低色温高显色性大功率白光LED的制备及其发光特性研究

用GaN基大功率蓝光LED芯片作为激发光源，分别用荧光粉转换法和红光LED补偿法制备了不同相关色温及显色指数的白光LED。对器件的发光特性研究表明，采用监光LED芯片激发单一黄色荧光粉，虽可以获得光通量和发光效率较高的白光LED，但其色温较高，显色性较差；在黄色荧光粉中添加红色荧光粉，由于光谱中红色成分的增加，可降低器件的色温，并提高器件的显色性，但由于目前红色荧光粉的转换效率较低，致使器件的整体发光效率不高；采用蓝光LED芯片激发黄色荧光粉，同时用红光LED进行补偿，通过调整蓝光和红光LED芯片的工作电流以及荧光粉的用量，可获得低色温和高显色性白光LED，而且整体发光效率较高。     

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.     

四芯片色温可调白光LED的研究

为了实现高光效、高显色性且色温可调的白光LED,对四种单基色蓝、绿、黄、红光LED的混光进行了研究.基于Yoshi-单色光模型和光的叠加原理,通过改变四种LED芯片的组合方式(峰值波长、相对光功率配比),对不同色温区的混合白光的显色指数(Ra)、色品质数(Qa)和光视效能(K)进行了仿真计算和光谱优化选择.结果表明:在2 700～6 500 K色温范围内,峰值波长为445 nm,500 nm,560 nm,620 nm的组合可以得到高Ra值和高Qa值;峰值波长为445 nm,535nm,590 nm,615 nm的组合可以得到较高K值.此外还分析了组合白光LED光谱参数对Ra、Qa、K及相关色温的影响.     

基于三通道脉冲宽度调制的LED调光调色

为了实现发光二极管(LED)的精确调光,根 据重心原理,结合脉冲宽度调制(PWM),推导出混合光的色品坐标 与占空比的函数关系;采用红/绿/蓝、红/绿/冷白和暖白/绿/蓝3种LED光源模块进行 实验验证,并且 以光效、显色指数和最大光通量3个指标对混光效果进行评价。实验结果表明:建议的计算 模型能精确地指导LED的光 色调节,混合光的色品坐标的设定值和测量值之间的误差小于0.002,色温误差在50 K以内。 用光谱丰富的 冷白和暖白LED分别代替红/绿/蓝光源模块中的蓝光和红光,能提高混合光的显色指数,暖 白/绿/蓝光源模块的混光效果最佳。     

荧光粉配比对大功率白光LED发光特性的影响

利用黄色、红色和黄绿色3种荧光粉混合的方法制备了一系列大功率平面发光LED光源,深入研究了黄色、红色和黄绿色3种荧光粉分别对大功率白光LED光源的发光效率、显色指数以及色温的影响规律。研究结果表明,随着黄色荧光粉含量的增加,其发光效率明显提高,最高可达140 lm/W,而显色指数和色温略有下降。随着红色荧光粉含量的增加,其显色指数明显提高,最高可达85,而发光效率和色温明显降低。随着黄绿色荧光粉含量的增加,其发光效率、显色指数以及色温均不同程度地略有下降,但是其对大功率白光LED的色容差起到很好的调节作用。     

实现色温自动控制的白光LED照明系统设计

荧光粉发光LED作为白光光源在照明领域有着广泛的应用。长时间工作,荧光粉发光LED将出现色温偏移现象。荧光粉发光LED的色温偏移与芯片衰减和荧光粉衰减有关。提出了一种能同时考虑芯片衰减和荧光粉衰减的数学模型。从理论上分析了芯片衰减和荧光粉衰减对荧光粉发光LED的色坐标及色温变化的影响。提出了一种利用蓝光LED与荧光粉发光LED混合,通过对蓝光LED进行负反馈控制,保证蓝光辐射在全白光中的辐射功率比值恒定,从而实现色温稳定的白光LED照明系统。     

双通道PWM的冷暖白光LED混色模型研究

LED光色度的动态调节是实现智能照明的基础, 采用冷暖白光LED和双通道脉冲宽度调制(PWM)法,基于1931CIE标准建立混合光源模型,推导出混合光源色坐标、相关色温 、最大亮度、显色指数与双通道调制脉冲 占空比比值的关系式。采用暖白光(色温3282 K)和冷白光(色温12930K)两种白光LED进行 混色实验, 通过微控制器输出PWM信号控制LED驱动电源,改变冷色光和暖色光的比重,得到的混合 光源色坐 标、最大亮度、相关色温及显色指数值与理论计算值吻合很好,证明了理论模型的正确性。 理论和实验结 果还表明,混合光源在双通道调制脉冲占空比比值为1的附近可得到低色温、高显色性和大 光通量的混合白光。     

可调色温的高显色指数LED白光光源的实验研究

采用暖白、绿、蓝LED混光和PWM调光技术,研究了光源的光谱、色温可调和显色指数特性。实验通过控制驱动电流的占空比,调节暖白、绿、蓝LED之间的光通量配比,实现了在3 000~6 500K范围内色温可调、Ra为85~95的高显色指数LED白光。混合光源的实验参数与理论计算值相一致。     

COB白光LED的光提取效率研究

针对LED高光效、高显色指数的要求,在分析LED光学性能的基础上,采用板上芯片(COB,Chip on Board)技术研究了表面涂覆硅胶量对COB白光LED的光通量、光效、色温和显色指数的影响,并提出一种高光效、高显色指数、低色温的白光LED封装方案,提高了COB白光LED的出光效率,实现了特定的光学分布,最终实现14 W COB封装结构下的白光LED,在电流密度为30 A/cm2时,其色温、显色指数及光效分别为4 900 K、82和125 lm/W.     

CdSe纳米材料对大功率白光LED显色性能的影响

利用CdSe纳米材料可以通过改变其大小和形状得到不同波段发射光谱的特点,在常规荧光粉中加入发射波长为630 nm的红色CdSe纳米材料,补充大功率白光LED光谱在深红波段的缺失.结果表明:引入红色CdSe纳米材料后,大功率白光LED的显色指数最高可到90左右,色温降低,但光效有所下降.这种方法为提高大功率白光LED显色指数提供了一种新的解决方案.     

LCD背光用LED的封装技术

We design a package patterned with red and green emitting phosphors excited by a blue LED to emit tri-basic mixing color.For high backlight display quality, we compare several phosphors.According to our measurements, green phosphors 0752G, 0753G and red phosphor 0763R are preferred for producing a good backlight source.Compared to RGB-LED backlight units, this frame typically benefits the lighting uniformity, and can sim-plify the structures.It also provides higher color render and better CCT than the traditional package method of a yellow phosphor with a blue chip.However, its light efficiency needs to be further improved for the use of backlights for LCDs.     

Correlated Color Temperature Tunable Multi-chip Light Emitting Diodes Light Source Design

One of the methods to derive white light from light emitting diodes（LEDs） is the multi-chip white LED technology, which mixes the light from red, green and blue LEDs. Introduced is an optimal algorithm for the spectrum design of the multi-chip white LEDs in this paper. It optimizes the selection of single color LEDs and drive current controlling, so that the multi-chip white LED achieves the target correlated color temperature （CCT）, as well as high luminous efficacy and good color rendering. A CCT tunable LED light source with four high-power LEDs is realized based on the above optimal design. Test results show that it maintains satisfactory color rendering and stable luminous efficacy across the whole CCT tuning range. Finally, discussed are the design improvement and the prospect of the future applications of the CCT tunable LED light source.     

近紫外芯片激发三基色荧光粉制作的白光LED

使用近紫外半导体芯片激发红绿蓝三基色荧光粉,制作了白光发光二极管（LED）,并研究了其光电特性。结果表明,采用发射峰值波长分别在613、495和451nm的红绿蓝荧光粉,在波长400nm左右半导体芯片激发下的白光LED,其显色指数Ra最大为82;使用YAG荧光粉代替绿色荧光粉后,Ra提高到93。测试结果还表明,当工作电...     

白光LED荧光粉研究及应用新进展

基于白光发光二极管技术的迅速发展以及荧光粉对白光LED器件的发光效率、显色性和使用寿命等性能的决定性影响,系统阐述了蓝光LED芯片激发用铝酸盐、硅酸盐、氮化物和氮氧化物系列黄色、红色和绿色荧光粉的研究进展和应用现状。探讨了上述荧光粉的研究重点、发展趋势和应用前景,指出需要进一步提高铝酸盐黄粉的发光效率,开发新型高光效氮化物和氮氧化物红粉和绿粉及其低成本制备技术,以满足高光效、高显色、低光衰型白光LED器件制作需要。     

荧光粉浓度和电流强度对白光LED特性的影响

讨论了荧光粉浓度及驱动电流强度对白光LED特性的影响。采用软件模拟实验和实际封装测试相结合的研究方法进行分析研究。对荧光粉浓度变化对白光LED光通量和相关色温(CCT)的影响进行了三维光线追迹模拟,并且进行了实际的封装验证。另外对白光LED的节温和显色性也做了深入细致的研究。研究结果表明:CCT随着荧光粉浓度的增大而减小,光通量则先上升后下降。同时由荧光粉浓度和驱动电流强度变化所引起的节温升高会降低荧光粉的转换效率。对显色性而言,采用高浓度荧光粉封装的白光LED有相对低的显色指数;并且显色指数随着驱动电流强度的增加而升高,最终趋于稳定。     

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.     

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.     

Improvement of emission efficiency and color rendering of high-power LED by controlling size of phosphor particles and utilization of different phosphors

White light can be produced by a combination of red, green and blue emitting diode chips or by the combination of a single diode chip with phosphors. Presently, more single chip white light-emitting diodes (LEDs) than multi-chip one are used because of their low cost, easily controlled circuitry, ease of maintenance and favorable luminescence efficiency. Since phosphors must be used as light converting materials in a single diode chip to obtain the desired emission, this study considers the problems encountered in using phosphors in LEDs. The proper application of phosphors in the package of LED can improve its efficiency, color rendering and thermal stability of luminescence. For example, a uniform size distribution of phosphors with red, green and blue emission helps to improve luminescence efficiency by preventing cascade excitation; the change in color with temperature can be overcome by counter-balancing red-shifting and blue-shifting phosphors; larger particles help to ensure the high efficiency of high-power LEDs, and costs can be reduced by using small particles size in low-power LED packaging because allows less phosphor to be used to obtain a particular efficiency.