Abstract
The high-power phosphor-based white-light-emitting diodes (LEDs) after thermal aging at 150°C and 500 hours are
studied experimentally. The white-light LEDs formed by three combinations of different thicknesses and concentrations
of the silicone YAG phosphor are 1 mm and 5.48%, 2mm and 3.2%, 3mm and 2.4%, respectively. The results showed
that the lumen loss, chromaticity (CIE) shift, and spectrum intensity reduction in yellow YAG phosphor of the highpower
white-light LEDs increased as the silicone YAG phosphor concentration increased. These were due to that the
transmittance loss and the refractive index variation of the silicone YAG phosphor increased as the aging time increased
and resulted in lower emission efficiency of the high-power white-light LEDs. However, the lumen loss and CIE shift
did not significantly depend on the thickness of the silicone YAG phosphor. The likely cause for the transmittance
reduction and refractive index variation increased is that the thermal effect increased after thermal aging. As a result, the
key of high-power phosphor-based white-light LEDs module package related degradation mode under thermal aging
was identified as the decay of the silicone YAG phosphor, evidenced by secondary-ion mass spectroscopy (SIMS)
analyses. This study clearly indicates that in order to maintain luminous power and minimize color shift of the highpower
white-light LEDs modules, a lower concentration of the YAG phosphor for use in packaging of the phosphorbased
white-light LEDs modules is essential.
