Semiconductor nanoparticles, method for producing semiconductor nanoparticles, and light emitter

Abstract

Provided are semiconductor nanoparticles that are formed of Ag-Ge-S compound semiconductors. In the semiconductor nanoparticles, the content ratio, in terms of molar ratio, of the Ag component to the Ge component is 1.0 or more and less than 7.5, preferably 1.8 or more and less than 7.3. The average particle size is 9 nm or less and the difference between the maximum and minimum particle sizes is regulated to 3 nm or less. These semiconductor nanoparticles emit light in the near-infrared region of 700-1000 nm. The semiconductor nanoparticles are synthesized at a reaction temperature of 150°C or higher and lower than 250°C, preferably at 220°C or lower. The compound semiconductors may be used as a core particle on the surface of which a coating layer is formed. Also provided is a light emitter that contains these semiconductor nanoparticles. Due to this configuration, achieved are semiconductor nanoparticles that are safe and easy to handle and can emit light in the near-infrared region, a method for producing the semiconductor nanoparticles, and a light emitter that can be applied to various fields such as civilian goods, medical uses and healthcare drugs.

Description

[Technical Field]

[0001] The present invention relates to semiconductor nanoparticles, a method for producing semiconductor nanoparticles, and a light-emitting body, and more specifically to semiconductor nanoparticles made of compound semiconductors containing Ag, Ge, and S as main components, a method for producing the same, and a light-emitting body containing the semiconductor nanoparticles. [Background technology]

[0002] Compound semiconductors, which combine two or more different elements, have attracted attention because of the variety of properties they offer. In particular, semiconductor nanoparticles, which are made by nanoparticleizing compound semiconductors, are essential materials for luminescent materials today, and various beneficial properties can be obtained by changing the element content ratio or by ultra-fine-particleizing them to 10 nm or less to exhibit quantum size effects. From this perspective, research and development into these nanoparticles is actively underway, with the aim of applying them to a variety of fields, including consumer, medical, and healthcare pharmaceuticals.

[0003] For example, Non-Patent Document 1 describes the structure and properties of Qdot nanocrystals (Qdot is a trade name) manufactured by Thermo Fisher Scientific.

[0004] That is, Non-Patent Document 1 describes nanocrystals that have a core-shell structure in which the core is made of CdSe or CdTe and the shell is made of ZnS, and the surface of the ZnS is coated with a polymer compound containing a carboxylate group (-COO) (see Fig. 6.6.1 and the "Structural Properties" section of the same document).

[0005] This non-patent document 1 describes that by controlling the core size of the nanocrystals, it is possible to obtain emission spectra with different peak wavelengths in the range of 525 to 800 nm, and that the smaller the particle size, the shorter the wavelength of the light emitted. Therefore, according to this non-patent document 1, it is thought that it is possible to obtain nanocrystals with various emission properties by varying the particle size even with the same composition (see Fig. 6.6.5, "Spectroscopic Properties" in the same document).

[0006] Furthermore, Patent Document 1 proposes a light emitter formed of nanoparticles made of a compound semiconductor containing Ag, In, and Se components, which has a peak wavelength of emission intensity in the range of 700 nm to 1400 nm and a half-value width of the peak wavelength of 100 nm or less.

[0007] In Patent Document 1, a steep and sharp emission spectrum with a half-width of 100 nm or less is obtained in the near-infrared region of 700 nm to 1400 nm. Patent Document 1 obtains a light emitter that has good light transmittance particularly in the wavelength region of 700 to 1000 nm, which is known as the "biological window," and attempts to obtain a light emitter suitable as a labeling agent (biomarker) for biological substances that constitute living organisms.

[0008] Furthermore, Patent Document 2 proposes a light-emitting body containing nanoparticles made of a compound semiconductor containing at least Ag, In, and Se components, in which a hydrophilic coating is formed on the surface of the nanoparticles and the nanoparticles are dispersed in water, and the light-emitting body has a peak wavelength of emission intensity in the range of 650 nm to 1000 nm and a half-value width at the peak wavelength of 100 nm or less.

[0009] In Patent Document 2, the light emitter is dispersed in water with the nanoparticle surface made hydrophilic, so that nonpolar organic solvents that are harmful to cells are not adsorbed onto biological tissue, and a steep and sharp emission spectrum with a half-width of 100 nm or less is obtained in the near-infrared region of 650 nm to 1000 nm. Moreover, in Patent Document 2, a coating is formed on the surface of the nanoparticles to inactivate the surface, thereby obtaining an emission quantum yield of 10% or more. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] WO 2017 / 126164 (Claim 1, paragraph

[0033] , Table 1, etc.) [Patent Document 2] WO 2020 / 246297 (claims 1, 3, paragraph

[0024] , table 1, etc.) [Non-patent literature]

[0011] [Non-Patent Document 1] "Qdot Nanocrystals - Section 6.6", [online], Thermo Fisher Scientific, Inc., [Retrieved January 11, 2022], Internet <URL: https: / / www.thermofisher.com / jp / ja / home / references / molecular-probes-the-handbook / ultrasensitive-detection-technology / qdot-nanocrystal-technology.html> Summary of the Invention [Problem to be solved by the invention]

[0012] However, the above-mentioned prior art documents contain toxic elements such as Cd, Se, and In in the nanoparticles, which necessitates toxic substance management and health management for manufacturing workers, limiting their application to practical fields such as consumer products, medical and healthcare pharmaceuticals, etc.

[0013] That is, Non-Patent Document 1 contains Cd, a known harmful substance, in the core material that constitutes the nanocrystals, which places a heavy burden on the environment and makes it difficult to apply to various fields, including the biomedical field.

[0014] Furthermore, Patent Documents 1 and 2 contain selenium and indium components that are inherently toxic. Although selenium constitutes part of enzymes and proteins in the body and acts as an antioxidant, it is toxic and can cause symptoms of poisoning if taken in chronic excess. Therefore, it must be managed and handled as a poison. Furthermore, while in the past it was considered a relatively safe substance, in recent years its toxicity has been confirmed, necessitating health management, particularly for production workers, over a long period of time, and presenting safety and handling problems.

[0015] Therefore, it is desirable to develop new semiconductor nanoparticles that can replace these components such as Cd, Se, and In, that do not require toxic substance control or strict health management for manufacturing workers, that are safe and easy to handle, and that can be easily applied in practical fields such as consumer products, medical and healthcare pharmaceuticals.

[0016] The present invention has been made in consideration of the above circumstances, and aims to provide semiconductor nanoparticles that are safe and easy to handle and capable of emitting light in the near-infrared region, a method for producing the semiconductor nanoparticles, and a light-emitting body that uses the semiconductor nanoparticles and can be applied to various fields such as consumer products, medical care, and healthcare pharmaceuticals. [Means for solving the problem]

[0017] The present inventors have conducted extensive research into compound semiconductors containing Ag, Ge, and S as their main components, instead of the above-mentioned Cd, In, or Se, which do not require strict regulations on toxic substance control or the health management of manufacturing workers, are relatively easy to handle, and are highly safe.As a result, they have discovered that by reducing the Ag component among these components below the stoichiometric ratio and setting the content ratio of the Ag component to the Ge component, converted into a molar ratio, to 1.0 or more and less than 7.5, it is possible to obtain semiconductor nanoparticles with an average particle size of 9 nm or less, which allows the quantum size effect to be exhibited, and which are capable of emitting light in the near-infrared region.

[0018] The present invention was made based on this finding, and the semiconductor nanoparticles of the present invention are characterized in that they are formed of a compound semiconductor containing Ag, Ge, and S components as main components, and that the content ratio of the Ag component to the Ge component, converted into a molar ratio, is 1.0 or more and less than 7.5, and that the average particle size is 9 nm or less.

[0019] Here, the average particle size refers to the arithmetic mean value of the equivalent circle diameter of each particle.

[0020] This eliminates the need for toxic substance management or long-term health management of manufacturing workers, and makes it possible to obtain semiconductor nanoparticles that are safe and easy to handle, emit light in the near-infrared region, and whose emission wavelength can be controlled.

[0021] In addition, in the semiconductor nanoparticles of the present invention, the content ratio is preferably 1.8 or more and 7.3 or less in terms of molar ratio.

[0022] Furthermore, the semiconductor nanoparticles of the present invention preferably have a difference between the maximum and minimum particle diameters of 3 nm or less.

[0023] This makes it possible to obtain high-quality semiconductor nanoparticles with uniform particle size.

[0024] Furthermore, the semiconductor nanoparticles of the present invention are preferably capable of emitting light in the wavelength range of 700 to 1000 nm.

[0025] This allows the semiconductor nanoparticles to emit light in the near-infrared region of 700 to 1000 nm, and therefore can be obtained with good optical transparency without affecting the human body even when irradiated with the living body.

[0026] The compound semiconductors described above are ultrafine particles with an average particle size of 9 nm or less, and since a large number of atoms are located on the particle surfaces of the compound semiconductors, many defects exist on the particle surfaces. These surface defects cause energy loss, which may result in a deterioration of the light-emitting properties.

[0027] However, as a result of intensive research, the inventors have found that the light-emitting properties can be improved by coating the surfaces of particles made of the above-mentioned compound semiconductor with a material having a larger band gap energy than the compound semiconductor, thereby forming a core-shell structure.

[0028] That is, the semiconductor nanoparticles of the present invention preferably have a core-shell structure in which a coating layer made of a material having a larger band gap energy than the compound semiconductor is formed on the surface of a core particle made of the compound semiconductor.

[0029] This allows the coating layer to seal surface defects on the core particle, suppressing energy loss. Moreover, because the band gap energy of the coating layer is larger than that of the core particle, light can be emitted without loss of luminescence from the core particle, thereby enabling the production of semiconductor nanoparticles with improved luminescence properties.

[0030] In the semiconductor nanoparticles of the present invention, the coating layer is mainly composed of periodic table It is preferable that the magnetic material is formed of a compound containing at least one element Z1 selected from the group of elements belonging to groups 12, 13, and 14 of the periodic table, and at least one element Z2 selected from the group of elements belonging to group 16 of the periodic table.

[0031] The compounds containing the above-mentioned element Z1 and element Z2 are widely used as various shell materials, and have a larger band gap energy than the core particle, so that the light emission from the core particle is not lost and it is possible to easily improve the light emission properties.

[0032] Furthermore, in the semiconductor nanoparticles of the present invention, the element Z1 preferably includes at least one selected from the group consisting of Zn, Ga, Sn, and Ge, and the element Z2 preferably includes at least one selected from the group consisting of S and O.

[0033] In addition, the semiconductor nanoparticles of the present invention preferably have a plurality of coating layers formed in the form of layers on the particle surface.

[0034] This allows the coating layer to be densified, which makes it possible to more effectively suppress energy loss and further improve the light-emitting properties.

[0035] Furthermore, the inventors have conducted extensive research into the manufacturing method of the above-mentioned semiconductor nanoparticles, and have found that by reacting an Ag-Ge-S mixed solution prepared so that the Ag to Ge content ratio in the final product is 1.0 or more and less than 7.5 in molar ratio terms at 150°C or more and less than 250°C, preferably 220°C or less, the particle generation reaction proceeds effectively and semiconductor nanoparticles with an average particle size of 9 nm or less can be easily obtained.

[0036] That is, the method for producing semiconductor nanoparticles according to the present invention is a method for producing semiconductor nanoparticles containing a compound semiconductor whose main components are Ag, Ge, and S components, and is characterized by comprising the steps of weighing out Ag compounds, Ge compounds, and S compounds so that the content ratio (Ag / Ge) of the Ag component to the Ge component in the compound semiconductor is 1.0 or more and less than 7.5 in terms of molar ratio, dissolving the weighed amounts in a solvent to produce an Ag-Ge-S mixed solution, and heating the Ag-Ge-S mixed solution to a reaction temperature of 150°C or more and less than 250°C to produce a compound semiconductor having an average particle size of 9 nm or less.

[0037] This allows the particle production reaction to proceed effectively, making it possible to easily obtain semiconductor nanoparticles with an average particle size of 9 nm or less.

[0038] In the method for producing semiconductor nanoparticles of the present invention, the reaction temperature is preferably 220° C. or lower.

[0039] In the method for producing semiconductor nanoparticles of the present invention, the nanoparticles are preferably dispersed in a non-polar solvent, and the non-polar solvent is preferably chloroform.

[0040] This makes it possible to obtain semiconductor nanoparticles that are stably dispersed in a non-polar solvent such as chloroform.

[0041] In the method for producing semiconductor nanoparticles of the present invention, the Ag compound preferably includes silver N,N-diethyldithiocarbamate.

[0042] Furthermore, in the method for producing semiconductor nanoparticles of the present invention, the Ge compound preferably includes a reaction product of a hydroxy acid and a germanium oxide, and the hydroxy acid preferably includes glycolic acid.

[0043] Furthermore, in the method for producing semiconductor nanoparticles of the present invention, the S compound preferably includes thiourea.

[0044] In the method for producing semiconductor nanoparticles of the present invention, the solvent preferably contains a combination of an aliphatic amine having a boiling point higher than the reaction temperature and a fat-soluble thiol.

[0045] This allows Ag compounds, Ge compounds, and S compounds to be dissolved in a high-boiling point solvent that is stable at high temperatures, making it possible to produce a chemically stable Ag-Ge-S mixed solution.

[0046] In the method for producing semiconductor nanoparticles of the present invention, the aliphatic amines preferably include oleylamine.

[0047] In the method for producing semiconductor nanoparticles of the present invention, the fat-soluble thiols preferably include 1-dodecanethiol.

[0048] Furthermore, in the method for producing semiconductor nanoparticles of the present invention, it is preferable to prepare a plurality of raw material-containing compounds for forming a coating layer having a larger band gap energy than the compound semiconductor, mix the compound semiconductor with the plurality of raw material-containing compounds, and subject the mixture to a heat treatment to form a coating layer on the surface of a core particle made of the compound semiconductor, thereby producing semiconductor nanoparticles with a core-shell structure.

[0049] This allows for the efficient production of semiconductor nanoparticles with a core-shell structure and improved luminescence properties.

[0050] Further, in the method for producing semiconductor nanoparticles of the present invention, the raw material-containing compound is periodic table and a Z2 compound containing at least one element Z1 selected from the group of elements belonging to Group 16 of the periodic table, and the Z1 compound preferably includes a Zn compound such as bis(2,4-pentanedionato)zinc(II), and the Z2 compound preferably includes an S compound such as thiourea.

[0051] Furthermore, in the method for producing semiconductor nanoparticles of the present invention, even in the case of semiconductor nanoparticles having a core-shell structure, they are preferably dispersed in a non-polar solvent such as chloroform.

[0052] The light-emitting body according to the present invention is characterized by containing the semiconductor nanoparticles.

[0053] As a result, the light-emitting body can emit light in the near-infrared region, and therefore, for example, by binding the light-emitting body to biological tissue and irradiating the tissue with excitation light from outside the organism, it is possible to observe the tissue morphology of the organism. [Effects of the Invention]

[0054] The semiconductor nanoparticles of the present invention are formed from a compound semiconductor containing Ag, Ge, and S components as main components, and the content ratio of the Ag component to the Ge component is 1.0 or more and less than 7.5 in terms of molar ratio, and the average particle size is 9 nm or less. Therefore, there is no need to strictly regulate toxic substance management or health management of manufacturing workers, and semiconductor nanoparticles can be obtained that are safe and easy to handle, can emit light in the near-infrared region, and the emission wavelength can be controlled.

[0055] Furthermore, according to the method for producing semiconductor nanoparticles of the present invention, there is provided a method for producing semiconductor nanoparticles formed of a compound semiconductor containing Ag, Ge, and S components as main components, the method comprising the steps of: weighing out precursor Ag compounds, Ge compounds, and S compounds so that the content ratio (Ag / Ge) of the Ag component to the Ge component in the semiconductor nanoparticles is equal to or greater than 1.0 and less than 7.5 in terms of molar ratio; dissolving the weighed amounts in a solvent to produce an Ag-Ge-S mixed solution; and heating the Ag-Ge-S mixed solution to a reaction temperature of equal to or greater than 150°C and less than 250°C to produce semiconductor nanoparticles having an average particle size of 9 nm or less. This allows the particle generation reaction to proceed effectively, and semiconductor nanoparticles having an average particle size of 9 nm or less can be easily obtained.

[0056] Furthermore, since the luminescent material of the present invention contains the semiconductor nanoparticles, the luminescent material can emit light in the near-infrared region. Therefore, for example, by binding the luminescent material to biological tissue and irradiating it with excitation light from outside the living body, it is possible to observe the tissue morphology of the living body. [Brief explanation of the drawings]

[0057] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment (first embodiment) of semiconductor nanoparticles according to the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a second embodiment of semiconductor nanoparticles according to the present invention. [Figure 3] FIG. 10 is a schematic diagram showing a modified example of the second embodiment. [Figure 4]This is a TEM image of sample number 1. [Figure 5] This is a TEM image of sample number 2. [Figure 6] This is a TEM image of sample number 3. [Figure 7] This is a TEM image of sample number 4. [Figure 8] This is a TEM image of sample number 5. [Figure 9] This is a TEM image of sample number 6. [Figure 10] This is a TEM image of sample number 9. [Figure 11] Photographs of samples Nos. 2, 8, and 9 are shown. [Figure 12] FIG. 1 shows the absorption spectrum profile of sample number 1. [Figure 13] FIG. 1 shows the absorption spectrum profile of sample number 2. [Figure 14] FIG. 1 shows the absorption spectrum profile of sample number 3. [Figure 15] FIG. 1 shows the absorption spectrum profile of sample number 4. [Figure 16] FIG. 1 shows the absorption spectrum profile of sample number 5. [Figure 17] FIG. 1 shows the absorption spectrum profile of sample number 6. [Figure 18] FIG. 1 shows the emission spectrum profile of sample number 1. [Figure 19] FIG. 1 shows the emission spectrum profile of sample number 2. [Figure 20] FIG. 1 shows the emission spectrum profile of sample number 3. [Figure 21] FIG. 1 shows the emission spectrum profile of sample number 4. [Figure 22] FIG. 1 shows the emission spectrum profile of sample number 5. [Figure 23] FIG. 1 shows the emission spectrum profile of sample number 6. [Figure 24]FIG. 10 is a diagram showing the relationship between the reaction temperature and the absorption spectrum profile for sample number 2. [Figure 25] FIG. 10 is a graph showing the relationship between the reaction temperature and the emission spectrum profile for sample number 2. [Figure 26] This is a TEM image of sample number 12. [Figure 27] 1 is a histogram showing the particle size distribution of sample number 12. [Figure 28] FIG. 1 shows the absorption spectrum profiles of sample No. 11 and sample No. 12. [Figure 29] FIG. 1 shows the emission spectrum profiles of sample No. 11 and sample No. 12. DETAILED DESCRIPTION OF THE INVENTION

[0058] Next, an embodiment of the present invention will be described in detail.

[0059] (First embodiment) 1 is a schematic diagram showing one embodiment (first embodiment) of semiconductor nanoparticles according to the present invention, in which the semiconductor nanoparticles 11 are formed of a compound semiconductor containing Ag, Ge, and S components as main components (hereinafter referred to as an "Ag-Ge-S-based compound semiconductor"). The semiconductor nanoparticles have a molar content ratio of Ag to Ge (hereinafter referred to as "Ag / Ge molar content ratio") of 1.0 or more and less than 7.5, and an average particle size of 9 nm or less.

[0060] This makes it possible to obtain semiconductor nanoparticles that emit light in the near-infrared region of 700 to 1000 nm and whose emission wavelength can be controlled, without using elements that have a high environmental impact and require strict toxic substance control and health management of manufacturing workers.

[0061] In other words, compound semiconductors are essential materials for luminescent substances, but as mentioned in the section [Problems to be Solved by the Invention], conventionally, highly toxic Cd components, Se components that can cause poisoning if taken in excess, and In components that require long-term health management for manufacturing workers have been used as constituents of compound semiconductors, making them inferior in safety and ease of handling.

[0062] Meanwhile, compound semiconductors containing Ag, Ge, and S with a stoichiometric composition expressed as Ag8GeS6 have been known for some time. These component elements do not require strict control like Cd, Se, and In, and are safe and easy to handle. Therefore, semiconductor nanoparticles formed from Ag-Ge-S compound semiconductors are promising as replacements for AgInSe2 and CdSe.

[0063] Therefore, in this embodiment, the semiconductor nanoparticles are formed from an Ag-Ge-S compound semiconductor, and the molar ratio of Ag to Ge is set to 1.0 or more and less than 7.5 for the reasons described below.

[0064] In recent years, semiconductor nanoparticles of this type have been attracting attention for their application as biomarkers (labeling agents) for biological substances constituting living organisms. In this case, it has traditionally been considered preferable to generate fluorescence in the near-infrared region (700 to 1700 nm). That is, in the visible light region (400 to 700 nm), which has shorter wavelengths than the near-infrared region, absorption by biological components such as hemoglobin is high. Furthermore, as wavelengths increase beyond 1700 nm, absorption by water increases, making it difficult for light to penetrate efficiently within living organisms. In contrast, the near-infrared region (700 to 1700 nm), particularly the 700 to 1000 nm region, has high optical transparency within living organisms and is considered a wavelength range suitable for bioimaging applications.

[0065] However, as mentioned above, the stoichiometric composition of Ag-Ge-S compound semiconductors is Ag8GeS6, and the stoichiometric ratio of the Ag / Ge molar ratio is 8. On the other hand, the absorption edge wavelength of Ag8GeS6 is approximately 900 nm, and therefore the emission wavelength, especially its maximum wavelength, may exceed 1000 nm, which may make it difficult to obtain highly accurate biological information even when irradiated onto biological tissue.

[0066] That is, when photon energy is applied to this type of semiconductor nanoparticle, the semiconductor nanoparticle absorbs light, and electrons in the ground state valence band are excited to the conduction band, forming holes in the valence band. The excited electrons are then attracted to the ground state valence band where holes exist by Coulomb force, and the electrons and holes recombine to emit light. In this case, to achieve high-efficiency light emission, it is preferable to bring the emission wavelength as close as possible to the absorption edge wavelength. However, when electrons return from the excited state to the valence band, part of the photon energy is usually consumed as vibrational energy, etc., resulting in a shift called the Stokes shift between the absorption wavelength and the emission wavelength. Therefore, the emission wavelength of semiconductor nanoparticles is longer than the absorption edge wavelength. However, with a stoichiometric Ag / Ge molar ratio of "8," the absorption edge wavelength is approximately 900 nm as described above, and the emission wavelength, especially its maximum wavelength, may exceed 1000 nm. This may result in poor light transmittance in vivo even when irradiated to biological tissue, making it difficult to obtain highly accurate biological information.

[0067] On the other hand, if the molar ratio Ag / Ge is adjusted so that the molar amount of Ag contained is less than the stoichiometric ratio, the absorption edge wavelength can be shifted to the shorter wavelength side, around 650 to 800 nm, thereby making it possible to emit light in the wavelength range of 700 to 1000 nm, which has good light transmittance to living organisms.

[0068] However, if the molar ratio Ag / Ge is less than 1.0, the Ag component will be extremely low, which may hinder the reaction for producing nanoparticles and make it impossible to obtain an Ag-Ge-S based compound semiconductor.

[0069] On the other hand, if the molar ratio of Ag / Ge is 7.5 or more, the luminescence quantum yield (the proportion of photons emitted as light among the photons absorbed by the nanoparticles) will be less than 0.5%, which may result in a decrease in luminescence efficiency.

[0070] Therefore, in this embodiment, the contents of the Ag component and the Ge component are adjusted so that the molar ratio Ag / Ge is 1.0 or more and less than 7.5, preferably 1.8 or more and 7.3 or less.

[0071] Furthermore, in this embodiment, the semiconductor nanoparticles have an average particle size of 9 nm or less.

[0072] In other words, semiconductor nanoparticles that are ultrafine, with an average particle size of approximately 10 nm or less, generally exhibit a quantum size effect, in which the band gap energy increases as the particle size decreases, and even when using semiconductor materials with the same component composition, the light absorption and emission wavelengths can be controlled over a wide range.

[0073] Therefore, in this embodiment, the average particle size of the semiconductor nanoparticles is controlled to 9 nm or less by adjusting the reaction conditions such as the reaction temperature and reaction time, which enables the quantum size effect to be exhibited, and by varying the average particle size, it becomes possible to vary the emission wavelength as needed within the wavelength range of 700 to 1000 nm.

[0074] The present inventors have reacted an Ag component with an S component to produce an Ag-S-based compound semiconductor that does not contain a Ge component. However, as will be described in detail in the Examples below, the product grains grew and became coarse, and it was confirmed that the average grain size exceeded 9 nm.

[0075] Furthermore, the variation in particle size of the semiconductor nanoparticles is preferably suppressed so that the difference between the maximum value Dmax and the minimum value Dmin is 3 nm or less, more preferably 2.6 nm or less.

[0076] This makes it possible to obtain stable, high-quality semiconductor nanoparticles with uniform particle size and good dispersibility.

[0077] Thus, the present semiconductor nanoparticles are formed from a compound semiconductor containing Ag, Ge, and S components as main components, and the content ratio of the Ag component to the Ge component is 1.0 or more and less than 7.5 in terms of molar ratio, and the average particle size is 9 nm or less. Therefore, there is no need to strictly regulate the management of toxic and hazardous substances or the health of workers, and it is possible to obtain semiconductor nanoparticles that are safe and easy to handle, emit light in the near-infrared region, and the emission wavelength can be controlled.

[0078] Next, one embodiment of the method for producing the semiconductor nanoparticles will be described in detail.

[0079] First, to obtain a Ge compound as a Ge source, for example, a hydroxy acid is reacted with a Ge oxide. Here, the hydroxy acid is not particularly limited as long as it is a carboxylic acid containing a hydroxy group, and examples thereof include glycolic acid (HOCH2COOH), lactic acid (CH3CH(OH)COOH), malic acid (HOOCCH(OH)CH2COOH), and glycerin (HOCH2CH(OH)COOH). Furthermore, the Ge oxide is also not particularly limited, but germanium(IV) oxide (GeO2) is usually preferred.

[0080] Then, predetermined amounts of hydroxy acid and Ge oxide are weighed out, and these weighed materials are mixed in highly pure water or ultrapure water. The mixture is heated and stirred in an oil bath adjusted to a predetermined temperature (e.g., 100°C), thereby causing a reaction between the hydroxy acid and Ge oxide, and then evaporated and dried to obtain a Ge compound.

[0081] Next, an Ag compound serving as an Ag source and an S compound serving as an S source are prepared. The Ag compound is not particularly limited, and examples thereof include organic acid silver compounds such as silver N,N-diethyldithiocarbamate (AgS2CN(C2H5)2) (hereinafter referred to as "AgDDTC") and silver acetate (Ag(OCOCH3), and inorganic acid silver compounds such as silver nitrate (AgNO3) and silver sulfate (Ag2SO4). The S compound may be, for example, thiourea (SC(NH2)2).

[0082] Then, the Ag compound, Ge compound, and S compound are weighed out so that the molar ratio Ag / Ge contained in the semiconductor nanoparticles, which are the final product, is 1.0 or more and less than 7.5, preferably 1.8 or more and 7.3 or less.

[0083] Next, these weighed materials are dissolved in a solvent to prepare an Ag-Ge-S mixed solution. Here, as the solvent, a high-boiling solvent that is chemically stable and has a boiling point higher than the reaction temperature described below can be preferably used. For example, a mixed solution of high-boiling aliphatic amines and fat-soluble thiols can be used. Here, as the aliphatic amines, hexylamine (CH 13 NH2), heptylamine (C7H 15 NH2), octylamine (C8H 17 NH2), nonylamine (C9H 19 NH2), decylamine (C 10 H 21 NH2), dodecylamine (C 12 H 25 NH2), tetradecylamine (C 14 H 29 NH2), pentadecylamine (C 15 H 31 NH2), hexadecylamine (C 16 H 33 NH2), heptadecylamine (C 17 H 35 NH2), octadecylamine (C 18 H 37 NH2), oleylamine (C8H 17 CH=CHC8H 16 Among these aliphatic amines, oleylamine, which is liquid at room temperature and has a high boiling point of about 350°C, can be used particularly preferably.

[0084] In addition, as fat-soluble thiols, aliphatic thiols, dithiols, and aromatic thiols can be used. Among these fat-soluble thiols, 1-dodecanethiol (C ) having a high boiling point of about 270°C is particularly preferred. 12 H25 SH) can be used with particular preference.

[0085] Next, the Ag-Ge-S mixed solution is degassed under reduced pressure and then substituted with nitrogen. The reaction is then carried out by heat treatment at a predetermined reaction temperature to obtain a reaction product. The reaction temperature is preferably 150°C or higher but lower than 250°C. A reaction temperature lower than 150°C is too low, making it difficult for the particle-forming reaction to proceed. On the other hand, a reaction temperature higher than 250°C accelerates particle growth, resulting in coarse particles and potentially making it difficult to obtain dispersed, stable nanoparticles.

[0086] Therefore, as described above, the reaction temperature is preferably 150°C or higher and lower than 250°C, and more preferably 150°C or higher and 220°C or lower.

[0087] The reaction time is not particularly limited, but can be set to, for example, about 5 to 20 minutes. Particle growth can also be controlled by changing the reaction time, thereby adjusting the particle size to within a range of 9 nm or less. By adjusting the average particle size in this way, the emission wavelength fluctuates due to the quantum size effect, allowing the peak wavelength of the emission intensity to be controlled.

[0088] Furthermore, by controlling the above-mentioned reaction conditions (reaction temperature and reaction time), the molar ratio Ag / Ge can be adjusted. That is, even if the amounts of Ag compound, Ge compound, and S compound charged are the same, by changing the reaction conditions, it is possible to control not only the average particle size but also the molar ratio Ag / Ge within the range of the present invention.

[0089] The reaction mixture is then left to cool to room temperature, and then centrifuged to separate it into a supernatant and a precipitate. The supernatant is collected and the precipitate is discarded. A poor solvent such as methanol, ethanol, acetone, or acetonitrile is then added to the supernatant to produce a precipitate, which is then centrifuged again to separate and collect the precipitate.

[0090] It is preferable to repeat the procedure of adding a poor solvent, centrifuging, and recovering the precipitate several times, thereby producing a highly pure precipitate that does not contain impurities such as other phases.

[0091] Next, by dissolving this precipitate in a non-polar solvent such as chloroform, toluene, or hexane, the nanoparticles formed from Ag-Ge-S compound semiconductors are stably dispersed in the non-polar solvent, thereby producing a nanoparticle dispersion solution.

[0092] Thus, the method for producing semiconductor nanoparticles of the present invention includes the steps of weighing out an Ag compound, a Ge compound, and an S compound so that the content ratio of the Ag component to the Ge component in the resulting semiconductor nanoparticles is 1.0 or more and less than 7.5 in terms of molar ratio, dissolving the weighed material in a solvent to produce an Ag-Ge-S mixed solution, and heating the Ag-Ge-S mixed solution to a reaction temperature of 150°C or more and less than 250°C to produce semiconductor nanoparticles having an average particle size of 9 nm or less.Therefore, the particle production reaction proceeds effectively, and semiconductor nanoparticles having an average particle size of 9 nm or less can be easily obtained.

[0093] Furthermore, since the light-emitting body containing the semiconductor nanoparticles emits light in the near-infrared region with a wavelength of 700 to 1000 nm, it can be suitably applied to bioimaging technology as a labeling agent (biomarker) for biological substances. That is, the light-emitting body containing the semiconductor nanoparticles is adsorbed to biological tissue, and the light-emitting body is irradiated with near-infrared light to cause the light-emitting body to emit light. The image is dynamically analyzed, biological information is detected, and it becomes possible to efficiently confirm the effects of medication and the state of cells in regenerative medicine, cancer treatment, etc.

[0094] (Second embodiment)

[0095] FIG. 2 is a schematic diagram showing a second embodiment of semiconductor nanoparticles according to the present invention.

[0096] In this second embodiment, the Ag-Ge-S compound semiconductor obtained in the first embodiment is used as a core particle 11, and a coating layer (shell layer) 12 having a band gap energy larger than that of the core particle 11 is formed on the surface of the core particle 11, forming a core-shell structure. This makes it possible to obtain semiconductor nanoparticles with improved luminescence properties.

[0097] That is, when photon energy is applied to the Ag-Ge-S compound semiconductor serving as the core particle 11, as described in the first embodiment, the Ag-Ge-S compound semiconductor absorbs the light, electrons in the ground state valence band are excited to the conduction band, and holes are formed in the valence band. The excited electrons are then attracted by Coulomb force to the ground state valence band where holes exist, and the electrons and holes recombine to emit light.

[0098] However, as described above, the Ag-Ge-S-based compound semiconductor is an ultrafine particle with an average particle size of 9 nm or less. Because a large number of atoms are present on the particle surface of the compound semiconductor, the Ag-Ge-S-based compound semiconductor core particle 11 has many defects in its crystal structure on its surface. These defects create various energy levels, i.e., defect levels, between bands. Therefore, when excited electrons absorb light and transition from the conduction band to the valence band, the excited electrons return to the valence band while undergoing vibrational relaxation without emitting light due to the defect levels. This can lead to non-radiative deactivation, in which electrons that transition to the valence band do not emit light even when they recombine with holes, potentially resulting in a degradation of the luminescence characteristics. Therefore, to further improve the luminescence characteristics, it is necessary to reduce the surface defects of the core particle 11 and suppress non-radiative deactivation. To achieve this, it is considered preferable to form a coating layer (shell layer) 12 on the surface of the core particle 11 to seal the surface defects.

[0099] However, if the upper end of the band gap energy of the shell material forming the coating layer 12 is lower than the lower end of the band gap energy (lower end of the conduction band) of the core particle 11, the excited electrons will transition from the conduction band to a low energy level at the upper end of the band gap of the shell material, and then from this low energy level to the ground state valence band, resulting in a loss of light emission from the core particle 11.

[0100] Therefore, in this second embodiment, by forming a coating layer 12 having a band gap energy larger than the band gap energy of the core particle 11 on the surface of the core particle 11, it is possible to avoid loss of light emission from the core particle 11 and effectively seal surface defects of the core particle 11, thereby reducing non-radiative deactivation and suppressing energy loss, thereby enabling improvement of the light emission characteristics.

[0101] The shell material for forming the coating layer 12 is not particularly limited as long as it has a band gap energy larger than that of the core particle 11 (Ag—Ge—S compound semiconductor) as described above. For example, the main component is periodic table A compound containing at least one element Z1 selected from the group of elements belonging to groups 12, 13, and 14 of the periodic table and at least one element Z2 selected from the group of elements belonging to group 16 of the periodic table can be used. Element Z1 can be at least one element selected from the group of Zn, Ga, Sn, and Ge, and element Z2 can be at least one element selected from the group of S and O. AgGeS6, which is the stoichiometric composition of an Ag-Ge-S-based compound semiconductor, has a band gap energy of approximately 1.45 eV, so ZnS with a band gap energy of approximately 3.7 eV and GaS3 with a band gap energy of approximately 3.4 eV are suitable for the shell material.

[0102] Next, the method for producing semiconductor nanoparticles according to the second embodiment will be described in detail.

[0103] First, a dispersion of core particles made of an Ag-Ge-S compound semiconductor is prepared by the same method and procedure as in the first embodiment.

[0104] A predetermined amount of core particles is then collected from the core particle dispersion and thoroughly degassed. A solvent such as oleylamine is heated and stirred while being degassed under vacuum, and cooled to room temperature to prepare a dry solvent.

[0105] Next, a compound containing a plurality of raw materials for forming the coating layer 12 is prepared.

[0106] The raw material containing compounds include Zn, Ga, Sn, etc. periodic table A Z1 compound containing at least one element Z1 selected from Groups 12, 13, and 14, and a Z2 compound containing at least one element Z2 selected from Group 16 of the periodic table, to which S, O, etc. belong, can be used.

[0107] Among these compounds containing raw materials, Zn compounds containing Zn and S compounds containing S can be preferably used.

[0108] Here, the Zn compound is not particularly limited, and examples thereof include inorganic acid salts of Zn such as zinc acetate (Zn(CH3COO)2), zinc chloride (ZnCl2), zinc nitrate (Zn(NO3)2), and zinc iodide (ZnI2); zinc oleate (Zn(CH8H8O)2); 17 CH=CHC7H 14 COO)2), zinc myristate (Zn(C 13 H 27 Zn fatty acid salts such as COO)2) can be used, and bis(2,4-pentanedionato)zinc(II) represented by the chemical formula (1) can be preferably used.

[0109] [ka]

[0110] Moreover, as the S compound, thiourea (SC(NH2)2) can be preferably used.

[0111] Then, predetermined amounts of the core particles and the above-mentioned multiple raw material-containing compounds are weighed, these weighed materials are mixed, and after nitrogen substitution, the dry solvent is added to obtain a mixed solution. This mixed solution is then heat-treated at a temperature of about 50°C for a predetermined time. This results in a reaction product (core-shell particles) in which coating layers 12 having a larger band gap energy than the core particles 11 are formed on the surfaces of the core particles 11.

[0112] Next, this reaction product is left to cool for a predetermined time, and then centrifuged to remove coarse particles and separate it into a supernatant and a precipitate, using methods and procedures similar to those of the first embodiment.The supernatant is collected and the precipitate is discarded.A poor solvent such as methanol, ethanol, acetone, or acetonitrile is then added to the supernatant to produce a precipitate, which is then centrifuged again to discard the supernatant and separate and collect the precipitate.

[0113] As in the first embodiment, it is preferable to repeat the steps of adding a poor solvent, centrifuging, and recovering the precipitate several times, thereby removing coarse particles and producing an ultrafine precipitate that does not contain impurities such as heterogeneous phases.

[0114] Next, this precipitate is dried in the air and then dissolved in a non-polar solvent such as chloroform, toluene, or hexane, whereby the core-shell structured semiconductor nanoparticles are stably dispersed in the non-polar solvent, thereby producing a nanoparticle dispersion solution (core-shell particle dispersion solution) according to the second embodiment.

[0115] The core-shell structure of the semiconductor nanoparticles can be confirmed by performing a compositional analysis to detect the components of the shell material, and then observing the core particle 11 alone and the semiconductor nanoparticles under an electron microscope to compare their average particle diameters. The core-shell structure can also be confirmed by performing elemental analysis at regular intervals linearly from the edge of the semiconductor nanoparticles using an electron microscope. That is, in semiconductor nanoparticles with a core-shell structure, a large amount of shell components is detected near the edge, and a large amount of core components is detected near the center, so the core-shell structure can also be confirmed by such elemental analysis.

[0116] FIG. 3 is a schematic diagram of semiconductor nanoparticles showing a modified example of the second embodiment.

[0117] In this modification, a plurality of coating layers 12, 13 are formed in layers on the particle surface of the core particle 11 to form a core-shell-shell structure. The coating layers 12, 13 may be formed of the same material or different materials as long as they are made of materials having a band gap energy larger than that of the core particle 11.

[0118] By forming multiple coating layers 12, 13 on the particle surface of core particle 11 in this manner, core particle 11 is covered with a high-density coating, which makes it possible to further inactivate the surface, further suppress energy loss, and further improve luminescence properties. Also, although two coating layers 12, 13 are formed on the particle surface of core particle 11 in Figure 3, it is also preferable to form multiple coating layers of three or more layers.

[0119] Furthermore, like the first embodiment, the light-emitting body containing the semiconductor nanoparticles also emits light in the near-infrared region with a wavelength of 700 to 1000 nm, and therefore can be suitably applied to bioimaging technology as a labeling agent for biological substances.

[0120] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely one embodiment of the present invention, and it goes without saying that modifications are possible without departing from the spirit of the invention. For example, the semiconductor nanoparticles (core particles) may be formed of a compound semiconductor containing Ag, Ge, and S as the main components, and the molar ratio Ag / Ge and average particle size may satisfy the above-described ranges. This does not exclude substances that are inevitably mixed in during the manufacturing process, and any additives may be included as long as they do not affect the properties.

[0121] Furthermore, the light emitter containing the semiconductor nanoparticles of the present invention can be used as a labeling agent for biological substances as described above, and can also be used as a light source for exciting markers in vivo. For example, by filling the sealing portion of a blue light-emitting diode or an ultraviolet light-emitting diode with the semiconductor nanoparticles of the present invention, the semiconductor nanoparticles are excited by the blue light-emitting diode or the ultraviolet light-emitting diode and emit light in the near-infrared region of 700 to 1400 nm, and can be used as light in this wavelength region to excite markers in vivo.

[0122] Furthermore, the semiconductor nanoparticles can also be used as a sensitizing filter that increases the sensitivity of night-vision cameras, and can contribute to improving the sensitivity of night-vision cameras.

[0123] In addition, in the second embodiment described above, a coating layer is formed on the surface of the core particle to improve the luminescence properties, but the luminescence properties can also be improved by capping the surface of the core particle with a surface protective agent to remove surface defects as much as possible.

[0124] Next, examples of the present invention will be described in detail. [Example]

[0125] [Sample Preparation] (Sample No. 1) First, we prepared germanium glycolate (Ge(OCH2COO)2(HO)2) as a Ge source by using 97% pure glycolic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 99.99% pure germanium(IV) oxide (manufactured by Kojundo Chemical Research Institute, Ltd.).

[0126] Then, 1.25 g of glycolic acid and 0.5 g of germanium (IV) oxide were weighed out, and these weighed amounts were added to 25 cm of ultrapure water. 3 The mixture was placed in a three-neck flask along with a stirrer tip, and heated in an oil bath at 100°C for 1 hour while stirring with a magnetic stirrer to obtain a colorless, transparent mixed solution. This mixed solution was then evaporated and dried to obtain germanium glycolate.

[0127] Next, AgDDTC (manufactured by Dojindo Laboratories) was prepared as the Ag source, 98% pure thiourea (manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared as the S source, and 50% pure oleylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 98% pure 1-dodecanethiol (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) were prepared as the solvent.

[0128] Then, 0.075 mmol of AgDDTC, 0.046 mmol of germanium glycolate, and 0.100 mmol of thiourea were placed in test tubes, and 2.75 cm of oleylamine was added to each test tube. 3 , 1-dodecanethiol 0.25cm 3 The above was added together with a stirrer chip and stirred to prepare an Ag-Ge-S mixed solution.

[0129] Next, the inside of the test tube was degassed under reduced pressure, and then replaced with nitrogen gas. The mixture was heated at a reaction temperature of 200° C. for 10 minutes while stirring with a magnetic stirrer, thereby obtaining a black-brown suspension (reaction product).

[0130] The suspension was then air-cooled to room temperature and then centrifuged at 4000 rpm for 5 minutes to separate the supernatant and the precipitate. The supernatant was collected and the precipitate was discarded. Next, 3 cm of methanol was added to the collected supernatant. 3The mixture was centrifuged again at 4000 rpm for 5 minutes to separate the supernatant from the precipitate, and the supernatant was discarded. 3 The mixture was centrifuged again at 4000 rpm for 5 minutes to separate the supernatant from the precipitate, and the supernatant was discarded. The precipitate was then redispersed in chloroform (purity 99.5%, manufactured by Tokyo Chemical Industry Co., Ltd.) as a non-polar solvent to prepare sample number 1 (nanoparticle dispersion solution).

[0131] After the solvent was dried off, the sample of sample number 1 was subjected to a composition analysis using a scanning electron microscope-energy dispersive X-ray spectroscopy (hereinafter referred to as "SEM-EDX") (manufactured by Horiba, Ltd., EMAX Energy). The composition formula was determined to be Ag 38.2 Ge 21.2 S 40.6 The molar ratio of Ag / Ge was 1.8.

[0132] (Sample No. 2) Sample No. 2 was prepared using the same method and procedure as Sample No. 1, except that 0.025 mmol of AgDDTC, 0.043 mmol of germanium glycolate, and 0.100 mmol of thiourea were weighed out. After drying the solvent, Sample No. 2 was subjected to composition analysis using SEM-EDX, as in Sample No. 1. The composition formula was Ag 42.9 Ge 12.7 S 44.4 The molar ratio of Ag / Ge was 3.4.

[0133] (Sample No. 3) Sample No. 3 was prepared using the same method and procedure as Sample No. 1, except that 0.050 mmol of AgDDTC, 0.0375 mmol of germanium glycolate, and 0.100 mmol of thiourea were weighed out. After drying the solvent, Sample No. 3 was subjected to composition analysis using SEM-EDX, as in Sample No. 1. The composition formula was Ag 47.5 Ge 12.4 S 12.4 The molar ratio of Ag / Ge was 3.8.

[0134] (Sample No. 4) Sample No. 4 was prepared using the same method and procedure as Sample No. 1, except that 0.100 mmol of AgDDTC, 0.025 mmol of germanium glycolate, and 0.100 mmol of thiourea were weighed out. After drying the solvent, Sample No. 4 was subjected to composition analysis using SEM-EDX, as in Sample No. 1. The composition formula was found to be Ag 48.3 Ge 11.6 S 40.1 The molar ratio of Ag / Ge was 4.2.

[0135] (Sample No. 5) Sample No. 5 was prepared using the same method and procedure as Sample No. 1, except that 0.010 mmol of AgDDTC, 0.0475 mmol of germanium glycolate, and 0.100 mmol of thiourea were weighed out. After drying the solvent, Sample No. 5 was subjected to composition analysis using SEM-EDX, as in Sample No. 1. The composition formula was found to be Ag 37.8 Ge 8.73 S 53.5 The molar ratio of Ag / Ge was 4.3.

[0136] (Sample No. 6) Sample No. 6 was prepared using the same method and procedure as Sample No. 1, except that 0.133 mmol of AgDDTC, 0.017 mmol of germanium glycolate, and 0.100 mmol of thiourea were weighed out. After drying the solvent, Sample No. 6 was subjected to composition analysis using SEM-EDX, as in Sample No. 1. The composition formula was found to be Ag 51.3 Ge 7.01 S 38.2 The molar ratio of Ag / Ge was 7.3.

[0137] (Sample No. 7) A black-brown suspension was obtained using the same method and procedure as Sample No. 1, except that 0.133 mmol of AgDDTC, 0.017 mmol of germanium glycolate, and 0.100 mmol of thiourea were weighed out. The suspension was then air-cooled to room temperature and then centrifuged at 4,000 rpm for 5 minutes to separate the supernatant and precipitate. The supernatant was discarded, and the precipitate was recovered. Next, 3 cm of methanol was added to the recovered precipitate. 3 The mixture was centrifuged again at 4000 rpm for 5 minutes to separate the supernatant from the precipitate, and the supernatant was discarded. 3 The supernatant was discarded, and the resulting precipitate was re-dispersed in chloroform to prepare sample No. 7.

[0138] Next, as with sample number 1, the solvent was dried off and then composition analysis was performed using SEM-EDX. The composition formula was Ag 54.5 Ge 7.30 S 38.2 The molar ratio of Ag / Ge was 7.5.

[0139] (Sample No. 8) An attempt was made to prepare nanoparticles with the composition formula Ge2S using the same method and procedure as sample number 1, except that 0.050 mmol of germanium glycolate and 0.100 mmol of thiourea were weighed out and AgDDTC was not included in the sample. However, when the reaction product of germanium glycolate and thiourea was centrifuged as described above and then dispersed in chloroform, only a trace amount of white particles was confirmed, as described below. This sample was designated sample number 8.

[0140] (Sample No. 9) Sample No. 9 was prepared using the same method and procedure as Sample No. 1, except that 0.200 mmol of AgDDTC and 0.100 mmol of thiourea were weighed out and no germanium glycolate was contained in the sample.

[0141] [Sample evaluation] (Particle size measurement) For each of samples Nos. 1 to 6 and 9, a transmission electron microscope (hereinafter referred to as "TEM") (Hitachi High-Technologies Corporation, H-7650) was used to take a TEM image, and the area of ​​100 randomly selected particles was measured. Next, the circle-equivalent diameter of each particle was calculated from the measurements and the arithmetic mean was taken to determine the average particle size. Furthermore, the difference between the maximum particle size Dmax and the minimum particle size Dmin was calculated. Note that for sample No. 8, no nanoparticles were observed to be generated, and the particle size could not be measured.

[0142] (Measurement of absorption spectrum, emission spectrum, and emission quantum yield) The absorption spectrum of each of the samples Nos. 1 to 6 was measured using a diode array spectrophotometer (8453a manufactured by Agilent Technologies).

[0143] Furthermore, for each of the samples Nos. 1 to 6, an absolute luminescence quantum yield measurement apparatus (C9920-03 manufactured by Hamamatsu Photonics KK) was used to measure the emission spectrum and luminescence quantum yield at room temperature of 25° C. Furthermore, for the sample No. 7, the luminescence quantum yield was measured using the above-mentioned absolute luminescence quantum yield measurement apparatus.

[0144] (Evaluation of measurement results) 4 to 10 show TEM images of Samples Nos. 1 to 6 and 9. FIG.

[0145] Sample No. 9, which did not contain a Ge component, yielded coarse semiconductor particles with a particle size of 10 nm or more, as shown in Figure 10, whereas Samples Nos. 1 to 6, which contained a Ge component, yielded nanoparticle-shaped semiconductor particles with reduced particle size variation and uniformly or approximately uniformly dispersed, as shown in Figures 4 to 9. In other words, it was found that the Ge component contributes to nanoparticle formation in Ag-Ge-S-based compound semiconductors.

[0146] FIG. 11 shows the reaction products dispersed in chloroform, where (a) shows sample number 2, (b) shows sample number 8, and (c) shows sample number 9.

[0147] Sample No. 8 did not contain any Ag components and was simply a reaction between germanium glycolate and thiourea. As a result, as shown in Figure 11(b), only a small amount of ultrafine white particles was observed, and it was confirmed that no precipitates were formed and no nanoparticles were produced.

[0148] For sample number 9, black particles were obtained by reacting AgDTTC with thiourea. These black particles dispersed in chloroform but immediately precipitated, as shown in Figure 11(c).

[0149] On the other hand, as shown in Fig. 11(a), a black-brown precipitate dispersed in chloroform was obtained from sample number 2. Although not shown, similar black-brown precipitates were also obtained from samples 1 and 3 to 7.

[0150] Table 1 shows the composition formula, molar ratio Ag / Ge, average particle size, difference between maximum particle size Dmax and minimum particle size Dmin, and luminescence quantum yield for each of Samples 1 to 9. For Samples 8 and 9, the composition formula of the compound to be prepared is listed.

[0151] [Table 1]

[0152] Sample No. 9 did not contain Ge components, and as described above, the particles became coarse, with the average particle size being 17.4 nm, far exceeding 9 nm. The difference between the maximum particle size Dmax and the minimum particle size Dmin was also 5.8 nm, resulting in a large variation, and it was found that there was a risk that the quantum size effect would not be fully achieved.

[0153] As described above, sample No. 7 produced a dark brown precipitate, similar to samples Nos. 1 to 6. However, since the molar ratio of Ag / Ge was 7.5, meaning that the molar amount of Ag component relative to the Ge component was high, the luminescence quantum yield was as low as 0.4%, and it was found that sufficient luminescence efficiency could not be obtained.

[0154] In contrast, as shown in Table 1, samples 1 to 6 had a molar Ag / Ge ratio of 1.8 to 7.3, which is within the range of the present invention, and therefore had an average particle size of 6.2 to 7.0 nm, allowing for nanoparticles of 9 nm or less. Furthermore, the difference between the maximum particle size Dmax and the minimum particle size Dmin was 1.6 to 2.6 nm, suppressing it to 3 nm or less. Furthermore, as shown in Table 1, the luminescence quantum efficiency was 0.7 to 1.2%, indicating that a luminescence quantum yield of 0.5% or more could be obtained.

[0155] 12 to 17 show the absorption spectra of each of the samples Nos. 1 to 6, with the horizontal axis representing wavelength (nm) and the vertical axis representing absorption coefficient (au). Note that in these absorption spectra, the absorption coefficient on the vertical axis has been normalized to the same standard so that the characteristics of each sample can be compared and evaluated.

[0156] 12 to 17, Samples 1 to 6 all have similar characteristics. That is, the absorption coefficient decreases along a continuous curve as the wavelength increases, and the wavelength of the trailing edge is approximately 800 nm in all cases. Therefore, this wavelength is considered to be the absorption edge wavelength.

[0157] 18 to 23 show the emission spectra of each of Samples 1 to 6, with the horizontal axis representing wavelength (nm) and the vertical axis representing emission intensity (au). As with the absorption spectra, the emission intensity on the vertical axis of these emission spectra is normalized to the same standard so that the characteristics of each sample can be compared and evaluated.

[0158] 18 to 23, it is clear that samples 1 to 6 emit light in the wavelength region of 1000 nm or less, which is at or near the absorption edge wavelength or longer than the absorption edge wavelength. In particular, samples 1, 2, and 4 (FIGS. 18, 19, and 21) were confirmed to have a mountain-shaped peak in emission intensity near 820 to 850 nm, which is near the absorption edge wavelength.

[0159] From the above, it was found that even Ag-Ge-S-based compound semiconductors that do not contain components such as Cd, Se, or In can emit light in the near-infrared region of 700 to 1000 nm by specifying the molar ratio Ag / Ge and the average particle size.Since the average particle size is also 9 nm or less, it is possible to exhibit the quantum size effect, and semiconductor nanoparticles that are safe and easy to handle and can be applied to a variety of fields can be obtained. [Example]

[0160] Samples were prepared using different reaction temperatures during synthesis, and the properties of each sample were evaluated. Similar to sample 2, 0.025 mmol of AgDDTC, 0.043 mmol of germanium glycolate, and 0.1 mmol of thiourea were weighed out, and the reaction temperatures were varied to 150°C (sample 2a), 220°C (sample 2b), and 250°C (sample 3). The samples were prepared using the same method and procedure as sample 1.

[0161] Next, the absorption spectrum and emission spectrum of each of the samples 2a to 2c were measured using the same method and procedure as in Example 1.

[0162] 24 shows the absorption spectra of samples 2a to 2c, with the horizontal axis representing wavelength (nm) and the vertical axis representing absorption coefficient (au). For comparison, the absorption spectrum of sample 2 is also shown.

[0163] 25 shows the emission spectra of samples 2a to 2c, with the horizontal axis representing wavelength (nm) and the vertical axis representing emission intensity (au). For comparison, the emission spectrum of sample 2 is also shown.

[0164] 24 and 25, the absorption coefficient and emission intensity on the vertical axis are normalized to the same standard so that the characteristics of each sample can be compared and evaluated. Therefore, the emission spectrum of sample number 2 is characteristically identical to the emission spectrum in FIG.

[0165] As is clear from FIG. 24, like sample number 2, samples 2a to 2c also have profiles in which the absorption edge wavelength is approximately 800 nm.

[0166] As shown in Figure 25, all of Samples 2a to 2c and 2 emit light in the near-infrared region with a wavelength of 700 to 1000 nm. In particular, Sample 2a, for which the reaction temperature was 150°C, exhibited a more pronounced peak in the emission intensity than Samples 2, 2b, and 2c, demonstrating favorable emission characteristics. Thus, it was confirmed that the reaction for producing semiconductor nanoparticles proceeded effectively by carrying out the reaction at 150°C, resulting in exceptionally favorable emission characteristics. [Example]

[0167] A core-shell structured sample (sample number 12) was prepared and its properties were compared with those of the core particle sample (sample number 11) and evaluated.

[0168] [Sample preparation] (Sample No. 11) As with sample number 2, 0.025 mmol of AgDDTC, 0.043 mmol of germanium glycolate, and 0.1 mmol of thiourea were placed in test tubes, and 2.75 cm of oleylamine was added to each test tube. 3 , 1-dodecanethiol 0.25cm 3 was added together with a stirrer tip to prepare an Ag-Ge-S mixed solution.

[0169] Next, the inside of the test tube was degassed under reduced pressure, and then replaced with nitrogen gas. The mixture was heated at a reaction temperature of 150° C. for 20 minutes while stirring with a magnetic stirrer, thereby obtaining a black-brown suspension (reaction product).

[0170] Thereafter, the same procedures as those for Sample No. 1 in Example 1 were followed: adding methanol, centrifuging, and recovering the precipitate. The resulting precipitate was redispersed in chloroform to prepare Sample No. 11 (core particle dispersion solution).

[0171] (Sample No. 12) For sample number 11, a sample of 5 nmol in terms of particle number was collected in a test tube and subjected to degassing treatment under reduced pressure for approximately 10 hours.

[0172] Furthermore, the oleylamine used as the solvent in Example 1 was heated and stirred at 100° C. for 1 hour while being degassed under reduced pressure, and then air-cooled to room temperature, thereby obtaining dry oleylamine.

[0173] Next, a Zn compound and an S compound were prepared as raw material-containing compounds. Here, bis(2,4-pentanedionato)zinc(II) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the Zn compound, and thiourea (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the S compound. 2.63 mg of bis(2,4-pentanedionato)zinc(II) and 0.75 mg of thiourea were added to the test tube containing the sample of sample number 11, and then the air was replaced with nitrogen gas. Next, 3 cm of the dried oleylamine was added to the test tube. 3 This mixed solution was then heated at 50°C for 15 minutes to obtain a reaction product.

[0174] The reaction mixture was then left to cool for 20 minutes, and then centrifuged at 4000 rpm for 5 minutes to separate the mixture into a supernatant and a precipitate. The supernatant was collected, and the precipitate was discarded. Next, 3 cm of methanol was added to the collected supernatant. 3 The mixture was centrifuged again at 4000 rpm for 5 minutes to separate the supernatant from the precipitate, and the supernatant was discarded. 3 The supernatant was discarded and the resulting precipitate was dried in the air. After that, the resulting precipitate was diluted with 2 cm of chloroform. 3 The mixture was dispersed in the following manner to prepare sample number 12 (core-shell particle dispersion solution).

[0175] [Sample evaluation] Fig. 26 is a TEM image of sample number 12. As is clear from Fig. 26, sample number 12, like sample numbers 1 to 6, was found to produce nanoparticulate semiconductor particles in which particle size variation was suppressed and which were uniformly or approximately uniformly dispersed.

[0176] For each of Samples 11 and 12, TEM images were taken, and the areas of 100 randomly selected particles were measured, and the equivalent-circle diameters of each particle were calculated from the measurements and the arithmetic mean was taken to determine the average particle size. The standard deviation σ of each sample was also calculated.

[0177] Next, for each of the samples Nos. 11 and 12, composition analysis was carried out using SEM-EDX in the same manner as in Example 1, and the Zn content in the sample was determined.

[0178] Furthermore, for each of the samples Nos. 11 and 12, the absorption spectrum and emission spectrum were measured in the same manner and procedure as in Example 1, and the emission quantum yield was calculated.

[0179] Table 2 shows the measurement results.

[0180] [Table 2]

[0181] The average particle size was determined from the TEM images of sample No. 12 and sample No. 11 (not shown). As shown in Table 2, the average particle size of sample No. 11 was 4.00 nm, while that of sample No. 12 was 4.89 nm, indicating that sample No. 12 had a larger average particle size than sample No. 11. This is thought to be because, in sample No. 12, bis(2,4-pentanedionato)zinc(II) and thiourea were added to the core particle sample of sample No. 11 and then heat-treated, forming a coating layer on the surface of the core particle, which resulted in the larger average particle size.

[0182] Note that sample No. 11 had the same charge amount as sample No. 2, but because the reaction conditions were different, the average particle size was 4.00 nm, which was smaller than that of sample No. 2 (5.7 nm). That is, sample No. 2 was reacted at a high reaction temperature of 200°C, which promoted particle growth and resulted in a coarse average particle size of 5.7 nm, whereas sample No. 11 was reacted at a reaction temperature of 150°C, which appears to have suppressed excessive particle growth and resulted in ultrafine particles with an average particle size of 4.00 nm.

[0183] Furthermore, as shown in Table 2, the standard deviation σ of sample No. 11 was 0.66 nm, while that of sample No. 12 was 0.65 nm, and it was found that sample No. 12 was able to secure a standard deviation σ almost equivalent to that of sample No. 11.

[0184] Fig. 27 is a histogram of sample number 12. In the figure, the horizontal axis represents particle size (nm) and the vertical axis represents frequency (%).

[0185] As shown in FIG. 27, the particle size distribution of sample No. 12 had a mountain-shaped peak, and it was found that the particles were spherical and dispersed almost uniformly.

[0186] Furthermore, the composition analysis results for sample number 12 were Ag: 23.5 atomic %, Ge: 4.6 atomic %, Zn: 26.4 atomic %, and S: 45.5 atomic %. That is, sample number 11 did not contain a Zn component, and therefore was substantially free of such a Zn component, whereas sample number 12 contained 26.4 atomic % of the Zn component. That is, from this composition analysis result, it was confirmed that sample number 12 was a semiconductor nanoparticle with a core-shell structure in which a shell layer (coating layer) made of ZnS was formed on the surface of a core particle.

[0187] As mentioned above, sample No. 11 had the same charge amount as sample No. 2, but the molar Ag / Ge ratio was also higher than that of sample No. 2. Specifically, as a result of composition analysis, sample No. 11 had 32.7 atomic % Ag, 7.9 atomic % Ge, and 59.4 atomic % S, resulting in a molar Ag / Ge ratio of 4.1, whereas sample No. 2 had 42.9 atomic % Ag, 12.7 atomic % Ge, and 44.4 atomic % S, resulting in a molar Ag / Ge ratio of 3.4 (see Example 1, Table 1). Therefore, sample No. 11 had a higher molar Ag / Ge ratio than sample No. 2. This is thought to be because sample No. 2 was heat-treated at a reaction temperature of 200°C, while sample No. 11 was heat-treated at a reaction temperature of 150°C. It was also found that by changing the reaction conditions in this way, not only the average particle size but also the molar ratio of the reactants could be controlled.

[0188] Figure 28 shows the absorption spectrum profiles of sample No. 11 and sample No. 12. The spectra are normalized to the same standard so that the characteristics of both samples can be compared and evaluated. In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents absorption coefficient (au).

[0189] 28, Sample No. 11 and Sample No. 12 show almost the same absorption spectrum. In particular, there is no difference in characteristics in the region near the absorption edge wavelength of 800 nm, and therefore it was confirmed that the formation of a shell layer (coating layer) does not change the absorption spectrum of the compound semiconductor forming the core particle.

[0190] Figure 29 shows the emission spectrum profiles of sample No. 11 and sample No. 12. The spectra are normalized to the same standard so that the characteristics of both samples can be compared and evaluated. In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents emission intensity (au).

[0191] As is clear from Figure 29, Sample No. 12 exhibits improved luminescence intensity compared to Sample No. 11. Furthermore, as shown in Table 2, Sample No. 12 exhibited improved luminescence quantum yield, from 3.1% for Sample No. 11 to 5.9% for Sample No. 12. Specifically, Sample No. 12 has core particles coated with ZnS (bandgap energy: approximately 3.7 eV), which has a larger bandgap energy than the Ag-Ge-S compound semiconductor of Sample No. 11 (approximately 1.45 eV). This allows light to be emitted without loss of luminescence from the core particles. Furthermore, because the surface defects of the core particles are sealed with the coating layer, surface defects are reduced, making it possible to suppress non-radiative deactivation processes. This has confirmed that the luminescence quantum yield can be improved, and semiconductor nanoparticles with high luminescence intensity and improved luminescence properties can be obtained. [Industrial Applicability]

[0192] By forming semiconductor nanoparticles from Ag-Ge-S compound semiconductors with an Ag / Ge molar ratio of 1.0 or more but less than 7.5, preferably 1.8 or more but less than 7.3, and an average particle size of 9 nm or less, they can emit light in the near-infrared region of 700 to 1000 nm, have a low environmental impact, and do not require special precautions regarding toxic substances or the health of manufacturing workers. These semiconductor nanoparticles are easy to handle and can be used in a variety of industrial fields, such as as a labeling agent for biological materials in bioimaging technology, a light source, or a sensitizing filter for night-vision cameras. By giving these semiconductor nanoparticles a core-shell structure, light emitters with improved luminous efficiency can be realized. [Explanation of symbols]

[0193] 11 Semiconductor nanoparticles, core particles 12 Covering layer 13 Covering layer

Claims

1. The semiconductor layer is made of a compound semiconductor containing Ag, Ge, and S as its main components, a content ratio of the Ag component to the Ge component, converted into a molar ratio, of 1.0 or more and less than 7.5; Semiconductor nanoparticles having an average particle size of 9 nm or less.

2. 2. The semiconductor nanoparticles according to claim 1, wherein the content ratio is 1.8 or more and 7.3 or less in terms of molar ratio.

3. 3. The semiconductor nanoparticles according to claim 1, wherein the difference between the maximum and minimum particle diameters is 3 nm or less.

4. 3. The semiconductor nanoparticles according to claim 1 or 2, which are capable of emitting light in the wavelength range of 700 to 1000 nm.

5. The semiconductor nanoparticle according to claim 1 or 2, characterized in that a coating layer made of a material having a band gap energy larger than that of the compound semiconductor is formed on the surface of a core particle made of the compound semiconductor, thereby forming a core-shell structure.

6. The semiconductor nanoparticle according to claim 5, characterized in that the coating layer is formed from a compound whose main component contains at least one element Z1 selected from the group of elements belonging to groups 12, 13, and 14 of the periodic table, and at least one element Z2 selected from the group of elements belonging to group 16 of the periodic table.

7. 7. The semiconductor nanoparticles according to claim 6, wherein the element Z1 includes at least one element selected from the group consisting of Zn, Ga, Sn, and Ge.

8. 7. The semiconductor nanoparticles according to claim 6, wherein the element Z2 includes at least one element selected from the group consisting of S and O.

9. 6. The semiconductor nanoparticle according to claim 5, wherein the coating layer is formed in a layered form on the surface of the core particle.

10. A method for producing semiconductor nanoparticles containing a compound semiconductor mainly composed of an Ag component, a Ge component, and an S component, comprising: weighing out an Ag compound, a Ge compound, and an S compound so that the content ratio of the Ag component to the Ge component in the compound semiconductor is equal to or greater than 1.0 and less than 7.5 in terms of molar ratio, and dissolving the weighed materials in a solvent to prepare an Ag-Ge-S mixed solution; and heating the Ag—Ge—S mixed solution to a reaction temperature of 150° C. or higher but lower than 250° C. to synthesize a compound semiconductor having an average particle size of 9 nm or less.

11. 11. The method for producing semiconductor nanoparticles according to claim 10, wherein the reaction temperature is 220° C. or less.

12. 12. The method for producing semiconductor nanoparticles according to claim 10, wherein the semiconductor nanoparticles are dispersed in a non-polar solvent.

13. 13. The method for producing semiconductor nanoparticles according to claim 12, wherein the non-polar solvent is chloroform.

14. 11. The method for producing semiconductor nanoparticles according to claim 10, wherein the Ag compound includes silver N,N-diethyldithiocarbamate.

15. 11. The method for producing semiconductor nanoparticles according to claim 10, wherein the Ge compound includes a reaction product of a hydroxy acid and a germanium oxide.

16. 16. The method for producing semiconductor nanoparticles according to claim 15, wherein the hydroxy acid includes glycolic acid.

17. 11. The method for producing semiconductor nanoparticles according to claim 10, wherein the S compound includes thiourea.

18. 11. The method for producing semiconductor nanoparticles according to claim 10, wherein the solvent contains a combination of an aliphatic amine having a boiling point higher than the reaction temperature and a fat-soluble thiol.

19. 19. The method for producing semiconductor nanoparticles according to claim 18, wherein the aliphatic amines include oleylamine.

20. 20. The method for producing semiconductor nanoparticles according to claim 18 or 19, wherein the fat-soluble thiols include 1-dodecanethiol.

21. 12. The method for producing semiconductor nanoparticles according to claim 10 or 11, further comprising the steps of: preparing a plurality of compounds containing raw materials for forming a coating layer having a larger band gap energy than the compound semiconductor; mixing the compound semiconductor with the plurality of compounds containing raw materials; and subjecting the mixture to a heat treatment to form a coating layer on the surface of a core particle made of the compound semiconductor, thereby producing semiconductor nanoparticles having a core-shell structure.

22. 22. The method for producing semiconductor nanoparticles according to claim 21, wherein the raw material-containing compound comprises a Z1 compound containing at least one element Z1 selected from the group of elements belonging to Groups 12, 13, and 14 of the periodic table, and a Z2 compound containing at least one element Z2 selected from the group of elements belonging to Group 16 of the periodic table.

23. 23. The method for producing semiconductor nanoparticles according to claim 22, wherein the Z1 compound includes a Zn compound, and the Z2 compound includes an S compound.

24. 24. The method for producing semiconductor nanoparticles according to claim 23, wherein the Zn compound contains bis(2,4-pentanedionato)zinc(II).

25. 24. The method for producing semiconductor nanoparticles according to claim 23, wherein the S compound includes thiourea.

26. 22. The method for producing semiconductor nanoparticles according to claim 21, wherein the semiconductor nanoparticles are dispersed in a non-polar solvent.

27. 27. The method for producing semiconductor nanoparticles according to claim 26, wherein the non-polar solvent is chloroform.

28. A light-emitting body comprising the semiconductor nanoparticles according to claim 1.

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