Up-conversion composite nanocrystal and green preparation method thereof

Abstract

The invention discloses an up-conversion composite nanocrystal and a green preparation method thereof, a nanocapsule which takes a high polymer material as a shell and is internally coated with an up-conversion precursor solution is obtained by using a water-in-oil miniemulsion technology, and then the up-conversion composite nanocrystal material is obtained through solvent volatilization and confinement crystallization in the nanocapsule. According to the method, green preparation of the up-conversion nanocrystal under mild conditions is realized, the reaction temperature is 50 DEG C, all organic solvents can be recycled, a small amount of water is used as a volatile solvent, and high-corrosion chemicals are not involved. Meanwhile, the obtained up-conversion composite nanocrystal can obtain high quantum yield under low energy density, and the quantum yield can reach 15.5% under the energy density of 10 W cm <-2 >. The preparation method provided by the invention is suitable for preparing any composite nanocrystal of the rare earth doped upconversion material with high solubility.

Description

Technical Field

[0001] The present invention relates to the field of solid luminescent materials, in particular to an up-conversion composite nanocrystal and a green preparation method thereof. Background Art

[0002] Upconversion materials can convert low-energy near-infrared light into high-energy visible light. As luminescent materials, they offer advantages such as being unaffected by background fluorescence and having high signal penetration. Rare-earth-doped upconversion nanocrystals, in particular, offer a narrow fluorescence spectrum, high chemical stability, no photobleaching, and minimal requirements for excitation sources. They have found applications in bioluminescent labeling, photodynamic therapy, photocatalysis, solid-state lasers, solar cells, sensors, LED devices, and super-resolution microscopy. However, compared to bulk upconversion materials, the high surface area of ​​nanocrystals leads to significant quenching of fluorescence energy by surface defects, significantly reducing their quantum yield and limiting their further applications. This presents a major challenge in the application of upconversion nanocrystals. Furthermore, the current preparation conditions for upconversion nanocrystals are demanding. The commonly used hot injection method involves temperatures exceeding 200°C and the use of highly toxic and corrosive reagents such as ammonium fluoride, resulting in high manufacturing costs and posing certain safety and environmental risks. Therefore, the development of low-cost, green methods for the preparation of high-quantum-yield upconversion nanocrystals is urgently needed to enhance their market potential.

[0003] Polymer materials possess a rich variety of organic functional groups, a wide range of tunable absorption and vibrational energy levels, and controllable aggregation states. If composite nanocrystals with upconversion materials encapsulated within a polymer shell could be prepared, surface defects could be passivated through coordination between the polymer and the upconversion material, while luminescence efficiency could be enhanced through energy transfer between specific functional groups and the upconversion nanocrystal. Furthermore, the good solubility of heavy halogen elements with low phonon energy could allow for solution-based preparation, thus opening the door to the green production of upconversion nanocrystals. Regarding the preparation of composite materials of polymers and upconversion nanocrystals, aside from the use of polymers to modify nanocrystals to improve their stability and biocompatibility (e.g., invention patents CN104804739A and CN116407650A), there are currently no public reports on the green production of upconversion composite nanocrystals with high quantum yields using polymer nanoencapsulation. Summary of the Invention

[0004] The present invention aims to address the low luminescence efficiency of upconversion nanocrystals, the limited approach to improving their efficiency, and the stringent synthesis conditions. The present invention also provides an upconversion composite nanocrystal and its green preparation method. Specifically, utilizing water-in-oil miniemulsion technology, nanocapsules containing a polymer shell and an upconversion precursor solution are obtained. Solvent evaporation then allows confined crystallization within the nanocapsule to yield the upconversion composite nanocrystal. This method not only utilizes the abundant organic functional groups in the polymer to regulate the crystallization process of the upconversion nanocrystals, reducing surface defects and improving luminescence efficiency by controlling surface defects, but also generates energy coupling and surface coordination effects at the resulting solid-solid interface, further enhancing upconversion efficiency through these two mechanisms. Of particular note, this method leverages the low phonon energy of heavy halogen metal halides to minimize nonradiative relaxation through this low phonon energy mechanism. Furthermore, it leverages the advantages of solution preparation, resulting in mild reaction conditions and fully solvent-recyclable solvents. This provides a new approach to the green preparation of upconversion nanocrystals.

[0005] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0006] The present invention provides an upconversion composite nanocrystal, comprising an upconversion material, a polymer coating material, and a surfactant, wherein the mass percentages of the components are as follows:

[0007] Upconversion materials: 0.1-90%;

[0008] Polymer coating material: 0.1~99.8%;

[0009] Surfactant: 0.01~50%.

[0010] As a preferred embodiment of the present invention, the up-conversion material includes a crystal matrix doped with rare earth elements.

[0011] As a preferred embodiment of the present invention, the crystal matrix contains one or more of the following ions: Li + , Na + , K + , Rb + , Cs + , Sr 2+ , Mg 2+ , Be 2+ , Ca 2+ , Ba 2+ , Cl - , Br - , I - , Yb 3+ , Gd 3+ , Y3+ .

[0012] As a preferred embodiment of the present invention, the rare earth element doping includes one or more of the following ions: Yb 3+ , Nd 3 + , Er 3+ , Ho 3+ , Tm 3+ .

[0013] As a preferred embodiment of the present invention, the polymer coating material includes a water-soluble component and an oil-soluble component.

[0014] As a preference of the present invention, the water-soluble component contains one or more of thiol, hydroxyl or amino functional groups, the number of the thiol is two or more, the number of the hydroxyl is two or more, and the number of the amino is two or more.

[0015] As a preference of the present invention, the oil-soluble component contains one or both of isocyanate groups and double bond functional groups, the number of the isocyanate groups is two or more, and the number of the double bonds is two or more.

[0016] As a preferred embodiment of the present invention, the surfactant is one or more of polyglycerol ricinoleate, Span 80, Span 83, and polyethylene glycol (30) dipolyhydroxystearate.

[0017] Another aspect of the present invention provides a green preparation method for upconversion composite nanocrystals, comprising the following steps:

[0018] Step 1, dissolving the water-soluble components of the upconversion material and the polymer coating material in water to obtain an aqueous phase;

[0019] Step 2, dissolving the surfactant in an organic solvent to obtain an oil phase;

[0020] Step 3, after mixing the water phase and the oil phase, the mixed system is subjected to high shear treatment to obtain an oil-in-water nanoemulsion;

[0021] Step 4, dissolving the oil-soluble component of the polymer material in an organic solvent to obtain a crosslinker solution;

[0022] Step 5: slowly dropwise adding the crosslinking agent solution into the oil-in-water nanoemulsion obtained by high shearing, and through polymerization reaction, obtaining polymer nanocapsules with an internal water phase coating.

[0023] Step 6: Dry the nanocapsules coated with the water phase to remove moisture and obtain upconversion composite nanocrystals.

[0024] As a preferred embodiment of the present invention, the high shear treatment is achieved by an ultrasonic disruptor, a high-speed stirrer or a micro-jet high-pressure homogenizer.

[0025] As a preference of the present invention, the organic solvent is one or more of cyclohexane, n-hexane, toluene, ethyl acetate, butyl acetate, dichloromethane, and chloroform.

[0026] The beneficial effects of the present invention are:

[0027] 1. Achieve green preparation of upconversion nanocrystals under mild conditions. The reaction temperature is 50°C, all organic solvents are recyclable, the volatile solvent is a small amount of water, and no highly corrosive chemicals are involved.

[0028] 2. The obtained upconversion composite nanocrystals can achieve high quantum yield at low energy density, and the -2 At an energy density of 1.5 %, the quantum yield can reach 15.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a transmission electron microscope photograph of the upconversion composite nanocrystal prepared in Example 1;

[0030] Figure 2 The upconversion composite nanocrystals prepared in Example 1 were irradiated with 980nm infrared light (3W cm -2 ) emits bright upconversion fluorescence;

[0031] Figure 3 XRD patterns of the upconversion composite nanocrystals prepared in Examples 1 to 5;

[0032] Figure 4 The upconversion composite nanocrystals prepared in Examples 1 to 5 were irradiated with 980nm infrared light (3W cm -2 ) upconversion fluorescence spectra under .

[0033] Figure 5 The upconversion composite nanocrystals prepared in Examples 1 to 5 were irradiated with a 980nm laser (10W cm -2 ) under the upconversion quantum yield diagram. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the implementation method of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0036] Example 1

[0037] A method for preparing upconversion composite nanocrystals comprises the following steps:

[0038] In 2 g of pure water, 2.36 g of cesium chloride, 1.35 g of gadolinium chloride hexahydrate, 0.26 g of ytterbium chloride hexahydrate, 0.026 g of erbium chloride hexahydrate and 150 mg of hydroxyethyl modified starch were dissolved in 2 g of water to obtain an aqueous phase. In 16 g of cyclohexane, 200 mg of polyethylene glycol (30) dipolyhydroxystearate was dissolved to obtain an oil phase. After the aqueous phase and the oil phase were mixed, the mixed system was subjected to high shear treatment using an ultrasonic crusher. At this time, 850 mg of diphenylmethane diisocyanate (MDI) was dissolved in 3 g of cyclohexane to obtain a crosslinker solution. The crosslinker solution was slowly added dropwise to the mixed system after high shear treatment. After 72 h of polymerization reaction, nanocapsules with an upconversion precursor solution coated inside were obtained. The nanocapsules were dried in a vacuum oven at 60 °C to finally obtain upconversion composite nanocrystals with a polymer material as the shell and an upconversion material coated inside. Figure 1 This is a transmission electron microscope photo of the upconversion composite nanocrystal prepared in this example. Figure 2 The upconversion composite nanocrystals prepared in this example were irradiated with 980nm infrared light (3W cm -2 ) emits bright upconversion fluorescence.

[0039] Example 2

[0040] A method for preparing upconversion composite nanocrystals comprises the following steps:

[0041] In 2 g of pure water, 2.36 g of cesium chloride, 1.35 g of gadolinium chloride hexahydrate, 0.26 g of ytterbium chloride hexahydrate, 0.026 g of erbium chloride hexahydrate, and 300 mg of hydroxyethyl-modified starch were dissolved in 2 g of water to obtain an aqueous phase. In 16 g of cyclohexane, 200 mg of Span 80 was dissolved to obtain an oily phase. After mixing the aqueous and oily phases, the mixture was subjected to high shear using an ultrasonicator. At this point, 700 mg of polyphenylpolymethylene polyisocyanate (PAPI) was dissolved in 3 g of cyclohexane to obtain a crosslinker solution. The crosslinker solution was slowly added dropwise to the high-shear mixture. After 72 hours of polymerization, nanocapsules coated with the upconversion precursor solution were obtained. The nanocapsules were dried in a vacuum oven at 60°C to obtain upconversion composite nanocrystals with a polymer shell and the upconversion material encapsulated within.

[0042] Example 3

[0043] A method for preparing upconversion composite nanocrystals comprises the following steps:

[0044] In 2 g of pure water, 2.36 g of cesium chloride, 1.35 g of gadolinium chloride hexahydrate, 0.26 g of ytterbium chloride hexahydrate, 0.026 g of erbium chloride hexahydrate, and 450 mg of hydroxyethyl-modified starch were dissolved in 2 g of water to obtain an aqueous phase. In 16 g of cyclohexane, 200 mg of Span 83 was dissolved to obtain an oily phase. After mixing the aqueous and oily phases, the mixture was subjected to high shear using an ultrasonicator. At this point, 550 mg of polyphenylpolymethylene polyisocyanate (PAPI) was dissolved in 3 g of cyclohexane to obtain a crosslinker solution. The crosslinker solution was slowly added dropwise to the high-shear mixture. After 72 hours of polymerization, nanocapsules coated with the upconversion precursor solution were obtained. The nanocapsules were dried in a vacuum oven at 60°C to obtain upconversion composite nanocrystals with the polymer shell and the upconversion material encapsulated within.

[0045] Example 4

[0046] A method for preparing upconversion composite nanocrystals comprises the following steps:

[0047] In 2 g of pure water, 2.36 g of cesium chloride, 1.35 g of gadolinium chloride hexahydrate, 0.26 g of ytterbium chloride hexahydrate, 0.026 g of erbium chloride hexahydrate, and 600 mg of hydroxyethyl-modified starch were dissolved in 2 g of water to obtain an aqueous phase. In 16 g of cyclohexane, 200 mg of Span 80 was dissolved to obtain an oily phase. After mixing the aqueous and oily phases, the mixture was subjected to high shear using an ultrasonicator. At this point, 400 mg of toluene diisocyanate (TDI) was dissolved in 3 g of cyclohexane to obtain a crosslinker solution. The crosslinker solution was slowly added dropwise to the high-shear mixture. After a 72-hour polymerization reaction, nanocapsules coated with the upconversion precursor solution were obtained. The nanocapsules were dried in a vacuum oven at 60°C to obtain upconversion composite nanocrystals with a polymer shell and the upconversion material encapsulated within.

[0048] Example 5

[0049] A method for preparing upconversion composite nanocrystals comprises the following steps:

[0050] In 2 g of pure water, 2.36 g of cesium chloride, 1.35 g of gadolinium chloride hexahydrate, 0.26 g of ytterbium chloride hexahydrate, 0.029 g of thulium chloride hexahydrate, and 750 mg of hydroxyethyl-modified starch were dissolved in 2 g of water to obtain an aqueous phase. In 16 g of cyclohexane, 200 mg of Span 80 was dissolved to obtain an oily phase. After mixing the aqueous and oily phases, the mixture was subjected to high shear using an ultrasonicator. At this point, 250 mg of polyphenylpolymethylene polyisocyanate (PAPI) was dissolved in 3 g of cyclohexane to obtain a crosslinker solution. The crosslinker solution was slowly added dropwise to the high-shear mixture. After 72 hours of polymerization, nanocapsules coated with the upconversion precursor solution were obtained. The nanocapsules were dried in a vacuum oven at 60°C to obtain upconversion composite nanocrystals with a polymer shell and the upconversion material encapsulated within.

[0051] Example 6

[0052] A method for preparing upconversion composite nanocrystals comprises the following steps:

[0053] In 2 g of pure water, 2.36 g of cesium chloride, 1.35 g of gadolinium chloride hexahydrate, 0.26 g of ytterbium chloride hexahydrate, and 0.031 g of holmium chloride hexahydrate were dissolved. 450 mg of hydroxyethyl-modified starch was also dissolved in 2 g of water to obtain an aqueous phase. In 16 g of cyclohexane, 200 mg of Span 80 was dissolved to obtain an oil phase. After mixing the aqueous and oil phases, the mixture was subjected to high shear using an ultrasonicator. At this point, 550 mg of polyphenylpolymethylene polyisocyanate (PAPI) was dissolved in 3 g of cyclohexane to obtain a crosslinker solution. The crosslinker solution was slowly added dropwise to the high-shear mixture. After 72 hours of polymerization, nanocapsules coated with the upconversion precursor solution were obtained. The nanocapsules were dried in a vacuum oven at 60°C to obtain upconversion composite nanocrystals with a polymer shell and the upconversion material encapsulated within.

[0054] Performance Characterization

[0055] The up-conversion composite nanocrystals prepared in Examples 1 to 5 were subjected to XRD diffraction analysis and fluorescence emission spectrum analysis (980 nm infrared light (3 W cm -2 ), quantum yield test (980nm laser irradiation (10W cm -2 ) and obtain Figure 3 XRD pattern of upconversion composite nanocrystals; Figure 4 The upconversion composite nanocrystals were illuminated by 980nm infrared light (3Wcm -2 ) up-conversion fluorescence spectra under ; Figure 5 The upconversion composite nanocrystals were irradiated with 980 nm laser (10 W cm -2) under the upconversion quantum yield diagram.

[0056] Although the present invention is described herein with reference to illustrative embodiments of the present invention, the above embodiments are merely preferred embodiments of the present invention, and the embodiments of the present invention are not limited to the above embodiments. It should be understood that those skilled in the art can design many other modifications and implementations, which will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. An upconversion composite nanocrystal, characterized in that: It includes up-conversion material, polymer coating material and surfactant, and the mass percentage of each component is as follows: up-conversion material: 0.1-90%; polymer coating material: 0.1-99.8%; surfactant: 0.01-50%.

2. The upconversion composite nanocrystal according to claim 1, characterized in that: The up-conversion material includes a crystal matrix and rare earth element doping.

3. The upconversion composite nanocrystal according to claim 2, characterized in that: The crystal matrix contains one or more of the following ions: Li + , Na + , K + , Rb + , Cs + , Sr 2+ , Mg 2+ , Be 2+ , Ca 2+ , Ba 2+ , Cl - , Br - , I - , Yb 3+ , Gd 3+ , Y 3+ .

4. The upconversion composite nanocrystal according to claim 2, characterized in that: The rare earth element doping includes one or more of the following ions: Yb 3+ , Nd 3+ , Er 3+ , Ho 3+ , Tm 3+ .

5. The upconversion composite nanocrystal according to claim 1, characterized in that: The polymer coating material includes a water-soluble component and an oil-soluble component.

6. The upconversion composite nanocrystal according to claim 5, characterized in that: The water-soluble component contains one or more of thiol, hydroxyl or amino functional groups, the number of the thiol is two or more, the number of the hydroxyl is two or more, and the number of the amino is two or more.

7. The upconversion composite nanocrystal according to claim 5, characterized in that: The oil-soluble component contains one or both of isocyanate groups and double bond functional groups, the number of the isocyanate groups is two or more, and the number of the double bonds is two or more.

8. The upconversion composite nanocrystal according to claim 1, characterized in that: The surfactant is one or more of polyglycerol ricinoleate, Span 80, Span 83, and polyethylene glycol (30) dipolyhydroxystearate.

9. A green preparation method for upconversion composite nanocrystals, characterized in that: The following steps are involved: Step 1, dissolving the water-soluble components of the upconversion material and the polymer coating material in water to obtain an aqueous phase; Step 2, dissolving the surfactant in an organic solvent to obtain an oil phase; Step 3, after mixing the water phase and the oil phase, the mixed system is subjected to high shear treatment to obtain an oil-in-water nanoemulsion; Step 4, dissolving the oil-soluble component of the polymer material in an organic solvent to obtain a crosslinker solution; Step 5, slowly adding the crosslinking agent solution dropwise to the oil-in-water nanoemulsion obtained by high shearing, and obtaining a polymer nanocapsule with an internal water phase coating through polymerization reaction; Step 6: Dry the nanocapsules coated with the water phase to remove moisture and obtain upconversion composite nanocrystals.

10. The green preparation method of upconversion composite nanocrystals according to claim 9, characterized in that: The high shear treatment is achieved by an ultrasonic disruptor, high-speed stirring or micro-jet high-pressure homogenizer.

11. The green preparation method of upconversion composite nanocrystals according to claim 9, characterized in that: The organic solvent in step 2 is one or more of cyclohexane, n-hexane, toluene, ethyl acetate, butyl acetate, dichloromethane, and chloroform.

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