Excitation Range Research Articles

The optical properties of In2S3 films in the far-infrared spectral range

Optical reflection spectra of In2S3 thin films (180 – 730 nm) deposited on glass substrates are measured by infrared spectroscopy using the synchrotron radiation of BESSY II storage ring in the spectral range of 30 – 8000 cm−1. The aim of the study is to find the influence of different substrate and post-annealing temperatures on the electron and phonon systems of In2S3 films deposited on glass. Clear features in the reflectance spectra for the studied films have been found mainly in the phonon excitation range 100 – 400 cm−1. The experimental dielectric functions ε(ω) of In2S3 films are found to be in good agreement with the calculated ones obtained for In2S3 crystals within the density functional theory. The dielectric functions ε(ω) of the films in the range of 100 – 400 cm−1 depend substantially on the post-annealing temperature. This indicates a transition of the film from the amorphous to the crystalline state. The thorough analysis of the frequency dependence of the reflection coefficient R(ω) and optical conductivity σ(ω) in the wavenumber range of 30 – 130 cm−1 allowed us to reveal the distributed electron states in In2S3 films.

Optical and thermal properties of rare earth-doped K4 Ca(PO4 )2 phosphor.

The luminescent properties and energy transfer (ET) mechanism in the Ln3+ pair of the RE3+ (RE = Eu3+ , Ce3+ , Dy3+ and Sm3+ ) doped K4 Ca(PO4 )2 phosphor were successfully investigated using a conventional high-temperature solid-state reaction. In the near infrared (NIR) range, Ce3+ -doped K4 Ca(PO4 )2 phosphor exhibited a UV-Vis. emission band, whereas K4 Ca(PO4 )2 :Dy3+ exhibited characteristic emission bands centred at 481 and 576 nm in the near-ultraviolet excitation range. The possibility of ET from Ce3+ to Dy3+ in K4 Ca(PO4 )2 phosphor was confirmed by a significant increase in the photoluminescence intensity of the Dy3+ ion based on the spectral overlap of acceptor and donor ions. X-ray diffraction, Fourier-transform infrared and thermogravimetric analysis/differential thermal analysis TGA/DTA were carried out to study phase purity, presence of functional groups and amount of weight loss under different temperature regimes. Therefore, the RE3+ -doped K4 Ca(PO4 )2 phosphor may be a stable phosphor host for light-emitting diode applications.

A Time Frequency Domain Based Approach for Ball Grid Array Solder Joint Fatigue Analysis Using Global Local Modeling Technique

AbstractThe fatigue life prediction of the electronic packages under dynamic loading conditions is an increasingly important area of research, with direct application in packaging industries. Current life prediction methodologies are, in general, developed through a finite element (FE) model that is correlated using an experimental data measured through sweep sine testing. The frequency response function (FRF) generated by using a sweep sine testing may suffer from leakage and windowing of the signal may not work correctly, which results in the shift in the amplitude and the resonance frequencies of the package. In consequence, there will be a significant deviation between the actual and the predicted natural frequencies and the amplitude of vibration response in the given excitation range, resulting in the longer time to fail the package during the laboratory based/virtual durability testing. Thus, it is necessary to develop a suitable validation technique in time/frequency domain to address this issue. In this paper, the step sine testing procedure is utilized to validate the FE model of a test vehicle consisting of a board level ball grid array chip package and the resonance-based fatigue testing is performed in the FE-based simulation. The global–local modeling approach is utilized to model the test vehicle and the volume average von Mises stress is used to predict the life of the solder joint. Following the numerical simulations, fatigue test is carried out in the test vehicle at the first resonance frequency obtained from the step sine test. Experimental results show that there are full openings of the corner balls in a very short interval of time. The results of the life prediction from the FE model and from experiments are comparable to each other thus validating the proposed methodology.

Effects of initial three-dimensional electron energy distribution on terahertz Bloch oscillations in a biased semiconductor superlattice

We investigate how the initial three-dimensional energy distribution of electrons created by femtosecond pump pulses in a biased semiconductor superlattice affects terahertz Bloch oscillations, which imitate a step response to a bias electric field. The emitted terahertz waveforms are well reproduced from a damped oscillation current with capacitive nature, exhibiting shorter relaxation times and worse temporal resolutions for central pump photon energies that are outside the range of ordinary electron excitation into the conduction first miniband. This indicates that in-plane excess energy changes the relaxation time via scattering processes, while partial use of the pump pulse spectrum reduces the temporal resolution.

The flow around a forced cylinder between two parallel walls

The vortex induced vibrations of a cylinder tightly confined in a narrow channel were numerically studied in two dimensions. Attached to a linear spring and subject to hydrodynamic forces and torques, the circular cylinder is free to move in both the cross-flow and in-line directions as well as to rotate about its axis. Low mass ratios and moderate Reynolds numbers were considered. The cases where boundaries, either physical or numerical, are far from the cylinder have deserved much attention, and share some of the phenomenology observed in the system here studied. As the upstream flow is increased, the tightly confined system shows an initial branch, followed by a synchronization or lock-in region that ends in a decoherence region. Nevertheless, within the lock-in region, no clear upper and lower branches appear when the cylinder is placed in a narrow channel, instead the system's behavior sensibly depends on the mass ratio. We managed to find a modified Strouhal parameter that collapses the range of excitation for the reduced masses considered and suggests a scaling for the system's natural frequency in the medium. Results offer a portrait of the motion, forces, and flow around the cylinder under such constrains.

Making Eu2+- and Sm2+-Doped Borates Fit for Solar Energy Applications

Despite the development of many luminescent materials for various applications, only a few of these phosphors are applicable for solar energy generation applications. This study used the conventional solid-state reaction method to synthesize different strontium borate compounds codoped with divalent europium and samarium ions. The material was optimized by varying the experimental procedure, the molar ratio of the boron, and the molar ratios of both codopants. Strontium hexaborate doped with a relatively high europium concentration and a low samarium concentration (Sr0.89B6O10:Eu0.1, Sm0.01) gave the optimum optical properties. These properties included a broad excitation range from 220 to 600 nm containing contributions from divalent europium and samarium ions. The material exhibited strong and narrow emission in the region from 650 to 850 nm following radiative transitions within the divalent samarium ions. The internal luminescence quantum efficiency of the optimized material was 79% (λex = 508.5 nm). There was no spectral overlap between the excitation and emission spectra, thereby reducing the reabsorption probability. These marked characteristics make this phosphor material appropriate for use as a solar radiation converter or for use in luminescent solar concentrators.

Driving a Third Generation Molecular Motor with Electrons Across a Surface.

Excitation of single molecules with electrons tunneling between a sharp metallic tip of a scanning tunneling microscope and a metal surface is one way to study and control dynamics of molecules on surfaces. Electron tunneling induced dynamics may lead to hopping, rotation, molecular switching, or chemical reactions. Molecular motors that convert rotation of subgroups into lateral movement on a surface can in principle also be driven by tunneling electrons. For such surface-bound motor molecules the efficiency of motor action with respect to electron dose is still not known. Here, the response of a molecular motor containing two rotor units in the form of overcrowded alkene groups to inelastic electron tunneling has been examined on a Cu(111) surface in ultrahigh vacuum at 5 K. Upon vibrational excitation, switching between different molecular conformations is observed, including conversion of enantiomeric states of chiral conformations. Tunneling at energies in the range of electronic excitations causes activation of motor action and movement across the surface. The expected unidirectional rotation of the two rotor units causes forward movements but with a low degree of translational directionality.

Composite pulses for optimal robust control in two-level systems

In this work, we put forward an approach of constructing the optimal composite pulse sequence for robust population transfer in two-level systems. This approach is quite universal and applicable to a variety of systems, because the modulation parameters of composite pulses are obtained by minimizing the homemade cost function rather than nullifying the error coefficients of the transition probability. Specifically, we design different forms of the cost function for implementing optimal robustness with respect to the single or multiple errors. When slightly adjusting the constraints of the cost function, this approach can be easily extended to achieve arbitrary population transfer. The numerical results demonstrate that the optimized sequences are immune from various systematic errors, allowing us to produce a broadening excitation range of the transition probability. Therefore, this work offers an optimal robust design for controlling quantum states in error-prone environments.

UV/blue/green converted efficient red-NIR photoluminescence in Cr incorporated MgAl2O4 nanocrystals: Site selective emission tailored through cation inversion and intrinsic defects

The UV/visible activated near-infrared (NIR) phosphors have many applications in solid state lighting, night vision devices and bio-imaging. The early research reported the red-NIR emitting phosphors doped with Cr3+ centers upon visible light excitation. Here, in this work the intense red-NIR emission and color tuning is achieved for broad excitation range (UV/blue/green) through Cr dopant induced defect centers and cation inversion in MgCr Al2O4 ( = 0.5, 1, 3, 5 and 10 mol%) nanocrystals. The Cr3+ doped MgAl2O4 nanocrystals were synthesized by combustion method through stoichiometric substitution of Mg by Cr, while most of the Cr3+ ions occupied the octahedral sites of spinel host with the formation of antisite defects, Cr3+ clusters, magnesium and oxygen vacancies. These defect centers were probed through Rietveld refinement, photoluminescence (PL), x-ray photoelectron and nuclear magnetic resonance spectra analyses. At UV excitation, the intrinsic defects played an interesting role in exhibiting the blue-violet emission attributed to host lattice defects and red-NIR emission attributed to strong/weak ligand field octahedral Cr3+ sites, via charge transfer to Cr3+ ions. The PL spectra evinced the enhanced red-NIR emission intensity upon 266 nm excitation than upon blue and green light excitation. Further, the weak ligand field site emission is found to be dominating with increase in doping concentration. Thus, Cr doped MgAl2O4 nanocrystals showed their potency of exhibiting the intense red-NIR emission and color tuning (from red purple to bluish purple and then to red color) upon UV/blue/green excitation.

Double Impact-Based Piezoelectric Energy Harvester for Low-Frequency Operation

This article presents a theoretical, numerical, and experimental study of a frequency upconverting (FUC) piezoelectric vibration energy harvester with a single low-frequency resonator that impacts twice per oscillation cycle on a single high-frequency unimorph generator. The model’s relevant physical aspects are specially designed to enhance the electrical output power over a wide-frequency range in the low-frequency excitation. The proposed double impact strategy allows obtaining a nearly constant output voltage, in contrast to typical upconverting mechanisms whose output voltage decays quickly in time. The device is safe from fatigue and can be used in high acceleration scenarios because the large displacements are limited by the generating beam, which acts as a natural stopper in an upward and downward directions. The prototype is designed to obtain a low value of optimal resistance with enhanced broadband performance below 25 Hz. The double impact FUC energy harvester’s performance is improved by adjusting the gap distance, the thickness of the generating beam, and the tip mass of the driving beam. The harvester reports 1428- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> peak output power at 20 Hz and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400 ~\mu \text{W}$ </tex-math></inline-formula> of average power for a usable bandwidth from 17.5 to 22 Hz in health monitoring systems.

Building in biologically appropriate multifunctionality in aqueous copper indium selenide-based quantum dots.

Advanced nanoplatforms equipped with different functional moieties for theranostics hold appealing promise for reshaping precision medicine. The reliable construction of an individual nanomaterial with intrinsic near-infrared (NIR) photofunction and magnetic domains is much desired but largely unexplored in a direct aqueous synthesis system. Herein, we develop an aqueous phase synthetic strategy for Mn2+ doping of ZnS shell grown on Zn-Cu-In-Se core quantum dots (ZCISe@ZnS:Mn QDs), providing the optimal NIR fluorescence quantum efficiency of up to 18.9% and meanwhile efficiently introducing paramagnetic domains. The relaxometric properties of the water-soluble Mn-doped QDs make them desirable for both the longitudinal and transverse (T1 and T2) magnetic resonance (MR) contrast enhancement due to the shell lattice-doped Mn2+ ions with slow tumbling rates and favoured spin-proton dipolar interactions with surrounding water molecules. Surprisingly, the incorporation of Mn2+ ions into the shell is found to significantly enhance the production of reactive oxygen species (ROS) by combining both the chemodynamic and photodynamic processes upon NIR light irradiation, showing great potential for efficient photo-assisted ablation of cancer cells. Furthermore, a broad-spectrum excitation range beneficial for bright NIR fluorescence imaging of breast cancer has been proven and offers high flexibility in the choice of incident light sources. Multiparametric MR imaging of the brain has also been successfully demonstrated in vivo.

Synthesis, structure, and photoelectric properties of a novel zero-dimensional organic-inorganic hybrid perovskite (C6H9N2)2MnI4

Organic metal halides (OMHs) have attracted considerable attention in the field of materials science because of their low cost, easy structure adjustment, and excellent optoelectronic properties. In this study, we synthesized a new organic manganese halide single-crystal, viz. (C6H9N2)2MnI4. The single crystal belongs to the triclinic crystal system with a centrosymmetric P-1 space group. The optical bandgap (2.21 eV) of yellow (C6H9N2)2MnI4 is close to the narrow bandgap and has a wide excitation range, with an optimal excitation wavelength of 468 nm. Among reported tetrahedrally coordinated manganese-based OMHs luminescent materials, yellow-green fluorescence emission is rare. (C6H9N2)2MnI4 also has a high fluorescence quantum efficiency of 67% and a fluorescence lifetime of 44 μs, and can be used to fabricate a light-emitting diode (LED) device with a luminous efficiency of 9.61 lm/W, thus expanding the applications of organic manganese halide materials.

Tuning of motor outputs produced by spinal stimulation during voluntary control of torque directions in monkeys.

Spinal stimulation is a promising method to restore motor function after impairment of descending pathways. While paresis, a weakness of voluntary movements driven by surviving descending pathways, can benefit from spinal stimulation, the effects of descending commands on motor outputs produced by spinal stimulation are unclear. Here, we show that descending commands amplify and shape the stimulus-induced muscle responses and torque outputs. During the wrist torque tracking task, spinal stimulation, at a current intensity in the range of balanced excitation and inhibition, over the cervical enlargement facilitated and/or suppressed activities of forelimb muscles. Magnitudes of these effects were dependent on directions of voluntarily produced torque and positively correlated with levels of voluntary muscle activity. Furthermore, the directions of evoked wrist torque corresponded to the directions of voluntarily produced torque. These results suggest that spinal stimulation is beneficial in cases of partial lesion of descending pathways by compensating for reduced descending commands through activation of excitatory and inhibitory synaptic connections to motoneurons.

Effects of low-dose radiation on human blood components after in vitro exposure to gamma radiation from 137Cs radioactivity

This current study was designed to determine the effects of in vitro exposure to radioactive cesium-137 on human blood components. Whole blood samples were given a radiation dose of 0.02, 0.05, 0.1, 0.2, and 0.3 mGy of gamma radiation using a 137Cs radioactive standard source. The whole blood samples that were exposed to 0 mGy served as sham-controls. The spectrofluoroscopic technique was used to determine the autofluorescence spectrum of protein in plasma or red blood cells by using excitation wavelength and range of emission wavelengths at 280 nm and 300–550 nm, respectively. The hemolysis of red blood cells was evaluated by determination of the release of hemoglobin from the red blood cells to the supernatant. Complete blood counts were also determined in whole blood. The results showed that there was no change in the ratio of fluorescence emission intensity at 340 nm of wavelength of protein extract from irradiated whole blood or red blood cells compared to the corresponding non-irradiated control. The hemolysis value did not change in irradiated whole blood when compared to the corresponding non-irradiated group. In addition, complete blood count values in irradiated groups did not differ from non-irradiated group. These current results suggested that there were no harmful effects of the low-dose gamma radiation from radioactive 137Cs on blood components when human whole blood was exposed to gamma radiation in an in vitro condition.

Short-term plasticity as a mechanism to regulate and retain multistability

Short-term synaptic plasticity of recurrent synapses has previously been shown to control and tune the balance of excitation and inhibition. Still, the precise mechanisms whereby short-term plasticity contributes to the coexistence and stabilization of neural firing are subtle and remain elusive. Here, we present a Wang–Buzsáki neural network to investigate the combined effect of short-term plasticity and recurrent inhibition on generating various firing patterns and dynamical retention. The resulting statistical analysis of both voltage trajectories and spike trains reveals two functional roles of short-term plasticity to neuronal dynamics. First, we find that recurrent inhibitory connections can be a possible mechanism to regulate neural firing at the given excitatory level. Secondly, we further find that neural networks of the excitatory population possess the ability to retain and stabilize various neural firing patterns with a broader range of excitation. Our findings pave the way to understanding the role of short-term plasticity in producing and maintaining multiple firing patterns.

Mn2+ doped BaAl11O16N phosphors with narrow band green emission and superior thermal stability for backlighting display applications

Here, BaAl11O16N: Mn2+ green phosphor was synthesized by a two-step high-temperature solid-phase method, and its phase structure, morphology and photoluminescence properties were studied in detail. The phosphor has a wide excitation range of 240–500 nm, and the most effective excitation bands are in the blue spectral regions, indicating that BaAl11O16N: Mn2+ green phosphor can be effectively excited by the commercial blue LED chip. Under the excitation of ultraviolet and blue light, the BaAl11O16N: Mn2+ phosphor shows bright green light emission, with a peak of 514 nm and a half peak width of about 31 nm. The emission properties with temperature change show that the BaAl11O16N: Mn2+ phosphor has good thermal stability and excellent color stability. The white light-emitting diode (a blue InGaN chip combined with BaAl11O16N: 0.25Mn2+ phosphor and a commercial K2SiF6: Mn4+ phosphor) exhibits a NTSC value of 119.3%. Therefore, it can be concluded that the BaAl11O16N: Mn2+ phosphor the ideal choice for wide color gamut backlight as a potential efficient phosphor with green narrow-band emission.

Double Perovskite Mn4+-Doped La2CaSnO6/La2MgSnO6 Phosphor for Near-Ultraviolet Light Excited W-LEDs and Plant Growth.

Non-rare earth doped oxide phosphors with far-red emission have become one of the hot spots of current research due to their low price and excellent physicochemical stability as the red component in white light-emitting diodes (W-LEDs) and plant growth. Herein, we report novel Mn4+-doped La2CaSnO6 and La2MgSnO6 phosphors by high-temperature solid-phase synthesis and analyzed their crystal structures by XRD and Rietveld refinement. Their excitation spectra consist of two distinct excitation bands with the dominant excitation range from 250 to 450 nm, indicating that they possess strong absorption of near-ultraviolet light. Their emission is located around 693 and 708 nm, respectively, and can be absorbed by the photosensitive pigments Pr and Pfr, proving their great potential for plant growth. Finally, the prepared samples were coated with 365 nm UV chips to fabricate far-red LEDs and W-LEDs with low correlation color temperature (CCT = 4958 K/5275 K) and high color rendering index (Ra = 96.4/96.6). Our results indicate that La2CaSnO6:Mn4+ and La2MgSnO6:Mn4+ red phosphors could be used as candidate materials for W-LED lighting and plant growth.

Two-Photon Excitation Spectra of Various Fluorescent Proteins within a Broad Excitation Range.

Two-photon excitation fluorescence laser-scanning microscopy is the preferred method for studying dynamic processes in living organ models or even in living organisms. Thanks to near-infrared and infrared excitation, it is possible to penetrate deep into the tissue, reaching areas of interest relevant to life sciences and biomedicine. In those imaging experiments, two-photon excitation spectra are needed to select the optimal laser wavelength to excite as many fluorophores as possible simultaneously in the sample under consideration. The more fluorophores that can be excited, and the more cell populations that can be studied, the better access to their arrangement and interaction can be reached in complex systems such as immunological organs. However, for many fluorophores, the two-photon excitation properties are poorly predicted from the single-photon spectra and are not yet available, in the literature or databases. Here, we present the broad excitation range (760 nm to 1300 nm) of photon-flux-normalized two-photon spectra of several fluorescent proteins in their cellular environment. This includes the following fluorescent proteins spanning from the cyan to the infrared part of the spectrum: mCerulean3, mTurquoise2, mT-Sapphire, Clover, mKusabiraOrange2, mOrange2, LSS-mOrange, mRuby2, mBeRFP, mCardinal, iRFP670, NirFP, and iRFP720.

Numerical simulations of a 15MW wind turbine on a concrete TLP with rigid pipe tendons

In this work, we analyze the stability of a concrete TLP platform with a square hull, designed for a 15 MW wind turbine. We verify the natural frequencies in the different degrees of freedom (DOFs) and two ultimate state design load cases (DLC) via two independent models, one in HAWC2+WAMIT from DTU and one in Orcaflex+AQWA from Bluenewables (BN). The decay tests show that the platform eigenfrequencies are outside of the main wave excitation range, and that the models predict the same natural periods within ±5%, with a maximum deviation 20% for the roll period (2.4 s vs. 2.23 s). In the ultimate load states (DLC 1.6 and 6.1), the platform motions are mainly driven by the wind and wave forcing. A small resonance is observed for the pitch motion, driven by the aerodynamic loads, and for the surge, driven by the difference-frequency components of the second-order wave excitation force. The tendons tension reaches a maximum of Nmax = 30 MN for DLC 6.1 (HS = 10.9 m, Tp = 14.0 s, Vref = 42.3ms−1). In both DLC 6.1 and DLC 1.6 the tendons are far from the compression limit, with a safety margin of ≈ 8 MN for the analyzed test cases.

Static vs. Dynamic Representations and the Mediating Role of Behavioral Affect on E-Learning Outcomes

Online learning has become increasingly commonplace, including the replacement and augmentation of traditional in-residence education, as well as ad-hoc training systems and just-in-time knowledge dissemination. However, design for instructional media to facilitate performance has relied on an inadequate understanding of the behavioral affect elicited from these designs. To investigate the degree to which excitement and engagement are predictive of individual learning outcomes in an online learning setting, we evaluate an experiment with two instructional representations (static and dynamic) using learning materials for a semaphore signaling system. We examine the excitement and engagement levels of the participants using electroencephalography (EEG) as potential mediators. Learning outcomes are measured by the evaluation scores of knowledge retention. We consider several structural equation models (SEMs) to see the underlying relationship between instructional representation, excitement, engagement, and learning outcomes. Notably, the models indicate the full mediation of behavioral affect on learning outcomes, in which both the range of excitement and the maximum level of engagement are mediating effects. This article illustrates the potential for biometrically measured affect aid in the modeling and understanding of how instructional design features ultimately impact performance.