Semiconductor nanocrystalline population and preparation method thereof

Abstract

The invention provides a semiconductor nanocrystalline population and a preparation method thereof. The crystal form of the semiconductor nanocrystal group is wurtzite single crystals, the semiconductor nanocrystal group comprises cadmium and selenium, and at least 85% of semiconductor nanocrystals in the semiconductor nanocrystal group do not have lattice stacking faults.

Description

Technical Field

[0001] The present disclosure relates to the technical field of semiconductor nanocrystal synthesis, and in particular, to a semiconductor nanocrystal group and a preparation method thereof. Background Art

[0002] Colloidal semiconductor nanocrystals are nanometer-sized fragments of the corresponding bulk crystals, synthesized and processed in solution with excellent control over size and size distribution. Due to their nanoscale lattice size, their optical and optoelectronic properties are not only closely related to size (i.e., quantum confinement effects), but are also sensitive to the perfection of their internal lattice, crystal facet structure, and facet-ligand interfaces. Although CdSe nanocrystals have been extensively studied and greatly developed, the synthesis of wurtzite CdSe nanocrystals with control over these aspects remains challenging. Summary of the invention

[0003] The purpose of the present disclosure is to provide a new group of wurtzite semiconductor nanocrystals with few lattice faults.

[0004] According to a first aspect of the present disclosure, a semiconductor nanocrystal group is provided, wherein the crystal form of the semiconductor nanocrystal group is wurtzite single crystal, the semiconductor nanocrystal group comprises cadmium and selenium, and at least 85% of the semiconductor nanocrystals in the semiconductor nanocrystal group have no lattice stacking faults.

[0005] Optionally, the surface ligand of the semiconductor nanocrystal comprises fatty acid zinc.

[0006] Optionally, the number of C atoms in the fatty acid zinc is less than or equal to 22 and greater than or equal to 2.

[0007] Optionally, when the semiconductor nanocrystal group is a nanosphere or a near-nanosphere or a near-nanorod or a nanorod or a nanowire, the XRD test result of the semiconductor nanocrystal group is and The ratio of the peak area of ​​the above semiconductor nanocrystal group to the peak area of ​​the above semiconductor nanocrystal group is 0.38 to 0.44; optionally, the test results of the above semiconductor nanocrystal group using the Cu target are The 2theta peak position is 42.1±0.5 degrees, and the Q value peak position is

[0008] Optionally, when the semiconductor nanocrystal group is nanospheres or near-nanospheres, the average aspect ratio of the semiconductor nanocrystal group is 0.8-1.6, and the average particle size is 3-20 nm; preferably, the particle size distribution deviation of the semiconductor nanocrystal group is less than or equal to 10%.

[0009] Optionally, the size of the semiconductor nanocrystal group can be extended along the c-axis, and the average aspect ratio of the semiconductor nanocrystal group is 1.4 to 40, and the average particle size is 5 to 15 nm.

[0010] Optionally, when the semiconductor nanocrystal group is a nanosphere or a near-nanosphere or a near-nanorod or a nanorod or a nanowire, the fluorescence half-peak width of the semiconductor nanocrystal group is 19 to 38 nm.

[0011] Optionally, the size of the semiconductor nanocrystal group can be extended along the c-axis, and when the morphology of the semiconductor nanocrystal group is near nanorods or nanorods or nanowires, the average aspect ratio of the semiconductor nanocrystal group is 1.4 to 18;

[0012] Optionally, through high-resolution transmission electron microscopy, the semiconductor nanocrystal group has a flat non-polar Crystal face.

[0013] According to a second aspect of the present disclosure, a method for preparing a semiconductor nanocrystal group is provided, the preparation method comprising:

[0014] A: mixing a first zinc precursor and a first fatty acid in a first container and heating them, reacting them at a first temperature to obtain a clear mixture, and then adding a reaction medium to the first container to obtain a first mixture; or mixing a first zinc precursor, a first fatty acid, and a reaction medium in a first container and heating them, reacting them at a first temperature to obtain a clear first mixture; or mixing a first zinc precursor, a first fatty acid, and a reaction medium in a first container and heating them, reacting the first mixture at a first temperature to obtain a clear mixture, and then adding the reaction medium to obtain a first mixture;

[0015] B: raising the first temperature to a second temperature or reacting at the first temperature for a first time, and then adding trialkylphosphine to the first container for a second time; after the reaction, a product system containing fatty acid zinc is obtained, wherein the fatty acid zinc is used as a ligand for subsequent reactions;

[0016] C: mixing a first cation precursor, a trialkylphosphine, the reaction medium and a second fatty acid and heating them to react to obtain a second mixture, wherein the molar ratio of the fatty acid zinc in B to the cation in the first cation precursor is greater than or equal to 5; and the first cation precursor includes cadmium;

[0017] D: preparing a third mixture containing an anion precursor, a trialkylphosphine and the above reaction medium; the above anion precursor includes selenium;

[0018] E1: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, to obtain a product system containing a first semiconductor nanocrystal group; or

[0019] E2: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, and adding the second mixture and the third mixture simultaneously for multiple times during the third time period to obtain a product system containing a first semiconductor nanocrystal group; or

[0020] E3: adding the second mixture and the third mixture into the first container simultaneously and in multiple times, reacting at a third temperature for a third time, to obtain a product system containing a first semiconductor nanocrystal group; or

[0021] E4: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, and then reacting at a fourth temperature for a fourth time, to obtain a product system containing a first semiconductor nanocrystal group;

[0022] Among them, the obtained product system includes a first semiconductor nanocrystal group accounting for more than 40% in number, and the first semiconductor nanocrystal group is a wurtzite single crystal; and the molar ratio of the cation of the first cationic precursor and the anion of the anionic precursor added to the first container is 0.9:1 to 4:1.

[0023] Optionally, the reaction medium is squalane, and the first zinc precursor is basic zinc carbonate, zinc oxide or fatty acid zinc with 2 to 22 carbon atoms; preferably, the molar concentration of zinc ions in the first mixture is 25 to 200 mmol / L; preferably, the molar concentration of cations in the second mixture is 2.5 to 10 mmol / L.

[0024] Optionally, the molar ratio of the trialkylphosphine added to the above B to the zinc element in the above first zinc precursor is 2:1 to 9:1. Preferably, the molar concentration of the trialkylphosphine in the above first mixture is 112 to 448 mmol / L.

[0025] Optionally, the first fatty acid includes a plurality of fatty acids with different carbon chain lengths or only one fatty acid; preferably, the first fatty acid includes capric acid and stearic acid; preferably, the second fatty acid is capric acid, dodecanoic acid or oleic acid.

[0026] Optionally, in the above B, the above first time is 0 to 4.5 hours; optionally, the above second time is 0 to 4.5 hours.

[0027] Optionally, the second temperature is greater than or equal to 310°C and less than or equal to 350°C.

[0028] Optionally, the third temperature is greater than 290°C.

[0029] Optionally, the above-mentioned E2 includes: injecting the above-mentioned second mixture and the above-mentioned third mixture into the above-mentioned first container in sequence, and when the crystal nuclei in the above-mentioned first container are formed, adding the above-mentioned second mixture and the above-mentioned third mixture into the above-mentioned first container in multiple times, respectively, and obtaining a product system containing the above-mentioned first semiconductor nanocrystal group after reacting for a certain period of time; preferably, in the above-mentioned E2~E4, the above-mentioned multiple additions are in the form of dropwise addition.

[0030] Optionally, the preparation method further comprises F: separating and purifying the first semiconductor nanocrystal group from any product system of E1 to E4.

[0031] Optionally, the preparation method further comprises F: separating and purifying a first semiconductor nanocrystal group from any product system of E1 to E4 as a seed crystal for a subsequent reaction, and removing the non-single-crystal wurtzite single crystal.

[0032] Optionally, the preparation method further includes G: preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, the reaction medium and a third fatty acid; preparing a sixth mixture containing the anion precursor, the trialkyl phosphine and the reaction medium; preparing a seventh mixture containing a second zinc precursor, a fourth fatty acid, a trialkyl phosphine and the reaction medium, wherein the seventh mixture reacts in a second container at a fifth temperature to obtain an eighth mixture containing fatty acid zinc; injecting the fourth mixture into the second container, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple times of adding are in a dropwise manner; heating the reaction at the fifth temperature for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

[0033] Optionally, the fifth temperature is greater than or equal to 270°C and less than or equal to 330°C; the fourth fatty acid includes one fatty acid or multiple fatty acids with different carbon chain lengths; preferably, the fourth fatty acid includes capric acid and oleic acid, or capric acid and erucic acid, or capric acid, oleic acid and erucic acid.

[0034] Optionally, the preparation method further comprises, when the average particle size of the first semiconductor nanocrystal group is greater than or equal to 5 nm, the average aspect ratio is greater than or equal to 1.4, and there is no excess cadmium in the first container; or when the average aspect ratio of the second semiconductor nanocrystal group is greater than or equal to 1.4, and there is no excess cadmium in the second container, annealing the first semiconductor nanocrystal group or the second semiconductor nanocrystal group at a sixth temperature for a sixth time, and the semiconductor nanocrystal group has a flat non-polar surface after the annealing treatment. Crystal face.

[0035] Optionally, the sixth temperature is greater than or equal to 330° C. and less than or equal to 350° C.; preferably, the sixth time is not less than 0.5 hours.

[0036] Optionally, the second semiconductor nanocrystal group is non-spherical in shape, and the preparation method further comprises H: spheroidizing the second semiconductor nanocrystal group.

[0037] Optionally, the above-mentioned H includes: after obtaining the above-mentioned second semiconductor nanocrystal group, adding a ninth mixture in situ into the above-mentioned second container, and performing annealing treatment at a sixth temperature for a sixth time, wherein the above-mentioned ninth mixture is obtained by mixing the above-mentioned second cation precursor, trialkylphosphine, the above-mentioned reaction medium and the fifth fatty acid and heating the mixture for reaction.

[0038] Optionally, the preparation method further includes G': preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, the reaction medium and a third fatty acid; preparing a sixth mixture containing the anion precursor, the trialkyl phosphine and the reaction medium; preparing a seventh mixture containing a second zinc precursor, a third cation precursor, a fourth fatty acid, a trialkyl phosphine and the reaction medium, adding the seventh mixture to a second container at a fifth temperature for reaction to obtain a seventh mixture containing fatty acid zinc and fatty acid cadmium; injecting the fourth mixture into a second container containing the seventh mixture, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple times of addition are in a dropwise manner; heating the reaction at the sixth temperature for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

[0039] Optionally, the molar ratio of the cadmium element in the seventh mixture to the zinc element in the seventh mixture is 0.1:1 to 0.25:1, and the shape of the second semiconductor nanocrystal group is spherical.

[0040] Optionally, the preparation method further includes G": preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing the second cation precursor, trialkyl phosphine, the reaction medium and the third fatty acid; preparing a sixth mixture containing the anion precursor, trialkyl phosphine and the reaction medium; a seventh mixture free of trialkyl phosphine obtained by reacting the second zinc precursor and the fourth fatty acid in the reaction medium, or a seventh mixture free of zinc obtained by reacting the trialkyl phosphine and the fourth fatty acid in the reaction medium, or a seventh mixture containing cadmium obtained by reacting the second zinc precursor, the third cation precursor, the trialkyl phosphine and the fourth fatty acid in the reaction medium; injecting the fourth mixture into a second container containing the seventh mixture, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple times of adding are in a dropwise manner; heating the reaction at a fifth temperature for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

[0041] Optionally, the molar concentration of the free first fatty acid remaining after the reaction of the first fatty acid and the first zinc precursor is 25-400 mmol / L, or the ratio of the amount of the free first fatty acid to the amount of the zinc element of the first zinc precursor is 2.5-10; BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings constituting part of the present application are used to provide a further understanding of the present disclosure. The exemplary embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure. In the drawings:

[0043] Figure 1 A transmission electron microscope (TEM) image of one embodiment of the present disclosure is shown, and the inset is a size distribution statistical graph.

[0044] Figure 2 The ultraviolet-visible absorption and fluorescence emission spectra of one embodiment of the present disclosure are shown.

[0045] Figure 3 A high resolution transmission electron microscopy (HRTEM) image of one embodiment of the present disclosure is shown.

[0046] Figure 4 An X-ray diffraction (XRD) pattern of one embodiment of the present disclosure and a theoretically simulated XRD pattern are shown.

[0047] Figure 5 An HRTEM image of branched nanocrystals according to one embodiment of the present disclosure is shown.

[0048] Figure 6 XRD patterns of two products of one embodiment of the present disclosure are shown.

[0049] Figure 7 The left and right figures show the TEM images corresponding to the products of the two embodiments of the present disclosure, Figure 7 The middle figure shows the effect of heating (preheating) time on the number ratio of spherical and branched nanocrystals.

[0050] Figure 8 The left figure shows the variation curve between heating time and peak area ratio; the right figure shows the XRD patterns of the products of two examples of the present disclosure.

[0051] Fig. 9 The XRD patterns of the products of some embodiments of the present disclosure are shown, and the inset is the corresponding HRTEM pattern.

[0052] Fig.10 TEM images of products obtained from the same seed crystal under different reaction conditions in some embodiments of the present disclosure are shown.

[0053] Fig.11 XRD patterns of products of some examples of the present disclosure are shown.

[0054] Fig.12 HRTEM images of the products of some examples of the present disclosure are shown.

[0055] Fig.13 TEM and HRTEM images of a product according to an embodiment of the present disclosure are shown.

[0056] Fig.14 TEM and HRTEM images of a product according to an embodiment of the present disclosure are shown.

[0057] Fig.15 TEM and HRTEM images of a product according to an embodiment of the present disclosure are shown.

[0058] Fig.16 TEM and HRTEM images of a product according to an embodiment of the present disclosure are shown.

[0059] Fig.17 TEM images of the products of some examples of the present disclosure are shown.

[0060] Fig.18 The UV-visible absorption and fluorescence emission spectra of the products of some embodiments of the present disclosure are shown, and the inset is a curve showing the change between the average diameter and the fluorescence half-maximum width (PL FWHM).

[0061] Fig.19 The UV-visible absorption and fluorescence emission spectra of the product of one embodiment of the present disclosure before and after separation are shown, and the inset is the corresponding TEM image.

[0062] Fig. 20 XRD patterns of products of some examples of the present disclosure are shown.

[0063] Fig.21 TEM and HRTEM images of a product before annealing according to an embodiment of the present disclosure are shown.

[0064] Fig. 22 XRD patterns of products of some examples of the present disclosure are shown. DETAILED DESCRIPTION

[0065] Various exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present disclosure.

[0066] The following description of at least one exemplary embodiment is in fact merely illustrative and is in no way intended to limit the present disclosure and its application or use. That is, the structures and methods herein are shown in an exemplary manner to illustrate different embodiments of the structures and methods in the present disclosure. However, those skilled in the art will appreciate that they merely illustrate exemplary ways of the present disclosure that can be implemented, rather than exhaustive ways. In addition, the drawings need not be drawn to scale, and some features may be enlarged to illustrate the details of specific components.

[0067] In addition, technologies, methods, and apparatus known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, such technologies, methods, and apparatus should be considered part of the authorization specification.

[0068] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0069] As used herein, the word "exemplary" means "serving as an example, instance, or illustration" rather than as a "model" to be exactly copied. Any implementation described as exemplary herein is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, the present disclosure is not to be limited by any expressed or implied theory given in the technical field, background, summary, or detailed description.

[0070] When the terms "about" or "substantially" are used in this specification with respect to a numerical value, it is intended that the relevant numerical value include a manufacturing or operating tolerance (eg, ±10%, ±5%) around the stated numerical value.

[0071] In addition, the terms "first", "second" and the like may also be used herein for reference purposes only, and thus are not intended to be limiting. For example, the terms "first", "second" and other such numerical terms referring to structures or elements do not imply a sequence or order unless the context clearly indicates otherwise.

[0072] It should also be understood that when the term “include / comprises” is used in this document, it indicates the presence of the specified features, integers, steps, operations, units and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, units and / or components and / or their combinations.

[0073] In this disclosure, the term "provide" is used in a broad sense to cover all ways of obtaining an object, and thus "providing an object" includes but is not limited to "purchasing", "preparing / manufacturing", "arranging / setting up", "installing / assembling", and / or "ordering" an object, etc.

[0074] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present disclosure. As used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0075] The "semiconductor nanocrystal" of the present application is sometimes abbreviated as "nanocrystal", and both have the same meaning. The "spherical" of the nanocrystal described in the present application is not a perfect sphere, which is the same as the general understanding of those skilled in the art. When the semiconductor nanocrystal particles have a spherical shape, the size of the semiconductor nanocrystal particles can be a diameter. The size of the semiconductor nanocrystal particles (or crystal seeds) can be measured by, for example, a transmission electron microscope (TEM).

[0076] Herein, "in situ" means within a container where the product system containing the semiconductor nanocrystals exists.

[0077] Similar to other types of colloidal II-VI and III-V semiconductor nanocrystals, CdSe can also be synthesized as stable zinc blende (fcc) or wurtzite (hcp) structures. The two structures have the same coordination number, atomic stacking factor, and very similar lattice bond energy (the difference between the two crystal structures is only 1.4 meV / unit for bulk CdSe), so obtaining single-crystalline nanocrystals of these two structures is the biggest challenge in the field of quantum dot synthesis. Although not true single crystals, the synthesis of monodisperse zinc blende CdSe nanocrystals with controllable lattice stacking fault type and single crystal plane structure has recently been reported, showing unusual optical properties, especially in the weakly confined size regime. Probably due to their electrical, optical, and optoelectronic properties in the visible light window, wurtzite CdSe nanocrystals have been the most sought-after in size and shape controlled synthesis, but their progress has lagged significantly behind that of the corresponding zinc blende nanocrystals. Fundamentally, lattice stacking faults occur randomly along the unique axis (c-axis) of wurtzite cadmium selenide nanocrystals, and this lattice defect seriously affects the crystal plane structure and optical performance of the nanocrystals.

[0078] Based on the above considerations, the first aspect of the present disclosure provides a semiconductor nanocrystal group, which is a spherical wurtzite single crystal. The semiconductor nanocrystal group includes cadmium and selenium, and more than 85% of the semiconductor nanocrystals in the semiconductor nanocrystal group have no lattice faults.

[0079] The thermal stability of II-VI semiconductor nanocrystal wurtzite structure is generally higher than that of sphalerite structure. The inventors creatively thought of using fatty acid zinc as ligands, taking advantage of the fact that the zinc-selenium bond is stronger than the cadmium-selenium bond, slightly weakening the strong control of the surface ligand on the nanocrystals, while ensuring the weak coordination of fatty acid zinc on the surface, stabilizing the size dispersion and morphology characteristics of the nanocrystals, and thus successfully producing monodisperse and high-quality single crystal wurtzite nanocrystals. The method for observing lattice stacking faults is high-resolution transmission electron microscopy.

[0080] The surface ligands of semiconductor nanocrystals are not limited, because ligand exchange can be carried out after the semiconductor nanocrystal group is prepared.

[0081] Replace various ligands.

[0082] In some preferred embodiments, more than 90% of the semiconductor nanocrystals in the semiconductor nanocrystal population have no lattice stacking faults, and more preferably, 100% have no lattice stacking faults.

[0083] In some embodiments, the surface ligands of the semiconductor nanocrystals include fatty acid zinc.

[0084] In some embodiments, the fatty acid zinc ligand is mainly coordinated to the non-polar crystal face of the wurtzite single crystal. In some embodiments, the dominant ligand of the wurtzite single crystal is fatty acid zinc, and the surface ligands also include fatty acid cadmium and fatty acid radicals. In some embodiments, a small amount of weakly coordinated TOP (directly coordinated to the surface or connected to the metal carboxylate) is also included.

[0085] In some embodiments, the fatty acid radical in the fatty acid zinc can be an alkyl carboxylic acid without a branched chain, such as acetic acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, stearic acid, oleic acid, eicosanoic acid, erucic acid, and octacosanoic acid.

[0086] In some embodiments, the number of C atoms in the fatty acid zinc is less than or equal to 18 and greater than or equal to 2. In some embodiments, the number of C atoms in the fatty acid zinc is 10-18.

[0087] In some embodiments, the fatty acid radical in the fatty acid zinc may be a branched alkyl carboxylic acid, thereby forming an entropic ligand.

[0088] In some embodiments, the fatty acid radical in the fatty acid zinc can be a dicarboxylic acid or polycarboxylic acid ligand, such as dodecenylsuccinic acid.

[0089] In some embodiments, the semiconductor nanocrystal is a core that is not coated with a shell. In some embodiments, the zinc element is only present on the surface of the crystal, that is, only in the ligand. In some embodiments, the mass ratio of the zinc element of the fatty acid zinc to all the metal elements in the semiconductor nanocrystal does not exceed 15%; in some embodiments, the zinc element does not exceed 2% after the fatty acid zinc ligand is replaced by other ligands. This mass ratio is related to the degree of purification. The higher the degree of purification, the lower the proportion.

[0090] In some embodiments, the semiconductor nanocrystal further comprises one or more of sulfur, zinc, and tellurium. In other embodiments, the semiconductor nanocrystal further comprises a doping element. In some embodiments, the semiconductor nanocrystal is a core-shell structure.

[0091] In some embodiments, the XRD test results of the semiconductor nanocrystal group are and The ratio of the peak areas is 0.38 to 0.44. and The ratio of the peak areas of represents the perfection of the wurtzite crystal form. Within this range, the higher the perfection of the wurtzite crystal form of the nanocrystal is. In some embodiments, the XRD test results of the semiconductor nanocrystal group are and The ratio of the peak areas is 0.4 to 0.44.

[0092] In some embodiments, the XRD test results of the semiconductor nanocrystal group are The 2theta peak position is 42.1±0.5 degrees (Cu target), and the Q value peak position (Q=4πsin(θ) / λ) is The semiconductor nanocrystal is a core that is not coated by a shell layer. The aforementioned peak position may change with the coating of the shell layer.

[0093] In some embodiments, the semiconductor nanocrystal is a wurtzite single crystal, and the size of the semiconductor nanocrystal can be extended along the c-axis, with an average aspect ratio of 0.8-40.

[0094] In some embodiments, the size of the semiconductor nanocrystal group can be extended along the c-axis. When the semiconductor nanocrystal group is a nanosphere or a near-nanosphere, the average aspect ratio of the semiconductor nanocrystal group is 0.8 to 1.6, and the average particle size is 3 to 20 nm. In some preferred embodiments, the semiconductor nanocrystal group is a nanosphere, and the deviation of its particle size distribution is less than or equal to 10%. In other embodiments, the average aspect ratio of the semiconductor nanocrystal group is 1.4 to 40, and the average particle size is 5 to 15 nm. At this time, the semiconductor nanocrystal group is in the shape of a nanorod or a nanowire, and the deviation of its particle size distribution is less than or equal to 30%.

[0095] The "particle size" mentioned in this application refers to the diameter of the nanocrystal or the average value of the length through the centroid (perpendicular to the c-axis direction). The "aspect ratio" mentioned in this application refers to the ratio of the longest length parallel to the c-axis to the diameter of the nanocrystal perpendicular to the c-axis or the average value of the length through the centroid. The average particle size of the semiconductor nanocrystal group is determined according to the type, optical properties and photoelectric properties of the semiconductor nanocrystal to be synthesized.

[0096] In some embodiments, when the semiconductor nanocrystal group is a nanosphere or a near-nanosphere or a nanorod or a nanowire, the fluorescence half-peak width of the semiconductor nanocrystal group is 19-38 nm. This fluorescence half-peak width provides a basis for the application of quantum dots in display.

[0097] In other embodiments, the semiconductor nanocrystal group has no lattice stacking faults at all. A nanocrystal group without lattice stacking faults can be synthesized by controlling the synthesis method, and specifically refer to the second aspect of the present disclosure.

[0098] In some embodiments, the semiconductor nanocrystal population is 31 P NMR test shows that there is basically no organic phosphine ligand. Weak organic phosphine ligands include trioctylphosphine (TOP), tributylphosphine (TBP), trioctylphosphine oxide (TOPO), etc. It is possible that these organic phosphine ligands are separated out during the preparation of semiconductor nanocrystals due to their weak coordination ability; strong organic phosphine ligands include octylphosphonic acid, diphenylphosphine, etc., and these organic phosphine ligands are very rare as impurities in the raw materials, so no similar signals appear.

[0099] In some embodiments, the shape of the semiconductor nanocrystal group is not particularly limited, and can be, for example, spherical, quasi-spherical, polyhedral, pyramidal, multi-footed, or cubic, nanorod, nanowire, or a combination thereof. In some preferred embodiments, the shape of the semiconductor nanocrystal is nanowire or nanorod or spherical.

[0100] In some embodiments, semiconductor nanocrystals have atomically flat nonpolar The surface is more conducive to the study of self-assembly and surface structure. Through high-resolution transmission electron microscopy, semiconductor nanocrystals have flat non-polar Crystal face.

[0101] In some embodiments, the size of the semiconductor nanocrystal group may be extended along the c-axis. When the morphology of the semiconductor nanocrystal group is near nanorods, nanorods or nanowires, the average aspect ratio of the semiconductor nanocrystal group is 1.4-18.

[0102] The present application provides a semiconductor nanocrystal composition, which comprises the above-mentioned semiconductor nanocrystal group and a semiconductor nanocrystal group having branches on the surface.

[0103] In some embodiments, the number of branched semiconductor nanocrystal groups accounts for less than or equal to 60%, or less than or equal to 50%, or less than or equal to 40%, or less than or equal to 30%, or less than or equal to 20%, or less than or equal to 10%.

[0104] In some embodiments, the XRD test results of the semiconductor nanocrystal composition are and In some preferred embodiments, the XRD test results of the semiconductor nanocrystal composition are as follows: and The ratio of the peak areas is 0.38 to 0.44.

[0105] From a synthetic point of view, the key difference between the two types of zinc blende and wurtzite CdSe nanocrystals may lie in their low-index crystal face structure, which originates from their lattice symmetry. In a symmetry-matched shape, a single-crystal zinc blende CdSe nanocube can form six identical {100} polar faces coordinated by the same surface ligands, that is, the same cadmium surface site is coordinated only with chelated fatty acid ligands. In contrast, wurtzite CdSe nanocrystals have a unique polar c-axis, and it is impossible to form nanocrystals with all equivalent low-index faces. For example, perpendicular to the c-axis, the (0001) and The wurtzite crystal plane is terminated by cadmium ions and selenium ions respectively. Parallel to the c-axis, and The wurtzite crystal faces of the series are all non-polar, but their atomic stacking patterns are different from each other. In order to accommodate these highly diverse crystal faces during nucleation and growth, the synthesis of wurtzite CdSe nanocrystals is usually carried out in a complex ligand system, which usually includes one (or more) components that cannot distinguish between the two crystal structures, resulting in the random formation of stacking faults in wurtzite CdSe nanocrystals. Specifically, fatty amines and cadmium phosphonates are considered to be necessary neutral ligands for the synthesis of wurtzite CdSe nanocrystals. Fatty amines, usually together with common cation precursors such as fatty acid cadmium, are very weak ligands for CdSe nanocrystals and can hardly compete with fatty acid cadmium (or fatty acid salt) ligands with similar concentrations, which may lead to the production of a mixture of zinc blende and wurtzite crystal forms during the nucleation stage. Although cadmium phosphonates, as strong ligands, are widely considered to be the best choice for the synthesis of wurtzite CdSe nanocrystals, they cannot prevent the formation of stacking faults, and their extremely low reactivity and inability to be replaced by other ligands hinder further purification, epitaxy and application.

[0106] Based on the above considerations, according to another aspect of the present application, a method for preparing a semiconductor nanocrystal group is provided, the preparation method comprising:

[0107] A: A first zinc precursor and a first fatty acid are mixed and heated in a first container, a clear mixture is obtained after reaction at a first temperature, and then a reaction medium is added to the first container to obtain a first mixture; or a first zinc precursor, a first fatty acid, and a reaction medium are mixed and heated in a first container, a clear first mixture is obtained after reaction at a first temperature; or a first zinc precursor, a first fatty acid, and a reaction medium are mixed and heated in a first container, a clear mixture is obtained after the first mixture reacts at a first temperature, and the reaction medium is added to obtain a first mixture.

[0108] The first temperature should be sufficient to allow the first zinc precursor and the first fatty acid to react and to obtain a clear and transparent solution at this temperature.

[0109] B: Raising the first temperature to a second temperature or reacting at the first temperature for a first time, and then adding trialkylphosphine into the first container to react for a second time; after the reaction, a product system containing fatty acid zinc is obtained, wherein the fatty acid zinc serves as a ligand for subsequent reactions.

[0110] During nucleation, the semiconductor nanocrystal group with a wurtzite structure is more afraid of free fatty acids than the semiconductor nanocrystal group with a zinc blende structure, and the residual first fatty acid will dissolve the small wurtzite nuclei, thereby greatly reducing the yield of the wurtzite nanocrystals. Maintaining the reaction mixture at the second temperature (greater than the first temperature) for the first time can slowly and controllably consume most of the excess first fatty acid while ensuring the complete dissolution of the first zinc precursor, thereby significantly improving the yield and relative yield of the wurtzite nanocrystal group.

[0111] In B, the addition of trialkylphosphine can effectively stabilize the fatty acid zinc and slow down the consumption of free free acid. Therefore, in the final stage of preparing the fatty acid zinc ligand, the addition of trialkylphosphine can prevent the uncontrolled decomposition of fatty acid zinc when the free fatty acid is less.

[0112] C: A first cation precursor, a trialkylphosphine, the reaction medium and a second fatty acid are mixed and heated to react to obtain a second mixture, wherein the molar ratio of the fatty acid zinc in B to the cation in the first cation precursor is greater than or equal to 5; and the first cation precursor includes a cadmium element.

[0113] In C, the prepared second mixture can maintain a transparent and clear state at room temperature, which is convenient for storage and use. At the same time, the molar ratio of zinc in the fatty acid zinc to the cation in the first cation precursor is greater than or equal to 5. The primary reason is that the fatty acid cadmium or carboxylate group prefers to coordinate to the {111} crystal face family of the sphalerite structure. Therefore, for when Cd 2+ concentration, especially the excess Cd that has not reacted with the anion precursors. 2+ When the concentration is high, more sphalerite structures will appear during nucleation, resulting in a relatively small number of components in single crystal wurtzite. At the same time, since the bond strength of cadmium-selenium is higher than that of zinc-selenium, more fatty acid zinc is needed to weaken the bond strength of Cd 2+ (such as fatty acid cadmium) has an effect on nucleation, so under preferred conditions, the molar concentration of fatty acid zinc is at least 5 times greater than that of fatty acid cadmium.

[0114] D: preparing a third mixture containing an anion precursor, a trialkylphosphine and the reaction medium; the anion precursor includes selenium;

[0115] The introduction of trialkylphosphine in the preparation of anion precursor improves the controllability and repeatability of nucleation at high temperature. It should be noted that there is no order requirement for the four steps A to D.

[0116] E1: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, to obtain a product system containing a first semiconductor nanocrystal group; or

[0117] E2: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, and adding the second mixture and the third mixture simultaneously in multiple times during the third time period to obtain a product system containing a first semiconductor nanocrystal group; or

[0118] E3: adding the second mixture and the third mixture into the first container simultaneously and in multiple times, reacting at a third temperature for a third time, to obtain a product system containing a first semiconductor nanocrystal group; or

[0119] E4: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, and then reacting at a fourth temperature for a fourth time, to obtain a product system containing a first semiconductor nanocrystal group;

[0120] The obtained product system includes a first semiconductor nanocrystal group accounting for more than 40% of the first semiconductor nanocrystal group, and the first semiconductor nanocrystal group is wurtzite; and the molar ratio of the cation of the first cation precursor to the anion of the anion precursor added to the first container is 0.9:1 to 4:1. The molar ratio of the cation (such as fatty acid cadmium) to the anion is not less than 0.9, because the anion will react with the fatty acid zinc in the first mixture to generate zinc selenide.

[0121] In E1 to E4, adding the second mixture at the third temperature first can prevent the third mixture from reacting with zinc in the first mixture in advance. After the third mixture is injected, the cadmium and selenium in the first container react immediately and form nuclei.

[0122] In E1, a nanocrystal group closest to the nucleation process can be obtained, with a size of 3nm. In order to obtain a nanocrystal group of a specific size, the second mixture and the third mixture can be injected or added (dripped) in equal molar amounts at the third temperature or cooled to the fourth temperature for multiple times to achieve the purpose of homogeneous epitaxy. E2 performs in-situ epitaxy on the basis of E1 to obtain a larger spherical or nearly spherical nanocrystal group.

[0123] In E3, the second mixture and the third mixture are directly added (dropped) in multiple times, which can effectively reduce the amount of nucleation, and the concentration of fatty acid zinc and the concentration of precursor relative to each nanocrystal group are greatly increased, thereby achieving the synthesis of nanorods.

[0124] In E4, less second mixture and third mixture are injected to reduce the amount of nucleation, and the temperature is lowered to the fourth temperature for homoepitaxial growth, which can also achieve the synthesis of nanorods.

[0125] At least 85%, 90%, or 100% of the first semiconductor nanocrystal group obtained above has no lattice stacking faults.

[0126] In some embodiments, the ratio of the amount of the free acid of the first fatty acid to the amount of the zinc element of the first zinc precursor is 2.5 to 10, or the molar concentration of the free first fatty acid remaining after the reaction of the first fatty acid and the first zinc precursor is 25 to 400 mmol / L. The concentration of the in situ prepared fatty acid zinc ligand in A is sufficiently high, usually greater than 10 times the first cation precursor (such as fatty acid cadmium) used in C below. The reduction of free fatty acids should itself be conducive to the nucleation of nanocrystals, thereby increasing the total yield of wurtzite nanocrystals, but in order to ensure that the first zinc precursor such as Zn 5 (CO 3 ) 2 (OH) 6 The decomposition of the thermal decomposition products formed in situ is thorough (when the free fatty acid is less, the fatty acid zinc is easily pyrolyzed to form zinc oxide at high temperature). The first fatty acid added in the in situ preparation of the fatty acid zinc in A needs to be excessive. In the case of an excess of the first fatty acid, the small zinc oxide nanoparticles can be easily redissolved into fatty acid zinc, and the free fatty acids are consumed.

[0127] In some embodiments, the reaction medium of each step is a non-coordinating solvent, such as squalane, liquid paraffin, trioctylamine, 1-18 selenium, vaseline, etc. When selecting the reaction medium, its boiling point and melting point are considered, and it needs to match the reaction conditions. In the above reaction, the reaction medium of each link is the same, which is conducive to the control of the reaction. In some embodiments, the reaction medium is squalane.

[0128] In some embodiments, the first zinc precursor in A is basic zinc carbonate, zinc oxide, or a fatty acid zinc with 2 to 22 carbon atoms. In some embodiments, the first zinc precursor can be zinc oxide or zinc acetate (if acetic acid is generated, an additional acetic acid removal operation is required). At the same time, the corresponding fatty acid zinc can also be directly used as the first zinc precursor while maintaining the same free acid concentration.

[0129] In some embodiments, the first cation precursor is a fatty acid cadmium with 10 to 18 carbon atoms, such as cadmium decanoate, cadmium dodecanoate, and cadmium oleate.

[0130] In some preferred embodiments, the molar concentration of zinc ions in the first mixture is 25 to 200 mmol / L. 2+ ) concentration is low, the product is prone to have obvious zinc blende structure and lattice faults, thereby reducing the yield of the first semiconductor nanocrystal group.

[0131] In some embodiments, the first fatty acid added to A is a saturated fatty acid, which can be an unbranched alkyl carboxylic acid, such as acetic acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, stearic acid, oleic acid, eicosanoic acid, erucic acid, and octacosanoic acid.

[0132] In some embodiments, considering the long preheating time (the sum of the first time and the second time), the first fatty acid is preferably a saturated fatty acid. It should be noted that short-chain fatty acid zinc will lead to the production of large-sized wurtzite nanocrystals in the nucleation stage, and long-chain fatty acids will make the process of preparing fatty acid zinc longer, so the first fatty acid can be reasonably selected according to actual needs.

[0133] In some embodiments, the first fatty acid includes a plurality of fatty acids of different carbon chain lengths or only one fatty acid.

[0134] In some embodiments, the first fatty acid comprises two fatty acids, thereby forming an entropic ligand. In some preferred embodiments, the first fatty acid comprises capric acid and stearic acid.

[0135] In some embodiments, the first fatty acid can be a branched alkyl carboxylic acid, thereby forming an entropic ligand.

[0136] In some embodiments, the first fatty acid can be a dicarboxylic acid or a polycarboxylic acid ligand, such as dodecenylsuccinic acid.

[0137] In some embodiments, the second fatty acid is decanoic acid or dodecanoic acid or oleic acid or a mixture thereof. The cation precursors such as cadmium decanoate, cadmium dodecanoate, cadmium oleate, etc. can be dispersed in a mixture of a reaction medium and trialkylphosphine at room temperature to obtain a transparent and clear solution, which is convenient for the introduction of the second mixture.

[0138] In some embodiments, the trialkyl phosphine is selected from TOP or TBP. In some embodiments, the phosphonic acid impurities in the trialkyl phosphine do not exceed 3%, and preferably, the other organic phosphine impurities in the trialkyl phosphine do not exceed 10%. In A to D, trialkyl phosphine is introduced. The prior art believes that various impurities in trialkyl phosphine, mainly including phosphine oxide, phosphine hydride, phosphonic acid and its decomposition products, will seriously affect the synthesis of spherical cadmium selenide nanocrystal groups. However, the inventors have experimentally confirmed that phosphine oxide and phosphine hydride have no observable adverse effects on the formation of wurtzite nanocrystal groups without stacking fault defects. Phosphonic acid is generally considered to be helpful in the formation of wurtzite nanocrystal groups, but it makes wurtzite single crystals less (the number of branched crystals increases), and at the same time induces stacking faults. The purity requirements of the above trialkyl phosphine can be appropriately reduced, reducing the cost of raw material procurement. When the raw materials are inspected at the warehouse, only the phosphonic acid impurities in the trialkyl phosphine can be paid attention to, reducing the inspection cost.

[0139] In some embodiments, the molar ratio of the trialkylphosphine added to B to the zinc element in the first zinc precursor is 2:1 to 9:1. When the trialkylphosphine is less, similar to the sphalerite cadmium selenide system, the sphalerite morphology will be obvious under TEM, and the XRD The peak area is relatively low; when there is too much trialkyl phosphine, it will combine with the coordinated fatty acid zinc and cause it to fall off the surface, which will cause the size distribution of the nanocrystal group to deteriorate significantly; at the same time, when there is more trialkyl phosphine, the concentration of organic phosphine impurities, especially octylphosphonic acid (OPA) in it will also increase, which will cause obvious stacking faults in the nanocrystal group under this system.

[0140] In some embodiments, in B, the molar concentration of trialkylphosphine in the first mixture is 112-448 mmol / L. Adding a sufficient amount of trialkylphosphine to the fatty acid zinc solution containing sufficient fatty acid can stabilize the system at the target reaction temperature. In some preferred embodiments, the concentration of trialkylphosphine is 50-250 mmol / L, which can obtain a stacking fault-free wurtzite nanocrystal population and significantly increase the proportion of the wurtzite nanocrystal population. Low trialkylphosphine, XRD spectrum The degree of perfection is reduced; without trialkylphosphine, wurtzite nanocrystals cannot be obtained. Excessive trialkylphosphine helps the detachment of surface fatty acid zinc ligands, which in turn weakens the effect of fatty acid zinc ligands in the nucleation process and cannot achieve growth without stacking faults (stack faults).

[0141] In some embodiments, in B, the first time is 0 to 4.5 hours; optionally, the second time is 0 to 4.5 hours. As the first time and the second time are extended, the content of the free first fatty acid is gradually reduced, and the output and relative yield of the wurtzite semiconductor nanocrystal group product are gradually increased. In some preferred embodiments, the first time is 3.5 hours and the second time is 1 hour.

[0142] If preheating is not performed (i.e., the first time and the second time are both 0), the concentration of the semiconductor nanocrystal group generated in E is relatively low. At this time, increasing the concentration of fatty acid zinc can make the fatty acid zinc more effectively coordinated on the non-polar surface of the semiconductor nanocrystal group, especially the non-polar Crystal plane, so that the semiconductor nanocrystal group is significantly elongated along the c-axis, and the synthesis of nanorods or even nanowires is achieved. Nanorods can also be synthesized by adding (such as dripping) the precursor for nucleation in multiple times instead of injecting the precursor for nucleation, because when the precursor is added in multiple times, the cadmium precursor and selenium precursor involved in the nucleation are relatively small. By reducing the amount of semiconductor nanocrystal group nucleation, the concentration of fatty acid zinc distributed to the surface of each semiconductor nanocrystal group can be significantly increased.

[0143] In some preferred embodiments, in C, the molar concentration of the cations in the second mixture is 2.5-10 mmol / L. When the concentration of anions in the third mixture is kept constant, it is found that as the concentration of Cd in the second mixture increases, 2+ As the molar concentration of (such as fatty acid cadmium) gradually increases, the XRD patterns of the products At the same time, more spherical nanocrystals have a sphalerite structure and obvious stacking faults. In the XRD diagram, the diffraction peaks of the wurtzite cadmium selenide nanocrystals are becoming less and less significant. Even if the molar concentrations of anions and cations in the second and third mixtures are kept equal and the molar concentrations of both are increased, the XRD patterns of the products are The ratio will also decrease, because all fatty acid cadmium cannot be consumed instantly during nucleation, resulting in an increase in the number of branched nanocrystals with sphalerite as the core.

[0144] In some embodiments, in C, the molar concentration of the second fatty acid in the second mixture is four times the molar concentration of the cation, and the molar concentration of the trialkylphosphine is twice the molar concentration of the cation.

[0145] In some embodiments, during nucleation, the molar ratio of cadmium in the second mixture to selenium in the third mixture is 0.9:1 to 4:1.

[0146] In some embodiments, in D, the second temperature is greater than or equal to 310°C and less than or equal to 350°C, and preferably the second temperature is equal to 330°C.

[0147] In some embodiments, the second temperature is equal to the third temperature. In some embodiments, the fourth temperature is greater than or equal to 270°C and less than or equal to 330°C.

[0148] In some embodiments, in E4, after reacting at the third temperature for the third time (nucleation), the temperature can be lowered to the fourth temperature to achieve low-temperature growth. The growth process has a low temperature requirement, and the product is a nanorod. It is speculated that the low temperature enhances the protection of the surface fatty acid zinc for the crystal surface on the non-polar side, thus making it easier for the semiconductor nanocrystal group to grow along the c-axis.

[0149] In E, the reaction temperature (third temperature) should be selected at a temperature where the output of wurtzite nanocrystals accounts for a high proportion, and the reactivity of the reactants should be considered. Insufficient reactivity can easily cause self-nucleation in the subsequent homoepitaxial growth stage, affecting the monodispersity of the crystals in the product. In some embodiments, the third temperature is greater than 290°C, preferably greater than or equal to 310°C and less than or equal to 350°C.

[0150] In some embodiments, E2 includes: injecting the second mixture and the third mixture into the first container in sequence, and when the crystal nuclei in the first container are formed, adding the second mixture and the third mixture into the first container in multiple times, and obtaining a product system containing a first semiconductor nanocrystal group after a certain reaction time.

[0151] The third time can be determined according to the desired fluorescence peak position. In some embodiments, in E2 to E4, the method of adding in multiple times is dropwise addition, which can be constant-speed dropwise addition. The dropwise addition rate of cadmium and / or selenium can be 0.5 to 3 mmol / h. The dropwise addition rates of cadmium and selenium can be different, such as cadmium is less than the dropwise addition rate of selenium, but the amount of substance added per unit time is the same for both. The above-mentioned dropwise addition rate is mainly referred to the preparation of the embodiment of the present application. If the production is scaled up, it needs to be increased in proportion.

[0152] In some embodiments, when the second mixture and the third mixture are injected or added into the container in multiple times, the amount of cadmium added to the second mixture is the same as the amount of selenium added to the third mixture in a single time or in the same unit time.

[0153] In some embodiments, the average particle size of the first semiconductor nanocrystal group is 5-15 nm. In some embodiments, the first semiconductor nanocrystal group is a nanosphere or a near-nanosphere or a near-nanorod or a nanorod or a nanowire.

[0154] In some embodiments, the preparation method further includes F: separating and purifying the first semiconductor nanocrystal group from any product system of E1 to E4.

[0155] In other embodiments, the product system containing the first semiconductor nanocrystal group includes more than 50%, 60%, 65%, 70%, 75%, 80%, 85% or 90% of single crystal wurtzite crystal group type crystals.

[0156] In other embodiments, the product system containing the first semiconductor nanocrystal group includes more than 80% of single crystal wurtzite crystal group type crystals.

[0157] In other embodiments, the preparation method further includes F: separating and purifying a first semiconductor nanocrystal group from any product system of E1 to E4 as a crystal group seed for subsequent reactions, and removing non-single crystal wurtzite crystals.

[0158] In some embodiments, the non-single crystal wurtzite crystal group type crystal has a sphalerite core and a wurtzite arm. Since the sizes and shapes of the two nanocrystal groups are very different, the precipitate where the branched nanocrystal group is located and the supernatant where the spherical nanocrystal group is located are easily separated. The non-wurtzite crystal group type crystal does not emit light.

[0159] The fifth time is determined according to the desired fluorescence peak position. In some embodiments, after obtaining the second semiconductor nanocrystal group, other precursors can be added to the first container to perform shell coating.

[0160] In other embodiments, after F, the preparation method further includes G: preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, the reaction medium and a third fatty acid; preparing a sixth mixture containing the anion precursor, a trialkyl phosphine and the reaction medium; preparing a seventh mixture containing a second zinc precursor, a fourth fatty acid, a trialkyl phosphine and the reaction medium, wherein the seventh mixture reacts in a second container at a fifth temperature to obtain an eighth mixture containing fatty acid zinc; injecting the fourth mixture into the second container, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple additions are in the form of drops; heating the reaction at the fifth temperature for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

[0161] In some embodiments, the third fatty acid is capric acid, dodecanoic acid, oleic acid, erucic acid, or a mixture thereof in different proportions. Thus, the second cation precursor of decanate can be dispersed in a mixture of a reaction medium and a trialkylphosphine at room temperature to obtain a transparent and clear solution.

[0162] In some embodiments, optionally, the molar concentration of the second fatty acid in the fifth mixture is four times the cation concentration, and the concentration of the trialkylphosphine is twice the cation concentration.

[0163] In some other embodiments, in G, the fifth temperature is greater than or equal to 270°C and less than or equal to 330°C.

[0164] In some embodiments, in G, the fourth fatty acid comprises one fatty acid or a plurality of fatty acids of different carbon chain lengths. In some preferred embodiments, the fourth fatty acid comprises capric acid and oleic acid, or capric acid and erucic acid, or capric acid, oleic acid and erucic acid.

[0165] In some embodiments, in G, in the eighth mixture, the molar concentration of the zinc ions is 50-100 mM.

[0166] In some embodiments, in G, in the eighth mixture, the molar concentration of the trialkylphosphine is 224 mM.

[0167] In some embodiments, the preparation method further comprises annealing the first or second semiconductor nanocrystal group. Since nanocrystals tend to grow dynamically at a faster dripping rate or a lower temperature, the modification of certain crystal faces by the ligand is not perfect, which results in the nanocrystals not having a thermally stable flat crystal face. After annealing, the presence of a large amount of fatty acid zinc promotes the intramolecular ripening of the nanocrystals, forming a flat non-polar surface that is conducive to the coordination of fatty acid zinc. Nanorods with uniform size distribution and atomically flat crystal surfaces are beneficial to the study of surface ligands and are also more conducive to the directional self-assembly of nanocrystals.

[0168] In some embodiments, after E (E1-E4), the preparation method further comprises, when the average particle size of the first semiconductor nanocrystal group is greater than or equal to 5nm, the average aspect ratio is greater than or equal to 1.4, and there is no excess cadmium element in the first container, annealing the first semiconductor nanocrystal group at a sixth temperature for a sixth time, wherein the semiconductor nanocrystal group has a flat non-polar surface after the annealing treatment. Crystal face.

[0169] In some embodiments, after G, the preparation method further comprises, when the average aspect ratio of the second semiconductor nanocrystal group is greater than or equal to 1.4 and there is no excess cadmium element in the second container, treating the second semiconductor nanocrystal group at a sixth temperature

[0170] The semiconductor nanocrystal group has a flat non-polar surface after the annealing treatment. Crystal face.

[0171] In some embodiments, the sixth temperature is greater than or equal to 330° C. and less than or equal to 350° C. In some embodiments, the sixth time is not less than 0.5 hours.

[0172] In some embodiments, after F, the preparation method also includes G': preparing a fourth mixture containing a first semiconductor nanocrystal group and a reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, a reaction medium and a second fatty acid; preparing a sixth mixture containing an anion precursor, a trialkyl phosphine and a reaction medium; preparing a seventh mixture containing a second zinc precursor, a third cation precursor, a fourth fatty acid, a trialkyl phosphine and the reaction medium, wherein the seventh mixture is added to a second container for reaction at a fifth temperature to obtain a seventh mixture containing fatty acid zinc and fatty acid cadmium; injecting the fourth mixture into a second container containing the seventh mixture, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably adding them in multiple times in a dropwise manner; at a sixth temperature, heating the reaction for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

[0173] In some embodiments, in G', the molar dropping rates of the fifth mixture and the sixth mixture are the same, such as 0.02 mmol / h.

[0174] In some embodiments, in G', the sixth temperature is greater than or equal to 330°C and less than or equal to 350°C.

[0175] In some embodiments, in G′, the molar ratio of the cadmium element in the second container to the zinc element in the second container is 0.1:1 to 0.25:1, and the shape of the second semiconductor nanocrystal group is spherical.

[0176] In some embodiments, the second cation precursor is a fatty acid cadmium with 10 to 18 carbon atoms, such as cadmium decanoate, cadmium dodecanoate, and cadmium oleate.

[0177] In some embodiments, the third cation precursor is a fatty acid cadmium with 2 to 18 carbon atoms, such as cadmium acetate, cadmium decanoate, cadmium dodecanoate, cadmium oleate; or cadmium oxide.

[0178] In some embodiments, after F, the preparation method further includes G": preparing a fourth mixture containing a first semiconductor nanocrystal group and a reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, a reaction medium and a second fatty acid; preparing a sixth mixture containing an anion precursor, a trialkyl phosphine and a reaction medium; a seventh mixture free of trialkyl phosphine obtained by reacting a second zinc precursor and a third fatty acid in a reaction medium, or a seventh mixture free of zinc obtained by reacting a trialkyl phosphine and a third fatty acid in a reaction medium; injecting the fourth mixture into a second container containing the seventh mixture, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably in multiple times in a dropwise manner; heating the reaction at a fifth temperature for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group. In the growth stage, trialkyl phosphine, fatty acid zinc, and trace amounts of cadmium (with a molar ratio of less than or equal to 0.25:1 to zinc) have no effect or little effect on the crystallinity of the semiconductor nanocrystal group, so there are multiple ways (without adding these substances) to perform homoepitaxial growth.

[0179] In some embodiments, in G", the molar dropping rates of the fifth mixture and the sixth mixture are the same, such as 0.02-0.1 mmol / h.

[0180] In some embodiments, in G", the fifth temperature is greater than or equal to 270°C and less than or equal to 330°C.

[0181] In some embodiments, in G", in the fifth mixture, optionally, the molar concentration of the cation is 0.04-0.1 mmol / L.

[0182] In some embodiments, in G", in the sixth mixture, the molar concentration of anions is equal to the molar concentration of cations in the fifth mixture, or the amount of anions added to the sixth mixture is ensured to be the same as the amount of cations added to the fifth mixture.

[0183] In some embodiments, in F, G, G', G", the fatty acid carbon chain length of the fourth fatty acid is 10 to 28. In some embodiments, the fourth fatty acid is one or more of capric acid, dodecanoic acid, tetradecanoic acid, stearic acid, oleic acid, behenic acid, erucic acid, and octacosanoic acid. In some embodiments, the fourth fatty acid includes one fatty acid or multiple fatty acids with different carbon chain lengths. In some embodiments, the fourth fatty acid includes capric acid and oleic acid.

[0184] In some embodiments, the second zinc precursor is basic zinc carbonate, zinc oxide, or a fatty acid zinc with 2 to 18 C. In some embodiments, the first zinc precursor can be zinc oxide or zinc acetate (if acetic acid is produced, an additional acetic acid removal operation is required), and while maintaining the same free acid concentration, the corresponding fatty acid zinc can also be directly used as the second zinc precursor.

[0185] In G, G', G", the separated single crystal wurtzite first semiconductor nanocrystal group is used for homoepitaxial growth, and the constrained conditions, such as the concentration of fatty acid zinc, the concentration of fatty acid cadmium, the concentration of trialkyl phosphine, temperature, the concentration of free fatty acid, etc., only have a significant effect on the nucleation process, and have little effect on the homoepitaxial growth process. When the separated single crystal wurtzite semiconductor nanocrystal group is grown under the above extreme conditions, the crystallinity will not be significantly deteriorated.

[0186] In some embodiments, the surface of the first or second semiconductor nanocrystal population obtained by separation and purification or without separation and purification is subjected to ligand exchange treatment. In some embodiments, the ligand exchange treatment is performed using oleic acid.

[0187] In some embodiments, the second semiconductor nanocrystal group is non-spherical in shape, and the preparation method further includes H: spheroidizing the second semiconductor nanocrystal group. The spheroidizing treatment is beneficial to the non-directional self-assembly of the nanocrystal group and the theoretical study of its optical properties.

[0188] In some embodiments, H comprises: after obtaining the second semiconductor nanocrystal group, adding a ninth mixture in situ in the second container, and performing annealing treatment at a sixth temperature for a sixth time, wherein the ninth mixture is obtained by mixing a third cation precursor, a trialkylphosphine, the reaction medium and a fifth fatty acid and heating the mixture for reaction. The ninth mixture may be the same as or slightly different from the second mixture, and its preparation raw materials may refer to the second mixture described above. Spheroidization may be achieved by adding cadmium elements and annealing in the reaction system.

[0189] In some embodiments, the molar ratio of the cadmium element in the ninth mixture added to the zinc element in the second container before the ninth mixture is added is 0.1:1 to 0.25:1. The second semiconductor nanocrystal group is spherical (or nanosphere).

[0190] After obtaining the second semiconductor nanocrystal group, if the product system containing the second semiconductor nanocrystal group has been cooled to ambient temperature, the ninth mixture is added to the second container and then the temperature is raised again for annealing. If the product system containing the second semiconductor nanocrystal group has not been cooled to ambient temperature, the reaction temperature is adjusted from the fifth temperature to the sixth temperature.

[0191] In some embodiments, the sixth temperature for spheroidization is greater than or equal to 330° C. and less than or equal to 350° C. In some preferred embodiments, in order to obtain a good spheroidization effect, the sixth time is not less than 0.5 hours.

[0192] In some embodiments, the method further includes exchanging ligands on the first semiconductor nanocrystal population or the second semiconductor nanocrystal population, such as replacing fatty acid zinc ligands.

[0193] Hereinafter, the embodiments are described in more detail with reference to specific examples. However, they are illustrative examples of the present disclosure, and the present disclosure is not limited thereto.

[0194] Chemicals. Trioctylphosphine (TOP, 97%) was purchased from Strem. Basic zinc carbonate (Zn 5 (CO 3 ) 2 (OH) 6 , 97%) was purchased from Thermo Fisher Scientific. Cadmium nitrate tetrahydrate (98%), selenium powder (Se, 200 mesh, 99.999%), oleic acid (HO1, 90%), myristic acid (HMy, 98%), lauric acid (HLa, 98%), capric acid (HDe, 99.9%), octylamine (99%), oleylamine (70%), tri-n-octylphosphine oxide (TOPO, 90%) were purchased from Sigma-Aldrich. Squalane (95%) and stearic acid (HSt, 99%) were purchased from TCI. Cadmium oxide (CdO, 99.99%), tetramethylammonium hydroxide (10wt.%, methanol) and diphenylphosphine (DPP, 93%), octylphosphonic acid (OPA, 98%) were purchased from Aladdin. All organic solvents were purchased from Sinopharm Reagent Company. All chemicals were used directly without further purification. In addition, FA in the abbreviation refers to various types of fatty acids or fatty acid salts.

[0195] Cadmium decanoate (CdDe 2) was synthesized. The synthesis process was modified according to the literature. Cadmium nitrate tetrahydrate (4 mmol) was dissolved in methanol (10 mL) in a 20 mL centrifuge tube. Decanoic acid (8 mmol) and tetramethylammonium hydroxide (7.6 mmol) were dissolved in 20 mL methanol in a 50 mL centrifuge tube. The former solution was quickly added to the latter solution, and the mixture was stirred vigorously. The appearance of a white precipitate indicated the formation of CdDe 2 , the mixture was refrigerated at 0 °C for 30 min to obtain more product. The precipitate was washed at least four times with 25 mL of methanol and once with 20 mL of n-hexane, and then dried in vacuum at room temperature overnight.

[0196] Prepare Cd precursor solution. Add CdDe into squalane (1.8740 g, 2.3 mL). 2 Powder (0.3184 g, 0.7 mmol), HDe (0.4823 g, 2.8 mmol) and TOP (0.5188 g, 1.4 mmol) were used to prepare 0.2 M CdDe 2 The mixture was stirred at 95°C to obtain a clear solution. 0.04M CdDe 2 The preparation process of the solution is similar to this, except that the composition of the precursor solution is changed, namely CdDe 2 (0.1820 g, 0.4 mmol), HDe (0.0689 g, 0.4 mmol), HO1 (0.3390 g, 1.2 mmol), TOP (0.2966 g, 0.8 mmol) and squalane (7.4410 g, 9.2 mL).

[0197] Preparation of Se precursor solution. Se powder (0.0790 g, 1 mol) was added to TOP (0.8314 g, 1 mL) to prepare 0.5 M TOPSe solution. It was then ultrasonicated to make a transparent solution, and then squalane (0.8044 g, 1 mL) was added to the mixture. A 0.04 M TOPSe solution was prepared using Se powder (0.0316 g, 0.4 mmol), TOP (0.3326 g, 0.4 mL) and squalane (7.7799 g, 9.6 mL) according to similar procedures.

[0198] Example 1: Zn 5 (CO 3 ) 2 (OH) 6(0.2mmol), HDe (1.8mmol), HSt (1.8mmol) and 8mL squalane were placed in a 50mL three-necked flask. After stirring and bubbling argon for 10 minutes, the mixture was heated to 250°C to obtain a colorless solution, and then 10mL squalane was injected into the hot solution. After heating to 330°C and maintaining for 3.5 hours, 2mL TOP was injected. After maintaining at 330°C for another hour, the pre-prepared 0.2M CdDe 2 The solution (0.25 mL, 0.05 mmol) and 0.5 M TOPSe solution (0.1 mL, 0.05 mmol) were then rapidly injected into the reaction solution. After rapid nucleation for 1 minute, 0.2 M CdDe 2 The solution and 0.5MTOPSe solution were added to the reaction bottle at a rate of 15.00mL / h and 6.00mL / h, respectively. The reaction was stopped when the CdSe nanocrystals reached the specified PL peak or size. Generally, the PL peak was about 620nm 5 minutes after the addition of the growth solution and about 655nm after 10 minutes. Take an equal amount of sample (about 0.2mL) and dissolve it in toluene for UV-vis, PL and TEM analysis to monitor the reaction. After the reaction, the mixture was cooled to room temperature.

[0199] In other embodiments, the preheating time, the amount of basic zinc carbonate, TOP, cadmium precursor solution and selenium precursor solution, and the temperature are changed accordingly. For specific changes, see Table 1. " / " represents the same as Example 1 and is not listed again. In order to compare the differences between products under different conditions, unless otherwise specified, the PL peak of the product under all conditions is 655±2nm.

[0200] Table 1

[0201]

[0202]

[0203]

[0204] In Examples 12-17, 23-26, 31-32, 34-40, and 44-45, after the second mixture and the third mixture were injected, no dripping was continued, but the reaction was stopped after 5 minutes of in-situ reaction, so the PL peak value was not necessarily 655 nm.

[0205] Example 46, the difference from Example 1 is that no preheating is performed and 0.2M CdDe is used at the start of the reaction. 2 The solution and 0.5MTOPSe solution were not injected but directly dripped at a rate of 15.00mL / h and 6.00mL / h, respectively.

[0206] Example 47, the difference from Example 1 is that the injected 0.2M CdDe 2 The molar amount of the solution and the 0.5M TOPSe solution were reduced to 20% respectively, and the temperature was quickly lowered to 270°C after injection. After rapid nucleation for 1 minute, 0.2M CdDe 2 The solution and 0.5 M TOPSe solution were added dropwise into the reaction flask at a rate of 15.00 mL / h and 6.00 mL / h, respectively.

[0207] Example 48, the difference from Example 1 is that the injected 0.2M CdDe 2 The molar amount of the solution and the 0.5M TOPSe solution were reduced to 30% respectively, and the temperature was quickly lowered to 270°C after injection. After rapid nucleation for 1 minute, 0.2M CdDe 2 The solution and 0.5 M TOPSe solution were added dropwise into the reaction flask at a rate of 15.00 mL / h and 6.00 mL / h, respectively.

[0208] Example 49 differs from Example 1 in that the injected TOP is doped with 1.5 mol % of octylphosphonic acid OPA.

[0209] Example 50 differs from Example 1 in that the injected TOP is doped with 1.5 mol % of diphenylphosphine DPP.

[0210] Example 51 is different from Example 1 in that the injected TOP is doped with 3 mol % of trioctylphosphine oxide TOPO.

[0211] Separation of two groups of nanocrystals. When the synthetic product is cooled to 100°C, 2 mL of octylamine is injected into the reaction solution. The solution is naturally cooled to room temperature and evenly divided into two 50 mL centrifuge tubes. A certain proportion of ethyl acetate, acetone, ethanol and other extractants (precipitants) are added to each centrifuge tube to precipitate the nanocrystals from the original solution. The purified precipitate is dispersed in 1.5 mL of toluene, 0.5 mL of octylamine and 2 mL of methanol, heated at 80°C for 3 minutes, and then the turbid liquid is centrifuged at 4000 rpm for 15 seconds, and the supernatant (which may contain white floccules) is quickly removed while hot. Repeat the above thermal purification operation until there is no white floccules or white precipitates in the supernatant after cooling. Disperse the precipitate in 3 mL of toluene at room temperature, and add 50 μL of oleylamine to disperse the nanocrystals. Continue to drip acetonitrile into the solution until the solution becomes turbid. The mixture was centrifuged at 12000rpm for 7 minutes to separate the nanocrystals into two morphologies, namely spherical nanocrystals in the supernatant and branched nanocrystals in the precipitate. The supernatant was collected with a syringe and detected with UV-visible light. If there is still an absorption tail on the low-energy side, the precipitation is repeated and separated with acetonitrile. To remove large-sized branched nanocrystals. In order to serve as a seed for synthesizing weakly confined wurtzite cadmium selenide nanocrystals, the precipitate is separated from the toluene solution using acetonitrile as a precipitation reagent, and the spherical nanocrystals are dispersed in squalane. Typically, 8.0nm spherical wurtzite cadmium selenide nanocrystal seeds are dispersed in 4.5mL of squalane to obtain a reddish-brown solution with an absorbance of about 120 at 350nm.

[0212] Seeded homoepitaxial growth of wurtzite cadmium selenide nanocrystals.

[0213] Example 52: Zn 5 (CO 3 ) 2 (OH) 6 (0.05mmol), HDe (0.5mmol), HO1 (0.5mmol) and 4.3mL of squalane were placed in a 25mL three-necked flask. After stirring and bubbling argon for 10 minutes, the mixture was heated to 250°C to obtain a colorless solution, and then 0.5mL of TOP was injected into the hot solution. It was heated to 330°C again, and the squalane solution containing seeds (usually 0.2mL was taken from 4.5mL of seed solution) was quickly injected into the reaction solution. 0.04M TOPSe solution and 0.04M CdDe 2 The solution was added to the reaction bottle by two injection pumps at the same speed, and the addition speed was 1.00 mL / h. When the CdSe nanocrystals reached the specified PL peak or size, the reaction stopped.

[0214] Example 53: The difference from Example 50 is that the growth reaction temperature is 270°C.

[0215] Example 54: The difference from Example 50 is that the reaction base liquid raw material is Zn 5 (CO 3 ) 2 (OH) 6 (0.05 mmol), CdO (0.05 mmol), HDe (0.55 mmol), HO1 (0.55 mmol) and 4.3 mL of squalane.

[0216] Example 55: The difference from Example 50 is that the raw materials of the reaction base liquid are HDe (0.25 mmol), HO1 (0.25 mmol) and 4.3 mL of squalane.

[0217] Example 56: The difference from Example 50 is that 0.5 mL TOP is not injected.

[0218] Example 57: The difference from Example 50 is that 0.04M TOPSe solution and 0.04M CdDe 2 The solution was added to the reaction bottle by two injection pumps at the same speed, and the addition speed was 0.50 mL / h.

[0219] Example 58: The difference from Example 55 is that after reaching the specified peak position or size, 200 μL of pre-made 0.2M CdDe 2 The solution was then annealed at 330°C for 60 minutes, and then the reaction was stopped.

[0220] Example 59: The difference from Example 55 is that the raw material of the reaction base liquid is Zn 5 (CO 3 ) 2 (OH) 6 (0.05 mmol), CdO (0.05 mmol), HDe (0.55 mmol), HO1 (0.55 mmol) and 4.3 mL of squalane.

[0221] Example 60: The difference from Example 50 is that 0.04M TOPSe solution and 0.04M CdDe 2 The solutions were added into the reaction bottle by two injection pumps at the same speed, which was 2.00 mL / h. The growth reaction temperature was 270°C.

[0222] Example 61: The difference from Example 58 is that after reaching the specified peak position or size, the temperature is raised to 330°C and maintained for 60 minutes for annealing treatment, and then the reaction is stopped.

[0223] Measurements and characterization. PL spectra were recorded by an Agilent Cary Eclipse G9800A spectrophotometer. UV-Vis spectra were recorded by an Agilent Cary 4000 UV-Vis spectrophotometer. PL excitation spectra were measured by an EdinburghInstruments FLS920 spectrometer. TEM images of nanocrystals deposited on copper grids with ultrathin carbon films were obtained on a Hitachi 700 transmission electron microscope at 100 kV. The diameters of spherical nanocrystals of all sizes were calculated from the projected area of ​​the TEM images. High-resolution TEM images were taken on a JEM 2100F transmission electron microscope at 200 kV. XRD measurements of nanocrystal powders uniformly placed on single-crystalline silicon wafers were performed on a Rigaku Ultimate-IV X-ray diffractometer under the measurement conditions of 40 kV / 30 mA and Cu Kα line. Some of these data were acquired on a Bruker D8 Advance X-ray diffractometer for more precise testing and repeatability verification.

[0224] Simulated XRD patterns. The XRD patterns were simulated based on the structure constructed using Python 3.12. Thermal effects were incorporated into the structure by randomly shifting cadmium (Cd) and selenium (Se) atoms from their equilibrium positions, as suggested by the literature. This displacement was calculated using a standard deviation of The function of scattering intensity is calculated as follows:

[0225]

[0226] The function of the scattering intensity is related to the scattering parameter (S, S = 2sin(θ) / λ). 0 ,f(S),r k and p(r k ) represent the incident light intensity, scattering influence factor, interatomic distance and the number of occurrences of the specific interatomic distance rk respectively.

[0227] The product result information of each example is shown in Table 2. Missing data are marked with "NA", and data that cannot be counted due to small morphological differences are marked with "x".

[0228] Table 2

[0229]

[0230]

[0231]

[0232]

[0233] The various optical characterizations of the product obtained in Example 1 (average particle size of about 8.0±0.6 nm) are shown in Figures 1 to 4 , Figure 1 It can be seen that 98% of the crystals are single crystal wurtzite-type spherical cadmium selenide nanocrystals, and 2% of the crystals are non-single crystal wurtzite-type branched cadmium selenide nanocrystals. The average particle size deviation of 98% of the single crystal wurtzite-type cadmium selenide nanocrystals is 7%. Figure 2 From the UV-visible spectrum and fluorescence emission spectroscopy, it can be seen that the product has a narrow fluorescence half-width (64meV) and a fluorescence peak at 655nm. Figure 3 The left and right sides show the

[0001] crystal direction and The high-resolution TEM image of the crystal direction is confirmed to be a spherical morphology from two mutually perpendicular directions, and No obvious stacking faults were observed in the crystal direction. Spherical nanocrystals can be separated from branched nanocrystals by simple separation operations. Figure 4 The XRD pattern of the spherical wurtzite-type cadmium selenide nanocrystals (supernatant) separated from the product is shown, and it can be seen that the diffraction patterns of the spherical wurtzite-type cadmium selenide nanocrystals and the simulated cadmium selenide wurtzite crystals without any stacking faults are different. Figure 10 According to the literature, if a portion of the unit cells have stacking faults, then the experimental results of the unit cells within a given size range will deviate greatly from the calculated results without stacking faults. Most of the deviations can be explained by the wurtzite lattice. and The calculated XRD pattern of perfect wurtzite nanocrystals with a size of 8.0 nm is well consistent with the experimental results, so it can be considered that the spherical nanocrystals from the supernatant are single crystal wurtzite. The diffraction peaks of sphalerite (220) are almost identical to each other and are far away from other diffraction peaks, so we can and The peak area ratio between the peaks is defined as a simple quantitative indicator to measure the perfection of the wurtzite structure. and The peak area ratio is used as a reference.

[0234] Figure 5 The high-resolution TEM image of the branched nanocrystals in the precipitation is shown. It can be seen that it has a zinc blende crystal (ZB) core and two wurtzite crystal (WZ) arms. The main part (arms) of the branched nanocrystals do not have stacking faults. However, even so, the branched nanocrystals have a zinc blende structure in the core. and The ratio is still ~17% lower than the standard value (see Figure 6 ).

[0235] Although TOP is used in large quantities in the synthesis of fatty acid zinc ligands, the sample (spherical wurtzite nanocrystals) separated and purified in Example 1 was 31 P NMR measurements did not detect TOP and possible derivatives, indicating that although TOP is a ligand for free aliphatic zinc, neither TOP alone nor TOP bound to aliphatic zinc can serve as an effective surface ligand.

[0236] The TEM images of the nanocrystals obtained in Examples 1 and 2 are shown in Figure 7 Right picture, left picture, Figure 7 The middle figure shows the relationship between the preheating time and the production ratio of spherical nanocrystals and branched nanocrystals. It can be seen that appropriately extending the preheating time can increase the ratio of spherical nanocrystals. and The relationship between peak area ratio and preheating time can be found in Figure 8 Left picture. Figure 8 The right figure is a comparison of the XRD patterns of Example 1 and Example 2. The increase in preheating time can effectively increase the yield of spherical wurtzite products, thus making and The peak area ratio increased slightly.

[0237] The XRD patterns of the nanocrystals obtained in Examples 1, 18, and 30 are shown in Fig. 9 , Fig. 9 The inset is the high-resolution electron micrograph of the corresponding nanocrystal. In the absence of TOP and when the fatty acid cadmium concentration is high, obvious stacking faults and different degrees of sphalerite structure will appear.

[0238] TEM images of the nanocrystals obtained in Examples 1, 52, 53, 54, 55, and 56 are shown in Fig.10 , where the left, middle and right pictures in the first row correspond to Example 53, Example 1 and Example 52 respectively; the left, middle and right pictures in the second row correspond to Example 54, Example 55 and Example 56 respectively. Different reaction conditions resulted in crystals of different shapes. Fig.11 It can be seen that they all have perfect XRD patterns, and the roots are all single crystal wurtzite nanocrystals. Fig.12 Shows nanocrystals of different shapes The high-resolution TEM image of the crystal orientation also verified that it has no lattice stacking faults.

[0239] The TEM images and high-resolution TEM images of the nanocrystals obtained in Example 57, Example 58 or Example 59, Example 61, and Example 16 are respectively shown in Fig.13 , Fig.14 , Fig.15 , Fig.16 Example 57 yields short nanorods, and its high-resolution TEM image is shown in Fig.13 , from

[0001] crystal direction and Crystal orientation confirms that the side is flat Crystal face family, Examples 58 and 59 obtained spherical nanocrystals, and their high-resolution TEM images are shown in Fig.14 The nanorods obtained in Example 61 and the nanowires obtained in Example 16 both showed a smooth Side. Four morphologies No stacking faults were found in the high-resolution TEM of the crystal directions.

[0240] Example 59 TEM images of nanocrystals with different average diameters obtained after different reaction times are shown in Fig.17 . Fig.18 The UV-visible absorption patterns of different nanocrystals are shown, with the inset being the relationship between size and fluorescence half-maximum width (PL FWHM).

[0241] Fig.19 The product obtained in Example 1 is shown in TEM images, UV-visible absorption spectra, and fluorescence spectra of the product before centrifugation (original product) and two kinds of separations (supernatant and precipitate) after centrifugation. The branched nanocrystals in the precipitate hardly emit light, and the branched nanocrystals have significant absorption on the low-energy side, resulting in a special, wide absorption tail in the UV absorption spectrum of the stock solution. The higher the proportion of branched nanocrystals, the more obvious the tail will be, which can be used as a semi-quantitative basis for quickly judging the relative proportion of branched nanocrystals in products of the same size from the spectrum.

[0242] The XRD patterns of the nanocrystals of Example 1, Example 49, Example 50 and Example 51 are shown in Fig. 20 The impurities that may exist in TOP will affect the yield of single crystal wurtzite. For example, adding a trace amount of OPA (Example 49) will significantly increase the branched part of the nanocrystals. Other trace impurities, such as TOPO (Example 51) and DPP (Example 50), basically do not affect the morphology, size, and crystallinity of the final product.

[0243] The TEM image and high-resolution TEM image of Example 60 are shown in Fig.21 , is Example 61 ( Fig.15 ) The morphology before annealing for 60 minutes has obvious dynamic growth characteristics, but it is also a single crystal wurtzite structure.

[0244] Fig. 22 The XRD patterns of spherical nanocrystals with different average diameters are shown. The sample with an average diameter of 3.3 nm cannot be effectively separated because the branched nanocrystals are similar in size to the spherical nanocrystals. Therefore, the XRD patterns are divided according to the average diameter of the sample. After the peaks return to one, and The peak is slightly lower.

[0245] For the convenience of explanation, the zinc blende structure is abbreviated as ZB and the wurtzite structure is abbreviated as WZ in the drawings.

[0246] Although some specific embodiments of the present disclosure have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. The various embodiments disclosed herein may be combined in any manner without departing from the spirit and scope of the present disclosure. It should also be understood by those skilled in the art that various modifications may be made to the embodiments without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims

1. A semiconductor nanocrystal group, characterized in that: The crystal form of the semiconductor nanocrystal group is wurtzite single crystal, the semiconductor nanocrystal group includes cadmium and selenium, and at least 85% of the semiconductor nanocrystals in the semiconductor nanocrystal group have no lattice stacking fault.

2. The semiconductor nanocrystal group according to claim 1, characterized in that: The surface ligand of the semiconductor nanocrystal includes fatty acid zinc. Preferably, the number of C atoms in the fatty acid zinc is less than or equal to 22 and greater than or equal to 2.

3. The semiconductor nanocrystal group according to claim 1, characterized in that: When the semiconductor nanocrystal group is a nanosphere or a near-nanosphere or a near-nanorod or a nanorod or a nanowire, the XRD test result of the semiconductor nanocrystal group is and The ratio of the peak area of ​​the semiconductor nanocrystal group to the peak area of ​​the semiconductor nanocrystal group is 0.38 to 0.44; Optionally, the test results of the semiconductor nanocrystal group XRD using Cu target The 2theta peak position is 42.1±0.5 degrees, and the Q value peak position is 4. The semiconductor nanocrystal group according to claim 1, characterized in that: When the semiconductor nanocrystal group is a nanosphere or a near-nanosphere, the average aspect ratio of the semiconductor nanocrystal group is 0.8-1.6, and the average particle size is 3-20 nm; preferably, the particle size distribution deviation of the semiconductor nanocrystal group is less than or equal to 10%.

5. The semiconductor nanocrystal group according to claim 1, characterized in that: The size of the semiconductor nanocrystal group can be extended along the c-axis, and the average aspect ratio of the semiconductor nanocrystal group is 1.4 to 40, and the average particle size is 5 to 15 nm.

6. The semiconductor nanocrystal group according to claim 1, characterized in that: When the semiconductor nanocrystal group is a nanosphere or a near-nanosphere or a near-nanorod or a nanorod or a nanowire, the fluorescence half-peak width of the semiconductor nanocrystal group is 19 to 38 nm.

7. The semiconductor nanocrystal group according to claim 1, characterized in that: The size of the semiconductor nanocrystal group can be extended along the c-axis. When the morphology of the semiconductor nanocrystal group is near nanorods, nanorods or nanowires, the average aspect ratio of the semiconductor nanocrystal group is 1.4 to 18. Through high-resolution transmission electron microscopy observation, preferably, the semiconductor nanocrystal group has a flat non-polar Crystal face.

8. A method for preparing a semiconductor nanocrystal group, characterized in that: The preparation method comprises: A: mixing a first zinc precursor and a first fatty acid in a first container and heating them, reacting them at a first temperature to obtain a clear mixture, and then adding a reaction medium to the first container to obtain a first mixture; or mixing a first zinc precursor, a first fatty acid, and a reaction medium in a first container and heating them, reacting them at a first temperature to obtain a clear first mixture; or mixing a first zinc precursor, a first fatty acid, and a reaction medium in a first container and heating them, reacting the first mixture at a first temperature to obtain a clear mixture, and then adding the reaction medium to obtain a first mixture; B: raising the first temperature to a second temperature or reacting at the first temperature for a first time, and then adding trialkylphosphine to the first container for a second time; after the reaction, a product system containing fatty acid zinc is obtained, wherein the fatty acid zinc is used as a ligand for subsequent reactions; C: mixing a first cation precursor, a trialkylphosphine, the reaction medium and a second fatty acid and heating them to react to obtain a second mixture, wherein the molar ratio of the fatty acid zinc in B to the cation in the first cation precursor is greater than or equal to 5; The first cation precursor includes cadmium element; D: preparing a third mixture containing an anion precursor, a trialkylphosphine and the reaction medium; the anion precursor includes selenium; E1: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, to obtain a product system containing a first semiconductor nanocrystal group; or E2: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, and adding the second mixture and the third mixture simultaneously in multiple times during the third time period to obtain a product system containing a first semiconductor nanocrystal group; or E3: adding the second mixture and the third mixture into the first container simultaneously and in multiple times, reacting at a third temperature for a third time, to obtain a product system containing a first semiconductor nanocrystal group; or E4: adding the second mixture and the third mixture to the first container in sequence, reacting at a third temperature for a third time, and then reacting at a fourth temperature for a fourth time, to obtain a product system containing a first semiconductor nanocrystal group; Among them, the obtained product system includes a first semiconductor nanocrystal group accounting for more than 40% in number, and the first semiconductor nanocrystal group is a wurtzite single crystal; and the molar ratio of the cation of the first cation precursor and the anion of the anion precursor added to the first container is 0.9:1 to 4:

1.

9. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The reaction medium is squalane, and the first zinc precursor is basic zinc carbonate, zinc oxide or fatty acid zinc with 2 to 22 carbon atoms; preferably, the molar concentration of zinc ions in the first mixture is 25 to 200 mmol / L; preferably, the molar concentration of cations in the second mixture is 2.5 to 10 mmol / L.

10. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The molar ratio of the trialkylphosphine added to the B to the zinc element in the first zinc precursor is 2:1 to 9:

1. Preferably, the molar concentration of the trialkylphosphine in the first mixture is 112 to 448 mmol / L.

11. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The first fatty acid includes a plurality of fatty acids with different carbon chain lengths or only one fatty acid; preferably, the first fatty acid includes capric acid and stearic acid; preferably, the second fatty acid is capric acid, dodecanoic acid or oleic acid.

12. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: In B, the first time is 0 to 4.5 hours; preferably, the second time is 0 to 4.5 hours.

13. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The second temperature is greater than or equal to 310°C and less than or equal to 350°C; preferably, the third temperature is greater than 290°C.

14. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The E2 comprises: injecting the second mixture and the third mixture into the first container in sequence; when the crystal nuclei in the first container are formed, adding the second mixture and the third mixture into the first container respectively in multiple times; after reacting for a certain period of time, a product system containing the first semiconductor nanocrystal group is obtained; preferably, in E2 to E4, the multiple additions are in the form of drops.

15. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The preparation method further includes F: separating and purifying the first semiconductor nanocrystal group from any product system of E1 to E4.

16. The method for preparing a semiconductor nanocrystal group according to claim 8, further comprising F: separating and purifying a first semiconductor nanocrystal group from any product system of E1 to E4 as a seed for a subsequent reaction, and removing the non-single-crystal wurtzite single crystal.

17. The method for preparing a semiconductor nanocrystal group according to claim 15, characterized in that: The preparation method also includes G: preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, the reaction medium and a third fatty acid; preparing a sixth mixture containing the anion precursor, a trialkyl phosphine and the reaction medium; preparing a seventh mixture containing a second zinc precursor, a fourth fatty acid, a trialkyl phosphine and the reaction medium, wherein the seventh mixture reacts in a second container at a fifth temperature to obtain an eighth mixture containing fatty acid zinc; injecting the fourth mixture into the second container, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple times of adding are in a dropwise manner; at the fifth temperature, heating the reaction for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

18. The method for preparing a semiconductor nanocrystal group according to claim 17, characterized in that: The fifth temperature is greater than or equal to 270°C and less than or equal to 350°C; the fourth fatty acid includes one fatty acid or multiple fatty acids with different carbon chain lengths; preferably, the fourth fatty acid includes capric acid and oleic acid, or capric acid and erucic acid, or capric acid, oleic acid and erucic acid.

19. The method for preparing a semiconductor nanocrystal group according to claim 8 or 17, characterized in that: The preparation method further includes, when the average particle size of the first semiconductor nanocrystal group is greater than or equal to 5nm, the average aspect ratio is greater than or equal to 1.4, and there is no excess cadmium element in the first container; or when the average aspect ratio of the second semiconductor nanocrystal group is greater than or equal to 1.4, and there is no excess cadmium element in the second container, annealing the first semiconductor nanocrystal group or the second semiconductor nanocrystal group at a sixth temperature for a sixth time, and the semiconductor nanocrystal group has a flat non-polar surface after the annealing treatment. Crystal face.

20. The semiconductor nanocrystal group according to claim 19, characterized in that: The sixth temperature is greater than or equal to 330° C. and less than or equal to 350° C.; preferably, the sixth time is not less than 0.5 hours.

21. The method for preparing a semiconductor nanocrystal group according to claim 17, characterized in that: The second semiconductor nanocrystal group is non-spherical in shape, and the preparation method further includes H: spheroidizing the second semiconductor nanocrystal group.

22. The method for preparing a semiconductor nanocrystal group according to claim 21, characterized in that: The H comprises: after obtaining the second semiconductor nanocrystal group, adding a ninth mixture in situ into the second container, and performing annealing treatment at a sixth temperature for a sixth time, wherein the ninth mixture is obtained by mixing the second cation precursor, trialkylphosphine, the reaction medium and the fifth fatty acid and heating the mixture for reaction.

23. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The preparation method also includes G': preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, the reaction medium and a third fatty acid; preparing a sixth mixture containing the anion precursor, a trialkyl phosphine and the reaction medium; preparing a seventh mixture containing a second zinc precursor, a third cation precursor, a fourth fatty acid, a trialkyl phosphine and the reaction medium, adding the seventh mixture to a second container at a fifth temperature for reaction to obtain a seventh mixture containing fatty acid zinc and fatty acid cadmium; injecting the fourth mixture into a second container containing the seventh mixture, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple times of addition are in the form of drops; at the sixth temperature, heating the reaction for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

24. The method for preparing a semiconductor nanocrystal group according to claim 23, characterized in that: The molar ratio of the cadmium element in the seventh mixture to the zinc element in the seventh mixture is 0.1:1 to 0.25:1, and the shape of the second semiconductor nanocrystal group is spherical.

25. The method for preparing a semiconductor nanocrystal group according to claim 15, characterized in that: The preparation method also includes G": preparing a fourth mixture containing the first semiconductor nanocrystal group and the reaction medium; preparing a fifth mixture containing a second cation precursor, a trialkyl phosphine, the reaction medium and a third fatty acid; preparing a sixth mixture containing the anion precursor, the trialkyl phosphine and the reaction medium; a seventh mixture free of trialkyl phosphine obtained by reacting the second zinc precursor and the fourth fatty acid in the reaction medium, or a seventh mixture free of zinc obtained by reacting the trialkyl phosphine and the fourth fatty acid in the reaction medium, or a seventh mixture containing cadmium obtained by reacting the second zinc precursor, the third cation precursor, the trialkyl phosphine and the fourth fatty acid in the reaction medium; injecting the fourth mixture into a second container containing the seventh mixture, and adding the fifth mixture and the sixth mixture to the second container in multiple times, preferably, the multiple times of adding are in a dropwise manner; heating the reaction at a fifth temperature for a fifth time to complete homoepitaxial growth to obtain a second semiconductor nanocrystal group.

26. The method for preparing a semiconductor nanocrystal group according to claim 8, characterized in that: The molar concentration of the free first fatty acid remaining after the reaction of the first fatty acid and the first zinc precursor is 25-400 mmol / L, or the ratio of the amount of the free first fatty acid to the amount of the zinc element of the first zinc precursor is 2.5-10.

Images