Ultra-High Thermal-Stable Glass Phosphor Layer for Phosphor-Converted White Light-Emitting Diodes

A glass phosphor layer with ultra-high thermal stability appropriate for phosphor-converted white light-emitting diodes (PC-WLEDs) is demonstrated. The results showed PC-WLEDs utilizing the high thermal stable glass phosphor maintained good thermal stability in lumen, chromaticity, and transmittance characteristics under the thermal aging condition up to 350 degrees C. This is a considerable high operating temperature for a phosphor layer in the PC-WLEDs. The lumen degradation, chromaticity shift, and transmittance loss in the glass-based PC-WLEDs under thermal aging at 150 degrees C, 250 degrees C, 350 degrees C, and 450 degrees C are also presented and compared with those of silicone-based PC-WLEDs under thermal aging at 150 degrees C and 250 degrees C. The result clearly demonstrated that the glass-based PC-WLEDs exhibited better thermal stability in lumen degradation, chromaticity shift, and transmittance loss than the silicone-based PC-WLEDs. The advantages of glass encapsulation in high-temperature operation of the PC-WLEDs could be explained that the glass transition temperature of the glass phosphor (567 degrees C) was much higher than it of silicone (150 degrees C). The newly developed ultra-high thermal-stable glass is essentially critical to the application of LED modules in the area where the high-power, high-temperature and absolute reliability are required for use in the next-generation solid-state lighting.