摘要
荧光粉的性能在很大程度上可以影响到LED产品的光效.关于荧光粉涂覆工艺如何影响LED的光效已经有很多研究,但是关于荧光粉层的位置对LED热学和光学性能的研究还比较少.本文采用了一种在线测试的方法,研究了高温加速实验中荧光粉层位于不同位置时对LED光效衰减的影响.通过制备荧光粉片,实现LED模块中荧光粉层的不同位置分布.对比实验结果表明,采用荧光粉片的LED模块光效衰减较小,在散热条件良好的情况下,荧光粉的发热对其光效影响不大.对于普通涂覆的大功率LED模块而言,要提高性能,其封装内部需要更好的热设计.
High power white light-emitting diode（LED） has been widely used in our daily life due to its extraordinary characteristics of high luminous efficiency, low power consumption, long lifetime and environment protection. Among all the technologies to produce white light, phosphor converting scheme is most popular. In this mode, part of the blue light emitted by LED chip is converted into yellow light by phosphor layer. Then a white output light of blue and yellow light mixture is obtained. The conversion ability of phosphor layer can determine LED＇s performance parameters including luminous efficiency, correlative color temperature, angular color uniformity, etc. When one of the parameters does not meet the requirement（like relative light output drops below 70%）, the LED fails. Therefore, LED＇s reliability is greatly affected by phosphor layer＇s property. Previous study shows that the conversion efficacy of phosphor exhibits exponential degradation as temperature increases. The decrease of phosphor＇s conversion efficacy can induce light output decrease and deteriorate the reliability. Thus, for phosphor converted LED（pc-LED）, thermal management is of great importance. In conventional phosphor coating process, phosphor gel is directly dispensed onto the LED chip. When the LED is working, heat generated by the chip is accumulated due to the poor heat conduction of phosphor layer, resulting in the phosphor temperature rise. Besides, the phosphor＇s self-heating can also cause phosphor temperature rise. To solve this problem, some researchers used remote phosphor coating to reduce the influence of heat produced by chip. The phosphor layer was moved away from the chip to avoid contact. It means that the phosphor layer＇s location can have an effect on pc-LED＇s reliability. In this paper, the phosphor layer＇s location was further controlled by phosphor slice. The phosphor slices were prepared by mold to keep specific size. An online testing method was adopted to investigate the effect of phosphor layer＇s location on LED＇s lumen maintenance under accelerated temperature life test. Three cases were aged under temperature of 120oC, namely blue LED module without phosphor layer, white LED module by conventional phosphor coating and white LED module by combining blue LED module and phosphor slice. The lumen maintenance was monitored and recorded every 30 s. After 30 h of aging, the light output of three cases of modules got stabilized. The results showed that the relative light output of conventional packaged white LED module had a 30% drop, while that of the white LED module by using phosphor slice only dropped 2.7%. The reason behind the phenomenon was well explained. Compared with the conventional phosphor layer, phosphor slice was away from the chip so that the heat generated by chip would not affect the phosphor temperature. Apart from this, the phosphor slice was in the air and the good heat dissipation can reduce the influence of phosphor self-heating. Thus, the temperature of phosphor slice was much lower than that of the conventional one and the reliability was somewhat enhanced. To sum up, the effect of phosphor layer＇s location on LED＇s luminous depreciation was studied by online testing system in this paper. Phosphor slices were prepared to achieve various phosphor location and comparison experiments were conducted. The results showed that white LED module with phosphor slice had better reliability. The reason was attributed to the good heat dissipation property of phosphor slice. This work presented an attempt for improving LED＇s reliability. For conventional packaged LED, better heat dissipation design was needed to improve the performance.
出处
《科学通报》
EI
CAS
CSCD
北大核心
2017年第12期1302-1306,共5页
Chinese Science Bulletin
基金
国家自然科学基金(51576078
51376070)资助
关键词
LED
光效衰减
加速实验
荧光粉位置
在线测试
light-emitting diode（LED）
luminous depreciation
accelerated life test
phosphor layer＇s location
online test
