化学共沉淀法合成YAG:Eu~(3+)红色荧光粉及其光致发光性质

采用化学共沉淀法合成YAG∶Eu3+红色荧光粉,利用XRD、荧光光谱和激光粒度仪等表征荧光粉晶体结构、光致发光、粒径分布等。结果表明,当煅烧温度为1000℃时,荧光粉YAG晶相趋于稳定,无中间相的形成,合成温度比传统高温固相法降低近500℃;随着煅烧温度升高,荧光粉光致发光峰强度增大,但峰值波长并不随煅烧温度升高而发生移动;前驱体中添加表面活性剂PEG后,荧光粉粒径为1.3μm左右,且粒径分布范围窄;助熔剂NaF能够显著提高荧光粉的光致发光强度,但过量则会出现浓度猝灭,其最佳添加量为4%。     

Research on lumen depreciation related to LED packages by in-situ measurement method

In this paper, lumen depreciation of LED in reliability experiment was monitored by in-situ measurement method. The partial LED flux on the receiving surface of fiber cable was captured, and it was proportional to the total luminous flux of LED light source when we provided an exact distance. The high temperature operating life test was used to find the weakness elements of LED packages with a limiting maximum temperature stress of 125 °C. Four kinds of packaged samples were constituted with difference components, and the lumen depreciations were presented. Combined with the lumen depreciation data and sampling inspection, the results could be summed up as follows: (i) the luminous flux of LED chip had a steady and slow depreciation, however, that of the samples coated with the phosphor–silicone composites had an initial sharp decline and then reach the stable state. (ii) The samples of only chip encapsulated by silicone and those of commercial white LEDs were carbonized on the center surface between chip and materials of encapsulant. As a conclusion, the silicone as an LED encapsulant could induce flaws, the material properties in larger coefficient of thermal expansion (CTE) and stronger adhesion should be considered in the package design stage, and the degradation of phosphor–silicone composites led to a fast light energy loss during the initial high temperature aging test, and then reached up to steady.     

Color shift acceleration on mid-power LED packages

Mid-power LED packages are now widely used in many indoor illumination applications due to several advantages. Temperature stress, humidity stress and current stress were experimentally designed and performed to accelerate the color shift of mid-power LED packages and color shift mechanisms have been discussed based on the color shift results obtained from measurements. Conclusions could be drawn:

• -Linear function fitting demonstrates a good linear relationship between color shift (Δu′ Δv′) and aging time almost for all the aging conditions. We can extrapolate the color shift Δu′ and Δv′ based on the fitted regression equations and then make the prediction for the total color shift Δu′v′.
• -Current stress can induce a different failure mode. Peak intensity reduction analysis reveals that the current stress accelerates the degradation of LED die.
• -Humidity test induced a substantial color shift both in u′ and v′. The u′ has an increased degradation rate after aging of 3000 h at 85%RH & 85 °C, there should be different degradation mechanisms during the whole humidity test. The molecular structure decomposition of silicone plates and then follows the silicone carbonization due to the long-term (3000 h) accumulated high localized temperature aging.

     

蓝光LEDs的转换荧光粉发光效率的测量

本文研究了YAG:Ce荧光粉的色点红移的现象.当YAG晶格点阵中的Y被 Gd 激发或添加了Pr作为 Ce 的共同催化剂时就会发生这种现象.测量了在(Y,Gd)AG:Ce和YAG:Ce,Pr荧光粉样品内部的效率,其激发光线的波长为 470 nm.其结果表明这两种荧光粉的发光效率分别随着Gd和Pr聚集而降低.SrGa2S4:Eu.是另外一种常用的转换蓝光 LED 的颜色的荧光粉.室温下,这种荧光粉效率很高,理论上其发光效率比 YAG:Ce 的发光效率高出 33%.对这种荧光粉效率的测量结果表明其制作过程是影响性能的主要因素.将这种荧光粉印刷在放在-个或多个蓝光 LED 前面的屏幕的表面,测得其发光效率高达 364 lm/W.     

白光LED的实现及荧光粉材料的选取

主要介绍了目前主流白光LED的封装方法,简述了各种方法的原理及优缺点。重点介绍了蓝光芯片与黄光荧光粉混合实现白光LED的机制。通过测试芯片发射谱、不同荧光粉材料的激发和发射谱,重点研究了蓝色芯片与黄色荧光粉材料的光谱匹配性,讨论了荧光粉材料的选取对器件的电学、光学性能的影响。     

Accelerated life test of high power white light emitting diodes based on package failure mechanisms

Accelerated life tests of high-power white light emitting diodes (LEDs) were conducted under an unbiased highly accelerated temperature and humidity test (HAST) and a normal aging test. The conditions in the unbiased HAST were 110 °C-85% RH, 130 °C-85% RH without bias. During the aging, the degradation mechanisms of optical power reduction and degradation of 455 mm blue wavelengths that were better than phosphors related yellow emission bands were observed. The microscopy analysis showed that this effect could be ascribed to the bubbling and discoloration of the silicone encapsulating material of the package. It is thought that these features are also responsible for the optical power reduction and thermal resistance increase.     

Fabrication of High-power White LEDs and White Light Uniformity Testing

As the blue and yellow lights are complementary colors, a blue InGaN LED chip is coated hy a yellow phosphor film to generate white light based on luminescence conversion mechanism. The emitted light of a blue LED is used as the primary source for exciting fluorescent material such as cerium doped yttrium aluminum garnet with the formula Y3Al2O12 ： Ce^3＋ （in short： YAG ： Ce^3＋ ）. The matching of the spectrum of the blue LED chips and the YAG ： Ce^3＋ yellow phosphor is studied to improve the conversion efficiency. The packaging methods and manufacturing processes for high power single chip-white LEDs are introduced. The uniformity of the output white light is investigated. Based on the characteristics of the high power white LEDs, some approaches and processes are suggested to improve the light uniformity when they are fabricated. The effectiveness of those approaches on the improvement of LEDs is discussed in detail and some interesting conclusions are also presented.     

大功率集成LED光转换光源的研制

介绍了一种应用远程激发技术的大功率集成LED光转换光源,通过使用固晶区无绝缘层的镜面铝基板进行集成封装蓝光LED光源,即COB光源。所制蓝光光源与远程激发荧光粉模块结合制成LED光转换光源。利用镜面铝基板的高导热系数,解决多种LED封装形式下芯片点亮温度过高、光源衰减快的问题。采用LED荧光高分子模块与蓝光芯片分离结合的远程激发技术制成白光光源,解决荧光粉分布不均、热老化、色偏移问题。通过与传统粉胶封装方式制得的大功率集成LED器件比较测试,该种光源具有防眩光、光色均匀度高、长寿命、节能和环保的优点,从而具有更广泛的用途。     

功率型白光LED可靠性的实验及仿真建模研究

快速推广LED产品到照明市场最主要的障碍在于长期的可靠性测试问题。由于长期的LED可靠性测试不符合快速且低成本的要求,因此本实验对白光LED进行步进式加速寿命老化测试,步进式环境温度从55oC到145oC变化。同时,对LED进行结温测试,并使用COMSOL仿真软件进行温度场分布仿真来模拟器件的发热情况,结果表明荧光胶处的温度高于LED芯片温度。在长期老化之后,对LED的光度进行测量,可以对LED的失效机理进行分析。通过研究温度对LED的光谱功率分布衰减的影响及光通量衰减的影响,发现在经过近3500 h的老化之后,LED的光衰很严重,表明电流及高温对LED的影响是极大的。     

Targeting Cooling for Quantum Dots in White QDs‐LEDs by Hexagonal Boron Nitride Platelets with Electrostatic Bonding

Although quantum dots (QDs) show excellent advantages in flexible wavelength‐tuning and high color rendering capability in white light‐emitting diodes (WLEDs) lighting and display applications, the less‐than‐one quantum efficiency inevitably gives rise to a non‐negligible heat generation problem, which induces high‐temperature quenching issues of QDs and severely hinders their potential applications. Efficient heat dissipation for these nanoscale QDs is challenging since these nanoparticle “heat sources” are usually embedded in a low‐thermal conductivity polymer matrix. In this work, this problem is attempted by targeting cooling of the QDs in the silicone matrix by electrostatically bonding the hexagonal boron nitride (hBN) platelets onto QDs without sacrificing the optical performance of WLEDs. The red‐emissive QDs/hBN composites are mixed with yellow‐emissive phosphor to fabricate QDs/hBN‐WLEDs. Due to the effective heat transfer channels established by the QDs/hBN in the silicone, the heat could be dissipated efficiently to ambient air, and the working temperature of WLEDs is reduced by 22.7 °C at 300 mA. The QDs/hBN‐WLEDs still maintain a high luminous efficiency of 108.5 lm W^?1 and a high color rendering index of Ra > 95, R9 > 90, showing that the present strategy can improve heat dissipation without sacrificing the optical performance.     

不同粒径YAG荧光粉对LED封装光源的影响研究

挑选国内某知名荧光粉企业的三种YAG荧光粉作为研究对象,三种样品的激发光谱相同,中心粒径(D50分别为9.3、13.6、16.7μ用这三种荧光粉,在相同粉胶质量比,相同点胶量的情况下,使用3014型号支架,制作出白光LED灯珠样品。使用分光分度计分别测量老化前后样品的各项光学参数。试验结果显示:随着荧光粉中心粒径的增大,色温向着高色温方向移动;当色温相同时,随着中心粒径的增大,光通量随之增大,使用100 mA电流加速老化一个星期情况下,随着荧光粉粒径的增大,光衰逐渐减小。     

驱动电流对大功率白光LED荧光粉转换效率的影响

对4种1W白光功率LED进行了100～900mA的变驱动电流光学特性试验。分析了荧光粉转换效率随驱动电流变化的内在机理,一是由于驱动电流增大导致蓝光芯片内量子限制斯塔克效应引起峰值波长蓝移,致使蓝光与荧光粉的匹配程度降低;二是由于驱动电流增大导致器件温度升高,荧光粉的非辐射增多,且其激发态能级分裂加剧,导致部分能量降低,黄光波长出现红移现象。通过分析上述两种因素的综合作用,得出了荧光粉转换效率随驱动电流变化的规律,并据此提出改进白光LED驱动电流特性的建议。     

激光器免温控泵浦源的多波长选择理论

为了实现激光器在一定温度范围内LD泵浦源免温控稳定工作,具有较高并且稳定的泵浦光吸收效率,分析了DPL激光器中LD发射谱和Nd:YAG增益介质吸收谱的特点及匹配问题,据此提出了一种激光器免温控泵浦源的多波长选择理论和方法,同时增加泵浦光吸收长度克服Nd:YAG吸收谱和LD波长失配的不利影响。优化设计了一个波长为802.35 nm@25℃、813.15 nm@25℃和810.95 nm@25℃的三波长LD泵浦方案,计算结果表明:在一定吸收长度下,多波长泵浦光吸收效率可达73.96%,并且在-15.7~65.7℃宽温度波动范围内,激光器输出能量不稳定度优于5%。同时还模拟分析了增益介质吸收长度和掺杂浓度对泵浦光吸收效率的影响。     

YAG荧光屏的制作与性能

介绍一种YAG荧光屏的结构、制作以及性能。YAG荧光屏不同于传统玻璃荧光屏的一个显著特点就是以具有高热导率、高机械强度、良好绝缘性和透光性的单晶YAG代替玻璃作为荧光屏粉层衬底。我们在YAG衬底上采用离心沉淀法制作荧光粉层;有机膜采用手工旋涂法工艺制作;铝膜采用真空电阻蒸发法制作,并讨论了铝膜的最佳厚度选取。3英寸红、绿、蓝荧光屏在0.5mA电流、29kV电压下亮度分别是6.2×10     

高功率高可靠性9XX nm激光二极管

为了提高半导体激光二极管的输出功率和可靠性,通过在有源区两侧势垒层和波导层之间引入高禁带宽度的GaAsP,抑制有源区载流子的泄漏,极大地改善了器件的性能。研究结果表明:在10~40℃温度范围内器件特征温度从原来的150 K提高至197.37 K(-75.76℃),峰值波长随温度的漂移系数为0.207 nm/℃;条宽200μm、腔长2000μm的9XX nm激光二极管可靠性工作的最大输出功率高达14.4 W;器件在注入电流为7 A时取得71.8%的最大电光转换效率,斜率效率为1.21 W/A。器件在恒定电流下的加速老化测试显示激光二极管可靠性工作寿命达2000 h以上。     

Synergetic Excess PbI2 and Reduced Pb Leakage Management Strategy for 24.28% Efficient,Stable and Eco-Friendly Perovskite Solar Cells

Introducing excess PbI₂ has proven to be an effective in situ passivation strategy for enhancing efficiency of perovskite solar cells (PSCs). Nevertheless, the photoinstability and hysteresis are still tough issues owing to the photolysis nature of PbI₂. Moreover, the humidity-related degradation of perovskite films is also a difficult territory to cover in such an in situ passivation strategy. Herein, a synergistic strategy is reported via initiatively inducing vertical graded PbI₂ distribution (GPD) in the whole perovskite film and capping a cis-Ru(H₂dcbpy)(dnbpy)(NCS)₂ (Z907) internal encapsulation (IE) layer on the surface to ameliorate the above issues. The GPD design can enhance luminescence, prolong carrier lifetimes, ascertaining the improvement of efficiency and elimination of photoinstability in the PSCs. Besides, the introduced IE layer not only can promote the moisture and thermal resistance, but also inhibit Pb leakage and ion migration in the PSCs. Through the synergetic regulations, the resultant PSCs exhibit an impressive open circuit voltage (V_OC) of 1.253 V, fill factor of 81.25%, and power conversion efficiency (PCE) of 24.28%. Moreover, the PSCs maintain 91% of its initial PCE at relative humidity of 85% after 500 h aging and 94% under continuous heating at 85 °C after 750 h aging.     

Accelerated testing for failures of tantalum capacitors

This study focused on the use of accelerated testing to find out why tantalum capacitors fail. Stress effects of humidity, temperature, and ripple voltage were examined in different combinations. Results show that a standard 85/85 test with combined enhanced moisture and temperature does not result in failure of tantalum capacitors in 2500 h. However, with added ripple voltage, failures may occur in a relatively short time. High relative humidity and high temperature both affect water diffusion, but apparently increased ripple voltage in 85/85 testing causes tantalum capacitor characteristics to weaken and capacitors to fail. The paper elaborates on the possible reasons.     

层压封装平面LED光源的耐候实验

研究了层压封装的平面LED光源在高温高湿与水下环境的可靠性。平面LED光源采用标准层压工艺封装,对封装后的LED模组进行高温高湿耐候试验与水下环境试验,并与未封装的LED模组进行对比实验。实验结果表明,在环境温度为80℃、相对湿度为80%,模组工作电流为300 mA,连续33天高温高湿条件下,层压封装的平面LED模组的照度变化和温度均高于未封装的LED模组。在40℃水下环境下连续工作400 h,层压封装的平面LED模组的照度略有变化,且光衰小于1%。因此,层压封装能有效阻断外界高温高湿环境对LED模组可靠性的影响,更适合在常温水下照明应用。     

基于蓝光LED的白光器件:用于固体发光的小颗粒YAG:Ce型荧光粉的合成

文章介绍了小颗粒 YAG:Ce 荧光粉的三种合成方法.这种荧光粉受到蓝光 LED 发出的光线的激发会发出黄光.在合成的 pcLEDs 里,蓝光和黄光混合形成了白光.本文解释了这种涂有 YAG:Ce 荧光粉的 pcLED 的色点的依赖性以及通过添加修复晶格点阵的催化剂以改变这种依赖型的方法.另外,文章还讨论了 Ce3 聚集中心的YAG:Ce 荧光粉的效率的测量、烧成温度、激发波长.