Light color conversion materials and light color conversion inks

Abstract

The present invention provides a photochromic conversion material and a photochromic conversion ink. The photochromic conversion material includes quantum dots and a crosslinkable cholesteric liquid crystal material. The crosslinkable cholesteric liquid crystal material coats the quantum dots. After crosslinking, the crosslinkable cholesteric liquid crystal material has Bragg diffraction characteristics, and can simultaneously reflect blue light with a wavelength between 400 nm and 480 nm and allow the blue light to penetrate.

Description

Technical Field

[0001] The present invention relates to a light color conversion material and a light color conversion ink. Background Art

[0002] Quantum dots (QDs) are semiconductor materials with a nanoscale size (usually less than 100 nm) and a crystal structure, and they can include hundreds to thousands of atoms. Quantum dots have characteristics such as high fluorescence brightness, high color purity (half-wave width less than 50 nm), good light stability and thermal stability, and thus have been widely used in display devices. However, how to improve the quantum efficiency and light color conversion efficiency of quantum dots remains an extremely important topic in this technology. Summary of the Invention

[0003] According to an embodiment of the present invention, the light color conversion material includes quantum dots and a crosslinkable cholesterol liquid crystal material. The crosslinkable cholesterol liquid crystal material coats the quantum dots. After crosslinking, the crosslinkable cholesterol liquid crystal material has Bragg diffraction characteristics and can simultaneously reflect blue light with a wavelength between 400 nm and 480 nm and allow the blue light to penetrate.

[0004] According to an embodiment of the present invention, the light color conversion ink includes a solvent and a light color conversion material dispersed in the solvent. The light color conversion material includes quantum dots and a crosslinkable cholesterol liquid crystal material. The crosslinkable cholesterol liquid crystal material coats the quantum dots. After crosslinking, the crosslinkable cholesterol liquid crystal material has Bragg diffraction characteristics and can simultaneously reflect blue light with a wavelength between 400 nm and 480 nm and allow the blue light to penetrate.

[0005] To make the present invention more obvious and understandable, specific embodiments are hereinafter given and described in detail in conjunction with the accompanying drawings. Brief Description of the Drawings

[0006] Figure 1 It is a graph showing the relationship between the light transmittance / reflection rate and the light wavelength of the crosslinkable cholesterol liquid crystal material in the light color conversion material according to an embodiment of the present invention. Detailed Description of the Embodiments

[0007] In an embodiment of the present invention, after the photochromic conversion material is irradiated with light having a wavelength between 400 nm and 480 nm (such as blue light), it can simultaneously reflect the incident light and be penetrated by the incident light. After multiple reflections and couplings of the incident light, diffraction resonance (i.e., Bragg diffraction) will be formed. In this way, the incident light having the wavelength range can break through the energy gap barrier of the quantum dots, thereby increasing the absorption amount of the incident light by the photochromic conversion material, and thus making the photochromic conversion material have a high optical density (OD). As a result, the excitation conversion of the quantum dots increases, thereby increasing the fluorescence emission intensity and the photochromic conversion efficiency. The photochromic conversion material of the embodiment of the present invention will be described in detail below.

[0008] The photochromic conversion material of the embodiment of the present invention includes quantum dots and a crosslinkable cholesteric liquid crystal material. The cholesteric liquid crystal material coats the quantum dots, so that a layer of cholesteric liquid crystal material covers the surface of the quantum dots. In this embodiment, the crosslinkable cholesteric liquid crystal material has Bragg diffraction characteristics after crosslinking, and can simultaneously reflect blue light having a wavelength between 400 nm and 480 nm and be penetrated by the blue light. In this embodiment, "the cholesteric liquid crystal material can simultaneously reflect light having a wavelength between 400 nm and 480 nm and be penetrated by the light after crosslinking" means that the cholesteric liquid crystal material has the characteristics of selective reflection / penetration for light having a wavelength between 400 nm and 480 nm after crosslinking. The light having a wavelength between 400 nm and 480 nm is, for example, blue light. Refer to Figure 1 When the photochromic conversion material is irradiated with light having a wavelength between 400 nm and 480 nm after crosslinking, the crosslinkable cholesteric liquid crystal material can simultaneously reflect the light and be penetrated by the light after crosslinking.

[0009] In this embodiment, the cholesteric liquid crystal material includes an optically active substance and a nematic liquid crystal monomer having a photopolymerizable acrylic functional group.

[0010] In one embodiment, the optically active substance may be a compound represented by at least one of [Formula 1-1] to [Formula 1-16].

[0011]

[0012]

[0013]

[0014]

[0015] In one embodiment, the nematic liquid crystal monomer having a photopolymerizable acrylic functional group may be a compound represented by [Formula 2] to [Formula 7]. The above compounds can be used alone or in combination of two or more.

[0016]

[0017]

[0018] The optically active substance can be mixed with a nematic liquid crystal monomer having a photopolymerizable acrylic functional group to prepare the photochromic conversion material of the embodiment of the present invention, but the present invention is not limited thereto.

[0019] In addition, the quantum dots can be any well-known quantum dot materials, and the present invention does not limit this. For example, the quantum dots can be single-core quantum dots, core-shell quantum dots or alloy-type quantum dots. The materials of the quantum dots can be II-VI group compounds, III-V group compounds or IV-VI group compounds. The II-VI group compound is, for example, CdSe, the III-V group compound is, for example, InP, and the IV-VI group compound is, for example, PbS, but the present invention is not limited thereto. Structurally, the quantum dots can have ligands, monomer layers, polymer layers, inorganic layers or combinations thereof, and the shape can be dot-shaped, rod-shaped, polygonal or irregular, but the present invention is not limited thereto.

[0020] The photochromic conversion material of the embodiment of the present invention can be mixed into a solvent to prepare the photochromic conversion ink of the embodiment of the invention. The solvent can be toluene, cyclopentanone, cyclohexanone, propylene glycol methyl ether acetate (PGMEA) or methyl ethyl ketone (MEK). For example, the photochromic conversion material of the embodiment of the present invention can be mixed into toluene to obtain a photochromic conversion ink having a solid content of 30%, but the present invention is not limited thereto.

[0021] Coating the photochromic conversion ink of the embodiment of the present invention on a substrate and performing light irradiation treatment can cause a crosslinking reaction of the crosslinkable cholesteric liquid crystal material. After the solvent in the photochromic conversion ink volatilizes, a photochromic conversion layer of the embodiment of the present invention can be formed. The photochromic conversion layer formed by the photochromic conversion ink of the embodiment of the present invention can have a high optical density, so the light emission intensity and the photochromic conversion efficiency are improved. Applying it to the light-emitting component of a display can make the display have a better display effect.

[0022] The effects of the photochromic conversion layer of the embodiment of the present invention will be described below with experimental examples and comparative examples.

[0023] Quantum dots

[0024] Green core-shell quantum dots and red core-shell quantum dots purchased from Taiwan NanoCrystal (TWNC) are used, where the material of the core is CdSe and the material of the shell is ZnS. The emission wavelengths of the green core-shell quantum dots and the red core-shell quantum dots are 528 nm and 630 nm respectively, the full widths at half maximum are 19 nm and 25 nm respectively, and the quantum efficiencies of both are greater than 90%.

[0025] Crosslinkable cholesterol liquid crystal material

[0026] A crosslinkable cholesterol liquid crystal material is prepared by mixing the optically active substance represented by [Formula 1-1] with the nematic liquid crystal monomer represented by [Formula 6], where the addition concentration of the optically active substance accounts for about 6% of the content of the nematic liquid crystal monomer, so that the crosslinkable cholesterol liquid crystal material has the characteristics of being able to simultaneously reflect light with wavelengths between 400 nm and 480 nm and being penetrated by the light after crosslinking.

[0027] Photochromic conversion ink

[0028] <Experimental Example>

[0029] The quantum dots and the crosslinkable cholesterol liquid crystal material are mixed to obtain a photochromic conversion material. The photochromic conversion material is added to toluene and sonicated for 2 hours to disperse, so that the crosslinkable cholesterol liquid crystal material crosslinks and coats the quantum dots to prepare a photochromic conversion ink.

[0030] <Comparative Example>

[0031] Isodecyl acrylate and 1,6-hexanediol diacrylate are first mixed, then quantum dots and toluene are added, and sonicated for 2 hours to disperse to prepare a photochromic conversion ink with a solid content of 30 wt.%.

[0032] Photochromic conversion layer

[0033] The photochromic conversion inks of the experimental example and the comparative example are respectively coated on a polyethylene terephthalate (PET) film with a thickness of 50 μm at a rotation speed of 200 rpm. After drying at 90 °C, exposure is carried out with a UV 365 nm light source (dose: 500 mJ) to form a photochromic conversion layer with a thickness of 9 μm to 10 μm.

[0034] Emission intensity test and optical density test

[0035] The light conversion layers of the experimental examples and comparative examples were irradiated with a blue light-emitting diode (LED) (maximum wavelength of approximately 447 nm), and the maximum emission intensity (relative to the same blue light condition) at the wavelength position where the quantum dots were converted and emitted light (green light at approximately 528 nm and red light at approximately 630 nm) was measured with a spectrometer (Ocean Optics USB4000 Spectrometer). The extinction degree of the light conversion layer with respect to the blue light-emitting diode, that is, the so-called optical density (OD), was calculated. The results are shown in Table 1.

[0036] The optical density (OD) was calculated as follows, where intensity 1 is the light intensity of the original blue light and intensity 2 is the remaining blue light intensity after passing through the light conversion layer.

[0037] OD = -log(intensity 2 / intensity 1)

[0038] Table 1

[0039]

[0040] * Green quantum dots were used in Experimental Examples 1, 2, 3 and Comparative Examples 1, 2, 3, and red quantum dots were used in Experimental Examples 4, 5, 6 and Comparative Examples 4, 5, 6.

[0041] It can be clearly seen from Table 1 that in the light conversion layer formed of the light conversion material of the embodiment of the present invention, since the light conversion material contains a crosslinkable cholesterol liquid crystal material (which has Bragg diffraction characteristics after crosslinking), it can simultaneously reflect and be penetrated by the blue light with a wavelength between 400 nm and 480 nm, so that the incident light with a wavelength between 400 nm and 480 nm can break through the energy gap barrier of the quantum dots, thereby increasing the absorption amount of the incident light by the light conversion layer, making the light conversion layer have a higher optical density, and thus increasing the emission intensity and the light conversion efficiency.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photochromic conversion ink, comprising: a solvent; and a photochromic conversion material dispersed in the solvent, wherein the photochromic conversion material comprises: quantum dots; and a crosslinkable cholesteric liquid crystal material coating the quantum dots, wherein the crosslinkable cholesteric liquid crystal material has a Bragg diffraction property after crosslinking and can simultaneously reflect blue light with a wavelength between 400 nm and 480 nm and allow the blue light to penetrate, and the crosslinkable cholesteric liquid crystal material comprises an optically active substance and a nematic liquid crystal monomer having a photopolymerizable acrylic functional group.

2. The optical color conversion ink according to claim 1, characterized in that, The quantum dots include single-core quantum dots, core-shell quantum dots or alloy-type quantum dots.

3. The light color conversion ink according to claim 1, wherein The solvent includes toluene, cyclopentanone, cyclohexanone, propylene glycol methyl ether acetate or methyl ethyl ketone.

4. The light color conversion ink according to claim 1, characterized in that, The optically active substance includes a compound represented by at least one of [Formula 1-1] to [Formula 1-16], 5. The light color conversion ink according to claim 1, wherein the nematic liquid crystal monomer having a photopolymerizable acrylic functional group includes a compound represented by at least one of [Formula 2] to [Formula 7], 6. The light color conversion ink according to claim 1, wherein the material of the quantum dots includes II-VI group compounds, III-V group compounds or IV-VI group compounds.

Images