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.

Date Published: 13 February 2008
PDF: 10 pages
Proc. SPIE 6910, Light-Emitting Diodes: Research, Manufacturing, and Applications XII, 691011 (13 February 2008); doi: 10.1117/12.760906

Published in SPIE Proceedings Vol. 6910:
Light-Emitting Diodes: Research, Manufacturing, and Applications XII
Klaus P. Streubel; Heonsu Jeon, Editor(s)