Preparation method of two-dimensional semiconductor nanocrystal

Abstract

The invention discloses a preparation method of two-dimensional semiconductor nanocrystals, and relates to the technical field of semiconductor luminescent materials. The preparation method comprises the following steps: adding a tellurium (Te) precursor solution and a sulfur (S) source into a cadmium (Cd) precursor solution, and carrying out gradient heating reaction in an inert atmosphere to obtain the two-dimensional semiconductor nanocrystals (CdTeS NPLs), the cadmium precursor solution is obtained by reacting a cadmium source, a ligand and a solvent in an inert atmosphere. The CdTeS NPLs disclosed by the invention has the characteristics of good quantum yield and green light emission performance, and has a very good application prospect in green light emission materials as a novel two-dimensional semiconductor nanocrystal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor light-emitting materials, in particular to a preparation method of two-dimensional semiconductor nanocrystals. BACKGROUND

[0002] Atomically flat semiconductor nanocrystals (NPLs), also known as colloidal quantum wells, are a class of semiconductor light-emitting materials with great potential in the next generation of optoelectronic devices. They have the following unique characteristics: narrow emission bandwidth (~ 40 meV), super large phonon strength and ultrafast fluorescence lifetime, extremely large linear and nonlinear absorption cross section, and suppressed Auger recombination. The above advantages make it have broad application prospects in the field of photons such as photovoltaics, photodetectors, light-emitting diodes (LEDs) and lasers.

[0003] However, the main problem faced by such nanocrystals is how to maintain their two-dimensional morphology with atomic thickness. Uniform alloying of nanocrystals without changing the vertical thickness is one of the effective ways to further adjust their optical properties. The advantage of alloyed nanocrystals is that by precisely controlling the amount of added precursor, their optoelectronic properties can be predicted in advance. Moreover, alloying can not only adjust the optical properties, but also control the lattice strain and structural defects. However, the current development of two-dimensional semiconductor nanocrystals is still insufficient - related research mainly focuses on cadmium sulfide-selenium nanocrystals, and the existing synthesis method for other cadmium sulfide-tellurium nanocrystals (such as cadmium sulfide-tellurium nanocrystals) is still limited. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of two-dimensional semiconductor nanocrystals to solve the problems existing in the prior art. The two-dimensional semiconductor nanocrystals of the present application have good quantum yield and green light emission performance.

[0005] To achieve the above purpose, the present application provides the following scheme: One of the technical solutions of the present application: a preparation method of two-dimensional semiconductor nanocrystals (CdTeS NPLs), comprising the following steps: adding tellurium (Te) precursor solution and sulfur (S) source in the cadmium (Cd) precursor solution, and performing gradient temperature reaction under inert atmosphere to obtain the two-dimensional semiconductor nanocrystals; The cadmium precursor solution is obtained by reacting cadmium source, ligand and solvent under inert atmosphere.

[0006] The application synthesizes cadmium precursor under inert atmosphere, then mixes with sulfur source and tellurium precursor solution in a certain proportion, and then obtains two-dimensional semiconductor nanocrystal CdTeS NPLs through gradient temperature reaction.

[0007] Further, the cadmium source includes cadmium acetate.

[0008] Further, the ligand includes myristic acid.

[0009] Myristic acid is selected as the cadmium ligand, the molecular chain length of which is moderate, the steric hindrance is small, and the structure is simpler than that of stearic acid and oleic acid, which is not only beneficial to the reaction, but also can play a surface modification role, thereby stabilizing the nanosheet (i.e. two-dimensional semiconductor nanocrystal) and forming relatively uniform nanosheets.

[0010] Further, the solvent includes octadecene (ODE).

[0011] Further, the sulfur source includes hexamethyldisilathiane.

[0012] Further, the tellurium precursor solution is obtained by reacting tellurium powder and tri-n-octylphosphine (TOP) under inert atmosphere.

[0013] Further, the preparation steps of the tellurium precursor solution include: mixing tellurium powder and tri-n-octylphosphine, vacuumizing and then filling nitrogen, then heating to 290-310 ℃ under nitrogen atmosphere, and then performing heat preservation reaction to obtain the tellurium precursor solution.

[0014] Further, the molar ratio of the tellurium powder and the tri-n-octylphosphine is 1:2-5, preferably 1:4.5.

[0015] Further, the operation of vacuumizing and then filling nitrogen is repeated at least 3 times, and the vacuumizing time of each time is 10-20 min.

[0016] Further, the heat preservation reaction time is 35-40 min, preferably 40 min.

[0017] Further, the operation of vacuumizing and then filling nitrogen is carried out at room temperature.

[0018] Further, the preparation step of the cadmium precursor solution comprises: mixing the cadmium source, the ligand and the solvent, vacuumizing at 30-40℃, then filling with nitrogen, then heating to 180-240℃ under nitrogen atmosphere, reacting for 0.5-1 h, then cooling to 100-120℃, vacuumizing for 1-2 h, then filling with nitrogen, and cooling to 30-40℃ under nitrogen atmosphere, then vacuumizing again at 30-40℃, then filling with nitrogen, to obtain the cadmium precursor solution.

[0019] Further, the molar ratio of the cadmium source to the ligand is 1:1-3.

[0020] Further, the molar ratio of the cadmium source to the solvent is 1:30-40.

[0021] Preferably, the heating is performed under nitrogen atmosphere at 180℃ for 1 h.

[0022] Further, the operation of vacuumizing at 30-40℃ and then filling with nitrogen is repeated for at least 3 times, and the vacuumizing time is 10-20 min each time.

[0023] Further, the operation of vacuumizing at 40℃ and then filling with nitrogen is repeated for at least 3 times, and the vacuumizing time is 10-20 min each time.

[0024] Further, the molar ratio of the tellurium element contained in the tellurium precursor solution to the sulfur element contained in the sulfur source is 0.2-1.8:1.8-0.2.

[0025] Preferably, the molar ratio of the tellurium element contained in the tellurium precursor solution to the sulfur element contained in the sulfur source is 1.4:0.6.

[0026] Further, the molar ratio of the cadmium element contained in the cadmium precursor solution to the tellurium element contained in the tellurium precursor solution + the sulfur element contained in the sulfur source is 0.6-1.0:2.

[0027] Preferably, the molar ratio of the cadmium element contained in the cadmium precursor solution to the tellurium element contained in the tellurium precursor solution + the sulfur element contained in the sulfur source is 0.8:2.

[0028] Further, the gradient temperature reaction is specifically 100 / 120 / 140 / 160 / 180 ℃ each temperature for 10-30 min (i.e. after reaction at 100 ℃ for 10-30 min, the temperature is increased to 120 ℃ for 10-30 min, then the temperature is increased to 140 ℃ for 10-30 min, then the temperature is increased to 160 ℃ for 10-30 min, then the temperature is increased to 180 ℃ for 10-30 min), or 100 / 120 / 140 / 160 / 180 / 200 ℃ each temperature for 10-30 min, or 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ each temperature for 10-30 min.

[0029] Preferably, the gradient temperature reaction is specifically 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ each temperature for 15 min.

[0030] Preferably, the two-dimensional semiconductor nanocrystals are prepared in a standard Schlenk line, and the more specific preparation steps include: The tellurium powder and tri-n-octylphosphine (molar ratio of 1:2-5, preferably 1:4.5) are placed in a three-necked flask; under room temperature stirring conditions, the operation of repeatedly vacuuming and then filling with nitrogen is repeated at least 3 times, each time for 10-20 min; then the solution is heated to 290-310 ℃ under a nitrogen atmosphere, and a constant temperature reaction is maintained at this temperature, during which a black Te powder is observed to gradually dissolve to obtain a light yellow clear transparent solution, and after constant temperature reaction for 35-40 min (preferably 40 min), the solution is cooled to room temperature, vacuumed for 30 min, and a tellurium precursor solution is obtained; The cadmium source (cadmium acetate), ligand (myristic acid) and solvent (octadecene) are placed in a three-necked flask (molar ratio of cadmium source to ligand is 1:1-3), and under 30-40 ℃, the operation of repeatedly vacuuming and then filling with nitrogen is repeated at least 3 times, each time for 10-20 min; then the solution is heated to 180-240 ℃ (preferably 180 ℃) for 0.5-1 h (preferably 1 h) under a nitrogen atmosphere; after the reaction is completed, the temperature is cooled to 100-120 ℃, vacuumed for 1-2 h, then filled with nitrogen, and cooled to 30-40 ℃ under a nitrogen atmosphere, then the operation of repeatedly vacuuming and then filling with nitrogen is repeated at least 3 times, each time for 10-20 min, and a cadmium precursor solution is obtained; The tellurium precursor solution is added to the cadmium precursor solution, mixed, and then the sulfur source (the sulfur source is hexamethyldisilthiane, and the molar ratio of the cadmium element contained in the cadmium precursor solution to the tellurium element contained in the tellurium precursor solution plus the sulfur element contained in the sulfur source is 0.6-1.0:2, preferably 0.8:2; the molar ratio of the tellurium element contained in the tellurium precursor solution to the sulfur element contained in the sulfur source is 0.2-1.8:1.8-0.2, preferably 1.4:0.6) is added, and then a gradient temperature reaction (100 / 120 / 140 / 160 / 180℃, each temperature for 10-30 min, or 100 / 120 / 140 / 160 / 180 / 200℃, each temperature for 10-30 min, or 100 / 120 / 140 / 160 / 180 / 200 / 220℃, each temperature for 10-30 min; preferably 100 / 120 / 140 / 160 / 180 / 200 / 220℃, each temperature for 15 min) is performed to obtain the two-dimensional semiconductor nanocrystals.

[0031] The sulfur source and the tellurium are added to the cadmium precursor solution, and then a gradient temperature reaction is performed, that is, the two-dimensional semiconductor nanocrystals are synthesized by a one-pot method, the process flow is simpler, and the relative quantum yield of the obtained CdTeS NPLs is higher.

[0032] Preferably, after the gradient temperature reaction is completed, the steps of purification and drying are further included, specifically: the reaction solution is dissolved in toluene, and ethanol is added to precipitate for 5-15 min, and then centrifuged for 3-8 min; the precipitate collected by centrifugation is again dissolved in toluene, and ethanol is added to precipitate for 5-15 min, and then centrifuged for 3-8 min; the steps are repeated three times, and then the precipitate collected by centrifugation in the third time is dried.

[0033] The CdTeS NPLs synthesized by the method are a novel ternary alloy two-dimensional nanocrystal structure, have a specific composition (the chemical formula can be defined as CdTe x S 1-x wherein x is 0.1-0.9, preferably 0.7) or size (the lateral size of a single CdTeS nanosheet is about 15-30 nm), and the relative quantum yield can reach 40%.

[0034] The second technical scheme of the present application: a two-dimensional semiconductor nanocrystal prepared by the method for preparing a two-dimensional semiconductor nanocrystal.

[0035] Further, the two-dimensional semiconductor nanocrystal is a green light emitting material.

[0036] Further, the green light emitting wavelength of the two-dimensional semiconductor nanocrystal is 520-530 nm.

[0037] Preferably, the two-dimensional semiconductor nanocrystals have a green emission wavelength of 526 nm.

[0038] The two-dimensional semiconductor nanocrystals of the present application can be used as green emission materials for the preparation of photovoltaic devices, photodetectors, light emitting diodes or lasers.

[0039] The following technical effects are disclosed by the present application: The present application synthesizes cadmium precursor under inert atmosphere, then mixes with sulfur source and tellurium precursor solution in a certain proportion, and then obtains two-dimensional semiconductor nanocrystals CdTeS NPLs through gradient temperature reaction. Through the cooperation of Cd, Te and S, in addition to adjusting the optical properties, the lattice strain and structural defects can also be controlled to enhance the luminescence and improve the quantum yield.

[0040] Experiments show that the two-dimensional semiconductor nanocrystals CdTeS NPLs provided by the present application have an emission wavelength in the range of 520-530 nm, and a half-width of about 23 nm. It has good quantum yield and green emission characteristics, and has broad application prospects in the fields of photovoltaics, photodetectors, light emitting diodes (LED) and lasers. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0042] Figure 1 XRD pattern of CdTeS NPLs prepared for Example 1.

[0043] Figure 2 TEM pattern of CdTeS NPLs prepared for Example 1.

[0044] Figure 3 Absorption spectrum and emission spectrum of CdTeS NPLs prepared for Example 1.

[0045] Figure 4 Absorption spectrum and emission spectrum of products under different gradient temperature reaction processes prepared for Example 1.

[0046] Figure 5 Absorption spectrum and emission spectrum of CdS NPLs prepared for Comparative Example 1.

[0047] Figure 6 Absorption spectrum and emission spectrum of CdTe NPLs prepared for Comparative Example 2.

[0048] Figure 7 Absorption and emission spectra of CdTeS NPLs prepared for Comparative Example 3.

[0049] Figure 8 Absorption and emission spectra of CdTeS NPLs prepared for Comparative Example 4. DETAILED DESCRIPTION

[0050] Various example embodiments of the present application will now be described in detail with reference to certain figures. Such description, however, is to be considered in all respects only as illustrative, and not restrictive.

[0051] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where particular ranges of values are given, understand that each intervening value, to the upper or lower limit of the ranges is also specifically included. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is also encompassed. The upper and lower limits of these smaller ranges can independently be included or excluded in the range, and are also encompassed.

[0052] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict, the present specification will control.

[0053] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples presented herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application.

[0054] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0055] It should be noted that the present application does not describe in detail the conventional operations in the art and is not the focus of the present application.

[0056] If room temperature is mentioned in the following examples and comparative examples of the present application, it specifically refers to 20-30 °C.

[0057] The raw materials used in the following examples and comparative examples of the present application are all commercially available unless otherwise specified.

[0058] The preparation processes of the following examples and comparative examples of the present application are all carried out in a standard Schlenk line to ensure that the reaction is not interfered by oxygen and water and to accurately control the reaction atmosphere.

[0059] Example 1 A two-dimensional semiconductor nanocrystal (CdTeS NPLs) is prepared by the following steps: (1) Synthesis of tellurium precursor solution (Te-TOP) 0.384 g (3.0 mmol) of Te powder and 4.970 g (13.4 mmol) of TOP were weighed into a 25 mL three-necked flask; under room temperature stirring, the operation of repeated vacuuming and nitrogen filling was repeated for 3 times, each time for 10 min, and the total vacuuming time was 30 min; then the solution was heated to 300 ℃ under nitrogen atmosphere, and kept constant temperature reaction at this temperature; during the reaction process, it was observed that the black Te powder was gradually dissolved to obtain a light yellow clear transparent solution; after constant temperature reaction for 40 min, the solution was cooled to room temperature, vacuumed for 30 min, and the obtained solution was the Te-TOP solution (i.e. the tellurium precursor solution), which was transferred to a storage bottle for standby.

[0060] (2) Preparation of CdTeS NPLs The cadmium acetate dihydrate (0.2132 g, 0.8 mmol), myristic acid (0.2285 g, 1.0 mmol) and octadecene (8.0 g, 31.7 mmol) were stirred and placed in a three-necked flask, which was repeatedly vacuumed and filled with nitrogen for 3 times at 40 ℃, each time for 10 min; then the solution was heated to 180 ℃ for 1 h under the nitrogen atmosphere; after the reaction, the temperature was lowered to 120 ℃, and the vacuum was applied for 1 h, then the nitrogen was filled, and the temperature was lowered to 40 ℃ under the nitrogen atmosphere, then the operation of repeatedly vacuuming and filling with nitrogen was repeated for 3 times, each time for 10 min, to obtain a cadmium precursor solution; then the Te-TOP solution (280 μL, containing Te 0.14 mmol) was added, mixed, and then the hexamethyldisilathiane (13 μL, containing S 0.06 mmol) was added, and a gradient temperature rising reaction was carried out, specifically, 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ for 15 min at each temperature, after the reaction at each temperature (before the temperature was raised for the next stage reaction), 200 μL of the reaction solution was dissolved in 1 mL of toluene, and 2 mL of ethanol was added to precipitate for 10 min, and then centrifuged at 9000 rpm for 5 min, the precipitate collected by centrifugation was dissolved in 1 mL of toluene again, and 2 mL of ethanol was added to precipitate for 10 min, and then centrifuged at 9000 rpm for 5 min, and the operation was repeated for 3 times, and then the precipitate collected by centrifugation for the third time was dried to obtain the product at different gradient temperature rising reaction processes.

[0061] The XRD characterization results of the CdTeS NPL prepared according to the above method (the product obtained after 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ for 15 min at each temperature, specifically CdTe 0.7 S 0.3 The XRD characterization results of the CdTeS NPL prepared according to the above method (the product obtained after 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ for 15 min at each temperature, specifically CdTe

[0062] The black curve in the XRD data graph is the XRD test result of the sample, which is well matched with the crystal standard card of CdTe sphalerite crystal type (located at the bottom of the X axis, light blue solid line); the crystal standard card of CdS sphalerite crystal type is shown at the bottom of the X axis (dark green solid line), and there is a certain matching degree with the measured results of the sample. It can be inferred from the XRD characterization results that the structure of the sample is based on sphalerite CdTe, and part of the Te atoms are replaced by S atoms; at the same time, the proportion of doped S elements is low, because the diffraction peaks in the XRD spectrum do not present a high degree of matching with the CdS sphalerite standard card, only weak characteristic peak signals can be observed, which further confirms that the S atoms are doped in the form of a small amount, and not form an independent CdS phase.

[0063] Figure 2 The TEM images of the CdTeS NPLs (products obtained after 15 min of reaction at each of the temperatures 100 / 120 / 140 / 160 / 180 / 200 / 220 °C) prepared in this example show that the nanosheets exhibit a clear stacking aggregation feature, with the sheet layers overlapping and closely assembling to form continuous and compact assembly regions. The layered or stacked morphology of the nanosheets can be observed, and the boundaries between the sheets are relatively blurred due to the dense stacking. This significant vertical stacking is speculated to be driven by the interactions between the sheets, such as van der Waals forces or ligand-mediated interactions, which promote the self-assembly of the nanosheets during sample preparation or processing. From the TEM images, it can also be further seen that the lateral size of the individual CdTeS nanosheets is about 15-30 nm, exhibiting an ultrathin two-dimensional sheet-like morphology. Figure 2

[0064] Figure 3 The absorption spectrum (UV) and emission spectrum (PL) of the CdTeS NPLs (products obtained after 15 min of reaction at each of the temperatures 100 / 120 / 140 / 160 / 180 / 200 / 220 °C) prepared in this example, with the inset being a fluorescence photo, show from the absorption spectrum that the first exciton characteristic absorption peak of the CdTeS NPLs is at 513 nm, and the second exciton characteristic absorption peak is at 454 nm. From the emission spectrum, it can be seen that the emission peak half-width of the CdTeS NPLs is about 23 nm, the emission wavelength is 526 nm, and the CdTeS NPLs can emit a narrow emission bandwidth green light, with a relative quantum yield of 40%.

[0065] Figure 4 The absorption spectrum and emission spectrum of the products obtained at different gradient temperature reaction processes prepared in this example show that the first exciton peak of the sample obtained after the gradient temperature is increased to 160 °C is 429 nm, and the first exciton peak of the sample obtained after the gradient temperature is increased to 180 °C is shifted to 513 nm, indicating that the CdTeS NPLs are synthesized when the gradient temperature is increased to 180 °C. In addition, comparing the emission spectra of the sample obtained after the gradient temperature is increased to 180 °C, the sample obtained after the gradient temperature is increased to 200 °C, and the sample obtained after the gradient temperature is increased to 220 °C, it can be seen that the tailing of the sample obtained after the gradient temperature is increased to 220 °C is significantly improved compared to the tailing of the sample obtained after the gradient temperature is increased to 180 °C and the sample obtained after the gradient temperature is increased to 200 °C (spectrum tailing will destroy optical uniformity, mask intrinsic properties, and also reduce energy utilization efficiency), and therefore, it is preferred that the reaction is carried out for 15 min at each of the temperatures 100 / 120 / 140 / 160 / 180 / 200 / 220 °C. ​

[0066] Comparative Example 1 A CdS NPLs was prepared by the following steps: Under stirring, cadmium acetate dihydrate (0.2132 g, 0.8 mmol), myristic acid (0.2285 g, 1.0 mmol) and 8.0 g of octadecene (ODE) were placed in a three-necked flask, and the operation of vacuumizing for 10 min and then filling with nitrogen was repeated 3 times at 40 ℃. Then the solution was heated to 180 ℃ for 1 h under nitrogen. After the reaction, the temperature was lowered to 120 ℃, and the operation of vacuumizing for 10 min and then filling with nitrogen was repeated 3 times. Then hexamethyldisilathiane (13 μL, containing S 0.06 mmol) was added, and a gradient temperature reaction was carried out. Specifically, the reaction was carried out at 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ for 15 min, respectively. After the reaction at each temperature (before the temperature was raised for the next stage of reaction), 200 μL of the reaction solution was dissolved in 1 mL of toluene, and 2 mL of ethanol was added for precipitation for 10 min, followed by centrifugation at 9000 rpm for 5 min. The precipitate collected by centrifugation was dissolved in 1 mL of toluene again, and 2 mL of ethanol was added for precipitation for 10 min, followed by centrifugation at 9000 rpm for 5 min. The operation was repeated 3 times. The precipitate collected by centrifugation in the third time was dried to obtain the product at different gradient temperature reaction processes.

[0067] Figure 5 The absorption spectrum (UV) and the emission spectrum (PL) of the CdS NPLs prepared in this comparative example (the product obtained after the reaction at 100 / 120 / 140 / 160 / 180 / 200 ℃ for 15 min, respectively) were shown in the following figures. As can be seen from the absorption spectrum, the first exciton characteristic absorption peak was at 406 nm, and the second exciton characteristic absorption peak was at 373 nm. As can be seen from the emission spectrum, the fluorescence intensity of the CdS NPLs was very low, and the defect emission was obvious.

[0068] Comparative Example 2 A CdTe NPLs was prepared by the following steps: (1) Synthesis of tellurium precursor solution (Te-TOP) The synthesis step was the same as step (1) of Example 1.

[0069] (2) Preparation of CdTe NPLs CdO (8.07 mmol) and 10 mL of propionic acid were added into a flask; under nitrogen atmosphere, heating at 70 ℃ for 1 hour until the solid was completely dissolved to obtain a colorless solution; after stopping heating, adding acetone to precipitate the product as a white solid; filtering the precipitate, washing with acetone, and vacuum drying for 12 hours to obtain cadmium propionate; 130 mg of cadmium propionate (0.5 mmol) obtained above, 80 μL of oleic acid (0.25 mmol), and 10 mL of octadecene (ODE) were added into a 50 mL three-necked flask, vacuum degassed and magnetically stirred at 95 ℃ for 2 hours. Under nitrogen atmosphere, heating to 210 ℃, then quickly adding 200 μL of TOP-Te solution (containing Te 0.1 mmol) to react for 30 minutes, and sampling for testing.

[0070] Figure 6 The absorption spectrum (UV) and emission spectrum (PL) of the CdTe NPLs prepared in this comparative example were shown in the figures. From the absorption spectrum, the first exciton characteristic absorption peak was at 504 nm, and the second exciton characteristic absorption peak was at 455 nm. From the emission spectrum, it can be seen that the fluorescence intensity of the CdTe NPLs was very low, almost close to no fluorescence.

[0071] Comparative Example 3 The same as Example 1, except that the gradient heating reaction process was changed to directly heating to 220 ℃ for 15 minutes.

[0072] Figure 7 The absorption spectrum (UV) and emission spectrum (PL) of the CdTeS NPLs prepared in this comparative example were shown in the figures. It can be seen that the emission peak was at 526 nm. In addition, the emission spectrum of the CdTeS NPLs was compared with the emission spectrum of the sample obtained after the gradient heating to 220 ℃ for 15 minutes in Example 1. Figure 4 It can be found that the tailing phenomenon of the CdTeS NPLs prepared in this comparative example was obvious, indicating that the fluorescence performance was not as good as the sample obtained after the gradient heating to 220 ℃ for 15 minutes in Example 1.

[0073] Comparative Example 4 (1) Synthesis of tellurium precursor solution (Te-TOP) The synthesis step was the same as step (1) of Example 1.

[0074] (2) Preparation of CdTeS NPLs The cadmium acetate dihydrate (0.2132 g, 0.8 mmol), oleic acid (316 μL, 1.0 mmol) and octadecene (8.0 g, 31.7 mmol) were stirred and placed in a three-necked flask, which was subjected to vacuum-nitrogen cycle for 3 times at 40 ℃, each time for 10 min; then the solution was heated to 180 ℃ for 1 h under nitrogen atmosphere; after the reaction, the temperature was decreased to 120 ℃, and the flask was subjected to vacuum-nitrogen cycle for 1 h; then the temperature was decreased to 40 ℃ under nitrogen atmosphere, and the flask was subjected to vacuum-nitrogen cycle for 3 times, each time for 10 min, to obtain a cadmium precursor solution; then the Te-TOP solution (280 μL, containing Te 0.14 mmol) was added, and the mixture was stirred; then hexamethyldisilathiane (13 μL, containing S 0.06 mmol) was added, and the mixture was subjected to gradient temperature rising reaction, specifically, the mixture was reacted at 100 / 120 / 140 / 160 / 180 / 200 ℃ for 15 min, respectively; after the reaction, 200 μL of the reaction solution was dissolved in 1 mL of toluene, and 2 mL of ethanol was added for precipitation for 10 min; then the mixture was centrifuged at 9000 rpm for 5 min; the precipitate collected by centrifugation was dissolved in 1 mL of toluene again, and 2 mL of ethanol was added for precipitation for 10 min; then the mixture was centrifuged at 9000 rpm for 5 min; the operation was repeated for 3 times; and the precipitate collected by centrifugation in the third time was dried to obtain the CdTeS NPLs.

[0075] Figure 8 The absorption spectrum (UV) and the emission spectrum (PL) of the CdTeS NPLs prepared in the present example can be seen, and the emission peak is 526 nm. In addition, the emission spectrum of the CdTeS NPLs prepared in the present example is compared with the emission spectrum of the sample obtained after the gradient temperature rising to 200 ℃ in Example 1, and it can be found that the tailing phenomenon of the CdTeS NPLs prepared in the present example is obvious, which indicates that the fluorescence performance of the CdTeS NPLs prepared in the present example is not as good as that of the sample obtained after the gradient temperature rising to 200 ℃ in Example 1. Figure 4

[0076] It can be seen from the comparison between the example and the present example that the luminescence of the CdTeS NPLs of the present application has the characteristics of greatly reduced half-peak width and improved quantum yield, and the CdTeS NPLs have good application prospect as green light emitting materials.

[0077] The above-described examples are only used to describe the preferred modes of the present application, and do not limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application.​

Claims

1. A method for preparing two-dimensional semiconductor nanocrystals, characterized in that, Includes the following steps: Tellurium precursor solution and sulfur source are added to cadmium precursor solution, and a gradient temperature increase reaction is carried out under an inert atmosphere to obtain the two-dimensional semiconductor nanocrystals. The cadmium precursor solution is obtained by reacting a cadmium source, ligand, and solvent under an inert atmosphere.

2. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 1, characterized in that, The cadmium source includes cadmium acetate; And / or, the ligand includes myristic acid; And / or, the solvent includes octadecene; And / or, the sulfur source includes hexamethyldisilthane; And / or, the tellurium precursor solution is obtained by reacting tellurium powder and tri-n-octylphosphine under an inert atmosphere.

3. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 2, characterized in that, The preparation steps of the tellurium precursor solution include: mixing tellurium powder and tri-n-octylphosphine, evacuating and then filling with nitrogen, then heating to 290-310 °C under a nitrogen atmosphere and maintaining the temperature to obtain the tellurium precursor solution.

4. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 3, characterized in that, The molar ratio of tellurium powder to tri-n-octylphosphine is 1:2-5; And / or, the operation of purging with nitrogen after vacuuming is repeated at least 3 times, with each vacuuming operation lasting 10-20 minutes; And / or, the heat preservation reaction time is 35-40 min.

5. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 1, characterized in that, The preparation steps of the cadmium precursor solution include: mixing the cadmium source, ligand and solvent, evacuating at 30-40 °C and then purging with nitrogen, then heating to 180-240 °C under a nitrogen atmosphere and reacting for 0.5-1 h, cooling to 100-120 °C after the reaction, evacuating for 1-2 h and then purging with nitrogen, then cooling to 30-40 °C under a nitrogen atmosphere, then evacuating again at 30-40 °C and purging with nitrogen to obtain the cadmium precursor solution.

6. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 5, characterized in that, The molar ratio of the cadmium source to the ligand is 1:1-3; And / or, the operation of evacuating at 30-40 °C and then purging with nitrogen shall be repeated at least 3 times, with each evacuation lasting 10-20 min; And / or, the operation of evacuating again at 30-40 °C and then purging with nitrogen is repeated at least 3 times, with each evacuation lasting 10-20 min.

7. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 1, characterized in that, The molar ratio of tellurium in the tellurium precursor solution to sulfur in the sulfur source is 0.2-1.8:1.8-0.2; And / or, on a molar ratio, the cadmium content in the cadmium precursor solution: the tellurium content in the tellurium precursor solution + the sulfur content in the sulfur source = 0.6-1.0:

2.

8. The method for preparing two-dimensional semiconductor nanocrystals as described in claim 1, characterized in that, The gradient heating reaction specifically involves reacting at 100 / 120 / 140 / 160 / 180 ℃ for 10-30 min, or at 100 / 120 / 140 / 160 / 180 / 200 ℃ for 10-30 min, or at 100 / 120 / 140 / 160 / 180 / 200 / 220 ℃ for 10-30 min.

9. A two-dimensional semiconductor nanocrystal prepared by a method according to any one of claims 1-8.

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