Semiconductor nanoparticles mainly composed of agcu chalcogen compound

Abstract

This invention relates to semiconductor nanoparticles comprising AgCu chalcogenide compounds composed of Ag, Cu, and chalcogenide elements (Ch), expressed by the following formula. This invention includes Te as an essential chalcogenide element. By utilizing Te, which has a relatively large mass among the chalcogenide elements, the photoresponse characteristics are shifted to the longer wavelength side. The semiconductor nanoparticles of this invention contain at least 90 atomic percent AgCu chalcogenide compounds, and the absorption wavelength at the longer wavelength side of the absorption spectrum is 1200 nm or more. AgxCuyChz (where Ch is a chalcogenide element, x, y, z are the atomic numbers of Ag, Cu, and chalcogenide elements, 0.2 ≦ z / (x+y) ≦ 1, and 1.0 ≦ x / y ≦ 10.0).

Description

Technical Field

[0001] This invention relates to semiconductor nanoparticles with AgCu chalcogenides as the main component. Specifically, it relates to semiconductor nanoparticles made of AgCu chalcogenides containing Te as an essential chalcogenide element, which exhibit suitable photoresponse in the long wavelength region. Prior Technology

[0002] Semiconductors exhibit quantum confinement effects by being fabricated into nanoscale particles, displaying a band gap corresponding to their particle size. Therefore, by controlling the composition and particle size of semiconductor nanoparticles and adjusting the band gap, the emission and absorption wavelengths can be arbitrarily set. Semiconductor nanoparticles utilizing this property are also known as quantum dots (QDs) and are expected to be used in various technological fields. Examples of applications for semiconductor nanoparticles include their use in light-emitting elements and fluorescent materials in display devices and bio-related substance detection labeling materials.

[0003] This is because, in addition to controlling the emission wavelength by adjusting the aforementioned particle size, semiconductor nanoparticles also exhibit sufficiently narrow and stable emission peak widths compared to organic dyes. Furthermore, besides controlling the absorption wavelength, semiconductor nanoparticles also possess high quantum efficiency and a high extinction coefficient. Due to these properties, semiconductor nanoparticles are being explored for use in photoelectric conversion elements and light-receiving elements mounted in solar cells and various photosensors.

[0004] In particular, semiconductor nanoparticles are expected to be used as light-receiving elements in optical sensors operating in the near-infrared (NIR) and short-wave infrared (SWIR) regions. Light sensors capable of responding to light in these longer wavelength regions are incorporated into LIDAR (Light Detection and Ranging) and SWIR image sensors. LIDAR is a remote sensing system used in autonomous driving, drones, and ships, and has become an important device in the development of autonomous driving technology in recent years. Recently, LIDAR has also been applied to facial recognition technology and augmented reality (AR) technology in smartphones and tablets. Furthermore, SWIR image sensors are predicted to see increased demand in areas such as food inspection, agriculture, and drones.

[0005] As with the aforementioned optical devices, the light-receiving elements of sensors have so far mostly been Si thin films. However, sensors made of Si thin films suffer from a significant decrease in sensitivity in the long wavelength region above 900 nm, making them unsuitable for these applications. Therefore, the development of light-receiving elements utilizing semiconductor nanoparticles is highly anticipated.

[0006] Regarding the composition of semiconductor nanoparticles, several semiconductor compounds have been reviewed to date. Metal chalcogenides such as PbS, PbSe, CdHgTe, Ag2S, Ag2Se, Ag2Te, AgInSe2, AgInTe2, CuInSe2, CuInTe2, and InAs are known semiconductor compounds exhibiting photoresponsiveness in the long-wavelength regions of the near-infrared (NIR) and short-wave infrared (SWIR) regions (Patent Documents 1-4). The applicant has also disclosed semiconductor nanoparticles with AgAuS-based compounds as the main component in Patent Document 5. [Previous Technical Documents] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2004-243507 [Patent Document 2] Japanese Patent Application Publication No. 2004-352594 [Patent Document 3] Japanese Patent Application Publication No. 2017-014476 [Patent Document 4] International Publication No. WO2020 / 054764 [Patent Document 5] Japanese Patent No. 7269591 Summary of the Invention

[0008] [The problem the invention aims to solve] While the aforementioned semiconductor compounds exhibit photoresponsiveness in the desired wavelength range, many present obstacles for their application in display devices and biomarkers, as described earlier. For example, the European RoHS Directive (which restricts the use of certain hazardous substances in electrical and electronic equipment) imposes restrictions on the use of Pb in such equipment from an environmental perspective. Therefore, semiconductor nanoparticles made from compounds containing Pb as a metallic component are unlikely to see widespread use in the electrical and electronic fields. Furthermore, the application of semiconductor nanoparticles in bio-related fields also presents challenges in utilizing compounds containing heavy metals such as Cd and Hg.

[0009] Furthermore, while the aforementioned semiconductor compounds exhibit photoresponsiveness in the long-wavelength region, the demand for semiconductor compounds capable of displaying photoresponsiveness at even longer wavelengths is continuously increasing. The recent development of autonomous driving technology in automobiles has been remarkable, necessitating responses to levels of autonomous driving (Levels 4 and 5) that do not require driver intervention. In this context, the photoresponsiveness of LiDAR in the longer wavelength region, which is less affected by sunlight and natural light, is crucial. Therefore, it can be said that quantum dot technology is still in the research stage. Consequently, there is a need for semiconductor nanoparticles that can exhibit photoresponsiveness in the longer wavelength region while also considering practicality.

[0010] This invention was made against the aforementioned background, and proposes semiconductor nanoparticles made from novel semiconductor compounds with appropriate photoresponsiveness while taking into account practicality for various regulations. In particular, this invention proposes semiconductor nanoparticles that exhibit appropriate light absorption characteristics in the long wavelength regions of the near-infrared (NIR) and short-wave infrared (SWIR) regions, while also emitting light. [Methods used to solve problems]

[0011] In reviewing solutions to the aforementioned problems, the inventors focused on semiconductor nanoparticles made from AgAuS compounds, which are related to the prior art of the applicant in this case (Patent Document 5). From the perspective of regulations regarding environmental impact and toxicity, Ag and Au are suitable metals, and AgAuS compounds are semiconductor compounds capable of exhibiting photoresponsiveness. However, the photoresponsiveness of conventional AgAuS compound nanoparticles in the near-infrared (NIR) and short-wave infrared (SWIR) regions remains problematic. In the aforementioned prior art of the applicant, by adding metals such as In to the AgAuS compound to utilize AgAuS-based multi-component compounds, the absorption wavelength of the semiconductor nanoparticles can be shifted to the longer wavelength side.

[0012] The inventors used the aforementioned AgAuS compounds, specifically transition metal chalcogenides, as a reference and simultaneously achieved photoresponsivity in the long wavelength region of transition metal chalcogenides based on a two-directional approach.

[0013] Scheme 1 uses Te (tellurium), an element with a mass greater than S (sulfur), as a necessary component of the chalcogenide group. The reason for this is that by increasing the mass of the chalcogenide group that combines with the transition metals, the orbital energy difference between the transition metal elements and the chalcogenide group elements decreases when the compound is formed, thereby shifting the photoresponse to the longer wavelength side.

[0014] Therefore, the second approach involves optimizing the transition metal composition of the chalcogenide compounds. Specifically, it involves using a combination of Ag and Cu instead of Ag and Au. Since Cu and Au are both Group 11 elements and have the same electronic structure, the resulting chalcogenide compounds have the potential to become suitable optical semiconductors. Furthermore, because Cu is one of the essential elements for the human body, it exhibits good biocompatibility.

[0015] Therefore, the inventors investigated the possibility of synthesizing nanoparticles of AgCu chalcogenides with Te as an essential chalcogenide element and their photoresponsiveness (hereinafter, chalcogenides are sometimes simply referred to as Ch). The results revealed AgCu chalcogenides that exhibit both light absorption and emission in the long wavelength region above 1200 nm, leading to the invention of this invention.

[0016] That is, the present invention is a semiconductor nanoparticle, which is a semiconductor nanoparticle comprising AgCu chalcogenide compound represented by the following formula, which is composed of Ag, Cu and chalcogenide (Ch) elements, wherein the aforementioned chalcogenide elements include Te as an essential chalcogenide element, and the present invention comprises more than 90 atomic percent of the aforementioned AgCu chalcogenide compound.

[0017] AgxCuyChz (In the formula, Ch is a chalcogenide, x, y, z are the number of atoms of Ag, Cu, and chalcogenide, 0.2≦z / (x+y)≦1.0, and 1.0≦x / y≦10.0).

[0018] The following describes the composition and manufacturing method of the nanoparticles of the present invention, which use AgCu chalcogenide compounds, in which Te is an essential chalcogenide element, as the main component.

[0019] A. The composition of the semiconductor nanoparticles of this invention A-1. Chemical Composition of Semiconductor Nanoparticles As described above, the semiconductor nanoparticles of this invention are mainly composed of AgCu chalcogenides. When the atomic numbers of Ag, Cu, and the chalcogenide element Ch are set as x, y, and z, respectively, the AgCu chalcogenide compound can be represented by AgxCuyChz. Therefore, 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 scope of the inventors' review, AgCu chalcogenide nanoparticles falling within this composition range exhibit superior light absorption characteristics in the long wavelength region above 1200 nm. Furthermore, AgCu chalcogenide nanoparticles within this composition range can also exhibit light emission. Therefore, by changing the atomic ratio x / y of Ag and Cu, the photoresponse characteristics of the AgCu chalcogenide nanoparticles can be changed. The atomic ratio x / y of Ag to Cu is preferably 3.0 to 5.0, thereby allowing emission peaks to be observed in a long wavelength range above 1200 nm.

[0020] In this invention, the chalcogenide (Ch) element in the AgCu chalcogenide compound is Te, which is an essential chalcogenide. As mentioned above, by using Te, which has a relatively large mass among the chalcogenide elements, the wavelength of the displayed light response can be shifted to the longer wavelength side. In the AgCu chalcogenide compound of this invention, the chalcogenide elements are bonded in a manner that compensates for the charge of the transition metals Ag and Cu. Therefore, the ratio of the number of chalcogenide atoms z to the number of transition metal atoms (x+y) 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] Furthermore, since Te is essential as the chalcogenide element in the AgCu chalcogenide compound of the present invention, it can consist solely of Te, but may also include other chalcogenide elements besides Te. When the AgCu chalcogenide compound of the present invention contains other chalcogenide elements besides Te, the presence of chalcogenide elements in the protective agent or solvent used during synthesis is due to their bonding with the transition metal component together with Te. S or Se are preferred as other chalcogenide elements that can be included together with Te in this process. When the AgCu chalcogenide compound of the present invention contains other chalcogenide elements besides Te and the number of Te atoms is set to zTe, the ratio of the number of Te atoms (zTe) to the number of all chalcogenide elements (z), zTe / z, is preferably 0.2 to 0.4, more preferably 0.25 to 0.35. As will be described later, in the inventors' review, when Te and other chalcogenide elements are included as chalcogenide elements, the light absorption characteristics change with the atomic ratio of Te.

[0022] Furthermore, the composition of the AgCu chalcogenides described above refers to the overall composition of the AgCu chalcogenides in semiconductor nanoparticles. The AgCu chalcogenides used in this invention can be composed of a single phase or multiple phases. For example, when the chalcogenide element is only Te, it can become an AgCu chalcogenide (AgxCuyTez). The specific chemical composition depends on the valence of Ag, Cu, and Te. There are several examples, such as AgCuTe (x=1, y=1, z=1) and AgCuTe2 (x=1, y=1, z=2), etc., which are stoichiometric chalcogenides. Moreover, when the chalcogenide contains S and / or Se in addition to Te, there are chalcogenides with such stoichiometric compositions (AgCuS (x=1, y=1, z=1) and AgCuSe (x=1, y=1, z=1), etc.). The AgCu chalcogenides in the semiconductor nanoparticles of this invention are composed of compounds with stoichiometric compositions in a single-phase or multi-phase mixture. Furthermore, it may also include compounds that do not constitute the aforementioned stoichiometric compositions. In the entirety of the AgCu chalcogenides in the semiconductor nanoparticles, x, y, and z only need to be within the ranges described above.

[0023] The semiconductor nanoparticles of this invention use AgCu chalcogenides as the main component and are composed of at least 90 atomic% AgCu chalcogenides. The semiconductor nanoparticles may be composed solely of AgCu chalcogenides. More preferably, the semiconductor nanoparticles contain at least 95 atomic% AgCu chalcogenides. The semiconductor nanoparticles of this invention sometimes contain elements other than Ag, Cu, and Te (which are essential chalcogenides) that constitute the AgCu chalcogenides. For example, the semiconductor nanoparticles may sometimes contain elements that constitute the solvent used in the synthesis of the AgCu chalcogenides and elements contained in the precursors of Ag, Cu, and Te used as raw materials. Examples of elements that may be included other than Ag, Cu, and chalcogenides that are essential constituent elements include C, P, Cl, Br, and I, etc., and the content of these elements in the semiconductor nanoparticles is permissible if it does not reach 10% by mass. Furthermore, the composition values ​​of compounds and elements shown herein are values ​​related to the semiconductor nanoparticles and do not include the content of the protective agents and their constituent elements described later.

[0024] A-2. Structure of the semiconductor nanoparticles of the present invention As described above, the AgCu chalcogenides applicable in this invention are composed of a single phase or multiple phases. As a type of semiconductor nanoparticle formed by multiple phases, it can be configured as a so-called core-shell structure. Examples of core-shell structures include a core (core compound) composed of AgCu chalcogenides containing Ag, Cu, and Te, and a shell (shell compound) composed of AgCu chalcogenides with a different composition than the core compound or a compound that does not contain any of Ag, Cu, or Te, with the shell compound covering at least a portion of the surface of the core compound. Alternatively, the multiple phases may not be a regular combination as in a core-shell structure, but rather a random distribution of multiple phases with different compositions. Furthermore, "rich in Cu," "rich in Ag," and "rich in Te" refers to a phase in which the composition ratio of Cu, Ag, and Te is greater than 50 atoms.

[0025] In addition to spherical shapes, the semiconductor nanoparticles of this invention can also be cubic or rod-shaped. The spherical and cubic semiconductor nanoparticles preferably have an average particle size of 2 nm to 20 nm. The particle size of the semiconductor nanoparticles is related to the bandgap adjustment effect caused by the quantum confinement effect. To maximize the better light absorption characteristics resulting from the bandgap adjustment, the aforementioned average particle size is preferred. The average particle size of the semiconductor nanoparticles is obtained by observing multiple (preferably 100 or more) particles using an electron microscope such as a TEM, measuring the particle size of each particle, and calculating the average number of particles. Furthermore, the particle size can be measured as the average of the major axis and minor axis.

[0026] Furthermore, scanning transmission electron microscopy (STEM) is preferred for analyzing the composition and structure of semiconductor nanoparticles in this invention. In particular, a high-angle scattering annular dark field scanning transmission electron microscope (HAADF-STEM) can be used to obtain scattering images that reflect the composition information of nanoparticles. By combining it with energy dispersive X-ray spectrometers (EDS, EDX), the distribution of Ag, Cu, and Te and the overall composition of the nanoparticles can be determined.

[0027] A-3. Photoresponsiveness of the semiconductor nanoparticles of the present invention As described so far, semiconductor nanoparticles adjust their band gap and change their photoresponse based on the quantum confinement effect corresponding to their particle size. Regarding the light absorption characteristics of the semiconductor nanoparticles of this invention, the absorption wavelength at the long wavelength side of the preferred absorption spectrum is 1200 nm or higher. This allows the semiconductor nanoparticles to absorb light from the visible light region to the near-infrared region. More preferably, the absorption wavelength at the long wavelength side of the semiconductor nanoparticles of this invention can be 1400 nm or higher.

[0028] Furthermore, the semiconductor nanoparticles of this invention can also exhibit emission phenomena. In this emission spectrum, emission peaks can be seen in the wavelength range above 1000 nm. As a preferred embodiment, the semiconductor nanoparticles of this invention can exhibit emission peaks in the long wavelength region above 1200 nm, and more preferably above 1400 nm.

[0029] A-4. Utilization of the Semiconductor Nanoparticles of the Invention By coating and supporting the semiconductor nanoparticles of the present invention on a suitable substrate / carrier, they can be applied to various applications such as the aforementioned optical sensor elements. The composition, shape, and size of the substrate or carrier are not particularly limited. Examples of substrates on plates or foils / films include glass, quartz, silicon, ceramics, or metals. Examples of granular or powdered carriers include inorganic oxides such as ZnO, TiO2, WO3, SnO2, In2O3, and Al2O3. Alternatively, the semiconductor nanoparticles can be supported on the aforementioned inorganic oxide carrier and then fixed to the substrate.

[0030] Furthermore, when coating or supporting semiconductor nanoparticles onto a substrate / carrier, as mentioned above, solutions, slurries, or inks in which the semiconductor nanoparticles are dispersed in a suitable dispersion medium are mostly used. Chloroform, toluene, cyclohexane, hexane, etc., can be used as the dispersion medium for such solutions. Further, coating methods for solutions containing semiconductor nanoparticles can include dip coating and spin coating, and various methods such as drop casting, impregnation, and adsorption can be used as the supporting methods.

[0031] Furthermore, the semiconductor nanoparticles of the present invention preferably contain a protective agent to suppress aggregation during their synthesis process or when dispersed in a dispersion medium as described above. Preferably, the protective agent is at least one of the following: alkylamines with 4 to 20 carbon atoms in the alkyl chain, alkenylamines with 4 to 20 carbon atoms in the alkenyl chain, alkylcarboxylic acids with 3 to 20 carbon atoms in the alkyl chain, alkenylcarboxylic acids with 3 to 20 carbon atoms in the alkenyl chain, or alkylthiols with 4 to 20 carbon atoms in the alkyl chain. This protective agent is bonded to the surface of the semiconductor nanoparticles and coats at least a portion thereof, and the aggregation of the semiconductor nanoparticles is suppressed in the dispersion to obtain a homogeneous solution. Furthermore, in the semiconductor nanoparticle synthesis step, nanoparticles with an appropriate average particle size are synthesized by adding the protective agent together with the raw materials to the reaction system. The protective agent can be used alone or in combination with the aforementioned alkylamines, alkenylamines, alkylcarboxylic acids, alkenylcarboxylic acids, and alkylthiols.

[0032] B. Method for manufacturing semiconductor nanoparticles according to the present invention Next, the method for manufacturing the semiconductor nanoparticles of the present invention will be described. The inventors have discovered that, in the synthesis of the AgCu chalcogenide compound with the above-described composition, it is preferable to use compounds containing Ag, Cu, and Te as precursors (Ag precursor, Cu precursor, Te precursor), and to introduce these precursors into the same reaction system and simultaneously heat them for reaction. The method for manufacturing semiconductor nanoparticles using this AgCu chalcogenide compound synthesis method will be described below.

[0033] B-1. Raw materials (Ag precursor, Cu precursor, Te precursor) Ag precursors, Cu precursors, and Te precursors used as raw materials are suitable for Ag salts or Ag complexes, Cu salts or Cu complexes, and Te compounds, respectively. The Ag precursors and Cu precursors are preferably salts or complexes containing monovalent Ag and monovalent Cu.

[0034] As Ag precursors, Ag salts or Ag complexes are suitable. Preferably, Ag precursors are salts or complexes containing monovalent Ag. Preferred specific examples of 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] Cu salts or Cu complexes are suitable as Cu precursors. Preferred Cu precursors are salts or complexes containing monovalent Cu. However, salts or complexes containing divalent Cu can also be used as Cu precursors. This is because during the synthesis of semiconductor nanoparticles, divalent Cu is reduced to monovalent Cu by the solvent or coexisting Te precursors. Preferred examples of Cu precursors include copper acetate, copper chloride, copper iodide, and copper bromide.

[0036] Te compounds that serve as Te precursors include those containing tellurium oxide (TeO2), telluric acid (Te(OH)6), sodium tellurite (Na2TeO3), and others.

[0037] Formation of the reaction system of B-2.AgCu chalcogenides In the synthesis of AgCu chalcogenides, a single reaction system is formed by mixing the aforementioned Ag, Cu, and Te precursors before proceeding with the reaction. At this time, the individually prepared Ag, Cu, and Te precursors can be mixed sequentially, with no particular restriction on the mixing order. Furthermore, a mixture of the Ag precursor and Cu precursor (the transition metal component of the AgCu chalcogenide) can be modified into a metal source precursor, and then mixed with the Te precursor to form the reaction system.

[0038] The atomic ratio (x / y) of Ag to Cu in the synthesized AgCu chalcogenide (AgxCuyChz) can be adjusted by the ratio of the amount of Ag precursor to Cu precursor fed in. When the number of Ag atoms in the Ag precursor is set to a and the number of Cu atoms in the Cu precursor is set to b, the ratio of the amount of Ag atoms fed in is preferably set to 1 to 10, more preferably 2 to 4, when the number of Ag atoms in the Ag precursor is set to a is 'a' and the number of Cu atoms in the Cu precursor is 'b'.

[0039] Furthermore, the amount of Te precursor fed into the reaction system may affect the number of Te atoms (zTe) in the chalcogenides of the synthesized AgCu chalcogenide (AgxCuyChz). According to the present inventors' review, when the number of Te atoms in the Te precursor is set as c, and the number of Cu atoms in the Cu precursor is set as b, the ratio (c / b: hereinafter sometimes referred to as the Te feed ratio) is preferably set to 0.1 to 2 and less, more preferably 0.1 to 1 and less.

[0040] Furthermore, as described above, the semiconductor nanoparticles of the present invention are preferably bonded to the AgCu chalcogenide compound with a protective agent. Moreover, when the protective agent contains a chalcogenide element, that chalcogenide element can form part of the chalcogenide element in the AgCu chalcogenide compound of the present invention. Therefore, it is preferable to add the protective agent together with the Ag precursor, Cu precursor, and Te precursor to the above-described reaction system. As a protective agent, it is preferable to add at least one of the following: an alkylamine with 4 to 20 carbon atoms in its alkyl chain, an alkenylamine with 4 to 20 carbon atoms in its alkenyl chain, an alkylcarboxylic acid with 3 to 20 carbon atoms in its alkyl chain, an alkenylcarboxylic acid with 3 to 20 carbon atoms in its alkenyl chain, or an alkylthiol with 4 to 20 carbon atoms in its alkyl chain.

[0041] The reaction system used in the synthesis of semiconductor nanoparticles can also generate nanoparticles without solvents, but it is preferable to use a solvent. When using a solvent, octadecene, tetradecane, oleic acid, oleylamine, dodecyl mercaptan, or mixtures thereof are suitable.

[0042] Synthesis conditions of B-3. AgCu chalcogenides AgCu chalcogenide nanoparticles were synthesized by heating a reaction system consisting of Ag precursor, Cu precursor, Te precursor, and a protecting agent. The heating temperature (reaction temperature) was set between 100°C and 200°C. The synthesis reaction was difficult to proceed below 100°C. On the other hand, above 200°C, nanoparticles with unstable shapes were formed. A more suitable reaction temperature was between 100°C and 150°C.

[0043] Furthermore, the reaction time (heating time) can be adjusted according to the amount of raw materials fed in, but it is preferably between 5 minutes and 120 minutes. More preferably, the reaction time is 10 minutes or more, and even more preferably 15 minutes or more. Also, it is preferable to stir the reaction system between the synthesis reactions of AgCu chalcogenide nanoparticles.

[0044] After the synthesis reaction of AgCu chalcogenide nanoparticles is completed, the reaction system can be cooled and recovered as semiconductor nanoparticles if necessary. At this time, a weak solvent such as alcohol (ethanol, methanol, etc.) can be added to precipitate the nanoparticles, or the semiconductor nanoparticles can be precipitated and recovered by centrifugation, etc. Then, the particles are temporarily washed with alcohol (ethanol, methanol, etc.) and uniformly dispersed in a good solvent such as chloroform. [Invention Effects]

[0045] As described above, the present invention relates to semiconductor nanoparticles primarily composed of AgCu chalcogenides (AgxCuyChz), for which Te is an essential chalcogenide element. The semiconductor nanoparticles of the present invention possess suitable photoresponsibility and are practically applicable considering regulations and other factors. The semiconductor nanoparticles of the present invention can be used as photoreceiving and emitting elements in the long-wavelength regions of the near-infrared (NIR) and short-wave infrared (SWIR) regions. Simple Explanation of the Diagram

[0046] [Figure 1] is a TEM image of semiconductor nanoparticles synthesized from AgCu chalcogenides (AgxCuyChz) in the first embodiment. [Figure 2] shows the absorption spectrum of the semiconductor nanoparticles synthesized from AgCu chalcogenides (AgxCuyChz) in the first embodiment. [Figure 3] shows the emission spectrum of the semiconductor nanoparticles synthesized from AgCu chalcogenides (AgxCuyChz) in the first embodiment. [Figure 4] shows the absorption spectrum of the semiconductor nanoparticles synthesized from AgCu chalcogenides (AgxCuyChz) in the second embodiment. [Figure 5] shows the emission spectrum of semiconductor nanoparticles synthesized from AgCu chalcogenides (AgxCuyChz) in the second embodiment. [Figure 6] is a TEM image of semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) synthesized by changing the heating temperature in the third embodiment. [Figure 7] shows the absorption spectrum of semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) synthesized by changing the heating temperature in the third embodiment. [Figure 8] shows the emission spectrum of semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) synthesized by changing the heating temperature in the third embodiment. [Figure 9] is a TEM image of semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) synthesized by varying the reaction time in the third embodiment. [Figure 10] shows the absorption spectrum of semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) synthesized by varying the reaction time in the third embodiment. [Figure 11] shows the emission spectrum of semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) synthesized by varying the reaction time in the third embodiment. Implementation

[0047] First Embodiment: The following describes an embodiment of the present invention. In this embodiment, semiconductor nanoparticles made of AgCu chalcogenides (AgxCuyChz) are synthesized, their appearance is confirmed, and their photoresponse characteristics are evaluated. In another embodiment, nanoparticles of AgCu chalcogenides with varying atomic ratios (x / y) of Ag and Cu are synthesized.

[0048] In this embodiment, the synthesis system for semiconductor nanoparticles formed from AgCu chalcogenides is pre-adjusted to a mixture of Ag precursor and Cu precursor containing transition metal components as the metal source precursor. Subsequently, the metal source precursor is mixed with Te precursor and reacted to synthesize semiconductor nanoparticles.

[0049] Silver acetate (Ag(OAc)) as an Ag precursor and copper acetate (Cu(OAc)) as a Cu precursor were dissolved and mixed in 3 mL of 1-dodecylthiol (DDT) as a solvent / protecting agent to prepare a metal source precursor. The total content of Ag and Cu in the solution was set to 0.08 mmol (metal conversion). Then, silver acetate and copper acetate were mixed to achieve Ag feed ratios (a / b) of 3 / 1, 2.5 / 1.5, 2 / 2, and 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 / protecting agent, and the solution of the Te precursor was adjusted by heating at 100°C for 5 minutes under nitrogen atmosphere.

[0050] To synthesize AgCu chalcogenide nanoparticles, a solution of metal source precursors (Ag, Cu) was first heated at 150°C for 5 minutes under nitrogen atmosphere. Then, a Te precursor solution was injected into the solution using a syringe. Subsequently, the reaction was heated at 150°C for 15 minutes under nitrogen atmosphere with stirring. After the reaction was complete, the mixture was cooled and centrifuged at 4000 rpm for 5 minutes to separate the supernatant and precipitate. Then, 4 cm³ of ethanol / toluene (as a weak solvent) was added to the supernatant to produce a precipitate, which was then recovered by centrifugation at 4000 rpm for 5 minutes to obtain the AgCu chalcogenide nanoparticles.

[0051] The AgCu chalcogenide nanoparticles obtained from the above operations were dispersed in 3 cm³ of chloroform to obtain a dispersion of semiconductor nanoparticles composed of AgCu chalcogenide. This dispersion was then transferred to a sample vial, purged with nitrogen, and stored under light-protected conditions.

[0052] [TEM Observation of Semiconductor Nanoparticles] TEM observations were performed on the semiconductor nanoparticles synthesized from AgCu chalcogenides (Ag feed ratios: 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5) in this embodiment. Figure 1 shows TEM images of each semiconductor nanoparticle fabricated in this embodiment (magnification referenced to the scale bars of each photograph). Referring to Figure 1, the AgCu chalcogenides synthesized with an Ag feed ratio of 3 / 1 show more slightly spherical nanoparticles. As the Ag feed ratio decreases (the proportion of Cu increases), there is a tendency for an increase in amorphous nanoparticles.

[0053] Compositional Analysis of Semiconductor Nanoparticles Compositional analysis was performed on the semiconductor nanoparticles (Ag feed ratios: 3 / 1, 2.5 / 1.5, 2 / 2, 1.5 / 2.5) synthesized in this embodiment using SEM-EDS. Table 1 shows the compositional results of each semiconductor nanoparticle. The compositional analysis results are expressed as atomic percent relative to the total number of nanoparticles in this embodiment and 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) calculated based on the compositional analysis results, and the ratio z / (x+y) of the number of chalcogenide atoms (z) to the number of transition metal atoms (x+y).

[0054]

[0055] As shown in Table 1, due to the increase in the Ag feed ratio (a / b), the ratio (x / y) of the number of Ag atoms (x) to the number of Cu atoms (y) in the AgCu chalcogenide compound naturally increases. Furthermore, it is confirmed that even if the Ag feed ratio changes, the ratio (x+y) of the number of chalcogenide atoms (z) to the number of transition metal atoms (Ag and Cu) does not change significantly. Moreover, it is confirmed that the AgCu chalcogenide compound synthesized in this embodiment must contain Te as a chalcogenide element and S as another chalcogenide element. Furthermore, except for No. 4, even if the Ag feed ratio changes, the number of Te atoms relative to the total number of chalcogenide elements (zTe / z) does not change significantly. The AgCu chalcogenide compound of No. 4 has the smallest Ag feed ratio (a / b: 1.5 / 2.5), and according to TEM observations (Figure 1), two-phase separation is observed, suggesting that this is the only difference in tendency.

[0056] [Determination of absorption and emission spectra] Secondly, to evaluate the photoresponsivity of each semiconductor nanoparticle, absorption and emission spectra were measured. Absorption spectroscopy was performed using a UV-Vis spectrophotometer (Agilent Technologies, Inc., Agilent 8453), with the wavelength range set to 400 nm–1600 nm. Emission spectroscopy was performed using a diode array spectrophotometer (PMA-12, C10027-02) manufactured by Hamamatsu Photonics Co., Ltd. The sample was adjusted with chloroform solution (n=1.4429) to an absorbance of 0.1 at 365 nm before measurement.

[0057] The absorption spectrum measurement results of each semiconductor nanoparticle manufactured in this embodiment are shown in Figure 2, and the emission spectrum measurement results are shown in Figure 3. Furthermore, the absorption wavelength and emission peak wavelength of each semiconductor nanoparticle on the long wavelength side based on these measurements are shown in Table 2.

[0058]

[0059] Referring to the absorption spectrum measurements in Figure 2 and Table 2, all semiconductor nanoparticles exhibit light absorption characteristics in the region above 1400 nm. Furthermore, in all cases, a smaller peak, considered an exciton peak, is observed in the wavelength range of 800 nm to 950 nm, while an absorption peak is also observed near 1400 nm. Regarding the composition of AgCu chalcogenides (AgxCuyChz), if a change is observed due to the atomic ratio of Ag to Cu (x / y), the absorption end shifts towards longer wavelengths as x / y increases and the atomic ratio of Ag increases.

[0060] Furthermore, the semiconductor nanoparticles of this embodiment have all been confirmed to exhibit emission. Referring to the emission spectrum measurements in Figure 3 and Table 2, emission peaks in the wavelength region above 1000 nm can be confirmed. In particular, the emission peak wavelength of the semiconductor nanoparticle (No. 1), which has a higher Ag atomic ratio, falls on the long wavelength side. An emission peak was observed in this semiconductor nanoparticle in the region above 1200 nm.

[0061] Based on the above evaluation results of photoresponse, it can be said that the semiconductor nanoparticles synthesized in this embodiment, made of AgCu chalcogenides, exhibit good light absorption in the long wavelength region with an absorption end above 1200 nm. In particular, the AgCu chalcogenide nanoparticles (x / y=4) with an Ag feed ratio of 3 / 1 in No. 1 have a long wavelength absorption end wavelength above 1500 nm, and their luminescence characteristics also show good peak wavelengths above 1200 nm.

[0062] Second Embodiment: In this embodiment, semiconductor nanoparticles composed of AgCu chalcogenides of various compositions are synthesized by adjusting the Te feed ratio. The synthesis method of the semiconductor nanoparticles used in this embodiment is basically the same as that in the first embodiment. A solution of the Te precursor is added to a solution of the metal source precursor and heated / reacted to obtain AgCu chalcogenide nanoparticles. In this embodiment, the amount of Te precursor is adjusted so that the Te feed 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, is 1 / 4, 1 / 2, 1 / 1, or 2 / 1, for the synthesis reaction. After synthesis, separation / purification is performed in the same manner as in the first embodiment to obtain AgCu chalcogenide nanoparticles. The Ag feed ratio (a / b) is set to 3 / 1, and other reaction conditions are the same as in the first embodiment.

[0063] Compositional Analysis of Semiconductor Nanoparticles Compositional analysis was performed on the semiconductor nanoparticles (Te feed ratios: 1 / 4, 1 / 2, 1 / 1, 2 / 1) synthesized from AgCu chalcogenides in this embodiment using SEM-EDS. The compositional results of each semiconductor nanoparticle are shown in Table 3.

[0064]

[0065] Referring to Table 3, even with an increase in the Te feed ratio (c / b), the ratio (z / (x+y)) of the number of chalcogenide atoms (z) to the number of transition metal atoms (Ag, Cu) does not change significantly. The increase in the Te feed ratio leads to an increase in the proportion of Te atoms relative to the total number of chalcogenide atoms (zTe / z). Furthermore, an increase in the Te feed ratio also shows a tendency to decrease the atomic ratio x / y of Ag and Cu.

[0066] [Determination of absorption and emission spectra] Next, absorption and emission spectra were measured to evaluate the photoresponsivity of each semiconductor nanoparticle manufactured in this embodiment. The measurement methods were the same as those in the first embodiment. The measurement results are shown in Figures 4 and 5, and the absorption wavelength and emission peak wavelength of each semiconductor nanoparticle on the long wavelength side are shown in Table 4.

[0067]

[0068] Referring to the absorption spectrum measurements in Figure 4 and Table 4, all semiconductor nanoparticles with varying Te feed ratios exhibited an exciton peak simultaneously around 1400 nm. Furthermore, the long-wavelength absorption ends all fell within the region above 1500 nm. In particular, the semiconductor nanoparticle (No. 5) with a relatively low Te feed ratio (the atomic ratio of Te in AgCu chalcogenides is relatively low) showed a further increase in the absorption wavelength.

[0069] Referring to the emission spectrum measurements 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) showed the same trend with no significant differences. No clear peaks were observed for semiconductor nanoparticle No. 8, which had a higher Te feed ratio (c / b: 2 / 1).

[0070] Third embodiment: In this embodiment, the photoresponsivity of semiconductor nanoparticles obtained by changing the synthesis conditions of AgCu chalcogenide nanoparticles is examined.

[0071] First, the effect of temperature before and after the formation of the reaction system is examined. Here, in the synthesis steps of AgCu chalcogenide nanoparticles in 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) are adjusted. Specifically, AgCu chalcogenide nanoparticles are synthesized under three conditions: (i) T1=T2=150℃, (ii) T1=150℃, T2=120℃, and (iii) T1=T2=120℃. The heating times in this examination are the same as in the first embodiment.

[0072] Furthermore, in this embodiment, the effect of heating time (reaction time) after adding the Te precursor solution to the metal source precursor solution was also examined. In this examination, reaction times were set to 5 min, 10 min, 20 min, 40 min, and 80 min to synthesize AgCu chalcogenide nanoparticles. The heating temperature in this examination was set to T1=T2=120℃.

[0073] In each review, the synthesis methods / conditions other than the above reaction conditions are the same as those in the first embodiment, and the Ag feed ratio (a / b) is set to 3 / 1.

[0074] Regarding the review results of this embodiment, firstly, the temperatures before and after the formation of the reaction system will be explained. Figure 6 is a TEM image of the AgCu chalcogenide nanoparticles synthesized under the heating conditions described in (i) to (iii) above. The TEM image shows that under condition (iii), where the heating temperatures (T1 and T2) before and after the formation of the reaction system are both 120°C, nanoparticles with stable particle shapes were synthesized. Furthermore, the shape of the nanoparticles tends to be unstable under heating conditions including 150°C.

[0075] Therefore, compositional analysis was performed on semiconductor nanoparticles under conditions (i) (T1=T2=150℃) and (iii) (T1=T2=120℃) with the same thermal temperature before and after the formation of the reaction system. The results are shown in Table 5. As can be seen from Table 5, although the shapes of these AgCu chalcogenide nanoparticles differ, their compositions are not significantly different.

[0076]

[0077] Furthermore, the results of the absorption and emission spectra of these two semiconductor nanoparticles are shown in Figures 7 and 8 and Table 6.

[0078]

[0079] If we observe the absorption spectrum measurement results in Figure 7 and Table 6, the absorption characteristics of the semiconductor nanoparticles under the heating conditions (i) and (iii) are generally similar curves. However, the semiconductor nanoparticles in (iii), whose heating temperature before and after the formation of the reaction system is set to 120°C, exhibit significantly stronger absorption peaks and longer absorption wavelengths. Next, referring to the emission spectrum measurement results in Figure 8 and Table 6, the emission peak wavelength of the semiconductor nanoparticles in (iii), whose heating temperature before and after the formation of the reaction system is set to 120°C, shifts significantly (by more than 200 nm) to the longer wavelength side.

[0080] Secondly, the results of the review regarding the effect of reaction time are explained. Figure 9 shows TEM images of AgCu chalcogenide nanoparticles synthesized with reaction times ranging from 5 min to 40 min (T1=T2=120℃). As can be seen from Figure 9, by setting the reaction time to a longer duration, the particle shape approaches spherical. Furthermore, the compositional analysis results of these semiconductor nanoparticles using EDS are shown in Table 7. Referring to Table 7, even with an increased reaction time, the atomic ratio (z / (x+y)) of the transition metal components (Ag, Cu) and chalcogen elements did not show a significant difference. Moreover, the atomic ratio (x / y) of Ag in the transition metal components also did not differ significantly within the range of 3.0 to 5.0.

[0081]

[0082] The absorption spectra of AgCu chalcogenide nanoparticles synthesized with reaction times set to 5 min to 40 min (T1=T2=120℃) are shown in Figure 10, the emission spectra are shown in Figure 11, and these are summarized in Table 8.

[0083]

[0084] If we observe the absorption spectrum in Figure 10, we can see that, apart from the reaction time of 80 minutes, the absorption characteristics of each semiconductor nanoparticle are not significantly different. Furthermore, if we observe the emission spectrum measurement results in Figure 11, we can see that, similar to the absorption spectrum results, the emission spectrum curves are not different, and the emission peak wavelengths are almost the same.

[0085] In summary, regarding the synthesis conditions examined in this embodiment, it can be stated that a lower temperature of 120°C is preferable to 150°C (first embodiment) for both the heating temperature of the metal source precursor and the reaction temperature. Furthermore, regarding the reaction time, a longer reaction time is preferable to achieve particle sphericity, but differences in properties other than particle shape are minimal. The reaction time can be set relatively flexibly. While the synthesis conditions for semiconductor nanoparticles should be adjusted according to the concentrations of transition metals / chalcogenides in the metal source precursor and the Te precursor, as well as the scale of the reaction system, the results of this embodiment can be used as a reference. [Industrial Applicability]

[0086] As explained above, the semiconductor nanoparticles formed from the AgCu chalcogenide of this invention exhibit excellent photoresponsivity. This AgCu chalcogenide can also be considered in compliance with regulations and to avoid the use of heavy metals. The semiconductor nanoparticles of this invention are expected to be used in light-emitting elements, fluorescent materials, and photoelectric conversion elements and light-receiving elements mounted in solar cells and photosensors, etc., for use in display devices and bio-related substance detection labeling materials. In particular, this invention improves the light absorption characteristics in the long wavelength regions of the near-infrared (NIR) and short-wave infrared (SWIR) regions. Therefore, this invention is particularly useful in the light-receiving elements of LIDAR and SWIR image sensors, where near-infrared responsiveness is crucial.

Claims

1. A semiconductor nanoparticle comprising an AgCu chalcogenide compound composed of Ag, Cu, and chalcogenide (Ch) represented by the following formula, wherein the aforementioned chalcogenide includes Te as an essential chalcogenide, and comprises at least 90 atomic percent of the aforementioned AgCu chalcogenide compound, AgxCuyChz (where Ch is a chalcogenide, x, y, z are the atomic number of Ag, Cu, and chalcogenide, 0.2≦z / (x+y)≦1, and 1.93≦x / y≦10.0).

2. The semiconductor nanoparticles of claim 1, wherein the chalcogen elements constituting the aforementioned AgCu chalcogen compound include chalcogen elements other than Te, and the aforementioned other chalcogen elements are S and Se.

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

4. Semiconductor nanoparticles as claimed in claim 1 or 2, wherein the nanoparticles contain more than 99 atomic percent of the aforementioned AgCu chalcogenide compound.

5. The semiconductor nanoparticles of claim 1 or 2 have an average particle size of 2 nm or more but less than 20 nm.

6. The semiconductor nanoparticles of claim 1 or 2, wherein at least one of the following as a protective agent is bonded to the surface: an alkylamine with an alkyl chain of 4 to 20 carbon atoms, an alkenylamine with an alkenyl chain of 4 to 20 carbon atoms, an alkylcarboxylic acid with an alkyl chain of 3 to 20 carbon atoms, an alkenylcarboxylic acid with an alkenyl chain of 3 to 20 carbon atoms, or an alkylthiol with an alkyl chain of 4 to 20 carbon atoms.

7. The semiconductor nanoparticles of claim 1 or 2 have an absorption wavelength of 1200 nm or more at the long wavelength side of their absorption spectrum.

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

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