Quantum dots and methods for manufacturing 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] This invention relates to cadmium-free quantum dots and a method for producing the same. [Background technology]

[0002] Quantum dots are inorganic nanoparticles composed of several thousand to tens of thousands of atoms, with a particle size of several nanometers to tens of thousands of nanometers. Because quantum dots emit fluorescence and are of the nano-order, they are also called fluorescent nanoparticles; because their composition is derived from semiconductor materials, they are also called semiconductor nanoparticles; and because their structure has a specific crystalline structure, they are also called nanocrystals.

[0003] Quantum dots are composed of positively charged metal atoms and negatively charged nonmetallic or semimetallic atoms, which are bonded together by ionic or covalent bonds. The ionic nature of the bond depends on the combination of properties of the metal and semimetallic atoms.

[0004] Quantum dots can have their emission wavelengths varied depending on their particle size and composition. Quantum dot performance is expressed by metrics such as fluorescence quantum yield (QY) and fluorescence 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 convert them to emit light in a specific wavelength range. Furthermore, these absorption and emission wavelengths can be controlled by the structure, composition, and size of the quantum dot, allowing them to be used in a variety of applications by leveraging these characteristics.

[0006] For example, when quantum dots are used as wavelength conversion materials in the visible light region, one of their characteristics is a wide range of colors that can be expressed, i.e., a high color gamut. In achieving a high color gamut using quantum dot wavelength conversion materials in the visible light region, the important optical properties are the fluorescence quantum yield and the fluorescence full width at half maximum.

[0007] Conventionally, highly efficient quantum dots have primarily contained cadmium (Cd). Quantum dots containing Cd have the advantages of high fluorescence quantum yield and a narrow fluorescence half-width. However, due to the toxicity of Cd, its use is restricted in many countries, which has been a major obstacle to practical application.

[0008] In response to this, the development of quantum dots that do not contain Cd is being considered in many cases. For example, the following patent document describes AIS or AIGS-based quantum dots or AISe or AIGSe-based quantum dots containing Ag, In, and S, or Ag, In, Ga, and S, or Ag, In, Se, or Ag, In, Ga, and Se. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-025201 [Patent Document 2] Japanese Patent Publication No. 2018-039971 [Patent Document 3] Japanese Patent Publication No. 2018-044142 [Patent Document 4] Japanese Patent Publication 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 [Overview of the project] [Problems that the invention aims to solve]

[0011] As described above, although research and development of chalcopyrite-based quantum dots that do not contain cadmium (Cd) is progressing, none of these quantum dots have yet reached a level of performance that would allow them to replace Cd-based quantum dots in terms of fluorescence full width at half maximum (FWHM) and fluorescence quantum yield.

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

[0013] Furthermore, the present invention aims to provide a method for manufacturing quantum dots that enables the mass production of the above-mentioned quantum dots. [Means for solving the problem]

[0014] The quantum dots of the present invention are ZnAgIn x Ga 1-x S y Se 1-yA quantum dot consisting of a system (0≦x<1, 0≦y≦1), exhibiting fluorescence characteristics such as a fluorescence full width at half maximum of 33 nm or less and a fluorescence quantum yield of 70% or more in the green wavelength range to the red wavelength range, wherein the quantum dot has a core-shell structure consisting of a core and a shell covering the core, and Zn is included in the shell.

[0015] The present invention provides a method for manufacturing quantum dots using ZnAgIn x Ga 1-x S y Se 1-y The system consists of (0≦x<1, 0≦y≦1), and after forming a core, a Zn-containing shell is formed to cover the core, thereby synthesizing quantum dots that exhibit fluorescence characteristics of 70% or more with a fluorescence half-width of 33 nm or less and a fluorescence quantum yield in the green wavelength range to the red wavelength range. [Effects of the Invention]

[0016] According to the quantum dots of the present invention, quantum dots with uniform composition, particle shape, and size can be synthesized, thereby narrowing the fluorescence half-width and increasing the fluorescence quantum yield.

[0017] Furthermore, the quantum dots of the present invention allow for the synthesis of quantum dots having a desired emission wavelength depending on the application.

[0018] Furthermore, since quantum dots with a narrow half-width can be synthesized at emission wavelengths suitable for the purpose, when used as wavelength conversion materials, it is possible to improve the color gamut.

[0019] Furthermore, the quantum dot manufacturing method of the present invention makes it possible to synthesize quantum dots with a narrow fluorescence half-width and that do not contain Cd in a manner that enables mass production. [Brief explanation of the drawing]

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

Modes for Carrying Out the Invention

[0021] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist. In this specification, the notation "~" means including its lower limit value and upper limit value.

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

[0023] In this embodiment, the quantum dot 5 is AgIn x Ga 1-x S y Se 1-y system, or ZnAgIn x Ga 1-x S y Se 1-y system (0 ≦ x < 1, 0 ≦ y ≦ 1). The quantum dot 5 in this embodiment is preferably a nanocrystal that contains at least silver (Ag), gallium (Ga), sulfur (S), or silver (Ag), gallium (Ga), and selenium (Se), and does not contain cadmium (Cd). Further, the quantum dot 5 can also contain indium (In) or zinc (Zn) in addition to Ag, Ga, S, or Ag, Ga, Se.

[0024] Here, "nanocrystal" refers to nanoparticles having a particle size of several nanometers to several tens of nanometers. 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 quantum dot 5 is preferably in the range of Ag / Ga = 0.05 or more and 10 or less. Furthermore, the ratio Ag / Ga is more preferably in the range of 0.05 or more and 5 or less, and even more preferably in the range of 0.1 or more and 3 or less.

[0026] The ratio of Zn to Ga that can be included in quantum dot 5 is preferably in the range of Zn / Ga = 0.1 to 10. More preferably, the ratio Zn / Ga is 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 fluorescence wavelength can be adjusted from the green wavelength range to the red wavelength range. In particular, in this embodiment, the fluorescence wavelength can be appropriately adjusted within the range of 400 nm to 700 nm. In this embodiment, the fluorescence 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 suppresses aggregation of the quantum dots 5 and allows the desired optical properties to be exhibited. The ligands that can be used in the reaction are not particularly limited, but the following ligands are typical 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, Lauryl acid:C 11 H 23 COOH, Decanoic acid: C9H 19 COOH, octanoic acid: C7H 15 COOH (3) Thiol type Octadecanthiol: 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:C8H 17 SH (4) Phosphine systems Trioctylphosphine:(C8H 17 )3P, Triphenylphosphine:(C6H5)3P, Tributylphosphine:(C4H9)3P (5) Phosphine oxide systems Trioctylphosphine oxide: (C8H 17 )3P=O, triphenylphosphine oxide: (C6H5)3P=O, tributylphosphine oxide: (C4H9)3P=O

[0030] The characteristic features of the quantum dot 5 of this embodiment will now be described. The quantum dot 5 of this embodiment exhibits fluorescence characteristics in the green wavelength range to the red wavelength range, with a fluorescence half-width of 45 nm or less and a fluorescence quantum yield of 35% or more.

[0031] Here, "fluorescence half-width" refers to the full width at half maximum (FWHM), which indicates the spread of the fluorescence wavelength at half the peak intensity of the fluorescence intensity in the fluorescence spectrum. Furthermore, the fluorescence FWHM is preferably 35 nm or less. More preferably 30 nm or less. Even more preferably 25 nm or less. By narrowing the fluorescence FWHM in this way, it is possible to improve the wide color gamut.

[0032] In this embodiment, the fluorescence quantum yield of the quantum dot 5 is more preferably 40% or higher, even more preferably 60% or higher, even more preferably 70% or higher, and most preferably 80% or higher. Thus, in this embodiment, the fluorescence quantum yield of the quantum dot can be increased.

[0033] Thus, 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 a quantum dot system (0≦x<1, 0≦y≦1), the fluorescence full width at half maximum (FWHM) can be narrowed from the green wavelength range to the red wavelength range, and the fluorescence quantum yield can be increased.

[0034] In this embodiment, the fluorescence wavelength can be freely controlled to approximately 400 nm to 700 nm. The quantum dot 5 in this embodiment is a solid solution based on Ag, Ga, In, and Zn as cationic raw materials, and Se and S as anionic 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 dot 5. For this reason, the fluorescence wavelength is preferably 400 nm to 480 nm for blue emission, more preferably 410 nm to 470 nm, and even more preferably 420 nm to 460 nm. For green emission, it is preferably 500 nm to 560 nm, more preferably 510 nm to 550 nm, and even more preferably 520 nm to 540 nm. For red emission, it is preferably 600 nm to 660 nm, more preferably 610 nm to 650 nm, and even more preferably 620 nm to 640 nm.

[0035] In this embodiment, as described above, it is possible to control the fluorescence wavelength from 400 nm to 700 nm, but green or red emission is preferred as the wavelength conversion material in the visible light region.

[0036] In this context, chalcopyrite is generally a material that exhibits defect emission with a fluorescence half-width of 45-80 nm. In contrast, the quantum dot 5 of this embodiment has a narrow fluorescence half-width, a high fluorescence quantum yield, and a fluorescence lifetime that can be made much shorter than that of defect emission. Based on these characteristics, it is presumed that the quantum dot 5 of this embodiment exhibits band-edge emission.

[0037] In particular, the quantum dot 5 of this embodiment has 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. Thus, it is possible to achieve characteristics of a narrow fluorescence half-width and high fluorescence quantum yield not only at green fluorescence wavelengths (around 510 to 540 nm) but also at 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 coated on 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 fluorescence full width at half maximum of the quantum dot 5 shown in Figure 1B is 45 nm or less, and the fluorescence quantum yield is 35% or more.

[0039] The core 5a of the quantum dot 5 shown in Figure 1B is the nanocrystal shown in Figure 1A. Therefore, it is preferable that the core 5a be formed from a nanocrystal containing Ag, Ga, S, or Ag, Ga, Se, but not Cd. The shell 5b, like the core 5a, does not contain cadmium (Cd). The material of the shell 5b is not particularly limited, 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] Furthermore, the shell 5b may be in a state of solid solution on the surface of the core 5a. In Figure 1B, the boundary between the core 5a and the shell 5b is shown with a dotted line, which means that it is acceptable whether or not the boundary between the core 5a and the shell 5b can be confirmed by analysis. The ZnAgIn mentioned above 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, the presence of Zn suggests that the core 5a is covered by the shell 5b.

[0041] The quantum dot 5 shown in Figure 1B, like Figure 1A, allows for free control of its fluorescence wavelength, ranging from approximately 400 nm to 700 nm, or from approximately 500 nm to 650 nm.

[0042] In this embodiment, fluorescence is emitted even with only a core made of AgGaS, AgGaSe, AgGaInS, or AgGaInSe, so shell coating is not necessarily required. However, by adopting a core-shell structure, it is possible to expect a further increase in fluorescence quantum yield while keeping the fluorescence full width at half maximum narrow. Furthermore, fluorescence is observed whether or not In is included. For example, in green fluorescence quantum dots, the inclusion of In results in good emission characteristics, but even without In, emission occurs, although the fluorescence full width at half maximum tends to be slightly larger. Specifically, emission has been confirmed with AgGaS.

[0043] Furthermore, generally, when Zn is used, the difference in valence (Zn is divalent, Ag is monovalent, and Ga or In is trivalent) tends to result in defect emission and a broader fluorescence full width at half maximum. However, in this embodiment, as will be shown in the experiments described later, even with post-addition of Zn, the fluorescence quantum yield can be increased while maintaining a narrow fluorescence full width at half maximum. In other words, it is possible to improve the emission characteristics by using Zn. Next, the method for manufacturing the quantum dot 5 of this embodiment will be described.

[0044] The method for manufacturing quantum dots in 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 method is characterized by synthesizing quantum dots consisting of a system (0≦x<1, 0≦y≦1) that exhibit fluorescence characteristics such as a fluorescence half-width of 45 nm or less and a fluorescence quantum yield of 35% or more in the green wavelength range to the red wavelength range.

[0045] First, in this embodiment, an organosilver compound, an organogallium compound, and sulfur or selenium are used for one-pot heating synthesis, or an organosilver compound, an organoindium compound, an organogallium compound, and sulfur or selenium are used.

[0046] In this process, the reaction temperature is set to a range of 100°C to 320°C to synthesize AgGaS, AgGaSe, AgGaInS, or AgGaInSe. However, a lower reaction temperature of 280°C or below is preferable.

[0047] Furthermore, in this embodiment, an organosilver compound or an inorganic silver compound is used as the raw material for Ag. While not particularly limited, for example, silver acetate: AgOAc, silver nitrate: AgNO3, as halides, silver chloride: AgCl, silver bromide: AgBr, silver iodide: AgI, and as carbamate salts, silver diethyldithiocarbamate: Ag(SC(=S)N(C2H5)2), silver dimethyldithiocarbamate: Ag(SC(=S)N(CH3)2), etc. can be used.

[0048] Furthermore, in this embodiment, the above-mentioned Ag raw material may be added directly to the reaction solution, or it may be dissolved in an organic solvent beforehand to obtain a solution of a certain concentration, which can then be used as the Ag raw material solution.

[0049] Furthermore, in this embodiment, an organic indium compound or an inorganic indium compound is used as a raw material for In. While not particularly limited, for example, indium acetate: In(OAc)3, indium nitrate: InNO3, indium acetylacetonate: In(acac)3, as a halide, indium chloride: InCl3, silver bromide: InBr3, indium iodide: InI3, and as a carbamate salt, indium diethyldithiocarbamate: In[(SC(=S)N(C2H5)2]3, indium dimethyldithiocarbamate: In[(SC(=S)N(CH3)2)]3, etc. can be used.

[0050] Furthermore, in this embodiment, an organic indium compound or an inorganic indium compound is used as the raw material for Ga. Although not particularly limited, for example, gallium acetate: Ga(OAc)3, gallium nitrate: GaNO3, gallium acetylacetonate: Ga(acac)3, as a halide, gallium chloride: GaCl3, gallium bromide: GaBr3, gallium iodide: Ga2I3, and as a carbamate salt, gallium diethyldithiocarbamate: Ga[(SC(=S)N(C2H5)2]3, etc., can be used.

[0051] Furthermore, in this embodiment, the In raw material or Ga raw material may be added directly to the reaction solution, or it may be dissolved in an organic solvent beforehand to obtain a solution of a certain concentration, and then used as the In raw material solution or Ga raw material solution.

[0052] Furthermore, in this embodiment, organic sulfur compounds such as thiols can be used as raw materials 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:C8H 17 SH, etc.

[0053] In particular, when synthesizing AgGaS or AgInGaS, the sulfur raw material species contributes significantly to the fluorescence properties. In this embodiment, it is preferable to use S-ODE raw materials obtained by dissolving sulfur in octadecene:ODE, disulfide-based or thiuram-based S raw materials, or S-OLAm / DDT obtained by dissolving sulfur in oleylamine and dodecanethiol. Of these, S-ODE raw materials can obtain a fluorescence half-width of 40 nm or less and a fluorescence quantum yield of 40% or more, but even better properties can be obtained by using disulfides. Examples include diphenyl disulfide, dibenzyl disulfide, isopropyl xanthogen disulfide, and 4,4'-dithiodimorpholine. Furthermore, even better fluorescence properties can be obtained by using thiuram-based raw materials. Examples include thiuram disulfide, dipentamethylenethiuram tetrasulfide, tetraethyl thiuram disulfide, and tetramethyl thiuram disulfide. In addition, the sulfurous raw material may also be a raw material having a structure in which multiple sulfur atoms are linked together (―S―)n, or a raw material having a structure in which nitrogen (NS-), carbon (CS-), etc., is attached to sulfur.

[0054] Furthermore, in this embodiment, organic selenium compounds (organo-chalcogen compounds) can be used as raw materials for Se. For example, trioctylphosphine selenide, which is obtained by dissolving selenium in trioctylphosphine: (C8H 17 )3P=Se, or tributylphosphine selenide ((C4H9)3P=Se) obtained by dissolving selenium in tributylphosphine, or a solution obtained by dissolving selenium in a high-boiling point solvent that is a long-chain hydrocarbon such as octadecene can be used.

[0055] When synthesizing AgGaSe or AgInGaSe, the selenium raw material species significantly contribute to the fluorescence characteristics. In particular, a solution (Se-OLAm / DDT) in which Se is dissolved in a mixture of oleylamine and dodecanethiol exhibits good luminescence characteristics. Ordinary chalcopyrite-based quantum dots can confirm two types of luminescence in the initial stage of luminescence: a PL spectrum considered to be band-edge luminescence and a PL spectrum considered to be defect luminescence. In most cases, the ratio of the luminescence intensities is such that the band-edge luminescence / defect luminescence is 10 or less. Subsequently, as the reaction progresses further, the intensity of the defect luminescence gradually decreases, and often, the intensity of the band-edge luminescence increases accordingly. However, when using Se-DDT / OLAm as the Se source as in this embodiment, it shows a single peak from the initial stage of luminescence, the band-edge luminescence / defect luminescence is 10 or more, and almost no peak considered to be defect luminescence can be confirmed. Also, the fluorescence lifetime is as short as 20 ns or less until it reaches 1 / e, and only a peak that is not defect luminescence can be confirmed in the initial stage of luminescence.

[0056] Also, in this embodiment, an organozinc compound or an inorganic zinc compound is used as the raw material of Zn. Organozinc compounds and inorganic zinc compounds are raw materials that are stable in air and easy to handle. The structure of the organozinc compound and the inorganic zinc compound is not particularly limited. For example, the following organozinc compounds and inorganic zinc compounds can be used. Zinc acetate: Zn(OAc)2 as an acetate, zinc nitrate: Zn(NO3)2, and as fatty acid salts, zinc stearate: Zn(OC(=O)C 17 H 35 [ )2, zinc oleate: Zn(OC(=O)C 17 H 33 [ )2, zinc palmitate: Zn(OC(=O)C 15 H 31 [ )2, zinc myristate: Zn(OC(=O)C 13 H 27 [ )2, zinc dodecanoate: Zn(OC(=O)C 11 H 23 [)2, zinc acetylacetonate: Zn(acac)2, as halides, zinc chloride: ZnCl2, zinc bromide: ZnBr2, zinc iodide: ZnI2, 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 a one-pot process without isolating or purifying the precursor.

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

[0059] However, as shown in Figure 1B, the fluorescence quantum yield can be further increased by coating the core 5a, which is made of nanocrystals, with the shell 5b.

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

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

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

[0063] In the quantum dot manufacturing method of this embodiment, after forming initial reaction particles, predetermined elements are added later to synthesize the dots, and it is preferable that the initial reaction particles do not contain In. Specifically, the particles formed in the initial reaction that do not contain In, such as AgGaS or AgGaSe, have the best luminescence properties.

[0064] Generally, inclusion of In from the initial stages of the reaction is performed, and the In / Ga ratio is adjusted. However, the quantum dots in this embodiment aim to suppress compositional variations and be synthesized with the smallest possible composition. Therefore, it is preferable that In is not included in the initial reaction. As a result, it is presumed that a narrow fluorescence half-width can be obtained.

[0065] In the case of green fluorescent quantum dots, it is preferable that the quantum dots ultimately contain In, and In can be incorporated during the reaction process. However, the inclusion of In is not essential for green fluorescent quantum dots; for example, emission has been confirmed with AgGaS without In, although the fluorescence full width at half maximum is slightly broadened.

[0066] Furthermore, in this embodiment, when adding Zn to the quantum dots, it is preferable to add Zn while paying attention to the following points. Firstly, Zn is not added during the initial reaction but added in the final step. This is because if Zn is included inside the particle, there is a risk that defect emission will be dominant, or that only defect emission may be observed. Therefore, by adding Zn in the final step, the aim is to react only on the particle surface. Secondly, Zn is added at a low temperature. Here, low temperature means around 150 to 200°C. If the temperature at which Zn is added is high, the Zn will react inside the particle, which is likely to result in defect emission. Therefore, in order to limit the reaction to the particle surface, it is preferable to react only on the particle surface at a low temperature.

[0067] Furthermore, in this embodiment, when synthesizing AgGaSe, it is preferable that the Se raw material is Se-OLAm / DDT. This effectively suppresses defect luminescence.

[0068] Furthermore, when synthesizing AgGaS, instead of dissolving sulfur powder, which is commonly used, thiuram-based, particularly tetraethyl thiuram disulfide, is preferable as it can yield good luminescence properties.

[0069] Furthermore, while the centrifugation process separates larger and smaller particles, the process of adding toluene or ethanol and then centrifuging allows for variations in aggregation depending on the surface ligands of the quantum dots, even if the particle sizes are uniform, by controlling the ratio of toluene or ethanol. This ratio can be controlled to quantum dots:toluene:ethanol = 1:0.5 to 2:0.5 to 2. Methanol may also be used instead of ethanol. As a result, quantum dots with high fluorescence quantum yield and quantum dots with low fluorescence quantum yield can be separated. Subsequently, adding TOP to the separated quantum dots can further improve the fluorescence quantum yield.

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

[0071] The applications of the quantum dot 5 shown in Figure 1 are not particularly limited, but some specific examples are given below.

[0072] Figure 2 is a schematic diagram of an LED device using quantum dots according to this embodiment. As shown in Figure 2, the LED device 1 of this embodiment is composed of a housing case 2 having a bottom surface 2a and side walls 2b surrounding the bottom surface 2a, an LED chip (light-emitting element) 3 placed on the bottom surface 2a of the housing case 2, and a fluorescent layer 4 filled inside the housing case 2 and sealing the upper side of the LED chip 3. Here, the upper side is the direction in which the light emitted from the LED chip 3 is emitted from the housing case 2, and is the direction opposite to the bottom surface 2a with respect to the LED chip 3.

[0073] The LED chip 3 is placed on a base wiring board (not shown), which may constitute the bottom surface of the housing case 2. As the base board, for example, a configuration in which a wiring pattern is formed on a substrate such as glass epoxy resin can be presented.

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

[0075] As shown in Figure 2, the fluorescent layer 4 is formed of 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 are dispersed in this embodiment may also contain a fluorescent substance other than the quantum dots 5. Examples of fluorescent substances include sialon-based materials and KSF(K2SiF6:Mn 4+ While red phosphors and other materials are available, the material is not particularly limited.

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

[0078] The LED device using quantum dots of the present embodiment can be applied to a display device. FIG. 3 is a longitudinal sectional view of a display device using the LED device shown in FIG. 2. As shown in FIG. 3, the display device 50 includes a plurality of LED devices 20 and a display unit 54 such as a liquid crystal display facing each LED device 20. Each LED device 20 is disposed on the back side of the display unit 54. Each LED device 20 has a structure in which an LED chip is sealed with a resin in which a large number of quantum dots 5 are diffused, similar to the LED device 1 shown in FIG. 2.

[0079] As shown in FIG. 3, the plurality of LED devices 20 are supported by a support 52. Each LED device 20 is arranged at a predetermined interval. The LED devices 20 and the support 52 constitute a backlight 55 for the display unit 54. The support 52 is not particularly limited in shape or material, such as being sheet-like, plate-like, or case-like. As shown in FIG. 3, a light diffusion plate 53 or the like may be interposed between the backlight 55 and the display unit 54.

[0080] By applying the quantum dots 5 with a narrow fluorescence half-width in the present embodiment to the LED device shown in FIG. 2, the display device shown in FIG. 3, etc., it becomes possible to effectively improve the light emission characteristics of the device.

[0081] Further, a resin composition in which the quantum dots 5 of the present embodiment are dispersed in a resin can also be formed into a sheet shape or a film shape. Such a sheet or film can be incorporated into, for example, a backlight device.

Examples

[0082] Hereinafter, the effects of the present invention will be described with reference to examples and comparative examples of the present invention. Note that the present invention is not limited by the following examples.

[0083] <Raw materials> In the experiment, AgIn x Ga 1-x [[ID=X]] y Se 1-y system or ZnAgIn x Ga​1-x S y Se 1-y The following raw materials were used to synthesize quantum dots of the system (0≦X<1, 0≦Y≦1). (solvent) Octadecene: Manufactured by Aldrich Corporation Oleylamine: Manufactured by 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: Manufactured by Aldrich Corporation (Indium raw material) Indium acetate: Manufactured by Shinko Chemical Industry Co., Ltd. Diethyldithiocarbamate indium: 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: Manufactured by Kishida Chemical Co., Ltd. Tetraethyl thiuram disulfide: Manufactured by Sanshin Chemical Industry Co., Ltd. Dipentamethylenethuram 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 Corporation F-2700 Ultraviolet-Visible Spectrophotometer: Hitachi V-770 Quantum yield measurement device: QE-1100, manufactured by Otsuka Electronics Co., Ltd. Scanning-line electron microscope (SEM): Hitachi SU9000

[0084] [Example 1] In a 300 mL reaction vessel, 1.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0085] This solution was dissolved at 120°C for 5 minutes, and then 1.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added. 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

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

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

[0089] Subsequently, the QD dispersion solution was washed with toluene and ethanol, and the redispersion process using TOP was repeated twice. The resulting QD dispersion solution was then measured using a fluorescence spectrometer. As a result, as shown in Figure 4, optical properties were obtained with a fluorescence wavelength of 539 nm, a fluorescence full width at half maximum of 35.4 nm, and a quantum yield of 75%.

[0090] [Example 2] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0091] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving dipentamethylenethuram tetrasulfide (DPTT) in oleylamine (OLAm) was added. The temperature was then increased from 120°C to 200°C and the mixture was 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0093] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0094] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 526 nm, a fluorescence full width at half maximum of 35.5 nm, and a quantum yield of 34%.

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

[0096] [Example 3] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0097] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving 4,4'-dithiodimorpholine (DTDM) in oleylamine (OLAm) was added. 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0099] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

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

[0101] Subsequently, the QD dispersion solution was washed with toluene and ethanol, and the redispersion process using TOP was repeated twice. The resulting QD dispersion solution was then measured using a fluorescence spectrometer. As a result, as shown in Figure 6, optical properties were obtained with a fluorescence wavelength of 527.5 nm, a fluorescence full width at half maximum of 36.9 nm, and a quantum yield of 56%.

[0102] [Example 4] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0103] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving isopropyl xanthogen disulfide in oleylamine (OLAm) was added. 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0105] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0106] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 530 nm, a fluorescence full width at half maximum of 37 nm, and a quantum yield of 40%.

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

[0108] [Example 5] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0109] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetramethylthiuram disulfide (TMTDS) in oleylamine (OLAm) was added. The temperature was then increased from 120°C to 200°C and the mixture was 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0111] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0112] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 542 nm, a fluorescence full width at half maximum of 36.5 nm, and a quantum yield of 54%.

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

[0114] [Example 6] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0115] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added. The temperature was then increased from 120°C to 200°C and the mixture was 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0117] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0118] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 546 nm, a fluorescence full width at half maximum of 29.3 nm, and a quantum yield of 39%.

[0119] Subsequently, the QD dispersion solution was washed with toluene and ethanol, and the redispersion process using TOP was repeated twice. The resulting QD dispersion solution was then measured using a fluorescence spectrometer. As a result, as shown in Figure 9, optical properties were obtained with a fluorescence wavelength of 548.5 nm, a fluorescence full width at half maximum of 30.5 nm, and a quantum yield of 59%.

[0120] [Example 7] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0121] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide in oleylamine (OLAm) was added. 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] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0124] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 546 nm, a fluorescence full width at half maximum of 36.5 nm, and a quantum yield of 55%.

[0125] Subsequently, the QD dispersion solution was washed with toluene and ethanol, and the redispersion process using TOP was repeated twice. The resulting QD dispersion solution was then measured using a fluorescence spectrometer. As a result, as shown in Figure 10, the optical properties obtained 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] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

[0128] To the resulting reaction solution, 321.8 mg of indium acetate (In(OAc)) and 2.25 ml of 0.2 M S-ODE were added, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0129] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0130] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 523 nm, a fluorescence full width at half maximum of 36.5 nm, and a quantum yield of 25%.

[0131] Subsequently, the QD dispersion solution was washed with toluene and ethanol, and the redispersion process using TOP was repeated twice. The resulting QD dispersion solution was then measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 522 nm, a fluorescence full width at half maximum of 38 nm, and a quantum yield of 46%.

[0132] [Example 9] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0133] This solution was dissolved at 120°C for 5 minutes, and then 1 ml of a 0.2 M solution of sulfur (S) obtained by dissolving sulfur (S) in octadecene (ODE) was added. The temperature was then increased from 120°C to 200°C and the mixture was 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 salt, and the mixture was heated again at 270°C for 10 minutes with stirring.

[0135] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and myristic acid (MA) in octadecene (ODE) in 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). This mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0136] The resulting reaction solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 534 nm, a fluorescence full width at half maximum of 36 nm, and a quantum yield of 33%.

[0137] Subsequently, the QD dispersion solution was washed with toluene and ethanol, and the redispersion process using TOP was repeated twice. The resulting QD dispersion solution was then measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 534 nm, a fluorescence full width at half maximum of 40 nm, and a quantum yield of 45%.

[0138] [Example 10] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0139] This solution was dissolved at 120°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added. The temperature was then increased from 120°C to 200°C and the mixture was 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 heated again at 270°C for 10 minutes with stirring.

[0141] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) in 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 mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0142] Subsequently, 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. After washing with toluene and ethanol, the QD dispersion solution was redispersed with toluene and measured using a fluorescence spectrometer. The results showed optical properties of 536.5 nm fluorescence wavelength, 29.4 nm fluorescence half-width, and 71% quantum yield.

[0143] [Example 11] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0144] This solution was dissolved at 200°C for 5 minutes, and 1 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added to it. 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 heated again 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 then redispersed with 10 ml of OLAm.

[0147] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) in 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 mixture was then added dropwise over 50 minutes to a solution being heated at 270°C with stirring. After the addition was complete, the mixture was heated with stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0148] Subsequently, 3 ml of TOP was added and heated at 200°C for 10 minutes. The resulting reaction solution was then cooled to room temperature. After washing with toluene and ethanol, the QD dispersion solution was redispersed with TOP and 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] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0150] This solution was dissolved at 200°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added. 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 obtained by dissolving indium acetate (In(OAc)3) in octadecene (ODE) and oleic acid (OLAc), and 1.125 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE) were added, and the mixture was heated again at 300°C for 10 minutes with stirring.

[0152] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) in 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) were mixed and added dropwise over 50 minutes to a solution being heated with stirring at 300°C. After the addition was complete, the mixture was heated with stirring for 20 minutes, and the resulting reaction solution was cooled to room temperature.

[0153] Subsequently, 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. The resulting reaction solution was then cooled to room temperature.

[0154] Subsequently, the reaction solution was centrifuged at 5500 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] Subsequently, 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 5500 rpm for 3 minutes (wash separation). The QD dispersion solution, redispersed with toluene, was measured using a fluorescence spectrometer. Wash separation is a process that controls the degree of aggregation due to differences in ligand coordination to the quantum dots by adjusting the ratio of toluene and ethanol. By going through centrifugation and wash separation, only quantum dots with well-balanced ligand coordination can be recovered, resulting in good emission characteristics (high quantum yield). As a result, as shown in Figure 12, optical properties were obtained with a fluorescence wavelength of 537.5 nm, a fluorescence half-width of 25 nm, and a quantum yield of 63%.

[0156] [Example 13] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0157] This solution was dissolved at 200°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added. 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 obtained by dissolving indium acetate (In(OAc)3) in octadecene (ODE) and oleic acid (OLAc), and 1.8 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE) were added, and the mixture was heated again at 290°C for 10 minutes with stirring.

[0159] Subsequently, 3.6 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in octadecene (ODE) in 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) were mixed and added dropwise over 80 minutes to a solution being heated with stirring at 290°C. After the addition was complete, the mixture was heated with stirring for 10 minutes, and the resulting reaction solution was cooled to room temperature.

[0160] Subsequently, the reaction solution was centrifuged at 5500 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] Subsequently, 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 5500 rpm for 3 minutes. The QD dispersion solution, redispersed with toluene, was measured using a fluorescence spectrometer. As a result, as shown in Figure 13, optical properties were obtained with a fluorescence wavelength of 531.0 nm, a fluorescence half-width of 29.3 nm, and a quantum yield of 85%.

[0162] [Example 14] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0163] This solution was dissolved at 200°C for 5 minutes, and then 0.5 ml of a 0.4 M solution obtained by dissolving tetraethyl thiuram disulfide (TETDS) in oleylamine (OLAm) was added. 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 obtained by dissolving indium acetate (In(OAc)3) in octadecene (ODE) and oleic acid (OLAc), and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene (ODE) were added, and the mixture was heated again at 290°C for 10 minutes with stirring.

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

[0166] Subsequently, the reaction solution was centrifuged at 5500 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 5500 rpm for 3 minutes. Then, 2 ml of ethanol was added to the supernatant, and the mixture was centrifuged again at 5500 rpm for 3 minutes. The QD dispersion solution, redispersed with toluene, was measured using a fluorescence spectrometer. As a result, optical properties were obtained with a fluorescence wavelength of 529.5 nm, a fluorescence half-width of 30.8 nm, and a quantum yield of 71%.

[0168] Subsequently, the resulting reaction solution was heated at 200°C for 5 minutes. Then, 2 ml of a solution prepared by mixing 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 while stirring the solution at 200°C. The resulting reaction solution was then 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 5500 rpm for 3 minutes. Then, 2 ml of ethanol was added to the supernatant, and the mixture was centrifuged again at 5500 rpm for 3 minutes. The QD dispersion solution, redispersed with toluene, was measured using a fluorescence spectrometer. As a result, as shown in Figure 14, optical properties were obtained with a fluorescence wavelength of 528 nm, a fluorescence half-width of 31 nm, and a quantum yield of 84%.

[0170] [Example 15] In a 100 mL reaction vessel, 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

[0172] The resulting reaction solution was centrifuged at 5500 rpm for 3 minutes to precipitate the quantum dots. The precipitated quantum dots were redispersed with toluene, methanol and ethanol were added, and the mixture was centrifuged again at 5500 rpm for 3 minutes to precipitate the QDs once more. Then, 9.5 ml of OLAm was added to the precipitated QDs and the mixture was redispersed.

[0173] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) in a molar ratio of Ga:OLAc = 1:1.5 was mixed with 0.64 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT). This mixture was then added dropwise over 20 minutes to a solution being heated at 290°C with stirring. After the addition was complete, the mixture was heated with stirring for 100 minutes, and the resulting reaction solution was cooled to room temperature. The solution obtained at this time was measured using a fluorescence spectrometer, and the optical properties were found to be a fluorescence wavelength of 639 nm and a fluorescence half-width of 28.5 nm.

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

[0175] Two ml of trioctylphosphine (TOP) was added to two ml of the resulting reaction solution. The precipitate was then removed by centrifugation. 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 full width at half maximum of 33 nm, and a quantum yield of 76%.

[0176] [Example 16] In a 100 mL reaction vessel, 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

[0178] The resulting reaction solution was centrifuged at 5500 rpm for 3 minutes to precipitate the quantum dots. The precipitated quantum dots were redispersed with toluene, methanol and ethanol were added, and the mixture was centrifuged again at 5500 rpm for 3 minutes to precipitate the QDs once more. Then, 9.5 ml of OLAm was added to the precipitated QDs and the mixture was redispersed.

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

[0180] Then, 8 ml of TOP was added and heated at 150°C for 5 minutes. Next, 0.34 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) was added and heated at 150°C for 40 minutes. Finally, 0.17 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution obtained by dissolving sulfur (S) in oleylamine (OLAm) and dodecanethiol (DDT) were added and heated at 150°C for 40 minutes. Afterward, it was cooled to room temperature.

[0181] 0.4 ml of trioctylphosphine (TOP) was added to 2 ml of the resulting reaction solution. The precipitate was then removed by centrifugation. The resulting solution was measured using a fluorescence spectrometer. The optical properties obtained were a fluorescence wavelength of 639 nm, a fluorescence full width at half maximum of 30.5 nm, and a quantum yield of 56%.

[0182] [Example 17] In a 100 mL reaction vessel, 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

[0184] The resulting reaction solution was centrifuged at 5500 rpm for 3 minutes to precipitate the quantum dots. The precipitated quantum dots were redispersed with toluene, methanol and ethanol were added, and the mixture was centrifuged again at 5500 rpm for 3 minutes to precipitate the QDs once more. Then, 9.5 ml of OLAm was added to the precipitated QDs and the mixture was redispersed.

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

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

[0187] 0.4 ml of trioctylphosphine (TOP) was added to 2 ml of the resulting reaction solution. The precipitate was then removed by centrifugation. 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] In a 100 mL reaction vessel, 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

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

[0191] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) in a molar ratio of Ga:OLAc = 1:1.5 was mixed with 0.64 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT). This mixture was then added dropwise over 20 minutes to a solution being heated at 290°C with stirring. After the addition was complete, the mixture was heated with stirring 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 obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) was added and heated at 150°C for 20 minutes. Finally, 0.6 ml of a 0.4 M solution obtained by dissolving zinc acetate (Zn(OAc)2) in oleic acid (OLAc) and oleylamine (OLAm) was added and heated at 150°C for 20 minutes. Then, 0.17 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution obtained by dissolving sulfur (S) in oleylamine (OLAm) and dodecanethiol (DDT) were added and the mixture was heated at 150°C for 20 minutes. After that, 0.6 ml of a 0.4 M solution obtained by dissolving zinc acetate (Zn(OAc)2) in oleic acid (OLAc) and oleylamine (OLAm) was added and the mixture was heated at 150°C for 20 minutes. After that, it was cooled to room temperature.

[0193] 0.4 ml of trioctylphosphine (TOP) was added to 2 ml of the resulting reaction solution. The precipitate was then removed by centrifugation. 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] In a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm), 0.25 ml of a 0.02 M solution obtained by dissolving gallium acetylacetonate (Ga(acac)3) and 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

[0195] This solution was dissolved at 150°C for 5 minutes, and then 0.36 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) was added. The mixture was then stirred for 10 minutes. After the resulting reaction solution was cooled to room temperature, it was heated at 320°C with stirring for 60 minutes. 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 with toluene and washed with methanol and ethanol. Then, 9.5 ml of OLAm was added and the mixture was redispersed.

[0197] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) in 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 then added dropwise over 30 minutes to a solution being heated at 260°C with stirring. After the addition was complete, the mixture was heated with stirring for 150 minutes, and the resulting reaction solution was cooled to room temperature.

[0198] Subsequently, 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 the mixture was heated at 150°C for 20 minutes. Then, 3 ml of trioctylphosphine (TOP) was added and the mixture was 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 the mixture was heated at 150°C for 20 minutes.

[0199] 0.4 ml of trioctylphosphine (TOP) was added to 2 ml of the resulting reaction solution. The precipitate was then removed by centrifugation. 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] In a 100 mL reaction vessel, 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

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

[0203] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride (GaCl3) and oleic acid (OLAc) in oleylamine (OLAm) in 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 then added dropwise over 10 minutes to a solution being heated at 290°C with stirring. After the addition was complete, the mixture was heated with stirring 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. Next, 0.34 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) was added and heated at 150°C for 20 minutes. Finally, 0.3 ml of a 0.8 M solution obtained by dissolving zinc acetate (Zn(OAc)2) in oleic acid (OLAc) and trioctylphosphine (TOP) was added and heated at 150°C for 20 minutes. Then, 0.17 ml of a 0.7 M solution obtained by dissolving selenium (Se) in oleylamine (OLAm) and dodecanethiol (DDT) and 0.15 ml of a 0.8 M solution obtained by dissolving sulfur (S) in oleylamine (OLAm) and dodecanethiol (DDT) were added and the mixture was heated at 150°C for 20 minutes. After that, 0.3 ml of a 0.8 M solution obtained by dissolving zinc acetate (Zn(OAc)2) in oleic acid (OLAc) and trioctylphosphine (TOP) was added and the mixture was heated at 150°C for 20 minutes. After that, it was cooled to room temperature.

[0205] 0.4 ml of trioctylphosphine (TOP) was added to 2 ml of the resulting reaction solution. The precipitate was then removed by centrifugation. 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 full width at half maximum of 23.9 nm, and a quantum yield of 75%.

[0206] [Comparative Example 1] In a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving 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) were added. The mixture was then heated with stirring under an inert gas (N2) atmosphere to dissolve the starting materials.

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

[0208] To the obtained reaction solution, 27.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 was added as a carbamate, and it was heated again at 260 °C for 10 minutes while stirring.

[0209] Thereafter, 2 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and myristic acid: MA in octadecene: ODE so that the 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. 3.5 ml of the solution was added dropwise over 50 minutes onto the solution being heated while stirring at 260 °C. After completion of the dropwise addition, it was heated while stirring for 70 minutes, and the obtained reaction solution was cooled to room temperature.

[0210] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, as shown in Fig. 20, optical properties with a fluorescence wavelength of about 641 nm and a fluorescence half-width of about 33.8 nm were obtained. The fluorescence quantum yield was a very low value that could not be measured.

[0211] As shown in Table 1 below, the initial particle composition, post-added elements, fluorescence wavelength, fluorescence half-width, and fluorescence quantum yield (PLQY) in each example were summarized. Table 2 summarizes the main differences based on Example 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, In was not included in the initial particle composition, and good characteristics were obtained in all cases. On the other hand, in Comparative Example 1, In was included in the initial particle composition, and in particular, the fluorescence quantum yield was a very low value that could not be observed.

[0215] For the "post-added elements", it includes the composition of the shell covering the core surface. However, as a result of the analysis by TEM-EDX, a clear core-shell structure could not be confirmed, and it was found that all the added raw materials were in a mixed crystal state. However, as described above, by not including In in the particles that can be synthesized by reacting initially, good properties have been obtained for all of them. Therefore, the "initial particle composition" and the "post-added elements" are described separately.

[0216] Also, in Example 16, it does not contain Zn, while Example 17 contains Zn, but better property results were obtained for Example 17 compared to Example 16.

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

[0218] Also, as shown in Table 1, it is possible to adjust the fluorescence wavelength within the range of 400 nm to 700 nm, and it was found that quantum dots with green emission can be synthesized by Examples 1 to 14, and quantum dots with red emission can be synthesized by Examples 15 to 20.

[0219] In contrast, for the AIS-based quantum dots described in the patent literature, from the green wavelength region to the red wavelength region, the fluorescence half-width is 45 nm or more, or the fluorescence quantum yield is 35% or less. Quantum dots of the AgIn x Ga 1-x S y Se 1-y system, or the ZnAgIn x Ga 1-x S y Se 1-y system (0 ≦ x < 1, 0 ≦ y ≦ 1) could not be obtained.

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

[0221] As shown in Figure 21, it was found that a large number of quantum dots can be mass-produced with a nearly uniform particle size.

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

[0223] According to the present invention, for example, quantum dots exhibiting high-brightness green fluorescence or red fluorescence can be stably obtained. Furthermore, 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.

[0224] This application is based on Japanese Patent Application No. 2019-153204, filed on August 23, 2019. All of its contents are included here.

Claims

1. ZnAgJan ｘ Ga １－ｘ S ｙ See １－ｙ A quantum dot consisting of a system (0 ≤ x < 1, 0 ≤ y ≤ 1), In the green to red wavelength range, it exhibits fluorescence characteristics with a fluorescence half-width of 33 nm or less and a fluorescence quantum yield of 70% or more. The quantum dot has a core-shell structure consisting of a core and a shell covering the core, and Zn is included in the shell. A quantum dot characterized by the following features.

2. The quantum dot according to claim 1, characterized in that it contains at least Zn, Ag, Ga, and S, or Zn, Ag, Ga, and Se, but does not contain Cd.

3. The quantum dot according to claim 1 or 2, characterized in that the shell is made of ZnS.

4. The quantum dot according to claim 1, characterized in that the core is made of AgInGaS or AgGaSe.

5. A quantum dot according to any one of claims 1 to 4, characterized in that the fluorescence wavelength is in the range of 400 nm to 700 nm.

6. The quantum dot according to any one of claims 1 to 5, characterized in that 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. ZnAgJan ｘ Ga １－ｘ S ｙ See １－ｙ The system consists of (0 ≤ x < 1, 0 ≤ y ≤ 1), After forming the core, a shell containing Zn is formed to cover the core. A method for producing quantum dots, characterized by synthesizing quantum dots that exhibit fluorescence characteristics such as a fluorescence half-width of 33 nm or less and a fluorescence quantum yield of 70% or more in the green wavelength range to the red wavelength range.

Images