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Phosphor Temperature and Degradation in High Power White Light Emitting Diodes
Keywords: white light emitting diodes, phosphor temperature, phosphor degradation
Thermal management is critical in determining the performance and reliability of high power phosphor-converted white light-emitting diodes (LEDs). It is well known that heat accumulation in the junction of the LED chip leads to degradation of the chip. In our previous work, it is shown that heat generation in the phosphor material (Ce:YAG) makes the average temperature in the phosphor-silicone mixture layer higher than the temperature in the chip junction. In this work, the local heating effect of phosphors in white LEDs with different phosphor placement and concentration was studied by both simulation and experiment. First of all, heat loads on each individual component of the studied 1W LED emitters were obtained from an optical simulation. Then a thermal simulation was performed to investigate the heating effect of individual phosphor particles. Meanwhile, the junction temperature and the board temperature were measured for correction purpose. The phosphor was preheated alone at the calculated temperature. After packaging, the luminous output of the LED emitter was measured. The result shows a reduction in lumen output, which proves that phosphor degradation caused by localized heating exists in the LED emitters.
Bohan Yan, Student
University of California, Irvine
Irvine, CA

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