Rare earth-activated aluminum nitride powders and method of making

• US 7,935,325 B2
• Filed: 12/20/2006
• Issued: 05/03/2011
• Est. Priority Date: 01/31/2006
• Status: Expired due to Fees

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG), Regents of the University of California (University of California)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG), Regents of the University of California (University of California)
• Inventors: Han, Bing, Talbot, Jan B., Mishra, Kailash A., Tao, Jonathan H., Raukas, Madis, Klinedinst, Keith A.
• Primary Examiner(s): Mayes; Melvin C
• Assistant Examiner(s): Gregorio; Guinever S
• Application Number:
  US12/161,017
• Publication Number:
  US 20090252667A1
• Time in Patent Office: 1,595 Days
• Field of Search: None
• US Class Current: 423/263
• CPC Class Codes: C01B 21/072 with aluminium
• CPC Class Codes: C01P 2002/52 containing elements as dopants
• CPC Class Codes: C01P 2002/54 one element only
• CPC Class Codes: C01P 2002/84 by UV- or VIS- data
• CPC Class Codes: C04B 2235/3224 Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
• CPC Class Codes: C04B 2235/465 Ammonia
• CPC Class Codes: C04B 2235/9661 Colour
• CPC Class Codes: C04B 35/581 based on aluminium nitride
• CPC Class Codes: C09K 11/0883 Arsenides; Nitrides; Phosphides
• CPC Class Codes: C09K 11/77066 Aluminium Nitrides or Aluminium Oxynitrides
• CPC Class Codes: C09K 11/77346 Aluminium Nitrides or Aluminium Oxynitrides
• CPC Class Codes: C09K 11/77496 Aluminium Nitrides or Aluminium Oxynitrides
• CPC Class Codes: C09K 11/77926 Aluminium Nitrides or Aluminium Oxynitrides

Abstract

Rare earth-activated aluminum nitride powders are made using a solution-based approach to form a mixed hydroxide of aluminum and a rare earth metal, the mixed hydroxide is then converted into an ammonium metal fluoride, preferably a rare earth-substituted ammonium aluminum hexafluoride ((NH₄)₃Al_1-xRE_xF₆), and finally the rare earth-activated aluminum nitride is formed by ammonolysis of the ammonium metal fluoride at a high temperature. The use of a fluoride precursor in this process avoids sources of oxygen during the final ammonolysis step which is a major source of defects in the powder synthesis of nitrides. Also, because the aluminum nitride is formed from a mixed hydroxide co-precipitate, the distribution of the dopants in the powder is substantially homogeneous in each particle.

Claims

1. A method of making a rare earth-activated aluminum nitride, comprising:

(a) forming an aqueous mixture containing aluminum and a rare earth metal;

(b) precipitating a mixed hydroxide of aluminum and the rare earth metal;

(c) reacting the mixed hydroxide with ammonium fluoride to form a fluoride compound of aluminum and the rare earth metal;

(d) drying the fluoride compound; and

(e) reacting the dried fluoride compound with ammonia gas to form the rare earth-activated aluminum nitride.

2. The method of claim 1 wherein the rare earth metal is selected from Dy, Tb, Eu, Tm, Ho, Sm, Er, Nd, Pr, Gd, and combinations thereof.

3. The method of claim 1 wherein the rare earth metal is selected from Dy, Tb, Eu, Tm, and combinations thereof.

4. The method of claim 1 wherein the aqueous mixture is formed by dissolving aluminum nitrate and a nitrate of the rare earth metal.

5. The method of claim 4 wherein the mixed hydroxide is precipitated by adding ammonium hydroxide to the aqueous mixture.

6. The method of claim 1 wherein the mixed hydroxide is reacted with a stoichiometric excess of ammonium fluoride at about 80°

C.

7. The method of claim 1 wherein the fluoride compound is reacted with ammonia gas at about 900°

C.

8. The method of claim 1 wherein the fluoride compound is a hexafluoride compound.

9. The method of claim 1 wherein the mixed hydroxide is filtered to produce a filtrate and rinsed until there is no change in the pH of the filtrate.

10. A method of making a rare earth-activated aluminum nitride, comprising:

(a) forming an aqueous mixture by dissolving aluminum nitrate and a nitrate of a rare earth metal;

(b) precipitating a mixed hydroxide of aluminum and the rare earth metal by adding ammonium hydroxide to the aqueous mixture;

(c) reacting the mixed hydroxide with a stoichiometric excess of ammonium fluoride at an elevated temperature to form a hexafluoride compound of aluminum and the rare earth metal;

(d) drying hexafluoride compound; and

(e) reacting the dried hexafluoride compound with ammonia gas to form the rare earth-activated aluminum nitride.

11. The method of claim 10 wherein the rare earth metal is selected from Dy, Tb, Eu, Tm, Ho, Sm, Er, Nd, Pr, Gd, and combinations thereof.

12. The method of claim 10 wherein the rare earth metal is selected from Dy, Tb, Eu, Tm, and combinations thereof.

13. The method of claim 10 wherein the hexafluoride compound is reacted with ammonia gas at about 900°

C.

14. The method of claim 13 wherein the mixed hydroxide is reacted with the excess ammonium fluoride at about 80°

C.

15. The method of claim 14 wherein the rare earth metal is selected from Dy, Tb, Eu, Tm, and combinations thereof.

16. The method of claim 10 wherein the mixed hydroxide is filtered to produce a filtrate and rinsed until there is no change in the pH of the filtrate.