SEMICONDUCTOR NANOPARTICLES CONTAINING AgCu CHALCOGEN COMPOUND AS MAIN COMPONENT

Abstract

The present invention relates to semiconductor nanoparticles comprising an AgCu chalcogen compound that contains Ag, Cu, and a chalcogen element (Ch) and is represented by formula. The present invention essentially contains Te as the chalcogen element. By applying Te having a relatively large mass among the chalcogen elements, the optical response characteristics are shifted to the long wavelength side. The semiconductor nanoparticles according to the present invention contain 90 atom% or more of the AgCu chalcogen compound, and has an absorption edge wavelength on the long wavelength side in the absorption spectrum of 1,200 nm or more. In the formula, Ch is a chalcogen element. x, y, and z represent the number of atoms of Ag, Cu and the chalcogen element, respectively, and 0.2≤z(x+y)≤1. In addition, 1.0≤x / y≤10.0.

Description

Semiconductor nanoparticles based on AgCu chalcogen compounds

[0001] The present invention relates to semiconductor nanoparticles mainly composed of an AgCu chalcogen compound, and more particularly to semiconductor nanoparticles made of an AgCu chalcogen compound that contain Te as an essential chalcogen element and have suitable photoresponsiveness in the long wavelength region.

[0002] When semiconductors are made into nanoscale particles, they exhibit a quantum confinement effect and exhibit a band gap that corresponds to the particle size. Therefore, by adjusting the band gap by controlling the composition and particle size of the semiconductor nanoparticles, it becomes possible to arbitrarily set the emission wavelength and absorption wavelength. Semiconductor nanoparticles that utilize this property are also called quantum dots (QDs), and are expected to be used in various technical fields. Examples of applications of semiconductor nanoparticles that are being considered include light-emitting elements and fluorescent materials used in display devices and marker substances for detecting biological substances.

[0003] This is because semiconductor nanoparticles have the ability to control the emission wavelength by adjusting the particle size as described above, and also have a sufficiently narrow and stable emission peak width compared to organic dyes. Furthermore, in addition to being able to control the absorption wavelength, semiconductor nanoparticles also have the properties of high quantum efficiency and a high absorption coefficient. Due to these properties, semiconductor nanoparticles are also being considered for use in photoelectric conversion elements and light-receiving elements mounted on solar cells, various optical sensors, etc.

[0004] In particular, semiconductor nanoparticles are expected to be applied to the light receiving elements of optical sensors that are compatible with the near-infrared region (NIR) and short-wave infrared region (SWIR). Optical sensors that can handle light in these long wavelength regions are installed in LIDAR (Light Detection and Ranging) and SWIR image sensors. LIDAR is a remote sensing system for autonomous driving automobiles, drones, ships, etc., and has become an important device in the recent development of autonomous driving technology. Recently, LIDAR has also been applied to facial recognition technology and augmented reality (AR) technology in smartphones, tablets, etc. Furthermore, SWIR image sensors are a device whose demand is expected to increase in the future in fields such as food inspection, agriculture, and drones.

[0005] Until now, silicon thin films have often been used as light-receiving elements in sensors for optical devices such as those described above. However, sensors based on silicon thin films have a significant drop in sensitivity in the long wavelength range of 900 nm or longer, making them unsuitable for the above applications. Therefore, there is hope for the development of light-receiving elements that use semiconductor nanoparticles.

[0006] Several semiconductor compounds have been investigated for the composition of semiconductor nanoparticles. Semiconductor compounds that have photoresponsiveness in the long wavelength region of the near infrared region (NIR) and short wave infrared region (SWIR) include PbS, PbSe, CdHgTe, and Ag. ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２ Metal chalcogenide compounds of Ag, InAs, etc. are known (Patent Documents 1 to 4). The applicant of the present application also discloses semiconductor nanoparticles containing an AgAuS-based compound as a main component in Patent Document 5.

[0007] Japanese Patent Application Laid-Open No. 2004-243507 Japanese Patent Application Laid-Open No. 2004-352594 Japanese Patent Application Laid-Open No. 2017-014476 International Publication No. WO2020 / 054764 Japanese Patent No. 7269591

[0008] Although the above-mentioned semiconductor compounds have photoresponsiveness in the desired wavelength range, many of them have obstacles when considering applications such as the display devices and markers for detecting biological substances mentioned at the beginning. For example, the European RoHS Directive (Restriction of the use of certain hazardous substances in electrical and electronic equipment) restricts the use of Pb in electrical and electronic equipment from the perspective of environmental impact. Therefore, semiconductor nanoparticles made of compounds containing Pb as a metal component are unlikely to be widely used in the electrical and electronic fields. Furthermore, when considering the use of semiconductor nanoparticles in biological fields, it is also difficult to use compounds containing heavy metals such as Cd and Hg.

[0009] Furthermore, while the semiconductor compounds described above have photoresponsiveness in the long-wavelength region, there is a growing demand for compounds that can exhibit photoresponsiveness at even longer wavelengths. Recent advances in autonomous driving technology for automobiles have been remarkable, and it is necessary to support autonomous driving levels (levels 4 and 5) that do not require a driver to drive. In this case, it is important for LIDAR to have a response in the longer wavelength region, which is less susceptible to the influence of sunlight and natural light. Therefore, quantum dot technology can be said to be still in the research stage. Therefore, semiconductor nanoparticles that can exhibit response in the longer wavelength region while taking practicality into consideration are needed.

[0010] The present invention has been made under the above-mentioned background, and proposes semiconductor nanoparticles made of a novel semiconductor compound that take into consideration practical applicability to various regulations and have suitable photoresponsiveness. In particular, the present invention proposes semiconductor nanoparticles that exhibit suitable light absorption properties in the long wavelength regions of the near-infrared region (NIR) and short-wave infrared region (SWIR) and are also capable of emitting light.

[0011] In investigating a solution to the above-mentioned problem, the present inventors focused on semiconductor nanoparticles made of AgAuS compounds, which are related to the prior art (Patent Document 5) of the present applicant. Ag and Au are metals that can be suitably used in terms of regulatory compliance, such as environmental impact and toxicity, and AgAuS compounds are semiconductor compounds that can exhibit photoresponsiveness. However, conventional AgAuS compound nanoparticles have issues with photoresponsiveness in the infrared region (NIR) and shortwave infrared region (SWIR). In the above-mentioned prior art of the present applicant, a metal such as In is added to the AgAuS compound to create an AgAuS-based multi-component compound, thereby shifting the absorption wavelength of the semiconductor nanoparticles to longer wavelengths.

[0012] The present inventors have taken the above-mentioned prior art AgAuS compound as a transition metal chalcogen compound into consideration and have attempted to impart photoresponsiveness in the long wavelength region to a transition metal chalcogen compound based on a two-pronged approach.

[0013] The first approach is to use Te (tellurium), an element with a larger mass than S (sulfur), as an essential component of the chalcogen element. This is because increasing the mass of the chalcogen element bonded to the transition metal reduces the orbital energy difference between each transition metal element and the chalcogen element when a compound is formed, which is presumed to shift the photoresponse to longer wavelengths.

[0014] The second approach is to optimize the transition metal component of the chalcogen compound, specifically, to use a combination of Ag and Cu instead of the combination of Ag and Au. Cu is a Group 11 element like Au and has a similar electronic structure, so it has the potential to become a suitable optical semiconductor when made into a chalcogen compound. Furthermore, Cu is one of the essential elements of the human body, so it has good biocompatibility.

[0015] Therefore, the present inventors investigated the feasibility of synthesizing nanoparticles of an AgCu chalcogen compound containing Te as an essential chalcogen element and the photoresponsiveness of the nanoparticles (hereinafter, the chalcogen element may be referred to as Ch.) As a result, they discovered an AgCu chalcogen compound that has optical absorption characteristics with an absorption edge in the long wavelength region of 1200 nm or more and can also exhibit a luminescence phenomenon, leading to the present invention.

[0016] That is, the present invention provides semiconductor nanoparticles containing an AgCu chalcogen compound represented by the following formula, which is 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] (In the formula, Ch is a chalcogen element. x, y, and z are the atomic numbers of Ag, Cu, and the chalcogen element, respectively, and 0.2≦z / (x+y)≦1.0. Also, 1.0≦x / y≦10.0.)

[0018] The structure of semiconductor nanoparticles containing an AgCu chalcogen compound containing Te as an essential chalcogen element as a main component according to the present invention and a method for producing the same will be described below.

[0019] A. Structure 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 are mainly composed of an AgCu chalcogen compound. This AgCu chalcogen compound has the following structure: Ag, Cu, and the chalcogen element Ch are x, y, and z, respectively. ｘ Cu ｙ Ch ｚIt can be expressed as follows. Regarding the composition of the AgCuCh compound, the ratio (atomic ratio) of the number of Ag atoms x to the number of Cu atoms y is 1.0≦x / y≦10.0. Within the range investigated by the inventors, AgCu chalcogen compound nanoparticles within this composition range exhibit favorable light absorption characteristics in the long wavelength region of 1200 nm or more. Furthermore, AgCu chalcogen compound nanoparticles within this composition range can also emit light. Furthermore, by changing the atomic ratio x / y of Ag to Cu, the photoresponse characteristics of the AgCu chalcogen compound nanoparticles change. It is more preferable that the atomic ratio x / y of Ag to Cu is 3.0 or more and 5.0 or less, thereby allowing an emission peak to be observed in the long wavelength region of 1200 nm or more.

[0020] The chalcogen element (Ch) of the AgCu chalcogen compound used in the present invention is a chalcogen element that essentially contains Te. As described above, by using Te, which has a relatively large mass among chalcogen elements, the wavelength exhibiting photoresponsiveness can be shifted to a longer wavelength. In the AgCu chalcogen compound of the present invention, the chalcogen element is bonded to the transition metals Ag and Cu so as to achieve charge compensation. The ratio of the number of atoms z of the chalcogen element to the number of atoms (x + y) of the transition metal components (Ag and Cu) satisfies 0.2≦z / (x + y)≦1.0. This atomic ratio z / (x + y) is preferably 0.3 to 0.7 (0.3≦z / (x + y)≦0.7), and more preferably 0.5 to 0.7 (0.5≦z / (x + y)≦0.7).

[0021] Furthermore, since Te is an essential chalcogen element in the AgCu chalcogen compound of the present invention, it may contain only Te, but may also contain other chalcogen elements other than Te. The reason why the AgCu chalcogen compound of the present invention contains other chalcogen elements in addition to Te is that when a chalcogen element is contained in a protective agent, solvent, etc. used in the synthesis process, this chalcogen element bonds with the transition metal component together with Te. As other chalcogen elements that may be contained together with Te in such a process, S or Se are preferred. When the AgCu chalcogen compound of the present invention contains other chalcogen elements other than Te, and the number of Te atoms is z, ＴｅWhen the number of atoms of Te (z) is Ｔｅ ) ratio z Ｔｅ / 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, the inventors' studies have shown that when other chalcogen elements are contained in addition to Te as a chalcogen element, the light absorption characteristics change depending on the atomic ratio of Te.

[0022] The composition of the AgCu chalcogen compound described above refers to 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 multiple phases. For example, when the chalcogen element is Te only, the AgCu chalcogen compound (Ag ｘ Cu ｙ Te ｚ ) can have several specific chemical compositions depending on the valence of Ag, Cu, and Te, such as AgCuTe (x = 1, y = 1, z = 1) and AgCuTe ２ (x=1, y=1, z=2). When S and / or Se are contained in addition to Te as chalcogen elements, chalcogen compounds with stoichiometric compositions for these elements (AgCuS (x=1, y=1, z=1) and AgCuSe (x=1, y=1, z=1) etc.) are also available. The AgCu chalcogen compound in the semiconductor nanoparticles of the present invention is composed of these stoichiometric compounds in a single phase or a multi-phase mixture. It may also contain compounds that do not have the above-mentioned stoichiometric composition. It is sufficient that x, y, and z are within the above-mentioned ranges in the entire AgCu chalcogen compound in the semiconductor nanoparticles.

[0023] The semiconductor nanoparticles according to the present invention are primarily composed of an AgCu chalcogen compound, with 90 atomic % or more of the AgCu chalcogen compound. The semiconductor nanoparticles may be composed solely of an AgCu chalcogen compound. More preferably, 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 essential chalcogen elements Ag, Cu, and Te that constitute the AgCu chalcogen compound. For example, the semiconductor nanoparticles may contain elements contained in the solvent used to synthesize the AgCu chalcogen compound or elements contained in the precursors of the raw materials Ag, Cu, and Te. Elements that may be contained in addition to the essential constituent elements Ag, Cu, and chalcogen elements include C, P, Cl, Br, I, etc., and the content of these elements in the semiconductor nanoparticles is acceptable as long as it is less than 10 mass %. Note that the composition values ​​of the compounds and elements shown here are values ​​related to the semiconductor nanoparticles and do not include the content of the protective agent and its constituent elements, which will be 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 multiple phases. Semiconductor nanoparticles composed of multiple phases can have a so-called core-shell structure. An example of a core-shell structure is a structure comprising 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 or a compound not containing Ag, Cu, or Te, whose composition is different from that of the core compound, and the shell compound covers at least a portion of the surface of the core compound. Furthermore, instead of a regular combination of multiple phases like the core-shell structure, multiple phases with different compositions may be randomly distributed. Cu-rich, Ag- and Te-rich, and the terms "Cu-rich" and "Ag- and Te-rich" mean that the composition ratio of Cu, Ag, and Te in the phase is greater than 50 atomic %.

[0025] The shape of the semiconductor nanoparticles according to the present invention may be spherical, cubic, or rod-shaped. The spherical or cubic semiconductor nanoparticles 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 band gap adjustment effect due to the quantum confinement effect. The above average particle size is preferable for achieving favorable light absorption characteristics through band gap adjustment. The average particle size of the semiconductor nanoparticles can be obtained by observing a plurality of semiconductor nanoparticles (preferably 100 or more) using an electron microscope such as a TEM, measuring the particle size of each particle, and calculating the particle number average. The particle size can be measured as the average value of the major axis and minor axis.

[0026] Furthermore, a scanning transmission electron microscope (scanning TEM) can be suitably used in analyzing the composition and structure of the semiconductor nanoparticles according to the present invention. In particular, a high-angle annular dark-field scanning transmission microscope (HAADF-STEM) can provide a scattering image that reflects the compositional information of the nanoparticles, and by combining it with an energy dispersive X-ray spectrometer (EDS, EDX) or the like, it is possible to understand the distribution of Ag, Cu, and Te and the composition of the entire nanoparticles.

[0027] A-3. Photoresponsiveness of semiconductor nanoparticles according to the present invention As described above, the band gap of semiconductor nanoparticles is adjusted by the quantum confinement effect according to the particle size, and the photoresponsiveness changes. Regarding the light absorption characteristics of the semiconductor nanoparticles according to the present invention, the absorption edge wavelength on the long wavelength side of the absorption spectrum is preferably 1200 nm or more. This allows the semiconductor nanoparticles to exhibit absorption for light in the visible light region to the near-infrared region. In a more preferred 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] Furthermore, the semiconductor nanoparticles according to the present invention can also exhibit a luminescence phenomenon. In this case, the emission spectrum exhibits an emission peak in a wavelength region of 1000 nm or more. In a preferred embodiment, the semiconductor nanoparticles according to the present invention can exhibit an emission peak in a long wavelength region of 1200 nm or more, more preferably 1400 nm or more.

[0029] A-4. Use of the semiconductor nanoparticles according to the present invention By coating and supporting the semiconductor nanoparticles according to the present invention on an appropriate substrate or carrier, they can be used in various applications such as the above-mentioned optical sensor elements. There are no particular limitations on the structure, shape, or dimensions of the substrate or carrier. Examples of substrates in the form of a plate or foil or film include glass, quartz, silicon, ceramics, or metal. In addition, examples of granular or powdered carriers include ZnO, TiO ２ , W.O. ３ , SnO ２ , In ２ O ３ , Al ２ O ３ The semiconductor nanoparticles may be supported on the inorganic oxide support and then fixed to a substrate.

[0030] Furthermore, when semiconductor nanoparticles are applied to or supported on a substrate or carrier, a solution, slurry, or ink in which semiconductor nanoparticles are dispersed in an appropriate dispersion medium is often used, as described above. Chloroform, toluene, cyclohexane, hexane, or the like can be used as the dispersion medium for this solution. Dipping and spin coating methods can be used as methods for applying the semiconductor nanoparticle solution, and various methods such as dropping, impregnation, and adsorption can be used as methods for supporting the semiconductor nanoparticles.

[0031] The semiconductor nanoparticles according to the present invention preferably contain a protective agent to suppress aggregation during their synthesis or when dispersed in a dispersion medium as described above. This protective agent is preferably at least one of alkylamines having an alkyl chain carbon number of 4 to 20, alkenylamines having an alkenyl chain carbon number of 4 to 20, alkylcarboxylic acids having an alkyl chain carbon number of 3 to 20, alkenylcarboxylic acids having an alkenyl chain carbon number of 3 to 20, and alkanethiols having an alkyl chain carbon number of 4 to 20. These protective agents bond to the surface of the semiconductor nanoparticles to coat at least a portion of them, suppressing aggregation of the semiconductor nanoparticles in the dispersion and forming a uniform solution. Furthermore, adding a protective agent to the reaction system together with the raw materials in the semiconductor nanoparticle synthesis process allows the synthesis of nanoparticles with a suitable average particle size. The protective agent can be any of the alkylamines, alkenylamines, alkylcarboxylic acids, alkenylcarboxylic acids, and alkanethiols, either singly or in combination.

[0032] B. Method for Producing Semiconductor Nanoparticles According to the Present Invention Next, a method for producing semiconductor nanoparticles according to the present invention will be described. The present inventors have discovered that, in the synthesis of an AgCu chalcogen compound having the above-described composition, it is preferable to use compounds containing Ag, Cu, and Te as precursors (Ag precursor, Cu precursor, Te precursor), introduce these precursors into the same reaction system, and heat and react them simultaneously. Below, a method for producing semiconductor nanoparticles using this AgCu chalcogen compound synthesis method will be described.

[0033] B-1. Raw materials (Ag precursor, Cu precursor, Te precursor) The Ag precursor, Cu precursor, and Te precursor used as raw materials are, respectively, an Ag salt or Ag complex, a Cu salt or Cu complex, and a Te compound. The Ag precursor and Cu precursor are preferably salts or complexes containing monovalent Ag and monovalent Cu.

[0034] The Ag precursor is preferably an Ag salt or an Ag complex. The Ag precursor is preferably a salt or complex containing monovalent Ag. Specific examples of suitable Ag precursors include silver acetate (Ag(OAc)), silver nitrate, silver carbonate, silver oxide, silver oxalate, silver chloride, silver iodide, silver (I) cyanide, and silver diethyldithiocarbamate.

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

[0036] The Te compound that can be used as a Te precursor is tellurium oxide (TeO ２ ), telluric acid (Te(OH) ６ ), sodium tellurite (Na ２ TeO ３ Te compounds such as tetraethoxysilane, ...

[0037] B-2. Formation of a reaction system of an AgCu chalcogen compound When synthesizing an AgCu chalcogen compound, the above-mentioned Ag precursor, Cu precursor, and Te precursor are mixed to form a single reaction system, which is then reacted. At this time, the Ag precursor, Cu precursor, and Te precursor that have been prepared separately may be mixed sequentially, and the order of mixing is not particularly limited. Alternatively, a mixture of an Ag precursor and a Cu precursor that will become the transition metal component of the AgCu chalcogen compound may be prepared as a metal source precursor, and the metal source precursor and Te precursor may be mixed to form a reaction system.

[0038] The synthesized AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚThe atomic ratio (x / y) of Ag to Cu in the AgCu chalcogen compound of the present invention can be adjusted by adjusting the ratio of the amounts of the Ag precursor and the Cu precursor charged. The ratio of the amounts charged for synthesizing the AgCu chalcogen compound of the present invention, in which the atomic ratio (x / y) of Ag to Cu falls within a predetermined range, is preferably set so that the ratio (a / b: hereinafter, referred to as the Ag charge ratio) is 1 or more and 10 or less, and more preferably 2 or more and 4 or less, where a is the number of Ag atoms in the Ag precursor and b is the number of Cu atoms in the Cu precursor.

[0039] The amount of Te precursor in the reaction system is determined by the amount of AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ The number of Te atoms in the chalcogen element (z Ｔｅ According to the studies of the present inventors, when the number of Te atoms in the Te precursor is c and the number of Cu atoms in the Cu precursor is b, the ratio thereof (c / b: hereinafter, this ratio may be referred to as the Te charging ratio) is preferably set to 0.1 or more and 2 or less, more preferably 0.1 or more and 1 or less.

[0040] Furthermore, as described above, the semiconductor nanoparticles of the present invention preferably have a protective agent bonded to the AgCu chalcogen compound. Furthermore, when this protective agent contains a chalcogen element, the chalcogen element can form 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, Cu precursor, and Te precursor. As the protective agent, it is preferable to add at least one of alkylamines having an alkyl chain carbon number of 4 to 20, alkenylamines having an alkenyl chain carbon number of 4 to 20, alkylcarboxylic acids having an alkyl chain carbon number of 3 to 20, alkenylcarboxylic acids having an alkenyl chain carbon number of 3 to 20, and alkanethiols having an alkyl chain carbon number of 4 to 20.

[0041] Although the reaction system for synthesizing semiconductor nanoparticles can produce nanoparticles without a solvent, it is preferable to use a solvent. When a solvent is used, octadecene, tetradecane, oleic acid, oleylamine, dodecanethiol, or a mixture thereof can be used.

[0042] B-3. ​​AgCu chalcogen compound synthesis conditions AgCu chalcogen compound nanoparticles are synthesized by heating a reaction system consisting of an Ag precursor, a Cu precursor, a Te precursor, and a protective agent. The heating temperature (reaction temperature) at this time is 100°C or higher and 200°C or lower. If the temperature is lower than 100°C, the synthesis reaction does not proceed easily. On the other hand, if the temperature 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] The reaction time (heating time) can be adjusted depending on the amount of raw materials charged, but 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. It is preferable to stir the reaction system while the synthesis reaction of AgCu chalcogen compound nanoparticles proceeds.

[0044] After the synthesis reaction of AgCu chalcogen compound nanoparticles is completed, the reaction system can be cooled as necessary and recovered as semiconductor nanoparticles. At this time, the nanoparticles can be precipitated by adding alcohol (ethanol, methanol, etc.) as a poor solvent, or the semiconductor nanoparticles can be precipitated and recovered by centrifugation or the like, and the particles can be further washed with alcohol (ethanol, methanol, etc.) and then uniformly dispersed in a good solvent such as chloroform.

[0045] As described above, the present invention provides an AgCu chalcogen compound (AgCu chalcogen compound) containing Te as an essential chalcogen element. ｘ Cu ｙ Ch ｚThe semiconductor nanoparticles according to the present invention have favorable photoresponsiveness and are practical in view of usage regulations, etc. The semiconductor nanoparticles according to the present invention can be used in applications such as light receiving elements and light emitting elements in the long wavelength region of the near infrared region (NIR) and short wave infrared region (SWIR).

[0046] The AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ TEM image of semiconductor nanoparticles made of AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ ) is a measurement result of the absorption spectrum of the semiconductor nanoparticles composed of the AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ... ｘ Cu ｙ Ch ｚ ) and the absorption spectrum of the semiconductor nanoparticles composed of the AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ ) was synthesized by changing the heating temperature in the third embodiment. ｘ Cu ｙ Ch ｚ TEM image of semiconductor nanoparticles made of AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ ) was synthesized by changing the heating temperature in the third embodiment. ｘ Cu ｙ Ch ｚ ) was synthesized by changing the reaction time in the third embodiment. ｘ Cuｙ Ch ｚ TEM images of semiconductor nanoparticles made of AgCu chalcogen compounds (Ag ｘ Cu ｙ Ch ｚ ) was synthesized by changing the reaction time in the third embodiment. ｘ Cu ｙ Ch ｚ ) and the emission spectrum of semiconductor nanoparticles.

[0047] First Embodiment: Hereinafter, an embodiment of the present invention will be described. In this embodiment, a AgCu chalcogen compound (Ag ｘ Cu ｙ Ch ｚ In this embodiment, nanoparticles of an AgCu chalcogen compound were synthesized by varying the atomic ratio of Ag to Cu (x / y).

[0048] In this embodiment, the semiconductor nanoparticles made of an AgCu chalcogen compound were synthesized by preparing a mixture of an Ag precursor and a Cu precursor, which serve as transition metal components, in advance as a metal source precursor, and then mixing and reacting the metal source precursor with a Te precursor to synthesize the semiconductor nanoparticles.

[0049] A metal source precursor was prepared by dissolving and mixing silver acetate (Ag(OAc)) as an Ag precursor and copper acetate (Cu(OAc)) as a Cu precursor in 3 mL of 1-dodecanethiol (DDT), a solvent and protective agent. At this time, the total content of Ag and Cu in the solution was set to 0.08 mmol in terms of metal. Then, silver acetate and copper acetate were mixed so that the Ag charging ratio (a / b) was 3 / 1, 2.5 / 1.5, 2 / 2, or 1.5 / 2.5. While this metal source precursor was being prepared, tellurium oxide (TeO ２ 0.2 mmol of Te precursor was dissolved in 2 mL of DDT, a solvent and protective agent, and heated at 100° C. for 5 minutes in a nitrogen atmosphere to prepare a Te precursor solution.

[0050] To synthesize AgCu chalcogen compound nanoparticles, first, a solution of metal source precursors (Ag, Cu) was heated at 150°C for 5 minutes under a nitrogen atmosphere. Then, the Te precursor solution was injected into the solution using a syringe. After that, the reaction temperature was set to 150°C under a nitrogen atmosphere, and the mixture was stirred while being heated for 15 minutes. After the reaction was completed, the mixture was allowed to cool and then centrifuged at 4000 rpm for 5 minutes to separate the supernatant and precipitate. Then, 4 cm of ethanol / toluene was added to the supernatant as a poor solvent. ３ After adding the mixture to cause precipitation, the mixture was centrifuged at 4000 rpm for 5 minutes to collect the precipitate, thereby obtaining AgCu chalcogen compound nanoparticles.

[0051] The AgCu chalcogen compound nanoparticles obtained by the above procedure were dissolved in 3 cm of chloroform. ３ This dispersion was transferred into a sample bottle, and the atmosphere was replaced with nitrogen, and the bottle was then stored in a refrigerator in a dark place.

[0052] [TEM Observation of Semiconductor Nanoparticles] TEM observation was performed on semiconductor nanoparticles composed of the AgCu chalcogen compound synthesized in this embodiment (Ag charge ratio: 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5). Figure 1 shows TEM images of each semiconductor nanoparticle produced in this embodiment (see the scale bar in each photograph for magnification). Referring to Figure 1, in the AgCu chalcogen compound synthesized with an Ag charge ratio of 3 / 1, many nearly spherical nanoparticles are observed. As the Ag charge ratio decreases (the proportion of Cu increases), there is a tendency for the number of amorphous nanoparticles to increase accordingly.

[0053] [Composition Analysis of Semiconductor Nanoparticles] Composition analysis was performed by SEM-EDS analysis on semiconductor nanoparticles composed of an AgCu chalcogen compound synthesized in this embodiment (Ag charging ratio: 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5). The measurement results of the composition of each semiconductor nanoparticle are shown in Table 1. In this embodiment and each of the following embodiments, the results of the composition analysis are expressed in atomic % relative to the total nanoparticles. 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]

[0055] As can be seen from Table 1, an increase in the Ag charge ratio (a / b) naturally increases the ratio (x / y) of the number of Ag atoms (x) to the number of Cu atoms (y) in the AgCu chalcogen compound. It was also confirmed that the ratio of the number of atoms (z) of the chalcogen elements to the number of atoms (x+y) of the transition metal components (Ag and Cu) does not vary significantly even when the Ag charge ratio is changed. It was also confirmed that the AgCu chalcogen compounds synthesized in this embodiment contain Te as an essential chalcogen element, while also containing S as another chalcogen element. Furthermore, with the exception of No. 4, the ratio of the number of Te atoms to the total number of chalcogen elements (z) was 0.01. Ｔｅ The AgCu chalcogen compound No. 4 has the smallest Ag ratio (a / b: 1.5 / 2.5), and the TEM observation results ( FIG. 1 ) show that two phases are separated, which is thought to be the only difference in the tendency.

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

[0057] The measurement results of the absorption spectrum of each semiconductor nanoparticle produced in this embodiment are shown in Figure 2, and the measurement results of the emission spectrum are shown in Figure 3. In addition, 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 are shown in Table 2.

[0058]

[0059] Referring to the absorption spectrum measurement results in FIG. 2 and Table 2, all of the semiconductor nanoparticles have optical absorption characteristics that show an absorption edge in the region of 1400 nm or more. In addition, all of them show a small peak that is thought to be an exciton peak in the wavelength range of 800 nm to 950 nm, while an absorption peak appears around 1400 nm. ｘ Cu ｙ Ch ｚ Regarding the composition of ), when the atomic ratio of Ag to Cu (x / y) is examined, a shift of the absorption edge to the long wavelength side is observed as x / y increases and the atomic ratio of Ag increases.

[0060] Furthermore, it was confirmed that all of the semiconductor nanoparticles of this embodiment exhibited luminescence. Referring to the measurement results of the emission spectrum in FIG. 3 and Table 2, an emission peak was confirmed in the wavelength region of 1000 nm or more. In particular, the emission peak wavelength of the semiconductor nanoparticles (No. 1) with a high Ag atomic ratio was on the long wavelength side. An emission peak was observed in the region of 1200 nm or more for these semiconductor nanoparticles.

[0061] From the above evaluation results of photoresponsiveness, it can be said that the semiconductor nanoparticles composed of the AgCu chalcogen compound synthesized in this embodiment have an absorption edge of 1200 nm or more and exhibit good light absorption properties in the long wavelength region. In particular, the AgCu chalcogen compound nanoparticles No. 1 with an Ag content of 3 / 1 (x / y = 4) had a long wavelength absorption edge wavelength of 1500 nm or more and also showed good emission characteristics with a peak wavelength of 1200 nm or more.

[0062] Second Embodiment: In this embodiment, semiconductor nanoparticles composed of AgCu chalcogen compounds of various compositions were synthesized by adjusting the Te charge ratio. The semiconductor nanoparticle synthesis method applied in this embodiment is basically the same as that in the first embodiment. A solution of a Te precursor was added to a solution of a metal source precursor, and the solution was heated and reacted to obtain nanoparticles of an AgCu chalcogen compound. In this embodiment, the amount of Te precursor added was adjusted to perform the synthesis reaction so that the Te charge ratio (c / b), which is the ratio of the number of Te atoms in the Te precursor, c, to the number of Cu atoms in the metal source precursor, b, was 1 / 4, 1 / 2, 1 / 1, or 2 / 1. After synthesis, the nanoparticles were separated and purified in the same manner as in the first embodiment to obtain nanoparticles of an AgCu chalcogen compound. The Ag charge ratio (a / b) was 3 / 1, and the other reaction conditions were the same as in the first embodiment.

[0063] [Composition Analysis of Semiconductor Nanoparticles] The composition of the semiconductor nanoparticles (Te content ratio: 1 / 4, 1 / 2, 1 / 1, 2 / 1) composed of the AgCu chalcogen compound synthesized in this embodiment was analyzed by SEM-EDS. The measurement results of the composition of each semiconductor nanoparticle are shown in Table 3.

[0064]

[0065] Referring to Table 3, even if the Te charging ratio (c / b) increases, there is no significant change in 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 (Ag, Cu) (x+y). Ｔｅ In addition, an increase in the Te content 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 to evaluate the photoresponsiveness of each semiconductor nanoparticle produced in this embodiment. These measurement methods were the same as in the first embodiment. The results of these measurements are shown in Figures 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]

[0068] Referring to the absorption spectrum measurement results in Figure 4 and Table 4, in all of the semiconductor nanoparticles with different Te loading ratios, an absorption peak appears near 1400 nm while showing an exciton peak. The long-wavelength absorption edge is in the region of 1500 nm or more in all cases. In particular, the semiconductor nanoparticles (No. 5) with a low Te loading ratio (low atomic ratio of Te in the AgCu chalcogen compound) showed a further shift in the absorption edge wavelength.

[0069] Referring to the emission spectrum measurement results in Figure 5 and Table 4, the emission spectrum curves of semiconductor nanoparticles No. 5 to No. 7 (c / b: 1 / 4 to 1 / 1) show similar trends with little difference. Semiconductor nanoparticle No. 8, which had a high Te loading ratio (c / b: 2 / 1), did not show a clear peak.

[0070] Third Embodiment: In this embodiment, the photoresponsiveness of semiconductor nanoparticles obtained when the synthesis conditions for AgCu chalcogen compound nanoparticles were changed was examined.

[0071] First, the influence of temperature before and after the formation of a reaction system was investigated. 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 (reaction temperature: T2) after adding the Te precursor solution were adjusted. Specifically, AgCu chalcogen compound nanoparticles were synthesized under three conditions: (i) T1 = T2 = 150°C, (ii) T1 = 150°C and T2 = 120°C, and (iii) T1 = T2 = 120°C. The heating times in each study were the same as those in the first embodiment.

[0072] In this embodiment, the effect of the heating time (reaction time) after adding the Te precursor solution to the metal source precursor solution was also investigated. In this investigation, AgCu chalcogen compound nanoparticles were synthesized with reaction times of 5, 10, 20, 40, and 80 minutes. The heating temperatures in this investigation were T1 = T2 = 120°C.

[0073] In each study, the synthesis method and conditions other than the above-mentioned reaction conditions were the same as those in the first embodiment, and the Ag feed ratio (a / b) was 3 / 1.

[0074] Regarding the results of the study of this embodiment, first, the temperature before and after the formation of the reaction system will be described. FIG. 6 is a TEM image of AgCu chalcogen compound nanoparticles synthesized under the heating conditions (i) to (iii) described above. This TEM image shows that nanoparticles with a stable particle shape are synthesized under the condition (iii) in which the heating temperatures (T1 and T2) before and after the formation of the reaction system are both 120°C. Furthermore, the shape of the nanoparticles tends to become unstable when heating is performed at 150°C.

[0075] Therefore, composition analysis was performed by EDS on semiconductor nanoparticles prepared under conditions (i) (T1 = T2 = 150°C) and (iii) (T1 = T2 = 120°C), in which the heating temperatures before and after the formation of the reaction system were the same. The results are shown in Table 5. Table 5 shows that these AgCu chalcogen compound nanoparticles differ in particle shape, but do not differ significantly in composition.

[0076]

[0077] The measurement results of the absorption and emission spectra of these two semiconductor nanoparticles are shown in FIGS.

[0078]

[0079] Looking at the absorption spectrum measurement results in Figure 7 and Table 6, the absorption characteristics of the semiconductor nanoparticles under heating conditions (i) and (iii) form similar curves overall. However, in the semiconductor nanoparticles (iii) where the heating temperature was 120°C before and after the formation of the reaction system, the absorption peak intensity is clearly stronger and the absorption edge wavelength is also longer. Furthermore, looking at the emission spectrum measurement results in Figure 8 and Table 6, the emission peak wavelength of the semiconductor nanoparticles (iii) where the heating temperature was 120°C before and after the formation of the reaction system is significantly shifted (by 200 nm or more) to the longer wavelength side.

[0080] Next, the results of an investigation into the effect of reaction time will be described. FIG. 9 is a TEM image of AgCu chalcogen compound nanoparticles synthesized over a reaction time of 5 to 40 minutes (T1 = T2 = 120°C). It can be seen from FIG. 9 that the particle shape becomes closer to a sphere as the reaction time increases. Furthermore, the results of composition analysis of these semiconductor nanoparticles by EDS are shown in Table 7. Referring to Table 7, it can be seen that even if the reaction time increases, there is no significant difference in the atomic ratio (z / (x+y)) of the transition metal components (Ag, Cu) to the chalcogen elements. Furthermore, the atomic ratio (x / y) of Ag in the transition metal components does not vary significantly within the range of 3.0 to 5.0.

[0081]

[0082] For AgCu chalcogen compound nanoparticles synthesized with a reaction time of 5 to 40 minutes (T1 = T2 = 120°C), the absorption spectrum measurement results are shown in Figure 10 and the emission spectrum measurement results are shown in Figure 11, and these are summarized in Table 8.

[0083]

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

[0085] To summarize the results of the study on the synthesis conditions investigated in this embodiment, it can be said that a relatively low temperature of 120°C is more preferable for the heating temperature and reaction temperature of the metal source precursor compared to 150°C (first embodiment). Furthermore, a longer reaction time is preferable because it results in spherical particles, but there is little difference in properties other than the particle shape. It is believed that the reaction time can be set relatively freely. The synthesis conditions for semiconductor nanoparticles should be adjusted depending on the concentrations of the 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 used as a reference.

[0086] As described above, semiconductor nanoparticles made of an AgCu chalcogen compound according to the present invention can exhibit excellent photoresponsiveness. This AgCu chalcogen compound is also designed to comply with usage regulations and avoid the use of heavy metals. The semiconductor nanoparticles according to the present invention are expected to be applied to light-emitting elements and fluorescent materials used in display devices and marker substances for detecting biological substances, as well as photoelectric conversion elements and photodetectors mounted in solar cells, optical sensors, and the like. In particular, the present invention aims to improve light absorption characteristics in the long wavelength regions of the near-infrared region (NIR) and shortwave infrared region (SWIR). For this reason, the present invention is particularly useful for photodetectors applied to LIDAR and SWIR image sensors, among the above-mentioned optical elements, in which responsiveness in the near-infrared region is important.

Claims

1. Semiconductor nanoparticles containing an AgCu chalcogen compound represented by the following formula, which is composed of Ag, Cu, and a chalcogen element, wherein the chalcogen element contains Te as an essential chalcogen element, and the AgCu chalcogen compound accounts for 90 atomic % or more of the semiconductor nanoparticles. (In the formula, Ch is a chalcogen element. x, y, and z are the atomic numbers 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 elements constituting the AgCu chalcogen compound include chalcogen elements other than Te, the other chalcogen elements being S and Se.

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

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

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

6. Semiconductor nanoparticles according to claim 1 or 2, having at least one of the following protective agents bonded to the surface: alkylamines having an alkyl chain carbon number of 4 to 20, alkenylamines having an alkenyl chain carbon number of 4 to 20, alkylcarboxylic acids having an alkyl chain carbon number of 3 to 20, alkenylcarboxylic acids having an alkenyl chain carbon number of 3 to 20, and alkanethiols having an alkyl chain carbon number of 4 to 20.

7. The semiconductor nanoparticles according to claim 1 or 2, having an absorption edge wavelength on the long wavelength side of the absorption spectrum of 1,200 nm or more.

8. The semiconductor nanoparticles according to claim 1 or 2, which have an emission spectrum with a peak wavelength of 1000 nm or more.

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