Nanoparticles, ink composition, and method for producing the ink composition

Abstract

The objective is to improve the dispersibility of nanoparticles in polar solvents by modifying the ligands applied to their surface. [Solution] The nanoparticles of the present invention are nanoparticles having a ligand on their surface, wherein the ligand contains a phosphate-based ligand. In the present invention, it is preferable that the phosphate-based ligand contains a comb-type polymer. Furthermore, in the present invention, it is preferable that the ligand further contains a thiol-based ligand.

Description

Technical Field

[0001] The present invention relates to nanoparticles with improved dispersibility in polar solvents, an ink composition containing the quantum dots, and a method for producing the ink composition.

Background Art

[0002] Patent Document 1 discloses an invention related to a dispersion containing quantum dots and an inkjet ink composition using the same. In Patent Document 1, a polymer dispersant having an amine value of 5 mgKOH / g or more is used to enhance the dispersibility of quantum dots.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object is to improve the ligand provided on the surface of the nanoparticles to enhance the dispersibility in polar solvents.

Means for Solving the Problems

[0005] The nanoparticles of the present invention are nanoparticles having a ligand on the surface, and the ligand contains a phosphoric acid-based ligand.

[0006] The method for producing an ink composition according to the present invention includes a step of synthesizing nanoparticles having a nonpolar ligand on the surface, a step of substituting the nonpolar ligand with a polar ligand, and a step of dispersing the nanoparticles having the polar ligand in a polar solvent.

Effects of the Invention

[0007] The nanoparticles of the present invention can improve dispersibility in polar solvents and enhance optical properties. [Brief explanation of the drawing]

[0008] [Figure 1] This is an illustrative diagram illustrating the decentralization needed to explain the conventional challenges. [Figure 2] This is a schematic diagram of the quantum dot (nanoparticle) in this embodiment. [Figure 3] This is an illustrative diagram of a comb-shaped polymer. [Figure 4] This is a step diagram showing the manufacturing process of the ink composition of this embodiment. [Figure 5] This is an illustrative diagram showing the dispersion in this embodiment. [Figure 6] This is a conceptual diagram of a display device using the ink composition of this embodiment. [Figure 7] This is a schematic diagram showing the experimental results of a visual inspection-based dispersion state evaluation test. [Figure 8] This is a schematic diagram of a fluorescence intensity measuring device. [Figure 9] This graph shows the relationship between measurement time and integrated intensity in reliability evaluation (room temperature lighting test). [Modes for carrying out the invention]

[0009] One embodiment of the present invention (hereinafter abbreviated as "Embodiment") will be described in detail below. However, the present invention is not limited to the following embodiment and can be implemented with various modifications within the scope of its gist. In this specification, the notation "~" includes the lower and upper limits.

[0010] <Background leading to the present invention> Quantum dots are inorganic nanoparticles composed of several thousand to tens of thousands of atoms, with a particle size of several nanometers to tens of thousands of nanometers. Because quantum dots emit fluorescence and are of the nano-order, they are also called fluorescent nanoparticles; because their composition is derived from semiconductor materials, they are also called semiconductor nanoparticles; and because their structure has a specific crystalline structure, they are also called nanocrystals.

[0011] In recent years, quantum dots, which can selectively control emission wavelengths, have been increasingly adopted in displays to improve color reproduction. Quantum dots can have their emission wavelengths varied depending on the particle size and composition.

[0012] Quantum dots are incorporated, for example, into the color conversion layer (wavelength conversion layer) of a display. The color conversion layer is formed by coating or exposing an ink composition in which quantum dots are added to a monomer that serves as a resist resin. Therefore, improving the dispersibility of quantum dots in the monomer leads to an improvement in optical properties.

[0013] Conventional challenges will be explained using Figure 1. Figure 1A is an image of the quantum dot synthesis solution 20. As shown in Figure 1A, a large number of nonpolar ligands 11 are attached to the surface of the quantum dot 10.

[0014] Examples of nonpolar ligands 11 include 1-octadecene (ODE), dodecanethiol (DDT), oleic acid (OAc), oleylamine (OAm), and trioctyl phosphate (TOP).

[0015] For example, a quantum dot 10 having a nonpolar ligand 11 is dispersed in a solvent 21 of 1-octadecene (ODE).

[0016] As shown in FIG. 1B, when the quantum dots 10 shown in FIG. 1A are washed and mixed in toluene 22, they can be dispersed in toluene 22. However, as shown in FIG. 1C, when the quantum dots 10 shown in FIG. 1A are washed and added to the polar solvent 23, it was found that the quantum dots 10 were unevenly distributed and aggregated, and could not be dispersed in the polar solvent 23.

[0017] Therefore, when the color conversion layer is formed using the ink composition containing the quantum dots 10 in the monomer of the polar solvent 23, there is a problem that the optical characteristics of the display deteriorate because the quantum dots 10 are not properly dispersed in the color conversion layer.

[0018] Therefore, in the present embodiment, attention was paid to the ligand provided on the surface of the quantum dots, and by improving the ligand, the dispersibility in the polar solvent was enhanced.

[0019] <Regarding the quantum dots in the present embodiment> FIG. 2 is a schematic diagram of the quantum dots 1 in the present embodiment. As shown in FIG. 2, the quantum dots 1 are nanocrystals composed of a core 2 made of semiconductor nanoparticles, a shell 3 formed on the surface of the core 2, and a ligand 4 formed on the surface of the shell 3.

[0020] Here, the “nanocrystal” refers to nanoparticles having a particle diameter of about several nm to several tens of nm. In the present embodiment, a large number of quantum dots 1 can be generated with a substantially uniform particle diameter.

[0021] The quantum dots 1 are formed in a substantially spherical shape, but they do not have to be perfect spheres. In the present embodiment, if the aspect ratio (length-to-width ratio) is about 0.8 to 1.2, they are included in a substantially spherical shape. Also, the boundary between the core 2 and the shell 3 is not clear, and a substantially boundary can be estimated by composition analysis or the like.

[0022] The combination of core 2 and shell 3 is not limited, but core 2 can be ZnSe, ZnTe, ZnSeTe, InP, GdSe, AgInGaS, etc., and shell 3 can be ZnS, etc. Furthermore, shell 3 may have multiple layers, for example, ZnTeSe / ZnSe / ZnS, or a buffer may be interposed between core 2 and shell 3. It is preferable that core 2 and shell 3 do not contain Cd. It is also preferable that they do not contain P. Organophosphorus compounds are expensive and easily oxidized in air, which destabilizes their synthesis and can easily lead to increased costs, unstable fluorescence properties, and complicated manufacturing processes.

[0023] As shown in Figure 2, numerous ligands (organic ligands) 4 are coordinated to the surface of quantum dot 1 (the surface of shell 3).

[0024] <Regarding the characteristic configuration of quantum dot 1 in this embodiment> The first characteristic is that the ligand 4 attached to the surface of the quantum dot 1 contains a phosphate ligand. Therefore, its chemical structure has the following formula 1.

[0025] [ka]

[0026] The phosphate ligand (phosphate polymer) may be a linear polymer or a comb-type polymer as shown in Figure 3, but a comb-type polymer is preferred. As shown in Figure 3, a comb-type polymer is a polymer having a linear main chain 5 with side chains 6 at predetermined intervals. Using a comb-type polymer can further improve dispersibility in polar solvents.

[0027] The molecular weight of the phosphate ligand is preferably between 700 and 6000, and more preferably between 1000 and 5000. Furthermore, the comb-shaped polymer shown in Figure 3 has relatively long side chains 6, and the molecular weight ratio of side chains 6 to the total molecular weight (if there are multiple side chains 6, the ratio of the molecular weights of all side chains 6 combined) is preferably between 20% and 50%, and more preferably between 30% and 45%. Note that the ● in Figure 3 represents functional groups (adsorbent groups) adsorbed on the quantum dot surface.

[0028] Furthermore, it is preferable that the side chains 6 are arranged at approximately regular intervals relative to the main chain 5. As an example, the molecular formula and SMILES notation of a phosphate ligand are shown below.

[0029] [ka]

[0030] [ka]

[0031] [ka]

[0032] [ka]

[0033] In this embodiment, it has been proven in experiments described later that the presence of a phosphate-based ligand among the polar ligands dramatically improves the dispersibility of quantum dot 1 in polar solvents.

[0034] Furthermore, in this embodiment, it is preferable that ligand 4 includes a thiol ligand along with a phosphate ligand. By mixing the phosphate ligand and the thiol ligand in this way, it becomes possible to more effectively improve dispersibility in polar solvents. While not limited to these, thiol ligands with the following structural formulas can be selected.

[0035] [ka]

[0036] [ka]

[0037] While there is no limit to the mass ratio of phosphate ligands to thiol ligands, it is preferable that there are more thiol ligands than phosphate ligands. The mass ratio of thiol ligands to phosphate ligands is preferably 1.0 to 3.0, and more preferably 1.5 to 2.5. The addition of thiols has the effect of improving optical properties such as QY. By increasing the amount of thiol added, the optical properties in the dispersed state can be effectively maintained (suppression of retention rate decrease).

[0038] At least one ligand 4 has a molecular weight of 500 or more. Phosphate ligands meet this requirement, but thiol ligands do not. However, ligands with a molecular weight of 500 or more are not limited to phosphate ligands only.

[0039] In this embodiment, some nonpolar ligands may be present. While not limited to nonpolar ligands, examples include 1-octadecene (ODE), dodecanethiol (DDT), oleic acid (OAc), oleylamine (OAm), and trioctyl phosphate (TOP). In this embodiment, when the quantum dots are synthesized, nonpolar ligands are attached to the surface as ligands, and then the nonpolar ligands are replaced with polar ligands. At this time, some nonpolar ligands may remain, without all of them being replaced by polar ligands.

[0040] <Regarding the ink composition of this embodiment> The ink composition in this embodiment comprises a quantum dot 1 having the ligand 4 described above, and a polar solvent, wherein the quantum dot 1 is dispersed in the polar solvent.

[0041] Quantum dot 1 contains a phosphate-based ligand as a polar ligand on its surface, preferably the phosphate-based ligand is a comb-type polymer as shown in Figure 3, and may also contain a thiol-based ligand.

[0042] The polar solvent preferably contains at least one solvent (resin) with the structural formula shown below.

[0043] [ka]

[0044] Furthermore, in this embodiment, in addition to the polar solvent mentioned above, acrylic resins, polyurethane resins, polyester resins, polyolefin resins, polycarbonate resins, polyethyleneimine resins, epoxy resins, thioether resins, etc., can be added as dispersion resins. In addition, as a polyfunctional thiol, pentaerythritol tetrakis(3-mercaptopropionate (PEMP)) can be included.

[0045] In this embodiment, when the quantum yield in the quantum dot synthesis solution (where the ligand is a nonpolar ligand) is defined as QY1, and then, after a washing step and substitution with a polar ligand, the quantum yield in the dispersion (where the ligand is a polar ligand) obtained by dispersing in a polar solvent is defined as QY2, the retention rate of the quantum yield, expressed as (QY2 / QY1) × 100 (%), can be made 60% or more, preferably 65% ​​or more, more preferably 70% or more, even more preferably 80% or more, even more preferably 85% or more, and most preferably 90% or more.

[0046] <Regarding the method for producing the ink composition in this embodiment> In this embodiment, the ink composition can be manufactured by the process shown in Figure 4. First, a synthesis solution (unwashed) containing the synthesized quantum dots is prepared (Step ST1). Existing methods can be applied to synthesize the quantum dots.

[0047] In this process, nonpolar ligands are coordinated to the surface of the quantum dots. Examples of nonpolar ligands, though not limited to them, include 1-octadecene (ODE), dodecanethiol (DDT), oleic acid (OAc), oleylamine (OAm), and trioctyl phosphate (TOP). The solvent in the synthesis solution is a nonpolar solvent such as 1-octadecene (ODE).

[0048] Next, toluene, ethanol, etc. are added to the synthesis solution, and the mixture is centrifuged to remove the supernatant liquid, allowing the quantum dots to precipitate. Then, ethanol, acetone, etc. are added.

[0049] Next, a polar ligand (dispersant) is added to replace the nonpolar ligands on the quantum dot surface with polar ligands (Step ST2). Then, hexane or the like is added to disperse the mixture, and the mixture is centrifuged to remove the supernatant, allowing the quantum dots to precipitate. Finally, acetone or the like is added to disperse the mixture.

[0050] Next, the quantum dots having polar ligands are dispersed in a polar solvent (step ST3). This allows for the production of a quantum dot ink composition in which quantum dots are dispersed in a polar solvent.

[0051] Figure 5A is an illustrative diagram showing the dispersion state of the quantum dot synthesis solution (unwashed), Figure 5B is an illustrative diagram showing the state after washing and dispersion in toluene, and Figure 5C is an illustrative diagram showing the state after dispersion in a polar solvent.

[0052] In Figures 5A and 5B, quantum dots 10, each having numerous nonpolar ligands 11 attached to its surface, are dispersed in a nonpolar solvent 21 or toluene 22. Figure 5A corresponds to step ST1 in Figure 4.

[0053] Between Figure 5B and Figure 5C, there is a ligand exchange step ST2. Therefore, in Figure 5C, the ligand 4 attached to the surface of quantum dot 1 is a polar ligand, specifically a phosphate ligand, or there are multiple types of ligand 4, and at least one of ligand 4 has a molecular weight of 500 or more, or is a comb-type polymer.

[0054] In Figures 5A to 5C, quantum dots 1 and 10 can be dispersed in the solvent, and in particular, as shown in Figure 5C, the state in which quantum dot 1 is dispersed in the polar solvent 23 can be appropriately maintained.

[0055] Thus, in the method for producing the ink composition of this embodiment, by adding a step in step ST2 in Figure 4 in which a nonpolar ligand is replaced with a polar ligand, the dispersibility in the polar solvent 23 can be effectively improved in step ST3 in Figure 4.

[0056] <Applications of Quantum Dot 1> Figure 6 is a cross-sectional view of a display device using the ink composition containing quantum dots according to this embodiment. The display device is configured as a micro-LED (Light Emitting Diode) display 30.

[0057] As shown in Figure 6, the microLED display 30 includes a plurality of display pixels 31a, 31b, and 31c. For example, the display pixel 31a shown in Figure 6 is a red display pixel, the display pixel 31b is a green display pixel, and the display pixel 31c is a blue display pixel. As shown in Figure 6, multiple light-emitting elements 33 are arranged on the substrate 32. For example, each light-emitting element 33 is a blue-emitting micro-LED.

[0058] As shown in Figure 6, the internal spaces of the partitions 34 for the red display pixels 31a and green display pixels 31b are filled with color conversion layers 35a and 35b. As shown in Figure 6, within the color conversion layers, red quantum dots 36 and green quantum dots 37 are dispersed in the red display pixels 31a and green display pixels 31b, respectively. Each quantum dot 36, 37 is dispersed in the resin 38.

[0059] As shown in Figure 6, a color filter layer 40 is provided on the surfaces of the color conversion layers 35a and 35b via a barrier layer 39. The color filter layer 40 comprises a red filter layer 40a, a green filter layer 40b, and a blue filter layer 40c. As shown in Figure 6, microlenses 41a to 41c can be provided on the surface of the color filter layer 40. The microlenses 41a to 41c are light-transmitting.

[0060] In this embodiment, the ink composition of this embodiment can be used in the color conversion layers 35a and 35b. In the ink composition, quantum dots are appropriately dispersed in a polar solvent, and therefore, even in the color conversion layers 35a and 35b shown in Figure 6, each quantum dot 36 and 37 can be appropriately dispersed within the resin 38. As a result, the optical properties of the display device can be maintained in good condition. [Examples]

[0061] The effects of the present invention will be explained below with reference to examples and comparative examples of the present invention. However, the present invention is not limited in any way by the following examples.

[0062] <Regarding the types of ligands and resins> The ligands and resins used in the experiment are shown in Tables 1, 2, and 3 below.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] The chemical formulas of comb-type phosphate polymer 1, comb-type phosphate polymer 2, comb-type phosphate polymer 3, comb-type phosphate polymer 4, thiol 2-1, thiol 2-2, thiol 2-3, and carboxylic acid 1, carboxylic acid 2, and carboxylic acid 3, as shown in Tables 1 and 2, are shown below.

[0067] [ka]

[0068] [ka]

[0069] [ka]

[0070] <Example 1> In Example 1, quantum dots were synthesized with nonpolar ligands attached to their surface. When substituting the nonpolar ligands with polar ligands, thiol 2 (amount added: 0.1 mL) and linear phosphate polymer (amount added: 0.2 mL) shown in Table 1 were added to produce quantum dots. Then, an ink composition was prepared by dispersing the quantum dots in DCP-M.

[0071] <Example 2> In Example 2, quantum dots were synthesized with nonpolar ligands attached to their surface. When substituting the nonpolar ligands with polar ligands, thiol 1 (amount added: 0.05 mL) and comb-type phosphate polymer 1 (amount added: 0.02 mL) shown in Table 1 were added to produce quantum dots. Then, an ink composition was prepared by dispersing the quantum dots in DCP-M.

[0072] <Example 3> In Example 3, quantum dots were synthesized with nonpolar ligands attached to their surface. When substituting the nonpolar ligands with polar ligands, thiol 2 (amount added: 0.05 mL) and comb-type phosphate polymer 1 (amount added: 0.02 mL), as shown in Table 1, were added to produce quantum dots. Then, an ink composition was prepared by dispersing the quantum dots in DCP-M.

[0073] <Example 4> In Example 4, quantum dots were synthesized with a nonpolar ligand attached to their surface. When substituting the nonpolar ligand with a polar ligand, thiol 1 (amount added: 0.05 mL) and comb-type phosphate polymer 1 (amount added: 0.02 mL) shown in Table 1 were added to produce quantum dots. Then, an ink composition was prepared by dispersing the quantum dots in the polar solvent of the following formula (11).

[0074] [ka]

[0075] <Example 5> In Example 5, quantum dots were synthesized with nonpolar ligands attached to their surface. When substituting the nonpolar ligands with polar ligands, the linear phosphate polymers shown in Table 1 (amount added: 0.2 mL) were added to produce the quantum dots. Then, an ink composition was prepared by dispersing the quantum dots in DCP-M.

[0076] <Example 6> In Example 6, quantum dots were synthesized with nonpolar ligands attached to their surface. When substituting the nonpolar ligands with polar ligands, the comb-type phosphate polymer 1 shown in Table 1 (amount added: 0.02 mL) was added to produce quantum dots. Then, an ink composition was prepared by dispersing the quantum dots in DCP-M.

[0077] <Comparative Example 1> In Comparative Example 1, quantum dots with nonpolar ligands attached to their surface were synthesized, and then thiol 2 (amount added: 0.5 mL) from Table 1 was added. However, the dots aggregated and could not be dispersed in a polar solvent.

[0078] <Comparative Example 2> In Comparative Example 2, quantum dots with nonpolar ligands attached to their surface were synthesized, and then thiol 1 (amount added: 0.2 mL) from Table 1 was added. However, the dots aggregated and could not be dispersed in a polar solvent.

[0079] <Comparative Example 3> In Comparative Example 3, quantum dots with nonpolar ligands attached to their surface were synthesized, and then a carboxylic acid polymer (amount added: 0.02 mL) was added. However, the dots aggregated and could not be dispersed in a polar solvent.

[0080] <Comparative Example 4> In Comparative Example 4, quantum dots with nonpolar ligands attached to their surface were synthesized, and when a carboxylic acid polymer (amount added: 0.02 mL) and thiol 2 (amount added: 0.02 mL) shown in Table 1 were added, aggregation occurred, and the dots could not be dispersed in a polar solvent.

[0081] <Comparative Example 5> In Comparative Example 5, quantum dots with nonpolar ligands attached to their surface were synthesized, and when a carboxylic acid polymer (amount added: 0.02 mL) and thiol 1 shown in Table 1 (amount added: 0.02 mL) were added, aggregation occurred, and the quantum dots could not be dispersed in a polar solvent.

[0082] <Visual assessment of the distributed state> The dispersion state of each ink composition in Examples 1-6, Comparative Examples 1-5, and the Reference Example was visually evaluated. In the experiment, each ink composition was filled into a transparent case and placed on a sheet of paper with three black lines, and it was evaluated whether the three lines could be seen through the ink composition. Figure 7 is a schematic diagram showing the experimental results of the visual dispersion state evaluation test. Figure 7 is a rasterized (square black and white dot) photographic image of each ink composition taken from directly above.

[0083] As shown in Figure 7, Examples 1-6 showed the highest transparency, and the three black lines were clearly visible. In the reference example, some turbidity was present, but the three black lines were still visible, indicating that the dispersion of quantum dots was maintained to some extent. In the reference example, the amount of linear phosphate polymer added was reduced compared to Example 5.

[0084] In contrast, comparative examples 1-5 showed turbidity and aggregation, and the three black lines could not be seen through them. This indicated a significant deterioration in the dispersibility of the quantum dots.

[0085] <Measurement of Quantum Yield (QY)> The measurement was performed using an absolute quantum yield meter with an integrating sphere. The measurement device used was the QE-1100 quantum efficiency measurement system manufactured by Otsuka Electronics Co., Ltd.

[0086] In the experiment, the quantum yield QY1 of the quantum dot synthesis solution (unwashed) and the quantum yield QY2 of the dispersion of quantum dots in a polar solvent were measured, and the retention rate ((QY2 / QY1) × 100 (%)) was determined. Note that for the comparative examples, it was not possible to disperse the quantum dots in a polar solvent, so the retention rate was only determined for Examples 1-4. The experimental results are shown in Table 1 below.

[0087] <Reliability evaluation (room temperature lighting test)> As shown in Figure 8, a QD resin layer 43 sandwiched between cover glass 42 and 44 was mounted on a jig 41 incorporating a blue LED (wavelength 450 nm) 40, and the fluorescence intensity was measured using a measuring instrument with an integrating sphere 45.

[0088] In the experiment, a 30mA current was passed through a blue LED 40 to light it up. The light (excitation light) was absorbed by the QD resin layer 43, converted into light with a wavelength corresponding to the band gap, and fluoresced. The fluorescence intensity was measured over time, and its changes were observed.

[0089] Figure 9 is a graph showing the relationship between measurement time and integrated intensity. Integrated intensity is the value obtained by integrating the fluorescence intensity.

[0090] In the experiment, QD resin layers 43 were formed using the ink compositions of Example 2, Example 3, and Example 4, and reliability evaluation (room temperature illumination test) was performed. In addition, as reference examples 1 to 3, QD resin layers 43 were formed using ink compositions in which quantum dots were mixed with IBOA (acrylate monomer), and reliability evaluation (room temperature illumination test) was performed.

[0091] As shown in Figure 9, Examples 2, 3, and 4 all demonstrated excellent stability, showing minimal change in fluorescence intensity over time with respect to light irradiation (excitation light at 450 nm). This indicates that substitution with phosphate-based and thiol-based ligands improved dispersibility in polar solvents. In particular, the dispersibility in a polar solvent mixed with DCP-M and PEMP was excellent, and it was found that the change in fluorescence intensity over time was minimized. Table 4 below shows the experimental results illustrating the dispersibility of Examples 1-6 and Comparative Examples 1-5.

[0092] [Table 4]

[0093] As shown in Table 4, Comparative Examples 1 to 5 all aggregated when the ligands were replaced and could not be dispersed in the polar solvent. However, in this example, all samples exhibited high dispersibility in the polar solvent, and the retention rate ((QY2 / QY1) × 100 (%)) obtained by measuring the quantum yield QY1 of the quantum dot synthesis solution (unwashed) and the quantum yield QY2 of the dispersion of quantum dots in the polar solvent could be increased to 80% or more, preferably 85% or more, and more preferably 90% or more.

[0094] In this example, it was found that the ligand has a phosphate ligand, and it is preferable to have a phosphate ligand alone, or to have a thiol ligand in addition. Furthermore, it was found that the phosphate ligand is preferably a comb-type polymer. [Explanation of symbols]

[0095] 1, 10: Quantum dots 2: Core 3: Shell 4: Ligand 5: Main chain 6: Side chain 11 :Nonpolar ligand 20:Synthetic liquid 21: Nonpolar solvents 22: Toluene 23: Polar solvents 30: Micro LED display 31a: Red display pixels 31b: Green display pixels 31c: Display pixels 32: Circuit board 33: Light-emitting element 34: Bulkhead 35a, 35b: Color conversion layer 36: Red quantum dot 37: Green quantum dot 39: Barrier layer 40: Blue LED 40: Color filter layer 42, 44: Cover glass 43:QD resin layer 45: Integrating sphere 46: Jig

Claims

1. Nanoparticles having ligands on their surface, The ligand includes a phosphate ligand. Nanoparticles characterized by the following features.

2. The phosphate ligand includes a comb-type polymer. The nanoparticles according to claim 1.

3. The ligand further includes a thiol ligand. The nanoparticles according to claim 1.

4. The nanoparticles according to claim 1 are dispersed in a polar solvent. An ink composition characterized by the following features.

5. A step of synthesizing nanoparticles having a nonpolar ligand on their surface, The step of replacing the nonpolar ligand with a polar ligand, A step of dispersing the nanoparticles having a polar ligand in a polar solvent, A method for producing an ink composition characterized by having the following:

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