CN115181568B - Synthesis of a multilayer core-shell structured composite nanostructured dual-mode luminescent material - Google Patents

Abstract

The invention discloses a rare earth down-converting red light-upconverting green light multilayer core-shell structure nano luminescent material and a preparation method thereof. Firstly, rare earth ions Gd ³⁺ and Eu ³⁺ are uniformly coated on the surface of SiO ₂ microspheres by using a urea homogeneous precipitation method, and then the SiO ₂ shell layer is coated by a method of weak alkaline hydrolysis of tetraethyl orthosilicate, and a core-shell structure precursor SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ is obtained after high-temperature calcination; rare earth ions Gd ³⁺ , Yb ³⁺ , and Er ³⁺ are coated on the surface of the precursor by using a urea hydrolysis method, and the SiO ₂ shell layer is further coated by a method of weak alkaline hydrolysis of tetraethyl orthosilicate, and the obtained product is dispersed in a mixed solution of H ₂ O and ethylene glycol, and ammonium metavanadate is added to make VO ₄ ³⁺ and inner layer RE ³⁺ (RE=Gd ³⁺ , Yb ³⁺ , Er ³⁺ ) and finally calcined at high temperature to obtain multilayer core-shell structure SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ microspheres. The prepared luminescent microspheres have the characteristics of uniform particle size, strong luminescence, good dispersibility, etc., saving rare earth resources, low cost, and environmentally friendly preparation method, simple equipment, high conversion rate, easy industrial production, etc.

Description

Synthesis of a multilayer core-shell structured composite nano dual-mode luminescent material

Technical Field

The present invention belongs to the field of rare earth oxide-vanadate composite nano-luminescent materials, and relates to a composite synthesis method of a multi-layer core-shell structured SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ composite nano-luminescent material (wherein Gd ₂ O ₃ :Eu is a cubic phase and GdVO ₄ :Yb,Er is a tetragonal phase structure), in particular to a method for synthesizing a core-shell structured nano-scale composite luminescent material having both down-conversion (DC) red light cubic phase Gd ₂ O ₃ :Eu and up-conversion (UC) green light tetragonal phase GdVO ₄ :Yb,Er by a low-temperature, low-cost, environmentally friendly method.

Background technique

Due to the unique electronic layer structure of rare earth elements, rare earth compounds exhibit many excellent optical, electrical and magnetic functions, especially rare earth elements have spectral properties that are unmatched by general elements. Rare earth oxides and vanadates are widely used in optoelectronic communications, glass manufacturing industry, display lighting, catalysis, fluorescent probes and other fields due to their high thermal stability, chemical stability and mechanical stability. Recently, core-shell multi-level nanomaterials have the properties of both core materials and shell materials, and their magnetic, optical, mechanical, thermal, electrical and catalytic properties can be improved by regulating the size and composition of their core and shell materials for application in various fields. The research on rare earth oxide and vanadate core-shell multi-level nano/micro materials has potential application prospects. At present, there are few reports on rare earth oxide and vanadate core-shell multi-mode luminescent materials, which mainly focus on the synthesis of dual-mode luminescent materials by uniformly mixing multiple rare earth elements with UC and DC properties into the same material. The synthesis mainly adopts high-temperature hydrothermal synthesis using organic templates or organic solvents, such as reported in T. Vairapperumal, M.Lakshmi, RV Kumar, SK J, MA Kumar, J. Lumin . 2020, 217 , 116761; L.Wang, H. Chen, D. Zhang, D. Zhao, W. Qin, Mater. Lett . 2011, 65 , 504-506; P.Kumar, J. Dwivedi, BK Gupta, J. Mater. Chem. C. 2014, 2 , 10468-10475; AKSingh, SK Singh, BK Gupta, R. Prakash, SB Rai, Dalton. Trans. 2013, 42 , 1065-1072. and other literature. These methods have the disadvantages of complex synthesis methods or non-reusable raw materials, high raw material prices, and environmental pollution; and the rare earth elements with UC and DC properties are uniformly mixed into the same material to obtain dual-mode luminescent materials, resulting in cross relaxation between lanthanide elements, which reduces the luminescence intensity and other disadvantages, which are not conducive to large-scale production and application. Rare earth elements with DC and UC properties are respectively doped into the inner layer or outer layer of the core-shell structure, and _SiO2 shells are used in the middle to avoid cross relaxation between lanthanide elements and thus improve the luminescence intensity. _SiO2 is non-toxic and inexpensive. Using _SiO2 as a core material can save resources; using _SiO2 as a shell material can not only protect the rare earth luminescence center from environmental interference and improve the light efficiency, but also reduce the concentration quenching between rare earth ions and improve the biocompatibility of the sample. Therefore, it is of great significance to develop a low-temperature, low-cost, and environmentally friendly method to synthesize nano/micron multi-level structure oxide and vanadate composite materials with multi-mode luminescence performance of core-shell structure using _SiO2 as core and shell materials.

Summary of the invention

The purpose of the present invention is to provide a _{method for synthesizing a non-toxic, low-cost and size-adjustable rare earth oxide and vanadate core-shell structure SiO 2 @Gd 2} O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ composite nano-luminescent material with SiO 2 as core and shell materials, wherein the material has both down-conversion red light and up-conversion green light emission.

The specific steps for preparing the core-shell structure SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ composite nanoluminescent material are as follows:

1. Preparation of SiO2 _microspheres : Add 4 mL _H2O and 35 mL anhydrous ethanol to a 100 mL round-bottom flask, and adjust the pH to 8-9 with aqueous ammonia. Stir continuously in an oil bath to keep the temperature at 50 ºC, then drop 1.7 mL of ethyl orthosilicate. After 6-8 hours of reaction, centrifuge the reaction solution and dry it at 60-80 ºC for 4-8 hours to obtain _SiO2 microspheres with a diameter of ~105 nm.

2. Preparation of SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres: Weigh 0.2 g of the SiO ₂ microspheres prepared above into a 100 mL round-bottom flask, add a certain amount of deionized H ₂ O and anhydrous ethanol, and then ultrasonically disperse for 8~10 min, add a certain amount of Gd(NO ₃ ) ₃ ·6H ₂ O and Eu(NO ₃ ) ₃ ·6H ₂ O in a molar ratio of 95%:5%, stir for 5 min, then add 0.3 g of urea, stir for 20~30 min to fully dissolve it, reflux in an oil bath at 85 ºC for 12~18 h, centrifuge the reaction solution, and dry the product at a temperature range of 60~80°C for 4~8 hours to obtain the precursor SiO ₂ @RE. Then weigh 0.2 g of the precursor SiO ₂ @RE white powder into a 100 mL beaker, add a certain amount of deionized H ₂ O and anhydrous ethanol for ultrasonic dispersion for 3-5 minutes, adjust the pH value to 8~9, transfer to an oil bath and stir, add a certain amount of tetraethyl orthosilicate dropwise, react at room temperature for 3 hours, and then centrifuge and separate. The product is placed in a muffle furnace and calcined at 900 ºC for 4 hours to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres.

3. Preparation of SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ microspheres: Weigh 0.2 g of the prepared SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres into a 100 mL round-bottom flask, add a certain amount of deionized H ₂ O and anhydrous ethanol, and then ultrasonically disperse for 10 min. Then, add 0.78 mmol Gd(NO ₃ ) ₃ ·6H ₂ O, 0.20 mmol Yb(NO ₃ ) ₃ ·6H ₂ O, 0.02 mmolEr(NO ₃ ) ₃ ·6H ₂ O and 0.3 g urea in sequence, stir to dissolve, and reflux in an oil bath at 85 ºC for 12 h. After the reaction was completed, the reaction solution was centrifuged and dried at 60°C to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE=Gd ³⁺ ,Yb ³⁺ ,Er ³⁺ ) microspheres.

Weigh 0.2 g of SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE = Gd ³⁺ , Yb ³⁺ , Er ³⁺ ) microspheres into a 100 mL beaker, add 4 mL H ₂ O, 30 mL anhydrous ethanol and 0.6 mL ammonia water, add 100 μL of tetraethyl orthosilicate after ultrasonic dispersion, react at room temperature for 3 h, then centrifuge and separate, wash with water and alcohol, and then dry to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE = Gd ³⁺ , Yb ³⁺ , Er ³⁺ )@SiO ₂ precursor microspheres.

Weigh 0.2 g of the obtained SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE = Gd ³⁺ , Yb ³⁺ , Er ³⁺ )@SiO ₂ precursor microspheres into a 100 mL round-bottom flask, add 15 mL H ₂ O and 20 mL ethylene glycol, and then ultrasonically disperse for 10 min, then add a certain amount of ammonium metavanadate, and reflux in an oil bath at 100~125 ºC for 6~12 h. After the reaction is completed, the obtained brown-yellow suspension is centrifuged and dried at 60 ºC. Finally, the dried powder is placed in a muffle furnace and calcined at 900 ºC for 4 h to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ microspheres. (The water used in the patent of this invention is deionized water)

The material preparation method of the present invention is environmentally friendly, has simple equipment and simple synthesis steps; the raw materials are inexpensive and no expensive surfactant is required as a template; it has the characteristics of not using toxic and harmful organic solvents, not polluting the environment, saving energy, having a high conversion rate, and being easy for industrial production, and is an ideal green process with good repeatability.

Description of the drawings:

Figures 1a and 1b are the XRD spectra and TEM images of the SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ product corresponding to Example 1, respectively. Figures 1c and 1d are the XRD spectra and TEM images of the SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ product corresponding to Example 2, respectively. The red and blue lines in the XRD graph are the cubic phase Gd ₂ O ₃ standard card JCPDS No. 12-0797 and the square phase GdVO ₄ standard card JCPDS No. 17-0260, respectively. It can be seen from the figure that the samples obtained in the two embodiments are mixed phases of cubic phase Gd ₂ O ₃ and square phase GdVO ₄ , and the crystallinity is good. The TEM image shows that the samples obtained in the two embodiments have a clear multilayer core-shell structure and good dispersibility.

Figure 2 is the up-conversion emission spectrum of the synthesized SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ sample. From this figure, it can be seen that the synthesized sample has good up-conversion luminescence performance, and the strongest emission peak is located at 552nm, which is green light emission.

Figure 3 is the down-conversion fluorescence spectrum of the synthesized SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ sample. From this figure, it can be seen that the synthesized sample has good down-conversion fluorescence performance, and the strongest emission peak is located at 619nm, which is red light emission.

Figure 4 shows the CIE chromaticity coordinates of the synthesized SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ sample and the luminescence photograph of the sample water dispersion. From this figure, it can be seen that the sample has good up-conversion green light and down-conversion red light luminescence performance.

Detailed ways:

Embodiment 1

(1) Add 4 mL of H ₂ O and 35 mL of anhydrous ethanol to a 100 mL round-bottom flask, and adjust the pH value to 8-9 with aqueous ammonia. Stir continuously in an oil bath to keep the temperature at 50 ºC, then add 1.7 mL of ethyl orthosilicate dropwise. After reacting for 6-8 hours, centrifuge the reaction solution, wash it with water and anhydrous ethanol three times, and dry it at 60-80 ºC for 4-8 hours to obtain SiO ₂ microspheres with a diameter of ~105 nm.

(2) Weigh 0.2 g of SiO ₂ microspheres with a diameter of ~105 nm and disperse them in 20 mL H ₂ O and 15 mL anhydrous ethanol, add 0.3 g of urea, 0.95 mmol Gd(NO ₃ ) ₃ ·6H ₂ O and 0.05 mmol Eu(NO ₃ ) ₃ ·6H ₂ O, stir at room temperature for 30 min to dissolve, react in an oil bath at 85°C for 12 hours, centrifuge, wash with water and anhydrous ethanol three times, and dry at 60 ºC to obtain SiO ₂ @RE precursor. Weigh 0.2 g of SiO ₂ @RE precursor, add 4 mL H ₂ O, 30 mL anhydrous ethanol and 0.6 mL ammonia water, ultrasonically disperse, add 100 μL of tetraethyl orthosilicate, react at room temperature for 3 h, centrifuge, wash with water and anhydrous ethanol three times, and dry at 60 ºC to obtain SiO ₂ @RE@SiO ₂ precursor. The SiO ₂ @RE@SiO ₂ precursor was placed in a muffle furnace and heated from room temperature to 900°C at a heating rate of 9°C/min and calcined for 4 h to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres.

(3) Weigh 0.2 g SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres into a 100 mL round-bottom flask, add 20 mL H ₂ O and 15 mL anhydrous ethanol, and disperse under ultrasonication for 10 min. Then add 0.78 mmol Gd(NO ₃ ) ₃ ·6H ₂ O, 0.20 mmol Yb(NO ₃ ) ₃ ·6H ₂ O, 0.02 mmol Er(NO ₃ ) ₃ ·6H ₂ O and 0.3 g urea in sequence. Stir and dissolve. Reverse the reaction in an oil bath at 85 ºC for 12 h, then centrifuge and wash with water and anhydrous ethanol three times. Then dry at 60 ºC to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE = Gd ³⁺ , Yb ³⁺ , Er ³⁺ ) microspheres. Take 0.2 g of SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE=Gd ³⁺ ,Yb ³⁺ ,Er ³⁺ ) microspheres in a 100 mL beaker, add 4 mL H ₂ O, 30 mL anhydrous ethanol and 0.6 mL ammonia water, add 100 μL of tetraethyl orthosilicate after ultrasonic dispersion, react at room temperature for 3 h, then centrifuge and wash three times with water and anhydrous ethanol, then dry at 60 ºC to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE@SiO ₂ (RE=Gd ³⁺ ,Yb ³⁺ ,Er ³⁺ ) precursor microspheres.

0.2 g of SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE@SiO ₂ (RE=Gd ³⁺ ,Yb ³⁺ ,Er ³⁺ ) precursor microspheres were weighed into a 100 mL round-bottom flask, 15 mL of H ₂ O and 20 mL of ethylene glycol were added, and ultrasonic dispersion was performed for 10 min. Then 0.15 g of ammonium metavanadate was added, and the mixture was refluxed in an oil bath at 125 ºC for 6 h, centrifuged, washed with water and anhydrous ethanol for 3 times, and dried at 60 ºC. The dried sample was placed in a muffle furnace and heated from room temperature to 900°C at a heating rate of 9 °C/min for 4 h to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ microspheres.

Embodiment 2

(1) Add 4 mL of H ₂ O and 35 mL of anhydrous ethanol to a 100 mL round-bottom flask, and adjust the pH value to 8-9 with aqueous ammonia. Stir continuously in an oil bath to keep the temperature at 50 ºC, then add 1.7 mL of ethyl orthosilicate dropwise. After reacting for 6-8 hours, centrifuge the reaction solution, wash it with water and anhydrous ethanol three times, and dry it at 60-80 ºC for 4-8 hours to obtain SiO ₂ microspheres with a diameter of ~105 nm.

(2) Weigh 0.2 g of SiO ₂ microspheres with a diameter of ~105 nm and disperse them in 25 mL H ₂ O and 10 mL anhydrous ethanol, add 0.3 g of urea, 0.475 mmol Gd(NO ₃ ) ₃ ·6H ₂ O and 0.025 mmol Eu(NO ₃ ) ₃ ·6H ₂ O, stir at room temperature for 20 min to dissolve, react in an oil bath at 85°C for 18 hours, centrifuge, wash with water and anhydrous ethanol three times, and dry at 80 ºC to obtain SiO ₂ @RE precursor. Weigh 0.2 g of SiO ₂ @RE precursor, add 2 mL H ₂ O, 30 mL anhydrous ethanol and 0.6 mL ammonia water, ultrasonically disperse, add 100 μL of tetraethyl orthosilicate, react at room temperature for 6 h, centrifuge, wash with water and anhydrous ethanol three times, and dry at 80 ºC to obtain SiO ₂ @RE@SiO ₂ precursor. The SiO ₂ @RE@SiO ₂ precursor was placed in a muffle furnace and heated from room temperature to 900°C at a heating rate of 9°C/min and calcined for 4 h to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres.

(3) Weigh 0.2 g SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ microspheres into a 100 mL round-bottom flask, add 20 mL H ₂ O and 15 mL anhydrous ethanol, and disperse under ultrasonication for 10 min. Then add 0.78 mmol Gd(NO ₃ ) ₃ ·6H ₂ O, 0.20 mmol Yb(NO ₃ ) ₃ ·6H ₂ O, 0.02 mmol Er(NO ₃ ) ₃ ·6H ₂ O and 0.3 g urea in sequence. Stir and dissolve. Reverse the reaction in an oil bath at 85 ºC for 12 h, and then centrifuge. Wash the mixture three times with water and anhydrous alcohol, and then dry it at 80 ºC to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE ( ^RE = Gd ³⁺ , Yb ³⁺ , Er ³⁺ ) microspheres. Weigh 0.2 g of SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE=Gd ³⁺ ,Yb ³⁺ ,Er ³⁺ ) microspheres into a 100 mL beaker, add 4 mL of H ₂ O, 30 mL of anhydrous ethanol and 0.6 mL of ammonia water, add 100 μL of tetraethyl orthosilicate after ultrasonic dispersion, react at room temperature for 3 h and then centrifuge. Wash three times with water and anhydrous ethanol and then dry at 80 ºC to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE@SiO ₂ (RE=Gd ³⁺ ,Yb ³⁺ ,Er ³⁺ ) precursor microspheres.

0.2 g SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @RE (RE = Gd ³⁺ , Yb ³⁺ , Er ³⁺ ) @SiO ₂ precursor microspheres were weighed into a 100 mL round-bottom flask, 15 mL H ₂ O and 20 mL ethylene glycol were added, and ultrasonic dispersion was performed for 10 min. Then 0.10 g ammonium metavanadate was added, and the mixture was refluxed in an oil bath at 100 ºC for 12 h, centrifuged, washed with water and anhydrous ethanol three times, and dried at 60 ºC. The dried sample was placed in a muffle furnace and heated from room temperature to 900°C at a heating rate of 9 °C/min for 4 h to obtain SiO ₂ @Gd ₂ O ₃ :Eu@SiO ₂ @GdVO ₄ :Yb,Er@SiO ₂ microspheres.

Claims (3)

1. A synthetic method of a SiO ₂@Gd₂O₃:Eu@SiO₂@GdVO₄:Yb,Er@SiO₂ composite nano luminescent material with a multilayer core-shell structure capable of emitting down-converted red light and up-converted green light is characterized in that: (1) By means ofSynthesizing SiO ₂ microsphere with a core diameter of 105nm by a method, depositing rare earth ions Gd ³⁺ and Eu ³⁺ on the surface of the SiO ₂ microsphere by a urea hydrolysis coprecipitation method, and coating a SiO ₂ shell layer with a thickness of 8nm by an ethyl orthosilicate hydrolysis method to obtain the SiO ₂@RE@SiO₂ microsphere; (2) Then, rare earth ions Gd ³⁺、Yb³⁺ and Er ³⁺ are deposited on the surface of the SiO ₂@RE@SiO₂ microsphere by utilizing a urea hydrolysis coprecipitation method, and SiO ₂ shell layers with the thickness of 8nm are coated; (3) The GdVO ₄:Yb and Er layers are formed by combining VO ₄ ^3- ions with inner rare earth ions Gd ³⁺、Yb³⁺ and Er ³⁺, gdVO ₄:Yb and Er layers are obtained by calcining at 900 ℃ to obtain the multi-layer core-shell structure SiO ₂@Gd₂O₃:Eu@SiO₂@GdVO₄:Yb,Er@SiO₂ composite nano luminescent material with down-conversion red light emission Gd ₂O₃:Eu layers and up-conversion green light emission, and the specific process conditions are as follows:

(1) Adding 4mL of H ₂ O and 35mL of absolute ethyl alcohol into a 100mL round-bottom flask, regulating the pH value to 8-9 by ammonia water, continuously stirring in an oil bath kettle to keep the temperature at 50 ℃, then dropwise adding 1.7mL of tetraethoxysilane, centrifugally separating reaction liquid after reacting for 6-8 hours, washing water and absolute ethyl alcohol for 3 times, and drying at 60-80 ℃ for 4-8 hours to obtain SiO ₂ microspheres with the diameter of 105 nm;

(2) 0.2g of SiO ₂ microsphere with the diameter of 105nm is weighed and dispersed in 20mL of H ₂ O and 15mL of absolute ethyl alcohol, 0.3g of urea and 0.95mmol of Gd (NO ₃)₃·6H₂ O and 0.05mmol of Eu (NO ₃)₃·6H₂ O are added, stirred and dissolved at normal temperature, reacted in an oil bath at 85 ℃ for 12 hours, centrifugally separated, washed by water and absolute ethyl alcohol for 3 times and dried at 60 ℃, 0.2g of dried sample is weighed, 4mL of H ₂ O, 30mL of absolute ethyl alcohol and 0.6mL of ammonia water are added, 100 mu L of tetraethoxysilane is added after ultrasonic dispersion, centrifugally separated after reaction for 3 hours at normal temperature, washed by water and absolute ethyl alcohol for 3 times and dried to obtain a precursor of SiO ₂@Gd³⁺,Eu³⁺@SiO₂, and then the precursor is calcined at 900 ℃ for 4 hours in a muffle furnace to obtain SiO ₂@Gd₂O₃:Eu@SiO₂ microsphere;

(3) Weighing 0.2g of SiO ₂@Gd₂O₃:Eu@SiO₂ microsphere into a 100mL round bottom flask, adding 20mL of H ₂ O and 15mL of absolute ethyl alcohol, performing ultrasonic dispersion for 10min, sequentially adding 0.78mmol Gd(NO₃)₃·6H₂O、0.20mmol Yb(NO₃)₃·6H₂O、0.02mmol Er(NO₃)₃·6H₂O and 0.3g of urea, stirring for dissolution, performing reflux reaction at 85 ℃ in an oil bath for 12H, performing centrifugal separation, washing with water and absolute ethyl alcohol for 3 times, and drying at 60 ℃ to obtain SiO ₂@Gd₂O₃:Eu@SiO₂@Gd³⁺,Yb³⁺,Er³⁺ microsphere; weighing 0.2g of SiO ₂@Gd₂O₃:Eu@SiO₂@Gd³⁺,Yb³⁺,Er³⁺ microsphere in a 100mL beaker, adding 4mL of H ₂ O, 30mL of absolute ethyl alcohol and 0.6mL of ammonia water, performing ultrasonic dispersion, then dropwise adding 100 mu L of tetraethoxysilane, reacting at normal temperature for 3H, centrifuging, washing with water and absolute ethyl alcohol for 3 times, and drying at 60 ℃ to obtain SiO ₂@Gd₂O₃:Eu@SiO₂@Gd³⁺,Yb³⁺,Er³⁺@SiO₂ precursor microsphere; and weighing 0.2g SiO₂@Gd₂O₃:Eu@SiO₂@Gd³⁺,Yb³⁺,Er³⁺@SiO₂ precursor microspheres in a 100mL round-bottom flask, adding 15mL of H ₂ O and 20mL of ethylene glycol, performing ultrasonic dispersion for 10min, adding 0.15g of ammonium metavanadate, performing reflux reaction at 125 ℃ in an oil bath for 6H, centrifuging, washing with water and absolute ethyl alcohol for 3 times, drying at 60 ℃, and finally placing the dried powder in a muffle furnace, heating to 900 ℃ from room temperature at a heating rate of 9 ℃/min, and calcining for 4H to obtain the SiO ₂@Gd₂O₃:Eu@SiO₂@GdVO₄:Yb,Er@SiO₂ microspheres.

2. The method for synthesizing the SiO ₂@Gd₂O₃:Eu@SiO₂@GdVO₄:Yb,Er@SiO₂ composite nano luminescent material with the multilayer core-shell structure capable of emitting down-converted red light and up-converted green light, which is characterized in that: the diameter of the SiO ₂ core used is 105nm; the SiO ₂ microsphere surface is deposited with rare earth ions Gd ³⁺ and Eu ³⁺, and then the surface is coated with a SiO ₂ shell layer with the thickness of 8nm, so as to avoid fluorescence quenching caused by cross relaxation phenomenon with the rare earth ions Gd ³⁺、Yb³⁺ and Er ³⁺ coated subsequently.

3. The method for synthesizing the SiO ₂@Gd₂O₃:Eu@SiO₂@GdVO₄:Yb,Er@SiO₂ composite nano luminescent material with the multilayer core-shell structure capable of emitting down-converted red light and up-converted green light, which is characterized in that: after rare earth ions Gd ³⁺、Yb³⁺ and Er ³⁺ are deposited on the surface of SiO ₂@Gd₂O₃:Eu@SiO₂ microsphere by urea hydrolysis, siO ₂ shell layer with the thickness of 8nm is coated, and GdVO ₄:Yb and Er are coated on the surface of SiO ₂@Gd₂O₃:Eu@SiO₂ microsphere by ammonium metavanadate substitution reaction to obtain the multilayer core-shell structure product.