Radiative Energy Transfer Research Articles

Efficient Photon Extraction in Top-Emission Organic Light-Emitting Devices Based on Ampicillin Microstructures.

The desire to enhance the efficiency of organic light-emitting devices (OLEDs) has driven to the investigation of advanced materials with fascinating properties. In this work, the efficiency of top-emission OLEDs (TEOLEDs) is enhanced by introducing ampicillin microstructures (Amp-MSs) with dual phases (α-/β-phase) that induce photoluminescence (PL) and electroluminescence (EL). Moreover, Amp-MSs can adjust the charge balance by Fermi level (EF ) alignment, thereby decreasing the leakage current. The decrease in the wave-guided modes can enhance the light outcoupling through optical scattering. The resulting TEOLED demonstrates a record-high external quantum efficiency (EQE) (maximum: 68.7% and average: 63.4% at spectroradiometer; maximum: 44.8% and average: 42.6% at integrating sphere) with a wider color gamut (118%) owing to the redshift of the spectrum by J-aggregation. Deconvolution of the EL intensities is performed to clarify the contribution of Amp-MSs to the device EQE enhancement (optical scattering by Amp-MSs: 17.0%, PL by radiative energy transfer: 9.1%, and EL by J-aggregated excitons: 4.6%). The proposed TEOLED outperforms the existing frameworks in terms of device efficiency.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions.

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

Ultralong-Lived Up-Conversional Room-Temperature Afterglow Materials with a Polyvinyl Alcohol Substrate

Room-temperature afterglow (RTA) materials have a wide range of applications in imaging, lighting, and therapy, due to their long lifetime and persistent luminescence after the light source is removed. Additionally, near-infrared light with low energy and a high penetration rate ensures its irreplaceable importance in imaging and therapy. Thus, it is vital to design RTA materials excited by NIR. In the present study, we select up-conversion nanoparticles (UCNPs) as the donor and add them into hybrids, obtained by dispersing coronene tetra-carboxylate salt (CS) into a polyvinyl alcohol (PVA)-substrate through a series of mixing methods. Through radiation energy transfer between the donor UCNPs and the acceptor CS, a kind of RTA film with a photoluminescence lifetime of more than 2 s under NIR excitation was successfully achieved, and these films could maintain persistent naked-eye-distinguishable luminescence after withdrawing the excitation light source. Furthermore, the films obtained from UCNP doping into CS/PVA hybrids were found to exhibit better RTA performance than those from smearing. This idea of up-conversion afterglow broadens the tuning and application scope for polymer-based luminescent materials.

Vibrational energy estimation of cracked composite beams using radiative energy transfer method

An energy flow model based on the radiative energy transfer method (RETM) is established for the high-frequency response prediction of finite composite beams with edge cracks. The Timoshenko beam theory is applied to derive the motion governing equations of the beam. The composite beam is divided into several components in line with its multiple cracks. Cracks and boundary conditions are modeled as elastic springs. Spring stiffnesses at the cracks are obtained by the inverse of the flexibility coefficients from the fracture mechanics theory. Power reflection and transmission coefficients through the cracks are derived through wave propagation analysis. The response of the beam loaded by a high-frequency point force is described by vibrational energy density and intensity. The energy response of each part of the beam is contributed by the rays emitted from the actual source set at load point and then, reflected or transmitted through the fictitious sources at cracks. Fictitious sources are determined by the energy balance equations at cracks and boundaries. Numerical examples show that the energy distributions of the multi-cracked composite beams are well predicted by the proposed approach.

The Highly Efficient Inorganic SrF<sub>2</sub>:Gd<sup>3+</sup>, Eu<sup>3+ </sup>Phosphor for Mercury Free Fluorescence Lamps

The strong vacuum ultraviolet (VUV) radiation absorption and energy transfer mechanism is detected in SrF2: Gd3+, Eu3+ fluoride phosphor. The phosphor is synthesized by a wet chemical method followed by reactive atmospheric process (RAP). The Powder XRD analysis shows structural purity. The photoluminescence characteristics of SrF2:Gd3+, Eu3+ phosphor is studied using the remote access of 4B8 window (VUV beamline) of the Beijing Synchrotron Radiation Facility (BSRF) China. In this paper the mechanism of Energy transfer from the Gd3+ to Eu3+ through the cross relaxation process is investigated. The down-conversion of energy from VUV (142 nm) to visible with quantum efficiency (QE) around 124% has been detected. The PL excitation and emission characteristics of the prepared phosphor advocates it as a prominent material for the applications in mercury free fluorescent lighting (MFFL) & Plasma Display Panel.

Modeling overcontact binaries

Context. In the realm of massive stars, strong binary interactions are commonplace. One extreme case is that of overcontact systems, which are expected to be part of the evolution of all stars evolving towards a merger and hypothesized as playing a role in the formation of binary black holes. However, important simplifications are made to model the evolution of overcontact binaries. The deformation from tidal forces is almost always put aside, and even rotation is frequently ignored in such models. Yet, both observations and theory have shown that overcontact stars are tidally deformed to a great extent, leaving a potentially important effect on the outer layers unaccounted for in models. Furthermore, in eclipsing binaries where radii can be determined to high precision, the question of how large the effect of tidal deformation is on the inferred properties of stellar models is still uncertain. Aims. We aim to consistently model overcontact binary stars in a one-dimensional (1D) stellar evolution code. To that end, we developed the required methodology to represent tidally distorted stars in 1D evolution codes. Methods. Using numerical methods, we computed the structure correction factors to the 1D spherical stellar structure equations of hydrostatic equilibrium and radiative energy transfer due to the binary Roche potential. We then compared them to existing results and the structure corrections of single, rotating stars. We implemented the new structure correction factors in the stellar evolution code MESA and explored several case studies. We compared the differences between our simulations: when no rotation is included, when we treat rotation using single star corrections (only accounting for centrifugal deformation), or when we use tidal deformation. Results. We find that ignoring rotation in deformed detached eclipsing binaries can produce a radius discrepancy of up to 5%. The difference between tidal and single star centrifugal distortion models is more benign at 1%, showing that single rotating star models are a suitable approximation of tidally deformed stars in a binary system. In overcontact configurations, we find a similar 5% variation in surface properties as a result of tidal distortion with respect to non-rotating models, showing that it is inappropriate to model binary stars filling their Roche lobe significantly as non-rotating.

Enhanced Effects of Chronic Restraint-Induced Psychological Stress on Total Body Fe-Irradiation-Induced Hematopoietic Toxicity in Trp53-Heterozygous Mice.

Humans are exposed to both psychological stress (PS) and radiation in some scenarios such as manned deep-space missions. It is of great concern to verify possible enhanced deleterious effects from such concurrent exposure. Pioneer studies showed that chronic restraint-induced PS (CRIPS) could attenuate Trp53 functions and increase gamma-ray-induced carcinogenesis in Trp53-heterozygous mice while CRIPS did not significantly modify the effects on X-ray-induced hematopoietic toxicity in Trp53 wild-type mice. As high-linear energy transfer (LET) radiation is the most important component of space radiation in causing biological effects, we further investigated the effects of CRIPS on high-LET iron-particle radiation (Fe)-induced hematopoietic toxicity in Trp53-heterozygous mice. The results showed that CRIPS alone could hardly induce significant alteration in hematological parameters (peripheral hemogram and micronucleated erythrocytes in bone marrow) while concurrent exposure caused elevated genotoxicity measured as micronucleus incidence in erythrocytes. Particularly, exposure to either CRISP or Fe-particle radiation at a low dose (0.1 Gy) did not induce a marked increase in the micronucleus incidence; however, concurrent exposure caused a significantly higher increase in the micronucleus incidence. These findings indicated that CRIPS could enhance the deleterious effects of high-LET radiation, particularly at a low dose, on the hematopoietic toxicity in Trp53-heterozygous mice.

On chip random lasing performance of the acceptor dye in a specially designed linear and zig zag array of microdroplets with intrinsic disorder

We demonstrate high-quality on chip random lasing of the acceptor dye using a specially designed dynamic linear array of microdroplets with unconventional shapes that do not support the whispering gallery modes. The intrinsic disorder in the droplet array consequent to its dynamic nature is utilized in achieving the randomness in the lasing emission without deliberately adding the disorder as in ordinary random laser systems. The novelty of the generated structure is illustrated by comparing its emission characteristics with two other arrays made of microspheres and microtriangular droplets arranged in a zig zag fashion. We show that only the linear array of microdroplets supports lasing in the acceptor emission. The design of the array structure allows to further reduce the lasing threshold drastically either by incorporating the radiative energy transfer or by tuning the number of acceptor dye molecules. The highly directional, well-controlled, and intense emission of weakly emitting dye generated on chip without the aid of conventional methods opens up a new scheme of random lasing generation mediated by microdroplets.

Engineering Radiative Energy Transfer and Directional Excitonic Emission in van der Waals Heterostructures

AbstractControlling excitonic energy transfer in 2D van der Waals (vdW) heterostructures is crucial for photonic and optoelectronic applications. Recent studies suggest that the interlayer energy transfer in vdW heterostructures is strongly correlated with the vertical interlayer spacing. However, the interlayer coupling with large separations (>20 nm) when the radiative energy transfer is dominant has not been studied yet. In this case, excitons as radiative dipole sources are able to control the light field. Here, the thickness dependency of radiative energy transfer in vertical vdW heterostructures of WS2 (tungsten disulfide)/hBN (hexagonal boron nitride)/WS2 is studied. The excitonic emission of WS2/hBN and WS2/hBN/WS2 heterostructures is engineered with the intensity ratios of heterostructures to monolayers ranging from 5% to 250%. More importantly, by changing the stacking order to control whether forward or backward emission is collected, a controllable directivity of the excitonic emission from 0.6 to 6.0 is achieved. In theory, the tunability to high‐index/mid‐index interferences and dipole–dipole far‐field coupling is attributed. The outcomes of the study on the radiative energy transfer of vdW heterostructures containing 1Ls (monolayers) with excitonic effects and MLs (multilayers) with high refractive indices will pave the way toward the realization of all vdW nanophotonics.

An SRAM SEU Cross Section Curve Physics Model

Static random access memories (SRAMs) are prone to a single-event upset (SEU), also known as soft errors, due to transient noise caused by a single strike of radiation. Beam testing has been extensively used to measure the SEU cross section of SRAMs as a function of the linear energy transfer (LET) of charged particle radiation. The evolution of the cross section as a function of LET is called the cross section curve, which plays a vital role in upset rate analysis for hardness assurance. Various analytical models have been developed to describe SRAM SEU cross-section curves, and they have proven to be useful in reducing the cost of beam testing as well as revealing the physics behind test results. However, they involve arbitrary parameters, which make it challenging to predict cross-section curves without any beam results. Moreover, the current method of analyzing cross-section curves or the LET dependence of cross sections relies on a model different from that is used in the analysis of power-supply-voltage dependence, which is becoming increasingly important because of the demand for low-power operation. To overcome these problems, this paper proposes a unified equation that describes both LET and the power-supply-voltage dependence of SRAM SEU cross sections. It comprises only parameters that are physically clear and familiar to SEU researchers. As well as giving possible constraints, comparisons with data from the literature suggest it can be applied to SRAMs fabricated in bulk and silicon-on-insulator (SOI) processes across generations from the early 1000-nm-scale to the current 10-nm-scale technology nodes.

Influence of Hydrogen Bonds and π–π Interactions on the Fluorescence of Crystalline (N-Alkylpyridyl)enamino-pyrrolo[2,3-b]quinoxalin-2-one Derivatives

This paper presents the relationship between the fluorescent properties of (E/Z)-(N-alkylpyridyl)enamino-pyrrolo[2,3-b]quinoxalin-2-one derivatives in the crystalline state and the molecular packing governed by the conformation of the molecules, hydrogen bonding, and π–π interactions. In particular, the type of 2-pyridyl alkyl chain (2-Py(CH2)n with n = 0,1,2) is responsible for the molecular packing and influences the fluorescence properties of crystalline pyrrolo[2,3-b]quinoxalines. The molecules studied exhibit permanent dipole moments that, in the crystalline phases, promote either the formation of dimers with an antiparallel orientation or stacks with a parallel dipole moment orientation. In dimers and stacks, the main observed interaction is the π–π type. The conformations of both (E)- and (Z)-enamines are stabilized by intramolecular hydrogen bonds from the NH group of the enamine to either the nitrogen atom N4 of the quinoxaline (E)-diastereoisomer or the oxygen atom of the amide carbonyl group in the (Z)-diastereoisomer. When an additional intramolecular hydrogen bond from the enamine NH group to the pyridyl nitrogen atom forms, it affects the conformation of the molecules, causing the reorientation of the molecular permanent dipole moment. Density functional theory (DFT) calculations performed for two neighboring molecules in dimers or stacks indicate two charge transfer mechanisms: intra- and intermolecular mechanisms. For centrosymmetric dimers, charge transfer occurs within each component molecule (intramolecular charge transfer). For stacks with molecules arranged by translation and noncentrosymmetric dimers, charge transfer is of an intermolecular nature. Higher absolute fluorescence quantum yields (Φf = 12.06–13.77%) are exhibited by the (E-diastereoisomers, which contain methylene or ethylene chains and form either translational stacks of the molecules or noncentrosymmetric dimers. The lowest absolute fluorescence quantum yields (Φf = 3.80–4.00%) are typical for the centrosymmetric dimers present in crystalline (Z)-(N-pyridyl)enaminopyrrolo[2,3-b]quinoxaline and (E)-(N-ethylpyridyl)enamino-pyrrolo[2,3-b]quinoxaline. The fluorescence liftimes τ were determined for single crystals of the studied phases (from 13.3 to 15.6 ns) and revealed one single process of radiative energy transfer.

Universal Theory of Light Scattering of Randomly Oriented Particles: A Fluctuational-Electrodynamics Approach for Light Transport Modeling in Disordered Nanostructures.

Disordered nanostructures are commonly encountered in many nanophotonic systems, from colloid dispersions for sensing to heterostructured photocatalysts. Randomness, however, imposes severe challenges for nanophotonics modeling, often constrained by the irregular geometry of the scatterers involved or the stochastic nature of the problem itself. In this Article, we resolve this conundrum by presenting a universal theory of averaged light scattering of randomly oriented objects. Specifically, we derive expansion-basis-independent formulas of the orientation-and-polarization-averaged absorption cross section, scattering cross section, and asymmetry parameter, for single or a collection of objects of arbitrary shape. These three parameters can be directly integrated into traditional unpolarized radiative energy transfer modeling, enabling a practical tool to predict multiple scattering and light transport in disordered nanostructured materials. Notably, the formulas of average light scattering can be derived under the principles of fluctuational electrodynamics, allowing the analogous mathematical treatment to the methods used in thermal radiation, nonequilibrium electromagnetic forces, and other associated phenomena. The proposed modeling framework is validated against optical measurements of polymer composite films with metal-oxide microcrystals. Our work may contribute to a better understanding of light–matter interactions in disordered systems, such as plasmonics for sensing and photothermal therapy, photocatalysts for water splitting and CO2 dissociation, photonic glasses for artificial structural colors, and diffuse reflectors for radiative cooling, to name just a few.

A review of atmospheric individual particle analyses: Methodologies and applications in environmental research

Aerosol ultra-fine and nano-particles are playing essential roles in the evolution of the Earth environment because of their deep connections to the chemical conversions and solar radiation energy transfer in the atmosphere, and have also become an urgent public concern in recent years due to their adverse health effects. Electron microscopes, as major tools being able to accurately identify the physical and chemical characteristics of individual particles in micron and submicron size, have been widely used in aerosol studies, although some barriers remain for their low efficiency and high cost. In this work, current understandings on the physical and chemical characteristics, mixing state and heterogeneous chemical reactions of individual aerosol particles, mainly obtained with electron microscopes, are reviewed. First, the techniques of individual particle analyses are briefly summarized and their advantages and disadvantages are discussed. Then, the morphology and composition of major atmospheric particle types obtained with these techniques and how the information was used to identify particle sources are introduced. The effects of aerosol particles on the environment, climate, human health, and global geochemical cycles are also discussed based on the data from individual particle analyses. Finally, challenges faced in individual particle studies are prospected.

Non-equilibrium radiation modeling in a gas kinetic simulation code

Radiation modeling is implemented in the highly parallel gas kinetic, open-source plasma simulation suite PICLas. A photon Monte Carlo approach for three-dimensional radiative energy transfer is developed. Since these kind of solvers have the disadvantage of high computational costs and statistical fluctuations, these points are addressed by specific adaptations to the solver. An approach to simulate axisymmetric problems is presented as well as noise reducing methods. Results are compared to a semi-infinite black body radiating cylinder, where an analytical solution is known, and a good agreement for both, three-dimensional and axisymmetric simulations is demonstrated. It is also shown that the implemented noise reducing methods can reduce statistical fluctuations. To calculate radiative properties in terms of emission and absorption coefficients, a line-by-line method is implemented and compared with good agreement to results obtained with other well-established radiation codes. The FIRE II reentry is used as a test case for a simulation combined with DSMC. Unidirectional coupling with the developed radiation modules shows good results compared to measured values as well as in performance scaling.

Development of bright orange-reddish color emitting material from Sm3+-doped Y2O3 based borosilicate glasses for solid state lighting materials

The glass having B2O3-Na2O-Y2O3-SiO2:Sm2O3 were fabricated to study its various Spectroscopic and radiative properties. For NBS-glass samples the trend for JO-parameters Ω4 > Ω2 > Ω6 except NBS-01 glass sample. The experimental (βexp) branching ratio are compared with theoretical (βcal) branching ratio and are in agreement with each other. The obtained values of the color-coordinates for NBS-Sm samples are located within orange-reddish region. The CCT-value for all NBS-Sm glasses are 1720 K. IH study suggest the dipole type of interaction between Sm3+-ions. The possible reason for this non-exponential behavior is non radiative energy transfer through resonance energy transfer between Sm3+−ions and cross relaxation between different energy levels of Sm3+-ions in NBS-glass matrix. The Study suggest the potential of NBS-Sm glass in advance display devices application emitting orange-reddish color.

Theoretical and experimental estimation of the relative optically stimulated luminescence efficiency of an optical-fiber-based BaFBr:Eu detector for swift ions

ABSTRACT The reliability of dose assessment with radiation detectors is an important feature in various fields, such as radiotherapy, radiation protection, and high-energy physics. However, many detectors irradiated by high linear energy transfer (LET) radiations exhibit decreased efficiency called the quenching effect. This quenching effect depends not only on the particle LET but also strongly on the ion species and its microscopic pattern of energy deposition. Recently, a computational method for estimating the relative efficiency of luminescence detectors has been proposed following the analysis of microdosimetric specific energy distributions simulated using the particle and heavy ion transport code system (PHITS). This study applied the model to estimate the relative optically stimulated luminescence (OSL) efficiency of BaFBr:Eu detectors. Additionally, we measured the luminescence intensity of BaFBr:Eu detectors exposed to 4He, 12C, and 20Ne ions to verify the calculated data. The model reproduced the experimental data in the cases of adopting a microdosimetric target diameter of approximately 30–50 nm. The calculated relative efficiency exhibits ion-species dependence in addition to LET. This result shows that the microdosimetric calculation from specific energy is a successful method for accurately understanding the results of OSL measurements with BaFBr:Eu detectors irradiated by various particles.

A Universal Strategy for Tunable Persistent Luminescent Materials via Radiative Energy Transfer

AbstractIn this work, a universal strategy for solid, solution, or gel state organic persistent luminescent materials via radiative energy transfer is proposed. The persistent luminescence (τ>0.7 s) could be remotely regulated between different colors by controlling the isomerization of the energy acceptor. The function relies on the simple radiative energy transfer (reabsorption) mechanism, rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. And the “apparent lifetime” for the energy acceptor is the same as the lifetime of the energy donor, which was different with a traditional radiative energy transfer process. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers a simple, feasible, and universal way to construct various persistent luminescent materials in solid, solution, and gel states.

A Universal Strategy for Tunable Persistent Luminescent Materials via Radiative Energy Transfer.

In this work, a universal strategy for solid, solution, or gel state organic persistent luminescent materials via radiative energy transfer is proposed. The persistent luminescence (τ>0.7 s) could be remotely regulated between different colors by controlling the isomerization of the energy acceptor. The function relies on the simple radiative energy transfer (reabsorption) mechanism, rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. And the "apparent lifetime" for the energy acceptor is the same as the lifetime of the energy donor, which was different with a traditional radiative energy transfer process. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers a simple, feasible, and universal way to construct various persistent luminescent materials in solid, solution, and gel states.

Luminescence photomodulation of nanospheres with CdSe/ZnS quantum dots in polymer films

The results of studies of the spectral-kinetic (absorption and fluorescent) characteristics of the polymer nanospheres created by us (containing luminescent inorganic CdSe/ZnS quantum dots and photochromic diarylethene molecules) incorporated into a polymer film are presented. A reversible modulation of the fluorescence intensity of quantum dots, caused by the photoisomerization of diarylethene molecules, was found. It is shown that nanospheres in polymer matrices exhibit higher efficiencies of both photoinduced modulation of QD radiation and Forster resonance energy transfer (FRET) from QDs to the cyclic isomer of DAE as compared to solutions. The results can be used, for example, to create luminescent photocontrolled panels based on films containing fluorescent nanoparticles. Keywords: photochromism, fluorescence, quantum dot, Forster resonance energy transfer, polymer nanospheres, polymer films

White emission of polymeric luminescent compositions doped with boron chelates

Multicomponent polymeric luminescent compositions doped with β-diketonates of boron difluoride were obtained, which can be used to produce white light by cascade radiative energy transfer. The white light is obtained by using the RGB model. The compositions containing four luminophores showed high color rendering values (color rendering index >80, 2776 K). Two luminescent transitions were realized in the obtained compositions for the red dye (R): S1-> S0, associated with cascade radiative energy transfer along the chain of luminophores, and S2-> S1->S0, directly excited by UV radiation. The luminous characteristics of the obtained compositions indicate the possibility of using polymeric luminescent compositions doped with β-diketonate boron difluoride in emergency and indoor lighting devices. Keywords: β-diketonates of boron difluoride, luminescence, polymer compositions, energy transfer, white light, illumination.