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Heavy Atom Effect of Selenium for Metal-Free Phosphorescent Light-Emitting Diodes
摘要： Room-temperature phosphorescence from metal-free purely organic molecules has recently gained much interest. We devised metal-free organic phosphors by incorporating selenium (Se) to promote spin?orbit coupling by its nonmetal heavy atom effect. The Se-based organic phosphors showed bright phosphorescent emission in organic light-emitting diodes (OLEDs) and photo-excited phosphorescence in an amorphous film state. Large orbital angular momentum change (ΔL) during the electron transition process and heavy atom effect of Se render a PL quantum yield of 0.33 ± 0.01 and a high external quantum efficiency (EQE) of 10.7 ± 0.14% in phosphorescent LEDs. This work demonstrates the rational molecular design of metal-free organic phosphorescent emitters with Se as an alternative novel class of materials to the conventional organometallic phosphors for OLEDs.
关键词： organic light-emitting diodes,spin?orbit coupling,selenium,metal-free organic phosphors,phosphorescent LEDs,room-temperature phosphorescence
更新于2025-09-23 15:19:57
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Suppressing Efficiency Roll-Off at High Current Densities for Ultra-Bright Green Perovskite Light-Emitting Diodes
摘要： Perovskite light-emitting diodes (PeLEDs) have undergone rapid development in the last several years with external quantum efficiencies (EQE) reaching over 21%. However, most PeLEDs still suffer from severe efficiency roll-off (droop) at high injection current densities, thus limiting their achievable brightness and presenting a challenge to their use in laser diode applications. In this work, we show that the roll-off characteristics of PeLEDs are affected by a combination of charge injection imbalance, nonradiative Auger recombination, and Joule heating. To realize ultrabright and efficient PeLEDs, several strategies have been applied. First, we designed an energy ladder to balance the electron and hole transport. Second, we optimized perovskite materials to possess reduced Auger recombination rates and improved carrier mobility. Third, we replaced glass substrates with sapphire substrates to better dissipate joule heat. Finally, by applying a current-focusing architecture, we achieved PeLEDs with a record luminance of 7.6 Mcd/m2. The devices can be operated at very high current densities (J) up to ~ 1 kA/cm2. Our work suggests a broad application prospect of perovskite materials for high-brightness LEDs and ultimately a potential for solution-processed electrically pumped laser diodes.
关键词： Joule heat,efficiency roll-off,Auger recombination,charge injection balance,high injection current density,ultrahigh brightness,perovskite light emitting diodes
更新于2025-09-23 15:19:57
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Inactivation of Salmonella and Quality Changes in Wheat Flour after Pulsed Light-Emitting Diode (LED) Treatments
摘要： Several low water activity (aw) foods have been recently associated with Salmonella related outbreaks and recalls. The use of high intensity light pulses generated by light-emitting diodes (LEDs) is a novel approach to achieve microbial inactivation. This study compares the ability of light emitted by LEDs at wavelengths of 275, 365, 395, and 455 nm to inactivate microorganisms at different environmental relative humidity (RH) conditions. The exposure to LED radiant energy of 1199 J/cm2 at wavelengths of 365, 395, and 455 nm resulted in Salmonella reductions of 2.22, 2.48, and 1.61 logs CFU/g, respectively. Reductions in Salmonella cell counts of 1.07, 2.42, 3.67, and 2.64 CFU/g were observed in wheat flour after 60 min of 275, 365, 395, and 455 nm LED treatments, respectively, at 25°C and an RH of 75%. Significant drying, oxidation of gluten proteins, and changes in the secondary structure of gluten were observed after LED treatments at all the light wavelengths tested. Significant color change of wheat flour was observed for all wavelengths LED except 275 nm. The results of this study will aid selection of LED wavelengths appropriate for inactivating microorganisms in low aw foods. This study presents the potential of LED treatment for simultaneous drying and microbial decontamination of foods.
关键词： gluten oxidation,Salmonella,light-emitting diodes,low water activity foods,microbial inactivation,wheat flour
更新于2025-09-23 15:19:57
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Suppression of dislocation-induced spiral hillocks in MOVPE-grown AlGaN on face-to-face annealed sputter-deposited AlN template
摘要： AlGaN films were grown on face-to-face annealed sputter-deposited AlN/sapphire (FFA Sp-AlN) templates via metalorganic vapor phase epitaxy (MOVPE), and the growth behavior of the AlGaN films was investigated. The sapphire substrates with small off-cut exhibited poor surface flatness of AlGaN grown on the FFA Sp-AlN templates owing to the formation of large hillock structures. To understand the origin of these hillock structures, the crystallinity and surface morphology of conventional fully MOVPE-grown AlN/sapphire (MOVPE-AlN) templates and the FFA Sp-AlN template were comprehensively studied. The screw- and mixed-type threading dislocation density of the FFA Sp-AlN template was estimated to be approximately 1.8 × 106 cm?2, which was two orders of magnitude lower than that of the MOVPE-AlN template. Consequently, the uniquely observed growth of the hillock structures in the FFA Sp-AlN templates was attributed to their low density of screw- and mixed-type threading dislocations. The large surface off-cut sapphire substrates suppressed the hillock structures on the FFA Sp-AlN templates. The improvement in surface flatness resulted in better optical properties of multiple quantum wells grown on the AlGaN layer. These results demonstrate a promising method for achieving highly efficient and cost effective AlGaN based deep ultraviolet light-emitting diodes.
关键词： AlGaN,MOVPE,deep ultraviolet light-emitting diodes,hillock structures,FFA Sp-AlN
更新于2025-09-23 15:19:57
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The Photothermal Stability Study of Quantum Dots Embedded in Sodium Chlorides
摘要： An e?cient and useful method for the incorporation of colloidal quantum dots (QDs) into ionic matrices is demonstrated. We prepared three di?erent synthesis methods, which are traditional saturated-salt water, methanol-assisted, and ethanol-assisted methods. The continuous thermal and photonic stress tests indicate that the high temperature, instead of photonic excitation stress, is more detrimental to the illumination capability of the quantum dots. While the traditional saturated-salt water synthesis and methanol-assisted method are quite e?ective in low temperature and low photon excitation intensity, the quantum dots sealed by the ethanol-assisted method cannot hold under all conditions. An over-1000-h aging test can provide crucial information for the longevity of these quantum dots, and more than 10,000 h of lifetime can be expected.
关键词： light-emitting diodes,quantum-well,nanomaterials,-wire and -dot devices
更新于2025-09-23 15:19:57
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LED illumination and plant growth regulatorsa?? effects on growth and phenolic acids accumulation in Moluccella laevis L. in vitro cultures
摘要： Moluccella laevis L. (Lamiaceae) is an annual ornamental plant, naturally occurring in the areas of Western and Central Asia (Irano-Turanian area). It is a popular ornamental species, but its phytochemical profile remains poorly studied. This study presents the first report on in vitro cultures of M. laevis. The influence of two types of illumination and plant growth regulators (PGRs) supplementation on the morphogenetic response and the content of phenolic compounds were examined. Shoots were cultured on Murashige and Skoog (MS) solid basal medium. White light or photosynthetic active radiation (PAR) as well as three concentrations of 6-benzylaminopurine (BA) 2, 3 or 4 μM and one of the three auxins: 1-naphthaleneacetic acid (NAA), indole-3-acetic acid (IAA) or 4-amino-3,5,6-trichloropicolinic acid (picloram—PIC) at concentration of 0.5 μM were used for shoot proliferation. The highest number of axillary shoots per explant (3.4) was obtained for shoots grown on MS medium supplemented with 3-μM BA and 0.5-μM NAA under PAR light. However, the effect of PGRs treatment on shoot growth and development was stronger than the influence of light. The phytochemical analysis using Ultra-Performance Liquid Chromatography–Mass Spectrometry allowed identification of four hydroxycinnamic acids (caffeic, ferulic, rosmarinic, chlorogenic) and two cyanidin glycosides (cyanidin 3-O-galactoside, and cyanidin 3-O-malonylglucoside) in shoot clusters and callus tissue.
关键词： Light emitting diodes,Irish bells,Phenolic acids,Shoot cultures
更新于2025-09-23 15:19:57
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Saturated red phosphorescent Iridium(III) complexes containing phenylquinoline ligands for efficient organic light-emitting diodes
摘要： Saturated red iridium phosphors are strongly desired for application in organic light-emitting diodes (OLEDs). Most of the reported iridium complexes with 2-arylquinoline or its derivatives as cyclometalating ligands are orange-red phosphorescent with peak wavelength below 620 nm. Herein trifluoromethyl (CF3) or Fluorine (F) is introduced into the 6-site of quinoline ring to design and synthesize the cyclometalated ligands 2-phenyl-6-CF3/F-quinoline (CF3-phq or F-phq) and heteroleptic iridium complexes Ir(CF3-phq)2(acac) (Ir-1), Ir(CF3-phq)2(tmd) (Ir-2), Ir(F-phq)2(acac) (Ir-3) and Ir(F-phq)2(tmd) (Ir-4). Owing to the electron-deficient feature of CF3 and F, the electron affinity of these complexes are increased, the corresponding LUMOs are pulled downwards, and the phosphorescence of CF3-containing iridium complexes are saturated red with peaks at 627–632 nm in photoluminescence. At the same time, by varying the ancillary ligand from acetylacetonate (acac) to 2,2,6,6-tetrametylheptane-3,5-dionate (tmd), the emitting performance are dramatically improved. As a result, the Ir(CF3-phq)2(tmd) based red OLED realized pure red electroluminescence with Commision Internationale de L’Eclairage (CIE) coordinates of (0.67, 0.33) with a high brightness of 12695 cd m?2 and a maximum external quantum efficiency of 14.96%, respectively, which maintained as high as 9.62% at a practical luminance of 1000 cd m?2. This is the first example of saturated red iridium phosphors with structure modification at the 6-site of quinoline ring of 2-phenylquinoline ligand.
关键词： Iridium complex,Phosphorescent organic light emitting diodes (PhOLEDs),Saturated red,2-Phenylquinoline,Trifluoromethyl
更新于2025-09-23 15:19:57
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Efficient and Stable CdSe/CdS/ZnS Quantum Rods-in-Matrix Assembly for White LED Application
摘要： CdSe/CdS core-shell quantum rods (QRs) are a promising prospect in optoelectronic applications but usually have a relatively low quantum efficiency and stability. Here, we report on an efficient and stable CdSe/CdS/ZnS QRs-in-matrix assembly (QRAs) by growing and embedding CdSe/CdS QRs in ZnS matrices. Structural characterizations show that the CdSe/CdS QRs are encapsulated and interconnected by ZnS in the QRAs structure. The stable ZnS encapsulation renders the CdSe/CdS QRs high quantum efficiency (QE) up to 85%. The QRAs also present high photo- and thermal-stability and can preserve 93% of the initial QE at 100°C. The QRAs powder presents a light degradation of only 2% under continuous excitation for 100 h, displaying profound potential in optoelectronic applications. White light-emitting diodes (WLEDs) are fabricated by packaging the QRAs powder as phosphor on top of blue GaN chip. The WLED shows high optical performance and light quality.
关键词： stability,assembly,light-emitting diodes,quantum rod,core-shell
更新于2025-09-23 15:19:57
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Efficient inkjet-printed blue OLED with boosted charge transport using host doping for application in pixelated display
摘要： Inkjet-printing is a desirable technology for organic light emitting diodes (OLEDs) owing to its compatibility with large-area low-cost full-color pixelated displays. In this work, we proposed a strategy to fabricate highly efficient inkjet-printed blue OLEDs by introducing 3,5-bis(N-car-bazolyl)benzene (mCP) as the host material into organic light emitting layers. By carefully tailoring the weight ratio of mCP to poly[(9,9-dioctyl-2,7-fluorene)-co-(dibenzothiophene-S,S-dioxide)] (PFSO), the device demonstrated superior charge transport capability, leading to balanced charge transport and optimized efficiency. Furthermore, in combination with modifying the mCP: PFSO ink formulation, a low-roughness organic emissive film on Poly(ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) layer was achieved. The performance of the inkjet-printed device has been significantly improved with nearly five times, which exhibits a maximum luminance and an external quantum efficiency of 3743 cd/m2 and 5.03%, respectively. The icing on the cake is that we fabricated a 3-inch blue OLED array device successfully with a brightness uniformity of 92.7%, which shows promising potential in realizing simple structure large-area and high-efficient OLEDs by inkjet printing.
关键词： Blue,Organic light emitting diodes,Charge transport,Inkjet-printing
更新于2025-09-23 15:19:57
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Electrochemically-stable ligands bridge the photoluminescence-electroluminescence gap of quantum dots
摘要： Colloidal quantum dots are promising emitters for quantum-dot-based light-emitting-diodes. Though quantum dots have been synthesized with ef?cient, stable, and high colour-purity photoluminescence, inheriting their superior luminescent properties in light-emitting-diodes remains challenging. This is commonly attributed to unbalanced charge injection and/or interfacial exciton quenching in the devices. Here, a general but previously overlooked degradation channel i.e., operando electrochemical reactions of surface ligands with injected charge carriers, is identi?ed. We develop a strategy of applying electrochemically-inert ligands to quantum dots with excellent luminescent properties to bridge their photoluminescence-electroluminescence gap. This material-design principle is general for boosting electroluminescence ef?ciency and lifetime of the light-emitting-diodes, resulting in record-long operational lifetimes for both red-emitting light-emitting-diodes (T95 > 3800 h at 1000 cd m?2) and blue-emitting light-emitting-diodes (T50 > 10,000 h at 100 cd m?2). Our study provides a critical guideline for the quantum dots to be used in optoelectronic and electronic devices.
关键词： electroluminescence,light-emitting-diodes,photoluminescence,Colloidal quantum dots,electrochemical stability
更新于2025-09-23 15:19:57