Emission Mode Research Articles

Pressure‐Promoted Self‐Trapped Exciton Emission and White‐Light Harvesting in Lead Halide Metal–Organic Frameworks at Ambient Conditions

AbstractLead halide metal−organic frameworks (MOFs) possess unique advantages in preparing single‐component white‐light‐emitting (WLE) materials due to their broadband emission based on self‐trapping excitons (STEs). However, in order to obtain high‐quality white light emission, challenges remain in adjusting and optimizing the color temperature and color coordinates of broadband STE emission. Herein, we have achieved tunable color emission and high‐quality white light emission with Commission International de l'Eclairage coordinates of (0.32, 0.38) and color temperature of 5777 K at ambient conditions in TMOF‐8(Cl) through pressure treatment. The irreversible lattice distortion after pressure treatment reduces the distance between [PbCl]+ unit and TDC2− unit. The enhanced hydrogen bonding interactions and electronic coupling between the Pb‐s orbitals and ligand energy levels turn on the charge transfer (CT) channel from [PbCl]+ unit to TDC2− unit. Adjusting the degree of lattice distortion can achieve the regulation of the relative intensity of STE and CT emission, thereby obtaining tunable color emission and high‐quality white light emission. This study provides a new perspective on the modulation of broadband STE emission in MOFs materials and a new platform for the development of high‐quality single‐component WLE materials.

Thermal emission modulation of fabrication-friendly, free-form metasurfaces via explainable deep-learning Bayesian optimization

Free-form metasurfaces with superimposed transformative meta-atoms provide a versatile platform to realize cross-band thermal emission control. However, design and manufacturing of free-form metasurfaces is extremely challenging, owing to the complex and fractal sub-wavelength topology. Here, we address these two issues by proposing an explainable deep-learning Bayesian optimization (DeepBO) framework to realize a library of fabrication-friendly, free-form metasurfaces with different light–matter interaction bandwidths. The DeepBO requires only 50 training data and is capable of screening high-dimensional design space of 1043 thermal photonic structure candidates with bandwidths from 0.3 to 3.2 eV. We unfold the black-box of deep-learning process by pattern recognition and identify the sub-space key features in the high-dimensional design space, which provides insights for thermal photonic metasurface design. We showcase the design and manufacturing of the broadband solar absorber and the narrowband thermophotovoltaic emitter with record-high spectral efficiency. The spectral selectivity of the fabricated free-form metasurface matches well with the design. The fabrication-friendly, free-form metasurfaces realized in this work can be generalized to thermal emitters for broad-ranges applications in energy and sensing.

Collective single-photon emission and energy transfer in thin-layer dielectric and plasmonic systems

Abstract We study the collective photon decay of multiple quantum emitters embedded in a thin high-index dielectric layer such as hexagonal boron nitride (hBN), with and without a metal substrate. We first explore the significant role that guided modes including surface plasmon modes play in the collective decay of identical single-photon emitters (super- and subradiance). Surprisingly, on distances relevant for collective emission, the guided or surface-plasmon modes do not always enhance the collective emission. We identify configurations with inhibition, and others with enhancement of the dipole interaction due to the guided modes. We interpret our results in terms of local and cross densities of optical states. In the same structure, we show a remarkably favorable configuration for enhanced Förster resonance energy transfer between a donor and acceptor in the dielectric layer on a metallic substrate. We compare our results to theoretical limits for energy transfer efficiency.

Quasi‐Periodic Emissions in Saturn's Magnetosphere and Their Effects on Electrons

AbstractInvestigations into quasiperiodic (QP) whistler mode emissions within Saturn's magnetosphere have uncovered distinctive characteristics of these emissions, which display a nearly periodic rising tone structure in the wave spectrogram, characterized by modulation periods of several minutes. These QP emissions are predominantly observed at low L‐shells around 5 and near the magnetic equator. Utilizing a quasi‐linear analysis framework, we evaluate the effects of these waves on the dynamics of energetic electrons. Our analysis suggests that these QP emissions can efficiently cause the loss of electrons within the energy range from 10 to 60 keV over a timescale of tens of minutes. By incorporating these findings into Fokker‐Planck simulations, we find minimal acceleration effects. This study is the first to examine QP emissions and their implications for energetic electron dynamics in Saturn's magnetosphere, highlighting their potentially significant contribution to the magnetospheric processes and dynamics.

Adding colour to ion-selective membranes.

An idea of using ion-exchanger salt containing optically active cations to prepare ion-selective membranes is proposed. Although the presence of an ion-exchanger in the composition of neutral ionophore based sensors is necessary, the choice of available salts for cation-selective sensors preparation, is usually limited to sodium or potassium compounds. In this work we propose application of an alternative salt, using a cation optically active both in absorption and emission mode as a mobile one. Thus, coloured ion-selective membranes can be obtained. This in turn opens new possibilities of monitoring the state of the receptor layer as well as allows direct analytical application of ion-selective membranes in simple optical mode with all benefits related to eliminating the necessity of using reference electrodes. As a model system Nile blue derivative of tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ion-exchanger was prepared and used to obtain potassium or calcium selective sensors. Selective exchange of ions between the membrane and solution, leading to an increase in optical signal of the solution, can be used to quantify the presence of analyte ions. Thus the sensor pretreatment process is becoming a source of analytical information. The applicability of this approach was verified in determining the presence of potassium ions in the vast majority of interfering ions, e.g. present as impurities in the reagent grade calcium chloride. The resulting potassium ions contents was well comparable with values obtained in course of ICP-MS approach.

Natural discharge of carbon from the extremely arid land: The mode and amount of CO2 emission based on earth-air exchange

Natural discharge of carbon from the extremely arid land: The mode and amount of CO2 emission based on earth-air exchange

Cylindrically bent Laue analyzer in an X-ray Raman/emission spectrometer: performance tests and a comparison with spherically bent Bragg analyzers.

The performances of a spherically bent Bragg analyzer and a cylindrically bent Laue analyzer in an X-ray Raman/emission spectrometer are compared. The reflectivity and energy resolution are evaluated from the intensity of the elastic scattering and the width of the energy distribution on a SiO2 glass sample. Widely used, Bragg analyzers display excellent performance at the photon energy E ≤ 10 keV. However, at higher E, the reflectivity and the resolution gradually deteriorate as E increases, showing poor performance above 20 keV. On the other hand, the reflectivity of the Laue analyzer gradually increases at E> 10 keV, displaying excellent reflectivity and good resolution around 20 keV. The Laue analyzer is suitable for X-ray absorption spectroscopy in high-energy-resolution fluorescence-detection mode or X-ray emission spectroscopy on 4d transition metal compounds. Furthermore, the X-ray Raman features of the lithium K-edge in LiF and the oxygen K-edge feature in H2O, measured by nine Bragg analyzers (2 m radius) at E ≃ 9.9 keV and by five Laue analyzers (1.4 m radius) at E ≃ 19.5 keV, have been compared. Similar count rates and resolutions are observed.

Shedding new light on quadrupolar 1,4-dihydropyrrolo[3,2-b]pyrroles: impact of electron-deficient scaffolds over emission.

In this work, we disclose a series of seven quadrupolar centrosymmetric 1,4-dihydropyrrolo[3,2-b]pyrroles (DHPPs) linked to the two peripheral, strongly electron-accepting heterocycles such as benzoxadiazole, benzothiadiazole and benzoselenadiazole. This represents the first study probing the influence of electron-deficient heterocycles, rather that small electron-withdrawing substituents, on photophysics of DHPPs. These new acceptor-donor-acceptor hybrid dyes exhibit an appreciable combination of photophysical properties including absorption maxima in the range of 470-620 nm, and emission in the range of 500-720 nm with fluorescence quantum yields reaching 0.88. We discovered that the presence of two 7-nitro-benzoxadiazolyl substituents at positions 2 and 5 of DHPP core, evokes a strong fluorescence in non-polar solvents shifted to 639 nm. This is the most bathochromically shifted emission for quadrupolar, centrosymmetric chromophore bearing exclusively biaryl linkages. Interestingly, 1,2,4,5-tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole (TAPP) possessing 4-benzothiadiazolyl groups is strongly emitting in the crystalline state (fluorescence quantum yield = 0.43). The combined photophysical and crystallographic studies point towards existence of intermolecular hydrogen bonds which modify the dihedral angles between the donor and acceptor moieties as a primary reason for this strong emission. Small structural alteration via the replacement of two 2,1,3-benzoxadiazole scaffolds with 2,1,3-benzoxadiazole-2-oxide moieties causes >103 decrease in the fluorescence intensity. Computational studies point out to strong charge transfer originating from exceptionally large dihedral angles as the pivotal reason of this phenomenon. Although internal conversion originating from the charge-transfer state is the prevailing non-radiative deactivation mechanism, intersystem crossing also plays a role. The rational design of DHPPs that enables modulation of emission will advance their applicability.

Detection of the Orbital Modulation of Fe Kα Fluorescence Emission in Centaurus X-3 Using the High-resolution Spectrometer Resolve on board XRISM

Detection of the Orbital Modulation of Fe Kα Fluorescence Emission in Centaurus X-3 Using the High-resolution Spectrometer Resolve on board XRISM

Luminescence Color Control Based on Inter Molecular Excited Energy Transfer Induced by Electrochromic Reaction

Electrochemical switching of luminescence color, i.e., electrofluorochromism, has received increasing attention because of its extensive applications. We have reported photo- and electrochemical- functional materials enabling dual reflective and emissive function by combining EC materials and luminescent lanthanide(III) complex. This modulation of emission is caused by control of photoexcitation energy transfer from the luminescent lanthanide(III) complex to EC material. In this study, we investigate the combination of a luminescent EC molecule and a blue luminescent molecule to achieve electrochemical control of luminescence color by controlling the energy transfer through an electrochromic reaction. We employed a functional leuco dye (Yellow-1), which shows yellow coloration and green emission by electrochemical oxidation, and 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT), which shows strong blue luminescence upon photoexcitation. Using this combination, the blue photoluminescence of the BBT molecule can be electrochemically modulated by the EC reaction of the Yellow-1 molecule, allowing the control of the luminescence color between blue and green emissions through electrochemical reactions.

Directional emission with super narrow divergence from perforated elliptical microdisk

In this work, a perforated polymeric elliptical microcavity is investigated by using the finite difference time domain (FDTD) method, highly directional laser emission with a far-field divergence angle of 2.57°, which is achieved without spoiling Q much. Further simulation analyses reveal that the far-field profile is insensitive to the deformation parameter of the hole, demonstrating the device is robust. In addition, the position of the hole and deformation parameter of the elliptical microcavity is vital for optimizing the far-field profile. Our work has provided an effective way to achieve directional whispering gallery mode emission with super narrow divergence, which will be important in integrated optics, optical communication and biochemical sensing.

Fluorescence temperature dependent behaviors of Eu3+/Mn4+ co-doping cubic and hexagonal ZnO-TiO2 compounds: Application in high sensitive optical thermometers

ZnTiO3:Eu3+,Mn4+ phosphors with hexagonal and cubic structure are synthesized by solvothermal method. The structure of ZnTiO3 depends on precursors and the annealing temperature. Inverse spinel Zn2TiO4 phase reveals the highest thermostability compared with cubic ZnTiO3 and hexagonal ZnTiO3 phases. The different phases of ZnTiO3 crystals exhibit different photoluminescence properties. The forbidden transition of 4A2g→2T2g for Mn4+ is observed in Zn2TiO4 and hexagonal ZnTiO3 (h-ZnTiO3) due to the decreased symmetry. The zero photon line (ZPL) assigned to 2Eg→4A2g transition of Mn4+ is absent in all type ZnTiO3 phases. A sharp emission peak at 714 nm assigned to ν6 (Stokes emission) mode of Mn4+ in h-ZnTiO3 is present when the temperature was below 270 K, and increases sharply in intensity with the temperature decreasing. The similar PL spectra of cubic ZnTiO3 and Zn2TiO4 co-doped with Eu3+ and Mn4+ show a wide emission band composed of Stokes and anti-Stokes modes. The calculated nephelauxetic parameter increases from 0.84 to 1.03 and 1.18 for Mn4+ in h-ZnTiO3, cubic ZnTiO3 and Zn2TiO4, respectively, indicating the covalency decreasing, which causes the red shift of ZPL in h-ZnTiO3. The Mn4+ emissions show stronger temperature dependence than that of Eu3+, especially for that in h-ZnTiO3 matrix. Based on the fluorescence intensity ratio between IEu3+ and IMn4+, the highest relative temperature sensitivity of 2.46 %K−1 is observed in cubic ZnTiO3 (c-ZnTiO3) and Zn2TiO4. Under the excitation at 550 nm, the highest relative sensitivity of 2.9 %K−1 is achieved in c- and h-ZnTiO3 mixed phases.

X-ray communication system with high-repetition-rate pulsed X-ray source and LYSO(Ce) and YAP(Ce) scintillators

X-ray communication offers significant advantages over traditional microwave methods due to its shorter wavelength and higher theoretical bandwidth, enabling efficient space communication and penetration through complex electromagnetic environments. However, current systems face limitations in X-ray emission modulation and high-precision timing detection. To meet the high-frequency transmission demands of space missions, we developed a pulsed X-ray emission source capable of high-frequency modulation. Additionally, we identified specific scintillators with distinct advantages for different transmission frequency ranges, allowing for performance optimization. Experimental results demonstrated a successful transmission rate of 10 MHz, validating the feasibility of MHz-frequency X-ray communication.

Investigation of Lamb wave modes recognition and acoustic emission source localization for steel plate based on golden jackal optimization VMD parameters and CWT

Accurate identification of Lamb wave modes in acoustic emission(AE) signals propagating on steel plates is crucial for precise source localization. In this paper, we propose a novel method that optimizes variational mode decomposition(VMD) parameters using golden jackal optimization(GJO) and identifies Lamb wave modes on steel plates through continuous wavelet transform(CWT). The Hsu-Nielsen source(HNS) is employed as the AE source. The minimum permutation entropy of the AE signal is used as the optimization objective, with GJO adaptively determining the optimal mode number (K) and penalty factor (α) for VMD. The maximum correlation coefficient method is applied to reconstruct the AE waveform, and both A0 and S0 Lamb wave modes are identified in the wavelet time–frequency domain using CWT. Furthermore, an AE source localization algorithm based on the time difference of arrival and the geometric relationship between two sensors is developed, utilizing the group velocity of the S0 mode. The proposed method effectively identifies acoustic wave modes, achieving an average relative localization error of approximately 0.48% for HNS.

Molecular Aggregation to and from Disaggregation of an Organic Emitter for Strategic Emission Modulation

Abstract“Aggregation‐caused fluorescence quenching” is a well‐established phenomenon by now. The procedure from aggregation to disaggregation usually causes a revival of emission signals, and thus affords an interesting new path to design “turn‐on” optical probes. For this purpose, the photophysics, energetics and dynamics of supra‐molecular encapsulation induced disaggregation of a self‐assembled bis‐indole derivative, 3,3’‐bisindolyl(phenyl)methane (BIPM), and its further reaggregation are reported herein. Compared to disaggregation strategies, its reverse process, reaggregation, has received much less attention so far. The gamma‐cyclodextrin (γ‐CD) molecules were found to be effective in disaggregating the BIPM associations and emission enhancement, whereas, the incorporation of guanidine hydrochloride (Gnd‐HCl) into the aqueous solution of disaggregated BIPM monomers in γ‐CD environment resulted in probe reaggregation leading to quenching of the restored emission. Here, γ‐CD and Gnd‐HCl can be considered as the molecular modulators of BIPM fluorescence based on the disaggregation–reaggregation mechanisms. The spectroscopic and thermodynamic findings associated with the disaggregation‐reaggregation processes might be insightful in reversible controlling of molecular aggregation and the associated optical properties for diverse applications.

Strain-Induced Tunable and Field-Free Spintronic THz Emitters Based on Flexible Substrate Heterostructures.

Spintronic THz emitters have been widely studied due to their advantages of broadband frequency, high efficiency, and easy fabrication. The spintronic THz signal is proportional to the magnetization of the ferromagnetic (FM) layer and requires an external magnetic field to maximize the THz signal intensity. Recently, a field-free emitter was designed based on a CoFeB/IrMn3 heterostructure via the exchange bias between two films. However, field-free spintronic THz emitters based on a common FM/nonmagnetic metal structure are rare. Here, we fabricate a tunable and field-free THz emitter with giant THz emission modulation ability based on a polyimide/CoFeB/Pt heterostructure. The THz emission can be modulated by changing the curvature radius of the polyimide substrate. After the emitter is forward bent, the THz radiation without an external magnetic field is stronger than in the flat state with a field, which we attribute to in-plane magnetic anisotropy on the FM layer induced by the tensile strain. When we curve the emitter backward, the THz intensity decreases sharply. Moreover, the modulation (ΔS/Smax) of the THz wave from the forward-curved and backward-curved emitter is over 95%, and the device shows good cyclic repeatability. We provide a novel way to design field-free spintronic THz sources, and flexible devices are promising for application in THz devices.

Design of Nanosecond Pulse Laser Diode Array Driver Circuit for LiDAR

The pulse laser emission circuit plays a crucial role as the emission unit of time-of-flight (TOF) LiDAR. This paper proposes a nanosecond-level pulse laser diode array drive circuit for LiDAR, primarily aimed at addressing the issue of high-speed scanning drive for the laser diode array at the emission end of solid-state LiDAR. Based on the single pulse laser diode drive circuit, this paper innovatively designs a circuit that includes modules such as a boost circuit, linear power supply, high-speed gate driver, GaN field-effect transistor, and pulse narrowing circuit, realizing an 8-channel laser diode array drive circuit. This circuit can achieve a pulse laser array drive with a single channel operating frequency of greater than 100 kHz, an output pulse width of less than 5 ns, a peak power greater than 75 W, and a channel switching time that does not exceed 1 μs. A field programmable gate array (FPGA) is used to control the operation of this circuit and perform a series of performance tests. Experimental results show that this circuit has a high repetition rate, large output power, a narrow pulse width, and fast switching speeds, making it highly suitable for use in the optical emission module of solid-state LiDAR.

Bias-controlled modulation for monolithic III-nitride optoelectronic integration.

III-nitride multi-quantum well (MQW) diodes can modulate the light emitted by another diode with the same MQW structure by varying the bias voltage owing to the spectral overlap between the electroluminescence spectrum and spectral responsivity curve of the MQW diodes. Here, we investigate bias-controlled modulation by monolithically integrating an optical transmitter, waveguide, electro-absorption modulator (EAM), and slot grating coupler on a silicon-based III-nitride platform using compatible fabrication processes. The modulated light is coupled into a fiber, which is direct to a photodiode for characterization. The bandwidths of forward-biased emission modulation and reverse-biased absorption modulation are of the same order of magnitude, with the latter exhibiting significant performance improvements. In addition, real-time video signal transmission was achieved using an EAM, which provides a meaningful reference for modulation applications of silicon-based GaN optoelectronic integrated systems.

The influence of structural defects on the electrical and infrared emission properties of VO2 thin films

Defect engineering is widely used in the modification of transition metal oxides. In this study, defects are introduced into the polycrystalline VO2 film by the energetic Ar ion irradiation, and the influence of structural defects on the electrical and infrared emission properties of VO2 thin films have been investigated. The decrease in electrical switching ratio with the increase of defect ratio (displacement per atom (dpa)) can be described as R10°C/R90°C=2.032×(dpa+0.005)−1.8069, while the infrared modulation performance is Δε=−0.119×ln(dpa+0.061). The dpa thresholds of the electrical switching ratio and the infrared modulation performance are ηdpaRR = 0.005/atom and ηdpaΔε = 0.0426/atom, respectively, indicating that the electrical switching ratio of VO2 films is more responsive to defects than the infrared modulation performance. The relationship between transition temperature and defect ratio has be determined. Concerning electrical properties, the heating phase transition temperature can be described as TMITHeating=25.88−10.93×ln(dpa+0.01); while for infrared emission modulation, the heating phase transition temperature is given by Tε−MITHeating=31.65−8.18×ln(dpa+0.01). While reducing the phase transition temperature, the VO2 thin films still exhibit an electrical switching ratio of more than two orders of magnitude and obvious infrared modulation performance. It not only offers a viable solution for broadening the application scope of VO2 but also contributes to understanding the role of defects in VO2 thin films for further research.

Creating respiratory pathogen-free environments in healthcare and nursing-care settings: a comprehensive review.

Hospital- and nursing-care-acquired infections are a growing problem worldwide, especially during epidemics, posing a significant threat to older adults in geriatric settings. Intense research during the COVID-19 pandemic highlighted the prominent role of aerosol transmission of pathogens. Aerosol particles can easily adsorb different airborne pathogens, carrying them for a long time. Understanding the dynamics of airborne pathogen transmission is essential for controlling the spread of many well-known pathogens, like the influenza virus, and emerging ones like SARS-CoV-2. Particles smaller than 50 to 100µm remain airborne and significantly contribute to pathogen transmission. This review explores the journey of pathogen-carrying particles from formation in the airways, through airborne travel, to deposition in the lungs. The physicochemical properties of emitted particles depend on health status and emission modes, such as breathing, speaking, singing, coughing, sneezing, playing wind instruments, and medical interventions. After emission, sedimentation and evaporation primarily determine particle fate. Lung deposition of inhaled aerosol particles can be studied through in vivo, in vitro, or in silico methods. We discuss several numerical lung models, such as the Human Respiratory Tract Model, the LUng Dose Evaluation Program software (LUDEP), the Stochastic Lung Model, and the Computational Fluid Dynamics (CFD) techniques, and real-time or post-evaluation methods for detecting and characterizing these particles. Various air purification methods, particularly filtration, are reviewed for their effectiveness in healthcare settings. In the discussion, we analyze how this knowledge can help create environments with reduced PM2.5 and pathogen levels, enhancing safety in healthcare and nursing-care settings. This is particularly crucial for protecting older adults, who are more vulnerable to infections due to weaker immune systems and the higher prevalence of chronic conditions. By implementing effective airborne pathogen control measures, we can significantly improve health outcomes in geriatric settings.