Novel rare earth up-conversion luminescence two-dimensional MOFs (Metal-Organic Frameworks) material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of new materials, and discloses a novel rare earth up-conversion luminescence two-dimensional MOFs material, a preparation method and an application, the chemical formula of the basic building unit of the novel rare earth up-conversion luminescence two-dimensional MOFs material is C21H19N2O19Ln2, and the novel rare earth up-conversion luminescence two-dimensional MOFs material is marked as Ln-PMA MOFs; the two-dimensional layered material is prepared by adopting a low-temperature solvothermal method, deprotonated 1, 2, 4, 5-benzene tetracarboxylic acid (PMA) and rare earth Ln < 3 + > are self-assembled to synthesize Ln-PMA MOFs with a novel two-dimensional layered structure, Yb < 3 + > ions are co-doped with Ho < 3 + >, Tb < 3 + > or Eu < 3 + > ions respectively to obtain a series of double-rare-earth doped two-dimensional layered MOFs, and the double-rare-earth doped two-dimensional layered MOFs can be used for preparing the double-rare-earth doped two-dimensional layered MOFs. The luminescent material has multi-mode emission performance of up-conversion luminescence and down-transfer luminescence, and can be widely applied to the fields of security anti-counterfeiting, optical information storage, biological imaging and the like.

Description

Technical Field

[0001] The present invention relates to the field of new material technology, and in particular to a novel rare earth up-conversion luminescent two-dimensional MOFs material, a preparation method and an application thereof. Background Art

[0002] Anti-counterfeiting technology is an effective means to prevent and suppress counterfeiting. Anti-counterfeiting labels based on luminescent materials are a hot topic in the current anti-counterfeiting field. Existing studies have shown that metal-organic frameworks (MOFs) with luminescent properties are a new type of luminescent material developed in recent years. They are stable structures formed by metal ions or metal ion clusters in organic molecular skeleton structures, where the metal ions can be rare earth or transition metal ions. Such materials generally have high porosity, large specific surface area and structural designability. That is, luminescent MOFs materials have shown broad application prospects in the fields of security anti-counterfeiting and bioimaging due to their unique optical properties and versatility. However, a lot of targeted research is still needed in its specific product design and application fields, and its complex preparation methods must also be improved before they can be applied industrially.

[0003] Existing two-dimensional luminescent metal–organic frameworks (2D MOFs) are a class of MOFs materials with unique structures. Their coordination network only extends on the two-dimensional plane and forms a layered stacking structure through weak interactions such as van der Waals forces. This type of material not only inherits the high specific surface area, porosity and structural designability of traditional MOFs, but also exhibits significant surface effects due to its two-dimensional structural characteristics, thus giving it excellent optical properties and showing wide application potential in the fields of sensing, optoelectronic devices, catalysis, etc. Especially in the field of information storage, its multi-mode luminescence characteristics provide new ideas for the development of high-density and high-security optical storage technology. Rare earth luminescent MOFs can significantly improve the stability and security of information storage because the metal-centered rare earth ions have unique ff electron transition characteristics (such as narrow emission peaks, long luminescence lifetimes, strong resistance to photobleaching, and a spectrum that covers ultraviolet light to near-infrared light).

[0004] At present, the research on two-dimensional luminescent MOFs mainly focuses on the field of down-shifting luminescence. Down-shifting luminescence is usually a process in which a material absorbs high-energy photons (such as ultraviolet light) and emits low-energy photons (such as visible light). Researchers have successfully developed a variety of two-dimensional MOF materials with down-shifting luminescence by introducing rare-earth metal ions (such as Eu³⁺, Tb³⁺) and organic ligands with strong absorption characteristics (such as aromatic carboxylic acids, porphyrins, etc.). However, although significant progress has been made in down-shifting luminescence of two-dimensional MOFs, due to various technical difficulties, the research on upconversion luminescence of two-dimensional MOFs is still very limited, and no relevant product and specific application reports have been found. The inability to achieve upconversion luminescence in two-dimensional MOFs makes it impossible for the material to use low-energy stimulation sources such as near-infrared light to trigger its luminescence, lacking an "invisible" excitation means in the field of information anti-counterfeiting. Upconversion luminescence refers to the process in which a material absorbs low-energy photons (long wavelength, such as near-infrared light) and emits high-energy photons (short wavelength, such as visible light). This anti-Stokes luminescence has irreplaceable advantages in biological imaging, anti-counterfeiting technology, and information storage.

[0005] Therefore, researching a new upconversion luminescent two-dimensional MOF material, designing a unique product structure, and simplifying its preparation method, and further applying it to the fields of security anti-counterfeiting, optical information storage, and biological imaging have great industrial value. Summary of the Invention

[0006] In view of the above deficiencies of existing security anti-counterfeiting and biological imaging materials in the prior art, the present invention provides a new rare-earth upconversion luminescent two-dimensional MOF material, a preparation method, and an application. Through the coordinated improvement of the targeted MOF product structure design and material synthesis method, the limitation of traditional two-dimensional MOFs being limited to down-shifting luminescence is broken through, and a new near-infrared light-responsive upconversion luminescent material is developed; at the same time, by optimizing reaction conditions, adjusting the ratio of precursors and other processing steps, the purity of the Ln-PMA MOF material is effectively improved, and it can be synthesized under the conditions of low-temperature solvothermal, realizing the acquisition of high-purity MOF materials under safe and simple reaction conditions, which can meet the requirements of industrial production; it has great application value in the fields of security anti-counterfeiting, optical information storage, and biological imaging.

[0007] To achieve the above object, the technical solution provided by the present invention is: A new rare-earth upconversion luminescent two-dimensional MOF material, the chemical formula of its basic building unit is C 21 H 19 N2O 19Ln2, denoted as Ln-PMA MOFs.

[0008] This new rare-earth upconversion luminescent two-dimensional MOFs material belongs to the monoclinic system with the space group P121 / c1; the asymmetric unit of Ln-PMA MOFs contains 2 rare-earth cations Ln 3+ , 1.5 molecules of 1,2,4,5-benzenetetracarboxylic acid (PMA), 2 coordinated N,N-dimethylformamide (DMF) molecules and 2 coordinated water molecules; the two Ln 3+ both adopt an eight-coordinate geometric structure, but their coordination environments are slightly different; Ln1 and Ln2 are connected by two carboxylic acid bridges from one PMA molecule to form a binuclear unit, and these units are connected along the b-axis and c-axis by the PMA ligand and form a two-dimensional layered structure under the capping action of DMF, which is stacked along the a-axis.

[0009] A preparation method of the new rare-earth upconversion luminescent two-dimensional MOFs material, characterized in that it comprises the following steps: (1) Weigh a set amount of rare-earth salt, add it to a test tube, add deionized water according to a set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40 KHz until the solution in the bottle is clear and transparent to form a uniform first dispersion; (2) Weigh a set amount of PMA ligand, add it to a test tube, add DMF according to a set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40 KHz until the solution in the bottle is clear and transparent to form a uniform second dispersion; (3) Transfer the above first dispersion and second dispersion to a glass bottle, place the glass bottle in an ultrasonic oscillator for ultrasonic treatment, the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40 KHz until the solution in the bottle is clear and transparent to form a uniform third dispersion; (4) Seal the glass bottle containing the third dispersion, put it in an oven and keep the temperature at 70 - 90 °C, react for 10 - 24 hours, and the rare-earth Ln 3+ self-assembles with PMA to form two-dimensional MOFs; then naturally cool to room temperature, filter and collect the produced flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours, and control the temperature at 60 - 70 °C to obtain a high-purity Ln-MOFs material The rare-earth salt in the step (1) is one of rare-earth nitrate and rare-earth chloride. The rare-earth ion is Y 3+ , La 3+ , Ce3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Yb 3+ , Lu 3+ one, two or more of; In step (1), relative to 0.9 - 1.2 mmol of rare earth salt, the amount of deionized water used is 4 - 7 mL.

[0010] In step (2), relative to 0.9 - 1.2 mmol of PMA, the amount of DMF used is 4 - 7 mL, An application of a preparation method of the novel rare earth up - conversion luminescent two - dimensional MOFs material, which has both up - conversion and down - conversion multi - mode luminescence properties and has important application values in the fields of optical information storage, security anti - counterfeiting and biological imaging.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. The rare earth up - conversion luminescent two - dimensional MOFs material, preparation method and application provided by the present invention break through the limitation of traditional two - dimensional MOFs which are limited to down - conversion luminescence by synchronously improving the targeted two - dimensional MOFs product design method and material synthesis method, and develop a near - infrared light - responsive up - conversion luminescent material; by optimizing reaction conditions, adjusting precursor ratios and other post - treatment steps, the purity of the Ln - PMA MOFs material is effectively improved, and high - purity MOFs material can be obtained under safe and simple reaction conditions to meet the requirements of industrial production.

[0012] 2. The rare earth up - conversion luminescent two - dimensional MOFs material and preparation method provided by the present invention are self - assembled and synthesized in a glass bottle under the condition of low - temperature solvothermal. Its method steps are simple, the operation is convenient, the reaction conditions are easy to control, the cost is low, the obtained product has high repeatability, and there is no pollution to the environment, which is easy to industrialize.

[0013] 3. The rare-earth upconversion luminescent two-dimensional MOFs material provided by the present invention can achieve upconversion luminescence in two-dimensional MOFs, obtain visible light by near-infrared light excitation, and then integrate upconversion luminescence and downshifting luminescence to achieve multimode regulation emission of two-dimensional MOFs, greatly expanding its application dimension in the field of information storage; and this material has high purity, good reproducibility, environmental friendliness, stable structure and properties, and has rich and stable pores, which is suitable as a carrier for gases, quantum dots, nanoparticles, organic small molecule drugs or dyes, etc., and has broad application prospects in many fields such as catalysis, adsorption separation, and optics, electricity, and magnetism.

[0014] 4. The rare-earth upconversion luminescent two-dimensional MOFs material provided by the present invention has few types of raw materials, a simple and efficient preparation process, high reproducibility, has multi-mode emission characteristics, can respond to excitation light of different wavelengths at the same time, and has advantages such as upconversion / downshifting dual-mode luminescence, and can be widely applied to technical fields such as security anti-counterfeiting, optical information storage, and biological imaging based on upconversion / downshifting dual modes.

[0015] 5. The product provided by the present invention has a unique structure, a simple preparation process, is easy to produce, and has high reproducibility; the material provided by the present invention can respond to excitation light of different wavelengths and can be widely applied to fields such as optical anti-counterfeiting and information security storage.

[0016] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram and a scanning electron microscope (SEM) photograph of the Yb-PMA MOFs material obtained in Example 1 of the present invention; Figure 2 It is a powder X-ray diffraction pattern and a fluorescence spectrum diagram of the 20% Ho,Yb-PMA MOFs material obtained in Example 2 of the present invention under the excitation of a 980 nm laser light source.

[0018] Figure 3 It is a fluorescence spectrum diagram of the 20% Tb,Yb-PMA MOFs material obtained in Example 3 of the present invention under the excitation of 980 nm and 330 nm light sources respectively.

[0019] Figure 4 It is a fluorescence spectrum diagram of the 30% Eu,Yb-PMA MOFs material obtained in Example 4 of the present invention under the excitation of 980 nm and 330 nm light sources respectively.

[0020] The present invention will be described in detail below in conjunction with the accompanying drawings and examples. Specific Embodiments

[0021] Basic implementation example

[0022] A novel rare-earth upconversion luminescent two-dimensional MOFs material, the chemical formula of its basic building unit is C 21 H 19 N2O 19 Ln2, denoted as Ln-PMA MOFs; this material belongs to the monoclinic system, and the space group is P121 / c1; the asymmetric unit of Ln-PMA MOFs contains 2 rare-earth cations Ln 3+ , 1.5 molecules of 1,2,4,5-benzenetetracarboxylic acid (PMA), 2 coordinated N,N-dimethylformamide (DMF) molecules and 2 coordinated water molecules; the two Ln 3+ both adopt an eight-coordinate geometric structure, but their coordination environments are slightly different; Ln1 and Ln2 are connected by two carboxylic acid bridges from one PMA molecule to form a binuclear unit, and these units are connected along the b-axis and c-axis by the PMA ligand and form a two-dimensional layered structure under the capping action of DMF, which is stacked along the a-axis.

[0023] The preparation method of the novel rare-earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1) Weigh a set amount of rare-earth salt, add it to a test tube, add deionized water according to a set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40 KHz until the solution in the bottle is clear and transparent to form a uniform first dispersion; The rare-earth salt is one of rare-earth nitrate and rare-earth chloride; The rare-earth ion is Y 3+ , La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Yb 3+ , Lu 3+ one, two or more of them; Relative to 0.9 - 1.2 mmol of rare-earth salt, the dosage of deionized water is 4 - 7 mL; (2) Weigh a set amount of PMA ligand, add it to a test tube, add DMF in a set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C and the time at 15 minutes. Set the ultrasonic frequency to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform second dispersion; For 0.9 - 1.2 mmol of PMA, the amount of DMF used is 4 - 7 mL; (3) Transfer the above first dispersion and second dispersion to a glass bottle, place the glass bottle in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C and the time at 15 minutes. Set the ultrasonic frequency to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform third dispersion; (4) Seal the glass bottle containing the third dispersion, put it in an oven and keep the temperature at 70 - 90 °C for reaction for 10 - 24 hours. The rare earth Ln 3+ self - assembles with PMA to form two - dimensional MOFs; then naturally cool to room temperature, filter and collect the resulting flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours, with the temperature controlled at 60 - 70 °C, and thus obtain high - purity Ln - MOFs materials.

[0024] An application of the preparation method of the novel rare - earth up - conversion luminescent two - dimensional MOFs material. Based on its combined up - conversion and down - transfer multi - mode luminescent properties, it has important industrial application value in the fields of optical information storage, security anti - counterfeiting and biological imaging.

[0025] The following specifically describes the implementation manners of the present invention. Unless otherwise specified, the equipment and materials used are all commercially available.

[0026] Example 1 A novel rare - earth up - conversion luminescent two - dimensional MOFs material, preparation method and application are specific selections and refinements of the basic embodiment.

[0027] See the appendix Figure 1 , the rare - earth up - conversion luminescent two - dimensional MOFs material provided in this example is specifically the Yb - PMA MOFs material.

[0028] The Yb - PMA MOFs material provided in this example has the chemical formula of C 21 H 19 N2O 19 Yb2 for its basic building unit, denoted as Yb - PMA MOFs.

[0029] The Yb-PMA MOFs material belongs to the monoclinic system with the space group P121 / c1; the asymmetric unit of Yb-PMA MOFs contains 2 rare earth cations Yb 3+ , 1.5 molecules of 1,2,4,5-benzenetetracarboxylic acid (PMA), 2 coordinated N,N-dimethylformamide (DMF) molecules and 2 coordinated water molecules; the two Yb 3+ both adopt an octahedral coordination geometry, but their coordination environments are slightly different; Yb1 and Yb2 are connected by two carboxylic acid bridges from one PMA molecule to form a binuclear unit, and these units are connected along the b-axis and c-axis by the PMA ligand and form a two-dimensional layered structure under the capping action of DMF, which is stacked along the a-axis (see Figure 1).

[0030] The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1) Weigh 1 mmol of YbCl3·6H2O and add it to a test tube. Add 5 mL of deionized water according to the set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes, and set the ultrasonic frequency to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform first dispersion; (2) Weigh 1 mmol of the PMA ligand and add it to a test tube. Add 5 mL of DMF according to the set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes, and set the ultrasonic frequency to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform second dispersion; (3) Transfer the above first dispersion and second dispersion to a glass bottle. Place the glass bottle in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes, and set the ultrasonic frequency to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform third dispersion; (4) Seal the glass bottle containing the third dispersion and put it into an oven to maintain a temperature of 70 - 90 °C for 10 - 24 hours. The rare earth Yb 3+ self-assembles with PMA to form two-dimensional MOFs; then naturally cool to room temperature, filter and collect the resulting flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven and vacuum dry them for 8 hours at a temperature controlled at 60 - 70 °C to obtain a high-purity Yb-PMA MOFs material.

[0031] The method of this example makes full use of the conditions of low-temperature heating and self-generated pressure. The deprotonated PMA and Yb 3+Ionic self-assembly forms two-dimensional MOFs. The flaky crystals collected from the bottom of the reaction vessel were named Yb-PMAMOFs. In this example, by optimizing the reaction conditions, adjusting the precursor ratio and other processing steps, the purity of the Yb-PMA MOFs material was effectively improved. This strategy provides a new idea for the synthesis of high-purity rare earth two-dimensional metal-organic framework materials.

[0032] As Figure 1 shown, where (a) is a schematic structural diagram of Yb-PMA MOFs crystals, showing that Yb-PMA MOFs have a two-dimensional layered structure and abundant pores, with a spatial effect, and can be used as carriers for gas molecules, quantum dots, nanoparticles, organic small molecule drugs or dyes, etc., and have broad application prospects in many fields such as catalysis, adsorption separation, and optics, electricity, and magnetism; (b) is a scanning electron microscope (SEM) photograph of Yb-PMA MOF, showing that the Yb-PMA MOFs material is a high-quality two-dimensional layered crystal.

[0033] Example 2 The novel rare earth upconversion luminescent two-dimensional MOFs material, preparation method and application provided in this example are basically the same as those in Example 1, except that the novel rare earth metal-organic framework material is specifically 20% Ho,Yb-PMAMOFs material.

[0034] The 20% Ho,Yb-PMA MOFs material provided in this example has a chemical formula of C 21 H 19 N2O 19 Yb 1.6 Ho 0.4 , denoted as 20% Ho,Yb-PMA MOFs.

[0035] The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1) Weigh 0.2 mmol of HoCl3×6H2O and 0.8 mmol of YbCl3×6H2O, add them to a test tube, add 5 mL of deionized water according to the set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform first dispersion; (2) Weigh 1 mmol of PMA ligand, add it to a test tube, add 5 mL of DMF according to the set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform second dispersion; (3) Transfer the above first dispersion liquid and second dispersion liquid into a glass bottle, place the glass bottle in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C, the time being 15 minutes, and the ultrasonic frequency set at 40 KHz until the solution in the bottle is clear and transparent, forming a uniform third dispersion liquid; (4) Seal the glass bottle containing the third dispersion liquid, put it into an oven and maintain the temperature at 70 - 90 °C for reaction for 10 - 24 hours, and rare earth Ho 3+ and Yb 3+ self-assemble with PMA to form two-dimensional MOFs; then naturally cool to room temperature, filter and collect the resulting flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours, with the temperature controlled at 60 - 70 °C, and high-purity 20% Ho,Yb-PMA MOFs material is obtained.

[0036] As Figure 2 shown, the 20% Ho,Yb-PMA MOFs material mainly emits red light under the excitation of a 980 nm laser light source, with the peak at 650 nm.

[0037] Example 3 The novel rare earth upconversion luminescent two-dimensional MOFs material, preparation method and application provided in this example are basically the same as those in Example 1, and the difference lies in that the novel rare earth metal-organic framework material is specifically 20% Tb,Yb-PMA MOFs material.

[0038] The 20% Tb,Yb-PMA MOFs material provided in this example has the chemical formula of C 21 H 19 N2O 19 Yb 1.6 Tb 0.4 , denoted as 20% Tb,Yb-PMA MOFs.

[0039] The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1) Weigh 0.2 mmol of TbCl3×6H2O and 0.8 mmol of YbCl3×6H2O, add them into a test tube, add 5 mL of deionized water according to the set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C, the time being 15 minutes, and the ultrasonic frequency set at 40 KHz until the solution in the bottle is clear and transparent, forming a uniform first dispersion liquid; (2) Weigh 1 mmol of the PMA ligand and add it to a test tube. Add 5 mL of DMF according to the set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the frequency of the ultrasonic wave to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform second dispersion liquid. (3) Transfer the above first dispersion liquid and second dispersion liquid to a glass bottle. Place the glass bottle in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the frequency of the ultrasonic wave to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform third dispersion liquid. (4) Seal the glass bottle containing the third dispersion liquid and put it in an oven at a temperature of 70 - 90 °C for reaction for 10 - 24 hours. The rare earth elements Tb 3+ and Yb 3+ self-assemble with PMA to form two-dimensional MOFs. Then, let it cool naturally to room temperature, filter and collect the resulting flaky crystals. Wash them three times with DMF and absolute ethanol respectively. Finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours at a temperature controlled at 60 - 70 °C to obtain a high-purity 20% Tb,Yb-PMA MOFs material.

[0040] As Figure 3 shown, the 20% Tb,Yb-PMA MOFs material has upconversion / downconversion dual-mode luminescence, showing green upconversion emission under 980 nm excitation ( Figure 3 a), while showing downconverted green luminescence under 330 nm light source excitation ( Figure 3 b), and the strongest emission peak is located at 545 nm.

[0041] Example 4 The novel rare earth upconversion luminescent two-dimensional MOFs material, preparation method and application provided in this example are basically the same as those in Example 1, except that the novel rare earth metal-organic framework material is specifically a 30% Eu,Yb-PMAMOFs material.

[0042] The 30% Eu,Yb-PMA MOFs material provided in this example has the chemical formula of C 21 H 19 N2O 19 Yb 1.4 Eu 0.6 for the basic building unit, denoted as 30% Eu,Yb-PMA MOFs.

[0043] The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1) Weigh 0.3 mmol of EuCl3×6H2O and 0.7 mmol of YbCl3×6H2O, add them to a test tube, add 5 mL of deionized water according to the set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C and the time for 15 minutes, and set the ultrasonic frequency to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform first dispersion; (2) Weigh 1 mmol of PMA ligand, add it to a test tube, add 5 mL of DMF according to the set ratio, place the test tube in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C and the time for 15 minutes, and set the ultrasonic frequency to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform second dispersion; (3) Transfer the above first dispersion and second dispersion to a glass bottle, place the glass bottle in an ultrasonic oscillator for ultrasonic treatment, with the temperature at 25 - 30 °C and the time for 15 minutes, and set the ultrasonic frequency to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform third dispersion; (4) Seal the glass bottle containing the third dispersion, put it in an oven and keep the temperature at 70 - 90 °C, react for 10 - 24 hours, and the rare earth Eu 3+ and Yb 3+ self-assemble with PMA to form two-dimensional MOFs; then naturally cool to room temperature, filter and collect the resulting flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours, with the temperature controlled at 60 - 70 °C, to obtain a high-purity 30% Eu,Yb-PMA MOFs material.

[0044] As Figure 4 shown, the 30% Eu,Yb-PMA MOFs material has upconversion / downconversion dual-mode luminescence. Under 980 nm excitation, it mainly shows red light emission ( Figure 4 a), and also emits red light under 330 nm light source excitation ( Figure 4 b), and the strongest emission peak is located at 615 nm.

[0045] Example 5 The novel rare earth upconversion luminescent two-dimensional MOFs material, preparation method and application provided in this example are basically the same as those in Example 1, except that the novel rare earth metal-organic framework material is specifically the Er-PMA MOFs material.

[0046] The Er-PMA MOFs material provided in this example has the chemical formula of C 21 H 19 N2O 19Er2, denoted as Er-PMA MOFs.

[0047] The preparation method of the novel rare-earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1) Weigh 1 mmol of ErCl3×6H2O and add it to a test tube. Add 5 mL of deionized water according to a set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the ultrasonic frequency to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform first dispersion; (2) Weigh 1 mmol of PMA ligand and add it to a test tube. Add 5 mL of DMF according to a set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the ultrasonic frequency to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform second dispersion; (3) Transfer the above first dispersion and second dispersion to a glass bottle. Place the glass bottle in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the ultrasonic frequency to 40 KHz until the solution in the bottle is clear and transparent, forming a uniform third dispersion; (4) Seal the glass bottle containing the third dispersion and put it in an oven at a temperature of 70 - 90 °C for 10 - 24 hours. The rare earth Er 3+ self-assembles with PMA to form two-dimensional MOFs; then naturally cool to room temperature, filter and collect the resulting flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours at a temperature controlled at 60 - 70 °C to obtain a high-purity Er-PMA MOFs material.

[0048] Example 6 The novel rare-earth upconversion luminescent two-dimensional MOFs material, its preparation method and its application provided in this example are basically the same as those in Example 1, except that this novel rare-earth metal-organic framework material is specifically Tm-PMA MOFs material.

[0049] The Tm-PMA MOFs material provided in this example has a chemical formula of C 21 H 19 N2O 19 Tm2, denoted as Tm-PMA MOFs.

[0050] The preparation method of the novel rare-earth upconversion luminescent two-dimensional MOFs material includes the following steps: (1)Weigh 1 mmol of TmCl3·6H2O and add it to a test tube. Add 5 mL of deionized water according to the set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the frequency of the ultrasonic wave to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform first dispersion. (2)Weigh 1 mmol of PMA ligand and add it to a test tube. Add 5 mL of DMF according to the set ratio. Place the test tube in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the frequency of the ultrasonic wave to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform second dispersion. (3)Transfer the above first dispersion and second dispersion to a glass bottle. Place the glass bottle in an ultrasonic oscillator for ultrasonic treatment at a temperature of 25 - 30 °C for 15 minutes. Set the frequency of the ultrasonic wave to 40 KHz until the solution in the bottle becomes clear and transparent, forming a uniform third dispersion. (4)Seal the glass bottle containing the third dispersion and put it in an oven at a temperature of 70 - 90 °C for reaction for 10 - 24 hours. The rare earth Tm 3+ self - assembles with PMA to form two - dimensional MOFs; then cool it naturally to room temperature, filter and collect the resulting flaky crystals; wash them three times with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying for 8 hours at a temperature controlled at 60 - 70 °C to obtain the high - purity Tm - PMA MOFs material.

[0051] The novel rare - earth up - conversion luminescent two - dimensional MOFs materials, preparation methods and applications provided by the above embodiments of the present invention focus on breaking through the limitation that traditional two - dimensional MOFs are limited to down - conversion luminescence by synchronously improving the targeted MOFs product design method and material synthesis method, and developing near - infrared light - responsive up - conversion luminescent materials; optimizing reaction conditions, adjusting the ratio of precursors and other treatment steps effectively improve the purity of the Ln - PMA MOFs materials; synthesizing under the conditions of low - temperature solvothermal method to achieve obtaining high - purity MOFs materials under safe and simple reaction conditions to meet the needs of industrial production.

[0052] The rare earth upconversion luminescent two-dimensional MOF materials provided by the above embodiments of the present invention have high purity, good reproducibility, environmental friendliness, stable structures and properties, and have rich and stable pores, which are suitable as carriers for gases, quantum dots, nanoparticles, organic small molecule drugs or dyes, etc., and have broad application prospects in many fields such as catalysis, adsorption separation, and optics, electricity, and magnetism. The rare earth upconversion luminescent two-dimensional MOF materials provided by the present invention use few types of raw materials, have a simple and efficient preparation process, high reproducibility, and can respond to excitation lights of different wavelengths, and have advantages such as upconversion / downconversion dual-mode luminescence, and can be widely applied to fields such as upconversion / downconversion dual-mode optical anti-counterfeiting and information security storage.

[0053] The preparation process provided by the present invention is simple, easy to produce, and has high reproducibility; the materials provided by the present invention have multi-mode emission characteristics, can respond to excitation lights of different wavelengths, and can be widely applied to fields such as optical anti-counterfeiting and information security storage.

[0054] It should be particularly noted that the present invention is not limited to the above embodiments. Within the scope recorded in the present invention, other new rare earth metal-organic framework materials, preparation methods and applications obtained by using other components, ratios and preparation process conditions can all achieve the technical effects recorded in the present invention, so the application documents of the present invention will not list them one by one.

[0055] As mentioned above, these are only the preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Any person skilled in the art can make many possible changes or equivalent changes to the technical solutions of the present invention within the scope of the technical solutions of the present invention by using the methods and technical contents disclosed above. Therefore, any equivalent modifications made according to the structure, construction and principle of the present invention without departing from the content of the technical solution of the present invention should be covered by the protection scope of the present invention.

Claims

1. A novel rare earth upconversion luminescent two-dimensional MOFs material, characterized in that, The chemical formula of its basic building unit is C 21 H 19 N2O 19 Ln2, denoted as Ln-PMA MOFs.

2. The novel rare earth upconversion luminescent two-dimensional MOFs material according to claim 1, wherein The material belongs to the monoclinic system with the space group P121 / c1; the asymmetric unit of Ln-PMA MOFs contains two rare-earth cations Ln 3+ , 1.5 molecules of 1,2,4,5-benzenetetracarboxylic acid (PMA), 2 coordinated N,N-dimethylformamide (DMF) molecules and 2 coordinated water molecules; two Ln 3+ both adopt an eight-coordinate geometric structure, but their coordination environments are slightly different; Ln1 and Ln2 are connected by two carboxylate bridges from one PMA molecule to form a binuclear unit, and these units are connected along the b-axis and c-axis by PMA ligands and form a two-dimensional layered structure under the capping action of DMF, stacking along the a-axis.

3. A method for preparing the novel rare earth upconversion luminescent two-dimensional MOFs material according to one of claims 1 or 2, characterized in that, It includes the following steps: (1) Weigh a set amount of rare earth salt, add it to a test tube, add deionized water in a set ratio, and place the test tube in an ultrasonic oscillator for ultrasonic treatment until the solution in the bottle is clear and transparent, forming a uniform first dispersion; (2) Weigh a set amount of PMA ligand, add it to a test tube, add DMF in a set ratio, and place the test tube in an ultrasonic oscillator for ultrasonic treatment until the solution in the bottle is clear and transparent, forming a uniform second dispersion; (3) Transfer the above first dispersion and second dispersion to a glass bottle, and place the glass bottle in an ultrasonic oscillator for ultrasonic treatment until the solution in the bottle is clear and transparent, forming a uniform third dispersion; (4) Seal the glass bottle containing the third dispersion liquid, place it in an oven and let it stand still. The rare earth Ln 3+ self-assembles with PMA to form two-dimensional MOFs; then cool it to room temperature, filter and collect the resulting flaky crystals; wash the flaky crystals with DMF and absolute ethanol respectively; finally, place the flaky crystals in a vacuum drying oven for vacuum drying to obtain high-purity Ln-MOFs materials.

4. The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material according to claim 3, characterized in that, The rare earth salt in step (1) is one of rare earth nitrate and rare earth chloride; The rare earth ion is Y 3+ , La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Yb 3+ , Lu 3+ or one, two or more of them.

5. The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material according to claim 3, characterized in that, The conditions for ultrasonic treatment in step (1): the temperature is 25 - 30 °C, the time is 15 minutes, and the frequency of the ultrasonic wave is set to 40KHz.

6. The preparation method of the novel rare-earth upconversion luminescent two-dimensional MOFs material according to claim 3, wherein, In step (1), relative to 0.9 - 1.2 mmol of rare earth salt, the amount of deionized water used is 4 - 7 mL; in step (2), relative to 0.9 - 1.2 mmol of PMA, the amount of DMF used is 4 - 7 mL.

7. The preparation method of the novel rare earth upconversion luminescent two-dimensional MOFs material according to claim 3, characterized in that, In step (4), specifically, it is placed in an oven to maintain a temperature of 70 - 90 °C, and reacted for 10 - 24 hours to synthesize flaky crystals, then naturally cooled to room temperature, and the generated flaky crystals are collected by filtration; the flaky crystals are washed three times with DMF and absolute ethanol respectively; placed in a vacuum drying oven for vacuum drying for 8 hours, and the temperature is controlled at 60 - 70 °C to obtain the two-dimensional Ln-PMA MOFs material.

8. Application of the novel rare earth upconversion luminescent two-dimensional MOFs material according to claim 1 or 2 in the fields of security anti-counterfeiting, optical information storage, and biological imaging.

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