Long-wave Excitation Research Articles

Excitation wavelength-dependent long-afterglow Sb, Mn-doped CsCdCl3 perovskite for anti-counterfeiting applications

Multi-color fluorescent anti-counterfeiting technology possesses a wide range of application prospects. However, there is still a challenge on the development of new single-component multi-color fluorescent materials related to the excitation wavelength. Herein, we report an efficient multi-peak luminescent material, Sb3+, Mn2+ co-doped CsCdCl3, which emission with a long afterglow is related to the excitation wavelength. There are two independent energy transfer channels of Mn2+ under short- and long-wave excitation. Under 357 nm excitation, dual-emission is observed at 506 and 590 nm attributed to the 3P1–1S0 and 4T1-6A1 transitions of [SbCl6]3- and Mn2+ ions, respectively. Under 254 nm excitation, the microcrystals have orange emission. Excitation wavelength-dependent and tunable dual-emission associated with the host self-captured excitons and [SbCl6]3- to Mn2+ energy transfer. The microcrystal's afterglow time at room temperature is 3500 s, which is attributed to the modulation of the trap for Mn2+. These results indicate that the material has potential applications in the field of multicolor fluorescent anti-counterfeiting.

Anti-stokes fluorescence of phycobilisome and its complex with the orange carotenoid protein

Phycobilisomes (PBSs) are giant water-soluble light-harvesting complexes of cyanobacteria and red algae, consisting of hundreds of phycobiliproteins precisely organized to deliver the energy of absorbed light to chlorophyll chromophores of the photosynthetic electron-transport chain. Quenching the excess of excitation energy is necessary for the photoprotection of photosynthetic apparatus. In cyanobacteria, quenching of PBS excitation is provided by the Orange Carotenoid Protein (OCP), which is activated under high light conditions. In this work, we describe parameters of anti-Stokes fluorescence of cyanobacterial PBSs in quenched and unquenched states. We compare the fluorescence readout from entire phycobilisomes and their fragments. The obtained results revealed the heterogeneity of conformations of chromophores in isolated phycobiliproteins, while such heterogeneity was not observed in the entire PBS. Under excitation by low-energy quanta, we did not detect a significant uphill energy transfer from the core to the peripheral rods of PBS, while the one from the terminal emitters to the bulk allophycocyanin chromophores is highly probable. We show that this direction of energy migration does not eliminate fluorescence quenching in the complex with OCP. Thus, long-wave excitation provides new insights into the pathways of energy conversion in the phycobilisome.

Evolution of instability modes and spreading characteristics of a planar jet flow under long-wave excitations

Switching phenomenon and parametric resonance have been identified in near field flows subjected to high-frequency controlled perturbations. This study reports the correlation between switching phenomenon, parametric resonance, and spreading characteristics caused by the instability modes after the end of the potential core of a planar jet (far field). Two periodically oscillating strips were used to control perturbations in free shear layers and three different long-wave excitations (i.e., symmetric, antisymmetric, and one-sided) were imposed at the excitation frequency (fe). The excitation frequency was fixed relative to the preferred mode frequency (fp) at fe = fp/4. To investigate the evolution of coherent structures, frequency spectral analysis and phase correlation were applied to hot-wire anemometer measurements. Under symmetric excitation, the instability mode of vortical structures is observed twice at mode switching, retaining the in-phase pattern. Jet puffing occurs when the cross correlation R12(0) is positive at the far field. These features cause vortex shedding to remain symmetric and suppresses the flapping motion of the jet. However, out-of-phase behavior reoccurs under antisymmetric and one-sided excitations and the cross correlation R12(0) becomes a negative after the end of the potential core. As a result, flapping motion is enhanced and the jet spreads wider after the end of the potential core.

Laboratory experiments on the influence of stratification and a bottom sill on seiche damping

Abstract. The damping of water surface standing waves (seiche modes) and the associated excitation of baroclinic internal waves are studied experimentally in a quasi-two-layer laboratory setting with a topographic obstacle at the bottom representing a seabed sill. We find that topography-induced baroclinic wave drag contributes markedly to seiche damping in such systems. Two major pathways of barotropic–baroclinic energy conversions were observed: the stronger one – involving short-wavelength internal modes of large amplitudes – may occur when the node of the surface seiche is situated above the close vicinity of the sill. The weaker, less significant other pathway is the excitation of long waves or internal seiches along the pycnocline that may resonate with the low-frequency components of the decaying surface forcing.

Ultrafast dynamics and mechanisms of non-stationary absorption in thin gallium selenide samples

Herein, the dynamics and mechanisms of induced absorption in thin samples of gallium selenide under various excitation conditions are studied using femtosecond kinetic spectroscopy. We have registered several types of induced changes including induced absorption on free charge carriers (“hot” and thermalized electrons), bleaching and absorption due to the population of near-edge trap or exciton states, as well as rapid changes in the absorption of probing radiation in the region of the overlap of the exciting and probing pulses due to two-quantum two-frequency interband transitions. The time ranges of the relaxation processes are estimated. It is shown that when using relatively low-intensity long-wave excitation (790 nm), the resonant excitation of the near-edge states occurs mainly due to two-quantum two-frequency transitions followed by the formation of the dynamic equilibrium between bound and free electrons in the time range up to 5 ps. When electrons are excited deeply into the conduction band with the formation of hot free electrons and their subsequent thermalization to the bottom of the conduction band in the time range up to 1 ps, the population of the near-edge states and the establishment of the dynamic equilibrium between bound and free electrons is realized in the same time range (5 ps) as when they are excited “from below”.

Influence of long-wave deviations on the quasi-static and dynamic excitation behavior at higher speeds

The scarcity of fossil fuels and increasing oil prices are among the factors that have led to a rising ownership of electric cars [1]. Noise reduction also plays a major role primarily in the drive train of motor vehicles. Noise and vibration excitation differ between a combustion engine and an electric motor. While the disturbing noises of auxiliaries, e.g. gear noise, have been largely masked by combustion engines, theses noises are no longer masked due to the use of electric motors [2]. Therefore, gear noise is perceived more pronounced. Considering the subjective perception and the excitation by rotational frequencies, that fall into the sensitive hearing range of high-speed gearboxes, the focus must be increasingly placed on manufacturing and assembly related long-wave deviations, such as wobble, pitch errors and eccentricities.This report investigates the effects of long-wave deviations of gears in gearboxes on the excitation and noise behavior. Quasi-static investigations were carried out to verify the influences of long-wave deviations on the long-wave excitation behavior. Therefore, the transmission error was measured, which describes the rotational fluctuation between input and output and represents the excitation.This investigation verifies according to the simulativ investigation by Brecher et al. that there is no transmission error dependency on the load [3]. In addition, this investigation proves the macro geometry-independent long-wave excitation in case of eccentricity. The reason for the invariant excitation behavior lies in the effective deviation in the gear mesh which in this case is independent of the mentioned parameters.In addition to the quasi-static tests, investigations of the structure-borne noise were carried out at higher speeds (input rotational speed up to nIn = 11,500 rpm). For these investigations, a two-stage gearbox with a test gear set was used and two different eccentricities and wobbles were manufactured. The analysis of these investigations confirm an increased excitation as a result of the deviations. Especially in natural frequency ranges, the excitation in the first rotational order is amplified by the considered long-wave deviations.The experimental results prove the importance of a function-oriented tolerance system for long-wave deviations, which lead to corresponding long-wave excitations. Furthermore, the findings constitute the first basis for the derivation of these tolerance limits.

Research on Dynamic of Urban Rail Vehicle of Variable Speed and Long-wave Excitation Conditions

Research on Dynamic of Urban Rail Vehicle of Variable Speed and Long-wave Excitation Conditions

Oxygen Vacancy Effect on Photoluminescence Properties of Self-Activated Yttrium Tungstate

A series of single-phase yttrium tungstate powders were synthesized through solid-state reaction under air or argon atmosphere. All powders showed broad band emission in the visible light region, and the argon-calcined samples presented strong near-infrared luminescence. Moreover, the long-wave excitation bands peaking at 340, 378, 380, 490, and 523 nm depended critically on the calcination atmosphere and temperature. The emergence of these new excitation bands was ascribed to different oxygen vacancy concentrations with the analysis of the first-principle calculation, Raman and X-ray absorption fine structure spectra. The oxygen vacancies caused the reduction of the average coordination number of tungsten, and the position of the localized energy band changed with the oxygen vacancy concentration. Finally, a schematic photoluminescence excitation model was proposed via anion and cation charge transfer. The obtained results promise to be very useful in interpreting self-activated tungstate luminescence mechanism. They can also serve as guide line for tuning the luminescence performance of yttrium tungstate and related materials.

Observations of fluorescent and biological aerosol at a high-altitude site in central France

Abstract. Total bacteria, fungal spore and yeast counts were compared with ultraviolet-light-induced fluorescence (UV-LIF) measurements of ambient aerosol at the summit of the Puy de Dôme (PdD) mountain in central France (1465 m a.s.l), which represents a background elevated site. Bacteria, fungal spores and yeast were enumerated by epifluorescence microscopy (EFM) and found to number 2.2 to 23 L−1 and 0.8 to 2 L−1, respectively. Bacteria counts on two successive nights were an order of magnitude larger than in the intervening day. A wide issue bioaerosol spectrometer, version 3 (WIBS-3) was used to perform UV-LIF measurements on ambient aerosol sized 0.8 to 20 μm. Mean total number concentration was 270 L−1 (σ = 66 L−1), found predominantly in a size mode at 2 μm for most of the campaign. Total concentration (fluorescent + non-fluorescent aerosol) peaked at 500 L−1 with a size mode at 1 μm because of a change in air mass origin lasting around 48 h. The WIBS-3 features two excitation and fluorescence detection wavelengths corresponding to different biological molecules, although non-biological interferents also contribute. The mean fluorescent particle concentration after short-wave (280 nm; associated with tryptophan) excitation was 12 L−1 (σ = 6 L−1), and did not vary much throughout the campaign. In contrast, the mean concentration of particles fluorescent after long-wave (370 nm; associated with NADH) excitation was 95 L−1 (σ = 25 L−1), and a nightly rise and subsequent fall of up to 100 L−1 formed a strong diurnal cycle in the latter. The two fluorescent populations exhibited size modes at 3 μm and 2 to 3 μm, respectively. A hierarchical agglomerative cluster analysis algorithm was applied to the data and used to extract different particle factors. A cluster concentration time series representative of bacteria was identified. This was found to exhibit a diurnal cycle with a maximum peak appearing during the day. Analysis of organic mass spectra recorded using an aerosol mass spectrometer (AMS; Aerodyne Inc.) suggests that aerosol reaching the site at night was more aged than that during the day, indicative of sampling the residual layer at night. Supplementary meteorological data and previous work also show that PdD lies in the residual layer/free troposphere at night, and this is thought to cause the observed diurnal cycles in organic-type and fluorescent aerosol particles. Based on the observed disparity between bacteria and fluorescent particle concentrations, fluorescent non-PBA is likely to be important in the WIBS-3 data and the surprisingly high fluorescent concentration in the residual layer/free troposphere raises questions about a ubiquitous background in continental air during the summer.

Plasmonic Enhancement of Molecular Fluorescence near Silver Nanoparticles: Theory, Modeling, and Experiment

Metal-enhanced fluorescence of molecular probes in plasmonic nanostructures offers highly sensitive chemical and biomedical analyses, but a comprehensive theory of the phenomenon is far from being complete. In this study, a systematic theoretical analysis is provided for overall luminescence enhancement/quenching for fluorophores near silver spherical nanoparticles. The approach accounts for local intensity enhancement, radiative and nonradiative rates modification, light polarization, molecule position, and its dipole moment orientation. Numerical modeling has been performed for fluorescein-based labels (e.g., Alexa Fluor 488) widely used in biomedical studies and development. The maximal enhancement exceeding 50 times is predicted for nanoparticle diameter 50 nm, the optimal excitation wavelength being 370 nm. For long-wave excitation, bigger particles are more efficient. The experiments with a fluorescein isothiocyanate conjugate of bovine serum albumin confirmed theoretical predictions. The results pr...

Luminescence excitation spectra of TbX 3 (X = Cl −, Br −, I −)

A systematic study of the excitation spectrum of TbX 3 (X = Cl −, Br −, I −) is presented in this work. In general, the excitation spectra of TbX 3 can be divided into three major regions: (1) the short-wave host lattice absorption region, (2) the intermediate absorption region where the Tb 3+ 4f 8 → 4f 75d 1 interconfigurational excitation transition are located, and (3) the long-wave excitation region where the Tb 3+ 4f 8 → 4f 8 intraconfigurational excitation transition are located. The high spin and the low spin components of the Tb 3+ interconfigurational excitation transition are clearly identified in the case of TbCl 3. The luminescence of TbX 3 (X = Cl −, Br −, I −) is dominated by emission transitions emanating from the Tb 3+ 5D 4 state. A comparative study of the optical properties of TbX 3 (X = Cl −, Br −, I −) with the properties of the Tb 3+ ion in several halide host lattices is presented. Further, a comparative study of the fundamental host lattice optical transitions in terbium halides and other halide materials is also presented.

Short-wave excitations in non-local Gross-Pitaevskii model

Abstract We show that a non-local form of the Gross-Pitaevskii equation describes not only long-wave excitations, but also the short-wave ones in Bose-condensate systems. At certain parameter values, the excitation spectrum mimics the Landau spectrum of quasi-particle excitations in superfluid helium with roton minimum. The excitation wavelength, at which the roton minimum exists, is close to the inter-particle interaction range. We determine how the roton gap and the effective roton mass depend on the interaction potential parameters, and show that the existence domain of the spectrum with a roton minimum is reduced if one accounts for an inter-particle attraction.

Vortical structure evolutions and spreading characteristics of a plane jet flow under anti-symmetric long-wave excitation

The vortical evolutions and spreading characteristics of a low-speed plane jet under anti-symmetric long-wave excitations are investigated experimentally. The perturbation is introduced with two oscillating strips located at the nozzle exit. The experiments were operated at Reynolds number of 8.2 × 10 3 based on the nozzle exit height. Mixing and spreading properties are influenced obviously by long-wave excitation after the end of potential core. The increments of half-width, momentum thickness, and volume flow rate depend on the excitation frequency. The results of flow visualization also reveal the dependence of excitation frequency. The power spectra of fluctuating velocities shows that the evolution of coherent structure is significantly influenced by the long-wave excitation in the downstream, but it is similar to the natural jet in the near field. The long-wave excitation at certain frequencies can promote large-scaled anti-symmetric vortical structures in the far field.

Luminescence of Molecules with Internal Charge Transfer upon Longwave Excitation

We have studied the spectral properties of luminescence of laurdan molecules in glycerin upon excitation at the red edge of the absorption band at different temperatures. The most significant red-wave shift of the spectra (∼10 nm) for the longwave band of dual fluorescence is observed depending on the excitation wavelength at a low temperature of 260 K when a solvent forms a fairly rigid matrix. At the same time, at increased temperatures of up to 370 K a small bathochromic shift and a change in the shape of the luminescence bands are also recorded reliably. Changes in the excitation spectra were observed when luminescence was recorded in the bands of the LE- and CT states. The difference spectrum responsible for the additional absorption that does not make a contribution to the longwave luminescence component has been isolated. The decay kinetics of both luminescence components have been measured and their expansions in decay constants have been analyzed. The experimental dependences obtained point to the complex mechanism of inhomogeneous broadening of spectra.

Diluted quasi-one-dimensional classical antiferromagnets.

We consider the effect of the exchange disordering, mainly the nonmagnetic dilution, on the low-temperature properties of the quasi-one-dimensional classical antiferromagnets. Dynamic susceptibility expansion in defect concentration shows that even a low level of doping substantially changes the spin-wave stiffness and the transverse susceptibility. We investigate the nonperturbative concentration dependencies of the spin-wave velocities and susceptibility arising when the impurity concentration exceeds the small characteristic value ${\mathit{x}}_{0}$= \ensuremath{\surd}${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$/${\mathit{J}}_{\mathrm{\ensuremath{\parallel}}}$ . A general result, pertinent to the true three-dimensional antiferromagnets as well, concerns the excitation spectrum of the disordered nonfrustrated antiferromagnets with nonfluctuating anisotropy. In this case the hydrodynamical description of long-wave excitations breaks down, and the spin waves with energies near the anisotropy gap are overdamped.

New highly fluorescent ketocyanine polarity probes

The syntheses and spectral properties of three new and highly fluorescent solvent polarity probes are described. They are found to be extremely sensitive to solvent polarity in that spectral red shifts in both absorption and fluorescence spectra occur upon increasing solvent polarity. Excitation and emission data of the dyes in a set of different polar solvents are given. The emission data are compared with the standard ET N values of solvent polarity and a linear correlation is obtained over a wide range. The origin of the unusual solvatochromic properties is discussed in terms of the resonance structures of this new group of molecular probes. Their outstanding features include high spectral sensitivity to polarity, high molar absorptivities, high fluorescence quantum yields, longwave excitation and emission, insignificant quenching by oxygen, and a sufficient stability in aqueous solution. Therefore, the new probes are considered to be advantageous over other polarity probes used so far in probing biochemical and biological systems.

Plasmon excitations in Josephson arrays and thin superconducting layers.

Long-wave excitations in Josephson arrays are investigated. The existence of excitations with square root or acoustic dispersion law, like plasmons in two-dimensional electron gas, is predicted. Observation of such excitations with frequency much lower than the frequency of the superconducting gap \ensuremath{\Delta}/\ensuremath{\Elzxh} is possible by use of a grating and the same far infrared or microwave techniques used for detection of the plasmons in semiconductor microstructures.

A Lagrangian model for wave-induced harbour oscillations

A set of equations in the Lagrangian description are derived for the propagation of long gravity waves in two horizontal directions for the purpose of determining the response of harbours with sloping boundaries to long waves. The equations include terms to account for weakly nonlinear and dispersive processes. A finite element formulation for these equations is developed which treats the propagation of transient waves in regions of arbitrary shape with vertical or sloping boundaries. Open boundaries are treated by specifying the wave elevation along the boundary or by applying a radiation boundary condition to absorb the waves leaving the computational domain. Nonlinear aspects of the interaction of long gravity waves with sloping boundaries and frequency dispersion due to non-hydrostatic effects are investigated. Results from the model are then compared with laboratory experiments of the response to long-wave excitation of a narrow rectangular harbour with a depth that decreases linearly from the entrance to the shore line.

Fluorometric continuous kinetic assay of α-chymotrypsin using new protease substrates possessing long-wave excitation and emission maxima

A direct and continuous kinetic method for the fluorometric determination of α-chymotrypsin and trypsin is described, and 2-aminoacridone (2-AA) is introduced as a promising new fluorophore in analytical biochemistry. N-Succinyl- and N-glutaryl-phenylalanine as well as N-benzoylarginine were coupled to 2-AA via a peptide bond and the resulting fluorogenic substrates are shown to be cleaved by the two enzymes. Since the substrate and product of hydrolysis have quite different spectral properties, the increase in the long-wave fluorescence of 2-AA (measured at 570 nm under 450-nm excitation) is a parameter for the enzyme activity. Chymotrypsin (0.5 μg/ml) and trypsin (0.1 μg/ml) were detectable in a 3-min assay. The major advantages of the new substrates over existing ones are the analytical wavelengths which are distinctly outside the background fluorescence of most biological matter and the somewhat faster reaction rates which can reduce the time of analysis.

Systems of particles with random mass

The kinetic and spectral properties of systems with random mass are considered. The conductivity sigma 0 of an electron gas with random effective mass is calculated in the coherent potential approximation. The authors show that the low-lying long-wave excitations of this system are described by the non-linear matrix sigma -model. The density of states of a two-dimensional electron gas with random mass in a perpendicular strong magnetic field is calculated.