Nitride and oxy-nitride cerium based phosphor materials for solid-state lighting applications

• US 20070075629A1
• Filed: 10/02/2006
• Published: 04/05/2007
• Est. Priority Date: 09/30/2005
• Status: Abandoned Application

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Le Toquin, Ronan, Cheetham, Anthony
• Application Number:
  US11/541,755
• Publication Number:
  US 20070075629A1
• Time in Patent Office: Days
• US Class Current: 313/503
• CPC Class Codes: C09K 11/0883 Arsenides; Nitrides; Phosphides
• CPC Class Codes: C09K 11/77217 Silicon Nitrides or Silicon Oxynitrides
• CPC Class Codes: C09K 11/77218 Silicon Aluminium Nitrides or Silicon Aluminium Oxynitrides
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: H05B 33/14 characterised by the chemical or physical composition or the arrangement of the electroluminescent material , or by the simultaneous addition of the electroluminescent material in or onto the light source
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

Three new cerium (Ce) based phosphor materials based on nitride and oxy-nitride compounds emit yellow or blue to green photons upon excitation by ultraviolet (UV) or blue light radiation. The two yellow emitting compounds belong to the quartenary Ca—Al—Si—N system with distinct structures. These bright yellow phosphors can be used for white light applications by combining either a blue light emitting diode (LED) and a yellow phosphor, a blue LED and green-orange phosphors, or an ultraviolet (UV) LED with three phosphors, i.e., red, blue and green (RGB) phosphors. The bright blue-green phosphor, which may be described by Sr₂SiO_4-δN_δ, can be used in the UV LED plus 3 RGB phosphors setup.

Claims

1. An apparatus for solid state lighting applications, comprising:

a light emitting diode (LED); and

a luminescent cerium (Ce) compound comprising a Ce³⁺ doped compound from the quartenary Ca—

Al—

Si—

N system;

wherein the luminescent Ce compound emits yellow light when excited by radiation from the LED.

2. The apparatus of claim 1, wherein the luminescent Ce compound has an excitation spectrum comprising wavelengths smaller than 430 nm.

3. The apparatus of claim 1, wherein the radiation is ultraviolet (UV) or blue light radiation.

4. The apparatus of claim 1, wherein the LED is a blue LED and the luminescent Ce compound emits the yellow light for use in white light applications with the blue LED.

5. A composition of matter, comprising:

a luminescent cerium (Ce) compound that emits yellow light when excited by radiation, wherein the luminescent Ce compound is a Ce³⁺ doped compound from the quartenary Ca—

Al—

Si—

N system.

6. The composition of matter of claim 5, wherein the radiation is ultraviolet (UV) or blue light radiation.

7. The composition of matter of claim 5, wherein the luminescent Ce compound emits the yellow light for use in white light applications with a blue light emitting diode (LED).

8. The composition of matter of claim 5, wherein the luminescent Ce compound is based on a nitride or oxy-nitride compound.

9. The composition of matter of claim 5, wherein the luminescent Ce compound is described by the formula:

M_xSi_yAl_zN_w-δ

O_δ

;

Ce³⁺

wherein x≈

y≈

z≈

1, w=3, M is calcium (Ca), strontium (Sr), magnesium (Mg), or lanthanide (Ln) elements, and 0≦

δ

<

3.

10. The composition of matter of claim 9, wherein alkaline earths are substituted for M.

11. The composition of matter of claim 9, wherein cerium (Ce) ions are substituted for Ca with a concentration ranging from 0.01 to 20%.

12. The composition of matter of claim 9, wherein yttrium (Y) or lanthanide (Ln) elements are substituted for M with simultaneous replacement of silicon (Si) by aluminium (Al) or gallium (Ga) for charge compensation.

13. The composition of matter of claim 9, wherein silicon (Si) is partially substituted by germanium (Ge).

14. The composition of matter of claim 5, wherein the luminescent Ce compound has an orthorhombic unit cell having parameters a=5.6477(13) Å

, b=9.5201(26) Å and

c=4.9967(13) Å

.

15. The composition of matter of claim 5, wherein the luminescent Ce compound has a broad excitation band from 375 to 475 nm with a maximum at around 420 nm.

16. The composition of matter of claim 15, wherein the luminescent Ce compound, upon excitation at 420 nm, has an emission band centered at around 540 nm with a full width at half maximum of about 100 nm from 500 to 600 nm.

17. The composition of matter of claim 5, wherein the luminescent Ce compound has an orthorhombic cell with parameters a=9.92 Å

, b=9.11 Å and

c=7.33 Å

.

18. The composition of matter of claim 5, wherein the luminescent Ce compound has an emission maximum in the range 520-620 nm.

19. The composition of matter of claim 18, wherein the luminescent Ce compound has an excitation maximum in the range 420-500 nm.

20. A method for creating a luminescent cerium (Ce) compound, comprising the steps of:

(a) mixing stoichiometric amounts of (1) Ca₃N₂ or Ca metal, (2) AlN, (3) Si₃N₄, Si₂N₂NH, or Si(NH)₂, and (4) Ce to create a mixture, wherein the Ce is in the form of a metal, nitride, or oxide;

(b) weighing and grinding the mixture in conditions of [O₂]<

1 parts per million (ppm) and [H₂O]<

1 ppm in order to prevent oxidation or hydrolysis; and

(c) heating the mixture to a temperature between 1450°

C. and 1600°

C. under flowing hydrogen and nitrogen (H₂/N₂) with a ratio of 5;

95 at 0.2 to 0.5 liters per minute.

21. The method of claim 20, further comprising mixing the stoichiometric amounts of (1) Ca₃N₂ or Ca metal, (2) AlN, (3) Si₃N₄, Si₂N₂NH or Si(NH)₂, with a Ca:

Al;

Si ratio of 1;

1;

1, and adding less than 2% strontium.

22. An apparatus for solid state lighting applications, comprising:

a light emitting diode (LED); and

a luminescent cerium (Ce) compound that emits blue-green light when excited by radiation from the light emitting diode.

23. The apparatus of claim 22, wherein the radiation is ultraviolet (UV) or blue light radiation.

24. The apparatus of claim 22, wherein the LED is an ultraviolet (UV) LED and the luminescent Ce compound emits the blue-green light for use in white light applications with the UV LED in combination with red, green and blue (RGB) phosphors.

25. A composition of matter, comprising:

a luminescent cerium (Ce) compound that emits blue-green light when excited by radiation.

26. The composition of matter of claim 25, wherein the radiation is ultraviolet (UV) or blue light radiation.

27. The composition of matter of claim 25, wherein the luminescent Ce compound is used for white light applications in combination with one or more ultraviolet (UV) light emitting diodes (LEDs) with red, green and blue (RGB) phosphors.

28. The composition of matter of claim 25, wherein the luminescent Ce compound is based on a nitride or oxy-nitride compound.

29. The composition of matter of claim 25, wherein the luminescent Ce compound is described by the formula:

M₂SiO_4δ

N_δ

wherein M is strontium (Sr) and 0≦

δ

<

4.

30. The composition of matter of claim 29, wherein alkaline earths are substituted for M.

31. The composition of matter of claim 29, wherein silicon (Si) is partially substituted by germanium (Ge).

32. The composition of matter of claim 25, wherein the luminescent Ce compound has an orthorhombic structure with a space group Pnmb with refined cell parameters of about a=5.6671(3) Å

, b=7.0737(4) Å and

c=9.7359(5) Å

A.

33. The composition of matter of claim 25, wherein the luminescent Ce compound has an excitation peak with a width of about 80 nm, which leads to efficient excitation from 330 up to 400 nm.

34. The composition of matter of claim 25, wherein the luminescent Ce compound has an emission peak that is varied from 450 to 500 nm depending on synthesis conditions, a percentage of Ce or substitution of Sr by larger cations such as Ba.

35. The composition of matter of claim 25, wherein the luminescent Ce compound has an emission peak with a width of about 80 nm.

36. The composition of matter of claim 25, wherein the luminescent Ce compound is prepared by:

preparing a reactive mix of Ce doped SrO and SiO₂ nanopowders by dissolution of stoichiometric amounts of Sr(NO₃)₂ and Ce(NO₃)₃ in water with Si(OC₂H₅)₄, wherein a coprecipitation of Sr and Ce oxalate at 60°

C. is performed in a slightly basic environment in order to gel Si(OC₂H₅)₄ and a resulting dried powder is calcined at 750°

C. for 2 hours; and

mixing the (Sr,Ce)—

Si—

O thoroughly with Si₃N₄ to create a powder mixture and firing the powder mixture twice in a tube furnace at a temperature of 1350°

C. under flowing N₂ at 1 to 4 liters per minute.