Quantum dots

Abstract

The purpose of the present invention is to provide: a method for producing a quantum dot in which a large amount of Zn can be contained on the surface; and a quantum dot. The method for producing a quantum dot according to the present invention comprises a step for generating a core containing at least Ag, Ga, S or Ag, Ga, and Se, and a step for coating the surface of the core with a shell, and in the step for coating the shell, the surface of the core is coated with GaS and then Zn is added. Preferably, the ZnS is coated after the GaS is coated. It is preferable that Cd and In are not contained in the core and the shell.

Description

[0001] This application is a divisional application of the PCT application entering the Chinese national phase, with an international application date of December 24, 2021, a date of entry into the Chinese national phase of August 24, 2023, a national application number of 202180094613.4, and an invention name of “Quantum Dot Manufacturing Method and Quantum Dots”. Technical Field

[0002] The invention relates to a method for manufacturing quantum dots with a core / shell structure and the quantum dots. Background Art

[0003] Quantum dots are inorganic nanoparticles with diameters ranging from a few nanometers to tens of nanometers, composed of thousands to tens of thousands of atoms. Quantum dots emit fluorescence and are called fluorescent nanoparticles due to their nanoscale size. They are also called semiconductor nanoparticles because they are composed of semiconductor materials, or nanocrystals because they have a specific crystalline structure.

[0004] Quantum dots are composed of positively charged metal atoms and negatively charged non-metal or semi-metal atoms, which are bonded together by either ionic or covalent bonds. The ionic nature of the bond depends on the combination of the properties of the metal and semi-metal atoms.

[0005] Quantum dots can vary their emission wavelength depending on their particle size and composition. Examples of quantum dot performance include fluorescence quantum yield (QY) and fluorescence full width at half maximum (FWHM).

[0006] One of the properties of quantum dots is photoluminescence. Quantum dots absorb wavelengths in a specific range and convert them into light, emitting light at wavelengths in that specific range. Furthermore, the absorption and emission wavelengths can be controlled by the structure, composition, and size of the quantum dots, allowing their characteristics to be flexibly utilized for various applications.

[0007] For example, when quantum dots are used as wavelength conversion materials in the visible light region, one of their characteristics is a wide range of colors that can be expressed, i.e., a high color gamut. Important optical properties for achieving a high color gamut using quantum dot-based wavelength conversion components in the visible light region are fluorescence quantum yield and fluorescence half-value width.

[0008] Previously, high-efficiency quantum dots (QDs) primarily contained cadmium (Cd). These QDs offer the advantages of high fluorescence quantum yields and narrow fluorescence half-value widths. However, due to the toxicity of Cd, its use is restricted in various countries, presenting a major obstacle to its practical application.

[0009] Meanwhile, the development of quantum dots that do not contain Cd has also been widely discussed. For example, the following patent documents describe quantum dots based on AIS or AIGS, or quantum dots based on AISe or AIGSe, containing Ag, In, S, or Ag, In, Ga, S, or Ag, In, Se, or Ag, In, Ga, Se.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-025201

[0013] Patent Document 2: Japanese Patent Application Publication No. 2018-039971

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-044142

[0015] Patent Document 4: Japanese Patent Application Publication No. 2018-141141

[0016] Patent Document 5: WO2018 / 159699

[0017] Non-patent literature

[0018] Non-Patent Literature 1: NPG Asia Materials, volume 10.2018, pp. 713-726

[0019] Non-patent document 2: ACS Publications 2018, 10, 49, 41844-41855

[0020] Non-patent literature 3: ACS Publications Nano Mater. 2020, 3, 3275-3287

[0021] Non-patent document 4: The Journal of Physical Chemistry Letters; Ligand-InducedLuminescence Transformation in AgInS2Nanoparticles: From Defect Emission toBand-Edge Emission Summary of the Invention

[0022] Problems to be solved by the invention

[0023] However, when Zn is used in AgGaS or AgInGaS, defect emission occurs due to the difference in valence (Zn is divalent, Ag is monovalent, and Ga or In is trivalent), and the fluorescence half-value width tends to increase.

[0024] Furthermore, even if Zn is added to AgGaS or AgInGaS after the Zn is not contained, the cationic species easily diffuse into the particles. Therefore, Zn easily diffuses into the core, resulting in defect emission.

[0025] Therefore, the present invention has been made in view of this point, and an object of the present invention is to provide a method for producing quantum dots and quantum dots capable of containing a large amount of Zn on the surface.

[0026] Solutions to Problems

[0027] The method for manufacturing quantum dots of the present invention is characterized in that it includes: a process of generating a core containing at least Ag, Ga, S or Ag, Ga, Se; and a process of coating the surface of the core with a shell, in which Zn is added after GaS is coated on the surface of the core.

[0028] The quantum dots of the present invention are characterized in that they have a core containing at least Ag, Ga, S or Ag, Ga, Se and a shell covering the surface of the core; the shell contains at least Zn; and exhibit fluorescence characteristics with a fluorescence half-value width of less than 35 nm and a fluorescence quantum yield of more than 70%.

[0029] Effects of the Invention

[0030] According to the method for producing quantum dots of the present invention, a shell containing a large amount of Zn can be used to coat the surface of a core containing at least Ag, Ga, S or Ag, Ga, Se, thereby producing quantum dots with edged luminescence and a fluorescence half-width of less than 35 nm with high precision. The quantum dots of the present invention can maintain edged luminescence while containing a large amount of Zn on the surface. In this way, the shell containing a large amount of Zn can be appropriately coated on the surface of the core, thereby improving the stability of the fluorescence properties and maintaining a high fluorescence quantum yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of quantum dots in an embodiment of the present invention.

[0032] Figure 2 Schematic diagram of an LED device using quantum dots according to an embodiment of the present invention.

[0033] Figure 3It is a longitudinal cross-sectional view of a display device using the LED device in the embodiment of the present invention.

[0034] Figure 4 This is a conceptual diagram showing a process for producing quantum dots according to an embodiment of the present invention.

[0035] Figure 5 This is the X-ray diffraction (XRD) spectrum in Example 1.

[0036] Figure 6 PL spectra in Examples 1 and 2.

[0037] Figure 7 (a) is a photograph of the TEM-EDX analysis results (Se+S and Ag+Zn) in Example 1, and (b) is a partial schematic diagram of (a).

[0038] Figure 8 (a) is a photograph of the analysis results of high-resolution STEM in Example 2, and (b) is a partial schematic diagram of (a).

[0039] Figure 9 (a) is a photograph of the TEM-EDX analysis results (Ag+Zn) in Example 2, and (b) is a partial schematic diagram of (a).

[0040] Figure 10 (a) is a photograph of the TEM-EDX analysis results (Zn) in Example 1 and the comparative example, and (b) is a partial schematic diagram of (a).

[0041] Figure 11 PL spectra of Example 3 and Comparative Example 2.

[0042] Figure 12 (a) is a photograph of the TEM-EDX analysis results (Ag+Ga) of the core of Example 3, (b) is a fluorescence (Photoluminescence: PL) spectrum of the core of Example 3, and (c) is a partial schematic diagram of (a). DETAILED DESCRIPTION

[0043] Hereinafter, an embodiment of the present invention (hereinafter referred to as "embodiment") is described in detail. In addition, the present invention is not limited to the following embodiment, and various modifications can be made within the scope of its purpose. In addition, the expression "to" in this specification means that the lower limit and upper limit are included.

[0044] Figure 1 Schematic diagram of quantum dots in this embodiment. Figure 1 The quantum dots 5 shown are nanocrystals that do not contain Cd.

[0045] In this embodiment, quantum dots 5 have a core / shell structure consisting of a core 5a and a shell 5b covering the surface of the core 5a. The core 5a preferably contains nanocrystals of at least silver (Ag), gallium (Ga), sulfur (S), or Ag, Ga, and selenium (Se). However, it is preferred that the core 5a does not contain cadmium (Cd) or In.

[0046] Furthermore, the core 5a may contain copper (Cu) or indium (In). The Ga / In ratio is preferably 5 or more, more preferably 10 or more, and even more preferably 30 or more.

[0047] Shell 5b, covering the surface of core 5a, is also preferably free of cadmium (Cd) and indium (In), similar to core 5a. In this embodiment, shell 5b contains a large amount of zinc (Zn). Specifically, shell 5b is preferably composed of zinc sulfide (ZnS), zinc selenide (ZnSe), zinc gallium selenide (ZnGa2Se4), or zinc gallium sulfide (ZnGa2S4). ZnS is preferred. Shell 5b may also be dissolved in the surface of core 5a.

[0048] Shell 5b may also contain copper (Cu) or indium (In). Specifically, shell 5b is preferably composed of copper sulfide (CuS), copper selenide (CuSe), indium sulfide (In2S3), indium selenide (In2Se3), indium zinc selenide (ZnIn2Se4), indium zinc sulfide (ZnIn2S4), copper indium sulfide (CuIn2S4), or copper indium selenide (CuIn2Se4). Shell 5b may also be solid-solution-coated on the surface of core 5a.

[0049] The quantum dot 5 of this embodiment can be appropriately coated with a shell 5b such as ZnS or ZnGa2S4 on the surface of the core 5a of AgGaSe or AgGaS. This embodiment can suppress the diffusion of Ag contained in the core 5a into the shell 5b. In addition, when the core 5a contains Se, the Se contained in the core 5a and the S contained in the shell 5b can be appropriately separated. In addition, the diffusion of Zn contained in the shell 5b into the interior of the core 5a can also be suppressed.

[0050] Furthermore, in the present embodiment, the shell 5 b may further contain gallium (Ga), or GaS or GaSe may be interposed between the core 5 a and the shell 5 b as the first layer of the shell.

[0051] Here, "nanocrystals" refer to nanoparticles having a particle size of about several nm to several tens of nm. This embodiment can produce a large number of quantum dots 5 with a substantially uniform particle size.

[0052] This embodiment can increase the amount of Zn present on the surface of quantum dots 5. Specifically, the Zn content is 5% or more by weight relative to the total quantum dots 5, preferably 10% or more, and more preferably 20% or more. While the upper limit is not specified, it is, for example, approximately 40%.

[0053] The Ga / In ratio of the entire quantum dot 5 is preferably 10 or more, more preferably 30 or more, and even more preferably 50 or more. The Ga / Zn ratio is preferably 1 or less, more preferably 0.5 or less.

[0054] like Figure 1 As shown, it is preferred that a large number of organic ligands 11 be coordinated to the surface of the quantum dots 5. This can suppress the aggregation of the quantum dots 5, thereby enabling the desired optical properties to be exhibited. The ligands that can be used in the reaction are not particularly limited, but the following ligands are representative examples.

[0055] (1) Aliphatic primary amine series

[0056] 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

[0057] (2) Fatty acid series

[0058] 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, octanoic acid: C7H 15 COOH

[0059] (3) Thiol series

[0060] Octadecanethiol: C 18 H 37 SH, hexadecanethiol: C 16 H 33SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, octyl mercaptan: C8H 17 SH

[0061] (4) Phosphine series

[0062] Trioctylphosphine: (C8H 17 )3P, triphenylphosphine: (C6H5)3P, tributylphosphine: (C4H9)3P

[0063] (5) Phosphine oxide series

[0064] Trioctylphosphine oxide: (C8H 17 )3P=O, triphenylphosphine oxide: (C6H5)3P=O, tributylphosphine oxide: (C4H9)3P=O

[0065] (6) Alcohol series

[0066] Oleyl alcohol: C 18 H 36 O

[0067] It is also preferred to coordinate with an inorganic ligand mixed with an organic ligand. This can further suppress surface defects in the quantum dots, resulting in higher optical properties. The ligand is not particularly limited, but halogens such as F, Cl, Br, and I are representative examples.

[0068] Next, a method for producing quantum dots will be described. This embodiment aims to produce quantum dots that exhibit band-edge luminescence and stabilize their luminescence properties by increasing the amount of Zn contained in the shell 5b. Furthermore, this embodiment also achieves band-edge luminescence using only the core 5a. This point will be discussed later.

[0069] Conventional methods for producing quantum dots include coating the surface of AgGaSe with a shell containing Se and then adding Zn. However, according to this embodiment, the amount of Zn on the core surface can be increased by the following method. Specifically, the quantum dot production method of this embodiment is characterized by the following.

[0070] (1) comprising the steps of generating a core 5a containing at least Ag, Ga, S or Ag, Ga, Se and covering the surface of the core 5a with a shell 5b,

[0071] (2) The process of coating the shell 5b is to coat the surface of the core 5a with GaS and then add Zn. The valence of GaS is not considered here. x S y(x=1-2, y=1-6), for example, GaS or Ga2S3. In addition, when GaSe is coated on the core surface, GaS or Ga2S3 can also be used. x Se y (x=1-2, y=1-6), for example, represented by GaSe or Ga2Se3. "Addition of Zn" includes addition of Zn alone, ZnS, ZnSe, ZnGa2Se4, and ZnGa2S4.

[0072] In this embodiment, it is preferable to coat the surface of the core 5 a with GaS and then with ZnS. Figure 4 FIG. 5 is a conceptual diagram of the manufacturing process of the quantum dot 5 of this embodiment. Figure 4 As shown in the left figure, after the AgGaSe core is generated, Figure 4 As shown in the central figure, the GaS shell is coated on the surface of the AgGaSe core. Then, Zn is added, as shown in Figure 4 As shown in the right figure, a ZnS shell is obtained. Figure 4 As shown in the center figure, the GaS shell covering the surface of the AgGaSe core is a crucial shell that prevents Zn from diffusing into the interior of the core 5a during the subsequent Zn addition. Furthermore, it is believed that Ga after Zn addition is released from the shell to the outside through dissolution and cleaning processes, reducing the amount remaining within the shell. However, Ga can also be contained within the shell. In other words, the shell can also be ZnGa2S4. Alternatively, the GaS shell can be interposed between the AgGaSe core and the ZnS shell. In other words, the shell can also have a two-layer structure of GaS / ZnS.

[0073] Alternatively, in this embodiment, it is preferable that Ga in GaS is cation-exchanged with Zn to form a ZnS shell. Figure 4 The particle size of AgGaSe / GaS in the central figure is Figure 4 The particle sizes of the AgGaS / ZnS in the right image are confirmed to be nearly identical by TEM-EDX analysis. This suggests that the ZnS shell covering the AgGaS surface is formed by cation exchange. Thus, cation exchange or anion solid solution can produce quantum dots with a core-shell structure that maintains the same particle size and exhibits a high surface Zn content.

[0074] In the previous preparation method, even if ZnS coating is implemented, Zn will immediately diffuse into the interior of the core and become defect luminescence, and large-scale ZnS coating cannot be implemented. In contrast, the present embodiment can confirm the crystallinity of ZnS obtained by adding Zn after GaS coating. In the shell coating, oleylamine is used, for example, but it is believed that oleylamine will become a ligand that hinders the shell coating. In fact, it is known that when a GaS coating operation without XRD shift is implemented, it will immediately become defect luminescence when Zn is added. In contrast, in the present embodiment, for example, non-amine DDT (dodecanethiol) is used in the shell coating. In addition to DDT, ODE can also be used. However, as long as oleylamine is not the main solvent, it can also be contained. In addition, as shown in the experimental results described later, it can be seen that after using DDT, XRD will shift during the GaS coating process. In this way, the present embodiment uses GaS in a DDT (or ODE) solvent, so that the coating can be completed without Ag diffusing to the surface.

[0075] The above-described method for producing quantum dots 5 according to this embodiment suppresses the diffusion of Ag contained in core 5a into the shell. Furthermore, the inclusion of Se contained in core 5a allows for the proper separation of Se in core 5a from S contained in shell 5b. Furthermore, the method for producing quantum dots 5 according to this embodiment increases the amount of Zn contained in shell 5b. While not particularly limited, the amount of Zn contained in quantum dots 5 can be adjusted to 5% or more, preferably 10% or more, and more preferably 20% or more by weight.

[0076] The method for producing quantum dots will be described in detail. First, in this embodiment, an organic silver compound, an organic gallium compound, and selenium are synthesized by heating in one pot.

[0077] At this time, AgGaSe is synthesized by setting the reaction temperature in the range of 100° C. to 320° C. The reaction temperature is preferably lower, 280° C. or lower.

[0078] In this embodiment, an organic silver compound or an inorganic silver compound is used as a raw material for Ag. Although not particularly limited, examples thereof include silver acetate (AgOAc) and silver nitrate (AgNO3). Halides include silver chloride (AgCl), silver bromide (AgBr), and silver iodide (AgI). Carbamates include silver diethyldithiocarbamate (Ag(SC(=S)N(C2H5)2) and silver dimethyldithiocarbamate (Ag(SC(=S)N(CH3)2).

[0079] In this embodiment, the above-mentioned Ag raw material may be directly added to the reaction solution, but it may be dissolved in an organic solvent in advance to form a solution having a certain concentration and used as an Ag raw material solution.

[0080] In this embodiment, an organic gallium compound or an inorganic gallium compound is used as a raw material of Ga. Although not particularly limited, for example, gallium acetate: Ga(OAc)3, gallium nitrate: GaNO3, and gallium acetylacetonate: Ga(acac)3 can be used. As halides, gallium chloride: GaCl3, gallium bromide: GaBr3, and gallium iodide: Ga2I3 can be used. As carbamates, gallium diethyldithiocarbamate: Ga[(SC(=S)N(C2H5)2]3 can be used.

[0081] In this embodiment, the Ga raw material may be directly added to the reaction solution, but it may be dissolved in an organic solvent in advance to form a solution having a certain concentration, and then used as the Ga raw material solution.

[0082] In addition, in this embodiment, an organic selenium compound (organic sulfide compound) can be used as a raw material of Se. For example, trioctylphosphine selenium (C8H) obtained by dissolving selenium in trioctylphosphine can be used. 17 )3P=Se, or tributylphosphine selenide formed by dissolving selenium in tributylphosphine: (C4H9)3P=Se, or a solution formed by dissolving selenium in a high-boiling-point solvent such as octadecene, a long-chain hydrocarbon. When synthesizing AgGaSe, the type of selenium raw material contributes greatly to the fluorescence characteristics. In particular, the solution formed by dissolving Se in a mixture of oleylamine and dodecanethiol (Se-OLAm / DDT) shows good luminescence characteristics. In the initial stage of luminescence, conventional chalcopyrite-based quantum dots can be confirmed to have two types of luminescence: a PL spectrum believed to be band-edge luminescence and a PL spectrum believed to be defect luminescence, and the luminescence intensity ratio of the band-edge luminescence / defect luminescence is almost below 10. Then, as the reaction proceeds, the intensity of the defect luminescence gradually decreases, and with this, the intensity of the band-edge luminescence also increases. However, when Se-DDT / OLAm is used as the Se source as in this embodiment, the luminescence is a single peak from the initial stage, the band-edge luminescence / defect luminescence is above 10, and the peak believed to be defect luminescence is almost not confirmed. In addition, the fluorescence half-value width is below 30nm. The fluorescence lifetime is also shortened to less than 20 ns until it reaches 1 / e, and only the peak of non-defective emission can be confirmed at the initial stage of emission.

[0083] Next, this embodiment can further increase the fluorescence quantum yield by coating the surface of the core 5a composed of nanocrystals with a shell 5b. As described above, this embodiment first coats the surface of the core with GaS and then adds Zn. Here, the Ga source is as described above.

[0084] In this embodiment, organic sulfur compounds such as mercaptans can be used as the raw material of S. For example, octadecyl mercaptan: C 18 H37 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, octyl mercaptan: C8H 17 SH, etc. In addition, S-ODE raw materials obtained by dissolving sulfur in octadecene:ODE, S-DDT raw materials obtained by dissolving sulfur in dodecanethiol, disulfide-based and thiuram-based S raw materials, and S-OLAm / DDT obtained by dissolving S in oleylamine and dodecanethiol can be used. The S raw material is not particularly limited.

[0085] In addition, organic zinc compounds and inorganic zinc compounds are used as Zn sources. Organic zinc compounds and inorganic zinc compounds are raw materials that are stable even in the air and easy to handle. In addition, this raw material can also be used as a ligand. Although the structure of the organic zinc compound and inorganic zinc compound is not particularly limited, for example, the organic zinc compounds and inorganic zinc compounds shown below can be used. As acetate, zinc acetate: Zn(OAc)2, zinc nitrate: Zn(NO3)2, and as fatty acid salt, 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, zinc chloride: ZnCl2, zinc bromide: ZnBr2, zinc iodide: ZnI2, zinc carbamate can be used as diethyldithiocarbamate zinc: Zn(SC(=S)N(C2H5)2)2, dimethyldithiocarbamate zinc: Zn(SC(=S)N(CH3)2)2, dibutyldithiocarbamate zinc: Zn(SC(=S)N(C4H9)2)2, etc.

[0086] Furthermore, in this embodiment, quantum dots can be obtained in one pot without separating and purifying the precursor.

[0087] Furthermore, after the core-shell structure is established, purification is performed using a specific solvent. For example, trioctylphosphine (TOP) can be used, but high fluorescence quantum yields can be achieved without TOP. Furthermore, TOP can be included as a ligand. Furthermore, in this embodiment, the resulting reaction solution can also be centrifuged.

[0088] Although the above-mentioned method for manufacturing quantum dots generates AgGaSe cores, cores containing at least Ag, Ga, and S can be generated. The Ag raw material, Ga raw material, and S raw material at this time are as described above. In addition, Cu and In may also be contained in the core. In addition, regarding the shell, it is believed that when ZnSe or ZnGa2Se4 is ultimately desired to be obtained, the shell of the first layer is preferably GaSe. However, it is also possible to coat ZnS or ZnGaS after the GaSe coating. In addition, it is believed that when the shell of the first layer is GaS, a shell containing ZnS or ZnGa2S4 or both can be ultimately obtained. However, it is also possible to coat ZnSe or ZnGaSe after the GaS coating.

[0089] In this embodiment, after coating with GaS, a ZnS shell may be coated by cation exchange between Ga and Zn.

[0090] The method for producing quantum dots in this embodiment is to form a core and then synthesize a shell by adding a predetermined element. In can be included in the initial stage of the core generation reaction, but it is preferably not included. This can achieve good luminescence properties.

[0091] In addition, in the present embodiment, when Zn is preferably contained in the quantum dots, Zn is added by paying attention to the following points. First, Zn is not added during the initial reaction but added in the final process. This is because when Zn is contained inside the particles, defect luminescence may dominate or only defect luminescence may be confirmed. Therefore, the purpose of adding Zn in the final process is to react only on the surface of the particles. The second is to add Zn at a low temperature. Here, low temperature refers to about 150 to 250°C. When the temperature when adding Zn is high temperature, Zn reacts until the inside of the particles, so it is easy to become defect luminescence. Therefore, in order for the reaction to stay on the surface of the particles, it is preferred to react only on the surface of the particles at a low temperature.

[0092] In addition, in this embodiment, when synthesizing AgGaSe, it is preferred that gallium acetylacetonate: Ga(acac) 3 be used as the Ga raw material, because better light emitting characteristics can be obtained compared to gallium chloride.

[0093] The Se raw material is preferably Se-OLAm / DDT, which can effectively suppress defect emission.

[0094] In addition, the fluorescence quantum yield can be further improved by adding TOP to the isolated quantum dots, but the addition of TOP is not required.

[0095] As described above, according to the quantum dot production method of this embodiment, the surface of a core containing at least Ag, Ga, S, or Ag, Ga, Se, can be appropriately coated with a shell containing a large amount of Zn. This allows for the high-precision production of quantum dots exhibiting band-edge luminescence with a fluorescence half-width of 35 nm or less, and is also feasible for mass production. This embodiment enables the core to be appropriately coated with a ZnS shell, thereby improving the stability of the fluorescence properties and achieving a high fluorescence quantum yield, specifically a fluorescence quantum yield of 70% or greater.

[0096] Band-edge luminescence is explained. In this embodiment, band-edge luminescence is achieved not only with core-shell structures but also with core monomers. In the inventions described in patent documents, band-edge luminescence has not been confirmed for quantum dots from Groups 11, 13, and 16, and neither has band-edge luminescence been confirmed for core monomers. In each patent document, a shell operation is performed to achieve band-edge luminescence.

[0097] Furthermore, it is conceivable that the core can emit edge-emitting light by performing a surface treatment based on the shell coating process, as defined in various patent and non-patent literatures, rather than shell coating. Furthermore, the quantum dots of this embodiment can be realized without surface treatment of the core that emits edge-emitting light. Otherwise, the quantum dots realized in this embodiment have the same characteristics as conventional core-shell structures.

[0098] The core-shell structure of conventional quantum dots represents a structure of quantum dots in which the core and shell are composed of clearly different elements and separated particles as a whole. In addition, another feature is that the shell coating shows an XRD peak position different from the core. The characteristics of this core-shell structure cannot be proved by the method defined as shell coating in various patent documents and non-patent literature. On the other hand, the quantum dots of the present embodiment are crystallized quantum dots in which Ag, Ga, or Se in the core and Zn or S in the shell are clearly separated. After shell coating, the XRD peak position changes, similar to the previous quantum dots. Thus, the quantum dots of the present embodiment are the first to achieve clear shell-coated quantum dots.

[0099] Furthermore, in this embodiment, even if the emission intensity is not high in the core alone and the core-shell structure is not formed, the fluorescence half-value width can be narrowed and band-edge emission can be confirmed.

[0100] In addition, by appropriately adjusting the particle size and composition of the quantum dots 5, the fluorescence wavelength can be controlled within the green to red range in this embodiment. Therefore, the fluorescence wavelength for green emission is preferably 500 nm to 560 nm, more preferably 510 nm to 550 nm, and even more preferably 520 nm to 540 nm. Furthermore, for red emission, the fluorescence wavelength is preferably 600 nm to 660 nm, more preferably 610 nm to 650 nm, and even more preferably 620 nm to 640 nm.

[0101] Furthermore, in this embodiment, as described above, the fluorescence wavelength can be adjusted within the range of 500 nm to 700 nm.

[0102] The quantum dots 5 of this embodiment exhibit fluorescence characteristics with a fluorescence half-value width of 35 nm or less and a fluorescence quantum yield (Quantum Yield) of 70% or more.

[0103] Here, "fluorescence half-value width" refers to the full width at half maximum (FWHM) of the fluorescence wavelength at half the peak intensity of the fluorescence intensity in the fluorescence spectrum. Furthermore, the FWHM is preferably 35 nm or less. Furthermore, the FWHM is more preferably 30 nm or less. This narrows the FWHM, thereby enhancing high color gamut.

[0104] The fluorescence quantum yield of the quantum dots 5 of this embodiment is preferably 70% or higher, more preferably 80% or higher, and even more preferably 90% or higher. Thus, this embodiment can improve the fluorescence quantum yield of the quantum dots.

[0105] Chalcopyrite is a material that typically emits defect-induced luminescence with a fluorescence half-width of 70 to 100 nm. In contrast, the quantum dots 5 of this embodiment exhibit a narrow fluorescence half-width, a high fluorescence quantum yield, and a fluorescence lifetime significantly shorter than that of defect-induced luminescence. These characteristics indicate that the quantum dots 5 of this embodiment exhibit band-edge luminescence.

[0106] In the above-described method for producing quantum dots according to the present embodiment, Cu may be added when generating AgGaSe cores or AgGaS cores.

[0107] As a raw material for Cu, an organic copper compound or an inorganic copper compound is used. Although not particularly limited, examples thereof include copper acetate: Cu(OAc)2, copper nitrate: Cu(NO3)2, halides such as copper chloride: CuCl2, copper bromide: CuBr2, and silver iodide: CuI2. Carbamates such as copper diethyldithiocarbamate: Cu(SC(=S)N(C2H5)2)2 and copper dimethyldithiocarbamate: Cu(SC(=S)N(CH3)2)2 can be used.

[0108] In the present embodiment, the above-mentioned Cu raw material may be directly added to the reaction solution, but it may be dissolved in an organic solvent in advance and used as a solution having a certain concentration as a Cu raw material solution.

[0109] During nucleation, it is thought that Cu acts as a catalyst. Specifically, according to the results of TEM-EDX analysis, quantification of Cu is difficult, and XRD results show that equivalent results are obtained regardless of the presence or absence of Cu addition. Therefore, it is speculated that Cu acts as a catalyst rather than being dissolved in the elements that constitute the nucleus.

[0110] During nucleation, the addition of Cu can increase the quantum yield (QY) to the same or higher level, and reduce the fluorescence half-value width to the same or lower level, compared to the case where Cu is not added. Depending on the application of quantum dots, better results can be obtained by adding Cu. Although not particularly limited Figure 1 The uses of the quantum dots 5 shown are as follows, but several specific examples are listed below.

[0111] Figure 2 Schematic diagram of an LED device using quantum dots of this embodiment. Figure 2 As shown, the structure includes: a storage container 2 having a bottom surface 2a and side walls 2b surrounding the bottom surface 2a; an LED chip (light-emitting element) 3 arranged on the bottom surface 2a of the storage container 2; and a fluorescent layer 4 filled in the storage container 2 and sealing the upper surface side of the LED chip 3. Here, the upper surface side refers to the direction in which light emitted by the LED chip 3 is emitted from the storage container 2, that is, the direction opposite to the bottom surface 2a with respect to the LED chip 3.

[0112] The LED chip 3 may be arranged on a base wiring board (not shown), which constitutes the bottom portion of the storage container 2. The base board may be a base material such as glass epoxy resin with a wiring pattern formed thereon, for example.

[0113] The LED chip 3 is a semiconductor element that emits light when a voltage is applied in the forward direction, and has a basic structure in which a P-type semiconductor layer and an N-type semiconductor layer are connected via a PN junction. Figure 2As shown, the fluorescent layer 4 is formed of a resin 6 in which a large number of quantum dots 5 are dispersed.

[0114] The resin composition in which the quantum dots 5 of this embodiment are dispersed may contain the quantum dots 5 and fluorescent substances other than the quantum dots 5. Examples of fluorescent substances include hybrid ceramics, KSF (K2SiF6: Mn 4+ ) red phosphor, etc., but the material is not particularly limited.

[0115] The resin 6 constituting the fluorescent layer 4 is not particularly limited, and may be 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.

[0116] The LED device using the quantum dots of this embodiment can be suitably used in a display device. Figure 3 For use Figure 2 A longitudinal cross-sectional view of a display device of an LED device is shown. Figure 3 As shown, the display device 50 is configured to include 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 arranged on the back side of the display unit 54. Figure 2 The LED device 1 shown similarly has a structure in which an LED chip is sealed with a resin in which a large number of quantum dots 5 are diffused.

[0117] like Figure 3 As shown, 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 a display unit 54. The support 52 is in the form of a sheet, a plate, or a container, and the shape and material are not particularly limited. Figure 3 As shown, a light diffusion plate 53 or the like may be interposed between the backlight 55 and the display unit 54 .

[0118] By applying the quantum dots 5 having a narrow fluorescence half-value width in this embodiment to Figure 2 The LED device shown, Figure 3 The display device shown, etc., can effectively improve the light-emitting characteristics of the device.

[0119] Furthermore, the resin composition in which the quantum dots 5 of this embodiment are dispersed in a resin can be formed into a sheet or film. Such a sheet or film can be incorporated into a backlight device, for example.

[0120] Example

[0121] Hereinafter, the effects of the present invention will be described by way of examples and comparative examples of the present invention. However, the present invention is not limited in any way by the following examples.

[0122] <Raw Materials>

[0123] In the experiment, the following raw materials were used to synthesize quantum dots composed of a core / shell structure of AgGaSe / ZnS.

[0124] (Solvent)

[0125] Oleylamine: manufactured by Kao Co., Ltd.

[0126] Dodecanethiol: manufactured by Kao Co., Ltd.

[0127] (Silver raw material)

[0128] Silver acetate: manufactured by Aldrich Corporation

[0129] (Gallium raw materials)

[0130] Gallium acetylacetonate: Made by Tokyo Chemical Industry Co., Ltd.

[0131] (selenium)

[0132] Selenium: Shinko Chemical Industry Co., Ltd.

[0133] (Zinc)

[0134] Zinc acetate: manufactured by Kishida Chemical Co., Ltd.

[0135] Zinc bromide: manufactured by KISHIDA Chemical Co., Ltd.

[0136] (Sulfur raw materials)

[0137] Sulfur: manufactured by Kishida Chemical Co., Ltd.

[0138] <Measurement equipment>

[0139] Fluorescence spectrometer: F-2700 manufactured by JASCO Corporation

[0140] Quantum yield measurement device: QE-1100 manufactured by Otsuka Electronics Co., Ltd.

[0141] Scanning line electron microscope (SEM): SU9000 manufactured by Hitachi, Ltd.

[0142] X-ray diffraction apparatus (XRD): Bruker D2 PHASER

[0143] [Example 1]

[0144] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) dissolved in oleylamine (OLAm), 36.7 mg of gallium acetylacetonate (Ga(acac)3), 20.0 mL of oleylamine (OLAm), and 2.0 mL of dodecanethiol (DDT) were placed. The mixture was then heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0145] This solution was dissolved at 150°C for 10 minutes, and 0.3 ml of a 0.7 M solution of selenium (Se) dissolved in a 5:2 volume ratio mixed solvent of dodecanethiol:DDT and oleylamine:OLAm was added. The temperature was then raised from 150°C to 320°C, and stirred for a total of 10 minutes. The resulting reaction solution was then cooled to room temperature.

[0146] The reaction solution was centrifuged at 5500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene, and after adding ethanol, the precipitate was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 10.0 ml of dodecanethiol:DDT. The precipitate obtained here was measured using an X-ray diffraction (XRD) device. The results are shown in FIG. Figure 5 In the figure, it is represented as A.

[0147] The dispersion was placed in a 100 mL reaction vessel and heated at 270°C for 10 minutes under an inert gas (N2) atmosphere. A 0.4 M solution of sulfur (S) dissolved in dodecanethiol (DDT) and a 0.1 M solution of gallium acetylacetonate (Ga(acac)3) dissolved in oleyl alcohol (OLOH) were added dropwise in five portions every 10 minutes. The resulting reaction solution was then cooled to room temperature.

[0148] Toluene and ethanol were added to the reaction solution, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 10.0 ml of dodecanethiol:DDT. The precipitate obtained here was measured using an X-ray diffraction (XRD) device. The results are shown in Figure 5 In the figure, it is represented as B.

[0149] This dispersion was placed in a 100 mL reaction vessel and heated at 180°C for 10 minutes under an inert gas (N2) atmosphere. A 0.2 M solution of zinc bromide (ZnBr2) dissolved in dodecanethiol:DDT and a 0.4 M solution of sulfur (S) dissolved in dodecanethiol:DDT were added dropwise five times, alternating every 10 minutes. The resulting reaction solution was then cooled to room temperature.

[0150] Fluorescence Half-Width and Quantum Yield Experiments

[0151] The QD dispersion solution was measured by a fluorescence spectrometer and a quantum efficiency measurement system. Figure 6 As shown in FIG, the fluorescence wavelength is 637.5 nm, the fluorescence half-value width is 32.11 nm, and the quantum yield is 76%. In addition, the precipitate obtained here was measured using an X-ray diffraction (XRD) device. The results are shown in FIG. Figure 5 In the example, it is represented as C.

[0152] <Analysis results of X-ray diffraction (XRD) equipment>

[0153] exist Figure 5 The maximum peaks of the results of XRD analysis of samples A, B, and C obtained in each synthesis process are shown in FIG. Based on the results, it can be confirmed that the XRD peaks of A to B are shifted to the high-angle side. In this synthesis process, the sample obtained by adding Ga and S to the AgGaSe2 (sample A) obtained as the core is B. In addition, the sample obtained by adding Zn and S to the sample B obtained here is C. In this synthesis process, it can also be confirmed that the XRD peaks of B to C are further shifted to the high-angle side. From the observation of such peak shifts, it can be inferred that the Ag contained in the core does not diffuse into the shell and is able to cover the shell containing a large amount of Zn.

[0154] TEM-EDX analysis results

[0155] The results of TEM-EDX analysis of the quantum dots of Example 1 (observation images) are shown in FIG. Figure 7 . Figure 7 (a) is a photograph of the TEM-EDX analysis results (Se+S and Ag+Zn). Figure 7 (b) is Figure 7 Partial schematic diagram of (a). Figure 7 The dotted line in (b) indicates the vicinity of the boundary between the core and the shell (it does not indicate a clear boundary). Figure 9 The same will be true in the future. Figure 7 The observation image on the left is the analysis result of Se+S. Figure 7The observation image on the right is the analysis result of Ag+Zn. These experimental results show that Se and S exist separately, specifically, S exists around Se. Furthermore, Ag and Zn exist separately, specifically, Zn exists around Ag. It can be seen that Se and Ag are primarily contained in the core, while S and Zn are primarily contained in the shell. This prevents the diffusion of components contained in the core into the shell, and similarly, prevents the diffusion of components contained in the shell into the core.

[0156] [Example 2]

[0157] The same manufacturing operation as in Example 1 was followed, but the same operation was performed until GaS coating, and Zn was added to the obtained particles 9 times. The quantum dot dispersion solution was measured by a fluorescence spectrometer and a quantum efficiency measurement system. The results were as follows: Figure 6 The optical characteristics shown are a fluorescence wavelength of 630 nm, a fluorescence half-value width of 34 nm, and a maximum quantum yield of 94%.

[0158] High-resolution STEM results

[0159] The results of high-resolution STEM analysis of the quantum dots of Example 2 are shown in FIG. Figure 8 . Figure 8 (a) is a photograph of the analysis results of high-resolution STEM in Example 2, Figure 8 (b) is Figure 8 Partial diagram of (a). Confirm Figure 8 When the particles are crystalline, the crystal lattice can be confirmed from the entire particle. Based on this result, it can be inferred that the shell is crystallized and the diffusion of the Ag contained in the core and the Zn contained in the shell is suppressed.

[0160] TEM-EDX analysis results

[0161] The results of TEM-EDX analysis of the quantum dots of Experimental Example 2 (observation images) are shown in FIG. Figure 9 . Figure 9 (a) is a photograph of the TEM-EDX analysis results (Ag+Zn) in Example 2. Figure 9 (b) is Figure 9 Partial schematic diagram of (a). Figure 9 The observed image is the analysis result of Ag + Zn. From this observed image, it can be seen that Zn exists around Ag, which can inhibit the diffusion of components contained in the core to the shell, and similarly inhibit the diffusion of components contained in the shell to the core.

[0162] <Zn content measurement results>

[0163] Figure 101 and 2 show the results of Zn content analysis by TEM-EDX. Figure 10 (a) is a photograph of the TEM-EDX analysis results (Zn) in Example 1 and the comparative example. Figure 10 (b) is Figure 10 Partial schematic diagram of (a). Figure 10 The observation image on the left side is Comparative Example 1. Figure 10 The observation image on the right side is Example 1. Comparative Example 1 is different from the above experimental example. Figure 4 In the process of the central figure, the first shell is coated with oleylamine solvent. Figure 4 On the other hand, the embodiment is the above-mentioned experimental example 1, that is, through Figure 4 The fabrication steps to generate quantum dots are shown.

[0164] according to Figure 10 The experimental results shown confirmed that Example 1 contained a larger amount of Zn on the core surface than Comparative Example 1, and that GaS and ZnS could be appropriately coated on the surface of AgGaSe.

[0165] The Zn content in the quantum dots of Comparative Example 1, Example 1, and Example 2 was measured. The Zn content in Comparative Example 1 was approximately 1%, in Example 1 approximately 5%, and in Example 2 approximately 10%. It can be seen that the Zn content in Examples 1 and 2 was several to ten times greater than that in Comparative Example 1. Furthermore, the Zn content in Example 2 was nearly double that in Example 1. This is due to the increased number of Zn post-addition steps in Example 2.

[0166] [Example 3]

[0167] In a 100 mL reaction vessel, 1.8 mL of a 0.2 M solution of silver acetate (Ag(OAc)) dissolved in oleylamine (OLAm), 0.2 mL of a 0.2 M solution of copper acetate (Cu(OAc)2) dissolved in oleylamine (OLAm), 0.2644 mg of gallium acetylacetonate (Ga(acac)3), 20.0 mL of oleylamine (OLAm), and 4.0 mL of dodecanethiol (DDT) were placed. The mixture was then heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0168] This solution was dissolved at 150°C for 10 minutes, and 1.43 ml of a 0.7 M solution of selenium (Se) dissolved in a 5:2 volume ratio mixed solvent of dodecanethiol:DDT and oleylamine:OLAm was added. The temperature was then raised from 150°C to 320°C, and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0169] The resulting reaction solution was centrifuged at 5500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene, and after adding ethanol, the solution was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 10.0 ml of dodecanethiol:DDT.

[0170] This dispersion was placed in a 100 mL reaction vessel and heated at 270°C for 5 minutes under an inert gas (N2) atmosphere. 0.25 mL of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol / DDT and 1.3 mL of a 0.1 M solution of gallium acetylacetonate (Ga(acac)3) dissolved in oleyl alcohol / OLOH were mixed. Heating was continued for a total of 60 minutes. The resulting reaction solution was then cooled to room temperature.

[0171] Toluene and ethanol were added to the obtained reaction solution, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate, which was then redispersed in 10.0 ml of dodecanethiol:DDT.

[0172] This dispersion was placed in a 100 mL reaction vessel and heated at 200°C for 5 minutes under an inert gas (N2) atmosphere. 2.0 mL of a 0.8 M solution of zinc bromide (ZnBr2) dissolved in dodecanethiol:DDT and 2.0 mL of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol:DDT were mixed and added dropwise at 0.4 mL intervals over 10 minutes. Heating was continued for a total of 120 minutes. The resulting reaction solution was cooled to room temperature.

[0173] The QD dispersion solution was measured using a fluorescence spectrometer. The results showed optical characteristics of a fluorescence wavelength of 623.5 nm, a fluorescence half-value width of 34.70 nm, and a quantum yield of 76%.

[0174] [Example 4]

[0175] In a 300 mL reaction vessel, 5.4 mL of a 0.2 M solution of silver acetate (Ag(OAc)) dissolved in oleylamine (OLAm), 0.88092 g of gallium acetylacetonate (Ga(acac)3), 120.0 mL of oleylamine (OLAm), and 11 mL of dodecanethiol (DDT) were placed. The mixture was then heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0176] This solution was dissolved at 150°C for 15 minutes, and 4.29 ml of a 0.7 M solution of selenium (Se) dissolved in a 5:2 volume ratio mixed solvent of dodecanethiol:DDT and oleylamine:OLAm was added. The temperature was then raised from 150°C to 320°C, and stirred for a total of 25 minutes. The resulting reaction solution was then cooled to room temperature.

[0177] The resulting reaction solution was centrifuged at 5500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene, ethanol was added, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was again redispersed with toluene, ethanol was added, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 60.0 ml of dodecanethiol / DDT.

[0178] This dispersion was placed in a 300 mL reaction vessel and heated at 270°C for 5 minutes under an inert gas (N2) atmosphere. 0.1 mL of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol:DDT was mixed and heated for 20 minutes. Next, 1.2 mL of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol:DDT and 6.0 mL of a 0.1 M solution of gallium acetylacetonate (Ga(acac)3) dissolved in oleyl alcohol:OLOH were mixed and added dropwise in five portions of 1.44 mL over 10 minutes. Heating was continued for a total of 50 minutes. The resulting reaction solution was then cooled to room temperature.

[0179] Toluene, ethanol, and methanol were added to the resulting reaction solution, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate, which was then redispersed in 87.5 ml of octadecene: ODE and 10 ml of trioctylphosphine: TOP.

[0180] The dispersion was placed in a 300 mL reaction vessel and heated at 240°C for 5 minutes under an inert gas (N2) atmosphere. The mixture was then mixed with 10 mL of a 0.8 M solution of zinc acetate:Zn(OAc)2 dissolved in a 1:1 volume ratio of trioctylphosphine:TOP and oleic acid:OLAc. The mixture was then mixed with 0.4 mL of a 4 N solution of octadecene:ODE (6.7 mL), trioctylphosphine:TOP (2.3 mL), dodecanethiol:DDT (1.0 mL), and hydrogen chloride:HCl dissolved in ethyl acetate:C4H8O2. The mixture was then added dropwise in eight portions of 2.25 mL every 10 minutes. The mixture was heated for a total of 80 minutes. The resulting reaction solution was cooled to room temperature.

[0181] The QD dispersion solution was measured using a fluorescence spectrometer. The results showed optical characteristics of a fluorescence wavelength of 622.5 nm, a fluorescence half-value width of 36.1 nm, and a quantum yield of 91%.

[0182] [Example 5]

[0183] In a 100 mL reaction vessel, 0.45 mL of a 0.2 M solution of silver acetate (Ag(OAc)) dissolved in oleylamine (OLAm), 0.0734 g of gallium acetylacetonate (Ga(acac)3), 10.0 mL of oleylamine (OLAm), 0.917 mL of dodecanethiol (DDT), and 0.0643 mL of a 0.7 M solution of selenium (Se) dissolved in a 1:1 volume ratio mixed solvent of dodecanethiol (DDT) and oleylamine (OLAm) were placed. The mixture was then heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0184] This solution was dissolved at 320°C for 1.25 minutes, and 1 ml of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol (DDT) was mixed and heated for 60 minutes. The resulting reaction solution was then cooled to room temperature.

[0185] Toluene and ethanol were added to the resulting reaction solution, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene, and ethanol was added, followed by centrifugation at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 5.0 ml of dodecanethiol:DDT and centrifuged at 5500 rpm for 3 minutes to obtain a precipitate.

[0186] The dispersion was placed in a 100 mL reaction vessel and heated at 240°C for 3 minutes under an inert gas (N2) atmosphere. A 0.2 M solution of zinc bromide (ZnBr2) dissolved in dodecanethiol (DDT) and 0.53 mL of trioctylphosphine (TOP) were mixed and added dropwise in three portions of 0.506 mL every 10 minutes. The heating lasted for a total of 30 minutes. The resulting reaction solution was cooled to room temperature.

[0187] The QD dispersion solution was measured using a fluorescence spectrometer. As a result, optical characteristics were obtained, including a fluorescence wavelength of 540.5 nm and a fluorescence half-value width of 39.0 nm.

[0188] [Comparative Example 2]

[0189] In a 100 mL reaction vessel, 1.8 mL of a 0.2 M solution of silver acetate (Ag(OAc)) dissolved in oleylamine (OLAm), 0.2 mL of a 0.2 M solution of copper acetate (Cu(OAc)2) dissolved in oleylamine (OLAm), 0.2644 mg of gallium acetylacetonate (Ga(acac)3), 20.0 mL of oleylamine (OLAm), and 4.0 mL of dodecanethiol (DDT) were placed. The mixture was then heated while stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0190] This solution was dissolved at 150°C for 10 minutes, and 1.43 ml of a 0.7 M solution of selenium (Se) dissolved in a 5:2 volume ratio mixed solvent of dodecanethiol:DDT and oleylamine:OLAm was added. The temperature was then raised from 150°C to 320°C, and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0191] The resulting reaction solution was centrifuged at 5500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene, and after adding ethanol, the precipitate was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 10.0 ml of dodecanethiol:DDT.

[0192] The dispersion was placed in a 100 mL reaction vessel and heated at 270°C for 5 minutes under an inert gas (N2) atmosphere. 0.25 mL of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol (DDT) was mixed. After heating for 20 minutes, the resulting reaction solution was cooled to room temperature.

[0193] Hexane and ethanol were added to the obtained reaction solution, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate, which was then redispersed in 10.0 ml of dodecanethiol:DDT.

[0194] This dispersion was placed in a 100 mL reaction vessel and heated at 200°C for 5 minutes under an inert gas (N2) atmosphere. 2.0 mL of a 0.8 M solution of zinc bromide (ZnBr2) dissolved in dodecanethiol (DDT) and 2.0 mL of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol (DDT) were mixed and added dropwise at 0.4 mL intervals every 10 minutes. The mixture was heated for a total of 120 minutes. The resulting reaction solution was cooled to room temperature.

[0195] The QD dispersion solution was measured using a fluorescence spectrometer. The results showed optical characteristics of a fluorescence wavelength of 631.0 nm, a fluorescence half-value width of 36.24 nm, and a quantum yield of 96%.

[0196] <About Shelled Quantum Dots Formed by Cation Exchange>

[0197] Example 3 is an experimental example in which GaS coating was performed, and Comparative Example 2 is an experimental example in which GaS coating was not performed. Figure 11 (a) and (b) are the fluorescence (Photoluminescence: PL) spectra in Example 3 and Comparative Example 2. Figure 11 (b) is to Figure 11 An enlarged view of a portion of (a).

[0198] like Figure 11As shown in (b), Comparative Example 2 shows a shorter luminescence spectrum around 500-550 nm compared to Example 3. This is presumably because in Comparative Example 2, when ZnS as a shell material was added to avoid GaS coating, Zn exchanged cations with the core cation species such as Ag, Cu, and Ga.

[0199] In contrast, it is found that Example 3 can suppress short-wavelength emission compared to Comparative Example 2 by adding the ZnS raw material after GaS coating.

[0200] Therefore, it is inferred that the Zn added later did not diffuse into the core via the coating GaS.

[0201] Based on the above experimental results, it is believed that Ga and Zn after GsS coating are transformed into ZnS through cation exchange. In addition, since the particle size of AgGaSe / GaS particles and AgGaSe / ZnS particles is almost unchanged, it can also be speculated that Ga and Zn are cation exchanged or anion solid solution.

[0202] Regarding nuclear band-edge luminescence

[0203] EDX analysis was performed on the core of Example 3. The experimental results are shown in Figure 12 Middle (a). Figure 12 (c) is a partial schematic diagram of (a). Figure 12 As shown in (a), Ga (blue) and Ag (purple) are distributed almost equally in the core, which is considered to be a core-shell structure. Figure 12 (b) is the fluorescence (Photoluminescence: PL) spectrum of the core of Example 3. Figure 12 As shown in (b), it can be seen that the fluorescence half-value width of the emission spectrum is narrow.

[0204] It can be seen from this example that the core monomer also emits light with an edge.

[0205] <About the Catalytic Effect of Cu>

[0206] Although embodiment 3 is to carry out the interpolation of Cu when generating core, in the result of TEM-EDX analysis, the correct quantitative of Cu is difficult.In addition, in XRD, no matter have or not add Cu, all can obtain equal result.Therefore infer that Cu plays a role as catalyst than being dissolved in the element that constitutes core.

[0207] Industrial applicability

[0208] According to the present invention, for example, quantum dots that exhibit high-brightness green or red fluorescence can be stably obtained. Moreover, by applying the quantum dots of the present invention to LEDs, backlight devices, display devices, etc., excellent luminescence properties can be obtained in each device.

[0209] This application is based on Japanese Patent Application No. 2020-217158 filed on December 25, 2020, and Japanese Patent Application No. 2021-53070 filed on March 26, 2021, the contents of which are incorporated herein by reference in their entirety.

Claims

1. A quantum dot, characterized in that The quantum dot has a core and a shell, wherein the core contains at least Cu, Ag, Ga, S or Cu, Ag, Ga, Se, and the shell covers the surface of the core. The shell contains at least Zn, The fluorescence characteristics of the invention are that the fluorescence half-value width is less than 35nm and the fluorescence quantum yield is more than 70%.

2. The quantum dot according to claim 1, characterized in that The shell consists of ZnS.

3. The quantum dot according to claim 1 or claim 2, characterized in that The core and the shell do not contain Cd and In.

4. The quantum dot according to claim 1 or claim 2, characterized in that The fluorescence wavelength is in the range of 400nm to 700nm.

5. The quantum dot according to claim 1 or claim 2, characterized in that Nucleomonomers show band-edge luminescence.

Images