Rare earth up-conversion luminescent material with three-layer core-shell structure as well as preparation method and application of rare earth up-conversion luminescent material

Abstract

The invention provides a three-layer core-shell structure rare earth up-conversion luminescent material as well as a preparation method and application thereof, and relates to the technical field of luminescent materials. The invention provides a rare earth up-conversion luminescent material with a three-layer core-shell structure. NaYF4: Er < 3 + > is taken as a core, NaYF4: Yb < 3 + > is taken as a middle shell layer, and NaYF4 is taken as an outer shell layer. The novel three-layer core-shell structure provided by the invention can reduce the surface defects of the material, solves the problem that the material is easy to quench, has strong single-band red light emission performance, greatly improves the up-conversion luminescence performance of the material compared with the existing material, shows excellent luminescence performance and good biological stability, and is suitable for industrial production. The material can be applied to the fields of biomedicine, infrared detection and the like, and a new material is provided for further expanding the application of the material in the light-emitting field.

Description

Technical Field

[0001] The present invention relates to the technical field of luminescent materials, and particularly relates to a rare earth upconversion luminescent material with a three-layer core-shell structure, a preparation method thereof, and an application thereof. Background Art

[0002] Rare earth ion-doped upconversion micro-nano luminescent materials have attracted extensive attention from researchers due to their unique luminescent properties such as large Stokes shift and narrow-band emission. In recent years, researchers have enhanced and regulated the upconversion luminescence intensity and spectral characteristics of materials through various methods such as ion co-doping technology and constructing core-shell structures. For example, there have been reports on core-shell structures such as NaYF 4 :Gd / Tm / Er@CdTe, NaYF 4 :Er / Yb / Gd@NaGdF 4 、NaYF 4 :Er / Yb@NaGdF 4 However, due to the existence of surface defects in the above luminescent materials, the materials are prone to quenching. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a rare earth upconversion luminescent material with a three-layer core-shell structure, a preparation method thereof, and an application thereof. The rare earth upconversion luminescent material with a three-layer core-shell structure provided by the present invention can reduce the surface defects of the material, and the material is not prone to quenching.

[0004] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a rare earth upconversion luminescent material with a three-layer core-shell structure, having a core-middle shell-outer shell structure, with NaYF 4 :Er 3+ as the core, NaYF 4 :Yb 3+ as the middle shell layer, and NaYF 4 as the outer shell layer.

[0006] Preferably, the molar content of Er element in the NaYF 4 :Er 3+ and NaYF 4 :Yb 3+ is 1-10%.

[0007] Preferably, the molar content of Yb element in the NaYF 4 :Er 3+ and NaYF 4 :Yb 3+ is 10-19%.

[0008] Preferably, the thickness of the core is 60-70 nm, the thickness of the middle shell layer is 5-10 nm, and the thickness of the outer shell layer is 5-10 nm.

[0009] The present invention also provides a preparation method of the three-layer core-shell structured rare earth upconversion luminescent material described in the above technical solution, including the following steps:

[0010] (1) Mix an aqueous NaOH solution, oleic acid, ethanol, a yttrium source, a ytterbium source, NaF and NaYF 4 :Er 3+ nanomaterials, carry out a solvothermal reaction, and form a NaYF 4 :Er 3+ layer on the surface of the nanomaterials to obtain NaYF 4 :Yb 3+ ; 4 :Er 3+ @NaYF 4 :Yb 3+ ;

[0011] (2) Mix an aqueous NaOH solution, oleic acid, ethanol, a yttrium source, NaF and NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ and carry out a solvothermal reaction to form a NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ layer on the surface to obtain the three-layer core-shell structured rare earth upconversion luminescent material. 4

[0012] Preferably, in step (1), the molar ratio of the NaF and NaYF 4 :Er 3+ nanomaterials is 1:1-2;

[0013] The molar ratio of the NaF and NaOH in the aqueous NaOH solution is 1:0.4-6; the concentration of the aqueous NaOH solution is 0.2-0.5 g / mL;

[0014] The molar ratio of the NaF and yttrium in the yttrium source is 1:0.1-2; the yttrium source includes yttrium oxide and / or yttrium salt;

[0015] The molar ratio of the NaF and ytterbium in the ytterbium source is 1:0.02-0.5; the ytterbium source includes ytterbium oxide and / or ytterbium salt;

[0016] The ratio of the amount of substance of the NaF and the volume of ethanol is 1 mmol:1.25-2 mL;

[0017] The molar ratio of the amount of substance of NaF to the volume of oleic acid is 1 mmol: 2.5 - 5 mL;

[0018] The temperature of the solvothermal reaction is 180 - 200 °C, the time is 8 - 10 h, and the pressure is 2 - 3 MPa.

[0019] Preferably, in step (2), the molar ratio of NaF to NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ is 1:1 - 2;

[0020] The molar ratio of the amount of substance of NaF to NaOH in the NaOH aqueous solution is 1:0.4 - 6; the concentration of the NaOH aqueous solution is 0.2 - 0.5 g / mL;

[0021] The molar ratio of the amount of substance of NaF to yttrium in the yttrium source is 1:0.1 - 2; the yttrium source includes yttrium oxide and / or yttrium salt;

[0022] The molar ratio of the amount of substance of NaF to the volume of ethanol is 1 mmol: 1.25 - 2 mL;

[0023] The molar ratio of the amount of substance of NaF to the volume of oleic acid is 1 mmol: 2.5 - 5 mL;

[0024] The temperature of the solvothermal reaction is 180 - 200 °C, the time is 8 - 10 h, and the pressure is 2 - 3 MPa.

[0025] Preferably, the preparation method of the NaYF 4 :Er 3+ nanomaterial comprises the following steps:

[0026] Perform a solvothermal reaction on the NaOH aqueous solution, oleic acid, ethanol, yttrium source, erbium source, and NaF to obtain NaYF 4 :Er 3+ nanomaterial.

[0027] Preferably, the molar ratio of the amount of substance of NaF to NaOH in the NaOH aqueous solution is 1:0.4 - 6; the concentration of the NaOH aqueous solution is 0.2 - 0.5 g / mL;

[0028] The molar ratio of the amount of substance of NaF to yttrium in the yttrium source is 1:0.1 - 2; the yttrium source includes yttrium oxide and / or yttrium salt;

[0029] The molar ratio of the amount of substance of NaF to erbium in the erbium source is 1:0.004 - 0.1; the erbium source includes erbium oxide and / or erbium salt;

[0030] The molar amount of NaF and the volume of ethanol are in a ratio of 1 mmol: 1.25 - 2 mL;

[0031] The molar amount of NaF and the volume of oleic acid are in a ratio of 1 mmol: 2.5 - 5 mL;

[0032] The temperature of the solvothermal reaction is 180 - 200 °C, the time is 8 - 10 h, and the pressure is 2 - 3 MPa.

[0033] The present invention also provides an application of the three - layer core - shell structure rare - earth up - conversion luminescent material described in the above technical solution or the three - layer core - shell structure rare - earth up - conversion luminescent material prepared by the preparation method described in the above technical solution in infrared detection or the preparation of biomedical materials.

[0034] The present invention provides a three - layer core - shell structure rare - earth up - conversion luminescent material (denoted as NaYF 4 :Er 3+ @NaYF 4 :Yb 3 + @NaYF 4 ), which has a core - middle - shell - outer - shell structure. Taking NaYF 4 :Er 3+ as the core, taking NaYF 4 :Yb 3+ as the middle - shell layer, and taking NaYF 4 as the outer - shell layer. The present invention uses the NaYF 4 :Er 3+ core and the NaYF 4 :Yb 3+ middle - shell layer as the sensitization layer. By virtue of the organic combination of the active NaYF 4 :Yb 3+ middle - shell layer and the core NaYF 4 :Er 3+ , the interfacial energy transfer between Yb 3+ ions in the sensitization layer and Er 3+ in the host lattice further improves the emission intensity of red and green light of Er 3+ ions. The outer - shell layer NaYF 4 plays a role in reducing surface defects. The novel three - layer core - shell structure provided by the present invention can reduce the surface defects of the material, solve the problem of easy quenching of the material, has strong single - band red - light emission performance, and the up - conversion luminescence performance of the material is greatly improved compared with existing materials, providing new materials for further expanding its application in the luminescence field. The three - layer core - shell structure rare - earth up - conversion luminescent material provided by the present invention exhibits excellent luminescence performance and good biological stability, and can be applied to fields such as biomedicine and infrared detection.

[0035] Through the effective comparison of the up-conversion emission spectra intensities of different structures, the optimal enhancement structure system and ion doping concentration are explored. Description of the Drawings

[0036] Figure 1 Transmission electron microscope image of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Example 1;

[0037] Figure 2 Transmission electron microscope image of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ prepared in Example 1;

[0038] Figure 3 Transmission electron microscope image of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Example 1;

[0039] Figure 4 Up-conversion luminescence spectrum of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Example 1;

[0040] Figure 5 Up-conversion luminescence spectra of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Examples 1-6;

[0041] Figure 6 Up-conversion luminescence spectrum of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 and NaYF 4 :Er@NaYF 4 :Yb and NaYF 4 :Er 3+ / Yb 3+Upconversion luminescence spectra of the nanoparticles;

[0042] Figure 7 NaYF prepared for Example 1 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 Quantum yield graph;

[0043] Figure 8 NaYF prepared for Comparative Example 1 4 :Er 3+ / Yb 3+ Quantum yield graph;

[0044] Figure 9 NaYF prepared for Example 1 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 and NaYF 4 :Er@NaYF 4 :Yb and NaYF prepared for Comparative Example 1 4 :Er 3+ / Yb 3+ XRD pattern of the nanoparticles. Detailed implementation mode

[0045] The present invention provides a rare earth upconversion luminescent material with a three-layer core-shell structure, having a core-middle shell-outer shell structure, with NaYF 4 :Er 3+ as the core, NaYF 4 :Yb 3+ as the middle shell layer, and NaYF 4 as the outer shell layer.

[0046] In the present invention, the molar content of Er element in the NaYF 4 :Er 3+ and NaYF 4 :Yb 3+ is preferably 1 to 10, and can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% in specific embodiments.

[0047] In the present invention, the molar content of Er element in the NaYF 4 :Er 3+ and NaYF 4 :Yb 3+The molar content of Yb element is preferably 10-19%, and in specific embodiments, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0048] In the present invention, the NaYF 4 :Er 3+ and NaYF 4 :Yb 3+ The total molar content of Er element and Yb element is preferably 20%.

[0049] In the present invention, the thickness of the core is preferably 60-75 nm, and in specific embodiments, it can be 60 nm, 62 nm, 65 nm, 68 nm or 70 nm.

[0050] In the present invention, the thickness of the intermediate shell layer is preferably 5-10 nm, and in specific embodiments, it can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm. In the present invention, the mass ratio of the core to the intermediate shell layer is preferably 10-15:1, and in specific embodiments, it can be 10:1, 11:1, 12:1, 13:1, 14:1, or 15:1.

[0051] In the present invention, the thickness of the outer shell layer is 5-10 nm, and in specific embodiments, it can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm. In the present invention, the mass ratio of the core to the intermediate shell layer and the outer shell layer is preferably 10-15:1, and in specific embodiments, it can be 10:1, 11:1, 12:1, 13:1, 14:1, or 15:1.

[0052] In the present invention, the three-layer core-shell structured rare earth upconversion luminescent material is preferably a nanorod structure.

[0053] The present invention also provides a preparation method of the three-layer core-shell structured rare earth upconversion luminescent material described in the above technical solution, including the following steps:

[0054] (1) Mix an aqueous NaOH solution, oleic acid, ethanol, a yttrium source, a ytterbium source, NaF and a NaYF 4 :Er 3+ nanomaterial, carry out a solvothermal reaction, and form a NaYF 4 :Er 3+ layer on the surface of the NaYF 4 :Yb 3+ nanomaterial to obtain NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ ;

[0055] (2) Mix an aqueous NaOH solution, oleic acid, ethanol, a yttrium source, NaF, and NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ and conduct a solvothermal reaction to form a layer of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ on the surface to obtain the rare earth upconversion luminescent material with a three - layer core - shell structure. 4

[0056] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0057] First, the preparation method of the NaYF 4 :Er 3+ nanomaterials will be described in detail below.

[0058] In the present invention, the preparation method of the NaYF 4 :Er 3+ nanomaterials preferably includes the following steps: Mix an aqueous NaOH solution, oleic acid, ethanol, a yttrium source, an erbium source, and NaF and conduct a solvothermal reaction to obtain the NaYF 4 :Er 3+ nanomaterials.

[0059] In the present invention, the NaYF 4 :Er 3+ nanomaterials preferably include NaYF 4 :Er 3+ nanorods.

[0060] In the present invention, the molar ratio of NaOH in the NaF and the aqueous NaOH solution is preferably 1:0.4 - 6, and in specific embodiments, it can be 1:0.4, 1:1, 1:1.5, 1:1.875, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, or 1:6. In the present invention, the concentration of the aqueous NaOH solution is preferably 0.2 - 0.5 g / mL, and in specific embodiments, it can be 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, or 0.5 g / mL.

[0061] ​In the present invention, the molar ratio of yttrium in the NaF and yttrium source is preferably 1:0.1 to 2, and in specific embodiments, it can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2. In the present invention, the yttrium source preferably includes yttrium oxide and / or yttrium salt; the yttrium oxide is preferably Y 2 O 3 ; the yttrium salt preferably includes YF 3 、YF 4 and Y(NO 3 )·6H 2 O, or one or more of them.

[0062] In the present invention, the molar ratio of erbium in the NaF and erbium source is preferably 1:0.004 to 0.1, and in specific embodiments, it can be 1:0.004, 1:0.005, 1:0.008, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09 or 1:0.1. In the present invention, the erbium source preferably includes erbium oxide and / or erbium salt; the erbium oxide is preferably Er 2 O 3 ; the erbium salt preferably includes ErF 3 、ErF 4 and Er(NO 3 )·5H 2 O, or one or more of them.

[0063] In the present invention, the ratio of the amount of substance of NaF to the volume of ethanol is preferably 1 mmol:1.25 to 2 mL, and in specific embodiments, it can be 1 mmol:1.25 mL, 1 mmol:1.3 mL, 1 mmol:1.4 mL, 1 mmol:1.5 mL, 1 mmol:1.6 mL, 1 mmol:1.7 mL, 1 mmol:1.8 mL, 1 mmol:1.9 mL or 1 mmol:2 mL.

[0064] In the present invention, the ratio of the amount of substance of NaF to the volume of oleic acid is preferably 1 mmol:2.5 to 5 mL, and in specific embodiments, it can be 1 mmol:2.5 mL, 1 mmol:3 mL, 1 mmol:3.5 mL, 1 mmol:4 mL, 1 mmol:4.5 mL or 1 mmol:5 mL.

[0065] In the present invention, the mixing preferably includes: first stirring and mixing ethanol, oleic acid and an aqueous NaOH solution to obtain a mixed solution; second stirring and mixing the mixed solution with a yttrium source, an erbium source and NaF to obtain a gel-like mixture. In the present invention, the time for the first stirring and mixing is preferably 30 to 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min or 60 min. In the present invention, the time for the second stirring and mixing is preferably 30 to 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min or 60 min. In the present invention, the temperature for the mixing is preferably room temperature.

[0066] In the present invention, the temperature for the solvothermal reaction is preferably 180 to 200 °C, and in specific embodiments, it can be 180 °C, 185 °C, 190 °C, 195 °C or 200 °C; the time for the solvothermal reaction is preferably 8 to 10 h, and in specific embodiments, it can be 8 h, 8.5 h, 9 h, 9.5 h or 10 h; the pressure for the solvothermal reaction is preferably 2 to 3 MPa, and in specific embodiments, it can be 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa or 3 MPa; the solvothermal reaction is preferably carried out in a stainless steel autoclave.

[0067] After completing the solvothermal reaction, the present invention preferably further includes: performing solid-liquid separation on the reaction system obtained from the solvothermal reaction, washing the obtained solid component with ethanol and then drying it to obtain NaYF 4 :Er 3+ nanomaterials. In the present invention, the number of times of washing with ethanol is preferably 3 to 5 times, and in specific embodiments, it can be 3 times, 4 times or 5 times. In the present invention, the temperature for drying is preferably 60 to 80 °C, and in specific embodiments, it can be 60 °C, 65 °C, 70 °C, 75 °C or 80 °C; the time for drying is preferably 6 to 8 h, and in specific embodiments, it can be 6 h, 6.5 h, 7 h, 7.5 h or 8 h.

[0068] The present invention mixes an aqueous NaOH solution, oleic acid, ethanol, a yttrium source, a ytterbium source, NaF and NaYF 4 :Er 3+ nanomaterials, performs a solvothermal reaction, and forms a NaYF 4 :Er 3+ layer on the surface of the NaYF 4 :Yb 3+ to obtain NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ .

[0069] In the present invention, the molar ratio of the NaF and NaYF 4 :Er 3+ nanomaterials is preferably 1:1 to 2, and may be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2 in specific embodiments.

[0070] In the present invention, the molar ratio of NaOH in the NaF and NaOH aqueous solution is preferably 1:0.4 to 6, and may be 1:0.4, 1:1, 1:1.5, 1:1.875, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5 or 1:6 in specific embodiments. In the present invention, the concentration of the NaOH aqueous solution is preferably 0.2 to 0.5 g / mL, and may be 0.2 g / mL, 0.3 g / mL, 0.4 g / mL or 0.5 g / mL in specific embodiments.

[0071] In the present invention, the molar ratio of yttrium in the NaF and yttrium source is preferably 1:0.1 to 2, and may be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2 in specific embodiments. In the present invention, the yttrium source preferably includes yttrium oxide and / or yttrium salt; the yttrium oxide is preferably Y 2 O 3 ; the yttrium salt preferably includes YF 3 , YF 4 and / or Y(NO 3 )·6H 2 O.

[0072] In the present invention, the molar ratio of ytterbium in the NaF and ytterbium source is preferably 1:0.02 to 0.5, and may be 1:0.02, 1:0.04, 1:0.045, 1:0.05, 1:0.8, 1:0.1, 1:0.2, 1:0.3, 1:0.4 or 1:0.5 in specific embodiments. In the present invention, the ytterbium source preferably includes one or more of ytterbium oxide, ytterbium fluoride and ytterbium salt; the ytterbium oxide is preferably Yb 2 O 3 ; the ytterbium salt preferably includes YbF 3 and / or Yb(NO 3 )·5H 2 O.

[0073] In the present invention, the molar amount of NaF and the volume of ethanol are preferably in a ratio of 1 mmol: 1.25 - 2 mL, and in specific embodiments, it can be 1 mmol: 1.25 mL, 1 mmol: 1.3 mL, 1 mmol: 1.4 mL, 1 mmol: 1.5 mL, 1 mmol: 1.6 mL, 1 mmol: 1.7 mL, 1 mmol: 1.8 mL, 1 mmol: 1.9 mL or 1 mmol: 2 mL.

[0074] In the present invention, the molar amount of NaF and the volume of oleic acid are preferably in a ratio of 1 mmol: 2.5 - 5 mL, and in specific embodiments, it can be 1 mmol: 2.5 mL, 1 mmol: 3 mL, 1 mmol: 3.5 mL, 1 mmol: 4 mL, 1 mmol: 4.5 mL or 1 mmol: 5 mL.

[0075] In the present invention, the temperature of the solvothermal reaction is preferably 180 - 200 °C, and in specific embodiments, it can be 180 °C, 185 °C, 190 °C, 195 °C or 200 °C; the time of the solvothermal reaction is preferably 8 - 10 h, and in specific embodiments, it can be 8 h, 8.5 h, 9 h, 9.5 h or 10 h; the pressure of the solvothermal reaction is preferably 2 - 3 MPa, and in specific embodiments, it can be 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa or 3 MPa; the solvothermal reaction is preferably carried out in a stainless steel autoclave.

[0076] In the present invention, the mixing preferably includes: stirring and mixing ethanol, oleic acid and an aqueous NaOH solution for the third time to obtain a mixed solution; stirring and mixing the mixed solution with a yttrium source, a ytterbium source and NaF for the fourth time, and then stirring and mixing with a NaYF 4 :Er 3+ nano - material for the fifth time to obtain a gel - like mixture. In the present invention, the time of the third stirring and mixing is preferably 30 - 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min or 60 min. In the present invention, the time of the fourth stirring and mixing is preferably 30 - 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min or 60 min. In the present invention, the time of the fifth stirring and mixing is preferably 30 - 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min or 60 min. In the present invention, the temperature of the mixing is preferably room temperature.

[0077] After the solvothermal reaction is completed, the present invention preferably further comprises: performing solid-liquid separation on the reaction system obtained by the solvothermal reaction, washing the obtained solid component with ethanol and then drying to obtain NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ In the present invention, the number of ethanol washing is preferably 3 times. In the present invention, the drying temperature is preferably 80° C.; and the drying time is preferably 6 hours.

[0078] Get NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ Then, the present invention combines NaOH aqueous solution, oleic acid, ethanol, yttrium source, NaF and NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ Mix and perform solvothermal reaction in NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ NaYF formed on the surface 4 layer to obtain the three-layer core-shell structure rare earth up-conversion luminescent material.

[0079] In the present invention, the NaF and NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ The molar ratio of is preferably 1:1-2, and in specific embodiments can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2;

[0080] In the present invention, the molar ratio of NaOH in the NaF and NaOH aqueous solutions is preferably 1:0.4-6, and in specific embodiments, it can be 1:0.4, 1:1, 1:1.5, 1:1.875, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5 or 1:6. In the present invention, the concentration of the NaOH aqueous solution is preferably 0.2-0.5 g / mL, and in specific embodiments, it can be 0.2 g / mL, 0.3 g / mL, 0.4 g / mL or 0.5 g / mL.

[0081] In the present invention, the molar ratio of yttrium in the NaF and yttrium source is preferably 1:0.1 to 2, and in specific embodiments, it can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2. In the present invention, the yttrium source preferably includes yttrium oxide and / or yttrium salt; the yttrium oxide is preferably Y 2 O 3 ; the yttrium salt preferably includes YF 3 、YF 4 and Y(NO 3 )·6H 2 O, one or more of them.

[0082] In the present invention, the ratio of the amount of substance of NaF to the volume of ethanol is preferably 1 mmol: 1.25 to 2 mL, and in specific embodiments, it can be 1 mmol: 1.25 mL, 1 mmol: 1.3 mL, 1 mmol: 1.4 mL, 1 mmol: 1.5 mL, 1 mmol: 1.6 mL, 1 mmol: 1.7 mL, 1 mmol: 1.8 mL, 1 mmol: 1.9 mL or 1 mmol: 2 mL.

[0083] In the present invention, the ratio of the amount of substance of NaF to the volume of oleic acid is preferably 1 mmol: 2.5 to 5 mL, and in specific embodiments, it can be 1 mmol: 2.5 mL, 1 mmol: 3 mL, 1 mmol: 3.5 mL, 1 mmol: 4 mL, 1 mmol: 4.5 mL or 1 mmol: 5 mL.

[0084] In the present invention, the mixing preferably includes: stirring and mixing ethanol, oleic acid and NaOH aqueous solution sixthly to obtain a mixed solution; stirring and mixing the mixed solution with the yttrium source and NaF seventhly, and then with NaYF 4 :Er 3+ @NaYF 4 :Yb 3+Perform the eighth stirring and mixing to obtain a gel-like mixture. In the present invention, the time for the sixth stirring and mixing is preferably 30 to 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min, or 60 min. In the present invention, the time for the seventh stirring and mixing is preferably 30 to 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min, or 60 min. In the present invention, the time for the eighth stirring and mixing is preferably 30 to 60 min, and in specific embodiments, it can be 30 min, 40 min, 50 min, or 60 min. In the present invention, the temperature for the mixing is preferably room temperature.

[0085] In the present invention, the temperature for the solvothermal reaction is preferably 180 to 200 °C, and in specific embodiments, it can be 180 °C, 185 °C, 190 °C, 195 °C, or 200 °C; the time for the solvothermal reaction is preferably 8 to 10 h, and in specific embodiments, it can be 8 h, 8.5 h, 9 h, 9.5 h, or 10 h; the pressure for the solvothermal reaction is preferably 2 to 3 MPa, and in specific embodiments, it can be 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa, or 3 MPa; the solvothermal reaction is preferably carried out in a stainless steel autoclave.

[0086] After completing the solvothermal reaction, the present invention preferably further includes: performing solid-liquid separation on the reaction system obtained from the solvothermal reaction, washing the obtained solid component with ethanol and then drying it to obtain a three-layer core-shell structured rare earth upconversion luminescent material. In the present invention, the number of times for washing with ethanol is preferably 3 times. In the present invention, the temperature for drying is preferably 80 °C; the time for drying is preferably 6 h.

[0087] The present invention also provides the application of the three-layer core-shell structured rare earth upconversion luminescent material described in the above technical solution or the three-layer core-shell structured rare earth upconversion luminescent material prepared by the preparation method described in the above technical solution in infrared detection or the preparation of biomedical materials. The three-layer core-shell structured rare earth upconversion luminescent material provided by the present invention exhibits excellent luminescent properties and good biological stability, and can be applied to fields such as biomedicine and infrared detection. The three-layer core-shell structured rare earth upconversion luminescent material provided by the present invention provides an important experimental reference for the related research on constructing materials with excellent single-band red light emission, and provides a new way for further broadening the single-band red light emission of rare earth fluorides.

[0088] In order to further illustrate the present invention, the following examples are used to describe in detail the three-layer core-shell structured rare earth upconversion luminescent material provided by the present invention, its preparation method and application, but they should not be construed as limiting the protection scope of the present invention.

[0089] Among the raw materials used in the following examples and comparative examples, the purity of YNO 3 ·6H 2 O is 99.9%, the purity of ErNO 3 ·6H 2 O is 99.9%, the purity of Yb(NO 3 ) 3 ·5H 2 O is 99.9%, and the purity of other raw materials is above analytical pure grade.

[0090] Example 1

[0091] (1) Preparation of NaYF 4 :Er 3+ nanorods

[0092] At room temperature, 10 mL of ethanol and 20 mL of oleic acid were added to 3 mL of an aqueous NaOH solution with a concentration of 0.2 g / mL, and the mixture was stirred for 30 min to obtain a transparent mixture. Then, 1.6 mmol of Y(NO 3 ) 3 ·6H 2 O, 0.04 mmol of Er(NO 3 ) 3 ·5H 2 O and 8 mmol of NaF were added, and the mixture was stirred for 30 min. The resulting gel-like mixture was transferred to a stainless-steel autoclave and heated at 160 °C for 10 h. After solid-liquid separation, the obtained solid component was washed with ethanol three times and dried at 80 °C for 6 h to obtain NaYF 4 :Er 3+ nanorods.

[0093] (2) Preparation of NaYF 4 :Er@NaYF 4 :Yb

[0094] At room temperature, 10 mL of ethanol and 20 mL of oleic acid were added to 3 mL of an aqueous NaOH solution with a concentration of 0.2 g / mL, and the mixture was stirred for 30 min to obtain a transparent mixture. Then, 1.6 mmol of Y(NO 3 ) 3 ·6H 2 O, 0.36 mmol of Yb(NO 3 ) 3 ·5H 2 O and 8 mmol of NaF were added, and the mixture was stirred for 30 min. Then, the NaYF 4 :Er 3+Nanorods, continue stirring for 30 min. Transfer the obtained gel-like mixture to a stainless-steel autoclave and heat at 160 °C for 10 h. Separate the solid and liquid phases, wash the obtained solid component with ethanol three times, and dry at 80 °C for 6 h to obtain NaYF with a nanocore-shell structure 4 :Er@NaYF4:Yb.

[0095] (3) Preparation of rare-earth conversion nanophosphor (NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 )

[0096] At room temperature, add 10 mL of ethanol and 20 mL of oleic acid to 3 mL of an aqueous NaOH solution with a concentration of 0.2 g / mL, stir for 30 min to obtain a transparent mixture, add 1.6 mmol of Y(NO 3 ) 3 ·6H 2 O and 8 mmol of NaF, stir for 30 min, add the NaYF4:Er@NaYF prepared in step (1) 4 :Yb, continue stirring for 30 min. Transfer the obtained gel-like mixture to a stainless-steel autoclave and heat at 160 °C for 10 h. Separate the solid and liquid phases, wash the obtained solid component with ethanol three times, and dry at 80 °C for 6 h to obtain NaYF with a core-middle shell-outer shell structure 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 (i.e., NaYF 4 :0.02Er 3+ @NaYF 4 :0.18Yb 3+ @NaYF 4 , where 0.02 means the molar percentage of Er 3+ in the core and middle shell layers is 2%, and 0.18 means the molar percentage of Yb 3+ in the core and middle shell layers is 18%).

[0097] Example 2

[0098] Prepare NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 , the difference from Example 1 is only that: Er(NO 3 )3 ·5H 2 The dosage of O is 0.02 mmol, and Yb(NO 3 ) 3 ·5H 2 The dosage of O is 0.38 mmol, and NaYF 4 :0.01Er 3 + @NaYF 4 :0.19Yb 3+ @NaYF 4 .

[0099] Example 3

[0100] Prepare NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 according to the method of Example 1. The difference from Example 1 is only that: the dosage of Er(NO 3 ) 3 ·5H 2 O is 0.08 mmol, and the dosage of Yb(NO 3 ) 3 ·5H 2 O is 0.32 mmol, and NaYF 4 :0.04Er 3 + @NaYF 4 :0.16Yb 3+ @NaYF 4 .

[0101] Example 4

[0102] Prepare NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 according to the method of Example 1. The difference from Example 1 is only that: the dosage of Er(NO 3 ) 3 ·5H 2 O is 0.12 mmol, and the dosage of Yb(NO 3 ) 3 ·5H 2 O is 0.28 mmol, and NaYF 4 :0.06Er 3 + @NaYF 4 :0.14Yb 3+ @NaYF4 .

[0103] Example 5

[0104] Prepare NaYF according to the method of Example 1 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 , the difference from Example 1 is only that: the dosage of Er(NO 3 ) 3 ·5H 2 O is 0.2 mmol, and the dosage of Yb(NO 3 ) 3 ·5H 2 O is 0.2 mmol, to obtain NaYF 4 :0.1Er 3+ @NaYF 4 :0.1Yb 3+ @NaYF 4 .

[0105] Comparative Example 1

[0106] Preparation of NaYF without core-shell structure 4 :Er 3+ / Yb 3+ nanoparticles

[0107] At room temperature, add 10 mL of ethanol and 20 mL of oleic acid to 3 mL of NaOH aqueous solution with a concentration of 0.2 g / mL, stir for 30 min to obtain a transparent mixture, add 1.6 mmol of Y(NO 3 ) 3 ·6H 2 O, 0.04 mmol of Er(NO 3 ) 3 ·5H 2 O, 0.36 mmol of Yb(NO 3 ) 3 ·5H 2 O and 8 mmol of NaF, stir for 30 min, transfer the obtained gel-like mixture to a stainless steel autoclave, heat at 160 °C for 10 h, perform solid-liquid separation, wash the obtained solid component with ethanol 3 times, and dry at 80 °C for 6 h to obtain NaYF without core-shell structure 4 :Er 3+ / Yb 3+ (NaYF 4 :0.02Er 3+ / 0.18Yb 3+ ) nanoparticles.

[0108] Figures 1 - 3 The transmission electron microscope image of the NaYF prepared in Example 1 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 shows that NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 exhibits a nanorod-like structure. The thickness of the NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 rod is about 75 nm. The thickness of the core NaYF 4 :Er 3+ is about 65 nm, the thickness of the middle layer NaYF 4 :Yb 3+ is about 5 nm, and the thickness of the shell layer NaYF 4 is about 5 nm.

[0109] Using an external 980 nm laser as the light source, fluorescence emission spectroscopy tests were performed on the NaYF prepared in Example 1 4 :Er 3+ 、NaYF 4 :Er@NaYF 4 :Yb and NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4

[0110] Figure 4 The upconversion luminescence spectrum of the NaYF prepared in Example 1 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 shows that in NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 Er emits green light in the range of 510 - 560 nm. The energy level transition corresponding to 530 nm is 2 H 11 / 2 - 4 I 15 / 2 and the energy level transition corresponding to 540 nm is​4 S 3 / 2 - 4 I 15 / 2 , emits red light at 635 - 680 nm, and the corresponding energy level transition is 4 F 9 / 2 - 4 I 15 / 2 .

[0111] Figure 5 The upconversion luminescence spectra of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Examples 1 - 6. The total molar mass ratio of Er 3+ and Yb 3+ is 20% and remains constant. When Er 3+ is 0.02, its ratio is 10%. When Er 3+ is 0.1, its ratio is 50%. It can be seen that when the Er 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 ion content in NaYF 3+ increases from 10% to 50%, its upconversion luminescence intensities at red and green lights are significantly greater than those of NaYF 4 :Er 3+ / Yb 3+ . Even when the Er 3+ content increases to 50%, no obvious concentration quenching occurs.

[0112] Figure 6 The upconversion luminescence spectra of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Example 1, NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ and the upconversion luminescence spectra of the NaYF 4 :Er 3+ / Yb 3+ nanoparticles prepared in Comparative Example 1. It can be seen that NaYF 4 :Er 3+ @NaYF 4 :Yb 3 + @NaYF 4The upconversion luminescence intensity is greater than that of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ , because the outermost NaYF 4 effectively reduces surface defects or non-radiative energy transfer between rare earth ions and surface functional groups of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ nanorods. The upconversion luminescence intensity of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ is higher than that of NaYF 4 :Er 3+ / Yb 3+ nanoparticles, which is mainly attributed to the interfacial energy transfer from Yb 4 to Er 3+ in NaYF 4 :Er 3+ @NaYF 3+ :Yb 3+ .

[0113] Figure 7 Figure of the fluorescence quantum yield of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 prepared in Example 1, Figure 8 Figure of the fluorescence quantum yield of NaYF 4 :Er 3+ / Yb 3+ nanoparticles prepared in Comparative Example 1. As can be seen from Figures 7-8, under 980 nm laser excitation, obvious green (about 517-563 nm) and red (about 640-675 nm) regions are obtained. The quantum yield is the integral region of the emission light / the integral region of the excitation light. The fluorescence quantum yield of NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 is 4.26%, ， and the fluorescence quantum yield of NaYF 4 :Er 3+ / Yb 3+ nanoparticles is 1.82%.

[0114] Figure 9 Figure of NaYF 4 :Er3+ @NaYF 4 :Yb 3+ @NaYF 4 and NaYF 4 :Er@NaYF 4 :Yb and the NaYF prepared in Comparative Example 1 4 :Er 3+ / Yb 3+ XRD patterns of the nanoparticles. As can be seen from the figure, NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 and NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ and the NaYF prepared in Comparative Example 1 4 :Er 3+ / Yb 3+ nanoparticles have the same main diffraction peaks, and correspond one by one to the crystal phase of the hexagonal NaYF 4 standard card JCPDS NO28-1192, which proves indirectly that NaYF 4 :Er 3 + @NaYF 4 :Yb 3+ @NaYF 4 , NaYF 4 :Er 3+ @NaYF 4 :Yb 3+ and NaYF 4 :Er 3+ / Yb 3+ nanoparticles are successfully synthesized.

[0115] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A three-layer core-shell rare earth upconversion luminescent material having a core-middle shell-outer shell structure, with NaYF4:Er 3+ As the core, NaYF4:Yb 3+ as the middle shell and NaYF4 as the outer shell.

2. The three-layer core-shell structure rare earth upconversion luminescent material according to claim 1, characterized in that: The NaYF4:Er 3+ and NaYF4:Yb 3+ The molar content of the Er element is 1 to 10%.

3. The three-layer core-shell structure rare earth upconversion luminescent material according to claim 1, characterized in that: The NaYF4:Er 3+ and NaYF4:Yb 3+ The molar content of Yb element is 10-19%.

4. The three-layer core-shell structure rare earth up-conversion luminescent material according to any one of claims 1 to 3, characterized in that: The thickness of the core is 60-70 nm, the thickness of the middle shell is 5-10 nm, and the thickness of the outer shell is 5-10 nm.

5. The method for preparing the three-layer core-shell structure rare earth up-conversion luminescent material according to any one of claims 1 to 4, comprising the following steps: (1) NaOH aqueous solution, oleic acid, ethanol, yttrium source, ytterbium source, NaF and NaYF4:Er 3+ Nanomaterials were mixed and solvothermally reacted in NaYF4:Er 3+ NaYF4:Yb formed on the surface of nanoparticles 3+ layer, and obtain NaYF4:Er 3+ @NaYF4:Yb 3+ ; (2) NaOH aqueous solution, oleic acid, ethanol, yttrium source, NaF and NaYF4:Er 3+ @NaYF4:Yb 3+ Mix and perform solvothermal reaction in NaYF4:Er 3+ @NaYF4:Yb 3+ A NaYF4 layer is formed on the surface to obtain the three-layer core-shell structure rare earth up-conversion luminescent material.

6. The preparation method according to claim 5, characterized in that: In step (1), the NaF and NaYF4:Er 3+ The molar ratio of nanomaterials is 1:1-2; The molar ratio of NaF to NaOH in the aqueous solution of NaOH is 1:0.4-6; the concentration of the aqueous solution of NaOH is 0.2-0.5 g / mL; The molar ratio of yttrium in the NaF and yttrium source is 1:0.1-2; the yttrium source includes yttrium oxide and / or yttrium salt; The molar ratio of NaF to ytterbium in the ytterbium source is 1:0.02-0.5; the ytterbium source includes ytterbium oxide and / or ytterbium salt; The ratio of the amount of NaF to the volume of ethanol is 1 mmol: 1.25-2 mL; The ratio of the amount of NaF to the volume of oleic acid is 1 mmol: 2.5-5 mL; The temperature of the solvent thermal reaction is 180-200° C., the time is 8-10 hours, and the pressure is 2-3 MPa.

7. The preparation method according to claim 5, characterized in that: In step (2), the NaF and NaYF4:Er 3+ @NaYF4:Yb 3+ The molar ratio is 1:1-2; The molar ratio of NaF to NaOH in the aqueous solution of NaOH is 1:0.4-6; the concentration of the aqueous solution of NaOH is 0.2-0.5 g / mL; The molar ratio of yttrium in the NaF and yttrium source is 1:0.1-2; the yttrium source includes yttrium oxide and / or yttrium salt; The ratio of the amount of NaF to the volume of ethanol is 1 mmol: 1.25-2 mL; The ratio of the amount of NaF to the volume of oleic acid is 1 mmol: 2.5-5 mL; The temperature of the solvent thermal reaction is 180-200° C., the time is 8-10 hours, and the pressure is 2-3 MPa.

8. The preparation method according to claim 5 or 6, characterized in that: The NaYF4:Er 3+ The method for preparing the nanomaterial comprises the following steps: NaOH aqueous solution, oleic acid, ethanol, yttrium source, erbium source and NaF are subjected to solvothermal reaction to obtain NaYF4:Er 3+ Nanomaterials.

9. The preparation method according to claim 8, characterized in that: The molar ratio of NaF to NaOH in the aqueous solution of NaOH is 1:0.4-6; the concentration of the aqueous solution of NaOH is 0.2-0.5 g / mL; The molar ratio of yttrium in the NaF and yttrium source is 1:0.1-2; the yttrium source includes yttrium oxide and / or yttrium salt; The molar ratio of NaF to erbium in the erbium source is 1:0.004-0.1; the erbium source includes erbium oxide and / or erbium salt; The ratio of the amount of NaF to the volume of ethanol is 1 mmol: 1.25-2 mL; The ratio of the amount of NaF to the volume of oleic acid is 1 mmol: 2.5-5 mL; The temperature of the solvent thermal reaction is 180-200° C., the time is 8-10 hours, and the pressure is 2-3 MPa.

10. Use of the three-layer core-shell structure rare earth up-conversion luminescent material according to any one of claims 1 to 4 or the three-layer core-shell structure rare earth up-conversion luminescent material prepared by the preparation method according to any one of claims 5 to 9 in infrared detection or preparation of biomedical materials.

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