功率型白光LED光学特性退化分析

将GaN基蓝光芯片涂敷YAG荧光粉和透明硅胶制成额定功率为1 W的白光发光二极管(LED)，对其施加900mA的电流应力，在老化过程中测量白光LED的主要光学参数，考察其光学特性的退化情况。经过4 200 h的老化，样品光通量退化为初始值的15%~18% 。样品的漏电流明显增大，表明芯片有源区缺陷密度提高，但光谱分布图中蓝光部分的辐射量未减少，仅观察到黄光部分辐射量的减少，推断出YAG荧光粉的转换效率降低。同时，从原理上分析了样品色温逐渐增大，显色指数基本不变的原因，对大功率白光LED在照明领域的应用有一定的借鉴意义。

Analysis on the Degradation of Optical Properties of High Power White LED

One watt white light emitting diodes (LEDs) were made by GaN-based blue light chips. The chips were coated by YAG phosphor and transparent silica gel. Current of 900 mA as electrical stress was carried on the LED samples and the optical properties of the samples were observed by measuring the main optical parameters during the aging test. After 4 200 hours of aging, the luminous flux rate of LEDs declined by a factor between 15% and 18%. Changes in I-V curves indicated the increase in leakage current, which were caused by the increase in defect density. Radiant flux of the blue light drawn from the spectrogram didn’t decrease while the yellow light decreased obviously, which implies the degradation of conversion efficiency of YAG phosphor. Reasons for the increase in color temperature and keeping constant in color rendering index (CRI) were theoretically analyzed. The results of the experiment will provide a reference to the illumination applications of the high power white LED.