Optically-regulated optical emission using colloidal quantum dot nanocrystals
The present invention relates to the emission of light which occurs in proportion with an electrical signal, an optical signal, or the combination of both. The emission of light may occur due to the passage of current through a light-emitting polymer, or due to energy transfer of excitons from this polymer to light-emitting quantum dots. Optical sensitivity is achieved through the inclusion of another species of quantum dots whose absorption is generally at longer wavelengths relative to the light-emitting material. Light incident upon the device results in an enhanced current flow in the presence of an applied bias, and thus enhanced excitation of the light-emitting moity is achieved in proportion with the optical power absorbed by the light-absorbing moity. Two device architectures are presented, one based on a mutilayer structure in which the functions of light absorption and light emission are separated, and the other in which these functions are integrated within a single active region.
1. A device for detecting light in a pre-selected wavelength range and converting the detected light into light of at least one pre-selected wavelength and emitting the light at said at least one pre-selected wavelength, comprising:
a substrate and a first electrically conducting electrode layer on the substrate;
a first layer of first nanocrystals located on the first electrically conducting electrode layer which absorb light in said pre-selected wavelength range;
at least one second layer of second nanocrystals which emit light at said at least one pre-selected wavelength located on the first layer of first nanocrystals; and
a second electrically conducting electrode layer on the at one least second layer of second nanocrystals,
wherein at least one of said substrate and first electrically conducting electrode layer and said second electrically conducting electrode layer is substantially transparent to the light in the pre-selected wavelength range and light at the at least one pre-selected wavelength, and
wherein when the light in said pre-selected wavelength range is incident on said first layer of first nanocrystals a photocurrent is responsively produced when a voltage is applied between the first and second electrically conducting electrode layers, and
wherein said photocurrent acts to pump the at least one second layer of the second nanocrystals which responsively emit light at the at least one pre-selected wavelength.
2. The device according to claim 1 including
a first layer located between said first electrically conducting electrode layer and said first layer of first nanocrystals, wherein the first layer is selected from a group comprising a conducting layer, a semiconducting layer, and an insulating layer,
a second layer located between said first layer of first nanocrystals and said at least one second layer of second nanocrystals, wherein the second layer is selected from a group comprising a conducting layer, a semiconducting layer, and an insulating layer,
wherein said first and second layers function to regulate the transport of electrons and holes into the first and at least one second layers of nanocrystals.
3. The device according to claim 1 wherein the first nanocrystals are of a material and size, each of which is selected so that said first nanocrystals absorb light in said pre-selected wavelength range, and wherein the second nanocrystals are substantially monodisperse and are of a material and size, each of which is selected so that said second nanocrystals emits at the at least one pre-selected wavelength.
4. The device according to claim 1 wherein an areal concentration N 1 of said first nanocrystals is such that N 1 a 2 >1 where a is a radius of the first nanocrystals, and wherein an a real concentration N 2 of said second nanocrystals is such that N 2 b 2 >>1 where b is a radius of the second nanocrystals.
5. The device according to claim 1 wherein the first and the at least one second nanocrystals are made of the same material, and wherein the first nanocrystals have a first pre-selected mean diameter selected so that the first nanocrystals absorb light in said pre-selected wavelength range, and wherein the second nanocrystals are substantially monodisperse and have a second pre-selected mean diameter so that the second nanocrystals emit light at the at least one pre-selected wavelength.
6. The device according to claim 1 wherein the pre-selected wavelength range is in a spectral region selected from a group comprising an infrared spectral region and a visible spectral region, and wherein the at least one pre-selected wavelength is a visible wavelength but at a higher wavelength than wavelengths in said visible spectral region.
7. The device according to claim 6 wherein the semiconducting layer is selected from the group consisting of poly(2-methoxy-5-(2′-ethyl-hexyloxy-)-p-phenylene vinylene) (MEH-PPV) and associated poly-phenylene-vinylene derivatives, polyfluorine (PFO) and associated polyfluorine derivatives, and poly-thiophenes, poly(3-octyl-thiophene) (P3HT), poly(9,9-dioctyifluorene-co-bitiophene) (F8T2), and wherein the insulating layer is selected from the group consisting of PMMA (poly-methyl-methacrylate) and insulating dielectrics selected from a group comprising inorganic and mixed organ-inorganic dielectrics, SiO 2 , SiO, and SiN x O y , and wherein the conducting layer is selected from the group consisting of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), and doped MEH-PPV and doped PPV (poly-phenylene-vinylene).
8. The device according to claim 2 wherein the first layer located between said first electrically conducting electrode layer and said first layer of first nanocrystals is poly(p-phenylenevinylene) (PPV).
9. The device according to claim 1 wherein the first and the second nanocrystals are selected from the group consisting of inorganic semiconductors.
10. The device according to claim 9 wherein the first and the second nanocrystals are selected from the group consisting of III-V semiconductors and IV-VI semiconductors.
11. The device according to claim 10 wherein the III-V semiconductors are InAs, and wherein the IV-VI semiconductors are selected from the group consisting of PbSe, CdS and CdSe.
12. The device according to claim 1 wherein the first and the second nanocrystals have a core/shell structure comprising a core made of a pre-selected type of material and a shell material surrounding the core made of a different pre-selected type of material.
13. The device according to claim 12 wherein the nanocrystals with the core/shell structure are ZnS(CdSe).
14. The device according to claim 1 wherein the first and the second nanocrystals are PbS nanocrystals.
15. The device according to claim 1 wherein the at least one second layer of second nanocrystals is two or more layers of nanocrystals, each layer including nanocrystals of a pre-selected size for emitting light of wavelengths different from all the other layers of nanocrystals.
16. The device according to claim 1 wherein the first and second nanocrystals have pre-selected ligands attached to a surface of the first and the second nanocrystals.
17. The device according to claim 16 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are selected from the group consisting of oleate, hexylamine, octylamine, dodecylamine, octadecylamine, tri-octyl phosphine oxide, butylamine, and pyridine.
18. The device according to claim 16 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are octadecylamine (C18).
19. The device according to claim 1 including a light source for illuminating the first and at least one second layers of the first and the nanocrystals, the light source emitting light at one or more pre-selected wavelengths for selective absorption by the first and the nanocrystals.
20. The device according to claim 1 wherein at least one of the first and the nanocrystals has a core/shell structure comprising a core made of a pre-selected type of material and a shell material surrounding the core made of a different pre-selected type of material.
21. The device according to claim 20 wherein the nanocrystals with the core/shell structure are ZnS(CdSe).
22. The device according to claim 1 wherein the nanocrystals have a size in a range from about 1 to about 20 nm.
23. The device according to claim 1 wherein the nanocrystals have a size in a range from about 2 to about 10 nm.
24. The device according to claim 1 wherein said second layer of the second nanocrystals include two or more types of nanocrystals, wherein each type are of a material and size, each of which is selected so that each type of nanocrystal emits light of pre-selected wavelengths in the visible or infrared, or combinations thereof.
25. A device for detecting light in a pre-selected wavelength range and converting the detected light into light of at least one pre-selected wavelength and emitting the light at said at least one pre-selected wavelength, comprising:
a substrate and a first electrically conducting electrode layer on the substrate;
a polymer matrix located on the first electrically conducting electrode layer, the polymer matrix containing a mixture of nanocrystals, the mixture including at least,
first nanocrystals which absorb light in a pre-selected wavelength range, and
a light emitting member located in the polymer matrix which emits light at said at least one pre-selected wavelength; and
a second electrically conducting electrode layer located on the polymer matrix,
wherein at least one of said substrate and first electrically conducting electrode layer and said second electrically conducting electrode layer is substantially transparent to the light in the pre-selected wavelength range and light at said at least one pre-selected wavelength,
wherein when light in the pre-selected wavelength range is incident on the polymer matrix and absorbed by the first nanocrystals, a photocurrent is responsively produced when a voltage is applied between the first and second electrically conducting electrode layers, and
wherein said photocurrent acts to pump the light emitting member, which responsively emit light at said at least one pre-selected wavelength.
26. The device according to claim 25 wherein the light emitting member located in the polymer matrix which emits light at said at least one pre-selected wavelength is the polymer matrix itself.
27. The device according to claim 25 wherein the light emitting member located in the polymer matrix which emits light at the at least one pre-selected wavelength includes second nanocrystals encapsulated in said polymer matrix which emit light at said at least one pre-selected wavelength.
28. The device according to claim 25 wherein the pre-selected wavelength range is an infrared or visible spectral region, and wherein the at least one pre-selected wavelength is a visible wavelength but at a higher wavelength than wavelengths in said visible spectral region.
29. The device according to claim 27 wherein an areal concentration N 1 of said first nanocrystals is such that N 1 a 2 >>1 where a is a radius of the first nanocrystals, and wherein an areal concentration N 2 of the second nanocrystals is such that N 2 b 2 >>1 where b is a radius of the second nanocrystals.
30. The device according to claim 27 wherein the first nanocrystals are of a material and mean diameter, each of which is selected so that said first nanocrystals absorb light in said pre-selected wavelength range, and wherein the second nanocrystals are substantially monodisperse and are of a material and mean diameter, each of which is selected so that the nanocrystals emit light at the at least one pro-selected wavelength.
31. The device according to claim 27 wherein the first and the second nanocrystals are made of the same material, and wherein the first nanocrystals have a first pre-selected mean diameter selected so that the first nanocrystals absorb light in said pre-selected wavelength range, and wherein the second nanocrystals are substantially monodisperse and have a pre-selected mean diameter so that the second nanocrystals emit light at the at least one pre-selected wavelength.
32. The device according to claim 25 wherein the polymer matrix serves the function of allowing the electronic transport of at least one of electrons and holes.
33. The device according to claim 25 wherein the polymer matrix comprises semiconducting polymers selected from the group consisting of MEH-PPV and associated poly-phenylene-vinylene derivatives, PFO and associated polyflnorine derivatives, and poly-thiophenes including P3HT and P3OT.
34. The device according to claim 25 herein the first nanocrystals are selected from the group consisting of inorganic semiconductors.
35. The device according to claim 27 wherein the second nanocrystals are selected from the group consisting of inorganic semiconductors.
36. The device according to claim 35 wherein the first and the second nanocrystals are selected from the group consisting of III-V semiconductors and IV-VI semiconductors.
37. The device according to claim 36 wherein the III-V semiconductors are InAs, and wherein the IV-VI semiconductors are selected from the group consisting of PbSe, CdS and CdSe.
38. The device according to claim 27 wherein the first and the second nanocrystals are colloidal PbS nanocrystals.
39. The device according to claim 25 wherein the polymer matrix is poly(p-phenylenevinylene) (PPV).
40. The device according to claim 25 wherein the first nanocrystals have pre-selected ligands attached to a surface of the first nanocrystals.
41. The device according to claim 27 wherein the second nanocrystals have pre-selected ligands attached to a surface of the second nanocrystals.
42. The device according to claim 41 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are selected from the group consisting of oleate, hexylamine, octylamine, dodecylamine, octadecylamine, tri-octyl phosphine oxide and pyridine.
43. The device according to claim 42 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are octadecylamine (C18).
44. The device according to claim 25 including a light source for illuminating the first nanocrystals, the light source emitting light at one or more pre-selected wavelengths for absorption by the first nanocrystals.
45. The device according to claim 25 wherein the nanocrystals have a core/shell structure comprising a core made of a pre-selected type of material and a shell material surrounding the core made of a different pre-selected type of material.
46. The device according to claim 45 wherein the nanocrystals with the core/shell structure are ZnS(CdSe).
47. The device according to claim 25 wherein the nanocrystals have a size in a range from about 1 to about 20 nm.
48. The device according to claim 25 wherein the nanocrystals have a size in a range from about 2 to about 10 nm.
49. The device according to claim 25 including a conducting, semiconducting or insulating layer located between the first electrode layer and the polymer matrix functioning to regulate the transport of electrons and holes into the polymer matrix.
50. A method for detecting light in a pre-selected wavelength range and converting the detected light into light of at least one pre-selected wavelength and emitting the light at said at least one pre-selected wavelength, comprising the steps of:
applying a pre-selected voltage across a polymer matrix located between first and second electrode layers, said polymer matrix containing
first nanocrystals which absorb light in a pre-selected wavelength range, and
a light emitting member that emits light at said at least one pre-selected wavelength; and
wherein at least one of said first and second electrode layers is substantially transparent to the light in the pre-selected wavelength range and the light of at said at least one pre-selected wavelength, and
wherein when the light in the pre-selected wavelength range is incident on the polymer matrix and absorbed by the first nanocrystals, a photocurrent is responsively produced when said pre-selected voltage is applied between the first and second electrode layers, and
wherein said photocurrent acts to pump the light emitting member located in the polymer matrix which responsively emits light at said at least one pre-selected wavelength.
51. The method according to claim 50 wherein said light emitting member located in the polymer matrix which emits light at said at least one pre-selected wavelength is the polymer matrix itself.
52. The method according to claim 50 wherein the light emitting member located in the polymer matrix which emits light at said at least one pre-selected wavelength includes second nanocrystals encapsulated in said polymer matrix which emits light at said at least one pre-selected wavelength.
53. The method according to claim 50 wherein the pre-selected wavelength range is an infrared or visible spectral region, and wherein the light at said at least one pre-selected wavelength is a visible wavelength but at a higher wavelength than wavelengths in said visible spectral region.
54. The method according to claim 50 wherein an areal concentration N 1 of said first nanocrystals respectively is such that N 1 a 2 >>1 where a is a radius of the first nanocrystals.
55. The method according to claim 52 wherein an areal concentration N 2 of the second nanocrystals is such that N 2 b 2 >>1 where b is a radius of the second nanocrystals.
56. The method according to claim 50 wherein the first nanocrystals are made of a material and have a size, both of which are selected so that said first nanocrystals absorb light in said pre-selected wavelength range.
57. The method according to claim 52 wherein the second nanocrystals are substantially monodisperse and are made of a material and have a size, both of which are selected so that the second nanocrystals emit light at said at least one pre-selected wavelength.
58. The method according to claim 52 wherein the second nanocrystals include two or more types of nanocrystals, wherein each type are of a material and monodisperse size, each of which is selected so that each of said types of nanocrystal emits light of pre-selected wavelengths in the visible or infrared, or combinations thereof.
59. The method according to claim 52 wherein the first and the second nanocrystals have pre-selected ligands attached to a surface of the first and the second nanocrystals.
60. The method according to claim 59 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are selected from the group consisting of oleate, hexylamine, octylamine, dodecylarnine, octadecylamine, tri-octyl phosphine oxide, butylamine, and pyridine.
61. The method according to claim 59 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are octadecylamine (C18).
62. A method for detecting light in a pre-selected wavelength range and converting the detected light into light of at least one pre-selected wavelength and emitting the light at said at least one pre-selected wavelength, comprising the steps of:
applying a pre-selected voltage across a structure which includes
first and second electrically conducting electrode layers, and
located between the first and second electrode layers, a first layer of first nanocrystals on said first electrode layer which absorb light in said pre-selected wavelength range, and
at least one second layer of second nanocrystals on the layer of first nanocrystals which emit light at said at least one pre-selected wavelength, and
said second electrically conducting electrode layer being located on the at least one second layer of nanocrystals;
wherein at least one of said first and second electrode layers is substantially transparent to light in the pre-selected wavelength range and light at said at least one pre-selected wavelength; and
wherein when light in said pre-selected wavelength range is incident on said first layer of first nanocrystals a photocurrent is responsively produced when a voltage is applied between said first and second electrode layers, and
wherein said photocurrent acts to pump the at least one second layer of second nanocrystals which responsively emit light at said at least one pre-selected wavelength.
63. The method according to claim 62 wherein the laminate structure includes a second conducting, semiconducting or insulating layer located between the first electrically conducting electrode layer and said first layer of first nanocrystals, said first and second conducting, semiconducting or insulating layer functioning to regulate transport of electrons and holes into said first and at least one second layers of nanocrystals.
64. The method according to claim 62 wherein the pre-selected wavelength range is an infrared or visible spectral region, and wherein the at least one pre-selected wavelength is a visible wavelength but at a higher wavelength than wavelengths in said visible spectral region.
65. The method according to claim 62 wherein an areal concentration N 1 of said first nanocrystals respectively is such that N 1 a 2 >>1 where a is a radius of the first nanocrystals, and wherein an areal concentration N 2 of said second nanocrystals is such that N 2 b 2 >>1 where b is a radius of the second nanocrystals.
66. The method according to claim 62 wherein the first nanocrystals are made of a material and have a size, both of which are selected so that said first nanocrystals absorb light in said pre-selected wavelength range, and wherein the second nanocrystal are substantially monodisperse and are made of a material and have a size, both of which are selected so that the second nanocrystals emit light at the at least one pre-selected wavelength.
67. The method according to claims 62 wherein said second layer of the second nanocrystals include two or more types of nanocrystals, wherein each type are of a material and size, each of which is selected so that each type of nanocrystal emits light of pre-selected wavelengths in the visible or infrared, or combinations thereof.
68. The method according to claim 62 including a first conducting, semiconducting or insulating layer located between said first electrically conducting electrode layer and said first layer of first nanocrystals, a second conducting, semiconducting or insulating layer located between said first layer of first nanocrystals and said at least one second layer of second nanocrystals, wherein said first and second conducting, semiconducting or insulating layers function to regulate the transport of electrons and holes into the first and at least one second layers of nanocrystals.
69. The method according to claim 62 wherein the first and the second nanocrystals have pre-selected ligands attached to a surface of the first and the second nanocrystals.
70. The method according to claim 69 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are selected from the group consisting of oleate, hexylamine, octylamine, dodecylarnine, octadecylamine, tri-octyl phosphine oxide, butylamine, and pyridine.
71. The method according to claim 69 wherein the pre-selected ligands attached to the surface of the first and the second nanocrystals are octadecylamine (C18).