白光照明LED灯温度特性的研究

分析了荧光粉转换型白光LED照明光源色坐标、显色指数、色温和发光效率与驱动电流和温度的关系。驱动电流的增加将引起蓝光波峰的长移，并随电流的增大而增大；但其对色坐标、色温和显色指并未引起较大的变化，而发光效率发生下降，主要原因为蓝光波峰的红移导致荧光粉与激发波长的不匹配，引起荧光粉发光效率的下降，这个现象在不同环境温度下的发光也得到证实，实验结果认为LED的驱动电流为20mA，温度低于50℃时具有较好的发光效率，而显色指数要通过增加红色成分来改善。     

白光LED用LiBaBO3:Eu2+材料发光特性研究

采用高温固相法制备了LiBaBO3:Eu2+绿色发光材料.测量了Eu2+浓度为1 mol%时样品的激发与发射光谱,其发射光谱为双峰宽谱,主峰分别为482和507 nm,与理论计算值符合很好;监测482 nm发射峰时,对应激发光谱的峰值为287和365 nm,监测507 nm发射峰时,对应的激发峰为365和405 nm.研究了Eu2+浓度对材料发射光谱的影响,结果显示,随Eu2+浓度的增大,蓝、绿发射峰均发生了红移,当Eu2+浓度大于3 mol%时,蓝色发射峰消失,只有绿色发射峰存在.测量了LiBaBO3:Eu2+材料发光强度随Eu2+浓度的变化情况,结果显示随Eu2+浓度的增大发光强度呈现先增大后减小的趋势,在Eu2+浓度为3 mol%时到达峰值,根据Dexter理论,其浓度猝灭机理为电偶极-偶极相互作用.     

白光LED极限流明效率的计算

对蓝光芯片加黄色荧光粉制备白光LED方法的流明效率进行了理论计算。根据光度学原理,我们考虑到视觉函数V(λ)的修正,以色坐标为x=0.325,y=0.332,显色指数为81.5,色温为5 914 K的白光LED发光光谱为依据,计算了白光LED流明效率的理论极限:得出每瓦白光LED辐射光功率产生的光通量为298.7 lm,白光LED发射的总光子数为2.7×10¹⁸。在理想情况下,注入一个电子-孔穴对产生一个蓝光光子,设荧光粉的量子效率为1,因此,注入的电子-孔穴对数亦等于白光光子数,进而计算出白光LED每辐射1 W的光功率所需的电功率为1.51 W,上述白光LED发光光谱对应的白光LED的电-光转换的理论极限流明效率为197.8 lm/W。     

色坐标对白光LED光通量的影响

研究了在蓝光芯片加黄色荧光粉制备白光LED方法中,色坐标位置对光通量的影响。在同样蓝光功率条件下,我们对标准白光点(色坐标x=0.33±0.05,y=0.33±0.05)附近不同色坐标位置的光通量进行了计算。假设(0.325,0.332)位置流明效率为100 lm/W,计算得出,最大光通量对应的色坐标位置为(0.35,0.38),光通量为112 lm;最小光通量对应的色坐标位置为(0.29,0.28),光通量为93.5 lm。相对于100 lm的变化幅度达到18.5%。通过与实验数据的对比和分析,进一步验证了白光LED光通量随色坐标增大而增加的这一趋势。     

温度和电流对白光LED发光效率的影响

对大功率白光LED发光效率进行了研究,得出温度和电流对LED发光效率的影响:随着温度的升高,势阱中辐射复合几率降低,从而降低了发光效率;电流的升高,使更多的非平衡载流子穿过势垒,降低了发光效率。LED工作时,过高的工作温度或者过大的工作电流都会产生明显的光衰:如果LED工作温度超过芯片的承载温度,这将会使LED的发光效率快速降低,产生明显的光衰,并且对LED造成永久性破坏;如果LED的工作电流超过芯片的饱和电流,也会使LED发光效率快速降低,产生明显的光衰。并且LED所能承载的温度与饱和电流有一定关系,散热良好的装置可以使LED工作温度相对降低些,饱和电流也可以更大,LED也就可以在相对较大的电流下工作。     

白光LED光学仿真中的相关色温计算

光学仿真是白光LED照明设计中的一个重要方法,但色度分布的光学仿真中计算量太过庞大,以致在一般计算条件下无法得到可靠的仿真结果。为解决这一问题,本文利用色度转换关系和逐点法计算色温,引入数值拟合和像素合成两种处理方法,有效降低了光学仿真结果的涨落。通过对处理结果和实验结果在照度和相关色温两方面的对比,两种处理方法的有效性得到证明,大幅提升了基于色度配光的光学仿真计算效率。     

新一代照明光源白光LED的发展概况

1概述 目前，常见照明光源存在一定的不足：真空器件体积大，易碎，发光效率低；日光灯短波紫外线激发波长更长的红绿蓝荧光粉发光，发光效率低，寿命短．体积小，效率高，能耗低，寿命长成为对未来新一代照明光源的基本要求，并且要使光源光谱的分布尽量接近太阳光谱，才能与眼睛的特性相匹配．满足这一条件最好方法就是用两种或多种色光合成白光．     

Ba3Tb(BO3)3:Ce3+:一种白光LED用绿色荧光粉

采用高温固相法合成了Ba3Tb(BO3)3和Ba3Tb(BO3)3:Ce3+两种绿色荧光粉,并研究了材料的发光性质.Ba3Tb(BO3)2材料呈多峰发射,发射峰位于439,493,547,589和629 nm,分别对应Tb3+的5D3→7F4和5D4→7F1=6,5,4,3跃迁发射,主峰为547 nm;监测547 nm发射峰,所得激发光谱由4f75d1宽带吸收(200-330 nm)和4f4f电子吸收(330-400 nm)组成,主峰为380 nm.以Ce3+激活Ba3Tb(BO3)3,所得Ba3Tb(BO3)3:Ce3+与Ba3Tb(BO3),材料的发射光谱分布相同,但发射强度明显增强,说明Ce3+对Tb3+产生了很好的敏化作用;监测547 nm最强发射峰,所得激发光谱为宽带,主峰位于360 nm.改变H3BO3量,Ba3Tb(BO3)3:Ce3+材料的发射强度随之变化,当H3BO3过量15 wt%时,发射强度最大.上述研究结果表明Ba3Tb(BO3)3:Ce3+是一种很好的适于UV-LED管芯激发的白光LED用绿色荧光粉.     

白光LED衰减的光谱分析

为了研究白光LED衰减的机理,通过试验跟踪并分析了采用YAG荧光粉、荧光粉晶片、RGB三合一方式封装的PLCC-4型白光LED,以及采用YAG荧光粉封装的大功率白光LED的发射光谱老化衰减曲线。试验在相同的环境下,对上述四种类型的白光LED进行了通电老化,同一类型白光LED老化电流及时间相同,老化完成后测试其光谱分布。通过分析光谱分布曲线的变化来研究白光中各色光的衰减情况,通过对比各色光的衰减情况来推断白光LED的衰减原因。分析表明白光LED的衰减主要是由蓝光LED的衰减及荧光粉的猝灭引起:采用YAG荧光粉、采用荧光粉晶片及RGBLED封装的白光LED衰减特性基本相同,白光的衰减主要是由蓝光的衰减引起;大功率白光LED与PLCC-4型白光LED衰减特性稍有不同,白光的衰减除了因蓝光的衰减外,还有荧光粉的衰减所引起的白光衰减,而蓝光的衰减所占比例至少不低于80%。通过上述分析可以进一步推断:在散热条件足够理想的情况下,白光LED的衰减主要由蓝光的衰减引起,而随着系统温度的提升,荧光粉的衰减将加剧白光LED的衰减。所得结果将为白光LED的应用及进一步对白光LED衰减原因的研究提供了参考。     

涂敷红、绿荧光粉的白光LED显色性研究

通过蓝光发光二极管(LED)芯片激发红、绿两种荧光粉制作白光LED,首先保持两种荧光粉的配比不变,依次从2700～13000 K改变相关色温,发现在某一色温段时,显色指数达到最高.然后依次改变两种荧光粉的配比,重复试验,发现不同的荧光粉配比,达到最高显色指数所对应的色温段不同.试验结果表明,通过合理匹配红、绿荧光粉和硅胶三者之间的比例.可以实现在2700～13000 K之间的任一色温区,显色指数均能达到90以上,在4000 K以下的低色温区,显色指数可达到96.基于此.通过选择和匹配LED蓝光芯片、荧光粉的激发、发射波长,以及它们之间的比例关系,可以实现在任意色温段使显色指数最大化的白光LED光谱设计.     

Nano-plasmon enhancement effect on MWIR light emitting diode performance

We observed a significant increase in electro luminescence from GaSb based mid-wave infrared (MWIR) LED device through coupling with localized surface plasmon of a single layer Au nano-particles. We fabricated an interband cascade (IC) LED device with nine cascade active/injection layers with InAs/Ga_1−x In_xSb/InAs quantum well (QW) active region. Thin Au plasmon layer of 20 nm thickness is deposited on top anode electrode by e-beam technique, which resulted in 100% increase in light output for 50 μm square mesa device. We also observed a reduction in the device turn on voltage and increase in the apparent black body emission temperature due to nano-structure surface plasmon layer.     

新型有机白光器件的初步研究

白光有机电致发光器件(WOLED)具备很多天然的技术优点,可以应用在下一代照明设备上,因此正成为研究的新热点.但是由于传统的多层或单层WOLED结构受染料浓度和载流子传输难以控制等因素的限制,使进一步优化器件效率和白光色度稳定成为WOLED发展的瓶颈.本工作针对传统WOLED存在的上述问题,设计制备了新型的具有颜色互补的黄色和蓝色发光条纹,交替排列所组成的WOLED器件,并且分析了黄光—蓝光条纹尺寸和改变照射角度对器件光照稳定性的影响. 关键词： 白光 色度稳定 效率 条纹结构     

Blue light emitting diode exceeding 100% quantum efficiency

InGaN/GaN light‐emitting diodes (LEDs) are known to exhibit a strongly non‐uniform vertical carrier distribution within the multi‐quantum well (MQW) active region. We propose to eliminate “dark” quantum wells by insertion of multiple tunnel junctions into the MQW which allow for the repeated use of electrons and holes for photon generation. In good agreement with available measurements, we demonstrate by self‐consistent numerical simulation that such tunnel junction LED design promises quantum efficiencies as high as 250% as well as a strongly enhanced output power at high input power, compared to conventional LED concepts.

     

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5~nm/5~nm) film deposition. The surface morphology of wafers and the current--voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.     

Optical design of adjustable light emitting diode for different lighting requirements

<正>Light emitting diode(LED) sources have been widely used for illumination.Optical design,especially freedom compact lens design is necessary to make LED sources applied in lighting industry,such as large-range interior lighting and small-range condensed lighting.For different lighting requirements,the size of target planes should be variable.In our paper we provide a method to design freedom lens according to the energy conservation law and Snell law through establishing energy mapping between the luminous flux emitted by a Lambertian LED source and a certain area of the target plane.The algorithm of our design can easily change the radius of each circular target plane,which makes the size of the target plane adjustable.Ray-tracing software Tracepro is used to validate the illuminance maps and polar-distribution maps.We design lenses for different sizes of target planes to meet specific lighting requirements.     

Effect of encapsulation technology on organic light emitting diode lifetime

A kind of green organic light-emitting diodes (OLED) was prepared via vacuum thermal evaporation, of which the multilayer structure was indium-tin oxide (ITO)/copper-phthalocyanine (CuPc) (200 Å)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD) (600 Å)/N′-diphenyl-N,N′-tris(8-hydroxyquinoline) aluminium (Alq3) (400 Å):10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-(l)benzopyropyrano(6,7,8-i, j)quinolizin-11-one (C545T) (2%)/Alq3 (200 Å)/LiF (10 Å)/Al (1000 Å). And we used both traditional glass encapsulation and thin film encapsulation (TFE) technologies to protect the device, reducing impact of vapor and oxygen. Organic film offered an excellent surface morphology, while inorganic film was nearly a perfect barrier to vapor and oxygen. Both of them constituted the encapsulation unit of TFE. According to the results of acceleration life test, the operation lifetime of device using TFE was 22% less than that of device using traditional glass cap encapsulation. So, the technology of TFE should be optimized further, and the quality of TFE needs a great improvement. There is a long way to go and a lot of hard work before realizing flexible display with OLED, but the dream will be true one day.     

热真空环境下LED发光效率的实验研究

为了研究LED的发光效率在实际空间环境下的变化,对LED的发光效率在热真空环境下进行实验研究,测定LED光学样机在大气环境中以及在热真空环境中的温升及硅光电池电流变化情况,并分析其结点温度与光强的对应关系,得出LED的输出光效随着结点温度的升高而降低的结论。分析比较了在大气、热真空环境条件下的光效输出随结点温度变化的异同,验证了在大气中比在真空环境中光效下降较慢。     

Transport and luminescence phenomena in electroformed silicon nitride-based light emitting diode

Abstract

Hydrogenated amorphous silicon nitride-based heterojunction pin diode was electroformed under sufficiently high forward bias stress leading to its instant nanocrystallization at room temperature. In order to investigate the origin of the accompanying bright visible light emission, current-voltage and electroluminescence (EL) characteristics of the electroformed diode were scanned over temperature. Electrical transport mechanism was analysed in the low, medium and high electric field regimes. Temperature and field dependence of thermal activation energy were discussed. EL characteristics were studied using the spectral energy distribution and the injection current dependence of its intensity. Thermal quenching data of EL and photoluminescence intensities were compared. Finally, the relationship between the electrical transport and luminescence phenomena was attempted to be interpreted within the frame of a self-consistent model.     

A novel yellow phosphor for white light emitting diodes

This paper reports that a novel yellow phosphor, LiSrBO₃:Eusup>2+, was synthesized by the solid-state reaction. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (360 and 400~nm) and blue (425 and 460~nm) light, and exhibits a satisfactory yellow performance (565~nm). The role of concentration of Eusup>2+ on the emission intensity in LiSrBO₃ is studied, and it is found that the critical concentration is 3 mol\%, and the concentration self-quenching mechanism is the dipole--dipole interaction according to the Dexter theory. White light emitting diodes were generated by using an InGaN chip (460~nm or 400~nm) with LiSrBO₃:Eusup>2+ phosphor, the CIE chromaticity is (x=0.341, y=0.321) and (x=0.324, y=0.318), respectively. Therefore, LiSrBO₃:Eusup>2+ is a promising yellow phosphor for white light emitting diodes.     

Luminescence characteristics of Eu3+ activated borate phosphor for white light emitting diode

In this paper, the Sr₃Y₂ (BO₃)₄:Eu³⁺ phosphor was synthesized by high temperature solid-state reaction method and the luminescence characteristics were investigated. The emission spectrum exhibits one strong red emission at 613nm corresponding to the electric dipole ⁵D₀--⁷F₂ transition of Eu³⁺ under 365nm excitation, this is because Eu³⁺ substituted for Y³⁺ occupied the non-centrosymmetric position in the crystal structure of Sr₃Y₂ (BO₃)₄. The excitation spectrum indicates that the phosphor can be effectively excited by ultraviolet (254nm, 365nm and 400nm) and blue (470nm) light. The effect of Eu³⁺ concentration on the red emission of Sr₃Y₂ (BO₃)₄:Eu³⁺ was measured, the result shows that the emission intensities increase with increasing Eu³⁺ concentration, then decrease. The Commission Internationale del'Eclairage chromaticity (x, y) of Sr₃Y₂(BO₃)₄:Eu³⁺ phosphor is (0.640,0.355) at 15 mol% Eu³⁺.