Quantum dot composition

Abstract

The present invention provides a technology that makes it possible to easily perform ligand exchange. Provided is a quantum dot composition that is used to produce ligand-exchanged quantum dots by replacing at least a portion of ligands. A quantum dot composition according to the present invention comprises quantum dots, a solvent, and halogen ions, wherein: each quantum dot includes a core-shell particle that includes a core and a shell layer which covers the core and ligands that are coordinated to the surface of the core-shell particle; the shell layer includes Zn and S; the ligands include a first ligand that is a thiol and a second ligand that is at least one compound selected from the group consisting of amines, fatty acids, phosphine-based compounds, and alcohols; and the molar fraction of the first ligand to the ligands is within the range of 0.001-0.1.

Description

Quantum dot composition

[0001] This disclosure relates to quantum dot compositions.

[0002] In recent years, quantum dots have been used in various fields such as solar cells and display devices. A quantum dot includes, for example, a core-shell particle containing a core and a shell layer covering it, and a ligand coordinated to the surface of this particle. The ligand improves properties such as the dispersibility, stability, and storage of the quantum dot. For example, Patent Document 1 describes that quantum dots containing a specific ligand exhibit excellent viscosity stability in the dispersion liquid containing them. Patent Document 2 also describes that quantum dots containing a specific ligand can achieve high external quantum efficiency.

[0003] Japanese Patent Publication No. 2023-107228, International Publication No. 2023 / 127163

[0004] This disclosure aims to provide a technology that enables easy ligand substitution.

[0005] According to one aspect of the present invention, a quantum dot composition is provided for use in producing ligand-substituted quantum dots by substituting at least a portion of a ligand, comprising a quantum dot, a solvent, and a halogen ion, wherein the quantum dot comprises a core-shell particle having a core and a shell layer covering the core, and a ligand coordinated to the surface of the core-shell particle, the shell layer comprising Zn and S, and the ligand comprising a first ligand which is a thiol and a second ligand which is one or more compounds selected from the group consisting of amines, fatty acids, phosphine compounds and alcohols, and the mole fraction of the first ligand to the ligand is in the range of 0.001 or more and 0.1 or less.

[0006] According to another aspect of the present invention, a quantum dot composition is provided in which the halogen ion is a chloride ion or a bromide ion.

[0007] According to yet another aspect of the present invention, the halogen ion is a chloride ion, and a quantum dot composition according to the above aspect is provided, comprising the chloride ion in the form of zinc chloride.

[0008] According to yet another aspect of the present invention, a quantum dot composition relating to any of the above aspects is provided, wherein the first ligand is 1-dodecanethiol.

[0009] According to yet another aspect of the present invention, a quantum dot composition is provided relating to either of the above aspects, wherein the second ligand is oleic acid and trioctylphosphine.

[0010] According to yet another aspect of the present invention, a quantum dot composition is provided in which the concentration of the halogen ions in the quantum dot composition is in the range of 0.0005 mol / L or more and 0.05 mol / L or less, according to any of the above aspects.

[0011] According to yet another aspect of the present invention, a quantum dot composition according to any of the above aspects is provided, wherein the shell layer further comprises Te.

[0012] According to yet another aspect of the present invention, a quantum dot composition is provided which, according to any of the above aspects, the first ligand has an alkyl chain, and the main chain of the alkyl chain has eight or more carbon atoms.

[0013] According to yet another aspect of the present invention, a quantum dot composition is provided which is any of the above aspects wherein the second ligand has an alkyl chain, and the number of carbon atoms in the main chain of the alkyl chain of the second ligand is 8 or more.

[0014] According to yet another aspect of the present invention, a ligand-substituted quantum dot composition is provided, wherein at least a portion of the ligand contained in the quantum dot composition according to any of the above aspects is substituted with a third ligand which is one or more compounds selected from the group consisting of thiols, amines, and zinc halides.

[0015] According to yet another aspect of the present invention, a ligand-substituted quantum dot composition is provided, wherein 0.95 to 0.999 mole fractions of the ligand contained in the quantum dot composition are substituted with the third ligand.

[0016] A method for producing a ligand-substituted quantum dot composition is provided, which includes substituting at least one of the ligands contained in the quantum dot composition according to any of the above aspects with a third ligand which is one or more compounds selected from the group consisting of thiols, amines, and zinc halides.

[0017] According to yet another aspect of the present invention, a method for producing a ligand-substituted quantum dot composition is provided, wherein 0.95 to 0.999 mole fractions of the ligand contained in the quantum dot composition are replaced with the third ligand.

[0018] This disclosure provides a technology that enables easy ligand substitution.

[0019] Embodiments of the present invention will be described below. The embodiments described below are more specific to any of the above aspects. The matters described below can be incorporated into each of the above aspects, either individually or in combination.

[0020] Furthermore, the embodiments shown below illustrate configurations for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited by the material, shape, and structure of the components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims described in the claims.

[0021] <1> Quantum dot composition The quantum dot composition according to one embodiment of the present invention is used to produce ligand-substituted quantum dots by substituting at least a portion of the ligand. The quantum dot composition comprises quantum dots, a solvent, and halogen ions.

[0022] A quantum dot comprises a core-shell particle containing a core and a shell layer covering the core, and a ligand coordinated to the surface of the core-shell particle.

[0023] The core contains, for example, zinc (Zn), sulfur (S), tellurium (Te), or selenium (Se). The core is, for example, a combination of Zn and Te, a combination of Zn and Se, a combination of Zn, S, and Te, a combination of Zn, Se, and S, a combination of Zn, Te, and Se, or a combination of Zn, Te, Se, and S.

[0024] The shell layer contains Zn and S. The shell layer may further contain Te. The shell layer contains, for example, a combination of Zn and S, or a combination of Zn, S, and Te. A part of the shell layer may be solid-soluted in the core. Also, the shell layer may consist of a single layer or may consist of a plurality of layers.

[0025] The core-shell particles may contain elements other than the above elements, but preferably do not contain at least one of cadmium (Cd) and phosphorus (P). Since Cd is a harmful substance, it is preferable that the core-shell particles, quantum dots, and quantum dot compositions do not contain Cd. Also, when an organic phosphorus compound is used as a raw material for the core-shell particles, the organic phosphorus compound is likely to be oxidized in the air, so the synthesis of quantum dots is likely to be destabilized. In this case, an increase in cost, destabilization of fluorescence characteristics, and complication of the manufacturing process are likely to occur. Also, in the above case, the cost is likely to increase also from the point that the organic phosphorus compound is expensive.

[0026] The ligand contains a first ligand and a second ligand. The first ligand is a thiol. The thiol preferably contains an alkyl chain. The alkyl chain is preferably linear. Also, the number of carbon atoms in the main chain of the alkyl chain is preferably 8 or more. When the number of carbon atoms in the main chain of the alkyl chain is 8 or more, the dispersibility of the quantum dots is particularly excellent. The thiol is, for example, octadecanethiol (C １０ , １２ , ２５ H ３７ SH), hexadecanethiol (C １６ H ３３ SH), tetradecanethiol (C １４ H ２９ SH), dodecanethiol (C １２ H ２５ SH), decanethiol (C １０ H２１ SH), or octanthiol (C ８ H １７ The first ligand is preferably 1-dodecanethiol.

[0027] The second ligand is one or more compounds selected from the group consisting of amines, fatty acids, phosphine compounds, and alcohols. The second ligand preferably contains an alkyl chain. Furthermore, the number of carbon atoms in the main chain of the alkyl chain is preferably eight or more. When the number of carbon atoms in the main chain of the alkyl chain is eight or more, the dispersibility of quantum dots is excellent.

[0028] The amine is, for example, an aliphatic amine. The aliphatic amine is preferably a primary amine. The aliphatic amine is, for example, oleylamine (C １８ H ３５ NH ２ ), stearyl(octadecyl)amine (C １８ H ３７ NH ２ ), dodecyl(lauryl)amine (C １２ H ２５ NH ２ ), decylamine (C １０ H ２１ NH ２ ), or octylamine (C ８ H １７ NH ２ )

[0029] The fatty acid may be saturated or unsaturated. For example, the fatty acid is 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 (C ９ H １９ COOH), or octanoic acid (C ７ H １５ It is COOH.

[0030] Phosphine compounds are phosphine and compounds containing phosphine. ３ It is a compound represented as (where P is phosphorus and R is a hydrocarbon group). A phosphine is, for example, trioctylphosphine ((C ８ H １７ ) ３ P), triphenylphosphine ((C ６ H ５ ) ３ P), or tributylphosphine ((C) ４ H ９ ) ３ P) is correct.

[0031] Compounds containing phosphine are, for example, phosphine oxides. Phosphine oxides include, for example, trioctylphosphine oxide ((C) ８ H １７ ) ３ P=O), triphenylphosphine oxide ((C ６ H ５ ) ３ P=O) or tributylphosphine oxide ((C) ４ H ９ ) ３ P=O). The phosphine compound is preferably trioctylphosphine oxide.

[0032] Alcohols include, for example, oleyl alcohol (C １８ H ３６ O) is correct.

[0033] The second ligand is preferably oleic acid and trioctylphosphine.

[0034] The mole fraction of the first ligand relative to the ligand is in the range of 0.001 to 0.1. Preferably, this mole fraction is in the range of 0.008 to 0.08. If this mole fraction is too small, the photoluminescence quantum yield (hereinafter referred to as PL quantum yield) tends to be low. If this mole fraction is too large, ligand substitution is less likely to occur.

[0035] The above mole fractions can be obtained, for example, by the following method. First, the quantum dot composition is separated into supernatant and precipitate using an ultracentrifuge. Next, the supernatant is removed, and the precipitate, dried at room temperature, is heated to generate gas. Next, the generated gas is collected using liquid nitrogen and analyzed using gas chromatography-mass spectrometry. Next, each of the compounds detected by the analysis is quantified to obtain the number of moles. Then, the mole fraction of the first ligand relative to all detected compounds is obtained. In this way, the mole fraction of the first ligand relative to the ligand is obtained.

[0036] Furthermore, the mole fraction of the second ligand can also be obtained using the same method as described above. Additionally, by applying the above method to the ligand-substituted quantum dot composition described later, the mole fraction of the third ligand can also be obtained. The mole fraction of the third ligand is also called the ligand substitution rate.

[0037] The solvent is, for example, a hydrocarbon. Examples of solvents include alkanes such as n-hexane and n-octane, 1-octadecene, or toluene.

[0038] Halogen ions, for example, fill in defects in the shell layer. Some of the halogen ions may be free in the solvent.

[0039] Halogen ions may be included in the quantum dot composition in the form of halides. For example, the halogen ion may be a chloride ion, and the chloride ion may be included in the quantum dot composition in the form of zinc chloride. When the chloride ion is included in the quantum dot composition in the form of zinc chloride, at least a portion of the zinc chloride is ionized into chloride ions and zinc ions. The chloride may be hydrogen chloride or hydrochloric acid. Alternatively, the chloride may be zinc chloride and hydrochloric acid.

[0040] The halogen ions are preferably chloride ions or bromide ions. The bromide ions may be included in the quantum dot composition, for example, in the form of zinc bromide.

[0041] The halogen ion concentration in the quantum dot composition is preferably in the range of 0.0005 mol / L to 0.05 mol / L, and more preferably in the range of 0.001 mol / L to 0.03 mol / L. If the halogen ion concentration is too low, it is difficult to achieve a high PL quantum yield. If the halogen ion concentration is too high, ligand substitution is difficult to occur. This will be discussed later. Also, if the halide concentration is too high, the quantum dots tend to aggregate and precipitate.

[0042] <2> Method for Manufacturing Quantum Dot Compositions Below, an example of a method for manufacturing the quantum dot composition described above will be explained.

[0043] First, prepare a copper compound, an organic chalcogen compound or a chalcogen-containing solution, and a thiol as the first ligand. The copper compound may be an organic copper compound or an inorganic copper compound.

[0044] Organocopper compounds include, for example, copper acetate, copper fatty acid, or copper acetylacetonate. Specifically, organocopper compounds include copper(I) acetate (Cu(OAc)) and copper(II) acetate ((Cu(OAc)) ２ ), 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 ), or copper acetylacetonate (Cu(acac) ２ )

[0045] Inorganic copper compounds are, for example, copper halides. Examples of copper halides include copper(I) chloride (CuCl) and copper(II) chloride (CuCl). ２ ), copper(I) bromide (CuBr), copper(II) bromide (CuBr ２ ), copper(I) iodide (CuI), or copper(II) iodide (CuI)２ )

[0046] The organic chalcogen compound is, for example, an organic selenium compound or an organic tellurium compound. The organic selenium compound is, for example, trioctylphosphine selenide ((C ８ H １７ )) ３ P = Se) obtained by dissolving selenium in trioctylphosphine, or tributylphosphine selenide ((C ４ H ９ )) ３ P = Se.

[0047] The organic tellurium compound is, for example, trioctylphosphine telluride ((C ８ H １７ )) ３ P = Te) obtained by dissolving tellurium in trioctylphosphine, tributylphosphine telluride ((C ４ H ９ )) ３ P = Te), or a dialkylditelluride such as diphenylditelluride ((C ６ H ５ )) ２ Te ２ )) (R2Te ２ ).

[0048] The chalcogen-containing solution is a solution obtained by dissolving a chalcogen in an organic solvent. The chalcogen-containing solution is, for example, a solution (Se-ODE solution) obtained by dissolving selenium at a high temperature in a solvent having a high boiling point, such as a long-chain hydrocarbon such as octadecene, or a solution (Se-DDT / OLA m solution) obtained by dissolving selenium in oleylamine and dodecanethiol.

[0049] Next, a copper compound, an organic chalcogen compound or a chalcogen-containing solution, and thiol as the first ligand are stirred while heating to synthesize a copper chalcogenide. Hereinafter, the synthesized copper chalcogenide is also referred to as a precursor. The copper chalcogenide is, for example, copper telluride (Cu ２ Te), copper sulfide telluride (Cu ２TeS), copper sulfide selenide telluride (Cu ２ TeSeS), copper selenide (Cu ２ Se), or copper selenide sulfide (Cu ２ It is SeS.

[0050] The solvent in the above synthesis is, for example, a hydrocarbon, ester compound, aliphatic amine, fatty acid, or phosphine. The solvent is preferably one with a high boiling point. Examples of solvents include octadecene, t-butylbenzene, and butyl butyrate (C). ４ H ９ COOC ４ H ９ ), or benzyl butyrate (C ６ H ５ CH ２ COOC ４ H ９ )

[0051] The synthesis of copper chalcogenides is preferably carried out in a range of 160°C to 250°C, preferably in a range of 160°C to 220°C, and preferably in a range of 160°C to 200°C.

[0052] The amount of thiol added is preferably such that the amount of sulfur (S) relative to chalcogen is within the range of 1 equivalent to 50 equivalents, and more preferably within the range of 5 equivalents to 20 equivalents.

[0053] When thiols are added during the synthesis of copper chalcogenides, sulfur (S) can be dissolved in the core. When S is dissolved in the core, quantum dots with high luminescence intensity can be obtained.

[0054] Next, a zinc compound is added to the reaction solution containing the copper chalcogenide. This induces a metal exchange reaction between the copper in the copper chalcogenide and the zinc. The zinc compound may be an organozinc compound or an inorganic zinc compound.

[0055] Organozinc compounds include, for example, zinc acetate (Zn(OAc) ２ ); zinc nitrate (Zn(NO) ３ ) ２ ); Zinc stearate (Zn(OC(=O)C １７ H３５ ) 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 ) and zinc dodecanoate (Zn(OC(=O)C １１ H ２３ ) ２ ) and other fatty acid zinc; or zinc acetylacetonate (Zn(acac) ２ )

[0056] Inorganic zinc compounds include, for example, zinc chloride (ZnCl). ２ ), zinc bromide (ZnBr ２ ) and zinc iodide (ZnI ２ Zinc halides such as ) and zinc diethyldithiocarbamate (Zn(SC(=S)N(C) ２ H ５ ) ２ ) ２ ), zinc dimethyldithiocarbamate (Zn(SC(=S)N(CH ３ ) ２ ) ２ ), dibutyldithiocarbamate zinc (Zn(SC(=S)N(C ４ H ９ ) ２ ) ２ Zinc carbamate such as ) can be used.

[0057] The above metal exchange reaction is preferably carried out in the range of 180°C to 280°C, and more preferably in the range of 180°C to 250°C. The core is formed in this manner.

[0058] Next, to the obtained solution, a chalcogen-containing solution containing a chalcogen different from the chalcogen contained in the aforementioned organic chalcogen compound and chalcogen-containing solution, or an organic chalcogen compound and a zinc compound, are added and stirred while heating. This synthesizes core-shell particles.

[0059] Next, the obtained core-shell particles, halide, and second ligand or raw material for the second ligand are heated and stirred under an inert gas atmosphere, and then the resulting solution is cooled. It is preferable that the concentration of halogen ions in the resulting solution is within the range described above. In this case, the mass of the halide in the resulting solution is, for example, 0.05% by mass or less.

[0060] The halide is, for example, at least one of zinc chloride and hydrochloric acid. When hydrochloric acid is used as the halide, the shape of the quantum dots can be adjusted by etching with hydrochloric acid.

[0061] For example, oleylamine (OLAm), oleic acid (OLA), and trioctylphosphine (TOP) can be used as raw materials for the second ligand.

[0062] Heating is carried out, for example, within a range of 100°C to 250°C. The heating time is carried out, for example, within a range of 10 minutes to 120 minutes. The method for manufacturing the quantum dot composition has been described above.

[0063] In the method described above, quantum dots are synthesized via precursor synthesis and metal exchange reactions. Compared to synthesizing quantum dots without precursor synthesis and metal exchange reactions, this method does not require the use of reagents that are difficult to handle. Therefore, quantum dots can be synthesized safely and stably using the method described above. Furthermore, quantum dots can be obtained in a single pot using the method described above.

[0064] Furthermore, it is preferable that the amount of residual Cu in the quantum dots be low. For example, the amount of residual Cu in the quantum dots is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 10 ppm or less.

[0065] Furthermore, the raw material for the second ligand may be added during the synthesis of copper chalcogenides, metal exchange reactions, and shell layer synthesis. Additionally, halides may be added during the metal exchange reactions and shell layer synthesis.

[0066] <3> Method for Manufacturing Ligand-Substituted Quantum Dot Compositions Below, an example of a method for manufacturing ligand-substituted quantum dot compositions using the above-described quantum dot compositions will be explained.

[0067] First, a third ligand is added to the quantum dot composition described above. The third ligand is, for example, one or more compounds selected from the group consisting of thiols, amines, and zinc halides. The thiol is, for example, hexanethiol (C ６ H １３ It is SH). The thiol may be the same as the first ligand. The amine may be the same as the amine that can be used as the second ligand, for example. The zinc halide is, for example, zinc chloride.

[0068] The addition of the third ligand is preferably carried out under an inert gas atmosphere, such as nitrogen. The third ligand is preferably added such that the mass of the third ligand relative to the mass of the quantum dot is in the range of 5 to 25.

[0069] Next, the quantum dot composition to which the third ligand has been added is subjected to ultrasonic cleaning. Subsequently, toluene and ethanol are added to the quantum dot composition, thereby inducing precipitation.

[0070] Next, the obtained solution and precipitate are centrifuged, and then the supernatant is removed. Then, the sequence of adding toluene and ethanol, centrifuging, and removing the supernatant is repeated three times. Next, toluene is added to the obtained precipitate. In this way, a ligand-substituted quantum dot composition is obtained.

[0071] According to the above method, a ligand-substituted quantum dot composition can be obtained in which all or part of the ligands contained in the quantum dot composition are substituted with a third ligand. In the ligand-substituted quantum dot composition, it is preferable that 0.95 to 0.999 mole fractions of the ligands contained in the quantum dot composition are substituted with the third ligand, that is, the ligand substitution rate is in the range of 0.95 to 0.999, and more preferably in the range of 0.95 to 0.975.

[0072] For example, when a thiol is used as the third ligand, the ligand-substituted quantum dot composition may contain a ligand in which the thiol group of the third ligand is replaced by a halogen ion. For example, when a quantum dot composition containing a chloride ion as the halogen ion is used and hexanethiol is used as the third ligand, the ligand-substituted quantum dot composition may contain chlorohexane as the ligand. This chloride ion is thought to be a chloride ion derived from the quantum dot composition before ligand substitution. The mole fraction of such a ligand relative to the total ligand is, for example, in the range of 0.01 to 0.2.

[0073] Furthermore, as mentioned above, if the concentration of halogen ions in the quantum dot composition is too high, ligand substitution is less likely to occur. For example, when a thiol is added to the quantum dot composition as a third ligand when the concentration of halogen ions is too high, sulfides are easily formed. In this case, the sulfides are more likely to coordinate to the core-shell particles. Specifically, when 1-hexanethiol is added to the quantum dot composition as a third ligand, dihexyl disulfide is more likely to coordinate to the shell layer. This can be confirmed, for example, by thermal desorption gas chromatography-mass spectrometry.

[0074] The number of times the above sequence is repeated may be two or less, or four or more.

[0075] <4> Effects: Quantum dots are used, for example, in devices that convert optical signals into electrical signals, such as display devices and solar cells. For example, in a display device that uses a QLED (Quantum dot Light Emitting Diode) as a light-emitting element, it is necessary to adjust the composition of the ligand of the quantum dot according to the energy levels of the light-emitting layer containing the light-emitting element and the adjacent hole transport layer and electron transport layer.

[0076] The quantum dot compositions described above can be easily modified, for example, by substituting at least a portion of the ligand depending on the design of the desired display device. The inventors consider the reasons for this to be as follows.

[0077] The quantum dot described above contains a thiol as the first ligand and one or more compounds selected from the group consisting of amines, fatty acids, phosphine compounds, and alcohols as the second ligand. The thiol has a high coordination ability to Zn contained in the shell layer. On the other hand, amines, fatty acids, phosphine compounds, and alcohols have a lower coordination ability to Zn compared to thiols. The mole fraction of the first ligand relative to the ligand contained in the quantum dot described above is in the range of 0.001 to 0.1. Therefore, in the quantum dot described above, substitution from the first ligand to the third ligand described above is unlikely to occur, but substitution from the second ligand to the third ligand described above is likely to occur. For this reason, ligand substitution is easy with the quantum dot composition described above.

[0078] Furthermore, the quantum dot composition described above also exhibits excellent luminescence properties. The inventors consider the reason for this to be as follows: The quantum dot described above contains thiol as the first ligand within the above-mentioned range. Quantum dots containing thiol as a ligand have a high PL quantum yield. And, as described above, substitution from the first ligand to the third ligand is unlikely to occur, so ligand-substituted quantum dots also have a high PL quantum yield.

[0079] Furthermore, in the quantum dot composition described above, halogen ions fill in the defects in the shell layer, which is expected to achieve a high PL quantum yield.

[0080] The tests conducted in connection with the present invention are described below.

[0081] <1> Production of quantum dot compositions and ligand-substituted quantum dot compositions <1.1> Example 1 First, quantum dot compositions were produced. Specifically, quantum dot compositions were produced by the following method.

[0082] First, in a 300 mL reaction vessel, add copper acetate (Cu(OAc)) ２546 mg of ) was added along with 9 mL of dodecanethiol (DDT), 9 mL of oleylamine (OLAm), and 57 mL of octadecene (ODE). These were then dissolved by heating under a nitrogen atmosphere while stirring.

[0083] Next, 8.4 mL of 0.3 M Se-DDT / OLAm solution was added to the obtained solution, and the mixture was heated at 220°C for 10 minutes while stirring. After that, the obtained solution (Cu ２ Se(S) was cooled to room temperature.

[0084] Next, ethanol was added to the obtained solution to form a precipitate. Then, the obtained solution and precipitate were centrifuged, and the supernatant was removed. Next, octadecene (ODE) was added to the reaction vessel and the precipitate was dispersed. In this way, Cu ２ A Se(S)-ODE solution was obtained.

[0085] Next, Cd ２ In Se(S)-ODE solution, zinc chloride (ZnCl ２ 4092 mg of ZnSe was added along with 60 mL of trioctylphosphine (TOP) and 2.4 mL of oleylamine (OLAm). These were then stirred at 220°C for 30 minutes under a nitrogen atmosphere. The resulting solution (ZnSe) was then cooled to room temperature.

[0086] Next, ethanol was added to the obtained solution to induce precipitation. Then, the obtained solution and precipitate were centrifuged, and the supernatant was removed. Next, octadecene (ODE) was added to the reaction vessel and the precipitate was dispersed. In this way, a ZnSe(S)-ODE solution was obtained.

[0087] Next, zinc chloride (ZnCl) is added to the ZnSe(S)-ODE solution. ２ 4092 mg of ZnSe(S) was added along with 30 mL of trioctylphosphine (TOP) and 3 mL of oleylamine (OLAm). These were then stirred at 280°C for 30 minutes under a nitrogen atmosphere. The resulting solution (ZnSe(S)) was then cooled to room temperature.

[0088] Next, 15 mL of 0.1 M S-DDT / OLAm solution was added to the obtained solution, and the mixture was heated at 220°C for 30 minutes with stirring. After that, the obtained solution (ZnSe(S)) was cooled to room temperature.

[0089] Next, ethanol was added to the obtained solution to induce precipitation. Then, the obtained solution and precipitate were centrifuged, and the supernatant was removed. Next, octadecene (ODE) was added to the reaction vessel and the precipitate was dispersed. In this way, a ZnSe(S)-ODE solution was obtained.

[0090] Next, zinc chloride (ZnCl) is added to the ZnSe(S)-ODE solution. ２ 2052 mg of ZnSe(S) was added along with 36 mL of trioctylphosphine (TOP) and 1.2 mL of oleylamine (OLAm). These were then stirred at 230°C for 60 minutes under a nitrogen atmosphere. The resulting solution (ZnSe(S)) was then cooled to room temperature.

[0091] As described above, a quantum dot composition according to Example 1 was obtained.

[0092] Next, 5 mL of 1-hexanethiol was added to 50 mL of the obtained quantum dot composition under a nitrogen atmosphere. These were then washed with 38 kHz ultrasound for 15 minutes.

[0093] Next, under an atmospheric environment, 25 mL of toluene was added to the obtained solution, followed by 200 mL of ethanol to induce precipitation. Then, the obtained solution and precipitate were centrifuged, and the supernatant was removed. Centrifugation was performed at 5500 rpm for 5 minutes.

[0094] Next, 25 mL of toluene was added to the obtained solution, followed by 20 mL of ethanol to induce precipitation. The obtained solution and precipitate were then centrifuged, and the supernatant was removed. The sequence of adding toluene and ethanol, followed by centrifugation and removal of the supernatant was then repeated twice. Centrifugation was performed at 5500 rpm for 5 minutes.

[0095] Next, toluene was added to the resulting precipitate. In this way, a ligand-substituted quantum dot composition was obtained.

[0096] <1.2> Example 2 The ligand-substituted quantum dot composition according to Example 2 was produced by the same method as the method for producing the ligand-substituted quantum dot composition according to Example 1, except that 1-octanthiol was used instead of 1-hexanethiol.

[0097] <1.3> Example 3 The ligand-substituted quantum dot composition according to Example 3 was produced by the same method as the method for producing the ligand-substituted quantum dot composition according to Example 1, except that the amount of zinc chloride added to the ZnSe(S)-ODE solution was changed from 2052 mg to 440 mg.

[0098] <1.4> Comparative Example 1 A ligand-substituted quantum dot composition according to Comparative Example 1 was produced by the same method as the method for producing the ligand-substituted quantum dot composition according to Example 1, except that the amount of dodecanethiol was changed from 9 mL to 0.2 mL.

[0099] <1.5> Comparative Example 2 A ligand-substituted quantum dot composition according to Comparative Example 2 was produced by the same method as the method for producing the ligand-substituted quantum dot composition according to Example 1, except that the amount of zinc chloride added to the ZnSe(S)-ODE solution was changed from 2052 mg to 0 mg.

[0100] <1.6> Comparative Example 3 A ligand-substituted quantum dot composition according to Comparative Example 3 was produced by the same method as the method for producing the ligand-substituted quantum dot composition according to Example 1, except that the amount of zinc chloride added to the ZnSe(S)-ODE solution was changed from 2052 mg to 0 mg, and 1-octanthiol was used instead of 1-hexanethiol.

[0101] <1.7> Comparative Example 4 A ligand-substituted quantum dot composition according to Comparative Example 4 was produced by the same method as the method for producing the ligand-substituted quantum dot composition according to Example 1, except that the amount of dodecanethiol was changed from 9 mL to 43 mL.

[0102] <2> Evaluation <2.1> Mole fractions For each of the quantum dot compositions and ligand-substituted quantum dot compositions according to Examples 1 to 3 and Comparative Examples 1 to 4, the ligand mole fraction was obtained using the method described above.

[0103] <2.2> PL quantum yield The PL quantum yield was measured for each of the quantum dot compositions and ligand-substituted quantum dot compositions according to Examples 1 to 3 and Comparative Examples 1 to 4 using an absolute PL quantum yield measuring device (product name: C11347, manufactured by Hamamatsu Photonics). For the quantum dot compositions, hexane was used as the solvent and the concentration of the quantum dot composition was set to 0.01% by mass. For the ligand-substituted quantum dot compositions, toluene was used as the solvent and the concentration of the ligand-substituted quantum dot composition was set to 0.01% by mass. The excitation wavelength was set to 350 nm.

[0104] <2.3> Ligand Substitution Rates For each of the ligand-substituted quantum dot compositions according to Examples 1 to 3 and Comparative Examples 1 to 4, the ligand substitution rate for the third ligand was obtained. This ligand substitution rate was defined as the ratio of the number of moles of the third ligand to the total number of moles of all ligands.

[0105] The results of the above evaluation are shown in Table 1 below.

[0106]

[0107] In Table 1, "DDT," "TOP," "ODE," "HEX," and "OCT" represent dodecanethiol, trioctylphosphine, octadecene, 1-hexanethiol, and 1-octanthiol, respectively. As shown in Table 1, the PL quantum yield of the quantum dot compositions according to Examples 1 to 3 was 60% or higher. Furthermore, the ligand substitution rate of the ligand-substituted quantum dot compositions according to Examples 1 to 3 was 90% or higher, and they exhibited excellent luminescence properties. On the other hand, although the ligand-substituted quantum dot compositions according to Comparative Examples 1 to 3 achieved a high ligand substitution rate, their PL quantum yield was 60% or lower. Furthermore, although the ligand-substituted quantum dot composition according to Comparative Example 4 had a PL quantum yield of 60% or higher, its ligand substitution rate was less than 90%.

Claims

1. A quantum dot composition for use in producing ligand-substituted quantum dots by substituting at least a portion of a ligand, comprising a quantum dot, a solvent, and a halogen ion, wherein the quantum dot comprises a core-shell particle having a core and a shell layer covering the core, and a ligand coordinated to the surface of the core-shell particle, the shell layer comprising Zn and S, and the ligand comprising a first ligand which is a thiol and a second ligand which is one or more compounds selected from the group consisting of amines, fatty acids, phosphine compounds, and alcohols, and the mole fraction of the first ligand to the ligand is in the range of 0.001 or more and 0.1 or less.

2. The quantum dot composition according to claim 1, wherein the halogen ion is a chloride ion or a bromide ion.

3. The quantum dot composition according to claim 2, wherein the halogen ion is a chloride ion, and the chloride ion is contained in the form of zinc chloride.

4. The quantum dot composition according to any one of claims 1 to 3, wherein the first ligand is 1-dodecanethiol.

5. The quantum dot composition according to any one of claims 1 to 4, wherein the second ligand is oleic acid and trioctylphosphine.

6. The quantum dot composition according to any one of claims 1 to 5, wherein the concentration of the halogen ion in the quantum dot composition is in the range of 0.0005 mol / L or more and 0.05 mol / L or less.

7. The quantum dot composition according to any one of claims 1 to 6, wherein the shell layer further comprises Te.

8. The quantum dot composition according to any one of claims 1 to 7, wherein the first ligand has an alkyl chain, and the main chain of the alkyl chain has 8 or more carbon atoms.

9. The quantum dot composition according to any one of claims 1 to 8, wherein the second ligand has an alkyl chain, and the number of carbon atoms in the main chain of the alkyl chain of the second ligand is 8 or more.

10. A ligand-substituted quantum dot composition comprising a quantum dot composition according to any one of claims 1 to 9, wherein at least a portion of the ligand contained in the quantum dot composition is substituted with a third ligand which is one or more compounds selected from the group consisting of thiols, amines, and zinc halides.

11. The ligand-substituted quantum dot composition according to claim 10, wherein 0.95 to 0.999 mole fractions of the ligand contained in the quantum dot composition are substituted with the third ligand.

12. A method for producing a ligand-substituted quantum dot composition, comprising substituting at least one of the ligands contained in the quantum dot composition according to any one of claims 1 to 9 with a third ligand which is one or more compounds selected from the group consisting of thiols, amines, and zinc halides.

13. A method for producing a ligand-substituted quantum dot composition according to claim 12, wherein 0.95 to 0.999 mole fractions of the ligand contained in the quantum dot composition are replaced with the third ligand.

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