Long persistence red phosphors and method of making

• US 6,419,854 B1
• Filed: 01/04/2000
• Issued: 07/16/2002
• Est. Priority Date: 06/16/1998
• Status: Expired due to Fees

• Current Assignee: Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Zaremba, Diane, Yocom, Perry Niel
• Primary Examiner(s): KOSLOW, CAROL M
• Application Number:
  US09/477,307
• Time in Patent Office: 924 Days
• Field of Search: 252/361.45, 428/403, 428/404, 428/407
• US Class Current: 252/301.40S
• CPC Class Codes: C09K 11/7731 with alkaline earth metals
• CPC Class Codes: C09K 11/7786 with alkaline earth metals
• CPC Class Codes: C09K 11/7788 Oxyhalogenides
• CPC Class Codes: Y10T 428/2991 Coated
• CPC Class Codes: Y10T 428/2993 Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]
• CPC Class Codes: Y10T 428/2998 including synthetic resin or polymer

Abstract

Long persistence phosphors based on strontium sulfide and activated with a divalent rare earth such as europium and a trivalent rare earth that does not change valence in a strontium sulfide host, and including oxygen and a halide, have long persistence and emit in the red-to-orange colors of the spectrum.

Claims

1. A long persistence, red-emitting phosphor comprising the formula SrS:

Eu;

M.O.X wherein M is a trivalent rare earth that does not change valence in the SrS host, and X is a halogen.

2. A phosphor according to claim 1 wherein X is chlorine.

3. A phosphor according to claim 1 wherein X is bromine.

4. A phosphor according to claim 1 wherein M is a trivalent rare earth that does not change valence in the SrS host that is selected from the group consisting of praeseodymium, neodymium, gadolinium, terbium, dysprosium, holmium, erbium and lutetium.

5. A phosphor according to claim 4 wherein the trivalent rare earth is erbium.

6. A phosphor according to claim 1 encapsulated in a water-impervious coating.

7. A phosphor according to claim 1 produced in powdered form wherein the powder particles are encapsulated in a water impervious coating.

8. A method of making a phosphor having the formula SrS:

Eu;

M.O.X wherein M is a trivalent rare earth that does not change valence in the SrS host and X is a halogen comprising

a) mixing strontium sulfate doped with europium and one or more trivalent rare earths that does not change valence in a SrS host with a hydrocarbon and sulfur in a closed inert crucible;

b) heating the mixture at about 900 to 1200°

C. and

c) heating the product with sulfur, a hydrocarbon and an ammonium halide to form SrS;

Eu;

M.O.X wherein M and X have the meanings given above.

9. A method according to claim 8 wherein the halogen is chlorine.

10. A method according to claim 8 wherein M is a trivalent rare earth selected from the group consisting of praeseodymium, neodymium, gadolinium, terbium, holmium, erbium and lutetium.

11. A method according to claim 8 wherein the trivalent rare earth is terbium.

12. A phosphor comprising a long persistence, red-emitting strontium sulfide doped with europium and a coactivator M where M is a rare earth ion selected from the group consisting of:

praseodymium, neodymium, gadolinium, terbium, dysprosium, holmium, erbium and lutetium.

13. The phosphor of claim 12 further comprising OX where X is a halogen.

14. The phosphor of claim 13 wherein M and OX are present in a stoichiometric ratio of between 1:

1-4 for M;

OX.

15. The phosphor of claim 13 where X is selected from the group consisting of:

chlorine and bromine.

16. The phosphor of claim 12 wherein M is praseodymium.

17. The phosphor of claim 12 wherein M is neodymium.

18. The phosphor of claim 12 wherein M is gadolinium.

19. The phosphor of claim 12 wherein M is terbium.

20. The phosphor of claim 12 wherein M is dysprosium.

21. The phosphor of claim 12 wherein M is holmium.

22. The phosphor of claim 12 wherein M is erbium.

23. The phosphor of claim 12 wherein M is lutetium.

24. The phosphor according to claim 12 further comprising a water impervious coating.

25. The phosphor according to claim 12 wherein red to orange-red colored light is emitted after a light source is removed.

26. The phosphor according to claim 12 further comprising oxygen.

27. The phosphor according to claim 26 wherein M and oxygen (O) are present in a stoichiometric ratio of between 1:

1-3 for M;

O.

28. The phosphor according to claim 12 further comprising halogen.

29. The phosphor according to claim 28 wherein M and halogen (X) are present in a