Quantum dot

Abstract

To provide a cadmium-free quantum dot having a narrow fluorescence half-width.SOLUTION: A quantum dot of the present invention does not comprise Cd, and is characterized in that a core is formed of ZnTe, ZnTeS, ZnTeSe, or ZnTeSeS. Furthermore, in the present invention, it is preferable that the quantum dot has a core-shell structure in which a nanocrystal serves as the core and a surface of the core is coated with a shell, and the shell is formed of ZnSe or ZnS.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to cadmium-free quantum dots.

Background Art

[0002] Quantum dots are nanoparticles composed of about several hundreds to several thousands of atoms and having a particle size of about several nm to several tens of nm. Quantum dots are also called fluorescent nanoparticles, semiconductor nanoparticles, or nanocrystals.

[0003] The emission wavelength of quantum dots can be variously changed depending on the particle size and composition of the nanoparticles. Further, examples of the performance of quantum dots include fluorescence quantum yield (Quantum Yield: QY) and fluorescence full width at half maximum (Full Width at Half Maximum: FWHM). When quantum dots are used as a wavelength conversion material in the visible light region, the most significant feature is that the range of colors that can be expressed is wide, that is, a high color gamut. Therefore, in the high color gamut achieved by a wavelength conversion member in the visible light region using quantum dots, an important optical property is the fluorescence full width at half maximum.

[0004] Conventionally used highly efficient quantum dots mainly contained cadmium (Cd). Quantum dots containing Cd have the advantages of high fluorescence quantum yield and narrow fluorescence full width at half maximum. On the other hand, due to the toxicity of Cd, its use is regulated in various countries, which has been a major obstacle to practical application.

[0005] On the other hand, the development of Cd-free quantum dots that do not contain Cd has also been extensively studied. One of the typical ones is chalcopyrite-based Copper Indium Sulfide (CuInS2): CIS-based quantum dots (see, for example, Patent Document 1). However, since the luminescence principle is defect luminescence, its optical properties are not higher than those of Cd-based quantum dots, and generally the fluorescence full width at half maximum is 80 to 100 nm or more. The same applies to chalcopyrite-based quantum dots other than CIS, and so far, the synthesis of chalcopyrite-based quantum dots with a fluorescence full width at half maximum below 60 nm has not been reported.

[0006] Another typical Cd-free quantum dot is Indium Phosphide (InP): InP-based quantum dots (see, for example, Patent Document 1). However, InP-based quantum dots have a wider fluorescence full width at half maximum compared to CdSe-based quantum dots, and so far, the synthesis of InP-based quantum dots with a fluorescence full width at half maximum below 35 nm has not been reported.

[0007] Also, zinc selenide (ZnSe) is known as a cadmium-free quantum dot, but since ZnSe has a band gap of 2.7 eV, it is impossible to emit light of green or higher wavelengths using only ZnSe.

[0008] As another zinc-based quantum dot, zinc telluride (ZnTe) can be considered, but there are not many reported examples regarding its solution synthesis.

[0009] In Non-Patent Document 1 below, a direct synthesis method of ZnTe using an organozinc compound and trialkylphosphine telluride is described in detail. Although the ZnTe obtained in this paper has been studied in detail, such as the absorption shifting to the long wavelength side with particle growth, none of the ZnTe synthesized in this paper has fluorescence properties.

[0010] In addition, in Non-Patent Document 2 below, ZnTe with a sphalerite structure was synthesized using an organozinc compound and Te reduced by super hydride (Lithium triethylborohydride: LiBHEt3) as raw materials. By variously examining the reaction conditions, research on controlling the morphology of ZnTe nanoparticles has been reported. The synthesis method is characterized by using super hydride, which is highly reactive and difficult to use in mass production. In this paper, details of the particle morphology, crystal structure, and absorption spectrum of the obtained ZnTe are reported, but there is no description regarding the fluorescence characteristics.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Non-Patent Documents

[0012]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] As described above, although the research and development of quantum dots containing no Cd such as CIS-based and InP-based ones are progressing, the fluorescence half-width of any of the quantum dots is large.

[0014] In addition, regarding the above-mentioned ZnTe, in the synthesis method by direct synthesis, in order to enhance the reactivity of the zinc raw material, for example, diethylzinc (Et2Zn) is generally used. However, since diethylzinc has high reactivity and ignites in air, it must be handled under an inert gas stream. Thus, the handling and storage of the raw material are difficult, and the reaction using it also involves risks such as heat generation and ignition, making it unsuitable for mass production.

[0015] Also, in a reaction system using an organic zinc raw material such as a fatty acid salt or zinc halide with low reactivity, although ZnTe is generated, the particle generation is insufficient or there are many structural defects. For this reason, there has been a problem that generally no fluorescence is observed in the purified nanoparticles.

[0016] In the manufacturing method of ZnTe quantum dots with a narrow fluorescence half-width, there has been no reported example where fluorescence was confirmed by a safe method that enables mass production.

[0017] The present invention has been made in view of such a point, and an object thereof is to provide a cadmium-free quantum dot with a narrow fluorescence half-width.

[0018] Another object of the present invention is to provide a manufacturing method of quantum dots that safely and mass-producibly synthesizes the above-mentioned quantum dots.

Means for Solving the Problems

[0019] The present invention is characterized in that it does not contain Cd, and the core is formed of ZnTe, ZnTeS, ZnTeSe, or ZnTeSeS.

[0020] In the present invention, it is preferable that the quantum dot has a core-shell structure with a nanocrystal as the core and a shell covering the surface of the core, and the shell is formed of ZnSe or ZnS.

[0021] In the present invention, it is preferable that the fluorescence half-width is 40 nm or less. In the present invention, it is preferable that the fluorescence wavelength is in the range of 400 nm or more and 650 nm or less.

[0022] In the present invention, it is preferable that the copper chalcogenide is synthesized by a metal exchange reaction using a copper chalcogenide as a precursor. In the present invention, it is preferable that a copper chalcogenide as a precursor is synthesized from an organocopper compound or an inorganic copper compound and an organic chalcogen compound, and the quantum dots are synthesized using the precursor. In the present invention, it is preferable that the core is formed of ZnTe and the remaining amount of Cu is 100 ppm or less.

Advantages of the Invention

[0023] According to the quantum dots of the present invention, quantum dots with uniform particle shapes and sizes can be synthesized, so that the fluorescence half-width can be narrowed and the improvement of the high color gamut can be achieved.

[0024] Further, according to the method for producing quantum dots of the present invention, quantum dots with a narrow fluorescence half-width and not containing Cd can be synthesized safely and in a mass-producible manner.

Brief Description of the Drawings

[0025]

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Modes for Carrying Out the Invention

[0026] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof.

[0027] FIG. 1 is a schematic diagram of a quantum dot in the present embodiment. The quantum dot 5 shown in FIG. 1A is a cadmium-free nanocrystal.

[0028] In the present embodiment, the quantum dot 5 is preferably a nanocrystal containing zinc and tellurium (hereinafter referred to as Zn and Te), or zinc, tellurium and sulfur (hereinafter referred to as Zn, Te and S), or zinc, tellurium, selenium and sulfur (referred to as Zn, Te, Se and S). Note that a nanocrystal containing zinc, tellurium and selenium may also be used. Alternatively, the quantum dot 5 may be a nanocrystal containing zinc and selenium.

[0029] The quantum dot 5 has fluorescence characteristics due to band-edge emission and exhibits a quantum size effect due to the size of its particles.

[0030] Here, the "nanocrystal" refers to nanoparticles having a particle size of about several nm to several tens of nm. In the present embodiment, a large number of quantum dots 5 can be generated with a substantially uniform particle size.

[0031] Zn and Te, or Zn, Te and S, Zn, Te, S and Se, or Zn and Se contained in the quantum dot 5 are the main components, and elements other than these elements may be included. However, it is preferable that neither cadmium (Cd) nor phosphorus (P) is included. Since organophosphorus compounds are expensive and easily oxidized in air, synthesis becomes unstable, leading to an increase in cost, instability of fluorescence characteristics, and complexity of the manufacturing process.

[0032] The quantum dots 5 of this embodiment have a fluorescence half-width of 40 nm or less. The "fluorescence half-width" refers to the full width at half maximum (FWHM) indicating the spread of the fluorescence wavelength at an intensity that is half of the peak value of the fluorescence intensity in the fluorescence spectrum. Further, the fluorescence half-width is preferably 30 nm or less. Further, the fluorescence half-width is preferably 28 nm or less. Further, the fluorescence half-width is more preferably 26 nm or less. Further, the fluorescence half-width is still more preferably 25 nm or less. Further, the fluorescence half-width is even more preferably 23 nm or less. Thus, since the fluorescence half-width can be narrowed, improvement in high color gamut can be achieved. In this embodiment, as will be described later, as a reaction system for synthesizing the quantum dots 5, after synthesizing copper chalcogenide as a precursor, a metal exchange reaction is performed on the precursor. By manufacturing the quantum dots 5 based on such an indirect synthesis reaction, the fluorescence half-width can be narrowed, and specifically, a fluorescence half-width of 40 nm or less (preferably 30 nm or less) can be obtained.

[0033] As shown in FIG. 1A, it is preferable that a large number of organic ligands 11 are coordinated on the surface of the quantum dots 5. Thereby, aggregation of the quantum dots 5 can be suppressed, and the intended optical properties are exhibited. The ligands that can be used in the reaction are not particularly limited, and for example, the following ligands can be mentioned as typical ones. Aliphatic primary amine-based, oleylamine: C 18 H 35 NH2, stearyl (octadecyl) amine: C 18 H 37 NH2, dodecyl (lauryl) amine: C 12 H 25 NH2, decylamine: C 10 H 21 NH2, octylamine: C8H 17 NH2 Fatty acid, oleic acid: C 17 H 33 COOH, stearic acid: C 17 H 35 COOH, palmitic acid: C 15 H 31COOH, Myristic Acid: C 13 H 27 COOH, Lauric Acid: C 11 H 23 COOH, Decanoic Acid: C9H 19 COOH, Octanoic Acid: C7H 15 COOH Thiol-based, Octadecanethiol: C 18 H 37 SH, Hexadecanethiol: C 16 H 33 SH, Tetradecanethiol: C 14 H 29 SH, Dodecanethiol: C 12 H 25 SH, Decanethiol: C 10 H 21 SH, Octanethiol: C8H 17 SH Phosphine-based, Trioctylphosphine: (C8H 17 )3P, Triphenylphosphine: (C6H5)3P, Tributylphosphine: (C4H9)3P Phosphine Oxide-based, Trioctylphosphine Oxide: (C8H 17 )3P=O, Triphenylphosphine Oxide: (C6H5)3P=O, Tributylphosphine Oxide: (C4H9)3P=O

[0034] In this embodiment, the ligand is not limited to monofunctional small molecules, and it is also possible to use bifunctional, trifunctional, tetrafunctional or higher polyfunctional oligomers and polymers.

[0035] The fluorescence quantum yield of the quantum dots 5 in this embodiment is 5% or more. Further, the fluorescence quantum yield is more preferably 10% or more, and even more preferably 20% or more. Thus, in this embodiment, the fluorescence quantum yield of the quantum dots can be increased.

[0036] In this embodiment, the fluorescence wavelength can be freely controlled to about 400 nm or more and 650 nm or less. For example, the quantum dot 5 in this embodiment is a solid solution based on ZnTe using a chalcogen element in addition to zinc. In this embodiment, by adjusting the particle size of the quantum dot 5 and the composition of the quantum dot 5, the fluorescence wavelength can be controlled from blue to green to yellow to red. Therefore, the fluorescence wavelength is preferably 400 nm or more, and more preferably 430 nm or more. Further, as red emission, the fluorescence wavelength is preferably 650 nm or less, and as green emission, it is more preferably 580 nm or less.

[0037] In this embodiment, as described above, the fluorescence wavelength can be controlled from blue to red. However, as a wavelength conversion material in the visible light region, green or red emission is preferable.

[0038] The quantum dot 5 shown in FIG. 1B has a core-shell structure having a core 5a and a shell 5b coated on the surface of the core 5a. As shown in FIG. 1B, it is preferable that a large number of organic ligands 11 are coordinated on the surface of the quantum dot 5. Further, the fluorescence half-width of the quantum dot 5 shown in FIG. 1B is 40 nm or less. The fluorescence half-width is preferably 30 nm or less.

[0039] The core 5a of the quantum dot 5 shown in FIG. 1B is the nanocrystal shown in FIG. 1A. Therefore, the core 5a is preferably formed of ZnTe, ZnTeS, ZnTeSeS, ZnSe, or ZnSeS. The shell 5b does not contain cadmium (Cd) as in the case of the core 5a. The shell 5b is not particularly limited in terms of material, but is formed of, for example, zinc selenide (ZnSe), zinc sulfide (ZnS), or the like.

[0040] Note that the shell 5b may be in a state of being solid-solubilized on the surface of the core 5a. In FIG. 1B, the boundary between the core 5a and the shell 5b is shown by a dotted line, which indicates that it may or may not be possible to confirm the boundary between the core 5a and the shell 5b by analysis.

[0041] The quantum dot 5 shown in FIG. 1B can also freely control the fluorescence wavelength to about 400 nm or more and 650 nm or less, similar to FIG. 1A.

[0042] Subsequently, a method for manufacturing the quantum dot 5 of the present embodiment will be described.

[0043] First, in the present embodiment, a copper chalcogenide (precursor) is synthesized from an organic copper compound or an inorganic copper compound and an organic chalcogen compound. Specifically, as the precursor, copper telluride: Cu2Te, copper telluride sulfide: Cu2TeS, copper telluride selenide sulfide: Cu2TeSeS, copper selenide: Cu2Se, or copper selenide sulfide: Cu2SeS is preferably used.

[0044] In the present embodiment, ZnTe core alone emits fluorescence, but in order to increase the fluorescence intensity of the quantum dot, it is preferable to dissolve S in ZnTe. Therefore, in the synthesis of Cu2Te as the precursor, it is preferable to add thiol in an amount of 1 to 50 equivalents with respect to Te, and in order to obtain a quantum dot with higher fluorescence intensity, it is more preferable to add 5 to 20 equivalents. Thereby, Cu2TeS and Cu2TeSeS can be obtained. Thiol is not limited, but for example, octadecanethiol: C 18 H 37 SH, hexadecanethiol: C 16 H 33 SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, octanethiol: C8H 17 SH, etc.

[0045] Here, in this embodiment, the Cu raw material of Cu2Te is not particularly limited, and for example, the following organic copper reagents or inorganic copper reagents can be used. That is, copper(I) acetate Cu(OAc), copper(II) acetate: Cu(OAc)2 as acetates, and copper stearate: Cu(OC(=O)C 17 H 35 )2, copper oleate: Cu(OC(=O)C 17 H 33 )2, copper myristate: Cu(OC(=O)C 13 H 27 )2, copper dodecanoate: Cu(OC(=O)C 11 H 23 )2, copper acetylacetonate: Cu(acac)2, and as halides, both monovalent and divalent compounds can be used, such as copper(I) chloride: CuCl, copper(II) chloride: CuCl2, copper(I) bromide: CuBr, copper(II) bromide: CuBr2, copper(I) iodide: CuI, copper(II) iodide: CuI2, etc.

[0046] In this embodiment, tellurium uses an organotellurium compound (organic chalcogen compound) as a raw material. Although the structure of the compound is not particularly limited, for example, trioctylphosphine telluride obtained by dissolving tellurium in trioctylphosphine: (C8H 17 )3P=Te, or tributylphosphine telluride obtained by dissolving tellurium in tributylphosphine: (C4H9)3P=Te, etc. can be used. Also, dialkylditellurides such as diphenylditelluride: (C6H5)2Te2: R2Te2 can also be used.

[0047] Also, in this embodiment, when selenium is dissolved, selenium uses an organic selenium compound (organic chalcogen compound) as a raw material. Although the structure is not particularly limited, for example, trioctylphosphine selenide obtained by dissolving selenium in trioctylphosphine: (C8H 17)3P=Se, or tributylphosphine selenide obtained by dissolving selenium in tributylphosphine: (C4H9)3P=Se, or a solution obtained by dissolving selenium at a high temperature in a high-boiling-point solvent such as octadecene, a long-chain hydrocarbon, can be used.

[0048] In this embodiment, an organic copper compound or an inorganic copper compound and an organic chalcogen compound are mixed and dissolved. As the solvent, octadecene can be used as a high-boiling saturated hydrocarbon or unsaturated hydrocarbon. In addition to this, t-butylbenzene can be used as an aromatic high-boiling solvent, butyl butyrate: C4H9COOC4H9, benzyl butyrate: C6H5CH2COOC4H9, etc. can be used as high-boiling ester solvents, but it is also possible to use an aliphatic amine compound, a fatty acid compound, or an aliphatic phosphorus compound as the solvent.

[0049] At this time, the reaction temperature is set in the range of 160 °C or higher and 250 °C or lower to synthesize a copper chalcogenide (precursor). Note that the reaction temperature is preferably 160 °C or higher and 220 °C or lower, which is lower, and more preferably 160 °C or higher and 200 °C or lower, which is even lower.

[0050] Also, in this embodiment, there is no particular limitation on the reaction method, but in order to obtain quantum dots with a narrow half-width, it is important to synthesize Cu2Te, Cu2TeS, Cu2TeSeS, Cu2Se, Cu2SeS with uniform particle sizes. For this reason, in the synthesis of the precursors Cu2Te, or Cu2TeS, Cu2TeSeS, Cu2Se, Cu2SeS, it is preferable to quickly add a tellurium raw material solution, or a mixed solution of a tellurium raw material and a selenium raw material, or a selenium raw material, to the heated organic copper raw material solution.

[0051] In addition, in this embodiment, in order to obtain ZnTe or ZnSe with high fluorescence intensity as the core, it is important to dissolve sulfur (S) in the core. Therefore, for example, in the synthesis of Cu2Te as a precursor, it is preferable to add thiol in an amount of 1 to 50 equivalents with respect to Te, and more preferably 5 to 20 equivalents in order to obtain quantum dots with high fluorescence intensity. Although not particularly limited to thiol, for example, octadecanethiol: C 18 H 37 SH, hexadecanethiol: C 16 H 33 SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, octanethiol: C8H 17 SH, etc.

[0052] Next, as raw materials for ZnTe, ZnTeS, ZnTeSeS, ZnSe, or ZnSeS, an organozinc compound or an inorganic zinc compound is prepared. The organozinc compound and the inorganic zinc compound are raw materials that are stable in air and easy to handle. Although the structure of the organozinc compound and the inorganic zinc compound is not particularly limited, in order to efficiently perform the metal exchange reaction, it is preferable to use a zinc compound with high ionic properties. For example, the following organozinc compounds and inorganic zinc compounds can be used. That is, zinc acetate: Zn(OAc)2 as an acetate, zinc nitrate: Zn(NO3)2, and as fatty acid salts, zinc stearate: Zn(OC(=O)C 17 H 35 )2, zinc oleate: Zn(OC(=O)C 17 H 33 )2, zinc palmitate: Zn(OC(=O)C 15 H 31 )2, zinc myristate: Zn(OC(=O)C 13 H 27 )2, zinc dodecanoate: Zn(OC(=O)C 11 H 23)2. Zinc acetylacetonate: Zn(acac)2, as halides, zinc chloride: ZnCl2, zinc bromide: ZnBr2, zinc iodide: ZnI2, and as zinc carbamate, zinc diethyldithiocarbamate: Zn(SC(=S)N(C2H5)2)2, zinc dimethyldithiocarbamate: Zn(SC(=S)N(CH3)2)2, zinc dibutyldithiocarbamate: Zn(SC(=S)N(C4H9)2)2, etc. can be used.

[0053] Subsequently, the above-mentioned organic zinc compound or inorganic zinc compound is added to the reaction solution in which the precursor of the copper chalcogenide is synthesized. Thereby, a metal exchange reaction between copper (Cu) of the copper chalcogenide and zinc (Zn) occurs. It is preferable to cause the metal exchange reaction at 180 °C or higher and 280 °C or lower. Further, it is more preferable to cause the metal exchange reaction at a lower temperature, 180 °C or higher and 250 °C or lower.

[0054] In addition, in the present embodiment, when performing metal exchange, a compound having an auxiliary role of releasing the metal of the precursor into the reaction solution by coordination or chelation or the like is required.

[0055] Examples of the compound having the above-mentioned role include ligands capable of forming a complex with copper. For example, phosphorus-based ligands, amine-based ligands, and sulfur-based ligands are preferable, and among them, phosphorus-based ligands are more preferable because of their high efficiency.

[0056] Thereby, the metal exchange between Cu and Zn is appropriately performed, and quantum dots with a narrow fluorescence half-width based on Zn and Te or Zn and Se can be produced.

[0057] In addition, the metal exchange with Cu-Zn preferably proceeds quantitatively. In order to improve the optical properties of the produced ZnTe or ZeSe, it is preferable to reduce the residual amount of Cu in ZnTe or ZnSe. The residual amount of Cu is preferably 100 ppm, more preferably 50 ppm, and ideally 10 ppm or less.

[0058] In this embodiment, a copper chalcogenide is synthesized from an organic copper compound or an inorganic copper compound and an organic chalcogen compound as a precursor, and quantum dots are synthesized by metal exchange using the precursor. Thus, in this embodiment, first, quantum dots are synthesized through the synthesis of the precursor, and ZnTe and ZnSe are not directly synthesized. By such an indirect synthesis method, it is not necessary to use reagents that are too reactive and dangerous to handle, and it is possible to safely and stably synthesize ZnTe-based quantum dots and ZnSe-based quantum dots with a narrow full width at half maximum.

[0059] Further, in this embodiment, it is possible to obtain desired quantum dots by performing Cu-Zn metal exchange in one pot without isolating and purifying the precursor.

[0060] Further, in this embodiment, the synthesized quantum dots exhibit fluorescence characteristics without performing various treatments such as washing, isolation and purification, coating treatment, or ligand exchange.

[0061] However, as shown in FIG. 1B, the fluorescence quantum yield can be further increased by coating the core 5a made of nanocrystals such as ZnTe, ZnTeS, or ZnTeSeS with the shell 5b.

[0062] Further, in this embodiment, it is possible to synthesize a core / shell structure at the precursor stage. For example, when zinc selenide (ZnSe) is used for the shell structure, the copper chalcogenide of the precursor is Cu2Te / Cu2Se. By continuously adding a Te raw material and a Se raw material in one reaction vessel for synthesis and then performing Cu-Zn metal exchange, it is possible to obtain ZnTe / ZnSe.

[0063] In this embodiment, by using Cu2Te, Cu2TeS, or Cu2TeSeS as a precursor and performing Cu-Zn metal exchange, not only ZnTe, ZnTeS, or ZnTeSeS nanocrystals can be synthesized, but also, for example, by using Cu2Te / Cu2Se as a precursor and performing Cu-Zn metal exchange, it is possible to synthesize ZnTe / ZnSe having a core-shell structure. Similarly, one-pot synthesis of a solid solution having a core-shell structure is also possible.

[0064] In this embodiment, although Cu2Te, Cu2TeS, or Cu2TeSeS is mainly used as the precursor, by performing Cu-Zn metal exchange in the same manner with Cu2Se, Cu2SeS, or Cu2S, it is possible to obtain nanocrystals such as ZnSe, ZnSeS, or ZnS.

[0065] The uses of the quantum dots 5 shown in FIG. 1 are not particularly limited, but several specific examples are given below.

[0066] FIG. 2 is a schematic diagram of an LED device using the quantum dots of this embodiment. As shown in FIG. 2, the LED device 1 of this embodiment includes a storage case 2 having a bottom surface 2a and a side wall 2b surrounding the periphery of the bottom surface 2a, an LED chip (light-emitting element) 3 disposed on the bottom surface 2a of the storage case 2, and a fluorescent layer 4 filled in the storage case 2 and sealing the upper surface side of the LED chip 3. Here, the upper surface side is the direction in which the light emitted from the LED chip 3 is emitted from the storage case 2, and indicates the direction opposite to the bottom surface 2a with respect to the LED chip 3.

[0067] The LED chip 3 is disposed on a base wiring board (not shown), and the base wiring board may constitute the bottom portion of the storage case 2. As the base board, for example, a configuration in which a wiring pattern is formed on a base material such as glass epoxy resin can be presented.

[0068] The LED chip 3 is a semiconductor element that emits light when a voltage is applied in the forward direction, and has a basic configuration in which a P-type semiconductor layer and an N-type semiconductor layer are PN-junctioned.

[0069] As shown in FIG. 2, the fluorescent layer 4 is formed of a resin 6 in which a large number of quantum dots 5 are dispersed.

[0070] In addition, the resin composition in which the quantum dots 5 in the present embodiment are dispersed may contain a fluorescent substance different from the quantum dots 5 and the quantum dots 5. Examples of the fluorescent substance include cyan-based and KSF (K2SiF6:Mn 4+ ) red phosphors, etc., but the material is not particularly limited.

[0071] The resin 6 constituting the fluorescent layer 4 is not particularly limited, but polypropylene (PP), polystyrene (PS), acrylic resin, methacrylate resin, MS resin, polyvinyl chloride (PVC), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethylpentene, liquid crystal polymer, epoxy resin, silicone resin, or a mixture thereof can be used.

[0072] The LED device using the quantum dots of the present embodiment can be applied to a display device. FIG. 3 is a longitudinal sectional view of a display device using the LED device shown in FIG. 2. As shown in FIG. 3, the display device 50 includes a plurality of LED devices 20 and a display unit 54 such as a liquid crystal display facing each LED device 20. Each LED device 20 is disposed on the back side of the display unit 54. Each LED device 20 has a structure in which an LED chip is sealed with a resin in which a large number of quantum dots 5 are diffused, similar to the LED device 1 shown in FIG. 2.

[0073] As shown in FIG. 3, a plurality of LED devices 20 are supported by a support 52. Each LED device 20 is arranged at a predetermined interval. Each LED device 20 and the support 52 constitute a backlight 55 for the display unit 54. The support 52 is not particularly limited in shape or material, such as being sheet-like, plate-like, or case-like. As shown in FIG. 3, a light diffusion plate 53 or the like may be interposed between the backlight 55 and the display unit 54.

[0074] By applying the quantum dots 5 with a narrow fluorescence half-width in the present embodiment to the LED device shown in FIG. 2, the display device shown in FIG. 3, etc., it is possible to effectively improve the light emission characteristics of the device.

Example

[0075] Hereinafter, the effects of the present invention will be described with reference to examples and comparative examples of the present invention. Note that the present invention is not limited by the following examples.

[0076] <Raw materials> In the present invention, the following raw materials were used to synthesize cadmium-free quantum dots.

[0077] Solvent Octadecene: manufactured by Aldrich Co., Ltd., manufactured by Idemitsu Kosan Co., Ltd. Oleylamine: manufactured by Kao Corporation Oleic acid: manufactured by Kao Corporation

[0078] Zinc chloride: manufactured by Aldrich Co., Ltd. Zinc iodide: manufactured by Aldrich Co., Ltd. Zinc acetate dihydrate: manufactured by Ikoma Chemical Co., Ltd. Zinc acetate anhydrous: manufactured by Aldrich Co., Ltd. Tellurium (4N: 99.99%): manufactured by Shinsei Chemical Co., Ltd., or manufactured by Aldrich Selenium (4N: 99.99%): manufactured by Shinsei Chemical Co., Ltd., or manufactured by Aldrich Sulfur: manufactured by Kishida Chemical Co., Ltd.

[0079] Trioctylphosphine: manufactured by Kitakyo Chemical Co., Ltd. Trioctylphosphine oxide: manufactured by Aldrich Tetradecane: manufactured by Tokyo Chemical Industry Co., Ltd. (TCI) Triphenyl phosphite: manufactured by Aldrich Hexadecylamine: manufactured by NOF Corporation Dodecanethiol: manufactured by Arkema

[0080] <Measuring instrument> Fluorescence spectrometer: F-2700 manufactured by JASCO Corporation UV-visible spectrophotometer: V-770 manufactured by Hitachi, Ltd. Quantum yield measurement device: QE-1100 manufactured by Otsuka Electronics Co., Ltd. X-ray diffractometer (XRD): D2 PHASER manufactured by Bruker Scanning electron microscope (SEM): SU9000 manufactured by Hitachi, Ltd.

[0081] [Example 1] In a 100 mL reaction vessel, 36.3 mg of copper acetate anhydrous: Cu(OAc)2, 0.5 mL of dodecanethiol: DDT, 0.1 mL of oleylamine: OLAm, and 4 mL of octadecene: ODE were placed. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0082] To this solution, 0.2 mL of a tellurium-trioctylphosphine solution: Te-TOP solution (0.5 M) was added, and it was heated while stirring at 220 °C for 10 minutes. The obtained reaction solution (Cu2Te) was cooled to room temperature.

[0083] Thereafter, 273 mg of zinc chloride: ZnCl2, 3 mL of trioctylphosphine: TOP, and 0.1 mL of oleylamine: OLAm were added to the reaction solution, and it was heated while stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere.

[0084] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, as shown in Figure 4, optical properties with a fluorescence wavelength of about 518.5 nm and a fluorescence half-width of about 24.3 nm were obtained.

[0085] Further, ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Then, toluene was added to the precipitate to disperse it, obtaining a dispersion solution of ZnTe particles.

[0086] [Example 2] Into a 100 mL reaction vessel, 36.3 mg of copper(II) acetate anhydrous: Cu(OAc)2, 63.8 μL of hexadecanethiol: HDT, 0.1 mL of oleylamine: OLAm, and 10 mL of octadecene: ODE were placed. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0087] To this solution, 0.2 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M) was added, and it was heated while stirring at 200 °C for 10 minutes.

[0088] The obtained reaction solution was cooled to room temperature. Then, 273 mg of zinc chloride: ZnCl2, 3 mL of trioctylphosphine: TOP, and 0.1 mL of oleylamine: OLAm were added to the reaction solution. Then, under an inert gas (N2) atmosphere, it was heated while stirring at 250 °C for 15 minutes.

[0089] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, as shown in Figure 5, optical properties with a fluorescence wavelength of about 510.0 nm and a fluorescence full width at half maximum of about 22.3 nm were obtained.

[0090] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Then, toluene was added to the precipitate to disperse it, obtaining a dispersion solution of ZnTe particles.

[0091] [Example 3] Into a 100 mL reaction vessel, 36.3 mg of copper(II) acetate anhydrous: Cu(OAc)2 and 5 mL of dodecanethiol: DDT were placed. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0092] To this solution, 0.2 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M) was added, and the mixture was heated with stirring at 220 °C for 20 minutes. The resulting reaction solution was cooled to room temperature. Then, 273 mg of zinc chloride: ZnCl2, 3 mL of trioctylphosphine: TOP, and 0.2 mL of oleylamine: OLAm were added to the reaction solution. And it was heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere.

[0093] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, as shown in Fig. 6, optical properties with a fluorescence wavelength of about 529.5 nm and a fluorescence half-width of about 26.1 nm were obtained.

[0094] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Then, toluene was added to the precipitate and dispersed to obtain a particle solution of ZnTeS.

[0095] [Example 4] 72.7 mg of copper acetate anhydrous: Cu(OAc)2, 0.4 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M), 0.2 mL of trioctylphosphine selenide: Se-TOP solution (1 M), 1 mL of dodecanethiol: DDT, and 8 mL of octadecene: ODE were placed in a 100 mL reaction vessel, and heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0096] This solution was heated with stirring at 220 °C for 10 minutes, then 0.2 mL of oleylamine: OLAm was added, and it was heated with stirring at 220 °C for 5 minutes. The resulting reaction solution was cooled to room temperature. Then, 546 mg of zinc chloride: ZnCl2, 6 mL of trioctylphosphine: TOP, and 0.2 mL of oleylamine: OLAm were added to the reaction solution, and it was heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere.

[0097] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 522.5 nm and a fluorescence half-width of 24.9 nm were obtained (Fig. 7).

[0098] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to collect the precipitate. Toluene was added to the precipitate and dispersed to obtain a ZnTeSeS particle dispersion solution.

[0099] [Example 5] Into a 100 mL reaction vessel, 36.3 mg of copper acetate anhydrous: Cu(OAc)2, 0.2 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M), 0.5 mL of dodecanethiol: DDT, and 4 mL of octadecene: ODE were placed, and heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0100] This solution was heated with stirring at 180 °C for 10 minutes, and then 0.1 mL of oleylamine: OLAm was added, and heated with stirring at 180 °C for 5 minutes. The obtained reaction solution was cooled to room temperature. Then, 273 mg of zinc chloride: ZnCl2, 3 mL of trioctylphosphine: TOP, and 0.1 mL of oleylamine: OLAm were added to the reaction solution, and heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere.

[0101] This solution was cooled to room temperature, 546 mg of zinc chloride: ZnCl2 was added, and heated with stirring at 220 °C for 60 minutes under an inert gas (N2) atmosphere.

[0102] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 542.0 nm and a fluorescence half-width of 27.8 nm were obtained (Figure 8).

[0103] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to collect the precipitate. Toluene was added to the precipitate and dispersed to obtain a ZnTe particle dispersion solution.

[0104] [Example 6] Into a 100 mL reaction vessel, 36.3 mg of copper acetate anhydrous: Cu(OAc)2, 0.2 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M), and 4 mL of dodecanethiol: DDT were placed, and heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0105] This solution was heated while stirring at 220 °C for 10 minutes, and then 0.1 mL of oleylamine: OLAm was added, and it was heated while stirring at 220 °C for 10 minutes. The obtained reaction solution was cooled to room temperature. Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to collect the precipitate. 4 mL of ODE and 0.1 mL of OLAm were added to the precipitate and dispersed to obtain a CuTe(S) particle dispersion solution.

[0106] Thereafter, 273 mg of zinc chloride: ZnCl2 and 3 mL of trioctylphosphine: TOP were added to the reaction solution, and it was heated while stirring at 220 °C for 20 minutes under an inert gas (N2) atmosphere. Further, 0.5 mL of zinc octanoate solution (0.2 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of additionally adding zinc octanoate and performing heating and stirring was performed a total of 2 times.

[0107] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 520.5 nm and a fluorescence half-width of 22.4 nm were obtained (Figure 9).

[0108] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to collect the precipitate. Toluene was added to the precipitate and dispersed to obtain a ZnTeS particle dispersion solution.

[0109] [Example 7] 0.091 g of copper(II) acetate anhydrous: Cu(OAc)2, 0.625 mL of dodecanethiol: DDT, 0.625 mL of trioctylphosphine: TOP, 0.194 g of trioctylphosphine oxide: TOPO, and 10 mL of tetradecane were placed in a 100 mL reaction vessel, and heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0110] To this solution, 0.5 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M) and 0.125 mL of oleylamine: OLAm were added, and the mixture was heated with stirring at 200 °C for 15 minutes. The resulting reaction solution was cooled to room temperature. Then, 0.685 g of zinc chloride: ZnCl2, 7.5 mL of trioctylphosphine: TOP, 0.25 mL of oleylamine: OLAm, and 0.066 mL of triphenyl phosphite were added to the reaction solution, and the mixture was heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Further, 1.25 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding additional zinc octanoate and performing heating and stirring was carried out a total of 2 times.

[0111] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 502.0 nm and a fluorescence half-width of 17.9 nm were obtained (Figure 13).

[0112] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate to disperse it, obtaining a ZnTe particle dispersion solution.

[0113] [Example 8] To a 100 mL reaction vessel, 0.8 mL of copper oleate: Cu(OLAc)2 (0.5 M), 0.4 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M), 2 mL of Se-ODE solution (0.1 M), 1 mL of dodecanethiol: DDT, and 6.2 mL of octadecene: ODE were added, and the mixture was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0114] This solution was heated while stirring at 220 °C for 10 minutes, and then 0.2 mL of oleylamine: OLAm was added, and it was heated while stirring at 220 °C for 5 minutes. The resulting reaction solution was cooled to room temperature. Then, 0.546 g of zinc chloride: ZnCl2, 6 mL of trioctylphosphine: TOP, and 0.2 mL of oleylamine: OLAm were added to the reaction solution, and it was heated while stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Furthermore, 0.5 mL of zinc octanoate solution (0.2 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding additional zinc octanoate and performing heating and stirring was carried out a total of 2 times.

[0115] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 522.5 nm and a fluorescence half-width of 23.1 nm were obtained (Figure 14).

[0116] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate to disperse it, obtaining a ZnTeSe particle dispersion solution.

[0117] [Example 9] 0.182 g of copper(II) acetate anhydrous: Cu(OAc)2, 1 mL of tellurium-trioctylphosphine: Te-TOP solution (0.5 M), 0.439 mL of Se-DDT / OLAm solution (0.285 M), 2.5 mL of dodecanethiol: DDT, 0.25 mL of oleylamine: OLAm, 0.387 g of trioctylphosphine oxide: TOPO, and 20 mL of octadecene: ODE were placed in a 100 mL reaction vessel, and it was heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0118] This solution was heated while stirring at 180 °C for 20 minutes. The resulting reaction solution was cooled to room temperature. Then, 1.37 g of zinc chloride: ZnCl2, 15 mL of trioctylphosphine: TOP, and 0.5 mL of oleylamine: OLAm were added to the reaction solution, and it was heated while stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Further, 2.5 mL of a zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding additional zinc octanoate and performing heating and stirring was carried out a total of 2 times.

[0119] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 496.5 nm and a fluorescence half-width of 21.3 nm were obtained (Figure 15).

[0120] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate and dispersed to obtain a ZnTeSe particle dispersion solution.

[0121] [Example 10] 0.091 g of copper(II) acetate anhydrous: Cu(OAc)2, 0.625 mL of dodecanethiol: DDT, 0.625 mL of trioctylphosphine: TOP, 0.194 g of trioctylphosphine oxide: TOPO, and 10 mL of octadecene: ODE were placed in a 100 mL reaction vessel, and it was heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0122] To this solution, 0.5 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M), 0.25 mL of Se-TOP solution (1 M), and 0.125 mL of oleylamine: OLAm were added, and the mixture was heated with stirring at 180 °C for 20 minutes. The resulting reaction solution was cooled to room temperature. Then, 0.685 g of zinc chloride: ZnCl2, 7.5 mL of trioctylphosphine: TOP, 0.25 mL of oleylamine: OLAm, and 0.066 mL of triphenyl phosphite were added to the reaction solution, and the mixture was heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Further, 1.25 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding additional zinc octanoate and performing heating and stirring was carried out a total of 2 times.

[0123] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 495.0 nm and a fluorescence half-width of 18.7 nm were obtained (Figure 16).

[0124] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate to disperse it, resulting in a ZnTeSe particle dispersion solution.

[0125] [Example 11] 0.091 g of copper(II) acetate anhydrous: Cu(OAc)2, 1.25 mL of dodecanethiol: DDT, 0.625 mL of trioctylphosphine: TOP, and 10 mL of octadecene: ODE were placed in a 100 mL reaction vessel, and the mixture was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0126] To this solution, 0.5 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M) and 0.125 mL of oleylamine: OLAm were added, and the mixture was heated with stirring at 200 °C for 15 minutes. Further, 1.25 mL of Se-ODE solution (0.1 M) was added, and stirring was continued at 200 °C for 15 minutes. The operation of adding the Se-ODE solution (0.1 M) additionally and performing heating and stirring was carried out twice in total, and the obtained reaction solution was cooled to room temperature. Thereafter, 0.685 g of zinc chloride: ZnCl2, 7.5 mL of trioctylphosphine: TOP, and 0.25 mL of oleylamine: OLAm were added to the reaction solution, and the mixture was heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Further, 1.25 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding zinc octanoate additionally and performing heating and stirring was carried out twice in total.

[0127] After the obtained reaction solution was cooled to room temperature, toluene and ethanol were added to cause precipitation, and centrifugation was performed to recover the precipitate. 11 mL of octadecene: ODE was added to the precipitate and dispersed to obtain a ZnTe / ZnSe particle ODE dispersion solution.

[0128] To the obtained ODE dispersion solution, 0.685 g of zinc chloride: ZnCl2, 7.5 mL of trioctylphosphine: TOP, and 0.25 mL of oleylamine: OLAm were added, and the mixture was heated with stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Further, 1.25 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding zinc octanoate additionally and performing heating and stirring was carried out twice in total.

[0129] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 517.0 nm and a fluorescence half-width of 20.1 nm were obtained (Figure 17).

[0130] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate and dispersed to obtain a ZnTe / ZnSe particle dispersion solution.

[0131] [Example 12] In a 100 mL reaction vessel, 0.091 g of copper(II) acetate anhydrous: Cu(OAc)₂, 1.25 mL of dodecanethiol: DDT, 0.625 mL of trioctylphosphine: TOP, and 10 mL of octadecene: ODE were added. While stirring under an inert gas (N₂) atmosphere, the mixture was heated to dissolve the raw materials.

[0132] To this solution, 0.5 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M) and 0.125 mL of oleylamine: OLAm were added, and the mixture was heated while stirring at 200 °C for 15 minutes. Further, 1.25 mL of Se-ODE solution (0.1 M) was added, and after stirring at 200 °C for 15 minutes, 1.25 mL of S-ODE solution (0.1 M) was added, and stirring was continued at 200 °C for 15 minutes. After cooling the resulting reaction solution to room temperature, 0.685 g of zinc chloride: ZnCl₂, 7.5 mL of trioctylphosphine: TOP, and 0.25 mL of oleylamine: OLAm were added to the reaction solution, and while stirring under an inert gas (N₂) atmosphere, the mixture was heated at 220 °C for 30 minutes. Further, 1.25 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding zinc octanoate additionally and performing heating and stirring was carried out a total of 2 times.

[0133] After cooling the resulting reaction solution to room temperature, toluene and ethanol were added to cause precipitation, and centrifugation was performed to recover the precipitate. 11 mL of octadecene: ODE was added to the precipitate and dispersed to obtain a ZnTe / ZnSe / ZnS particle ODE dispersion solution.

[0134] To the obtained ODE dispersion solution, 0.685 g of zinc chloride: ZnCl₂, 7.5 mL of trioctylphosphine: TOP, and 0.25 mL of oleylamine: OLAm were added, and while stirring under an inert gas (N₂) atmosphere, the mixture was heated at 220 °C for 30 minutes. Further, 1.25 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding zinc octanoate additionally and performing heating and stirring was carried out a total of 2 times.

[0135] As a result of measuring the obtained reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of 513.0 nm and a fluorescence half-width of 21.6 nm were obtained (Figure 18).

[0136] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate and dispersed to obtain a ZnTe / ZnSe / ZnS particle dispersion solution.

[0137] [Example 13] Into a 100 mL reaction vessel, 0.182 g of copper acetate anhydrous: Cu(OAc)₂, 1 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M), 2.5 mL of dodecanethiol: DDT, and 20 mL of octadecene: ODE were placed. Then, while stirring under an inert gas (N₂) atmosphere, it was heated to dissolve the raw materials.

[0138] This solution was heated while stirring at 180 °C for 10 minutes, and then 0.25 mL of oleylamine: OLAm was added, and it was heated while stirring at 180 °C for 10 minutes. The obtained reaction solution was cooled to room temperature. Then, 1.37 g of zinc chloride: ZnCl₂, 15 mL of trioctylphosphine: TOP, and 0.25 mL of oleylamine: OLAm were added to the reaction solution, and it was heated while stirring at 220 °C for 30 minutes under an inert gas (N₂) atmosphere. Further, 2.5 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of additionally adding zinc octanoate and performing heating and stirring was performed a total of 2 times. Then, the obtained reaction solution (ZnTeS) was cooled to room temperature.

[0139] To 10 mL of the reaction solution, 0.241 g of hexadecylamine: HDA was added, and it was heated with stirring at 220 °C for 5 minutes under an inert gas (N2) atmosphere. Further, 2 mL of trioctylphosphine: TOP, 0.125 mL of Se-TOP (1 M), and 0.375 mL of S-TOP (1 M) were mixed, 0.25 mL of this mixture was added to the reaction solution, and stirring was continued at 220 °C for 10 minutes. The operation of adding the mixed solution and performing heating and stirring was carried out 10 times in total. Then, 1 mL of zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding zinc octanoate additionally and performing heating and stirring was carried out 2 times in total.

[0140] As a result of measuring the obtained reaction solution with a fluorescence spectrometer and a quantum efficiency measurement system, optical properties with a fluorescence wavelength of 522.5 nm, a fluorescence half-width of 27.3 nm, and a quantum yield of about 12% were obtained (Figure 19).

[0141] Ethanol was added to the obtained reaction solution to cause precipitation, centrifugation was performed to recover the precipitate, and toluene was added to the precipitate to disperse it, obtaining a ZnTeS / ZnSeS particle dispersion solution.

[0142] [Example 14] 0.182 g of copper(II) acetate anhydrous: Cu(OAc)2, 1 mL of tellurium trioctylphosphine: Te-TOP solution (0.5 M), 0.439 mL of Se-DDT / OLAm solution (0.285 M), 2.5 mL of dodecanethiol: DDT, 0.25 mL of oleylamine: OLAm, 0.387 g of trioctylphosphine oxide: TOPO, and 20 mL of octadecene: ODE were placed in a 100 mL reaction vessel, and it was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0143] This solution was heated while stirring at 180 °C for 20 minutes. The resulting reaction solution was cooled to room temperature. Then, 1.37 g of zinc chloride (ZnCl2), 15 mL of trioctylphosphine (TOP), 0.5 mL of oleylamine (OLAm), and 0.131 mL of triphenyl phosphite were added to the reaction solution, and it was heated while stirring at 220 °C for 30 minutes under an inert gas (N2) atmosphere. Further, 2.5 mL of a zinc octanoate solution (0.1 M) was added, and stirring was continued at 220 °C for 10 minutes. The operation of adding additional zinc octanoate and performing heating and stirring was carried out a total of 2 times. Then, the resulting reaction solution (ZnTeSeS) was cooled to room temperature.

[0144] To 10 mL of the reaction solution, 0.241 g of hexadecylamine (HDA) was added, and it was heated while stirring at 240 °C for 5 minutes under an inert gas (N2) atmosphere. Further, 1.125 mL of trioctylphosphine (TOP), 0.031 mL of Se-TOP (1 M), and 0.094 mL of S-TOP (1 M) were mixed, 0.125 mL of this mixture was added to the reaction solution, and stirring was continued at 240 °C for 5 minutes. The operation of adding additional mixed solution and performing heating and stirring was carried out a total of 10 times. Then, 0.5 mL of a zinc octanoate solution (0.1 M) was added, and stirring was continued at 240 °C for 5 minutes. The operation of adding additional zinc octanoate and performing heating and stirring was carried out a total of 2 times.

[0145] As a result of measuring the obtained reaction solution with a fluorescence spectrometer and a quantum efficiency measurement system, optical properties with a fluorescence wavelength of 532.0 nm, a fluorescence half-width of 27.6 nm, and a quantum yield of approximately 20% were obtained (Figure 20).

[0146] Ethanol was added to the obtained reaction solution to cause precipitation, and centrifugation was performed to recover the precipitate. Toluene was added to the precipitate to disperse it, obtaining a ZnTeSeS / ZnSeS particle dispersion solution.

[0147] [Example 15] 100 mL of a reaction vessel was charged with 72.7 mg of copper acetate anhydrous: Cu(OAc)₂, 0.5 mL of dodecanethiol: DDT, 0.1 mL of oleylamine: OLAm, and 10 mL of octadecene: ODE. Then, while stirring under an inert gas (N₂) atmosphere, it was heated to dissolve the raw materials.

[0148] To this solution, 0.65 mL of a trioctylphosphine telluride: Te-TOP solution (0.5 M) was added, and it was heated while stirring at 220 °C for 5 minutes. Then, 0.1 mL of a trioctylphosphine selenide: Se-TOP solution (1 M) was added, and it was heated while stirring at 220 °C for 5 minutes. The resulting reaction solution was cooled to room temperature.

[0149] To this reaction solution, 550 mg of zinc chloride: ZnCl₂, 6 mL of trioctylphosphine: TOP, and 0.2 mL of oleylamine: OLAm were added, and it was heated while stirring at 220 °C for 15 minutes and at 280 °C for 110 minutes under an inert gas (N₂) atmosphere.

[0150] Then, 1 mL of a solution obtained by mixing 12 mL of zinc octanoate (0.4 M) and 1.1 mL of DDT was added dropwise, and it was heated while stirring at 280 °C for 60 minutes.

[0151] As a result of measuring the resulting reaction solution with a fluorescence spectrometer, optical properties with a fluorescence wavelength of about 610 nm and a fluorescence half-width of about 38.5 nm were obtained (Figure 21).

[0152] Ethanol was added to the resulting reaction solution to cause precipitation, and centrifugation was performed to collect the precipitate. Toluene was added to the precipitate to disperse it, obtaining a ZnTe / ZnSe particle dispersion solution.

[0153] [Example 16] 100 mL of a reaction vessel was charged with 131 mg of copper acetylacetonate: Cu(acac)₂, 1.5 mL of dodecanethiol: DDT, 4.75 mL of oleylamine: OLAm, and 6.25 mL of octadecene: ODE. Then, while stirring under an inert gas (N₂) atmosphere, it was heated to dissolve the raw materials.

[0154] To this solution, 1.75 mL of a Se-DDT / OLAm solution (0.3 M) was added, and the mixture was heated with stirring at 220 °C for 10 minutes. The resulting reaction solution (Cu2Se(S)) was cooled to room temperature.

[0155] Ethanol was added to the Cu2Se reaction solution to cause precipitation, and the precipitate was collected by centrifugation. ODE was added to the precipitate to disperse it.

[0156] Subsequently, 682 mg of zinc chloride: ZnCl2, 5 mL of trioctylphosphine: TOP, and 0.5 mL of oleylamine: OLAm were added to the ZnSe(S)-ODE solution, and the mixture was heated with stirring at 280 °C for 120 minutes under an inert gas (N2) atmosphere. The resulting reaction solution (ZnSe(S)) was cooled to room temperature.

[0157] As a result of measuring the obtained reaction solution with a fluorescence spectrometer and a quantum efficiency measurement system, optical properties with a fluorescence wavelength of about 446.0 nm, a fluorescence half-width of about 16.6 nm, and a quantum yield of about 30.6% were obtained (Figure 22).

[0158] Ethanol was added to the obtained reaction solution to cause precipitation, and the precipitate was collected by centrifugation. Toluene was added to the precipitate to disperse it, obtaining a ZnSe particle dispersion solution.

[0159] [Comparative Example 1] 91.7 mg of zinc acetate anhydrous: Zn(OAc)2, 10 mL of octadecene: ODE, 3 mL of oleylamine: OLAm, and 3 mL of trioctylphosphine: TOP were placed in a 100 mL reaction vessel. Then, the mixture was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0160] To this solution, 0.5 mL of a trioctylphosphine telluride solution: Te-TOP solution (0.5 M) was added, and the mixture was heated with stirring at 280 °C for 10 minutes. The reaction solution changed to a turbid suspension ranging from light yellow to reddish-brown, and the resulting solution was irradiated with a black light at 365 nm, but no fluorescence was observed.

[0161] [Comparative Example 2] Into a 100 mL reaction vessel, 68.1 mg of anhydrous zinc chloride: ZnCl2, 10 mL of octadecene: ODE, 3 mL of oleylamine: OLAm, and 3 mL of trioctylphosphine: TOP were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0162] To this solution, 0.5 mL of a trioctylphosphine telluride solution: Te-TOP solution (0.5 M) was added, and it was heated while stirring at 280 °C for 10 minutes. The reaction solution changed from a pale yellow to a reddish-brown suspension, and the resulting solution was irradiated with a black light at 365 nm, but no fluorescence was observed at all.

[0163] [Comparative Example 3] Into a 100 mL reaction vessel, 316.2 mg of zinc stearate: Zn(OC(C=O)C 17 H 35 )2, 10 mL of octadecene, 3 mL of oleylamine: OLAm, and 3 mL of trioctylphosphine: TOP were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0164] To this solution, 0.5 mL of a trioctylphosphine telluride solution: Te-TOP solution (0.5 M) was added, and it was heated while stirring at 280 °C for 10 minutes. The reaction solution changed from a pale yellow to a reddish-brown suspension, and the resulting solution was irradiated with a black light at 365 nm, but no fluorescence was observed at all.

[0165] [Comparative Example 4] Into a 100 mL reaction vessel, 314.2 mg of zinc oleate: Zn(OC(=O)C 17 H 33 )2, 10 mL of octadecene: ODE, 3 mL of oleylamine: OLAm, and 3 mL of trioctylphosphine: TOP were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0166] To this solution, 0.5 mL of a trioctylphosphine telluride solution: Te-TOP solution (0.5 M) was added, and the mixture was heated with stirring at 280 °C for 10 minutes. The reaction solution changed from a pale yellow to a reddish-brown suspension, and the resulting solution was irradiated with a black light at 365 nm, but no fluorescence was observed.

[0167] Table 1 shown below summarizes the synthesis raw materials, precursor synthesis conditions, metal exchange reaction conditions, shell coating conditions, fluorescence wavelength, and fluorescence half-width in Examples 1 to 16.

[0168] [Table 1] TIFF2025113295000003.tif167154TIFF2025113295000004.tif186155TIFF2025113295000005.tif215163TIFF2025113295000006.tif109163

[0169] As shown in Table 1, in the examples, the fluorescence half-width was 40 nm or less in all cases. Also, it was found that the fluorescence half-width could be made 30 nm or less, further, the fluorescence half-width could be made 28 nm or less, and furthermore, it was possible to control the fluorescence half-width to about 25 nm or less.

[0170] Also, as shown in Table 1, it was found that the fluorescence wavelength could be adjusted within the range of 400 nm to 650 nm.

[0171] Also, as shown in Table 1, it was found that quantum dots emitting green light according to Examples 1 to 14 or red light according to Example 15 could be synthesized.

[0172] Also, the dispersion solution of ZnTe particles of Example 1 was measured using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Figure 10 shows the measurement results of the scanning electron microscope (SEM), and Figure 11 shows the measurement results of the X-ray diffractometer (XRD).

[0173] In addition, the dispersion solution of Cu2Te particles in Example 1 was measured using a scanning electron microscope (SEM). The results are shown in FIG. 12.

[0174] As shown in FIGS. 10 and 12, it was found that the particle diameters of ZnTe particles as quantum dots and Cu2Te as a precursor could be generated almost uniformly.

[0175] In addition, from the peak values of the XRD spectrum of ZnTe shown in FIG. 11, it was proved that a ZnTe solid solution was formed.

[0176] In the present invention, not only Cu2Te but also Cu2Se and Cu2S can be used as a precursor. According to Example 16, ZnSe with a narrow full width at half maximum of blue light emission could be obtained using Cu2Se as a precursor.

[0177] In addition, it is known from ICP analysis that the ZnSe obtained using Cu2Se as a precursor contains Cu at 100 ppm or less with respect to Zn.

[0178] Also in this embodiment, since ZnTe is obtained using Cu2Te as a precursor, it is considered that Cu is contained. From this, by adjusting the Cu-Zn metal exchange reaction, Zn 1-x Cu x It is also possible to obtain quantum dots of CuTe(X<0.001) (X is the ratio of the number of moles of Cu to the total number of moles of Zn and Cu).

Industrial Applicability

[0179] According to the present invention, for example, quantum dots showing high-intensity green fluorescence can be stably obtained. By applying the quantum dots of the present invention to an LED, a backlight device, a display device, etc., excellent light emission characteristics can be obtained in each device.

[0180] This application is based on Japanese Patent Application No. 2017-145269 filed on July 27, 2017 and Japanese Patent Application No. 2017-198667 filed on October 12, 2017. The entire contents of these applications are incorporated herein by reference.

Claims

1. A quantum dot characterized by not containing Cd and having a core formed of ZnTe, ZnTeS, ZnTeSe, or ZnTeSeS.

2. The quantum dot has a core-shell structure with a nanocrystal as the core and a shell coated on the surface of the core, The quantum dot according to claim 1, wherein the shell is formed of ZnSe or ZnS.

3. The quantum dot according to claim 2, wherein the fluorescence full width at half maximum is 40 nm or less.

4. The quantum dot according to any one of claims 1 to 3, wherein the fluorescence wavelength ranges from 400 nm to 650 nm.

5. The quantum dot according to any one of claims 1 to 4, characterized in that it is synthesized by a metal exchange reaction using a copper chalcogenide as a precursor.

6. The quantum dot according to any one of claims 1 to 5, characterized in that a copper chalcogenide as a precursor is synthesized from an organic copper compound or an inorganic copper compound and an organic chalcogen compound, and the quantum dot is synthesized using the precursor.

7. The quantum dot according to any one of claims 1 to 6, characterized in that the core is formed of ZnTe and the residual amount of Cu is 100 ppm or less.

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