JP2019085575A - Semiconductor nanoparticle and manufacturing method therefor - Google Patents

Abstract

To provide a semiconductor nanoparticle having a constitution providing a band edge light emission from ternary system or quaternary system quantum dots obtained as a low toxicity component and a manufacturing method therefor.SOLUTION: There is provided a semiconductor nanoparticle having a core and a shell covering a surface of the core, large in band gap energy and hetero jointed with the core, and emitting when light is irradiated, the core is a semiconductor containing M, Mand Z, Mis at least one kind of element selected from a group consisting of Ag, Cu and Au, Mis at least one kind of element selected from a group consisting of Al, Ga, In and Tl, Z is at least one kind of element selected from a group consisting of S, Se and Te, the shell is a semiconductor containing the XIII group elements and the XVI group elements.SELECTED DRAWING: None

Description

  The present disclosure relates to a semiconductor nanoparticle and a method of manufacturing the same, and a light emitting device using the semiconductor nanoparticle.

  As a white light emitting device used for a backlight of a liquid crystal display device, a device using light emission of a quantum dot (also called a semiconductor quantum dot) has been proposed. Semiconductor particles are known to exhibit a quantum size effect when their particle size is, for example, 10 nm or less, and such nanoparticles are called quantum dots. The quantum size effect is a phenomenon in which each band of valence band and conduction band considered to be continuous in bulk particles becomes discrete when the particle size is nanosize, and the band gap energy changes according to the particle size. Point to

  A quantum dot absorbs light and emits light corresponding to its band gap energy, and thus can be used as a wavelength conversion material in a light emitting device. A light emitting device using quantum dots is proposed, for example, in Patent Documents 1 and 2. Specifically, a part of the light emitted from the LED chip is absorbed by the quantum dots, and light of another color is emitted, and the light emitted from the quantum dots and the LED chip not absorbed by the quantum dots It has been proposed that white light be obtained by mixing with In these patent documents, it is proposed to use quantum dots of group 12-16, such as CdSe and CdTe, and group 14-16, such as PbS and PbSe. Patent Document 3 proposes a wavelength conversion film using a core-shell structured semiconductor quantum dot not containing these elements, in consideration of the toxicity of the compound containing Cd and Pb. The core shell formation is also described in Non-Patent Document 1.

JP, 2012-212862, A JP, 2010-177656, A WO 2014/129067

Chem, Commun. 2010, vol. 46, pp 2082-2084

  One of the advantages of using quantum dots in light emitting devices is that light of a wavelength corresponding to the band gap can be obtained as a relatively narrow half width peak. However, among the quantum dots proposed as a wavelength conversion substance, light of a wavelength corresponding to the band gap, that is, one whose band edge emission has been confirmed is represented by Group 12 to Group 14 such as CdSe. It is a quantum dot consisting of a binary semiconductor. However, band edge emission has not been confirmed for ternary quantum dots, in particular, quantum dots of group 11-group 13-group 16.

  The light emitted from the group 11-group 13-group 16 quantum dots has a broad emission peak because it originates from defect levels on the particle surface or inside or from donor-acceptor pair recombination. Therefore, the half width is wide and the light emission life is also long. Such light emission is not particularly suitable for light emitting devices used in liquid crystal display devices. This is because light emission with a narrow half bandwidth having peak wavelengths corresponding to three primary colors (RGB) is required for a light emitting device used for a liquid crystal display device in order to ensure high color reproducibility. Therefore, although ternary quantum dots can be made to have a low toxicity composition, their practical use has not been advanced.

  Embodiments of the present invention aim to provide a semiconductor nanoparticle and a method of manufacturing the same, which has a configuration in which band edge emission can be obtained from ternary or quaternary quantum dots that can have a low toxicity composition. Do.

An embodiment according to the present invention comprises a core, and a shell covering the surface of the core and having a band gap energy larger than that of the core and having a heterojunction with the core, and emitting light when irradiated with light. The core is a semiconductor containing M ¹ , M ² and Z, M ¹ is at least one element selected from the group consisting of Ag, Cu and Au, and M ² is Al And at least one element selected from the group consisting of Ga, In and Tl, and Z is at least one element selected from the group consisting of S, Se and Te, and the shell is substantially composed of It is a semiconductor nanoparticle which is a semiconductor which consists of a group 13 element and a group 16 element.

Furthermore, an embodiment according to the present invention is 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 and Au, and M ² is A semiconductor comprising at least one element selected from the group consisting of Al, Ga, In and Tl, and Z being at least one element selected from the group consisting of S, Se and Te; Preparing a dispersion dispersed in a solvent,
A compound containing a Group 13 element and a single substance of a Group 16 element or a compound containing a Group 16 element are added to the dispersion, and the Group 13 element and the substance are substantially added to the surface of the primary semiconductor nanoparticle. A method for producing semiconductor nanoparticles, comprising forming a layer of a semiconductor comprising a Group 16 element.

  In the semiconductor nanoparticle of the embodiment according to the present invention, the surface of the core made of a specific ternary semiconductor is made of a semiconductor containing a Group 13 element and a Group 16 element having a larger band gap energy than the semiconductor. It is characterized by being covered with a shell. This feature makes it possible to obtain emission with a short emission lifetime, that is, band edge emission, which has not been conventionally obtained with the ternary quantum dots. This semiconductor nanoparticle can be made to have a composition that does not contain Cd and Pb that are considered to be highly toxic, and is also applicable to products for which the use of Cd or the like is prohibited. It is. Therefore, this semiconductor nanoparticle can be suitably used as a wavelength conversion material of a light emitting device used for a liquid crystal display etc., and as a biomolecule marker. Furthermore, according to the above-described method for producing semiconductor nanoparticles, it is possible to relatively easily produce ternary semiconductor nanoparticles giving band edge emission.

It is a XRD pattern of the primary semiconductor nanoparticle (core) produced in Example 1. It is the emission spectrum of the semiconductor nanoparticle of the core-shell structure produced in Example 1. FIG. It is an absorption and excitation spectrum of the semiconductor nanoparticle of the core-shell structure produced in Example 1. FIG. It is an emission spectrum of the primary semiconductor nanoparticle (core) produced in Example 1. It is an absorption spectrum of the primary semiconductor nanoparticle (core) produced in Example 1. FIG. 7 is an emission spectrum of the core-shell structured semiconductor nanoparticle produced in Example 2. FIG. FIG. 7 is an absorption and excitation spectrum of the core-shell structured semiconductor nanoparticle produced in Example 2. FIG. FIG. 7 shows an emission spectrum of the core-shell structured semiconductor nanoparticle produced in Example 3. FIG. FIG. 16 is an absorption and excitation spectrum of the core-shell structured semiconductor nanoparticle produced in Example 3. FIG. It is the emission spectrum of the semiconductor nanoparticle produced by the comparative example 1. FIG. It is an absorption spectrum of the semiconductor nanoparticle produced by the comparative example 1. FIG. It is an emission spectrum of the semiconductor nanoparticle produced by Example 4A-4D. It is an emission spectrum of the semiconductor nanoparticle produced by Example 5A-5F. It is a graph which shows the relation between the peak intensity of band edge luminescence of semiconductor nanoparticles produced in Examples 4A to 4D and Examples 5A to 5F and the retention time. It is a graph which shows the relationship between the peak wavelength of band edge emission of the semiconductor nanoparticle produced by Example 4A-4D and Example 5A-5F, and retention time. It is a HRTEM image of the semiconductor nanoparticle produced by Example 5F. It is an HAADF image of the semiconductor nanoparticle produced by Example 5F. FIG. 16 is an emission spectrum of the core-shell structured semiconductor nanoparticle produced in Example 6. FIG. 7 is an absorption spectrum of the core-shell structured semiconductor nanoparticle produced in Example 6. FIG.

  Hereinafter, embodiments will be described in detail. However, the present invention is not limited to the mode shown below. Further, the matters described in each of the embodiments and the modifications thereof can be applied to the other embodiments and modifications unless otherwise noted.

(Outline of this embodiment)
The present inventors have found that there is band-edge emission for ternary quantum dots, in particular, for group 11-group 13-group 16 quantum dots, which are manufactured by a general manufacturing method. Since it has not been confirmed, the configuration for obtaining band edge emission from this quantum dot was examined. In the process of the study, the inventors examined the possibility that band edge emission can be obtained by changing the state of the surface of the ternary to quaternary quantum dots, and in particular, It was studied to change the surface condition by coating the surface with an appropriate semiconductor. As a result, it has been found that band edge light emission can be obtained from the quantum dots by covering a ternary or quaternary quantum dot with a semiconductor containing a Group 13 element and a sixteenth element, and this embodiment It came to
In addition, about CdSe in which band end light emission is confirmed, in order to make the band end light emission stronger, the structure which coat | covers the surface with CdS etc. is already proposed. In addition, a configuration in which the surface of a ternary quantum dot is coated with ZnS or ZnSe is also proposed. However, by using ternary or quaternary quantum dots as cores whose band edge emission does not occur or band edge emission is hardly observed in the emission spectrum, the surface of the core is covered with a shell made of a specific semiconductor. There has been no report so far that band edge emission can be obtained.

The semiconductor nanoparticle of this embodiment is 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 and Au, and M ² is The surface of a core comprising a semiconductor comprising at least one element selected from the group consisting of Al, Ga, In and Tl, and Z being at least one element selected from the group consisting of S, Se and Te A semiconductor comprising a Group 13 element and a Group 16 element is covered by a shell having a band gap energy larger than that of the core, and the shell is in a heterojunction with the core. In the following, first, the core (ternary system and quaternary system) and the shell will be described.

[core]
(Ternary core)
The core consisting of a ternary semiconductor is a semiconductor nanoparticle because it consists of a semiconductor containing M ¹ , M ² and Z and is itself in the form of particles.
Here, M ¹ is at least one element selected from the group consisting of Ag, Cu and Au, preferably Ag or Cu, and particularly preferably Ag. When M ¹ is Ag, synthesis of the core (corresponding to primary semiconductor nanoparticles used in the production method described later) is facilitated. Two or more elements may be contained as M ¹ .
The crystal structure of the core may be at least one selected from the group consisting of tetragonal, hexagonal and orthorhombic.

M ² is at least one element selected from the group consisting of Al, Ga, In and Tl, preferably In or Ga, and particularly preferably In. In is preferable because it hardly generates a by-product. Two or more elements may be contained as M ² .

  Z is at least one element selected from the group consisting of S, Se and Te, preferably S. The core in which Z is S has a wider band gap as compared with the core in which Z is Se or Te, and thus it is preferable because light emission in the visible light region is easily given. Two or more elements may be contained as Z.

The combination of M ¹ , M ² and Z is not particularly limited. The combination of M ¹ , M ² and Z (M ¹ / M ² / Z) is preferably Cu / In / S, Ag / In / S, Ag / In / Se, and Ag / Ga / S.

A semiconductor that contains the above specific element and whose crystal structure is tetragonal, hexagonal, or orthorhombic is generally represented by the composition formula of M ¹ M ² Z ₂ , the literature, etc. It is introduced in A semiconductor represented by the composition formula of M ¹ M ² Z ₂ which has a hexagonal crystal structure is a wurtzite type, and a semiconductor having a tetragonal crystal structure is a chalcopyrite type. The crystal structure is identified, for example, by measuring the XRD pattern obtained by X-ray diffraction (XRD). Specifically, an XRD pattern obtained by simulating an XRD pattern obtained from the core, which is known as that of a semiconductor nanoparticle represented by the composition of M ¹ M ² Z ₂ , or a crystal structure parameter Compare with. If the known pattern and the simulated pattern match the core pattern, the crystalline structure of the semiconductor nanoparticle can be said to be the crystalline structure of the matched known or simulated pattern.
In the aggregate of semiconductor nanoparticles, plural types of semiconductor nanoparticles having different core crystal structures may be mixed. In that case, peaks derived from a plurality of crystal structures are observed in the XRD pattern.

However, a core composed of a ternary semiconductor is not actually of the stoichiometric composition represented by the above general formula, and in particular, the ratio of the number of atoms of M ^{1 to} the number of atoms of M ² (M ¹ / M ² ) is smaller than one. Also, the sum of the number of atoms of M ^{1 and} the number of atoms of M ² may not be the same as the number of atoms of Z. In the semiconductor nanoparticle of the present embodiment, the core made of a ternary semiconductor may be made of such a non-stoichiometric semiconductor. In the present specification, for a semiconductor containing a specific element, “-” is used to connect constituent elements as in the case of M ¹ -M ² -Z, regardless of whether it is the stoichiometric composition or not. The semiconductor composition is represented by the equation.

The core may consist essentially of only M ¹ , M ² and Z. Here, the term "substantially" is used in consideration of unavoidable inclusion of elements other than M ¹ , M ² and Z due to the mixing of impurities and the like.

Alternatively, the core may contain other elements. For example, part of M ² may be substituted by another metal element. The other metal element may be a +3 metal ion, specifically, Cr, Fe, Al, Y, Sc, La, V, Mn, Co, Ni, Ga, In, Rh, Ru , One or more elements selected from Mo, Nb, W, Bi, As and Sb. The amount of substitution is preferably 10% or less, where the number of atoms combining M ² and a substitution element is 100%.

(Quaternary core)
The core composed of a quaternary semiconductor is composed of a semiconductor containing M ¹ , M ² , M ³ and Z, and is itself a semiconductor nanoparticle like the core composed of a ternary semiconductor. The crystal structure of the core made of a quaternary semiconductor may be at least one selected from the group consisting of tetragonal, hexagonal and orthorhombic. In an assembly of nanoparticles, plural types of nanoparticles having different core crystal structures may be mixed. In that case, peaks derived from a plurality of crystal structures are observed in the XRD pattern.
Since M ¹ , M ² and Z are as described in relation to the ternary core, their description is omitted here.
M ³ is at least one element selected from the group consisting of Zn and Cd. M ³ is preferably Zn. If M ³ is Zn, the semiconductor nanoparticles of the present embodiment can be provided as having a low toxicity composition. In addition, even when Cd is employed, the amount of Cd can be reduced as compared to a binary core using Cd, and therefore, it can be provided as a composition having a low toxicity.

The combination of M ¹ , M ² , M ³ and Z (M ¹ / M ² / M ³ / Z) is not particularly limited. The combination of M ¹ , M ² , M ³ and Z (M ¹ / M ² / M ³ / Z) is preferably Cu / In / Zn / S, Ag / In / Zn / S.

In general, a semiconductor that contains the above four specific elements and whose crystal structure is tetragonal, hexagonal, or orthorhombic is (M ¹ M ² ) _x M ³ _y Z ₂ (wherein , X + y = 2) are introduced in the literature and the like. That is, the semiconductor represented by this composition formula is ^one in which M ³ is doped in the semiconductor represented by the composition formula of M ¹ M ² Z ₂ described in relation to the core composed of the ternary semiconductor, or It can be said that M ¹ M ² Z ₂ and M ³ Z form a solid solution.

Even when made of a semiconductor of a four-component, in fact, the core and not of the stoichiometric composition represented by the above general formula, in particular the ratio of the number of atoms atoms pairs M ² of M ¹ (M ¹ / M ² ) is smaller than one. Also, x + y may not be 2. In the semiconductor nanoparticle of the present embodiment, the core made of quaternary semiconductor may be made of such a non-stoichiometric semiconductor. Therefore, in the present specification, even in the case of a quaternary semiconductor, it does not matter whether it has a stoichiometric composition or not, as in the case of M ¹ -M ² -M ³ -Z, the constituent elements The semiconductor composition may be expressed by a formula connected by "-".
The method of identifying the crystal structure of the quaternary semiconductor is as described in relation to the core made of the ternary semiconductor.

The core consisting of a quaternary semiconductor substantially consists only of M ¹ , M ² , M ³ and Z. Here, the term "substantially" is used in consideration of unavoidable inclusion of elements other than M ¹ , M ² _, M ³ and Z due to the contamination of impurities and the like. Alternatively, the core made of quaternary semiconductor may contain other elements.

For example, part of M ² may be substituted by another metal element. Examples of the other metal elements and their substitution amounts are as described in relation to the ternary core, and thus the description thereof is omitted here.

In addition / or a part of M ³ may be replaced by another metal element. The other metal element may be a +2 metal ion, and specifically, Co, Ni, Pd, Sr, Ba, Fe, Cr, Mn, Cu, Cd, Rh, W, Ru, Pb And at least one element selected from Sn, Mg and Ca. The amount of substitution is preferably 10% or less, where the number of atoms combining M ³ and a substitution element is 100%.

[shell]
In the present embodiment, the shell is a semiconductor having a band gap energy larger than that of the semiconductor constituting the core, and is a semiconductor substantially composed of a Group 13 element and a Group 16 element. The Group 13 elements include B, Al, Ga, In, and Tl, and the Group 16 elements include O, S, Se, Te, and Po. 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. Specifically, “substantially” means that the ratio of elements other than the Group 13 element and the Group 16 element is, for example, 5 when the total number of atoms of all the elements contained in the shell is 100%. It shows that it is less than%.

  Although the band gap energy of the semiconductor constituting the core depends on the composition thereof, a group 11-group 13-group 16 ternary semiconductor or a quaternary semiconductor based on this is generally one. A semiconductor having a band gap energy of 0 eV to 3.5 eV, in particular consisting of Ag-In-S, has a band gap energy of 1.8 eV to 1.9 eV and is a semiconductor consisting of Ag-In-Zn-S Have a band gap energy of 1.8 eV to 3.9 eV. Therefore, the shell may be configured by selecting the composition and the like according to the band gap energy of the semiconductor that constitutes the core. Alternatively, the core may be designed such that the band gap energy of the semiconductor constituting the core is smaller than that of the shell, if the composition of the shell and the like are previously determined.

  Specifically, the shell may have a band gap energy of, for example, 2.0 eV to 5.0 eV, in particular 2.5 eV to 5.0 eV. In addition, the band gap energy of the shell is larger than that of the core by, for example, about 0.1 eV to 3.0 eV, particularly about 0.3 eV to 3.0 eV, and more particularly about 0.5 eV to 1.0 eV It may be. When the difference between the band gap energy of the shell and the band gap energy of the core is small, the ratio of light emission other than the band edge light emission may increase in the light emission from the core, and the band edge light emission ratio may be small.

  Furthermore, the band gap energies of the core and shell are preferably selected such that at the core-shell heterojunction, the band gap energy of the shell provides a type-I band alignment that sandwiches the band gap energy of the core. By forming the type-I band alignment, band edge emission from the core can be better obtained. In type-I alignment, a barrier of at least 0.1 eV is preferably formed between the band gap of the core and the band gap of the shell, in particular 0.2 eV or more, more particularly 0.3 eV or more A barrier may be formed. The upper limit of the barrier is, for example, 1.8 eV, in particular 1.1 eV. When the barrier is small, in the light emission from the core, the ratio of light emission other than the band edge light emission may be increased, and the ratio of the band edge light emission may be decreased.

  In the present embodiment, the shell may contain In or Ga as a Group 13 element. In addition, in the present embodiment, the shell may contain S as a Group 16 element. A semiconductor containing In or Ga or containing S tends to be a semiconductor having a band gap energy larger than that of a group 11-group 13-group 16 ternary semiconductor.

The shell may also be one in which the crystal system of the semiconductor conforms to that of the semiconductor of the core, and the lattice constant may be the same as or similar to that of the semiconductor of the core. A shell made of a semiconductor which is familiar with the crystal system and whose lattice constant is close (here, the lattice constant of the shell is close to the lattice constant of the core is close to that of the core) has good core circumference. May cover. For example, Ag-In-S which is a ternary semiconductor of Group 11-Group 13-Group 16 is generally a tetragonal system, but as a crystal system familiar to this, a tetragonal system, An orthorhombic system is mentioned. When the Ag-In-S semiconductor is tetragonal, its lattice constant is 5.828 Å, 5.828 Å, 11.19 Å, and the shell covering it is tetragonal or cubic. Preferably, the lattice constant or a multiple thereof is close to the lattice constant of the Ag-In-S semiconductor.
Alternatively, the shell may be amorphous (amorphous).

  Whether or not an amorphous (amorphous) shell is formed can be confirmed by observing the semiconductor nanoparticles of the core-shell structure of the present embodiment by HAADF-STEM. Specifically, a part having a regular pattern (for example, a stripe pattern or a dot pattern) is observed in the center, and a part not observed as having a regular pattern around it is observed in HAADF-STEM. Be done. According to HAADF-STEM, those having a regular structure such as crystalline material are observed as an image having a regular pattern, and those having no regular structure such as an amorphous material are: It is not observed as an image having a regular pattern. Therefore, when the shell is amorphous, the shell is observed as a distinctly different part from the core (having a crystal structure such as tetragonal system as described above) observed as an image having a regular pattern be able to.

  Also, when the core is made of Ag-In-S and the shell is made of GaS, the shell is darker than the core in the image obtained by HAADF-STEM because Ga is an element lighter than Ag and In. It tends to be observed.

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

  On the other hand, it is preferable that the shell does not constitute a solid solution with the core. When the shell forms a solid solution with the core, both become integral and the mechanism of the present embodiment of covering the core with the shell and changing the surface state of the core to obtain band edge emission can not be obtained. For example, it is confirmed that band edge emission can not be obtained from the core even if the surface of the core made of Ag-In-S is covered with zinc sulfide (Zn-S) of the stoichiometric composition or non-stoichiometric composition. ing. Zn-S satisfies the above condition in terms of the band gap energy in relation to Ag-In-S, and gives a type-1 band alignment. Nevertheless, it is inferred that the band edge emission could not be obtained from the particular semiconductor because the particular semiconductor and ZnS form a solid solution and the core-shell interface disappears.

The shell may include, but is limited to, a combination of In and S, a combination of Ga and S, or a combination of In, Ga and S as a combination of Group 13 elements and Group 16 elements. is not. The combination of In and S may be in the form of indium sulfide, the combination of Ga and S may be in the form of gallium sulfide, and the combination of In, Ga and S is indium gallium sulfide Good. The indium sulfide constituting the shell in this embodiment may not be of the stoichiometric composition (In ₂ S ₃ ), and in that sense, in the present specification, the indium sulfide is limited to the formula InS _x (x is an integer) May be represented by any arbitrary number, for example, 0.8 to 1.5). Similarly, gallium sulfide may not be of stoichiometric composition (Ga ₂ S ₃ ), in which sense gallium sulfide may be represented herein by the formula GaS _x (where x is not limited to any integer, for example It may be represented by 0.8 to 1.5). The indium gallium sulfide may have a composition represented by In _{2 (1-y)} Ga 2 _y S ₃ (where y is any number greater than 0 and less than 1), or In _a Ga _{1- a} S _b (a is any number greater than 0 and less than 1 and b is any number not limited to an integer) may be represented.

Indium sulfide has a band gap energy of 2.0 eV to 2.4 eV, and in the case where the crystal system is cubic, its lattice constant is 10.775 Å. Gallium sulfide has a band gap energy of about 2.5 eV to 2.6 eV, and a lattice constant of 5.215 Å for a crystal system having a tetragonal system. However, the crystal systems etc. described herein are all report values, and the shell does not necessarily satisfy these report values in the actual semiconductor nanoparticles of core-shell structure.
Indium sulfide and gallium sulfide can be selected from the group 11-group 13-group 16 ternary or quaternary semiconductors, in particular when Ag-In-S or Ag-In-Zn-S is the core. It is preferably used as a semiconductor constituting a shell. In particular, gallium sulfide is preferably used because of its large band gap energy. When using gallium sulfide, stronger band edge emission can be obtained as compared to using indium sulfide.

  The shell may have its surface modified with any compound. When the surface of the shell is an exposed surface of the core-shell structured semiconductor nanoparticle, by modifying the surface, the nanoparticle can be stabilized to prevent aggregation or growth of the semiconductor nanoparticle, and / Alternatively, the dispersibility of the semiconductor nanoparticles in the solvent can be improved.

  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 or the like. As a C4-C20 hydrocarbon group, saturated aliphatic carbonization, such as n-butyl group, isobutyl group, n-pentyl group, n-hexyl group, octyl group, decyl group, dodecyl group, hexadecyl group, octadecyl group, etc. Hydrogen group; unsaturated aliphatic hydrocarbon group such as oleyl group; alicyclic hydrocarbon group such as cyclopentyl group and cyclohexyl group; aromatic hydrocarbon group such as phenyl group, benzyl group, naphthyl group and naphthylmethyl group etc. Among these, saturated aliphatic hydrocarbon groups and unsaturated aliphatic hydrocarbon groups are preferable. The nitrogen-containing compounds include amines and amides, the sulfur-containing compounds include thiols, and the oxygen-containing compounds include fatty acids.

  As a surface modifier, the nitrogen-containing compound which has a C4-C20 hydrocarbon group is preferable. Such nitrogen-containing compounds are, for example, alkylamines such as n-butylamine, isobutylamine, n-pentylamine, n-hexylamine, octylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, and alkenyls such as oleylamine It is an amine. In particular, n-tetradecylamine is preferred from the viewpoint that it is easy to obtain high purity and that the boiling point exceeds 290 ° C.

  The surface modifier is also preferably a sulfur-containing compound having a hydrocarbon group having 4 to 20 carbon atoms. Such sulfur-containing compounds are, for example, n-butanethiol, isobutanethiol, n-pentanethiol, n-hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol and the like.

  The surface modifier may be used 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. .

[Core shell structure]
The configuration of the core-shell structured semiconductor nanoparticle of the present embodiment, which comprises the core and the shell described above, will be described below.

  The semiconductor nanoparticles of the core-shell structure of the present embodiment may have, for example, an average particle size of 50 nm or less. The average particle size may be in the range of 1 nm to 20 nm, in particular in the range of 1 nm to 10 nm.

  The average particle size of the nanoparticles may be determined, for example, from a TEM image taken using a transmission electron microscope (TEM). Specifically, the particle diameter of the nanoparticles is a line segment connecting any two points on the outer periphery of the particle observed in the TEM image, and the longest one of the line segments passing through the center of the particle Point to.

  However, when the particles have a rod-like shape, the length of the short axis is regarded as the particle size. Here, rod-shaped particles are observed as quadrilateral including a rectangular shape (the cross section has a circle, an ellipse, or a polygonal shape), an elliptical shape, or a polygonal shape (for example, a shape like a pencil) Refers to those in which the ratio of the major axis length to the minor axis length is greater than 1.2. For rod-shaped particles, in the case of an elliptical shape, the long axis length refers to the longest line segment connecting any two points on the outer periphery of the particle, and in the case of a rectangular or polygonal shape And the longest one of the line segments parallel to the longest side among the sides defining the outer periphery and connecting any two points on the outer periphery of the particle. The length of the short axis refers to the longest line segment that is orthogonal to the line segment defining the length of the long axis among the line segments connecting any two points on the outer periphery.

  As for the average particle size, TEM images at 50,000 to 150,000 times are acquired at three or more locations on an arbitrarily selected grid, and in each of the acquired TEM images, the particle sizes of all measurable nanoparticles are measured, Let it be the arithmetic mean of their particle sizes. Here, "measurable" particles are those in which the entire particle can be observed in the TEM image. Therefore, in the TEM image, a part of the particle is not included in the imaging range, and particles that are “broken” are not measurable. The number of TEM images is 3 or more, and the total number of nanoparticles contained in the selected TEM image is 100 or more. Therefore, for example, although it appears that three TEM images contain 100 or more nanoparticles, in reality the number of nanoparticles does not reach 100, it is necessary to increase the number of imaging points. Alternatively, even if two TEM images contain 100 or more nanoparticles, the measurement of the average particle diameter of the nanoparticles is performed using three or more TEM images.

  In core-shell structured semiconductor nanoparticles, the core may have an average particle size of, for example, 10 nm or less, in particular 8 nm or less. The average particle size of the core may be in the range of 2 nm to 10 nm, in particular in the range of 2 nm to 8 nm, more particularly in the range of 2 nm to 6 nm, or in the range of 4 nm to 10 nm, 5 nm to 8 nm. When the average particle size of the core is too large, it is difficult to obtain the quantum size effect and it is difficult to obtain band edge emission.

  The shell may have a thickness of 0.1 nm or more. The thickness of the shell may be in the range of 0.1 nm to 50 nm, in particular in the range of 0.1 nm to 20 nm, more in particular in the range of 0.2 nm to 10 nm. Alternatively, the thickness of the shell may be in the range of 0.1 nm to 3 nm, in particular in the range of 0.3 nm to 3 nm. If the thickness of the shell is too small, the effect of covering the core by the shell is not sufficiently obtained, and band edge emission becomes difficult to obtain.

  The average particle size of the core and the thickness of the shell may be determined by observing semiconductor nanoparticles of the core-shell structure, for example, by HAADF-STEM. In particular, when the shell is amorphous, HAADF-STEM can easily determine the thickness of the shell that is likely to be observed as a part different from the core. In that case, the particle size of the core can be determined according to the method described above for the semiconductor nanoparticles. If the thickness of the shell is not constant, the smallest thickness is taken as the thickness of the shell in the particle.

  Alternatively, the average particle size of the core may be pre-measured prior to coating with the shell. Then, the average particle size of the core-shell structure semiconductor nanoparticles may be measured, and the difference between the average particle size and the average particle size of the core measured in advance may be determined to determine the thickness of the shell.

  The semiconductor nanoparticles of this embodiment emit light when irradiated with light, and specifically, when irradiated with ultraviolet light, visible light or infrared light, light having a wavelength longer than the irradiated light Emit The emission of the semiconductor nanoparticles of the present embodiment may be fluorescence or may contain fluorescence. In that case, the semiconductor nanoparticle of the present embodiment can function as a fluorescent substance that emits fluorescence. In addition, the semiconductor nanoparticle of the present embodiment is not covered with a band edge emission when it is not covered with a shell due to the fact that the core is covered with a shell containing an element of a specific group. Band edge emission can be provided. Specifically, for example, when irradiated with ultraviolet light, visible light, or infrared light, the semiconductor nanoparticle of the present embodiment has light emission of a wavelength longer than that of the irradiated light, and the light emission of the main component It is possible to emit light with a lifetime of 200 ns or less and / or a half width of the emission spectrum of 50 nm or less. Here, the "emission life" refers to the life of emission measured using a device called a fluorescence lifetime measurement device as in the examples described later.

The “emission lifetime of the main component” is determined according to the following procedure. First, semiconductor nanoparticles are irradiated with excitation light to emit light, and the decay (afterglow) of light having a wavelength in the vicinity of the peak of the emission spectrum, for example, in the range of (peak wavelength ± 50 nm) Measure the change. The change over time is measured from the time when the irradiation of the excitation light is stopped. The obtained attenuation curve is generally a sum of a plurality of attenuation curves derived from relaxation processes such as light emission and heat. Therefore, in the present embodiment, assuming that the light emission intensity is I (t), assuming that three components (that is, three attenuation curves) are included, the parameter is set so that the attenuation curve can be expressed by the following equation. Do the fitting. Parameter fitting is performed using dedicated software.
_{I (t) = A 1 exp} (-t / τ 1) + A 2 exp (-t / τ 2) + A 3 exp (-t / τ 3)

In the above equation, τ ₁ , τ ₂ and τ ₃ of each component are the time required for the emission intensity to decay to 1 / e (36.8%) of the initial level, which corresponds to the emission lifetime of each component Do. Let τ ₁ , τ ₂ , and τ ₃ be in ascending order of light emission lifetime. Also, A ₁ , A ₂ and A ₃ are contribution rates of the respective components. In the present embodiment, the emission lifetime τ of the main component is 200 ns or less, when the main component is the one with the largest integral value of the curve represented by A _x exp (−t / τ _x ). Such emission is assumed to be band edge emission. In addition, when identifying the principal component, A _x × τ _x obtained by integrating the value of t of A _x exp (−t / τ _x ) from 0 to infinity is compared, and this value is the largest. As the main component.

  In the present embodiment, assuming that the attenuation curve of light emission includes three, four, or five components, the attenuation curve drawn by the equation obtained by performing parameter fitting and the actual attenuation curve The difference is not so different. Therefore, in the present embodiment, the number of components included in the light emission decay curve is assumed to be three in order to obtain the light emission lifetime of the main component, thereby avoiding complication of parameter fitting.

  Band edge emission may be obtained with defect emission. Defective light emission generally has a long light emission lifetime and a broad spectrum, and has its peak on the longer wavelength side than the band edge light emission. Alternatively, the semiconductor nanoparticles of the present embodiment may emit only defect light and may not emit band edge light. Even in such semiconductor nanoparticles, the core is covered with the shell, so that electrical defects on the surface are eliminated, so that the material performs charge separation for the purpose of photoelectric conversion and suppresses recombination ( In particular, the constituent material of the solar cell is more suitable and useful.

  In the band edge light emission in which the semiconductor nanoparticles of the present embodiment emit light, the intensity and the position of the peak can be changed by changing the particle size of the semiconductor nanoparticles. For example, if the particle size of the semiconductor nanoparticles is made smaller, the intensity of the band edge emission (the ratio of the band edge emission / defect emission intensity) can be made larger. In addition, when the particle size of the semiconductor nanoparticles is further reduced, the peak wavelength of band edge emission tends to shift to the short wavelength side. Furthermore, the smaller the particle size of the semiconductor nanoparticles, the smaller the half bandwidth of the spectrum of band edge emission tends to be.

  In addition, it is preferable that the semiconductor nanoparticle of the present embodiment is one whose absorption spectrum or excitation spectrum (also referred to as fluorescence excitation spectrum) exhibits an exciton peak. The exciton peak is a peak obtained by exciton generation, and the fact that this is expressed in the absorption spectrum or excitation spectrum means that the particle is suitable for band edge emission with small particle size distribution and few crystal defects. Means The sharper the exciton peak, the more the particles with less particle size having crystal defects are included in the aggregate of semiconductor nanoparticles, and hence the half width of light emission becomes narrower and the light emission efficiency is improved. is expected. In the absorption spectrum or excitation spectrum of the semiconductor nanoparticle of the present embodiment, an exciton peak is observed, for example, in the range of 350 nm to 1000 nm. The excitation spectrum for observing the presence or absence of an exciton peak may be measured by setting the observation wavelength near the peak wavelength.

[Method for producing core-shell structured semiconductor nanoparticles]
The semiconductor nanoparticle of the core-shell structure of the present embodiment is
-Preparing a dispersion in which a core semiconductor nanoparticle (herein, the core before being coated with a shell is conveniently referred to as a "primary semiconductor nanoparticle") is dispersed in a solvent; A dispersion containing a compound containing the same element as a source of the Group 13 element and a compound containing the same element or the same element as a source of the Group 16 element, to form a primary semiconductor nano Forming a semiconductor layer substantially consisting of a Group 13 element and a Group 16 element on the surface of the particle.

(Preparation of primary semiconductor nanoparticles)
The primary semiconductor nanoparticles correspond to the above core, and in the case of a ternary system, they are nanoparticles consisting of a semiconductor containing M ¹ , M ² and Z, and in the case of a quaternary system. Is a nanoparticle consisting of a semiconductor containing M ¹ , M ² , M ³ and Z. As the primary semiconductor nanoparticles, commercially available ones may be used as they are, or those experimentally produced may be used, or M ¹ source, M ² source, and Z source, and optionally, may be used. It may be produced by reacting an M ³ source. In the manufacturing method of the present embodiment, it is not necessary to immediately carry out coating with a shell after producing the primary semiconductor nanoparticles, and separately produced primary semiconductor nanoparticles may be used with time.

Ternary primary semiconductor nanoparticles are converted to a complex, for example, by mixing a salt of element M ^1, a salt of element M ² and a ligand having element Z as a coordination element, and heat treating this complex May be produced by a method including The type of M ¹ salt and M ² salt is not particularly limited, and may be either an organic acid salt or an inorganic acid salt. Specifically, the salt may be any of a nitrate, an acetate, a sulfate, a hydrochloride, and a sulfonate, preferably an organic acid such as an acetate. The organic acid salt has high solubility in an organic solvent, and the reaction can be more uniformly progressed.

  When Z is sulfur (S), examples of the ligand having Z as a coordination element include β-dithiones such as 2,4-pentanedithione; 1,2-bis (trifluoromethyl) ethylene- Dithiols such as 1,2-dithiol; diethyl dithiocarbamate; thiourea.

  When Z is tellurium (Te), a ligand having Z as a coordination element is, for example, diallyl telluride or dimethyl ditelluride. When Z is selenium (Se), examples of a ligand having Z as a coordination element include dimethyl diselenocarbamic acid and 2- (dimethylamino) ethaneselenol.

The complex is obtained by mixing a salt of M ^1, a salt of M ² , and a ligand having Z as a coordination element. The formation of the complex may be carried out by mixing the aqueous solution of the salt of M ^{1 and} the salt of M ² with the aqueous solution of the ligand, or alternatively, the salt of M ¹ , the salt of M ² and the ligand It may be carried out by a method of charging by mixing in an organic solvent (in particular, a highly polar organic solvent such as ethanol). The organic solvent may be a surface modifier, or a solution comprising a surface modifier. The preparation ratio of the salt of M ^1, the salt of M ² and the ligand having Z as a coordination element is 1: 1: 2 (molar ratio) corresponding to the composition formula of M ¹ M ² Z ₂ Is preferred.

The resulting complex is then heat treated to form primary semiconductor nanoparticles. The heat treatment of the complex may be carried out by precipitating and separating the obtained complex, drying it to a powder, and heating the powder at a temperature of 100 ° C. to 300 ° C., for example. In this case, the primary semiconductor nanoparticles obtained by heat treatment are preferably heat-treated in a solvent which is a surface modifier or a solvent containing a surface modifier to further modify the surface thereof. Alternatively, the heat treatment of the complex may be carried out by heating the complex obtained as a powder, for example, at a temperature of 100 ° C. to 300 ° C. in a solvent that is a surface modifier, or a solvent that includes a surface modifier. Alternatively, in the case of forming a complex by a method in which the salt of M ^1, the salt of M ² and the ligand are introduced into an organic solvent and mixed, a solvent containing a surface modifier or a surface modifier is used. The formation of the complex, the heat treatment and the surface modification may be carried out sequentially or simultaneously by carrying out heat treatment after introducing the salt and the ligand.

Alternatively, the primary semiconductor nanoparticles may be formed by introducing a salt of M ^1, a salt of M ² , and a compound serving as a source of Z into an organic solvent. Alternatively, the organic solvent is reacted with a salt of M ¹ to form a complex, and then the organic solvent is reacted with a salt of M ² to form a complex, and these complex and a source of Z The reaction product may be produced by a method of causing crystal growth of the obtained reactant. The salt of M ^{1 and} the salt of M ² are as described in relation to the preparation method including the formation of the above complex. The organic solvent which reacts with these salts to form a complex is, for example, an alkylamine having 4 to 20 carbon atoms, an alkenylamine, an alkylthiol, an alkenylamine, an alkyl phosphine or an alkenyl phosphine. These organic solvents eventually become surface modifications of the resulting primary semiconductor nanoparticles. These organic solvents may be used in combination with other organic solvents. Also in this production method, the preparation ratio of the salt of M ¹ , the salt of M ² and the compound serving as the source of Z is 1: 1: 2 (molar ratio corresponding to the composition formula of M ¹ M ² Z ₂ It is preferable to set it as

  The compound serving as a source of Z is, for example, sulfur, thiourea, thioacetamide, alkylthiol when Z is sulfur (S). When Z is tellurium (Te), for example, a Te-phosphine complex obtained by heat-treating a mixture obtained by adding a Te powder to trialkylphosphine at 200 to 250 ° C. is used as a compound serving as a Z source. It may be used. When Z is selenium (Se), for example, a Se-phosphine complex obtained by heat-treating a mixture obtained by adding Se powder to trialkylphosphine at 200 to 250 ° C. is used as a compound serving as a Z source. It may be used.

Alternatively, the method of producing the primary semiconductor nanoparticles may be a so-called hot injection method. In the hot injection method, a compound (for example, a salt of M ^1, a salt of M ² , etc.) serving as a supply source of each element constituting the primary semiconductor nanoparticles in a solvent heated to a temperature in the range of 100 ° C. to 300 ° C. A liquid (also referred to as a precursor solution) in which a compound serving as a source of H and Z (or a ligand having a coordination element of Z) dissolved or dispersed therein is introduced in a relatively short time (for example, on the order of milliseconds) Thus, it is a method of producing semiconductor nanoparticles in which many crystal nuclei are generated in the initial stage of reaction. Alternatively, in the hot injection method, a compound serving as a source of a part of elements may be dissolved or dispersed in an organic solvent in advance, and this may be heated, and then precursor solutions of other elements may be added. . If the solvent is a surface modifier or a solvent containing a surface modifier, surface modification can be performed simultaneously. According to the hot injection method, nanoparticles having a smaller particle size can be produced.

  The surface modifiers that modify the surface of the primary semiconductor nanoparticles are as described above in relation to the shell. The surface modification of the primary semiconductor nanoparticles stabilizes the particles and prevents their aggregation or growth, and / or improves their dispersibility in the solvent. When the primary semiconductor nanoparticles are surface modified, the shell grows when the surface modifier is released. Therefore, in the finally obtained core-shell structure nanoparticles, the surface modifier that modifies the primary semiconductor nanoparticles is not usually present on the surface of the core (the interface between the core and the shell).

  In any of the production methods, primary semiconductor nanoparticles are produced under an inert atmosphere, particularly under an argon atmosphere or a nitrogen atmosphere. This is to reduce or prevent the oxide by-product and the oxidation of the surface of the primary semiconductor nanoparticles.

When primary semiconductor nanoparticles are added to M ¹ , M ² and Z to further include M ³ , ie, quaternary, in the preparation of the primary semiconductor nanoparticles described above, M ³ The salt is used together with the salt of M ^{1 and} the salt of M ² . The preparation ratio of the salt of M ^1, the salt of M ^2, the salt of M ³ , and the compound that is a source of Z or a ligand having Z as a coordination element is (M ¹ M ² ) _x M ³ _y Te It is preferable to set it as x: x: y: 2 (molar ratio) corresponding to the compositional formula of the stoichiometry composition of ₂ (in Formula, x + y = 2). The salt of M ³ may be either an organic acid salt or an inorganic acid salt. Specifically, the salt of M ³ may be any of nitrate, acetate, sulfate, hydrochloride and sulfonate. Others are the same as in the method for producing ternary primary semiconductor nanoparticles, and thus the detailed description thereof is omitted here.

When the ternary or quaternary semiconductor nanoparticles have a composition in which a part of M ² is substituted by another metal element, the other metal elements are produced in the production of the primary semiconductor nanoparticles. Use the salt of In that case, the preparation ratio of the salt of M ^{2 and} the salt of the metal element is adjusted so that the substitution amount of the metal element is as desired. Similarly, in the case of producing quaternary semiconductor nanoparticles, when it is assumed that the composition of M ³ is partially replaced with another metal element, the other semiconductor nanoparticles are produced during production of the primary semiconductor nanoparticles. The salt of the metal element of

  The ternary or quaternary primary semiconductor nanoparticles produced by the above method may be separated from the solvent after completion of the reaction, and may be further purified as required. The separation is performed, for example, by preparing the particles, centrifuging the mixture, and removing the supernatant. Purification is carried out by adding alcohol to the supernatant, centrifuging to precipitate, removing the precipitate (or removing the supernatant), and drying the separated precipitate by, for example, vacuum degassing or natural drying, Or you may implement by the method of making it melt | dissolve in an organic solvent. Purification (addition of alcohol and centrifugation) may be performed multiple times as necessary. As alcohols used for purification, lower alcohols such as methanol, ethanol, n-propanol and the like may be used. When the precipitate is dissolved in an organic solvent, chloroform, toluene, cyclohexane, hexane, pentane, octane or the like may be used as the organic solvent.

  If the primary semiconductor nanoparticles are purified and then dried, drying may be performed by vacuum degassing, or may be performed by natural drying, or alternatively, may be performed by a combination of vacuum degassing and natural drying . Natural drying may be carried out, for example, by leaving it in the atmosphere at normal temperature and pressure, and in that case, it may be left for 20 hours or more, for example, about 30 hours.

(Dispersion liquid of primary semiconductor nanoparticles)
When the primary semiconductor nanoparticles are coated with a shell, a dispersion in which this is dispersed in an appropriate solvent is prepared, and a semiconductor layer to be a shell in the dispersion is formed. In the liquid in which the primary semiconductor nanoparticles are dispersed, since the scattered light does not occur, the dispersion is generally obtained as a transparent (colored or colorless) one. The solvent in which the primary semiconductor nanoparticles are dispersed is not particularly limited, and may be any organic solvent (in particular, a highly polar organic solvent such as ethanol) as in the preparation of the primary semiconductor nanoparticles. The organic solvent may be a surface modifier, or a solution comprising a surface modifier. For example, the organic solvent may be at least one selected from nitrogen-containing compounds having a hydrocarbon group having 4 to 20 carbon atoms, which are surface modifiers described in relation to the shell, or It may be at least one selected from sulfur-containing compounds having 20 hydrocarbon groups, or at least one hydrocarbon selected from nitrogen-containing compounds having 4 to 20 carbon atoms and having 4 to 20 carbon atoms It may be a combination with at least one selected from sulfur-containing compounds having a group. As the nitrogen-containing compound, in particular, n-tetradecylamine is preferable in that particularly high purity compounds are easily available and the boiling point exceeds 290 ° C. Specific organic solvents include oleylamine, n-tetradecylamine, dodecanethiol, or combinations thereof.

  The dispersion of primary semiconductor nanoparticles may be prepared such that the proportion of particles in the dispersion is, for example, 0.02% by mass to 1% by mass, in particular 0.1% by mass to 0.6% by mass. . If the proportion of particles in the dispersion is too small, it becomes difficult to recover the product by the poor solvent aggregation / precipitation process, and if it is too large, the proportion of Ostwald ripening and collision coalescence of the material constituting the core increases. The diameter distribution tends to be wide.

(Formation of shell)
The formation of the layer of the semiconductor to be the shell is carried out by adding a compound containing a Group 13 element and a compound containing a single Group 16 element or a compound containing a Group 16 element to the above dispersion liquid.
The compound containing a Group 13 element is a source of a Group 13 element, and examples thereof include organic salts, inorganic salts, and organic metal compounds of the Group 13 element. Specifically, examples of the compound containing a Group 13 element include nitrates, acetates, sulfates, hydrochlorides, sulfonates and acetylacetonato complexes, preferably organic salts such as acetates, or organic metals It is a compound. Organic salts and organometallic compounds have high solubility in organic solvents, and are likely to promote the reaction more uniformly.

  The simple substance of the Group 16 element or the compound containing the Group 16 element is a source of the Group 16 element. For example, when sulfur (S) is used as a constituent element of the shell as a Group 16 element, elemental sulfur such as high purity sulfur can be used, or n-butanethiol, isobutanethiol, n-pentanethiol Thiols such as n-hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol and the like, disulfides such as dibenzyl disulfide, and sulfur-containing compounds such as thiourea and thiocarbonyl compounds can be used.

  When oxygen (O) is used as the constituent element of the shell as the group 16 element, alcohols, ethers, carboxylic acids, ketones, and N oxide compounds may be used as the group 16 element source. When selenium (Se) is used as a constituent element of the shell as a Group 16 element, elemental selenium, selenium selenide phosphine oxide, organic selenium compounds (dibenzyl diselenide and diphenyl diselenide) or hydrides, etc. The compounds may be used as a Group 16 element source. When tellurium (Te) is used as the constituent element of the shell as the Group 16 element, tellurium alone, tellurium phosphine oxide, or a hydride may be used as the source of the Group 16 element.

  The method for adding the Group 13 element source and the Group 16 element source to the dispersion is not particularly limited. For example, a mixed solution in which a Group 13 element source and a Group 16 element source are dispersed or dissolved in an organic solvent may be prepared, and this mixed solution may be added to the dispersion little by little, for example, by a dropping method. In this case, the mixture may be added at a rate of 0.1 mL / hr to 10 mL / hr, in particular 1 mL / hr to 5 mL / hr. The mixture may also be added to the heated dispersion. Specifically, for example, the temperature of the dispersion is raised so that the peak temperature is 200 ° C. to 290 ° C., and after the peak temperature is reached, the mixed solution is added little by little while maintaining the peak temperature. Then, the shell layer may be formed by a method of lowering the temperature (slow injection method). The peak temperature may be maintained as necessary after the addition of the mixture is finished.

  If the peak temperature is too low, the surface modifier that is modifying the primary semiconductor nanoparticles may not be sufficiently detached, or the chemical reaction for shell formation may not proceed sufficiently, and so on. May be insufficient. If the peak temperature is too high, the primary semiconductor nanoparticles may be altered, and even if a shell is formed, band edge emission may not be obtained. The time for maintaining the peak temperature may be a total of 1 minute to 300 minutes, particularly 10 minutes to 60 minutes after the addition of the mixture is started. The retention time of the peak temperature is selected in relation to the peak temperature, a longer shell time if the peak temperature is lower, and a shorter shell time if the peak temperature is higher, a good shell layer Is easy to form. The temperature raising rate and the temperature lowering rate are not particularly limited, and the temperature may be lowered by, for example, leaving the heat source (for example, an electric heater) off after holding for a predetermined time at the peak temperature.

  Alternatively, the entire Group 13 element source and Group 16 element source may be added directly to the dispersion. Then, the semiconductor layer serving as the shell may be formed on the surface of the primary semiconductor nanoparticles by heating the dispersion to which the Group 13 element source and the Group 16 element source are added (heating-up method). Specifically, for example, the dispersion to which the Group 13 element source and the Group 16 element source are added is gradually heated to have a peak temperature of 200 ° C. to 290 ° C .; After holding for 300 minutes for a minute, heating may be performed by gradually lowering the temperature. The temperature rising rate may be, for example, 1 ° C./min to 50 ° C./min, and the temperature falling rate may be, for example, 1 ° C./min to 100 ° C./min. Alternatively, heating may be performed so as to reach a predetermined peak temperature without particularly controlling the temperature rising rate, or temperature lowering may not be performed at a constant rate, but may be performed by leaving the heat source to be off and leaving it to cool. Good. Problems when the peak temperature is too low or too high are as described in the method of adding the above mixture.

  According to the heating up method, semiconductor nanoparticles having a core-shell structure giving stronger band edge emission tend to be obtained as compared with the case of forming a shell by the slow injection method.

Whatever method is used to add the Group 13 element source and the Group 16 element source, the preparation ratio of the two corresponds to the stoichiometric composition ratio of the compound semiconductor consisting of the Group 13 element and the Group 16 element. Is preferred. For example, when an In source is used as a Group 13 element source and an S source is used as a Group 16 element source, the preparation ratio is 1: 1.5 (In: S corresponding to the composition formula of In ₂ S ₃ It is preferable to set it as Similarly, when a Ga source is used as a Group 13 element source and an S source is used as a Group 16 element source, the preparation ratio is 1: 1.5 (Ga :: corresponding to the composition formula of Ga ₂ S ₃ It is preferable to set it as S). However, the feed ratio does not necessarily have to be the stoichiometric composition ratio, and when the raw material is charged in excess of the target shell production amount, for example, the Group 16 element source is For example, the feed ratio may be 1: 1 (13: 16).

In addition, the preparation amount is selected in consideration of the amount of primary semiconductor nanoparticles contained in the dispersion so that a shell of a desired thickness is formed on the primary semiconductor nanoparticles present in the dispersion. For example, the compound semiconductor of the stoichiometry composition which consists of a group 13 element and a group 16 element produces 0.01mmol-10mmol, especially 0.1mmol-1mmol to the substance mass 10nmol as a particle of the primary semiconductor nanoparticle As noted, the loadings of the Group 13 element source and the Group 16 element source may be determined. However, the amount of substance as a particle is the molar amount when one particle is regarded as a large molecule, and the number of nanoparticles contained in the dispersion is the Avogadro number (N _A = 6.022 × It is equal to the value divided by 10 ²³ ).

  In the manufacturing method of this embodiment, n-tetra is used as a dispersion, using indium acetate or gallium acetylacetonato as a Group 13 element source, and using elemental sulfur or dibenzyl disulfide as a Group 16 element source. Preferably, decylamine is used to form a shell comprising indium sulfide or gallium sulfide.

When dibenzyl disulfide is used as a Group 16 element source (sulfur source) in the heating up method, the shell is sufficiently formed even if the retention time after reaching the peak temperature is short (for example, 20 minutes or more and 30 minutes or less) It is easy to obtain semiconductor nanoparticles that give strong band edge emission. When a shell is formed using elemental sulfur, semiconductor nanoparticles with strong band edge emission are difficult to obtain if the retention time after reaching the peak temperature is short, but if the retention time is extended (eg, 40 minutes or more, particularly 50) The upper limit is, for example, 60 minutes or more), and semiconductor nanoparticles having strong band edge emission can be easily obtained. In addition, when sulfur is used for a longer holding time, it is possible to obtain band edge light emission with higher emission intensity than semiconductor nanoparticles manufactured using dibenzyl disulfide. Furthermore, according to the heating up method using elemental sulfur, by prolonging the retention time, the intensity of the broad peak derived from the defect emission gives an emission spectrum sufficiently smaller than the intensity of the peak of the band edge emission. Semiconductor nanoparticles are obtained. Furthermore, regardless of the type of sulfur source, the peak of band edge emission emitted from the obtained semiconductor nanoparticles tends to shift to the longer wavelength side as the retention time becomes longer.
In addition, when n-tetradecylamine is used as the dispersion in the heating up method, semiconductor nanoparticles giving an emission spectrum in which the intensity of a broad peak derived from defect emission is sufficiently smaller than the intensity of a peak of band edge emission Is obtained.
The above tendency is significant when using a gallium source as a Group 13 element source.

  Thus, a shell is formed to form a core-shell semiconductor nanoparticle. The obtained core-shell structure semiconductor nanoparticles may be separated from the solvent, and may be further purified and dried as needed. The method of separation, purification and drying is as described above in relation to the primary semiconductor nanoparticles, and thus the detailed description thereof is omitted here.

(Light emitting device)
Next, as another embodiment according to the present invention, a light emitting device using the semiconductor nanoparticles of the core-shell structure described above will be described.
A light emitting device which is an embodiment of the present invention is a light emitting device including a light conversion member and a semiconductor light emitting element, and the light conversion member includes the semiconductor nanoparticles of the core-shell structure described above. According to this light emitting device, for example, the semiconductor nanoparticles of the core-shell structure absorb a part of the light emitted from the semiconductor light emitting element to emit light of a longer wavelength. Then, the light from the semiconductor nanoparticle of the core-shell structure and the remainder of the light emission 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, a semiconductor light emitting element that emits blue-violet light or blue light having a peak wavelength of about 400 nm to 490 nm is used, and semiconductor nanoparticles having a core-shell structure that absorbs blue light to emit yellow light are used. For example, a light emitting device that emits white light can be obtained. Alternatively, a white light emitting device can be obtained by using two types of semiconductor nanoparticles having a core-shell structure, one that absorbs blue light and emits green light and the other that absorbs blue light and emits red light. it can.
Alternatively, even in the case of using semiconductor nanoparticles of three types of core-shell structures that use a semiconductor light emitting element that emits ultraviolet light with a peak wavelength of 400 nm or less and that absorbs ultraviolet light to emit blue light, green light, and red light, respectively. A white light emitting device can be obtained. In this case, it is preferable that the semiconductor nanoparticles absorb and convert all the light from the light emitting element so that the ultraviolet light emitted from the light emitting element does not leak to the outside.

Alternatively, white light is emitted by using semiconductor nanoparticles having a peak wavelength of about 490 nm to 510 nm and emitting blue light as the semiconductor nanoparticles having a core-shell structure. You can get the device.
Alternatively, if a semiconductor light emitting element that emits red light with a wavelength of 700 nm to 780 nm is used and a semiconductor nanoparticle having a core-shell structure that absorbs red light and emits near infrared light, near infrared light is emitted. A light emitting device can also be obtained.

The core-shell semiconductor nanoparticles may be used in combination with other semiconductor quantum dots, or may be used in combination with other non-quantum phosphors (eg, organic phosphors or inorganic phosphors). Other semiconductor quantum dots are, for example, binary semiconductor quantum dots described in the Background section. A garnet-based phosphor such as an aluminum garnet-based phosphor can be used as the phosphor that is not a quantum dot. Examples of garnet phosphors include yttrium-aluminum-garnet phosphors activated with cerium and lutetium-aluminum-garnet phosphors activated with cerium. In addition, nitrogen-containing calcium aluminosilicate phosphor activated with europium and / or chromium, silicate phosphor activated with europium, β-SiAlON phosphor, nitride phosphor such as CASN or SCASN, etc. Rare earth nitride phosphors such as LnSi ₃ N 11 or LnSiAlON, oxynitrides such as BaSi ₂ O ₂ N ₂ : Eu, or Ba ₃ Si ₆ O ₁₂ N ₂ : Eu, CaS, SrGa ₂ S ₄ type, SrAl ₂ O ₄ system, 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 A K ₂ SiF ₆ : Mn phosphor or the like as a fluoride complex phosphor can be used.

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

Alternatively, another example of the light conversion member is a resin 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 device is disposed on a flat substrate. It is a member.
Alternatively, still another example of the light conversion member is a case where a resin member containing a reflective material is filled around the semiconductor light emitting element so that the upper end thereof is flush with the semiconductor light emitting element. It is the resin member formed in flat form by predetermined thickness on the upper part of the resin member containing the said semiconductor light emitting element and the said reflecting material.

The light conversion member may be in contact with the semiconductor light emitting element or may be provided apart from the semiconductor light emitting element. Specifically, the light conversion member may be a pellet-like member, a sheet member, a plate-like member or a rod-like member disposed apart from the semiconductor light emitting device, or a member provided in contact with the semiconductor light emitting device, for example It may be a sealing member, a coating member (a member covering a light emitting element provided separately from the mold member), or a mold member (for example, a member having a lens shape).
In the case of using semiconductor nanoparticles of two or more types of core-shell structure that emit light of different wavelengths in a light emitting device, semiconductor nanoparticles of the two or more types of core-shell structure are mixed in one light conversion member. Alternatively, two or more light conversion members including 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-like or stripe-like pattern on a plane.

An LED chip is mentioned as a semiconductor light emitting element. The LED chip may include one or more semiconductor layers selected from the group consisting of GaN, GaAs, InGaN, AlInGaP, GaP, SiC, and ZnO. Violet light, the semiconductor light emitting element which emits blue light, or ultraviolet light, is preferably represented in the general formula _{In X Al Y Ga 1-X} -Y N (0 ≦ X, 0 ≦ Y, X + Y <1) It is preferable that a GaN-based compound be provided as a semiconductor layer.

The light emitting device of the present embodiment is preferably incorporated into a liquid crystal display as a light source. Since the band edge emission by semiconductor nanoparticles of the core-shell structure has a short emission life, a light emitting device using this is suitable for a light source of a liquid crystal display device which requires a relatively fast response speed. Moreover, the semiconductor nanoparticle of the core-shell structure of the present embodiment can exhibit a light emission peak with a small half width as band edge light emission. Thus, in the light emitting device:
-A blue semiconductor light emitting device is used to obtain blue light having a peak wavelength in the range of 420 nm to 490 nm, and a semiconductor nanoparticle having a core-shell structure has a peak wavelength in the range of 510 nm to 550 nm, preferably 530 nm to 540 nm Light and red light having a peak wavelength in the range of 600 nm to 680 nm, preferably 630 to 650 nm; or
-In a light emitting device, ultraviolet light having a peak wavelength of 400 nm or less is obtained by a semiconductor light emitting element, and blue light having a peak wavelength of 430 nm to 470 nm, preferably 440 to 460 nm, and a peak wavelength By using green light of 510 nm to 550 nm, preferably 530 to 540 nm, and red light with a peak wavelength in the range of 600 to 680 nm, preferably 630 to 650 nm, without using dark color filters A liquid crystal display device with good reproducibility can be obtained. The light emitting device of this embodiment is used, for example, as a direct type backlight or as an edge type backlight.

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

Example 1
(1) Preparation of Primary Semiconductor Nanoparticles (Ag-In-S) Silver acetate (AgOAc), indium acetate (In (OAc) ₃ ) 0.4 mmol each, thiourea 0.8 mmol, 11.8 mL oleylamine, And 0.2 mL of 1-dodecanethiol are placed in a two-necked flask and vacuum degassed (3 min at normal temperature), and then reaches 200 ° C. at a temperature rise rate of 10 ° C./min under an Ar atmosphere The temperature rose to the end. The obtained suspension was allowed to cool, and then subjected to centrifugation (radius 150 mm, 2500 rpm, 10 minutes) to remove the supernatant deep red solution. To this was added methanol until precipitation of nanoparticles was generated, and subjected to centrifugation (radius 150 mm, 2500 rpm, 3 minutes), and the precipitate was vacuum dried at room temperature to obtain semiconductor nanoparticles (primary semiconductor nanoparticles) .

The XRD pattern of the obtained primary semiconductor nanoparticles was measured and compared with tetragonal (chalcopyrite type) AgInS ₂ , hexagonal (wurtzite type) AgInS ₂ , and orthorhombic AgInS ₂ . The measured XRD pattern is shown in FIG. From XRD pattern, the crystal structure of the primary semiconductor nanoparticles have been found to be substantially the same structure as AgInS ₂ tetragonal. The XRD pattern was measured using a powder X-ray diffractometer (trade name: SmartLab) manufactured by RIGAKU CO., LTD. (The same in the following experimental examples).

Further, the shape of the obtained primary semiconductor nanoparticles is observed using a transmission electron microscope (TEM, manufactured by Hitachi High-Technologies Corp., trade name H-7650), and the average particle diameter is 80 to 200,000. It measured from the TEM image of double. Here, high resolution carbon HRC-C10 STEM Cu100P grid (Oken Shoji Co., Ltd.) was used as a TEM grid, and the shape of the obtained particles was spherical or polygonal.
The average particle size is selected from three or more TEM images, and among the nanoparticles contained in them, all measurable ones, that is, those in which the image of the particle is broken at the edge of the image are excluded For all particles, the particle size was measured and determined by the method of determining the arithmetic mean. In all the examples and comparative examples including the present example, three or more TEM images were used to measure the particle size of a total of 100 or more nanoparticles.
The average particle size of the primary semiconductor nanoparticles was 5.3 nm.

It was 52.2 micromol when the substance mass of the indium contained in the primary semiconductor nanoparticle obtained by (1) was calculated | required by ICP emission spectroscopy (Shimadzu Corporation, ICPS-7510) measurement.
The volume of the primary semiconductor nanoparticles when the average particle size is 5.3 nm is calculated to be 77.95 nm ³ when spherical. In addition, since the unit cell volume of the silver sulfide indium crystal in the case of tetragonal is calculated to be 0.38 nm ³ (lattice constant 5.828 Å, 5.828 Å, 11.19 Å), the volume of the primary semiconductor nanoparticles is By dividing by unit cell volume, it is calculated that 205 unit cells are contained in one primary semiconductor nanoparticle. Next, one unit cell of silver indium sulfide crystal in the case of tetragonal contains 4 indium atoms, so that 820 indium atoms are contained per nanoparticle. Is calculated.
The substance mass of the primary semiconductor nanoparticles as nanoparticles is calculated to be 63.6 nmol by dividing the substance mass of indium by the number of indium atoms per nanoparticle.

(2) Coating of shell With the primary semiconductor nanoparticles obtained in (1) as a core, of these, 20 nmol of the substance weight as nanoparticles in a mixed solvent of 5.9 mL of oleylamine and 0.1 mL of dodecanethiol A dispersed dispersion was obtained, which was kept at 200 ° C. under an Ar atmosphere. Separately, indium acetate (In (OAc) ₃ ) 0.8 mmol (233 mg) and sulfur powder 1.2 mmol (38.4 mg) are added to 8 mL of oleylamine, and stirred for 10 minutes at 100 ° C. Sulfur powder was dissolved to obtain a mixed solution. The mixture was added dropwise to the heated dispersion at a rate of 5 mL / h (0.5 mmol / h based on In) at 5 ml. At the end of the addition of the mixture, the heat source is turned off and the reaction solution is allowed to cool to room temperature, and then methanol is added to the solution to obtain precipitates of core-shell structure semiconductor nanoparticles, followed by centrifugation (radius 150 mm) The solid component was recovered by 2500 rpm for 3 minutes. The product was dissolved in chloroform and various measurements were performed. The average particle size of the shell-coated particles was measured. The average particle size of the core-shell semiconductor nanoparticles is 11.4 nm, and the difference between the average particle size of the primary semiconductor nanoparticles and the thickness of the shell Was about 3.0 nm on average.

(3) Measurement of absorption, emission and excitation spectrum The emission, absorption and excitation spectrum were measured. The results are shown sequentially in FIG. 2 and FIG.
The emission spectrum was measured at an excitation wavelength of 500 nm using a multichannel spectrometer (manufactured by Hamamatsu Photonics Co., Ltd., trade name: PMA12). The absorption spectrum was measured at a wavelength of 350 nm to 850 nm using an ultraviolet visible near infrared spectrophotometer (manufactured by Nippon Bunko, trade name V-670). The excitation spectrum was measured at an observation wavelength of 593 nm and 780 nm (corresponding to the peak observed in the emission spectrum) using a fluorescence spectrophotometer (Fluoromax-4 manufactured by Horiba, Ltd.).
As shown in FIG. 2, in the semiconductor nanoparticle of the core-shell structure obtained in Example 1, a sharp emission peak having a half width of about 38 nm was observed around 593 nm. Further, as shown in FIG. 3, in the excitation spectrum at the observation wavelength of 593 nm, an exciton peak was observed at around 540 nm. As reference, the emission spectrum and absorption spectrum of primary semiconductor nanoparticles (Ag-In-S) are shown in FIG. 4 and FIG. The emission spectrum of Ag-In-S not coated with a shell is a broad peak having a peak around 820 nm, and no exciton peak was observed in the absorption and excitation spectrum.

In Example 1, the light emission lifetime of the light emission observed as a sharp peak was measured. The luminescence lifetime is measured using a fluorescence lifetime measuring device (trade name: Quantaurus-Tau) manufactured by Hamamatsu Photonics Co., Ltd., by irradiating light with a wavelength of 470 nm as excitation light to semiconductor nanoparticles having a core-shell structure to produce sharp luminescence. The decay curve of the luminescence around the peak wavelength of the peak was determined. The obtained attenuation curve was divided into three components by parameter fitting using fluorescence lifetime measurement / analysis software U11487-01 manufactured by Hamamatsu Photonics Co., Ltd. As a result, τ ₁ , τ ₂ and τ ₃ and contribution rates of each component (A ₁ , A ₂ and A ₃ ) were as shown in Table 1 below.

  As shown in Table 1, the main component (τ3, A3) was 121.7 ns, but the component (τ2, A2) with a light emission lifetime of 28.0 ns was also observed at the same level of intensity. The emission lifetime is fluorescence emitted from CdSe (nanoparticles) whose band edge emission has been confirmed, and was about the same as the fluorescence lifetime (30 ns to 60 ns) of the component having the largest contribution rate.

(Example 2)
Among primary semiconductor nanoparticles produced by the same procedure as in Example 1, a dispersion liquid in which 10 nmol of the substance weight as nanoparticles was dispersed in 12 mL of oleylamine was obtained, and was maintained at 260 ° C. in Ar atmosphere. . Separately, gallium acetylacetonato (Ga (acac) ₃ ) and sulfur powder are added to oleylamine to a concentration of 0.1 mmol / mL and 0.15 mmol / mL, respectively, and stirred at 100 ° C. for 10 minutes Then, gallium acetylacetonate and sulfur powder were dissolved to obtain a mixed solution. To the heated dispersion, 4 ml of the mixture was dropped at a rate of 5 mL / h (0.5 mmol / h based on Ga). When the addition of the mixture is completed, the heat source is turned off and the reaction solution is allowed to cool to room temperature, and then methanol is added to the solution to obtain precipitates of core-shell semiconductor nanoparticles, which are centrifuged (radius 150 mm, The solid component was recovered by 2500 rpm, 3 minutes). The product was dissolved in chloroform and various measurements were performed.
Moreover, when the average particle diameter of the particle | grains coat | covered with shell was measured, the average particle diameter of the semiconductor nanoparticle of core-shell structure was 6.65 nm. The average particle size of the primary semiconductor nanoparticles produced in this example was 5.99 nm, and from this difference, the thickness of the shell was about 0.33 nm on average.

  Although the primary semiconductor nanoparticles were produced in the same procedure as in Example 1, the average particle size is different from that produced in Example 1. This is considered to be due to the fact that the time until starting heating after reagent mixing is slightly different from that of Example 1, and that the substance mass of the silver-thiol complex which is expected to be generated during this time is different. The same can be said for the following embodiments.

An emission spectrum (excitation wavelength: 450 nm), an absorption spectrum, and an excitation spectrum at observation wavelengths of 580 nm and 730 nm were measured using the same apparatus as that used in Example 1. The results are shown in FIG. 6 and FIG. As shown in FIG. 6, in the semiconductor nanoparticle of the core-shell structure obtained in Example 2, a sharp emission peak having a half width of about 39 nm was observed around 584 nm. Further, as shown in FIG. 7, in the excitation spectrum at the observation wavelength of 580 nm, an exciton peak was observed at around 530 nm.
In addition, using the same multi-channel spectrometer (excitation wavelength: 450 nm) as in Example 1, the emission quantum yield at a sharp peak (530-650 nm) considered to be band edge emission was measured: 1.9% Met.
In addition, when the light emission lifetime of the light emission observed as a sharp peak was measured in the same manner as in Example 1, τ ₁ , τ ₂ , and τ ₃ , and the contribution rates of the respective components (A ₁ , A ₂ and A ₃ ) was as shown in Table 2 below. As shown in Table 2, the light emission lifetime of the main component (τ ₂ , A ₂ ) was 39.1 ns.

(Example 3)
Among the primary semiconductor nanoparticles prepared by the same procedure as in Example 1, 30 nmol of the substance weight as nanoparticles, 0.1 mmol of gallium acetylacetonato (Ga (acac) ₃ ), and 0.05 mmol of dibenzyl disulfide 12 mL of oleylamine was placed in a flask, heated to 260 ° C. at a temperature rising rate of 10 ° C./min, held at 260 ° C. for 20 minutes, and then cooled with the heat source off. Then, methanol was added to the solution to obtain a precipitate of core-shell semiconductor nanoparticles, and the solid component was recovered by centrifugation (radius 150 mm, 2500 rpm, 3 minutes). The product was dissolved in chloroform and various measurements were performed.
Moreover, when the average particle diameter of the particle | grains covered with the shell was measured, the average particle diameter of the semiconductor nanoparticle of core-shell structure was 8.0 nm. The average particle size of the primary semiconductor nanoparticles produced in this example was 6.0 nm, and from this difference, the thickness of the shell was about 1 nm on average.

The emission spectrum (excitation wavelength: 450 nm), absorption spectrum, and excitation spectrum were measured using the same apparatus as that used in Example 1. The results are shown sequentially in FIG. 8 and FIG. As shown in FIG. 8, in the semiconductor nanoparticle of the core-shell structure obtained in Example 3, a sharp emission peak having a half width of about 39 nm was observed around 586 nm. Further, as shown in FIG. 9, in the excitation spectrum at the observation wavelength of 585 nm, an exciton peak was observed at around 535 nm. Moreover, when the light emission quantum yield was measured like Example 2, the light emission quantum yield was 14.3%.
In addition, when the light emission lifetime of the light emission observed as a sharp peak was measured in the same manner as in Example 1, τ ₁ , τ ₂ , and τ ₃ , and the contribution rates of the respective components (A ₁ , A ₂ and A ₃ ) was as shown in Table 3 below. As shown in Table 3, the light emission lifetime of the main component (τ ₂ , A ₂ ) was 51.4 ns.

When the emission spectra of the semiconductor nanoparticles obtained in Example 1 and the semiconductor nanoparticles obtained in Example 2 are compared, in Example 2, the emission intensity of the sharp peak (intensity of band edge emission) is The emission intensity of the broad peak (the intensity of defect emission) was clearly larger. From this, it can be seen that shell formation by GaS _x is more advantageous to obtain band edge emission from the core than shell formation by InS _x .

  When the luminescence quantum yields of the semiconductor nanoparticles obtained in Example 2 and the semiconductor nanoparticles obtained in Example 3 were compared, it was confirmed that Example 3 was 7.5 times as large as Example 2. It was done. In addition, at the time of shell formation, the thickness of the shell was as large as about 1 nm in Example 3 despite the fact that the molar ratio to the primary semiconductor nanoparticles of the Ga source for shell formation is the same. Taking these into consideration, when dibenzyl disulfide is used as a sulfur source, the shell covers the surface of the core without interruption and surface defects of the core are effectively removed, whereby the intensity of band edge emission is increased. It is guessed that it became bigger.

(Comparative example 1)
Among the primary semiconductor nanoparticles produced in the same procedure as in Example 1, 10 nmol of the substance weight as nanoparticles was dispersed in 12 mL of oleylamine to obtain a dispersion, which was maintained at 260 ° C. in an Ar atmosphere. Separately, zinc acetate (Zn (OAc) ₂ ) and sulfur powder are respectively added to be 0.1 mmol / mL in oleylamine, and zinc acetate and sulfur powder are dissolved by heating at 100 ° C. for 10 minutes. The mixture was allowed to obtain a mixed solution. The mixture was dropped in 2 ml at a rate of 5 mL / h (0.5 mmol / h based on Zn) to the heated dispersion. When the addition of the mixture is completed, the heat source is turned off and the reaction solution is allowed to cool to room temperature, and then methanol is added to the solution to obtain precipitates of core-shell semiconductor nanoparticles, which are centrifuged (radius 150 mm, The solid component was recovered by 2500 rpm, 3 minutes). This was dissolved in chloroform, and using the same apparatus as that used in Example 1, the emission spectrum (excitation wavelength: 450 nm) and the absorption spectrum were measured. The results are shown in FIG. 10 and FIG.

  As shown in FIG. 10, in the nanoparticles obtained in Comparative Example 1, a sharp emission peak as seen in Examples 1 to 3 was not observed, and a broad spectrum was observed. That is, although ZnS has a larger band gap energy than Ag-In-S and can give a type-1 band alignment, no band edge emission was observed. This is considered to be because solid solution was formed between core-shells and core-shell structure was not formed.

(Examples 4A to 4D)
Among the primary semiconductor nanoparticles prepared by the same procedure as in Example 1, 30 nmol of the substance weight as nanoparticles, 0.1 mmol of gallium acetylacetonato (Ga (acac) ₃ ), and 0.05 mmol of dibenzyl disulfide 12 mL of oleylamine was placed in a flask and heated to 260 ° C. at a heating rate of 10 ° C./min. Immediately after the temperature reached 260 ° C. (Example 4A), after holding at 260 ° C. for 10 minutes (Example 4B), 20 minutes (Example 4C), and 30 minutes (Example 4D) respectively, the heat source was turned off. It was allowed to cool. Thereafter, the liquid containing the reaction product was centrifuged (radius 150 mm, 2500 rpm, 10 minutes), and the supernatant was removed. To this was added methanol until precipitation of nanoparticles occurred, and the mixture was centrifuged (radius 150 mm, 2500 rpm, 5 minutes) to recover a solid component. The product was dissolved in chloroform and various measurements were performed.

(Examples 5A to 5F)
Among the primary semiconductor nanoparticles prepared by the same procedure as in Example 1, 30 nmol of the substance weight as nanoparticles, 0.1 mmol of gallium acetylacetonato (Ga (acac) ₃ ), 0.15 mmol of sulfur, and oleylamine 12 mL was placed in a flask and heated to 260 ° C. at a heating rate of 10 ° C./min. Immediately after reaching 260 ° C. (Example 5A), each at 260 ° C. for 10 minutes (Example 5B), 30 minutes (Example 5C), 40 minutes (Example 5D), 50 minutes (Example 5E), 60 After holding for a minute (Example 5F), the heat source was turned off and allowed to cool. Thereafter, the liquid containing the reaction product was centrifuged (radius 150 mm, 2500 rpm, 10 minutes), and the supernatant was removed. To this was added methanol until precipitation of nanoparticles occurred, and the mixture was centrifuged (radius 150 mm, 2500 rpm, 5 minutes) to recover a solid component. The product was dissolved in chloroform and various measurements were performed.

  The emission spectrum (excitation wavelength: 400 nm) of the semiconductor nanoparticles obtained in Examples 4A to 4D and Examples 5A to 5F was obtained using the same apparatus as that used in Example 1. The emission spectra are shown in FIG. 12 (Examples 4A to 4D) and FIG. 13 (Examples 5A to 5F). In each of the drawings, the emission spectrum of the primary semiconductor nanoparticle (core) not having a shell formed is also shown as a reference example.

  As shown in FIG. 12, among the examples 4A to 4C in which the shell was formed using dibenzyl disulfide as a sulfur source, the peak intensity of the band edge emission was the largest in the example 4C (retention time: 20 minutes). Example 4D (30 minutes retention time) showed lower peak edge emission intensity than Example 4C. From this, it was found that when the shell is formed using dibenzyl disulfide, the band edge emission intensity can be improved by a relatively short retention time. This can also be confirmed by FIG. 14 which shows the relationship between the peak intensity of the band edge emission of Examples 4A to 4C and the retention time.

  As shown in FIG. 13, among the examples 5A to 5F in which a shell was formed using a sulfur simple substance as a sulfur source, the peak intensity of band edge emission was the largest in example 5E (retention time: 50 minutes). From this, it can be seen that when the shell is formed using sulfur alone as the sulfur source, a long retention time is required to obtain particles of core-shell structure with a higher peak intensity of band edge emission. This can also be confirmed by FIG. 14 which shows the relationship between the peak intensity of the band edge emission of Examples 5A to 5F and the retention time. In addition, as shown in FIG. 14, when sulfur is used alone to increase the retention time to form a shell, band edge emission larger than the maximum value of the peak intensity of band end emission achieved when using dibenzyl disulfide is obtained. Peak intensity can be achieved.

  Furthermore, as shown in FIG. 13, when the shell is formed by using sulfur alone to extend the holding time, the intensity of the band edge emission (the ratio of the band edge emission / defect emission intensity) can be further increased. (In particular, Examples 5E, 5F).

  FIG. 15 is a graph showing the relationship between the peak wavelength of band edge emission and the retention time for Examples 4A to 4D and Examples 5A to 5F. It is understood that the peak wavelength shifts to the long wavelength side as the retention time becomes longer in any case where dibenzyl disulfide and sulfur alone are used.

[Observation by HRTEM and HAADF]
The core-shell structure semiconductor nanoparticles of Example 5F were observed by HRTEM and HAADF (manufactured by Nippon Denshi, trade name ARM-200F). The HRTEM image is shown in FIG. 16 and the HAADF image is shown in FIG. In any case, a crystalline core having a regular pattern and a shell having no regular pattern located around the same are observed, and it is observed that the shell is amorphous in the semiconductor nanoparticles of Example 5F. The

[Analysis by XPS]
The semiconductor nanoparticles having a core-shell structure of Example 5F were analyzed by X-ray photoelectron spectroscopy (manufactured by Shimadzu Corporation, trade name KRATOS AXIS-165X). Silver and indium correspond to the position of sulfide when comparing the peak position derived from 3d orbital to the database, and sulfur corresponds to the position of metal sulfide when comparing the peak position derived from 2p orbital to the database It confirmed that it corresponded. In addition, regarding gallium, it was not possible to confirm that it is a sulfide because a sulfide database was not available, but the peak position derived from the 3d orbital of gallium is clearly different from metallic gallium, and gallium oxide and gallium selenide It was confirmed that it is likely to be a sulfide because

[Analysis by energy dispersive X-ray analyzer]
The atomic percentage of each element contained in the semiconductor nanoparticles having a core-shell structure of Example 5F was analyzed by an energy dispersive X-ray analyzer (trade name: OCTANE, manufactured by EDAX). The results are shown in Table 4. When the composition is AgInS ₂ · Ga ₂ S ₃ , the atomic percentage of sulfur calculated from the results of Ag and Ga in Table 4 is 53.9 (17.2 × 2 + 13.1 ÷ 2 × 3 = 53.9 And a good match to the values of S in Table 4.

(Example 6)
(1) Preparation of Primary Semiconductor Nanoparticles (Ag-In-S) Silver acetate (AgOAc), indium acetate (In (OAc) ₃ ) 0.4 mmol each, thiourea 0.8 mmol, 35.8 mmol n- Tetradecylamine and 0.2 mL of 1-dodecanethiol were put in a two-necked flask, vacuum degassed (3 min at normal temperature), and then Ar was heated at a temperature rising rate of 5 ° C./min. The temperature was raised until it reached 150 ° C. The resulting suspension is allowed to cool, a small amount of hexane is added around around 90 ° C., and the mixture is centrifuged (radius 150 mm, 4000 rpm, 10 minutes), and the dark red solution as a supernatant is taken out. The To this was added methanol until precipitation of nanoparticles was generated, and subjected to centrifugation (radius 150 mm, 2500 rpm, 3 minutes), and the precipitate was vacuum dried at room temperature to obtain semiconductor nanoparticles (primary semiconductor nanoparticles) .

(2) Coating of shell With the primary semiconductor nanoparticles obtained in (1) as a core, of these, 30 nmol by substance weight as nanoparticles, 0.1 mmol of gallium acetylacetonato (Ga (acac) ₃ ), The flask was charged with 0.15 mmol of sulfur and 36.48 mmol of n-tetradecylamine, heated to 260 ° C. at a temperature rising rate of 10 ° C./min, and maintained at 260 ° C. for 50 minutes, after which the heating source was It was turned off and allowed to cool. Then, methanol was added to the solution to obtain a precipitate of core-shell semiconductor nanoparticles, and the solid component was recovered by centrifugation (radius 150 mm, 2500 rpm, 3 minutes). The product was dissolved in chloroform and various measurements were performed.
Moreover, when the average particle diameter of the particle | grains covered with the shell was measured, the average particle diameter of the semiconductor nanoparticle of core-shell structure was 8.6 nm. The average particle size of the primary semiconductor nanoparticles produced in this example was 7.1 nm, and from this difference, the thickness of the shell was about 0.75 nm on average.

  The emission spectrum (excitation wavelength: 450 nm) and absorption spectrum were measured using the same apparatus as that used in Example 1. The results are sequentially shown in FIG. 18 and FIG. As shown in FIG. 18, in the semiconductor nanoparticle of the core-shell structure obtained in Example 6, a sharp emission peak having a half width of about 28 nm was observed around 581 nm. Further, as shown in FIG. 19, in the excitation spectrum at the observation wavelength of 585 nm, an exciton peak was observed at around 535 nm. In addition, using the same multi-channel spectrometer (excitation wavelength: 450 nm) as in Example 1, the emission quantum yield at a sharp peak (530-630 nm) considered to be band edge emission was measured to be 21.1%. Met.

  Embodiments according to the present invention are semiconductor nanoparticles capable of band edge emission, and can be used as a wavelength conversion material of a light emitting device or as a biomolecular marker.

Claims (16)

A semiconductor nanoparticle comprising: a core; and a shell covering a surface of the core and having a band gap energy larger than that of the core and heterojunction with the core, and emitting light when irradiated with light.
The core is 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 and Au, and M ² is Al, Ga, In And at least one element selected from the group consisting of and T1, and Z is at least one element selected from the group consisting of S, Se and Te;
Semiconductor nanoparticles, wherein the shell is a semiconductor substantially consisting of a Group 13 element and a Group 16 element.   The semiconductor nanoparticle according to claim 1, wherein the shell contains In as the group 13 element.   The semiconductor nanoparticle according to claim 1, wherein the shell contains Ga as the group 13 element.   The semiconductor nanoparticle according to claim 2 or 3, wherein the shell contains S as the group 16 element. Wherein the core comprises Ag as ^{M 1,} it contains In as ^{M 2,} the semiconductor nanoparticles according to claim 1 comprising S as Z. It said core further comprises a M ^3, is M ^3, is at least one element selected from the group consisting of Zn and Cd, semiconductor nanoparticles according to any one of claims 1-5.   The semiconductor nanoparticle of any one of Claims 1-6 which has a peak whose half value width of an emission spectrum is 50 nm or less.   The semiconductor nanoparticle of any one of Claims 1-7 whose light emission lifetime is 200 ns or less.   The semiconductor nanoparticle according to any one of claims 1 to 8, wherein the excitation or absorption spectrum of the semiconductor nanoparticle exhibits an exciton peak. 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 and Au, and M ² is composed of Al, Ga, In and Tl A dispersion is prepared by dispersing, in a solvent, primary semiconductor nanoparticles consisting of a semiconductor which is at least one element selected from the group and Z is at least one element selected from the group consisting of S, Se and Te. To do,
A compound containing a Group 13 element and a single substance of a Group 16 element or a compound containing a Group 16 element are added to the dispersion, and the Group 13 element and the substance are substantially added to the surface of the primary semiconductor nanoparticle. A method of producing semiconductor nanoparticles, comprising forming a layer of a semiconductor comprising a Group 16 element.   The method for producing a semiconductor nanoparticle according to claim 10, wherein the compound containing a Group 16 element is dibenzyl disulfide.   After adding the compound containing the Group 13 element and the single substance of the Group 16 element or the compound containing the Group 16 element to the dispersion, the dispersion is kept at a constant speed in the range of 200 ° C. to 290 ° C. The manufacturing method of the semiconductor nanoparticle of Claim 10 or 11 including holding for a fixed time at the said peak temperature, after making it heat up to the peak temperature which exists inside.   The method for producing semiconductor nanoparticles according to claim 12, wherein the single substance of the Group 16 element is a single substance of sulfur, and the time during which the dispersion liquid is held at the peak temperature is 40 minutes or more and 60 minutes or less.   The manufacturing method of the semiconductor nanoparticle of any one of Claims 10-13 in which the said dispersion liquid contains n-tetradecyl amine. A light emitting device comprising a light conversion member and a semiconductor light emitting element, wherein the light conversion member includes the semiconductor nanoparticle according to any one of claims 1 to 9.   The light emitting device according to claim 15, wherein the semiconductor light emitting element is an LED chip.