Electroluminescent phosphor powder with D50 value of less than 12 μm and method of making
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 μm, and more preferably less than 10 μm. 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 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. The step of inducing defects may be accomplished by milling, mulling or sonification of the mixture.
1. 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.
2. The method of claim 1 , wherein the step of inducing defects includes sonification of the mixture.
3. The method of claim 1 , wherein the first mixture is preliminarily fired at a temperature in a range of about 1020° C. to about 1100° C. for about 65 minutes to about 85 minutes.
4. The method of claim 3 , wherein the preliminary firing is at a temperature of about 1085° C. for about 75 minutes.
5. The method of claim 1 , wherein the first step firing is at a temperature of about 1050° C. for about 40 minutes.
6. The method of claim 1 , wherein the second step firing is at a temperature of about 730° C. for about 2¼ hours.
7. The method of claim 5 , wherein the second step firing is at a temperature of about 730° C. for about 2¼ hours.
8. An electroluminescent phosphor powder comprising particles of a copper-activated zinc sulfide electroluminescent phosphor having a particle size distribution having a D50 value of less than 12 μm, wherein the powder when operated at 100V and 400 Hz in an electroluminescent lamp has a brightness of at least about 10 fL.
9. The electroluminescent phosphor powder of claim 8 , wherein the brightness is at least about 15 fL.
10. The electroluminescent phosphor powder of claim 8 , wherein the brightness is at least about 25 fL.
11. An electroluminescent lamp, comprising: a first electrode, a second electrode, a first dielectric layer containing a dielectric material, and a second dielectric layer containing an electroluminescent phosphor, the dielectric layers being located between the first and second electrodes and the phosphor comprising copper-activated zinc sulfide particles that have a size distribution with a D50 value of less than 12 μm, wherein the lamp when operated at 100V and 400 Hz has a brightness of at least about 10 fL.
12. The electroluminescent lamp of claim 11 , wherein the brightness is at least about 15 fL.
13. The electroluminescent lamp of claim 11 , wherein the brightness is at least about 25 fL.
14. The electroluminescent phosphor powder of claim 8 , wherein the phosphor particles further contain chlorine, manganese or both.