Semiconductor nanoparticles containing agtes compound as main component

Abstract

To provide a semiconductor nanoparticle which has improved light absorption characteristics in a long wavelength region and can suitably cope with a near infrared region and a short wave infrared region.SOLUTION: The present invention relates to a semiconductor nanoparticle containing an AgTeS compound composed of Ag, Te, and S as essential constituent elements. The AgTeS compound constituting the semiconductor nanoparticles is represented by the following formula. The semiconductor nanoparticles according to the present invention contain 90 atom% or more of the AgTeS compound. The long-wavelength-side absorption-edge wave length is equal to or longer than 1100nm. In addition, the semiconductor nanoparticles according to the present invention can also emit light. (In the formula, x, y, and z are the numbers of atoms of Ag, Te, and S, and 0.5 ≤ x / (x + y + z) ≤ 0.7.). In addition, 0.3 ≤ y / (y + z) ≤ 0.99. ) SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to semiconductor nanoparticles mainly composed of an AgTeS compound, and more specifically to semiconductor nanoparticles made of an AgTeS compound that have favorable photoresponsiveness in the long wavelength region and whose photoresponsiveness can be controlled by adjusting the composition. [Background technology]

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

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

[0004] In particular, semiconductor nanoparticles are expected to be applied to the light-receiving elements of optical sensors that operate in the near-infrared (NIR) and shortwave infrared (SWIR) regions. Optical sensors that can detect light in these long wavelength regions are installed in LIDAR (Light Detection and Ranging) and SWIR image sensors. LIDAR is a remote sensing system used in autonomous driving vehicles, drones, ships, and other applications, 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 and tablets. Furthermore, demand for SWIR image sensors is expected to increase in the future in fields such as food inspection, agriculture, and drones.

[0005] In particular, autonomous driving technology using LIDAR has shown remarkable development, and it is expected that it will be possible to support autonomous driving levels (levels 4 and 5) that do not require a driver to drive. In order to support advanced autonomous driving levels, it is important that LIDAR is less susceptible to the effects of sunlight and natural light, and that it has a response in the longer wavelength range.

[0006] On the other hand, silicon thin films have often been used as light-receiving elements in sensors for optical devices up to now, but sensors using 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.

[0007] Given the above background, the development of light-receiving elements using semiconductor nanoparticles is expected in the future, and several semiconductor compounds are being investigated. Here, metal chalcogenide compounds such as PbS, PbSe, CdHgTe, Ag2S, Ag2Se, Ag2Te, AgInSe2, AgInTe2, CuInSe2, CuInTe2, and InAs are known as semiconductor compounds that are photoresponsive in the long wavelength region of the near-infrared region (NIR) and short-wave infrared region (SWIR) (Patent Documents 1 to 4). The applicant of the present application also discloses semiconductor nanoparticles mainly composed of AgAuS-based compounds in Patent Document 5. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-243507 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-352594 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-014476 [Patent Document 4] International Publication No. WO2020 / 054764 [Patent Document 5] Patent No. 7269591 Summary of the Invention [Problem to be solved by the invention]

[0009] Although the semiconductor compounds mentioned above exhibit photoresponsiveness in the desired wavelength range, many of them present obstacles when considering applications such as display devices and biomarkers, as mentioned at the beginning of this article. For example, the European RoHS Directive restricts the use of Pb in electrical and electronic devices due to its environmental impact. Therefore, semiconductor nanoparticles made from 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 bio-related fields, it is also difficult to use compounds containing heavy metals such as Cd and Hg.

[0010] Furthermore, although the semiconductor compounds exemplified in each of the above patent documents are said to have photosensitivity in the long wavelength region, there are few specific manufacturing examples and evaluation cases regarding their photosensitivity characteristics. In Patent Documents 1 and 2, although many of the semiconductor compounds listed above are described, there are no specific manufacturing examples or evaluation results regarding their response characteristics in the long wavelength region. Also, although the nanoparticles composed of the semiconductor compounds described in the above patent documents show the possibility of response in the wavelength range up to around 1400 nm, in LIDAR etc., there may be a requirement for photosensitivity in a further longer wavelength region in the future. In this regard, it can be said that quantum dot technology is still in the research stage, and it is necessary to clarify specific semiconductor compounds and semiconductor nanoparticles that can exhibit photosensitivity in a longer wavelength region while considering practicality.

[0011] Therefore, the present invention proposes a specific configuration and manufacturing method of semiconductor nanoparticles composed of a novel semiconductor compound having suitable photosensitivity while considering practicality for various regulations. In particular, the present invention presents semiconductor nanoparticles that exhibit suitable light absorption characteristics in the long wavelength region of the near-infrared region (NIR) and short-wave infrared region (SWIR), and can also emit light.

Means for Solving the Problems

[0012] Many of the compounds having opto-semiconductor characteristics in each of the above-described prior arts are chalcogen compounds of transition metals. And, there is a correlation between the photosensitivity characteristics of transition metal chalcogen compounds and the mass (atomic weight) of the chalcogen element. That is, by increasing the mass of the chalcogen element, the orbital energy difference between the transition metal element and the chalcogen element of the transition metal chalcogenide compound is reduced, and thereby it is presumed that the photosensitivity shifts to the longer wavelength side. Looking at the above-described semiconductor compounds, for example, in the Ag compounds of Ag2S, Ag2Se, and Ag2Te, since the mass of the chalcogen element is S < Se < Te, the absorption wavelengths of these Ag compounds also shift to the longer wavelength side in this order.

[0013] Based on the above findings, the present inventors attempted to synthesize compounds of one or more transition metals and various chalcogenide elements, and focused on transition metal chalcogenide compounds composed of Ag, a transition metal, and two chalcogen elements, Te and S. According to the present inventors, the photoresponsiveness (absorption edge wavelength) of AgTeS compounds can be varied over a wide range by changing the ratio of Te to S among the chalcogen elements constituting the compound. This ability to control the absorption edge wavelength can enable application to optical devices for various applications, including LIDAR. Furthermore, Ag is known as a metal with bactericidal and antibacterial properties, is nontoxic, and has good biocompatibility. Therefore, Ag chalcogen compounds can also comply with various regulations. Based on these findings, the present inventors conceived the present invention of semiconductor nanoparticles primarily composed of AgTeS compounds.

[0014] That is, the present invention relates to semiconductor nanoparticles containing an AgTeS compound represented by the following formula, which is made of Ag, Te, and S, and which contain 90 atomic % or more of the AgTeS compound.

[0015] [ka] (wherein x, y, and z are the numbers of Ag, Te, and S atoms, respectively, and 0.5≦x / (x+y+z)≦0.7. Also, 0.3≦y / (y+z)≦0.99.)

[0016] The structure and production method of semiconductor nanoparticles containing an AgTeS compound as a main component according to the present invention will be described below.

[0017] A. Structure of the semiconductor nanoparticles according to the present invention A-1. Chemical composition of semiconductor nanoparticles As described above, the semiconductor nanoparticles according to the present invention are mainly composed of an AgTeS compound. When the numbers of Ag, Te, and S atoms are x, y, and z, respectively, this AgTeS compound has the following structure: x Te y S z It can be expressed as:

[0018] As described above, the AgTeS compound used in the present invention is composed of two chalcogen elements, Te and S. Among the chalcogen elements, S is an element with a relatively small mass, while Te is an element with a large mass. The relationship between the mass of the chalcogen element and the photoresponsiveness of the chalcogenide compound is as described above, and it is believed that the present invention makes it possible to adjust the wavelength exhibiting photoresponsiveness by using chalcogen elements with opposite masses.

[0019] The AgTeS compound constituting the semiconductor nanoparticles according to the present invention has photoresponsive characteristics that correspond to its composition. Specifically, the absorption wavelength of the AgTeS compound shifts proportionally to the longer wavelength side as the atomic ratio of Te to the chalcogen elements (Te and S), (y / (y+z)) (the ratio of the number of Te atoms to the number of chalcogen elements), increases. Here, in the present invention, AgTeS compounds having a Te atomic ratio y / (y+z) of 0.30 or more exhibit absorption wavelengths of 1100 nm or more. The Te atomic ratio y / (y+z) is more preferably 0.40 or more. The upper limit of y / (y+z) is 0.99 or less, preferably 0.90 or less. AgTeS compound nanoparticles within this composition range can also emit light.

[0020] In the AgTeS compound of the present invention, the Ag atomic ratio x / (x+y+z) is set to 0.5≦x / (x+y+z)≦0.7. It is preferable that the range of the Ag atomic ratio is relatively narrow. The inventors have confirmed that the photoresponse characteristics can be adjusted by changing the above-mentioned y / (y+z) within this range for the number of Ag atoms. It is more preferable that x / (x+y+z) is 0.55 or more and 0.65 or less.

[0021] The atomic ratio ((y+z) / (x+y+z)) of the chalcogen elements (Te and S) in the AgTeS compound is the remainder (1.0-(x / (x+y+z))) of the above-mentioned atomic ratio of Ag. The atomic ratios of Te and S, y / (x+y+z) and z / (x+y+z), respectively, are preferably 0.1≦y / (x+y+z)≦0.4 and 0.01≦z / (x+y+z)≦0.3. More preferably, they are 0.14≦y / (x+y+z)≦0.37 and 0.04≦z / (x+y+z)≦0.28.

[0022] The semiconductor nanoparticles according to the present invention are primarily composed of an AgTeS compound having the composition range described above, and are composed of 90 atomic % or more of the AgTeS compound. The semiconductor nanoparticles may be composed solely of the AgTeS compound. Semiconductor nanoparticles preferably contain 95 atomic % or more of the AgTeS compound. The semiconductor nanoparticles according to the present invention may contain elements other than Ag, Te, and S, which constitute the AgTeS compound. For example, the semiconductor nanoparticles may contain elements contained in the solvent used to synthesize the AgTeS compound or in the precursors that serve as the raw materials for Ag and Te. Elements that may be contained in addition to the essential constituent elements Ag, Te, and S include C, P, Cl, Br, and I. 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.

[0023] The composition of the AgTeS compound described above refers to the overall composition of the AgTeS compound in the semiconductor nanoparticles. The AgTeS compound used in the present invention may be composed of only an alloy phase of the same composition, or may be composed of alloy phases of multiple compositions. It is sufficient that x, y, and z fall within the above-mentioned ranges for the entire AgTeS compound in the semiconductor nanoparticles. The composition of this AgTeS compound can be obtained by performing composition analysis on multiple locations on the semiconductor nanoparticles and calculating the average value.

[0024] Furthermore, semiconductor nanoparticles composed of multiple alloy phases may have a so-called core-shell structure. An example of a core-shell structure is a structure consisting of a core (core compound) made of an AgTeS compound containing Ag, Te, and S, and a shell (shell compound) made of an AgTeS compound or a compound not containing any of Ag, Te, and S, with the shell compound covering 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.

[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 may be related to the band gap adjustment effect due to the quantum confinement effect. The above-mentioned 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 diameter (long axis) and the minor diameter (short axis).

[0026] Furthermore, a scanning transmission electron microscope (Scanning TEM) can be suitably used to analyze the composition and structure of the semiconductor nanoparticles according to the present invention. In particular, a High Angle Annular Dark Field Scanning TEM (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, Te, and S and the overall composition of the nanoparticles.

[0027] A-2. Photoresponsiveness of the semiconductor nanoparticles according to the present invention As described above, the responsiveness of semiconductor nanoparticles varies depending on the composition of the AgTeS compound, which is the main constituent, in particular the atomic ratio of Te (y / (y+z)). 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 in the range of 1100 nm to 2100 nm. This allows the semiconductor nanoparticles to exhibit absorption for light in the visible to 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 1300 nm or more.

[0028] The semiconductor nanoparticles according to the present invention may also exhibit a luminescence phenomenon. In this case, the emission spectrum exhibits a peak emission wavelength in the wavelength region of 1300 nm or more. In a more preferred embodiment, the semiconductor nanoparticles according to the present invention can exhibit a peak emission wavelength in the long wavelength region of 1500 nm or more.

[0029] A-3. 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 optical sensor elements described above. There are no particular limitations on the configuration, shape, or dimensions of the substrate or carrier. Examples of plate-shaped, foil-like, or film-like substrates include glass, quartz, silicon, ceramics, and metals. Examples of granular or powdery carriers include inorganic oxides such as ZnO, TiO2, WO3, SnO2, In2O3, and Al2O3. Alternatively, the semiconductor nanoparticles may be supported on the inorganic oxide carrier and then fixed to the substrate.

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

[0031] The semiconductor nanoparticles according to the present invention may contain a protective agent to suppress aggregation during the synthesis process or when dispersed in a dispersion medium as described above. The action and composition of the protective agent will be described in detail below. The protective agent binds to the surface of the semiconductor nanoparticles to coat at least a portion thereof, suppressing aggregation of the semiconductor nanoparticles in the dispersion liquid and forming a uniform solution, etc. Furthermore, by adding the protective agent to the reaction system together with the raw materials in the semiconductor nanoparticle synthesis process, nanoparticles with a suitable average particle size are synthesized. Although excess of this protective agent is removed by treatment such as washing after the synthesis of the semiconductor nanoparticles, some of it may remain and be bound to the surface of the semiconductor nanoparticles.

[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 inventors of the present invention have proposed a method for synthesizing the AgTeS compound having the above-described composition, in which compounds containing Ag and Te are used as precursors (Ag precursor, Te precursor), and the Ag precursor and Te precursor are introduced into the same reaction system containing a protective agent containing S, and are then heated simultaneously to react with each other. Hereinafter, a method for producing semiconductor nanoparticles using this AgTeS compound synthesis method will be described.

[0033] B-1. Raw materials (Ag precursor, Te precursor) The Ag precursor used as the raw material is preferably an Ag salt or an Ag 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 cyanide(I) salt, and silver diethyldithiocarbamate.

[0034] The Te precursor may be a Te compound, specifically, tellurium oxide (TeO2), telluric acid (Te(OH)6), sodium tellurite (Na2TeO3), or the like.

[0035] The protective agent is added to the surface of AgTeS compound nanoparticles synthesized in the reaction system to suppress nanoparticle aggregation. In addition, in the present invention, the protective agent also functions as a sulfur source for the synthesis of the AgTeS compound. Therefore, a protective agent containing S is used in the present invention. As this protective agent, at least one of thiols having 4 to 20 carbon atoms, sulfides having 4 to 20 carbon atoms, thioesters having 4 to 20 carbon atoms, and thioketones having 4 to 20 carbon atoms is preferred. More preferred protective agents are thiols having 4 to 20 carbon atoms and having an alkyl group, sulfanyl group, or the like as a substituent. Specifically, dodecanethiol, octanethiol, decanethiol, undecanethiol, and nonanethiol are preferred. These protective agents can be used alone or in combination.

[0036] B-2. Formation of AgTeS compound reaction system In the synthesis of the AgTeS compound, the Ag precursor and Te precursor are mixed to form a single reaction system, which is then reacted. Furthermore, a protective agent containing S coexists in this reaction system. The reaction system may be formed by mixing separate solutions of the Ag precursor and Te precursor, each containing a protective agent, or by dispersing the Ag precursor and Te precursor in a solvent and then mixing the protective agent.

[0037] The synthesized AgTeS compound (Ag x Te y S zThe composition (x, y, z) of the AgTeS compound can be adjusted by the amounts of the Ag precursor and the Te precursor. In particular, the Te atomic ratio y / (y + z) can be adjusted by the ratio of the number of Te atoms (b) in the Te precursor to the number of Ag atoms (a) in the Ag precursor (b / a: hereinafter, this ratio is referred to as the Te charge ratio). As the Te charge ratio (b / a) increases, an AgTeS compound with a larger y / (y + z) is synthesized. This is because the number of S atoms contributing to the synthesis of the AgTeS compound decreases as the number of Te atoms in the reaction system increases. The Te charge ratio (b / a) when synthesizing the AgTeS compound of the present invention is preferably 1 / 8 or more and 6 / 8 or less. Furthermore, the Te charge ratio for setting y / (y + z) within the preferred range (0.4 or more and 0.90 or less) is more preferably 4 / 8 or more and 6 / 8 or less.

[0038] The reaction system for synthesizing semiconductor nanoparticles can be formed using a solvent, but it can also be formed without a solvent. For example, if a solvent that is liquid at the reaction temperature and can dissolve the Ag precursor and the Te precursor, such as the protective agent dodecanethiol, is used, the reaction system can be formed without a solvent. In addition, when a solvent is used, octadecene, tetradecane, oleic acid, oleylamine, or a mixture thereof can be used.

[0039] B-3. ​​Synthesis conditions of AgTeS compound nanoparticles Nanoparticles of the AgTeS compound are synthesized by heating a reaction system consisting of an Ag precursor, a Te precursor, and a protective agent. The heating temperature (reaction temperature) is set to 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.

[0040] 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 AgTeS compound nanoparticles proceeds.

[0041] After the synthesis reaction of AgTeS compound nanoparticles is completed, the reaction system can be cooled as needed and the nanoparticles can be recovered. At this time, the nanoparticles can be precipitated by adding a poor solvent such as alcohol (ethanol, methanol, etc.), or the semiconductor nanoparticles can be precipitated and recovered by centrifugation or the like, and the particles can be washed with alcohol (ethanol, methanol, etc.) and then uniformly dispersed in a good solvent such as chloroform. [Effects of the Invention]

[0042] As described above, the present invention provides an AgTeS compound (AgTeS), which is an Ag chalcogenide compound composed of two chalcogen elements, Te and S. x Te y S z The semiconductor nanoparticles according to the present invention have favorable photoresponsiveness, and the photoresponsive properties can be controlled by adjusting the composition (Te atomic ratio: y / (y+z)). Furthermore, the semiconductor nanoparticles according to the present invention are practical and biocompatible, taking into consideration usage regulations and the like. 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). [Brief explanation of the drawings]

[0043] [Figure 1] TEM image of semiconductor nanoparticles made of AgTeS compound synthesized in this embodiment. [Figure 2] 1 shows the results of measuring the absorption spectrum of semiconductor nanoparticles made of an AgTeS compound synthesized in this embodiment. [Figure 3]1 shows the results of measuring the emission spectrum of semiconductor nanoparticles made of an AgTeS compound synthesized in this embodiment. [Figure 4] 1 is a graph showing the relationship between the Te atomic ratio (y / (y+z)) and the UV-λmax wavelength of semiconductor nanoparticles made of an AgTeS compound synthesized in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0044] Hereinafter, an embodiment of the present invention will be described. In this embodiment, an AgTeS compound (Ag x Te y S z ) were synthesized, and their photoresponsive properties were evaluated. At this time, nanoparticles of AgTeS compounds were synthesized with varying atomic ratios (y / (y+z)) of Te and chalcogen elements. In the synthesis of the AgTeS compound in this embodiment, a reaction system was formed by mixing a solution of an Ag precursor and a protective agent with a solution of a Te precursor and a protective agent.

[0045] A test tube purged with nitrogen was charged with 67 mg of silver acetate (Ag(OAc)) as an Ag precursor and 3 mL of 1-dodecanethiol (DDT) as a protective agent, and the mixture was left at room temperature for 1 minute, then heated at 120°C for 5 minutes to prepare an Ag precursor solution. This Ag precursor solution was kept at 120°C until the next synthesis step.

[0046] Separately, 160 mg of tellurium oxide (TeO2) as the Te precursor and 2 mL of the protective agent DDT were added to a similarly nitrogen-purged test tube. The mixture was left at room temperature for 1 minute, then heated at 120°C for 5 minutes and allowed to cool to room temperature for 15 minutes. Next, this Te precursor mixture was filtered through a 0.2 μm filter to remove precipitates, and an equimolar amount of tri-n-octylphosphine ([CH3(CH2)7]3P:TOP) was added to the filtrate to prepare the Te precursor solution. The addition of TOP to the Te precursor promotes the formation of AgTeS compounds by improving and stabilizing the Te atoms.

[0047] The synthesis of AgTeS compound nanoparticles was performed by injecting the Te precursor solution (room temperature) with a syringe into the Ag precursor solution maintained at 120°C to form a reaction system. In this embodiment, the injection amount of the Te precursor solution was changed to adjust the Te charge ratio (b / a), which is the ratio of the number of Te atoms to the number of Ag atoms, to 1 / 8, 2 / 8, 4 / 8, and 6 / 8. The synthesis of AgTeS compound nanoparticles with a Te charge ratio (b / a) of 4 / 8 was performed three times under the same conditions.

[0048] In the synthesis process, regardless of the Te content, the color of the Ag precursor solution changed (yellow to brown) the moment the Te precursor solution was added dropwise, and AgTeS compound nanoparticles were synthesized. After the synthesis reaction, the resulting AgTeS compound nanoparticle dispersion was allowed to cool for 15 minutes and return to room temperature. The supernatant and precipitate were then separated by centrifugation at 4000 rpm for 5 minutes, and the precipitate was recovered to obtain AgTeS compound nanoparticles.

[0049] The AgTeS compound nanoparticles obtained by the above procedure were dissolved in 3 cm of chloroform. 3 The resulting mixture was dispersed in a solution containing semiconductor nanoparticles made of an AgTeS compound.

[0050] [TEM observation of AgTeS compound nanoparticles] TEM observation was performed on the semiconductor nanoparticles composed of the AgTeS compound synthesized in this embodiment. Figure 1 shows TEM images of the semiconductor nanoparticles (Te content ratio: 2 / 8, 4 / 8, 6 / 8) produced in this embodiment (see the scale bar in each photograph for magnification). Referring to Figure 1, at each Te content ratio, approximately spherical AgTeS compound nanoparticles were formed. In addition, some of the nanoparticles had a connected rod shape.

[0051] [Composition analysis of semiconductor nanoparticles] Composition analysis was performed by SEM-EDS analysis on semiconductor nanoparticles composed of the AgTeS compound (Te charging ratios: 1 / 8, 2 / 8, 4 / 8, 6 / 8) synthesized in this embodiment. This composition analysis was performed on multiple randomly selected locations on the semiconductor nanoparticles, and the average value was used as the composition of the AgTeS compound. The measurement results for 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 entire nanoparticle. Table 1 also shows the atomic ratios of Ag, Te, and S in the AgTeS compound, and the atomic ratio of Te to the chalcogen elements (y / (y+z)), calculated based on the composition analysis results.

[0052] [Table 1]

[0053] As can be seen from Table 1, the atomic ratio of Te to chalcogen elements (y / (y+z)) in the AgTeS compound increases with an increase in the Te charge ratio (b / a). The number of Te atoms in the reaction system increases, resulting in Te in the AgTeS compound. On the other hand, it is believed that the number of S atoms supplied from the protective agent during the synthesis reaction decreases by the amount of Te added. Furthermore, the Ag atomic ratio (x / (x+y+z)) fluctuates little even when the Te charge ratio is changed. Furthermore, three syntheses were performed with a Te charge ratio (b / a) of 4 / 8, and it was confirmed that there was no significant difference in the compositions (Nos. 3 to 5). The results of the composition analysis indicated that the semiconductor nanoparticles contained P derived from the TOP (phosphine) used during synthesis, but the amount (atomic %) was extremely small, as can be seen from the analytical values. It can be seen that the semiconductor nanoparticles synthesized in this embodiment are essentially composed of the AgTeS compound.

[0054] [Measurement of absorption and emission spectra] Next, to evaluate the photoresponse of each semiconductor nanoparticle, absorption spectra were measured using a UV-visible spectrophotometer (Agilent Technologies, Inc., Agilent 8453) in the wavelength range of 700 nm to 2200 nm.

[0055] Regarding the properties of the AgTeS compound nanoparticles produced in this embodiment, the measurement results of the absorption spectrum are shown in FIG. 2 and the measurement results of the emission spectrum are shown in FIG. 3. Furthermore, the wavelength (UV-λ max ) are shown in Table 2.

[0056] [Table 2]

[0057] Regarding the optical properties of the AgTeS compound nanoparticles produced in this embodiment, first, the light absorption properties will be examined. Referring to FIG. 2 and Table 2, all of the AgTeS compound nanoparticles synthesized in this embodiment have UV-λ max was observed in the region above 1100 nm. It was also confirmed that the optical absorption characteristics of AgTeS compound nanoparticles can be changed by adjusting the composition (y / (y+z)). Table 2 shows the relationship between the atomic ratio of Te to chalcogen elements (y / (y+z)) and the UV-λ of AgTeS compound nanoparticles. max The relationship between the UV-λ and the AgTeS compound nanoparticles is shown in Figure 4. max shifts linearly to the longer wavelength side as the Te atomic ratio (y / (y+z)) increases. This good linear trend indicates that the photoresponse characteristics of AgTeS compound nanoparticles can be well controlled by adjusting their composition. It is also believed possible to synthesize AgTeS compound nanoparticles with an absorption edge wavelength in the 1500-1600 nm range.

[0058] Emission spectra were measured using a diode array spectrophotometer (PMA-12, C10027-02) manufactured by Hamamatsu Photonics K.K. The sample was prepared in a chloroform solution (n = 1.4429) and adjusted so that the absorbance at 365 nm was 0.1. Emission spectra were measured for semiconductor nanoparticles No. 1 to No. 5. Based on the absorption spectrum measurement results, semiconductor nanoparticle No. 6 is expected to have an emission spectrum peak in the long wavelength region, but accurate measurement was difficult due to the limitations of the measurement equipment, so it was not measured. The emission spectrum measurement results for each semiconductor nanoparticle are shown in Figure 3, and the emission spectrum peak (PL-λmax) is shown in Table 3.

[0059] [Table 3]

[0060] From the measurement results of the emission spectrum peak (PL-λmax) in Table 3, it was confirmed that all of the semiconductor nanoparticles measured in this embodiment exhibited emission. These nanoparticles were confirmed to have emission peak wavelengths in the wavelength range of 1300 nm or more. In particular, semiconductor nanoparticles with a high Te atomic ratio (Te content ratio: 4 / 8) exhibited emission peak wavelengths in the range of 1500 nm or more. [Industrial Applicability]

[0061] As described above, semiconductor nanoparticles made of the AgTeS compound according to the present invention can exhibit excellent photoresponsiveness. This AgTeS 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 and optical sensors. 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). Therefore, the present invention is particularly useful for photodetectors applied to LIDAR and SWIR image sensors, among the above-mentioned optical elements, where responsiveness in the near-infrared region is important.

Claims

1. The semiconductor nanoparticles contain an AgTeS compound represented by the following formula, which is composed of Ag, Te, and S, and the semiconductor nanoparticles contain the AgTeS compound in an amount of 90 atomic % or more. 【Chemistry 1】 (In the formula, x, y, and z are the numbers of Ag, Te, and S atoms, respectively, and 0.5≦x / (x+y+z)≦0.

7. Also, 0.3≦y / (y+z)≦0.99.)

2. 2. The semiconductor nanoparticles according to claim 1, wherein the AgTeS compound satisfies 0.1≦y / (x+y+z)≦0.4 and 0.01≦z / (x+y+z)≦0.

3.

3. 3. The semiconductor nanoparticles according to claim 1, wherein the average particle size is 2 nm or more and 20 nm or less.

4. 3. The semiconductor nanoparticle according to claim 1, wherein at least one of thiols having 4 to 20 carbon atoms, sulfides having 4 to 20 carbon atoms, thioesters having 4 to 20 carbon atoms, and thioketones having 4 to 20 carbon atoms is bonded to the surface as a protective agent.

5. 3. The semiconductor nanoparticles according to claim 1, wherein the long-wavelength absorption edge wavelength of the absorption spectrum is 1100 nm or more.

6. 3. The semiconductor nanoparticles according to claim 1, wherein the peak wavelength of the emission spectrum is 1,300 nm or more.

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