WO2023287886A1

WO2023287886A1 - Tunable illumination device

Info

Publication number: WO2023287886A1
Application number: PCT/US2022/036966
Authority: WO
Inventors: Jason Hartlove
Original assignee: Nanosys, Inc.
Priority date: 2021-07-13
Filing date: 2022-07-13
Publication date: 2023-01-19

Abstract

An illumination device, a method of operating the illumination device, and a display device are disclosed. The illumination device may include a control circuit configured to determine a set of signals based on a target color temperature. Further, the illumination device may include at least two types of light emitting diodes (LEDs) configured to emit source lights based on the set of signals. Further still, the illumination device may include a housing having a phosphor coating with multiple luminescent nanostructures configured to emit, based on the source lights, an output light corresponding to the target color temperature.

Description

TUNABLE ILLUMINATION DEVICE

BACKGROUND OF THE INVENTION

Field

[0001] The present disclosure relates to illumination devices having phosphor coatings with luminescent nanostructures such as quantum dots (QDs).

Background

[0002] One or more of the following references may be related: EP Patent Document No.

2749813; US Patent No. 10,219,345; U.S. Patent Publication No. : 2019/0280043; WO2018157166; U.S. Patent No. 6,357,889; U.S. Patent No. 8,362,507; and U.S. Patent No. 10,154,560

[0003] Circadian lighting, or lighting which substantially matches the spectrum of sunlight throughout the day, is an emerging field which is believed to provide multiple health benefits. In particular, the reduction of the exposure for people indoors to blue light during the day and especially into the evening hours is believed to result in improvement in the sleep cycle which has in turn been linked to improved cardio-vascular health, reduction in cancer rates and many other benefits. In contrast, cool fluorescent or cool white LED lighting frequently used in factory conditions has recently been identified by the World Health Organization (WHO) as a carcinogen.

[0004] In order to provide white light from LED sources, conventional phosphor materials such as yttrium aluminum garnet (YAG) have been used. However, the resultant spectrum from these phosphors provides too much blue light energy and too little red- light energy to substantially match the spectrum of daylight. As a result, the so-called color temperature of most LED lights are cool, in the range of about 3000K-4000K. Even those which are in the warmer range such as about 2700K have too little red component and still far too much blue component to be suitable to substantially match the spectrum of sunlight, which is continuously variable during the day.

[0005] These solutions also lack the ability to be continuously variable as the emission spectra is fixed based on the amount of phosphor loading and the phosphor emission characteristics at the time of manufacture. Because the options in terms of the spectral characteristics of conventional phosphors are also limited, the ability to provide light at wavelengths throughout the visible spectra is also reduced.

BRIEF SUMMARY

[0006] Accordingly, there is need for illumination devices that output light with a color temperature that substantially matches the color temperature of sunlight throughout the day. Embodiments herein describe the use of multiple types of LEDs and a phosphor coating with luminescent nanostructures (NS) ( e.g quantum dots (QDs) to construct an illumination device that outputs light with a tunable color temperature (i.e., tunable emissions spectrum).

[0007] One or more embodiments are directed towards an illumination device. The illumination device includes a control circuit configured to determine a first plurality of signals based on a first target color temperature. Further, the illumination device includes a plurality of light emitting diodes (LEDs) (e.g., at least two types of LEDs) configured to emit a first plurality of source lights based in the first plurality of signals. Further still, the illumination device includes a housing comprising a phosphor coating with a plurality of luminescent nanostructures configured to emit, based on the first plurality of source lights, a first output light corresponding to the first target color temperature.

[0008] One or more embodiments are directed towards a method for operating an illumination device associated with a phosphor coating comprising a plurality of luminescent nanostructures. The method includes determining, based on a first target color temperature, a first plurality of signals for a plurality of light emitting diodes (LEDs) (e.g., at least two types of LEDs). Further, the method includes emitting a first plurality of source lights by driving the plurality of LEDs with the first plurality of signals. Further still, the method includes emitting, by the phosphor coating and based on the first plurality of source lights, a first output light corresponding to the first target color temperature.

[0009] 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

[0010] FIG. 1 shows an illumination device in accordance with one or more embodiments.

[0011] FIG. 2 shows an illumination device in accordance with one or more embodiments.

[0012] FIG. 3 shows a circuit board in accordance with one or more embodiments.

[0013] FIG. 4 and FIG. 5 show example spectra in accordance with one or more embodiments.

[0014] FIG. 6 shows a cross-sectional structure of a barrier layer coated luminescent nanostructure (NS) in accordance with one or more embodiments.

[0015] FIG. 7 shows a cross-sectional view of a NS film in accordance with one or more embodiments.

[0016] FIG. 8 shows a flowchart for operating an illumination device in accordance with one or more embodiments.

[0017] FIG’s 9 and 10 show schematically a display device in accordance with one or more embodiments.

[0018] FIG. 11 shows schematically, in cross-section, a display device in accordance with one or more embodiments.

[0019] FIG. 12 shows schematically a system incorporating the display device, in accordance with one or more embodiments.

[0020] The features and advantages of the present disclosure/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

[0021] 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 disclosure. It will be apparent to a person skilled in the pertinent art that this disclosure 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The term “substantially” as used herein indicates the value of a given quantity varies by ±1% to ±5% of the value.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The term “primary emission peak wavelength” as used herein refers to the wavelength at which the emission spectrum exhibits the highest intensity.

[0036] 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.

[0037] The terms “specular reflectors,” “specularly reflective surfaces,” “reflective surfaces,” and “reflective coatings” are used herein to refer to elements, materials, and/or surfaces capable of specular reflection.

[0038] 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.

[0039] The term “nanostructure (NS) film” is used herein to refer to a film having luminescent nanostructures.

[0040] 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. [0041] 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

[0042] One or more embodiments are directed towards an illumination device that emits an output light with a color temperature that substantially matches a target color temperature (e.g., the color temperature of sunlight at a given time of the day). The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of a color comparable to that of the light source. The illumination device is continuously tunable such that output lights with different color temperatures can be emitted at different times. The illumination device can include different types (i.e., different colors) of light emitting diodes (LEDs) within a housing that is at least partially covered with a phosphor coating having luminescent nanostructures (NSs) (e.g., quantum dots (QDs)). The output light is a function of the source lights emitted by the LEDs and the absorption/emission properties of the phosphor coating.

[0043] FIG. 1 shows an illumination device 100 in accordance with one or more embodiments. Illumination device 100 has multiple components including a circuit board 110, multiple types of LEDs (e.g., LED type A 105 A, LED type B 105B), and a housing 125. Each of these components is discussed below.

[0044] In one or more embodiments, the different types of LEDs 105 correspond to different colors. For example, LEDs 105 can include LED type A 105A, which can correspond to a white LED, and LED type B 105B, which can correspond to a violet LED. Although FIG. 1 only shows two types of LEDs, in other embodiments, there can be three or more types of LEDs. Further, there can be any number of LEDs of a specific LED type included in LEDs 105. For example, there can be 4 white LEDs and 7 violet LEDs.

[0045] In one or more embodiments, light emitted by an LED is referred to as source light. Accordingly, the intensity of source light from an LED is a function of the signal (e.g., electric current) driving the LED. Those skilled in the art, having the benefit of this detailed description, will appreciate that source light from different types of LEDs will have different emissions spectra (discussed below). [0046] In one or more embodiments, LEDs 105 are disposed on circuit board 110 (e.g., a printed circuit board). LEDs 105 can be clustered into groups of any size on circuit board 110, with each group containing LEDs 105 of only the same type or of different types. Additionally or alternatively, LEDs 105 can be disposed on circuit board 110 randomly or according to any pattern. All LEDs can be disposed on the same side of circuit board 100. Alternatively, LEDs can be scattered across multiple sides of circuit board 100.

[0047] In one or more embodiments, circuit board 110 and LEDs 105 are located within housing 125 ( i.e ., housing 125 fully or partially encloses circuit board 110 and LEDs 105). As shown in FIG. 1, housing 125 can have a tube shape. In other embodiments, housing 125 can have a lightbulb shape (e.g., any known bulb shape), a rectangular shape, a pyramid shape, a cone shape, a polygon shape, etc. As well as a more conventional light bulb applications, the illumination device is in examples configured for use as a lighting panel which has a planar light emission surface and is for illuminating an area such as at least part of a wall, ceiling or window, or for example for illuminating, from behind, an advert of an advertising panel. Although FIG. 1 shows circuit board 110 as being centered (or approximately centered) within housing 125, in other embodiments, circuit board 110 can be disposed on housing 125 itself. For example, circuit board 110 can have a curved shape and can be disposed on a curved surface of housing 125.

[0048] In one or more embodiments, housing 125 includes a phosphor coating 115 with luminescent NSs (e.g., QDs). Phosphor coating 115 can be disposed/deposited on the entire housing 125. Alternatively, phosphor coating 115 can be disposed/deposited only on a portion of housing 125. Housing 125 can be composed of a glass substrate and the phosphor coating 115 can be disposed/deposited on a layer of the glass substrate. Additionally or alternatively, phosphor coating 115 can be placed on housing 125 via a vapor deposition method. Phosphor coating 115 can correspond to a nanostructure film disposed on housing 125. Moreover, phosphor coating 115 may correspond to a separate component that fully or partially covers housing 125.

[0049] Luminescent NSs such as 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. Accordingly, in one or more embodiment, phosphor coating 115 is configured to emit the output light of illumination device 100 (i.e., light that appears to be coming from illumination device 100). Phosphor coating 115 can absorb incident light (e.g., source lights from LEDs) and re-emit the light at different wavelengths, thereby generating the output light (discussed below). The emission spectrum of phosphor coating 115 depends on the types, sizes, and concentrations of the luminescent NSs (e.g., QDs).

[0050] In one or more embodiments, a portion of housing 125 is covered by reflector coating A 120A. Reflector coating A 120A may be composed of one or more materials including polished aluminum, aluminized Mylar sheets, aluminum foils, glossy and matte based paints and polymer coatings including white, off white and other colors depending on the desired color tone, etc. Reflector coating A 120A can be disposed/deposited on housing 125. Reflector coating A 120A is configured to reflect all or most source light that strikes it and thus ensure that source light only leaves housing 125 via phosphor coating 115 (discussed below). Thus, reflector coating A 120A improves the efficiency of illumination device 100 by increasing light emitted from illumination device 100. In one or more embodiments, any portion of housing 125 that is not covered by the phosphor coating 115 is covered by reflector coating A 120A. For example, as shown in FIG. 1, half (or approximately half) of housing 125 is covered by phosphor coating 115, while the other half is covered by reflector coating A 120A. As discussed, the one or more locations of reflector coating A 120 A can be selected to increase the output light from illumination device 100.

[0051] FIG. 2 shows illumination device 100 in accordance with one or more embodiments. As shown in FIG. 2, housing 125 of illumination device 100 is covered by alternating strips of phosphor coating 115 and reflective coating A 120A. These strips are only one possible pattern for disposing phosphor coating 115 and reflective coating A 120A on housing 125. Other patterns can be composed of a repeated shape (e.g., hexagon, diamond, triangle), where shapes composed of phosphor coating 115 abut shapes composed of reflective coating A 120 A.

[0052] FIG. 3 shows a circuit board 310 in accordance with one or more embodiments.

Circuit board 310 can correspond to circuit board 110, discussed above in reference to FIG. 1. As shown in FIG. 3, the different types of LEDs 105 are disposed on circuit board 310. As also shown in FIG. 3, reflective coating B 120B is disposed on circuit board 310. Reflective coating B 120 B and reflective coating A 120A can be composed of the same material or different material. Like reflector coating A 120 A, reflector coating B 120B is configured to reflect all or most source light that strikes it and thus increase the likelihood that source light only leaves housing 125 via phosphor coating 115. In one or more embodiments, reflector coating B 120B and LEDs 105 are disposed on the same side of circuit board 310. Alternatively, reflector coating B 120B is disposed on a different side of circuit board 310 than LEDs 105. Additionally or alternatively, reflector coating B 120B is disposed on multiple sides of circuit board 310. The one or more locations of reflector coating B 120B can be selected to increase the output light from illumination device 100.

[0053] In one or more embodiments, control circuit 130 is also disposed on circuit board

310. Alternatively, control circuit 130 can be disposed on housing 125. Control circuit 130 is configured to generate and drive LEDs 105 with signals (e.g., electrical currents).

In one or more embodiments, control circuit 130 is connected to one or more sensors (not shown) and can measure the color temperature of light (e.g., sunlight or ambient light).

In one or more embodiments, control circuit 130 can implement (in hardware or software) one or more clocks (discussed below). In one or more embodiments, control circuit 130 can implement (in hardware or software) one more repositories (e.g., memory locations, flat files, databases, lookup tables, arrays, hard drives, etc.) storing values for generating the signals that drive LEDs 105. The input value to the lookup tables can be a time (from the clocks) and/or the measured color temperature associated with the one or more sensors (discussed below). Control circuit 130 can include circuitry for sending and receiving wireless communication. As shown in FIG. 3, in one or more embodiments, reflective coating B 120B covers control circuit 130. For example, control circuit 130 can be encased and reflective coating B 120B covers the enclosure in which control circuit 130 is located. Although FIG. 3 shows the control circuit 130 as being located on the same side of circuit board 310 as LEDs 105, in other embodiments, control circuit 130 and LEDs 105 are located on different sides of circuit board 310.

[0054] In one or more embodiments, the output light emitted by illumination device 100

(i.e., the light that appears to be coming from illumination device 100) has a color temperature. The color temperature of the output light is a function of the color spectrum of the output light. Phosphor coating 115 emits the output light in response to being struck by source light generated by one or more of LEDs 105. The color spectrum of the output light, and thus the color temperature of the output light, is a function of at least: (i) the color spectrum of source light emitted by each type of LED; (ii) the intensity of the source light emitted by each type of LED; and (iii) the emission spectrum (e.g., emission peaks) of the phosphor coating 115. As discussed above, the intensity of the source light from an LED is a function of the signal (e.g., electrical current) driving the LED. As also discussed above, the emission spectrum of phosphor coating 115 is a function of the size and density of the luminescent NSs (e.g., QDs). Accordingly, once the emission spectrum is chosen (e.g., through at least the size and density of the luminescent NSs) and the different types of LEDs have been selected, the color temperature of the output light can be changed by changing the signals driving the different types of LEDs (which changes the intensity of source light emitted from each type of LED).

[0055] FIG. 4 shows an example in accordance with one or more embodiments.

Specifically, FIG. 4 shows an example emission spectrum 405A for source light emitted from LED type A 105 A (e.g., white LED), an example emission spectrum 405B for source light emitted from LED type B 105B (e.g., violet LED), and an example emission spectrum 415 for phosphor coating 115. As shown in FIG. 4, the emission spectrum 415 has a relatively lower output 422 in the low green range (about 510nm) and a higher output 424 in the deep red range (about 650nm)

[0056] FIG. 5 shows an example in accordance with one or more embodiments. FIG. 5 shows three emission spectra 590 associated with three different output lights emitted by illumination device 100. Each of the three different output lights is generated using one or more of the LED types (discussed in FIG. 4) and phosphor coating 115 with the emission spectrum 415 (also discussed in FIG. 4).

[0057] The top emission spectrum 590A corresponds to output light generated using only type A LEDs 105 A (e.g., white LEDs) and phosphor coating 115. In other words, type B LEDs 105B (e.g., violet LEDs) are turned off in order to generate this output light. The output light has a color temperature that is slightly warmer than the color temperature produced by white LED itself because some of the blue light from the white LED is absorbed by phosphor coating 115 and emitted as either green or red light. The color temperature of the output light (i.e., Color Temp A) is in excess of about 5000 K. This color temperature approximates morning sunlight.

[0058] The bottom emission spectrum 590C corresponds to output light generated using only type B LEDs 105B (e.g., violet LEDs) and the phosphor coating 115. In other words, type A LEDs 105A (e.g., white LEDs) are turned off in order to generate this output light. Nearly all of the violet light is absorbed by the green and red quantum dots in phosphor coating 115 as they will have a high absorption at this lower wavelength.

The color temperature of this output light (i.e., Color Temp C) is less than about 3000 K. This color temperature approximates later afternoon sunlight.

[0059] The middle emission spectrum 590B corresponds to output light generated using type A LEDs 105A (e.g., white LEDs), type B LED 105B (e.g., violet LEDs), and phosphor coating 115. The color temperature of this output light (i.e., Color Temp B) will vary between about 3000 K and about 5000 K and can be controlled by varying the intensity of the source light emitted by different types of LEDs 105. This range of color temperatures approximates afternoon sunlight.

[0060] FIG. 8 shows a flowchart in accordance with one or more embodiments. The flowchart of FIG. 8 depicts a process for operating illumination device 100. For example, the process depicted in FIG. 8 can be executed so that an output light is emitted by illumination device 100 with a color temperature that substantially matches a target (e.g., desired) color temperature. One or more of the steps in FIG. 8 can be executed by control circuit 130. In one or more embodiments, one or more of the steps shown in FIG. 8 can be omitted, repeated, and/or performed in a different order than the order shown in FIG.

8. Accordingly, the scope of the disclosure should not be considered limited to the specific arrangement of steps shown in FIG. 8.

[0061] In Step 805, a target color temperature is obtained. The target color temperature can be obtained by the control circuit 130. The target color temperature can be obtained over a network with wired and/or wireless segments. In one or more embodiments, the target color temperature is the color temperature of sunlight at the current time. Accordingly, the target color temperature can be obtained using sensors that are exposed to sunlight (e.g., sensors on the exterior of a building). Additionally or alternatively, the target color temperature can be obtained by first determining the current time of day (e.g., by accessing a clock, obtaining the current time of day over a network, etc.) and then accessing a repository (e.g., lookup table) that stores the color temperatures of sunlight at different times.

[0062] In Step 810, signals (e.g., electric currents) for the different types of LEDs in illumination device 100 are determined based on the target color temperature. As discussed above, the illumination device 100 includes at least two different types of LEDs 105. One or more of these different types of LEDs are driven with a signal (e.g., electric current) in order for illumination device 100 to emit an output light having (or approximating) the target color temperature. The control circuit 130 can include a repository storing signal values (e.g., 0mA, 2.1mA, 10mA, etc.) for the different types of LEDs for a variety of target color temperatures. In other words, the repository stores the signal values that should be used to drive different types of LEDs in order to end up with output light substantially matching the target color temperature. The target color temperature can be a criterion for searching the repository and retrieving the signal values for the different types of LEDs. Additionally or alternatively, a time (e.g., 3:00pm) corresponding to the target color temperature (e.g., of sunlight) can be a criterion for searching the repository and retrieving the signal values for the different types of LEDs.

[0063] In embodiments where control circuit 130 has a repository, those skilled in the art, having the benefit of this detailed description, will appreciate that the signal values stored in the repository (and possibly retrieved in Step 810) are determined/calculated in advance (e.g., before execution of the process in FIG. 8). Moreover, these signal values are dependent on different LED types 105 (and their color spectra) in the illumination device 100 and the absorption/emission properties of phosphor coating 115. For example, it can be determined in advance (e.g., before execution of the process in FIG. 6) that driving the white LEDs with 1.5 mA and driving the violet LEDs with 2.1 mA results in an output light from illumination device 100 with a color temperature of 3500 K. Accordingly, these values (i.e., 1.5 mA, 2.1 mA, 3500 K) would be stored in the repository. If the target color temperature obtained in Step 805 is 3500 K, the 1.5 mA and 2.1 mA needed to achieve an output light having (or approximating) a color temperature of 3500K would be determined by accessing the repository.

[0064] In Step 815, the LEDs emit source light based on the signals (e.g., electric currents). In other words, the LEDs are driven with the signals determined in Step 810. The different types of LEDs can correspond to different colors (e.g., white, violet, etc.) and the magnitude of the signal driving an LED impacts the intensity of the source light emitted by the LED. One or more LEDs can be driven with a signal of 0 mA (i.e., the LEDs are turned off). As discussed above, the source light can be reflected by one or more reflective coatings 120. As also discussed above, the source light from different types of LEDs have different emission spectra.

[0065] In Step 820, an output light is emitted by illumination device 100. Specifically, the output light is emitted by phosphor coating 115 of illumination device 100. The output light is emitted in response to the source light (directly from LEDs 105 or reflected off reflective coatings 120) being absorbed by the phosphor coating 115 and re-emitted with different wavelengths. The emission spectrum of the output light, and thus the color temperature of the output light, is a function of at least: (i) the emission spectrum of source light emitted by each type of LED; (ii) the intensity of the source light emitted by each type of LED; and (iii) the emission spectrum (e.g., emission peaks) of the phosphor coating 115. As discussed above, the signal values for the LEDs are determined such that the output light corresponds to the target color temperature. In other words, the output light has a color temperature that substantially matches the target color temperature.

[0066] In Step 825, it is determined whether there is a new target color temperature. For example, there might be a new target color temperature if a predetermined amount of time has passed (e.g., 2.5 hours) since the last target color determined was obtained. Additionally or alternatively, a new target color temperature can be received over a network at any time. When it is determined that there is a new color temperature, the process returns to Step 810. When it is determined that there is not a new color temperature, the process can end.

[0067] In one or more embodiments, the illumination device 100 can be located indoors (e.g., inside a home, an office, a factory, a laboratory, an underground facility, an airplane, etc.) and the output light can be used to illuminate the indoor space. The process depicted in FIG. 8 can be executed such that the output light effectively tracks the sunlight (i.e., illumination device 100 is continuously tunable to track or mimic the color temperature of sunlight), which can improve the quality of life of those present (e.g., improve sleep cycle, improve car dio- vascular health, reduce the likelihood of cancer, etc.). Additionally or alternatively, the process depicted in FIG. 8 can be used to replicate sunlight when no sunlight is present (e.g., the facility is underground, the facility has no windows, a night or graveyard shift at a factory, etc.). EXAMPLE EMBODIMENTS OF A BARRIER LAYER COATED NANOSTRUCTURE

[0068] FIG. 6 illustrates a cross-sectional structure of a barrier layer coated luminescent nanostructure (NS) 600, according to an embodiment. The phosphor coating 115 can have many of these luminescent nanostructures 600. A quantum dot is one example of NS 600. 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 can 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 can improve structural and optical stability and QY of NS 601 compared to undoped NSs.

[0069] Core 602 can have a size of less than 20 nm in diameter, according to an embodiment. In another embodiment, core 602 can 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.

[0070] Shell 604 surrounds core 602 and is disposed on outer surface of core 602. Shell 604 can include cadmium sulfide (CdS), zinc cadmium sulfide (ZnCdS), zinc selenide sulfide (ZnSeS), and zinc sulfide (ZnS). In an embodiment, shell 604 can have a thickness 604t, for example, one or more monolayers. In other embodiments, shell 604 can have a thickness 604t between about 1 nm and about 5 nm. Shell 604 can be utilized to help reduce the lattice mismatch with core 602 and improve the QY of NS 601. Shell 604 can 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.

[0071] In alternate embodiments, NS 601 can 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 disclosure. 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 disclosure.

[0072] 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 604a of shell 604. In embodiments of NS 601 having one or more shells, barrier layer 606 can 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 can 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.

[0073] 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 can have a thickness 606t ranging from about 8 nm to about 15 nm in various embodiments. [0074] As illustrated in FIG. 6, barrier layer coated NS 600 can additionally or optionally include a plurality of ligands or surfactants 608, according to an embodiment. Ligands or surfactants 608 can 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 can include hydrophilic or polar heads 608a and hydrophobic or non-polar tails 608b. The hydrophilic or polar heads 608a can be bound to barrier layer 606. The presence of ligands or surfactants 608 can 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 can drop. Ligands or surfactants 608 can 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.

[0075] 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.

[0076] 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).

[0077] 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.

[0078] In some embodiments, NSs 601 and/or 600 can 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 can be synthesized to emit light in the green and/or yellow range. In some embodiments, NSs 601 and/or 600 can be synthesized emit light in the blue, indigo, violet, and/or ultra-violet range. In some embodiments, NSs 601 and/or 600 can 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.

[0079] NSs 601 and/or 600 can be synthesized to display a high QY. In some embodiments, NSs 601 and/or 600 can be synthesized to display a QY between 80% and 95% or between 85% and 90%.

[0080] Thus, according to various embodiments, NSs 600 can 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

[0081] FIG. 7 illustrates a cross-sectional view of a NS film 700, according to an embodiment. In some embodiments, the phosphor coating 115 can be similar to NS film 700.

[0082] NS film 700 can include a plurality of barrier layer coated core-shell NSs 600

(FIG. 6) and a matrix material 710, according to an embodiment. NSs 600 can 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 can be uniformly distributed throughout matrix material 710 in an embodiment, though in other embodiments NSs 600 can 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 can have a size distribution.

[0083] In an embodiment, NSs 600 can 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 can 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.

[0084] Matrix material 710 can 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 that 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 can completely surround each of the NSs 600. The matrix material 710 can be flexible in applications where a flexible or moldable NS film 700 is desired. Alternatively, matrix material 710 can include a high-strength, non-flexible material.

[0085] Matrix material 710 can include polymers and organic and inorganic oxides. Suitable polymers for use in matrix material 710 can 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 can 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 that combine with ligand amines (e.g., APS or PEI ligand amines) to form epoxy, and the like.

[0086] In some embodiments, matrix material 710 includes scattering microbeads such as Ti02 microbeads, ZnS microbeads, or glass microbeads that may improve photo conversion efficiency of NS film 700. In some embodiments, matrix material 710 can include fluorescent material.

[0087] In another embodiment, matrix material 710 can 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 can be curable with UV or thermal curing methods to facilitate roll-to-roll processing.

[0088] According to some embodiments, NS film 700 can 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.

[0089] According to some embodiments, the formation of NS film 700 can 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 can have a thickness less than about 75 pm, for example, in a range from about 70 pm to about 40 pm, from about 65 pm to about 40 pm, from about 60 pm to about 40 pm, or form about 50 pm to about 40 pm. In some embodiments, NS film 700 has a thickness less than about 10 pm. In some embodiments, the formation of NS film 700 can 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 can 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

[0090] 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.

[0091] 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.

[0092] 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. Patent No. 7,374,807; U.S. Patent Application Ser. No. 10/796,832, filed Mar. 10, 2004; U.S. Patent. 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.

[0093] 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, AIN, A1P, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AIN, A1P, 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, Cul, Si3N4, Ge3N4, A1203, (Al, Ga, In)2 (S, Se, Te)3, A12CO, and an appropriate combination of two or more such semiconductors.

[0094] 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.

[0095] 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. Patent No. 8,283,412; U.S. Patent Publication No. 2008/0237540; U.S. Patent Publication No. 2010/0110728; U.S. Patent No. 8,563,133; U.S. Patent No. 7,645,397; U.S. Patent No. 7,374,807; U.S. Patent No. 6,949,206; U.S. Patent No. 7,572,393; and U.S. Patent 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.

[0096] 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.

[0097] Down-converting NSs (for example, as disclosed in U.S. Patent 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).

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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, AIN, A1P, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AIN, A1P, 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, PbSe, PbTe, CuP, CuCl, CuBr, Cul, Si3N4, Ge3N4, A1203, (Al, Ga, In)2 (S, Se, Te)3, AICO, and shell luminescent NSs for use in the practice of the present disclosure 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.

[0103] 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 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.

[0104] 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 pm in wavelength, and the infrared spectrum may comprise light between about 750 nm to about 300 pm in wavelength.

[0105] 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.

[0106] 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. EXAMPLE EMBODIMENTS RELATED TO A DISPLAY DEVICE

[0107] The illumination device of examples described above can be configured for use in a display device (e.g., a display panel, display unit, or display screen), for incorporation into apparatus using a display device to display information to a user.

[0108] FIG. 9 shows schematically a display device 900 of various examples which will be described in more detail later. The display device comprises an illumination device in accordance with examples described herein and a display device control system 950 The display device control system comprises the control circuit 930 of the illumination device (e.g., the control circuit is part of a display control circuit board outside of the housing of the illumination device). The display device control system is configured to switch the display device between at least a first display mode and a second display mode. In the first display mode the illumination device, in particular the plurality of LEDs, is switched to output light of a first color temperature, for displaying a given image. And in the second display mode the illumination device is switched to output light of a second color temperature, for displaying the same given image. In other words for the same image to be displayed, color temperature of the image is different depending on the first or second display mode. The first color temperature , e.g., corresponds with the first target color temperature described earlier, and the second color , e.g., corresponds with the second target color temperature described earlier. The first display mode is for example a day mode (e.g., for a user to view the display device during the day, e.g., from sunrise to sunset) and the second display mode is for example a night mode (e.g., for a user to view the display device during the night, e.g., from sunset to sunrise) with fewer or no wavelengths of light emitted in the range 380 to 460 nanometers (nm) (and hence a warmer emitted color temperature) compared with the day mode. The display device may be switched to the second display mode to help reduce a user’s exposure to light in the wavelength range 380 to 460 nm, ahead of a period of sleep, to aid the user falling asleep and sleeping well.

[0109] The illumination device is , e.g., configured for illuminating one or more picture element of the display device, or for acting as a plurality of picture elements. A picture element is , e.g., a sub-pixel or pixel of a display device. A display device typically comprises a plurality of picture elements independently controllable for the display device to display an image. The picture elements are arranged according to a pattern, e.g., as an array, matrix or grid, as shown for example in FIG. 9 by numeral 952. A display device capable of displaying a color image typically has a plurality of pixels, with each pixel comprising a plurality of sub-pixels; e.g., a pixel comprises a red (R) sub-pixel, a green (G) sub-pixel and a blue (B) sub-pixel which together function as an RGB pixel. There may be additional, independently controllable, sub-pixels, e.g., a white (W) sub pixel, to give an RGBW pixel. FIG. 9 illustrates schematically a matrix of RGB sub pixels.

[0110] Examples of such a display device will now be described with FIG. 10. The display device comprises: an illumination device 1056 in accordance with examples described previously, and a light modulator 1054 configured to modulate light emitted by the illumination device, for displaying an image. The light modulator has an array of light modulator regions to modulate light from the illumination device. Each light modulator region of the array of light modulator regions corresponds with a respective picture element 952 of the display device. So, for example, when viewing a viewing side of the display device for displaying an image to a user’s eye 1058, a perimeter of one light modulator region determines an extent of one picture element such as those shown in FIG. 9. The phosphor coating is , e.g., planar, with an extent covered by the array of light modulator regions, so that each light modulator region can be illuminated by the illumination device.

[0111] The display device control system is configured to control the array of light modulator regions for the display device to output an image. Each light modulator region is independently controllable, to modulate the amount of light transmitted from the illumination device to the viewing side, for each picture element. Thus one light modulator region may be switched to transmit less light (a darker state) than another light modulator region (a lighter state), so that with appropriate light modulation across the array of light modulator regions (and therefore the picture elements) the display device can display a desired image.

[0112] FIG. 11 shows in cross-section elements of a first class of the first examples. This class uses liquid crystal (LC) molecules for light modulation. By applying an electric field of appropriate magnitude to electrodes of a light modulator region, an orientation of the LC molecules can be changed to modulate light output by a respective picture element 1152, for displaying an image on a viewing side 1153. Various elements of such a display device will now be described using FIG. 11, but it is to be appreciated that many alternative constructions of a light modulator using LC molecules will be envisaged by the skilled person, in accordance with further examples.

[0113] The light modulator 1154 is stacked on the illumination device 1156, each of which is in accordance with examples described previously. Starting from the lowest layer shown, the illumination device comprises a substrate 1158 (e.g., of glass), a circuitry layer 1160 (e.g., comprising a circuit board as described earlier) on the substrate, and a plurality of LEDs connected to the circuitry layer including a first type of LED 1162 and a second type of LED 1164. The plurality of LEDs is configured and positioned, e.g., as an array of LEDs overlapped by the phosphor coating, to illuminate the phosphor coating 1166 comprising the luminescent nanostructures described previously. Between the LEDs and the phosphor coating is one or more layer, e.g., a diffuser 1168 to distribute light from the LEDs more evenly across the phosphor coating, and/or alignment layer using , e.g., prisms to align light from the LEDs with each picture element 1152. Further such diffuser and/or alignment layers may be used between the phosphor coating and the light modulator.

[0114] In other examples, instead of the array of LEDs, there is a light guide overlapped by the phosphor coating (which is , e.g., planar) and at least one LED of the plurality of LEDs is positioned along at least part of a perimeter of the light guide, to illuminate the phosphor coating via the light guide. This may be referred to as a so-called edge-lit light guide. In some such examples, or other examples, there is a light diffuser overlapped by the phosphor coating (which is , e.g., planar), and/or there is a light diffuser with a phosphor (, e.g., QDs) embedded within the light diffuser so as to function as the phosphor coating.

[0115] On the illumination device is the light modulator 1154 which, starting from the lowest layer shown, comprises a polarizer layer 1169 to linearly polarize light output by the phosphor coating. The polarizing layer 1169 is on a substrate 1170 (e.g., glass), a circuitry layer 1172 is on the substrate 1170, and is connected to an array of electrodes (e.g., of indium tin oxide (ITO)) 1174 each of which is electrically insulated from each other and has an extent which determines a shape and size of each picture element. On the electrodes there is a layer 1176 comprising LC molecules, the LC molecules and their density in the layer selected to provide a required rotation of linearly polarized light from the phosphor coating in accordance with a magnitude of applied electric field. An alignment layer 1178 is in contact with the layer comprising LC molecules, to align the LC molecules in contact with the alignment layer with a particular orientation. There is another linear polarizer layer 1180 orientated to linearly polarize light at an orientation , e.g., perpendicular to the polarizer layer 1169 described above. Each picture element also comprises a color filter 1182, in these examples between the alignment layer and the another linear polarizer layer. By appropriate choice of the color filter for each picture element, an RGB pixel (of three sub-pixel picture elements) can be made. On the another linear polarizer layer is a substrate 1186 (e.g., of glass). There is an electrode 1184 with an extent to cover more than one (e.g., all) picture elements, which may be referred to as a common electrode. This is shown between the alignment layer and the color filters.

[0116] FIG. 11 illustrates four picture elements 1152 so for some examples does not illustrate all picture elements of a display device. Thus it is to be appreciated that the plurality of LEDs of the illumination device has more than one pair of LED types as shown in FIG. 11. For example, for a repeating RGB sub-pixel pattern across the array, a pair of LEDs (one of each type) may be located in each green picture element of the display device. In other examples it is to be appreciated that the LEDs of the illumination device may be located differently; for example, in a different color picture element; there may be fewer of one type of LED compared with another type across the array; or one type of LED may be located in one color of picture element whereas another type of LED may be located in a different color of picture element across the array. The density and positioning of the LEDs depends at least partly on the shape and size of the picture elements of the display, but also the illumination characteristics of each LED and any layers such as a diffuser or reflector for transmitting light from the LEDs to the phosphor coating. In some such examples, each LED of the plurality of LEDs of the illumination device is configured to illuminate a plurality of picture elements (e.g., 50 to 100 or several thousands) of the display device. Each plurality of picture elements can be considered a zone, with a so-called mini-LED configuration, with each zone in some examples being independently controllable compared with other zones. Switching different zones differently can improve contrast, e.g., by switching off one zone to give a darker black, and may be referred to as “local dimming”. [0117] The first type of LED of the illumination device in some examples is LED type B referred to earlier, and the second type of LED of the illumination device in some examples is LED type A referred to earlier. The first type of LED is for example configured to emit light with a peak wavelength in the range of 380 to 460 nanometers. The second type of LED is for example configured to emit white light. Such a second type of LED is , e.g., a blue LED with a phosphor layer to emit white light in response to absorbing blue light from the LED, or is , e.g., a so-called triplet LED comprising red, green and blue sub-LEDs. The plurality of luminescent nanostructures in the phosphor coating 1166 comprises for example a first type of nanostructure configured to: to absorb light with a first peak wavelength in the range of 380 to 460 nanometers, to emit light with a first wavelength (e.g., green), and not to emit light in the range of 380 to 460 nanometers. In some further examples, the plurality of luminescent nanostructures comprises a second type of nanostructure configured to: to absorb light with a second peak wavelength in the range of 380 to 460 nanometers, to emit light with a second wavelength (e.g., red), different from the first wavelength, not to emit light with the first wavelength, and not to emit light in the range of 380 to 460 nanometers. Note that an LED may emit light with more than one peak wavelength, so a peak may be a local peak.

[0118] The circuitry layers 1174 and 1160 are each connected to the display device control system, and are configured for control of the illumination device and the light modulator by the display device control system to output a desired image. The circuitry layer 1174 of the light modulator is for example configured for so-called active matrix control of the light modulator regions, by using a switching element (e.g., a thin film transistor (TFT)) per picture element, and appropriate application of electrical signals to the source and gate terminals of each TFT, to set each light modulator region to transmit a desired amount of light emitted by the phosphor coating. The circuitry layer 1160 of the illumination device is configured so that, for example, all LEDs of one type of LED can be controlled together, and all LEDs of another type of LED can be controlled together.

In some examples each LED of one or multiple types of LED can be controlled independently of each other. Depending on the number of LEDs and their layout, the circuitry layer 1160 may even comprise switching elements (e.g., TFTs) for active matrix control of the LEDs. [0119] The display device control system 1150 is connected to the circuitry layers and the common electrode by signal lines indicated with dashed lines. The display device control system has for example a data input 1190 for receiving data representative of one or more images for the display device to display. As the skilled person will appreciate the display device control system comprises the control circuit of the illumination device (which may be located on a circuit board separate from the circuitry layer 1160 of the illumination device, or may alternatively be located as part of the circuitry layer 1160). As the skilled person will appreciate, the display device control system comprises circuitry for (and based on data representative of an image to be displayed) determining and applying appropriate electrical signals to the electrodes and LEDs of the light modulator and the illumination device.

[0120] As the skilled person will appreciate, the magnitude of voltage applied between the common electrode and the electrode of a light modulator region of a given picture element, and therefore the size of the applied electric field, determines a rotational orientation of the LC molecules through the picture element relative to the alignment set by the alignment layer and also relative to the linear polarizer layers. Thus the extent of light modulation of each light modulator region can be controlled, and in turn the amount of light transmitted from the phosphor coating either aligned with the alignment layer or at least partly rotated in orientation relative to the alignment layer.

[0121] As explained earlier, the display device control system can switch the illumination device to a first display mode or a second display mode, e.g., based on a sensor detecting a change in a color temperature of ambient light (e.g., sunlight) or a clock signal (e.g., a current time of day). In known display devices, e.g., those using LC molecules, a night mode displays images with a warmer color temperature by controlling LC molecules of blue sub-pixels to reduce or block the amount of light transmitted through the blue sub pixel. This approach however consumes energy to generate white light for transmission through the blue sub-pixel despite the blue sub-pixel being switched to transmit less or no light. In contrast, by using the illumination device of the present examples, the display device control system can switch the display device between the first and second display modes without controlling the array of light modulator regions to change the color temperature of light output by the display device. Thus the light modulator regions for the B sub-pixels do not need to be adjusted to change the color temperature output by the display device.

[0122] Moreover, at some color temperatures, the emission of the LEDs of the illumination device in combination with the phosphor coating comprises less luminescence at wavelengths that are within the high-absorbance wavebands associated with a color filter of a sub-pixel. For example, for a warmer color temperature, the emission of the LEDs of the illumination device in combination with the phosphor coating emission comprises less blue luminescence that would be within the high- absorbance wavebands associated with the green and the red color filters in the green and red sub-pixels; therefore less energy from the LEDs in combination with the phosphor layer is absorbed by the green and red filters. Thus a greater proportion of the luminescence is emitted from the illumination device, compared with known devices using LEDs emitting white light and at least partly closing a blue sub-pixel.

[0123] As the skilled person will appreciate, further classes of examples are envisaged which have a light modulator in combination with an illumination device, but which use a different technology (e.g., microelectromechanical (MEMs) or electrophoretic technology) than LC molecules for light modulation.

[0124] Examples are further envisaged where the LEDs of the illumination device itself are controlled to modulate light output by each picture element, rather than using a separate light modulator in combination with the illumination device. For example, each sub-pixel of the illumination device described above using FIG. 11 may comprise a blue LED (e.g., LED type B), and a plurality of sub-pixels may be illuminated by one white LED (e.g., LED type A), or instead a green and a red LED. By appropriate control of each blue LED and the green and red LEDs, a color temperature of an image output by the display device can be adjusted e.g., switched between the first display mode and the second display mode.

[0125] The display device of examples described above may be incorporated into apparatus comprising: the display device, at least one processor; and at least one memory at least one memory comprising computer program instructions, the at least one memory and the computer program instructions operable to, with the at least one processor, control the display device control system for controlling the display device to output an image. In some examples the at least memory and the computer program instructions are operable to, with the at least one processor, control the display device control system for switching the display device between at least the first display mode and the second display mode. And in other examples, the at least memory and the computer program instructions are operable to, with the at least one processor, transmit to the display device control system data indicative of at least one of a time of day, a color temperature of ambient light or a color temperature of sunlight.

[0126] The apparatus is for example an electronic device comprising the display device of examples for display an image to a user. Such an electronic device is for example a television, a computer monitor, a tablet computing device, a laptop computing device, a mobile telecommunications device, a portable (e.g., mobile) device, an electronic reader device, a watch or a satellite navigation device. A system diagram illustrating an example of a basic hardware architecture of the apparatus is shown in FIG. 12, such as a tablet computing device. Note that in other implementations some of the components shown in FIG. 12 are not present; for example for a computer monitor implementation, the system storage and/or battery may not be present. The apparatus 1 includes at least one processor 2 connected to and therefore in data communication with for example: a display device control system 4 (e.g., according to examples described earlier), a communications system 6, a user input system 8, a power system 10 and system storage 12. The display device control system is connected to and is therefore in data communication with the display device 14. The at least one processor 2 is for example a general purpose processor, a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any suitable combination thereof designed to perform the functions described herein. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The processor may be coupled, via one or more buses, to read information from or write information to one or more memories, for example those of the system storage 12. The at least one processor may additionally, or in the alternative, contain memory, such as processor registers. [0127] The display device control system 4 for example includes driver components, for use in applying a voltage to any of the picture elements, to address different such picture elements. In examples the light modulator regions of the picture elements are driven using an active matrix control scheme and the display device control system is configured to control switching elements such as thin film transistors (TFTs) of the display device 1 via circuitry to control the picture elements. The circuitry may include signal and control lines. For example, the display device control system may include display drivers such as display column drivers and display row drivers.

[0128] The communications system for example is configured for the apparatus to communicate with for example a computing device via a data network, for example a computer network such as the Internet, a local area network, a wide area network, a telecommunications network, a wired network, a wireless network, or some other type of network. The communications system may further for example comprise an input/output (I/O) interface, such as a universal serial bus (USB) connection, a Bluetooth or infrared connection, or a data network interface for connecting the apparatus to a data network such as any of those described above. Content data as described later may be transferred to the apparatus via the communications system.

[0129] The user input system may include for example an input device for receiving input from a user of the apparatus. Example input devices include, but are not limited to, a keyboard, a rollerball, buttons, keys, switches, a pointing device, a mouse, a joystick, a remote control, an infrared detector, a voice recognition system, a bar code reader, a scanner, a video camera (possibly coupled with video processing software to, e.g., detect hand gestures or facial gestures), a motion detector, a microphone (possibly coupled to audio processing software to, e.g., detect voice commands), or other device capable of transmitting information from a user to the device. The input device may also take the form of a touch-screen associated with the display device, in which case a user responds to prompts on the display device by touch. The user may enter textual information through the input device such as the keyboard or the touch-screen.

[0130] The apparatus may also include a user output system (not illustrated) including for example an output device for providing output to a user of the apparatus. Examples include, but are not limited to, a printing device, an audio output device including for example one or more speakers, headphones, earphones, alarms, or haptic output devices. The output device may be a connector port for connecting to one of the other output devices described, such as earphones.

[0131] The power system for example includes power circuitry 16 for use in transferring and controlling power consumed by the apparatus. The power may be provided by a mains electricity supply or from a battery 18, via the power circuitry. The power circuitry may further be used for charging the battery from a mains electricity supply.

[0132] The system storage 12 includes at least one memory, for example at least one of volatile memory 20 and non-volatile memory 22 and may comprise a non-transitory computer readable storage medium. The volatile memory may for example be a Random Access Memory (RAM). The non-volatile (NV) memory may for example be a solid state drive (SSD) such as Flash memory, or Read Only Memory (ROM). Further storage technologies may be used, for example magnetic, optical or tape media, compact disc (CD), digital versatile disc (DVD), Bluray or other data storage media. The volatile and/or non-volatile memory may be removable or non-removable.

[0133] Any of the memories may store data for controlling the apparatus, for example components or systems of the apparatus. Such data may for example be in the form of computer readable and/or executable instructions, for example computer program instructions. Therefore, the at least one memory and the computer program instructions may be configured to, with the at least one processor, control the display device control system for controlling the display device to output an image.

[0134] In the example of FIG. 12, the volatile memory 20 stores for example display device data 24 which is indicative of an image to be provided by the display device 14. The processor 2 may transmit data, based on the display device data, to the display device control system 4 which in turn outputs signals to the display device for applying voltages to the picture elements, for displaying an image. The non-volatile memory 22 stores for example program data 24 and/or content data 26. The program data is for example data representing computer executable instructions, for example in the form of computer software, for the apparatus to run applications or program modules for the apparatus or components or systems of the apparatus to perform certain functions or tasks, and/or for controlling components or systems of the apparatus. For example, application or program module data includes any of routines, programs, objects, components, data structures or similar. The content data is for example data representing content for example for a user; such content may represent any form of media, for example text, at least one image or a part thereof, at least one video or a part thereof, at least one sound or music or a part thereof. Data representing an image or a part thereof is for example representative of an image to be provided by at least one picture element of the display device. Such data may include content data of one type, but may instead include a mixture of content data of different types, for example a movie may be represented by data including at least image data and sound data.

[0135] Various methods are envisaged of fabricating and/or assembling an illumination device of examples described here, a display device described herein, and apparatus described herein comprising the display device. For example, a method of assembling the display device comprises providing the illumination device (e.g., pre-assembled), providing the light modulator (e.g., pre-assembled), positioning the array of light modulator regions relative to the plurality of LEDs, for the display device, and bonding the illumination device to the light modulator. A method of assembling the apparatus for example comprises providing the display device and connecting the at least one processor to the display device control system.

[0136] It is envisaged that the illumination device described above as part of a display device may in other examples be used independently as an illumination device (with an appropriate control system, but , e.g., without a light modulator) for an interior lighting application.

[0137] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. [0138] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An illumination device, comprising: a control circuit configured to determine a first plurality of signals based on a first target color temperature; a plurality of light emitting diodes (LEDs) configured to emit a first plurality of source lights based in the first plurality of signals, wherein the plurality of LEDs comprises at least two types of LEDs; and a housing comprising a phosphor coating with a plurality of luminescent nanostructures configured to emit, based on the first plurality of source lights, a first output light corresponding to the first target color temperature.

2. The illumination device of claim 1, further comprising: a circuit board, wherein the plurality of LEDs are disposed on the circuit board, and wherein the plurality of luminescent nanostructures comprises quantum dots.

3. The illumination device of clam 2, wherein: the circuit board is disposed on a first portion of the housing; and the phosphor coating is disposed on a second portion of the housing.

4. The illumination device of claim 2, further comprising: a first reflector coating configured to reflect the first plurality of source lights.

5. The illumination device of claim 4, wherein: the first reflector coating is disposed on a first portion of the housing; and the phosphor coating is disposed on a second portion of the housing.

6. The illumination device of claim 5, wherein: the circuit board comprises a first side facing the first reflector coating and a second side facing the phosphor coating; and the plurality of LEDs are disposed on the first side.

7. The illumination device of claim 4, further comprising: a second reflector coating disposed on the circuit board and configured to reflect the first plurality of source lights.

8. The illumination device of claim 4, further comprising: a second reflector coating covering the control circuit disposed on the circuit board and configured to reflect the first plurality of source lights.

9. The illumination device of claim 4, wherein the first reflector coating and the phosphor coating are disposed as alternating strips on the housing.

10. The illumination device of claim 1, wherein the housing comprises at least one selected from a group consisting of a tube shape and a bulb shape.

11. The illumination device of claim 1, wherein the housing comprises a glass substrate and the phosphor coating is inside the glass substrate.

12. The illumination device of claim 1, wherein: the control circuit is further configured to generate a second plurality of signals based on a second target color temperature; the plurality of LEDs is further configured to emit a second plurality of source lights based on the second plurality of signals; the phosphor coating is further configured to emit, based on the second plurality of source lights, a second output light that approximates the second target color temperature.

13. The illumination device of claim 12, wherein: the first target color temperature corresponds to a color temperature of sunlight at a first time of day; and the second target color temperature corresponds to the color temperature of sunlight at a second time of day.

14. The illumination device of any preceding claim, wherein: the at least two types of LEDs comprise a first type of LED configured to emit light with a peak wavelength in the range of 380 to 460 nanometers; and the plurality of luminescent nanostructures comprises a first type of nanostructure configured: to absorb light with a first peak wavelength in the range of 380 to 460 nanometers, to emit light with a first wavelength, and not to emit light in the range of 380 to 460 nanometers.

15. The illumination device of claim 14, wherein: the plurality of luminescent nanostructures comprises a second type of nanostructure configured: to absorb light with a second peak wavelength in the range of 380 to 460 nanometers, to emit light with a second wavelength, different from the first wavelength, not to emit light with the first wavelength, and not to emit light in the range of 380 to 460 nanometers.

16. The illumination device of claim 14 or 15, wherein: the at least two types of LEDs comprise a second type of LED configured to emit white light.

17. The illumination device of any preceding claim, wherein: the phosphor coating is planar, and the plurality of LEDs is configured as an array of LEDs to illuminate the phosphor coating.

18. The illumination device of any of claims 1 to 16, comprising at least one of: i) a light guide, wherein: the phosphor coating is planar, and at least one LED of the plurality of LEDs is positioned along a perimeter of the light guide, to illuminate the phosphor coating via the light guide, or ii) a light diffuser, wherein: the phosphor coating is planar, and/or a phosphor is embedded within the light diffuser..

19. A display device comprising: the illumination device of any preceding claim; and a display device control system comprising the control circuit of the illumination device and configured to switch the display device between at least: a first display mode, with the illumination device outputting light of a first color temperature; and a second display mode, with the illumination device outputting light of a second color temperature.

20. The display device of claim 19, comprising: a light modulator comprising an array of light modulator regions to modulate light from the illumination device, each light modulator region of the array of light modulator regions corresponding with a respective picture element of the display device, wherein the display device control system is configured to control the array of light modulator regions for the display device to output an image.

21. The display device of claim 20, wherein each light modulator region of the array of light modulator regions respectively comprises: liquid-crystal (LC) molecules; and electrodes positioned for applying an electric field, under control of the display device control system, to change an orientation of the LC molecules and modulate light output by the respective picture element.

22. The display device of any of claims 19 to 21, wherein each LED of the plurality of LEDs of the illumination device is configured to illuminate a plurality of picture elements of the display device.

23. The display device of any of claims 19 to 22, wherein: the display device control system is configured to switch the display device between the first display mode and the second display mode without controlling the array of light modulator regions to change the color temperature of light output by the display device.

24. Apparatus comprising: the display device of any of claims 19 to 23; at least one processor; and at least one memory comprising computer program instructions, the at least one memory and the computer program instructions operable to, with the at least one processor, control the display device control system for controlling the display device to output an image.

25. Apparatus of claim 24, wherein the at least memory and the computer program instructions are operable to, with the at least one processor, control the display device control system for switching the display device between at least the first display mode and the second display mode.

26. Apparatus of claim 24 or 25, wherein the at least memory and the computer program instructions are operable to, with the at least one processor, transmit to the display device control system data indicative of at least one of a time of day, a color temperature of ambient light or a color temperature of sunlight.

27. A method of assembling the display device of any of claims 20 to 23, comprising: providing the illumination device; providing the light modulator; positioning the array of light modulator regions relative to the plurality of LEDs, for the display device; and bonding the illumination device to the light modulator.

28. A method of assembling the apparatus of any of claims 24 to 26, comprising: providing the display device; and connecting the at least one processor to the display device control system.

29. A method for operating an illumination device associated with a phosphor coating comprising a plurality of luminescent nanostructures, comprising: determining, based on a first target color temperature, a first plurality of signals for a plurality of light emitting diodes (LEDs), wherein the plurality of LEDs comprises at least two types of LEDs; emitting a first plurality of source lights by driving the plurality of LEDs with the first plurality of signals; and emitting, by the phosphor coating and based on the first plurality of source lights, a first output light corresponding to the first target color temperature.

30. The method of claim 29, further comprising: obtaining a second target color temperature; determining, based on the second target color temperature, a second plurality of signals for a plurality of LEDs; emitting a second plurality of source lights by driving the plurality of LEDs with the second plurality of signals; and emitting, by the phosphor coating and based on the second plurality of source lights, a second output light corresponding to the second target color temperature.

31. The method of claim 30, wherein: obtaining the first target color temperature comprises determining a color temperature of sunlight at a first time of day; and obtaining the second target color temperature comprises determining the color temperature of sunlight at a second time of day.

32. The method of claim 31, further comprising: reflecting, by a first reflector coating, the first plurality of source lights, wherein the plurality of LEDs are disposed on a circuit board, wherein the circuit board is within a housing of the illumination device, and wherein the plurality of luminescent nanostructures comprises quantum dots.

33. The method of claim 32, further comprising: reflecting, by a second reflector coating, the first plurality of source lights, wherein the first reflector coating is disposed on a first portion of the housing, wherein the phosphor coating is disposed on a second portion of the housing, and wherein the second reflector coating is disposed on the circuit board.

34. The method of claim 32, further comprising: reflecting, by a second reflector coating, the first plurality of source lights, wherein the first reflector coating is disposed on a first portion of the housing, wherein the phosphor coating is disposed on a second portion of the housing, wherein the first plurality of signals are determined by a control circuit disposed on the circuit board, and wherein the second reflector coating covers the control circuit.

35. The method of claim 32, wherein the first reflector coating and the phosphor coating are disposed as alternating strips on the housing.