Color conversion particles

Abstract

The color conversion particle comprises a core and a shell that includes the core and absorbs excitation light, and the color conversion particle emits light at the core or at the interface between the core and the shell upon receiving the irradiated excitation light. The shell is composed of chalcogenide perovskite, and the core and the shell have an energy band alignment that exhibits a Stokes shift.

Description

Technical Field

[0001] The present invention relates to color converting particles. Background Art

[0002] Color conversion using wavelength conversion (down conversion) has been widely used in lighting, display devices, solar cells, etc., which converts excitation light incident on an object from the outside into light with a longer wavelength and emits it. In this color conversion, for example, a phosphor to which an activator is added is sometimes used. However, conventional phosphors have limitations in terms of controllability of emission wavelength, emission peak width, and number of peaks (color purity). For example, in applications such as display devices that require high color purity at a specific wavelength, there are many issues that need to be improved.

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

[0004] In this core-shell quantum dot, the core material is selected from, for example, Cd(S, Se), InP, APbX3 (A = Cs, MA; X = Cl, Br, I). In addition, the shell material is, for example, Zn(S, Se), A'2PbX4 (A' = OA), etc. Here, MA is methylammonium and OA is octylammonium. In addition, non-patent literatures 1 and 2 disclose core-shell quantum dots using halide perovskites represented by CsPbBr3.

[0005] Prior art literature

[0006] Non-patent literature

[0007] Non-patent literature 1: S. Bera et al., "Perovskite Nanocrystal Heterostructures: Synthesis, Optical Properties, and Applications", ACS Energy Lett. 5, 2858-2872 (2020).

[0008] Non-patent document 2: "Challenges and Opportunities in Designing Perovskite Nanocrystal Heterostructures", ACS Energy Lett.5, 2253-2255 (2020). Summary of the invention

[0009] Problem that the invention aims to solve

[0010] CdSe, one of the materials for the core-shell quantum dots, contains Cd, which is regulated by RoHHS, and is toxic. Therefore, InP has been developed as a substitute for Cd(S,Se), but InP contains In, a rare metal, and there are problems in terms of material durability and luminous efficiency. On the other hand, halide perovskites represented by CsPbBr have high absorbance and luminous efficiency, but the material durability is insufficient.

[0011] In addition, quantum dots have a small size of several nanometers, so their absorbance is small. On the other hand, if the size of quantum dots is increased to improve absorbance, the quantum size effect may be lost, and the loss due to reabsorption of luminescence may increase, resulting in a decrease in luminescence efficiency.

[0012] The present invention has been made in view of the above circumstances, and provides color conversion particles that achieve high absorbance and high luminous efficiency while ensuring durability.

[0013] Means used to solve problems

[0014] A color conversion particle according to one embodiment of the present invention comprises a core and a shell that includes the core and absorbs excitation light, and emits light at the core or at an interface between the core and the shell upon receiving the irradiated excitation light. The shell is composed of chalcogenide perovskite, and the core and the shell have a band alignment that exhibits a Stokes shift.

[0015] Effects of the Invention

[0016] According to the color conversion particle of the present invention, high absorbance and high luminous efficiency can be achieved while ensuring durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram showing a configuration example of the color conversion particles according to the present embodiment.

[0018] Figure 2 This is a graph showing an example of the relationship between the shell thickness and the absorptivity of the excitation light.

[0019] Figure 3 This is a graph showing an example of the relationship between excitation energy and particle radius.

[0020] Figure 4 : is a diagram showing an example of the alignment of the energy bands of the core and the shell.

[0021] Figure 5 : is a diagram showing an example of the alignment of the energy bands of the core and the shell.

[0022] Figure 6 : is a diagram showing an example of the alignment of the energy bands of the core and the shell.

[0023] Figure 7 It is a diagram showing a modification of the color conversion particle of the present embodiment.

[0024] Figure 8 It is a diagram showing a modification of the color conversion particle of the present embodiment.

[0025] Fig. 9 It is a diagram showing the energy band alignment of the core and the shell in the example.

[0026] Fig.10 It is a figure which shows the result of the simulation of Example.

[0027] Fig.11 It is a diagram showing the distribution curves of the light absorption coefficients of BaZrS3 and SrZrS3 and the PL emission spectrum of BaZrS3.

[0028] Fig.12 This is a diagram showing the correspondence between the combination of core and shell materials in Examples and Comparative Examples, the type of band alignment, and the appearance of Stokes shift. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments will be described with reference to the drawings.

[0030] In the embodiments, in order to make the description easy to understand, the structure or elements other than the main part of the present invention are simplified or omitted. In addition, in the drawings, the same elements are marked with the same symbols. It should be noted that in the drawings, the shape, size, etc. of each element are schematically shown and do not represent the actual shape, size, etc.

[0031] <Structure of Color Conversion Particles>

[0032] Figure 1 (a) is a schematic diagram showing a configuration example of the color conversion particles according to the present embodiment.

[0033] The color conversion particle 10 is a particle having an overall shape of nanometer scale, and performs color conversion by absorbing incident excitation light and re-emitting (emitting light) in the form of light having different energy (wavelength).

[0034] The color conversion particle 10 has a core 11 as a light emitting part and a shell 12 as a light absorbing part. The shell 12 contains one or more cores 11 therein. The color conversion particle 10 is formed by partially or entirely covering each core 11 with the shell 12 from the outside.

[0035] In the color conversion particle 10, the core 11 and the shell 12 are provided separately, and the chalcogenide perovskite described later is used as the material of the shell 12. This achieves high absorbance of the excitation light by the shell 12 and improves the durability of the color conversion particle 10. This will be described later.

[0036] In addition, in the core 11 and the shell 12, the energy E at the lower end of the conduction band c and the energy E at the upper end of the valence band v The band alignment of 1.1 and 1.2 is a relationship that causes the Stokes shift to appear. The band alignment of the core 11 and the shell 12 will be described later.

[0037] Furthermore, by adjusting the band gap between the core 11 and the shell 12, the shell 12 can be provided with a property of transmitting light emitted from the core 11. Thus, in the color conversion particle 10, it is possible to suppress the light generated in the core 11 from being reabsorbed by the shell 12.

[0038] <Shell 12>

[0039] (Shell material)

[0040] The shell 12 is composed of chalcogenide perovskite, which is a semiconductor material that absorbs a target excitation light wavelength and generates excited carriers.

[0041] Chalcogenide perovskite is a semiconductor formed of a perovskite crystal structure group containing a chalcogen element (S, Se, Te) at the X site, and also includes a material in which a part of the X site is replaced with oxygen (O).

[0042] The above-mentioned perovskite represents a group of substances having a cubic crystal structure with a BX6 octahedron as a skeleton shown in the chemical formula ABX3, and can obtain a tetragonal or orthorhombic crystal structure by accompanying lattice distortion. In addition, in the same ABX3 composition, multiple stable crystal structures have been revealed in computational science. These crystal structures range from structures close to perovskites to significantly different structures. In addition, as derived structures, there are Ruddlesden-Popper-type and Dion-Jacobson-type layered perovskites based on the perovskite structure, and double perovskite crystal structures in which different elements are alternately arranged at the B site.

[0043] In this specification, the above-mentioned crystal structures are collectively referred to as "perovskite crystal structure group".

[0044] The perovskite crystal structure group specifically includes substances having the following crystal structures.

[0045] Cubic perovskite, tetragonal perovskite, GdFeO3 orthorhombic, YScS3 orthorhombic, NH4CdCl3 orthorhombic, BaNiO3 hexagonal, FePS3 monoclinic, PbPS3 monoclinic, CeTmS3 monoclinic, Ruddlesden-Popper layered perovskite, Dion-Jacobson layered perovskite, double perovskite.

[0046] It should be noted that the crystal structure and electronic structure of the perovskite crystal structure group change depending on the composition and synthesis conditions, and the photoelectric properties and chemical characteristics change. Therefore, the composition and conditions are selected so as to obtain a crystal structure suitable for the purpose.

[0047] For example, materials having cubic perovskite, tetragonal perovskite, GdFeO3-type orthorhombic perovskite, Ruddlesden-Popper-type layered perovskite, and double perovskite structures have excellent photoelectric and chemical properties. In addition, by setting the structure to a Dion-Jacobson-type layered perovskite, the chemical stability can be further improved.

[0048] In particular, it is known that a substance having a crystal structure of a GdFeO3 type orthorhombic perovskite represented by ABX3 (A=Group 2, B=Group 4) has excellent photoelectric properties represented by a high light absorption coefficient.

[0049] In addition, the chemical formula of chalcogenide perovskite can be composed of ABX3, A'2A n-1 B n X 3n+1 ,A”A”’B”2X7,A”A2B”3X 10 ,A2BB'X6 indicates.

[0050] 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). In addition, n is set to a positive integer. It should be noted that A and A', B and B' can be the same element. In addition, A, A', A", A"', B, B', B", and X respectively include elements obtained by mixing elements in their respective groups in arbitrary ratios.

[0051] As an example, the chalcogenide perovskite represented by the chemical formula ABX3 includes the following substances. In the following example, X is selected from (S, Se) as the dominant material among the chalcogen elements, A is selected from (Sr, Ba) as the dominant material among the Group 2 elements, and B is selected from (Zr, Hf) as the dominant material among the Group 4 elements.

[0052] SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, BaHfSe3.

[0053] In addition, as an example, from the chemical formula A'2A n-1 B n X 3n+1 The chalcogenide perovskite represented includes the following substances: X is selected from (S, Se) as the dominant material among chalcogen elements, A and A' are selected from (Sr, Ba) as the dominant material among Group 2 elements, and B is selected from (Zr, Hf) as the dominant material among Group 4 elements.

[0054] Sb 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 、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+ 1Hf n S 3n+1 , Sr n+1 Hf n Se 3n+1 、Ba2Sr n-1 Hf nS 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 .

[0055] These chalcogenide perovskites can also be composed of (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 Indicates (wherein x, x', y, and z are each a value greater than or equal to 0 and less than or equal to 1).

[0056] It should be noted that the preferred materials among the above X, A, A′, and B are materials having a band gap suitable for use in light-emitting devices, display devices, lighting devices, etc. that emit visible light when applied to the color conversion particle 10 .

[0057] In chalcogenide perovskites, by partially replacing constituent elements with elements of the same or different groups, it is possible to control carrier concentration or crystal structure, and adjust other physical and chemical properties. For example, Group 1 elements can be replaced by Groups 1 and 2, Group 2 elements can be replaced by Groups 1, 2, and 3, Group 3 elements can be replaced by Groups 2, 3, and 4, Group 4 elements can be replaced by Groups 3, 4, and 5, and Group 16 elements can be replaced by Groups 15, 16, and 17.

[0058] The advantages of chalcogenide perovskite include the following.

[0059] Chalcogenide perovskites have the characteristics of large light absorption coefficient and excellent luminescence performance (luminous efficiency, half-peak width). In addition, the distribution curve of the light absorption coefficient of chalcogenide perovskites stands up steeply at the band edge. Therefore, chalcogenide perovskites have the characteristic of high absorbance near the band gap edge.

[0060] Therefore, the shell 12 of the chalcogenide perovskite has high absorbance and can efficiently absorb the excitation light.

[0061] In addition, chalcogenide perovskites have high chemical stability and excellent durability against external environments and stimuli such as air, moisture, heat, and light. Therefore, the shell 12 of chalcogenide perovskites has high durability, and degradation of the shell 12 itself and the core 11 located inside can be suppressed.

[0062] In addition, chalcogenide perovskites are also advantageous in that they do not contain toxic elements and are therefore highly safe, and that they do not contain rare metals and therefore have low raw material costs.

[0063] (Band gap of shell)

[0064] Next, the band gap of the shell 12 using chalcogenide perovskite will be described.

[0065] In the color conversion particle, the light emitted at the core or the interface between the core and the shell is extracted to the outside through the shell. Therefore, the shell needs to transmit the emitted light. If the emitted light is absorbed in the shell, the luminous efficiency of the color conversion particle decreases corresponding to the degree of absorption. Therefore, the band gap of the shell is preferably greater than the energy of the emitted light.

[0066] The shell 12 using chalcogenide perovskite can effectively absorb ultraviolet excitation light (wavelength 365nm) generated by GaN (Eg~3.4eV) LED when the band gap is less than 3.4eV. In addition, the shell 12 using chalcogenide perovskite can effectively absorb blue excitation light (wavelength 460nm) generated by InGaN LED and OLED when the band gap is less than 2.7eV.

[0067] Therefore, in order to absorb light having a wavelength of 365 nm or longer, the band gap of the shell 12 is preferably 3.4 eV or less. Alternatively, in order to absorb light having a wavelength of 460 nm or longer, the band gap of the shell 12 is preferably 2.7 eV or less.

[0068] Here, ZnS (Eg ~ 3.6eV; wavelength 340nm) which is usually used for the shell of the previous quantum dots cannot absorb the above excitation light. Therefore, when the shell of ZnS is used, the Stokes shift will not be manifested due to the above excitation light. Similarly, ZnSe has a band gap of 2.7eV (wavelength 460nm), so it can absorb ultraviolet excitation light, but the absorption of blue excitation light is weak.

[0069] In summary, it can be seen that the conventional materials cannot fully absorb the excitation light due to the low light absorption coefficient near the band gap edge, and the absorbance of the shell becomes lower than that of chalcogenide perovskite.

[0070] (shell thickness)

[0071] In addition, the lower limit and the upper limit of the thickness of the shell 12 are defined from the following viewpoints.

[0072] First, the shell 12 as the light absorbing portion is required to have a thickness sufficient to absorb the excitation light.

[0073] Figure 2 This is a graph showing the calculation of the absorptivity of 460 nm excitation light (blue light) with respect to the thickness of the shell 12 using the light absorption coefficient of SrZrS 3 , which is a typical chalcogenide perovskite material. Figure 2 The vertical axis represents the absorbance of 460nm excitation light. Figure 2 The horizontal axis represents the thickness (nm) of the shell 12 .

[0074] Figure 2 The absorption rate of blue light is shown to be about 4% at 2nm, about 10% at 5nm, about 20% at 10nm, about 46% at 30nm, about 64% at 50nm, and about 87% at 100nm.

[0075] As the use of the color conversion particles 10, it is generally assumed that a large amount of the color conversion particles 10 are contained in a film, a coating film, a resin, etc. and used as a color conversion material. Figure 2 If each shell 12 has a thickness of at least 2 nm, sufficient absorbance can be achieved as a whole for the color conversion material to which the plurality of color conversion particles are applied.

[0076] Specifically, when applied to a color conversion film, assuming that there are more than 100 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 color conversion film can fully absorb blue light.

[0077] Second, if the shell 12 is too thick, photoexcited carriers will be deactivated due to recombination before reaching the core 11, and the light emission efficiency will be reduced.

[0078] Here, if we estimate the diffusion length of carriers based on the conductivity of SrHfS3, a typical chalcogenide perovskite material, the maximum is about 30nm. Figure 2 , blue light is absorbed by about 98% at a thickness of 200nm. If it is assumed that the light-excited carriers absorbed at a depth of 200nm in the shell 12 diffuse with a diffusion length of 30nm, when the depth direction is further away from the position of the depth of 200nm in the shell 12 by more than 100nm, the carriers that can reach it almost disappear. Therefore, if the shell 12 is thicker than 300nm, the light-excited carriers cannot reach the core 11, and the luminous efficiency is reduced. Therefore, the thickness of the shell 12 is in the range of more than 2nm and less than 300nm.

[0079] From the viewpoint of suppressing the recombination of photoexcited carriers, if the shell 12 can fully absorb the excitation light, the thickness of the shell 12 is preferably thinner, for example, the thickness of the shell 12 is preferably greater than 2 nm and less than 50 nm. When the thickness of the shell 12 is 50 nm, about 64% of blue light is absorbed. In the case of increasing the absorption of light without sacrificing the distance of carrier diffusion, the thickness of the shell 12 is preferably up to 50 nm.

[0080] When the thickness of the shell 12 is 30 nm, the absorption of blue light is reduced to about 46%, but because it is within the range of the diffusion length of the carriers, more carriers can move to the core, which can improve the luminous efficiency. In addition, when the thickness of the shell 12 is 10 nm, only about 20% of the blue light is absorbed, but it is thin enough compared to the diffusion length of the carriers, so most of the carriers move to the core, which can further improve the luminous efficiency. Therefore, if the thickness of the shell 12 is preferably set to a range of 2 nm or more and 30 nm or less (absorption rate of blue light: about 4%-about 46%), and more preferably set to a range of 2 nm or more and 10 nm or less (absorption rate of blue light: about 4%-about 20%), it is possible to take into account both sufficient absorption of blue light and good carrier movement to the core 11.

[0081] <Nucleus 11>

[0082] The core 11 is a light-emitting particle made of a semiconductor material that generates fluorescence of a target emission wavelength by excitation light. The core 11 as a light-emitting particle generates an electron energy level transition having energy corresponding to the target emission wavelength.

[0083] When semiconductors are used in luminescent particles, the emission is basically the fluorescence emitted when electrons excited to the conduction band recombine with holes in the valence band. Therefore, the emission wavelength in the luminescent particle is equivalent to the band gap energy E of the bulk. g，bulk .

[0084] If the particle size of the light-emitting particle becomes smaller, the quantum size effect caused by the confinement of the electrons becomes prominent, and the energy levels of the electrons become discrete. In this case, the energy (band gap) of the lowest excited state E ex Greater than E g，bulk , and depends on the particle size. That is, if the particle size of the luminescent particle becomes smaller, the luminescent wavelength shifts to the short wavelength side compared to the bulk state, and the luminescent wavelength changes according to the particle size. By utilizing this property, the luminescent wavelength of the luminescent particle can be controlled.

[0085] Specifically, the E of a luminous particle with radius r is ex It is given by the following formula. It should be noted that μ represents the reduced mass of the exciton, E b，ex represents the exciton binding energy, r B represents the exciton Bohr radius.

[0086]

Mathematical formula 1

[0087]

[0088] μ, E b，ex 、r B are given by the following formulas, where ε is the dielectric constant of the luminescent particle. * e is the effective mass of the electron, m * h is the effective mass of the hole.

[0089]

Mathematical formula 2

[0090]

[0091]

[0092]

[0093] Figure 3 It represents E when μ = 0.1 and ε = 10. ex Plot of the dependence on r. Figure 3 The vertical axis represents E ex / E g，bulk , Figure 3 The horizontal axis represents r / r B As the radius r of the luminous particle decreases and approaches r B , E ex The value of E g，bu1k And if r is r B Below, then E ex The value of increases significantly (quantum size effect).

[0094] Using the characteristics of the quantum size effect, based on r determined by the above formula B A light-emitting particle having a particle size in a range where the emission wavelength depends on the particle size is called a "quantum dot". On the other hand, a light-emitting particle having a particle size in a range where the emission wavelength hardly depends on the particle size is called a "non-quantum dot".

[0095] It should be noted that the particle size that shows the quantum size effect varies depending on the parameters μ and ε. For a typical semiconductor, if μ = 0.1 and ε = 10, then r = 3r B The particle size (radius) boundary at which the quantum size effect appears is around . Figure 3 In the figure, the boundary is indicated by a dotted line.

[0096] As mentioned above, the particle size at which the quantum size effect appears in the luminescent particle is basically determined by the exciton Bohr radius r B However, the quantum size effect is also related to the dielectric constant of the material and the effective mass of the electron hole. ex Therefore, it is actually difficult to uniquely describe the boundary between quantum dots and non-quantum dots using particle size and other physical properties.

[0097] Here, consider the typical physical property values ​​(m e * =0.3m0,m h * =0.5m0,ε=6ε0,E g，bulk =1.93eV) calculated from the lowest excitation energy E ex It should be noted that the above m0 is the mass of the electron.

[0098] In the case of BaZrS3, the effective particle radius of a typical quantum size is considered to be about 7.5 nm. Therefore, in the case of BaZrS3, particles with a particle size of 15 nm or less are considered to be quantum dots, and particles with a particle size of more than 15 nm are considered to be non-quantum dots.

[0099] The core 11 of this embodiment may be any of the above-mentioned quantum dots and non-quantum dots.

[0100] 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. In addition, in the case of a quantum dot, the core 11 has high luminous efficiency and a narrow peak.

[0101] However, in order to make the emission wavelength (color) consistent, strict particle size control is required, and the manufacture of quantum dots requires a high degree of manufacturing technology. In addition, quantum dots lack chemical stability due to their tiny particles, and are prone to condensation, regrowth, and decomposition, so the surface needs to be protected. In addition, the electronic state of quantum dots is discrete, so the state density of the valence band and the conduction band are small, and the light absorption coefficient becomes smaller than that of the bulk.

[0102] On the other hand, when the core 11 is a non-quantum dot, that is, when a relatively large particle is used to utilize bulk luminescence without showing quantum size effect, the problems of stability and light absorption are alleviated. However, in a non-quantum dot, the emission wavelength of the core 11 is determined by E g，bulk Therefore, in order to adjust the emission wavelength, it is necessary to change the composition and crystal structure to make E g，bulk change.

[0103] As described above, quantum dots and non-quantum dots have their own advantages and disadvantages, so as the composition of the core 11, an appropriate composition can be selected from quantum dots and non-quantum dots according to the situation and purpose. In addition, the size that produces the quantum size effect varies depending on the material, so the particle size of the core 11 is appropriately set according to the physical properties of the material.

[0104] On the other hand, in order to suppress the reabsorption of the core 11, the particle size of the core 11 is preferably small. For example, when the particle size of BaZrS3 is 200nm, 10% of the red light with a wavelength of 630nm generated by another BaZrS3 core arranged nearby is absorbed. Therefore, the particle size of the core 11 is preferably 200nm or less.

[0105] In addition, if the particle size of the core 11 is set to 50 nm or less under the above conditions, the reabsorption of red light with a wavelength of 630 nm becomes 3%, and if the particle size of the core 11 is set to 25 nm or less, the reabsorption of red light with a wavelength of 630 nm can be suppressed to 2% or less. Therefore, the particle size of the core 11 is preferably 50 nm or less, and more preferably 25 nm or less.

[0106] In addition, the particle size at which the core 11 can stably exist is preferably 1 nm or more.

[0107] Therefore, the particle diameter of the core 11 is preferably 1 nm or more and 200 nm or less.

[0108] (Material for Core 11)

[0109] As the material of the core 11, for example, a substance in which an activator that becomes a luminescent center (luminescent ion) is added to a matrix crystal of an oxide, nitride, etc. (so-called activated phosphor), Group II-VI semiconductors, Group III-V semiconductors, Group I-III-VI semiconductors, Group I-II-IV-VI semiconductors, Group IV-VI semiconductors, halide perovskite semiconductors, oxide perovskites, organic-inorganic perovskites, Si, carbon materials or mixed crystal compounds thereof can be used.

[0110] Alternatively, chalcogenide perovskite may be used as the material of the core 11 .

[0111] High luminescence performance can be expected by using a chalcogenide perovskite core 11 having an excellent light absorption coefficient. In addition, from the viewpoint of affinity with the constituent elements of the shell, the matching of the crystal structure and the lattice constant, the defects at the interface between the core 11 and the shell 12 are reduced, and non-luminescent recombination is reduced, so higher luminescence efficiency can be expected.

[0112] As an example, in the case where chalcogenide perovskite is used as the material of the core 11 , a substance different from the material of the shell 12 may be selected from the substances listed below.

[0113] SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, BaHfSe3, Sr2Ba n- 1Zr 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 、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

[0114] The chalcogenide perovskite applicable to the core 11 can also be composed of (Sr x Ba 1-x )(Zr y Hf 1-y )(S z Se 1-z )3 or (Srx’ Ba 1-x’ )2(Sr x Ba 1-x ) n-1 (Zr y Hf 1-y ) n (S z Se 1-z ) 3n+1 Indicates (wherein x, x', y, and z are each a value greater than or equal to 0 and less than or equal to 1).

[0115] These substances are advantageous materials in that, when used as the core 11 of the color conversion particle 10 , they have a band gap suitable for use in light-emitting devices, display devices, lighting devices, and the like that emit visible light.

[0116] <Band Alignment of Core 11 and Shell 12>

[0117] As described above, in the core 11 and the shell 12, the energy E at the lower end of the conduction band c and the energy E at the upper end of the valence band v The band alignment becomes the relationship that makes the Stokes shift appear.

[0118] Stokes shift originally refers to the energy difference between the energy state of electrons excited by light and the energy state of electrons when they release energy and emit light in a single substance, and is observed as the difference in the maximum energy position of the absorption spectrum and the emission spectrum.

[0119] For heterogeneous structured nanoparticles such as the color conversion particle 10 of the present embodiment, by designing appropriate band alignment at the heterogeneous interface, an "apparent Stokes shift", i.e., an energy difference between the absorption spectrum end and the emission spectrum peak, can be generated. In this specification, the apparent Stokes shift generated in heterogeneous structured nanoparticles is sometimes referred to as Stokes shift.

[0120] Figure 4 , Figure 5 , Figure 6 An example of the energy band alignment between the core 11 and the shell 12 is shown.

[0121] exist Figure 4 , Figure 5 , Figure 6 In each figure, the top indicates the direction of increasing energy, and the central rectangle indicates the band gap E of core 11. g_core , the rectangles on both sides represent the band gap E of shell 12 g_shell The upper side of the central rectangle represents the energy E at the lower end of the conduction band of core 11. c_core The bottom of the central rectangle represents the energy E at the top of the valence band of core 11. v_core The upper sides of the rectangles on both sides represent the energy E at the lower end of the conduction band of shell 12.c_she1l The bottom sides of the rectangles on both sides represent the energy E of the upper end of the valence band of shell 12. v_shell .

[0122] In addition, Figure 4 , Figure 5 , Figure 6 In each figure, the curve drawn on the upper side of the rectangle represents the distribution of electrons, and the curve drawn on the bottom side of the rectangle represents the distribution of holes. In addition, the downward arrow in the figure represents the energy difference of the light emission process, and the upward arrow in the figure represents the energy difference of the light absorption (excitation) process. When the energy difference of the light absorption process is greater than the energy difference of the light emission process, the Stokes shift appears.

[0123] exist Figure 4 In (a)-(e), the band gap E of shell 12 g_shell Both are larger than the band gap E of core 11 g_core (E g_shell >E g_core ). On the other hand, Figure 5 In (a)-(e), the band gap E of shell 12 g_shell are smaller than the band gap E of core 11 g_core (E g_shell <E g_core ). In addition, Figure 6 In (a)-(c), the band gap E of shell 12 g_shell The band gap E of core 11 g_core Equal(E g_shell =E g_core ). It should be noted that regarding E c_core With E c_shel1 The size relationship and E v_core With E v_shell The size relationship, in Figure 4 , Figure 5 , Figure 6 are marked separately in each figure.

[0124] The Stokes shift is Figure 4 (a)-(e), Figure 5 (a), (e), Figure 6 The color conversion particles of this embodiment have Figure 4 (a)-(e), Figure 5 (a), (e), Figure 6 The energy band alignment of the color conversion particle of this embodiment satisfies the energy E of the lower end of the conduction band of the shell 12. c_shell The energy E above the lower end of the conduction band of core 11 c_core, or the energy E at the upper end of the valence band of shell 12 v_shel1 The energy E is lower than the upper end of the valence band of nucleus 11. v_core At least one of the conditions (i.e., E c_shell >E c_core 、E v_shell <E v_core Any of, or E c_she1l >E c_core and E v_she1l <E v_core ).

[0125] Figure 4 The band alignments (Type I and Quasi-Type II) of (b), (c), and (d) all satisfy the energy E of the lower end of the conduction band of shell 12. c_shell is the energy E at the lower end of the conduction band of core 11 c_core The energy E of the upper end of the valence band of shell 12 is above v_shell is the energy E at the upper end of the valence band of nucleus 11 v_core The following conditions (i.e., in E g_shell >E g_core When E c_shell ≥E c_core And E v_shel1 ≤E v_core ).

[0126] exist Figure 4 In the case of Type I shown in (c), electrons and holes are confined in the core 11 and recombination (nuclear luminescence) occurs in the core 11. In Type I, holes and electrons are localized in the core 11, so the overlap of wave functions is large and the luminescence efficiency is high. Therefore, as the energy band alignment of the core 11 and the shell 12, the structure of Type I is most preferred. Figure 4 The materials of the core 11 and the shell 12 of Type I shown in (c) include, for example, a combination of BaZrS 3 for the core 11 and SrZrS 3 for the shell 12.

[0127] Figure 4 Quasi-Type II (where E g_shell >E g_core ), one of the carriers, holes or electrons, extends to the shell, so the luminous efficiency is lower than that of Type I. However, in Figure 4 In (b) and (d), even so, another type of carrier is locally present in the core, so the luminous efficiency is high, second only to Type I and is preferred. Figure 4 The materials of the core 11 and shell 12 of Quasi-Type II shown in (b) and (d) include, for example, Figure 4The core 11 shown in (b) is a combination of BaHfS 3 and the shell 12 is CaZrS 3.

[0128] In addition, Figure 4 (a), (e), Figure 5 (a), (e), Figure 6 In the energy band alignment of (a) and (c) (Type II), electrons and holes are separated in the core 11 and the shell 12, so it is difficult to emit light based on inter-band recombination compared to Type I. However, in Type II, it is possible that recombination occurs at the interface between the core 11 and the shell 12 (interface emission), which is higher than the E of the shell 12. g The small energy difference thus shows up as a Stokes shift.

[0129] In the case of Type II, light emission occurs at the interface between the core 11 and the shell 12, so the overlap of wave functions is small and the light emission efficiency is lower than that of Type I. In addition, it is believed that the interface recombination is sometimes accompanied by non-light emitting recombination via interface defects, so the light emission efficiency is also lowered in this regard.

[0130] However, Type II band alignment is advantageous in that it can achieve a wide range of emission wavelengths, and is expected to be used in near-infrared luminescent materials and the like. Figure 4 (a), (e), Figure 5 (a), (e), Figure 6 The materials of the core 11 and shell 12 of Type II shown in (a) and (c) include, for example, Figure 4 The core 11 shown in (a) is a combination of BaZrS3 and the shell 12 is CaZrS3.

[0131] In addition, if Figure 4 As shown in (a)-(e), if the band gap E of shell 12 is g_shell Greater than the band gap E of core 11 g_core (E g_shell >E g_core ), the light emitted by the core 11 is hardly absorbed by the shell 12 and is emitted to the outside. As a result, the reabsorption loss in the shell 12 is suppressed, and the luminous efficiency of the color conversion particle 10 can be further improved.

[0132] exist Figure 6 In (a) and (c), the band gap E of shell 12 g_shell The band gap E of core 11 g_core Equal(E g_shell =E g_core ). Therefore, in Figure 6 In the case of (a) and (c), Figure 4 (a)-(e) g_shell >Eg_core ), the light emitted by the core 11 is easily reabsorbed by the shell 12, and the reabsorption loss becomes larger. Therefore, the luminous efficiency of the color conversion particle 10 becomes lower. It should be noted that if Figure 5 The band gap E of shell 12 is as shown in (a) and (e). g_shell Smaller than the band gap E of core 11 g_core (E g_shell <E g_core ) Figure 6 Comparing the cases (a) and (c) of Figure 6 In the cases of (a) and (c), the amount of light reabsorbed by the shell 12 is small, and the reabsorption loss is suppressed, so that the light emission efficiency of the color conversion particle 10 can be improved.

[0133] It should be noted that the color conversion particle 10 can take various states depending on the combination of the material of the core 11 and the material of the shell 12. The material of the core 11 and the material of the shell 12 exemplified above are sulfides, but they can also be selenides or solid solutions. If they are also included, various states can be achieved, and there are combinations of the materials of the core 11 and the shell 12 that show excellent luminescent properties.

[0134] <Particle Diameter of Color Conversion Particles 10>

[0135] Here, when ink in which the color conversion particles 10 are dispersed in a solvent is applied by, for example, an inkjet method, if the particle size of the color conversion particles 10 is too large, the nozzle may be clogged. In other coating methods, the large particle size of the color conversion particles 10 may also become a process problem.

[0136] For the reasons described above, the particle diameter of the color conversion particles 10 is preferably 1000 nm or less.

[0137] <Method for Manufacturing Color Conversion Particles 10>

[0138] Next, a method for producing the color conversion particle 10 will be described. The color conversion particle 10 is produced by performing a synthesis step of the shell 12 after a synthesis step of the core 11 .

[0139] (Synthesis Step of Core 11)

[0140] In the synthesis process of the core 11, the core 11 as the nano luminescent particle is generated by a known method such as hot injection method, solvothermal method, hydrothermal method, continuous flow process synthesis method, CHM (composite-hydroxide-mediated method), temperature rise method, gas phase synthesis, solid phase synthesis, mechanochemical synthesis, etc. As the material of the core 11, for example, the above-mentioned substances can be used.

[0141] In addition, chalcogenide perovskite may also be used as the material of the core 11. In this case, the core 11 may be synthesized by reacting a precursor compound in a solution, mixing and heating a precursor powder in an inert atmosphere or air, or mixing and heating a metal precursor powder in an inert atmosphere and reacting it with a chalcogen precursor gas.

[0142] When the core 11 is synthesized by reacting precursor compounds in a solution, for example, a hot injection method, a temperature rising method, a solvothermal method, a hydrothermal method, a CHM method, a continuous flow process synthesis method, or the like can be applied.

[0143] (Shell 12 Synthesis Step)

[0144] In the step of synthesizing the shell 12, the shell 12 of the chalcogenide perovskite is synthesized on the surface of the core 11 obtained in the above step. In this step, the nano-luminescent particles that become the core 11 and the precursor of the chalcogenide perovskite are mixed in a solvent using a one-pot synthesis method or a hot injection method. Thus, the color conversion particle 10 having a core-shell structure in which the surface of the core 11 is covered with the shell 12 of the chalcogenide perovskite is synthesized. It should be noted that as a method of synthesizing the shell other than the solution, the shell 12 can also be generated by, for example, gas phase synthesis based on drum sputtering.

[0145] As an example, a case where the shell 12 of chalcogenide perovskite ABX3 in which A and B respectively contain group II and group IV elements is synthesized by the hot injection method will be described.

[0146] In this case, a first solution and a second solution are prepared, wherein the first solution contains nano-luminescent particles that become cores, a precursor compound containing a group II element, a precursor compound containing a group IV element, and a solvent, and the second solution contains a precursor compound containing a chalcogen element and a solvent. Then, for the first solution, the second solution is put into a reaction vessel at a temperature in the range of 150°C to 350°C, and the reaction is maintained in the reaction vessel at the above temperature for 1 second to 100 hours. Thus, a compound having a target core-shell structure is synthesized by undergoing a process in which the shell material grows on the nanoparticles used in the reaction. After the reaction is completed, the target is recovered after washing with an organic solvent or water.

[0147] Examples of the precursor compound containing the Group II element include the following precursor compounds.

[0148] Metal powders, metal alkoxides, metal carboxylates, metal nitrates, metal perchlorates, metal sulfates, metal acetylacetonates, metal halides, metal hydroxides, metal halides, and combinations thereof.

[0149] Examples of the precursor compound containing the Group IV element include the following precursor compounds.

[0150] Metal powders, metal alkoxides, metal carboxylates, metal nitrates, metal perchlorates, metal sulfates, metal acetylacetonates, metal halides, metal hydroxides, metal halides, and combinations thereof.

[0151] Examples of the precursor compound containing a chalcogen element include the following compounds.

[0152] Metal sulfides (including selenide or telluride);

[0153] Carbon disulfide (including selenide or telluride);

[0154] Sulfide, hydrogen selenide, hydrogen telluride and other sulfide hydrogens;

[0155] Thiol compounds (including selenide or telluride);

[0156] Phosphine compounds such as trioctylphosphine sulfide (including selenide or telluride);

[0157] Thiourea (including seleno or telluron derivatives);

[0158] Sulfur, selenium, tellurium,

[0159] Or a substance obtained by dispersing these compounds in a solvent such as an amine, an acid, a hydrocarbon, or the like, and a combination thereof.

[0160] Examples of the solvent include the following solvents.

[0161] Typically, an organic solvent or water is used, wherein the organic solvent comprises at least one of the following compounds:

[0162] Primary amines, secondary amines, and tertiary amines having organic groups such as hydrocarbon groups;

[0163] Aromatic hydrocarbons;

[0164] Nitrogen-containing heterocyclic compounds, oxygen-containing heterocyclic compounds, sulfur-containing heterocyclic compounds, selenium-containing heterocyclic compounds, tellurium-containing heterocyclic compounds;

[0165] Aliphatic hydrocarbons;

[0166] Phosphine compounds having organic groups such as hydrocarbon groups;

[0167] Phosphine oxide compounds having organic groups such as hydrocarbon groups;

[0168] A compound having an alcohol, an aldehyde, a carboxylic acid, or a thio group, a seleno group, or a tellurium group thereof.

[0169] Furthermore, combinations of these solvents.

[0170] The heating of the solution includes reacting the chalcogen precursor to form chalcogen hydride. In addition, the reaction of the solution includes synthesizing under an inert atmosphere or an atmospheric atmosphere. In addition, the reaction of the solution can use a microreactor to synthesize the target in a continuous flow process.

[0171] In addition, in the synthesis of the above-mentioned shell 12, the nanoluminescent particles that become the core 11 can be synthesized first, and the shell 12 can be synthesized continuously, or the shell precursor can be added to the reaction container when the nanoluminescent particles are synthesized to synthesize the color conversion particles 10 having the target core-shell structure.

[0172] <External Structure of Color Conversion Particle 10>

[0173] In addition, if Figure 1 As shown in (b), the color conversion particle 10 may have a shell 13 as a protective layer and a ligand 14 as an outer structure.

[0174] (Shell 13)

[0175] The shell 13 is a protective layer that covers the semiconductor particles formed by the core 11 and the shell 12 from the outside. The shell 13 is provided to further improve the durability of the color conversion particle 10 by suppressing the degradation of the semiconductor particles due to contact with oxygen and protecting the semiconductor particles from chemical interactions with the outside. In addition, the shell 13 has the property of transmitting the excitation light as the target and the luminescence of the core 11.

[0176] The housing 13 is formed by a known method using a chemically stable material such as silicon dioxide, glass, an oxide insulator, or a resin.

[0177] For example, when the outer shell 13 is formed 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 forming an inorganic oxide by a thermal curing reaction using a sol-gel method, for example.

[0178] In addition, the outer shell 13 may be a layer containing a resin or a modified polysilazane. Polysilazane is a polymer having a silicon-nitrogen bond and is a solid solution of SiO2, Si3N4 and an intermediate solid solution of the two formed by Si-N, Si-H, NH, etc. x N y When the outer shell 13 is formed of a resin, it is preferably formed of a water-soluble resin such as a polyvinyl alcohol resin from the viewpoint of ease of production.

[0179] In addition, the outer shell 13 may have a multilayer structure including both a layer of a metal oxide and a layer containing a resin or a modified polysilazane or the like.

[0180] (ligand 14)

[0181] The ligand 14 is an organic modifying molecule for modifying the surface of the color conversion particle 10 , and is provided so as to be bonded to the outer surface of the color conversion particle 10 or to cover the color conversion particle 10 .

[0182] The ligand 14 has the function of isolating the color conversion particles 10 to improve dispersibility and preventing regrowth and destruction caused by contact between the color conversion particles 10. The ligand 14 also has the function of suppressing surface defects of the shell 12 and improving luminous efficiency by capping dangling bonds.

[0183] As the modified organic molecule of the ligand 14, a modified organic molecule having a structure of 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 phosphonyl group, a sulfone group, an amine group, etc. can be used. Examples of such modified organic molecules include sodium hexametaphosphate, sodium laurate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, triethanolamine lauryl sulfate, lauryl diethanolamide, dodecyltrimethylammonium chloride, trioctylphosphine, trioctylphosphine oxide, and the like.

[0184] In addition, it is preferable to use a compound having a hydrophilic group and a hydrophobic group in the molecule as the modified organic molecule of the ligand 14. Thus, the color conversion particle 10 can be coated with the ligand 14 by both chemical bonding such as coordination bonding by heteroatoms and bonding based on physical adsorption. As such a modified organic molecule, a compound having a non-polar hydrocarbon terminal as a hydrophobic group and an amino group as a hydrophilic group, i.e., an amine, can be cited. In the case where the hydrophilic group of the modified organic molecule is an amine, the amine can be firmly bonded to the metal element.

[0185] In addition, the modified organic molecule as the ligand 14 preferably has a heteroatom. By making the modified organic molecule have a heteroatom, electrical polarity is generated between the heteroatom and the carbon atom, and the modified organic molecule can be firmly bonded to the surface on the outer surface of the color conversion particle. Here, "heteroatom" refers to all atoms except hydrogen atoms and carbon atoms.

[0186] <Modification Example of Color Conversion Particles>

[0187] Next, refer to Figure 7 , Figure 8 A modification of the color conversion particle 10 will be described. Figure 7 , Figure 8 In the schematic diagram of the color conversion particle 10 shown in FIG. 1 , only the core 11 and the shell 12 are shown unless otherwise specified. However, the color conversion particles 10 may also be Figure 1The example (b) also has a shell 13 and a ligand 14 .

[0188] For example, Figure 7 As shown in (a) of FIG. 1 , the shell 12 of the color conversion particle 10 does not necessarily have to cover the entire core 11 , and a portion of the core 11 may be exposed to the outside.

[0189] For example, Figure 7 As shown in (b), the color conversion particle 10 may have a structure in which a plurality of shells 12 are stacked on the outside of a core 11. By using materials with different compositions, crystal structures, etc. as the materials of each shell 12, the light absorption characteristics and light emission characteristics of the color conversion particle 10 as a whole can be adjusted. Figure 7 In the example (b) of FIG. 1 , two layers of shells 12 a and 12 b are stacked on the core 11 , but the shell 12 of the color conversion particle 10 may be three or more layers.

[0190] Figure 7 The color conversion particle 10 having the multilayer shells 12 a and 12 b shown in (b) can be formed by heating a solution containing semiconductor particles having the shells 12 a formed on the core 11 and other shell precursors.

[0191] For example, Figure 7 As shown in (c), the color conversion particle 10 may have a structure including a plurality of cores 11 in a shell 12. If a plurality of cores 11 are included in the shell 12, the effective thickness of the shell 12 in the color conversion particle 10 increases, and the durability of the color conversion particle 10 can be improved. In addition, by using materials having different compositions, crystal structures, etc. in the respective cores 11, the light absorption characteristics and light emission characteristics of the color conversion particle 10 as a whole can be adjusted.

[0192] exist Figure 7 In the example (c), a structure including three cores 11 in the shell 12 is shown, but the number of cores 11 included in the shell 12 can be changed appropriately. In addition, in the color conversion particle 10 having a plurality of cores 11, any of the cores 11 may be partially exposed outside the shell 12.

[0193] In addition, the color conversion particle 10 may include a plurality of cores 11 in a shell 12, and the shell 12 may have a plurality of layers. Figure 7 As shown in (d), the outer side of the shell 12a including the plurality of cores 11 may be further covered with the shell 12b. Figure 7 A shell is further laminated on the outer side of the shell 12b of (d).

[0194] For example, Figure 7 As shown in (e), a plurality of cores 11 each covered with a shell 12a may be covered with a shell 12b and integrated to form a color conversion particle 10. Figure 7 In the example (e), each shell 12 a may include a plurality of cores 11 .

[0195] In addition, the core 11 of the color conversion particle 10 may also contain a light absorbing material 17 made of the same material as the shell 12. Figure 7 As shown in (f), the outer side of the light absorbing material 17 may be covered by the core 11. It should be noted that the material of the light absorbing material 17 can be any material that can be selected as the material of the shell 12, and the shell 12 covering the core 11 and the light absorbing material 17 may not be composed of the same material.

[0196] As described above, in the structure of the stacked core having the light absorbing material 17 inside, the light absorbing material 17 (the same material as the shell 12) located inside the core 11 can be used to absorb the excitation light that has passed through the outer shell 12, thereby improving the excitation light absorption rate. In addition, in the structure of the stacked core having the light absorbing material 17 inside, the light-emitting efficiency can be improved by effectively confining the photoexcited carriers in the narrow region of the core 11 sandwiched by the material of the shell 12.

[0197] In addition, the energy band alignment of the light absorbing material 17 and the core 11 is preferably Type I, and the energy band alignment of the core 11 and the shell 12 is also preferably Type I. For example, a combination of the light absorbing material 17 being SrZrS3 and the core 11 being BaZrS3 can be cited, and a material combination in which the shell 12 is further SrZrS3 can be cited. As another example, a combination of the light absorbing material 17 being SrHfS3 and the core 11 being BaHfS3 can be cited, and a material combination in which the shell 12 is further SrHfS3 can be cited. It should be noted that the light absorbing material 17 may be a material other than chalcogenide perovskite as long as the energy band alignment of the light absorbing material 17 and the core 11 shows a Stokes shift.

[0198] In addition, the color conversion particle 10 may have a hollow structure having a void 16 inside. Figure 8 As shown in (a), one or more voids 16 may be formed in the core 11. Alternatively, Figure 8 As shown in (b), in the color conversion particle 10 having the outer shell 13 outside the shell 12, a gap 16 can be formed between the shell 12 and the outer shell 13. By forming the gap 16 that does not absorb light or emit light inside the color conversion particle 10, the optical characteristics and shape of the color conversion particle 10 can be adjusted.

[0199] Figure 8The hollow structure color conversion particle 10 shown in (a) and (b) can be manufactured, for example, as follows. First, organic matter such as fullerene and carbon nanotubes and soluble salts are added simultaneously during synthesis to generate semiconductor particles containing organic matter and salts. Then, the organic matter or salt is dissolved using a solvent, or the organic matter or salt is ashed at high temperature, thereby obtaining the hollow structure color conversion particle 10.

[0200] In addition, foreign matter that does not absorb or emit light, such as an insulator or other composition, may be included in the core 11 or shell 12 of the color conversion particle 10. By including such foreign matter in the core 11 or shell 12, for example, the luminous efficiency of the color conversion particle 10 can be improved by scattering light, and the shape of the color conversion particle 10 can be adjusted.

[0201] In addition, if Figure 8 As shown in (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 vertical direction (depth direction) relative to the interface. The physical properties and chemical properties of the core 11 or shell 12 continuously change in a gradient manner in the depth direction, thereby improving the matching of the lattice and reducing lattice defects. As a result, non-luminescent recombination is reduced, and the luminous efficiency of the color conversion particle can be improved.

[0202] It should be noted that the above-mentioned gradient structure can be produced, for example, by the same method as in the case of producing the multi-layered core 11 and shell 12 .

[0203] In addition, in the present invention, the shape of the color conversion particles to be synthesized is not particularly limited. For example, spherical, elongated, star-shaped, polyhedral, pyramidal, tetrapod, tetrahedral, flake-shaped, conical, or irregularly shaped cores 11 and / or color conversion particles 10 may be synthesized.

[0204] Hereinafter, the effects of the color conversion particle 10 according to the present embodiment will be described.

[0205] The color conversion particle 10 of this embodiment includes a core 11 and a shell 12 that includes the core 11 and absorbs excitation light. The color conversion particle 10 receives the irradiated excitation light and generates light emission at the core 11 or at the interface between the core 11 and the shell 12. Chalcogenide perovskite, which is a material of the shell 12, has the characteristics of high light absorption coefficient and excellent durability. Therefore, in this embodiment, since the core 11 is covered with the shell 12 of the chalcogenide perovskite, the color conversion particle 10 has high durability against heat and other interference. In addition, compared with conventional quantum dots, the color conversion particle 10 is less likely to cause performance degradation even if the ligand is separated due to heat or other interference.

[0206] In addition, the core 11 and the shell 12 have an energy band alignment showing a Stokes shift. In this embodiment, the difference in band edge transition energy between the shell 12 and the core 11 is utilized, and the shell 12 of the chalcogenide perovskite with high absorbance is used to transfer photoexcited carriers to the core 11, so that the photoexcited carriers enclosed in the core 11 are recombined to emit light.

[0207] In this embodiment, the shell 12 of chalcogenide perovskite is formed outside the core 11, so that the part responsible for absorption and the part responsible for light emission are separated in the color conversion particle 10. As a result, a large Stokes shift can be obtained, and absorbance can be obtained by the shell 12 without increasing the size of the core 11. Therefore, the reabsorption loss of light emission caused by the core 11 can be suppressed, and high absorbance and high light emission efficiency can be achieved.

[0208] In addition, as described above, the color conversion particle 10 of the present embodiment has high absorbance and luminous efficiency, and therefore, compared with conventional quantum dots, the desired color conversion function can be achieved with a smaller amount. In other words, for example, when the color conversion particle 10 of the present embodiment is applied to the color conversion layer of a device other than a display device or lighting, the color conversion layer can be thinned and the yield rate can be improved. In the formation of the color conversion layer, the probability of the occurrence of defects in the film-making process increases due to repeated film-making processes, resulting in a decrease in the yield rate of the color conversion layer. Conversely, if the color conversion layer can be thinned, the film-making process can be reduced, and thus the effective defect rate of the color conversion layer can be reduced.

[0209] In addition, if the band gap of the shell 12 is made larger than the band gap of the core 11, the light emitted by the core 11 is hardly absorbed by the shell 12 and is emitted to the outside, so that the reabsorption loss in the shell can also be suppressed. That is, when the band gap of the shell 12 is larger than the band gap of the core 11, the absorbance can be increased by making the shell 12 thicker without increasing the reabsorption loss, so the luminous efficiency of the color conversion particle 10 can be further improved.

[0210] In addition, if the band gap of the shell 12 is set to 3.4 eV or less, the ultraviolet excitation light (wavelength 365 nm) generated by the GaN LED can be effectively absorbed. In this case, by using a single ultraviolet LED and the color conversion particle 10 that converts the color into RGB colors by the ultraviolet excitation light, it is possible to emit light of each color of RGB without using LEDs (light sources) with multiple emission wavelengths, thereby simplifying the light-emitting element.

[0211] Furthermore, if the core 11 is made of chalcogenide perovskite, the absorbance and durability of the core 11 can be improved, and the light emission efficiency can be further improved by reducing defects at the core-shell interface.

[0212] <Product Form and Application Example of Color Conversion Particle 10>

[0213] Next, the product form and application examples of the color conversion particle 10 are described. The product form of the color conversion particle 10 includes powder, solution, film, sheet, etc. In addition, as an application example of the color conversion particle 10, application to various devices is assumed.

[0214] (powder)

[0215] The powder is a powder in which the color conversion particles 10 are in an agglomerated state. Hereinafter, the color conversion particles 10 are sometimes referred to as primary particles, and the particles in which the color conversion particles 10 are in an agglomerated state are referred to as secondary particles. The sizes of the primary particles and the secondary particles are not particularly limited, and the primary particles are preferably in the range of 5nm-1000nm. In addition, ligands may be imparted to the surfaces of the primary particles and the secondary particles. In order to improve the properties such as the luminescent properties, the dispersibility of the color conversion particles, and the film forming properties, other materials may be added to the powder of the color conversion particles 10 as additives.

[0216] The use of the powder of the color conversion particles 10 is not particularly limited. For example, the powder may be dispersed in a solvent to make a solution, dispersed in a resin or solid medium to make a composite, sintered to make a sputtering target, or directly used as a vapor deposition source in a powder state.

[0217] (Solution)

[0218] The solution is a solution in which the color conversion particles 10 are dispersed in a solvent. The sizes of the primary particles and the secondary particles are not particularly limited, and the primary particles are preferably in the range of 5nm-1000nm. In addition, "dispersed" means that the color conversion particles 10 are floating or suspended in the solvent, and a part of them may have settled. In addition, ligands may be given to the surfaces of the primary particles and the secondary particles.

[0219] The solvent of the solution may be one or more solvents. Examples of the solvent include the following solvents, but the invention is not limited thereto.

[0220] Esters such as water, methyl formate, ethyl formate, propyl formate, amyl formate, methyl acetate, ethyl acetate, and amyl 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 phenethyl ether; 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, Alcohols such as 2-trifluoroethanol 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 dichloromethane and chloroform; organic solvents having a hydrocarbon group such as n-pentane, cyclohexane, n-hexane, benzene, toluene, and xylene; dimethyl sulfoxide, etc.

[0221] Furthermore, in order to improve the light emitting characteristics, dispersibility of the color conversion particles 10, film forming properties and the like, an acid, an alkali or a binder material may be added as an additive to the above solution.

[0222] In addition, the use of the above-mentioned solution is not particularly limited. For example, it can be used for film formation using coating, spraying, blade coating (other solution film formation methods), preparation of a composite using a composite with a solid dispersion medium, or preparation of a device using the same.

[0223] (film)

[0224] The thin film is a thin film in which the color conversion particles 10 are condensed into a planar state. The size of the primary particles and the secondary particles is not particularly limited, and the primary particles are preferably in the range of 5nm-1000nm. In addition, ligands may be imparted to the surfaces of the primary particles and the secondary particles. In order to improve the luminescent properties and the dispersibility of the color conversion particles 10, other materials may be added as additives to the above-mentioned thin film.

[0225] The method for preparing the above-mentioned thin film is not particularly limited. For example, the thin film can be prepared by coating, spraying, blade coating, inkjet and other film-forming methods based on solution film formation, or vacuum processes such as sputtering and vacuum evaporation. In addition, the color conversion particles 10 can be formed into a film by coating or other methods, and then sintered or other treatments are performed to make the particle shape not maintained.

[0226] (Sheet)

[0227] The sheet is a sheet in which the dispersion medium in which the color conversion particles 10 are dispersed is in a planar state. The size of the primary particles and the secondary particles is not particularly limited, and the primary particles are preferably in the range of 5nm to 1000nm. In addition, ligands may be added to the surfaces of the primary particles and the secondary particles.

[0228] The material used as the dispersion medium of the sheet can be any polymer known to those skilled in the art for this purpose. In a suitable embodiment, the polymer is substantially translucent or substantially transparent.

[0229] For example, polymers that can be used as dispersion media for sheets include, but are not limited to, polyvinyl butyral, polyvinyl acetate, silicone, and silicone derivatives. In addition, silicone derivatives include, but are 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, etc.

[0230] In order to improve the light emitting characteristics and the dispersibility of the color conversion particles 10, other materials such as silica fine particles and the solvent described in the above solution may be added as additives to the above sheet.

[0231] 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 ink containing the color conversion particles 10 with a dispersion medium or a precursor thereof and applying the mixture.

[0232] (Device)

[0233] As the use of the color conversion particle 10, or the above-mentioned powder, solution, film, sheet, it is envisioned that it is applied to the down conversion of ultraviolet light or blue light in various devices. As the types of devices, for example, light-emitting devices such as LEDs and organic ELs, display devices including the light-emitting devices, lighting devices including the light-emitting devices, image sensors, photoelectric conversion devices, bioluminescent markers, etc. can be cited.

[0234] <Example>

[0235] Hereinafter, examples of the color conversion particles of the present invention will be described.

[0236] In the color conversion particles of the embodiment, the material of the core is BaZrS3, and the material of the shell is SrZrS3. That is, the core and shell of the color conversion particles of the embodiment are chalcogenide perovskite, which is an example of an optimal combination of materials for exhibiting Stokes shift. As described above, when the core and shell are chalcogenide perovskite, the interface defects between the core and the shell are reduced, and high luminous efficiency can be expected.

[0237] Fig. 9 This is a diagram showing the alignment of the energy bands of shell / core / shell in the color conversion particles of the embodiment. The origin of the energy on the vertical axis is set to the vacuum energy level. The physical property values ​​of the core and shell are determined based on the reference "Y. Nishigaki et al., Sol. RRL 1900555 (2020)" and the reference "K. Hanzawa et al., J. Am. Chem. Soc. 141, 5343 (2019)" and other experimental result reports.

[0238] like Fig. 9 As shown, regarding the energy band alignment of the shell and core in the embodiment, the E c Lower than the shell E c , nuclear E v Higher than the shell E v , thus becoming Type I. Therefore, in the configuration of the embodiment, it is expected that the shell absorbs the excitation light, and the excited carriers move to the core and recombine, thereby performing core luminescence. In addition, in the embodiment, due to the band gap E of the shell g Greater than the core band gap E g , so the suppression of reabsorption losses in the shell is also expected.

[0239] In the embodiment, one-dimensional simulation was performed using software (SCAPS-1D) regarding light absorption and light emission of the color conversion particles. Fig.10 It is a figure which shows the result of the simulation of Example. Fig.10 The horizontal axes of the respective graphs represent the one-dimensional positions in the diameter direction of the color conversion particles.

[0240] In the simulation, the core diameter was set to 20 nm, the shell thickness was set to 50 nm, and the excitation light wavelength was set to 450 nm blue light, with an illumination of 100 mW / cm 2 Incident from one side (left side of the figure).

[0241] Fig.10 (a) represents the E of the color conversion particle c Distribution curve, Fig.10 (b) represents the E of the color conversion particle v Distribution curve. The energy on the vertical axis is expressed in Fermi energy E F As a benchmark.

[0242] exist Fig.10 In (a), the E of the core range (the horizontal axis value is in the range of 50nm-70nm) c E below the shell range c In addition, Fig.10 (b), the range of the kernel E v E above the shell range v .and, Fig.10 The distribution curves of (a) and (b) are Fig. 9 The band alignment shown is in good agreement.

[0243] Fig.10 (c) shows the carrier concentration distribution curve of the color conversion particles. Fig.10 The solid line in (c) represents the electron distribution curve. Fig.10 The dotted line in (c) represents the distribution curve of holes.

[0244] exist Fig.10 In (c), the carrier density in the core range (the horizontal axis value is in the range of 50nm-70nm) is higher than that in the shell range. Fig.10 As can be seen from (c), carriers excited by light absorbed by the shell efficiently move to the core and are confined in the core.

[0245] Fig.10 (d) represents the generation rate and recombination rate of carriers. Fig.10 The dashed line in (d) represents the distribution curve of the carrier generation rate. Fig.10 The solid line in (d) represents the distribution curve of the carrier recombination rate.

[0246] like Fig.10 As shown in (d), the carrier generation rate is highest on the left side of the figure where the excitation light is incident. In addition, since the light absorption coefficient of chalcogenide perovskite is very large, the carrier generation rate decreases sharply as it moves to the right side of the figure. It can be seen that most of the carrier excitation based on light absorption occurs within the range of 0nm-50nm shell.

[0247] On the other hand, the carrier recombination rate shows a high value in the core range (the value of the horizontal axis is in the range of 50nm-70nm), and in the shell range, the value is almost zero. In other words, the luminescence caused by the recombination of carriers is almost entirely caused by the photoexcited carriers that move to the core.

[0248] Therefore, according to the simulation results, it can be seen that the transport of photoexcited carriers from the shell to the core and the confinement of photoexcited carriers in the core occur efficiently.

[0249] 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 light absorption coefficients of BaZrS3 and SrZrS3 and the PL (Photoluminescence) emission peak of BaZrS3 are calculated respectively.

[0250] Fig.11 It is a diagram showing the distribution curves of the light absorption coefficients of BaZrS3 and SrZrS3 and the PL emission spectrum of BaZrS3. Fig.11 The horizontal axis represents wavelength.

[0251] PL emission spectrum of BaZrS3 as the core material ( Fig.11 The solid line in the middle shows a sharp emission peak with a half-width of about 30 nm. This is because the absorption edge (the rise of the light absorption coefficient near the band edge) of chalcogenide perovskite is very steep.

[0252] in addition, Fig.11 The single-dot dash line represents the distribution curve of the light absorption coefficient of BaZrS3. Fig.11 The dashed line represents the distribution curve of the light absorption coefficient of SrZrS 3. In the region where the lower part of the distribution curve of the light absorption coefficient overlaps with the distribution curve of the PL emission spectrum, the luminescence can be reabsorbed.

[0253] That is, it is known that if color conversion is performed using only BaZrS3 as the core material, the luminescence can be reabsorbed. Therefore, in the case of the core of BaZrS3, if the particle size is increased to increase the absorbance, the reabsorption also increases, so the absorbance and the loss of reabsorption are in a trade-off relationship.

[0254] On the other hand, the distribution curve of the light absorption coefficient of SrZrS 3 hardly overlaps with the lower part of the distribution curve of the PL emission spectrum of BaZrS 3. Therefore, it can be seen that when a shell of SrZrS 3 is applied to a core of BaZrS 3, reabsorption in the shell hardly occurs.

[0255] In the embodiment, the color conversion particles are set to a core-shell structure, and the absorbance of the excitation light is obtained by SrZrS3, which is a shell material with a larger band gap than BaZrS3 as the core. Therefore, in the configuration of the embodiment, the absorbance can be obtained by thickening the shell without increasing the reabsorption loss.

[0256] Fig.12 : is a graph showing the correspondence between the combination of core and shell materials in Examples and Comparative Examples, the type of band alignment, and the appearance of Stokes shift. Fig.12, for 16 combinations (4×4=16) in which four materials, SrZrS 3 , BaZrS 3 , SrHfS 3 , and BaHfS 3 , are used as core and shell materials, the types of band alignment and the presence or absence of the Stokes shift are correlated and shown.

[0257] exist Fig.12 In the example, the combination of materials showing Stokes shift (Yes) is an example, and the combination of materials not showing Stokes shift (No) is a comparative example. Fig.12 In the case where the core and the shell are made of the same material, the type of band alignment is flat, and no Stokes shift is observed in these cases.

[0258] exist Fig.12 In the case where the core material is SrZrS3 and the shell material is BaZrS3, the type of band alignment is Inverse Type I, and Stokes shift does not appear in this combination. On the other hand, when the core material is SrZrS3 and the shell material is SrHfS3 or BaHfS3, the type of band alignment is Type II, and Stokes shift appears in these combinations.

[0259] exist Fig.12 In the case where the core material is BaZrS3 and the shell material is SrZrS3, the type of band alignment is Type I. In addition, when the core material is BaZrS3 and the shell material is SrHfS3 or BaHfS3, the type of band alignment is Type II. Stokes shift is shown in all these combinations.

[0260] exist Fig.12 In the case where the core material is SrHfS3 and the shell material is SrZrS3 or BaZrS3, the type of band alignment is Type II, and Stokes shift is shown in all of these combinations. On the other hand, when the core material is SrHfS3 and the shell material is BaHfS3, the type of band alignment is Inverse Type I, and Stokes shift is not shown in this combination.

[0261] exist Fig.12 In the case where the core material is BaHfS3 and the shell material is SrZrS3 or BaZrS3, the type of band alignment is Type II. In addition, when the core material is BaHfS3 and the shell material is SrHfS3, the type of band alignment is Type I. Stokes shift is shown in all these combinations.

[0262] It should be noted that when the core material is BaZrS3 and the shell material is SrZrS3, and when the core material is BaHfS3 and the shell material is SrHfS3, since the type of band alignment is Type I, color conversion particles with particularly excellent luminescence characteristics can be obtained.

[0263] As described above, the embodiments of the present invention are described, but the embodiments are presented as an example and are not intended to limit the scope of the present invention. The embodiments can be implemented in various ways other than those described above, and various omissions, substitutions, changes, etc. can be made without departing from the scope of the present invention. The embodiments and their variations are included in the scope and spirit of the present invention, and the inventions and their equivalents described in the claims are also included in the scope and spirit of the present invention.

[0264] In addition, this application claims priority based on Japanese Patent Application No. 2020-195058 filed on November 25, 2020, and all contents of Japanese Patent Application No. 2020-195058 are incorporated herein by reference.

[0265] Description of Reference Numerals

[0266] 10…Color conversion particles

[0267] 11…nuclear

[0268] 12, 12a, 12b…shell

[0269] 13…Housing

[0270] 14…Ligand

[0271] 16…Gap

Claims

1. A color conversion particle, comprising: nuclear; and a shell that contains the core and absorbs the excitation light, The color conversion particle receives the irradiated excitation light and generates light emission at the core or at the interface between the core and the shell. The shell is composed of a chalcogenide perovskite, The core is composed of a chalcogenide perovskite different from that of the shell, The core and the shell have a band alignment exhibiting a Stokes shift, The band alignment satisfies the energy E of the lower end of the conduction band of the shell c_shell The energy E above the lower end of the conduction band of the nucleus c_core , or the energy E at the upper end of the valence band of the shell v_shell energy E below the upper end of the valence band of the nucleus v_core At least one of the conditions, The chalcogenide perovskite constituting the shell is (Sr x Ba 1-x )(Zr y Hf 1-y )(S z Se 1-z ) 3, among which, x, y, and z are values ​​greater than or equal to 0 and less than or equal to 1, respectively. The chalcogenide perovskite constituting the core and different from the shell is (Sr x Ba 1-x )(Zr y Hf 1-y )(S z Se 1-z )3, where x, y, and z are values ​​greater than 0 and less than 1, Among them, the chalcogen elements refer to S, Se, and Te.

2. The color conversion particle according to claim 1, wherein The chalcogenide perovskite constituting the shell is any one selected from SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, and BaHfSe3.

3. The color conversion particle according to claim 1, wherein The band gap of the shell is larger than the band gap of the core.

4. The color conversion particle according to claim 3, wherein The band alignment satisfies the energy E of the lower end of the conduction band of the shell c_shell The energy E above the lower end of the conduction band of the nucleus c_core , and the energy E of the upper end of the valence band of the shell v_shell energy E below the upper end of the valence band of the nucleus v_core conditions.

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

6. The color conversion particle according to claim 1, wherein The shell has a thickness of 2 nm or more and 300 nm or less.

7. The color conversion particle according to claim 6, wherein The shell has a thickness of 2 nm or more and 50 nm or less.

8. The color conversion particle according to claim 7, wherein: The shell has a thickness of 2 nm or more and 30 nm or less.

9. The color conversion particle according to claim 7, wherein: The shell has a thickness of 2 nm or more and 10 nm or less.

10. The color conversion particle according to claim 1, wherein The shell has a plurality of layers.

11. The color conversion particle according to claim 1, wherein The shell comprises a plurality of the cores.

12. The color conversion particle according to claim 1, wherein The core contains light absorbing material.

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

14. The color conversion particle according to claim 1, wherein At least one of the shell or the core has a structure in which physical properties change in a gradient shape in a depth direction.

15. The color conversion particle according to claim 1, wherein The chalcogenide perovskite constituting the core and different from the shell is any one selected from SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, and BaHfSe3.

16. The color conversion particle according to claim 1, wherein The core is BaZrS3, and the shell is SrZrS3.

17. The color conversion particle according to claim 1, wherein The core is BaHfS3, and the shell is SrHfS3. 18 . A powder comprising the color conversion particles according to claim 1 .

19. A solution comprising the color conversion particle according to any one of claims 1 to 17. 20 . A thin film comprising the color conversion particles according to claim 1 .

21. A sheet comprising the color conversion particles according to any one of claims 1 to 17.

22. A device comprising the color conversion particle according to any one of claims 1 to 17.

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