Quantum dot

Abstract

The purpose of the present invention is to provide a quantum dot having a shell structure that is suitable for group I-III-VI chalcopyrite-type semiconductor nanoparticles.　A quantum dot (1) according to the present invention comprises a core (2) that includes a group I-III-VI chalcopyrite structure and a shell (4) that contains Zn-S, and is characterized by comprising, between the core (2) and the shell (4), a first buffer layer (3) that has a lattice constant between the lattice constant of the core (2) and the lattice constant of the shell (4).

Description

quantum dots

[0001] The present invention relates to quantum dots comprising I-III-VI chalcopyrite-type semiconductor nanoparticles.

[0002] Patent Documents 1 and 2 disclose quantum dots comprising chalcopyrite-type semiconductor nanoparticles of Group I-III-VI.

[0003] Patent Document 1 specifies that the quantum dots are semiconductors having a core-shell structure, the shell containing a Group 13 element and a Group 16 element, and the proportion of elements other than the Group 13 element and the Group 16 element is 5% or less when the total number of atoms of all elements contained in the shell is taken as 100%.

[0004] Patent Document 2 discloses that quantum dots may have a core-shell structure, and the shell is formed of, for example, indium sulfide, gallium sulfide, aluminum sulfide, zinc sulfide, indium selenide, gallium selenide, aluminum selenide, or zinc selenide.

[0005] Patent No. 6464215 JP 2022-120222 A

[0006] Chalcopyrite-type semiconductor nanoparticles of Group I-III-VI elements have attracted attention as quantum dots that emit green or red light.

[0007] However, when a shell made of ZnS is formed on the core surface in order to enhance the emission intensity, differences in crystal structure and mismatches in lattice constants occur between the I-III-VI chalcopyrite-type semiconductor nanoparticles and the ZnS, resulting in a broad emission spectrum and a deterioration in the emission characteristics.

[0008] The present invention has been made in view of the above points, and has as its object to provide quantum dots having a shell structure suitable for Group I-III-VI chalcopyrite-type semiconductor nanoparticles.

[0009] The quantum dot of the present invention is characterized by having a core having a group I-III-VI chalcopyrite structure and a shell containing Zn—S, and including a first buffer layer between the core and the shell, the first buffer layer having a lattice constant between the lattice constants of the core and the shell.

[0010] According to the quantum dots of the present invention, a first buffer layer for adjusting the lattice constant is provided between a core having a chalcopyrite structure of Group I-III-VI and a shell containing Zn—S, thereby enabling heteroepitaxial growth and providing quantum dots with good light-emitting properties.

[0011] 1A and 1B are schematic diagrams of quantum dots according to an embodiment of the present invention, in which (a) shows a chalcopyrite structure and (b) shows a zincblende structure. 2A and 2B are longitudinal sectional views of a light-emitting device according to an embodiment of the present invention.

[0012] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the invention. In this specification, the expression "to" means that the lower limit and upper limit are included.

[0013] <Background to the Invention> Quantum dots are inorganic nanoparticles composed of several thousand to tens of thousands of atoms and having a particle diameter of several to tens of nanometers. Quantum dots emit light and are also called luminescent nanoparticles because their size is on the nanometer order, semiconductor nanoparticles because their composition is derived from semiconductor materials, or nanocrystals because their structure has a specific crystalline structure.

[0014] In recent years, quantum dot materials, which can selectively control the emission wavelength, have been increasingly adopted in displays to improve color reproduction. Quantum dots can vary the emission wavelength in various ways depending on the particle size and composition.

[0015] High-efficiency quantum dots that have been used up to now have mainly contained Cd. Quantum dots containing Cd have the advantages of high luminescence quantum yield and narrow emission half-width. However, due to the toxicity of Cd, their use is restricted in various countries, which has been a major obstacle to their practical application. Therefore, there is a demand for switching to quantum dot materials that do not use Cd.

[0016] For example, to emit green light using a Cd-free InP-based material, the particle size must be extremely small, making it impractical. For this reason, I-III-VI chalcopyrite-type semiconductor nanoparticles have attracted attention as a better alternative to InP-based materials. I-III-VI chalcopyrite-type semiconductor nanoparticles are band-edge emitting materials with narrow emission half-widths.

[0017] However, it has been found that coating I-III-VI chalcopyrite semiconductor nanoparticles with a ZnS shell in order to enhance the emission intensity results in a deterioration of the emission characteristics, such as a broadened emission spectrum, a wider emission half-width, and a lower quantum yield.

[0018] This is thought to be due to defects caused by the difference in crystal structure between the I-III-VI group chalcopyrite semiconductor nanoparticles and ZnS and a mismatch in lattice constant.

[0019] (Regarding differences in crystal structure and mismatches in lattice constants) When quantum dots are formed with a core-shell structure, it is thought that good light-emitting properties can be obtained by heteroepitaxial growth from the core to the shell so that no crystal defects occur.

[0020] For example, in conventional CdSe / ZnS quantum dots capable of green light emission, CdSe and ZnS have the same zinc blende structure (see Figure 2(b)). Therefore, there is no difference in crystal structure or mismatch in lattice constant between the two, making heteroepitaxial growth possible.

[0021] In addition, InP, a Cd-free quantum dot capable of green emission, also has a zinc blende structure. Therefore, even if ZnS is directly coated on the surface of an InP core, theoretically, there would be no difference in the crystal structure or mismatch in lattice constant. However, this would require the particle size of the InP core to be extremely small, which poses a problem that makes it impossible to achieve.

[0022] In contrast, the chalcopyrite structure of Group I-III-VI elements is a structure in which zinc blende is doubled in the c-axis direction, as shown in Figure 2(a). Therefore, if the surface of Group I-III-VI chalcopyrite-type semiconductor nanoparticles is directly coated with a ZnS shell, a mismatch in lattice constants occurs, which is thought to prevent heteroepitaxial growth. This results in a broadened emission spectrum, an increased emission half-width, and a decreased quantum yield (QY).

[0023] <Layer Structure of Quantum Dots in the Present Embodiment> Fig. 1 is a schematic diagram of a quantum dot 1 in the present embodiment. As shown in Fig. 1, the quantum dot 1 is a nanocrystal comprising a core 2 made of a chalcopyrite-type semiconductor nanoparticle of a group I-III-VI, a first buffer layer 3 formed on the surface of the core 2, and a shell 4 formed on the surface of the first buffer layer 3 and constituting the outermost shell.

[0024] Here, the term "nanocrystal" refers to nanoparticles having a particle diameter of about several nanometers to several tens of nanometers. In this embodiment, a large number of quantum dots 1 can be produced with a substantially uniform particle diameter.

[0025] The quantum dots 1 are formed in a substantially spherical shape, but do not have to be perfectly spherical. In this embodiment, an aspect ratio (length-to-length ratio) of approximately 0.8 to 1.2 is considered to be substantially spherical. Furthermore, the boundaries between the core 2 and the first buffer layer 3 and between the first buffer layer 3 and the shell 4 are not clear, and the approximate boundaries can be estimated by composition analysis or the like.

[0026] (Core 2) Core 2 is composed of a chalcopyrite structure of I-III-VI groups shown in FIG. 2(a). Group I contains Ag and may contain a portion of Cu. Group III contains Ga and may contain a portion of In. Group VI contains either S or Se, or both. Core 2 is composed of (Ag １－ｘ Cu Ｘ )-(In ｙ Ga １－ｙ )-(S ｚ Se １－ｚ ) ２ It can be expressed as the system (0≦x<1, 0≦y<1, 0≦z≦1). Note that the "-" in the chemical formula indicates that the atomic ratio between the elements connecting it does not have to be the stoichiometric composition ratio.

[0027] In the green-emitting quantum dot 1, the core 2 is Ag-(In ｙ Ga １－ｙ )-S ２ It is preferable that the system (0≦y<1) (referred to as "AIGS") is made up of the following: Preferably, 0<y<1, more preferably 0.1≦y≦0.5, and even more preferably 0.2≦y≦0.4.

[0028] In green-emitting quantum dots, a second buffer layer made of Ag—Ga—S (referred to as “AGS”) is preferably formed on the surface of the AIGS. The second buffer layer functions as a buffer layer, but in this embodiment, it is referred to as the “second buffer layer” to distinguish it from the first buffer layer 3. In this embodiment, the first buffer layer 3 is formed on the surface of the second buffer layer made of AGS. By providing AGS in the second buffer layer, the constituent elements of the first buffer layer 3 are less likely to penetrate into the core 2, thereby suppressing deterioration of the light-emitting characteristics. In particular, Zn contained in the first buffer layer 3 can be prevented from penetrating into the core 2.

[0029] Alternatively, in the red-emitting quantum dot 1, the core 2 is (Ag １－ｘ Cu ｘ )-Ga-Se ２ It is preferable that the quantum dots for red light emission are made of the system (0≦x<1). １－ｘ Cu ｘ )-Ga-Se２ Directly on the surface of the core 2 of the system, a first buffer layer 3, described below, can be formed.

[0030] (First Buffer Layer 3) The first buffer layer 3 has a lattice constant between the lattice constant of the core 2 and the lattice constant of the shell 4. By interposing the first buffer layer 3, whose lattice constant is adjusted in this way, between the core 2 and the shell 4, heteroepitaxial growth can be promoted, and the light-emitting properties can be improved, particularly, the light-emitting half-width can be narrowed and the quantum yield (QY) can be increased.

[0031] The first buffer layer 3 is preferably formed by doping Zn into a chalcopyrite structure of the I-III-VI group. ｕ Zn １－２ｕ Ga ｕ )-S ２ (0<u<0.5) (referred to as "AZGS"). By doping with Zn, part of Ag (Group I) and Ga (Group III) are replaced with Zn. As a result, in the chalcopyrite structure shown in FIG. 2(a), part of Group I and Group III elements are replaced with Zn, and Zn appears on the crystal surface. The lattice constant of the first buffer layer 3 becomes the lattice constant between the core 2 and the shell 4, and the lattice constant mismatch between the core 2 and the shell 4 can be reduced.

[0032] It is preferable to adjust Zn to 0.01 mmol to 0.6 mmol, preferably 0.01 mmol to 0.2 mmol, per 1 mmol of Ag. That is, the Zn / Ag molar ratio is 0.01 to 0.6, preferably 0.01 to 0.2 mmol. Furthermore, when Ag is 1 mmol, Ga is approximately 1 mmol to 3 mmol. That is, the Ga / Ag molar ratio is 1 to 3.

[0033] (Shell 4) Shell 4 forms the outermost shell of the quantum dot and contains Zn—S (referred to as "ZnS"). Shell 4 may contain constituent elements other than Zn and S, and in this case, it still has a zinc blende structure. However, shell 4 is preferably made of ZnS. In this embodiment, using ZnS for shell 4 makes it possible to enhance the emission intensity.

[0034] ZnS has a zinc blende structure as shown in FIG. 2( b). However, the crystal structure of the first buffer layer 3 in contact with the ZnS is not the chalcopyrite structure shown in FIG. 2( a). The crystal is deformed closer to the zinc blende structure by Zn doping. This reduces crystal distortion between the core 2 having the chalcopyrite structure and the shell 4 having the zinc blende structure, promoting heteroepitaxial growth. As a result, it becomes possible to appropriately achieve the effect of using ZnS in the outermost shell (enhanced luminescence intensity).

[0035] It is preferable that a large number of organic ligands are coordinated to the surface of the quantum dot 1 (surface of the shell 4). This makes it possible to suppress aggregation of the quantum dots 1 and to achieve the desired optical properties. There are no particular limitations on the ligands that can be used in the reaction, but the following ligands are representative examples:

[0036] (1) Aliphatic primary amine 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 , octylamine: C ８ H １７ NH ２

[0037] (2) Fatty acid 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 １９COOH, octanoic acid: C ７ H １５ COOH

[0038] (3) Thiol-based octadecanethiol: C １８ H ３７ SH, hexanedecanethiol: C １６ H ３３ SH, tetradecanethiol: C １４ H ２９ SH, dodecanethiol: C １２ H ２５ SH, decanethiol: C １０ H ２１ SH, octanethiol: C ８ H １７ SH (4) Phosphine system Trioctylphosphine: (C ８ H １７ ) ３ P, triphenylphosphine: (C ６ H ５ ) ３ P, tributylphosphine: (C ４ H ９ ) ３ P

[0039] (5) Phosphine oxide system Trioctylphosphine oxide: (C ８ H １７ ) ３ P═O, triphenylphosphine oxide: (C ６ H ５ ) ３ P═O, tributylphosphine oxide: (C ４ H ９ ) ３ P=O

[0040] <Regarding the physical properties and characteristic values ​​of the quantum dots 1> The average particle diameter of the quantum dots 1 is approximately 3 nm to 15 nm, preferably 5 nm to 15 nm, preferably 5 nm to 12 nm, and more preferably 5 nm to 10 nm. Furthermore, the particle diameter error among multiple quantum dots 1 can be kept to approximately ±2 nm, making it possible to manufacture quantum dots 1 with uniform particle diameters. For example, when several tens to several hundred quantum dots 1 are randomly selected and the difference between the maximum and minimum particle diameters is measured, it is possible to keep it to approximately 2 nm.

[0041] The emission wavelength of the quantum dots 1 is preferably about 470 nm to 800 nm. In this embodiment, quantum dots 1 that emit green to red light with high luminance can be stably obtained.

[0042] The emission half width of the quantum dot 1 is 50 nm or less, preferably 45 nm or less, more preferably 40 nm or less, even more preferably 35 nm or less, and most preferably 33 nm or less.

[0043] The "emission half width" refers to the full width at half maximum, which indicates the spread of the emission wavelength at half the intensity of the peak emission intensity in the emission spectrum. In this way, in the present embodiment, the emission half width can be narrowed, thereby improving the color gamut.

[0044] The luminescence quantum yield of the quantum dots 1 of this embodiment is preferably 40% or more, more preferably 50% or more, even more preferably 55% or more, even more preferably 60% or more, and most preferably 65% ​​or more. In this way, this embodiment can increase the luminescence quantum yield of the quantum dots 1.

[0045] <Method for Manufacturing Quantum Dots 1> Next, a method for manufacturing the quantum dots 1 of this embodiment will be described. A method for manufacturing green light-emitting quantum dots will be described.

[0046] An organic silver compound, an organic indium compound, an organic gallium compound, and sulfur are heated and synthesized in one pot, and the AIGS particles are separated by centrifugation, and the AIGS particles are dispersed in toluene or the like.

[0047] At this time, Ag—In—Ga—S is synthesized at a reaction temperature set within the range of, for example, 100° C. to 320° C. Note that the reaction temperature is preferably set lower, at 300° C. or lower.

[0048] In this embodiment, an organic silver compound or an inorganic silver compound is used as a raw material for Ag. Although not particularly limited, for example, silver acetate (AgOAc) or silver nitrate (AgNO) ３ , as halides, silver chloride: AgCl, silver bromide: AgBr, silver iodide: AgI, as carbamates, silver diethyldithiocarbamate: Ag(SC(=S)N(C ２ H ５ ) ２ ), silver dimethyldithiocarbamate: Ag(SC(=S)N(CH ３ ) ２ ), etc. can be used.

[0049] In this embodiment, the Ag raw material may be added directly to the reaction solution, or may be dissolved in an organic solvent in advance to a certain concentration and used as the Ag raw material solution.

[0050] In this embodiment, an organic indium compound or an inorganic indium compound is used as a raw material for In. Although not particularly limited, for example, indium acetate: In(OAc) ３ , indium nitrate: InNO ３ , indium acetylacetonate: In(acac) ３ , as a halide, indium chloride: InCl ３ , silver bromide: InBr ３ , indium iodide: InI ３ , and indium diethyldithiocarbamate as a carbamate: In[(SC(=S)N(C ２ H ５ ) ２ ] ３ , indium dimethyldithiocarbamate: In[(SC(=S)N(CH ３ ) ２ )] ３ , etc. can be used.

[0051] In this embodiment, an organic indium 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: GaNO ３, gallium acetylacetonate: Ga(acac) ３ , as a halide, gallium chloride: GaCl ３ , gallium bromide: GaBr ３ , gallium iodide: Ga ２ I ３ , and gallium diethyldithiocarbamate as a carbamate: Ga[(SC(=S)N(C ２ H ５ ) ２ ] ３ , etc. can be used.

[0052] In this embodiment, the In source material or the Ga source material may be added directly to the reaction solution, or may be dissolved in an organic solvent in advance to prepare a solution of a certain concentration, which may then be used as the In source solution or the Ga source solution.

[0053] In this embodiment, an organic sulfur compound such as thiol can be used as a raw material for S. For example, octadecanethiol:C １８ H ３７ SH, hexanedecanethiol: C １６ H ３３ SH, tetradecanethiol: C １４ H ２９ SH, dodecanethiol: C １２ H ２５ SH, decanethiol: C １０ H ２１ SH, octanethiol: C ８ H １７ SH, etc.

[0054] The type of sulfur raw material contributes significantly to the luminescence characteristics. In this embodiment, it is preferable to use an S-ODE raw material in which sulfur is dissolved in octadecene (ODE), a disulfide-based or thiuram-based S raw material, or S-OLAm / DDT in which S is dissolved in oleylamine and dodecanethiol. Among these, the use of disulfides rather than S-ODE raw materials can provide better luminescence characteristics (emission half-width and quantum yield). Examples include diphenyl disulfide, dibenzyl disulfide, isopropyl xanthogen disulfide, and 4,4'-dithiodimorpholine. Furthermore, the use of thiuram raw materials can provide even better luminescence characteristics. Examples include thiuram disulfide, dipentamethylene thiuram tetrasulfide, tetraethyl thiuram disulfide, and tetramethyl thiuram disulfide. Alternatively, the S raw material may be a raw material having a structure (—S—)n in which multiple sulfur atoms are linked together, or a raw material having a structure in which nitrogen (N—S—), carbon (C—S—), etc. are attached to sulfur.

[0055] Next, an AGS source (solution) obtained by adding an organic silver compound, an organic gallium compound, and sulfur is added to the AIGS reaction solution to coat the surface of the AIGS with AGS, and then the mixture is centrifuged to precipitate AIGS / AGS particles, which are then dispersed in toluene or the like.

[0056] Next, an organic silver compound, an organic zinc compound, an organic gallium compound, and sulfur are added to the AIGS / AGS reaction solution to coat the surface of the AIGS / AGS with AZGS, and then the mixture is centrifuged to precipitate the AIGS / AGS / AZGS particles, which are then dispersed in toluene or the like.

[0057] As the source of Zn, an organic zinc compound or an inorganic zinc compound is used. The organic zinc compound or inorganic zinc compound is a source that is stable in air and easy to handle. The structure of the organic zinc compound or inorganic zinc compound is not particularly limited, but for example, the organic zinc compound or inorganic zinc compound shown below can be used. As an acetate, zinc acetate: Zn(OAc) ２ , zinc nitrate: Zn(NO ３ ) ２ , as fatty acid salts, zinc stearate: Zn(OC(=O)C１７ 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 a halide, zinc chloride: ZnCl ２ , zinc bromide: ZnBr ２ , zinc iodide: ZnI ２ , zinc carbamate is zinc diethyldithiocarbamate: Zn(SC(=S)N(C ２ H ５ ) ２ ) ２ , zinc dimethyldithiocarbamate: Zn(SC(=S)N(CH ３ ) ２ ) ２ , zinc dibutyldithiocarbamate: Zn(SC(=S)N(C ４ H ９ ) ２ ) ２ etc. can be used.

[0058] In the case of AZGS, the amount of Zn doped into the I-III-VI chalcopyrite structure is changed by adjusting the amount of organic gallium compound added when forming the first buffer layer, and specifically, Zn partially replaces the I and III positions of the chalcopyrite structure, so that the lattice constant of the first buffer layer becomes an intermediate value between that of the chalcopyrite structure and that of the zinc blende structure.

[0059] Finally, an organic zinc compound and sulfur are added to the AIGS / AGS / AZGS reaction solution to coat the surface of AZGS with ZnS, and the mixture is centrifuged to precipitate the AIGS / AGS / AZGS / ZnS particles, which are then dispersed in toluene or the like.

[0060] The above describes a method for producing green-emitting quantum dots, but red-emitting quantum dots can also be produced in a similar manner. Note that in the case of red-emitting quantum dots, the step of forming an AGS on the second buffer layer is not necessary.

[0061] <Application of Quantum Dots 1> The application of the quantum dots 1 of this embodiment is not particularly limited, but may be, for example, a light emitting device as shown in FIG.

[0062] The light-emitting device 10 shown in Fig. 3 includes a light-emitting element 12 and a wavelength conversion sheet 13. The light-emitting element 12 is, for example, an LED chip. As shown in Fig. 3, a diffusion plate 15, a wavelength conversion sheet 13, and various optical sheets 16 and 17 are stacked at predetermined intervals on the light-emitting side (upper direction in the figure) of each light-emitting element 12. The optical sheets 16 and 17 are, for example, brightness enhancement films or lenses, but are not particularly limited thereto.

[0063] In this embodiment, the light-emitting element 12 is adjusted to be able to emit blue light or light obtained by mixing blue light with visible light other than blue. This allows the light-emitting element 12 to emit blue light or near-white light (approximately white light). Here, "near-white light" refers to light that is close to white light, such as reddish white light, yellowish white light, bluish white light, or greenish white light.

[0064] In this embodiment, the wavelength conversion sheet 13 includes red-light-emitting quantum dots and green-light-emitting quantum dots.

[0065] In this embodiment, the light L1 emitted from the light emitting element 12 is attenuated and converted by the red-emitting quantum dots and green-emitting quantum dots contained in the wavelength conversion sheet, so that white light L2 can be emitted from the surface of the light emitting device.

[0066] The wavelength conversion sheet 13 of this embodiment is a sheet-like object containing quantum dots having I-III-VI group chalcopyrite semiconductor nanoparticles, the quantum dots being dispersed in a resin. For example, the wavelength conversion sheet 13 may be formed on at least one surface of a substrate film (not shown). The substrate film is not particularly limited, but is preferably a PET (polyethylene terephthalate) film from the viewpoints of light transparency, ease of handling, and adhesion to the wavelength conversion sheet 13. Alternatively, a PEN (polyethylene naphthalate) film may be used instead of the PET film or PE film.

[0067] The effects of the present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0068] Experimental Example 1 In Example 1, quantum dots composed of AIGS / AGS / AZGS / ZnS were produced. AIGS was the core, AGS was the second buffer layer, AZGS was the first buffer layer, and ZnS was the shell. The quantum dots shown in Experimental Example 1 were green-emitting quantum dots.

[0069] Experimental Example 2 In Experimental Example 2, quantum dots made of AIGS / ZnS were produced. AIGS was the core and ZnS was the shell. Unlike Experimental Example 1, Experimental Example 2 did not include the second buffer layer and the first buffer layer.

[0070] Experimental Example 3 In Experimental Example 3, quantum dots composed of AIGS / AGS / ZnS were produced. AIGS was the core, AGS was the second buffer layer, and ZnS was the shell. Unlike Experimental Example 1, Experimental Example 3 did not include the first buffer layer.

[0071] Experimental Example 4 In Experimental Example 4, quantum dots composed of AgCuGaSe / AZGS / ZnS were produced. AgCuGaSe was the core, AZGS was the first buffer layer, and ZnS was the shell. The quantum dots shown in Experimental Example 4 were red-emitting quantum dots.

[0072] <Measurement of Emission Wavelength and Emission Half Width> The emission wavelength and emission half width of a measurement sample in which quantum dots were dispersed in toluene were measured using an emission spectrometer (F-2700 manufactured by JASCO Corporation).

[0073] <Measurement of quantum yield (QY)> The quantum yield of a measurement sample in which quantum dots were dispersed in toluene was measured using a quantum yield measurement device (QE-1100 manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were as follows: Absorption coefficient: 0.35 to 0.5, Excitation light: 450 nm, Measurement range: 470 to 800 nm

[0074] <Manufacturing Process of QD Dispersion in Experimental Example 1> 0.42 g of silver iodide (AgI) and 0.42 g of gallium acetylacetonate (Ga(acac)) were placed in a 300 mL reaction vessel. ３ 0.88 g, 6.0 ml of dodecanethiol (DDT), and 120 ml of oleylamine (OLAm) were added, and an inert gas (N ２ ) and heated at 220°C under an atmosphere.

[0075] Thereafter, 6 ml of a 0.4 M solution of tetrathiuram disulfide (TETDS) dissolved in oleylamine was added, and the mixture was heated for 40 minutes, after which the resulting reaction solution was cooled to room temperature.

[0076] The resulting reaction solution was added with indium acetate: In(OAc) ３ 6 ml of a 0.2 M solution obtained by dissolving oleic acid (OLAc) and octadecene (ODE) and 18 ml of a 0.2 M solution obtained by dissolving sulfur (S) in octadecene were added, and an inert gas (N ２ ) atmosphere at 300°C for 30 minutes.

[0077] Then, gallium chloride: GaCl ３ 14.4 ml of a 0.2 M solution obtained by dissolving the above in oleic acid and octadecene was added, and an inert gas (N ２ ) and heated at 300° C. for 40 minutes in an atmosphere. Thereafter, the resulting reaction solution was cooled to room temperature.

[0078] The resulting reaction solution was centrifuged, and the supernatant was collected. Toluene and ethanol were then added, and the mixture was centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate. The precipitate was then re-dispersed in toluene.

[0079] The QD dispersion solution (AIGS solution) was measured using an emission spectrometer, and the optical properties were as follows: emission wavelength: 540.5 nm, emission half-width: 31.0 nm, and quantum yield: 35.0%.

[0080] In a 300 mL reaction vessel, 120 ml of the toluene dispersion solution and oleylamine (OLAm) were added and purged with an inert gas (N ２ ) atmosphere at 260°C to form gallium chloride: GaCl ３ A mixture of 14.4 ml of a 0.2 M solution obtained by dissolving sulfur in oleic acid and octadecene and 7.2 ml of a 0.2 M solution obtained by dissolving sulfur in octadecene was added five times at 10-minute intervals. The reaction solution was then cooled to room temperature.

[0081] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0082] 1.27 ml of a 0.4 M solution of silver acetate (AgOAc) dissolved in oleylamine and gallium acetylacetonate (Ga(acac) ３ 0.42 g, 4.5 ml of dodecanethiol (DDT), and 5.77 ml of oleylamine (OLAm) were mixed in an inert gas (N ２ The resulting solution was heated at 150°C under atmospheric pressure for 10 minutes, and then 4.5 ml of a 0.8 M solution of sulfur (S) dissolved in dodecanethiol (DDT) was added and heated for 5 minutes. The resulting reaction solution (AGS source) was then cooled to room temperature.

[0083] In a 300 mL reaction vessel, 45 ml of the toluene dispersion solution (a solution in which the AIGS core was surface-treated with GaS), 45 ml of octadecene (ODE), and 45 ml of oleylamine (OLAm) were added under an inert gas atmosphere (N ２ ) and heated at 290°C under atmospheric pressure.

[0084] After that, the resulting reaction solution AGS source was filled with an inert gas (N ２) atmosphere at 290°C, gallium chloride: GaCl was added six times at 20 minute intervals. ３ A mixture of 4.8 ml of a 0.2 M solution obtained by dissolving sulfur in oleic acid and octadecene and 2.4 ml of a 0.2 M solution obtained by dissolving sulfur in octadecene was added six times at 10-minute intervals. The reaction solution was then cooled to room temperature.

[0085] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0086] The QD dispersion solution (AIGS / AGS solution) was measured using an emission spectrometer, and the optical properties were as follows: emission wavelength: 536.0 nm, emission half-width: 32.0 nm, and quantum yield: 56.0%.

[0087] The toluene dispersion solution, 35 ml of octadecene (ODE), and 1 ml of trioctylphosphine (TOP) were placed in a 300 mL reaction vessel and purged with an inert gas (N ２ The mixture was heated to 160° C. under a 10-minute atmosphere, and a 0.2 M solution of sulfur (S) in octadecene was added four times at 10-minute intervals. The reaction solution was then cooled to room temperature.

[0088] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0089] In a 300 mL reaction vessel, the toluene dispersion solution, 40 ml of oleylamine (OLAm), 2.64 ml of octadecene (ODE), and zinc acetate (Zn(OAc)) were added. ２ 0.046 g of gallium acetylacetonate: Ga(acac) ３ 2.34 ml of a solution containing 0.41 g of sulfur (S), 0.06 g of oleylamine (OLAm), and 3.5 ml of dodecanethiol (DDT) dissolved therein, and 0.23 ml of a 0.4 M solution obtained by dissolving silver acetate (AgOAc) in oleylamine were added, and the mixture was purged with an inert gas (N ２ ) atmosphere at 160° C. for 50 minutes. Thereafter, the resulting reaction solution was cooled to room temperature.

[0090] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0091] The QD dispersion solution (AIGS / AGS / AZGS solution) was measured using an emission spectrometer, and the optical properties were observed to be an emission wavelength of 537.5 nm, an emission half-width of 30.0 nm, and a quantum yield of 18.0%.

[0092] In a 300 mL reaction vessel, the toluene dispersion solution, 21.8 ml of octadecene: ODE, 32.3 ml of trioctylphosphine::TOP, 15.8 ml of oleic acid: OLAc, and zinc acetate: Zn(OAc) were added. ２ A mixture of 4.8 ml of a 0.8 M solution obtained by dissolving trioctylphosphine: TOP in oleic acid, 0.88 ml of a 2.2 M solution obtained by dissolving sulfur: S in trioctylphosphine, and 3.36 ml of octadecene: ODE was added, and an inert gas (N ２ ) and heated at 130° C. for 30 minutes in an atmosphere. Thereafter, the resulting reaction solution was cooled to room temperature.

[0093] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0094] The QD dispersion solution (AIGS / AGS / AZGS / ZnS solution) was measured using an emission spectrometer, and the optical properties were observed to be an emission wavelength of 536.5 nm, an emission half-width of 33.0 nm, and a quantum yield of 65.0%.

[0095] <Production process of QD dispersion in Experimental Example 4> 120 ml of oleylamine (OLAm) was placed in a 300 mL reaction vessel and purged with an inert gas (N ２ ) atmosphere at 310 °C, and 2.70 ml of a 0.4 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm) and copper (II) acetate anhydride (Cu(OAc)) were added. ２ 0.60 ml of a 0.2 M solution obtained by dissolving in oleylamine: OLAm and gallium acetylacetonate: Ga(acac) ３A mixture of 4.84 ml of a solution obtained by dissolving 0.88 g of ammonium hydroxide and 0.24 g of selenium in 2.15 ml of oleylamine (OLAm) and 2.15 ml of dodecanethiol (DDT) and 12.0 ml of dodecanethiol (DDT) was added and heated for 10 minutes, after which the resulting reaction solution was cooled to room temperature.

[0096] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0097] This dispersion and oleylamine (OLAm) were placed in a 300 mL reaction vessel and an inert gas (N ２ ) and heated at 290° C. for 60 minutes in an atmosphere. Thereafter, the resulting reaction solution was cooled to room temperature.

[0098] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0099] The QD dispersion solution (AgCuGaSe solution) was measured using an emission spectrometer, and the optical properties were observed to be an emission wavelength of 627.2 nm, an emission half-width of 30.4 nm, and a quantum yield of 6.6%.

[0100] In a 300 mL reaction vessel, the toluene dispersion solution and 20 ml of oleylamine (OLAm) were added and purged with an inert gas (N ２ ) atmosphere at 310°C to obtain gallium acetylacetonate: Ga(acac) ３ 0.40 g of zinc acetate: Zn(OAc) ２　 A mixture of 4.88 mL of a solution obtained by dissolving 0.05 g of ammonium hydroxide and 0.06 g of sulfur (S) in 6.3 mL of oleylamine (OLAm) and 3.5 mL of dodecanethiol (DDT), and 0.63 mL of a 0.4 M solution obtained by dissolving silver acetate (Ag(OAc)) in oleylamine (OLAm) was added sequentially and heated for 100 minutes. The resulting reaction solution was then cooled to room temperature.

[0101] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0102] The QD dispersion solution (AgCuGaSe / AZGS solution) was measured using an emission spectrometer, and the optical properties were observed to be an emission wavelength of 626.0 nm, an emission half-width of 26.9 nm, and a quantum yield of 11.8%.

[0103] In a 300 mL reaction vessel, the toluene dispersion solution, 5.79 g of zinc carbamate: ZDEC, and 5.79 g of zinc acetate: Zn(OAc) ２　 2.94 g of octadecene, 48 ml of ODE, 20 ml of dodecanethiol, 48 ml of trioctylphosphine, and 80 ml of sulfur were dissolved in octadecene, and the resulting solution was mixed with an inert gas (N ２ ) and heated at 180° C. for 60 minutes in an atmosphere. Thereafter, the resulting reaction solution was cooled to room temperature.

[0104] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0105] The QD dispersion solution (a solution of AgCuGaSe / AZGS surface-treated with ZnS) was measured using an emission spectrometer, and the optical properties were observed to be an emission wavelength of 627.7 nm, an emission half-width of 28.9 nm, and a quantum yield of 44.8%.

[0106] In a 300 mL reaction vessel, the toluene dispersion solution, 22 mL of oleic acid (OLAc), 30 mL of dodecanethiol (DDT), and 44 mL of trioctylphosphine (TOP) were added and purged with an inert gas (N ２ ) atmosphere at 220°C to obtain zinc acetate: Zn(OAc) ２ 19.2 ml of a 0.8 M solution obtained by dissolving trioctylphosphine: TOP and oleic acid, 3.52 ml of a 2.2 M solution obtained by dissolving sulfur: S in trioctylphosphine, 12.8 ml of dodecanethiol: DDT, and 0.64 ml of a mixture of hydrochloric acid / ethyl acetate: HCl / EtOAc were successively added, and the mixture was heated for 100 minutes.

[0107] Then, trioctylphosphine:TOP was added and heated for 20 minutes, and the resulting reaction solution was cooled to room temperature.

[0108] Toluene and ethanol were added to the resulting reaction solution, which was then centrifuged at 7,500 rpm for 3 minutes to obtain a precipitate, which was then re-dispersed in toluene.

[0109] The QD dispersion solution (AgCuGaSe / AZGS / ZnS solution) was measured using an emission spectrometer, and the optical properties were observed to be an emission wavelength of 629.7 nm, an emission half-width of 30.0 nm, and a quantum yield of 82.1%.

[0110] The experimental results of Experimental Examples 1 to 4 are shown in Table 1 below.

[0111]

[0112] As shown in Table 1, in Experimental Examples 1 and 4, in which the first buffer layer (AZGS) was interposed between the core and the shell, it was found that the emission full width at half maximum (FWHM) could be made smaller and the quantum yield (QY) could be made larger than in Experimental Examples 2 and 3.

[0113] Thus, Experimental Examples 1 and 4 were able to obtain better light emission characteristics than Experimental Examples 2 and 3. In Experimental Examples 1 and 4, it is presumed that the interposition of the first buffer layer having a lattice constant between the core and shell enabled heteroepitaxial growth, resulting in an improved emission spectrum, a smaller full width at half maximum (FWHM), and an increased quantum yield (QY).

[0114] <Experiments on Molar Ratio of AZGS in First Buffer Layer> Experiments were conducted in which the molar amount of AZGS added as the first buffer layer was changed in Experimental Examples 5 to 9 shown in Tables 2 and 3. Note that each molar amount shown in the tables indicates the amount added (input amount) during synthesis.

[0115]

[0116] All of these experimental examples were green-emitting quantum dots, and were manufactured in accordance with the manufacturing method of Experimental Example 1 described above. Note that in Experimental Examples 5 to 9, no shell ZnS film was formed. Therefore, the quantum yield (QY) values ​​were low. Among the experimental examples shown in Tables 2 and 3, Experimental Examples 6, 7, and 8 exhibited favorable luminescence characteristics. It was found that all of these could narrow the full width at half maximum (FWHM) of luminescence and obtain a high quantum yield (QY). Furthermore, Experimental Example 8 was able to achieve a smaller average particle size.

[0117] <Experiment on GaS Surface Treatment> In the above-mentioned Experimental Example 1, the AIGS cores in the QD dispersion solution (AIGS solution) were subjected to a GaS surface treatment (hereinafter referred to as the "first GaS surface treatment"), followed by the addition of an AGS source. After the AGS source was added, a GaS surface treatment (hereinafter referred to as the "second GaS surface treatment") was performed. The molar ratio of Ga to S in the first and second GaS surface treatments was 2:1.

[0118] In Experimental Example 10, the core-shell layer structure was the same as in Experimental Example 1, but the molar ratio of Ga to S during the first GaS surface treatment was 4:1. Specifically, the QD dispersion solution (AIGS solution) was diluted with gallium chloride:GaCl ３ A mixture of 9.6 L of a 0.2 M solution of sulfur (S) in oleic acid and octadecene and 2.4 mL of a 0.2 M solution of sulfur (S) in octadecene was added six times at 10-minute intervals. In Experimental Example 10, the molar ratio of Ga to S during the second GaS surface treatment was 2:1, the same as in Experimental Example 1.

[0119] As shown in Table 4, the particle diameter in Experimental Example 10 was slightly larger than that in Experimental Example 1, which resulted in a slight shift in the emission wavelength toward the longer wavelength side. Furthermore, Experimental Example 10 achieved a smaller emission half-width and a higher emission quantum yield compared to Experimental Example 1. This is presumably due to more effective promotion of heteroepitaxial growth between the core and shell. In Experimental Example 10, the Ga molar ratio during the first GaS surface treatment was increased compared to Experimental Example 1 (Ga:S ratio changed from 2:1 to 4:1). This likely allowed the lattice constant of the AIGS surface to be closer to that of AGS, thereby reducing the lattice mismatch at the interface. As a result, AGS grew appropriately, and degradation of the emission characteristics was more effectively suppressed. Furthermore, in Experimental Example 10, increasing the Ga ratio likely reduced defects in the AIGS core. For example, when the presence or absence of GaS treatment was examined, the quantum yield (QY) was improved with GaS treatment. This suggests that trivalent Ga vacancies exist in the AIGS core, and that increasing the Ga ratio in the GaS treatment can fill more of the defects in the AIGS core, thereby reducing defects at the core-shell interface and improving the optical properties after shell formation.

[0120] <Another Example Based on the Core-Shell Layer Structure of Experimental Example 4> Experimental Example 11 shown in Table 5 below differs from Experimental Example 4 in the conditions of the ZnS surface treatment and the ZnS shell. First, the differences in the ZnS surface treatment will be described. That is, in Experimental Example 11, a toluene dispersion solution (ACGSe / AZGS), 9.6 mL of ODE, 9.6 mL of TOP, and 4 mL of DDT were added to a 100 mL scale reaction vessel, and while the temperature was raised to 190°C, 3.9 mL of Zn source material (0.8 M) and 15.9 mL of S source material (0.2 M) were dissolved. In practice, the Zn source material and the S source material were added alternately in three cycles so as to achieve the above-mentioned addition amounts. The Zn source material was Zn(OAc). ２ The powder was dissolved in OLAc and TOP solution, and the S raw material was prepared by dissolving S powder in ODE. Then, the mixture was cooled to room temperature and washed with toluene and ethanol.

[0121] Next, differences in the ZnS shell conditions will be described. In Example 11, 7.5 mL of DDT, 11 mL of TOP, and 2.75 mL of OLAc were added to a 100 mL toluene dispersion solution (a solution in which ACGSe / AZGS was surface-treated with ZnS), and the mixture was heated to 240°C. Then, 3.3 mL of S source (0.8 M) was added, and the mixture was maintained at 240°C for 10 minutes and cooled to room temperature. The mixture was then heated to 220°C, and 1.72 mL of ZnS source (1) was added three times at 10-minute intervals. Furthermore, 1.37 mL of ZnS source (2) was added three times at 10-minute intervals. Then, 6 mL of TOP was added, and the mixture was maintained at 220°C for 20 minutes, after which the mixture was cooled to room temperature and washed with toluene and ethanol. Here, the S raw material was prepared by dissolving S powder in DDT, the ZnS raw material (1) was prepared by dissolving 0.8M of Zn raw material and 2.2M of S raw material (S powder + TOP) in DDT, and the ZnS raw material (2) was prepared by dissolving 0.8M of Zn raw material and 2.2M of S raw material (S powder + TOP) in DDT, with the Zn ratio being higher than that of the ZnS raw material (1).

[0122] In Experimental Example 12 shown in Table 5 below, the core conditions were different from those in Experimental Example 11. Specifically, the amount of GaSe raw material used for the core was increased by 0.75 times.

[0123] In Experimental Example 13 shown in Table 5 below, a GaS surface treatment process was added to Experimental Example 11. Specifically, 90 mL of OLAm and 90 mL of ODE were added to a 300 mL QD dispersion (AgCuGaSe solution) and heated to 290°C. A mixed source of 12.48 mL of Ga source (0.2M) and 6.24 mL of S source (0.2M) was added six times in 2.4 mL increments at 10-minute intervals while maintaining the temperature at 290°C. The mixture was then cooled to room temperature and washed. The Ga source (0.2M) was GaCl ３ was dissolved in ODE and OLAc, and the S raw material (0.2 M) was prepared by dissolving S powder in ODE.

[0124] The experimental results of Experimental Examples 11 to 13 are shown in Table 5 below.

[0125] In Experimental Examples 11 to 13, the QY was increased compared to Experimental Example 4. In Experimental Examples 11 and 13, the particle diameter was reduced compared to Experimental Example 4.

[0126] This application is based on Japanese Patent Application No. 2024-124574, filed on July 31, 2024, the contents of which are incorporated herein in their entirety.

Claims

1. A quantum dot having a core made of a group I-III-VI chalcopyrite structure and a shell containing Zn—S, characterized in that it includes a first buffer layer between the core and the shell, the first buffer layer having a lattice constant between the lattice constants of the core and the shell.

2. The core is (Ag １－ｘ Cu Ｘ )-(In ｙ Ga １－ｙ )-(S ｚ Se １－ｚ ) ２ Quantum dot according to claim 1, characterized in that it consists of the system (0≦x<1, 0≦y<1, 0≦z≦1).

3. The core is Ag—(In ｙ Ga １－ｙ )-S ２ Quantum dot according to claim 1, characterized in that it consists of the system (0≦y<1).

4. The quantum dot according to claim 3, characterized in that a second buffer layer made of Ag-Ga-S is formed on the surface of the core, and the first buffer layer is formed on the surface of the second buffer layer.

5. The core is (Ag １－ｘ Cu ｘ )-Ga-Se ２ Quantum dots according to claim 1, characterized in that they consist of the system (0≦x<1).

6. The quantum dot according to claim 1, wherein the first buffer layer is formed by doping Zn into a group I-III-VI chalcopyrite structure.

7. The first buffer layer is (Ag ｕ Zn １－２ｕ Ga ｕ )-S ２ 7. The quantum dot according to claim 6, wherein u is a function of 0<u<0.

5.

8. The quantum dot according to claim 1, characterized in that the fluorescence wavelength is 470 nm or more and 800 nm or less.

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