Improvement in the moisture stability of CaS:Eu phosphor applied in light-emitting diodes by titania surface coating

A sol-gel coating process was applied to improve the moisture stability of CaS:Eu phosphor used in light-emitting diode (LED). Titania conformal coating on the surface of phosphor particles was conducted by the hydrolysis and condensation of titanium isopropoxide. The humidity resistance test in the state of LED package including pristine phosphor or coated phosphor was carried out. As a result, titania surface coating prevented the drastic decrease in light output power and electrical open failure originating from the phosphor decomposition by reaction with moisture. Therefore, it was concluded that titania conformal coating layer played a role as a barrier against the moisture and prolonged the lifetime of pristine phosphor.