SEMICONDUCTOR NANOPARTICLE INCLUDING Ag Cu CHALCOGEN COMPOUND AS PRINCIPAL CONSTITUENT

Abstract

To provide a semiconductor nanoparticle excellent in light response characteristic, particularly light absorbing characteristic, and capable of being favorably used in a near infrared region and in a short wave infrared region.SOLUTION: The present invention is related to a semiconductor nanoparticle including a chalcogen compound, which contains Ag, Cu and a chalcogen element (Ch), and is represented by the following formula. The present invention indispensably contains Te as a chalcogen compound. The light response characteristic is shifted to a long wave length side by applying Te having a relatively large mass in chalcogen elements. The semiconductor nanoparticle pertaining to the present invention contains 90 atom% or more of an Ag Cu chalcogen compound, and has an absorption edge wavelength of a long wavelength side of an absorption spectrum of 1,200 nm or more. In the formula, Cu is a chalcogen element. x, y, z are atomic numbers of Ag, Cu, and a chalcogen element, and 0.2≤z / (x+y)≤1 is satisfied. Also, 1.0≤x / y≤10.0 holds for x and y.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to semiconductor nanoparticles mainly composed of an AgCu chalcogen compound. Specifically, it relates to semiconductor nanoparticles composed of an AgCu chalcogen compound containing Te as an essential chalcogen element and having suitable optical responsiveness in the long wavelength region.

Background Art

[0002] When a semiconductor is made into nanoparticles on the nanoscale, the quantum confinement effect is exhibited, and it shows 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 called quantum dots (QD) and are expected to be utilized in various technical fields. As application examples of semiconductor nanoparticles, for example, light-emitting elements used in display devices and marker substances for detecting bio-related substances, and their utilization as fluorescent substances are being studied.

[0003] In addition to the emission wavelength being controllable by the above-mentioned particle size adjustment, the emission peak width of semiconductor nanoparticles is sufficiently narrow and stable compared to organic dyes. Furthermore, semiconductor nanoparticles have the properties of having a high quantum efficiency and a high extinction coefficient in addition to being able to control the absorption wavelength. Due to these properties, the use of semiconductor nanoparticles in photoelectric conversion elements and light-receiving elements mounted on solar cells and various optical sensors is also being studied.

[0004] In particular, semiconductor nanoparticles are expected to be applied to light-receiving elements of optical sensors corresponding to the near-infrared region (NIR) and short-wave infrared region (SWIR). Optical sensors capable of responding to light in these long-wavelength regions are mounted on LIDAR (Light Detection and Ranging) and SWIR image sensors. LIDAR is a remote sensing system used in automotive autonomous driving, drones, ships, etc., and has become an important device in the development of recent autonomous driving technologies. Recently, LIDAR has also been applied to face recognition technology and augmented reality (AR) technology in smartphones, tablets, etc. In addition, SWIR image sensors are devices whose demand is expected to increase in the future in fields such as food inspection, agriculture, and drones.

[0005] For the light-receiving elements of the sensors of the above optical devices, there have been many application examples of Si thin films so far. However, since sensors using Si thin films have a significant decrease in sensitivity in the long-wavelength region of 900 nm or more, they are difficult to be compatible with the above applications. Therefore, the development of light-receiving elements using semiconductor nanoparticles is expected.

[0006] Regarding the composition of semiconductor nanoparticles, several semiconductor compounds have been studied so far. As semiconductor compounds having optical responsiveness in the long-wavelength regions of the near-infrared region (NIR) and short-wave infrared region (SWIR), metal chalcogenide compounds such as PbS, PbSe, CdHgTe, Ag2S, Ag2Se, Ag2Te, AgInSe2, AgInTe2, CuInSe2, CuInTe2, and InAs are known (Patent Documents 1 to 4). The applicant of the present application has also disclosed semiconductor nanoparticles mainly composed of AgAuS-based compounds in Patent Document 5.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] Although the above-described semiconductor compound has photoreactivity in a desired wavelength region, considering its application to uses such as the display device and the marker for detecting biomolecules described at the beginning, many of them have factors that become obstacles. For example, Pb is restricted in the use in electrical and electronic equipment from the viewpoint of environmental load by the European RoHS Directive (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment). Therefore, it is difficult to expect wide use of semiconductor nanoparticles composed of a compound containing Pb as a metal component in the electrical and electronic fields. Also, considering the use of semiconductor nanoparticles in the biological field, it is difficult to use compounds containing heavy metals such as Cd and Hg.

[0009] In addition, although the above-described semiconductor compound has photoreactivity in the long wavelength region, there is an increasing demand for a compound that can exhibit photoreactivity on the longer wavelength side. The recent development of the automatic driving technology of automobiles is remarkable, and it is necessary to correspond to the automatic driving levels (levels 4 and 5) that do not assume driving by a driver. In this case, for LIDAR, responsiveness in a longer wavelength region that is less affected by sunlight and natural light is important. Therefore, it can be said that the quantum dot technology is still in the research stage. And, considering practicality, semiconductor nanoparticles that can exhibit responsiveness in a longer wavelength region are required.

[0010] The present invention has been made under the above background, and while considering practicality with respect to various regulations, proposes semiconductor nanoparticles composed of a novel semiconductor compound having suitable photoreactivity. In particular, the present invention presents semiconductor nanoparticles that exhibit suitable light absorption characteristics in the long wavelength regions of the near-infrared region (NIR) and short-wavelength infrared region (SWIR) and can also emit light.

Means for Solving the Problems

[0011] In examining means for solving the above problems, the present inventors focused on semiconductor nanoparticles composed of an AgAuS compound related to the prior art (Patent Document 5) by the applicant of the present application. Ag and Au are metals that can be suitably used from the viewpoint of compliance with regulations such as environmental load and toxicity, and the AgAuS compound is a semiconductor compound that can exhibit photoreactivity. However, the conventional AgAuS compound nanoparticles had problems with photoreactivity in the infrared region (NIR) and short-wavelength infrared region (SWIR). In the prior art of the applicant of the present application described above, by adding a metal such as In to the AgAuS compound and applying an AgAuS-based multi-component compound, the absorption wavelength of the semiconductor nanoparticles is shifted to the longer wavelength side.

[0012] While referring to the transition metal chalcogenide compound, the AgAuS compound, which is the above prior art, the present inventors aimed to impart photoreactivity in the long wavelength region to the transition metal chalcogenide compound based on a two-way approach.

[0013] The first approach is to apply Te (tellurium), an element with a larger mass than S (sulfur), as an essential component as the chalcogen element. This is because by increasing the mass of the chalcogen element that binds to the transition metal, the orbital energy difference between each transition metal element and the chalcogen element when forming a compound is reduced, and it is presumed that the photoreactivity is thereby shifted to the longer wavelength side.

[0014] And as a second approach, it is the optimization of the transition metal component of the chalcogen compound. Specifically, it is to apply a combination of Ag and Cu instead of a combination of Ag and Au. Since Cu is a Group 11 element like Au and has a similar electronic structure, it has the potential to be a suitable optical semiconductor when formed into a chalcogen compound. And since Cu is one of the essential elements for the human body, it has good biocompatibility.

[0015] Therefore, the present inventors examined the possibility of synthesizing nanoparticles of an AgCu chalcogen compound having Te as an essential chalcogen element and its optical responsiveness (hereinafter, the chalcogen element may be referred to as Ch). As a result, an AgCu chalcogen compound having a light absorption characteristic having an absorption edge in a long wavelength region of 1200 nm or more and capable of exhibiting a light emission phenomenon was found, leading to the present invention.

[0016] That is, the present invention is semiconductor nanoparticles containing an AgCu chalcogen compound represented by the following formula composed of Ag, Cu, and a chalcogen element, wherein the chalcogen element contains Te as an essential chalcogen element, and the semiconductor nanoparticles contain 90 atomic% or more of the AgCu chalcogen compound.

[0017] [Chemical formula] (In the formula, Ch is a chalcogen element. x, y, and z are the number of atoms of Ag, Cu, and the chalcogen element, respectively, and 0.2 ≤ z / (x + y) ≤ 1.0. Also, 1.0 ≤ x / y ≤ 10.0.

[0018] Hereinafter, the configuration and production method of semiconductor nanoparticles mainly composed of an AgCu chalcogen compound having Te as an essential chalcogen element according to the present invention will be described.

[0019] A. Configuration of the semiconductor nanoparticles according to the present invention A-1. Chemical composition of the semiconductor nanoparticles As described above, the semiconductor nanoparticles according to the present invention mainly contain an AgCu chalcogen compound. In this AgCu chalcogen compound, when the number of atoms of Ag, Cu, and chalcogen element Ch are x, y, and z, respectively, Ag x Cu y Ch z can be represented by. Regarding the composition of the AgCuCh compound, the ratio (atomic ratio) of the number of atoms x of Ag to the number of atoms y of Cu is 1.0 ≦ x / y ≦ 10.0. In the range studied by the present inventors, the nanoparticles of the AgCu chalcogen compound within this composition range exhibit suitable light absorption characteristics in the long wavelength region of 1200 nm or more. Further, the AgCu chalcogen compound nanoparticles within this composition range can also exhibit luminescence. And by changing the atomic ratio x / y of Ag and Cu, the optical response characteristics of the AgCu chalcogen compound nanoparticles change. The atomic ratio x / y of Ag and Cu is more preferably 3.0 or more and 5.0 or less, whereby a luminescence peak can be observed in the long wavelength region of 1200 nm or more.

[0020] The chalcogen element (Ch) of the AgCu chalcogen compound applied in the present invention is a chalcogen element that requires Te. As described above, by applying Te, which has a relatively large mass among chalcogen elements, the wavelength showing photoreactivity can be shifted to the long wavelength side. In the AgCu chalcogen compound of the present invention, the chalcogen element is bonded so as to compensate for the charge with respect to Ag and Cu, which are transition metals. And the ratio of the number of atoms z of the chalcogen element to the number of atoms (x + y) of the transition metal component (Ag and Cu) satisfies 0.2 ≦ z / (x + y) ≦ 1.0. This atomic ratio z / (x + y) is preferably 0.3 or more and 0.7 or less (0.3 ≦ z / (x + y) ≦ 0.7), and more preferably 0.5 or more and 0.7 or less (0.5 ≦ z / (x + y) ≦ 0.7).

[0021] In addition, since it is stated that the chalcogen element in the AgCu chalcogen compound of the present invention must include Te, it may be only Te, or may contain other chalcogen elements other than Te. In the AgCu chalcogen compound of the present invention, when other chalcogen elements are contained in addition to Te, it is due to the fact that when the protective agent, solvent, etc. used in the synthesis process contain chalcogen elements, these combine with the transition metal component together with Te. As other chalcogen elements that can be contained together with Te in such a process, S or Se is preferable. When the AgCu chalcogen compound of the present invention contains other chalcogen elements other than Te, and the number of Te atoms is z Te when, the ratio z Te ) of the number of Te atoms (z Te ) to the total number of chalcogen atoms (z) is preferably 0.2 or more and 0.4 or less, and more preferably 0.25 or more and 0.35 or less. As will be described later, in the studies by the present inventors, when other chalcogen elements are contained together with Te as the chalcogen element, the optical absorption characteristics change depending on the atomic ratio of Te.

[0022] Note that the composition of the AgCu chalcogen compound described above is the overall composition of the AgCu chalcogen compound in the semiconductor nanoparticles. The AgCu chalcogen compound applied to the present invention may be composed of a single phase or may be composed of a plurality of phases. For example, when the chalcogen element is only Te, the AgCu chalcogen compound (Ag x Cu y Te z) The specific chemical compositions that can be obtained include several depending on the valences of Ag, Cu, and Te. There are stoichiometric chalcogen compounds such as AgCuTe (x = 1, y = 1, z = 1) and AgCuTe2 (x = 1, y = 1, z = 2). Also, when S and / or Se are included in addition to Te as chalcogen elements, there are stoichiometric chalcogen compounds for these (such as AgCuS (x = 1, y = 1, z = 1) and AgCuSe (x = 1, y = 1, z = 1)). The AgCu chalcogen compound in the semiconductor nanoparticles of the present invention is composed of these compounds with stoichiometric compositions in a single-phase or a mixed state of multiple phases. Also, it may contain compounds that do not have the above stoichiometric compositions. In the entire AgCu chalcogen compound in the semiconductor nanoparticles, it is sufficient that x, y, and z are within the range of the above conditions.

[0023] The semiconductor nanoparticles according to the present invention have an AgCu chalcogen compound as the main component and are composed of 90 atomic% or more of the AgCu chalcogen compound. The semiconductor nanoparticles may consist only of the AgCu chalcogen compound. It is more preferable that the semiconductor nanoparticles contain 95 atomic% or more of the AgCu chalcogen compound. The semiconductor nanoparticles according to the present invention may contain elements other than the chalcogen elements essential for Ag, Cu, and Te that constitute the AgCu chalcogen compound. For example, the constituent elements of the solvent when synthesizing the AgCu chalcogen compound and the elements contained in the respective precursors of Ag, Cu, and Te as raw materials may be contained in the semiconductor nanoparticles. Examples of elements that may be contained in addition to the essential constituent elements Ag, Cu, and the chalcogen elements include C, P, Cl, Br, I, etc. The content of these elements in the semiconductor nanoparticles is acceptable if it is less than 10 mass%. Note that the composition values of the compounds and elements shown here are values regarding the semiconductor nanoparticles and do not include the content of the protective agent and its constituent elements described later.

[0024] A-2. Structure of the semiconductor nanoparticles according to the present invention As described above, the AgCu chalcogen compound applied to the present invention is composed of a single phase or a plurality of phases. As an aspect of semiconductor nanoparticles composed of a plurality of phases, a so-called core-shell structure can be adopted. Examples of the core-shell structure include a core (core compound) composed of an AgCu chalcogen compound containing Ag, Cu, and Te, and a shell (shell compound) composed of an AgCu chalcogen compound having a composition different from that of the core compound or a compound not containing any of Ag, Cu, and Te, and the shell compound covers at least a part of the surface of the core compound. Further, even if it is not a regular combination of a plurality of phases such as a core-shell structure, a plurality of phases having different compositions may be randomly distributed. Note that Cu-rich, Ag, and Te-rich mean that the composition ratios of Cu, Ag, and Te in the phase are greater than 50 atomic%.

[0025] The shape of the semiconductor nanoparticles according to the present invention may be spherical, cubic, or rod-shaped in addition to the spherical shape. The semiconductor nanoparticles having a spherical or cubic shape 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 adjustment effect of the band gap due to the quantum confinement effect. In order to exhibit suitable light absorption characteristics by adjusting the band gap, it is preferable to have the above-mentioned average particle size. The average particle size of the semiconductor nanoparticles can be obtained by observing a plurality (preferably 100 or more) of semiconductor nanoparticles with an electron microscope such as TEM, measuring the particle size and the like of each particle, and calculating the number average. Note that the particle size can be measured as the average value of the major axis (long axis) and the minor axis (short axis).

[0026] In addition, in the analysis of the composition and structure of the semiconductor nanoparticles according to the present invention, a scanning transmission electron microscope (Scanning TEM) can be preferably used. In particular, according to a high-angle annular dark-field scanning transmission microscope (High Angle Annular Dark Field Scanning TEM: HAADF-STEM), a scattering image reflecting the composition information of the nanoparticles can be obtained, and by combining with an energy dispersive X-ray spectrometer (EDS, EDX), etc., the distribution state of Ag, Cu, and Te and the composition of the whole nanoparticles can be grasped.

[0027] A-3. Photoresponsivity of Semiconductor Nanoparticles According to the Present Invention As described above, the bandgap of semiconductor nanoparticles is adjusted by the quantum confinement effect according to the particle size, and the photoresponsivity changes. Regarding the light absorption characteristics of the semiconductor nanoparticles according to the present invention, it is preferable that the absorption edge wavelength on the long wavelength side of the absorption spectrum is 1200 nm or more. Thereby, the semiconductor nanoparticles exhibit absorbability to light in the visible light region to the near infrared region. As a more preferable embodiment, the semiconductor nanoparticles according to the present invention can have an absorption edge wavelength on the long wavelength side of 1400 nm or more.

[0028] In addition, the semiconductor nanoparticles according to the present invention can also exhibit a light emission phenomenon. In the light emission spectrum at this time, a light emission peak is observed in a wavelength range of 1000 nm or more. As a preferable embodiment, the semiconductor nanoparticles according to the present invention can exhibit a light emission peak in a long wavelength region of 1200 nm or more, more preferably 1400 nm or more.

[0029] A-4. Modes of Use of Semiconductor Nanoparticles According to the Present Invention By appropriately coating and supporting the semiconductor nanoparticles according to the present invention on an appropriate base material or carrier, they can be applied to various uses such as the above-described optical sensor elements. There are no particular restrictions on the configuration, shape, and dimensions of this base material or carrier. Examples of the base material on a plate-like or foil / film include glass, quartz, silicon, ceramics, or metal. Examples of the granular / 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 base material.

[0030] When applying and supporting semiconductor nanoparticles on a substrate or carrier, as described above, a solution, slurry, or ink in which the semiconductor nanoparticles are dispersed in an appropriate dispersion medium is often used. As the dispersion medium for this solution or the like, chloroform, toluene, cyclohexane, hexane, etc. can be applied. And as the coating method for the solution of semiconductor nanoparticles or the like, dipping, spin coating method, and as the supporting method, various methods such as dropping method, impregnation method, adsorption method, etc. can be applied.

[0031] In addition, the semiconductor nanoparticles according to the present invention preferably contain a protective agent in order to suppress aggregation during the synthesis process and when dispersed in a dispersion medium as described above. As this protective agent, at least one of an alkylamine having 4 or more and 20 or less carbon atoms in the alkyl chain, an alkenylamine having 4 or more and 20 or less carbon atoms in the alkenyl chain, an alkylcarboxylic acid having 3 or more and 20 or less carbon atoms in the alkyl chain, an alkenylcarboxylic acid having 3 or more and 20 or less carbon atoms in the alkenyl chain, and an alkanethiol having 4 or more and 20 or less carbon atoms in the alkyl chain is preferable. These protective agents bind to the surface of the semiconductor nanoparticles and cover at least a part thereof, suppressing the aggregation of the semiconductor nanoparticles in the dispersion to form a uniform solution or the like. Further, by adding a protective agent to the reaction system together with the raw materials in the synthesis step of the semiconductor nanoparticles, nanoparticles having a suitable average particle size are synthesized. In addition, the protective agent can be applied alone or in combination of two or more of the above-mentioned alkylamine, alkenylamine, alkylcarboxylic acid, alkenylcarboxylic acid, and alkanethiol.

[0032] B. Method for manufacturing semiconductor nanoparticles according to the present invention Next, the method for manufacturing semiconductor nanoparticles according to the present invention will be described. The present inventors have found that the synthesis of the AgCu chalcogen compound having the above-described composition preferably uses compounds containing the respective constituent elements of Ag, Cu, and Te as precursors (Ag precursor, Cu precursor, Te precursor), introducing them into the same reaction system and heating them simultaneously to cause a reaction. Hereinafter, the method for manufacturing semiconductor nanoparticles applying this synthesis method of the AgCu chalcogen compound will be described.

[0033] B-1. Raw materials (Ag precursor, Cu precursor, Te precursor) As the Ag precursor, Cu precursor, and Te precursor serving as raw materials, an Ag salt or Ag complex, a Cu salt or Cu complex, and a Te compound are respectively applied. As for the Ag precursor and Cu precursor, salts or complexes containing monovalent Ag and monovalent Cu are preferable.

[0034] As the Ag precursor, an Ag salt or Ag complex is applied. The Ag precursor is preferably a salt or complex containing monovalent Ag. Preferable specific examples of the Ag precursor include silver acetate (Ag(OAc)), silver nitrate, silver carbonate, silver oxide, silver oxalate, silver chloride, silver iodide, silver(I) cyanide salt, silver diethyldithiocarbamate, and the like.

[0035] As the Cu precursor, a Cu salt or Cu complex is applied. The Cu precursor is preferably a salt or complex containing monovalent Cu. However, as for the Cu precursor, a salt or complex containing divalent Cu can also be used. This is because divalent Cu is reduced to monovalent Cu by a solvent, a coexisting Te precursor, etc. during the synthesis process of semiconductor nanoparticles. Preferable specific examples of the Cu precursor include copper acetate, copper chloride, copper iodide, copper bromide, and the like.

[0036] As the Te compound serving as the Te precursor, Te compounds such as tellurium oxide (TeO2), telluric acid (Te(OH)6), and sodium tellurite (Na2TeO3) can be applied.

[0037] B-2. Formation of reaction system of AgCu chalcogen compound In the synthesis of the AgCu chalcogen compound, after forming a single reaction system in which the above-mentioned Ag precursor, Cu precursor, and Te precursor are mixed, the reaction is carried out. At this time, the separately prepared Ag precursor, Cu precursor, and Te precursor may be sequentially mixed, and the mixing order is not particularly limited. Also, a mixture of the Ag precursor and Cu precursor, which are the transition metal components of the AgCu chalcogen compound, may be adjusted as a metal source precursor, and the metal source precursor and the Te precursor may be mixed to form a reaction system.

[0038] The atomic ratio (x / y) of Ag to Cu in the synthesized AgCu chalcogen compound (Ag x Cu y Ch z ) can be adjusted by the ratio of the charged amounts of the Ag precursor and the Cu precursor. For the charged amount ratio for synthesizing the AgCu chalcogen compound of the present invention with the atomic ratio (x / y) of Ag to Cu within a predetermined range, when the number of Ag atoms in the Ag precursor is a and the number of Cu atoms in the Cu precursor is b, it is preferable to set their ratio (a / b: hereinafter, this ratio is referred to as the Ag charged ratio) to be 1 or more and 10 or less, and more preferably 2 or more and 4 or less.

[0039] In addition, the charged amount of the Te precursor in the reaction system can affect the number of Te atoms (z x Cu y Ch z ) in the chalcogen element of the synthesized AgCu chalcogen compound (Ag Te ). According to the study by the present inventors, when the number of Te atoms in the Te precursor is c and based on the number of Cu atoms b in the above-mentioned Cu precursor, it is preferable to set their ratio (c / b: hereinafter, this ratio is sometimes referred to as the Te charged ratio) to be 0.1 or more and 2 or less, and more preferably 0.1 or more and 1 or less.

[0040] Also, as described above, it is preferable that the semiconductor nanoparticles of the present invention have a protective agent bonded to the AgCu chalcogen compound. Further, when this protective agent contains a chalcogen element, the chalcogen element can form a part of the chalcogen element of the AgCu chalcogen compound of the present invention. Therefore, it is preferable to add a protective agent to the above-mentioned reaction system together with the Ag precursor, the Cu precursor, and the Te precursor. As the protective agent, it is preferable to add at least any 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, and an alkanethiol having an alkyl chain carbon number of 4 or more and 20 or less.

[0041] In the reaction system for synthesizing semiconductor nanoparticles, it is possible to generate nanoparticles without a solvent, but it is preferable to use a solvent. When using a solvent, octadecene, tetradecane, oleic acid, oleylamine, dodecanethiol, or a mixture thereof can be applied.

[0042] Synthesis conditions of B-3.AgCu chalcogen compound AgCu chalcogen compound nanoparticles are synthesized by heating a reaction system composed of an Ag precursor, a Cu precursor, a Te precursor, and a protective agent. The heating temperature (reaction temperature) at this time is set to be 100°C or higher and 200°C or lower. If it is less than 100°C, the synthesis reaction hardly proceeds. On the other hand, if it exceeds 200°C, nanoparticles with unstable particle shapes may be formed. A more suitable reaction temperature is 100°C or higher and 150°C or lower.

[0043] Also, the reaction time (heating time) can be adjusted according to the charged amount of raw materials, etc., but it is preferably 5 minutes or more and 120 minutes or less. The reaction time is more preferably 10 minutes or more, and even more preferably 15 minutes or more. During the progress of the synthesis reaction of AgCu chalcogen compound nanoparticles, it is preferable to stir the reaction system.

[0044] After the completion of the synthesis reaction of AgCu chalcogen compound nanoparticles, the reaction system can be cooled as necessary and recovered as semiconductor nanoparticles. At this time, an alcohol (ethanol, methanol, etc.) serving as a poor solvent can be added to precipitate the nanoparticles, or the semiconductor nanoparticles can be precipitated and recovered by centrifugation or the like. After washing the particles once with an alcohol (ethanol, methanol, etc.), they can be uniformly dispersed in a good solvent such as chloroform.

Advantages of the Invention

[0045] As described above, the present invention is an AgCu chalcogen compound (Ag x Cu y Ch zIt is a semiconductor nanoparticle having [the substance in parentheses] as a main component. The semiconductor nanoparticle according to the present invention has suitable photoreactivity and also has practicality considering usage restrictions and the like. And the semiconductor nanoparticle according to the present invention can be applied to uses such as light receiving elements and light emitting elements in the long wavelength region of the near infrared region (NIR) and the short wavelength infrared region (SWIR).

Brief Description of Drawings

[0046]

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Mode for Carrying Out the Invention

[0047] First Embodiment : Hereinafter, embodiments of the present invention will be described. In this embodiment, semiconductor nanoparticles composed of an AgCu chalcogen compound (Ag x Cu y Ch z ) were synthesized, and their appearance and the like were confirmed, and their photoreactive properties were evaluated. In this embodiment, nanoparticles of an AgCu chalcogen compound with a changed atomic ratio (x / y) of Ag and Cu were synthesized.

[0048] The synthesis of semiconductor nanoparticles composed of an AgCu chalcogen compound in this embodiment was carried out by previously preparing a mixture of an Ag precursor and a Cu precursor as transition metal components as a metal source precursor, and then mixing and reacting the metal source precursor and a Te precursor to synthesize semiconductor nanoparticles.

[0049] Silver acetate (Ag(OAc)) was used as the Ag precursor, and copper acetate (Cu(OAc)) was used as the Cu precursor. They were dissolved and mixed in 3 mL of 1-dodecanethiol (DDT) as a solvent and a protecting agent to prepare a metal source precursor. At this time, the total content of Ag and Cu in the solution was set to be 0.08 mmol in terms of metal. Then, silver acetate and copper acetate were mixed so that the charging ratio (a / b) of Ag was 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5. While preparing this metal source precursor, 0.2 mmol of tellurium oxide (TeO2) was dissolved in 2 mL of DDT as a solvent and a protecting agent, and heated at 100 ° C for 5 minutes under a nitrogen atmosphere to prepare a solution of the Te precursor.

[0050] The synthesis of AgCu chalcogenide compound nanoparticles was carried out as follows: First, a solution of metal source precursors (Ag, Cu) was heated at 150 °C for 5 minutes under a nitrogen atmosphere. Then, the above Te precursor solution was injected into it with a syringe. After that, while stirring, the reaction temperature was set at 150 °C and heated for 15 minutes under a nitrogen atmosphere. After the reaction was completed, it was allowed to cool and then centrifuged at 4000 rpm for 5 minutes to separate the supernatant and the precipitate. Then, ethanol / toluene was added to the supernatant as a poor solvent at 4 cm 3 to cause precipitation, and then centrifuged at 4000 rpm for 5 minutes to recover the precipitate, obtaining AgCu chalcogenide compound nanoparticles.

[0051] The AgCu chalcogenide compound nanoparticles obtained by the above operations were dispersed in 3 cm of chloroform 3 to obtain a dispersion of semiconductor nanoparticles composed of AgCu chalcogenide compounds. This dispersion was transferred to a sample bottle, subjected to nitrogen substitution, and then stored refrigerated in the dark.

[0052] [TEM Observation of Semiconductor Nanoparticles] TEM observation was performed on the semiconductor nanoparticles (Ag charging ratios: 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5) composed of the AgCu chalcogenide compound synthesized in this embodiment. Figure 1 shows the TEM images of each semiconductor nanoparticle manufactured in this embodiment (the magnification can be referred to the scale bar of each photo). Referring to Figure 1, in the AgCu chalcogenide compound synthesized with an Ag charging ratio of 3 / 1, many substantially spherical nanoparticles are observed. As the Ag charging ratio decreases (the proportion of Cu increases), accordingly, the number of amorphous nanoparticles tends to increase.

[0053] [Composition Analysis of Semiconductor Nanoparticles] For the semiconductor nanoparticles composed of AgCu chalcogen compounds synthesized in this embodiment (Ag charging ratio: 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5), composition analysis by SEM-EDS was performed. The measurement results of the composition of each semiconductor nanoparticle are shown in Table 1. The results of the composition analysis are expressed in atomic% with respect to the entire nanoparticles in this embodiment and each of the following embodiments. Table 1 also shows the ratio x / y of the number of Ag atoms (x) to the number of Cu atoms (y) and the ratio z / (x + y) of the number of atoms of the chalcogen element (z) to the number of atoms of the transition metal component (x + y) calculated based on the composition analysis results.

[0054]

Table 1

[0055] As can be seen from Table 1, with the increase in the Ag charging ratio (a / b), naturally, the ratio (x / y) of the number of Ag atoms (x) to the number of Cu atoms (y) in the AgCu chalcogen compound increases. Also, regarding the ratio of the number of atoms of the chalcogen element (z) to the number of atoms of the transition metal component (Ag and Cu) (x + y), it is confirmed that there is no significant variation even when the Ag charging ratio changes. And it is confirmed that the AgCu chalcogen compound synthesized in this embodiment contains S as another chalcogen element while having Te as an essential chalcogen element. Furthermore, except for No. 4, (z Te / z) of the total chalcogen element of the Te atom number does not show significant variation even when the Ag charging ratio changes. The AgCu chalcogen compound of No. 4 has the smallest Ag charging ratio (a / b: 1.5 / 2.5). Referring to the results of TEM observation (Figure 1), phase separation into two phases is observed, and it is considered that only this shows a different tendency.

[0056] [Measurement of Absorption Spectrum and Emission Spectrum] Next, in order to evaluate the optical responsiveness of each semiconductor nanoparticle, absorption spectrum measurement and emission spectrum measurement were performed. The absorption spectrum was measured using an ultraviolet-visible spectrophotometer (manufactured by Agilent Technologies, Agilent 8453) with a wavelength range of 400 nm to 1600 nm. Also, for the emission spectrum, a diode array spectrophotometer (PMA-12, C10027-02) manufactured by Hamamatsu Photonics K.K. was used. The sample was adjusted with a chloroform solution (n = 1.4429) so that the absorbance at 365 nm was 0.1 and then measured.

[0057] The measurement results of the absorption spectra of each semiconductor nanoparticle manufactured in this embodiment are shown in Fig. 2, and the measurement results of the emission spectra are shown in Fig. 3. Also, Table 2 shows the absorption edge wavelength on the long wavelength side and the peak wavelength of the emission spectrum of each semiconductor nanoparticle measured based on these.

[0058]

Table 2

[0059] Referring to the measurement results of the absorption spectra in Fig. 2 and Table 2, all semiconductor nanoparticles have light absorption characteristics showing an absorption edge in the region of 1400 nm or more. Also, in all cases, an absorption peak appears around 1400 nm while showing a small peak considered to be an exciton peak at a wavelength of 800 nm to 950 nm. Regarding the composition of the AgCu chalcogen compound (Ag x Cu y Ch z ), when looking at the change according to the atomic ratio (x / y) of Ag and Cu, a shift to the long wavelength side of the absorption edge is observed as x / y increases and the atomic ratio of Ag becomes higher.

[0060] In addition, in the semiconductor nanoparticles of the present embodiment, the emission of light has been confirmed in all cases. Referring to the measurement results of the emission spectra in Fig. 3 and Table 2, emission peaks in the wavelength range of 1000 nm or more were confirmed. In particular, the emission peak wavelength of the semiconductor nanoparticles (No. 1) with a high atomic ratio of Ag is on the longer wavelength side. In these semiconductor nanoparticles, emission peaks in the region of 1200 nm or more were observed.

[0061] From the above evaluation results of the optical responsiveness, it can be said that the semiconductor nanoparticles composed of the AgCu chalcogenide compound synthesized in the present embodiment have an absorption edge of 1200 nm or more and exhibit good light absorption in the long wavelength region. In particular, the AgCu chalcogenide compound nanoparticles (x / y = 4) with an Ag charging ratio of 3 / 1 of No. 1 have an absorption edge wavelength on the long wavelength side of 1500 nm or more and also show good emission characteristics with a peak wavelength of 1200 nm or more.

[0062] Second Embodiment :In the present embodiment, semiconductor nanoparticles composed of AgCu chalcogenide compounds with various compositions were synthesized by adjusting the charging ratio of Te. The method for synthesizing the semiconductor nanoparticles applied in the present embodiment is basically the same as that of the first embodiment. A solution of a Te precursor was added to a solution of a metal source precursor, and heating and reaction were carried out to obtain nanoparticles of an AgCu chalcogenide compound. In the present embodiment, the charging amount at the time of adding the Te precursor was adjusted so that the Te charging ratio (c / b), which is the ratio of the number of Te atoms c in the Te precursor to the number of Cu atoms b in the metal source precursor, was 1 / 4, 1 / 2, 1 / 1, and 2 / 1, and the synthesis reaction was carried out. After synthesis, separation and purification were carried out in the same manner as in the first embodiment to obtain nanoparticles of an AgCu chalcogenide compound. The Ag charging ratio (a / b) was set to 3 / 1, and the other reaction conditions were the same as those of the first embodiment.

[0063] [Composition Analysis of Semiconductor Nanoparticles] For the semiconductor nanoparticles (Te charging ratios: 1 / 4, 1 / 2, 1 / 1, 2 / 1) composed of the AgCu chalcogenide compound synthesized in the present embodiment, composition analysis by SEM-EDS analysis was performed. The measurement results of the composition of each semiconductor nanoparticle are shown in Table 3.

[0064]

Table 3

[0065] Referring to Table 3, even when the Te charging ratio (c / b) increases, there is no significant change in the ratio (z / (x + y)) of the number of atoms (z) of the chalcogen element to the number of atoms (x + y) of the transition metal components (Ag, Cu). The increase in the Te charging ratio leads to an increase in the ratio (z Te / z) of the number of Te atoms to the total number of atoms of the chalcogen element. Also, it can be observed that the increase in the Te charging ratio also tends to lead to a decrease in the atomic ratio x / y of Ag to Cu.

[0066] [Measurement of Absorption Spectrum and Emission Spectrum] Next, absorption spectrum measurement and emission spectrum measurement were performed as evaluations of the optical responsiveness of each semiconductor nanoparticle manufactured in this embodiment. These measurement methods are the same as those in the first embodiment. The results of these measurements are shown in FIGS. 4 and 5, and the absorption edge wavelength on the long wavelength side and the peak wavelength of the emission spectrum of each semiconductor nanoparticle are shown in Table 4.

[0067]

Table 4

[0068] Referring to the measurement results of the absorption spectra in FIGS. 4 and Table 4, in any of the semiconductor nanoparticles with the Te charging ratio changed, an absorption peak appears around 1400 nm while showing an exciton peak. And the absorption edge on the long wavelength side is in the region of 1500 nm or more in all cases. In particular, for the semiconductor nanoparticles (No. 5) with a low Te charging ratio (low atomic ratio of Te in the AgCu chalcogen compound), a further red shift of the absorption edge wavelength was observed.

[0069] Referring to the measurement results of the emission spectra in FIGS. 5 and Table 4, the emission spectrum curves of the semiconductor nanoparticles of No. 5 to No. 7 (c / b: 1 / 4 to 1 / 1) show a similar trend and the differences are not significant. For the semiconductor nanoparticles of No. 8 with a high Te charging ratio (c / b: 2 / 1), no distinct peak was observed.

[0070] Third Embodiment : In this embodiment, the optical responsiveness of semiconductor nanoparticles obtained when changing the synthesis conditions of AgCu chalcogen compound nanoparticles was examined.

[0071] First, the influence of temperature before and after the reaction system is formed was examined. Here, in the synthesis process of AgCu chalcogen compound nanoparticles of the first embodiment, the heating temperature (T1) of the metal source precursor solution before adding the Te precursor solution to the metal source precursor solution and the heating temperature after adding the Te precursor solution (reaction temperature: T2) were adjusted. Specifically, AgCu chalcogen compound nanoparticles were synthesized under three conditions: (i) T1 = T2 = 150 °C, (ii) T1 = 150 °C, T2 = 120 °C, and (iii) T1 = T2 = 120 °C. The heating time in each of these examinations was the same as that in the first embodiment.

[0072] Also, in this embodiment, the influence of the heating time (reaction time) after adding the Te precursor solution to the metal source precursor solution was also examined. In this examination, AgCu chalcogen compound nanoparticles were synthesized with the reaction time set to 5 min, 10 min, 20 min, 40 min, and 80 min. The heating temperature in this examination was set to T1 = T2 = 120 °C.

[0073] In addition, in each examination, the synthesis methods and conditions other than the above-described reaction conditions were the same as those in the first embodiment, and the Ag charging ratio (a / b) was set to 3 / 1.

[0074] Regarding the examination results of this embodiment, first, the temperature before and after the reaction system formation will be described. Fig. 6 is a TEM image of AgCu chalcogen compound nanoparticles synthesized under the heating conditions of (i) to (iii) described above. From this TEM image, it can be seen that nanoparticles with a stable particle shape are synthesized under the condition of (iii) where both the heating temperatures (T1 and T2) before and after the reaction system formation are 120 °C. And the shape of the nanoparticles tends to become unstable by including heating at 150 °C.

[0075] Therefore, for semiconductor nanoparticles under the conditions (i) where the heating temperature before and after the reaction system formation is the same (T1 = T2 = 150 °C) and (iii) (T1 = T2 = 120 °C), composition analysis was performed by EDS. The results are shown in Table 5. From Table 5, it was found that although there are differences in particle shape, there are no significant differences in composition among these AgCu chalcogenide compound nanoparticles.

[0076]

Table 5

[0077] In addition, the measurement results of the absorption spectra and emission spectra of these two semiconductor nanoparticles are shown in Figs. 7, 8 and Table 6.

[0078]

Table 6

[0079] Looking at the measurement results of the absorption spectra in Fig. 7 and Table 6, the absorption characteristics of the semiconductor nanoparticles under the heating conditions (i) and (iii) are generally similar curves. However, for the semiconductor nanoparticles in (iii) where the heating temperature before and after the reaction system formation is 120 °C, the intensity of the absorption peak is clearly stronger, and the absorption edge wavelength is also at a longer wavelength. Then, referring to the measurement results of the emission spectra in Fig. 8 and Table 6, the emission peak wavelength in the semiconductor nanoparticles in (iii) where the heating temperature before and after the reaction system formation is 120 °C is significantly shifted to the longer wavelength side (more than 200 nm).

[0080] Next, the results of examining the influence of reaction time will be described. Fig. 9 shows TEM images of AgCu chalcogen compound nanoparticles synthesized with the reaction time ranging from 5 min to 40 min (T1 = T2 = 120 °C). From Fig. 9, it can be seen that by increasing the reaction time, the particle shape approaches a spherical shape. Also, Table 7 shows the results of compositional analysis of these semiconductor nanoparticles by EDS. Referring to Table 7, even when the reaction time increases, there is no significant difference in the atomic ratio (z / (x + y)) between the transition metal components (Ag, Cu) and the chalcogen element. Also, the atomic ratio (x / y) of Ag in the transition metal components is not much different within the range of 3.0 to 5.0.

[0081]

Table 7

[0082] Regarding the AgCu chalcogen compound nanoparticles synthesized with the reaction time ranging from 5 min to 40 min (T1 = T2 = 120 °C), the measurement results of the absorption spectrum are shown in Fig. 10, the measurement results of the emission spectrum are shown in Fig. 11, and a summary of these is shown in Table 8.

[0083]

Table 8

[0084] Looking at the absorption spectrum in Fig. 10, except for a reaction time of 80 min, there is no significant difference in the absorption characteristics of each semiconductor nanoparticle. Also, looking at the measurement results of the emission spectrum in Fig. 11, similar to the results of the absorption spectrum, there is no difference in the emission spectrum curve, and it can be said that the emission peak wavelengths are almost the same.

[0085] Summarizing the examination results regarding the synthesis conditions studied in this embodiment, it can be said that regarding the heating temperature of the metal source precursor and the reaction temperature, it is more preferable to set them to 120°C, which is relatively low compared to 150°C (First Embodiment). Also, regarding the reaction time, although it is preferable that spheroidization of the particles is observed by making the reaction time long, there are few differences in characteristics other than the outer shape of the particles. It is considered that the reaction time can be set relatively freely. The synthesis conditions of the semiconductor nanoparticles should be adjusted according to the concentrations of transition metal and chalcogen elements in the metal source precursor and Te precursor and the scale of the reaction system, but the results of this embodiment can be referred to.

Industrial Applicability

[0086] As described above, the semiconductor nanoparticles composed of the AgCu chalcogen compound according to the present invention can exhibit good optical responsiveness. This AgCu chalcogen compound also takes into account compliance with usage restrictions and avoidance of the use of heavy metals. 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 bio-related substances, and photoelectric conversion elements and light-receiving elements mounted on solar cells and optical sensors. In particular, the present invention aims to improve the light absorption characteristics in the long wavelength regions of the near-infrared region (NIR) and short-wavelength infrared region (SWIR). Therefore, the present invention is particularly useful for light-receiving elements applied to LIDAR and SWIR image sensors, which place importance on responsiveness in the near-infrared region among the above-described light elements.

Claims

1. Semiconductor nanoparticles containing an AgCu chalcogen compound represented by the following formula and composed of Ag, Cu, and a chalcogen element, wherein the chalcogen element contains Te as an essential chalcogen element, and the semiconductor nanoparticles contain 90 atomic% or more of the AgCu chalcogen compound. 【Chemical 1】 (In the formula, Ch is a chalcogen element. x, y, and z are the number of atoms of Ag, Cu, and the chalcogen element, respectively, and 0.2 ≦ z / (x + y) ≦ 1. Also, 1.0 ≦ x / y ≦ 10.0.)

2. The semiconductor nanoparticles according to Claim 1, wherein the chalcogen element constituting the AgCu chalcogen compound contains other chalcogen elements other than Te, and the other chalcogen elements are S and Se.

3. The semiconductor nanoparticles according to Claim 2, wherein the ratio of the number of atoms of Te to the number of atoms of the chalcogen element constituting the AgCu chalcogen compound is 0.2 or more and 0.4 or less.

4. The semiconductor nanoparticles according to Claim 1 or Claim 2, which contain 99 atomic% or more of the AgCu chalcogen compound.

5. The semiconductor nanoparticles according to Claim 1 or Claim 2, having an average particle diameter of 2 nm or more and 20 nm or less.

6. The semiconductor nanoparticles according to Claim 1 or Claim 2, wherein 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, and an alkanethiol having 4 to 20 carbon atoms in the alkyl chain is bonded to the surface as a protective agent.

7. The semiconductor nanoparticles according to Claim 1 or Claim 2, having an absorption edge wavelength on the long wavelength side of the absorption spectrum of 1200 nm or more.

8. The semiconductor nanoparticles according to Claim 1 or Claim 2, having a peak wavelength of the emission spectrum of 1000 nm or more.

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