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Changing Light with Phosphor

Patent

US8937332

Owner

OSRAM GmbH

Filing Date

January 31, 2012

Priority Date

February 04, 2011

Portfolio

Lighting - OSRAM

Intro

Emission wavelengths of garnet phosphors can be shifted by growing a monocrystalline phosphor film on a substrate that has a slightly different parameter than the film. The strain induced 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 in the film growth direction.

Claims

1. A wavelength converter for an LED, comprising: a substrate of monocrystalline garnet having a cubic crystal structure, a first lattice parameter an...
  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.  
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Abstract

A wavelength converter for an LED is described that comprises a substrate of monocrystalline garnet having a cubic crystal structure, a first lattice ...
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.
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Phosphor Expert
June 28, 2018

It would be an advantage for both white and single color pc-LEDs to be able to adjust the emission colors of available garnet-based phosphors without having to change their composition.
Applications: Yttrium Aluminum Garnet LED phosphors could be a match. They are high efficiency phosphors suitable for coating LEDs with high CCT.
Companies: LED phosphor producers

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