High humidity resistance of high-power white-light-emitting diode modules employing Ce:YAG doped glass

The reliability study of thermal shock and damp heat tests for high-power white-light-emitting diode modules (WLEDMs) incorporating Ce:YAG doped glass, instead of conventional Ce:YAG doped silicone, as a phosphor layer is presented. The Ce:YAG doped glass as a phosphor layer is used for the glass to possess high transition temperature (T_g) of 750°C that can exhibit higher thermal stability and humidity resistance than conventional silicone. A comparison study of lumen loss, chromaticity shift, and transmittance loss of high-power WLEDWs with Ce:YAG doped glass and Ce:YAG doped silicone under thermal shock and damp heat tests was performed. The damp heat results showed that the high-power WLEDWs with Ce:YAG doped glass at 2~8 wt% doping concentrations exhibited 67~69%, 49~65%, and 35~67% better improvements than doped silicone for the lumen loss, chromaticity shift, and transmittance loss, respectively. The damp heat test demonstrated the larger improvement of glass doped in transmittance loss. The thermal shock results showed that the high-power WLEDWs with Ce:YAG doped glass at 2~8 wt% doping concentrations exhibited 57~68%, 53~58%, and 58~67% better improvements than doped silicone for the lumen loss, chromaticity shift, and transmittance loss, respectively. These results demonstrated that the Ce:YAG doped glass exhibited higher humidity resistance than the Ce:YAG doped silicone under damp heat and thermal shock tests. A better thermal stability and humidity resistance of doped glass phosphor layer may be beneficial to the many applications where the LED modules with high-power and high reliability are demanded.