3 February 2009 Decay of lumen and chromaticity of high-power phosphor-converted white-light-emitting diodes in thermal aging
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Abstract
In this paper, we would like to report the following two subjects:(1) Thermal decay mechanisms of phosphor-doped silicone in high power phosphor-converted white light emitting diode (PC-WLED) module and (2) Thermal aging variations of light profile and output power of blue LED modules having a polycarbonate lens and silicone as an encapsulant. Although silicone degradation attributed to the final thermal degradation, it is not a dominant factor until a much thicker silicone is employed in PC-LEDs. The major degradation mechanism of the PC-LEDs results from the higher doping concentration of Ce:YAG in silicone. However, the negligible difference of fluorescent lifetimes among the test samples before and after thermal aging (at 150°C for 500hrs) eliminated any significant quenching processes that existed in our aged samples. The emission spectra suggest that a higher doping concentration in silicone causes a higher degree of loss at the emission wavelength of Ce:YAG, namely 570nm. Therefore, minimizing any mismatch of the refractive index, thermal expansion , and chemistry between the phosphor and the silicone is a new sign of improving thermal reliability for high power PC-LEDs. Thermal aging variations of light profile and output power of LED modules fabricated by three manufacturers (namely, Type I, II, and III) were investigated experimentally and numerically. Both experimental results and simulation results suggested that improving the lens/ encapsulant materials and packaging designs are essential to not only greatly extend the product lifetime but also enhance the light quality of LED modules as illumination sources. Index Terms -High-powered phosphor-converted white-light-emitting diodes (PC-WLEDs), lumen loss, chromaticity shift, silicone, polycarbonate, thermal aging, etc.
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Jau-Sheng Wang, Jau-Sheng Wang, Chun-Chin Tsai, Chun-Chin Tsai, Ming-Hung Chen, Ming-Hung Chen, Yi-Cheng Hsu, Yi-Cheng Hsu, Hung-Lieh Hu, Hung-Lieh Hu, Chao-Wei Lee, Chao-Wei Lee, Wood-Hi Cheng, Wood-Hi Cheng, } "Decay of lumen and chromaticity of high-power phosphor-converted white-light-emitting diodes in thermal aging", Proc. SPIE 7231, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XIII, 72310O (3 February 2009); doi: 10.1117/12.807560; https://doi.org/10.1117/12.807560
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