Quantum dot

Abstract

The object of the present invention is to provide Cd-free chalcopyrite quantum dots that have a narrow fluorescence half-width and a high fluorescence quantum yield. The quantum dots of the present invention are AgIn x Ga 1-x S y Se 1-y system, or ZnAgIn x Ga 1-x S y Se 1-y The quantum dots are composed of the system (0≦x<1, 0≦y≦1) and are characterized by exhibiting fluorescent properties in the green to red wavelength range, with a fluorescence half-width of 45 nm or less and a fluorescence quantum yield of 35% or more.

Description

Technical Field

[0001] The present invention relates to cadmium-free quantum dots and a method for manufacturing the same.

Background Art

[0002] Quantum dots are inorganic nanoparticles composed of about several thousand to several tens of thousands of atoms and having a particle size of about several nm to a dozen or so nm. Since quantum dots emit fluorescence and their size is on the nano order, they are called fluorescent nanoparticles. Since their composition is derived from a semiconductor material, they are called semiconductor nanoparticles, or since their structure has a specific crystal structure, they are also called nanocrystals.

[0003] Quantum dots are composed of metal atoms having a positive charge and non-metal or semi-metal atoms having a negative charge, and the metal atoms and semi-metal atoms are bonded by an ionic bond or a covalent bond. The ionic nature of the bond depends on the combination of the properties of the metal atoms and semi-metal atoms.

[0004] The emission wavelength of quantum dots can be variously changed depending on the particle size and composition of the particles. Examples of properties representing the performance of quantum dots include fluorescence quantum yield (QY) and full width at half maximum (FWHM).

[0005] One of the performances of quantum dots is photoluminescence. Quantum dots can absorb light of a specific wavelength region and convert it into light of a specific region and emit light. Further, the absorption wavelength and emission wavelength can be controlled by the structure, composition, and size of the quantum dots, and they can be used for various applications taking advantage of this feature.

[0006] For example, when quantum dots are used as a wavelength conversion material in the visible light region, one of their features is that the range of colors that can be expressed is wide, that is, a high color gamut can be achieved. In realizing the high color gamut by a wavelength conversion member in the visible light region using such quantum dots, important optical properties are the fluorescence quantum yield and the fluorescence half-width.

[0007] Conventionally, the highly efficient quantum dots that have been used mainly contained cadmium (Cd). Quantum dots containing Cd have the advantages of a high fluorescence quantum yield and a narrow fluorescence half-width. On the other hand, due to the toxicity of Cd, its use is regulated in various countries, which has been a major obstacle to practical applications.

[0008] In contrast, the development of quantum dots that do not contain Cd has also been studied extensively. For example, the following patent documents describe AIS or AIGS-based quantum dots containing Ag, In, and S, or Ag, In, Ga, and S, or AISe or AIGSe-based quantum dots containing Ag, In, and Se, or Ag, In, Ga, and Se.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0010]

Non-Patent Document 1

[0011] As described above, although the research and development of chalcopyrite-based quantum dots containing no Cd has progressed, none of the quantum dots has reached the performance that should replace Cd-based quantum dots from the viewpoints of fluorescence full-width at half-maximum and fluorescence quantum yield.

[0012] The present invention has been made in view of such points, and an object thereof is to provide a chalcopyrite-based quantum dot that does not contain Cd and has a narrow fluorescence full-width at half-maximum and a high fluorescence quantum yield.

[0013] Another object of the present invention is to provide a method for producing quantum dots that can synthesize the above-described quantum dots in a mass-producible manner. [Means for Solving the Problems]

[0014] The quantum dots of the present invention are ZnAgIn x Ga 1-x S y Se 1-yA quantum dot composed of a system (0 ≦ x < 1, 0 ≦ y ≦ 1), having 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, and the ratio of Ag to Ga is in the range of Ag / Ga = 0.05 or more and 10 or less, and the ratio of Zn to Ga is in the range of Zn / Ga = 0.1 or more and 10 or less ri , The quantum dot has a core-shell structure of a core and a shell covering the core, and Zn is included in the shell. characterized by this.

[0015] The method for manufacturing the quantum dot of the present invention 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), and is characterized by synthesizing a quantum dot that exhibits fluorescence characteristics with 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.

Advantages of the Invention

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

[0017] Also, according to the quantum dot of the present invention, quantum dots having a target emission wavelength can be synthesized according to the application.

[0018] Also, according to the quantum dot of the present invention, since quantum dots with a narrow half-width can be synthesized at an emission wavelength according to the purpose, when used as a wavelength conversion material, an improvement in high color gamut can be achieved.

[0019] Also, according to the method for manufacturing the quantum dot of the present invention, it is possible to synthesize quantum dots with a narrow fluorescence half-width and not containing Cd in a mass-producible method.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Embodiment for Carrying Out the Invention

[0021] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof. In this specification, the notation "~" means including the lower limit value and the 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-yIt is a quantum dot composed of a system (0≦x<1, 0≦y≦1). The quantum dot 5 in this embodiment preferably contains at least silver (Ag), gallium (Ga), and sulfur (S), or silver (Ag), gallium (Ga), and selenium (Se), and is a nanocrystal that does not contain cadmium (Cd). Further, the quantum dot 5 can also contain indium (In) or zinc (Zn) in addition to Ag, Ga, and S, or Ag, Ga, and Se.

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

[0025] The ratio of Ag to Ga contained in the quantum dot 5 is preferably in the range of Ag / Ga = 0.05 or more and 10 or less. Further, 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 contained in the quantum dot 5 is preferably in the range of Zn / Ga = 0.1 or more and 10 or less. The ratio Zn / Ga is more preferably in the range of 0.1 or more and 5 or less. By controlling this ratio, it becomes 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 or more and 700 nm or less. In this embodiment, it is also possible to adjust the fluorescence wavelength within the range of 500 nm or more and 650 nm or less.

[0028] As shown in Fig. 1A, it is preferable that a large number of organic ligands (ligands) 11 are coordinated on the surface of the quantum dots 5. This can suppress the aggregation of the quantum dots 5 and enable the expression of the desired optical properties. The ligands that can be used in the reaction are not particularly limited, and for example, the following ligands can be mentioned as representative ones.

[0029] (1) Aliphatic primary amine-based Oleylamine: C 18 H 35 NH2, Stearyl (octadecyl) amine: C 18 H 37 NH2, Dodecyl (lauryl) amine: C 12 H 25 NH2, Decylamine: C 10 H 21 NH2, Octylamine: C8H 17 NH2 (2) Fatty acid-based Oleic acid: C 17 H 33 COOH, Stearic acid: C 17 H 35 COOH, Palmitic acid: C 15 H 31 COOH, Myristic acid: C 13 H 27 COOH, Lauric acid: C 11 H 23 COOH, Decanoic acid: C9H 19 COOH, Octanoic acid: C7H 15 COOH (3) Thiol-based Octadecanethiol: C 18 H 37 SH, Hexadecanethiol: C 16 H 33 SH, Tetradecanethiol: C 14 H 29 SH, Dodecanethiol: C 12 H 25 SH, Decanethiol: C 10 H 21 SH, Octanethiol: C8H 17 SH (4) Phosphine-based Trioctylphosphine: (C8H 17 )3P, Triphenylphosphine: (C6H5)3P, Tributylphosphine: (C4H9)3P (5) Phosphine oxide-based Trioctylphosphine oxide: (C8H 17 )3P=O, Triphenylphosphine oxide: (C6H5)3P=O, Tributylphosphine oxide: (C4H9)3P=O

[0030] The characteristic part of the quantum dot 5 of this embodiment will be described. The quantum dot 5 of this embodiment exhibits fluorescence characteristics with 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.

[0031] Here, the "fluorescence half-width" refers to the full width at half maximum (FWHM) indicating the spread of the fluorescence wavelength at half the intensity of the peak value of the fluorescence intensity in the fluorescence spectrum. Also, the fluorescence half-width is preferably 35 nm or less. More preferably, the fluorescence half-width is 30 nm or less. Still more preferably, the fluorescence half-width is 25 nm or less. Thus, since the fluorescence half-width can be narrowed, improvement in high color gamut can be achieved.

[0032] The fluorescence quantum yield of the quantum dot 5 of this embodiment is more preferably 40% or more, still more preferably 60% or more, even more preferably 70% or more, and most preferably 80% or more. 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-yIn a quantum dot of the system (0 ≦ x < 1, 0 ≦ y ≦ 1), it is possible to narrow the fluorescence half-width and increase the fluorescence quantum yield from the green wavelength region to the red wavelength region.

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

[0035] Note that in this embodiment, as described above, it is possible to control the fluorescence wavelength to 400 nm or more and 700 nm or less, but for a wavelength conversion material in the visible light region, green or red light emission is preferred.

[0036] Here, chalcopyrite is generally a material that emits defective fluorescence with a fluorescence half-width of 45 to 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 very short compared to defective fluorescence. From such characteristics, it is presumed that the quantum dot 5 of this embodiment emits band-edge fluorescence.

[0037] In particular, the quantum dots 5 of the present embodiment can synthesize quantum dots 5 having a fluorescence full width at half maximum of 30 μm or less, a fluorescence quantum yield of 80% or more, and a fluorescence wavelength in the range of 510 nm or more and 650 nm or less. In this way, not only the green fluorescence wavelength (around 510 to 540 nm), but also the red fluorescence wavelength (around 610 to 650 nm) can achieve the characteristics of a narrow fluorescence full width at half maximum and a high fluorescence quantum yield.

[0038] The quantum dots 5 shown in FIG. 1B have a core-shell structure having a core 5a and a shell 5b coated on the surface of the core 5a. As shown in FIG. 1B, it is preferable that a large number of organic ligands 11 are coordinated on the surface of the quantum dots 5. Further, the fluorescence full width at half maximum of the quantum dots 5 shown in FIG. 1B is 45 nm or less, and the fluorescence quantum yield is 35% or more.

[0039] The core 5a of the quantum dots 5 shown in FIG. 1B is the nanocrystal shown in FIG. 1A. Therefore, the core 5a is preferably formed of a nanocrystal containing Ag, Ga, S, or Ag, Ga, Se and not containing Cd. The shell 5b, like the core 5a, does not contain cadmium (Cd). The shell 5b is not particularly limited in terms of material, and examples thereof include indium sulfide, gallium sulfide, aluminum sulfide, zinc sulfide, indium selenide, gallium selenide, aluminum selenide, and zinc selenide. At this time, as the Ga source, gallium chloride, gallium bromide, or gallium iodide is preferably used.

[0040] Note that the shell 5b may be in a state of being solid-solubilized on the surface of the core 5a. In FIG. 1B, the boundary between the core 5a and the shell 5b is shown by a dotted line, which indicates that it does not matter whether the boundary between the core 5a and the shell 5b can be confirmed by analysis or not. ZnAgIn listed above x Ga 1-x S y Se 1-y In the quantum dots of the ZnAgInGaSSe system (0 ≦ x < 1, 0 ≦ y ≦ 1), even if the core-shell structure cannot be confirmed, it can be presumed that the core 5a is covered with the shell 5b by containing Zn.

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

[0042] In this embodiment, since the core composed of AgGaS, AgGaSe, AgGaInS or AgGaInSe alone can emit fluorescence, the shell coating is not necessarily required. However, by adopting a core-shell structure, a further increase in the fluorescence quantum yield can be expected while the fluorescence half-width remains narrow. Also, regarding In, fluorescence can be observed whether it is contained or not. For example, in the case of green fluorescent quantum dots, good emission characteristics are provided by containing In, but even if In is not contained, fluorescence is emitted although the fluorescence half-width tends to be somewhat larger. Specifically, emission from AgGaS has been confirmed.

[0043] Generally, when Zn is used, defective emission occurs due to the difference in valence (Zn is divalent, Ag is monovalent, Ga and In are trivalent), and the fluorescence half-width tends to widen. However, in this embodiment, as shown in the experiment described later, even if Zn is post-added, the fluorescence quantum yield can be increased while the fluorescence half-width remains narrow. That is, by using Zn, it becomes possible to improve the emission characteristics. Subsequently, the manufacturing method of the quantum dots 5 of this embodiment will be described.

[0044] The manufacturing method of the quantum dots of this embodiment is characterized by synthesizing quantum dots having 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, which are composed of an AgIn x Ga 1-x S y Se 1-y system, or a ZnAgIn x Ga 1-x S y Se 1-y system (0 ≦ x < 1, 0 ≦ y ≦ 1).

[0045] First, in this embodiment, an organic silver compound, an organic gallium compound, and sulfur or selenium, or an organic silver compound, an organic indium compound, an organic gallium compound, and sulfur or selenium are heated and synthesized in one pot.

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

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

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

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

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

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

[0052] In addition, in this embodiment, an organic sulfur compound such as thiol can be used as a raw material for S. For example, octadecanethiol: C 18 H 37 SH, hexadecanethiol: 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 source species greatly contribute to the fluorescence characteristics. In this embodiment, it is preferable to use an S-ODE source in which sulfur is dissolved in octadecene: ODE, a disulfide-based or thiuram-based S source, or S-OLAm / DDT in which S is dissolved in oleylamine and dodecanethiol. Among these, with the S-ODE source, a fluorescence half-width of 40 nm or less and a fluorescence quantum yield of 40% or more can be obtained, but even better characteristics can be obtained by using disulfide. For example, diphenyldisulfide, dibenzyldisulfide, isopropylxanthogen disulfide, and 4,4'-dithiodimorpholine. Also, even better fluorescence characteristics can be obtained by using a thiuram-based source. For example, thiuram disulfide, dipentamethylenethiuram tetrasulfide, tetraethylthiuram disulfide, tetramethylthiuram disulfide, etc. Additionally, the S source may also be a source having a structure in which multiple sulfurs are linked together (―S―)n or a source having a structure in which nitrogen (N-S-), carbon (C-S-), etc. are attached to sulfur.

[0054] Also, in this embodiment, an organic selenium compound (organic chalcogen compound) can be used as the Se source. For example, trioctylphosphine selenide in which selenium is dissolved in trioctylphosphine: (C8H 17 )3P=Se, or tributylphosphine selenide in which selenium is dissolved in tributylphosphine: (C4H9)3P=Se, or a solution in which selenium is dissolved in a high-boiling solvent such as octadecene, which is a long-chain hydrocarbon, can be used.

[0055] When synthesizing AgGaSe or AgInGaSe, the type of selenium raw material significantly contributes 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. In ordinary chalcopyrite-based quantum dots, two types of luminescence can be confirmed 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 luminescence intensity ratio is such that band-edge luminescence / defect luminescence is 10 or less. Subsequently, as the reaction progresses further, the intensity of defect luminescence gradually decreases, and often, the intensity of band-edge luminescence also 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 the peak that is not defect luminescence can be confirmed in the initial stage of luminescence.

[0056] In addition, in this embodiment, an organozinc compound or an inorganic zinc compound is used as the raw material for 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 can be used. As zinc carbamate, 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] In addition, in this embodiment, it is possible to obtain quantum dots in one pot without isolating and purifying the precursor.

[0058] In addition, in this embodiment, the synthesized quantum dots exhibit fluorescence characteristics without performing various treatments such as washing, isolation and purification, coating treatment, or ligand exchange.

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

[0060] In addition, after having a core-shell structure, by purifying with a specific solvent, the fluorescence quantum yield can be further increased. For example, trioctylphosphine (TOP), etc.

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

[0062] In addition, in this embodiment, by mixing toluene, methanol, ethanol, acetone, etc. into the synthesized reaction solution and centrifuging to remove the aggregates, quantum dots with more excellent luminescence characteristics can be obtained.

[0063] In the method for manufacturing quantum dots according to this embodiment, after forming initial reaction particles, a predetermined element is added later for synthesis. At this time, it is preferable that In is not contained in the initial stage of the reaction. Specifically, the particles formed in the initial stage of the reaction are preferably AgGaS or AgGaSe that do not contain In, which exhibit the best luminescence characteristics.

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

[0065] In addition, for quantum dots with green fluorescence, it is preferably a quantum dot containing In finally, and In can be included in the reaction process. However, in quantum dots with green fluorescence, containing In is not essential. For example, although the fluorescence half-width is slightly broadened, luminescence has been confirmed with AgGaS without containing In.

[0066] Also, in this embodiment, when including Zn in the quantum dots, it is preferable to add Zn while paying attention to the following points. First, Zn is not added during the initial reaction but is added in the final step. This is because if Zn is contained inside the particles, defect luminescence may be dominant, or there is a risk that only defect luminescence can be confirmed. Therefore, in the final step, the aim is to react only on the particle surface by adding Zn. The second is to add Zn at a low temperature. Here, the low temperature means about 150 to 200 °C. When the temperature at which Zn is added is high, Zn reacts to the inside of the particles, so it is likely to result in defect luminescence. Therefore, in order to stop at the reaction on the particle surface, it is preferable to react only on the particle surface at a low temperature.

[0067] Also, in this embodiment, when synthesizing AgGaSe, the Se raw material is preferably Se-OLAm / DDT. Thereby, defect luminescence can be effectively suppressed.

[0068] Also, when synthesizing AgGaS, instead of using sulfur powder which is generally used, a thiuram-based material, particularly tetraethylthiuram disulfide, is preferable as it can obtain good luminescence characteristics.

[0069] Also, the centrifugation step is a step of separating large particles from small particles. However, in the centrifugation step with the addition of toluene or ethanol, even if the particle sizes are uniform, by controlling the ratio of toluene or ethanol, the degree of aggregation can be changed due to the difference in the surface ligands of the quantum dots. At that time, it can be controlled at a ratio of quantum dots:toluene:ethanol = 1:0.5 - 2:0.5 - 2. Note that methanol may be used instead of ethanol. As a result, it is possible to separate into quantum dots with a high fluorescence quantum yield and quantum dots with a low fluorescence quantum yield. After that, by adding TOP to the separated quantum dots, it is possible to further improve the fluorescence quantum yield.

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

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

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

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

[0074] The 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 PN-junctioned.

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

[0076] In addition, the resin composition in which the quantum dots 5 are dispersed in the present embodiment may contain a fluorescent substance different from the quantum dots 5 and the quantum dots 5. Examples of the fluorescent substance include sialon-based and KSF (K2SiF6:Mn 4+ ) red phosphors, but 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, methacrylic resin, MS resin, polyvinyl chloride (PVC), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethylpentene, liquid crystal polymer, epoxy resin, silicone resin, or a mixture thereof can be used.

[0078] The LED device using quantum dots according to this 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 this embodiment to the LED device shown in FIG. 2, the display device shown in FIG. 3, etc., it is possible to effectively improve the light emission characteristics of the device.

[0081] In addition, a resin composition in which the quantum dots 5 of this 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. It should be noted that the present invention is not limited by the following examples.

[0083] <Raw materials> In the experiment, AgIn x Ga 1-x S y Se 1-y system or ZnAgIn x Ga1-x S y Se 1-y The following raw materials were used in synthesizing quantum dots of the system (0 ≦ X < 1, 0 ≦ Y ≦ 1). (Solvent) Octadecene: manufactured by Aldrich Co., Ltd. Oleylamine: manufactured by Kao Corporation Dodecanethiol: manufactured by Kao Corporation Oleic acid: manufactured by Kao Corporation, Lunac O-V Trioctylphosphine: manufactured by Hokko Chemical Industry Co., Ltd. (Silver raw material) Silver acetate: manufactured by Aldrich Co., Ltd. (Indium raw material) Indium acetate: manufactured by Shinsei Chemical Industry Co., Ltd. Indium diethyldithiocarbamate: synthetic raw material by the inventors (Gallium raw material) Gallium chloride: manufactured by Shinsei Chemical Industry Co., Ltd. Gallium acetylacetonate: manufactured by Tokyo Chemical Industry Co., Ltd. (Sulfur raw material) Sulfur: manufactured by Kishida Chemical Co., Ltd. Tetraethylthiuram disulfide: manufactured by Sanshin Chemical Industry Co., Ltd. Dipentamethylene thiuram 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 instrument> Fluorescence spectrometer: F-2700 manufactured by JASCO Corporation Ultraviolet-visible spectrophotometer: V-770 manufactured by Hitachi, Ltd. Quantum yield measuring device: QE-1100 manufactured by Otsuka Electronics Co., Ltd. Scanning electron microscope (SEM): SU9000 manufactured by Hitachi, Ltd.

[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, 165 mg of gallium acetylacetonate: Ga(acac)3, 28.5 mL of oleylamine: OLAm, and 1.5 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, the mixture was heated to dissolve the raw 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 tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added thereto. Thereafter, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Then, the resulting reaction solution was cooled to room temperature.

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

[0087] Thereafter, 9 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 13.5 mL of a mixed solution of 4.5 mL of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE were added dropwise over 50 minutes onto the solution being heated while stirring at 270 °C. After completion of the dropwise addition, the mixture was heated while stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

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

[0089] Thereafter, the QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in Figure 4, optical properties with a fluorescence wavelength of 539 nm, a fluorescence half-width of 35.4 nm, and a quantum yield of 75% were obtained.

[0090] [Example 2] Into a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw 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 dipentamethylenethiuram tetrasulfide (DPTT) in oleylamine: OLAm was added thereto. Thereafter, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0092] To the obtained reaction solution, 41.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2] as a carbamate was added, and it was heated again at 270 °C for 10 minutes while stirring.

[0093] Thereafter, 4.5 mL of a mixed solution of 3 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 was added dropwise over 50 minutes onto the solution being heated while stirring at 270 °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.

[0094] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 526 nm, a fluorescence half-width of 35.5 nm, and a quantum yield of 34% were obtained.

[0095] Subsequently, the QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in Fig. 5, optical properties with a fluorescence wavelength of 526.5 nm, a fluorescence half-width of 34.8 nm, and a quantum yield of 54% were obtained.

[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, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 mL of dodecanethiol: DDT were added. Then, it was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0097] This solution was dissolved at 120 °C for 5 minutes, and 0.5 mL of a 0.4 M solution obtained by dissolving 4,4'-dithiobis(morpholine) (DTDM) in oleylamine: OLAm was added thereto. Then, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Thereafter, the obtained reaction solution was cooled to room temperature.

[0098] 41.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 as a carbamate was added to the obtained reaction solution, and it was heated again at 270 °C for 10 minutes while stirring.

[0099] Subsequently, 4.5 mL of a mixed solution obtained by mixing 3 mL of a 0.1 M solution of gallium chloride: GaCl3 and myristic acid: MA dissolved in octadecene: ODE so that the molar ratio of Ga: MA = 1: 3 and 1.5 mL of a 0.2 M solution of sulfur: S dissolved in octadecene: ODE was added dropwise over 50 minutes onto the solution being heated with stirring at 270 °C. After completion of the dropwise addition, it was heated with stirring for 70 minutes, and the obtained reaction solution was cooled to room temperature.

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

[0101] Subsequently, the QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in Fig. 6, optical properties with a fluorescence wavelength of 527.5 nm, a fluorescence half-width of 36.9 nm, and a quantum yield of 56% were obtained.

[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, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw 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 thereto. Then, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Subsequently, the obtained reaction solution was cooled to room temperature.

[0104] To the obtained reaction solution, 41.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 was added as a carbamate, and it was heated again at 270 °C for 10 minutes while stirring.

[0105] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and myristic acid: MA in octadecene: ODE such that the molar ratio of Ga: MA is 1: 3, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE were mixed to obtain 4.5 ml of a solution, which was added dropwise onto a solution being heated with stirring at 270 °C over 50 minutes. After completion of the dropwise addition, 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 with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 530 nm, a fluorescence half-width of 37 nm, and a quantum yield of 40% were obtained.

[0107] Subsequently, a QD dispersion solution obtained by repeating the operations of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in Figure 7, optical properties with a fluorescence wavelength of 532 nm, a fluorescence half-width of 36.9 nm, and a quantum yield of 65% were obtained.

[0108] [Example 5] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were added. Then, the mixture was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

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

[0110] To the obtained reaction solution, 41.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 was added as a carbamate, and the mixture was heated again at 270 °C for 10 minutes while stirring.

[0111] Subsequently, 3 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 4.5 ml of a mixed solution of 1.5 ml of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE were added dropwise over 50 minutes onto the solution being heated at 270 °C while stirring. After completion of the dropwise addition, the mixture was heated while stirring for 70 minutes, and the obtained reaction solution was cooled to room temperature.

[0112] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 542 nm, a fluorescence half-width of 36.5 nm, and a quantum yield of 54% were obtained.

[0113] Subsequently, a QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in Figure 8, optical properties with a fluorescence wavelength of 542 nm, a fluorescence half-width of 36.5 nm, and a quantum yield of 71% were obtained.

[0114] [Example 6] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were added. Then, the mixture was heated while stirring under an inert gas (N2) atmosphere to dissolve the raw 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 tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added thereto. Thereafter, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Thereafter, the resulting reaction solution was cooled to room temperature.

[0116] To the resulting reaction solution, 341.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 as a carbamate was added, and it was heated again at 270 °C for 10 minutes while stirring.

[0117] Thereafter, 4.5 ml of a mixed solution obtained by dissolving 3 ml of a 0.1 M solution of gallium chloride: GaCl3 and oleic acid: OLAc in octadecene: ODE so that the molar ratio of Ga: MA = 1: 3 and 1.5 ml of a 0.2 M solution of sulfur: S in octadecene: ODE was added dropwise over 50 minutes onto the solution being heated while stirring at 270 °C. After completion of the dropwise addition, it was heated while stirring for 70 minutes, and the resulting reaction solution was cooled to room temperature.

[0118] The resulting reaction solution was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 546 nm, a fluorescence half-width of 29.3 nm, and a quantum yield of 39% were obtained.

[0119] Thereafter, the QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in FIG. 9, optical properties with a fluorescence wavelength of 548.5 nm, a fluorescence half-width of 30.5 nm, and a quantum yield of 59% were obtained.

[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, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw 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 tetraethylthiuram disulfide in oleylamine: OLAm was added thereto. Thereafter, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0122] To the obtained reaction solution, 21.8 mg of indium acetate: In(OAc)3 and 0.75 mL of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE were added, and it was heated with stirring at 270 °C for 10 minutes.

[0123] Thereafter, 3 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, and 4.5 mL of the mixed solution was added dropwise over 50 minutes onto the solution being heated with stirring at 270 °C. After completion of the dropwise addition, it was heated with stirring for 70 minutes, and the obtained reaction solution was cooled to room temperature.

[0124] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 546 nm, a fluorescence half-width of 36.5 nm, and a quantum yield of 55% were obtained.

[0125] Thereafter, a QD dispersion solution obtained by repeating the operations of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, as shown in FIG. 10, optical properties with a fluorescence wavelength of 546.5 nm, a fluorescence half-width of 36.2 nm, and a quantum yield of 81% were obtained.

[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, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

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

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

[0129] Thereafter, 4.5 mL of a mixed solution obtained by mixing 3 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 was added dropwise over 50 minutes onto the solution being heated while stirring at 270 °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.

[0130] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 523 nm, a fluorescence half-width of 36.5 nm, and a quantum yield of 25% were obtained.

[0131] Thereafter, the QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 522 nm, a fluorescence half-width of 38 nm, and a quantum yield of 46% were obtained.

[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, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

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

[0134] To the obtained reaction solution, 41.9 mg of indium diethyldithiocarbamate: In[SC(=S)N(C2H5)2]3 as a carbamate was added, and it was heated again at 270 °C for 10 minutes while stirring.

[0135] Thereafter, 4.5 mL of a mixed solution obtained by mixing 3 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 was added dropwise over 50 minutes onto the solution being heated while stirring at 270 °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.

[0136] The obtained reaction solution was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 534 nm, a fluorescence half-width of 36 nm, and a quantum yield of 33% were obtained.

[0137] Thereafter, the QD dispersion solution obtained by repeating the operation of washing with toluene and ethanol and redispersing with TOP twice was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 534 nm, a fluorescence half-width of 40 nm, and a quantum yield of 45% were obtained.

[0138] [Example 10] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 73.4 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.3 ml of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw 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 tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added thereto. Then, the temperature was raised from 120 °C to 200 °C and stirred for a total of 20 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0140] To the obtained 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 it was heated again at 270 °C for 10 minutes while stirring.

[0141] Then, 4.5 ml of a mixed solution of 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in octadecene: ODE so that the molar ratio of Ga: OLAc = 1: 1.5 and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE was added dropwise over 50 minutes onto the solution being heated while stirring at 270 °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.

[0142] Subsequently, 3 ml of TOP was added, and the mixture was heated at 200 °C for 10 minutes. The resulting reaction solution was cooled to room temperature. Then, it was washed with toluene and ethanol, and the QD dispersion solution redispersed in toluene was measured with a fluorescence spectrometer. As a result, optical properties with a fluorescence wavelength of 536.5 nm, a fluorescence full width at half maximum of 29.4 nm, and a quantum yield of 71% were obtained.

[0143] [Example 11] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 91.8 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

[0144] This solution was dissolved at 200 °C for 5 minutes, and then 1 ml of a 0.4 M solution obtained by dissolving tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added, and it was heated while stirring for 40 minutes. Then, the resulting reaction solution was 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 it was heated again at 270 °C for 10 minutes while stirring.

[0146] The resulting reaction solution was washed with 3 ml of toluene and 30 ml of ethanol, and 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 so that the molar ratio of Ga: OLAc = 1: 1.5, and 1.5 ml of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE were mixed to obtain 4.5 ml of a solution, which was added dropwise onto a solution being heated with stirring at 270 °C over 50 minutes. After completion of the dropping, 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 the mixture was heated at 200 °C for 10 minutes. The resulting reaction solution was cooled to room temperature. Then, it was washed with toluene and ethanol and redispersed with TOP, and the QD dispersion solution was measured with a fluorescence spectrometer. As a result, as shown in Fig. 11, optical properties with a fluorescence wavelength of 530.5 nm, a fluorescence half-width of 38 nm, and a quantum yield of 86% were obtained.

[0149] [Example 12] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 55 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were added. Then, the mixture was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0150] This solution was dissolved at 200 °C for 5 minutes, and 0.5 ml of a 0.4 M solution obtained by dissolving tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added thereto. Then, it was heated with stirring at 200 °C for 40 minutes. Then, the resulting reaction solution was 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 with stirring at 300 °C for 10 minutes.

[0152] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in octadecene: ODE such that the molar ratio of Ga: OLAc is 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 the resulting solution was added dropwise over 50 minutes onto a solution being heated while stirring at 300 °C. After completion of the dropwise addition, the mixture was heated while 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 while stirring at 200 °C for 30 minutes, and the resulting reaction solution was cooled to room temperature.

[0154] Subsequently, the reaction solution was centrifuged at 5500 rpm for 3 minutes using a centrifuge, 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, and the resulting reaction solution was 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 (washing and separation), and the QD dispersion solution redispersed with toluene was measured using a fluorescence spectrometer. Note that the washing and separation step controls the degree of aggregation due to differences in the ligands coordinated to the quantum dots according to the ratio of toluene and ethanol and separates them. By undergoing centrifugation and washing and separation, only quantum dots with ligands coordinated in a well-balanced manner can be recovered, and good luminescence characteristics (high quantum yield) can be obtained. As a result, as shown in Figure 12, optical characteristics with a fluorescence wavelength of 537.5 nm, a fluorescence full width at half maximum of 25 nm, and a quantum yield of 63% were obtained.

[0156] [Example 13] Into a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 73.4 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw 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 tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added thereto. Thereafter, it was heated with stirring at 200 °C for 40 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0158] To the obtained 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 it was heated again with stirring at 290 °C for 10 minutes.

[0159] Thereafter, a solution prepared by mixing 3.6 mL of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in octadecene: ODE so that the molar ratio of Ga: OLAc = 1:3, 1.8 mL of a 0.2 M solution obtained by dissolving sulfur: S in octadecene: ODE, and 2.7 mL of oleylamine: OLAm was added dropwise over 80 minutes onto the solution being heated with stirring at 290 °C. After completion of the dropwise addition, it was heated with stirring for 10 minutes, and the obtained reaction solution was cooled to room temperature.

[0160] Thereafter, the reaction solution was centrifuged at 5500 rpm for 3 minutes using a centrifuge, and the supernatant was recovered. 3 mL of TOP was added to the recovered supernatant, and it was heated at 180 °C for 10 minutes, and the obtained reaction solution was 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, followed by centrifugation. Then, 2 ml of ethanol was added to the supernatant, and centrifugation was performed 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 Fig. 13, optical properties with a fluorescence wavelength of 531.0 nm, a fluorescence half-width of 29.3 nm, and a quantum yield of 85% were obtained.

[0162] [Example 14] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 73.4 mg of gallium acetylacetonate: Ga(acac)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were placed. Then, while stirring under an inert gas (N2) atmosphere, the mixture was heated to dissolve the raw 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 tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm was added thereto. Subsequently, it was heated with stirring at 200 °C for 40 minutes. Then, the obtained reaction solution was cooled to room temperature.

[0164] To the obtained 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 with stirring at 290 °C for 10 minutes.

[0165] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in oleylamine: OLAm such that the molar ratio of Ga: OLAc is 1:3, 0.5 ml of a 0.4 M solution obtained by dissolving tetraethylthiuram disulfide (TETDS) in oleylamine: OLAm, and 3 ml of oleylamine: OLAm were added dropwise over 80 minutes onto a solution being heated while 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.

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

[0168] Subsequently, the resulting reaction solution was heated at 200 °C for 5 minutes, and 0.075 ml of an 0.8 M solution obtained by dissolving zinc acetate: Zn(OAc)2 in oleic acid: OLAc and trioctylphosphine: TOP, 0.6 ml of a 0.2 M solution obtained by dissolving sulfur: S in trioctylphosphine: TOP, and 2 ml of a solution obtained by mixing 1.325 ml of oleylamine: OLAm were added dropwise over 120 minutes onto a solution being heated while stirring at 200 °C. The resulting reaction solution was cooled to room temperature.

[0169] To 1 ml of the obtained reaction solution, 1 ml of toluene and 1.6 ml of ethanol were added, and centrifuged at 5500 rpm for 3 minutes. Then, 2 ml of ethanol was added to the supernatant, centrifuged at 5500 rpm for 3 minutes, and the QD dispersion solution redispersed with toluene was measured with a fluorescence spectrometer. As a result, as shown in Fig. 14, optical properties with a fluorescence wavelength of 528 nm, a fluorescence half-width of 31 nm, and a quantum yield of 84% were obtained.

[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, 55.5 mg of gallium acetylacetonate: Ga(acac)3, 20 mL of oleylamine: OLAm, and 3 ml of dodecanethiol: DDT were placed. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw materials.

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

[0172] The obtained reaction solution was centrifuged at 5500 rpm for 3 minutes with a centrifuge to precipitate the quantum dots. The precipitated quantum dots were redispersed with toluene, methanol and ethanol were added, and then centrifuged at 5500 rpm for 3 minutes with a centrifuge to precipitate the QD again. Then, 9.5 ml of OLAm was added to the precipitated QD for redispersion.

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

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

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

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

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

[0178] The obtained reaction solution was centrifuged at 5500 rpm for 3 minutes using a centrifuge to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene, methanol and ethanol were added, and then it was centrifuged at 5500 rpm for 3 minutes using a centrifuge to precipitate the QD again. Thereafter, 9.5 ml of OLAm was added to the precipitated QD and redispersion was carried out.

[0179] Thereafter, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in oleylamine: OLAm so that the molar ratio of Ga: OLAc was 1: 1.5 and 3.64 ml of a mixed solution of 0.64 ml of a 0.7 M solution obtained by dissolving selenium: Se in oleylamine: OLAm and dodecanethiol: DDT were added dropwise over 30 minutes onto the solution being heated with stirring at 290 °C. After completion of the dropwise addition, it was heated with stirring for 90 minutes, and the obtained reaction solution was cooled to room temperature.

[0180] Thereafter, 8 ml of TOP was added and heated at 150 °C for 5 minutes. Then, 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. 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 heated at 150 °C for 40 minutes. Thereafter, it was cooled to room temperature.

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

[0182] [Example 17] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 55.5 mg of gallium acetylacetonate: Ga(acac)3, 20 mL of oleylamine: OLAm, and 3 ml of dodecanethiol: DDT were placed. Then, it was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

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

[0184] The obtained reaction solution was centrifuged at 5500 rpm for 3 minutes with a centrifuge to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene, methanol and ethanol were added, and then centrifuged at 5500 rpm for 3 minutes with a centrifuge to precipitate the QD again. Then, 9.5 ml of OLAm was added to the precipitated QD for redispersion.

[0185] Subsequently, 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in oleylamine: OLAm so that the molar ratio of Ga: OLAc = 1: 1.5, and 0.64 ml of a 0.7 M solution obtained by dissolving selenium: Se in oleylamine: OLAm and dodecanethiol: DDT were mixed, and 3.64 ml of the mixed solution was added dropwise onto a solution heated with stirring at 290 °C over 30 minutes. After completion of the dropwise addition, the mixture was heated with stirring for 90 minutes, and the resulting reaction solution was cooled to room temperature.

[0186] Subsequently, 8 ml of TOP was added and heated at 150 °C for 5 minutes. Then, 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. Then, 0.3 ml of an 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 an 0.8 M solution obtained by dissolving sulfur: S in oleylamine: OLAm and dodecanethiol: DDT were added and heated at 150 °C for 20 minutes. Then, 0.3 ml of an 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. Subsequently, it was cooled to room temperature.

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

[0188] [Example 18] Into a 100 mL reaction vessel, 0.5 mL of a 0.2 M solution obtained by dissolving silver acetate: AgOAc in oleylamine: OLAm, 55.5 mg of gallium acetylacetonate: Ga(acac)3, 20 mL of oleylamine: OLAm, and 3 mL of dodecanethiol: DDT were added. Then, while stirring under an inert gas (N2) atmosphere, it was heated to dissolve the raw 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 thereto. Then, it was stirred for 10 minutes. After the obtained reaction solution was cooled to room temperature, it was heated while stirring at 320 °C for 20 minutes. Then, it was cooled to room temperature.

[0190] The obtained reaction solution was centrifuged to precipitate the quantum dots. The precipitated quantum dots were redispersed in toluene and washed with methanol and ethanol. Then, 9.5 mL of OLAm was added for redispersion.

[0191] Thereafter, 3 mL of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in oleylamine: OLAm so that the molar ratio of Ga: OLAc = 1: 1.5, and 3.64 mL of a mixed solution of 0.64 mL of a 0.7 M solution obtained by dissolving selenium: Se in oleylamine: OLAm and dodecanethiol: DDT were added dropwise over 20 minutes onto the solution being heated while stirring at 290 °C. After completion of the dropwise addition, it was heated while stirring for 100 minutes, and the obtained reaction solution was cooled to room temperature.

[0192] Subsequently, 8 ml of TOP was added and heated at 150 °C for 5 minutes. Then, 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. 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 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 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 heated at 150 °C for 20 minutes. Then, it was cooled to room temperature.

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

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

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

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

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

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

[0199] To 2 ml of the obtained reaction solution, 0.4 ml of trioctylphosphine: TOP was added. Then, centrifugation was performed to remove the precipitate. The obtained solution was measured with a fluorescence spectrometer. As a result, as shown in Fig. 18, optical properties with a fluorescence wavelength of 631 nm, a fluorescence half-width of 25 nm, and a quantum yield of 67% were obtained.

[0200] [Example 20] To a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 55.5 mg of gallium acetylacetonate: Ga(acac)3, 20 mL of oleylamine: OLAm, and 3 ml of dodecanethiol: DDT were added. Then, it was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

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

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

[0203] Then, 3.5 ml of a mixed solution obtained by mixing 3 ml of a 0.1 M solution obtained by dissolving gallium chloride: GaCl3 and oleic acid: OLAc in oleylamine: OLAm so that the molar ratio of Ga: OLAc = 1: 1.5 and 0.5 ml of a 0.8 M solution obtained by dissolving sulfur: S in oleylamine: OLAm and dodecanethiol: DDT was added dropwise over 10 minutes onto the solution being heated with stirring at 290 °C. After completion of the dropwise addition, it was heated with stirring for 110 minutes, and the obtained reaction solution was cooled to room temperature.

[0204] Subsequently, 8 ml of TOP was added and heated at 150 °C for 5 minutes. Then, 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. After that, 0.3 ml of an 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 an 0.8 M solution obtained by dissolving sulfur: S in oleylamine: OLAm and dodecanethiol: DDT were added and heated at 150 °C for 20 minutes. After that, 0.3 ml of an 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. Subsequently, it was cooled to room temperature.

[0205] To 2 ml of the obtained reaction solution, 0.4 ml of trioctylphosphine: TOP was added. Then, centrifugation was performed to remove the precipitate. The obtained solution was measured with a fluorescence spectrometer. As a result, as shown in Fig. 19, optical properties with a fluorescence wavelength of 633 nm, a fluorescence half-width of 23.9 nm, and a quantum yield of 75% were obtained.

[0206] [Comparative Example 1] Into a 100 mL reaction vessel, 0.5 ml of a 0.2 M solution obtained by dissolving silver acetate: Ag(OAc) in oleylamine: OLAm, 29 mg of indium acetate: In(OAc)3, 9.5 mL of oleylamine: OLAm, and 0.5 ml of dodecanethiol: DDT were put. Then, it was heated with stirring under an inert gas (N2) atmosphere to dissolve the raw materials.

[0207] This solution was dissolved at 120 °C for 5 minutes, and then 1 ml of a 0.2 M solution (S-ODE) obtained by dissolving sulfur: S in octadecene: ODE was added. Then, while raising the temperature from 120 °C to 200 °C, it was heated with stirring for a total of 20 minutes. The obtained 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 the mixture was heated again at 260 °C for 10 minutes with stirring.

[0209] Thereafter, 3.5 ml of a mixed solution obtained by dissolving 2 ml of a 0.1 M solution of 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 of sulfur: S in octadecene: ODE was added dropwise over 50 minutes onto the solution being heated with stirring at 260 °C. After completion of the dropwise addition, the mixture was heated with 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 value so low that it 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 value so low that it could not be observed.

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

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

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

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

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

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

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

[0222] Also, the results (observation images) of analyzing the quantum dots of Example 15 by TEM-EDX are shown in FIG. 22. FIG. 23 is a partial schematic diagram of the observation image shown in FIG. 22. As shown in FIGS. 22 and 23, it was found that the more Zn was detected, the darker the color was detected, and Zn mainly existed on the surface of the quantum dots.

Industrial Applicability

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

[0224] This application is based on Japanese Patent Application No. 2019-153204 filed on August 23, 2019. The entire contents thereof are incorporated herein by reference.

Claims

Claim 1 ZnAgIn ｘ Ga １－ｘ S ｙ Se １－ｙ Quantum dots composed of the system (0 ≦ x < 1, 0 ≦ y ≦ 1), exhibiting fluorescence characteristics with a fluorescence half-width of 33 nm or less and a fluorescence quantum yield of 70% or more in the green wavelength region to the red wavelength region, the ratio of Ag to Ga is in the range of Ag / Ga = 0.05 or more and 10 or less, and the ratio of Zn to Ga is in the range of Zn / Ga = 0.1 or more and 10 or less, the quantum dot has a core-shell structure of a core and a shell covering the core, and Zn is contained in the shell, characterized quantum dot. Claim 2 The quantum dot according to claim 1, characterized by containing at least Zn, Ag, Ga, and S, or Zn, Ag, Ga, and Se, and not containing Cd. Claim 3 The quantum dot according to claim 1 or claim 2, characterized in that the fluorescence wavelength is in the range of 400 nm or more and 700 nm or less. Claim 4 The quantum dot according to claim 1, 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 or more and 650 nm or less.

Images