WO2021039727A1

WO2021039727A1 - Semiconductor nanoparticles, production method for same, and light-emitting device

Info

Publication number: WO2021039727A1
Application number: PCT/JP2020/031860
Authority: WO
Inventors: 鳥本　司; 達矢亀山; 千恵宮前; 桑畑　進; 太郎上松; 大祐小谷松
Original assignee: 国立大学法人東海国立大学機構; 国立大学法人大阪大学; 日亜化学工業株式会社
Priority date: 2019-08-26
Filing date: 2020-08-24
Publication date: 2021-03-04
Also published as: JPWO2021039727A1

Abstract

Provided is a production method for core/shell-type semiconductor nanoparticles that are capable of band-edge light emission and have excellent light emission efficiency. The production method for the core/shell-type semiconductor nanoparticles involves: obtaining a mixture that includes cores, at least one compound that includes at least one first element selected from the group that consists of Al, Ga, In, and Tl, and at least one simple substance of or compound that includes at least one second element selected from the group that consists of S, Se, and Te; and performing a heat treatment on the mixture to produce the core/shell-type semiconductor nanoparticles. The mixture includes the compound(s) that include the first element(s) and the simple substance(s) of or compound(s) that include the second element(s) such that the ratio of the total number of atoms of the first element(s) to the sum of the total number of atoms of the first element(s) and the total number of atoms of the second element(s) is greater than 0.5.

Description

Semiconductor nanoparticles and their manufacturing methods and light emitting devices

The present disclosure relates to semiconductor nanoparticles, a method for producing the same, and a light emitting device.

It is known that semiconductor particles exhibit a quantum size effect when the particle size is, for example, 10 nm or less, and such nanoparticles are called quantum dots (also called semiconductor quantum dots). The quantum size effect is a phenomenon in which the bands of the valence band and the conduction band, which are considered to be continuous in bulk particles, become discrete when the particle size is nano-sized, and the band gap energy changes according to the particle size. Point to.

Since the quantum dots can absorb light and convert the wavelength into light corresponding to the band gap energy, a white light emitting device utilizing the light emission of the quantum dots has been proposed (for example, Japanese Patent Application Laid-Open No. 2012-212862). (See Japanese Patent Application Laid-Open No. 2010-177656). Further, core-shell type semiconductor nanoparticles capable of emitting band-end light and having a low toxicity composition and a method for producing the same have been proposed (see, for example, Japanese Patent Application Laid-Open No. 2018-0414242).

Semiconductor nanoparticles with higher luminous efficiency are required as quantum dots that exhibit band-end emission. One aspect of the present disclosure is to provide a method for producing semiconductor nanoparticles capable of band-end emission and having excellent luminous efficiency.

The first aspect is a method for producing core-shell type semiconductor nanoparticles. The production method is a core containing a semiconductor containing ^{M 1} , M ² ^{and Z, wherein M 1} is at least one element selected from the group consisting of Ag, Cu, Au and an alkali metal, and at least Ag. Is included, M ² is at least one element selected from the group consisting of Al, Ga, In and Tl, and contains at least one of In and Ga, and Z is from the group consisting of S, Se and Te. Preparing a core containing at least one selected element, a core, at least one compound containing at least one selected element from the group consisting of Al, Ga, In and Tl, and S. , Se and Te to obtain a mixture containing at least one element of the second element selected from the group consisting of Se and Te and at least one compound containing the second element, and heat-treating the mixture to obtain core-shell type semiconductor nanoparticles. Including to get. The mixture is a compound containing the first element and a simple substance of the second element or a compound containing the second element, and the total atoms of the first element relative to the total number of atoms of the first element and the total number of atoms of the second element. Include in a mixed ratio where the ratio of numbers is greater than 0.5.

The second aspect is a core-shell type semiconductor nanoparticle having a core and a shell arranged on the surface of the core and emitting light by irradiation with light. The core ^{comprises a semiconductor containing M 1} , M ² and Z, where M ¹ is at least one element selected from the group consisting of Ag, Cu, Au and alkali metals, containing at least Ag and M ² Is at least one element selected from the group consisting of Al, Ga, In and Tl, contains at least one of In and Ga, and Z is at least one element selected from the group consisting of S, Se and Te. Contains the elements of. The core has ^{a total M 1} content of 10 mol% or more and 30 mol% or less, ^{a total M 2} content of 15 mol% or more and 35 mol% or less, and a total Z content of 35. It is more than mol% and less than 55 mol%. The shell is substantially composed of a first element, which is at least one selected from the group consisting of Al, Ga, In and Tl, and a second element, which is at least one selected from the group consisting of S, Se and Te. , O element.

The third aspect is a light emitting device including a light conversion member containing the core-shell type semiconductor nanoparticles and a semiconductor light emitting element.

According to one aspect of the present disclosure, it is possible to provide a method for producing semiconductor nanoparticles capable of band-end emission and having excellent luminous efficiency.

It is a figure which shows the absorption spectrum of the core-shell type semiconductor nanoparticles. It is a figure which shows the emission spectrum of the core-shell type semiconductor nanoparticles. It is a figure which shows the absorption spectrum of the core-shell type semiconductor nanoparticles. It is a figure which shows the emission spectrum of the core-shell type semiconductor nanoparticles.

In the present specification, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .. Further, the content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments shown below exemplify core-shell type semiconductor nanoparticles, a method for producing the same, and a light emitting device for embodying the technical idea of the present invention, and the present invention is the core-shell type shown below. It is not limited to semiconductor nanoparticles, their manufacturing methods, and light emitting devices.

Method for producing core-shell type semiconductor nanoparticles The method for producing core-shell type semiconductor nanoparticles includes a preparatory step for preparing a core, a mixing step for obtaining a mixture containing a core and a shell-forming material, and a heat treatment of the mixture for core-shell type semiconductor nanoparticles. Includes a heat treatment step to obtain. The core contains a semiconductor containing ^{element M 1} , element M ^{2 and element Z.} The element M ¹ contains at least one selected from the group consisting of silver (Ag), copper (Cu), gold (Au) and alkali metals, and contains at least Ag. The element M ² contains at least one selected from the group consisting of aluminum (Al), gallium (Ga), indium (In) and thallium (Tl), and contains at least one of In and Ga. Element Z comprises at least one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te). The mixture is selected from the group consisting of the core and at least one compound containing the first element, which is at least one selected from the group consisting of Al, Ga, In and Tl as the shell-forming material, and the group consisting of S, Se and Te. It contains at least one element of the second element and at least one compound containing the second element. The mixture comprises a compound containing the first element (hereinafter, also referred to as a first element source) and a simple substance of the second element or a compound containing a second element (hereinafter, also referred to as a second element source). It is included in a mixing ratio in which the ratio of the total number of atoms of the first element to the total number of total atoms of the element and the total number of atoms of the second element is greater than 0.5.

In the method for producing core-shell type semiconductor nanoparticles, when forming a shell on the core surface, the first element source and the second element source, which are shell-forming materials, are used, and the content of the first element is changed to the second element. On the other hand, core-shell type semiconductor nanoparticles having excellent light emission efficiency can be produced by heat-treating the mixture contained in an excess amount on a molar basis. This can be considered, for example, because the first element contained in excess reacts with an element other than the second element, for example, oxygen to form a shell.

Core preparation step In the core preparation step, a core containing a semiconductor containing ^{element M 1} , element M ^{2 and element Z is prepared.} The core may be semiconductor nanoparticles. The core may be appropriately selected from commercially available semiconductor nanoparticles and prepared, or semiconductor nanoparticles having a desired composition may be produced and prepared.

The element M ¹ constituting the core contains Ag and may further contain at least one element selected from the group consisting of Cu, Au and alkali metals. The alkali metal in the element M ¹ includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and the like. Since the alkali metal can be a monovalent cation like Ag, it can replace a part of Ag in the composition of the semiconductor nanoparticles. In particular, Li has an ionic radius similar to that of Ag and is preferably used. In the composition of semiconductor nanoparticles, for example, by substituting a part of Ag with an alkali metal, for example, the band gap is widened and the emission peak wavelength is shifted to a short wavelength. The element M ² contains at least one of In and Ga, and may further contain at least one element selected from the group consisting of Al and Tl. The element Z contains at least one element selected from the group consisting of S, Se and Te, and may contain at least S.

The core may be, for example, ^{semiconductor nanoparticles containing Ag as the element M 1} , at least one of In and Ga as the element M ^{2, and S as the element Z.} Further, the core may be, for example, semiconductor nanoparticles having a composition represented by the following formula (1).
M ¹ _q M ² Z _{(q + 3) / 2} (1)
Here, 0.2 <q ≦ 1.2.

The core semiconductor nanoparticles can be manufactured by the following manufacturing method. For example, the first core production method includes a raw material preparation step for obtaining a first raw material mixture ^{containing a salt containing the element M 1} , a salt containing the element M ^{2, a source of the element Z, and an organic solvent.} It may include a heat treatment step of heat-treating the first raw material mixture to obtain semiconductor nanoparticles. Further, the second core production method comprises a raw material preparation step for obtaining a second raw material mixture ^{containing a salt containing the element M 1} , a salt containing the element M ^{2, and an organic solvent, and a predetermined raw material mixture.} It may include a heating step of heating to a temperature and an addition step of adding a source of element Z to the heated second raw material mixture.

In the first core production method, ^{a salt containing the element M 1} , a salt containing the element M ² , and a source of the element Z are simultaneously charged into an organic solvent to prepare a first raw material mixture. The core may be manufactured by heat-treating. According to this method, semiconductor nanoparticles as a core can be synthesized in one pot with good reproducibility by a simple operation. Further, the organic solvent and the ^{salt containing the element M 1} are reacted to form a complex, and then the organic solvent and the ^{salt containing the element M 2} are reacted to form a complex, and these complexes and the element Z are formed. The core may be produced by a method of reacting with the source of the above and growing the obtained reaction product into crystals. In this case, the heat treatment may be carried out at the stage of reacting with the source of element Z.

The salt containing the element M ¹ and the salt containing the element M ² may be either an organic acid salt or an inorganic acid salt. Specifically, examples of the inorganic acid salt include nitrates, sulfates, hydrochlorides, sulfonates and the like. Examples of the organic acid salt include formate, acetate, oxalic acid, and acetylacetonate salt. The salt containing the element M ¹ and the salt containing the element M ² are preferably at least one selected from the group consisting of these, and more preferably organic acid salts such as acetate and acetylacetonate. It is considered that the organic acid salt has a high solubility in an organic solvent and the reaction can be easily carried out more uniformly.

Among the sources of element Z, examples of the source of S include elemental sulfur and sulfur-containing compounds. Specific examples of the urea-containing compound include β-dithiones such as 2,4-pentanedithione; dithiols such as 1,2-bis (trifluoromethyl) ethylene-1,2-dithiol; diethyldithiocarbamide acid. Dialkyldithiocarbamide salts such as salts; thiourea, monoalkylthiourea, 1,3-dialkylthiourea, 1,1-dialkylthiourea, 1,1,3-trialkylthiourea, 1,1,3,3- Examples thereof include alkylthiourea having an alkyl group having 1 to 18 carbon atoms such as tetraalkylthiourea.

Examples of the Se supply source include elemental selenium; Se-containing compounds such as selenourea, selenoacetamide, and alkylselenol. Examples of the Te supply source include tellurium simple substance, Te-phosphine complex, and alkyltelrol.

Examples of the organic solvent include amines having a hydrocarbon group having 4 to 20 carbon atoms, for example, alkylamines having 4 to 20 carbon atoms or alkenylamines, for example, thiols having a hydrocarbon group having 4 to 20 carbon atoms, for example, 4 carbon atoms. 20 alkylthiols or alkenylthiols, such as phosphines having a hydrocarbon group having 4 to 20 carbon atoms, such as alkylphosphine or alkenylphosphine having 4 to 20 carbon atoms, are selected from the group consisting of these. It is preferable to contain at least one type. These organic solvents may, for example, surface-modify the resulting semiconductor nanoparticles, for example. The organic solvent may be used in combination of two or more, for example, at least one selected from thiols having a hydrocarbon group having 4 to 20 carbon atoms and an amine having a hydrocarbon group having 4 to 20 carbon atoms. A mixed solvent in combination with at least one of the above is used. These organic solvents may be mixed with other organic solvents and used. When the organic solvent contains the thiol and the amine, the volume ratio of the thiol to the amine (thiol / amine) is, for example, greater than 0 and 1 or less, preferably 0.007 or more and 0.2 or less.

The first raw material mixture ^{comprises at least one salt containing the element M 1} , at least one salt containing the element M ^2, and at least one source of the element Z without reacting with each other. It may be contained, or may be contained as a complex formed from these. Further, the first raw material mixture contains ^{an M 1} complex formed from a salt containing ^{the element M 1} ^{, an M 2} complex formed from a salt containing the element M ² , a complex formed from a source of the element Z, and the like. It may be a thing. Complex formation is carried out, for example, ^{by mixing a salt containing the element M 1} , a salt containing the element M ² , and a source of the element Z in a suitable organic solvent. Further, the mixed atmosphere may be an inert gas atmosphere, for example, an argon atmosphere, a nitrogen atmosphere, or the like. By creating an inert gas atmosphere, by-production of oxides can be reduced or prevented.

In the first raw material mixture, the ratio of the total number of atoms ^{of the element M 1} ^{(M 1} / M ² ) to the total number of atoms of the ^{element M 2} contained in the composition is, for example, 0.1 or more and 2.5 or less. It is preferably 0.2 or more and 2.0 or less, and more preferably 0.3 or more and 1.5 or less. Further, in the composition of the first raw material mixture, the ratio of the number of atoms of In to the total number of atoms of In and Ga (In / (In + Ga)) is, for example, 0.1 or more and 1.0 or less, preferably 0.1 or more. It is 0.25 or more and 0.99 or less. Further, in the composition of the first raw material mixture, the ^{ratio (M 1} / Z) of the total number of atoms ^{of the element M 1 to} the total number of atoms of the element Z is, for example, 0.27 or more and 1.0 or less. It is preferably 0.35 or more and 0.5 or less. By using the source of each element so that the composition of the first raw material mixture satisfies these conditions, it is possible to generate semiconductor nanoparticles that easily give band-end emission.

The heat treatment step in the first production method is a one-step heat treatment step in which the first raw material mixture is heat-treated at a predetermined temperature, but after the heat treatment at the first temperature, the heat treatment is performed at a second temperature higher than the first temperature. It may be a two-step heat treatment step of heat treatment. By performing the heat treatment in two steps, for example, semiconductor nanoparticles having better reproducibility and relatively high intensity of band-end emission can be produced. Here, the heat treatment at the first temperature and the heat treatment at the second temperature may be continuously performed, or the heat treatment may be performed by lowering the temperature after the heat treatment at the first temperature and then raising the temperature to the second temperature. Good.

When the heat treatment of the first raw material mixture is performed in a one-step heat treatment step, the heat treatment temperature may be, for example, 180 ° C. or higher, preferably 200 ° C. or higher or 260 ° C. or higher. The heat treatment temperature may be, for example, 370 ° C. or lower, preferably 350 ° C. or lower or 320 ° C. or lower. The heat treatment time may be, for example, 1 minute or longer, preferably 5 minutes or longer, and more preferably 7 minutes or longer. The heat treatment time may be, for example, 120 minutes or less, preferably 60 minutes or less, more preferably 30 minutes or less, or 20 minutes or less.

Further, when the heat treatment of the first raw material mixture is performed in a two-step heat treatment step, the first temperature may be, for example, 30 ° C. or higher, preferably 100 ° C. or higher. The first temperature may be, for example, 200 ° C. or lower, preferably 180 ° C. or lower. The heat treatment time at the first temperature may be, for example, 1 minute or longer, preferably 5 minutes or longer, and more preferably 10 minutes or longer. The heat treatment time at the first temperature may be, for example, 120 minutes or less, preferably 60 minutes or less, and more preferably 30 minutes or less.

The second temperature may be, for example, 180 ° C. or higher, preferably 200 ° C. or higher. The second temperature may be, for example, 370 ° C or lower, preferably 350 ° C or lower. The heat treatment time at the second temperature may be, for example, 1 minute or longer, preferably 5 minutes or longer, and more preferably 10 minutes or longer. The heat treatment time at the second temperature may be, for example, 120 minutes or less, preferably 60 minutes or less, and more preferably 30 minutes or less.

The heat treatment time is defined as the start time of the heat treatment when the temperature reaches a predetermined temperature, and the end time of the heat treatment at the predetermined temperature when the operation for lowering or raising the temperature is performed. The rate of temperature rise until reaching a predetermined temperature may be, for example, 1 ° C./min or more and 100 ° C./min or less, or 1 ° C./min or more and 50 ° C./min or less. The temperature lowering rate after the heat treatment is, for example, 1 ° C./min or more and 100 ° C./min or less, and may be cooled if necessary, or the heat source may be stopped and allowed to cool.

The atmosphere in the heat treatment step is preferably a rare gas atmosphere such as argon or an inert atmosphere such as a nitrogen atmosphere. By heat treatment in an inert atmosphere, by-production of oxides can be suppressed.

The preparation process of the second core manufacturing method, to prepare at least one salt containing the element M ^1, and at least one salt containing the element M ^2, the second raw material mixture containing an organic solvent. The second raw material mixture can be prepared by mixing a salt ^{containing the element M 1} and a salt containing the element M ^{2 with an organic solvent.} Further, the second raw material mixture may be prepared by mixing ^{a salt containing the element M 1} or a salt containing the element M ² with an organic solvent, and then mixing the remaining components. The obtained second raw material mixture may be in a solution state without undissolved substances in a heated state. Further, the mixed atmosphere may be an inert gas atmosphere, for example, an argon atmosphere, a nitrogen atmosphere, or the like. By creating an inert gas atmosphere, by-production of oxides can be reduced or prevented.

^{The salt containing the element M 1} used in the second core manufacturing method, the salt containing the element M ² and the organic solvent are the same as those used in the first core manufacturing method.

The second raw material mixture may ^{contain at least one salt containing the element M 1} and at least one salt containing the element M ² without reacting with each other, and is formed from these. It may be contained as a complex. Further, the second raw material mixture may ^{contain an M 1} complex formed from a salt containing ^{the element M 1} ^{, an M 2} complex formed from a salt containing the element M ^2, and the like. The complex formation is carried out, for example, by mixing a salt ^{containing the element M 1} and a salt containing the element M ^{2 in a suitable organic solvent.}

In the second raw material mixture, the ratio of the total number of atoms ^{of the element M 1} ^{(M 1} / M ² ) to the total number of atoms of the ^{element M 2} contained in the composition is, for example, 0.1 or more and 2.5 or less. It is preferably 0.2 or more and 2.0 or less, and more preferably 0.3 or more and 1.5 or less. Further, in the composition of the second raw material mixture, the ratio of the number of atoms of In to the total number of atoms of In and Ga (In / (In + Ga)) is, for example, 0.1 or more and 1.0 or less, preferably 0.1 or more. It is 0.25 or more and 0.99 or less. By using the source of each element so that the composition of the mixture satisfies these conditions, it is possible to generate semiconductor nanoparticles that easily give band-end emission.

In the temperature raising step in the second core manufacturing method, the prepared second raw material mixture is heated to a temperature in the range of, for example, 120 ° C. or higher and 300 ° C. or lower. The temperature reached by raising the temperature is preferably 125 ° C. or higher, more preferably 130 ° C. or higher, further preferably 135 ° C. or higher, and preferably 175 ° C. or lower, more preferably 160 ° C. or lower, still more preferably 150 ° C. or lower. Is. The rate of temperature rise is, for example, 1 ° C./min or more and 50 ° C./min or less, preferably 10 ° C./min or more and 50 ° C./min or less.

The atmosphere in the step of raising the temperature of the second raw material mixture is preferably an inert gas atmosphere, for example, an argon atmosphere, a nitrogen atmosphere, or the like. By creating an inert gas atmosphere, by-production of oxides can be reduced or prevented.

The adding step in the second core manufacturing method, the second raw material mixture is heated to a predetermined temperature, while maintaining a predetermined temperature, for the number of atoms of the element M ¹ in the mixture supply source of the element Z The elements are gradually added so that the rate of increase in the ratio of the number of atoms of element Z is, for example, 10 / min or less. The rate of increase in the ratio of the number of Z atoms to the number ^{of M 1} atoms in the mixture ^{(Z / M 1} ratio) is, for example, the Z / M ¹ ratio at a given time subtracted from the ^{Z / M 1 ratio after that unit time.} , Calculated by dividing the unit time by the minute conversion value. The unit time is arbitrarily selected from, for example, 1 second to 1 minute. ^{The rate of increase in the ratio of the number of Z atoms to the number of M 1} atoms in the second raw material mixture is preferably 0.0001 / min or more and 2 / min or less from the viewpoint of controlling the particle growth of the generated particles. More preferably 0.0001 / min or more and 1 / min or less, further preferably 0.001 / min or more and 0.2 / min or less, and particularly preferably 0.001 / min or more and 0.1 / min or less. is there. Further, it is preferably 0.0002 / min or more and 2 / min or less, and more preferably 0.002 / min or more and 0.2 / min or less.

The total amount of the source of the element Z is the amount of atomic ratio of the element Z on the final atomic number of the element M ¹ in the resulting mixture becomes 0.1 to 5.0, preferably The amount is 1.0 or more and 2.5 or less. The time required for adding the source of element Z may be, for example, 1 minute or longer, preferably 5 minutes or longer, more preferably 15 minutes or longer, still more preferably 20 minutes or longer, and preferably 120 minutes or longer. Below, it is more preferably 60 minutes or less, still more preferably 40 minutes or less.

The total amount of the source of the element Z is, when the amount of atomic ratio of the element Z for atomic elements M ¹ in the mixture is 0.1 or more and 2.5 or less, an increase in Z / M ¹ ratio The rate is, for example, 0.0001 / min or more and 1 / min or less, preferably 0.001 / min or more and 0.1 / min or less. The total amount of the source of the element Z is, when the amount of atomic ratio of the element Z for atomic elements M ¹ in the mixture is 5.0 or less beyond 2.5, Z / M ^The rate of increase of 1 ratio is, for example, 0.0002 / min or more and 2 / min or less, preferably 0.002 / min or more and 0.2 / min or less.

The source of element Z may be added so that the amount added per unit time is substantially the same over the required time. That is, the unit amount obtained by dividing the total addition amount of the source of the element Z by the number obtained by dividing the required time by the unit time may be added as the addition amount per unit time. The unit time can be, for example, 1 second, 5 seconds, 10 seconds, 30 seconds or 1 minute. The source of element Z may be added continuously or stepwise. The source of element Z may also be added to the mixture, for example, under an inert gas atmosphere.

The source of element Z is the same as the source of element Z used in the first core manufacturing method. In particular, in the second core production method, a sulfur-containing compound soluble in an organic solvent is preferable as a source of element Z, and alkylthiourea is preferably used from the viewpoint of solubility and reactivity, and 1,3-alkylthio is used. Urea is more preferably used. The alkyl group of the alkylthiourea preferably has 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, still more preferably 1 to 4 carbon atoms, and even more preferably 1 to 3 carbon atoms. If the alkylthiourea has multiple alkyl groups, they may be the same or different.

The source of element Z may be added to a second raw material mixture that has been heated as a simple substance of element Z or a solution in which a compound containing element Z is dispersed or dissolved in an organic solvent. Since the source of the element Z is a solution of a compound containing the element Z, the amount of the element Z added per unit time in the addition step can be easily controlled, and the semiconductor nanoparticles having a narrower particle size distribution can be easily controlled. Can be efficiently manufactured.

Examples of the organic solvent for dissolving the compound containing the element Z, which is the source of the element Z, include the same as the above-mentioned organic solvent. For example, an amine having a hydrocarbon group having 4 or more and 20 or less carbon atoms. Can be used.

When the source of the element Z is a solution of a compound containing the element Z, the concentration of the compound containing the element Z is, for example, 1 mmol / L or more and 500 mmol / L or less, preferably 10 mmol / L or more and 50 mmol / L or less.

The second core manufacturing method may further include a heat treatment step of heat-treating the mixture after the addition of the source of element Z is completed at a temperature in the range of 120 ° C. or higher and 300 ° C. or lower. The temperature of the heat treatment may be the same as or different from the temperature at which the mixture is heated. From the viewpoint of quantum yield, the heat treatment temperature is, for example, 120 ° C. or higher and 300 ° C. or lower, preferably 125 ° C. or higher and 175 ° C. or lower, more preferably 130 ° C. or higher and 160 ° C. or lower, and further preferably 135 ° C. or higher and 150 ° C. or lower. Is.

The heat treatment time is, for example, 3 seconds or more, preferably 5 minutes or more, 10 minutes or more, or 20 minutes or more from the viewpoint of the quantum efficiency of the semiconductor nanoparticles. The upper limit of the heat treatment time is not particularly limited, but can be, for example, 60 minutes or less. The time for heat treatment is defined as the start time of the heat treatment when the temperature reaches a predetermined temperature (for example, the time when the temperature reaches 140 ° C. in the case of 140 ° C.), and the end time of the heat treatment when the operation for lowering the temperature is performed.

The atmosphere of the heat treatment is preferably an inert gas atmosphere, for example, an argon atmosphere or a nitrogen atmosphere. By creating an inert gas atmosphere, by-production of oxides can be reduced or prevented.

The second core manufacturing method may include a cooling step of lowering the temperature of the solution containing the semiconductor nanoparticles following the above-mentioned step. The cooling step starts when the operation for lowering the temperature is performed and ends when the temperature is cooled to 50 ° C. or lower.

The cooling step may include a period in which the temperature lowering rate is 50 ° C./min or more from the viewpoint of suppressing the production of silver sulfide from the unreacted Ag salt. For example, after performing the operation for lowering the temperature, the temperature can be set to 50 ° C./min or more at the time when the lowering of the temperature starts.

The atmosphere of the cooling step is preferably an inert gas atmosphere, for example, an argon atmosphere or a nitrogen atmosphere. By creating an inert gas atmosphere, by-production of oxides can be reduced or prevented.

The first core manufacturing method or the second core manufacturing method may further include a separation step of separating the obtained semiconductor nanoparticles from the solution, and may further include a purification step, if necessary. In the separation step, for example, the solution containing the semiconductor nanoparticles may be subjected to centrifugation to take out the supernatant liquid containing the semiconductor nanoparticles. In the purification step, for example, the supernatant obtained in the separation step may be subjected to centrifugation by adding an appropriate organic solvent such as alcohol, and the semiconductor nanoparticles may be taken out as a precipitate. The semiconductor nanoparticles can also be taken out by volatilizing the organic solvent from the supernatant liquid. The removed precipitate may be dried by, for example, vacuum degassing or natural drying, or a combination of vacuum degassing and natural drying. Natural drying may be carried out, for example, by leaving it in the air at normal temperature and pressure, and in that case, it may be left for 20 hours or more, for example, about 30 hours. Moreover, the taken-out precipitate may be dispersed in a suitable organic solvent.

In the first core manufacturing method or the second core manufacturing method, the purification step by adding an organic solvent such as alcohol and centrifuging may be carried out a plurality of times as necessary. As the alcohol used for purification, a lower alcohol having 1 to 4 carbon atoms such as methanol, ethanol and n-propyl alcohol may be used. When the precipitate is dispersed in an organic solvent, a halogen-based solvent such as chloroform, a hydrocarbon solvent such as toluene, cyclohexane, hexane, pentane, or octane may be used as the organic solvent.

Mixing step In the mixing step in the method for producing core-shell type semiconductor nanoparticles, the prepared core contains a compound containing at least one first element selected from the group consisting of Al, Ga, In and Tl (first element source). ), And at least one element of the second element selected from the group consisting of S, Se and Te, and at least one compound containing the second element (second element source), which are the total atoms of the first element. The shell is mixed at a mixing ratio in which the ratio of the total number of atoms of the first element to the total number of the total number of atoms of the second element (hereinafter, also referred to as the first element ratio) is greater than 0.5, for example. Obtain a forming mixture. The first element ratio in the shell-forming mixture is preferably 0.6 or more, or 0.7 or more. The upper limit of the first element ratio is, for example, less than 1, preferably 0.98 or less or 0.95 or less.

The shell-forming mixture may be obtained by mixing the prepared core, the first element source, and the second element source in an organic solvent. The organic solvent can be at least one selected from nitrogen-containing compounds having a hydrocarbon group having 4 or more and 20 or less carbon atoms, or a sulfur-containing compound having a hydrocarbon group having 4 or more and 20 or less carbon atoms. It can be at least one selected and may be a mixture thereof.

The prepared core may form a shell-forming mixture as a dispersion. In a liquid in which a core of semiconductor nanoparticles is dispersed, scattered light is not generated, so that the dispersion liquid is generally obtained as transparent (colored or colorless). The solvent for dispersing the core can be any organic solvent as in the case of producing the core. For example, the organic solvent can be at least one selected from nitrogen-containing compounds having a hydrocarbon group having 4 or more and 20 or less carbon atoms, or a sulfur-containing compound having a hydrocarbon group having 4 or more and 20 or less carbon atoms. It can be at least one selected from, or a sulfur-containing compound having at least one selected from a nitrogen-containing compound having a hydrocarbon group having 4 or more and 20 or less carbon atoms and a hydrocarbon group having 4 or more and 20 or less carbon atoms. It can be combined with at least one selected from. The nitrogen-containing compound is preferably higher than the reaction temperature because it is easily available and has a boiling point of more than 290 ° C. Specific organic solvents include oleylamine and n-tetra. Examples thereof include decylamine, dodecanethiol, or a combination thereof.

In the core dispersion, the concentration of particles in the dispersion is, for example, 5.0 × ^10-8 mol / liter or more and 5.0 × 10 ^-4 mol / liter or less, particularly 1.0 × ^10-7 mol / liter. It may be prepared so as to be liter or more and 5.0 × 10 ^{-5 mol / liter or less.} When the proportion of particles in the dispersion is 5.0 × ^10-8 mol / liter or more, the product tends to be easily recovered by the aggregation / precipitation process with a poor solvent. Further, when the content is 5.0 × 10 ^-4 mol / liter or less, Ostwald ripening of the materials constituting the core and fusion due to collision are suppressed, and there is a tendency that the widening of the particle size distribution can be suppressed. The particle concentration is calculated based on the number of particles contained in the dispersion liquid divided by the Avogadro's number.

The first element source is a compound containing at least one of Group 13 elements selected from the group consisting of Al, Ga, In and Tl, and is, for example, an organic acid salt, an inorganic acid salt, or an organic metal compound of the first element. And so on. Specific examples of the first element source include inorganic acid salts such as nitrates, sulfates, hydrochlorides and sulfonates; and organic acid salts such as acetates and acetylacetonate complexes, preferably acetates and acetylacetates. It is an organic acid salt such as a nat complex. It is considered that the organic acid salt has a high solubility in an organic solvent and the reaction can be easily carried out more uniformly.

The first element source may be a salt containing at least one of In and Ga. The salt containing at least one of In and Ga may be an organic acid salt such as an acetate or an acetylacetonate complex, an inorganic acid salt such as a sulfate, a hydrochloride or a sulfonate, or the like. It may preferably be an acetate, an acetylacetonate complex or the like.

The second element source is a simple substance of a group 16 element selected from the group consisting of S, Se and Te, or a compound containing a group 16 element. For example, when S is a constituent element of the shell as the second element, the sulfur source is a single sulfur such as high-purity sulfur, or n-butanethiol, isobutanethiol, n-pentanethiol, n-hexanethiol, octane. Thiols such as thiols, decanethiols, dodecanethiols, hexadecanethiols and octadecanethiols, disulfides such as dibenzyl sulfide, thioureas, alkylthioureas such as 1,3-dimethylthiourea, and sulfur-containing compounds such as thiocarbonyl compounds. Good. Among them, when thiourea, alkylthiourea or the like is used as a sulfur source, a shell is sufficiently formed and core-shell type semiconductor nanoparticles that give strong band-end emission can be easily obtained.

When Se is a constituent element of the shell as the second element, selenium alone or a compound such as selenium phosphine oxide, an organic selenium compound (dibenzyl diselenide, diphenyl diselenide, etc.) or a hydride is used. It may be used as a second element source. When Te is a constituent element of the shell as the second element, tellurium alone, tellurium phosphine oxide, or hydride may be used as the second element source.

The shell-forming mixture may contain an alkali metal salt in addition to the first element source and the second element source. Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and the like. The alkali metal salt may be either an organic acid salt or an inorganic acid salt. Specifically, examples of the salt include nitrates, acetates, sulfates, hydrochlorides, sulfonates, acetylacetonate salts and the like, and preferably at least one selected from the group consisting of these. More preferably, it is an organic acid salt such as acetate.

When the shell-forming mixture contains an alkali metal salt, the charging ratio of the alkali metal salt to the first element source may be, for example, 0.1 or more and 5 or less, or 0.2 or more and 4 or less. The charging ratio of the second element source to the total sum of the alkali metal salt and the first element source may be, for example, 0.3 or more and 3 or less, or 0.5 or more and 2 or less.

The amount of the first element source and the second element source charged in the shell-forming mixture takes into consideration the amount of core contained in the dispersion liquid so that a shell having a desired thickness is formed in the core existing in the dispersion liquid. You may select it. For example, a semiconductor compound having a stoichiometric composition composed of the first element and the second element is produced in an amount of 0.1 μmol or more and 10 mmol or less, particularly 5 μmol or more and 1 mmol or less, based on a substance amount of 10 nmol as core particles. The amount of the 1-element source and the 2nd element source may be determined. However, the amount of substance as a particle is the molar amount when one particle is regarded as a huge molecule, and the number of nanoparticles contained in the dispersion is the Avogadro's number (NA = 6.022 × 10). Equal to the value divided by ^23).

The content of the first element source with respect to the amount of substance of the core in the shell-forming mixture is, for example, 1.6 or more, preferably 1.6 ×, as the molar ratio of the first element source to the number of particles (mol) of the core. is 10 ³ or more, more preferably 1 × 10 ⁴ or more, and for example 2.5 × 10 ⁵ or less, preferably 1.3 × 10 ⁵ or less. The content of the second element source to the content of the core, as the molar ratio of the second element sources for the number of particles of the core (moles), for example, at 5.3 × 10 or more, preferably 5.3 × 10 ² or more , and the addition is for example 8.5 × 10 ⁴ or less, preferably 4.3 × 10 ⁴ or less.

Heat Treatment Step In one aspect of the heat treatment step in the method for producing core-shell type semiconductor nanoparticles, for example, the shell-forming mixture is heat-treated at a predetermined temperature to form a semiconductor layer as a shell on the surface of the semiconductor nanoparticles as a core. To obtain core-shell type semiconductor nanoparticles (heat treatment-up method). Specifically, the shell-forming mixture is gradually heated so that its peak temperature is 200 ° C. or higher and 310 ° C. or lower, held at the peak temperature for a predetermined time, and then gradually lowered. You can. The heating rate may be, for example, 1 ° C./min or more and 50 ° C./min or less, but 50 ° C./min or more and 100 ° C. up to 200 ° C. It is preferably less than / minute. Further, when it is desired to further raise the temperature to 200 ° C. or higher, the temperature is preferably 1 ° C./min or higher and 5 ° C./min or lower thereafter. The temperature lowering rate may be, for example, 1 ° C./min or more and 50 ° C./min or less. When the peak temperature is equal to or higher than the above temperature, the surface modifier that modifies the semiconductor nanoparticles is sufficiently desorbed, or the chemical reaction for shell formation proceeds sufficiently, and so on, the semiconductor layer (shell). ) Tends to be well formed. When the peak temperature is equal to or lower than the above temperature, deterioration of the semiconductor nanoparticles is suppressed, and good band-end emission tends to be obtained. The time for maintaining the peak temperature can be, for example, 1 minute or more and 300 minutes or less, particularly 10 minutes or more and 120 minutes or less. The peak temperature retention time is selected in relation to the peak temperature, with a longer retention time when the peak temperature is lower and a shorter retention time when the peak temperature is higher, a better shell layer. Is easy to form.

Another aspect of the heat treatment step in the method for producing core-shell type semiconductor nanoparticles is that even in a one-step heat treatment step in which the shell-forming mixture is heat-treated at a predetermined temperature, the heat treatment is performed at the first temperature and then from the first temperature. It may be a two-step heat treatment step in which the heat treatment is performed at a high second temperature. By performing the heat treatment in two steps, for example, core-shell type semiconductor nanoparticles having better reproducibility and high intensity of band-end emission can be produced. Here, the heat treatment at the first temperature and the heat treatment at the second temperature may be continuously performed, or the heat treatment may be performed by lowering the temperature after the heat treatment at the first temperature and then raising the temperature to the second temperature. Good.

When the heat treatment of the shell-forming mixture is performed in a two-step heat treatment step, the first temperature may be, for example, 30 ° C. or higher, preferably 100 ° C. or higher. The first temperature may be, for example, 200 ° C. or lower, preferably 180 ° C. or lower. The heat treatment time at the first temperature may be, for example, 1 minute or longer, preferably 5 minutes or longer, and more preferably 7 minutes or longer. The heat treatment time at the first temperature may be, for example, 120 minutes or less, preferably 60 minutes or less, more preferably 30 minutes or less, or 20 minutes or less.

The second temperature may be, for example, 180 ° C. or higher, preferably 200 ° C. or higher. The second temperature may be, for example, 350 ° C. or lower, preferably 330 ° C. or lower or 310 ° C. or lower. The time of the heat treatment at the second temperature may be, for example, 1 minute or longer, preferably 5 minutes or longer, more preferably 10 minutes or longer or 20 minutes or longer. The heat treatment time at the second temperature may be, for example, 120 minutes or less, preferably 90 minutes or less, more preferably 60 minutes or less, or 40 minutes or less.

The heat treatment time is defined as the start time of the heat treatment when the temperature reaches a predetermined temperature, and the end time of the heat treatment at the predetermined temperature when the operation for lowering or raising the temperature is performed. The rate of temperature rise until the temperature reaches a predetermined temperature is, for example, 1 ° C./min or more and 100 ° C./min or less, or 1 ° C./min or more and 50 ° C./min or less. The temperature lowering rate after the heat treatment is, for example, 1 ° C./min or more and 100 ° C./min or less, and may be cooled if necessary, or the heat source may be stopped and allowed to cool.

In this way, a shell is formed to form core-shell type semiconductor nanoparticles having a core-shell structure. The resulting core-shell semiconductor nanoparticles may be separated from the solvent and, if necessary, further purified and dried. Since the methods of separation, purification, and drying are as described above in relation to the method for producing cores of semiconductor nanoparticles, detailed description thereof will be omitted here.

In one embodiment, the method for producing core-shell type semiconductor nanoparticles may include a step of adding an oxygen source to the shell-forming mixture. That is, the method for producing core-shell type semiconductor nanoparticles may include a core preparation step, a mixing step, and a heat treatment step, and the mixing step may include obtaining a shell-forming mixture containing an oxygen source. When the shell-forming mixture subjected to the heat treatment step contains an oxygen source, core-shell type semiconductor nanoparticles having higher luminous efficiency can be produced.

In the present embodiment, the shell-forming mixture obtained in the mixing step contains an oxygen source. In the mixing step, the prepared core is mixed with the first element source, the second element source and the oxygen source to obtain a shell-forming mixture.

In one embodiment, the method for producing core-shell type semiconductor nanoparticles may include a step of adding an oxygen source to the shell-forming mixture in the heat treatment step. That is, the method for producing core-shell type semiconductor nanoparticles may include a core preparation step, a mixing step, and a heat treatment step, and the heat treatment step may include adding an oxygen source to the shell-forming mixture. By adding an oxygen source to the mixture for forming a shell in a heated state, core-shell type semiconductor nanoparticles having higher luminous efficiency can be produced.

In the present embodiment, an oxygen source is added while heat-treating the shell-forming mixture obtained in the mixing step. When the shell formation is performed by a one-step heat treatment, the oxygen source may be added during the heat treatment at the peak temperature, during the temperature rise to the peak temperature, or during the temperature decrease from the peak temperature. .. When the heat treatment for shell formation is performed in two steps, an oxygen source may be added during the heat treatment at the first temperature, an oxygen source may be added after the heat treatment at the first temperature, and during the heat treatment at the second temperature. An oxygen source may be added. Further, in addition to the addition of the oxygen source in the heat treatment step, the shell-forming mixture before the heat treatment may contain the oxygen source in advance.

In one embodiment, the method for producing core-shell type semiconductor nanoparticles may include a step of bringing an oxygen source into contact with the core-shell type semiconductor nanoparticles obtained in the heat treatment step. That is, the method for producing core-shell type semiconductor nanoparticles includes a core preparation step, a mixing step, and a heat treatment step, and even if the core-shell type semiconductor nanoparticles obtained after the heat treatment step are brought into contact with an oxygen source. Good. By bringing an oxygen source into contact with the core-shell type semiconductor nanoparticles obtained from the shell-forming mixture and introducing oxygen atoms into the shell, core-shell type semiconductor nanoparticles having higher luminous efficiency can be produced.

In this embodiment, an oxygen source is brought into contact with the core-shell type semiconductor nanoparticles obtained in the heat treatment step to introduce oxygen atoms into the shell. The core-shell type semiconductor nanoparticles that are brought into contact with the oxygen source may be unrefined after the heat treatment step, or may be purified. Further, the core-shell type semiconductor nanoparticles that are brought into contact with the oxygen source may be obtained from a shell-forming mixture containing the oxygen source, and may be obtained by adding the oxygen source to the shell-forming mixture in the heat treatment step. You can.

The oxygen source is not particularly limited as long as oxygen atoms can be introduced into the composition of the shell. Specific examples of the oxygen source include a compound containing an oxygen atom and a gas containing an oxygen atom. Examples of the compound containing an oxygen atom include water, alcohol and the like, and at least one selected from the group consisting of these is preferable. Examples of the gas containing an oxygen atom include oxygen gas and ozone gas, and at least one selected from the group consisting of these is preferable. The oxygen source may be added by dissolving or dispersing a compound containing an oxygen atom in the shell-forming mixture, or by blowing a gas containing an oxygen atom into the shell-forming mixture.

In the case of water, for example, the amount of oxygen source added or used is 6000 ppm or less, preferably 3000 ppm or less, or 1000 ppm or less with respect to the weight of the solvent.

When the shell surface of the core-shell type semiconductor nanoparticles is modified with a specific modifier described later, the core-shell type semiconductor nanoparticles obtained by the above production method may be subjected to the modification step. In the modification step, the core-shell type semiconductor nanoparticles are brought into contact with a specific modifier containing phosphorus (P) having a negative oxidation number to modify the shell surface of the core-shell particles. As a result, core-shell type semiconductor nanoparticles exhibiting band-end emission with a better quantum yield are produced.

The contact between the core-shell type semiconductor nanoparticles and the specific modifier can be performed, for example, by mixing the dispersion liquid of the core-shell type semiconductor nanoparticles and the specific modifier. Further, the core-shell particles may be mixed with a liquid specific modifier. The solution may be used as the specific modifier. The dispersion liquid of the core-shell type semiconductor nanoparticles is obtained by mixing the core-shell type semiconductor nanoparticles with an appropriate organic solvent. Examples of the organic solvent used for dispersion include halogen solvents such as chloroform; aromatic hydrocarbon solvents such as toluene; and aliphatic hydrocarbon solvents such as cyclohexane, hexane, pentane, and octane. The concentration of the amount of substance in the dispersion liquid of the core-shell type semiconductor nanoparticles is, for example, 1 × 10 ^-7 mol / L or more and 1 × 10 ^-3 mol / L or less, preferably 1 × 10 ^-6 mol / L or more 1 × 10 ^-4 mol / L or less.

The amount of the specific modifier used for the core-shell type semiconductor nanoparticles is, for example, 1-fold or more and 50,000-fold or less in terms of molar ratio. Further, a dispersion liquid of core-shell type semiconductor nanoparticles having a concentration of a substance amount of 1.0 × 10 ^-7 mol / L or more and 1.0 × 10 ^-3 mol / L or less in the dispersion liquid of core-shell type semiconductor nanoparticles is used. In this case, the dispersion liquid and the specific modifier may be mixed in a volume ratio of 1: 1000 to 1000: 1.

The temperature at the time of contact between the core-shell type semiconductor nanoparticles and the specific modifier is, for example, −100 ° C. or higher and 100 ° C. or lower, or 30 ° C. or higher and 75 ° C. or lower. The contact time may be appropriately selected according to the amount of the specific modifier used, the concentration of the dispersion liquid, and the like. The contact time is, for example, 1 minute or more, preferably 1 hour or more, 100 hours or less, preferably 48 hours or less. The atmosphere at the time of contact is, for example, an atmosphere of an inert gas such as nitrogen gas or rare gas.

Core-shell type semiconductor nanoparticles The core-shell type semiconductor nanoparticles include a core and a shell arranged on the surface of the core, and emit light when irradiated with light. The core may be semiconductor nanoparticles containing ^{element M 1} , element M ^{2 and element Z.} M ¹ is at least one element selected from the group consisting of silver (Ag), copper (Cu), gold (Au) and alkali metals, and contains at least Ag. M ² is at least one element selected from the group consisting of aluminum (Al), gallium (Ga), indium (In) and thallium (Tl), and contains at least one of In and Ga. Z contains at least one element selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te). The composition of the core is such that ^{the total content of M 1} is 10 mol% or more and 30 mol% or less, ^{the total content of M 2} is 15 mol% or more and 35 mol% or less, and the total content of Z is. Is 35 mol% or more and 55 mol% or less. The shell is substantially composed of a first element, which is at least one selected from the group consisting of Al, Ga, In and Tl, and a second element, which is at least one selected from the group consisting of S, Se and Te. , Oxygen (O) element.

In the core-shell type semiconductor nanoparticles, the core itself contains semiconductor nanoparticles, and the shell is composed of oxygen elements in addition to the first and second elements, so that excellent light emission efficiency can be achieved. it can. The core-shell type semiconductor nanoparticles have an emission peak wavelength in the range of 500 nm or more and 1000 nm or less by irradiation with light having a wavelength in the range of 200 nm or more and less than 500 nm, and the half width in the emission spectrum is, for example, 250 meV or less. It emits light. The half width is preferably 200 meV or less, more preferably 150 meV or less. The lower limit of this half width is, for example, 30 meV or more. When the half-value width is 250 meV or less, the half-value width is 73 nm or less when the emission peak wavelength is 600 nm, and when the emission peak wavelength is 700 nm, the half-value width is 100 nm or less and the emission peak wavelength is 800 nm. In the case, it means that the full width at half maximum is 130 nm or less, and it means that the core-shell type semiconductor nanoparticles emit light at the band end.

Core-shell type semiconductor nanoparticles containing Ag, at least one of In and Ga, S, Se or Te in the composition of the core and the first element, the second element and the oxygen element in the composition of the shell have the shape and shape. Due to its size, it gives band edge emission. Further, the core-shell type semiconductor nanoparticles can have a composition that does not contain Cd and Pb, which are considered to be highly toxic, and can be applied to products and the like whose use of Cd and the like is prohibited. Therefore, the semiconductor nanoparticles can be suitably used as a wavelength conversion substance for a light emitting device used in a liquid crystal display device, as a biomolecule marker, or the like.

The total content of Ag, Cu, Au and alkali metals in the composition of the core is, for example, 10 mol% or more and 30 mol% or less, preferably 15 mol% or more and 25 mol% or less. The total content of Al, Ga, In and Tl in the composition of the core is, for example, 15 mol% or more and 35 mol% or less, preferably 20 mol% or more and 30 mol% or less. The total content of S, Se and Te in the composition of the core is, for example, 35 mol% or more and 55 mol% or less, preferably 40 mol% or more and 55 mol% or less.

When the core contains In and Ga, the ratio of the number of atoms of In to the sum of the number of atoms of In and Ga in the composition (In / (In + Ga)) is, for example, 0.01 or more and 1.0 or less, which is preferable. Is 0.1 or more and 0.99 or less. The ratio of the sum of the atomic numbers of Ag to the sum of the atomic numbers of In and Ga in the core composition (Ag / (In + Ga)) is, for example, 0.3 or more and 1.2 or less, preferably 0.5. It is 1.1 or less. When the core contains S, the ratio of the number of atoms of S to the sum of the numbers of atoms of Ag, In and Ga in the composition of the core (S / (Ag + In + Ga)) is, for example, 0.8 or more and 1.5 or less. It is preferably 0.9 or more and 1.2 or less.

The composition of the core is identified by, for example, energy dispersive X-ray analysis (EDX), fluorescent X-ray analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, and the like. The composition ratio of (Ag) / (In + Ga), S / (Ag + In + Ga) and the like is calculated based on the composition identified by any of these methods.

In the composition of the core, Ag may be partially substituted and contain at least one element of Cu and Au, but it is preferably composed substantially of Ag. Here, "substantially" means that the ratio of elements other than Ag to Ag is, for example, 10 mol% or less, preferably 5 mol% or less, and more preferably 1 mol% or less.

When the core contains an alkali metal, the alkali metal content is, for example, less than 30 mol%, preferably 1 mol% or more and 25 mol% or less. The atomic number ratio of alkali metal to the atomic sum of Ag in an atomic and alkali metal in the composition of the core ^{^{(M a) (M a)}} (M a / (Ag + M a)) , for example, less than 1 Yes, preferably 0.8 or less, more preferably 0.4 or less, still more preferably 0.2 or less. The ratio is, for example, greater than 0, preferably 0.05 or more, and more preferably 0.1 or more. The alkali metal preferably contains at least Li, and is preferably substantially Li. Here, "substantially" means that the ratio of the alkali metal other than Li to Li is, for example, 10 mol% or less, preferably 5 mol% or less, and more preferably 1 mol% or less. ..

In the composition of the core, at least one of In and Ga may be partially substituted to contain at least one element of Al and Tl, but is substantially composed of at least one of In and Ga. Is preferable. Here, "substantially" means that the ratio of elements other than In or Ga to In and Ga is, for example, 10 mol% or less, preferably 5 mol% or less, and more preferably 1 mol% or less. Means.

When the core contains S, S may be partially substituted and contain at least one element of Se and Te, or may be substantially composed of S. Here, "substantially" means that the ratio of the element other than S to S is, for example, 10 mol% or less, preferably 5 mol% or less, and more preferably 1 mol% or less.

The core may consist substantially of at least one of Ag, In and Ga, and only S. Here, the term "substantially" is used in consideration of the fact that elements other than Ag, In, Ga and S are inevitably contained due to the mixing of impurities and the like.

The crystal structure of the core may include at least one selected from the group consisting of tetragonal, hexagonal and orthorhombic crystals. For example, semiconductor nanoparticles containing Ag, In, and S and whose crystal structure is tetragonal, hexagonal, or orthorhombic are generally represented by the composition formula of _{AgInS 2 in the literature.} Etc. are introduced. The core according to the present embodiment can be considered, for example, in which a part of In, which is a Group 13 element, is replaced with Ga, which is also a Group 13 element. The composition of the core may be represented by, for example, Ag-In-Ga-S or the like.

Semiconductor nanoparticles represented by a composition formula such as Ag-In-Ga-S having a hexagonal crystal structure are of the wurtzite type, and semiconductors having a tetragonal crystal structure are calcopyrite. It is a type. The crystal structure is identified, for example, by measuring the XRD pattern obtained by X-ray diffraction (XRD) analysis. Specifically, the XRD pattern obtained from the semiconductor nanoparticles is a known XRD pattern assuming that the semiconductor nanoparticles are represented by the composition of _{AgInS 2, or an XRD pattern obtained by simulating from crystal structure parameters.} Compare. If any of the known patterns and simulation patterns match the pattern of the semiconductor nanoparticles, it can be said that the crystal structure of the semiconductor nanoparticles is the crystal structure of the matching known or simulation pattern.

In the core aggregate, some cores having different crystal structures may be mixed. In that case, in the XRD pattern, peaks derived from a plurality of crystal structures are observed.

The core may have, for example, an average particle size of 50 nm or less. The average particle size of the core may be, for example, 20 nm or less, 10 nm or less, or less than 10 nm. When the average particle size of the core is 50 nm or less, the quantum size effect tends to be easily obtained, and band-end emission tends to be easily obtained. The lower limit of the average particle size of the core is, for example, 1 nm.

The particle size of the core can be determined from, for example, a TEM image taken with a transmission electron microscope (TEM). Specifically, it is a line segment connecting arbitrary two points on the outer circumference of a particle observed in a TEM image of a certain particle, and is the length of the longest line segment passing through the inside of the particle. Let it be the particle size of the particles.

However, if the particles have a rod shape, the length of the minor axis is regarded as the particle size. Here, the rod-shaped particles have a minor axis and a major axis orthogonal to the minor axis in the TEM image, and the ratio of the length of the major axis to the length of the minor axis is larger than 1.2. .. The rod-shaped particles are observed in a TEM image as, for example, a rectangular shape including a rectangular shape, an elliptical shape, a polygonal shape, or the like. The shape of the cross section, which is a plane orthogonal to the long axis of the rod shape, may be, for example, a circle, an ellipse, or a polygon. Specifically, for rod-shaped particles, the length of the major axis refers to the length of the longest line segment connecting any two points on the outer circumference of the particle in the case of an elliptical shape. , Rectangular or polygonal, refers to the length of the longest line segment that is parallel to the longest side that defines the outer circumference and connects any two points on the outer circumference of the particle. .. The length of the minor axis refers to the length of the longest line segment that is orthogonal to the line segment that defines the length of the major axis among the line segments connecting arbitrary two points on the outer circumference.

The average particle size of the core is measured by measuring the particle size of all measurable particles observed in the TEM image of 50,000 times or more and 150,000 times or less, and used as the arithmetic mean of those particle sizes. Here, the measurable particles are those in which the entire particles can be observed in the TEM image. Therefore, in the TEM image, a part of the TEM image is not included in the imaging range, and particles that are cut off are not measurable. When the number of measurable particles contained in one TEM image is 100 or more, the average particle size is obtained using the TEM image. On the other hand, when the number of measurable particles contained in one TEM image is less than 100, the imaging location is changed to further acquire the TEM image, and 100 or more measurable particles included in two or more TEM images are possible. The particle size of the particles is measured to obtain the average particle size.

The core, which is a semiconductor nanoparticle, may be capable of emitting light at the band end. The core may emit light having an emission peak wavelength in the range of 500 nm or more and 650 nm or less by irradiating light having a wavelength in the range of 200 nm or more and less than 500 nm. The full width at half maximum in the emission spectrum of the core is 250 meV or less, preferably 200 meV or less, and more preferably 150 meV or less. The lower limit of this half width is, for example, 30 meV or more. When the half-value width is 250 meV or less, the half-value width is 73 nm or less when the emission peak wavelength is 600 nm, and when the emission peak wavelength is 700 nm, the half-value width is 100 nm or less and the emission peak wavelength is 800 nm. In the case, it means that the half width is 130 nm or less, and it means that the semiconductor nanoparticles emit light at the band end.

The core may give other light emission, for example, defective light emission, in addition to the band end light emission. Defect emission generally has a long emission lifetime, has a broad spectrum, and has a peak on the longer wavelength side than band-end emission. When both band-end emission and defect emission can be obtained, it is preferable that the intensity of band-end emission is larger than the intensity of defect emission.

The peak position of the band end emission of the core can be changed by changing at least one of the shape of the core and the average particle size, particularly by changing the average particle size. For example, if the average particle size of the core is made smaller, the bandgap energy becomes larger due to the quantum size effect, and the peak wavelength of the band edge emission can be shifted to the short wavelength side.

Further, in the band end emission of the core, the emission peak wavelength can be changed by changing the composition of the core. For example, shifting the emission peak wavelength of band-end emission to the short wavelength side by increasing the Ga ratio (Ga / (In + Ga)), which is the ratio of the number of atoms of Ga to the sum of the number of atoms of In and Ga in the composition. Can be done. Further, for example, select the Li or the like as an alkali metal, ^{M a} ratio ^(M a / a atomic ratio of alkali metal ^{(M a)} with respect to the atomic sum of Ag and alkali metal ^{(M a)} in the composition ( Ag + M ^a)) it is possible to shift the emission peak wavelength of the band edge emission to the short wavelength side by the increase. Further, for example, by substituting a part of S in the composition with Se and increasing the S ratio (S / (S + Se)), which is the ratio of the number of atoms of S to the sum of the number of atoms of S and Se, the band end emission is emitted. The emission peak wavelength of is can be shifted to the short wavelength side.

The absorption spectrum of the core may show exciton peaks. The exciton peak is a peak obtained by exciton generation, and the fact that it is expressed in the absorption spectrum means that the core particle group is composed of particles suitable for band-end emission with a small particle size distribution and few crystal defects. It means that it has been done. Further, the steeper the exciton peak, the more particles having the same particle size and less crystal defects are contained in the aggregate of core particles. Therefore, if the exciton peak is steep, the half width of light emission is expected to be narrowed, and the luminous efficiency is expected to be improved. In the absorption spectrum of the core, exciton peaks are observed, for example, in the range of 350 nm or more and 900 nm or less.

The core may emit light having an emission peak wavelength on the longer wavelength side than the exciton peak of the absorption spectrum by Stokes shift. When the absorption spectrum of the core shows an exciton peak, the energy difference between the exciton peak and the emission peak wavelength is, for example, 300 meV or less.

The core-shell type semiconductor nanoparticles have a core-shell structure in which the semiconductors constituting the shell are arranged on the surface of the core. The shell is a semiconductor having a band gap energy larger than that of the semiconductor constituting the core, and is composed of at least one first element selected from the group consisting of Group 13 elements Al, Ga, In and Tl, and the first element. It is composed of a semiconductor containing at least one second element selected from the group consisting of Group 16 elements S, Se and Te, and an oxygen element. The semiconductor constituting the shell may contain only one type or two or more types of Group 13 elements, and may contain only one type or two or more types of Group 16 elements.

The shell may be substantially composed of a semiconductor composed of a first element, a second element and an oxygen element. Here, "substantially" means that the ratio of elements other than the first element, the second element and the oxygen element is, for example, 10% when the total number of atoms of all the elements contained in the shell is 100%. Hereinafter, it is shown that it is preferably 5% or less, more preferably 1% or less.

The shell may be configured by selecting its composition or the like according to the bandgap energy of the semiconductor constituting the core described above. Alternatively, if the composition of the shell or the like is determined in advance, the core may be designed so that the bandgap energy of the semiconductor constituting the core is smaller than that of the shell. For example, a semiconductor made of Ag—In—S has a bandgap energy of about 1.8 eV or more and 1.9 eV or less.

Specifically, the semiconductor constituting the shell may have, for example, a bandgap energy of 2.0 eV or more and 5.0 eV or less, or 2.5 eV or more and 5.0 eV or less. The bandgap energy of the shell is, for example, 0.1 eV or more and 3.0 eV or less, 0.3 eV or more and 3.0 eV or less, or 0.5 eV or more and 1.0 eV or less larger than the band gap energy of the core. It may be. When the difference between the bandgap energy of the semiconductors constituting the shell and the bandgap energy of the semiconductors constituting the core is equal to or greater than the above lower limit value, the proportion of light emitted from the core other than the band edge light emission decreases, and the band The rate of edge emission tends to be large.

Further, the bandgap energy of the semiconductors constituting the core and the shell is selected so that the bandgap energy of the shell provides the bandgap energy of type-I that sandwiches the bandgap energy of the core in the heterojunction of the core and the shell. Is preferable. By forming the band alignment of type-I, the band edge emission from the core can be obtained better. In type-I alignment, it is preferable that a barrier of at least 0.1 eV is formed between the band gap of the core and the band gap of the shell, for example, a barrier of 0.2 eV or more, or 0.3 eV or more. May be formed. The upper limit of the barrier is, for example, 1.8 eV or less, and particularly 1.1 eV or less. When the barrier is at least the above lower limit value, the ratio of light emission other than band-end light emission tends to decrease and the ratio of band-end light emission tends to increase in light emission from the core.

The semiconductor constituting the shell may contain In or Ga as the first element. Further, the semiconductor constituting the shell may contain S as a second element. Further, the semiconductor constituting the shell may contain an oxygen (O) element. Semiconductors containing In or Ga, S and O tend to be semiconductors having a bandgap energy larger than that of the core described above.

The crystal system of the semiconductor of the shell may be familiar to the crystal system of the semiconductor of the core, and the lattice constant of the shell may be the same as or close to that of the semiconductor of the core. A shell made of semiconductors, which is familiar to the crystal system and has a close lattice constant (here, a multiple of the shell's lattice constant is close to the core's lattice constant but also has a close lattice constant), has a good circumference of the core. May be covered. Further, the shell may be amorphous.

Whether or not an amorphous shell is formed can be confirmed by observing semiconductor nanoparticles having a core-shell structure with HAADF-STEM. When an amorphous shell is formed, specifically, a portion having a regular pattern (for example, a striped pattern, a dot pattern, etc.) is observed in the central portion, and a regular pattern is observed around the portion. A portion that is not observed as having a pattern is observed in HAADF-STEM. According to HAADF-STEM, a substance having a regular structure such as a crystalline substance is observed as an image having a regular pattern, and a substance having no regular structure such as an amorphous substance is observed. It is not observed as an image with a regular pattern. Therefore, when the shell is amorphous, the shell is observed as a part clearly different from the core (which has a crystal structure such as a tetragonal system as described above) observed as an image having a regular pattern. be able to.

Further, when the shell is composed of Ga—SO, the shell is observed as a darker image than the core in the image obtained by HAADF-STEM because Ga is an element lighter than Ag and In contained in the core. Tend to be.

Whether or not an amorphous shell is formed can also be confirmed by observing the semiconductor nanoparticles having the core-shell structure of the present embodiment with a high-resolution transmission electron microscope (HRTEM). In the image obtained by HRTEM, the core part is observed as a crystal lattice image (an image having a regular pattern), the shell part is not observed as a crystal lattice image, and black and white contrast is observed, but it is regular. The pattern is observed as an invisible part.

On the other hand, the shell is preferably made of a semiconductor that does not form a core and a solid solution. When the shell forms a solid solution with the core, the two become one, and the mechanism of obtaining band-end emission by covering the core with the shell and changing the surface state of the core may not be obtained.

The shell may include, but is not limited to, a combination of In and S, a combination of Ga and S, or a combination of In and Ga and S as combinations of the first and second elements. .. The combination of In and S may have a shell containing indium sulfide, and the combination of Ga and S may have a shell containing gallium sulfide, and the combination of In, Ga and S. The combination may be in the form of a shell containing indium gallium sulfide. The indium sulfide that can constitute the shell _{does not have to have a stoichiometric composition (In 2} S ₃ ), and in that sense, indium sulfide is the formula InS _x (x is any number not limited to an integer, for example 0. It may be represented by (8 or more and 1.5 or less). Similarly, gallium sulfide _{does not have to have a stoichiometric composition (Ga 2} S ₃ ), and in that sense, gallium sulfide has the formula GaS _x (x is any number not limited to an integer, for example 0.8 or more. It may be represented by (1.5 or less). Indium gallium sulfide _{may have a composition represented by In 2 (1-y)} Ga _2y S ₃ (y is any number greater than 0 and less than 1), or In _a Ga _{1-. It may be represented by a} S _b (a is any number greater than 0 and less than 1 and b is any number not limited to an integer).

The form of the oxygen element constituting the shell is not clear, but may be, for example, Ga-OS, Ga ₂ O _3, or the like.

The bandgap energy of indium sulfide is 2.0 eV or more and 2.4 eV or less, and the lattice constant of indium sulfide having a cubic crystal system is 1.0775 nm. The bandgap energy of gallium sulfide is about 2.5 eV or more and 2.6 eV or less, and the lattice constant of gallium sulfide having a tetragonal crystal system is 0.5215 nm. However, the crystal systems and the like described here are all reported values, and in the semiconductor nanoparticles having an actual core-shell structure, the shell does not necessarily include a semiconductor satisfying these reported values.

In the semiconductor nanoparticles having a core-shell structure, the thickness of the shell may be in the range of 0.1 nm or more and 50 nm or less, in the range of 0.1 nm or more and 10 nm or less, and particularly in the range of 0.3 nm or more and 3 nm or less. When the thickness of the shell is at least the above lower limit value, the effect of covering the core with the shell can be sufficiently obtained, and band-end light emission with excellent luminous efficiency can be easily obtained.

The surface of the core-shell type semiconductor nanoparticles may be modified with any compound. Compounds that modify the surface of semiconductor nanoparticles are also called surface modifiers. The surface modifier has, for example, a function of stabilizing core-shell type semiconductor nanoparticles to prevent particle aggregation or growth, a function of improving the dispersibility of core-shell type semiconductor nanoparticles in a solvent, and a function of core-shell type semiconductor nanoparticles. It has at least one function of compensating for surface defects and improving light emission efficiency.

The surface modifier is, for example, a nitrogen-containing compound having a hydrocarbon group having 4 to 20 carbon atoms, a sulfur-containing compound having a hydrocarbon group having 4 to 20 carbon atoms, and an oxygen-containing compound having a hydrocarbon group having 4 to 20 carbon atoms. It may be a compound, a phosphorus-containing compound having a hydrocarbon group having 4 to 20 carbon atoms, or the like. Examples of the hydrocarbon group having 4 to 20 carbon atoms include saturated aliphatic hydrocarbon groups such as a butyl group, an isobutyl group, a pentyl group, a hexyl group, an octyl group, an ethylhexyl group, a decyl group, a dodecyl group, a hexadecyl group and an octadecyl group; Unsaturated aliphatic hydrocarbon group such as oleyl group; alicyclic hydrocarbon group such as cyclopentyl group and cyclohexyl group; aromatic hydrocarbon group having 6 to 10 carbon atoms such as phenyl group and naphthyl group; benzyl group and naphthylmethyl Examples thereof include an arylalkyl group such as a group, of which a saturated aliphatic hydrocarbon group and an unsaturated aliphatic hydrocarbon group are preferable. Examples of the nitrogen-containing compound include amines and amides, examples of the sulfur-containing compound include thiols and the like, examples of the oxygen-containing compound include fatty acids and the like, and examples of the phosphorus-containing compound include phosphines and phosphine oxides. Kind and the like.

As the surface modifier, a nitrogen-containing compound having a hydrocarbon group having 4 to 20 carbon atoms is preferable. Examples of such nitrogen-containing compounds include alkylamines such as butylamine, isobutylamine, pentylamine, hexylamine, octylamine, ethylhexylamine, decylamine, dodecylamine, hexadecylamine and octadecylamine, and alkenylamines such as oleylamine. ..

As the surface modifier, a sulfur-containing compound having a hydrocarbon group having 4 to 20 carbon atoms is also preferable. Examples of such sulfur-containing compounds include butanethiol, isobutanethiol, pentanethiol, hexanethiol, octanethiol, ethylhexanethiol, decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol and the like.

The surface modifier may be used alone or in combination of two or more different ones. For example, one compound selected from the nitrogen-containing compounds exemplified above (for example, oleylamine) and one compound selected from the sulfur-containing compounds exemplified above (for example, dodecanethiol) may be used in combination. ..

The shell surface of the core-shell type semiconductor nanoparticles may be modified with a surface modifier containing phosphorus (P) having a negative oxidation number (hereinafter, also referred to as “specific modifier”). Since the surface modifier of the shell contains the specific modifier, the quantum efficiency in band-end emission of the semiconductor nanoparticles of the core-shell structure is further improved.

The specific modifier contains P having a negative oxidation number as a Group 15 element. The oxidation number of P becomes -1 when one hydrogen atom or hydrocarbon group is bonded to P, and becomes +1 when one oxygen atom is bonded by a single bond, and changes in the substitution state of P. For example, the oxidation number of P in trialkylphosphine and triarylphosphine is -3, and that in trialkylphosphine oxide and triarylphosphine oxide is -1.

The specific modifier may contain other Group 15 elements in addition to P having a negative oxidation number. Examples of other Group 15 elements include N, As, Sb and the like.

The specific modifier may be, for example, a phosphorus-containing compound containing a hydrocarbon group having 4 or more and 20 or less carbon atoms. The hydrocarbon group having 4 to 20 carbon atoms includes n-butyl group, isobutyl group, n-pentyl group, n-hexyl group, octyl group, ethylhexyl group, decyl group, dodecyl group, tetradecyl group, hexadecyl group and octadecyl group. Linear or branched saturated aliphatic hydrocarbon groups such as groups; Linear or branched unsaturated aliphatic hydrocarbon groups such as oleyl groups; Alicyclic hydrocarbon groups such as cyclopentyl groups and cyclohexyl groups; Aromatic hydrocarbon groups such as a phenyl group and a naphthyl group; arylalkyl groups such as a benzyl group and a naphthylmethyl group may be mentioned, and among these, a saturated aliphatic hydrocarbon group and an unsaturated aliphatic hydrocarbon group are preferable. When the specific modifier has a plurality of hydrocarbon groups, they may be the same or different.

Specifically, as the specific modifier, tributylphosphine, triisobutylphosphine, tripentylphosphine, trihexylphosphine, trioctylphosphine, tris (ethylhexyl) phosphine, tridecylphosphine, tridodecylphosphine, tritetradecylphosphine, trihexadecyl Phosphine, trioctadecylphosphine, triphenylphosphine, tributylphosphine oxide, triisobutylphosphine oxide, trypentylphosphine oxide, trihexylphosphine oxide, trioctylphosphine oxide, tris (ethylhexyl) phosphine oxide, tridecylphosphine oxide, tridodecylphosphine oxide , Tritetradecylphosphine oxide, trihexadecylphosphine oxide, trioctadecylphosphine oxide, triphenylphosphine oxide and the like, and at least one selected from the group consisting of these is preferable.

Light-emitting device The light-emitting device includes an optical conversion member and a semiconductor light-emitting element, and the optical conversion member includes the core-shell type semiconductor nanoparticles described above. According to this light emitting device, for example, a part of the light emitted from the semiconductor light emitting element is absorbed by the core-shell type semiconductor nanoparticles to emit light having a longer wavelength. Then, the light from the core-shell type semiconductor nanoparticles and the rest of the light emitted from the semiconductor light emitting element are mixed, and the mixed light can be used as the light emission of the light emitting device.

Specifically, if a semiconductor light emitting device that emits bluish purple light or blue light having a peak wavelength of about 400 nm or more and 490 nm or less is used, and a semiconductor nanoparticle that absorbs blue light and emits yellow light is used. A light emitting device that emits white light can be obtained. Alternatively, a white light emitting device can also be obtained by using two types of semiconductor nanoparticles, one that absorbs blue light and emits green light, and one that absorbs blue light and emits red light.

Alternatively, even when a semiconductor light emitting element that emits ultraviolet rays having a peak wavelength of 400 nm or less is used and three types of semiconductor nanoparticles that absorb ultraviolet rays and emit blue light, green light, and red light are used, the white light emitting device is used. Can be obtained. In this case, it is desirable that all the light from the light emitting element is absorbed by the semiconductor nanoparticles and converted so that the ultraviolet rays emitted from the light emitting element do not leak to the outside.

Alternatively, if a semiconductor light emitting device that emits bluish green light having a peak wavelength of about 490 nm or more and 510 nm or less is used, and if the semiconductor nanoparticles that absorb the above bluish green light and emit red light are used, white light is emitted. You can get the device.

Alternatively, if a semiconductor light emitting element that emits red light having a wavelength of 700 nm or more and 780 nm or less is used, and if semiconductor nanoparticles that absorb red light and emit near infrared rays are used, a light emitting device that emits near infrared rays is used. You can also get.

Core-shell semiconductor nanoparticles may be used in combination with other semiconductor quantum dots, or may be used in combination with other non-quantum dot phosphors (eg, organic or inorganic phosphors). The other semiconductor quantum dots are, for example, the dual-system semiconductor quantum dots described in the background technology section. As a phosphor that is not a quantum dot, a garnet-based phosphor such as an aluminum garnet-based phosphor can be used. Examples of the garnet phosphor include a cerium-activated yttrium-aluminum-garnet-based phosphor and a cerium-activated lutetium-aluminum-garnet-based phosphor. In addition, a nitrogen-containing calcium aluminosilicate-based phosphor activated with europium and / or chromium, a silicate-based phosphor activated with europium, a β-SiAlON-based phosphor, a nitride-based phosphor such as CASN-based or SCASN-based, Rare earth nitride-based phosphors such as _{LnSi 3} N ₁₁ _{series or LnSi AlON series, BaSi 2} O ₂ N ₂ : Eu series or Ba ₃ Si ₆ O ₁₂ N ₂ : Acid nitride based phosphors such as Eu series, CaS series, SrGa ₂ S ₄ type, SrAl2O4 based, sulfide-based phosphor of ZnS-based, etc., chloro silicate-based phosphor, SrLiAl ₃ N _4: Eu _phosphor, SrMg 3 _SiN 4: Eu phosphor, activated with manganese fluoride As a complex phosphor, K ₂ SiF ₆ : Mn phosphor or the like can be used.

In the light emitting device, the light conversion member containing the core-shell type semiconductor nanoparticles may be, for example, a sheet or a plate-shaped member, or a member having a three-dimensional shape. An example of a member having a three-dimensional shape is that in a surface mount type light emitting diode, when a semiconductor light emitting element is arranged on the bottom surface of a recess formed in a package, the recess is formed to seal the light emitting element. It is a sealing member formed by filling with a resin.

Another example of the light conversion member is a resin member formed so as to surround the upper surface and the side surface of the semiconductor light emitting device with a substantially uniform thickness when the semiconductor light emitting element is arranged on a flat substrate. is there. Alternatively, another example of the light conversion member is the case where a resin member containing a reflective material is filled around the semiconductor light emitting device so that the upper end forms the same plane as the semiconductor light emitting device. It is a resin member formed in a flat plate shape with a predetermined thickness on the upper part of the resin member including the semiconductor light emitting element and the reflective material.

The light conversion member may be in contact with the semiconductor light emitting element or may be provided away from the semiconductor light emitting element. Specifically, the light conversion member may be a pellet-shaped member, a sheet member, a plate-shaped member, or a rod-shaped member arranged apart from the semiconductor light-emitting element, or a member provided in contact with the semiconductor light-emitting element, for example. , A sealing member, a coating member (a member that covers a light emitting element provided separately from the mold member), or a mold member (including, for example, a member having a lens shape).

Further, when two or more types of core-shell type semiconductor nanoparticles exhibiting light emission of different wavelengths are used in the light emitting device, the two or more types of semiconductor nanoparticles may be mixed in one light conversion member. Alternatively, two or more optical conversion members containing only one type of quantum dot may be used in combination. In this case, the two or more types of light conversion members may form a laminated structure, or may be arranged as a dot-shaped or striped pattern on a plane.

Examples of the semiconductor light emitting element include an LED chip. The LED chip may include one or more semiconductor layers selected from the group consisting of GaN, GaAs, InGaN, AlInGaP, GaP, SiC, ZnO and the like. The semiconductor light emitting device that emits blue-violet light, blue light, or ultraviolet light is, for example, _{a GaN-based device whose composition is represented by In X} Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, X + Y <1). It is provided with a compound as a semiconductor layer.

The light emitting device is preferably incorporated in a liquid crystal display device as a light source. Since band-end emission by core-shell type semiconductor nanoparticles has a short emission lifetime, a emission device using this is suitable as a light source for a liquid crystal display device that requires a relatively fast response speed. Further, the core-shell type semiconductor nanoparticles of the present embodiment may exhibit an emission peak having a small half-value width as band-end emission. Therefore, in the light emitting device, the blue semiconductor light emitting element is used to obtain blue light having a peak wavelength in the range of 420 nm or more and 490 nm or less, and the semiconductor nanoparticles have a peak wavelength in the range of 510 nm or more and 550 nm or less, preferably 530 nm or more and 540 nm or less. The green light inside and the red light having a peak wavelength in the range of 600 nm or more and 680 nm or less, preferably 630 nm or more and 650 nm or less are obtained. Alternatively, in the light emitting device, the semiconductor light emitting element is used to obtain ultraviolet light having a peak wavelength of 400 nm or less, and the semiconductor nanoparticles have a peak wavelength of 430 nm or more and 470 nm or less, preferably 440 nm or more and 460 nm or less. It is intended to obtain green light of 510 nm or more and 550 nm or less, preferably 530 nm or more and 540 nm or less, and red light having a peak wavelength in the range of 600 nm or more and 680 nm or less, preferably 630 nm or more and 650 nm or less. As a result, a liquid crystal display device having good color reproducibility can be obtained without using a dark color filter. The light emitting device is used, for example, as a direct type backlight or an edge type backlight.

Alternatively, a sheet, plate-shaped member, or rod made of resin, glass, or the like containing core-shell type semiconductor nanoparticles may be incorporated in the liquid crystal display device as an optical conversion member independent of the light emitting device.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
Preparation of semiconductor nanoparticles (core) 0.0833 mmol of silver acetate ( _{AgOAc), 0.05 mmol of acetylacetonatoindium (In (acac) 3} )), 0.075 mmol of acetylacetonatogallium (Ga (acac) ₃ ) ) And 0.2292 mmol of sulfur powder were added to a mixed solution of ^{0.25 cm 3} of 1-dodecanethiol and 2.75 cm ^{3 of oleylamine and dispersed.} The dispersion was placed in a test tube together with a stirrer, subjected to nitrogen substitution, and then heat-treated at 300 ° C. for 10 minutes while stirring the contents in the test tube under a nitrogen atmosphere. After the heat treatment, the obtained suspension was allowed to cool, and then subjected to centrifugation (radius 146 mm, 4000 rpm, 5 minutes), and the precipitate was taken out. To this, 3 ml of methanol was added, and the mixture was centrifuged (radius 146 mm, 4000 rpm, 5 minutes) to precipitate semiconductor nanoparticles, and the supernatant was discarded. Further, 3 ml of ethanol was added thereto, and the mixture was centrifuged under the same conditions to precipitate semiconductor nanoparticles. The precipitate was taken out, dried, and then dispersed in chloroform to obtain a core dispersion as a semiconductor nanoparticle dispersion.

Preparation of core-shell type semiconductor nanoparticles The obtained semiconductor nanoparticles dispersion ^{was separated so as to contain 1 × 10-5} mmol of semiconductor nanoparticles, and dried under reduced pressure. To this, 0.16 mmol of acetylacetonatogallium (Ga (acac) ₃ ) and 0.0533 mmol of thiourea were weighed, and 3.0 mL of oleylamine (moisture value of 480 ppm) was added to replace the inside of the test tube with nitrogen. After the nitrogen substitution, the contents in the test tube were stirred in a nitrogen atmosphere, and the first stage heat treatment was performed at 150 ° C. for 10 minutes, and the second stage heat treatment was performed at 300 ° C. for 30 minutes. Allowed to cool to room temperature. The precipitate was removed by centrifugation (4000 rpm, 5 minutes). The supernatant was filtered through a membrane filter having a pore size of 0.20 μm. Methanol was added and centrifuged (4000 rpm, 5 minutes), and ethanol was added to the obtained precipitate and centrifuged (4000 rpm, 5 minutes) to obtain core-shell type semiconductor nanoparticles as a precipitate.

(Examples 2 to 4 and Comparative Example 1)
Core-shell type semiconductor nanoparticles were obtained in the same manner as in Example 1 except that the preparation composition at the time of producing the core-shell type semiconductor nanoparticles and the heating time in the second stage were changed as shown in Table 1.

(Average particle size)
The shapes of the core-shell type semiconductor nanoparticles obtained in Examples 1 to 4 and Comparative Example 1 were observed using a transmission electron microscope (TEM, manufactured by Hitachi High-Technologies Corporation, trade name H-7650), and were also observed. The average particle size was measured from a TEM image of 80,000 to 200,000 times. Here, as the TEM grid, the trade name high resolution carbon HRC-C10 STEM Cu100P grid (Oken Shoji Co., Ltd.) was used. The shape of the obtained particles was spherical or polygonal. For the average particle size, select 3 or more TEM images, and among the nanoparticles contained in these, a total of 100 or more particle sizes excluding those in which the image of the particles is cut off at the edge of the image. Was measured, and the arithmetic mean was calculated.

(Absorption / light emission characteristics)
The absorption spectrum and the emission spectrum of the core-shell type semiconductor nanoparticles obtained in Examples 1 to 4 and Comparative Example 1 were measured. The absorption spectrum was measured using a diode array spectrophotometer (manufactured by Agilent Technologies, trade name Agent 8453A) with a wavelength of 190 nm or more and 1100 nm or less. The emission spectrum was measured at an excitation wavelength of 365 nm using a multi-channel spectroscope (manufactured by Hamamatsu Photonics, trade name PMA11). The absorption spectrum is shown in FIG. 1 and the emission spectrum is shown in FIG. Emission peak wavelength (band-end emission) of steep emission peaks observed in each emission spectrum, half-value width of band-end emission, emission quantum yield of band-end emission, and Stokes shift of band-end emission (obtained from absorption spectrum) Table 2 shows the energy value of the absorption peak minus the energy value of the emission peak obtained from the emission spectrum). From Table 2, it was confirmed that the core-shell type semiconductor nanoparticles obtained in Examples 1 to 4 had a higher band-end emission quantum yield than Comparative Example 1.

(Example 5)
Preparation of core-shell type semiconductor nanoparticles The semiconductor nanoparticles dispersion obtained in Example 1 was ^{separated so as to contain 1 × 10-5} mmol of semiconductor nanoparticles, and dried under reduced pressure. To this, 0.16 mmol of acetylacetonatogallium (Ga (acac) 3) and 0.0533 mmol of thiourea were weighed, and 3.0 mL of dehydrated oleylamine (water value 50 ppm) was added to replace the inside of the test tube with nitrogen. After performing nitrogen substitution, heat treatment at 150 ° C. for 10 minutes was performed as the first stage heat treatment while stirring the contents in the test tube under a nitrogen atmosphere, and then 5.35 × ^10-5 mol of pure water was added. After the addition, the heat treatment was carried out at 300 ° C. for 30 minutes as the second step heat treatment, and then allowed to cool at room temperature for 45 minutes. The precipitate was removed by centrifugation (4000 rpm, 5 minutes). The supernatant was filtered through a membrane filter having a pore size of 0.20 μm. Methanol was added and centrifuged (4000 rpm, 5 minutes), and ethanol was added to the obtained precipitate and centrifuged (4000 rpm, 5 minutes) to obtain core-shell type semiconductor nanoparticles as a precipitate.

(Examples 6 to 9, Comparative Example 2)
A core-shell type semiconductor nanoparticle dispersion liquid was obtained in the same manner as in Example 1 except that the amount of pure water added was changed as shown in Table 3.

The average particle size and light emission characteristics of the core-shell type semiconductor nanoparticles obtained in Examples 5 to 9 and Comparative Example 2 were measured in the same manner as in Example 1. The results are shown in Table 4. Further, FIG. 3 shows an absorption spectrum and FIG. 4 shows an emission spectrum. From Table 3, it was confirmed that the core-shell type semiconductor nanoparticles obtained in Examples 5 to 9 had a higher band-end emission quantum yield than Comparative Example 2.

(Example 10)
The core-shell type semiconductor nanoparticles obtained in Example 7 were dispersed in chloroform to prepare a dispersion. Subsequently, the same amount of trioctylphosphine (TOP) as the dispersion was added and mixed, and then allowed to stand at room temperature for 24 hours to obtain a dispersion of TOP-modified core-shell type semiconductor nanoparticles. When the emission characteristics of the TOP-modified core-shell type semiconductor nanoparticles were measured in the same manner as in Example 1, the quantum yield of band-end emission was 88.8%.

The entire disclosure of Japanese Patent Application No. 2019-153625 (filed on August 26, 2019) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

Claims

A core containing a semiconductor containing M 1 , M 2 and Z, wherein M 1 is at least one element selected from the group consisting of Ag, Cu, Au and alkali metals, containing at least Ag and M. 2 is at least one element selected from the group consisting of Al, Ga, In and Tl, contains at least one of In and Ga, and Z is at least 1 selected from the group consisting of S, Se and Te. Preparing a core containing the seed element and
At least one compound containing the core, at least one selected from the group consisting of Al, Ga, In and Tl, and at least one compound containing the first element, and at least one selected from the group consisting of S, Se and Te. To obtain a mixture containing a simple substance of the second element and at least one compound containing the second element,
The mixture is heat-treated to obtain core-shell semiconductor nanoparticles.
The mixture contains the compound containing the first element and the simple substance of the second element or the compound containing the second element with respect to the total number of atoms of the first element and the total number of atoms of the second element. A method for producing core-shell type semiconductor nanoparticles, which comprises a mixing ratio in which the ratio of the total number of atoms of the first element is greater than 0.5.
The production method according to claim 1, wherein the mixture contains an added oxygen source.
The production method according to claim 1 or 2, wherein the heat treatment comprises adding an oxygen source to the mixture.
The production method according to any one of claims 1 to 3, which comprises contacting an oxygen source with the core-shell type semiconductor nanoparticles obtained by the heat treatment.
The core comprises a core and a shell disposed on the surface of the core, wherein the core comprises a semiconductor containing M 1 , M 2 and Z, and M 1 is selected from the group consisting of Ag, Cu, Au and alkali metals. At least one element, containing at least Ag, and M 2 being at least one element selected from the group consisting of Al, Ga, In and Tl, containing at least one of In and Ga. Z contains at least one element selected from the group consisting of S, Se and Te.
The core has a total M 1 content of 10 mol% or more and 30 mol% or less, a total M 2 content of 15 mol% or more and 35 mol% or less, and a total Z content of Z. 35 mol% or more and 55 mol% or less,
The shell is substantially a first element that is at least one selected from the group consisting of Al, Ga, In and Tl, and a second element that is at least one selected from the group consisting of S, Se and Te. And O element
Core-shell type semiconductor nanoparticles that emit light when irradiated with light.
A light emitting device including a light conversion member containing the core-shell type semiconductor nanoparticles according to claim 5 and a semiconductor light emitting device.
The light emitting device according to claim 6, wherein the semiconductor light emitting element is an LED chip.