White light illumination system with improved color output

• US 6,538,371 B1
• Filed: 03/27/2000
• Issued: 03/25/2003
• Est. Priority Date: 03/27/2000
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Srivastava, Alok Mani, Comanzo, Holly Ann, Duggal, Anil Raj
• Primary Examiner(s): Patel, Nimeshkumar D.
• Assistant Examiner(s): CLOVE, THELMA S
• Application Number:
  US09/534,575
• Time in Patent Office: 1,093 Days
• Field of Search: 252/301.4 H, 252/301.4 R, 313/486, 313/467, 313/502, 445/24, 438/116, 438/127
• US Class Current: 313/486
• CPC Class Codes: C09K 11/7774 Aluminates
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/12044 OLED
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

There is provided a white light illumination system including a blue LED and a luminescent material. The system color output is improved when a line connecting the LED color coordinates and the luminescent material color coordinates approximates the Black Body Locus on the CIE chromatically diagram. The LED may have a peak emission wavelength between 470 and 500 nm. The luminescent material may be (Y_1−x−zGd_xCe_z)₃Al₅O₁₂, where 0.7>x>0.4 and 0.1>z>0.

Claims

1. A white light illumination system comprising a radiation source and a luminescent material, wherein:

an emission spectrum of the radiation source represents a first point on a CIE chromaticity diagram;

an emission spectrum of the luminescent material represents a second point on the CIE chromaticity diagram;

a first line connecting the first point and the second point approximates a Black Body Locus on the CIE chromaticity diagram; and

radiation emitted by the system approximates the Black Body Locus on the CIE chromaticity diagram substantially independent of a thickness of the luminescent material for color temperatures ranging from 4000 K to 6000 K.

2. The system of claim 1, wherein the radiation source comprises a light emitting diode.

3. The system of claim 2, wherein the first line intersects the Black Body Locus twice.

4. The system of claim 2, wherein the first line is tangential to the Black Body Locus.

5. The system of claim 2, wherein:

a third point and a fourth point on the first line are located less than 0.01 y-units away from the Black Body Locus on the CIE chromaticity diagram;

the third point corresponds to a first color temperature; and

the fourth point corresponds to a second color temperature which is at least 2000 K greater than the first color temperature.

6. The system of claim 5, wherein the third point and the fourth point on the first line are located less than 0.005 y-units away from the Black Body Locus on the CIE chromaticity diagram.

7. The system of claim 6, wherein the first color temperature is 4000 K and the second color temperature is 6000K.

8. The system of claim 2, wherein:

a) the luminescent material comprises;

(A<sub>1−

x</sub>Gd_x)₃D₅E₁₂;

Ce,

wherein A comprises at least one of Y, Lu, Sm and La;

D comprises at least one of Al, Ga, Sc and In;

E comprises oxygen; and

x>

0.4; and

b) a peak emission wavelength of the light emitting diode is greater than 470 nm.

9. The system of claim 8, wherein the luminescent material comprises (Y₁₋

x−

zGd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0.

10. The system of claim 9, wherein the luminescent material further contains fluorine.

11. The system of claim 9, wherein the luminescent material comprises a (Y_0.37Gd_0.6Ce_0.03)₃Al₅O₁₂ phosphor.

12. The system of claim 8 wherein the light emitting diode contains at least one semiconductor layer comprising GaN, ZnSe and SiC having a peak emission wavelength greater than 470 nm but less than 500 nm.

13. The system of claim 12, wherein the light emitting diode peak emission wavelength is 475 to 480 nm.

14. The system of claim 12, wherein the light emitting diode comprises an InGaN p-n junction.

15. The system of claim 8, wherein:

the luminescent material comprises (Y<sub>1−

x−

z</sub>Gd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0; and

the light emitting diode peak emission wavelength is greater than 470 nm but less than 500 nm.

16. The system of claim 15, 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 luminescent material is phosphor coated over a surface of the light emitting diode;

b) the luminescent material is phosphor interspersed in the encapsulating material;

c) the luminescent material is a phosphor coated onto the shell;

or

d) the luminescent material is a scintillator overlying a surface of the light emitting diode.

17. The system of claim 2, wherein the CIE color coordinates of a radiation emitted by the system range from x=0.31 and y=0.33 to x=0.44 and y=0.4.

18. The system of claim 1, wherein the radiation source comprises one of a laser diode or a radiative gas discharge in a plasma display or in a fluorescent lamp.

57. The system of claim 1, wherein an emission spectrum of the system is represented by a point on the first line.

19. A white light illumination system comprising:

a) a luminescent material, comprising;

(A<sub>1−

x</sub>Gd_x)₃D₅E₁₂;

Ce,

wherein A comprises at least one of Y, Lu, Sm and La;

D comprises at least one of Al, Ga, Sc and In;

E comprises oxygen; and

x>

0.4;

b) a light emitting diode having a peak emission wavelength greater than 470 nm; and

wherein radiation emitted by the system approximates a Black Body Locus on a CIE chromaticity diagram substantially independent of a thickness of the luminescent material for color temperatures ranging from 4000 K to 6000 K.

20. The system of claim 19, wherein the luminescent material consists essentially of (Y₁₋

x−

zGd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0.

21. The system of claim 20, wherein the luminescent material further contains fluorine.

22. The system of claim 20, wherein the luminescent material comprises a (Y_0.37Gd_0.6Ce_0.03)₃Al₅O₁₂ phosphor.

23. The system of claim 19, wherein the light emitting diode comprises an InGaN p-n junction having a peak emission wavelength greater than 470 nm but less than 500 nm.

24. The system of claim 23, wherein the light emitting diode peak emission wavelength is 475 to 480 nm.

25. The system of claim 19, wherein:

the luminescent material comprises (Y<sub>1−

x−

z</sub>Gd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0; and

the light emitting diode peak emission wavelength is greater than 470 nm but less than 500 nm.

26. The system of claim 25, 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 luminescent material is a phosphor coated over a surface of the light emitting diode;

b) the luminescent material is a phosphor interspersed in the encapsulating material;

c) the luminescent material is a phosphor coated onto the shell;

or

d) the luminescent material is a scintillator overlying a surface of the light emitting diode.

27. The system of claim 20, wherein CIE color coordinates of a radiation emitted by the system range from x=0.31 and y=0.33 to x=0.44 and y=0.4.

28. A method of making a white light illumination system containing a radiation source and a luminescent material, comprising:

selecting a first line which approximates a Black Body Locus on a CIE chromaticity diagram;

forming the radiation source, wherein an emission spectrum of the radiation source is represented by a first point on the first line; and

forming the luminescent material, wherein an emission spectrum of the luminescent material is represented by a second point on the first line.

29. The method of claim 28, wherein the radiation source comprises a light emitting diode.

30. The method of claim 29, wherein the first line intersects the Black Body Locus twice.

31. The method of claim 29, wherein the first line is tangential to the Black Body Locus.

32. The method of claim 29, wherein:

a third point and a fourth point on the first line are located less than 0.01 y-units away from the Black Body Locus on the CIE chromaticity diagram;

the third point corresponds to a first color temperature; and

the fourth point corresponds to a second color temperature which is at least 2000 K greater than the first color temperature.

33. The method of claim 32 wherein:

the third point and the fourth point on the first line are located less than 0.005 y-units away from the Black Body Locus on the CIE chromaticity diagram.

34. The method of claim 33, wherein the first color temperature is 4000 K and the second color temperature is 6000K.

35. The method of claim 29, wherein:

a) the luminescent material comprises;

(A<sub>1−

x</sub>Gd_x)₃D₅E₁₂;

Ce,

wherein A comprises at least one of Y, Lu, Sm and La;

D comprises at least one of Al, Ga, Sc and In;

E comprises oxygen; and

x>

0.4; and

b) a peak emission wavelength of the light emitting diode is greater than 470 nm.

36. The method of claim 35, wherein:

the luminescent material comprises (Y<sub>1−

x−

z</sub>Gd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0; and

the light emitting diode peak emission wavelength is greater than 470 nm but less than 500 nm.

37. The method of claim 36, wherein the luminescent material comprises a (Y_0.37Gd_0.6Ce_0.03)₃Al₅O₁₂ phosphor and the light emitting diode comprises an InGaN p-n junction having a peak emission wavelength of 475 to 480 nm.

38. The method of claim 35, wherein the step of forming the luminescent material comprises:

mixing a Y₂O₃ powder, a CeO₂ powder, an Al₂O₃ powder, a GdO₂ powder and an AlF₃ flux to form a first powder;

sintering the first powder in a reducing atmosphere to form a sintered body; and

converting the sintered body into a second powder.

39. The method of claim 38, wherein:

the step of forming the light emitting diode comprises;

placing a light emitting diode into a shell; and

filling the shell with an encapsulating material;

and wherein the step of forming the luminescent material further comprises;

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

b) interspersing the second powder in the encapsulating material;

or

c) coating a suspension of the second powder and a solvent onto the shell and drying the suspension.

40. The method of claim 29, wherein the radiation emitted by the system approximates the Black Body Locus on the CIE chromaticity diagram substantially independent of a thickness of the luminescent material for color temperatures ranging from 4000 K to 6000 K.

41. The method of claim 29, wherein the step of forming the light emitting diode comprises:

selecting an existing light emitting diode having an emission spectrum represented by the first point on the first line; and

placing the light emitting diode into the illumination system.

42. The method of claim 29, wherein the step of forming the luminescent material comprises:

selecting an existing luminescent material having an emission spectrum represented by the second point on the first line; and

placing the luminescent material into the illumination system.

43. The method of claim 29, further comprising forming at least one of plural light emitting diodes and plural luminescent materials based on a single step of selecting the first line which approximates the Black Body Locus.

44. The method of claim 28, wherein the radiation source comprises one of a laser diode or a radiative gas discharge in a plasma display or in a fluorescent lamp.

45. A method of making a white light illumination system containing a radiation source and a luminescent material, comprising:

selecting the radiation source whose emission spectrum represents a first point on a CIE chromaticity diagram;

selecting the luminescent material whose emission spectrum represents a second point on the CIE chromaticity diagram, such that a first line connecting the first point and the second point approximates a Black Body Locus on the CIE chromaticity diagram; and

placing the radiation source and the luminescent material into the white light illumination system.

46. The method of claim 45, wherein:

the radiation source comprises a light emitting diode; and

the luminescent material comprises a phosphor.

47. The method of claim 46, wherein the first line intersects the Black Body Locus twice.

48. The method of claim 46, wherein the first line is tangential to the Black Body Locus.

49. The method of claim 46, wherein:

a third point and a fourth point on the first line are located less than 0.01 y-units away from the Black Body Locus on the CIE chromaticity diagram;

the third point corresponds to a first color temperature; and

the fourth point corresponds to a second color temperature which is at least 2000 K greater than the first color temperature.

50. The method of claim 49, wherein:

the third point and the fourth point on the first line are located less than 0.005 y-units away from the Black Body Locus on the CIE chromaticity diagram.

51. The method of claim 50, wherein the first color temperature is 4000 K and the second color temperature is 6000K.

52. The method of claim 46, wherein:

a) the luminescent material comprises;

(A<sub>1−

x</sub>Gd_x)₃D₅E₁₂;

Ce,

wherein A comprises at least one of Y, Lu, Sm and La;

D comprises at least one of Al, Ga, Sc and In;

E comprises oxygen; and

x>

0.4; and

b) a peak emission wavelength of the light emitting diode is greater than 470 nm.

53. The method of claim 52, wherein:

the luminescent material comprises (Y<sub>1−

x−

z</sub>Gd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0; and

the light emitting diode peak emission wavelength is greater than 470 nm but less than 500 nm.

54. The method of claim 53, wherein the luminescent material comprises a (Y_0.37Gd_0.6Ce_0.03)₃Al₅O₁₂ phosphor and the light emitting diode comprises an InGaN p-n junction having a peak emission wavelength of 475 to 480 nm.

55. The method of claim 46, wherein:

the step of placing the radiation source and the luminescent material into the white light illumination system comprises;

placing the light emitting diode into a shell; and

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

b) interspersing a phosphor powder and an encapsulating material in a shell;

or

c) coating a suspension of the phosphor powder and a solvent onto the shell and drying the suspension.

56. The method of claim 45, wherein the radiation emitted by the system approximates the Black Body Locus on the CIE chromaticity diagram substantially independent of a thickness of the luminescent material for color temperatures ranging from 4000 K to 6000 K.

58. A white light illumination system comprising a radiation source and a luminescent material, wherein:

an emission spectrum of the radiation source represents a first point on a CIE chromaticity diagram;

the radiation source comprises a light emitting diode having a peak emission wavelength of 475 to 480 nm;

an emission spectrum of the luminescent material represents a second point on the CIE chromaticity diagram; and

a first line connecting the first point and the second point approximates a Black Body Locus on the CIE chromaticity diagram.

59. The system of claim 58, wherein the luminescent material comprises (Y₁₋

x−

zGd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0.

60. A white light illumination system comprising:

a) a luminescent material, comprising;

(A<sub>1−

x</sub>Gd_x)₃D₅E₁₂;

Ce,

wherein A comprises at least one of Y, Lu, Sm and La;

D comprises at least one of Al, Ga, Sc and In;

E comprises oxygen; and

x>

0.4;

b) a light emitting diode having a peak emission wavelength of 475 to 480 nm.

61. The system of claim 60, wherein:

the light emitting diode comprises an InGaN p-n junction; and

the luminescent material comprises (Y<sub>1−

x−

z</sub>Gd_xCe_z)₃Al₅O₁₂;

0.7>

x>

0.4; and

0.1>

z>

0.