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Electrical and Environmental Degradation Causes and Effects in Polyfluorene-Based Polymer Light-Emitting Diodes
摘要： We report on the degradation mechanism of polymer light-emitting diodes (PLEDs) kept in the environment with no encapsulation. The device structure is indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/poly?uorene/aluminum (Al) fabricated by a simple solution-processed method. Its physical, optical and electrical properties were measured over time in order to explore factors resulting in device instability. The sustained decrease in current density and electroluminescence, as well as the appearance of dark spots and electrode delamination, reveal that the device performance tends to degrade in the atmosphere gradually. To clarify the effect of the external electric ?eld on the device degradation process, a device with lower threshold voltage was fabricated and its performance was recorded with and without bias voltage. Also, when the Al cathode of a completely ruined blue PLED was re-deposited, the device started to emit green light, con?rming the irreversible chemical structural changes occurred in the active layer. Noticeably, in addition to cathode delamination, we observed that the rate of luminescence degradation in fabricated PLEDs is more than two times faster than that of the current density. The detailed study of the stability issue in PLEDs, presented in this work, can have great potential importance in the fabrication of other organic electronic devices such as organic solar cells and organic photodetectors due to similar instability factors.
关键词： Degradation,dark spot,luminescence,polymer light-emitting diode
更新于2025-09-23 15:19:57
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Antimicrobial photodynamic therapy with Bixa orellana extract and blue LED in the reduction of halitosisa??A randomized, controlled clinical trial
摘要： This study aimed to evaluate the reduction of halitosis when using antimicrobial photodynamic therapy (aPDT) with Bixa orellana extract and blue light-emitting diode (LED). Methods: Forty-four UNINOVE students or employees with a diagnosis of sulfide (H2S) ≥ 112 ppb in gas chromatography were selected. The patients were randomly divided in groups: Group 1 (n=15): aPDT with annatto and LED; Group 2 (n=14): tongue scraping; Group 3 (n=15): tongue scraping and aPDT. For aPDT, a was Bixa orellana extract used in a concentration of 20% w/v (Fórmula e A??o?, S?o Paulo, Brazil) on the tongue for 2 minutes, associated with a blue-violet LED (Valo Cordless Ultradent? Products, Inc., South Jordan, UT, USA) (395-480 nm). Six points were irradiated on the back of the tongue, at wavelength 395-480 nm for 20 seconds, energy of 9.6 J and radiant energy of 6.37 J/cm2 per point. The results were compared before, immediately after treatment and 7 days after. The Friedman test was used for the intragroup analysis and the Kruskal Wallis test for the intergroup analysis. Results: In all groups, there was a difference between baseline and the value immediately after the treatment. In Groups 1 and 3, there was no difference between the baseline and the 7 days control. Conclusion: There was an immediate reduction of halitosis, but the reduction was not maintained after 7days.
关键词： Light emitting diode,Photodynamic therapy,Bixa orellana,Halitosis
更新于2025-09-23 15:19:57
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Efficient near ultraviolet organic light-emitting diode based on PVK material doped with BCPO molecules
摘要： Near ultraviolet organic light-emitting diodes (NUV-OLEDs) have a wide range of applications. However, when large band-gap polymer of PVK was used as the emitting material, its poor electron transportation capability resulted in a large amount of charge accumulation on both sides of light-emitting layer/electron-transporting layer interface of the device, hence generating intense electroplex emission and seriously reducing the e?ciency of NUV light-emitting. In order to solve this issue, BCPO molecules were doped in PVK with certain concentrations, forming PVK:BCPO mixing light-emitting layers. As compared with pure PVK, electron transportation capability was apparently increased in PVK:BCPO mixing layers. On one hand, charge accumulation at the interface was substantially weakened, and the electroplex emission was inhibited. On the other hand, transportations of electron and hole carriers became more balanced in light-emitting layer. Both of these improvements e?ectively promoted device performance. At appropriate BCPO doping concentration, the external quantum e?ciency of PVK:BCPO-based NUV-OLEDs reached the maximum value of ～2.6 %. Further experimental progress would bring it closer to the practical application in future.
关键词： Electroplex,Near ultraviolet,E?ciency,Organic light-emitting diode
更新于2025-09-23 15:19:57
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Prominent Heat Dissipation in Perovskite Light-Emitting Diodes with Reduced Efficiency Droop for Silicon-Based Display
摘要： Solution-processed perovskite light-emitting diodes (LEDs) possess outstanding optoelectronic properties for potential solid-state display applications. However, poor device stability results in significant efficiency droop partly being ascribed to Joule heating when LEDs are operated at high current densities. Herein, we used monocrystal silicon (c-Si) as substrate and charge injection layer to alleviate the thermal affection in perovskite LED (PeLED). By incorporating silicon oxide (SiOx) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4’-(N-(4-butylphenyl) (TFB) layer to tune the charge injection balance in c-Si-based device, a PeLED achieves an external quantum efficiency of 2.12% with a current efficiency of 6.06 cd A-1. Benefiting from excellent heat dissipation of c-Si, the PeLEDs display reduced efficiency droop and extended operational lifetime. Furthermore, both electroluminescent (EL) dynamic information display and static pattern displays of c-Si-based PeLED have been successfully demonstrated. These results reveal the feasibility of potential practical c-Si-based PeLEDs with reduced efficiency droop for EL display applications.
关键词： efficiency droop,silicon substrate,perovskite light-emitting diode,display application,heat dissipation
更新于2025-09-23 15:19:57
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Nanoplatelet-Based Light-Emitting Diode and Its Use in All-Nanocrystal LiFi-like Communication
摘要： Since colloidal nanocrystals (NCs) were integrated as green and red sources for LCD displays, the next challenge for quantum dots has been their use in electrically driven light emitting diodes (LEDs). Among various colloidal nanocrystals, nanoplatelets (NPLs) appeared as promising candidates for light emitting devices because their two-dimensional shape allows a narrow luminescence spectrum, directional emission and high light extraction. To reach high quantum efficiency it is critical to grow core/shell structures. High temperature growth of the shells seems to be a better strategy than previously reported low temperature approaches to obtain bright NPLs. Here, we synthesize CdSe/CdZnS core/shell NPLs whose shell alloy content is tuned to optimize the hole injection in the LED structure. The obtained LED has exceptionally low turn-on voltage, long-term stability (>3100 h at 100 Cd.m-2), external quantum efficiency above 5% and luminance up to 35000 cd.m-2. We study the low-temperature performance of the LED and find that there is a delay of droop in terms of current density as temperature decreases. In the last part of the paper, we design a large LED (56 mm2 emitting area) and test its potential for LiFi-like communication. In such approach, the LED is not only a lightning source but also used to transmit a communication signal to a PbS quantum dot solar cell used as a broad band photodetector. Operating conditions compatible with both lighting and information transfer have been identified. This work paves the way toward an all nanocrystal-based communication setup.
关键词： efficiency droop,nanoplatelets,electronic transport,light emitting diode,nanocrystal-based communication
更新于2025-09-23 15:19:57
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Effect of Horizontal p-n Junction on Optoelectronics Characteristics in InGaN-Based Light-Emitting Diodes with V-shaped Pits
摘要： Two InGaN-based light-emitting diodes (LEDs) with and without pre-layer were prepared, and both had a similar multi-quantum well (MQW) structure with four green QWs near n-GaN and one blue QW close to p-GaN. The pre-layer established large V-shaped pits in MQWs. In addition to the regular vertical p-n junction along c-axis, a kind of horizontal p-n junction created by n-type MQWs and p-GaN filled in V-shaped pits was introduced. And the effect of the horizontal p-n junction on optoelectronics characteristics, including photoluminescence, electroluminescence, and ??-??, were discussed. The horizontal p-n junction creates a strong horizontal built-in electric field which can effectively separate the photogenerated carriers in the QW close to p-GaN, leading to the absence of photoluminescence from the QW close to p-GaN. The horizontal p-n junction also provides a path for hole injection, which changes the turn-on order of QW, and reduces the voltage of the LED with large V-shaped pits. These results suggest a new thought of analyzing and designing InGaN-based LEDs with V-shaped pits.
关键词： light-emitting diode,V-shaped pit,indium gallium nitride,built-in electric field
更新于2025-09-23 15:19:57
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Inactivation of <i>Pseudomonas aeruginosa</i> Biofilms by 405-Nanometer-Light-Emitting Diode Illumination
摘要： Biofilm formation by Pseudomonas aeruginosa contributes to its survival on surfaces and represents a major clinical threat because of the increased tolerance of biofilms to disinfecting agents. This study aimed to investigate the efficacy of 405-nm light-emitting diode (LED) illumination in eliminating P. aeruginosa biofilms formed on stainless steel coupons under different temperatures. Time-dependent killing assays using planktonic and biofilm cells were used to determine the antimicrobial and antibiofilm activity of LED illumination. We also evaluated the effects of LED illumination on the disinfectant susceptibility, biofilm structure, extracellular polymeric substance (EPS) structure and composition, and biofilm-related gene expression of P. aeruginosa biofilm cells. Results showed that the abundance of planktonic P. aeruginosa cells was reduced by 0.88, 0.53, and 0.85 log CFU/mL following LED treatment for 2 h compared with untreated controls at 4, 10, and 25°C, respectively. For cells in biofilms, significant reductions (1.73, 1.59, and 1.68 log CFU/cm2) were observed following LED illumination for 2 h at 4, 10, and 25°C, respectively. Moreover, illuminated P. aeruginosa biofilm cells were more sensitive to benzalkonium chloride or chlorhexidine compared with untreated cells. Scanning electron microscopy and confocal laser scanning microscopic observation indicated that both the biofilm structure and EPS structure were disrupted by LED illumination. Further, reverse transcription-quantitative PCR revealed that LED illumination downregulated the transcription of several genes associated with biofilm formation. These findings suggest that LED illumination has the potential to be developed as an alternative method for prevention and control of P. aeruginosa biofilm contamination.
关键词： light-emitting diode,disinfectant,extracellular polymeric substances,biofilm-related genes,Pseudomonas aeruginosa,biofilm
更新于2025-09-23 15:19:57
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Luminous Intensity Field Optimization for Antiglare LED Desk Lamp without Second Optical Element
摘要： This study proposes a model of a light module with an optimized luminous intensity ?eld for realizing an antiglare light-emitting diode (LED) desk lamp without a second optical element. We simulated di?erent luminous intensity ?eld pro?les to analyze the uni?ed glare rating (UGR) and illumination uniformity performance of a desk lamp. The spatial e?ect of UGR and the illumination uniformity a?ect eye comfort. The light module was set to di?erent beam angles without a second optical element, louver structure, and re?ective element on the luminaire to compare di?erent UGRs and uniformity values for evaluating human eye comfort. The simulation and experimental results indicated that the luminous intensity curve for a beam angle of 90? achieved an illumination uniformity of 80% and a UGR of 18.1 at a height of 45 cm, thus realizing a human-friendly antiglare desk lamp.
关键词： light-emitting diode,second optical element,uni?ed glare rating,desk lamp,antiglare
更新于2025-09-23 15:19:57
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Double Metal Oxide Electron Transport Layers for Colloidal Quantum Dot Light-Emitting Diodes
摘要： The performance of colloidal quantum dot light-emitting diodes (QD-LEDs) have been rapidly improved since metal oxide semiconductors were adopted for an electron transport layer (ETL). Among metal oxide semiconductors, zinc oxide (ZnO) has been the most generally employed for the ETL because of its excellent electron transport and injection properties. However, the ZnO ETL often yields charge imbalance in QD-LEDs, which results in undesirable device performance. Here, to address this issue, we introduce double metal oxide ETLs comprising ZnO and tin dioxide (SnO2) bilayer stacks. The employment of SnO2 for the second ETL significantly improves charge balance in the QD-LEDs by preventing spontaneous electron injection from the ZnO ETL and, as a result, we demonstrate 1.6 times higher luminescence efficiency in the QD-LEDs. This result suggests that the proposed double metal oxide ETLs can be a versatile platform for QD-based optoelectronic devices.
关键词： metal oxide,light emitting diode (LED),SnO2 nanoparticles,quantum dot (QD),double electron transport layer (ETL)
更新于2025-09-23 15:19:57
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Room-temperature operation of near-infrared light-emitting diode based on Tm-doped GaN with ultra-stable emission wavelength
摘要： Near-infrared (NIR) light with a wavelength of 650–950 nm is used for various biomedical applications. Although NIR emitters are typically based on GaAs-related materials, they contain toxic elements, and the emission wavelength can easily shift during the device operation due to temperature changes and current injection levels. On the other hand, Tm3t, which is one of the rare-earth ions, can generate ultra-stable NIR luminescence with a wavelength of (cid:1)800 nm, based on 3H4 – 3H6 transitions in a 4f shell, and we have recently focused on Tm-doped GaN (GaN:Tm) based light-emitting diodes (LEDs) as novel NIR emitters. In this paper, we present a demonstration of a NIR-LED based on GaN:Tm grown by the organometallic vapor phase epitaxy method with optimized growth conditions and structures, where the parasitic reaction is well suppressed. NIR luminescence from the GaN:Tm-based LED is derived from 3H4 – 3H6 transitions of Tm3t ions and consists of three dominant peaks at 795, 806, and 814 nm. The turn-on voltage of the NIR-LED is (cid:1)6:9 V, and it is significantly lower than the previously reported electroluminescent devices based on GaN:Tm with impact ionization processes. From a current dependence of the electroluminescence spectra and temperature-dependent photoluminescence for the NIR-LED, the peak shifts are determined to be ,7:6 pm/mA and (cid:1)1:3 pm/K, respectively.
关键词： Tm-doped GaN,ultra-stable emission wavelength,Near-infrared,organometallic vapor phase epitaxy,light-emitting diode
更新于2025-09-23 15:19:57