfer processes take place on timescales ranging from femtoseconds to nanoseconds, and can be monitored in real time via time-resolved fluorescence spectroscopy. This method is widely used for measurements on unicellular photosynthetic organisms, isolated photosynthetic membranes, and individual complexes. Measurements on intact leaves remain a challenge due to their high structural heterogeneity, high scattering, and high optical density, which can lead to optical artefacts. However, detailed information on the dynamics of these early steps, and the underlying structure–function relationships, is highly informative and urgently required in order to get deeper insights into the physiological regulation mechanisms of primary photosynthesis. Here, we describe a current methodology of time-resolved fluorescence measurements on intact leaves in the picosecond to nanosecond time range. Principles of fluorescence measurements on intact leaves, possible sources of alterations of fluorescence kinetics and the ways to overcome them are addressed. We also describe how our understanding of the organisation and function of photosynthetic proteins and energy flow dynamics in intact leaves can be enriched through the application of time-resolved fluorescence spectroscopy on leaves. For that, an example of a measurement on Zea mays leaves is presented.

Steady state and time–resolved luminescence of Tb3+/Ce3+ doped ABS-BGP glasses

ABS-BGP (Al2O3-B2O3-SiO2-BaCO3-Gd2O3-P2O5) glasses doped with different concentrations of Ce3+ and Tb3+ were prepared by high temperature melting method. The luminescent properties using steady state and time-resolved luminescence were investigated. The time-resolved luminescence was studied by pulse photo- and cathodoluminescence type of excitation. The strong “blue” emission due to radiation transition of Ce3+ ions under selective excitation in nanosecond time range was recorded. The decay time of Tb3+ ions under the electron beam excitation at 542 nm is 2.2 ms. It was demonstrated that the luminescence efficiency does not depend on the Ce3+ concentration excited by the LED chip. The decay kinetics are characterized by a single exponential function with the decay time τ = 30 ns under photoexcitation. However there are two components of luminescence decay τ1 = 35 ns, τ2 = 540 ns when excited by a flow of electrons. The difference in luminescence decay kinetics under various type of excitation was discussed. The results indicate that ABS-BGP glasses would be excellent candidate for visible luminescent device applications.

Research of luminophores afterglow under influence of pulsed X-ray radiation of nanosecond duration

The work describes an investigation of afterglow of various luminophores under influence of pulsed X-ray radiation of nanosecond duration. As a source of radiation a pulsed X-ray “Yasen 01” apparatus is applied. Maximum impulse current of an X-ray tube is 300 A. Maximum electron energy is 120 keV. Half-height pulse duration of an X-ray burst is about 30 ns. A pulse repetition rate is up to 4 kHz. Two types of X-ray luminophores based on gadolinium oxysulfide Gd2O2S:Tb and cesium iodide CsI:Tl have been investigated. The novelty of the work is use of a fast-acting solid-state semiconductor photomultiplier. It allows recording changes of luminophores luminosity in the nanosecond time range. The photomultiplier is characterized by having two discreet outputs for measuring quickly and slowly time-changing light flows. Presence of two signal outputs allows recording changes of luminophores luminosity both during fast nanosecond excitation and during long-time afterglow. Obtained data about the nature of afterglow of investigated luminophores makes it possible to select the best one for use in conjunction with a pulsed X-ray apparatus with a high pulse repetition rate.

Type-II photon avalanche associated with interband transitions in crystals: dependences of transmission on incident light intensity

Light transmission in a type-II photon avalanche model based on interband transitions in crystals is studied. For various laser radiation durations and different material thicknesses, the transmission dependences on the intensity of the incident light j0 are obtained. It is shown that the transmission decreases sharply with increasing j0. Thus, in the nanosecond time range, an effective attenuation of radiation with j0≈30–150 kW/cm2 at lengths of 10−2–10−1 cm can be obtained.

Spectroscopy of divalent samarium in alkaline-earth fluorides

Optical spectra (absorption, luminescence, decay of emission, spectra with time resolution) of Sm2+ ions in alkaline-earth fluoride crystals (CaF2, SrF2, BaF2) in the wavelength range 120–900 nm at 7–300 K were studied. By additive coloration of about 60% of the original Sm3+ is converted to Sm2+.One component of the decay of the Sm2+ emission was observed in BaF2 crystals with a lifetime of 16 ms (a slow component) and in CaF2 crystals with a lifetime of 1.3 μs (fast component) at low temperature. In SrF2 crystals, two decay of luminescence components are found in the millisecond and nanosecond time range. The luminescence spectra of the slow and fast components in CaF2, SrF2, BaF2 are similar, which confirms their attribution to forbidden 4f-4f and allowed 5d-4f transitions, respectively. The results obtained made it possible to clarify the position of the excited levels of Sm2+ 4f(5D0) and 5d(eg) relative to the bottom of the conduction band of alkaline-earth fluorides.

Luminescent properties of MgAl2O4 ceramics doped with rare earth ions fabricated by spark plasma sintering technique

MgAl2O4 ceramics doped with rare earth ions (Eu2+ and Ce3+ ions) were fabricated by spark plasma sintering technique. A complex characterization of the crystalline and defect structure of the ceramic by XRD was carried out. Absorption, excitation, photo- and cathodoluminescence spectra were studied. The photoluminescence spectrum shifts to the blue region with a maximum at λem = 475 nm for the MAS:0.1Ce ceramics. The nature of this luminescence can be caused by the radiative transitions in the cerium ion 5d–4f. The emission spectrum of MAS:0.1Eu has a “green” band emission in range of 400–700 nm centered around 500 nm, which can be ascribed to the allowed 4f65d1→4f7 (5d–4f) transition of Eu2+. In the millisecond time range, simultaneously with the emission of the complex host centers, the impurity luminescence bands of the chromium ion are recorded. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63–3.82 eV caused by F-type centers. It was demonstrated that the Eu2+ and Ce3+ ions lead to change the intensity ratio of the luminescence bands. The luminescence decay kinetics of synthesized spinel ceramics in nano- and millisecond time range were investigated in detail.

Simulations of short pulse laser-matter interaction in case of tight focusing onto thin film

Studies of ultra-fast laser-matter interaction are important for many applications. Such interaction triggers extreme physical processes which are localized in the range from ~10 nanometers to micron spatial scales and developing within picosecond−nanosecond time range. Thus the experimental observations are difficult and methods of applied mathematics are necessary to understand these processes. Here we describe our simulation approaches and present solutions for a laser problem significant for applications. Namely, the processes of melting, a liquid jet formation, and its rupture are considered. Motion with the jet is caused by a short ~0.1−1 ps pulse illuminating a small spot on a surface of a thin ~10 − 100 nm film deposited onto substrate. We find the 5-fold symmetry structures in the frozen jet and appearance of very sharp tip of the jet.

Investigation of the aluminum phthalocyanine nanoparticles colloidal solutions pH-dependent photoluminescence kinetics in pico- and nanosecond time range

In this study, the fluorescence intensity decay of aluminum phthalocyanine nanoparticles colloidal solutions at different pH was investigated. Hamamatsu Streak-Camera (C10627 - 13 Hamamatsu Photonics) with picosecond temporal resolution (15 ps) was used to carry out the measurements. For excitation we used Hamamatsu Picosecond Light Pulser PLP - 10 with 637 nm wavelength and 65 ps pulse duration. The changes in fluorescence decay kinetics were found during the experiment. The number of fluorescence lifetime components and duration of lifetimes depends on pH. At pH 2 the presence of two fluorescence lifetimes was recorded: the first one was 5 ns, which corresponded to the molecular form in solution, and 1.5 ns, which corresponded to bound state of phthalocyanine molecules. This work is a preparatory step towards a model which describes the interaction of aluminum phthalocyanine nanoparticles with environment in biological tissue.

Electric strength of hydrogen in the nanosecond time range

We have obtained information in breakdown voltage U br of gas discharges as a function of gas pressure p and voltage surge of the discharge gap in the subnanosecond time interval. The experiments are made in a uniform electric field. The working gas is hydrogen. The pressure is varied from 0.1 to 6.0 MPa. The experiment is started at the minimal discharge gap width d = 0.15 mm. Then, d is increased with a step of 0.1–0.2 mm at a fixed gas pressure (0.1, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 MPa) until the discharge gap does not experience breakdown. It is found that an increase in pressure from 5.0 to 6.0 MPa increases the breakdown voltage in hydrogen by 40–170% depending on the discharge gap width. The results are plotted in the U br vs. pd coordinates. It is shown that the charge similarity law is violated in the subnanosecond range. For the same product of pressure by the discharge gap, the breakdown voltage substantially depends on the gas pressure in the gap.

Note: Design of a full photon-timing recorder down to 1-ns resolution for fluorescence fluctuation measurements.

A photon timing recorder was realized in a field programmable gate array to capture all timing data of photons on multiple channels with down to a 1-ns resolution and to transfer all data to a host computer in real-time through universal serial bus with more than 10 M events/s transfer rate. The main concept is that photon time series can be regarded as a serial communication data stream. This recorder was successfully applied for simultaneous measurements of fluorescence fluctuation and lifetime of near-infrared dyes in solution. This design is not only limited to the fluorescence fluctuation measurement but also applicable to any kind of photon counting experiments in a nanosecond time range because of the simple and easily modifiable design.

Band structure engineering via piezoelectric fields in strained anisotropic CdSe/CdS nanocrystals.

Strain in colloidal heteronanocrystals with non-centrosymmetric lattices presents a unique opportunity for controlling optoelectronic properties and adds a new degree of freedom to existing wavefunction engineering and doping paradigms. We synthesized wurtzite CdSe nanorods embedded in a thick CdS shell, hereby exploiting the large lattice mismatch between the two domains to generate a compressive strain of the CdSe core and a strong piezoelectric potential along its c-axis. Efficient charge separation results in an indirect ground-state transition with a lifetime of several microseconds, almost one order of magnitude longer than any other CdSe/CdS nanocrystal. Higher excited states recombine radiatively in the nanosecond time range, due to increasingly overlapping excited-state orbitals. k̇p calculations confirm the importance of the anisotropic shape and crystal structure in the buildup of the piezoelectric potential. Strain engineering thus presents an efficient approach to highly tunable single- and multiexciton interactions, driven by a dedicated core/shell nanocrystal design.