Nanocluster-based white-light-emitting material employing surface tuning

• US 7,235,190 B1
• Filed: 09/02/2004
• Issued: 06/26/2007
• Est. Priority Date: 09/02/2004
• Status: Active Grant

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Thoma, Steven G., Abrams, Billie L., Wilcoxon, Jess P.
• Primary Examiner(s): KOSLOW, CAROL M
• Application Number:
  US10/933,069
• Time in Patent Office: 1,027 Days
• Field of Search: 252/301.6 S, 252/301.35
• US Class Current: 252/301.60S
• CPC Class Codes: C09K 11/02 Use of particular materials as binders, particle coatings or suspension media therefor
• CPC Class Codes: C09K 11/565 with zinc cadmium
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 977/773 Nanoparticle, i.e. structure having three dimensions of 100 nm or less
• CPC Class Codes: Y10S 977/824 Group II-VI nonoxide compounds, e.g. CdxMnyTe
• CPC Class Codes: Y10S 977/834 Optical properties of nanomaterial, e.g. specified transparency, opacity, or index of refraction

Abstract

A method for making a nanocrystal-based material capable of emitting light over a sufficiently broad spectral range to appear white. Surface-modifying ligands are used to shift and broaden the emission of semiconductor nanocrystals to produce nanoparticle-based materials that emit white light.

Claims

1. A method for making a white-light-emitting material, comprising:

forming a solution of CdS nanocrystals;

reacting a surface of said CdS nanocrystals with a surface-modifying compound to form a solution of surface-dominated light-emitting nanoparticles;

aging said surface-dominated light-emitting nanoparticles to broaden a light-emission spectrum of said surface-dominated light-emitting nanoparticles to produce a white-light-emitting material, wherein said solution of CdS nanocrystals is formed by an inverse micelle method.

2. The method of claim 1, wherein a Cd salt used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of cadmium nitrate, cadmium chloride, cadmium iodide, and cadmium perchlorate.

3. The method of claim 1, wherein a sulfide source used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of ammonium sulfide, hydrogen sulfide, lithium sulfide, and sodium sulfide.

4. The method of claim 1, wherein a first solvent used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of alkanes, aromatic hydrocarbons, ethers, cyclic ethers, tetrahydrofuran, and alcohols containing at least 8 carbon atoms.

5. The method of claim 1, wherein a first surfactant used to form said solution of CdS nanocrystals by said inverse micelle method comprises an anionic surfactant.

6. The method of claim 1, wherein a first surfactant used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of AOT, quaternary ammonium salts comprising alkyl chains containing 16 or more carbon atoms, and alkylated polyethers of the formula CH₃(CH₂)_m(CH₂CH₂O)_nOH where m is at least 8 and n is at least 4.

7. A method for making a white-light-emitting material, comprising:

forming a solution of CdS nanocrystals;

reacting a surface of said CdS nanocrystals with a surface-modifying compound to form a solution of surface-dominated light-emitting nanoparticles; and

aging said surface-dominated light-emitting nanoparticles to broaden a light-emission spectrum of said surface-dominated light-emitting nanoparticles to produce a white-light-emitting material, wherein the step of forming said solution of CdS nanocrystals comprises dissolving a plurality of preformed CdS nanocrystals in a solvent solution.

8. The method of claim 7, wherein said solvent solution comprises a second solvent and a second surfactant.

9. The method of claim 8, wherein said second surfactant is selected from the group consisting of AOT, quaternary ammonium salts comprising alkyl chains containing at least 16 carbon atoms, and alkylated polyethers of the formula CH₃(CH₂)_m(CH₂CH₂O)_nOH where m is at least 8 and n is at least 4.

10. The method of claim 8, wherein said second solvent is selected from the group consisting of alkyl hydrocarbons, aromatic hydrocarbons, and alcohols containing 8 or more carbon atoms.

11. A method for making a white-light-emitting material, comprising:

forming a solution of CdS nanocrystals;

reacting a surface of said CdS nanocrystals with a surface-modifying compound to form a solution of surface-dominated light-emitting nanoparticles;

a aging said surface-dominated light-emitting nanoparticles to broaden a light-emission spectrum of said surface-dominated light-emitting nanoparticles to produce a white-light-emitting material, and encapsulating said aged surface-dominated light-emitting nanoparticles with an encapsulant to produce a white-light-emitting material.

12. The method of claim 11, wherein said solution of CdS nanocrystals is formed by an inverse micelle method.

13. The method of claim 12, wherein a Cd salt used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of cadmium nitrate, cadmium chloride, cadmium iodide, and cadmium perchlorate.

14. The method of claim 12, wherein a sulfide source used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of ammonium sulfide, hydrogen sulfide, lithium sulfide, and sodium sulfide.

15. The method of claim 12, wherein a fourth solvent used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of alkanes, tetrahydrofuran, alcohols containing at least 8 carbon atoms, octyl ether, and benzyl ether.

16. The method of claim 12, wherein a third surfactant used to form said solution of CdS nanocrystals by said inverse micelle method comprises an anionic surfactant.

17. The method of claim 12, wherein a third surfactant used to form said solution of CdS nanocrystals by said inverse micelle method is selected from the group consisting of AOT, quaternary ammonium salts comprising alkyl chains containing at least 16 carbon atoms, and alkylated polyethers of the formula CH₃(CH₂)_m(CH₂CH₂O)_nOH where m is at least 8 and n is at least 4.

18. The method of claim 11, wherein a method for forming said solution of CdS nanocrystals comprises dissolving a plurality of preformed CdS nanocrystals in a solvent solution.

19. The method of claim 18, wherein said solvent solution comprises a fifth solvent and a fourth surfactant.

20. The method of claim 19, wherein said fourth surfactant is selected from the group consisting AOT, quaternary ammonium salts comprising alkyl chains containing at least 10 carbon atoms, and alkylated polyethers of the formula CH₃(CH₂)_m(CH₂CH₂O)_nOH where m is at least 8 and n is at least 4.

21. The method of claim 19, wherein said fifth solvent is selected from the group consisting of alkyl hydrocarbons containing between 5 and 16 carbon atoms, ethers, cyclic ethers, tetrahydrofuran, and alcohols containing at least 6 carbon atoms.

22. The method of claim 11, wherein said surface-modifying compound comprises an electron-donating ligand.

23. The method of claim 11, wherein said surface-modifying compound is selected from a group consisting of thiols, amines, and phosphines.

24. The method of claim 11, wherein said encapsulant is selected from the group consisting of AOT, tri-octyl phosphine, an ormosil, a silica glass, a silicone, and an epoxy.

25. A method for making a white-light-emitting material, comprising:

forming a solution of CdS nanocrystals in a solvent solution;

reacting a surface of said CdS nanocrystals with a surface-modifying compound to form a solution of surface-dominated light-emitting nanoparticles;

aging said solution of said surface-dominated light-emitting nanoparticles to broaden a light-emission spectrum of said surface-dominated light-emitting nanoparticles to form a solution of aged surface-dominated light-emitting nanoparticles;

applying said solution to a surface;

and

evaporating said solvent from said solution of aged surface-dominated light-emitting nanoparticles to form a film containing said aged surface-dominated light-emitting nanoparticles to produce a white-light-emitting material.

26. The method of claim 25, wherein said surface-modifying compound is selected from a group consisting of thiols, amines, and phosphines.

27. The method of claim 25, wherein said solvent solution comprises a solvent and a surfactant.

28. The method of claim 27, wherein said surfactant is selected from the group consisting of AOT, quaternary ammonium salts comprising alkyl chains containing 16 or more carbon atoms, and alkylated polyethers of the formula CH₃(CH₂)_m(CH₂CH₂O)_nOH where m is at least 8 and n is at least 4.

29. The method of claim 27, wherein said solvent is selected from the group consisting of alkanes, aromatic hydrocarbons, ethers, cyclic ethers, tetrahydrofuran, and alcohols containing at least 8 carbon atoms.

30. A method for making a white-light-emitting material comprising:

combining approximately 2 wt % Li₄[S₄Cd₁₀(SC₆H₅)₁₆] with approximately 98 wt % (aminopropyl)methylsiloxane-dimethylsiloxane copolymer to form a mixture;

deaerating the mixture;

heating the mixture to an elevated temperature to form a plurality of CdS nanocrystals; and

combining the mixture with an encapsulant precursor solution to form a nanoparticle-containing precursor solution.

31. The method of claim 30, wherein said elevated temperature is between 100°

C. and 250°

C.

32. The method of claim 30, further comprising curing the nanoparticle-containing precursor solution to form a white-light-emitting material.