Quantum dot synthesis method

Abstract

To provide a method for improving the quantum yield of luminescence while changing the emission wavelength of quantum dots that are composed of cesium and group 14 metals (lead, tin) halides.SOLUTION: A method for synthesizing quantum dots includes a first step of forming quantum dots with a perovskite structure of composition CsMX3 (Cs: cesium, M: group 14 metal, X: first halogen), with each particle encased in ligands; and a second step of adding a ligand substance, which can act as a ligand for quantum dots, and a halide of a second halogen different from the first halogen and a group 14 metal to a solution in which the quantum dots are dispersed. This process synthesizes quantum dots with a perovskite structure that have emission wavelengths different from those of the quantum dots with the CsMX3 composition.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for synthesizing quantum dots, and more particularly to a method for synthesizing perovskite quantum dots of cesium and a halide of a Group 14 metal (lead, tin). [Background technology]

[0002] Colloidal perovskite quantum dots (quantum dots having a perovskite nanocrystal structure) have recently attracted attention as fluorescent materials with high luminescence quantum yields (photoluminescence quantum yield: the ratio of the number of photons emitted by a material to the number of photons absorbed by the material) and with a relatively wide tunable emission wavelength range (hereinafter, unless otherwise specified, the term "quantum dots" refers to perovskite quantum dots). Quantum dots are expected to be useful in optoelectronic applications such as displays, light-emitting diodes, and solar cells. Regarding such quantum dots, Non-Patent Document 1 describes a method for synthesizing quantum dots composed of cesium and lead halides using inexpensive commercially available materials. This document also demonstrates that the emission wavelength of quantum dots can be tuned in the visible light region by adjusting the halogen elements used in the formation of the nanocrystals that will become the quantum dots. Non-Patent Document 2 reports that when a lead halide or an ammonium halide salt of a halogen element other than bromine (Br) is added to synthesized quantum dots with a composition of CsPbBr3, the bromine in the quantum dots is replaced with chlorine or iodine, and the luminescence quantum yield decreases, but the luminescence wavelength shifts to the shorter or longer wavelength side. Also, Non-Patent Document 3 reports that the luminescence quantum yield improves by adding PbBr2 and DDAB (didodecyldimethylammonium bromide) after the formation of quantum dots with a composition of CsPbBr3. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] L. Protesescu, et al, “Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut” Nano Lett. 2015, 15, 3692-3696 [Non-patent document 2] QA Akkerman, et al, “Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions”, J. Am. Chem. Soc. 2015, 137, 10276-10281 [Non-patent document 3] MI Bodnarchuk, et al, “Rationalizing and Controlling the Surface Structure and Electronic Passivation of CesiumLead Halide Nanocrystals”, ACS Energy Lett. 2019, 4, 63-74 Summary of the Invention [Problem to be solved by the invention]

[0004] In the research of the present inventors, it was found that after forming quantum dots of cesium and a Group 14 metal (lead, tin) halide, adding a halide salt of a Group 14 metal element and a halogen element different from the halogen element in the composition of the formed quantum dots, and a ligand material capable of stabilizing the colloidal state by coordinating to the surface of the quantum dots, to a solution in which the quantum dots are dispersed, can change the emission wavelength of the quantum dots and significantly increase the emission quantum yield. This phenomenon is extremely advantageous when using quantum dots in the field of optoelectronics. This finding is utilized in the present invention.

[0005] Thus, one object of the present invention is to provide a method for improving the luminescence quantum yield of quantum dots of cesium and Group 14 metal (lead, tin) halides while changing the emission wavelength of the quantum dots. [Means for solving the problem]

[0006] According to one aspect of the present invention, the above problem is solved by a method for synthesizing quantum dots, comprising the steps of: a first step of forming quantum dots having a perovskite structure with a composition of CsMX3 (Cs: cesium, M: Group 14 metal, X: first halogen), each particle of which is covered with a ligand; a second step of adding a ligand substance usable as a ligand for the quantum dots and a halide of a second halogen different from the first halogen and a Group 14 metal to the solution in which the quantum dots are dispersed; a method for synthesizing quantum dots with a perovskite structure having an emission wavelength different from that of the quantum dots having the composition CsMX3, This is achieved by:

[0007] In the above-described configuration of the present invention, the "quantum dots" are nanocrystals having a perovskite structure with a CsMX3 composition. The nanocrystal particles are prepared in a state where they are coated with ligands and dispersed in an organic solvent. The quantum dot formation method in the first step may be basically the same as the method described in Non-Patent Document 1. The ligand may be any substance that can be used as a ligand for quantum dots with a perovskite structure with a CsMX3 composition, typically oleic acid and oleylamine. The Group 14 metal M may be selected from lead (Pb) and tin (Sn). The first halogen X may be selected from bromine (Br), fluorine (F), chlorine (Cl), and iodine (I). The CsMX3 composition may typically be CsPbBr3. In the first step, the quantum dots may typically be prepared in a state where they are dispersed as colloids in an organic solvent such as hexane.

[0008] In the second step, the "ligand substance usable as a quantum dot ligand" may be selected from any substance that coordinates around each quantum dot particle and stabilizes the colloidal state. Examples of such substances include salts of halogens and cations having hydrocarbon chains and a charge at one end. Specifically, the hydrocarbon chain cation having a suitable number of carbon atoms (approximately 9 to 16) and whose charge is independent of pH is advantageously used, and preferably, a cation having two or three hydrocarbon chains. In an embodiment, the quaternary ammonium cation used may be, but is not limited to, didodecyldimethylammonium ion. The didodecyldimethylammonium ion may be used as didodecyldimethylammonium bromide or didodecyldimethylammonium chloride. On the other hand, the "halide of a second halogen different from the first halogen and a Group 14 metal" may specifically be a lead halide or a tin halide, and the second halogen is a halogen different from the first halogen used in the quantum dots formed in the first step. That is, when the first halogen used in the quantum dots is bromine Br, the second halogen may be chlorine Cl, iodine I, or fluorine F. Therefore, when the composition of CsMX3 is CsPbBr3, the halide of the second halogen and a Group 14 metal may be PbCl2, PbI2, SnCl2, or SnI2. The ligand substance and halide to be added to the solution in which the quantum dots formed in the first step are dispersed may be added by mixing a solution in which the ligand substance and halide are dispersed in an organic solvent such as toluene with the solution in which the quantum dots are dispersed.

[0009] In an embodiment of the method of the present invention, in a first step, quantum dots having a perovskite structure with a composition of CsPbBr3 are prepared in a colloidal state dispersed in an organic solvent, with each particle coated with oleic acid and oleylamine as the ligands, and in a second step, a solution in which didodecyldimethylammonium bromide or didodecyldimethylammonium chloride and PbCl2 are dispersed in an organic solvent may be mixed with the solution in which the quantum dots are dispersed.

[0010] As described above, adding a halide of a second halogen and a Group 14 metal, and a ligand substance usable as a quantum dot ligand, to a solution containing dispersed quantum dots formed by the first step results in the synthesis of quantum dots with an emission wavelength different from that of the quantum dots formed by the first step, and the resulting quantum dots have an emission quantum yield significantly higher than that of the quantum dots formed by the first step. Experiments conducted by the inventors of the present invention have shown that, for example, quantum dots formed by the first step with a composition of CsPbBr3 have an emission wavelength of approximately 518 nm and an emission quantum yield of 50-60%, whereas quantum dots obtained by the second step exhibit an emission wavelength shift to a range of 495-513 nm and an emission quantum yield of 70-90%, depending on the amount of ligand substance and halide added. It has also been found that the increased emission quantum yield of quantum dots obtained by the method of the present invention is generally maintained for at least two weeks.

[0011] In the above configuration, it has been found that the emission wavelength of the quantum dots obtained through the second step changes more significantly as the amounts of the ligand substance and the halide added increase. Therefore, the amounts of the ligand substance and the halide added to the solution in which the quantum dots formed in the first step are dispersed may be adjusted so that light of the desired emission wavelength is obtained from the quantum dots. Specifically, for example, when a Group 14 metal chloride is added to quantum dots formed using bromine, it has been found that the larger the amount added, the more the emission wavelength of the quantum dots shifts to the shorter wavelength side. Therefore, if it is desired to shift the emission wavelength of the quantum dots to the shorter wavelength side, the amount of Group 14 metal chloride added may be increased. [Effects of the Invention]

[0012] Thus, according to the present invention, in a method for synthesizing quantum dots, after forming quantum dots having a perovskite structure with a composition of CsMX3 and each particle covered with a ligand, a ligand substance that can be used as a ligand for the quantum dots and a halide of a Group 14 metal and a second halogen (different from the first halogen X) are added, thereby making it possible to obtain quantum dots with a different emission wavelength from the quantum dots formed in the first step and with an increased emission quantum yield. With this configuration, quantum dots that stably have a higher emission quantum yield and emit light of a wavelength selected from a wider wavelength range can be obtained, and it is expected that the usefulness of quantum dots will be further enhanced.

[0013] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0014] [Figure 1]FIG. 1(A) is a schematic diagram showing the formation of quantum dots in the first step of the method of synthesizing quantum dots according to the present invention, in which a cesium oleate (Cs-OA) solution is mixed with a solution containing a Group 14 metal halide (lead bromide PbBr), oleic acid (OA), and oleylamine (OAm). FIG. 1(B) is a schematic diagram of quantum dots formed in the first step of the method of the present invention. FIG. 1(C) is a schematic diagram showing the preparation of quantum dots with a shifted emission wavelength and increased emission quantum yield in the second step of the method of the present invention, in which a ligand substance and a Group 14 metal halide are mixed with the solution containing the quantum dots formed in the first step. FIG. 1(D) is a schematic diagram of quantum dots formed in the second step of the method of the present invention. [Figure 2] Figures 2(A) and (B) are graphs showing the peak wavelength (PLP) and luminescence quantum yield (PLQY) of the quantum dots formed in the second step of the method of the present invention. (A) shows the case where didodecyldimethylammonium bromide was used as the ligand substance, and (B) shows the case where didodecyldimethylammonium chloride was used as the ligand substance. In the figure, ○ indicates the value immediately after synthesis (fr), △ indicates the value five days after synthesis (5d), ◇ indicates the value one week after synthesis (1w), and × indicates the value two weeks after synthesis (2w). The numbers in the figure indicate the amount (μl) of the mixture of the ligand substance and Group 14 metal halide added to the solution (1 ml) in which the quantum dots were dispersed. S indicates the case where no mixture was added. [Explanation of symbols]

[0015] 10...Three-necked flask 12...Mantle heater 14...Temperature sensor 16...Syringe 18...Pneumatic transport pipe BEST MODE FOR CARRYING OUT THE INVENTION

[0016] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0017] Synthesis of quantum dots In the synthesis of quantum dots according to this embodiment, (1) the formation of quantum dots (first step) and (2) the modification of the properties of the quantum dots (second step) are carried out. Each step will be described in more detail below.

[0018] (1) Formation of quantum dots (first step) In this embodiment, quantum dots are formed by mixing a Group 14 metal halide and cesium in a nonpolar solvent in the presence of a ligand substance having a hydrocarbon group, such as oleic acid (OA) or oleylamine (OAm), to form quantum dots, which are nanocrystalline structures with a perovskite structure. The quantum dot formation process may be essentially the same as that described in Non-Patent Document 1. Specifically, the following steps are performed: (a) preparing a solution of a cesium fatty acid salt, such as cesium oleate; (b) preparing a solution of a Group 14 metal halide; (c) preparing a mixture of ligand substances; (d) mixing the Group 14 metal halide solution with the ligand substance mixture; (e) injecting a fatty acid cesium solution into the Group 14 metal halide-ligand substance solution (forming quantum dots); and (f) purifying the quantum dots.

[0019] In each step, the cesium fatty acid salt solution (a) is prepared by dissolving cesium carbonate (CsCO3) and a fatty acid in a nonpolar solvent such as 1-octadecene (ODE) by heating to approximately 120°C under vacuum. The fatty acid may be any fatty acid that can be used as a quantum dot ligand, and oleic acid is typically used. The Group 14 metal halide solution (b) is prepared by dissolving a Group 14 metal halide in a nonpolar solvent such as 1-octadecene (ODE) by heating to approximately 120°C under vacuum. The Group 14 metal halide is typically lead bromide (PbBr2), but is not limited thereto and may also be lead fluoride, lead chloride, lead iodide, tin fluoride, tin chloride, tin bromide, or tin iodide. The ligand substance mixture (c) is prepared by heating and mixing a ligand substance having a hydrocarbon group to approximately 130°C. The ligand substance may be any substance that can be coordinated to the surface of quantum dots in an organic solvent to make the quantum dots in a colloidal state, such as oleic acid (OA) or oleylamine (OAm) (see Non-Patent Document 3). Then, such a ligand substance mixture is subsequently dispersed (d) in the solution of the Group 14 metal halide (b).

[0020] Subsequently, the cesium fatty acid salt solution (a) is injected into the solution in which the Group 14 metal halide and ligand substance mixture are dispersed, thereby forming quantum dots (e) that are nanocrystalline particles with a perovskite structure having a composition of CsMX3 (Cs: cesium, M: Group 14 metal, X: first halide), each particle covered with a ligand such as OA or OAm. In this process, as schematically illustrated in Figure 1(A), a mixture of the Group 14 metal halide and ligand substance mixture (PbBr2,OA-OAm / ODE) contained in a three-neck flask 10 may be heated under a nitrogen atmosphere using a mantle heater 12 or the like, and the cesium fatty acid salt solution (Cs-OA / ODE) may be injected using a syringe 16, and the two solutions may be mixed. As a result, quantum dots Qd having a composition such as CsPbBr3 are formed with ligands L such as OA and OAm coordinated around them, as shown in FIG. 1(B).

[0021] Once the quantum dots are formed, any material that did not form the quantum dots can be removed by an optional purification process such as centrifugation, as in the experimental example described below, and the quantum dots are prepared in a colloidal state dispersed in an organic solvent such as hexane (f).

[0022] (2) Modifying the properties of quantum dots (second step) As described above, once quantum dots have been formed, a salt of a Group 14 metal and a halogen (second halogen) of an elemental species different from the halogen (first halogen) constituting the formed quantum dots, and a ligand substance are added to the solution in which the quantum dots are dispersed.

[0023] Specifically, in this process, a mixture solution of a Group 14 metal halide salt and a ligand substance is first prepared. Any substance usable as a quantum dot ligand may be used as the ligand substance. More specifically, the ligand substance may be a salt of a halogen and a cation having a hydrocarbon chain and a charge at one end. Such a cation may be selected from those having characteristics such as an appropriate number of carbon atoms in the hydrocarbon chain (approximately 9 to 16) and an independency of the charge on pH. Specific examples of such cations include, but are not limited to, quaternary ammonium cations having a hydrocarbon chain with the above carbon number. In an embodiment, the ligand substance may be didodecyldimethylammonium bromide (DDAB), didodecyldimethylammonium chloride (DDAC), tridodecylmethylammonium iodide (TDAI), or the like. Meanwhile, the Group 14 metal halide salt added to the solution of formed quantum dots is selected from any Group 14 metal halide salt different from the halide salt used in the first process. Specifically, for example, when PbBr2 is used in the first step, other halide salts of Group 14 metals such as PbCl2, PbI2, SnCl2, or SnI2 may be used. The mixed solution of the halide salt of the Group 14 metal and the ligand substance is prepared by stirring the halide salt of the Group 14 metal and the ligand substance in an organic solvent such as toluene while heating.

[0024] Then, a mixture solution of a Group 14 metal halide salt and a ligand substance is injected into the quantum dot dispersion solution. In this process, as shown in FIG. 1C, a mixture solution of a Group 14 metal halide salt and a ligand substance (e.g., a PbCl3, DDAB toluene solution) is injected into a quantum dot dispersion solution (e.g., a CsPbBr3 hexane solution) contained in a three-neck flask 10 using a syringe 16. The resulting solution is then heated and stirred under a nitrogen atmosphere using a mantle heater 12 or the like. As a result, as shown in FIG. 1D, a portion of the first halogen (e.g., Br) in the quantum dot Qd composition is replaced with a second halogen (e.g., Cl), and the newly added ligand substance L (e.g., DDA) is coordinated around the quantum dots.

[0025] Thereafter, the quantum dot dispersion is prepared in the same manner as above, by removing materials that did not form quantum dots by any purification process such as centrifugation, and the quantum dots are dispersed in a colloidal state in an organic solvent such as toluene.

[0026] As described in the experimental examples below, the amount and type of the mixture solution of a Group 14 metal halide salt and a ligand substance injected into the quantum dot dispersion prepared in the first step affect the shift in the emission wavelength peak of the quantum dots and the increase in the luminescence quantum yield. Experiments have shown that the greater the amount of the mixture solution of a Group 14 metal halide salt and a ligand substance injected, the greater the shift in the emission wavelength peak. Therefore, the amount of the mixture solution of a Group 14 metal halide salt and a ligand substance injected can be adjusted to obtain the desired emission wavelength peak. Furthermore, it has been observed that an excessive amount of the ligand substance, such as DDA, tends to reduce the increase in the luminescence quantum yield. Therefore, it is preferable to adjust the amount of the ligand substance to an appropriate amount.

[0027] Thus, according to the configuration of this embodiment, as shown in the results of the experimental example described below (FIG. 2), the quantum dot dispersion prepared in the first step of this embodiment has a quantum dot luminescence quantum yield of 50-60%, whereas the quantum dot dispersion obtained through the second step of this embodiment has a quantum dot luminescence quantum yield of 70-90%, and the peak emission wavelength is shifted from the initial quantum dot luminescence wavelength peak depending on the injection amount of the mixture solution of the Group 14 metal halide salt and the ligand substance. Furthermore, the quantum dot luminescence quantum yield is maintained for at least about two weeks. These features are expected to further expand the range of applications for quantum dots.

[0028] In order to verify the effectiveness of the present invention described above, the following experiments were carried out. It should be understood that the following examples are merely illustrative of the effectiveness of the present invention and do not limit the scope of the present invention. [Example]

[0029] According to the method of this embodiment described above, quantum dots were synthesized and the emission wavelength and emission quantum yield were measured as follows. All of the substances used were chemical substances.

[0030] 1. Formation of quantum dots (first step) (a) Preparation of cesium fatty acid (cesium oleate) solution A three-necked flask was charged with 60 mL of 1-octadecene, 0.6 g of cesium carbonate (CsCO3), and 2.13 g of oleic acid (OA). After evacuating, the flask was stirred with a magnetic stirrer at room temperature for 2 minutes, and then heated to 120°C and stirred for 30 minutes to prepare a cesium oleate solution. (b) Preparation of Group 14 metal halide (PbBr2) solution In another three-necked flask, 20 mL of 1-octadecene and 0.318 g of PbBr2 were placed, and after evacuating, the mixture was stirred with a magnetic stirrer at room temperature for 10 minutes, and then heated to 120°C and stirred for 60 minutes to prepare a PbBr2 solution. (c) Preparation of Ligand Substance Mixture 2.68 g of oleic acid (OA) and 3 mL of oleylamine (OAm) were placed in a beaker and stirred for 1 minute, and then heated to 130° C. and stirred for 30 minutes to obtain an OA-OAm mixture. (d) Mixing the Group 14 metal halide solution with the ligand material mixture (b) 4.2 ml of the OA-OAm mixture was injected into the PbBr2 solution in the three-neck flask using a syringe, the solution was mixed, and the flask was evacuated to a vacuum for 30 minutes and maintained as is. (e) Injection of fatty acid cesium solution into Group 14 metal halide-ligand material solution (d) The three-necked flask was placed under a nitrogen atmosphere and heated to 190°C, and 3.2 mL of cesium oleate solution was injected using a syringe. Five seconds after injection, the three-necked flask was cooled in ice water for 30 seconds. This resulted in the formation of quantum dots, which were perovskite nanocrystals with a composition of CsPbBr3 and coordinated with OA and OAm. (f) Purification of quantum dots After cooling the three-neck flask, the resulting product was mixed with an equal amount of methyl acetate, and the mixture was centrifuged at 9300 rpm for 4 minutes and 30 seconds to collect the precipitate, which was then dried. The dried precipitate was then dispersed in hexane to a concentration of 50 mg / mL, refrigerated for 2 hours, and then centrifuged at 4000 rpm for 2 minutes to collect the supernatant, which was then stored as a quantum dot dispersion.

[0031] 2. Modifying the properties of quantum dots (second step) (a) Preparation of a mixed solution of a Group 14 metal halide salt and a ligand substance PbCl was used as the Group 14 metal halide salt, and didodecyldimethylammonium bromide (DDAB) or didodecyldimethylammonium chloride (DDAC) was used as the ligand substance. 27.8 mg of PbCl, 92 mg of DDAB or 83.64 mg of DDAC, and 3 ml of toluene were placed in a screw bottle and stirred at 40°C for 46 hours to prepare a mixed solution of the halide salt and the ligand substance. (b) Injection of a mixture solution of halide salt and ligand substance into the quantum dot dispersion. 1 ml of quantum dot dispersion was placed in a three-neck flask, and 100-600 μl of a mixed solution of halide salt and ligand substance was injected using a syringe. The mixture was then stirred for 1 hour at 40°C under a nitrogen atmosphere. During this process, some of the Br in the quantum dots was replaced with Cl, and DDAB or DDAC became ligands and coordinated around the quantum dots. (f) Purification of quantum dots 1 ml of methyl acetate was added to the quantum dot dispersion in the three-neck flask and mixed. The mixed solution was centrifuged at 9300 rpm for 3 minutes, the precipitate was dispersed in 1 ml of toluene, and centrifuged at 4000 rpm for 2 minutes. The supernatant was collected and saved as a new quantum dot dispersion.

[0032] (Measurement of luminescence quantum yield) The peak emission wavelength and emission quantum yield of the quantum dot solution were measured using an absolute PL quantum yield measurement system, Quantaurus-QY Cl1347-01 (Hamamatsu Photonics Co., Ltd.). The excitation light wavelength was set to 400 nm.

[0033] As shown in Figure 2(A), the quantum dots prepared in the first step (S in the figure) exhibited a peak emission wavelength of approximately 518 nm and a quantum yield of 50-60%. In contrast, when PbCl2 and DDAB were added in the second step, the peak emission wavelength of the quantum dots shifted to shorter wavelengths within the range of 513 nm to 495 nm, and the quantum yield increased to 70-90%, depending on the amount of PbCl2 added. The shift in the peak emission wavelength of the quantum dots increased with increasing amounts of PbCl2. These characteristics were maintained for two weeks after the preparation of the quantum dots. Furthermore, as shown in Figure 2(B), when PbCl2 and DDAC were added in the second step, the peak emission wavelength of the quantum dots shifted to shorter wavelengths with increasing amounts of the PbCl2 and DDAC mixed solution. However, when the amount of the mixed solution added was 250 μl, the luminescence quantum yield increased to approximately 80%, but when the amount of the mixed solution added was 500 μl, the luminescence quantum yield decreased.

[0034] The above results show that when a ligand-covered quantum dot with a perovskite nanocrystal structure having a CsMX3 composition is added with a Group 14 metal halide of a halogen different from that constituting the quantum dot and a ligand substance, the emission wavelength of the quantum dot shifts and the emission quantum yield can be increased, provided that the amount added is not excessive.

[0035] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. 1. A method for synthesizing quantum dots, comprising: CsMX ３ a first step of forming quantum dots having a perovskite structure with a composition of (Cs: cesium, M: Group 14 metal, X: first halogen), each particle being covered with a ligand; a second step of adding a ligand substance usable as a ligand for the quantum dots and a halide of a Group 14 metal and a second halogen different from the first halogen to the solution in which the quantum dots are dispersed; Including, In the first step, the quantum dot particles are dispersed in an organic solvent in a colloidal state, coated with oleic acid and oleylamine as the ligands, and in the second step, the ligand substance is didodecyldimethylammonium bromide. In the second step, the quantum dot dispersion solution is mixed with a solution in which the ligand substance and a halide of the second halogen and a Group 14 metal are dispersed in an organic solvent in a liquid ratio of 10 to 1 to 6, so that the amount of the ligand substance and the halide added is in a range that increases the luminescence quantum yield of the quantum dots. ３ A method for synthesizing quantum dots with a perovskite structure that emit light at a wavelength different from that of the quantum dots having the composition of formula (1).

2. 1. A method for synthesizing quantum dots, comprising: CsMX ３ a first step of forming quantum dots having a perovskite structure with a composition of (Cs: cesium, M: Group 14 metal, X: first halogen), each particle being covered with a ligand; a second step of adding a ligand substance usable as a ligand for the quantum dots and a halide of a Group 14 metal and a second halogen different from the first halogen to the solution in which the quantum dots are dispersed; Including, In the first step, the quantum dot particles are dispersed in an organic solvent in a colloidal state, coated with oleic acid and oleylamine as the ligands, and in the second step, the ligand substance is didodecyldimethylammonium chloride. In the second step, the quantum dot dispersion solution is mixed with a solution in which the ligand substance and a halide of the second halogen and a Group 14 metal are dispersed in an organic solvent in a liquid ratio of 4:1, so that the amounts of the ligand substance and the halide added are in a range that increases the luminescence quantum yield of the quantum dots, thereby producing the CsMX ３ A method for synthesizing quantum dots with a perovskite structure that emit light at a wavelength different from that of the quantum dots having the composition of formula (1).

3. 3. The method of claim 1 or 2, wherein the CsMX ３ The composition is CsPbBr ３ and the halide of the second halogen and a Group 14 metal is PbCl ２ or PbI ２ or SnCl ２ or SnI ２ How to be.

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