Method of providing storage dielectric of phosphor particles coated with secondary emissive material

DETAILED DESCRIPTION I claim: 1.
A method of manufacture of a charge image storage dielectric capable of bistable storage of a charge image formed thereon, comprising the steps of: coating a plurality of particles of phosphor material with a secondary emissive-forming substance; and heating the coated phosphor particles to form a secondary electron emissive material from said substance and to bond said secondary emissive material to the outer surface of said phosphor particles whereby a storage dielectric is formed with said secondary emissive material being substantially uniformly distributed throughout said storage dielectric.
2.
A method in accordance with claim 1 in which the coating step includes dissolving the secondary emissive-forming substance in water, mixing the phosphor particles with the resulting solution to provide a slurry, and drying the slurry to remove the water and leave a coating of said substance on said phosphor particles.
3.
A method in accordance with claim 1 in which the coating step includes dissolving a first substance in water, mixing the phosphor particles with the resulting solution to form a slurry, mixing a second substance with the slurry which reacts with said first substance to produce the secondary emissive-forming substance, and causes said secondary emissive-forming substance to precipitate onto the phosphor particles to form a coating, and filtering the slurry to remove the coated phosphor particles.
4.
A method in accordance with claim 1 in which the phosphor material is manganese activated zinc orthosilicate and the secondary electron emissive material is magnesium oxide formed by coating the phosphor particles with a magnesium compound and heating the coated particles in a oxygen-containing atmosphere.
5.
A method in accordance with claim 4 in which the heating temperature is less than about 900.
degree.
C.
6.
A method in accordance with claim 1 in which the storage dielectric is applied to a support member after the phosphor particles are coated with secondary emissive material to produce a storage target capable of bistable storage of a charge image