Patent Publication Number: US-11029559-B2

Title: Nanostructure based display devices

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application incorporates by reference in their entirety U.S. Provisional Appl. No. 62/550,394, filed Aug. 25, 2017. 
    
    
     BACKGROUND OF THE INVENTION 
     Field 
     The present invention relates to display devices including phosphor films having luminescent nanostructures such as quantum dots (QDs). 
     Background 
     Luminescent nanostructures (NSs) such as quantum dots (QDs) represent a class of phosphors that have the ability to emit light at a single spectral peak with narrow line width, creating highly saturated colors. It is possible to tune the emission wavelength based on the size of the NSs. The NSs are used to produce a NS film that may be used as a color down conversion layer in display devices (e.g., liquid crystal display (LCD) device, organic light emitting diode (OLED) display device). The use of a color down conversion layer in emissive displays can improve the system efficiency by down-converting white light, blue light, or ultra-violet (UV) light to a more reddish light, greenish light, or both before the light passes through a color filter. This use of a color down conversion layer may reduce loss of light energy due to filtering. 
     NSs may be used as the conversion material due to their broad absorption and narrow emission spectra. Because, the density of NSs required for such application is very high in a very thin color down conversion layer of about 3 μm-6 μm, NSs prepared using current methods suffer from quenching of their optical properties when the NSs are closely packed next to each other in a thin NS film. As such, current NS-based display devices using NS films as color down conversion layers suffer from low quantum yield (QY). 
     One of the factors used to define the image quality of a display device is the color gamut coverage of standard RGB color spaces such as Rec. 2020, Rec. 709, DCI P3, NTSC, or sRGB provided by the display device.  FIG. 1  illustrates a definition of color gamut coverage of a display device. In  FIG. 1 , area  101  formed between 1976 CIE color coordinates  101   a - 101   c  represents the color gamut of a standard RGB color space (e.g., Rec. 2020) on the 1976 CIE u′-v′ chromaticity diagram  100 . Area  102  formed between 1976 CIE color coordinates  102   a - 102   c  represents the color gamut of the display device on the 1976 CIE u′-v′ chromaticity diagram  100 . Color gamut coverage of the display device may be defined as a ratio of the overlapping area  103  between areas  101  and  102  to area  101 . The wider the color gamut coverage of a display device, the wider is the range of colors identifiable by the human eye (i.e., the visible spectrum) rendered by the display device, and hence, improves the image quality of the display device assuming the other factors contributing to the image quality are optimized. 
     Current display devices suffer from a trade-off between achieving the desired brightness (e.g., brightness required by high dynamic range (HDR) imaging standards) and the desired color gamut coverage (e.g., greater than 85%) of the standard RGB color spaces. For example, some display devices suffer about 30% loss in brightness in order to achieve over 90% DCI P3 color gamut coverage. Hence, with current technology, loss of brightness in display devices would be significantly higher in order to achieve color gamut coverage of color spaces that are even wider than DCI P3 (e.g., Rec. 2020). 
     Another disadvantage suffered by current display devices is the leakage of unconverted light through conversion materials (e.g., NS films) of the display devices that negatively affects the color gamut coverage of the display devices. For example, some display devices suffer from leakage of unwanted blue light through their green and/or red pixels. This may occur when blue light incident on the conversion material from a blue light source is not fully absorbed and converted into green and/or red light by the conversion material. 
     SUMMARY 
     Accordingly, there is need for display devices with improved color gamut coverage and with less of a trade-off between achieving the desired color gamut coverage of the wide RGB color spaces and the desired brightness. 
     According to an embodiment, a display device includes a backlight unit having a light source and a liquid crystal display (LCD) module. The LCD module includes a phosphor film and a filter element. The phosphor film is configured to receive a primary light, from the light source, having a first peak wavelength and to convert a portion of the primary light to emit a secondary light having a second peak wavelength. The second peak wavelength is different from the first peak wavelength. The filter element is optically coupled to the phosphor film and is configured to allow the secondary light to pass through the filter element and to block an unconverted portion of the primary light from passing through the filter element. 
     According to an embodiment, a display device includes an organic light emitting diode (OLED), a phosphor film, and a filter element. The phosphor film is configured to receive a primary light, from the OLED, having a first peak wavelength and to convert a portion of the primary light to emit a secondary light having a second peak wavelength. The second peak wavelength is different from the first peak wavelength. The filter element is optically coupled to the phosphor film and is configured to allow the secondary light to pass through the filter element and to block an unconverted portion of the primary light from passing through the filter element. 
     According to an embodiment, a display device includes an array of pixels. A pixel of the array of the pixels includes a sub-pixel having a quantum dot film and a filter element. The QD film is configured to receive a primary light having a first peak wavelength and to convert a portion of the primary light to emit a secondary light having a second peak wavelength. The second peak wavelength is different from the first peak wavelength. The filter element is disposed on the quantum dot film and is configured to allow the secondary light to pass through the filter element and to block an unconverted portion of the primary light from passing through the filter element. 
     Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present embodiments and, together with the description, further serve to explain the principles of the present embodiments and to enable a person skilled in the relevant art(s) to make and use the present embodiments. 
         FIG. 1  is a CIE 1976 u′v′ chromaticity diagram of Rec. 2020 color gamut and a color gamut of a display device. 
         FIGS. 2-3  are exploded cross-sectional views of liquid crystal display (LCD) devices, according to an embodiment. 
         FIG. 4  is an exploded cross-sectional view of an organic light emitting diode (OLED) display device, according to an embodiment. 
         FIG. 5  is an exploded cross-sectional view of a pixel of an OLED display device, according to an embodiment. 
         FIG. 6  is a schematic of a cross-sectional view of a nanostructure, according to an embodiment. 
         FIG. 7  is a schematic of a nanostructure film, according to an embodiment. 
     
    
    
     The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Although specific configurations and arrangements may be discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the pertinent art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the present invention. It will be apparent to a person skilled in the pertinent art that this invention can also be employed in a variety of other applications beyond those specifically mentioned herein. It should be appreciated that the particular implementations shown and described herein are examples and are not intended to otherwise limit the scope of the application in any way. 
     It is noted that references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure or characteristic is described in connection with an embodiment, it would be within the knowledge of one skilled in the art to effect such feature, structure or characteristic in connection with other embodiments whether or not explicitly described. 
     All numbers in this description indicating amounts, ratios of materials, physical properties of materials, and/or use are to be understood as modified by the word “about,” except as otherwise explicitly indicated. 
     In embodiments, the term “display device” refers to an arrangement of elements that allow for the visible representation of data on a display screen. Suitable display screens may include various flat, curved or otherwise-shaped screens, films, sheets or other structures for displaying information visually to a user. Display devices described herein may be included in, for example, display systems encompassing a liquid crystal display (LCD), televisions, computers, mobile phones, smart phones, personal digital assistants (PDAs), gaming devices, electronic reading devices, digital cameras, tablets, wearable devices, car navigation systems, and the like. 
     The term “about” as used herein indicates the value of a given quantity varies by ±10% of the value. For example, “about 100 nm” encompasses a range of sizes from 90 nm to 110 nm, inclusive. 
     The term “substantially” as used herein indicates the value of a given quantity varies by ±1% to ±5% of the value. 
     In embodiments, the term “forming a reaction mixture” or “forming a mixture” refers to combining at least two components in a container under conditions suitable for the components to react with one another and form a third component. 
     In embodiment, the terms “light guide plate,” “light guide,” and “light guide panel” are used interchangeably and refer to an optical component that is suitable for directing electromagnetic radiation (light) from one position to another. 
     In embodiments, the term “optically coupled” means that components are positioned such that light is able to pass from one component to another component without substantial interference. 
     The term “nanostructure” as used herein refers to a structure having at least one region or characteristic dimension with a dimension of less than about 500 nm. In some embodiments, the nanostructure has a dimension of less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 20 nm, or less than about 10 nm. Typically, the region or characteristic dimension will be along the smallest axis of the structure. Examples of such structures include nanowires, nanorods, nanotubes, branched nanostructures, nanotetrapods, tripods, bipods, nanocrystals, nanodots, QDs, nanoparticles, and the like. Nanostructures can be, e.g., substantially crystalline, substantially monocrystalline, polycrystalline, amorphous, or a combination thereof. In some embodiments, each of the three dimensions of the nanostructure has a dimension of less than about 500 nm, less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 20 nm, or less than about 10 nm. 
     The term “QD” or “nanocrystal” as used herein refers to nanostructures that are substantially monocrystalline. A nanocrystal has at least one region or characteristic dimension with a dimension of less than about 500 nm, and down to the order of less than about 1 nm. The terms “nanocrystal,” “QD,” “nanodot,” and “dot,” are readily understood by the ordinarily skilled artisan to represent like structures and are used herein interchangeably. The present invention also encompasses the use of polycrystalline or amorphous nanocrystals. 
     The term “heterostructure” when used with reference to nanostructures refers to nanostructures characterized by at least two different and/or distinguishable material types. Typically, one region of the nanostructure comprises a first material type, while a second region of the nanostructure comprises a second material type. In certain embodiments, the nanostructure comprises a core of a first material and at least one shell of a second (or third etc.) material, where the different material types are distributed radially about the long axis of a nanowire, a long axis of an arm of a branched nanowire, or the center of a nanocrystal, for example. A shell can but need not completely cover the adjacent materials to be considered a shell or for the nanostructure to be considered a heterostructure; for example, a nanocrystal characterized by a core of one material covered with small islands of a second material is a heterostructure. In other embodiments, the different material types are distributed at different locations within the nanostructure; e.g., along the major (long) axis of a nanowire or along a long axis of arm of a branched nanowire. Different regions within a heterostructure can comprise entirely different materials, or the different regions can comprise a base material (e.g., silicon) having different dopants or different concentrations of the same dopant. 
     As used herein, the term “diameter” of a nanostructure refers to the diameter of a cross-section normal to a first axis of the nanostructure, where the first axis has the greatest difference in length with respect to the second and third axes (the second and third axes are the two axes whose lengths most nearly equal each other). The first axis is not necessarily the longest axis of the nanostructure; e.g., for a disk-shaped nanostructure, the cross-section would be a substantially circular cross-section normal to the short longitudinal axis of the disk. Where the cross-section is not circular, the diameter is the average of the major and minor axes of that cross-section. For an elongated or high aspect ratio nanostructure, such as a nanowire, the diameter is measured across a cross-section perpendicular to the longest axis of the nanowire. For a spherical nanostructure, the diameter is measured from one side to the other through the center of the sphere. 
     The terms “crystalline” or “substantially crystalline,” when used with respect to nanostructures, refer to the fact that the nanostructures typically exhibit long-range ordering across one or more dimensions of the structure. It will be understood by one of skill in the art that the term “long range ordering” will depend on the absolute size of the specific nanostructures, as ordering for a single crystal cannot extend beyond the boundaries of the crystal. In this case, “long-range ordering” will mean substantial order across at least the majority of the dimension of the nanostructure. In some instances, a nanostructure can bear an oxide or other coating, or can be comprised of a core and at least one shell. In such instances it will be appreciated that the oxide, shell(s), or other coating can but need not exhibit such ordering (e.g. it can be amorphous, polycrystalline, or otherwise). In such instances, the phrase “crystalline,” “substantially crystalline,” “substantially monocrystalline,” or “monocrystalline” refers to the central core of the nanostructure (excluding the coating layers or shells). The terms “crystalline” or “substantially crystalline” as used herein are intended to also encompass structures comprising various defects, stacking faults, atomic substitutions, and the like, as long as the structure exhibits substantial long range ordering (e.g., order over at least about 80% of the length of at least one axis of the nanostructure or its core). In addition, it will be appreciated that the interface between a core and the outside of a nanostructure or between a core and an adjacent shell or between a shell and a second adjacent shell may contain non-crystalline regions and may even be amorphous. This does not prevent the nanostructure from being crystalline or substantially crystalline as defined herein. 
     The term “monocrystalline” when used with respect to a nanostructure indicates that the nanostructure is substantially crystalline and comprises substantially a single crystal. When used with respect to a nanostructure heterostructure comprising a core and one or more shells, “monocrystalline” indicates that the core is substantially crystalline and comprises substantially a single crystal. 
     The term “ligand” as used herein refers to a molecule capable of interacting (whether weakly or strongly) with one or more faces of a nanostructure, e.g., through covalent, ionic, van der Waals, or other molecular interactions with the surface of the nanostructure. 
     The term “quantum yield” (QY) as used herein refers to the ratio of photons emitted to photons absorbed, e.g., by a nanostructure or population of nanostructures. As known in the art, quantum yield is typically determined by a comparative method using well-characterized standard samples with known quantum yield values. 
     The term “primary emission peak wavelength” as used herein refers to the wavelength at which the emission spectrum exhibits the highest intensity. 
     The term “full width at half-maximum” (FWHM) as used herein refers to refers to a measure of spectral width. In the case of an emission spectrum, a FWHM can refer to a width of the emission spectrum at half of a peak intensity value. 
     The term Forster radius used herein is also referred as Forster distance in the art. 
     The terms “luminance” and “brightness” are used herein interchangeably and refer to a photometric measure of a luminous intensity per unit area of a light source or an illuminated surface. 
     The terms “specular reflectors,” “specularly reflective surfaces,” and “reflective surfaces” are used herein to refer to elements, materials, and/or surfaces capable of specular reflection. 
     The term “specular reflection” is used herein to refer to a mirror-like reflection of light (or of other kinds of wave) from a surface, when an incident light hits the surface. 
     The term “nanostructure (NS) film” is used herein to refer to a film having luminescent nanostructures. 
     The term “red sub-pixel” is used herein to refer to an area of a pixel that emits light having a primary emission peak wavelength in the red wavelength region of the visible spectrum. In some embodiments, the red wavelength region may include wavelengths ranging from about 620 nm to about 750 nm. 
     The term “green sub-pixel” is used herein to refer to an area of a pixel that emits light having a primary emission peak wavelength in the green wavelength region of the visible spectrum. In some embodiments, the green wavelength region may include wavelengths ranging from about 495 nm to about 570 nm. 
     The term “blue sub-pixel” is used herein to refer to an area of a pixel that emits light having a primary emission peak wavelength in the blue wavelength region of the visible spectrum. In some embodiments, the blue wavelength region may include wavelengths ranging from about 435 nm to about 495 nm. 
     The term “emissive surface of a sub-pixel” is used herein to refer to a surface of a topmost layer of the sub-pixel from which light is emitted towards a display screen of a display device. 
     The published patents, patent applications, websites, company names, and scientific literature referred to herein are hereby incorporated by reference in their entirety to the same extent as if each was specifically and individually indicated to be incorporated by reference. Any conflict between any reference cited herein and the specific teachings of this specification shall be resolved in favor of the latter. Likewise, any conflict between an art-understood definition of a word or phrase and a definition of the word or phrase as specifically taught in this specification shall be resolved in favor of the latter. 
     Technical and scientific terms used herein have the meaning commonly understood by one of skill in the art to which the present application pertains, unless otherwise defined. Reference is made herein to various methodologies and materials known to those of skill in the art. 
     Overview 
     This disclosure provides various embodiments of nanostructure-based display devices that help to improve or eliminate existing trade-offs between achieving the desired brightness and the desired color gamut in display devices. These various embodiments also help to improve display performance such as color gamut coverage of the nanostructure-based display devices by reducing or substantially eliminating leakage of unwanted light through one or more pixels of the display devices. 
     Example Embodiments of a Liquid Crystal Display (LCD) Device 
       FIG. 2  illustrates a schematic of an exploded cross-sectional view of an LCD display device  200 , according to an embodiment. A person of ordinary skill in the art will recognize that the view of display device in  FIG. 2  is shown for illustration purposes and may not be drawn to scale. LCD display device  200  may include a backlight unit (BLU)  202  and an LCD module  204 , according to an embodiment. 
     BLU  202  may include an optical cavity  212  and an array of LEDs  210  (e.g., white LEDs, blue LEDs, or a combination thereof) coupled to optical cavity  212 . Optical cavity  212  may include a top side  203 , a bottom side  205 , sidewalls  207 , and a closed volume confined by top side  203 , bottom side  205 , and sidewalls  207 . LEDs  210  may be coupled to a top surface  205   a  of bottom side  205  within the closed volume. LEDs  210  may be configured to provide a primary light (e.g., a blue light, or a white light) that may be processed through LCD module  204  and subsequently, transmitted to and distributed across a display screen  230  of LCD display device  200 . In some embodiments, LEDs  210  may comprise blue LEDs that emit in the range from about 440 nm to about 470 nm. In some embodiments, LEDs  210  may comprise white LEDs that emit in the range from about 440 nm to about 700 nm or other possible light wavelength ranges. In an embodiment, the array of LEDs  210  may comprise a two-dimensional array of LEDs that are spread across an area of top surface  205   a  and the area may be equal to the surface area of display screen  230 . 
     It should be noted that even though two sidewalls  207  are shown in  FIG. 2 , a person skilled in the art would understand that optical cavity  212  may include any number of sidewalls  207 , according to various embodiments. For example, optical cavity  212  may have a cuboid shape and may include four sidewalls similar to sidewalls  207 . Optical cavity  212  is not restricted to being cuboid in shape or having other straight-sided shapes. Optical cavity  212  may be configured to be any type of geometric shape, such as but not limited to cylindrical, trapezoidal, spherical, or elliptical, according to various embodiments, without departing from the spirit and scope of the present invention. It should also be noted that the rectangular cross-sectional shape of optical cavity  212 , as illustrated in  FIG. 2 , is for illustrative purposes, and is not limiting. Optical cavity  212  may have other cross-sectional shapes (e.g., trapezoid, oblong, rhomboid), according to various embodiments, without departing from the spirit and scope of the present invention. 
     Top side  203  of optical cavity  212  may be configured to be an optically diffusive and transmissive layer such that light from LEDs  210  may exit optical cavity  212  through top side  203  with a substantially uniform distribution of brightness across top surface  203   a  of top side  203 . In an embodiment, top side  203  may include optically transparent areas and optically translucent areas that are strategically arranged over LEDs  210  to provide the substantially uniform distribution in light brightness exiting top side  203 . In another embodiment, top side  203  may include pores of varying sizes in diameters and optically translucent areas that are strategically arranged to provide the substantially uniform distribution in light brightness exiting top side  203 . 
     Bottom side  205  and/or sidewalls  207  may be constructed from one or more materials (e.g., metals, non-metals, and/or alloys) that are configured to have specularly reflective top surface  205   a  and/or specularly reflective side wall interior surfaces  207   a , respectively. For example, top surface  205   a  and/or side wall interior surfaces  207   a  may be mirror-like surfaces having mirror-like reflection properties. In some embodiments, top surface  205   a  and/or side wall interior surfaces  207   a  may be completely specularly reflective or partially specularly reflective and partially scattering. In some other embodiments, top surface  205   a  and/or side wall interior surfaces  207   a  include diffuse reflectors. 
     In alternate embodiments, optical cavity  212  may include specular reflectors  209  coupled to sidewall interior surfaces  207   a . Specular reflectors  209  may be coupled to sidewall interior surfaces  207   a  using optically transparent adhesive. The optically transparent adhesive may comprise tape, various glues, polymeric compositions such as silicones, etc. Additional optically transparent adhesive may include various polymers, including, but not limited to, poly(vinyl butyral), poly(vinyl acetate), epoxies, and urethanes; silicone and derivatives of silicone, including, but not limited to, polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane, fluorinated silicones and vinyl and hydride substituted silicones; acrylic polymers and copolymers formed from monomers including, but not limited to, methylmethacrylate, butylmethacrylate, and laurylmethacrylate; styrene based polymers; and polymers that are cross linked with difunctional monomers, such as divinylbenzene, according to various examples. 
     Specularly reflective top surface  205   a  and side wall interior surfaces  207   a  and specular reflectors  209  may substantially minimize absorption of light from LEDs  210  through bottom side  205  and/or side walls  207  and thus, substantially minimize loss of luminance within optical cavity  212  and increase light output efficiency of BLU  202 . 
     In alternate embodiments, BLU  202  may further include one or more brightness enhancement films (BEFs) (not shown) disposed between optical cavity  212  and LCD module  204 . The one or more BEFs may have reflective and/or refractive films, reflective polarizer films, light extraction features, light recycling features, prism films, groove films, grooved prism films, prisms, pitches, grooves, or other suitable brightness enhancement features. The brightness-enhancing features of BEFs may be configured to reflect a portion of the primary light (e.g., blue light from optical cavity  212 ) back toward optical cavity  212 , thereby providing recycling of the primary light. 
     LCD module  204  may be configured to process the light received from BLU  202  to desired characteristics for transmission to and distribution across display screen  230 . In some embodiments, LCD module  204  may include one or more polarizing filters, such as first and second polarizing filters  214  and  222 , one or more optically transparent substrates such as first and second optically transparent substrates  216  and  228 , switching devices  218 . 1  through  218 . 6  arranged in a 2-D array on first substrate  216 , a liquid crystal (LC) solution layer  220 , a plurality of pixels such as pixels  224 . 1  and  224 . 2  arranged in a 2-D array, and display screen  230 . 
     In some embodiments, pixel  224 . 1  may include sub-pixels  226 . 1  through  226 . 3  and pixel  224 . 2  may include sub-pixels  226 . 4  through  226 . 6 . In some embodiments, each of pixels  224 . 1  and  224 . 2  may be tri-chromatic, for example, having red sub-pixels  226 . 1  and  226 . 4 , green sub-pixels  226 . 2  and  226 . 5 , and blue sub-pixels  226 . 3  and  226 . 6 , respectively. 
     The term “red sub-pixel” is used herein to refer to an area of a pixel that emits light having a primary emission peak wavelength in the red wavelength region of the visible spectrum. In some embodiments, the red wavelength region may include wavelengths ranging from about 620 nm to about 750 nm. The term “green sub-pixel” is used herein to refer to an area of a pixel that emits light having a primary emission peak wavelength in the green wavelength region of the visible spectrum. In some embodiments, the green wavelength region may include wavelengths ranging from about 495 nm to about 570 nm. The term “blue sub-pixel” is used herein to refer to an area of a pixel that emits light having a primary emission peak wavelength in the blue wavelength region of the visible spectrum. In some embodiments, the blue wavelength region may include wavelengths ranging from about 435 nm to about 495 nm. 
     The arrangement order of red, green, and blue sub-pixels  226 . 1  through  226 . 6  in respective pixels  224 . 1  and  224 . 2  is illustrative and is not limiting. The red, green, and blue sub-pixels in each of pixels  224 . 1  and  224 . 2  may be arranged in any order with respect to each other. In some embodiments, pixels  224 . 1  and/or  224 . 2  may be monochromatic having either red, green, or blue sub-pixels  226 . 1  through  226 . 6 . The number of pixels and switching devices shown in  FIG. 2  are illustrative and are not limiting. LCD module  204  may have any number of switching devices and pixels without departing from the spirit and scope of this disclosure. 
     Light from BLU  202  may be polarized through first polarizing filter  214  and the polarized light may be transmitted to LC solution layer  220 . LC solution layer  220  may include LCs  232  having rod-shaped molecules that may act as shutters to control the amount of light transmission from LC solution layer  220 . In some embodiments, LCs  232  may be arranged in a 3-D array. Columns  234 . 1  through  234 . 6  of the 3-D array of LCs may be independently controlled by respective switching devices  218 . 1  through  218 . 6 . In some embodiments, switching devices  218 . 1  through  218 . 6  may comprise transistors, such as, for example, thin film transistors (TFTs). By controlling LCs  232 , the amount of light travelling from columns  234 . 1  through  234 . 6  to respective sub-pixels  226 . 1  through  226 . 6  may be controlled, and consequently, the amount of light transmitting from sub-pixels  226 . 1  through  226 . 6  is controlled. 
     LCs  232  may be twisted to varying degrees depending on the voltage applied to columns  234 . 1  through  234 . 6  by respective switching devices  218 . 1  through  218 . 6 . By controlling the twisting of LCs  232 , the polarization angle of light passing through LC solution layer  220  may be controlled. Light leaving LC solution layer  220  may then pass through second polarizing filter  222  that may be positioned at 90 degrees with respect to first polarizing filter  214 . The angle of polarization of the light leaving LC solution layer  220  and entering second polarizing filter  222  may determine how much of the light is able to pass through and exit from second polarizing filter  222 . Second polarizing filter  222  may attenuate the light, block the light, or allow the light to pass without attenuation based on its angle of polarization. 
     Portions of light travelling through columns  234 . 1  through  234 . 6  of LCs and exiting out of second polarizing filter  222  may then enter respective ones of sub-pixels  226 . 1  through  226 . 6 . These portions of light may undergo a stage of color filtering through the respective ones of sub-pixels  226 . 1  through  226 . 6  to achieve the desired optical characteristics for light distribution across display screen  230 . In some embodiments, each of sub-pixels  226 . 1  through  226 . 6  may include a phosphor film  236  that may filter the portions of light entering sub-pixels  226 . 1  through  226 . 6 . 
     Phosphor films  236  may include luminescent nanostructures such as QDs (e.g., QD  600  described with reference to  FIG. 6 ), according to some embodiments. Phosphor films  236  may be down-converters, where the portions of light (also referred as primary light) entering the respective ones of sub-pixels  226 . 1  through  226 . 6  may be absorbed, for example, by the luminescent nanostructures in phosphor films  236  and re-emitted as secondary light having a lower energy or longer wavelength than the primary light. 
     In some embodiments, phosphor films  236  of red sub-pixels  226 . 1  and  226 . 4  may include luminescent nanostructures that absorb the primary light and emit a first secondary light having a primary emission peak wavelength in the red wavelength region of the visible spectrum light. In some embodiments, phosphor films  236  of green sub-pixels  226 . 2  and  226 . 5  may include luminescent nanostructures that absorb the primary light and emit a second secondary light having a primary emission peak wavelength in the green wavelength region of the visible spectrum light. In some embodiments, phosphor films  236  of blue sub-pixels  226 . 3  and  226 . 6  may include luminescent nanostructures that absorb the primary light and emit a third secondary light having a primary emission peak wavelength in the blue wavelength region of the visible spectrum light. In alternate embodiments, blue sub-pixels  226 . 3  and  226 . 6  may have non-phosphor films instead of phosphor films  236 . The non-phosphor films may exclude luminescent nanostructures such as QDs and may be optically transmissive to blue light when BLU  202  has blue LEDs  210 , as there is no need for down-conversion of primary light from blue LEDs  210  for blue sub-pixels  226 . 3  and  226 . 6 . In such alternate embodiments, instead of light blocking elements  238 , blue sub-pixels  226 . 3  and  226 . 6  may also have non-phosphor films that are optically transmissive to blue light. 
     In some embodiments, phosphor films  236  may be segmented films that are placed adjacent to each other on second polarizing filter  222  or on an optically transparent substrate (not shown). The segmented phosphor films  236  may be placed in a manner such that there is negligible gap at interfaces between adjacent phosphor films  236  to prevent leakage of primary light through the interfaces. In alternate embodiments, each of phosphor films  236  may be different regions of a continuous phosphor film. 
     Additionally, each of sub-pixels  226 . 1  through  226 . 6  may include a light blocking element  238  disposed on phosphor film  236 , according to some embodiments. The secondary light emitting from phosphor films  236  may be filtered through corresponding ones of light blocking elements  238  before travelling to display screen  230 . 
     Light blocking elements  238  may be configured to allow the secondary light (e.g., first, second, and/or third secondary light discussed above) to pass and to block portions of the primary light (e.g., blue light) that are not absorbed by phosphor films  236  and down-converted to the secondary light. The unwanted portions of primary light that may have leaked out of phosphor films  236  may be blocked by absorbing and/or scattering them. Leakage of the unconverted primary light from phosphor films  236  to display screen  230  may adversely affect the color gamut coverage of LCD display device  200 . The use of light blocking elements  238  to prevent such leakage may also help to reduce the manufacturing cost of LCD display device  200  by reducing the density of luminescent nanostructures included in phosphor films  236 . The density of luminescent nanostructures may be reduced as instead of using the luminescent nanostructures to absorb substantially all portions of the primary light, any portions of primary light not absorbed in phosphor films  236  may be filtered out by light blocking elements  238 . 
     Light blocking elements  238  may be also configured to tune the spectral emission widths (also referred as width of emission spectrum) of the secondary light (e.g., first, second, and/or third secondary light discussed above) to achieve a desired color gamut coverage of LCD display device  200 . Tuning of the spectral emission widths may require absorbing one or more wavelengths from the secondary light to narrow their spectral emission widths to achieve the desired color gamut coverage without significant decrease in brightness. For example, there may be less than 10% (e.g., about 8%, about 5%, about 3%, or about 1%) decrease in brightness due to this tuning process compared to display devices without light blocking elements  238 . As the secondary light from phosphor films  236  having luminescent nanostructures such as QDs typically exhibit narrow spectral emission widths, the tuning process may not require absorption of wide range of wavelengths to achieve the desired color gamut coverage as required in current non-QD based display devices to achieve similar color gamut coverage. 
     Wide spectral emission width is one of the limitations in current non-QD based display devices (e.g., YAG-phosphor based display devices) in achieving wide color gamut coverage of, for example, the Rec. 2020 color space. Use of absorbing elements such as light blocking elements  238  in current non-QD based display devices may achieve wide color gamut coverage (e.g., 80-90% Rec. 2020 color gamut coverage), but at the cost of significant decrease in brightness. Such decrease in brightness may not only adversely affect the image quality of the current display devices, but also fail to meet the brightness level required under the HDR imaging standards. 
     Light blocking elements  238  may include one or more non-phosphor materials. That is, the one or more non-phosphor materials exhibit optical absorption properties and/or optical scattering properties, but do not exhibit optical emission properties. The one or more non-phosphor materials may be selected based on their optical absorption properties to absorb and/or on their scattering properties to scatter only the one or more wavelengths or range of wavelengths that require absorbing and/or scattering during the above described blocking and tuning processes. In some embodiments, the one or more non-phosphor materials may include the same absorption property. In some embodiment, each of the one or more non-phosphor materials includes an absorption property different from each other. 
     The one or more non-phosphor materials may be selected such that they may be inexpensively disposed on phosphor films  236  or any other layer/structure of LCD display device  200  to form light blocking elements  238 . For example, the one or more non-phosphor materials may be dye (e.g., narrow band organic Exciton P491 dye), ink, paint, polymeric material, an/or any material that may be sprayed, painted, spin-coated, printed, or any other suitable low temperature (e.g., below 100° C.) deposition method. Printing may be done using, for example, a plotter, an inkjet printer, or a screen printer. In some embodiments, the one or more non-phosphor materials may be directly disposed on phosphor films  238 . In some embodiments, the one or more non-phosphor materials may be scattering materials that include films or particles (e.g., particles having diameters ranging from about 100 nm to about 500 μm) of titanium oxide, zinc oxide, zinc sulfide, silicone, or a combination thereof. In some embodiments, light blocking elements  238  may include a substrate having the one or more non-phosphor materials disposed on it. 
     In some embodiments, light blocking elements  238  may be segmented films that are placed adjacent to each other on phosphor films  236  or on an optically transparent substrate (not shown). The segmented light blocking elements  238  may be placed in a manner such that there is negligible gap at interfaces between adjacent light blocking elements  238 . In alternate embodiments, each of light blocking elements  238  may be different regions of a continuous film placed on phosphor films  236 . Thus,  FIG. 2  is not depicted to scale. 
     In some embodiments, light blocking elements  238  may not be a separate structure as shown in  FIG. 2 , but may be included in phosphor films  236 . That is, phosphor films  236  may be a composite film comprising the luminescent nanostructures, as described above, along with light blocking elements  238 . The one or more non-phosphor materials of light blocking elements  238  such as dye, ink, paint, polymeric material, scattering materials (e.g., particles having diameters ranging from about 100 nm to about 500 μm), or a combination thereof may be incorporated or embedded in a matrix of phosphor films  236 . The one or more non-phosphor materials may include nanostructured materials that may be dispersed in a matrix of phosphor films  236 . These nanostructured materials may exhibit optical absorption properties and/or optical scattering properties and may not exhibit any optical emission properties. In some embodiments, light blocking elements  238  may be included in optically transparent substrate  228 , which may also be configured to provide environmental sealing to the underlying layers and/or structures of LCD module  204  and/or BLU  202 . In alternate embodiments, light blocking elements  238  may be included in second polarizing filter  222 , which may be positioned between substrate  228  and phosphor films  236 . In some embodiments, light blocking elements  238  may be dichroic filters that, for example, may reflect the primary light (e.g., blue light) while transmitting the secondary light. 
     Display screen  230  may be configured to generate images. Display screen  230  may be a touch screen display, according to an embodiment. LCD display device  200  may further include one or more medium materials (not shown) disposed between any of the adjacent elements in LCD display device  200 , for example between optical cavity  212  and LCD module  204 , on either sides of LC solution layer  220 , or between any other elements of LCD display device  200 . The one or more medium materials may include, but not limited to, substrates, a vacuum, air, gas, optical materials, adhesives, optical adhesives, glass, polymers, solids, liquids, gels, cured materials, optical coupling materials, index-matching or index-mismatching materials, index-gradient materials, cladding or anti-cladding materials, spacers, epoxy, silica gel, silicones, brightness-enhancing materials, scattering or diffuser materials, reflective or anti-reflective materials, wavelength-selective materials, wavelength-selective anti-reflective materials, or other suitable medium material. Suitable materials may include silicones, silicone gels, silica gel, epoxies (e.g., Loctite™ Epoxy E -30CL), acrylates (e.g., 3M™ Adhesive 2175). The one or more medium materials may be applied as a curable gel or liquid and cured during or after deposition, or pre-formed and pre-cured prior to deposition. Curing methods may include UV curing, thermal curing, chemical curing, or other suitable curing methods known in the art. Index-matching medium materials may be chosen to minimize optical losses between elements of BLU  202  and LCD module  204 . 
     LCD display device  200  may have a geometric shape, such as but not limited to cylindrical, trapezoidal, spherical, or elliptical, according to various embodiments, without departing from the spirit and scope of the present invention. LCD display device  200  is not restricted to being cuboid in shape or having other straight-sided shapes. It should be noted that the rectangular cross-sectional shape of LCD display device  200  is for illustrative purposes, and is not limiting. LCD display device  200  may have other cross-sectional shapes (e.g., trapezoid, oblong, rhomboid), according to various embodiments, without departing from the spirit and scope of the present invention. It should also be noted that even though optical cavity  212 , substrates  216  and  228 , polarizing filter  214  and  222 , and display screen  230  are shown in  FIG. 2  to have similar dimensions along X-axis, a person skilled in the art would understand that each of these components may have dimensions different from each other in one or more directions, according to various embodiments. 
       FIG. 3  illustrates a schematic of an exploded cross-sectional view of an edge-lit LCD display device  300 , according to an embodiment. LCD display device  300  may include a BLU  302  and LCD module  204 . Elements in  FIG. 3  with the same annotations as elements in  FIG. 2  are described above. 
     BLU  302  may include an LED  310  (e.g., a blue LED), a light guide plate (LGP)  312 , and a reflector  308 . BLU  302  may be configured to provide a primary light (e.g., a blue light) that may be processed through LCD module  204  and subsequently, transmitted to and distributed across display screen  230 . The blue LED may emit in the range from about 440 nm to about 470 nm. According to an embodiment, the blue LED may be, for example, a GaN LED that emits blue light at a wavelength of 450 nm. 
     LGP  312  may include fiber optic cables, polymeric or glass solid bodies such as plates, films, containers, or other structures, according to some embodiments. The size of LGP  312  may depend on the ultimate application and characteristics of LED  310 . The thickness of LGP  312  may be compatible with thickness of LED  310 . The other dimensions of LGP  312  may be designed to extend beyond the dimensions of LED  310 , and may be on the order of 10&#39;s of millimeters, to 10&#39;s to 100&#39;s of centimeters. 
     In some embodiments, the materials of LGP  312  may include polycarbonate (PC), poly methyl methacrylate (PMMA), methyl methacrylate, styrene, acrylic polymer resin, glass, or other suitable LGP materials. Suitable manufacturing methods for LGP  312  may include injection molding, extrusion, or other suitable embodiments. LGP  312  may be configured to provide uniform primary light emission, such that primary light entering LCD module  204  may be of uniform color and brightness. LGP  312  may include a substantially uniform thickness over the entire LGP  312  surface. Alternatively, LGP  312  may have a wedge-like shape. In some embodiments, LGP  312  may be optically coupled to LED  310  and may be physically connected to or detached from LED  310 . For physically connecting LGP  312  to LED  310 , optically transparent adhesive may be used (not shown). 
     In some embodiments, BLU  302  may include an array of LEDs (not shown), each of which may be similar to LED  310  in structure and function. The array of LEDs may be adjacent to LGP  312  and may be configured to provide the primary light to LCD module  204  for processing and for subsequent transmission to display screen  230  as discussed above with reference to  FIG. 2 . 
     In some embodiments, reflector  308  may be configured to increase the amount of light that is emitted from LGP  312 . Reflector  308  may comprise a suitable material, such as a reflective mirror, a film of reflector particles, a reflective metal film, or other suitable conventional reflectors. In some embodiments, reflector  308  may include a white film. In some embodiments, reflector  308  may include additional functionality or features, such as scattering, diffuser, or brightness-enhancing features. 
     Example Embodiments of an Organic Light Emitting Diode (OLED) Display Device 
       FIG. 4  illustrates a schematic of an exploded cross-sectional view of an organic light emitting diode (OLED) display device  400 , according to an embodiment. OLED display device  400  may include a back plate  418 , a plurality of pixels  424  arranged in a 2-D array on back plate  418 , and a transmissive cover plate  430 , according to an embodiment. The number of pixels shown in  FIG. 4  is illustrative and is not limiting. OLED display device  400  may have any number pixels without departing from the spirit and scope of this disclosure. 
     Cover plate  430  may serve as display screen to generate images and/or may be configured to provide environmental sealing to underlying structures of OLED display device  400 . Cover plate  430  may be also configured to be an optically transparent substrate on which other components (e.g., electrode) of OLED display device  400  may be disposed. In some embodiments, pixels  424  may be tri-chromatic having red, green, and blue sub-pixels. In some embodiments, pixels  424  may be monochromatic having either red, green, or blue sub-pixels. In some embodiments, OLED display device  400  may have a combination of both tri-chromatic and monochromatic pixels  424 . 
     OLED display device  400  may further include control circuitry (not shown) of pixels  424 . Pixels  424  may be independently controlled by switching devices such as, for example, thin film transistors (TFTs). OLED display device  400  may have a geometric shape, such as but not limited to cylindrical, trapezoidal, spherical, or elliptical, according to various embodiments, without departing from the spirit and scope of the present invention. It should be noted that even though back plate  418 , array of pixels  424 , and cover plate  430  are shown in  FIG. 4  to have similar dimensions along X-axis, a person skilled in the art would understand that each of these components may have dimensions different from each other in one or more directions, according to various embodiments. 
       FIG. 5  illustrates an exploded cross-sectional view of a tri-chromatic pixel  524  of an OLED display device, according to an embodiment. One or more of pixels  424  of OLED display device  400  of  FIG. 4  may have a configuration similar to pixel  524 . Pixel  524  may include a red sub-pixel  540 , a green sub-pixel  542 , and a blue sub-pixel  544 . The arrangement order of red, green, and blue sub-pixels  540 ,  542 , and  544  is illustrative and is not limiting. The red, green, and blue sub-pixels  540 ,  542 , and  544  may be arranged in any order with respect to each other. 
     Each of red, green, and blue sub-pixels  540 ,  542 , and  544  may include a light source  546  (e.g., a blue OLED or a UV OLED) and a light blocking element  548 . The above discussion of light blocking elements  238  applies to light blocking elements  548  unless mentioned otherwise. 
     Red sub-pixel  540  may further include a phosphor film  550  disposed on an emitting surface of light source  546  of red sub-pixel  540 . Phosphor film  550  may have luminescent nanostructures such as QDs (e.g., QD  600  described with reference to  FIG. 6 ) that absorb primary light from light source  546  of red sub-pixel  540  and emit red light having a primary emission peak wavelength in the red wavelength region of the visible spectrum. 
     Green sub-pixel  542  may further include a phosphor film  552  disposed on an emitting surface of light source  546  of green sub-pixel  542 . Phosphor film  552  may have luminescent nanostructures such as QDs (e.g., QD  600  described with reference to  FIG. 6 ) that absorb primary light from light source  546  of green sub-pixel  542  and emit green light having a primary emission peak wavelength in the green wavelength region of the visible spectrum. 
     Blue sub-pixel  544  may further include a phosphor film  554  disposed on an emitting surface of light source  546  of blue sub-pixel  544 , according to an embodiment. Phosphor film  554  may have luminescent nanostructures such as QDs (e.g., QD  600  described with reference to  FIG. 6 ) that absorb primary light from light source  546  and emit blue light having a primary emission peak wavelength in the blue wavelength region of the visible spectrum. In alternate embodiments, blue sub-pixel  544  may have a non-phosphor film instead of phosphor film  554 . The non-phosphor film may exclude luminescent nanostructures such as QDs and may be optically transmissive to blue primary light of light source  546 . In such alternate embodiments, instead of light blocking elements  548 , blue sub-pixel  544  may also have a non-phosphor film that is optically transmissive to blue light. 
     Light blocking elements  548  may be configured to filter the red, green, and blue lights emitted from respective phosphor films  550 ,  552 , and  554  before travelling to a cover plate such as cover plate  430  of  FIG. 4 . Light blocking elements  548  may be configured to allow the red, green, and blue light from respective phosphor films  550 ,  552 , and  554  to pass and to block portions of primary light from light source  546  that are not absorbed by phosphor films  550 ,  552 , and  554 , and down-converted to the red, green, and blue light, respectively. The unwanted portions of the primary light that may have leaked out of phosphor films  550 ,  552 , and  554  may be blocked by absorbing and/or scattering them. Light blocking elements  548  may be also configured to tune the spectral emission widths (also referred as width of emission spectrum) of the red, green, and blue light emitted from respective phosphor films  550 ,  552 , and  554  to achieve a desired color gamut coverage of OLED display device  400 . 
     In some embodiments, light blocking elements  548  may not be a separate structure as shown in  FIG. 5 , but may be included in phosphor films  550 ,  552 , and  554 . That is, phosphor films  550 ,  552 , and  554  may be composite films comprising the luminescent nanostructures, as described above, along with light blocking elements  548 . The one or more non-phosphor materials of light blocking elements  548  such as dye, ink, paint, polymeric material, scattering materials (e.g., particles having diameters ranging from about 100 nm to about 500 μm), or a combination thereof may be incorporated or embedded in matrices of phosphor films  550 ,  552 , and  554 . The one or more non-phosphor materials may include nanostructured materials that may be dispersed in matrices of phosphor films  550 ,  552 , and  554 . These nanostructured materials may exhibit optical absorption properties and/or optical scattering properties and may not exhibit any optical emission properties. 
     Example Embodiments of a Barrier Layer Coated Nanostructure 
       FIG. 6  illustrates a cross-sectional structure of a barrier layer coated luminescent nanostructure (NS)  600 , according to an embodiment. In some embodiments, a population of NS  600  may be included in phosphor films  236 ,  550 ,  552 , and/or  554 . Barrier layer coated NS  600  includes a NS  601  and a barrier layer  606 . NS  601  includes a core  602  and a shell  604 . Core  602  includes a semiconducting material that emits light upon absorption of higher energies. Examples of the semiconducting material for core  602  include indium phosphide (InP), cadmium selenide (CdSe), zinc sulfide (ZnS), lead sulfide (PbS), indium arsenide (InAs), indium gallium phosphide, (InGaP), cadmium zinc selenide (CdZnSe), zinc selenide (ZnSe) and cadmium telluride (CdTe). Any other II-VI, III-V, tertiary, or quaternary semiconductor structures that exhibit a direct band gap may be used as well. In an embodiment, core  602  may also include one or more dopants such as metals, alloys, to provide some examples. Examples of metal dopant may include, but not limited to, zinc (Zn), Copper (Cu), aluminum (Al), platinum (Pt), chrome (Cr), tungsten (W), palladium (Pd), or a combination thereof. The presence of one or more dopants in core  602  may improve structural and optical stability and QY of NS  601  compared to undoped NSs. 
     Core  602  may have a size of less than 20 nm in diameter, according to an embodiment. In another embodiment, core  602  may have a size between about 1 nm and about 5 nm in diameter. The ability to tailor the size of core  602 , and consequently the size of NS  601  in the nanometer range enables photoemission coverage in the entire optical spectrum. In general, the larger NSs emit light towards the red end of the spectrum, while smaller NSs emit light towards the blue end of the spectrum. This effect arises as larger NSs have energy levels that are more closely spaced than the smaller NSs. This allows the NS to absorb photons containing less energy, i.e. those closer to the red end of the spectrum. 
     Shell  604  surrounds core  602  and is disposed on outer surface of core  602 . Shell  604  may include cadmium sulfide (CdS), zinc cadmium sulfide (ZnCdS), zinc selenide sulfide (ZnSeS), and zinc sulfide (ZnS). In an embodiment, shell  604  may have a thickness  604   t , for example, one or more monolayers. In other embodiments, shell  604  may have a thickness  604   t  between about 1 nm and about 5 nm. Shell  604  may be utilized to help reduce the lattice mismatch with core  602  and improve the QY of NS  601 . Shell  604  may also help to passivate and remove surface trap states, such as dangling bonds, on core  602  to increase QY of NS  601 . The presence of surface trap states may provide non-radiative recombination centers and contribute to lowered emission efficiency of NS  601 . 
     In alternate embodiments, NS  601  may include a second shell disposed on shell  604 , or more than two shells surrounding core  602 , without departing from the spirit and scope of the present invention. In an embodiment, the second shell may be on the order of two monolayers thick and is typically, though not required, also a semiconducting material. Second shell may provide protection to core  602 . Second shell material may be zinc sulfide (ZnS), although other materials may be used as well without deviating from the scope or spirit of the invention. 
     Barrier layer  606  is configured to form a coating on NS  601 . In an embodiment, barrier layer  606  is disposed on and in substantial contact with outer surface  604   a  of shell  604 . In embodiments of NS  601  having one or more shells, barrier layer  606  may be disposed on and in substantial contact with the outermost shell of NS  601 . In an example embodiment, barrier layer  606  is configured to act as a spacer between NS  601  and one or more NSs in, for example, a solution, a composition, and/or a film having a plurality of NSs, where the plurality of NSs may be similar to NS  601  and/or barrier layer coated NS  600 . In such NS solutions, NS compositions, and/or NS films, barrier layer  606  may help to prevent aggregation of NS  601  with adjacent NSs. Aggregation of NS  601  with adjacent NSs may lead to increase in size of NS  601  and consequent reduction or quenching in the optical emission properties of the aggregated NS (not shown) including NS  601 . In further embodiments, barrier layer  606  provides protection to NS  601  from, for example, moisture, air, and/or harsh environments (e.g., high temperatures and chemicals used during lithographic processing of NSs and/or during manufacturing process of NS based devices) that may adversely affect the structural and optical properties of NS  601 . 
     Barrier layer  606  includes one or more materials that are amorphous, optically transparent and/or electrically inactive. Suitable barrier layers include inorganic materials, such as, but not limited to, inorganic oxides and/or nitrides. Examples of materials for barrier layer  606  include oxides and/or nitrides of Al, Ba, Ca, Mg, Ni, Si, Ti, or Zr, according to various embodiments. Barrier layer  606  may have a thickness  606   t  ranging from about 8 nm to about 15 nm in various embodiments. 
     As illustrated in  FIG. 6 , barrier layer coated NS  600  may additionally or optionally include a plurality of ligands or surfactants  608 , according to an embodiment. Ligands or surfactants  608  may be adsorbed or bound to an outer surface of barrier layer coated NS  600 , such as on an outer surface of barrier layer  606 , according to an embodiment. The plurality of ligands or surfactants  608  may include hydrophilic or polar heads  608   a  and hydrophobic or non-polar tails  608   b . The hydrophilic or polar heads  608   a  may be bound to barrier layer  606 . The presence of ligands or surfactants  608  may help to separate NS  600  and/or NS  601  from other NSs in, for example, a solution, a composition, and/or a film during their formation. If the NSs are allowed to aggregate during their formation, the quantum efficiency of NSs such as NS  600  and/or NS  601  may drop. Ligands or surfactants  608  may also be used to impart certain properties to barrier layer coated NS  600 , such as hydrophobicity to provide miscibility in non-polar solvents, or to provide reaction sites (e.g., reverse micellar systems) for other compounds to bind. 
     A wide variety of ligands exist that may be used as ligands  608 . In some embodiments, the ligand is a fatty acid selected from lauric acid, caproic acid, myristic acid, palmitic acid, stearic acid, and oleic acid. In some embodiments, the ligand is an organic phosphine or an organic phosphine oxide selected from trioctylphosphine oxide (TOPO), trioctylphosphine (TOP), diphenylphosphine (DPP), triphenylphosphine oxide, and tributylphosphine oxide. In some embodiments, the ligand is an amine selected from dodecylamine, oleylamine, hexadecylamine, and octadecylamine. In some embodiments, the ligand is trioctylphosphine (TOP). In some embodiments, the ligand is oleylamine. In some embodiments, the ligand is diphenylphosphine. 
     A wide variety of surfactants exist that may be used as surfactants  608 . Nonionic surfactants may be used as surfactants  608  in some embodiments. Some examples of nonionic surfactants include polyoxyethylene (5) nonylphenylether (commercial name IGEPAL CO-520), polyoxyethylene (9) nonylphenylether (IGEPAL CO-630), octylphenoxy poly(ethyleneoxy)ethanol (IGEPAL CA-630), polyethylene glycol oleyl ether (Brij 93), polyethylene glycol hexadecyl ether (Brij 52), polyethylene glycol octadecyl ether (Brij S10), polyoxyethylene (10) isooctylcyclohexyl ether (Triton X-100), and polyoxyethylene branched nonylcyclohexyl ether (Triton N-101). 
     Anionic surfactants may be used as surfactants  608  in some embodiments. Some examples of anionic surfactants include sodium dioctyl sulfosuccinate, sodium stearate, sodium lauryl sulfate, sodium monododecyl phosphate, sodium dodecylbenzenesulfonate, and sodium myristyl sulfate. 
     In some embodiments, NSs  601  and/or  600  may be synthesized to emit light in one or more various color ranges, such as red, orange, and/or yellow range. In some embodiments, NSs  601  and/or  600  may be synthesized to emit light in the green and/or yellow range. In some embodiments, NSs  601  and/or  600  may be synthesized emit light in the blue, indigo, violet, and/or ultra-violet range. In some embodiments, NSs  601  and/or  600  may be synthesized to have a primary emission peak wavelength between about 605 nm and about 650 nm, between about 510 nm and about 550 nm, or between about 300 nm and about 480 nm. 
     NSs  601  and/or  600  may be synthesized to display a high QY. In some embodiments, NSs  601  and/or  600  may be synthesized to display a QY between 80% and 95% or between 85% and 90%. 
     Thus, according to various embodiments, NSs  600  may be synthesized such that the presence of barrier layer  606  on NSs  601  does not substantially change or quench the optical emission properties of NSs  601 . 
     Example Embodiments of a Nanostructure Film 
       FIG. 7  illustrates a cross-sectional view of a NS film  700 , according to an embodiment. In some embodiments, phosphor films  236 ,  550 ,  552 , and/or  554  may be similar to NS film  700 . 
     NS film  700  may include a plurality of barrier layer coated core-shell NSs  600  ( FIG. 6 ) and a matrix material  710 , according to an embodiment. NSs  600  may be embedded or otherwise disposed in matrix material  710 , according to some embodiments. As used herein, the term “embedded” is used to indicate that the NSs are enclosed or encased within matrix material  710  that makes up the majority component of the matrix. It should be noted that NSs  600  may be uniformly distributed throughout matrix material  710  in an embodiment, though in other embodiments NSs  600  may be distributed according to an application-specific uniformity distribution function. It should be noted that even though NSs  600  are shown to have the same size in diameter, a person skilled in the art would understand that NSs  600  may have a size distribution. 
     In an embodiment, NSs  600  may include a homogenous population of NSs having sizes that emit in the blue visible wavelength spectrum, in the green visible wavelength spectrum, or in the red visible wavelength spectrum. In other embodiments, NSs  600  may include a first population of NSs having sizes that emit in the blue visible wavelength spectrum, a second population of NSs having sizes that emit in the green visible wavelength spectrum, and a third population of NSs that emit in the red visible wavelength spectrum. 
     Matrix material  710  may be any suitable host matrix material capable of housing NSs  600 . Suitable matrix materials may be chemically and optically compatible with NSs  600  and any surrounding packaging materials or layers used in applying NS film  700  to devices. Suitable matrix materials may include non-yellowing optical materials which are transparent to both the primary and secondary light, thereby allowing for both primary and secondary light to transmit through the matrix material. In an embodiment, matrix material  710  may completely surround each of the NSs  600 . The matrix material  710  may be flexible in applications where a flexible or moldable NS film  700  is desired. Alternatively, matrix material  710  may include a high-strength, non-flexible material. 
     Matrix material  710  may include polymers and organic and inorganic oxides. Suitable polymers for use in matrix material  710  may be any polymer known to the ordinarily skilled artisan that can be used for such a purpose. The polymer may be substantially translucent or substantially transparent. Matrix material  710  may include, but not limited to, epoxies, acrylates, norbornene, polyethylene, poly(vinyl butyral):poly(vinyl acetate), polyurea, polyurethanes; silicones and silicone derivatives including, but not limited to, amino silicone (AMS), polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane, silsesquioxanes, fluorinated silicones, and vinyl and hydride substituted silicones; acrylic polymers and copolymers formed from monomers including, but not limited to, methylmethacrylate, butylmethacrylate, and laurylmethacrylate; styrene-based polymers such as polystyrene, amino polystyrene (APS), and poly(acrylonitrile ethylene styrene) (AES); polymers that are crosslinked with bifunctional monomers, such as divinylbenzene; cross-linkers suitable for cross-linking ligand materials, epoxides which combine with ligand amines (e.g., APS or PEI ligand amines) to form epoxy, and the like. 
     In some embodiments, matrix material  710  includes scattering microbeads such as TiO2 microbeads, ZnS microbeads, or glass microbeads that may improve photo conversion efficiency of NS film  700 . In some embodiments, matrix material  710  may include light blocking elements such as light blocking elements  238  and/or  548  described above with reference to  FIGS. 2-3 and 5 . 
     In another embodiment, matrix material  710  may have low oxygen and moisture permeability, exhibit high photo- and chemical-stability, exhibit favorable refractive indices, and adhere to outer surfaces of NSs  600 , thus providing an air-tight seal to protect NSs  600 . In another embodiment, matrix material  710  may be curable with UV or thermal curing methods to facilitate roll-to-roll processing. 
     According to some embodiments, NS film  700  may be formed by mixing NSs  600  in a polymer (e.g., photoresist) and casting the NS-polymer mixture on a substrate, mixing NSs  600  with monomers and polymerizing them together, mixing NSs  600  in a sol-gel to form an oxide, or any other method known to those skilled in the art. 
     According to some embodiments, the formation of NS film  700  may include a film extrusion process. The film extrusion process may include forming a homogenous mixture of matrix material  710  and barrier layer coated core-shell NSs such as NS  600 , introducing the homogenous mixture into a top mounted hopper that feeds into an extruder. In some embodiments, the homogenous mixture may be in the form of pellets. The film extrusion process may further include extruding NS film  700  from a slot die and passing extruded NS film  700  through chill rolls. In some embodiments, the extruded NS film  700  may have a thickness less than about 75 μm, for example, in a range from about 70 μm to about 40 μm, from about 65 μm to about 40 μm, from about 60 μm to about 40 μm, or form about 50 μm to about 40 μm. In some embodiments, NS film  700  has a thickness less than 10 μm. In some embodiments, the formation of NS film  700  may optionally include a secondary process followed by the film extrusion process. The secondary process may include a process such as co-extrusion, thermoforming, vacuum forming, plasma treatment, molding, and/or embossing to provide a texture to a top surface of NS film  700 . The textured top surface NS film  700  may help to improve, for example defined optical diffusion property and/or defined angular optical emission property of NS film  700 . 
     Example Embodiments of Luminescent Nanostructures 
     Described herein are various compositions having luminescent nanostructures (NSs). The various properties of the luminescent nanostructures, including their absorption properties, emission properties and refractive index properties, may be tailored and adjusted for various applications. 
     The material properties of NSs may be substantially homogenous, or in certain embodiments, may be heterogeneous. The optical properties of NSs may be determined by their particle size, chemical or surface composition. The ability to tailor the luminescent NS size in the range between about 1 nm and about 15 nm may enable photoemission coverage in the entire optical spectrum to offer great versatility in color rendering. Particle encapsulation may offer robustness against chemical and UV deteriorating agents. 
     Luminescent NSs, for use in embodiments described herein may be produced using any method known to those skilled in the art. Suitable methods and example nanocrystals are disclosed in U.S. Pat. No. 7,374,807; U.S. patent application Ser. No. 10/796,832, filed Mar. 10, 2004; U.S. Pat. No. 6,949,206; and U.S. Provisional Patent Application No. 60/578,236, filed Jun. 8, 2004, the disclosures of each of which are incorporated by reference herein in their entireties. 
     Luminescent NSs for use in embodiments described herein may be produced from any suitable material, including an inorganic material, and more suitably an inorganic conductive or semiconductive material. Suitable semiconductor materials may include those disclosed in U.S. patent application Ser. No. 10/796,832, and may include any type of semiconductor, including group II-VI, group III-V, group IV-VI and group IV semiconductors. Suitable semiconductor materials may include, but are not limited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SuS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI, Si 3 N 4 , Ge 3 N 4 , Al 2 O 3 , (Al, Ga, In) 2  (S, Se, Te) 3 , Al 2 CO, and an appropriate combination of two or more such semiconductors. 
     In certain embodiments, the luminescent NSs may have a dopant from the group consisting of a p-type dopant or an n-type dopant. The NSs may also have II-VI or III-V semiconductors. Examples of II-VI or III-V semiconductor NSs may include any combination of an element from Group II, such as Zn, Cd and Hg, with any element from Group VI, such as S, Se, Te and Po, of the Periodic Table; and any combination of an element from Group III, such as B, Al, Ga, In, and Tl, with any element from Group V, such as N, P, As, Sb and Bi, of the Periodic Table. 
     The luminescent NSs, described herein may also further include ligands conjugated, cooperated, associated or attached to their surface. Suitable ligands may include any group known to those skilled in the art, including those disclosed in U.S. Pat. No. 8,283,412; U.S. Patent Publication No. 2008/0237540; U.S. Patent Publication No. 2010/0110728; U.S. Pat. No. 8,563,133; U.S. Pat. No. 7,645,397; U.S. Pat. No. 7,374,807; U.S. Pat. No. 6,949,206; U.S. Pat. No. 7,572,393; and U.S. Pat. No. 7,267,875, the disclosures of each of which are incorporated herein by reference. Use of such ligands may enhance the ability of the luminescent NSs to incorporate into various solvents and matrixes, including polymers. Increasing the miscibility (i.e., the ability to be mixed without separation) of the luminescent NSs in various solvents and matrixes may allow them to be distributed throughout a polymeric composition such that the NSs do not aggregate together and therefore do not scatter light. Such ligands are described as “miscibility-enhancing” ligands herein. 
     In certain embodiments, compositions having luminescent NSs distributed or embedded in a matrix material are provided. Suitable matrix materials may be any material known to the ordinarily skilled artisan, including polymetic materials, organic and inorganic oxides. Compositions described herein may be layers, encapsulants, coatings, sheets or films. It should be understood that in embodiments described herein where reference is made to a layer, polymeric layer, matrix, sheet or film, these terms are used interchangeably, and the embodiment so described is not limited to any one type of composition, but encompasses any matrix material or layer described herein or known in the art. 
     Down-converting NSs (for example, as disclosed in U.S. Pat. No. 7,374,807) utilize the emission properties of luminescent nanostructures that are tailored to absorb light of a particular wavelength and then emit at a second wavelength, thereby providing enhanced performance and efficiency of active sources (e.g., LEDs). 
     While any method known to the ordinarily skilled artisan may be used to create luminescent NSs, a solution-phase colloidal method for controlled growth of inorganic nanomaterial phosphors may be used. See Alivisatos, A. P., “Semiconductor clusters, nanocrystals, and quantum dots,” Science 271:933 (1996); X. Peng, M. Schlamp, A. Kadavanich, A. P. Alivisatos, “Epitaxial growth of highly luminescent CdSe/CdS Core/Shell nanocrystals with photostability and electronic accessibility,”  J. Am. Chem. Soc.  30:7019-7029 (1997); and C. B. Murray, D. J. Norris, M. G. Bawendi, “Synthesis and characterization of nearly monodisperse CdE (E=sulfur, selenium, tellurium) semiconductor nanocrystallites,”  J Am. Chem. Soc.  115:8706 (1993), the disclosures of which are incorporated by reference herein in their entireties. 
     According to an embodiment, CdSe may be used as the NS material, in one example, for visible light down-conversion, due to the relative maturity of the synthesis of this material. Due to the use of a generic surface chemistry, it may also possible to substitute non-cadmium-containing NSs. 
     In semiconductor NSs, photo-induced emission arises from the band edge states of the NS. The band-edge emission from luminescent NSs competes with radiative and non-radiative decay channels originating from surface electronic states. X. Peng, et al.,  J Am. Chem. Soc.  30:7019-7029 (1997). As a result, the presence of surface defects such as dangling bonds provide non-radiative recombination centers and contribute to lowered emission efficiency. An efficient and permanent method to passivate and remove the surface trap states may be to epitaxially grow an inorganic shell material on the surface of the NS. X. Peng, et al.,  J. Am. Chem. Soc.  30:701 9-7029 (1997). The shell material may be chosen such that the electronic levels are type 1 with respect to the core material (e.g., with a larger bandgap to provide a potential step localizing the electron and hole to the core). As a result, the probability of non-radiative recombination may be reduced. 
     Core-shell structures may be obtained by adding organometallic precursors containing the shell materials to a reaction mixture containing the core NSs. In this case, rather than a nucleation event followed by growth, the cores act as the nuclei, and the shells may grow from their surface. The temperature of the reaction is kept low to favor the addition of shell material monomers to the core surface, while preventing independent nucleation of nanocrystals of the shell materials. Surfactants in the reaction mixture are present to direct the controlled growth of shell material and to ensure solubility. A uniform and epitaxially grown shell may be obtained when there is a low lattice mismatch between the two materials. 
     Example materials for preparing core-shell luminescent NSs may include, but are not limited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P, Co, Au, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTc, BeS, BcSe, BcTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, Pb Se, PbTe, CuP, CuCl, CuBr, CuI, Si 3 N 4 , Ge 3 N 4 , Al 2 O 3 , (Al, Ga, In) 2  (S, Se, Te) 3 , AlCO, and shell luminescent NSs for use in the practice of the present invention include, but are not limited to, (represented as Core/Shell), CdSe/ZnS, InP/ZnS, InP/ZnSe, PbSe/PbS, CdSe/CdS, CdTe/CdS, CdTe/ZnS, as well as others. 
     Luminescent NSs for use in the embodiments described herein may be less than about 100 nm in size, and down to less than about 2 nm in size and invention absorb visible light. As used herein, visible light is electromagnetic radiation with wavelengths between about 380 and about 780 nanometers that is visible to the human eye. Visible light can be separated into the various colors of the spectrum, such as red, orange, yellow, green, blue, indigo and violet. Blue light may comprise light between about 435 nm and about 495 nm, green light may comprise light between about 495 nm and 570 nm and red light may comprise light between about 620 nm and about 750 nm in wavelength. 
     According to various embodiments, the luminescent NSs may have a size and a composition such that they absorb photons that are in the ultraviolet, near-infrared, and/or infrared spectra. The ultraviolet spectrum may comprise light between about 100 nm to about 400 nm, the near-infrared spectrum may comprise light between about 750 nm to about 100 μm in wavelength, and the infrared spectrum may comprise light between about 750 nm to about 300 μm in wavelength. 
     While luminescent NSs of other suitable material may be used in the various embodiments described herein, in certain embodiments, the NSs may be ZnS, InAs, CdSe, or any combination thereof to form a population of nanocrystals for use in the embodiments described herein. As discussed above, in further embodiments, the luminescent NSs may be core/shell nanocrystals, such as CdSe/ZnS, InP/ZnSe, CdSe/CdS or InP/ZnS. 
     Suitable luminescent nanostructures, methods of preparing luminescent nanostructures, including the addition of various solubility-enhancing ligands, can be found in Published U.S. Patent Publication No. 2012/0113672, the disclosure of which is incorporated by reference herein in its entirety. 
     It is to be understood that while certain embodiments have been illustrated and described herein, the claims are not to be limited to the specific forms or arrangement of parts described and shown. In the specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. Modifications and variations of the embodiments are possible in light of the above teachings. It is therefore to be understood that the embodiments may be practiced otherwise than as specifically described.