Color conversion particles

Abstract

Color-converting particles possess a core and a shell containing the core that absorbs excitation light. When irradiated by excitation light, they emit light at the core or the interface between the core and the shell. The shell is composed of chalcogenide perovskite, and the core and shell have a band arrangement that enables Stokes shift.

Description

Technical Field

[0001] This invention relates to a color-converting particle. Prior Technology

[0002] Background Technology Color conversion has been widely used in lighting and display devices, solar cells, and other applications. It utilizes wavelength conversion (down-conversion) to transform excitation light incident on an object into longer wavelength light before its release. For this type of color conversion, phosphors with added activators are sometimes used. However, conventional phosphors have limitations in the controllability of emission wavelength, emission peak width, and peak number (color purity). For example, there are many issues that need improvement when applied to applications such as display devices that require high color purity at specific wavelengths.

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

[0004] For this type of core-shell quantum dot, for example, the core material is selected from Cd (S, Se), InP, APbX3 (A=Cs, MA; X=Cl, Br, I). Furthermore, for example, the shell material is Zn (S, Se) and A'2PbX4 (A'=OA). Here, MA is methylammonium, and OA is octylammonium. Furthermore, Non-Patent Literature 1 and 2 disclose core-shell quantum dots using halide perovskites, represented by CsPbBr3. Prior technology 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

[0006] Invention Summary The problem the invention aims to solve CdSe, one of the core-shell quantum dot materials mentioned above, contains Cd, which is toxic due to its RoHS regulated content. Therefore, InP has been developed as an alternative to Cd (S, Se), but InP, in addition to containing the rare metal In, still faces challenges in terms of material durability and luminescence efficiency. On the other hand, while halide perovskites, represented by CsPbBr, have high absorbance and luminescence efficiency, their durability is still insufficient.

[0007] Furthermore, quantum dots are extremely small, only a few nanometers in size, resulting in very low absorbance. On the other hand, if the size of quantum dots is increased to improve absorbance, there is a risk that the luminous efficiency will decrease due to the loss of quantum size effect and increased loss caused by reabsorption of light.

[0008] The present invention was made in view of the above-mentioned situation and can provide a color conversion particle that achieves high light absorption and high luminous efficiency while ensuring durability. The means to solve the problem

[0009] The color-converting particle of this invention has a core and a shell containing the core and absorbing excitation light. When irradiated by excitation light, it emits light in the core or at the interface between the core and the shell. The shell is composed of chalcogenide perovskites, and the core and shell have a band alignment that enables Stokes shift. Invention Effects

[0010] According to the color-converting particles of the present invention, high light absorption and high luminous efficiency can be achieved while ensuring durability. Simple Explanation of the Diagram

[0011] Figure 1 is a schematic diagram showing an example of the structure of the color-converting particles in this embodiment. Figure 2 is a graph showing an example of the relationship between shell thickness and excitation light absorption rate. Figure 3 is a graph showing an example of the relationship between excitation energy and particle radius. Figure 4 is a diagram showing an example of the band arrangement of the core and shell. Figure 5 is a diagram showing an example of the band arrangement of the core and shell. Figure 6 is a diagram showing an example of the band arrangement of the core and shell. Figure 7 is a diagram showing a variation of the color-converting particles of this embodiment. Figure 8 is a diagram showing a variation of the color-converting particles of this embodiment. Figure 9 is a diagram showing the band arrangement of the core and shell of an embodiment. Figure 10 is a diagram showing the simulation results of an embodiment. Figure 11 is a graph showing the light absorption coefficients of BaZrS3 and SrZrS3 and the PL emission spectrum of BaZrS3. Figure 12 is a diagram showing the correspondence between the material combination of the core and shell of the embodiment and the type of band arrangement and the performance of Stokes displacement. Implementation

[0012] Forms used to implement inventions The implementation will now be described with reference to the drawings. In this embodiment, to make the description easier to understand, structures or elements other than the main parts of the invention are simplified or omitted. Furthermore, in the illustrations, the same elements are given the same symbols. Also, in the illustrations, the shapes and dimensions of each element are shown schematically, not in their actual form or size.

[0013] <The Structure of Color-Converting Particles> Figure 1(a) is a schematic diagram showing an example of the structure of the color-converting particles in this embodiment. The color-converting particles 10 are nano-sized particles that absorb incident excitation light and convert it into light with different energy (wavelength), and then release it again (emit light), thereby performing color conversion.

[0014] The color-converting particle 10 has a core 11 for emitting light and a shell 12 for absorbing light. The shell 12 contains one or more cores 11 inside. Furthermore, each core 11 is partially or completely covered by the shell 12 from the outside to form the color-converting particle 10.

[0015] In the color-converting particle 10, the core 11 and the outer shell 12 are constructed separately, and the material of the outer shell 12 is a chalcogenide perovskite, which will be described later. This allows the outer shell 12 to achieve high absorbance of excitation light and improves the durability of the color-converting particle 10. This point will be discussed later.

[0016] Furthermore, regarding the core 11 and the outer shell 12, the band arrangement of the energy Ec at the lower end of the conduction band and the energy Ev at the upper end of the valence band exhibits a Stokes shift relationship. The band arrangement of the core 11 and the outer shell 12 will be discussed later. Furthermore, by adjusting the band gap between the core 11 and the outer shell 12, the outer shell 12 can be endowed with the property of allowing light emitted by the core 11 to pass through. In this way, the color-converting particles 10 can suppress the light generated by the core 11 from being absorbed again by the outer shell 12.

[0017] <Outer Shell 12> (Materials of the outer shell) The outer shell 12 is made of chalcogenide perovskite, a semiconductor material, which can absorb the desired excitation wavelength and generate excitation carriers. Chalcogenide perovskites are semiconductors composed of perovskite crystal structures containing chalcogen elements (S, Se, Te) at the X site, and also include some of the X sites that are substituted with oxygen (O).

[0018] The aforementioned perovskites refer to a group of materials represented by the chemical formula ABX3, possessing a cubic crystal structure with a BX6 octahedral framework, and potentially exhibiting tetragonal or orthorhombic crystal structures due to lattice distortion. Furthermore, computational studies have shown a majority of stable crystal structures within the same ABX3 composition. These crystal structures encompass structures similar to perovskites as well as quite different structures. Moreover, regarding derived structures, Ruddlesden-Popper type and Dion-Jacobson type layered perovskites based on the perovskite structure already exist, as well as bis-perovskites with alternating elements at the B crystal sites. In this specification, the crystal structures described above are collectively referred to as the "perovskite crystal structure group".

[0019] Specifically, the perovskite crystalline structure group includes substances with the following crystalline 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. Furthermore, the crystal structure group of perovskites varies depending on the composition and synthesis conditions, resulting in changes in crystal structure and electronic structure, as well as electronic and chemical properties. Therefore, the composition and conditions should be selected in a way that yields a suitable crystal structure for the desired purpose.

[0020] For example, materials with cubic, tetragonal, GdFeO3-type orthorhombic perovskite, Ruddlesden-Popper-type layered perovskite, and double perovskite structures exhibit excellent photoelectric and chemical properties. Furthermore, chemical stability can be further enhanced by fabricating Dion-Jacobson-type layered perovskite structures. It is known that substances with the crystal structure of GdFeO3 type orthorhombic perovskite, as shown in ABX 3 (A = Group 2, B = Group 4), have excellent photoelectric properties, starting with high light absorption coefficient.

[0021] In addition, the chemical formulas of chalcogenide perovskites can be represented as ABX 3, A' 2A n-1B nX 3n+1, A''A'''B'' 2X 7, A''A 2B'' 3X 10, and A 2BB'X 6. In the above chemical formulas, X represents a chalcogenide (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). Furthermore, let n be a positive integer. Also, A and A', and B and B' can be the same element. Furthermore, A, A', A'', A''', B, B', B'', and X are mixtures of elements from their respective groups in any proportion.

[0022] For example, chalcogenide perovskites represented by the chemical formula ABX 3 include the following substances. In the following examples, X is selected from the dominant materials of the chalcogen group (S, Se), A is selected from the dominant materials of Group 2 elements (Sr, Ba), and B is selected from the dominant materials of Group 4 elements (Zr, Hf). SrZrS 3, SrZrSe 3, SrHfS 3, SrHfSe 3, BaZrS 3, BaZrSe 3, BaHfS 3, BaHfSe 3.

[0023] Furthermore, in one example, chalcogenide perovskites represented by the chemical formula A' 2A n-1B nX 3n+1 contain the following substances: X is selected from the dominant materials of the chalcogen group (S, Se), A and A' are selected from the dominant materials of Group 2 elements (Sr, Ba), and B is selected from the dominant materials of Group 4 elements (Zr, Hf). Sr 2Ba n-1Zr nS 3n+1, Sr 2Ba n-1Zr nSe 3n+1, Sr n+1Zr nS 3n+1, Sr n+1Zr nSe 3n+1, Ba 2Sr n-1Zr nS 3n+1, Ba 2Sr n-1Zr nSe 3n+1, Ba n+1Zr nS 3n+1, Ba n+1Zr nSe 3n+1、Sr 2Ba n-1Hf nS 3n+1、Sr 2Ba n-1Hf nSe 3n+1、Sr n+1Hf nS 3n+1、Sr n+1Hf nSe 3n+1、Ba 2Sr n-1Hf nS 3n+1、Ba 2Sr n-1Hf nSe 3n+1、Ba n+1Hf nS 3n+1、Ba n+1Hf nSe 3n+1.

[0024] These chalcogenide perovskites can also be expressed as (Sr xBa 1-x)(Zr yHf 1-y)(S zSe 1-z) 3 or (Sr x'Ba 1-x') 2(Sr xBa 1-x) n-1(Zr yHf 1-y) n(S zSe 1-z) 3n+1 (but x, x', y, and z are each values ​​greater than 0 and less than 1).

[0025] Furthermore, the superior materials among X, A, A', and B mentioned above refer to materials with band gaps that are suitable for emitting visible light in applications such as light-emitting devices, display devices, and lighting devices when applied to color-converting particles 10.

[0026] Chalcogenide perovskites can have their carrier concentration or crystal structure, as well as other physical and chemical properties, adjusted by partially substituting constituent elements with elements from the same or different groups. For example, Group 1 elements can be substituted with Group 1 or 2 elements, Group 2 elements with Group 1, 2, or 3 elements, Group 3 elements with Group 2, 3, or 4 elements, Group 4 elements with Group 3, 4, or 5 elements, and Group 16 elements with Group 15, 16, or 17 elements.

[0027] The special characteristics of chalcogenide perovskites can be listed below. Chalcogenide perovskites have high light absorption coefficients, resulting in excellent luminescent properties (luminous efficiency and half-width at half-maximum). Furthermore, the light absorption coefficient profile of chalcogenide perovskites shows a sharp increase at the band edge. Therefore, chalcogenide perovskites exhibit very high absorbance near the band gap edge. Therefore, the outer shell 12 of the chalcogenide perovskite has high absorbance and can efficiently absorb excitation light.

[0028] Furthermore, chalcogenide perovskites exhibit high chemical stability and excellent durability against external environmental factors and stimuli such as atmosphere, moisture, heat, and light. Therefore, the high durability of the outer shell 12 of chalcogenide perovskites can inhibit the deterioration of both the outer shell 12 itself and the inner core 11. Furthermore, chalcogenide perovskites are highly safe because they do not contain toxic elements, and they are also advantageous in terms of low raw material costs because they do not contain rare metals.

[0029] (Gap in the outer shell) Next, the band gap of the outer shell 12 of the chalcogenide perovskite will be explained. In color-converting particles, light emitted at the core or core-shell interface is absorbed by the shell and transmitted to the outside. Therefore, the shell must allow the emitted light to pass through. If absorption of emitted light occurs within the shell, the absorbed portion will be reflected in a decrease in the luminous efficiency of the color-converting particle. Therefore, the band gap of the shell should preferably be above the energy of the emitted light.

[0030] When the casing 12 uses a chalcogenide perovskite, it can effectively absorb the ultraviolet excitation light (wavelength 365nm) of GaN (Eg~3.4eV) LEDs when the band gap is below 3.4eV. In addition, when the casing 12 uses a chalcogenide perovskite, it can effectively absorb the blue excitation light (wavelength 460nm) of InGaN LEDs and OLEDs when the band gap is below 2.7eV. Therefore, in order to absorb light with wavelengths above 365 nm, the band gap of the outer casing 12 should preferably be below 3.4 eV. Alternatively, in order to absorb light with wavelengths above 460 nm, the band gap of the outer casing 12 should preferably be below 2.7 eV.

[0031] Therefore, ZnS (Eg ~ 3.6 eV; wavelength 340 nm), a known quantum dot commonly used in enclosures, cannot absorb the aforementioned excitation light. Consequently, when using a ZnS enclosure, it will not exhibit a Stokes shift due to the excitation light. Similarly, while ZnSe, with a band gap of 2.7 eV (wavelength 460 nm), can absorb ultraviolet excitation light, its absorption of blue excitation light is very weak. It can be seen that, in either case, conventional materials have a low light absorption coefficient near the band gap edge, which prevents them from fully absorbing excitation light. Compared to chalcogenide perovskites, the light absorption of the outer shell is reduced.

[0032] (Thickness of the outer shell) Furthermore, the lower and upper limits of the thickness of the outer casing 12 are determined from the following perspectives. First, the outer shell 12 of the light-absorbing part needs to have a thickness that can fully absorb the excitation light.

[0033] Figure 2 is a graph that uses the light absorption coefficient of a representative chalcogenide perovskite material, namely SrZrS3, to calculate the absorption rate of 460 nm excitation light (blue light) relative to the thickness of the outer shell 12. 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 outer shell 12. As shown in Figure 2, the absorption rate of blue light is approximately 4% at 2nm, approximately 10% at 5nm, approximately 20% at 10nm, approximately 46% at 30nm, approximately 64% at 50nm, and approximately 87% at 100nm.

[0034] Regarding the application of color conversion particles 10, it is generally envisioned that thin films, coatings, resins, etc., contain a large number of color conversion particles 10 to be used as color conversion materials. In this case, referring to Figure 2, if each shell 12 has a thickness of at least 2nm, then the color conversion material using a large number of color conversion particles can achieve sufficient light absorption as a whole. Specifically, when applied to color conversion films, it is envisioned that there are more than 100 color conversion particles 10 in the thickness direction of the color conversion film. If the thickness of the outer shell 12 is 2nm, since each color conversion particle 10 can absorb about 4% of blue light, the aforementioned color conversion film can fully absorb blue light.

[0035] Second, if the outer shell 12 is too thick, the photoexcitation carriers will recombine and become inactive before reaching the core 11, thus reducing the luminescence efficiency.

[0036] Therefore, if we estimate the carrier diffusion length based on the conductivity of a representative chalcogenide perovskite material, SrHfS3, it would be around 30 nm at its longest. Furthermore, as shown in Figure 2, approximately 98% of blue light is absorbed at a thickness of 200 nm. If we assume that carriers excited by the absorbed light at a depth of 200 nm diffuse with a diffusion length of 30 nm, then once the carriers move 100 nm further away from the 200 nm depth of the shell 12, all reachable carriers will disappear. Therefore, if the shell 12 is thicker than 300 nm, photoexcited carriers will not be able to reach the core 11, and the luminous efficiency will decrease. Thus, the thickness of the shell 12 is in the range of 2 nm or more and 300 nm or less.

[0037] From the perspective of suppressing photoexcited carrier recombination, if the outer shell 12 can sufficiently absorb the excitation light, its thickness should be thinner. For example, the thickness of the outer shell 12 should be above 2 nm and below 50 nm. When the thickness of the outer shell 12 is 50 nm, it will absorb approximately 64% of the blue light. To increase light absorption without sacrificing the carrier diffusion distance, the thickness of the outer shell 12 should be up to 50 nm.

[0038] When the thickness of the outer shell 12 is 30 nm, although the blue light absorption will decrease to approximately 46%, it will fall within the carrier diffusion length range, allowing more carriers to move towards the core and thus improving luminous efficiency. Furthermore, when the thickness of the outer shell 12 is 10 nm, although it only absorbs about 20% of the blue light, it is thin enough compared to the carrier diffusion length, allowing almost all carriers to move towards the core and further improving luminous efficiency. Therefore, the thickness of the outer shell 12 should ideally be between 2 nm and 30 nm (blue light absorption rate: approximately 4%-approximately 46%), and more preferably between 2 nm and 10 nm (blue light absorption rate: approximately 4%-approximately 20%), thus balancing sufficient blue light absorption with good carrier movement towards the core 11.

[0039] <Kernel 11> The core 11 is a light-emitting particle made of semiconductor material, which can generate fluorescence of the desired emission wavelength by excitation light. The core 11 used as a light-emitting particle causes displacement between electronic energy levels, and the displacement between electronic energy levels has energy corresponding to the desired emission wavelength.

[0040] When luminescent particles are made of semiconductors, the fluorescence emitted when electrons excited in the conduction band recombine with holes in the valence band is used for luminescence. Therefore, the emission wavelength of the luminescent particles is equivalent to the bulk band gap energy Eg,bulk.

[0041] If the particle size of the luminescent particles decreases, the quantum size effect caused by confined electrons becomes significant, and the energy levels of the electrons become discrete. At this point, the energy (band gap) Eex of the lowest excited state becomes greater than Eg,bulk, and becomes dependent on the particle size. That is, if the particle size of the luminescent particles decreases, the emission wavelength will shift towards shorter wavelengths compared to the bulk state, and the emission wavelength will change depending on the particle size. This property can be used to control the emission wavelength of the luminescent particles.

[0042] Specifically, the exciton exciton energy Eex of a luminous particle with radius r can be given by the following formula. Additionally, μ represents the exciton transduction mass, Eb,ex represents the exciton binding energy, and rB represents the exciton Bohr radius.

[0043] [Mathematical Expression 1]

[0044] Using ε as the dielectric constant of the luminescent particle, μ, Eb, ex, and rB can be given by the following formulas. Furthermore, m * e is the effective mass of the electron, and m * h is the effective mass of the hole.

[0045] [Mathematical Expression 2]

[0046] Figure 3 is a graph showing the dependence of Eex on r when μ=0.1 and ε=10. The vertical axis of Figure 3 represents Eex / Eg,bulk, and the horizontal axis represents r / rB. As the radius r of the luminescent particle decreases and approaches rB, the value of Eex increases slowly from Eg,bulk. Then, once r becomes below rB, the value of Eex increases significantly (quantum size effect).

[0047] Utilizing the aforementioned quantum size effect, and based on the rB defined in the above formula, luminescent particles whose particle size falls within the range where the emission wavelength and particle size are dependent are called "quantum dots". On the other hand, luminescent particles whose particle size falls within the range where the emission wavelength and particle size are almost independent are called "non-quantum dots". Furthermore, the particle size exhibiting quantum size effects varies depending on the parameters μ and ε. However, if we assume μ=0.1 and ε=10 for a typical semiconductor, then approximately r=3rB will become the boundary for the particle size (radius) exhibiting quantum size effects. This boundary is represented by a dashed line in Figure 3.

[0048] As mentioned above, for luminescent particles, the particle size exhibiting quantum size effects is essentially characterized by its relationship with the exciton Boltzmann radius rB. However, the manifestation of quantum size effects is also related to the dielectric constant of the material and the effective mass of electron holes, and the variation of the E ex value is continuous. Therefore, it is practically difficult to unambiguously represent the boundary between quantum dots and non-quantum dots through particle size and other physical properties.

[0049] Therefore, the particle radius dependence of the lowest excitation energy Eex is considered using typical physical properties of the representative chalcogenide perovskite material BaZrS3 (mee*=0.3m0, mh*=0.5m0, ε=6ε0, Eg,bulk=1.93eV). Also, m0 is the electron mass mentioned above. In the case of BaZrS3, it is conceivable that the particle radius exhibiting typical quantum size effects is approximately 7.5 nm. Therefore, in the case of BaZrS3, it is conceivable that particles with a diameter of less than 15 nm are quantum dots, and particles with a diameter greater than 15 nm are non-quantum dots.

[0050] The core 11 of this embodiment can be any of the aforementioned quantum dots and non-quantum dots. When the core 11 is a quantum dot, it has the advantage of being able to control the emission wavelength (color) by changing the particle size of the same material. In addition, when it is a quantum dot, the core 11 has high luminous efficiency and a narrower peak. However, to achieve uniform emission wavelengths (colors), precise particle size control is required, necessitating highly advanced manufacturing techniques for quantum dots. Furthermore, due to their tiny size, quantum dots lack chemical stability and are prone to aggregation, regrowth, and decomposition, thus requiring surface protection. Additionally, because the electronic states of quantum dots are discrete, with low density of states in both the valence and conduction bands, their light absorption coefficient is smaller compared to bulk materials.

[0051] On the other hand, when the core 11 is a non-quantum dot, that is, when relatively large particles are used to emit light using bulk material without exhibiting quantum size effects, the problems of stability and light absorption can be reduced. However, for non-quantum dots, since the emission wavelength of the core 11 depends on E g,bulk, it will be necessary to change the composition and crystal structure to change E g,bulk in order to adjust the emission wavelength.

[0052] As mentioned above, both quantum dots and non-quantum dots have their advantages and disadvantages. As for the core 11, it is only necessary to select the appropriate one from quantum dots and non-quantum dots according to the situation and application. In addition, the size that can produce quantum size effect varies depending on the material. Therefore, the particle size of the core 11 is appropriately set according to the material properties.

[0053] On the other hand, in order to suppress the reabsorption of the core 11, the particle size of the core 11 should be small. For example, in the case of BaZrS 3, when the particle size is 200 nm, it will absorb 10% of the red light with a wavelength of 630 nm generated by other BaZrS 3 cores located nearby. Therefore, the particle size of the core 11 should be below 200 nm.

[0054] Furthermore, under the above conditions, if the particle size of the core 11 is below 50 nm, the reabsorption of red light at a wavelength of 630 nm is 3%; if the particle size of the core 11 is below 25 nm, the reabsorption of red light at a wavelength of 630 nm can be controlled below 2%. Therefore, the particle size of the core 11 should preferably be below 50 nm, and even more preferably below 25 nm.

[0055] Furthermore, in terms of the particle size at which the core 11 can exist stably, a size of 1 nm or larger is preferable. In summary, the particle size of kernel 11 should be above 1nm and below 200nm.

[0056] (Materials for Kernel 11) For example, materials for core 11 can include substances containing activators that can form luminescent centers (luminescent ions) added to the parent crystals such as oxides and nitrides (so-called activated phosphors), II-VI semiconductors, III-V semiconductors, I-III-VI semiconductors, I-II-IV-VI semiconductors, IV-VI semiconductors, halide perovskite semiconductors, oxide perovskites, organic-inorganic perovskites, Si, carbon materials or mixed crystal compounds thereof.

[0057] In addition, the material for core 11 can also be a chalcogenide perovskite. High luminescence performance can be expected by using a chalcogenide perovskite core 11 with excellent light absorption coefficient. Furthermore, from the viewpoint of affinity with the constituent elements of the shell and integration of crystal structure and lattice constant, the use of a chalcogenide perovskite core 11 reduces defects at the interface between the core 11 and the shell 12, thereby reducing the recombination of non-luminescent elements, and thus higher luminescence efficiency can be expected.

[0058] In one instance, when the material of the core 11 is a chalcogenide perovskite, it may be selected from the following listed materials that are different from the material of the outer shell 12. SrZrS 3, SrZrSe 3, SrHfS 3, SrHfSe 3, BaZrS 3, BaZrSe 3, BaHfS 3, BaHfSe 3, Sr 2Ba n-1Zr nS 3n+1, Sr 2Ba n-1Zr nSe 3n+1, Sr n+1Zr nS 3n+1, Sr n+1Zr nSe 3n+1、Ba 2Sr n-1Zr nS 3n+1、Ba 2Sr n-1Zr nSe 3n+1、Ba n+1Zr nS 3n+1、Ba n+1Zr nSe 3n+1、Sr 2Ba n-1Hf nS 3n+1、Sr 2Ba n-1Hf nSe 3n+1、Sr n+1Hf nS 3n+1, Sr n+1Hf nSe 3n+1, Ba 2Sr n-1Hf nS 3n+1, Ba 2Sr n-1Hf nSe 3n+1, Ba n+1Hf nS 3n+1, Ba n+1Hf nSe 3n+1.

[0059] The same applies to the chalcogenide perovskite in the core 11 and the shell 12. It can also be represented by (Sr xBa 1-x)(Zr yHf 1-y)(S zSe 1-z) 3 or (Sr x'Ba 1-x') 2(Sr xBa 1-x) n-1(Zr yHf 1-y) n(S zSe 1-z) 3n+1 (but x, x', y, and z are each values ​​above 0 and below 1). When these materials are applied to the core 11 of the color-converting particle 10, they are advantageous materials from the viewpoint that their band gap is suitable for emitting visible light in light-emitting devices, display devices, lighting devices, etc.

[0060] <Band Arrangement of Core 11 and Shell 12> As mentioned above, in the core 11 and the outer shell 12, the energy band arrangement of the lower conduction band energy Ec and the upper valence band energy Ev exhibits a relationship that allows for the Stokes shift.

[0061] Stokes shift originally referred to the energy difference between the energy state of an electron excited by light and the energy state of an electron that emits light when it releases energy. It was observed as the difference between the maximum energy positions of the absorption and emission spectra. Heterostructure nanoparticles such as the color conversion particles 10 of the present embodiment can generate an "apparent Stokes shift" by designing an appropriate energy band arrangement on the heterojunction interface, that is, creating an energy difference between the absorption spectrum end and the emission spectrum peak. In the specification of the present invention, the apparent Stokes shift generated by nanoparticles of the heterostructure is sometimes simply referred to as the Stokes shift.

[0062] Figures 4, 5, and 6 show examples of the energy band arrangements of the core 11 and the shell 12. In each of Figures 4, 5, and 6, the upward direction represents the direction of increasing energy. The central rectangle represents the band gap Eg_core of the core 11, and the two side rectangles represent the band gap Eg_shell of the shell 12. The upper side of the central rectangle represents the lower energy Ec_core of the conduction band of the core 11, and the bottom side of the central rectangle represents the upper energy Ev_core of the valence band of the core 11. The upper side of the two side rectangles represents the lower energy Ec_shell of the conduction band of the shell 12, and the bottom side of the two side rectangles represents the upper energy Ev_shell of the valence band of the shell 12.

[0063] In addition,in each of Figures 4, 5, and 6, the curve drawn on the upper side of the rectangle represents the electron distribution, and the curve drawn on the bottom side of the rectangle represents the hole distribution. In addition, the downward arrow in the figure represents the energy difference in the light emission process, and the upward arrow in the figure represents the energy difference in the light absorption (excitation) process. When the energy difference in the light absorption process is greater than the energy difference in the light emission process, the Stokes shift will be manifested.

[0064] In Figures 4(a)-(e), the band gap Eg_shell of the shell 12 is greater than the band gap Eg_core of the core 11 (Eg_shell > Eg_core). On the other hand, in Figures 5(a)-(e), the band gap Eg_shell of the shell 12 is less than the band gap Eg_core of the core 11 (Eg_shell < Eg_core). In addition, in Figures 6(a)-(c), the band gap Eg_shell of the shell 12 is equal to the band gap Eg_core of the core 11 (Eg_shell = Eg_core). Regarding the size relationship between Ec_core and Ec_shell and the size relationship between Ev_core and Ev_shell, they are respectively described in each of Figures 4, 5, and 6.

[0065] The Stokes shift is manifested in the energy band alignments (Type I (First Type), Quasi-Type II (Quasi-Second Type), and Type II (Second Type)) shown in FIGS. 4(a)-(e), FIGS. 5(a), (e), and FIGS. 6(a), (c). Therefore, the color conversion particles of the present embodiment have any one of the energy band alignments in FIGS. 4(a)-(e), FIGS. 5(a), (e), and FIGS. 6(a), (c). The energy band alignment of the color conversion particles of the present embodiment satisfies at least any one of the following conditions: the lower energy of the conduction band of the outer shell 12, E c_shell, is higher than the lower energy of the conduction band of the inner core 11, E c_core, and the upper energy of the valence band of the outer shell 12, E v_shell, is lower than the upper energy of the valence band of the inner core 11, E v_core (that is, any one of E c_shell > E c_core and E v_shell < E v_core, or E c_shell > E c_core and E v_shell < E v_core).

[0066] The energy band alignments (Type I and Quasi-Type II) in FIGS. 4(b), (c), (d) all satisfy the following conditions: the lower energy of the conduction band of the outer shell 12, E c_shell, is above the lower energy of the conduction band of the inner core 11, E c_core, and the upper energy of the valence band of the outer shell 12, E v_shell, is below the upper energy of the valence band of the inner core 11, E v_core (that is, when E g_shell > E g_core, E c_shell ≧ E c_core and E v_shell ≦ E v_core).

[0067] In the case of Type I shown in FIG. 4(c), electrons and holes are confined in the inner core 11 and recombination (inner core luminescence) is induced within the inner core 11. In the case of Type I, since holes and electrons are locally present in the inner core 11, the overlap of the wave functions is large and the luminescence efficiency is high. Therefore, the energy band alignment of the inner core 11 and the outer shell 12 is best in the structure of Type I. Examples of the materials of the inner core 11 and the outer shell 12 in Type I shown in FIG. 4(c) include: a combination where the inner core 11 is BaZrS 3 and the outer shell 12 is SrZrS 3.

[0068] As shown in Figures 4(b) and (d), in Quasi-Type II (but Eg_shell > Eg_core), carriers of either holes or electrons diffuse into the shell, resulting in lower luminous efficiency compared to Type I. However, even so, in Figures 4(b) and (d), carriers of the other type of electron are locally present in the core, thus the luminous efficiency remains relatively high, second only to Type I. The materials of the core 11 and shell 12 in Quasi-Type II shown in Figures 4(b) and (d) can be, for example, a combination of BaHfS3 for the core 11 and CaZrS3 for the shell 12 shown in Figure 4(b).

[0069] Furthermore, in the band arrangements (Type II) of Figures 4(a), (e), 5(a), (e), 6(a), and (c), electrons and holes are separated in the core 11 and the shell 12, making it less likely to induce inter-band recombination luminescence compared to Type I. However, in Type II, there is a possibility of recombination (interfacial luminescence) at the interface between the core 11 and the shell 12, resulting in a smaller energy difference (Eg) than that of the shell 12, thus exhibiting Stokes shift.

[0070] In Type II, the light emission occurs at the interface between the core 11 and the shell 12, resulting in less overlap of the wave functions and lower luminous efficiency compared to Type I. Furthermore, interface recombination is sometimes accompanied by non-luminous recombination involving interface defects, which also suggests a decrease in luminous efficiency. It is obvious that even in terms of the band arrangement of Type II, it is still advantageous from the point of view that a wide range of emission wavelengths can be achieved, and it can be expected to be applied to near-infrared luminescent materials, etc. The materials of the core 11 and shell 12 of Type II shown in Figures 4(a), (e), 5(a), (e), 6(a), and (c) can be, for example, a combination of core 11 being BaZrS3 and shell 12 being CaZrS3 as shown in Figure 4(a).

[0071] Furthermore, as shown in Figures 4(a)-(e), if the band gap Eg_shell of the outer shell 12 is made larger than the band gap Eg_core of the core 11 (Eg_shell>Eg_core), then the light emitted by the core 11 will hardly be absorbed by the outer shell 12 and released to the outside. In this way, the reabsorption loss of the outer shell 12 is suppressed, and the luminous efficiency of the color conversion particles 10 can be further improved.

[0072] In FIGS. 6(a) and 6(c), the band gap Eg_shell of the shell 12 is equal to the band gap Eg_core of the core 11 (Eg_shell = Eg_core). Therefore, compared with the cases in FIGS. 4(a)-(e) (Eg_shell > Eg_core), in the cases of FIGS. 6(a) and 6(c), the light emitted by the core 11 is more likely to be reabsorbed by the shell 12, increasing the reabsorption loss. As a result, the luminous efficiency of the color conversion particles 10 is reduced. Additionally, when comparing the case where the band gap Eg_shell of the shell 12 is less than the band gap Eg_core of the core 11 (Eg_shell < Eg_core), as shown in FIGS. 5(a) and 5(e), with the cases of FIGS. 6(a) and 6(c), the reabsorption loss in the cases of FIGS. 6(a) and 6(c) is suppressed because less light is reabsorbed by the shell 12, and the luminous efficiency of the color conversion particles 10 can be improved.

[0073] In addition, the color conversion particles 10 can take various states through the combination of the materials of the core 11 and the shell 12. Although the materials of the core 11 and the shell 12 exemplified above are sulfides, they can also be selenides and solid solutions. By including these substances, various states can be achieved, and there are material combinations of the core 11 and the shell 12 that exhibit excellent luminous characteristics.

[0074] <Particle diameter of the color conversion particles 10> Here, when coating ink in which the color conversion particles 10 are dispersed in a solvent using, for example, an inkjet method, if the particle diameter of the color conversion particles 10 is too large, it will cause nozzle blockage. Even for other coating methods, the large particle diameter of the color conversion particles 10 may pose a problem in the process. For the above reasons, the particle diameter of the color conversion particles 10 should be 1000 nm or less. <000029​​​​​​​​​​In the synthesis of core 11, conventional methods such as thermal injection, solvothermal, hydrothermal, continuous flow process, CHM (composite-hydroxide-mediated), heating, gas-phase synthesis, solid-phase synthesis, and mechanochemical synthesis can be used to generate core 11, which belongs to nanoluminescent particles. The materials used for core 11 can be, for example, the substances mentioned above.

[0077] In addition, the material of core 11 can also be chalcogenide perovskite. In this case, core 11 can be synthesized by reacting precursor compounds in solution, or by mixing and heating precursor powders in an inert gas environment or in the atmosphere, or by mixing and heating metal precursor powders in an inert gas environment and reacting them with chalcogen precursor gases. When synthesizing the core 11 by reacting the precursor compound in solution, for example, methods such as hot injection, heating, solvothermal, hydrothermal, CHM, and continuous process synthesis can be used.

[0078] (Synthesis steps for shell 12) The synthesis step of the outer shell 12 involves synthesizing a chalcogenide perovskite outer shell 12 on the surface of the core 11 obtained in the above steps. In this step, a one-pot synthesis method and a hot-injection method are used, where the nanoluminescent particles of the core 11 are mixed with the chalcogenide perovskite precursor in a solvent. This synthesizes color-converting particles 10 with a core-shell structure, where the surface of the core 11 is coated with a chalcogenide perovskite outer shell 12. Alternatively, in addition to solution-based methods, the outer shell 12 can also be generated through vapor-phase synthesis, such as using barrel sputtering.

[0079] The following example illustrates the use of the hot-injection method to synthesize the outer shell 12 of chalcogenide perovskite ABX 3, in which A and B are composed of group II and group IV elements, respectively. At this point, a first solution and a second solution are prepared. The first solution contains the nanoluminescent particles that will become the core, a precursor compound containing a group II element, a precursor compound containing a group IV element, and a solvent. The second solution contains a precursor compound containing a chalcogenide element and a solvent. Next, the second solution is added to the reaction vessel at a temperature ranging from 150°C to 350°C, and the reaction is carried out at the aforementioned temperature for 1 second to 100 hours. In this process, the shell material grows on the nanoparticles used in the reaction, and the desired core-shell structure is synthesized. After the reaction is complete, the target compound is recovered after washing with an organic solvent or water.

[0080] The precursor compounds containing Group II elements mentioned above can be listed as follows: Metal powders, metal alkoxides, metal carboxylates, metal nitrates, metal perchlorates, metal sulfates, metal acetoacetones, metal halides, metal hydroxides, metal halides, and combinations thereof.

[0081] The precursor compounds containing group IV elements can be listed below: Metal powders, metal alkoxides, metal carboxylates, metal nitrates, metal perchlorates, metal sulfates, metal acetoacetones, metal halides, metal hydroxides, metal halides, and combinations thereof.

[0082] The precursor compounds containing chalcogens can be listed below: Metal sulfides (including selenium-substituted or tellurium-substituted compounds); Carbon disulfide (including selenium-substituted or tellurium-substituted compounds); Hydrogen sulfide, hydrogen selenide, hydrogen telluride, and other sulfide hydrogens; Thiol compounds (including selenium-substituted or tellurium-substituted compounds); Phosphine compounds such as trioctylphosphine sulfide (with selenium or tellurium substituted derivatives); Thiourea (including selenium-substituted or tellurium-substituted derivatives); Sulfur, selenium, tellurium; Alternatively, a substance formed by dispersing such compounds in solvents such as amines, acids, hydrocarbons, etc., and combinations thereof.

[0083] The solvents mentioned above can be listed as follows: Primary, secondary, and tertiary amines possessing 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 containing organic groups such as hydrocarbon groups; Phosphine oxide compounds containing organic groups such as hydrocarbon groups; Alcohols, aldehydes, carboxylic acids, or compounds having thiolated, selenium-substituted, or tellurium-substituted groups; A commonly used organic solvent or water, or a combination of such solvents, containing at least one of the above.

[0084] The heating of the above solution involves reacting the chalcogenide precursors to form hydrogen chalcogenide. Furthermore, the reaction of the above solution involves synthesis under an inert gas environment or atmospheric conditions. Moreover, the reaction of the above solution can also be performed using a microreactor and a continuous flow process to synthesize the target compound.

[0085] Furthermore, the synthesis of the aforementioned shell 12 can be carried out by first synthesizing the nano-luminescent particles that will become the core 11 and then continuously synthesizing the shell 12. Alternatively, a shell precursor can be added to the reaction vessel during the synthesis of the nano-luminescent particles to synthesize the desired color-converting particles 10 with a core-shell structure.

[0086] <External Structure of Color-Converting Particle 10> Furthermore, as shown in Figure 1(b), the color-converting particle 10 may also have an outer shell 13 and ligands 14 as an external structure, which serve as a protective layer.

[0087] (Outer shell 13) The outer shell 13 is a protective layer that covers the semiconductor particles consisting of the core 11 and the shell 12 from the outside. The outer shell 13 is provided to suppress the degradation of semiconductor particles caused by contact with oxygen, and to further improve the durability of the color conversion particles 10 by protecting the semiconductor particles from external chemical interactions. In addition, the outer shell 13 has the property of allowing the excitation light for the purpose and the light emission of the core 11 to be transmitted. The outer shell can be formed using chemically stable substances such as silicon dioxide, glass, oxide insulators, and resins, and using conventional methods.

[0088] For example, when the outer shell 13 is formed of a metal oxide, materials such as silicon oxide, zirconium oxide, titanium oxide, and aluminum oxide can be used. Regarding the outer shell 13 containing metal oxides, for example, it can be formed by using a thermosetting reaction of melt-gel to form inorganic oxides.

[0089] Furthermore, the outer shell 13 can also be a layer containing resin or a polysilazane modifier. Polysilazane is a polymer with silicon-nitrogen bonds, and is an inorganic polymer of ceramic precursors composed of Si-N, Si-H, NH, etc., and containing SiO2, Si3N4, and the intermediate solid solution SiOxNy, etc. Furthermore, when forming the outer shell 13 with resin, water-soluble resins such as polyvinyl alcohol resins are preferable from the perspective of ease of manufacturing. In addition, the outer shell 13 can also be a multi-layered structure, which includes a metal oxide layer and a layer containing resin or polysilazane modified material.

[0090] (Cognate 14) The ligand 14 is an organic modifier molecule that modifies the surface of the color conversion particle 10, and is configured by binding to the outer surface of the color conversion particle 10 or covering the color conversion particle 10. The ligand 14 not only facilitates the isolation of color-converting particles 10 from each other to improve dispersion, but also prevents regrowth and damage caused by contact between the color-converting particles 10. In addition, the ligand 14 also functions to suppress surface defects of the shell 12 through capping of dangling bonds, thereby improving luminous efficiency.

[0091] The modified organic molecule used as ligand 14 can be a substance having a nitrogen-containing functional group, a sulfur-containing functional group, an acidic group, a amide group, a phosphono group, a phosphonooxide group, a hydroxyl group, a straight-chain alkyl group, a carboxyl group, a phosphonopropyl group, a sulfonic acid group, an amino group, etc. Examples of such modified organic molecules include sodium hexametaphosphate, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, triethanolamine lauryl sulfate, lauryl diethanolamine, dodecyl trimethylammonium chloride, trioctylphosphine, and trioctylphosphine oxide.

[0092] Furthermore, the modified organic molecule used as ligand 14 should preferably be a compound with both hydrophilic and hydrophobic groups in its molecule. In this way, the ligand 14 can be coated with the color-changing particle 10 through both chemical bonding via coordination bonds (similar to heteroatoms) and bonding via physical adsorption. Examples of such modified organic molecules include amines, which are compounds with a nonpolar hydrocarbon terminal 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 strongly bond with metal elements.

[0093] Furthermore, the modified organic molecule used as ligand 14 should preferably have heteroatoms. By incorporating heteroatoms into the modified organic molecule, an electrical polarity can be generated between the heteroatom and the carbon atom, and the modified organic molecule can be strongly bonded to the surface of the color-converting particle. Here, "heteroatoms" refers to all atoms other than hydrogen and carbon atoms.

[0094] <Example of a variation of color-converting particles> Next, referring to Figures 7 and 8, a variation of the color-converting particle 10 will be described. Furthermore, in the schematic diagrams of the color-converting particle 10 shown in Figures 7 and 8, only the core 11 and the outer shell 12 are shown unless otherwise stated. However, these color-converting particles 10, like the example in Figure 1(b), may also have an outer shell 13 and ligands 14.

[0095] For example, as shown in Figure 7(a), the outer shell 12 of the color-converting particle 10 may not completely cover the core 11, and a part of the core 11 may be exposed on the outside.

[0096] For example, as shown in Figure 7(b), the color-converting particle 10 can be constructed by stacking multiple shells 12 around a core 11. By using different materials with different compositions and crystal structures as the materials for each shell 12, the overall light absorption and light emission properties of the color-converting particle 10 can be adjusted. The example in Figure 7(b) shows an example of two shells 12a and 12b stacked on the core 11, but the shells 12 of the color-converting particle 10 can also have three or more layers.

[0097] The color-converting particles 10 with multi-layered shells 12a and 12b shown in Figure 7(b) can be formed by heating a solution containing semiconductor particles with shells 12a already formed on the core 11 and other shell precursors.

[0098] For example, as shown in Figure 7(c), the color-converting particle 10 can also have a structure in which a plurality of cores 11 are contained within the outer shell 12. If a plurality of cores 11 are contained within the outer shell 12, the thickness of the effective outer shell 12 in the color-converting particle 10 is increased, which can improve the durability of the color-converting particle 10. In addition, the overall light absorption and light emission characteristics of the color-converting particle 10 can be adjusted by using materials with different compositions and crystal structures for each core 11. The example in Figure 7(c) shows a structure in which the outer shell 12 contains three cores 11, but the number of cores 11 contained in the outer shell 12 can be varied. In addition, in the color-converting particles 10 with a plurality of cores 11, any one core 11 may be partially exposed outside the outer shell 12.

[0099] Furthermore, the color-converting particles 10 can also have a structure in which the shell 12 contains a plurality of cores 11 and the shell 12 has a plurality of layers. For example, as shown in FIG7(d), the outer side of the shell 12a containing a plurality of cores 11 can be further covered by the shell 12b. In addition, the outer side of the shell 12b in FIG7(d) can also be further laminated with a shell. For example, as shown in Figure 7(e), a color-converting particle 10 can be integrally formed by covering each of the plurality of cores 11 covered by the shell 12b with the shell 12b. Alternatively, in the example of Figure 7(e), the shell 12a can also be something that contains a plurality of cores 11.

[0100] Furthermore, the core 11 of the color-converting particle 10 may also include a light-absorbing material 17 made of the same material as the outer shell 12. For example, as shown in FIG7(f), the outer side of the light-absorbing material 17 may be covered by the core 11. Alternatively, for example, the material of the light-absorbing material 17 need only be a material that can be used as the material of the outer shell 12, and the outer shell 12 covering the core 11 and the light-absorbing material 17 may also be made of the same material. In the layered core structure with light-absorbing material 17 as described above, the light-absorbing material 17 (made of the same material as the outer shell 12) located inside the core 11 can absorb the excitation light transmitted through the outer shell 12, thereby increasing the excitation light absorption rate. Furthermore, in the layered core structure with light-absorbing material 17, photoexcitation carriers can be effectively confined to the very narrow region of the core 11, which is enclosed by the material of the outer shell 12, thereby improving luminous efficiency.

[0101] Furthermore, the band arrangement of the light-absorbing material 17 and the core 11 should preferably be Type I, and more specifically, the band arrangement of the core 11 and the shell 12 should also preferably be Type I. For example, a combination of light-absorbing material 17 being SrZrS3 and core 11 being BaZrS3 could be used, and a further example is a combination of shell 12 being SrZrS3. Other examples include a combination of light-absorbing material 17 being SrHfS3 and core 11 being BaHfS3, and a further example is a combination of shell 12 being SrHfS3. Additionally, the band arrangement of the light-absorbing material 17 and core 11 only needs to be a combination of materials capable of exhibiting Stokes shift; the light-absorbing material 17 can also be a material other than chalcogenide perovskites.

[0102] Furthermore, the color-converting particle 10 can also have a hollow structure with internal gaps 16. For example, as shown in FIG8(a), one or more gaps 16 can be formed within the core 11. Alternatively, as shown in FIG8(b), in a color-converting particle 10 having an outer shell 13 outside the outer shell 12, a gap 16 can be formed between the outer shell 12 and the outer shell 13. By forming gaps 16 inside the color-converting particle 10 that do not exhibit light absorption or emission, the optical properties and shape of the color-converting particle 10 can be adjusted.

[0103] The hollow color-conversion particles 10 shown in Figures 8(a) and (b) can be manufactured, for example, as follows. First, semiconductor particles containing organic matter and salt are generated by simultaneously adding organic materials such as fullerenes and carbon nanotubes and soluble salts during synthesis. Then, the organic matter or salt is dissolved in a solvent, or the organic matter or salt is ashed at high temperature, thereby obtaining the hollow color-conversion particles 10.

[0104] Furthermore, the core 11 or shell 12 of the color-converting particle 10 may contain foreign matter that does not exhibit light absorption and light emission, such as insulators or other components. By including such foreign matter in the core 11 or shell 12, the luminous efficiency of the color-converting particle 10 can be improved by means of light scattering, and the shape of the color-converting particle 10 can be adjusted.

[0105] Furthermore, as shown in Figure 8(c), the core 11 or shell 12 of the color-converting particle 10 can 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 a direction perpendicular to the interface (depth direction). By allowing the physical and chemical properties of the core 11 or shell 12 to continuously change in a gradient-like manner in the depth direction, the lattice integration is improved, and lattice defects are reduced. This reduces non-luminescent recombination, thereby improving the luminescence efficiency of the color-converting particle. Furthermore, the aforementioned gradient structure can be manufactured using the same methods as when manufacturing a multi-layered core 11 and shell 12.

[0106] Furthermore, the shape of the color-converting particles synthesized in this invention is not particularly limited. Cores 11 and / or color-converting particles 10 with shapes such as spheres, strips, stars, polyhedra, pyramids, tetrapods, tetrahedrons, small plates, cones, and irregular shapes can be synthesized.

[0107] The following describes the effects of the color-converting particles 10 in this embodiment. The color-converting particle 10 of this embodiment has a core 11 and a shell 12 containing the core 11 and absorbing excitation light. Upon irradiation with excitation light, it emits light in the core 11 or at the interface between the core 11 and the shell 12. The chalcogenide perovskite material of the shell 12 has high light absorption coefficient and excellent durability. Therefore, in this embodiment, since the core 11 is covered by the chalcogenide perovskite shell 12, the color-converting particle 10 has high durability against heat and other disturbances. Furthermore, compared to conventional quantum dots, the color-converting particle 10 is less prone to performance degradation even if ligands detach due to heat or other disturbances.

[0108] Furthermore, the core 11 and the shell 12 have a band arrangement that enables Stokes shift. In this embodiment, the difference in band edge transition energy between the shell 12 and the core 11 is utilized to transport photoexcitation carriers to the core 11 through the chalcogenide perovskite shell 12 with high light absorption, so that the photoexcitation carriers that have been confined to the core 11 recombine and emit light. In this embodiment, by forming a chalcogenide perovskite shell 12 outside the core 11, the absorption portion and the emission portion of the color-converting particle 10 are separated. This allows for a significant capture of the Stokes shift, enabling absorption to be gained through the shell 12 without increasing the size of the core 11. Therefore, high absorbance and high luminous efficiency can be achieved while suppressing the emission reabsorption loss caused by the core 11.

[0109] Furthermore, the color conversion particles 10 of this embodiment, as described above, possess high light absorption and luminous efficiency. Therefore, compared to conventional quantum dots, a smaller quantity can be used to achieve the desired color conversion function. In other words, for example, when the color conversion particles 10 of this embodiment are applied to color conversion layers in devices other than display devices and lighting, thin-film processing of the color conversion layer and improved yield can be achieved. During the formation of the color conversion layer, the probability of defects in the film-forming process increases due to repeated film-forming processes, resulting in a lower yield of the color conversion layer. Conversely, if the color conversion layer can be thinned, the film-forming process can be reduced, thereby reducing the defect rate of the color conversion layer in practice.

[0110] Furthermore, if the band gap of the outer shell 12 is larger than the band gap of the core 11, the light 12 emitted by the core 11 will hardly be absorbed by the outer shell and will be released to the outside, thus suppressing the reabsorption loss of the outer shell. That is, when the band gap of the outer shell 12 is larger than the band gap of the core 11, the outer shell 12 can be thickened to gain light absorption without increasing the reabsorption loss, thereby further improving the luminous efficiency of the color conversion particles 10.

[0111] Furthermore, if the band gap of the housing 12 is below 3.4 eV, it can effectively absorb the ultraviolet excitation light (wavelength 365 nm) of the GaN LED. At this time, by using a single ultraviolet LED and color conversion particles 10 that can be converted into various RGB colors by ultraviolet excitation light, it is possible to emit light of various RGB colors without using LEDs (light sources) with multiple emission wavelengths, thus simplifying the light-emitting element. Furthermore, if the core 11 is made of chalcogenide perovskite, the light absorption and durability of the core 11 can be improved, and the defects at the core-shell interface can be reduced, thereby further improving the luminous efficiency.

[0112] <Examples of Product Forms and Applications of Color-Converting Particles 10> Secondly, examples of the product forms and applications of the color conversion particles 10 will be described. Examples of product forms of the color conversion particles 10 include powder, solution, film, and sheet. Furthermore, regarding applications of the color conversion particles 10, they can be envisioned for use in various devices.

[0113] (powder) The powder is a product in which the color-converting particles 10 are aggregated. Hereinafter, the color-converting particles 10 are sometimes referred to as primary particles, and the aggregated form of the color-converting particles 10 is referred to as secondary particles. The size of the primary and secondary particles is not particularly limited, but the primary particles are preferably in the range of 5 nm to 1000 nm. In addition, ligands can also be imparted to the surface of the primary and secondary particles. In order to improve the luminescence properties, dispersibility and film-forming properties of the color-converting particles, other materials can also be added to the powder of color-converting particles 10 as additives.

[0114] Furthermore, the applications of the color conversion particles 10 powder are not particularly limited. For example, it can be dispersed in solvents to make solutions, dispersed in resins and solid media to make composites, made into sintered bodies for use as sputtering targets, or directly used as a source for evaporation in powder form.

[0115] (solution) The solution consists of color conversion particles 10 dispersed in the solvent. The size of the primary and secondary particles is not particularly limited, but the primary particles are preferably in the range of 5 nm to 1000 nm. Furthermore, "dispersed" means that the color conversion particles 10 are floating or suspended in the solvent, and some precipitation is also possible. In addition, ligands can be assigned to the surfaces of the primary and secondary particles.

[0116] The solution may use one or more solvents. Examples of solvents are given below, but are not limited to: 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 tributyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dimethylethane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, and phenethyl ether; and ethers such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tributanol, 1-pentanol, 2-methyl-2-butanol, methoxypropanol, diacetone alcohol, cyclohexanol, 2-fluoroethanol, and 2,2-ethylhexanol. 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 with amide groups such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, acetamide, and N,N-dimethylacetamide; organic solvents with nitrile groups such as acetonitrile, isobutyronitrile, propionitrile, and methoxyacetonitrile; organic solvents with carbonate groups such as ethyl carbonate and propyl carbonate; organic solvents with halogenated hydrocarbon groups such as dichloromethane and chloroform; organic solvents with hydrocarbon groups such as n-pentane, cyclohexane, n-hexane, benzene, toluene, and xylene; and dimethyl sulfoxide, etc.

[0117] In addition, to improve the luminescence properties, the dispersibility of the color conversion particles 10, and the film-forming properties, the above solution may also be supplemented with acids, alkalis, or binder materials. Furthermore, the applications of the above solutions are not particularly limited. For example, they can be used for: film formation using coating, spraying, doctor blade methods (and other solution film formation methods); and for the production of composites by combining with solid dispersion media; or for the production using such equipment.

[0118] (film) The thin film is a structure in which the color-converting particles 10 are aggregated into a planar form. The size of the primary and secondary particles is not particularly limited, but the primary particles are preferably in the range of 5 nm to 1000 nm. Furthermore, ligands can be imparted to the surfaces of the primary and secondary particles. To improve the luminescence properties and the dispersibility of the color-converting particles 10, other materials can also be added as additives to the aforementioned thin film.

[0119] The method for preparing the aforementioned thin film is not particularly limited. For example, it can be prepared using coating, spraying, doctor blade, inkjet, and other solution-based film preparation methods, or using vacuum processes such as sputtering and vacuum evaporation. Furthermore, it is also possible to prepare the color conversion particles 10 using coating or other methods, and then use other treatments such as firing to achieve a state in which the particle shape is not maintained.

[0120] (Sheet) The sheet material is a planar dispersion medium for dispersing the colored conversion particles 10. The size of the primary and secondary particles is not particularly limited, but the primary particles are preferably in the range of 5nm-1000nm. In addition, ligands can be imparted to the surface of the primary and secondary particles.

[0121] The material used as the dispersion medium for the sheet can be any polymer suitable for this purpose and known to those skilled in the art. In a suitable embodiment, this polymer is almost translucent or almost transparent. For example, polymers that can be used as dispersion media for sheets include polyvinyl butyral, polyvinyl acetate, polysiloxanes, and polysiloxane derivatives, but are not limited to these. Furthermore, polysiloxane derivatives include polyphenylmethylsiloxanes, polyphenylalkylsiloxanes, polydiphenylsiloxanes, polydialkylsiloxanes, fluorinated polysiloxanes, vinyl- and hydrogenated polysiloxanes, ionomers, polyethylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polypropylene, polyester, polycarbonate, polystyrene, polyacrylonitrile, ethylene vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-methacrylic acid copolymer films, and nylon, but are not limited to these.

[0122] To improve the luminescence properties and the dispersibility of the color conversion particles 10, silicon dioxide microparticles and other materials such as the solvents described in the solution section can be added to the above-mentioned sheet as additives. The method of manufacturing the aforementioned sheet is not particularly limited. For example, the sheet can be manufactured by kneading and stretching powder with a dispersion medium, or by mixing ink containing color conversion particles 10 with a dispersion medium or its precursor and then coating it.

[0123] (equipment) Regarding the use of color-converting particles 10 or the aforementioned powders, solutions, films, and sheets, it is conceivable that they can be applied to the downconversion of ultraviolet or blue light in various devices. Examples of such devices include light-emitting devices such as LEDs and organic ELs, display devices containing such light-emitting devices, lighting devices containing such light-emitting devices, image sensors, photoelectric conversion devices, and bioluminescent markers.

[0124] <Example> The following describes an embodiment of the color-converting particles of the present invention. The core material of the color-converting particles in this embodiment is BaZrS3, and the shell material is SrZrS3. That is, the color-converting particles in this embodiment represent an example of an optimal material combination where the core and shell are chalcogenide perovskites exhibiting Stokes shift. As mentioned above, when the core and shell are chalcogenide perovskites, interface defects between the core and shell are reduced, and high luminous efficiency can be expected.

[0125] Figure 9 is a diagram showing the band structure of the shell / core / shell in a color-converting particle of an embodiment. The origin of the vertical axis is the vacuum level. The physical properties of the core and shell were determined with reference to "Y. Nishigaki et al., Sol. RRL 1900555 (2020)" and "K. Hanzawa et al., J. Am. Chem. Soc. 141, 5343 (2019)", and by incorporating other experimental results.

[0126] As shown in Figure 9, in the band arrangement of the shell and core in the embodiment, the core's Ec is lower than the shell's Ec, and the core's Ev is higher than the shell's Ev, thus it is Type I. Therefore, in the structure of the embodiment, it is expected that the shell will absorb excitation light, and the excited carriers will move towards the core and recombine to achieve core luminescence. Furthermore, since the band gap Eg of the shell is larger than that of the core in the embodiment, it is also expected that the reabsorption loss of the shell will be suppressed.

[0127] In this embodiment, the light absorption and emission of the color-converting particles were simulated using software (SCAPS-1D) in one dimension. Figure 10 is a graph showing the simulation results of this embodiment. The horizontal axis of each graph in Figure 10 represents the one-dimensional position of the color-converting particles along their diameter direction.

[0128] In the simulation, the core diameter was set to 20 nm and the shell thickness was set to 50 nm. In addition, the wavelength of the excitation light was set to 450 nm blue light, and the excitation light was set to be incident from one side (left side of the figure) with an illuminance of 100 mW / cm2.

[0129] Figure 10(a) shows the Ec curve of the color-converting particle, and Figure 10(b) shows the Ev curve of the color-converting particle. The vertical axis energy is based on the Fermi energy EF. In Figure 10(a), the Ec of the core region (horizontal axis value in the range of 50nm-70nm) is lower than that of the outer shell region. Furthermore, in Figure 10(b), the Ev of the core region is higher than that of the outer shell region. The curves in Figures 10(a) and (b) are quite consistent with the band arrangement shown in Figure 9.

[0130] Figure 10(c) shows the carrier concentration distribution of color-converting particles. The solid line in Figure 10(c) represents the electron curve, and the dashed line in Figure 10(c) represents the hole curve. In Figure 10(c), the carrier density in the core region (horizontal axis value in the range of 50nm-70nm) is higher than that in the outer shell region. Therefore, it can be seen from Figure 10(c) that carriers excited by light absorbed by the outer shell are effectively moved 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) represents the carrier generation rate curve, and the solid line in Figure 10(d) represents the carrier recombination rate curve.

[0132] As shown in Figure 10(d), the carrier generation rate is highest on the left side of the excitation light incident diagram. Furthermore, due to the very large light absorption coefficient of chalcogenide perovskites, the carrier generation rate decreases sharply as the light travels towards the right side of the diagram. This indicates that carrier excitation caused by light absorption almost entirely occurs within the outer shell range of 0 nm to 50 nm.

[0133] On the other hand, the carrier recombination rate shows a high value across the core range (horizontal axis value in the range of 50nm-70nm), while the value is almost zero in the shell range. That is, the luminescence caused by carrier recombination is almost entirely caused by photoexcitation of carriers that have moved to the core. Therefore, the simulation results show that the photoexcitation carrier transport from the shell to the core and the photoexcitation carrier confinement towards the core have been effectively induced.

[0134] Furthermore, based on the optical coefficients of BaZrS3 and SrZrS3 shown in “Y. Nishigaki et al., Sol. RRL 1900555 (2020).”, the light absorption coefficients of BaZrS3 and SrZrS3 and the PL (Photoluminescence) emission peak of BaZrS3 were calculated respectively.

[0135] Figure 11 is a graph showing the light absorption coefficients of BaZrS3 and SrZrS3, as well as the PL emission spectrum of BaZrS3. The horizontal axis of Figure 11 represents wavelength.

[0136] The PL emission spectrum of the core material BaZrS3 (solid line in Figure 11) shows a sharp emission peak with a half-width of about 30 nm. This is due to the very steep absorption edge (the jump in the light absorption coefficient near the band edge) of the chalcogenide perovskite.

[0137] Furthermore, the dashed line in Figure 11 represents the light absorption coefficient curve of BaZrS3, and the dashed line in Figure 11 represents the light absorption coefficient curve of SrZrS3. In the region where the lower part of these light absorption coefficient curves overlaps with the PL emission spectrum curve, the emitted light can be reabsorbed.

[0138] In other words, it can be seen that if only the core material BaZrS3 is used for color conversion, the light emission can be reabsorbed. Therefore, when using the core material BaZrS3, if the particle size is increased in order to gain absorbance, the reabsorption will also increase. Thus, there is a trade-off between the absorbance and the reabsorption loss.

[0139] On the other hand, the lower halves of the absorption coefficient curve of SrZrS3 and the PL emission spectrum curve of BaZrS3 almost do not overlap. Therefore, it can be concluded that when the shell of SrZrS3 is applied to the core of BaZrS3, the shell hardly undergoes reabsorption.

[0140] In the embodiments, the color-converting particles are fabricated into a core-shell structure, and the shell material SrZrS3, which has a larger band gap than the BaZrS3 core, is used to gain the absorbance of the excitation light. Therefore, with the structure of the embodiments, the absorbance can be gained by thickening the shell without increasing the reabsorption loss.

[0141] Figure 12 is a diagram showing the correspondence between the material combinations of the core and shell in the embodiments and comparative examples, and the band arrangement type and Stokes shift behavior. In Figure 12, for the 16 combinations (4×4=16) of applying the four materials SrZrS3, BaZrS3, SrHfS3, and BaHfS3 to the core and shell materials, the band arrangement type and the presence or absence of Stokes shift behavior are respectively linked and represented.

[0142] In Figure 12, the material combination showing Stokes displacement (Yes) is an example, and the material combination not showing Stokes displacement (No) is a comparative example. Here, when the core and shell are made of the same material in Figure 12, the band arrangement type is Flat in both cases, and neither of these cases shows Stokes displacement.

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

[0144] In Figure 12, when the core material is BaZrS3 and the shell material is SrZrS3, the band arrangement type is Type I. Furthermore, when the core material is BaZrS3 and the shell material is either SrHfS3 or BaHfS3, the band arrangement type is Type II. Both of these combinations exhibit Stokes shift.

[0145] In Figure 12, when the core material is SrHfS3 and the shell material is SrZrS3 or BaZrS3, the band arrangement type is Type II, and both combinations exhibit Stokes shift. On the other hand, when the core material is SrHfS3 and the shell material is BaHfS3, the band arrangement type is Inverse Type I, and Stokes shift is not exhibited in this combination.

[0146] In Figure 12, when the core material is BaHfS3 and the shell material is SrZrS3 or BaZrS3, the band arrangement type is Type II. Furthermore, when the core material is BaHfS3 and the shell material is SrHfS3, the band arrangement type is Type I. Any of these combinations exhibits a Stokes shift.

[0147] In addition, 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 band arrangement type is Type I in either case, color-converting particles with excellent luminescence properties can be obtained.

[0148] Although the embodiments of the present invention have been described above, these embodiments are merely illustrative examples and are not intended to limit the scope of the present invention. Embodiments may be implemented in various ways other than those described above, and various omissions, substitutions, and modifications may be made without departing from the spirit of the present invention. The embodiments and their variations are included within the scope and spirit of the present invention. At the same time, the invention described in the claims and its equivalents are also included within the scope and spirit of the present invention.

[0149] Furthermore, this application asserts priority based on Japanese Patent Application No. 2020-195058, which was filed on November 25, 2020, and incorporates the entire contents of Japanese Patent Application No. 2020-195058.

[0150] 10: Color-converting particles 11: Kernel 12, 12a, 12b: Outer shell 13: Outer shell 14: Coordinators 16: Gap 17: Light-absorbing materials

Claims

1. A color-converting particle having a core and a shell containing the core and absorbing excitation light, and emitting light upon irradiation by the excitation light in the core or at the interface between the core and the shell; wherein the shell is composed of a chalcogenide perovskite; and wherein the core and the shell have a band arrangement capable of exhibiting Stokes shift; wherein the band arrangement satisfies at least one of the following conditions: the lower conduction band energy Ec_shell of the shell is higher than the lower conduction band energy Ec_core of the core; and the upper valence band energy Ev_shell of the shell is lower than the upper valence band energy Ev_core of the core; and the band gap of the shell is larger than the band gap of the core.

2. The color-converting particles of claim 1, wherein the aforementioned chalcogenide perovskite has any of the following crystal structures: cubic perovskite, tetragonal perovskite, GdFeO3-type orthorhombic perovskite, Ruddlesden-Popper-type layered perovskite, Dion-Jacobson-type layered perovskite, and double perovskite.

3. The color-changing particles as requested in item 1, wherein the chemical formula of the aforementioned chalcogenide perovskite is ABX3 or A'2An-1BnX3n+1 (A and A' are group 2 elements, B is group 4 elements, X is a chalcogenide element, but n is an integer greater than or equal to 1).

4. The color-changing particles as requested in item 3, wherein the chemical formula of the aforementioned chalcogenide perovskite is ABX3 (A is a group 2 element, B is a group 4 element, and X is a chalcogenide element).

5. The color-changing particles as claimed in claim 3, wherein the aforementioned A, A', B, and X comprise elements of their respective families mixed in any ratio.

6. The color changing particles of claim 1, including the aforementioned sulfide powders selected from CaTiS3, CaTiSe3, CaTiTe3, CaZrS3, CaZrSe3, CaZrTe3, CaHfS3, CaHfSe3, CaHfTe3, SrTiS3, SrTiSe3, SrTiTe3, SrZrS3 , SrZrSe3, SrZrTe3, SrHfS3, SrHfSe3, SrHfTe3, BaTiS3, BaTiSe3, BaTiTe3, BaZrS3, BaZrSe3, BaZrTe3, BaHfS3, BaHfSe3, BaHfTe3, Ca2Ban-1TinS3n+ 1, Ca2Ban-1TinSe3n+1, Ca2Ban-1TinTe3n+1, Ca2Ban-1ZrnS3n+1, Ca2Ban-1ZrnSe3n+1, Ca2Ban-1ZrnTe3n+1, Ca2Ban-1HfnS3n+1, Ca2Ban-1HfnSe3n+ 1, Ca2Ban-1HfnTe3n+1, Ca2Srn-1TinS3n+1, Ca2Srn-1TinSe3n+1, Ca2Srn-1TinTe3n+1, Ca2Srn-1ZrnS3n+1, Ca2Srn-1ZrnSe3n+1, Ca2Srn-1ZrnTe3n+ 1, Ca2Srn-1HfnS3n+1, Ca2Srn-1HfnSe3n+1, Ca2Srn-1HfnTe3n+1, Sr2Can-1TinS3n+1, Sr2Can-1TinSe3n+1, Sr2Can-1TinTe3n+1, Sr2Can-1ZrnS3n+1 , Sr2Can-1ZrnSe3n+1, Sr2Can-1ZrnTe3n+1, Sr2Can-1HfnS3n+1, Sr2Can-1HfnSe3n+1, Sr2Can-1HfnTe3n+1, Sr2Ban-1TinS3n+1, Sr2Ban-1TinSe3n+1 , Sr2Ban-1TinTe3n+1, Sr2Ban-1ZrnS3n+1, Sr2Ban-1ZrnSe3n+1, Sr2Ban-1ZrnTe3n+1, Sr2Ban-1HfnS3n+1, Sr2Ban-1HfnSe3n+1, Sr2Ban-1HfnTe3n+1 , Ba2Can-1TinS3n+1, Ba2Can-1TinSe3n+1, Ba2Can-1TinTe3n+1, Ba2Can-1ZrnS3n+1, Ba2Can-1ZrnSe3n+1, Ba2Can-1ZrnTe3n+1, Ba2Can-1HfnS3n+1,Ba2Can-1HfnSe3n+1, Ba2Can-1HfnTe3n+1, Ba2Srn-1TinS3n+1, Ba2Srn-1TinSe3n+1, Ba2S rn-1TinTe3n+1, Ba2Srn-1ZrnS3n+1, Ba2Srn-1ZrnSe3n+1, Ba2Srn-1ZrnTe3n+1, Ba2Srn-1H fnS3n+1、Ba2Srn-1HfnSe3n+1、Ba2Srn-1HfnTe3n+1、Can+1TinS3n+1、Can+1TinSe3n+1、Can +1TinTe3n+1、Can+1ZrnS3n+1、Can+1ZrnSe3n+1、Can+1ZrnTe3n+1、Can+1HfnS3n+1、Can+1H fnSe3n+1、Can+1HfnTe3n+1、Srn+1TinS3n+1、Srn+1TinSe3n+1、Srn+1TinTe3n+1、Srn+1Zrn S3n+1、Srn+1ZrnSe3n+1、Srn+1ZrnTe3n+1、Srn+1HfnS3n+1、Srn+1HfnSe3n+1、Srn+1HfnTe3 Any one of the following: n+1, Ban+1TinS3n+1, Ban+1TinSe3n+1, Ban+1TinTe3n+1, Ban+1ZrnS3n+1, Ban+1ZrnSe3n+1, Ban+1ZrnTe3n+1, Ban+1HfnS3n+1, Ban+1HfnSe3n+1, Ban+1HfnTe3n+1 (but n is an integer greater than or equal to 1).

7. The color-changing particles as claimed in claim 1, wherein the aforementioned chalcogenide perovskite is (CaxSrx'Ba1-x-x')(TiyZry'Hf1-y-y')(SzSez'Te1-z-z')3 or (CawSrw'Ba1-w-w')2(CaxSrx'Ba1-x-x')n-1(TiyZry'Hf1-y-y')n(SzSez'Te1-z-z')3n+1 (but w, w', x, x', y, y', z, z' are each values ​​greater than 0 and less than 1, and w+w'≦1, x+x'≦1, y+y'≦1, z+z'≦1).

8. The color-converting particle of request item 1, wherein the aforementioned band arrangement satisfies the following conditions: the lower conduction band energy Ec_shell of the aforementioned shell is higher than the lower conduction band energy Ec_core of the aforementioned core, and the upper valence band energy Ev_shell of the aforementioned shell is lower than the upper valence band energy Ev_core of the aforementioned core.

9. The color-converting particles of claim 1, wherein the band gap of the aforementioned shell is 3.4 eV or less.

10. The color-converting particles of claim 1, wherein the thickness of the aforementioned shell is more than 2 nm and less than 300 nm.

11. The color-converting particles of claim 10, wherein the thickness of the aforementioned shell is 2 nm or more and 50 nm or less.

12. The color-converting particles of claim 11, wherein the thickness of the aforementioned shell is more than 2 nm and less than 30 nm.

13. The color-converting particles of claim 11, wherein the thickness of the aforementioned shell is more than 2 nm and less than 10 nm.

14. The color-changing particle as claimed in claim 1, wherein the aforementioned shell has multiple layers.

15. The color-changing particle as in claim 1, wherein the aforementioned shell contains a plurality of the aforementioned cores.

16. The color-converting particles of claim 1, wherein the aforementioned core contains a light-absorbing material.

17. The color-changing particle of claim 1, wherein at least one of the aforementioned shell and the aforementioned core contains foreign matter or voids.

18. The color-changing particle of claim 1, wherein at least one of the aforementioned shell and the aforementioned core has a structure in which physical properties change in a gradient direction in the depth direction.

19. The color-changing particle of claim 1, wherein the aforementioned core is composed of a chalcogenide perovskite, which is different from the aforementioned outer shell.

20. The color-changing particles of claim 19, wherein the chalcogenide perovskite system other than the aforementioned shell is selected from SrZrS3, SrZrSe3, SrHfS3, SrHfSe3, BaZrS3, BaZrSe3, BaHfS3, BaHfSe3, Sr2Ban-1ZrnS3n+1, Sr2Ban-1ZrnSe3n+1, Srn+1ZrnS3n+1, Srn+1ZrnSe3n+1, Ba2Srn-1ZrnS ... Any one of rnSe3n+1, Ban+1ZrnS3n+1, Ban+1ZrnSe3n+1, Sr2Ban-1HfnS3n+1, Sr2Ban-1HfnSe3n+1, Srn+1HfnS3n+1, Srn+1HfnSe3n+1, Ba2Srn-1HfnS3n+1, Ba2Srn-1HfnSe3n+1, Ban+1HfnS3n+1, and Ban+1HfnSe3n+1 (but n is an integer greater than or equal to 1).

21. The color-changing particles of claim 19, wherein the chalcogenide perovskite, which is different from the aforementioned shell, is (SrxBa1-x)(ZryHf1-y)(SzSe1-z)3 or (Srx'Ba1-x')2(SrxBa1-x)n-1(ZryHf1-y)n(SzSe1-z)3n+1 (but x, x', y, and z are each values ​​greater than 0 and less than 1).

22. The color-changing particle as requested in item 20, wherein the aforementioned core is BaZrS3 and the aforementioned shell is SrZrS3.

23. The color-changing particle as requested in item 20, wherein the aforementioned core is BaHfS3 and the aforementioned shell is SrHfS3.

24. A powder comprising color-converting particles as claimed in any one of claims 1 to 23.

25. A solution comprising color-converting particles as claimed in any one of claims 1 to 23.

26. A thin film comprising color-converting particles as claimed in any one of claims 1 to 23.

27. A sheet comprising color-changing particles as described in any one of claims 1 to 23.

28. A device comprising color-converting particles as described in any one of claims 1 to 23.

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