Method for manufacturing quantum dots and quantum dots

Abstract

The 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. The method for producing quantum dots of the present invention is characterized in that it includes a step of generating a core containing at least Ag, Ga, S or containing Ag, Ga, Se and a step of coating the surface of the core with a shell, and in the step of coating the shell, Zn is added after the surface of the core is coated with GaS. Preferably, ZnS is coated after coating GaS. Preferably, Cd and In are not contained in the core and the shell.

Description

Technical Field

[0001] The invention relates to a method for manufacturing quantum dots with a core / shell structure and the quantum dots. Background Art

[0002] Quantum dots are inorganic nanoparticles with a particle size of several nanometers to tens of nanometers, which are composed of thousands to tens of thousands of atoms. Quantum dots emit fluorescence, and because of their nanometer size, they are called fluorescent nanoparticles. Because their composition is derived from semiconductor materials, they are also called semiconductor nanoparticles, or because their structure has a specific crystal structure, they are also called nanocrystals.

[0003] Quantum dots are composed of positively charged metal atoms and negatively charged non-metal or semi-metal atoms, which are bonded to each other by ionic or covalent bonds. The ionic nature of the bond depends on the combination of the properties of the metal atom and the semi-metal atom.

[0004] Quantum dots can change the emission wavelength in various ways depending on the particle size and composition of the particles. Examples of the performance of quantum dots include fluorescence quantum yield (QY) and fluorescence half-value width (FWHM).

[0005] One of the properties of quantum dots is photoluminescence. Quantum dots can absorb wavelengths in a specific wavelength range and convert them into wavelengths in a specific range to emit light. In addition, the absorption wavelength and the emission wavelength can be controlled according to the structure, composition, and size of the quantum dots, and their characteristics can be flexibly utilized for various purposes.

[0006] For example, when quantum dots are used as wavelength conversion materials in the visible light region, one of the characteristics thereof is that the range of colors that can be expressed is wide, i.e., high color gamut. In the high color gamut achieved by the wavelength conversion component in the visible light region using the quantum dots, important optical properties are the fluorescence quantum yield and the fluorescence half-value width.

[0007] In the past, the high-efficiency quantum dots that have been used mainly contain cadmium (Cd). Cd-containing quantum dots have the advantages of high fluorescence quantum yield and narrow fluorescence half-value width. On the other hand, due to the toxicity of Cd, various countries have restricted its use, which has become a major obstacle to its practical application.

[0008] On the other hand, the development of quantum dots that do not contain Cd has also been widely discussed. For example, the following patent documents describe quantum dots of AIS or AIGS series or quantum dots of AISe or AIGSe series containing Ag, In, S, or Ag, In, Ga, S, or Ag, In, Se, or Ag, In, Ga, Se.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2017-025201

[0012] Patent Document 2: Japanese Patent Application Publication No. 2018-039971

[0013] Patent Document 3: Japanese Patent Application Publication No. 2018-044142

[0014] Patent Document 4: Japanese Patent Application Publication No. 2018-141141

[0015] Patent Document 5: WO2018 / 159699

[0016] Non-patent literature

[0017] Non-patent literature 1: NPG Asia Materials volume 10.2018, pp713-726

[0018] Non-patent document 2: ACS Publications 2018, 10, 49, 41844-41855

[0019] Non-patent literature 3: ACS Publications Nano Mater. 2020, 3, 3275-3287

[0020] Non-patent literature 4: The Journal of Physical Chemistry Letters; Ligand-InducedLuminescence Transformation in AgInS 2 Nanoparticles:From Defect Emission toBand-Edge Emission Summary of the invention

[0021] Problems to be solved by the invention

[0022] 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 be widened.

[0023] Furthermore, even if Zn is added to AgGaS or AgInGaS so that it does not contain Zn, the cationic species easily diffuse into the particles. Therefore, Zn easily diffuses into the core, resulting in defect emission.

[0024] 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.

[0025] Solutions to Solve Problems

[0026] 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.

[0027] 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 they exhibit fluorescence characteristics with a fluorescence half-value width of less than 35nm and a fluorescence quantum yield of more than 70%.

[0028] Effects of the Invention

[0029] According to the method for manufacturing 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, and quantum dots with band-edge luminescence having a fluorescence half-value width of less than 35nm can be manufactured with high precision. According to the quantum dots of the present invention, it is possible to maintain band-edge luminescence and to make the surface contain a large amount of Zn. In this way, a shell with a large amount of Zn can be appropriately coated on the surface of the core, thereby improving the stability of the fluorescence characteristics, and further maintaining a high fluorescence quantum yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of quantum dots in an embodiment of the present invention.

[0031] Figure 2 Schematic diagram of an LED device using quantum dots according to an embodiment of the present invention.

[0032] Figure 3 It is a longitudinal cross-sectional view of a display device using the LED device in the embodiment of the present invention.

[0033] Figure 4This is a conceptual diagram showing a process for producing quantum dots according to an embodiment of the present invention.

[0034] Figure 5 This is the X-ray diffraction (XRD) spectrum in Example 1.

[0035] Figure 6 : The fluorescence (Photoluminescence: PL) spectra in Examples 1 and 2.

[0036] 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).

[0037] 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).

[0038] Fig. 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).

[0039] Fig.10 (a) is a photograph of the analysis results (Zn) of TEM-EDX in Example 1 and the comparative example, and (b) is a partial schematic diagram of (a).

[0040] Fig.11 2 are the fluorescence (Photoluminescence: PL) spectra in Example 3 and Comparative Example 2.

[0041] Fig.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

[0042] 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 embodiments, and various modifications can be made within the scope of its purpose. In addition, the expression "to" in this specification means including the meaning of its lower limit and upper limit.

[0043] Figure 1 Schematic diagram of quantum dots in this embodiment. Figure 1 The quantum dot 5 shown in A is a nanocrystal that does not contain Cd.

[0044] In this embodiment, the quantum dot 5 is a core / shell structure of a core 5a and a shell 5b covering the surface of the core 5a. The core 5a preferably contains at least silver (Ag), gallium (Ga), sulfur (S) or nanocrystals of Ag, Ga, and selenium (Se). However, it is preferred that the core 5a does not contain cadmium (Cd) or In.

[0045] In addition, 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 further preferably 30 or more.

[0046] The shell 5b covering the surface of the core 5a is also preferably free of cadmium (Cd) and indium (In) as the core 5a. In the present embodiment, the shell 5b contains a large amount of zinc (Zn). Specifically, the shell 5b is preferably made of zinc sulfide (ZnS), zinc selenide (ZnSe), zinc gallium selenide (ZnGaSe), etc. 2 Se 4 ), zinc gallium sulfide (ZnGa 2 S 4 ) is formed. Among them, ZnS is preferred. In addition, the shell 5b may be in a state of being solid-solutioned on the surface of the core 5a.

[0047] In addition, the shell 5b may also contain copper (Cu) and indium (In). Specifically, the shell 5b is preferably made of copper sulfide (CuS), copper selenide (CuSe), indium sulfide (In 2 S 3 ), Indium Selenide (In 2 Se 3 ), indium zinc selenide (ZnIn 2 Se 4 ), indium zinc sulfide (ZnIn 2 S 4 ), copper indium sulfide (CuIn 2 S 4 ), copper indium selenide (CuIn 2 Se 4 ) structure. In addition, the shell 5b may be in a state of being solid-solution-solubilized on the surface of the core 5a.

[0048] The quantum dot 5 of this embodiment can be appropriately coated with ZnS or ZnGa on the surface of the core 5a of AgGaSe or AgGaS. 2 S 4 The present 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.

[0049] In the present embodiment, gallium (Ga) may be contained in the shell 5 b , or GaS or GaSe may be interposed between the core 5 a and the shell 5 b as the first layer of the shell.

[0050] Here, "nanocrystal" refers to nanoparticles having a particle diameter of about several nm to several tens of nm. In this embodiment, a large number of quantum dots 5 can be generated with a substantially uniform particle diameter.

[0051] This embodiment can increase the amount of Zn present on the surface of the quantum dot 5. Specifically, the amount of Zn has a weight ratio of 5% or more, preferably 10% or more, and more preferably 20% or more relative to the entire quantum dot 5. Although the upper limit is not limited, for example, the upper limit is about 40%.

[0052] Furthermore, the Ga / In ratio of the entire quantum dot 5 is preferably 10 or more, more preferably 30 or more, and further preferably 50 or more. Furthermore, the Ga / Zn ratio is preferably 1 or less, and more preferably 0.5 or less.

[0053] like Figure 1 As shown, it is preferred that many organic ligands 11 are coordinated on 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 for the reaction are not particularly limited, but for example, the following ligands can be listed as representative ligands.

[0054] (1) Aliphatic primary amine series

[0055] Oleylamine: C 18 H 35 NH 2 , Stearyl (octadecyl) amine: C 18 H 37 NH 2 , Dodecyl (lauryl) amine: C 12 H 25 NH 2 , Decylamine: C 10 H 21 NH 2 , Octylamine: C 8 H 17 NH 2

[0056] (2) Fatty acid series

[0057] Oleic acid: C 17 H 33 COOH, stearic acid: C 17 H 35 COOH, palmitic acid: C 15 H 31 COOH, myristic acid: C 13H 27 COOH, lauric acid: C 11 H 23 COOH, decanoic acid: C 9 H 19 COOH, octanoic acid: C 7 H 15 COOH

[0058] (3) Thiol series

[0059] Octadecanethiol: C 18 H 37 SH, hexadecyl mercaptan: C 16 H 33 SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decamethicone: C 10 H 21 SH, Octanethiol: C 8 H 17 SH

[0060] (4) Phosphine series

[0061] Trioctylphosphine: (C 8 H 17 ) 3 P, triphenylphosphine: (C 6 H 5 ) 3 P, tributylphosphine: (C 4 H 9 ) 3 P

[0062] (5) Phosphine oxide series

[0063] Trioctylphosphine oxide: (C 8 H 17 ) 3 P=O, triphenylphosphine oxide: (C 6 H 5 ) 3 P=O, tributylphosphine oxide: (C 4 H 9 ) 3 P=O

[0064] (6) Alcohol series

[0065] Oleyl alcohol: C 18 H 36 O

[0066] It is also preferred that the inorganic ligand is coordinated with the organic ligand. This can further suppress the surface defects of the quantum dots, thereby showing higher optical properties. The ligand is not particularly limited, but halogens such as F, Cl, Br, and I are representative examples.

[0067] Next, the method for manufacturing quantum dots is described. The purpose of this embodiment is to display band-edge luminescence and increase the amount of Zn contained in the shell 5b, so as to realize a method for manufacturing quantum dots with stabilized luminescence characteristics. In addition, this embodiment can also realize band-edge luminescence only by the core 5a. This point will be described later.

[0068] Conventionally, as an example of a method for producing quantum dots, for example, a shell containing Se is coated on the surface of AgGaSe and then Zn is added. However, according to this embodiment, the amount of Zn on the core surface can be increased by the following method. That is, the method for producing quantum dots of this embodiment is characterized by the following.

[0069] (1) comprising the steps of generating a core 5a containing at least Ag, Ga, S or Ag, Ga, Se and coating the surface of the core 5a with a shell 5b,

[0070] (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 to 2, y = 1 to 6), for example, GaS or Ga 2 S 3 In addition, the case where GaSe is coated on the core surface can also be represented by Ga x Se y (x=1-2, y=1-6), for example, GaSe or Ga 2 Se 3 "Zn addition" includes the addition of Zn monomer, ZnS, ZnSe, ZnGa 2 Se 4 , ZnGa 2 S 4 Added.

[0071] In the present embodiment, it is preferred that the surface of the core 5 a is coated 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 of the figure, the GaS shell is coated on the surface of the AgGaSe core. Then, Zn is added later, as shown in Figure 4 As shown in the right figure, a ZnS shell is obtained. Figure 4As shown in the central figure of FIG. 5 , the GaS shell covering the surface of the AgGaSe core is an important shell for preventing Zn from diffusing into the core 5a when Zn is added next. In addition, it is believed that Ga after Zn addition is separated from the shell to the outside through the dissolution and cleaning process, and the remaining amount in the shell is reduced, but Ga can also be contained in the shell. That is, the shell can also become ZnGa 2 S 4 Alternatively, the GaS shell may be interposed between the AgGaSe core and the ZnS shell. That is, the shell may also have a two-layer structure of GaS / ZnS.

[0072] Alternatively, in this embodiment, it is preferable that Ga of GaS is cation-exchanged with Zn to be coated with a ZnS shell. Figure 4 The central figure shows the particle size of AgGaSe / GaS and Figure 4 The particle sizes of AgGaS / ZnS in the right figure are confirmed by TEM-EDX analysis results to be almost the same. This can also be inferred that the ZnS shell coated on the surface of AgGaS is coated by cation exchange. In this way, through cation exchange or anion solid solution, it is possible to synthesize quantum dots with a core-shell structure with no change in particle size and a large amount of surface Zn.

[0073] In the previous preparation method, even if ZnS coating is implemented, Zn will immediately diffuse into 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.

[0074] According to the manufacturing method of the quantum dot 5 of the present embodiment described above, the diffusion of Ag contained in the core 5a into the shell can be suppressed, and the Se contained in the core 5a can be appropriately separated from the S contained in the shell 5b. Moreover, according to the manufacturing method of the quantum dot 5 of the present embodiment, the amount of Zn contained in the shell 5b can be increased. Although not particularly limited, as a weight ratio, the amount of Zn in the quantum dot 5 can be adjusted to 5% or more, preferably 10% or more, and more preferably 20% or more.

[0075] 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.

[0076] 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 a lower temperature of 280° C. or less.

[0077] In addition, in this embodiment, as a raw material of Ag, an organic silver compound or an inorganic silver compound is used. Although not particularly limited, for example, silver acetate: AgOAc, silver nitrate: AgNO 3 As the halide, silver chloride: AgCl, silver bromide: AgBr, silver iodide: AgI can be used, and as the carbamate, silver diethyldithiocarbamate: Ag(SC(=S)N(C 2 H 5 ) 2 ), silver dimethyldithiocarbamate: Ag(SC(=S)N(CH 3 ) 2 )wait.

[0078] In the present 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 and used as a solution having a certain concentration as the Ag raw material solution.

[0079] 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) can be used. 3 , Gallium nitrate: GaNO 3 、Gallium acetylacetonate: Ga(acac) 3 As the halogenide, gallium chloride can be used: GaCl 3 , Gallium bromide: GaBr 3 , Gallium iodide: Ga 2 I 3 As the carbamate, gallium diethyldithiocarbamate can be used: Ga[(SC(=S)N(C 2 H 5 ) 2 ] 3 wait.

[0080] In the present 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.

[0081] 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 prepared by dissolving selenium in trioctylphosphine can be used: (C 8 H 17 ) 3 P=Se, or tributylphosphine selenide obtained by dissolving selenium in tributylphosphine: (C 4 H 9 ) 3 P=Se, or a solution obtained by dissolving selenium in a high boiling point solvent of a long-chain hydrocarbon such as octadecene. When synthesizing AgGaSe, the type of selenium raw material contributes greatly to the fluorescence characteristics. In particular, a solution obtained by dissolving Se in a mixture of oleylamine and dodecanethiol (Se-OLAm / DDT) shows good luminescence characteristics. In the initial stage of luminescence, two types of luminescence can be confirmed in the conventional chalcopyrite-based quantum dots, namely, the PL spectrum considered to be band edge luminescence and the PL spectrum considered to be defect luminescence, and the luminescence intensity ratio is almost below 10. Then, by further undergoing the reaction, the intensity of the defect luminescence gradually decreases, and with this, the intensity of the band edge luminescence also increases in most cases. However, as in the present embodiment, when Se-DDT / OLAm is used as a Se source, it is a single peak from the initial stage of luminescence, the band edge luminescence / defect luminescence is above 10, and the peak considered to be defect luminescence can hardly be confirmed. In addition, the fluorescence half-value width is below 30nm. The fluorescence lifetime is also short to below 20ns until it becomes 1 / e, and only the peak of non-defect luminescence can be confirmed at the initial stage of luminescence.

[0082] Next, in this embodiment, the surface of the core 5a composed of nanocrystals is coated with a shell 5b, thereby further increasing the fluorescence quantum yield. As described above, in this embodiment, the surface of the core is first coated with GaS and then Zn is added. Here, the Ga source is as described above.

[0083] In this embodiment, an organic sulfur compound such as mercaptan can be used as a raw material of S. For example, octadecanethiol: C 18 H 37 SH, hexadecyl mercaptan: C 16 H 33 SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decamethicone: C 10 H 21 SH, Octanethiol: C 8 H 17SH, 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.

[0084] In addition, an organic zinc compound or an inorganic zinc compound is used as a Zn source. The organic zinc compound or the inorganic zinc compound is a raw material that is stable even in 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 or the inorganic zinc compound is not particularly limited, for example, the organic zinc compound or the inorganic zinc compound shown below can be used. Zinc acetate can be used as an acetate: Zn(OAc) 2 、Zinc nitrate: Zn(NO 3 ) 2 As fatty acid salt, zinc stearate can be used: 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 myristic acid: 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 can be used as a halogenide: ZnCl 2 , Zinc bromide: ZnBr 2 , Zinc iodide: ZnI 2 As zinc carbamate, zinc diethyldithiocarbamate can be used: Zn(SC(=S)N(C 2 H 5 ) 2 ) 2 、Zinc dimethyldithiocarbamate: Zn(SC(=S)N(CH 3 ) 2 ) 2 、Zinc dibutyl dithiocarbamate: Zn(SC(=S)N(C 4 H 9 ) 2 ) 2 wait.

[0085] Furthermore, in the present embodiment, quantum dots can be obtained in one pot without separating and purifying the precursor.

[0086] In addition, after having a core-shell structure, it is purified with a specific solvent. For example, trioctylphosphine (TOP) can be used, but a high fluorescence quantum yield can be obtained without TOP. In addition, TOP can be included as a ligand. In addition, in this embodiment, the synthesized reaction solution can also be centrifuged.

[0087] 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 materials, Ga raw materials, and S raw materials at this time are as described above. In addition, Cu and In can also be contained in the core. In addition, regarding the shell, it is believed that when ZnSe or ZnGa is finally obtained, 2 Se 4 In the case of GaSe, the shell of the first layer is preferably GaSe. However, it is also possible to coat ZnS or ZnGaS after GaSe coating. In addition, it is believed that when the shell of the first layer is GaS, a ZnS or ZnGaS-containing 2 S 4 However, it is also possible to coat ZnSe or ZnGaSe after coating with GaS.

[0088] In this embodiment, after coating with GaS, a ZnS shell may be coated by cation exchange between Ga and Zn.

[0089] The method for producing quantum dots in this embodiment is to synthesize the shell by adding a predetermined element after forming the core. In may be contained in the initial stage of the reaction of core generation, but preferably, In is not contained. This can obtain good luminescence characteristics.

[0090] 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, the first is to add Zn in the final process without adding Zn in the initial reaction. This is because, when Zn is contained inside the particles, defect luminescence may dominate or only defect luminescence can 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 a 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.

[0091] In addition, in this embodiment, when synthesizing AgGaSe, it is preferred that the Ga raw material use gallium acetylacetonate: Ga(acac) 3 , compared with gallium chloride, it can obtain better luminescence properties.

[0092] The Se raw material is preferably Se-OLAm / DDT, which can effectively suppress defect emission.

[0093] In addition, the fluorescence quantum yield can be further improved by adding TOP to the separated quantum dots, but the addition of TOP is not necessary.

[0094] As described above, according to the method for manufacturing quantum dots 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. Thus, quantum dots with edge-emitting fluorescence having a fluorescence half-value width of less than 35nm can be manufactured with high precision, and can be mass-produced. This embodiment can appropriately coat the core with a shell composed of ZnS, thereby improving the stability of the fluorescence characteristics, thereby obtaining a high fluorescence quantum yield, specifically a fluorescence quantum yield of more than 70%.

[0095] Band-edge luminescence is described. In this embodiment, not only the core-shell structure but also the core monomer can achieve band-edge luminescence. Here, in the inventions described in the patent documents, especially for quantum dots of Groups 11-13-16, band-edge luminescence is not confirmed, and band-edge luminescence is not confirmed for core monomers. In each patent document, a shell operation is performed to obtain band-edge luminescence.

[0096] In addition, it is conceivable that the method defined as shell coating in each patent document and each non-patent document is implemented by performing a surface treatment of the core based on the shell coating operation instead of shell coating, so that the core emits light with an edge. Moreover, the quantum dot of this embodiment is realized without performing a surface treatment on the core with edge emission. In addition, the quantum dot realized in this embodiment is a quantum dot having the same characteristics as the conventional core-shell structure.

[0097] 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 XRD peak position different from the core is displayed by shell coating. The characteristics of the core-shell structure cannot be proved by the method defined as shell coating in various patent documents and non-patent documents. 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 in the same way as conventional quantum dots. Thus, the quantum dots of the present embodiment are quantum dots that can achieve clear shell coating for the first time.

[0098] 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.

[0099] In addition, the present embodiment can control the fluorescence wavelength to green to red by appropriately adjusting the particle size of the quantum dots 5 and the composition of the quantum dots 5. Therefore, the fluorescence wavelength is preferably 500 nm to 560 nm as green luminescence, more preferably 510 nm to 550 nm, and further preferably 520 nm to 540 nm. In addition, as red luminescence, it is preferably 600 nm to 660 nm, more preferably 610 nm to 650 nm, and further preferably 620 nm to 640 nm.

[0100] In addition, in this embodiment, as described above, the fluorescence wavelength can also be adjusted within the range of 500 nm to 700 nm.

[0101] The quantum dot 5 of this embodiment exhibits fluorescence characteristics with a fluorescence half-value width of 35 nm or less and a fluorescence quantum yield (Quantum Yield) of 70% or more.

[0102] Here, "fluorescence half-value width" refers to the half-value full width (Full Width that Half Maximum) of the fluorescence wavelength that represents half the intensity of the peak value of the fluorescence intensity in the fluorescence spectrum. In addition, the fluorescence half-value width is preferably less than 35nm. In addition, the fluorescence half-value width is more preferably less than 30nm. In this way, the fluorescence half-value width can be narrowed, so that the high color gamut can be improved.

[0103] The fluorescence quantum yield of the quantum dot 5 of this embodiment is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. In this way, this embodiment can improve the fluorescence quantum yield of the quantum dot.

[0104] Chalcopyrite is generally a defect luminescent material with a fluorescence half-value width of 70 to 100 nm. In contrast, the quantum dot 5 of the present embodiment has a narrow fluorescence half-value width, a high fluorescence quantum yield, and a fluorescence lifetime much shorter than that of defect luminescence. Based on such characteristics, it can be inferred that the quantum dot 5 of the present embodiment is a quantum dot with edge luminescence.

[0105] In the above-described method for producing quantum dots according to the present embodiment, Cu may be added when generating the AgGaSe core or the AgGaS core.

[0106] As the raw material of Cu, an organic copper compound or an inorganic copper compound is used. Although not particularly limited, for example, copper acetate: Cu(OAc) can be used. 2 、Copper nitrate: Cu(NO 3 ) 2 , Copper chloride can be used as halogenide: CuCl 2 , Copper bromide: CuBr 2 , Silver iodide: CuI2 As carbamate, copper diethyldithiocarbamate can be used: Cu(SC(=S)N(C 2 H 5 ) 2 ) 2 , Copper dimethyl dithiocarbamate: Cu(SC(=S)N(CH 3 ) 2 ) 2 wait.

[0107] 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 the Cu raw material solution.

[0108] When the nucleus is generated, it is considered that Cu plays a role as a catalyst. That is, according to the results of TEM-EDX analysis, it is difficult to quantify Cu. In addition, in XRD, the same results can be obtained regardless of whether Cu is added. Therefore, it is speculated that Cu plays a role as a catalyst rather than being dissolved in the elements constituting the nucleus.

[0109] During nucleation, the addition of Cu can increase the quantum yield (QY) to the same level or higher than that without Cu addition, and can reduce the fluorescence half-value width to the same level or lower. Depending on the application of quantum dots, better results can be obtained by adding Cu. Although not particularly limited Figure 1 The uses of quantum dots 5 are shown, but several specific examples are listed below.

[0110] Figure 2 Schematic diagram of an LED device using quantum dots of this embodiment. Figure 2 As shown, the storage container 2 is composed of: a storage container 2 having a bottom surface 2a and a side wall 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 the light emitted by the LED chip 3 is emitted from the storage container 2, that is, the opposite direction to the bottom surface 2a relative to the LED chip 3.

[0111] The LED chip 3 may be disposed on a base wiring substrate (not shown) that constitutes the bottom portion of the storage container 2. As the base substrate, for example, a structure in which a wiring pattern is formed on a base material such as glass epoxy resin can be suggested.

[0112] 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 of a P-type semiconductor layer and an N-type semiconductor layer connected by PN. Figure 2As shown, the fluorescent layer 4 is formed of a resin 6 in which a large number of quantum dots 5 are dispersed.

[0113] 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 (K 2 SiF 6 :Mn 4+ ) red phosphor, etc., but the material is not particularly limited.

[0114] The resin 6 constituting the fluorescent layer 4 is not particularly limited, and polypropylene (PP), polystyrene (PS), acrylic resin (Acrylic resin), methacrylate resin (Methacrylate), MS resin, polyvinyl chloride (PVC), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethylpentene, liquid crystal polymer, epoxy resin (Epoxy resin), silicone resin (Silicone resin) or a mixture thereof may be used.

[0115] 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 as shown. Figure 3 As shown in FIG. 1 , 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.

[0116] like Figure 3 As shown, a plurality of LED devices 20 are supported by a support body 52. ​​Each LED device 20 is arranged at a predetermined interval. Each LED device 20 and the support body 52 form a backlight 55 for a display unit 54. The support body 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 .

[0117] 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.

[0118] 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 a film. Such a sheet or a film can be incorporated into a backlight device, for example.

[0119] Example

[0120] Hereinafter, the effects of the present invention will be described by way of examples of the present invention and comparative examples. In addition, the present invention is not limited to the following examples at all.

[0121] <Raw materials>

[0122] In the experiment, the following raw materials were used to synthesize quantum dots composed of a core / shell structure of AgGaSe / ZnS.

[0123] (Solvent)

[0124] Oleylamine: manufactured by Kao Co., Ltd.

[0125] Dodecanethiol: manufactured by Kao Corporation

[0126] (Silver raw material)

[0127] Silver acetate: manufactured by Aldrich Corporation

[0128] (Gallium raw materials)

[0129] Gallium acetylacetonate: Made by Tokyo Chemical Industry Co., Ltd.

[0130] (selenium)

[0131] Selenium: Shinko Chemical Industry Co., Ltd.

[0132] (Zinc)

[0133] Zinc acetate: manufactured by KISHIDA Chemical Co., Ltd.

[0134] Zinc bromide: manufactured by KISHIDA Chemical Co., Ltd.

[0135] (Sulfur raw materials)

[0136] Sulfur: manufactured by KISHIDA Chemical Co., Ltd.

[0137] <Measurement equipment>

[0138] Fluorescence spectrometer: F-2700 manufactured by JASCO Corporation

[0139] Quantum yield measurement device: QE-1100 manufactured by Otsuka Electronics Co., Ltd.

[0140] Scanning electron microscope (SEM): SU9000 manufactured by Hitachi Ltd.

[0141] X-ray diffraction device (XRD): D2 PHASER manufactured by Bruker

[0142] [Example 1]

[0143] In a 100 mL reaction container, 0.5 ml of a 0.2 M solution of silver acetate: Ag(OAc) dissolved in oleylamine: OLAm, and gallium acetylacetonate: Ga(acac) were placed. 3 36.7 mg, oleylamine: OLAm20.0 mL, dodecanethiol: DDT 2.0 ml. Then, under inert gas (N 2 ) atmosphere while stirring and heating to dissolve the raw materials.

[0144] The 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 mixed solvent of dodecanethiol:DDT and oleylamine:OLAm at a volume ratio of 5:2 was added. Then, the temperature was raised from 150° C. to 320° C. and stirred for a total of 10 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0145] The obtained reaction solution was centrifuged at 5500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene, and after adding ethanol, it was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. Then, the precipitate was redispersed in 10.0 ml of dodecanethiol: DDT. In addition, 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 A.

[0146] The dispersion was placed in a 100 mL reaction container and stirred under an inert gas (N 2 ) atmosphere for 10 minutes at 270°C, and 0.15 ml of a 0.4 M solution of sulfur (S) dissolved in dodecanethiol (DDT) and gallium acetylacetonate (Ga(acac)) were added dropwise 5 times every 10 minutes. 3 The obtained reaction solution was cooled to room temperature.

[0147] 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. 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.

[0148] The dispersion was placed in a 100 mL reaction container and stirred under an inert gas (N 2 ) atmosphere at 180°C for 10 minutes, and zinc bromide was added dropwise 5 times every 10 minutes: ZnBr 2 0.1 ml of a 0.2 M solution obtained by dissolving sulfur in dodecanethiol:DDT and 0.1 ml of a 0.4 M solution obtained by dissolving sulfur:S in dodecanethiol:DDT. Then, the obtained reaction solution was cooled to room temperature.

[0149] <Experiments on fluorescence half-value width and quantum yield>

[0150] The QD dispersion solution was measured by a fluorescence spectrometer and a quantum efficiency measurement system. The results are as follows: Figure 6 As shown in the figure, the fluorescence wavelength is 637.5nm, the fluorescence half-value width is 32.11nm, 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 Figure 5 It is represented as C in the text.

[0151] <Analysis results of X-ray diffraction (XRD) equipment>

[0152] 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. From this result, it can be confirmed that the XRD peaks of A to B are shifted to the high-angle side. In this synthesis process, the AgGaSe obtained as the core 2 (Sample of A) and the sample obtained by adding Ga and S is B. In addition, with respect to the sample of B obtained here, the sample obtained by adding Zn and S is C. In this synthesis process, it can also be confirmed that the XRD peaks from B to C are further shifted to the high angle side. From the shift of such peaks, it can be inferred that Ag contained in the core does not diffuse into the shell, and can cover the shell containing a large amount of Zn.

[0153] <TEM-EDX analysis results>

[0154] The results (observation images) of the TEM-EDX analysis of the quantum dots of Example 1 are shown in 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). Fig. 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 7 The observation image on the right side is the analysis result of Ag+Zn. According to the experimental results, Se and S exist separately, specifically, S exists around Se. In addition, it can be seen that Ag and Zn exist separately, specifically, Zn exists around Ag. It can be seen that Se and Ag are mainly contained in the core, and S and Zn are mainly contained in the shell. In this way, it is possible to suppress the diffusion of components contained in the core to the shell, and similarly, it is possible to suppress the diffusion of components contained in the shell to the core.

[0155] [Example 2]

[0156] The same manufacturing operation as in Example 1 was followed, but the same operation was performed until GaS coating, and the operation of post-adding Zn to the obtained particles was performed 9 times. The quantum dot dispersion solution was measured by a fluorescence spectrometer and a quantum efficiency measurement system. As a result, the following can be obtained: 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%.

[0157] <High-resolution STEM results>

[0158] The results of high-resolution STEM analysis of the quantum dots in Example 2 are shown in 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 schematic diagram of (a). Confirm Figure 8 When the particles are crystalline, the crystal lattice can be confirmed from the whole 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.

[0159] <TEM-EDX analysis results>

[0160] The results (observation images) of the TEM-EDX analysis of the quantum dots of Experimental Example 2 are shown in FIG. Fig. 9 . Fig. 9 (a) is a photograph of the TEM-EDX analysis results (Ag+Zn) in Example 2. Fig. 9 (b) is Fig. 9Partial schematic diagram of (a). Fig. 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 suppress the diffusion of components contained in the core to the shell, and similarly, can suppress the diffusion of components contained in the shell to the core.

[0161] <Measurement results of Zn content>

[0162] Fig.10 The figure shows the results of analyzing the amount of Zn by TEM-EDX. Fig.10 (a) is a photograph of the TEM-EDX analysis results (Zn) in Example 1 and Comparative Example, Fig.10 (b) is Fig.10 Partial schematic diagram of (a). Fig.10 The observation image on the left side is Comparative Example 1. Fig.10 The observation image on the right side is Example 1. Comparative Example 1 is different from the above-mentioned experimental example. Figure 4 In the process of the central figure, the first layer of the shell is coated with oleylamine solvent. Figure 4 In the process of the right figure, Zn is added later. On the other hand, the embodiment is the above-mentioned experimental example 1, that is, Figure 4 Shown are the fabrication steps to generate quantum dots.

[0163] according to Fig.10 The experimental results shown confirmed that Example 1 contained a larger amount of Zn on the surface of the core than Comparative Example 1, and that GaS and ZnS could be appropriately coated on the surface of AgGaSe.

[0164] The amount of Zn contained in the quantum dots of the above-mentioned Comparative Example 1, Example 1 and Example 2 was measured, and the amount of Zn contained in Comparative Example 1 was about 1%, the amount of Zn contained in Example 1 was about 5%, and the amount of Zn contained in Example 2 was about 10%. It can be seen that the amount of Zn contained in Examples 1 and 2 was increased by several times to about 10 times compared with Comparative Example 1. In addition, the amount of Zn contained in Example 2 was doubled compared with Example 1. This is because the number of Zn post-addition steps was increased in Example 2.

[0165] [Example 3]

[0166] In a 100 mL reaction container, 1.8 ml of a 0.2 M solution of silver acetate: Ag(OAc) dissolved in oleylamine: OLAm and 1.8 ml of copper acetate: Cu(OAc) were placed. 2 Dissolve in oleylamine: OLAm to obtain a 0.2M solution 0.2 ml, acetylacetonate gallium: Ga(acac) 3 0.2644 mg, oleylamine: OLAm20.0 mL, dodecanethiol: DDT 4.0 ml. Then, under inert gas (N 2) atmosphere while stirring and heating to dissolve the raw materials.

[0167] The solution was dissolved at 150°C for 10 minutes, and 1.43 ml of a 0.7 M solution obtained by dissolving selenium:Se in a mixed solvent of dodecanethiol:DDT and oleylamine:OLAm at a volume ratio of 5:2 was added. Then, the temperature was raised from 150°C to 320°C, and stirring was performed for a total of 20 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0168] The obtained 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. Then, the precipitate was redispersed in 10.0 ml of dodecanethiol:DDT.

[0169] The dispersion was placed in a 100 mL reaction container and stirred under an inert gas (N 2 ) atmosphere at 270°C for 5 minutes, and mixed 0.25 ml of a 0.8 M solution obtained by dissolving sulfur: S in dodecanethiol: DDT, and acetylacetonate gallium: Ga(acac) 3 Dissolve in oleyl alcohol:OLOH to obtain 1.3 ml of a 0.1 M solution. Heat for a total of 60 minutes. Then, cool the obtained reaction solution to room temperature.

[0170] 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.

[0171] The dispersion was placed in a 100 mL reaction vessel and heated under an inert gas (N 2 ) atmosphere at 200°C for 5 minutes, and mix the zinc bromide: ZnBr 2 2.0 ml of a 0.8 M solution obtained by dissolving sulfur in dodecanethiol:DDT and 2.0 ml of a 0.8 M solution obtained by dissolving sulfur:S in dodecanethiol:DDT were added dropwise at a rate of 0.4 ml every 10 minutes. The heating was continued for a total of 120 minutes. The resulting reaction solution was cooled to room temperature.

[0172] The QD dispersion solution was measured by a fluorescence spectrometer. As a result, 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% were obtained.

[0173] [Example 4]

[0174] In a 300 mL reaction container, 5.4 ml of a 0.2 M solution of silver acetate: Ag(OAc) dissolved in oleylamine: OLAm, and gallium acetylacetonate: Ga(acac) were placed.3 0.88092g, oleylamine: OLAm120.0mL, dodecanethiol: DDT 11ml. Then, under inert gas (N 2 ) atmosphere while stirring and heating to dissolve the raw materials.

[0175] The solution was dissolved at 150°C for 15 minutes, and 4.29 ml of a 0.7 M solution obtained by dissolving selenium:Se in a mixed solvent of dodecanethiol:DDT and oleylamine:OLAm in a volume ratio of 5:2 was added. Then, the temperature was raised from 150°C to 320°C, and stirring was performed for a total of 25 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0176] The obtained 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 precipitate was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was redispersed with toluene again, ethanol was added, and the precipitate was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. Then, the precipitate was redispersed in 60.0 ml of dodecanethiol: DDT.

[0177] The dispersion was placed in a 300 mL reaction container and stirred under an inert gas (N 2 ) atmosphere at 270°C for 5 minutes, mixed with 0.1 ml of a 0.8 M solution of sulfur: S dissolved in dodecanethiol: DDT, and heated for 20 minutes. Then, mixed with 1.2 ml of a 0.8 M solution of sulfur: S dissolved in dodecanethiol: DDT and gallium acetylacetonate: Ga(acac) 3 Dissolve 6.0 ml of a 0.1 M solution obtained by dissolving in oleyl alcohol:OLOH, and add dropwise 5 times at 1.44 ml every 10 minutes. Heat for a total of 50 minutes. Then, cool the resulting reaction solution to room temperature.

[0178] Toluene, ethanol and methanol 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 87.5 ml of octadecene: ODE and 10 ml of trioctylphosphine: TOP.

[0179] The dispersion was placed in a 300 mL reaction vessel and heated under an inert gas (N 2 ) atmosphere at 240°C for 5 minutes, and mix zinc acetate: Zn(OAc) 2 10 ml of a 0.8 M solution of trioctylphosphine:TOP and oleic acid:OLAc in a volume ratio of 1:1 was dissolved, 6.7 ml of octadecene:ODE, 2.3 ml of trioctylphosphine:TOP, 1.0 ml of dodecanethiol:DDT, and hydrogen chloride:HCl were dissolved in ethyl acetate:C 4 H8 O 2 0.4 ml of a 4N solution was added dropwise in 8 portions at a rate of 2.25 ml every 10 minutes. The heating was continued for a total of 80 minutes. The resulting reaction solution was cooled to room temperature.

[0180] The QD dispersion solution was measured by a fluorescence spectrometer. As a result, 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% were obtained.

[0181] [Example 5]

[0182] In a 100 mL reaction container, 0.45 ml of a 0.2 M solution of silver acetate: Ag(OAc) dissolved in oleylamine: OLAm, and gallium acetylacetonate: Ga(acac) were placed. 3 0.0734 g, 10.0 mL of oleylamine: OLAm, 0.917 ml of dodecanethiol: DDT, and 0.0643 ml of a 0.7 M solution obtained by dissolving selenium: Se in a mixed solvent of dodecanethiol: DDT and oleylamine: OLAm at a volume ratio of 1:1. Then, under an inert gas (N 2 ) atmosphere while stirring and heating to dissolve the raw materials.

[0183] The 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.

[0184] 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. The precipitate was redispersed with toluene, and ethanol was added, and the mixture was centrifuged at 7500 rpm for 3 minutes to obtain a precipitate. The precipitate was then redispersed in 5.0 ml of dodecanethiol:DDT. The precipitate was centrifuged at 5500 rpm for 3 minutes to obtain a precipitate.

[0185] The dispersion was placed in a 100 mL reaction vessel and heated under an inert gas (N 2 ) atmosphere at 240°C for 3 minutes, and mix the zinc bromide: ZnBr 2 Dissolve 2 ml of a 0.2 M solution of dodecanethiol:DDT and 0.53 ml of trioctylphosphine:TOP, and add dropwise 3 times at 0.506 ml every 10 minutes. Heat for a total of 30 minutes. Cool the resulting reaction solution to room temperature.

[0186] The QD dispersion solution was measured by a fluorescence spectrometer. As a result, optical characteristics of a fluorescence wavelength of 540.5 nm and a fluorescence half-value width of 39.0 nm were obtained.

[0187] [Comparative Example 2]

[0188] In a 100 mL reaction container, 1.8 ml of a 0.2 M solution of silver acetate: Ag(OAc) dissolved in oleylamine: OLAm and 1.8 ml of copper acetate: Cu(OAc) were placed. 2 Dissolve in oleylamine: OLAm to obtain a 0.2M solution 0.2 ml, acetylacetonate gallium: Ga(acac) 3 0.2644 mg, oleylamine: OLAm20.0 mL, dodecanethiol: DDT 4.0 ml. Then, under inert gas (N 2 ) atmosphere while stirring and heating to dissolve the raw materials.

[0189] The solution was dissolved at 150°C for 10 minutes, and 1.43 ml of a 0.7 M solution obtained by dissolving selenium:Se in a mixed solvent of dodecanethiol:DDT and oleylamine:OLAm at a volume ratio of 5:2 was added. Then, the temperature was raised from 150°C to 320°C and stirred for a total of 20 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0190] The obtained 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. Then, the precipitate was redispersed in 10.0 ml of dodecanethiol:DDT.

[0191] The dispersion was placed in a 100 mL reaction vessel and heated under an inert gas (N 2 ) atmosphere for 5 minutes at 270°C, and 0.25 ml of a 0.8 M solution of sulfur: S dissolved in dodecanethiol:DDT was mixed. After heating for 20 minutes, the obtained reaction solution was cooled to room temperature.

[0192] 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.

[0193] The dispersion was placed in a 100 mL reaction vessel and heated under an inert gas (N 2 ) atmosphere at 200°C for 5 minutes, and mix the zinc bromide: ZnBr 2 2.0 ml of a 0.8 M solution obtained by dissolving sulfur in dodecanethiol:DDT and 2.0 ml of a 0.8 M solution obtained by dissolving sulfur:S in dodecanethiol:DDT were added dropwise at a rate of 0.4 ml every 10 minutes. The heating was continued for a total of 120 minutes. The resulting reaction solution was cooled to room temperature.

[0194] The QD dispersion solution was measured by a fluorescence spectrometer. As a result, 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% were obtained.

[0195] <About the formation of shelled quantum dots by cation exchange>

[0196] 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. Fig.11 (a) and (b) are the fluorescence (Photoluminescence: PL) spectra in Example 3 and Comparative Example 2. Fig.11 (b) is to Fig.11 An enlarged view of a portion of (a).

[0197] like Fig.11 As shown in (b), the emission spectrum of Comparative Example 2 can be confirmed near the short wavelength of 500-550nm compared with Example 3. It is speculated that this is because when ZnS raw material as a shell is added in Comparative Example 2 in order not to cover GaS, Zn and Ag, Cu, Ga, etc., which are cationic species of the core, are exchanged for cations.

[0198] On the other hand, it can be seen that Example 3 can suppress short-wavelength light emission compared with Comparative Example 2 by adding the ZnS raw material after GaS coating.

[0199] Therefore, it is inferred that the Zn added later did not diffuse into the core through the coated GaS.

[0200] 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 inferred that Ga and Zn undergo cation exchange or anion solid solution.

[0201] <About nuclear band-edge luminescence>

[0202] EDX analysis was performed on the core of Example 3. The experimental results are shown in Fig.12 Middle (a). Fig.12 (c) is a partial schematic diagram of (a). Fig.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. Fig.12 (b) is the fluorescence (Photoluminescence: PL) spectrum of the core of Example 3. Fig.12 As shown in (b), it can be seen that the fluorescence half-value width of the emission spectrum is narrow.

[0203] It can be seen from this example that the core monomer will also emit light with an edge.

[0204] <About the Catalytic Effect of Cu>

[0205] Although embodiment 3 is to carry out the addition of Cu when generating core, in the result of TEM-EDX analysis, the correct quantification 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 constituting core.

[0206] Industrial Applicability

[0207] According to the present invention, for example, quantum dots showing high-brightness green fluorescence 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 characteristics can be obtained in each device.

[0208] 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 thereof are incorporated herein in their entirety.

Claims

1. A method for manufacturing quantum dots, It is characterized in that include: A step of generating a core containing at least Ag, Ga, S or Ag, Ga, Se; as well as A step of coating the surface of the core with a shell, In the step of coating the shell, GaS is coated on the surface of the core and then Zn is added to coat the core with ZnS.

2. The method for producing quantum dots according to claim 1, It is characterized in that After being coated with GaS, Ga and Zn undergo cation exchange to form ZnS.

3. The method for producing quantum dots according to claim 1 or 2, It is characterized in that Cu is added when the core is generated.

4. The method for producing quantum dots according to claim 1 or 2, It is characterized in that The core and the shell do not contain Cd and In.

5. The method for producing quantum dots according to claim 1 or 2, It is characterized in that As the Ga raw material, gallium acetylacetonate (Ga(acac) 3 ).

6. A quantum dot, It is characterized in that A core containing at least Ag, Ga, S or Ag, Ga, Se and a shell covering the surface of the core; The shell has at least Zn; GaS or GaSe is contained between the core and the shell composed of ZnS, The fluorescence characteristics show a fluorescence half-value width below 35nm and a fluorescence quantum yield above 70%.

7. The quantum dot according to claim 6, It is characterized in that The core and the shell do not contain Cd and In.

8. The quantum dot according to claim 6 or 7, It is characterized in that The fluorescence wavelength is in the range of 400nm to 700nm.

9. The quantum dot according to claim 6 or 7, It is characterized in that Nuclear monomers show band-edge luminescence.

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