Patent ID: 7291291

Claim:
A method of making an electroluminescent phosphor powder comprising 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 μm; 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° C. to about 1080° 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° C. to about 850° 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 μm.