Forming technology of boiling structure on evaporation surface of phase-change heat sink for high-power light emitting diode

Boiling structures on evaporation surface of red copper sheet with a diameter (D) of 10 mm and a wall thickness (h) of 1 mm were processed by the ploughing-extrusion (P-E) processing method, which is one part of the phase-change heat sink for high power (HP) light emitting diode (LED). The experimental results show that two different structures of rectangular- and triangular-shaped micro-grooves are formed in P-E process. When P-E depth (ap), interval of helical grooves (dp) and rotation speed (n) are 0.12 mm, 0.2 mm and 100 r/min, respectively, the boiling structures of triangular-shaped grooves with the fin height of 0.15 mm that has good evaporation performance are obtained. The shapes of the boiling structures are restricted by dp and ap, and dp is determined by n and amount of feed (f). The ploughing speed has an important influence on the formation of groove structure in P-E process.

High power and high reliability GaN/InGaN flip-chip light-emitting diodes

High-power and high-reliability GaN/InGaN flip-chip light-emitting diodes （FCLEDs） have been demonstrated by employing a flip-chip design, and its fabrication process is developed. FCLED is composed of a LED die and a submount which is integrated with circuits to protect the LED from electrostatic discharge （ESD） damage. The LED die is flip-chip soldered to the submount, and light is extracted through the transparent sapphire substrate instead of an absorbing Ni/Au contact layer as in conventional GaN/InGaN LED epitaxial designs. The optical and electrical characteristics of the FCLED are presented. According to ESD IEC61000-4-2 standard （human body model）, the FCLEDs tolerated at least 10 kV ESD shock have ten times more capacity than conventional GaN/InGaN LEDs. It is shown that the light output from the FCLEDs at forward current 350mA with a forward voltage of 3.3 V is 144.68 mW, and 236.59 mW at 1.0A of forward current. With employing an optimized contact scheme the FCLEDs can easily operate up to 1.0A without significant power degradation or failure. The li.fe test of FCLEDs is performed at forward current of 200 mA at room temperature. The degradation of the light output power is no more than 9% after 1010.75 h of life test, indicating the excellent reliability. FCLEDs can be used in practice where high power and high reliability are necessary, and allow designs with a reduced number of LEDs.

High color rendering index white organic light-emitting diode using levofloxacin as blue emitter

Levofloxacin （LOFX）, which is well-known as an antibiotic medicament, was shown to be useful as a 452-nm blue emitter for white organic light-emitting diodes （OLEDs）. In this paper, the fabricated white OLED contains a 452-nm blue emitting layer （thickness of 30 nm） with 1 wt% LOFX doped in CBP （4,4＇-bis（carbazol-9-yl）biphenyl） host and a 584-nm orange emitting layer （thickness of 10 nm） with 0.8 wt% DCJTB （4-（dicyanomethylene）-2-tert-butyl-6-（1,1,7,7- tetramethyljulolidin-4-yl-vinyl）-4H-pyran） doped in CBE which are separated by a 20-nm-thick buffer layer of TPBi （2,2＇,2＂-（benzene-1,3,5-triyl）-tri（1-phenyl-lH-benzimidazole）. A high color rendering index （CRI） of 84.5 and CIE chromaticity coordinates of （0.33, 0.32）, which is close to ideal white emission CIE （0.333, 0.333）, are obtained at a bias voltage of 14 V. Taking into account that LOFX is less expensive and the synthesis and purification technologies of LOFX are mature, these results indicate that blue fluorescence emitting LOFX is useful for applications to white OLEDs although the maximum current efficiency and luminance are not high. The present paper is expected to become a milestone to using medical drug materials for OLEDs.

Analysis on electrical characteristics of high-voltage GaN-based light-emitting diodes

In order to investigate their electrical characteristics, high-voltage light-emitting-diodes （HV-LEDs） each contain- ing four cells in series are fabricated. The electrical parameters including varying voltage and parasitic effect are studied. It is shown that the ideality factors （IFs） of the HV-LEDs with different numbers of cells are 1.6, 3.4, 4.7, and 6.4. IF increases linearly with the number of cells increasing. Moreover, the performance of the HV-LED with failure cells is examined, The analysis indicates that the failure cell has a parallel resistance which induces the leakage of the failure cell. The series resistance of the failure cell is 76.8 Ω, while that of the normal cell is 21.3 Ω. The scanning electron microscope （SEM） image indicates that different metal layers do not contact well. It is hard to deposit the metal layers in the deep isolation trenches. The fabrication process of HV-LEDs needs to be optimized.

High-Sensitivity Ozone Sensing Using 280 nm Deep Ultraviolet Light-Emitting Diode for Detection of Natural Hazard Ozone

Recently ozone is one of natural hazards which comes from cars, industry using ozone for sterilization of organic and inorganic materials and for water purification. So, ozone sensing becomes very important, and convenient and accurate ozone sensor is required. A new high sensitivity ozone sensing system using an deep ultra-violet light emitting diode (DUV-LED) operated at the wavelength of 280 nm has been successfully constructed. The fabrication of diode operated at 280 nm is much easier than that of DUV-LED operated at Hg lamp wavelength of 254 nm. The system is compact and possible to sense the ozone concentration less than 0.1 ppm with an accuracy of 0.5% easily with low power DUV-LED of around 200 micro Watts operated at 280 nm without any data processing circuit.

Pure blue and white light electroluminescence in a multilayer organic light-emitting diode using a new blue emitter

We characterized the 6,12-bis{[N-（3,4-dimethylphenyl）-N-（2,4,5-trimethylphenyl）]amino} chrysene （BmPAC）, which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device （WOLED） with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer （BEML） in front of the orange light emitting layer （YEML） to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light.

Highly Efficient and Stable Hybrid White Organic Light Emitting Diodes with Controllable Exciton Behavior by a Mixed Bipolar Interlayer

Highly efficient and stable hybrid white organic light-emitting diodes （HWOLEDs） with a mixed bipolar interlayer between fluorescent blue and phosphorescent yellow emitting layers are demonstrated. The bipolar interlayer is a mixture of p-type diphenyl （l0-phenyl-lOH-spiro [acridine-9,9＇-fluoren]-3Lyl） phosphine oxide and n-type 2＇,2- （1,3,5-benzinetriyl）-tris（1-phenyl-l-H-benzimidazole）. The electroluminance and Commission Internationale de l＇Eclairage （CIE1931） coordinates＇ characteristics can be modulated easily by adjusting the ratio of the hole- predominated material to the electron-predominated material in the interlayer. The hybrid WOLED with a p-type：n-type ratio of 1：3 shows a maximum current efficiency and power efficiency of 61.1 ed/A and 55.8 lm/W, respectively, with warm white CIE coordinates of （0.34, 0.43）. The excellent efficiency and adaptive CIE coordi- nates are attributed to the mixed interlayer with improved charge carrier balance, optimized exciton distribution, and enhanced harvesting of singlet and triplet excitons.

Internal quantum efficiency drop induced by the heat generation inside of light emitting diodes (LEDs)

The reasons for low output power of AlGalnP Light Emitting Diodes （LEDs） have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency （EQE） has serious impaction on the internal quantum efficiency （IQE）, because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.

Evaluation and Enhanced Use of Light Emitting Diodes for Hydroponics

Hydroponic farming is a viable and economical farming method,which can produce safe and healthy greens and vegetables conveniently and at a relatively low cost.It is essential to provide supplemental lighting for crops grown in greenhouses to meet the daily light requirement,Daily Light Integral(DLI).The present paper investigates how effectively and efficiently LEDs can be used as a light source in hydroponics.It is important for a hydroponic grower to assess the requirement of photo synthetically active radiation(PAR)or the Photosynthetic Photon Flux Density(PPFD),in a greenhouse,and adjust the quality and quantity of supplemental lighting accordingly.A Quantum sensor(or PAR sensor)can measure PAR more accurately than a digital light meter,which measures the light intensity or illuminance in the SI unit Lux,but a PAR sensor is relatively expensive and normally not affordable by an ordinary farmer.Therefore,based on the present investigation and experimental results,a very simple way to convert light intensity measured with a Lux meter into PAR is proposed,using a simple conversion factor(41.75 according to the present work).This allows a small-scale hydroponic farmer to use a simple and inexpensive technique to assess the day to day DLI values of PAR in a greenhouse accurately using just an inexpensive light meter.The present paper also proposes a more efficient way of using LED light panels in a hydroponic system.By moving the LED light panels closer to the crop,LED light source can use a fewer number of LEDs to produce the same required daily light requirement and can increase the efficiency of the power usage to more than 80%.Specifically,the present work has determined that it is important to design more efficient vertically movable LED light panels with capabilities of switching individual LEDs on and off,for the use in greenhouses.This allows a user to control the number of LEDs that can be lit at a particular time,as required.By doing so it is possible to increase the efficiency of a LED lighting system by reducing its cost of the electricity usage.

Efficient top-emitting white organic light emitting device with an extremely stable chromaticity and viewing-angle

In this paper,we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic lightemitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer.With a 24-nm out-coupling layer,the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area.By introducing an efficient electron blocking layer tris（1phenylpyrazolato,N,C2 ＇）iridium（III）（Ir（ppz） 3） to confine the exciton recombination area,the current efficiency and the colour stability of the device are effectively improved.A white emission with the Ir（ppz） 3 layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V,and the Commission Internationale de L＇Eclairage（CIE） chromaticity coordinates are almost constant during a large voltage change of 6 V-11 V.There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45,with a CIE x,y coordinate variation of only（±0.0025,±0.0008）.Even at a large viewing angle（75）,the CIE x,y coordinate change is as small as（±0.0087,±0.0013）.

Fabrication of high-voltage light emitting diodes with a deep isolation groove structure

In order to connect several independent LEDs in series, inductively coupled plasma （ICP） deep etching of GaN is required for isolation. The GaN-based high-voltage （HV） LEDs with a 5 μm deep isolation groove and an acceptable mesa sidewall angle of 79.2° are fabricated and presented. The surface morphology and construction profile of the etched groove are characterized by laser microscopy and scanning electron microscopy. After contact metal formation and annealing, the electrical properties are evaluated by I-V characteristics. The trend of the I-V curve has good accordance with conventional LEDs. The contact resistance of HV LEDs is also tested and was reduced by 4.6 Ω compared to conventional LEDs, while the output power increased by 5 W. The results show that this technique can be applied to practical fabrication.

GaN-based high-voltage light-emitting diodes with backside reflector

High-voltage light-emitting diodes （HV-LED） with backside reflector, including Ti305/SiO2 distributed Bragg reflector （DBR） or hybrid reflector combining DBR and Al or Ag metal layer, are investigated using Monte Carlo ray tracing method. The hybrid reflector leads to more enhancement of light-extraction efficiency （LEE）. Moreover, the LEE can also be improved by redesigning the thicknesses of DBR. HV-LED with four redesigned DBR pairs （4-MDBR）, and those with a hybrid reflector combining 4-MDBR and Al metal layer （4-MDBR-Al）, are fabricated. Compared to 4-MDBR, the enhancement of light-output power induced by 4-MDBR-A1 is 4.6%, which is consistent with the simulated value of 4.9%.

Novel high-brightness tunneling-regenerated multi-activeregion AlGaInP light-emitting diode

In order to resolve the prevailing problems in conventional light-emitting diodes (LEDs), novel high-efficiency tunneling-regenerated multi-active-region (TRMAR) LEDs are proposed, which have such advantages as low heat generation, carrier overflow level and non-radiation re-combination rate and whose quantum efficiency and the output optical power can be scaled with the number of the active regions. Experiments show that the on-axis luminous intensity of TRMAR LEDs increases linearly with the number of active regions. The novel LEDs have high quantum efficiency under low current injection and their maximum on-axis luminous intensity exceeds 5 candelas at 20 mA current injection at the peak wavelength of 625 nm with a 15?angle cap.

Enhancement of light output powers of GaN-based light emitting diodes with textured indium tin oxide transparent layer by using corrosive liquid

In order to promote the light output powers of GaN-based light emitting diodes (LEDs), two kinds of novel corrosive liquidshave been developed in this paper to roughen the surface of the indium tin oxide (ITO) current spreading layer of LEDs. As aresult, the textured transparent ITO layer greatly enhanced the external quantum efficiency of the LEDs. Provided that a wafersample was dipped in a kind of corrosive liquid developed by us for only about 60 s, the light output powers of the LEDs canbe promoted by 24.7%, compared with conventional GaN-based LEDs. It is obvious that the presented method is simple, rapidand cost-effective.

A CO_2 laser rapid-thermal-annealing SiO_x based metal-oxide-semiconductor light emitting diode

Enhanced near-infrared （NIR） electroluminescence （EL） of a metal-oxide-semiconductor light emitting device （MOSLED） made on CO2 laser-annealed SiOx film is demonstrated. An EL power of near 50 nW from CO2 laser rapid-thermal-annealing （RTA） MOSLED under a biased voltage of 85 V and a current density of 2.3 mA/cm^2 is preliminarily reported.

Optimization of organic light emitting diode for HAT-CN based nano-structured device by study of injection characteristics at anode/organic interface

To increase the current density of the hole only device, 1, 4, 5, 8, 9, 11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) material has been inserted in the device at the indium tin oxide (ITO)/organic interface. Since HATCN molecule can withdraw electrons, it can alter electronic properties of the electrodes and hence inserted between the organic/metal interfaces. This paper deals with the optimization of the thickness of organic-metal layers to enhance the efficiency. Also, efforts have been made to increase the current density and reduce the operating voltage of the device. The material 2, 7-bis [N, N-bis (4- methoxy-phenyl) amino]-9, 9-spirobifluorene (Meo-Spiro-TPD) is used to simulate the hole only device because it is a thermally stable hole transport material. Simulated results shows that better current density values can be achieved compared to fabricated one by optimizing the organic metal layer thickness. The best optimized layer thickness of 22 nm for Alq3, 25 nm for *CBP doped with Ir(ppy)3, 9 nm for Meo-Spiro TPD and 4 nm for HAT-CN which results in current density of 0.12 A/cm2 with a reduction in operating voltage by approximately 2 V.

KEAP1-NRF2/HO-1通路介导LED红光促高糖诱导下人牙周膜干细胞成骨分化及减轻氧化损伤

目的探讨Kelch样ECH相关蛋白1-核因子E2相关因子2/血红素加氧酶-1(Kelch-like ECH associated protein 1-nuclear factor erythroid 2-related factor 2/heme oxygenase-1,KEAP1-NRF2/HO-1)通路介导发光二极管(light-emitting diode,LED)红光对高糖诱导下人牙周膜干细胞(human periodontal ligament stem cells,hPDLSCs)成骨分化和氧化损伤的影响,为LED红光在细胞抗氧化损伤中的应用提供依据。方法流式细胞术、碱性磷酸酶(alkaline phosphatase,ALP)染色和茜素红染色鉴定hPDLSCs;高糖预处理hPDLSCs 48 h,用1、3、5 J/cm^(2)LED红光照射细胞,CCK-8实验选择促细胞增殖率高的辐射曝光量进行后续实验。将hPDLSCs分为对照组、高糖组、高糖+光照组;ALP染色、ALP活性检测、茜素红染色和半定量分析检测成骨分化能力,qRT-PCR和Western blot检测细胞成骨相关基因ALP、Runt相关转录因子2(runt-related transcription factor 2,RUNX2)、成骨细胞特异性转录因子(osterix,OSX)基因和蛋白表达;qRT-PCR检测相关抗氧化酶基因超氧化物歧化酶2(superoxide dismutase 2,SOD2)、过氧化氢酶(catalase,CAT)表达;荧光显微镜观察和流式细胞术测定细胞内活性氧簇(reactive oxygen species,ROS)水平;ELISA检测细胞上清液中肿瘤坏死因子-α(tumor necrosis factor-α,TNF-α)、白细胞介素-1β(interleukin-1β,IL-1β)水平。以NRF2特异性抑制剂ML385抑制NRF2通路,ALP染色、ALP活性检测细胞早期成骨分化能力,q RT-PCR检测早期成骨分化标志物ALP、RUNX2、OSX基因表达,Western blot检测细胞KEAP1、NRF2、HO-1蛋白表达水平。结果选择促高糖诱导下hPDLSCs增殖率最高的5 J/cm^(2)辐射曝光量进行后续实验(P<0.05)。5 J/cm^(2)LED红光促进高糖诱导下hPDLSCs的成骨分化(P<0.05),上调ALP、RUNX2、OSX的基因与蛋白表达(P<0.05),上调SOD2、CAT基因表达(P<0.05),降低细胞ROS水平(P<0.05),减少细胞上清液中TNF-α、IL-1β水平(P<0.05)。ML385抑制NRF2通路,细胞ALP活性降低(P<0.05),ALP、RUNX2、OSX基因表达下降(P<0.05),KEAP1蛋白表达上升(P<0.05),NRF2、HO-1蛋白表达下降(P<0.05)。结论LED红光可能通过KEAP1-NRF2/HO-1通路促进高糖诱导下hPDLSCs增殖和成骨分化,减轻氧化损伤。

Ce/Tb/Sm共掺杂CaO-B_2O_3-SiO_2发光玻璃的白光发射及其发光颜色调控

用高温熔融法制备了Ce/Tb/Sm三元共掺杂的CaO-B2O3-SiO2发光玻璃材料,并使用荧光分光光度计和CIE色度坐标对其光谱学和发光特性进行了研究.结果表明:在374nm激发下,在Ce/Tb/Sm三元共掺杂发光玻璃的发射光谱中同时观测到了蓝光、绿光和红橙光的发射带,这些发射带的混合实现了白光的全色发射显示.此外,Ce/Tb/Sm三元共掺杂发光玻璃的发光颜色随着Tb4O7含量的减小从绿光逐渐过渡到白光,显示出发光颜色的可调节性,极大地扩展了其在白光发光二极管中的应用.