Emission Spectra Research Articles

A two-dimensional thin film structure with spectral selective emission capability suitable for high-temperature environments

Spectral selective emission materials, characterized by their high emission efficiency within specific wavelength ranges, play a crucial role in various fields such as infrared stealth and radiative cooling. In this study, leveraging the tunneling effect of ultrathin metal layers and the impedance matching principle, we designed a one-dimensional multilayer thin film structure composed of Mo/Ge/Al. This design successfully achieved spectral selective emission within the 3-14 μm infrared spectrum range, showcasing superior high-temperature infrared stealth capabilities. Research findings indicate that the infrared atmospheric window (ε3-5 μm=0.40, ε8-14 μm=0.30) maintains a low emissivity within the temperature range from room temperature to 400°C, while high emissivity in non-infrared atmospheric windows (ε5-8 μm=0.81) enables radiative cooling. The use of high emissivity in the non-infrared atmospheric window reduced the surface temperature of this structure by 15.3°C compared to untreated Si substrate under similar heating conditions. The temperature reduction was 34.1°C when compared to a Si substrate coated with a 200 nm Al film. This straightforward and easily scalable structure not only presents novel solutions for applications in infrared stealth and radiative cooling but also holds vast potential for diverse fields including military, aerospace, and industrial manufacturing, injecting fresh impetus and possibilities into technological advancement.

Luminescent color modulation of Zn/BaAl2O4:0.2%Eu phosphors for LED application

Spinel-type aluminate (ZnAl2O4) doped with europium (Eu) ions has garnered considerable attention in the field of luminescence. This study explores a series of Zn/BaAl2O4:0.2%Eu phosphors (x=0∼0.25, x is for the mole fraction of BaAl2O4), fabricated through a high temperature solid-phase reaction method in air or reduction environment. In the case of phosphors synthesized in air, the photoluminescence emission (PL) spectra show a series of sharp emission peaks at 570nm, 589nm, 620nm, 660nm, and 710nm, which are generated by the 5D0-7FJ (J = 0, 1, 2, 3, 4) level transitions in Eu3+. Time-resolved photoluminescence and X-ray photoelectron spectroscopy (XPS) characteristics also validate the presence of Eu3+ in samples synthesized in air. An intriguing observation is the abnormally strong emission peak at 570nm under 346nm excitation, originating from the Eu3+5D0-7F0 level transition. For x=0.15, the corresponding CIE color coordinate is (0.3246, 0.3449), suggesting its potential application as a mono-doped and uni-matrix white phosphor. On the other hand, phosphors synthesized in reduction environment exhibit PL spectra with a wide emission band spanning from 400nm to 550nm, resulting from the electric-dipole-allowed transition of f-d state of Eu2+. The partial substitution of Zn2+ with Ba2+ significantly enhances the Eu2+ luminescence intensity. Moreover, an elevation of the mole fraction of Zn/BaAl2O4:0.2%Eu leads to a notable redshift (450nm→500nm) in the emission peaks of Eu2+ caused by lattice expansion, providing the adjustability of emitting color.

Research on multicolor luminescence, structural and energy transfer in Dy/Eu co-doped fluoroborate glasses for W-LEDs

The composition of 50B2O3-20Al2O3-5Na2O-10Bi2O3-15CaF2-xDy-yEu (x = 0.1，0.5，1.0，1.5，2.0，3.0 mol%; y = 0, 0.1, 0.3, 0.5, 0.7, 1.0 mol%) (BACDE) glass were prepared using the traditional melt quenching process. The structure of the BACDE glass was analyzed using XRD analysis and Fourier infrared spectroscopy. The photoluminescence spectra show that concentration quenching occurs when Dy concentration is higher than 1.0mol% in fluoroborate glass. By varying the excitation circumstances and obtaining emission spectra at three distinct excitation wavelengths (364, 382, and 395 nm), the luminescence characteristics of BACDE glass were examined. The results indicate that when excited at 364 nm, the luminescence of the BACDE glass is close to the white region, a controlled color shift is achieved within a certain range. The spectral superposition and fluorescence attenuation spectra of Dy3+ emission and Eu3+ absorption demonstrate the energy transfer from Dy3+ to Eu3+, and the main transfer mechanism is the electric dipole-electric dipole interaction. The most optimal chromaticity coordinates for the BACDE glass samples were (0.3832,0.3858), (0.3672,0.3949), with a color temperature (CCT) of approximately 3992K at 364 nm excitation. By controlling the Dy/Eu content, BACDE glass can exhibit warm white, and light reddish-orange glow. Thus, Eu3+/Dy3+ co-doped BACDE glasses have potential applications in white luminescent materials and dimmable materials.

Preparation of fluorescent carbon dots by flow-assisted melt polymerization for tetracycline detection in medical wastewater

Tetracycline (TC) is one of the most important therapeutic drugs that is widely used in hospitals. However, its harmful effects on human health and various ecosystems cannot be ignored. Owing to its poor metabolic activity and low biodegradability, TC commonly discharges as the parent compound and accumulates readily in sludges and soils by precipitation from wastewater, which can induce the evolution of antibiotic-resistant bacteria; therefore, it has been listed as one of the new pollutants with potential ecotoxicological risk. The control measures and environmental management of TC pollutants in environmental water samples require precise determination of TC pollutant concentrations. Carbon dots (CDs) are an emerging type of fluorescent material with numerous advantages such as easy preparation, low cost, low toxicity, and good biocompatibility. Consequently, they have attracted widespread attention in the field of TC detection. Herein, we synthesized TE-CDs with good blue-fluorescence performance via flow-assisted melt polymerization using tricarboxylic acid and ethylenediamine as raw precursors. The morphology and structure of the prepared TE-CDs were characterized. The transmission electron microscopy (TEM) results showed that the prepared TE-CDs were well dispersed, with an average diameter of (2.43±0.48) nm. The X-ray diffraction (XRD) results showed that the TE-CDs had an amorphous carbon structure. Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations showed that the surface of the TE-CDs was rich in hydrophilic groups, such as amino, hydroxyl, and carboxyl groups, which indicated that TE-CDs had good water solubility and were advantageous for detecting TC in medical wastewater. Subsequently, the optical properties of the TE-CDs were investigated. The fluorescence emission spectra of the TE-CDs were recorded at various excitation wavelengths. The emission spectra of the TE-CDs exhibited excitation wavelength dependence and when the excitation wavelength changes from 300 nm to 400 nm, their fluorescence intensity decreased to varying degrees. The TE-CDs exhibited optimal fluorescence intensity at an excitation wavelength of 368 nm, while the emission wavelength was 448 nm. TC could effectively quench the blue fluorescence of the CDs, and by utilizing this property, the detection of TC concentration could be achieved. After the addition of TC, the fluorescence of the system immediately reached an extreme value, and no significant change was observed within 10 min. An incubation time of 20 s was selected to obtain precise results. Additionally, the TE-CDs exhibited stable fluorescence intensity over a wide pH range. The fluorescence stability of the TE-CDs was investigated, and no significant change in fluorescence intensity was observed after standing for 10 d, indicating that the prepared TE-CDs had excellent fluorescence stability. The fluorescence intensity of the TE-CDs decreased to varying degrees within the range of 2-200 mg/L TC until complete quenching occurred. TC mass concentration in the range of 4-20 mg/L showed a good linear relationship (R2=0.9978) with the fluorescence quenching intensity of the TE-CDs. The limit of detection was 0.2 mg/L. A preliminary investigation was undertaken to explore the quenching mechanism of the TE-CDs fluorescence by TC. Upon addition of TC, a significant reduction in the fluorescence lifetime of the TE-CDs was observed. During the quenching process, no new substances were observed by UV absorption spectroscopy. Additionally, no significant changes in the 1H NMR spectra of the TE-CDs were noted before and after the addition of TC, indicating the absence of an interaction between the TE-CDs and TC. Therefore, the quenching mechanism may involve dynamic quenching. The selectivity and anti-interference ability of the developed method were evaluated; in the presence of interfering substances, TC quenched the fluorescence of the TE-CDs, indicating that the TE-CDs had good selectivity and anti-interference performance towards TC. The method was applied to the quantitative detection of TC in medical wastewater, with recoveries of 96.5%-119.8% and relative standard deviations of 0.8%-2.6%. In conclusion, the analytical performance of the proposed method is comparable with that of previously reported detection methods; moreover, the method has the advantages of low operational cost, simple preparation process, time-saving, and good repeatability. Therefore, the TE-CDs can be used as chemical sensors for the detection of TC in medical wastewater and have good practical applications.

Computational chemistry facilitates the development of second near-infrared xanthene-based dyes.

The dyes in the second near-infrared (NIR-II) region play a crucial role in advancing imaging technology. However, developing small-molecule dyes in NIR-II poses a significant bottleneck to meet the substantial demands in biological fields, which may be attributed to the lack of a rational design strategy. Herein, we designed a series of rhodamine analogs with more red-shifted emission by replacing the oxygen-bridge atom in xanthene-based dyes with -C(CH3)2, -Si(CH3)2, -SO2, and -P(O)Ph. We investigated the frontier molecular orbital, electrostatic potential surfaces, the interaction region indicator, electron-hole distribution, and absorption and emission spectrum of xanthene-based dyes using (time-dependent) density functional theory. Our results demonstrated that these designed small molecular dyes exhibit long emission wavelengths covering 1377-1809nm. We expected these findings to enable the targeted design of long-wavelength rhodamines. Geometry optimization of dyes in the ground and excited states was carried out at ω-B97XD/Def2SVP level using Gaussian 16 A03. The absorption and emission wavelengths were evaluated using 13 functional, including TPSSH, O3LYP, B3LYP*, B3LYP, PBE0, MPW1B95, PBE-1/3, PBE38, MPWB1K, MN15, BHandHLYP, ω-B97XD, and CAM-B3LYP.

Dual metal-organic-frameworks mediated resonance energy transfer for ultrasensitive electrochemiluminescence immunosensing.

Anelectrochemiluminescence (ECL) biosensor for carcinoembryonic antigen (CEA) based on electrochemiluminescence resonance energy transfer (ECL-RET) was designed. Tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) was used as an energy donor for ECL-RET, and an Au nanoparticle-modified MOF framework (AuCoFe MOF) was used as an energy receptor for ECL-RET. The ECL emission spectra of Ru(bpy)32+ were in the range 550 to 680nm, and a zinc oxalate MOF encapsulating Ru(bpy)32+ (Ru@ Zn oxalate MOF) was prepared. The UV-vis absorption spectrum of AuCoFe MOF ranges from 280 to 700nm and overlaps with emission spectra of Ru@Zn oxalate MOF, which is critical for RET. The AuCoFe MOF-Ab2 bioconjugate, target CEA antigen, and the Ru@Zn oxalate MOF-Ab1 bioconjugate together form a sandwich structure, resulting in quenching of the ECL signal of Ru@Zn oxalate MOF by AuCoFe MOF. Under the optimized experimental conditions, the ECL-RET sensor exhibited excellent analytical performance in CEA detection with a linear range of 1.0 × 10-13 to 1.0 × 10-8mgmL-1; the minimum limit of detection is 1.4 × 10-14mgmL-1 (S/N = 3); and its recoveries of spiked samples ranging from 99.1 to 100.7%. The developed sensor has excellent stability, reproducibility, and specificity and is suitable for the detection of CEA in human serum and has the potential to provide sensitive detection of other biomarkers of diseases.

Assessing methods for telluric removal on atmospheric retrievals of high-resolution optical exoplanetary transmission spectra

Recent advancements in ultra-stable ground-based high-resolution spectrographs have propelled ground-based astronomy to the forefront of exoplanet detection and characterisation. However, the resultant transmission and emission spectra of exoplanetary atmospheres are inevitably contaminated by telluric absorption and emission lines due to the light's transmission through the Earth's atmosphere above the observatory. Retrieving accurate atmospheric parameters depends on accurate modelling and removal of this telluric contamination while preserving the faint underlying exoplanet signal. There exist many methods to model telluric contamination, whether directly modelling the Earth's transmission spectrum via radiative transfer modelling, or using a principal component analysis (PCA)-like reconstruction to fit the time-invariant features of a spectrum, and removing these models from the observations. We aimed to assess the efficacy of these various telluric removal methods in preserving the underlying exoplanetary spectra. We compared two of the most common telluric modelling and removal methods molecfit and the PCA-like algorithm SysRem using planetary transmission spectra injected into three high-resolution optical observations taken with ESPRESSO. These planetary signals were injected at orbital periods of P = 2 days and P = 12 days, resulting in differing changes in radial velocity during transit. We then retrieved various injected atmospheric model parameters in order to determine the efficacy of the telluric removal methods, as well as their effect on the transmission spectra of exoplanets with varying orbital architectures. For the close-in, high velocity injected signal, we found that SysRem performed better for species that are also present in the Earth's atmosphere--with accurate and precise retrieval of atmospheric abundances and $T$-$P$ profiles, across each of the datasets. As we moved to slower moving signals at larger orbital separations, for one of the three datasets SysRem dampened the planetary H$_2$O signal, leaving the retrieved abundance value unconstrained. In contrast, the H$_2$O signal was preserved for the telluric modelling method molecfit . However, this behaviour was not ubiquitous across all three of the injected datasets, with another dataset showing a more precise H$_2$O/Fe ratio when preprocessed with SysRem . These conflicts highlight the importance of testing individual high-resolution dataset reduction routines independently to ensure real exoplanetary signals are preserved.

High-sensitivity multi-gas detection using dual-ridge metasurface emitters with polarization-distinguishable emission spectra

The metasurface thermal emitter offers an energy-efficient, compact, and sensitive solution as a radiation source for non-contact gas detection, enabling the “molecular fingerprint” technique to be widely applied, from medical diagnostics to environmental monitoring. However, most narrowband emitters are designed for a single target gas, hindering the miniaturization of multi-gas detection systems. In this work, a one-dimensional dual-ridge grating emitter is employed, achieving dual-band and tri-band polarization-distinguishable emission spectra through the excitation of Fabry-Perot (FP) resonances and quasi-bound states in the continuum (qBICs). These emission spectra can be readily matched to multiple non-overlapping absorption peaks of gases such as CH4, CO2, CO, NO, and NH3 within the 3–6 µm range, thereby reducing the impact of mixed gases on measurements. Compared to conventional metal-dielectric-metal structures, the use of a single metal layer results in lower material losses, enabling higher Q-factors and more pronounced directional radiation intensity variations. Furthermore, adjusting the asymmetry to modulate the qBIC-excited absorption peaks does not affect the Q-factor of the FP resonance absorption, thus achieving high-sensitivity multi-band gas detection. This work provides a promising approach for the miniaturization and integration of multi-gas channel detection, facilitating more accurate and sensitive sensing strategies.

Gan Photonic Crystals: Spectral Dynamics in UV, X‐Ray, and Alpha Radiation

In this work, a comparative analysis of gallium nitride (GaN) thin films is conducted, both with and without photonic crystal (PhC) structures, focusing on their scintillation and photoluminescence properties. GaN's suitability for diverse optoelectronic and radiation detection applications is analyzed, and this study examines how PhC implementation can enhance these properties. Methodologically, the emission spectra is analyzed from 5.9 keV X‐ray sources, decay curves, pulse height spectra in response to 241Am 5.5 MeV alpha‐rays, and photoluminescence spectra induced by UV excitation. The findings demonstrate a substantial increase in quantum efficiency for PhC GaN, nearly tripling the light yield that of conventional plain GaN thin films under the UV excitation. The enhancement is predominantly attributed to the PhC GaN's proficiency in guiding light at 550 nm, a feature indicative of its spectral filtering capabilities, as detailed in the study. Furthermore, side‐band scintillations, stemming from inherent materials like Chromium that generate scintillations at diverse wavelengths, are effectively mitigated. A key finding of this study is the effective detection of light not only at the rear but also along the lateral sides of the films, offering new possibilities for radiation detector design and architecture.

A Novel Carbon Dot-Bromothymol Blue System for Ratiometric Colorimetric-Fluorometric Sensing of Glutathione in Urine: A Smartphone-Compatible Approach.

This study presents a novel dual-modal approach for glutathione (GSH) detection using blue and yellow dual-emission carbon dots (BY-CDs) and bromothymol blue (BTB) at pH 8.0. The method employs both colorimetric and fluorometric detection modes, offering a new perspective on GSH quantification. BTB's blue coloration induces selective fluorescence quenching of the CDs' 610nm emission peak, with minimal effect on the 445nm peak. Upon GSH addition, the quinonoid structure (blue color) of BTB transforms to its benzenoid form (yellow color). This transformation triggers fluorescence restoration at 610nm and significant quenching at 445nm, enabling ratiometric fluorescence analysis (F610/F445). Concurrently, colorimetric detection is also ratiometric, based on measuring the ratio between the emerging yellow color peak (435nm) and the decreasing blue color peak (618nm) (A435/A618). The state-of-the-art aspect of this detection method lies in the strategic choice of dual-emission CDs and a dye with distinct absorption spectra that closely match the emission spectra of the CDs. This unique combination allows for dual detection with opposite responses in the two detection modes, enhancing selectivity and reliability. The probe was thoroughly characterized, and its detection mechanism was elucidated using various spectroscopic techniques. The method shows excellent linearity, a broad detection range, and low detection limits for both fluorometry (0.02 - 10.0μM, 5.88nM) and colorimetry (1.0 - 35.0μM, 301.25nM). Additionally, a smartphone-based platform was developed for colorimetric GSH determination, enhancing the method's potential for on-site analysis. The assay's practicality was validated through successful application to human urine samples, yielding excellent recovery values (97.33% to 99.13%).

Spectrum Broadening Due to Nonselective Linear Absorption

The position and linewidth of an emission spectrum reflect the physical properties of the luminophor. So, keeping the spectrum from distortion is very important in its measurement. However, we find that the spectrum linewidth will be broadened when the near-infrared radiation from a sodium lamp passes through a nonselective linear absorbing filter. This counterintuitive linewidth-broadening phenomenon is obvious when the residual light power after the filter is low enough, typically lower than 2.48×10−4 μW. This novel linewidth-broadening effect is different from the well-known Lorentzian, Doppler, and Voigt broadening, and is likely to be more independent evidence of the discrete wavelet structure of classical plane light waves. The effect is significant in high-sensitivity spectroscopy measurements, for example streak camera spectroscopy and Raman spectroscopy experiments. In addition, this effect may also be significant for cosmological research.

Impact of Carbon Tax on Renewable Energy Development and Environmental–Economic Synergies

Global warming caused by greenhouse gas emissions has become a worldwide environmental problem, posing a great threat to human survival. As the world’s largest emitter of carbon dioxide, China has pledged to reach peak carbon emissions by no later than 2030 and carbon neutrality by 2060. It is found that a carbon tax is a powerful incentive to reduce carbon emissions and promote an energy revolution, but it may have negative socio-economic impacts. Therefore, based on China’s 2020 input–output table, this paper systematically investigates the impacts of a carbon tax on China’s economy, carbon emissions, and energy by applying a computable general equilibrium model to determine the ideal equilibrium between socio-economic and environmental objectives. Based on energy use characteristics, we subdivided the energy sector into five major sectors: coal, oil, natural gas, thermal power generation, and clean power. The results show that when the carbon emission reduction target is less than 15%, that is, when the equilibrium carbon tax price is less than 54 yuan/ton, the implementation of a carbon tax policy can significantly reduce carbon emission and fossil fuel energy consumption, while only slightly reducing economic growth rate, and can achieve the double dividend of environment and economy. Moreover, because the reduction of coal consumption has the greatest impact on reducing carbon emissions, the ad valorem tax rate on coal after the carbon tax is imposed is the highest because coal has the highest carbon emission coefficient among fossil fuels. In addition, as an emerging clean energy source, hydrogen energy is the ideal energy storage medium for achieving clean power generation in power systems. If hydrogen energy can be vigorously developed, it is expected to greatly accelerate the deep decarbonization of power, industry, transportation, construction, and other fields.

On the in-situ determination of the effective secondary electron emission coefficient in low pressure capacitively coupled radio frequency discharges based on the electrical asymmetry effect

Abstract We present a method for the in-situ determination of the effective secondary electron emission coefficient (SEEC, γ) in a capacitively coupled plasma (CCP) source based on the γ-dependence of the DC self-bias voltage that develops over the plasma due to the Electrical Asymmetry Effect (EAE). The EAE is established via the simultaneous application of two consecutive radio-frequency harmonics (with a varied phase angle) for the excitation of the discharge. Following the measurement of the DC self-bias voltage experimentally, Particle-in-Cell/Monte Carlo Collision (PIC/MCC) simulations coupled with a diffusion-reaction-radiation (DRR) code to compute the argon atomic excited level dynamics are conducted with a sequence of SEEC values. The actual γ for the given discharge operating conditions is found by searching for the best match between the experimental and computed values of the DC self-bias voltage. The γ ≈ 0.07 values obtained this way are in agreement with typical literature data for the working gas of argon and the electrode material of stainless steel in the CCP source. The method can be applied for a wider range of conditions, as well as for different electrode materials and gases to reveal the effective SEEC for various physical settings and discharge operating conditions.

Molecular and Clinical Characterization of a Cohort of Autosomal Recessive Sensorineural Hearing Loss in Egyptian Patients

Hearing loss (HL) is one of the most common health problems worldwide. Autosomal recessive non-syndromic sensorineural hearing loss (ARNSHL) represents a large portion of congenital hereditary HL. Our study was conducted on 13 patients from 13 unrelated families. The majority of patients presented with congenital severe to profound bilateral sensorineural HL. All patients were subjected to detailed family history and three-generation pedigree analysis to exclude any environmental cause and to ensure an autosomal recessive mode of inheritance. Molecular analysis was performed using the whole exome sequencing (WES) technique for the recruited patients. Three variants in the MYO7A and OTOF genes were reported for the first time in patients with ARNSHL (one nonsense, one frameshift, and one splice variant). Ten previously reported variants were detected in seven genes (GJB2, MYO15A, BSND, OTOF, CDH23, SLC26A4, and TMIE). They varied between missense, nonsense, frameshift, and splice variants. This study expands the molecular spectrum of two types of autosomal recessive deafness (types 2 and 9).

Influence of Hydrogen Additive on Electrophysical Parameters and Emission Spectra of Tetrafluoromethane Plasma

The influence of the addition of hydrogen on the electrophysical parameters and emission spectra of tetrafluoromethane under conditions of a direct current glow discharge has been studied. It has been established that gas temperature changes nonlinearly with increasing proportion of hydrogen in the plasma-forming mixture. The emission spectra of tetrafluoromethane plasma with hydrogen were obtained and analyzed. It is shown that plasma radiation is represented by atomic and molecular components, and the dependences of the line radiation intensities on the external conditions of the discharge are determined by the excitation of emitting states during direct electron impacts.

An adaptive prediction method for carbon emissions of power systems containing new energy based on least-squares support vector machine

Aiming at the problem of high volatility and intermittency of new energy-containing power systems, which affects the prediction accuracy of carbon emissions, we study the adaptive prediction method of carbon emissions of a new energy-containing power system based on a least-squares support vector machine. The carbon emission coefficients of the nodes of the new energy-containing power system are determined based on the trend analysis method. Historical carbon emissions and carbon emission coefficients of the power system are collected, and the rough set method is used to simplify the carbon emission attributes and obtain a simplified attribute set for carbon emission prediction. The least-squares support vector mechanism is used to construct the carbon emission prediction model, and the simplified attribute set is used as the input of the carbon emission prediction model. The whale optimization algorithm was selected to determine the optimal parameters of the least-squares support vector machine through the process of encircling prey, hunting behavior, searching for predation, and adaptively optimizing the least-squares support vector machine to output carbon emission prediction results. The experimental results show that the method can accurately predict the carbon emissions of the power system, and the mean square error of the carbon emissions prediction is lower than 7.

Donor-Acceptor-Donor Dyads with Electron-Rich π-Extended Azahelicenes to Panchromatic Absorbing Dyes.

Panchromatic dyes have been highly useful in the realm of optical devices. Here, we report that panchromatic dyes with heterohelicenes have been successfully synthesized using a donor-acceptor strategy. Our synthesis resulted in the creation of π-extended aza[5]helicene oligomers with butadiyne linkages, which displayed bathochromically shifted absorption and emission spectra. The solvent-dependent optical measurements revealed the intramolecular charge transfer characteristic of these molecules, and theoretical calculations described the biased molecular orbitals on the azahelicene units that generated the charge-transfer characteristic. Encouraged by these results, we also prepared donor-acceptor-donor dyads using azahelicenes and dimide derivatives, resulting in panchromatic absorbing characteristics covering the range from 250 nm to 800 nm. Theoretical calculations showed the presence of mixed charge-transfer transitions and localized transitions on the azahelicene units, which led to a broad light-absorbing property covering the near IR region. Additionally, we conducted measurements of circular dichroism and circularly polarized luminescence for the obtained products. The g-values were reduced by oligomerization, indicating that the lowest energy transitions were allowed in nature.

Stable Xanthene Radicals and Their Heavy Chalcogen Analogues Showing Tunable Doublet Emission from Green to Near-infrared.

Organic luminescent radicals, unlike traditional closed-shell fluorescent emitters, exhibit distinct luminescence mechanisms, offering promising potential for optoelectronic devices. To date, stable luminescent radicals have predominantly been confined to polychlorinated triphenylmethyl radicals, underscoring the need for new platforms to expand their emission spectra. In this study, we report the synthesis of stable 9-aryl-substituted xanthene radicals and their heavy chalcogen analogues (1a-c and 2a-c), which exhibited excellent chemical stability and emission ranging from green to near-infrared (527~714 nm). Notably, the selenium-substituted radical (1c) demonstrates a significantly enhanced photoluminescence quantum yield of 41% when doped into its precursor solid. Additionally, the introduction of methoxyphenyl groups has largely enhanced the stability of the radical, showcasing an excellent photostability with the longest half-life of around 1792 h. The high internal quantum efficiency of up to 81% was further validated in organic light-emitting diode. This study introduces a novel class of stable carbon-centered radicals with high tunability and functionality for photoelectric applications.

Stable Xanthene Radicals and Their Heavy Chalcogen Analogues Showing Tunable Doublet Emission from Green to Near‐infrared

Organic luminescent radicals, unlike traditional closed‐shell fluorescent emitters, exhibit distinct luminescence mechanisms, offering promising potential for optoelectronic devices. To date, stable luminescent radicals have predominantly been confined to polychlorinated triphenylmethyl radicals, underscoring the need for new platforms to expand their emission spectra. In this study, we report the synthesis of stable 9‐aryl‐substituted xanthene radicals and their heavy chalcogen analogues (1a‐c and 2a‐c), which exhibited excellent chemical stability and emission ranging from green to near‐infrared (527~714 nm). Notably, the selenium‐substituted radical (1c) demonstrates a significantly enhanced photoluminescence quantum yield of 41% when doped into its precursor solid. Additionally, the introduction of methoxyphenyl groups has largely enhanced the stability of the radical, showcasing an excellent photostability with the longest half‐life of around 1792 h. The high internal quantum efficiency of up to 81% was further validated in organic light‐emitting diode. This study introduces a novel class of stable carbon‐centered radicals with high tunability and functionality for photoelectric applications.

The glow of axion quark nugget dark matter

Context. The existence of axion quark nuggets is a potential consequence of the axion field, which provides a possible solution to the charge-conjugation parity violation in quantum chromodynamics. In addition to explaining the cosmological discrepancy of matter-antimatter asymmetry and a visible-to-dark-matter ratio of Ωdark/Ωvisible ≃ 5, these composite compact objects are expected to represent a potentially ubiquitous electromagnetic background radiation by interacting with ordinary baryonic matter. We conducted an in-depth analysis of axion quark nugget-baryonic matter interactions in the environment of the intracluster medium in the constrained cosmological Simulation of the LOcal Web (SLOW). Aims. Here, we aim to provide upper limit predictions on electromagnetic counterparts of axion quark nuggets in the environment of galaxy clusters by inferring their thermal and non-thermal emission spectrum originating from axion quark nugget-cluster gas interactions. Methods. We analyzed the emission of axion quark nuggets in a large sample of 161 simulated galaxy clusters using the SLOW simulation. These clusters are divided into a sub-sample of 150 galaxy clusters, ordered in five mass bins ranging from 0.8 to 31.7 × 1014 M⊙, along with 11 cross-identified galaxy clusters from observations. We investigated dark matter-baryonic matter interactions in galaxy clusters in their present stage at the redshift of z = 0 by assuming all dark matter consists of axion quark nuggets. The resulting electromagnetic signatures were compared to thermal Bremsstrahlung and non-thermal cosmic ray (CR) synchrotron emission in each galaxy cluster. We further investigated individual frequency bands imitating the observable range of the WMAP, Planck, Euclid, and XRISM telescopes for the most promising cross-identified galaxy clusters hosting detectable signatures of axion quark nugget emission. Results. We observed a positive excess in the low- and high-energy frequency windows, where thermal and non-thermal axion quark nugget emission can significantly contribute to (or even outshine) the emission of the intracluster medium (ICM) in frequencies up to νT ≲ 3842.19 GHz and νT ϵ [3.97, 10.99] × 1010GHz, respectively. Emission signatures of axion quark nuggets are found to be observable if CR synchrotron emission of individual clusters is sufficiently low. The degeneracy in the parameters contributing to an emission excess makes it challenging to offer predictions with respect to pinpointing specific regions of a positive axion quark nugget excess; however, a general increase in the total galaxy cluster emission is expected based on this dark matter model. Axion quark nuggets constitute an increment of 4.80% of the total galaxy cluster emission in the low-energy regime of νT ≲ 3842.19 GHz for a selection of cross-identified galaxy clusters. We propose that the Fornax and Virgo clusters represent the most promising candidates in the search for axion quark nugget emission signatures. Conclusions. The results from our simulations point towards the possibility of detecting an axion quark nugget excess in galaxy clusters in observations if their signatures can be sufficiently disentangled from the ICM radiation. While this model proposes a promising explanation for the composition of dark matter, with the potential to have this outcome verified by observations, we propose further changes that are aimed at refining our methods. Our ultimate goal is to identify the extracted electromagnetic counterparts of axion quark nuggets with even greater precision in the near future.