Double-frequency excitation red fluorescence up-conversion nano material and preparation method thereof

Abstract

The invention provides a double-frequency excitation red fluorescence up-conversion nano material and a preparation method thereof, the up-conversion luminescent material comprises a luminescent core and an inert shell coating the luminescent core, the chemical formula of the luminescent core is beta-NaYF4: 2% Er < 3 + >, 60% Yb < 3 + >; the chemical formula of the inert shell is beta-NaYF4. Therefore, the material with the core-shell structure can emit red upconversion fluorescence under the common excitation of near-infrared light with two different wavelengths of (940-1000) nm and (1520-1550) nm, and the upconversion luminescent material with the luminescent core-inert shell two-layer structure can obviously improve the luminous intensity of dual-frequency common excitation compared with a mononuclear material.

Description

Technical Field

[0001] The present invention belongs to the cross-technical field of true three-dimensional display, up-conversion luminescence and nano core-shell material preparation, and specifically relates to a dual-frequency excitation red fluorescence up-conversion luminescent material and a preparation method thereof. Background Art

[0002] The importance of the human visual system in information acquisition is self-evident, because the information we obtain through vision accounts for 80% of the overall information. This makes the eyes one of the main channels for us to obtain information from the outside world. With the continuous advancement of science and technology, we can enjoy a variety of images from various channels, such as the Internet. Although most of these images are based on two-dimensional (2D) display and provide relatively rich visual information, they always lack something important, namely the depth information of objects. This is one of the reasons why we are so eager for true three-dimensional display technology. Therefore, researchers have been exploring ways to fully reflect the information of objects. True three-dimensional display technology should be able to accurately reflect the brightness, color and depth information of objects. Once we achieve low-cost, high-quality three-dimensional stereoscopic display technology, it will cause a major change in human visual information acquisition.

[0003] As a new type of fluorescent material, upconversion materials have many advantages. Compared with other fluorescent materials, it has the characteristics of anti-Stokes luminescence, that is, it can be excited by low-energy light and then emit high-energy light. Upconversion materials composed of rare earth elements are usually excited by infrared light, which means that there is no interference with the image caused by visible light excitation. However, when solid-state upconversion materials are used as display carriers, their size is often limited, making it difficult to achieve large-scale spatial three-dimensional display. Despite this, as an emerging display technology, upconversion materials still have great research potential and can bring us more innovations and breakthroughs in the future.

[0004] Since it does not require head-mounted equipment and can meet people's requirements for true three-dimensional display, naked-eye stereoscopic display technology has gradually become a research hotspot in recent years. Naked-eye stereoscopic display technology includes spatial three-dimensional display, spectroscopic three-dimensional display, holographic three-dimensional display, etc. Spatial three-dimensional display technology, also known as spatial volumetric three-dimensional display technology, divides the display space into many regularly arranged voxel points, activates the specified voxels through a specific addressing method, and thus displays a fixed pattern in space. Spectroscopic stereoscopic display technology is based on the principle of binocular parallax of the human eye, similar to polarization stereoscopic display technology. Since the left and right eyes receive images with parallax respectively, the brain will automatically synthesize a three-dimensional pattern. Holographic three-dimensional display technology uses the principle of interference to record all the information of an object and diffraction to read the information of the object to achieve three-dimensional display. Current three-dimensional display technologies have their own advantages and disadvantages, so most of them are under research and improvement.

[0005] Today's society has a growing demand for energy efficiency, display technology, biomedical applications and environmental protection. The study of color luminescence based on upconversion materials is of great significance because it can solve many real-life problems. First, by using upconversion materials, the efficiency of light energy conversion can be improved, especially in energy conversion devices such as solar cells, which will help reduce energy consumption and promote the development of renewable energy. Secondly, the research on color luminescent materials helps to improve the color performance and luminous effect of LED display screens, enhance the visual experience and quality of electronic products, and also help to reduce energy consumption and the generation of electronic waste. In addition, the application of upconversion materials can also be extended to the biomedical field, such as bioluminescent imaging and biomarkers, providing new tools and methods for medical diagnosis and treatment. Finally, by developing environmentally friendly lighting technologies, such as using upconversion materials to prepare more efficient fluorescent lamps and LED lamps, energy consumption and carbon emissions can be reduced, which helps to protect the environment and mitigate the impact of climate change. Summary of the invention

[0006] The present invention aims to improve at least one of the above technical problems at least to some extent.

[0007] In order to improve the above problems, the present invention provides a dual-frequency excitation red fluorescence up-conversion nanomaterial, wherein the up-conversion luminescent material comprises a luminescent core and an inert shell covering the luminescent core, wherein the chemical formula of the luminescent core is β-NaYF4: Er3+, Yb3+; and the chemical formula of the inert shell is β-NaYF4. Thus, the core-shell structured material of the present invention can emit high-brightness red up-conversion luminescence under the co-excitation of two different wavelengths of near-infrared light of (940~1000)nm and (1520~1550)nm, and the up-conversion luminescent material of the luminescent core-inert shell two-layer structure can significantly improve the luminescence intensity of dual-frequency co-excitation compared with the single-core material.

[0008] According to an embodiment of the present invention, in the luminescent core, the molar amount of Er3+ is (0.5~3.0)% of the total molar amount of β-NaYF4, Er3+ and Yb3+; in the luminescent core, the molar amount of Yb3+ is (55~65)% of the total molar amount of β-NaYF4, Er3+ and Yb3+.

[0009] According to an embodiment of the present invention, in the inert shell, the molar amount of Y3+ is 100% of the total molar amount of β-NaYF4.

[0010] The present invention also provides a method for the dual-frequency excitation red fluorescence up-conversion nanomaterial as described above, the method comprising: preparing a luminescent core β-NaYF4: Er3+, Yb3+; using the obtained luminescent core β-NaYF4: Er3+, Yb3+ as a crystal core, coating the outer layer of the luminescent core with an inert shell β-NaYF4, and obtaining a luminescent core-inert shell structure β-NaYF4: Er3+, Yb3+@β-NaYF4; obtaining an up-conversion luminescent material β-NaYF4: Er3+, Yb3+@β-NaYF4 with a core-shell structure. Thus, the up-conversion luminescent material prepared by the method has all the characteristics and advantages of the up-conversion luminescent material described above, which will not be repeated here. In addition, the method also has the advantages of simple operation and low production cost, and is suitable for large-scale industrial production.

[0011] According to an embodiment of the present invention, the preparation of the luminescent core β-NaYF4:Er3+,Yb3+ includes: mixing a first rare earth salt with oleic acid and 1-octadecene, reacting to generate a first rare earth oleic acid complex, mixing the first rare earth oleic acid complex with a methanol solution containing a first sodium source and a first fluorine source, and reacting after the methanol evaporates to obtain a luminescent core β-NaYF4:Er3+,Yb3+; wherein the first rare earth salt includes a Y-containing rare earth salt, an Er-containing rare earth salt, and a Yb-containing rare earth salt; preparing a luminescent core-inert shell structure β-NaYF 4:Er3+,Yb3+@β-NaYF4 includes: mixing a second rare earth salt with oleic acid and 1-octadecene, reacting to generate a second rare earth oleic acid complex, adding the luminescent core β-NaYF4:Er3+,Yb3+ as a crystal nucleus to the second rare earth oleic acid complex, adding a methanol solution containing a second sodium source and a second fluorine source, and reacting after the methanol evaporates to obtain a luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, wherein the second rare earth salt includes a Y-containing rare earth salt.

[0012] According to an embodiment of the present invention, when preparing the luminescent core β-NaYF4:Er3+,Yb3+, the ratio of the first rare earth salt to oleic acid and 1-octadecene is 1 mmol:(5~12)mL:(10~20)mL; when preparing the luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, the ratio of the second rare earth salt to oleic acid and 1-octadecene is 1 mmol:(10~20)mL:(10~15)mL.

[0013] According to an embodiment of the present invention, the first rare earth salt and the second rare earth salt are one of rare earth chloride salt and trifluoroacetic acid rare earth salt; the first sodium source and the second sodium source are NaOH; the first fluorine source and the second fluorine source are NH4F.

[0014] According to an embodiment of the present invention, when preparing the luminescent core β-NaYF4:Er3+,Yb3+, the ratio of the first rare earth salt to the first sodium source, the first fluorine source, and methanol is 1mmol:(1.5~3.5)mmol:(3~5)mmol:(8~12)mL; when preparing the luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, the ratio of the second rare earth salt to the second sodium source, the second fluorine source, and methanol is 1mmol:(1.5~3.5)mmol:(3~5)mmol:(8~12)mL.

[0015] According to an embodiment of the present invention, when preparing the luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, the molar ratio of the second rare earth salt to the luminescent core β-NaYF4:Er3+,Yb3+ is 1:(0.9~1.3). BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of a dual-frequency red up-conversion luminescent material in one embodiment of the present invention.

[0017] Figure 2 It is a flow chart of a method for preparing a dual-frequency red up-conversion luminescent material in one embodiment of the present invention.

[0018] Figure 3 This is a morphology image taken by a scanning electron microscope of the dual-frequency red up-conversion luminescent material prepared in Example 1 of the present invention.

[0019] Figure 4 This is a fluorescence image of the dual-frequency red up-conversion luminescent material prepared in Example 1 of the present invention under the co-excitation of a 1530nm laser and a 980nm laser. DETAILED DESCRIPTION

[0020] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific technology or conditions are indicated in the embodiments, the technology or conditions described in the literature in this area or the product instructions are used. The reagents used are not indicated by the manufacturer, and are all conventional products that can be purchased from the market.

[0021] The dual-frequency red up-conversion luminescent material provided by the present invention is referred to Figure 1, the dual-frequency red up-conversion luminescent material comprises a luminescent core and an inert shell covering the luminescent core, the chemical formula of the luminescent core is β-NaYF4:Er3+,Yb3+; the chemical formula of the inert shell is β-NaYF4. Therefore, the dual-frequency red material of the core-shell structure of the present invention can emit high-brightness red up-conversion luminescence under the co-excitation of two different wavelengths of near-infrared light of (940~1000)nm and (1520~1550)nm. Compared with the uncoated β-NaYF4:Er3+,Yb3+, the luminescence intensity of the core-shell structure material of the present invention is increased by nearly 1.5 times. Specifically, in the inner layer structure β-NaYF4:Er3+,Yb3+@β-NaYF4 of the present invention, Er3+ is isolated from the space by coating, thereby reducing the influence of Er3+'s own concentration quenching and improving the up-conversion luminescence intensity; on the other hand, it can reduce the surface defects of the material, reduce non-radiative transitions, and improve the absorption of near-infrared light inside and outside the material, thereby improving the up-conversion luminescence intensity of dual-frequency co-excitation.

[0022] According to an embodiment of the present invention, in the luminescent core, the molar amount of Er3+ is (0.5%~3.0%) of the total molar amount of β-NaYF4, Er3+ and Yb3+. As a result, the luminescent core can have a stronger dual-frequency excitation up-conversion luminescence intensity. If the doping ratio of Er3+ in the luminescent core is too small, there will be too few luminescent centers and the up-conversion luminescence intensity of dual-frequency excitation will be low. If the doping ratio of Er3+ in the luminescent core is too large, concentration quenching of Er3+ itself will occur, resulting in a decrease in the up-conversion luminescence intensity of dual-frequency excitation.

[0023] According to an embodiment of the present invention, in the luminescent core, the molar amount of Yb3+ is (55% to 65%) of the total molar amount of β-NaYF4, Er3+ and Yb3+. As a result, the luminescent core can have a strong dual-frequency red excitation up-conversion luminescence intensity. After the Yb3+ ions replace the Y3+ ions in the lattice, the electron charge density on the surface of the crystal increases. Due to the increase in charge row, the change in the surface electron charge density of small-sized nanocrystals can slow down the diffusion of negatively charged F- ions to the surface, thereby resulting in an adjustable reduction in the size of NaYF4 nanocrystals. Smaller nanocrystals have relatively more surface quenching sites, which leads to enhanced non-radiative energy relaxation of the luminescent center, thereby inhibiting up-conversion luminescence.

[0024] The upconversion luminescent material according to the embodiment of the present invention has the following advantages: (1) The upconversion luminescent material in the present invention reasonably utilizes the core-shell structure to successfully passivate the surface of the single-core structure upconversion nanomaterial, and the doped Er3+ ions are confined in the internal core space, and the high-energy vibration generated by the reaction of the surface ions with the surrounding environment, thereby suppressing the luminescence quenching caused. The red fluorescence upconversion process of the core-shell structure is significantly more efficient than that of the single-core structure. (2) The core / inert shell nanostructure designed by the present invention, the Yb3+ ions doped in the core can promote the absorption of near-infrared red light by the NaYF4:Yb / Er core; improve the utilization rate of the dual-frequency excitation red fluorescence upconversion nanomaterial for near-infrared light at (940~1000)nm and (1520~1550)nm, so that the upconversion luminescent material has excellent performance of high brightness and high contrast.

[0025] The present invention also provides a method for preparing the dual-frequency excitation red fluorescence upconversion nanomaterial as described above, referring to Figure 2 The method comprises: S100, preparing a luminescent core β-NaYF4:Er3+,Yb3+.

[0026] According to an embodiment of the present invention, the luminescent core β-NaYF4:Er3+,Yb3+ can be prepared by a solvothermal method. Specifically, step S100 includes: mixing a first rare earth salt with oleic acid and 1-octadecene, reacting to generate a first rare earth oleic acid complex, mixing the first rare earth oleic acid complex with a methanol solution containing a first sodium source and a first fluorine source, and reacting after the methanol evaporates to obtain the luminescent core β-NaYF4:Er3+,Yb3+; wherein the first rare earth salt includes a Y-containing rare earth salt, an Er-containing rare earth salt, and a Yb-containing rare earth salt.

[0027] According to an embodiment of the present invention, in the reaction of generating the first rare earth oleic acid complex, the reaction is carried out under the protection of an inert gas, the reaction temperature is (150°C~160°C), the reaction time is 30 minutes, and after the reaction of generating the first rare earth oleic acid complex is completed, the method further comprises: cooling the reaction system to (40°C~50°C), adding a methanol solution containing a first sodium source and a first fluorine source under vigorous stirring, and keeping warm at (40°C~50°C) for 0.5 hours; heating to (100°C~120°C) and keeping warm for 10 minutes to remove all methanol; rapidly heating to 294~300°C and keeping warm for 1.5 hours, and cooling to room temperature; centrifuging the reaction solution with an ethanol solution at a speed of 8000r / min for 10 minutes, collecting the precipitate, and washing it three times with a mixture of cyclohexane and anhydrous ethanol, and finally dispersing the product in cyclohexane to obtain β-NaYF4:Er3+,Yb3+.

[0028] According to some embodiments of the present invention, the contents of the components in the Y-containing rare earth salt, the Er-containing rare earth salt, and the Yb-containing rare earth salt in the first rare earth salt are weighed according to the stoichiometric ratio of the luminescent core β-NaYF4:Er3+,Yb3+. Specifically, since the molar amount of Er3+ in the luminescent core is (0.5%~3.0%) of the total molar amount of β-NaYF4, Er3+ and Yb3+, and the molar amount of Yb3+ is (55%~65%) of the total molar amount of β-NaYF4, Er3+ and Yb3+, the first rare earth salt should satisfy: the percentage of the molar amount of Er in the Er-containing rare earth salt to the sum of the molar amount of Y in the Y-containing rare earth salt, the molar amount of Er in the Er-containing rare earth salt, and the molar amount of Yb in the Yb-containing rare earth salt is (0.5%~3.0%), and the percentage of the molar amount of Yb in the Yb-containing rare earth salt to the sum of the molar amount of Y in the Y-containing rare earth salt, the molar amount of Er in the Er-containing rare earth salt, and the molar amount of Yb in the Yb-containing rare earth salt is (55%~65%).

[0029] According to an embodiment of the present invention, when preparing the luminescent core β-NaYF4:Er3+,Yb3+, the ratio of the first rare earth salt to oleic acid and 1-octadecene is 1 mmol:(5-12) mL:(10-20) mL. Under this condition, the first rare earth salt is rapidly dissolved and the first rare earth oleic acid complex is generated.

[0030] According to an embodiment of the present invention, the first rare earth salt is one of rare earth chloride salt and trifluoroacetic acid rare earth salt; the first sodium source is NaOH; and the first fluorine source is NH4F.

[0031] According to an embodiment of the present invention, when preparing the luminescent core β-NaYF4:Er3+,Yb3+, the ratio of the first rare earth salt to the first sodium source, the first fluorine source, and methanol is 1 mmol:(1.5-3.5) mmol:(3-5) mmol:(8-12) mL. Under this condition, the generation of the luminescent core β-NaYF4:Er3+,Yb3+ is favorable.

[0032] S200, using the obtained luminescent core β-NaYF4:Er3+,Yb3+ as a crystal core, coating the outer layer of the luminescent core with an inert shell β-NaYF4, and obtaining a luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4.

[0033] According to an embodiment of the present invention, a luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4 can be prepared by a solvothermal method. Specifically, step S200 includes: mixing a second rare earth salt with oleic acid and 1-octadecene, reacting to generate a second rare earth oleic acid complex, adding the luminescent core β-NaYF4:Er3+,Yb3+ as a seed crystal to the second rare earth oleic acid complex, adding a methanol solution containing a second sodium source and a second fluorine source, and after the methanol evaporates, reacting to obtain a luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, wherein the second rare earth salt includes a Y-containing rare earth salt.

[0034] According to an embodiment of the present invention, in the reaction of generating the second rare earth oleic acid complex, the reaction is carried out under the protection of an inert gas, the reaction temperature is (150°C~160°C), the reaction time is 30 minutes, and after the reaction of generating the second rare earth oleic acid complex is completed, the method further comprises: cooling the reaction system to (40°C~50°C), adding seed crystals β-NaYF4:Er3+,Yb3+ under vigorous stirring, stirring for 5 minutes, and then adding a methanol solution containing a second sodium source and a second fluorine source. , (40℃~50℃) and keep warm for 0.5h; heat to (100℃~120℃) and keep warm for 10min to remove all methanol; quickly heat to 294-300℃ and keep warm for 1.5h, then cool to room temperature; centrifuge the reaction solution with ethanol solution at a speed of 8000r / min for 10 minutes, collect the precipitate, and wash it three times with a mixture of cyclohexane and anhydrous ethanol. The final product is dispersed in cyclohexane to obtain a luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4.

[0035] According to some embodiments of the present invention, the content of each component in the Y-containing rare earth salt in the second rare earth salt is weighed according to the stoichiometric ratio of the inert shell β-NaYF4. Specifically, since the molar amount of Y3+ in the inert shell is 100% of the total molar amount of β-NaYF4 and Y3+, the second rare earth salt should satisfy: the percentage of the molar amount of Y in the Y-containing rare earth salt to the total molar amount of the rare earth salt is 100%.

[0036] According to an embodiment of the present invention, when preparing the luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, the ratio of the second rare earth salt to oleic acid and 1-octadecene is 1 mmol:(5-12) mL:(10-20) mL. Under this condition, the second rare earth salt is rapidly dissolved and the second rare earth oleic acid complex is generated.

[0037] According to an embodiment of the present invention, the second rare earth salt is one of rare earth chloride salt and trifluoroacetic acid rare earth salt; the second sodium source is NaOH; and the second fluorine source is NH4F.

[0038] According to an embodiment of the present invention, when preparing the luminescent core-inert shell structure β-NaYF4: Er3+, Yb3+@β-NaYF4, the ratio of the second rare earth salt to the second sodium source, the second fluorine source, and methanol is 1mmol: (1.5~3.5)mmol: (3~5)mmol: (8~12)mL. Under this condition, the formation of the luminescent core-inert shell structure β-NaYF4: Er3+, Yb3+@β-NaYF4 is favorable.

[0039] According to an embodiment of the present invention, when preparing the luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4, the ratio of the second rare earth salt to the luminescent core β-NaYF4:Er3+,Yb3+ is 1:(0.9~1.3). Under this condition, the formation of the luminescent core-inert shell structure β-NaYF4:Er3+,Yb3+@β-NaYF4 is favorable.

[0040] The present invention coats the rare earth luminescent material layer by layer through a solvent thermal method, so that the structure of each coating layer can be complete and uniform, and the thickness and number of the coating layers can be directional controlled, and the structure of the up-conversion luminescent material can be flexibly adjusted and optimized.

[0041] The present invention is further described below in conjunction with specific examples. The raw materials of the examples and comparative examples can be obtained from commercial sources or prepared by known methods.

[0042] Example 1.

[0043] The core-shell dual-frequency excitation upconversion luminescent material is composed of a luminescent core and an inert shell, the luminescent core structure is β-NaYF4: 2% Er3+, 60% Yb3+, and the inert shell structure is β-NaYF4. The chemical expression of the core-shell dual-frequency red excitation upconversion luminescent material is: β-NaYF4: 2% Er3+, 60% Yb3+@β-NaYF4.

[0044] The preparation method of the dual-frequency excitation up-conversion luminescent material of the core-shell structure includes:

[0045] (1) Preparation of luminescent core β-NaYF4: 2% Er3+, 60% Yb3+; 0.38mmol YCl3, 0.02mmol ErCl3, 0.6mmol YbCl3·6H2O were added to a mixed solvent of 6mL oleic acid and 15mL 1-octadecene, and inert gas was introduced to deoxygenate, and the mixture was kept at (150℃~160℃) for 30min until the rare earth salt was completely dissolved to obtain a rare earth oleic acid complex, and then the temperature was lowered to (40℃~50℃); 10mL of 2.5mmol NaOH and 4mmol NH4F methanol solution, (40℃~50℃) keep warm for 0.5h; heat to (100℃~120℃) and keep warm for 10min to remove methanol; quickly heat to 295℃ and keep warm for 1.5h, then cool to room temperature; centrifuge the reaction solution with ethanol solution at 8000r / min for 10 minutes, collect the precipitate, and wash it three times with a mixture of cyclohexane and anhydrous ethanol. The final product is dispersed in 4mL cyclohexane to obtain the luminescent core β-NaYF4: 2% Er3+, 60% Yb3+.

[0046] (2) Preparation of a luminescent core-inert shell structure β-NaYF4: 2% Er3+, 60% Yb3+@β-NaYF4; Using the luminescent core β-NaYF4: 2% Er3+, 60% Yb3+@β-NaYF4 prepared in step (1) as a crystal core, a luminescent core-inert shell structure β-NaYF4: 2% Er3+, 60% Yb3+@β-NaYF4 was prepared by a solvothermal method. Specifically, the preparation of luminescent core-inert shell structure of β-NaYF4: 2% Er3+, 60% Yb3+@β-NaYF4 includes: adding 1.0mmol YCl3·6H2O to a mixed solvent of 6mL oleic acid and 15mL 1-octadecene, introducing an inert gas to deoxygenate, keeping warm at (150℃~160℃) for 30min until the rare earth salt is completely dissolved to obtain a rare earth oleic acid complex, and cooling to (40℃~50℃); adding the crystal core β-NaYF4: 2% Er3+, 60% Yb3+ dissolved in 4mL cyclohexane in step (1) under vigorous stirring, stirring for 5min, and then adding 10mL of methanol solution containing 2.5mmol NaOH and 4mmol NH4F, and keeping warm at (40℃~50℃) for 0.5h; heating to (100℃~120℃) and keeping warm for 10min to remove all methanol; rapidly heating to 295℃ Keep warm for 1.5 hours and cool to room temperature; centrifuge the reaction solution with ethanol at a speed of 8000r / min for 10 minutes, collect the precipitate, and wash it three times with a mixture of cyclohexane and anhydrous ethanol. The final product is dispersed in 4mL cyclohexane to obtain luminescent core-inert shell structure β-NaYF4: 2% Er3+, 60% Yb3+@β-NaYF4.

[0047] Example 2.

[0048] A dual-frequency red excitation up-conversion luminescent material of a core-shell structure was prepared by referring to the method of Example 1, except that in the luminescent core prepared in Example 2, the molar amount of Er3+ was 0.5% of the total molar amount of β-NaYF4, Er3+ and Yb3+, and the molar amount of Yb3+ was 60% of the total molar amount of β-NaYF4, Er3+ and Yb3+. The chemical expression of the dual-frequency red excitation up-conversion luminescent material of the core-shell structure prepared in Example 2 is: β-NaYF4: 0.5% Er3+, 60% Yb3+@β-NaYF4.

[0049] Example 3.

[0050] The core-shell dual-frequency red excitation up-conversion luminescent material was prepared by referring to the method of Example 1, except that in the luminescent core prepared in Example 3, the molar amount of Er3+ was 1.0% of the total molar amount of β-NaYF4, Er3+ and Yb3+, and the molar amount of Yb3+ was 60% of the total molar amount of β-NaYF4, Er3+ and Yb3+. The chemical expression of the core-shell dual-frequency red excitation up-conversion luminescent material prepared in Example 3 is: β-NaYF4: 1.0% Er3+, 60% Yb3+@β-NaYF4.

[0051] Example 4.

[0052] The core-shell structured dual-frequency red excitation up-conversion luminescent material was prepared by referring to the method of Example 1, except that in the luminescent core prepared in Example 4, the molar amount of Er3+ was 1.5% of the total molar amount of β-NaYF4 and Er3+, and the molar amount of Yb3+ was 60% of the total molar amount of β-NaYF4, Er3+ and Yb3+. The chemical expression of the core-shell structured dual-frequency red excitation up-conversion luminescent material prepared in Example 4 is: β-NaYF4: 1.5% Er3+, 60% Yb3+@β-NaYF4.

[0053] Example 5.

[0054] The core-shell dual-frequency red excitation up-conversion luminescent material was prepared by referring to the method of Example 1, except that in the luminescent core prepared in Example 4, the molar amount of Er3+ was 2.5% of the total molar amount of β-NaYF4 and Er3+, and the molar amount of Yb3+ was 60% of the total molar amount of β-NaYF4, Er3+ and Yb3+. The chemical expression of the core-shell dual-frequency red excitation up-conversion luminescent material prepared in Example 4 is: β-NaYF4: 2.5% Er3+, 60% Yb3+@β-NaYF4.

[0055] Example 6.

[0056] The core-shell structured dual-frequency red excitation up-conversion luminescent material was prepared by referring to the method of Example 1, except that in the luminescent core prepared in Example 4, the molar amount of Er3+ was 3.0% of the total molar amount of β-NaYF4 and Er3+, and the molar amount of Yb3+ was 60% of the total molar amount of β-NaYF4, Er3+ and Yb3+. The chemical expression of the core-shell structured dual-frequency red excitation up-conversion luminescent material prepared in Example 4 is: β-NaYF4: 3% Er3+, 60% Yb3+@β-NaYF4.

[0057] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0058] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. Dual-frequency excitation red fluorescence upconversion nanomaterial, characterized in that: include: A luminescent core, wherein the chemical formula of the luminescent core is β-NaYF4:Er3+,Yb3+; An inert shell is coated on the surface of the luminescent core, and the chemical formula of the inert shell is β-NaYF4.

2. The dual-frequency excitation red fluorescence upconversion nanomaterial according to claim 1, characterized in that: The diameter of the luminescent core is 20-25 nm.

3. The dual-frequency excitation red fluorescence upconversion nanomaterial according to claim 1, characterized in that: The thickness of the inert shell is 5 to 10 nm.

4. The dual-frequency excitation red fluorescence upconversion nanomaterial according to claim 1, characterized in that: In the luminescent core, the molar amount of Er3+ is 0.5-3.0% of the total molar amount of Y3+, Er3+ and Yb3+, and the molar amount of Yb3+ is 55%-65% of the total molar amount of Y3+, Er3+ and Yb3+.

5. The dual-frequency excitation red fluorescence upconversion nanomaterial according to claim 1, characterized in that: In the inert shell, the molar amount of Y3+ is 100%.

6. A method for preparing the dual-frequency excitation red fluorescence upconversion nanomaterial according to any one of claims 1 to 5, characterized in that: include: (1) mixing a first rare earth salt, oleic acid, 1-octadecene, a first fluorine source, and a first sodium source to obtain a luminescent core having a general formula of β-Na-YF4:Er3+,Yb3+; (2) The luminescent core of the general formula β-NaYF4:Er3+,Yb3+ obtained in step (1) is mixed with a second rare earth salt, the oleic acid, the 1-octadecene, the second fluorine source and the second sodium source to form an inert shell of the general formula β-NaYF4 on the surface of the luminescent core, so as to obtain a luminescent core / inert shell nanocrystal of the general formula β-NaYF4:Er3+;Yb3+@β-NaYF4.

7. The method according to claim 6, characterized in that The first rare earth salt and the second rare earth salt independently include at least one of a rare earth chloride salt and a rare earth nitrate salt.

8. The method according to claim 6, characterized in that The first fluorine source and the second fluorine source include at least one of ammonium fluoride, potassium fluoride, lithium fluoride, sodium fluoride and sodium trifluoroacetate.

9. Optionally, the first sodium source and the second sodium source include at least one of sodium hydroxide, sodium fluoride, sodium acetate and sodium trifluoroacetate.

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