Degradation mechanism analysis for phosphor/silicone composites aged under high temperature and high humidity condition

High power phosphor-converted white light emitting diodes (pc-WLEDs) are proposed to substitute the traditional lighting sources owing to their benefits in high luminous efficiency, low power consumption, long lifetime and environmentally friendly. Currently, the most effective approach to fabricate a pc-WLED package is to cover the phosphor/silicone composites on a blue LED chip using the deposition or thermal-pressing technology. The mechanism for generating white light from pc-white LEDs is a combination of blue light emitted by an LED chip and the excited yellow light from phosphors. In that case, the phosphor/silicone composite coated on the LED chip is always exposed under the environment of high temperature and high humidity. This study investigates the long-term degradation failure mechanisms of phosphor/silicone composites aged under the high temperature and high humidity condition. Three composites are prepared by mixing three widely used phosphor powders with silicone respectively. According to the SEM/EDX and FTIR analysis and simulated experiment, it shows that the degradation of phosphor/silicone composites aged under the high temperature & high humidity condition is related to the change of its pH value, which can degrade both the light-conversion efficiency of phosphors and the transmittance of silicone.