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High thermal stability of phosphor-converted white light-emitting diodes (PC-WLEDs) using Ce:YAG-doped glass (CeYDG), instead of conventional Ce:YAG-doped silicone (CeYDS), as a PC layer is proposed and fabricated. The proposed CeYDG possesses host stability as glass and retains desired fluorescence as Ce:YAG. The CeYDG employed in the PC-WLED test demonstrates better performances than conventional CeYDS, including lumen loss, chromaticity shift, transmittance loss, and peak emission intensity undergoing three industry-standard reliability tests at either high (8 wt%) or low (2 wt%) doping concentrations of Ce:YAG. While the CeYDG reveals better stability than the CeYDS, we expect even better performance after refining the glass composition and fabrication process for CeYDG due to current processing facility limitations. However, this study clearly demonstrates the feasibility and advantages of adapting glass as a PC layer in PC-WLED modules that can potentially provide higher reliability and better performance for high-end LEDs, particularly in the area where strict reliability is highly required and in the environment where silicone fails to stand for long.

Decay of radiation pattern and optical spectrum of high-power LED modules fabricated by different manufacturers after a thermal-aging test were investigated experimentally and numerically. Samples were aged at 65degC, 85degC, and 95degC under a constant current of 350 mA. The results showed that the radiation pattern of the LED modules at the two view angles of plusmn(45deg ~ 75deg) decreased more than the other angles as aging time increased. This was due to the reduction of optical power from corner shape of lens. Due to the degradation of lens material after thermal aging, the center wavelength of the LED spectrum shifted 5 nm. Furthermore, the radius curvature of plastic lens was observed to have 6-70 mum contraction as aging times increased. The key module package related to the decrease of power density, the change of radiation pattern, and the shift of optical spectrum in high-power LED modules under thermal aging were due to the degradation of lens material and lens structure. Both experimental and simulated results clearly indicated that improving the lens structure and lens material is essential to extend the operating life of the high-power LED modules. This study may provide practical LED package guidelines in low-cost consumer applications.