Wavelength converter for an LED and LED containing same

• US 8,937,332 B2
• Filed: 01/31/2012
• Issued: 01/20/2015
• Est. Priority Date: 02/04/2011
• Status: Expired due to Fees

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Inventors: Kundaliya, Darshan, Raukas, Madis, Scotch, Adam M., Hamby, David, Mishra, Kailash, Stough, Matthew
• Primary Examiner(s): DANG, PHUC T
• Application Number:
  US13/982,667
• Publication Number:
  US 20130313603A1
• Time in Patent Office: 1,085 Days
• Field of Search: 257/98.99, 117/108
• US Class Current: 257/98
• CPC Class Codes: C09K 11/7701 Chalogenides
• CPC Class Codes: C09K 11/7774 Aluminates
• CPC Class Codes: C30B 23/025 characterised by the substrate
• CPC Class Codes: C30B 23/066 Heating of the material to be evaporated
• CPC Class Codes: C30B 29/68 Crystals with laminate structure, e.g. "superlattices"
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree

Abstract

A wavelength converter for an LED is described that comprises a substrate of monocrystalline garnet having a cubic crystal structure, a first lattice parameter and an oriented crystal face. An epitaxial layer is formed directly on the oriented crystal face of the substrate. The layer is comprised of a monocrystalline garnet phosphor having a cubic crystal structure and a second lattice parameter that is different from the first lattice parameter wherein the difference between the first lattice parameter and the second lattice parameter results in a lattice mismatch within a range of ±15%. The strain induced in the phosphor layer by the lattice mismatch shifts the emission of the phosphor to longer wavelengths when a tensile strain is induced and to shorter wavelengths when a compressive strain is induced. Preferably, the wavelength converter is mounted on the light emitting surface of a blue LED to produce an LED light source.

Claims

1. A wavelength converter for an LED, comprising:

a substrate of monocrystalline garnet having a cubic crystal structure, a first lattice parameter and an oriented crystal face; and

an epitaxial layer formed directly on the oriented crystal face of the substrate, the layer comprising a monocrystalline garnet phosphor having a cubic crystal structure and a second lattice parameter that is different from the first lattice parameter, the difference between the first lattice parameter and the second lattice parameter resulting in a lattice mismatch within a range of about −

3.1% to −

15%.

2. The wavelength converter of claim 1 wherein the garnet phosphor is a cerium-activated garnet phosphor having a composition represented by a formula A₃B₅O₁₂:

Ce, wherein A is Y, Sc, La, Gd, Lu, or Tb and B is Sc, Al or Ga.

3. The wavelength converter of claim 2 where the garnet phosphor is selected from Y₃Al₅O₁₂:

Ce or Lu₃Al₅O₁₂;

Ce.

4. The wavelength converter of claim 2 wherein the substrate is GGG (111).

5. The wavelength converter of claim 2 wherein the phosphor contains from about 0.001 to about 0.1 moles cerium per mole of phosphor.

6. The wavelength converter of claim 2 wherein the phosphor contains from about 0.005 to about 0.05 moles cerium per mole of phosphor.

7. The wavelength converter of claim 2 wherein the garnet phosphor is Lu₃Al₅O₁₂:

Ce and the substrate is GGG (111).

8. The wavelength converter of claim 3 wherein the substrate is GGG (111).

9. The wavelength converter of claim 3 wherein the phosphor contains from about 0.1 at.% Ce to about 10 at.% Ce.

10. The wavelength converter of claim 3 wherein the phosphor contains from about 0.5 at.% Ce to about 5 at.% Ce.

11. The wavelength converter of claim 1 wherein the garnet phosphor has a composition represented by a formula selected from:

(i) (A₁A₂′

)(B₂B₃′

)O₁₂;

Eu,Bi wherein A=Y, La, Gd;

A′

=Na, K, Li;

B=Mg, Ca, Sr, Ba; and

B′

=V, Ti, Sc, Nb, Zr;

(ii) A₃B₂B₃′

O₁₂;

Mg,Ce wherein A=Ca, Sr, Ba;

B=Sc, Ti, V, Nb; and

B′

=Si, Ge, Ga, Al, Sn, In;

or

(iii) (AA′

)₃(BB′

)₅O₁₂ wherein A=Y, La, Lu, Gd;

A′

=Mg, Ca, Sr, Ba; and

B or B′

, Al, Si, Ge.

12. The wavelength converter of claim 1 wherein the garnet phosphor is represented by the formula (A₁A₂′

)(B₂B₃′

)O₁₂—

;

Eu,Bi wherein A is Y, La, Gd;

A′

is Na, K, Li;

B is Mg, Ca, Sr, Ba; and

B′

is V, Ti, Sc, Nb, Zr or the garnet phosphor is represented by the formula A₃B₂B₃′

O₁₂;

Mg,Ce wherein A is Ca, Sr, Ba;

B is Sc, Ti, V, Nb; and

B′

is Si, Ge, Ga, Al, Sn, In.

13. An LED light source comprising:

an LED and a wavelength converter mounted on a light emitting surface of the LED, the wavelength converter converting at least a portion of the light emitted by the LED into light having a longer wavelength, the wavelength converter comprising;

a substrate of monocrystalline garnet having a cubic crystal structure, a first lattice parameter and an oriented crystal face; and

an epitaxial layer formed directly on the oriented crystal face of the substrate, the layer comprising a monocrystalline garnet phosphor having a cubic crystal structure and a second lattice parameter that is different from the first lattice parameter, the difference between the first lattice parameter and the second lattice parameter resulting in a lattice mismatch within a range of about −

3.1% to −

15%.

14. The LED light source of claim 13 wherein the garnet phosphor is a cerium-activated garnet phosphor having a composition represented by a formula A₃B₅O₁₂:

Ce, wherein A is Y, Sc, La, Gd, Lu, or Tb and B is Sc, Al or Ga.

15. The LED light source of claim 13 wherein the garnet phosphor is selected from Y₃Al₅O₁₂:

Ce or Lu₃Al₅O₁₂;

Ce.

16. The LED light source of claim 13 wherein the garnet phosphor is Lu₃Al₅O₁₂:

Ce and the substrate is GGG (111).

17. The LED light source of claim 13 wherein the garnet phosphor is represented by the formula (A₁A₂′

)(B₂B₃′

)O₁₂;

Eu,Bi wherein A is Y, La, Gd;

A′

is Na, K, Li;

B is Mg, Ca, Sr, Ba; and

B′

is V, Ti, Sc, Nb, Zr or the garnet phosphor is represented by the formula A₃B₂B₃′

O₁₂;

Mg,Ce wherein A is Ca, Sr, Ba;

B is Sc, Ti, V, Nb; and

B′

is Si, Ge, Ga, Al, Sn, In.

18. The LED light source of claim 13 wherein the LED emits light having a wavelength in a range from 420 nm to 490 nm.