A method for preparing large-size near-infrared luminescent indium phosphide quantum dots

Abstract

The present invention relates to the synthesis and energy technology fields of colloidal quantum dots, and in particular to a method for preparing large-scale near-infrared luminescent indium phosphide quantum dots. The method includes: adding In(I)Cl, tri-n-octylphosphine, oleylamine, and pseudo-halogen ammonium salt to react, heating and vacuuming to remove excess gas; the pseudo-halogen ammonium salt is thermally decomposed to produce pseudo-halogen ions, indirectly producing In-pseudo-halogen bonds; the temperature continues to rise, a phosphorus source is injected, and the reaction can obtain near-infrared luminescent InP quantum dots, with an emission peak at around 780nm, and a particle size of the prepared InP quantum dots of 10.5±1.3nm; then purifying and encapsulating the shell layer to obtain InP / ZnS / ZnS. The present invention adopts a safe and environmentally friendly pseudo-halogen ammonium salt in-situ treatment method, and the pseudo-halogen ions produced etch off the surface oxygen-containing groups of the indium phosphide quantum dots. After encapsulating the double-shell, the yield of the InP quantum dots is improved.

Description

Technical Field

[0001] The present invention relates to the field of synthesis and energy technology of colloidal quantum dots, and in particular to a method for preparing large-sized near-infrared luminescent indium phosphide quantum dots. Background Art

[0002] Indium phosphide (InP) quantum dots (QDs) are considered one of the most viable alternatives to cadmium-based QDs due to their low toxicity, tunable light from the visible to the near-infrared (NIR), limited emission spectra, and competitive optical properties. Innovative synthetic methods have been developed to reduce the cost and environmental impact of InP QD production while enhancing photophysical properties. However, the emission peak of InP-based QDs typically lies below ∼750 nm, and the current luminescence intensity in the NIR range remains significantly lower than that in the visible region. Various efforts have been made to extend the emission spectrum of InP QDs. For example, transition metal ion doping strategies, such as Cu-doped InP, have been developed to extend the emission range. While these doping strategies demonstrate easy tuning of NIR emission, this emission mechanism is believed to inherently limit the maximum brightness of the emitter and increase the emission peak width. Meanwhile, creating core-shell InP QDs with type-II or inverted type-I band gaps can also provide tunable emission to extend the wavelength. However, these complex structures are associated with lattice mismatch in the heterostructure, resulting in a longer photoluminescence lifetime and lower luminescence intensity. In this sense, directly increasing the size of quantum dots appears to be a simple and feasible technique to extend the emission range.

[0003] InP is a III-V semiconductor with a bulk bandgap energy of 1.35 eV, making it possible to synthesize quantum dots that emit in the near-infrared region. However, as the size increases, the generation of internal and surface defects increases significantly, which contributes to a reduction in luminescence intensity. Furthermore, due to the strong covalency of the In-P bond, the nucleation and growth reaction rates of InP quantum dots are difficult to control. Therefore, the production of large-scale InP quantum dots that emit near-infrared luminescence is difficult. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing large-sized near-infrared luminescent indium phosphide quantum dots. In(I)Cl and pseudohalogen ammonium salts are combined to synthesize InP quantum dots with near-infrared emission (emission peak at 780nm) and narrow half-maximum width (45nm), which makes up for the defects of InP quantum dots in near-infrared emission, as well as the problems of large half-maximum width and low fluorescence quantum yield in near-infrared emission.

[0005] The technical solutions adopted are:

[0006] A method for preparing large-sized near-infrared luminescent indium phosphide quantum dots comprises the following steps:

[0007] (1) adding pseudohalogen ammonium salt to the reaction of In(I)Cl, tri-n-octylphosphine, and oleylamine, heating, and vacuuming to remove excess gas;

[0008] (2) During the heating process, the pseudohalogen ammonium salt decomposes to produce pseudohalogen ions, indirectly generating In-pseudohalogen bonds;

[0009] The temperature is further increased, a phosphorus source is injected, and the reaction is continued for 30 to 60 minutes to obtain near-infrared luminescent InP quantum dots. The particle size of the synthesized InP quantum dots is 10.5±1.3nm.

[0010] (3) Purification: After the temperature drops to room temperature, ethanol is added and centrifuged to remove impurities. The resulting precipitate is dissolved in hexane and the purification is repeated to produce pure InP quantum dots.

[0011] (4) The purified InP quantum dots are wrapped with two layers of ZnS to obtain InP / ZnS / ZnS with a higher fluorescence quantum yield.

[0012] Preferably, in step (1), the pseudohalogen is CN - 、NCO - 、SCN - 、NCO - 、O2 2- OH - 、SeCN - HCOO - 、CH3COO - IO4 - TFSI - PF6 - 、BF4 - 、SeO4 2- Any of .

[0013] Preferably, in step (1), the molar ratio of In(I)Cl, NH4PF6, and tri-n-octylphosphine is 25:20 to 35:35; and the volume ratio of the mole of In(I)Cl to oleylamine is 0.25 mmol:4.5 ml.

[0014] Preferably, in step (1), the heating temperature is 50-60°C.

[0015] Preferably, in step (2), the phosphorus source is an inorganic phosphide or an organic phosphide, wherein the inorganic phosphide is any one of indium triphosphide, phosphine, elemental phosphorus, and indium phosphate, and the organic phosphide is an organic phosphate ester or an organic phosphorus amine, preferably (DMA)3P. The temperature for injecting (DMA)3P is 220°C.

[0016] Preferably, in step (3), centrifugal separation is performed at 4000-4500 rpm; and the purification is repeated 3-5 times.

[0017] Preferably, in step (4), the method of InP encapsulating ZnS is:

[0018] a. The obtained InP quantum was diluted with ODE and vacuumed to remove excess water, vented with nitrogen and heated, and a Zn(DDTC)2 solution was injected. After the temperature rose, it was allowed to react for 5 to 10 minutes to wrap the first layer of ZnS.

[0019] b. The temperature continues to rise, and Zn(St)2 solution is injected again. After reacting for 20 to 30 minutes, 1-DDT is injected. The zinc and sulfur ion exchange coating process is repeated in a cycle until the shell reaches a certain thickness, that is, the second layer of ZnS is wrapped.

[0020] As a further preference, in step a, the temperature for injecting Zn(DDTC)2 is 110-120°C; and the temperature for carrying out the reaction is 200°C.

[0021] As a further preference, in step a, the method for preparing the Zn(DDTC)2 solution is to mix Zn(DDTC)2 with oleylamine and stir them uniformly by ultrasonication; wherein the molar ratio of Zn(DDTC)2 to oleylamine is 0.1 mmol / ml.

[0022] As a further preference, in the step b, a zinc precursor is added to ODE, heated to a temperature in the range of 170-200° C. and stirred to dissolve evenly; the molar ratio of the zinc precursor to the ODE is 1.2 mmol:5 ml; wherein the zinc precursor is any one of zinc oxide, zinc acetate, zinc stearate, zinc chloride, zinc bromide, and zinc iodide.

[0023] As a further preference, in the step b, the temperature of the injected zinc precursor solution is 240°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In the present invention, an in-situ active pseudo-halogen auxiliary method is used to prepare high-brightness near-infrared InP quantum dots, and a method for direct synthesis of indium (I) halide and aminophosphine is introduced. An in-situ active pseudo-halogen and ammonium root dual protection method is adopted to produce large-sized InP quantum dots with a near-infrared emission region. The particle size of the synthesized InP quantum dots is 10.5±1.3nm. The activity from the inorganic pseudo-halogen ammonium salt can effectively reduce the reactivity of indium ions and change the nucleation and growth process of InP quantum dots. At the same time, the coexistence of ammonium roots and pseudo-halogen ions can simultaneously etch the surface oxide in situ, hinder the formation of traps, and induce directional growth in the entire growth process of InP quantum dots. After wrapping the double shell, not only the yield of InP quantum dots is improved, but also the optical properties of InP are improved.

[0026] Experimental results show that the prepared InP quantum dots have an emission linewidth of up to 45 nm and a near-infrared emission wavelength of approximately 780 nm. Furthermore, a double-shell zinc sulfide layer encapsulation of the InP quantum dots was constructed to enhance luminescence intensity, resulting in a fluorescence quantum yield (PLQY) exceeding 50%. Finally, an intrinsically stretchable, high-power color conversion film constructed using an InP quantum dot / polymer composite exhibits excellent near-infrared luminescence conversion capability and scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Transmission electron microscope photograph and size distribution diagram of large-sized InP quantum dots synthesized by adding ammonium hexafluorophosphate in the present invention.

[0028] Figure 2 The maximum fluorescence peak of InP prepared by adding different moles of pseudohalogen ammonium salt using the method of the present invention is changed.

[0029] Figure 3 This is a graph showing the change in the position of the InP emission peak generated by the present invention at different reaction times and after adding different molar numbers of pseudohalogen ammonium salts.

[0030] Figure 4 A comparison chart of the changes in absorption intensity, fluorescence intensity and yield of single-shell and double-shell InP quantum dots.

[0031] Figure 5 (Left) Changes in the mechanical properties of the InP quantum dots prepared by the present invention after mixing with SEBS; (Right) EL spectra and light conversion illustrations of the InP-based color conversion layer at different currents (top left). DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention in any way. Unless otherwise specified, the methods, reagents and equipment used in the present invention are conventional methods, reagents and equipment in the art, and the reagents and equipment can be obtained from commercial sources.

[0033] Example 1

[0034] A method for preparing large-sized near-infrared luminescent indium phosphide quantum dots is described. In a 50 mL three-necked round-bottom flask, 7.5 mg (0.25 mmol) of InCl3, 0.15 mL (0.35 mmol) of tri-n-octylphosphine, and 4.5 mL of oleylamine are added. The pseudohalogen ammonium salt added is ammonium hexafluorophosphate (0.2 mmol). The flask is evacuated at 50°C for 30 minutes until no bubbles form. The solution is then immediately heated to 220°C under argon.

[0035] Upon reaching 220°C, 0.19 mL of (DMA) 3P diluted in 0.25 mL of ODE was immediately injected. The reaction temperature was maintained at 220°C for 60 minutes. After 1 hour, the temperature was lowered to room temperature, 30 mL of ethanol was added, and the mixture was centrifuged at 4000 rpm to eliminate contaminants. The resulting precipitate was dissolved in hexane, and the purification process was repeated three more times to produce pure InP quantum dots.

[0036] InCl can be replaced by InI or InBr, and the preparation method and steps are the same as those in Example 1.

[0037] Example 2

[0038] The molar amount of ammonium hexafluorophosphate added was 0.25 mmol. Other matters not mentioned were the same as those in Example 1.

[0039] Example 3

[0040] The molar amount of ammonium hexafluorophosphate added was 0.30 mmol. Other matters not mentioned were the same as those in Example 1.

[0041] Example 4

[0042] The molar amount of ammonium hexafluorophosphate added was 0.35 mmol. Other details not mentioned were the same as those in Example 1.

[0043] like Figure 1 As shown, the transmission electron microscope photograph of large-sized InP quantum dots synthesized by adding ammonium hexafluorophosphate in Example 1 of the present invention, and the size distribution diagram in the upper right corner show that the particle size of the synthesized InP quantum dots is 10.5±1.3 nm.

[0044] like Figure 2 As shown, by changing the molar number of ammonium hexafluorophosphate, the highest fluorescence peak of InP obtained is changed from 730 nm (0.2 mmol) to 780 nm (0.35 mmol).

[0045] Test Example 1

[0046] The preparation steps were as described in Example 1, and the luminescence peak positions of the InP samples generated after adding (DMA)3P and reacting for 1 min, 5 min, 10 min, 30 min, and 60 min were recorded respectively.

[0047] The preparation steps were as described in Example 2, and the luminescence peak positions of the InP samples generated after adding (DMA)3P and reacting for 1 min, 5 min, 10 min, 30 min, and 60 min were recorded respectively.

[0048] The preparation steps were as described in Example 3, and the luminescence peak positions of the InP samples generated after adding (DMA)3P and reacting for 1 min, 5 min, 10 min, 30 min, and 60 min were recorded respectively.

[0049] The preparation steps were as described in Example 4, and the luminescence peak positions of the InP samples generated after adding (DMA)3P and reacting for 1 min, 5 min, 10 min, 30 min, and 60 min were recorded respectively.

[0050] like Figure 3 As shown in the figure, the change of the emission peak position of InP generated after adding (DMA)3P at different reaction times and adding different molar numbers of pseudohalogen ammonium salts, it can be seen that the luminescence range of quantum dots gradually red-shifts with the increase of quantum dot size.

[0051] Test Example 2

[0052] The method for preparing InP quantum dots is the same as that in Example 1, and then the shell layer is wrapped.

[0053] Purified InP quantum dots and 4ml of ODE were placed in a 50ml three-necked container. The mixture was degassed at room temperature for 60 minutes to remove water, oxygen, and residual hexane. The reaction was then flooded with nitrogen and further heated to 120°C. 0.1mmol of Zn(DDTC)2 and 2ml of OAm were added to grow an initial surface coating of the ZnS shell, forming a thin first shell layer, namely InP / ZnS.

[0054] Then, 0.4 mL of zinc precursor solution, i.e., an ODE solution (0.25 mM) of zinc stearate (Zn(St)2), was introduced, the temperature was raised to 240 ° C and maintained for 20 minutes. 0.2 mL of 1-DDt was continuously injected to construct a second layer of ZnS shell, and the zinc and sulfur ion exchange coating process was repeated. The thickness of the second shell was controlled according to time. Finally, the process was stopped by cooling the mixture to room temperature. The InP / ZnS / ZnS quantum dots were then precipitated once with acetone, redispersed in toluene, and stored for the next step of device development.

[0055] like Figure 4 As shown in the figure, the absorption intensity, fluorescence intensity and photoluminescence yield of the InP / ZnS quantum dots wrapped in single shell and double shell are tested. It can be seen that the photoluminescence yield of the InP / ZnS / ZnS quantum dots wrapped in double shell is significantly improved.

[0056] Test Example 3

[0057] The prepared InP was applied to prepare an InP QDs@SEBS elastomer assembled into a near-infrared light conversion film. The resulting NIR-LED device is a transparent prestine SEBS and InP / SEBS composite film made from a combination of an intrinsically stretchable InP quantum dot / SEBS composite and a high-power blue GaN chip.

[0058] The stress-strain curves of QDs / SEBS and pristine SEBS films were measured to evaluate the tensile mechanical properties. Figure 5 As shown in the left figure, the fabricated intrinsically stretchable InP quantum dot / SEBS film exhibits better stretchability than the original SEBS film. We combined the InP / ZnS / ZnS-based quantum dot phosphor with a commercial blue GaN chip (emission band peak at 450nm) to fabricate a near-infrared color conversion device. The electroluminescence current spectrum of the near-infrared color conversion device is shown in Figure 1. Figure 5 As shown on the right, when a blue LED is turned on, the blue electroluminescence generated by the blue LED chip pumps the solution-based quantum dots, generating PL in the near-infrared spectral region. The intrinsically stretchable InP QDs@SEBS composite film exhibits significant near-infrared emission ranging from 660 to 900 nm. When the injection current is increased from 8 mA to 269 mA, the light intensity spectrum remains essentially unchanged, with a slight red shift in the PL peak position at 10 nm, demonstrating its suitability for use as a stretchable near-infrared light-conversion film.

[0059] The meanings of the English abbreviations used in this application are as follows.

[0060] Indium chloride: InCl; Indium bromide: InBr; Indium iodide: InI; In(I)Cl: Indium chloride (iodide);

[0061] Ammonium hexafluorophosphate: NH4PF6;

[0062] Tris(dimethylamino)phosphine: (DMA)3P;

[0063] Zinc diethyldithiocarbamate: Zn(DDTC)2;

[0064] Zinc stearate: Zn(St)2;

[0065] Oleylamine: OAm;

[0066] Cyanide ion: CN - ;

[0067] Cyanate ion: NCO - ;

[0068] Thiocyanate ion: SCN-;

[0069] Cyanol ion: NCO - ;

[0070] Hydrogen peroxide ion: O2 2- ;

[0071] Hydroxyl ion: OH-;

[0072] Selenocyanate ion: SeCN-;

[0073] Iodate ion: IO4 -

[0074] Selenium oxyphosphate ion: SeO4 2- ;

[0075] Formate ion: HCOO - ;

[0076] Acetic acid and ion: CH3COO - ;

[0077] Bistrifluoromethanesulfonyl imide ion: TFSI - ;

[0078] Hexafluorophosphate ion: PF6 - ;

[0079] Boron tetrafluoride ion: BF4 - ;

[0080] n-Dodecanethiol: 1-DDt;

[0081] 1-Octadecene: ODE.

[0082] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing large-sized near-infrared luminescent indium phosphide quantum dots, characterized in that: The method comprises the following steps: (1) In a three-necked round-bottom flask, add In(I)Cl, tri-n-octylphosphine, and oleylamine, then add pseudohalogen ammonium salt to the reaction mixture, heat, and evacuate to remove excess gas; (2) During the heating process, the pseudohalogen ammonium salt decomposes to produce pseudohalogen ions, indirectly generating In-pseudohalogen bonds; The temperature continues to rise, a phosphorus source is injected, and the reaction is continued for 30 to 60 minutes to obtain near-infrared luminescent InP quantum dots. (3) Purification: After the temperature drops to room temperature, ethanol is added and centrifuged to remove impurities. The resulting precipitate is dissolved in hexane and the purification is repeated to produce pure InP quantum dots. (4) Wrapping the purified InP quantum dots with two layers of ZnS to obtain InP / ZnS / ZnS; Wherein, the pseudohalogen is either PF6⁻ or BF4⁻; The molar ratio of In(I)Cl, pseudohalogenated ammonium salt, and tri-n-octylphosphine is 25:20 to 35:35; the volume ratio of In(I)Cl to oleylamine is 0.25 mmol:4.5 ml; and the heating temperature is 50-60°C. The temperature of the injected phosphorus source is 220° C.; the phosphorus source is (DMA)3P.

2. The method for preparing large-sized near-infrared luminescent indium phosphide quantum dots according to claim 1, characterized in that: In the step (3), centrifugation is performed at 4000-4500 rpm; the purification is repeated 3-5 times.

3. The method for preparing large-sized near-infrared luminescent indium phosphide quantum dots according to claim 1, characterized in that: In step (4), the method of InP encapsulating ZnS is: a. The obtained InP quantum was diluted with ODE and vacuumed to remove excess water, purged with nitrogen and heated, and a Zn(DDTC)2 solution was injected. After the temperature rose, it was allowed to react for 5 to 10 minutes to wrap the first layer of ZnS. b. The temperature continues to rise, and the zinc precursor solution is injected. After reacting for 20 to 30 minutes, 1-DDT is injected to wrap the second layer of ZnS.

4. The method for preparing large-sized near-infrared luminescent indium phosphide quantum dots according to claim 3, characterized in that: In the step a, the temperature for injecting Zn(DDTC)2 is 110-120°C; and the temperature for carrying out the reaction is 200°C.

5. The method for preparing large-sized near-infrared luminescent indium phosphide quantum dots according to claim 3, characterized in that: In step a, the Zn(DDTC)2 solution is prepared by mixing Zn(DDTC)2 with oleylamine and stirring them uniformly by ultrasonication; wherein the molar ratio of Zn(DDTC)2 to oleylamine is 0.1 mmol / ml.

6. The method for preparing large-sized near-infrared luminescent indium phosphide quantum dots according to claim 3, characterized in that: In the step b, a zinc precursor is added to ODE, heated to a temperature in the range of 170-200° C., and stirred to dissolve uniformly; the molar ratio of the zinc precursor to the ODE is 1.2 mmol:5 ml; wherein the zinc precursor is any one of zinc oxide, zinc acetate, zinc stearate, zinc chloride, zinc bromide, and zinc iodide.

7. The method for preparing large-sized near-infrared luminescent indium phosphide quantum dots according to claim 3, characterized in that: In the step b, the temperature of the injected zinc precursor solution is 240°C.

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