Quantum dot, and production method of the same

Abstract

To provide a chalcopyrite-based quantum dot narrow in a fluorescence half-value width, high in a fluorescence quantum yield, and containing no Cd.SOLUTION: A quantum dot comprises a ZnAgInxGa1-xSySe1-y (0≤x<1, 0≤y≤1) based compound, where fluorescence characteristics of a fluorescence half-value width of 33 nm or less, and a fluorescence quantum yield of 70% or more are exhibited in a green wave length region to a red wave length region, the quantum dot is a core shell structure comprising a core, and a shell covering the shell, and Z is included in the shell.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to cadmium-free quantum dots and methods for producing the same. [Background technology]

[0002] Quantum dots are inorganic nanoparticles composed of thousands to tens of thousands of atoms and with diameters of several to tens of nanometers. Quantum dots emit fluorescence and are also called fluorescent nanoparticles because they are nanometer-order in size, semiconductor nanoparticles because their composition is derived from semiconductor materials, or nanocrystals because they have a specific crystalline structure.

[0003] Quantum dots consist of positively charged metal atoms and negatively charged non-metallic or metalloid atoms, which are bonded together by either ionic or covalent bonds, depending on the combined properties of the metal and metalloid atoms.

[0004] Quantum dots can vary their emission wavelength depending on their particle size and composition. Quantum dot performance can be measured by their fluorescence quantum yield (QY) and full width at half maximum (FWHM).

[0005] One of the properties of quantum dots is photoluminescence. Quantum dots can absorb wavelengths in a specific wavelength range and emit light by converting them into other wavelengths in a specific range. Furthermore, the absorption and emission wavelengths can be controlled by the structure, composition, and size of the quantum dots, and these characteristics can be utilized for a variety of purposes.

[0006] For example, when quantum dots are used as wavelength conversion materials in the visible light region, one of their characteristics is that they can express a wide range of colors, i.e., a wide color gamut. In realizing a wide color gamut using quantum dots in the visible light region, the important optical properties are the fluorescence quantum yield and the fluorescence half-width.

[0007] Previously, highly efficient quantum dots mainly contained cadmium (Cd). Cd-containing quantum dots have the advantages of high fluorescence quantum yield and narrow fluorescence half-width. However, due to the toxicity of Cd, their use is restricted in various countries, which has been a major barrier to their practical application.

[0008] In response to this, many studies are being conducted on the development of quantum dots that do not contain Cd. For example, the following patent documents describe AIS or AIGS quantum dots or AISe or AIGSe quantum dots that contain Ag, In, and S, or Ag, In, Ga, and S, or Ag, In, and Se, or Ag, In, Ga, and Se. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2017-025201 [Patent Document 2] Japanese Patent Application Publication No. 2018-039971 [Patent Document 3] Japanese Patent Application Laid-Open No. 2018-044142 [Patent Document 4] Japanese Patent Application Laid-Open No. 2018-141141 [Patent Document 5] WO2018 / 159699 [Non-patent literature]

[0010] [Non-Patent Document 1] NPG Asia Materials volume 10. 2018, pp713-726 [Non-patent document 2] ACS Publications 2018,10,49,41844-41855 [Non-patent document 3] ACS Publications Nano Mater. 2020, 3, 3275-3287 [Non-patent document 4] The Journal of Physical Chemistry Letters; Ligand-Induced Luminescence Transformation in AgInS2 Nanoparticles: From Defect Emission to Band-Edge Emission Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, although research and development of Cd-free chalcopyrite-based quantum dots is progressing, none of the quantum dots has achieved the performance required to replace Cd-based quantum dots in terms of fluorescence half-width and fluorescence quantum yield.

[0012] The present invention has been made in view of the above points, and has an object to provide Cd-free chalcopyrite quantum dots that have a narrow fluorescence half-width and a high fluorescence quantum yield.

[0013] Another object of the present invention is to provide a method for producing quantum dots that synthesizes the quantum dots in a manner that allows for mass production. [Means for solving the problem]

[0014] The quantum dots of the present invention are ZnAgIn x Ga 1-x S y Se 1-yThe quantum dots are of the system (0≦x<1, 0≦y≦1) and exhibit fluorescent properties in the green to red wavelength range, with a fluorescence half-width of 33 nm or less and a fluorescence quantum yield of 70% or more, and are characterized in that the quantum dots have a core-shell structure consisting of a core and a shell covering the core, and Zn is contained in the shell.

[0015] The method for producing quantum dots of the present invention is x Ga 1-x S y Se 1-y The system (0≦x<1, 0≦y≦1) is characterized in that after a core is formed, a shell containing Zn is formed to cover the core, and quantum dots are synthesized that exhibit fluorescent properties in the green to red wavelength range, with a fluorescence half-width of 33 nm or less and a fluorescence quantum yield of 70% or more. [Effects of the Invention]

[0016] According to the quantum dots of the present invention, quantum dots having uniform composition, particle shape and size can be synthesized, and therefore the fluorescence half-width can be narrowed and the fluorescence quantum yield can be increased.

[0017] Furthermore, according to the quantum dots of the present invention, quantum dots having a desired emission wavelength depending on the application can be synthesized.

[0018] Furthermore, according to the quantum dots of the present invention, quantum dots with narrow half-widths can be synthesized with emission wavelengths suited to the purpose, and therefore, when used as wavelength conversion materials, it is possible to improve the color gamut.

[0019] Furthermore, according to the method for producing quantum dots of the present invention, it is possible to synthesize quantum dots that have a narrow fluorescence half-width and do not contain Cd by a method that allows for mass production. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of a quantum dot according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram of an LED device using quantum dots according to an embodiment of the present invention. [Figure 3] 1 is a vertical cross-sectional view of a display device using an LED device according to an embodiment of the present invention. [Figure 4] 1 shows a photoluminescence (PL) spectrum of AgInGaS in Example 1. [Figure 5] 10 is a PL spectrum of AgInGaS in Example 2. [Figure 6] 10 is a PL spectrum of AgInGaS in Example 3. [Figure 7] 10 is a PL spectrum of AgInGaS in Example 4. [Figure 8] 10 is a PL spectrum of AgInGaS in Example 5. [Figure 9] 10 is a PL spectrum of AgInGaS in Example 6. [Figure 10] 10 is a PL spectrum of AgInGaS in Example 7. [Figure 11] 13 is a PL spectrum of AgInGaS in Example 11. [Figure 12] 13 is a PL spectrum of AgInGaS in Example 12. [Figure 13] 13 is a PL spectrum of AgInGaS in Example 13. [Figure 14] 13 is a PL spectrum of ZnAgInGaS in Example 14. [Figure 15] 10 is a PL spectrum of ZnAgGaSeS in Example 15. [Figure 16] 10 is a PL spectrum of ZnAgGaSeS in Example 17. [Figure 17] 10 is a PL spectrum of ZnAgGaSeS in Example 18. [Figure 18] 13 is a PL spectrum of ZnAgInGaSeS in Example 19. [Figure 19] 10 is a PL spectrum of ZnAgGaSeS in Example 20. [Figure 20]1 shows a PL spectrum of ZnAgInGaS in Comparative Example 1. [Figure 21] 10 is a scanning electron microscopy (SEM) photograph of AgInGaS in Example 7. [Figure 22] 10 is a photograph showing the results of TEM-EDX analysis in Example 15. [Figure 23] FIG. 23 is a partial schematic view of FIG. 22. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. The present invention is not limited to the following embodiment, and can be practiced in various modifications within the scope of the gist. In this specification, the notation "to" means that the lower limit and upper limit are included.

[0022] 1A is a schematic diagram of a quantum dot according to this embodiment. The quantum dot 5 shown in FIG. 1A is a nanocrystal that does not contain Cd.

[0023] In this embodiment, the quantum dots 5 are AgIn x Ga 1-x S y Se 1-y system, or ZnAgIn x Ga 1-x S y Se 1-y The quantum dots 5 are quantum dots made of the system (0≦x<1, 0≦y≦1). The quantum dots 5 in this embodiment are preferably nanocrystals containing at least silver (Ag), gallium (Ga), and sulfur (S), or silver (Ag), gallium (Ga), and selenium (Se), but not cadmium (Cd). The quantum dots 5 may also contain Ag, Ga, and S, or Ag, Ga, and Se, and further indium (In) or zinc (Zn).

[0024] Here, "nanocrystal" refers to nanoparticles having a particle size of about several nm to several tens of nm. In this embodiment, a large number of quantum dots 5 can be produced with a substantially uniform particle size.

[0025] The ratio of Ag to Ga contained in the quantum dots 5 is preferably in the range of Ag / Ga=0.05 to 10. Furthermore, the ratio Ag / Ga is more preferably in the range of 0.05 to 5, and even more preferably in the range of 0.1 to 3.

[0026] The ratio of Zn to Ga that can be contained in the quantum dots 5 is preferably in the range of Zn / Ga = 0.1 to 10. The ratio Zn / Ga is more preferably in the range of 0.1 to 5. By controlling this ratio, it is possible to adjust the emission wavelength.

[0027] In this embodiment, the fluorescent wavelength can be adjusted from the green wavelength region to the red wavelength region. In particular, in this embodiment, the fluorescent wavelength can be appropriately adjusted within the range of 400 nm to 700 nm. In this embodiment, the fluorescent wavelength can also be adjusted within the range of 500 nm to 650 nm.

[0028] As shown in Figure 1A, it is preferable that a large number of organic ligands 11 are coordinated to the surface of the quantum dots 5. This makes it possible to suppress aggregation of the quantum dots 5 and to achieve the desired optical properties. There are no particular limitations on the ligands that can be used in the reaction, but the following ligands are representative examples:

[0029] (1) Aliphatic primary amines 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 21NH2, Octylamine: C8H 17 NH2 (2) Fatty acid type 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: CH 19 COOH, octanoic acid: CH 15 COOH (3) Thiol-based Octadecanethiol: C 18 H 37 SH, hexanedecanethiol: C 16 H 33 SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, Octanethiol: CH 17 SH (4) Phosphine Trioctylphosphine: (C8H 17 )3P, triphenylphosphine: (C6H5)3P, tributylphosphine: (C4H9)3P (5) Phosphine oxides Trioctylphosphine oxide: (C8H 17 )3P=O, triphenylphosphine oxide: (C6H5)3P=O, tributylphosphine oxide: (C4H9)3P=O

[0030] The following describes the characteristic features of the quantum dots 5 of this embodiment. The quantum dots 5 of this embodiment exhibit fluorescent properties, with a fluorescence half-width of 45 nm or less and a fluorescence quantum yield of 35% or more in the green to red wavelength range.

[0031] Here, "fluorescence half-width" refers to the full width at half maximum, which indicates the spread of the fluorescence wavelength at half the intensity of the peak fluorescence intensity in the fluorescence spectrum. The fluorescence half-width is preferably 35 nm or less. The fluorescence half-width is more preferably 30 nm or less. The fluorescence half-width is even more preferably 25 nm or less. In this way, the fluorescence half-width can be narrowed, thereby improving the color gamut.

[0032] The fluorescence quantum yield of the quantum dots 5 of this embodiment is more preferably 40% or more, even more preferably 60% or more, even more preferably 70% or more, and most preferably 80% or more. Thus, this embodiment can increase the fluorescence quantum yield of the quantum dots.

[0033] In this way, in this embodiment, AgIn x Ga 1-x S y Se 1-y system, or ZnAgIn x Ga 1-x S y Se 1-y In quantum dots of the system (0≦x<1, 0≦y≦1), the fluorescence half-width can be narrowed in the green to red wavelength region, and the fluorescence quantum yield can be increased.

[0034] In this embodiment, the fluorescence wavelength can be freely controlled to approximately 400 nm or more and 700 nm or less. The quantum dots 5 in this embodiment are solid solutions based on Ag, Ga, In, and Zn as cation raw materials and Se and S as anion raw materials. In this embodiment, the fluorescence wavelength can be controlled from blue to green to red by appropriately adjusting the particle size and composition of the quantum dots 5. Therefore, for blue emission, the fluorescence wavelength is preferably 400 nm or more and 480 nm or less, more preferably 410 nm or more and 470 nm or less, and even more preferably 420 nm or more and 460 nm or less. For green emission, the fluorescence wavelength is preferably 500 nm or more and 560 nm or less, more preferably 510 nm or more and 550 nm or less, and even more preferably 520 nm or more and 540 nm or less. For red emission, the fluorescence wavelength is preferably 600 nm or more and 660 nm or less, more preferably 610 nm or more and 650 nm or less, and even more preferably 620 nm or more and 640 nm or less.

[0035] In this embodiment, as described above, the fluorescent wavelength can be controlled to 400 nm or more and 700 nm or less, but as a wavelength conversion material in the visible light region, green or red light emission is preferred.

[0036] Here, chalcopyrite is generally a material that emits defect light with a fluorescence half-width of 45 to 80 nm. In contrast, the quantum dots 5 of this embodiment have a narrow fluorescence half-width, a high fluorescence quantum yield, and a fluorescence lifetime that is much shorter than that of defect light. From these characteristics, it is presumed that the quantum dots 5 of this embodiment emit band edge light.

[0037] In particular, quantum dots 5 of this embodiment can be synthesized that have a fluorescence half-width of 30 μm or less, a fluorescence quantum yield of 80% or more, and a fluorescence wavelength in the range of 510 nm to 650 nm. In this way, it is possible to achieve the characteristics of a narrow fluorescence half-width and a high fluorescence quantum yield not only for green fluorescence wavelengths (around 510 to 540 nm) but also for red fluorescence wavelengths (around 610 to 650 nm).

[0038] The quantum dot 5 shown in Figure 1B has a core-shell structure having a core 5a and a shell 5b covering the surface of the core 5a. As shown in Figure 1B, it is preferable that a large number of organic ligands 11 are coordinated to the surface of the quantum dot 5. Furthermore, the quantum dot 5 shown in Figure 1B has a fluorescence half-width of 45 nm or less and a fluorescence quantum yield of 35% or more.

[0039] The core 5a of the quantum dot 5 shown in FIG. 1B is the nanocrystal shown in FIG. 1A. Therefore, the core 5a is preferably formed of a nanocrystal containing Ag, Ga, and S, or Ag, Ga, and Se, but not Cd. The shell 5b, like the core 5a, does not contain cadmium (Cd). The shell 5b may be made of any material, but examples include indium sulfide, gallium sulfide, aluminum sulfide, zinc sulfide, indium selenide, gallium selenide, aluminum selenide, and zinc selenide. In this case, it is preferable to use gallium chloride, gallium bromide, or gallium iodide as the Ga source.

[0040] The shell 5b may be in a state of being solid-solutioned on the surface of the core 5a. In FIG. 1B, the boundary between the core 5a and the shell 5b is shown by a dotted line, but this means that it does not matter whether the boundary between the core 5a and the shell 5b can be confirmed by analysis or not. x Ga 1-x S y Se 1-y In quantum dots of the system (0≦x<1, 0≦y≦1), even if a core-shell structure cannot be confirmed, it can be assumed that the core 5a is coated with the shell 5b due to the inclusion of Zn.

[0041] As with the quantum dots 5 shown in FIG. 1A, the fluorescence wavelength can also be freely controlled to about 400 nm or more and 700 nm or less, or about 500 nm or more and 650 nm or less.

[0042] In this embodiment, a shell coating is not necessarily required because the core alone, consisting of AgGaS, AgGaSe, AgGaInS, or AgGaInSe, emits fluorescence. However, by using a core-shell structure, a further increase in fluorescence quantum yield can be expected while maintaining a narrow fluorescence half-width. Furthermore, fluorescence can be observed whether or not In is included. For example, green fluorescent quantum dots have good luminescence properties when they contain In, but they also emit light even without In, although the fluorescence half-width tends to be somewhat larger. Specifically, luminescence has been confirmed with AgGaS.

[0043] Furthermore, when Zn is used, differences in valence (divalent Zn, monovalent Ag, and trivalent Ga or In) generally result in defective emission, which tends to broaden the fluorescence half-width. However, in this embodiment, as shown in the experiments described below, even when Zn is added later, the fluorescence quantum yield can be increased while the fluorescence half-width remains narrow. In other words, the use of Zn makes it possible to improve the emission characteristics. Next, a method for producing the quantum dots 5 of this embodiment will be described.

[0044] The quantum dot manufacturing method of this embodiment is AgIn x Ga 1-x S y Se 1-y system, or ZnAgIn x Ga 1-x S y Se 1-y The system (0≦x<1, 0≦y≦1) is characterized by the synthesis of quantum dots that exhibit fluorescent properties in the green to red wavelength range, with a fluorescence half-width of 45 nm or less and a fluorescence quantum yield of 35% or more.

[0045] First, in this embodiment, a compound is synthesized in one pot by heating from an organic silver compound, an organic gallium compound, and sulfur or selenium, or from an organic silver compound, an organic indium compound, an organic gallium compound, and sulfur or selenium.

[0046] At this time, AgGaS, AgGaSe, AgGaInS or AgGaInSe is synthesized at a reaction temperature set in the range of 100° C. to 320° C. Note that the reaction temperature is preferably set at a lower temperature of 280° C. or less.

[0047] In this embodiment, an organic silver compound or an inorganic silver compound is used as the Ag raw material, and although not particularly limited, examples thereof include silver acetate (AgOAc), silver nitrate (AgNO), halides such as silver chloride (AgCl), silver bromide (AgBr), and silver iodide (AgI), and carbamates such as silver diethyldithiocarbamate (Ag(SC(=S)N(C2H5)2) and silver dimethyldithiocarbamate (Ag(SC(=S)N(CH3)2).

[0048] In this embodiment, the Ag raw material may be added directly to the reaction solution, or may be dissolved in an organic solvent in advance to a certain concentration and used as the Ag raw material solution.

[0049] In this embodiment, an organic indium compound or an inorganic indium compound is used as a raw material for In. While not particularly limited, examples include indium acetate: In(OAc)3, indium nitrate: InNO3, and indium acetylacetonate: In(acac)3; halides include indium chloride: InCl3, silver bromide: InBr3, and indium iodide: InI3; and carbamates include indium diethyldithiocarbamate: In[(SC(=S)N(C2H5)2]3 and indium dimethyldithiocarbamate: In[(SC(=S)N(CH3)2)]3.

[0050] In this embodiment, an organic indium compound or an inorganic indium compound is used as a Ga source material. Although not particularly limited, examples include gallium acetate: Ga(OAc)3, gallium nitrate: GaNO3, and gallium acetylacetonate: Ga(acac)3; halides include gallium chloride: GaCl3, gallium bromide: GaBr3, and gallium iodide: Ga2I3; and carbamates include gallium diethyldithiocarbamate: Ga[(SC(=S)N(C2H5)2]3.

[0051] In this embodiment, the In source material or Ga source material may be added directly to the reaction solution, or may be dissolved in an organic solvent in advance to prepare a solution of a certain concentration, which may then be used as the In source material solution or Ga source material solution.

[0052] In this embodiment, an organic sulfur compound such as thiol can be used as a raw material for S. For example, octadecanethiol:C 18 H 37 SH, hexanedecanethiol: C 16 H 33 SH, tetradecanethiol: C 14 H 29 SH, dodecanethiol: C 12 H 25 SH, decanethiol: C 10 H 21 SH, Octanethiol: CH 17 SH, etc.

[0053] In particular, when synthesizing AgGaS or AgInGaS, the sulfur source species significantly contributes to the fluorescent properties. In this embodiment, it is preferable to use an S-ODE source in which sulfur is dissolved in octadecene (ODE), a disulfide-based or thiuram-based S source, or S-OLAm / DDT in which S is dissolved in oleylamine and dodecanethiol. Among these, the S-ODE source can achieve a fluorescent half-width of 40 nm or less and a fluorescent quantum yield of 40% or more. However, using a disulfide can achieve even better properties. Examples include diphenyl disulfide, dibenzyl disulfide, isopropyl xanthogen disulfide, and 4,4'-dithiodimorpholine. Furthermore, using a thiuram source can achieve even better fluorescent properties. Examples include thiuram disulfide, dipentamethylene thiuram tetrasulfide, tetraethyl thiuram disulfide, and tetramethyl thiuram disulfide. Alternatively, the S raw material may be a raw material having a structure (-S-)n in which multiple sulfur atoms are linked together, or a raw material having a structure in which nitrogen (NS-), carbon (CS-), etc. are attached to sulfur.

[0054] In this embodiment, an organic selenium compound (organic chalcogen compound) can be used as a raw material for Se. For example, trioctylphosphine selenide (C8H2O5), in which selenium is dissolved in trioctylphosphine, can be used. 17 )3P=Se, or tributylphosphine selenide: (C4H9)3P=Se, in which selenium is dissolved in tributylphosphine, or a solution of selenium dissolved in a high-boiling solvent, such as a long-chain hydrocarbon, such as octadecene, can be used.

[0055] When synthesizing AgGaSe or AgInGaSe, the selenium source species contributes significantly to the fluorescent properties. In particular, a solution (Se-OLAm / DDT) in which Se is dissolved in a mixture of oleylamine and dodecanethiol exhibits excellent luminescence properties. Typical chalcopyrite-based quantum dots exhibit two types of PL spectrum at the initial stage of emission: band-edge PL and defect PL. The PL intensity ratio (band-edge / defect PL) is usually less than 10. Subsequently, as the reaction progresses, the intensity of the defect PL gradually decreases, and the intensity of the band-edge PL often increases accordingly. However, when Se-DDT / OLAm is used as the Se source in this embodiment, a single peak is observed from the initial stage of emission, with the band-edge / defect PL ratio being greater than 10, and almost no peaks considered to be defect PL are observed. Furthermore, the fluorescence lifetime is short, less than 20 ns, until the fluorescence reaches 1 / e, and only peaks other than defect PL are observed at the initial stage of emission.

[0056] In this embodiment, an organic zinc compound or an inorganic zinc compound is used as a raw material for Zn. The organic zinc compound or inorganic zinc compound is a raw material that is stable in air and easy to handle. There are no particular limitations on the structure of the organic zinc compound or inorganic zinc compound, but for example, the organic zinc compound and inorganic zinc compound shown below can be used. As acetate salts, zinc acetate: Zn(OAc)2, zinc nitrate: Zn(NO3)2, and as fatty acid salts, zinc stearate: Zn(OC(=O)C 17 H 35 )2, Zinc oleate: Zn(OC(=O)C 17 H 33 )2, Zinc palmitate: Zn(OC(=O)C 15 H 31 )2, Zinc myristate: Zn(OC(=O)C 13 H 27 )2, Zinc dodecanoate: Zn(OC(=O)C 11 H 23)2, zinc acetylacetonate: Zn(acac)2, as halides, zinc chloride: ZnCl2, zinc bromide: ZnBr2, zinc iodide: ZnI2, as zinc carbamates, zinc diethyldithiocarbamate: Zn(SC(=S)N(C2H5)2)2, zinc dimethyldithiocarbamate: Zn(SC(=S)N(CH3)2)2, zinc dibutyldithiocarbamate: Zn(SC(=S)N(C4H9)2)2, etc. can be used.

[0057] Furthermore, in this embodiment, quantum dots can be obtained in one pot without isolating and purifying the precursor.

[0058] Furthermore, in this embodiment, the synthesized quantum dots exhibit fluorescent properties without undergoing various treatments such as washing, isolation and purification, coating treatment, and ligand exchange.

[0059] However, the fluorescence quantum yield can be further increased by coating the nanocrystal core 5a with a shell 5b, as shown in FIG. 1B.

[0060] Furthermore, after the core-shell structure is formed, the fluorescence quantum yield can be further increased by purifying the compound with a specific solvent, such as trioctylphosphine (TOP).

[0061] In addition, in this embodiment, quantum dots with better luminescence properties can be obtained by centrifuging the synthesized reaction solution.

[0062] In addition, in this embodiment, quantum dots with better luminescence properties can be obtained by mixing toluene, methanol, ethanol, acetone, etc. with the synthesized reaction solution and removing the aggregates by centrifugation.

[0063] In the quantum dot manufacturing method of this embodiment, after forming the initial reaction particles, a predetermined element is added later for synthesis, and at this time, it is preferable that the initial reaction does not contain In. Specifically, the particles formed in the initial reaction are AgGaS or AgGaSe that do not contain In, which have the best light-emitting properties.

[0064] Generally, In is included from the initial stage of the reaction and the In / Ga ratio is adjusted, but the quantum dots of this embodiment are synthesized with as little composition as possible, while suppressing compositional variations. Therefore, it is preferable that In is not included in the initial reaction. As a result, it is presumed that light emission characteristics with a narrow fluorescence half-width can be obtained.

[0065] It is preferable that green fluorescent quantum dots ultimately contain In, and In can be included during the reaction process. However, it is not essential that green fluorescent quantum dots contain In; for example, emission has been confirmed with AgGaS without containing In, although the fluorescence half-width is somewhat broadened.

[0066] Furthermore, in this embodiment, when Zn is incorporated into the quantum dots, it is preferable to add Zn while taking the following points into consideration. First, Zn is not added during the initial reaction but is added in the final step. This is because if Zn is contained inside the particles, defect luminescence may predominate, or only defect luminescence may be observed. Therefore, by adding Zn in the final step, the purpose is to cause a reaction only on the particle surface. Second, Zn is added at a low temperature. Here, low temperature means approximately 150 to 200°C. If the temperature when Zn is added is high, Zn will react all the way to the inside of the particles, which is likely to result in defect luminescence. Therefore, it is preferable to cause the reaction only on the particle surface at a low temperature in order to limit the reaction to the particle surface.

[0067] In this embodiment, when synthesizing AgGaSe, the Se raw material is preferably Se-OLAm / DDT, which can effectively suppress defect luminescence.

[0068] Furthermore, when synthesizing AgGaS, rather than dissolving the commonly used sulfur powder, thiuram-based compounds, particularly tetraethylthiuram disulfide, are preferred as they can provide good luminescence properties.

[0069] The centrifugation process separates large and small particles. Even if the particle size is uniform, the centrifugation process using toluene or ethanol can alter the degree of aggregation due to differences in the surface ligands of the quantum dots by controlling the ratio of toluene and ethanol. The ratio can be controlled at a quantum dot:toluene:ethanol ratio of 1:0.5-2:0.5-2. Methanol can also be used instead of ethanol. As a result, quantum dots with high fluorescence quantum yields and quantum dots with low fluorescence quantum yields can be separated. Then, adding TOP to the separated quantum dots can further improve the fluorescence quantum yield.

[0070] As described above, according to the quantum dot manufacturing method of this embodiment, it is possible to synthesize Cd-free quantum dots that have a narrow fluorescence half-width and a high fluorescence quantum yield in a mass-producible manner.

[0071] The uses of the quantum dots 5 shown in FIG. 1 are not particularly limited, but some specific examples are given below.

[0072] Fig. 2 is a schematic diagram of an LED device using quantum dots according to this embodiment. As shown in Fig. 2, the LED device 1 according to this embodiment comprises a storage case 2 having a bottom surface 2a and a sidewall 2b surrounding the periphery of the bottom surface 2a, an LED chip (light-emitting element) 3 disposed on the bottom surface 2a of the storage case 2, and a fluorescent layer 4 filled in the storage case 2 and sealing the upper surface side of the LED chip 3. Here, the upper surface side refers to the direction in which light emitted from the LED chip 3 is emitted from the storage case 2, and indicates the direction opposite the bottom surface 2a of the LED chip 3.

[0073] The LED chip 3 is disposed on a base wiring substrate (not shown), which may form the bottom surface of the storage case 2. The base substrate may be, for example, a substrate made of glass epoxy resin or the like, on which a wiring pattern is formed.

[0074] The LED chip 3 is a semiconductor element that emits light when a forward voltage is applied, and has a basic configuration in which a P-type semiconductor layer and an N-type semiconductor layer are PN junctioned.

[0075] As shown in FIG. 2, the fluorescent layer 4 is formed from a resin 6 in which a large number of quantum dots 5 are dispersed.

[0076] Furthermore, the resin composition in which the quantum dots 5 of this embodiment are dispersed may contain the quantum dots 5 and a fluorescent material other than the quantum dots 5. The fluorescent material may be a sialon-based material or KSF (K2SiF6:Mn 4+ ) red phosphor, etc., but the material is not particularly limited.

[0077] The resin 6 constituting the fluorescent layer 4 is not particularly limited, but examples thereof include polypropylene (PP), polystyrene (PS), acrylic resin, methacrylic resin, MS resin, polyvinyl chloride (PVC), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethylpentene, liquid crystal polymer, epoxy resin, silicone resin, and mixtures thereof.

[0078] The LED device using quantum dots of this embodiment can be applied to display devices. Fig. 3 is a longitudinal cross-sectional view of a display device using the LED device shown in Fig. 2. As shown in Fig. 3, a 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 disposed on the back side of the display unit 54. Each LED device 20 has a structure in which an LED chip is sealed with a resin in which a large number of quantum dots 5 are diffused, similar to the LED device 1 shown in Fig. 2.

[0079] As shown in Fig. 3, a plurality of LED devices 20 are supported by a support 52. The LED devices 20 are arranged at predetermined intervals. The LED devices 20 and the support 52 together form a backlight 55 for a display unit 54. The support 52 is not particularly limited in shape or material, and may be in the form of a sheet, plate, or case. As shown in Fig. 3, a light diffusion plate 53 or the like may be interposed between the backlight 55 and the display unit 54.

[0080] By applying the quantum dots 5 having a narrow fluorescence half-width in this embodiment to the LED device shown in Figure 2 or the display device shown in Figure 3, it is possible to effectively improve the light-emitting characteristics of the device.

[0081] Furthermore, a 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, for example, a backlight device. [Example]

[0082] The effects of the present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0083] <Raw materials> In the experiment, AgIn x Ga 1-x S y Se 1-y system or ZnAgIn x Ga1-x S y Se 1-y The following raw materials were used to synthesize quantum dots in the system (0≦X<1, 0≦Y≦1). (solvent) Octadecene: Aldrich Oleylamine: Kao Corporation Dodecanethiol: manufactured by Kao Corporation Oleic acid: Lunac OV manufactured by Kao Corporation Trioctylphosphine: manufactured by Hokko Chemical Co., Ltd. (Silver raw material) Silver acetate: Aldrich (Indium raw material) Indium acetate: manufactured by Shinko Chemical Industry Co., Ltd. Indium diethyldithiocarbamate: a synthetic raw material by the inventors (Gallium raw material) Gallium chloride: manufactured by Shinko Chemical Industry Co., Ltd. Gallium acetylacetonate: manufactured by Tokyo Chemical Industry Co., Ltd. (sulfur raw material) Sulfur: Kishida Chemical Co., Ltd. Tetraethylthiuram disulfide: manufactured by Sanshin Chemical Industry Co., Ltd. Dipentamethylenethiuram tetrasulfide: manufactured by Sanshin Chemical Industry Co., Ltd. Isopropyl xanthogen disulfide: manufactured by Sanshin Chemical Industry Co., Ltd. Tetramethylthiuram disulfide: manufactured by Sanshin Chemical Industry Co., Ltd. <Measuring equipment> Fluorescence spectrometer: JASCO F-2700 UV-visible spectrophotometer: Hitachi V-770 Quantum yield measurement device: Otsuka Electronics QE-1100 Scanning electron microscope (SEM): Hitachi SU9000

[0084] [Example 1] A 300 mL reaction vessel was charged with 1.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 3165 mg of gallium acetylacetonate (Ga(acac)), 28.5 mL of oleylamine (OLAm), and 1.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0085] This solution was dissolved at 120°C for 5 minutes, and 1.5 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0086] To the resulting reaction solution, 125.7 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0087] Thereafter, 13.5 ml of a solution obtained by mixing 9 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 4.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, was added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0088] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 539 nm, fluorescence half-width: 35 nm, and fluorescence quantum yield: 49%.

[0089] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 4, the optical properties were as follows: a fluorescence wavelength of 539 nm, a fluorescence half-width of 35.4 nm, and a quantum yield of 75%.

[0090] [Example 2] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0091] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution obtained by dissolving dipentamethylenethiuram tetrasulfide (DPTT) in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0092] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0093] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0094] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 526 nm, fluorescence half-width: 35.5 nm, and quantum yield: 34%.

[0095] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 5, the optical properties were a fluorescence wavelength of 526.5 nm, a fluorescence half-width of 34.8 nm, and a quantum yield of 54%.

[0096] [Example 3] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0097] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution of 4,4'-dithiodimorpholine (DTDM) in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0098] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0099] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0100] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 526 nm, fluorescence half-width: 37.5 nm, and quantum yield: 41%.

[0101] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 6, the optical properties were a fluorescence wavelength of 527.5 nm, a fluorescence half-width of 36.9 nm, and a quantum yield of 56%.

[0102] [Example 4] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0103] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution of isopropyl xanthogen disulfide in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0104] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0105] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0106] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 530 nm, fluorescence half-width: 37 nm, and quantum yield: 40%.

[0107] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 7, the optical properties were as follows: a fluorescence wavelength of 532 nm, a fluorescence half-width of 36.9 nm, and a quantum yield of 65%.

[0108] [Example 5] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0109] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution of tetramethylthiuram disulfide (TMTDS) in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0110] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0111] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0112] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 542 nm, fluorescence half-width: 36.5 nm, and quantum yield: 54%.

[0113] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 8, the optical properties were a fluorescence wavelength of 542 nm, a fluorescence half-width of 36.5 nm, and a quantum yield of 71%.

[0114] [Example 6] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0115] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0116] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0117] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the addition was complete, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0118] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 546 nm, fluorescence half-width: 29.3 nm, and quantum yield: 39%.

[0119] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 9, the optical properties were as follows: a fluorescence wavelength of 548.5 nm, a fluorescence half-width of 30.5 nm, and a quantum yield of 59%.

[0120] [Example 7] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0121] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution obtained by dissolving tetraethylthiuram disulfide in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0122] To the resulting reaction solution, 0.75 ml of a 0.2 M solution obtained by dissolving indium acetate: In(OAc)321.8 mg and sulfur: S in octadecene: ODE was added, and the mixture was heated at 270° C. for 10 minutes with stirring.

[0123] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0124] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 546 nm, fluorescence half-width: 36.5 nm, and quantum yield: 55%.

[0125] The QD dispersion was then washed twice with toluene and ethanol and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 10, the optical properties were a fluorescence wavelength of 546.5 nm, a fluorescence half-width of 36.2 nm, and a quantum yield of 81%.

[0126] [Example 8] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0127] This solution was dissolved at 120°C for 5 minutes, and 1 ml of a 0.2 M solution (S-ODE) obtained by dissolving sulfur (S) in octadecene (ODE) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0128] To the resulting reaction solution, 21.8 mg of indium acetate (In(OAc)3) and 2.25 ml of 0.2 M S-ODE were added, and the mixture was again heated at 270° C. for 10 minutes with stirring.

[0129] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0130] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 523 nm, fluorescence half-width: 36.5 nm, and quantum yield: 25%.

[0131] The QD dispersion was then washed twice with toluene and ethanol, and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer, revealing the following optical properties: a fluorescence wavelength of 522 nm, a fluorescence half-width of 38 nm, and a quantum yield of 46%.

[0132] [Example 9] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0133] This solution was dissolved at 120°C for 5 minutes, and 1 ml of a 0.2 M solution (S-ODE) obtained by dissolving sulfur (S) in octadecene (ODE) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0134] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0135] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, were mixed and added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0136] The resulting reaction solution was measured using a fluorescence spectrometer, and the optical properties were as follows: fluorescence wavelength: 534 nm, fluorescence half-width: 36 nm, and quantum yield: 33%.

[0137] The QD dispersion was then washed twice with toluene and ethanol, and redispersed in TOP. The resulting solution was measured using a fluorescence spectrometer, revealing the following optical properties: a fluorescence wavelength of 534 nm, a fluorescence half-width of 40 nm, and a quantum yield of 45%.

[0138] [Example 10] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 373.4 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.3 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0139] This solution was dissolved at 120°C for 5 minutes, and 0.5 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto. The temperature was then raised from 120°C to 200°C and stirred for a total of 20 minutes. The resulting reaction solution was then cooled to room temperature.

[0140] To the resulting reaction solution, 0.375 ml of a 0.2 M solution obtained by dissolving indium acetate (In(OAc)3) in oleylamine (OLAm) and oleic acid (OLAc) and 1.225 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE) were added, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0141] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) to a molar ratio of Ga:OLAc = 1:1.5 was mixed with 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE). This 4.5 ml solution was added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0142] After that, 3 ml of TOP was added, and the mixture was heated at 200 °C for 10 minutes. The resulting reaction solution was then cooled to room temperature. The mixture was then washed with toluene and ethanol, and the QD dispersion solution was redispersed in toluene. The resulting QD dispersion solution was measured using a fluorescence spectrometer. The optical characteristics were a fluorescence wavelength of 536.5 nm, a fluorescence half-width of 29.4 nm, and a quantum yield of 71%.

[0143] [Example 11] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 391.8 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0144] This solution was dissolved at 200°C for 5 minutes, and 1 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto, and the mixture was heated with stirring for 40 minutes. The resulting reaction solution was then cooled to room temperature.

[0145] To the resulting reaction solution, 0.375 ml of a 0.2 M solution obtained by dissolving indium acetate (In(OAc)3) in oleylamine (OLAm) and oleic acid (OLAc) and 0.375 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE) were added, and the mixture was again heated at 270°C for 10 minutes with stirring.

[0146] The resulting reaction solution was washed with 3 ml of toluene and 30 ml of ethanol, and re-dispersed in 10 ml of OLAm.

[0147] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) to a molar ratio of Ga:OLAc = 1:1.5 was mixed with 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE). This 4.5 ml solution was added dropwise over 50 minutes to the solution being heated with stirring at 270°C. After the completion of the addition, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0148] After that, 3 ml of TOP was added, and the mixture was heated at 200 °C for 10 minutes. The resulting reaction solution was then cooled to room temperature. The mixture was then washed with toluene and ethanol, and the QD dispersion solution redispersed in TOP was measured using a fluorescence spectrometer. As shown in Figure 11, the optical properties obtained were a fluorescence wavelength of 530.5 nm, a fluorescence half-width of 38 nm, and a quantum yield of 86%.

[0149] [Example 12] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 355 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0150] This solution was dissolved at 200°C for 5 minutes, and 0.5 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto. The mixture was then heated at 200°C for 40 minutes with stirring. The resulting reaction solution was then cooled to room temperature.

[0151] To the resulting reaction solution, 0.375 ml of a 0.2 M solution of indium acetate (In(OAc)3) in octadecene (ODE) and oleic acid (OLAc) and 1.125 ml of a 0.2 M solution of sulfur (S) in octadecene (ODE) were added, and the mixture was again heated at 300°C for 10 minutes with stirring.

[0152] Then, a solution containing 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) to a molar ratio of Ga:OLAc = 1:3, 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE), and 0.141 ml of oleylamine (OLAm) was added dropwise over 50 minutes to the solution being heated with stirring at 300 °C. After the addition was complete, the solution was heated with stirring for 20 minutes, and then cooled to room temperature.

[0153] Thereafter, 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE) was added, and the mixture was heated at 200° C. for 30 minutes with stirring, and the resulting reaction solution was cooled to room temperature.

[0154] The reaction solution was then centrifuged at 5,500 rpm for 3 minutes, and the supernatant was collected. 3 ml of TOP was added to the collected supernatant, and the mixture was heated at 200°C for 10 minutes. The resulting reaction solution was then cooled to room temperature.

[0155] Next, 1 ml of toluene and 1.5 ml of ethanol were added to 1 ml of the reaction solution and centrifuged. 2 ml of ethanol was added to the supernatant and centrifuged at 5,500 rpm for 3 minutes (washing separation). The QD dispersion solution redispersed in toluene was measured using a fluorescence spectrometer. Note that washing separation refers to a separation process in which the degree of aggregation due to differences in ligand coordination with the quantum dots is controlled by adjusting the ratio of toluene and ethanol. Through centrifugation and washing separation, only quantum dots with well-balanced ligand coordination were recovered, resulting in excellent luminescence properties (high quantum yield). As a result, optical properties were obtained, such as a fluorescence wavelength of 537.5 nm, a fluorescence half-width of 25 nm, and a quantum yield of 63%, as shown in Figure 12.

[0156] [Example 13] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 373.4 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0157] This solution was dissolved at 200°C for 5 minutes, and 0.5 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto. The mixture was then heated at 200°C for 40 minutes with stirring. The resulting reaction solution was then cooled to room temperature.

[0158] To the resulting reaction solution, 0.6 ml of a 0.2 M solution of indium acetate (In(OAc)3) in octadecene (ODE) and oleic acid (OLAc) and 1.8 ml of a 0.2 M solution of sulfur (S) in octadecene (ODE) were added, and the mixture was again heated at 290°C for 10 minutes with stirring.

[0159] Then, a solution containing 3.6 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) to a molar ratio of Ga:OLAc = 1:3, 1.8 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE), and 2.7 ml of oleylamine (OLAm) was added dropwise over 80 minutes to the solution being heated with stirring at 290 °C. After the addition was complete, the solution was heated with stirring for 10 minutes, and then cooled to room temperature.

[0160] The reaction solution was then centrifuged at 5,500 rpm for 3 minutes, and the supernatant was collected. 3 ml of TOP was added to the collected supernatant, and the mixture was heated at 180°C for 10 minutes. The resulting reaction solution was then cooled to room temperature.

[0161] Next, 1 ml of the reaction solution was mixed with 1 ml of toluene and 1.5 ml of ethanol, and the mixture was centrifuged. 2 ml of ethanol was added to the supernatant, and the mixture was centrifuged at 5,500 rpm for 3 minutes. The QD dispersion solution was redispersed in toluene and measured using a fluorescence spectrometer. As shown in Figure 13, the optical properties obtained were a fluorescence wavelength of 531.0 nm, a fluorescence half-width of 29.3 nm, and a quantum yield of 85%.

[0162] [Example 14] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 373.4 mg of gallium acetylacetonate (Ga(acac)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0163] This solution was dissolved at 200°C for 5 minutes, and 0.5 ml of a 0.4 M solution of tetraethylthiuram disulfide (TETDS) in oleylamine (OLAm) was added thereto. The mixture was then heated at 200°C for 40 minutes with stirring. The resulting reaction solution was then cooled to room temperature.

[0164] To the resulting reaction solution, 0.5 ml of a 0.2 M solution of indium acetate (In(OAc)3) in octadecene (ODE) and oleic acid (OLAc) and 1.5 ml of a 0.2 M solution of sulfur (S) in octadecene (ODE) were added, and the mixture was again heated at 290°C for 10 minutes with stirring.

[0165] Then, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine:OLAm to a molar ratio of Ga:OLAc = 1:3, 0.5 ml of a 0.4 M solution obtained by dissolving tetraethylthiuram disulfide (TETDS) in oleylamine:OLAm, and 3 ml of oleylamine:OLAm were added dropwise over 80 minutes to the solution heated with stirring at 290°C. After the addition was complete, the solution was heated with stirring for 10 minutes, and then cooled to room temperature.

[0166] The reaction solution was then centrifuged at 5,500 rpm for 3 minutes, and the supernatant was collected. 3 ml of TOP was added to the collected supernatant, and the mixture was heated at 180°C for 10 minutes. The resulting reaction solution was then cooled to room temperature.

[0167] To 1 ml of the resulting reaction solution, 1 ml of toluene and 1.5 ml of ethanol were added, and the mixture was centrifuged at 5,500 rpm for 3 minutes. 2 ml of ethanol was then added to the supernatant, and the mixture was centrifuged at 5,500 rpm for 3 minutes. The QD dispersion solution was redispersed in toluene and measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 529.5 nm, a fluorescence half-width of 30.8 nm, and a quantum yield of 71%.

[0168] The resulting reaction solution was then heated at 200°C for 5 minutes, and 2 ml of a solution containing 0.075 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP), 0.6 ml of a 0.2 M solution of sulfur (S) dissolved in trioctylphosphine (TOP), and 1.325 ml of oleylamine (OLAm) was added dropwise over 120 minutes onto the solution, which was heated with stirring at 200°C, and the resulting reaction solution was cooled to room temperature.

[0169] To 1 ml of the resulting reaction solution, 1 ml of toluene and 1.6 ml of ethanol were added, and the mixture was centrifuged at 5,500 rpm for 3 minutes. 2 ml of ethanol was then added to the supernatant, and the mixture was centrifuged at 5,500 rpm for 3 minutes. The QD dispersion solution redispersed in toluene was measured using a fluorescence spectrometer. As shown in Figure 14, the optical properties obtained were a fluorescence wavelength of 528 nm, a fluorescence half-width of 31 nm, and a quantum yield of 84%.

[0170] [Example 15] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm), 355.5 mg of gallium acetylacetonate (Ga(acac)), 20 mL of oleylamine (OLAm), and 3 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0171] This solution was dissolved at 150°C for 5 minutes, and 0.36 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto. The mixture was then stirred for 10 minutes. The resulting reaction solution was cooled to room temperature and then heated at 320°C for 20 minutes with stirring. The mixture was then cooled to room temperature.

[0172] The resulting reaction solution was centrifuged at 5,500 rpm for 3 minutes to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene, and methanol and ethanol were added. The mixture was then centrifuged at 5,500 rpm for 3 minutes to precipitate the QDs again. 9.5 ml of OLAm was then added to the precipitated QDs and they were redispersed.

[0173] Next, 3 mL of a 0.1 M solution (GaCl3: oleylamine: OLAm) of gallium chloride and oleic acid (OLAc) in a molar ratio of 1:1.5 Ga:OLAc was mixed with 0.64 mL of a 0.7 M solution (Se: oleylamine: OLAm and dodecanethiol: DDT). This 3.64 mL solution was added dropwise over 20 minutes to the stirred solution heated at 290 °C. After the addition was complete, the solution was heated with stirring for 100 minutes, and then cooled to room temperature. The resulting solution was measured using a fluorescence spectrometer, revealing a fluorescence wavelength of 639 nm and a fluorescence half-width of 28.5 nm.

[0174] Then, 8 ml of TOP was added and heated at 200°C for 5 minutes. 1 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) was mixed with 1 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT). 2 ml of this mixed solution was added dropwise over 20 minutes onto the solution, which was being stirred and heated at 200°C. After the addition was complete, the solution was heated with stirring for 130 minutes, and then cooled to room temperature.

[0175] To 2 ml of the resulting reaction solution, 2 ml of trioctylphosphine:TOP was added. The mixture was then centrifuged to remove the precipitate. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 15, the optical properties obtained were a fluorescence wavelength of 642 nm, a fluorescence half-width of 33 nm, and a quantum yield of 76%.

[0176] [Example 16] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm), 355.5 mg of gallium acetylacetonate (Ga(acac)), 20 mL of oleylamine (OLAm), and 3 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0177] This solution was dissolved at 150°C for 5 minutes, and 0.36 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto. The mixture was then stirred for 10 minutes. The resulting reaction solution was cooled to room temperature and then heated at 320°C for 20 minutes with stirring. The mixture was then cooled to room temperature.

[0178] The resulting reaction solution was centrifuged at 5,500 rpm for 3 minutes to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene, and methanol and ethanol were added. The mixture was then centrifuged at 5,500 rpm for 3 minutes to precipitate the QDs again. 9.5 ml of OLAm was then added to the precipitated QDs and they were redispersed.

[0179] Then, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) to a molar ratio of Ga:OLAc = 1:1.5, and 0.64 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) were mixed and added dropwise over 30 minutes to the solution being heated with stirring at 290°C. After the addition was complete, the solution was heated with stirring for 90 minutes, and then cooled to room temperature.

[0180] Then, 8 ml of TOP was added and heated at 150°C for 5 minutes. 0.34 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto and heated at 150°C for 40 minutes. 0.17 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) were added thereto and heated at 150°C for 40 minutes. The mixture was then cooled to room temperature.

[0181] To 2 ml of the resulting reaction solution, 0.4 ml of trioctylphosphine:TOP was added. The solution was then centrifuged to remove the precipitate. The resulting solution was measured using a fluorescence spectrometer. As a result, the optical properties obtained were a fluorescence wavelength of 639 nm, a fluorescence half-width of 30.5 nm, and a quantum yield of 56%.

[0182] [Example 17] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm), 355.5 mg of gallium acetylacetonate (Ga(acac)), 20 mL of oleylamine (OLAm), and 3 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0183] This solution was dissolved at 150°C for 5 minutes, and 0.36 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto. The mixture was then stirred for 10 minutes. The resulting reaction solution was cooled to room temperature and then heated at 320°C for 20 minutes with stirring. The mixture was then cooled to room temperature.

[0184] The resulting reaction solution was centrifuged at 5,500 rpm for 3 minutes to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene, and methanol and ethanol were added. The mixture was then centrifuged at 5,500 rpm for 3 minutes to precipitate the QDs again. 9.5 ml of OLAm was then added to the precipitated QDs and they were redispersed.

[0185] Then, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) to a molar ratio of Ga:OLAc = 1:1.5, and 0.64 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) were mixed and added dropwise over 30 minutes to the solution being heated with stirring at 290°C. After the addition was complete, the solution was heated with stirring for 90 minutes, and then cooled to room temperature.

[0186] Then, 8 ml of TOP was added and heated at 150°C for 5 minutes. 0.34 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto and heated at 150°C for 20 minutes. After that, 0.3 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) was added thereto and heated at 150°C for 20 minutes. 0.17 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) were added to the mixture and heated at 150°C for 20 minutes. 0.3 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) was then added and heated at 150°C for 20 minutes. The mixture was then cooled to room temperature.

[0187] To 2 ml of the resulting reaction solution, 0.4 ml of trioctylphosphine:TOP was added. The resulting solution was then centrifuged to remove the precipitate. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 16, the optical properties obtained were a fluorescence wavelength of 633 nm, a fluorescence half-width of 27 nm, and a quantum yield of 81%.

[0188] [Example 18] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate (AgOAc) in oleylamine (OLAm), 355.5 mg of gallium acetylacetonate (Ga(acac)), 20 mL of oleylamine (OLAm), and 3 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0189] This solution was dissolved at 150°C for 5 minutes, and 0.36 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto. The mixture was then stirred for 10 minutes. The resulting reaction solution was cooled to room temperature and then heated at 320°C for 20 minutes with stirring. The mixture was then cooled to room temperature.

[0190] The resulting reaction solution was centrifuged to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene and washed with methanol and ethanol. 9.5 ml of OLAm was then added and redispersed.

[0191] Then, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) to a molar ratio of Ga:OLAc = 1:1.5, and 0.64 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) were mixed and added dropwise over 20 minutes to the solution being heated and stirred at 290°C. After the addition was complete, the mixture was heated and stirred for 100 minutes, and the resulting reaction solution was cooled to room temperature.

[0192] Then, 8 ml of TOP was added and heated at 150°C for 5 minutes. 0.34 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added and heated at 150°C for 20 minutes. 0.6 ml of a 0.4 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and oleylamine (OLAm) was added and heated at 150°C for 20 minutes. 0.17 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) were added to the mixture and heated at 150°C for 20 minutes. 0.6 ml of a 0.4 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and oleylamine (OLAm) was then added and heated at 150°C for 20 minutes. The mixture was then cooled to room temperature.

[0193] To 2 ml of the resulting reaction solution, 0.4 ml of trioctylphosphine:TOP was added. The solution was then centrifuged to remove the precipitate. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 17, the optical properties obtained were a fluorescence wavelength of 630.5 nm, a fluorescence half-width of 24.5 nm, and a quantum yield of 70%.

[0194] [Example 19] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm), 53.3 mg of gallium acetylacetonate (Ga(acac)3), 0.25 mL of a 0.02 M solution obtained by dissolving indium acetylacetonate (In(acac)3) in oleylamine (OLAm) and oleic acid (OLAc), 9.5 mL of oleylamine (OLAm), and 2.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0195] This solution was dissolved at 150°C for 5 minutes, and 0.36 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto. The mixture was then stirred for 10 minutes. The resulting reaction solution was cooled to room temperature and then heated at 320°C for 60 minutes with stirring. It was then cooled to room temperature.

[0196] The resulting reaction solution was centrifuged to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene and washed with methanol and ethanol. 9.5 ml of OLAm was then added and redispersed.

[0197] Then, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) to a molar ratio of Ga:OLAc = 1:1.5 was mixed with 0.57 ml of a 0.8 M solution obtained by dissolving sulfur (S) in oleylamine (OLAm) and dodecanethiol (DDT). This mixture was added dropwise over 30 minutes to the solution being heated and stirred at 260°C. After the addition was complete, the mixture was heated and stirred for 150 minutes, and the resulting reaction solution was cooled to room temperature.

[0198] Next, 0.15 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) and 0.15 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) were added and heated at 150 °C for 20 minutes. 3 ml of trioctylphosphine (TOP) was then added and heated at 150 °C for 10 minutes. 0.15 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) and 0.15 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) were added and heated at 150 °C for 20 minutes.

[0199] To 2 ml of the resulting reaction solution, 0.4 ml of trioctylphosphine:TOP was added. The resulting solution was then centrifuged to remove the precipitate. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 18, the optical properties obtained were a fluorescence wavelength of 631 nm, a fluorescence half-width of 25 nm, and a quantum yield of 67%.

[0200] [Example 20] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm), 355.5 mg of gallium acetylacetonate (Ga(acac)), 20 mL of oleylamine (OLAm), and 3 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0201] This solution was dissolved at 150°C for 5 minutes, and 0.36 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto. The mixture was then stirred for 10 minutes. The resulting reaction solution was cooled to room temperature and then heated at 320°C for 20 minutes with stirring. The mixture was then cooled to room temperature.

[0202] The resulting reaction solution was centrifuged to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene and washed with methanol and ethanol. 9.5 ml of OLAm was then added and redispersed.

[0203] Then, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) to a molar ratio of Ga:OLAc = 1:1.5 was mixed with 0.5 ml of a 0.8 M solution obtained by dissolving sulfur (S) in oleylamine (OLAm) and dodecanethiol (DDT). This mixture was added dropwise over 10 minutes to the solution being heated and stirred at 290°C. After the addition was complete, the mixture was heated and stirred for 110 minutes, and the resulting reaction solution was cooled to room temperature.

[0204] Then, 8 ml of TOP was added and heated at 150°C for 5 minutes. 0.34 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) was added thereto and heated at 150°C for 20 minutes. After that, 0.3 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) was added thereto and heated at 150°C for 20 minutes. 0.17 ml of a 0.7 M solution of selenium (Se) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution of sulfur (S) dissolved in oleylamine (OLAm) and dodecanethiol (DDT) were added to the mixture and heated at 150°C for 20 minutes. 0.3 ml of a 0.8 M solution of zinc acetate (Zn(OAc)2) dissolved in oleic acid (OLAc) and trioctylphosphine (TOP) was then added and heated at 150°C for 20 minutes. The mixture was then cooled to room temperature.

[0205] To 2 ml of the resulting reaction solution, 0.4 ml of trioctylphosphine:TOP was added. The resulting solution was then centrifuged to remove the precipitate. The resulting solution was measured using a fluorescence spectrometer. As shown in Figure 19, the optical properties obtained were a fluorescence wavelength of 633 nm, a fluorescence half-width of 23.9 nm, and a quantum yield of 75%.

[0206] [Comparative Example 1] A 100 mL reaction vessel was charged with 0.5 mL of a 0.2 M solution of silver acetate (Ag(OAc)) in oleylamine (OLAm), 329 mg of indium acetate (In(OAc)), 9.5 mL of oleylamine (OLAm), and 0.5 mL of dodecanethiol (DDT). The mixture was heated under an inert gas (N2) atmosphere with stirring to dissolve the raw materials.

[0207] This solution was dissolved at 120°C for 5 minutes, and 1 ml of a 0.2 M solution (S-ODE) obtained by dissolving sulfur (S) in octadecene (ODE) was added thereto. The temperature was then increased from 120°C to 200°C while stirring for a total of 20 minutes. The resulting reaction solution was cooled to room temperature.

[0208] To the resulting reaction solution, 327.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] was added as a carbamate, and the mixture was again heated at 260°C for 10 minutes with stirring.

[0209] Then, 2 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene:ODE to a molar ratio of Ga:MA = 1:3 was mixed with 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene:ODE, and 3.5 ml of this solution was added dropwise over 50 minutes to the solution being heated with stirring at 260°C. After the addition was complete, the solution was heated with stirring for 70 minutes, and then cooled to room temperature.

[0210] The resulting reaction solution was measured using a fluorescence spectrometer. As a result, the optical characteristics were as shown in Figure 20, with a fluorescence wavelength of approximately 641 nm and a fluorescence half-width of approximately 33.8 nm. The fluorescence quantum yield was too low to be measured.

[0211] The initial particle composition, subsequently added elements, fluorescence wavelength, fluorescence half-width, and fluorescence quantum yield (PLQY) for each example are summarized in Table 1. Table 2 also summarizes the main differences between Examples 1 (green QD) and 15 (red QD).

[0212] [Table 1]

[0213] [Table 2]

[0214] As shown in Table 1, in Examples 1 to 18 and 20, the initial particle composition did not contain In, and all of them obtained good characteristics. On the other hand, in Comparative Example 1, the initial particle composition contained In, and in particular, the fluorescence quantum yield became an unobservably low value.

[0215] "Later-added elements" include the composition of the shell that covers the core surface, but TEM-EDX analysis revealed that a clear core-shell structure could not be confirmed and that all of the added raw materials were mixed crystals. However, as mentioned above, by not including In in the particles synthesized by the initial reaction, good properties were obtained in all cases, and for this reason, "initial particle composition" and "later-added elements" are listed separately.

[0216] Furthermore, Example 16 did not contain Zn, and Example 17 contained Zn, but Example 17 provided better characteristics than Example 16.

[0217] As shown in Table 1, in all of the Examples, it was found that the fluorescence half-width could be set to 45 nm or less, preferably 30 nm or less, and the fluorescence quantum yield could be set to 35% or more, preferably 70% or more.

[0218] Furthermore, as shown in Table 1, it was found that the fluorescence wavelength could be adjusted within the range of 400 nm to 700 nm, and that green-emitting quantum dots could be synthesized in Examples 1 to 14, and red-emitting quantum dots could be synthesized in Examples 15 to 20.

[0219] In contrast, the AIS quantum dots described in the patent documents have a fluorescence half-width of 45 nm or more or a fluorescence quantum yield of 35% or less in the green to red wavelength range. x Ga 1-x S y Se 1-y system, or ZnAgIn x Ga 1-x S y Se 1-y We were unable to obtain quantum dots in the system (0≦x<1, 0≦y≦1).

[0220] Furthermore, the dispersion of AgInGaS particles in Example 7 was measured using a scanning electron microscope (SEM), and Fig. 21 shows the measurement results using the scanning electron microscope (SEM).

[0221] As shown in FIG. 21, it was found that a large number of quantum dots with approximately uniform particle diameters could be mass-produced.

[0222] Furthermore, the results (observed image) of TEM-EDX analysis of the quantum dots of Example 15 are shown in Figure 22. Figure 23 is a partial schematic diagram of the observed image shown in Figure 22. As shown in Figures 22 and 23, the more Zn was detected, the darker the detected color, indicating that Zn was mainly present on the surface of the quantum dots. [Industrial Applicability]

[0223] According to the present invention, quantum dots that exhibit, for example, high-intensity green or red fluorescence can be stably obtained. By applying the quantum dots of the present invention to LEDs, backlight devices, display devices, etc., excellent light-emitting properties can be obtained in each device.

[0224] This application is based on Japanese Patent Application No. 2019-153204, filed on August 23, 2019, the contents of which are incorporated herein in their entirety.

Claims

1. ZnAgIn ｘ Ga １－ｘ S ｙ Se １－ｙ A quantum dot consisting of the system (0≦x<1, 0≦y≦1), exhibiting fluorescent properties in the green to red wavelength range, with a fluorescence half-width of 33 nm or less and a fluorescence quantum yield of 70% or more; The quantum dots have a core-shell structure including a core and a shell covering the core, and Zn is contained in the shell. Quantum dots characterized by:

2. 2. The quantum dot according to claim 1, comprising at least Zn, Ag, Ga, and S, or Zn, Ag, Ga, and Se, but not Cd.

3. 3. The quantum dot according to claim 1, wherein the shell is made of ZnS.

4. 2. The quantum dot according to claim 1, wherein the core is made of AgInGaS or AgGaSe.

5. 5. The quantum dot according to claim 1, wherein the fluorescence wavelength is in the range of 400 nm to 700 nm.

6. 6. The quantum dot according to claim 1, wherein the fluorescence half-width is 30 nm or less, the fluorescence quantum yield is 80% or more, and the fluorescence wavelength is in the range of 510 nm to 650 nm.

7. ZnAgIn ｘ Ga １－ｘ S ｙ Se １－ｙ It consists of the system (0≦x<1, 0≦y≦1), forming a core, and then forming a shell containing Zn to cover the core; A method for producing quantum dots, comprising synthesizing quantum dots that exhibit fluorescent properties in which the fluorescence half-width is 33 nm or less and the fluorescence quantum yield is 70% or more in the green to red wavelength range.

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