Highly luminescent nanostructures and methods of producing same

1. A composition comprising a population of nanostructures, which population displays a photoluminescence quantum yield of 70% or greater, wherein a photoluminescence spectrum of the population has a full width at half maximum of 50 nm or less, and an emission maximum between 450 nm and 750 nm, and wherein the nanostructures comprise InP/ZnS x Se 1-x /ZnS core/shell quantum dots, wherein 0<x<1.

2. The composition of claim 1 , wherein x is 0.25≦x≦0.75.

3. The composition of claim 1 , wherein the InP cores have an average diameter between about 15 Å and about 20 Å.

4. The composition of claim 1 , wherein the ZnS x Se 1-x shell is about 0.5 monolayer thick and the ZnS shell is about 2.0 monolayers thick.

5. The composition of claim 1 , comprising a C5-C8 carboxylic acid ligand bound to the nanostructures, which ligand is an unbranched alkyl carboxylic acid.

6. A composition comprising a population of nanostructures, which population displays a photoluminescence quantum yield of 75% or greater, wherein the nanostructures are InP/ZnS x Se 1-x /ZnS core/shell quantum dots, where 0<x<1, and are substantially free of Ga; and wherein a photoluminescence spectrum of the population has an emission maximum between 450 nm and 750 nm and a full width at half maximum of 60 nm or less.

7. The composition of claim 6 , wherein 0.25<x<0.75.

8. The composition of claim 6 , wherein the InP cores have an average diameter between about 15 Å and about 20 Å.

9. The composition of claim 8 , wherein the ZnS x Se 1-x shell is about 0.5 monolayer thick and the ZnS shell is about 2.0 monolayers thick.

10. A composition comprising a population of nanostructures, which population displays a photoluminescence quantum yield of 65% or greater, wherein a photoluminescence spectrum of the population has an emission maximum between 600 nm and 650 nm, and wherein the nanostructures comprise InP/ZnS x Se 1-x /ZnS core/shell quantum dots, where 0<x<1.

11. The composition of claim 10 , wherein 0.25≦x≦0.75.

12. The composition of claim 10 , wherein the InP cores have an average diameter between about 25 Å and about 30 Å.

13. The composition of claim 12 , wherein the ZnS x Se 1-x shell is about 0.5 monolayer thick and the ZnS shell is about 2.0 monolayers thick.

14. The composition of claim 10 , comprising a C5-C8 carboxylic acid ligand bound to the nanostructures, which ligand is an unbranched alkyl carboxylic acid.

15. The composition of claim 14 , comprising a dicarboxylic or polycarboxylic acid ligand bound to the nanostructures.

16. A population of InP/ZnS x Se 1-x /ZnS core/shell quantum dots, where 0.25≦x≦0.75, wherein the ZnS x Se 1-x shell is between about 0.3 and about 1.0 monolayer thick and the ZnS shell is between about 1.0 and about 3.0 monolayers thick.

17. The population of claim 16 , wherein the ZnS x Se 1-x shell is about 0.5 monolayer thick and the ZnS shell is about 2.0 monolayers thick.

18. The population of claim 16 , wherein the InP cores have an average diameter between about 15 Å and about 20 Å or between about 25 Å and about 30 Å.

19. A method for production of core/shell nanostructures where the shell comprises at least two layers, the method comprising:

providing InP nanostructure cores;

providing a first set of one or more precursors and reacting the precursors to produce a first layer of the shell, which first layer comprises ZnS x Se 1-x , where 0.25≦x≦0.75; and

then providing a second set of one or more precursors and reacting the precursors to produce a second layer of the shell, which second layer comprises ZnS.

20. The method of claim 19 , wherein the InP cores have an average diameter between about 15 Å and about 20 Å or between about 25 Å and about 30 Å.

21. The method of claim 19 , wherein the first set of precursors comprises diethyl zinc, bis(trimethylsilyl)selenide, and hexamethyldisilthiane, and wherein the second set of precursors comprises diethyl zinc and hexamethyldisilthiane.

22. A method for enriching InP nanostructures, the method comprising:

producing InP nanostructures in solution;

removing the InP nanostructures from the solution in which they were produced;

then suspending the InP nanostructures in at least one solvent and contacting the suspended nanostructures with a first precursor at a temperature of 200-230° C. to enrich the nanostructures, which first precursor comprises In.

23. The method of claim 22 , wherein the InP nanostructures have an average diameter between about 15 Å and about 20 Å or between about 25 Å and about 30 Å.

24. The method of claim 22 , wherein the first precursor is an indium carboxylate or indium laurate.

25. The method of claim 22 , comprising, after contacting the suspended nanostructures with the first precursor, adding one or more second precursors and reacting the second precursors to form a shell.

26. The method of claim 25 , comprising adding a nanostructure ligand and reacting the second precursors in the presence of the ligand to form the shell.

27. The method of claim 26 , wherein the ligand is a C5-C8 carboxylic acid ligand.

28. The method of claim 26 , comprising, after forming the shell, exchanging the ligand with a dicarboxylic or polycarboxylic acid ligand.

29. The method of claim 25 , wherein adding one or more second precursors and reacting the second precursors to form the shell comprises:

providing a first set of one or more second precursors and reacting them to produce a first layer of the shell, which first layer comprises ZnS x Se 1-x where 0.25≦x≦0.75, wherein the first set of second precursors comprises diethyl zinc, bis(trimethylsilyl)selenide, and hexamethyldisilthiane; and

then providing a second set of one or more second precursors and reacting them to produce a second layer of the shell, which second layer comprises ZnS, and wherein the second set of second precursors comprises diethyl zinc and hexamethyldisilthiane.