Method for in-situ synthesis of high-quality HgTe colloidal quantum dots

Abstract

The invention discloses a method for in-situ synthesis of high-quality HgTe colloidal quantum dots, and relates to a quantum dot technology, in particular to a preparation method of HgTe colloidal quantum dots (CQDs). The invention provides a novel passivator (PFGA) for retarding the nucleation rate in quantum dot synthesis, the size uniformity of HgTe CQDs (colloidal quantum dots) synthesized in situ is improved, the synthesis steps are simplified, and the operation steps are simplified for optimizing the subsequent HgTe CQDs ligand modification process. The in-situ synthesized HgTe CQDs have the advantages of uniform particle size, excellent exciton absorption peak, stable wavelength expansion, excellent optical performance and good atmospheric stability.

Description

Technical Field

[0001] The present invention relates to quantum dot technology, and in particular to a method for preparing HgTe colloidal quantum dots (CQDs). Background Art

[0002] Colloidal quantum dots (CQDs) are semiconductor nanocrystals with a size of 2-20 nm and a surface coating smaller than their exciton Bohr radius. These are "quasi-zero-dimensional" nanomaterials containing thousands of atoms and carrying a surface charge. The coating of one or more long-chain organic ligands protects the quantum dots and improves their dispersion, ensuring their stability in solution.

[0003] Secondary hot injection is a method for preparing colloidal quantum dots (CQDs). It involves rapidly injecting a solution containing a quantum dot precursor into a hot solvent, causing the precursor to decompose and form the quantum dots. This method has been widely studied for its ability to rapidly produce high-quality quantum dots. However, this method also has some drawbacks, such as difficulty in temperature control and very short reaction times, which make precise control difficult and lead to uneven size distribution of the quantum dots. Summary of the Invention

[0004] The present invention aims to provide a method for in-situ synthesis of HgTe colloidal quantum dots, which is prepared by ligand exchange and spin coating, and the method is simple and efficient.

[0005] The method for in-situ synthesis of high-quality HgTe colloidal quantum dots is characterized by the following steps: S1, HgCl2, oleylamine and hexafluoropentadiene (PFGA) were mixed at 70-120 o C, stirring and heating, while the reaction vessel is evacuated and filled with argon to form an oleylamine-Hg solution; S2, the reaction is complete, at 70-120 o C in an Ar atmosphere, the system was injected twice. The first time, 100 μL of 1 mmol non-metallic precursor trioctylphosphine tellurium (TOP-Te) was injected within 1 minute and held for 1-3 minutes to complete nucleation. Then, the second non-metallic precursor injection was started, and 200 μL of a 0.2 mmol TOP-Te and oleylamine solution was added within 1 minute and held for 3-5 minutes to complete growth. During the two injections, the system temperature was kept constant at the reaction temperature, and the temperature overshoot was maintained between ±3°C. S3, after the second injection reaction has lasted for 3-5 minutes, a mixture of tetrachloroethylene and mercaptopropionic acid (MPA) as purifying agents is added and stirred until cooled to room temperature to fully purify the surface of the quantum dots; S4, performing reverse precipitation centrifugation and washing on the purified quantum dots in isopropanol and acetone to obtain a quantum dot solution; S5, vacuum drying the quantum dot precipitate after centrifugal purification to obtain a solid powder of HgTe quantum dots.

[0006] The solid powder of the HgTe quantum dots is dissolved in a non-polar solvent such as n-octane to prepare HgTe colloidal quantum dot ink of a specific concentration.

[0007] In-situ synthesis of HgTe CQDs (colloidal quantum dots) is a method for generating quantum dots in situ within a specific matrix or reaction system. In-situ synthesis primarily involves reacting precursors at a predetermined location (such as on the surface or within another material) to form HgTe quantum dots. This method allows for better control of the location and distribution of the quantum dots and may also generate unique interactions with the matrix. This method utilizes a mixture of PFGA (hexafluoroglutaric acid) with a solution of mercuric chloride and oleylamine, followed by heating and dehydration. Due to the unique structure of hexafluoroglutaric acid, with a main structure length of approximately 4.98 Å, the interatomic distance between Hg atoms in the HgTe CQD crystal structure is approximately 5.8 Å, similar to that of PFGA. This allows PFGA to pin the HgTe CQDs, reducing surface defects, improving carrier mobility, and simplifying secondary solution processing, facilitating film formation.

[0008] The in situ synthesized HgTe CQDs have uniform particle size, excellent exciton absorption peak, stable wavelength extension, excellent optical properties and good atmospheric stability.

[0009] The technical effects and advantages of the present invention are: (1) The preparation method is simple, effective and reproducible; (2) The prepared HgTe CQDs have sharp exciton absorption peaks and uniform sizes; (3) At the same temperature, the exciton absorption peak position of HgTe CQDs is longer and the wavelength is easier to extend. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 TEM image of HgTe CQDs in Example 1 at a reaction system temperature of 70°C.

[0011] Figure 2 The exciton absorption peak of HgTe CQDs is sharp when the reaction system temperature is 70℃ and 80℃.

[0012] Figure 3 The chemical structure diagram of PFGA in Example 1 and the bonding mechanism diagram of PFGA and HgTe CQDs.

[0013] Figure 4 The TEM image and physical image of HgTe CQDs placed in the atmosphere at a reaction system temperature of 70°C in Example 1; Among them, Figure (a) is the picture after 2 days of placement, Figure (b) is the picture after 30 days of placement, and Figure (c) is the picture after 100 days of placement.

[0014] Figure 5 This is the XRD pattern of HgTe CQDs in Example 1; The horizontal axis represents the diffraction angle, and the vertical axis represents the signal intensity.

[0015] Figure 6 This is the XPS structural characterization result of HgTe CQDs; The horizontal axis represents the binding energy, and the vertical axis represents the signal intensity.

[0016] Among them, Figure (a) is the full XPS spectrum; Figure (b) is the 3d orbital diagram of Te; Figure (c) is the 4f orbital diagram of Hg.

[0017] Figure 7 This is the TEM image of HgTe colloidal quantum dots prepared by secondary hot injection at a reaction system temperature of 80°.

[0018] Figure 8 This is the TEM image of HgTe colloidal quantum dots prepared by secondary hot injection at a reaction system temperature of 90°.

[0019] Figure 9 This is a TEM image of traditional HgTe CQDs colloidal quantum dots that are not synthesized in situ. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below through specific embodiments, but it should not be understood that the scope of the present invention is limited to the following examples.

[0021] Example 1: A method for in-situ synthesis of high-quality HgTe colloidal quantum dots, the specific steps are as follows: S1. To prepare a 1 M TOPTe solution, 1.276 g tellurium powder (10 mmol) and 10 mL TOP were mixed in a 100 mL three-necked flask in a glove box and transferred to a Schlenk tube system. After three cycles of purging and degassing with argon, the mixture was heated to 100 °C under vacuum and degassed at this temperature for 1 h.

[0022] S2, purge the culture flask with argon and heat to 280 °C. Stir the dark green slurry at this temperature until all the tellurium powder is dissolved. Then remove the heating mantle and allow the flask to cool to room temperature under ambient conditions. Filter the resulting yellow solution through a 0.22 µm filter and transfer it to the glove box.

[0023] S3, using a two-shot injection method, in a 100 mL three-necked flask, 135 mg of HgCl2, 15 mL of oleylamine, and 25 mg of hexafluoropentadiene (PFGA) were degassed at 120 °C for 2 h to form an oleylamine-Hg solution.

[0024] In step S4, in an Ar atmosphere at 80°C, 100 μL of 1 mmol TOPTe was first injected and reacted for 1 minute to complete nucleation. In the second step, 200 μL of a mixed solution containing 0.2 mmol TOPTe and oleylamine was slowly injected within one minute.

[0025] S5, after the reaction was carried out for 5 minutes, the reaction was purified with a mixture of 15 mL tetrachloroethylene and 60 μL mercaptopropionic acid (MPA) and cooled naturally to room temperature.

[0026] S6, the quantum dot solution is subjected to reverse precipitation centrifugation and washing in isopropyl alcohol and acetone to obtain quantum dot particle powder.

[0027] S7, adding several polar solvents to the HgTe CQDs powder and shaking to dissolve it, to obtain a HgTe CQDs solution.

[0028] The solvent of the TOP-Te solution is TOP and Te powder dissolved, and the solution is filtered using a 0.22 μm filter.

[0029] The solution was purged with argon in a culture flask and heated for pyrolysis, and then filtered through a 0.22 µm filter.

[0030] In step S3, HgCl2, oleylamine and hexafluoropentadiene (FPGA) are dissolved to form an oleylamine-Hg solution.

[0031] As described in step S4, 100 μL of 1 mmol TOPTe was rapidly injected and reacted for one minute to complete the nucleation. In the second step, 200 μL of a mixed solution containing 0.2 mmol TOPTe and oleylamine was slowly injected over one minute.

[0032] The reaction was quenched with a mixture of 15 mL of tetrachloroethylene and 60 μL of mercaptopropionic acid (MPA) as described in step S5 and allowed to cool to room temperature.

[0033] The reverse precipitation centrifugation washing is performed in isopropanol and acetone in step S6, with a centrifugal speed of 8000 rpm / min and a centrifugal time of 5 min.

[0034] The non-polar solvents in step S7 are n-octane and tetrachloroethylene, and the shaking time is 30 seconds.

[0035] The HgTe quantum dots of this embodiment, such as Figure 1 As shown in Figure 2, HgTe CQDs have good single uniformity and high dispersion. Figure 2 As shown in FIG, the method of the present invention has a sharp exciton absorption peak, a large peak-to-valley ratio, and a high-quality synthesized quantum dot. Figure 3 As shown in the figure, PFGA (hexafluoroglutaric acid) can be pinned on it, reducing its surface defects, improving carrier mobility, and reducing its secondary solution processing process. Figure 4 As shown in Figure 2, HgTe CQDs have the best stability after 30 days. Figure 5 As shown in , its (110) and (111) crystal planes are obvious. Figure 6 As shown, the peaks of Hg's 4f orbital and Te's 3d orbital are obvious.

[0036] from Figure 7 、 8 It can be seen that compared with the traditional secondary hot injection synthesis, the synthesis of the present invention is more stable, the crystallinity and size uniformity of the quantum dots are better, the atmospheric stability is better, and the wavelength expansion is more stable. Figure 9 It can be seen that the in situ synthesis of PFGA slows down the nucleation rate of quantum dots, improves size uniformity, reduces the subsequent ligand modification process, and has lower environmental requirements.

[0037] Example 2: A method for in-situ synthesis of high-quality HgTe colloidal quantum dots, the specific steps are as follows: S1, put the prepared HgCl2 powder, oleylamine and hexafluoropentadiene (PFGA) into a three-necked flask and place it on a magnetic stirring heating mantle at 120 o C, and simultaneously the bottle is vacuumed and filled with argon through a double-row tube system, specifically: After vacuuming for 1 hour, aerate for 5 minutes, and repeat this operation at least 3 times to completely expel the residual water and air in the system and achieve the water-free and oxygen-free environment required by the experiment; S2. After the deoxygenation process is completed, turn off the vacuum pump, open the inflation knob and slowly introduce Ar into the system. Observe and ensure that bubbles slowly overflow from the bubbler to ensure that the entire reaction is carried out under the protection of an inert atmosphere. Then set the temperature of the electric heating mantle to cool the reaction system to 70°C, the reaction temperature, and keep it at this temperature for at least half an hour to ensure that the temperature of each part of the entire solution system is uniform. S3, the first rapid injection of 100 μL of 1 mmol Top-Te in 1 minute of the non-metallic precursor trioctylphosphine telluride (TOP-Te) was started, and the injection was maintained for 1-3 minutes to allow for the rapid formation of monomers and crystal nuclei; then the second slow injection of the non-metallic precursor was started using a microinjection pump, and 200 μL of 0.2 mmol Top-Te was slowly added within 1 minute to promote the gradual growth of the crystal nuclei and the ripening process of the quantum dots; during the two injections, the system temperature was maintained at the reaction temperature, and the temperature overshoot was maintained at ±3 o Between C; S4, after three minutes of the secondary injection reaction, add anhydrous isopropyl alcohol as a purifying agent and stir until the system cools to room temperature to fully purify the surface of the quantum dots; then start cooling. When the system temperature cools to room temperature, centrifuge and purify the quantum dot stock solution in the three-necked flask using the antisolvent method. Repeat the purification process 2-3 times; S5, vacuum drying the quantum dot precipitate after centrifugal purification to obtain a solid powder of HgTe quantum dots. The solid powder of HgTe quantum dots is dissolved in a non-polar solvent such as n-octane to prepare a HgTe colloidal quantum dot solution of a specific concentration.

Claims

1. A method for in situ synthesis of high-quality HgTe colloidal quantum dots, characterized in that Here are the steps: S1, HgCl2, oleylamine and hexafluoropentadiene (PFGA) were mixed at 70-120 o C, stirring and heating, while the reaction vessel is evacuated and filled with argon for protection, to react to form an oleylamine-Hg solution; S2, the reaction is complete, at 70-120 o C in an Ar atmosphere, the system was injected twice. The first time, 100 μL of 1 mmol non-metallic precursor trioctylphosphine tellurium (TOP-Te) was injected within 1 minute and maintained for 1-3 minutes to complete nucleation. Then, the second non-metallic precursor injection was started, and 200 μL of a 0.2 mmol mixed solution of TOP-Te and oleylamine was added within 1 minute. During the two injections, the system temperature was kept constant at the reaction temperature, and the temperature overshoot was maintained between ±3°C. S3, after the second injection reaction has lasted for 3-5 minutes, a mixture of tetrachloroethylene and mercaptopropionic acid (MPA) as a purifying agent is added and stirred until cooled to room temperature to fully purify the surface of the quantum dots; S4, performing reverse precipitation centrifugation and washing on the purified quantum dots in isopropanol and acetone to obtain a quantum dot solution; S5, vacuum drying the quantum dot precipitate after centrifugal purification to obtain a solid powder of HgTe quantum dots.

2. The method for in-situ synthesis of high-quality HgTe colloidal quantum dots according to claim 1, characterized in that The solid powder of the HgTe quantum dots is dissolved in a non-polar solvent such as n-octane to prepare HgTe colloidal quantum dot ink of a specific concentration.

3. The method for in-situ synthesis of high-quality HgTe colloidal quantum dots according to claim 1, characterized in that The solvent of the TOP-Te solution is a solution of TOP and Te powder, and the solution is filtered using a 0.22 μm filter.

4. The method for in-situ synthesis of high-quality HgTe colloidal quantum dots according to claim 1, characterized in that The reverse precipitation centrifugal washing was carried out in the isopropanol and acetone, the centrifugal speed was 8000 rpm / min, and the centrifugal time was 1 min.

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