Preparation method and application of high-stability Cs3Bi2X9 lead-free halide core-shell nanocrystals

Abstract

The application discloses a preparation method and application of high-stability lead-free halide core-shell nanocrystals and belongs to the field of semiconductor material preparation. The nanocrystal core layer is and the shell layer is an in-situ grown anatase phase / amorphous phase. Tetrabutyl titanate is used as a single titanium source, and one-step coating is carried out through precursor solution preparation-titanium source in-situ hydrolysis-anti-solvent induction-post treatment. Optionally, a chelating agent can be introduced to passivate defects, and a polymer+inorganic dense layer double-coating can be used to strengthen the stability. The oxygen-free preparation conditions are optimized, and one or mixed halogen nanocrystals can be prepared by passing nitrogen gas throughout the whole process, so that the problems of poor water oxygen and thermal stability of traditional nanocrystals are solved. In-situ coating forms an interface bonding, and the fluorescence retention rate is greater than or equal to 80% in air for three months, and the Cl / Br phase can reach greater than or equal to 90%. The process is simple and easy to scale, and the material can be widely applied to the fields of photocatalysis, flexible X-ray imaging, LED, photoelectric detection and the like, and has significant academic and industrial application values.

Description

Technical Field

[0001] The nanocrystals of this invention can be widely used in photocatalysis, flexible X-ray imaging, LED devices, photoelectric detection and other fields. The preparation process is simple, low-cost and easy to scale up, and has extremely high academic value and industrial application prospects. Background Technology

[0002] (X=Cl, Br, I) As a new type of lead-free halide quantum dot material, it has effectively overcome the toxicity defects of traditional lead-based perovskite quantum dots with its unique advantages such as low toxicity, tunable band gap (2.0-3.02 eV) and high optical absorption coefficient. It has attracted much attention in optoelectronic fields such as photoelectric detection, photocatalysis and light-emitting devices, and has broad practical application prospects.

[0003] However, Quantum dots themselves suffer from severe stability defects; their surface ligands are prone to desorption, resulting in persistently high surface defect density. When exposed to air, water, or moderate temperatures, they are highly susceptible to ion migration, phase separation, and crystal structure collapse, leading to fluorescence quenching and severely limiting their widespread application in practical scenarios. Currently, regarding... There have been relevant studies on the stabilization methods of quantum dots, mainly including polymer coating, inorganic shell post-coating and matrix embedding, but all of them have obvious shortcomings: (1) polymer coating has limited barrier properties and poor long-term stability; (2) traditional inorganic shells (such as , (2) Most of the post-coating processes are used, and the core-shell interface is loosely bonded, which easily forms voids and becomes water and oxygen permeation channels; (3) Although titanium-based coating has high barrier properties and chemical inertness, the existing technologies are mostly prepared in steps, and the hydrolysis rate of titanium source is difficult to control, which easily leads to uneven shell and agglomeration, and does not address the specific problems. Optimize the process to meet the special stability requirements of the I phase (especially).

[0004] Therefore, it is necessary to develop a method that is simple to manufacture, has a tight interface, and balances optical performance with stability in various environments. The stabilization method for nanocrystals has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In response to existing technologies The present invention addresses the problems of poor stability of lead-free halide nanocrystals, diverse titanium sources in the coating process, uncontrollable hydrolysis rate, loose core-shell interface bonding, and the reliance on glove boxes for I-phase nanocrystal preparation, which hinders large-scale production. It provides a high-stability solution. Preparation methods and applications of lead-free halide core-shell nanocrystals.

[0006] This invention uses tetrabutyl titanate as a single titanium source and achieves its slow hydrolysis. The shell is coated in situ in one step, forming a dense layer. Interface bonding is achieved; simultaneously, the oxygen-free preparation conditions are optimized, eliminating the harsh glove box operation and using only nitrogen protection throughout the process, which meets the oxygen-free preparation requirements of I-phase or high I-content mixed halogen nanocrystals, significantly reducing the production threshold. This invention further introduces defect passivation and dual-coating strategies, significantly improving the water and oxygen stability, thermal stability, and optical properties of the nanocrystals, achieving ultra-long-term stability with a fluorescence retention rate of ≥85% in air for 3 months.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a highly stable An in-situ coating preparation method for lead-free halide nanocrystals, wherein X is one or more of Cl, Br, and I, using tetrabutyl titanate as a single titanium source, and achieving the coating through slow hydrolysis of tetrabutyl titanate. In-situ coating is performed when X is I or a mixed halogen with I content ≥50%. The entire preparation process is carried out under nitrogen protection, eliminating the need for a glove box environment. The nanocrystals have a core-shell structure, with the core layer being... Lead-free halides, with an in-situ grown anatase / amorphous shell. The preparation method includes four steps: precursor solution preparation, titanium source addition, core-shell structure induction, and post-treatment. It can further introduce chelating agents to passivate defects and polymer + inorganic dense layer double coating to enhance stability.

[0008] Furthermore, the specific steps of the preparation method are as follows:

[0009] Step 1, Preparation of precursor solution: Purge high-purity nitrogen gas (purity ≥99.99%) into the reaction vessel for at least 30 minutes to fully purge the air from the vessel; then react CsX with... The molar ratio of CsX to CsX is 2.9–3.1:2. Dissolve Prepare a mixed solution with a concentration of 0.1-0.22 M in DMF, dimethyl sulfoxide (DMSO), or a mixture thereof; under continuous nitrogen protection, add [the following to the mixed solution]. The precursor solution was prepared by stirring at 55-65°C for 25-40 min until the solution became clear, with each of fatty acids and fatty amines at 4-6 vol% as ligands.

[0010] Step 2, Titanium Source Addition: Under continuous nitrogen protection, dilute tetrabutyl titanate 9–11 times with anhydrous ethanol, and slowly add it to the precursor solution at a rate of 1–2.5 drops / second, according to a Ti:Bi molar ratio of 0.4–1.1; stir at room temperature for 30–70 min to allow the tetrabutyl titanate to slowly hydrolyze and uniformly adsorb onto the substrate. On the surface of the precursor, form The precursor is coated; optionally, after slow hydrolysis of tetrabutyl titanate, 4-6 mM acetylacetone chelating agent is added under nitrogen protection, and stirring is continued for 8-12 min to passivate defects on the nanocrystal surface.

[0011] Step 3, Core-shell structure induction: Under continuous nitrogen protection, towards... The precursor is rapidly injected with 4-6 times its volume of one or more of toluene, chloroform, or n-hexane as an antisolvent to rapidly induce the formation of a core-shell structure using the antisolvent effect; after stirring for 8-12 min, it is centrifuged at 7000-9000 rpm for 4-6 min and the bottom precipitate is collected.

[0012] Step 4, Post-treatment: Under continuous nitrogen protection, the precipitate is vacuum dried at 55–65℃ for 10–14 h to remove residual solvent and obtain the in-situ precipitate. Covered Lead-free halide nanocrystals; when X is I or a mixed halide with I content ≥50%, after drying, it needs to be annealed at 70–85℃ for 25–35 min under a nitrogen atmosphere to further strengthen the core-shell interface bonding; optionally, after drying, the nanocrystals are subjected to double coating modification, first preparing 1–2 nm nanocrystals by atomic layer deposition (ALD). An inorganic dense layer is then spin-coated with a 3–5 wt% PMMA chloroform solution (3000 rpm, 30 s) to form a 300–500 nm polymer outer layer, further enhancing stability.

[0013] This invention also protects the high stability prepared by the above method. Lead-free halide nanocrystals, wherein the nanocrystals have a particle size <50 nm and a core-shell structure, with the core layer being... Pure phase, with an anatase / amorphous shell. , The shell thickness is 5–10 nm, and the core-shell interface is void-free and forms Covalent bonding effectively blocks water and oxygen permeation channels. This nanocrystal exhibits excellent optical properties, with a photoluminescence quantum yield (PLQY) ≥20%, and its stability has been significantly improved. After storage at 25℃ and 50% RH in air for 3 months, the fluorescence retention rate is ≥85%. The fluorescence retention rate of the Cl / Br phase after heating at 130℃ for 2 h is ≥80%, and the fluorescence retention rate of the I phase after heating at 95℃ for 2 h is ≥80%. After soaking in deionized water for 24 h, it still retains more than 70% of the fluorescence intensity.

[0014] This invention also protects the aforementioned high stability The application of lead-free halide nanocrystals: These nanocrystals can be widely used in photocatalysis, flexible X-ray imaging, LED devices, photoelectric detection and other fields. The preparation process is simple, the equipment requirements are low, and it is easy to scale up production, making it suitable for industrial applications.

[0015] The beneficial effects of the present invention include at least the following:

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. Single Titanium Source + Slow Hydrolysis for Precise and Controllable Coating: This invention uses tetrabutyl titanate as a single titanium source and achieves slow hydrolysis by controlling its dropping rate and stirring time. This avoids the problem of uneven hydrolysis rates caused by using multiple titanium sources, thus enabling... shell in The precursor grows uniformly on the surface, and the shell thickness is controllable and free from agglomeration, which greatly improves the repeatability and controllability of the coating process.

[0018] 2. In-situ coating achieves dense interfacial bonding, overcoming the bottleneck of long-term stability: This is accomplished in one step through "precursor solution preparation - in-situ hydrolysis of titanium source - antisolvent induction - post-treatment". In-situ coating of the shell, after slow hydrolysis of tetrabutyl titanate Direct formation on the precursor surface Covalent bonding, with no gaps at the core-shell interface and tight bonding, effectively avoids the problems of shell detachment and water and oxygen permeation in traditional post-coating processes, fundamentally improving the stability of nanocrystals and achieving ultra-long-term stability with a fluorescence retention rate of ≥85% in air for 3 months.

[0019] 3. Nitrogen protection replaces glove box, significantly lowering the industrialization threshold: For the preparation of I-phase or high I-content mixed halogen nanocrystals, this invention abandons the traditional harsh glove box operation and can achieve oxygen-free preparation by using nitrogen protection throughout the process. The equipment cost is low, the operation is simple, and there is no need for complex anhydrous and oxygen-free environment control, which greatly improves the operability of the process and the potential for large-scale production.

[0020] 4. Enhance performance through multiple collaborative strategies: By introducing... Fatty acid / fatty amine ligands regulate nanocrystal growth; acetylacetone chelating agents are added to passivate surface defects. (Optional) Double coating further enhances the barrier effect, achieving a synergistic improvement in optical performance and stability. The nanocrystalline PLQY is ≥20%, and its water, oxygen, and thermal stability are significantly better than existing materials.

[0021] 5. Simple process and easy to scale up production: The preparation method of this invention is a one-step in-situ coating process with a single titanium source and simple operation. It does not require complex step-by-step equipment, the reaction conditions are mild and highly controllable, the reagents used are inexpensive and readily available, and the steps such as centrifugation and drying are all routine industrial operations. It can also achieve large-scale preparation under nitrogen protection, making it suitable for industrial production.

[0022] 6. Wide range of applications: This invention has a wide range of applications. Lead-free halide nanocrystals are lead-free and environmentally friendly, with excellent photoelectric properties and ultra-long-term stability. They can be widely used in photocatalysis, flexible X-ray imaging, LED devices, photoelectric detection and other fields. They exhibit excellent performance, especially in blue LED devices, and have extremely high academic value and industrial application prospects. Attached Figure Description

[0023] Figure 1 is TEM image of nanocrystals;

[0024] Figure 2 is TEM image of nanocrystals;

[0025] Figure 3 is TEM image of nanocrystals;

[0026] Figure 4 shows the results immediately after preparation and after 3 months of storage. Nanocrystals and Comparison of PL spectra of nanocrystals;

[0027] Figure 5 shows the results after preparation and storage for 3 months. Nanocrystals and Comparison of PL spectra of nanocrystals;

[0028] Figure 6 shows the results immediately after preparation and after 3 months of storage. Nanocrystals and Comparison of PL spectra of nanocrystals.

[0029] Figure 7 for XRD pattern of nanocrystals

[0030] Explanation of reference numerals in Figures 1-3: In Figures 1-3, the core layer is... Lead-free halides, shell is The core-shell interface is free of voids; in Figure 4-6, 0 Day is the sample that has just been prepared, and 90 Day is the sample that has been stored at 25℃ and 50% RH in air for 3 months. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Note: When X is I or a mixed halogen with I content ≥50%, the preparation process in the following embodiments is carried out under nitrogen protection throughout, without the need for a glove box environment; all embodiments use tetrabutyl titanate as a single titanium source, achieved through its slow hydrolysis. In-situ wrapping.

[0032] Example 1: An in-situ Cover Preparation methods of nanocrystals

[0033] Preparation of precursor solution: Purge high-purity nitrogen (99.99% purity) into a three-necked flask for 30 minutes to purge air; then react CsBr with... The molar ratio is 3:2. Weigh out 0.3 mmol CsBr (0.0567 g) and 0.2 mmol CsBr (0.2 mmol). (0.0978g) was dissolved in 10 mL of DMF; under continuous nitrogen protection, 5 vol% (0.5 mL each) of oleic acid and oleylamine were added, and the mixture was magnetically stirred at 60°C for 30 min until the solution was clear to obtain the precursor solution;

[0034] Titanium source addition: Under continuous nitrogen protection, 0.2 mmol of tetrabutyl titanate (0.0616 g) was diluted 10 times with anhydrous ethanol (volume ratio 1:9) and slowly added to the precursor solution at a dropping rate of 1.5 drops / second. The mixture was stirred at room temperature for 40 min to allow the tetrabutyl titanate to slowly hydrolyze, forming... Encapsulating precursors;

[0035] Core-shell structure induction: Under continuous nitrogen protection, 50 mL of toluene (5 times the volume) was rapidly injected, stirred vigorously for 10 min, and then centrifuged at 8000 rpm for 5 min, and the orange-yellow precipitate at the bottom was collected;

[0036] Post-treatment: Under continuous nitrogen protection, the precipitate was placed in a vacuum drying oven and dried at 60°C for 12 h to obtain... Core-shell nanocrystalline powder.

[0037] Characterization results:

[0038] 1. Morphology and structure: From Figure 1 TEM images show that the nanocrystals are spherical with a particle size of 8-10 nm and a TiO2 shell thickness of 1 nm. Figure 7 XRD pattern analysis indicates that the core layer is Pure phase (PDF#97-009-6723), with an anatase shell. (PDF# 97-015-4605);

[0039] 2. Optical performance: Figure 4 The PL spectrum shows that The nanocrystal emission peak is located at 420 nm, with a full width at half maximum (FWHM) of 28 nm and PLQY = 23% (integrating sphere method).

[0040] 3. Stability: From Figure 4 It can be seen from this that The nanocrystals retained 91.2% fluorescence after being stored at 25°C and 50% RH in air for 3 months.

[0041] Example 2: An in-situ Cover Preparation methods of nanocrystals

[0042] Preparation of precursor solution: Purge high-purity nitrogen (99.99% purity) into a three-necked flask for 30 minutes to purge air; then react CsCl with... The molar ratio is 3:2. Weigh out 0.3 mmol CsCl (0.0366 g) and 0.2 mmol CsCl. (0.0586g) was dissolved in 10 mL of DMSO; under continuous nitrogen protection, 5 vol% (0.5 mL each) of lauric acid and dodecylamine were added, and the mixture was magnetically stirred at 58°C for 35 min until the solution was clear to obtain the precursor solution;

[0043] Titanium source addition: Under continuous nitrogen protection, 0.2 mmol of tetrabutyl titanate (0.0616 g) was diluted 10 times with anhydrous ethanol (volume ratio 1:9) and slowly added to the precursor solution at a dropping rate of 1.2 drops / second. The mixture was stirred at room temperature for 45 min to allow the tetrabutyl titanate to slowly hydrolyze, forming... Encapsulating precursors;

[0044] Core-shell structure induction: Under continuous nitrogen protection, 50 mL of acetone (5 times the volume) was rapidly injected, and the mixture was stirred vigorously for 12 min. Then, the mixture was centrifuged at 7500 rpm for 5 min, and the white precipitate at the bottom was collected.

[0045] Post-treatment: Under continuous nitrogen protection, the precipitate was placed in a vacuum drying oven and dried at 60°C for 12 h to obtain... Core-shell nanocrystalline powder.

[0046] Characterization results:

[0047] 1. Morphology and Structure: TEM images in Figure 2 show that the nanocrystals are spherical with a particle size of 2 nm. Due to the extremely small particle size... The shell was not observable; XRD pattern analysis indicated that the core layer was... Pure phase (PDF#97-008-3412);

[0048] 2. Optical performance: Figure 5 The PL spectrum shows that The nanocrystal emission peak is located at 370 nm, with a full width at half maximum (FWHM) of 28 nm and PLQY = 23% (integrating sphere method).

[0049] 3. Stability: From Figure 5 It can be seen from this that The nanocrystals retained 90.4% fluorescence after being stored at 25°C and 50% RH in air for 3 months.

[0050] Example 3: An in-situ Cover Preparation methods of nanocrystals

[0051] Preparation of precursor solution: Purge high-purity nitrogen into a three-necked flask for 40 minutes to purge air; prepare CsI solution according to the formula. The molar ratio is 3.05:2. Weigh out 0.305 mmol CsI (0.0641 g) and 0.2 mmol CsI. (0.1178 g) was dissolved in 10 mL of DMSO; under continuous nitrogen protection, the mixture was stirred for 35 min until clear to obtain the precursor solution;

[0052] Titanium source addition: Under continuous nitrogen protection, 0.22 mmol of tetrabutyl titanate was diluted 10 times with anhydrous ethanol and added dropwise to the precursor solution at 1 drop / second. The mixture was stirred at room temperature for 50 min to allow slow hydrolysis of the tetrabutyl titanate. Then, 0.005 mL of 5 mM acetylacetone was added, and stirring was continued for 10 min to passivate defects and form... Encapsulating precursors;

[0053] Core-shell structure induction: Under continuous nitrogen protection, 50 mL of n-hexane was rapidly injected, stirred for 12 min, centrifuged at 7500 rpm for 5 min, and the black precipitate was collected;

[0054] Post-treatment: Under continuous nitrogen protection, the precipitate was placed in a vacuum drying oven and dried at 60°C for 12 h to obtain... Core-shell nanocrystalline powder.

[0055] Characterization results:

[0056] 1. Morphology and structure: From Figure 3 TEM images show that the nanocrystals are spherical with a particle size of 1 nm. Due to their extremely small particle size... The shell was not observable; XRD pattern analysis indicated that the core was... Pure phase (PDF#97-041-0726);

[0057] 2. Optical performance: Figure 6 The PL spectrum shows that The nanocrystal emission peak is located at 405 nm, with a full width at half maximum (FWHM) of 28 nm and PLQY = 23% (integrating sphere method).

[0058] 3. Stability: From Figure 6 It can be seen from this that The nanocrystals retained 80% of their fluorescence after being stored at 25°C and 50% RH in air for 3 months.

[0059] Comparative Example 1: Uncovered Nanocrystals

[0060] Preparation method: Except for the absence of tetrabutyl titanate, the other steps are the same as in Example 1.

[0061] Characterization results: such as Figure 4 As shown, The fluorescence retention rate of the nanocrystals was only 2.1% after 3 months of storage in air;

[0062] Comparative Example 2: Uncovered Nanocrystals

[0063] Preparation method: Except for the absence of tetrabutyl titanate, the other steps are the same as in Example 2.

[0064] Characterization results: such as Figure 5 As shown, The fluorescence retention rate of the nanocrystals was only 2.4% after 3 months of storage in air;

[0065] Comparative Example 3: Uncovered Nanocrystals

[0066] Preparation method: Except for the absence of tetrabutyl titanate, the other steps are the same as in Example 3.

[0067] Characterization results: such as Figure 6 As shown, The fluorescence retention rate of nanocrystals was only 10% after 3 months of storage in air;

[0068] Key characterization methods description

[0069] 1. Morphology and structure characterization: The core-shell structure, particle size and shell thickness of the nanocrystals were observed using a transmission electron microscope (TEM, JEOL JEM-2100); the crystal phase was analyzed using an X-ray diffractometer (XRD, Bruker D8 Advance) under the following test conditions: Cu Kα radiation, λ=0.154 nm, 2θ=10-60°.

[0070] 2. Optical performance characterization: The PL spectrum and photoluminescence quantum yield (PLQY) were measured using a fluorescence spectrophotometer (Horiba FluoroMax-4) combined with an integrating sphere, with an excitation wavelength of 365 nm.

[0071] 3. Air stability: Place the sample in a constant temperature and humidity chamber at 25℃ and 50% RH, and test it regularly for 3 months to calculate the fluorescence retention rate;

[0072] Industrial Application Prospects

[0073] High stability of the present invention Lead-free halide nanocrystals are lead-free and environmentally friendly. In-situ coating is achieved through the slow hydrolysis of tetrabutyl titanate, a single titanium source, solving the problems of traditional methods. The core problems of nanocrystals include high sensitivity to water and oxygen, poor thermal stability, and unsatisfactory long-term stability. This invention addresses these issues by replacing the glove box with nitrogen protection, significantly lowering the preparation threshold for I-phase nanocrystals and achieving ultra-long-term stability with a fluorescence retention rate of ≥85% for 3 months in air. The preparation process is simple, low-cost, and easily scalable, making it widely applicable in photocatalysis, flexible X-ray imaging, LED devices, and photoelectric detection. It shows significant advantages in blue LED devices and flexible X-ray flat panel detectors, and is expected to replace traditional lead-based perovskite materials for industrialization, promoting the industrial development of lead-free optoelectronic materials.

[0074] Scope of protection

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly stable A method for preparing and applying lead-free halide core-shell nanocrystals, characterized in that, Includes the following steps: Step (1), Preparation of precursor solution: After purging the air by introducing nitrogen gas into the reaction vessel, proceed with CsX and... The molar ratio of CsX to CsX is 2.9–3.1:

2. Dissolve Prepare a mixed solution with a concentration of 0.1–0.22 M in DMF, dimethyl sulfoxide (DMSO), or a mixture thereof, and add [the following solvent] under continuous nitrogen purging. 4-6 vol% fatty acids and fatty amines were used as ligands, and the mixture was stirred at 55-65℃ for 25-40 min until the solution became clear to obtain the precursor solution. Wherein, X is any one of I, Br, and Cl; Optionally, when X=I, the solvent is (DMF), when X = Br or Cl, the solvent is dimethyl sulfoxide (DMSO); The nanocrystals have a core-shell structure, with the core layer being... Lead-free halides, with an anatase or amorphous shell. Using tetrabutyl titanate as the sole titanium source, the slow hydrolysis of tetrabutyl titanate is used to achieve... In-situ coating: When X is I or a mixed halogen with I content ≥50%, the entire preparation process is carried out under nitrogen protection, without the need for a glove box environment. Step (2), Titanium source addition: Under continuous nitrogen protection, dilute tetrabutyl titanate 9-11 times with anhydrous ethanol, and add it to the precursor solution described in step 1 at a dropping rate of 1-2.5 drops / second according to a Ti:Bi molar ratio of 0.4-1.

1. Stir at room temperature for 30-70 min to allow the tetrabutyl titanate to slowly hydrolyze and form Encapsulating precursors; Step (3), Core-shell structure induction: Under continuous nitrogen protection, proceed as described in step 2. Rapidly inject 4-6 times the volume of one or more of toluene, chloroform, or n-hexane as an antisolvent into the coating precursor, stir for 8-12 min, centrifuge at 7000-9000 rpm for 4-6 min, and collect the precipitate. Optionally, when X=I, the antisolvent is n-hexane, and when X=Br or Cl, the antisolvent is toluene; Step (4), Post-treatment: Under continuous nitrogen protection, the precipitate obtained in step 3 is vacuum dried at 55-65℃ for 10-14 h to obtain in-situ... Covered Lead-free halide nanocrystals; when X is I or a mixed halide with I content ≥50%, it needs to be annealed at 70-85℃ for 25-35 min under a nitrogen atmosphere after drying.

2. The preparation method according to claim 1, characterized in that, In step (1), optionally, the The fatty acid is one or both of lauric acid and oleic acid. Fatty amines are one or both of dodecylamine and oleylamine.

3. The preparation method according to claim 1, characterized in that, In step (2), after the slow hydrolysis of tetrabutyl titanate, a chelating agent, namely acetylacetone, is added to the system under nitrogen protection at a concentration of 4-6 mM. Stirring is continued for 8-12 min to passivate defects on the nanocrystal surface.

4. The preparation method according to claim 1, characterized in that, In step (4), after drying, the nanocrystals can be double-coated and modified. First, 1-2 nm nanocrystals are prepared by atomic layer deposition (ALD). An inorganic dense layer is then spin-coated with a 3-5 wt% polymethyl methacrylate (PMMA) chloroform solution to form a 300-500 nm polymer outer layer.

5. The preparation method according to claim 1, characterized in that, The Lead-free halide nanocrystals with a particle size <50 nm The shell thickness is 5-10 nm, and the core-shell interface is void and forms Covalent bonding.

6. A highly stable preparation made by the method of any one of claims 1-5 Lead-free halide nanocrystals, characterized in that, The nanocrystals have a core-shell structure, with the core layer being... Pure phase, with an anatase / amorphous shell. The fluorescence retention rate is ≥85% after 3 months of storage at 25℃ and 50% RH in air. The fluorescence retention rate of the Cl / Br phase is ≥80% after heating at 130℃ for 2 hours, and the fluorescence retention rate of the I phase is ≥80% after heating at 95℃ for 2 hours.

7. A high-stability solution as described in claim 6 The application of lead-free halide nanocrystals is characterized by, The nanocrystals are applied in one or more of the fields of photocatalysis, flexible X-ray imaging, LED devices, and photoelectric detection.

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