Monodisperse core/shell and other complex structured nanocrystals and methods of preparing the same

• US 20050129947A1
• Filed: 01/22/2004
• Published: 06/16/2005
• Est. Priority Date: 01/22/2003
• Status: Active Grant

• Current Assignee: The Board of Trustees of the University of Arkansas (University of Arkansas System)
• Original Assignee: The Board of Trustees of the University of Arkansas (University of Arkansas System)
• Inventors: Li, Jainqing, Peng, Xiaogang, Battaglia, David, Wang, Y. Andrew, Wang, Yunjun
• Granted Patent: US 7,767,260 B2
• Time in Patent Office: Days
• US Class Current: 428/403
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C09K 11/02 Use of particular materials as binders, particle coatings or suspension media therefor
• CPC Class Codes: C09K 11/025 non-luminescent particle coatings or suspension media
• CPC Class Codes: C09K 11/565 with zinc cadmium
• CPC Class Codes: C09K 11/703 with zinc or cadmium
• CPC Class Codes: C09K 11/7414 with zinc or cadmium
• CPC Class Codes: C09K 11/7492 Arsenides; Nitrides; Phosphides
• CPC Class Codes: C09K 11/883 with zinc or cadmium
• CPC Class Codes: C30B 29/605 Products containing multiple oriented crystallites, e.g. columnar crystallites
• CPC Class Codes: C30B 7/00 Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions from molten solvents C30B9/00; by normal or gradient freezing C30B11/00; under a protective fluid C30B27/00
• CPC Class Codes: G01N 33/588 with semiconductor nanocrystal label, e.g. quantum dots
• CPC Class Codes: H01L 31/0352 characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
• CPC Class Codes: H01L 31/036 characterised by their crystalline structure or particular orientation of the crystalline planes
• CPC Class Codes: H01L 33/18 within the light emitting region
• CPC Class Codes: H01L 33/28 containing only elements of Group II and Group VI of the Periodic Table
• CPC Class Codes: H01S 3/169 Nanoparticles, e.g. doped nanoparticles acting as a gain material
• CPC Class Codes: H01S 5/30 Structure or shape of the active region; Materials used for the active region
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

The present invention provides new compositions containing naearly monodisperse colloidal core/shell semiconductor nanocrystals with high photoluminescence quantum yields (PL QY), as well as other complex structured semiconductor nanocrystals. This invention also provides new synthetic methods for preparing these nanocrystals, and new devices comprising these compositions. In addition to core/shell semiconductor nanocrystals, this patent application also provides complex semiconductor nanostructures, quantum shells, quantum wells, doped nanocrystals, and other multiple-shelled semiconductor nanocrystals.

Claims

1. A composition comprising core/shell nanocrystals, wherein:

the nanocrystals comprise a core material and a shell material overcoating the core material, each of which is independently selected from a II/VI compound or a III/V compound,

the band gap of the core material is less than the band gap of the shell material; and

the thickness of the shell material is from 1 to about 15 monolayers.

2. The composition of claim 1, wherein the thickness of the shell material is from 3 to about 15 monolayers.

3. The composition of claim 1, wherein the thickness of the shell material is from 5 to about 15 monolayers.

4. The composition of claim 1, wherein the core/shell nanocrystals exhibit a type-I band offset or a type-II band offset.

5. The composition of claim 1, wherein the core material is selected from CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, HgSe, HgS, HgTe, ZnO, CdO, GaAs, InAs, GaP, or InP;

the shell material is selected from CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, HgSe, HgS, HgTe, ZnO, CdO, GaAs, InAs, GaP, or InP; and

the shell material is different from the core material.

6. The composition of claim 1, wherein the core/shell nanocrystals comprise CdSe/CdS, CdSe/ZnSe, CdSe/ZnS, CdS/ZnS, CdTe/CdSe, CdTe/CdS, CdTe/ZnTe, CdTe/ZnSe, CdTe/ZnS, ZnSe/ZnS, ZnTe/CdS, ZnTe/ZnSe, InAs/InP, InAs/CdSe, InAs/CdS, InAs/ZnS, InP/CdS, InP/ZnS, InP/ZnSe, InAs/InP/CdS, or a mixture thereof.

7. The composition of claim 1, wherein the as-prepared core/shell nanocrystals exhibit a photoluminescence quantum yield (PL QY) up to about 40%.

8. The composition of claim 1, wherein the core/shell nanocrystals luminesce at a wavelength from about 400 to about 1000 nm.

9. The composition of claim 1, wherein the core/shell nanocrystals exhibit a photoluminescence emission line characterized by a FWHM of about 50 nm or less.

10. The composition of claim 1, wherein the core/shell nanocrystals exhibit a photoluminescence emission line characterized by a FWHM of about 40 nm or less.

11. The composition of claim 1, wherein the core/shell nanocrystals exhibit a photoluminescence emission line characterized by a FWHM of about 28 nm or less when the core material comprises CdSe.

12. The composition of claim 1, wherein the core/shell nanocrystals are characterized by a size distribution having a standard deviation no greater than about 15% of a mean diameter of the population of core/shell nanocrystals.

13. A light-emitting diode comprising the composition of claim 1.

14. A biological labeling agent comprising the composition of claim 1.

15. A photoelectric device comprising the composition of claim 1.

16. A solar cell comprising the composition of claim 1.

17. A laser comprising the composition of claim 1.

18. A composition comprising nanocrystalline, core/shell quantum shells, wherein:

the quantum shells comprise a core material and a shell material overcoating the core material;

the core material comprises a stable, nanometer-sized inorganic solid;

the shell material overcoating the core material is selected from a II/VI compound or a III/V compound;

the band gap of the core material is greater than the band gap of the shell material;

the thickness of the shell material is from 1 to about 15 monolayers; and

the as-prepared quantum shells having the shell thickness greater than 1 monolayer exhibit a photoluminescence that is substantially limited to a bandgap emission, with a photoluminescence quantum yield (PL QY) up to about 20%.

19. The composition of claim 18, wherein the core material comprises a II/VI compound or a III/V compound.

20. The composition of claim 18, wherein photogenerated excitons are radially confined in the shell of the quantum shells.

21. The composition of claim 18, wherein the quantum shells exhibit a type-I band offset.

22. The composition of claim 18, wherein the core of the quantum shells comprise an insulator.

23. The composition of claim 18, wherein quantum shells comprise CdS/CdSe, CdS/InP, CdS/CdTe, ZnS/CdS, ZnS/CdSe, ZnS/ZnSe, ZnS/CdTe, ZnSe/CdSe, ZnSe/InP, CdS/InAs, CdSe/InAs, ZnSe/InAs, ZnS/InAs, InP/InAs, or a mixture thereof.

24. The composition of claim 18, wherein the quantum shells luminesce at a wavelength from about 400 to about 1000 nm.

25. The composition of claim 18, wherein the quantum shells exhibit a photoluminescence emission line characterized by a FWHM of about 50 nm or less.

26. The composition of claim 18, wherein the quantum shells exhibit a photoluminescence emission line characterized by a FWHM of about 40 nm or less.

27. The composition of claim 18, wherein the quantum shells exhibit a photoluminescence emission line characterized by a FWHM of about 35 nm or less.

28. The composition of claim 18, wherein the quantum shells are characterized by a size distribution having a standard deviation no greater than about 15% of a mean diameter of the population of core/shell nanocrystals.

29. A light-emitting diode comprising the composition of claim 18.

30. A biological labeling agent comprising the composition of claim 18.

31. A photoelectric device comprising the composition of claim 18.

32. A laser comprising the composition of claim 18.

33. A composition comprising nanocrystalline, core/shell/shell quantum wells, wherein:

the quantum wells comprise a core material, a first shell material overcoating the core material, and a second shell material overcoating the first shell material;

the core material comprises a stable, nanometer-sized inorganic solid;

the first shell material and the second shell material are independently selected from a II/VI compound or a III/V compound;

the band gap of the first shell material is less than the band gap of the core material and less than the band gap of the second shell material; and

the as-prepared quantum wells exhibit a photoluminescence that is substantially limited to a bandgap emission, with a photoluminescence quantum yield (PL QY) up to about 50%.

34. The composition of claim 33, wherein the core material comprises a II/VI compound or a II/V compound.

35. The composition of claim 33, wherein the core material comprises an insulator.

36. The composition of claim 33, wherein the quantum wells comprise CdS/CdSe/CdS, CdS/CdSe/ZnSe, CdS/CdSe/ZnS, ZnSe/CdSe/CdS, ZnSe/CdSe/ZnSe, ZnSe/CdSe/ZnS, ZnS/CdSe/ZnS, ZnS/CdSe/CdS, ZnS/CdSe/ZnSe, ZnS/CdS/ZnS, ZnS/ZnSe/ZnS, CdS/InP/CdS, CdS/InP/ZnSe, CdS/InP/ZnS, ZnSe/InP/ZnSe, ZnSe/InP/CdS, ZnSe/InP/ZnS, ZnS/InP/ZnS, ZnS/InP/CdS, ZnS/InP/ZnSe, CdS/InAs/CdS, CdS/InAs/ZnSe, CdS/InAs/ZnS, ZnSe/InAs/ZnSe, ZnSe/InAs/CdS, ZnSe/InAs/ZnS, ZnS/InAs/ZnS, ZnS/InAs/CdS, ZnS/InAs/ZnSe, CdSe/InAs/CdSe, CdSe/InAs/CdS, CdSe/InAs/ZnS, CdSe/InAs/ZnSe, InAs/InP/CdS, or a mixture thereof.

37. The composition of claim 33, wherein the core material and the second shell material are the same.

38. A light-emitting diode comprising the composition of claim 33.

39. A biological labeling agent comprising the composition of claim 33.

40. A photoelectric device comprising the composition of claim 33.

41. A laser comprising the composition of claim 33.

42. A composition comprising nanocrystalline, core/multiple shell quantum wells, wherein:

the quantum wells comprise a core material, a first shell material overcoating the core material, a second shell material overcoating the first shell material, and optionally comprising additional shell materials sequentially overcoating underlying shells;

the core material comprises a stable, nanometer-sized inorganic solid;

the first shell material and the second shell material are independently selected from a II/VI compound or a III/V compound;

any additional shells are independently selected from a II/VI compound or a III/V compound; and

the band gap of any shell material is less than the band gap of the both adjacent core or shell materials, or greater than the band gap of the both adjacent core or shell materials.

43. The composition of claim 42, wherein the core material comprises a II/VI compound or a III/V compound.

44. The composition of claim 42, wherein the core material of the quantum wells comprises an insulator.

45. A composition comprising radially-doped, core/multiple shell nanocrystals wherein:

the radially-doped nanocrystals comprise a core material, a first shell material overcoating the core material, a second shell material overcoating the first shell material, and a third shell material overcoating the second shell material;

the core material comprises a compound of the formula M¹_aE¹_b, wherein M¹ is selected from a group II or group III metal;

E¹ is selected from a non-metal; and

a and b are dictated by the stoichiometry of the compound;

the first shell material comprises a compound of the formula M¹_a-cM²_cE¹_b, wherein M² is selected from at least one transition metal;

0≦

c<

a; and

M² is different than M¹;

the second shell material comprises a compound of the formula M³_d-fM⁴_fE³_e, wherein M³ is selected from a group II or group III metal;

M⁴ is selected from a transition metal, a rare earth metal, or a mixture thereof;

d and e are dictated by the stoichiometry of the compound M³_dE³_e; and

0≦

f<

d;

the third shell material comprises a compound of the formula M⁵_g-iM⁶_iE⁵_h, wherein M⁵ is selected from a group II or group III metal;

M⁶ is selected from a transition metal, a rare earth metal, or a mixture thereof;

g and h are dictated by the stoichiometry of the compound M⁵_gE⁵_h; and

0≦

i<

g;

wherein the bandgap of the third shell material is greater than the bandgap of the core material, greater than the bandgap of the first shell material, and greater than the bandgap of the second shell materials; and

wherein the thicknesses of the first shell material, the second shell material, and the third shell material are independently varied between 0 and 15 monolayers.

46. The composition of claim 45, wherein:

a) i) M¹ is selected from Zn, Cd, or Hg, and E¹ is selected from O, S. Se, or Te;

or

ii) M¹ is selected from Ga and In, and E¹ is selected from N, P and As; and

b) M² is selected from Mn, Fe, Co, Ni, Pd, Pt, Cu, Al, Ag, or Au, or a rare earth metal.

47. The composition of claim 45, wherein M¹_aE¹_b is selected from CdSe, CdS, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, InAs, InP, GaAs, GaP, ZnO, CdO, HgO, In₂O₃, TiO₂, or a rare earth oxide.

48. The composition of claim 45, wherein the radially-doped, core/multiple shell nanocrystals comprise ZnSe/Zn_a-cM²_cSe/ZnSe, ZnSe/Zn_a-cM²_cSe/ZnS, ZnO/Zn_a-cM²_cO/ZnO, ZnO/Zn_a-cM²_cO/ZnS, TiO₂/Ti_a-cM²_cO₂/TiO₂, and wherein M² is selected from Mn, Fe, Co, Ni, Pd, Pt, Al, Cu, Ag, or Au, or a rare earth metal.

49. A composition comprising core/shell/shell dual-emitting nanocrystals, wherein:

the nanocrystals comprise a core material, a first shell material overcoating the core material, and a second shell material overcoating the first shell material, each of which is independently selected from a II/VI compound or a III/V compound;

the band gap of the first shell material is greater than the band gap of the core material and greater than the band gap of the second shell material; and

the as-prepared dual-emitting nanocrystals exhibit a photoluminescence comprising two bandgap emission peaks.

50. The composition of claim 49, wherein the dual-emitting nanocrystals further comprise at least one additional shell material sequentially overcoating underlying shells, wherein:

the additional shell materials are independently selected from a II/VI compound or a III/V compound; and

the band gap of the additional shell materials are greater than the band gap of the second shell material.

51. A composition comprising core/shell/shell/shell dual-emitting nanocrystals, wherein:

the nanocrystals comprise a core material, a first shell material overcoating the core material, a second shell material overcoating the first shell material, and a third shell material overcoating the second shell material, each of which is independently selected from a II/VI compound or a III/V compound;

the band gap of the first shell material and the band gap of the third shell material are less than the band gap of the core material and are less than the band gap of the second shell material; and

the as-prepared dual-emitting nanocrystals exhibit a photoluminescence comprising two bandgap emissions.

52. The composition of claim 51, wherein the dual-emitting nanocrystals further comprise at least one additional shell material sequentially overcoating underlying shells, wherein:

the additional shell materials are independently selected from a II/VI compound or a III/V compound; and

the band gap of the additional shell materials are greater than the band gap of the second shell material.

53. A composition comprising core/multiple shell nanocrystals, wherein:

the nanocrystals comprise a core material, a first shell material overcoating the core material, a second shell material overcoating the first shell material, a third shell material overcoating the second shell material, a fourth shell material overcoating the third shell material, and optionally additional shells overcoating underlying shells, each of which is independently selected from a II/VI compound or a III/V compound;

the band gap of any shell material is less than the band gap of the both adjacent core or shell materials, or greater than the band gap of the both adjacent core or shell materials.

54. A population of nanocrystals comprising a plurality of nanocrystals, wherein:

each nanocrystal comprises a core material and the shell material overcoating the core material, each of which is independently selected from a II/VI compound or a III/V compound,

wherein the band gap of the core material is less than the band gap of the shell material;

wherein the population of nanocrystals is substantially monodisperse; and

wherein the plurality of nanocrystals exhibit a photoluminescence quantum yield (PL QY) of greater than or equal to about 20%.

55. The population of nanocrystals of claim 54, wherein:

the core material is selected from CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, HgSe, HgS, HgTe, ZnO, CdO, GaAs, InAs, GaP, or InP;

the shell material is selected from CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, HgSe, HgS, HgTe, ZnO, CdO, GaAs, InAs, GaP, or InP; and

the shell material is different from the core material.

56. The population of nanocrystals of claim 54, wherein the plurality of nanocrystals exhibit a photoluminescence quantum yield (PL QY) of greater than or equal to about 30%.

57. The population of nanocrystals of claim 54, wherein the plurality of cores has a size distribution having a standard deviation no greater than about 20% of a mean diameter of the population.

58. A method for preparing core/shell nanocrystals having the formula M¹X¹/M²X², comprising:

a) providing a solution of core nanocrystals of the formula M¹X¹;

b) forming a first monolayer of a shell material M²X² by contacting the core nanocrystals, in an alternating manner, with a cation (M²) precursor solution in an amount effective to form a monolayer of the cation, and an anion (X²) precursor solution in an amount effective to form a monolayer of the anion; and

c) optionally forming subsequent monolayers of shell material M²X² by contacting the core/shell nanocrystals, in an alternating manner, with a cation (M²) precursor solution in an amount effective to form a monolayer of the cation, and an anion (X²) precursor solution in an amount effective to form a monolayer of the anion;

wherein M¹X¹ comprises a stable, nanometer-sized inorganic solid;

wherein M²X² is selected from a II/VI compound or a III/V compound; and

wherein M¹X¹ and M²X² are different.

59. A method for preparing core/shell nanocrystals having the formula M¹X¹/M²X², comprising:

a) providing a solution of core nanocrystals of the formula M¹X¹;

b) forming at least one monolayer of a shell material M²X² by contacting the core nanocrystals, in an alternating manner, with a cation (M²) precursor solution in an amount effective to form a monolayer of the cation, and an anion (X²) precursor solution in an amount effective to form a monolayer of the anion;

wherein M¹X¹ comprises a stable, nanometer-sized inorganic solid;

wherein M²X² is selected from a II/VI compound or a III/V compound; and

wherein M¹X¹ and M²X² are different.

60. The method of claim 59, M²X² comprises a II/VI compound or a III/V compound.

61. The method of claim 59, wherein the cation (M²) precursor solution is contacted with the core nanocrystals before the anion (X²) precursor 25 solution is contacted with the core nanocrystals.

62. The method of claim 59, wherein the anion (X²) precursor solution is contacted with the core nanocrystals before the cation (M²) precursor solution is contacted with the core nanocrystals.

63. The method of claim 59, further comprising purifying the core/shell nanocrystals.

64. The method of claim 59, wherein M¹X¹ and M²X² are independently selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, ZnO, CdO, InP, InAs, GaAs, or GaP.

65. The method of claim 59, wherein the cation precursor solution comprises a metal oxide, a metal halide, a metal nitride, a metal ammonia complex, a metal amine, a metal amide, a metal imide, a metal carboxylate, a metal acetylacetonate, a metal dithiolate, a metal carbonyl, a metal cyanide, a metal isocyanide, a metal nitrile, a metal peroxide, a metal hydroxide, a metal hydride, a metal ether complex, a metal diether complex, a metal triether complex, a metal carbonate, a metal phosphate, a metal nitrate, a metal nitrite, a metal sulfate, a metal alkoxide, a metal siloxide, a metal thiolate, a metal dithiolate, a metal disulfide, a metal carbamate, a metal dialkylcarbamate, a metal pyridine complex, a metal bipyridine complex, a metal phenanthroline complex, a metal terpyridine complex, a metal diamine complex, a metal triamine complex, a metal diimine, a metal pyridine diimine, a metal pyrazolylborate, a metal bis(pyrazolyl)borate, a metal tris(pyrazolyl)borate, a metal nitrosyl, a metal thiocarbamate, a metal diazabutadiene, a metal dithiocarbamate, a metal dialkylacetamide, a metal dialkylformamide, a metal formamidinate, a metal phosphine complex, a metal arsine complex, a metal diphosphine complex, a metal diarsine complex, a metal oxalate, a metal imidazole, a metal pyrazolate, a metal-Schiff base complex, a metal porphyrin, a metal phthalocyanine, a metal subphthalocyanine, a metal picolinate, a metal piperidine complex, a metal pyrazolyl, a metal salicylaldehyde, a metal ethylenediamine, a metal triflate compound, or any combination thereof.

66. The method of claim 59, wherein the cation precursor comprises a metal oxide, a metal carbonate, a metal bicarbonate, a metal sulfate, a metal sulfite, a metal phosphate, metal phosphite, a metal halide, a metal carboxylate, a metal hydroxide, a metal alkoxide, a metal thiolate, a metal amide, a metal imide, a metal alkyl, a metal aryl, a metal coordination complex, a metal solvate, a metal salt, or a combination thereof.

67. The method of claim 59, wherein the cation precursor solution optionally comprises a ligand selected from a fatty acid, an fatty amine, a phosphine, a phosphine oxide, a phosphonic acid, a phosphinic acid, a sulphonic acid, or any combination thereof, any one of which having up to about 30 carbon atoms.

68. The method of claim 59, wherein the anion precursor comprises an element, a covalent compound, an ionic compound, or a combination thereof.

69. A method for preparing core/shell/shell nanocrystals having the formula M¹X¹/M²X²/M³X³ comprising:

a) providing a solution of core nanocrystals of the formula M¹X¹;

b) forming at least one monolayer of a first shell material M²X² by contacting the core nanocrystals, in an alternating manner, with a first cation (M²) precursor solution in an amount effective to form a monolayer of the first cation, and a first anion (X²) precursor solution in an amount effective to form a monolayer of the first anion; and

c) forming at least one monolayer of a second shell material M³X³ by contacting the core nanocrystals, in an alternating manner, with a second cation (M³) precursor solution in an amount effective to form a monolayer of the second cation, and an second anion (X³) precursor solution in an amount effective to form a monolayer of the first anion;

wherein M¹X¹ comprises a stable, nanometer-sized inorganic solid;

wherein M²X² and M³X³ are independently selected from a II/VI compound or a III/V compound; and

wherein M¹X¹, M²X², and M³X³ are different.

70. The method of claim 69, M²X² comprises a II/VI compound or a III/V compound.

71. The method of claim 69, wherein the cation (M²) precursor solution is contacted with the core nanocrystals before the anion (X²) precursor solution is contacted with the core nanocrystals.

72. The method of claim 69, wherein the anion (X²) precursor solution is contacted with the core nanocrystals before the cation (M²) precursor solution is contacted with the core nanocrystals.

73. The method of claim 69, further comprising purifying the core/shell nanocrystals.

74. The method of claim 69, wherein M¹X¹, M²X², and M³X³ are independently selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, ZnO, CdO, InP, InAs, GaAs, or GaP.

75. The method of claim 69, wherein the cation precursor solution comprises a metal oxide, a metal halide, a metal nitride, a metal ammonia complex, a metal amine, a metal amide, a metal imide, a metal carboxylate, a metal acetylacetonate, a metal dithiolate, a metal carbonyl, a metal cyanide, a metal isocyanide, a metal nitrile, a metal peroxide, a metal hydroxide, a metal hydride, a metal ether complex, a metal diether complex, a metal triether complex, a metal carbonate, a metal phosphate, a metal nitrate, a metal nitrite, a metal sulfate, a metal alkoxide, a metal siloxide, a metal thiolate, a metal dithiolate, a metal disulfide, a metal carbamate, a metal dialkylcarbamate, a metal pyridine complex, a metal bipyridine complex, a metal phenanthroline complex, a metal terpyridine complex, a metal diamine complex, a metal triamine complex, a metal diimine, a metal pyridine diimine, a metal pyrazolylborate, a metal bis(pyrazolyl)borate, a metal tris(pyrazolyl)borate, a metal nitrosyl, a metal thiocarbamate, a metal diazabutadiene, a metal dithiocarbamate, a metal dialkylacetamide, a metal dialkylformamide, a metal formamidinate, a metal phosphine complex, a metal arsine complex, a metal diphosphine complex, a metal diarsine complex, a metal oxalate, a metal imidazole, a metal pyrazolate, a metal-Schiff base complex, a metal porphyrin, a metal phthalocyanine, a metal subphthalocyanine, a metal picolinate, a metal piperidine complex, a metal pyrazolyl, a metal salicylaldehyde, a metal ethylenediamine, a metal triflate compound, or any combination thereof.

76. The method of claim 69, wherein the cation precursor comprises a metal oxide, a metal carbonate, a metal bicarbonate, a metal sulfate, a metal sulfite, a metal phosphate, metal phosphite, a metal halide, a metal carboxylate, a metal hydroxide, a metal alkoxide, a metal thiolate, a metal amide, a metal imide, a metal alkyl, a metal aryl, a metal coordination complex, a metal solvate, a metal salt, or a combination thereof.

77. The method of claim 69, wherein the cation precursor solution optionally comprises a ligand selected from a fatty acid, an fatty amine, a phosphine, a phosphine oxide, a phosphonic acid, a phophinic acid, a sulphonic acid, or any combination thereof, any one of which having up to about 30 carbon atoms.

78. The method of claim 69, wherein the anion precursor comprises an element, a covalent compound, an ionic compound, or a combination thereof.

79. A method for preparing radially-doped core/shell/shell nanocrystals having the formula M¹_xE_y/M¹_x-zM²_zE_y/M¹_x-qM³_qE_y, comprising:

a) providing a solution of core nanocrystals of the formula M¹_xE_y, wherein M¹ is selected from a metal, E is selected from a non-metal, and x and y are dictated by the stoichiometry of the compound;

b) forming at least one monolayer of a doped first shell material of the formula M¹_x-zM²_zE_y by contacting the core nanocrystals, in an alternating manner, with a cation precursor solution in an amount effective to form a monolayer of the first cation doped with the second cation, and a first anion (X²) precursor solution in an amount effective to form a monolayer of the first anion;

wherein the cation precursor solution comprises a first cation (M¹) precursor, a second cation (M²) precursor, or a combination thereof, and

wherein M² is selected from a transition metal or a mixture thereof, 0≦

z<

x, and M² is different than M¹;

c) forming at least one monolayer of a second shell material of the formula M¹_x-qM³_qE_y by contacting the core/shell nanocrystals, in an alternating manner, with a first cation precursor solution in an amount effective to form a monolayer of the first cation, and an second anion (X³) precursor solution in an amount effective to form a monolayer of the first anion;

wherein the first cation precursor solution optionally comprises a third cation (M³) precursor selected from a transition metal, a rare earth metal, or a mixture thereof, and

wherein 0≦

q<

x, and x is not equal to q when M² is the same as M³; and

d) optionally repeating steps b and c to form additional shells overcoating the second shell.

80. The method of claim 79, wherein M¹E is selected from a II/VI compound or a III/V compound.

81. The method of claim 79, wherein q is 0.

82. A composition comprising core/shell nanocrystals having the formula M¹X¹/M²X², prepared by the method of:

a) providing a solution of core nanocrystals of the formula M¹x¹;

b) forming a first monolayer of a shell material M²X² by contacting the core nanocrystals, in an alternating manner, with a cation (M²) precursor solution in an amount effective to form a monolayer of the cation, and an anion (X²) precursor solution in an amount effective to form a monolayer of the anion; and

c) optionally forming subsequent monolayers of shell material M²X² by contacting the core/shell nanocrystals, in an alternating manner, with a cation (M²) precursor solution in an amount effective to form a monolayer of the cation, and an anion (X²) precursor solution in an amount effective to form a monolayer of the anion;

wherein the cation precursor solution optionally contains at least one ligand, and wherein the anion precursor solution optionally contains at least one ligand;

wherein M¹X¹ comprises a stable, nanometer-sized inorganic solid;

wherein M²X² is selected from a II/VI compound or a III/V compound; and

wherein M¹X¹ and M²X² are different.

83. A composition comprising radially-doped, core/multiple shell nanocrystals, comprising:

1) a core material having the formula M¹_a-cM²_cE¹_b, wherein;

a) M¹ is selected from a metal, E¹ is selected from a non-metal, and a and b are dictated by the stoichiometry of the compound M¹_aE¹_b;

b) M² is selected from a transition metal, a rare earth metal, or a mixture thereof; and

M² is different than M¹; and

c) 0≦

c<

a;

2) an optional first shell material overcoating the core material, having the formula M³_d-fM⁴_fE³_e, wherein;

a) M³ is selected from a metal, E³ is selected from a non-metal, and d and e are dictated by the stoichiometry of the compound M³_dE³_e;

b) M⁴ is selected from a transition metal, a rare earth metal, or a mixture thereof; and

M⁴ is different than M³; and

c) 0≦

f<

d;

3) an optional second shell material overcoating the optional first shell material, having the formula M⁵_g-iM⁶_iE⁵_h, wherein;

a) M⁵ is selected from a metal, E⁵ is selected from a non-metal, and g and h are dictated by the stoichiometry of the compound M⁵_gE⁵_h;

b) M⁶ is selected from a transition metal, a rare earth metal, or a mixture thereof; and

M⁶ is different than M⁵; and

c) 0≦

i<

g;

4) an optional third shell material overcoating the optional second shell material, having the formula M⁷_j-lM⁸_lE⁷_k, wherein;

a) M⁷ is selected from a metal, E⁷ is selected from a non-metal, and j and k are dictated by the stoichiometry of the compound M⁷_jE⁷_k;

b) M⁸ is selected from a transition metal, a rare earth metal, or a mixture thereof; and

M⁸ is different than M⁷; and

c) 0≦

l<

j; and

5) an optional fourth shell material overcoating the optional third shell material, having the formula M⁹_m-oM¹⁰_oE⁹_n, wherein;

a) M⁹ is selected from a metal, E⁹ is selected from a non-metal, and m and n are dictated by the stoichiometry of the compound M⁹_mE⁹_n;

b) M¹⁰ is selected from a transition metal, a rare earth metal, or a mixture thereof; and

M¹⁰ is different than M⁹; and

c) 0≦

o<

m.

84. The composition of claim 83, wherein M¹_aE¹_b, M³_dE³_e, M⁵_gE⁵_h, M⁷_jE⁷_k, and M⁹_mE⁹_n are independently selected from a II/VI compound or a III/V compound.

85. The composition of claim 83, wherein the thickness of the first shell material, the second shell material, the third shell, and the fourth shell material are independently varied between 1 and about 15 monolayers.

86. The composition of claim 83, wherein the band gap of any shell material is less than the band gap of the both adjacent core or shell materials, or greater than the band gap of the both adjacent core or shell materials.

87. The composition of claim 83, wherein:

a) i) M¹, M³, M⁵, M⁷, and M⁹ are independently selected from Zn, Cd, or Hg, and E¹, E³, E⁵, E⁷, and E⁹ are independently selected from O, S. Se, or Te;

or

ii) M¹, M³, M⁵, M⁷, and M⁹ are independently selected from Ga and In, and E¹, E³, E⁵, E⁷, and E⁹ are independently selected from N, P and As; and

b) M², M⁴, M⁶, M⁸, and M¹⁰ are independently selected from Mn, Fe, Co, Ni, Pd, Pt, Cu, Al, Ag, or Au, or a rare earth metal.

88. The composition of claim 83, wherein M¹_aE¹_b, M³_dE³_e, M⁵_gE⁵_h, M⁷_jE⁷_k, and M⁹_mE⁹_n are independently selected from CdSe, CdS, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, InAs, InP, GaAs, GaP, ZnO, CdO, HgO, In₂O₃, TiO₂, or a rare earth oxide.

89. The composition of claim 83, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b.

90. The composition of claim 83, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e.

91. The composition of claim 83, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h.

92. The composition of claim 83, wherein:

a) the nanocrystals comprise a core material, a first shell material, and a second material; and

have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h; and

b) the nanocrystals comprise ZnSe/Zn_d-fM⁴_fSe/ZnSe, ZnSe/Zn_d-fM⁴_fSe/ZnS, ZnO/Zn_d-fM⁴_fO/ZnO, ZnO/Zn_d-fM⁴_fO/ZnS, TiO₂/Ti_d-fM⁴_fO₂/TiO₂, and wherein M⁴ is selected from Mn, Fe, Co, Ni, Pd, Pt, Cu, Al, Ag, or Au, or a rare earth metal.

93. The composition of claim 83, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h/M⁷_j-lM⁸_lE⁷_k.

94. The composition of claim 83, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h/M⁷_j-lM⁸_lE⁷_k.

95. The composition of claim 83, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h/M⁷_j-lM⁸_lE⁷_k/M⁹_m-oM¹⁰_oE⁹_n.

96. A method for preparing radially-doped core/multiple shell nanocrystals comprising a doped core material having the formula M¹_a-cM²_cE¹_b, an optional doped first shell material having the formula M³_d-fM⁴_fE³_e and overcoating the core material, an optional doped second shell material having the formula M⁵_g-iM⁶_iE⁵_h and overcoating the first core material, an optional doped third shell material having the formula M⁷_j-lM⁸_lE⁷_k and overcoating the second core material, and an optional doped fourth shell material having the formula M⁹_m-oM¹⁰_oE⁹_n and overcoating the third core material, comprising:

a) providing a solution of core nanocrystals of the formula M¹_aE¹_b, wherein M¹ is selected from a metal, E¹ is selected from a non-metal, and a and b are dictated by the stoichiometry of the compound;

b) optionally forming at least one monolayer of a doped core material of the formula M¹_a-cM²_cE¹_b by contacting the nanocrystals, in an alternating manner, with a first cation precursor solution in an amount effective to form a monolayer of a first cation M¹, optionally doped with a second cation M², and a first anion (E¹) precursor solution in an amount effective to form a monolayer of the first anion;

wherein the first cation precursor solution comprises a first cation (M¹) precursor and an optional second cation (M²) precursor; and

wherein M² is selected from a transition metal, a rare earth metal, or a mixture thereof;

M² is different than M¹; and

0≦

c<

a;

c) optionally forming at least one monolayer of a doped first shell material of the formula M³_d-fM⁴_fE³_e by contacting the nanocrystals, in an alternating manner, with a second cation precursor solution in an amount effective to form a monolayer of a third cation M³, optionally doped with a fourth cation M⁴, and a second anion (E³) precursor solution in an amount effective to form a monolayer of the second anion;

wherein the second cation precursor solution comprises a third cation (M³) precursor and an optional fourth cation (M⁴) precursor; and

wherein M³ is selected from a metal, E³ is selected from a non-metal, and d and e are dictated by the stoichiometry of the compound M³_dE³_e;

wherein M⁴ is independently selected from a transition metal, a rare earth metal, or a mixture thereof;

M⁴ is different than M³; and

0≦

f<

d;

d) optionally repeating step c to form optional doped shells M⁵_g-iM⁶_iE⁵_h, M⁷_j-lM⁸_lE⁷_k, and M⁹_m-oM¹⁰_oE⁹_n, wherein M⁵, M⁷, and M⁹ are independently selected from a metal;

M⁶, M⁸, and M¹⁰ are independently selected from a transition metal, a rare earth metal, or a mixture thereof;

E⁵, E⁷, and E⁹ are independently selected from a non-metal;

g and h are dictated by the stoichiometry of the compound M⁵_gE⁵_h;

j and k are dictated by the stoichiometry of the compound M⁷_jE⁷_k, m and n are dictated by the stoichiometry of the compound M⁹_mE⁹_n;

0≦

i<

g;

0≦

l<

j; and

0≦

o<

m.

97. The method of claim 96, wherein M¹_aE¹_b, M³_dE³_e, M⁵_gE⁵_h, M⁷_jE⁷_k, and M⁹_mE⁹_n are independently selected from a II/VI compound or a III/V compound.

98. The method of claim 96, wherein the thickness of the first shell material, the second shell material, the third shell, and the fourth shell material are independently varied between 1 and about 15 monolayers.

99. The method of claim 96, wherein the band gap of any shell material is less than the band gap of the both adjacent core or shell materials, or greater than the band gap of the both adjacent core or shell materials.

100. The method of claim 96, wherein:

a) i) M¹, M³, M⁵, M⁷, and M⁹ are independently selected from Zn, Cd, or Hg, and E¹, E³, E⁵, E⁷ and E⁹ are independently selected from O, S. Se, or Te;

or

ii) M¹, M³, M⁵, M⁷, and M⁹ are independently selected from Ga and In, and E¹, E³, E⁵, E⁷, and E⁹ are independently selected from N, P and As; and

b) M², M⁴, M⁶, M⁸, and M¹⁰ are independently selected from Mn, Fe, Co, Ni, Pd, Pt, Cu, Al, Ag, or Au, or a rare earth metal.

101. The method of claim 96, wherein M¹_aE¹_b, M³_dE³_e, M⁵_gE⁵_h, M⁷_jE⁷_k, and M⁹_mE⁹_n are independently selected from CdSe, CdS, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, InAs, InP, GaAs, GaP, ZnO, CdO, HgO, In₂O₃, TiO₂, or a rare earth oxide.

102. The method of claim 96, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b.

103. The method of claim 96, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e.

104. The method of claim 96, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h.

105. The method of claim 96, wherein:

a) the nanocrystals comprise a core material, a first shell material, and a second material; and

have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h; and

b) the nanocrystals comprise ZnSe/Zn_d-fM⁴_fSe/ZnSe, ZnSe/Zn_d-fM⁴_fSe/ZnS, ZnO/Zn_d-fM⁴_fO/ZnO, ZnO/Zn_d-fM⁴_fO/ZnS, TiO₂/Ti_d-fM⁴_fO₂/TiO₂, and wherein M⁴ is selected from Mn, Fe, Co, Ni, Pd, Pt, Cu, Al, Ag, or Au, or a rare earth metal.

106. The method of claim 96, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h/M⁷_j-lM⁸_lE⁷_k.

107. The method of claim 96, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h/M⁷_j-lM⁸_lE⁷_k.

108. The method of claim 96, wherein the nanocrystals have the formula M¹_a-cM²_cE¹_b/M³_d-fM⁴_fE³_e/M⁵_g-iM⁶_iE⁵_h/M⁷_j-lM⁸_lE⁷_k/M⁹_m-oM¹⁰_oE⁹_n.