| Summary: | 碩士 === 國立中山大學 === 光電工程學系研究所 === 99 === A Ce:YAG-doped glass phosphor layer instead of conventional Ce:YAG-doped silicone phosphor layer as phosphor-converted white-light emitting diodes (PC-WLEDs) is demonstrated. The advantage of employing doped glass encapsulation in high power PC-WLEDs could be explained the material property of glass transition temperature of 750℃ was higher than silicone of 150℃.
The lumen degradation, chromaticity shift, color temperature change, transmittance, and fluorescence spectrum in glass and silicone based high-power PC-WLEDs under thermal aging at 150℃, 200℃, and 250℃ is compared and presented. Under highest temperature of 250℃, the glass and silicone encapsulation base d PC-WLEDs exhibited 8.15% and 38.85% in lumen loss, 1.07 and 7.32 in chromaticity shift, 856 K and 3666 K in color temperature change, 4.21% and 28.1% in transmittance loss, respectively. However, the excitation spectrum altered as slight as emission spectrum before and after experiments.
After aging test, the mean-time-to-failure (MTTF) evaluation of glass and silicone encapsulation materials for PC-WLEDs in accelerated thermal tests is also compared and presented by the using of Weibull distribution and Arrhenius equation. The MTTF of PC-WLEDs is defined the lumen decayed to 90%. The results showed that the glass as encapsulation material of PC-WLEDs exhibited higher MTTF than the silicone encapsulation by about 4.81, 5.92, and 7.53 times in lumen loss at 150℃, 200℃, and 250℃, respectively.
The results of the lumen loss, chromaticity shift, and MTTF investigations demonstrated that the thermal-stability performance of the glass based PC-WLEDs were better than silicone based PC-WLEDs at 150℃, 200℃, and 250℃. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to the many applications where the LED modules with high power and high reliability are demanded.
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