Radiative Channels Research Articles

Спектрально-люминесцентные свойства и фотолиз заряженных форм бисфенола А

The spectral luminescent properties and photolysis of the ionic forms (neutral, cationic and anionic) of bisphenol A have been studied experimentally and by methods of quantum chemistry. Calculations and experiment have shown that, in comparison with a neutral form, no new absorption bands appear in the absorption spectra of ionic form in the range 200–600 nm. The polar solvent (water) shifts the absorption spectrum bands of ionic forms towards low energies. In this case, the shift of the absorption spectrum of the cation is insignificant, and the shift of the anion is significant with an increase in the intensity of the absorption bands. The low quantum yield of fluorescence of ionic form is explained by the prevalence of the efficiency of singlet-triplet conversion over the efficiency of the radiation channel of decay of the fluorescent state. The low quantum yield of fluorescence of the anionic form is due not only to the effective singlet-triplet conversion, but also to the low efficiency of the radiative decay of the fluorescent state of the anion caused by a change in its orbital nature. Calculations have shown that the potential curves of the excited states of bisphenol A and its ionic forms have a significant potential barrier to photolysis. The increase in the efficiency of the process of photodissociation of the bisphenol A anion is caused by a noticeable decrease in the potential barrier and an increase in the overlap of the absorption spectra of the bisphenol A anion and solar radiation.

J-Aggregation Enhanced Thermally Activated Delayed Fluorescence for Amplified Spontaneous Emission

Modulation of excited-state energy-level structures through controlled molecular-stacking arrangement provides an effective strategy to tuning fluorescence and thermally activated delayed fluorescence (TADF) amplified spontaneous emission (ASE), but remains a critical challenge. Herein, we demonstrated the regulation of fluorescence and TADF ASE in organic crystalline polymorphs by controlling the excited-state dynamics through aggregate effects. Experimental and theoretical studies show that green crystals emit green fluorescence ASE while red crystals emit red TADF ASE, because higher degree of J-aggregation in red crystals significantly results in a substantial decrease of energy gaps between singlet and triplet to 0.24 eV for the realization of reverse intersystem crossing process. Our results suggest that molecular packing presents a powerful approach to tailor the radiative channels and fundamentally important to tuning fluorescence and TADF ASE in pure organic crystals.

Methodological aspects of the presentation of information security threats recognition signs in the context of improving technical intelligence

Formulation of the problem. The completeness of the characteristics of one of the most serious threats to the security of information today – its leakage through the transient electromagnetic pulse emanation standard (TEMPEST) from computer equipment (CE) is determined not only by the number of detectable signs of leakage but also by several other parameters characterizing the dynamics of the implementation of such a threat. The established patterns in the scenarios of violators’ actions associated with the use of technical reconnaissance equipment (TRQ) to intercept informative TEMPEST signals from computer equipment made it possible to form a model of all possible options for using TRQ to obtain confidential information processed by computer equipment. The proposed model provides the implementation of the methodological principles of the recognition theory for a more complete characterization of threats of information leakage through the channels of spurious electromagnetic radiation and interference from CE in the process of their detection.Objective. Development of methodological grounds for presenting signs of the violator’s implementation of certain functions associated with the use of technical reconnaissance equipment to intercept informative signals of spurious electromagnetic radiation and interference from computer equipment as signs that identify the most significant conditions for the recognition and prevention of such threats.Results. Methodological solutions for the identification of three states significant for the prevention of threats are given based on the structuring of the functional representation of the intruder’s actions to implement such threats. Mathematical models for assessing the predicted amount of information disclosed in the process of intercepting TEMPEST informative signals from computer equipment, and assessing the level of security threats in case of interception of information are also presented.Practical significance. The paper presents the main options for the operation of a complex of programs for recognizing threats of information leakage through TEMPEST channels from computer equipment developed within the framework of the presented methodology.

Fluoroindate glasses co-doped with Pr3+/Er3+ for near-infrared luminescence applications

Fluoroindate glasses co-doped with Pr3+/Er3+ ions were synthesized and their near-infrared luminescence properties have been examined under selective excitation wavelengths. For the Pr3+/Er3+ co-doped glass samples several radiative and nonradiative relaxation channels and their mechanisms are proposed under direct excitation of Pr3+ and/or Er3+. The energy transfer processes between Pr3+ and Er3+ ions in fluoroindate glasses were identified. In particular, broadband near-infrared luminescence (FWHM = 278 nm) associated to the 1G4 → 3H5 (Pr3+), 1D2 → 1G4 (Pr3+) and 4I13/2 → 4I15/2 (Er3+) transitions of rare earth ions in fluoroindate glass is successfully observed under direct excitation at 483 nm. Near-infrared luminescence spectra and their decays for glass samples co-doped with Pr3+/Er3+ are compared to the experimental results obtained for fluoroindate glasses singly doped with rare earth ions.

Preclinical Challenges in Proton Minibeam Radiotherapy: Physics and Biomedical Aspects

The concept of spatial fractionation in radiotherapy was developed for better sparing of normal tissue in the entrance channel of radiation. Spatial fractionation utilizing proton minibeam radiotherapy (pMBRT) promises to be advantageous compared to X-ray minibeams due to higher dose conformity at the tumor. Preclinical in vivo experiments conducted with pMBRT in mouse ear models or in rat brains support the prospects, but the research about the radiobiological mechanisms and the search for adequate application parameters delivering the most beneficial minibeam therapy is still in its infancy. Concerning preclinical research, we consider glioma, non-small cell lung cancer and hepatocellular carcinoma as the most promising targets and propose investigating the effects on healthy tissue, especially neuronal cells and abdominal organs. The experimental setups for preclinical pMBRT used so far follow different technological approaches, and experience technical limitations when addressing the current questions in the field. We review the crucial physics parameters necessary for proton minibeam production and link them to the technological challenges to be solved for providing an optimal research environment. We consider focusing of pencil or planar minibeams in a scanning approach superior compared to collimation due to less beam halos, higher peak-to-valley dose ratios and higher achievable dose rates. A possible solution to serve such a focusing system with a high-quality proton beam at all relevant energies is identified to be a 3 GHz radio-frequency linear accelerator. We propose using a 16 MeV proton beam from an existing tandem accelerator injected into a linear post-accelerator, boosted up to 70 MeV, and finally delivered to an imaging and positioning end-station suitable for small animal irradiation. Ion-optical simulations show that this combination can generate focused proton minibeams with sizes down to 0.1 mm at 18 nA mean proton current - sufficient for all relevant preclinical experiments. This technology is expected to offer powerful and versatile tools for unleashing structured and advanced preclinical pMBRT studies at the limits and also has the potential to enable a next step into precision tumor therapy.

Hybrid Metal-Dielectric Metasurfaces for Refractive Index Sensing.

Hybrid metal-dielectric nanostructures have recently gained prominence because they combine strong field enhancement of plasmonic metals and the several low-loss radiation channels of dielectric resonators, which are qualities pertaining to the best of both worlds. In this work, an array of such hybrid nanoantennas is successfully fabricated over a large area and utilized for bulk refractive index sensing with a sensitivity of 208 nm/RIU. Each nanoantenna combines a Si cylinder with an Al disk, separated by a SiO2 spacer. Its optical response is analyzed in detail using the multipoles supported by its subparts and their mutual coupling. The nanoantenna is further modified experimentally with an undercut in the SiO2 region to increase the interaction of the electric field with the background medium, which augments the sensitivity to 245 nm/RIU. A detailed multipole analysis of the hybrid nanoantenna supports our experimental findings.

Indirect Measurements of n- and p-Induced Reactions of Astrophysical Interest on Oxygen Isotopes

Observations of abundances and isotopic ratio determinations in stars yield powerful constraints on stellar models. In particular, the oxygen isotopic ratios are of particular interest because they are affected not only by nucleosynthesis but also by mixing processes. This review is focused on the measurements via the Trojan Horse Method (THM) that have been carried out to investigate the low-energy cross sections of proton and neutron-induced reactions on 17O as well as the proton-induced reaction on 18O, overcoming extrapolation procedures and enhancement effects due to electron screening. The (p,a) reactions induced on these oxygen isotopes are of paramount importance for the nucleosynthesis in many stellar sites, including red giants (RGs), asymptotic giant branch (AGB) stars, massive stars, and classical novae. The indirect measurement of the 17O(p,a)14N reaction was performed. The strength of the narrow resonance at 65 keV was evaluated and it was used to renormalize the corresponding resonance strength in the 17O+p radiative capture channel. The reaction rate was evaluated for both the 17O(p,a)14N and the 17O(p,g)18F, and a significant difference of 30% and 20% with respect to the literature was found in the temperature range relevant for RG, AGB and massive stars nucleosynthesis. Regarding the 18O(p,a)15N reaction, the strength of the 20 keV resonance was extracted, which is the main contribution to the reaction rate for astrophysics. This approach allowed us to improve the data accuracy of a factor 8.5, as it is based on the measured strength instead of extrapolations or spectroscopic measurements. Finally, the 17O(n,a)14C reaction was studied because of its role during the s-process nucleosynthesis as a possible neutron poison. This study represents the extension of THM to resonant neutron-induced reactions. In this measurement, the subthreshold level centered at -7 keV in the center-of-mass, corresponding to the 8.039 MeV 18O excited level, was observed. Moreover, the THM measurements showed a clear agreement with the available direct measurements because of the additional contribution of the 8.121 MeV 18O level, strongly suppressed in direct measurements because of its l=3 angular momentum. The contributions to the total reaction rate were than evaluated for future astrophysical applications.

Luminescence of a Two-Particle Complex from a Spherical Quantum Dot and Plasmon Nanoglobule in an External Magnetic Field

Based on a specially created theoretical model, frequency dependences of the luminescence intensity of the two-component “exciton-activated semiconductor quantum dot (QD)–plasmon nanoparticle (NP)” system in a constant magnetic field are calculated. In contrast to previous models, it goes beyond the scope of the approximation of dipole polarizability of a spherical NP. The induced NP dipole moment was calculated taking into account the inhomogeneous character of the field created by the QD containing an exciton. It is shown that, with a change in induction of the external magnetic field, one can observe transformation of exciton luminescence spectra of such system as a result of the exciton–plasmon interaction between cluster particles and magnetization of the NP electron plasma. The competition of radiative and nonradiative decay channels of the excited state of a two-particle complex is taken into account. It is shown that, in rate spectra of the nonradiative energy transfer from the QD to the NP, as well as of spontaneous emission of the nanocomplex, stripes of higher order multipole transitions are formed in addition to dipole stripes; they are split into doublet components in the magnetic field.

Construction and optimization of ecological network in Xi'an based on landscape analysis

Ecological network can connect fragmented habitat patches to increase the connectivity among landscapes, which plays an important role to landscapes and ecological problems caused by urbanization. In this study, the ecological networks of Xi'an City were constructed using landscape pattern index and morphological spatial pattern analysis to reveal landscape pattern features. The performance of the network was evaluated with the gravity model to provide an optimization strategy. The landscape richness index was relatively high, with significant differences of landscape patterns between north and south parts. The ecological sources were predominated in the south and east areas, while a higher comprehensive resistance with low connectivity was found in the north and central areas. The ecological corridors were unevenly distributed, with the radiation channels derived from hydrological analysis providing a supplementary role. Furthermore, ecological networks could be optimized by introducing other ecological sources, supplementing stepping stones, and repairing fracture points, to reduce the problems of uneven distribution of ecological sources, the excessively long ecological corridors in local regions, and the obstruction of road networks. Our optimization method provided an optional way to assist urban planning of Xi'an City.

Kinetic effects in parallel electron energy transport channels in the scrape-off layer

We present an analysis of parallel electron energy transport in the scrape-off layer (SOL), considering the convective and conductive channels, as well as the radiation and neutral inelastic energy transfer channels involving atomic deuterium. Kinetic effects in both equilibria and conductive transients are explored by utilizing the capability of the SOL-KiT code to treat electrons as either a fluid or kinetically. We find kinetic effects in multiple channels, with an emphasis on those occurring during the investigated conductive transients. Energetic electron effects in the heat flux, as well as a modification of ionization rates of up to 40% compared to Maxwellian rates during perturbations in detached conditions, are reported and discussed.

Manipulating light radiation from a topological perspective

Manipulating radiation is important for a variety of optoelectronic applications, such as on-chip lasers, energy-efficient grating couplers, and antennas for light detection and ranging. Although designing and optimizing those optoelectronic devices are usually believed to be an engineering-oriented task, recent research reveals that the principles underlying radiation manipulation are closely connected to the concept of topology—the study of properties that are invariant under continuous deformations. In this review, we summarize a series of advances of the physics, phenomena, and applications related to radiation manipulation, in which topological concepts were adopted. Radiation could carry energy escaping from the system, breaking the energy conservation. The non-Hermiticity of such systems brings quite different physical consequences when comparing with the Hermitian counterparts and, hence, also results in the emergence of many interesting and extraordinary phenomena. In particular, it is found that the perfect trapping of light can still be realized in such non-Hermitian systems because of the photonic realization of bound states in the continuum. The fundamental nature of bound states in the continuum has been identified to be topological: they are essentially topological defects of the polarization vector field in momentum space, depicted by a kind of topological invariant named topological charges. Therefore, manipulation of radiation channels can be realized by controlling the topological charge evolution in momentum space. It is also demonstrated that the photonic states accompanied with different topological charges generate vortex beams with unique far-field radiation patterns, and ultra-fast switching of such vortex beams is demonstrated according to this principle. The progresses of topological photonics upon light radiation show that the topology is not just mathematical convenience for depicting photonic systems, but has brought realistic consequences in manipulating light and will boost the applications of photonics and optoelectronics in many aspects.

Accounting for the interference component in the technical channel of information leakage of spurious electromagnetic radiation in the video path with diversity reception

National standards of Ukraine, other legal documents of the system of technical protection of information propose to protect information that is a state and other secret on the objects of information activities of organizations and institutions of all forms of ownership. One of the dangerous technical channels of information leakage is the channel of incidental electromagnetic radiation of the video path of electronic computing equipment. An important element of such a channel is the means of radio and radio intelligence used by the stakeholder to intercept spurious electromagnetic radiation. Intelligence tools are evolving and improving. One of the ways to improve the use of intelligence is the remote reception of incidental electromagnetic radiation. When assessing the possibilities of spaced reception, it is also necessary to take into account the phenomena of interference of the signal reflected from the earth's surface with the signal of direct propagation from the computer to the reconnaissance antennas.The article is devoted to the analysis of the need to take into account the interference multiplier of electromagnetic field propagation when estimating the possibility of conducting reconnaissance of incidental electromagnetic radiation at spaced reception. Approaches to take into account the factors influencing the interference of PEMV are identified. The components of the quantitative model of the technical channel of information leakage are proposed, which allow taking into account the factors influencing the signal/noise ratio of the signal perceived by the intelligence equipment.

Structural characterization and photoluminescence of (Gd1-xErx)2O3 nanophosphors synthesized by co-precipitation of layered precursors

In this paper, the layered (Gd1-xErx)2(OH)5NO3·nH2O (LGEH) with a variable content of erbium were synthesized by controlled double-jet precipitation (CDJP) at a constant pH value. The effect of pH co-precipitation on the morphology, crystallinity, porosity of the LGEH, as well as on the spectral-luminescent properties of oxide nanophosphors obtained by their heat treatment is significant. We have found that the samples with the lowest disordering and the highest of photoluminescence (PL) intensity of Er3+ ions are obtained from amorphous sponge-like precursor co-precipitated at pH 9.5. The PL of nanostructural (Gd1-xErx)2O3 depends on both structural-morphology properties and samples composition. It was also found that efficiency of radiative and non-radiative relaxation channels for excited Er3+ ions mainly depends on three factors: nanocrystals size, specific surface area and erbium concentration. For explanation of the PL behavior in the green and red spectral ranges, the energy diagram showing the intracenter energy transitions and intercenter energy migration in synthesized nanophosphors was proposed.

Parametric dependence of bound states in the continuum on periodic structures

Bound states in the continuum (BICs) have some unusual properties and important applications in photonics. A periodic structure sandwiched between two homogeneous media is the most popular platform for observing BICs and realizing their applications. Existing studies on BICs assume the periodic structure has a ${C}_{2}$ rotational symmetry about the axis perpendicular to the periodic layer. It is known that all BICs turn to resonant states with finite quality factors if the periodic structure is perturbed by a generic perturbation breaking the ${C}_{2}$ symmetry, and a typical BIC continues to exist if the perturbation keeps the ${C}_{2}$ symmetry. We study how typical BICs depend on generic structural parameters. For a class of BICs with one opening radiation channel, we show that in the plane of two generic parameters, the BICs exist continuously as a curve. Consequently, BICs can exist on periodic structures without the ${C}_{2}$ symmetry, and they can be found by tuning a single structural parameter. The result is established analytically by a perturbation theory with two independent perturbations and validated by numerical examples. Our study reveals a much larger family for BICs on periodic structures, and provides new opportunities for future applications.

X-ray spectra of the Fe-L complex

The Hitomi results for the Perseus cluster have shown that accurate atomic models are essential to the success of X-ray spectroscopic missions and just as important as the store of knowledge on instrumental calibration and astrophysical modeling. Preparing the models requires a multifaceted approach, including theoretical calculations, laboratory measurements, and calibration using real observations. In a previous paper, we presented a calculation of the electron impact cross sections on the transitions forming the Fe-L complex. In the present work, we systematically tested the calculation against cross-sections of ions measured in an electron beam ion trap experiment. A two-dimensional analysis in the electron beam energies and X-ray photon energies was utilized to disentangle radiative channels following dielectronic recombination, direct electron-impact excitation, and resonant excitation processes in the experimental data. The data calibrated through laboratory measurements were further fed into a global modeling of the Chandra grating spectrum of Capella. We investigated and compared the fit quality, as well as the sensitivity of the derived physical parameters to the underlying atomic data and the astrophysical plasma modeling. We further list the potential areas of disagreement between the observations and the present calculations, which, in turn, calls for renewed efforts with regard to theoretical calculations and targeted laboratory measurements.

Quantum Hamiltonian for the surface charge density on a ring torus and radiative decay of plasmons

Photon scattering and the ensuing excitation of surface plasmons in single rings, single composite rings, and many-ring systems was recently shown to provide dispersion and field distributions [K. V. Garapati et al., J. Phys. Commun. 2, 015031 (2018)] of potential for specific applications in particle and molecular trapping [R. Alaee et al., Appl. Phys. Lett. 109, 141102 (2016); M. Salhi et al., Phys. Rev. A 92, 033416 (2015)], in addition to metamaterials and sensing. Following photon or electron interactions with metallic nanorings, both radiative and nonradiative decay channels are important in the consideration of the nanoparticle as a photon or phonon source, and in related applications. Here, we quantize the electronic normal modes of the ring torus and obtain the radiative decay of plasmons. Due to a geometry-related complexity, we employ a perturbation approach to obtain analytical expressions for the radiative decay channel for a vacuum bounded single solid nanoring. In quantizing the fields, the frequency spectrum of the charge density normal modes of the nanoring is obtained and shown to agree with the exact quasistatic plasmon dispersion relations. Higher-order corrections beyond the presented zero- and first-order calculations may be obtained following the presented results. The results are of potential interest in quantum sensing such as entangling photons and plasmons, or plasmons and trapped molecules.

Charge‐Carrier Trapping and Radiative Recombination in Metal Halide Perovskite Semiconductors

AbstractTrap‐related charge‐carrier recombination fundamentally limits the performance of perovskite solar cells and other optoelectronic devices. While improved fabrication and passivation techniques have reduced trap densities, the properties of trap states and their impact on the charge‐carrier dynamics in metal‐halide perovskites are still under debate. Here, a unified model is presented of the radiative and nonradiative recombination channels in a mixed formamidinium‐cesium lead iodide perovskite, including charge‐carrier trapping, de‐trapping and accumulation, as well as higher‐order recombination mechanisms. A fast initial photoluminescence (PL) decay component observed after pulsed photogeneration is demonstrated to result from rapid localization of free charge carriers in unoccupied trap states, which may be followed by de‐trapping, or nonradiative recombination with free carriers of opposite charge. Such initial decay components are shown to be highly sensitive to remnant charge carriers that accumulate in traps under pulsed‐laser excitation, with partial trap occupation masking the trap density actually present in the material. Finally, such modelling reveals a change in trap density at the phase transition, and disentangles the radiative and nonradiative charge recombination channels present in FA0.95Cs0.05PbI3, accurately predicting the experimentally recorded PL efficiencies between 50 and 295 K, and demonstrating that bimolecular recombination is a fully radiative process.

Bound states in the continuum (BIC) accompanied by avoided crossings in leaky-mode photonic lattices

Abstract When two nonorthogonal resonances are coupled to the same radiation channel, avoided crossing arises and a bound state in the continuum (BIC) appears with appropriate conditions in parametric space. This paper presents numerical and analytical results on the properties of avoided crossing and BIC due to the coupled guided-mode resonances in one-dimensional (1D) leaky-mode photonic lattices with slab geometry. In symmetric photonic lattices with up-down mirror symmetry, Friedrich–Wintgen BICs with infinite lifetime are accompanied by avoided crossings due to the coupling between two guided modes with the same transverse parity. In asymmetric photonic lattices with broken up-down mirror symmetry, quasi-BICs with finite lifetime appear with avoided crossings because radiating waves from different modes cannot be completely eliminated. We also show that unidirectional-BICs are accompanied by avoided crossings due to guided-mode resonances with different transverse parities in asymmetric photonic lattices. The Q factor of a unidirectional-BIC is finite, but its radiation power in the upward or downward direction is significantly smaller than that in the opposite direction. Our results may be helpful in engineering BICs and avoided crossings in diverse photonic systems that support leaky modes.

Two-dimensional electron bound hole photoluminescence in GaAs in perpendicular magnetic fields

The photoluminescence of quasi two-dimensional (2D) electrons in modulation doped AlxGa1 − xAs-GaAs single heterostructure recombining with bound holes was studied at liquid helium temperatures in magnetic fields up to 9 T. Luminescence contributions from the ground and a weakly populated first excited 2D subband were observed as well as bulk-like contributions from the GaAs buffer. The 2D subband and the bulk signals are linked and oscillate with the magnetic field strength. It is not the filling factor that rules but the alignment of the two subband Landau-ladders paired with intersubband scattering that drives an oscillatory behavior of the subband populations. Asymmetric Landau-level transition line shapes indicate a perturbed 2D electron system. We performed a detailed analyses of Landau-level dependent line strengths, positions and half widths and compared the experiment with calculations of subband energies and transition matrix elements. The total electron density is not fixed in our experiment but decreases with magnetic field strength. This might indicate that the 2D system exchanges electrons with a reservoir and/or that the correlation between radiative and nonradiative recombination channels vary strongly with the magnetic field strength.

Divertor impurity seeding with a new feedback control scheme for maintaining good core confinement in grassy-ELM H-mode regime with tungsten monoblock divertor in EAST

Small perturbations and strong impurity exhaust capability associated with the small grassy ELMs render the grassy-ELM regime a suitable candidate for achieving steady-state H-mode operation with a radiative divertor, especially in a metal-wall device, such as the Experimental Advanced Superconducting Tokamak (EAST). As the degradation of pedestal performance with excessive divertor impurity seeding or accumulation tends to be accompanied with significantly increased radiation near the divertor X point, feedback control of the absolute extreme ultraviolet (AXUV) radiation near the X point has been employed to maintain the confinement property in EAST. However, the absolute value of the AXUV radiation at the outer target varies with plasma conditions as during the divertor detachment process. Thus, a new feedback-control scheme has been recently developed and applied to grassy-ELM H-mode plasmas in EAST to achieve stationary partial detachment while maintaining good global energy confinement with H 98,y2 >1. In this scheme, electron temperatures (T et) measured by divertor Langmuir probes are used to identify the onset of detachment, and then the plasma control system (PCS) switches to the feedback control of one channel of AXUV radiation near the X point, where a steep gradient in the radiation profile is present. The feedback is performed through pulse-width-modulated duty cycle of a piezo valve to seed impurities with mixed gas (50% Ne and 50% D2) from the outer target plate near the strike point in the upper tungsten monoblock divertor. T et near the strike point is maintained in the range of 5–8 eV, and peak surface temperature on the outer target plate (T IR,peak) is suppressed and maintained at ∼180 °C, based on infrared camera measurements. The plasma stored energy maintains nearly constant over the entire feedback-control period. It thus offers a highly promising plasma control scenario suitable for long-pulse high-performance H-mode operation in EAST, which is potentially applicable to future steady-state fusion reactors as an integrated solution for the control of both ELM-induced transient and steady-state divertor heat loads while maintaining good core confinement.