Semiconductor nanoparticles composed of AgAuS-based compounds

Abstract

The present invention provides semiconductor nano-particles comprising semiconductor crystals of a compound containing Ag, Au and S as essential constituent elements. An AgAuS-based compound constituting the semiconductor nano-particles contains Ag, Au and S in a total amount of 95% by mass or more. The compound is preferably an AgAuS three-component compound represented by general formula: Ag(nx)Au(ny)S(nz). In the formula, n represents an arbitrary positive integer; x, y and z respectively represent number-based content ratios of Ag, Au and S atoms in the compound, and independently represent a real number satisfying the following formula 0 < x,y,z ≦ 1; and x / y is 1 / 7 to 7 inclusive.

Description

Technical Field

[0001] The present invention relates to semiconductor nanoparticles composed of AgAuS-based compounds. More specifically, it relates to ternary compounds composed of Ag, Au, and S, and semiconductor nanoparticles having a novel structure.

Background Art

[0002] Semiconductors exhibit the quantum confinement effect when made into nanoparticles on the nanoscale and show a bandgap corresponding to the particle size. Therefore, by controlling the composition and particle size of semiconductor nanoparticles to adjust the bandgap, the emission wavelength and absorption wavelength can be arbitrarily set. Semiconductor nanoparticles utilizing this property are also referred to as quantum dots (QD) and are expected to be utilized in various technical fields.

[0003] For example, semiconductor nanoparticles are being studied for use as light-emitting elements, fluorescent substances, etc. used in display devices and marker substances for detecting biological-related substances. As described above, in addition to being able to freely control the emission wavelength by controlling the particle size, the emission peak width of semiconductor nanoparticles is sufficiently narrower than that of organic dyes and is more stable than organic dyes under excitation light irradiation. Therefore, applications to light-emitting elements and the like can be expected.

[0004] Also, semiconductor nanoparticles are expected to be used in photoelectric conversion elements and light-receiving elements mounted on solar cells, optical sensors, etc. In addition to being able to control the absorption wavelength by the particle size, they also have the characteristics of having a high quantum efficiency and a high absorption coefficient. Due to this property, semiconductor nanoparticles can contribute to the miniaturization and thinning of semiconductor devices.

[0005] As specific configurations of semiconductor nanoparticles, there are known semiconductor nanoparticles composed of binary compound semiconductors such as group 12-group 16 compound semiconductors like CdS, CdSe, CdTe, and group 14-group 16 compound semiconductors like PbS, PbSe, and ternary compound semiconductors such as group 11-group 13-group 16 compound semiconductors like AgInTe2 (Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] Semiconductor nanoparticles that are being applied to the various uses described above are still in the research stage, and the optimal ones, including their manufacturing methods, have not been found. Under these circumstances, there is a great demand for the development of nanoparticles applying a novel compound semiconductor having the above-described specific properties due to the quantum confinement effect and properties in practical aspects such as biocompatibility (low-toxicity composition). The present invention has been made under the above background, and provides semiconductor nanoparticles composed of a novel compound semiconductor not found in the composition examples reported so far, which have appropriate light-emitting and light-absorbing properties and also biocompatibility.

Means for Solving the Problems

[0008] The present invention for solving the above problems is semiconductor nanoparticles composed of a semiconductor crystal of a compound containing Ag, Au, and S as essential constituent elements, wherein the total content of Ag, Au, and S in the compound is 95% by mass or more.

[0009] In conventional research examples, Ag and Au have each been used as constituent elements of semiconductor nanoparticles separately, but there are no specific studies on the characteristics when ternary compound semiconductors containing both Ag and Au are made into nanoparticles. In this regard, according to the studies of the present inventors, it has been confirmed that AgAuS-based compound semiconductors exhibit suitable light-emitting and light-absorbing characteristics by nanoparticle formation and adjustment of the compositions of Ag and Au.

[0010] Also, both Ag and Au are chemically relatively stable metals and have long been known as metals with biocompatibility. And S is an essential element of the living body and an element with biocompatibility. Therefore, AgAuS-based compound semiconductors can also be expected to be applied to fluorescent substances and the like used in the human body such as markers and DNA chips.

[0011] Hereinafter, semiconductor nanoparticles composed of AgAuS-based compound semiconductors according to the present invention and a method for manufacturing the same will be described.

[0012] A Composition of the Semiconductor Nanoparticles According to the Present Invention As described above, the semiconductor nanoparticles according to the present invention are semiconductor nanoparticles composed of a compound having Ag, Au, and S as essential constituent elements. The compound composed of Ag, Au, and S is specifically, as a general formula, Ag (nx) Au (ny) S (nz) which is an AgAuS ternary compound represented by. At this time, n is an arbitrary positive integer. x, y, and z indicate the ratios of the number of atoms of Ag, Au, and S in the compound, and are real numbers such that 0 < x, y, z ≦ 1. Also, regarding the atomic number ratios x and y of Ag and Au, x / y is 1 / 7 or more and 7 or less. The atomic number ratio z of S is, as described above, a real number such that 0 < z ≦ 1, but it is preferably a real number having z ≧ (x + y) / 2.

[0013] The AgAuS-based compounds in the present invention include, more specifically, Ag1Au7S4, AgAu3S2, Ag3Au5S4, AgAuS, Ag5Au3S4, Ag3AuS2, and Ag7AuS4. These AgAuS-based compounds with specific compositions are compounds with a stoichiometric composition where nx, ny, and nz are integers. However, the compounds constituting the semiconductor nanoparticles of the present invention are not limited to such compounds with a stoichiometric composition.

[0014] Also, regarding the atomic ratios x and y of Ag and Au, it is more preferable that x / y is 0.3 or more and 3.6 or less. Further, it is more preferable that x / (x + y) is a real number of 0.33 or more and 0.78 or less. Among the AgAuS-based compounds with the stoichiometric compositions listed above, AgAuS, Ag5Au3S4, and Ag3AuS2 meet these conditions. Semiconductor nanoparticles composed of these compounds have a relatively high emission quantum yield and exhibit more effective characteristics as light-emitting elements and the like.

[0015] As described above, the semiconductor nanoparticles according to the present invention are composed of an AgAuS-based compound represented by Ag (nx) Au (ny) S (nz) This AgAuS-based compound is not necessarily composed of a single phase and may be composed of a mixed phase. For example, a mixed phase of the AgAuS-based compound with the stoichiometric composition described above (such as Ag3AuS2) and an AgAuS-based compound that does not have a stoichiometric composition (Ag (nx) Au (ny) S (nz) : nx, ny, nz are real numbers that are not integers within the above range) may be acceptable.

[0016] The semiconductor nanoparticles according to the present invention are composed of semiconductor crystals of a compound having the above structure with Ag, Au, and S as essential constituent elements. The total content of Ag, Au, and S in this semiconductor crystal is 95% by mass or more. Elements that may be contained in addition to the essential constituent elements Ag, Au, and S include Ge, Si, Sn, Pb, O, Se, Te, etc. These elements are acceptable if they are less than 5% by mass. However, it is preferable that the total content of Ag, Au, and S in the compound is 99% by mass or more, and more preferably 99.9% by mass or more. Here, the composition value of the compound is the value of the semiconductor crystal itself in the semiconductor nanoparticles and does not include the components of the protective agent described later.

[0017] The semiconductor nanoparticles according to the present invention preferably have an average particle size of 2 nm or more and 20 nm or less. The particle size of the semiconductor nanoparticles is related to the adjusting action of the bandgap due to the quantum confinement effect. In order to exhibit suitable light emission and light absorption characteristics by adjusting the bandgap, it is preferable to have the above average particle size. The average particle size of the semiconductor nanoparticles can be obtained by observing a plurality (preferably 100 or more) of particles with an electron microscope such as TEM, measuring the particle size of each particle, and calculating the number average.

[0018] In addition, in the semiconductor nanoparticles according to the present invention, as a protective agent, at least one of an alkylamine having 4 to 20 carbon atoms in the alkyl chain, an alkenylamine having 4 to 20 carbon atoms in the alkenyl chain, an alkylcarboxylic acid having 3 to 20 carbon atoms in the alkyl chain, an alkenylcarboxylic acid having 3 to 20 carbon atoms in the alkenyl chain, an alkanethiol having 4 to 20 carbon atoms in the alkyl chain, a trialkylphosphine having 4 to 20 carbon atoms in the alkyl chain, a trialkylphosphine oxide having 4 to 20 carbon atoms in the alkyl chain, triphenylphosphine, and triphenylphosphine oxide is preferably bonded to the particle surface. When handling semiconductor nanoparticles, it is often made into a solution (sometimes referred to as a slurry or ink) in which the semiconductor nanoparticles are dispersed in an appropriate dispersion medium. The above protective agent is useful for suppressing the aggregation of semiconductor nanoparticles in the solution to form a uniform solution or the like. Further, the protective agent acts also in forming nanoparticles having a suitable average particle size by being added to the reaction system together with the raw materials in the synthesis step of the AgAuS compound. Incidentally, the protective agent can be applied by using the above alkylamine, alkenylamine, alkylcarboxylic acid, alkenylcarboxylic acid, alkanethiol, trialkylphosphine, trialkylphosphine oxide, triphenylphosphine, and triphenylphosphine oxide alone or in combination of a plurality of them.

[0019] As described above, depending on the particle size of the semiconductor nanoparticles, the band gap is adjusted by the quantum confinement effect, and the light absorption characteristics change. In the semiconductor nanoparticles according to the present invention, those having an absorption edge wavelength on the long wavelength side of the absorption spectrum of 600 nm or more are preferable. Thereby, the semiconductor nanoparticles have absorbability and responsiveness to light in the visible region to the near-infrared region.

[0020] By appropriately applying and supporting the semiconductor nanoparticles according to the present invention on a suitable substrate or carrier, they can be applied to various applications such as light-emitting elements described above. There are no particular restrictions on the composition, shape, and dimensions of this substrate or carrier. Examples of the substrate on a plate or foil include glass, quartz, silicon, ceramics, or metal. Also, examples of the granular or powdery carrier include inorganic oxides such as ZnO, TiO2, WO3, SnO2, In2O3, and Al2O3. Further, the semiconductor nanoparticles may be supported on the inorganic oxide carrier and further fixed to the substrate.

[0021] Also, when applying and supporting the semiconductor nanoparticles on the substrate or carrier, as described above, a solution, slurry, or ink in which the semiconductor nanoparticles are dispersed in a suitable dispersion medium is often used. As the dispersion medium for this solution, etc., chloroform, toluene, cyclohexane, hexane, etc. can be applied. And as the coating method for the solution of the semiconductor nanoparticles, etc., dipping, spin coating method, and as the supporting method, various methods such as dropping method, impregnation method, adsorption method, etc. can be applied.

[0022] B Method for manufacturing semiconductor nanoparticles according to the present invention The semiconductor nanoparticles applying the AgAuS-based compound semiconductor according to the present invention can be manufactured by mixing an Ag precursor, an Au precursor, and, if necessary, an S precursor which is a sulfur source in a reaction solvent, and heating the reaction system composed of these at a temperature of 100°C or higher and 200°C or lower. As described above, it is preferable to add at least one of an alkylamine having an alkyl chain carbon number of 4 or more and 20 or less, an alkenylamine having an alkenyl chain carbon number of 4 or more and 20 or less, an alkylcarboxylic acid having an alkyl chain carbon number of 3 or more and 20 or less, an alkenylcarboxylic acid having an alkenyl chain carbon number of 3 or more and 20 or less, an alkanethiol having an alkyl chain carbon number of 4 or more and 20 or less, a trialkylphosphine having an alkyl chain carbon number of 4 or more and 20 or less, a trialkylphosphine oxide having an alkyl chain carbon number of 4 or more and 20 or less, triphenylphosphine, and triphenylphosphine oxide as a protective agent to the reaction system.

[0023] As the Ag precursor and Au precursor used as raw materials, an Ag salt or Ag complex and an Au salt or Au complex are respectively applied. The Ag precursor and Au precursor are preferably salts or complexes containing monovalent Ag and monovalent Au. However, for the Au precursor, a precursor containing trivalent Au can be used. This is because trivalent Au is reduced to monovalent Au by a solvent or a coexisting sulfur compound during the synthesis process of the semiconductor nanoparticles. Further, as the Ag precursor and Au precursor, it is preferable to apply a complex having a ligand containing at least one sulfur (S) atom. In that case, the sulfur atom contained in the ligand of the Ag complex and / or Au complex can be used as the sulfur source of the AgAuS-based compound, and the compound can be synthesized.

[0024] Suitable Ag precursors include silver acetate (Ag(OAc)), silver nitrate, silver carbonate, silver oxide, silver oxalate, silver chloride, silver iodide, silver(I) cyanide salt, etc. Also, suitable Au precursors include Au resinate (C 10 H 18 Au2S2:CAS68990-27-2), chloro(dimethyl sulfide)gold(I) ((CH3)2SAuCl), gold(I) iodide, gold(I) sulfite salt, chloroauric acid(III), gold(III) acetate, gold(I) cyanide salt, gold(III) cyanide salt, 1,10-phenanthroline gold(III), etc. Also, as the sulfur compound serving as the S precursor, in addition to elemental sulfur, compounds such as thiourea, alkylthiourea, thioacetamide, alkanethiol, and compounds such as β-dithiones, dithiols, xanthate salts, and diethyldithiocarbamate salts can be applied. Note that even if the Ag complex and Au complex are complexes having a ligand containing an S atom, an S compound may be added.

[0025] Here, the composition of the synthesized AgAuS-based compound (general formula Ag (nx) Au (ny) S (nz)(x, y) in it can be adjusted by the mixing ratio (charged atomic ratio) of the Ag precursor and the Au precursor. To obtain a suitable AgAuS-based compound, regarding the charged amount of the Ag precursor and the charged amount of the Au precursor, when the ratio of the metal atoms contained therein (Ag:Au) is set as a:b, it is preferable to set a:b within the range of 0.78:0.22 to 0.14:0.86 in atomic ratio. Also, regarding the amount of S (c) in the reaction system, it is preferably 0.25 or more and 4 or less in atomic ratio with respect to the total number of atoms of Ag and Au in the reaction system. However, regarding the sulfur source, even if there is excess S in the reaction system, the influence on the composition of the AgAuS-based compound is small.

[0026] The reaction system in the synthesis of semiconductor nanoparticles can be generated without a solvent, or a solvent may be used. When using a solvent, octadecene, tetradecane, oleic acid, oleylamine, dodecanethiol, or a mixture thereof, etc. can be applied.

[0027] The heating temperature (reaction temperature) of the reaction system composed of the Ag precursor, the Au precursor, the S precursor, and the protective agent is set to 50°C or higher and 200°C or lower. If it is less than 50°C, the synthesis of the AgAuS-based compound hardly proceeds. On the other hand, if it exceeds 200°C, there are problems such as Au forming nanoparticles alone and the possibility that a compound with the desired composition may not be generated. The average particle size of the semiconductor nanoparticles increases with the increase in the reaction temperature, but it rarely exceeds a suitable average particle size within the above temperature range. A more suitable reaction temperature is 100°C or higher and 165°C or lower. Also, the heating time (reaction time) can be adjusted according to the charged amount of the raw materials, but it is preferably 1 minute or more and 60 minutes or less. Incidentally, during the synthesis reaction of the semiconductor nanoparticles, it is preferable to stir the reaction system.

[0028] After the synthesis reaction of the semiconductor nanoparticles is completed, the reaction system is cooled as necessary, and the semiconductor nanoparticles are recovered. At this time, an alcohol (ethanol, methanol, etc.) serving as a non-solvent is added to precipitate the nanoparticles, or the semiconductor nanoparticles are precipitated and recovered by centrifugation or the like. After the particles are once washed with an alcohol (ethanol, methanol, etc.), they may be uniformly dispersed in a good solvent such as chloroform.

Advantages of the Invention

[0029] As described above, the present invention relates to semiconductor nanoparticles composed of an AgAuS-based compound. The AgAuS-based compound has a novel composition as a constituent component of semiconductor nanoparticles, but exhibits suitable optical properties when formed into nanoparticles. In addition, since its constituent elements are low-toxic elements having biocompatibility, in addition to general semiconductor devices such as light-emitting elements, applications to markers used in living organisms can also be expected.

Brief Description of the Drawings

[0030]

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Figure 17

Embodiments for Carrying Out the Invention

[0031] First Embodiment: Hereinafter, embodiments of the present invention will be described. In this embodiment, by adjusting the mixing ratio of the Ag precursor and the Au precursor, AgAuS-based compounds (Ag (nx) Au (ny) S (nz) ) of various compositions were produced. Then, for the produced semiconductor nanoparticles, TEM observation and XRD analysis were performed to confirm the average particle size and crystal structure, and then measurement of the absorption spectrum and emission spectrum was performed. The schematic of the manufacturing process of the Ag (nx) Au (ny) S (nz) semiconductor nanoparticles is shown in Fig. 1.

[0032] As the Ag precursor as a raw material, silver acetate (Ag(OAc)), as the Au precursor, Au resinate (C 10 H 18 Au2S2: see the following chemical formula), and 0.2 mmol of thiourea as the S precursor were weighed and put into a test tube. Further, 100 mm of 1-dodecanethiol (DDT) as a protective agent 3 and 2900 mm of oleylamine (OLA) as a solvent 3 were added.

[0033]

Chemical formula

[0034] In this embodiment, while the total amount of silver acetate and Au resinate was 0.4 mmol, the metal atom charging atomic ratio (a:b) of Ag:Au was adjusted. In this embodiment, a:b = 1.0:0, 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, 0.14:0.86, 0:1.0 At seven charging atomic ratios of (nx) Au (ny) S (nz)It was decided to synthesize the compound. Then, each precursor, protective agent, solvent, and stir bar were placed in a test tube, and after nitrogen substitution was performed three times, the reaction temperature was set to 150 °C with a hot stirrer, and stirring was carried out while heating for 10 minutes. After the reaction was completed, it was allowed to cool for 30 minutes and then transferred to a small test tube, and centrifuged at 4000 rpm for 5 minutes to separate the supernatant and the precipitate.

[0035] After that, methanol was added as a non-solvent to the supernatant at 4000 mm 3 to cause precipitation, and centrifuged at 4000 rpm for 5 minutes to recover the precipitate. Ethanol was further added to this precipitate at 4000 mm 3 to disperse it, and then centrifuged under the same conditions to remove by-products and solvents for purification. The precipitate (semiconductor nanoparticles) thus obtained was dispersed in chloroform at 4000 mm 3 to obtain a dispersion of semiconductor nanoparticles of the AgAuS-based compound (Ag (nx) Au (ny) S (nz) ). This dispersion was transferred to a sample bottle, nitrogen substitution was performed, and then stored refrigerated under light shielding.

[0036] [TEM Observation and Measurement of Average Particle Size] TEM observation was performed on the manufactured semiconductor nanoparticles (a:b = 1.0:0, 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, 0.14:0.86, 0:1.0 ). Figure 2 shows the TEM image of the semiconductor nanoparticles manufactured in this embodiment (the magnification can be referred to the scale bar (10 nm) of each photograph). It was confirmed from each TEM image that substantially spherical semiconductor nanoparticles were synthesized.

[0037] Based on these TEM images, the average particle size of the semiconductor nanoparticles of each composition was measured and calculated. In particle size measurement, the particle size was determined for all measurable semiconductor nanoparticles included in the TEM images, and the average particle size and standard deviation were calculated. The results are shown in FIG. 3. The error bars in each plot indicate the standard deviation. From FIG. 3, it can be seen that the average particle size of the semiconductor nanoparticles produced in this embodiment is in the range of 2 nm to 5 nm. In terms of the ratio of Ag and Au, particles with a:b=0:1 (Au2S) tend to have a small particle size, but there are no significant differences otherwise.

[0038] [Composition analysis of semiconductor nanoparticles] In addition to the above TEM observation, ICP analysis was performed to analyze the composition of the semiconductor nanoparticle samples. The ICP analysis was performed using an Agilent Technologies Co., Ltd. After pretreatment by microwave acid decomposition using 5110, measurements were performed at RF power: 1.2 kW, plasma gas flow rate: 12 L / min, and auxiliary gas flow rate: 1.0 L / min. Table 1 shows the analysis results for seven types of semiconductor nanoparticles with Ag and Au atomic ratios (a:b) of a:b = 1.0:0, 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, 0.14:0.86, and 0:1.0. Table 1 shows that the atomic ratios (x:y:z) of the semiconductor nanoparticles produced in this embodiment are close to the atomic ratios (a:b) of the metal precursors, although they do not completely match. The cation / anion ratio ((x+y) / (2z)) showed a value of 0.78 to 0.95, and the semiconductor particles were composed of a non-stoichiometric composition lacking cations. In addition, the semiconductor nanoparticles synthesized in this embodiment had a total concentration of Ag, Au, and S in the AgAuS compound of 100 mass %.

[0039] [Table 1]

[0040] [XRD analysis] XRD analysis was performed on each semiconductor nanoparticle. The XRD analyzer was Ultima IV manufactured by Rigaku Corporation, with characteristic X-rays being CuKα rays and the analysis condition being 1° / min. Figure 4 shows the diffraction patterns of the seven types of nanoparticles manufactured in this embodiment. Furthermore, among them, the enlarged diffraction patterns of three types of nanoparticles with the charged atomic ratios (a:b) of Ag and Au being a:b = 0:1.0, 0.60:0.40, and 0:1.0 are shown in FIGS. 5a to 5c. From FIG. 5c, peaks that match the diffraction pattern of Au2S are obtained for the semiconductor nanoparticles with the charged atomic ratio of 0:1.0. Also, from FIG. 5a, for the semiconductor nanoparticles with the charged atomic ratio of 1.0:0, although there is a partial mismatch in the peaks on the high-angle side, peaks around 35 to 37 °C derived from the diffraction of Ag2S are observed. On the other hand, referring to FIG. 5b, for the semiconductor nanoparticles with the charged atomic ratio of 0.60:0.40, in addition to the peaks derived from Ag3AuS2, peaks derived from 1.43 Au 0.66 S were observed. From this, it is considered that the composition of the entire compound of this semiconductor nanoparticle is Ag n(0.68) Au n(0.32) S n(0.6) (x = 0.68, y = 0.32, z = 0.60), but it may be composed of a mixed phase of Ag3AuS2 and Ag 1.43 Au 0.66 S.

[0041] Then, referring to FIG. 4, it is confirmed that in the semiconductor nanoparticles with the charged metal ratios (Ag:Au) of a:b = 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, and 0.14:0.86, as the ratio of Ag increases and the ratio of Au decreases, the peak pattern gradually changes from Au2S to Ag2S. From the XRD analysis of this embodiment, although it has not reached the determination of the structure and composition of the solid solution of the particles synthesized at each charged atomic ratio or the determination of the composition and abundance when mixtures coexist, it can be confirmed that crystalline particles could be synthesized in any charged composition.

[0042] [Measurement of Absorption Spectrum and Emission Spectrum] Next, the absorption spectrum and emission spectrum were measured for each semiconductor nanoparticle. The absorption spectrum was measured using an ultraviolet-visible spectrophotometer (manufactured by Agilent Technologies, Agilent 8453) in the wavelength range of 400 nm to 1100 nm as shown in Fig. 6 is the measurement result of the absorption spectrum of the semiconductor nanoparticles of this embodiment.

[0043] The emission spectrum was measured using a fluorescence spectrophotometer (manufactured by Hamamatsu Photonics K.K., PMA-12) with an excitation wavelength of 365 nm. At this time, the sample was adjusted to have an absorbance of 0.1 at 365 nm with a chloroform solution (n = 1.4429) and then measured.

[0044] Also, for the measurement of the emission quantum yield, an absolute PL quantum yield device (manufactured by Hamamatsu Photonics K.K., C9920-03) was used. When emission was observed at a long wavelength of 1000 nm or more, the emission spectrum was measured using a multi-channel spectrophotometer (manufactured by Hamamatsu Photonics K.K., PMA-12 (model numbers: C10027-02 (wavelength range 350 to 1100 nm) and 10028-01 (wavelength range 900 to 1650 nm))). At this time, the sample was adjusted to have an absorbance of 0.1 at 700 nm with a chloroform solution (n = 1.4429) and then measured. The excitation wavelength was set to 700 nm. For the calculation of the emission quantum yield, for the emission spectrum measured with the fluorescence spectrophotometer, the emission spectrum of an ethanol solution (n = 1.3618) of indocyanine green (ICG: Φ = 13.2%), which is a near-infrared emitting organic fluorescent dye, was measured as a standard sample, and the emission quantum yield of each sample was calculated by the relative method using the following formula.

[0045]

Equation

[0046] The emission spectra of the semiconductor nanoparticles of the present embodiment measured and calculated as described above are shown in FIGS. 7 and 8. FIG. 9 shows the relationship between the charged atomic ratio a:b and the long-wavelength side absorption edge wavelength of the semiconductor nanoparticles of the present embodiment obtained from FIG. 6. FIG. 10 shows the relationship between the charged atomic ratio a:b and the emission quantum yield of the semiconductor nanoparticles of the present embodiment obtained from FIGS. 7 and 8.

[0047] From FIG. 9, for semiconductor nanoparticles with a:b = 1.0:0 (Ag2S) and 0.78:0.22, the absorption edge wavelength reached a long wavelength region of 1100 nm or more and could not be accurately measured. The absorption edge wavelength shifted to the short wavelength side once as the Ag ratio decreased compared to a:b = 0.78:0.22, and reached the shortest wavelength (660 nm) when a:b = 0.45:0.55. When the Ag ratio decreased further than this, the absorption edge wavelength shifted to the long wavelength side again, and was estimated to be 970 nm for particles with a:b = 0:1.0 (Au2S). It was confirmed that the absorption edge wavelength of the semiconductor nanoparticles composed of Ag (nx) Au (ny) S (nz) in the present invention is 600 nm or more.

[0048] Also, from FIG. 10, it can be seen that the emission quantum yield of the semiconductor nanoparticles of the present embodiment is maximized in the vicinity of the charged atomic ratio a:b = 0.60:0.40. In the semiconductor nanoparticles composed of Ag (nx) Au (ny) S (nz) in the present invention, when a:b = 1.0:0 or 0:1.0 is used as a reference example (Ag2S or Au2S), those synthesized with a:b = 0.33:0.67 to 0.78:0.22 are considered to be particularly suitable. And from Table 1, the semiconductor nanoparticles manufactured with the above-mentioned suitable charged atomic ratio have atomic ratios (x, y) of Ag and Au such that x / (x + y) is 0.46 to 0.78, that is, x / y is 0.85 to 3.5.

[0049] Second Embodiment : In the present embodiment, silver acetate and gold resinate are used, while fixing the charged atomic ratio (a:b) of metal atoms at 0.60:0.40, and changing the reaction temperature during synthesis to Ag (nx)Au (ny) S (nz) Semiconductor nanoparticles composed of a compound were produced, and the average particle size, absorption spectrum, and emission spectrum were measured. Ag (nx) Au (ny) S (nz) The manufacturing process of the semiconductor nanoparticles is basically the same as that of the first embodiment. In FIG. 1, the total amount of silver acetate and Au resinate was set to 0.4 mmol, and the reaction system was formed with the respective metal charge atomic ratios a:b being 0.60:0.40. Then, semiconductor nanoparticles were produced under five conditions of reaction temperatures of 100°C, 125°C, 150°C, 165°C, and 175°C.

[0050] [TEM Observation and Measurement of Average Particle Size] For the semiconductor nanoparticles produced at each reaction temperature, TEM observation was performed in the same manner as in the first embodiment. FIG. 11 shows the TEM images of each semiconductor nanoparticle. From FIG. 11, the generation of substantially spherical nanoparticles is also confirmed in this embodiment. Also, FIG. 12 shows the relationship between the reaction temperature and the average particle size measured for each semiconductor nanoparticle. It can be seen that the particle size of the semiconductor nanoparticles increases as the reaction temperature rises. This is considered to be due to the promotion of crystal growth by the increase in the reaction temperature.

[0051] [Measurement of Absorption Spectrum and Emission Spectrum] The absorption spectrum and emission spectrum were measured for each semiconductor nanoparticle. These measurement methods were the same as those in the first embodiment.

[0052] The measurement results of the absorption spectrum of the semiconductor nanoparticles of this embodiment are shown in FIG. 13. Also, FIG. 14 shows the relationship between the reaction temperature and the absorption edge wavelength on the long wavelength side obtained from the measurement results of the absorption spectrum. From FIG. 14, even when the reaction temperature changes, the absorption edge wavelength of the semiconductor nanoparticles is not greatly affected and is approximately constant at 650 - 750 nm. It was confirmed that the absorption edge wavelength of the semiconductor nanoparticles produced in this embodiment is also 600 nm or more.

[0053] Also, the emission spectrum of the semiconductor nanoparticles of this embodiment is shown in Fig. 15. From Fig. 15, it can be seen that at reaction temperatures of 100 to 165 °C, the emission peak wavelength of the semiconductor nanoparticles is 700 to 800 nm and hardly changes. At 175 °C, no emission peak was detected. Fig. 16 shows the relationship between the reaction temperature and the emission quantum yield of the semiconductor nanoparticles of this embodiment. According to Fig. 16, from 100 °C to 150 °C, the emission quantum yield of the obtained semiconductor nanoparticles increased as the reaction temperature increased. On the other hand, when the reaction temperature was further increased to 165 °C and 175 °C, the emission quantum yield of the obtained semiconductor nanoparticles decreased conversely.

[0054] [XRD analysis] Furthermore, XRD analysis was performed on the semiconductor nanoparticles obtained at reaction temperatures of 125 °C, 150 °C, and 165 °C. The analysis conditions are the same as those in the first embodiment. Fig. 17 shows the diffraction patterns of the respective semiconductor nanoparticles. From Fig. 17, it was found that the semiconductor nanoparticles produced at 165 °C had higher crystallinity because each diffraction peak became sharp. Considering this together with the above measurement results of the average particle size, it is suggested that the promotion of crystal growth due to the increase in the reaction temperature enhances the crystallinity along with the increase in the particle size of the semiconductor nanoparticles. From the above, the semiconductor nanoparticles according to the present invention can be produced at a reaction temperature of 100 °C to 175 °C, but a more suitable reaction temperature is considered to be 165 °C or lower from the viewpoint of the emission quantum yield.

Industrial Applicability

[0055] As described above, the semiconductor nanoparticles composed of the AgAuS-based compound according to the present invention and having a novel composition can exhibit good optical properties. Also, the AgAuS-based compound is a low-toxic compound having biocompatibility. The semiconductor nanoparticles according to the present invention are expected to be applied to light-emitting elements, fluorescent substances used in display devices and marker substances for detecting biological-related substances, and photoelectric conversion elements and light-receiving elements mounted on solar cells and optical sensors.

[0056] In addition, based on the present invention, semiconductor nanoparticles capable of exhibiting light emission and light absorption characteristics in the near-infrared region can also be obtained. In recent years, as photoelectric conversion elements that emphasize responsiveness in the near-infrared region, there are light receiving elements applied to LIDAR (Light Detection and Ranging) and near-infrared (SWIR) image sensors. The semiconductor nanoparticles according to the present invention are expected to be applied to photoelectric conversion elements that operate in such a near-infrared region.

Claims

1. Semiconductor nanoparticles composed of a semiconductor crystal of a compound containing Ag, Au, and S as essential components, wherein the total content of Ag, Au, and S in the compound is 95% by mass or more, the compound is represented by the general formula Ag(nx)Au(ny)S(nz), and is a semiconductor nanoparticle which is a ternary AgAuS compound of monovalent Ag, monovalent Au, and S. Here, in the general formula, n is an arbitrary positive integer. x, y, and z represent the ratios of the number of atoms of Ag, Au, and S in the compound, and are real numbers such that 0 < x, y, z ≤ 1. Also, x / y is 1 / 7 or more and 7 or less.

2. The semiconductor nanoparticles according to claim 1, wherein z is a real number satisfying z ≥ (x + y) / 2.

3. The semiconductor nanoparticles according to claim 1 or claim 2, wherein the value of x / (x + y) is a real number of 0.33 or more and 0.78 or less.

4. The semiconductor nanoparticles according to any one of claims 1 to 3, having an average particle diameter of 2 nm or more and 20 nm or less.

5. The semiconductor nanoparticles according to any one of claims 1 to 4, wherein at least one of an alkylamine having an alkyl chain with 4 to 20 carbon atoms, an alkenylamine having an alkenyl chain with 4 to 20 carbon atoms, an alkylcarboxylic acid having an alkyl chain with 3 to 20 carbon atoms, an alkenylcarboxylic acid having an alkenyl chain with 3 to 20 carbon atoms, an alkanethiol having an alkyl chain with 4 to 20 carbon atoms, a trialkylphosphine having an alkyl chain with 4 to 20 carbon atoms, a trialkylphosphine oxide having an alkyl chain with 4 to 20 carbon atoms, triphenylphosphine, and triphenylphosphine oxide is bonded to the surface.

6. The semiconductor nanoparticles according to any one of claims 1 to 5, having an absorption edge wavelength on the long wavelength side of the absorption spectrum of 600 nm or more.

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