针对中功率蓝光及相应的白光LED器件进行加速老化实验,并具体分析了器件中硅胶和绿红混合荧光粉等封装材料对老化行为的影响和失效机理。在测试器件的光电老化行为之后, 利用反射光谱和飞行时间二次离子质谱对失效器件进行了结构分析。结果表明, 温度和湿度对蓝光和白光器件老化行为具有不同的影响。对于中功率蓝光LED而言, 其光衰的主要原因是由于S、Cl等元素的引入及氧化等因素引起的黄化导致了透明硅胶反射率的下降。而对于绿红混合荧光粉组成的中功率白光LED来说, 其光衰和色漂问题主要归结于在高温特别是高湿环境下工作, 器件中荧光粉和硅胶等封装材料发生了一些化学反应, 使荧光粉发生分解, 并引起了荧光转换效率的下降。

Highly stress tests were carried out for mid-power GaN-based LEDs encapsulated with silicone and green/red mixed phosphors. Except for the optical and electrical measurement, the reflection spectroscopy and time of flight-secondary ion mass spectrometry (TOF-SIMS) were also used to investigate the failure mechanism. Our results show that the high temperature and humidity play an important role in determining the failure mode for mid-power blue and white LEDs. The decrease of the blue emission is related to the degradation of the transparent silicone and the reflectivity by the oxidation and the contamination of sulfide and chlorine. While the dissolution of the phosphors in white LEDs will lead to the decrease of the conversion efficiency and deteriorate the photometric and colorimetric properties of mid-power white LEDs.