A shell-less indium phosphide quantum dot based on in-situ passivation with orthophosphate and its preparation method

Abstract

This invention belongs to the field of nanomaterials technology, specifically relating to a shell-less indium phosphide quantum dot based on in-situ passivation with orthophosphate and its preparation method. Using indium and phosphorus sources as raw materials, this invention synthesizes indium phosphide core quantum dots under an inert atmosphere, followed by in-situ passivation treatment with polyphosphoric acid. The polyphosphoric acid is hydrolyzed to generate orthophosphate ions, which strongly coordinate with the indium active sites on the quantum dot surface to form a stable passivation layer, efficiently eliminating surface defect states. This method eliminates the need for epitaxial growth of a shell, is simple in process, has mild conditions, and is easy to scale up. The prepared shell-less indium phosphide quantum dots achieve a photoluminescence quantum yield of over 90%, with an optimal yield approaching 100%. The emission peak position is stable without shift, and air stability and anti-photoaging performance are significantly improved. This method solves the problems of low quantum yield, poor stability, and complex preparation of traditional indium phosphide quantum dots, and can be widely used in optoelectronic devices such as light-emitting diodes, photodetectors, biofluorescent labels, and lasers.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a shell-less indium phosphide quantum dot based on in-situ passivation with orthophosphate and its preparation method. Background Technology

[0002] Indium phosphide (InP) quantum dots, as a novel environmentally friendly fluorescent nanomaterial, align with the global trend of green and low-carbon development by being free of toxic heavy metals such as cadmium and lead. They exhibit irreplaceable application potential in several cutting-edge fields, including display panels, solid-state lighting, biofluorescent labeling, photoelectric detection, solar cells, and lasers. Compared to traditional heavy metal-containing quantum dots, InP quantum dots not only possess excellent size-dependent luminescence properties, wide color gamut coverage, and good biocompatibility, but also effectively avoid the environmental pollution and biotoxicity problems caused by heavy metals, making them a research hotspot in the field of nanomaterials in recent years. However, due to unsaturated coordination, InP quantum dots have numerous dangling bonds and defect sites on their surface atoms. These surface defects trigger strong nonradiative recombination processes, resulting in a generally low photoluminescence quantum yield (PLQY), typically only 5%–15%. Furthermore, their poor chemical and photostability, coupled with their susceptibility to degradation under ambient air and light conditions, significantly limits their industrial application in practical devices.

[0003] Currently, the industry has conducted extensive research on modification techniques for InP quantum dot surface defects, and various passivation modification methods have emerged, but all have significant technical limitations. Among them, halide or fluoride surface treatment is a relatively simple passivation method. It mainly achieves partial passivation by coordinating halide ions (such as Cl⁻, Br⁻) or fluoride ions (F⁻) with unsaturated metal sites on the quantum dot surface. However, its passivation effect is limited, typically only increasing the photoluminescence quantum yield to around 30%, and it easily causes a 5-10 nm shift in the quantum dot emission peak position, failing to meet the application requirements of high-performance devices. Furthermore, the ligand binding force on the quantum dot surface after passivation by this method is weak, and it is easily detached during subsequent device fabrication processes (such as spin coating and vapor deposition), further affecting the stability and lifespan of the device, making it difficult to meet the stringent requirements of industrial production.

[0004] To further improve the luminescence performance and stability of InP quantum dots, epitaxial growth of a shell to construct a core-shell structure has become the mainstream modification strategy. Common shell materials include group II-VI semiconductors such as ZnS, ZnSe, and CdS. This method grows a semiconductor shell on the surface of the InP core quantum dot, which can effectively passivate defect sites on the core surface and form a heterojunction structure to suppress nonradiative recombination, thereby significantly improving quantum yield and stability. The PLQY of some core-shell InP quantum dots can be increased to over 80%. However, this process has problems such as complex operation, long reaction cycle, and high production cost. Shell growth usually requires staged control of temperature, reaction time, and raw material ratio. Moreover, problems such as lattice mismatch and interface defects are prone to occur during shell growth, leading to fluctuations in the optical performance of quantum dots and poor batch-to-batch consistency. At the same time, shell growth has extremely high requirements for the control of reaction conditions, requiring precise control of parameters such as the purity of the inert atmosphere, stirring speed, and raw material drop acceleration rate, making it difficult to achieve large-scale mass production and failing to meet the actual needs of industrial production.

[0005] Therefore, developing a surface modification technology for InP quantum dots that is simple to process, efficient in passivation, low in cost, and capable of large-scale production, in order to solve the core problems of low quantum yield and poor stability, has become a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a shell-less indium phosphide quantum dot based on in-situ passivation with polyphosphate and its preparation method. By using polyphosphate in-situ passivation treatment, surface defects of quantum dots can be efficiently eliminated without the need for epitaxial growth of a shell, significantly improving their luminescence performance and stability. The prepared quantum dots have a particle size of 3-5 nm, a particle size distribution variation coefficient ≤15%, and a photoluminescence quantum yield ≥90%. After being stored in air at 25°C and 50% relative humidity for 30 days, the photoluminescence quantum yield retention rate is >90%. At the same time, the preparation process is simplified, production costs are reduced, and the large-scale preparation of shell-less InP quantum dots is realized, providing technical support for their industrial application in the field of optoelectronic devices.

[0007] The technical solution adopted is as follows: A method for preparing shell-less indium phosphide (InP) quantum dots based on in-situ passivation with orthophosphate includes the following steps: (1) Synthesis of indium phosphide core quantum dots: Mix the indium source, coordination solvent and non-coordination solvent, and stir with a magnetic stirrer for 10-15 minutes until a uniform and transparent mixed solution is formed. This ensures that the indium source is fully dissolved in the solvent system and avoids uneven quantum dot size distribution caused by excessively high local concentrations. The reaction was carried out under an inert atmosphere by adding a phosphorus source. After the reaction was completed, the reaction vessel was placed in an ice-water bath and rapidly cooled to room temperature. After purification, indium phosphide core quantum dots were obtained. (2) In-situ passivation treatment: The indium phosphide core quantum dots obtained in step (1) are dispersed in an organic solvent, polyphosphoric acid (PPA) is added, and a passivation reaction is carried out under heating conditions. After the reaction is completed, the indium phosphide quantum dots without shell are obtained by purification.

[0008] Preferably, in step (1), the indium source is selected from at least one of indium chloride (InCl3), indium acetate (In(CH3COO)3), and indium nitrate (In(NO3)3), with indium chloride being preferred, as it has good solubility, high reactivity, and easy purity control, which can ensure uniform nucleation of quantum dots and reduce the introduction of impurities; The phosphorus source is selected from at least one of tert-butylphosphine dichloride (t-BuPCl2), tri(dimethylamine)phosphine (P(NMe2)3), trioctylphosphine (TOP), tri(diethylamine)phosphine (P(NEt2)3), and tri(trimethylsilyl)phosphine (P(TMS)3), with tert-butylphosphine dichloride being preferred. It has moderate reactivity, readily reacts with indium sources to generate InP cores, and the byproducts are easy to remove, thus not adversely affecting the quantum dot performance. The coordination solvent is selected from at least one of oleylamine (OAm), octadecylamine (ODA), hexadecylamine (HDA), oleic acid (OA), and myristic acid, with oleylamine being preferred. It has strong coordination ability, can effectively stabilize the surface of InP quantum dots, prevent quantum dot aggregation, and is easily replaced by polyphosphoric acid, which facilitates subsequent passivation treatment. The noncoordination solvent is selected from at least one of octadecene (ODE), hexadecene, liquid paraffin, dioctyl ether, and eicosene, with octadecene being preferred. It has a high boiling point, stable chemical properties, can provide a stable reaction environment, and does not react with the raw materials, making it easy to control the reaction temperature. The passivation reagent is polyphosphoric acid (PPA) with a purity of ≥98%. After hydrolysis, it can generate orthophosphate anions, which strongly coordinate with the indium active sites on the surface of InP quantum dots to form a stable passivation layer. It is also widely available and inexpensive, making it suitable for large-scale applications. The purification reagents are anhydrous ethanol and toluene, both of analytical grade. Anhydrous ethanol is used for the precipitation and separation of quantum dots, and toluene is used for the dispersion of quantum dots. The combination of the two can effectively remove excess ligands and by-products, ensuring the purity of quantum dots. The inert atmosphere is argon or nitrogen, with a purity ≥99.99%.

[0009] Preferably, in step (1), the ratio of the indium source, the coordinating solvent, and the non-coordinating solvent is (0.2–1) mmol : (5–10) mL : (10–15) mL. This ratio can effectively control the nucleation rate and growth process of quantum dots, ensuring that the prepared InP core quantum dots have uniform size and good dispersion.

[0010] Preferably, before adding the phosphorus source in step (1), an inert atmosphere should be introduced for 5 to 10 minutes to completely remove the air and oxygen in the flask and avoid the interference of oxygen and moisture on the synthesis of quantum dots. The mixture was degassed under vacuum at 100–120°C and 0.08–0.1 MPa for 20–30 min, and then heated to 160–180°C under an inert atmosphere before the phosphorus source was injected. The phosphorus source is pre-dissolved in octadecene, and the injection time is controlled within 10 seconds, with a reaction time of 3–6 minutes after injection. This ensures that the phosphorus source is rapidly and uniformly dispersed in the system, avoiding excessively high local concentrations that could lead to quantum dot aggregation. After the phosphorus source is injected, the reaction begins immediately. During the reaction, the solution color can be observed to gradually change from colorless to pale yellow, then orange-yellow, and finally orange-red or dark red. This color change indicates that the InP core quantum dots have been successfully generated, and their size gradually increases with reaction time. After the preset reaction time is reached, the three-necked flask is immediately placed in an ice-water bath for rapid cooling to room temperature, quickly terminating the reaction to prevent excessive quantum dot growth and uneven size. The resulting product is a crude solution of indium phosphide core quantum dots. This crude solution contains unreacted raw materials, ligands, and a small amount of byproducts, requiring purification.

[0011] Preferably, in step (1), the purification includes: adding anhydrous ethanol to the reaction solution for precipitation, shaking vigorously for 5 to 10 minutes, centrifuging to collect the precipitate, redispersing the precipitate in toluene, adding anhydrous ethanol again, centrifuging, and repeating the washing 2 to 3 times.

[0012] Specifically: Add 3-5 times the volume of anhydrous ethanol to the crude solution, shake vigorously for 5-10 min to allow the quantum dots to precipitate fully, then place it in a high-speed centrifuge and centrifuge at 8000-12000 r / min for 5-10 min, and collect the precipitate at the bottom; redisperse the precipitate in toluene, add anhydrous ethanol again to precipitate, centrifuge, and repeat washing 2-3 times until excess ligands and reaction byproducts are removed. Finally, disperse the purified InP core quantum dots in toluene and store it under argon protection at 0-4℃ for later use to avoid oxidative degradation of the quantum dots.

[0013] Preferably, the amount of polyphosphoric acid added in step (2) satisfies the molar ratio of phosphorus atoms to indium elements in polyphosphoric acid of 0.5 to 10:1.

[0014] Preferably, in step (2), the passivating agent is polyphosphoric acid with a purity ≥98%; The passivation reaction conditions were as follows: reaction temperature 80–200℃, reaction time 40–90 min, heating rate 2–5℃ / min, and stirring speed 300–500 r / min. Continuous stirring was maintained during the reaction to ensure uniform reaction. A significant increase in the fluorescence intensity of the solution was observed during the reaction, gradually changing from weak fluorescence to strong fluorescence, indicating that the orthophosphate passivation layer had been successfully formed on the quantum dot surface, and surface defects were effectively eliminated.

[0015] Preferably, in step (2), the dropping rate of the polyphosphoric acid is 0.1 to 1 mL / min.

[0016] Preferably, in step (2), the purification includes: adding anhydrous ethanol to precipitate, centrifuging to collect the precipitate, and then washing it 2 to 3 times with a toluene / ethanol mixed solution; finally, dispersing the purified quantum dots in one or more mixed organic solvents of toluene, n-hexane or cyclohexane, and storing them under argon protection; wherein the volume ratio of toluene to ethanol is 1:1.

[0017] This invention prepares a shell-less indium phosphide quantum dot based on in-situ passivation with orthophosphate. Its particle size is 3–5 nm, the full width at half maximum (FWHM) of its emission spectrum is ≤40 nm, and the photoluminescence quantum yield is ≥90%, reaching over 98% under optimal conditions, approaching 100%, far exceeding that of traditional unpassivated InP quantum dots (below 15%) and halide passivated quantum dots (around 30%). The emission peak position is basically consistent with the unpassivated InP core quantum dot, with no significant shift (shift ≤3 nm), and the emission spectrum has a narrow FWHM (≤40 nm), indicating uniform quantum dot size distribution and stable optical performance. Tunable emission can be achieved in the visible light region (450–650 nm). By controlling the size of the InP core quantum dot (3–5 nm), continuous emission from blue-green to red light can be achieved, adapting to the application requirements of different optoelectronic devices.

[0018] The stability of the in-situ passivated indium phosphide quantum dots prepared by this invention is significantly improved. After long-term storage in air (25°C, 50% relative humidity) for 30 days, the photoluminescence quantum yield (PLQY) retention rate is >90%, and the luminescence intensity shows no significant decay. After continuous irradiation with 365 nm LED (50 W) high-power ultraviolet light for 180 min, the PL intensity retention rate is ≥85%, which is far superior to traditional unpassivated quantum dots (PL intensity decays by more than 50% after 60 min of irradiation) and core-shell structured quantum dots (PL intensity retention rate is about 75% after 180 min of irradiation). It also exhibits good dispersibility in organic solvents such as toluene and n-hexane, and no obvious agglomeration phenomenon is observed after 6 months of storage, demonstrating excellent chemical stability.

[0019] The present invention prepares a shell-less indium phosphide quantum dot based on in-situ passivation of orthophosphate. It has good structure and dispersibility, uniform particle size distribution, and coefficient of variation ≤15%. Characterization by transmission electron microscopy (TEM) shows that the quantum dots are spherical, well dispersed, and without obvious agglomeration. The thickness of the surface orthophosphate passivation layer is uniform (about 0.5~1 nm), which is tightly bonded to the InP core and has no obvious interface defects.

[0020] This invention prepares a shell-less indium phosphide quantum dot based on in-situ passivation with orthophosphate, which is environmentally friendly and suitable for mass production. The preparation process does not use toxic heavy metals such as cadmium and lead, and no harmful byproducts are generated, meeting the requirements of green environmental protection. The product can be stably dispersed in common organic solvents, which facilitates subsequent device fabrication processes such as spin coating and printing. The entire preparation process is simple and mild, requiring no complex equipment, and can achieve large-scale mass production. The production cost is reduced by more than 30% compared with core-shell structure quantum dots.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High passivation efficiency and significantly improved optical performance: Through in-situ passivation with polyphosphate orthophosphate, the photoluminescence quantum yield of InP quantum dots can be increased from about 15% to more than 90%, with the best approaching 100%, solving the core problem of low quantum yield of traditional InP quantum dots; at the same time, the emission peak position is kept stable, without blue shift / red shift phenomenon, and the emission spectrum has a narrow half-width at half-maximum, with optical performance superior to existing passivation technologies.

[0022] (2) Excellent stability and extended service life: The orthophosphate passivation layer is strongly coordinated with the indium sites on the quantum dot surface and is tightly bound, which can effectively isolate oxygen and moisture, greatly improving the stability of quantum dots in air storage and ultraviolet light environment. The PLQY retention rate in air is >90% after 30 days, and the PL intensity retention rate in ultraviolet light is ≥85% after 180 min. The service life is more than 5 times longer than that of unpassivated quantum dots, meeting the long-term use requirements of actual devices.

[0023] (3) Simple process and easy to scale up production: No epitaxial growth shell is required. The synthesis and passivation of quantum dots can be completed in just two steps. The steps are few and the operation is simple. The reaction conditions are mild and no high temperature and high pressure are required. The equipment requirements are low. The raw materials are widely available and inexpensive. The purification process is simple and can achieve large-scale production. This solves the problems of complex process, high cost and difficulty in mass production of existing core-shell structure quantum dots.

[0024] (4) High product purity and good dispersibility: By optimizing the raw material ratio and purification process, the prepared shell-less InP quantum dots have high purity and no excess ligands and by-product residues; the particle size is uniform, the dispersibility is good, and there is no obvious agglomeration. They can be directly used for the preparation of optoelectronic devices without additional dispersion treatment, thus improving the device preparation efficiency.

[0025] (5) Environmentally friendly and free of heavy metals, with a wide range of applications: The preparation process does not use toxic heavy metals, and the products do not contain harmful substances such as cadmium and lead, which is in line with the trend of green and environmentally friendly development. Quantum dots have adjustable optical properties and excellent stability, and can be widely used in many fields such as light-emitting diodes, photodetectors, solar cells, biological fluorescent labeling materials, and lasers, with broad application prospects.

[0026] (6) Good batch-to-batch consistency: By precisely controlling the reaction parameters of each step (temperature, time, raw material ratio, stirring speed, etc.), the quantum dots prepared in different batches can be made stable in performance, with batch-to-batch PLQY deviation ≤5% and size distribution variation coefficient ≤15%, which meets the quality control requirements of industrial production. Attached Figure Description

[0027] Figure 1 This is a flowchart of the preparation method of the present invention.

[0028] Figure 2 The absorption / fluorescence spectra of different PPA:In molar ratios are shown in this invention; where (a) is an InP quantum dot with a size of about 3 nm; and (b) is an InP quantum dot with a size of about 5 nm.

[0029] Figure 3 The following are stability comparison charts; (a) shows the PL intensity comparison after 30 days of air exposure; (b) shows the stability comparison of 365nm LED (50W) under UV irradiation.

[0030] Figure 4 The optical properties of quantum dots of different sizes under optimal conditions of this invention; wherein, (a) is the absorption / fluorescence spectrum of InP quantum dots with a size of about 3 nm; (b) is the absorption / fluorescence spectrum of InP quantum dots with a size of about 5 nm; and (c) is a bar chart comparing quantum yield before and after treatment. Detailed Implementation

[0031] The accompanying drawings are for illustrative purposes only; the present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] All raw materials used in this invention are of analytical grade or higher purity and were purchased from commercial sources. Unless otherwise specified, all instruments used are those used in routine experiments or tests.

[0033] Example 1 like Figure 1As shown, a method for preparing shell-less indium phosphide (InP) quantum dots based on in-situ passivation with orthophosphate includes the following steps: (1) Synthesis of indium phosphide core quantum dots.

[0034] Select a 100 mL three-necked flask and add 0.2 mmol of indium chloride (InCl3, 99.99% purity), 5 mL of oleylamine (OAm, 98% purity), and 15 mL of octadecene (ODE, 90% purity) sequentially. Secure the flask in a constant-temperature heating mantle, insert a magnetic stir bar, and connect the argon gas delivery line and vacuum device. Turn on the magnetic stir bar and set the stirring speed to 400 rpm for 10 minutes, until a homogeneous and transparent mixed solution is formed.

[0035] First, argon gas is introduced into the three-necked flask at a flow rate of 50 mL / min for 8 minutes to completely purge air and oxygen from the flask. Then, the vacuum apparatus is turned on, and the system temperature is slowly heated to 120°C. Vacuum degassing is then performed at 0.1 MPa for 30 minutes, with continuous stirring to ensure complete removal of moisture and oxygen. After degassing, argon gas is maintained (flow rate 50 mL / min), the vacuum is stopped, and heating continues to slowly raise the system temperature to 180°C. Once the temperature stabilizes (fluctuation ≤2°C), the phosphorus source is ready to be injected.

[0036] Accurately weigh 0.4 mmol of tert-butylphosphine dichloride (t-BuPCl2, 98% purity) and dissolve it in 2 mL of octadecene. Use a 1 mL microsyringe to rapidly inject this phosphorus source solution into the reaction system, controlling the injection time at 8 seconds. After injection, continuously stir (400 rpm) for 5 minutes. During the reaction, the solution color gradually changed from colorless to pale yellow, then orange-yellow, and finally orange-red, indicating that the InP core quantum dots had been successfully generated.

[0037] After reacting for 5 min, immediately remove the three-necked flask from the heating mantle and place it in an ice-water bath to rapidly cool to room temperature to terminate the reaction. Add 15 mL of anhydrous ethanol (99.7% purity) to the obtained crude solution and shake vigorously for 8 min to allow the InP core quantum dots to precipitate fully. Place the mixture in a high-speed centrifuge and centrifuge at 10000 r / min for 8 min, collecting the orange-red precipitate at the bottom.

[0038] The precipitate was redispersed in 5 mL of toluene, and 15 mL of anhydrous ethanol was added again. The mixture was shaken, centrifuged, and washed twice to remove excess oleylamine ligands and unreacted raw materials. Finally, the purified InP core quantum dots were dispersed in 10 mL of toluene and stored at 0–4 °C under argon protection. Characterization showed that the emission peak of the InP core quantum dots was approximately 520 nm, the initial PLQY was approximately 15%, the particle size was approximately 3 nm, and the coefficient of variation of particle size distribution was 12%.

[0039] (2) In-situ passivation treatment.

[0040] Take 10 mL of the prepared InP core quantum dot toluene dispersion (indium content of 0.05 mmol) into a 50 mL reaction flask, place a magnetic stir bar in it, connect an argon gas delivery tube, introduce argon gas (flow rate 30 mL / min), turn on the magnetic stir bar, stir at 300 r / min for 10 min to make the quantum dots uniformly dispersed in toluene.

[0041] Accurately measure 0.05 mmol of polyphosphoric acid (PPA, 98% purity) and slowly add it to the reaction flask using a 1 mL microsyringe at a dropping rate of 0.5 mL / min. Stir continuously during the addition to ensure uniform dispersion of the polyphosphoric acid in the system. After the addition is complete, slowly increase the temperature of the reaction system at a rate of 3 °C / min until it reaches 120 °C. Maintain this temperature for 60 min, stirring continuously (300 rpm). A significant increase in the fluorescence intensity of the solution can be observed, changing from weak orange-red fluorescence to strong orange-red fluorescence.

[0042] After the reaction is complete, turn off the heating mantle and allow the reaction system to cool naturally to room temperature. Add 20 mL of anhydrous ethanol to the reaction solution and shake vigorously for 8 min to allow the passivated quantum dots to precipitate fully. Place the mixture in a high-speed centrifuge and centrifuge at 9000 r / min for 6 min, collecting the precipitate at the bottom.

[0043] The precipitate was washed with 15 mL of a toluene / ethanol mixture (1:1, v / v), shaken for 5 min, and then centrifuged. The washing was repeated twice to remove excess polyphosphoric acid and reaction byproducts. Finally, the purified shell-less indium phosphide quantum dots were dispersed in 8 mL of toluene and stored under argon protection at 0–4 °C.

[0044] Performance test results: Characterization showed that the photoluminescence quantum yield (PLQY) of the shell-less indium phosphide quantum dots prepared in this embodiment was 98%, and the emission peak position was 520 nm, consistent with that before passivation, without shift; the particle size was approximately 3.2 nm, the particle size distribution variation coefficient was 11%, and the dispersibility was good; after being stored in air at 25°C and 50% relative humidity for 30 days, the PLQY retention rate was 92%; after continuous irradiation with a 365 nm LED (50 W) for 180 min, the PL intensity retention rate was 88%; TEM characterization showed that the quantum dots were spherical, the surface passivation layer was clearly visible, and there was no obvious agglomeration.

[0045] Example 2 A method for preparing shell-less indium phosphide (InP) quantum dots based on in-situ passivation of orthophosphate is disclosed. The only difference between this method and Example 1 is that the molar ratio of polyphosphoric acid to In (PPA:In) is 3:1. All other steps, raw materials and parameters are exactly the same as in Example 1.

[0046] Specific differences in steps: (2) In the in-situ passivation treatment, accurately measure 0.15 mmol of polyphosphoric acid and add it to the reaction flask at a dropping rate of 0.5 mL / min. The other passivation conditions (temperature, time, stirring speed, etc.) are the same as in Example 1.

[0047] Performance test results: The PLQY of the shell-less indium phosphide quantum dots prepared in this embodiment is approximately 95%, the emission peak position is 521 nm with an offset of 1 nm; the particle size is approximately 3.3 nm, and the particle size distribution variation coefficient is 12%; the PLQY retention rate in air for 30 days is approximately 92%; the PL intensity retention rate after 180 min of ultraviolet irradiation is 86%; the quantum dots have good dispersion and the surface passivation layer is uniform.

[0048] Example 3 A method for preparing shell-less indium phosphide (InP) quantum dots based on in-situ passivation of orthophosphate is different from Example 1 only in that the reaction temperature of the in-situ passivation treatment is 160°C, while the other steps, raw materials and parameters are exactly the same as those in Example 1.

[0049] Specific differences in steps: (2) In the in-situ passivation treatment, after adding polyphosphoric acid, the reaction system is heated to 160°C and reacted at a constant temperature for 60 min. The remaining passivation conditions (molar ratio, dropping rate, stirring speed, etc.) are the same as in Example 1.

[0050] Performance test results: The PLQY of the shell-less indium phosphide quantum dots prepared in this embodiment is approximately 96%, the emission peak position is 520 nm, and there is no shift; the particle size is approximately 3.2 nm, and the particle size distribution variation coefficient is 11%; the PLQY retention rate in air for 30 days is approximately 91%; the PL intensity retention rate after 180 min of ultraviolet irradiation is 87%; the passivation layer on the quantum dot surface is denser, and the stability is slightly better than that of Example 1.

[0051] Comparative Example 1 This comparative example provides a method for preparing indium phosphide quantum dots. The only difference from Example 1 is that the molar ratio of polyphosphoric acid to In (PPA:In) is 0.2:1. All other steps, raw materials and parameters are exactly the same as in Example 1.

[0052] Specific differences in steps: (2) In the in-situ passivation treatment, 0.01 mmol of polyphosphoric acid was accurately measured and added to the reaction flask at a dropping rate of 0.5 mL / min. The remaining passivation conditions were the same as in Example 1.

[0053] Performance test results: Due to insufficient polyphosphoric acid content, the quantum dots prepared in this comparative example were not sufficiently passivated, and a large number of defect sites still existed on the surface. The PLQY was approximately 45%, the emission peak position was 523 nm with a shift of 3 nm, the particle size was approximately 3.2 nm, and the particle size distribution variation coefficient was 14%. The PLQY retention rate in air for 30 days was approximately 60%, and the PL intensity retention rate after 180 min of UV irradiation was approximately 50%. The quantum dots showed slight aggregation and poor stability.

[0054] Comparative Example 2 This comparative example provides a method for preparing indium phosphide quantum dots. The only difference from Example 1 is that the molar ratio of polyphosphoric acid to In (PPA:In) is 15:1. All other steps, raw materials, and parameters are exactly the same as in Example 1.

[0055] Specific differences in steps: (2) In the in-situ passivation treatment, 0.75 mmol of polyphosphoric acid was accurately measured and added to the reaction flask at a dropping rate of 0.5 mL / min. The remaining passivation conditions were the same as in Example 1.

[0056] Performance test results: Due to excessive polyphosphoric acid, the quantum dots prepared in this comparative example underwent an overreaction, resulting in the formation of excessive orthophosphate on the surface of some quantum dots, leading to quantum dot aggregation. The PLQY was approximately 85%, the emission peak was 515 nm with a slight blue shift of 5 nm, the particle size was approximately 4.0 nm, and the particle size distribution variation coefficient was 18%. The PLQY retention rate in air for 30 days was approximately 80%, and the PL intensity retention rate after 180 min of UV irradiation was approximately 75%. The poor dispersibility of the quantum dots affected their practical applications.

[0057] Comparative Example 3 This comparative example provides a method for preparing indium phosphide quantum dots. The only difference from Example 1 is that the reaction temperature for in-situ passivation treatment is 60°C, while the remaining steps, raw materials, and parameters are exactly the same as in Example 1.

[0058] Specific differences in steps: (2) In the in-situ passivation treatment, after adding polyphosphoric acid, the reaction system is heated to 60°C and reacted at a constant temperature for 60 min. The remaining passivation conditions are the same as in Example 1.

[0059] Performance test results: Due to the low passivation temperature, the polyphosphoric acid hydrolysis of the quantum dots prepared in this comparative example was insufficient, resulting in an inadequate amount of orthophosphate and poor passivation effect. The PLQY was approximately 60%, the emission peak position was 522 nm with a shift of 2 nm, the particle size was approximately 3.3 nm, and the particle size distribution variation coefficient was 15%. The PLQY retention rate in air for 30 days was approximately 70%, and the PL intensity retention rate after 180 min of UV irradiation was approximately 65%. The passivation layer on the surface of the quantum dots was incomplete, resulting in poor stability.

[0060] Using core QDs as a control, the reaction conditions and product performance of Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0061] Table 1 Comparison of reaction conditions and product properties between Examples 1-3 and Comparative Examples 1-3 As shown in Table 1, as tested in Example 1, the passivation effect was optimal when the PPA:In molar ratio was 1:1 and the reaction temperature was 120°C. PLQY increased significantly from 15% to 98%, while the luminescence peak position remained unchanged.

[0062] Effect of ratio: If the ratio is too low (comparative example 1), the passivation will be insufficient; if the ratio is too high (comparative example 2), it may lead to excessive reaction, slightly affecting the crystal surface structure, causing spectral shift and efficiency reduction.

[0063] Temperature effect: If the temperature is too low (Comparative Example 3), the reaction kinetics are insufficient and the passivation is incomplete; excellent results can be obtained in the temperature range of 120℃~160℃.

[0064] Stability: The quantum dots passivated by the method of the present invention (such as in Examples 1-3) have a long-term stability that is far superior to that of the unpassivated core quantum dots.

[0065] The above embodiments fully demonstrate the effectiveness, superiority, and wide process window of the polyphosphoric acid in-situ passivation method provided by the present invention. Those skilled in the art can optimize and adjust the process parameters through conventional experiments within the scope disclosed in this invention (e.g., PPA:In molar ratio 0.5–10:1, reaction temperature 80℃–200℃) to obtain high-performance indium phosphide quantum dots far exceeding those of existing technologies.

[0066] Combination such as Figure 2As shown, polyphosphoric acid of different molar ratios was used to treat indium phosphide (PPA:In = 0.2:1, 1:1, 3:1, 15:1) quantum dots of different sizes. It can be seen that the fluorescence intensity of indium phosphide quantum dots of different sizes was not high before treatment with an appropriate amount of polyphosphoric acid, but the fluorescence intensity was significantly improved after treatment.

[0067] like Figure 3 As shown, the product prepared in Example 1 was directly subjected to stability testing with InP quantum dots. It can be seen that the stability of the quantum dots treated with polyphosphoric acid in Example 1 of the present invention was greatly improved under both conditions.

[0068] like Figure 4 As shown, the normalized optical absorption and photoluminescence spectra of indium phosphide quantum dots (InP-PPA) with different sizes treated with polyphosphoric acid at a molar ratio (PPA:In=1:1) of approximately 3 nm (a) and 5 nm (b) are compared with those of InP quantum dots. Figure (c) is a bar chart showing the quantum yield changes of the two types of indium phosphide quantum dots of different sizes before (InP) and after (InP-PPA) treatment with polyphosphoric acid. Before polyphosphoric acid treatment, the fluorescence intensity of indium phosphide quantum dots of different sizes was not high, but after treatment, the fluorescence intensity increased significantly, more than doubling, and the quantum yield increased to over 90%.

[0069] Example 4 A method for preparing shell-less indium phosphide (InP) quantum dots based on in-situ passivation of orthophosphate is different from Example 1 only in that the indium source is indium acetate (In(CH3COO)3) and the phosphorus source is tris(dimethylamine)phosphine (P(NMe2)3). The remaining steps, raw material ratios and parameters are exactly the same as those in Example 1.

[0070] Specific differences in steps: (1) In the preparation of InP core quantum dots, 0.2 mmol indium chloride was replaced with 0.2 mmol indium acetate, and 0.4 mmol tert-butylphosphine chloride was replaced with 0.4 mmol tris(dimethylamine)phosphine. The rest of the synthesis conditions were the same as in Example 1.

[0071] Performance test results: The PLQY of the shell-less indium phosphide quantum dots prepared in this embodiment is approximately 94%, the emission peak position is 522 nm with an offset of 2 nm; the particle size is approximately 3.4 nm, and the particle size distribution variation coefficient is 13%; the PLQY retention rate in air for 30 days is approximately 90%; the PL intensity retention rate after 180 min of ultraviolet irradiation is 86%; the quantum dots have good dispersion and stable optical properties.

[0072] Example 5 A method for preparing shell-less indium phosphide (InP) quantum dots based on in-situ passivation of orthophosphate is different from Example 1 only in that the coordinating solvent is oleic acid and the non-coordinating solvent is hexadecene. All other steps, raw material ratios and parameters are exactly the same as in Example 1.

[0073] Specific differences in steps: (1) In the preparation of InP core quantum dots, 5 mL of oleylamine was replaced with 5 mL of oleic acid, and 15 mL of octadecene was replaced with 15 mL of hexadecene. The rest of the synthesis conditions were the same as in Example 1.

[0074] Performance test results: The PLQY of the shell-less indium phosphide quantum dots prepared in this embodiment is approximately 93%, the emission peak position is 519 nm with an offset of 1 nm; the particle size is approximately 3.1 nm, and the particle size distribution variation coefficient is 12%; the PLQY retention rate in air for 30 days is approximately 89%; the PL intensity retention rate after 180 min of ultraviolet irradiation is 85%; the quantum dots have good dispersibility and can be stably dispersed in toluene.

[0075] Comparative Example 4 This comparative example provides a method for preparing indium phosphide quantum dots without in-situ passivation with polyphosphoric acid. The remaining steps, raw materials, and parameters are exactly the same as in Example 1.

[0076] Specific differences: The in-situ passivation treatment in step (2) is omitted, and the InP core quantum dots purified in step (1) are directly dispersed in toluene as the final product.

[0077] Performance test results: The unpassivated InP quantum dots prepared in this comparative example have many surface defects, with PLQY≈15% and an emission peak position of 520 nm; the particle size is about 3.0 nm, and the particle size distribution variation coefficient is 12%; the PLQY retention rate in air for 30 days is ≈30%; after 60 min of UV irradiation, the PL intensity decreases by more than 50%, and after 60 min, the PL intensity is only 45% of the initial value; the quantum dots are easily oxidized in air, and the dispersibility gradually deteriorates, which cannot meet the requirements of practical applications.

[0078] Comparative Example 5 This comparative example provides a method for preparing core-shell structured InP / ZnS quantum dots, employing a traditional epitaxial shell growth strategy. The specific steps are as follows: (1) Preparation of InP core quantum dots: The same as step (1) in Example 1 was used to obtain InP core quantum dots with PLQY≈15% and emission peak position of 520 nm.

[0079] (2) ZnS shell growth: The InP core quantum dot toluene dispersion was placed in a three-necked flask and heated to 150°C under argon protection. A mixed solution of Zn source (zinc acetate) and S source (sodium thiosulfate) was slowly added dropwise. The reaction was carried out at a constant temperature for 120 min. After cooling, the mixture was purified to obtain InP / ZnS core-shell quantum dots.

[0080] Performance test results: The InP / ZnS core-shell quantum dots prepared in this comparative example had a PLQY of approximately 85%, an emission peak position of 525 nm with a shift of 5 nm, a particle size of approximately 4.5 nm, and a particle size distribution variation coefficient of 16%. The PLQY retention rate in air for 30 days was approximately 75%. The PL intensity retention rate after 180 min of UV irradiation was approximately 75%. The preparation process was complex, with a long reaction cycle (shell growth required 120 min), and the production cost was 35% higher than that of Example 1, with poor batch-to-batch consistency.

[0081] As can be seen from the comparison between Examples 4-5 and Comparative Examples 4-5, the shell-less indium phosphide quantum dot preparation method provided by the present invention can significantly improve quantum yield and stability by passivating with polyphosphate in situ without epitaxial growth of a shell. Moreover, the process is simple, low-cost, and easy to scale up, and its overall performance is superior to the prior art.

[0082] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a shell-free indium phosphide quantum dot based on orthophosphate in-situ passivation, characterized in that, Includes the following steps: (1) Synthesis of indium phosphide core quantum dots: Indium source, coordinating solvent and non-coordinating solvent were mixed and heated under an inert atmosphere. Phosphorus source was added to carry out the reaction. After the reaction was completed, the reaction vessel was placed in an ice-water bath to cool to room temperature. After purification, indium phosphide core quantum dots were obtained. (2) In-situ passivation treatment: The indium phosphide core quantum dots obtained in step (1) are dispersed in an organic solvent, polyphosphoric acid is added, and a passivation reaction is carried out under heating conditions. After the reaction is completed, the indium phosphide quantum dots without shell are obtained by purification.

2. The preparation method of the shell-free indium phosphide quantum dots based on orthophosphate in-situ passivation according to claim 1, characterized in that, In step (1), the indium source is selected from at least one of indium chloride, indium acetate, and indium nitrate, and the phosphorus source is selected from at least one of tert-butylphosphine dichloride, tris(dimethylamine)phosphine, trioctylphosphine, tris(diethylamine)phosphine, and tris(trimethylsilyl)phosphine. The coordinating solvent is selected from at least one of oleylamine, octadecylamine, hexadecylamine, oleic acid, and myristic acid; the non-coordinating solvent is selected from at least one of octadecene, hexadecene, liquid paraffin, dioctyl ether, and eicosene. The inert atmosphere is argon or nitrogen, with a purity ≥99.99%.

3. The method according to claim 2, wherein the method is characterized by, In step (1), the ratio of the indium source, the coordinating solvent and the non-coordinating solvent is (0.2-1) mmol : (5-10) mL : (10-15) mL.

4. The preparation method of the shell-free indium phosphide quantum dots based on orthophosphate in-situ passivation according to claim 1, characterized in that, Before adding the phosphorus source in step (1), the mixture is first degassed under vacuum at 100-120℃ and 0.08-0.1MPa for 20-30 min, and then heated to 160-180℃ under inert atmosphere before the phosphorus source is injected. The phosphorus source is pre-dissolved in octadecene, the injection time is controlled within 10 seconds, and the reaction time after injection is 3 to 6 minutes.

5. The method according to claim 1, wherein the method is characterized by: In step (1), the purification includes: adding anhydrous ethanol to the reaction solution for precipitation, shaking vigorously for 5 to 10 minutes, centrifuging to collect the precipitate, redispersing the precipitate in toluene, adding anhydrous ethanol again, centrifuging, and washing 2 to 3 times.

6. The method according to claim 1, wherein the method is characterized by: The amount of polyphosphoric acid added in step (2) satisfies the molar ratio of phosphorus atoms to indium elements in polyphosphoric acid of 0.5 to 10:

1.

7. The method according to claim 1, wherein the method is characterized by, In step (2), the passivation reagent is polyphosphoric acid with a purity ≥98%; The passivation reaction conditions are as follows: reaction temperature 80–200℃, reaction time 40–90 min, heating rate 2–5℃ / min, and stirring speed 300–500 r / min.

8. The method for preparing shell-less indium phosphide quantum dots based on in-situ passivation of orthophosphate according to claim 1, characterized in that, In step (2), the dropping rate of the polyphosphoric acid is 0.1 to 1 mL / min.

9. The method for preparing shell-less indium phosphide quantum dots based on in-situ passivation of orthophosphate according to claim 1, characterized in that, In step (2), the purification includes: adding anhydrous ethanol to precipitate, centrifuging to collect the precipitate, and then washing it 2 to 3 times with a toluene / ethanol mixed solution; finally, dispersing the purified quantum dots in one or more mixed organic solvents of toluene, n-hexane or cyclohexane, and storing them under argon protection; wherein the volume ratio of toluene to ethanol is 1:

1.

10. A shell-less indium phosphide quantum dot based on orthophosphate in-situ passivation prepared by the preparation method according to any one of claims 1-9, characterized in that, The quantum dots have a particle size of 3–5 nm, a particle size distribution variation coefficient of ≤15%, a full width at half maximum (FWHM) of emission spectrum of ≤40 nm, and a photoluminescence quantum yield of ≥90%.

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