湿热环境下LED荧光粉的性能退化规律及机理研究

Degradation Mechanism Analysis for LED Phosphors under Hygrothermal Environment

摘要:

由于基于钇铝石榴石基（YAG）黄色荧光粉的大功率白光发光二极管（LED）显色指数偏低，采用多基色荧光粉混合制备高显色白光LED已受到业内接受，然而不同荧光粉性能差异造成LED光-色-热性能的稳定性和可靠性等问题已经备受关注。本文选用制备高品质白光LED所常用黄、红、橙三种荧光粉，研究其在高温高湿老化试验和浸水模拟饱和水环境实验中的发光性能、发热性能、晶体结构和微观颗粒形貌变化规律，分析不同荧光粉的性能退化机理。研究表明：1）在湿热环境下荧光粉易与水发生反应产生OH-，提升湿环境pH值，引起主体晶体结构结晶度下降，晶格振动增强，光致发热能量增加，诱发热猝灭效应；同时荧光粉表面粗化效应增加蓝光散射，降低蓝光吸收和转化效率；2）在浸水模拟实验的饱和水环境中，荧光粉的发光性能和发热性能变化规律与高温高湿长期老化试验结果一致，可以有效评估LED荧光粉在湿热环境下可靠性。

关键词:白光LED;荧光粉;高温高湿;浸水模拟实验;失效机理

Abstract:

Due to the low color rendering of high-power white light-emitting diodes (LEDs) based on yttrium aluminum garnet-based (YAG) yellow phosphors, high color-rendering white LEDs by mixing multiple-phosphors have been accepted by LED industry. However, the difference of phosphors can result in the luminous-chromatic-thermal stability and reliability problems in LED packages. This study selects yellow, red and orange phosphors used in high color rendering white packages, analyzes their luminescence and thermal properties, crystal structures and micro morphologies during both the high temperature and high moisture ageing test and the water-soaking test, and finally figures out the degradation mechanisms of different phosphors. The results show that: 1) the hydrolysis reaction of phosphors under hygrothermal environment produces OH- and increases the environment’s pH, that can lower the crystallinity of phosphor hosts, increase the lattice vibration and light-induced heat, and enhance the thermal quenching effect of phosphors. Meanwhile, the surface roughening of phosphor particles can increase the blue light scattering and lower its absorption and conversion efficiency. 2) the degradation trends of both luminescence and thermal properties of phosphors under the water-soaking test are similar to those aged under high temperature and high moisture ageing test. So it is an effective method to assess the reliability of LED phosphors under hygrothermal environment.

Key words:White LED; Phosphors; Hygrothermal environment; Water-soaking; Degradation mechanisms