Method for producing core / shell semiconductor nanoparticles

Abstract

Provided is a method for producing core / shell semiconductor nanoparticles, which is characterized by having a shell formation step in which a core particle or an intermediate particle of a core / shell semiconductor nanoparticle having one or more shells, a dispersion medium, and a shell precursor are mixed and reacted so as to form a shell on at least a part of the surface of the core particle or the intermediate particle of a core / shell semiconductor nanoparticle having one or more shells, thereby obtaining a core / shell semiconductor nanoparticle. The method for producing core / shell semiconductor nanoparticles is also characterized in that the dispersion medium contains an ester compound. The present invention is capable of providing a method for producing core / shell semiconductor nanoparticles, with which it is possible to increase the quantum efficiency of core / shell semiconductor nanoparticles.

Description

Method for Producing Core / Shell-Type Semiconductor Nanoparticles

[0001] The present invention relates to a method for producing core / shell-type semiconductor nanoparticles.

[0002] Semiconductor nanoparticles that are so small that the quantum confinement effect appears have a bandgap that depends on the particle size. Excitons formed in semiconductor nanoparticles by means such as photoexcitation and charge injection emit photons of energy corresponding to the bandgap upon recombination. Therefore, by appropriately selecting the composition and particle size of the semiconductor nanoparticles, light emission at a desired wavelength can be obtained.

[0003] Semiconductor nanoparticles are being tried for various applications such as display applications, biological labeling applications, and solar cell applications. In particular, for display applications, semiconductor nanoparticles are being formed into films and used as wavelength conversion layers.

[0004] As semiconductor nanoparticles, Cd chalcogenide semiconductor nanoparticles and semiconductor nanoparticles based on InP are known (for example, Patent Documents 1 to 3). In particular, research on Cd-based semiconductor nanoparticles represented by Cd chalcogenides has been actively conducted in this field since relatively early on.

[0005] U.S. Patent Application Publication No. 2015 / 083969, U.S. Patent No. 9169435, U.S. Patent No. 9884993

[0006] Cd chalcogenide semiconductor nanoparticles have the advantage that the change in emission wavelength due to particle size change is relatively gentle compared to InP-based semiconductor nanoparticles, so it is easy to adjust the emission wavelength.

[0007] However, although Cd chalcogenide semiconductor nanoparticles with relatively high quantum efficiency have been obtained, further improvement in quantum efficiency is required when they are used in applications that emphasize light conversion efficiency such as display applications.

[0008] Also, for InP-based semiconductor nanoparticles, further improvement in quantum efficiency is required.

[0009] Therefore, an object of the present invention is to provide a method for producing core / shell semiconductor nanoparticles that can increase the quantum efficiency of the core / shell semiconductor nanoparticles.

[0010] As a result of diligent research to solve the above problems, the present inventors have found that core / shell type semiconductor nanoparticles with high quantum efficiency can be obtained by a method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to form a shell on at least a part of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound, and thus the present invention has been completed. In other words, the present invention (1) provides a method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to form a shell on at least a part of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound.

[0011] Furthermore, the present invention (2) provides a method for producing core / shell type semiconductor nanoparticles according to (1), characterized in that the ester compound is an ester compound having an aromatic ring.

[0012] Furthermore, the present invention (3) provides a method for producing core / shell type semiconductor nanoparticles according to (1), characterized in that the ester compound is an ester compound that does not have an aromatic ring.

[0013] Furthermore, the present invention (4) provides a method for producing core / shell type semiconductor nanoparticles according to (1), characterized in that the ester compound is an ester compound having an aromatic ring and an ester compound not having an aromatic ring.

[0014] Furthermore, the present invention (5) provides a method for producing core / shell type semiconductor nanoparticles according to any of (1) to (4), characterized in that the core particles mixed in the shell formation step are a dispersion of core particles.

[0015] Furthermore, the present invention (6) provides a method for producing core / shell type semiconductor nanoparticles according to (5), characterized in that the temperature of the dispersion of the core particles is 200°C to 380°C.

[0016] Furthermore, the present invention (7) provides a method for producing core / shell type semiconductor nanoparticles according to any of (1) to (6), characterized in that the core particles of the core / shell type semiconductor nanoparticles contain Cd and Se.

[0017] Furthermore, the present invention (8) provides a method for producing core / shell type semiconductor nanoparticles according to any of (1) to (7), characterized in that the shell of the core / shell type semiconductor nanoparticle contains Cd and S.

[0018] Furthermore, the present invention (9) provides a method for producing the core / shell type semiconductor nanoparticles of (8), characterized in that the shell of the core / shell type semiconductor nanoparticles further contains Zn and S.

[0019] Furthermore, the present invention (10) provides a method for producing core / shell type semiconductor nanoparticles according to any of (1) to (9), characterized in that the reaction temperature in the shell formation step is 200°C to 380°C.

[0020] According to the present invention, it is possible to provide a method for producing core / shell type semiconductor nanoparticles that can increase the quantum efficiency of the core / shell type semiconductor nanoparticles.

[0021] The core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention are semiconductor nanoparticles having a core particle and one or more layers of shell formed on at least a part of the surface of the core particle. In the core / shell type semiconductor nanoparticles, the shell only needs to be at least one layer, and examples include core / shell type semiconductor nanoparticles consisting of a core particle and one layer of shell, core / shell type semiconductor nanoparticles consisting of a core particle and two layers of shell, and core / shell type semiconductor nanoparticles consisting of a core particle and three or more layers of shell.

[0022] Core particles related to core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention include core particles containing Cd and a chalcogen element. Because the core particles related to the core / shell type semiconductor nanoparticles contain Cd and a chalcogen element, the change in emission wavelength due to particle size changes is relatively gradual, making it easier to adjust the emission wavelength. Examples of chalcogen elements include Se, S, and Te. In particular, when the core particles contain Cd and Se, it is preferable in that monodisperse particles with high color purity are easily obtained. When the core particles are core particles containing Cd and a chalcogen element, the core particles may inevitably or intentionally contain elements such as P, N, Si, Al, and Zn, as long as it does not impair the scope of the present invention.

[0023] When the core particles of the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention contain Cd and a chalcogen element, the shell of the core / shell type semiconductor nanoparticle mainly contains S, Cd and / or Zn. When the shell mainly contains S, Cd and / or Zn, the shell may, in addition to S, Cd and / or Zn, inevitably or intentionally contain elements such as P, N, Si, F, Cl, and Br, to the extent that it does not impair the scope of the present invention.

[0024] In the case where the core particles of the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention contain Cd and a chalcogen element, the shell form of the core / shell type semiconductor nanoparticles may include, for example, a shell containing CdS. Another example of a shell form is a shell containing ZnS. These shells do not need to have a stoichiometric composition and may have an elemental concentration gradient within the shell.

[0025] Core particles related to core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention include core particles containing In and P. By using core particles related to core / shell type semiconductor nanoparticles that contain In and P, it is possible to obtain light-emitting particles while reducing environmental impact. When the core particles are core particles containing In and P, the core particles may inevitably or intentionally contain elements such as P, N, Zn, S, Si, F, Cl, and Br, as long as it does not impair the scope of the present invention.

[0026] When the core particles of the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention are core particles containing In and P, the shell of the core / shell type semiconductor nanoparticles mainly contains Zn and S and / or Se. When the shell mainly contains Zn and S and / or Se, the shell may, inevitably or intentionally, contain elements other than Zn and S and / or Se, as long as it does not impair the scope of the present invention.

[0027] In the case where the core particles of the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention are core particles containing In and P, the shell form of the core / shell type semiconductor nanoparticles can be, for example, a shell containing ZnSe. Another shell form can be a shell containing ZnS. Yet another shell form can be a shell containing ZnSeS. These shell forms do not need to have a stoichiometric composition and may have an elemental concentration gradient within the shell.

[0028] The average particle size of the core particles in the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention is preferably 1 to 20 nm. When the average particle size of the core particles is 1 to 20 nm, excitation light of 450 nm can be converted into light with a wavelength of 500 to 680 nm. In this invention, the average particle size of the core particles is determined by calculating the area circle equivalent diameter (Heywood diameter) of 10 or more particles from a particle image observed by a transmission electron microscope (TEM).

[0029] Examples of shell configurations include a shell consisting of two or more layers, where the innermost core shell is made of CdS. Another example of a shell configuration is one in which the innermost first shell is made of CdS, and the second shell covering the outer surface of the first shell is made of ZnS.

[0030] The average particle size of the core / shell semiconductor nanoparticles obtained by the method for producing core / shell semiconductor nanoparticles of the present invention is not particularly limited, but is preferably 2 to 30 nm, and particularly preferably 2 to 25 nm. When the average particle size of the core / shell semiconductor nanoparticles is 2 to 30 nm, excitation light of 450 nm can be converted into light with a wavelength of 500 to 680 nm. In this invention, the average particle size of the core / shell semiconductor nanoparticles is determined by calculating the area circle equivalent diameter (Heywood diameter) of 10 or more particles from a particle image observed by a transmission electron microscope (TEM).

[0031] The quantum efficiency (QY) of the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention is 90% or higher, preferably 92% or higher, and more preferably 94% or higher. Although the mechanism is not clear, the inventors believe that uniform shell formation is promoted by using an ester compound having an aromatic ring as the dispersion medium in the shell formation process.

[0032] The full width at half maximum (FWHM) of the emission spectrum of the core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention is preferably 30 nm or less, and particularly preferably 29 nm or less. The FWHM of the core / shell type semiconductor nanoparticles of the present invention is 30 nm or less, and particularly preferably 29 nm or less, resulting in high color purity, making them suitable for display applications.

[0033] The core / shell semiconductor nanoparticles obtained by the method for producing core / shell semiconductor nanoparticles of the present invention may have their shell surfaces modified with ligands to stabilize dispersion in the matrix and / or impart weather resistance. Furthermore, if necessary, the ligand modifying the core / shell semiconductor nanoparticles may be replaced with another ligand to enhance dispersibility in dispersion media of different polarities. Additionally, the ligand-modified core / shell semiconductor nanoparticles of the present invention can bind to other structures through the ligand.

[0034] The core / shell type semiconductor nanoparticles obtained by the method for producing core / shell type semiconductor nanoparticles of the present invention may have an oxide layer on their surface. The oxide that forms the oxide layer is not particularly limited as long as it is within the range that the effects of the present invention are achieved, and examples include oxides of Si, Ti, and Al.

[0035] The present invention relates to a method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells with a dispersion medium and a shell precursor to form a shell on at least a portion of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound.

[0036] Furthermore, the first embodiment of the present invention is a method for producing core / shell type semiconductor nanoparticles in which the ester compound contained in the dispersion medium is an ester compound having an aromatic ring. In other words, the first embodiment of the present invention is a method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to form a shell on at least a part of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound having an aromatic ring.

[0037] Furthermore, the second embodiment of the present invention is a method for producing core / shell type semiconductor nanoparticles in which the ester compound contained in the dispersion medium is an ester compound that does not have an aromatic ring. In other words, the second embodiment of the present invention is a method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to form a shell on at least a part of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound that does not have an aromatic ring.

[0038] Furthermore, the third embodiment of the present invention is a method for producing core / shell type semiconductor nanoparticles in which the ester compound contained in the dispersion medium is a combination of an ester compound having an aromatic ring and an ester compound not having an aromatic ring. In other words, the third embodiment of the present invention is a method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to form a shell on at least a part of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound having an aromatic ring and an ester compound not having an aromatic ring.

[0039] In the following description, the first embodiment of the method for producing core / shell type semiconductor nanoparticles, the second embodiment of the method for producing core / shell type semiconductor nanoparticles, and the third embodiment of the method for producing core / shell type semiconductor nanoparticles of the present invention differ mainly in whether the ester contained in the dispersion medium is an ester having an aromatic ring, an ester without an aromatic ring, or a combination of an ester having an aromatic ring and an ester without an aromatic ring, but there are also common points. Therefore, the differences will be described by referring to the first embodiment of the method for producing core / shell type semiconductor nanoparticles, the second embodiment of the method for producing core / shell type semiconductor nanoparticles, or the third embodiment of the method for producing core / shell type semiconductor nanoparticles of the present invention, and the common points will be described by referring to the first embodiment of the method for producing core / shell type semiconductor nanoparticles, the second embodiment of the method for producing core / shell type semiconductor nanoparticles, and the third embodiment of the method for producing core / shell type semiconductor nanoparticles of the present invention collectively as the method for producing core / shell type semiconductor nanoparticles of the present invention.

[0040] The present invention provides a method for producing core / shell type semiconductor nanoparticles, which includes a shell formation step.

[0041] The shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention is a step of mixing an intermediate particle of a core particle or a core / shell type semiconductor nanoparticle having one or more shells, a dispersion medium, and a shell precursor, and reacting them to form a shell on at least a part of the surface of the intermediate particle of the core particle or the core / shell type semiconductor nanoparticle having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles.

[0042] Examples of the core particles used in the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention include core particles containing Cd and a chalcogen element. Since the change in the emission wavelength due to the change in the particle size is relatively gentle when the core particles are core particles containing Cd and a chalcogen element, it becomes easier to adjust the emission wavelength. Examples of the chalcogen element include Se, S, and Te. In particular, when the core particles contain Cd and Se, it is preferable in that monodisperse particles with high color purity are easily obtained. When the core particles are core particles containing Cd and a chalcogen element, the core particles can contain elements such as P, N, Si, Al, and Zn unavoidably or intentionally within a range not impairing the scope of the present invention.

[0043] Examples of the core particles used in the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention include core particles containing In and P. Since the core particles are core particles containing In and P, particles capable of emitting light can be obtained while reducing the environmental load. When the core particles are core particles containing In and P, the core particles can contain elements such as P, N, Zn, S, Si, F, Cl, and Br unavoidably or intentionally within a range not impairing the scope of the present invention.

[0044] The average particle size of the core particles is preferably 1 to 20 nm. When the average particle size of the core particles is 1 to 20 nm, excitation light of 450 nm can be converted into light having a wavelength of 500 to 680 nm. In the present invention, the average particle size of the core particles is determined by calculating the particle sizes of 10 or more particles as the equivalent diameter of the area circle (Heywood diameter) for the particle image observed by a transmission electron microscope (TEM).

[0045] Note that the core particles may be obtained by any method. For example, known methods include the hot injection method, the flow reactor method, and the like.

[0046] The intermediate particles of the core / shell type semiconductor nanoparticles having one or more shells used in the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention are intermediate particles used in the production of core / shell type semiconductor nanoparticles in which two or more shells are formed on the core. For example, when a first layer shell is formed on the core particles to obtain intermediate particles of core / first layer shell type semiconductor nanoparticles, and then a second layer shell is formed on the obtained intermediate particles of core / first layer shell type semiconductor nanoparticles to produce core / first layer shell / second layer shell type semiconductor nanoparticles having two shells, the intermediate particles of core / first layer shell type semiconductor nanoparticles correspond to the intermediate particles of core / shell type semiconductor nanoparticles having one or more shells used in the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention. Further, for example, when producing core / first layer shell / second layer shell / third layer shell type semiconductor nanoparticles having three shells, the intermediate particles of core / first layer shell type semiconductor nanoparticles and the intermediate particles of core / first layer shell / second layer shell type semiconductor nanoparticles obtained in the production process correspond to the intermediate particles of core / shell type semiconductor nanoparticles having one or more shells used in the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention.

[0047] The composition of the core and the shell in the intermediate particles of the core / shell type semiconductor nanoparticles having one or more shells used in the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention is adjusted so as to be the composition of the core / shell type semiconductor nanoparticles to be produced.

[0048] The shell precursor used in the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention is appropriately selected depending on the composition of the shell to be formed. Examples of Cd precursors include cadmium oxide, cadmium chloride, cadmium acetate, or cadmium oleate and other cadmium carboxylates. Examples of Se precursors include trialkylphosphine selenide, selenol, Se-TBP solution and Se-TOP solution obtained by dispersing selenium powder in tributylphosphine (TBP) or trioctylphosphine (TOP). Examples of S precursors include trioctylphosphine sulfide, tributylphosphine sulfide, thiols, and bis(trimethylsilyl) sulfide. Examples of Zn precursors include zinc acetate, zinc propionate, zinc myristate, zinc oleate and other zinc carboxylates.

[0049] For example, in the case where the core particle contains Cd and a chalcogen element, and a shell mainly containing S, Cd, and / or Zn is formed, the shell precursor mainly contains an S precursor and a Cd precursor and / or a Zn precursor. Also, for example, in the case where the core particle contains In and P, and a shell mainly containing Zn, S, and / or Se is formed, the shell precursor mainly contains a Zn precursor and an S precursor and / or a Se precursor.

[0050] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention, the amount of shell precursor used is appropriately selected depending on the thickness of the shell to be formed.

[0051] The dispersion medium used in the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention is a dispersion medium for dispersing core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells before mixing with the shell precursor, and is the dispersion medium used when carrying out the shell formation reaction.

[0052] The dispersion medium used in the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention contains an ester compound. The content of the ester compound in the dispersion medium used in the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and more preferably 5.0% by mass or more. By having the content of the ester compound in the dispersion medium within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased.

[0053] The dispersion medium used in the shell formation step of the first embodiment of the present invention for producing core / shell type semiconductor nanoparticles contains an ester compound having an aromatic ring, but does not contain an ester without an aromatic ring. Ester compounds are generally substances obtained by the dehydration condensation of a carboxylic acid and an alcohol, but the group having the aromatic ring in the ester compound having an aromatic ring may be a group derived from either a carboxylic acid or an alcohol. By including an ester compound having an aromatic ring in the dispersion medium used in the shell formation step, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased. In particular, when the ester compound having an aromatic ring is an ester compound in which both the group derived from the carboxylic acid and the group derived from the alcohol have aromatic rings, the resulting core / shell type semiconductor nanoparticles exhibit very high quantum efficiency. Although the mechanism is not clear, the inventors believe that the inclusion of an ester compound having an aromatic ring in the dispersion medium during the shell formation step promotes uniform shell formation.

[0054] Examples of ester compounds having an aromatic ring include benzyl carboxylates such as benzyl acetate, benzyl butyrate, and benzyl phenylacetate; alkyl benzoates such as octyl benzoate; benzyl benzoate; and phenethyl benzoate. Of these, octyl benzoate, benzyl phenylacetate, benzyl benzoate, and phenethyl benzoate are preferred because they yield core / shell type semiconductor nanoparticles with high quantum efficiency even when added at relatively low temperatures in the dispersion medium. The ester compound having an aromatic ring may be a single compound or a combination of two or more compounds.

[0055] Ester compounds having an aromatic ring are preferably those with a boiling point of 200°C or higher at 1 atm, and more preferably those with a boiling point of 210°C or higher, as they are less likely to volatilize during the shell formation process.

[0056] The dispersion medium used in the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention may contain compounds other than ester compounds having an aromatic ring, such as carboxylic acids, amines, and phosphines.

[0057] In the shell formation step of the first embodiment of the present invention, the content of the aromatic ring-containing ester compound in the dispersion medium is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and more preferably 5.0% by mass or more. By having the content of the aromatic ring-containing ester compound in the dispersion medium within the above range, the quantum efficiency of the core / shell-type semiconductor nanoparticles can be increased.

[0058] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention, the amount of dispersion medium used is preferably 5 to 2000, more preferably 5 to 1500, in terms of the molar ratio to Cd in the core particles when the core particles contain Cd and a chalcogen element, and in terms of the molar ratio to In in the core particles when the core particles contain In and P. By using an amount of dispersion medium within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased.

[0059] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention, the amount of ester compound having an aromatic ring used is preferably 5 to 500, more preferably 5 to 300, in terms of the molar ratio to Cd in the core particles when the core particles contain Cd and a chalcogen element, and in terms of the molar ratio to In in the core particles when the core particles contain In and P. By using an ester compound having an aromatic ring within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased. When using two or more ester compounds having aromatic rings as a dispersion medium, the above amount refers to the total amount of ester compounds having aromatic rings used.

[0060] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention, when an ester compound having an aromatic ring is used as a dispersion medium, a substance having an aromatic ring derived from the dispersion medium may coordinate as a ligand to the surface of the core / shell type semiconductor nanoparticles. Examples of substances having an aromatic ring derived from the dispersion medium include decomposition products of esters, or by-products of precursors or additives in the manufacturing process of core / shell type semiconductor nanoparticles. There are no particular limitations, but examples include alkylbenzenes such as nonadecylbenzene and n-octylbenzene, aromatic alcohols such as benzyl alcohol, and aromatic carboxylic acids such as phenylacetic acid and benzoic acid.

[0061] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention, the core particles may be in the form of a dispersion of core particles. That is, a dispersion of core particles may be used as the core particles in the shell formation step. Preferably, the dispersion of core particles is one in which the core particles are dispersed in an organic dispersion medium such as octadecene. In this case, the shell formation step may be carried out not only by simply replacing the core particles with a dispersion of core particles as described above, but also by adding a dispersion medium and a shell precursor to the dispersion of core particles. When adding a dispersion medium and a shell precursor to a dispersion of core particles, there are no particular limitations on the order, but it is preferable that the shell precursor be added in the presence of the dispersion of core particles and the dispersion medium.

[0062] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention, when mixing a dispersion of core particles as core particles, it is preferable that the dispersion of core particles is heated. The temperature of the dispersion of core particles is preferably 200°C to 380°C, more preferably 220°C to 350°C, and even more preferably 250°C to 350°C. It is believed that by having the temperature of the dispersion of core particles within the above range, the reaction activity with the dispersion medium and the shell precursor is increased, and a uniform shell can be formed.

[0063] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the first embodiment of the present invention, the reaction temperature of the shell formation reaction is preferably 200°C to 380°C, more preferably 220°C to 350°C, and even more preferably 250°C to 350°C. It is believed that by having the reaction temperature of the shell formation reaction within the above range, the reaction activity with the dispersion medium and the shell precursor is increased, and a uniform shell can be formed.

[0064] The dispersion medium used in the shell formation step of the second embodiment of the present invention for manufacturing core / shell type semiconductor nanoparticles contains an ester compound without an aromatic ring, but does not contain an ester having an aromatic ring. Ester compounds are generally substances obtained by the dehydration condensation of a carboxylic acid and an alcohol, but in ester compounds without an aromatic ring, neither the group derived from the carboxylic acid nor the group derived from the alcohol has an aromatic ring. By including an ester compound without an aromatic ring in the dispersion medium used in the shell formation step, the resulting core / shell type semiconductor nanoparticles exhibit high quantum efficiency. Although the mechanism is not clear, the inventors believe that the inclusion of an ester compound without an aromatic ring in the dispersion medium during the shell formation step promotes uniform shell formation.

[0065] Examples of ester compounds without aromatic rings include alkyl carboxylates such as cyclohexyl acetate and ethyl oleate. Of these, cyclohexyl acetate and ethyl oleate are preferred because, when added at a relatively high temperature in the dispersion medium, a core / shell with high quantum efficiency can be obtained. The ester compound without aromatic rings may be a single compound or a combination of two or more compounds.

[0066] Ester compounds without aromatic rings are less likely to volatilize during the shell formation process, and it is preferable that their boiling point at 1 atm be 170°C or higher, and more preferably 180°C or higher. If the addition temperature of the ester compound is higher than the boiling point of the ester compound, rapid boiling of the ester compound can be suppressed by adding it not by itself, but together with a compound described later or an additional dispersion medium.

[0067] The dispersion medium used in the shell formation step of the second embodiment of the present invention for the method of producing core / shell type semiconductor nanoparticles may contain compounds other than ester compounds that do not have an aromatic ring, such as carboxylic acids, amines, and phosphines.

[0068] In the shell formation step of the second embodiment of the present invention for producing core / shell type semiconductor nanoparticles, the content of the ester compound without an aromatic ring in the dispersion medium is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and more preferably 5.0% by mass or more. By having the content of the ester compound without an aromatic ring in the dispersion medium within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased.

[0069] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the second embodiment of the present invention, the amount of dispersion medium used is preferably 5 to 2000, more preferably 5 to 1500, in terms of the molar ratio to Cd in the core particles when the core particles contain Cd and a chalcogen element, and in terms of the molar ratio to In in the core particles when the core particles contain In and P. By using an amount of dispersion medium within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased.

[0070] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the second embodiment of the present invention, the amount of ester compound without aromatic rings used is preferably 5 to 500, more preferably 5 to 300, in terms of the molar ratio to Cd in the core particles when the core particles contain Cd and a chalcogen element, and in terms of the molar ratio to In in the core particles when the core particles contain In and P. By using an amount of ester compound without aromatic rings within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased. When two or more ester compounds without aromatic rings are used as a dispersion medium, the above amount refers to the total amount of ester compounds without aromatic rings used.

[0071] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the second embodiment of the present invention, if an ester compound without an aromatic ring is used as the dispersion medium, core / shell type semiconductor nanoparticles with high quantum efficiency can be obtained.

[0072] In the shell formation step of the second embodiment of the present invention for manufacturing core / shell type semiconductor nanoparticles, the core particles may be in the form of a dispersion of core particles. That is, a dispersion of core particles may be used as the core particles in the shell formation step. Preferably, the dispersion of core particles is one in which the core particles are dispersed in an organic dispersion medium such as octadecene. In this case, the shell formation step may be carried out not only by simply replacing the core particles with a dispersion of core particles as described above, but also by adding a dispersion medium and a shell precursor to the dispersion of core particles. When adding a dispersion medium and a shell precursor to a dispersion of core particles, there are no particular limitations on the order, but it is preferable that the shell precursor be added in the presence of the dispersion of core particles and the dispersion medium.

[0073] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles according to the second embodiment of the present invention, when mixing a dispersion of core particles as core particles, it is preferable that the dispersion of core particles is heated. The temperature of the dispersion of core particles is preferably 280°C to 380°C, more preferably 290°C to 350°C, and even more preferably 300°C to 350°C. It is believed that the reaction activity with the dispersion medium and the shell precursor is increased when the temperature of the dispersion of core particles is within the above range, allowing for the uniform formation of the shell.

[0074] In the shell formation step of the second embodiment of the present invention for manufacturing core / shell type semiconductor nanoparticles, the reaction temperature of the shell formation reaction is preferably 280°C to 380°C, more preferably 290°C to 350°C, and even more preferably 300°C to 350°C. It is believed that by having the reaction temperature of the shell formation reaction within the above range, the reaction activity with the dispersion medium and the shell precursor is increased, and a uniform shell can be formed.

[0075] The dispersion medium used in the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles includes an ester compound having an aromatic ring and an ester compound not having an aromatic ring. The ester compound having an aromatic ring contained in the dispersion medium used in the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles is the same as the ester compound having an aromatic ring in the first embodiment of the present invention for producing core / shell type semiconductor nanoparticles. Furthermore, the ester compound not having an aromatic ring contained in the dispersion medium used in the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles is the same as the ester compound not having an aromatic ring in the second embodiment of the present invention for producing core / shell type semiconductor nanoparticles.

[0076] The dispersion medium used in the shell formation step of the third embodiment of the present invention for the method of producing core / shell type semiconductor nanoparticles may contain compounds such as carboxylic acids, amines, and phosphines, in addition to ester compounds having an aromatic ring and ester compounds not having an aromatic ring.

[0077] In the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles, the total content of ester compounds having an aromatic ring and ester compounds not having an aromatic ring in the dispersion medium is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and more preferably 5.0% by mass or more. By having the content of ester compounds not having an aromatic ring in the dispersion medium within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased.

[0078] In the dispersion medium used in the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles, the content of ester compounds having an aromatic ring and ester compounds not having an aromatic ring in the dispersion medium is preferably 1:100 to 100:1 by mass ratio, more preferably 1:50 to 100:1, and more preferably 1:1 to 100:1.

[0079] In the shell formation step of the third embodiment of the present invention for manufacturing core / shell type semiconductor nanoparticles, the amount of dispersion medium used is 5 to 2000, more preferably 5 to 1500, in terms of the molar ratio to Cd in the core particles when the core particles contain Cd and a chalcogen element, and in terms of the molar ratio to In in the core particles when the core particles contain In and P. By using an amount of dispersion medium within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased.

[0080] In the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles, the total amount of ester compounds having aromatic rings and ester compounds not having aromatic rings used is preferably 5 to 500, more preferably 5 to 300, in terms of the molar ratio to Cd in the core particles when the core particles contain Cd and a chalcogen element, and in terms of the molar ratio to In in the core particles when the core particles contain In and P. By having the total amount of ester compounds having aromatic rings and ester compounds not having aromatic rings within the above range, the quantum efficiency of the core / shell type semiconductor nanoparticles can be increased. When two or more ester compounds having aromatic rings are used as the dispersion medium, the above amount refers to the total amount of ester compounds having aromatic rings used. When two or more ester compounds not having aromatic rings are used as the dispersion medium, the above amount refers to the total amount of ester compounds not having aromatic rings used.

[0081] In the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles, using an ester compound having an aromatic ring and an ester compound not having an aromatic ring as a dispersion medium can increase the quantum efficiency of the core / shell type semiconductor nanoparticles.

[0082] In the shell formation step of the third embodiment of the present invention for manufacturing core / shell type semiconductor nanoparticles, the core particles may be in the form of a dispersion of core particles. That is, in the shell formation step, a dispersion of core particles may be used as the core particles. Preferably, the dispersion of core particles is one in which the core particles are dispersed in an organic dispersion medium such as octadecene. In this case, the shell formation step may be carried out not only by simply replacing the core particles with a dispersion of core particles as described above, but also by adding a dispersion medium and a shell precursor to the dispersion of core particles. When adding a dispersion medium and a shell precursor to a dispersion of core particles, there are no particular limitations on the order, but it is preferable that the shell precursor be added in the presence of the dispersion of core particles and the dispersion medium.

[0083] In the shell formation step of the third embodiment of the present invention for producing core / shell type semiconductor nanoparticles, when mixing a dispersion of core particles as core particles, it is preferable that the dispersion of core particles is heated. The temperature of the dispersion of core particles is preferably 250°C to 380°C, more preferably 270°C to 350°C, and even more preferably 290°C to 350°C. It is believed that the reaction activity with the dispersion medium and the shell precursor is increased when the temperature of the dispersion of core particles is within the above range, allowing for the uniform formation of the shell.

[0084] In the shell formation step of the third embodiment of the method for producing core / shell type semiconductor nanoparticles of the present invention, the reaction temperature of the shell formation reaction is preferably 250°C to 380°C, more preferably 270°C to 350°C, and even more preferably 290°C to 350°C. It is believed that by having the reaction temperature of the shell formation reaction within the above range, the reaction activity with the dispersion medium and the shell precursor is increased, and a uniform shell can be formed.

[0085] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention, core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor are mixed and a shell formation reaction is carried out. In the shell formation process, a method for mixing core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to carry out a shell formation reaction includes, for example, (i) first mixing core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor, and then heating to cause a reaction; (ii) heating a mixture of core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells and a dispersion medium, and reacting while adding a shell precursor; (iii) heating a mixture of a dispersion medium and a shell precursor, and reacting while adding core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells; and (iv) heating the dispersion medium while reacting while adding core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells and a shell precursor, respectively.

[0086] In the shell formation step of the method for producing core / shell type semiconductor nanoparticles of the present invention, a mixed precursor, which is a pre-mixed mixture of precursors of each element that forms the shell, may be mixed as the shell precursor, or the precursors of each element that forms the shell may be mixed separately as shell precursors. When a mixed precursor, which is a pre-mixed mixture of precursors of each element that forms the shell, is mixed, the shell precursors can react uniformly with the core particles, enabling uniform shell formation. When the precursors of each element that forms the shell are mixed separately, it is possible to prevent the precursors of each element from reacting before the shell formation step, thereby suppressing the generation of by-products.

[0087] In this way, core / shell type semiconductor nanoparticles are obtained by performing the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention.

[0088] In the method for producing core / shell type semiconductor nanoparticles of the present invention, in order to form two or more shells of different compositions on a core particle, the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention can be performed using a shell precursor to obtain the composition of each shell in the formation of each shell. For example, in order to form a first layer shell on a core particle, the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention is performed to obtain an intermediate particle of core / first layer shell type semiconductor nanoparticles. Then, in order to form a second layer shell on the obtained intermediate particle of core / first layer shell type semiconductor nanoparticles, the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention is performed to obtain a core / first layer shell / second layer shell type semiconductor nanoparticle having two shells. Furthermore, for example, in order to form a first layer shell on a core particle, a shell formation step according to the method for manufacturing core / shell type semiconductor nanoparticles of the present invention is performed to obtain an intermediate particle of core / first layer shell type semiconductor nanoparticles. Then, in order to form a second layer shell on the obtained intermediate particle of core / first layer shell type semiconductor nanoparticles, a shell formation step according to the method for manufacturing core / shell type semiconductor nanoparticles of the present invention is performed. ... Then, in order to form an nth layer shell on the obtained intermediate particle of core / first layer shell / second layer shell / ... / (n-1)th layer shell type semiconductor nanoparticles, a shell formation step according to the method for manufacturing core / shell type semiconductor nanoparticles of the present invention is performed to obtain a core / first layer shell / second layer shell / ... / nth layer shell type semiconductor nanoparticle having n layers of shells.

[0089] Furthermore, in the method for producing core / shell type semiconductor nanoparticles of the present invention, by applying the method for producing core / shell type semiconductor nanoparticles of the present invention when forming a shell that is directly formed on the surface of the core particle, core / shell type semiconductor nanoparticles with high quantum efficiency can be obtained.

[0090] In the method for producing core / shell type semiconductor nanoparticles of the present invention, in order to form two or more shells on a core particle, the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention can be performed in at least one of the shell formations. For example, in a method for producing core / shell type semiconductor nanoparticles in which a first layer shell is formed on a core particle to obtain an intermediate particle of the core / first layer shell type semiconductor nanoparticle, then a second layer shell is formed on the obtained intermediate particle of the core / first layer shell type semiconductor nanoparticle, ... and then an nth layer shell is formed on the obtained intermediate particle of the core / first layer shell / second layer shell / ... / (n-1)th layer shell type semiconductor nanoparticle to obtain a core / first layer shell / second layer shell / ... / nth layer shell type semiconductor nanoparticle having n layers of shells, the shell formation step according to the method for producing core / shell type semiconductor nanoparticles of the present invention can be performed in at least one of the shell formations.

[0091] After obtaining core / shell semiconductor nanoparticles using the method for producing core / shell semiconductor nanoparticles of the present invention, the surface of the shell can be modified with a ligand to stabilize the dispersion of the obtained core / shell semiconductor nanoparticles in a matrix and / or to impart weather resistance. Furthermore, if necessary, after obtaining core / shell semiconductor nanoparticles using the method for producing core / shell semiconductor nanoparticles of the present invention and then surface-modifying them with a ligand, the ligand modifying the core / shell semiconductor nanoparticles can be replaced with another ligand to improve dispersibility in dispersion media of different polarities. Additionally, after obtaining core / shell semiconductor nanoparticles using the method for producing core / shell semiconductor nanoparticles of the present invention and then surface-modifying them with a ligand, the ligand-modified core / shell semiconductor nanoparticles can be bound to other structures via the ligand.

[0092] The method for producing core / shell type semiconductor nanoparticles of the present invention allows for the formation of an oxide layer on the surface of core / shell type semiconductor nanoparticles after obtaining them. The oxide used to form the oxide layer is not particularly limited as long as it is within the range that achieves the effects of the present invention, and examples include oxides of Si, Ti, and Al.

[0093] The present invention will be described below based on specific experimental examples, but the present invention is not limited to these.

[0094] Semiconductor nanoparticles were fabricated according to the following method, and the composition and optical properties of the obtained semiconductor nanoparticles were measured.

[0095] (Example 1) <Cadmium oleate (Cd(Ol) ２ Synthesis of ) > First, 20 mmol of tetramethylammonium hydroxide pentahydrate and 6.4 mL of oleic acid (OAc) were added to 50 mL of methanol, and the mixture was stirred to form a homogeneous solution A. Next, 10 mmol of cadmium acetate hydrate was added to 50 mL of methanol, and the mixture was stirred to form a homogeneous solution B. Then, solution B was slowly added to solution A with stirring, and a milky white cadmium oleate precipitate was formed. After adding all the mixture, the solution was stirred for 20 minutes. Finally, the precipitate was centrifuged about three times with methanol and dried in a vacuum oven at 40°C. The dried cadmium oleate was stored in a vial.

[0096] <Preparation of Selenium Precursor> 10 mmol of Se powder was dissolved in 2.4 g of tributylphosphine (TBP) to prepare a 0.1 mol / L TBP-Se solution, which was then diluted with 6.9 g of octadecene (ODE) to obtain the selenium precursor.

[0097] <Preparation of mixed precursor> First, 0.3 mmol of cadmium oleate and 0.6 mmol of S powder were added to a vial (5 mL). Subsequently, 1.5 mmol of oleylamine, 1.5 mmol of octanoic acid, and 2.26 mL of ODEN were added to the vial to prepare a total of 3 mL of mixed precursor solution. The mixed solution was ultrasonically dispersed at 50°C and stored after complete dissolution.

[0098] <Synthesis of CdSe core particles> 0.2 mmol of cadmium oxide (CdO) and 0.8 mmol of stearic acid were added to a three-necked flask containing 10 mL of ODEN, and the flask was then mounted on a heating magnetic stirrer. The three-necked flask was degassed at room temperature for 30 minutes, and then heated at 270°C for 1 hour under a nitrogen atmosphere until the liquid turned pale yellow. It was cooled to room temperature, and 0.5 g of trioctylphosphine oxide (TOPO) and 1.5 g of amine stearate were added to the above solution. Then, it was heated to 60°C and stirred to completely dissolve the solid, and then degassed again until there were no more bubbles in the solution. Next, N ２ The mixture was transferred to a three-necked flask, stirred for 10 minutes, and then heated to 290°C. At this temperature, 1 mL of TBP-Se solution was rapidly injected, and after injection, the temperature was lowered to 250°C over 5 minutes, and then cooled to room temperature. The precipitate was centrifuged 1-2 times with 5 mL of hexane and 15 mL of ethanol.

[0099] <Synthesis of CdSe / CdS Core / Shell Semiconductor Nanoparticles> 7.5 mL of ODÉ and 40 mg of CdSe core particles were placed in a three-necked flask, and the flask was mounted on a heated magnetic stirrer. The mixture was degassed at 150°C for 30 minutes until no more bubbles remained in the solution. Then, under a nitrogen atmosphere, the temperature was increased to 300°C at a rate of 10°C / min, and when the temperature of the mixture reached 280°C, a mixed solution of 0.9 g of benzyl acetate and 1 mL of ODÉ was added, while simultaneously injecting 3 mL of mixed precursor at a rate of 1.5 mL / h. At the same rate, the temperature was increased to 310°C, held for 15 minutes, and then cooled to room temperature. The obtained CdSe / CdS core / shell semiconductor nanoparticles were centrifuged 1-2 times with 5 mL of hexane and 15 mL of ethanol to obtain CdSe / CdS core / shell semiconductor nanoparticles.

[0100] (Example 2) <Synthesis of CdSe / CdS / ZnS core / shell type semiconductor nanoparticles> 0.6 mmol of sulfur powder and 2 mL of trioctylphosphine (TOP) were placed in a 5 mL test flask and dispersed and dissolved before sonication to obtain a sulfur precursor. Next, 0.7 mmol of zinc acetate dihydrate was added to a three-necked flask along with 2 mL of oleic acid (OAc) and 6 mL of ODÉ, and the flask was mounted on a heating magnetic stirrer. The mixture was degassed at 120°C for 30 minutes, and then heated at 250°C for 1 hour under a nitrogen atmosphere to completely dissolve the solid. The solution was then cooled to 70°C, and a hexane solution of CdSe / CdS dispersed in 1 mL of hexane from Example 1 was quickly poured into the flask. After degassing for 30 minutes, the mixture was heated to 250°C under a nitrogen atmosphere. Next, the precursor was slowly injected into the solution at a rate of 0.1 mL / min and reacted for a further 40 minutes after the injection process. The solution was cooled to room temperature and centrifuged once or twice using 5 mL of hexane and 15 mL of ethanol to obtain CdSe / CdS / ZnS core / shell semiconductor nanoparticles. The obtained CdSe / CdS / ZnS core / shell semiconductor nanoparticles were dispersed in 4 mL of hexane.

[0101] (Example 3) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 2, except that 0.15 g of benzyl acetate was used instead of 0.9 g of benzyl acetate added in the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 2.

[0102] (Example 4) CdSe / CdS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 1, except that 1.0 g of benzyl butyrate was used instead of 0.9 g of benzyl acetate and 1 mL of ODE added to the synthesis of the CdSe / CdS core / shell type semiconductor nanoparticles in Example 1.

[0103] (Example 5) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 2, except that 1.0 g of benzyl butyrate was used instead of 0.9 g of benzyl acetate and 1 mL of ODE added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 2.

[0104] (Example 6) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that 1.4 g of octyl benzoate was used instead of 1.0 g of benzyl butyrate added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 5.

[0105] (Example 7) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that 0.23 g of benzyl phenylacetate was used instead of 1.0 g of benzyl butyrate added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 5.

[0106] (Example 8) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that 1.35 g of benzyl phenylacetate was used instead of 1.0 g of benzyl butyrate added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 5.

[0107] (Example 9) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that 6.75 g of benzyl phenylacetate was used instead of 1.0 g of benzyl butyrate added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 5.

[0108] (Example 10) CdSe / CdS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 1, except that 1.3 g of benzyl benzoate was used instead of 0.9 g of benzyl acetate and 1 mL of ODE added in the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles in Example 1.

[0109] (Example 11) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 5, except that 1.3 g of benzyl benzoate was used instead of 1.0 g of benzyl butyrate added in Example 5.

[0110] (Example 12) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 5, except that 6.5 g of benzyl benzoate was used instead of 1.0 g of benzyl butyrate added in Example 5.

[0111] (Example 13) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 5, except that 13.0 g of benzyl benzoate was used instead of 1.0 g of benzyl butyrate added in Example 5.

[0112] (Example 14) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 5, except that 0.43 g of benzyl benzoate was used instead of 1.0 g of benzyl butyrate added in Example 5.

[0113] (Example 15) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 5, except that 0.22 g of benzyl benzoate was used instead of 1.0 g of benzyl butyrate added in Example 5.

[0114] (Example 16) The method for preparing CdSe core particles was the same as in Example 1, and the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles was carried out as follows. CdSe core particles in 7.5 mL of ODEE were placed in a three-necked flask. The flask was then mounted on a heating magnetic stirrer. The mixture was degassed at 150°C for 30 minutes until no more bubbles remained in the solution. The temperature was raised to 300°C at a rate of 10°C / min under a nitrogen atmosphere, and then 1.3 g of benzyl benzoate was added. Subsequently, 3 mL of mixed precursor was injected, and the temperature was simultaneously raised to 310°C at the same rate, held for 15 minutes, and then cooled to room temperature. The obtained CdSe / CdS core / shell type semiconductor nanoparticles were centrifuged once or twice with 5 mL of hexane and 15 mL of ethanol to obtain CdSe / CdS core / shell type semiconductor nanoparticles.

[0115] (Example 17) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that the synthesis of the CdSe / CdS core / shell type semiconductor nanoparticles in Example 5 was performed using the synthesis method of Example 16.

[0116] (Example 18) The method for producing CdSe core particles was the same as in Example 1, and the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles was carried out as follows. 7.5 mL of ODE and 40 mg of CdSe core particles were placed in a three-necked flask, and the flask was mounted on a heated magnetic stirrer. The mixture was degassed at 150°C for 30 minutes until no more bubbles remained in the solution. Then, under a nitrogen atmosphere, the temperature was raised to 280°C at a rate of 10°C / min, and when the temperature of the mixture reached 260°C, 1.3 g of benzyl benzoate was added, while simultaneously injecting 3 mL of mixed precursor at a rate of 1.5 mL / h. At the same time, the temperature was raised to 290°C at the same rate, held for 15 minutes, and then cooled to room temperature. The obtained CdSe / CdS core / shell type semiconductor nanoparticles were centrifuged 1 to 2 times with 5 mL of hexane and 15 mL of ethanol. The CdSe / CdS core / shell type semiconductor nanoparticles obtained by centrifugation were dispersed in hexane to obtain a hexane solution. Subsequently, the synthesis of CdSe / CdS / ZnS core / shell type semiconductor nanoparticles was carried out in the same manner as in Example 2 to obtain CdSe / CdS / ZnS core / shell type semiconductor nanoparticles.

[0117] (Example 19) The method for preparing CdSe core particles was the same as in Example 1, and the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles was carried out as follows. CdSe core particles in 7.5 mL of ODEE were placed in a three-necked flask. The flask was then mounted on a heated magnetic stirrer. The mixture was degassed at 150°C for 30 minutes until no more bubbles remained in the solution. While raising the temperature to 300°C at a rate of 10°C / min under a nitrogen atmosphere, 1.3 g of benzyl benzoate was added when the temperature of the mixture reached 260°C. Then, 3 mL of mixed precursor was injected, and at the same rate the temperature was raised to 310°C, held for 15 minutes, and then cooled to room temperature. The obtained CdSe / CdS core / shell type semiconductor nanoparticles were centrifuged once or twice with 5 mL of hexane and 15 mL of ethanol to obtain CdSe / CdS core / shell type semiconductor nanoparticles. Subsequently, the synthesis of CdSe / CdS / ZnS core / shell type semiconductor nanoparticles was carried out in the same manner as in Example 2, and CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained.

[0118] (Example 20) The method for producing CdSe core particles was the same as in Example 1, and the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles was carried out as follows. CdSe core particles in 7.5 mL of ODE were placed in a three-necked flask. The flask was then mounted on a heating magnetic stirrer. The mixture was degassed at 150°C for 30 minutes until no more bubbles remained in the solution. The temperature was raised to 310°C at a rate of 10°C / min under a nitrogen atmosphere, and then 1.3 g of benzyl benzoate was added. After that, 3 mL of mixed precursor was injected, the temperature was raised to 310°C, held for 15 minutes, and then cooled to room temperature. The obtained CdSe / CdS core / shell type semiconductor nanoparticles were centrifuged once or twice with 5 mL of hexane and 15 mL of ethanol to obtain CdSe / CdS core / shell type semiconductor nanoparticles. Subsequently, the synthesis of CdSe / CdS / ZnS core / shell type semiconductor nanoparticles was carried out in the same manner as in Example 2, and CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained.

[0119] (Example 21) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 20, except that 6.5 g of benzyl benzoate was used instead of 1.3 g of benzyl benzoate added in the synthesis of the CdSe / CdS core / shell type semiconductor nanoparticles in Example 20.

[0120] (Example 22) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that 1.35 g of phenethyl benzoate was used instead of 1.0 g of benzyl butyrate added in the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 5.

[0121] (Example 23) The method for preparing CdSe core particles was the same as in Example 1, and the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles was carried out as follows. CdSe core particles in 7.5 mL of ODEE were placed in a three-necked flask. The flask was then mounted on a heating magnetic stirrer. The mixture was degassed at 150°C for 30 minutes until no more bubbles remained in the solution. The temperature was raised to 300°C at a rate of 10°C / min under a nitrogen atmosphere, and then 0.85 g of cyclohexyl acetate and 1 mL of ODEE were added. Subsequently, 3 mL of mixed precursor was injected, and the temperature was simultaneously raised to 310°C at the same rate, held for 15 minutes, and then cooled to room temperature. The obtained CdSe / CdS core / shell type semiconductor nanoparticles were centrifuged once or twice with 5 mL of hexane and 15 mL of ethanol to obtain CdSe / CdS core / shell type semiconductor nanoparticles.

[0122] (Example 24) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 2, except that the synthesis of CdSe / CdS core / shell type semiconductor nanoparticles was performed using the synthesis method of Example 23.

[0123] (Example 25) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 5, except that 1.8 g of ethyl oleate was used instead of 1.0 g of benzyl butyrate added in the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 5.

[0124] (Comparative Example 1) CdSe / CdS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 1, but without adding 0.9 g of benzyl acetate, which was added in Example 1.

[0125] (Comparative Example 2) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were synthesized in the same manner as in Example 1, but without adding 0.9 g of benzyl acetate, which was added in Example 2, and with the other steps being the same.

[0126] (Comparative Example 3) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 1, except that 12.5 g of oleyl alcohol was used instead of 0.9 g of benzyl acetate added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 2.

[0127] (Comparative Example 4) CdSe / CdS / ZnS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 1, except that 0.5 g of oleic acid was used instead of 0.9 g of benzyl acetate added to the synthesis of the CdSe / CdS / ZnS core / shell type semiconductor nanoparticles in Example 2.

[0128] (Comparative Example 5) CdSe / CdS core / shell type semiconductor nanoparticles were obtained in the same manner as in Example 1, except that 0.7 g of benzoic acid was used instead of 0.9 g of benzyl acetate added to the synthesis of the CdSe / CdS core / shell type semiconductor nanoparticles in Example 1. The CdSe / CdS core / shell type semiconductor nanoparticles obtained in Comparative Example 5 showed significantly reduced luminescence, and their optical properties could not be adequately measured. The synthesis of CdSe / CdS / ZnS core / shell type semiconductor nanoparticles was carried out in the same manner as in Example 2, but no nanoparticles with adequately measurable optical properties were obtained.

[0129] The optical identification of the obtained core / shell type semiconductor nanoparticles was measured as follows. The obtained core / shell type semiconductor nanoparticles were dispersed in octane, and the concentration of the semiconductor nanoparticles was adjusted so that the absorption rate of the dispersion was 20-30%, and this was injected into a measurement cell. For the measurement, a fluorescence quantum efficiency measurement system (Otsuka Electronics: QE-2100) was used, and a single 450 nm light was used as the excitation light, and the emission spectrum was obtained by irradiating the sample with the excitation light. From the emission spectrum obtained here, the fluorescence quantum efficiency (QY), full width at half maximum (FWHM), and emission peak wavelength (PWL) were calculated from the re-excitation corrected emission spectrum, which excludes the re-excitation fluorescence emission spectrum of the portion that was re-excited and emitted fluorescence. The results of fluorescence quantum efficiency (QY), full width at half maximum (FWHM), and emission peak wavelength (PWL) for each sample are shown in Tables 1 to 3.

[0130]

[0131]

[0132]

[0133] In the table, "boiling point" refers to the boiling point at 1 atm. "Ratio to core Cd (mol ratio)" refers to the molar ratio of the ester compound used as the dispersion medium to the Cd in the core particles. The composition shows the composition of the core particles and the shell, and indicates the composition of "core particle / first layer shell" or "core particle / first layer shell / second layer shell".

[0134] In the shell formation process, Examples 1 to 22, which used an ester having an aromatic ring as the dispersion medium, yielded CdSe / CdS core / shell type semiconductor nanoparticles or CdSe / CdS / ZnS core / shell type semiconductor nanoparticles with higher QY compared to Comparative Example 1, which did not use an ester as the dispersion medium.

[0135] In the shell formation process, Examples 23 to 25, which used an ester without an aromatic ring as the dispersion medium, yielded CdSe / CdS core / shell type semiconductor nanoparticles or CdSe / CdS / ZnS core / shell type semiconductor nanoparticles with higher QY compared to Comparative Example 1, which did not use an ester as the dispersion medium.

Claims

1. A method for producing core / shell type semiconductor nanoparticles, comprising a shell formation step of mixing and reacting core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, a dispersion medium, and a shell precursor to form a shell on at least a portion of the surface of the core particles or intermediate particles of core / shell type semiconductor nanoparticles having one or more shells, thereby obtaining core / shell type semiconductor nanoparticles, wherein the dispersion medium contains an ester compound.

2. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the ester compound is an ester compound having an aromatic ring.

3. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the ester compound is an ester compound that does not have an aromatic ring.

4. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the ester compound is an ester compound having an aromatic ring and an ester compound not having an aromatic ring.

5. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the core particles mixed in the shell formation step are a dispersion of core particles.

6. The method for producing core / shell type semiconductor nanoparticles according to claim 5, characterized in that the temperature of the dispersion of the core particles is 200°C to 380°C.

7. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the core particles of the core / shell type semiconductor nanoparticles contain Cd and Se.

8. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the shell of the core / shell type semiconductor nanoparticle contains Cd and S.

9. The method for producing core / shell type semiconductor nanoparticles according to claim 8, characterized in that the shell of the core / shell type semiconductor nanoparticle further comprises Zn and S.

10. The method for producing core / shell type semiconductor nanoparticles according to claim 1, characterized in that the reaction temperature in the shell formation step is 200°C to 380°C.

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