Light emitting device incorporating a luminescent material

• US 7,042,020 B2
• Filed: 02/14/2003
• Issued: 05/09/2006
• Est. Priority Date: 02/14/2003
• Status: Expired due to Term

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Negley, Gerald H.
• Primary Examiner(s): Tran, Minhloan
• Assistant Examiner(s): MONDT, JOHANNES P
• Application Number:
  US10/248,754
• Publication Number:
  US 20040159849A1
• Time in Patent Office: 1,180 Days
• Field of Search: 257 79-103, 372 43- 50
• US Class Current: 257/98
• CPC Class Codes: H01L 33/501 characterised by the materials, e.g. binder

Abstract

A light emitting device uses a source of exciting radiation such as an light emitting diode to excite a photo luminescent material to provide a source of visible light. The photo luminescent material is loaded into a low density material such as a xerogel or an aerogel which is adjacent the source of exciting radiation

Claims

1. A semiconductor based light emitting device comprising:

a light emitting diode that emits an exciting radiation;

a porous matrix covering at least a portion of said light emitting diode, and a substance loaded into said porous matrix which emits a responsive radiation upon interaction with the exciting radiation emitted by said diode.

2. A light emitting device according to claim 1 wherein said porous matrix is in direct contact with said diode.

3. A light emitting device according to claim 1 wherein said matrix has a porosity of at least about 50 percent by volume.

4. A light emitting device according to claim 1 wherein said matrix has a porosity of at least about 70 percent by volume.

5. A light emitting device according to claim 1 wherein said matrix has a porosity of at least about 90 percent by volume.

6. A light emitting device according to claim 1 wherein the concentration of said loaded substance in said porous matrix is sufficient to produce a desired emission of visible light at the desired level of exciting radiation while avoiding overloading the porous matrix to the point of structural disadvantage.

7. A light emitting device according to claim 1 wherein said diode emits electromagnetic radiation in a frequency selected from the group consisting of the ultraviolet, visible and infrared portions of the electromagnetic spectrum.

8. A light emitting device according to claim 1 wherein said light emitting diode has an active layer selected from the group consisting of gallium nitride, indium gallium nitride and indium aluminum gallium nitride.

9. A light emitting device according to claim 1 wherein said porous matrix is substantially transparent with respect to said exciting radiation and said responsive radiation.

10. A light emitting device according to claim 1 wherein said porous matrix comprises a sol gel material.

11. A light emitting device according to claim 10 wherein said porous matrix is selected from the group consisting of aerogels and xerogels.

12. A light emitting device according to claim 10 wherein said sol gel material comprises a silica compound.

13. A light emitting device according to claim 12 wherein said silica compound comprises methacryloxypropyltrimethoxysilane.

14. A light emitting device according to claim 10 wherein said sol gel material has a density between about 0.01 g/cm³ and 1.6 g/cm³.

15. A light emitting device according to claim 10 wherein said sol gel material has a pore size distribution of between about 1 nm and 500 nm.

16. A light emitting device according to claim 10 wherein said so gel material has a surface area of at least 100 m²/g.

17. A light emitting device according to claim 1 wherein said radiation responsive substance is a phosphor.

18. A light emitting device according to claim 17 wherein said phosphor emits light within the visible portion of the spectrum in response to the exciting radiation from said diode.

19. A light emitting device according to claim 17 wherein said phosphor is in the form of particles between about 0.001 microns and about 20 microns.

20. A light emitting device according to claim 17 wherein said phosphor is selected from the group consisting of oxide-based phosphors;

sulfide-based phosphors;

iodide-based phosphors;

garnet-based phosphors; and

mixtures of two or more or these.

21. A lamp comprising the light emitting device according to claim 1.

22. A pixel comprising the light emitting device according to claim 1.

23. A display comprising the light emitting device according to claim 1.

24. A light emitting device according to claim 1 wherein said diode is selected from the group consisting of homojunctions, single heterojunctions, and double heterojunctions.

25. A light emitting device according to claim 1 wherein said diode includes a feature selected from the group consisting of quantum wells, multiple quantum wells, and superlattice structures.

65. A light emitting device according to claim 18 wherein said light emitting diode emits light within the visible portion of the spectrum having a first color, and wherein said phosphor emits light having a second color that is different from said first color, and wherein said first and second colors blend together so that the device emits light having a color that is different from said first and second colors.

66. A Light emitting device according to claim 20 wherein said phosphor comprises yttrium aluminum garnet (YAG).

67. A light emitting device according to claim 20 wherein said phosphor comprises a sulfide-based phosphor.

26. A light emitting device comprising:

a light emitting diode that emits an exciting radiation, said light emitting diode having a silicon carbide substrate and an active layer that includes at least one Group III nitride;

a porous matrix covering at least a portion of said light emitting diode, and a photoluminescent material loaded into said porous matrix which emits visible light upon interaction with the exciting radiation emitted by said diode.

27. A light emitting device according to claim 26 wherein said porous matrix is in direct contact with said diode.

28. A light emitting device according to claim 26 wherein said diode emits electromagnetic radiation in a frequency selected from the group consisting of the ultraviolet, visible and infrared electromagnetic spectrum.

29. A light emitting device according to claim 26 wherein said porous matrix is substantially transparent with respect to said exciting radiation and visible light.

30. A light emitting device according to claim 26 wherein said porous matrix is a sol gel material.

31. A light emitting device according to claim 30 wherein said porous matrix is an aerogel.

32. A light emitting device according to claim 30 wherein said porous matrix is a xerogel.

33. A light emitting device according to claim 26 wherein said photoluminescent material is a phosphor.

34. A light emitting device according to claim 33 wherein said phosphor is selected from the group consisting of oxide-based phosphors;

sulfide-based phosphors;

iodide-based phosphors;

garnet-based phosphors; and

mixtures of two or more or these.

35. A lamp comprising the light emitting device according to claim 26.

36. A pixel comprising the light emitting device according to claim 26.

37. A display comprising the light emitting device according to claim 26.

38. A light emitting device according to claim 26 wherein said light emitting diode has an active layer selected from the group consisting of gallium nitride, indium gallium nitride and indium aluminum gallium nitride.

68. A light emitting device according to claim 33 wherein said diode emits light within the visible portion of the spectrum having a first color, and wherein said phosphor emits visible light having a second color that is different from said first color, and wherein said first and second colors blend together so that the device emits light having a color that is different from said first and second colors.

69. A light emitting device according to claim 34 wherein said phosphor comprises yttrium aluminum garnet (YAG).

70. A light emitting device according to claim 34 wherein said phosphor comprises a sulfide-based phosphor.

39. A light emitting device comprising:

a laser diode that emits an exciting radiation, said laser diode having a silicon carbide substrate and an active layer that includes at least one Group III nitride;

a porous matrix covering at least a portion of said laser diode, and a photoluminescent material loaded into said porous matrix which emits a responsive radiation upon interaction with the exciting radiation emitted by said laser diode.

40. A light emitting device according to claim 39 wherein said light emitting diode has an active layer selected from the group consisting of gallium nitride, indium gallium nitride and indium aluminum gallium nitride.

41. A light emitting device according to claim 39 wherein said porous matrix is in direct contact with said diode.

42. A light emitting device according to claim 39 wherein said porous matrix is a sol gel substantially transparent with respect to said exciting radiation and visible light.

43. A light emitting device according to claim 42 wherein said sol gel is selected from the group consisting of aerogels and xerogels.

44. A light emitting device according to claim 39 wherein said photoluminescent material comprises a phosphor selected from the group consisting of oxide-based phosphors;

sulfide-based phosphors;

iodide-based phosphors;

garnet-based phosphors; and

mixtures of two or more or these.

71. A light emitting device according to claim 39 wherein said laser diode emits light within the visible portion of the spectrum having a first color, and wherein said photoluminescent material is a phosphor and emits light within the visible portion of the spectrum having a second color that is different from said first color, and wherein said first and second colors blend together so that the device emits light having a color that is different from said first and second colors.

72. A light emitting device according to claim 44 wherein said phosphor comprises yttrium aluminum garnet (YAG).

73. A light emitting device according to claim 44 wherein said phosphor comprises a sulfide-based phosphor.

45. A semiconductor-based light emitting device comprising:

a light emitting diode that includes a single crystal silicon carbide substrate a porous matrix on said diode and selected from the group consisting of aerogels and xerogels; and

a phosphor loaded in said matrix and that responds to the emission from said diode with a secondary emission of a different wavelength.

46. A light emitting device according to claim 45 wherein said porous matrix is directly on said diode.

47. A light emitting device according to claim 45 wherein said matrix has a porosity of at least about 50 percent by volume.

48. A light emitting device according to claim 45 wherein said matrix has a porosity of at least about 70 percent by volume.

49. A light emitting device according to claim 45 wherein said matrix has a porosity of at least about 90 percent by volume.

50. A light emitting device according to claim 45 wherein said phosphor is present in said matrix in an amount of between about one milligram and one gram per cubic centimeter.

51. A light emitting device according to claim 45 wherein said porous matrix is substantially transparent with respect to said exciting radiation and said responsive radiation.

52. A light emitting device according to claim 45 wherein said porous matrix comprises a silica compound.

53. A light emitting device according to claim 52 wherein said silica compound comprises methacryloxypropyltrimethoxysilane.

54. A light emitting device according to claim 52 wherein said silica compound has a density between about 0.01 g/cm³ and 1.6 g/cm³.

55. A light emitting device according to claim 52 wherein said silica compound has a pore size distribution of between about 1 nm and 500 nm.

56. A light emitting device according to claim 52 wherein said silica compound has a surface area of at least 100 m²/g.

57. A light emitting device according to claim 45 wherein said phosphor is present in said matrix in the form of particles between about 0.001 microns and about 20 microns.

58. A light emitting device according to claim 45 wherein said phosphor is selected from the group consisting of oxide-based phosphors;

sulfide-based phosphors;

iodide-based phosphors;

garnet-based phosphors; and

mixtures of two or more or these.

59. A lamp comprising the light emitting device according to claim 45.

60. A pixel comprising the light emitting device according to claim 45.

61. A display comprising the light emitting device according to claim 45.

62. A light emitting device according to claim 45 wherein said diode is selected from the group consisting of homojunctions, single heterojunctions, and double heterojunctions.

63. A light emitting device according to claim 45 wherein said diode includes a feature selected from the group consisting of quantum wells, multiple quantum wells, and superlattice structures.

64. A light emitting device according to claim 45 wherein said light emitting diode has an active layer selected from the group consisting of gallium nitride, indium gallium nitride and indium aluminum gallium nitride.

74. A light emitting device according to claim 45 wherein said light emitting diode emits light within the visible portion of the spectrum having a first color, and wherein said phosphor emits light within the visible portion of the spectrum having a second color that is different from said first color, and wherein said first and second colors blend together so that the device emits light having a color that is different from said first and second colors.

75. A light emitting device according to claim 58 wherein said phosphor comprises yttrium aluminum garnet (YAG).

76. A light emitting device according to claim 58 wherein said phosphor comprises a sulfide-based phosphor.