Quantum dots

Abstract

The purpose of the present invention is to provide a quantum dot having a core-shell structure capable of realizing a type I structure in a ZnTe core. The quantum dot according to the present invention has a core-shell structure that does not contain cadmium, and is characterized in that the core contains Zn and Te, and the shell contains Mg and S. According to the invention, the quantum dot is characterized in that the quantum dot is composed of a core / MgS containing Zn and Te, a core / MgS containing Zn and Te, a core / ZnMgS / MgS containing Zn and Te, a core / MgS / ZnS containing Zn and Te, a core / ZnMgS / MgS / ZnS containing Zn and Te, a core / MgS / ZnO containing Zn and Te, or a core / ZnMgS / MgS / ZnO containing Zn and Te.

Description

Technical Field

[0001] This invention relates to cadmium-free ZnTe-based quantum dots. Background Technology

[0002] Quantum dots are nanoparticles with a diameter of several nm to tens of nm, consisting of hundreds to thousands of atoms. Quantum dots are also known as fluorescent nanoparticles, semiconductor nanoparticles, or nanocrystals.

[0003] Quantum dots can vary the emission wavelength depending on the particle size and composition of the nanoparticles. Other parameters representing the performance of quantum dots include fluorescence quantum yield (QY) and full width at half maximum (FWHM). When quantum dots are used as wavelength conversion materials in the visible light region, their most prominent characteristic is a wide range of colors they can represent, i.e., high color gamut. Therefore, in achieving high color gamut in wavelength conversion components using quantum dots in the visible light region, the important optical property is the fluorescence half width.

[0004] Previously used high-efficiency quantum dots mainly contained cadmium (Cd). Cd-containing quantum dots have the advantages of high fluorescence quantum yield and narrow fluorescence half-width. However, due to the toxicity of Cd, its use is restricted in various countries, which has become a major obstacle to its practical application.

[0005] In contrast, the development of Cd-free quantum dots has also been extensively studied. One representative example is the chalcopyrite-based Copper Indium Sulfide (CuInS2): a CIS-based quantum dot (see, for example, Patent Document 1). However, due to its defect-based luminescence mechanism, its optical properties are not as high as those of Cd-based quantum dots, typically exhibiting a fluorescence half-width of 80–100 nm or higher. The same applies to chalcopyrite-based quantum dots other than CIS; to date, no chalcopyrite-based quantum dots with a fluorescence half-width below 60 nm have been reported.

[0006] In addition, another representative of Cd-free quantum dots is indium phosphide (InP): InP-based quantum dots (see, for example, Patent Document 1). However, compared with CdSe-based quantum dots, InP-based quantum dots have a wider fluorescence half-width, and the synthesis of InP-based quantum dots with a fluorescence half-width of less than 35 nm has not been reported to date.

[0007] In addition, zinc selenide (ZnSe) is known as a cadmium-free quantum dot, but ZnSe has a band gap of 2.7 eV, so green light cannot be produced by using ZnSe alone.

[0008] Zinc telluride (ZnTe) could be considered as another zinc-based quantum dot, but there are few reports on its solution synthesis.

[0009] Non-Patent Literature 1 described in detail a direct synthesis method of ZnTe using organozinc compounds and trialkylphosphine tellurides. Although the absorption shift towards longer wavelengths with particle growth was studied in detail in the paper, the ZnTe synthesized in that paper did not exhibit fluorescence properties.

[0010] Furthermore, in Non-Patent Literature 2 below, the synthesis of zincblende-structured ZnTe was carried out using Te reduced by an organozinc compound and Super-Hydride (Lithium triethylborhydride: LiBHEt3) as a starting material. Studies on controlling the morphology of ZnTe nanoparticles through various investigations of reaction conditions were reported. The use of Super-Hydride, which is highly reactive and difficult to use in mass production, is a characteristic of the synthesis method. In this paper, the particle morphology, crystal structure, and absorption spectrum of the obtained ZnTe are reported in detail, but fluorescence properties are not described.

[0011] Existing technical documents Patent documents Patent Document 1: International Publication No. 2007 / 060889 Non-patent literature Non-patent document 1: Journal of Materials Chemistry. C, 2014, 2, 2877Synthesis and properties of ZnTe and ZnTe / ZnS core / shell semiconductor nanocrystals Non-patent literature 2: Journal of Physical Chemistry C, 2008, 112(14), pp 5454-5458 Shape-Control of ZnTe Nanocrystal Growth in Organic Solution Summary of the Invention

[0012] The problem that the invention aims to solve Cadmium-free quantum dots include InP and AgInGaS. Among them, ZnTe is a candidate with a small fluorescence half-width, but it has not yet been commercialized.

[0013] The present invention is made in view of this purpose, and its object is to provide a quantum dot having a core-shell structure capable of realizing a type I structure in a ZnTe core.

[0014] Methods for solving problems The quantum dots of the present invention are characterized in that they are cadmium-free core-shell quantum dots, wherein the core contains at least Zn and Te, and the shell contains at least Mg and S.

[0015] Invention Effects The quantum dots of the present invention enable the realization of Type I structures. Attached Figure Description

[0016] Figure 1 is a schematic diagram of quantum dots in an embodiment of the present invention.

[0017] Figure 2A This is an energy level diagram when using quantum dots with a core-shell structure.

[0018] Figure 2B This is an energy level diagram when using quantum dots with a core-shell structure.

[0019] Figure 2C This is an energy level diagram when using quantum dots with a core-shell structure.

[0020] Figure 2D This is an energy level diagram when using quantum dots with a core-shell structure.

[0021] Figure 2E This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0022] Figure 2F This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0023] Figure 2G This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0024] Figure 2H This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0025] Figure 2I This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0026] Figure 2J This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0027] Figure 2K This is one implementation of an energy level diagram of quantum dots composed of a core-shell structure of type I.

[0028] Figure 3A This indicates the MgS synthesis process.

[0029] Figure 3B This is a schematic diagram of the ZnMgS synthesis.

[0030] Figure 4 This is a schematic diagram illustrating an application example of a sheet material containing sub-dots according to this embodiment.

[0031] Figure 5 This is the photoluminescence (PL) spectrum of ZnTe in Example 1.

[0032] Figure 6 This is the PL spectrum of ZnTe in Example 2.

[0033] Figure 7 This is the PL spectrum of ZnTeS in Example 3.

[0034] Figure 8 This is the PL spectrum of ZnTeSeS in Example 4.

[0035] Figure 9 This is the PL spectrum of ZnTe in Example 5.

[0036] Figure 10 This is the PL spectrum of ZnTeS in Example 6.

[0037] Figure 11 This is a scanning electron microscope (SEM) image of ZnTe from Example 1.

[0038] Figure 12 This is the X-ray diffraction (XRD) spectrum of ZnTe in Example 1.

[0039] Figure 13 This is a SEM image of Cu2Te from Example 1.

[0040] Figure 14 This is the PL spectrum of ZnTe in Example 7.

[0041] Figure 15 This is the PL spectrum of ZnTeSe in Example 8.

[0042] Figure 16 This is the PL spectrum of ZnTeSe in Example 9.

[0043] Figure 17 This is the PL spectrum of ZnTeSe in Example 10. Detailed Implementation

[0044] Hereinafter, one embodiment of the present invention (hereinafter referred to as "Embodiment") will be described in detail. Furthermore, the present invention is not limited to the following embodiment, and various modifications can be made within its scope.

[0045] Figure 1 is a schematic diagram of the quantum dot in this embodiment. Figure 1A The quantum dot 5 shown is a Cd-free nanocrystal.

[0046] In this embodiment, the quantum dot 5 is preferably a nanocrystal containing zinc and tellurium (hereinafter referred to as Zn, Te), or zinc, tellurium and sulfur (hereinafter referred to as Zn, Te, S), or zinc, tellurium, selenium and sulfur (hereinafter referred to as Zn, Te, Se, S). Alternatively, it may be a nanocrystal containing zinc, tellurium and selenium.

[0047] Quantum dot 5 exhibits fluorescence properties based on band-edge emission and displays quantum size effects depending on the size of its particles.

[0048] Here, "nanocrystals" refers to nanoparticles with a particle size of approximately several nm to tens of nm. In this embodiment, multiple quantum dots 5 can be generated with a substantially uniform particle size.

[0049] The quantum dot 5 contains Zn and Te, or Zn, Te and S, Zn, Te and Se, or Zn, Te, S and Se as main components, and may also contain elements other than these. However, it does not contain Cd, and preferably does not contain phosphorus (P). Organophosphorus compounds are expensive and easily oxidized in air, thus their synthesis is unstable, which can lead to increased costs, unstable fluorescence properties, and complicated manufacturing processes. In this embodiment, it is preferable that it does not contain PoHS-restricted substances.

[0050] The fluorescence half-width at half-maximum (WWHM) of the quantum dot 5 in this embodiment is 40 nm or less. "Fluorescence half-width at half-maximum" refers to the full width at half-maximum (WWHM) of the fluorescence wavelength at half the peak intensity of the fluorescence spectrum. Preferably, the WWHM is 30 nm or less. More preferably, it is 28 nm or less. More preferably, it is 26 nm or less. Even more preferably, it is 25 nm or less. Even more preferably, it is 23 nm or less. This narrowing of the WWHM results in an improved color gamut. In this embodiment, as the reaction system for synthesizing the quantum dot 5, a copper chalcogenide is synthesized as a precursor, followed by a metal exchange reaction. By manufacturing the quantum dot 5 based on this indirect synthesis reaction, the fluorescence half-width can be narrowed; specifically, a WWHM of 40 nm or less (preferably 30 nm or less) can be obtained.

[0051] like Figure 1A As shown, preferably, a plurality of organic ligands 11 are coordinated on the surface of the quantum dot 5. This suppresses the aggregation of the quantum dots 5 and allows them to exhibit the desired optical properties. The ligands that can be used for the reaction are not particularly limited; for example, the following ligands can be cited as representative ligands.

[0052] Aliphatic primary amines, oleylamines: 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 acids, oleic acid: C 17 H 33 COOH, stearic acid: C 17 H 35 COOH, palmitic acid: C 15 H 31 COOH, myristic acid: C 13 H 27 COOH, Lauric acid: C 11 H 23 COOH, Decanoic acid: C9H 19 COOH, Caprylic acid: C7H 15 COOH Thiol series, octadecylthiol: C 18 H 37 SH, hexadecylthiol: C 16 H 33 SH, tetradecylthiol: C 14 H 29 SH, dodecylthiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, Octanethiol: C8H 17 SH Phosphine series, trioctylphosphine: (C8H 17 3P, triphenylphosphine: (C6H5)3P, tributylphosphine: (C4H9)3P Phosphine oxide series, trioctylphosphine oxide: (C8H 17 3P=O, Triphenylphosphine oxide: (C6H5)3P=O, Tributylphosphine oxide: (C4H9)3P=O In this embodiment, the ligand is not limited to a single-functional small molecule, but can also be a multifunctional oligomer or polymer with two, three, four or more functions.

[0053] In this embodiment, the fluorescence quantum yield of quantum dot 5 is 5% or more. Furthermore, the fluorescence quantum yield is more preferably 10% or more, even more preferably 20% or more, even more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, and most preferably 60% or more. Thus, according to this embodiment, the fluorescence quantum yield of the quantum dot can be improved.

[0054] According to this embodiment, the fluorescence wavelength can be freely controlled to approximately 490 nm or higher and 550 nm or lower. For example, the quantum dot 5 in this embodiment is a solid solution based on ZnTe, which uses chalcogenide elements in addition to zinc. In this embodiment, by adjusting the particle size and composition of the quantum dot 5, the fluorescence wavelength can be controlled to be green.

[0055] Figure 1B The quantum dot 5 shown is a core-shell structure having a core 5a and a shell 5b covering the surface of the core 5a. For example... Figure 1B As shown, preferably, a plurality of organic ligands 11 are coordinated on the surface of the quantum dot 5. Furthermore, Figure 1B The fluorescence half-width of the quantum dot 5 shown is less than 40 nm. Preferably, the fluorescence half-width is less than 30 nm.

[0056] Figure 1B The nucleus 5a of quantum dot 5 shown is Figure 1A The nanocrystals shown are as follows. Therefore, the core 5a is preferably formed of ZnTe, ZnTeS, ZnTeSe, or ZnTeSeS. The shell 5b, like the core 5a, does not contain cadmium (Cd).

[0057] In this embodiment, shell 5b preferably contains Mg and S. Shell 5b is preferably MgS or ZnMgS.

[0058] Shell 5b can also be in a state of solid solution dissolved on the surface of core 5a. Figure 1B In the diagram, the boundary between the nucleus 5a and the shell 5b is shown by a dashed line. However, this means that the boundary between the nucleus 5a and the shell 5b can be confirmed by analysis or it cannot be confirmed; either case is acceptable.

[0059] In this embodiment, the quantum dot 5 forms a shell 5b on the surface of the core 5a, separated by a buffer layer. The buffer layer is a region in which at least some or all of the elements constituting the core 5a are mixed with at least some or all of the elements constituting the shell 5b.

[0060] Thus, as an example, the quantum dot 5 in this embodiment is composed of ZnTe / ZnMgS / MgS.

[0061] In this embodiment, a core-shell structure is formed by including a buffer layer. That is, the buffer layer can be regarded as the first layer of the shell.

[0062] MgS and ZnMgS used as shells are easily hydrolyzed. Therefore, it is preferable to form a thin coating (protective layer) on the surface of MgS or ZnMgS.

[0063] As an example, the quantum dot 5 in this embodiment is composed of ZnTe / MgS / ZnS, ZnTe / ZnMgS / MgS / ZnS, ZnTe / MgS / ZnO, or ZnTe / ZnMgS / MgS / ZnO. In this structure, ZnS or ZnO is a coating (protective layer), and the shell is MgS or ZnMgS.

[0064] In the case of quantum dots having a core-shell structure, it becomes Figures 2A-2D Any energy level diagram in the [concept]. In the case of a light-emitting element, the shell of the core-shell structure is important in enhancing the quantum confinement effect. In particular, [the following is preferred]. Figure 2A The type I structure shown has a higher LUMO energy in the shell than in the core, and a lower HOMO energy in the shell than in the core. That is, the quantum dot in this embodiment preferably has a type I core-shell structure.

[0065] Here, it is known that a core-shell structure of ZnTe / ZnS will not result in a Type I structure. Therefore, in this embodiment, a shell is formed using MgS to stably control the structure to Type I.

[0066] That is, by setting it to Figures 2E to 2K The core-shell structured quantum dots shown can form type I structures, enabling an increase in fluorescence quantum yield. For example, it is known that in the aforementioned ZnTe / ZnS, the fluorescence quantum yield becomes quite low, but... Figures 2E to 2K The quantum dots with the core-shell structure shown can dramatically increase the fluorescence quantum yield to tens of percent or more, preferably more than 50%.

[0067] like Figure 2E As shown, the core is ZnSe or ZnSeTe. Zn and Te are the main components, but Se may also be present in small amounts. The amount of Se (molar amount) is less than that of Zn and Te. The same applies in other embodiments. Figure 2E In this study, ZnMgS is used as the shell. Therefore, the LUMO energy of the shell is higher than that of the core, while the HOMO energy of the shell is lower than that of the core, enabling the formation of type I structures.

[0068] exist Figure 2FIn the core, the shell uses MgS and ZnMgS. Based on energy levels, ZnMgS is positioned between the core and MgS, resulting in a stepped energy level distribution in both the LUMO and HOMO processes. This allows for efficient recombination of holes and electrons, improving luminescence efficiency. Consequently, the fluorescence quantum yield can be more effectively increased. Furthermore, the ZnMgS layer, as an intermediate layer, can also be considered a buffer layer, constituting the first layer of the shell.

[0069] exist Figure 2G In this embodiment, a MgS shell is formed around the core. This also allows for the formation of a Type I structure, which can improve the fluorescence quantum yield. Figure 2E and Figure 2G Both consist of a single shell, but which shell to use can be determined by the method of forming Type I structure, the composition of the nucleus, and its energy levels.

[0070] Figure 2H In this embodiment, a MgS shell is formed around the core, and then ZnS is formed on the surface of the shell. In this embodiment, the ZnS layer is thinner than the MgS layer, and ZnS serves as a protective layer. That is, since ZnMgS is chemically fragile (easily hydrolyzed, etc.), it is preferable to form a protective layer. Using ZnS as the protective layer provides both protection for ZnMgS and stable luminescence efficiency, which is preferred.

[0071] The thickness of the ZnS layer can be thinner than the thickness of the shell. ZnS preferably covers the entire surface of the shell in a generally uniform manner, but local deficiencies are also permissible.

[0072] Furthermore, if the ZnS of the protective layer as in this embodiment is compared with the ZnS of the shell, the relationship becomes that the lower end of the conductive band of the shell > the lower end of the conductive band of the protective layer, and the lower end of the valence band of the shell < the lower end of the valence band of the protective layer.

[0073] Figure 2I Is setting ZnS as Figure 2F The outermost layer of the implementation method. This allows for the protection of chemically fragile MgS and the attainment of stable luminescence efficiency.

[0074] Figure 2J It is a replacement Figure 2H An example of using ZnO as a protective layer instead of ZnS. Figure 2K It is a replacement Figure 2J This is an example of using ZnO as a protective layer for ZnS. In either case, ZnO can effectively protect the chemically fragile MgS.

[0075] The thickness of the ZnO layer can be thinner than the thickness of the shell. ZnO preferably covers the entire surface of the shell in a generally uniform manner, but it is also permissible to have local deficiencies.

[0076] Next, the manufacturing method of the quantum dot 5 in this embodiment will be described.

[0077] First, in this embodiment, copper chalcogenides (precursors) are synthesized from organic copper compounds or inorganic copper compounds and organic chalcogenide compounds. Specifically, copper telluride: Cu₂Te, or copper telluride sulfide: Cu₂TeS, or copper telluride selenide sulfide: Cu₂TeSeS are preferred precursors. Additionally, copper telluride may contain a small amount of Se.

[0078] In this embodiment, fluorescence is emitted only by the ZnTe core, but to improve the fluorescence intensity of the quantum dots, it is preferable to dissolve S in ZnTe. Therefore, in the synthesis of Cu2Te as a precursor, it is preferable to add 1 to 50 equivalents of thiol relative to Te, and more preferably 5 to 20 equivalents to obtain quantum dots with higher fluorescence intensity. This allows the production of Cu2TeS and Cu2TeSeS. The thiol is not limited, but octadecylthiol is used for example: C 18 H 37 SH, hexadecylthiol: C 16 H 33 SH, tetradecylthiol: C 14 H 29 SH, dodecylthiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, Octanethiol: C8H 17 SH, etc.

[0079] In this embodiment, the Cu raw material for Cu2Te is not particularly limited, and for example, organic copper reagents and inorganic copper reagents described below can be used. That is, as acetate, copper acetate (I)Cu(OAc) and copper acetate (II)Cu(OAc)2 can be used, and as fatty acid salt, copper stearate:Cu(OC(=O)C can be used. 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, as a halide, can be used in both monovalent and divalent forms. It can be copper chloride (I): CuCl, copper chloride (II): CuCl2, copper bromide (I): CuBr, copper bromide (II): CuBr2, copper iodide (I): CuI, copper iodide (II): CuI2, etc.

[0080] In this embodiment, an organotelluric compound (organochalcogenide compound) is used as the raw material. The structure of the compound is not particularly limited; for example, a trioctylphosphine telluride containing tellurium dissolved in trioctylphosphine can be used: (C8H 17 )3P=Te, or tributylphosphine telluride dissolved in tributylphosphine: (C4H9)3P=Te, etc. Alternatively, diphenyl ditelluride: (C6H5)2Te2 and other dialkyl ditelluride: R2Te2 can also be used.

[0081] In this embodiment, when selenium is dissolved in a solid solution, an organoselenium compound (organochalcogenide compound) is used as the raw material. The structure is not particularly limited; for example, a trioctylphosphine selenide containing selenium dissolved in trioctylphosphine can be used: (C8H 17 )3P=Se, or tributylphosphine selenide (C4H9)3P=Se dissolved in tributylphosphine, or a solution of selenium dissolved in octadecene, a long-chain hydrocarbon, at high temperature.

[0082] In this embodiment, an organocopper compound or an inorganic copper compound is mixed with an organochalcogenide compound and dissolved. Octadecene can be used as a solvent, specifically a high-boiling-point saturated or unsaturated hydrocarbon. Alternatively, tert-butylbenzene can be used as an aromatic high-boiling-point solvent, and butyl butyrate (C4H9COOC4H9) or benzyl butyrate (C6H5CH2COOC4H9) can be used as a high-boiling-point ester solvent. Aliphatic amine compounds, fatty acid compounds, or aliphatic phosphorus compounds can also be used as solvents.

[0083] At this point, the reaction temperature is set to a range of 160°C or higher and 250°C or lower to synthesize copper chalcogenides (precursors). Furthermore, the reaction temperature is preferably a lower range of 160°C or higher and 220°C or lower, and more preferably a further lower range of 160°C or higher and 200°C or lower.

[0084] Furthermore, in this embodiment, the reaction method is not particularly limited. In order to obtain quantum dots with narrow half-widths, it is important to synthesize Cu2Te, Cu2TeS, and Cu2TeSeS with uniform particle size. Therefore, in the synthesis of Cu2Te or Cu2TeS, Cu2TeSeS as precursors, it is preferable to rapidly add a tellurium raw material solution, or a mixture of tellurium and selenium raw materials, or a mixture of selenium raw materials, relative to the heated organic copper raw material solution.

[0085] Furthermore, in this embodiment, it is important to dissolve sulfur (S) in the core to obtain ZnTe with high fluorescence intensity. Therefore, for example, in the synthesis of Cu2Te as a precursor, it is preferable to add 1 to 50 equivalents of thiol relative to Te, and more preferably 5 to 20 equivalents to obtain quantum dots with high fluorescence intensity. The thiol is not particularly limited, and for example, octadecylthiol: C 18 H 37 SH, hexadecylthiol: C 16 H 33 SH, tetradecylthiol: C 14 H 29 SH, dodecylthiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, Octanethiol: C8H 17 SH, etc.

[0086] Next, organozinc compounds and inorganic zinc compounds are prepared as raw materials for ZnTe, ZnTeS, and ZnTeSeS. These organozinc compounds and inorganic zinc compounds are stable in air and easy to handle. There are no particular limitations on the structure of the organozinc compounds and inorganic zinc compounds; however, for efficient metal exchange reactions, zinc compounds with high ionicity are preferred. For example, the following organozinc compounds and inorganic zinc compounds can be used: zinc acetate: Zn(OAc)2, zinc nitrate: Zn(NO3)2, and zinc stearate: Zn(OC(=O)C, as fatty acid salts. 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 a halide, can be zinc chloride: ZnCl2, zinc bromide: ZnBr2, zinc iodide: ZnI2. As zinc carbamate, can be diethyldithiocarbamate: Zn(SC(=S)N(C2H5)2)2, dimethyldithiocarbamate: Zn(SC(=S)N(CH3)2)2, dibutyldithiocarbamate: Zn(SC(=S)N(C4H9)2)2, etc.

[0087] Next, the aforementioned organozinc compound and inorganic zinc compound are added to the reaction solution containing the precursor of the copper chalcogenide. This leads to a metal exchange reaction between copper (Cu) and zinc (Zn) of the copper chalcogenide. The metal exchange reaction preferably occurs at a temperature above 180°C and below 280°C. More preferably, the metal exchange reaction occurs at a lower temperature of above 180°C and below 250°C.

[0088] In addition, in this embodiment, when performing metal exchange, a compound is required that has an auxiliary function of releasing the precursor metal into the reaction solution through coordination or chelation.

[0089] Compounds exhibiting the aforementioned effects include ligands capable of forming complexes with copper. Phosphorus-based ligands, amine-based ligands, and thio-based ligands are preferred, with phosphorus-based ligands being particularly preferred due to their high efficiency.

[0090] Therefore, by appropriately performing metal exchange between Cu and Zn, it is possible to fabricate quantum dots with narrow fluorescence half-widths based on Zn and Te.

[0091] Furthermore, the metal exchange with Cu-Zn is preferably carried out quantitatively. To improve the optical properties of the resulting ZnTe, it is also preferable to reduce the residual Cu content in ZnTe. The residual Cu content is preferably 100 ppm, more preferably 50 ppm, and ideally below 10 ppm.

[0092] In this embodiment, copper chalcogenides are synthesized using organocopper compounds or inorganic copper compounds and organochalcogenide compounds as precursors. Metal exchange is then performed using these precursors to synthesize quantum dots. Thus, in this embodiment, quantum dots are first synthesized via precursor synthesis, rather than directly synthesizing ZnTe. This indirect synthesis method avoids the use of highly reactive and hazardous reagents, enabling the safe and stable synthesis of ZnTe-based quantum dots with narrow half-widths.

[0093] Furthermore, in this embodiment, Cu-Zn metal exchange can be performed in one pot without separating or purifying the precursors to obtain the desired quantum dots.

[0094] Furthermore, in this embodiment, the synthesized quantum dots exhibit fluorescence properties even without undergoing various treatments such as washing, separation and purification, coating treatment, or ligand exchange.

[0095] But through such Figure 1B As shown, covering a core 5a with a shell 5b composed of nanocrystals such as ZnTe, ZnTeSe, ZnTeS, or ZnTeSeS can further increase the fluorescence quantum yield.

[0096] In this embodiment, a shell 5b made of MgS is used to cover the surface of the core 5a. Figure 3A The synthesis process of MgS is shown.

[0097] like Figure 3A As shown, ODE (4 ml) containing a ZnTe core was heated to 210 °C, and Mg(Ac)₂ (2 mmol), OLAm (4 ml), and ODE (12 ml) were added at a rate of 4 ml per hour. The temperature was then increased to 240 °C and maintained for 1 hour, followed by a reduction to 230 °C, and the addition of Mg(St)₂ (2 mmol), OLAm (5 mmol), ODE (10 ml), and DDT (5 ml) at a rate of 4 ml per hour. The mixture was then maintained at 230 °C for 0.5 hours. Subsequently, the mixture was repeatedly precipitated and washed with ethanol, and finally dispersed in hexane or chloroform. This yielded quantum dots with a core-shell structure composed of ZnTe / MgS.

[0098] Alternatively, MgS can also be formed through cation exchange. For example, in the case of using MgS in a shell structure, ZnTe / MgS can be obtained by preparing ZnTe / Cu2S and performing Cu-Mg metal exchange.

[0099] In addition, in this embodiment, the variable lower conductor end (Ec) of ZnTe can also be adjusted by ligand exchange.

[0100] Figure 3B This is a schematic diagram illustrating the synthesis of the shell or buffer layer of ZnMgS. For example, OLA (34 ml) is added to a solution containing a ZnTe or ZnSeTe core and heated to 300°C while stirring.

[0101] Next, inject TOP (6.4 mL) and 1M TOP-S (3.2 mL), followed immediately by rapid addition of a total of 3.2 mL of diethylzinc and di-n-butylmagnesium (refer to...). Figure 3B ).

[0102] Furthermore, the film thickness of the ZnMgS shell can be adjusted by the number of times TOP-S, diethylzinc, and di-n-butylmagnesium are added.

[0103] The quantum dot 5 in this embodiment can be configured into a composition containing quantum dots dispersed in a resin. The resin composition may contain quantum dots 5 and a fluorescent substance different from the quantum dots 5. As the fluorescent substance, silane-based or KSF (K2SiF6:Mn) fluorescent substances are available. 4 + Red fluorescent materials, etc., are allowed, but there are no specific restrictions on the materials used.

[0104] The resin used to disperse quantum dots 5 is not particularly limited and can be polypropylene (PP), polystyrene (PS), acrylic resin, methacrylate, MS resin, polyvinyl chloride (PVC), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethylpentene, liquid crystal polymer, epoxy resin, silicone resin, or mixtures thereof.

[0105] The composition containing sub-dots in this embodiment can be applied to display devices. The QD sheet of this embodiment can be effectively applied to backlighting in display applications, for example, for... Figure 4 The Mini LED, QD OLED, and μLED shown are also effective.

[0106] Example The effects of the present invention will be described below through embodiments and comparative examples. Furthermore, the present invention is not limited to the following embodiments.

[0107] <Ingredients> In this invention, the following raw materials are used in the synthesis of cadmium-free quantum dots.

[0108] solvent Octadecene: Aldrich Co., Ltd., Idemitsu Kosan Co., Ltd. Oleylamine: manufactured by Kao Co., Ltd. Oleic acid: Manufactured by Kao Corporation Zinc chloride: manufactured by Aldrich Corporation Zinc iodide: manufactured by Aldrich Co., Ltd. Zinc acetate dihydrate: manufactured by Ikoma Chemical Co., Ltd. Zinc acetic anhydride: Aldrich Co., Ltd. Tellurium (4N: 99.99%): Manufactured by Shinshin Chemical Co., Ltd. or Aldrich Corporation. Selenium (4N: 99.99%): Manufactured by Shinshin Chemical Co., Ltd. or Aldrich Corporation. Sulfur: Manufactured by KISHIDA Chemical Co., Ltd. Trioctylphosphine: manufactured by Hokko Chemical Co., Ltd. Trioctylphosphine oxide: Manufactured by Aldrich Tetradecane: Produced by Tokyo Chemical Industry Co., Ltd. (TCI) Triphenyl phosphite: manufactured by Aldrich Cetylamine: manufactured by NOF Co., Ltd. Dodecanethiol: manufactured by Arkema <Measuring Instruments> Fluorescence spectrometer: F-2700 manufactured by Japan Spectrophotometer Co., Ltd. UV-Vis spectrophotometer: Hitachi, Ltd. V-770 Quantum Yield Measurement Apparatus: Otsuka Electron Co., Ltd. QE-1100 X-ray diffraction (XRD) apparatus: Bruker D2 PHASER Scanning electron microscope (SEM): Hitachi SU9000 [Example 1] Add copper acetic anhydride (Cu(OAc)2) 236.3 mg, dodecyl mercaptan (DDT) 0.5 mL, oleylamine (OLAm) 0.1 mL, and octadecene (ODE) 4 mL to a 100 mL reaction vessel. Then, under an inert gas atmosphere (N2), heat while stirring to dissolve the raw materials.

[0109] Add 0.2 mL of trioctylphosphine telluride:Te-TOP solution (0.5 M) to the solution and heat at 220 °C with stirring for 10 minutes. Cool the resulting reaction solution (Cu2Te) to room temperature.

[0110] Then, zinc chloride (ZnCl2) 273 mg, trioctylphosphine (TOP) 3 mL, and oleylamine (OLAm) 0.1 mL were added to the reaction solution. The mixture was heated at 220 °C for 30 minutes with stirring under an inert gas (N2) atmosphere.

[0111] The obtained reaction solution was analyzed using a fluorescence spectrometer. The results are as follows: Figure 5 As shown, optical properties with a fluorescence wavelength of approximately 518.5 nm and a fluorescence half-width of approximately 24.3 nm were obtained.

[0112] In addition, ethanol is added to the obtained reaction solution to produce a precipitate, which is then recovered by centrifugation. Toluene is then added to the precipitate to disperse it, thus preparing a dispersion solution of ZnTe particles.

[0113] [Example 2] Add copper acetic anhydride (Cu(OAc)2) 236.3 mg, hexadecyl mercaptan (HDT) 63.8 μL, oleylamine (OLAm) 0.1 mL, and octadecene (ODE) 10 mL to a 100 mL reaction vessel. Then, heat while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0114] Add 0.2 mL of trioctylphosphine telluride: Te-TOP solution (0.5 M) to the solution and heat at 200 °C with stirring for 10 minutes.

[0115] The resulting reaction solution was cooled to room temperature. Then, zinc chloride (ZnCl2) 273 mg, trioctylphosphine (TOP) 3 mL, and oleylamine (OLAm) 0.1 mL were added to the reaction solution. The mixture was then heated at 250 °C for 15 minutes with stirring under an inert gas (N2) atmosphere.

[0116] The obtained reaction solution was measured using a fluorescence spectrometer, and the results are as follows: Figure 6 As shown, optical properties with a fluorescence wavelength of approximately 510.0 nm and a fluorescence half-width of approximately 22.3 nm were obtained.

[0117] Ethanol was added to the resulting reaction solution to produce a precipitate, which was then recovered by centrifugation. Toluene was then added to the precipitate to disperse it, yielding a dispersion of ZnTe particles.

[0118] [Example 3] Add 36.3 mg of copper acetic anhydride (Cu(OAc)2) and 5 mL of dodecyl mercaptan (DDT) to a 100 mL reaction vessel. Then, heat while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0119] Add 0.2 mL of trioctylphosphine telluride:Te-TOP solution (0.5 M) to the solution and heat at 220 °C with stirring for 20 minutes. Cool the resulting reaction solution to room temperature. Then, add 273 mg of zinc chloride:ZnCl2, 3 mL of trioctylphosphine:TOP, and 0.2 mL of oleylamine:OLAm to the reaction solution. Then, heat at 220 °C with stirring for 30 minutes under an inert gas (N2) atmosphere.

[0120] The obtained reaction solution was measured using a fluorescence spectrometer, and the results are as follows: Figure 7 As shown, optical properties with a fluorescence wavelength of approximately 529.5 nm and a fluorescence half-width of approximately 26.1 nm were obtained.

[0121] Ethanol was added to the resulting reaction solution to produce a precipitate, which was then recovered by centrifugation. Toluene was then added to the precipitate to disperse it, thus preparing a ZnTeS particle solution.

[0122] [Example 4] Add 272.7 mg of copper acetic anhydride (Cu(OAc)), 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 dodecyl mercaptan (DDT), and 8 mL of octadecene (ODE) to a 100 mL reaction vessel, and heat while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0123] The solution was heated at 220°C with stirring for 10 minutes, then 0.2 mL of oleylamine (OLAm) was added, and the mixture was heated at 220°C with stirring 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 the mixture was heated at 220°C with stirring for 30 minutes under an inert gas (N2) atmosphere.

[0124] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 522.5 nm and a fluorescence half-width of 24.9 nm. Figure 8 ).

[0125] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTeSeS particle dispersion solution.

[0126] [Example 5] Add copper acetic anhydride (Cu(OAc)) 236.3 mg, trioctylphosphine telluride (Te-TOP solution, 0.5 M) 0.2 mL, dodecyl mercaptan (DDT) 0.5 mL, and octadecene (ODE) 4 mL to a 100 mL reaction vessel. Stir and heat under an inert gas (N2) atmosphere to dissolve the raw materials.

[0127] The solution was heated at 180°C with stirring for 10 minutes, then 0.1 mL of oleylamine (OLAm) was added, and the mixture was heated at 180°C with stirring for 5 minutes. The resulting 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 the mixture was heated at 220°C with stirring for 30 minutes under an inert gas (N2) atmosphere.

[0128] The solution was cooled to room temperature, and 546 mg of zinc chloride (ZnCl2) was added. The mixture was then heated at 220°C for 60 minutes with stirring under an inert gas (N2) atmosphere.

[0129] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 542.0 nm and a fluorescence half-width of 27.8 nm. Figure 9 ).

[0130] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTe particle dispersion solution.

[0131] [Example 6] Add copper acetic anhydride (Cu(OAc)) 236.3 mg, trioctylphosphine telluride (Te-TOP solution, 0.5 M) 0.2 mL, and dodecyl mercaptan (DDT) 4 mL to a 100 mL reaction vessel. Stir and heat under an inert gas (N2) atmosphere to dissolve the raw materials.

[0132] The solution was heated at 220°C with stirring for 10 minutes, then 0.1 mL of oleylamine (OLAm) was added, and the mixture was heated at 220°C with stirring for another 10 minutes. The resulting reaction solution was cooled to room temperature. Ethanol was added to the resulting reaction solution to produce a precipitate, which was then collected by centrifugation. 4 mL of ODE and 0.1 mL of OLAm were added to the precipitate to disperse it, thus preparing a CuTe(S) particle dispersion solution.

[0133] Then, zinc chloride (ZnCl2) 273 mg and trioctylphosphine (TOP) 3 mL were added to the reaction solution, and the mixture was heated at 220 °C with stirring for 20 minutes under an inert gas (N2) atmosphere. Next, 0.5 mL of zinc octoate solution (0.2 M) was added, and the mixture was stirred continuously at 220 °C for 10 minutes. This heating and stirring process was repeated twice with the addition of additional zinc octoate.

[0134] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 520.5 nm and a fluorescence half-width of 22.4 nm. Figure 10 ).

[0135] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTeS particle dispersion solution.

[0136] [Example 7] Add copper acetic anhydride (Cu(OAc)2) 0.091 g, dodecyl mercaptan (DDT) 0.625 mL, trioctylphosphine (TOP) 0.625 mL, trioctylphosphine oxide (TOPO) 0.194 g, and tetradecane 10 mL to a 100 mL reaction vessel. Stir and heat under an inert gas (N2) atmosphere to dissolve the raw materials.

[0137] Add 0.5 mL of trioctylphosphine telluride:Te-TOP solution (0.5 M) and 0.125 mL of oleylamine:OLAm to the solution, and heat at 200 °C with stirring for 15 minutes. Cool the resulting reaction solution to room temperature. Then, add 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 to the reaction solution, and heat at 220 °C with stirring for 30 minutes under an inert gas (N2) atmosphere. Next, add 1.25 mL of zinc octoate solution (0.1 M), and continue stirring at 220 °C for 10 minutes. Repeat the heating and stirring process twice with the addition of zinc octoate.

[0138] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 502.0 nm and a fluorescence half-width of 17.9 nm. Figure 14 ).

[0139] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTe particle dispersion solution.

[0140] [Example 8] Add 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 dodecyl mercaptan: DDT, and 6.2 mL of octadecene: ODE to a 100 mL reaction vessel. Stir and heat under an inert gas (N2) atmosphere to dissolve the raw materials.

[0141] The solution was heated at 220°C with stirring for 10 minutes, then 0.2 mL of oleylamine (OLAm) was added, and the mixture was heated at 220°C with stirring 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 the mixture was heated at 220°C with stirring for 30 minutes under an inert gas (N2) atmosphere. Next, 0.5 mL of zinc octoate solution (0.2M) was added, and the mixture was stirred continuously at 220°C for 10 minutes. This heating and stirring process was repeated twice with the addition of additional zinc octoate.

[0142] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 522.5 nm and a fluorescence half-width of 23.1 nm. Figure 15 ).

[0143] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTeSe particle dispersion solution.

[0144] [Example 9] Add 20.182 g of copper acetic anhydride (Cu(OAc)), 1 mL of trioctylphosphine telluride (Te-TOP solution, 0.5 M), 0.439 mL of Se-DDT / OLAm solution (0.285 M), 2.5 mL of dodecyl mercaptan (DDT), 0.25 mL of oleylamine (OLAm), 0.387 g of trioctylphosphine oxide (TOPO), and 20 mL of octadecene (ODE) to a 100 mL reaction vessel. Stir and heat under an inert gas (N2) atmosphere to dissolve the raw materials.

[0145] The solution was heated at 180°C with stirring for 20 minutes. The resulting reaction solution was cooled to room temperature. Then, zinc chloride (ZnCl2) 1.37 g, trioctylphosphine (TOP) 15 mL, and oleylamine (OLAm) 0.5 mL were added to the reaction solution, and the mixture was heated at 220°C with stirring for 30 minutes under an inert gas (N2) atmosphere. Next, 2.5 mL of zinc octoate solution (0.1 M) was added, and the mixture was stirred continuously at 220°C for 10 minutes. This heating and stirring process was repeated twice with the addition of additional zinc octoate.

[0146] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 496.5 nm and a fluorescence half-width of 21.3 nm. Figure 16 ).

[0147] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTeSe particle dispersion solution.

[0148] [Example 10] Add copper acetic anhydride (Cu(OAc)2) 0.091g, dodecyl mercaptan (DDT) 0.625mL, trioctylphosphine (TOP) 0.625mL, trioctylphosphine oxide (TOPO) 0.194g, and octadecene (ODE) 10mL to a 100mL reaction vessel. Stir and heat under an inert gas (N2) atmosphere to dissolve the raw materials.

[0149] Add 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 to the solution, and heat at 180 °C with stirring for 20 minutes. Cool the resulting reaction solution to room temperature. Then, add 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 to the reaction solution, and heat at 220 °C with stirring for 30 minutes under an inert gas (N2) atmosphere. Next, add 1.25 mL of zinc octoate solution (0.1 M), and continue stirring at 220 °C for 10 minutes. Repeat the heating and stirring process twice with the addition of zinc octoate.

[0150] The obtained reaction solution was measured using a fluorescence spectrometer, and the optical properties were obtained with a fluorescence wavelength of 495.0 nm and a fluorescence half-width of 18.7 nm. Figure 17 ).

[0151] Ethanol was added to the obtained reaction solution to produce a precipitate. The precipitate was recovered by centrifugation. Toluene was added to the precipitate to disperse it, thus preparing a ZnTeSe particle dispersion solution.

[0152] In the embodiments, the fluorescence half-width is 40 nm or less. It is also known that the fluorescence half-width can be 30 nm or less, further 28 nm or less, and further controlled to approximately 25 nm or less.

[0153] Furthermore, it is known that green-emitting quantum dots can be synthesized.

[0154] In addition, the dispersion solution of ZnTe particles in Example 1 was measured using a scanning electron microscope (SEM) and an X-ray diffraction (XRD) apparatus. Figure 11 These are the results of measurements taken using a scanning electron microscope (SEM). Figure 12It is the result of X-ray diffraction (XRD) measurement.

[0155] In addition, the dispersion solution of Cu₂Te particles from Example 1 was measured using scanning electron microscopy (SEM). The results are shown in... Figure 13 .

[0156] like Figure 11 and Figure 13 As shown, ZnTe particles as quantum dots and Cu2Te as precursors were generated with approximately uniform particle sizes.

[0157] In addition, by Figure 12 The peak values ​​in the XRD spectrum of ZnTe shown indicate the formation of a ZnTe solid solution.

[0158] Industrial availability According to the present invention, quantum dots exhibiting high brightness green fluorescence can be stably obtained, for example. Furthermore, by applying the quantum dots of the present invention to LEDs, backlight devices, display devices, etc., excellent light-emitting characteristics can be obtained in each device.

[0159] This application is based on Japan Patent Application No. 2023-170558, filed on September 29, 2023. Its entire contents are contained herein.

Claims

1. A quantum dot, characterized in that, It is a cadmium-free core-shell quantum dot, wherein the core contains at least Zn and Te, and the shell contains at least Mg and S.

2. The quantum dot according to claim 1, characterized in that, The quantum dots are composed of a core / MgS containing Zn and Te, a core / MgS containing Zn and Te, a core / ZnMgS / MgS containing Zn and Te, a core / MgS / ZnS containing Zn and Te, a core / ZnMgS / MgS / ZnS containing Zn and Te, a core / MgS / ZnO containing Zn and Te, or a core / ZnMgS / MgS / ZnO containing Zn and Te.

3. The quantum dot according to claim 1, characterized in that, The fluorescence wavelength is 490nm~550nm.

4. The quantum dot according to claim 1, characterized in that, The core-shell structure is a type I structure.

Images