Quantum dot and preparation method therefor, and device comprising quantum dot

Abstract

The present disclosure provides a Group II-VI core-shell quantum dot and a preparation method therefor. A quantum dot shell having a gradient alloy structure is gradually grown by using a precursor that has a reactivity gradient. The gradient alloy structure has a band gap that gradually increases from inside to outside, thereby solving the problem of difficulty in epitaxial growth caused by a decrease in the surface activity of a quantum dot along with an increase in the size thereof. By using zinc halide and octanethiol to regulate crystal facets, the proportion of polar facets on the surface of the quantum dot is increased, and the stability of the quantum dot is significantly improved. Moreover, provided is a low-cadmium quantum dot core. A hot-injection method is used to perform nucleation and growth of ZnSe at a high temperature, a cadmium precursor is then added after the stable nucleation of ZnSe, and cadmium / zinc ion exchange is performed by utilizing the binding energy of selenium / cadmium that is stronger than that of selenium / zinc, thereby forming a CdZnSe ternary core, which can solve the problem of it being difficult for blue-light quantum dots that use CdZnSe as a light-emitting core to cover the pure blue band.

Description

Quantum dots, methods of making the same, and devices including quantum dots TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of nanomaterials, and in particular to a quantum dot, a method of making the same, and a light-emitting device including the quantum dot. BACKGROUND

[0002] A quantum dot is a semiconductor nanomaterial that can confine an exciton in three-dimensional space. Quantum dots have a specific band gap according to their composition and size, and thus can be excited by absorbing light from an excitation source and can emit light of a specific wavelength corresponding to the band gap energy of the quantum dot. Due to its excellent properties such as high quantum efficiency, narrow excitation spectrum, high optical stability, long fluorescence lifetime, and good solution processing compatibility, quantum dots have great application potential in high-quality displays. The quantum dots that are currently being researched for display applications mainly emit blue light and are II-VI semiconductor quantum dots. Quantum dot light-emitting diodes are devices that use quantum dots as light-emitting materials, and have the advantages of lower energy consumption, higher color purity, and wider color gamut. Therefore, quantum dot light-emitting technology has become the most promising next-generation self-emitting display technology. SUMMARY

[0003] According to an aspect of the present disclosure, a quantum dot of core-shell structure is provided, including a group II element and a group VI element, wherein the quantum dot shell has a gradient alloy structure with a band gap that increases from the inside to the outside.

[0004] In some embodiments, the quantum dot shell includes a first nanocrystal shell layer located on the quantum dot core, the first nanocrystal shell layer including a first II-VI compound, and a second nanocrystal shell layer located on a side of the first nanocrystal shell layer away from the quantum dot core, the second nanocrystal shell layer including a second II-VI compound, wherein the band gap of the second nanocrystal shell layer is greater than the band gap of the first nanocrystal shell layer.

[0005] In some embodiments, the quantum dot shell further includes a third nanocrystal shell layer located between the first nanocrystal shell layer and the second nanocrystal shell layer, the third nanocrystal shell layer including a third II-VI compound, the third II-VI compound being an alloy of the first II-VI compound and the second II-VI compound, wherein the band gap of the third nanocrystal shell layer is greater than the band gap of the first nanocrystal shell layer, and the band gap of the third nanocrystal shell layer is less than the band gap of the second nanocrystal shell layer.

[0006] In some embodiments, the first II-VI compound includes ZnSe, the second II-VI compound includes ZnS, and the third II-VI compound includes ZnSeS.

[0007] In some embodiments, the radius of the quantum dot core is 1.3 nm ± 0.3 nm, the thickness of the first nanocrystal shell is 1.6 nm ± 0.1 nm, the thickness of the second nanocrystal shell is 0.9 nm ± 0.1 nm, and the thickness of the third nanocrystal shell is 1.1 nm ± 0.1 nm.

[0008] In some embodiments, the quantum dot has a spherical shape.

[0009] In some embodiments, the quantum dot shell further includes a fourth nanocrystal shell located on the side of the second nanocrystal shell away from the quantum dot core, wherein the composition of the fourth nanocrystal shell is the same as that of the second nanocrystal shell.

[0010] In some embodiments, the second nanocrystal shell and the fourth nanocrystal shell are both composed of ZnS, the ratio of Zn to S in the second nanocrystal shell is 1:1, and the ratio of Zn to S in the fourth nanocrystal shell is 1:1-2:1.

[0011] In some embodiments, the quantum dot has a cubic shape.

[0012] In some embodiments, the crystal plane of the quantum dot is <100> Crystal facets.

[0013] In some embodiments, the structure of the quantum dot shell is ZnSe / ZnSeS / ZnS / ZnS or ZnSe / ZnSeS / ZnS or ZnSe / ZnS / ZnS.

[0014] In some embodiments, the quantum dot includes a quantum dot body and a ligand coordinated on the quantum dot body, wherein the ligand is an ionic ligand.

[0015] In some embodiments, the ligand is a carboxylic acid or a halogen.

[0016] In some embodiments, the quantum dot core contains the element cadmium (Cd), and the quantum dot emits light at a wavelength less than 470 nm.

[0017] In some embodiments, the quantum dot core is composed of CdZnSe or CdSe / CdZnSe.

[0018] In some embodiments, the emission peak is adjustable between 450nm and 470nm, and the full width at half maximum (FWHM) is less than 30nm.

[0019] In some embodiments, the molar amount of Cd accounts for 0.5%-2% of the total molar amount of quantum dots.

[0020] According to another aspect of this disclosure, a quantum dot light-emitting device is provided, comprising a quantum dot according to any one of the embodiments described above.

[0021] According to another aspect of this disclosure, a method for preparing group II-VI core-shell quantum dots is provided, comprising: preparing a quantum dot core; preparing a first nanocrystal shell on the quantum dot core; preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core; wherein the band gap of the second nanocrystal shell is larger than the band gap of the first nanocrystal shell.

[0022] In some embodiments, preparing a first nanocrystal shell on the quantum dot core includes: reacting a first cation precursor and a first anion precursor in a solution containing the quantum dot core at a first temperature to generate the first nanocrystal shell; preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core includes: adding a second cation precursor and a second anion precursor, and reacting the second cation precursor and the second anion precursor at a first temperature to generate the second nanocrystal shell, wherein the first cation precursor and the second cation precursor have different reactivity.

[0023] In some embodiments, the first cationic precursor includes one or more of long-chain zinc carboxylate with a C number greater than 12, the second cationic precursor includes one or more of short-chain zinc carboxylate with a C number less than 6, the first anionic precursor includes selenium, and the second anionic precursor includes sulfur.

[0024] In some embodiments, after the first nanocrystal shell is prepared on the quantum dot core and before the second nanocrystal shell is prepared on the side of the first nanocrystal shell away from the quantum dot core, the method further includes: preparing a third nanocrystal shell on the first nanocrystal shell.

[0025] In some embodiments, preparing a third nanocrystal shell on the first nanocrystal shell includes: after the first nanocrystal shell has grown, adding a third cation precursor and a third anion precursor, and reacting the third cation precursor and the third anion precursor at a first temperature to generate the third nanocrystal shell, wherein the third anion precursor includes a mixed solution of the first anion precursor and the second anion precursor.

[0026] In some embodiments, the third cationic precursor comprises one or more of medium-chain zinc carboxylate with a C number of 6-12.

[0027] In some embodiments, the first temperature ranges from 305 to 315°C.

[0028] In some embodiments, after preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core, the method further includes preparing a fourth nanocrystal shell on the side of the second nanocrystal shell away from the quantum dot core.

[0029] In some embodiments, preparing a fourth nanocrystal shell on the side of the second nanocrystal shell away from the quantum dot core includes: after the second nanocrystal shell has grown, adding a fourth cation precursor and a fourth anion precursor, and reacting the fourth cation precursor and the fourth anion precursor at a second temperature to generate the fourth nanocrystal shell, wherein the composition of the fourth nanocrystal shell is the same as that of the second nanocrystal shell.

[0030] In some embodiments, the fourth cation precursor includes zinc halide, and the fourth anion precursor includes octylthiol.

[0031] In some embodiments, the preparation of quantum dot nuclei includes: rapidly adding a fifth anion precursor to a fifth cation precursor at a second temperature, causing the fifth cation precursor to react with the fifth anion precursor for a first time period to form a first quantum dot nucleus.

[0032] In some embodiments, the preparation of quantum dot nuclei further includes: after forming the first quantum dot nuclei, adding a sixth cation precursor at a second temperature to form a second quantum dot nuclei; wherein the cation in the sixth cation precursor is different from the cation in the fifth cation precursor, and the binding energy between the cation in the sixth cation precursor and the fifth anion is higher than the binding energy between the cation in the fifth cation precursor and the fifth anion, and the second quantum dot nuclei is a ternary nucleus formed by partially replacing the cation in the first quantum dot nucleus with the cation in the sixth cation precursor.

[0033] In some embodiments, the second temperature ranges from 295 to 305°C.

[0034] In some embodiments, the components of the fifth cation precursor are the same as those of the first cation precursor, and the components of the fifth anion precursor are the same as those of the first anion precursor.

[0035] In some embodiments, the first cation precursor includes an excess of a fifth cation precursor remaining during the formation of the quantum dot core.

[0036] In some embodiments, the fifth cation precursor includes one or more of long-chain zinc carboxylate with a C number greater than 12, the fifth anion precursor includes selenium, and the sixth cation precursor includes cadmium carboxylate.

[0037] In some embodiments, the molar ratio of zinc carboxylate to cadmium carboxylate is 20:1 to 50:1.

[0038] In some embodiments, the first time period is in the range of 2-10 minutes. Attached Figure Description

[0039] The exemplary embodiments of this disclosure will be described in detail below with reference to the accompanying drawings, in which:

[0040] Figure 1A shows a simplified structural schematic diagram of a II-VI group core-shell quantum dot according to an embodiment of the present disclosure;

[0041] Figure 1B shows a simplified structural schematic diagram of another II-VI group core-shell quantum dot according to an embodiment of the present disclosure;

[0042] Figure 1C shows a simplified structural schematic diagram of another II-VI group core-shell quantum dot according to an embodiment of the present disclosure;

[0043] Figure 2 shows a transmission electron microscope image of the quantum dot nucleus ZnSe;

[0044] Figure 3 shows a transmission electron microscope image of the quantum dots after ZnSe shell coating;

[0045] Figure 4 shows a transmission electron microscope image of the quantum dots after ZnSeS / ZnS shell coating;

[0046] Figure 5 shows a transmission electron microscope image of the quantum dots after being coated with the fourth nanocrystal shell ZnS.

[0047] Figure 6 shows a high-resolution transmission electron microscope image and a lattice Fourier transform diagram of the quantum dots after being coated with the fourth nanocrystal shell ZnS.

[0048] Figure 7 shows a flowchart of a method 700 for preparing group II-VI core-shell quantum dots;

[0049] Figure 8 shows a flowchart of another preparation method 800 for group II-VI core-shell quantum dots;

[0050] Figure 9 shows a flowchart of another preparation method 900 for group II-VI core-shell quantum dots;

[0051] Figure 10 shows the different absorption spectra as the reaction proceeds during the synthesis of the quantum dot shell;

[0052] Figure 11 shows the different absorption spectra as the reaction proceeds during the synthesis process;

[0053] Figure 12 shows a schematic diagram of the atomic stacking structure on the surface of quantum dots before and after crystal plane modulation;

[0054] Figure 13 shows the absorption spectrum as it evolves over time during the growth of quantum dots;

[0055] Figure 14 shows a schematic diagram of the quantum dot synthesis steps according to an embodiment of the present disclosure;

[0056] Figure 15 shows a fluorescence quantum efficiency test graph of blue quantum dots obtained according to an embodiment of the present disclosure;

[0057] Figure 16 shows a transient fluorescence test pattern of blue quantum dots obtained according to an embodiment of the present disclosure;

[0058] Figure 17 shows a fluorescence quantum efficiency test graph of blue quantum dots obtained according to an embodiment of the present disclosure;

[0059] Figure 18 shows a fluorescence quantum efficiency test graph of blue quantum dots obtained according to an embodiment of the present disclosure;

[0060] Figure 19 shows an EQE-voltage diagram of a blue QLED device based on quantum dots according to an embodiment of the present disclosure;

[0061] Figure 20 shows an EQE-brightness diagram of a blue QLED device based on quantum dots according to an embodiment of the present disclosure;

[0062] Figure 21 shows a comparison of the quantum dot emission spectra before and after the addition of zinc halide;

[0063] Figure 22 shows a schematic diagram of the synthesis steps of a quantum dot core according to an embodiment of the present disclosure;

[0064] Figure 23 shows a spectrum of a quantum dot obtained according to an embodiment of the present disclosure;

[0065] Figure 24 shows a spectrum of a quantum dot obtained according to an embodiment of the present disclosure;

[0066] Figure 25 shows a spectrum of a quantum dot obtained according to an embodiment of the present disclosure;

[0067] Figure 26 shows a spectrum of a quantum dot obtained according to an embodiment of the present disclosure; and

[0068] Figure 27 shows a spectrum of a quantum dot obtained according to an embodiment of the present disclosure.

[0069] It should be understood that the accompanying drawings are merely schematic illustrations of exemplary embodiments of the present disclosure and are not intended to limit the present disclosure, nor need they be drawn to scale. Furthermore, in the drawings, the same or similar components are indicated by the same or similar reference numerals. Detailed Implementation

[0070] The technical solutions of the embodiments of this disclosure will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0071] Before formally describing the technical solutions of the embodiments of this disclosure, the terms used in the embodiments of this disclosure are explained and defined as follows to help those skilled in the art to more clearly understand the technical solutions of the embodiments of this disclosure.

[0072] In embodiments of this disclosure, terms such as "reactivity" and "activity" refer to the degree of reactivity of a chemical reagent or precursor solution in a chemical reaction. Higher reactivity or activity indicates a greater likelihood of participation in the reaction. For example, a reactant with high reactivity refers to a reactant with a relatively high degree of reactivity, while a reactant with low reactivity refers to a reactant with a relatively low degree of reactivity. The terms "reactivity" and "activity" are used interchangeably herein.

[0073] In the embodiments of this disclosure, the first, second, third, fourth, fifth, and sixth cation precursors each include a corresponding solute and solvent. Any two of these cation precursors may include the same or different solutes, and any two of these cation precursors may include the same or different solvents. Furthermore, these cation precursors can provide the same or different cations for the growth of quantum dot cores or quantum shells. Similarly, the first, second, third, fourth, and fifth anion precursors each include a corresponding solute and solvent. Any two of these anion precursors may include the same or different solutes, and any two of these cation precursors may include the same or different solvents. Furthermore, these cation precursors can provide the same or different anions for the growth of quantum dot cores or quantum shells. Here, the terms "first," "second," "third," "fourth," "fifth," and "sixth" are used only to distinguish one precursor from another and do not represent the preparation or reaction order of the precursors, nor do they constitute a limitation on the individual precursors. The precursors in this disclosure can be obtained through preparation or purchase. For example, the applicant may prepare the first cation precursor, second cation precursor, third cation precursor, fourth cation precursor, fifth cation precursor, and sixth cation precursor, as well as the first anion precursor, second anion precursor, third anion precursor, fourth anion precursor, and fifth anion precursor, themselves, or may prepare the first cation precursor, second cation precursor, third cation precursor, fourth cation precursor, fifth cation precursor, and sixth cation precursor, as well as the first anion precursor, second anion precursor, third anion precursor, fourth anion precursor, and fifth anion precursor, in cooperation with other companies or enterprises. The required first, second, third, fourth, fifth, and sixth cation precursors, as well as the first, second, third, fourth, and fifth anion precursors, may be purchased from other companies or enterprises, or obtained by any other suitable means. In this disclosure, the terms "precursor" and "precursor precursor" are used interchangeably herein.

[0074] In this disclosure, “Group II” refers to Group IIA and Group IIB, and examples of Group II metals can be Cd, Zn, Hg and Mg, but are not limited thereto.

[0075] In this disclosure, “VI family” refers to the VIA family, and examples of it may include, but are not limited to, S, Se and Te.

[0076] Quantum dots (QDs), as a novel luminescent material, have advantages such as high light purity, high luminescence quantum efficiency, adjustable luminescence color, and long lifespan, making them a research hotspot for novel LED luminescent materials.

[0077] Quantum dot light-emitting diodes (QLEDs) made from blue quantum dots generally suffer from an efficiency roll-off problem, rooted in a high Auger recombination rate. Under high current, the probability of nonradiative recombination of quantum dots increases, leading to a rapid decrease in the device's luminous efficiency. Those skilled in the art have attempted to reduce the Auger recombination rate of quantum dots by using a shell with a gradually decreasing potential barrier. However, during quantum dot growth, as the quantum dot size increases, the surface energy gradually decreases, causing the epitaxial growth rate of the shell to gradually decline. Using highly reactive precursors may induce self-nucleation.

[0078] In view of this, embodiments of this disclosure provide a core-shell structured quantum dot, wherein the quantum dot shell has a gradient alloy structure, the gradient alloy structure having a band gap that increases gradually from the inside to the outside, and without obvious interlayer interfaces. The gradient alloy shell can be grown stepwise using a precursor with varying reactivity gradients to solve the problem of decreased surface activity of quantum dots as size increases, which makes epitaxial growth difficult.

[0079] In this disclosure, the gradient alloy structure may have at least two nanocrystal shells. For example, two nanocrystal shells with two gradient band gaps may be grown using two precursors with different reactivity; or three nanocrystal shells with three gradient band gaps may be grown stepwise using three precursors with varying reactivity; or four nanocrystal shells with four gradient band gaps may be grown stepwise using four precursors with varying reactivity.

[0080] The quantum dot shell with gradient alloy structure proposed in this disclosure is applicable to any quantum dot core. The following embodiments are illustrated using a core-shell structure quantum dot of group II-VI as an example.

[0081] Figure 1A shows a simplified structural diagram of a group II-VI core-shell quantum dot according to an embodiment of the present disclosure. The quantum dot 10 includes a quantum dot core 100 and a quantum dot shell 110, wherein the quantum dot shell 110 includes: a first nanocrystalline shell layer 101 located on the quantum dot core 100, the first nanocrystalline shell layer may include a first group II-VI compound; and a second nanocrystalline shell layer 102 located on the side of the first nanocrystalline shell layer 101 away from the quantum dot core 100, the second nanocrystalline shell layer may include a second group II-VI compound; wherein the band gap of the second nanocrystalline shell layer 102 is larger than the band gap of the first nanocrystalline shell layer 101. Exemplarily, the first group II-VI compound may be ZnSe, and the second group II-VI compound may be ZnS.

[0082] Figure 1B shows a simplified structural diagram of another group II-VI core-shell quantum dot according to an embodiment of the present disclosure. The quantum dot 10 includes a quantum dot core 100 and a quantum dot shell 110, wherein the quantum dot shell includes: a first nanocrystalline shell layer 101 located on the quantum dot core 100, the first nanocrystalline shell layer may include a first group II-VI compound; a second nanocrystalline shell layer 102 located on the side of the first nanocrystalline shell layer 101 away from the quantum dot core 100, the second nanocrystalline shell layer may include a second group II-VI compound; and a third nanocrystalline shell layer 103 located between the first nanocrystalline shell layer 101 and the second nanocrystalline shell layer 102, the third nanocrystalline shell layer may include a third group II-VI compound, the third group II-VI compound being an alloy of the first group II-VI compound and the second group II-VI compound. The band gap of the third nanocrystalline shell layer 103 is larger than the band gap of the first nanocrystalline shell layer 101, and the band gap of the third nanocrystalline shell layer 103 is smaller than the band gap of the second nanocrystalline shell layer 102. For example, the first II-VI compound can be ZnSe, the second II-VI compound can be ZnS, and the third II-VI compound can be ZnSeS.

[0083] In embodiments where the quantum dot shell comprises a first nanocrystalline shell, a second nanocrystalline shell, and a third nanocrystalline shell, the quantum dots have a spherical shape. Taking a CdZnSe / ZnSe / ZnSeS / ZnS quantum dot structure as an example, Figure 2 shows a transmission electron microscope (TEM) image of the CdZnSe quantum dot core, Figure 3 shows a TEM image of the quantum dots after being coated with a ZnSe shell, and Figure 4 shows a TEM image of the quantum dots after being coated with a ZnSeS / ZnS shell. As shown in Figures 2-4, the particle size of the ZnSe core is approximately 2 nm, the particle size of the quantum dots after being coated with a ZnSe shell is approximately 5 nm, and the particle size of the quantum dots after being coated with a ZnSeS / ZnS shell is approximately 10 nm. The gradual increase in quantum dot particle size demonstrates the occurrence of epitaxial growth in each shell. Simultaneously, the significant increase in quantum dot size indicates that the problem of decreased surface activity of quantum dots with increasing size, leading to difficulty in epitaxial growth, can be overcome by adjusting the precursor activity.

[0084] The quantum dots provided in this disclosure have a band gap that increases from the inside to the outside and no obvious interlayer interface, which can effectively improve the photoluminescence quantum yield (PLQY) of the quantum dots.

[0085] In the embodiments of this disclosure, the radius of the quantum dot core is 1.3 nm ± 0.3 nm, that is, the radius of the quantum dot core ranges from 1 to 1.6 nm. For example, the radius of the quantum dot core can be 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, etc.; the thickness of the first nanocrystal shell is 1.6 nm ± 0.1 nm, that is, the thickness of the first nanocrystal shell ranges from 1.5 to 1.7 nm. For example, the thickness of the first nanocrystal shell can be 1.5 nm, 1.6 nm, etc. The thickness of the second nanocrystal shell is 0.9nm ± 0.1nm, that is, the thickness range of the second nanocrystal shell is 0.8nm-1.0nm. For example, the thickness of the second nanocrystal shell can be 0.8nm, 0.9nm, 1.0nm, etc. The thickness of the third nanocrystal shell is 1.1nm ± 0.1nm, that is, the thickness range of the third nanocrystal shell is 1nm-1.2nm. For example, the thickness of the third nanocrystal shell can be 1nm, 1.1nm, 1.2nm, etc.

[0086] Researchers also discovered that the surface of spherical quantum dots is covered by different crystal planes. For nonpolar crystal planes, surface atoms are usually connected to electrically neutral ligands (L-type ligands) via coordinate bonds. Because L-type ligand bonds are relatively weak, a desorption-adsorption equilibrium exists in solution, making it easy for ligands to be lost during purification, dilution, etc., leading to defect exposure and affecting the fluorescence quantum yield. Using metal halides during quantum dot shell growth can passivate the cation polar planes, inhibiting their growth, while simultaneously promoting the growth of other crystal planes and their transformation into cation polar planes. However, the small steric hindrance of metal halides can cause significant ion exchange, leading to lattice defects.

[0087] In view of this, this disclosure proposes a scheme for controlling the crystal facets of quantum dots. First, ZnS epitaxial growth is performed using short-chain zinc salts and trioctylphosphine-sulfur. Then, zinc halides and octyl mercaptan are used for crystal facet control. By employing two zinc precursors with different reactivity, the transformation of quantum dots from spherical to cubic shapes can be ensured while ion exchange occurs between homogeneous ZnS molecules, preventing lattice defects. Halogen ions in zinc halides, such as chloride ions, act as X-type ligands to coordinate the cation polar facets and passivate the growth of those facets, causing other facets to gradually evolve into cation polar facets as well.

[0088] Figure 1C shows a simplified structural schematic diagram of another group II-VI core-shell quantum dot according to an embodiment of the present disclosure. The quantum dot 10 includes a quantum dot core 100 and a quantum dot shell 110, wherein the quantum dot shell includes: a first nanocrystalline shell layer 101 located on the quantum dot core 100, the first nanocrystalline shell layer including a first group II-VI compound; a second nanocrystalline shell layer 102 located on the side of the first nanocrystalline shell layer 101 away from the quantum dot core 100, the second nanocrystalline shell layer including a second group II-VI compound; a third nanocrystalline shell layer 103 located between the first nanocrystalline shell layer 101 and the second nanocrystalline shell layer 102, the third nanocrystalline shell layer including a third group II-VI compound, the third group II-VI compound being an alloy of the first group II-VI compound and the second group II-VI compound; and a fourth nanocrystalline shell layer 104 located on the side of the second nanocrystalline shell layer 102 away from the quantum dot core 100, the composition of the fourth nanocrystalline shell layer 104 being the same as the composition of the second nanocrystalline shell layer 102. The band gap of the third nanocrystal shell 103 is larger than that of the first nanocrystal shell 101, and the band gap of the third nanocrystal shell 103 is smaller than that of the second nanocrystal shell 102. For example, the first II-VI compound can be ZnSe, the second II-VI compound can be ZnS, the third II-VI compound can be ZnSeS, and the composition of the fourth nanocrystal shell 104 is the same as that of the second nanocrystal shell 102, i.e., it is also ZnS. The ratio of Zn to S in the second nanocrystal shell is 1:1, and the ratio of Zn to S in the fourth nanocrystal shell is 1:1 to 2:1.

[0089] In embodiments where the quantum dot shell comprises a first nanocrystal shell, a second nanocrystal shell, a third nanocrystal shell, and a fourth nanocrystal shell, the quantum dots have a cubic shape. Taking a quantum dot with a core / ZnSe / ZnSeS / ZnS / ZnS structure as an example, Figure 5 shows a transmission electron microscope image of the quantum dot after being coated with the fourth nanocrystal shell (ZnS). Compared to Figure 4 before the fourth nanocrystal shell (ZnS), the size of the quantum dot after coating with the fourth nanocrystal shell (ZnS) does not change significantly, but the shape changes from spherical to cubic, indicating that ion exchange and surface crystal plane reshaping mainly occurred at this stage. Figure 6 shows a high-resolution transmission electron microscope image and a lattice Fourier transform diagram of the quantum dot after being coated with the fourth nanocrystal shell (ZnS). Based on the lattice arrangement and interatomic spacing analysis, the entire crystal plane is a single... <100> The presence of only one crystal facet, and the absence of other crystal faces, indicates that the proportion of cation polar faces in the quantum dots was significantly increased through crystal facet modulation of the fourth nanocrystal shell.

[0090] Increasing the proportion of cation polar faces can enhance the coverage of X-type ligands on the quantum dot surface. Since X-type ligands have strong coordination ability, they are less prone to detaching from the quantum dot surface during purification due to process variations, thus significantly improving the stability of the quantum dots.

[0091] In this embodiment of the disclosure, the quantum dot surface that has undergone crystal plane modulation is <100> The polar facets are surface-coordinated with ionic ligands such as carboxylic acids and halogens, which have high bond energies and are environmentally stable. At the same time, the reduction in the proportion of nonpolar facets also reduces the proportion of phosphine ligands coordinated with them, eliminating the influence of the weak bond energy and easy oxidation characteristics of phosphine ligands.

[0092] Currently, the main blue quantum dot emitting cores are CdZnSe, CdZnS, and ZnSeTe. CdZnS is easily synthesized in the blue light band due to its wide bandgap. ZnSeTe is cadmium-free, but its performance still lags behind cadmium-containing materials. CdZnSe, with its narrower bandgap compared to CdZnS, exhibits a higher Zn / Cd ratio in the blue light band, making it a low-cadmium material with excellent performance, combining the advantages of both CdZnS and ZnSeTe to some extent. However, due to the strong binding energy between Se and Cd, narrow-bandgap CdSe emitting cores are easily formed, making it difficult to control the emission band of CdZnSe within the pure blue light band (<475nm).

[0093] In view of this, this disclosure proposes a cadmium-low blue quantum dot. ZnSe nucleation and growth are performed at high temperature using a hot-injection method. Subsequently, a cadmium precursor is added to the stable ZnSe nucleation site, and cadmium / zinc ion exchange is carried out using the stronger binding energy of selenium / cadmium compared to selenium / zinc, thereby forming a CdZnSe ternary nucleus. This approach not only solves the problem that blue quantum dots with CdZnSe as the luminescent nucleus cannot cover the pure blue light band, but also, the gradient alloy luminescent nucleus structure formed by the ion exchange reaction is expected to further reduce the Auger recombination rate of the quantum dots.

[0094] Using the CdZnSe quantum dot cores provided in this disclosure, the emission peak can be tunable in the range of 450nm-470nm, with a full width at half maximum (FWHM) of less than 30nm.

[0095] Combined with the quantum dot shell provided in the aforementioned embodiments, the structure of the quantum dot can be CdZnSe / ZnSe / ZnS, that is, a ternary alloy core encased in two layers of gradient alloy shell; or the quantum dot structure can be CdZnSe / ZnSe / ZnSeS / ZnS, that is, a ternary alloy core encased in three layers of gradient alloy shell; or the quantum dot structure can be CdZnSe / ZnSe / ZnSeS / ZnS / ZnS, that is, a ternary alloy core encased in four layers of gradient alloy shell.

[0096] In the cadmium-low blue quantum dots provided in this disclosure, the molar amount of Cd accounts for 0.5%-2% of the total molar amount of the quantum dots. For example, the molar amount of Cd as a percentage of the total molar amount of the quantum dots can be 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, etc.

[0097] In some embodiments, the quantum dot core can be composed of CdSe / CdZnSe. A zinc precursor, rather than a sulfur precursor, is added during the early stages of CdSe seed formation to form a gradient alloy-coated small-sized CdSe / CdZnSe luminescent core, which is then further coated to complete the shell growth. The advantage of this approach is that it can further increase the distance between the luminescent core and surface defects, improving quantum dot performance. However, the disadvantage is that it requires controlling the CdSe luminescent core with a narrow intrinsic bandgap to an extremely small size to achieve blue light emission, which presents significant synthesis challenges.

[0098] This disclosure also provides a quantum dot light-emitting device, including quantum dots of any of the above embodiments. The light-emitting device made using the above quantum dots, such as a blue QLED device, can achieve an external quantum efficiency (EQE) of 20% while having no efficiency roll-off.

[0099] This disclosure also provides a method for preparing group II-VI core-shell quantum dots. Figure 7 shows a flowchart of a preparation method 700 for group II-VI core-shell quantum dots. As shown in Figure 7, the preparation method 700 includes the following steps: preparing a quantum dot core; preparing a first nanocrystalline shell on the quantum dot core; preparing a second nanocrystalline shell on the side of the first nanocrystalline shell away from the quantum dot core, wherein the band gap of the second nanocrystalline shell is larger than the band gap of the first nanocrystalline shell.

[0100] In some embodiments, the step of preparing a first nanocrystal shell on the quantum dot core includes: reacting a first cation precursor and a first anion precursor in a solution containing the quantum dot core at a first temperature to generate the first nanocrystal shell. Here, reacting the first cation precursor and the first anion precursor at the first temperature to generate the first nanocrystal shell includes two scenarios. In the first scenario, the first cation is an excess cation precursor remaining from the step of preparing the quantum dot core; in this case, only the first anion precursor needs to be added when preparing the first nanocrystal shell, thus simplifying the preparation process. In the second scenario, there is no excess cation remaining from the quantum dot core preparation process, or the cation precursor for preparing the quantum dot core is different from the cation precursor for preparing the first nanocrystal shell; in this case, both the first cation precursor and the first anion precursor need to be added when preparing the first nanocrystal shell.

[0101] In some embodiments, the step of preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core includes: adding a second cation precursor and a second anion precursor, and reacting the second cation precursor and the second anion precursor at a first temperature to generate the second nanocrystal shell, wherein the first cation precursor and the second cation precursor have different reactivity.

[0102] In some embodiments, the first cationic precursor comprises one or more of long-chain zinc carboxylate with a carbon number greater than 12, such as zinc carboxylate with carbon numbers of 13, 14, 15, 16, 17, 18, etc. The long-chain zinc carboxylate may include unsaturated long-chain carboxylates (such as zinc oleate) and saturated long-chain carboxylates. The second cationic precursor comprises one or more of short-chain zinc carboxylate with a carbon number less than 6, such as zinc carboxylate with carbon numbers of 1, 2, 3, 4, 5. The short-chain zinc carboxylate may be, for example, zinc formate, zinc acetate, zinc propionate, zinc butyrate, etc. The first anionic precursor comprises selenium, and the second anionic precursor comprises sulfur.

[0103] Figure 8 shows a flowchart of another preparation method 800 for group II-VI core-shell quantum dots. As shown in Figure 8, after preparing a first nanocrystal shell on the quantum dot core and before preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core, the preparation method 800 further includes: preparing a third nanocrystal shell on the first nanocrystal shell.

[0104] In some embodiments, the step of preparing a third nanocrystal shell on the first nanocrystal shell includes: after the first nanocrystal shell has grown, adding a third cation precursor and a third anion precursor, and reacting the third cation precursor and the third anion precursor at a first temperature to generate the third nanocrystal shell, wherein the third anion precursor includes a mixed solution of the first anion precursor and the second anion precursor.

[0105] In some embodiments, the third cationic precursor comprises one or more medium-chain zinc carboxylate species with 6-12 carbon atoms, such as zinc carboxylate species with 7, 8, 9, 10, or 11 carbon atoms. Medium-chain zinc carboxylate species may be, for example, zinc laurate, zinc decanoate, zinc octanoate, etc.

[0106] In the embodiments of this disclosure, the first nanocrystalline shell, the second nanocrystalline shell, and the third nanocrystalline shell can all be prepared at a first temperature, which ranges from 305 to 315°C. Those skilled in the art will understand that, considering the temperature control accuracy and stability of the heating equipment, as well as steps such as adding solutions during the preparation process, the temperature of the reaction system will fluctuate to some extent. In the embodiments of this disclosure, in the steps of preparing the first, second, and third nanocrystalline shells, the temperature of the heating equipment can be set to 310°C, and the actual temperature of the reaction system is approximately in the range of 305-315°C. That is to say, the first, second, and third nanocrystalline shells are all prepared within the approximately 305-315°C range, and it is not required that the first, second, and third nanocrystalline shells be prepared at exactly the same temperature.

[0107] Figure 9 shows a flowchart of another method 900 for preparing group II-VI core-shell quantum dots. As shown in Figure 9, after preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core, the method further includes preparing a fourth nanocrystal shell on the side of the second nanocrystal shell away from the quantum dot core.

[0108] In some embodiments, preparing a fourth nanocrystal shell on the side of the second nanocrystal shell away from the quantum dot core includes: after the second nanocrystal shell has grown, adding a fourth cation precursor and a fourth anion precursor, and reacting the fourth cation precursor and the fourth anion precursor at a second temperature to generate the fourth nanocrystal shell, wherein the composition of the fourth nanocrystal shell is the same as that of the second nanocrystal shell.

[0109] In some embodiments, the fourth cation precursor includes zinc halide, and the fourth anion precursor includes octylthiol.

[0110] Taking the ZnSe / ZnSeS / ZnS / ZnS quantum dot shell as an example, Figure 10 shows the different absorption spectra during the synthesis of the quantum dot shell as the reaction proceeds. As shown in Figure 10, the absorption in the short-wavelength band gradually increases with the epitaxial growth of different shell layers, proving that the epitaxial growth of quantum dots with different shell layers proceeds smoothly. At the same time, with the increase of the number of coating layers, the characteristic peaks of the absorption spectrum gradually become smoother, indicating that the shell components are gradually alloyed, and a gradient alloy shell coating is achieved.

[0111] Figure 11 shows the different absorption spectra during the synthesis process. In Figure 11, the first exciton absorption peak has been normalized, so the absorbance is positively correlated with the shell bandgap and thickness. During the quantum dot synthesis stage, as the reaction proceeds, the inner shell of the quantum dot gradually thickens, showing an increase in absorption at 300-400 nm. In Figure 11, "inner shell" refers to the first nanocrystalline shell ZnSe and the second nanocrystalline shell ZnSeS. The "ZnS epitaxial growth process" in Figure 11 refers to the process of epitaxially growing the third nanocrystalline shell by adding short-chain zinc carboxylate and thio-trioctylphosphine, which shows a significant increase in short wavelengths below 350 nm in the absorption spectrum, corresponding to the epitaxial growth of the wide bandgap material ZnS. The “crystal plane control process” in Figure 11 refers to the process of adding zinc halide and octylthiol to generate the fourth nanocrystalline shell ZnS. The absorption spectrum shows a slight change in the ZnS composition, which proves that the epitaxial growth of ZnS in the previous step reduced the overall effect of ion exchange and avoided the destruction of the inner lattice order.

[0112] Referring back to Figures 5 and 6, the size of the quantum dots did not change significantly after being coated with the fourth nanocrystalline shell of ZnS, but the shape changed from spherical to cubic, indicating that ion exchange and surface crystal plane reshaping mainly occurred at this stage. Based on the lattice arrangement and interatomic spacing analysis, the entire crystal plane is a single... <100> The presence of only one crystal facet, and the absence of other crystal faces, indicates that the proportion of cation polar faces in the quantum dots was significantly increased through crystal facet modulation of the fourth nanocrystal shell.

[0113] Figure 12 shows a schematic diagram of the atomic packing structure on the surface of the quantum dot before and after crystal facet manipulation. Before crystal facet manipulation, the surface of the spherical quantum dot consists of different crystal faces. <111> , <110> , <100> After covering and crystal plane manipulation, the quantum dots changed from spherical to cubic, and the entire crystal plane became a single shape. <100> The quantum dots have no other crystal faces, and the proportion of cation polar faces is greatly increased by crystal facet modulation.

[0114] The above describes a method for preparing quantum dot shells with gradient alloy structures. Quantum dot shells with gradient alloy structures prepared by this method are applicable to any quantum dot core.

[0115] In order to control the emission band of blue quantum dots to the pure blue light band, this disclosure also proposes a method for preparing quantum dot cores.

[0116] In some embodiments, the steps for preparing quantum dot nuclei include: rapidly adding a fifth anion precursor to a fifth cation precursor at a first temperature, causing the fifth cation precursor and the fifth anion precursor to react at a second temperature for a first time period to form a first quantum dot nucleus; and after forming the first quantum dot nucleus, adding a sixth cation precursor at a second temperature to form a second quantum dot nucleus. The cation in the sixth cation precursor is different from the cation in the fifth cation precursor, and the binding energy between the cation in the sixth cation precursor and the fifth anion is higher than the binding energy between the cation in the fifth cation precursor and the fifth anion. The second quantum dot nucleus is a ternary nucleus formed by partially replacing the cation in the first quantum dot nucleus with the cation in the sixth cation precursor. The first quantum dot nucleus can be considered an intermediate in the final formation of the second quantum dot nucleus. In this embodiment, the first time period can range from 2 to 10 minutes, for example, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, etc.

[0117] In the embodiments of this disclosure, both the fourth nanocrystal shell and the quantum dot core can be prepared at a second temperature, which ranges from 295 to 305°C. Those skilled in the art will understand that, considering the temperature control accuracy and stability of the heating equipment, as well as steps such as adding solutions during the preparation process, the temperature of the reaction system will fluctuate to some extent. In the embodiments of this disclosure, in the steps of preparing the fourth nanocrystal shell and the quantum dot core, the temperature of the heating equipment can be set to 300°C, and the actual temperature of the reaction system is approximately in the range of 295-305°C. That is to say, both the fourth nanocrystal shell and the quantum dot core are prepared within the approximate range of 295-305°C, and it is not required that both the fourth nanocrystal shell and the quantum dot core be prepared at exactly the same temperature.

[0118] Figure 13 shows the absorption spectra of quantum dots evolving over time during growth. In Figure 13, the dashed box on the left indicates the growth of ZnSe, and the dashed box on the right indicates the growth of ZnCdSe. For clarity, Figure 13 also shows magnified views of the corresponding portions of the two dashed boxes. Curves 1, 2, 4, 5, 6, 7, 8, 9, and 10 represent the absorption spectra of quantum dots obtained after 1 minute, 2 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes of reaction, respectively. As shown in Figure 13, from 1 to 4 minutes, the absorption peak around 340 nm gradually increases as the reaction proceeds, indicating the nucleation and growth of ZnSe during this stage. Five minutes later, with the addition of the cadmium precursor, an absorption peak appeared in the blue light region of the visible spectrum (450nm-470nm). The absorption peak slowly red-shifted with time, indicating that zinc / cadmium ion exchange occurred after the cadmium precursor was injected at this stage, forming a CdZnSe ternary nucleus. As the reaction proceeded, cadmium gradually accumulated towards the nucleus center, causing the spectrum to gradually red-shift.

[0119] In some embodiments, the composition of the fifth cation precursor is the same as that of the first cation precursor, and the composition of the fifth anion precursor is the same as that of the first anion precursor. That is, the composition of the first quantum dot core is the same as that of the first nanocrystal shell described above. In this case, if an excess of the fifth cation precursor is added during the formation of the quantum dot core, then no additional first cation precursor needs to be added in the step of forming the first nanocrystal shell. The remaining fifth cation precursor after the nucleation step can be used as the first cation precursor for forming the first nanocrystal shell.

[0120] In some embodiments, the fifth cation precursor includes one or more of long-chain zinc carboxylate with a carbon number greater than 12, such as zinc carboxylate with 13, 14, 15, 16, 17, 18, etc. The long-chain zinc carboxylate may include unsaturated long-chain carboxylates (such as zinc oleate) and saturated long-chain carboxylates. The fifth anion precursor includes selenium. The sixth cation precursor includes cadmium carboxylate. Cadmium carboxylate may include saturated cadmium carboxylate (e.g., cadmium stearate, cadmium laurate, cadmium myristate, cadmium behenate, etc.) and unsaturated cadmium carboxylate (e.g., cadmium oleate). The molar ratio of zinc carboxylate to cadmium carboxylate is 20:1 to 50:1. For example, the molar ratio of zinc carboxylate to cadmium carboxylate is 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, etc. In this embodiment, the first quantum dot core formed by the zinc carboxylate precursor and the selenium precursor is ZnSe, and the second quantum dot core formed by adding the cadmium carboxylate precursor is CdZnSe.

[0121] This method for preparing quantum dot nuclei involves first nucleating and growing ZnSe at high temperatures, then adding a cadmium precursor based on the stable ZnSe nucleation. Utilizing the stronger binding energy of selenium / cadmium compared to selenium / zinc, cadmium / zinc ion exchange occurs, resulting in the formation of a CdZnSe ternary nucleus. This approach not only solves the problem of blue quantum dots with CdZnSe luminescent nuclei failing to cover the pure blue light band, but also, the gradient alloy luminescent nucleus structure formed by the ion exchange reaction is expected to further reduce the Auger recombination rate of quantum dots.

[0122] Below, several specific embodiments of methods for preparing quantum dots are given, using the following examples: a solution of zinc carboxylate as the first cation precursor, a solution of zinc carboxylate as the second cation precursor, a solution of zinc carboxylate as the third cation precursor, a solution of zinc halide as the fourth cation precursor, a solution of selenium as the first anion precursor, a solution of sulfur as the second anion precursor, a mixed solution of the first and second anion precursors as the third cation precursor, a solution of octylthiol as the fourth anion precursor / a solution of zinc carboxylate as the fifth cation precursor, and a solution of cadmium carboxylate as the sixth cation precursor / a solution of selenium as the fifth anion precursor.

[0123] First, the preparation methods of various cationic and anionic precursors are introduced.

[0124] Preparation of long-chain zinc carboxylate solutions: For unsaturated long-chain zinc carboxylates (e.g., zinc oleate), zinc acetate is weighed quantitatively in a three-necked flask, and oleic acid is added. The mixture is first degassed, then heated to 170°C and reacted for 10 minutes. The mixture is then cooled and held at 100°C for later use. For saturated carboxylates, long-chain zinc carboxylate is weighed quantitatively and dispersed in an octadecene solution. The solution is heated to 120°C and stirred to form a transparent suspension for later use. Long-chain zinc carboxylates refer to zinc carboxylates with a carbon chain greater than 12 carbon atoms. The concentration range of the long-chain zinc carboxylate solution is 0.1–1 mol / L, optionally 0.2 mol / L.

[0125] Preparation of medium-chain zinc carboxylate solution: Quantitatively weigh medium-chain zinc carboxylate and disperse it in an octadecene solution. Heat to 120℃ and stir to obtain a transparent suspension for later use. Medium-chain zinc carboxylate refers to zinc carboxylate with 6-12 carbon atoms in its carbon chain, such as laurate, decanoate, and octanoate. The concentration range of medium-chain zinc carboxylate is 0.1-1 mol / L, optionally 0.2 mol / L.

[0126] Preparation of short-chain zinc carboxylate: Weigh out a quantitative amount of short-chain zinc carboxylate and place it in a glass weighing vessel or spatula for later use. Short-chain zinc carboxylate refers to zinc carboxylate with fewer than 6 carbon atoms in its carbon chain, such as formate, acetate, propionate, butyrate, etc.

[0127] Preparation of zinc halide solution: Weigh out a quantitative amount of solid zinc halide and dissolve it in acetone. Shake thoroughly to form an emulsion, then aspirate the solution into a syringe for later use. Zinc chloride, such as zinc chloride, zinc bromide, or zinc iodide, can be used.

[0128] Preparation of selenium-trioctylphosphine solution: Selenium powder is added to trioctylphosphine and dissolved by ultrasonication to form a colorless and transparent solution. The solution is then drawn into a syringe for later use. Generally, the concentration range of selenium-trioctylphosphine solution is 0.1-1 mol / L, and optionally, the concentration range is 0.2 mol / L.

[0129] Preparation of sulfur-trioctylphosphine solution: Sulfur powder is added to trioctylphosphine and dissolved by ultrasonication to form a colorless and transparent solution. The solution is then drawn into a syringe for later use. Generally, the concentration range of sulfur-trioctylphosphine solution is 0.1-1 mol / L, and optionally, the concentration range is 0.2 mol / L.

[0130] Preparation of octetrazol-octadecene solution: Octetrazol is quantitatively diluted with octadecene solution, and the solution is drawn into a syringe for later use. Generally, the concentration range of octetrazol-octadecene solution is 0.1-1 mol / L, and optionally, the concentration range is 0.2 mol / L.

[0131] Preparation of saturated cadmium carboxylate solution: Cadmium stearate is mixed with octadecene and stirred at 120°C to form a suspension for later use. Optionally, cadmium carboxylate salts such as cadmium laurate, cadmium myristate, and cadmium behenate can also be used.

[0132] Preparation of unsaturated carboxylic acid cadmium solution: Taking cadmium oleate as an example, cadmium oxide is mixed with octadecene oleate, degassed first, then heated to 200℃ and reacted for 30 minutes, then cooled and kept at 100℃ for later use.

[0133] The following describes in detail specific embodiments of quantum dot preparation, using a quantum dot structure of CdZnSe / ZnSe / ZnSeS / ZnS / ZnS as an example. Figure 14 shows a schematic diagram of the quantum dot synthesis steps according to an embodiment of the present disclosure. Figure 22 shows a schematic diagram of the quantum dot core synthesis steps according to an embodiment of the present disclosure.

[0134] Examples one through five below are specific embodiments of the quantum dot core CdZnSe.

[0135] Example 1

[0136] First, using a double-row tube system, zinc acetate, oleic acid, and octadecene were added to a three-necked flask and subjected to vacuum degassing to remove water, oxygen, and low-boiling-point organic components from the system. The flask was then connected to a nitrogen atmosphere, and the reaction was heated to produce a zinc oleate solution.

[0137] Then, the zinc oleate solution was heated to 300°C, and the selenium precursor solution was quickly injected into the flask using a syringe, with timing started, to allow for the nucleation and growth of zinc selenide quantum dots. After a period of reaction, a cadmium oleate precursor suspension was quickly injected into the flask using a syringe. Taking advantage of the higher binding energy of cadmium selenide compared to zinc selenide, cadmium / zinc ion exchange was performed to form CdZnSe ternary nuclei.

[0138] In Example 1, zinc oleate precursor and cadmium oleate precursor were used, with a zinc / cadmium ratio of 40:1. Figure 23 shows the spectrum of the quantum dots obtained in Example 1. As shown in Figure 23, the emission peak of the quantum dots is 460 nm and the full width at half maximum (FWHM) is less than 30 nm.

[0139] Example 2

[0140] The preparation conditions for Example 2 were the same as those for Example 1, except that the zinc / cadmium ratio was adjusted to 30:1. Figure 24 shows the spectrum of the quantum dots obtained in Example 2. As shown in Figure 24, the emission peak of the quantum dots is 465 nm and the full width at half maximum (FWHM) is less than 30 nm.

[0141] Example 3

[0142] The preparation conditions for Example 3 were the same as those for Example 1, except that cadmium stearate precursor was used instead of cadmium oleate precursor, and the zinc / cadmium ratio was 50:1. Figure 25 shows the spectrum of quantum dots obtained in Example 3. As shown in Figure 25, the emission peak of the quantum dots is 450 nm, and the full width at half maximum (FWHM) is less than 30 nm.

[0143] Example 4

[0144] The preparation conditions for Example 4 were the same as those for Example 1, except that cadmium stearate precursor was used instead of cadmium oleate precursor, and the zinc / cadmium ratio was 40:1. Figure 26 shows the spectrum of the quantum dots obtained in Example 4. As shown in Figure 26, the emission peak of the quantum dots was 460 nm, and the full width at half maximum (FWHM) was less than 30 nm.

[0145] Example 5

[0146] The preparation conditions in Example 4 were the same as in Example 1, except that cadmium stearate precursor was used instead of cadmium oleate precursor, and the zinc / cadmium ratio was 25:1. Figure 27 shows the spectrum of the quantum dots obtained in this example. As shown in Figure 27, the emission peak of the quantum dots is 470 nm, and the full width at half maximum (FWHM) is less than 30 nm.

[0147] In another embodiment, quantum dot cores with a CdSe / CdZnSe structure can also be prepared. A zinc precursor is added during the early stages of CdSe seed formation to form a gradient alloy-coated small-sized CdSe / CdZnSe luminescent core, which is then further coated to complete the shell growth. The advantage of this approach is that it can further increase the distance between the luminescent core and surface defects, improving quantum dot performance. However, the disadvantage is that it requires controlling the CdSe luminescent core with a narrow intrinsic bandgap to an extremely small size to achieve blue light emission, which presents significant synthesis challenges.

[0148] The quantum dot nucleus preparation method disclosed herein employs a hot-injection method for ZnSe nucleation and growth at high temperatures. Subsequently, a cadmium precursor is added to the stable ZnSe nucleation site, and cadmium / zinc ion exchange is performed using the stronger binding energy of selenium / cadmium compared to selenium / zinc, thereby forming a CdZnSe ternary nucleus. This approach not only solves the problem that blue quantum dots with CdZnSe as the luminescent nucleus cannot cover the pure blue light band, but also, the gradient alloy luminescent nucleus structure formed by the ion exchange reaction is expected to further reduce the Auger recombination rate of the quantum dots.

[0149] Examples six to eight below are specific examples of preparing ZnSe / ZnSeS / ZnS / ZnS shells based on CdZnSe cores.

[0150] Example 6

[0151] After the CdZnSe core growth is complete, the temperature is raised to 310℃, and a selenium-trioctylphosphine solution is slowly injected using a syringe pump to perform epitaxial growth of the ZnSe shell. Generally, the injection rate is 2-6 mL / h, optionally 5 mL / h. The zinc oleate added during the nucleation stage is in excess, so no additional cationic precursor is required.

[0152] Then, after the ZnSe shell has grown, a mixed solution of selenium-trioctylphosphine and thio-trioctylphosphine is slowly injected using a syringe pump to perform epitaxial growth of the ZnSeS shell. Generally, the injection rate is 2-6 mL / h, optionally 5 mL / h. During the continuous injection of the anionic precursor, zinc laurate as a cationic precursor for the ZnSeS shell is injected into the flask at equal intervals using a syringe, with an injection interval of 10-15 minutes, optionally 10 minutes.

[0153] Then, after the ZnSeS shell has grown completely, open the sealed rubber stopper and quickly pour the zinc acetate from the weighing boat or spatula into the flask. Next, slowly inject the thio-trioctylphosphine solution using a syringe pump to continue the epitaxial growth of the ZnS shell. Generally, the injection rate is 2-6 mL / h, optionally 5 mL / h.

[0154] Then, after the first ZnS shell has grown, the temperature is adjusted to 300°C, the sealed rubber stopper is opened, and a zinc chloride-acetone solution is slowly injected into the flask using a syringe. During injection, the pressure in the flask needs to be carefully controlled because the acetone rapidly vaporizes. Subsequently, an octetane-octadecene solution is injected to perform the epitaxial growth of the second ZnS shell. Generally, the injection rate is 2-6 mL / h, optionally 5 mL / h. Referring to Figure 11, the growth of the first ZnS shell corresponds to the ZnS epitaxial growth process in Figure 11, and the growth of the second ZnS shell corresponds to the crystal facet manipulation process in Figure 11.

[0155] Finally, after injecting the octetrate-octadecene solution, remove the heat source and allow the flask to cool naturally to room temperature. Remove the quantum dot solution and purify it. The purification process for the quantum dot stock solution can be as follows: Transfer the pre-prepared quantum dot stock solution into a centrifuge tube, add an equal volume of n-hexane solution, and then use ethanol as the antisolvent for purification. The ratio of ethanol to stock solution + n-hexane should be controlled at 0.5:1 to 1:1 until the solution becomes turbid. Place the tube in a centrifuge for purification, typically at 5000 rpm to 10000 rpm for 5 to 10 minutes. After centrifugation, discard the supernatant and disperse the precipitate on the tube wall in a non-polar solvent, such as n-hexane or toluene. Repeat the above steps twice with the antisolvent to obtain the quantum dot solution.

[0156] In Example 6, zinc oleate was used as the long-chain zinc carboxylate, zinc laurate as the medium-chain zinc carboxylate, zinc acetate as the short-chain zinc carboxylate, and zinc chloride as the zinc chloride. The fluorescence quantum efficiency (PLQY) of the blue quantum dots prepared in Example 6 reached 95%. Figure 15 shows the fluorescence quantum efficiency test graph of the blue quantum dots obtained according to this example. Figure 16 shows the transient fluorescence test graph of the quantum dots obtained according to this example. As shown in Figure 16, the transient fluorescence of the quantum dots exhibits single exponential decay.

[0157] Example 7

[0158] The preparation conditions of Example 7 were the same as those of Example 6, except that zinc decanoate was used as a medium-chain zinc carboxylate. The fluorescence quantum efficiency (PLQY) of the blue quantum dots prepared in Example 7 reached 85%. Figure 17 shows the fluorescence quantum efficiency test graph of the blue quantum dots obtained according to this example.

[0159] Example 8

[0160] The preparation conditions for Example 8 were the same as those for Example 6, except that zinc octoate was used as a medium-chain zinc carboxylate. The fluorescence quantum efficiency (PLQY) of the blue quantum dots prepared in Example 8 reached 100%. Figure 18 shows the fluorescence quantum efficiency test graph of the blue quantum dots obtained according to this example.

[0161] The preparation method disclosed herein overcomes the problem of decreased surface activity of quantum dots as size increases, which hinders epitaxial growth, by adjusting the precursor activity. The prepared quantum dot shell has a band gap that gradually increases from the inside to the outside and no obvious interlayer interface, which can effectively improve the photoluminescence quantum yield (PLQY) of the quantum dots.

[0162] Example 9

[0163] In Example 9, a blue QLED device was fabricated using the blue quantum dots prepared in Example 8, achieving an external quantum efficiency of 20%. Figure 19 shows the EQE-voltage diagram of the blue QLED device from Example 9. The emission peak of this blue QLED device is located at 465 nm, conforming to the blue color gamut coordinates of the Rec.2020 display standard. Figure 20 shows the EQE-brightness diagram of the blue QLED device from Example 9. Due to the gradient alloy shell coating, the brightness of this blue QLED device reaches 40000 Cd / m². 2 The efficiency did not roll off at high brightness, demonstrating good stability.

[0164] The researchers also conducted specific experiments to study the effects of ZnS epitaxial growth and crystal plane manipulation processes on the stability of quantum dots.

[0165] Comparative Example 1

[0166] In Comparative Example 1, the epitaxial growth and crystal plane manipulation proposed in this disclosure were not performed, i.e., the prepared quantum dot structure was core / ZnSe / ZnSeS. Table 1 shows the PLQY of the quantum dot solution obtained in Comparative Example 1 under three conditions. As shown in Table 1, although the pre-prepared quantum dots had a high PLQY (80%), after three purification processes, the PLQY was only 23%, and after the original solution was exposed to air, the PLQY also decreased to 46%. This indicates that quantum dots that have not undergone the epitaxial growth and crystal plane manipulation treatment proposed in this disclosure lack stability to both the process and the environment, and the PLQY decreases significantly after purification or exposure to air.

[0167] Table 1

[0168] Comparative Example 2

[0169] In Comparative Example 2, the epitaxial growth and crystal plane manipulation proposed in this disclosure were not performed; that is, the prepared quantum dot structure was core / ZnSe / ZnSeS. Trioctylphosphine ligand was added after one purification. Table 2 shows the PLQY of the quantum dot solution obtained in Comparative Example 3 under three conditions. As shown in Table 2, after one purification and the addition of trioctylphosphine ligand, the PLQY showed a significant rebound (72%), approaching the original solution PLQY (80%). This indicates that the instability of the quantum dot process and environment stems from the exposure of surface defects caused by the shedding and oxidation of the phosphine ligand.

[0170] Table 2

[0171] Comparative Example 3

[0172] In Comparative Example 3, the first ZnS shell was epitaxially grown (i.e., epitaxial growth using a solution of short-chain zinc carboxylate and trioctylphosphine), but no crystal plane manipulation was performed. Table 3 shows the PLQY of the quantum dot solution obtained in Comparative Example 3 under three conditions. As shown in Table 3, the epitaxial growth of the first ZnS shell further improved the original solution PLQY (85%), but after three purification processes, the PLQY was only 28%, and the PLQY also decreased to 53% after the original solution was exposed to air. The stability of the quantum dots to the purification process and environment was not improved, indicating that this implementation method only increased the thickness of the shell layer and did not improve the shedding and oxidation of phosphine ligands after purification and exposure to air.

[0173] Table 3

[0174] Comparative Example 4

[0175] In Comparative Example 4, epitaxial growth of the second ZnS shell was performed (i.e., crystal facet control was achieved using zinc halide and octyl mercaptan), but the epitaxial growth of the first ZnS shell was not performed. Table 4 shows the PLQY of the quantum dot solution obtained in Comparative Example 4 under three conditions. As shown in Table 4, crystal facet control alone reduced the PLQY of the original solution to only 32%. Figure 21 shows a comparison of the quantum dot emission spectra before and after the addition of zinc halide. As shown in Figure 21, the spectrum showed a significant blue shift after the addition of zinc halide, indicating that the addition of the highly reactive zinc halide precursor caused ion exchange between the precursor and the inner shell, resulting in interfacial defects between the quantum dot core and shell. Referring to Table 4, it can also be seen that the crystal facet control process effectively enhanced the process and environmental stability of the quantum dots; the PLQY after purification and exposure to air did not decrease significantly compared to the original solution.

[0176] Table 4

[0177] Example 10

[0178] In Example 10, both epitaxial growth of the first ZnS shell (i.e., epitaxial growth using a short-chain zinc carboxylate and trioctylphosphine solution) and epitaxial growth of the second ZnS shell (i.e., crystal facet control using zinc halide and octyl mercaptan) were performed. Table 5 shows the PLQY of the quantum dot solution obtained in Example 10 under three conditions. As shown in Table 5, after the epitaxial growth of the first ZnS shell and the crystal facet control treatment of the second ZnS shell, the quantum dots not only achieved a high PLQY of 97% in the original solution, but also maintained a PLQY of over 90% after three purifications and exposure to air. Combined with the transmission electron microscopy characterization in Figures 4, 5, and 6, it is shown that the growth of the first ZnS shell increased the thickness of the ZnS, the first ZnS shell controlled the crystal facets of the quantum dots, and the quantum dots transformed from spherical to cubic, with the quantum dot surface being... <100> The polar facets are coordinated with ligands that are highly bond-energetic and environmentally stable, such as carboxylic acids and halogens. Simultaneously, the reduced proportion of nonpolar facets also decreases the proportion of phosphine ligands coordinated with them, eliminating the influence of their inherently weak bond energy and easy oxidation characteristics.

[0179] Table 5

[0180] The quantum dot crystal facet control scheme proposed in this disclosure first uses short-chain zinc salt and trioctylphosphine-sulfur for ZnS epitaxial growth, and then uses zinc halide and octyl mercaptan for crystal facet control. By using two zinc precursors with different reactivity, the transformation of quantum dots from spherical to cubic can be ensured while ion exchange occurs between homogeneous ZnS, without causing lattice defects. Halogen ions in zinc halide, such as chloride ions, act as X-type ligands to coordinate the cation polar facet and passivate the growth of that facet, causing other faces to gradually evolve into cation polar faces as well.

[0181] In the accompanying drawings, the thickness of certain areas and layers may be exaggerated for clarity. The same reference numerals in the figures denote the same or similar structures, and therefore their detailed descriptions are omitted. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the description of this disclosure to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details described, or other methods, components, materials, etc., can be employed. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring the main technical concept of this disclosure.

[0182] It will be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, areas, layers, and / or parts, these elements, components, areas, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, component, area, layer, or part from another. Therefore, the first element, component, area, layer, or part discussed above may be referred to as the second element, component, area, layer, or part without departing from the teachings of this disclosure.

[0183] Spatial relative terms such as “row,” “column,” “below,” “above,” “left,” “right,” etc., may be used herein for ease of description to describe the relationship between one element or feature illustrated in the figures and another element(s). It will be understood that these spatial relative terms are intended to cover different orientations of the device in use or operation other than those depicted in the figures. For example, if the device in the figure is flipped, then an element described as “below other elements or features” will be oriented “above other elements or features.” Thus, the exemplary term “below” can cover both orientations above and below. Devices may be oriented in other ways (rotated 90 degrees or otherwise) and the spatial relative descriptors used herein will be interpreted accordingly. Additionally, it will be understood that when a layer is referred to as “between two layers,” it may be the only layer between those two layers, or there may be one or more intermediate layers.

[0184] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprising” and / or “including”, when used in this specification, specify the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. In the description of this specification, references to the terms “one embodiment,” “another embodiment,” etc., mean that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this disclosure. The illustrative expressions of the foregoing terms in this specification do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine the different embodiments or examples described herein and the features of the different embodiments or examples without contradiction.

[0185] It will be understood that when a component or layer is referred to as "on another component or layer," "connected to another component or layer," "coupled to another component or layer," or "adjacent to another component or layer," it may be directly on another component or layer, directly connected to another component or layer, directly coupled to another component or layer, or directly adjacent to another component or layer, or there may be intermediate components or layers. Conversely, when a component is referred to as "directly on another component or layer," "directly connected to another component or layer," "directly coupled to another component or layer," or "directly adjacent to another component or layer," no intermediate components or layers exist. However, in any case, "on" or "directly on" should not be interpreted as requiring a layer to completely cover the layer below.

[0186] Embodiments of this disclosure are described herein with reference to illustrative illustrations (and intermediate structures) of idealized embodiments. Therefore, variations in the illustrated shapes should be expected, for example, as a result of manufacturing techniques and / or tolerances. Consequently, embodiments of this disclosure should not be construed as limited to the specific shapes of the regions illustrated herein, but should include, for example, shape deviations due to manufacturing processes. Thus, the regions illustrated are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of a device and are not intended to limit the scope of this disclosure.

[0187] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the relevant field and / or the context of this specification, and will not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0188] As those skilled in the art will understand, although the steps of the methods in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order unless the context clearly indicates otherwise. Additional or alternatively, multiple steps may be combined into a single step, and / or a single step may be broken down into multiple steps. Furthermore, other method steps may be inserted between steps. Inserted steps may represent improvements to the method described herein, or may be unrelated to the method. Moreover, a given step may not be fully completed before the next step begins.

[0189] "At least one of A, B and C" has the same meaning as "at least one of A, B or C", both including the following combinations of A, B and C: only A, only B, only C, combinations of A and B, combinations of A and C, combinations of B and C, and combinations of A, B and C.

[0190] "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.

[0191] As used herein, “about,” “approximately,” or “approximately” includes the stated value and the average value within an acceptable range of deviation from the given value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the given quantity (i.e., the limitations of the measurement system).

[0192] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A core-shell quantum dot comprising group II and group VI elements, wherein the quantum dot shell has a gradient alloy structure having a band gap that increases from the inside to the outside.

2. The quantum dot according to claim 1, wherein the quantum dot shell comprises: A first nanocrystal shell is located on the quantum dot core, and the first nanocrystal shell comprises a first group II-VI compound; as well as A second nanocrystal shell located on the side of the first nanocrystal shell away from the quantum dot core, the second nanocrystal shell comprising a second group II-VI compound; The band gap of the second nanocrystal shell is greater than that of the first nanocrystal shell.

3. The quantum dot according to claim 2, wherein the quantum dot shell further comprises: A third nanocrystal shell is located between the first and second nanocrystal shells, the third nanocrystal shell comprising a third group II-VI compound, which is an alloy of the first and second group II-VI compounds. The band gap of the third nanocrystal shell is greater than that of the first nanocrystal shell, and the band gap of the third nanocrystal shell is smaller than that of the second nanocrystal shell.

4. The quantum dot according to claim 3, wherein the first group II-VI compound comprises ZnSe, the second group II-VI compound comprises ZnS, and the third group II-VI compound comprises ZnSeS.

5. The quantum dot according to claim 4, wherein the radius of the quantum dot core is 1.3 nm ± 0.3 nm, the thickness of the first nanocrystal shell is 1.6 nm ± 0.1 nm, the thickness of the second nanocrystal shell is 0.9 nm ± 0.1 nm, and the thickness of the third nanocrystal shell is 1.1 nm ± 0.1 nm.

6. The quantum dot according to any one of claims 1-5, wherein the quantum dot has a spherical shape.

7. The quantum dot according to claim 6, wherein the quantum dot shell further comprises: A fourth nanocrystal shell is located on the side of the second nanocrystal shell away from the quantum dot core, and the composition of the fourth nanocrystal shell is the same as that of the second nanocrystal shell.

8. The quantum dot according to claim 7, wherein the second nanocrystal shell and the fourth nanocrystal shell are both composed of ZnS, the ratio of Zn to S in the second nanocrystal shell is 1:1, and the ratio of Zn to S in the fourth nanocrystal shell is 1:1-2:

1.

9. The quantum dot according to claim 7 or 8, wherein the quantum dot has a cubic shape.

10. The quantum dot according to claim 9, wherein the crystal plane of the quantum dot is... <100> Crystal facets.

11. The quantum dot according to claim 1 or 2, wherein the structure of the quantum dot shell is ZnSe / ZnSeS / ZnS / ZnS or ZnSe / ZnSeS / ZnS or ZnSe / ZnS / ZnS.

12. The quantum dot according to claim 10, comprising a quantum dot body and ligands coordinated on the quantum dot body, wherein, The ligand is an ionic ligand.

13. The quantum dot according to claim 12, wherein the ligand is a carboxylic acid or a halogen.

14. The quantum dot according to any one of claims 1-11, wherein the quantum dot core contains the element cadmium (Cd), and the quantum dot emits light at a wavelength less than 470 nm.

15. The quantum dot according to claim 14, wherein the composition of the quantum dot core is CdZnSe or CdSe / CdZnSe.

16. The quantum dot according to claim 15, wherein the emission peak is adjustable in the range of 450nm-470nm and the full width at half maximum (FWHM) is less than 30nm.

17. In the quantum dot according to claim 15, the molar amount of Cd accounts for 0.5%-2% of the total molar amount of the quantum dot.

18. A quantum dot light-emitting device comprising a quantum dot according to any one of claims 1-17.

19. A method for preparing group II-VI core-shell quantum dots, comprising: Preparation of quantum dot cores; A first nanocrystal shell is prepared on the quantum dot core; A second nanocrystal shell is prepared on the side of the first nanocrystal shell away from the quantum dot core; The band gap of the second nanocrystal shell is greater than that of the first nanocrystal shell.

20. The method according to claim 19, wherein, The preparation of the first nanocrystal shell on the quantum dot core includes: reacting a first cation precursor and a first anion precursor in a solution containing the quantum dot core at a first temperature to generate the first nanocrystal shell; Preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core includes: adding a second cation precursor and a second anion precursor, and reacting the second cation precursor and the second anion precursor at a first temperature to generate the second nanocrystal shell. The first cation precursor and the second cation precursor have different reactivity.

21. The method according to claim 20, wherein, The first cationic precursor includes one or more of long-chain zinc carboxylate with a C number greater than 12, the second cationic precursor includes one or more of short-chain zinc carboxylate with a C number less than 6, the first anionic precursor includes selenium, and the second anionic precursor includes sulfur.

22. The method according to claim 21, further comprising, after preparing a first nanocrystal shell on the quantum dot core and before preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core: A third nanocrystal shell is prepared on the first nanocrystal shell.

23. The method according to claim 22, wherein, The preparation of a third nanocrystal shell on the first nanocrystal shell includes: after the first nanocrystal shell is grown, adding a third cation precursor and a third anion precursor, and reacting the third cation precursor and the third anion precursor at a first temperature to generate the third nanocrystal shell, wherein the third anion precursor includes a mixed solution of the first anion precursor and the second anion precursor.

24. The method according to claim 23, wherein, The third cationic precursor includes one or more of medium-chain zinc carboxylate with 6-12 carbon atoms.

25. The method according to claim 20 or 23, wherein, The first temperature range is 305-315℃.

26. The method according to claim 19, further comprising, after preparing a second nanocrystal shell on the side of the first nanocrystal shell away from the quantum dot core: A fourth nanocrystal shell is prepared on the side of the second nanocrystal shell away from the quantum dot core.

27. The method according to claim 26, wherein, The preparation of a fourth nanocrystal shell on the side of the second nanocrystal shell away from the quantum dot core includes: after the second nanocrystal shell has grown, adding a fourth cation precursor and a fourth anion precursor, and reacting the fourth cation precursor and the fourth anion precursor at a second temperature to generate the fourth nanocrystal shell, wherein the composition of the fourth nanocrystal shell is the same as that of the second nanocrystal shell.

28. The method according to claim 27, wherein, The fourth cation precursor includes zinc halide, and the fourth anion precursor includes octylthiol.

29. The method according to any one of claims 19-28, wherein, The preparation of quantum dot cores includes: At the second temperature, the fifth anion precursor is rapidly added to the fifth cation precursor, so that the fifth cation precursor reacts with the fifth anion precursor to form the first quantum dot nucleus during the first time period.

30. The method of claim 29, further comprising: After the first quantum dot nucleus is formed, a sixth cation precursor is added at a second temperature to form the second quantum dot nucleus; The cation in the sixth cation precursor is different from the cation in the fifth cation precursor, and the binding energy between the cation in the sixth cation precursor and the fifth anion is higher than the binding energy between the cation in the fifth cation precursor and the fifth anion. The second quantum dot core is a ternary core formed by partially replacing the cation in the first quantum dot core with the cation in the sixth cation precursor.

31. The method according to claim 29 or 30, wherein the second temperature ranges from 295 to 305°C.

32. The method according to claim 29, wherein, The components of the fifth cation precursor are the same as those of the first cation precursor, and the components of the fifth anion precursor are the same as those of the first anion precursor.

33. The method according to claim 32, wherein, The first cation precursor includes an excess of the fifth cation precursor remaining during the formation of the quantum dot nucleus.

34. The method according to claim 30, wherein, The fifth cation precursor includes one or more of long-chain zinc carboxylate with a C number greater than 12, the fifth anion precursor includes selenium, and the sixth cation precursor includes cadmium carboxylate.

35. The method according to claim 34, wherein, The molar ratio of zinc carboxylate to cadmium carboxylate is 20:1 to 50:

1.

36. The method according to claim 29, wherein, The first time period is in the range of 2-10 minutes.

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