Color conversion particles

Abstract

These color conversion particles comprise a core, and a shell that encapsulates the core and absorbs excitation light. The color conversion particles receive irradiated excitation light and emit light in the core or at the interface of the core and the shell. The shell is configured from a chalcogenide perovskite, and the core and the shell have a band alignment that manifests a Stokes shift.

Description

[Technical Field]

[0001] The present invention relates to color conversion particles. [Background technology]

[0002] Color conversion using wavelength conversion (down-conversion), in which excitation light incident on an object from the outside is converted into light with a longer wavelength and then emitted, has been widely used in lighting, display devices, solar cells, and other applications. For example, phosphors containing added activators are sometimes used in this type of color conversion. However, conventional phosphors have limitations in the controllability of the emission wavelength, emission peak width, and number of peaks (color purity). Therefore, there are many issues that need to be addressed when applying them to applications requiring high color purity at specific wavelengths, such as display devices.

[0003] On the other hand, in recent years, core-shell quantum dots, which utilize quantum effects to solve the above problems, have attracted attention and are being applied in various fields. Core-shell quantum dots are tiny semiconductor particles with a diameter of several nanometers, and have a structure in which a core, which functions as a light-emitting portion, is covered from the outside by a shell, which functions as a carrier confinement layer and a light-absorbing portion.

[0004] In this type of core-shell quantum dot, the core material is selected from, for example, Cd(S,Se), InP, and APbX3 (A = Cs,MA; X = Cl, Br, I). The shell material is, for example, Zn(S,Se) or A'2PbX4 (A' = OA), where MA is methylammonium and OA is octylammonium. Non-Patent Documents 1 and 2 disclose core-shell quantum dots using halide perovskite, typified by CsPbBr3. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] S. Bera et al., “Perovskite Nanocrystal Heterostructures: Synthesis, Optical Properties, and Applications”, ACS Energy Lett. 5, 2858-2872 (2020). [Non-patent document 2] “Challenges and Opportunities in Designing Perovskite Nanocrystal Heterostructures”, ACS Energy Lett. 5, 2253-2255 (2020). Summary of the Invention [Problem to be solved by the invention]

[0006] CdSe, one of the materials for the core-shell quantum dots mentioned above, contains Cd, which is restricted by RoHS, and is toxic. For this reason, InP was developed as an alternative to Cd(S,Se), but InP contains the rare metal In and has issues with material durability and luminescence efficiency. On the other hand, halide perovskites, such as CsPbBr, have high absorbance and luminescence efficiency, but their material durability is insufficient.

[0007] Furthermore, quantum dots have a small absorbance due to their small size of a few nanometers, but increasing the size of quantum dots to increase absorbance raises concerns that the quantum size effect will be lost and that luminescence efficiency will decrease due to increased loss due to reabsorption of emitted light.

[0008] The present invention has been made in view of the above circumstances, and provides color conversion particles that ensure durability and achieve high absorbance and high luminous efficiency. [Means for solving the problem]

[0009] A color conversion particle according to one embodiment of the present invention comprises a core and a shell that surrounds the core and absorbs excitation light, and emits light at the core or at the interface between the core and the shell upon irradiation with excitation light. The shell is made of a chalcogenide perovskite, and the core and shell have a band alignment that produces a Stokes shift. The band alignment is determined by the energy E of the lower edge of the conduction band of the shell. c_shell is the energy E at the bottom of the conduction band of the core c_core or the energy E of the top of the valence band of the shell v_shell is the energy E at the top of the valence band of the core v_core The band gap of the shell is larger than the band gap of the core. [Effects of the Invention]

[0010] The color conversion particles of the present invention ensure durability and can achieve high absorbance and high luminous efficiency. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are schematic diagrams showing examples of the configuration of color conversion particles according to an embodiment of the present invention. [Figure 2] 10 is a graph showing an example of the relationship between the shell thickness and the absorptance of excitation light. [Figure 3] 1 is a graph showing an example of the relationship between excitation energy and particle radius. [Figure 4] FIG. 1 shows an example of core and shell band alignment. [Figure 5] FIG. 1 shows an example of core and shell band alignment. [Figure 6] FIG. 1 shows an example of core and shell band alignment. [Figure 7] 10A and 10B are diagrams showing modified examples of color conversion particles according to the present embodiment. [Figure 8] 10A and 10B are diagrams showing modified examples of color conversion particles according to the present embodiment. [Figure 9] FIG. 1 is a diagram showing the band alignment of the core and shell in an example. [Figure 10] FIG. 10 is a diagram showing the results of a simulation of an example. [Figure 11] FIG. 1 shows the optical absorption coefficients of BaZrS3 and SrZrS3, and the respective profiles of the PL emission spectrum of BaZrS3. [Figure 12] FIG. 1 is a diagram showing the correspondence between combinations of core and shell materials and the type of band alignment and the occurrence of Stokes shift in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment will be described with reference to the drawings. In the embodiments, in order to make the explanation easier to understand, structures or elements other than the main parts of the present invention will be described in a simplified or omitted manner. Furthermore, in the drawings, the same elements are given the same reference numerals. Note that the shapes, dimensions, etc. of each element in the drawings are shown schematically and do not represent the actual shapes, dimensions, etc.

[0013] <Color conversion particle structure> FIG. 1(a) is a schematic diagram showing an example of the configuration of color conversion particles according to this embodiment. The color conversion particles 10 have an overall particle shape on the nanometer scale, and perform color conversion by absorbing incident excitation light and re-emitting (emitting) it as light with a different energy (wavelength).

[0014] The color conversion particle 10 has a core 11 as a light-emitting portion and a shell 12 as a light-absorbing portion. The shell 12 contains one or more cores 11 therein. The color conversion particle 10 is formed by covering part or all of each core 11 from the outside with the shell 12.

[0015] In the color conversion particle 10, the core 11 and the shell 12 are provided separately, and the material for the shell 12 is a chalcogenide perovskite, which will be described later. This allows the shell 12 to have high absorbance for the excitation light, and also improves the durability of the color conversion particle 10. This will be described later.

[0016] In addition, the energy E c and the energy at the top of the valence band, E v The band alignment between the core 11 and the shell 12 is such that a Stokes shift occurs. The band alignment between the core 11 and the shell 12 will be described later. Furthermore, by adjusting the band gap between the core 11 and the shell 12, it is possible to impart to the shell 12 the property of transmitting the light emitted in the core 11. This makes it possible to prevent the light generated in the core 11 from being reabsorbed by the shell 12 in the color conversion particle 10.

[0017] <Shell 12> (Shell material) The shell 12 is made of chalcogenide perovskite, which is a semiconductor material that absorbs the target excitation light wavelength and generates excited carriers. Chalcogenide perovskites are semiconductors consisting of a group of perovskite crystal structures containing chalcogen elements (S, Se, Te) at the X site, and also include those in which part of the X site is replaced with oxygen (O).

[0018] Perovskites, as mentioned above, are a group of substances with a cubic crystal structure based on a BX6 octahedron, represented by the chemical formula ABX3. Due to lattice distortion, they can take on tetragonal or orthorhombic crystal structures. Furthermore, several stable crystal structures have been shown to exist for the same ABX3 composition through computational science. These crystal structures range from structures close to perovskite to structures that are quite different. Furthermore, derivative structures exist, such as Ruddlesden-Popper and Dion-Jacobson layered perovskites based on the perovskite structure, as well as double perovskite crystal structures in which different elements are alternately arranged at the B site. In this specification, the above crystal structures are collectively referred to as the "perovskite crystal structure group."

[0019] The perovskite crystal structure group specifically includes substances having the following crystal structures: Cubic perovskite, tetragonal perovskite, GdFeO3-type orthorhombic, YScS3-type orthorhombic, NH4CdCl3-type orthorhombic, BaNiO3-type hexagonal, FePS3-type monoclinic, PbPS3-type monoclinic, CeTmS3-type monoclinic, Ruddlesden-Popper-type layered perovskite, Dion-Jacobson-type layered perovskite, double perovskite The perovskite crystal structure group changes its crystal structure and electronic structure depending on the composition and synthesis conditions, which in turn changes its optoelectronic and chemical properties. Therefore, the composition and synthesis conditions are selected to obtain a crystal structure suitable for the purpose.

[0020] For example, materials with cubic perovskite, tetragonal perovskite, GdFeO3-type orthorhombic perovskite, Ruddlesden-Popper-type layered perovskite, and double perovskite structures have excellent optoelectronic and chemical properties. Furthermore, by using a Dion-Jacobson-type layered perovskite structure, chemical stability can be further improved. In particular, materials with a GdFeO3-type orthorhombic perovskite crystal structure, represented by ABX3 (A = Group 2, B = Group 4), are known to have excellent photoelectron properties, including a high optical absorption coefficient.

[0021] The chemical formula of chalcogenide perovskite is ABX3,A'2A n-1 B n X 3n+1 , A''A'''B''2X7, A''A2B''3X 10 , which can be expressed as A2BB'X6. In the above chemical formula, X represents a chalcogen element (S, Se, Te). A and A' represent Group 2 elements (Ca, Sr, Ba), A'' represents Group 1 elements (Li, Na, K, Rb, Cs), and A''' represents Group 3 elements (rare earth elements) and Bi. B and B' represent Group 4 elements (Ti, Zr, Hf), and B'' represents Group 5 elements (V, Nb, Ta). Also, n is a positive integer. Note that A and A', and B and B' may be the same element. Also, A, A', A'', A''', B, B', B'', and X include mixtures of elements from each group in any ratio.

[0022] As an example, chalcogenite perovskite represented by the chemical formula ABX3 includes the following materials: In the following example, X is selected from the predominant chalcogen elements (S, Se), A is selected from the predominant Group 2 elements (Sr, Ba), and B is selected from the predominant Group 4 elements (Zr, Hf). SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, BaHfSe3

[0023] As an example, the chemical formula A'2A n-1 B n X 3n+1 Chalcogenite perovskites expressed as follows include the following materials: X is selected from the dominant chalcogen elements (S, Se), A and A' are selected from the dominant Group 2 elements (Sr, Ba), and B is selected from the dominant Group 4 elements (Zr, Hf). Sr2Ba n-1 Zr n S 3n+1 , Sr2Ba n-1 Zr n Se 3n+1 , Sr n+1 Zr n S 3n+1 , Sr n+1 Zr n Se 3n+1 , Ba2Sr n-1 Zr n S 3n+1 , Ba2Srn-1 Zr n Se 3n+1 , Ba n+1 Zr n S 3n+1 , Ba n+1 Zr n Se 3n+1 , Sr2Ba n-1 Hf n S 3n+1 , Sr2Ba n-1 Hf n Se 3n+1 , Sr n+1 Hf n S 3n+1 , Sr n+1 Hf n Se 3n+1 , Ba2Sr n-1 Hf n S 3n+1 , Ba2Sr n-1 Hf n Se 3n+1 , Ba n+1 Hf n S 3n+1 , Ba n+1 Hf n Se 3n+1

[0024] These chalcogenide perovskites (Sr x Ba 1-x )(Zr y Hf 1-y )(S z Se 1-z )3 or (Sr x’ Ba 1-x’ )2(Sr x Ba 1-x ) n-1 (Zr y Hf 1-y ) n (S z Se 1-z ) 3n+1 (where x, x', y, and z are each a value between 0 and 1).

[0025] The dominant materials for X, A, A', and B described above are materials that, when applied to the color conversion particles 10, have a band gap suitable for applications that emit visible light, such as light-emitting devices, display devices, and lighting devices.

[0026] In chalcogenide perovskites, the carrier concentration, crystal structure, and other physical and chemical properties can be controlled by partial substitution of constituent elements with elements from the same or different groups. For example, elements from group 1 can be substituted with elements from groups 1 and 2, elements from group 2 with elements from groups 1, 2, and 3, elements from group 3 with elements from groups 2, 3, and 4, elements from group 4 with elements from groups 3, 4, and 5, and elements from group 16 with elements from groups 15, 16, and 17.

[0027] The features of chalcogenide perovskites include the following: Chalcogenide perovskites have a large optical absorption coefficient and excellent luminescence performance (luminous efficiency, half-width). In addition, the optical absorption coefficient profile of chalcogenide perovskites rises steeply at the band edge. Therefore, chalcogenide perovskites have the characteristic of high absorbance near the band gap edge. Therefore, the chalcogenide perovskite shell 12 has high absorbance and can efficiently absorb the excitation light.

[0028] Furthermore, chalcogenide perovskite has high chemical stability and is highly resistant to external environments and stimuli such as air, moisture, heat, and light. Therefore, the chalcogenide perovskite shell 12 is highly durable and can suppress deterioration of the shell 12 itself and the core 11 inside. Furthermore, chalcogenide perovskites are advantageous in that they are highly safe because they do not contain toxic elements, and the raw material costs are low because they do not contain rare metals.

[0029] (shell band gap) Next, the band gap of the shell 12 using chalcogenide perovskite will be described. In color conversion particles, light emitted at the core or core-shell interface passes through the shell and is extracted to the outside. Therefore, the shell must be transparent to the emitted light. If the emitted light is absorbed in the shell, the luminous efficiency of the color conversion particles will decrease accordingly. Therefore, it is preferable that the band gap of the shell is equal to or greater than the energy of the emitted light.

[0030] Shell 12 using chalcogenide perovskite can effectively absorb ultraviolet excitation light (wavelength 365 nm) from GaN (Eg ~ 3.4 eV) LEDs when the band gap is 3.4 eV or less. Also, shell 12 using chalcogenide perovskite can effectively absorb blue excitation light (wavelength 460 nm) from InGaN LEDs or OLEDs when the band gap is 2.7 eV or less. Therefore, the band gap of the shell 12 is preferably 3.4 eV or less to absorb light with a wavelength of 365 nm or more, or 2.7 eV or less to absorb light with a wavelength of 460 nm or more.

[0031] Here, ZnS (Eg ~ 3.6 eV; wavelength 340 nm), which is commonly used for the shell of conventional quantum dots, cannot absorb the above excitation light. Therefore, in the case of a shell using ZnS, the above excitation light does not produce a Stokes shift. Similarly, since the band gap of ZnSe is 2.7 eV (wavelength 460 nm), it can absorb ultraviolet excitation light, but its absorption of blue excitation light is weak. In any case, conventional materials have low optical absorption coefficients near the band gap edge, so they are unable to sufficiently absorb the excitation light, resulting in lower shell absorbance compared to chalcogenide perovskites.

[0032] (shell thickness) The upper and lower limits of the thickness of the shell 12 are determined from the following viewpoints. First, the shell 12, which is the light absorbing portion, is required to have a thickness that allows it to sufficiently absorb the excitation light.

[0033] Figure 2 is a graph showing the calculated absorption rate of 460 nm excitation light (blue light) versus the thickness of the shell 12, using the optical absorption coefficient of SrZrS3, a typical chalcogenide perovskite material. The vertical axis of Figure 2 represents the absorption rate of 460 nm excitation light, and the horizontal axis of Figure 2 represents the thickness (nm) of the shell 12. The absorptance of blue light shown in Figure 2 was approximately 4% at 2 nm, approximately 10% at 5 nm, approximately 20% at 10 nm, approximately 46% at 30 nm, approximately 64% at 50 nm, and approximately 87% at 100 nm.

[0034] The color conversion particles 10 are usually expected to be used as a color conversion material by incorporating a large number of color conversion particles 10 into a film, coating, resin, etc. In this case, as shown in Figure 2, if each shell 12 has a thickness of at least 2 nm, sufficient absorbance can be achieved for the entire color conversion material to which a large number of color conversion particles are applied. Specifically, when applied to a color conversion film, it is assumed that there are 100 or more color conversion particles 10 in the thickness direction of the color conversion film. If the thickness of the shell 12 is 2 nm, one color conversion particle 10 can absorb about 4% of blue light, so the above color conversion film can sufficiently absorb blue light.

[0035] Secondly, if the shell 12 is too thick, photoexcited carriers will recombine and be deactivated before reaching the core 11, resulting in a decrease in luminous efficiency.

[0036] Here, the carrier diffusion length is estimated to be approximately 30 nm at most based on the electrical conductivity of SrHfS3, a typical chalcogenide perovskite material. Also, Figure 2 shows that approximately 98% of blue light is absorbed at a thickness of 200 nm. Assuming that carriers excited by light absorbed at a depth of 200 nm in the shell 12 diffuse over a diffusion length of 30 nm, if the shell 12 is further away from the 200 nm depth position by more than 100 nm in the depth direction, almost no carriers can reach the core 11. Therefore, if the shell 12 is thicker than 300 nm, photoexcited carriers cannot reach the core 11, resulting in reduced luminous efficiency. Therefore, the thickness of the shell 12 is in the range of 2 nm to 300 nm.

[0037] From the viewpoint of suppressing recombination of photoexcited carriers, it is preferable that the thickness of shell 12 is as thin as possible as long as shell 12 can sufficiently absorb the excitation light, and for example, the thickness of shell 12 is preferably 2 nm to 50 nm. When the thickness of shell 12 is 50 nm, approximately 64% of blue light is absorbed. To increase light absorption without sacrificing the distance over which carriers diffuse, it is preferable that the thickness of shell 12 be up to 50 nm.

[0038] When the shell 12 is 30 nm thick, the absorption of blue light is reduced to approximately 46%, but because this is within the carrier diffusion length, more carriers can move to the core, thereby improving luminous efficiency. When the shell 12 is 10 nm thick, the absorption of blue light is only approximately 20%, but because this is sufficiently thinner than the carrier diffusion length, most of the carriers move to the core, thereby improving luminous efficiency. Therefore, the thickness of the shell 12 is preferably in the range of 2 nm to 30 nm (blue light absorption rate: approximately 4% to approximately 46%), and more preferably in the range of 2 nm to 10 nm (blue light absorption rate: approximately 4% to approximately 20%), thereby achieving both sufficient absorption of blue light and good carrier movement to the core 11.

[0039] <Core 11> The core 11 is a light-emitting particle made of a semiconductor material that emits fluorescence of a desired emission wavelength when exposed to excitation light. The core 11 as a light-emitting particle generates transitions between electron levels with energy corresponding to the desired emission wavelength.

[0040] When a semiconductor is used as a light-emitting particle, the fluorescence emitted when electrons excited to the conduction band recombine with holes in the valence band is used as the light emission. Therefore, the emission wavelength of the light-emitting particle is determined by the band gap energy E g,bulk is equivalent to

[0041] When the particle size of the luminescent particles becomes small and the quantum size effect due to the confinement of electrons becomes significant, the energy levels of the electrons become discrete. In this case, the energy of the lowest excited state (band gap) E ex is E g,bulk The emission wavelength becomes larger than that in the bulk state and depends on the particle size. In other words, as the particle size of the luminescent particles decreases, the emission wavelength shifts to shorter wavelengths than in the bulk state, and the emission wavelength changes depending on the particle size. By utilizing this property, it is possible to control the emission wavelength of the luminescent particles.

[0042] Specifically, E of a luminous particle with radius r ex is given by the following equation, where μ is the exciton-reduced mass and E b,ex denotes the exciton binding energy, and r B denotes the exciton Bohr radius.

[0043]

number

[0044] μ,E b,ex ,r B are given by the following equations, where ε is the dielectric constant of the light-emitting particle. * e is the effective mass of the electron, and m * h is the effective mass of the hole.

[0045]

number

[0046] Figure 3 shows the E when μ=0.1 and ε=10. ex The vertical axis of Figure 3 is the E ex / E g,bulk The horizontal axis of Figure 3 shows r / r B The radius r of the luminous particle becomes smaller and B As it approaches E ex The value of E g,bulk It gradually increases from rB If it becomes below E ex The value of increases significantly (quantum size effect).

[0047] By utilizing the characteristics of the quantum size effect, the r determined by the above formula B Based on this, light-emitting particles having a particle size in a range in which the emission wavelength depends on the particle size are called "quantum dots." On the other hand, light-emitting particles having a particle size in a range in which the emission wavelength is almost independent of the particle size are called "non-quantum dots." The particle size at which the quantum size effect appears varies depending on the parameters μ and ε. For a typical semiconductor, if μ=0.1 and ε=10 are assumed, then r=3r B This is the boundary of the particle size (radius) at which the quantum size effect appears. In Figure 3, this boundary is indicated by a dashed line.

[0048] As mentioned above, the particle size at which the quantum size effect appears in a luminescent particle is basically the exciton Bohr radius r B The quantum size effect is characterized by the relationship between the dielectric constant of the material and the effective mass of the electron and hole, and E ex The change in the value of is also continuous. Therefore, it is actually difficult to express the boundary between quantum dots and non-quantum dots uniquely in terms of particle size or other physical properties.

[0049] Here, the typical physical properties (m e * =0.3m0, m h * =0.5m0, ε=6ε0, E g,bulk = 1.93 eV) ex Consider the particle radius dependence of m0 above, which is the mass of the electron. In the case of BaZrS3, the typical quantum size particle radius is considered to be approximately 7.5 nm. Therefore, in the case of BaZrS3, particles with a diameter of 15 nm or less are considered quantum dots, and particles with a diameter of more than 15 nm are considered non-quantum dots.

[0050] The core 11 of this embodiment may be either the quantum dot or non-quantum dot described above. When the core 11 is a quantum dot, there is an advantage that the emission wavelength (color) can be controlled by changing the particle size of the same substance. Also, in the case of quantum dots, the luminous efficiency of the core 11 is high and the peak is narrow. However, precise particle size control is necessary to align the emission wavelength (color), and the production of quantum dots requires advanced manufacturing technology. Furthermore, quantum dots have poor chemical stability due to their tiny size, and they easily aggregate, re-grow, or decompose, so their surfaces must be protected. Furthermore, quantum dots have discrete electronic states, so the density of states in both the valence band and conduction band is small, resulting in a smaller optical absorption coefficient compared to bulk materials.

[0051] On the other hand, if the core 11 is a non-quantum dot, that is, if a relatively large particle is used and bulk emission is utilized without manifesting the quantum size effect, the stability and light absorption problems are alleviated. However, for non-quantum dots, the emission wavelength of the core 11 is E g,bulk Therefore, to adjust the emission wavelength, E g,bulk It becomes necessary to change

[0052] As described above, quantum dots and non-quantum dots both have their advantages and disadvantages, so an appropriate quantum dot or non-quantum dot structure can be selected depending on the situation and application as the configuration of core 11. Furthermore, the dimensions that produce the quantum size effect differ depending on the material, so the particle size of core 11 is set appropriately depending on the physical properties of the material, etc.

[0053] On the other hand, to suppress re-absorption by core 11, it is preferable that the particle size of core 11 is small. For example, when BaZrS3 has a particle size of 200 nm, it absorbs 10% of red light with a wavelength of 630 nm generated by another BaZrS3 core placed nearby. Therefore, it is preferable that the particle size of core 11 is 200 nm or less.

[0054] Furthermore, under the above conditions, if the particle size of core 11 is 50 nm or less, the re-absorption of red light with a wavelength of 630 nm is 3%, and if the particle size of core 11 is 25 nm or less, the re-absorption of red light with a wavelength of 630 nm can be suppressed to 2% or less. Therefore, the particle size of core 11 is preferably 50 nm or less, and more preferably 25 nm or less.

[0055] Furthermore, the particle size at which the core 11 can exist stably is preferably 1 nm or more. From the above, it is preferable that the particle size of the core 11 is 1 nm or more and 200 nm or less.

[0056] (Core 11 material) Examples of materials that can be used for the core 11 include substances (so-called activated phosphors) in which an activator that serves as a luminescent center (luminescent ion) is added to a host crystal such as an oxide or nitride, II-VI group semiconductors, III-V group semiconductors, I-III-VI group semiconductors, I-II-IV-VI group semiconductors, IV-VI group semiconductors, halide perovskite semiconductors, oxide perovskites, organic-inorganic perovskites, Si, carbon materials, and mixed crystal compounds thereof.

[0057] The material of the core 11 can also be chalcogenide perovskite. The core 11 using chalcogenide perovskite, which has an excellent optical absorption coefficient, is expected to have high luminescence performance. Furthermore, the core 11 using chalcogenide perovskite reduces defects at the interface between the core 11 and the shell 12 and reduces non-radiative recombination due to its affinity with the constituent elements of the shell and the matching between the crystal structure and lattice constant, so that higher luminous efficiency can be expected.

[0058] For example, when chalcogenide perovskite is used as the material for the core 11, a material different from that for the shell 12 can be selected from the following substances. SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, BaHfSe3, Sr2Ba n-1 Zr nS 3n+1 , Sr2Ba n-1 Zr n Se 3n+1 , Sr n+1 Zr n S 3n+1 , Sr n+1 Zr n Se 3n+1 , Ba2Sr n-1 Zr n S 3n+1 , Ba2Sr n-1 Zr n Se 3n+1 , Ba n+1 Zr n S 3n+1 , Ba n+1 Zr n Se 3n+1 , Sr2Ba n-1 Hf n S 3n+1 , Sr2Ba n-1 Hf n Se 3n+1 , Sr n+1 Hf n S 3n+1 , Sr n+1 Hf n Se 3n+1 , Ba2Sr n-1 Hf n S 3n+1 , Ba2Sr n-1 Hf n Se 3n+1 , Ba n+1 Hf n S 3n+1 , Ba n+1 Hf n Se 3n+1

[0059] The chalcogenide perovskites applicable to the core 11, as well as the shell 12, are (Sr x Ba 1-x )(Zr y Hf 1-y )(S z Se 1-z )3 or (Sr x’ Ba 1-x’ )2(Sr x Ba 1-x ) n-1 (Zr y Hf1-y ) n (S z Se 1-z ) 3n+1 (where x, x', y, and z are each a value between 0 and 1). These substances are advantageous materials in that, when applied to the core 11 of the color conversion particle 10, they have a band gap suitable for applications that emit visible light, such as light-emitting devices, display devices, and lighting devices.

[0060] <Band alignment of core 11 and shell 12> As mentioned above, the energy E c and the energy at the top of the valence band, E v The band alignment is such that a Stokes shift occurs.

[0061] The Stokes shift originally refers to the energy difference between the energy state of photoexcited electrons and the electronic state when they emit energy and emit light in a single substance, and is observed as the difference in the maximum energy positions of the absorption spectrum and emission spectrum. In heterostructure nanoparticles such as the color conversion particle 10 of this embodiment, an "apparent Stokes shift," i.e., an energy difference between the absorption spectrum edge and the emission spectrum peak, can be generated by designing an appropriate band alignment at the heterointerface. In this specification, the apparent Stokes shift generated in heterostructure nanoparticles is sometimes simply referred to as the Stokes shift.

[0062] 4, 5 and 6 show examples of band alignment between the core 11 and the shell 12. In each of Figures 4, 5, and 6, the upward direction indicates the direction of increasing energy, and the central rectangle indicates the band gap E g_core The rectangles on both sides indicate the band gap E of shell 12. g_shell The upper side of the central rectangle represents the energy E c_core The base of the central rectangle is the energy E at the top of the valence band of the core 11.v_core The top edges of the rectangles on both sides indicate the energy E c_shell The bottom of the rectangle on both sides is the energy E at the top of the valence band of shell 12. v_shell Shows.

[0063] In Figures 4, 5, and 6, the curve drawn on the top side of the rectangle indicates the distribution of electrons, and the curve drawn on the bottom side of the rectangle indicates the distribution of holes. The downward arrows in the figures indicate the energy difference in the emission process, and the upward arrows in the figures indicate the energy difference in the absorption (excitation) process. A Stokes shift occurs when the energy difference in the absorption process is larger than the energy difference in the emission process.

[0064] In Figure 4(a)-(e), the band gap E g_shell are the band gap E of Core 11 g_core is greater than (E g_shell >E g_core ) On the other hand, in Figure 5(a)-(e), the band gap E g_shell are the band gap E of Core 11 g_core is smaller than (E g_shell <E g_core ) In addition, in Figure 6(a)-(c), the band gap E g_shell are the band gap E of Core 11 g_core is equal to (E g_shell =E g_core ). In addition, E c_core and E c_shell The relationship between the magnitudes of E v_core and E v_shell The magnitude relationship is shown in Figures 4, 5, and 6, respectively.

[0065] The Stokes shift occurs in the band alignments (Type I, Quasi-Type II, and Type II) shown in Figures 4(a)-(e), 5(a), (e), 6(a), and (c). Therefore, the color conversion particles of this embodiment have any of the band alignments shown in Figures 4(a)-(e), 5(a), (e), and 6(a) and (c). The band alignment of the color conversion particles of this embodiment occurs when the energy E c_shell is the energy E at the bottom of the conduction band of the core 11 c_core or the energy E of the top of the valence band of shell 12 v_shell is the energy E at the top of the valence band of the core 11 v_core or lower than E c_shell >E c_core , E v_shell <E v_core Either one of or E c_shell >E c_core and E v_shell <E v_core ).

[0066] The band alignments (Type I and Quasi-Type II) in Fig. 4(b), (c), and (d) are the energy E c_shell is the energy E at the bottom of the conduction band of the core 11 c_core Now, the energy E at the top of the valence band of shell 12 v_shell is the energy E at the top of the valence band of the core 11 v_core The following conditions are satisfied (i.e., E g_shell >E g_core When E c_shell ≧E c_core And E v_shell ≦E v_core ).

[0067] In the case of Type I shown in Figure 4(c), electrons and holes are confined in the core 11 and recombine (core emission) occurs within the core 11. In Type I, holes and electrons are localized in the core 11, resulting in large overlap of wave functions and high emission efficiency. Therefore, the Type I configuration is the most preferable in terms of band alignment between the core 11 and shell 12. Examples of materials for the core 11 and shell 12 of Type I shown in Figure 4(c) include a combination of BaZrS3 for the core 11 and SrZrS3 for the shell 12.

[0068] Quasi-Type II (where E g_shell >E g_core In Quasi-Type II shown in Figures 4(b) and (d), one of the carriers, holes or electrons, spreads to the shell, resulting in a lower luminous efficiency than Type I. However, in Figures 4(b) and (d), the other carrier is still localized in the core, resulting in a relatively high luminous efficiency, making it the second most preferable after Type I. An example of the materials for the core 11 and shell 12 of Quasi-Type II shown in Figures 4(b) and (d) is the combination of BaHfS3 for the core 11 and CaZrS3 for the shell 12 shown in Figure 4(b).

[0069] In addition, in the band alignment (Type II) shown in Figures 4(a), (e), 5(a), (e), 6(a), and (c), electrons and holes are separated into the core 11 and the shell 12, so light emission due to interband recombination is less likely to occur compared to Type I. However, in Type II, recombination (interface emission) may occur at the interface between the core 11 and the shell 12, and the E g Since the energy difference is smaller than the

[0070] In the case of Type II, light emission occurs at the interface between the core 11 and shell 12, so the overlap of the wave functions is small and the light emission efficiency is lower than that of Type I. In addition, interface recombination can be accompanied by non-radiative recombination via interface defects, which is also thought to be a factor in the lower light emission efficiency. However, Type II band alignment is advantageous in that it can achieve a wide range of emission wavelengths, and is expected to be applied to near-infrared luminescent materials, etc. Examples of materials for the Type II core 11 and shell 12 shown in Figures 4(a), (e), 5(a), (e), 6(a), and (c) include the combination of BaZrS3 for the core 11 and CaZrS3 for the shell 12 shown in Figure 4(a).

[0071] As shown in Figures 4(a)-(e), the band gap E g_shell The band gap E of Core 11 g_core Make it larger than (E g_shell >E g_core ), the light emitted in the core 11 is emitted to the outside without being absorbed by the shell 12. This suppresses re-absorption loss in the shell 12, and the luminous efficiency of the color conversion particle 10 can be further improved.

[0072] In Figure 6(a) and (c), the band gap E g_shell is the band gap E of Core 11 g_core is equal to (E g_shell =E g_core ). Therefore, in the cases of Fig. 6(a) and (c), the cases of Fig. 4(a)-(e) (E g_shell >E g_core ), the light emitted from the core 11 is easily reabsorbed by the shell 12, resulting in a large reabsorption loss. This reduces the luminous efficiency of the color conversion particle 10. Note that, as shown in FIGS. 5(a) and 5(e), the band gap E g_shell is the band gap E of Core 11 g_core is smaller than (E g_shell <E g_core 6(a) and (c) with the cases of Figures 6(a) and (c), in the cases of Figures 6(a) and (c), less light is reabsorbed in the shell 12, suppressing reabsorption loss, thereby improving the luminous efficiency of the color conversion particles 10.

[0073] The color conversion particles 10 can be in various states depending on the combination of the materials for the core 11 and the shell 12. The materials for the core 11 and the shell 12 exemplified above are sulfides, but they may also be selenides or solid solutions. Including these, various states can be realized, and there are combinations of the materials for the core 11 and the shell 12 that exhibit excellent light-emitting properties.

[0074] <Particle size of color conversion particles 10> When applying ink in which color conversion particles 10 are dispersed in a solvent using, for example, an inkjet method, if the particle size of the color conversion particles 10 is too large, it can cause nozzle clogging. In other application methods as well, the large particle size of the color conversion particles 10 can pose a problem in the process. For the reasons above, it is preferable that the particle size of the color conversion particles 10 be 1000 nm or less.

[0075] <Method of manufacturing color conversion particles 10> Next, a description will be given of a method for producing the color conversion particles 10. The color conversion particles 10 are produced by synthesizing the core 11 and then synthesizing the shell 12.

[0076] (Core 11 synthesis process) In the synthesis process of the core 11, the core 11, which is a nano-luminescent particle, is produced by a known method such as a hot injection method, a solvothermal method, a hydrothermal method, a continuous flow process synthesis method, a composite-hydroxide-mediated (CHM) method, a heat-up method, a gas-phase synthesis, a solid-phase synthesis, or a mechanochemical synthesis. The material of the core 11 may be, for example, the above-mentioned substances.

[0077] Furthermore, chalcogenide perovskite may be used as the material for core 11. In this case, core 11 may be synthesized by reacting precursor compounds in a solution, by mixing and heating precursor powders in an inert atmosphere or in the air, or by mixing and heating metal precursor powders in an inert atmosphere and reacting them with chalcogen precursor gas. When synthesizing the core 11 by reacting a precursor compound in a solution, for example, a hot injection method, a heat-up method, a solvothermal method, a hydrothermal method, a CHM method, a continuous flow process synthesis method, or the like can be applied.

[0078] (Shell 12 synthesis process) In the shell 12 synthesis step, a chalcogenide perovskite shell 12 is synthesized on the surface of the core 11 obtained in the above step. In this step, a one-pot synthesis method or a hot injection method is applied to mix nano-luminescent particles that will become the core 11 with a chalcogenide perovskite precursor in a solvent. This synthesizes color conversion particles 10 having a core-shell structure in which the surface of the core 11 is covered with a chalcogenide perovskite shell 12. As a shell synthesis method other than using a solution, the shell 12 may also be produced by gas-phase synthesis, for example, by barrel sputtering.

[0079] As an example, a case will be described in which the hot injection method is applied to synthesize a shell 12 of chalcogenide perovskite ABX3, in which A and B are group II and group IV elements, respectively. In this case, a first solution containing core nanoparticles, a precursor compound containing a Group II element, a precursor compound containing a Group IV element, and a solvent, and a second solution containing a precursor compound containing a chalcogen element and a solvent are prepared. The second solution is then added to the first solution in a reaction vessel at a temperature ranging from 150°C to 350°C, and the reaction is allowed to proceed at the aforementioned temperature for 1 second to 100 hours. This allows the shell material to grow on the nanoparticles used in the reaction, synthesizing the desired compound with a core-shell structure. After the reaction is complete, the target product is recovered after washing with an organic solvent or water.

[0080] Examples of the precursor compounds containing the above-mentioned Group II elements include the following. Metal powders, metal alkoxides, metal carboxylates, metal nitrates, metal perchlorates, metal sulfates, metal acetylacetonates, metal halides, metal hydroxides, metal halides, and combinations thereof

[0081] Examples of the precursor compounds containing the above-mentioned Group IV elements include the following. Metal powders, metal alkoxides, metal carboxylates, metal nitrates, metal perchlorates, metal sulfates, metal acetylacetonates, metal halides, metal hydroxides, metal halides, and combinations thereof

[0082] Examples of the precursor compounds containing the chalcogen elements include the following. Metal sulfides (including selenium- or tellurium-substituted ones); Carbon disulfide (including selenium- or tellurium-substituted forms); hydrogen chalcogenides such as hydrogen sulfide, hydrogen selenide, and hydrogen telluride; Thiol compounds (including selenium- or tellurium-substituted ones); Phosphine compounds (including selenium- or tellurium-substituted ones) such as trioctylphosphine sulfide; Thiourea (including selenium- or tellurium-substituted forms); Sulfur, selenium, tellurium, Or, dispersions of these compounds in solvents such as amines, acids, hydrocarbons, etc., and combinations thereof.

[0083] Examples of the solvent include the following: primary amines, secondary amines, and tertiary amines having organic groups such as hydrocarbon groups; aromatic hydrocarbons; Nitrogen-containing heterocyclic compounds, oxygen-containing heterocyclic compounds, sulfur-containing heterocyclic compounds, selenium-containing heterocyclic compounds, tellurium-containing heterocyclic compounds; Aliphatic hydrocarbons; Phosphine compounds having organic groups such as hydrocarbon groups; Phosphine oxide compounds having organic groups such as hydrocarbon groups; alcohols, aldehydes, carboxylic acids, or compounds having sulfur-substituted, selenium-substituted, or tellurium-substituted groups thereof; A commonly used organic solvent containing at least one of the following, or water, or a combination of these solvents.

[0084] Heating the solution may involve reacting a precursor of the chalcogen element to form hydrogen chalcogenide. The reaction of the solution may involve synthesis under an inert atmosphere or in air. Furthermore, the reaction of the solution may involve synthesis of the target product in a continuous flow process using a micro reactor.

[0085] Furthermore, in synthesizing the above-mentioned shell 12, nano-luminescent particles that will become the core 11 may be synthesized first, and then the shell 12 may be synthesized continuously, or a shell precursor may be added to the reaction vessel used to synthesize the nano-luminescent particles, and color conversion particles 10 having the desired core-shell structure may be synthesized.

[0086] <External structure of color conversion particles 10> Furthermore, as shown in FIG. 1(b), the color conversion particles 10 may have an outer shell 13 as a protective layer and a ligand 14 as an external structure.

[0087] (Outer shell 13) The outer shell 13 is a protective layer that covers the semiconductor particles, which are made up of the core 11 and the shell 12. The outer shell 13 is provided to suppress deterioration of the semiconductor particles due to contact with oxygen and to protect the semiconductor particles from chemical interactions with the outside, thereby further improving the durability of the color conversion particles 10. The outer shell 13 also has the property of transmitting the target excitation light and the light emitted from the core 11. The outer shell 13 is formed by a known method using a chemically stable material such as silica, glass, an oxide insulator, or a resin.

[0088] For example, when the outer shell 13 is made of a metal oxide, silicon oxide, zirconium oxide, titanium oxide, aluminum oxide, etc. can be used as the material. The outer shell 13 containing a metal oxide can be formed by a method of forming an inorganic oxide by a thermosetting reaction using a sol-gel method, for example.

[0089] The outer shell 13 may also be a layer containing a resin or a modified polysilazane. Polysilazane is a polymer with silicon-nitrogen bonds, and is SiO2, Si3N4, and an intermediate solid solution SiO2, which are composed of Si-N, Si-H, NH, etc. x N y The outer shell 13 is a ceramic precursor inorganic polymer containing, for example, etc. When the outer shell 13 is made of a resin, it is preferably made of a water-soluble resin such as a polyvinyl alcohol resin for ease of production. The outer shell 13 may have a multi-layer structure including both a metal oxide layer and a layer containing a resin or a modified polysilazane.

[0090] (Ligand 14) The ligands 14 are organic modifying molecules that modify the surface of the color conversion particles 10, and are bonded to the outer surfaces of the color conversion particles 10 or provided so as to coat the color conversion particles 10. The ligands 14 improve dispersibility by making it easier to separate the color conversion particles 10 from one another, and also function to prevent regrowth or destruction due to contact between the color conversion particles 10. The ligands 14 also function to suppress surface defects of the shell 12 by capping the tangling bonds, thereby improving luminous efficiency.

[0091] The modified organic molecule used as ligand 14 may have a structure containing a nitrogen-containing functional group, a sulfur-containing functional group, an acidic group, an amide group, a phosphine group, a phosphine oxide group, a hydroxyl group, a linear alkyl group, a carboxyl group, a phosphonic group, a sulfonic group, an amine group, etc. Examples of such modified organic molecules include sodium hexametaphosphate, sodium laurate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, triethanolamine lauryl sulfate, lauryl diethanolamide, dodecyltrimethylammonium chloride, trioctylphosphine, and trioctylphosphine oxide.

[0092] Furthermore, it is preferable to use a compound having both hydrophilic and hydrophobic groups in the molecule as the modified organic molecule used as the ligand 14. This allows the color-converting particles 10 to be coated with the ligand 14 through both chemical bonds, such as coordinate bonds between heteroatoms, and bonds through physical adsorption. Examples of this type of modified organic molecule include amines, which are compounds having a nonpolar hydrocarbon end as a hydrophobic group and an amino group as a hydrophilic group. When the hydrophilic group of the modified organic molecule is an amine, the amine can bond strongly to the metal element.

[0093] Furthermore, the modified organic molecule serving as the ligand 14 preferably contains a heteroatom. By containing a heteroatom in the modified organic molecule, electrical polarity is generated between the heteroatom and the carbon atom, allowing the modified organic molecule to be firmly bonded to the outer surface of the color-converting particle. Here, "heteroatom" refers to all atoms except hydrogen and carbon atoms.

[0094] <Modification of Color Conversion Particles> Next, modified examples of the color conversion particle 10 will be described with reference to Figures 7 and 8. In the schematic diagrams of the color conversion particle 10 shown in Figures 7 and 8, only the core 11 and shell 12 are shown unless otherwise specified. However, these color conversion particles 10 may each have an outer shell 13 and ligands 14, similar to the example in Figure 1(b).

[0095] For example, as shown in FIG. 7(a), the shell 12 of the color conversion particle 10 does not necessarily have to cover the entire core 11, and part of the core 11 may be exposed to the outside.

[0096] For example, as shown in Fig. 7(b), the color conversion particle 10 may have a structure in which a single core 11 is covered with a plurality of layered shells 12. By using materials with different compositions or crystal structures for the shells 12, it is possible to adjust the absorption and emission characteristics of the entire color conversion particle 10. In the example of Fig. 7(b), two layers of shells 12a and 12b are layered on the core 11, but the color conversion particle 10 may have three or more layers of shells 12.

[0097] The color conversion particles 10 having multiple shells 12a and 12b shown in FIG. 7(b) can be formed by heating a solution containing semiconductor particles having a shell 12a formed on a core 11 and another shell precursor.

[0098] For example, as shown in Figure 7(c), the color conversion particle 10 may have a structure in which multiple cores 11 are contained within a shell 12. If multiple cores 11 are contained within the shell 12, the effective thickness of the shell 12 in the color conversion particle 10 increases, improving the durability of the color conversion particle 10. Furthermore, by using materials with different compositions, crystal structures, etc. for each core 11, the light absorption and light emission characteristics of the color conversion particle 10 as a whole can be adjusted. 7(c) shows a structure in which three cores 11 are contained within the shell 12, but the number of cores 11 contained in the shell 12 can be changed as appropriate. Furthermore, in a color conversion particle 10 having multiple cores 11, any one of the cores 11 may be partially exposed to the outside of the shell 12.

[0099] Furthermore, the color conversion particle 10 may have a structure in which a plurality of cores 11 are contained within a shell 12, and the shell 12 has a plurality of layers. For example, as shown in Fig. 7(d), the outside of a shell 12a containing a plurality of cores 11 may be further coated with a shell 12b. Note that a further shell may be layered on the outside of the shell 12b in Fig. 7(d). For example, as shown in Fig. 7(e), a plurality of cores 11, each coated with a shell 12a, may be coated with a shell 12b and integrated to form a color conversion particle 10. In the example of Fig. 7(e), each shell 12a may contain a plurality of cores 11.

[0100] Furthermore, the core 11 of the color conversion particle 10 may contain a light-absorbing material 17 made of the same material as the shell 12. For example, as shown in Fig. 7(f), the light-absorbing material 17 may be coated on the outside with the core 11. Note that the material of the light-absorbing material 17 may be any material that can be selected as the material of the shell 12, and the shell 12 that covers the core 11 and the light-absorbing material 17 do not have to be made of the same material. In the laminated core structure having the light-absorbing material 17 inside as described above, the excitation light that has passed through the outer shell 12 is absorbed by the light-absorbing material 17 (the same material as the shell 12) inside the core 11, thereby improving the excitation light absorption rate. Furthermore, in the laminated core structure having the light-absorbing material 17 inside, photoexcited carriers are effectively confined in the narrow region of the core 11 sandwiched between the materials of the shell 12, thereby improving the luminous efficiency.

[0101] Furthermore, the band alignment between the light-absorbing material 17 and the core 11 is preferably Type I, and further, the band alignment between the core 11 and the shell 12 is also preferably Type I. For example, a combination of the light-absorbing material 17 as SrZrS3 and the core 11 as BaZrS3 can be mentioned, and further, a combination of the shell 12 as SrZrS3 can be mentioned. Another example is a combination of the light-absorbing material 17 as SrHfS3 and the core 11 as BaHfS3 can be mentioned, and further, a combination of the shell 12 as SrHfS3 can be mentioned. Note that the light-absorbing material 17 may be a material other than a chalcogenide perovskite as long as the band alignment between the light-absorbing material 17 and the core 11 is a combination of materials that exhibit a Stokes shift.

[0102] Furthermore, the color conversion particles 10 may have a hollow structure with voids 16 inside. For example, as shown in FIG. 8(a), one or more voids 16 may be formed inside the core 11. Alternatively, as shown in FIG. 8(b), in a color conversion particle 10 having an outer shell 13 outside a shell 12, voids 16 may be formed between the shell 12 and the outer shell 13. By forming voids 16 inside the color conversion particle 10 that do not absorb or emit light, it is possible to adjust the optical properties and shape of the color conversion particle 10.

[0103] The hollow color-converting particles 10 shown in Figures 8(a) and 8(b) can be manufactured, for example, as follows. First, an organic substance such as fullerene or carbon nanotubes or a soluble salt is added during synthesis to produce semiconductor particles containing the organic substance or salt. Then, the organic substance or salt is dissolved in a solvent or incinerated at high temperature to obtain the hollow color-converting particles 10.

[0104] Furthermore, the core 11 or shell 12 of the color conversion particle 10 may contain foreign matter that does not absorb or emit light, such as an insulator or other composition. By including such foreign matter in the core 11 or shell 12, it is possible to improve the luminous efficiency of the color conversion particle 10 by scattering light, for example, or to adjust the shape of the color conversion particle 10.

[0105] Furthermore, as shown in Figure 8(c), the core 11 or shell 12 of the color conversion particle 10 may have a gradient structure in which physical properties such as composition, crystal structure, lattice constant, density, crystal orientation, carrier concentration, band gap, defect density, dielectric constant, and conductivity continuously change in the direction perpendicular to the interface (depth direction). Continuously changing the physical and chemical properties of the core 11 or shell 12 in a gradient manner in the depth direction improves lattice matching and reduces lattice defects. This reduces non-radiative recombination and improves the luminous efficiency of the color conversion particle. The gradient structure can be manufactured by the same method as that used to manufacture the multi-layer core 11 and shell 12, for example.

[0106] Furthermore, in the present invention, the shape of the synthesized color conversion particles is not particularly limited. For example, cores 11 and / or color conversion particles 10 can be synthesized in the shape of spheres, elongates, stars, polyhedra, pyramids, tetrapods, tetrahedra, platelets, cones, or irregular shapes.

[0107] The effects of the color conversion particles 10 of this embodiment will be described below. The color conversion particle 10 of this embodiment includes a core 11 and a shell 12 that surrounds the core 11 and absorbs excitation light. When irradiated with excitation light, the core 11 or the interface between the core 11 and the shell 12 emits light. The chalcogenide perovskite that is the material of the shell 12 has a high light absorption coefficient and excellent durability. Therefore, in this embodiment, the core 11 is covered with the chalcogenide perovskite shell 12, making the color conversion particle 10 highly durable against heat and other disturbances. Furthermore, compared to conventional quantum dots, the color conversion particle 10 is less susceptible to performance degradation even when ligands are released due to heat or other disturbances.

[0108] Furthermore, the core 11 and the shell 12 have a band alignment that produces a Stokes shift. In this embodiment, by utilizing the difference in band edge transition energy between the shell 12 and the core 11, photoexcited carriers are transported to the core 11 by the chalcogenide perovskite shell 12, which has high absorbance, and the photoexcited carriers confined in the core 11 are recombined to emit light. In this embodiment, the chalcogenide perovskite shell 12 is formed on the outside of the core 11, thereby separating the absorption portion from the emission portion in the color conversion particle 10. This allows a large Stokes shift to be achieved, and the absorbance can be increased by the shell 12 without increasing the size of the core 11. Therefore, it is possible to achieve high absorbance and high luminous efficiency while suppressing re-absorption loss of emission by the core 11.

[0109] Furthermore, because the color conversion particles 10 of this embodiment have high absorbance and luminous efficiency as described above, they can achieve the desired color conversion function with a smaller amount than conventional quantum dots, etc. In other words, when the color conversion particles 10 of this embodiment are used as color conversion layers in display devices, lighting, and other devices, it is possible to reduce the thickness of the color conversion layer and improve the yield. When forming a color conversion layer, repeating the film formation process multiple times increases the probability of defects occurring in the film formation process, resulting in a decrease in the yield of the color conversion layer. Conversely, if the color conversion layer can be made thinner, the film formation process can be reduced, thereby reducing the effective defect rate of the color conversion layer.

[0110] Furthermore, if the band gap of shell 12 is made larger than the band gap of core 11, the light emitted in core 11 is emitted to the outside without being absorbed by shell 12, and re-absorption loss in the shell can also be suppressed. In other words, if the band gap of shell 12 is larger than the band gap of core 11, it becomes possible to increase the thickness of shell 12 and increase absorbance without increasing re-absorption loss, and therefore the luminous efficiency of color conversion particle 10 can be further improved.

[0111] Furthermore, if the band gap of the shell 12 is set to 3.4 eV or less, ultraviolet excitation light (wavelength 365 nm) from a GaN LED can be effectively absorbed. In this case, by using a single ultraviolet LED and color conversion particles 10 that convert colors into each of the RGB colors using ultraviolet excitation light, it is possible to emit each of the RGB colors without using LEDs (light sources) with multiple emission wavelengths, thereby simplifying the light-emitting element. Furthermore, when the core 11 is made of chalcogenide perovskite, the absorbance and durability of the core 11 can be increased, and the luminous efficiency can be further improved by reducing defects at the core-shell interface.

[0112] <Product forms and application examples of Color Conversion Particles 10> Next, we will explain the product forms and application examples of the color-converting particles 10. Product forms of the color-converting particles 10 include powder, solution, thin film, and sheet. Furthermore, as an example of application of the color-converting particles 10, application to various devices is envisioned.

[0113] (powder) The powder is an aggregate of color conversion particles 10. Hereinafter, the color conversion particles 10 will be referred to as primary particles, and the aggregate of color conversion particles 10 will be referred to as secondary particles. There are no particular restrictions on the size of the primary particles and secondary particles, but primary particles are preferably in the range of 5 nm to 1000 nm. Ligands may also be attached to the surfaces of the primary particles and secondary particles. To improve properties such as luminescence characteristics, dispersibility of the color conversion particles, and film-forming properties, other materials may be added as additives to the powder of color conversion particles 10.

[0114] Furthermore, there are no particular limitations on the uses of the powder of color conversion particles 10. For example, they may be dispersed in a solvent to prepare a solution, dispersed in a resin or solid medium to prepare a composite, sintered to be used as a sputtering target, or used as a powder directly as a source for evaporation or the like.

[0115] (solution) The solution is a state in which the color conversion particles 10 are dispersed in a solvent. There are no particular restrictions on the size of the primary particles and secondary particles, but the primary particles are preferably in the range of 5 nm to 1000 nm. Furthermore, "dispersed" refers to a state in which the color conversion particles 10 are floating or suspended in the solvent, although some may have settled. Furthermore, ligands may be attached to the surfaces of the primary particles and secondary particles.

[0116] The solution may contain one or more solvents, including, but not limited to, the following: Water, esters such as methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, and pentyl acetate; ketones such as γ-butyrolactone, acetone, dimethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; ethers such as diethyl ether, methyl tert-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, and phenetole; methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol, methoxypropanol, diacetone alcohol, cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, and 2,2,2-trifluoroethanol. alcohols such as ethanol and 2,2,3,3-tetrafluoro-1-propanol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, and triethylene glycol dimethyl ether; organic solvents having an amide group such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetamide, and N,N-dimethylacetamide; organic solvents having a nitrile group such as acetonitrile, isobutyronitrile, propionitrile, and methoxyacetonitrile; organic solvents having a carbonate group such as ethylene carbonate and propylene carbonate; organic solvents having a halogenated hydrocarbon group such as methylene chloride and chloroform; organic solvents having a hydrocarbon group such as n-pentane, cyclohexane, n-hexane, benzene, toluene, and xylene; dimethyl sulfoxide, etc.

[0117] In order to improve the light-emitting properties, dispersibility of the color conversion particles 10, film-forming properties, and other properties, an acid, a base, a binder material, or the like may be added as an additive to the above solution. The use of the solution is not particularly limited. For example, the solution may be used for film formation by a coating method, a spray method, a doctor blade method (or other solution film formation methods), for preparing a composite by combining with a solid dispersion medium, or for preparing a device using the same.

[0118] (thin film) The thin film is a state in which the color conversion particles 10 are aggregated in a planar form. There are no particular restrictions on the size of the primary particles and secondary particles, but the primary particles are preferably in the range of 5 nm to 1000 nm. Ligands may be attached to the surfaces of the primary particles and secondary particles. Other materials may be added to the thin film as additives to improve properties such as luminescence characteristics and dispersibility of the color conversion particles 10.

[0119] The method for producing the thin film is not particularly limited. For example, the thin film may be produced by coating, spraying, doctor blade, inkjet, or other solution film-forming methods, or by vacuum processes such as sputtering and vacuum deposition. Furthermore, the color-converting particles 10 may be formed into a film by coating or other methods, and then may be baked or otherwise treated to lose their particle shape.

[0120] (sheet) The sheet is a planar dispersion medium containing dispersed color conversion particles 10. There are no particular restrictions on the size of the primary particles and secondary particles, but the primary particles are preferably in the range of 5 nm to 1000 nm. Ligands may be attached to the surfaces of the primary particles and secondary particles.

[0121] The material used as the dispersion medium for the sheet can be any polymer known to those skilled in the art for such purposes. In a suitable embodiment, such polymers are substantially translucent or substantially transparent. For example, polymers that can be used as the dispersion medium for the sheet include, but are not limited to, polyvinyl butyral, polyvinyl acetate, silicones, and silicone derivatives, including, but not limited to, polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane, fluorinated silicones, vinyl- and hydride-substituted silicones, ionomers, polyethylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polypropylene, polyester, polycarbonate, polystyrene, polyacrylonitrile, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-methacrylic acid copolymer film, nylon, and the like.

[0122] In order to improve properties such as the light emitting properties and the dispersibility of the color conversion particles 10, other materials such as silica fine particles or the solvents described above for the solution may be added to the sheet as additives. The method for producing the sheet is not particularly limited. For example, the sheet may be produced by kneading powder and a dispersion medium and stretching the mixture, or by mixing an ink containing the color-changing particles 10 with a dispersion medium or a precursor thereof and applying the mixture.

[0123] (device) The color conversion particles 10, or the above-mentioned powders, solutions, films, and sheets, can be used for down-conversion of ultraviolet light, blue light, etc. in various devices. Examples of such devices include light-emitting devices such as LEDs and organic ELs, display devices including such light-emitting devices, lighting devices including such light-emitting devices, image sensors, photoelectric conversion devices, and bioluminescent tags.

[0124] <Example> Examples of the color conversion particles of the present invention will now be described. In the color conversion particles of the embodiment, the core material is BaZrS3 and the shell material is SrZrS3. In other words, the color conversion particles of the embodiment have a core and a shell made of chalcogenide perovskite, which corresponds to an example of the best material combination for exhibiting a Stokes shift. As described above, when the core and the shell are made of chalcogenide perovskite, interfacial defects between the core and the shell are reduced, and high luminous efficiency can be expected.

[0125] Figure 9 shows the shell / core / shell band alignment in the color conversion particles of the example. The origin of the energy on the vertical axis is the vacuum level. The physical properties of the core and shell were determined by referring to the literature "Y. Nishigaki et al., Sol. RRL 1900555 (2020)" and "K. Hanzawa et al., J. Am. Chem. Soc. 141, 5343 (2019)" and by comprehensively examining other experimental results.

[0126] As shown in FIG. 9, the band alignment between the shell and the core in the example is such that the E c is the shell E c Lower, core E v is the shell E v Since the band gap E of the shell is higher than that of the core, it is classified as Type I. Therefore, in the configuration of the example, it is expected that excitation light is absorbed in the shell, and the excited carriers move to the core and recombine, resulting in core emission. g is the core band gap E g Since it is larger than the α value, it is expected that the reabsorption loss in the shell will be suppressed.

[0127] In the examples, one-dimensional simulations were performed using software (SCAPS-1D) to analyze the absorption and emission of color conversion particles. Figure 10 shows the results of the simulations. The horizontal axis in each diagram in Figure 10 represents the one-dimensional position in the diameter direction of the color conversion particle.

[0128] In the simulation, the core diameter was set to 20 nm, the shell thickness to 50 nm, and the excitation light wavelength was set to 450 nm blue light with an irradiance of 100 mW / cm. 2 The excitation light was set to enter from one side (the left side of the figure).

[0129] Figure 10(a) shows the E c 10(b) shows the E v The vertical axis shows the Fermi energy E F is the standard. In Fig. 10(a), the E c is the shell range E c Also, in Fig. 10(b), the E v is the shell range E v 10(a) and (b) are in good agreement with the band alignment shown in FIG.

[0130] Figure 10(c) shows the carrier concentration distribution of the color conversion particles, where the solid line indicates the electron profile and the dashed line indicates the hole profile. In Figure 10(c), the carrier density in the core range (50-70 nm on the horizontal axis) is higher than that in the shell range, which indicates that the carriers excited by the light absorbed in the shell are effectively transported to the core and confined there.

[0131] Figure 10(d) shows the carrier generation rate and recombination rate. The dashed line in Figure 10(d) shows the profile of the carrier generation rate, and the solid line in Figure 10(d) shows the profile of the carrier recombination rate.

[0132] As shown in Figure 10(d), the carrier generation rate is highest on the left side of the figure, where the excitation light is incident. Furthermore, because the optical absorption coefficient of chalcogenide perovskite is very large, the carrier generation rate drops sharply as one moves to the right side of the figure. It can be seen that most of the carrier excitation due to optical absorption occurs within the 0-50 nm shell range.

[0133] On the other hand, the carrier recombination rate is high throughout the core range (50-70 nm on the horizontal axis) and is nearly zero in the shell range, meaning that light emission due to carrier recombination is mostly caused by photoexcited carriers that have moved to the core. Therefore, the simulation results show that the transport of photoexcited carriers from the shell to the core and the confinement of photoexcited carriers in the core occur effectively.

[0134] In addition, based on the optical coefficients of BaZrS3 and SrZrS3 shown in the above-mentioned "Y. Nishigaki et al., Sol. RRL 1900555 (2020)," the optical absorption coefficients of BaZrS3 and SrZrS3 and the photoluminescence (PL) emission peak of BaZrS3 were calculated.

[0135] Fig. 11 shows the optical absorption coefficients of BaZrS3 and SrZrS3 and the profiles of the PL emission spectrum of BaZrS3. The horizontal axis in Fig. 11 represents wavelength.

[0136] The PL spectrum of the core material, BaZrS3 (solid line in Figure 11), shows a sharp emission peak with a half-width of approximately 30 nm, which is due to the extremely steep absorption edge (the rise of the optical absorption coefficient near the band edge) of chalcogenide perovskite.

[0137] The dashed line in Fig. 11 shows the profile of the optical absorption coefficient of BaZrS3, and the dashed line in Fig. 11 shows the profile of the optical absorption coefficient of SrZrS3. In the region where the tails of these optical absorption coefficient profiles overlap with the profile of the PL emission spectrum, the emitted light can be reabsorbed.

[0138] This means that if color conversion is performed using only the core material, BaZrS3, the emitted light may be reabsorbed. Therefore, in the case of a BaZrS3 core, increasing the particle size to increase absorbance also increases reabsorption, so there is a trade-off between the magnitude of absorbance and the loss of reabsorption.

[0139] On the other hand, the profile of the optical absorption coefficient of SrZrS3 barely overlaps with the profile of the PL emission spectrum of BaZrS3, indicating that when a SrZrS3 shell is applied to a BaZrS3 core, there is almost no reabsorption in the shell.

[0140] In this example, the color conversion particles have a core-shell structure, and the absorbance of excitation light is increased by the shell material, SrZrS3, which has a larger band gap than the core material, BaZrS3. Therefore, in this example, it is possible to increase the absorbance by thickening the shell without increasing the re-absorption loss.

[0141] Fig. 12 shows the relationship between combinations of core and shell materials, band alignment types, and occurrence of Stokes shift in Examples and Comparative Examples. Fig. 12 shows the band alignment types and whether or not a Stokes shift occurs for 16 combinations (4 × 4 = 16) when four materials, SrZrS3, BaZrS3, SrHfS3, and BaHfS3, are used as the core and shell materials.

[0142] In Fig. 12, the combination of materials that exhibits a Stokes shift (Yes) is an example, and the combination of materials that does not exhibit a Stokes shift (No) is a comparative example. In Fig. 12, when the core and shell are made of the same material, the band alignment type is Flat, and in these cases, a Stokes shift does not appear.

[0143] In Figure 12, when the core material is SrZrS3 and the shell material is BaZrS3, the band alignment type is Inverse Type I, and this combination does not exhibit a Stokes shift. On the other hand, when the core material is SrZrS3 and the shell material is SrHfS3 or BaHfS3, the band alignment type is Type II, and these combinations all exhibit a Stokes shift.

[0144] In Figure 12, when the core material is BaZrS3 and the shell material is SrZrS3, the band alignment type is Type I. When the core material is BaZrS3 and the shell material is SrHfS3 or BaHfS3, the band alignment type is Type II. All of these combinations exhibit a Stokes shift.

[0145] In Figure 12, when the core material is SrHfS3 and the shell material is SrZrS3 or BaZrS3, the band alignment type is Type II, and a Stokes shift occurs in all of these combinations. On the other hand, when the core material is SrHfS3 and the shell material is BaHfS3, the band alignment type is Inverse Type I, and no Stokes shift occurs in this combination.

[0146] In Figure 12, when the core material is BaHfS3 and the shell material is SrZrS3 or BaZrS3, the band alignment type is Type II. Also, when the core material is BaHfS3 and the shell material is SrHfS3, the band alignment type is Type I. All of these combinations result in a Stokes shift.

[0147] In addition, when the core material is BaZrS3 and the shell material is SrZrS3, or when the core material is BaHfS3 and the shell material is SrHfS3, the band alignment type is Type I, so color conversion particles with particularly excellent luminescence properties can be obtained.

[0148] Although the embodiments of the present invention have been described above, they are presented as examples and are not intended to limit the scope of the present invention. The embodiments can be implemented in various forms other than those described above, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the present invention. The embodiments and their modifications are included within the scope and spirit of the present invention, and the inventions described in the claims and their equivalents are also included within the scope and spirit of the present invention.

[0149] This application also claims priority based on Japanese Patent Application No. 2020-195058, filed on November 25, 2020, and the entire contents of Japanese Patent Application No. 2020-195058 are incorporated herein by reference. [Explanation of symbols]

[0150] 10...Color conversion particles 11...Core 12, 12a, 12b...Shell 13...Outer shell 14...Ligand 16...Void

Claims

1. The core and a shell that surrounds the core and absorbs excitation light, emitting light at the core or at the interface between the core and the shell in response to the irradiated excitation light; the shell is composed of a chalcogenide perovskite; the core and the shell have a band alignment that exhibits a Stokes shift, the band alignment satisfies at least one of the conditions that an energy E c_shell of the lower edge of the conduction band of the shell is higher than an energy E c_core of the lower edge of the conduction band of the core, or an energy E v_shell of the upper edge of the valence band of the shell is lower than an energy E v_core of the upper edge of the valence band of the core, The bandgap of the shell is larger than the bandgap of the core Color transformation particles.

2. The chalcogenide perovskite may be a cubic perovskite, a tetragonal perovskite, or GdFeO 3 The perovskite has one of the following crystal structures: orthorhombic perovskite, Ruddlesden-Popper layered perovskite, Dion-Jacobson layered perovskite, or double perovskite. The color conversion particle according to claim 1 .

3. The chemical formula of the chalcogenide perovskite is ABX 3 or A' 2 A n-1 B n X 3n+1 (A and A' are elements of Group 2, B is an element of Group 4, and X is a chalcogen element, where n is an integer of 1 or more) The color conversion particle according to claim 1 or 2.

4. The A, A', B, and X each include a mixture of elements from each group in any ratio. The color conversion particle according to claim 3 .

5. The chalcogenide perovskite is CaTiS 3 ,CaTiSe 3 ,CaTiTe 3 ,CaZrS 3 ,CaZrSe 3 ,CaZrTe 3 ,CaHfS 3 ,CaHfSe 3 ,CaHfTe 3 ,SrTiS 3 ,SrTiSe 3 ,SrTiTe 3 ,SrZrS 3 ,SrZrSe 3 ,SrZrTe 3 ,SrHfS 3 ,SrHfSe 3 ,SrHfTe 3 ,BaTiS 3 ,BaTiSe 3 ,BaTiTe 3 ,BaZrS 3 ,BaZrSe 3 ,BaZrTe 3 ,BaHfS 3 ,BaHfSe 3 ,BaHfTe 3 ,Ca 2 Ba n-1 Ti n S3 n+1 ,Ca 2 Ba n-1 Ti n Se 3n+1 ,Ca 2 Ba n-1 Ti n Te 3n+1 ,Ca 2 Ba n-1 Zr n S 3n+1 ,Ca 2 Ba n-1 Zr n Se 3n+1 ,Ca 2 Ba n-1 Zr n Te 3n+1 ,Ca 2 Ba n-1 Hf n S 3n+1 ,Ca 2 Ba n-1 Hf n Se 3n+1 ,That 2 Ba n-1 Hf n Te 3n+1 ,That 2 Sr n-1 Ti n S 3n+1 ,That 2 Sr n-1 Ti n Se 3n+1 ,That 2 Sr n-1 Ti n Te 3n+1 ,That 2 Sr n-1 Zr n S 3n+1 ,That 2 Sr n-1 Zr n Se 3n+1 ,That 2 Sr n-1 Zr n Te 3n+1 ,That 2 Sr n-1 Hf n S 3n+1 ,That 2 Sr n-1 Hf n Se 3n+1 ,That 2 Sr n-1 Hf n Te 3n+1 ,Sr 2 Ca n-1 Ti n S 3n+1 ,Sr 2 Ca n-1 Ti n Se 3n+1 ,Sr 2 Ca n-1 Ti n Te 3n+1 ,Sr 2 Ca n-1 Zr n S 3n+1 ,Sr 2 Ca n-1 Zr n Se 3n+1 ,Sr 2 Ca n-1 Zr n Te 3n+1 ,Sr 2 Ca n-1 Hf n S 3n+1 ,Sr 2 Ca n-1 Hf n Se 3n+1 ,Sr 2 Ca n-1 Hf n Te 3n+1 ,Sr 2 Ba n-1 Ti n S 3n+1 ,Sr 2 Ba n-1 Ti n Se 3n+1 ,Sr 2 Ba n-1 Ti n Te 3n+1 ,Sr 2 Ba n-1 Zr n S 3n+1 ,Sr 2 Ba n-1 Zr n Se 3n+1 ,Sr 2 Ba n-1 Zr n Te 3n+1 ,Sr 2 Ba n-1 Hf n S3 n+1 ,Sr 2 Ba n-1 Hf n Se 3n+1 ,Sr 2 Ba n-1 Hf n Te 3n+1 ,Ba 2 Ca n-1 Ti n S 3n+1 ,Ba 2 Ca n-1 Ti n Se 3n+1 ,Ba 2 Ca n-1 Ti n Te 3n+1 ,Ba 2 Ca n-1 Zr n S 3n+1 ,Ba 2 Ca n-1 h n ｳe 3n+1 ,Ba 2 Ca n-1 h n Te 3n+1 ,Ba 2 Ca n-1 ｨf n ﳳ 3n+1 ,Ba 2 Ca n-1 ｨf n ｳe 3n+1 ,Ba 2 Ca n-1 ｨf n Te 3n+1 ,Ba 2 3r n-1 Ti n ﳳ 3n+1 ,Ba 2 3r n-1 Ti n ｳe 3n+1 ,Ba 2 3r n-1 Ti n Te 3n+1 ,Ba 2 3r n-1 h n ﳳ 3n+1 ,Ba 2 3r n-1 h n ｳe 3n+1 ,Ba 2 3r n-1 h n Te 3n+1 ,Ba 2 3r n-1 ｨf n ﳳ 3n+1 ,Ba 2 3r n-1 ｨf n ｳe 3n+1 ,Ba 2 3r n-1 ｨf n Te 3n+1 ,Ca n+1 Ti n ﳳ 3n+1 ,Ca n+1 Ti n ｳe 3n+1 ,Ca n+1 Ti n Te 3n+1 ,Ca n+1 h n ﳳ 3n+1 ,Ca n+1 Zr n Se 3n+1 ,Ca n+1 Zr n Te 3n+1 ,Ca n+1 Hf n S 3n+1 ,Ca n+1 Hf n Se 3n+1 ,Ca n+1 Hf n Te 3n+1 ,Sr n+1 Ti n S3 n+1 ,Sr n+1 Ti n Se 3n+1 ,Sr n+1 Ti n Te 3n+1 ,Sr n+1 Zr n S 3n+1 ,Sr n+1 Zr n Se 3n+1 ,Sr n+1 Zr n Te 3n+1 ,Sr n+1 Hf n S 3n+1 ,Sr n+1 Hf n Se 3n+1 ,Sr n+1 Hf n Te 3n+1 ,Ba n+1 Ti n S 3n+1 ,Ba n+1 Ti n Se 3n+1 ,Ba n+1 Ti n Te 3n+1 ,Ba n+1 Zr n S 3n+1 ,Ba n+1 Zr n Se 3n+１ ,Ba n+1 Zr n Te 3n+1 ,Ba n+1 Hf n S 3n+1 ,Ba n+1 Hf n Se 3n+1 , Ba n+1 Hf n Te 3n+1 (where n is an integer of 1 or more), The color conversion particle according to claim 1 .

6. The chalcogenide perovskite is (Ca x Sr x’ Ba 1-x-x’ ) (Ti y Zr y’ Hf 1-y-y’ ) (S z Se z’ Te 1-z-z’ ) 3 or (Ca w Sr w’ Ba 1-w-w’ ) 2 (Ca x Sr x’ Ba 1-x-x’ ) n-1 (Ti y Zr y’ Hf 1-y-y’ ) n (S z Se z’ Te 1-z-z’ ) 3n+1 (wherein w, w', x, x', y, y', z, and z' are each a value between 0 and 1, inclusive, w+w'≦1, x+x'≦1, y+y'≦1, and z+z'≦1, and n is an integer of 1 or greater.) The color conversion particle according to claim 1 .

7. The band alignment is determined by the energy E c_shell is the energy E of the lower end of the conduction band of the core c_core The energy E of the top of the valence band of the shell is higher than v_shell is the energy E of the top of the valence band of the core v_core Meet lower requirements The color conversion particle according to claim 1 .

8. The band gap of the shell is 3.4 eV or less. The color conversion particle according to claim 1 .

9. The thickness of the shell is 2 nm or more and 300 nm or less. The color conversion particle according to claim 1 .

10. The thickness of the shell is 2 nm or more and 50 nm or less. The color conversion particle according to claim 9 .

11. The thickness of the shell is 2 nm or more and 30 nm or less. The color conversion particle according to claim 10.

12. The thickness of the shell is 2 nm or more and 10 nm or less. The color conversion particle according to claim 10.

13. The shell has multiple layers The color conversion particle according to claim 1 .

14. The shell includes a plurality of the cores. The color conversion particle according to claim 1 .

15. The core contains a light-absorbing material. The color conversion particle according to claim 1 .

16. At least one of the shell and the core contains foreign matter or voids The color conversion particle according to claim 1 .

17. At least one of the shell and the core has a structure in which physical properties change in a gradient manner in the depth direction. The color conversion particle according to claim 1 .

18. The core is composed of a chalcogenide perovskite different from the shell, The chalcogenide perovskite different from the shell is SrZrS 3 , SrZrSe 3 , SrHfS 3 , SrHfSe 3 , BaZrS 3 , BaZrSe 3 , BaHfS 3 , BaHfSe 3 , Sr 2 Ba n-1 Zr n S 3n+1 , Sr 2 Ba n-1 Zr n Se 3n+1 , Sr n+1 Zr n S 3n+1 , Sr n+1 Zr n Se 3n+1 , Ba 2 Sr n-1 Zr n S 3n+1 , Ba 2 Sr n-1 Zr n Se 3n+1 , Ba n+1 Zr n S 3n+1 , Ba n+1 Zr n Se 3n+1 , Sr 2 Ba n-1 Hf n S 3n+1 , Sr 2 Ba n-1 Hf n Se 3n+1 , Sr n+1 Hf n S 3n+1 , Sr n+1 Hf n Se 3n+1 , Ba 2 Sr n-1 Hf n S 3n+1 , Ba 2 Sr n-1 Hf n Se 3n+1 , Ba n+1 Hf n S 3n+1 , Ba n+1 Hf n Se 3n+1 18. The color conversion particle according to claim 1, wherein n is an integer of 1 or more.

19. The core is composed of a chalcogenide perovskite different from the shell, The chalcogenide perovskite different from the shell is (Sr x Ba 1-x ) (Zr y Hf 1-y ) (S z Se 1-z ) 3 or (Sr x’ Ba 1-x’ ) 2 (Sr x Ba 1-x ) n-1 (Zr y Hf 1-y ) n (S z Se 1-z ) 3n+1 (where x, x', y, and z are each a value between 0 and 1, and n is an integer greater than or equal to 1.) The color conversion particle according to claim 1 .

20. A powder comprising the color conversion particles according to any one of claims 1 to 19.

21. A solution comprising the color conversion particles according to any one of claims 1 to 19.

22. A thin film comprising the color conversion particles according to any one of claims 1 to 19.

23. A sheet comprising the color conversion particles according to any one of claims 1 to 19.

24. A device comprising color conversion particles according to any one of claims 1 to 19.

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