Moisture resistant electroluminescent phosphor with high initial brightness and method of making
An electroluminescent (EL) phosphor is described wherein each individual phosphor particle is encapsulated in an inorganic coating, preferably aluminum oxyhydroxide. The encapsulated phosphor shows an extreme insensitivity to atmospheric moisture and suffers only minor loss of initial brightness in lamps. The method of applying the coating is a hybrid process, which involves EL phosphor particles first being coated with a thin inorganic film using an atomic layer deposition (ALD) method in a fluidized bed wherein the precursors are introduced sequentially in repeated cycles, subsequently followed by an additional coating layer applied by a chemical vapor deposition (CVD) method in which the precursors are introduced simultaneously.
1. A coated electroluminescent phosphor, comprising: individual particles of a zinc sulfide-based electroluminescent phosphor wherein each particle is encapsulated in an aluminum oxyhydroxide coating, wherein the aluminum content of the coated electroluminescent phosphor is from 1 wt % to about 2.5 wt %, the phosphor exhibiting a retained initial brightness of at least 90% and having a moisture resistance equivalent to a CVD-coated phosphor having an aluminum oxyhydroxide coating wherein the aluminum content of the CVD coated phosphor is 3.8 weight percent.
2. The coated phosphor of claim 1 wherein the aluminum content of the coated electroluminescent phosphor is about 2.2 weight percent.