JP7622356B2 - Quantum dots, quantum dot precursors, and methods for producing quantum dots - Google Patents

Description

The present invention relates to quantum dots, quantum dot precursors, and methods for producing quantum dots.

Quantum dots are nanoparticles composed of hundreds to thousands of atoms and with diameters of several nm to tens of nm. Quantum dots are also called fluorescent nanoparticles, semiconductor nanoparticles, or nanocrystals. Quantum dots have the characteristic that the emission wavelength can be changed in various ways depending on the particle size and composition of the nanoparticles.

The performance of quantum dots can be expressed by the fluorescence quantum yield (QY) and the fluorescence full width at half maximum (FWHM). When quantum dots are used as wavelength conversion materials in the visible light region, their most significant feature is the wide range of colors that can be expressed, i.e., a wide color gamut. In order to achieve a wide color gamut using quantum dots, it is important to narrow the fluorescence full width at half maximum.

Representative materials for green or red quantum dots with this high fluorescence quantum yield and narrow fluorescence half-width include cadmium selenide (CdSe) quantum dots using cadmium (Cd), or ZnCdSeS, which is made up of four elements, with zinc (Zn) or sulfur (S) dissolved in the quantum dots.

For example, in Non-Patent Document 1, quantum dots of CuSe consisting of a copper (Cu) and selenium (Se) compound are synthesized, and then metal-exchanged with zinc (Zn) or cadmium (Cd) to obtain quantum dots of ZnSe or CdSe. However, there is no report showing good luminescence properties using the metal-exchange method.

J. Am. Chem. Soc. (2015) 137 29 9315-9323

As described above, although research and development of Cd-based quantum dots is progressing, no Cd-based quantum dots have been reported that have been produced using the metal exchange method (cation exchange method) and have luminescence characteristics of a fluorescence wavelength of 400 to 800 nm and a fluorescence half-width of 35 nm or less.

The present invention has been made in view of these points, and aims to provide a method for mass-producing Cd-based quantum dots that are safe and can be produced using Cd-based quantum dots with narrow fluorescence half-widths, quantum dot precursors, and a metal exchange method that allows synthesis at low temperatures.

The method for producing quantum dots in the present invention is characterized by synthesizing Cu ₂ Se or Cu ₂ SeS as a precursor from an organic copper compound or an inorganic copper compound and an organic chalcogen compound, simultaneously adding a zinc compound and a cadmium compound to perform metal exchange between the copper of Cu ₂ Se or Cu ₂ SeS and the cadmium and zinc, and synthesizing a quantum dot core consisting of CdZnSe with a Zn/Cd molar ratio of 10 to 20 or CdZnSeS with a Zn/Cd molar ratio of 10 to 20 and a S/Se molar ratio of more than 0 and 0.2 or less , having a fluorescence half-width of 35 nm or less and an average particle size of 2 nm to 10 nm.

The Cd-based quantum dots of the present invention can narrow the fluorescence half-width and improve the color gamut.

In addition, the quantum dot manufacturing method of the present invention makes it possible to safely manufacture Cd-based quantum dots with narrow fluorescence half-widths in a manner that allows for mass production.

Fig. 1A is a schematic diagram of a quantum dot according to an embodiment of the present invention, and Fig. 1B is a schematic diagram of a quantum dot according to an embodiment of the present invention different from that of Fig. 1A. 1 is a photoluminescence (PL) spectrum of CdSe in Example 1. 1 is a PL spectrum of ZnCdSe in Example 2. 1 is a PL spectrum of ZnCdSe in Example 3. 1 is a PL spectrum of ZnCdSe in Example 4. 1 is a PL spectrum of ZnCdSeS in Example 5. 1 is an X-ray diffraction (XRD) spectrum of CdSe in Example 1. 1 is an XRD spectrum of ZnCdSe in Example 2. 1 is an XRD spectrum of ZnCdSe in Example 3. 1 is an XRD spectrum of ZnCdSe in Example 4. 1 is an XRD spectrum of ZnCdSeS in Example 5. 1 is a scanning electron microscope (SEM) photograph of CdSe in Example 1. 1 is a SEM photograph of ZnCdSe in Example 2. 1 is a SEM photograph of ZnCdSe in Example 3. 1 is a SEM photograph of ZnCdSe in Example 4. 1 is a SEM photograph of ZnCdSeS in Example 5.

In recent years, research and development of Cd-based quantum dots has progressed. Conventionally, there are many syntheses in which each raw material is directly reacted. In the direct synthesis method, there is a synthesis method in which synthesis is performed at high temperatures or an organic zinc compound such as diethyl zinc (Et ₂ Zn) is used to increase reactivity. However, even when synthesis is performed at high temperatures or a highly reactive reagent such as diethyl zinc is used, there is a risk of heat generation or fire during the reaction. Therefore, it is not suitable for mass production from a safety standpoint.

The inventors have therefore developed Cd-based quantum dots that have a narrow fluorescence half-width and emit blue to red fluorescence, using a cation exchange method that allows synthesis at low temperatures. In addition, they have made it possible to synthesize quantum dots using a method that allows for mass production and is highly safe.

One embodiment of the present invention (hereinafter, abbreviated as "embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and can be practiced with various modifications within the scope of the gist. In addition, the notation "to" includes both the lower limit and the upper limit as a range.

Figures 1A and 1B are schematic diagrams of quantum dots in this embodiment.

Quantum dot 1 shown in FIG. 1A is a nanocrystal containing cadmium (Cd) and selenium (Se), or cadmium (Cd), zinc (Zn), and selenium (Se), or cadmium (Cd), zinc (Zn), selenium (Se), and sulfur (S), or cadmium (Cd), zinc (Zn), and sulfur (S).

Quantum dot 1 has fluorescent properties due to band-edge emission, and because the particles are nano-sized, they exhibit a quantum size effect.

Here, "nanocrystal" refers to nanoparticles with a particle size of about several nm to several tens of nm. In this embodiment, a large number of quantum dots 1 can be produced with a roughly uniform particle size.

The quantum dot 1 contains Cd and Zn, Cd, Zn and Se, or Cd, Zn, Se and S, or Cd, Zn and S as its main components, but may contain elements other than these elements.

The quantum dot 1 of this embodiment has a fluorescence half-width of 35 nm or less. "Fluorescence half-width" refers to the full width at half maximum, which indicates the spread of the fluorescence wavelength at half the intensity of the peak value of the fluorescence intensity in the fluorescence spectrum. The fluorescence half-width is preferably 32 nm or less. The fluorescence half-width is more preferably 30 nm or less. The fluorescence half-width is even more preferably 25 nm or less. The fluorescence half-width is even more preferably 20 nm or less. In this way, in this embodiment, the fluorescence half-width can be narrowed, thereby improving the color gamut.

In this embodiment, as described later, the reaction system for synthesizing quantum dots 1 is such that copper chalcogenide is synthesized as a precursor, and then a metal exchange reaction (cation exchange reaction) is performed on the precursor. By producing quantum dots 1 based on such an indirect synthesis reaction, the fluorescence half-width can be narrowed, and specifically, a fluorescence half-width of 35 nm or less can be achieved.

It is preferable that a large number of organic ligands 2 are coordinated to the surface of the quantum dots 1. This makes it possible to suppress aggregation between the quantum dots 1, and to develop the desired optical properties. There are no particular limitations on the ligands that can be used in the reaction, but the following ligands are representative examples:

₍ 1 ₎ Aliphatic primary amines _{Oleylamine: C18H35NH2 ,} stearyl (octadecyl) _amine : _C18H37NH2 , _dodecyl (lauryl) _{amine : C12H25NH2 , decylamine} : _C10H21NH2 , _octylamine : _C8H17NH2
(2) Fatty Acids 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 (dodecanoic) acid: C ₁₁ H ₂₃ COOH, decanoic acid: C ₉ H ₁₉ COOH, octanoic acid: C ₇ H ₁₅ COOH
₍ 3) Thiols: Octadecanethiol: _C18H37SH , hexanedecanethiol: _C16H33SH , tetradecanethiol: _{C14H29SH , dodecanethiol : C12H25SH} , decanethiol _{: C10H21SH} , _octanethiol : _C8H17SH
(4) Phosphine-based compounds: Trioctylphosphine: (C ₈ H ₁₇ ) ₃ P, triphenylphosphine: (C ₆ H ₅ ) ₃ P, tributylphosphine: (C ₄ H ₉ ) ₃ P
(5) Phosphine oxide series Trioctylphosphine oxide: (C ₈ H ₁₇ ) ₃ P═O, triphenylphosphine oxide: (C ₆ H ₅ ) ₃ P═O, tributylphosphine oxide f: (C ₄ H ₉ ) ₃ P═O

In this embodiment, the quantum dot 1 has a fluorescence quantum yield of 10% or more. In addition, the fluorescence quantum yield is more preferably 30% or more, and even more preferably 50% or more. In this way, in this embodiment, the fluorescence quantum yield of the quantum dot 1 can be increased.

In this embodiment, the average particle size of the quantum dots 1 is 2 nm or more and 10 nm or less. The average particle size of the quantum dots 1 is preferably 3 nm or more and 9 nm or less, and more preferably 4 nm or more and 8 nm or less. The "average particle size" is calculated by averaging the diameters of all particles of 10 or more (preferably 200 or more) calculated as equivalent circle diameters.

In addition, the particle size of the quantum dots 1 in this embodiment is preferably within the range of ±2 nm of the average particle size. In this way, in this embodiment, it is possible to generate a large number of quantum dots 1 with very uniform particle sizes.

In this embodiment, the fluorescence wavelength can be freely controlled to about 400 nm or more and 700 nm or less. The quantum dot 1 in this embodiment is a solid solution based on ZnCdSeS using chalcogen elements. In this embodiment, the fluorescence wavelength can be controlled by adjusting the particle size of the quantum dot 1 and the composition of the quantum dot 1. In this embodiment, the fluorescence wavelength can be set to 450 nm or more. Note that in this embodiment, the fluorescence wavelength can be controlled to blue to red.

The quantum dot 1 shown in FIG. 1B has a core-shell structure having a core 1a and a shell 1b coated on the surface of the core 1a. As shown in FIG. 1B, it is preferable that a large number of organic ligands 2 are coordinated to the surface of the quantum dot 1.

The core 1a of the quantum dot 1 shown in FIG. 1B is the nanocrystal shown in FIG. 1A. Therefore, the core 1a is preferably formed of Cd and Se, Cd, Zn and Se, or Cd, Zn, Se and S, or Cd, Zn and S. The shell 1b may be formed of any material, for example, zinc sulfide (ZnS).

The shell 1b may be in a state of being solidified on the surface of the core 1a. In FIG. 1B, the boundary between the core 1a and the shell 1b is shown by a dotted line, but this means that the boundary between the core 1a and the shell 1b may or may not be confirmed by analysis. In this embodiment, the core alone containing Cd and Se, Cd, Zn, and Se, or Cd, Zn, Se, and S, or Cd, Zn, and S, is characterized by emitting fluorescence.

The quantum dot 1 shown in FIG. 1B can also have a fluorescence half-width of 32 nm or less, similar to that of FIG. 1A. Moreover, it is more preferable that the fluorescence half-width is 25 nm or less. Furthermore, the fluorescence wavelength can be freely controlled to be 400 nm or more and 700 nm or less. And in this embodiment, it is possible to control the fluorescence wavelength to blue.

Next, a method for producing the quantum dot 1 of this embodiment will be described. First, in this embodiment, a copper chalcogenide (precursor) is synthesized from an organic copper compound or an inorganic copper compound and an organic chalcogen compound. Specifically, the precursor is preferably copper selenide: Cu ₂ Se or copper selenide sulfide: Cu ₂ SeS.

In this embodiment, the Cu raw material for Cu ₂ Se is not particularly limited, but for example, the following organic copper reagents or inorganic copper reagents can be used. That is, as acetates, copper acetate (I) Cu(OAc) and copper acetate (II): Cu(OAc) ₂ are usable; as fatty acid salts, copper stearate: Cu(OC(=O)C ₁₇ H ₃₅ ) ₂ , copper oleate: Cu(OC(=O)C ₁₇ H ₃₃ ) ₂ , copper myristate: Cu(OC(=O)C ₁₃ H ₂₇ ) ₂ , copper dodecanoate: Cu(OC(=O)C ₁₁ H ₂₃ ) ₂ , and copper acetylacetonate: Cu(acac) ₂ are usable; as halides, both monovalent and divalent compounds can be used, and as such, copper chloride (I): CuCl, copper chloride (II): CuCl ₂ , copper bromide (I): CuBr, and copper bromide (II): CuBr ₂ are usable. , copper (I) iodide: CuI, copper (II) iodide: _CuI2 , etc. can be used.

In this embodiment, an organic selenium compound (organic chalcogenide) is used as the raw material for selenium. In particular, a solution (Se-DDT/OLAm) in which selenium is dissolved in a mixture of oleylamine and dodecanethiol shows good luminescence characteristics after cation exchange. In addition, trioctylphosphine selenide: (C ₈ H ₁₇ ) ₃ P=Se in which sulfur is dissolved in a high-boiling point solvent that is a long-chain phosphine-based hydrocarbon such as trioctylphosphine, or tributylphosphine selenide: (C ₄ H ₉ ) ₃ P=Se in which selenium is dissolved in tributylphosphine, can be used. Alternatively, a solution (Se-ODE) in which selenium is dissolved at high temperature in a high-boiling point solvent that is a long-chain hydrocarbon such as octadecene can be used.

In this embodiment, an organic copper compound or an inorganic copper compound is mixed with an organic chalcogen compound and dissolved. As the solvent, octadecene can be used as a high boiling point saturated or unsaturated hydrocarbon. In addition, t-butylbenzene can be used as an aromatic high boiling point solvent, butyl butyrate: C ₄ H ₉ COOC ₄ H ₉ , benzyl butyrate: C ₆ H ₅ CH ₂ COOC ₄ H ₉ , etc. can be used as a high boiling point ester solvent, but it is also possible to use an aliphatic amine-based or fatty acid-based compound, an aliphatic phosphorus-based compound, or a mixture of these as the solvent.

At this time, the reaction temperature is set to a range of 120°C or higher and 250°C or lower to synthesize copper chalcogenide (precursor). Note that the reaction temperature is preferably lower, 120°C or higher and 200°C or lower, and even lower, 120°C or higher and 150°C or lower, is more preferable.

In this embodiment, the reaction method is not particularly limited, but in order to obtain quantum dots with a narrow fluorescence half-width, it is important to synthesize _Cu2Se and _Cu2SeS with uniform particle size. For example, in this embodiment, it is preferable that the particle size of the copper chalcogenide (precursor) is uniform within a range of ±2 nm of the average particle size. The definition of the average particle size is as described above.

The sulfur (S) used in the synthesis of _Cu2SeS can be a solution (S-TOP) in which sulfur is dissolved in a high-boiling solvent such as a thiol or a long-chain phosphine-based hydrocarbon such as trioctylphosphine, a solution (S-ODE) in which sulfur is dissolved in a high-boiling solvent such as a long-chain hydrocarbon such as octadecene, or a solution (S-DDT/OLAm) in which sulfur is dissolved in a mixture of oleylamine and dodecanethiol. In particular, the _thiol is not limited, but examples thereof include _{octadecanethiol} : _C18H37SH , _{hexanedecanethiol : C16H33SH} , tetradecanethiol _{: C14H29SH} , dodecanethiol: _C12H25SH , decanethiol: _C10H21SH , _octanethiol : _C8H17SH , and benzenethiol: C6H5SH.

In this embodiment, the fluorescence wavelength can be freely controlled in the range of 400 nm to 700 nm while maintaining the fluorescence half-width of 32 nm or less of the quantum dots by changing the addition ratio of selenium and sulfur, which are anion species used in the synthesis of the copper chalcogenide precursor. Even if the particle size and cation species (Zn or Cd) are the same, if the S ratio of the precursor is high, the wavelength will be short. Specifically, the target wavelength can be targeted by controlling the molar ratio of sulfur to selenium (S/Se). In this embodiment, the target wavelength is mainly 450 to 550 nm, and good results are obtained by adjusting S/Se to < 0.2. Here, the molar ratio includes 0, in which case the quantum dots do not contain sulfur. By adjusting the molar ratio of sulfur to selenium in the range of more than 0 and less than 0.2, the quantum dots can contain both selenium and sulfur.

Next, an organic zinc compound or an inorganic zinc compound is prepared as a raw material for ZnCdSe or ZnCdSeS. The organic zinc compound or inorganic zinc compound is a raw material that is stable in air and easy to handle. There are no particular limitations on the structure of the organic zinc compound or inorganic zinc compound, but in order to efficiently carry out the metal exchange reaction, it is preferable to use a zinc compound with high ionicity. For example, the organic zinc compounds and inorganic zinc compounds shown below can be used.

The zinc raw materials include acetates such as zinc acetate: Zn(OAc) ₂ and zinc nitrate: Zn(NO ₃ ) ₂ , fatty acid salts such as 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 , and zinc acetylacetonate: Zn(acac) ₂ , and halides such as zinc chloride: ZnCl ₂ , zinc bromide: ZnBr ₂ , and zinc iodide: ZnI _{2 .} 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.

Cadmium raw materials include acetate salts such as cadmium acetate: Cd(OAc) ₂ , cadmium nitrate: Cd(NO ₃ ) ₂ , and fatty acid salts such as cadmium stearate: Cd(OC(═O)C ₁₇ H ₃₅ ) ₂ , cadmium oleate: Cd(OC(═O)C ₁₇ H ₃₃ ) ₂ , cadmium palmitate: Cd(OC(═O)C ₁₅ H ₃₁ ) ₂ , cadmium myristate: Cd(OC(═O)C ₁₃ H ₂₇ ) ₂ , cadmium dodecanoate: Cd(OC(═O)C ₁₁ H ₂₃ ) ₂ , and cadmium acetylacetonate: Cd(acac) _{2 .} As halides, cadmium chloride: _CdCl2 , cadmium bromide: _CdBr2 , cadmium iodide: _CdI2 , and as cadmium carbamates, cadmium diethyldithiocarbamate: Cd(SC(=S)N( _C2H5 ) ₂ ) ₂ , cadmium dimethyldithiocarbamate: Cd(SC(=S)N( _CH3 ) _{2 ) 2} , cadmium dibutyldithiocarbamate: _Cd (SC(=S)N( _C4H9 ) ₂ ) ₂ , etc. can be used.

Then, the organic zinc compound or inorganic zinc compound is added to the reaction solution in which the copper chalcogenide precursor has been synthesized. This causes a metal exchange reaction between the copper (Cu) of the copper chalcogenide and zinc (Zn) and cadmium (Cd). It is preferable to cause the metal exchange reaction at a temperature of 140°C or higher and 300°C or lower. It is more preferable to cause the metal exchange reaction at a lower temperature, 140°C or higher and 240°C or lower, and even more preferable to cause the metal exchange reaction at an even lower temperature, 140°C or higher and 180°C or lower.

In this embodiment, the metal exchange reaction between Cu and Zn and Cd proceeds quantitatively. If the precursor Cu remains in the nanocrystal, it acts as a dopant and emits light through a different emission mechanism, widening the fluorescence half-width. Therefore, it is preferable that the nanocrystal does not contain the precursor Cu. However, by using a precursor such as CuSe, particles with a better shape and more uniform particle size than the conventional directly synthesized ZnCdSe can be produced. In addition, by checking for residual Cu, it is possible to determine whether or not this method has been used. The amount of residual Cu is measured by ICP (inductively coupled plasma) emission spectroscopy.

In addition, the above describes the metal exchange reaction between Cu and Zn and Cd, but it is possible to produce quantum dots 1 containing Cd and Se by metal exchange between Cu and Cd.

In addition, in this embodiment, when performing metal exchange, a compound is required that plays an auxiliary role in liberating the precursor metal into the reaction solution by coordination or chelating, etc.

Compounds having the above-mentioned role include ligands capable of forming a complex with Cu. For example, phosphorus-based ligands, amine-based ligands, and sulfur-based ligands are preferred, and among these, phosphorus-based ligands are even more preferred due to their high efficiency.

This allows the metal exchange between Cu and Cd, or between Cu and Cd and Zn, to be carried out appropriately, and quantum dots with narrow fluorescence half-widths based on Cd and Se, Zn, Cd and Se, Zn, Cd, Se and S, or Cd, Zn and S can be mass-produced with high safety.

In addition, in the metal exchange reaction, good characteristics can be obtained by simultaneously exchanging two or more metal species. There is no particular limitation on the metal species, but two or more can be selected from Zn, Cd, Mg, Mn, Ag, In, Ga, Al, etc. In this embodiment, however, Cd is an essential element. For example, in this embodiment, if only Cd is metal exchanged in the precursor of copper chalcogenide to synthesize CdSe, and then Zn is added, good luminescence characteristics cannot be obtained (Comparative Example 1). Therefore, as in this embodiment, it is preferable to add two or more cation species (Zn and Cd in this embodiment) at the same time (Examples 2 to 5).

In addition, in this embodiment, by changing the ratio of zinc and cadmium, which are cationic species used during metal exchange, the fluorescence wavelength can be freely controlled in the range of 400 nm to 700 nm while maintaining a fluorescence half-width of 32 nm or less. For example, in this embodiment, when ZnCdSe is synthesized with the ratio of the amount of zinc substance to the amount of cadmium substance being in the range of 10 to 20 in terms of the amount of zinc compound and cadmium compound added, it is possible to control the fluorescence wavelength in the range of 450 nm to 600 nm while maintaining a fluorescence half-width of 35 nm or less.

In this embodiment, in the amounts of zinc compound and cadmium compound added, it is preferable to adjust the molar ratio of the amount of zinc substance to the amount of cadmium substance (Zn/Cd) to a range of 30 or less. In this embodiment, a molar ratio of 0 is also included. In this case, zinc is not included in the quantum dots. In addition, when both cadmium and zinc are included in the quantum dots, the molar ratio is preferably 5 to 25, and more preferably 10 to 20 (Examples 2 to 5).

In this embodiment, quantum dots are synthesized by synthesizing a copper chalcogenide as a precursor from an organic copper compound or an inorganic copper compound and an organic chalcogen compound, and then performing metal exchange using the precursor. In this way, in this embodiment, quantum dots are synthesized first through the synthesis of a precursor, and are not directly synthesized. Unlike direct synthesis, this indirect synthesis makes it easier to control the reaction rate, and does not require difficult reaction control to achieve a uniform particle size. In addition, indirect synthesis does not require the use of reagents that are too highly reactive and dangerous to handle, as in direct synthesis. Therefore, compared to direct synthesis, the reaction is easier to control during production, making it possible to safely and stably synthesize CdSe, ZnCdSe, ZnCdS, or ZnCdSeS quantum dots with narrow fluorescence half-widths.

In addition, in this embodiment, it is possible to obtain the desired quantum dots by performing metal exchange between Cu-Zn and Cd in one pot without isolating and purifying the precursor. On the other hand, the precursor copper chalcogenide may be isolated and purified before use.

In addition, in this embodiment, the synthesized quantum dots exhibit fluorescent properties without undergoing various processes such as washing, isolation and purification, coating, and ligand exchange.

However, as shown in Figure 1B, the fluorescence quantum yield can be further increased by covering the core 1a made of nanocrystals such as CdSe, ZnCdSe, ZnCdS, or ZnCdSeS with a shell 1b such as ZnS.

In this embodiment, the core/shell structure can be synthesized at the precursor stage, for example, by synthesizing Cu ₂ Se/Cu ₂ S with a precursor copper chalcogenide, followed by metal exchange of Cu-Zn and Cd to obtain ZnCdSe/ZnCdS.

In this embodiment, the S raw material used for the shell structure is not particularly limited, but the following raw materials are representative:

Thiols: 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: C ₈ H ₁₇ SH, benzenethiol: C ₆ H ₅ SH, or a solution (S-TOP) in which sulfur is dissolved in a high-boiling solvent that is a long-chain phosphine-based hydrocarbon such as trioctylphosphine, a solution (S-ODE) in which sulfur is dissolved in a high-boiling solvent that is a long-chain hydrocarbon such as octadecene, or a solution (S-DDT/OLAm) in which sulfur is dissolved in a mixture of oleylamine and dodecanethiol can be used.

The applications of the quantum dots 1 shown in Figures 1A and 1B are not particularly limited, but for example, the quantum dots 1 of this embodiment that emit blue fluorescence can be applied to wavelength conversion members, lighting members, backlight devices, display devices, etc.

The quantum dot 1 of this embodiment is applied to a wavelength conversion member, an illumination member, a backlight device, a display device, etc., and when photoluminescence (PL) is used as the light emission principle, it is possible to emit blue fluorescence by UV irradiation from a light source. Alternatively, when electroluminescence (EL) is used as the light emission principle, or when quantum dots emit all three primary colors by other methods, it is possible to make a light emitting element that emits blue fluorescence using the quantum dot 1 of this embodiment. In this embodiment, a light emitting element (full color LED) that includes the quantum dot 1 of this embodiment that emits blue fluorescence, together with quantum dots that emit green fluorescence and quantum dots that emit red fluorescence, can be used to emit white light.

The wavelength conversion member is formed in a sheet, film, or molded body. For example, a molded body in which quantum dots are dispersed in a resin is stored in a container having a storage space by pressing or the like. At this time, it is preferable that the refractive index of the molded body is smaller than the refractive index of the container. As a result, a part of the light that enters the molded body is totally reflected by the inner wall of the container. Therefore, the amount of light leaking to the outside from the side of the container can be reduced. By applying the quantum dots with a narrow fluorescence half-width in this embodiment to wavelength conversion members, lighting members, backlight devices, display devices, and the like, it is possible to effectively improve the light emission characteristics.

The effects of the present invention will be explained below using examples and comparative examples. Note that the present invention is not limited in any way by the following examples.

<Ingredients>
In the present invention, the following raw materials were used to synthesize quantum dots.
<Solvent>
Octadecene: Idemitsu Kosan Co., Ltd.: Linearen (registered trademark) 18
Oleylamine: Farmin (registered trademark) O-V, manufactured by Kao Corporation
Trioctylphosphine: manufactured by Hokko Chemical Co., Ltd. Dodecanethiol: manufactured by Kao Corporation: Thiokalcol (registered trademark), or manufactured by Aldrich Co., Ltd. <Metal>
Anhydrous copper (II) acetate: manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd. Zinc chloride: manufactured by Kishida Chemical Co., Ltd. Cadmium acetate dihydrate: manufactured by Ikoma Chemical Co., Ltd. Selenium (4N: 99.99%): manufactured by Shinko Chemical Industry Co., Ltd. Sulfur: manufactured by Kishida Chemical Co., Ltd. <Measuring equipment>
Fluorescence spectrometer: F-2700 manufactured by JASCO Corporation
Ultraviolet-visible spectrophotometer: Hitachi V-770
Quantum yield measurement device: Otsuka Electronics Co., Ltd. QE-1100
X-ray diffraction device (XRD): Bruker D2 PHASER
Scanning electron microscope (SEM): Hitachi SU9000

[Example 1]
91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed in a 100 mL reaction vessel, and the mixture was heated at 150° C. for 5 minutes under stirring in an inert gas (N ₂ ) atmosphere to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 10 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 986 mg of cadmium acetate dihydrate (Cd(OAc) _2.2H2O ), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° _C for 10 minutes under an inert gas ( _N2 ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene and ethanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 mL of octadecene (ODE) was added to disperse the precipitate.

Then, 986 mg of cadmium acetate dihydrate (Cd(OAc) _2.2H2O ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated at 180° _C for 10 minutes under an inert gas ( _N2 ) atmosphere while stirring. The resulting reaction solution was cooled to room temperature. As a result, CdSe quantum dots were obtained in the reaction solution.

The resulting reaction solution was measured using a fluorescence spectrometer and a quantum efficiency measurement system. As a result, the optical characteristics obtained were a fluorescence wavelength of about 670 nm and a fluorescence half-width of about 32 nm, as shown in Figure 2.

The reaction solution obtained was also measured using an XRD device. The results are shown in Figure 7. Figure 12 shows a scanning electron microscope (SEM) photograph of the reaction solution obtained. From this, the average particle size was found to be 6.1 nm.

[Example 2]
91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed in a 100 mL reaction vessel, and the mixture was heated at 150° C. for 5 minutes under stirring in an inert gas (N ₂ ) atmosphere to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 10 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 504 mg _{of zinc chloride (ZnCl2), 98.6 mg of cadmium acetate dihydrate (Cd(OAc)2.2H2O ) ,} 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180°C for 30 minutes under an inert gas ( _N2 ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene and ethanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated at 180° C. for 30 minutes under stirring in an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature. As a result, ZnCdSe quantum dots were obtained in the reaction solution.

The resulting reaction solution was measured using a fluorescence spectrometer and a quantum efficiency measurement system. As a result, as shown in Figure 3, optical characteristics were obtained, such as a fluorescence wavelength of about 490 nm, a fluorescence half-width of about 20 nm, and a quantum yield of 53%. In addition, in the amounts of zinc compound and cadmium compound added, the molar ratio of the amount of zinc substance to the amount of cadmium substance (Zn/Cd ratio) was 20.

The reaction solution obtained was also measured using an XRD device. The results are shown in Figure 8. A scanning electron microscope (SEM) photograph of the reaction solution obtained is shown in Figure 13. The average particle size was found to be 5.8 nm. It was found that the average particle size in Examples 1 and 2 was similar, but the fluorescence wavelengths were different. This suggests that the fluorescence wavelength changes depending on the composition.

[Example 3]
91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed in a 100 mL reaction vessel, and the mixture was heated at 150° C. for 5 minutes under stirring in an inert gas (N ₂ ) atmosphere to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 10 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 147.9 mg of cadmium acetate dihydrate (Cd(OAc) _{2.2H 2} O), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene and ethanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated at 180° C. for 30 minutes under stirring in an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature. As a result, ZnCdSe quantum dots were obtained in the reaction solution.

The resulting reaction solution was measured using a fluorescence spectrometer and a quantum efficiency measurement system. As a result, as shown in Figure 4, optical characteristics were obtained, such as a fluorescence wavelength of about 510 nm, a fluorescence half-width of about 22 nm, and a quantum yield of 56%. In addition, in the amounts of zinc compound and cadmium compound added, the molar ratio of the amount of zinc substance to the amount of cadmium substance (Zn/Cd ratio) was 13.

The resulting reaction solution was measured using an XRD device. The results are shown in Figure 9. Figure 14 shows a scanning electron microscope (SEM) photograph of the resulting reaction solution. The average particle size was found to be 5.8 nm. Since the average particle size in Example 3 was similar to those in Examples 1 and 2, it is believed that the fluorescence wavelength changes depending on the composition.

[Example 4]
91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed in a 100 mL reaction vessel, and the mixture was heated at 150° C. for 5 minutes under stirring in an inert gas (N ₂ ) atmosphere to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 60 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 197.2 mg of cadmium acetate dihydrate (Cd(OAc) _{2.2H 2} O), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene and ethanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated at 180° C. for 30 minutes under stirring in an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature. As a result, ZnCdSe quantum dots were obtained in the reaction solution.

The resulting reaction solution was measured using a fluorescence spectrometer and a quantum efficiency measurement system. As a result, as shown in Figure 5, optical characteristics were obtained, such as a fluorescence wavelength of about 532 nm, a fluorescence half-width of about 23 nm, and a quantum yield of 52%. In addition, in the amounts of zinc compound and cadmium compound added, the molar ratio of the amount of zinc substance to the amount of cadmium substance (Zn/Cd ratio) was 10.

The resulting reaction solution was measured using an XRD device. The results are shown in Figure 10. Figure 15 shows a scanning electron microscope (SEM) photograph of the resulting reaction solution. The average particle size was found to be 7.3 nm. Since the average particle size in Example 4 was similar to those in Examples 1 to 3, it is believed that the fluorescence wavelength changes depending on the composition.

[Example 5]
91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed in a 100 mL reaction vessel, and the mixture was heated at 150° C. for 5 minutes under stirring in an inert gas (N ₂ ) atmosphere to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated with stirring at 150°C for 10 minutes. Then, 0.5 mL of a 0.1 M solution obtained by dissolving sulfur (S) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added, and the mixture was heated with stirring at 150°C for 5 minutes. The resulting reaction solution was cooled to room temperature.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 147.9 mg of cadmium acetate dihydrate (Cd(OAc) _{2.2H 2} O), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene and ethanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated at 180° C. for 30 minutes under stirring in an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature. As a result, ZnCdSeS quantum dots were obtained in the reaction solution.

The resulting reaction solution was measured using a fluorescence spectrometer and a quantum efficiency measurement system. As a result, the optical characteristics obtained were a fluorescence wavelength of about 477 nm and a fluorescence half-width of about 22 nm, as shown in Figure 6.

In Example 5, when the copper chalcogenide precursor was synthesized, two types of anion species, selenium and sulfur, were present, and the molar ratio of the amount of sulfur substance to the amount of selenium substance (S/Se ratio) was 0.125.
In addition, in the amounts of the zinc compound and the cadmium compound added, the molar ratio of the amount of zinc substance to the amount of cadmium substance (Zn/Cd ratio) was 13.

The resulting reaction solution was measured using an XRD device. The results are shown in Figure 11. Figure 16 shows a scanning electron microscope (SEM) photograph of the resulting reaction solution. The average particle size was found to be 5.5 nm. Since the average particle size in Example 5 was similar to those in Examples 1 to 5, it is believed that the fluorescence wavelength changes depending on the composition.

[Comparative Example 1]
91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed in a 100 mL reaction vessel, and the mixture was heated at 150° C. for 5 minutes under stirring in an inert gas (N ₂ ) atmosphere to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 10 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 98.6 mg of cadmium acetate dihydrate (Cd(OAc) _2.2H2O ), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° _C for 30 minutes under an inert gas ( _N2 ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene and ethanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.
The resulting reaction solution was measured with a fluorescence spectrometer, but no luminescence was observed.

[Comparative Example 2]
A 100 mL reaction vessel was charged with 98.6 mg of cadmium acetate dihydrate (Cd(OAc) _2.2H2O ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE). The mixture was heated at 150° _C for 5 minutes under an inert gas ( _N2 ) atmosphere while stirring to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 10 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene, ethanol, and methanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.
The reaction solution thus obtained was measured using a fluorescence spectrometer, and the optical characteristics were that the fluorescence wavelength was about 512 nm and the fluorescence half-width was about 40 nm.

[Comparative Example 3]
In _a 100 mL reaction vessel, 91 mg of anhydrous copper acetate (Cu(OAc) ₂ ), 197.2 mg of cadmium acetate dihydrate (Cd(OAc) _2.2H2O ), 4.8 mL of oleylamine (OLAm), and 7.75 mL of octadecene (ODE) were placed. Then, the mixture was heated at 150°C for 5 minutes under an inert gas ( _N2 ) atmosphere while stirring to dissolve the raw materials.

1.4 mL of a 0.285 M solution obtained by dissolving selenium (Se) powder in dodecanethiol (DDT) and oleylamine (OLAm) was added to this solution, and the mixture was heated at 150°C for 30 minutes with stirring. The resulting reaction solution was cooled to room temperature.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 10 mL of trioctylphosphine (TOP), and 0.4 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.

Toluene, ethanol, and methanol were added to this reaction solution to generate a precipitate, which was then centrifuged to recover the precipitate, and 12 ml of octadecene (ODE) was added to disperse the precipitate.

Then, 504 mg of zinc chloride (ZnCl ₂ ), 5 mL of trioctylphosphine (TOP), and 0.5 mL of oleylamine (OLAm) were added, and the mixture was heated with stirring at 180° C. for 30 minutes under an inert gas (N ₂ ) atmosphere. The resulting reaction solution was cooled to room temperature.
The reaction solution thus obtained was measured using a fluorescence spectrometer, and the optical characteristics were that the fluorescence wavelength was about 542.5 nm and the fluorescence half-width was about 52 nm.

The composition, average particle size, fluorescence wavelength, fluorescence half-width, and fluorescence quantum yield (QY) for the above-mentioned Examples 1 to 5 and Comparative Examples 1 to 3 are summarized in Table 1 below. All composition values are in mmol.

As shown in Table 1, in this example, the fluorescence half-width was 35 nm or less in all cases. It was also found that the fluorescence half-width could be reduced to 32 nm or less, and that in the case of ZnCdSe-based quantum dots or ZnCdSeS-based quantum dots, the fluorescence half-width could be reduced to 25 nm or less, and furthermore, that it was possible to control it to 20 nm or less. On the other hand, in the comparative examples, Comparative Example 2 and Comparative Example 3, which showed fluorescence, the fluorescence half-width was 40 nm or more, and it was found that a narrow fluorescence half-width could not be obtained.

Furthermore, as shown in Table 1, in the examples, it was found that the fluorescent wavelength could be adjusted within the range of 400 nm to 700 nm. It was also found that the fluorescent wavelength could be adjusted within the range of 450 nm to 700 nm.

As shown in Table 1, in the examples, it was found that the average particle size of the quantum dots could be adjusted within the range of 2 nm to 10 nm. In addition, the particle sizes of 95% or more of the quantum dots were within the range of ±2 nm of the average particle size, and it was found that a large number of quantum dots could be produced with very uniform particle sizes.

The quantum dot particle dispersions of Examples 1 to 5 were measured using an X-ray diffraction (XRD) device and a scanning electron microscope (SEM). Figures 7 to 11 show the results of the X-ray diffraction (XRD) device measurement, and Figures 12 to 16 show the results of the scanning electron microscope (SEM) measurement.

Figure 7 shows not only the XRD spectrum of Example 1 (CdSe quantum dots), but also the XRD spectrum of ZnSe particles as quantum dots after cation exchange for reference. As shown in Figure 7, it was confirmed that the peak values of Example 1 and ZnSe are different.

In addition, it was confirmed that the peak values of the XRD spectrum of the ZnCdSe quantum dots shown in Figures 8 to 10 differ depending on the amount of Cd used. That is, as shown in Table 1, it was found that in Examples 2 to 4, the peak values of the XRD spectrum differ due to the different composition ratios of the cationic species Zn and Cd. In addition, the peak value of the XRD spectrum shown in Figure 9 of Example 3 differs from the peak value of the XRD spectrum shown in Figure 11 of Example 5, which is Example 3 to which sulfur (S) was added, and this confirmed that the peak value of the XRD spectrum differs due to the addition of sulfur (S).

As shown in each example, by adjusting the ratio of cadmium and zinc added as cationic species in the metal substitution method, it was found that the fluorescence wavelength of the quantum dots can be controlled in the range of 400 nm to 700 nm while maintaining the fluorescence half-width at 35 nm or less.

Specifically, in this embodiment, it was found that by adjusting the molar ratio of zinc to cadmium within a range of 30 or less, the fluorescence wavelength of the quantum dots can be freely adjusted within a range of 400 nm to 700 nm while maintaining the fluorescence half-width of the quantum dots at 35 nm or less.

In addition, as shown in each example, it was found that by adjusting the ratio of selenium and sulfur added as anion species when synthesizing the copper chalcogenide precursor, it is possible to control the fluorescence wavelength in the range of 400 nm to 700 nm while maintaining the fluorescence half-width of the quantum dots at 32 nm or less.

Specifically, in this embodiment, it was found that by adjusting the molar ratio of sulfur to selenium in the range of 0.2 or less, the fluorescence wavelength of the quantum dots can be freely adjusted in the range of 400 nm to 700 nm while maintaining the fluorescence half-width of the quantum dots at 35 nm or less.

According to the present invention, it is possible to stably obtain Cd-based quantum dots that emit blue to red fluorescence. Furthermore, by applying the quantum dots of the present invention to LEDs, backlight devices, display devices, etc., it is possible to obtain excellent light-emitting characteristics in each device.

1: quantum dot 1a: core 1b: shell 2: organic ligand

Claims (7)

synthesizing a precursor, Cu ₂ Se or Cu ₂ SeS, from an organic copper compound or an inorganic copper compound and an organic chalcogen compound;
A zinc compound and a cadmium compound are added at the same time to exchange the copper of _Cu2Se or _Cu2SeS with the cadmium and zinc,
or CdZnSe having a Zn/Cd molar ratio of 10 to 20 , or CdZnSeS having a Zn/Cd molar ratio of 10 to 20 and a S/Se molar ratio of greater than 0 and less than 0.2 ;
A method for producing quantum dots, comprising synthesizing quantum dot cores having a fluorescence half-width of 35 nm or less and an average particle size of 2 nm to 10 nm. 2. The method for producing quantum dots according to claim 1 , wherein the particle size of the precursor is within a range of ±2 nm of the average particle size. 3. The method for producing quantum dots according to claim 1, wherein the ratio of cadmium and zinc added as cationic species in the metal substitution method is adjusted to control the fluorescence wavelength of the quantum dots to within a range of 400 nm to 700 nm while maintaining the fluorescence half-width of the quantum dots to 35 nm or less . 4. The method for producing quantum dots according to claim 1, wherein the ratio of selenium and sulfur added as anion species when synthesizing the precursor is adjusted to control the fluorescence wavelength of the quantum dots to within a range of 400 nm to 700 nm while maintaining the fluorescence half-width of the quantum dots to 35 nm or less. 5. The method for producing quantum dots according to claim 1 , wherein the metal exchange reaction is carried out at a temperature of 140° C. or higher and 300° C. or lower. 6. The method for producing quantum dots according to claim 1 , wherein the precursor is synthesized at a reaction temperature of 120° C. or higher and 250° C. or lower. Cu as a precursor is prepared from an organic copper compound or an inorganic copper compound and an organic chalcogen compound. ₂ Se or Cu ₂ SeS is synthesized,
Zinc and cadmium compounds are added simultaneously to form Cu ₂ Se or Cu ₂ The copper of SeS is exchanged with cadmium and zinc,
The Zn/Cd molar ratio is CdZnSe having a molar ratio of 10 to 20, or the Zn/Cd molar ratio is CdZnSeS having a molar ratio of 10 to 20 and a molar ratio of S/Se of more than 0 to 0.2,
A quantum dot core having a fluorescence half-width of 35 nm or less, an average particle size of 2 nm to 10 nm, and a quantum yield of 50% or more was synthesized.
A quantum dot characterized by:

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