Cross-reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Application No. 63/162,349, filed March 17, 2021, the contents of which are incorporated herein by reference in its entirety.

BACKGROUND

[0002] This disclosure relates to the field of quantum dots, films and wafers containing quantum dots, methods of making the quantum dots and methods of using quantum dots.

[0003] A common use of quantum dots in display and lighting devices is to convert blue light from LEDs into other useful longer wavelengths in the visible range. In many instances, it is desirable to achieve near 100% blue light conversion on the distal (away from the blue source) side of the device with very little transmission of blue light. Efforts to achieve this in the past have included sandwiching the quantum dots in a polymer matrix between diffuser films to scatter the energizing light to maximize the number of photons that hit the quantum dots to maximize down-conversion. Alternatively, scattering beads may be added to the polymer matrix that contains the quantum dots to increase the number of photon hits. Sufficient down-conversion can be achieved with these methods so long as there is sufficient thickness of the quantum dot layer and scattering films to achieve long path lengths for the blue photons. There is a need in small devices to achieve maximum down-conversion in very thin path lengths in the 5-50 micron range. This is difficult to achieve with traditional methods as longer path lengths are required.

[0004] Much research has been devoted to improving the stability and useable life of quantum dots and their ease of manufacture and use. Applicants have developed several techniques and quantum dots that each contribute to improved stability, ease of manufacture, and/or ease of use; non- limiting examples of which include Nie (U.S. Patent Nos. 7,981,667 and US 8,420,155) and Qu (U.S. Patent No. 8.454,927). Some references disclose methods of making quantum dots that are tunable by stoichiometry, rather than by size.

[0005] Non-limiting examples include alloy-gradient quantum dots which can be particularly stable. These quantum dots are more stable than predecessor dots, benefit from ease of manufacture, since split second timing is no longer required to obtain the right size and therefore the desired emission wavelength. These quantum dots further benefit from uniform size, regardless of emission -wavelength, which allows for uniform handling and processing, which is not possible with size-tunable quantum dots, which require different sized quantum dots to achieve a spectrum of colors.

[0006] These stoichiometrically -tuned quantum dots were further stabilized by capping, in some instances with ZnS, resulting in a capped alloy-gradient stoichiometrically tuned quantum dot.

[0007] While this advance was, and remains, a significant advance in quantum dot science, further improvements to stability were sought. Particularly, quantum dots are sensitive to their immediate, proximate environment. Applicants found by passivating the surface of the quantum dot, particularly with atomic layers of A1203, stability improved. A passivation layer essentially places an optically neutral layer of armor around the quantum dot making increasing its stability. U.S. Patent No. 9,425,253 describes methods of combining the advances of the Nie and Qu disclosures with passivation to provide a more stable, long-lived, uniformly sized quantum dot.

[0008] Although very stable, well performing, and long-lived, the passivated quantum dots can still be difficult to handle and process, and remain sensitive to their immediate, proximate environment and could benefit from a stable electronic environment immediately proximate their outer surface (e.g. outside the passivation layer). Accordingly, more, better, and/or different ways of stabilizing quantum dots, regardless of type, particularly for optoelectronic applications is desired.

[0009] Further, additional methods of making the quantum dots, themselves, are always sought after. Summary

[0010] Some embodiments provide a membrane comprising: a Nanoporous Anodic Aluminum Oxide membrane coated with quantum dots, wherein the quantum dots are substantially evenly dispersed in transparent silica.

[0011] Some embodiments provide a membrane comprising: a Nanoporous Anodic Aluminum Oxide membrane coated with quantum dots, wherein the quantum dots are substantially evenly dispersed in a transparent polymer.

[0012] Some embodiments provide a membrane comprising: Nanoporous Anodic Aluminum Oxide membrane wherein the pores of the membrane are at least partially filled with quantum dots.

[0013] In some embodiments, the quantum dots are dispersed in transparent silica or polymer.

[0014] In some embodiments, the pores are substantially filled with quantum dots.

[0015] In some embodiments, the quantum dots comprise 11- VI- VI semiconductor nanocrystals according to the formula WYxZl-x; having a predetermined emission wavelength, wherein W is a Group II element, Y and Z are different Group VI elements, and 0<X<1.

[0016] In some embodiments, the Group II element is one or more selected from Cd, Zn and Hg.

[0017] In some 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.

[0018] Some embodiments provide a method of making Nanoporous Anodic Aluminum Oxide membranes containing quantum dots comprising: dispersing membrane discs in a dispersion containing a matrix and quantum dots to form a quantum dot - membrane composite, treating the dispersion to remove entrapped air and curing the quantum dot - membrane composite at a temperature and time sufficient for the matrix to become solid. [0019] In some embodiments, the quantum dots partially or substantially completely fill the voids or columns in the membrane.

[0020] In some embodiments, the matrix comprises a glass or an acrylate resin.

[0021] These and other embodiments will be readily appreciated by one of ordinary skill in the art upon reading this specification.

Brief Description of the Drawings

[0022] FIG. 1 is an electron micrograph of a non-limiting example of a Nanoporous Anodic Aluminum Oxide (NAAO) membrane that can be used in the various aspects of the disclosure.

[0023] FIG. 2 depicts a reaction scheme in accordance with various aspects of this disclosure.

Detailed Description

[0024] Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties, which the present disclosure desires to obtain. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0025] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0026] Also, it should be understood that any numerical range recited 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 and including the recited minimum value of 1 and the recited maximum value of 10; that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations.

[0027] Applicants have now discovered that, in some embodiments, uniformly coating the surface of Nanoporous Anodic Aluminum Oxide (NAAO) membranes with quantum dots and/or in other embodiments filling the pores of an NAAO with quantum dots, desirable photoluminescent emissions of the quantum dots can be achieved.

[0028] Described herein are methods for making quantum dot- containing NAAO membranes and using those membranes in devices to achieve desirable down-conversion, in some embodiments, where very thin path lengths are desired. These compositions and methods are applicable to various types of quantum dots and applicable, as non-limiting examples, to displays and lighting in handheld devices such as cellular phones and notebook computers.

[0029] As used herein, the singular forms "a", "an" and "the" include plural reference unless the context clearly dictates otherwise.

[0030] As used herein , the term “-acrylate resin " refers to polymers resulting from the polymerization of one or more acrylates and optionally one or more other polymerizable unsaturated molecules together with any (non-quantum dot) additives that may be blended into the polymer.

[0031] As used herein, the term "about" means plus or minus 10% of the numerical value of the number with which it is being used. As a non limiting example, about 50% means in the range of 45%- 55%.

[0032] As used herein, the term "composite" refers to materials that contain quantum dots and a polymer and/or glass and optionally a NAAO membrane combined into a matrix that includes quantum dots dispersed throughout the matrix. In some embodiments, the quantum dots are dispersed substantially evenly throughout the matrix. [0033] As used herein, the term “core/shell" means particles that have a quantum dot as a core and one or more shells or coatings generally uniformly surrounding the quantum dot core. Non-limiting examples of shell materials include Cd or Zn salts of S or Se and/or metal oxides.

[0034] The terms "include," "comprise," and "have" and their conjugates, as used herein, mean "include but not necessarily limited to."

[0035] As used herein, the term “glass” refers to a solid that possesses a noncrystalline or amorphous structure at the atomic scale and that exhibits a glass transition when heated towards the liquid state. In some embodiments herein, glass can refer to a noncrystalline amorphous solid that can be transparent, which, as non-limiting examples, can include silicate glasses based on silicon dioxide or quartz. In other embodiments, glass can refer to metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. Non-limiting examples of suitable polymer glasses include acrylic glass, polycarbonate and polyethylene terephthalate.

[0036] As used herein, the terms “Group II element" or “Group II metal” are meant to include one or more elements from the IUPAC group 2 of the periodic table selected from Cd, Zn and Hg, except when discussing “Cd-free” embodiments, in which case Group II element refers one or more elements from the IUPAC group 2 of the periodic table selected from Cu, Zn and Hg.

[0037] As used herein, the terms “Group III element" or “Group III metal” is meant to include one or more elements selected from In, Ga, Al, Tl, Sc and Y.

[0038] As used herein, the term "Group VI element" is meant to include one or more elements from the IUPAC group VI of the periodic table selected from S, Se, Te, Po, and O.

[0039] As used herein, the terms "nanoparticles", "nano crystals", and "passivated nanocrystals" refer to small structures in which the ordinary properties of their constituent materials are altered by their physical dimensions due to quantum-mechanical effects, often referred to as “quantum confinement”. For the sake of clarity, the use of these terms in this disclosure refers to objects possessing quantum-confinement properties, which are separated from one another in all three dimensions; enabling incorporation into liquids, vapors, or solids.

[0040] As used herein, the terms “nanoporous anodic aluminum oxide membrane” and “NAAO membrane”, in singular or plural, refer to self-organized materials with honeycomb-like structure often formed by electrochemical oxidation (anodization) of aluminum in acid electrolytes in conditions that balance the growth and the localized dissolution of aluminum oxide to form arrays of nanometer-sized pores, high density arrays of uniform and parallel pores. The diameter of the pores can be as low as 5 nanometers and as high as several hundred nanometers, and length can be controlled from few tens of nanometers to few hundred micrometers. In some embodiments, the pores can extend in the z direction the width of the membrane and in other embodiments part-way in the z direction a portion of the width of the membrane with the remainder containing clear A1203. A non- limiting example of a NAAO membrane useful in aspects of the disclosure is shown in FIG. 1.

[0041] As used herein, the terms "optional" or "optionally" mean that the subsequently described structure, event, or circumstance may or may not be present or occur, and that the description includes instances where the structure is present and where it is not or instances where the event occurs and instances where it does not.

[0042] As used herein, the term "polymer" is meant to encompass, without limitation, oligomers, homopolymers, copolymers and graft copolymers.

[0043] As used herein, the terms “quantum dots” and “QDs” refer to very small semiconductor particles, often only several nanometres in size, such that their optical and electronic properties often differ from those of larger particles. In many cases the quantum dot will emit light of specific wavelength or frequencies if electricity or light is applied to them, which can be precisely tuned by changing the quantum dots' size, shape, stoichiometry and/or material. QDs are often prepared by treating semiconductor nanocrystals. [0044] As used herein, the terms “semiconductor nanocrystals” and “SCNs” refer to tiny light-emitting particles on the nanometer scale that demonstrates the quantum confinement effect, which leads to spatial enclosure of the electronic charge carriers within the nanocrystal. This effect can take advantage of the size and shape of the SCNs to widely and precisely tune the energy of discrete electronic energy states and optical transitions.

[0045] As used herein, the terms “substantially free of cadmium”, “Cd-free” and “Cadmium free” mean that an SCN or quantum dot has no detectable amount of cadmium using conventional analytical methods known to those skilled in the art or less than 0.01 wt.% cadmium based on conventional analytical methods known to those skilled in the art.

[0046] Any semiconductor nanocrystals known in the art can be used as the core for the quantum dots for incorporation into the NAAO membranes described herein, non-limiting examples being the relevant semiconductor nanocrystals disclosed in International Published Patent Application WO 2017/201465 ; 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; 8,481,113; 8,648,524;

9,063,363; and 9,182,621 as well as U.S. Published Patent Application Nos. 2006/0036084; 2010/0270504; 2010/0283034; 2012/0039859;

2012/0241683; 2013/0335677; 2014/0131632; and 2014/0339497.

[0047] The quantum dots employed herein can include quantum dot, and can be: a) cadmium-containing or cadmium free b) alloy-gradient or non -gradient (i .e. homogenous) c) size -tunable, stoichiometrically-tmmble, or not, or d) any combination of these.

[0048] Some embodiments provide a method for synthesizing II- VI-VI semiconductor nanocrystals (SCNs) of the formula WYxZ(l-x) having a predetermined emission wavelength, where W is a Group II element, Y and Z are different Group VI elements, and 0<X<1. The methods include heating a II-VI-VI SCN precursor solution to a temperature sufficient to produce the II- VI- VI SCNs, where the II- VI- VI SCN precursor solution includes a Group II element, a first Group VI element, a second Group VI element, and a pH controller in one or more solvents, which include one or more C12 to C20 hydrocarbons and one or more fatty acids; and where the amount of pH controller is adjusted to provide the predetermined emission wavelength from the SCNs.

[0049] In some embodiments, the Group II element is one or more selected from Cd, Zn and Hg.

[0050] In some embodiments, each of the first Group VI element and the second Group VI element is independently one or more selected from S. Se, Te, Po, and O.

[0051] In some embodiments, the ci2 to C20 hydrocarbons are one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane and lcosane.

[0052] In some embodiments, the fatty acids are one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, o.-Linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0053] In some embodiments, the pH controller is an oxide or carboxylic acid salt of a Group II element.

[0054] In some embodiments, the pH controller is selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0055] In some embodiments, the II- VI- VI SCN precursor solution is prepared by dissolving the Group II element, the first Group VI element, and the second Group VI element in a solvent that includes the pH controller, octadecene and a fatty acid to provide the II- VI- VI SCN precursor solution.

[0056] In some embodiments, the II- VI- VI SCN precursor is prepared by preparing a first solution by dissolving the Group II element and the first Group VI element in a first solvent that includes octadecene and a fatty acid; preparing a second solution by dissolving the second Group VI element in a second solvent that includes octadecene; mixing the first and second solutions to provide a II-VI-VI SCN precursor solution: adding the pH controller to one or both of the first and second solutions; and mixing the first and second solutions to provide a II-VI-VI SCN precursor solution.

[0057] In some embodiments, the II-VI-VI SCN precursor solution is prepared by preparing a first solution by dissolving a Group II element in a first solvent that includes 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 that includes octadecene: adding the pH controller to one or both of the first and second solutions: and mixing the first and second solutions to provide a II-VI-VI SCN precursor solution.

[0058] In some embodiments, the II-VI-VI SCN precursor is prepared by: preparing a first solution by dissolving a Group II element in a first solvent that includes octadecene and a fatty acid; preparing a second solution by dissolving a first Group VI element in a second solvent that includes octadecene; preparing a third solution by dissolving a second Group VI element in a third solvent that includes tributylphosphine; adding the pH controller to one or more of the first, second, or third solutions; and mixing the first, second, and third solutions to provide a II-VI-VI SCN precursor solution.

[0059] In some embodiments, the fatty acid is oleic acid.

[0060] In some embodiments, the temperature is between about 270°C and 330°C.

[0061] Some embodiments provide II-VI-VI semiconductor nanocrystals made according to the methods disclosed herein.

[0062] Some embodiments provide a II-VI-VI semiconductor nanocrystal that includes Cd, S and Se, where in the nanocrystal has been modified by a zinc alkyl carboxylate pH controller.

[0063] Some embodiments provide a method of tuning a II-VI-VI semiconductor nanocrystal of known emission wavelength, the method includes: providing a II-VI-VI semiconductor nanocrystal having a known emission wavelength; heating the II-VI-VI semiconductor nanocrystal in a solution that includes a pH controller, one or more C12 to C20 hydrocarbons and one or more fatty acids to form an SCN solution; adding a solution that includes dialkyl zinc, hexaalkyldisilathiane and trialkylphosphine; and heating to a temperature sufficient to produce a capped II-VI-VI semiconductor nanocrystal; where the amount of pH controller is adjusted to provide a predetermined emission wavelength shift from the known emission wavelength of the II-VI-VI semiconductor nanocrystal.

[0064] In some embodiments, the C12 to C20 hydrocarbons are one or more selected from hexadecene, octadecene, eicosene, hexadecane, octadecane and icosane.

[0065] In some embodiments, the fatty acids are one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0066] In some embodiments, the pH controller is an oxide or carboxylic acid salt of a Group II element.

[0067] In some embodiments, the pH controller is selected from zinc salts of acetic acid, citric acid, lactic acid, propionic acid, butyric acid, tartaric acid, and valeric acid.

[0068] In some embodiments, the dialkyl zinc is dimethyl zinc, the hexaalkyldisilathiane is hexamethyldisilathiane and the trialkylphosphine is trioctylphosphiine.

[0069] In some embodiments, the temperature is between about 150° C and about 350° C.

[0070] Some embodiments provide a tuned II-VI-VI semiconductor nanocrystal made according to the methods disclosed herein.

[0071] Some embodiments provide a capped II-VI-VI semiconductor nanocrystal that includes: a core that includes a II-VI-VI semiconductor nanocrystal containing Cd, S and Se, wherein the nanocrystal has been modified by a zinc alkylcarboxylate; and a cap layer chosen from a layer containing ZnS, a layer containing A1203, and a multi layer cap that includes a first layer containing ZnS and a second layer containing A1203. [0072] Some embodiments provide a cadmium free "Cd-free" semiconductor nanocrystal that includes 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.

[0073] In some embodiments, the semiconductor nanocrystal does not contain cadmium.

[0074] In some embodiments, the Cd-free nanocrystal has an emission wavelength in the near ultra violet to far infrared range.

[0075] Some embodiments provide methods for synthesizing Cd- free semiconductor nanocrystals. The methods include: heating a precursor solution containing 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 together comprising one or more C12 to C20 hydrocarbons, one or more fatty acids and optionally one or more Cl to C22 alkyl thiols to a temperature sufficient to produce the Cd-free semiconductor nanocrystals.

[0076] In some embodiments, the Group II elements are one or more selected from Cu, Zn and Hg.

[0077] In some embodiments, the Group III elements are one or more selected from In, Ga, Al, and Tl.

[0078] In some embodiments, the Group VI elements are one or more selected from S, Se, Te, Po, and O.

[0079] In some embodiments, the C12 to C20 hydrocarbons are one or more selected from hexadecene, octadecene, cicosene, hexadecane, octadecane and icosane.

[0080] In some embodiments, the fatty acids are one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-Linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0081] In some embodiments, the fatty acid is oleic acid.

[0082] In some embodiments, the temperature is between about

270° C. and about 330° C. [0083] Some embodiments provide Cd-free semiconductor nanocrystals made according to the methods disclosed herein.

[0084] Some embodiments provide a Cd-free semiconductor nanocrystal that has been modified by a zinc alkylcarboxylate.

[0085] Some embodiments provide methods of capping a Cd-free semiconductor nanocrystal that includes: providing a Cd-free semiconductor nanocrystal; heating the Cd-free semiconductor nanocrystal in a solution containing one or more C12 to C20 hydrocarbons and one or more fatty acids to form an SCN solution; adding a solution containing dialkyl zinc, hexaalkyldisilathiane and trialkylphosphine; and heating to a temperature sufficient to produce a capped Cd-free semiconductor nanocrystal.

[0086] In some embodiments, the C12 to C20 hydrocarbons are one or more selected from hexadecene, octadecene, cicosene, hexadecane, octadecane and icosane.

[0087] In some embodiments, the fatty acids are one or more selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a-Linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and arachidic acid.

[0088] In some embodiments, the dialkyl zinc is dimethyl zinc, the hexaalkyldisilathiane is hexamethyldisilathiane and the trialkylphosphine is trioctylphosphine.

[0089] In some embodiments, the temperature is between about 150° C and about 350° C.

[0090] Some embodiments provide a capped Cd-free semiconductor nanocrystal including: a core containing a Cd-free semiconductor nanocrystal including a core of one or more group II elements, one or more group III elements, and one or more group VI elements, where the semiconductor nanocrystal is substantially free of cadmium, where the nanocrystal has been modified by a zinc alkylcarboxylate; a cap layer chosen from a layer containing ZnS and a layer containing A1203. [0091] In embodiments of the disclosure, the surface of a NAAO membrane is coated with quantum dots, which can be any described herein and/or derived from semiconductor nanocrystals or SCNs described herein. The quantum dots can be substantially evenly dispersed in transparent silica (glass).

[0092] In some embodiments, the quantum dots can be substantially evenly dispersed in a transparent polymer and coated onto the surface of the NAAO membrane.

[0093] In some embodiments, the pores of the NAAO membrane can be partially or completely filled with quantum dots dispersed in transparent silica or polymer.

[0094] A non-limiting example of Nanoporous Anodic Aluminum Oxide (NAAO) membranes useful in the disclosures herein is shown in FIG. 1.

[0095] In embodiments of the disclosure, the pore size of the NAAO membrane can be at least about 40, in some cases at least about 50 and in other cases at least about 60 nanometers and can be up to about 500, in some cases about 450, in other cases about 400, in some instances about 350 and in other instances about 300 nanometers. Those skilled in the art can chose an NAAO membrane pore size appropriate for the desired end use application. The NAAO membrane pore size can be any value or range between any of the values recited above.

[0096] In embodiments of the disclosure, the membrane thicknesses of the NAAO membrane can be at least about 10, in some cases at least about 20 and in other cases at least about 30 microns and can be up to about 250, in some cases about 200, in other cases about 175, in some instances about 150 and in other instances about 100 microns. Those skilled in the art can chose an NAAO membrane thickness appropriate for the desired end use application. The NAAO membrane thickness can be any value or range between any of the values recited above.

[0097] In embodiments of the disclosure, the pore size of the NAAO membrane can extend in the z direction at least 25%, in some cases at least 35%, and in other cases at least 45% of the width of the membrane and can extend up to 100%, in other cases up to 90%, and In other cases up to 80% of the width of the membrane. In embodiments, the portion less than 100% can contain clear A1203. Those skilled in the art can chose an NAAO membrane with pore depths in the z direction appropriate for the desired end use application. The NAAO membrane z direction pore depth can be any value or range between any of the values recited above.

[0098] In embodiments, structures containing quantum dots and NAAO membranes as described herein can have high light scattering properties for light sources emanating from a direction parallel to the long axis of the pores. In aspects of the disclosure, photoluminescent emissions of quantum dots applied to NAAO membranes as described herein have been observed.

[0099] In embodiments of the disclosure, structures containing quantum dots and NAAO membranes as described herein can have a difference in refractive index between the NAAO membrane and the applied quantum dot containing media, in many cases a glass or polymer. In these embodiments, light scattering of energizing light is maximized in the x and y directions. In these embodiments, photon hits on the quantum dots from the energizing light is maximized.

[0100] In embodiments of the disclosure, when the quantum dots are embedded in the cylindrical or hollow cylinders in the NAAO membranes, the quantum dot containing media can have a different refractive index than the supporting structure of the NAAO membrane and is oriented in the z direction (parallel to the pore axis). Emitted light from the quantum dots can be maximized in the z direction. In these embodiments photon hits can be maximized and light extraction in the preferred z direction can be improved. A benefit of these embodiments can be that the quantum dots can be sealed in a protective matrix within the structure.

[0101] In embodiments of the disclosure, the refractive index of the NAAO membrane can be at least about 1.6, in some cases at least about 1.65 and in other cases at least about 1.7 and can be up to about 1.9, in some cases about 1.85, in other cases about 1.8. Those skilled in the art can chose an NAAO membrane with a refractive index appropriate for the desired end use application. The NAAO membrane refractive index can be any value or range between any of the values recited above.

[0102] In embodiments of the disclosure, the refractive index of the applied quantum dot containing media can be at least about 1.4, in some cases at least about 1.45 and in other cases at least about 1.5 and can be up to about 1.65, in some cases about 1.6, in other cases about 1.55. Those skilled in the art can chose a quantum dot containing media with a refractive index appropriate for the desired end use application. The quantum dot containing media refractive index can be any value or range between any of the values recited above.

[0103] In some embodiments, the quantum dots are selected from core-shell quantum dots, Cd-free quantum dots, and stoichiometrically tuned quantum dots.

[0104] In some embodiments, the outermost layer of the quantum dots is selected from a capping layer and a passivation layer.

[0105] In some embodiments, the outermost layer is a ZnS capping layer.

[0106] In some embodiments, the outermost layer is an A1203 passivation layer.

[0107] In some embodiments, the quantum dot containing media includes quantum dots described herein and a polymer material that includes an acrylate resin containing units derived from polymerizing one or monomers according to the formula: where R1 is hydrogen or methyl and R2 is chosen from 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. [0108] In embodiments, the acrylic glass can include the acrylate resins described herein.

[0109] In embodiments, the quantum dot containing media provide a quantum dot containing polymer resin that contains a plurality of quantum dots each having an A1203 passivation layer; a polymer material cross- linked to the A1203 passivation layer, where the bond dissociation energy between the polymer material and the A1203 is greater than the energy required to reach the melt temperature of the cross-linked polymer.

[0110] Some embodiments of the quantum dot containing media include a quantum dot containing polymer resin that includes: a homogenous plurality of multicolor, same-sized alloy-gradient quantum dots each having a ZnS capping layer and an A1203 passivation layer: a polymer material cross-linked to the A1203 passivation layer, where the bond dissociation energy between the polymer material and the A1203 is greater than the energy required to reach the melt temperature of the crosslinked polymer.

[0111] Many embodiments relate to semiconductor nanocrystals that can be tuned to predetermined emission wavelengths.

[0112] In particular embodiments, the nanocrystalline particles have an emission wavelength in the near ultraviolet (UV) to far infrared (IR) range, and in particular, the visible range. More particularly, the quantum dots have an emission wavelength that can be from about 350 to about 750 nm.

[0113] Other embodiments provide a method for synthesizing semiconductor core shell nanoparticles that includes synthesizing a Cd-free semiconductor nanocrystal as described above, and coating it with a semiconductor shell with higher bandgap to improve the quantum efficiency and stability compared with the Cd-free semiconductor nanocrystals by themselves.

[0114] Further embodiments provide a method for synthesizing a Cd-free semiconductor nanocrystal having a semiconductor shell as described above and a second shell that acts as an insulator. [0115] In embodiments, the quantum dot cores have a similar surface area across the visible range. In some embodiments, the Cd-free quantum dots can be used in the methods described herein. Any Cd-free quantum dot can be used in the embodiments and aspects of this disclosure. In particular embodiments, the Cd-free quantum dots described in WO 2017/201465 are well-suited for use with the methods and applications disclosed herein.

[0116] In embodiments of the disclosure, core passivation can provide both confinement of the exciton wavefunction to the core and a physical barrier to water and oxygen.

[0117] In embodiments of the disclosure, the quantum dot containing media provides separation in space for the individual quantum dots to provide a stable electronic configuration outside the quantum dot volume that is conducive to photoluminescence, while itself being stable against photodegradation.

[0118] Combining these embodiments into usable materials can accelerate the acceptance of quantum dot based components for display and lighting applications.

The Core

[0119] It is a basic property of metal and semiconductor materials that their propensity for chemical reactions increases with an increase in surface area to mass. Thus, a 1cm cube of metal will simply heat up when exposed to flame while that same mass will ignite if ground to a micron sized powder. The same is true of QD cores with respect to environmental degradation and photodegradation. Quantum dots tuned by core size will differentially degrade due to the increased reactivity of smaller cores (blue- green emitters) versus larger cores (yellow-red emitters) because of a higher surface area to mass ratio. This is true in both situations of environmental attack by water and oxygen and under conditions of high photon flux where destructive free radicals are created on the QD surface. At the surface of quantum dots, there is a population of atoms that are incompletely part of the periodic three dimensional crystal lattice of the interior. These atoms have vacant or lone-pair electron orbitals. These dangling bonds are the source of undesired chemical reactions both with the external environment and in non-radiative carrier relaxation processes during the photoluminescent emission cycle in which electrons pool at these sites instead of recombining with a hole. This effect is magnified with smaller quantum dots that have a higher surface area/mass ratio than larger quantum dots.

[0120] Thus, in an optical device composed of multi-colored size- tuned quantum dots, it is likely that faster degradation of the quantum dots emitting at the low blue end of the visible spectrum will be observed over time, especially under conditions of exposure to water and oxygen combined with high photon flux. It is desirable to have all quantum dot cores in an optoelectronic device be of similar size.

[0121] This desired core configurations can be achieved by using quantum dots synthesized by the methods of Nie (US 7,981,667 and US 8,420,155) and Qu (US 8,454,927). These QDs are tuned by composition and not by size.

[0122] While same color size-tunable dots could be used, when considering the entire visible range, stoichiometrically-tuned quantum dots advantageously have the same size regardless of emission wavelength. Stoichiometrically-tuned quantum dots can be made in accordance with the Nie and Qu patents discussed above or other available methods. An improved method, involving the use of a pH controller to fine tune the emission wavelength is disclosed in International Patent Publication WO 2017/201465 Al, the relevant disclosure of which is incorporated herein by reference. Quantum dots made by the methods disclosed therein result in core/shell quantum dots having substantially the same size regardless of emission wavelength.

Capping (i.e. first passivation layer!

[0123] In embodiments, there are two methods to passivate the dangling bonds on the surface of quantum dots for higher quantum efficiency (QE) and improved photo/chemical stability: 1) passivating with low MW organic ligands or 2) passivating with inorganic shells. Passivation with organic ligands is simple and straightforward but the surface metal-organic ligands bond is relatively unstable and can be broken and displaced by chemical and/or photochemical reactions.

[0124] Passivation with inorganic shells is embodied by the well- known core-shell type of quantum dots, and is often referred to as "capping" such as with a ZnS shell. The surface passivation of QD cores with inorganic shells is more stable and has the additional desired effect of providing better confinement of the exciton wavefunction to the core, thus increasing QE. If a QD core is located within a shell material with a larger bandgap energy, the electron and hole wavefunctions are better confined to the core. The recombination probability of the two wavefunctions (electron and hole) increases while the non-radiative decay process via interaction with dangling bonds on the surface decreases.

[0125] These core-shell structures are improved with respect to QE and photostability (PS) but are still susceptible to chemical attack by water and oxygen from the environment.

[0126] This capping is present in traditional core-shell quantum dots, and can be applied to a number of quantum dots, including the Cd- Free quantum dots and stoichiometrically/pH controller tuned quantum dots.

Passivation (second layer)

[0127] In embodiments, it is desirable to provide a second shell of an even wider bandgap material over the first shell that would further confine the exciton wavefunction, 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. In embodiments, this can be realized by adding a second shell, a passivation layer, of A1203 as described in U.S. Patent No. 9.425.253, the relevant portions of which are hereby incorporated by reference. The bandgap of AI203 is between -3.5 and -11 which encompass the commonly used II-VI and Ill-V QD core and shell materials.

[0128] In addition to having a bandgap energy that encompasses the commonly used QD core-shell materials, A1203, at a thickness of 4-5 atomic layers, has the additional property of providing an absolute or near-absolute barrier to the diffusion of oxygen and water. This provides a high barrier of protection from chemical attack by water and oxygen on the sensitive core shell semiconductor materials.

[0129] In some embodiments, a core-shell quantum dot containing a coating a traditional CdSe/ZnS core-shell quantum dot with an A1203 passivation layer can be used in aspects of the disclosure.

Application of Quantum Dots to NAAO Membranes

[0130] In embodiments, the surface of the NAAO membrane as described above can be coated with any of the quantum dots described above such that they are substantially evenly dispersed in a glass. In some embodiments, the glass is a silica glass or an acrylic glass.

[0131] In embodiments, the surface of the NAAO membrane as described above can be coated with any of the quantum dots described above such that they are substantially evenly dispersed in a transparent polymer. In some embodiments, the transparent polymer can be an acrylate resin.

[0132] In embodiments, the pores of the NAAO structure are partially or completely filled with any of the quantum dots described above. In some embodiments, the quantum dots can be dispersed in a glass or transparent polymer described above. In these structures, there is a difference in refractive index between the NAAO membrane (as described above) and the coating or filling media (as described above).

[0133] In embodiments, this structure has a very high surface area per volume. This structure has high light scattering properties for light sources emanating from a direction parallel to the long axis of the NAAO membrane pores.

[0134] In embodiments, photoluminescent emission of quantum dots coated onto the surface of NAAO membranes occurs.

[0135] In embodiments, light scattering of energizing light is maximized in the x and y directions. This maximizes photon hits on the quantum dots from the energizing light. The quantum dots are embedded in a cylindrical or hollow cylinder material that has a different refractive index than the supporting structure and is oriented in the z direction (parallel to the pore axis). Emitted light from the quantum dots can be maximized in the z direction. Photon hits are maximized and light extraction in the preferred z direction can be improved. Additionally, the quantum dots are sealed in a protective matrix within the structure.

Processing

[0136] In embodiments, NAAO membrane discs as described above are dispersed in a dispersion of colloidal silica and quantum dots in an organic solvent and treated to remove any entrapped air. The resulting coated discs are cured at a temperature and time sufficient condense the silica matrix via the reaction depicted in FIG. 2.

[0137] In embodiments, NAAO membrane discs as described above are dispersed in a dispersion of a molten acrylic glass and quantum dots and treated to remove any entrapped air. The resulting coated discs are cured at a temperature and time sufficient to allow the acrylic glass to harden, encapsulating the quantum dot coated NAAO membrane.

[0138] In embodiments, NAAO membrane discs as described above are dispersed in a dispersion of a silica matrix, molten glass or acrylate resin and quantum dots and treated to remove any entrapped air and partially or substantially completely fill the voids or columns in the NAAO membrane. The resulting coated discs are cured at a temperature and time sufficient to allow the molten glass or acrylate resin to harden and/or cure, encapsulating the quantum dot filled NAAO membrane.

[0139] In embodiments, entrapped air can be removed using any suitable deaeration methods known in the art. Suitable methods include, but are not limited to sonication, membrane degasification, ultrasonic degassing, vacuum cycles, pressurization, centrifugation and combinations thereof.

[0140] In embodiments, the amount of quantum dots dispersed in a continuous phase, non-limiting examples including a silica matrix, a glass and an acrylate resin, can be at least about 1 , in some cases at least about 2 and in other cases at least about 3 mg QD/gram continuous phase and can be up to about 100, in some cases up to about 75, in other cases up to about 50, in some instances up to about 25 and in other instance up to about 10 mg QD/gram continuous phase. The amount of quantum dots dispersed in the continuous phase will vary based on the particular quantum dots, continuous phase, NAAO membrane and targeted end use. The amount of quantum dots dispersed in the continuous phase can be any value or range between any of the values recited above.

[0141] Aspects of this disclosure relate to semiconductor nanocrystals tuned to a predetem lined emission wavelength (i.e. a quantum dot). In some instances, the quantum dots may be a plurality of quantum dots containing a range of predetermined emission wavelengths. Particularly, in some embodiments, a plurality of quantum dots contains a homogenous mixture of quantum dots emitting a desired plurality of desired wavelengths.

[0142] Aspects of the present disclosure relate to films and 3-D structures comprising core/shell quantum dot particles dispersed in a glass or acrylate resin applied to a NAAO membrane as described herein. The films and 3-D structures provide the ability place 3-D structures onto commercially applicable equipment resulting in highly stable quantum dot - NAAO membrane composite films and 3D structures.

[0143] The disclosed films and 3-D structures can be used in display and lighting applications. In particular aspects, a single-coat down- conversion fil m (SCDCF) that includes a single layer of the quantum dot - NAAO membrane composite film, sandwiched between at least two transparent films and 3-D structures can be used. The single and multilayer films and 3-D structures enable a simpler and more cost effective product that provides at least the performance of more complicated structures.

[0144] The present disclosure will further be described 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.

Examples

[0145] NAAO membranes with a thickness of 50 microns and pore diameter of 200 nm were obtained from Whatman (Maidstone, UK).

SapphireTM quantum dots (Crystalplex, Pittsburgh, PA) were dispersed in a 30% dispersion of colloidal silica (10-15 nm particles) in toluene (Nissan Chemicals, Tokyo Japan) at a concentration of 5 mg QD/gram silica. 10% tetraethyl orthosilicate (Gelest, Morrisville, PA) was added and to the dispersion and the resultingl3 mm discs of the NAAO membranes were sonicated in this dispersion for 30 seconds to remove entrapped air. The discs were cured at 85°C for 30 minutes to condense the silica matrix via the reaction shown in FIG. 2. The resulting discs demonstrated very bright green and red quantum dot emission with minimal transmission of blue light in the z direction.

[0146] The fact that the disclosure or examples above are directed to specific combinations of particular quantum dots, particular capping, particular passivation layers, and a particular NAAO membranes is not meant to suggest that this disclosure is limited to those particular combinations. The disclosure is exemplary, and not limiting, in nature. Those of skill in the art will recognize variations of the theme without departing from the scope and spirit of this disclosure.