Cerium based phosphor materials for solid-state lighting applications

• US 20070159066A1
• Filed: 10/02/2006
• Published: 07/12/2007
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• 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
• Granted Patent: US 8,920,676 B2
• 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

A luminescent cerium (Ce) doped compound emitting bright red light, comprising a calcium silicate nitride ternary system, such as CaSiN_2δO_δ:Ce³⁺, that crystallizes in a face-centered cubic unit cell with a lattice parameter of ˜a=14.88 Å. The Ce doped compound can be used for white light applications either: (i) to enhance the light quality of the system based on a blue LED with a yellow or green phosphor, (ii) as an orange phosphor in combination with a blue LED and a green phosphor, or (iii) as a red phosphor in a setup comprising a ultraviolet (UV) LED and red, green and blue (RGB) phosphors. Substitution of smaller elements on the Ca site or larger elements on the Si site leads to a decrease of the emission wavelength towards the yellow or orange region.

Claims

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

a light emitting diode (LED); and

a luminescent cerium (Ce) compound that emits orange to red light when excited by radiation from the light emitting diode.

2. The apparatus of claim 1, wherein the light emitting diode is a blue light emitting diode and the luminescent cerium compound is used with the blue light emitting diode in combination with a yellow or green phosphor.

3. The apparatus of claim 1, wherein the light emitting diode is a blue light emitting diode and the luminescent cerium compound is used with the blue light emitting diode as an orange phosphor in combination with a green phosphor.

4. The apparatus of claim 1, wherein the light emitting diode is an ultraviolet (UV) light emitting diode and the luminescent cerium compound is used with the ultraviolet light emitting diode as a red phosphor in a group of red, green and blue (RGB) phosphors.

5. A composition of matter, comprising:

a luminescent cerium (Ce) compound that emits orange to red light when excited by radiation.

6. The composition of matter of claim 5, wherein the luminescent Ce compound is excited by wavelengths ranging from ultraviolet (UV) to green.

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

M_x(Si,Al)_yN<sub>z−

δ</sub>

O_δ

;

Ce³⁺

wherein x≈

y≈

1, z=2, 0≦

δ

<

2 and M is calcium (Ca), magnesium (Mg), strontium (Sr) or barium (Ba).

8. The composition of matter of claim 7, wherein germanium (Ge) is substituted for silicon (Si).

9. The composition of matter of claim 7, wherein M is yttrium (Y) or lanthanide (Ln) elements, and silicon (Si) is replaced by aluminum (Al) or gallium (Ga) for charge compensation.

10. The composition of matter of claim 7, wherein the luminescent Ce compound is a new phase in the calcium silicate nitride ternary system that crystallizes in a cubic unit cell.

11. The composition of matter of claim 10, wherein the luminescent Ce compound comprises CaSiN₂₋

δ

O_δ

;

Ce³⁺.

12. The composition of matter of claim 11, wherein substitution of smaller elements on the Ca site or larger elements on the Si site leads to a decrease of the emission wavelength towards the yellow or orange region.

13. The composition of matter of claim 7, wherein the luminescent Ce compound is made using the following steps:

(a) mixing stoichiometric amounts of;

(1) Ca₃N₂ or Ca metal, (2) AlN, (3) Si₃N₄ Si₂N₂NH, or Si(NH)₂, and (4) Ce as a rare earth source either as a metal, a nitride, or an oxide, in order to form a mixture;

(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 under flowing N₂ in conditions of 0.5 to 4 liters per minute to a temperature between 1300°

C. and 1500°

C.

14. The composition of matter of claim 5, wherein the luminescent compound is used with a blue light emitting diode in combination with a yellow or green phosphor.

15. The composition of matter of claim 5, wherein the luminescent Ce compound is used with a blue light emitting diode as an orange phosphor in combination with a green phosphor.

16. The composition of matter of claim 5, wherein the luminescent Ce compound is used with an ultraviolet (UV) light emitting diode as a red phosphor in a group of red, green and blue (RGB) phosphors.

17. A method for creating a luminescent 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) a rare earth source either as a metal, a nitride, or an oxide, in order to form a mixture;

(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 under flowing N₂ in conditions of 0.5 to 4 liters per minute to between 1300°

C. and 1500°

C.

18. The method of claim 17, wherein the rare earth source is cerium (Ce).