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24.3: <i>Invited Paper:</i> Printed Electrodes for All‐Solution‐Processed Inverted‐Structure OLEDs
摘要： A key enabling technology for all-printed organic light-emitting diodes is printing electrodes that can be used for anodes or cathodes for conventional or inverted device structures. In both device structures, the first bottom electrodes, which are either transparent or opaque depending on the device structure, are typically printed while the last top electrodes have been deposited by using a vacuum-based evaporation process because when the last top electrodes are fabricated by using a solution-based process, under organic layers are easily damaged during the fabrication process. Although so-called transfer printing process has been often reported for organic devices such as organic solar cells, it has been rarely applied for OLEDs. In addition, no fine patterning has been adopted in such printing processes. As part of our efforts towards all-printed OLEDs, inkjet-printed and/or transfer-printed, finely-patterned PEDOT:PSS electrodes have been investigated in our lab and most recent achievement will be reported in detail. In order to implement all-solution-processed OLEDs, we also studied the inverted-structure OLEDs, which showed comparable results to the conventional structure OLEDs with the vacuum-based deposited electrodes.
关键词： inverted structure,Organic light-emitting diode,OLED,PLED,inkjet-printing,transfer-printing,polymer light-emitting diode
更新于2025-09-19 17:13:59
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[IEEE 2018 International Conference on Recent Innovations in Electrical, Electronics & Communication Engineering (ICRIEECE) - Bhubaneswar, India (2018.7.27-2018.7.28)] 2018 International Conference on Recent Innovations in Electrical, Electronics & Communication Engineering (ICRIEECE) - Improvement of Uniformity of Illumination for Circular LED Arrangement in VLC System
摘要： Light emitting diode (LED) offers several advantageous properties that they can be used in many lighting applications. The optimal placement of LED lamps is very crucial for effective visible light communication (VLC). In this paper, different LED arrangements have been investigated and analyzed using MATLAB for estimating the illumination uniformity. To closely approximate the practical scenario, single bounce reflections from the walls has been considered for evaluating the results. The results show that the uniformity of illumination within the room significantly improves with the increase in the radius of the circular array of LEDs. The optimal arrangement of LEDs shows significantly better results than the other proposed arrangements.
关键词： visible light communication,Light emitting diode (LED),illuminance,uniformity
更新于2025-09-19 17:13:59
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Enhanced light-emitting diode induced fluorescence detection system with capillary electrophoresis
摘要： An enhanced fluorescence detection system of capillary electrophoresis (CE) was equipped with a concave silver mirror, by which the detection sensitivity of light-emitting diode induced fluorescence (LEDIF) can be increased greatly. The silver concave mirror and the cathode window in photomultiplier tube (PMT) were accurately set face to face at the same axis. When the two labeled tumor markers exactly moved to the center of detection window, the emission from analytes are excitated by LED source. Currently, the analytes may be regarded as a luminescent source point. When the source point exactly moves to the focus of the concave mirror, the emission of the labeled sample was collected effectively, enhanced by convergence and reflected by the concave mirror. Then it was sensitively detected by the PMT. The optical mechanism of enhancing detection sensitivity was explored. A simple comparative test on sensitivity was carried out, which aimed to compare sensitivity of the new detection system with concave mirror to that without concave mirror but the other conditions were kept the same. Two tumor markers labeled with FITC were selected for the test, using the simple LEDIF detect system. The results (LOD, 150 nM for L-Leu and L-Val) showed that the detection sensitivity matched with concave mirror reached more 16 times than the detection method without concave mirror.
关键词： Curvature radius,Light-emitting diode induced fluorescence,Tumor markers,Concave silver mirror,Polarized light,Highly sensitive optical detector
更新于2025-09-19 17:13:59
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Red-shift effect in multi-color LEDs based visible light communication
摘要： Visible light communication (VLC) is a short range wireless optical communication system that provides lighting and data transmission, simultaneously. Besides lighting, in order to obtain high data rates, color-shift keying (CSK) which modulates the intensity of light using multi-color light emitting diodes (LEDs) has been introduced in IEEE 802.15.7 VLC standard. In CSK-based VLC (VLC-CSK) systems, some parameters of LEDs such as junction temperature is affected by physical and operation conditions. Junction temperature variations change the power spectral density (PSD) of LEDs, which is known as red-shift effect. In this study, the red-shift effect is examined for the first-time in VLC-CSK systems. The obtained numerical results show that the red-shift effect may dramatically reduce the performance of optical communication system. To eliminate the negative effect of red-shift, an effective solution based on the power normalization is proposed at the receiver side.
关键词： Visible light communication (VLC),red-shift effect,color shift keying (CSK),light-emitting diode (LED)
更新于2025-09-19 17:13:59
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In the Right Light: Photodynamic Inactivation of Microorganisms Using a LED-Based Illumination Device Tailored for the Antimicrobial Application
摘要： Drug-resistant bacteria threaten the health of people world-wide and cause high costs to their health systems. According to Scientific American, the number of regrettable fatalities due to the bacteria that are resistant to conventional antibiotics will sum up to 300 million until 2050 if the problem is not tackled immediately. Photodynamic Inactivation (PDI) has proven effective against microorganisms irrespective of their resistance to conventional treatment, but for the translation into clinical practice, economic, homogenous and powerful light sources holding approval as medical devices are needed. In this study we present two novel light emitting diode (LED)-based lamps (Repuls7PDI-red and Repuls7PDI-blue) tailored for application in PDI and demonstrate their photodynamic efficiency upon using either methylene blue (MB), a photoactive compound widely used in PDI, or Sodium Magnesium Chlorophyllin (CHL), a water-soluble derivative of chlorophyll, which holds approval as food additive E140, against bacteria and fungi. Gram+ Staphylococcus aureus, Gram? Escherichia coli and the yeast Candida albicans serve as model systems. Repuls7PDI-red emits a wavelength of 635 nm and an intensity of 27.6 ± 2.4 mW·cm?2 at a distance of 13.5 cm between the light source and the target, while the Repuls7PDI-blue allows an exposure at 433 nm (within the range of violet light) (6.4 ± 0.5 mW·cm?2 at 13.5 cm). Methylene blue was photoactivated with the Repuls7PDI-red at 635 nm (25.6 J·cm?2) and allows for photokilling of E. coli by more than 6 log10 steps at a concentration of 10 μM MB. Using equal parameters, more than 99.99999% of S. aureus (20 μM MB) and 99.99% of C. albicans (50 μM MB) were killed. If blue light (Repuls7PDI-blue, 433 nm, 6.6 J·cm2) is used to trigger the production of reactive oxygen species (ROS), a photoinactivation of S. aureus (5 μM CHL, CFU reduction > 7 log10) and C. albicans (>7 log10) below the detection limit is achieved. PDI based on CHL (10 μM) using red light activation reduces the number of viable S. aureus by more than 6 log10. Our data prove that both LED-based light sources are applicable for Photodynamic Inactivation. Their easy-to-use concept, high light output and well-defined wavelength might facilitate the translation of PDI into clinical practice.
关键词： light emitting diode,photosensitizers,Photodynamic Inactivation,light source,natural substances
更新于2025-09-19 17:13:59
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Spirobifluorene-based oligopyridine derivatives as electron-transporting materials for green phosphorescent organic light-emitting diodes
摘要： The electron-transporting materials (ETMs), 2,7-bis(3,5-di(pyridin-3-yl)phenyl)-9,9'-spirobi[fluorene] (3-4PySF) and 2,7-bis(3,5-di(pyridin-4-yl)phenyl)-9,9'-spirobi[fluorene] (4-4PySF) were designed and synthesized by combining spirobifluorene moiety with di(pyridine-3-yl)phenyl and di(pyridine-4-yl)phenyl, respectively. The spirobifluorene moiety improves materials’ rigid twisted structure to ensure the morphological stability of amorphous film, and pyridine acts as electron acceptor to enhance electron-transporting ability of materials. The dependence of electron-transporting property on the position of substituted pyridine rings was studied. The melting point (Tm) of 4-4PySF is estimated to be 41 ℃ higher than that of 3-4PySF. And the higher current density in the electron only devices exhibited by 4-4PySF revealed the effect of nitrogen atom position on the charge-transporting properties. Green PhOLEDs based on bis(2-phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir(ppy)2tmd) as the emitter and 3-4PySF, 4-4PySF and 1,3,5-tris(N-phenylbenzimidazol-2-yl-benzene (TPBi) as ETMs were fabricated. Compared to the device based on the conventional ETM TPBi, the devices based on new ETMs exhibited a higher maximum external quantum efficiency (EQE) of 20.5% and a lower turn-on voltage (Von) of 2.6 V.
关键词： electron-transporting material,intermolecular interaction,oligopyridine,organic light-emitting diode,spirobifluorene
更新于2025-09-19 17:13:59
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Photocontrolled Iodine-Mediated Green Reversible-Deactivation Radical Polymerization of Methacrylates: Effect of Water in the Polymerization System
摘要： Photocontrolled iodine-mediated reversible-deactivation radical polymerization (RDRP) is a facile and highly efficient access to precision polymers. Herein, a facile photocontrolled iodine-mediated green RDRP strategy was successfully established in water by using 2-iodo-2-methylpropionitrile (CP-I) as the initiator and water-soluble functional monomers including poly(ethylene glycol) methyl ether methacrylate (PEGMA), 2-hydroxyethyl methacrylate (HEMA), and 2-hydroxypropyl methacrylate (HPMA) as the model monomers under blue-light-emitting diode (LED) irradiation at room temperature. Well-defined polymers (PPEGMA, PHEMA, PHPMA) with narrow polydispersities (1.09?1.21) were obtained, and amphiphilic block copolymers which can form nanospheres in situ in water (PPEGMA-b-poly(benzyl methacrylate) (PPEGMA-b-PBnMA) and PPEGMA-b-PHPMA) were prepared. To explore the role of water in our polymerization, control experiments were successfully carried out by using oil-soluble monomer methyl methacrylate (MMA) with the help of trace amounts of water. Notably, the green solvent—water—has an additionally positive effect in accelerating the polymerization and makes our polymerization system an environmentally friendly polymerization system. Therefore, this simple strategy conducted in the presence of water enables the green preparation of well-defined water-soluble or water-insoluble polymers and clean synthesis of amphiphilic copolymer nanoparticles in situ.
关键词： blue-light-emitting diode,water-soluble functional monomers,amphiphilic block copolymers,green solvent,RDRP,Photocontrolled iodine-mediated reversible-deactivation radical polymerization
更新于2025-09-19 17:13:59
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[IEEE 2019 Innovations in Power and Advanced Computing Technologies (i-PACT) - Vellore, India (2019.3.22-2019.3.23)] 2019 Innovations in Power and Advanced Computing Technologies (i-PACT) - A Novel Switched Capacitor based High Gain Boost Converter with efficient MPPT controller for LED Lighting Applications
摘要： The paper proposed a novel switched capacitor based high gain quadratic DC-DC boost converter with Perturb & Observe MPPT (Maximum Power Point Tracking) controller. The converter configuration is appropriate to be employed in fuel cell and solar photovoltaic systems. The presented converter topology is designed with solar powered switched capacitor based voltage lift technique to provide high voltage conversion ratio. Due to variable atmospheric conditions it’s very difficult to provide constant output to the LED (Light Emitting Diode) load. Even small change in the characteristics of LED that will effect to damage the load. Hence P&O (Perturb & Observe) MPPT controller is applying for the designed converter configuration in order to produce stable output with high gain under variable weather conditions. Due to high step up gain and symmetrical configuration of the circuit topology, the stress voltage across the power semiconductor devices is low. Hence, the metal oxide semiconductor field-effect transistor gives high performance with low ON state resistance. The design cost of the circuit is reduces because of using low voltage rating diodes. Also reverse recovery and conduction losses are low which improves the power conversion and efficiency of the converter. The principle of operation and steady state analysis of the circuit topology are conferred in detail. Finally a simulation experiment of proposed converter with 120Watts of LED load is simulated and verified with theoretical analysis.
关键词： High voltage conversion ratio,Switched Capacitor,LED (Light Emitting Diode),PWM (Pulse Width Modulation) control,MPPT(Maximum Power Point Tracking),SMPS (Switched Mode Power Supplies),P&O (Perturb &Observe)
更新于2025-09-19 17:13:59
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Package structure of polarized white chip-on-board light-emitting diode with high thermal conductivity
摘要： The package structure of high power white chip-on-board (COB) light-emitting diode (LED) is investigated. The temperature-dependent performance of the white COB LED combined with a polymeric wire-grid polarizer film (WGF) is optimized. The optimized packaging structure is with a modified phosphor resin layer encapsulated to blue COB LED and an optically transparent plate deposited on the modified phosphor resin layer. The modified phosphor resin comprises a mixture of yellow phosphor and AlN resin for reducing thermal resistance. Results show that the extinction ratio is 83 and the luminous efficacy is 61.4 lm/W at an input power of 8 W for the polarized white COB LED. Without the WGF, the luminous efficacy of the package structure of the COB LED is 90 lm/W.
关键词： Wire-grid polarizer,Packaging, polarization,Light-emitting diode,Chip-on-board
更新于2025-09-19 17:13:59
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Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates
摘要： We compared the e?ciency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the e?ciency droop characteristics using the rate equation model with reduced e?ective active volume. The e?ciency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum e?ciency was ?tted with the rate equation model, the e?ective active volume of the MQW on silicon was found to be ~1.45 times larger than that of the MQW on sapphire. The lower e?ciency droop in the LED on silicon could be attributed to its larger e?ective active volume compared with the LED on sapphire. The simulation results showed that the e?ective active volume decreased as the internal electric ?elds increased, as a result of the reduced overlap of the electron and hole distribution inside the quantum well and the inhomogeneous carrier distribution in the MQWs. The di?erence in the internal electric ?eld of the MQW between the LED on silicon and sapphire could be a major reason for the di?erence in the e?ective active volume, and consequently, the e?ciency droop.
关键词： e?ciency droop,rate equation,quantum well,light-emitting diode,GaN
更新于2025-09-19 17:13:59