Emission Peak Research Articles

Cyano‐Modified Multi‐Resonance Thermally Activated Delayed Fluorescent Emitters Towards Pure‐Green OLEDs with a CIEy Value of 0.74

AbstractThe development of pure‐green organic emitters with ideal emission peaks and ultra‐narrow full‐widths at half‐maximum (FWHMs) remains a formidable challenge. Herein, we report two new green emitters, CNBN and MCNBN, which achieve extremely narrow FWHMs by synergistic rigid π‐extension and cyano‐substitution of a sky‐blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) core. The introduction of cyano groups induces red‐shifts in the emission to the green region and dramatically minimizes the FWHMs. In toluene solution, CNBN and MCNBN exhibit narrowband emission with a maximum at 501 nm and 510 nm with ultra‐narrow FWHMs of 14 nm/0.066 eV and 15 nm/0.071 eV, respectively. Given the near‐unity photoluminescence quantum yields and almost 100 % horizontal dipole orientation, the electroluminescent (EL) devices based on CNBN and MCNBN deliver external quantum efficiencies (EQEs) exceeding 30 % with FWHMs of 16 nm/0.072 eV and 17 nm/0.080 eV, respectively. Notably, the MCNBN‐based device achieves pure‐green emission with a maximum at 517 nm with Commission Internationale de l’Éclairage coordinates of (0.17, 0.74), closely aligning with the BT.2020 green standard.

Photophysical Properties of Tandem Quantum Defects in Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNTs) are versatile near-infrared (NIR) fluorophores that can be chemically functionalized to create biosensors. Numerous noncovalent approaches were developed to detect analytes, but these design concepts can be susceptible to nonspecific binding and reduced stability. In contrast, covalent modification of SWCNTs with quantum defects can be utilized to tune their fluorescence properties and enable new molecular recognition concepts. Here, we present and assess four different synthetic pathways/sequences to modify SWCNTs covalently with both sp3 quantum defects and DNA-based guanine defects. We find that it is possible to create two defect types without disrupting the optical properties or chemical stability. Interestingly, the emission peak associated with sp3 defects (E11*) shifts around 3 nm when combined with guanine defects, indicating a coupling between the two defect types. However, it is far lower than the red-shift in bandgap-related emission (E11) by guanine quantum defects (40 nm). We furthermore demonstrate that combinations of defects can be used for (bio)sensing. In summary, the combination of multiple quantum defect types in SWCNTs provides a platform for multifunctional biosensors and a new design space that can be explored.

Synthesis and Characterization of Lignocellulose-Based Carbon Quantum Dots (CQDs) and Their Antimicrobial and Antioxidant Functionalities

Carbon quantum dots (CQDs) have recently drawn enormous attention due to not only their unique chemical, biological, and optical properties but also because a variety of renewable biomasses are readily utilized as carbon sources in their synthesis. This study investigated the synthesis, characterization, and functional evaluation of CQDs from unbleached mechanical pulp as a natural lignocellulosic resource. The CQDs were synthesized using a one-step hydrothermal synthesis with varying temperature, time, and pulp consistency. The resulting CQDs exhibit a spherical shape with a size distribution of 9.73 ± 0.82 nm and lattice parameters of 0.21 and 0.34 nm, indicating a graphite core. The photoluminescence spectra showed evident fluorescence characteristics, with an emission peak at 435 nm at an excitation wavelength of 370 nm. The as-prepared CQDs were also chemically composed of C=C and C=O bonds linked to the hydroxyl and carboxyl functional groups, which are typically found in lignocellulose-based CQDs. The CQDs demonstrated antibacterial activity exceeding 99.9% against E. coli at the lowest concentration of 0.75 mg/mL. Demonstrating its antioxidation property, the DPPH radical scavenging activity surpassed 90% with more than 40 µg/mL of the CQD solution.

A “Turn‐Off” Fluorescence Sensor Based on 1,1,2,2‐Tetraphenylethylene for the Selective Detection of Antiviral Agents

AbstractIn this study, we constructed a “turn‐off” fluorescence probe for the specific detection of antiviral agents by preparing stable reserve solutions of 1,1,2,2‐tetraphenylethylene (TPE), which notably exhibits the character of aggregation‐induced emission (AIE). The fluorescent molecules were systematically characterized. The maximum excitation and emission peaks were located at 281 and 440 nm, respectively. We discussed the fluorescence response between TPE and antiviral agents, as well as the effects of certain single‐variable factors. The % suppressed efficiency (%E) was calculated and the Stern–Volmer equation was analyzed. The results indicated that Cidofovir (CDV) can more effectively quench TPE based on the mechanism of internal filtration effect (IFE) and static quenching. We studied the linear correlation between fluorescence intensity and the concentration of CDV. The limit of detection (LOD) was found to be 0.2279 mg·L−1. The recovery rates of CDV in blank samples ranged from 93.22%–97.90%. Additionally, different letters “L” were written using the prepared solutions under ambient light and UV light, respectively, demonstrating that the written contents were both readable and easily erasable. The specific recognition of CDV using TPE lays the groundwork for detecting CDV residues, which holds promising prospects for practical detection.

Venus' O 5577 Å Oxygen Green Line: A Global Diffuse Proton‐Induced Aurora

AbstractThe Venusian O(1S–1D) 5577 Å “oxygen green line” has been an enigmatic feature of the Venusian atmosphere since its first attempted observation by the Venera spacecraft. Its first detection in 1999 and subsequent detections point to a unique auroral phenomena. However, the lack of (1D–3P) 6300 Å “oxygen red line” emission suggests that the green line originates from deep in the ionosphere, much lower than current models predict. Here, we present 16 years of ground‐based observations of the Venusian green line, comparing its behavior to the solar wind and spacecraft observations of the Venusian ionosphere. We find that all instances of green line emission occur during solar energetic particle (SEP) events, with a Matthews correlation coefficient of 0.93 between emission and the presence of SEPs. Coordinated observations between Venus Express and ground‐based observatories show enhanced nightside ionospheric peak densities during the time of green line emission, with the lowest peak occurring at 115 km near local midnight. Such high density yet low altitude peaks suggest the presence of highly energetic particle precipitation. Initial modeling indicates 50 keV protons are needed to penetrate to such low altitudes. Comparisons of solar wind data confirm that such protons are present during all green line detections and nightside ionosphere enhancements. The association of SEP storms with green line emission and low nightside ionospheric peaks indicates that the green line is a unique global diffuse aurora, likely originating deep in the ionosphere and driven by proton precipitation, something that could be common for all non‐magnetic planetary atmospheres.

Influence of zinc on electrochemical and photoluminescence properties of yttrium chromate nanoparticles

YCrO4: Zn (1-9 mol %) nanoparticles were synthesized using Aloe vera gel via a solution combustion method and subsequently calcined at 600 °C for 3 h. X-ray diffraction analysis confirmed a pure tetragonal crystal structure, indicative of high material quality, while surface morphology revealed irregularly shaped and sized nanoparticles that varied with dopant concentration. The crystallite size, calculated using Scherrer’s method, decreased from 14 nm to 9 nm, and the optical energy band gap narrowed from 2.93 eV to 2.75 eV with increasing zinc doping. Photoluminescence emission spectra, recorded under 310 nm excitation, displayed peaks centered at 483, 525, and 628 nm, with the violet-blue emission attributed to the recombination of zinc interstitial (Zni) and zinc vacancy (VZn) energy levels. The presence of oxygen vacancies contributed to the green emission peak, while red emissions resulted from band transitions between zinc interstitial and oxygen interstitial (Oi) defect levels within the host matrix. The CIE coordinates fell within the 1713 K region, with an average color-correlated temperature of 1730 K, indicating a warm LED output. Electrochemical studies demonstrated that the specific capacitance of YCrO4:Zn (1-9 mol%) nanoparticles ranged from 86.94 to 130.27 F/g at a scan rate of 10 mV/s, underscoring the significant influence of dopant concentration on the material’s electrochemical properties, as higher concentrations of Zn2+ in YCrO4 enhanced the charge storage capability, suggesting its potential for improved performance in energy storage applications.

Microwave Synthesis of Luminescent Recycled Glass Containing Dy2O3 and Sm2O3

This research studied the recycling of borosilicate glass wastes from damaged laboratory glassware. The luminescent glasses were prepared by doping glass waste powder with rare earth ions, namely, dysprosium ions (Dy3+) and samarium ions (Sm3+), as well as co-doping with Dy3+ and Sm3+ at a concentration of 2% by weight. The sintering process was conducted in a microwave oven for a duration of 15 min. The photoluminescence spectra of the doped glasses were obtained under excitation at 401 nm and 388 nm. The results showed that the emission characteristics depended on the doping concentrations of Dy3+ and Sm3+ and the excitation wavelengths. Upon excitation at 401 nm, the co-doped glasses exhibited the maximum emission peak of Sm3+ at 601 nm (yellowish and orange region in the CIE chromaticity diagram) due to the energy transition from 4G5/2 to 6H7/2. When excited at 388 nm, however, the emission spectra of the co-doped glasses were similar to the characteristic emission peaks of Dy3+ (white region in the CIE chromaticity diagram), but the peak position exhibits a red shift. This could be attributed to an increase in the amount of non-bridging oxygens (NBOs) by co-doping.

Spatial and seasonal variations of carbon emissions in an urban lake: Flux sensitivity and sampling optimization based on high-resolution measurements

Understanding the dynamics of pCO2 and pCH4 is important for evaluating carbon emissions from the aquatic environment. While temporal dynamics of pCO2 and pCH4 have been extensively studied, there is a noticeable gap in the literature concerning their spatial characteristics. In this study, we used boat-mounted sensors to directly measure pCO2 and pCH4 with high spatial resolution across seasons in Xuanwu Lake (XWL), an urban lake in Nanjing, China. Additionally, water chemistries were measured at selected sites for correlation analysis. Sensitivity analysis was performed to assess the effects of measurement location and density on carbon flux estimates.Results show that continuous on-board measurements innovatively captured the spatial distribution of pCO2 and pCH4. Both gases varied significantly across seasons, exhibiting pronounced spatial heterogeneity. Peak emissions occurred in summer, with the lowest CO2 in spring and CH4 in fall. Both pCO2 and pCH4 increased from the lake center to the shoreline, with the largest fluctuations near the shore. In total, XWL acted as a net source of CO2 and CH4, with mean diffusive fluxes of 11.4 ± 10.1 and 3.0 ± 0.3 mmol∙m−2∙d−1, respectively. Furthermore, sensitivity analysis showed that lake-wide flux calculations depend on measurement locations and sample size. pCO2 exhibited greater heterogeneity than pCH4, necessitating different sampling thresholds. The optimal threshold for capturing lake-wide CO2 flux was 18–30 samples per km2, while this density was sufficient for CH4 flux estimates. Our study highlights that both CO2 and CH4 exhibit significant spatial and temporal heterogeneity, necessitating high-resolution sampling for accurate flux assessments. The sampling strategy presented could guide future studies, as sampling in the intermediate zone effectively reduces the number of samples needed while maintaining accuracy.

Structural and optical properties of black silicon prepared by wet chemical etching

The study focuses on the optimization of black silicon fabrication via etching using a solution composed of KOH, NaOH, and Na2SiO3 at constant concentrations and varying durations. Surface morphology was analyzed using Field Emission Scanning Electron Microscopy (FE-SEM). The results showed that pyramidal structures were formed on the silicon surface with heights between 1.2 and 4.1 μm. The uniform distribution was confirmed by AFM images. The surface roughness decreased as the etching time increased; it was measured at 14.03 nm for 15 minutes and 5.59 nm for 30 minutes. The properties of photoluminescence (PL) were evaluated using a spectrometer and it was found that peak emission shifts to lower energies (red shift) when etching time is increased. Optical reflectivity decreases sharply when etching time is increased. Additionally, the longer the etching duration, the greater the energy gap of the material which increased from 1.25 eV to approximately 1.4 eV.

MTiTaO6: Cr3+ (M = Al3+, Ga3+, Sc3+) Phosphors with Ultra‐Broadband Excitation Spectra and Enhanced Near‐Infrared Emission for Solar Cells

AbstractAchieving ultra‐broadband absorption and enhancing the near‐infrared (NIR) emitting properties of NIR phosphors is a key challenge to realize its multiple applications, such as solar spectrum conversion, spectral analysis, and night vision. Here, a novel NIR phosphor system MTiTaO6: Cr3+ (M = Al3+, Ga3+, Sc3+), with an excitation spectrum as broad as 421 nm and enhanced NIR emission is reported. It is the widest excitation spectrum among the known Cr3+‐doped NIR phosphors. Structural and spectroscopic analysis shows that the ultra‐broadband excitation spectrum originates from the overlap of multiple luminescence centers. Additionally, the emission peak is red‐shifted from 816 to 871 nm with increasing M ion radius, and the emission intensity is enhanced, which not only makes the emission spectra more compatible with the response curve of c‐Si solar cells, but also gives it an advantage in NIR spectroscopy applications. Comparison of the excitation spectra with the solar spectrum and spectral analysis of the emission spectra of water and alcohol demonstrate its promising applications.

Polarity-sensitive pyrene fluorescent probes for multi-organelle imaging in living cells.

Polarity-sensitive probes (PAS) were synthesized through the attachment of azetidine and sulfonyl substituents to the pyrene fluorescent core. The emission peaks and fluorescence lifetimes of these PAS probes exhibit high sensitivity to polarity, enabling the visualization of microenvironmental characteristics and dynamics across multiple organelles.

Stepwise Planarizing Geometries of D–A Type Red Thermally Activated Delayed Fluorescence Molecules in Condensed States Toward High‐Efficiency Red/NIR OLEDs

AbstractQuasiplanar donor–acceptor (D–A) thermally activated delayed fluorescence (TADF) molecules are appealing candidates for efficient red/near‐infrared (NIR) emitters but have not been realized. Herein, for the first time, a stepwise approach to achieve this goal via a spiro‐locked C─C covalent bond linking strategy combined with the subtle management of intermolecular C─H···CN noncovalent bonds in condensed states is presented. This synergetic effect enables the newly developed molecule, DCN‐SAC, to not only attain nearly unity photoluminescence quantum yield, with a horizontal dipole ratio of up to 89% at 5 wt% doped conditions but also achieve a quasiplanar configuration with high‐exciton‐harvesting J‐aggregates under neat condensed conditions. The optimized organic light‐emitting diode (OLED) using DCN‐SAC as the dopant furnishes a topmost external quantum efficiency (EQE) of 38.7% at 631 nm among all red OLEDs based on TADF materials. More importantly, a DCN‐SAC‐based nondoped OLED affords a remarkable EQE of 12.6% with an emission peak at 730 nm, which sets a record‐breaking value among all previously reported nondoped TADF devices in the similar emission region. These findings reveal the effectiveness and great potential of stepwise planarity, presenting a new paradigm for developing high‐efficiency red/NIR TADF OLEDs.

White Fluorescent Carbon Dots for Specific Fe3+ Detection and Imaging Applications.

In recent years, carbon dots (CDs) with fluorescence imaging function have been widely used in biomedicine, electronic manufacturing and environmental monitoring. However, monochromatic fluorescence is often limited by the application environment and loses its effectiveness. Here, we carefully designed white fluorescent CDs (WF-CDs) by solvothermal method, which is used for fluorescence imaging applications under different environmental conditions. WF-CDs based on nitrogen doping can produce obvious emission peaks at 400 nm, 490 nm and 640 nm, respectively, corresponding to red, green and blue (RGB) bands in the three primary colors. The full wavelength emission was realized by changing the solvent types and pH values to adjust the emission peak intensity. WF-CDs can accurately detect Fe3+ concentration according to fluorescence extinction degree (fluorescence elimination rate reaches 95.34%). Furthermore, WF-CDs has practical applications in cell-level fluorescence imaging, near-infrared fluorescence imaging and ultraviolet anti-counterfeiting, and has broad application prospects in the fields of nano-medicine and industrial manufacturing.

The Observed Phase Space of Mass-loss History from Massive Stars Based on Radio Observations of a Large Supernova Sample

Abstract In this work, we study the circumstellar material (CSM) around massive stars, and the mass-loss rates depositing this CSM, using a large sample of radio observations of 325 core-collapse supernovae (CCSNe; only ~22% of them being detected). This sample comprises both archival data and our new observations of 99 CCSNe conducted with the AMI-LA radio array in a systematic approach devised to constrain the mass loss at different stages of stellar evolution. In the supernova (SN)–CSM interaction model, observing the peak of the radio emission of an SN provides the CSM density at a given radius (and therefore the mass-loss rate that deposited this CSM). On the other hand, limits on the radio emission, and/or on the peak of the radio emission provide a region in the CSM phase space that can be ruled out. Our analysis shows a discrepancy between the values of mass-loss rates derived from radio-detected and radio-nondetected SNe. Furthermore, we rule out mass-loss rates in the range of 2 × 10−6–10−4 M ⊙ yr−1 for different epochs during the last 1000 yr before the explosion (assuming wind velocity of 10 km s−1) for the progenitors of ~80% of the Type II supernovae (SNe II) in our sample. In addition, we rule out the ranges of mass-loss rates suggested for red supergiants for ~50% of the progenitors of SNe II in our sample. We emphasize here that these results take a step forward in constraining mass loss in winds from a statistical point of view.

Cyano-Modified Multi-Resonance Thermally Activated Delayed Fluorescent Emitters Towards Pure-Green OLEDs with a CIEy Value of 0.74.

The development of pure-green organic emitters with ideal emission peaks and ultra-narrow full-widths at half-maximum (FWHMs) remains a formidable challenge. Herein, we report two new green emitters, CNBN and MCNBN, which achieve extremely narrow FWHMs by synergistic rigid π-extension and cyano-substitution of a sky-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) core. The introduction of cyano groups induces red-shifts in the emission to the green region and dramatically minimizes the FWHMs. In toluene solution, CNBN and MCNBN exhibit narrowband emission with a maximum at 501 nm and 510 nm with ultra-narrow FWHMs of 14 nm/0.066 eV and 15 nm/0.071 eV, respectively. Given the near-unity photoluminescence quantum yields and almost 100 % horizontal dipole orientation, the electroluminescent (EL) devices based on CNBN and MCNBN deliver external quantum efficiencies (EQEs) exceeding 30 % with FWHMs of 16 nm/0.072 eV and 17 nm/0.080 eV, respectively. Notably, the MCNBN-based device achieves pure-green emission with a maximum at 517 nm with Commission Internationale de l'Éclairage coordinates of (0.17, 0.74), closely aligning with the BT.2020 green standard.

Biochemical evidence for the diversity of LHCI proteins in PSI-LHCI from the red alga Galdieria sulphuraria NIES-3638.

Red algae are photosynthetic eukaryotes whose light-harvesting complexes (LHCs) associate with photosystem I (PSI). In this study, we examined characteristics of PSI-LHCI, PSI, and LHCI isolated from the red alga Galdieria sulphuraria NIES-3638. The PSI-LHCI supercomplexes were purified using anion-exchange chromatography followed by hydrophobic-interaction chromatography, and finally by trehalose density gradient centrifugation. PSI and LHCI were similarly prepared following the dissociation of PSI-LHCI with Anzergent 3-16. Polypeptide analysis of PSI-LHCI revealed the presence of PSI and LHC proteins, along with red-lineage chlorophyll a/b-binding-like protein (RedCAP), which is distinct from LHC proteins within the LHC protein superfamily. RedCAP, rather than LHC proteins, exhibited tight binding to PSI. Carotenoid analysis of LHCI identified zeaxanthin, β-cryptoxanthin, and β-carotene, with zeaxanthin particularly enriched, which is consistent with other red algal LHCIs. A Qy peak of chlorophyll a in the LHCI absorption spectrum was blue-shifted compared with those of PSI-LHCI and PSI, and a fluorescence emission peak was similarly shifted to shorter wavelengths. Based on these results, we discuss the diversity of LHC proteins and RedCAP in red algal PSI-LHCI supercomplexes.

Enhanced optical response of n-type doped InAs quantum dots through interface state inactivation

Owing to the wide tuning range, high-temperature stability, flexible design, and fast recovery dynamics, quantum dots (QDs) have been widely used in many research fields, such as lasers, photodetectors, solar cells, and displays. Among these, III–V InAs/GaAs QDs are especially suited for infrared optoelectronic applications due to their strong working stability and enhanced light output efficiency. The doping technique has been admitted as a very effective method to enhance the modal gain and temperature insensitivity for InAs/GaAs QDs-based devices. Additionally, doping could modulate critical optical responses, like light absorption and carrier recovery dynamics, making these QDs ideal for ultrafast applications. In this work, p-type (Be) doping and n-type (Si) doping were introduced into multilayer QDs to mitigate the adverse effects of grown-in interface states, which were verified by temperature-dependent photoluminescence (PL) characterization. The results show a significant increase in PL intensity for n-doped samples, which was attributed to the effective suppression of interface states. This enhancement correlates with doping levels, with PL intensity increasing from 1.71 to 2.72 times as Si concentration rises from 1 × 1018/cm3 to 3 × 1018/cm3. In contrast, p-doped samples show a slight decrease in PL intensity and a 20 nm blueshift in PL emission peak, indicating different interdiffusion behaviors between In and Ga atoms compared to that in n-doped ones. By integrating with distributed Bragg mirrors, QD semiconductor saturable absorption mirrors were developed, where n-doped QDs presented superior performance in mode-locked ultrafast lasers with the shortest pulse width and highest output power.

Tuning optical and structural properties of polystyrene nanocomposites with rutile TiO₂ nanoparticles

ABSTRACT The surface morphology and structural properties of polystyrene (PS)/TiO₂ nanocomposites were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while optical properties were assessed via UV-Vis spectroscopy and Fluorescence measurements. SEM images revealed uniform dispersion of TiO₂ nanoparticles with sizes ranging from 48 to 58.5 nm in the PS matrix, showing no significant agglomeration. XRD analysis revealed a decrease in crystallite size with increasing TiO₂ concentration. UV-Vis spectra demonstrated a decrease in the band gap with increasing TiO₂ concentration, indicating a shift towards enhanced visible light absorption. PL spectra excited at 330 nm revealed distinct emission peaks, with significant increases in intensity at higher TiO₂ concentrations, particularly at 399 nm and 422.5 nm, corresponding to near-band-edge and defect-related emissions. FTIR analysis demonstrated that the incorporation of TiO₂ led to disruption of C-O bonds in the PS matrix, particularly at 10% TiO₂, suggesting strong interactions between the TiO₂ nanoparticles and the polymer, which may weaken the polymer backbone. Overall, these findings suggest that TiO₂ incorporation not only impacts crystallite size and strain but also enhances the optical and fluorescence properties of PS/TiO₂ nanocomposites.

Construct ZnSeTe/ZnTe Nanostructures with the Tunable Emission from 450 to 760 nm.

Developing heavy-metal-free materials with wide tunable emission is important to light-emitters. The alloying method is utilized in ZnSe magic size clusters (MSCs) with Te to form ZnSeTe and manipulate the band gap structure in ZnSe. The growth of ZnTe on alloyed ZnSeTe quantum dots (QDs) forms ZnSeTe/ZnTe core/shell nanostructures, showing the tunable photoluminescence emission peak from 450 to 760 nm with the different thicknesses of ZnTe shell. This is the record tunable range of 310 nm in the full visible and near-infrared spectra based on zinc chalcogenide nanostructures. Further coating thin ZnSe and ZnS shell on ZnSeTe/ZnTe core/shell nanostructures significantly improves the stability and quantum yield of nanoparticles. This work offers a new, cadmium-free material choice for optoelectronic devices aligning with environmental and performance requirements for modern applications.

Enhanced Spontaneous Emission Rate and Luminescence Intensity of CsPbBr3 Quantum Dots Using a High-Q Microdisk Cavity.

Perovskite quantum dots (QDs) are high-efficiency optoelectronic materials attracting great interest, but further improvement in the luminescence efficiency is crucial for their application. In this work, we enhance both the spontaneous emission rate and the photoluminescence (PL) intensity of CsPbBr3 QDs by coupling them to a high quality (Q) factor SiO2 microdisk cavity. Compared to conventional metal plasmonic cavities, the dielectric cavity structure suppresses the effects of quenching and energy transfer, which could introduce complex fluctuations and nonradiative decays. As such, we obtain a 5.9-fold enhancement of the PL intensity and a 5.6-fold enhancement of the emission rate. Moreover, the different enhancement behaviors for phonon sidebands allow us to further explore the different components in the broad emission peak of ensembled QDs. These results demonstrate the great potential of microdisk cavities in enhancing the luminescence in optoelectronic devices and exploring the exciton-photophysics of perovskite QDs.