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Abstract

There is presented an electroluminescent phosphor powder of copper-activated zinc sulfide particles that has a size distribution with a D50 value of less than 12 .mu.m, and more preferably less than 10 .mu.m. The powder is preferably made by a method that includes the steps of combining copper-doped zinc sulfide with sulfur, zinc oxide and a chloride-containing flux to form a first mixture; preliminarily firing the first mixture and milling the preliminarily fired first mixture to form a milled material having a D50 value of less than or equal to about 5 .mu.m; blending the milled material with sulfur, zinc oxide and a chloride-containing flux to form a second mixture; firing the mixture in a first firing step at a temperature in a range of about 1020.degree. C. to about 1080.degree. C. to form a hexagonal zinc sulfide material; inducing defects into the hexagonal zinc sulfide material; firing the hexagonal zinc sulfide material in a second firing step at a temperature in a range of about 650.degree. C. to about 850.degree. C. to form an electroluminescent phosphor; and sifting the electroluminescent phosphor to provide an electroluminescent phosphor powder comprising phosphor particles that have a size distribution with a D50 value of less than 12 .mu.m. The step of inducing defects may be accomplished by milling, mulling or sonification of the mixture.

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First Claim