Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/03—Printing inks characterised by features other than the chemical nature of the binder
  • C09D11/037—Printing inks characterised by features other than the chemical nature of the binder characterised by the pigment
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  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
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  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
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  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/66—Additives characterised by particle size
  • C09D7/67—Particle size smaller than 100 nm
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  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/56—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing sulfur
  • C09K11/562—Chalcogenides
  • C09K11/565—Chalcogenides with zinc cadmium
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  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/08—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials
  • C09K11/88—Luminescent materials, e.g. electroluminescent or chemiluminescent containing inorganic luminescent materials containing selenium, tellurium or unspecified chalcogen elements
  • C09K11/881—Chalcogenides
  • C09K11/883—Chalcogenides with zinc or cadmium
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional [2D] radiating surfaces
  • H05B33/14—Light sources with substantially two-dimensional [2D] radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source
  • H05B33/145—Arrangements of the electroluminescent material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/30—Sulfur-, selenium- or tellurium-containing compounds
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
  • G02B1/11—Anti-reflection coatings
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/0006—Arrays
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/08—Mirrors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/85—Packages
  • H10H20/851—Wavelength conversion means
  • H10H20/8511—Wavelength conversion means characterised by their material, e.g. binder
  • H10H20/8512—Wavelength conversion materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/85—Packages
  • H10H20/851—Wavelength conversion means
  • H10H20/8511—Wavelength conversion means characterised by their material, e.g. binder
  • H10H20/8512—Wavelength conversion materials
  • H10H20/8513—Wavelength conversion materials having two or more wavelength conversion materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/85—Packages
  • H10H20/852—Encapsulations
  • H10H20/854—Encapsulations characterised by their material, e.g. epoxy or silicone resins
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/701—Integrated with dissimilar structures on a common substrate
  • Y10S977/715—On an organic substrate
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/734—Fullerenes, i.e. graphene-based structures, such as nanohorns, nanococoons, nanoscrolls or fullerene-like structures, e.g. WS2 or MoS2 chalcogenide nanotubes, planar C3N4, etc.
  • Y10S977/753—Fullerenes, i.e. graphene-based structures, such as nanohorns, nanococoons, nanoscrolls or fullerene-like structures, e.g. WS2 or MoS2 chalcogenide nanotubes, planar C3N4, etc. with polymeric or organic binder
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/832—Nanostructure having specified property, e.g. lattice-constant, thermal expansion coefficient
  • Y10S977/834—Optical properties of nanomaterial, e.g. specified transparency, opacity, or index of refraction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/23—Sheet including cover or casing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/23—Sheet including cover or casing
  • Y10T428/239—Complete cover or casing

Definitions

• the present invention relates to nanocomposite matrixes, including polymeric layers comprising nanocrystals, and processes for preparing nanocrystal doped matrixes.
• High performance down-converting phosphor technologies will play a prominent role in the next generation of visible light emission, including high efficiency solid-state white lighting (SSWL).
• SSWL solid-state white lighting
• NIR near infrared
• L infrared
• NIR near infrared
• NIR ultraviolet
• L infrared
• Down-conversion from ultraviolet (UN) or blue light emitting semiconductor light emitting diodes (LEDs) into blue, red and green wavelengths offers a fast, efficient and cost-effective path for delivering commercially attractive white light sources.
• LEDs often suffer from reduced performance as a result of internal reflection of photons at the chip/coating interface.
• LEDs are encapsulated or coated in a polymeric material (which may comprise phosphors) to provide stability to the light-emitting chip.
• a polymeric material which may comprise phosphors
• these coatings are made by using an inorganic or organic coating that has a very different refractive index than the base material (i.e., the chip), which results in a detrimental optical effect due to the refractive index mismatch at the interface between the two materials.
• the temperature of the LED can reach in excess of 100°C.
• a compliant polymeric layer e.g., silicone
• this compliant layer is often further coated with a hard shell polymer.
• the resulting LED structure suffers loss of light at the chip/compliant polymer interface due to the lower refractive index of the polymer coating in relation to the LED.
• the refractive index of the compliant layer is increased, even greater loss will occur due at the high refractive index/low refractive index interface between the compliant polymer and the hard shell polymer due to internal reflection.
• the present invention fulfills these needs by providing polymeric nanocomposites that function as down-converting layers, photon-filtering layers and/or refractive index matching layers, by taking advantage of the ability to tailor nanocrystals to maximize their emission, absorption and refractive index properties.
• the present invention provides matrix materials doped with nanocrystals that have specific emission and/or absorption characteristics and also allow for specific tailoring of refractive indexes of the nanocomposites.
• the present invention provides polymeric layers comprising a polymer and semiconductor nanocrystals embedded within the polymer, wherein the nanocrystals have a size and a composition such that they absorb visible, ultraviolet, near-infrared and/or infrared light, and wherein the polymeric layers scatter a minimal portion of light that enters the layers.
• the polymer is silicone.
• the polymeric layers of the present invention can be used to coat optical devices (e.g., refractive lenses or reflective elements) or can be used to encapsulate active devices, such as a light emitting diodes (LEDs).
• the polymeric layers of the present invention that absorb visible light will absorb red light, blue light and/or green light.
• the nanocrystals utilized throughout the embodiments of the present invention will suitably be between about 1-10 nm in size, about 1-4 nm in size or about 1-3 nm in size and can further comprise miscibility-enhancing ligands attached to their surface to aid in mixing with the polymers.
• the polymeric layers of the present invention can have any effective refractive index between that of the pure polymer and the pure nanocrystals, and will suitably have an effective refractive index greater than about 1.5 and in certain embodiments about 1.8. In certain embodiments, the polymeric layers of the present invention will be greater than about 0.5 mm in thickeness
• the present invention provides polymeric layers comprising a polymer and semiconductor nanocrystals embedded within the polymer, wherein the polymeric layer has an effective refractive index greater than the polymer alone, and wherein the polymeric layer scatters a minimal portion of light that enters the polymeric layer.
• the polymeric layers will scatter less than about 50%, less than about 20% or less than about 15% of light that enters the polymeric layers.
• the nanocrystals will be ZnS nanocrystals and the polymeric layers will be greater than about 0.5 mm in thickness.
• the present invention provides polymeric layers that encapsulate an active device (e.g., an LED) that has an effective refractive index, ni.
• the layer comprises a polymer and semiconductor nanocrystals embedded within the polymer.
• the layer has an inner boundary in contact with the active device and an outer boundary in contact with a medium having an effective refractive index, n 2 , wherein the layer has an effective refractive index less than or equal to ni at the inner boundary and an effective refractive index greater than or equal to n at the outer boundary, h certain embodiments, effective refractive index ni will be greater than n 2 , suitably greater than about 1.5, and in certain embodiments about 1.8.
• the layer will have a nanocrystal density gradient, being highest at the inner boundary and lowest at the outer boundary. Suitably this nanocrystal density gradient will be linear throughout the polymeric layer.
• the present invention also provides processes for preparing polymeric layers, comprising mixing semiconductor nanocrystals at a first density with a solvent and a polymer to form a first mixture, coating a substrate material with the first mixture and evaporating the solvent to form the polymeric layer, wherein the polymeric layer has an effective refractive index of n ⁇ .
• the processes of the present invention can be used to prepare polymeric layers for coating active devices (e.g., LEDs), or optical devices (e.g., refractive lenses or reflective elements).
• active devices e.g., LEDs
• optical devices e.g., refractive lenses or reflective elements.
• the processes of the present invention can utilize nanocrystals which further comprise miscibility- enhancing ligands attached to their surface.
• the processes of the present invention can further comprise mixing semiconductor nanocrystals at a second density with a solvent and a polymer to form a second mixture, coating the substrate material with the second mixture and evaporating the solvent to form a second polymeric layer, wherein the second polymeric layer has an effective refractive index of n 2 .
• the processes can further til comprise repeating these steps with a third through density of fh semiconductor nanocrystals to produce third through i polymeric layers, wherein the third through i polymeric layers have effective refractive indices, n 3 through n;, respectively.
• the effective refractive index ni will be greater than n and the effective refractive index of the i th polymeric layer will be less than the effective refractive index of any other polymeric layer.
• the processes of the present invention can further comprise centrifuging the first mixture of semiconductor nanocrystals, solvent and polymer, to form a nanocrystal density gradient within the mixture prior to coating the substrate material.
• the coating can be via spin coating or screen printing.
• the nanocrystals used in the processes of the present invention can have a size and a composition such that they absorb light at a particular wavelength.
• the nanocrystals can be tuned so as to emit light at a particular wavelength.
• the process of the present invention can utilize semiconductor nanocrystals that comprise two or more different sizes or compositions and therefore can have different properties.
• the polymeric layers produced by the processes of the present invention will suitably be greater than about 0.5 mm in thickness.
• the present invention provides solid state white lighting devices comprising a power efficiency greater than 25 lm/W, suitably greater than 50 lm/W, greater than 100 lm/W, greater than 150 lm W, or greater than 200 lm/W.
• the solid state white lighting devices comprise a down converting nanocomposite that comprises two or more semiconductor nanocrystals tuned to emit light at one or more selected wavelengths.
• the solid state white lighting devices of the present invention will suitably provide a CRI of greater than about 80.
• the solid state white lighting devices comprise a matrix coupled to the two or more semiconductor nanocrystals via one or more chemical moieties.
• the present invention provides down converting nanocomposite devices, comprising two or more semiconductor nanocrystal phosphors of two or more sizes, the nanocrystal phosphors tuned to emit light at one or more selected wavelengths, and providing a CRI of greater than about 80; a matrix with a high index of refraction, low UN degradation and/or matched thermal expansion; and a chemical structure coupling the matrix to the nanocrystal phosphors.
• the two or more semiconductor nanocrystal phosphors will comprise a core-shell structure, wherein a shell (e.g., ZnS) provides a type I band gap with respect to a core.
• the core-shell nanocrystals of the present invention will suitably have a quantum efficiency of about 10% to about 90%.
• the two or more semiconductor nanocrystal phosphors are color matched and the matrix can comprise TiO .
• the nanocomposite can be layered on an LED substrate which comprises sapphire or SiC.
• the matrix will be a compliant layer that can withstand the thermal expansion that results when the LED heats up, and suitably will be silicone.
• the present invention provides polymeric layers, comprising a polymer; and semiconductor nanocrystals embedded within the polymer, wherein the nanocrystals have miscibility-enhancing ligands conjugated to their surface, and wherein the ligands comprise an alkane chain of between 6 and 18 carbons in length, hi suitable embodiments, the ligands can comprise an alkane chain of between 12 and 18 carbons in length.
• the polymer will suitably be silicone, and the semiconductor nanocrystals will suitably have a size between about 1-10 nm, and in certain embodiments will be ZnS nanocrystals.
• the polymeric layers will scatter a minimal portion of light that enters said polymeric layer.
• the layer will be greater than about 0.5 mm in thickness.
• FIG. 1 shows absorption and emission spectra for various nanocrystal radii showing continuous tailoring of the emission and absorption wavelengths.
• FIG. 2 shows a comparison of traditional thick phosphors integrated during packaging, and a nanocomposite down-converting layer integrated prior to dicing, according to one embodiment of the present invention.
• FIG. 3 shows the elimination of wasted light at the edges of the visible spectrum by using phosphor nanocrystals, compared to traditional phosphor edge losses.
• FIG. 4 shows the normalized intensity generated by mixing a continuum of nanocrystal sizes, creating broad-band white light.
• FIG. 5 shows a three color emitting LED in accordance with one embodiment of the present invention.
• FIG. 6 is a cross-sectional view of a polymeric layer in accordance with one embodiment of the present invention.
• FIG. 7 is a cross-sectional view of a polymeric layer having a nanocrystal density gradient in accordance with one embodiment of the present invention.
• FIG. 8 is a cross-sectional view of an optical device with a polymeric layer coating the device in accordance with one embodiment of the present invention.
• FIG. 9 is a plot showing the effective refractive index of various matrixes versus volume loading ratio of ZnS nanocrystals. [0035] FIG.
• FIG. 10 is a plot showing the effective refractive index of a silicone nanocomposite comprising ZnS nanocrystals as a function of wavelength.
• FIG. 11 is a cross-sectional view of a light emitting diode encapsulated within a polymeric layer in accordance with one embodiment of the present invention.
• FIG. 12 is a cross-sectional view of a light emitting diode encapsulated within a polymeric layer having a nanocrystal density gradient in accordance with one embodiment of the present invention.
• FIG. 13 is a traditional LED chip - silicon cap assembly.
• FIG. 14 is a nanocomposite - LED chip assembly in accordance with one embodiment of the present invention.
• FIG. 15 is a nanocomposite - LED chip assembly in accordance with one embodiment of the present invention.
• FIG. 16 is a plot of percent transmittance for a silicone nanocomposite comprising ZnS nanocrystals as a function of nanocrystals size.
• FIG. 17 is a plot of percent transmission for a silicone nanocomposite comprising ZnS nanocrystals as a function of wavelength.
• FIG. 18 shows a representation of a 3-part ligand, with a tail-group, a head group and a middle/body-group. [0044] FIG.
• FIG. 19 is an example ligand that can be conjugated to the nanocrystals of the present invention.
• FIGS. 20a-20n show examples, chemical synthesis, and NMR characterization of several example ligands in accordance with the present invention.
• FIG. 21 is a flowchart depicting processes for preparing polymeric layers in accordance with the present invention.
• FIG. 22 is a cross-sectional view of a polymeric layer comprising individual layers each with a different nanocrystal density gradient according to one embodiment of the present invention.
• FIG. 23 shows an X-Ray diffraction analysis of ZnS nanocrystals.
• FIG. 24 shows Transmission Electron Micrographs of ZnS nanocrystals.
• the present invention provides various polymeric nanocomposites comprising polymeric materials with embedded nanocrystals.
• the various properties of the nanocrystals including their absorption properties, emission properties and refractive index properties, are utilized to create nanocomposites that can be tailored and adjusted for various applications, hi one embodiment, the present invention provides applications of semiconductor nanocrystals that utilize their emission properties in down-conversion applications.
• the present invention combines two, non-electronically active properties of the same nanocrystals, by using the high absorption coefficient and relatively sharp band edge of the nanocrystals to filter light as a cutoff filter.
• the high refractive index of nanocrystals can also be used when mixed into low refractive index materials to create substantially transparent nanocomposites with effective refractive indexes matched to the substrates they are coating.
• the refractive index of the nanocomposite can be matched to a second, further encapsulating material.
• the present invention also provides for nanocomposites that combine two or more of these various properties in different configurations into the same nanocomposite.
• nanocrystal 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 on the order of less than about 1 nm.
• “about” means a value of ⁇ 10% of the stated value (e.g. "about 100 nm encompasses a range of sizes from 90 nm to 110 nm, inclusive).
• the terms “nanocrystal,” “nanodot,” “dot” and “quantum dot” are readily understood by the ordinarily skilled artisan to represent like structures and are used herein interchangeably.
• the present invention also encompasses the use of polycrystalline or amorphous nanocrystals.
• Nanocrystals can be substantially homogenous in material properties, or in certain embodiments, can be heterogeneous.
• the optical properties of nanocrystals can be determined by their particle size, chemical or surface composition. The ability to tailor the nanocrystal size in the range between about 1 nm and about 15 nm enables photoemission coverage in the entire optical spectrum to offer great versatility in color rendering. Particle encapsulation offers robustness against chemical and UN deteriorating agents.
• Nanocrystals for use in the present invention can be produced using any method known to those skilled in the art. Suitable methods are disclosed in U.S. Patent Application No. 10/796,832, filed March 10, 2004, U.S. Patent Application No. 10/656,910, filed September 4, 2003 and U.S. Provisional Patent Application No. 60/578,236, filed June 8, 2004, the disclosures of each of which are incorporated by reference herein in their entireties.
• the nanocrystals for use in the present invention can be produced from any suitable material, suitably an inorganic material, and more suitably an inorganic conductive or semiconductive material. Suitable semiconductor materials include those disclosed in U.S. Patent Application No.
• Suitable semiconductor materials include, but are not limited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P, B ⁇ , BP, BAs, A1 ⁇ , A1P, AlAs, AlSb, Ga ⁇ , GaP, GaAs, GaSb, hi ⁇ , InP, InAs, InSb, A1 ⁇ , A1P, AlAs, AlSb, Ga ⁇ , GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, Pb
• the semiconductor nanocrystals may comprise a dopant from the group consisting of: a p-type dopant or an n-type dopant.
• the nanocrystals useful in the present invention can also comprise II-VI or III-V semiconductors.
• II-VI or III-V semiconductor nanocrystals 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, Po, of the Periodic Table; and any combination of an element from Group III, such as B, Al, Ga, In, and Tl, with any element from Group V, such as N, P, As, Sb and Bi, of the Periodic Table.
• the nanocrystals useful in the present invention can also further comprise ligands conjugated, cooperated, associated or attached to their surface as described throughout.
• Suitable ligands include any group known to those skilled in the art, including those disclosed in U.S. Patent Application No. 10/656,910 and U.S. Provisional Patent Application No. 60/578,236.
• Use of such ligands can enhance the ability of the nanocrystals to incorporate into various solvents and matrixes, including polymers. Increasing the miscibility (i.e., the ability to be mixed without separation) of the nanocrystals in various solvents and matrixes allows them to be distributed throughout a polymeric composition such that the nanocrystals do not aggregate together and therefore do not scatter light.
• Such ligands are described as "miscibility-enhancing" ligands herein.
• nanocomposite refers to matrix materials comprising nanocrystals distributed or embedded therein.
• suitable matrix materials can be any material known to the ordinarily skilled artisan, including polymeric materials, organic and inorganic oxides.
• Nanocomposites of the present invention can be layers, encapsulants, coatings or films as described herein. It should be understood that in embodiments of the present invention where reference is made to a layer, polymeric layer, matrix, or nanocomposite, these terms are used interchangeably, and the embodiment so described is not limited to any one type of nanocomposite, but encompasses any matrix material or layer described herein or known in the art.
• the present invention provides a complete down- conversion system based on engineered nanocomposite materials for use with currently available blue LED excitation sources that dramatically improve the overall cost, performance and efficiency of SSWL.
• the down-converting nanocomposites of the present invention utilize the emission properties of nanocrystals 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).
• active sources e.g., LEDs
• the nanocrystals utilized in the down-converting applications of the present invention will be constructed and tailored so as to be highly emitting.
• this system produces SSWL that exceeds performance of the best traditional fluorescent and incandescent bulbs, with color rendering of greater than 80 and power efficiency of greater than 200 lm/W, at a cost of less than one U.S. dollar/khn.
• the luminous efficiency (measured in lm/W) is the efficiency of the conversion from electrical power (W) to optical power (W), combined with the efficiency of the conversion from optical power (W) to the luminous flux.
• ⁇ wp is the wall plug efficiency
• r ⁇ ⁇ um is the photopic efficiency/response of the human eye
• ⁇ ss is the stokes shift efficiency from converting a blue photon to a longer wavelength photon
• ⁇ iQE is the internal quantum efficiency of the phosphor
• ⁇ pa ckage is overall package efficiency and accounts for losses in light extraction efficiency from optical scattering (E os ), parasitic scattering (E pS ), total internal reflection (E T ⁇ R ), external packaging like the lead frame and submount (E exp ), etc.
• CCT or correlated color temperature refers to the human eye property of being optimally adapted to the sunlight spectral content.
• K Kelvin
• the chromaticity coordinates for R, G and B must fall near the black body radiation, for temperatures between 2000°C and 8000°C. Higher or lower than "optimum" temperatures register to the eye as too “cold” or too “warm” color hues.
• Color rendering has to do with the appearance of various object colors under a given source illumination, compared to that from a reference source.
• a collection of 14 sample colors of different saturation is customarily used for the color rendering index (CRT), which provides a quantitative measure on a scale of 1 to 100.
• CRT color rendering index
• Two sources of similar color temperature may produce widely varying CRIs. Low CRIs make colors unacceptable for illumination, while high CRI (>80) are acceptable for general illumination purposes.
• the present invention provides processes comprising: [0064] (1) A simulation model can be used to determine optimized nanocrystal mixtures for CRI, CCT, and luminous efficiency with targets of CRI>80, CCT about 4,000 K and efficiency of 200 lm/W. [0065] (2) Nanocrystals and nanocrystal component mixtures are synthesized with emission peak widths, peak maximums, and intensity ratios determined by simulation.
• a controlled nanocrystal phosphor nanocomposite including: (a) a surface ligand capable of achieving high (about 20% or more) loading density in the selected composite is produced; (b) a ligand exchange process to incorporate a 3-part ligand onto the nanocrystal is performed; (c) a homogeneous, non-phase separated TiO 2 nanocomposite with nanocrystal loading densities up to 20% by volume is produced; (d) quantum yield (QY) dependence on nanocrystal loading density in the nanocomposite is determined; (e) an index of refraction dependence on loading density in the nanocomposite and index-matching of the nanocomposite to blue LED substrate (e.g., sapphire and/or SiC) is determined; and (f) a relationship of loading density and film thickness to optimize refractive index matching and nanocomposite optical density is determined.
• QY quantum yield
• the simulation program incorporates an algorithm to determine the optimum spectral emission characteristics of nanocrystal component mixtures for simultaneous maximization of color rendering, color temperature and overall efficacy for production of white light.
• the approach provides a super- convergent, random search, optimization algorithm in the phosphor parameter space.
• the program seeks a combination of emission wavelengths that simultaneously maximizes luminous efficacy, color rendering (CRI) and color temperature (CCT), subject to the white-light chromaticity constrains calculated using standard CIE (Commission Internationale de PEclairage).
• CIE Commission Internationale de PEclairage
• the measured nanocrystal quantum efficiency, peak wavelength and emission spectral width are input parameters. Performance boundaries, as for example, efficacy no less than 90%, or CRI > 90, can also be applied for flexibility in the design.
• the number of required wavelengths i.e., nanocrystal sizes
• the number of required wavelengths is a variable that allows a determination of trade-offs between performance and manufacturing cost.
• a validation procedure with iteration cycles is adopted, whereby mixtures of nanocrystal components, of size, composition peak maximum, peak widths, mixture abundance, and internal quantum efficiency predicted by the simulation are manufactured.
• the resulting values of CRI and CCT are determined experimentally and compared with the predictions and adjustments are made as appropriate.
• the luminous efficiency is determined based on optical parameters including stoke shift efficiency, internal quantum efficiency and photopic response.
• the output of this procedure is the optimum number of emission colors, the precise center wavelengths of each color, the precise spectral width of each color and the exact relative intensity of each and the corresponding concentration based on excitation by, for example, a selected blue LED (about 460nm).
• the simulations described throughout can determine suitable emission characteristics for the nanocrystal.
• available solution phase synthetic techniques are used to fabricate core/shell nanocrystal phosphors and characterize mixtures as determined by the theoretical model.
• nanocrystal batches are fabricated with spectral characteristics generated by the theoretical model. Each distinct wavelength is synthesized separately and combined to produce the final mixture. Specific attention is paid to the center wavelength and the peak- width of each sample. In particular, narrow emission in the red avoids efficiency loss in the IR.
• a solution-phase mixture of nanocrystals is produced and characterized that has the appropriate composition to produce white light with CRI and CTT, matching that of the theoretical model when illuminated with blue excitation and total down- conversion efficiency comparable to that predicted by the model, assuming zero loss to other mechanisms in the process.
• synthesis occurs as an initial nucleation event that takes place over seconds, followed by crystal growth at elevated temperature for several minutes.
• Parameters such as the temperature, types of surfactants present, precursor materials, and ratios of surfactants to monomers can be modified so as to change the nature and progress of the reaction.
• the temperature controls the structural phase of the nucleation event, rate of decomposition of precursors, and rate of growth.
• the organic surfactant molecules mediate both solubility and control of the nanocrystal shape.
• the ratio of surfactants to monomer, surfactants to each other, monomers to each other, and the individual concentrations of monomers strongly influence the kinetics of growth.
• CdSe is used as the nanocrystal 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 is also possible to substitute non-cadmium-containing nanocrystals.
• the shell material can be chosen such that the electronic levels are type I 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 can be reduced.
• Core-shell structures are obtained by adding organometallic precursors containing the shell materials to a reaction mixture containing the core nanocrystal.
• the cores act as the nuclei, and the shells 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 ensure solubility.
• a uniform and epitaxially grown shell is obtained when there is a low lattice mismatch between the two materials.
• the spherical shape acts to minimize interfacial strain energy from the large radius of curvature, thereby preventing the formation of dislocations that could degrade the optical properties of the nanocrystal system.
• ZnS can be used as the shell material using known synthetic processes, resulting in a high-quality emission. As above, if necessary, this material can be easily substituted if the core material is modified.
• FIG. 1 represents the abso ⁇ tion and emission peaks for nanocrystals of increasing size (2 nm to 15 nm).
• the initial peak (lower wavelength) indicates the abso ⁇ tion wavelength and the later peak (higher wavelength) the emission wavelength in nm.
• the abso ⁇ tion and emission peak wavelengths shift from about 450 nm to about 700 nm, and can be tuned over this range.
• the vertical shaded bars on FIG. 1 indicate visible light wavelengths in the blue 100, green 102 and red 104 ranges.
• the width of the emission peak is determined by the size distribution of the sample. Peak widths down to 20 nm full width at half maximum (FWHM) can be achieved.
• the abso ⁇ tion spectrum of nanocrystals is very broad and intense, as typical of the bulk material, which is characteristically different than organic phosphors. Abso ⁇ tion coefficients are in excess of 55,000/cm (in the blue range of the spectrum) over the entire range of crystal sizes.
• core-shell nanocrystals can be made with quantum efficiencies as high as 90% (this does not take into account energy loss due to Stokes shift, but is simply the ratio of photons-in to photons-out).
• the present invention provides an engineerable down-converting system (see FIG. 2).
• Systems according to the present invention can comprise a nanocomposite down-converting layer that can be coated directly onto an LED wafer prior to dicing and packaging, eliminating the need for heterogeneous integration of the phosphor layer during packaging.
• the nanocomposite down-converting layer is suitably engineered from three components, including: (1) Semiconductor nanocrystal phosphors of one or more, suitably two or more, sizes tuned to emit at the required wavelength(s) and with the required spectral characteristics to optimize the color rendering index (CRT) and power conversion efficiency in the final device; (2) A host matrix (e.g., a polymer) selected for high index of refraction (generally about 1.5 or greater), low UV degradation and matched thermal expansion to the LED chip; and, (3) A unique nanocrystal surface chemistry that acts as the interface between the nanocrystals and the host matrix, allowing each element to be independently selected and tailored without impacting the other component. As shown in FIG. 2, such a down-converting nanocomposite phosphor layer 208 will take the place of phosphor 200 and phosphor encapsulant layer 206.
• FIG. 3 illustrates the emission range of the down-converting nanocomposites of the present invention, in the red region of a 2-color phosphor mix, compared to that resulting from traditional inorganic phosphors for white.
• Emission peaks 302 and 304 represent the emission spectra of a 2- color phosphor mix according to one embodiment of the present invention.
• Spectrum 306 represents the emission spectrum of traditional inorganic phosphors. Not only does the narrow emission prevent photon waste at the edges of the visible spectrum by the eye, but it also allows a superior optimization of color rendering index and power conversion efficiency.
• Wasted light region 308 demonstrates light emitted from traditional inorganic phosphors at the edges of the visible spectrum that is cut out by using the sha ⁇ emission peak 304.
• FIG. 4 illustrates the concept of fine-tuning the emission by using more than three emission colors, each with a specific, narrow, emission peak, to generate an overall emission spectrum with a superior color rendering index that can be as high as 100 for any color temperature.
• a balance between efficiency and CRI is a balance between efficiency and CRI.
• the exact number of colors, center wavelengths, relative concentrations and spectral widths can be determined theoretically to optimize both parameters simultaneously.
• green 500 and red 502 down-conversion layers can be patterned across LED chips 204 prior to dicing.
• This allows low-cost fabrication of 3-color emitting LEDs integrated into a single die, such that a single chip can be used to dynamically tune emission of the LED from monochromatic to white for any color temperature.
• the present invention provides formation of an integrated chip-level 3-color mixing-based SSWL for all lighting applications, at a cost point competitive with traditional lighting, but with far superior efficiency, performance and color engineering capability.
• Suitable matrixes for use in all embodiments of the present invention include polymers and organic and inorganic oxides.
• Suitable polymers for use in the matrixes of the present invention include any polymer known to the ordinarily skilled artisan that can be used for such a p pose. hi suitable embodiments, the polymer will be substantially translucent or substantially transparent.
• Such polymers include, but are not limited to, poly(vinyl butyral):poly( vinyl acetate), silicone and derivatives of silicone, including, but not limited to, polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane, fluorinated silicones and vinyl and hydride substituted silicones.
• the nanocrystals used the present invention can be embedded in a polymeric (or other suitable material, e.g., waxes, oils) matrix using any suitable method, for example, mixing the nanocrystals in a polymer and casting a film, mixing the nanocrystals with monomers and polymerizing them together, mixing the nanocrystals in a so-gel to form an oxide, or any other method known to those skilled in the art.
• the term "embedded” is used to indicate that the nanocrystals are enclosed within the polymer that makes up the majority component of the matrix.
• the thickness of the layers of the present invention can be controlled by any method known in the art, such as spin coating and screen printing.
• the various polymeric layers of the present invention can be any thickness required, suitably, the layers will be less than about 100 mm in thickness, and down to on the order of less than about 1 mm in thickness. In other embodiments, the polymeric layers of the present invention can be on the order of 10's to 100's of microns in thickness, hi one embodiment, the present invention provides nanocrystal doped layers that are greater than about 0.5 mm in thickness, and suitably will scatter only a minimal portion of light that enters the layer (see later for a discussion of scattering). In other embodiments, the layers will be between about 0.5 mm and about 50 mm in thickness.
• the nanocrystals can be embedded in the various matrixes at any loading ratio that is appropriate for the desired function.
• the nanocrystals will be loaded at a ratio of between about 0.001% and about 75% by volume depending upon the application, matrix and type of nanocrystals used.
• the appropriate loading ratios can readily be determined by the ordinarily skilled artisan and are described herein further with regard to specific applications.
• the present invention provides polymeric layers comprising a polymer and nanocrystals embedded within the polymer, such that the layers act as photon-filtering nanocomposites.
• the nanocrystals will be prepared from semiconductor materials, but any suitable material described throughout can be used to prepare the nanocrystals.
• the nanocrystals will have a size and a composition such that the nanocrystals absorb light of a particular wavelength or over a range of wavelengths.
• the nanocrystals utilized in these embodiments are tailored such that their abso ⁇ tion characteristics are enhanced or maximized, while their emission characteristics are minimized, i.e.
• the photon-filtering nanocomposites can also comprise nanocrystals that have high emission properties and emit light at a particular wavelength as discussed throughout.
• the present invention provides nanocomposites that comprise different types of nanocrystals such that the nanocomposites exhibit several, or all, of the properties discussed throughout, in a layer.
• FIG. 6 is a cross-sectional view of a polymeric layer 600 showing nanocrystals 604 embedded in polymer 602. Note that nanocrystals 604 are not to scale and are visibly represented for illustrative pu ⁇ oses only.
• the polymeric layers and nanocomposites of the present invention can also comprise nanocrystals of different sizes and compositions within the same layer.
• the nanocrystals can be distributed homogenously throughout the polymeric layer and nanocomposites (see FIG. 6). In other embodiments, the nanocrystals can be randomly distributed. In further embodiments, the nanocrystals can be distributed throughout the layer such that they form a nanocrystal density gradient throughout the layer (as discussed further in the refractive index section below).
• FIG 7, shows a cross-sectional view of a polymeric layer 700 with nanocrystals 604 embedded in polymer 602 in such a way that they form a nanocrystal density gradient from high density (lower portion of FIG. 7) to low density (upper portion of FIG. 7) within polymer 602.
• the photon-filtering polymeric layers and nanocomposites of the present invention can be used to coat, encapsulate, cover, be deposited on (or any other similar arrangement known to those skilled in the art) any substrate material.
• the polymeric layers of the present invention can be used to coat optical devices.
• the polymeric layers can be used to encapsulate active devices.
• FIG 8 is a cross-sectional view of an optical device 802 coated with polymer 602 comprising nanocrystals 604.
• Coated optical devices 800 according to such an embodiment can be used in any application where a filter or anti-reflective coating is desired on a refractive or reflective device.
• active devices can be any device known to the skilled artisan.
• an "active device” is one that requires a source of energy for its operation and has an output that is a function of present and past input signals.
• active devices include, but are not limited to, controlled power supplies, transistors, diodes, including light emitting diodes (LEDs), light detectors, amplifiers, transmitters and other semiconductor devices.
• the nanocrystals By controlling the size and composition of the nanocrystals used in the practice of the present invention, the nanocrystals will absorb light of a particular wavelength, or a particular range of wavelengths, while not scattering light.
• the ability to make nanocrystals out of different semiconductors, and control their size, allows for polymeric layers to be fabricated with nanocrystals that will absorb light from the UN, to visible, to near infrared (MR), to infrared (IR) wavelengths.
• Nanocrystals for use in the present invention will suitably be less than about 100 nm in size, and down to less than about 2 nm in size. In suitable embodiments, the nanocrystals of the present invention absorb visible light.
• 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.
• the photon-filtering nanocomposites of the present invention can be constructed so as to absorb light that makes up any one or more of these colors.
• the nanocomposites of the present invention can be constructed so as to absorb blue light, red light, or green light, combinations of such colors, or any colors in between.
• blue light comprises light between about 435 nm and about 500 nm
• green light comprises light between about 520 nm and 565 nm
• red light comprises light between about 625 nm and about 740 nm in wavelength.
• the ordinarily skilled artisan will be able to construct nanocomposites that can filter any combination of these wavelengths, or wavelengths between these colors, and such nanocomposites are embodied by the present invention.
• Polymeric layers that comprise nanocrystals that can absorb light of a particular wavelength, or range of wavelengths, will act as edge pass filters, absorbing light that is less than a certain wavelength.
• the photon-filtering nanocomposites can be constructed so as to absorb light that is less than about 565 nm (e.g., blue and green) and allowing wavelengths of light that are longer than about 565 nm (e.g., red) to pass through the polymeric layer.
• the nanocrystals 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 comprises light between about 100 nm to about 400 nm
• the near-infrared spectrum comprises light between about 750 nm to about 100 ⁇ m in wavelength
• the infrared spectrum comprises light between about 750 nm to about 300 ⁇ m in wavelength.
• the nanocrystals can be ZnS, InAs or CdSe nanocrystals.
• InAs nanocrystals (with a 1340 nm abso ⁇ tion peak) with TOP (tri-n-octylphosphine) ligands attached to their surface can be dissolved in a solvent such as toluene.
• Poly(vinyl butyral): ⁇ oly( vinyl acetate) (PVB:PVA) polymer can also be dissolved in toluene and the two solutions can be mixed together.
• a substrate can then be coated or encapsulated with the mixture and the toluene evaporated off.
• a thin film results that is non-light-scattering due to the size of the non- aggregated nanocrystals.
• Polymeric layers produced in such a manner will have an effective refractive index between that of either material by itself (i.e., the polymer or the nanocrystal material), which can be adjusted by modifying the loading ratio of the nanocrystals and the density of the nanocrystals at various points in the polymeric layer (see Refractive Index section for additional disclosure).
• a polymeric layer comprising such nanocrystals can act as an antireflective filter, absorbing light that is less than about 1340 nm in wavelength.
• CdSe nanocrystals (having an abso ⁇ tion peak at about 580 nm) with stearic acid ligands can be dissolved in a solvent such as toluene.
• ZnS nanocrystals with amine, carboxylic acid, phosphonic acid, phosphonate, phosphine, phosphine oxide or sulfur ligands can be dissolved in a solvent.
• a ligand exchange can then be performed in solution with a siloxane ligand and excess ligand can be removed.
• Nanocrystals can then be mixed with a polymer base, such as silicone, and a substrate material can then be coated or encapsulated. After curing, the film will have an effective refractive index between that of the polymer (e.g., silicone) and the nanocrystals, which can be adjusted by changing the loading ratio of the nanocrystals in the silicone.
• a polymeric layer will act as a filter absorbing light that is less than about 580 nm in wavelength (i.e., blue, green, yellow, orange, violet, UN light).
• overall light extraction relates to: (a) extraction from substrate 202 to phosphor encapsulant layer 206; and (b) from phosphor encapsulant layer 206 to air.
• the radius of the encapsulant layer is much larger than the emitting area (e.g., cm vs. mm) thus light rays inside the encapsulant layer that reach out in the radial direction impinge almost pe ⁇ endicular to the encapsulant layer surface ⁇ « ⁇ c and are extracted.
• the overall extraction is mainly limited by extraction from the substrate to the phosphor plane interface, taking advantage of the higher phosphor critical angle, due to the higher than air index of refraction.
• the present invention provides nanocomposite layers 208, that can bond to LED substrate 202, that have an effective refraction index of greater than 1.5.
• a matched-index passive layer e.g., a hard shell polymer
• the term "effective refractive index (n e )" is used to indicate that the polymeric layers of the present invention are composite materials, and thus, their effective refractive index is a result of the refractive index of all components of the layer.
• the term refractive index as used herein indicates the degree to which the nanocomposites of the invention bend light.
• the refractive index of the nanocomposites can be determined by the ratio of the speed of light in a vacuum divided by the speed of light in the nanocomposites.
• the polymeric layers of the present invention whether down- converting, photon-filtering, or refractive index matching, have an effective refractive index that can be controlled by the ratio, density, composition and size of the nanocrystals embedded within the matrix.
• FIG. 10 shows the effective refractive index of a silicone nanocomposite comprising 3 nm ZnS nanocrystals at 30% by volume as a function of wavelength. An effective refractive index of greater than about 1.77 is observed for all wavelengths from 300 nm to 700 nm.
• Control and tailoring of the effective refractive index allows the matrixes of the present invention to be utilized in applications where a layer having either a uniform or varying effective refractive index may be desired, for example as polymeric layers encapsulating LEDs.
• a polymeric layer is used to encapsulate the light emitting diode chip of an LED to provide protection to the chip.
• refractive index (n) differences between the high n of the LED chip and the generally low n of the polymeric encapsulant large amounts of light are lost due to light reflecting at the chip/polymer interface.
• the present invention therefore provides for a polymeric layer that has a refractive index higher than pure polymer that can approach or match the refractive index of the LED chip, thereby limiting the light lost at the chip/polymer interface.
• a polymeric layer that has a refractive index higher than pure polymer that can approach or match the refractive index of the LED chip, thereby limiting the light lost at the chip/polymer interface.
• FIG. 11 showing a cross-sectional view of an encapsulated light emitting diode 1100, in which polymer 602 comprising embedded nanocrystals 604 encapsulates LED chip 1106.
• Any active device including those discussed throughout, can be encapsulated in a similar mamier.
• FIGS. 11 and 12 showing specific LED structures are presented for illustrative purposes only, and any LED structure known to those skilled in the art can be similarly encapsulated.
• the effective refractive index of the polymeric layer can be any value between that of the pure matrix material (e.g., silicone at about 1.49, TiO 2 at about 1.5) and the nanocrystals themselves (e.g., up to about 3).
• the effective refractive index of the matrix will be greater than about 1.5, preferably between about 1.5 and about 2.5, and in certain embodiments the refractive index of the matrix will be about 1.8.
• a second polymeric layer can be added on top of the first layer.
• this second layer will be a "hard-shell" polymer and will have a refractive index that is lower than the LED chip.
• the present invention provides for a polymeric layer or polymeric encapsulant which has a density gradient of nanocrystals such that the effective refractive index of the polymeric layer matches both the chip and the hard shell polymer at their respective interfaces.
• the present invention provides polymeric layers that encapsulate an active device that has an effective refractive index, .
• the layer comprises a polymer and semiconductor nanocrystals embedded within the polymer, and has an inner boundary in contact with the active device and an outer boundary in contact with a medium that has an effective refractive index, n 2 .
• the layer has an effective refractive index less than or equal to m at the inner boundary and an effective refractive index greater than or equal to n 2 at the outer boundary.
• the active device will be an LED, though any active device, including those described throughout, can be encapsulated.
• ni will be greater than n .
• FIG. 12 shows a cross-sectional view of an LED encapsulated in such a polymeric layer.
• Encapsulated LED 1200 comprises polymeric layer 602 comprising embedded nanocrystals 604 encapsulating LED chip 1106.
• Hard shell polymer 1202 further coats polymeric layer 602 to provide additional structural integrity and protection to the LED.
• FIG 12 illustrates the nanocrystal density gradient throughout the thickness of polymeric layer 602, this gradient being highest at the boundary with LED chip 1106 and lowest at the boundary with hard shell polymer 1202.
• the effective refractive index is ni at the boundary with LED chip 1106 and the effective refractive index is n 2 at the boundary with hard shell polymer 1202.
• this nanocrystal density gradient will be substantially linear throughout the polymeric layer, though it can take any form throughout the thickness of the layer, e.g., cyclic, parabolic, etc.
• the effective refractive index of polymeric layer 602 will be greater than about 1.5 throughout the layer, and in certain embodiments will be about 1.8 (ni) at the interface with LED chip 1106 and about 1.5 (n 2 ) at the interface with hard shell polymer 1202.
• light emitting diodes often utilize LED chip 1106 covered by a drop or layer of silicone 1300 usually a few millimeters in diameter.
• silicone 1300 usually a few millimeters in diameter.
• the amount of nanocrystals required for a doped matrix a few millimeters think for each LED translates to rather large quantities of nanocrystals for mass production, thereby driving up the cost; and (2) the scattering from the nanocrystals throughout a think layer may make the matrix opaque for a path-length of a few millimeters.
• the present invention provides for a thin film of nanocomposite 1402 formed on the surface of an LED chip 1106, this thin film is then further capped with small hemispheres 1404 of the same nanocomposite. All of the light that enters the nanocomposite hits the composite/air interface at 90° and therefore does not suffer from any internal reflection.
• the thickness of the film and the diameter of the small caps can be chosen to satisfy the thermal compliance and other mechanical/thermal requirements.
• the thickness, t, of the film, and the diameter, d, of the small hemispheres can be in the range of l ⁇ 's-100's of nms to microns to millimeters.
• the thickness of the layer will be on the order of 10's of microns, for example about 10-50 microns.
• the diameter of the hemispheres is generally on the order of microns.
• the small hemispheres 1404 of nanocomposite can be further capped with a large hemisphere of silicone 1302, as illustrated in FIG. 15.
• the refractive index of the large hemisphere of silicone is not required for light extraction.
• nanocomposite films and hemispheres in this manner allows for the use of larger sized nanocrystals in comparison to those that can be used in conjunction with thicker pathlength films.
• nanocrystals on the order of 5-7 nm could be used with the thin film/hemisphere embodiments of the present invention, while nanocrystals on the order of about 3-5 nm could be required for thicker pathlength nanocomposites.
• the nanocrystals useful in the practice of the present invention can have a composition and a size such that they absorb light at a particular wavelength(s) and emit at a particular wavelength(s).
• the polymeric layers of the present invention can comprise combinations of nanocrystals that function in the various ways described herein.
• a nanocomposite of the present invention can comprise nanocrystals having specific, enhanced emission properties, others having specific, enhanced abso ⁇ tion properties but low emission properties, and the entire nanocomposite can be constructed such that the layer has a specific refractive index that is matched or tailored for a specific pmpose.
• the polymeric layers of the present invention can be used as encapsulants for active devices (e.g., LEDs) that emit light of a certain wavelength, filter out other wavelengths and have a refractive index appropriately matched to an active device and/or an additional substrate or coating.
• active devices e.g., LEDs
• the nanocrystals do not aggregate. That is, that they remain separate from each other in the polymeric layer and do not coalesce with one another to form larger aggregates. This is important, as individual crystals will not scatter light passing through the layer, while larger aggregated structures can create an opaque layer that can hinder the passage of light.
• the nanocomposites of the present invention will scatter a minimal portion of light that enters the various layers. It is desirable that the nanocomposites of the present invention scatter as little light as possible, such that the layers are substantially transparent or clear.
• the phrase “scatter a minimal portion of light,” means that the amount of light that enters the various nanocomposites of the invention from the incident side (the side that light is entering) is transmitted such that less than about 50% of this incident light is scattered by the nanocomposite.
• the amount of light that is scattered by the nanocomposite will be less than about 20%, less than about 15%, and approaching 0% of the light being transmitted.
• the factors that impact most significantly on the amount of light that is scattered by the nanocomposites are the size of the nanocrystals and their miscibility in the polymeric matrix, and hence their ability to remain separated.
• the size of the nanocrystals can be tailored by selecting specific semiconductor materials and then generating and processing the nanocrystals until the desired size is attained.
• the nanocrystals will suitably be between about 1 nm and about 20 nm in size. More suitably, between about 1 nm and about 10 nm, between about 1 nm and about 4 nm and most suitably between about 1 nm and about 3 nm.
• the percent transmittance of light can be tailored from between about 5% to about 100% (i.e. percent that is scattered can be tailored from between about 95% to about 0%). It is a significant advantage of the present invention that by generating nanocrystals that are between about 1 nm to about 4 nm, less than about 50% of the incident light is scattered by the nanocomposites of the present invention. As shown in FIG 16, by creating nanocrystals that are between about 1 nm and about 3 nm, scattering of less than 20%, approaching 15%, 10%, 5% and 0%, can be achieved. As demonstrated in FIG.
• a silicone nanocomposite comprising 3 nm ZnS nanocrystals and a layer with a 3 mm pathlength will scatter less than about 50% (i.e. transmit more than about 50%) of the incident light over the wavelength range 350 nm to 700 nm, scatter less than about 30% over the wavelength range 400 nm to 700 nm and scatter less than about 15% over the wavelength range 500 nm to 700 nm.
• the nanocomposites of the present invention two critical issues are: (1) achieving high miscibility of the nanocrystals in the host matrix, and (2) prevention of aggregation of the nanocrystals at a high concentration. Aggregation results in quenching of the emission, hence a lowering of the amount of light transmitted, as well as light scattering from the aggregates. Tuning the index of refraction of the overall composite layer also occurs at different nanocrystals loading densities. Since the nanocrystals have a refractive index of about 2.5 to about 3 and the host matrix is about 1.5 to about 2, matching of the refractive index of the LED substrate (typically sapphire or SiC) will eliminate an optical interface and losses from total internal reflection.
• the LED substrate typically sapphire or SiC
• a tailored, miscibility-enhancing ligand can be designed to bind, associate, coordinate, attach or conjugate to a nanocrystal, and to allow for controlled mixing and miscibility in the host matrix.
• the performance characteristics, including quantifying the effects on the internal quantum efficiency and light extraction efficiency are measured on nanocomposites of various loading densities and thicknesses.
• Dispersion of nanocrystals in a host matrix can be controlled by minimizing phase separation and aggregation that can occur when mixing the nanocrystals into the matrixes.
• a basic strategy of the present invention is to design a novel 3-part ligand, in which the head-group, tail-group and middle/body-group can each be independently fabricated and optimized for their particular function, and then combined into an ideally functioning complete surface ligand (see FIG 18; see FIG 19 for an example ligand).
• head group 1804 is selected to bind specifically to the semiconductor material of the nanocrystal (e.g., can be tailored and optimized for CdSe, ZnS or any other nanocrystal material).
• Tail group 1800 is designed to interact strongly with the matrix material and be miscible in the solvent utilized (and can, optionally, contain a linker group to the host matrix) to allow maximum miscibility and loading density in the host matrix without nanocrystal aggregation.
• Middle or body group 1802 is selected for specific electronic functionality (e.g., charge isolation).
• This multipart ligand strategy has been used for the fabrication of high loading density, non-fluorescent, polymer-CdSe nanorod composites in the development of hybrid inorganic-organic nanocomposite solar cells.
• significant modifications to the ligand are made due to differences in the two applications.
• the ligand is designed to be charge insulating (rather than charge conducting) and to provide retention of nanocrystal photoluminescence as well as to be compatible with a completely different matrix type (inorganic rather than organic polymers) and nanocrystal material type and shape.
• a benefit of this modular approach is the ability to rapidly evaluate new tail, head, and middle/body groups, hi the area of head groups (binding with the nanocrystal), there are available methods developed for the development of CdSe synthetic techniques. This includes an understanding of the binding of nanocrystals with phosphonic acids, amines, thiols, phosphines, and phosphine oxides.
• a tailored ligand can be optionally designed to bind strongly to the nanocrystal and to allow for mixing in a TiO host medium.
• the new ligand allows for dispersion control (solubility and processabihty) to facilitate inco ⁇ oration of the nanocrystals into solvents or host matrixes over a wide range of loading densities as necessary to achieve the optimal white light device performance characteristics and refractive index matching to the blue- LED.
• the ligand molecule can be synthesized using a generalized technique allowing three separate groups to be synthesized separately and then combined. Head groups of phosphonic acid, amines, carboxylic acids or thiol moieties can be used because of their affinity for the nanocrystal surface. Tail groups can contain terminal hydroxyl groups to tether the nanocrystal in a titania sol-gel matrix, or silicon groups to match a silicone polymer matrix.
• the middle/body unit is selected for charge insulation (e.g., large energy gap for both electrons and holes), and possible targets are identified using computer modeling. The modeling is performed using a Density Functional Theory (DFT) to model the bandgap of various target molecular structures for ligand design. The confirmation of the chemical identity and purity will be done using mass spectrometry, NMR and FTIR analysis.
• DFT Density Functional Theory
• the insulating group (middle/body unit) of the ligands can be selected from long-chain alkanes of various lengths and aromatic hydrocarbons, e.g., C6-C22 alkanes. Selection of the length of the body unit will depend on the desired characteristics of the final matrix and of the polymeric base being used. For example, in applications where it is desired that the matrix possess rheologic or other properties (e.g., mechanical/electical) similar to that of the polymeric base substance, a shorter chain (e.g., C6-C18) body unit can be selected.
• the use of a C12 body unit-based ligand on ZnS nanocrystals allows for increased loading of the ZnS nanocrystals at a ratio sufficient to achieve a refractive index of 1.7070 in a base of immersion oil (starting refractive index 1.5180), while still maintaining the grease like consistency of the oil.
• the use of shorter chain ligands allows for a lower volume fraction of nanocrystals to be used to achieve the same refractive index when compared to nanocrystals with longer chain ligands.
• the use of longer chain ligands can be used when it is desired that the final matrix possess properties closer to that of the ligand itself, rather than the base material.
• the ligand itself could be used to form the matrix material.
• Longer chain ligands also allow for additional spacing between the nanocrystals to keep them from aggregating in the base substrate.
• Figure 19 shows an example of a ligand with a phosphonic acid head group 1900, an aliphatic tail 1902 and an aromatic hydrocarbon body 1904.
• Appropriate choice of body and/or tail components are used to provide like functionality to the matrix to afford high concentrations of nanocrystals in siloxane polymer matrices.
• Refractive index (RI) tuning/matching can also be affected by the ligand. independent tuning of the tail or body components of the ligand to obtain a particular RI match with the polymer matrix can be achieved by varying the ligand chemistry appropriately.
• Head-Body-Tail affords freedom from any particular ensemble limitations.
• a phosphonate head group for nanocrystal binding, alkane body group for length adjustment/nanocrystal spacing and dimethyl silicone tail for silicone matrix compatibility can be synthesized as shown in FIG. 20b.
• An example of tuning the RI (increasing the value) can be realized by inco ⁇ oration of phenyl groups shown in FIG. 20a (similar to silicone polymers (from vendor Gelest Inc., 612 William Leigh Drive Tullytown, PA 19007-6308): DMS-H21 dimethylsiloxane vs.
• FIG. 20a illustrates several non-limiting example ligands with head-body-tail design. Matrix compatibility adjustments such as branching siloxane units can also be accommodated (FIG. 20b, molecule 3). Structure verification by NMR of synthesized precursors 1 and 2 in FIG. 20b is shown in FIGS. 20c-f.
• FIG. 20g shows additional examples of ligands and synthesis schemes in accordance with the present invention, including (from top to bottom) the use of trisiloxane, cyclic tetrasiloxane and branched siloxane tail groups in the generation of ligands.
• Carboxylic acid functionalization of these silicone surfactants is illustrated in FIG. 20g.
• Structure verification by NMR of a carboxylated trisiloxane ligand shown in FIG. 20g (ligand at top of page) is represented in FIGS. 20h-i.
• FIGs. 20j and 20n show further examples and synthesis schemes for the production of phosphonate functionalized silicone ligands. Structure verification by NMR of the bromide precursor shown in FIG. 20j is represented in FIG. 20k. FIGS. 201 and 20m represent NMR verification of the structure of the phosphonate ligand product.
• Ligand exchange to displace the surfactants can be done by mass action exchange in solution.
• the nanocrystals and the new ligand are co-dissolved in solvent and allowed to react for a specified time at elevated temperatures.
• the product is precipitated with alcohol to remove any excess unbound ligands and to remove the displaced synthesis surfactants.
• the attachment is confirmed by NMR analysis by redissolving the product into a deuterated NMR compatible solvent.
• Complexation of the ligand with the nanocrystal causes a shift and broadening in the spectrum compared to the free unbound molecule due to a hindered rotation.
• the present invention provides polymeric layers, comprising a polymer; and semiconductor nanocrystals embedded within the polymer, wherein the nanocrystals have miscibility-enhancing ligands conjugated to their surface, and wherein the ligands comprise an alkane chain of between 6 and 18 carbons in length.
• the ligands can comprise an alkane chain of between 12 and 18 carbons in length.
• the polymer will suitably be silicone, and the semiconductor nanocrystals will suitably have a size between about 1-10 nm, and in certain embodiments will be ZnS nanocrystals.
• the polymeric layers will scatter a minimal portion of light that enters said polymeric layer.
• the layer will be greater than about 0.5 mm in thickness.
• the present invention provides processes for preparing polymeric layers, comprising (a) mixing semiconductor nanocrystals at a first density with a solvent and a polymer to form a first mixture (2100), (b) coating a substrate material with the first mixture (2102), and (c) evaporating the solvent to form the polymeric layer (2104), wherein the polymeric layer has an effective refractive index ofni.
• the processes of the present invention can be used to coat active devices or optical devices.
• nanocrystals useful in the processes of the present invention can comprise miscibility-enhancing ligands conjugated, coordinated, attached, bound or otherwise associated to their surface. Any of the various types of nanocrystals discussed herein can be used in the processes of the present invention. For example, high emission nanocrystals, low emission/high abso ⁇ tion nanocrystals and low emission/low abso ⁇ tion nanocrystals can be used, hi certain embodiments, two or more different types of nanocrystals can be mixed with the solvent and polymer, thereby creating a composite that has several or all of the properties described herein.
• Refractive index matching applications can utilize any of the nanocrystals discussed throughout, depending on if the nanocomposite is also required to function as a down- converting layer or a filtering layer. In other applications, nanocrystals that have low emission/low abso ⁇ tion properties are useful in refractive index matching applications where refractive index effects only are desired.
• the processes of the present invention can further comprise (d) mixing semiconductor nanocrystals at a second density with a solvent and a polymer to form a second mixture (2106), (e) coating the substrate material with the second mixture (2108), and (f) evaporating the solvent to form a second polymeric layer (2110), wherein the second polymeric layer has an effective refractive index of n 2 .
• the processes of the present invention can further comprise repeating steps (d) through (f) with a third through i th density of semiconductor nanocrystals to produce third through i th polymeric layers, fh wherein the third through i polymeric layers have effective refractive indices, n through nj, respectively (2112).
• i refers to an integer.
• the present invention encompasses processes for producing polymeric layers which comprise any number of separate layers used to produce an overall layer, coating, or encapsulant.
• Each individual layer, 1 through i can comprise a different density of nanocrystals, nanocrystals of a different composition (i.e., high emission or high abso ⁇ tive properties), and nanocrystals of different sizes. As such, each layer can have a different effective refractive index and can have multiple and/or different properties and characteristics.
• an overall polymeric layer e.g., an encapsulating layer
• FIG. 1 An overall polymeric layer
• the effective refractive index of the 1 st layer, m (2200) will be greater than any other layer (2202, 2204, 2206), and the effective refractive index of the i th layer, m (2206), will be less than any other layer (2200, 2202, 2204).
• the processes of the present invention can be performed in the reverse order, i.e., where the nanocrystal density and thus the effective refractive index of the i th layer is higher than any other layer, and the effective refractive index of the first layer prepared, . , is less than any other layer.
• the density and effective refractive index of the individual layers can be the same, or can be prepared in such a manner that the overall effective refractive index of the polymeric layer varies throughout the layer, rather than in a graded fashion, as in FIG. 22.
• Suitable coating processes include, but are not limited to, spin coating and screen printing.
• spin coating consists of four stages.
• the first stage is the deposition of the coating fluid onto the substrate. It can be done using a nozzle that pours the coating solution out, or can be sprayed onto the surface, etc. Usually this dispense stage provides a substantial excess of coating solution compared to the amount that will ultimately be required in the final coating thickness.
• the second stage is when the substrate is accelerated up to its final, desired, rotation speed. The second stage is usually characterized by aggressive fluid expulsion from the substrate surface by the rotational motion. Ultimately, the substrate reaches its desired speed and the fluid is thin enough that the viscous shear drag exactly balances the rotational accelerations.
• the third stage is when the substrate is spinning at a constant rate and fluid viscous forces dominate fluid thinning behavior.
• This stage is characterized by gradual fluid thinning.
• Mathematical treatments of the flow behavior show that if the liquid exhibits Newtonian viscosity (i.e., is linear) and if the fluid thickness is initially uniform across the substrate (albeit rather thick), then the fluid thickness profile at any following time will also be uniform, leading to a uniform final coating.
• the fourth stage is when the substrate is spinning at a constant rate and solvent evaporation dominates the coating thinning behavior. As the prior stage advances, the fluid thickness reaches a point where the viscosity effects yield only rather minor net fluid flow. At this point, the evaporation of any volatile solvent species will become the dominant process occurring in the coating.
• the processes of the present invention can further comprise centrifuging the mixture produced in step 2100 to form a nanocrystal density gradient within the mixture prior to the coating in 2102.
• the use of centrifugation creates a gradient within the polymeric layer as nanocrystals separate in accordance with their inertia.
• Various centrifugation speeds or accelerations can be used to produce the nanocrystal density gradient in the polymeric layers and can readily be determined by those skilled in the art.
• the centrifugation speed selected depends on the size of the nanocrystals and the difference in density between the nanocrystals and the polymer solution prior to polymerization, and the centrifugal approach.
• Centrifugation can be for a short time at high speed and generate a gradient kinetically where the centrifugation step is timed based on a calculated or measured centrifugation rate.
• an equilibrium approach can be used where the flux of the nanocrystals toward the bottom of a centrifuge tube is matched to the flux of nanocrystals toward the top of the tube (due to diffusion). The diffusional flux is proportional to the concentration gradient of the nanocrystals.
• accelerations can be in the range of a few hundred times g to 100,000 times g, where g is the acceleration due to gravity (9.8 m/s 2 )
• g is the acceleration due to gravity (9.8 m/s 2 )
• the nanocrystals will spread out through the polymeric layer according to their inertia in response to the centrifugation and generate a gradient in the layer. Any other process known to those skilled in the art to generate gradients within polymers may also be used to create the polymeric layers of the present invention.
• the optical path length varies with distance from its center, where optical path length is defined as the product of the physical path length, thickness, and the refractive index, n, of the lens material.
• the refractive index, n is fixed and the thickness, varies.
• a lens can also be created by keeping the thickness, constant and varying the refractive index as a function of distance from the axis of the lens.
• Such a lens is called a Graded Index lens, or sometimes abbreviated as a GRIN lens.
• the methods of the present invention can also be used to create GRIN lenses.
• Polymer/nanocrystal blends can be used to make GRIN lenses due to the dramatic refractive index difference between nanocrystals (e.g., ZnS about 2.35) and optical plastics such as poly(methyl methacrylate) (PMMA) (refractive index about 1.45).
• PMMA poly(methyl methacrylate)
• a gradient pump can be used to inject a solution containing polymer monomers and nanocrystals into the center of a mold, and then nanocrystal concentration can be varied during the fill. The lens can then be cured and removed.
• polymeric nanocomposites of the present invention can be used in any application where the down-conversion, filtering, and/or refractive index characteristics of the composites are desired.
• Non-limiting examples of applications of polymeric nanocomposites with increased refractive indexes include:
• Plastic Eye Glass Lenses and Contacts The thickness of a lens is proportional to the refractive index of the material of which it made. The higher the refractive index, the thinner the lens. Normal glass has a refractive index of about 1.523 while an example plastic, such as CR39, has refractive index of 1.49. A plastic lens, although lighter in weight, is thicker than a glass lens of equivalent power.
• the refractive index can be increased beyond the level of glass to make ultra-thin lenses.
• the refractive index of contact lenses are about 1.40.
• the addition of even a small percentage of nanocrystals e.g., about 10% ZnS would increase the refractive index to about 1.5, therefore allowing for thinner lenses.
• Ligands such as those discussed throughout can be used to lock the nanocrystals in place in the polymeric layer.
• Suitable nanocrystal synthesis procedures include fabricating nanocrystal samples with specific spectral characteristics matched to those prescribed by the theoretical models of the present invention. This can include fabricating nanocrystals with tunable sizes and size distributions (e.g., sizes ranging from 1 - 20 nm in diameter producing emission peak wavelengths tunable between 460 and 640 nm with FWHM tunable from about 15 to about 100 nm). This in turn is used to synthesize nanocrystal mixtures identified by simulations that have the optimal emission characteristics. The simulation and core/shell nanocrystal procedure is typically performed in an iterative process.
• Type I core-shell nanocrystals of CdSe/ZnS can be synthesized by a two step process using a solution phase method, first with the fabrication of the core material followed by growth of the shell.
• Core CdSe nanocrystals are dispersed in TOPO and TOP to which a mixture of ZnEt 2 and (TMS) 2 S will be added at a temperature between 140°C to 220°C.
• ZnS shell coating thickness will be varied by changing precursor ratios and growth temperatures to obtain a umform surface coverage and to improve the quantum efficiency.
• the confirmation of shell growth will be done using XRD, EDX and TEM analysis.
• the optical properties of the individual nanocrystals are characterized by measurement of the UN- Vis abso ⁇ tion and photoluminescence spectra using a commercial UV-Vis spectrophotometer and a fluorometer. The excitation wavelength is matched to the blue LED (about 460 nm). Internal quantum efficiency of the nanocrystals in solution are calculated using internal reference standards. Nanocrystal component mixtures (solution phase) are formed by mixing the appropriate concentration ratios to match the predictions from the theoretical model. The emission and abso ⁇ tion information of these actual mixtures is then back-fed as an input into the simulation to validate (and to refine, if necessary) the model.
• the output of this procedure is a solution-phase mixture of nanocrystals that has the appropriate composition to produce white light with CRI and CTT matching that of the theoretical model when illuminated with blue excitation and total down-conversion efficiency comparable to that predicted by the model, assuming zero loss to other mechanisms in the process.
• FIG. 23 shows an X-Ray diffraction scan of ZnS nanocrystals produced according the present invention. The scan shows the presence of Zinc Sulfide with a mixture of wurtzite and zinc blend (spaelite) crystals.
• FIG. 24 shows a Transmission Electron Micrograph (TEM) of ZnS nanocrystals (about 4 nm diameter) produced according the present invention.
• the ZnS nanocrystals can be produced using any chain length hydrocarbon, for example C6-C22 alkane, depending on the application and desired properties.
• Heptamethyl cyclotetrasiloxane and 1,1,1,3,3,5,5-heptamethyl trisiloxane were purchased from Gelest (Morrisville, PA), distilled and stored in a storage flask using Schlenk technique before use.
• the volatiles were removed from the clear brown solution by rotational evaporator leaving an opaque brown oil.
• the product was distilled from the mixture by short path apparatus collecting the fraction with vapor temperature between 80 and 95°C and pressure ⁇ 20 mtorr.
• the product is a clear colorless oil (5.55 g or approximately 17 mmol and 57% yield) that typically contains about 50% acid and 50% anhydride.
• Complete conversion to the acid was accomplished by dissolution of the product mixture (2.00 g or approximately 6.2 mmol) in acetonitrile, 40 mL, followed by addition of pyridine (5.00 mL, 5.11 g, 64.6 mmol) and water (6.20 mL, 6.20 g, 33.4 mmol).
• reaction solution then slowly turned light brown and produced a small amount of heat. After about 2 hours, the reaction flask was sunounded by a thermostat controlled water bath that was heated to 35°C. The reaction solution was heated overnight. [0193] The volatiles were removed from the clear brown solution by rotational evaporator leaving an opaque brown oil.
• a column was packed with silica (230 - 400 mesh) in hexanes that was 30 mm in diameter and 150 mm long. After placing the crude product on the column, the column was eluted with hexane, 250 mL, followed by a mixed solvent of 1:1 ratio of ethyl acetate to hexane, 1500 mL. The elutant was collected in one fraction.
• Additional phosphonic acid-silicone ligands such as those shown in FIGs. 20a, 20j and 20n and disclosed throughout the present specification can be prepared using a procedure similar to that above.

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