Methods and devices using high efficiency alkaline earth metal thiogallate-based phosphors

• US 7,368,179 B2
• Filed: 04/13/2004
• Issued: 05/06/2008
• Est. Priority Date: 04/21/2003
• Status: Active Grant

• Current Assignee: Lightscape Materials, Inc., Stanley Electric Company Limited
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Tian, Yongchi, Zaremba, Diane, Yocom, Perry Niel
• Primary Examiner(s): Cano; Milton I.
• Assistant Examiner(s): Thompson; Camie S.
• Application Number:
  US10/823,288
• Publication Number:
  US 20040206973A1
• Time in Patent Office: 1,484 Days
• Field of Search: 257/40, 257/98, 428/690, 428/917, 252/301.4 S, 427/66, 427/67, 313/503, 313/506, 313/112
• US Class Current: 428/690
• CPC Class Codes: C09K 11/7731 with alkaline earth metals
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: Y10S 428/917 Electroluminescent

Abstract

The present invention provides a light emitting device comprising: a light output; a light source that produces light having a wavelengths of 530 nm or less; and a wavelength transformer located between the light source and the light output, where the wavelength transformer comprises Sr_1-xCa_xGa₂S₄: yEu²⁺·zGa₂S₃, where x is 0.0001 to 1, y is a value defining sufficient Eu²⁺ to provide luminescent emission, and z is 0.0001 to 0.2 based on the mole amount of Sr_xCa_1-xGa₂S₄, and where the wavelength transformer effectively increases the light at the light output, the light having a wavelength between 535 nm and 560 nm.

Claims

1. A light emitting device comprising:

a light output;

a light source producing light including wavelengths of 530 nm or less; and

a wavelength transformer located between the light source and the light output, comprising Sr_1-xCa_xGa₂S₄;

yEu²⁺·

zGa₂S₃, wherein;

x is 0.0001 to 1;

y is a value defining sufficient Eu²⁺ to provide luminescent emission;

z is 0.0001 to 0.2 based on the mole amount of Sr_xCa_1-xGa₂S₄; and

the wavelength transformer effectively increases the light at the light output, the light having a wavelength between 535 nm and 560 nm.

2. The light emitting device of claim 1, wherein z is 0.001 to 0.2.

3. The light emitting device of claim 1, wherein z is 0.001 to 0.1.

4. The light emitting device of claim 1, wherein y is 0.001 to 0.1 based on the mole amount of Sr_1-xCa_xGa₂S₄.

5. The light emitting device of claim 4, wherein y is 0.01 to 0.08.

6. The light emitting device of claim 4, wherein y is 0.01 to 0.04.

7. The light emitting device of claim 1, wherein the phosphor has an emission peak of 535 nm to 560 nm.

8. The light emitting device of claim 7, wherein the emission peak has a bandwidth of 50 nm or less under excitation with an emission source at 440 nm±

40 nm.

9. A method of making a strontium calcium thiogallate phosphor of formula Sr_1-xCa_xGa₂S₄:

yEu²⁺·

zGa₂S₃, wherein;

x is 0.0001 to 1;

y is a value defining sufficient Eu²⁺ to provide luminescent emission; and

z is 0.0001 to 0.2 based on the mole amount of Sr_1-xCa_xGa₂S₄, the method comprising;

forming a composition of sulfate salts of gallium, divalent europium, calcium and, if x is not 1, strontium; and

firing the composition under hydrogen sulfide.

10. The method of claim 9, wherein z is 0.001 to 0.2.

11. The method of claim 9, wherein an amount of gallium is tuned to the range of 0.1 to 7% in excess of the stoichiometric amount of Sr_xCa_1-xGa₂S₄:

yEu²⁺.

12. The method of claim 9, further comprising:

a second firing of the composition following the fixing under hydrogen sulfide.

13. The method of claim 12, wherein the firing under hydrogen sulfide is conducted at 500 to 850 degrees C.

14. The method of claim 13, wherein the second firing is conducted at 750 to 950 degrees C.

15. The method of claim 13, wherein the product of the firing under hydrogen sulfide is ground prior to the second firing.

16. The method of claim 9, wherein z is 0.001 to 0.1.

17. The method of claim 9, wherein y is 0.001 to 0.1 based on the mole amount of Sr_1-xCa_xGa₂S₄.

18. The method of claim 17, wherein y is 0.01 to 0.08.

19. The method of claim 18, wherein y is 0.01 to 0.04.

20. The method of claim 9, wherein the phosphor has an emission peak of 535 nm to 560 nm.

21. The method of claim 20, wherein the emission peak has a bandwidth of 50 nm or less under excitation with an emission source at 440 nm±

40 nm.