内外相结构的粉浆法制备白光LED

为了获得白光LED芯片表面上优质性能的荧光粉层,提出一种内外相结构的粉浆法。基于水溶性感光胶的平面涂层技术,采用四氢呋喃将硅胶均匀分散后,通过有机硅消泡剂乳化形成以聚乙烯醇(PVA)为外相,以憎水性粘合剂硅胶为内相的乳液。实验结果表明,这种粉浆具备硅胶的优良特性,提高了荧光粉层的物化性能,显影后在芯片表面得到均匀且厚度可控的平面涂层,改善了白光的均匀性,提高了芯片的出光效率。     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的白光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层.采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr3+在433.6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44.8～59 lm提高到了79.4～84.9 lm.     

功率型白光LED平面涂层技术研究

基于水溶性感光胶的白光LED表面涂层技术,阐述了含有荧光粉感光胶悬浮液的配比和封装结构对白光LED出光效率的影响,提出了相应的改进措施,通过实验证实提高了白光LED器件的整体性能.同时,对利用该法得到的功率型白光LED进行了光衰减测试,LED在700mA电流下点亮168 h后,光输出为初始光输出的95.95%,满足实用要求.     

提高基于粉浆法的功率型白光LEDs发光效率的研究

基于水溶性感光胶的自光LEDs平面涂层技术,在蓝光LED芯片表面上得到了可控的荧光粉层．采用降低粉浆中ADC的浓度和提高荧光粉的含量两种措施,减少Cr^3＋在433．6和620nm两处吸收对器件出光效率的影响;新配制的粉浆在暗室中静置3～5h,既可以提高器件的出光效率同时又避免了暗反应带来的影响;在蓝光LED表面上得到粉层后,再涂覆硅胶层,由于硅胶的折射率与粉层的更接近,不但使出光色调偏向蓝光区域而且有更多光子出射,光通量由未加硅胶层时的44．8～59lm提高到了79．4～84．9lm．     

白光LED荧光粉涂层用感光胶及其光化学反应

蓝光发光二极管(LED)芯片与黄色荧光粉组合,是一种实现白光LED的有效途径.采用粉浆法和光刻工艺,在蓝光LED芯片表面得到了一层平面黄色荧光粉层,实现了对荧光粉层的厚度和形状的控制,光谱测试显示所得器件达到了白光照明的要求.详细介绍了基于水溶性感光胶的荧光粉胶体的制备方法,并对其光化学反应的机理进行了初步探讨.     

高亮度高纯度白光LED封装技术研究

通过对高功率InGaN(蓝)LED倒装芯片结构+YAG荧光粉构成白光LED的分析,可以得出这种结构能提高发光效率和散热效果的结论。通过对白光LED的构成和电流/温度/光通量的分析,可知在蓝宝石衬底和环氧树脂的界面间涂敷一层硅橡胶能改善光的折射率。改进光学器件的封装技术,可以大幅度提高大功率LED的出光率(光通量)。     

粉浆法制备平面荧光粉涂层白光LED的技术改进

基于粉浆法制备白光LED能得到厚度可控的荧光粉层,改善了白光LED的均匀性.由于芯片长时间工作时表面的发热以及回流焊时的瞬间高温环境,聚乙烯醇(PVA)感光胶的颜色容易发生改变,影响了白光LED光效的稳定性.本文采用等离子体去胶,实验结果表明,通过该方法能有效去除感光胶,处理后的LED不会因为长时间工作荧光粉表面涂层的...     

荧光粉涂覆方式对白光LED光色指标的影响

文章采用TRACEPRO软件建立了三种白光LED的光学模型:(1)芯片直接涂覆荧光粉;(2)芯片涂覆硅胶后涂覆荧光粉层;(3)芯片涂覆荧光粉后涂覆硅胶层.通过改变荧光粉的摩尔浓度或硅胶厚度来考察白光LED的光色指标,如光通量、色温及显色指数的变化.研究结果表明:第一种和第二种涂覆方式中,光色指标随着荧光粉摩尔浓度或硅胶厚度的改变呈规律性变化;第三种涂覆方式中,色温及显色指数的变化趋势不稳定,第三种方式光通量高于前两种,最大值可达到87.31m.三种方式的显色指数在70左右.研究结论为白光LED工艺设计提供参考和依据.     

白光 LED 封装材料的光学特性对光通量的影响

封装材料的光学特性是影响白光 LED 光通量的主要因素之一,基于蒙特卡洛非序列光线追迹的方法,应用专业光学仿真软件 Lighttools 系统地研究了硅胶折射率、荧光粉颗粒粒径、反光杯表面反光类型及反光率几种光学特性条件下的白光 LED 光通量。研究结果表明：硅胶折射率存在最优值（n=1.48）使得白光 LED 光通量最大;在相同色温的前提下荧光粉颗粒粒径与光通量成反比关系;漫反射表面对于光通量的提高优于镜面反射,同时光通量均随着反光率的升高而升高,这些规律对于实际生产研究具有指导意义。     

折射率匹配对绿光发光二极管微显示光学性能影响

设计了用于发光二极管(LED)微显示器折射率匹配层结构,可以提高LED微显示器的光学性能。倒装结构的LED微显示器出光面为蓝宝石(折射率约1.76),它和空气的折射率(约为1.0)相差较大,会有很大一部分光因为全反射而反射回器件内部被吸收,导致器件的光效率降低。本文通过涂敷折射率匹配层硅胶(折射率约1.41～1.53)的方法,改变器件表层的折射率使其和空气的折射率相匹配,增加光逃逸锥角,从而提高器件的光效率。结果表明涂敷硅胶可以提高光效率约25.75%,在涂敷硅胶基础上盖玻璃片(折射率约1.47)可提高光效率约32.78%,且硅胶涂敷前后器件的电学、光学、结温稳定性好。尽管增加的是侧方向的光通量,但是其光效率的增加为高效率LED微显示的实现提供了参考依据。     

Phosphor Thermometry in White Light-Emitting Diodes

A method for the in situ measurement of phosphor temperature in high-power white light-emitting diodes (LEDs) was demonstrated. The method is based on the dependence of the fluorescence decay time in inorganic phosphors on temperature. The decay time was estimated using the frequency-domain technique, which relies on the measurement of the phase shift of the sinusoidal waveform of fluorescence relative to that of the photoexcitation, obtained by driving the LED at high-frequency current. LEDs containing a single phosphor ("cool-white") and a phosphor blend ("warm-white") were examined. By comparison of the phosphor temperature with that of the LED junction and metal mount, the character of the spatial profile of temperature within the LED packages was revealed     

大功率发光二极管的寿命试验及其失效分析

以GaN基蓝光LED芯片为基础光源制备了大功率蓝光LED,并通过荧光粉转换的方法制备了白光LED.对大功率蓝光和白光LED进行了寿命试验,并对其失效机理进行了分析.结果表明,大功率LED的光输出随时间的衰减呈指数规律,缺陷的生长和无辐射复合中心的形成,荧光粉量子效率的降低,静电的冲击,电极性能不稳定,以及封装体中各成分之间热膨胀系数失配引起的机械应力都可能导致大功率LED的失效.     

Overdriving reliability of chip scale packaged LEDs: Quantitatively analyzing the impact of component

The objective of this study is to quantitatively evaluate the impacts of LED components on the overdriving reliability of high power white LED chip scale packages (CSPs). The reliability tests under room temperature are conducted over 1000 h in this study on CSP LEDs with overdriving currents. A novel method is proposed to investigate the impact of various components, including blue die, phosphor layer, and substrate, on the lumen depreciation of CSP LEDs after aging test. The electro-optical measurement results show that the overdriving current can lead to both massive light output degradation and significant color shift of CSP LEDs. The quantitative analysis results show that the phosphor layer is the major contributor to the failure in early period aging test. For the long-term reliability, the degradations of phosphor and reflectivity of substrate contribute significantly on lumen depreciation. The proposed reliability assessment method with overdriving loadings can be usefully implemented for LED manufacturers to make a cost- and effective-decision before mass production.     

Preparation of GaN-on-Si based thin-film flip-chip LEDs

GaN based MQW epitaxial layers were grown on Si(111) substrate by MOCVD using AIN as the buffer layer.High light extraction LEDs were prepared by substrate transferring technology in combination with thin-film and flip-chip design.The blue and white 1.1×1.1 mm~2 LED lamps are measured.The optical powers and external quantum efficiency for silicone encapsulated blue lamp are 546 mW,and 50.3%at forward current of 350 mA, while the photometric light output for a white lamp packaged with standard YAG phosphor is 120.1 lm.     

Optical Analysis of Color Distribution in White LEDs With Various Packaging Methods

Uniform color distribution is essential for the packaging of light emitting diodes (LEDs). The Monte Carlo ray tracing method is applied to analyze the color distribution of white LEDs. Five packaging methods are investigated and the location of phosphor layer is varied. Results reveal that the packaging method is the primary factor affecting the color distribution and a nonreflector packaging method presents better color uniformity. The location of phosphor has a small impact on the color uniformity but remote location, if too far, can reduce the uniformity significantly. The reduction of color uniformity may exceed 88%.      

Luminous efficacy and color rendering index of high power white LEDs packaged by using red phosphor

We packaged a series of high power white LEDs by covering the blue LED chips with yellow phosphor, red phosphor and the two phosphors mixed by appropriate mass ratio, respectively, and discussed the excitation and emission spectrum of yellow phosphor and red phosphor and the characteristics of the LEDs. We found that the luminous efficacy of the white LEDs covered with the two phosphors mixed by appropriate mass ratio was lower than that of the white LEDs covered with yellow phosphor, but the color rendering index was improved observably.     

Methods of Increasing Luminous Efficiency of Phosphor-Converted LED Realized by Conformal Phosphor Coating

White light output was realized through combining a cerium-doped yttrium aluminum garnet (YAG:${hbox{Ce}}^{3+}$ ) phosphor with a gallium nitride (GaN)-based blue light-emitting diode (LED). In order to coat a phosphor layer of high quality on a GaN chip, the slurry coating technique was applied and investigated because of the coating efficiency and uniformity. The phosphor layer of conformal structure was realized on the LED chip with the self-exposure method. The influences of ammonium dichromate (ADC) as photosensitizer of photoresist in the slurry are discussed. Two methods are brought forward to reduce the absorption of Cr ions introduced by ADC. And experimental results indicate that these two methods are feasible to increase the luminous efficiency of white LEDs.