Excitation Range Research Articles

Introducing visible-light sensitivity into photocatalytic CeO2 nanoparticles by hybrid particle preparation exploiting plasmonic properties of gold: enhanced photoelectrocatalysis exemplified for hydrogen peroxide sensing.

In this report we combine the catalytic properties of CeO2 nanoparticles with their transduction ability for photoelectrochemical sensing. This study highlights the usage of CeO2 providing catalytic activity towards H2O2, but only with a limited excitation range in the UV for the construction of a sensing system. In order to improve the photoelectrocatalysis of CeO2 nanoparticles by extending their excitation to visible light, Au/CeO2 core/shell hybrid nanoparticles have been synthesized. The hybrid nanoparticles are fixed on electrodes, allowing for the generation of photocurrents, the direction of which can be controlled by the electrode potential (without bias). The application of the hybrid nanoparticles results in an enhanced photocurrent amplitude under white light illumination as compared to the pure CeO2 nanoparticles. Wavelength-dependent measurements confirm the participation of the Au core in the signal transduction. This can be explained by improved charge carrier generation within the hybrid particles. Thus, by using a plasmonic element the photoelectochemical response of a catalytic nanoparticle (i.e. CeO2) has been spectrally extended. The effect can be exploited for sensorial hydrogen peroxide detection. Here higher photocatalytic current responses have been found for the hybrid particles fixed to gold electrodes although the catalytic reduction has been comparable for both types of nanoparticles. Thus, it can be demonstrated that Au/CeO2 core-shell nanoparticles allow the utilization of visible light for photoelectrochemical hydrogen peroxide (H2O2) detection with improved sensitivity under white light illumination or application of such particles with only visible light excitation, which is not possible for pure CeO2. With help of the layer-by-layer (LbL) technique for nanoparticle immobilization, the electrode response can be adjusted and with a 5 layers electrode a low detection limit of about 3 μM H2O2 with a linear detection range up to 2000 μM is obtained.

RESULTS OF RESEARCHES OF DEHYDRATION OF SMALL DISPERSED ROCK MASS ON A VIBRATING DEVICE OF NEW DESIGN

Great difficulties arise when processing wet mineral raw materials less than 1 mm, and this problem is given large attention. There is an urgent need to dehydrate the final product of mining to a minimum percentage of moisture. Such raw material includes coal, which in the process of mining and processing forms a large number of small particles with a size of 1.0 ÷ 0.05 mm and, when enriched by froth flotation, is saturated with moisture, which complicates the subsequent use of coal. Also, for the processing of man-made deposits, consisting of ash and slag waste, they must be dewatered for subsequent complex processing, which consists in the use of magnetic separation and fine screening. Mechanical dewatering devices do not always provide the final moisture content required by the market today. Only free and loosely bound moisture is extracted by mechanical methods, and pore and capillary moisture is not removed. Therefore, various sources of heat are used as an auxiliary process for the dehydration of minerals. The article presents the results of studies of dehydration of finely dispersed rock mass on a vibration device of a new design. Intensification of the dewatering process is achieved due to the vertical conical screw and the creation of a vibroboiling layer. Preliminary studies have shown the effectiveness of the use of a transport-drying device, while it was possible to reduce the humidity in the finished product from 15% to 5%. According to the results of the experiments, it was found that during the operation of the transport-drying device, the layer thickness decreases from loading to unloading by 3 times, while the path of movement of the material along the working surface increases 2.5 times, the frequency range of vibration excitation from 1000-1200 rpm, the amplitude fluctuations are 4-5 mm and the temperature of the supplied air is 50-80 Сº. Thus, the proposed dewatering device can be used in the mining industry, since, in addition to transportation, it is also capable of dewatering wet material with sufficient efficiency.

Optoelectronic dynamic memristor systems based on two-dimensional crystals

Abstract Optical modulation of resistive switching in an optoelectronic memristor allows it to be optically controlled at ultra-high speed and ultra-low power consumption. Optical memristive systems with memory elements switched by electromagnetic radiation can be used in optically reconfigurable and tunable neural networks for neuromorphic computing and brain-inspired artificial intelligence systems. Two-dimensional (2D) crystals with unique electrical and optical properties demonstrate tremendous potential in the creation of highly efficient information and sensor systems for real-time data monitoring and processing. In this paper, we consider optoelectronic structures based on graphene, graphene oxide, and molybdenum disulfide for dynamic memristive signal processing. 2D optoelectronic memristor structures exhibit multiple states, which can be monitored in a wide range of optical excitations and used as sensors for pattern recognition and image processing. An optoelectronic dynamic memristive structure with quantum dots (QDs), controlled by ultrafast photoinduced structural phase transitions, is promising for creating information systems with stochastic data processing. The phase transition, controlled by charge and temperature, results in tunable periodic oscillations due to two state variables that exhibit chaotic behavior similar to that which occurs in a biological neuron network.

Nonlinear modeling and vibration mitigation of combined vortex-induced and base vibrations through energy harvesting absorbers

This study derives a nonlinear reduced-order model in order to evaluate the efficacy of an energy harvesting absorber at controlling base excitations, vortex-induced vibrations, and simultaneous base excitations and vortex-induced vibrations. Vibration absorbers are secondary systems that couple with a primary structure to dissipate the mechanical energy of vibrations. An energy harvesting absorber turns a portion of that dissipated energy into useful electrical energy which can be used to power small systems. The effects of various design parameters of the energy harvesting absorber on the behavior of the system is examined under different excitations. Next, an investigation of increasing the stiffness of the absorber is carried out with a goal of increasing the range in which meaningful energy can be harvested. Designs for the energy harvesting absorber are compared for their control of the system and their energy output when the system is subjected to concurrent base excitations and vortex-induced vibrations. Using an energy harvesting absorber tuned for vortex-induced vibrations provides the greatest reduction in amplitude and the most even power output over the range of wind speeds and base excitations.

Dispersion of the nonlinear susceptibility of MoS2 and WS2 from second-harmonic scattering spectroscopy

Dispersion of the absolute second-order susceptibility of both $\mathrm{Mo}{\mathrm{S}}_{2}$ and $\mathrm{W}{\mathrm{S}}_{2}$ is assessed on a wide spectral excitation range (710--1300 nm) by using second-harmonic scattering spectroscopy (SHS). SHS is an accurate ensemble measurement here applied on well-dispersed suspensions of monodisperse liquid-exfoliated nanosheets showing a high monolayer content. The as-derived, high susceptibility values shed light on the discrepancies between available literature values while evidencing resonances associated with the main excitonic transitions.

Nanoscale-Confined Terahertz Polaritons in a van der Waals Crystal.

Electromagnetic field confinement is crucial for nanophotonic technologies, since it allows for enhancing light-matter interactions, thus enabling light manipulation in deep sub-wavelength scales. In the terahertz (THz) spectral range, radiation confinement is conventionally achieved with specially designed metallic structures-such as antennas or nanoslits-with large footprints due to the rather long wavelengths of THz radiation. In this context, phonon polaritons-light coupled to lattice vibrations-in van der Waals (vdW) crystals have emerged as a promising solution for controlling light beyond the diffraction limit, as they feature extreme field confinements and low optical losses. However, experimental demonstration of nanoscale-confined phonon polaritons at THz frequencies has so far remained elusive. Here, it is provided by employing scattering-type scanning near-field optical microscopy combined with a free-electron laser to reveal a range of low-loss polaritonic excitations at frequencies from 8 to 12 THz in the vdW semiconductor α-MoO3 . In this study, THz polaritons are visualized with: i) in-plane hyperbolic dispersion, ii) extreme nanoscale field confinement (below λo ⁄75), and iii) long polariton lifetimes, with a lower limit of >2ps.

A study of photophoretic trapping exploiting motional resonances of trapped particles induced by wideband excitation

Photophoretic forces confine particles by a combination of levitation and active trapping. To generate the latter, the component of photophoretic force transverse to gravity generates a torque, which leads to complex rotation of the particle, thereby generating a restoring force. This force has not been understood quantitatively. In this paper, we study this component of photophoretic force by trapping a single absorbing particle using a loosely focused Gaussian laser beam and modulating the trap-center spatially using a superposition of multiple sinusoidal frequencies applied to the trapping beam. We vary the modulation amplitude in proportion to the excitation frequency so as to compensate for the reduced particle response at higher frequencies and thus obtain an almost constant response of the particle over the entire excitation range. We use the amplitude and phase response to determine the resonance frequency and the trap stiffness—which we study as a function of laser power and the intensity experienced by trapped particles of different sizes. We observe that, while the trapping stiffness is proportional to laser power, the optical intensity experienced by a particle at different powers is the same. This is reasonable in order to facilitate optical levitation but implies that the trap stiffness actually depends on an “effective intensity,” which may be a combination of the particle accommodation coefficient and the laser power.

Quantum Dots: An Emerging Tool for Point-of-Care Testing.

Quantum dots (QDs) are semiconductor crystals in the nanodimension having unique optical and electronic properties that differ from bulk material due to quantum mechanics. The QDs have a narrow emission peak, size-dependent emission wavelength, and broad excitation range which can be utilized for diverse biomedical applications such as molecular imaging, biosensing, and diagnostic systems. This article reviews the current developments of biomedical applications of QDs with special reference to point-of-care testing.

Breaking the Brightness Barrier: Design and Characterization of a Selected-Ion Fluorescence Measurement Setup with High Optical Detection Efficiency.

A quadrupole ion trap (QIT) mass spectrometer has been modified and coupled with tunable laser excitation and highly sensitive fluorescence detection systems to perform fluorescence studies on mass-selected ions. Gaseous ions, generated using nanoelectrospray ionization (nano-ESI), are trapped in the QIT that allows optical access for laser irradiation. The emitted fluorescence is collected from a 5.0 mm diameter hole drilled into the ring electrode of the QIT and is directed toward the detection setup. Due to the small inner diameter (7.07 mm) of the ring electrode and a relatively large opening for fluorescence collection, a fluorescence collection efficiency of 2.3% is achieved. After some losses in transmission, around 1.8% of the emitted fluorescence reaches the detectors, more than any other similar instrument reported in the literature. This improved fluorescence collection translates to a much shorter measurement time for a fluorescence signal. Another key feature of this setup is the ability to perform a variety of fluorescence experiments on trapped ions including excitation and emission spectroscopy, lifetime measurement, and ion imaging. The capabilities of the instrument are demonstrated by measuring fluorescence spectra of dyes and biomolecules labeled with dyes in a range of different excitation and emission wavelengths, quantum yields, m/z, and different polarities. A fluorescence lifetime measurement and ion image of trapped rhodamine 6G cations are also shown. With a wide array of functionality and high fluorescence detection performance, this setup provides an opportunity to study biomolecular structures and photophysics of fluorophores in well-controlled environments.

Time-resolved luminescence and excitation spectroscopy of co-doped Gd3Ga3Al2O12 scintillating crystals

Cerium doped Gd3Ga3Al2O12 (GGAG) single crystals as well as GGAG:Ce single crystals co-doped by divalent (Mg2+, Ca2+) and tetravalent (Zr4+, Ti4+) ions have been studied by means of time-resolved luminescence as well as the excitation luminescence spectroscopy in vacuum ultraviolet (VUV) and soft X-ray (XUV) spectral range. Tunable laser excitation was applied for time-resolved experiments in order to obtain luminescence decay curves under excitations in Ce3+, Gd3+ and excitonic absorption bands. The influence of the co-dopant ions on the Ce3+ luminescence decay kinetics is elucidated. The fastest luminescence decay was observed for the Mg2+ co-doped crystals under any excitation below bandgap energy indicating the perturbation of the 5d states of Ce3+ by Mg2+ ions. Synchrotron radiation was utilized for the luminescence excitation in the energy range from 4.5 to 800 eV. Special attention was paid to the analysis of Ce3+ excitation spectra in VUV and XUV spectral range where multiplication of electronic excitation (MEE) processes occur. Our results demonstrated that GGAG:Ce single crystals co-doped by Mg2+ ions as well as the GGAG:Ce crystal annealed in vacuum reveal the most efficient excitation of Ce3+ emission in VUV-XUV excitation range. The role of intrinsic defects in MEE processes in the co-doped as well as in the annealed GGAG:Ce single crystals is discussed.

Nonlocal Stimulation of Three-Magnon Splitting in a Magnetic Vortex.

We present a combined numerical, theoretical, and experimental study on stimulated three-magnon splitting in a magnetic disk in the vortex state. Our micromagnetic simulations and Brillouin-light-scattering results confirm that three-magnon splitting can be triggered even below threshold by exciting one of the secondary modes by magnons propagating in a waveguide next to the disk. The experiments show that stimulation is possible over an extended range of excitation powers and a wide range of frequencies around the eigenfrequencies of the secondary modes. Rate-equation calculations predict an instantaneous response to stimulation and the possibility to prematurely trigger three-magnon splitting even above threshold in a sustainable manner. These predictions are confirmed experimentally using time-resolved Brillouin-light-scattering measurements and are in a good qualitative agreement with the theoretical results. We believe that the controllable mechanism of stimulated three-magnon splitting could provide a possibility to utilize magnon-based nonlinear networks as hardware for neuromorphic computing.

Estimation Method of Fluorescent Donaldson Matrices Based on Multispectral Imaging Data

This paper proposes a compact and reliable method to estimate the bispectral Donaldson matrices of fluorescent objects by using multispectral imaging data. We suppose that an image acquisition system allows multiple illuminant projections to the object surface and multiple response channels in the visible range. The Donaldson matrix is modeled as a twodimensional array with the excitation range (350, 700 nm) and the reflection and emission ranges (400, 700 nm). The observation model is described using the spectral sensitivities of a camera and the spectral functions of reflectance, emission, and excitation. The problem of estimating the spectral functions is formulated as a least squares problem to minimize the residual error of the observations and the roughness of the spectral functions. An iterative algorithm is developed to obtain the optimal estimates of the whole spectral functions. The performance of the proposed method is examined in simulation experiments using multispectral imaging data in detail.

Optical properties of Pb2MoO5 and Pb2WO5 single crystals as materials for practical applications

The low-gradient Czochralski method was used to obtain lanarkite type Pb2MoO5 and Pb2WO5 crystals. Photoluminescence properties under UV excitation were studied, such as temperature dependences of decay time and excitation and emission spectra. The Pb2MoO5 crystals demonstrate intensive emission spectra in green range under 350 nm excitation and yellow-red range under 325 nm excitation. Pb2WO5 crystals exhibit green-blue luminescence under 400 nm excitation and green-yellow luminescence under 340 nm excitation. Photoluminescence spectra for investigated crystals show a short wavelength shoulder in violet spectral region near 400−420 nm. These violet component of photoluminescence for lead crystals are attribute to the transitions triplet states 1T1,2 of MoO42− and WO42-groups, respectively. The band gap of Pb2MoO5 and Pb2WO5 crystals were estimated from UV absorption spectrum and are equal to about 3.45 eV. Correlated color temperatures and color purity for both crystals at different excitations were calculated and the conclusion was made about the possibility of using such crystals in warm-white light emitted diodes and other solid-state lighting applications. Color chromaticity coordinates are shown on CIE1931. Temperature dependence of decay time constant allowed us to calculate sensitivity for non-contact thermometry applications.

Nonexponential Photoluminescence Dynamics in an Inhomogeneous Ensemble of Excitons in WSe2 Monolayers

The spectral and spatiotemporal dynamics of photoluminescence in monolayers of transition metal dichalcogenide WSe2 obtained by mechanical exfoliation on a Si/SiO2 substrate is studied over a wide range of temperatures and excitation powers. It is shown that the dynamics is nonexponential and, for times t exceeding ∼50 ps after the excitation pulse, is described by a dependence of the form 1/(t + t0). Photoluminescence decay is accelerated with a decrease in the temperature and in the energy of emitting states. It is shown that the observed dynamics cannot be described by a bimolecular recombination process, such as exciton—exciton annihilation. A model that describes the nonexponential photoluminescence dynamics by taking into account the spread of radiative recombination times of localized exciton states in a random potential gives good agreement with experimental data.

Crack Protective Layered Architecture of Lead-Free Piezoelectric Energy Harvester in Bistable Configuration.

Kinetic piezoelectric energy harvesters are used to power up ultra-low power devices without batteries as an alternative and eco-friendly source of energy. This paper deals with a novel design of a lead-free multilayer energy harvester based on BaTiO3 ceramics. This material is very brittle and might be cracked in small amplitudes of oscillations. However, the main aim of our development is the design of a crack protective layered architecture that protects an energy harvesting device in very high amplitudes of oscillations. This architecture is described and optimized for chosen geometry and the resulted one degree of freedom coupled electromechanical model is derived. This model could be used in bistable configuration and the model is extended about the nonlinear stiffness produced by auxiliary magnets. The complex bistable vibration energy harvester is simulated to predict operation in a wide range of frequency excitation. It should demonstrate typical operation of designed beam and a stress intensity factor was calculated for layers. The whole system, without presence of cracks, was simulated with an excitation acceleration of amplitude up to 1g. The maximal obtained power was around 2 mW at the frequency around 40 Hz with a maximal tip displacement 7.5 mm. The maximal operating amplitude of this novel design was calculated around 10 mm which is 10-times higher than without protective layers.

Interlayer Polarization Explains Slow Charge Recombination in Two-Dimensional Halide Perovskites by Nonadiabatic Molecular Dynamics Simulation.

Two-dimensional (2D) perovskites for applications in photovoltaics and optoelectronics are attracting a great deal of research interest. The nonradiative electron-hole (e-h) recombination is the major efficiency loss channel. Herein, we report a study of the thickness dependence of the e-h recombination dynamics in diamine-based 2D perovskite via ab initio NAMD. For multilayer structures, due to the emergence of spontaneous interlayer electric polarization, which is induced by the collective and correlated reorientation of methylammonium molecules, the electron and hole at the band edges are localized in different inorganic layers, suppressing the e-h recombination. Furthermore, a broad range of phonon excitation also inspired rapid pure dephasing related to the microscopic origin for longer recombination times. The combination of the two effects leads to the observation of a prolonged carrier lifetime in multilayer 2D perovskites, which is essential to understanding the nonradiative e-h recombination mechanism in such materials.

Near-UV-excitable, green-emitting Tb3+-based complexes

Light emitting diodes (LEDs) have become a very important source for ultraviolet light (UV) in various technical areas, the near UV range (NUV in the following) being particularly attractive due to the availability of high power emitters at very competitive cost for the spectral range between 350 and 400 nm. While numerous Eu3+ complexes are known now that can efficiently be exploited in this excitation range, corresponding green Tb3+ emitter complexes are hard to find. Tb3+ salts of fenamic acid and derivatives thereof are shown to be interesting candidates for applications using NUV excitation: on additional co-coordination with e.g. 5,5′‑dimethyl‑2,2′‑bipyridine, excitation maxima at 380 nm, at the same time maintaining high efficiencies, can be accomplished. Such coordination compounds hold the promise of being useful as versatile marker molecules in a variety of ‘soft’ chemical environments.

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: CO Excitation and Atomic Carbon in Star-forming Galaxies at z = 1–3

Abstract We investigate the CO excitation and interstellar medium (ISM) conditions in a cold gas mass-selected sample of 22 star-forming galaxies at z = 0.46–3.60, observed as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). Combined with Very Large Array follow-up observations, we detect a total of 34 CO transitions with J = 1 up to 8 (and an additional 21 upper limits, up to J = 10) and 6 and transitions (and 12 upper limits). The CO(2–1) and CO(3–2)-selected galaxies, at and 2.5, respectively, exhibit a range in excitation in their mid-J = 4, 5 and high-J = 7, 8 lines, on average lower than ( -brighter) BzK-color- and submillimeter-selected galaxies at similar redshifts. The former implies that a warm ISM component is not necessarily prevalent in gas mass-selected galaxies at . We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at z < 2 and z ≥ 2, finding and , respectively. From the models, we infer that the galaxies at z ≥ 2 have intrinsically higher excitation than those at z < 2. This fits a picture in which the global excitation is driven by an increase in the star formation rate surface density of galaxies with redshift. We derive a neutral atomic carbon abundance of , comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities (≥104 cm−3), consistent with the low-J CO excitation. Our results imply a decrease in the cosmic molecular gas mass density at z ≥ 2 compared to previous ASPECS measurements.

Application of Piezoelectric Wafer Active Sensors for Elastic Guided Wave Excitation and Detection in Structural Health Monitoring Systems for Elongated Constructions

At present, technologies for continuous ultrasonic monitoring of the state of extended structures using elastic guided waves excited and measured by an array of piezoelectric wafer active sensors are being actively developed. Guided waves interact with inhomogeneities (defects) of any nature, revealing their presence by reflected and scattered waves arising due to diffraction, while a change in their characteristics indicates the degradation of the strength properties of the material during operation. Based on measurements taken on laboratory samples, we demonstrate the capabilities of piezoelectric wafer active sensors to generate probing signals of various types and vary their amplitude-frequency characteristics in a wide frequency range. Mathematical modeling of wave processes is carried out within the framework of an integral approach based on an explicit integral and asymptotic representation of excited waves through the Fourier symbol of the Green’s matrix of the waveguide structure under consideration. The experimental measurements confirm the applicability of the simplified model developed on this basis for the two-mode excitation range of fundamental Lamb waves.

Superior Properties and Biomedical Applications of Microorganism-Derived Fluorescent Quantum Dots.

Quantum dots (QDs) are fluorescent nanocrystals with superb photo-physical properties. Applications of QDs have been exponentially increased during the past decade. They can be employed in several disciplines, including biological, optical, biomedical, engineering, and energy applications. This review highlights the structural composition and distinctive features of QDs, such as resistance to photo-bleaching, wide range of excitations, and size-dependent light emission features. Physical and chemical preparation of QDs have prominent downsides, including high costs, regeneration of hazardous byproducts, and use of external noxious chemicals for capping and stabilization purposes. To eliminate the demerits of these methods, an emphasis on the latest progress of microbial synthesis of QDs by bacteria, yeast, and fungi is introduced. Some of the biomedical applications of QDs are overviewed as well, such as tumor and microRNA detection, drug delivery, photodynamic therapy, and microbial labeling. Challenges facing the microbial fabrication of QDs are discussed with the future prospects to fully maximize the yield of QDs by elucidating the key enzymes intermediating the nucleation and growth of QDs. Exploration of the distribution and mode of action of QDs is required to promote their biomedical applications.