Semiconductor nanoparticle and method for producing the same

Abstract

To provide a semiconductor nanoparticle excellent in light resistance.SOLUTION: The semiconductor nanoparticle contains silver, indium, gallium, zinc and sulfur in its composition and emits light by light irradiation. When the semiconductor nanoparticle is approximated to a sphere and partitioned into a first region from the center to a position where the distance from the center is 79.4% of the radius and a second region from a position where the distance from the center is 79.4% of the radius to the surface, the value obtained by dividing the ratio of the abundance of zinc to the abundance of gallium in the second region by the ratio of the abundance of zinc to the abundance of gallium in the first region is greater than 1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to semiconductor nanoparticles and methods for making same. [Background technology]

[0002] It is known that semiconductor particles exhibit a quantum size effect when their particle size is, for example, 20 nm or less, and such nanoparticles are called quantum dots (also called semiconductor quantum dots). The quantum size effect refers to the phenomenon in which the valence band and conduction band, which are considered continuous in bulk particles, become discrete when the particle size is reduced to nanometers, and the band gap energy changes depending on the particle size.

[0003] Since quantum dots can absorb light and convert its wavelength into light corresponding to its band gap energy, white light-emitting devices utilizing quantum dot emission have been proposed. In this regard, an efficient method for producing ternary semiconductor nanoparticles capable of band-edge emission and low toxicity has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2022 / 191032 Summary of the Invention [Problem to be solved by the invention]

[0005] In semiconductor nanoparticles capable of band-edge emission, further improvement in durability is required. One aspect of the present disclosure aims to provide semiconductor nanoparticles with excellent light resistance and a method for producing the same. [Means for solving the problem]

[0006] The first aspect is a semiconductor nanoparticle that contains silver, indium, gallium, zinc, and sulfur in its composition and emits light when irradiated with light. When the semiconductor nanoparticle is approximated as a sphere and divided into a first region extending from the center to a position at 79.4% of the radius and a second region extending from the position at 79.4% of the radius to the surface, the ratio of the amount of zinc present in the first region to the amount of gallium present in the second region divided by the ratio of the amount of zinc present in the first region to the amount of gallium present in the first region is greater than 1.

[0007] A second aspect is a method for producing semiconductor nanoparticles, comprising: preparing first semiconductor nanoparticles containing silver, indium, gallium, and sulfur in their composition; and heat-treating a mixture containing the first semiconductor nanoparticles, a zinc source, and a sulfur source at a first temperature of 180°C or higher and 250°C or lower to obtain second semiconductor nanoparticles. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, it is possible to provide semiconductor nanoparticles having excellent light resistance and a method for producing the same. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are schematic diagrams illustrating the first and second regions of a semiconductor nanoparticle, in which (A) is a graph showing the amount of each element detected, and (B) is a schematic diagram showing a hemisphere of a semiconductor nanoparticle. [Figure 2] FIG. 1 shows the emission spectrum of semiconductor nanoparticles. [Figure 3] FIG. 1 is a diagram showing the results of a light resistance test of semiconductor nanoparticles. DETAILED DESCRIPTION OF THE INVENTION

[0010] As used herein, the term "process" refers not only to an independent process, but also to processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, the content of each component in a composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. Furthermore, the upper and lower limits of the numerical ranges described herein can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. The half-width of a phosphor refers to the wavelength width (full width at half maximum; FWHM) of the emission spectrum of the phosphor, where the emission intensity is 50% of the maximum emission intensity. The following describes embodiments of the present invention in detail. However, the following embodiments are intended to exemplify semiconductor nanoparticles and methods for producing the same, embodying the technical concept of the present invention. The present invention is not limited to the semiconductor nanoparticles and methods for producing the same. The components set forth in the claims are in no way limited to the components of the embodiments.

[0011] semiconductor nanoparticles The semiconductor nanoparticles contain silver (Ag), indium (In), gallium (Ga), zinc (Zn), and sulfur (S) in their composition and emit light when irradiated with light. When the semiconductor nanoparticles are approximated as a sphere and divided into a first region extending from the center to a position at 79.4% of the radius and a second region extending from the position at 79.4% of the radius to the surface, the relative abundance of zinc in the first region ( 1 R Zn / Ga ) and the relative abundance of zinc in the second region ( 2 R Zn / Ga ) divided by ( 2 R Zn / Ga / 1 R Zn / Ga (hereinafter also referred to as "zinc abundance ratio") is greater than 1. That is, in the semiconductor nanoparticles, the relative abundance of zinc is greater in the outer second region than in the inner first region.

[0012] Semiconductor nanoparticles can exhibit excellent light resistance by containing a large amount of zinc in the outer region of the particle. This can be explained, for example, as follows: In semiconductor nanoparticles, reversible ligand detachment occurs upon irradiation with light, and irreversible reactions such as surface oxidation proceed at the site where the ligand is detached, resulting in degradation. In the semiconductor nanoparticles of this embodiment, the surface is protected with a compound containing zinc and sulfur, which is thought to suppress irreversible degradation. Alternatively, it is thought that the placement of a semiconductor containing zinc and sulfur on the surface reduces surface defects, improving stability against light.

[0013] The zinc abundance ratio in the semiconductor nanoparticles may be, for example, greater than 1, and preferably 1.1 or greater. The zinc abundance ratio may be, for example, 10 or less. When the zinc abundance ratio is within the above range, the light resistance of the semiconductor nanoparticles tends to be further improved.

[0014] In a semiconductor nanoparticle approximated as a sphere, the first and second regions are defined at a distance from the center that is 79.4% of the radius. This means that the volumes of the first and second regions in the semiconductor nanoparticle approximated as a sphere are equal. The calculation of the spherical approximation of the semiconductor nanoparticle and the relative abundance of zinc in the first and second regions is performed as follows. For any cross section of the semiconductor nanoparticle, EDX analysis is performed using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) along the line connecting two points on the outer edge of the particle at the maximum distance, and a graph showing the detected amount of each element versus the analysis distance is obtained. The two positions that sandwich the position giving the maximum detected amount of sulfur are defined as the outer edge of the particle, the distance between these two positions is defined as the particle diameter, the midpoint between these two positions is defined as the particle center, and half the particle diameter is defined as the particle radius. In the EDX analysis, the detected amount of zinc from the particle center to a position 79.4% of the particle radius is divided by the detected amount of gallium, and the average value is defined as the relative abundance of zinc in the first region ( 1 R Zn / Ga) and the average value of the amount of zinc detected from the position 79.4% of the particle radius from the center of the particle to the outer edge of the particle divided by the amount of gallium detected was taken as the relative amount of zinc present in the second region ( 2 R Zn / Ga )

[0015] The first and second regions of a semiconductor nanoparticle will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating the first and second regions of a semiconductor nanoparticle. (A) is a graph showing the detected amount of each element, and (B) is a schematic diagram of a semiconductor nanoparticle 100 showing only a hemisphere. In graph A showing the detected amount of each element, detection position 4 corresponding to a detection amount 1 / 2H, which is half of the maximum detection amount H of sulfur (S), is defined as the outer edge 104 of the semiconductor nanoparticle 100. The line segment connecting the two detection positions 4 is defined as the particle diameter 106 of the semiconductor nanoparticle 100. Position 2, which equally divides the particle diameter 106, is defined as the center 102 of the semiconductor nanoparticle 100. The first region 10 is the region from the center 102 of the semiconductor nanoparticle 100 to a position corresponding to 79.4% of the radius, and the second region 20 is the region from the position corresponding to 79.4% of the radius of the semiconductor nanoparticle 100 to the outer edge 104.

[0016] In the semiconductor nanoparticles, there is more zinc in the outer second region than in the inner first region, but the distribution of other elements may differ from the distribution of zinc. For example, the semiconductor nanoparticles may have a ratio of indium abundance to gallium abundance in the first region ( 1 R In / Ga ) and the ratio of the indium abundance to the gallium abundance in the second region ( 2 R In / Ga ) divided by ( 2 R In / Ga / 1 R In / Ga (hereinafter also referred to as "indium abundance ratio") may be less than 1. That is, in the semiconductor nanoparticles, the relative abundance of indium may be greater in the inner first region than in the outer second region.

[0017] The indium abundance ratio in the semiconductor nanoparticles may be, for example, less than 1, preferably 0.8 or less, or 0.6 or less. The indium abundance ratio may be, for example, 0.3 or more. When the indium abundance ratio is within the above range, the luminescence intensity of the semiconductor nanoparticles tends to be further improved. The indium abundance ratio is calculated in the same manner as the zinc abundance ratio described above.

[0018] In one embodiment, the semiconductor nanoparticles may have a first semiconductor portion containing silver, indium, gallium, and sulfur in its composition, and a second semiconductor portion disposed on the surface of the first semiconductor portion and containing zinc and sulfur in its composition. The first semiconductor portion may have a region near the boundary with the second semiconductor portion having a composition further containing zinc, and the second semiconductor portion may have a region near the boundary with the first semiconductor portion having a composition further containing silver, indium, and gallium. That is, the first semiconductor portion and the second semiconductor portion may be in contact with each other, including a region in which they form a solid solution. Hereinafter, the semiconductor constituting the first semiconductor portion will also be referred to as the first semiconductor, and the semiconductor constituting the second semiconductor portion will also be referred to as the second semiconductor.

[0019] In the semiconductor nanoparticles, a second semiconductor portion containing zinc and sulfur may be disposed as an attachment on the surface of a first semiconductor portion, or a particle containing the first semiconductor may be coated with an attachment containing the second semiconductor. Furthermore, the semiconductor nanoparticles may have a core-shell structure in which, for example, a particle containing the first semiconductor serves as a core and an attachment containing the second semiconductor serves as a shell, with the shell disposed on the surface of the core.

[0020] The first semiconductor constituting the semiconductor nanoparticles contains silver (Ag), indium (In), gallium (Ga), and sulfur (S). Generally, semiconductors containing Ag, In, and S and having a tetragonal, hexagonal, or orthorhombic crystal structure are introduced in literature as being represented by the composition formula AgInS2. However, in reality, the composition is not stoichiometric as represented by the general formula above. In particular, the ratio of the number of Ag atoms to the number of In and Ga atoms (Ag / In+Ga) may be less than 1, or conversely, may be greater than 1. Furthermore, the sum of the number of Ag atoms and the number of In and Ga atoms may not be the same as the number of S atoms. Therefore, in this specification, when a semiconductor containing a specific element is used, and whether or not it has a stoichiometric composition is not an issue, the semiconductor composition may be expressed using a formula in which the constituent elements are connected by a "-", such as Ag-In-Ga-S. Therefore, the composition of the first semiconductor in this embodiment can be considered to be, for example, Ag—In—S and Ag—Ga—S, where some or all of the In, a Group 13 element, is replaced with Ga, also a Group 13 element.

[0021] Semiconductors containing the above elements that have a hexagonal crystal structure are known as wurtzite-type semiconductors, while those that have a tetragonal crystal structure are known as chalcopyrite-type semiconductors. The crystal structure can be identified, for example, by measuring the XRD pattern obtained by X-ray diffraction (XRD) analysis. Specifically, the XRD pattern obtained from the first semiconductor is compared with a known XRD pattern for semiconductor nanoparticles with a composition of AgInS2, or with an XRD pattern obtained by simulation using crystal structure parameters. If any of the known and simulated patterns matches the pattern of the first semiconductor, the crystal structure of the semiconductor nanoparticles can be said to be the crystal structure of the corresponding known or simulated pattern.

[0022] In an aggregate of nanoparticles made of a first semiconductor, nanoparticles containing first semiconductors of different crystal structures may be present. In this case, peaks derived from multiple crystal structures are observed in the XRD pattern. In one embodiment of nanoparticles made of a first semiconductor, the first semiconductor may be substantially tetragonal, and peaks corresponding to the tetragonal crystal structure may be observed, while peaks derived from other crystal structures may not be substantially observed.

[0023] The total Ag content in the composition of the first semiconductor may be, for example, 10 mol% to 30 mol%, and preferably 15 mol% to 25 mol%. The total In and Ga content in the composition of the first semiconductor may be, for example, 15 mol% to 35 mol%, and preferably 20 mol% to 30 mol%. The total S content in the composition of the first semiconductor may be, for example, 35 mol% to 55 mol%, and preferably 40 mol% to 55 mol%.

[0024] The first semiconductor contains at least Ag, and may be partially substituted to further contain at least one of Cu, Au, and an alkali metal, or may be substantially composed of Ag. Here, "substantially" indicates that the ratio of the number of atoms of elements other than Ag to the total number of atoms of Ag and elements other than Ag is, for example, 10% or less, preferably 5% or less, and more preferably 1% or less. Also, the first semiconductor may be substantially composed of Ag and an alkali metal (hereinafter referred to as M aThe first semiconductor may contain, for example, an alkali metal (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Alkali metals can form monovalent cations like Ag, and thus can substitute for a portion of Ag in the composition of the first semiconductor. Li, in particular, has an ionic radius similar to that of Ag and is preferably used. Substituting a portion of Ag in the composition of the first semiconductor can, for example, widen the band gap and shift the emission peak wavelength to a shorter wavelength. Although the details are unclear, it is believed that lattice defects in the first semiconductor are reduced, improving the internal quantum yield of band-edge emission. When the first semiconductor contains an alkali metal, it may contain at least Li.

[0025] The first semiconductor is Ag and alkali metal (M a When the first semiconductor contains Ag, the content of the alkali metal in the composition of the first semiconductor is, for example, greater than 0 mol % and less than 30 mol %, and preferably 1 mol % or more and 25 mol % or less. a ) relative to the total number of atoms of alkali metals (M a ) atomic number ratio (M a / (Ag+M a )) is, for example, less than 1, preferably 0.8 or less, more preferably 0.4 or less, and even more preferably 0.2 or less. The ratio is, for example, greater than 0, preferably 0.05 or more, and more preferably 0.1 or more.

[0026] The first semiconductor contains In and Ga, and may further contain at least one of Al and Tl by substitution of a portion thereof, or may be substantially composed of In and Ga. Here, "substantially" indicates that the ratio of the number of atoms of elements other than In and Ga to the total number of atoms of In, Ga, and elements other than In and Ga is, for example, 10% or less, preferably 5% or less, and more preferably 1% or less.

[0027] The ratio of the number of In atoms to the total number of In and Ga atoms in the first semiconductor (In / (In+Ga)) may be, for example, 0.01 or more and less than 1, and preferably 0.1 or more and 0.99 or less. When the ratio of the number of In atoms to the total number of In and Ga atoms is within a predetermined range, a short wavelength emission peak wavelength (for example, 545 nm or less) can be obtained. Furthermore, the ratio of the number of Ag atoms to the total number of In and Ga atoms (Ag / (In+Ga)) is, for example, 0.3 or more and 1.2 or less, and preferably 0.5 or more and 1.1 or less. The ratio of the number of S atoms to the total number of Ag, In, and Ga atoms (S / (Ag+In+Ga)) is, for example, 0.8 or more and 1.5 or less, and preferably 0.9 or more and 1.2 or less.

[0028] The first semiconductor may contain S, a portion of which may be substituted to further contain at least one of Se and Te, or may be substantially composed of S. Here, "substantially" indicates that the ratio of the number of atoms of elements other than S to the total number of atoms of S and elements other than S is, for example, 10% or less, preferably 5% or less, and more preferably 1% or less.

[0029] The first semiconductor may be substantially composed of Ag, In, Ga, S, and elements that partially replace the aforementioned elements. Here, the term "substantially" is used in consideration of the fact that elements other than Ag, In, Ga, S, and the elements partially replacing the aforementioned elements are inevitably included due to the inclusion of impurities, etc.

[0030] The first semiconductor may have a composition represented by the following formula (1), for example. (Ag p Ma (1-p) ) q In r Ga (1-r) S (q+3) / 2 (1) Here, p, q, and r satisfy 0 < p ≤ 1, 0.20 < q ≤ 1.2, and 0 < r < 1. M a represents an alkali metal.

[0031] The surface of the first semiconductor portion may be surface-modified with a gallium halide. By surface-modifying the surface of the first semiconductor portion with a gallium halide, the internal quantum efficiency of band-edge emission tends to improve. Specific examples of the gallium halide include gallium chloride, gallium fluoride, gallium bromide, gallium iodide, and the like.

[0032] The semiconductor nanoparticles may have a second semiconductor portion containing zinc and sulfur on the surface of the first semiconductor portion. The second semiconductor constituting the second semiconductor portion may be a semiconductor having a larger bandgap than the first semiconductor.

[0033] In the composition of the second semiconductor containing zinc (Zn) and sulfur (S) included in the second semiconductor portion, a part of Zn may be substituted with at least one Group 13 element selected from the group consisting of boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). Also, a part of S may be substituted with at least one Group 16 element selected from the group consisting of oxygen (O), selenium (Se), tellurium (Te), and polonium (Po).

[0034] The second semiconductor may be a semiconductor consisting essentially of Zn and S. Here, "consisting essentially of" means that when the total number of atoms of all elements contained in the second semiconductor containing Zn and S is 100%, the ratio of the number of atoms of elements other than Zn and S is, for example, 10% or less, preferably 5% or less, more preferably 1% or less.

[0035] The second semiconductor may have a crystal system similar to that of the first semiconductor, and its lattice constant may be the same as or close to that of the first semiconductor. A second semiconductor with a similar crystal system and a similar lattice constant (here, a second semiconductor whose lattice constant multiples are similar to that of the first semiconductor) may effectively coat the periphery of the first semiconductor. For example, the first semiconductor is generally tetragonal, but examples of similar crystal systems include tetragonal and orthorhombic. When Ag-In-S is tetragonal, its lattice constants are 0.5828 nm, 0.5828 nm, and 1.119 nm. The second semiconductor coating it is preferably tetragonal or orthorhombic, and its lattice constant or multiples thereof are similar to that of Ag-In-S. Alternatively, the second semiconductor may be amorphous.

[0036] The semiconductor nanoparticles may have an average particle size of, for example, 50 nm or less. From the viewpoints of ease of production and the internal quantum yield of band-edge emission, the average particle size is preferably in the range of 1 nm to 20 nm, more preferably 1.6 nm to 15 nm, and particularly preferably 2 nm to 10 nm.

[0037] The average particle size of semiconductor nanoparticles may be determined, for example, from a transmission electron microscope (TEM) image taken using a TEM. Specifically, the particle size of an individual particle refers to the longest line segment that connects any two points on the periphery of the particle observed in the TEM image and exists inside the particle. The average particle size of semiconductor nanoparticles is calculated as the arithmetic mean of the particle sizes of the individual particles.

[0038] However, when the particles have a rod shape, the length of the minor axis is considered to be the particle size. Here, rod-shaped particles refer to particles that have a minor axis and a major axis perpendicular to the minor axis in a TEM image, and the ratio of the length of the major axis to the length of the minor axis is greater than 1.2. Rod-shaped particles are observed in TEM images as, for example, quadrangular, including rectangular, elliptical, or polygonal shapes. The cross-sectional shape of the rod, which is a plane perpendicular to the major axis, may be, for example, circular, elliptical, or polygonal. Specifically, for rod-shaped particles, the length of the major axis refers to the length of the longest line segment connecting any two points on the periphery of the particle in the case of an elliptical shape; and in the case of a rectangular or polygonal shape, refers to the length of the longest line segment connecting any two points on the periphery of the particle that is parallel to the longest side defining the periphery. The length of the minor axis refers to the length of the longest line segment connecting any two points on the periphery that is perpendicular to the line segment defining the length of the major axis.

[0039] In the semiconductor nanoparticles, the first semiconductor portion may be particulate and may have an average particle size of, for example, 20 nm or less, particularly 15 nm or less, or less than 10 nm. The average particle size of the first semiconductor portion may be, for example, 1.5 nm or more and 20 nm or less, preferably 1.5 nm or more and less than 15 nm, or 1.5 nm or more and less than 10 nm. When the average particle size of the first semiconductor portion is equal to or less than the upper limit, it is easy to obtain a quantum size effect.

[0040] The average thickness of the second semiconductor portion in the semiconductor nanoparticles may be, for example, greater than 0 nm and not greater than 5 nm. The thickness of the second semiconductor portion may preferably be in the range of 0.1 nm to 20 nm, or in the range of 0.3 nm to 5 nm. When the thickness of the second semiconductor portion is equal to or greater than the lower limit, the effect of disposing the second semiconductor portion in the semiconductor nanoparticles is sufficiently obtained, and light resistance is likely to be improved.

[0041] The semiconductor nanoparticles preferably have a substantially tetragonal crystal structure. The crystal structure is identified by measuring the XRD pattern obtained by X-ray diffraction (XRD) analysis as described above. "Substantially tetragonal" means that the ratio of the height of the peak around 48°, which indicates hexagonal and orthorhombic crystals, to the height of the main peak around 26°, which indicates tetragonal crystals, is, for example, 10% or less, or 5% or less.

[0042] The second semiconductor containing Zn and S may be configured by selecting its composition and the like depending on the band gap energy of the first semiconductor. Alternatively, if the composition and the like of the semiconductor containing Zn and S are determined first, the first semiconductor may be designed so that its band gap energy is smaller than that of the semiconductor containing Zn and S. Generally, a semiconductor made of Ag-In-S has a band gap energy of 1.8 eV or more and 1.9 eV or less.

[0043] Specifically, the second semiconductor containing Zn and S may have a band gap energy of, for example, 2.0 eV to 5.0 eV, particularly 2.5 eV to 5.0 eV. The band gap energy of the second semiconductor containing Zn and S may be greater than the band gap energy of the first semiconductor by, for example, about 0.1 eV to 3.0 eV, particularly about 0.3 eV to 3.0 eV, and more particularly about 0.5 eV to 1.0 eV. When the difference between the band gap energy of the second semiconductor containing Zn and S and the band gap energy of the first semiconductor is equal to or greater than the lower limit, the proportion of emission other than band edge emission in the light emission from the semiconductor nanoparticles tends to decrease, and the proportion of band edge emission tends to increase.

[0044] The second semiconductor may contain oxygen (O) atoms. Semiconductors containing oxygen atoms tend to have a larger bandgap energy than the first semiconductor. The form of the second semiconductor containing oxygen atoms is not clear, but it may be, for example, Zn—OS, ZnO, etc.

[0045] The semiconductor nanoparticles may exhibit band edge emission having a peak emission wavelength in the wavelength range of 475 nm to 560 nm when irradiated with light from a light source having a peak emission wavelength in the range of, for example, 380 nm to 545 nm, and the range of the peak emission wavelength may be preferably 510 nm to 550 nm, and more preferably 525 nm to 535 nm. Furthermore, the semiconductor nanoparticles may have a half width in their emission spectrum of, for example, 45 nm or less, preferably 40 nm or less, or 30 nm or less. The lower limit of the half width may be, for example, 15 nm or more. Furthermore, it is preferable that the emission lifetime of the main component (band edge emission) is 200 ns or less.

[0046] Here, the "luminescence lifetime" refers to the lifetime of luminescence measured using a device known as a fluorescence lifetime measurement device. Specifically, the "luminescence lifetime of the main component" is determined according to the following procedure. First, semiconductor nanoparticles are irradiated with excitation light to cause them to emit light, and the time-dependent change in the decay (afterglow) of light with a wavelength near the peak of the emission spectrum, for example, a wavelength within ±50 nm of the peak wavelength, is measured. The time-dependent change is measured from the point at which irradiation with the excitation light is stopped. The resulting decay curve is generally the sum of multiple decay curves resulting from relaxation processes such as luminescence and heat. Therefore, in this embodiment, assuming that three components (i.e., three decay curves) are included, parameter fitting is performed so that the decay curve can be expressed by the following equation when the luminescence intensity is I(t). Parameter fitting is performed using dedicated software. I(t) = A1exp(-t / τ1) + A2exp(-t / τ2) + A3exp(-t / τ3)

[0047] In the above formula, τ1, τ2, and τ3 of each component are the time required for the emission intensity to decay to 1 / e (36.8%) of the initial value, which corresponds to the emission lifetime of each component. τ1, τ2, and τ3 are arranged in order of shortest emission lifetime. Also, A1, A2, and A3 are the contribution rates of each component. For example, A x exp(-t / τ xWhen the component with the largest integral value of the curve represented by A is selected as the main component, the luminescence lifetime τ of the main component is 200 ns or less. Such luminescence is presumed to be band edge luminescence. x exp(-t / τ x ) from 0 to infinity. x ×τ x The component with the largest value is selected as the principal component.

[0048] Note that the deviation between the decay curves drawn by equations obtained by parameter fitting assuming that the luminescence decay curve contains three, four, or five components and the actual decay curve is not significantly different. Therefore, in this embodiment, when determining the luminescence lifetime of the main component, the number of components contained in the luminescence decay curve is assumed to be three, thereby avoiding complication of parameter fitting.

[0049] The internal quantum yield of light emission from the semiconductor nanoparticles may be, for example, 40% or more, preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. The internal quantum yield is calculated at a temperature of 25°C using a quantum yield measurement device under the conditions of an excitation light wavelength of 450 nm and a fluorescence wavelength range of 475 nm to 800 nm.

[0050] The luminescence of semiconductor nanoparticles may include defect luminescence (e.g., donor-acceptor luminescence) in addition to band-edge luminescence, but preferably consists essentially of band-edge luminescence alone. Defect luminescence generally has a long luminescence lifetime, a broad spectrum, and a peak at a longer wavelength than band-edge luminescence. Here, "substantially consisting of band-edge luminescence alone" means that the purity of the band-edge luminescence component in the luminescence spectrum (hereinafter also referred to as "band-edge luminescence purity") is 40% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more. The upper limit of the purity of the band-edge luminescence component may be, for example, 100% or less, less than 100%, or 99% or less. The "purity of the band-edge luminescence component" is expressed by the following formula when the luminescence spectrum is separated into two peaks, a1 and a2, by performing parameter fitting on the luminescence spectrum assuming that the shapes of the band-edge luminescence peak and the defect luminescence peak follow a normal distribution, and the peaks are separated into two peaks, a1 and a2, respectively. Purity of band edge emission component (%) = a1 / (a1+a2)×100 If the emission spectrum does not contain any band-edge emission, i.e., if it contains only defect emission, it is 0%; if the peak areas of the band-edge emission and defect emission are the same, it is 50%; and if it contains only band-edge emission, it is 100%.

[0051] The internal quantum yield of band edge emission is defined as the internal quantum yield calculated using a quantum yield measurement device at a temperature of 25°C under the conditions of an excitation light wavelength of 450 nm and a fluorescence wavelength range of 475 nm to 800 nm, or the internal quantum yield calculated under the conditions of an excitation light wavelength of 365 nm and a fluorescence wavelength range of 450 nm to 950 nm, or the internal quantum yield calculated under the conditions of an excitation light wavelength of 450 nm and a fluorescence wavelength range of 500 nm to 950 nm, multiplied by the purity of the band edge emission component and divided by 100. The internal quantum yield of band edge emission of the semiconductor nanoparticles is, for example, 15% or more, preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more.

[0052] The peak position of the band-edge emission emitted by semiconductor nanoparticles can be changed by changing the particle size of the semiconductor nanoparticles. For example, decreasing the particle size of the semiconductor nanoparticles tends to shift the peak wavelength of the band-edge emission to shorter wavelengths. Furthermore, decreasing the particle size of the semiconductor nanoparticles tends to decrease the half-width of the spectrum of the band-edge emission.

[0053] When the semiconductor nanoparticles exhibit defect luminescence in addition to band-edge luminescence, the intensity ratio of the band-edge luminescence may be, for example, 0.75 or more, preferably 0.85 or more, more preferably 0.9 or more, and particularly preferably 0.93 or more, and the upper limit may be, for example, 1 or less, less than 1, or 0.99 or less. The intensity ratio of the band-edge luminescence is expressed by the following formula when the emission spectrum is separated into two peaks, the band-edge luminescence peak and the defect luminescence peak, by performing parameter fitting assuming that the shapes of the band-edge luminescence peak and the defect luminescence peak are normal distributions, and the maximum peak intensities are b1 and b2, respectively. Band edge emission intensity ratio = b1 / (b1+b2) The band-edge emission intensity ratio is 0 when the emission spectrum does not contain any band-edge emission, i.e., contains only defect emission; 0.5 when the maximum peak intensities of the band-edge emission and defect emission are the same; and 1 when only band-edge emission is contained.

[0054] The semiconductor nanoparticles preferably have an absorption spectrum or excitation spectrum (also referred to as a fluorescence excitation spectrum) that exhibits an exciton peak. The exciton peak is a peak obtained by exciton generation, and its appearance in the absorption spectrum or excitation spectrum indicates that the particles have a small particle size distribution and are suitable for band-edge emission with few crystal defects. The steeper the exciton peak, the more particles with uniform particle size and few crystal defects are contained in the semiconductor nanoparticle aggregate. Therefore, the half-width of the emission is narrower, and the luminous efficiency is expected to improve. In the absorption spectrum or excitation spectrum of the semiconductor nanoparticles of this embodiment, the exciton peak is observed, for example, within a range of 400 nm to 550 nm, preferably 430 nm to 500 nm. The excitation spectrum for determining the presence or absence of an exciton peak may be measured by setting the observation wavelength near the peak wavelength.

[0055] The surfaces of the semiconductor nanoparticles may be modified with a surface modifier. Specific examples of the surface modifier include amino alcohols having from 2 to 20 carbon atoms, ionic surface modifiers, nonionic surface modifiers, nitrogen-containing compounds having a hydrocarbon group having from 4 to 20 carbon atoms, sulfur-containing compounds having a hydrocarbon group having from 4 to 20 carbon atoms, oxygen-containing compounds having a hydrocarbon group having from 4 to 20 carbon atoms, phosphorus-containing compounds having a hydrocarbon group having from 4 to 20 carbon atoms, and halides of Group 2, Group 12, or Group 13 elements. The surface modifiers may be used alone or in combination of two or more different types.

[0056] Method for producing semiconductor nanoparticles The method for producing semiconductor nanoparticles may include a first step of preparing first semiconductor nanoparticles containing silver (Ag), indium (In), gallium (Ga), and sulfur (S) in its composition, and a second step of heat-treating a first mixture containing the first semiconductor nanoparticles, a zinc (Zn) source, and a sulfur (S) source at a temperature of 180°C or higher and 250°C or lower to obtain second semiconductor nanoparticles.

[0057] By heat-treating the prepared first mixture containing the first semiconductor nanoparticles, a zinc source, and a sulfur source, second semiconductor nanoparticles are produced in which a compound containing zinc and sulfur is disposed on the surface of the first semiconductor nanoparticles. The resulting second semiconductor nanoparticles have a narrow half-width in their emission spectrum and excellent light resistance. This is thought to be because, for example, the semiconductor containing zinc and sulfur is disposed on the surface, reducing surface defects and improving light stability.

[0058] In the first step, first semiconductor nanoparticles containing a first semiconductor containing Ag, In, Ga, and S are prepared. The first semiconductor nanoparticles may be prepared by obtaining desired semiconductor nanoparticles, for example, by transfer, or by manufacturing the desired semiconductor nanoparticles using the manufacturing method described below. The first semiconductor nanoparticles may be obtained by the methods described in, for example, WO 2018 / 159699, WO 2019 / 160094, or WO 2020 / 162622. Details of the manufacturing method of the first semiconductor nanoparticles will be described later.

[0059] In the second step, the first mixture containing the prepared first semiconductor nanoparticles, a zinc (Zn) source, and a sulfur (S) source is heat-treated at a temperature of 180°C or higher and 250°C or lower to obtain second semiconductor nanoparticles. In the second semiconductor nanoparticles, a compound containing zinc and sulfur may be disposed on at least a portion of the surface of the first semiconductor nanoparticles. The compound containing zinc and sulfur may be a semiconductor compound, may contain zinc sulfide, or may be a compound essentially consisting of zinc and sulfur. The compound containing zinc and sulfur may have a stoichiometric composition (e.g., ZnS), or may have a composition that differs from the stoichiometric composition.

[0060] Examples of the zinc source contained in the first mixture include zinc salts. The zinc salt may be either an organic acid salt or an inorganic acid salt. Specific examples of inorganic acid salts include halides, nitrates, sulfates, and sulfonates. Examples of organic acid salts include carboxylates such as formates, acetates, oleates, stearates, and oxalates, and complex salts such as acetylacetonates. The zinc salt may preferably contain at least one selected from the group consisting of these salts. Because of its high solubility in organic solvents and the more uniform progress of the reaction, it may more preferably contain at least one selected from the group consisting of organic acid salts such as carboxylates and acetylacetonates. The first mixture may contain one zinc salt alone or two or more zinc salts in combination.

[0061] The zinc source in the first mixture may contain a compound having a Zn-S bond. The Zn-S bond may be a covalent bond, an ionic bond, a coordinate bond, or the like. Examples of compounds having a Zn-S bond include zinc salts of sulfur-containing compounds, which may be organic acid salts of zinc, inorganic acid salts, organometallic compounds, and the like. Specific examples of sulfur-containing compounds include thiocarbamic acid, dithiocarbamic acid, thiocarbonates, dithiocarbonates (xanthogenic acid), trithiocarbonates, thiocarboxylic acids, dithiocarboxylic acids, and derivatives thereof. Among these, at least one selected from the group consisting of xanthogenic acid and its derivatives is preferred because it decomposes at relatively low temperatures. Specific examples of sulfur-containing compounds include aliphatic thiocarbamic acid, aliphatic dithiocarbamic acid, aliphatic thiocarbonates, aliphatic dithiocarbonates, aliphatic trithiocarbonates, aliphatic thiocarboxylic acids, and aliphatic dithiocarboxylic acids. Examples of aliphatic groups in these sulfur-containing compounds include alkyl groups and alkenyl groups having from 1 to 12 carbon atoms, preferably from 1 to 4 carbon atoms. The aliphatic thiocarbamic acid may include a dialkylthiocarbamic acid, the aliphatic dithiocarbamic acid may include a dialkyldithiocarbamic acid, and the aliphatic dithiocarbonate (aliphatic xanthic acid) may include an alkylxanthic acid. The alkyl group in the dialkylthiocarbamic acid and the dialkyldithiocarbamic acid may have, for example, 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms. The two alkyl groups in the dialkylthiocarbamic acid and the dialkyldithiocarbamic acid may be the same or different. Specific examples of the compound having a Zn-S bond include zinc bisdimethyldithiocarbamate, zinc bisdiethyldithiocarbamate (Zn(DDTC)2), zinc chlorodiethyldithiocarbamate, and zinc ethylxanthate (Zn(EX)2). The first mixture may contain one compound having a Zn-S bond alone, or two or more compounds in combination. The compound having a Zn-S bond in the first mixture may be both a zinc source and a sulfur source.

[0062] The zinc source in the first mixture may include at least one selected from the group consisting of zinc halide, zinc alkylxanthogenate, zinc dialkyldithiocarbamate, zinc carboxylate, etc. The number of carbon atoms in the alkyl group in the zinc alkylxanthogenate, zinc dialkyldithiocarbamate, and zinc alkylcarboxylate may be, for example, 1 or more and 18 or less, and preferably 1 or more and 4 or less.

[0063] The sulfur source in the first mixture can be elemental sulfur or a compound containing sulfur. Examples of sulfur sources include elemental sulfur such as high-purity sulfur, or sulfur-containing compounds such as alkylthiols having 4 to 18 carbon atoms, such as n-butanethiol, isobutanethiol, n-pentanethiol, n-hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, and octadecanethiol; disulfides such as dibenzyl disulfide and tetraalkylthiuram disulfide; thiourea, thiocarbonyl compounds, thiocarbamic acid, dithiocarbamic acid, thiocarbonates, dithiocarbonates (xanthic acid), trithiocarbonates, thiocarboxylic acids, dithiocarboxylic acids, and derivatives thereof. The sulfur source in the first mixture can also serve as a zinc source. For example, a compound having a Zn-S bond can serve as both the zinc source and the sulfur source in the first mixture.

[0064] The sulfur source in the first mixture may include at least one selected from the group consisting of zinc alkylxanthate, zinc dialkyldithiocarbamate, thiourea and its derivatives, tetraalkylthiuram disulfide, and elemental sulfur. Examples of thiourea derivatives include alkylthiourea and dialkylthiourea. The number of carbon atoms in the alkyl group in the zinc alkylxanthate, zinc dialkyldithiocarbamate, alkylthiourea, dialkylthiourea, tetraalkylthiuram disulfide, etc. may be, for example, 1 to 18, and preferably 1 to 4.

[0065] The contents of the zinc source and sulfur source in the first mixture may be selected in consideration of the amount of first semiconductor nanoparticles contained in the first mixture so that a compound containing zinc and sulfur in desired amounts is disposed on the surface of the first semiconductor nanoparticles. For example, the amounts of the zinc source and sulfur source may be determined so that 0.01 mmol to 10 mmol, particularly 0.1 mmol to 1 mmol, of a compound having a stoichiometric composition consisting of zinc and sulfur is produced per 10 nmol of the first semiconductor nanoparticles as a particle substance. However, the amount of substance as a particle is the molar amount when one first semiconductor nanoparticle is considered as a giant molecule, and the number of first semiconductor nanoparticles contained in the first mixture is determined by Avogadro's number (N A =6.022×10 23 ) divided by .

[0066] The content of the zinc source in the first mixture is, for example, such that the ratio of the number of moles of zinc contained in the zinc source to the number of moles of the first semiconductor nanoparticles is 5.0 × 10 3 Over 6.0 x 10 4 The amount may be less than or equal to 6.7×10 3 That's it, 1.5 x 10 4 or more, or 2.0 x 10 4 or more, and preferably 4.5×10 4 Below, 4.0 x 10 4 or less, or 3.0 x 10 4 The amount may be as follows:

[0067] The first mixture may contain an organic solvent. Examples of organic solvents in the first mixture include amines having a hydrocarbon group containing 4 to 20 carbon atoms, such as alkylamines or alkenylamines having 4 to 20 carbon atoms; thiols having a hydrocarbon group containing 4 to 20 carbon atoms, such as alkylthiols or alkenylthiols having 4 to 20 carbon atoms; and phosphines having a hydrocarbon group containing 4 to 20 carbon atoms, such as alkylphosphines or alkenylphosphines having 4 to 20 carbon atoms. Preferably, the first mixture contains at least one selected from the group consisting of these organic solvents. These organic solvents may ultimately be used to modify the surface of the resulting semiconductor nanoparticles. Two or more organic solvents may be used in combination; for example, a mixed solvent may be used that combines at least one thiol having a hydrocarbon group containing 4 to 20 carbon atoms with at least one amine having a hydrocarbon group containing 4 to 20 carbon atoms. These organic solvents may be used in combination with other organic solvents. When the organic solvent contains the thiol and the amine, the volume ratio of the thiol to the amine (thiol / amine) is, for example, greater than 0 and equal to or less than 1, and preferably equal to or greater than 0.007 and equal to or less than 0.2.

[0068] The content of the first semiconductor nanoparticles in the first mixture is, for example, 5.0 × 10 -8 mol / L or more 5.0 x 10 -5 mol / L or less, preferably 1.0×10 -7 mol / L or more, or 3.0 x 10 -7 mol / L or more, and preferably 2.5×10 -5 mol / L or less, 1.0 x 10 -5 mol / L or less, or 7.5 x 10 -6 It may be mol / L or less.

[0069] In the second step, the first mixture is heat-treated to obtain a heat-treated product containing second semiconductor nanoparticles. The heat treatment temperature may be, for example, 180°C or higher and 250°C or lower. The heat treatment may include a temperature-raising step of raising the temperature of the first mixture to a temperature in the range of 180°C or higher and 250°C or lower, and a synthesis step of heat-treating the first mixture at a temperature in the range of 180°C or higher and 250°C or lower for a predetermined time.

[0070] The temperature range in the temperature increase step of the first heat treatment step may be 180° C. or higher and 250° C. or lower, and preferably 190° C. or higher and 240° C. or lower. The temperature increase rate may be adjusted so that the maximum temperature during the temperature increase does not exceed the target temperature, and is, for example, 1° C. / min. or higher and 50° C. / min. or lower.

[0071] The heat treatment temperature in the synthesis step of the first heat treatment step may be 180°C or higher and 250°C or lower, and preferably 190°C or higher and 240°C or lower. The heat treatment time in the synthesis step may be, for example, 3 seconds or longer, and preferably 1 minute or longer, 10 minutes or longer, 30 minutes or longer, 60 minutes or longer, or 90 minutes or longer. The heat treatment time may be, for example, 300 minutes or shorter, and preferably 180 minutes or shorter, or 150 minutes or shorter. The heat treatment time in the synthesis step starts when the temperature set in the above-mentioned temperature range is reached (for example, when set to 200°C, the time when 200°C is reached), and ends when the temperature is lowered. The synthesis step makes it possible to obtain a dispersion containing second semiconductor nanoparticles in which a compound containing zinc and sulfur is arranged on the surface of first semiconductor nanoparticles.

[0072] The heat treatment is preferably performed in an inert gas atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the production of oxide by-products and the oxidation of the surfaces of the resulting semiconductor nanoparticles.

[0073] The method for producing semiconductor nanoparticles may further include a cooling step following the synthesis step, in which the temperature of the resulting dispersion containing semiconductor composite particles is lowered. The cooling step begins when the temperature lowering operation is performed and ends when the temperature has been cooled to 50°C or below. The cooling step may include a period in which the temperature lowering rate is 50°C / min or more. In particular, the rate may be 50°C / min or more when the temperature lowering operation is performed and the temperature lowering starts.

[0074] The cooling step is preferably performed in an inert gas atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the production of oxide by-products and the oxidation of the surfaces of the resulting semiconductor composite particles.

[0075] The method for producing semiconductor nanoparticles may further include a separation step of separating the second semiconductor nanoparticles from the heat-treated product obtained in the second step, and may further include a purification step as necessary. In the separation step, for example, the heat-treated product containing the second semiconductor nanoparticles may be centrifuged to extract a precipitate containing the second semiconductor nanoparticles. In the purification step, for example, an appropriate organic solvent such as alcohol may be added to the precipitate obtained in the separation step, followed by centrifugation to extract the second semiconductor nanoparticles as a precipitate. That is, the purification step may include mixing the heat-treated product with an organic solvent to obtain a second mixture, centrifuging the second mixture, and extracting the second semiconductor nanoparticles as a precipitate or dispersion by centrifugation. In addition, in the method for producing semiconductor nanoparticles, the purification step of adding an organic solvent and centrifuging may be performed multiple times as necessary.

[0076] The organic solvent used in the purification step may include an alcohol solvent. Examples of the alcohol solvent used in the purification step include lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, n-amyl alcohol, and isoamyl alcohol. The organic solvent used in the purification step may include halogenated solvents such as chloroform, dichloromethane, dichloroethane, trichloroethane, and tetrachloroethane, and hydrocarbon solvents such as toluene, cyclohexane, hexane, pentane, and octane. The liquid amount of the organic solvent used in the purification step may be, for example, a volume ratio of 0.1 to 10, preferably 0.4 to 2, relative to the liquid amount of the mixture.

[0077] The separation step in the method for producing semiconductor nanoparticles may involve volatilizing the organic solvent from the heat-treated product to extract second semiconductor nanoparticles. The second semiconductor nanoparticles extracted in the separation step and purification step may be dried, for example, by vacuum degassing, natural drying, or a combination of vacuum degassing and natural drying. Natural drying may be performed, for example, by leaving the nanoparticles in the atmosphere at room temperature and normal pressure, in which case they may be left for 20 hours or more, for example, about 30 hours. The extracted precipitate may also be dispersed in an appropriate organic solvent. When dispersing the precipitate in an organic solvent, examples of the organic solvent that may be used include halogen-based solvents such as chloroform, dichloromethane, dichloroethane, trichloroethane, and tetrachloroethane, and hydrocarbon-based solvents such as toluene, cyclohexane, hexane, pentane, and octane. The organic solvent in which the precipitate is dispersed may be a halogen-based solvent from the viewpoint of internal quantum yield.

[0078] First method for producing semiconductor nanoparticles The method for producing the first semiconductor nanoparticles may include a third step of heat-treating a third mixture containing a silver (Ag) salt, an indium (In) salt, a compound having a gallium (Ga)-sulfur (S) bond, a gallium halide, and an organic solvent to obtain the first semiconductor nanoparticles. The method for producing the first semiconductor nanoparticles may further include other steps in addition to the third step, as necessary.

[0079] The third step may include a mixing step of obtaining a third mixture containing an Ag salt, an In salt, a compound having a Ga-S bond, a gallium halide, and an organic solvent, and a heat treatment step of heat-treating the obtained third mixture to obtain first semiconductor nanoparticles.

[0080] By using a compound having a Ga-S bond as a supply source of Ga and S contained in the composition of the first semiconductor nanoparticles, it becomes easier to control the composition of the produced first semiconductor nanoparticles. Furthermore, by using a gallium halide, it becomes easier to control the particle size of the produced first semiconductor nanoparticles. From the above, it is believed that semiconductor nanoparticles that exhibit band-edge emission and high band-edge emission purity can be efficiently produced in one pot.

[0081] In the mixing step, a third mixture is prepared by mixing an Ag salt, an In salt, a compound having a Ga-S bond, a gallium halide, and an organic solvent. The mixing method in the mixing step may be appropriately selected from commonly used mixing methods.

[0082] The Ag salt and In salt in the third mixture may be either an organic acid salt or an inorganic acid salt. Specific examples of inorganic acid salts include nitrates, sulfates, hydrochlorides, and sulfonates. Examples of organic acid salts include formates, acetates, oxalates, and acetylacetonates. The Ag salt and In salt may preferably be at least one selected from the group consisting of these salts, and more preferably at least one selected from the group consisting of organic acid salts such as acetates and acetylacetonates, because these salts have high solubility in organic solvents and allow the reaction to proceed more uniformly. The first mixture may contain one Ag salt and one In salt, or two or more of each salt may be combined.

[0083] The Ag salt in the third mixture may contain a compound having an Ag-S bond, which can suppress the by-production of silver sulfide in the heat treatment step described below. The Ag-S bond may be a covalent bond, an ionic bond, a coordinate bond, or the like. Examples of compounds having an Ag-S bond include Ag salts of sulfur-containing compounds, which may be organic acid salts, inorganic acid salts, organometallic compounds, and the like. Examples of sulfur-containing compounds include thiocarbamic acid, dithiocarbamic acid, thiocarbonates, dithiocarbonates (xanthogenic acid), trithiocarbonates, thiocarboxylic acids, dithiocarboxylic acids, and derivatives thereof. Among these, at least one selected from the group consisting of xanthogenic acid and its derivatives is preferred because it decomposes at relatively low temperatures. Specific examples of sulfur-containing compounds are the same as those in the compound having a Ga-S bond. Specific examples of compounds having an Ag-S bond include silver dimethyldithiocarbamate, silver diethyldithiocarbamate (Ag(DDTC)), silver ethylxanthogenate (Ag(EX)), and the like.

[0084] The In salt in the third mixture may contain a compound having an In-S bond. The In-S bond may be any of a covalent bond, an ionic bond, a coordinate bond, and the like. Examples of compounds having an In-S bond include In salts of sulfur-containing compounds, which may be organic acid salts, inorganic acid salts, organometallic compounds, and the like. Specific examples of sulfur-containing compounds include thiocarbamic acid, dithiocarbamic acid, thiocarbonates, dithiocarbonates (xanthogenic acid), trithiocarbonates, thiocarboxylic acids, dithiocarboxylic acids, and derivatives thereof. Among these, at least one selected from the group consisting of xanthogenic acid and its derivatives is preferred because it decomposes at relatively low temperatures. Specific examples of sulfur-containing compounds are the same as those described above. Specific examples of compounds having an In-S bond include indium trisdimethyldithiocarbamate, indium trisdiethyldithiocarbamate (In(DDTC)), indium chlorobisdiethyldithiocarbamate, and indium ethylxanthogenate (In(EX)).

[0085] The third mixture includes a compound having a Ga-S bond. The Ga-S bond may be a covalent bond, an ionic bond, a coordinate bond, or the like. Examples of compounds having a Ga-S bond include Ga salts of sulfur-containing compounds, which may be organic acid salts of Ga, inorganic acid salts of Ga, organometallic compounds, and the like. Specific examples of sulfur-containing compounds include thiocarbamic acid, dithiocarbamic acid, thiocarbonates, dithiocarbonates (xanthogenic acid), trithiocarbonates, thiocarboxylic acids, dithiocarboxylic acids, and derivatives thereof. Among these, at least one selected from the group consisting of xanthogenic acid and its derivatives is preferred because it decomposes at relatively low temperatures. Specific examples of sulfur-containing compounds include aliphatic thiocarbamic acid, aliphatic dithiocarbamic acid, aliphatic thiocarbonates, aliphatic dithiocarbonates, aliphatic trithiocarbonates, aliphatic thiocarboxylic acids, and aliphatic dithiocarboxylic acids. Examples of aliphatic groups in these sulfur-containing compounds include alkyl groups and alkenyl groups having 1 to 12 carbon atoms. The aliphatic thiocarbamic acid may include a dialkylthiocarbamic acid, and the aliphatic dithiocarbamic acid may include a dialkyldithiocarbamic acid. The alkyl group in the dialkylthiocarbamic acid and the dialkyldithiocarbamic acid may have, for example, 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms. The two alkyl groups in the dialkylthiocarbamic acid and the dialkyldithiocarbamic acid may be the same or different. Specific examples of the compound having a Ga-S bond include gallium trisdimethyldithiocarbamate, gallium trisdiethyldithiocarbamate (Ga(DDTC)3), gallium chlorobisdiethyldithiocarbamate, and gallium ethylxanthogenate (Ga(EX)3). The third mixture may contain one compound having a Ga-S bond alone, or two or more compounds in combination.

[0086] The gallium halide in the third mixture may include gallium fluoride, gallium chloride, gallium bromide, gallium iodide, etc., and may contain at least one selected from the group consisting of these. The gallium halide may also contain at least gallium chloride. When the gallium halide contains gallium chloride, the gallium chloride content in the gallium halide may be, for example, 70 mol% or more, preferably 90 mol% or more, or 95 mol% or more, and preferably 100 mol% or less, or less than 100 mol%. The gallium halide may be used alone or in combination of two or more.

[0087] The third mixture may contain an organic solvent. Examples of organic solvents in the third mixture include amines having a hydrocarbon group containing 4 to 20 carbon atoms, such as alkylamines or alkenylamines having 4 to 20 carbon atoms, thiols having a hydrocarbon group containing 4 to 20 carbon atoms, such as alkylthiols or alkenylthiols having 4 to 20 carbon atoms, and phosphines having a hydrocarbon group containing 4 to 20 carbon atoms, such as alkylphosphines or alkenylphosphines having 4 to 20 carbon atoms. It is preferable to include at least one selected from the group consisting of these organic solvents. These organic solvents may ultimately be used to modify the surface of the resulting first semiconductor nanoparticles. Two or more organic solvents may be used in combination. For example, a mixed solvent may be used that combines at least one thiol having a hydrocarbon group containing 4 to 20 carbon atoms with at least one amine having a hydrocarbon group containing 4 to 20 carbon atoms. These organic solvents may be used in combination with other organic solvents. When the organic solvent contains the thiol and the amine, the volume ratio of the thiol to the amine (thiol / amine) is, for example, greater than 0 and equal to or less than 1, and preferably equal to or greater than 0.007 and equal to or less than 0.2.

[0088] The ratios of Ag, In, Ga, and S in the third mixture may be appropriately selected depending on the desired composition. In this case, the ratios of Ag, In, Ga, and S do not have to be stoichiometric. For example, the ratio of the number of moles of Ga to the total number of moles of In and Ga (Ga / (In+Ga)) may be 0.2 to 0.95, 0.4 to 0.9, or 0.6 to 0.9. For example, the ratio of the number of moles of Ag to the total number of moles of Ag, In, and Ga (Ag / (Ag+In+Ga)) may be 0.05 to 0.55. For example, the ratio of the number of moles of S to the total number of moles of Ag, In, and Ga (S / (Ag+In+Ga)) may be 0.6 to 1.6.

[0089] The third mixture may further contain an alkali metal salt. a Examples of alkali metal salts include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), with Li being preferred since its ionic radius is similar to that of Ag. Examples of alkali metal salts include organic acid salts and inorganic acid salts. Specific examples of inorganic acid salts include nitrates, sulfates, hydrochlorides, and sulfonates, while examples of organic acid salts include acetates and acetylacetonates. Of these, organic acid salts are preferred because of their high solubility in organic solvents.

[0090] If the third mixture contains an alkali metal salt, the ratio of the number of alkali metal atoms to the total number of Ag and alkali metal atoms (M a / (Ag+M a )) may be, for example, less than 1, preferably 0.8 or less, more preferably 0.4 or less, and even more preferably 0.2 or less. The ratio may be, for example, greater than 0, preferably 0.05 or more, and more preferably 0.1 or more.

[0091] The molar ratio of the content of the gallium halide to the Ag salt in the third mixture may be, for example, 0.01 or more and 1 or less, and from the viewpoint of the internal quantum yield, may be preferably 0.12 or more and 0.45 or less.

[0092] The concentration of the Ag salt in the third mixture may be, for example, 0.01 mmol / L or more and 500 mmol / L or less, and from the viewpoint of the internal quantum yield, may be preferably 0.05 mmol / L or more and 100 mmol / L or less, and more preferably 0.1 mmol / L or more and 50 mmol / L or less.

[0093] In the heat treatment step, the third mixture is heat-treated to obtain semiconductor nanoparticles. The heat treatment temperature may be, for example, 200°C or higher and 340°C or lower. The heat treatment step may include a temperature increase step in which the third mixture is heated to a temperature in the range of 200°C or higher and 340°C or lower, and a synthesis step in which the third mixture is heat-treated at a temperature in the range of 200°C or higher and 340°C or lower for a predetermined time.

[0094] The temperature range in the temperature increasing step of the heat treatment step may be 200° C. or higher and 340° C. or lower, and preferably 230° C. or higher and 320° C. or lower. The temperature increasing rate may be adjusted so that the maximum temperature during the temperature increase does not exceed the target temperature, and is, for example, 1° C. / min. or higher and 50° C. / min. or lower.

[0095] The heat treatment temperature in the synthesis step of the heat treatment step may be 200°C or higher and 340°C or lower, and preferably 230°C or higher and 320°C or lower. The heat treatment time in the synthesis step may be, for example, 3 seconds or longer, and preferably 1 minute or longer, 10 minutes or longer, 30 minutes or longer, 60 minutes or longer, or 90 minutes or longer. The heat treatment time may be, for example, 300 minutes or shorter, and preferably 180 minutes or shorter, or 150 minutes or shorter. The heat treatment time in the synthesis step starts when the temperature set in the above-mentioned temperature range is reached (for example, when set to 250°C, the time when 250°C is reached), and ends when the temperature-lowering operation is performed. A dispersion containing first semiconductor nanoparticles can be obtained by the synthesis step.

[0096] The heat treatment step is preferably performed in an inert gas atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the production of oxide by-products and the oxidation of the surfaces of the resulting first semiconductor nanoparticles.

[0097] The method for producing first semiconductor nanoparticles may further include, following the synthesis step, a cooling step of lowering the temperature of the resulting dispersion containing the first semiconductor nanoparticles. The cooling step begins when the temperature-lowering operation is performed and ends when the dispersion has cooled to 50°C or below.

[0098] The cooling step may include a period during which the temperature is lowered at a rate of 50°C / min or more in order to suppress the generation of silver sulfide from unreacted Ag salts. In particular, the rate may be 50°C / min or more at the start of the temperature lowering operation after the temperature lowering operation has been performed.

[0099] The cooling step is preferably performed in an inert gas atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the production of oxide by-products and the oxidation of the surfaces of the resulting first semiconductor nanoparticles.

[0100] The method for producing the first semiconductor nanoparticles may further include a separation step of separating the first semiconductor nanoparticles from the dispersion liquid, a purification step, etc. Details of the separation step and purification step are as described above.

[0101] The first semiconductor nanoparticles obtained as described above may be in the form of a dispersion or a dried powder. The first semiconductor nanoparticles exhibit band-edge emission and can exhibit high band-edge emission purity. The first semiconductor nanoparticles may be the semiconductor nanoparticles obtained in the third step described above, or may be the semiconductor nanoparticles obtained after the fourth step described below.

[0102] The fourth step may include a mixing step of obtaining a fourth mixture containing the semiconductor nanoparticles obtained in the third step described above and a gallium halide, and a heat treatment step of heat treating the obtained fourth mixture to obtain semiconductor nanoparticles.

[0103] By heat-treating the fourth mixture containing the first semiconductor nanoparticles and a gallium halide, it is possible to produce first semiconductor nanoparticles with improved band-edge emission purity and internal quantum yield.

[0104] In the mixing step, the first semiconductor nanoparticles and a gallium halide are mixed to obtain a fourth mixture. The fourth mixture may further contain an organic solvent. The organic solvent contained in the fourth mixture is the same as the organic solvent exemplified in the first step described above. When the fourth mixture contains an organic solvent, the concentration of the first semiconductor nanoparticles is, for example, 5.0 × 10 mol / L or more and 5.0 × 10 -5 mol / L or less, especially 1.0 x 10 -6 mol / L or more, 1.0 × 10 -5 The fourth mixture may be prepared so that the concentration of the first semiconductor nanoparticles is equal to or less than 1 mole / L, where the concentration is set based on the amount of substance as particles, as described above.

[0105] The details of the gallium halide in the fourth mixture are as described above. The molar ratio of the content of the gallium halide to the first semiconductor nanoparticles in the fourth mixture may be, for example, 0.01 or more and 50 or less, and preferably 0.1 or more and 10 or less.

[0106] The fourth mixture may further contain a sulfur source. The inclusion of a sulfur source can increase the quantum yield of band-edge emission and narrow the half-width of the emission spectrum. Examples of the sulfur source include elemental sulfur and sulfur-containing compounds. Examples of sulfur-containing compounds include alkylthiols having 4 to 18 carbon atoms, disulfide compounds, thiourea, thiocarbonyl compounds, thiocarbamic acid, dithiocarbamic acid, thiocarbonates, dithiocarbonates (xanthic acids), trithiocarbonates, thiocarboxylic acids, dithiocarboxylic acids, and derivatives thereof. The sulfur source in the fourth mixture may contain at least one selected from the group consisting of thiourea, thiourea derivatives, and compounds having a Ga-S bond. Examples of thiourea derivatives include alkylthioureas and dialkylthioureas. The alkyl group in the alkylthiourea may have, for example, 1 to 18 carbon atoms, preferably 1 to 4 carbon atoms. Specific examples of compounds having a Ga-S bond include gallium trisdimethyldithiocarbamate, gallium trisdiethyldithiocarbamate (Ga(DDTC)3), gallium chlorobisdiethyldithiocarbamate, and gallium ethylxanthogenate (Ga(EX)3).

[0107] When the fourth mixture contains a sulfur source, the molar ratio of sulfur contained in the sulfur source to the first semiconductor nanoparticles in the fourth mixture may be, for example, 0.01 or more and 50 or less, and preferably 0.1 or more and 10 or less.

[0108] In the heat treatment step, the fourth mixture is heat-treated to obtain semiconductor nanoparticles. The heat treatment temperature may be, for example, 200°C or higher and 320°C or lower. The heat treatment step may include a temperature increase step of increasing the temperature of the fourth mixture to a temperature in the range of 200°C or higher and 320°C or lower, and a modification step of heat-treating the fourth mixture at a temperature in the range of 200°C or higher and 320°C or lower for a predetermined time.

[0109] The heat treatment step may further include a preliminary heat treatment step of heat treating the fourth mixture at a temperature of 60° C. or higher and 100° C. or lower before the temperature increasing step. The heat treatment temperature in the preliminary heat treatment step may be, for example, 70° C. or higher and 90° C. or lower. The heat treatment time in the preliminary heat treatment step may be, for example, 1 minute or higher and 2 hours or lower, and preferably 5 minutes or higher or 1 hour or lower.

[0110] The temperature range in the temperature increase step of the heat treatment step may be 200° C. or higher and 320° C. or lower, and preferably 230° C. or higher and 290° C. or lower. The temperature increase rate may be adjusted so that the maximum temperature during the temperature increase does not exceed the target temperature, and may be, for example, 1° C. / min. or higher and 50° C. / min. or lower.

[0111] The heat treatment temperature in the modification step of the heat treatment process may be 200°C or higher and 320°C or lower, and preferably 230°C or higher and 290°C or lower. The heat treatment time in the modification step may be, for example, 3 seconds or longer, and preferably 1 minute or longer, 10 minutes or longer, 30 minutes or longer, 60 minutes or longer, or 90 minutes or longer. The heat treatment time may be, for example, 300 minutes or shorter, and preferably 180 minutes or shorter, or 150 minutes or shorter. The heat treatment time in the modification step starts when the temperature set in the above-mentioned temperature range is reached (for example, when the temperature is set to 250°C, the time when 250°C is reached), and ends when the temperature is lowered.

[0112] The heat treatment step is preferably performed in an inert gas atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the production of oxide by-products and the oxidation of the surfaces of the resulting semiconductor nanoparticles.

[0113] The fourth step may further include a cooling step of lowering the temperature of the resulting dispersion liquid containing semiconductor nanoparticles following the modification step, which starts when the temperature-lowering operation is performed and ends when the temperature has been cooled to 50°C or below.

[0114] The cooling step may include a period in which the temperature drop rate is 50°C / min or more. In particular, the temperature drop rate may be 50°C / min or more at the start of the temperature drop after the temperature drop operation has been performed.

[0115] The cooling step is preferably performed in an inert gas atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the production of oxide by-products and the oxidation of the surfaces of the resulting first semiconductor nanoparticles.

[0116] The invention according to the present disclosure may include, for example, the following aspects. [1] Semiconductor nanoparticles containing silver, indium, gallium, zinc, and sulfur in their composition, When the semiconductor nanoparticle is approximated as a sphere and divided into a first region from the center to a position at 79.4% of the radius and a second region from the center to the surface at a position at 79.4% of the radius, the ratio of the amount of zinc present in the first region to the amount of gallium present in the second region divided by the ratio of the amount of zinc present in the second region is greater than 1; Semiconductor nanoparticles that emit light when exposed to light.

[0117] [2] The semiconductor nanoparticles according to [1], wherein the ratio of the amount of indium present in the first region to the amount of gallium present in the second region divided by the ratio of the amount of indium present in the first region to the amount of gallium present in the second region is less than 1.

[0118] [3] The semiconductor nanoparticles according to [1] or [2], wherein the semiconductor nanoparticles have a peak emission wavelength in the range of 475 nm or more and 560 nm or less.

[0119] [4] The semiconductor nanoparticles according to any one of [1] to [3], wherein the half width of the emission spectrum is 40 nm or less.

[0120] [5] The semiconductor nanoparticles according to any one of [1] to [4], wherein the semiconductor nanoparticles have an internal quantum efficiency of 40% or more.

[0121] [6] The semiconductor nanoparticles according to any one of [1] to [5], each of which has a first semiconductor portion containing silver, indium, gallium, and sulfur in its composition, and a second semiconductor portion disposed on the surface of the first semiconductor portion and containing zinc and sulfur in its composition.

[0122] [7] The semiconductor nanoparticle according to [6], wherein the second semiconductor portion has an average thickness of more than 0 nm and not more than 5 nm.

[0123] [8] Preparing first semiconductor nanoparticles containing silver, indium, gallium, and sulfur; and heat-treating a mixture containing the first semiconductor nanoparticles, a zinc source, and a sulfur source at a first temperature of 180°C or higher and 250°C or lower to obtain second semiconductor nanoparticles.

[0124] [9] The method according to [8], wherein the zinc source comprises at least one selected from the group consisting of zinc halide, zinc alkylxanthate, zinc dialkyldithiocarbamate, and zinc carboxylate.

[0125]

[10] The method according to [8] or [9], wherein the sulfur source comprises at least one selected from the group consisting of zinc alkylxanthogenate, zinc dialkyldithiocarbamate, thiourea and its derivatives, tetraalkylthiuram disulfide, and elemental sulfur. [Example]

[0126] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0127] Example 1 Synthesis of AIGS semiconductor nanoparticles A mixture was obtained by mixing 0.340 mmol of silver ethylxanthate (Ag(EX)), 0.357 mmol of indium acetate (In(OAc)3), 0.680 mmol of gallium ethylxanthate (Ga(EX)3), and 0.051 mmol of gallium chloride with 20 mL of oleylamine (OLA). The mixture was then heat-treated at 310°C for 120 minutes under a nitrogen atmosphere while stirring. The resulting suspension was allowed to cool, yielding dispersion 1 containing AIGS semiconductor nanoparticles.

[0128] Separation process The dispersion 1 containing AIGS semiconductor nanoparticles obtained in the above step was centrifuged (radius 146 mm, 3800 rpm, 5 minutes), and the supernatant was removed to obtain a precipitate, which was then mixed with 5 mL of chloroform. The mixture was centrifuged (radius 146 mm, 3800 rpm, 5 minutes), and the supernatant was recovered. Another 5 mL of chloroform was added to the remaining precipitate, and the mixture was centrifuged (radius 146 mm, 3800 rpm, 5 minutes), and the supernatant was recovered. Next, 11 mL of methanol was added to the chloroform solution of the recovered supernatant and mixed. The mixture was centrifuged (radius 146 mm, 3800 rpm, 5 minutes), and precipitate 1 containing AIGS semiconductor nanoparticles was obtained.

[0129] Gallium chloride treatment The precipitate 1 containing AIGS semiconductor nanoparticles obtained in the separation step was mixed with 1.020 mmol of gallium chloride, 1.020 mmol of 1,3-dimethylthiourea, and 20 mL of oleylamine (OLA). The mixture was heat-treated at 270°C for 120 minutes while stirring under a nitrogen atmosphere. The resulting suspension was allowed to cool, yielding dispersion 2 containing AIGS semiconductor nanoparticles.

[0130] ZnS treatment Dispersion 2 containing AIGS semiconductor nanoparticles obtained in the gallium chloride treatment step was mixed with 0.255 mmol of zinc ethylxanthate (Zn(EX)2) and 0.765 mmol of zinc iodide. The mixture was heat-treated at 200°C for 120 minutes while stirring under a nitrogen atmosphere. The resulting suspension was allowed to cool, yielding Dispersion 3 containing AIGS semiconductor nanoparticles.

[0131] Comparative Example 1 Dispersion 2 containing AIGS semiconductor nanoparticles was obtained in the same manner as in Example 1, except that the steps up to the gallium chloride treatment step were carried out but the ZnS treatment step was not carried out.

[0132] Measurement of the emission spectrum of semiconductor nanoparticles The emission spectrum of the semiconductor nanoparticles obtained above was measured, and the band-edge emission peak wavelength, half-width, and internal quantum yield were calculated. The emission spectrum was measured at room temperature (25°C) using a quantum efficiency measurement system (Otsuka Electronics, product name QE-2100) with an excitation light wavelength of 450 nm and in the wavelength range from 300 nm to 950 nm. The internal quantum yield was calculated from the wavelength range from 475 nm to 800 nm. The results are shown in Table 1 and Figure 2.

[0133] Lightfastness Test The heat-treated material was dispersed in chloroform so that the absorbance at 450 nm was 0.150 (path length 1 cm) to prepare a sample for light resistance testing. This sample was irradiated with light at 450 nm at room temperature. The internal quantum efficiency was measured before and after light irradiation, and the internal quantum efficiency retention rate was calculated. The results are shown in Figure 3, and the internal quantum efficiency retention rate after 48 hours of irradiation is shown in Table 1.

[0134] [Table 1]

[0135] Table 1 and Figure 2 show that ZnS treatment does not result in any change in the luminescence properties. Furthermore, Table 1 and Figure 3 show that ZnS treatment can reduce the degradation of semiconductor nanoparticles due to light irradiation. This demonstrates that this method can improve the light resistance of AIGS semiconductor nanoparticles without deteriorating their luminescence properties. [Explanation of symbols]

[0136] 10 First area 20 Second area 100 Semiconductor Nanoparticles 102 center 104 outer edge

Claims

1. The semiconductor nanoparticles contain silver, indium, gallium, zinc, and sulfur in their composition, When the semiconductor nanoparticle is approximated as a sphere and divided into a first region from the center to a position at 79.4% of the radius and a second region from the center to the surface, a ratio of the amount of zinc present in the first region to the amount of gallium present in the second region divided by a ratio of the amount of zinc present in the second region to the amount of gallium present is greater than 1; Semiconductor nanoparticles that emit light when exposed to light.

2. 2. The semiconductor nanoparticle according to claim 1, wherein the ratio of the amount of indium present in the first region to the amount of gallium present in the second region divided by the ratio of the amount of indium present in the first region to the amount of gallium present in the second region is less than 1.

3. The semiconductor nanoparticles according to claim 1 or 2, wherein the semiconductor nanoparticles have a peak emission wavelength in the range of 475 nm to 560 nm.

4. 3. The semiconductor nanoparticles according to claim 1, wherein the half width of the emission spectrum of the semiconductor nanoparticles is 40 nm or less.

5. The semiconductor nanoparticles according to claim 1 or 2, wherein the semiconductor nanoparticles have an internal quantum efficiency of 40% or more.

6. The semiconductor nanoparticle according to claim 1 or 2, wherein the semiconductor nanoparticle has a first semiconductor portion containing silver, indium, gallium, and sulfur in its composition, and a second semiconductor portion disposed on the surface of the first semiconductor portion and containing zinc and sulfur in its composition.

7. The semiconductor nanoparticle according to claim 6 , wherein the second semiconductor portion has an average thickness of more than 0 nm and not more than 5 nm.

8. providing first semiconductor nanoparticles having a composition comprising silver, indium, gallium, and sulfur; and heat-treating a mixture containing the first semiconductor nanoparticles, a zinc source, and a sulfur source at a first temperature of 180°C or higher and 250°C or lower to obtain second semiconductor nanoparticles.

9. 9. The method according to claim 8, wherein the zinc source comprises at least one selected from the group consisting of zinc halide, zinc alkylxanthate, zinc dialkyldithiocarbamate, and zinc carboxylate.

10. 9. The method according to claim 8, wherein the sulfur source comprises at least one selected from the group consisting of zinc alkylxanthogenate, zinc dialkyldithiocarbamate, thiourea and its derivatives, tetraalkylthiuram disulfide, and elemental sulfur.

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