Failure Analysis of a Phosphor-Converted White Light-Emitting Diode due to the CaS:Eu Phosphor

Abstract

To improve the longevity of phosphor-converted white light-emitting diode (LED), CaS:Eu red phosphor is usually coated by SiO(2). The coating characteristics such as moisture resistance were found to be excellent and critically dependent upon the processing variables such as precursor concentration, pH value, and the temperature of the solution in case of the sol-gel process. Very interestingly, even though SiO(2)-coated CaS:Eu phosphor shows very strong moisture resistance, longevity of white LED is not improved that much when the coated phosphor applied to LED chip. Our consecutive experimental results show that the CaS:Eu particle is decomposed provoking a H(2)S gas release and silver pad under the chip is damaged by the H,S gas, which leads to the decrease of reflectivity and consequently luminance from the LED. [DOI: 10.1143/JJAP.47.3524]