Light-emitting material and method for producing the same

Abstract

The present invention provides a light emitting material having excellent durability. This light emitting material comprises second semiconductor nanoparticles, which comprise first semiconductor nanoparticles and an adhesive substance disposed on the surface of the first semiconductor nanoparticles and which emit light when irradiated with light, and a metal compound in which the second semiconductor nanoparticles are embedded. The first semiconductor nanoparticles contain M1, M2 and Z. M1 comprises at least one member selected from the group consisting of Ag, Cu, Au and alkali metals and Ag is necessarily contained therein. M2 comprises at least one member selected from the group consisting of Al, Ga, In and Tl and In and / or Ga are necessarily contained therein. Z comprises at least one member selected from the group consisting of S, Se and Te. The adhesive substance comprises a semiconductor which substantially comprises at least one member selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one member selected from the group consisting of S, O, Se and Te. The metal compound comprises Zn and / or Ga, together with S and / or O.

Description

[Technical Field]

[0001] The present disclosure relates to light-emitting materials and methods for making the same. [Background technology]

[0002] Core-shell semiconductor nanoparticles are characterized by high luminescence efficiency and a narrow half-width of the emission spectrum. Furthermore, by varying their particle size, the emitted color can be controlled over a wide wavelength range. These properties make them excellent for use in highly efficient, high-color-rendering lighting and wide-color-gamut displays. For these reasons, core-shell semiconductor nanoparticles are attracting attention as next-generation light-emitting materials. However, due to the high surface area-to-volume ratio of core-shell semiconductor nanoparticles, they have low chemical stability and are particularly susceptible to degradation by water, oxygen, etc. Therefore, methods for imparting barrier properties to nanoparticles are being investigated.

[0003] For example, WO 2013 / 041864 discloses a light-emitting device comprising luminescent particles in which semiconductor nanoparticles are embedded in a polymeric encapsulation medium, and a light-emitting layer in which the luminescent particles are embedded in a host matrix material. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to provide a light-emitting material with excellent durability. [Means for solving the problem]

[0005] The first aspect is a light-emitting material comprising second semiconductor nanoparticles (hereinafter also referred to as "core-shell type semiconductor nanoparticles") that contain first semiconductor nanoparticles (hereinafter also referred to as "core") and an attachment (hereinafter also referred to as "shell") disposed on the surface of the core and emit light upon irradiation with light, and a metal compound that embeds the core-shell type semiconductor nanoparticles. 1 , M 2 and Z. M 1is at least one selected from the group consisting of silver (Ag), copper (Cu), gold (Au) and alkali metals, and contains at least Ag. 2 is at least one selected from the group consisting of aluminum (Al), gallium (Ga), indium (In) and thallium (Tl), and includes at least one of In and Ga. Z includes at least one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te). The core is M 1 The total content of M is 10 mol % or more and 30 mol % or less, 2 The total content of is 15 mol% or more and 35 mol% or less, and the total content of Z is 35 mol% or more and 55 mol% or less. The shell substantially contains a semiconductor consisting of at least one selected from the group consisting of aluminum (Al), gallium (Ga), indium (In), thallium (Tl), and alkali metals, and at least one selected from the group consisting of sulfur (S), oxygen (O), selenium (Se), and tellurium (Te). The metal compound contains at least one of zinc (Zn) and gallium (Ga), and at least one of sulfur (S) and oxygen (O).

[0006] The second aspect is a method for producing a light-emitting material, which includes: preparing core-shell semiconductor nanoparticles that contain a core and a shell disposed on the surface of the core and that emit light when irradiated with light; obtaining a mixture containing the core-shell semiconductor nanoparticles, a compound containing at least one of Zn and Ga, a compound containing at least one of S and O, and a solvent; and obtaining from the mixture a metal compound that contains at least one of Zn and Ga and at least one of S and O and that embeds the core-shell semiconductor nanoparticles. 1 , M 2 and Z. M 1 is at least one selected from the group consisting of Ag, Cu, Au and alkali metals, and contains at least Ag. 2 is at least one selected from the group consisting of Al, Ga, In and Tl, and includes at least one of In and Ga. Z includes at least one selected from the group consisting of S, Se and Te. The core is M 1The total content of M is 10 mol % or more and 30 mol % or less, 2 The total content of is 15 mol% or more and 35 mol% or less, and the total content of Z is 35 mol% or more and 55 mol% or less. The shell essentially consists of at least one selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one selected from the group consisting of S, O, Se and Te. [Effects of the Invention]

[0007] According to one embodiment of the present invention, a light-emitting material with excellent durability can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a light-emitting material containing a metal compound that embeds core-shell semiconductor nanoparticles. [Figure 2] FIG. 1 is a schematic cross-sectional view showing an example of a light-emitting device. [Figure 3] FIG. 10 is a schematic cross-sectional view showing another example of the light emitting device. [Figure 4] FIG. 10 is a schematic cross-sectional view showing another example of the light emitting device. [Figure 5] 1 shows the emission spectrum of the light-emitting material according to Example 1. [Figure 6] 1 shows an emission spectrum of a light-emitting material according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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. Below, embodiments of the present invention are described in detail. However, the embodiments described below are merely illustrative of luminescent materials and methods for producing the same, embodying the technical concept of the present invention. The present invention is not limited to the luminescent materials and methods for producing the same. The components described in the claims are in no way limited to the components of the embodiments. The dimensions, materials, shapes, relative positions, etc. of the components described in the embodiments are not intended to limit the scope of the present invention, unless otherwise specified. These are merely illustrative examples.

[0010] luminescent materials The luminescent material includes second semiconductor nanoparticles and a metal compound that embeds the second semiconductor nanoparticles. The second semiconductor nanoparticles include first semiconductor nanoparticles and an attachment disposed on the surface of the first semiconductor nanoparticles. The attachment may cover the surface of the first semiconductor nanoparticles. Therefore, surface analysis of the second semiconductor nanoparticles may not detect elements that can only be contained in the first semiconductor nanoparticles (e.g., Ag). Hereinafter, for convenience, in this specification, the first semiconductor nanoparticles will be referred to as the core, the attachment as the shell, and the second semiconductor nanoparticles as core-shell type semiconductor nanoparticles.

[0011] The light-emitting material includes core-shell semiconductor nanoparticles that contain a core and a shell disposed on the surface of the core and emit light when irradiated with light, and a metal compound that embeds the core-shell semiconductor nanoparticles. 1 , M 2 and Z, where M 1 is at least one selected from the group consisting of Ag, Cu, Au and alkali metals, and may contain at least Ag. 2is at least one selected from the group consisting of Al, Ga, In and Tl, and may contain at least one of In and Ga. Z may contain at least one selected from the group consisting of S, Se and Te. The core is M 1 The total content of M is 10 mol % or more and 30 mol % or less, 2 The core-shell semiconductor nanoparticles may have a composition in which the total content of is 15 mol % or more and 35 mol % or less, and the total content of Z is 35 mol % or more and 55 mol % or less. The shell may essentially contain a semiconductor consisting of at least one selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one selected from the group consisting of S, O, Se and Te. The metal compound that embeds the core-shell semiconductor nanoparticles may contain at least one of Zn and Ga, and at least one of S and O.

[0012] When the luminescent material is composed of core-shell semiconductor nanoparticles having a specific structure and a specific metal compound that embeds the nanoparticles, the durability of the luminescent material is improved and deterioration of the luminescent properties of the luminescent material caused by water, oxygen, etc. in the environment is suppressed. The metal compound is thought to function, for example, as a matrix that embeds the core-shell semiconductor nanoparticles.

[0013] The core-shell semiconductor nanoparticles are at least partially embedded in a metal compound to form a light-emitting material, in which a plurality of particles may be embedded in the metal compound in an aggregated state, or individual particles may be embedded independently in the metal compound.

[0014] Here, examples of the configuration of luminescent materials will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of the luminescent material 1. The luminescent material 1 is composed of core-shell semiconductor nanoparticles 2 and a metal compound 3 in which the core-shell semiconductor nanoparticles 2 are embedded. In FIG. 1, the core-shell semiconductor nanoparticles 2 are embedded as individual particles or aggregated particles in the metal compound 3, which serves as a matrix. Some of the core-shell semiconductor nanoparticles 2 may be partially exposed from the surface of the metal compound 3. For simplicity of explanation, the core-shell semiconductor nanoparticles 2 are depicted as spherical in FIG. 1, but the shape of the core-shell semiconductor nanoparticles is not limited to a spherical shape. Furthermore, in FIG. 1, the metal compound 3 is depicted as cubic, but the shape of the metal compound 3 is not limited to a cubic shape.

[0015] Core-shell semiconductor nanoparticles Core-shell semiconductor nanoparticles are 1 , M 2 and Z, and a shell comprising a semiconductor essentially consisting of at least one selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one selected from the group consisting of S, O, Se and Te. 1 is at least one selected from the group consisting of Ag, Cu, Au and alkali metals, and may contain at least Ag. 2 is at least one selected from the group consisting of Al, Ga, In and Tl, and may contain at least one of In and Ga. Z may contain at least one selected from the group consisting of S, Se and Te. M when the core composition is 1 mol 1 The total content of M in the core composition may be, for example, 10 mol % or more and 30 mol % or less, and preferably 15 mol % or more and 25 mol % or less. 2 The total content of Z in the core composition may be, for example, from 15 mol% to 35 mol%, and preferably from 20 mol% to 30 mol%. The total content of Z in the core composition may be, for example, from 35 mol% to 55 mol%, and preferably from 40 mol% to 55 mol%.

[0016] The core composition is M1 M relative to the total number of atoms 2 The ratio of the total number of atoms (M 2 / M 1 ) is, for example, 0.5 or more and 10 or less, preferably 0.8 or more and 5 or less, and more preferably 0.9 or more and 2 or less. The composition of the core is 1 The ratio of the total number of atoms of Z to the total number of atoms of M (Z / M 1 ) is, for example, 1 or more and 10 or less, preferably 1.5 or more and 8 or less, and more preferably 2 or more and 3 or less. The core may be, for example, a compound represented by the composition formula: M 1 M 2 It may have a composition represented by Z2.

[0017] Semiconductor nanoparticles containing Ag, In, and S and having a tetragonal, hexagonal, or orthorhombic crystal structure are generally introduced in literature as those having the composition formula AgInS2. However, in reality, they do not have the stoichiometric composition represented by the above composition formula, and in particular M 1 M for the number of atoms 2 The ratio of the number of atoms (M 2 / M 1 ) may be smaller than 1, or may be larger than 1. Also, M 1 and M 2 The sum of the number of atoms in M may not be the same as the number of atoms in Z. Therefore, in this specification, when a semiconductor containing a specific element is used, it is not important whether it is a stoichiometric composition or not. 1 -M 2 The composition can sometimes be expressed as a formula in which the constituent elements are connected with "-", such as -Z.

[0018] Semiconductors containing the above elements that have a hexagonal crystal structure are called wurtzite-type, and semiconductors that have a tetragonal crystal structure are called chalcopyrite-type. 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 semiconductor nanoparticles is compared with a known XRD pattern for a semiconductor with a composition of AgInS2, or an XRD pattern obtained by simulation using crystal structure parameters. If any of the known and simulated patterns matches the pattern of the semiconductor contained in the core, the crystal structure of the core can be said to be the crystal structure of the corresponding known or simulated pattern.

[0019] In the aggregate of core semiconductor nanoparticles, semiconductor nanoparticles of different crystal structures, such as tetragonal, hexagonal, and orthorhombic, may be present. In this case, peaks derived from multiple crystal structures are observed in the XRD pattern. Since core-shell semiconductor nanoparticles are substantially composed of tetragonal crystals, peaks corresponding to tetragonal crystals are observed, and peaks derived from other crystal structures are not substantially observed.

[0020] M 1 M contains at least Ag, and may further contain at least one element selected from the group consisting of Cu, Au and alkali metals. 1 may be substantially composed of Ag, may be substantially composed of Ag and Cu, or may be substantially composed of Ag and alkali metal. Here, "substantially" means that the ratio of elements other than Ag, Cu and alkali metal to the total amount of Ag, Cu and alkali metal is, for example, 10 mol % or less, preferably 5 mol % or less, and more preferably 1 mol % or less. Here, M 1 The alkali metals included in the ion exchange reaction include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

[0021] M 1When Ag and Cu are contained, the ratio of the number of Cu atoms to the total number of Ag and Cu atoms (Cu / (Ag+Cu)) 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. Also, the ratio is, for example, greater than 0, preferably 0.05 or more, and more preferably 0.1 or more. 1 However, Ag and alkali metals (hereinafter referred to as M a When the silver and alkali metals (M a ) relative to the total number of atoms of alkali metals (M a ) atomic number ratio (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 is, for example, greater than 0, preferably 0.05 or more, and more preferably 0.1 or more.

[0022] M 2 contains at least one of In and Ga, and may further contain at least one selected from the group consisting of Al and Tl. 2 is preferably substantially composed of at least one of In and Ga. Here, "substantially" means that the ratio of elements other than In and Ga to the total of In and Ga is, for example, 10 mol % or less, preferably 5 mol % or less, and more preferably 1 mol % or less.

[0023] M 2 When the material contains at least one of In and Ga, the ratio of the number of Ga atoms to the total number of In and Ga atoms (Ga / (Ga+In)) may be, for example, 0.95 or less, and preferably 0.2 or more and 0.9 or less.

[0024] Z includes at least one element selected from the group consisting of S, Se, and Te. Z includes at least S, and may be partially substituted with at least one of Se and Te. Z is preferably substantially composed of S, Se, or Te. Here, "substantially" indicates that the ratio of elements other than Z to Z is, for example, 10 mol % or less, preferably 5 mol % or less, and more preferably 1 mol % or less.

[0025] M 1 , M 2 and Z combination (M 1 / M 2 Examples of / Z) include Cu / In / S, Ag / In / S, Ag / (In,Ga) / S, Ag / In / Se, Ag / (In,Ga) / Se, Ag / In / Te, Ag / (In,Ga) / Te, Ag / Ga / S, Ag / Ga / Se, Ag / Ga / Te, and the like.

[0026] The semiconductor contained in the core may be substantially composed of Ag, Cu, alkali metals, In, Ga, S, and elements partially substituted therewith. Here, the term "substantially" is used in consideration of the fact that elements other than Ag, Cu, alkali metals, In, Ga, S, and elements partially substituted therewith are inevitably included due to the inclusion of impurities, etc.

[0027] The core may have an average particle size of, for example, 10 nm or less, particularly 8 nm or less. The average particle size of the semiconductor nanoparticles may be in the range of 1.5 nm to 10 nm, particularly 1.7 nm to 7.5 nm. When the average particle size of the semiconductor nanoparticles is equal to or less than the upper limit, it is easy to obtain a quantum size effect.

[0028] The average particle size of semiconductor nanoparticles may be determined, for example, from a transmission electron microscope (TEM) image. Specifically, the particle size of semiconductor nanoparticles refers to the longest line segment that connects any two points on the periphery of a particle observed in a TEM image and exists within the particle.

[0029] The average particle size of semiconductor nanoparticles is determined by measuring the particle size of all measurable particles observed in a TEM image at magnifications of 50,000x to 150,000x and then calculating the arithmetic mean of those particle sizes. Here, "measurable" particles are those whose entire outline can be observed in a TEM image. Therefore, particles whose outline is "broken" and whose outline is not partly included in the imaging range in a TEM image are not measurable. If the number of measurable particles in a single TEM image is 100 or more, that TEM image is used to determine the average particle size. On the other hand, if the number of measurable particles in a single TEM image is less than 100, the imaging location is changed, additional TEM images are acquired, and the particle sizes of the 100 or more measurable particles in two or more TEM images are measured to determine the average particle size.

[0030] The shell may be composed of a semiconductor having a larger bandgap energy than the semiconductor constituting the core, and including at least one selected from the group consisting of a Group 13 element and an alkali metal, and a Group 16 element. The shell may be composed essentially of a semiconductor consisting of at least one selected from the group consisting of Al, Ga, In, Tl, and an alkali metal, and at least one selected from the group consisting of S, O, Se, and Te. Here, "substantially" means that, when the total number of atoms of all elements contained in the shell is taken as 100%, the proportion of atoms of elements other than Al, Ga, In, Tl, alkali metal, S, O, Se, and Te is, for example, 10% or less, preferably 5% or less, and more preferably 1% or less.

[0031] The shell may be configured by selecting its composition, etc., depending on the band gap energy of the semiconductor constituting the core. Alternatively, if the composition, etc., of the shell is determined first, the core may be designed so that the band gap energy of the semiconductor constituting the core is smaller than that of the shell. Generally, semiconductors made of Ag—In—S have a band gap energy of 1.8 eV or more and 1.9 eV or less.

[0032] Specifically, the semiconductor constituting the shell 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 shell may be greater than that of the core 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. If the difference between the band gap energy of the semiconductor constituting the shell and the band gap energy of the semiconductor constituting the core is equal to or greater than the lower limit, the proportion of emission other than band edge emission in the light emission from the core tends to decrease, and the proportion of band edge emission tends to increase.

[0033] Furthermore, the band gap energies of the semiconductors constituting the core and shell are preferably selected so as to provide type-I band alignment at the heterojunction between the core and shell, in which the band gap energy of the shell sandwiches the band gap energy of the core. Forming type-I band alignment allows for better band edge emission from the core. In type-I alignment, a barrier of at least 0.1 eV is preferably formed between the band gap of the core and the band gap of the shell, and may be, for example, 0.2 eV or more, or 0.3 eV or more. The upper limit of the barrier is, for example, 1.8 eV or less, particularly 1.1 eV or less. If the barrier is equal to or greater than the lower limit, the proportion of emission other than band edge emission in the emission from the core tends to decrease, and the proportion of band edge emission tends to increase.

[0034] The semiconductor constituting the shell may contain In or Ga as a Group 13 element. The shell may also contain S as a Group 16 element. Semiconductors containing In or Ga or containing S tend to be semiconductors with a larger band gap energy than the core. Furthermore, the semiconductor constituting the shell may contain oxygen (O). Semiconductors containing In or Ga, S, and O tend to be semiconductors with a larger band gap energy than the core.

[0035] The shell may have a semiconductor crystal system that is similar to that of the core semiconductor, and its lattice constant may be the same as or close to that of the core semiconductor. A shell made of a semiconductor with a similar crystal system and a similar lattice constant (here, a shell whose lattice constant multiples are close to that of the core is also considered to be close) may effectively cover the core. For example, the core described above is generally tetragonal, and examples of similar crystal systems include tetragonal and orthorhombic. When Ag-In-S is tetragonal, the lattice constants are 0.5828 nm, 0.5828 nm, and 1.119 nm, respectively. The shell that covers it is preferably tetragonal or cubic, and its lattice constant or a multiple thereof is close to that of Ag-In-S. Alternatively, the shell may be amorphous.

[0036] Whether or not an amorphous shell is formed can be confirmed by observing semiconductor nanoparticles with a core-shell structure using HAADF-STEM. When an amorphous shell is formed, specifically, a portion having a regular pattern (e.g., a striped or dotted pattern) is observed in the center, and a portion not observed as having a regular pattern is observed around it using HAADF-STEM. With HAADF-STEM, substances with a regular structure, such as crystalline substances, are observed as having a regular pattern, while substances without a regular structure, such as amorphous substances, are not observed as having a regular pattern. Therefore, if the shell is amorphous, the shell can be observed as a clearly different portion from the core (which may have a tetragonal or other crystalline structure, as described above), which is observed as having a regular pattern.

[0037] Furthermore, when the shell is made of Ga-S, Ga is a lighter element than the Ag, In, etc. contained in the core, so the shell tends to be observed as a darker image than the core in HAADF-STEM images.

[0038] Whether or not an amorphous shell is formed can also be confirmed by observing core-shell semiconductor nanoparticles with a high-resolution transmission electron microscope (HRTEM). In the images obtained with HRTEM, the core portion is observed as a crystal lattice image (an image with a regular pattern), while the shell portion is not observed as a crystal lattice image; a black-and-white contrast is observed, but the regular pattern is not visible.

[0039] On the other hand, it is preferable that the shell does not form a solid solution with the core. If the shell and core form a solid solution, the two become integrated, and band-edge emission may not be obtained. For example, it has been confirmed that band-edge emission from the core cannot be obtained even when the surface of a core made of Ag-In-S is covered with zinc sulfide (Zn-S) of stoichiometric or non-stoichiometric composition. Zn-S satisfies the above conditions regarding band gap energy with respect to Ag-In-S, providing type-I band alignment. Despite this, band-edge emission was not obtained from core-shell semiconductor nanoparticles. This is presumably because the core semiconductor and Zn-S form a solid solution, eliminating the core-shell interface.

[0040] The shell may contain, but is not limited to, a combination of In and S, a combination of Ga and S, or a combination of In, Ga, and S as a combination of Group 13 and Group 16 elements. The combination of In and S may be in the form of indium sulfide, and the combination of Ga and S may be in the form of gallium sulfide, and the combination of In, Ga, and S may be indium gallium sulfide. The indium sulfide constituting the shell does not have to be of stoichiometric composition (In2S3), and in this sense, indium sulfide is referred to herein as having the formula InS x (x is not limited to an integer and may be any number, for example, 0.8 to 1.5.) Similarly, gallium sulfide does not have to have a stoichiometric composition (Ga2S3), and in this sense, gallium sulfide is herein referred to as having the formula GaS x(x is not limited to an integer, but may be any number, for example, 0.8 to 1.5). Indium gallium sulfide is In 2(1-y) Ga 2y S3 (where y is any number greater than 0 and less than 1), or In p Ga (1-p) S q (p is any number greater than 0 and less than 1, and q is any number that is not limited to integers).

[0041] The form of the oxygen element that constitutes the shell is not clear, but it may be, for example, Ga-OS, Ga2O3, or the like.

[0042] Indium sulfide has a band gap energy of 2.0 eV to 2.4 eV, and when the crystal system is cubic, its lattice constant is 1.0775 nm. Gallium sulfide has a band gap energy of approximately 2.5 eV to 2.6 eV, and when the crystal system is tetragonal, its lattice constant is 0.5215 nm. However, the crystal systems described here are all reported values, and the shells of actual core-shell semiconductor nanoparticles do not necessarily meet these reported values.

[0043] Indium sulfide and gallium sulfide are preferably used as semiconductors constituting the shell disposed on the surface of the core. Gallium sulfide is particularly preferred because of its larger band gap energy. When gallium sulfide is used, stronger band edge emission can be obtained compared to when indium sulfide is used.

[0044] The core-shell semiconductor nanoparticles may have an average particle size of, for example, 50 nm or less. From the viewpoints of ease of production and the 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 8 nm, and particularly preferably 2 nm to 7.5 nm. The average particle size of the core-shell semiconductor nanoparticles is measured in the same manner as the average particle size of the semiconductor nanoparticles described above.

[0045] The shell thickness may be, for example, in the range of 0.1 nm to 50 nm, preferably in the range of 0.1 nm to 10 nm, and more preferably in the range of 0.3 nm to 3 nm. When the shell thickness is equal to or greater than the lower limit, the effect of the shell covering the core is sufficiently obtained, and band-edge emission is easily obtained.

[0046] The shell thickness may be determined by observing the core-shell semiconductor nanoparticles, for example, with HAADF-STEM. In particular, when the shell is amorphous, the shell thickness, which is easily observed as a part different from the core, can be easily determined with HAADF-STEM. When the shell thickness is not constant, the smallest thickness is taken as the shell thickness of the particle.

[0047] Alternatively, the average particle size of the cores may be measured in advance before coating with the shell, and the thickness of the shell may be determined by measuring the average particle size of the core-shell semiconductor nanoparticles and calculating the difference between the average particle size and the previously measured average particle size of the cores.

[0048] The core-shell 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 peak height at around 48°, which indicates hexagonal and orthorhombic crystals, to the main peak at around 26°, which indicates tetragonal crystals, is 10% or less.

[0049] When irradiated with ultraviolet light, visible light, infrared light, or other light, the core-shell semiconductor nanoparticles emit light with a longer wavelength than the irradiated light. Specifically, when irradiated with ultraviolet light, visible light, or infrared light, the semiconductor nanoparticles can emit light with a longer wavelength than the irradiated light, and the emission lifetime of the main component is 200 ns or less and / or the half-width of the emission spectrum is 70 nm or less.

[0050] When irradiated with light having a peak wavelength around 450 nm, the core-shell semiconductor nanoparticles may emit light having an emission peak wavelength in the range of 500 nm to 820 nm. The half-width of the emission peak in the emission spectrum may be, for example, 150 nm or less, preferably 100 nm or less, more preferably 70 nm or less, and particularly preferably 50 nm or less. The lower limit of the half-width may be, for example, 10 nm or more. The half-width may also be, for example, 250 meV or less, preferably 210 meV or less, and more preferably 190 meV or less. The lower limit of the half-width may be, for example, 35 meV or more.

[0051] The luminescence of core-shell 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 and a broad spectrum, with its 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 is 40% or more, preferably 60% or more. The "purity of the band-edge luminescence component" is expressed by the following formula when the peak in the luminescence spectrum is separated into two peaks, a band-edge luminescence peak and a defect luminescence peak, and their areas are a1 and a2, respectively. Note that the shape of each peak is assumed to be a normal distribution. 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%.

[0052] The quantum yield of band edge emission is measured using a quantum yield measurement device at an excitation wavelength of 450 nm and a temperature of 25°C, and is defined as the internal quantum yield calculated in the range of 506 nm to 882 nm multiplied by the purity of the band edge emission component and divided by 100. The quantum yield of band edge emission of core-shell semiconductor nanoparticles is, for example, 10% or more, and preferably 20% or more.

[0053] The peak position of the band-edge emission emitted by core-shell semiconductor nanoparticles can be changed by changing the particle size of the core-shell semiconductor nanoparticles. For example, when the particle size of the core-shell semiconductor nanoparticles is made smaller, the peak wavelength of the band-edge emission tends to shift to the shorter wavelength side. Furthermore, when the particle size of the core-shell semiconductor nanoparticles is made smaller, the half-width of the spectrum of the band-edge emission tends to become smaller.

[0054] The core-shell semiconductor nanoparticles also preferably exhibit an exciton peak in their absorption spectrum or excitation spectrum (also referred to as a fluorescence excitation spectrum). 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 core-shell semiconductor nanoparticle aggregate. Therefore, the half-width of the emission is narrower, and it is expected that the luminescence efficiency will be improved. In the absorption spectrum or excitation spectrum of the core-shell semiconductor nanoparticles, the exciton peak is observed, for example, within a range of 350 nm to 1000 nm. The excitation spectrum to determine the presence or absence of an exciton peak may be measured by setting the observation wavelength near the peak wavelength.

[0055] The shell surface of the core-shell 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, and phosphorus-containing compounds having a hydrocarbon group having from 4 to 20 carbon atoms. Two or more different surface modifiers may be used in combination.

[0056] The amino alcohol may be any compound having an amino group and an alcoholic hydroxyl group, and including a hydrocarbon group having 2 to 20 carbon atoms. The number of carbon atoms in the amino alcohol is preferably 10 or less, more preferably 6 or less. The hydrocarbon group constituting the amino alcohol may be derived from a hydrocarbon such as a linear, branched, or cyclic alkane, alkene, or alkyne. "Derived from a hydrocarbon" means that the amino alcohol is formed by removing at least two hydrogen atoms from a hydrocarbon. Specific examples of amino alcohols include aminoethanol, aminopropanol, aminobutanol, aminopentanol, aminohexanol, and aminooctanol. The amino group of the amino alcohol is bonded to the surface of the core-shell semiconductor nanoparticles, and the hydroxyl group is exposed on the opposite outermost surface of the particles, which changes the polarity of the core-shell semiconductor nanoparticles and is thought to improve dispersibility in alcoholic solvents (e.g., methanol, ethanol, propanol, butanol, etc.).

[0057] Examples of ionic surface modifiers include nitrogen-containing compounds, sulfur-containing compounds, and oxygen-containing compounds having an ionic functional group in the molecule. The ionic functional group may be either cationic or anionic, and preferably has at least a cationic group. Specific examples of surface modifiers and surface modification methods can be found in, for example, Chemistry Letters, Vol. 45, pp. 898-900, 2016.

[0058] The ionic surface modifier may be, for example, a sulfur-containing compound having a tertiary or quaternary alkylamino group. The number of carbon atoms in the alkyl group of the alkylamino group may be, for example, 1 to 4. The sulfur-containing compound may also be an alkyl or alkenyl thiol having 2 to 20 carbon atoms. Specific examples of the ionic surface modifier include hydrogen halide salts of dimethylaminoethanethiol, halogen salts of trimethylammoniumethanethiol, hydrogen halide salts of dimethylaminobutanethiol, and halogen salts of trimethylammoniumbutanethiol.

[0059] Examples of nonionic surface modifiers include nitrogen-containing compounds, sulfur-containing compounds, and oxygen-containing compounds having a nonionic functional group containing an alkylene glycol unit, an alkylene glycol monoalkyl ether unit, or the like. The number of carbon atoms in the alkylene group in the alkylene glycol unit may be, for example, 2 to 8, and preferably 2 to 4. The number of repeating alkylene glycol units may be, for example, 1 to 20, and preferably 2 to 10. The nitrogen-containing compound contained in the nonionic surface modifier may have an amino group, the sulfur-containing compound may have a thiol group, and the oxygen-containing compound may have a hydroxyl group. Specific examples of nonionic surface modifiers include methoxytriethyleneoxyethanethiol and methoxyhexaethyleneoxyethanethiol.

[0060] Examples of nitrogen-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms include amines and amides. Examples of sulfur-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms include thiols. Examples of oxygen-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms include carboxylic acids, alcohols, ethers, aldehydes, and ketones. Examples of phosphorus-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms include trialkylphosphines, triarylphosphines, trialkylphosphine oxides, and triarylphosphine oxides.

[0061] The content of the core-shell semiconductor nanoparticles in the light-emitting material may be, for example, from 0.01% by mass to 10% by mass, and preferably from 0.1% by mass to 5% by mass, relative to the total mass of the light-emitting material.

[0062] The metal compound constituting the light-emitting material contains at least one of Zn and Ga, and at least one of S and O, and embeds the core-shell semiconductor nanoparticles. The metal compound may be a compound substantially consisting of at least one of Zn and Ga, and at least one of S and O. Here, "substantially" means that, when the total number of atoms of all elements contained in the metal compound is taken as 100%, the proportion of the number of atoms of elements other than Zn, Ga, S, and O is, for example, 10% or less, preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less. The proportions of elements contained in the metal compound can be confirmed, for example, by ICP emission spectrometry for Zn, Ga, and S, and by elemental analysis by combustion for O. The metal compound may contain at least one selected from the group consisting of metal sulfides, metal oxysulfides, and metal oxides. The presence of at least one selected from the group consisting of metal sulfides, metal oxysulfides, and metal oxides in the metal compound can be confirmed, for example, by SEM-EPMA.

[0063] The metal sulfide may contain at least one of Zn and Ga, and S. When the metal sulfide is substantially composed of Zn and S, it may have a composition represented by ZnS. Here, "substantially" indicates that, when the total number of atoms of all elements contained in the metal sulfide is taken as 100%, the proportion of the number of atoms of elements other than Zn and S is, for example, 5% or less, preferably 3% or less, and more preferably 1% or less. Furthermore, when the metal sulfide is substantially composed of Ga and S, it may have a composition represented by Ga2S3. Here, "substantially" indicates that, when the total number of atoms of all elements contained in the metal sulfide is taken as 100%, the proportion of the number of atoms of elements other than Ga and S is, for example, 5% or less, preferably 3% or less, and more preferably 1% or less.

[0064] The metal oxysulfide may contain at least one of Zn and Ga, and S and O. When the metal oxysulfide is, for example, substantially composed of Zn, S, and O, ZnO x S (1-x)It may have a composition represented by (0 < X < 1). Here, "substantially" means that when the total number of atoms of all elements contained in the metal oxysulfide is 100%, the ratio of the number of atoms of elements other than Zn, S, and O is, for example, 5% or less, preferably 3% or less, more preferably 1% or less. Also, when the metal oxysulfide is substantially formed from Ga, S, and O, Ga2O x S (3-x) It may have a composition represented by (0 < X < 3). Here, "substantially" means that when the total number of atoms of all elements contained in the metal oxysulfide is 100%, the ratio of the number of atoms of elements other than Ga, S, and O is, for example, 5% or less, preferably 3% or less, more preferably 1% or less.

[0065] The metal oxide may contain at least one of Zn and Ga and O. When the metal oxide is substantially formed from, for example, Zn and O, it may have a composition represented by ZnO. Here, "substantially" means that when the total number of atoms of all elements contained in the metal oxide is 100%, the ratio of the number of atoms of elements other than Zn and O is, for example, 5% or less, preferably 3% or less, more preferably 1% or less. Also, when the metal oxide is substantially formed from Ga and O, it may have a composition represented by Ga2O3. Here, "substantially" means that when the total number of atoms of all elements contained in the metal oxide is 100%, the ratio of the number of atoms of elements other than Ga and O is, for example, 5% or less, preferably 3% or less, more preferably 1% or less.

[0066] The metal compound that embeds the core-shell type semiconductor nanoparticles may be a compound generated by a solution reaction as described later. The metal compound may be, for example, a sol-gel decomposition product obtained by reacting an organic acid salt or an inorganic acid salt of a metal with at least one of a sulfur-containing compound and an oxygen-containing compound at a low temperature of 100 °C or lower in the presence of water, alcohol, etc. The metal compound may be a crystalline substance or an amorphous substance. The crystalline state of the metal compound can be confirmed, for example, by X-ray diffraction.

[0067] Method for producing luminescent material The method for producing a luminescent material includes a preparation step of preparing core-shell semiconductor nanoparticles that contain a core and a shell disposed on the surface of the core and that emit light when irradiated with light, a mixing step of obtaining a mixture for producing the luminescent material that contains the core-shell semiconductor nanoparticles, a compound containing at least one of Zn and Ga, a compound containing at least one of S and O, and a solvent, and a synthesis step of obtaining, from the mixture for producing the luminescent material, a metal compound that contains at least one of Zn and Ga and at least one of S and O and that embeds the core-shell semiconductor nanoparticles. The core of the core-shell semiconductor nanoparticles is M 1 , M 2 and Z, M 1 , M 2 and Z, where M 1 is at least one selected from the group consisting of Ag, Cu, Au and alkali metals, and contains at least Ag. 2 is at least one selected from the group consisting of Al, Ga, In and Tl, and includes at least one of In and Ga. Z includes at least one selected from the group consisting of S, Se and Te. The core is M 1 The total content of M is 10 mol % or more and 30 mol % or less, 2 The shell may have a composition in which the total content of is 15 mol % or more and 35 mol % or less, and the total content of Z is 35 mol % or more and 55 mol % or less. The shell may consist essentially of at least one selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one selected from the group consisting of S, O, Se and Te.

[0068] A metal compound containing at least one of Zn and Ga as the metal is precipitated by reacting a compound containing at least one of S and O in the presence of core-shell semiconductor nanoparticles via a solvent. Because the metal compound precipitates while encapsulating the core-shell semiconductor nanoparticles, a light-emitting material can be efficiently produced by a solution reaction.

[0069] Preparation process In the preparation step, core-shell semiconductor nanoparticles are prepared. The core-shell semiconductor nanoparticles may be appropriately selected from commercially available products, or may be prepared by manufacturing core-shell semiconductor nanoparticles having desired properties. For methods of manufacturing core-shell semiconductor nanoparticles, reference can be made to the descriptions in, for example, JP 2018-044142 A, WO 2018 / 159699 A, WO 2019 / 160094 A, and U.S. Publication No. 2019 / 0345384 A. Specifically, for example, they can be manufactured as follows.

[0070] The first method for producing the core semiconductor nanoparticles is 1 and a salt containing M 2 and an organic solvent, elevating the temperature of the first mixture, and adding a source of Z to the heated mixture. 1 and a salt containing M 2 providing a second mixture comprising a salt comprising:

[0071] M used in the first and second manufacturing methods 1 Salts containing M 2 Examples of salts containing the above include organic acid salts and inorganic acid salts. Specific examples of inorganic acid salts include nitrates, sulfates, hydrochlorides, sulfonates, and carbonates. Examples of organic acid salts include acetates and acetylacetonates. Among these, organic acid salts are preferred because of their high solubility in organic solutions.

[0072] Examples of the source of Z used in the first and second production methods include Z alone and compounds containing Z. When Z is S, examples of the source of S include sulfur or a sulfur-containing compound. Specific examples of sulfur-containing compounds include β-dithiones such as 2,4-pentanedithione; dithiols such as 1,2-bis(trifluoromethyl)ethylene-1,2-dithiol; dialkyldithiocarbamates such as diethyldithiocarbamate; and alkylthioureas such as thiourea, 1,3-dialkylthiourea having an alkyl group having 1 to 18 carbon atoms, 1,1-dialkylthiourea, alkylthiourea, 1,1,3-trialkylthiourea, and 1,1,3,3-tetraalkylthiourea. As the source of S, sulfur-containing compounds that are soluble in organic solvents are preferred. From the viewpoints of solubility and reactivity, alkylthioureas are more preferred, and 1,3-dialkylthioureas are even more preferred. The alkyl group of the alkylthiourea preferably has 1 to 12 carbon atoms, more preferably 1 to 8, more preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. When the alkylthiourea has multiple alkyl groups, they may be the same or different.

[0073] When Z used in the first and second production methods is Se, examples of the source of Se include simple selenium and Se-containing compounds such as selenourea, selenoacetamide, and alkylselenol. When Z is Te, examples of the source of Te include simple tellurium and Te-containing compounds such as diallyl telluride and dimethyl ditelluride.

[0074] Examples of organic solvents used in the first and second production methods include amines having a hydrocarbon group containing 4 to 20 carbon atoms, particularly alkylamines or alkenylamines having 4 to 20 carbon atoms; thiols having a hydrocarbon group containing 4 to 20 carbon atoms, particularly alkylthiols or alkenylthiols having 4 to 20 carbon atoms; and phosphines having a hydrocarbon group containing 4 to 20 carbon atoms, particularly alkylphosphines or alkenylphosphines having 4 to 20 carbon atoms. These organic solvents can ultimately be used to modify the surface of the resulting semiconductor nanoparticles. Two or more of these organic solvents may be used in combination, and in particular, 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 also be used in combination with other organic solvents. Note that the organic solvent may be solid at room temperature as long as it dissolves at 120°C or higher.

[0075] M contained in the first mixture in the first manufacturing method 1 M of total number of atoms 2 to the total number of atoms (M 1 / M 2 ) may be, for example, 0.1 or more and 2 or less, preferably 0.5 or more and 1.2 or less. 1 The total concentration may be, for example, 1 mmol / L or more and 500 mmol / L or less, and preferably 10 mmol / L or more and 50 mmol / L or less.

[0076] In the temperature increase in the first production method, the prepared first mixture may be heated to a temperature in the range of 120°C or more and 300°C or less. The temperature reached by the temperature increase is preferably 125°C or more, more preferably 130°C or more, and even more preferably 135°C or more. The temperature reached by the temperature increase is preferably 175°C or less, more preferably 160°C or less, and even more preferably 150°C or less. The temperature increase rate may be, for example, 1°C / min or more and 50°C / min or less, and preferably 10°C / min or more and 50°C / min or less.

[0077] The atmosphere in which the temperature of the first mixture is increased in the first production method may be an inert gas atmosphere, and is preferably, for example, an argon atmosphere, a nitrogen atmosphere, etc. By using an inert gas atmosphere, it is possible to reduce or prevent the by-production of oxides.

[0078] In the first production method, the source of Z is added to the first mixture heated to a predetermined temperature, and the source of Z is added to the first mixture while maintaining the predetermined temperature. 1 The mixture is gradually added so that the rate of increase in the ratio of the number of Z atoms to the total number of M atoms is 10 / min or less. 1 The ratio of the number of Z atoms to the total number of M atoms (Z / M 1 The rate of increase of Z / M 1 The ratio is Z / M after that unit time. 1 The unit time is arbitrarily selected between 1 second and 1 minute. 1 From the viewpoint of controlling the particle growth of nanoparticles, the rate of increase in the ratio of the number of Z atoms to the total number of atoms is preferably 0.0001 / min to 2 / min, more preferably 0.0001 / min to 1 / min, even more preferably 0.001 / min to 0.2 / min, and particularly preferably 0.001 / min to 0.1 / min. Also, it is preferably 0.0002 / min to 2 / min, more preferably 0.002 / min to 0.2 / min, even more preferably 0.0025 / min to 0.19 / min, and particularly preferably 0.04 / min to 0.12 / min. Z / M 1 The rate of increase of the ratio may be, for example, 0.0001 / min or more, preferably 0.001 / min or more, more preferably 0.01 / min or more, and particularly preferably 0.04 / min or more. Z / M 1 The rate of increase of the ratio may be, for example, 5 / min or less, preferably 2 / min or less, more preferably 0.5 / min or less, or 0.25 / min or less.

[0079] The total amount of the source of Z added in the first production method is 1The amount of Z may be such that the ratio of the number of Z atoms to the total number of atoms is 0.1 or more and 5 or less, and preferably 1 or more and 2.5 or less. The time required for adding the Z source may be, for example, 1 minute or more, preferably 5 minutes or more, more preferably 15 minutes or more, and even more preferably 20 minutes or more. The time required may be, for example, 120 minutes or less, preferably 60 minutes or less, and more preferably 40 minutes or less.

[0080] The total amount of the source of Z added in the first production method is 1 When the ratio of the number of Z atoms to the total number of atoms of is 0.1 or more and 2.5 or less, Z / M 1 The rate of increase of the ratio may be, for example, 0.0001 / min or more and 1 / min or less, preferably 0.001 / min or more and 0.2 / min or less, more preferably 0.002 / min or more and 0.2 / min or less, even more preferably 0.0025 / min or more and 0.19 / min or less, and particularly preferably 0.04 / min or more and 0.12 / min or less. 1 When the ratio of the number of Z atoms to the total number of atoms of is more than 2.5 and 5.0 or less, Z / M 1 The rate of increase of the ratio may be, for example, 0.0002 / min or more and 2 / min or less, preferably 0.002 / min or more and 0.2 / min or less, more preferably 0.0025 / min or more and 0.19 / min or less, and even more preferably 0.04 / min or more and 0.12 / min or less.

[0081] In the first production method, the source of Z may be added so that the amount added per unit time is approximately the same over the required time. That is, the unit amount obtained by dividing the total amount of the source of Z by the required time divided by the unit time may be added as the amount added per unit time. The unit time may be, for example, 1 second, 5 seconds, 10 seconds, 30 seconds, or 1 minute. The source of Z may be added continuously or in stages. Alternatively, the source of Z may be added to the mixture under an inert gas atmosphere, for example.

[0082] In the first production method, the source of Z may be added to the mixture as a solution of a compound containing Z dissolved in an organic solvent. When the source of Z is a solution of a compound containing Z, the amount of the source of Z added per unit time in the addition step can be easily controlled, and semiconductor nanoparticles with a narrower particle size distribution can be efficiently produced.

[0083] Examples of the organic solvent for dissolving the compound containing Z in the first production method include the same organic solvents as those contained in the mixture described above, and for example, an amine having a hydrocarbon group having 4 to 20 carbon atoms can be used.

[0084] When the source of Z in the first manufacturing method is a solution of a compound containing Z, the concentration of the compound containing Z may be, for example, 1 mmol / L or more and 500 mmol / L or less, and preferably 10 mmol / L or more and 50 mmol / L or less.

[0085] The first production method may further include a heat treatment step of heat-treating the mixture after the addition of the Z source at a temperature in the range of 120°C to 300°C. The heat treatment temperature may be the same as or different from the temperature to which the mixture is heated. From the viewpoint of quantum yield, the heat treatment temperature may be, for example, 120°C to 300°C, preferably 125°C to 175°C, more preferably 130°C to 160°C, and even more preferably 135°C to 150°C.

[0086] The heat treatment time in the first manufacturing method may be, for example, 3 seconds or more, preferably 5 minutes or more, from the viewpoint of the quantum efficiency of the semiconductor nanoparticles. There is no particular upper limit to the heat treatment time, but it may be, for example, 60 minutes or less. The heat treatment time is defined as the start time of the heat treatment when a predetermined temperature is reached (for example, the time when 140°C is reached in the case of 140°C), and the end time of the heat treatment when the temperature is lowered.

[0087] The heat treatment atmosphere in the first production method may be an inert gas atmosphere, preferably an argon atmosphere or a nitrogen atmosphere, which can reduce or prevent the by-production of oxides and the oxidation of the surfaces of the obtained semiconductor nanoparticles.

[0088] The first method for producing semiconductor nanoparticles may include a cooling step of lowering the temperature of the solution containing semiconductor nanoparticles following the heat treatment. The cooling step begins when the temperature lowering operation is performed and ends when the solution has been cooled to 50°C or below.

[0089] The cooling step in the first production method is to remove unreacted M 1 M from salt 1 In order to suppress the formation of a compound containing Z, a period in which the temperature is lowered at a rate of 50°C / min or more may be included. For example, after the temperature lowering operation is performed, the temperature can be lowered at a rate of 50°C / min or more at the time when the temperature lowering starts.

[0090] The atmosphere in the cooling step in the first production method is preferably an inert gas atmosphere, such as an argon atmosphere or a nitrogen atmosphere, which can reduce or prevent the by-production of oxides and reduce or prevent the oxidation of the surfaces of the obtained semiconductor nanoparticles.

[0091] In the second manufacturing method, M 1 and a salt containing M 2 A second mixture is prepared containing a salt containing M, a source of Z, and an organic solvent. 1 and a salt containing M 2 The second mixture in the second production method may be obtained by mixing a salt containing M 1 and a salt containing M 2 Alternatively, a solution containing a salt containing the compound and an organic solvent may be prepared, and the solution may be heated and then the source of Z may be added to the heated solution. The heating temperature when the source of Z is added to the heated solution is, for example, 30°C or higher and 90°C or lower, and preferably 40°C or higher and 80°C or lower.

[0092] M contained in the second mixture in the second manufacturing method 1 M of total number of atoms 2 to the total number of atoms (M 1 / M 2 ) may be, for example, 0.1 or more and 2 or less, preferably 0.5 or more and 1.2 or less. 1 The total concentration may be, for example, 1 mmol / L or more and 500 mmol / L or less, and preferably 10 mmol / L or more and 50 mmol / L or less.

[0093] The heat treatment in the second production method may be a first heat treatment in which the second mixture is heated to a first temperature and maintained at that temperature for a predetermined period of time. The first temperature may be, for example, a temperature in the range of 200°C to 370°C. When the Z source contains S, the first temperature is preferably 260°C or higher and 320°C or lower, more preferably 290°C to 310°C. When the Z source contains Se, the first temperature is preferably 220°C or higher, more preferably 250°C or higher, and preferably 370°C or lower, more preferably 350°C or lower. M 2 When contains Ga, the first temperature is preferably 230°C or higher. The time for maintaining the predetermined temperature may be 1 minute or more and 180 minutes or less, preferably 5 minutes or more and 60 minutes or less. The heat treatment of the second mixture may be a second heat treatment performed at two or more temperatures. For example, the second mixture may be heated at a temperature in the range of 30°C or more and 190°C or less for 1 minute or more and 30 minutes or less, and then heated at the above-mentioned first temperature in the range of 200°C or more and 370°C or less for 1 minute or less and 60 minutes or less.

[0094] The heat treatment in the second production method may be a third heat treatment in which the second mixture is heated to a second temperature and maintained at that temperature for a predetermined period of time. The second temperature may be, for example, in the range of 125°C to 175°C, preferably 130°C to 160°C, and more preferably 135°C to 150°C. The temperature rise rate is, for example, 1°C / min to 50°C / min.

[0095] The time for maintaining the second temperature in the third heat treatment is preferably 3 seconds or more from the viewpoint of quantum efficiency. The upper limit of the maintenance time can be, for example, 60 minutes or less. The time for maintaining the predetermined temperature is defined as the start time of the heat treatment when the temperature set in the above-mentioned temperature range is reached, and the end time of the heat treatment when the temperature is lowered.

[0096] The atmosphere for the first, second, and third heat treatments in the second production method is preferably an inert atmosphere, particularly an argon or nitrogen atmosphere, which can reduce or prevent the by-production of oxides and the oxidation of the surfaces of the resulting semiconductor nanoparticles.

[0097] The second production method may include a cooling step of lowering the temperature of the solution containing semiconductor nanoparticles following the first, second, and third heat treatments. The cooling step begins when an operation for lowering the temperature is performed and ends when the temperature has been cooled to 50°C or below.

[0098] In the second production method, the cooling step is carried out to remove unreacted M 1 M from salt 1 In order to suppress the formation of compounds containing Z, it is preferable to include a period in which the temperature is lowered at a rate of 50°C / min or more. In particular, it is preferable that the temperature is lowered at a rate of 50°C / min or more at the time when the temperature lowering operation is started after the temperature lowering operation is performed.

[0099] The atmosphere in the cooling step in the second production method may be an inert atmosphere, preferably an argon atmosphere or a nitrogen atmosphere, which can reduce or prevent the by-production of oxides and the oxidation of the surfaces of the resulting semiconductor nanoparticles.

[0100] The first and second methods for producing core semiconductor nanoparticles described above may further include a separation step of separating the semiconductor nanoparticles from the solution, and may further include a purification step, if necessary. In the separation step, for example, a solution containing the semiconductor nanoparticles may be centrifuged to extract a supernatant containing the nanoparticles. In the purification step, for example, an appropriate organic solvent such as alcohol may be added to the supernatant obtained in the separation step, followed by centrifugation to extract the semiconductor nanoparticles as a precipitate. The semiconductor nanoparticles can also be extracted by volatilizing the organic solvent from the supernatant. The extracted precipitate 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 mixture in the air at room temperature and normal pressure, in which case it 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.

[0101] In the first and second methods for producing core semiconductor nanoparticles, a purification step involving the addition of an organic solvent such as alcohol and centrifugation may be performed multiple times as necessary. The alcohol used for purification may be a lower alcohol having 1 to 4 carbon atoms, such as methanol, ethanol, or n-propyl alcohol. When dispersing the precipitate in an organic solvent, the organic solvent may be a halogenated solvent such as chloroform, dichloromethane, dichloroethane, trichloroethane, or tetrachloroethane, or a hydrocarbon solvent such as toluene, cyclohexane, hexane, pentane, or octane. From the viewpoint of quantum yield, the organic solvent in which the precipitate is dispersed may be a halogenated solvent.

[0102] The method for producing core-shell semiconductor nanoparticles may be a production method including a preparation step of obtaining a third mixture by mixing a dispersion containing semiconductor nanoparticles obtained by the above-mentioned first and second methods for producing core semiconductor nanoparticles with a compound containing at least one element selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one element selected from the group consisting of S, O, Se and Te or a compound containing said element, and a shell formation step of heat-treating the third mixture.

[0103] Because light scattering does not occur in a liquid in which semiconductor nanoparticles are dispersed, the resulting dispersion is generally transparent (colored or colorless). The solvent for dispersing the semiconductor nanoparticles can be any organic solvent, as in the case of preparing semiconductor nanoparticles. The organic solvent can be a surface modifier or a solution containing a surface modifier. For example, the organic solvent can be at least one selected from nitrogen-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms, which are surface modifiers described in connection with the method for producing semiconductor nanoparticles. Alternatively, the organic solvent can be at least one selected from sulfur-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms. Alternatively, the organic solvent can be a combination of at least one selected from nitrogen-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms and at least one selected from sulfur-containing compounds having a hydrocarbon group with 4 to 20 carbon atoms. Nitrogen-containing compounds are preferably those with a boiling point higher than the reaction temperature, because particularly high-purity compounds are readily available and have a boiling point exceeding 290°C. Specific organic solvents include oleylamine, n-tetradecylamine, dodecanethiol, or a combination thereof.

[0104] The solvent for dispersing the semiconductor nanoparticles may contain a halogen-based solvent such as chloroform, or may be essentially a halogen-based solvent. Alternatively, after dispersing the semiconductor nanoparticles in a halogen-based solvent, the solvent may be exchanged with an organic solvent containing a surface modifier such as a nitrogen-containing compound to obtain a dispersion of semiconductor nanoparticles. Solvent exchange can be performed, for example, by adding a surface modifier to a dispersion of semiconductor nanoparticles containing a halogen-based solvent and then removing at least a portion of the halogen-based solvent. Specifically, for example, a dispersion containing a halogen-based solvent and a surface modifier can be heat-treated under reduced pressure to remove at least a portion of the halogen-based solvent, thereby obtaining a dispersion of semiconductor nanoparticles containing the surface modifier. The reduced pressure conditions and heat treatment temperature for the heat treatment under reduced pressure may be set so that at least a portion of the halogen-based solvent is removed and the surface modifier remains. Specifically, the reduced pressure conditions may be, for example, from 1 Pa to 2000 Pa, preferably from 50 Pa to 500 Pa. The heat treatment temperature may be, for example, from 20°C to 120°C, preferably from 50°C to 80°C.

[0105] The semiconductor nanoparticle dispersion has a particle concentration of, for example, 5.0 × 10 -7 5.0 x 10 moles / liter or more -5 moles / liter or less, especially 1.0 x 10 -6 moles / liter or greater, 1.0 x 10 -5 If the particle ratio in the dispersion is too small, it becomes difficult to recover the product by the aggregation and precipitation process in a poor solvent, while if it is too large, the rate of Ostwald ripening and fusion due to collision of the material that makes up the core increases, and the particle size distribution tends to become broader.

[0106] The compound containing at least one selected from the group consisting of Al, Ga, In, Tl, and alkali metals may be an organic salt, inorganic salt, organometallic compound, or the like of these elements. Examples of compounds containing these elements include nitrates, acetates, sulfates, hydrochlorides, sulfonates, acetylacetonate complexes, and the like, with organic salts such as acetates or organometallic compounds being preferred. This is because organic salts and organometallic compounds have high solubility in organic solvents, making it easier to promote the reaction more uniformly.

[0107] For example, when S is used as the shell constituent element, elemental sulfur such as high-purity sulfur can be used as at least one element selected from the group consisting of S, O, Se, and Te. Alternatively, sulfur-containing compounds such as thiols such as n-butanethiol, isobutanethiol, n-pentanethiol, n-hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, and octadecanethiol, disulfides such as dibenzyl sulfide, thiourea, alkylthioureas such as 1,3-dimethylthiourea, and thiocarbonyl compounds can be used. In particular, when alkylthioureas such as 1,3-dimethylthiourea are used as the Group 16 element source (sulfur source), sufficient shell formation is achieved, making it easier to obtain semiconductor nanoparticles that exhibit strong band-edge emission. When O is used as the shell constituent element, specific examples include compounds containing oxygen atoms, gases containing oxygen atoms, and the like. Examples of compounds containing oxygen atoms include water and alcohols, and at least one selected from the group consisting of these is preferred. Examples of the gas containing oxygen atoms include oxygen gas, ozone gas, etc., and at least one selected from the group consisting of these is preferred. The oxygen source may be added by dissolving or dispersing a compound containing oxygen atoms in the mixture for forming the shell, or by blowing a gas containing oxygen atoms into the mixture for forming the shell.

[0108] A method for producing core-shell semiconductor nanoparticles involves heating a dispersion containing core semiconductor nanoparticles until the peak temperature reaches 200°C or higher and 310°C or lower. After reaching the peak temperature, a mixture of the shell-forming elements or compounds dispersed or dissolved in an organic solvent is added in small amounts while maintaining the peak temperature. The temperature is then lowered to form the shell layer (a slow injection method). In this case, the heat treatment begins immediately after the dispersion containing semiconductor nanoparticles and the mixture are mixed to obtain a third mixture. The mixture may be added at a rate of 0.1 mL / hour to 10 mL / hour, particularly 1 mL / hour to 5 mL / hour. The peak temperature may be maintained as needed even after the addition of the mixture is complete.

[0109] If the peak temperature is above the above temperature, the surface modifier modifying the semiconductor nanoparticles is sufficiently removed, or the chemical reaction for shell formation is sufficiently advanced, which tends to result in sufficient formation of the semiconductor layer (shell). If the peak temperature is below the above temperature, alteration of the semiconductor nanoparticles is suppressed, and good band-edge emission tends to be obtained. The time for maintaining the peak temperature can be a total of 1 minute to 300 minutes, particularly 10 minutes to 120 minutes, from the start of addition of the mixed solution. The peak temperature maintenance time is selected in relation to the peak temperature; a longer maintenance time is used when the peak temperature is lower, and a shorter maintenance time is used when the peak temperature is higher, which tends to form a good shell layer. The temperature increase rate and temperature decrease rate are not particularly limited. The temperature decrease can be carried out, for example, by maintaining the peak temperature for a predetermined time, then stopping heating by a heat source (e.g., an electric heater), and allowing the mixture to cool.

[0110] Alternatively, a method for producing core-shell semiconductor nanoparticles may involve mixing a dispersion containing core semiconductor nanoparticles with a shell-forming element or compound to obtain a third mixture, followed by heat treatment of the third mixture to form a shell semiconductor layer on the surface of the semiconductor nanoparticles (heating-up method). Specifically, the third mixture may be gradually heated to a peak temperature of 200°C to 310°C, held at the peak temperature for 1 minute to 300 minutes, and then gradually cooled. The heating rate may be, for example, 1°C / min to 50°C / min, but is preferably 50°C / min to 100°C / min up to 200°C to minimize core deterioration caused by continued heat treatment in the absence of a shell. Furthermore, when the temperature is further increased to 200°C or higher, the subsequent heating rate is preferably 1°C / min to 5°C / min. The heating rate may be, for example, 1°C / min to 50°C / min. The advantages of the peak temperature being in the above range are as explained in the slow injection method.

[0111] The heating-up method tends to produce core-shell semiconductor nanoparticles that give stronger band-edge emission than when the shell is formed by the slow injection method.

[0112] The third mixture in the heating-up method may be prepared by mixing a dispersion of semiconductor nanoparticles containing a halogen-based solvent, an organic solvent such as a surface modifier, and a shell-forming unit or compound, and then removing at least a portion of the halogen-based solvent, for example, by heat treatment under reduced pressure. That is, the preparation step may include mixing a dispersion of semiconductor nanoparticles containing a halogen-based solvent, an organic solvent such as a surface modifier, and a shell-forming unit or compound to obtain a pre-mixture, and removing at least a portion of the halogen-based solvent from the pre-mixture to obtain a third mixture.

[0113] In either method, the feed ratio of the elements or compounds forming the shell may be determined in accordance with the stoichiometric ratio of a semiconductor compound consisting of at least one element selected from the group consisting of Al, Ga, In, Tl, and alkali metals and at least one element selected from the group consisting of S, O, Se, and Te, but does not necessarily have to be the stoichiometric ratio. For example, the feed ratio of at least one element selected from the group consisting of Al, Ga, In, Tl, and alkali metals to at least one element selected from the group consisting of S, O, Se, and Te can be 0.75 or more and 1.5 or less.

[0114] Furthermore, the amount of charge is selected taking into consideration the amount of semiconductor nanoparticles contained in the dispersion so that a shell of the desired thickness is formed on the semiconductor nanoparticles present in the dispersion. For example, the amount of shell-forming element or compound may be determined so that a compound semiconductor having a stoichiometric composition consisting of a Group 13 element and a Group 16 element is produced in an amount of 1 μmol to 10 mmol, particularly 5 μmol to 1 mmol, per 10 nmol of semiconductor nanoparticles. However, the amount of particle substance is the molar amount when one particle is considered as a giant molecule, and the number of semiconductor nanoparticles contained in the dispersion is determined by Avogadro's number (NA = 6.022 × 10 23 ) divided by .

[0115] In the method for producing core-shell semiconductor nanoparticles, it is preferable to form a shell containing indium sulfide or gallium sulfide using indium acetate or gallium acetylacetonate, sulfur elemental compound, thiourea or dibenzyl disulfide, and a mixture of oleylamine and dodecanethiol or oleylamine as a dispersion medium.

[0116] Furthermore, when a mixture of oleylamine and dodecanethiol or oleylamine is used as the dispersion liquid in the heating-up method, core-shell semiconductor nanoparticles tend to be obtained that give an emission spectrum in which the intensity of the broad peak derived from defect emission is sufficiently smaller than the intensity of the peak of band-edge emission. The above tendency is also significantly observed when a gallium source is used.

[0117] In this way, a shell is formed to form core-shell semiconductor nanoparticles having a core-shell structure. The obtained core-shell semiconductor nanoparticles having a core-shell structure may be separated from the solvent and, if necessary, further purified and dried. The methods for separation, purification, and drying are as described above in relation to the semiconductor nanoparticles, and therefore detailed description thereof will be omitted here.

[0118] Mixing process In the mixing step in the method for producing a luminescent material, a mixture for producing a luminescent material is obtained by mixing core-shell type semiconductor nanoparticles, a compound containing at least one of Zn and Ga, a compound containing at least one of S and O, and a solvent. The core-shell type semiconductor nanoparticles used in the mixing step may be in the form of a dispersion liquid.

[0119] Compounds containing at least one of Zn and Ga include organic acid salts and inorganic acid salts containing at least one of Zn and Ga. Specific examples of inorganic acid salts include nitrates, sulfates, hydrochlorides, sulfonates, and carbonates. Examples of organic acid salts include acetates and acetylacetonates. Among these, organic acid salts are preferred because of their high solubility in organic solutions. Examples of compounds containing S include the sulfur-containing compounds described above, as well as thioamides such as thioacetamide. Examples of compounds containing O include water, alcohols, and amino alcohols.

[0120] Examples of the solvent include water, alcohols having from 1 to 8 carbon atoms, alkylene glycols having from 2 to 8 carbon atoms, and other polyols such as glycerin. Specific examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, hexanol, octanol, and 2-ethylhexanol. The solvent may be a mixed solvent of water and alcohol, but it is preferable that the solvent is essentially alcohol, as this can suppress deterioration of the core-shell semiconductor nanoparticles. "Substantially" means that the content of components other than alcohol is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0121] The content of the core-shell semiconductor nanoparticles in the mixture for producing a light-emitting material may be, for example, 10 nanomoles / L to 10 micromoles / L, and preferably 100 nanomoles / L to 1 micromoles / L, as a concentration based on the amount of substance (number of particles) as nanoparticles. The content of the compound containing at least one of Zn and Ga in the mixture for producing a light-emitting material may be, for example, 1 millimoles / L to 1 mole / L, and preferably 10 millimoles / L to 200 millimoles / L. The content of the compound containing at least one of S and O in the mixture for producing a light-emitting material may be, for example, 1 millimoles / L to 1 mole / L, and preferably 10 millimoles / L to 200 millimoles / L.

[0122] The molar ratio of the content of the compound containing at least one of S and O to the content of the compound containing at least one of Zn and Ga in the mixture for producing the luminescent material may be, for example, 0.1 or more and 10 or less, and preferably 0.5 or more and 2 or less.

[0123] In the mixing step, for example, a compound containing at least one of S and O can be added to a mixture of a solution containing a compound containing at least one of Zn and Ga and a dispersion of core-shell type semiconductor nanoparticles to obtain a mixture for producing a light-emitting material. Alternatively, a compound containing at least one of Zn and Ga can be added to a mixture of a solution containing a compound containing at least one of S and O and a dispersion of core-shell type semiconductor nanoparticles to obtain a mixture for producing a light-emitting material. The mixing temperature may be, for example, 0°C or higher and 100°C or lower, and preferably 10°C or higher and 80°C or lower. The mixing atmosphere may be, for example, an inert atmosphere, and when only alcohol is used as the solvent, a dehydrated atmosphere is more preferable.

[0124] The method for producing a luminescent material may include a surface treatment step of contacting the core-shell semiconductor nanoparticles prepared in the preparation step with a surface modifier (hereinafter also referred to as a specific surface modifier) selected from the group consisting of an amino alcohol having from 2 to 20 carbon atoms, an ionic surface modifier, a nonionic surface modifier, a nitrogen-containing compound having a hydrocarbon group having from 4 to 20 carbon atoms, a sulfur-containing compound having a hydrocarbon group having from 4 to 20 carbon atoms, an oxygen-containing compound having a hydrocarbon group having from 4 to 20 carbon atoms, and a phosphorus-containing compound having a hydrocarbon group having from 4 to 20 carbon atoms.

[0125] The amino alcohol used in the surface treatment step may be a compound having 2 to 20 carbon atoms and containing an amino group and an alcoholic hydroxyl group. The amino alcohol preferably has 3 or more carbon atoms, and preferably 10 or less, and more preferably 6 or less. The hydrocarbon group constituting the amino alcohol may be derived from a hydrocarbon such as a linear, branched, or cyclic alkane, alkene, or alkyne. Specific examples of amino alcohols include aminoethanol, aminopropanol, aminobutanol, aminopentanol, aminohexanol, and aminooctanol. Contacting core-shell semiconductor nanoparticles with amyl alcohol can further improve the dispersibility of the core-shell semiconductor nanoparticles in a solvent, thereby producing a mixture for producing a light-emitting material with good dispersion stability. It is believed that the surface modifier, for example, adheres to the surface of the core-shell semiconductor nanoparticles to further improve their dispersibility in a solvent.

[0126] In the surface treatment step, for example, the core-shell semiconductor nanoparticles may be brought into contact with the specific surface modifier by mixing the core-shell semiconductor nanoparticles with the specific surface modifier. The ratio of the specific surface modifier to the core-shell semiconductor nanoparticles in the surface treatment step is, for example, 1 × 10 of the core-shell semiconductor nanoparticles. -8 The amount of contact may be 0.1 mL or more, preferably 0.5 mL or more and 10 mL or less, per mole. The contact temperature may be, for example, 0°C or more and 100°C or less, preferably 10°C or more and 80°C or less. The contact time may be, for example, 10 seconds or more and 10 days or less, preferably 1 minute or more and 1 day or less. The contact atmosphere may be an inert atmosphere, and an argon atmosphere or a nitrogen atmosphere is particularly preferred.

[0127] Light-emitting material synthesis process In the synthesis step, a metal compound that contains at least one of Zn and Ga and at least one of S and O and that embeds core-shell semiconductor nanoparticles is obtained from the mixture for producing the light-emitting material. The metal compound precipitates from the mixture for producing the light-emitting material while embedding the core-shell semiconductor nanoparticles through a synthesis reaction involving solvolysis (the so-called sol-gel method).

[0128] In the synthesis step, for example, the metal compound may be precipitated at room temperature (e.g., 25°C), or the metal compound may be precipitated by heat treatment. The heat treatment temperature may be, for example, less than 100°C, preferably 80°C or less, more preferably 60°C or less. The heat treatment temperature may be 0°C or higher, preferably 30°C or higher. The time required for the synthesis step may be, for example, 1 minute or more, preferably 10 minutes or more. The time required for the synthesis step may be, for example, 10 days or less, preferably 3 days or less. The atmosphere for the synthesis step is preferably an inert atmosphere, particularly an argon atmosphere or a nitrogen atmosphere. By using an inert atmosphere, a light-emitting material with better light-emitting properties can be obtained. Furthermore, when only alcohol is used as a solvent, a dehydrated atmosphere may be used.

[0129] The embedding rate of the core-shell semiconductor nanoparticles in the metal compound in the synthesis step may be, for example, 10% or more, and preferably 80% or more, and is determined by dividing the amount of core-shell semiconductor nanoparticles contained in the precipitated metal compound by the amount of core-shell semiconductor nanoparticles added to the mixture for producing the light-emitting material.

[0130] The method for producing a luminescent material may further include a separation step in which the metal compound produced in the synthesis step is separated from the solvent, and may further include a purification step as necessary. In the separation step, for example, the reaction solution containing the luminescent material may be centrifuged to recover the luminescent material as a precipitate. Alternatively, the precipitate of the luminescent material may be recovered by solid-liquid separation means such as filtration. In the purification step, for example, the precipitate obtained in the separation step may be washed with an organic solvent such as alcohol, and the washed precipitate may be dried.

[0131] Light-emitting device The light emitting device includes a light source having an emission peak wavelength in the ultraviolet to visible light range and the above-mentioned light emitting material. The light emitting device includes, for example, a light source having an emission peak wavelength in the range of 380 nm to 485 nm, and may further include other components as necessary. By including the light emitting material, the light emitting device can achieve excellent long-term reliability. In addition to the light source and the light emitting material, the light emitting device may also include a member that covers the light source.

[0132] The light source used has a peak emission wavelength in the short wavelength range of 380 nm to 485 nm. The peak emission wavelength of the light source is preferably 420 nm to 485 nm, and more preferably 440 nm to 480 nm. This allows the light-emitting material to be efficiently excited and visible light to be effectively utilized. Furthermore, by using a light source in this wavelength range, a light-emitting device with high emission intensity can be provided.

[0133] It is preferable to use a semiconductor light-emitting element (hereinafter simply referred to as "light-emitting element") as the light source. By using a semiconductor light-emitting element as the light source, it is possible to configure a light-emitting device that is highly efficient, has a high linearity of output relative to input, and is resistant to mechanical shocks and is stable. The light-emitting element may be one that has a semiconductor layer made of at least one kind selected from the group consisting of GaN, GaAs, InGaN, AlInGaP, GaP, SiC, ZnO, etc. The semiconductor light-emitting element that emits blue-violet light, blue light, or ultraviolet light is preferably a nitride-based compound (In X Al Y Ga 1-X-Y N, 0≦X, 0≦Y, X+Y≦1) as a semiconductor layer.

[0134] Details of the luminescent material included in the light-emitting device have been described above. The luminescent material may be contained in a member covering the light source, or may be disposed on the member covering the light source. By disposing the luminescent material on the light source, it is possible to absorb a portion of the light emitted from the light source and emit it as light with a longer wavelength. Furthermore, by having the light source have an emission peak wavelength in the range of 380 nm to 485 nm, it is possible to more effectively utilize the light emitted from the light source. In other words, it is possible to reduce the loss of light emitted from the light-emitting device, and it is possible to provide a highly efficient light-emitting device. The content of the luminescent material included in the light-emitting device can be appropriately selected depending on the light source, purpose, etc.

[0135] The light emitting device may contain a phosphor as needed in addition to the light emitting material. The phosphor may be any material that absorbs a portion of the light emitted from the light source and converts the wavelength of the light into light with a different wavelength from that of the light emitting material. The phosphor can be contained in a member that covers the light source to form the light emitting device. By including a phosphor, it is possible to provide light emitting devices with various color tones.

[0136] Examples of phosphors include nitride-based phosphors, oxynitride-based phosphors, and sialon-based phosphors that are activated primarily with a lanthanoid element such as Eu or Ce; alkaline earth halo apatite phosphors, alkaline earth metal borate halide phosphors, alkaline earth metal aluminate phosphors, alkaline earth silicates, alkaline earth sulfides, alkaline earth thiogallates, alkaline earth silicon nitrides, germanates, and fluoride complexes that are activated primarily with a lanthanoid element such as Eu or a transition metal element such as Mn; rare earth aluminates and rare earth silicates that are activated primarily with a lanthanoid element such as Ce; and inorganic and organic complexes that are activated primarily with a lanthanoid element such as Eu.

[0137] Specific examples of phosphors include (Ca,Sr,Ba)2SiO4:Eu, (Y,Gd)3(Ga,Al)5O 12:Ce, (Si,Al)6(O,N)8:Eu(β-sialon), SrGa2S4:Eu, (Ca,Sr)2Si5N8:Eu, CaAlSiN3:Eu, (Ca,Sr)AlSiN3:Eu, Lu3Al5O 12 : Ce, (Ca, Sr, Ba, Zn)8MgSi4O 16 Examples include (F,Cl,Br,I)2:Eu, K2(Si,Ti,Ge)F6:Mn, 3.5MgO·0.5MgF2·GeO2:Mn, and the like, and it is preferable to include at least one selected from the group consisting of these.

[0138] The member covering the light source is, for example, composed of at least one type of resin. The resin may be either a thermoplastic resin or a thermosetting resin. Specific examples of thermosetting resins include epoxy resin and silicone resin. The member covering the light source may contain the above-mentioned luminescent material, phosphor, etc. in addition to the resin, and may further contain other components as necessary. Examples of other components include fillers such as silica, barium titanate, titanium oxide, and aluminum oxide, light stabilizers, colorants, etc. When the fluorescent member contains, for example, a filler as another component, the content thereof may be 0.01% by mass to 20% by mass of the resin.

[0139] An example of the light emitting device according to this embodiment will be described with reference to FIGS. 2, 3 and 4. FIG.

[0140] 2, 3, and 4 are schematic cross-sectional views of light-emitting devices 10, 20, and 30, respectively, which are examples of surface-mounted light-emitting devices. Light-emitting devices 10, 20, and 30 include a light-emitting element 6 that emits light on the short wavelength side of visible light (e.g., in the range of 380 nm to 485 nm) and has an emission peak wavelength in the range of 440 nm to 480 nm, and a molded body 9 on which the light-emitting element 6 is mounted. The molded body 9 is formed by integrally molding leads 7 and a resin portion. The molded body 9 forms a recess having a bottom and side surfaces, and the light-emitting element 6 is disposed on the bottom surface of the recess. The light-emitting element 6 has a pair of positive and negative electrodes, which are electrically connected via leads 7 and wires 8, respectively. The light-emitting element 6 is covered with a covering member 4 containing resin. The covering member 4 not only functions to protect the light-emitting element 6 from the external environment but also can convert the wavelength of the light emitted by the light-emitting element 6.

[0141] In the light-emitting device 10 of FIG. 2, a light-emitting material 1 containing core-shell semiconductor nanoparticles 2 and a metal compound 3 is encapsulated in a covering member 4. In FIG. 2, the light-emitting material 1 is mixed in a substantially uniform ratio throughout the covering member 4. This makes it possible to obtain light with reduced color unevenness. Furthermore, when the light-emitting material 1 is encapsulated in the covering member 4, the light-emitting material 1 may be unevenly distributed within the covering member 4. For example, by arranging the light-emitting material 1 close to the light-emitting element 6, the wavelength of the light from the light-emitting element 6 can be efficiently converted, resulting in a light-emitting device with excellent luminous efficiency.

[0142] In the light emitting device 20 of Fig. 3, a wavelength converting member 5 encapsulating a light emitting material 1 containing core-shell semiconductor nanoparticles 2 and a metal compound 3 is disposed on the surface of a covering member 4. In Fig. 3, the light emitting element 6 and the light emitting material 1 encapsulated in the wavelength converting member 5 are disposed with a gap between them, so that the effect of heat generated from the light emitting element 6 on the light emitting material 1 can be suppressed.

[0143] In the light emitting device 30 of FIG. 4 , a wavelength conversion member 5 encapsulating a light emitting material 1 containing core-shell semiconductor nanoparticles 2 and a metal compound 3 is disposed on the upper surfaces of the covering member 4 and the molded body 9. This is expected to have the same suppression effect on the light emitting material 1 as the light emitting device 20 with respect to the effect of heat generated by the light emitting element 6 on the light emitting material 1. Furthermore, the light emitting device 30 can be produced by a method in which the wavelength conversion member 5 is manufactured collectively in a separate process and then attached to the components of the light emitting device 30 other than the wavelength conversion member 5, or by a method in which a slurry-like raw material for the wavelength conversion member 5 is spray-coated onto the components of the light emitting device 30 other than the wavelength conversion member 5 and then cured. Therefore, a reduction in manufacturing costs due to simplified processes and improved yields can also be expected.

[0144] Examples of applications of light-emitting devices include lighting fixtures; display devices such as monitors, displays, and radar; and light sources for liquid crystal display devices.

[0145] The light-emitting device can be used in, for example, lighting fixtures; displays such as displays and radar; and light sources for liquid crystal displays. Preferably, the light source is incorporated into a liquid crystal display. Because band-edge emission from a light-emitting material has a short emission lifetime, a light-emitting device using the material is suitable as a light source for a liquid crystal display device that requires a relatively fast response speed. Furthermore, the light-emitting material of this embodiment can exhibit an emission peak with a small half-width as band-edge emission. Therefore, the light-emitting device may have the following configurations. (1) A blue semiconductor light-emitting element is used to obtain blue light having a peak wavelength in the range of 420 nm to 490 nm, and a light-emitting material is used to obtain green light having a peak wavelength in the range of 510 nm to 550 nm, preferably 530 nm to 540 nm, and red light having a peak wavelength in the range of 600 nm to 680 nm, preferably 630 nm to 650 nm; or (2) a light-emitting device is used to obtain ultraviolet light having a peak wavelength of 400 nm or less, and a light-emitting material is used to obtain blue light having a peak wavelength in the range of 430 nm to 470 nm, preferably 440 nm to 460 nm, green light having a peak wavelength in the range of 510 nm to 550 nm, preferably 530 nm to 540 nm, and red light having a peak wavelength in the range of 600 nm to 680 nm, preferably 630 nm to 650 nm. These light-emitting device embodiments allow for a liquid crystal display device with good color reproducibility without the use of dark color filters. The light emitting device is used, for example, as a direct type backlight or an edge type backlight.

[0146] Alternatively, a sheet, plate-like member, or rod made of resin, glass, or the like containing a light-emitting material may be incorporated into the liquid crystal display device as a light conversion member independent of the light-emitting device. [Example]

[0147] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0148] Example 1 Synthesis of semiconductor nanoparticles In a reaction vessel, 0.4 mmol of silver acetate (AgOAc) and 0.4 mmol of indium acetate (In(OAc)3) were mixed with 8 mL of distilled and purified oleylamine (OLA), and dodecanethiol (1.25 mmol, 300 μL) was added to prepare Solution A. Separately, 0.8 mmol of 1,3-dimethylthiourea was dissolved in 2 mL of oleylamine to prepare Solution B. Solution A was degassed and replaced with an argon atmosphere and heated to 140 °C. Solution B was then added dropwise to Solution A over 30 minutes. The rate of increase in the ratio of S atoms to Ag atoms in the mixture was 0.067 / min. After the addition, the solution temperature was maintained at 140 °C for 30 minutes. The mixture was then allowed to cool to room temperature, and coarse particles were removed by centrifugation. Methanol was then added to the supernatant to precipitate the core semiconductor nanoparticles, which were then recovered by centrifugation. The recovered solid was dispersed in 1 mL of chloroform.

[0149] Synthesis of core-shell semiconductor nanoparticles 0.1 mmol of gallium acetylacetonate (Ga(acac)3) and 0.1 mmol of 1,3-dimethylthiourea were weighed and added to 8 mL of distilled and purified oleylamine. The chloroform dispersion of the semiconductor nanoparticles synthesized above was then added to the core particle dispersion (a nanoparticle concentration equivalent to 30 nmol). The resulting solution was degassed at approximately 60 °C and replaced with an argon atmosphere. The temperature was then rapidly increased to 230 °C (heating rate: approximately 60 °C / min). After 230 °C, the temperature was further increased to 280 °C at a rate of 2 °C / min and heat-treated at 280 °C for 30 minutes. The solution was then allowed to cool to room temperature, and methanol was added to precipitate the core-shell semiconductor particles. After washing, the resulting core-shell semiconductor nanoparticles were dispersed in chloroform.

[0150] Synthesis of luminescent materials A portion of the obtained chloroform dispersion of core-shell semiconductor nanoparticles was taken and methanol was added to the resulting solution to cause precipitation, and several mL of 4-amino-1-butanol was added and stirred at 60°C for 30 minutes to obtain liquid C in which core-shell semiconductor nanoparticles were dispersed.

[0151] 0.06 mL of the above solution C was added to 12 mL of 1-propanol containing 0.6 mmol of zinc acetate and 0.5 mL of 4-amino-1-butanol, and 0.6 mmol of thioacetamide was added while stirring at room temperature. Stirring was continued for one day, and then the precipitate was collected by centrifugation. The precipitate was washed with methanol and dried in a vacuum oven at 70°C to obtain the luminescent material of Example 1. The emission spectrum of the obtained luminescent material is shown in Figure 5. The emission spectrum was measured using a spectrofluorometer (JASCO Corporation, product name FP-8600) with an excitation wavelength of 450 nm and observation wavelengths set to 460 nm to 1010 nm.

[0152] Example 2 0.06 mL of Solution C obtained in Example 1 was added to 12 mL of 1-propanol containing 0.6 mmol of gallium acetylacetonate (Ga(acac)3) and 0.5 mL of 4-amino-1-butanol, and 0.6 mmol of thioacetamide was added while stirring at room temperature. After stirring for one day, the precipitate was collected by centrifugation. The precipitate was washed with methanol and dried in a vacuum oven at 70°C to obtain the luminescent material of Example 2. The emission spectrum of the obtained luminescent material is shown in Figure 6.

[0153] (Comparative Example 1) The chloroform dispersion of the core-shell type semiconductor nanoparticles obtained in Example 1 was used as the light emitting material of Comparative Example 1.

[0154] (Durability evaluation) The light-emitting material obtained above was stored in the air in a dark place, and then the light-emitting properties of the light-emitting material were visually observed.

[0155] The luminescent material of Example 1 maintained its luminescence after 20 days of storage at room temperature, but the luminescent color changed from orange to red over time. The luminescent material of Example 2 maintained the same yellow luminescence as the initial luminescence even after one month of storage at room temperature. On the other hand, the luminescent material of Comparative Example 1 exhibited a decrease in luminescence intensity within a few days even when stored in a refrigerator, and ceased to emit light within about two weeks.

[0156] It was confirmed that the luminescent materials of Examples 1 and 2, in which the core-shell semiconductor nanoparticles were embedded in a metal compound, had improved durability compared to Comparative Example 1, in which the core-shell semiconductor nanoparticles were not embedded. It was also confirmed that the luminescent material of Example 2, in which the core-shell semiconductor nanoparticles were embedded in gallium sulfide, had improved durability compared to the luminescent material of Example 1, in which the core-shell semiconductor nanoparticles were embedded in zinc sulfide.

[0157] The disclosure of Japanese Patent Application No. 2020-040093 (filing date: March 9, 2020) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0158] 1. Luminescent materials 2. Core-shell semiconductor nanoparticles 3 Metal compounds 6 Light-emitting element 10, 20, 30 Light-emitting device

Claims

1. second semiconductor nanoparticles that emit light when irradiated with light, the second semiconductor nanoparticles comprising first semiconductor nanoparticles and an attachment disposed on the surface of the first semiconductor nanoparticles; a metal compound that embeds the second semiconductor nanoparticles; The first semiconductor nanoparticles are １ , M ２ and Z, M １ is at least one selected from the group consisting of Ag, Cu, Au and alkali metals, and contains at least Ag; M ２ is at least one selected from the group consisting of Al, Ga, In, and Tl, and contains at least one of In and Ga; Z is at least one selected from the group consisting of S, Se, and Te; The first semiconductor nanoparticles are M １ The total content of M is 10 mol % or more and 30 mol % or less, ２ and a total content of Z is 35 mol% or more and 55 mol% or less, the deposit substantially contains a semiconductor consisting of at least one selected from the group consisting of Al, Ga, In, Tl, and alkali metals, and at least one selected from the group consisting of S, O, Se, and Te; the second semiconductor nanoparticles further comprise an amino alcohol on the surface thereof; The metal compound comprises at least one of Zn and Ga, and at least one of S and O.

2. A light emitting device comprising: a light source having an emission peak wavelength in the range of 380 nm to 485 nm; and the light emitting material according to claim 1.

3. providing second semiconductor nanoparticles that emit light when irradiated with light, the second semiconductor nanoparticles including first semiconductor nanoparticles and an attachment disposed on a surface of the first semiconductor nanoparticles; contacting the second semiconductor nanoparticles with an amino alcohol; obtaining a mixture comprising second semiconductor nanoparticles contacted with the amino alcohol, a compound comprising at least one of Zn and Ga, a compound comprising at least one of S and O, and a solvent; obtaining, from the mixture, a metal compound that contains at least one of Zn and Ga, and at least one of S and O, and that embeds the second semiconductor nanoparticles; The first semiconductor nanoparticles are １ , M ２ and Z, M １ is at least one selected from the group consisting of Ag, Cu, Au and alkali metals, and contains at least Ag; M ２ is at least one selected from the group consisting of Al, Ga, In, and Tl, and contains at least one of In and Ga; Z is at least one selected from the group consisting of S, Se, and Te; The first semiconductor nanoparticles are M １ The total content of M is 10 mol % or more and 30 mol % or less, ２ and a total content of Z is 35 mol% or more and 55 mol% or less, A method for producing a luminescent material, wherein the deposit essentially comprises a semiconductor consisting of at least one selected from the group consisting of Al, Ga, In, Tl and alkali metals, and at least one selected from the group consisting of S, O, Se and Te.

4. The method for producing a luminescent material according to claim 3 , wherein the solvent contains an alcohol.

5. 5. The method for producing a luminescent material according to claim 3, wherein the temperature for obtaining the metal compound is 0°C or higher and 100°C or lower.

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