Longevity Improvement of CaS:Eu Phosphor Using Polymer Binder Coating for White LED Application

Abstract

To improve the longevity of a phosphor converted white light-emitting diode (LED), the coating on CaS:Eu phosphor by using polymer binder was carried out. The coating characteristics were found to be critically dependent on the sort of monomer and temperature of the reaction during the polymerizing process. This process is found to avoid a hydrolysis reaction, which causes damage to CaS:Eu phosphor surface, which frequently occurs in the conventional sol-gel process. Field-emission scanning electron microscope images and transmission electron microscopy images showed that polymer binder coating of on CaS:Eu phosphor was very solid and could well serve as a protective layer against the moisture, which is critically detrimental to the development of commercial white LEDs. Significant optical stability, even after a moisture-contacting experiment, was observed in the case of coated phosphors. However, it was also found that the emission of from the CaS:Eu phosphor still remained influential to the longevity of an LED device because of a bottom Ag plate in our experimental regime.