Semiconductor nanoparticles mainly composed of AgTeS compounds

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. More specifically, it relates to semiconductor nanoparticles made of an AgTeS compound that have suitable photoresponsiveness in the long wavelength region and whose photoresponsiveness can be controlled by adjusting the composition. [Background technology]

[0002] Semiconductors exhibit quantum confinement effects when formed into nanoscale particles, resulting in a band gap that corresponds to the particle size. Therefore, by controlling the composition and particle size of semiconductor nanoparticles to adjust the band gap, 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 their use is expected in various technological fields. Examples of applications for semiconductor nanoparticles include their use in light-emitting elements used in display devices and marker materials for detecting bio-related substances, as well as in fluorescent materials.

[0003] In addition to the ability to control the emission wavelength by adjusting the particle size as described above, semiconductor nanoparticles have a sufficiently narrow and stable emission peak width compared to organic dyes. Furthermore, in addition to the ability to control the absorption wavelength, semiconductor nanoparticles also possess high quantum efficiency and a high extinction coefficient. Due to these characteristics, semiconductor nanoparticles are being considered for use as photoelectric conversion elements and photodetectors in solar cells and various types of photosensors.

[0004] In particular, semiconductor nanoparticles are expected to be applied as photodetectors in optical sensors that support the near-infrared (NIR) and short-wave infrared (SWIR) regions. Optical sensors capable of handling 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 vehicles, drones, and ships, 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. SWIR image sensors are also devices whose demand is expected to increase in the future in fields such as food inspection, agriculture, and drones.

[0005] In particular, autonomous driving technology utilizing LiDAR has shown remarkable progress, and it is expected to support autonomous driving levels (Levels 4 and 5) that do not rely on driver intervention in the future. Furthermore, in order to support advanced autonomous driving levels, LiDAR needs to be less affected by sunlight and natural light, and its responsiveness in the longer wavelength range will be crucial.

[0006] On the other hand, in the past, silicon thin films have often been used as photodetectors in optical devices. However, sensors using silicon thin films suffer a significant decrease in sensitivity in the long wavelength range above 900 nm, making them unsuitable for the aforementioned applications.

[0007] Given the above background, the development of photodetectors using semiconductor nanoparticles is expected in the future, and several semiconductor compounds are being investigated. Here, known semiconductor compounds that exhibit photoresponsiveness in the long wavelength regions of the near-infrared (NIR) and short-wave infrared (SWIR) regions include metal chalcogenide compounds such as PbS, PbSe, CdHgTe, Ag2S, Ag2Se, Ag2Te, AgInSe2, AgInTe2, CuInSe2, CuInTe2, and InAs (Patent Documents 1-4). The applicant of this 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 Publication No. 2004-243507 [Patent Document 2] Japanese Patent Publication No. 2004-352594 [Patent Document 3] Japanese Patent Publication No. 2017-014476 [Patent Document 4] International Publication No. WO2020 / 054764 [Patent Document 5] Patent No. 7269591 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] While the semiconductor compounds described above exhibit photoresponsiveness in the desired wavelength range, many have obstacles when considering their application to applications such as the display devices and biomarkers for detecting biological substances mentioned at the beginning. For example, the use of lead (Pb) in electrical and electronic equipment is restricted by the European RoHS directive from an environmental perspective. Therefore, semiconductor nanoparticles composed of compounds containing Pb as a metallic component are unlikely to be widely used in the electrical and electronic fields. Furthermore, considering the use of semiconductor nanoparticles in bio-related fields, the use of compounds containing heavy metals such as cadmium (Cd) and mercury (Hg) is also difficult.

[0010] Furthermore, although the semiconductor compounds exemplified in each of the above patent documents are said to have photoresponsivity in the long wavelength region, there are few specific manufacturing examples and evaluation cases regarding their photoresponse 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. In addition, although the nanoparticles composed of the semiconductor compounds described in the above patent documents show the possibility of responding in a wavelength range of around 1400 nm at maximum, for LIDAR and the like, there is a possibility that further responsiveness in a longer wavelength region will be required 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 responsiveness 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 photoresponsivity while considering practicality for various regulations. In particular, the present invention presents semiconductor nanoparticles that exhibit suitable light absorption characteristics in the long wavelength regions of the near-infrared region (NIR) and the short-wave infrared region (SWIR), and can also emit light.

Means for Solving the Problems

[0012] Many of the compounds having optical semiconductor characteristics in each of the above-mentioned prior arts are chalcogen compounds of transition metals. And there is a correlation between the photoresponse 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 it is presumed that the photoresponsivity is shifted to the long wavelength side accordingly. Looking at the above-mentioned 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 will also shift to the long wavelength side in this order.

[0013] Based on the above findings, the inventors of the present invention attempted to synthesize a compound of one or more transition metals and various chalcogenide elements, and as a result, focused on a transition metal chalcogenide compound of Ag, which is a transition metal, and two chalcogen elements of Te and S. According to the inventors of the present invention, by changing the abundance ratio of Te and S with respect to the chalcogen elements constituting the AgTeS compound, the AgTeS compound can widely vary the photo-responsiveness (absorption edge wavelength). This possibility of controlling the absorption edge wavelength can enable the corresponding application to optical devices for various uses in addition to LIDAR. Further, Ag is well-known as a metal having a bactericidal and antibacterial action, and has no toxicity and good biocompatibility. Therefore, the Ag chalcogen compound can also pass various regulations. Based on these examination results, the inventors of the present invention arrived at the present invention as semiconductor nanoparticles mainly composed of an AgTeS compound.

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

[0015]

Chemical formula

[0016] Hereinafter, the configuration and manufacturing method of the semiconductor nanoparticles mainly composed of the AgTeS compound according to the present invention will be described. <00…​​​​​​​​​​​​​​

[0018] As described above, the AgTeS compound applied in the present invention is composed of two chalcogen elements, Te and S. S is a relatively small element among chalcogen elements, while Te is a large element. The relationship between the mass of the chalcogen element and the photoresponsiveness of the chalcogenide compound is as described above, and in the present invention, it is thought that the wavelength at which the photoresponsiveness is exhibited can be adjusted by applying chalcogen elements with opposing masses.

[0019] The AgTeS compounds constituting the semiconductor nanoparticles according to the present invention have photoresponse characteristics depending on their composition. Specifically, as the atomic ratio of Te to chalcogen elements (Te and S) (y / (y+z)) increases, the absorption wavelength of the AgTeS compound shifts proportionally to longer wavelengths. In this invention, AgTeS compounds with a Te atomic ratio y / (y+z) of 0.30 or higher exhibit an absorption wavelength of 1100 nm or higher. A Te atomic ratio y / (y+z) of 0.40 or higher is more preferable. The upper limit of y / (y+z) is 0.99 or lower, but preferably 0.90 or lower. Furthermore, AgTeS compound nanoparticles within this composition range can also exhibit luminescence.

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

[0021] Furthermore, the atomic ratio of chalcogen elements (Te and S) in the AgTeS compound ((y+z) / (x+y+z)) is the remainder of the atomic ratio of Ag described above (1.0-(x / (x+y+z))). For the atomic ratios of Te and S, y / (x+y+z) and z / (x+y+z), it is preferable to set 0.1≦y / (x+y+z)≦0.4 and 0.01≦z / (x+y+z)≦0.3, respectively. 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 mainly consist of an AgTeS compound having the composition range described above, and are composed of 90 atomic percent or more of the AgTeS compound. The semiconductor nanoparticles may consist only of the AgTeS compound. It is more preferable that the semiconductor nanoparticles contain 95 atomic percent 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, elements that constitute the solvent used when synthesizing the AgTeS compound, or elements contained in the precursors that serve as raw materials for Ag and Te, may be contained in the semiconductor nanoparticles. Elements that may be included other than the essential constituent elements Ag, Te, and S include C, P, Cl, Br, I, etc., and the content of these elements in the semiconductor nanoparticles is acceptable if it is less than 10 mass%. Note that the composition values ​​of the compounds and elements shown here are values ​​for the semiconductor nanoparticles and do not include the content of the protective agent and its constituent elements 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 applied to this invention may consist only of alloy phases of the same composition, or it may consist of alloy phases of multiple compositions. It is sufficient that x, y, and z in the entire AgTeS compound in the semiconductor nanoparticles fall within the above conditions. This composition of the AgTeS compound can be obtained by performing compositional analysis on multiple locations in the semiconductor nanoparticles and calculating the average value.

[0024] Furthermore, semiconductor nanoparticles composed of multiple alloy phases may take the form of 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 with a different composition from the core compound, or a compound that does not contain any of Ag, Te, or S, with the shell compound covering at least a portion of the surface of the core compound. Moreover, even if there is no regular combination of multiple phases like in the core-shell structure, multiple phases with different compositions may be randomly distributed.

[0025] The semiconductor nanoparticles according to the present invention may be spherical, cube-shaped, or rod-shaped. For spherical and cube-shaped semiconductor nanoparticles, an average particle size of 2 nm to 20 nm is preferred. The particle size of the semiconductor nanoparticles may be related to the band gap adjustment effect due to the quantum confinement effect. To exhibit suitable light absorption characteristics through band gap adjustment, the above-mentioned average particle size is preferred. The average particle size of 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. Note that particle size can be measured as the average value of the major axis and minor axis.

[0026] Furthermore, a scanning transmission electron microscope (STEM) is suitably used for analyzing the composition and structure of semiconductor nanoparticles according to the present invention. In particular, a high-angle annular dark-field scanning transmission microscope (HAADF-STEM) can obtain scattering images that reflect the compositional information of the nanoparticles, and when combined with an energy-dispersive X-ray spectrometer (EDS, EDX), the distribution state of Ag, Te, and S, as well as the overall composition of the nanoparticles, can be determined.

[0027] A-2. Photoresponsiveness of semiconductor nanoparticles according to the present invention As described above, the responsiveness of semiconductor nanoparticles changes depending on the composition of the AgTeS compound, which is the main component, particularly the atomic ratio of Te (y / (y+z)). Regarding the optical 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. As a result, the semiconductor nanoparticles exhibit absorption for light from the visible light region to the near-infrared region. In a more preferred embodiment, the semiconductor nanoparticles according to the present invention can have an absorption edge wavelength on the long-wavelength side of 1300 nm or more.

[0028] Furthermore, the semiconductor nanoparticles according to the present invention may also exhibit a light emission phenomenon. In this case, the emission spectrum shows an emission peak wavelength in the wavelength range 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 range of 1500 nm or more.

[0029] A-3. Utilization of semiconductor nanoparticles according to the present invention The semiconductor nanoparticles according to the present invention can be applied to various applications such as the above-mentioned optical sensor elements by coating or supporting them on a suitable substrate or carrier. There are no particular restrictions on the composition, shape, or dimensions of the substrate or carrier. Examples of substrates in the form of plates, foils, or 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 may be supported on the inorganic oxide carrier and then fixed to the substrate.

[0030] Furthermore, when coating or supporting semiconductor nanoparticles on a substrate or support, as described above, solutions, slurries, or inks in which semiconductor nanoparticles are dispersed in an appropriate dispersion medium are often used. Suitable dispersion media for these solutions include chloroform, toluene, cyclohexane, and hexane. Various methods can be used for coating the semiconductor nanoparticle solution, such as dipping and spin coating, and for supporting the nanoparticles, such as dropping, impregnation, and adsorption.

[0031] Furthermore, the semiconductor nanoparticles according to the present invention may contain a protective agent to suppress aggregation during the synthesis process and when dispersed in a dispersion medium as described above. The details of the action and composition of the protective agent will be described later. The protective agent binds to the surface of the semiconductor nanoparticles and coats at least a portion of them, suppressing aggregation of the semiconductor nanoparticles in the dispersion liquid and resulting in a homogeneous solution. In addition, by adding the protective agent to the reaction system along with the raw materials during the semiconductor nanoparticle synthesis process, nanoparticles with a suitable average particle size are synthesized. Although excess amounts of this protective agent are removed by washing and other processes after the synthesis of the semiconductor nanoparticles, some may remain and bind 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 prefer that the synthesis of the AgTeS compound having the above composition utilizes compounds containing Ag and Te, respectively, as precursors (Ag precursor and Te precursor), and that the Ag precursor and Te precursor be introduced into the same reaction system containing a protective agent containing S, and simultaneously heated to react. The method for producing semiconductor nanoparticles using this AgTeS compound synthesis method will be described below.

[0033] B-1. Raw materials (Ag precursor, Te precursor) Preferably, the Ag precursor used as the raw material is an Ag salt or Ag complex containing monovalent Ag. Suitable 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 salt, and silver diethyldithiocarbamate.

[0034] Te compounds can be used as Te precursors, specifically Te compounds such as telluric acid (TeO2), telluric acid (Te(OH)6), and sodium tellurite (Na2TeO3).

[0035] The protective agent is added to suppress the aggregation of AgTeS compound nanoparticles synthesized in the reaction system by binding to their surface. In addition, in this invention, the protective agent also acts as a source of sulfur for the synthesis of the AgTeS compound. Therefore, a protective agent containing sulfur is applied in this invention. At least one of the following is preferred as the protective agent: thiols having 4 to 20 carbon atoms, sulfides having 4 to 20 carbon atoms, thioesters having 4 to 20 carbon atoms, or thioketones having 4 to 20 carbon atoms. More preferred protective agents are thiols having 4 to 20 carbon atoms having alkyl groups, sulfanyl groups, etc. as substituents, specifically dodecanethiol, octanthiol, decanethiol, undecanethiol, and nonanthiol. These protective agents can be applied individually or in combination.

[0036] B-2. Formation of reaction systems for AgTeS compounds In the synthesis of AgTeS compounds, a single reaction system is formed by mixing the Ag precursor and Te precursor described above before the reaction is carried out. Furthermore, a protective agent containing sulfur is present in this reaction system. The reaction system may be formed by mixing separate solutions in which the protective agent has been added to each of the Ag precursor and Te precursor, or by dispersing the Ag precursor and Te precursor in a solvent and then mixing in 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 amount of Ag precursor and Te precursor added. In particular, the atomic ratio of Te, y / (y+z), can be adjusted by the ratio of the number of Te atoms in the Te precursor (b) to the number of Ag atoms in the Ag precursor (a) (b / a: hereinafter referred to as the Te charging ratio). As the Te charging 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. When synthesizing the AgTeS compound of the present invention, the Te charging ratio (b / a) is preferably 1 / 8 or more and 6 / 8 or less. Furthermore, to set y / (y+z) within a suitable range (0.4 or more and 0.90 or less), the Te charging ratio is more preferably 4 / 8 or more and 6 / 8 or less.

[0038] The reaction system for the synthesis of semiconductor nanoparticles can be formed by applying a solvent, but it can also be formed without a solvent. For example, if the protective agent is dodecanethiol, as mentioned above, and is a liquid at the reaction temperature and can dissolve the Ag precursor and Te precursor, the reaction system can be formed without a solvent. If a solvent is to be applied, octadecene, tetradecane, oleic acid, oleylamine, or mixtures thereof can be used.

[0039] B-3. ​​Synthesis conditions for AgTeS compound nanoparticles AgTeS compound nanoparticles are synthesized by heating a reaction system consisting of an Ag precursor, a Te precursor, and a protective agent. The heating temperature (reaction temperature) should be between 100°C and 200°C. Below 100°C, the synthesis reaction is difficult to proceed. On the other hand, above 200°C, nanoparticles with unstable particle shapes may be formed. A more preferable reaction temperature is between 100°C and 150°C.

[0040] In addition, the reaction time (heating time) can be adjusted according to the charged amount of the raw materials, etc., but it is preferably 5 minutes or more and 120 minutes or less. The reaction time is more preferably 10 minutes or more, and still more preferably 15 minutes or more. During the synthesis reaction of the AgTeS compound nanoparticles, it is preferable to stir the reaction system.

[0041] After the completion of the synthesis reaction of the AgTeS compound nanoparticles, the reaction system can be cooled as necessary and recovered as semiconductor nanoparticles. At this time, alcohol (ethanol, methanol, etc.) serving as a poor solvent is added to precipitate the nanoparticles, or the semiconductor nanoparticles are precipitated and recovered by centrifugation or the like. After once washing the particles with alcohol (ethanol, methanol, etc.) or the like, they may be uniformly dispersed in a good solvent such as chloroform.

Advantages of the Invention

[0042] As described above, the present invention is a semiconductor nanoparticle mainly composed of an Ag chalcogenide compound, AgTeS compound (Ag x Te y S z ) composed of two chalcogen elements, Te and S. The semiconductor nanoparticles according to the present invention have suitable photoreactivity and can control the photoreactive characteristics by adjusting the composition (Te atomic ratio: y / (y + z)). In addition, the semiconductor nanoparticles according to the present invention also have practicality and biocompatibility considering usage regulations and the like. And the semiconductor nanoparticles according to the present invention can be applied to uses such as light receiving elements and light emitting elements in the long wavelength regions of the near infrared region (NIR) and the short wavelength infrared region (SWIR).

Brief Description of the Drawings

[0043] [Figure 1] TEM image of the semiconductor nanoparticles composed of the AgTeS compound synthesized in this embodiment. [Figure 2] Measurement result of the absorption spectrum of the semiconductor nanoparticles composed of the AgTeS compound synthesized in this embodiment. [Figure 3]Measurement results of the emission spectrum of semiconductor nanoparticles composed of the AgTeS compound synthesized in this embodiment. [Figure 4] A graph showing the relationship between the Te atom ratio (y / (y+z)) of semiconductor nanoparticles composed of the AgTeS compound synthesized in this embodiment and the wavelength UV-λmax. [Modes for carrying out the invention]

[0044] Embodiments of the present invention will be described below. In this embodiment, the AgTeS compound (Ag x Te y S z Semiconductor nanoparticles consisting of ) were synthesized and their photoresponsive properties were evaluated. At this time, nanoparticles of AgTeS compounds were synthesized by changing the atomic ratio (y / (y+z)) of Te to chalcogen element. In this embodiment, a reaction system was formed by mixing a solution of Ag precursor and protective agent with a solution of Te precursor and protective agent.

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

[0046] Meanwhile, in a test tube similarly purged with nitrogen, 160 mg of tellurium oxide (TeO2) as a Te precursor and 2 mL of DDT as a protective agent were added. After standing at room temperature for 1 minute, the mixture was heated at 120°C for 5 minutes and then allowed to cool to room temperature for 15 minutes. Next, this mixed solution of Te precursors was filtered through a filter (0.2 μm) to remove the precipitate, and tri-n-octylphosphine ([CH3(CH2)7"3P:TOP) was added to the filtrate in an equimolar amount relative to the Te to prepare the Te precursor solution. The reason for adding TOP to the Te precursor is to promote the formation of the AgTeS compound by improving and stabilizing the protective power of the Te atom.

[0047] The synthesis of AgTeS compound nanoparticles was carried out by injecting a Te precursor solution (at room temperature) into an Ag precursor solution maintained at 120°C using a syringe to form a reaction system. In this embodiment, the Te charge ratio (b / a), which is the ratio of Te atoms to Ag atoms, was adjusted to 1 / 8, 2 / 8, 4 / 8, and 6 / 8 by varying the amount of Te precursor solution injected. 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 added dropwise, indicating the synthesis of AgTeS compound nanoparticles. After the synthesis reaction, the dispersion of the obtained AgTeS compound nanoparticles was allowed to cool to room temperature for 15 minutes. Furthermore, centrifugation was performed at 4000 rpm for 5 minutes to separate the supernatant from the precipitate, and the precipitate was collected to obtain AgTeS compound nanoparticles.

[0049] The AgTeS compound nanoparticles obtained by the above procedure were dissolved in chloroform at a rate of 3 cm. 3 A dispersion of semiconductor nanoparticles consisting of an AgTeS compound was obtained by dispersing them in a solution.

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

[0051] [Compositional analysis of semiconductor nanoparticles] The semiconductor nanoparticles (Te content ratio: 1 / 8, 2 / 8, 4 / 8, 6 / 8) composed of the AgTeS compound synthesized in this embodiment were subjected to compositional analysis by SEM-EDS. This compositional analysis was performed at multiple randomly selected locations on the semiconductor nanoparticles, and the average value was used 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 the following embodiments, the results of the compositional analysis are expressed as atomic percentages 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 element (y / (y+z)) calculated based on the compositional analysis results.

[0052] [Table 1]

[0053] As can be seen from Table 1, increasing the Te charging 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, becoming Te in the AgTeS compound. On the other hand, it is thought that the number of S atoms supplied from the protective agent during the synthesis reaction decreases by the amount of Te increase. Furthermore, the atomic ratio of Ag (x / (x+y+z)) does not fluctuate much even when the Te charging ratio changes. In addition, three syntheses were performed with a Te charging ratio (b / a) of 4 / 8, and it was confirmed that there was no significant difference in their composition (No. 3 to No. 5). From the above compositional analysis, it can be seen that the semiconductor nanoparticles contain P derived from TOP (phosphine) used during synthesis, but as can be seen from the analytical values, the amount (atomic %) is very small. It can be seen that the semiconductor nanoparticles synthesized in this embodiment consist substantially of the AgTeS compound.

[0054] [Measurement of absorption and emission spectra] Next, absorption spectroscopy was performed to evaluate the photoresponsiveness of each semiconductor nanoparticle. Absorption spectroscopy was performed using an ultraviolet-visible spectrophotometer (Agilent Technologies, Inc., Agilent 8453) with a measurement wavelength range of 700 nm to 2200 nm.

[0055] The characteristics of the AgTeS compound nanoparticles produced in this embodiment are shown in Figure 2 for absorption spectra and in Figure 3 for emission spectra. Furthermore, the wavelengths (UV-λ) of the exxington peaks (exciton peaks) of each semiconductor nanoparticle measured based on these values ​​are also shown. max ) are shown in Table 2.

[0056] [Table 2]

[0057] First, we will examine the light absorption properties of the AgTeS compound nanoparticles produced in this embodiment. Referring to Figure 2 and Table 2, all of the AgTeS compound nanoparticles synthesized in this embodiment exhibit UV-λ max This was observed in the region above 1100 nm. Furthermore, it was confirmed that the light absorption properties 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 is shown in Figure 4. As can be seen from Figure 4, the UV-λ of AgTeS compound nanoparticles max The wavelength shifts linearly to longer wavelengths with increasing Te atom ratio (y / (y+z)). This good linearity suggests that the photoresponse properties of AgTeS compound nanoparticles can be well controlled by adjusting their composition. Furthermore, it is considered possible to synthesize AgTeS compound nanoparticles with absorption edge wavelengths 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 samples were adjusted in chloroform solution (n=1.4429) to an absorbance of 0.1 at 365 nm before measurement. Emission spectra were measured for semiconductor nanoparticles No. 1 to No. 5. Although semiconductor nanoparticle No. 6 is presumed to have an emission spectrum peak in the long-wavelength region based on its absorption spectrum, accurate measurement was difficult due to limitations of the measuring equipment, and therefore it was not included in the measurement. Figure 3 shows the emission spectrum results for each semiconductor nanoparticle, and Table 3 shows the emission spectrum peak (PL-λmax).

[0059] [Table 3]

[0060] Table 3 shows the emission spectrum peak (PL-λmax) measurement results, indicating that emission was confirmed in all semiconductor nanoparticles measured in this embodiment. Emission peak wavelengths were observed in the wavelength range of 1300 nm and above. In particular, semiconductor nanoparticles with a high Te atomic ratio (Te content: 4 / 8) showed emission peak wavelengths in the region of 1500 nm and above. [Industrial applicability]

[0061] As described above, the semiconductor nanoparticles made of the AgTeS compound according to the present invention can exhibit good photoresponsiveness. This AgTeS compound also takes into consideration compliance with usage regulations and avoidance of heavy metal use. The semiconductor nanoparticles according to the present invention are expected to have applications in light-emitting elements and fluorescent materials used in display devices and marker materials for detecting bio-related substances, as well as in photoelectric conversion elements and photodetectors mounted on solar cells and light sensors. In particular, the present invention aims to improve the light absorption characteristics in the long wavelength regions of the near-infrared (NIR) and short-wave infrared (SWIR) regions. For this reason, the present invention is particularly useful for photodetectors applied to LIDAR and SWIR image sensors, where responsiveness in the near-infrared region is important among the above-mentioned optical elements.

Claims

1. A semiconductor nanoparticle comprising an AgTeS compound represented by the following formula, consisting of Ag, Te, and S, wherein the semiconductor nanoparticle contains 90 atomic percent or more of the AgTeS compound. 【Chemistry 1】 (In the formula, x, y, and z are the number of atoms of Ag, Te, and S, respectively, and 0.55 ≤ x / (x + y + z) ≤ 0.

7. Also, 0.3 ≤ y / (y + z) ≤ 0.99.)

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

4. A semiconductor nanoparticle according to claim 1 or claim 2, wherein at least one of the following is bonded to the surface as a protective agent: thiols having 4 to 20 carbon atoms, sulfides having 4 to 20 carbon atoms, thioesters having 4 to 20 carbon atoms, or thioketones having 4 to 20 carbon atoms.

5. The semiconductor nanoparticle according to claim 1 or claim 2, wherein the long-wavelength absorption edge wavelength of the absorption spectrum is 1300 nm or longer.

6. The semiconductor nanoparticle according to claim 1 or claim 2, wherein the peak wavelength of the emission spectrum is 1500 nm or more.

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