Emission Mechanism Research Articles

Toward Sustainable Non‐Emitting Asphalts: Understanding Diffusion–Adsorption Mechanisms of Hazardous Organic Compounds

AbstractAdvancing sustainable materials requires addressing their environmental impacts, particularly emissions. This study contributes to the development of sustainable, non‐emitting asphalt by providing a detailed understanding of the diffusion and adsorption behaviors of hazardous organic compounds (HOCs) emitted from asphalt. Using molecular simulations and quantum analysis, it is investigated how the diffusion and adsorption characteristics of sulfur‐ and oxygen‐containing HOCs change as aging progresses in asphalt. The results show that oxidation reduces the diffusion rate of HOCs and increases their adsorption energy. Dispersion forces and electrostatic attractions are key mechanisms stabilizing HOCs within the asphalt matrix. As oxidation progresses, hydrogen bonding and polar interactions between asphaltenes and highly polar HOCs become dominant. Among the asphalt components, asphaltenes, followed by resins, have the most significant impact on HOC binding. Additionally, non‐aromatic HOCs exhibit higher diffusion rates than aromatic HOCs. These findings provide crucial insights into the emission mechanisms of asphalt over its service life and offer guidance for designing future, sustainable, emission‐free asphalts. By reducing harmful emissions, this research contributes to pollution control, improved air quality, and the broader goal of sustainable pavement development.

Nonlinear photoexcitation processes at a MAPbBr3/GaAs heterointerface

Abstract While a significant part of the solar energy lies in the infrared range, common semiconductors cannot absorb this part of the solar irradiance by direct band-to-band transitions, because the corresponding photon energies are below the bandgap energy. Two-step photon up-conversion (TPU) is one of the processes that allows us to harvest energy in the region below the bandgap, and one possible approach to realize a TPU-based solar cell is to use an AlGaAs/GaAs heterointerface with quantum dots in order to induce additional intraband transitions. On the other hand, here we report on the TPU phenomenon at a methylammonium lead bromide/gallium arsenide (MAPbBr3/GaAs) heterointerface without quantum dots. For this heterojunction, we observed high-energy photoemission by low-energy photoinjection, demonstrating the TPU. By using photoluminescence (PL) and time-resolved PL measurement techniques, we elucidate the mechanism of the PL emission from MAPbBr3 observed from MAPbBr3/GaAs samples. Through the comparisons of the experimental PL and TRPL results between the MAPbBr3/GaAs and MAPbBr3/Glass-substrate samples, we successfully distinguish the TPU phenomenon from the ordinal two-photon absorption of MAPbBr3. Our findings in the TPU at the MAPbBr3/GaAs heterointerface may help to realize quantum-dot-free photon up-conversion solar cells.

Host-Matrix Interactions and Molecular Functionalization: Shaping the Delayed Emission Properties of Indenophenanthridine Derivatives.

The advancement of organic room temperature phosphorescence (RTP) materials has attracted considerable interest owing to their extensive applications. Their distinct advantages, including a metal-free composition, low toxicity, and facile synthesis under ambient conditions, make them highly desirable. This study examines the delayed fluorescence (DF) and RTP of metal-free, amorphous indenophenanthridine (IND)-based derivatives (1-10) and provides insights into molecular functionalisation and host matrix effects on delayed emission (RTP and DF). IND derivatives have been used in bioimaging and organic analyte detections; however, their delayed emission mechanism photophysical processes are poorly understood. This work examines the derivatives' physicochemical properties and time-resolved photophysics to determine how molecular structure, host interaction, and delayed emission properties relate. The described IND compounds show RTP and/or TTA (triplet-triplet annihilation) delayed fluorescence depending on the host environment. This research lays the groundwork for designing and developing new materials with increased RTP efficiency for future applications by detailing the detailed RTP processes and the crucial function of the host matrix.

Scalable Synthesis of 2D ErOCl with Sub-meV Narrow Emissions at Telecom Band.

Van der Waals (vdWs) materials are promising candidates for hetero-integration with silicon photonics toward miniaturization and integration. VdWs materials like molybdenum telluride and black phosphorus, despite being prominent, exhibit air sensitivity, and their room temperature emissions can be significantly broadened by tens of meV. Here, a self-encapsulation strategy is developed to scalably synthesize robust 2D vdWs ErOCl with sub-meV narrow emissions at the telecom C-band. Diverse 2D rare earth materials are also grown via chemical vapor deposition (TmOCl, YbOCl, HoOCl, DyOCl, SmOCl, NdOCl, TbOCl, GdOCl, EuOCl, and PrOCl), demonstrating the strategy's generalizability. The as-grown ErOCl exhibits high crystalline quality and excellent ambientand thermal stability (300°C). Photoluminescence analysis reveals a series of narrow emissions across the visible to near-infrared spectrum. The ErOCl's emission at the telecom band is narrowest among 2D luminescent materials, and suitable for integrating with photonic chips. Temperature-dependent photoluminescence spectra facilitate the understanding of emission mechanisms, analyzed using a crystal field perturbation model. Moreover, these emissions can be tuned by external magnetic fields. This research not only pioneers a novel strategy for synthesizing 2D rare earth materials but also paves the way for innovative building blocks in the realm of on-chip optical communications.

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Probing the transient and time-variable sky

The study of transient and variable events, including novae, active galactic nuclei, and black hole binaries, has historically been a fruitful path for elucidating the evolutionary mechanisms of our universe. The study of such events in the millimeter and submillimeter is, however, still in its infancy. Submillimeter observations probe a variety of materials, such as optically thick dust, which are hard to study in other wavelengths. Submillimeter observations are sensitive to a number of emission mechanisms, from the aforementioned cold dust, to hot free-free emission, and synchrotron emission from energetic particles. Study of these phenomena has been hampered by a lack of prompt, high sensitivity submillimeter follow-up, as well as by a lack of high-sky-coverage submillimeter surveys. In this paper, we describe how the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST) could fill in these gaps in our understanding of the transient universe. We discuss a number of science cases that would benefit from AtLAST observations, and detail how AtLAST is uniquely suited to contributing to them. In particular, AtLAST’s large field of view will enable serendipitous detections of transient events, while its anticipated ability to get on source quickly and observe simultaneously in multiple bands make it also ideally suited for transient follow-up. We make theoretical predictions for the instrumental and observatory properties required to significantly contribute to these science cases, and compare them to the projected AtLAST capabilities. Finally, we consider the unique ways in which transient science cases constrain the observational strategies of AtLAST, and make prescriptions for how AtLAST should observe in order to maximize its transient science output without impinging on other science cases.

Unusual high fluorescence of a 7,7'-diazaisoindigo derivative: A photophysical study.

7,7'-Diazaisoindigos are π-conjugated compounds but with poor luminescence properties. Their poor luminescence is generally attributed to the twisting around the central C7-C7' bond in the excited state which favors non-radiative decay. We have found an unusual high fluorescence quantum yield (ΦF ≈ 15%) in a N,N‑Octyl-7,7'-diazaisoindigo derivative incorporating two triphenylamine (TPA) subunits at 5,5'-positions (called compound 12). There are very few examples of fluorescent 7,7'-diazaisoindigos have been reported and the emission mechanism is generally associated by the hindering of the rotation around the central C7-C7' bond. Unexpectedly, 12 also experiences a twisting around the central C7-C7' bond in the excited state but is highly emissive. The intense fluorescence emission of 12 was attributed to the coexistence of two TPA-7-azaoxindole subunits acting as two fluorophores into a single molecule. The fluorescence emission of 12 is also sensitive to the polarity of the solvent. The intramolecular charge transfer character of the excited state was studied combining spectroscopic and theoretical methods.

Facile synthesis of silicon quantum dots with photoluminescence in the near-ultraviolet to violet region via wet oxidation

We report a facile wet oxidation treatment to obtain SiQDs with PL emission in the NUVV region while elucidating their emission mechanism.

Crab pulsar: IXPE observations reveal unified polarization properties in the optical and soft X-ray bands

We present a phase-dependent analysis of the polarized emission from the Crab pulsar based on three sets of observations by the Imaging X-ray Polarimetry Explorer (IXPE). We found that a phenomenological model involving a simple linear transformation of the Stokes parameters adequately describes the IXPE data. This model enabled us to establish a connection between the polarization properties of the Crab pulsar in the optical and soft X-ray bands for the first time, which suggests a common underlying emission mechanism in these bands that likely is synchrotron radiation. In particular, the phase-dependent polarization degree in X-rays for the pure pulsar emission shows similar features, but is reduced by a factor ≈(0.46 − 0.56) compared to the optical band (when we accounted for the contribution of the knot in the optical), which implies an energy-dependent polarized emission. Using this model, we also studied the polarization angle swing in the X-rays and identified a potentially variable phase shift at the interpulse relative to the optical band, alongside a phase shift that is marginally consistent with zero and persists at the main pulse. While the origin of this variability is unknown and presents a new challenge for the theoretical interpretation, our findings suggest that the emission mechanism for the main pulse is likely located far from the neutron star surface, perhaps near to or beyond the light cylinder, and that it does not operate in the inner magnetosphere, where vacuum birefringence is expected to be at work. Ignoring the phase shifts would result in identical phase-dependent polarization angles between the optical and X-ray bands for the pure pulsar emission.

Luminescent Perovskite Quantum Dots: Progress in Fabrication, Modelling and Machine Learning Approaches for Advanced Photonic and Quantum Computing Applications

Luminescent metal halide quantum dots (QDs), particularly perovskite quantum dots (PQDs), garnered remarkable attention for unique optical properties as well as critical use for advanced photonic and electronic devices. This comprehensive review explores the synthesis, properties, and applications of PQDs, with a focus on their role in luminescent metal halide QD devices. The review begins by discussing advanced synthesis techniques and surface engineering strategies for PQDs, highlighting recent developments in the field. Structural and optical characterization techniques are then examined, emphasizing the importance of understanding quantum confinement effects and emission mechanisms in PQDs. The review also includes a discussion on modelling and simulation, discussing computational methods for predicting and optimizing PQD properties. Experimental studies and device fabrication techniques are discussed in detail, showcasing the progress made in integrating PQDs into optoelectronic devices. Advanced applications of PQDs in light-emitting devices, solar cells, sensors, and photodetectors are explored, highlighting their potential for efficiency enhancements and novel functionalities. A detailed discussion on the emerging role of machine learning (ML) in PQD research, focusing on its applications in materials discovery and device optimization are also included. This review explores the potential of luminescent PQDs for quantum computing applications, focusing on their role as qubits, quantum gates, and quantum memory devices, emphasising the latest advancements, challenges, and future prospects of integrating PQDs into quantum computing architectures. The review concludes with an overview of emerging trends and future directions in the field, emphasizing the need for continued research to unlock the full potential of PQDs in advanced photonic and electronic devices.

Elucidating the mechanism behind the significant changes in photoluminescence behavior after powder compression into a tablet.

Nonconventional luminogens have great potential for applications in fields like anti-counterfeiting encryption. But so far, the photoluminescence quantum yield (PLQY) of most of these powders is still relatively low and the persistent room temperature phosphorescence (p-RTP) emission is relatively weak. To improve their PLQY and p-RTP, pressing the powder into tablets has been preliminarily proven to be an effective method, but the specific mechanism has not been fully elucidated yet. Here, D-(+)-cellobiose has been chosen as the representative to study the problem. The results showed that the PLQY and p-RTP lifetimes of the tablet of D-(+)-cellobiose were improved compared to those of the powder. Using the mechanism of clustering-triggered emission (CTE) and theoretical calculations, it has been demonstrated that the enhanced molecular interactions after compression are the key reason, which result in the formation of cluster emission centers with stronger emission capabilities. And the combination of the powder and tablet has been proven to have application potential for advanced anti-counterfeiting encryption. The above results not only provide possible references for understanding the emission mechanism of small molecules and cellulose based emission materials, but also promote the process of more intuitive observation of emission centers for explaining emission mechanisms.

Replica Symmetry Breaking Reveals the Emission Mechanism of FRET-Assisted Random Laser

Replica Symmetry Breaking Reveals the Emission Mechanism of FRET-Assisted Random Laser

Multicomponent synthesis of stereogenic-at-boron fluorophores (BOSPYR) from boronic acids, salicylaldehydes, and 2-formylpyrrole hydrazones.

This work describes one-step syntheses of various stereogenic-at-boron fluorochromes (BOSPYR) via multicomponent reactions involving readily accessible boronic acids, salicylaldehydes, and 2-formylpyrrole hydrazones. The dyes absorb and emit in the visible region of the electromagnetic radiation, and are characterized by large Stokes shifts (2850-4930 cm-1) with weak fluorescence emissions (Φfl: 1.5-9.1%). Notably, the dimmed fluorescence of BOSPYRs recovers upon transition to viscous media (21-fold for 1a). The representative compound 1a exhibits clear Cotton effects with dissymmetry factors of ca. |gabs| ∼ 1.9 × 10-3 in the visible region, indicating efficient asymmetry induction to the chromophore. The X-ray molecular structure of 1a shows that the chromophore deviates from planarity by 17.2°, which may contribute significantly to the inherent chirality of the fluorophore. A computational examination of excited states by time-dependent density functional theory (TD-DFT) identifies the emission mechanism as arising from a locally-excited (LE) state.

Are stellar embryos in Perseus radio-synchrotron emitters? Statistical data analysis with Herschel and LOFAR paving the way for the SKA

Cosmic rays (CRs) are crucial to the chemistry and physics of star-forming regions. By controlling the ionization rate of molecular gas, they mediate the interaction between matter flows and interstellar magnetic fields, thereby regulating the entire star formation process, from the diffuse interstellar medium to the formation of stellar embryos, or cores. The electronic GeV component of CRs is expected to generate nonthermal synchrotron radiation, which should be detectable at radio frequencies across multiple physical scales. However, synchrotron emission from star-forming regions in the Milky Way has barely been observed to date. In this work, we present the first attempt to statistically detect synchrotron emission with the LOw Frequency ARray (LOFAR) at 144 MHz from the nearby Perseus molecular cloud (at a distance of ∼300 pc). We perform median stacking over 353 prestellar and 132 protostellar cores derived from the Herschel Gould Belt Survey. Using data from the LOFAR two meter sky survey (LoTSS) with an angular resolution of 20arcsec, we identify 18 potential protostellar candidates and 5 prestellar ones. However, we interpret these as extragalactic contamination in the Herschel catalog. Our statistical analysis of the remaining cores does not reveal any significant radio counterpart of prestellar and protostellar cores at levels of $5, μJy beam^-1 and 8, μ$Jy beam^-1 in the stacked maps, respectively. We discuss our non-detections in two ways. For protostellar cores, we believe that strong extinction mechanisms of radio emission, such as free-free absorption and the Razin-Tsytovich effect, may be at play. For prestellar cores, using analytical models of magnetostatic-isothermal cores, the lack of detection with LOFAR helps us constrain the maximum ordered magnetic-field strength statistically attainable by these objects, on the order of 100 μG. We predict that the statistical emission of the prestellar-core sample in Perseus seen by LoTSS should be detectable in only 9 hours and 4 hours with the Square Kilometre Array-Low (SKA-Low) array assemblies AA* and AA4, respectively.

Transverse deformation waves in the non-isothermal lithosphere‒asthenosphere system

The features of the occurrence and propagation of transverse deformation waves in the elastic lithosphere – viscous asthenosphere system under non-isothermal conditions are studied in the approximation of a thin layer. In this case, the phase transition at the boundary of the layers, due to temperature and pressure disturbances, plays an essential role. The qualitative and quantitative properties of propagation of disturbances of thermomechanical fields have been studied in the long-wave approximation. It is shown that due to the energy supply from the non-isothermal asthenosphere, weakly attenuated wave packets can occur, which spread over thousands of km with a characteristic speed of about 100 km/year. This allows them to be considered as a possible trigger mechanism for the massive emission of methane from frozen sedimentary rocks into the atmosphere.

Mechanisms of N2O Emission in Drip-Irrigated Saline Soils: Unraveling the Role of Soil Moisture Variation in Nitrification and Denitrification

Drip irrigation generates structural bodies in soil, forming layered structures with moisture content gradients. There are four typical soil moisture characteristic values in this concentric structure as saturation capacity (θs), field capacity (FC), 60% field capacity (60% FC), and 30% field capacity (30% FC). In this study, we simulated these four soil water characteristic values to conduct an indoor soil incubation experiment under three different incubation conditions: aerobic (O), aerobic with 10 pa acetylene (OC), and anaerobic (AO). The results indicate that in soil with saturated water content, denitrification under aerobic conditions leads to high N2O emissions; in soil at field holding capacity, nitrification under aerobic conditions dominates low N2O emissions, which is most conducive to N2O reduction and greenhouse gas emission mitigation; in soil with 60% of field holding capacity, denitrification under anaerobic conditions leads to high N2O emissions; and in soil with 30% of field holding capacity, microbial activity decreases, inhibiting nitrification, denitrification, and N2O emissions. Our research has found that when conducting aerobic drip irrigation in soil at field capacity (FC), denitrification was reduced by 99%, nitrification was increased by 70%, and microbial activity was enhanced by 5%. Therefore, during drip irrigation, the position and flow rate of the dripper should be controlled to reduce soil water saturation areas, maintain soil aeration, control soil moisture content below field holding capacity, promote the nitrification process, reduce N2O emissions, and improve soil nitrogen use efficiency. Our study elucidates the characteristics of nitrogen transformation and N2O emissions across various soil moisture contents within the soil water structure under drip irrigation conditions, providing a scientific basis for the formulation of precise irrigation management practices and strategies for efficient soil nitrogen utilization.

Multiwavelength Afterglow Analysis of GRB 221009A: Unveiling the Evolution of a Cooling Break in a Wind-like Medium

Abstract Gamma-ray bursts (GRBs) are the most energetic explosions in the Universe, and their afterglow emission provides an opportunity to probe the physics of relativistic shock waves in an extreme environment. Several key pieces for completing the picture of GRB afterglow physics are still missing, including jet properties, the emission mechanism, and particle acceleration. Here, we present a study of the afterglow emission of GRB 221009A, the most energetic GRB ever observed. Using optical, X-ray, and gamma-ray data up to approximately 2 days after the trigger, we trace the evolution of the multiwavelength spectrum and the physical parameters behind the emission process. The broadband spectrum is consistent with the synchrotron emission emitted by relativistic electrons with its index of p = 2.29 ± 0.02. We identify a break energy at keV and an exponential cutoff at GeV in the observed multiwavelength spectrum. The break energy increases in time from 16.0 − 4.9 + 7.1 keV at 0.65 days to 46.8 − 15.5 + 25.0 keV at 1.68 days, favoring a stellar-wind-like profile of the circumburst medium with k = 2.4 ± 0.1 as in ρ(r) ∝ r −k . The high-energy attenuation at around 0.4 to 4 GeV is attributed to the maximum of the particle acceleration in the relativistic shock wave. This study confirms that the synchrotron process can explain the multiwavelength afterglow emission and its evolution.

Effect of the buffer layer on the energy storage performance of Pb0.97La0.02Zr0.5Sn0.5O3 thin film

Lead thin film capacitors with high energy storage performance have attracted increasing interest in their applications in modern devices. In this study, the energy storage performances of Pb0.95La0.02(Zr0.5Sn0.5)O3 antiferroelectric thin films were enhanced by incorporating Al2O3 and HfO2 buffer layers. The electrical properties and energy storage characteristics of antiferroelectric thin films with different buffer layers were analyzed to study the impact of buffer layers on energy storage performance. After the incorporation of Al2O3 and HfO2 buffer layers, the breakdown field strength (Eb) of the films were significantly increased and the leakage current densities were greatly reduced with the ohmic conduction range widened at low electric fields. As a result, the energy storage density of films with Al2O3 and HfO2 buffer layers increased significantly from 10.07 to 31.54 and 22.63 J/cm3, respectively. By analyzing the leakage current, it was found that the Poole–Frenkel emission was significantly suppressed by the Al2O3 buffer layer, while the HfO2 buffer layer had a limited effect on the conduction mechanisms, which resulted in the better energy storage performance of those films with Al2O3 buffer layers. The results demonstrate that the improvement of energy storage performance is attributed to the leakage current emission mechanism affected by the buffer layer.

Intrinsic Multicolor Emissive Aliphatic Linear Polyphosphate Esters From the Charge-Transfer-Induced Enhanced Spatial Electronic Communication.

Unconventional fluorescent polymers are attracting increasing attention because of their excellent biocompatibility and wide applications. However, these polymers typically exhibit weak long-wavelength emission. Herein, three novel aliphatic linear polyphosphate esters are prepared via a one-pot polycondensation reaction. Such polymers can generate strong blue, green, yellow, and red fluorescence under different excitations. Experimental and theoretical results showed that the cluster of C═C and phosphate ester groups attracted the negative charge of isolated functional groups, and the alkane chains and hydrogen atoms also provided a negative charge for spatial electronic communication. Then, intrinsic fluorescence arises from the charge-transfer-induced enhanced spatial electronic communication. Additionally, these polymers show potential applications in fluorescence film, ion detection, bacteria imaging, and visualization of the NaCl crystallization process. This work provides a universal design strategy for developing strong long-wavelength emissive polymers and gains new insight into intrinsic emission mechanisms.

An Energy-Tunable Dual Emission Mechanism of the Hybridized Local and Charge Transfer (HLCT) and the Excited State Conjugation Enhancement (ESCE).

Molecular design of dual-fluorescent probes requires precise adjustment of the energy levels of two excited states and the energy barrier between them. While the hybridized local and charge-transfer (HLCT) state has been recently focused as an important excited state for high emission efficiency with a tunable energy level, a dual emission involving the HLCT state has been only achieved with the excited-state intramolecular proton transfer (ESIPT) system. Here, a series of dual-fluorescent molecules involving an HLCT excited state with the excited-state conjugation enhancement (ESCE) motif is presented as the first case. The energy level of the HLCT state has been adjusted by changing substituents and solvents, separately from the ESCE energy level. The HLCT-ESCE molecular design with tunable fluorescence properties proposes a new strategy for the development of advanced fluorescent probes.

The LimPa mission: a small mission proposal to characterize the enigmatic lunar dust exosphere

The lunar environment is known to be characterized by complex interactions between plasma, the exosphere, dust, and the surface. However, our understanding of the environment is limited due to the lack of experimental evidence. Here, we propose a small, low-cost mission to characterize the dust and exosphere environment of the Moon. Named the Limb Pathfinder (LimPa), this is a proof-of-concept mission aimed toward understanding the coupling between plasma, dust, and tenuous neutral atmosphere. The LimPa mission was proposed to a call for the Small Mission to the Moon issued by European Space Agency in 2023. LimPa is designed to examine the dust exosphere above the lunar polar regions by using an utterly novel remote-sensing technique to measure the solar wind hydrogen atoms—the solar wind protons that are neutralized to hydrogen atoms. Its goals are (1) to detect for the first time the neutralized solar wind hydrogen produced by exospheric gas and levitated dust; (2) to measure the height profiles of the levitated dust and exospheric gas densities; and (3) to determine the emission mechanism of the horizon glow. Our baseline design of the LimPa mission is a 12U CubeSat. Three highly matured instruments are used: an energetic neutral atom camera, a proton sensor, and a camera system. The LimPa CubeSat is proposed to be inserted into a circular lunar polar orbit, with an altitude of 100 km as a baseline. The Sun-pointing attitude will allow measurements of neutralized solar wind that are produced by the exosphere and dust grains above the polar regions. The nominal lifetime is for 3 months as a pathfinder mission. The LimPa mission will open a new window to remote characterization of the lunar dust exosphere environment above the poles, and will demonstrate that this monitoring can be achieved with a simple and low-cost instrument system and spacecraft operation. The concept to be proven by the LimPa mission will enable long-term monitoring of the fragile dust exosphere environment, which substantially impacts on lunar exploration and will be significantly altered by human activities.Graphical abstract