Core / shell-type semiconductor nanoparticle and method for manufacturing same

Abstract

These core / shell-type semiconductor nanoparticles each comprise: a core containing at least indium (In) and phosphorus (P); and a shell containing zinc (Zn) and sulfur (S) and / or selenium (Se). The core / shell-type semiconductor nanoparticles are characterized by: having stacking faults; containing a halogen; having a molar ratio of halogen to indium (In) of more than 15 but no more than 500 on an atomic basis; and having an average circularity of 0.820-1.000, which is found in a STEM image obtained by observation with a scanning transmission electron microscope. The present invention provides: core / shell-type semiconductor nanoparticles each comprising a core containing indium (In) and phosphorus (P) and a shell containing zinc (Zn) and sulfur (S) and / or selenium (Se); and a method for producing the same. With shells formed with high uniformity and having highly consistent shapes, the core / shell-type semiconductor nanoparticles exhibit a high luminous efficiency and a narrow FWHM even if stacking faults are present.

Description

Core / shell semiconductor nanoparticles and method for producing the same

[0001] The present invention relates to core / shell semiconductor nanoparticles and a method for producing the same.

[0002] Semiconductor nanoparticles (quantum dots: QDs) with minute particle diameters are used as wavelength conversion materials for displays. These semiconductor nanoparticles are minute particles that can exhibit the quantum confinement effect, and the band gap width varies depending on the size of the nanoparticles. Furthermore, excitons formed within the semiconductor particles by means of photoexcitation, charge injection, etc. recombine to emit photons with energy corresponding to the band gap. Therefore, by adjusting the crystal size of the semiconductor nanoparticles, it is possible to control the emission wavelength and obtain light emission of a desired wavelength.

[0003] QD devices that use semiconductor nanoparticles include a system in which blue light is whitened using a QD film obtained by forming semiconductor nanoparticles into a film, and the resulting white light is then converted into red, green, and blue through a color filter (QD film system), and a system in which blue light is directly converted into red and green using a QD color filter that uses semiconductor nanoparticles (QD color filter system).

[0004] An example of the device configuration of a QD color filter type QD device is described using FIG. 1. As shown in FIG. 1, blue light from a blue LED 1 (light source) is directly converted to red light or blue light is directly converted to green light using QD patterns (7, 8) without being converted to white light. The QD patterns (7, 8) are formed by patterning semiconductor nanoparticles dispersed in a resin, and their thickness is approximately 5 to 10 μm due to the structural limitations of the display. For blue light, blue light from the blue LED 1 (light source) is transmitted through a diffusion layer 9 containing a diffusing material. Note that the reference numeral 3 denotes a liquid crystal; the polarizing plate is omitted in FIG. 1.

[0005] An example of the device configuration of a QD film-type QD device will be described with reference to FIG. 2. As shown in FIG. 2, a blue LED 101 is used as the light source, and the blue light is first converted into white light. To convert blue light to white light, a QD film 102 formed by dispersing semiconductor nanoparticles in a resin and forming it into a film with a thickness of approximately 100 μm is preferably used. The white light obtained by a wavelength conversion layer such as the QD film 102 is further converted into red light, green light, and blue light by a color filter (R) 104, a color filter (G) 105, and a color filter (B) 106, respectively. Note that reference numeral 103 denotes a liquid crystal, and the polarizing plate is omitted in FIG. 2.

[0006] Among these, the QD color filter method has been attracting attention in recent years because it directly converts blue light into each color, increasing the wavelength conversion efficiency of the entire QD device.

[0007] Against this background, semiconductor nanoparticles are essentially required to have high quantum efficiency to increase the wavelength conversion efficiency of QD devices, and narrow half-width to prevent color mixing.

[0008] Known semiconductor nanoparticles include Cd chalcogenide semiconductor nanoparticles and InP-based semiconductor nanoparticles (see, for example, Patent Documents 1 to 3). Much research has been conducted on Cd-based semiconductor nanoparticles. This is because Cd-based semiconductor nanoparticles have high quantum efficiency and a relatively gradual change in emission wavelength due to particle size change, making it easy to adjust the emission wavelength.

[0009] However, in recent years, due to concerns about adverse effects on the environment and human body, there has been a growing demand for the development of non-Cd-based semiconductor nanoparticles. Examples of non-Cd-based semiconductor nanoparticles include InP-based semiconductor nanoparticles. However, InP-based semiconductor nanoparticles have problems in that they have lower quantum efficiency than Cd-based semiconductor nanoparticles, and the emission wavelength changes significantly with particle size, making it difficult to adjust the emission wavelength.

[0010] As InP-based semiconductor nanoparticles, for example, Patent Documents 4 to 6 disclose semiconductor nanoparticles having a core-shell structure formed of an InP core and a shell made of ZnSe and ZnS (hereinafter also referred to as an InP / ZnSe-ZnS core / shell structure), as well as semiconductor nanoparticles having an InP / ZnSe-ZnS core / shell structure containing a halogen. In these nanoparticles, attempts have been made to increase the absorbance, improve the quantum efficiency, and narrow the half-width.

[0011] US Patent Application Publication No. 2015 / 083969 US Patent No. 9,169,435 US Patent No. 9,884,993 US Patent Application Publication No. 2017 / 0306227 US Patent Application Publication No. 2015 / 0083969 US Patent Application Publication No. 2018 / 0301592

[0012] In recent years, in order to increase quantum efficiency and reduce FWHM, semiconductor nanoparticles with a core / shell structure formed of a core made of InP and a shell made of ZnSe or ZnSe and ZnS have been developed as one type of InP-based semiconductor nanoparticles.

[0013] Here, the core / shell structure of Cd-based semiconductor nanoparticles is such that both the core and shell are a combination of Group 12 and Group 16 elements, and therefore an alloy layer can be formed at the core-shell interface, which helps to alleviate the lattice mismatch at the core-shell interface.

[0014] However, in the core / shell structure of InP-based semiconductor nanoparticles, the ZnSe or ZnSe and ZnS that make up the shell are a combination of Group 12 and Group 16 elements, so when attempting to form a core / shell structure with InP, which is a combination of Group 13 and Group 15 elements, it is difficult to form an alloy layer at the interface between the core and shell, strain is likely to accumulate inside, and uniform shell growth is hindered. Furthermore, if the shell is not formed uniformly, problems such as low luminous efficiency and large FWHM occur.

[0015] Conventionally, the shell formation reaction has been carried out at high temperatures of 330 to 340°C in order to form a uniform shell. However, a special high-boiling point solvent is required to carry out the reaction at high temperatures. In addition, the high reaction temperature leads to the formation of by-products. This causes problems such as low luminous efficiency and a broad FWHM.

[0016] Adding a halogen during shell formation can reduce shell distortion. However, if a large amount of halogen is added during shell formation to eliminate distortion, a large amount of halogen will bond to the core or the surface of the particle having the shell formed on the core. This halogen reduces the particle dispersibility, causing the particles to aggregate during the shell formation reaction, resulting in a problem of a broadened FWHM.

[0017] Furthermore, the shell of semiconductor nanoparticles is formed in the shell-forming reaction so that the particle's surface energy becomes more stable. During this process, planar lattice defects called stacking faults may occur in the shell of the semiconductor nanoparticle. The presence of these stacking faults may also degrade the optical properties of the semiconductor nanoparticles.

[0018] Therefore, an object of the present invention is to provide core / shell semiconductor nanoparticles that are composed of a core containing In and P and a shell containing Zn and S and / or Se, and that have a high luminous efficiency and a narrow FWHM because the shell is highly uniformly formed and has a uniform shape, and a method for producing the same.

[0019] As a result of intensive research aimed at solving the above problems, the present inventors have found that, in a shell formation reaction in which a shell containing Zn and S and / or Se is formed on core particles containing In and P, (1) by using a primary amine as a dispersion medium, particle aggregation is reduced even when a large amount of halogen is used, thereby allowing a larger amount of halogen to be used, and (2) because the larger amount of halogen can be used, a shell with less distortion can be formed even at a low reaction temperature. Furthermore, (3) by using a zinc salt of a branched carboxylic acid as the shell source, core / shell semiconductor nanoparticles with a uniform shape can be obtained. Based on these findings, the present inventors have found that core / shell semiconductor nanoparticles comprising a core containing In and P and a shell containing Zn and S and / or Se can be obtained, and that, because the shell formation is highly uniform and the shape is uniform, core / shell semiconductor nanoparticles with high luminous efficiency and narrow FWHM can be obtained even if the core contains stacking faults, and have completed the present invention.

[0020] That is, the present invention (1) provides core / shell semiconductor nanoparticles having at least a core containing In and P and a shell containing Zn and S and / or Se, characterized in that the core / shell semiconductor nanoparticles contain a halogen, and the molar ratio of halogen to In is greater than 15 and not more than 900, calculated as atoms, and the average circularity of the core / shell semiconductor nanoparticles is 0.820 to 1.000 in an STEM image obtained by observation with a scanning transmission electron microscope.

[0021] The present invention (2) also provides the core / shell semiconductor nanoparticles according to (1), characterized in that the halogen contained in the core / shell semiconductor nanoparticles is chlorine or bromine.

[0022] The present invention (3) also provides the core / shell semiconductor nanoparticles according to (1) or (2), wherein the halogen contained in the core / shell semiconductor nanoparticles is chlorine.

[0023] The present invention (4) also provides core / shell semiconductor nanoparticles according to any one of (1) to (3), characterized in that the semiconductor nanoparticles have stacking faults.

[0024] The present invention (5) also provides the core / shell semiconductor nanoparticles according to any one of (1) to (4), characterized in that a primary amine ligand is coordinated to the surface of the core / shell semiconductor nanoparticles.

[0025] The present invention (6) also provides core / shell semiconductor nanoparticles according to any one of (1) to (5), characterized in that the mass ratio of the primary amine ligands to all ligands is greater than 0% and not more than 100%.

[0026] The present invention (7) also provides core / shell semiconductor nanoparticles according to any one of (1) to (6), characterized in that the SD value calculated from the particle size distribution in an STEM image obtained by scanning transmission electron microscope observation is 1.0 or less.

[0027] The present invention (8) also provides the core / shell semiconductor nanoparticles according to any one of (1) to (7), characterized in that the quantum efficiency (QY) of the core / shell semiconductor nanoparticles is 80% or more.

[0028] The present invention (9) also provides the core / shell semiconductor nanoparticles according to any one of (1) to (8), characterized in that the full width at half maximum (FWHM) of the emission spectrum of the core / shell semiconductor nanoparticles is 35 nm or less.

[0029] The present invention (10) also provides the core / shell semiconductor nanoparticles according to any one of (1) to (9), characterized in that the core / shell semiconductor nanoparticles have an emission peak wavelength of 610 nm or more and a full width at half maximum (FWHM) of the spectrum of the core / shell semiconductor nanoparticles of 35 nm or less.

[0030] The present invention (11) also provides the core / shell semiconductor nanoparticles according to any one of (1) to (10), characterized in that the core / shell semiconductor nanoparticles have an emission peak wavelength of less than 530 nm.

[0031] The present invention (12) also provides the core / shell semiconductor nanoparticles according to any one of (1) to (11), characterized in that the ratio of the absorbance at the absorption peak to the absorbance at 450 nm of the core / shell semiconductor nanoparticles is 1.1 or less.

[0032] The present invention (13) also provides a method for producing core / shell semiconductor nanoparticles, comprising: a dispersion preparation step of mixing core particles containing at least In and P and zinc halide with a dispersion medium mainly containing a primary amine to prepare a core particle dispersion; and a shell formation step of mixing a Zn source, an S source and / or a Se source with the core particle dispersion and reacting them to form shells on the core particles, thereby obtaining core / shell type semiconductor nanoparticles, wherein the zinc halide is at least ZnCl. ２ and the Zn source is a zinc salt of a branched-chain carboxylic acid.

[0033] The present invention (14) also provides the method for producing core / shell semiconductor nanoparticles according to (13), characterized in that the mass ratio of the core particles to the primary amine dispersion medium is 0.001 to 0.100 mass%.

[0034] The present invention (15) also provides the method for preparing a dispersion liquid, ２ The present invention also provides a method for producing core / shell semiconductor nanoparticles according to (13) or (14), characterized in that the amount of the mixed compound is more than 7.5 and 1000 or less in molar ratio to In in the core particles.

[0035] The present invention (16) also provides the method for producing core / shell semiconductor nanoparticles according to any one of (13) to (15), characterized in that the reaction temperature in the shell formation step is 260°C to 320°C.

[0036] The present invention (17) also provides a method for producing core / shell semiconductor nanoparticles according to any one of (13) to (16), characterized in that trismethylsilylphosphine is used in synthesizing the core particles.

[0037] According to the present invention, it is possible to provide core / shell semiconductor nanoparticles that are composed of a core containing In and P and a shell containing Zn and S and / or Se, and that have a high luminous efficiency and a narrow FWHM because the shell is highly uniformly formed and has a uniform shape, and a method for producing the same.

[0038] 1 is a schematic diagram showing a QD device; FIG. 2 is a schematic diagram showing a QD device; FIG. 3 is a scanning transmission electron microscope image (STEM image) of core / shell semiconductor nanoparticles according to this embodiment; FIG. 4 is a scanning transmission electron microscope image (STEM image) of core / shell semiconductor nanoparticles according to this embodiment; FIG. 5 is a scanning transmission electron microscope image (STEM image) of core / shell semiconductor nanoparticles according to this embodiment; FIG. 6 is an absorbance curve of core / shell semiconductor nanoparticles according to this embodiment and conventional core / shell semiconductor nanoparticles; FIG. 7 is an absorbance curve of core / shell semiconductor nanoparticles according to this embodiment and conventional core / shell semiconductor nanoparticles.

[0039] The core / shell semiconductor nanoparticles of the present invention are core / shell semiconductor nanoparticles having at least a core containing In and P and a shell containing Zn and S and / or Se, characterized in that the core / shell semiconductor nanoparticles contain a halogen, and the molar ratio of halogen to In is greater than 15 and not more than 500, calculated as atoms, and the average circularity of the core / shell semiconductor nanoparticles is 0.820 to 1.000 in an STEM image obtained by observation with a scanning transmission electron microscope.

[0040] In the following, unless otherwise specified, the symbol "to" indicating a range of values ​​indicates a range including the values ​​written before and after the symbol "to." In other words, "0 to △" means "0 or more and △ or less."

[0041] The core / shell semiconductor nanoparticles of the present invention are semiconductor nanoparticles with a core / shell structure having a core and one or more shell layers. The core / shell semiconductor nanoparticles of the present invention may have at least one shell layer, and examples of the core / shell semiconductor nanoparticles of the present invention include core / shell semiconductor nanoparticles consisting of a core and one shell layer, core / shell semiconductor nanoparticles consisting of a core and two shell layers, and core / shell semiconductor nanoparticles consisting of a core and three or more shell layers.

[0042] The core of the core / shell semiconductor nanoparticles of the present invention contains In and P. The core is primarily composed of In and P. In addition to In and P, the core may unavoidably or intentionally contain Zn, S, Se, Si, N, etc., within the scope of not impairing the effects of the present invention. The core may also contain Zn, S, or Se diffusing from the shell. The average particle diameter of the core is preferably 1.0 to 5.0 nm. When the average particle diameter of the core is 1.0 to 5.0 nm, excitation light of 450 nm can be converted into light having a wavelength of 500 to 670 nm. In the present invention, the average particle diameter of the core is determined by calculating the area-equivalent circle diameter (Heywood diameter) of at least 500 particles from particle images observed with a scanning transmission electron microscope (STEM).

[0043] The shell of the core / shell semiconductor nanoparticles of the present invention contains Zn and S and / or Se. The shell mainly contains Zn and S and / or Se. Furthermore, the shell may unavoidably or intentionally contain Te, Si, Ti, Al, N, etc. in addition to Zn, S, and / or Se, as long as the effects of the present invention are not impaired. Te is effective in increasing the absorbance of the semiconductor nanoparticles, and is preferably added in a molar ratio of 0.00 to 0.50 relative to the moles of S or Se.

[0044] An example of the shell is a shell formed of ZeS. The shell may contain Se, Te, Si, Ti, Al, N, etc. in addition to Zn and S. Another example of the shell is a shell formed of ZnSe. The shell may contain S, Te, Si, Ti, Al, N, etc. in addition to Zn and Se. Another example of the shell is a shell consisting of two or more layers, with the shell closest to the core being formed of ZeS. In addition to Zn and S, it may contain Se, Te, Si, Ti, Al, N, etc. Another example of the shell is a shell consisting of two or more layers, with the shell closest to the core being formed of ZnSe. In addition to Zn and Se, the shell may contain S, Te, Si, Ti, Al, N, etc. Another example of the shell is a shell having a first shell formed of ZnS and covering the outer surface of the core, and a second shell formed of ZnSe and covering the outer surface of the first shell. The first shell may contain Se, Te, Si, Ti, Al, N, etc. in addition to Zn and S. The second shell may contain S, Te, Si, Ti, Al, N, etc. in addition to Zn and Se. An example of the shell configuration is a shell having a first shell formed of ZnSe and covering the outer surface of the core, and a second shell formed of ZnS and covering the outer surface of the first shell. The first shell may contain S, Te, Si, Ti, Al, N, etc. in addition to Zn and Se. The second shell may contain Se, Te, Si, Ti, Al, N, etc. in addition to Zn and S.

[0045] In the core / shell semiconductor nanoparticles of the present invention, the molar ratio of P to In (P / In) is 0.40 to 1.50, preferably 0.50 to 1.30, calculated as atoms. When the molar ratio of P to In is within the above range, the quantum efficiency is high and the half-width is small.

[0046] In the core / shell semiconductor nanoparticles of the present invention, the molar ratio of Zn to In (Zn / In), calculated as an atom, is 8.00 to 50.00, preferably 10.00 to 30.00. When the molar ratio of Zn to In is within the above range, the quantum efficiency is high and the half-width is small.

[0047] The molar ratio of S to In (S / In) of the core / shell semiconductor nanoparticles of the present invention is 3.00 to 25.00, preferably 4.00 to 20.00. When the molar ratio of S to In is within the above range, the quantum efficiency is high and the half-width is small.

[0048] The molar ratio of Se to In (Se / In) of the core / shell semiconductor nanoparticles of the present invention is 5.00 to 25.00, preferably 8.00 to 20.00. When the molar ratio of Se to In is within the above range, the quantum efficiency is high and the half-width is small.

[0049] When the core / shell semiconductor nanoparticles of the present invention contain S and Se, the molar ratio of the total of S and Se to In ((S+Se) / In) is 8.00 to 40.00, preferably 9.00 to 30.00, in atomic terms. When the molar ratio of the total of S and Se to In is within the above range, the quantum efficiency is high and the half-width is small.

[0050] The core / shell semiconductor nanoparticles of the present invention contain a halogen. The halogen is present at the interface between the core and the shell in the core / shell semiconductor nanoparticles of the present invention. The halogen is In ３＋ and Zn ２＋The inventors speculate that this effect is due to the halogen atoms filling dangling bonds as linkages between the core particles, thereby enhancing the confinement effect on anions. Therefore, when the core / shell semiconductor nanoparticles of the present invention contain a halogen on the outer surface of the core particle, the halogen fills dangling bonds, eliminating defect levels and narrowing the half-width. Furthermore, in the core / shell semiconductor nanoparticles of the present invention, the halogen is also present inside the shell. Examples of halogen include F, Cl, Br, and I. Of these, Cl and Br are preferred as halogens because they narrow the half-width and make it easier to uniformly shape the nanoparticles. The core / shell semiconductor nanoparticles of the present invention preferably contain Cl as the halogen because this increases the fluorescence quantum efficiency of the semiconductor nanoparticles. In the core / shell semiconductor nanoparticles of the present invention, the halogen may be present inside the core particle, at the core-shell interface, inside the shell, or on the outer surface of the shell. However, the presence of the halogen at the core-shell interface and inside the shell in particular narrows the half-width and enhances the quantum efficiency.

[0051] In the core / shell semiconductor nanoparticles of the present invention, the molar ratio of halogen to In (halogen / In), in atomic terms, is greater than 15 and not more than 900, preferably 20 to 850. When the molar ratio of halogen to In is within the above range, the quantum efficiency is high, the half-width is small, and the Stokes shift is small. Note that when the core / shell semiconductor nanoparticles of the present invention contain two or more types of halogen, the molar ratio of halogen to In refers to the sum of the molar ratios of each of the two or more types of halogen to In.

[0052] In an STEM image obtained by observation of the core / shell semiconductor nanoparticles of the present invention using a transmission electron microscope, the average circularity of the core / shell semiconductor nanoparticles is 0.820 to 1.000, preferably 0.830 to 1.000. Circularity in an STEM image indicates how close the particle shape is to a circle, and is calculated by the following formula (1): Circularity = 4πA / P ２(1) (wherein A is the projected area of ​​the particle, and P is the perimeter of the projected image of the particle.) The closer the circularity value is to 1, the closer the particle is to a circle. The closer the circularity of core / shell semiconductor nanoparticles is to 1, the more isotropically the shell is formed. When the average circularity of core / shell semiconductor nanoparticles in an STEM image obtained by scanning transmission electron microscope observation is within the above range, a uniform shell can be formed on the surface of the core, and core / shell semiconductor nanoparticles with high fluorescence quantum efficiency can be obtained. In the production of core / shell semiconductor nanoparticles, if the shell formation is non-uniform when forming a shell on the surface of the core particle, or if core particles or particles in the process of forming a shell on the surface of the core particle aggregate in the dispersion medium during the shell formation reaction, particles with a circularity far from 1.000 will be generated, which will cause a decrease in fluorescence quantum efficiency or an increase in half-value width. In the present invention, the average circularity of core / shell semiconductor nanoparticles is determined by measuring the projected area and perimeter of the projected image for at least 500 particles in particle images observed with a scanning transmission electron microscope (STEM), calculating the circularity, and averaging these values ​​to determine the average circularity. The projected area and perimeter of the projected image of the particles are determined by analyzing the STEM images observed with a scanning transmission electron microscope. The analysis method involves dropping a dispersion of the core / shell semiconductor nanoparticles to be observed onto a grid, heating and annealing in a vacuum, and then observing. After determining the measurement scale for the particle image data obtained during observation using image processing software (ImageJ), the projected area and perimeter of the projected image of each particle are calculated for at least 500 particles. The circularity of each particle is determined from the resulting projected area and perimeter of the projected image of each particle.

[0053] Conventionally, many semiconductor nanoparticles have stacking faults inside the nanoparticles in order to stabilize their surface energy, and it has been thought that the presence of stacking faults can significantly reduce the optical properties of the nanoparticles. However, it has been confirmed that the core / shell semiconductor nanoparticles of the present invention have high optical properties even if they have stacking faults inside the nanoparticles. Furthermore, the core / shell semiconductor nanoparticles of the present invention may have an average number of stacking faults per particle of 0.50 to 10.00.

[0054] The presence or absence of stacking faults occurring in core / shell semiconductor nanoparticles can be observed using a scanning transmission electron microscope. Figures 3 to 5 are STEM images of core / shell semiconductor nanoparticles according to this embodiment. As indicated by the arrows in Figures 3 to 5, in the STEM images obtained by scanning transmission electron microscope observation, the locations where the atomic arrangement is misaligned correspond to stacking faults. The average number of stacking faults per particle is calculated by counting the number of stacking faults in each of the images of any 10 or more particles observed using a scanning transmission electron microscope, and dividing the total by the number of particles observed.

[0055] In an STEM image obtained by scanning transmission electron microscope observation of the core / shell semiconductor nanoparticles of the present invention, the average particle diameter of the core / shell semiconductor nanoparticles is not particularly limited, but is preferably 1.0 to 20.0 nm, and particularly preferably 1.0 to 10.0 nm. In the present invention, the average particle diameter of the core / shell semiconductor nanoparticles is determined by calculating the particle diameters of at least 500 particles in an image of particles observed with a scanning transmission electron microscope (STEM) as the area-equivalent circle diameter (Heywood diameter).

[0056] The core / shell semiconductor nanoparticles of the present invention exhibit a narrow particle size distribution. The SD value of the core / shell semiconductor nanoparticles calculated from particle images observed with a scanning transmission electron microscope (STEM) (the difference between the 90% number cumulative particle diameter D90 and the 10% number cumulative particle diameter D10 divided by the 50% number cumulative particle diameter D50, i.e., (D90-D10) / D50) is 1.00 or less, preferably 0.90 or less, and more preferably 0.80 or less. In the present invention, the particle size distribution is determined by arbitrarily selecting at least 500 particles from particle images observed with a scanning transmission electron microscope (STEM), calculating the particle diameter of each particle in terms of the area-equivalent circle diameter (Heywood diameter), determining the number-cumulative particle size distribution from the particle diameters of each particle obtained, and then determining the 10% cumulative particle diameter, 50% cumulative particle diameter, and 90% cumulative particle diameter from the obtained particle size distribution.

[0057] The core / shell semiconductor nanoparticles of the present invention can have primary amine ligands on their surfaces. When a primary amine is used as a dispersion medium for the core particles during the shell formation reaction in the production of the core / shell semiconductor nanoparticles of the present invention, the primary amine of the dispersion medium can serve as a ligand for the core / shell semiconductor nanoparticles of the present invention. Examples of primary amines include oleylamine and dodecylamine.

[0058] In the core / shell semiconductor nanoparticles of the present invention, the mass ratio of primary amine ligands to all ligands ((mass of primary amine ligands / total ligands)×100) is more than 0% and not more than 100%. In the present invention, the type and amount of ligands coordinated to the semiconductor nanoparticles can be determined by gas chromatography mass spectrometry (GC-MS). A calibration curve of the ligands thought to be coordinated to the semiconductor nanoparticles is prepared, and quantitative measurement is performed by the calibration curve method.

[0059] The Cd content of the core / shell semiconductor nanoparticles of the present invention is 100 ppm by mass or less, preferably 80 ppm by mass or less, and particularly preferably 50 ppm by mass or less.

[0060] The core / shell semiconductor nanoparticles of the present invention have an emission peak wavelength of 500 nm to 670 nm. The core / shell semiconductor nanoparticles of the present invention have characteristic optical properties, particularly when they are core / shell semiconductor nanoparticles that emit green light with an emission peak wavelength of less than 530 nm or core / shell semiconductor nanoparticles that emit red light with an emission peak wavelength of 610 nm or more.

[0061] The quantum efficiency (QY) of the core / shell semiconductor nanoparticles of the present invention is preferably 80% or more, particularly preferably 83% or more. Since the core / shell semiconductor nanoparticles of the present invention contain a halogen and further have a highly uniform shell formation, the resulting core / shell semiconductor nanoparticles can exhibit a high exciton confinement effect, leading to improved quantum efficiency. In particular, in green-emitting core / shell semiconductor nanoparticles having an emission peak wavelength of less than 530 nm, the small size of the core particles makes it difficult to uniformly form a shell with a high exciton confinement effect on the core particles, and it has traditionally been considered difficult to obtain core / shell semiconductor nanoparticles having an emission peak wavelength of less than 530 nm and a high quantum efficiency (QY). However, the core / shell semiconductor nanoparticles of the present invention make it possible to obtain core / shell semiconductor nanoparticles having an emission peak wavelength of less than 530 nm and a quantum efficiency (QY) of 80% or more.

[0062] The full width at half maximum (FWHM) of the emission spectrum of the core / shell semiconductor nanoparticles of the present invention is preferably 35 nm or less, particularly preferably 33 nm or less. When the full width at half maximum of the emission spectrum of the semiconductor nanoparticles is within the above range, highly pure light emission can be obtained at a desired emission wavelength. The core / shell semiconductor nanoparticles of the present invention facilitate uniform nanoparticle shape adjustment, allowing the full width at half maximum (FWHM) of the emission spectrum to be within the above range. In particular, it has been considered difficult to narrow the full width at half maximum (FWHM) of the emission spectrum for red-emitting core / shell semiconductor nanoparticles having an emission peak wavelength of 610 nm or more. However, the core / shell semiconductor nanoparticles of the present invention can achieve a full width at half maximum (FWHM) of the emission spectrum of 35 nm or less, despite having an emission peak wavelength of 610 nm or more.

[0063] The core / shell semiconductor nanoparticles of the present invention are characterized in that the ratio of the absorbance at the absorption peak to the absorbance at 450 nm is 1.1 or less. Semiconductor nanoparticles having a ratio of the absorbance at the absorption peak to the absorbance at 450 nm of 1.1 or less have low self-absorption, thereby enabling them to maintain a sharp emission spectrum or, when used in a device, to suppress emission loss due to self-absorption. The core / shell semiconductor nanoparticles of the present invention have an absorption peak top at 495 to 590 nm. In particular, green-emitting core / shell semiconductor nanoparticles having an emission peak wavelength of less than 530 nm have an absorption peak top at 495 to 515 nm. FIGS. 6 and 7 show absorbance curves for core / shell semiconductor nanoparticles of this embodiment. FIG. 6 shows the absorbance curve for core / shell semiconductor nanoparticles having an emission peak wavelength of 521 nm, and FIG. 7 shows the absorbance curve for core / shell semiconductor nanoparticles having an emission peak wavelength of 527 nm. The dashed line represents the absorbance curve of core / shell semiconductor nanoparticles obtained by a conventional method, and the solid line represents the absorbance curve of the core / shell semiconductor nanoparticles of this embodiment. In both figures, the absorbance curves are normalized by the absorbance at 450 nm. It can be seen that for all of the core / shell semiconductor nanoparticles of this embodiment, the ratio of the absorbance at the peak of the absorption spectrum to the absorbance at 450 nm is 1.1 or less.

[0064] The core / shell semiconductor nanoparticles of the present invention may have their shell surfaces modified with a ligand to stabilize their dispersion in a matrix. Furthermore, if necessary, the ligand with which the core / shell semiconductor nanoparticles of the present invention are modified may be exchanged for another ligand to enhance their dispersibility in solvents of different polarity. Furthermore, the core / shell semiconductor nanoparticles of the present invention that have been modified with a ligand can also be bound to other structures via the ligand.

[0065] The core / shell semiconductor nanoparticles of the present invention may have an oxide layer on the surface thereof. The oxide forming the oxide layer is not particularly limited as long as the effects of the present invention are achieved, and examples thereof include oxides of Si, Ti, and Al.

[0066] The core / shell semiconductor nanoparticles of the present invention are preferably produced by the following method for producing core / shell semiconductor nanoparticles of the present invention.

[0067] The method for producing core / shell semiconductor nanoparticles of the present invention comprises a dispersion preparation step of mixing core particles containing at least In and P and zinc halide with a dispersion medium mainly containing a primary amine to prepare a core particle dispersion, and a shell formation step of mixing a Zn source and an S source and / or a Se source with the core particle dispersion and reacting them to form shells on the core particles, thereby obtaining core / shell semiconductor nanoparticles, wherein the zinc halide is at least ZnCl ２ wherein the Zn source is a zinc salt of a branched-chain carboxylic acid.

[0068] The method for producing core / shell semiconductor nanoparticles of the present invention comprises a dispersion preparation step and a shell formation step.

[0069] The dispersion preparation step is a step of preparing a core particle dispersion by mixing core particles containing at least In and P and zinc halide with a dispersion medium mainly containing a primary amine.

[0070] The dispersion medium containing primarily primary amines is a reaction solvent for the shell formation reaction and is used to disperse core particles containing In and P or particles in the process of forming a shell on the surface of the core particles. Examples of primary amines include oleylamine and dodecylamine. The primary amine may be one or more types. Furthermore, by having the dispersion medium contain primarily primary amines, preferably by having the dispersion medium contain 50% or more by volume of primary amines, and more preferably by having the dispersion medium be primary amines (the content of primary amines in the dispersion medium being 100% by volume), the dispersion of core particles containing In and P or particles in the process of forming a shell on the surface of the core particles is improved in the shell formation reaction, thereby reducing particle aggregation and enabling the production of uniform core / shell semiconductor nanoparticles. On the other hand, if the dispersion medium is an amine other than a primary amine, such as a secondary amine or a tertiary amine, or a non-amine-based dispersion medium such as trioctylphosphine oxide, particle aggregation occurs during the shell formation reaction. In addition, a dispersion medium containing primarily a primary amine may contain a non-primary amine such as a secondary amine or a tertiary amine, or a dispersion medium other than an amine, together with the primary amine, but in this case, the above-mentioned effect can be obtained by the dispersion medium containing primarily a primary amine. "Containing primarily a primary amine" means that when multiple dispersion mediums are used, the volume fraction of the primary amine is the highest.

[0071] Core particles containing In and P are mainly composed of In and P. Furthermore, the core particles may unavoidably or intentionally contain Zn, S, Se, Si, N, etc. in addition to In and P, as long as the effects of the present invention are not impaired. The average particle diameter of the core particles is preferably 1.0 to 5.0 nm. When the average particle diameter of the core particles is 1.0 to 5.0 nm, excitation light of 450 nm can be converted into light having a wavelength of 500 to 650 nm. In the present invention, the average particle diameter of the core particles is determined by calculating the area-equivalent circle diameter (Heywood diameter) of at least 500 particles from particle images observed with a scanning transmission electron microscope (STEM).

[0072] In the core particle, the molar ratio of P to In (P / In) is 0.40 to 1.50, preferably 0.50 to 1.30, in terms of atoms. When the molar ratio of P to In is within the above range, the quantum efficiency is high and the half-width is small.

[0073] Although the method for producing core particles containing In and P is not particularly limited, it is preferable to synthesize them using a silylphosphine precursor such as trimethylsilylphosphine as the P source. In the method for producing core particles containing In and P, when a silylphosphine precursor such as trimethylsilylphosphine is used as the P source, the nuclei of core particles containing In and P are generated instantly upon addition of the precursor due to its high reactivity, so that core particles with a narrow particle size distribution are likely to be obtained. Another advantage is that gas generation due to decomposition of the precursor during the synthesis process can be suppressed.

[0074] In the dispersion preparation step, the amount of core particles containing In and P mixed into the dispersion medium containing mainly a primary amine is an amount such that the mass ratio of the core particles to the dispersion medium containing mainly a primary amine ((mass of core particles / mass of dispersion medium containing mainly a primary amine) × 100) is 0.001 to 0.100 mass%.

[0075] In the dispersion liquid preparation step, the zinc halide mixed with the dispersion medium containing mainly primary amine serves as a halogen source and a Zn source. In the dispersion liquid preparation step, when the zinc halide is mixed with the dispersion medium containing mainly primary amine, the zinc halide dissolves in the amine dispersion medium, and the dissolved halogen bonds to the surface of the core particles containing In and P. In the dispersion liquid preparation step, the zinc halide mixed with the dispersion medium containing mainly primary amine contains at least ZnCl ２ The zinc halide also includes zinc bromide (ZnBr ２ ), zinc fluoride (ZnF ２ ) can be included.

[0076] In the dispersion preparation step, the amount of zinc halide mixed is an amount such that the molar ratio of Zn in the zinc halide to In in the core particles containing In and P (number of moles of Zn in zinc halide / number of moles of In in the core particles) is more than 7.5 and 1000 or less, preferably 10 to 900. When the molar ratio of Zn to In is within the above range, the quantum efficiency is high and the half width is small.

[0077] In the dispersion preparation step, ZnCl ２ The amount of ZnCl mixed is determined based on the In content of the core particles containing In and P. ２ Molar ratio of Zn (ZnCl ２ The amount is such that the ratio (moles of Zn in the core particle / moles of In in the core particle) is greater than 7.5 and not more than 1000, preferably 10 to 900. ２ When the amount of the compound is within the above range, the quantum efficiency is high and the half-value width is small.

[0078] In the dispersion preparation step, the temperature when the core particles containing In and P and the zinc halide are mixed with the dispersion medium containing mainly a primary amine is 170°C to 240°C, preferably 180°C to 220°C.

[0079] In the dispersion preparation step, in addition to the core particles containing In and P and the zinc halide, a dispersant and the like can be mixed into a dispersion medium mainly containing a primary amine. Examples of the dispersant that can be used include known carboxylic acid-based dispersants, thiol-based dispersants, and phosphine-based dispersants.

[0080] In the dispersion preparation step, core particles containing In and P and zinc halide are mixed with a dispersion medium containing mainly a primary amine to obtain a core particle dispersion in which halogen is bonded to the surface of the core particles.

[0081] The shell formation step is a step of mixing a Zn source and an S source and / or a Se source with the core particle dispersion obtained by carrying out the dispersion preparation step, and causing a reaction to form a shell on the core particles, thereby obtaining core / shell type semiconductor nanoparticles.

[0082] In the shell formation step, a branched-chain zinc carboxylate is used as the Zn source. Compared to linear zinc carboxylates, branched-chain zinc carboxylates are bulkier, leading to interference between the branched chains during shell formation. This is thought to limit the amount of zinc present on the core surface in the reaction system, leading to relatively gradual shell formation and the formation of a uniform shell, resulting in a uniformly shaped core / shell semiconductor nanoparticle. Furthermore, the generation of by-products is suppressed, enabling the production of particles with a narrow particle size distribution. Furthermore, the formation of a uniform shell increases the fluorescence quantum efficiency of the resulting core / shell semiconductor nanoparticles, and the uniformly shaped core / shell semiconductor nanoparticles narrow the half-width of the resulting core / shell semiconductor nanoparticles. The number of carbon atoms in the branched-chain carboxylic acid in the zinc salt of the branched-chain carboxylic acid is preferably 4 to 20, more preferably 5 to 19. Examples of zinc salts of branched chain carboxylic acids include zinc salts of 2-ethylhexanoic acid, zinc salts of 3,5,5-trimethylhexanoic acid, zinc salts of 16-methylheptadecanoic acid, and zinc salts of neodecanoic acid.

[0083] The Zn source used in the shell formation step is preferably in the form of a solution at 25° C. and 1 atm. By being in the form of a solution at 25° C. and 1 atm, the Zn source can be added to the dispersion liquid without clogging a supply pipe, even when the Zn source is added gradually over a long period of time.

[0084] In the shell formation step, a Zn source and either an S source or a Se source, or both an S source and a Se source, are mixed into a core particle dispersion, and the Zn source is reacted with the S source and / or the Se source to carry out a shell formation reaction and form a shell on the core particle.

[0085] Examples of the S source include, but are not limited to, trioctylphosphine sulfide, tributylphosphine sulfide, thiols, and bis(trimethylsilyl) sulfide.

[0086] Examples of Se sources include, but are not limited to, trioctylphosphine selenide, tributylphosphine selenide, thiols, and bis(trimethylsilyl)selenide.

[0087] In the shell formation step, the amount of Zn source mixed into the core particle dispersion is an amount such that the molar ratio (Zn / In) of the total number of moles of Zn in the zinc halide mixed in the dispersion preparation step and Zn in the Zn source mixed in the shell formation step, relative to In in the core particles containing In and P, exceeds 15 and is not more than 2000, preferably 20 to 1600. When the molar ratio of Zn to In is within the above range, the quantum efficiency is high and the half width is small.

[0088] In the shell formation step, the Zn source can be added to the core particle dispersion liquid gradually. Alternatively, in the shell formation step, the Zn source may be added to the core particle dispersion liquid all at once. Conventionally, it was thought that when the Zn source is added to the core particle dispersion liquid gradually, the amount of zinc present on the core surface layer in the reaction system is limited compared to when the Zn source is added all at once, and therefore shell formation proceeds relatively slowly and a uniform shell is formed. However, in the method for producing core / shell semiconductor nanoparticles of the present invention, by performing the above-mentioned dispersion preparation step, it is possible to form a uniform shell whether the Zn source is added to the core particle dispersion liquid gradually or when the Zn source is added to the core particle dispersion liquid all at once.

[0089] In the present invention, the addition method of gradually adding a Zn source to a core particle dispersion liquid includes a continuous addition method in which the Zn source is continuously added to the core particle dispersion liquid, and a divided addition method in which the Zn source is divided into two or more portions and added to the core particle dispersion liquid. The continuous addition method in which the Zn source is continuously added to the core particle dispersion liquid is not particularly limited, and examples thereof include a method in which the outlet end of a Zn source supply pipe is positioned in the core particle dispersion liquid and the Zn source is continuously supplied from the Zn source supply pipe. The divided addition method in which the Zn source is divided into two or more portions and added to the core particle dispersion liquid is not particularly limited, and examples thereof include a method in which the Zn source is divided into n portions and added dropwise to the core particle dispersion liquid in small amounts n times (n is an integer).

[0090] In the shell formation step, the addition time when the Zn source is gradually added to the core particle dispersion is preferably 1 minute to 6 hours, and more preferably 5 minutes to 5 hours. In the present invention, the addition time when the Zn source is gradually added to the core particle dispersion refers to the time from when the addition of the Zn source to the core particle dispersion starts to when the addition is completed. For example, in the case of a continuous addition method in which the Zn source is continuously added to the core particle dispersion, the addition time refers to the time from when the supply of the Zn source to the core particle dispersion starts to when the supply of the Zn source is stopped. Furthermore, in the case of a divided addition method in which the Zn source is added to the core particle dispersion in two or more divided portions, the addition time refers to the time from when the first addition to the core particle dispersion is made to the last addition.

[0091] In the shell formation step, the rate of addition of Zn when the Zn source is successively added to the core particle dispersion is preferably 0.01 to 30 mol / hour, more preferably 0.05 to 28 mol / hour, in terms of atoms in the Zn source per gram of core particles in the core particle dispersion.

[0092] In the shell formation step, the Zn source can be added to the core particle dispersion liquid all at once. Adding all at once means that the time from the start of addition of the Zn source to the core particle dispersion liquid to the end of addition is within 1 minute. In the shell formation step, the addition time when the Zn source is added all at once to the core particle dispersion liquid is preferably 0.01 seconds to 1 minute, more preferably 0.05 seconds to 1 minute. In the present invention, the addition time when the Zn source is added all at once refers to the time from the start of addition of the Zn source to the core particle dispersion liquid to the end of addition.

[0093] In the shell formation step, the amount of the S source mixed into the core particle dispersion is an amount such that the molar ratio (S / In) of S in the S source to In in the core particles containing In and P is 0.01 to 25.00, and preferably 4.00 to 20.00. When the molar ratio of S to In is within the above range, the quantum efficiency is high and the half width is small.

[0094] In the shell formation step, the amount of the Se source mixed into the core particle dispersion is an amount such that the molar ratio (Se / In) of Se in the Se source to In in the core particles containing In and P is 5.00 to 40.00, preferably 8.00 to 30.00. When the molar ratio of Se to In is within the above range, the quantum efficiency is high and the half width is small.

[0095] When an S source and a Se source are mixed into the core particle dispersion in the shell formation step, the amounts of the S source and the Se source mixed are such that the molar ratio ((S+Se) / In) of the total number of moles of S in the S source and the number of moles of Se in the Se source relative to the In in the core particles containing In and P is 5.00 to 60.00, and preferably 9.00 to 40.00. When the molar ratio of the total number of moles of S and Se relative to In is within the above range, the quantum efficiency is high and the half width is small.

[0096] In the shell formation step, the S source and / or the Se source may be added to the core particle dispersion liquid sequentially, or in the shell formation step, the S source and / or the Se source may be added to the core particle dispersion liquid all at once.

[0097] In the present invention, the addition method for successively adding the S source and / or Se source to the core particle dispersion liquid includes a continuous addition method for continuously adding the S source and / or Se source to the core particle dispersion liquid, and a divided addition method for adding the S source and / or Se source to the core particle dispersion liquid in two or more divided portions. The continuous addition method for continuously adding the S source and / or Se source to the core particle dispersion liquid is not particularly limited, and examples thereof include a method in which the outlet end of a supply pipe for the S source and / or Se source is positioned in the core particle dispersion liquid, and the S source and / or Se source is continuously supplied from the supply pipe for the S source and / or Se source. The divided addition method for adding the S source and / or Se source to the core particle dispersion liquid in two or more divided portions is not particularly limited, and examples thereof include a method in which the S source and / or Se source is dropped into the core particle dispersion liquid in small amounts n times (n is an integer).

[0098] In the shell formation step, the addition time when the S source and / or Se source is gradually added to the core particle dispersion is preferably 1 minute to 6 hours, and more preferably 1 minute to 5 hours. In the present invention, the addition time when the S source and / or Se source is gradually added to the core particle dispersion refers to the time from when the addition of the S source and / or Se source to the core particle dispersion starts to when the addition is completed. For example, in the case of a continuous addition method in which the S source and / or Se source is continuously added to the core particle dispersion, the addition time refers to the time from when the supply of the S source and / or Se source to the core particle dispersion starts to when the supply of the S source and / or Se source is stopped. Furthermore, in the case of a divided addition method in which the S source and / or Se source is added to the core particle dispersion in two or more portions, the addition time refers to the time from when the first addition to the core particle dispersion is made to the last addition.

[0099] In the shell formation step, the addition rate of S and / or Se when the S source and / or Se source is successively added to the core particle dispersion is preferably 0.01 to 60 mol / hour, more preferably 0.01 to 50 mol / hour, in terms of atoms in the S source and / or Se source per 1 g of core particles in the core particle dispersion.

[0100] In the shell formation step, adding the S source and / or Se source to the core particle dispersion all at once means that the time from the start to the end of addition of the S source and / or Se source to the core particle dispersion is within 1 minute.

[0101] In the shell formation step, the addition time when the S source and / or Se source is added all at once to the core particle dispersion is preferably 0.01 second to 1 minute, more preferably 0.05 second to 1 minute. In the present invention, the addition time when the S source and / or Se source is added all at once refers to the time from the start of addition of the S source and / or Se source to the core particle dispersion to the end of addition.

[0102] In the shell formation step, the order of addition of the Zn source and the S source and / or Se source is not particularly limited. The Zn source may be added first, and then the S source and / or Se source may be added. Alternatively, the S source and / or Se source may be added first, and then the Zn source may be added. Alternatively, the addition may be performed so that the time period from the start to the end of the addition of the Zn source and the time period from the start to the end of the addition of the S source and / or Se source completely coincide or partially coincide.

[0103] In the shell formation step, the reaction temperature during the shell formation reaction is 260°C to 320°C, preferably 280°C to 320°C. When the reaction temperature during the shell formation reaction is within the above range, the generation of by-products during the shell formation reaction is reduced. On the other hand, if the reaction temperature during the shell formation reaction is below the above range, the shell formation reaction is difficult to occur, and if the reaction temperature exceeds the above range, the generation of by-products increases.

[0104] In the shell formation step, in addition to the Zn source, the S source and / or the Se source, a dispersant and the like can be mixed in. Examples of the dispersant that can be used include known carboxylic acid-based dispersants, thiol-based dispersants, and phosphine-based dispersants.

[0105] Then, a shell formation step is carried out to form a shell on the core particle, thereby obtaining core / shell type semiconductor nanoparticles consisting of a core containing In and P and a shell containing Zn and S and / or Se formed on the surface of the core.

[0106] In the method for producing core / shell semiconductor nanoparticles of the present invention, by using a dispersion medium containing primarily a primary amine as the dispersion medium for the core particles, particle aggregation can be minimized even when a large amount of halogen is introduced into the core particles or into particles in the process of forming a shell on the surface of the core particles. Therefore, since a large amount of halogen can be introduced during shell formation on the core particles, the reaction temperature can be lowered to form a uniform shell. Therefore, by increasing the halogen content of the core particles and core / shell semiconductor nanoparticles, a uniform shell can be formed, and core / shell semiconductor nanoparticles with a high average circularity can be obtained. Furthermore, since a uniform shell can be formed even at a low reaction temperature, the generation of by-products can be reduced. Furthermore, by using the method for producing core / shell semiconductor nanoparticles of the present invention, a uniform shell can be formed even on relatively small core particles, resulting in a high electron confinement effect and high quantum efficiency even for core / shell semiconductor nanoparticles with an emission peak of less than 530 nm.

[0107] In the method for producing core / shell semiconductor nanoparticles of the present invention, a dispersion medium containing mainly primary amines is used as the dispersion medium for the shell formation reaction, and therefore core / shell semiconductor nanoparticles whose surfaces are modified with primary amine ligands are obtained. In other words, the method for producing core / shell semiconductor nanoparticles of the present invention produces core / shell semiconductor nanoparticles having primary amine ligands. Furthermore, the primary amine ligands on the surfaces of the core / shell semiconductor nanoparticles obtained by the method for producing core / shell semiconductor nanoparticles of the present invention can be ligand-exchanged with other ligands. Known methods are used as the ligand exchange method.

[0108] The core / shell semiconductor nanoparticles obtained as described above can be purified. For example, the core / shell semiconductor nanoparticles can be precipitated from the solution by adding a polarity-reversing solvent such as acetone. The precipitated core / shell semiconductor nanoparticles can then be recovered by filtration or centrifugation. The recovered core / shell semiconductor nanoparticles can then be washed with additional solvent and redissolved. This purification procedure can be repeated, for example, two to four times, or until the desired purity is achieved. Other purification methods include, for example, coagulation, liquid-liquid extraction, distillation, electrodeposition, size exclusion chromatography, and ultrafiltration. These purification methods can be used alone or in combination.

[0109] Alternatively, an oxide layer can be formed on the surface of the core / shell semiconductor nanoparticles by adding a surfactant to the core / shell semiconductor nanoparticles obtained as described above, stirring, then adding an inorganic-containing composition, and stirring again. The surfactant is not particularly limited, and examples thereof include sodium dodecyl sulfate, sodium lauryl sulfate, n-butanol, and dioctyl sodium sulfosuccinate. The inorganic-containing composition is not particularly limited, and examples thereof include silane coupling agents, titanate coupling agents, and aluminate coupling agents. For example, after purifying the core / shell semiconductor nanoparticles, an aqueous solution containing a surfactant is added, and the mixture is mixed and stirred to form micelles. The formation of micelles is confirmed by the cloudiness of the mixture. The aqueous phase in which the micelles have formed is recovered, and the inorganic-containing composition is added thereto. The mixture is stirred at 10 to 30°C for 10 minutes to 6 hours. After removing unreacted materials, the mixture is purified again to obtain core / shell semiconductor nanoparticles having an oxide layer. The method for forming the outermost oxide layer is not limited to the above method, and for example, a method of adding an inorganic-containing composition during shell synthesis or other known methods may be used.

[0110] <Measurement> Elemental analysis of core / shell semiconductor nanoparticles can be performed using an inductively coupled plasma (ICP) or an X-ray fluorescence analyzer (XRF). In ICP measurement, purified core / shell semiconductor nanoparticles are dissolved in nitric acid, heated, and then diluted with water, and measured using an ICP optical emission analyzer (Shimadzu Corporation, ICPS-8100) by a calibration curve method. In XRF measurement, filter paper impregnated with the dispersion is placed in a sampling holder, and quantitative analysis is performed using an X-ray fluorescence analyzer (Rigaku Corporation, ZSX100e).

[0111] The optical properties of core / shell semiconductor nanoparticles can be measured using a fluorescence quantum efficiency measurement system (QE-2100, manufactured by Otsuka Electronics) and a visible-ultraviolet spectrophotometer (V670, manufactured by JASCO). An emission spectrum is obtained by irradiating a dispersion of core / shell semiconductor nanoparticles in a dispersion medium with excitation light. The fluorescence quantum efficiency (QY) and full width at half maximum (FWHM) are calculated from the re-excitation-corrected emission spectrum obtained by subtracting the re-excitation fluorescence emission spectrum of the fluorescence emitted by re-excitation from the obtained emission spectrum. Examples of dispersion media include normal hexane, octadecene, toluene, acetone, and PGMEA. The excitation light used for the measurement is a single light of 450 nm, and the concentration of semiconductor nanoparticles is adjusted so that the absorptance is 20 to 30%. Meanwhile, the absorption spectrum can be measured by irradiating a dispersion of core / shell semiconductor nanoparticles in a dispersion medium with ultraviolet to visible light.

[0112] The average particle size, average circularity, and SD value of the core / shell semiconductor nanoparticles can be calculated by observation using a scanning transmission microscope (JEM-ARM200F, manufactured by JEOL). First, a dispersion of the core / shell semiconductor nanoparticles is dropped onto a grid, annealed in vacuum, and then observed using the scanning transmission microscope (JEM-ARM200F, manufactured by JEOL). The vacuum level during observation is approximately 2 × 10 －５It is preferable to perform the measurement while maintaining the pressure at 200 Pa. Next, the projected area and perimeter of the projected image of each particle are calculated from the obtained image data using analysis software, and the circularity and average particle diameter of the core / shell semiconductor nanoparticles are determined for each particle from the obtained projected area and perimeter of the projected image of each particle. Furthermore, the SD value (the difference between the 90% cumulative particle diameter D90 and the 10% cumulative particle diameter D10 divided by the 50% cumulative particle diameter D50, i.e., (D90-D10) / D50) is determined from the particle size distribution (integrated number) of the core / shell semiconductor nanoparticles.

[0113] The type and amount of ligands coordinated to semiconductor nanoparticles can be identified by qualitative and quantitative analysis of functional groups by nuclear magnetic resonance spectroscopy (NMR) and infrared spectroscopy (IR), and by various types of chromatography.

[0114] It should be noted that the configurations, methods, procedures, processes, etc. described in this specification are merely examples and do not limit the present invention, and many variations are applicable within the scope of the present invention.

[0115] The present invention will be described below based on specific experimental examples, but the present invention is not limited to these.

[0116] Core / shell semiconductor nanoparticles were produced according to the following method, and the composition and optical properties of the obtained core / shell semiconductor nanoparticles were measured. <Preparation of Precursors> Precursors used for producing core / shell semiconductor nanoparticles were prepared as follows. Se precursor: 22 mmol of selenium powder and 10 mL of trioctylphosphine (TOP) were mixed in nitrogen and stirred until completely dissolved, yielding a 2.2 M Se precursor (trioctylphosphine selenide). S precursor: 22 mmol of sulfer powder and 10 mL of trioctylphosphine (TOP) were mixed in nitrogen and stirred until completely dissolved, yielding a 2.2 M S precursor (trioctylphosphine sulfide). Example 1: Green Core Formation Process Indium acetate (8.5 mmol), zinc acetate (3.2 mmol), myristic acid (20 mmol), and octadecene (50 mL) were mixed and heated to 120°C under vacuum (<20 Pa) and allowed to react for 4 hours. The reaction mixture was cooled to 35°C under a nitrogen atmosphere, and 10 mL of trioctylphosphine (TOP) and 10 mL of a P precursor (trismethylsilylphosphine 15 wt% TOP solution) were added. The mixture was heated to 300°C, and after InP nanoparticles had grown to the desired size, the mixture was quenched and the InP cores (green) were collected in a nitrogen-filled container.

[0117] <Shell Formation Process> In a glove box under a nitrogen atmosphere, 7.5 mL of oleylamine was added to a flask connected to a Schlenk line. Furthermore, the core (0.3 mmol in terms of In) and zinc chloride (12.0 mmol) obtained above were poured into the flask, heated to 180°C, and maintained for 60 minutes to obtain a core particle dispersion. Next, while the core particle dispersion was heated to 240°C at a rate of 1°C / min, a mineral spirit solution of zinc bis(2-ethylhexanoate) (Zn: 15%) (4.5 g) and the above-mentioned Se precursor (2.1 mL) were continuously added sequentially to the flask over the course of 1 hour. The addition rate of the Zn source at this time was 10.0 mmol / hour in terms of the molar amount of Zn. Next, the above-mentioned S precursor (1.5 mL) was continuously added to the flask over 1 hour, heated to 280 °C, and then cooled to room temperature to obtain InP / ZnSe / ZnS QDs (Green) as core / shell semiconductor nanoparticles. Next, acetone was added to the dispersion of InP / ZnSe / ZnS QDs (Green) obtained as above, resulting in the aggregation of InP / ZnSe / ZnS QDs (Green). After centrifugation (6000 rpm, 10 minutes), the supernatant was removed, and the InP / ZnSe / ZnS QDs (Green) were redispersed in heptane. This process was repeated to obtain purified InP / ZnSe / ZnS QDs (Green).

[0118] <Optical Property Measurement> The optical properties of the obtained core / shell semiconductor nanoparticles (QDs) were measured. The results are shown in Table 3. The optical properties were measured using a fluorescence quantum efficiency system (QE-2100, manufactured by Otsuka Electronics Co., Ltd.). The QDs were dispersed in heptane and irradiated with excitation light to obtain an emission spectrum. The re-excited fluorescence spectrum corresponding to the fluorescence emitted by re-excitation was removed from the obtained emission spectrum, and the fluorescence peak wavelength, fluorescence quantum efficiency (QY), and full width at half maximum (FWHM) were calculated from the excitation-corrected emission spectrum. The excitation light used for the measurement was a single light of 450 nm, and the dispersion liquid used had a QD dispersion concentration adjusted to achieve an absorptivity of 20-30%. The absorption spectrum of the core / shell semiconductor nanoparticles (QDs) was measured by irradiating the semiconductor nanoparticle dispersion liquid with light from 300 nm to 700 nm using a UV-visible spectrophotometer (V-570, manufactured by JASCO Corporation). The dispersion liquid used for measuring the absorption spectrum was a heptane dispersion medium, the concentration of which was adjusted so that the amount of semiconductor nanoparticles was 1 mg per mL. The ratio of the absorbance at the absorption peak to the absorbance at 450 nm of the obtained core / shell semiconductor nanoparticles was 0.91.

[0119] <Scanning Transmission Electron Microscope Observation> The obtained core / shell semiconductor nanoparticles (QDs) were observed using a scanning transmission electron microscope (JEOL, JEM-ARM200F). 20 μL of the obtained QDs in heptane dispersion was dropped onto a carbon-coated molybdenum grid (Oken Shoji) and annealed in vacuum using a heating holder (JEOL, EM31670SHTH) before observation. The accelerating voltage was 200 kV, and a double silicon drift detector (SDD) was used as the detector. The EDS collection angle was 1.7 steradians (sr.), the electron probe convergence half angle was 30 mrad, and the HAADF collection angle was 137-175 mrad. The vacuum level during observation was 2×10 －５ The temperature was maintained at 100 Pa.

[0120] Using the obtained image data, image processing software (ImageJ) was used to calculate the projected area and perimeter of the projected image of each particle for at least 500 particles. By determining the measurement scale used for image processing from the image used during measurement, it is possible to determine the specific length or area of ​​the particle. The circularity of each particle was calculated from the projected area and perimeter of the projected image of each particle obtained in this manner. The average particle diameter of core / shell semiconductor nanoparticles (QDs) was determined by calculating the particle diameter of at least 500 particles in terms of the area circle equivalent diameter (Heywood diameter) for particle images observed with a scanning transmission electron microscope (STEM). The analysis method involves dropping a dispersion of the core / shell semiconductor nanoparticles to be observed onto a grid, heating and annealing in a vacuum, and then observing. Using image processing software (ImageJ) to determine the measurement scale for the particle image data during observation, the projected area and perimeter of the projected image of each particle were calculated for at least 500 particles. The circularity of each particle was determined from the projected area and perimeter of the projected image of each obtained particle. Furthermore, D10, D50, and D90 were determined from the particle size distribution of the core / shell semiconductor nanoparticles (QD) obtained from particle images observed by a scanning transmission electron microscope (STEM), and the SD value ((D90-D10) / D50) was calculated. The average number of stacking faults per particle of the core / shell semiconductor nanoparticles (QD) was calculated by counting the number of stacking faults for each observation image of any 10 or more particles in an STEM image obtained by scanning transmission electron microscope observation, and dividing the total by the number of particles observed. The average number of stacking faults per particle of the obtained core / shell semiconductor nanoparticles was 3.6.

[0121] <Calculation of Ligand Coordination> The coordination amount of the ligand to the semiconductor nanoparticle composite was measured using a gas chromatography mass spectrometer (GCMS-QP2010). First, the purified semiconductor nanoparticle composite was dried at less than 100°C to obtain a dry powder, and then the dry powder of the semiconductor nanoparticle composite was loaded into the gas chromatography mass spectrometer. After heating at 300°C or higher and passing through a column together with a carrier gas, the coordination amount of the amine was calculated by a calibration curve method from the retention time and peak area of ​​the signal obtained by the detector.

[0122] <Composition Analysis> 1 mg of the purified semiconductor nanoparticle composite was added to a flask, and then nitric acid was added and the mixture was heated and dissolved by microwave irradiation. The resulting measurement solution was quantitatively analyzed using an ICP optical emission spectrometer (ICPE-9820: Shimadzu Corporation) and a calibration curve method. The atomic ratio of each element was calculated from the content of each element. <Halogen Amount> The halogen amount in the resulting core / shell semiconductor nanoparticles (QDs) was measured using a combustion ion chromatograph. 10 to 50 μL of a dispersion of core / shell semiconductor nanoparticles (QDs) (here, a dispersion medium adjusted to mg / mL) was added to the sample injection port and combusted. Since the ion content was measured from the resulting peak, the halogen amount relative to the core / shell semiconductor nanoparticles (QDs) was calculated from the weight of the added core / shell semiconductor nanoparticles (QDs) and the In amount measured by the ICP optical emission analysis described above.

[0123] Example 2 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that dodecylamine was used instead of oleylamine in the shell formation process. The average number of stacking faults per particle in the obtained core / shell semiconductor nanoparticles was 4.7.

[0124] Example 3 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that in the shell formation process, the mineral spirits solution (Zn: 15%) of zinc bis(2-ethylhexanoate) was changed to a mineral spirits solution (Zn: 15%) of zinc 3,5,5-trimethylhexanoate.

[0125] Example 4 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that in the shell formation process, a mineral spirits solution of zinc neodecanoate (Zn: 15%) was used instead of a mineral spirits solution of zinc bis(2-ethylhexanoate) (Zn: 15%). The ratio of the absorbance at the absorption peak to the absorbance at 450 nm of the obtained core / shell semiconductor nanoparticles was 1.00. The average number of stacking faults per particle of the obtained core / shell semiconductor nanoparticles was 5.1.

[0126] Example 5 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that the addition time of the mineral spirit solution (Zn: 15%) of zinc bis(2-ethylhexanoate) in the shell formation process was set to 1 minute or less. The ratio of the absorbance at the absorption peak to the absorbance at 450 nm of the obtained core / shell semiconductor nanoparticles was 0.88. The average number of stacking faults per particle of the obtained core / shell semiconductor nanoparticles was 4.2.

[0127] Example 6 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that the shell formation process was carried out by heating to 260° C. after adding the S precursor.

[0128] Example 7 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that the shell formation process was carried out by adding an S precursor and then heating to 300° C. The average number of stacking faults per particle in the obtained core / shell semiconductor nanoparticles was 3.5.

[0129] Example 8 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that zinc chloride (9.90 mol mm) and zinc bromide (2.10 mmol) were added instead of zinc chloride (12.0 mmol) in the shell formation process. The average number of stacking faults per particle in the obtained core / shell semiconductor nanoparticles was 6.1.

[0130] Example 9: Red Core Formation Process: Indium acetate (9.2 mmol), zinc acetate (1.2 mmol), myristic acid (30.0 mmol), and octadecene (30 mL) were mixed and heated to 120°C under vacuum (<20 Pa) for 4 hours to obtain an In precursor. The reaction mixture was cooled to 35°C under a nitrogen atmosphere, and 26.0 mL of trioctylphosphine (TOP) and 13.0 mL of the aforementioned P precursor (15 wt% trismethylsilylphosphine TOP solution) were added to prepare a core precursor. The resulting core precursor was heated to 300°C and quenched after InP particles had grown to the desired size, yielding InP particles. Next, 15 mL of octadecene and 10 mL of InP particles were added to a nitrogen-purged flask and heated to 290°C. A solution containing the above-mentioned In precursor and (15 wt % trismethylsilylphosphine TOP solution) was added to the flask at a rate of 0.015 mL / min until the absorption peak wavelength reached 585 nm, thereby obtaining an InP core (red).

[0131] <Shell formation process> In a glove box under a nitrogen atmosphere, 7.5 mL of oleylamine was added to a flask connected to a Schlenk line. Furthermore, the core (In equivalent: 0.12 mmol) and zinc chloride (9.9 mmol) obtained above were poured into the flask, heated to 200 °C, and maintained for 60 minutes to obtain a core dispersion preparation. While the temperature was raised to 300 °C at a rate of 1 °C / min, a mineral spirit solution of zinc bis(2-ethylhexanoate) (Zn: 15%) (4.36 g) and the above-mentioned Se precursor (3 mL) were continuously added sequentially to the flask over 1 hour. The addition rate of the Zn source at this time was 14.2 mmol / hour in terms of the molar amount of Zn. Next, the above-mentioned S precursor (0.5 mL) was continuously added to the flask over 30 minutes, heated to 280 °C, and then cooled to room temperature to obtain InP / ZnSe / ZnS QDs (Red) as core / shell semiconductor nanoparticles. Next, acetone was added to the dispersion of InP / ZnSe / ZnS QDs (Red) obtained as above, resulting in the aggregation of InP / ZnSe / ZnS QDs (Red). After centrifugation (6000 rpm, 10 minutes), the supernatant was removed, and the InP / ZnSe / ZnS QDs (Red) were redispersed in heptane. This process was repeated to obtain purified InP / ZnSe / ZnS QDs (Red). The average number of stacking faults per particle of the obtained core / shell semiconductor nanoparticles was 6.3.

[0132] Example 10 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 9, except that dodecylamine was used instead of oleylamine in the shell formation process. The average number of stacking faults per particle in the obtained core / shell semiconductor nanoparticles was 7.1.

[0133] Example 11 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 9, except that in the shell formation process, the mineral spirits solution (Zn: 15%) of zinc bis(2-ethylhexanoate) was changed to a mineral spirits solution (Zn: 15%) of zinc 3,5,5-trimethylhexanoate.

[0134] Example 12 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 9, except that in the shell formation process, a mineral spirits solution of zinc neodecanoate (Zn: 15%) was used instead of a mineral spirits solution of zinc bis(2-ethylhexanoate) (Zn: 15%). The average number of stacking faults per particle in the resulting core / shell semiconductor nanoparticles was 7.3.

[0135] Example 13 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 9, except that in the shell formation process, the time for adding the mineral spirit solution of zinc bis(2-ethylhexanoate) (Zn: 15%) was set to 1 minute or less.

[0136] Example 14 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 9, except that in the shell formation process, after adding the S precursor, heating was performed to 300° C. The average number of stacking faults per particle in the obtained core / shell semiconductor nanoparticles was 6.5.

[0137] Comparative Example 1 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that zinc chloride was not added in the shell formation process.

[0138] Comparative Example 2 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that dioctylamine was added instead of oleylamine in the shell formation process.

[0139] Comparative Example 3 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that trioctylamine was added instead of oleylamine in the shell formation process. The obtained InP / ZnSe / ZnS semiconductor nanoparticles had low luminescence intensity and were severely aggregated, making STEM observation impossible.

[0140] Comparative Example 4 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that oleylamine was not added in the shell formation process. The resulting InP / ZnSe / ZnS semiconductor nanoparticles had very low luminescence intensity and were severely aggregated, making STEM observation impossible.

[0141] Comparative Example 5 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 1, except that zinc oleate was used instead of zinc chloride in the shell formation process. The resulting InP / ZnSe / ZnS semiconductor nanoparticles had low luminescence intensity.

[0142] Comparative Example 6 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 6, except that in the shell formation process, zinc oleate was used instead of a mineral spirit solution (Zn: 15%) of zinc bis(2-ethylhexanoate) and the addition time of the zinc oleate was set to 1 minute or less. The obtained InP / ZnSe / ZnS semiconductor nanoparticles had a wide half-width of the emission spectrum and a wide particle size distribution.

[0143] Comparative Example 7 InP / ZnSe / ZnS semiconductor nanoparticles were obtained in the same manner as in Example 6, except that zinc oleate was used instead of the mineral spirits solution (Zn: 15%) of zinc bis(2-ethylhexanoate) in the shell formation process. The obtained InP / ZnSe / ZnS semiconductor nanoparticles had a wide half-width of the emission spectrum and a wide particle size distribution.

[0144] When a zinc salt of a linear carboxylic acid was used, semiconductor nanoparticles with high circularity were obtained, but the half-width of the emission spectrum was wide and the particle size distribution was also wide. Furthermore, when a zinc salt of a linear carboxylic acid was used, the dried powder of InP / ZnSe / ZnS semiconductor nanoparticles after synthesis was analyzed using an X-ray diffractometer, the presence of by-products such as zinc oxide was confirmed.

[0145]

[0146]

[0147]

[0148] 1, 101 Blue LED 3, 103 Liquid crystal 7, 8 QD patterning 9 Diffusion layer 11 Core 12 Shell 102 QD film 104 Color filter (R) 105 Color filter (G) 106 Color filter (B)

Claims

1. Core / shell semiconductor nanoparticles having a core containing at least In and P and a shell containing Zn and S and / or Se, wherein the core / shell semiconductor nanoparticles contain a halogen, and the molar ratio of halogen to In is greater than 15 and not more than 900, calculated on an atomic basis; and wherein the average circularity of the core / shell semiconductor nanoparticles is 0.820 to 1.000 in an STEM image obtained by observation with a scanning transmission electron microscope.

2. The core / shell semiconductor nanoparticles according to claim 1, wherein the halogen contained in said core / shell semiconductor nanoparticles is chlorine or bromine.

3. The core / shell semiconductor nanoparticles according to claim 1, wherein the halogen contained in said core / shell semiconductor nanoparticles is chlorine.

4. The core / shell semiconductor nanoparticles according to claim 1, wherein the semiconductor nanoparticles have stacking faults.

5. The core / shell semiconductor nanoparticles according to claim 1, wherein a primary amine ligand is coordinated to the surface of said core / shell semiconductor nanoparticles.

6. Core / shell semiconductor nanoparticles according to claim 1, characterized in that the mass ratio of the primary amine ligands to all ligands is greater than 0% and less than 100%.

7. Core / shell semiconductor nanoparticles according to claim 1, characterized in that the SD value calculated from the particle size distribution in an STEM image obtained by observation with a scanning transmission electron microscope is 1.0 or less.

8. The core / shell semiconductor nanoparticles according to claim 1, wherein the quantum efficiency (QY) of the core / shell semiconductor nanoparticles is 80% or more.

9. The core / shell semiconductor nanoparticles according to claim 1, wherein the full width at half maximum (FWHM) of the emission spectrum of said core / shell semiconductor nanoparticles is 35 nm or less.

10. The core / shell semiconductor nanoparticles according to claim 1, wherein the emission peak wavelength of the core / shell semiconductor nanoparticles is 610 nm or more, and the full width at half maximum (FWHM) of the spectrum of the core / shell semiconductor nanoparticles is 35 nm or less.

11. The core / shell semiconductor nanoparticles according to claim 1, wherein the peak emission wavelength of said core / shell semiconductor nanoparticles is less than 530 nm.

12. The core / shell semiconductor nanoparticles according to claim 1, wherein the ratio of the absorbance at the absorption peak to the absorbance at 450 nm of said core / shell semiconductor nanoparticles is 1.1 or less.

13. A method for producing core / shell semiconductor nanoparticles, comprising: a dispersion preparation step of mixing core particles containing at least In and P and zinc halide with a dispersion medium containing mainly a primary amine to prepare a core particle dispersion; and a shell formation step of mixing a Zn source, an S source and / or a Se source with the core particle dispersion and reacting them to form shells on the core particles, thereby obtaining core / shell type semiconductor nanoparticles, wherein the zinc halide is at least ZnCl ２ wherein the Zn source is a zinc salt of a branched-chain carboxylic acid.

14. The method for producing core / shell semiconductor nanoparticles according to claim 13, wherein the mass ratio of the core particles to the primary amine dispersion medium is 0.001 to 0.100 mass %.

15. The ZnCl ２ 14. The method for producing core / shell semiconductor nanoparticles according to claim 13, wherein the molar ratio of the amount of the compound to In in the core particles is greater than 7.5 and 1000 or less.

16. The method for producing core / shell semiconductor nanoparticles according to claim 13, wherein the reaction temperature in the shell formation step is 260°C to 320°C.

17. The method for producing core / shell semiconductor nanoparticles according to claim 13, characterized in that trismethylsilylphosphine is used in synthesizing the core particles.

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