Highly luminescent color-selective materials and method of making thereof

• US 6,207,229 B1
• Filed: 08/05/1999
• Issued: 03/27/2001
• Est. Priority Date: 11/13/1997
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Mikulec, Frederic Victor, Bawendi, Moungi, Jensen, Klavs F., Dabbousi, Bashir O., Rodriguez-Viejo, Javier
• Primary Examiner(s): LE, HOA T
• Application Number:
  US09/368,743
• Time in Patent Office: 600 Days
• Field of Search: 427/212, 427/215, 427/226, 427/592, 428/403
• US Class Current: 427/215
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01B 17/20 Methods for preparing sulfides or polysulfides, in general ammonium sulfides or polysulfides C01C; sulfides or polysulfides of metals, other than alkali metals, magnesium, calcium, strontium and barium, see the relevant groups of subclasses C01F or C01G, according to the metal
• CPC Class Codes: C01B 19/007 Tellurides or selenides of metals C01B19/002 takes precedence
• CPC Class Codes: C01P 2002/72 by d-values or two theta-values, e.g. as X-ray diagram
• CPC Class Codes: C01P 2002/84 by UV- or VIS- data
• CPC Class Codes: C01P 2004/04 obtained by TEM, STEM, STM or AFM
• CPC Class Codes: C01P 2004/52 highly monodisperse size distribution
• CPC Class Codes: C01P 2004/86 Thin layer coatings, i.e. the coating thickness being less than 0.1 time the particle radius
• CPC Class Codes: C01P 2006/60 Optical properties, e.g. expressed in CIELAB-values
• CPC Class Codes: C09K 11/883 with zinc or cadmium
• CPC Class Codes: Y10T 428/12028 Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.]
• CPC Class Codes: Y10T 428/12049 Nonmetal component
• CPC Class Codes: Y10T 428/12181 Composite powder [e.g., coated, etc.]
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

A coated nanocrystal capable of light emission includes a substantially monodisperse nanoparticle selected from the group consisting of CdX, where x=S, Se, Te and an overcoating of ZnY, where Y=S, Se, uniformly deposited thereon, said coated nanoparticle characterized in that when irradiated the particles exhibit photoluminescence in a narrow spectral range of no greater than about 60 nm, and most preferably 40 nm, at full width half max (FWHM). The particle size of the nanocrystallite core is in the range of about 20 Å to about 125 Å, with a deviation of less than 10% in the core. The coated nanocrystal exhibits photoluminescence having quantum yields of greater than 30%.

Claims

1. A method of preparing a coated nanocrystal capable of light emission, comprising:

introducing a substantially monodisperse core population, wherein each member of the core population comprises a first semiconductor material, and a precursor capable of thermal conversion into a second semiconductor material into a coordinating solvent, the monodisperse core population, when irradiated, emits light in a spectral range of no greater than about 60 nm full width half max (FWHM),

wherein the coordinating solvent is maintained at a temperature sufficient to convert the precursor into the second semiconductor material yet insufficient to substantially alter the monodispersity of the core population,

wherein the second semiconductor material has a band gap greater than the first semiconductor material, and

whereby an overcoating of the second semiconductor material is formed on a member of the core population.

2. The method of claim 1, further comprising:

monitoring the monodispersity of the nanocrystal.

3. The method of claim 2, wherein the temperature is increased in response to when monitoring indicates overcoating appears to stop.

4. The method of claim 1, wherein the temperature is lowered in response to a spreading of the size distribution as estimated from the absorption spectra.

5. The method of claim 1, wherein the first semiconductor material is selected from the group consisting of CdS, CdSe, CdTe, and mixtures thereof.

6. The method of claim 1, wherein the second semiconductor material is selected from the group consisting of ZnS, ZnSe, CdS, CdSe and mixtures thereof.

7. The method of claim 1, wherein the particle size of the core is in the range of about 20 Å

to about 125 Å

.

8. The method of claim 1, wherein the nanocrystal further comprises an organic layer on the nanocrystal outer surface.

9. The method of claim 8, wherein the organic layer is obtained by exposing the nanocrystal to an organic compound having affinity for the nanocrystal surface, whereby the organic compound displaces the coordinating solvent.

10. The method of claim 1, wherein the spectral range is no greater than about 40 nm FWHM.

11. The method of claim 1, wherein the coated nanocrystal exhibits photoluminescence having a quantum yield of greater than about 30%.

12. A method of preparing a coated nanocrystal capable of light emission, comprising:

introducing a substantially monodisperse core population, wherein each member of the population comprises a first semiconductor material, and a precursor capable of thermal conversion into a second semiconductor material into a coordinating solvent, the monodisperse first semiconductor core population exhibiting less than a 10% rms deviation in core diameter,

wherein the coordinating solvent is maintained at a temperature sufficient to convert the precursor into the second semiconductor material yet insufficient to substantially alter the monodispersity of the first semiconductor material,

wherein the second semiconductor material has a band gap greater than the first semiconductor material, and

whereby an overcoating of the second semiconductor material is formed on a member of the core population.

13. The method of claim 12, further comprising:

monitoring the monodispersity of the nanocrystal.

14. The method of claim 12, wherein the first semiconductor material is selected from the group consisting of CdS, CdSe, CdTe, and mixtures thereof.

15. The method of claim 12, wherein the second semiconductor material is selected from the group consisting of ZnS, ZnSe, CdS, CdSe and mixtures thereof.

16. The method of claim 12, wherein the particle size of the core is in the range of about 20 Å

to about 125 Å

.

17. The method of claim 12, wherein the nanocrystal further comprises an organic layer on the nanocrystal outer surface.

18. The method of claim 17, wherein the organic layer is obtained by exposing the nanocrystal to an organic compound having affinity for the nanocrystal surface, whereby the organic compound displaces the coordinating solvent.

19. The method of claim 12, wherein the monodisperse core population, when irradiated, emits light in a spectral range of no greater than about 60 nm full width half maximum (FWHM).

20. A method of preparing a coated nanocrystal capable of light emission, comprising:

introducing a substantially monodisperse core population, each member of which comprises a first semiconductor material, and a precursor capable of thermal conversion into a second semiconductor material into a coordinating solvent, the monodisperse core population exhibiting less than a 10% rms deviation in core diameter, and

overcoating the second semiconductor material on a member of the core population without substantially altering the monodispersity of the first semiconductor core.