阅读说明：本技术 量子点组合物 (Quantum dot compositions ) 是由 武贡笋 伊马德·纳萨尼 阿米尔卡·皮拉伊·纳雷能 于 2015-03-30 设计创作，主要内容包括：本发明公开了量子点(QD)的多相聚合物膜及其在发光器件(LED)中的用途。QD被吸收在分散在外部聚合物相内的主体基质中。主体基质是疏水性的并且与QD的表面相容。主体基质还可以包含防止QD聚集的支架材料。外部聚合物典型是更亲水的并且防止氧与QD接触。(Multiphase polymer films of Quantum Dots (QDs) and their use in Light Emitting Devices (LEDs) are disclosed. The QDs are absorbed in a host matrix dispersed within an outer polymer phase. The host matrix is hydrophobic and compatible with the surface of the QDs. The host matrix may also comprise a scaffolding material that prevents QD aggregation. The outer polymer is typically more hydrophilic and prevents oxygen from contacting the QDs.)

1. A light emitting device, comprising:

a primary light emitting element; and

a two-phase composition containing Quantum Dots (QDs) in optical communication with the primary light emitting element, the two-phase composition comprising:

a hydrophobic inner phase comprising a hydrophobic solvent selected from: fatty acid esters and ethers, isopropyl myristate, isopropyl palmitate, phenyl myristate, natural and synthetic oils, heat transfer liquids, fluorinated hydrocarbons, dibutyl sebacate, and diphenyl ether;

a population of QDs dispersed within the internal phase; and

a hydrophilic outer phase.

2. The light emitting device of claim 1, wherein the QD-containing two-phase composition is in the form of a film.

3. The light emitting device of claim 2, wherein the film is disposed between two gas isolation layers.

4. The light emitting device of claim 1, wherein the inner phase of the two-phase composition further comprises a scaffold material.

5. The light emitting device of claim 4, wherein the scaffold material is fumed silica, fumed alumina, a hydrophobic polymer, porous polymer beads, or a lipophilic sephadex.

6. The light emitting device of claim 1, wherein the outer phase of the two-phase composition is an epoxy resin.

7. The light emitting device of claim 1, wherein the outer phase of the two phase composition is a bisphenol a-epoxy resin.

8. The light emitting device of claim 1, wherein the outer phase of the two-phase composition comprises a polymer having a glass transition temperature above about 50 ℃.

9. The light emitting device of claim 1, wherein the outer phase of the two-phase composition comprises an epoxy-acrylate resin and one or more of: 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA) or carboxylic acid (meth) acrylates.

10. The light-emitting device of claim 9, wherein the carboxylic (meth) acrylate is any one of the following: 2-carboxyethyl methacrylate oligomer (CEMAO), 2-carboxyethyl acrylate oligomer (CEAO), Acrylic Acid (AA) or methacrylic acid (MMA).

11. A light emitting device, comprising:

a primary light emitting element; and

a two-phase composition containing Quantum Dots (QDs) in optical communication with the primary light emitting element, the two-phase composition comprising:

a hydrophobic inner phase comprising a hydrophobic solvent;

a population of QDs dispersed within the internal phase; and

an outer phase comprising an epoxy resin or a bisphenol A-epoxy resin.

12. The light emitting device of claim 11, wherein the QD-containing two-phase composition is in the form of a film.

13. The light emitting device of claim 12, wherein the film is disposed between two gas isolation layers.

14. The light emitting device of claim 11, wherein the inner phase of the two-phase composition further comprises a scaffold material.

15. The light emitting device of claim 11, wherein the scaffold material is fumed silica, fumed alumina, a hydrophobic polymer, porous polymer beads, or a lipophilic sephadex.

16. A light emitting device, comprising:

a primary light emitting element; and

a two-phase composition containing Quantum Dots (QDs) in optical communication with the primary light emitting element, the two-phase composition comprising:

a hydrophobic inner phase comprising a hydrophobic solvent;

a population of QDs dispersed within the internal phase; and

an outer phase comprising an epoxy-acrylate resin and one or more of: 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA) or carboxylic acid (meth) acrylates.

17. The light emitting device of claim 16, wherein the QD-containing two-phase composition is in the form of a film.

18. The light emitting device of claim 17, wherein the film is disposed between two gas isolation layers.

19. The light emitting device of claim 16, wherein the inner phase of the two-phase composition further comprises a scaffold material.

20. The light-emitting device of claim 16, wherein the carboxylic (meth) acrylate is any one of the following: 2-carboxyethyl methacrylate oligomer (CEMAO), 2-carboxyethyl acrylate oligomer (CEAO), Acrylic Acid (AA) or methacrylic acid (MMA).

Technical Field

The present invention relates to a light emitting device.

Background

Light Emitting Diodes (LEDs) are becoming more important for modern life and it is envisaged that they will become one of the main applications in many forms of illumination, such as automotive lights, traffic signals, general lighting, Liquid Crystal Display (LCD) backlights and display screens. Currently, LED devices are typically made of inorganic solid-state semiconductor materials. The material used to fabricate the LED determines the color of light produced by the LED. Each material emits light with a specific wavelength spectrum, i.e. with a specific color mixture. Common materials include AlGaAs (red), AlGaInP (orange-yellow-green), and AlGaInN (green-blue).

For many applications, there is a need for LEDs that produce white light, which is a mixture of basic colors (e.g., red, green, and blue), or that produce light that is not available when using typical LED semiconductor materials. Currently, the most common method of color mixing to produce a desired color, such as white, is to use a combination of phosphorescent materials placed on top of a solid state LED, whereby light from the LED ("primary light") is absorbed by the phosphorescent material and then re-emitted "secondary light" at a different frequency. The phosphorescent material "down-converts" a portion of the primary light.

Phosphorescent materials currently used in down conversion applications typically absorb UV or blue light and convert it to light having a longer wavelength, such as red or green light. A lighting device having a primary light source of blue color, such as a blue light emitting LED, in combination with a secondary phosphor emitting red and green light, may be used to generate white light.

The most commonly used phosphor materials are solid semiconductor materials such as trivalent rare earth doped oxides or halophosphates. By combining a blue-emitting LED with a green phosphor such as SrGa₂S₄:Eu₂ ²⁺And red phosphors such as SrSi₅Ni₈:Eu₂ ²⁺Or UV-emitting LEDs plus yellow phosphors such as Sr₂P₂O₇:Eu²⁺；Mu²⁺And a blue-green phosphor, a white emission can be obtained. White LEDs can also be manufactured by combining a blue LED with a yellow phosphor.

Several problems are associated with solid state down-converting phosphors. Color control and color rendering may be poor (i.e., Color Rendering Index (CRI) <75), resulting in an unpleasant light in many cases. Furthermore, it is difficult to adjust the hue of the emitted light; this is because the characteristic color emitted by any particular phosphor is a function of the material from which the phosphor is made. Some hues may not be available at all if no suitable material is present. There is therefore a need in the art for down-converting phosphors that have higher flexibility and better color rendering than currently available phosphors.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a light emitting device comprising: a primary light emitting element; and a Quantum Dot (QD) -containing two-phase composition in optical communication with the primary light-emitting element, the two-phase composition comprising: a hydrophobic inner phase comprising a hydrophobic solvent selected from: fatty acid esters and ethers, isopropyl myristate, isopropyl palmitate, phenyl myristate, natural and synthetic oils, heat transfer liquids, fluorinated hydrocarbons, dibutyl sebacate, and diphenyl ether; a population of QDs dispersed within the internal phase; and a hydrophilic outer phase.

According to a second aspect of the present invention, there is provided a light emitting device comprising: a primary light emitting element; and a Quantum Dot (QD) -containing two-phase composition in optical communication with the primary light-emitting element, the two-phase composition comprising: a hydrophobic inner phase comprising a hydrophobic solvent; a population of QDs dispersed within the internal phase; and an external phase comprising an epoxy resin or a bisphenol a-epoxy resin.

According to a third aspect of the present invention, there is provided a light emitting device comprising: a primary light emitting element; and a Quantum Dot (QD) -containing two-phase composition in optical communication with the primary light-emitting element, the two-phase composition comprising: a hydrophobic inner phase comprising a hydrophobic solvent; a population of QDs dispersed within the internal phase; and an external phase comprising an epoxy-acrylate resin and one or more of: 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA) or carboxylic acid (meth) acrylates.

Drawings

Fig. 1 illustrates a prior art system in which a QD-containing film is coated onto a transparent substrate.

Fig. 2 illustrates a QD-containing film coated with a gas barrier sheet.

Fig. 3 shows quantum yield versus time (QY) for QD films using IPM as the host phase and epoxy (OG142) as the outer phase.

Figure 4 shows the effect of different adhesion promoters in CN104 formulation on edge ingress (edge ingress) of the resulting QD film.

Figure 5 shows the stability of a two-phase QD film based on 20% HEA in CN104 resin.

Figure 6 shows the stability of a two-phase QD film using a 20% MAA/CN104 outer phase resin.

Figure 7 shows the stability of two-phase QD films based on IPM/polyisoprene inner phase and CN 104/20% HEA outer phase resins.

Detailed Description

There has been considerable interest in developing properties of compound semiconductor particles having a size of about 2-50nm, commonly referred to as Quantum Dots (QDs) or nanocrystals. These materials are commercially interesting because of their size-tunable electronic properties that can be used in many commercial applications.

The most studied semiconductor materials are chalcogenide II-VI materials, i.e. ZnS, ZnSe, CdS, CdSe, CdTe; especially CdSe, due to its tunability in the visible region of the spectrum. Repeatable processes for the large-scale production of these materials have been developed according to the "bottom up" technique, whereby particles are prepared using a "wet" chemical process, atom-by-atom (i.e., from molecule to cluster to particle).

Two fundamental factors, both related to the size of the individual semiconductor nanoparticles, are responsible for their unique properties. The first is a large surface to volume ratio. As the particles become smaller, the ratio of the number of surface atoms to the number of internal atoms increases. This results in the surface properties playing an important role in the bulk properties of the material. The second factor is the change in the electronic properties of the material when the material size is very small. At extremely small sizes, quantum confinement (quantum confinement) results in a gradual increase in the band gap of the material as the particle size decreases. This effect is a result of the confinement of "electrons in a box", which produces discrete energy levels similar to those observed in atoms and molecules, rather than continuous bands observed in the corresponding bulk semiconductor material. Thus, the "electrons and holes" generated by absorption of electromagnetic radiation are closer together than they are in the corresponding macrocrystalline material. This results in a narrow bandwidth emission depending on the particle size and composition of the nanoparticle material. Thus QDs have higher kinetic energy than the corresponding macrocrystalline material and therefore the energy of the first excitonic transition (band gap) increases as the particle size decreases.

QD nanoparticles of a single semiconductor material tend to have lower quantum efficiencies due to electron-hole recombination occurring at defects and dangling bonds (dangling bonds) located on the surface of the nanoparticles that may cause non-radiative electron-hole recombination. One way to eliminate such defects and dangling bonds on the inorganic surface of the QD is to grow a second inorganic material with a wide band gap and a small lattice mismatch with the core material on the surface of the core particle to produce a "core-shell" particle. Core-shell particles separate any carriers confined in the core from surface states that would otherwise act as non-radiative recombination centers. One example is QDs with a ZnS shell grown on the surface of a CdSe core.

Basic QD-based light emitting devices have been fabricated by embedding the fabricated QD colloid in an optically clear LED encapsulation medium, typically silicone or acrylate, which is then placed on top of a solid state LED. The use of QDs may have some significant advantages over the use of more conventional phosphors, such as the ability to tune the emission wavelength, strong absorption, improved color rendering, and low scattering.

For commercial application of QDs in next generation light emitting devices, QDs are preferably incorporated into LED encapsulant while remaining as fully monodisperse as possible and without significant quantum efficiency loss. The methods developed to date are problematic, especially because of the nature of current LED encapsulants. When formulated into current LED encapsulants, QDs may aggregate, thereby reducing the optical performance of the QDs. Furthermore, once the QDs are incorporated into the LED encapsulant, oxygen may migrate through the encapsulant to the surface of the QDs, which may lead to photo-oxidation and, as a result, a drop in Quantum Yield (QY).

One way to address the problem of oxygen migration to the QDs is to incorporate the QDs into a medium having low oxygen permeability to form "beads" of such material containing the QDs dispersed within the bead. The QD-containing beads may then be dispersed within the LED encapsulant. Examples of such systems are described in U.S. patent application No. 12/888,982 (publication No. 2011/0068322), filed on 9/23/2010, and 12/622,012 (publication No. 2010/0123155), filed on 11/19/2009, both of which are incorporated herein by reference in their entirety.

QD-containing films are described herein. Fig. 1 illustrates a prior art embodiment 100 in which a QD-containing film 101 is disposed on a transparent substrate 102. Such a film may be used to down-convert primary light 103 from a primary light source 104, for example, by absorbing the primary light 103 and emitting secondary light 105. A portion 106 of the primary light may also be transmitted through the film and the substrate such that all light emitted from the film and the substrate is a mixture of the primary and secondary light.

QD-containing films, such as film 101 in fig. 1, may be formed by dispersing the QDs in a polymeric resin material and forming a film of the material, typically using any method known in the art for making polymeric films. It has been found that QDs are generally more compatible with hydrophobic resins, such as acrylates, than more hydrophilic resins, such as epoxy resins. Therefore, polymer films made from QDs dispersed in acrylates tend to have higher initial Quantum Yields (QY) than QD films using hydrophilic resins such as epoxy resins. However, acrylates tend to be permeable to oxygen, while epoxy polymers and similar hydrophilic polymers tend to be more adept at excluding oxygen.

One alternative for achieving the high QY associated with QD-containing hydrophobic films while also maintaining the stability of the QY over time is to separate the film from oxygen by sandwiching the film between gas spacers, as illustrated in fig. 2. Fig. 2 illustrates a panel 200 having a polymer film 201 contained between gas barrier sheets 202 and 203. The polymer film 201 contains QDs dispersed throughout. The gas barrier sheets 202 and 203 serve to prevent oxygen from contacting the dispersed QDs. However, even in the embodiment illustrated in fig. 2, oxygen may permeate into the film at the edges 204, causing degradation of the QY of the film.

One solution to this problem is to isolate the sealing edge 204 with oxygen. However, doing so increases the cost of manufacturing the panel 200. Another option is to use a polymer 201 that is less permeable to oxygen. However, as explained above, QDs are generally poorly compatible with such polymer resins, and thus the optical properties of devices using such polymers are less than ideal.

Another option is to use a multiphase system where the QDs are suspended in a hydrophobic polymer, such as an acrylate, and the hydrophobic polymer is surrounded by a more oxygen impermeable material, such as an epoxy. For example, beads of acrylate-suspended QDs may be coated with epoxy. Typically, the QDs are suspended in an acrylate polymer, such as lauryl (meth) acrylate, and a crosslinker, such as trimethylolpropane tri (meth) acrylate. The polymer matrix is then cured, for example by using photocuring (typically using photoinitiators such as Igracure).

It has been found that suspending QDs in an acrylate matrix causes a large red-shift in the emission spectrum, which is generally undesirable. The red shift is believed to be due to two reasons. First, acrylate polymers are generally less hydrophobic than ligands attached to the surface of QDs. Slight incompatibility leads to a red shift. Furthermore, the emission tends to be further red-shifted as the acrylate polymer cures. The methods disclosed herein do not cause such red-shifted emissions.

The disclosed compositions and methods are based on forming a host matrix for the QDs, thereby maximizing the dispersion of the QDs in a hydrophobic environment that is highly compatible with the QD surface. One example of a suitable host matrix is isopropyl myristate (IPM). Hydrophobic compounds with a structure similar to IPM can be used as the host phase. Other examples include fatty acid esters and ethers, isopropyl myristate, isopropyl palmitate, phenyl myristate, natural and synthetic oils, heat transfer liquids, fluorinated hydrocarbons, dibutyl sebacate, and diphenyl ether.

Host matrices such as IPM and other hydrophobic materials described above have the advantage that they are compatible with the hydrophobic surface of the QD. Furthermore, the matrix is not cured. Both of these properties minimize the red shift. However, because they are not cured polymer matrices, such matrices tend to lack rigidity. To impart rigidity, and to disaggregate (i.e., space apart) the QDs within the host matrix, the nanoparticles dispersed in place may be immobilized using a scaffold or support material. The stent or support material may be any low polarity material with a high surface area. The scaffold material should be conducive to both spotting and solvent. Examples of suitable scaffolds or support materials are: fumed silica (Aerosil), fumed alumina, hydrophobic polymers (e.g., polyisoprene, cellulose esters, polyesters, polystyrene, porous polymer beads, and lipophilicitySephadex.

The QDs may be suspended in a hydrophobic host matrix together with a scaffold or support material. The suspension can then be used to make a two-phase system by forming an emulsion of the bulk phase with an outer phase, which is typically a more hydrophilic and oxygen impermeable material such as an epoxy resin. Examples of suitable external phase materials include epoxy resins, such as EPO-TEK OG142, which are commercially available one-component, low viscosity epoxy resins. Other suitable external phase materials include Sartomer CN104C80 (bisphenol a based oligomer diluted with hydroxyethyl acrylate (HEA) with photoinitiator and inhibitor).

According to some embodiments, high glass transition temperature epoxy resins facilitate oxygen barrier and stabilize polymer films at high temperatures. Acrylate-based bisphenol a epoxy resins exhibit fast cure rates. Hydroxy (meth) acrylates, such as 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA) or carboxylic (meth) acrylates such as 2-carboxyethyl (meth) acrylate oligomer (CEAO or CEMAO), Acrylic Acid (AA), methacrylic acid (MMA) are used in the formulation to improve adhesion to gas barrier films and to adjust resin viscosity without affecting the oxygen barrier properties of bisphenol a-epoxy acrylates. It should be noted that HPA (T)_g＝22℃)、HPMA(T_g76 ℃ C.) and HEMA (T_gThe polymer at 109 ℃) showed thermally responsive behavior in aqueous solution and became hydrophobic at temperatures ≥ 40 ℃, indicating that the film is less sensitive to humidity. High glass transition temperature (T of PMAA) was shown in some formulations with CN104_gThe temperature is 220 ℃; t of PAA_gPolymers of (meth) acrylic acid at 70-106 c are also advantageous to ensure that the film is stable at high temperatures.