Cadmium-free quantum dots, tunable quantum dots, quantum dot-containing polymers, articles containing them, films, and 3D structures, as well as methods for their preparation and use

Abstract

Quantum dot-containing polymer resins, and methods for making the polymer resins themselves, are provided. Cadmium-free and / or stoichiometrically controlled quantum dots are disclosed, as are methods for their fabrication. The inclusion of such quantum dots in a stabilized polymer matrix is ​​also disclosed. The polymer is selected for its strong binding affinity to the outer layer of the quantum dots, such that the bond dissociation energy between the polymer material and the quantum dots is greater than the energy required to reach the melting temperature of the cross-linked polymer.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 338,888, filed May 19, 2016, entitled Tunable Semiconductor Nanocrystals And Films And 3 - D Structures Containing Them; U.S. Provisional Patent Application No. 62 / 338,915, filed May 19, 2016, entitled Cadmium - Free Quantum Dots; and U.S. Provisional Patent Application No. 62 / 441,182, filed December 31, 2016, entitled Quantum Dot Containing Polymer And Methods Of Making The Same, the entire disclosures of which are hereby incorporated by reference herein in their entirety.

[0002] This disclosure relates to the fields of quantum dots, polymers containing quantum dots, methods of making quantum dots and polymers containing them, and methods of using them.

Background Art

[0003] Numerous studies have been conducted to improve the stability and shelf - life of quantum dots and the ease of their manufacture and use. The applicant has developed several techniques and quantum dots that respectively contribute to improved stability, ease of manufacture, and / or ease of use.

[0004] Nie (U.S. Patent Nos. 7,981,667 and 8,420,155) and Qu (U.S. Patent No. 8,454,927) (each of which is hereby incorporated by reference in its entirety) disclose methods for making quantum dots that are tunable by stoichiometry rather than by size. In particular, the alloy gradient quantum dots disclosed therein are particularly stable. These quantum dots are more stable than previously existing dots and benefit from ease of manufacture because they no longer require timing on the order of milliseconds to obtain an appropriate size and, thus, the desired emission wavelength. These quantum dots further benefit from a uniform size, regardless of the emission wavelength, and the uniform size enables uniform handling and processing, which is not possible with size-tunable quantum dots that require different sizes of quantum dots to obtain different colors.

[0005] These stoichiometrically tunable quantum dots are in some cases further stabilized by capping with ZnS, resulting in capped, alloy gradient, stoichiometrically tunable quantum dots.

[0006] This advance was and still is a significant advance in quantum dot science, but further improvements in stability were desired. In particular, quantum dots are sensitive to their surrounding proximal environment. The Applicant has discovered that the stability is greatly improved by passivating the surface of the quantum dots, in particular using atomic layers of Al2O3. The passivation layer essentially installs an optically neutral armor layer around the quantum dots, making the quantum dots very stable. Combining the disclosure of the advances of Nie (U.S. Patent Nos. 7,981,667 and 8,420,155) and Qu (U.S. Patent No. 8,454,927) with passivation results in the production of stable, long-lived, uniform-sized quantum dots. These concepts are incorporated into the Applicant's U.S. Patent No. 9,425,253 (which is hereby incorporated by reference).

[0007] While being highly stable, high-performance, and long-lasting, these passivated quantum dots are still difficult to handle and process and remain sensitive to the surrounding proximity environment, and would benefit from a stable electronic environment in direct proximity to the outer surface of the quantum dot (e.g., outside the passivation layer). Accordingly, there is a need for additional, better, and / or various ways to stabilize quantum dots, particularly for optoelectronic applications, regardless of type.

[0008] Furthermore, there is always a need for additional ways to fabricate the quantum dots themselves.

[0009] Here, the Applicant has discovered that by firmly binding a polymer to the outer surface of a quantum dot, the stability of the quantum dot can be maintained, among other things, under various severe manufacturing conditions such as extrusion, injection molding, and other techniques.

[0010] As further described below, in a specific embodiment, the polymer is selected to crosslink with the passivation layer (e.g., Al2O3) of the quantum dot such that the binding dissociation energy associated with the polymer / passivation layer is greater than the energy required to melt the crosslinked polymer. In other words, the bond between the polymer and the passivation layer is not broken at the extrusion (or other manufacturing) temperature. This strong bond essentially protects the quantum dots during melting operations such as extrusion and injection molding. Previously, quantum dots exposed to such temperatures would easily darken and their optoelectronic properties would be lost depending on the processing conditions. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] Methods for making quantum dot-containing polymer resins and the polymer resins themselves are described herein. These methods are applicable to various types of quantum dots as long as the polymer can bind firmly to the surface of the quantum dot. MEANS FOR SOLVING THE PROBLEMS

[0012] One embodiment is of a method for synthesizing II-VI-VI semiconductor nanocrystals (SCNs) of formula WY x Z (1-x) (wherein W is a Group II element, Y and Z are different Group VI elements, and 0 < X < 1), the method comprising heating an II-VI-VI SCN precursor solution to a temperature sufficient to form the II-VI-VI SCNs, where the II-VI-VI SCN precursor solution comprises a Group II element, a first Group VI element, a second Group VI element, and a pH adjuster in one or more solvents that together contain one or more C 12 ~C 20 hydrocarbons and one or more fatty acids, and providing a method in which the amount of the pH adjuster is adjusted to provide a predetermined emission wavelength from the SCNs.

[0013] In certain embodiments, the Group II element is one or more selected from Cd, Zn, and Hg.

[0014] In certain embodiments, each of the first Group VI element and the second Group VI element is one or more selected from S, Se, Te, Po, and O.

[0015] In certain embodiments, the C 12 ~C 20 hydrocarbons are one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0016] ​In certain embodiments, the fatty acid is one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0017] In certain embodiments, the pH adjuster is an oxide or carboxylate of a Group II element.

[0018] In certain embodiments, the pH adjuster is selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0019] In certain embodiments, the II-VI-VI SCN precursor solution is prepared by dissolving a Group II element, a first Group VI element, and a second Group VI element in a solvent containing a pH adjuster, octadecene, and a fatty acid to provide the II-VI-VI SCN precursor solution.

[0020] In certain embodiments, the II-VI-VI SCN precursor is prepared by: preparing a first solution by dissolving a Group II element and a first Group VI element in a first solvent containing octadecene and a fatty acid; preparing a second solution by dissolving a second Group VI element in a second solvent containing octadecene; mixing the first and second solutions to provide an II-VI-VI SCN precursor solution; and adding a pH adjuster to one or both of the first and second solutions.

[0021] In one embodiment, the II-VI-VI SCN precursor solution is prepared by a process of preparing a first solution by dissolving a Group II element in a first solvent containing octadecene and a fatty acid, a process of preparing a second solution by dissolving a first Group VI element and a second Group VI element in a second solvent containing octadecene, a process of adding a pH adjuster to one or both of the first and second solutions; and a process of mixing the first and second solutions to provide the II-VI-VI SCN precursor solution.

[0022] In one embodiment, the II-VI-VI SCN precursor is prepared by a process of preparing a first solution by dissolving a Group II element in a first solvent containing octadecene and a fatty acid; a process of preparing a second solution by dissolving a first Group VI element in a second solvent containing octadecene, a process of preparing a third solution by dissolving a second Group VI element in a third solvent containing tributylphosphine, a process of adding a pH adjuster to one or more of the first, second, or third solutions, and a process of mixing the first, second, and third solutions to provide the II-VI-VI SCN precursor solution.

[0023] In one embodiment, the fatty acid is oleic acid.

[0024] In one embodiment, the temperature is about 270°C to 330°C.

[0025] One embodiment provides II-VI-VI semiconductor nanocrystals fabricated according to the methods disclosed herein.

[0026] One embodiment provides II-VI-VI semiconductor nanocrystals comprising Cd, S, and Se, the nanocrystals being modified by an alkylcarboxylic acid zinc pH adjuster.

[0027] One embodiment is a method of tuning II-VI-VI semiconductor nanocrystals of a known emission wavelength, the method comprising providing II-VI-VI semiconductor nanocrystals having a known emission wavelength, and heating the II-VI-VI semiconductor nanocrystals in a solution containing a pH adjuster, one or more C 12 ~C 20 hydrocarbons, and one or more fatty acids to form an SCN solution, adding a solution containing dialkyl zinc, hexaalkyl disilathiane, and trialkyl phosphine, and heating to a temperature sufficient to produce capped II-VI-VI semiconductor nanocrystals, wherein the amount of the pH adjuster is adjusted to provide a predetermined emission wavelength shift from the known emission wavelength of the II-VI-VI semiconductor nanocrystals.

[0028] In one embodiment, the C 12 ~C 20 hydrocarbons are one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0029] In one embodiment, the fatty acids are one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0030] In one embodiment, the pH adjuster is an oxide or carboxylate of a Group II element.

[0031] In one embodiment, the pH adjuster is selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0032] In one embodiment, the dialkyl zinc is dimethyl zinc, the hexaalkyl disilathiane is hexamethyl disilathiane, and the trialkyl phosphine is trioctyl phosphine.

[0033] In certain embodiments, the temperature is from about 150 °C to 350 °C.

[0034] Certain embodiments provide tuned II-VI-VI semiconductor nanocrystals made according to the methods disclosed herein.

[0035] Certain embodiments include a core comprising a II-VI-VI semiconductor nanocrystal comprising Cd, S, and Se, a capped II-VI-VI semiconductor nanocrystal comprising a cap layer selected from the group consisting of a core modified with zinc alkylcarboxylate, a layer comprising ZnS, a layer comprising Al2O3, and a multilayer cap comprising a first layer comprising ZnS and a second layer comprising Al2O3.

[0036] Certain embodiments provide cadmium-free "Cd-free" semiconductor nanocrystals comprising one or more Group II elements, one or more Group III elements, and one or more Group VI elements, the semiconductor nanocrystals being substantially free of cadmium.

[0037] In certain embodiments, the semiconductor nanocrystals do not contain cadmium.

[0038] In certain embodiments, the Cd-free nanocrystals have emission wavelengths in the near ultraviolet to far infrared regions.

[0039] Certain embodiments are methods for synthesizing Cd-free semiconductor nanocrystals, comprising heating a precursor solution comprising one or more non-cadmium Group II elements, one or more Group III elements, and one or more Group VI elements in one or more solvents comprising one or more C 12 ~C 20 hydrocarbons, one or more fatty acids, and optionally one or more C1-C 22 alkylthiols to a temperature sufficient to produce Cd-free semiconductor nanocrystals.

[0040] In certain embodiments, the Group II element is one or more selected from Cu, Zn, and Hg.

[0041] In certain embodiments, the Group III element is one or more selected from In, Ga, Al, and Tl.

[0042] In certain embodiments, the Group VI element is one or more selected from S, Se, Te, Po, and O.

[0043] In certain embodiments, C 12 ~C 20 The hydrocarbon is one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0044] In certain embodiments, the fatty acid is one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0045] In certain embodiments, the fatty acid is oleic acid.

[0046] In certain embodiments, the temperature is about 270 °C to 330 °C.

[0047] Certain embodiments provide Cd-free semiconductor nanocrystals made according to the methods disclosed herein.

[0048] Certain embodiments provide Cd-free semiconductor nanocrystals modified with zinc alkylcarboxylate.

[0049] One embodiment is a method of capping a Cd-free semiconductor nanocrystal, the method comprising providing a Cd-free semiconductor nanocrystal; heating the Cd-free semiconductor nanocrystal in a solution containing one or more C 12 ~C 20 hydrocarbons and one or more fatty acids to form an SCN solution; adding a solution containing dialkylzinc, hexaalkyldisilathiane, and trialkylphosphine; and heating to a temperature sufficient to produce a capped Cd-free semiconductor nanocrystal.

[0050] In one embodiment, the C 12 ~C 20 hydrocarbon is one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0051] In one embodiment, the fatty acid is one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0052] In one embodiment, the dialkylzinc is dimethylzinc, the hexaalkyldisilathiane is hexamethyldisilathiane, and the trialkylphosphine is trioctylphosphine.

[0053] In one embodiment, the temperature is from about 150 °C to 350 °C.

[0054] One embodiment provides a capped Cd-free semiconductor nanocrystal comprising a core of a Cd-free semiconductor nanocrystal comprising a core of one or more Group II elements, one or more Group III elements, and one or more Group VI elements, wherein the semiconductor nanocrystal is substantially free of cadmium, the nanocrystal comprising a core modified with zinc alkylcarboxylate, a capping layer selected from the group consisting of a layer comprising ZnS, and a layer comprising Al2O3.

[0055] One embodiment provides a quantum dot-containing polymer resin comprising a plurality of quantum dots each having an outermost layer, and a polymer material crosslinked to the outermost layer such that the binding dissociation energy between the polymer material and the outermost layer is greater than the energy required to reach the melting temperature of the crosslinked polymer.

[0056] In one embodiment, the plurality of quantum dots are selected from core-shell quantum dots, Cd-free quantum dots, or stoichiometrically tuned quantum dots.

[0057] In one embodiment, the outermost layer is selected from a capping layer and a passivation layer.

[0058] In one embodiment, the outermost layer is a Zns capping layer.

[0059] In one embodiment, the outermost layer is an Al2O3 passivation layer.

[0060] In one embodiment, the polymer material is an acrylate resin comprising units derived from the polymerization of one or more monomers represented by the formula:

Chemical formula

[0061] In certain embodiments, the acrylate resin further has the following formula:

Chemical formula

[0062] Certain embodiments provide a quantum dot-containing polymer resin comprising a plurality of quantum dots each having an Al2O3 passivation layer and a polymer material crosslinked to the Al2O3 passivation layer, wherein the bond dissociation energy between the polymer material and Al2O3 is greater than the energy required to reach the melting temperature of the crosslinked polymer.

[0063] One embodiment provides a quantum dot-containing polymer resin comprising a plurality of uniform, multicolored, same-sized alloy gradient quantum dots each having a ZnS capping layer and an Al2O3 passivation layer; and a polymer material crosslinked to the Al2O3 passivation layer, wherein the binding dissociation energy between the polymer material and Al2O3 is greater than the energy required to reach the melting temperature of the crosslinked polymer.

[0064] One embodiment provides a quantum dot-containing polymer resin comprising a plurality of quantum dots each having a ZnS capping layer and an Al2O3 passivation layer; and a polymer material crosslinked to the Al2O3 passivation layer, wherein the binding dissociation energy between the polymer material and Al2O3 is greater than the energy required to reach the melting temperature of the crosslinked polymer.

[0065] One embodiment provides an article comprising at least one of a film, a multilayer film, or a 3D object containing a quantum dot-containing polymer, wherein the polymer is bound to the quantum dots such that the binding dissociation energy between the polymer material and the quantum dots is greater than the energy required to reach the melting temperature of the crosslinked polymer.

[0066] In certain embodiments, the quantum dot-containing polymer is suitable for conventional polymer handling and manufacturing techniques including, but not limited to, solution casting, injection molding, extrusion molding, and the like.

[0067] Embodiments relate to semiconductor nanocrystals that can be tuned to a predetermined emission wavelength.

[0068] In a specific embodiment, the nanocrystal particles have emission wavelengths in the near ultraviolet (UV) to far infrared (IR) region, particularly in the visible region. More specifically, the quantum dots can have emission wavelengths of about 350 to about 750 nm.

[0069] One embodiment provides a quantum dot core and a semiconductor nanocrystal modified by a zinc alkyl carboxylate such as zinc acetate.

[0070] A further embodiment provides a method for synthesizing semiconductor core / shell nanoparticles, the method comprising synthesizing the Cd-free semiconductor nanocrystal described above and coating it with a semiconductor shell having a higher bandgap to improve quantum efficiency and stability compared to the Cd-free semiconductor nanocrystal itself.

[0071] A further embodiment provides a method for synthesizing a Cd-free semiconductor nanocrystal having the semiconductor shell described above and a second shell that acts as an insulator.

[0072] Yet another embodiment relates to semiconductor nanocrystals, cores / shells, and core / shell / shell particles described herein dispersed in an acrylate resin and their films and 3-D structures. These films and 3-D structures provide the ability to cast films and 3-D structures in commercially applicable devices to produce highly stable quantum dot-polymer composite films and 3-D structures. The films and 3-D structures can be used for display and lighting applications. In a specific aspect, a single-coat down-conversion film (SCDF) and 3-D structure comprising a single layer of a quantum dot-polymer composite film sandwiched between at least two transparent films can be used. The single-layer and multi-layer films and 3-D structures of the present invention enable simpler and more cost-effective products that provide at least the performance of more complex structures.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0074] Here, the applicant has discovered that by firmly binding the polymer to the outer surface of the quantum dots, the stability of the quantum dots can be maintained under various severe manufacturing conditions such as, but not limited to, extrusion molding, injection molding, and other techniques.

[0075] As further described below, in a specific embodiment, the polymer is selected to crosslink with the passivation layer (e.g., Al2O3) of the quantum dots such that the binding dissociation energy associated with the polymer / passivation layer is greater than the energy required to melt the crosslinked polymer. In other words, the bond between the polymer and the passivation layer is not broken at the extrusion (or other manufacturing) temperature. This strong bond essentially protects the quantum dots during melting operations such as extrusion and injection molding. Previously, quantum dots exposed to such temperatures would easily darken and their optoelectronic properties would be lost depending on the processing conditions.

[0076] Methods for making quantum dots, quantum dot-containing polymer resins, and the polymer resins themselves are described herein. These methods are applicable to various types of quantum dots as long as the polymer can bind firmly to the surface of the quantum dots.

[0077] By firmly binding the polymer to the outer surface of quantum dots, particularly passivated quantum dots, the stability of the quantum dots can be maintained under various severe manufacturing conditions such as, but not limited to, extrusion molding, injection molding, casting molding, solution casting, and other techniques.

[0078] As further described below, in a specific embodiment, the polymer is selected to crosslink with the passivation layer of the quantum dots (e.g., Al2O3) such that the binding dissociation energy associated with the bond between the polymer and the passivation layer is greater than the energy required to melt the crosslinked polymer. In other words, the bond between the polymer and the passivation layer is not broken at the melting temperature that occurs, for example, during an extrusion (or other manufacturing) process. This strong bond essentially protects the quantum dots during melting operations such as extrusion and injection molding. Previously, quantum dots exposed to such temperatures would easily darken and their optoelectronic properties were lost depending on the processing conditions.

[0079] Methods for making quantum dot-containing polymer resins and the polymer resins themselves are described herein. These methods are applicable to various types of quantum dots as long as the polymer can strongly bind to the surface of the quantum dots.

[0080] As described above, improved stability was obtained using the polymers and methods disclosed herein with any quantum dot, whether the polymer was adjusted in terms of uniformity or alloy gradient, size, or stoichiometry, whether capped or uncapped, whether passivated or unpassivated, as long as the polymer can strongly bind to the outer surface of the quantum dots. However, achieving efficient and stable quantum dot (QD) photoluminescence over the visible region of light under a combined condition of a high photon flux and a chemically harmful external environment benefits from a multi-layered approach.

[0081] First, the QD cores should have similar surface areas across the visible region. Additionally, it is specifically contemplated that cadmium-free (Cd-free) quantum dots can also be used in the methods and polymers described herein. Any Cd-free quantum dots can be used, but those described in U.S. Provisional Patent Application No. 62 / 338,915, entitled Cadmium-Free Quantum Dots, the disclosure of which is incorporated herein by reference and described below, are well-suited for use with the methods and polymers disclosed herein.

[0082] Second, core passivation should provide both confinement of exciton waves to the core and a physical barrier to water and oxygen.

[0083] Third, a dispersion matrix that provides separation in the space for individual QDs must also provide a stable electronic configuration outside the QD volume that results in photoluminescence while being itself stable to photodegradation. Embodiments of these three elements in materials that are usable in the thermoplastic, thermosetting, and solution casting manufacture of optical components will accelerate the acceptance of quantum dot-based components for display and lighting applications.

[0084] 1. Core It is a fundamental property of metals and semiconductor materials that the tendency for chemical reactions increases with an increase in surface area per mass. Thus, while a 1 cm cube of metal simply gets hot when exposed to a flame, the same mass will ignite if pulverized into micron-sized powder. The same holds true for QD cores with respect to environmental degradation and photolysis. QDs tuned by core size will degrade differently due to the increased reactivity of smaller cores (blue-green emitters) relative to larger cores (yellow-red emitters) because of their higher surface area to mass ratio. This holds true in both situations: environmental attack by water and oxygen and under conditions of high photon flux where destructive free radicals are generated on the QD surface. At the surface of the QD, there is a population of atoms that are imperfectly part of the internal periodic 3D crystal lattice. These atoms have empty or lone pair orbits. These dangling bonds are responsible for unwanted chemical reactions with the external environment and unwanted chemical reactions in the non-radiative carrier relaxation process during the luminescence emission cycle where electrons accumulate at these sites instead of recombining with holes. This effect is magnified in smaller QDs that have a higher surface area / mass ratio than larger QDs.

[0085] Therefore, in optical devices composed of QDs tuned in polychromatic sizes, earlier degradation of QDs emitting at the blue end of the visible spectrum is likely to be observed over time, especially under conditions of exposure to water and oxygen combined with high photon flux. It is desirable for all QD cores in an optoelectronic device to be of a similar size.

[0086] This desired core structure can be achieved by using QDs synthesized by the methods of Nie (U.S. Patent Nos. 7,981,667 and 8,420,1550) and Qu (U.S. Patent No. 8,454,927). These QDs are tuned by composition rather than by size.

[0087] When considering the full visible range, size-adjustable dots of the same color can be used, but stoichiometrically tuned quantum dots advantageously have the same size regardless of the emission wavelength. Stoichiometrically tuned quantum dots can be made according to the patents of Nie and Qu described above or other available methods. An improved method involving the use of a pH adjuster to finely tune the emission wavelength is disclosed in U.S. Provisional Patent Application No. 62 / 338,888 entitled Tunable Semiconductor Nanocrystals And Films And 3-D Structures Containing Them, the disclosure of which is incorporated herein by reference and described below. The quantum dots made by the method disclosed therein result in core / shell quantum dots having substantially the same size regardless of the emission wavelength.

[0088] Capping (i.e., the first passivation layer) There are two ways to passivate dangling bonds on the surface of QDs for higher quantum efficiency (QE) and improved photo / chemical stability: 1) passivation by low MW organic ligands or 2) passivation by an inorganic shell. Passivation by organic ligands is simple and straightforward, but the surface metal-organic ligand bonds are relatively unstable and can be broken and lost by chemical and / or photochemical reactions. Passivation by an inorganic shell is carried out by the well-known core-shell type of QDs and is often referred to as "capping" by, for example, a ZnS shell. Surface passivation of the QD core by an inorganic shell is more stable and provides better confinement of exciton waves to the core, thus having the additional desired effect of increasing QE. When the QD core is located within a shell material having a larger bandgap energy, electron and hole waves are better confined by the core. While the recombination probability of the two waves (electrons and holes) increases, the non-radiative decay process via interaction with dangling bonds on the surface decreases. The bandgaps and electron energy levels for common II-VI, III-V, and II-VI semiconductors are shown in FIG. 1.

[0089] These core-shell structures are improved with respect to QE and photostability (PS), but are still sensitive to chemical attack by water and oxygen from the environment.

[0090] This capping exists in conventional core-shell quantum dots and can be applied to many quantum dots, including the Cd-free quantum dots and stoichiometrically / pH-adjusted quantum dots disclosed herein, as well as other quantum dots.

[0091] 2. Passivation (Second Layer): It is desirable to provide a second shell of a wider bandgap material than the first shell that can further confine the excitonic fluctuations, passivate the dangling bonds on the outer surface of the first shell material, and provide a physical barrier to the diffusion of water and oxygen.

[0092] This can be achieved by adding a passivation layer of a second shell, Al2O3, as described in U.S. Patent No. 9,425,253 (Qu and Miller), which is incorporated herein by reference. The bandgap of Al2O3, including commonly used II-VI and III-V QD core and shell materials, is -3.5 to -11 (Figure 2).

[0093] In addition to having a bandgap energy including commonly used QD core-shell materials, Al2O3 at a thickness of 4 to 5 atomic layers has the further property of providing an absolute or nearly absolute barrier to the diffusion of oxygen and water. This provides a high barrier for protection from chemical attack by water and oxygen on the sensitive core-shell semiconductor material.

[0094] Figure 3 shows the improved stability achieved by coating a conventional CdSe / ZnS core-shell quantum dot with an Al2O3 passivation layer.

[0095] 3. Dispersion matrix (i.e., polymer) The Al2O3 surface layer provides a unique opportunity for a synergistic effect to provide a matrix of a QD dispersion that is chemically and electronically stable at the QD / matrix interface. The surface of Al2O3 is characterized by a repeating pattern of electropositive and electronegative regions, as seen in Figures 4 and 5.

[0096] The QDs having an Al2O3 surface exhibit a very strong binding affinity for polymers having repeating carbonyl groups, such as organic ligands containing -COOH and -SH groups, and further polymers described in the disclosures of the present invention by Nulwala assigned to Crystalplex (both U.S. Provisional Patent Applications Nos. 62 / 338,888 and 62 / 338,915, filed May 19, 2016, and incorporated herein by reference) and U.S. patent application Ser. No. 14 / 725,658 (incorporated herein by reference). This strong binding confers a plurality of desirable effects on the resulting QD / ligand / polymer matrix.

[0097] 3.1 Stability of the electronic configuration immediately outside the QD volume It is known that the electronic configuration of the volume directly adjacent to the QD surface and extending to the exciton Bohr radius can affect the overall QE of the QD population (see X. Ji, D. Copenhaver, C. Sichmeller, and X. Peng, "Ligand bonding and dynamics on colloidal nanocrystals at room temperature: the case of alkylamines on CdSe nanocrystals," J. Am. Chem. Soc. 130(17), 5726 - 5735(2008); S. F. Wuister, C. de Mello Donega, and A. Meijerink, "Influence of Thiol Capping on the Exciton Luminescence and Decay Kinetics of CdTe and CdSe Quantum Dots," J. Phys. Chem. B 108(45), 17393 - 17397(2004)). This is commonly seen when exchanging small MW organic ligands on the QD surface. Changes in the luminescent QE are observed even when the QD nanocrystals are not physically changed by the process. What is needed is a local electronic configuration that results in a very stable boundary between the QD surface and the external matrix, which provides a high QE for the QD and remains unchanged even under extreme conditions of temperature, high photon flux, and a hostile chemical environment. This can be achieved by binding the Al2O3 surface of the QD to a polymer such as that disclosed by Nulwala. The total binding energy of the matrix polymer to the Al2O3 surface exceeds the energy of the extrusion process at 280 °C and can provide a stable QD / matrix boundary.

[0098] 3.2 Chemical stability of the QD / matrix boundary In addition to heat, the stability of the QD / matrix interface can also be impaired by the presence of oxygen free radicals. These destructive free radicals can be generated at the QD / matrix interface by the combination of a high photon flux and the presence of O2 molecules. The destructive radicals can lead to the breaking of covalent bonds (chain scission) in the polymer chains in the matrix and / or the breaking of multiple ionic bonds between the matrix polymer chains and the Al2O3 surface of the QDs.

[0099] The QD / matrix interface can be resistant to oxygen free radical attack by the combination of the excess of ionic bonds between the matrix polymer and the Al2O3 surface and the high O2 barrier properties inherent in the matrix polymer. Certain polymers, in particular, the homopolymer of cyclohexyl acrylate and the copolymers of cyclohexyl acrylate with methyl methacrylate or heptyl acrylate, have repeating carbonyl units that are oriented in 3D space such that the repeating distance of the electronegative carbonyl oxygen coincides with the repeating distance of the electropositive regions on the surface of Al2O3. This results in a very strong binding of the polymer to the Al2O3 surface due to the many binding sites per polymer chain.

[0100] Furthermore, these acrylic polymers have high O2 barrier properties. The combined effect of the QDs suspended in these matrices is a very stable binding of the polymer to the QD surface and minimal O2 diffusion to the binding sites.

[0101] 3.3 Stable Dispersion in the 3D Matrix Volume In addition to the chemical stability of the QD / matrix interface, the QDs must be sufficiently dispersed without aggregation in order to function properly in the luminescent mode.

[0102] The polymers described in 3.2, and others disclosed by Nulwala, disperse QDs in this way. This is because the polymer-QD bonds are more stable than the self-bonding of QD-QD. When bonded in this way, the QD / matrix remains stable throughout downstream processes such as thermoplastic, thermosetting, and solution casting operations. Furthermore, the physical properties of the polymer matrix can be improved by interaction with the QD nanoparticles. The physical cross-linking sites provided by the QDs can change and improve the physical properties of the polymer such as glass transition temperature, durometer, impact resistance, tensile strength, and chemical resistance.

[0103] 4. Processing 4.1 Preparation of the Composite The QD / polymer composite can be prepared by a plurality of methods.

[0104] The polymer can be polymerized in a continuous reactor, and the QDs can be introduced into the continuous flow either before or after complete polymerization. Next, the resulting QD / polymer composite stream is recovered, the solvent is removed for use as a thermoplastic material, and optical components can be produced. The solvent may be retained or added to produce a solution cast composite to produce an optical film.

[0105] The polymer can be fully polymerized and then mixed with the QDs in a suitable solvent. Mixing such as high shear mixing can be applied to increase the binding of the polymer to the QD surface. The QD / polymer composite can be left as such for use in solution casting film formation, or the solvent can be removed to produce a dried composite for thermoplastic processing to produce optical components.

[0106] The QDs can be suspended in a monomer or mixture of monomers, or a mixture of monomers and oligomers, or a mixture of monomers and polyfunctional monomers having a plurality of vinyl groups that produce cross-linking in the final polymer. This thermosetting material can be cured later by heat or ultraviolet light to produce the final optical components.

[0107] 4.1 Downstream Processing of the Composite Three commonly used processes for generating optical components from plastics are thermoplastic processing, thermosetting processing, and solution casting.

[0108] Included in these general categories are injection molding, extrusion, thermosetting potting, thermosetting films, solution cast films, solution cast inkjet printing, solution cast 3D printing, thermosetting inkjet printing, thermosetting 3D printing, thermoplastic 3D printing, and other techniques.

[0109] Unless an operating example or otherwise specifically indicated, all numerical values or expressions referring to amounts of ingredients, reaction conditions, etc. used in this specification and the claims should be understood to be modified in all instances by the term "about". Accordingly, unless there is a conflicting description, the numerical parameters set forth in the following specification and the appended claims are approximations that can vary depending on the desired properties sought by the present invention. At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter should be construed in light of the reported number of significant digits and by applying ordinary rounding techniques.

[0110] Although the numerical ranges and parameters indicating the broad scope of the present invention are approximations, the numerical values set forth in the specific examples are reported as accurately as possible. However, any numerical value inherently contains some degree of error necessarily resulting from the standard deviation found in their respective test measurements.

[0111] It should also be understood that any numerical range described herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between the recited minimum value of 1 and the recited maximum value of 10 (and including the end points); that is, all sub-ranges having a minimum value of 1 or more and a maximum value of 10 or less. Since the disclosed numerical ranges are continuous, they include any value between the minimum and maximum values. Unless otherwise specified, the various numerical ranges recited in this application are approximate values.

[0112] As used herein, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise.

[0113] As used herein, the term "about" means plus or minus 10% of the numerical value with which it is used. Thus, about 50% means in the range of 45% to 55%.

[0114] As used herein, the term "copolymer" means a polymer resulting from the polymerization of two or more polymerizable unsaturated molecules and is intended to include terpolymers, tetrapolymers, and the like.

[0115] As used herein, the term "core / shell" means a particle having a quantum dot with one or more shells or coatings that substantially uniformly surround the core and the quantum dot core. Non-limiting examples of shell materials include Cd or Zn salts of S or Se and / or metal oxides.

[0116] As used herein, the terms "include", "comprise", and "have" and variations thereof mean "including, but not necessarily limited to".

[0117] As used herein, the term "Group II element" is intended to include one or more elements from IUPAC Group 2 of the periodic table selected from Cd, Zn, and Hg, except when describing Cd-free embodiments, in which case the Group II element refers to one or more elements from IUPAC Group 2 of the periodic table selected from Cu, Zn, and Hg.

[0118] As used herein, the term "Group VI element" is intended to include one or more elements from IUPAC Group 16 of the periodic table selected from S, Se, Te, Po, and O.

[0119] As used herein, the terms "nanoparticle", "nanocrystal", and "passivated nanocrystal" refer to small structures whose normal properties of these constituent materials are altered by their physical dimensions due to a quantum mechanical effect often called "quantum confinement". For clarity, the use of these terms in this disclosure refers to objects having quantum confinement properties, which are separated from each other in all three dimensions; and which allow incorporation into a liquid, vapor, or solid.

[0120] "Optional" or "optionally" means that the structure, event, or situation described thereafter may or may not be present or occur, and that the description includes both the case where the structure is present and the case where it is not present, or the case where the event occurs and the case where it does not occur.

[0121] As used herein, the term "polymer" is intended to include, but is not limited to, oligomers, homopolymers, copolymers, and graft copolymers.

[0122] As used herein, the term "quantum dot" typically refers to nanocrystalline particles made from materials that are bulk semiconductors or insulating materials having tunable photophysical properties in the near ultraviolet (UV) to far infrared (IR) region, particularly in the visible region. In many embodiments of the present invention, the term "quantum dot" includes semiconductor nanocrystals (SCNs) containing transition metals (non-limiting examples are Cd and Zn), and anions from Group 16 of the IUPAC periodic table (non-limiting examples are Se, S, Te, and O).

[0123] As used herein, the term "composite" refers to a material comprising quantum dots and a polymer that are combined into a matrix containing quantum dots dispersed throughout the matrix. In certain embodiments, the quantum dots are substantially uniformly dispersed throughout the matrix.

[0124] Aspects of the present disclosure relate to semiconductor nanocrystals (i.e., quantum dots) tuned to a predetermined emission wavelength. In some cases, the quantum dots can be a plurality of quantum dots that include a range of predetermined emission wavelengths. In particular, in certain embodiments, the plurality of quantum dots contains a homogeneous mixture of quantum dots that emit a plurality of desired wavelengths.

[0125] Aspects of the present invention relate to films and 3-D structures containing core / shell quantum dot particles dispersed in an acrylate resin. These films and 3-D structures provide the ability to produce highly stable quantum dot-polymer composite films and 3-D structures by casting the film and installing the 3-D structure on a commercially applicable device. The films and 3-D structures of the present invention can be used for display and lighting applications. In a specific aspect, a single coat down conversion film (SCDF) and 3-D structure including a single layer of a quantum dot-polymer composite film sandwiched between at least two transparent films can be used. The single-layer and multi-layer films and 3-D structures of the present invention enable simpler and more cost-effective products that provide at least the performance of more complex structures.

[0126] Quantum dot core Any semiconductor nanocrystal known in the art can be used as a core for quantum dots for incorporation into the polymers described herein. Non-limiting examples include U.S. Patent Nos. 6,207,229; 6,322,901; 6,576,291; 6,821,337; 7,138,098; 7,825,405; 7,981,667; 8,071,359; 8,288,152; 8,288,153; 8,420,155; 8,454,927; 8,481,112; 8,481,113; 8,648,524; 9,063,363; and 9,182,621, as well as U.S. Patent Application Publication Nos. 2006 / 0036084; 2010 / 0270504; 2010 / 0283034; 2012 / 0039859; 2012 / 0241683; 2013 / 0335677; 2014 / 0131632; and 2014 / 0339497, and related semiconductor nanocrystals disclosed therein.

[0127] The quantum dots used herein can be any quantum dots, a) cadmium-containing or cadmium-free b) alloy-graded or non-graded (i.e., homogeneous) c) adjustable in size, stoichiometrically adjustable, or non-adjustable, or d) any combination thereof can be.

[0128] Furthermore, novel methods for fabricating quantum dots are envisioned herein. In particular, methods for fabricating stoichiometrically and pH-adjusted quantum dots of the same size and Cd-free quantum dots are disclosed herein, both per se and for incorporation into the polymers disclosed herein.

[0129] Thus, conventional core / shell quantum dots, such as commercially available ones, other Cd-free quantum dots, and stoichiometrically and pH-regulator adjusted quantum dots and Cd-free quantum dots of the same size as described and disclosed herein can be incorporated into polymers, as further described below.

[0130] Cd-free quantum dots As used herein, the term "Cd-free" means that the object so described is substantially free of cadmium, or made without cadmium, or contains no cadmium. For example, the terms "Cd-free semiconductor nanocrystals" and "Cd-free semiconductor quantum dots" refer to semiconductor nanocrystals or quantum dots that are substantially free of cadmium, made without cadmium, or contain no cadmium.

[0131] "Substantially free of cadmium" means containing less than 5% cadmium, less than 3% cadmium, less than 1%, less than 0.5%, less than 0.3%, less than 0.1%, or any range of values between any two of these values and any value therebetween.

[0132] As used herein, with respect to Cd-free quantum dots, the term "Group II element" is intended to include one or more elements from IUPAC Group 2 of the periodic table selected from Cu, Zn, and Hg.

[0133] As used herein, the term "Group III element" is intended to include one or more elements selected from In, Ga, Al, and Tl.

[0134] As used herein, the term "Group VI element" is intended to include one or more elements from IUPAC Group 16 of the periodic table selected from S, Se, Te, Po, and O.

[0135] In one embodiment, suitable Cd-free semiconductor nanocrystals that can provide useful quantum dot cores include, but are not limited to, II-II-III-VI semiconductor nanocrystals (SCNs) of the formula ABCD, where A is a Group II element, B is another Group II element, C is a Group III element, and D is a Group VI element.

[0136] In a specific embodiment, the Group II element can be one or more selected from Cu, Zn, and Hg, the Group III element can be one or more selected from In, Ga, and Al, and the Group VI element can be one or more selected from S, Se, Te, Po, and O.

[0137] In a specific embodiment, the Cd-free nanoparticles are ZnCuInS and / or ZnCuGaS.

[0138] In another specific embodiment, suitable semiconductor nanocrystals that can provide useful Cd-free quantum dot cores in the present invention include II-II-III-III-VI semiconductor nanocrystals (SCNs) of the formula ABCDE, where A is a first Group II element, B is a second Group II element, C is a first Group III element, D is a second Group III element, and E is a Group VI element.

[0139] In a further aspect of this specific embodiment, the Group II element can be one or more selected from Cu, Zn, and Hg, the Group III element can be selected from In, Ga, and Al, and the Group Vi element can be selected from S, Se, Te, Po, and O.

[0140] In a further specific aspect of this specific embodiment, the Cd-free nanoparticles are ZnCuInAlS and / or ZnCuInGaS.

[0141] In a further embodiment, suitable Cd-free semiconductor nanocrystals that can provide quantum dot cores useful in the present invention include II-II-III-VI-VI semiconductor nanocrystals (SCNs) of the formula ABCDE, where A is a first Group II element, B is a second Group II element, C is a Group III element, D is a first Group VI element, and E is a second Group element.

[0142] In aspects of this further embodiment, the Group II element(s) can be one or more selected from Cu, Zn, and Hg, the Group III element(s) are In, Ga, Al, and the Group VI element(s) can be selected from S, Se, Te, Po, and O.

[0143] In certain aspects of this further embodiment, the Cd-free nanoparticles are ZnCuInSSe, ZnCuGaSSe, ZnCuAlSSe, and combinations thereof.

[0144] In a further embodiment, suitable Cd-free semiconductor nanocrystals that can provide quantum dot cores useful in the present invention include II-II-III-III-VI-VI semiconductor nanocrystals (SCNs) of the formula ABCDEF, where A is a first Group II element, B is a second Group II element, C is a first Group III element, D is a second Group III element, D is a Group element, E is a first Group VI element, and F is a second Group VI element.

[0145] In aspects of this further embodiment, the Group II element(s) can be one or more selected from Cu, Zn, and Hg, the Group III element(s) can be one or more selected from In, Ga, Al, and the Group VI element(s) can be one or more selected from S, Se, Te, Po, and O.

[0146] In certain aspects of this further embodiment, the Cd-free nanoparticles can be ZnCuInAlSSe, ZnCuInGaSSe, ZnCuAlGaSSe, and combinations thereof.

[0147] Sources of Group II and Group III elements In certain embodiments, the sources of Group II and Group III elements are metal oxides.

[0148] In a specific embodiment, the sources of Group II and Group III elements can be selected from ZnO, CuO, In2O3, and Al2O3.

[0149] In certain embodiments, the sources of Group II and Group III elements are fatty acid salts.

[0150] In a specific embodiment, the Group II and Group III elements can be selected from ZnX, CuX, InX, and AlX. X can be a carboxylic acid having a chain length of C1-C22.

[0151] Any suitable carboxylic acid can be used. In certain embodiments, the carboxylic acid used can be one or more selected from acetic acid, propionic acid, butyric acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0152] In a specific embodiment, the carboxylic acid is oleic acid.

[0153] In a particular embodiment, the carboxylic acid is acetic acid.

[0154] Sources of Group VI elements In certain embodiments, the sources of Group VI elements are pure elemental powders.

[0155] In a specific embodiment, the Group VI elements can be selected from elemental S, Se, Te, Po, and O.

[0156] In certain embodiments, the sources of Group VI elements are Group VI element-containing molecules.

[0157] In a specific embodiment, the Group VI element is present as the corresponding thiolate of a monofunctional alkylthiol-containing molecule, such as an alkylthiol having a chain length of C1-C22, but not limited thereto.

[0158] In a particular embodiment, the Group VI element is the thiolate of 1-dodecanethiol.

[0159] In a specific embodiment, the Group VI element can be the dithiolate of a corresponding dithiol molecule, such as a dithiol molecule having a chain length of C1-C22, but not limited thereto.

[0160] Ligand In an embodiment, the Cd-free nanoparticles are coated with a ligand.

[0161] In a specific embodiment, the ligand can be selected from single-chain fatty acids having a chain length of C8-C22.

[0162] Any suitable fatty acid can be used. In an embodiment, the fatty acid used can be one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, caprylic acid, and arachidic acid.

[0163] In a particular embodiment, examples of the fatty acid ligand include caprylic acid or octanoic acid.

[0164] In a specific embodiment, the ligand can be selected from single-chain thiols having a chain length of C1-C22.

[0165] In a particular embodiment, an example of the ligand is 1-dodecanethiol.

[0166] In a specific embodiment, the ligand can be a mixture of a fatty acid and a long-chain thiol having a chain length of C1-C22.

[0167] In a particular embodiment, the ligand is a mixture of 1-dodecanethiol and octanoic acid.

[0168] Solvent In some embodiments, the solvent used for the synthesis of Cd-free nanoparticles comprises one or more C12-C20 hydrocarbons. In many embodiments, the precursor solution solvent can be selected according to the physical properties of the materials used in the precursor solution, and as required by the equipment available for the synthesis. In specific embodiments, typically, a high-boiling organic solvent having a boiling point above about 150 °C, in some cases above about 200 °C, and in other cases above about 225 °C is used.

[0169] In a specific embodiment, the solvent comprises one or more selected from octadecane, dodecane, hexadecane, and eicosane.

[0170] In some embodiments, tributylphosphine (TBP) is used as the solvent in the precursor solution. In other embodiments, a mixture of TBP and C12-C20 hydrocarbons is used in the precursor solution. In these embodiments, it can be advantageous to include TBP because TBP provides a strong dipole moment that can help dissolve Group VI elements. In many embodiments, the precursor solution solvent can be selected according to the physical properties of the materials used in the precursor solution, and as required by the equipment available for the synthesis.

[0171] Cd-free core synthesis One embodiment provides a method for synthesizing a Cd-free semiconductor nanocrystal core. The method includes heating a precursor solution comprising a desired mixture of a Group II element, a Group III element, and a Group VI element as described above in one or more solvents comprising one or more C12 - C20 hydrocarbons and one or more fatty acids to a temperature sufficient to produce a Cd-free semiconductor nanocrystal core.

[0172] In one embodiment, the emission wavelength of the synthesized Cd-free nanoparticles is determined by the molar ratio of the precursors, as well as the concentration in the C12 - C20 hydrocarbon solvent and the type of C12 - C20 hydrocarbon solvent. Once the appropriate amounts of the chemicals required for the synthesis are weighed, they are placed in a suitable reaction vessel. Without degassing, the temperature is raised to a level sufficient to initiate the reaction and maintained at that temperature for a period sufficient to equilibrate the reaction.

[0173] In one embodiment, the reaction temperature is at least about 200 °C, in some cases at least about 220 °C, in other cases at least about 240 °C, and in some cases at least about 250 °C, and can be up to about 300 °C, in some cases up to about 280 °C, and in other cases up to about 270 °C. The temperature used depends on the specific precursors and solvents being used. The reaction temperature can be any value or in the range between any of the values listed above.

[0174] In one embodiment, the reaction time is at least about 5 minutes, in some cases at least about 8 minutes, and in other cases at least about 9 minutes, and can be up to about 60 minutes, in some cases up to about 45 minutes, in other cases up to about 30 minutes, and in some cases up to about 15 minutes. The reaction time used depends on the specific precursors and solvents being used. The reaction time can be any value or in the range between any of the values listed above.

[0175] In a particular embodiment, the reaction time is about 10 minutes.

[0176] Core Purification Purification of the Cd-free nanoparticle core is performed to substantially reduce or remove unreacted precursors and by-products generated during the reaction. In certain embodiments, purification of the Cd-free nanoparticle core can be performed as follows. 1) Transfer the Cd-free nanoparticle core synthesis solution to a centrifuge tube and dilute its volume 7.5-fold with a 1:3 mixture of nonpolar and polar solvents (non-limiting examples are hexane and butanol). 2) Centrifuge the solution from (1) until a crystalline pellet forms and discard the supernatant. 3) Wash the crystals three times with a 1:3 mixture of nonpolar and polar solvents (non-limiting examples are hexane and methanol) using 6.5 times the volume of the original Cd-free nanoparticle core synthesis solution for each wash. First, add the nonpolar solvent to suspend the crystals and then add the polar solvent to precipitate it. 4) Suspend the crystals in a nonpolar solvent (non-limiting example is hexane) at 81% of the volume of the synthesis solution.

[0177] Unconventional QD: Tuning by Stoichiometry / pH Control The following embodiments relate to quantum dots made in accordance with the teachings of U.S. Provisional Patent Application No. 62 / 338,888 that use a pH adjuster in a method for stoichiometrically tuning QDs to help establish a desired emission wavelength.

[0178] In certain embodiments, the core is a II-VI-VI semiconductor nanocrystal (SCN) having a predetermined emission wavelength. In certain embodiments, these are prepared by heating a II-VI-VI SCN precursor solution containing a Group II element, a first Group VI element, a second Group VI element, and a pH adjuster to a temperature sufficient to form the II-VI-VI SCN in one or more solvents that together contain one or more C 12 ~C 20 hydrocarbons and one or more fatty acids. The amount of the pH adjuster is adjusted to provide a predetermined emission wavelength from the SCN.

[0179] Although not desiring to be bound by theory, Applicant believes that the use of oleic acid results in excellent quantum dots because oleic acid is particularly suitable for subsequent capping with ZnS.

[0180] Precursor solution In certain embodiments, suitable semiconductor nanocrystals that can provide quantum dot cores useful in the present invention include II-VI-VI semiconductor nanocrystals (SCNs) of the formula WYxZ(1-x) where W is a Group II element, Y and Z are different Group VI elements, and 0 < x < 1.

[0181] In specific embodiments, the Group II element can be one or more selected from Cd, Zn, and Hg, and the Group VI element can be one or more selected from S, Se, Te, Po, and O.

[0182] In certain embodiments, the source of the Group VI element is an organic material that is soluble in C12-C20 hydrocarbons and miscible with one or more fatty acids used to make the II-VI-VI SCN. In many embodiments, pure Group VI elements in powder form are used.

[0183] In specific embodiments, a desired predetermined emission wavelength to be emitted from the SCN is specified and the amount of pH adjuster is adjusted such that the resulting SCN has the predetermined emission wavelength.

[0184] pH adjuster In certain embodiments, the amount of pH adjuster is selected to adjust the emission maximum wavelength of the SCN to a desired predetermined emission wavelength. If a specific wavelength is desired, several synthetic reactions using different concentrations of pH adjuster and, optionally, different molar ratios of precursors are performed to create a calibration curve. Next, the required concentration of pH adjuster and, if determined, the required ratio of precursors are specified for the desired wavelength from the calibration curve.

[0185] In a specific embodiment of this implementation, the emission wavelength from the SCN, without a pH adjuster, can be any wavelength within the visible region, particularly, from about 400 nm to about 700 nm, and any wavelength between those values. That is, the SCN can be fabricated using a known emission wavelength. Next, by introducing a pH adjuster, the emission wavelength can be "adjusted" from its known emission wavelength to a desired predetermined wavelength.

[0186] When a pH adjuster is included in the precursor solution, the emission wavelength of the SCN changes to a longer wavelength. In certain embodiments, the SCN emission wavelength can increase by at least 3 nm, in some cases at least 5 nm, and in other cases at least 7 nm, and can increase by up to 25 nm, in some cases up to 20 nm, and in other cases up to 17 nm, per 0.1 weight percent of the pH adjuster included in the precursor solution. The amount of the SCN emission wavelength can be any value or within a range between any of the values listed above. The amount of increase in the SCN emission wavelength can vary based on the size of the semiconductor nanocrystal, the specific pH adjuster used, and the specific Group II and Group VI elements used. By manipulating these factors, the emission wavelength can be accurately adjusted to the desired emission wavelength.

[0187] The pH adjuster is included in the precursor solution at a level that provides an increase in the desired SCN emission wavelength, often referred to as "tuning" of the SCN. The pH adjuster can be present in the precursor solution at a level from about 0.01 weight percent of the precursor solution, in some cases about 0.1 weight percent of the precursor solution, in other cases about 0.15 weight percent of the precursor solution, and in some cases about 0.2 weight percent of the precursor solution, and can be up to about 1 weight percent of the precursor solution, in some cases up to about 0.9 weight percent of the precursor solution, in other cases up to about 0.8 weight percent of the precursor solution, and in some cases up to about 0.7 weight percent of the precursor solution. The amount of the pH adjuster is an amount sufficient to achieve the desired adjustment and typically does not exceed the amount that increases the SCN emission wavelength beyond the visible spectrum. The amount of the pH adjuster in the precursor solution can be any value or within a range between any of the values listed above.

[0188] Any pH adjuster that can maintain the desired pH and perform the emission wavelength adjustment described above can be used in the SCN solution. In certain embodiments, the pH adjuster can be an oxide or carboxylate of a Group II element. In a specific embodiment, the pH adjuster can be selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid. In a specific embodiment, the pH adjuster is an oxide or carboxylate of a Group II element.

[0189] In one aspect of the present invention, the pH adjuster is selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0190] In certain embodiments, the C12 - C20 hydrocarbon used in the SCN solution can be one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0191] In other embodiments, the fatty acid used in the SCN solution can be one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α - linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0192] Any pH adjuster that can maintain the desired pH and perform the emission wavelength adjustment described above can be used in the precursor solution. In certain embodiments, the pH adjuster can be an oxide or carboxylate of a Group II element. In a specific embodiment, the pH adjuster can be a salt of an acid selected from the group consisting of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid. In certain embodiments, the salt is a zinc salt of an acid selected from the group consisting of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0193] In an embodiment, the pH adjuster is soluble in one or more fatty acids used in the precursor solution.

[0194] Hydrocarbon solvent Any suitable C12-C20 hydrocarbon can be used in the precursor solution. In certain embodiments, the C12-C20 hydrocarbon in the precursor solution can include one or more hydrocarbons selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0195] In certain embodiments, tributylphosphine (TBP) is used as a solvent in the precursor solution. In other embodiments, a mixture of TBP and a C12-C20 hydrocarbon is used in the precursor solution. In these embodiments, it can be advantageous to include TBP because TBP provides a strong dipole moment that can help dissolve Group VI elements. In many embodiments, the precursor solution solvent can be selected according to the physical properties of the materials used in the precursor solution and as required by the equipment available for synthesis.

[0196] Fatty acid Any suitable fatty acid can be used in the precursor solution. In certain embodiments, the fatty acid used in the precursor solution can be one or more fatty acids selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0197] In a specific embodiment of the present invention, the fatty acid is oleic acid.

[0198] In a specific embodiment, the II-VI-VI SCN precursor is prepared by dissolving a Group II element, a first Group VI element, and a second Group VI element in a solvent containing a pH adjuster, octadecene, and a fatty acid to provide a II-VI-VI SCN precursor solution.

[0199] In other embodiments, the II-VI-VI SCN precursor is prepared by: preparing a first solution by dissolving a Group II element and a first Group VI element in a first solvent containing octadecene and a fatty acid; preparing a second solution by dissolving a second Group VI element in a second solvent containing octadecene; and mixing the first and second solutions to provide a II-VI-VI SCN precursor solution. In this embodiment, both the first and second solutions contain a pH adjuster.

[0200] In a further embodiment, the II-VI-VI SCN precursor is prepared by: preparing a first solution by dissolving a Group II element in a first solvent containing octadecene and a fatty acid; preparing a second solution by dissolving a first Group VI and a second Group VI element in a second solvent containing octadecene; and mixing the first and second solutions to provide a II-VI-VI SCN precursor solution. In this embodiment, both the first and second solutions contain a pH adjuster.

[0201] In a further embodiment, the II-VI-VI SCN precursor is prepared by a process comprising dissolving a Group II element in a first solvent containing octadecene and a fatty acid to prepare a first solution; dissolving a first Group VI element in a second solvent containing octadecene to prepare a second solution; dissolving a second Group VI element in a third solvent containing tributylphosphine to prepare a third solution; and mixing the first, second, and third solutions to provide a II-VI-VI SCN precursor solution. In this embodiment, one or more of the first, second, and third solutions contains a pH adjuster.

[0202] In all of the above embodiments, the II-VI-VI semiconductor nanocrystals are synthesized by heating the II-VI-VI SCN precursor solution to a temperature sufficient to form the desired quantum dot core. In an embodiment, the precursor solution temperature is at least 200 °C, in some cases at least 225 °C, in many cases at least 250 °C, and in many cases at least 270 °C, and can be up to about 400 °C, in some cases up to about 350 °C, and in other cases up to about 330 °C. The temperature at which the II-VI-VI semiconductor nanocrystals are grown varies depending on the specific Group II and Group VI elements, and the ratios used, as well as the solvents, fatty acids, and pH adjusters employed.

[0203] In all of the above embodiments, the II-VI-VI semiconductor nanocrystals are synthesized by heating the II-VI-VI SCN precursor solution to the temperature described above for at least a period sufficient to form the desired quantum dot core. In one embodiment, the reaction time is at least 40, in some cases at least 50, in many cases at least 60, and in many cases at least 70 minutes, and can be up to about 120, in some cases up to about 110, and in other cases up to about 100 minutes. The reaction time at which the II-VI-VI semiconductor nanocrystals are grown varies depending on the temperature, the specific Group II and Group VI elements, and the ratios used, as well as the solvents, fatty acids, and pH adjusters employed.

[0204] In a specific embodiment of the present invention, the quantum dot core can be prepared by selecting a Group II element soluble in a fatty acid. Non-limiting examples of suitable fatty acids are stearic acid and oleic acid. A pH adjuster, an oxide or acetate of the Group II element soluble in the fatty acid is used. The source of the Group VI element is selected to be soluble in an organic solvent that is miscible with the fatty acid used to dissolve the Group II. In this embodiment, the organic solvent can be tributylphosphine and / or octadecene.

[0205] In this embodiment, the pH or the electrical environment of the reaction system is determined by introducing a pH adjuster into the reaction system. The pH adjuster is selected based on having a negative or positive charge depending on the desired type of nanocrystal and the properties of the precursors being used; and is miscible with the reaction system being used. In a specific embodiment, the pH adjuster is zinc acetate.

[0206] In addition to this embodiment, once the pH adjuster, solvent, and elements are selected, solutions of those elements are prepared in aliquots, which are mixed together for nanocrystal synthesis. After mixing, the reaction is completed.

[0207] In this embodiment, the emission maximum is determined by 1) the molar ratio of six elements of two groups; and 2) the concentration of the PH adjuster.

[0208] The present invention provides a method for tuning a quantum dot core. A convenient method of the present invention for tuning the emission maximum wavelength of the resulting quantum dot core involves identifying a desired emission maximum. Once a specific wavelength is identified, several synthesis reactions with varying molar ratios of precursors and concentrations of pH adjusters can be carried out to identify the molar ratio of elements and the concentration of the pH adjuster that provide the desired wavelength. In many embodiments, a calibration curve can be created by performing the synthesis reactions outlined above using varying ratios of elements and concentrations of the pH adjuster. Once the calibration curve is created, the ratio of elements and the concentration of the pH adjuster for any desired emission maximum can be identified.

[0209] Some specific advantages of embodiments of the present invention include not having to rely on a specific reaction time. Once the pH adjuster and stock solution are prepared, aliquots of each are mixed together and can be stirred at a temperature sufficient to support crystal growth, in many embodiments from about 200 °C to about 400 °C, for about 40 to about 120 minutes. Advantageously, it is not important to terminate the reaction at a specific time. In accordance with the method according to the present invention, after the reaction is complete, the solution can be continuously stirred at the growth temperature without changing the final quantum dot core product. In many prior art methods of synthesizing nanocrystals, an additional reaction time of 1 to 5 seconds further significantly changes the product.

[0210] In a specific embodiment, the semiconductor material of the quantum dot core can have one or more gradients of the semiconductor material extending from the center of the nanocrystal or quantum dot to the outermost surface of the nanocrystal. Such nanocrystals or quantum dots are referred to herein as "concentration gradient quantum dots". For example, in one embodiment, a concentration gradient quantum dot having at least a first semiconductor and a second semiconductor can be prepared such that the concentration of the first semiconductor gradually increases from the center of the concentration gradient quantum dot to the surface of the quantum dot. In such an embodiment, the concentration of the second semiconductor can gradually decrease from the core of the concentration gradient quantum dot to the surface of the quantum dot. Without wishing to be bound by theory, the concentration gradient quantum dot can have a bandgap energy that is non-linearly related to the molar ratio of at least two semiconductors.

[0211] Concentration gradient quantum dots can be prepared from any semiconductor material known in the art, including the semiconductor materials listed above, and the concentration gradient quantum dots can be composed of two or more semiconductor materials. In a specific embodiment, the concentration gradient quantum dot can be an alloy of CdSeTe having the molecular formula CdS1-xTex, CdSSe having the molecular formula CdS1-xSex, CdSTe having the molecular formula CdS1-xTex, ZnSeTe having the molecular formula ZnSe1-xTex, ZnCdTe having the molecular formula Zn1-xCdxTe, CdHgS having the molecular formula Cd1-xHgxS, HgCdTe having the molecular formula HgCdTe, InGaAs having the molecular formula InGaS, GaAlAs having the molecular formula GaAlAs, or InGaN having the molecular formula InGaN, where x in each example can be any ratio between 0 and 1.

[0212] The methods described above provide various uncapped semiconductor nanocrystals, collectively referred to herein as quantum dot cores.

[0213] One embodiment provides a quantum dot core, particularly a II-VI-VI semiconductor nanocrystal prepared according to the methods described above.

[0214] One embodiment provides a quantum dot core and a II-VI-VI semiconductor nanocrystal comprising Cd, S, and Se, where the nanocrystal is modified by zinc alkylcarboxylate (such as zinc acetate). The quantum dot core and the II-VI-VI semiconductor nanocrystal generally correspond to the formula WYxZ(1-x), where W is a Group II element, Y and Z are different Group VI elements, and 0 < X < 1. In a specific embodiment, the quantum dot core and the II-VI-VI semiconductor nanocrystal have a predetermined emission wavelength.

[0215] The II-VI-VI semiconductor nanocrystals of the present invention may have any diameter as long as quantum confinement is achieved, and thus can be of any size. In some embodiments, the II-VI-VI semiconductor nanocrystals described herein have a primary particle diameter of less than about 10 nm. According to other embodiments, the II-VI-VI semiconductor nanocrystals have a primary particle diameter of about 1 to about 500 nm. In other embodiments, the primary particle diameter is about 1 to about 100 nm, and in still other embodiments, the primary particle diameter is about 5 to about 15 nm. As used herein, the term "primary particle" refers to the smallest distinguishable division in a particulate system. A primary particle can also be a subunit of an aggregate.

[0216] Standard core / shell quantum dots (CdSe / ZnS) Standard core / shell quantum dots of the CdSe / ZnS type were obtained from a commercial source. The quantum dots were processed to evaluate the stability of quantum dots with and without an Al2O3 passivation layer, and the stability of quantum dots with and without an Al2O3 passivation layer and with and without incorporation into the polymer matrix described herein. Figure 6 shows the results of these tests.

[0217] To evaluate the effect of the Al2O3 passivation layer, QDs with and without the Al2O3 passivation layer were directly coated (naked) on glass slides and exposed to 85 / 85 conditions (85 °C, 85% humidity). As seen in Figure 6, there were significant differences between the Al2O3 passivated QDs and those without Al2O3 passivation. Relative intensity is not necessarily important in this analysis, but the decrease in intensity of QDs without the Al2O3 passivation layer indicates QDs with much lower stability.

[0218] Figure 6 shows that core / shell QDs with or without the Al2O3 passivation layer benefit from incorporation into the polymers described later in this specification. Herein, QDs with and without the passivation layer were dispersed and embedded in the polymers described herein and tested under 85 / 85 test conditions. Figure 6 shows that dispersion in the polymer results in stable QDs for both samples. Thus, dispersion within the polymers disclosed herein results in stable QDs.

[0219] Shell growth (capping) of Cd-free nanoparticle cores Capping of the purified Cd-free nanoparticle cores can be carried out by the following method.

[0220] Method 1: Maintain an oxygen-free environment during the capping process. Take a sample of the purified Cd-free nanoparticle cores and perform the following steps. The amounts shown are per 0.1 mmol of Group II element in the Cd-free nanoparticle core solution. 1) Vacuum purge until the non-polar solvent has evaporated. 2) Add 4.00 g of trioctylphosphine oxide and vacuum purge for 10 minutes. Optionally, if a shell containing stearic acid is desired, 0.2 g of stearic acid can be added together with the trioctylphosphine oxide before performing the vacuum purge. 3) Heat to about 100 °C under reduced pressure for about 30 minutes, then to 200 °C under reduced pressure for 30 minutes. 4) Prepare a capping solution by mixing 40 μL of Zn(CH3)2, 80 μL of hexamethyldisilathiane (CAS No. 3385-94-2), and 2.00 mL of trioctylphosphine in an oxygen-free environment. 5) Drop the capping solution into solution (3) at about 200 - 220 °C over about 5 minutes for every 2.0 mL of trioctylphosphine used. 6) Stir under nitrogen at 200 °C for about 30 minutes to about 2 hours. 7) Cool the solution to room temperature.

[0221] A graph of the ratio of elements versus the emission wavelength can be created to provide a calibration curve. The calibration curve can be used to determine the appropriate ratio of elements necessary to obtain crystals that fluoresce at the desired wavelength.

[0222] Method 2: Fill a three-necked flask with a desired amount of zinc acetate, sulfur element, 1-dodecanethiol, octadecane, and octanoic acid to obtain a purified Cd-free nanoparticle core. Degas for about 20 minutes, then fill the flask with nitrogen and raise the temperature high enough for the reaction to proceed at that temperature for about 60 minutes.

[0223] Capping of Quantum Dot Cores Embodiments of the present invention relate to a method for capping semiconductor nanocrystals. Any of the quantum dot cores disclosed above herein can be used in the methods according to these embodiments. One or more of the semiconductor nanocrystals described above are provided and heated in a solution containing one or more C12 - C20 hydrocarbons and one or more fatty acids to form an SCN solution. A solution containing dialkylzinc, hexaalkyldisilathiane, and trialkylphosphine is added to the SCN solution and heated to a temperature sufficient to produce capped II-VI-VI semiconductor nanocrystals.

[0224] In a specific embodiment, a predetermined emission wavelength from the capped semiconductor nanocrystals is identified, and an amount of a pH adjuster that provides the predetermined emission wavelength from the capped semiconductor nanocrystals can be added.

[0225] In one embodiment, the amount of the pH adjuster is selected to adjust the emission peak wavelength of the capped SCN. When a specific wavelength is desired, several synthesis reactions using different concentrations of the pH adjuster and the specific SCN to be capped are performed to create a calibration curve. Next, the required concentration of the pH adjuster for the desired wavelength from the calibration curve is identified.

[0226] In a specific aspect of this embodiment, in the absence of the pH adjuster, the emission wavelength from the capped semiconductor nanocrystals can be any wavelength within the visible region, particularly from about 400 nm to about 700 nm, and any wavelength in between. When the pH adjuster is included in the SCN solution, the emission wavelength of the capped semiconductor nanocrystals changes to a longer wavelength. In one aspect of the present invention, the SCN emission wavelength can increase by at least 2 nm, in some cases at least 3 nm, and in other cases at least 4 nm, and can increase by up to 15, in some cases up to 12, and in other cases up to 10 nm per 0.1 weight percent of the pH adjuster included in the SCN solution. The amount of the capped semiconductor nanocrystal emission wavelength can increase and can be any value or in a range between any of the values listed above. The amount of the capped semiconductor nanocrystal emission wavelength increases and can vary based on the size of the capped semiconductor nanocrystals, the specific pH adjuster used, and the specific Group II and Group VI elements used.

[0227] The pH adjuster is included in the SCN solution at a level that provides an increase in the emission wavelength of the desired capped semiconductor nanocrystals, often referred to as "tuning" of the capped semiconductor nanocrystals. The pH adjuster may be present in the SCN solution at a level from about 0.01 to, in some cases, about 0.1, in other cases, about 0.15, and in some cases, about 0.2 weight percent of the SCN solution, and may be up to about 1, in some cases, up to about 0.9, in other cases, up to about 0.8, and in some cases, up to about 0.7 weight percent of the SCN solution. The amount of the pH adjuster is an amount sufficient to achieve the desired tuning and typically does not exceed an amount that increases the emission wavelength of the capped semiconductor nanocrystals beyond the visible spectrum. The amount of the pH adjuster in the SCN solution can be any value or in a range between any of the values listed above.

[0228] Any pH adjuster that can maintain the desired pH and perform the emission wavelength tuning described above can be used in the SCN solution. In certain embodiments, the pH adjuster can be an oxide or carboxylate salt of a Group II element. In specific embodiments, the pH adjuster can be selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid. In specific embodiments, the pH adjuster is an oxide or carboxylate salt of a Group II element.

[0229] In certain aspects of the invention, the pH adjuster is selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0230] In certain embodiments, the C12 - C20 hydrocarbon used in the SCN solution can be one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane, and icosane.

[0231] In other embodiments, the fatty acid used in the SCN solution can be one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0232] In an embodiment, the dialkyl zinc is dimethyl zinc, the hexaalkyl disilathiane is hexamethyl disilathiane, and the trialkyl phosphine is trioctyl phosphine.

[0233] In many embodiments, the temperature of the SCN solution containing dialkyl zinc, hexaalkyl disilathiane, and trialkyl phosphine is heated to about 150 °C to 350 °C to form the capped quantum dots.

[0234] The method described above herein provides capped semiconductor nanocrystals.

[0235] The capped semiconductor nanocrystals of the present invention can have any diameter as long as quantum confinement is achieved, and thus can be of any size. In some embodiments, the capped semiconductor nanocrystals described herein have a primary particle diameter of less than about 10 nm. According to other embodiments, the II-VI-VI semiconductor nanocrystals have a primary particle diameter of about 1 to about 500 nm. In other embodiments, the primary particle diameter is about 1 to about 100 nm, and in still other embodiments, the primary particle diameter is about 5 to about 15 nm. As used herein, the term "primary particle" refers to the smallest distinguishable division in a particulate system. A primary particle can also be a subunit of an aggregate.

[0236] Cd-free Al2O3 capping In certain embodiments, the passivation layer is applied to the capped Cd-free nanoparticle core prepared as described above. In these embodiments, an aluminum capping material is prepared by mixing trimethylaluminum and trioctylphosphine to form a capping solution. The capping solution is added to a solution of core / shell Cd-free nanoparticles at a temperature sufficient to grow a monolayer of aluminum on the surface of the core / shell Cd-free nanoparticles, providing an aluminum-coated core / shell Cd-free nanoparticle core. In specific embodiments, the monolayer can be at least 1 atom thick, in some cases at least 2 atom thick, and in other cases at least 3 atom thick, and can be up to 20 atom thick, in some cases up to 15 atom thick, in other cases up to 10 atom thick, and in some cases up to 5 atom thick. In many cases, the capping solution is mixed with a solution of the capped Cd-free nanoparticle core at a temperature from 100 °C, in some cases at least 150 °C, and in other cases at least 175 °C, and can be mixed at a temperature up to about 300 °C, in some cases up to about 250 °C, and in other cases up to about 225 °C. Next, the aluminum-coated, capped Cd-free nanoparticle core is allowed to stand in air at a temperature below 100 °C for a time sufficient to convert all or part of the monolayer of aluminum to a monolayer of Al2O3, oxidizing to provide a capped Cd-free nanoparticle core coated with aluminum oxide ("passivated core / shell Cd-free nanoparticles").

[0237] The method of making passivated core / shell Cd-free nanoparticles can, in certain embodiments, be further modified to obtain desired characteristics. For example, nanoparticle properties such as surface functionality, surface charge, particle size, zeta (ζ) potential, hydrophobicity, etc. can be optimized according to the specific use of the passivated nanocrystals. For example, in certain embodiments, the modified surface chemistry and small particle size can contribute to a reduction in the interparticle spacing. In other embodiments, the passivated nanoparticles are stable in water or other liquid media without substantial aggregation and substantial precipitation for at least 30 days, preferably at least 90 days, more preferably at least 120 days. The terms “stable” or “stabilized” mean that the solid component (i.e., the nanoparticles) has stability against aggregation and flocculation in a fluid-phase solution or suspension for a period of time sufficient to maintain the integrity of the compound and, preferably, useful for the purposes detailed herein. As used herein, the term “aggregation” refers to the formation of aggregates consisting of particulate subunits held together by relatively weak forces (e.g., van der Waals forces or capillary forces) that can split into particulate subunits, for example, during processing. The resulting structure is called an “aggregate”.

[0238] Passivated core / shell Cd-free nanoparticles can have any diameter as long as quantum confinement is achieved and thus can be of any size. In some embodiments, the passivated core / shell Cd-free nanoparticles described herein have a primary particle size of less than about 10 nm in diameter. According to other embodiments, the passivated core / shell Cd-free nanoparticles have a primary particle size of from about 1 nm to about 500 nm in diameter. In other embodiments, a primary particle size of from about 1 to about 100 nm in diameter, and in still other embodiments, a primary particle size of from about 5 nm to about 15 nm in diameter. As used herein, the phrase “primary particle” refers to the smallest distinguishable division in a particulate system. A primary particle can also be a subunit of an aggregate.

[0239] Passivation of Capped II-VI-VI Semiconductor Nanocrystals (e.g., Al2O3 Passivation) In certain embodiments, a passivation layer is applied to the capped II-VI-VI semiconductor nanocrystals prepared as described above. In these embodiments, an aluminum capping material is prepared by mixing trimethylaluminum and trioctylphosphine to form a capping solution. The capping solution is added to a solution of the core / shell nanocrystals at a temperature sufficient to grow a monolayer of aluminum on the surface of the core / shell nanocrystals to provide aluminum-coated core / shell nanocrystals. In specific embodiments, the monolayer can be at least 1 atom thick, in some cases at least 2, and in other cases at least 3 atom thick, and can be up to 20, in some cases up to 15, in other cases up to 10, and in some cases up to 5 atom thick. In many cases, the capping solution is mixed with a solution of the capped II-VI-VI semiconductor nanocrystals at a temperature from 100°C, in some cases at least 150°C, and in other cases at least 175°C, and can be mixed at a temperature up to about 300°C, in some cases up to about 250°C, and in other cases up to about 225°C. Next, the capped II-VI-VI semiconductor nanocrystals coated with aluminum are allowed to stand in air at a temperature below 100°C for a time sufficient to convert all or part of the monolayer of aluminum to a monolayer of Al2O3 and oxidized to provide capped II-VI-VI semiconductor nanocrystals coated with aluminum oxide ("passivated core / shell nanocrystals").

[0240] The method of making the passivated nanocrystals of the present invention can be further modified in certain embodiments to obtain desired characteristics. For example, nanoparticle characteristics such as surface functionality, surface charge, particle size, zeta (ζ) potential, hydrophobicity, etc. can be optimized according to the specific use of the passivated nanocrystals. For example, in certain embodiments, the modified surface chemistry and small particle size can contribute to a reduction in the interparticle gap. In other embodiments, the passivated nanoparticles are stable in water or other liquid media without substantial aggregation and substantial precipitation over at least 30 days, preferably over at least 90 days, more preferably over at least 120 days. The terms "stable" or "stabilized" mean that the solid component (i.e., the nanoparticles) has stability against aggregation and agglomeration in a solution or suspension in a fluid phase for a period of time sufficient to maintain the integrity of the compound and, preferably, useful for the purposes detailed herein. As used herein, the term "aggregation" refers to the formation of aggregates consisting of particulate subunits held together by relatively weak forces (e.g., van der Waals forces or capillary forces) that can split into particulate subunits, for example, during processing. The resulting structure is called an "aggregate".

[0241] The capped passivated nanocrystals of the present invention can have any diameter as long as quantum confinement is achieved and thus can be of any size. In some embodiments, the passivated nanocrystals described herein have a primary particle size of less than about 10 nm in diameter. According to other embodiments, the passivated nanocrystals have a primary particle size of about 1 to about 500 nm in diameter. In other embodiments, they have a primary particle size of about 1 to about 100 nm in diameter, and in still other embodiments, a primary particle size of about 5 to about 15 nm in diameter. As used herein, the phrase "primary particle" refers to the smallest distinguishable division in a particulate system. A primary particle can also be a subunit of an aggregate.

[0242] The above-described specific embodiments provide capped II-VI-VI semiconductor nanocrystals including a core comprising a II-VI-VI semiconductor nanocrystal containing Cd, S, and Se modified by zinc alkylcarboxylate, and a cap layer selected from a layer containing ZnS, a layer containing Al2O3, a layer containing ZnS, and a second layer containing Al2O3.

[0243] As a more specific, non-limiting description of the capped semiconductor nanocrystals according to the present invention, the sources of the various atoms should be soluble in fatty acids such as stearic acid or oleic acid. As a non-limiting example, oxides or acetates of Group 2 elements are often soluble in stearic acid. The sources of both Group VI elements should be selected to be soluble in an organic solvent that is miscible with the fatty acid used to dissolve the Group 2 element. Pure Group 6 elements in powder form are often suitable. Tributylphosphine (TBP) and octadecene are examples of solvents that are miscible with oleic acid. In many embodiments, TBP provides a strong dipole moment, if necessary, to dissolve the Group 6 element. The solvent can be selected depending on the physical properties of the elements and, if necessary, the equipment available for the synthesis.

[0244] In many embodiments, the pH, or electrical environment, of the reaction system is determined by introducing additional materials into the reaction system. These materials should 1) have a negative or positive charge depending on the type of nanocrystal desired and the properties of the precursors used; and 2) be miscible with the selected reaction system. In a specific embodiment, zinc acetate is the pH adjuster.

[0245] Continuing with this embodiment, it is important to recall that the method according to the present invention does not require the timing of a critical end point. The reaction can be completed. The emission maximum is determined not by the reaction time but by 1) the molar ratio of the six Group 2 elements; and 2) the concentration of the pH adjuster.

[0246] In addition to this embodiment and the above description, adjustment of the emission peak wavelength to a specific desired wavelength requires only a few synthetic reactions using different molar ratios of the precursors and the concentration of the pH adjuster. This enables fine-tuning of the molar ratio and the concentration of the pH adjuster to the desired wavelength.

[0247] In an embodiment, a calibration curve is created by performing several syntheses using different concentrations of the pH adjuster. A stock solution of the pH adjuster is prepared, aliquots thereof are mixed together, and stirred at a temperature high enough to support crystal growth. Suitable temperatures can be from about 200 °C to about 400 °C over about 40 to about 120 minutes. It is not important to end the reaction at a specific time. In an embodiment, once the reaction is complete, the solution can be stirred at the growth temperature without changing the product. As a non-limiting example, stirring at the growth temperature for 10, 20, and 30 minutes at temperature does not change the semiconductor nanocrystals, which are the final product, when a CdSeS system is used. As shown above, prior art methods of nanocrystal synthesis using an additional reaction time of 1 to 5 seconds significantly change the product.

[0248] The method of this embodiment produces uncapped semiconductor nanocrystals referred to as "cores". By capping the cores, the cores are made more stable and their quantum efficiency is increased. As a non-limiting example, capping with ZnS is known to those skilled in the art. It is useful but not essential to purify the crystals before capping the cores of this embodiment.

[0249] The cores according to this embodiment can first be purified by diluting the synthesis mixture 7.5 times its volume with a 1:3 mixture of hexane and butanol. This precipitates the nanocrystals, and then the nanocrystals can be pelleted by centrifugation. Next, the crystals are first suspended in hexane and then washed three times by adding three volumes of methanol, thereby precipitating the crystals again. After the last wash, the crystals are dissolved in hexane for capping.

[0250] Another specific embodiment provides a method for providing a capped CdSeS core. The method includes three steps: core synthesis, core purification, and core capping.

[0251] The specific core synthesis of this embodiment includes the following: 1A) Mix a pH adjuster and a precursor with octadecene and a fatty acid (oleic acid and / or stearic acid), thoroughly disperse nitrogen gas, and heat to about 250 - 350 °C until the solution becomes clear to prepare a desired amount of the pH adjuster and the precursor. 2A) Prepare a solution of sulfur and selenium in an oxygen - free environment and mix each aliquot to be added to the cadmium precursor solution such that the Cd:S:Se molar ratio is 2:X:(1 - X) (where 0 < X < 1) to obtain a desired fluorescence wavelength. 3A) Combine a mixture of sulfur and selenium with octadecene to form a solution that is about 45 - 50 volume percent of the cadmium precursor solution while maintaining an oxygen - free environment. 4A) Introduce the solution from step (3A) into the solution from step (1A) at 250 - 350 °C and then maintain a temperature of about 250 - 350 °C. Stir the resulting solution for about 40 - 120 minutes until the reaction is complete while maintaining an oxygen - free environment.

[0252] The obtained core is purified according to this specific embodiment using the following method: 1B) Transfer the core synthesis solution from step (4A) to a centrifuge tube and dilute it 7.5 times its volume with a 1:3 mixture of hexane and butanol. 2B) Centrifuge the mixture from (1B) until a crystalline pellet is formed and discard the supernatant. 3B) Wash the crystalline pellet from step (2B) three times with a 1:3 hexane:methanol using about 6.5 times the volume of the original core synthesis solution for each wash. Add hexane to suspend the crystals and then add methanol to precipitate the crystals. (4B) The precipitated crystals from process (3B) are suspended in hexane at about 75 - 85% of the volume of the synthesis solution.

[0253] The obtained purified core maintains an oxygen - free environment during the capping process. A sample of the purified core from process (4B) is taken and is capped according to this specific embodiment by using the following method (the amounts shown are used with about 0.1 mmol of cadmium in the core solution of process (4B)): (1C) Vacuum purge until substantially all of the hexane has evaporated. (2C) Add about 0.2 g of zinc acetate (pH adjuster), 10 ml of octadecene, and fatty acid, and vacuum purge for 10 minutes. (3C) Heat to about 75 - 125 °C for about 30 minutes, and then to about 175 - 225 °C for about 30 minutes. (4C) Prepare the capping solution by mixing about 35 - 45 μL of Zn(CH₃)₂, about 75 - 85 μL of hexamethyldisilathiane (CAS number 3385 - 94 - 2), and about 1.85 - 2.15 mL of trioctylphosphine in an anaerobic environment. (5C) Slowly add the capping solution from step (4C) into the solution from step (3C) over a period of about 4 - 6 minutes for every 2.0 mL of trioctylphosphine used. (6C) Stir the solution from step (5C) at 175 - 225 °C for about 1.5 - 2.5 hours under nitrogen. (7C) Cool the solution from (6C) to room temperature.

[0254] Polymer containing the capped quantum dot core As used herein, the term "acrylate" is intended to include esters of both acrylic acid and methacrylic acid, such as the corresponding alkyl esters often referred to as acrylates and methacrylates, and other esters that may contain one or more of N, P, Si, and S, which are intended to be encompassed by the term "acrylate". The acrylate as used herein has the following formula: [Chemical formula] (wherein R1 is hydrogen or methyl; R2 is selected from the group consisting of methyl; ethyl; propyl; dodecyl; steryl; isopropyl; butyl; isobutyl; pentyl; cyclopentyl; isopentyl; linear C 1~18 alkyl; linear, branched, and cyclic C 6~8 alkyl).

[0255] As used herein, the term "acrylate resin" refers to a polymer obtained from the polymerization of one or more acrylates, and optionally one or more other polymerizable unsaturated molecules, along with any (non-quantum dot) additives that can be mixed into the polymer.

[0256] Unless otherwise specified, all molecular weight values are determined using gel permeation chromatography (GPC) with appropriate polystyrene standards. Unless otherwise indicated, the molecular weight values shown herein are weight average molecular weights (Mw).

[0257] Various embodiments relate to polymers, resins, films, or 3-D structures that include the semiconductor nanocrystals described above, dispersed in an acrylate resin. Any suitable acrylate resin can be used in the present invention. Non-limiting examples of suitable acrylate resins include the following formula: [Chemical formula] (wherein R1 is hydrogen or methyl, R 2 is selected from the group consisting of methyl; ethyl; propyl; dodecyl; steryl; isopropyl; butyl; isobutyl; pentyl; cyclopentyl; isopentyl; linear, branched, and cyclic hexyl containing 1 to 18 carbon atoms; linear, branched, and cyclic heptyl; and linear, branched, and cyclic octyl), and includes repeating or monomer units derived from polymerizing one or more monomers represented by)

[0258] The compound of Formula I is herein referred to as an acrylate monomer.

[0259] The amount and type of acrylate monomer in the acrylate resin are determined based on the desired properties of the resulting film and / or 3-D structure or other product, and the specific semiconductor nanocrystals used in the film.

[0260] In certain embodiments, the acrylate resin is made from methyl methacrylate (i.e., R1 = R2 = methyl) and, optionally, one or more other monomers represented by Structure I. In this embodiment, the amount of methyl methacrylate can be at least 1%, in some cases at least 5%, in other cases at least 10%, in some cases at least 20%, and in other cases at least 25% based on the weight of the acrylate resin, and can be 100%, in some cases at most 95%, in other cases at most 90%, in some cases at most 80%, in other cases at most 70%, in some cases at most 60%, and in other cases at most 50%. The amount of methyl methacrylate in the acrylate resin can be any value or in the range between any of the values listed above.

[0261] In one embodiment, the acrylate resin is made from methyl acrylate (i.e., R1 = H, R2 = methyl) and, optionally, one or more other monomers represented by Structure I. In this embodiment, the amount of methyl acrylate can be at least 1%, in some cases at least 5%, in other cases at least 10%, in some cases at least 20%, and in other cases at least 25%, based on the weight of the acrylate resin, and can be 100%, in some cases at most 95%, in other cases at most 90%, in some cases at most 80%, in other cases at most 70%, in some cases at most 60%, and in other cases at most 50%. The amount of methyl acrylate in the acrylate resin can be any value or in a range between any of the values listed above.

[0262] The amount of methyl methacrylate and / or methyl acrylate in the acrylate resin is determined based on the desired properties of the resulting film or structure, and the specific capping or capping and passivating semiconductor nanocrystals used in the film.

[0263] In these embodiments, other acrylate monomers are used at a level such that they make up 100% of the total percentage of monomers used in the acrylate resin.

[0264] In certain embodiments, the acrylate resin is made from cyclohexyl acrylate (i.e., R1 = H, R2 = cyclohexyl) and, optionally, one or more other monomers represented by Structure I. In this embodiment, the amount of cyclohexyl acrylate can be at least 1%, in some cases at least 5%, in other cases at least 10%, in some cases at least 20%, and in other cases at least 25%, based on the weight of the acrylate resin, and can be 100%, in some cases at most 95%, in other cases at most 90%, in some cases at most 80%, in other cases at most 70%, in some cases at most 60%, and in other cases at most 50%. The amount of cyclohexyl acrylate in the acrylate resin can be any value or in a range between any of the values listed above. In these embodiments, other acrylate monomers are used at a level such that the total percentage of monomers used in the acrylate resin is 100%. The amount of cyclohexyl acrylate in the acrylate resin is determined based on the desired properties of the resulting film or structure and the specific capping or capping and passivating semiconductor nanocrystals used in the film.

[0265] Other embodiments include one or more acrylate monomers of Formula I in the following formula:

Chemical Formula

[0266] The monomers of Formulas II-V are referred to herein as nitrogen-containing monomers.

[0267] In a specific embodiment, the acrylate resin is made from one or more acrylate monomers and one or more nitrogen-containing monomers. In this embodiment, the amount of acrylate monomer can be at least 1%, in some cases at least 5%, in other cases at least 10%, in some cases at least 20%, and in other cases at least 25%, based on the weight of the acrylate resin, and can be up to 99%, in some cases up to 95%, in other cases up to 90%, in some cases up to 80%, in other cases up to 70%, in some cases up to 60%, and in other cases up to 50%. The amount and type of acrylate monomer in the acrylate resin, as well as the corresponding amount and type of nitrogen-containing monomer, can be any value or in the range between any of the values listed above. In these embodiments, the nitrogen-containing monomer is used at a level such that the total percentage of monomers used in the acrylate resin is 100%. The amount and type of acrylate monomer in the acrylate resin, as well as the amount and type of nitrogen-containing monomer, are determined based on the desired properties of the resulting film and the specific capping or capping and passivating semiconductor nanocrystals used in the film.

[0268] Other embodiments relate to films and 3-D structures containing the capping or capping and passivating 2-6-6 semiconductor nanocrystals described above, dispersed in a polymer obtained from polymerizing one or more acrylate monomers represented by Structure I and one or more nitrogen-containing monomers represented by one or more of Structures II, III, IV, and V.

[0269] In certain embodiments, the films and 3-D structures described herein can be prepared using any suitable method. Non-limiting examples of the preparation of the films and 3-D structures described herein include dispersing capped nanocrystals in a suitable solution of a polymer obtained from polymerizing one or more acrylate monomers represented by Structure I and / or one or more nitrogen-containing monomers represented by one or more of Structures II, III, IV, and V. Typically, an organic solvent is used for the polymer solution. Any good solvent for the polymer can be used, but a solvent that can be removed to facilitate film formation is often used. Suitable solvents include, but are not limited to, C6 - C20 linear, branched, and cyclic aliphatic and aromatic solvents. In a specific embodiment, hexane, octane, decene, benzene, toluene, and xylene are suitable solvents. The solution of the capped nanocrystals, polymer, and solvent is typically homogenized to uniformly disperse the capped nanocrystals in the polymer solution and then stretched into a film and the solvent is evaporated.

[0270] In certain embodiments, the nanocrystal / polymer composites described herein typically contain, for the composite, at least 0.0001 wt%, in some cases at least 0.01 wt%, in other cases at least 0.1 wt%, in some cases at least 1 wt% levels of nanocrystals, and in other cases at least 5 weight percent of nanocrystals, and can contain, for the composite, up to about 75%, in some cases about 60%, in other cases about 50%, in some cases about 40%, and in other cases about 30% weight percent of nanocrystals. The amount of nanocrystals is determined according to the intended end use, the specific nanocrystals used, as well as the specific polymer used. The amount of nanocrystals in the nanocrystal / polymer composite can be any value or in the range between any of the values listed above (e.g., 0.0001 to 75 wt% of the composite).

[0271] The nanocrystal / polymer composites of the present invention can also contain additives such as, for example, primary antioxidants (including vitamin E, hindered phenols, etc.); secondary antioxidants (such as phosphites and phosphonites); nucleating agents, plasticizers or processing aids (such as fluoroelastomers and / or polyethylene glycol-linked processing aids), acid scavengers, stabilizers, corrosion inhibitors, foaming agents, chain-breaking antioxidants, and other ultraviolet light absorbers, matting agents, antistatic agents, slip agents, anti-blocking agents, pigments, dyes and fillers, and curing agents such as peroxides. The specific additives used are selected so as not to interfere with the desired properties to be obtained from the nanocrystal / polymer composite.

[0272] These and other common additives in the composite industry can be present in the nanocrystal / polymer composite in certain embodiments in amounts of about 0.01 to about 50 wt%, in other embodiments in amounts of about 0.1 to about 20 wt%, and in yet other embodiments in amounts of about 1 to about 5 wt%, where the desired range can include any combination of any wt% upper limit and any wt% lower limit.

[0273] Films containing capped quantum dot cores and multilayer films and 3-D structures containing 3-D structures Various embodiments relate to multilayer films and 3-D structures including one or more layers including the capping or capping and passivating quantum dot cores described above. The quantum dot cores can be uncapped, capped, passivated, or any combination thereof.

[0274] As a non-limiting example, FIG. 7 shows a multilayer film 10 including a first layer 12, a last layer 16, and an intermediate layer 14, including a film including the capping or capping and passivating quantum dot cores described above. In certain embodiments, the first layer 12 and the last layer 16 can have a refractive index of at least 1.47, in some cases at least 1.5, and in other cases at least 1.52, and can have a refractive index of up to about 1.7, in some cases up to about 1.65, and in other cases up to about 1.6.

[0275] Generally, the multilayer films and 3-D structures according to the present invention as shown in FIG. 7 can be made by first dispersing quantum dots in a suitable solvent and dissolving a resin made from an acrylate resin, a resin including a nitrogen monomer, and / or an acrylate monomer and a nitrogen-containing monomer in the quantum dot dispersion. Next, the resulting dispersion is coated onto a first film and then dried. Next, a second film, and any subsequent films, are thermally laminated onto the surface of the first film coated with the dispersion.

[0276] In many prior art systems, the reabsorption behavior of quantum dots and the lack of resistance to environmental degradation of quantum dots have been addressed using multiple costly thin film structures. These structures are used to efficiently convert blue light from light emitting diodes ("LEDs") to longer wavelengths emitted from quantum dots ("downconversion") and to protect the quantum dots for long-term use in optoelectronic devices. Examples of such structures include blocking filters, dichroic layers, separation of quantum dots into multiple single-color layers, and other complex multiple thin film structures. However, these structures are complex and costly to manufacture.

[0277] The present invention disclosed herein provides a single coat downconversion film (SCDF) and a 3-D structure that includes a single layer 14 of a quantum dot-containing matrix sandwiched between two transparent films (12, 16), as illustrated by FIG. 7, which can be easily manufactured at low cost. The combination of maximum dispersion and refractive index (RI) matching enables a simple and cost-effective product that provides at least the performance of more complex structures. Thus, embodiments of the multilayer films and 3-D structures according to the present invention rely on the combination of maximum quantum dot dispersion and refractive index matching to obtain optimal performance.

[0278] Referring to FIG. 8, the luminescent mode quantum dots emit light isotropically (in all possible directions). In many applications, it is desirable for the light generated by the quantum dots to escape from the matrix in which the quantum dots are dispersed and move in a preferred direction. The simplest structure for achieving some degree of directivity is to coat a layer of quantum dots in a polymer matrix on a film of a material having a higher refractive index than the polymer matrix. Using quantum dots dispersed in a first material (20) having a lower refractive index (n1) than a second material (22) having a refractive index (n2), and an excitation source (24) coming from the opposite side of the second material (22) (i.e., through the first material 20), the percentage of light emitted isotropically from the QDs in the first material (20) is refracted towards the normal and preferentially emitted away from the excitation source compared to the case where n1 = n2. When a reflector is placed behind the excitation source, with each pass of the reflected light of the quantum dots, the light of the quantum dots is directed towards the normal and the directivity is amplified during each pass. When a sandwich is created with a first material (20) having a refractive index n1 laminated between two layers of a second material (22) having a refractive index n2, the light is further directed towards the normal with each pass.

[0279] A further embodiment is shown in FIG. 9, which shows a multilayer film 50 including a first layer 52 and a last layer 56, and an intermediate layer 54, including a film containing the capping or capping and passivating quantum dot cores described above. A first barrier layer 58 and a second barrier layer 60 are located between the intermediate layer 54 and the first layer 52, and between the intermediate layer 54 and the last layer 56, respectively. In a specific embodiment, the first layer 52 and the last layer 56 may have a refractive index of at least 1.47, in some cases at least 1.5, and in other cases at least 1.52, and may have a refractive index of up to about 1.7, in some cases up to about 1.65, and in other cases up to about 1.6.

[0280] Generally, as shown in FIG. 9, the multilayer film and 3-D structure according to the present invention can be produced by first dispersing quantum dots in a suitable solvent and then dissolving a resin made of an acrylate resin, a resin containing a nitrogen monomer, and / or an acrylate monomer and a nitrogen-containing monomer in the quantum dot dispersion. Next, the obtained dispersion is coated on a first barrier film and then dried. Next, a second barrier film is thermally laminated on the surface of the first barrier film coated with the dispersion. Next, suitable first and final films, and 3-D structures are thermally laminated on the first and second barrier films, and the 3-D structure.

[0281] In certain embodiments, referring to the first layer 12 and the last layer 16 in FIG. 7, and the first layer 52 and the last layer 56 in FIG. 9, the layers can be any suitable material independently selected from polyethylene, polycarbonate, polypropylene, modified cellulose resin, transparent polyvinyl chloride, acrylic resin, polysiloxane, epoxy resin, sapphire, quartz, and glass.

[0282] In many embodiments of the film and 3-D structure, the multilayer film and 3-D structure containing the capping or capping and passivating 2-6-6 semiconductor nanocrystals described above are advantageous compared to films and 3-D structures using crosslinked polymers that are often used in the art. The light stability of the resin used in the films and 3-D structures described herein provides quantum dots, as well as films and 3-D structures containing quantum dots, with improved photodegradation stability.

[0283] In many embodiments of the film and 3-D structures, the composite material is prepared by combining nanocrystals with a polymer during or after polymerization in a suitable solvent and then removing the solvent to produce a material consisting essentially of 95-100% solid material that is substantially solvent-free. This composite can then be injection molded, extruded, compression molded, transfer molded, pressed, or first melted and formed using a process that converts the composite into the desired 3-D shape. These 3-D parts are then used in optoelectronic devices.

[0284] The quantum dots described herein can be included in solutions, inks, films, resin pellets, and thermoplastic pellets.

[0285] Solutions containing the quantum dots described herein can be prepared simply by leaving the QDs in solution without drying or by placing the purified QDs in a suitable solution for later use.

[0286] As described above, the QDs can be embedded in a polymer matrix to form a film or 3-D structure. The composite (QD-matrix) can also be pelletized for later use as resin pellets or thermoplastic pellets, and then it can be used in subsequent molding processes just as conventional resin or polymer pellets are used.

[0287] QD can be incorporated into inks such as those suitable for inkjet printing, 3-D printing, or other printing technologies. The inks are generally prepared from the quantum dots described herein, mixed with a polymer such as the acrylate polymers described herein, and a solvent. Any suitable solvent such as toluene can be used, although not limited thereto. Other additives useful in the inks such as, although not limited thereto, flow agents, self-leveling agents, viscosity modifiers, de-bubbling agents, binders, surfactants, etc. can also be used. In certain embodiments, the polymer and solvent components account for from about 1% to about 80% of the ink composition. The quantum dots are present at about 0.1 mg to about 100 mg of quantum dots per gram of polymer.

[0288] The present invention is further illustrated by reference to the following examples. The following examples are merely illustrative and are not intended to be limiting. Unless otherwise indicated, all percentages are by weight unless otherwise specified.

Examples

[0289] Example A1 - 530 nm Cd-free Quantum Dots 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed. This reaction provided Cd-free quantum dots having an emission wavelength of about 530 nm.

[0290] Example A2 - 750 nm Cd-free Quantum Dots 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.05 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of oleic acid, and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0291] This reaction provided Cd-free ZnInCuS quantum dots with an emission wavelength of approximately 750 nm.

[0292] Examples A3 - A7: Cd-free N quantum dots with emission wavelengths of 530 - 750 nm By changing the Zn / Cu ratio, the emission wavelength of the Cd-free quantum dots can be adjusted to 530 - 750 nm.

[0293] In Examples 3 - 7, the reaction was carried out in the same manner as in Example 1, except that the amount of copper acetate used was as shown in Table 1, which shows the emission spectra obtained for some of the wavelengths.

[0294] [Table 1]

[0295] Figure 10 shows the emission spectra for some of the wavelengths.

[0296] Example A8 Capping by Method 1 In a glove box, a solution for the deposition of one or more layers of ZnS onto the Cd-free nanocrystals of Example 1 was prepared. If no change in the emission wavelength of the Cd-free nanocrystals was observed, the solution was slowly added to the nanocrystal solution. This addition process lasted for about 2 minutes.

[0297] The resulting solution was added to a 50 ml conical centrifuge tube, and 5 ml of hexane and 15 ml of butanol were added. After sonication for about 1 minute, 20 ml of methanol was added. The nanocrystals were centrifuged, and the supernatant was discarded. The nanocrystals were washed two more times with 10 ml of hexane, precipitated with 20 ml of methanol, and centrifuged again.

[0298] The purified nanocrystals were transferred to a three-neck round-bottom flask, and hexane was removed under reduced pressure. Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were added. The flask was evacuated for 10 minutes and heated to 100 °C for 30 minutes and then to 200 °C for 30 minutes. The capping material was prepared in a glove box as follows: 40 μl of dimethylzinc, 80 μl of hexamethyldisilathiane, and 4 ml of trioctylphosphine were mixed in a glass vial and sealed with a rubber stopper. The capping solution was placed in a syringe, removed from the glove box, and slowly injected into the core solution over at least 10 minutes. The resulting solution was stirred at 200 °C for 30 minutes, then removed from the heat and cooled to room temperature.

[0299] This example provided capped Cd-free nanocrystals.

[0300] Example A9 Capping by Method 2 0.25 g of the purified Cd-free core from Example 1 was placed in a three-neck flask together with 1 g of zinc acetate, 0.032 g of S, 2 ml of 1-dodecanethiol, 10 ml of ODE, and 2 ml of octanoic acid. Degassing was carried out for 20 minutes, then the flask was filled with nitrogen, the temperature was raised to 240 °C, and the reaction was allowed to proceed for about 60 minutes.

[0301] This example provided capped Cd-free nanocrystals.

[0302] Example A10 Al2O3 Capping In a glove box, a solution for the deposition of one or more layers of ZnS onto the Cd-free nanocrystals of Example 1 was prepared. If no change in the emission wavelength of the Cd-free nanocrystals was observed, the solution was slowly injected into the nanocrystal solution. This injection process lasted about 2 minutes.

[0303] The resulting solution was added to a 50 ml conical centrifuge tube, and 5 ml of hexane and 15 ml of butanol were added. After sonication for about 1 minute, 20 ml of methanol was added. The nanocrystals were centrifuged and the supernatant was discarded. The nanocrystals were further washed twice with 10 ml of hexane, precipitated with 20 ml of methanol, and centrifuged again. The purified capped Cd-free nanocrystals were suspended in hexane for further capping.

[0304] The purified nanocrystals were transferred to a three-neck round-bottom flask, and hexane was removed under reduced pressure. Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were added. The flask was purged with vacuum for 10 minutes, heated to 100 °C for 30 minutes, and then to 200 °C for 30 minutes. The capping material was prepared in a glove box as follows: 40 μl of dimethylzinc, 80 μl of hexamethyldisilathiane, and 4 ml of trioctylphosphine were mixed in a glass vial and sealed with a rubber stopper. The capping solution was placed in a syringe, taken out of the glove box, and slowly injected into the core solution over at least 10 minutes. The resulting solution was stirred at 200 °C for 30 minutes, then removed from the heat and cooled to room temperature.

[0305] Several monolayers of aluminum were grown on the capped Cd-free nanocrystals as follows. Aluminum capping material was prepared in a glove box by mixing 10 μl of trimethylaluminum and 1 ml of trioctylphosphine to form a capping solution, which was sealed with a rubber stopper. The capping solution was placed in a syringe, taken out of the glove box, slowly injected into the core / shell nanocrystal solution at 200 °C over about 5 minutes, then removed from the heat and cooled to 100 °C. At that point, the flask was opened to air, thereby slowly oxidizing the aluminum outer coating on the core / shell nanocrystals at 100 °C for 3 hours. Several monolayers of Al2O3 were coated on the core / shell nanocrystals to provide passivated core / shell Cd-free nanocrystals.

[0306] Example A11 - ZnCuGaS 0.25 g of zinc acetate, 0.3 g of gallium acetate, and 0.01 g of copper acetate were charged into a three - necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, and 2 ml of 1 - dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0307] This example provided Cd - free quantum dots having an emission wavelength of approximately 550 nm.

[0308] Example A12 - ZnCuAlS 0.25 g of zinc acetate, 0.3 g of aluminum acetate, and 0.01 g of copper acetate were charged into a three - necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, and 2 ml of 1 - dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0309] This example provided Cd - free quantum dots having an emission wavelength of approximately 490 nm.

[0310] Example A13 ZnCuInSSe 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.01 g of copper acetate were charged into a three - necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, 200 μl of TBP / Se solution (the concentration was 1 g / 10 ml), and 2 ml of 1 - dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0311] This example provided Cd - free quantum dots having an emission wavelength of approximately 550 nm.

[0312] Example A14 - ZnCuInGaS 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.1 g of gallium acetate, and 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0313] This example provided Cd-free quantum dots having an emission wavelength of about 560 nm.

[0314] Example A15-ZnCuInGaSSe 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.1 g of gallium acetate, 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, 200 μl of a TBP / Se solution (the concentration was 1 g / 10 ml), and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0315] This example provided Cd-free quantum dots having an emission wavelength of about 560 nm.

[0316] Example A16-ZnCuInAlS 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.1 g of aluminum acetate, 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0317] This example provided quantum dots having an emission wavelength of about 500 nm.

[0318] Example A17-ZnCuInAlSSe 0.25 g of zinc acetate, 0.3 g of indium acetate, 0.1 g of aluminum acetate, and 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, 200 μl of a TBP / Se solution (the concentration was 1 g / 10 ml), and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0319] This example provided quantum dots having an emission wavelength of about 540 nm.

[0320] Example A18-ZnCuGaAlS 0.25 g of zinc acetate, 0.3 g of gallium acetate, 0.1 g of aluminum acetate, and 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0321] This example provided quantum dots having an emission wavelength of about 500 nm.

[0322] Example A19-ZnCuGaAlSSe 0.25 g of zinc acetate, 0.3 g of gallium acetate, 0.1 g of aluminum acetate, and 0.01 g of copper acetate were charged into a three-necked flask together with 5 ml of octadecane, 0.5 ml of octanoic acid, 200 μl of a TBP / Se solution (the concentration was 1 g / 10 ml), and 2 ml of 1-dodecanethiol. Without degassing, the temperature was raised to 270 °C. After 10 minutes, the heat was removed.

[0323] This example provided quantum dots having an emission wavelength of about 540 nm.

[0324] Example B1: Qd Adjusted with a pH Adjusting Agent Core Synthesis In a three-necked round-bottom flask, zinc acetate (0.2 g) (as a pH adjuster), octadecene (80 mL) were mixed with oleic acid (4 mL) and added to CdO (0.512 g). The flask was flushed with 99.999% nitrogen for 20 minutes and then heated to 300 °C until the solution became clear. Stock solutions of selenium and sulfur were prepared in a glove box under 99.999% nitrogen. Selenium powder (1.00 g) was mixed with tributylphosphine (10.00 mL), and sulfur powder (0.050 g) was mixed with octadecene (20.00 mL). 200 μL of the selenium precursor was mixed with 20 mL of the sulfur precursor in a 20 mL glass vial, diluted to 2.00 mL with octadecene, and then added to the cadmium precursor via a syringe and stirred for 60 minutes or until no change in the emission wavelength was observed. This produced a core that fluoresced at 570 nm.

[0325] Examples B2 - B6 The same procedure as in Example B1 was performed for Examples B2 - B6, except that the amount of zinc acetate as a pH adjuster in the core synthesis was changed as shown in the following table.

[0326] [Table 2]

[0327] This data can be graphed to provide a calibration curve to determine the appropriate amount of zinc acetate for the desired wavelength by plotting the emission maximum on the Y-axis and zinc acetate on the X-axis. The calibration curve based on this data is shown in Figure 12.

[0328] Examples B7 - B11 The same procedure as in Example B1 was performed to produce cores for Examples B7 - B11. The cores were then subjected to purification and capping.

[0329] Purification The whole core solution was added to 80 mL of hexane and 180 mL of butanol. The resulting solution was centrifuged (2,680 G for 5 minutes), and the supernatant was discarded, leaving the nanocrystals. The nanocrystals were washed three times by suspending them in hexane (10 mL), precipitated with methanol (30 mL), and centrifuged (2,680 G for 10 minutes). Next, the crystals were suspended in 5 mL of hexane.

[0330] Capping The purified nanocrystals were transferred to a three-neck round-bottom flask, and the solvent (hexane) was removed under reduced pressure. Zinc acetate (see the following table), octadecene (20 ml), and oleic acid (10 ml) were added to the flask. The flask was purged with vacuum for 10 minutes, then heated to 100 °C for 30 minutes, and then further heated to 200 °C for 30 minutes. While heating the nanocrystals, the capping solution was prepared in a glove box as follows: Dimethylzinc (40 μL) was mixed with hexamethyldisilathiane (80 μL, CAS number 3385-94-2) and trioctylphosphine (2.00 mL). The capping solution was put into a syringe, taken out of the glove box, and added drop by drop to the nanocrystals over 5 minutes. The resulting solution was stirred at 200 °C for 2 hours and then cooled to room temperature.

[0331] The amount of zinc acetate (pH adjuster) was changed as shown in the following table in the capping process. The red shift after capping indicates that the thicker the shell, the longer the red shift. Thicker shell nanocrystals can enhance the photo-stability and chemical stability.

[0332]

Table 3

[0333] A calibration curve for the shift of the emission wavelength based on this data is shown in Figure 13.

[0334] Example B12 (Comparative Example) CdZnSSe nanocrystals were fabricated as follows. 0.16 mmol of CdO, 0.4 mmol of Zn(AC)2, 200 μl of oleic acid, and 8 ml of octadecene were added to a 100 ml three-necked round-bottom flask. The flask was connected to a vacuum, degassed for about 10 minutes, then filled with high-purity nitrogen, heated to 300 °C, and stirred until a colorless solution was formed. Stock solutions of sulfur and selenium were prepared in a glove box filled with 99.999% nitrogen. Selenium powder (1.00 g) was mixed with tributylphosphine (10.00 ml), and sulfur powder (0.05 g) was mixed with octadecene (25.00 ml). A certain amount of the above sulfur and selenium stock solutions were mixed together in a glass vial and diluted with octadecene to 4 ml to obtain a solution referred to herein as the input solution. The amounts of sulfur and selenium totaled 1 mmol, and the S to Se ratio was determined by the final emission wavelength of the obtained nanocrystals. The input solution was taken out of the glove box using a syringe and quickly injected into the Cd and Zn precursor solutions while raising the growth temperature to 270 °C. This temperature was maintained for 40 - 60 minutes to grow the nanocrystals to the desired size as determined by the desired emission wavelength.

[0335] In the glove box, the solution was prepared for use in depositing one or more layers of ZnS onto the prepared nanocrystals. If no change in the emission wavelength of the nanocrystals prepared above was observed, the solution was slowly injected into the nanocrystal solution. This injection process lasted about 2 minutes.

[0336] The obtained solution was added to a 50 ml conical centrifuge tube, and 5 ml of hexane and 15 ml of butanol were added. After sonication for about 1 minute, 20 ml of methanol was added. The nanocrystals were centrifuged and the supernatant was discarded. The nanocrystals were washed two more times with 10 ml of hexane, precipitated with 20 ml of methanol, and centrifuged again. The purified nanocrystals were suspended in hexane for further capping.

[0337] The purified nanocrystals were transferred to a three-neck round-bottom flask, and hexane was removed under reduced pressure. Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were added. The flask was vacuum purged for 10 minutes and heated to 100 °C for 30 minutes and then to 200 °C for 30 minutes. The capping material was prepared in a glove box as follows: 40 μl of dimethylzinc, 80 μl of hexamethyldisilathiane, and 4 ml of trioctylphosphine were mixed in a glass vial and sealed with a rubber stopper. The capping solution was placed in a syringe, removed from the glove box, and slowly injected into the core solution over at least 10 minutes. The resulting solution was stirred at 200 °C for 30 minutes, then removed from the heat and cooled to room temperature.

[0338] Examples B13 and B14 To compare the photostability of the nanocrystals fabricated in the present invention, nanocrystal-polymethylmethacrylate (PMMA) films were deposited and irradiated with an ultra-high-intensity blue (450 nm) LED to monitor the intensity decay. The nanocrystals were dispersed in a toluene solution of PMMA using a Brinkman Homogenizer, and then the films were coated using an Elcometer 4340 Automatic Film Applicator and dried at room temperature to fabricate the films. Thus, the nanocrystals (5 mg) from Examples B11 and B12 were added to PMMA (5 g) to fabricate thin films. Under an ultra-high-intensity blue (450 nm) LED for continuous irradiation. Figure 11 shows the results of the stability test (Example B13 contains the nanocrystals from Example B11, and Example B14 contains the nanocrystals from Example B12. The data demonstrate the photostability of the nanocrystals fabricated according to the present invention.

[0339] As can be seen from the figures, the film using the nanocrystals according to Example B11 in the PMMA film maintains luminescence for at least 120 minutes, while the nanocrystals of the comparative example of Example B12 in the PMMA film deteriorate significantly even after only 20 minutes.

[0340] Examples B15 - B20 The polymer was synthesized by radical polymerization in toluene. Various amounts of vinyl monomers (as shown in the following table showing the weight ratio of comonomers) were used for the polymerization. The monomers were dissolved in toluene (1 mL per 1 g of monomer). An initiator, azobisisobutyronitrile (AIBN, 0.5 wt% based on the monomer) was added. The mixture was purged with N2 for 30 minutes. Next, the mixture was heated to 70 °C and stirred overnight. The resulting product was a colorless viscous liquid. MMA = methyl methacrylate, BA = butyl acrylate, CHA = cyclohexyl acrylate, NNDMT = Formula V, where both R3 and R4 are methyl. The Mw and PDI values were determined by GPC using analytical standards.

[0341]

Table 4

[0342] Using a Brinkman Homogenizer, the nanocrystals of Example B11 were dispersed in the toluene solution of the polymers in Examples B15 - B20, and then a film was cast using an Elcometer 4340 Automatic Film Applicator and dried at room temperature as described in Examples B13 and B14 to produce a cast film. All except Example B18 produced acceptable films with improved stability as demonstrated in Example B13.

[0343] Using a Brinkman Homogenizer, the nanocrystals of Example B11 were dispersed in a toluene solution of the polymers in Examples B15 - B20. Next, in a vacuum oven, at 125 °C and a reduced pressure of 30 mmHg, the toluene was removed to produce an extruded film. Next, the obtained material was melted in a heating tube until it reached 175 °C, extruded onto a glass slide, and cooled to form a composite containing a concentration of 0.5 mg of nanocrystals per 1000 mg of polymer.

[0344] Example B21 The passivated CdZnSSe nanocrystals were prepared as follows. 0.16 mmol of CdO, 0.4 mmol of Zn(AC)2, 200 μl of oleic acid, and 8 ml of octadecene were added to a 100 ml three-necked round-bottom flask. The flask was connected to a vacuum, degassed for about 10 minutes, then filled with high-purity nitrogen, heated to 300 °C, and stirred until a colorless solution was formed. Stock solutions of sulfur and selenium were prepared in a glove box filled with 99.999% nitrogen. Selenium powder (1.00 g) was mixed with tributylphosphine (10.00 ml), and sulfur powder (0.05 g) was mixed with octadecene (25.00 ml). A certain amount of the above sulfur and selenium stock solutions were mixed together in a glass vial and diluted with octadecene to 4 ml to obtain a solution referred to herein as the input solution. The amounts of sulfur and selenium totaled 1 mmol, and the S to Se ratio was determined by the final emission wavelength of the obtained nanocrystals. The input solution was taken out of the glove box using a syringe and quickly introduced into the Cd and Zn precursor solutions while raising the growth temperature to 270 °C. This temperature was maintained for 40 - 60 minutes to grow the nanocrystals to the desired size as determined by the desired emission wavelength.

[0345] In the glove box, a solution was prepared for use in the deposition of one or more layers of ZnS onto the prepared nanocrystals. If no change in the emission wavelength of the nanocrystals prepared above was observed, the solution was slowly introduced into the nanocrystal solution. This introduction process lasted about 2 minutes.

[0346] The resulting solution was added to a 50 ml conical centrifuge tube, and 5 ml of hexane and 15 ml of butanol were added. After sonication for about 1 minute, 20 ml of methanol was added. The nanocrystals were centrifuged and the supernatant was discarded. The nanocrystals were washed two more times with 10 ml of hexane, precipitated with 20 ml of methanol, and centrifuged again. The purified nanocrystals were suspended in hexane for further capping.

[0347] The purified nanocrystals were transferred to a three-neck round-bottom flask, and hexane was removed under reduced pressure. Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were added. The flask was purged with vacuum for 10 minutes, heated to 100 °C for 30 minutes, and then to 200 °C for 30 minutes. The capping material was prepared in the glove box as follows: 40 μl of dimethylzinc, 80 μl of hexamethyldisilathiane, and 4 ml of trioctylphosphine were mixed in a glass vial and sealed with a rubber stopper. The capping solution was placed in a syringe, removed from the glove box, and slowly introduced into the core solution over at least 10 minutes. The resulting solution was stirred at 200 °C for 30 minutes, then removed from the heat and cooled to room temperature.

[0348] Several monolayers of aluminum were grown on the nanocrystals as follows. Aluminum capping material was prepared in a glove box by mixing 10 ul of trimethylaluminum and 1 ml of trioctylphosphine to form a capping solution, which was sealed with a rubber stopper. The capping solution was placed in a syringe, removed from the glove box, and slowly introduced into the core / shell nanocrystal solution at 220 °C for about 5 minutes. Next, it was removed from the heat and cooled to 100 °C. At that point, the flask was opened to air, thereby slowly oxidizing the aluminum outer coating on the core / shell nanocrystals at 100 °C for 1 hour. Several monolayers of Al2O3 were coated on the core / shell nanocrystals to provide passivated core / shell nanocrystals.

[0349] Example B22 A solution-cast film containing the passivated nanocrystals of Example B21 was prepared as follows: The passivated nanocrystals of Example 16 were added to a 50 / 50 w / w solution of cyclohexyl acrylate homopolymer and toluene. The Mw of the polymer was about 125,000. The passivated nanocrystals were added at a concentration of 0.5 mg of nanocrystals per gram of polymer. Next, the mixture was mixed for 2 minutes using a high-shear mixer (Brinkman, model number PT / 35). Next, the mixture was dried on a glass slide to a thickness of 0.5 mm.

[0350] Figure 14 shows the emission spectrum of a solution-cast film made using excitation at 450 nm and emission at the red wavelength of the spectrum.

[0351] Example B23 A melt-extruded film containing the passivated nanocrystals of Example B21 was prepared as follows: The passivated nanocrystals of Example B21 were added to a 50 / 50 w / w solution of cyclohexyl acrylate homopolymer (Mw about 125,000) in toluene. Next, the mixture was homogenized for 2 minutes using a high-shear mixer (Brinkman, model number PT / 35). The homogenized mixture was dried to form a nanocrystal / polymer composite, which was ground into small pieces of 1 - 5 mm, filled into a glass syringe, and heated to 175 °C. Next, the melted mixture was extruded on a glass slide to a thickness of 0.5 mm.

[0352] Figure 15 shows the emission spectrum of a melt-extruded film fabricated using excitation at 450 nm and emission at the red wavelength of the spectrum.

[0353] The present invention has been described with reference to some details of its specific embodiments. Such details are not intended to be construed as limitations on the scope of the present invention, except to the extent that they are included in the appended claims.

[0354] Examples of thermosetting resins: Examples of thermosetting acrylic formulations that cure in the presence of QD are as follows: 60% (by weight) of heptyl acrylate, 30% of cyclohexyl acrylate, 10% of trimethylolpropane triacrylate (TMPTA). To this, a thermal initiator such as 0.1% of benzoyl peroxide, and QD in the range of 0.001 - 20% wt / wt are added. The mixture is polymerized by heating to 85 °C for 10 minutes.

[0355] It is contemplated herein that any quantum dots can be subjected to the capping and passivation methods disclosed herein and further incorporated into the polymer matrices described herein. It is not intended that the present disclosure or the above examples relate to a particular combination of a particular quantum dot type, a particular capping, a particular passivation layer, and a particular polymer be construed to suggest that the present disclosure is limited to those particular combinations. The present disclosure is, in essence, exemplary and not limiting. Those skilled in the art will recognize variations of the subject matter without departing from the scope and spirit of the present disclosure.

Claims

1. A capped II-VI-VI semiconductor nanocrystal, a core comprising a II-VI-VI semiconductor nanocrystal containing Cd, S, and Se, wherein the nanocrystal is modified by zinc acetate, said core; a cap layer covering the core and containing ZnS; A capped II-VI-VI semiconductor nanocrystal comprising the same.

2. A nanocrystal / polymer composite, a plurality of the capped II-VI-VI semiconductor nanocrystals according to Claim 1; a polymer material crosslinked to the capped II-VI-VI semiconductor nanocrystals; A nanocrystal / polymer composite comprising the same.

3. In the nanocrystal / polymer composite according to Claim 2, the polymer material 【Chemical 1】 comprises an acrylate resin containing units derived from the polymerization of one or more monomers represented by wherein R １ is hydrogen or methyl, and R ２ is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, cyclopentyl, isopentyl, linear, branched, and cyclic hexyl, linear, branched, and cyclic heptyl, and linear, branched, and cyclic octyl A nanocrystal / polymer composite.

4. In the nanocrystal / polymer composite according to Claim 3, the acrylate resin further 【Chemical Formula 2】 comprises units derived from the polymerization of one or more acrylate monomers represented by wherein R ３ and R ４ each independently is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, cyclopentyl, isopentyl, C ６ to C １２ linear, branched, cyclic, and aromatic hydrocarbyl, and polyethylene glycol R ５ is selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, cyclopentyl, isopentyl, C ６ to C １２ linear, branched, cyclic, and aromatic hydrocarbyl, and polyethylene glycol A nanocrystal / polymer composite.

5. A plurality of the capped II-VI-VI semiconductor nanocrystals according to Claim 1.

6. An optical device comprising a plurality of the capped II-VI-VI semiconductor nanocrystals according to Claim 5.

7. An optoelectronic device comprising a plurality of the capped II-VI-VI semiconductor nanocrystals according to Claim 5.

8. An optical device comprising the nanocrystal / polymer composite according to Claim 2.

9. An optoelectronic device comprising the nanocrystal / polymer composite according to Claim 2.

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