To prolong the light emission life-span of an electroluminescent (EL) phosphor particle (ZnS:Cu, Cl), the phosphor particles were encapsulated with an antihumidity film and the relationship between the light emission life-span and the composition of the antihumidity film, as well as the film structure, was studied. The antihumidity films consisted of TiOx and SiOx which were deposited by chemical vapor deposition. This was achieved through hydrolysis of the TiCl4 and SiCl4 source precursors. The SiOx film did not exhibit antihumidity characteristics; however, antihumidity characteristics were confirmed in the TiOx film and the light emission life-span was prolonged. However, due to the effect of residual Cl in the TiOx film, the indium-tin oxide (ITO) electrode of the EL device deteriorated and substantial prolongation of the light emission life-span was not possible. On the basis of these findings, we deposited a SiOx film on the TiOx film, and attempted to prevent the ITO electrode from deteriorating due to residual Cl ions in the TiOx film. As a result of the introduction of a dual layer consisting of SiOx and TiOx films, the brightness half-life was prolonged to 200 h (at 40 degreesC, 90% humidity, 100 V 400 Hz). Thus, the life span of the phosphor has been expanded to approximately tenfold that of nonencapsulated phosphors.