Graphene-covered light-emitting nano composite material and preparation method thereof

Abstract

The invention relates to the technical field of photoelectric functional materials, in particular to a graphene-covered light-emitting nano composite material and a preparation method thereof. The graphene-covered light-emitting nano composite material comprises a rigid substrate, a rare earth light-emitting material layer and a graphene sealing layer which are sequentially arranged from bottom to top, wherein the rare earth luminescent material is rare earth luminescent nanocrystalline coated with a silicon dioxide layer, and the thickness of the silicon dioxide layer is 5-25nm. The graphene sealing layer prevents exogenous molecules from permeating and approaching the rare earth fluoride nanocrystals, so that a quenching effect caused by molecular bond resonance is avoided; the silicon dioxide spacing layer prevents the rare earth fluoride nanocrystal b-ALnF4: E (at) ALnF4 from making contact with graphene, and the quenching effect caused by energy transfer is weakened; the rigid substrate can be attached to the graphene to form a sealing structure. After the graphene-covered light-emitting nano composite material is immersed in pure water, the maximum light-emitting intensity retention rate can reach 66.5%, and the graphene-covered light-emitting nano composite material has important value in research and development of high-stability light-emitting nano elements, nano sensing detection elements and the like.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic functional materials technology, specifically to a graphene-coated luminescent nanocomposite material and its preparation method. Background Technology

[0002] Semiconductor quantum dots, rare-earth-doped nanocrystals, and other luminescent nanomaterials hold significant value in imaging displays and biosensing, but their luminescence efficiency is easily affected by the environment, a key factor limiting their application. For example, when luminescent nanoparticles encounter water molecules, a significant quenching effect occurs through non-radiative resonance energy transfer. Studies have shown that nanomaterials exposed to humid environments typically maintain only 10% of their original luminescence intensity. Graphene, as a two-dimensional material with high mechanical strength, good chemical stability, high light transmittance, and atomic-level thickness, is an ideal barrier material for physically blocking microscopic particles such as water molecules. Graphene has been used to construct miniature liquid sample cells, sealing aqueous samples and then placing them in a high-vacuum environment for transmission electron microscopy imaging. This indicates that graphene can effectively prevent water molecules from permeating across the membrane. However, if graphene is directly exposed to luminescent nanomaterials, the delocalized p-electron cloud of graphene generally leads to an interfacial charge transfer-type luminescence quenching effect. Therefore, how to utilize the physical barrier effect of graphene to isolate nano-luminescent materials while suppressing the luminescence quenching effect of graphene itself is an important opportunity and challenge for the development of solid-state high-quality nano-luminescent materials and high-performance optical devices. Summary of the Invention

[0003] To overcome the aforementioned technical difficulties, this invention provides a graphene-coated luminescent nanocomposite material and its preparation method. This invention uses a graphene sealing layer to prevent exogenous molecules (such as water molecules) from penetrating close to rare-earth fluoride nanocrystals, and employs a silica shell of appropriate thickness to coat the rare-earth luminescent nanomaterial b-ALnF4:E@ALnF4, using SiO2 as a physical spacer layer to weaken energy transfer between the rare-earth luminescent material and graphene, while simultaneously increasing the effective distance between the nanocrystals and exogenous molecules. The rare-earth luminescent nanoparticles are sealed within a sandwich structure composed of a silicon wafer and graphene, significantly improving their luminescence intensity retention rate in water-rich environments.

[0004] In a first aspect, the present invention provides a graphene-coated luminescent nanocomposite material, comprising, from top to bottom, a rigid substrate, a rare earth luminescent material layer, and a graphene sealing layer.

[0005] The rare earth luminescent material is a rare earth luminescent nanocrystal coated with a silicon dioxide layer, the thickness of which is 5-25 nm. Furthermore, the rigid substrate is selected from one of the following: monocrystalline silicon wafer, polycrystalline silicon wafer, thermally oxidized silicon wafer, quartz wafer, silicon nitride wafer, silicon carbide wafer, sapphire substrate, or glass wafer; preferably, the rigid substrate is a monocrystalline silicon wafer with a surface roughness of less than 0.5 nm.

[0006] Furthermore, the rare-earth luminescent nanocrystals are b-ALnF4:E@ALnF4, where A is selected from Li. + Na + K + One of them; Ln is selected from Y 3+ Gd 3+ La 3+ Lu 3+ At least one of them; E is selected from Nd 3+ Yb 3+ Tm 3+ Er 3+ At least one of the following; preferably, A is selected from Na. + Ln is selected from Y 3+ E is selected from Yb 3+ With Er 3+ .

[0007] Furthermore, the thickness of the silicon dioxide layer is 5-25 nm, or 5-21 nm, or 15-25 nm, or 6-12 nm, or 10-18 nm, or 2-28 nm, or 2-12 nm, or 6-8 nm, or 6.5 nm, or 21 nm.

[0008] Furthermore, the graphene sealing layer is a single layer of graphene or a multilayer of graphene.

[0009] Furthermore, the thickness of the graphene sealing layer is 0.3-3 nm, or 0.3-0.8 nm, or 0.3-0.5 nm, or 0.3-0.4 nm.

[0010] Secondly, the present invention provides a method for preparing graphene-coated luminescent nanocomposite materials, comprising the following steps: S1. Synthesis of rare-earth luminescent nanocrystals β-ALnF4:E@ALnF4, wherein A is selected from Li + Na + K + One of them; Ln is selected from Y 3+ Gd 3+ La 3+ Lu 3+ At least one of them; E is selected from Nd 3+ Yb 3+ Tm 3+ Er 3+ At least one of them; Further, the rare earth luminescent nanocrystals are prepared by the following method: Y(CF3COO)3, CF3COONa, and E(CF3COO)3 are added to a mixed solvent of oleic acid / oleylamine / octadecene, heated and stirred under a nitrogen atmosphere, and the product is collected by centrifugation after the thermal decomposition reaction is completed to obtain α-NaYF4:E nanocrystals; α-NaYF4:E and CF3COONa are added to a mixed solvent of oleic acid / octadecene, heated and stirred under a nitrogen atmosphere, and the product is collected by centrifugation after the thermal decomposition reaction is completed to obtain b-NaYF4:E nanocrystals; b-NaYF4:E nanocrystals are mixed with Y(CF3COO)3 and CF3COONa, added to a mixed solvent of oleic acid / octadecene, heated and stirred under a nitrogen atmosphere, and the product is collected by centrifugation after the thermal decomposition reaction is completed to obtain b-NaYF4:E@NaYF4 nanocrystals; Furthermore, the molar ratio of E(CF3COO)3 to Y(CF3COO)3 is b:(1-b), where the value of b is 0 < b < 0.5, or 0 < b < 0.3, or 0.1 < b < 0.3; or 0.2 < b < 0.25. Furthermore, E is selected from Nd 3+ Yb 3+ Tm 3+ Er 3+ One or two of them; Furthermore, the chemical formula of the rare-earth luminescent nanocrystals is: b-NaYF4:Yb,Er@NaYF4, where Yb 3+ doping ratio x%, 5 <x<99.5;Er 3+ The doping ratio y% is 0.5%. <y<5; S2. Synthesis of thin-layer SiO2 spacer shell: 0.1-0.6 g of surfactant CO-520 and 2-40 mg of rare earth fluoride nanocrystals were sequentially added to 1-5 ml of cyclohexane and ultrasonically mixed; 10-100 mL of alkaline solution was added and stirred to form a reverse microemulsion solution; 10-100 mL of tetraethyl orthosilicate (TEOS) was added and the mixture was sealed and stirred at room temperature for 24 h; then the product was centrifuged and washed sequentially with isopropanol and ethanol to obtain thin-layer SiO2-coated rare earth luminescent nanoparticles; Furthermore, the alkaline solution is selected from 13% ammonia solution; S3. Synthesis of thick SiO2 spacer shell: Take 2-40 mg of the thin SiO2-coated rare earth luminescent nanoparticles obtained in S2 and disperse them in 1-5 ml of ethanol; add 50-500 mL of alkaline solution and stir evenly; add 1-200 mL of tetraethyl orthosilicate (TEOS) and seal and stir for 15 h at room temperature; centrifuge and wash the product with ethanol and water in sequence to obtain thick SiO2-coated rare earth luminescent nanoparticles; Furthermore, the alkaline solution is selected from 25% ammonia solution; S4. Coating rare earth luminescent nanoparticles: Cut and polish silicon wafers, immerse them in a concentrated sulfuric acid-hydrogen peroxide mixture to remove surface stains and obtain a strongly hydrophilic surface; after rinsing the silicon wafers with deionized water, dry them for later use; spin-coat the surface of the silicon wafers with an aqueous solution of rare earth luminescent nanoparticles prepared in S2 or S3, and dry them at 70-90 ℃ to obtain a silicon substrate wafer with rare earth luminescent nanoparticles spread on it. S5. Applying a graphene sealing layer: Cut copper foil of appropriate size to support graphene, spin-coat a polymethyl methacrylate (PMMA) anisole solution onto the graphene surface, and dry the anisole; place the copper foil face down and float it on the surface of the copper etching solution until the copper foil is completely etched; transfer the floating graphene-PMMA film sequentially to dilute hydrochloric acid and then to pure water for rinsing; insert the composite silicon wafer obtained in S4 into the bottom of the aqueous solution and retrieve the graphene film from bottom to top; immerse the composite silicon wafer in acetone to dissolve the PMMA layer, and after thorough cleaning and drying, obtain a solid composite material of graphene sealing rare earth nanoluminescent particles.

[0011] In this invention, the graphene sealing layer prevents exogenous molecules (such as water molecules) from penetrating close to the rare-earth fluoride nanocrystals, thereby avoiding quenching effects caused by molecular bond resonance. The silica spacer layer prevents the rare-earth fluoride nanocrystals b-ALnF4:E@ALnF4 from contacting the graphene, while increasing the effective distance between the nanocrystals and exogenous molecules, thus weakening the quenching effect caused by energy transfer. The surface-polished rigid inorganic material substrate can adhere to the graphene to form a sealed structure and provide mechanical support. The graphene-coated luminescent nanocomposite material of this invention, after immersion in pure water, maintains a luminescence intensity retention rate of up to 66.5%, approximately three times that of the sample without the SiO2 spacer layer. This invention is of significant value for the research and development of highly stable luminescent nanodevices and nanosensor detection elements. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of the graphene-coated luminescent nanocomposite material of the present invention; Figure 2 Transmission electron microscopy image of b-NaYF4:Yb,Er@NaYF4 nanocrystals; Figure 3 Transmission electron microscopy image of b-NaYF4:Yb,Er@NaYF4@SiO2 nanoparticles; in, Figure 3 a represents nanoparticles covered with a thin SiO2 spacer shell. Figure 3 b represents nanoparticles covered with a thick SiO2 spacer shell; Figure 4The effects of surface ligands, SiO2 spacer shells, and graphene on the luminescence lifetime of rare earth nanoparticles under dry conditions; Figure 5 Scanning electron microscope images of graphene-coated luminescent nanocomposite material and a reference sample without spacers; Figure 6 The results show the anti-disturbance performance of graphene-coated luminescent nanocomposite material and a reference sample without spacers. in, Figure 6 a represents the luminescence intensity retention rate under immersion conditions, and 6b represents the luminescence lifetime retention rate under immersion conditions. Figure 7 The emission spectra of the graphene-coated luminescent nanocomposite material prepared in Example 1 under water immersion and drying conditions are shown. Detailed Implementation

[0013] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] This invention aims to develop solid-state composite nanomaterials with luminescent properties that are less susceptible to environmental quenching factors. The invention provides a graphene-coated luminescent nanocomposite material and its preparation method. Graphene's physical barrier effect protects the rare-earth fluoride nanocrystalline luminescent material b-ALnF4:E@ALnF4, preventing the penetration of exogenous molecules (such as water molecules) and avoiding quenching effects caused by molecular bond resonance. Simultaneously, a silica shell prevents the rare-earth fluoride nanocrystals from contacting the graphene, increasing the effective distance between the nanocrystals and exogenous molecules, thus weakening the quenching effect caused by energy transfer. Finally, a surface-polished rigid inorganic substrate supports the rare-earth luminescent nanoparticle layer and the graphene layer, and the rigid inorganic substrate and graphene form a sealed structure, sealing the rare-earth luminescent nanoparticles within the intermediate layer. Please refer to [link to relevant documentation]. Figure 1The graphene-coated luminescent nanocomposite material contains rare earth luminescent nanoparticles located within a sealing layer formed by the graphene and a rigid substrate. The sealed composite structure consists of, from bottom to top: a rigid substrate, a rare earth luminescent material layer, and a graphene sealing layer. The rare earth luminescent material is composed of rare earth luminescent nanocrystals and spacer shells. In some specific embodiments, the chemical composition of the rare earth luminescent nanocrystals is b-NaYF4:Yb,Er@NaYF4; In other specific embodiments, a method for preparing graphene-coated luminescent nanocomposite materials is provided, comprising the following steps: S1. Synthesis of rare earth-doped luminescent nanocrystals b-NaYF4:Yb,Er@NaYF4: CF3COONa, Y(CF3COO)3, Yb(CF3COO)3, and Er(CF3COO)3 were added to a mixed solvent of oleic acid / oleylamine / octadecene. The mixture was heated and stirred under a nitrogen atmosphere. After the thermal decomposition reaction was completed, the product was collected by centrifugation to obtain α-NaYF4:Yb,Er nanocrystals. α-NaYF4:Yb,Er and CF3COONa were added to a mixed solvent of oleic acid / octadecene. The mixture was heated and stirred under a nitrogen atmosphere. After the thermal decomposition reaction was completed, the product was collected by centrifugation to obtain α-NaYF4:Yb,Er nanocrystals. The product was collected by centrifugation to obtain b-NaYF4:Yb,Er nanocrystals. The b-NaYF4:Yb,Er nanocrystals were then mixed with Y(CF3COO)3 and CF3COONa, and added to a mixed solvent of oleic acid / octadecene. The mixture was heated and stirred under a nitrogen atmosphere. After the thermal decomposition reaction was completed, the product was collected by centrifugation to obtain b-NaYF4:Yb,Er@NaYF4 nanocrystals. The morphology of the nanoparticles prepared in this example was characterized using transmission electron microscopy (TEM). The TEM image of the b-NaYF4:Yb,Er@NaYF4 nanocrystals is shown below. Figure 2 As shown, the particles are spherical in shape. S2. Synthesis of a thin-layer SiO2 spacer shell: Surfactant CO-520 and b-NaYF4:Yb,Er@NaYF4 nanocrystals were sequentially added to cyclohexane and ultrasonically mixed. An appropriate amount of ammonia or other alkaline aqueous solution was added and stirred to form a reverse microemulsion solution. An appropriate amount of TEOS was added, and the mixture was sealed and stirred at room temperature for 24 h. The product was then centrifuged and washed sequentially with isopropanol and ethanol to obtain rare-earth luminescent nanoparticles coated with a thin layer of SiO2. The morphology of the nanoparticles prepared in this example was characterized using transmission electron microscopy (TEM). TEM images of the b-NaYF4:Yb,Er@NaYF4@SiO2 nanoparticles are shown below. Figure 3 As shown in a, a thin silica shell was formed on the surface of b-NaYF4:Yb,Er@NaYF4 nanocrystals; In some embodiments of this implementation, the amount of rare earth luminescent nanoparticles is 2-40 mg, the amount of surfactant CO-520 is 0.1-0.6 g, the amount of 13% ammonia water is 10-100 mL, the amount of TEOS is 10-100 mL, and the amount of cyclohexane is 5 mL. In some embodiments of this implementation, the thickness of the thin SiO2 spacer shell is 2-12 nm, or 6-12 nm, or 6-8 nm; In some preferred embodiments, the amount of rare earth luminescent nanoparticles is 10 mg, the amount of surfactant CO-520 is 0.4 g, the amount of 13% ammonia water is 50 mL, the amount of TEOS is 40 mL, and the amount of cyclohexane is 5 mL; the thickness of the thin SiO2 spacer shell is 6.5 nm. S3. Synthesis of thick SiO2 spacer shell: Take the thin SiO2-coated rare earth luminescent nanoparticles obtained in S2 and quantitatively disperse them in ethanol; add an appropriate amount of ammonia or other alkaline reagent aqueous solution and stir evenly; add an appropriate amount of TEOS and seal and stir for 15 h at room temperature; centrifuge and wash the product sequentially with ethanol and water to obtain thick SiO2-coated rare earth luminescent nanoparticles. The morphology of the nanoparticles prepared in this embodiment was characterized using transmission electron microscopy (TEM). TEM images of the b-NaYF4:Yb,Er@NaYF4@SiO2 nanoparticles are shown below. Figure 3 As shown in b, a thick silica shell is formed on the surface of b-NaYF4:Yb,Er@NaYF4 nanocrystals; In some embodiments of this implementation, the amount of rare earth luminescent nanoparticles used is 2-40 mg, the amount of 25% ammonia water used is 100-300 mL, the amount of TEOS used is 1-200 mL, and the amount of ethanol used is 5 mL.

[0016] In some embodiments of this implementation, the thickness of the thick SiO2 spacer shell is 12-28 nm, or 12-22 nm, or 19-22 nm.

[0017] In some preferred embodiments, the amount of rare earth luminescent nanoparticles is 10 mg, the amount of 25% ammonia water is 220 mL, the amount of TEOS is 100 mL, and the amount of ethanol is 5 mL; the thickness of the thick SiO2 spacer shell is 21 nm.

[0018] S4. Coating rare earth luminescent nanoparticles: Cut and polish silicon wafers, immerse them in a mixture of concentrated sulfuric acid and hydrogen peroxide to remove stains, rinse with deionized water to obtain hydrophilic silicon wafers, and dry them for later use; spin-coat the surface of the silicon wafers with an aqueous solution of rare earth luminescent nanoparticles prepared in S2 or S3, and dry them at 70-90 ℃ to obtain silicon wafers with rare earth luminescent nanoparticles spread on them. In some embodiments of this implementation, the mass concentration of the rare earth luminescent nanoparticle aqueous solution is 2-40 mg / mL, the amount of solution added to the substrate surface is 1-50 μL, the spin-coating speed is 200-4000 rpm, and the number of spin-coating cycles is one or more. In some preferred embodiments, the mass concentration of the rare earth luminescent nanoparticle aqueous solution is 10 mg / mL, the amount of solution added to the substrate surface is 20 μL, the spin-coating speed is 2000 rpm, the particles prepared in S2 are spin-coated three times, the particles prepared in S3 are spin-coated once, and the drying temperature is 70 ℃.

[0019] S5. Applying a graphene sealing layer: Cut copper foil of appropriate size to support graphene, spin-coat a polymethyl methacrylate (PMMA) anisole solution onto the graphene surface, and dry the anisole at 80 ℃; place the copper foil face down in copper etching solution and keep it floating until the copper foil is completely etched; transfer the floating graphene-PMMA film sequentially to dilute hydrochloric acid and pure water for floating and cleaning; insert the composite silicon wafer obtained in S4 into the bottom of the aqueous solution and retrieve the floating graphene film from bottom to top; immerse the composite silicon wafer in acetone to dissolve the PMMA layer, clean it multiple times, and then dry it to obtain rare earth nanoluminescent particles sealed with graphene.

[0020] In some embodiments of this implementation, the graphene film is made of a single layer or multiple layers of graphene film; the thickness of the graphene film is 0.3-3 nm, or 0.3-0.8 nm, or 0.3-0.5 nm, or 0.3-0.4 nm; in some preferred embodiments, the thickness of the single layer graphene film is 0.34 nm.

[0021] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention. Example 1

[0022] Preparation of α-NaYF4:E@NaYF4 nanocrystals: 1 mmol CF3COONa, 0.78 mmol Y(CF3COO)3, 0.2 mmol Yb(CF3COO)3, 0.02 mmol Er(CF3COO)3, 10 mmol oleic acid (OA), 10 mmol oleylamine (OAm), and 20 mmol octadecene (ODE) were transferred to a two-necked flask. The mixture was heated under vacuum for 10 min with stirring to remove moisture and oxygen. After vacuuming, nitrogen gas was introduced and continuously supplied. Once the pressure stabilized, the mixture was heated to 310 °C and maintained for 30 min. After cooling, 60 ml of ethanol was added, and the α-NaYF4:Yb,Er nanocrystal precipitate was collected by centrifugation. The α-NaYF4:Yb,Er nanocrystals were transferred to another two-necked flask, and 1 mmol CF3COONa, 20 mmol OA, and 20 mmol oleylamine (ODE) were added. ODE was performed, and the above dehydration, deoxygenation, and heating reaction were repeated to obtain b-NaYF4:Yb,Er nanocrystals. The b-NaYF4:Yb,Er nanocrystals were transferred to a new two-necked flask, and 2 mmol CF3COONa, 2 mmol Y(CF3COO)3, 20 mmol OA, and 20 mmol ODE were added. The above dehydration, deoxygenation, and heating reaction were repeated to obtain b-NaYF4:Yb,Er@NaYF4 nanocrystals. The solution was then diluted to 10 mL of cyclohexane.

[0023] Preparation of b-NaYF4:Yb,Er@NaYF4@SiO2 nanoparticles: 150 μL of b-NaYF4:Yb,Er@NaYF4 cyclohexane solution and 0.4 g CO-520 were added to 5 mL of cyclohexane and ultrasonically dispersed; 50 μL of 13% ammonia water was added and stirred to form a reverse microemulsion system; 40 μL of TEOS was added and the mixture was placed in a shaker at room temperature for 24 h; 40 mL of ethanol was added to disrupt the microemulsion system, and the nanoparticles with a 6.5 nm thick silica shell were obtained by centrifugation; the nanoparticles were dispersed in 5 mL of pure water.

[0024] Preparation of graphene-coated luminescent nanocomposite material: The above-mentioned nanoparticle solution was dropped onto the surface of a hydrophilic silicon wafer, and after rotating to remove excess solution, it was dried at 70 °C to obtain a silicon wafer coated with rare earth nanoparticles; a copper foil with a single layer of graphene film deposited on its surface was cut into appropriate sizes, and a 2% PMMA anisole solution was spin-coated onto its surface, and the anisole was dried at 80 °C; the copper foil was placed face down in a copper etching solution and kept floating until the copper foil was completely etched; the floating graphene-PMMA film was sequentially transferred to dilute hydrochloric acid and then to pure water for floating and cleaning; the silicon wafer was brought into contact with the graphene film floating on the surface of pure water from bottom to top, and slowly lifted to cover the surface of the silicon wafer with the graphene film, and dried at 100 °C for half an hour to remove residual moisture; the composite silicon wafer was immersed in acetone to dissolve the PMMA layer, and the acetone cleaning solution was changed every 30 minutes for three rounds of cleaning; the composite silicon wafer was removed and dried to obtain the graphene-coated luminescent nanocomposite material. Example 2

[0025] The preparation method is basically the same as in Example 1, except that the preparation method of rare earth-doped nanoparticles modified with silica layer is as follows: 150 μL of b-NaYF4 Yb,Er@NaYF4 solution is added to 5 mL of cyclohexane solution containing 0.4 g CO-520, 50 μL of 13% ammonia water is added and stirred to form a reverse microemulsion, then 40 μL of TEOS is added and the mixture is reacted on a shaker for 24 h, ethanol is added to break the emulsion and centrifuged, the resulting precipitate is washed and dissolved in 5 mL of ethanol, then 220 μL of 25% ammonia water and 100 μL of TEOS are added, the mixture is reacted on a shaker for 15 h and then centrifuged and washed to obtain nanoparticles coated with a silica shell with a thickness of 21 nm; the nanoparticles are dispersed in 5 mL of pure water.

[0026] Comparative Example 1 The preparation method is basically the same as in Example 1, except that a cyclohexane solution of b-NaYF4:Yb,Er@NaYF4 nanocrystals is used for silicon wafer coating. The nanocrystal surface only has oleic acid ligands and no SiO2 spacer layer.

[0027] Comparative Example 2 The preparation method is basically the same as in Example 1, except that a dimethylformamide (DMF) solution of b-NaYF4:Yb,Er@NaYF4 nanocrystals with oleic acid ligands removed is used for silicon wafer coating. There are no organic molecular ligands or SiO2 spacer layers on the nanocrystal surface. Graphene is in direct contact with the rare-earth luminescent nanocrystals. The ligand removal method for b-NaYF4:Yb,Er@NaYF4 nanocrystals is as follows: 0.5 mL of a cyclohexane solution of b-NaYF4:Yb,Er@NaYF4 nanocrystals is diluted to 2 mL; 2 mL of DMF and 50 mg of nitrosotetrafluoroborate (NOBF4) are added and the mixture is stirred for 10 min; the precipitate is separated by centrifugation and redispersed in 40 mL of DMF.

[0028] Test Example 1 The luminescence properties of the raw materials and products of Examples 1 and 2, as well as Comparative Examples 1 and 2, were tested. An Edinburgh FLS-1000 spectrometer was used. The samples were fixed on a solid sample holder and excited by a 980 nm laser at a power of 1 W and a frequency of 100 Hz. The luminescence decay curve of the 545 nm emission peak was measured, and the luminescence lifetime was obtained by fitting.

[0029] The luminescence lifetime test results are listed in Table 1, and the corresponding bar chart is shown below. Figure 4 After coating rare-earth luminescent nanoparticles with SiO2, the residual hydroxyl groups within the SiO2 layer cause a quenching effect, resulting in a shorter luminescence lifetime compared to the original state (oleic acid ligand adsorption) nanocrystals and ligand-free nanocrystals. However, after graphene coating, the luminescence lifetime of the original nanocrystals, ligand-free nanocrystals, and thin-layer SiO2-coated nanocrystals shows a significant reduction, while the luminescence lifetime of thick-layer SiO2-coated nanocrystals remains almost unchanged. This indicates that the SiO2 spacer layer effectively prevents energy transfer between the luminescent nanocrystals and graphene, and the blocking effect increases with increasing spacer layer thickness.

[0030] Table 1. Luminescence lifetime of rare earth nanoparticles before and after graphene coating

[0031] Test Example 2 The samples prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to structural characterization and luminescence performance retention tests. A silicon wafer carrying the sample was fixed between a glass slide and a coverslip. First, the luminescence intensity and lifetime of the sample in a dry state were tested. Then, deionized water was injected between the glass slides, and after immersing the sample in water for 5 minutes, its luminescence intensity and lifetime were tested while maintaining the immersion state. The spectrometer used was an Edinburgh FLS-1000, excited by a 980 nm laser at a power of 1 W and a frequency of 100 Hz. The luminescence decay curve of its 545 nm emission peak was measured, and the luminescence lifetime was obtained by fitting. Continuous excitation at a power of 1 W was used to collect the emission spectrum in the range of 500 nm-700 nm, and the integrated area was recorded as the luminescence intensity. The luminescence performance retention rate was defined as: immersion state test value / dry state test value.

[0032] like Figure 5 As shown in the figure, SEM morphological characterization reveals that the scanning electron beam can penetrate the graphene sealing layer and image the rare earth nanoparticles. Rare earth nanoparticles are densely distributed beneath the graphene sealing layer. The SiO2-coated nanoparticles (c, d) have a significantly increased diameter compared to the uncoated particles (a, b). At the damaged areas of the graphene sealing layer, a multi-layered twisted stacked structure of graphene can be observed; the presence or absence of graphene coverage causes a difference in SEM imaging contrast between the rare earth nanoparticles on both sides. Optical test results are listed in Table 2, and the retention rate of luminescence properties after immersion in water is shown in [Table 2]. Figure 6 .like Figure 6 As shown, in the absence of a SiO2 spacer layer, the luminescence lifetime and intensity of graphene-covered luminescent particles immersed in water decrease sharply, indicating that water molecules outside the graphene layer still cause luminescence quenching of the nanocrystals within the sealing layer through molecular bond resonance. Graphene-covered luminescent particles with a SiO2 spacer layer exhibit higher retention rates of luminescence intensity and lifetime. Furthermore, due to differences in the nanoparticle packing density and thickness on the silicon wafer surfaces of each sample, the absolute luminescence intensity is not comparable across samples, but the luminescence retention rate is comparable.

[0033] Table 2. Luminescence intensity and lifetime of graphene-coated luminescent nanocomposites before and after immersion in water.

[0034] Figure 7 The results show that the luminescence intensity of the sample in Example 1 before immersion in water was 2.41 × 10⁻⁶. 5 Even after being immersed in water, the luminous intensity of au can still reach 1.61 × 10⁻⁶. 5 au.

[0035] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. A graphene-coated luminescent nanocomposite, characterized by, The rigid substrate, the rare earth luminescent material layer and the graphene sealing layer are sequentially arranged from bottom to top; wherein the rare earth luminescent material is a rare earth luminescent nanocrystal wrapped with a silicon dioxide layer, and the thickness of the silicon dioxide layer is 5-25 nm.

2. The graphene-coated luminescent nanocomposite of claim 1, wherein, The rigid substrate is one of a single crystal silicon wafer, a polycrystalline silicon wafer, a thermal silicon oxide wafer, a quartz wafer, a silicon nitride wafer, a silicon carbide wafer, a sapphire wafer or a glass wafer, and the surface roughness is less than 0.5 nm.

3. The graphene-coated luminescent nanocomposite of claim 1, wherein, The thickness of the graphene sealing layer is 0.3-3 nm, or 0.3-0.8 nm, or 0.3-0.5 nm, or 0.3-0.4 nm.

4. The graphene-coated luminescent nanocomposite of claim 1, wherein, The rare-earth luminescent nanocrystal is β-ALnF 4： E@ALnF4, A is selected from one of Li + , Na + , K + ; Ln is selected from at least one of Y 3+ , Gd 3+ , La 3+ , Lu 3+ ; E is selected from at least one of Nd 3+ , Yb 3+ , Tm 3+ , Er 3+ .

5. The graphene-coated luminescent nanocomposite of claim 1, wherein, The thickness of the silicon dioxide layer is 5-25 nm, or 5-21 nm, or 15-25 nm, or 6-12 nm, or 10-18 nm, or 6.5 nm, or 21 nm.

6. The method for preparing graphene-coated luminescent nanocomposite material as described in claim 1, characterized in that, The method comprises the following steps: S1. Synthesis of rare earth luminescent nanocrystals β-ALnF 4： E@ALnF 4， wherein A is selected from one of Li + , Na + , K + ; Ln is selected from at least one of Y 3 + , Gd 3+ , La 3+ , Lu 3+ ; E is selected from at least one of Nd 3+ , Yb 3+ , Tm 3+ , Er 3+ ; S2. Synthesis of a thin-layer SiO2 spacer shell: sequentially add a surfactant CO-520 and a rare earth luminescent nanocrystal into cyclohexane and uniformly disperse; add an alkaline solution and stir to form a reverse microemulsion solution; add tetraethyl orthosilicate, seal and stir at room temperature for 15-24 h, then add an alcohol solution to destroy the microemulsion system and centrifugally separate to obtain rare earth luminescent nanoparticles coated with a thin-layer SiO2; S3. Synthesis of a thick-layer SiO2 spacer shell: take the rare earth luminescent nanoparticles coated with a thin-layer SiO2 prepared in S2, disperse in ethanol, add an alkaline solution and uniformly stir, add tetraethyl orthosilicate, seal and stir at room temperature for 15-24 h, then centrifugally separate to obtain rare earth luminescent nanoparticles coated with a thick-layer SiO2; S4. Coating of rare earth luminescent nanoparticles: dilute the rare earth luminescent nanoparticles prepared in S2 or S3, coat on the surface of a silicon wafer, and dry at 70-90 ℃ to obtain a silicon wafer with rare earth luminescent nanoparticles laid thereon; S5. Application of a graphene sealing layer: cut a copper foil of appropriate size to carry graphene, coat PMMA on the surface of the graphene, dry, and then float the copper foil substrate in copper etching solution until the copper foil completely disappears; sequentially transfer the floating graphene-PMMA film into dilute hydrochloric acid and pure water for cleaning; then contact the surface of the silicon wafer prepared in S4 with the floating graphene-PMMA film to make the graphene composite with the surface of the silicon wafer; immerse the graphene-composite silicon wafer in acetone to dissolve the PMMA layer, replace the acetone cleaning solution for multiple times, and then dry to obtain rare earth nanoluminescent particles covered with a graphene sealing layer.

7. The production method according to claim 6, characterized by, In S2, the rare earth doped nanocrystal is b-NaYF4:x%Yb, y%Er@NaYF4; wherein x=5-99.5 and y=0.5-5.

8. The preparation method according to claim 6, characterized in that, In the S1, the rare earth luminescent nanocrystals are prepared by adding Y(CF3COO)3, CF3COONa and E(CF3COO)3 into a mixed solvent of oleic acid / oleylamine / octadecene, heating and stirring under a nitrogen atmosphere, centrifuging to collect the product after the thermal decomposition reaction is completed, obtaining α-NaYF4:E nanocrystals; adding α-NaYF4:E and CF3COONa into a mixed solvent of oleic acid / octadecene, heating and stirring under a nitrogen atmosphere, centrifuging to collect the product after the thermal decomposition reaction is completed, obtaining b-NaYF4:E nanocrystals; mixing the b-NaYF4:E nanocrystals with Y(CF3COO)3 and CF3COONa, adding into a mixed solvent of oleic acid / octadecene, heating and stirring under a nitrogen atmosphere, centrifuging to collect the product after the thermal decomposition reaction is completed, obtaining b-NaYF4:E@NaYF4 nanocrystals.

9. The production method according to claim 8, characterized by, The molar ratio of E(CF3COO)3 to Y(CF3COO)3 in the S1 is b:(1-b), b is in the range of 0 3+ , Yb 3+ , Tm 3+ , Er 3+ , or two of them.

10. The production method according to claim 5, characterized by, In the S2, the concentration of the dispersion liquid obtained by dispersing the rare earth luminescent nanocrystals in cyclohexane is 0.02-0.12 g / ml; the ratio of the use amounts of the dispersion liquid, CO-520, tetraethyl orthosilicate and the alkaline solution is (1-5) ml:(0.1-0.6) g:(10-100) mL:(10-500) mL; and / or, in the S3, the concentration of the dispersion liquid obtained by dispersing the rare earth luminescent nanocrystals coated with a thin layer of SiO2 in ethanol is 0.4-8 mg / ml; the ratio of the use amounts of the dispersion liquid, CO-520, tetraethyl orthosilicate and the alkaline solution is (1-5) ml:(0.1-0.6) g:(10-100) mL:(10-500) mL.

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