SEMICONDUCTOR NANOPARTICLES COMPRISING AgTeS COMPOUND AS MAIN COMPONENT

Abstract

The present invention relates to semiconductor nanoparticles including an AgTeS compound containing Ag, Te, and S as essential constituent elements. The AgTeS compound forming the semiconductor nanoparticles is represented by the formula. In the formula, x, y, and z are respectively the numbers of Ag atoms, Te atoms, and S atoms and satisfy 0.5≤x / (x+y+z)≤0.7 and 0.3≤y / (y+z)≤0.99. The semiconductor nanoparticles according to the present invention include at least 90 at.% the AgTeS compound. The semiconductor nanoparticles according to the present invention have an absorption spectrum in which the longer-wavelength-side absorption-edge wavelength is 1,100 nm or longer. The semiconductor nanoparticles according to the present invention can emit light.

Description

Semiconductor nanoparticles mainly composed of AgTeS compounds

[0001] The present invention relates to semiconductor nanoparticles mainly composed of an AgTeS compound, and more particularly 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.

[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] 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 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] 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 for LIDAR to be less susceptible to the effects of sunlight and natural light and to have 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. However, 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] In light of 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, 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, Ag ２ S, Ag ２ Se, Ag ２ Te, AgInSe ２ , AgInTe ２ , CuInSe ２ , CuInTe ２Metal 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.

[0008] 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

[0009] 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 restricts the use of Pb in electrical and electronic devices 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.

[0010] Furthermore, although the semiconductor compounds exemplified in the above patent documents are said to have photoresponsiveness in the long wavelength region, there are few specific examples of their production and evaluation of their photoresponsiveness. Patent Documents 1 and 2 describe many of the semiconductor compounds listed above, but do not provide specific examples of their production or evaluation results of their response characteristics in the long wavelength region. Furthermore, while the nanoparticles made of the semiconductor compounds described in the above patent documents demonstrate the possibility of responding to wavelengths up to around 1400 nm, LIDAR and other applications may require response in even longer wavelength regions in the future. In this regard, quantum dot technology is still in the research stage, and it is necessary to identify specific semiconductor compounds and semiconductor nanoparticles that can exhibit response in longer wavelength regions while taking practicality into consideration.

[0011] Therefore, the present invention proposes a specific configuration and a manufacturing method for semiconductor nanoparticles made of a novel semiconductor compound that takes into consideration practical applicability to various regulations and has suitable photoresponsiveness. In particular, the present invention proposes semiconductor nanoparticles that exhibit suitable light absorption characteristics in the long wavelength regions of the near infrared region (NIR) and short wave infrared region (SWIR) and are also capable of emitting light.

[0012] Many of the compounds having optical semiconductor properties in the above-mentioned prior arts are transition metal chalcogen compounds. The photoresponsive properties of transition metal chalcogen compounds are correlated with the mass (atomic weight) of the chalcogen element. That is, it is presumed that increasing the mass of the chalcogen element reduces the orbital energy difference between the transition metal element and the chalcogen element of the transition metal chalcogen compound, thereby shifting the photoresponsiveness to the longer wavelength side. Looking at the above-mentioned semiconductor compounds, for example, Ag ２ S, Ag ２ Se, Ag ２ In Ag compounds of Te, the masses of the chalcogen elements are S<Se<Te, and therefore the absorption wavelengths of these Ag compounds also shift to the longer wavelength side in this order.

[0013] Based on the above findings, the 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 inventors, the photoresponsiveness (absorption edge wavelength) of AgTeS compounds can be varied over a wide range by changing the abundance ratio of Te and S among the chalcogen elements constituting the compound. This ability to control the absorption edge wavelength can enable compatibility with optical devices for various applications in addition to LIDAR. Furthermore, Ag is known as a metal with bactericidal and antibacterial properties, is non-toxic, and has good biocompatibility. Therefore, Ag chalcogen compounds can also comply with various regulations. Based on these findings, the inventors conceived the present invention of semiconductor nanoparticles primarily composed of AgTeS compounds.

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

[0015] (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.)

[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 the semiconductor nanoparticles As described above, the semiconductor nanoparticles according to the present invention are mainly composed of an AgTeS compound. This AgTeS compound has the following structure: where the number of Ag, Te, and S atoms is x, y, and z, respectively. 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 according to its composition. Specifically, in particular, as the atomic ratio of Te to chalcogen elements (Te and S) (the ratio of the number of Te atoms to the number of chalcogen element atoms) (y / (y+z)) increases, the absorption wavelength of the AgTeS compound shifts proportionally to the longer wavelength side. 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. Furthermore, the upper limit of y / (y+z) is 0.99 or less, preferably 0.90 or less. Furthermore, AgTeS compound nanoparticles within this composition range can also exhibit luminescence.

[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 can be said that the range in which the Ag atomic ratio can be set is relatively narrow. The present inventors have confirmed that, within this range, the number of Ag atoms can be adjusted by changing the above-mentioned y / (y + z). 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, 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 elements contained 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] In addition, 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 in which a core (core compound) is made of an AgTeS compound containing Ag, Te, and S, and a shell (shell compound) is made of an AgTeS compound or a compound that does not contain Ag, Te, or S, and the shell compound covers at least a portion of the surface of the core compound. In addition, 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. In order to achieve favorable light absorption characteristics through band gap adjustment, the above-mentioned average particle size is preferable. 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, Te, and S and the composition of the entire nanoparticles.

[0027] A-2. Photoresponsiveness of 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)). Looking at 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 light 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] 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 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 an emission peak 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 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, and metals. 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 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 have found that the synthesis of the AgTeS compound having the above-described composition preferably uses compounds containing Ag and Te as precursors (Ag precursor, Te precursor), introduces the Ag precursor and the Te precursor into the same reaction system containing a protective agent containing S, and reacts them by heating simultaneously. Below, a method for producing semiconductor nanoparticles that uses 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 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(I) cyanide, and silver diethyldithiocarbamate.

[0034] The Te precursor is a Te compound, specifically, tellurium oxide (TeO ２ ), telluric acid (Te(OH) ６ ), sodium tellurite (Na ２ TeO ３ Te compounds such as tetraethoxysilane, ...

[0035] The protective agent is added to the surface of AgTeS compound nanoparticles synthesized in the reaction system, thereby suppressing 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, in the present invention, a protective agent containing S is used. 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 a reaction system of AgTeS compound When synthesizing the AgTeS compound, the above-described 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 the Te precursor, each containing a protective agent, or by dispersing the Ag precursor and the 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 charged. 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 will be 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) in 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 by using a solvent, but it can also be formed without a solvent. For example, as long as it is liquid at the reaction temperature and can dissolve the Ag precursor and the Te precursor, such as the protective agent dodecanethiol, 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 for AgTeS Compound Nanoparticles Nanoparticles of 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) 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.

[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 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.

[0042] As described above, the present invention provides an AgTeS compound (Ag), 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)). The semiconductor nanoparticles according to the present invention are also 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).

[0043] TEM image of semiconductor nanoparticles made of the AgTeS compound synthesized in this embodiment. Measurement results of the absorption spectrum of semiconductor nanoparticles made of the AgTeS compound synthesized in this embodiment. Measurement results of the emission spectrum of semiconductor nanoparticles made of the AgTeS compound synthesized in this embodiment. Te atomic ratio (y / (y+z)) and wavelength UV-λ of semiconductor nanoparticles made of the AgTeS compound synthesized in this embodiment. ｍａｘ Graph showing the relationship between.

[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 of Te and chalcogen elements (y / (y+z)). 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] 67 mg of silver acetate (Ag(OAc)) as an Ag precursor and 3 mL of 1-dodecanethiol (DDT) as a protective agent were placed in a test tube that had been purged with nitrogen, and the mixture was left at room temperature for 1 minute and 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] On the other hand, in a test tube similarly purged with nitrogen, tellurium oxide (TeO ２ 160 mg of Te precursors and 2 mL of DDT (protecting agent) were added, and the mixture was left at room temperature for 1 minute, then heated at 120°C for 5 minutes, and then allowed to cool to room temperature for 15 minutes. Next, this Te precursor mixture was filtered through a filter (0.2 μm) to remove precipitates, and the filtrate was diluted with tri-n-octylphosphine ([CH ３ (CH ２ ) ７ " ３ A Te precursor solution was prepared by adding an equimolar amount of TOP to Te. The reason for adding TOP to the Te precursor is to promote the formation of AgTeS compounds by improving and stabilizing the protection of Te atoms.

[0047] The synthesis of AgTeS compound nanoparticles was carried out by injecting the Te precursor solution (room temperature) into the Ag precursor solution maintained at 120 ° C. with a syringe 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 carried out three times under the same conditions.

[0048] In the synthesis process, regardless of the Te charging ratio, the color of the Ag precursor solution changed (yellow to brown) the moment the Te precursor solution was dropped, and AgTeS compound nanoparticles were synthesized. After the synthesis reaction, the resulting AgTeS compound nanoparticle dispersion was allowed to cool for 15 minutes and returned to room temperature. Further, the mixture was centrifuged at 4000 rpm for 5 minutes to separate the supernatant and precipitate, and the precipitate was collected 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 dispersion of 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 each semiconductor nanoparticle (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 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 taken as the composition of the AgTeS compound. 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 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]

[0053] As can be seen from Table 1, an increase in the Te charge ratio (b / a) increases the atomic ratio of Te to chalcogen elements (y / (y+z)) in the AgTeS compound. 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 AgTeS compounds.

[0054] [Measurement of Absorption Spectrum and Emission Spectrum] Next, absorption spectrum was measured to evaluate the photoresponsiveness of each semiconductor nanoparticle. The absorption spectrum was measured using a UV-visible spectrophotometer (Agilent 8453, manufactured by Agilent Technologies, Inc.) in the measurement wavelength range of 700 nm to 2200 nm.

[0055] Regarding the characteristics 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) of the exxion peak of each semiconductor nanoparticle measured based on these is ｍａｘ ) are shown in Table 2.

[0056]

[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 ｍａｘwas observed in the region of 1100 nm or more. It was also confirmed that the light 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. As can be seen from Figure 4, ｍａｘ shifts linearly to the longer wavelength side as the Te atomic ratio (y / (y+z)) increases. This tendency for good linearity suggests 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 region.

[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 measurement equipment, so it was not included in the measurement. The measurement results of the emission spectrum of each semiconductor nanoparticle are shown in Figure 3, and the emission spectrum peak (PL-λmax) is shown in Table 3.

[0059]

[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.

[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, in which responsiveness in the near-infrared region is important.

Claims

1. Semiconductor nanoparticles containing an AgTeS compound represented by the following formula, which is composed of Ag, Te, and S, and which contain 90 atomic % or more of the AgTeS compound. (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. The semiconductor nanoparticles according to claim 1, wherein the AgTeS compound satisfies the conditions 0.1≦y / (x+y+z)≦0.4 and 0.01≦z / (x+y+z)≦0.

3.

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

4. Semiconductor nanoparticles according to claim 1 or claim 2, having at least one of the following protective agents bonded to the surface: 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.

5. The semiconductor nanoparticles according to claim 1 or 2, wherein the absorption edge wavelength on the long wavelength side of the absorption spectrum is 1100 nm or more.

6. The semiconductor nanoparticles according to claim 1 or 2, which have an emission spectrum with a peak wavelength of 1,300 nm or more.

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