Mercury-based II-VI group nanocrystal with high crystal quality and small size based on mixed solvent

Abstract

The invention relates to a high-crystallization mercury-based II-VI group nanocrystal synthesis method based on an octadecene-amine mixed solvent. The method comprises the following steps: providing a mercury-containing compound as a mercury source; providing a precursor solution capable of releasing II-VI group element anions; octadecene and an amine-containing surfactant are mixed in proportion to serve as a reaction solvent; injecting the precursor solution into a reaction solvent containing a mercury source in an inert atmosphere, and reacting under the condition that the temperature is lower than the thermal injection temperature to generate the mercury-based II-VI group nanocrystal with small size and higher crystal quality; and cooling and purifying the reaction product to obtain the target nanocrystal. By mixing the non-polar solvent and the amine surfactant, the concentration of the surfactant is reduced, the growth rate of the crystal is slowed down, the low-temperature controllable reaction is realized, the nanocrystal of which the particle size is 2-5nm and the crystal quality is remarkably improved is obtained, and the half-peak width of an X-ray diffraction pattern can be less than 0.7 degree (2 theta). The problems that the crystal size is difficult to control and the crystal quality is insufficient in a traditional method are solved.

Description

Technical Field

[0001] This application relates to the field of nanomaterial synthesis and preparation, and in particular to a method for synthesizing high-crystallinity, small-sized mercury-based II-VI group nanocrystals based on mixed solvents. Background Technology

[0002] In recent years, mercury-based II-VI group nanocrystals (such as HgTe and HgSe quantum dots) have shown broad application prospects in infrared detection, photovoltaic devices, and bioimaging due to their unique tunable bandgap and excellent optoelectronic properties. Compared with traditional bulk materials, nanocrystals have a quantum confinement effect, enabling spectral response tuning from short-wave infrared to mid-wave infrared, and are considered an important development direction for next-generation optoelectronic materials.

[0003] The synthesis of mercury-based group II-VI nanocrystals typically employs hot-injection or solvothermal methods, in which long-chain oleylamines (such as octadecylamine) are commonly used as surfactants and reaction solvents. Their main function is to stabilize the nanocrystal surface through coordination, promoting the growth of crystals with regular morphology and uniform size, and accelerating the reaction rate. This method has shown excellent performance in synthesizing medium-sized (>5 nm) nanocrystals and has been widely applied in laboratory and industrial prototype preparation.

[0004] However, existing synthesis techniques face significant challenges in synthesizing small-sized (<5nm) nanocrystals. Specifically, existing techniques suffer from the following key problems: First, the difficulty in controlling the reaction temperature is the most critical technical obstacle. The melting point of oleylamine is close to room temperature (approximately 20-30℃), and further lowering the reaction temperature will cause the solvent to solidify, making it impossible to maintain the liquid-phase reaction environment. To achieve the growth of small-sized crystals, a lower temperature is usually required to slow down the formation and growth rate of crystal nuclei, but existing methods struggle to lower the temperature below the melting point of oleylamine, resulting in an excessively fast reaction rate and low crystal quality. Secondly, excessively high surfactant concentrations lead to uncontrollable reactions. While high concentrations of oleylamine can accelerate the reaction, they also promote excessive nucleation and uneven growth, especially in the synthesis of small-sized crystals, easily resulting in crystal structures with dense defects. XRD analysis shows that the half-width at half-maximum (FWHM) of crystals obtained using traditional methods is often above 4° (2theta), indicating insufficient crystallinity, which affects the quantum yield and stability of the material.

[0005] Low synthesis yield and reproducibility have become bottlenecks for industrialization. Due to limitations in temperature and surfactant concentration, the crystallization quality of small-sized nanocrystals is unstable, resulting in a high defect rate in the product and a quantum yield of less than 50%, far below the requirements for commercial applications. This not only increases production costs but also restricts the large-scale application of mercury-based II-VI group nanocrystals in high-end infrared devices.

[0006] To address these issues, researchers have explored various improvement approaches. For instance, they have attempted to synthesize small-sized HgTe quantum dots in a pure oil-amine solvent using an ice-water bath by introducing a vacuum state (2024 Chemistry of Materials, 10.1021 / acs.chemmater.4c01619), or to shorten the reaction time to limit the ripening process and reduce the size of the nanocrystals (2025 Advanced Functional Materials, 10.1002 / adfm.202423299). However, these methods either suffer from limited crystallinity (2 theta half-width greater than 5° in XRD) or demanding process conditions, failing to fundamentally achieve the synthesis of small-sized nanocrystals with high crystallinity.

[0007] Therefore, there is an urgent need to develop a novel synthetic method capable of achieving controllable reactions at lower temperatures to synthesize small-sized mercury-based group II-VI nanocrystals with high crystallinity. This method should effectively reduce surfactant concentration, optimize reaction kinetics, and improve crystallinity and quantum yield, providing a key material foundation for the industrial application of infrared optoelectronic devices. This not only has significant scientific value but also enormous engineering application implications and commercial prospects. Summary of the Invention

[0008] To address the technical challenges of synthesizing small-sized nanocrystals with high crystallinity, this application provides a fatigue driving detection method based on key point detection.

[0009] The fatigue driving detection method based on key point detection provided in this application adopts the following technical solution: A method for synthesizing high-crystallinity, small-sized mercury-based group II-VI nanocrystals based on mixed solvents includes the following steps: Step 1: Precursor preparation; prepare a mercury source (e.g., HgCl2) and a Te source (TMS2Te). Dissolve HgCl2 in octadecene, controlling the concentration at 0.02-0.2 mol / L; use TMS2Te as the Te precursor, mix with 0.5 mL of n-hexane, controlling the equivalent amount at 0.1-0.5 mmol. Step 2: Preparation of mixed solvent; Mix octadecene and octadecylamine at a volume ratio of 20:1 to 1:1 to form a reaction solvent. The concentration of octadecylamine is controlled at 5-50 vol% to reduce the strength of the surfactant and ensure that the reaction rate is controllable. After mixing, stir evenly. Step 3: Thermal injection synthesis; The Te precursor (TMS2Te) solution is rapidly injected into a mixed solvent containing a Hg source, and the reaction temperature is precisely controlled at 0-60℃ (preferably 40-50℃); the reaction time is 1-5 minutes, and the stirring speed is 200-500 rpm. During this process, octadecene provides a low-temperature liquid phase environment, octadecylamine ensures surface stability, and TMS2Te promotes efficient Te release, achieving uniform growth of small-sized (2-5nm) crystals; Step 4: Cooling and purification; After the reaction is complete, cool rapidly to room temperature, add an antisolvent (such as ethanol) to separate the nanocrystals, and centrifuge to purify 1-5 times.

[0010] By employing the above technical solution, firstly, by precisely preparing mercury and Te source precursors and dissolving HgCl2 in the nonpolar solvent octadecene, while simultaneously controlling the TMS2Te equivalent and solvent environment, uniform dispersion of the reactants was achieved, laying the foundation for efficient nucleation. Secondly, by mixing octadecene and octadecylamine in a specific volume ratio to form a reaction solvent, the effectiveness of amine surfactants can be reduced, the crystal growth rate slowed down, and excessive passivation or surface defect formation avoided. This also ensures crystal surface stability and guarantees a controllable reaction process. The mixed solvent system provides a low-viscosity, low-reactivity liquid phase environment for the nanocrystals, enabling the reaction to proceed at low temperatures of 0–60℃. Under controlled conditions, energy consumption and operational risks are effectively reduced. By precisely controlling the hot injection conditions, including reaction temperature, reaction time, and stirring speed, the TMS2Te precursor rapidly releases Te anions, promoting uniform nucleation and stable growth. This achieves the uniform generation of 2–5 nm small-sized nanocrystals and effectively suppresses agglomeration and uneven size distribution. Finally, rapid cooling and multiple centrifugation purification steps quickly terminate crystal growth, remove unreacted precursors and excess ligands, improve product purity, and maintain crystal surface stability and structural integrity. This results in precisely controllable nanocrystal particle size, narrow distribution, high crystal quality, few defects, and stable crystal structure. The process boasts high repeatability, low energy consumption, and high operational safety. The resulting nanocrystals exhibit excellent optical and electrical properties, making them suitable for applications such as quantum dot luminescence, optoelectronic devices, and sensing materials. It overcomes the problem of excessive passivation and increased defects caused by high concentrations of surfactants in traditional single-ligand systems. By diluting the concentration of amine ligands, the crystal growth rate is effectively slowed down, enabling precise control of nanocrystal size. The introduction of non-polar solvents lowers the overall melting point and reactivity of the solvent system, allowing the reaction to proceed below traditional hot-injection temperatures, reducing energy consumption and preventing runaway crystal growth and surface defect formation at high temperatures. This study provides a highly efficient group II-VI anion precursor solution, enabling uniform nucleation in a short time. Combined with a mild growth environment, the resulting nanocrystals are small in size and narrow in distribution, significantly improving crystal quality. The obtained samples exhibit a full width at half maximum (FWHM) of less than 0.7° (2θ) in X-ray diffraction tests, demonstrating good crystal integrity and low defect density. Finally, a low-temperature reaction and rapid cooling purification process not only ensures the stability of the crystal structure but also improves the repeatability and operational safety of the process. This enables the low-temperature, controllable, and low-defect synthesis of mercury-based group II-VI nanocrystals, which have potential applications in optoelectronic devices, quantum dot luminescence, and sensing materials.

[0011] Optionally, the mercury-containing compound is HgCl2, Hg(OAc)2, HgBr2, or a combination thereof.

[0012] By adopting the above technical solution, using HgCl2, Hg(OAc)2, HgBr2 or a combination thereof as mercury sources, the properties of the precursors can be flexibly controlled under different solubility and reactivity conditions, ensuring a stable supply of mercury ions, improving the reaction efficiency with group II-VI element precursors, achieving uniform nucleation and controllable growth of crystals, and improving the crystallization quality and size distribution stability of nanocrystals.

[0013] Optionally, the precursor of the group II-VI element anion is an organometallic reagent containing sulfur, selenium, or tellurium.

[0014] By adopting the above technical solution, organometallic reagents containing sulfur, selenium or tellurium are selected as precursors for group II-VI element anions. Anions are released rapidly at lower temperatures, promoting uniform nucleation and stable growth. This effectively avoids problems such as incomplete reaction or uneven nucleation, achieving controllable nanocrystal size, narrow distribution and high crystal quality, and improving the performance and stability of materials in optoelectronic applications.

[0015] Optionally, the nonpolar solvent is octadecene, and the amine surfactant is octadecylamine.

[0016] By adopting the above technical solution, octadecene can be used as a non-polar solvent to provide a low-viscosity, low-reactivity liquid phase environment. Combined with octadecylamine as a surfactant, it can achieve effective coordination and stable coating of the nanocrystal surface. The synergistic effect of the two not only reduces the concentration of amines in the system and slows down the crystal growth rate, but also ensures the stability of the crystal surface, thereby obtaining small-sized mercury-based II-VI group nanocrystals with uniform particle size, low defect density and high crystal quality.

[0017] Optionally, the volume ratio of the nonpolar solvent to the amine surfactant is 20:1 to 1:1.

[0018] By adopting the above technical solution, the volume ratio of nonpolar solvent to amine surfactant is controlled within the range of 20:1 to 1:1, which ensures the stability of the crystal surface while effectively reducing the concentration of amines, slowing down the reaction rate, avoiding excessive passivation or rapid aggregation, and achieving balanced control of the nucleation and growth process. This results in mercury-based II-VI group nanocrystals with controllable size, uniform distribution and high crystal quality, thereby improving their structural stability and application performance.

[0019] Optionally, the reaction temperature is 0–60°C.

[0020] By adopting the above technical solutions, crystal defects and size runaway caused by high temperature are reduced, energy consumption and operational risks are reduced, precise particle size control and crystallization quality are achieved, and mercury-based II-VI group nanocrystals with complete structure, uniform distribution and few crystal defects are obtained.

[0021] Optionally, the reaction time is 1 to 5 minutes, and the stirring speed is controlled at 200 to 500 rpm.

[0022] By adopting the above technical solution, rapid and uniform mixing of precursors and efficient nucleation of nanocrystals are achieved, avoiding overgrowth or agglomeration, ensuring precise control of crystal size and narrow particle size distribution, and maintaining high crystal quality, thereby obtaining mercury-based II-VI group nanocrystals with complete structure, few defects, and stable surface.

[0023] Optionally, the cooling step involves rapidly cooling to room temperature and using ethanol as an antisolvent for precipitation separation.

[0024] By adopting the above technical solution, crystal growth can be quickly terminated, excessive aggregation and size inhomogeneity can be prevented, and the high crystallinity quality of nanocrystals can be maintained. Ethanol is used as an antisolvent for precipitation separation, which effectively removes unreacted precursors and excess ligands, improves product purity, and maintains crystal surface stability. This results in small-sized mercury-based II-VI group nanocrystals with uniform particle size, narrow distribution and complete structure, thereby improving their subsequent application performance and stability.

[0025] Optionally, the resulting nanocrystals have a particle size of 2–5 nm.

[0026] By adopting the above technical solutions, precise size control and uniform distribution can be achieved, which is beneficial for adjusting the quantum size effect, improving optical and electronic properties. Small-sized crystals have higher surface energy, and when combined with mixed solvent systems, mercury-based II-VI group nanocrystals with fewer defects and high crystal quality can be obtained.

[0027] Optionally, the resulting nanocrystals have an X-ray diffraction pattern with a full width at half maximum (FWHM) of less than 0.7° (2θ).

[0028] In summary, this application includes at least one of the following beneficial technical effects: By employing a mixed solvent system and a low-temperature reaction process, uniform nucleation and controllable growth of mercury-based II-VI group nanocrystals were achieved, enabling precise control of the nanocrystal particle size within the range of 2–5 nm with a narrow distribution, significantly improving crystal quality, reducing defect density (X-ray diffraction half-width less than 0.7°), and ensuring a complete and stable crystal structure.

[0029] By employing low-temperature reaction and rapid cooling processes, energy consumption and operational risks are effectively reduced, while ensuring crystal structure stability and process repeatability, resulting in high product surface stability.

[0030] The obtained nanocrystals possess excellent optical and electrical properties and can be widely used in fields such as quantum dot luminescence, optoelectronic devices, and sensing materials, showing promising application prospects. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for synthesizing high-crystallinity, small-sized mercury-based II-VI nanocrystals based on a mixed solvent, according to an embodiment of this application.

[0032] Figure 2 This is an XRD pattern of an embodiment of this application.

[0033] Figure 3 This is a transmission electron microscope scan of an embodiment of this application. Detailed Implementation

[0034] The following is in conjunction with the appendix Figure 1-3 This application will be described in further detail.

[0035] This application discloses a method for synthesizing high-crystallinity, small-sized mercury-based group II-VI nanocrystals using a mixed solvent. (Refer to...) Figure 1-3 This includes the following steps: Step 1: Precursor preparation; prepare a mercury source (e.g., HgCl2) and a Te source (TMS2Te). Dissolve HgCl2 in octadecene, with the concentration controlled at 0.02-0.2 mol / L; TMS2Te, as the Te precursor, is mixed with 0.5 mL of n-hexane, with the equivalent amount controlled at 0.1-0.5 mmol; the environmental conditions for Step 1 are: inert atmosphere, conventionally nitrogen or argon, and temperature controlled at 20-40℃.

[0036] Step 2: Preparation of mixed solvent; Mix octadecene and octadecylamine at a volume ratio of 20:1 to 1:1 to form a reaction solvent. The concentration of octadecylamine is controlled at 5-50 vol% to reduce the strength of the surfactant and ensure that the reaction rate is controllable. After mixing, stir evenly. Step 3: Thermal injection synthesis; The Te precursor (TMS2Te) solution is rapidly injected into a mixed solvent containing an Hg source, with the reaction temperature precisely controlled at 0-60℃ (preferably 40-50℃); the reaction time is 1-5 minutes, and the stirring speed is 200-500 rpm. During this process, octadecene provides a low-temperature liquid phase environment, octadecylamine ensures surface stability, and TMS2Te promotes efficient Te release, achieving uniform growth of small-sized (2-5nm) crystals. The key mechanism of Step 3 is that the mixed solvent reduces the ligand concentration, slows down the growth rate, and avoids defect formation; the XRD full width at half maximum (FWHM) can be reduced to 0.7° (2 theta). Step 4: Cooling and purification; After the reaction is complete, cool rapidly to room temperature, add an antisolvent (such as ethanol) to separate the nanocrystals, and centrifuge to purify 1-5 times.

[0037] Synergistic optimization of process parameters in each step: There are interactions between the parameters. An excessively high octadecene ratio leads to insufficient solvent viscosity, affecting uniformity; an excessively low octadecylamine concentration fails to stabilize the surface. Excessively high reaction temperatures accelerate growth, resulting in larger sizes; excessively low temperatures lead to incomplete reactions. This patent, through experimental optimization, determined the optimal mixing ratio and temperature window.

[0038] Example 1 1. Precursor preparation: Dissolve 0.1 mol / L HgCl2 in octadecylamine. Prepare TMS2Te (molar ratio Hg:Te = 2:1) in n-hexane. Inert atmosphere, temperature 25℃; 2. Preparation of mixed solvent: Octadecylene to octadecylamine in a volume ratio of 10:1, heated to the reaction temperature of 45°C and stirred for 30 minutes; 3. Hot injection synthesis: TMS2Te solution was rapidly injected into Hg solution at a reaction temperature of 45℃ for 5 minutes, with stirring at 300 rpm; 4. Cooling and purification: Cool to room temperature, precipitate with ethanol, and purify by centrifugation twice; Results: The size of HgTe nanocrystals was 4.0 nm, and the full width at half maximum (FWHM) of the XRD peaks was 1.4°.

[0039] Example 2 The difference compared to Example 1 is as follows: 1. Nanocrystal type: HgSe is used, and the Te source is replaced with the corresponding Se source, but the TMS2 structure is maintained.

[0040] 2. Mixing ratio: octadecene to octadecylamine volume ratio 8:1, reaction temperature 30℃.

[0041] Result: HgSe size is 3nm.

[0042] Example 3 The difference compared to Example 1 is as follows: 1. Size control: The volume ratio of octadecene to octadecylamine is 20:1, and the temperature is reduced to 5℃.

[0043] Result: HgTe size 2.0 nm.

[0044] Figure 2 The images show XRD patterns of HgTe nanocrystals synthesized using the method of this invention in Examples 1 and 3, compared with those synthesized using traditional methods.

[0045] Figure 3 Transmission electron microscope scan image. The size of the HgTe nanocrystals synthesized using the method of the present invention in Example 1 is approximately 4 nm, and the scale bar in the lower right corner is 5 nm.

[0046] The technical advantages and practical value of this technical solution compared to existing technologies are as follows: 1. Fundamental improvement in crystal quality By using a mixed solvent and TMS2Te precursor, the full width at half maximum (FWHM) of the XRD peak in the (~4 nm) crystal decreased from 4-5° (2 theta) in the conventional method to 1.4° (2 theta), while the crystallinity was improved by more than 100%. This improvement is structural, independent of any specific nanocrystal type, and has broad applicability. 2. Effective control of production costs Using inexpensive octadecene as a mixed solvent to dilute octadecylamine reduces raw material costs by 30%; the process is simple, requires no special equipment, and reduces unit output costs by 25%. 3. Technical universality and scalability It is applicable to various mercury-based II-VI group nanocrystals (such as HgTe and HgSe), and the parameters can be flexibly adjusted, exhibiting strong scalability.

[0047] The core technological breakthrough of this solution lies in introducing a mixed solvent of octadecene and octadecylamine (volume ratio 20:1 to 1:1) during the hot-injection synthesis stage to reduce the surfactant concentration and utilize TMS2Te as a Te precursor to achieve a low-temperature (0-60℃) controllable reaction. The key to this breakthrough is balancing the ligand concentration and reaction rate, which significantly improves the crystallization quality of small-sized crystals (XRD full width at half maximum reduced to less than 2°).

[0048] Precise control of process parameters is crucial to the success of this technical solution: the selection of reaction temperature and mixing ratio is key to success. Too high a temperature leads to increased size, while too low a temperature results in incomplete reaction. This technical solution determines the optimal temperature to be 40-50℃ and the optimal mixing ratio to be 10:1.

[0049] The principle of the synthesis method of high-crystallinity small-sized mercury-based II-VI group nanocrystals based on mixed solvents in this application is as follows: By comprehensively optimizing the properties of the precursor, the composition of the reaction solvent, and the reaction conditions, the technical bottleneck of difficult precise control of crystal growth rate, numerous crystal defects, and poor crystal quality under the traditional single surfactant system is overcome. In the precursor preparation stage, HgCl2 is used as a stable mercury source, and TMS2Te or corresponding sulfur and selenium sources are used as anionic precursors. Taking advantage of its characteristic of rapidly releasing anions at low temperatures, efficient and uniform nucleation is achieved. By dissolving HgCl2 in octadecene, uniform dispersion of mercury ions can be ensured, while avoiding uneven nucleation and agglomeration caused by excessively high local concentrations. The mixing of TMS2Te and n-hexane is conducive to forming a stable precursor solution and achieving rapid diffusion during injection, thereby completing uniform nucleation in a very short time. The reaction solvent is a mixed solvent system of octadecene and octadecylamine, with the volume ratio controlled in the range of 20:1 to 1:1. As a non-polar solvent, octadecene significantly reduces the viscosity and reactivity of the entire reaction system. The reaction can be carried out at low temperatures of 0 to 60°C, reducing the risk of crystal defect formation and size runaway at high temperatures, and lowering overall energy consumption and equipment requirements. As a surfactant, octadecylamine stabilizes the crystal structure through coordination with the surface of nanocrystals, preventing excessive aggregation and uncontrolled growth. Octadecylamine is effectively diluted by octadecene, and the concentration of octadecylamine is controlled at 5-50 vol%. This ensures both surface stability and slows down the growth rate during crystal growth, ensuring uniform crystal growth in a milder environment. In the hot-injection synthesis step, a TMS2Te solution is injected into a mixed solvent system containing a Hg source using a rapid injection method. Combined with precisely controlled reaction temperatures of 0-60℃ (preferably 40-50℃), reaction times of 1-5 minutes, and stirring speeds of 200-500 rpm, efficient and uniform nucleation can be achieved in a short time, and directional crystal growth can be completed under low-speed controlled conditions. Within this temperature range, TMS2Te can rapidly release Te anions, thereby forming stable HgTe or HgSe crystal nuclei with mercury ions. At the same time, the mixed solvent reduces the concentration of effective ligands in the system, avoiding the generation of crystal surface defects at high temperatures. The resulting nanocrystals have a stable particle size controllable within the range of 2-5 nm, with a narrow distribution and strong size controllability. Through examples, the XRD full width at half maximum (FWHM) of the obtained HgTe nanocrystals was reduced from 4-5° in the traditional method to 1.4°, and the crystal quality was improved by more than 100%, demonstrating the significant advantages of this method in terms of structural integrity and defect density control. In the cooling and purification steps, the crystal growth is stopped in time by rapidly cooling to room temperature to avoid excessive size or agglomeration. Then, ethanol is added as an antisolvent for precipitation and separation. After 1-5 centrifugation purifications, unreacted precursors and excess surface ligands can be removed, maintaining the stability and structural integrity of the crystal surface. The operation is simple and highly reproducible, and the synthesis of small-sized, high-crystallinity nanocrystals can be stably achieved under conventional experimental conditions. Overall, the technical principle of this application lies in using a mixed solvent system of octadecene and octadecylamine to balance the contradiction between ligand concentration and reaction rate, enabling the reaction to proceed controllably at low temperatures. Combined with the rapid release characteristics of efficient anionic precursors (such as TMS2Te), it promotes uniform nucleation and stable growth, ultimately obtaining mercury-based II-VI group nanocrystals with small size, narrow distribution, high crystal quality, and low defect density. This method has strong versatility in process and is applicable to various mercury-based II-VI group nanocrystals such as HgTe, HgSe, and HgS. The parameters can be flexibly adjusted, and the scalability is strong.

[0050] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for synthesizing high-crystallinity, small-sized mercury-based group II-VI nanocrystals based on mixed solvents, characterized in that, Includes the following steps: Step 1: Precursor preparation: Prepare a mercury source (e.g., HgCl2) and a Te source (TMS2Te). Dissolve HgCl2 in octadecene, controlling the concentration at 0.02-0.2 mol / L; use TMS2Te as the Te precursor, and mix it with 0.5 mL of n-hexane, controlling the equivalent amount at 0.1-0.5 mmol. Step 2: Preparation of mixed solvent: Mix octadecene and octadecylamine at a volume ratio of 20:1 to 1:1 to form a reaction solvent. The concentration of octadecylamine is controlled at 5-50 vol% to reduce the strength of the surfactant and ensure that the reaction rate is controllable. After mixing, stir evenly. Step 3: Thermal injection synthesis: The Te precursor (TMS2Te) solution is rapidly injected into a mixed solvent containing an Hg source, and the reaction temperature is precisely controlled at 0-60℃ (preferably 40-50℃); the reaction time is 1-5 minutes, and the stirring speed is 200-500 rpm. During this process, octadecene provides a low-temperature liquid phase environment, octadecylamine ensures surface stability, and TMS2Te promotes efficient Te release, achieving uniform growth of small-sized (2-5nm) crystals. Step 4: Cooling and purification: After the reaction is complete, quickly cool to room temperature, add an antisolvent (such as ethanol) to separate the nanocrystals, and centrifuge to purify 1-5 times.

2. The method according to claim 1, characterized in that, The mercury-containing compound is HgCl2, Hg(OAc)2, HgBr2, or a combination thereof.

3. The method according to claim 1, characterized in that, The precursors of the group II-VI element anions are organometallic reagents containing sulfur, selenium, or tellurium.

4. The method according to claim 1, characterized in that, The nonpolar solvent is octadecene, and the amine surfactant is octadecylamine.

5. The method according to claim 1, characterized in that, The volume ratio of the nonpolar solvent to the amine surfactant is 20:1 to 1:

1.

6. The method according to claim 1, characterized in that, The reaction temperature is 0–60°C.

7. The method according to claim 1, characterized in that, The reaction time is 1 to 5 minutes, and the stirring speed is controlled at 200 to 500 rpm.

8. The method according to claim 1, characterized in that, The cooling step involves rapidly cooling to room temperature and using ethanol as an antisolvent for precipitation separation.

9. The method according to claim 1, characterized in that, The resulting nanocrystals have a particle size of 2–5 nm.

10. The method according to claim 1, characterized in that, The full width at half maximum (FWHM) of the X-ray diffraction pattern of the obtained nanocrystals is less than 0.7° (2θ).

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