Aluminum fluoride flux synthesis method for producing cerium doped YAG

• US 6,409,938 B1
• Filed: 03/27/2000
• Issued: 06/25/2002
• Est. Priority Date: 03/27/2000
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Comanzo, Holly Ann
• Primary Examiner(s): KOSLOW, CAROL M
• Application Number:
  US09/534,576
• Time in Patent Office: 820 Days
• Field of Search: 252/301.4 R
• US Class Current: 252/301.40R
• CPC Class Codes: C09K 11/7774 Aluminates

Abstract

A method of making a YAG:Ce³⁺ phosphor includes adding an AlF₃ fluxing agent to a yttrium, cerium, aluminum and oxygen containing starting powder and sintering the powder in a weak reducing atmosphere generated by evaporating charcoal. The resulting phosphor has a luminosity of greater than 435 lumens per watt.

Claims

1. A phosphor comprising:

2. The phosphor of claim 1, wherein:

the phosphor luminosity is 435 to 453 lumens per watt;

the phosphor x color coordinate ranges from 0.435 to 0.446; and

the phosphor y color coordinate ranges from 0.537 to 0.545.

3. The phosphor of claim 2, comprising:

(Y<sub>1−

x−

z</sub>Ce_xGd_z)₃Al₅O₁₂, wherein 0.1>

x>

0 and 0.05>

z≧

0.

4. The phosphor of claim 3, comprising:

(Y_0.97Ce_0.03)₃Al₅O₁₂, wherein;

the phosphor luminosity is 453 lumens per watt;

the phosphor x color coordinate is 0.435; and

the phosphor y color coordinate is 0.545.

5. The phosphor of claim 3, comprising (Y_0.93Gd_0.05Ce_0.03)₃Al₅O₁₂, wherein:

the phosphor luminosity is 441 lumens per watt;

the phosphor x color coordinate is 0.446; and

the phosphor y color coordinate is 0.537.

6. The phosphor of claim 3, wherein at least a portion of the oxygen is substituted by fluorine from an AlF₃ flux.

7. A white light illumination system comprising a light emitting diode and the phosphor of claim 1.

8. The system of claim 7 wherein the light emitting diode contains at least one semiconductor layer comprising GaN, ZnSe or SiC having an emission wavelength greater than 400 nm but less than 500 nm.

9. The system of claim 7, further comprising a shell containing the light emitting diode and an encapsulating material between the shell and the light emitting diode, and wherein:

a) the phosphor is coated over a surface of the light emitting diode;

b) the phosphor is interspersed in the encapsulating material;

or

c) the phosphor is coated onto the shell.

10. A method of making a YAG:

Ce³⁺ phosphor, comprising;

combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF₃ to obtain a first mixture; and

heating the first mixture to form a solid YAG;

Ce³⁺ phosphor body, wherein the phosphor luminosity is greater than 435 lumens per watt.

11. The method of claim 10, wherein the YAG:

Ce³⁺ phosphor comprises;

12. The method of claim 11, wherein the phosphor comprises:

(Y<sub>1−

x−

z</sub>Ce_xGd_z)₃Al₅O₁₂, wherein 0.1>

x>

0 and 0.7>

z≧

0; and

further comprising fluorine incorporated from the AlF₃.

13. The method of claim 11, wherein:

the at least one powder comprises a first powder comprising yttrium and oxygen, a second powder comprising cerium and oxygen, and a third powder comprising aluminum and oxygen; and

AlF₃ comprises a fourth powder.

14. The method of claim 13, wherein:

the first powder comprises Y₂O₃;

the second powder comprises CeO₂; and

the third powder comprises Al₂O₃.

15. The method of claim 13, wherein the at least one powder further comprises a Gd₂O₃ powder.

16. The method of claim 13, wherein at least one of the first powder, the second powder and the third powder comprises an oxalate, hydroxide, carbonate or nitrate compound.

17. The method of claim 11, wherein the concentration of the fourth powder comprises between 2 and 20 mole percent per mole of the phosphor produced.

18. The method of claim 11, wherein the step of combining at least one powder comprises:

dissolving Y and Ce in an acid;

co-precipitating a first powder comprising Y, Ce and oxygen with oxalic acid; and

combining the first powder with an Al₂O₃ powder and an AlF₃ powder.

19. The method of claim 18, further comprising:

dissolving Gd in the acid; and

wherein the first powder further comprises Gd.

20. The method of claim 10, wherein the step of heating comprises sintering in a reducing atmosphere comprising carbon.

21. The method of claim 20, wherein the reducing atmosphere does not contain forming gas.

22. The method of claim 20, wherein the step of sintering comprises:

placing the first mixture into a first container; and

evaporating a carbon based fuel to obtain the reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide.

23. The method of claim 22, further comprising:

placing the carbon based fuel into a second container, wherein the carbon based fuel comprises activated charcoal;

placing the first container comprising a covered alumina crucible into the second container; and

raising the temperature of the second container to 1500°

C. for 6 hours.

24. The method of claim 22, wherein the step of heating comprises raising the temperature of the first container to 1000 to 1600°

C. for 2 to 10 hours.

25. A method of using a phosphor, comprising:

converting the solid phosphor body made by the process of claim 11 to a phosphor powder; and

placing the phosphor powder into an illumination system.

26. The method of claim 25, wherein the step of converting comprises at least one of dry milling, wet milling, jet milling or crushing.

27. The method of claim 25, wherein the step of placing the phosphor powder into the illumination system comprises placing the phosphor powder into a white light illumination system containing a light emitting diode, into a plasma display or into a fluorescent lamp.

28. The method of claim 27, wherein the step of placing the phosphor powder into a white light illumination system comprises:

a) coating a suspension of the phosphor powder and a solvent over a surface of the light emitting diode and drying the suspension;

b) interspersing the phosphor powder in an encapsulating material overlying the light emitting diode;

or

c) coating a suspension of the phosphor powder and a solvent onto a shell enclosing the light emitting diode and drying the suspension.

29. The method of claim 27, wherein the step of placing the phosphor powder into a plasma display or into a fluorescent lamp comprises:

coating a suspension of the phosphor powder and a solvent onto a surface of a lamp cover or onto a surface of a portion of a plasma display; and

drying the suspension.

30. The method of claim 10, wherein:

the step of combining comprises;

a) combining a Y₂O₃ powder, a CeO₂ powder and an Al₂O₃ powder with AlF₃ to form a first mixture;

or

b) dissolving Y and Ce in an acid, co-precipitating a first powder comprising Y, Ce and oxygen, and combining the first powder with an Al₂O₃ powder and an AlF₃ powder to form a first mixture;

or

c) combining yttrium, cerium and aluminum containing compounds selected from at least one of oxide, oxalate, hydroxide, carbonate and nitrate compounds with AlF₃ to form a first mixture;

the step of heating comprises;

a) placing the first mixture into a crucible;

b) raising the temperature of the crucible to 1000 to 1600°

C. for 2 to 10 hours; and

c) supplying a reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide into the crucible by evaporating activated charcoal to form a solid phosphor body comprising (Y<sub>1−

x−

z</sub>Ce_xGd_z)₃Al₅(O,F)₁₂, wherein 0.1>

x>

0 and 0.7>

z≧

0; and

further comprising converting the solid phosphor body into a phosphor powder.

31. The method of claim 30, wherein the step of combining comprises:

combining a Y₂O₃ powder, a CeO₂ powder and an Al₂O₃ powder with AlF₃ to form a first mixture.

32. A phosphor powder made by the process of claim 11.

33. An illumination system comprising a fluorescent lamp, a plasma display or a light emitting diode and the phosphor powder of claim 32.

34. A method of making a YAG:

Ce³⁺ phosphor, comprising;

combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF₃ to obtain a first mixture; and

sintering the first mixture in a reducing atmosphere comprising carbon to form a solid YAG;

Ce³⁺ phosphor body.

35. The method of claim 34, wherein the reducing atmosphere does not contain forming gas.

36. The method of claim 34, wherein the step of sintering comprises:

placing the first mixture into a first container; and

evaporating a carbon based fuel to obtain the reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide.

37. The method of claim 36, further comprising:

placing the carbon based fuel into a second container, wherein the carbon based fuel comprises activated charcoal;

placing the first container comprising a covered alumina crucible into the second container; and

raising the temperature of the second container to 1500°

C. for 6 hours.

38. The method of claim 36, wherein the step of sintering comprises raising the temperature of the first container to 1000 to 1600°

C. for 2 to 10 hours.

39. The method of claim 34, wherein the YAG:

Ce³⁺ phosphor comprises;

40. The method of claim 39, wherein:

the phosphor luminosity is 435 to 453 lumens per watt;

the phosphor x color coordinate ranges from 0.435 to 0.446; and

the phosphor y color coordinate ranges from 0.537 to 0.545.

41. The method of claim 39, wherein the step of combining comprises:

combining a Y₂O₃ powder, a CeO₂ powder and an Al₂O₃ powder with AlF₃ to form the first mixture.

42. A method of making a phosphor comprising:

combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF₃ to obtain a first mixture, wherein the step of combining comprises;

a) combining a Y₂O₃ powder, a CeO₂ powder and an Al₂O₃ powder with AlF₃ to form a first mixture;

or

b) dissolving Y and Ce in an acid, co-precipitating a first powder comprising Y, Ce and oxygen, and combining the first powder with an Al₂O₃ powder and an AlF₃ powder to form a first mixture;

or

c) combining yttrium, cerium and aluminum containing compounds selected from at least one of oxide, oxalate, hydroxide, carbonate and nitrate compounds with AlF₃ to form a first mixture;

heating the first mixture to form a solid phosphor body, wherein the step of heating comprises;

a) placing the first mixture into a crucible;

b) raising the temperature of the crucible to 1000 to 1600°

C. for 2 to 10 hours; and

c) supplying a reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide into the crucible by evaporating activated charcoal to form a solid phosphor body comprising (Y<sub>1−

x−

z</sub>Ce_xGd_z)₃Al₅(O,F)₁₂, wherein 0.1>

x>

0 and 0.7>

z≧

0; and

further comprising converting the solid phosphor body into a phosphor powder.

43. The method of claim 42, wherein the step of combining comprises:

combining a Y₂O₃ powder, a CeO₂ podwer and an Al₂O₃ powder with AlF₃ to form the first mixture.