Method of making electroluminescent phosphors with small particle sizes and powder with d50 value of no more than 10 micrometers

A method of making an electroluminescent phosphor powder comprising the steps of:

• combining copper-doped zinc sulfide with zinc oxide, sulfur and a chloride-containing flux to form a mixture;
• first firing the mixture at a temperature in a range of 1050-1150° C. for 25-90 minutes;
• first cooling the fired mixture to below 100° C. in less than about 60 minutes;
• mulling the cooled mixture to form a mulled mixture;
• second firing the mulled mixture at a temperature in a range of 700-850° C. for 1-4 hours;
• second cooling the fired mulled mixture to provide an electroluminescent powder comprising copper-activated zinc sulfide particles that have a D50 value of 12-17 μm;
• and
• elutriating the cooled mulled mixture to provide an electroluminescent powder comprising copper-activated zinc sulfide particles that have a size distribution with a D50 value of no more than 10 μm.

A method of making an electroluminescent phosphor powder comprising the steps of:

• combining copper-doped zinc sulfide with zinc oxide, sulfur and a chloride-containing flux to form a mixture;
• first firing the mixture at a first temperature in a range of 1050-1085° C. for 25-55 minutes;
• first cooling the fired mixture to below 100° C. in less than about 60 minutes;
• mulling the cooled mixture to form a mulled mixture;
• second firing the mulled mixture at a second temperature in a range of 700-850° C. for 1-4 hours;
• second cooling the fired mulled mixture;
• and
• screening the cooled mulled mixture to provide an electroluminescent powder comprising copper-acitvated zinc sulfide particles that have a size distribution with a D50 value of no more than 10 μm.