A NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and its synthesis method

Abstract

The present application provides a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and a synthesis method thereof. The synthesis method selects 4-bromobutyric acid and oleylamine as ligands, and can prepare a Cs4PbBr6 shell layer at room temperature. The synthesis method of the present application obtains a precursor solution by adding a saturated solution of N,N-dimethylacetamide dissolved with lead bromide and cesium bromide, and obtains a well-structured NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal material by adding an antisolvent and controlling the addition volume and temperature of the antisolvent. The synthesis method of the present application has simple process, good reproducibility and low cost, and meets environmental requirements. The NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal prepared by the present application has high-efficiency upconversion luminescence, and can make the upconversion light continuously tunable in the visible light range, and can further improve the environmental stability and structural stability of Cs4PbX6 nanocrystals.

Description

Technical Field

[0001] This application belongs to the technical field of nanomaterials. More specifically, it relates to a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and a synthesis method thereof. Background Art

[0002] Cs4PbBr6 nanocrystals have excellent optoelectronic properties such as high luminescence quantum yield, narrow full-width at half-maximum of the luminescence peak, and long carrier diffusion distance, making them have broad application prospects in fields such as solar cells, light-emitting diodes, lasers, and photodetectors. However, since Cs4PbX6 nanocrystals are ionic crystals, they have poor environmental stability and an unstable structure prone to phase change (turning into CsPbBr3 when exposed to water). NaYF4,Yb,Tm nanocrystals have high upconversion efficiency and good stability, and can emit stable and efficient upconversion light under the excitation of near-infrared lasers, and are widely used in anti-counterfeiting, biological fluorescence labeling, and biological therapy. However, the emission wavelength of its upconversion luminescence is only determined by the energy level position of the activator ions, resulting in a very fixed emission position and poor adjustability. Therefore, if Cs4PbBr6 and NaYF4,Yb,Tm nanocrystals are combined, high-efficiency upconversion luminescence can be obtained, the upconversion light can be continuously tunable in the visible light range, and at the same time, the environmental stability and structural stability of Cs4PbX6 nanocrystals can be further improved.

[0003] However, there are significant differences in growth kinetics and structural mismatches between these two materials. Therefore, there are still many problems in how to achieve the epitaxial growth of these two materials and successfully prepare a Cs4PbBr6 and NaYF4,Yb,Tm nanocrystal composite material. Summary of the Invention

[0004] The purpose of this application is to provide a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and a synthesis method thereof in view of the deficiencies of the prior art. The synthesis method has simple technology, low cost, and can realize the controllable preparation of NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal materials.

[0005] To achieve the above purpose, in the first aspect of this application, a synthesis method of NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals is provided, including the following steps:

[0006] Add octadecene and oleic acid to rare earth salts, evacuate and place them in an inert gas atmosphere, heat to the point where all the rare earth salts are dissolved and then cool to room temperature to obtain a rare earth salt solution; the rare earth salts include yttrium acetate, ytterbium acetate, and thulium acetate;

[0007] Ammonium fluoride and sodium hydroxide are dissolved in methanol to obtain an ammonium fluoride - sodium hydroxide / methanol solution;

[0008] The ammonium fluoride - sodium hydroxide / methanol solution is added to the rare earth salt solution, and moisture and oxygen in the reaction system are removed. The temperature is raised to 280 - 310 °C and the reaction is carried out for 1 - 2 h. After the product is cooled, the product is washed and the ligands on the surface of the nanocrystals are removed with dilute hydrochloric acid. Finally, the product is dispersed in N,N - dimethylacetamide to obtain an intermediate system;

[0009] Oleylamine and 4 - bromobutyric acid are added to the intermediate system, and a saturated solution of N,N - dimethylacetamide dissolving lead bromide and cesium bromide is added. The reaction is carried out at room temperature for 10 - 20 min to obtain a precursor solution;

[0010] An antisolvent solution is added to the precursor solution, and then the product is separated and washed to obtain NaYF4:Yb,Tm@Cs4PbBr6 core - shell structured nanocrystals.

[0011] Further, the rare earth salt solution contains 1 mmol of the rare earth salt, the added volume of octadecene is 10 - 20 mL, and the added volume of oleic acid is 5 - 10 mL.

[0012] Further, the dissolution temperature of the rare earth salt is 140 - 150 °C.

[0013] Further, in the ammonium fluoride - sodium hydroxide / methanol solution, the amount of ammonium fluoride is 4 - 5 mmol, the amount of sodium hydroxide is 2 - 3 mmol, and the volume of methanol is 8 - 12 mL.

[0014] Further, the temperature for removing moisture and oxygen in the reaction system is 120 - 150 °C and the time is 20 - 30 min.

[0015] Further, the pH value of the dilute hydrochloric acid is 0.5 - 3.

[0016] Further, in the intermediate system, the volume of N,N - dimethylacetamide is 1 - 2 mL.

[0017] Further, the added volume of oleylamine is 0.5 - 2 mL, and the added volume of 4 - bromobutyric acid is 0.11 - 0.77 mL; in the saturated solution of N,N - dimethylacetamide dissolving lead bromide and cesium bromide, the amounts of lead bromide and cesium bromide are 0.4 - 0.5 mmol, the volume of N,N - dimethylacetamide is 8 - 12 mL, and the concentrations of lead ions and cesium ions are both not less than 0.04 mmol / mL.

[0018] Further, 5-8 mL of the anti-solvent solution is added to every 0.5-1 mL of the precursor solution, and after heating to 40-60 °C, the product is separated and washed. The anti-solvent is any one of toluene, chlorobenzene, and ethyl acetate.

[0019] In the second aspect of the present application, a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal material is provided, which is prepared by using the synthesis method described in any one of the above.

[0020] Compared with the prior art, the present application has the following technical effects:

[0021] The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal in the present application selects 4-bromobutyric acid and oleylamine as ligands, and a Cs4PbBr6 shell layer can be prepared at room temperature. The synthesis method of the present application obtains a precursor solution by adding a saturated solution of N,N-dimethylacetamide dissolved with lead bromide and cesium bromide, and obtains a well-structured NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal material by adding an anti-solvent and controlling the added volume and temperature of the anti-solvent. The synthesis method of the present application has simple process, good reproducibility, low cost, and meets environmental requirements.

[0022] The NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal prepared in the present application has high-efficiency upconversion luminescence, and can make the upconversion light continuously adjustable in the visible light range. At the same time, it can further improve the environmental stability and structural stability of the Cs4PbX6 nanocrystal. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 a is the XRD pattern of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal prepared in Example 1 of the present application, and 1b is its EDS-mapping diagram;

[0025] Figure 2 a is the TEM image of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal prepared in Example 1 of the present application, Figure 2 b is Figure 2 the size distribution diagram of the nanocrystals in a;

[0026] Figure 3 Figure a shows the HRTEM image of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals prepared in Example 1 of this application. Figures 3b and 3c are the HRTEM image and FFT image of the area within the box in Figure 3a, respectively.

[0027] Figure 4 Figure shows the spectral graph and fluorescence photograph (upper) of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals prepared in Example 1 of this application under 980 nm excitation, and the fluorescence spectral graph and fluorescence photograph (lower) under 375 nm excitation.

[0028] Figure 5 Figure shows the high-resolution spectrum of the XPS etching of bromine element of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals prepared in Example 1 of this application. Detailed implementation manners

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer, the following further details this application in combination with examples. It should be understood that the specific examples described herein are only used to explain this application and are not used to limit this application.

[0030] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0031] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms of "a", "the" and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0032] The weights of the relevant components mentioned in the specification of the embodiments of this application not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the contents of the relevant components in the specification of the embodiments of this application are enlarged or reduced in proportion, they are within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass described in the specification of the embodiments of this application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0033] Example 1

[0034] Example 1 of this application provides a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and its synthesis method, including the following steps:

[0035] ① Weigh a total of 1 mmol of yttrium acetate, ytterbium acetate, and thulium acetate using an analytical balance and transfer them to a 100 mL four-necked flask. Add 15 mL of octadecene and 6 mL of oleic acid. Evacuate the flask and place it in a nitrogen atmosphere. Heat the mixture at a rate of 15 °C / min to 150 °C. After all the rare earth salts are dissolved, cool the mixture to room temperature (20 - 30 °C).

[0036] ② Dissolve 4 mmol of ammonium fluoride and 2.5 mmol of sodium hydroxide in 10 mL of methanol. Add the solution to the four-necked flask in step ① and react. Keep the temperature to remove moisture and oxygen in the system. Then heat the mixture at a rate of 20 °C / min to 300 °C and maintain the temperature for 1.5 hours. After the product cools down, wash the product and remove the surface ligands of the nanocrystals with dilute hydrochloric acid with a pH of 1. Finally, disperse the product in 2 mL of N,N-dimethylacetamide.

[0037] ③ Add the N,N-dimethylacetamide system obtained in step ② to a 50 mL flask. Add 1 mL of oleylamine and 0.66 mL of 4-bromobutyric acid. Add a 10 mL N,N-dimethylacetamide solution containing lead bromide and cesium bromide (c(PbBr2) = c(CsBr) = 0.04 mmol / mL) to the flask at a rate of 0.25 mL / min. After adding, react for 15 min to obtain a precursor.

[0038] ④ Take 1 mL of the precursor solution, add 5 mL of toluene, and heat to 40 °C. Then centrifuge the product at 9000 r / min, discard the supernatant, and disperse the product in chlorobenzene solution to obtain NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals.

[0039] The average particle size of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals prepared in this example is 33 nm, as shown in Figure 2 b; The TEM image is shown in Figure 2 a.

[0040] Example 2

[0041] Example 2 of this application provides a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and its synthesis method, including the following steps:

[0042] ① Weigh a total of 1 mmol of yttrium acetate, ytterbium acetate, and thulium acetate using an analytical balance and transfer them to a 100 mL four-necked flask. Add 20 mL of octadecene and 8 mL of oleic acid. Evacuate the flask and place it in a nitrogen atmosphere. Heat the mixture at a rate of 15 °C / min to 140 °C. After all the rare earth salts are dissolved, cool the mixture to room temperature (20 - 30 °C).

[0043] ② Dissolve 5 mmol of ammonium fluoride and 3 mmol of sodium hydroxide in 12 mL of methanol, add it to the four-necked flask in step ① for reaction, keep warm to remove moisture and oxygen in the system, then heat it up to 300 °C at a heating rate of 20 °C / min and hold for 1 hour. After the product is cooled, wash the product and remove the ligands on the surface of the nanocrystals with dilute hydrochloric acid with a pH of 0.5. Finally, disperse the product in 2 mL of N,N-dimethylacetamide;

[0044] ③ Add the N,N-dimethylacetamide system obtained in step ② to a 50 mL flask, add 0.5 mL of oleylamine and 0.11 mL of 4-bromobutyric acid, and add 9 mL of an N,N-dimethylacetamide solution (c(PbBr2)=c(CsBr)=0.04 mmol / mL) dissolved with lead bromide and cesium bromide to it at a rate of 0.25 mL / min. After adding, react for 10 min to obtain a precursor;

[0045] ④ Take 0.8 mL of the precursor solution, add 4 mL of toluene, and heat to 50 °C. Then centrifuge the product at 9000 r / min, discard the supernatant, and disperse the product in a toluene solution to obtain NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals.

[0046] Example 3

[0047] Example 3 of the present application provides a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal and its synthesis method, including the following steps:

[0048] ① Weigh a total of 1 mmol of yttrium acetate, ytterbium acetate and thulium acetate with an analytical balance into a 100 mL four-necked flask, add 12 mL of octadecene and 4 mL of oleic acid, evacuate and place it in a nitrogen atmosphere, heat it up to 145 °C at a heating rate of 15 °C / min, and cool it to room temperature (20 - 30 °C) after all the rare earth salts are dissolved;

[0049] ② Dissolve 3 mmol of ammonium fluoride and 2 mmol of sodium hydroxide in 8 mL of methanol, add it to the four-necked flask in step ① for reaction, keep warm to remove moisture and oxygen in the system, then heat it up to 300 °C at a heating rate of 20 °C / min and hold for 2 hours. After the product is cooled, wash the product and remove the ligands on the surface of the nanocrystals with dilute hydrochloric acid with a pH of 2. Finally, disperse the product in 3 mL of N,N-dimethylacetamide;

[0050] ③ Add the NN-dimethylacetamide system obtained in step ② into a 50 mL flask, add 1.5 mL of oleylamine and 0.77 mL of 4-bromobutyric acid, add 12 mL of NN-dimethylacetamide solution (c(PbBr2)=c(CsBr)=0.04 mmol / mL) dissolved with lead bromide and cesium bromide at a rate of 0.25 mL / min, react for 20 min to obtain a precursor;

[0051] ④ Take 1 mL of the precursor solution, add 8 mL of ethyl acetate, and heat to 60°C, then centrifuge the product at 9000 r / min, discard the supernatant, and disperse the product in ethyl acetate solution to obtain NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals.

[0052] The XRD spectrum and EDS spectrum of the NaYF4:Yb,Tm@Cs4PbBr6 nanocrystalline material prepared in Example 1 are shown in Figure 1 . Figure 1 The positions and relative intensities of the diffraction peaks shown in the XRD spectrum in a match those of the NaYF4:Yb,Tm@Cs4PbBr6 nanocrystalline material (ICSD No.:51917; ICSD No.:25124). Figure 1 The EDS-mapping spectrum in b shows that each element is evenly distributed in the prepared NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystals, indicating that the synthesized product is a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure material.

[0053] The single particle of NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal prepared in Example 1 was subjected to HRTEM analysis. The characterization results are shown in Figure 3 a. Figure 3 The spacing of the lattice fringes shown by HRTEM of a is and They can correspond to the (010) crystal plane of NaYF4:Yb,Tm and the (-351) crystal plane of Cs4PbBr6, respectively, and the FFT diagram (3c) can also confirm this point. This shows that the material prepared in Example 1 is a core-shell material.

[0054] The optical properties of the NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystals prepared in Example 1 were characterized. Figure 4 .from Figure 4 It can be seen that NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystals have bright green emission under 980nm and 375nm excitation. Figure 4It can be seen from the square illustration in [description] that the product has good dispersibility in the chlorobenzene solution.

[0055] The NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals prepared in Example 1 were tested by XPS etching. The results are shown in Figure 5 . Figure 5 It shows that the prepared NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals are relatively uniform core-shell structures, and verifies that the thickness of the outermost shell of the core-shell structure is 2 nm.

[0056] The above embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for synthesizing NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystals, characterized in that, It includes the following steps: Add octadecene and oleic acid to the rare earth salt, evacuate and place it in an inert gas atmosphere, heat it until all the rare earth salt is dissolved and then cool it to room temperature to obtain a rare earth salt solution; the rare earth salt includes yttrium acetate, ytterbium acetate, and thulium acetate; Dissolve ammonium fluoride and sodium hydroxide in methanol to obtain an ammonium fluoride - sodium hydroxide / methanol solution; Add the ammonium fluoride - sodium hydroxide / methanol solution to the rare earth salt solution, remove moisture and oxygen in the reaction system, heat it to 280 - 310 °C, react for 1 - 2 h, after the product is cooled, wash the product and remove the ligands on the surface of the nanocrystals with dilute hydrochloric acid, and finally disperse the product in N,N - dimethylacetamide to obtain an intermediate system; the pH value of the dilute hydrochloric acid is 0.5 - 3; Add oleylamine and 4 - bromobutyric acid to the intermediate system, and add a N,N - dimethylacetamide solution dissolving lead bromide and cesium bromide thereto at a rate of 0.25 mL / min. The concentrations of both lead bromide and cesium bromide are 0.04 mmol / mL. After adding, react at room temperature for 10 - 20 min to obtain a precursor solution; Add an anti - solvent solution to the precursor solution, then separate and wash the product to obtain NaYF4:Yb,Tm@Cs4PbBr6 core - shell structure nanocrystals; wherein, 5 - 8 mL of the anti - solvent solution is added to every 0.5 - 1 mL of the precursor solution, and after heating to 40 - 60 °C, the product is separated and washed. The anti - solvent is any one of toluene, chlorobenzene, and ethyl acetate.

2. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal according to claim 1, characterized in that, The rare earth salt solution contains 1 mmol of the rare earth salt, the added volume of octadecene is 10 - 20 mL, and the added volume of oleic acid is 5 - 10 mL.

3. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal according to claim 1, characterized in that, The dissolution temperature of the rare earth salt is 140 - 150 °C.

4. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal as described in claim 1, characterized in that, In the ammonium fluoride - sodium hydroxide / methanol solution, the amount of ammonium fluoride is 4 - 5 mmol, the amount of sodium hydroxide is 2 - 3 mmol, and the volume of methanol is 8 - 12 mL.

5. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal as described in claim 1, characterized in that, The temperature for removing moisture and oxygen in the reaction system is 120 - 150 °C, and the time is 20 - 30 min.

6. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal according to claim 1, characterized in that In the intermediate system, the volume of N,N - dimethylacetamide is 1 - 2 mL.

7. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal as described in claim 1, characterized in that, The added volume of oleylamine is 0.5 - 2 mL, and the added volume of 4 - bromobutyric acid is 0.11 - 0.77 mL.

8. The synthesis method of a NaYF4:Yb,Tm@Cs4PbBr6 core-shell structure nanocrystal as claimed in claim 1, wherein In the N,N - dimethylacetamide saturated solution dissolving lead bromide and cesium bromide, the amounts of lead bromide and cesium bromide are 0.4 - 0.5 mmol, and the volume of N,N - dimethylacetamide is 8 - 12 mL.

9. A NaYF4:Yb,Tm@Cs4PbBr6 core-shell structured nanocrystal, characterized in that, It is prepared by using the synthesis method described in any one of claims 1 - 8.

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