Post-treatment method of mercury-based II-VI group nanocrystal with protective layer formed by chemical oxidation

Abstract

The invention relates to a post-treatment method for a mercury-based II-VI group nanocrystal with a protective layer formed by chemical oxidation, and solves the problems of poor stability and photoelectric property degradation of the mercury-based II-VI group nanocrystal caused by surface oxidation, ligand desorption and environmental sensitivity. An oxide protection layer with the thickness of 1-3 nm is formed on the surface of the nanocrystal, the long-term stability and the photoelectric property of the nanocrystal are improved, and the method comprises the specific steps of centrifugal purification of the nanocrystal, preparation of an oxidizing agent solution, controllable oxidation reaction, functional ligand surface modification and purification treatment. The oxidation layer is ensured to be compact and stable by accurately adjusting the concentration of the oxidant, the reaction temperature and the reaction time. According to the method, oxygen and moisture permeation is effectively blocked, surface defects are reduced, the quantum yield and the photoelectric property are improved, and the method is widely applied to the fields of post-treatment of mercury-based II-VI group nanocrystals and photoelectric devices.

Description

Technical Field

[0001] This application relates to the field of chemical treatment of nanomaterial surfaces, and in particular to a post-treatment method for mercury-based II-VI nanocrystals that form a protective layer through chemical oxidation. Background Technology

[0002] Mercury-based group II-VI nanocrystals (such as HgTe and HgSe quantum dots) have significant applications in short-wave to mid-wave infrared detection, photovoltaic devices, and bioimaging due to their tunable band gaps and excellent infrared photoelectric properties. However, these nanocrystals face serious stability problems in practical applications, becoming a key bottleneck restricting their commercialization.

[0003] Currently, the stability issues of mercury-based II-VI group nanocrystals mainly manifest in the following aspects: First, the most prominent problem is the performance degradation caused by uncontrollable and continuous surface oxidation. Mercury-based nanocrystals are easily oxidized in air, especially when surface Te or Se atoms react with oxygen to form oxides such as TeO2 or SeO2. These oxides directly lead to a reduction in effective particle size, causing a blue shift in the cutoff edge; at the same time, they introduce deep-level defect states, leading to an increase in nonradiative recombination, significantly enhancing dark current noise and weakening photoelectric conversion efficiency.

[0004] Secondly, the aggregation problem caused by ligand desorption restricts device fabrication. Long-chain ligands such as oleylamine used in traditional synthesis have weak binding forces to the surface of nanocrystals, making them prone to desorption during solution processing or thin film preparation, leading to irreversible aggregation of the nanocrystals. TEM observations show that nanocrystals after ligand desorption form micron-sized aggregates within hours, losing the quantum confinement effect and completely losing their optical properties.

[0005] Third, poor environmental stability limits practical applications. Mercury-based nanocrystals are relatively sensitive to environmental factors such as humidity and temperature. In environments with relative humidity >50%, water molecules accelerate surface oxidation and ligand hydrolysis, causing performance to degrade by more than 80% within a week. At the device operating temperature (50-80℃), this degradation process is further accelerated, making it difficult for the device lifetime to meet practical requirements.

[0006] Fourth, existing protection methods have significant limitations. Researchers have tried various surface passivation strategies, including inorganic shell coating (such as ZnS and CdS), organic ligand exchange, and polymer encapsulation. However, these methods all have shortcomings: inorganic shell coating requires high-temperature treatment (>150℃), which easily leads to recrystallization and size increase of the core crystal, destroying the original quantum confinement effect. In addition, the uniformity of shell growth is difficult to control, often resulting in incomplete coating and ineffective water and oxygen barrier. Although organic ligand exchange is simple to operate, the binding force between the new ligand and the surface is still limited, and it is easy to re-desorb during subsequent device processing, resulting in short-lived protection. Although polymer encapsulation can provide a certain degree of physical isolation, the permeability and hygroscopicity of the polymer itself lead to poor long-term protection and significantly affect the charge transport performance of the nanocrystals.

[0007] Therefore, there is an urgent need to develop a novel post-processing method that can controllably form a dense and uniform protective layer on the surface of nanocrystals. This layer can effectively block oxygen and moisture while maintaining good optical and charge transport properties. Furthermore, the process should be mild and highly reproducible, providing key technical support for the practical application of mercury-based II-VI group nanocrystals. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, this application provides a post-processing method for mercury-based II-VI group nanocrystals that form a protective layer through chemical oxidation.

[0009] This application provides a post-processing method for mercury-based II-VI group nanocrystals that form a protective layer through chemical oxidation, employing the following technical solution: A post-treatment method for mercury-based group II-VI nanocrystals with a protective layer formed by chemical oxidation, the method comprising the following steps: Step 1: Pretreatment of nanocrystals. The newly synthesized mercury-based II-VI nanocrystals are dispersed in a non-polar solvent and purified by centrifugation to remove excess ligands and reaction byproducts. Step 2: Preparation of oxidant solution. Prepare the oxidant solution by selecting H2O2 or organic peroxide and adjusting the oxidant concentration and solvent type. Step 3: Controlled chemical oxidation treatment. The oxidant solution is added dropwise to the nanocrystal dispersion, and controlled oxidation is carried out under stirring conditions to form an oxide protective layer. Step 4: Surface ligand modification. Functional ligands are used to modify the oxide layer surface to enhance the protective effect. Step 5: Purification and stabilization. Purify the oxidized nanocrystals, remove excess oxidants and ligands, and disperse the nanocrystals in the target solvent or store them in an inert atmosphere.

[0010] By employing the above-mentioned technical solution, a post-treatment method for mercury-based II-VI group nanocrystals, which forms a protective layer through chemical oxidation, is developed. This method creates a dense oxide protective layer on the nanocrystal surface, enhancing its stability and photoelectric properties. First, the nanocrystal surface is oxidized under controlled conditions using a mild oxidant to form a self-limiting oxide layer that effectively blocks oxygen and moisture, preventing oxidation and degradation in air. Second, the oxide layer eliminates surface dangling bonds and defect states, reducing non-radiative recombination centers and improving quantum yield. Modification with functional ligands further enhances surface passivation, improving the photoelectric stability and adaptability of the nanocrystals. Precise control of the oxidant concentration, reaction temperature, and time ensures the oxidation reaction occurs only on the nanocrystal surface, preventing over-oxidation and crystal aggregation, and maintaining the structural integrity of the nanocrystals. Finally, desolventizing and centrifuging are used to remove excess oxidant and ligands, ensuring the purity of the nanocrystals and improving their performance and stability in practical applications.

[0011] Optionally, the nanocrystals are mercury-based group II-VI nanocrystals selected from HgTe, HgSe and their alloys.

[0012] By adopting the above technical solution, surface oxidation protection of mercury-based II-VI nanocrystals was achieved, which significantly improved the stability and photoelectric properties of the nanocrystals. The self-limiting growth characteristics of the oxide layer effectively prevented deep oxidation, and the surface passivation function reduced defect states and improved quantum yield.

[0013] Optionally, in step one, the concentration of the nanocrystal dispersion is controlled at 0.5-10 mg / mL, and pretreatment is performed under an inert atmosphere.

[0014] By adopting the above technical solution, excess ligands and byproducts are effectively removed, ensuring the cleanliness of the nanocrystal surface. This provides a good foundation for subsequent oxidation and ligand modification, avoids surface contamination, ensures precise control of the oxidation process, and improves the stability and photoelectric properties of the nanocrystals.

[0015] Optionally, the oxidant is an aqueous solution of H2O2 with a concentration range of 3%-30%, or tert-butyl hydroperoxide (TBHP) with a concentration of 5-50 mM.

[0016] By adopting the above technical solution, the oxidation depth can be precisely controlled to avoid over-oxidation. The flexible adjustment of different oxidant concentrations ensures the controllability of the oxidation process. A self-limiting and dense oxide layer is formed on the surface of the nanocrystals, providing effective protection. This optimizes the surface passivation effect of the nanocrystals and improves their stability and photoelectric properties.

[0017] Optionally, the molar ratio of oxidant to nanocrystals is controlled between 1:1 and 100:1 to precisely regulate the oxidation depth.

[0018] By adopting the above technical solution, precise control of oxide layer thickness can be achieved. The adjustable oxidation depth can ensure that the surface oxide layer is within the range of 1-3 nanometers, avoiding excessive oxidation or crystal structure damage, ensuring the stability and excellent photoelectric performance of nanocrystals, optimizing the passivation effect of nanocrystal surface, and improving its reliability for long-term use.

[0019] Optionally, the reaction temperature in step three is controlled at 0-40°C, preferably 15-25°C, and the reaction time is 5-60 minutes.

[0020] By adopting the above technical solution, a mild oxidation reaction is achieved, preventing excessive oxidation or crystal dissolution, avoiding damage to the nanocrystal structure, and maintaining the stability and performance of the nanocrystals.

[0021] Optionally, during the oxidation reaction, the Te / Se atoms on the surface of the nanocrystals are oxidized to TeO2 / SeO2, forming a dense oxide protective layer with a thickness of 1-3 nm.

[0022] By adopting the above technical solution, the protective layer has self-limiting growth characteristics, which can prevent further deep oxidation and ensure that the core structure of the nanocrystal is not damaged. The dense oxide layer effectively isolates the penetration of external oxygen and moisture, thereby improving the stability and photoelectric properties of the nanocrystal.

[0023] Optionally, the functional ligand described in step four is a short-chain thiol, phosphonic acid, or bifunctional ligand, and the ligand concentration is 1-20 times the quantum dot equivalent.

[0024] By adopting the above technical solution, the ligand concentration is controlled at 1-20 times the quantum dot equivalent, ensuring a strong bond between the ligand and the oxide layer, providing additional steric hindrance protection, avoiding the formation of surface defect states, significantly improving the passivation effect of the nanocrystal surface, and enhancing the quantum yield.

[0025] Optionally, the ligand provides additional surface protection by forming a strong bond with TeO2 or SeO2 in the oxide layer; The type, concentration, and reaction time of the oxidant are optimized based on the size and composition of the nanocrystals to achieve the best oxide layer performance. The oxide layer is an amorphous or low-crystallinity oxide with self-limiting growth characteristics, which can effectively prevent further deep oxidation. By controlling process parameters such as oxidant concentration, reaction temperature, and time, a dense oxide layer is formed, which can effectively block oxygen and moisture penetration and improve the stability of nanocrystals. The oxidized nanocrystals exhibit significant surface passivation, reducing surface defect states and improving quantum yield and photoelectric performance.

[0026] By adopting the above technical solution, the oxide layer provides additional protection by forming strong bonds with ligands on the surface, effectively preventing the generation of surface defects and unstable factors. The type, concentration, and reaction time of the oxidant are precisely optimized according to the size and composition of the nanocrystals to form the best oxide layer performance. The oxide layer is amorphous or low crystallinity and has self-limiting growth characteristics. It can form a uniform and dense oxide protective layer on the surface, preventing deep oxidation and effectively blocking the penetration of oxygen and moisture, improving the stability of nanocrystals in air, significantly passivating the surface of the oxidized nanocrystals, reducing surface defects, and significantly improving quantum yield and photoelectric properties.

[0027] Optionally, in step five, the oxidized nanocrystals are purified 2-4 times by precipitation with excess antisolvent and centrifugation, and then redispersed in a non-polar solvent and dried and stored in an inert atmosphere.

[0028] By adopting the above technical solution, excess oxidants and ligands are effectively removed, ensuring the purity and stability of the nanocrystal surface. The purified nanocrystals are redispersed in a non-polar solvent to ensure good dispersibility and processing adaptability, or they are dried and stored in an inert atmosphere to prevent moisture and oxygen in the air from affecting them.

[0029] In summary, this application includes at least one of the following beneficial technical effects: The self-limiting oxide layer formed by chemical oxidation effectively prevents further oxidation or degradation of the nanocrystal surface, blocks the penetration of external oxygen and moisture, thereby improving its stability and photoelectric properties in air.

[0030] The oxide layer thickness can be precisely controlled within the range of 1-3 nm to avoid excessive oxidation or crystal agglomeration, thus maintaining the structural integrity of the nanocrystals and their excellent optoelectronic properties.

[0031] By using functional ligands to modify the oxide layer, the surface passivation effect is enhanced, the surface defect states are reduced, and the quantum yield and photoelectric performance are improved.

[0032] The purification process removes excess oxidants and ligands, ensuring the purity of the nanocrystals and enabling them to exhibit higher processing adaptability and performance stability in practical applications.

[0033] The self-limiting growth characteristics of the oxide layer effectively prevent deep oxidation, maintain the stability of the nanocrystal core structure, and improve its long-term reliability and performance.

[0034] Improved stability The protective layer formed by controlled chemical oxidation can effectively prevent further deep oxidation, and the surface composition remains stable during long-term storage. In accelerated aging tests at 60% relative humidity and 25°C, the performance degradation rate of the treated nanocrystals is reduced by more than 10 times.

[0035] The passivation effect of the oxide layer can eliminate some surface defects, reduce the carrier concentration of some samples, and maintain the optimization of photoelectric performance. Attached Figure Description

[0036] Figure 1 This is a flowchart of an embodiment of this application.

[0037] Figure 2 This is a transmission electron microscope scan of HgTe nanocrystals synthesized using the method described in this application after oxidation.

[0038] Figure 3 This is a comparison chart of the stability test results of HgTe nanocrystals synthesized using the method described in this application. Detailed Implementation

[0039] The following is in conjunction with the appendix Figure 1-3 This application will be described in further detail.

[0040] This application discloses a post-processing method for mercury-based group II-VI nanocrystals that have formed a protective layer through chemical oxidation. (Refer to...) Figure 1 The method includes the following steps: Step 1: Disperse the newly synthesized mercury-based II-VI nanocrystals in a non-polar solvent and centrifuge to purify them, removing excess ligands and reaction byproducts. Centrifuge 1-3 times to remove excess ligands and reaction byproducts, ensuring surface cleanliness. Environmental conditions: inert atmosphere (glove box or nitrogen protection), temperature 15-30℃. Step 2: Prepare the oxidant solution. Select H2O2 or organic peroxide, and adjust the oxidant concentration and solvent type. Preferably, use an aqueous solution of H2O2 with a concentration of 3-30 wt% or tert-butyl hydroperoxide (TBHP) with a concentration of 5-50 mM. Dissolve the oxidant in a polar solvent (such as ethanol, isopropanol or acetonitrile) to prepare the oxidant solution. The molar ratio of oxidant to nanocrystals should be controlled between 1:1 and 100:1 to achieve precise control of the oxidation depth. Step 3: Controlled chemical oxidation treatment. The oxidant solution is added dropwise to the nanocrystal dispersion, and controlled oxidation is carried out under stirring conditions to form an oxide protective layer. Under continuous stirring (200-500 rpm), the oxidant solution was added dropwise to the nanocrystal dispersion at a rate of 0.1-1 mL / min. The reaction temperature was precisely controlled at 0-40℃ (preferably 15-25℃), and the reaction time was 5-60 minutes. Key process parameter control: The concentration of oxidant determines the thickness of the oxide layer. Too high a concentration leads to over-oxidation and agglomeration, while too low a concentration results in insufficient protection.

[0041] Reaction temperature: Low temperatures favor self-limiting oxidation and prevent deep oxidation; excessively high temperatures can cause crystals to dissolve. During this process, the Te / Se atoms on the surface of the nanocrystals are oxidized to TeO2 / SeO2, forming an amorphous or low-crystallinity oxide protective layer. The thickness of this layer is precisely characterized by high-resolution TEM and XPS depth analysis, ensuring that it is within the range of 1-3 nm. Step 4: Surface ligand modification. Functional ligands are used to modify the oxide layer surface to enhance the protective effect. Functional ligands include: short-chain thiols (such as 1,2-ethanedithiol EDT, 3-mercaptopropionic acid MPA). Phosphonic acid (such as dodecylphosphonic acid DDPA) bifunctional ligands (containing both thiol and carboxylic acid groups) have a ligand concentration of 1-20 times the quantum dot equivalent. The ligands are firmly anchored through strong bonding with the oxide layer (Te / Se-O- ligands), while providing additional steric protection. Step 5: Purify the oxidized nanocrystals, remove excess oxidant and ligands, and disperse the nanocrystals in the target solvent or store them in an inert atmosphere. During the process, excess antisolvent (such as ethanol or methanol) is added to precipitate the nanocrystals, followed by centrifugation (5000-10000 rpm, 5-10 minutes). The purification is repeated 2-4 times to remove excess oxidant and ligands. Finally, the nanocrystals are redispersed in the target solvent (such as n-hexane or tetrachloroethylene TCE) or dried and stored in an inert atmosphere.

[0042] Synergistic optimization of process parameters: There are complex interactions among the parameters. The type and concentration of oxidant need to be matched according to the size and composition of nanocrystals: Small-sized crystals (<3 nm) require milder oxidants and lower concentrations. Reaction temperature and time are inversely proportional; lower temperatures require longer reaction times to achieve the same degree of oxidation. The type of ligand must match the properties of the oxide layer: TeO2 tends to form strong bonds with thiol ligands, while SeO2 has a stronger affinity for phosphonic acid ligands. Through systematic experimental optimization, a quantitative relationship between oxidation conditions, oxide layer properties, and stability was established, ensuring the repeatability and controllability of the process.

[0043] This application proposes a post-treatment method for mercury-based II-VI nanocrystals based on controlled chemical oxidation. The method involves quantitatively oxidizing the surface of the nanocrystals with a mild oxidant at room temperature or low temperature to form a dense oxide protective layer. This is then combined with surface modification using functional ligands to achieve long-term stability and performance retention of the nanocrystals.

[0044] The technical principle of this application is as follows: The core of this method lies in using a mild oxidant (such as H2O2, organic peroxides, ozone, etc.) to oxidize the outermost Te / Se atoms of the nanocrystals under controlled conditions, forming a self-limiting oxide protective layer; this oxide layer has the following technical characteristics: 1. Self-limiting growth: The oxidation reaction only occurs in 1-3 atomic layers on the surface. After the oxide layer is formed, it will prevent further deep oxidation and protect the internal crystal structure. 2. Denseness: By controlling the concentration of oxidant, reaction temperature and time, the resulting oxide layer has a dense structure that can effectively block the penetration of oxygen and moisture; 3. Surface passivation: The oxide layer eliminates surface dangling bonds and defect states, reduces nonradiative recombination centers, and improves quantum yield; 4. Ligand anchoring sites: The oxide layer provides abundant oxygen atoms as ligand anchoring sites, enabling subsequently introduced functional ligands (such as thiols and phosphonates) to bind more firmly and enhancing overall stability.

[0045] The core of the technical solution in this application is to introduce a controllable chemical oxidation process in the post-processing stage of nanocrystals. Using mild oxidants (H2O2, organic peroxides, etc.) at room temperature or low temperature, the Te / Se atoms on the surface of the nanocrystals are selectively oxidized to form a dense oxide protective layer with a controllable thickness (1-3 nm). Combined with the surface modification of functional ligands, the long-term stability and excellent photoelectric performance are achieved.

[0046] The technological innovations of this application include: 1. Self-limiting oxidation mechanism: By precisely controlling the type, concentration, and reaction conditions of the oxidant, self-limiting growth of surface oxidation is achieved, avoiding the damage to the crystal core caused by excessive oxidation. 2. Dual protection of oxide layer and ligand: The oxide layer provides physical isolation and surface passivation, while the functional ligands are firmly anchored through strong bonding with the oxide layer, forming a synergistic protection system.

[0047] Key parameter combinations of the technical solution in this application: 1. Type and concentration of oxidant: H2O2 (3-30 wt%) or TBHP (5-50 mM), molar ratio 1:1-100:1; 2. Reaction temperature and time: 0-40℃ (preferably 15-25℃), 5-60 minutes; 3. Ligand modification: Thiols or phosphonates, concentration 0.1-10 vol% The synergistic optimization of the above parameters is the key to achieving a high-quality protective layer, and directly determines the final stability and performance.

[0048] An alternative to the technical solution of this application is to use plasma oxidation, which uses low-power oxygen plasma or ozone plasma to oxidize the surface of nanocrystals and form an oxide protective layer under vacuum or low-pressure atmosphere.

[0049] Advantages of the alternative: The oxidation process is more uniform, and the crystallinity of the oxide layer is controllable; Disadvantages of the alternative: It requires dedicated plasma equipment, which is costly; the process parameter window is narrow, making it prone to over-oxidation; it is not suitable for mass production and is applicable to laboratory research or small-batch high-end applications.

[0050] Example 1 Example 1 illustrates the modification of HgTe nanocrystals with thiol ligands based on H2O2 oxidation, demonstrating a typical process for mild oxidation of medium-sized HgTe nanocrystals using hydrogen peroxide (H2O2) and surface curing using short-chain thiols (EDT). Nanocrystal pretreatment: The synthesized HgTe nanocrystals (average particle size approximately 4.5 nm) were dispersed in anhydrous n-hexane. Excess synthesized ligands in the supernatant were removed by centrifugation (6000 rpm, 5 min), and the precipitate was redispersed in n-hexane to prepare a dark brown dispersion with a concentration of 5 mg / mL. All operations were performed in a nitrogen-filled glove box (oxygen content < 0.1 ppm, temperature 25 °C).

[0051] Preparation of oxidizing agent solution: A 30 wt% aqueous solution of H₂O₂ was diluted with anhydrous ethanol to prepare an ethanol solution with a H₂O₂ concentration of 0.1 M. Based on calculations, the molar ratio of oxidant to surface atoms of HgTe nanocrystals was set to approximately 10:1. Controlled chemical oxidation treatment: Under magnetic stirring (300 rpm), the above oxidant solution was added dropwise to the HgTe nanocrystal dispersion at a rate of 0.5 mL / min using a micro-injection pump. The reaction temperature was controlled at 20℃, and the reaction time was 30 minutes. Surface ligand modification: Immediately after the oxidation reaction is complete, an ethanol solution of 1,2-ethylenedithiol (EDT) is added to the reaction system. The amount of EDT added is 15 times the molar equivalent of the nanocrystals. Stirring continues for 10 minutes. Purification and stabilization: Excess anhydrous ethanol was added to the mixture as an antisolvent, causing the nanocrystals to flocculate and precipitate. The mixture was centrifuged at 8000 rpm for 5 minutes, and the supernatant was discarded. The "dispersion (n-hexane)-precipitation (ethanol)" step was repeated twice. The resulting HgTe nanocrystals with an oxide protective layer were redispersed in tetrachloroethylene (TCE) for subsequent infrared detector device fabrication. The average particle size of the oxidized quantum dots increased to 5 nm.

[0052] Example 2 The difference between Example 2 and Example 1 is that: HgTe was replaced with HgSe nanocrystals (average particle size approximately 8 nm).

[0053] Tert-butyl hydroperoxide (TBHP) was used instead of H2O2 at a concentration of 20 mM, increasing the molar ratio of oxidant to nanocrystals to 50:1.

[0054] Example 3 The difference between Example 3 and Example 1 is that: The reaction was carried out at 5°C (ice-water bath), with the reaction time shortened to 10 minutes and the dropping rate accelerated to 0.1 mL / min. The low temperature and short reaction time were intended to induce sub-monolayer oxidation of the crystal surface.

[0055] Comparative Example 1 Comparative Example 1 provides an unmodified HgTe nanocrystal as a reference sample; Synthesis and purification of nanocrystals: Post-processing of HgTe nanocrystals prepared using the exact same synthesis method as in Example 1 (blank control): The resulting HgTe nanocrystal precipitate was not subjected to the chemical oxidation treatment described in Example 1 (i.e., no oxidant was added), nor was it subjected to subsequent target ligand (such as thiols or phosphonic acids) substitution modification.

[0056] Final product state: The purified HgTe nanocrystals were redispersed in a nonpolar solvent to obtain an HgTe nanocrystal dispersion in which the original synthesized ligands were retained on the surface, which was used as the sample for Comparative Example 1.

[0057] Reference Figure 2 , Figure 2 This is a transmission electron microscope scan of the HgTe nanocrystals synthesized by the method of this application after oxidation. The HgTe nanocrystals synthesized by the method of this invention in Example 1 have a size of approximately 5 nm after oxidation, with a scale bar of 10 nm in the lower right corner.

[0058] Reference Figure 3 The stability (mobility performance) test comparison of HgTe nanocrystals synthesized using the method of this application is shown in the figure. The black dots represent Example 1 and the triangles represent Comparative Example 1. The figure shows that the curve of Example 1 is very stable.

[0059] The implementation principle of the post-treatment method for mercury-based II-VI nanocrystals to form a protective layer through chemical oxidation in this application embodiment is as follows: First, the newly synthesized mercury-based II-VI nanocrystals are dispersed in a non-polar solvent, and excess ligands and reaction byproducts are removed by centrifugation to ensure the cleanliness of the nanocrystal surface. Next, an oxidant solution is prepared, selecting H2O2 or an organic peroxide. The oxidation depth is precisely controlled by adjusting the oxidant concentration and solvent type (such as ethanol, isopropanol, or acetonitrile). Subsequently, the oxidant solution is added dropwise to the nanocrystal dispersion, and controlled chemical oxidation is carried out under continuous stirring to form a dense oxide protective layer. The oxidation reaction is carried out under precisely controlled temperature and time to ensure the thickness and uniformity of the oxide layer. To enhance the protective effect, the surface of the oxide layer is modified with functional ligands. The ligands form strong bonds with oxygen atoms in the oxide layer, improving the stability and photoelectric properties of the nanocrystals. Finally, the oxidized nanocrystals are purified by methods such as excess antisolvent precipitation and centrifugation to remove excess oxidants and ligands, ensuring their purity. The nanocrystals are then redispersed in the target solvent or stored in an inert atmosphere to prevent external environmental influences. This effectively improves the stability of mercury-based II-VI nanocrystals, prevents oxidative degradation, and enhances their photoelectric properties.

[0060] 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 post-processing method for mercury-based group II-VI nanocrystals with a protective layer formed by chemical oxidation, characterized in that: The method includes the following steps: Step 1: Pretreatment of nanocrystals. The newly synthesized mercury-based II-VI nanocrystals are dispersed in a non-polar solvent and purified by centrifugation to remove excess ligands and reaction byproducts. Step 2: Prepare the oxidant solution, choosing H2O2 or organic peroxide, and adjust the oxidant concentration and solvent type; Step 3: Controlled chemical oxidation treatment. The oxidant solution is added dropwise to the nanocrystal dispersion, and controlled oxidation is carried out under stirring conditions to form an oxide protective layer. Step 4: Surface ligand modification. Functional ligands are used to modify the oxide layer surface to enhance the protective effect. Step 5: Purification and stabilization. Purify the oxidized nanocrystals, remove excess oxidants and ligands, and disperse the nanocrystals in the target solvent or store them in an inert atmosphere.

2. The post-processing method according to claim 1, characterized in that: The nanocrystals mentioned therein are mercury-based group II-VI nanocrystals, selected from HgTe, HgSe and their alloys.

3. The post-processing method according to claim 1, characterized in that: In step one, the concentration of the nanocrystal dispersion is controlled at 0.5-10 mg / mL, and it is pretreated under an inert atmosphere.

4. The post-processing method according to claim 1, characterized in that: The oxidant is an aqueous solution of H2O2 with a concentration range of 3%-30%, or tert-butyl hydroperoxide (TBHP) with a concentration of 5-50 mM.

5. The post-processing method according to claim 1, characterized in that: The molar ratio of oxidant to nanocrystals is controlled between 1:1 and 100:1 to precisely regulate the oxidation depth.

6. The post-processing method according to claim 1, characterized in that: In step three, the reaction temperature is controlled at 0-40°C, preferably 15-25°C, and the reaction time is 5-60 minutes.

7. The post-processing method according to claim 1, characterized in that: During the oxidation reaction, the Te / Se atoms on the surface of the nanocrystals are oxidized to TeO2 / SeO2, forming a dense oxide protective layer with a thickness of 1-3 nm.

8. The post-processing method according to claim 1, characterized in that: The functional ligands mentioned in step four are short-chain thiols, phosphonic acids, or bifunctional ligands, and the ligand concentration is 1-20 times the quantum dot equivalent.

9. The post-processing method according to claim 1, characterized in that: The ligands provide additional surface protection by forming strong bonds with TeO2 or SeO2 in the oxide layer; The type, concentration, and reaction time of the oxidant are optimized based on the size and composition of the nanocrystals to achieve the best oxide layer performance. The oxide layer is an amorphous or low-crystallinity oxide with self-limiting growth characteristics, which can effectively prevent further deep oxidation. By controlling process parameters such as oxidant concentration, reaction temperature, and time, a dense oxide layer is formed, which can effectively block oxygen and moisture penetration and improve the stability of nanocrystals. The oxidized nanocrystals exhibit significant surface passivation, reducing surface defect states and improving quantum yield and photoelectric performance.

10. The post-processing method according to claim 1, characterized in that: In step five, the oxidized nanocrystals are purified 2-4 times by precipitation with excess antisolvent and centrifugation, and then redispersed in a non-polar solvent and dried and stored in an inert atmosphere.

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