Enhanced rare earth doped upconversion luminescent metal-organic framework material, preparation method and application

Abstract

The application belongs to the technical field of new materials, and discloses a reinforced rare earth doped upconversion luminescence metal organic framework material, a preparation method and application, a basic building unit of the material has a chemical formula of C4HO8Ln, and is recorded as Ln-MOFs, wherein the Ln site is jointly occupied by one, two or three different rare earth ions, including a sensitizing agent rare earth ion, an activator rare earth ion and an energy mediating node rare earth ion; the Ln-MOFs are prepared by a high-temperature solvothermal method, and a three-dimensional framework is constructed by taking rare earth ions as metal centers and oxalic acid and formic acid as organic ligands, wherein the formic acid is derived from in-situ decomposition of a DMF molecule under high temperature. Under excitation of 980 nm near-infrared light, the three-doped Ln-MOFs have a significantly improved upconversion luminescence intensity of Ho 3+ . The upconversion luminescence intensity of Ho 3+ is significantly improved by taking the energy mediating node. The material prepared by the application can be widely applied in the fields of optical anti-counterfeiting and information security storage.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to an enhanced rare-earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application. Background Technology

[0002] Rare-earth-based metal-organic frameworks (Ln-MOFs) are a class of crystalline porous materials with periodic network structures formed by the self-assembly of rare-earth ions or rare-earth clusters as metal nodes and organic ligands through coordination. These materials not only inherit the ultra-high specific surface area, flexibly designable pore structures, and diverse chemical modifiability of traditional metal-organic frameworks (MOFs), but also possess the characteristic 4f-4f electronic transition properties of rare-earth ions due to their use of rare-earth ions as metal nodes. This allows them to produce characteristic luminescence with narrow-band emission, large Stokes (or anti-Stokes) shifts, long fluorescence lifetimes (microseconds to milliseconds), and high color purity. Simultaneously, the 4f electron shell of rare-earth ions is influenced by the outer 5s²5p electrons... 6 The effective shielding of electrons results in higher coordination numbers (6–12, or even higher) compared to traditional MOFs, allowing for more flexible and varied coordination geometries. Furthermore, the stronger ionicity of the coordination bonds enables the connection of more organic ligands, inducing complex three-dimensional topological networks that are difficult to obtain with traditional MOFs. These advantages have made rare-earth metal-organic frameworks one of the most promising luminescent materials in recent years.

[0003] Currently, research on rare-earth upconversion luminescent MOFs mainly relies on dual-doped rare-earth ions to achieve upconversion luminescence. Upconversion luminescence is typically an anti-Stokes optical process where a material continuously absorbs two or more low-energy photons (such as near-infrared light) and emits a high-energy photon (such as visible or ultraviolet light) through energy transfer mechanisms such as energy transfer and excited-state absorption. In recent years, research on rare-earth upconversion luminescent MOFs has remained very limited, and has mostly focused on dual-doped rare-earth ion MOF systems. This research primarily involves designing crystal mesh structures using different organic ligands to alter the spatial distance between rare-earth ions, thereby optimizing energy transfer and achieving upconversion luminescence in rare-earth MOFs. In dual-doped rare-earth ion Ln-MOF systems, one rare-earth ion acts as a sensitizer (such as Yb). 3+ One type efficiently absorbs low-energy excitation light and transfers the energy to the activator; another type acts as an activator (such as Eu). 3+ 、Tb 3 + Ho 3+After receiving energy, lanthanides emit high-energy photons of the target wavelength. However, the crystallization process of MOFs is essentially a coordination-driven self-assembly process. When two or more rare-earth ions coexist in the same synthetic system, due to the extremely similar chemical properties of lanthanides, they tend to randomly occupy metal node positions in the framework. Therefore, the average distance and relative geometric orientation between the sensitizer and activator in the dual-doped rare-earth ion Ln-MOF system are often difficult to control precisely. Reverse energy transfer may also occur between the activator and sensitizer, resulting in upconversion luminescence in the dual-doped rare-earth ion Ln-MOF system often failing to achieve optimal luminescence performance. Therefore, new mechanisms and methods are needed to prepare new rare-earth ion Ln-MOF system materials to overcome these problems. Summary of the Invention

[0004] To address the limitations of existing dual-doped rare-earth ion upconversion luminescent Ln-MOFs materials, which suffer from limited energy transfer efficiency and are confined to a sensitizer-activator binary system, this invention provides an enhanced rare-earth-doped upconversion luminescent metal-organic framework material, its preparation method, and applications. By synergistically optimizing the design and synthesis process of Ln-MOFs materials and introducing an enhanced doped rare-earth ion system, the luminescence limitations of traditional binary systems are overcome, resulting in upconversion luminescent Ln-MOFs materials with superior energy transfer efficiency. In terms of the preparation method, by optimizing reaction conditions and controlling the rare-earth ion ratio, the yield and purity of Ln-MOFs materials are significantly improved. Furthermore, the preparation method eliminates the need for stirring, ultrasonication, and other processing steps, simplifying the operation process, reducing the complexity of the process, and minimizing reliance on specialized equipment. This allows for the acquisition of high-purity Ln-MOFs materials under simple conditions, thus meeting the needs of industrial production.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: An enhanced rare-earth-doped upconversion luminescent metal-organic framework material is characterized by the basic building block having the chemical formula C4HO8Ln, denoted as Ln-MOFs, wherein the Ln sites are occupied by one, two, or three different rare-earth ions; the one, two, or three rare-earth ions include sensitizer rare-earth ions, activator rare-earth ions, and energy-mediated node rare-earth ions, wherein the energy-mediated node rare-earth ions are used to transfer energy between the sensitizer rare-earth ions and the activator rare-earth ions to construct an enhanced upconversion luminescence energy transfer pathway; wherein the sensitizer rare-earth ion is Yb. 3+ The energy-mediated node rare earth ion is Tb. 3+ The activator rare earth ions are Ho. 3+ Or Eu 3+ .

[0006] A method for preparing the enhanced rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh a mixture of rare earth salts containing one, two or three different rare earth ions, wherein the one, two or three rare earth ions include sensitizer rare earth ions, activator rare earth ions and energy-mediated node rare earth ions, and add it to the inner liner of a reaction vessel made of polytetrafluoroethylene. (2) Weigh out the oxalic acid ligand and add it to the inner liner of the reactor; (3) In the reactor liner containing rare earth salts and oxalic acid ligands, N,N'-dimethylformamide solvent and deionized water are added in sequence according to the set ratio. The reactor liner is left to stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. The liner containing the dispersion is sealed according to the correct operating procedure of the reactor and placed in an oven. It is reacted at 140-170 °C for 48-72 hours to allow the DMF solvent to decompose in situ to produce formic acid. Rare earth Ln³⁺ self-assembles with deprotonated oxalic acid and formic acid to form three-dimensional MOFs. The product is cooled to room temperature and the blocky crystals are collected by filtration. The blocky crystals are washed with DMF and anhydrous ethanol respectively. Finally, the blocky crystals are placed in a vacuum drying oven and vacuum dried at 70-80 °C for 4-6 hours to obtain high-purity Ln-MOFs material.

[0007] An application of the enhanced rare-earth-doped upconversion luminescent metal-organic framework material in the fields of optical anti-counterfeiting and information security storage is disclosed. The material generates upconversion luminescence under 980 nm near-infrared light excitation, and the upconversion luminescence includes an energy transfer path from energy-mediated node rare-earth ions to activator rare-earth ions. The material also generates downconversion luminescence under 288 nm ultraviolet light excitation, realizing a downconversion / upconversion dual-mode optical anti-counterfeiting.

[0008] Compared with the prior art, the present invention has the following beneficial effects: 1. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its applications provided by this invention simultaneously improve the product design and material synthesis methods of traditional dual-doped rare-earth ion Ln-MOFs. It selectively chooses rare-earth ions with matching energy levels as energy transfer mediator nodes to enhance upconversion efficiency. In the sensitizer-activator system, based on the upconversion energy transfer strategy, a third rare-earth ion is introduced to construct tri-doped rare-earth ion Ln-MOFs, thereby overcoming the limitations of traditional dual-doped Ln-MOFs systems in terms of upconversion luminescence intensity and energy transfer efficiency, and developing highly efficient upconversion luminescent materials with near-infrared light response. Simultaneously, by optimizing reaction conditions and controlling the rare-earth ion ratio, the yield and purity of Ln-MOFs materials are effectively improved, enabling the acquisition of high-purity MOFs materials under simple reaction conditions, meeting the needs of industrial production.

[0009] 2. This invention introduces a third type of rare-earth ion with energy level matching as the energy-mediated node in a triple-doped energy transfer strategy, which can regulate and optimize the upconversion energy transfer efficiency of the double-doped rare-earth ion Ln-MOFs system. This strategy effectively suppresses multiphonon relaxation and cross-relaxation by intervening in the energy transfer path, finely controlling energy transfer, relaxation rate, and energy level difference. Simultaneously, it suppresses concentration quenching by diluting the spatial distribution of the activator and regulates the lattice field strength and coordination microenvironment, achieving efficient, multicolor tunable, and stable upconversion luminescence. These mechanisms deepen and expand the energy transfer process in Ln-MOFs. More importantly, they provide a theoretical basis for the rational design of rare-earth metal-organic framework materials and expand their application potential in advanced photonics.

[0010] 3. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material and its preparation method provided by this invention adopt a solvothermal synthesis route, eliminating the need for stirring, ultrasonication, or other auxiliary treatments, and enabling self-assembly synthesis in a reaction vessel. This method simplifies experimental steps, reduces operational difficulty, and minimizes reliance on experimental instruments. It has advantages such as simple steps, convenient operation, easy control of reaction conditions, low cost, high product reproducibility, and environmental friendliness, making it easy to industrialize.

[0011] 4. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material provided by this invention has the characteristics of high purity and stable structure and performance. This material contains abundant and stable porous structures, making it suitable as a carrier for substances such as gases, quantum dots, and nanoparticles, and it has broad application prospects in many fields such as catalysis, adsorption separation, and optics.

[0012] 5. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material provided by this invention uses fewer types of raw materials and can respond to excitation light of different wavelengths. It also has dual-mode luminescence characteristics of downconversion / upconversion and can be widely used in fields such as downconversion / upconversion dual-mode optical anti-counterfeiting and information security storage.

[0013] 6. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material provided by this invention achieves a novel energy transfer enhancement mechanism from terbium to holmium rare-earth upconversion luminescence through an unconventional combination of three-doped rare-earth ions, providing a new technical approach for designing energy transfer pathways in rare-earth-based upconversion luminescence systems. Attached Figure Description

[0014] Figure 1 These are a schematic diagram of the structure of the Yb-MOFs material obtained in Example 1 of this invention and a scanning electron microscope (SEM) image; Figure 2 These are the powder X-ray diffraction (PXRD) patterns of the 20%Ho, 20%Tb, 60%Yb-MOFs material obtained in Example 2 of this invention, and the powder X-ray diffraction (PXRD) patterns of Yb-MOFs simulated by the single crystal structure of the Yb-MOFs material.

[0015] Figure 3 This is the upconversion fluorescence spectrum of the 20%Ho, 20%Tb, 60%Yb-MOFs material obtained in Example 2 of this invention under excitation by a 980 nm laser source.

[0016] Figure 4 This is the upconversion fluorescence spectrum of the 40%Ho,60%Yb-MOFs material obtained in Comparative Example 1 of this invention under excitation by a 980 nm laser source.

[0017] Figure 5 These are the down-transfer / up-conversion fluorescence spectra of the 40%Tb, 60%Yb-MOFs material obtained in Comparative Example 2 of this invention under excitation by light sources of 288 nm and 980 nm, respectively. Detailed Implementation

[0018] The following is in conjunction with the appendix Figure 1-5 The present invention will be described in detail with reference to several embodiments and comparative examples. Unless otherwise specified, all equipment and materials used are commercially available.

[0019] Basic Implementation The enhanced rare-earth-doped upconversion luminescent metal-organic framework material provided in this embodiment has a basic building block with the chemical formula C4HO8Ln, denoted as Ln-MOFs. The Ln sites are occupied by one, two, or three different rare-earth ions. These one, two, or three rare-earth ions include sensitizer rare-earth ions, activator rare-earth ions, and energy-mediated node rare-earth ions. The energy-mediated node rare-earth ions are used to transfer energy between the sensitizer rare-earth ions and the activator rare-earth ions to construct an upconversion luminescence energy transfer pathway. The sensitizer rare-earth ion is Yb. 3+ The energy-mediated node rare earth ion is Tb. 3+ The activator rare earth ions are Ho. 3+ Or Eu 3+ .

[0020] When the Ln site is occupied by a single rare earth ion (single doping), it is the sensitizer rare earth ion Yb. 3+ .

[0021] When two rare earth ions co-occupy the Ln site (dual doping), they include both sensitizer rare earth ions and activator rare earth ions, wherein the activator rare earth ion is Ho. 3+ Or Eu 3+ .

[0022] When the Ln site is occupied by three rare earth ions (triple doping), the Ln site is dominated by Yb 3+ 、Tb 3+ and Ho 3+ Jointly occupied, of which Yb 3+ As a sensitizer, Tb 3+ As an energy-mediated node, Ho 3+ As an activator; the upconversion luminescence energy transfer pathway includes Tb 3+ to Ho 3+ Energy transfer to enhance Ho 3+ The upconversion luminescence intensity.

[0023] The doped material belongs to the orthorhombic crystal system with space group . Cmca The asymmetric unit of Ln-MOFs contains one rare earth cation Ln. 3+ 3 oxalic acid molecules and 2 formic acid molecules; the Ln 3+ The ion adopts an eight-coordinate geometry, and its coordination environment consists of six carboxyl oxygen atoms provided by three oxalic acid molecules and two oxygen atoms provided by two formic acid molecules; wherein, the oxalic acid ligand is connected to Ln in a bidentate bridging manner through a carboxylic acid group. 3+ The ions extend along the a-axis and c-axis, while the formic acid ligands extend the framework along the b-axis, together forming a three-dimensional framework structure.

[0024] A method for preparing the enhanced rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh a mixture of rare earth salts containing one, two, or three different rare earth ions, wherein the one, two, or three rare earth ions include sensitizing rare earth ions, activating rare earth ions, and energy-mediated node rare earth ions, and add it to the inner liner of a reaction vessel made of polytetrafluoroethylene; wherein the rare earth salt is a rare earth sulfate; and 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 three of the rare earth salts; the total molar amount of rare earth salts is 0.24 ~ 0.26 mmol; (2) Weigh out the oxalic acid ligand and add it to the inner liner of the reactor; wherein the amount of oxalic acid ligand is 0.48 ~ 0.52 mmol, the amount of DMF in step (3) is 5 ~ 8 mL, the amount of deionized water is 2.5 ~ 4 mL, and the volume ratio of DMF to deionized water is 2:1.

[0025] (3) In the reactor liner containing rare earth salts and oxalic acid ligands, N,N'-dimethylformamide solvent and deionized water are added sequentially according to the set ratio. The reactor liner is left to stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. The liner containing the dispersion is sealed according to the correct operating procedure of the reactor and placed in an oven. It is then reacted at 140-170 ℃ for 48-72 hours to allow the DMF solvent to decompose in situ to produce formic acid and rare earth Ln. 3+ Three-dimensional MOFs were formed by self-assembly with deprotonated oxalic acid and formic acid; the product was cooled to room temperature and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol, respectively; finally, the bulk crystals were placed in a vacuum drying oven and vacuum dried at 70-80 °C for 4-6 hours to obtain high-purity Ln-MOFs materials.

[0026] An application of the enhanced rare-earth-doped upconversion luminescent metal-organic framework material in the fields of optical anti-counterfeiting and information security storage is disclosed. The material generates upconversion luminescence under 980 nm near-infrared light excitation, and the upconversion luminescence includes an energy transfer path from energy-mediated node rare-earth ions to activator rare-earth ions. The material also generates downconversion luminescence under 288 nm ultraviolet light excitation, realizing a downconversion / upconversion dual-mode optical anti-counterfeiting.

[0027] Example 1 The enhanced rare-earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application provided in this embodiment are a detailed refinement of the basic embodiment.

[0028] See Figure 1 The rare-earth upconversion luminescent MOFs material provided in this embodiment is specifically a Yb-MOFs material.

[0029] The Yb-MOFs material provided in this embodiment has the chemical formula C4HO8Yb for its basic building block, and is denoted as Yb-MOFs.

[0030] This Yb-MOF material belongs to the orthorhombic crystal system, with space group [space group missing]. Cmca The asymmetric unit of Yb-MOFs contains one rare earth cation Yb. 3+ 3 oxalic acid molecules and 2 formic acid molecules; the Yb 3+ The ion adopts an eight-coordinate geometry, with its coordination environment consisting of six carboxyl oxygen atoms provided by three oxalic acid molecules and two oxygen atoms provided by two formic acid molecules. The oxalic acid ligand connects to Yb via a bidentate bridging mechanism through a carboxylic acid group. 3+ The ions extend along the a-axis and c-axis. The formic acid ligands extend the framework along the b-axis, together forming a three-dimensional framework structure (see Figure 1).

[0031] The preparation method of this enhanced rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh out 0.24 ~ 0.26 mmol of Yb2(SO4)3·8H2O and add it into the inner liner of the reactor made of polytetrafluoroethylene; (2) Weigh 0.48 ~ 0.52 mmol of oxalic acid ligand and add it to the inner liner of the reaction vessel made of polytetrafluoroethylene; (3) In the reactor liner containing Yb2(SO4)3·8H2O and oxalic acid ligand, add 5~8 mL of DMF solvent and 2.5~4 mL of deionized water in sequence according to the set ratio. Let the reactor liner stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. Seal the liner containing the dispersion according to the correct operating procedure of the reactor, place it in an oven to stand, heat, and react. Under high temperature conditions, the DMF solvent decomposes to release formic acid, and rare earth Yb... 3+ Three-dimensional MOFs were formed by self-assembly with oxalic acid and formic acid; then cooled to room temperature, and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol respectively; finally, the bulk crystals were placed in a vacuum drying oven for vacuum drying to obtain high-purity Yb-MOFs material.

[0032] The preparation method in this embodiment utilizes solvothermal and autogenous pressure conditions to deprotonated oxalic acid molecules and deprotonated formic acid molecules and Yb produced by the high-temperature decomposition of DMF solvent. 3+ Ion self-assembly formed rare-earth MOFs. We named the bulk crystals collected from the bottom of the reactor liner Yb-MOFs. This embodiment effectively improved the yield and purity of Yb-MOFs materials by optimizing reaction conditions and adjusting the rare-earth ion ratio, achieving the acquisition of high-purity MOFs materials under simple reaction conditions. This strategy provides a new technical approach for the synthesis of high-purity rare-earth upconversion luminescent metal-organic framework materials.

[0033] like Figure 1 As shown, (a) is a schematic diagram of the Yb-MOF crystal structure, showing that Yb-MOFs have abundant pores and close spatial distances between rare earth metal nodes, making them an effective platform for multi-doped rare earth systems. They can serve as carriers for gases, quantum dots, nanoparticles, etc., and have broad application prospects in catalysis, adsorption separation, and optics. (b) is a scanning electron microscope (SEM) image of Yb-MOFs, showing that the Yb-MOFs material is a high-quality three-dimensional bulk crystal. Figure 2 As shown, the main peak positions in the X-ray diffraction pattern of Yb-MOF powder were simulated using the single-crystal structure of Yb-MOFs.

[0034] Example 2 The enhanced rare earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application provided in this embodiment are basically the same as those in Example 1. The difference is that the enhanced rare earth metal-organic framework material is specifically a 20% Ho, 20% Tb, 60% Yb-MOFs material.

[0035] The 20%Ho, 20%Tb, 60%Yb-MOFs material provided in this embodiment has the chemical formula C4HO8Yb for its basic building blocks. 0.6 Tb 0.2 Ho 0.2 , denoted as 20%Ho, 20%Tb, 60%Yb-MOFs.

[0036] The preparation method of the enhanced rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh out 0.048 ~ 0.052 mmol of Ho2(SO4)3·8H2O, 0.048 ~ 0.052 mmol of Tb2(SO4)3·8H2O and 0.144 ~ 0.156 mmol of Yb2(SO4)3·8H2O and add them to the inner liner of the reaction vessel made of polytetrafluoroethylene; (2) Weigh 0.48 ~ 0.52 mmol of oxalic acid ligand and add it to the inner liner of the reaction vessel made of polytetrafluoroethylene; (3) In the reactor liner containing Ho2(SO4)3·8H2O, Tb2(SO4)3·8H2O, Yb2(SO4)3·8H2O, and oxalic acid ligand, add 5-8 mL of DMF solvent and 2.5-4 mL of deionized water in sequence according to the set ratio. Let the reactor liner stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. Seal the liner containing the dispersion according to the correct operating procedure of the reactor, place it in an oven to stand, heat, and react. Under high temperature conditions, the DMF solvent decomposes to release formic acid, and rare earth Ho2(SO4)3·8H2O is released into the reactor liner. 3+ 、Tb 3+ and Yb 3+ Three-dimensional MOFs were formed by self-assembly with oxalic acid and formic acid; then cooled to room temperature, and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol respectively; finally, the bulk crystals were placed in a vacuum drying oven for vacuum drying to obtain high-purity 20%Ho, 20%Tb, 60%Yb-MOFs material.

[0037] like Figure 2 As shown, by comparing the powder X-ray diffraction patterns of 20%Ho, 20%Tb, 60%Yb-MOFs with the simulated powder X-ray diffraction pattern of Yb-MOFs, no significant shift in the main peak positions was observed, proving that the introduction of rare earth ions into the triple-doped Ln-MOFs system did not alter the crystal structure and phase of the MOFs material itself. Figure 3 As shown, this 20%Ho, 20%Tb, 60%Yb-MOFs material mainly emits red light when excited by a 980 nm laser source, with a peak at 657 nm.

[0038] Comparative Example 1 The rare earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application provided in this comparative example are basically the same as those in Example 1. The difference is that the rare earth metal-organic framework material is specifically a 40% Ho, 60% Yb-MOFs material.

[0039] The 40%Ho,60%Yb-MOFs material provided in this comparative example has the chemical formula C4HO8Yb for its basic building blocks. 0.6 Ho 0.4 , denoted as 40%Ho, 60%Yb-MOFs.

[0040] The method for preparing the rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh 0.096 ~ 0.104 mmol of Ho2(SO4)3·8H2O and 0.144 ~ 0.156 mmol of Yb2(SO4)3·8H2O and add them to the inner liner of the reactor made of polytetrafluoroethylene; (2) Weigh 0.48 ~ 0.52 mmol of oxalic acid ligand and add it to the inner liner of the reaction vessel made of polytetrafluoroethylene; (3) In the reactor liner containing Ho2(SO4)3·8H2O, Yb2(SO4)3·8H2O and oxalic acid ligand, add 5~8 mL of DMF solvent and 2.5~4 mL of deionized water in sequence according to the set ratio. Let the reactor liner stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. Seal the liner containing the dispersion according to the correct operating procedure of the reactor, place it in an oven to stand, heat, and carry out the reaction. Under high temperature conditions, the DMF solvent decomposes to release formic acid, and rare earth Ho2(SO4)3·8H2O and Yb2(SO4)3·8H2O are released. 3+ and Yb 3+ Three-dimensional MOFs were formed by self-assembly with oxalic acid and formic acid; then cooled to room temperature, and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol respectively; finally, the bulk crystals were placed in a vacuum drying oven for vacuum drying to obtain high-purity 40%Ho,60%Yb-MOFs material.

[0041] The upconversion luminescence properties of the 40%Ho, 60%Yb-MOFs material were tested under the exact same test conditions as in Example 2. The test results are as follows: Figure 4 As shown, this 40%Ho,60%Yb-MOFs material mainly emits red light under 980 nm laser excitation, with a peak at 657 nm. By... Figure 3 and Figure 4By comparing the upconversion fluorescence spectra, it can be seen that Ho in the triple-doped system of Example 2 3+ The upconversion luminescence intensity is significantly enhanced compared to the dual-doped system in Comparative Example 1.

[0042] Comparative Example 2 The rare earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application provided in this comparative example are basically the same as those in Example 1. The difference is that the rare earth metal-organic framework material is specifically 40% Tb and 60% Yb-MOFs.

[0043] The 40%Tb,60%Yb-MOFs material provided in this comparative example has the chemical formula C4HO8Yb for its basic building blocks. 0.6 Tb 0.4 It is denoted as 40%Tb,60%Yb-MOFs.

[0044] The method for preparing the rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh 0.096 ~ 0.104 mmol of Tb2(SO4)3·8H2O and 0.144 ~ 0.156 mmol of Yb2(SO4)3·8H2O and add them to the inner liner of the reactor made of polytetrafluoroethylene; (2) Weigh 0.48 ~ 0.52 mmol of oxalic acid ligand and add it to the inner liner of the reaction vessel made of polytetrafluoroethylene; (3) In the reactor liner containing Tb2(SO4)3·8H2O, Yb2(SO4)3·8H2O and oxalic acid ligand, add 5~8 mL of DMF solvent and 2.5~4 mL of deionized water in sequence according to the set ratio. Let the reactor liner stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. Seal the liner containing the dispersion according to the correct operating procedure of the reactor, place it in an oven to stand, heat, and carry out the reaction. Under high temperature conditions, the DMF solvent decomposes to release formic acid and rare earth Tb. 3+ and Yb 3+ Three-dimensional MOFs were formed by self-assembly with oxalic acid and formic acid; then cooled to room temperature, and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol respectively; finally, the bulk crystals were placed in a vacuum drying oven for vacuum drying to obtain high-purity 40%Tb,60%Yb-MOFs material.

[0045] The upconversion luminescence properties of the 40%Tb,60%Yb-MOFs material were tested under the exact same test conditions as in Example 2. The test results are as follows: Figure 5As shown, this 40%Tb,60%Yb-MOFs material exhibits dual-mode emission (down-conversion / up-conversion), emitting green light under excitation by a 288 nm ultraviolet light source and a 980 nm near-infrared light source, with the main emission peak located at 545 nm. By... Figure 3 and Figure 5 By comparing the upconversion fluorescence spectra, it can be seen that Tb in the triple-doped system of Example 2... 3+ The upconversion luminescence intensity is relatively weaker compared to the dual-doped system in Comparative Example 2. This is in contrast to the Ho-doped system in Example 2. 3+ The phenomenon of enhanced upconversion luminescence intensity proves that in Yb , Tb , Tb in the triple-doped Ho-MOF material system 3+ As an energy-mediated node, a system was constructed using Tb 3+ ®Ho 3+ A novel upconversion luminescence energy transfer pathway, where energy is transferred from Tb 3+ Passed to Ho 3+ This makes Tb 3+ Upconversion luminescence reduction Ho 3+ Enhanced upconversion luminescence. This study demonstrates that the targeted introduction of energy-mediated rare-earth ions with energy level matching into the triple-doped system can significantly optimize the upconversion luminescence energy transfer efficiency of the traditional dual-doped system, thereby enhancing upconversion luminescence and overcoming the limitations of the traditional dual-doped Ln-MOF system in terms of upconversion luminescence intensity and energy transfer efficiency.

[0046] Example 3 The novel enhanced rare-earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application provided in this embodiment are basically the same as those in Example 1. The difference is that the novel rare-earth metal-organic framework material is specifically a Ho,Tm,Yb-MOFs material.

[0047] The Ho,Tm,Yb-MOFs material provided in this embodiment has the chemical formula of C4HO8Ln (Ln is Ho,Tm,Yb) as its basic building block, and is denoted as Ho,Tm,Yb-MOFs.

[0048] The preparation method of the enhanced rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh out 0.24 ~ 0.26 mmol of Ln2(SO4)3·8H2O (Ln is Ho, Tm, Yb), and add the three rare earth sulfates in any proportion to the inner liner of the reactor made of polytetrafluoroethylene. (2) Weigh 0.48 ~ 0.52 mmol of oxalic acid ligand and add it to the inner liner of the reaction vessel made of polytetrafluoroethylene; (3) In the reactor liner containing Ho2(SO4)3·8H2O, Tm2(SO4)3·8H2O, Yb2(SO4)3·8H2O, and oxalic acid ligand, add 5-8 mL of DMF solvent and 2.5-4 mL of deionized water in sequence according to the set ratio. Let the reactor liner stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. Seal the liner containing the dispersion according to the correct operating procedure of the reactor, place it in an oven to stand, heat, and react. Under high temperature conditions, the DMF solvent decomposes to release formic acid, and rare earth Ho2(SO4)3·8H2O is released into the reactor liner. 3+ Tm 3+ and Yb 3+ Three-dimensional MOFs were formed by self-assembly with oxalic acid and formic acid; then cooled to room temperature, and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol respectively; finally, the bulk crystals were placed in a vacuum drying oven for vacuum drying to obtain high-purity Ho,Tm,Yb-MOFs materials.

[0049] Example 4 The enhanced rare earth-doped upconversion luminescent metal-organic framework material, its preparation method, and its application provided in this embodiment are basically the same as those in Example 1. The difference is that the enhanced rare earth metal-organic framework material is specifically an Eu,Tb,Yb-MOF material.

[0050] The Eu,Tb,Yb-MOFs material provided in this embodiment has the chemical formula of C4HO8Ln (Ln represents Eu, Tb, and Yb) as its basic building block, and is denoted as Eu,Tb,Yb-MOFs.

[0051] The preparation method of the enhanced rare-earth-doped upconversion luminescent metal-organic framework material includes the following steps: (1) Weigh out 0.24 ~ 0.26 mmol of Ln2(SO4)3·8H2O (Ln is Eu, Tb, Yb), and add the three rare earth sulfates in any proportion to the inner liner of the reactor made of polytetrafluoroethylene. (2) Weigh 0.48 ~ 0.52 mmol of oxalic acid ligand and add it to the inner liner of the reaction vessel made of polytetrafluoroethylene; (3) In the reactor liner containing Eu2(SO4)3·8H2O, Tb2(SO4)3·8H2O, Yb2(SO4)3·8H2O, and oxalic acid ligand, add 5-8 mL of DMF solvent and 2.5-4 mL of deionized water in the specified proportions. Let the reactor liner stand to allow the contents to mix thoroughly until the solution is clear and transparent, forming a uniform dispersion. Seal the liner containing the dispersion according to the correct operating procedure for the reactor, place it in an oven to stand, heat, and react. Under high temperature conditions, the DMF solvent decomposes to release formic acid and rare earth Eu. 3+ 、Tb 3+ and Yb 3+ Three-dimensional MOFs were formed by self-assembly with oxalic acid and formic acid; then cooled to room temperature, and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol respectively; finally, the bulk crystals were placed in a vacuum drying oven for vacuum drying to obtain high-purity Eu,Tb,Yb-MOFs materials.

[0052] The enhanced rare-earth-doped upconversion luminescent metal-organic framework materials, their preparation methods, and applications disclosed in the above embodiments and comparative examples of this invention focus on overcoming the limitations of traditional dual-doped rare-earth ion upconversion luminescent Ln-MOF materials, which are confined to sensitizer-activator systems, by simultaneously improving targeted MOF product design and material synthesis methods. This leads to the development of triple-doped rare-earth ion upconversion luminescent Ln-MOF materials with superior energy transfer efficiency. Optimizing reaction conditions and adjusting rare-earth ion ratios effectively improves the yield and purity of Ln-MOF materials. Synthesis is performed without the need for stirring or ultrasonic treatment, simplifying experimental steps and reducing operational difficulty, thus reducing the use of experimental instruments and enabling the acquisition of high-purity MOF materials under simple reaction conditions to meet the needs of industrial production.

[0053] The enhanced rare-earth-doped upconversion luminescent metal-organic framework (Ln-MOFs) materials, their preparation methods, and applications provided in the above embodiments of the present invention have the chemical formula C4HO8Ln as the basic building block, denoted as Ln-MOFs (Ln represents one, two, or three rare-earth ions). The preparation method of these upconversion luminescent Ln-MOFs is a high-temperature solvothermal method, utilizing rare-earth ions as metal centers and oxalic acid and formic acid as organic ligands to form a network. The formic acid originates from the decomposition of DMF molecules at high temperatures. Under heating and autogenous pressure, deprotonated oxalic acid and formic acid react with rare-earth Ln... 3+ A series of Ln-MOFs doped with different rare earth ions were synthesized through ion self-assembly. 3+ Ions and Tb 3+ Or Ho 3+Co-doping yielded two types of dual-doped rare-earth ion Ln-MOFs (Yb,Tb-MOFs and Yb,Ho-MOFs) exhibiting characteristic upconversion luminescence; further, Yb... 3+ 、Tb 3+ and Ho 3+ Triple-doped rare-earth ion Ln-MOFs (Yb) were obtained by co-doping with three rare-earth ions. , Tb , Ho-MOFs), which simultaneously exhibit Tb 3+ and Ho 3+ The upconversion luminescence properties of its Tb 3+ The upconversion luminescence of Ho is relatively weak, while Ho 3+ The upconversion luminescence of the Ln-MOFs is significantly enhanced compared to that of the corresponding dual-doped rare-earth ion Yb,Ho-MOFs. The preparation method provided by this invention is simple, easy to operate, and reproducible; by controlling different ratios of the rare-earth triple-doped components, the previously unreported upconversion luminescence of Tb-doped Ln-MOFs is achieved. 3+ ®Ho 3+ The upconversion light transmission path optimizes energy transfer efficiency and can be widely used in fields such as optical anti-counterfeiting and information security storage.

[0054] The enhanced rare-earth-doped upconversion luminescent metal-organic framework materials provided in the above embodiments of the present invention have high purity, good reproducibility, environmental friendliness, and stable structure and performance. They have abundant and stable pores, making them suitable as carriers for gases, quantum dots, nanoparticles, etc., and have broad application prospects in many fields such as catalysis, adsorption separation, and optics.

[0055] The enhanced rare-earth-doped upconversion luminescent metal-organic framework material provided by this invention uses fewer types of raw materials and has a simple and efficient preparation process. It can respond to excitation light of different wavelengths and has the advantages of downconversion / upconversion dual-mode luminescence. It can be widely used in downconversion / upconversion dual-mode optical anti-counterfeiting, information security storage and other fields.

[0056] The enhanced rare-earth-doped upconversion luminescent metal-organic framework material provided by this invention achieves a novel energy transfer mechanism of rare-earth upconversion luminescence through a combination of three non-traditional rare-earth ions, providing a new technical approach for designing energy transfer pathways in rare-earth-based upconversion luminescence systems.

[0057] It should be noted that the present invention is not limited to the above-described embodiments. Within the scope of the present invention, other novel rare earth metal-organic framework materials, preparation methods and applications obtained by using other components, proportions and preparation process conditions can all achieve the technical effects described in the present invention. Therefore, the present invention application documents will not list them one by one.

[0058] The above description is merely a preferred embodiment and comparative example of the present invention, and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations or equivalent embodiments and comparative examples of the present invention using the methods and techniques disclosed above, without departing from the scope of the present invention. Therefore, all equivalent modifications made based on the structure, construction, and principles of the present invention without departing from the scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. An enhanced rare-earth-doped upconversion luminescent metal-organic framework material, characterized in that, The basic building block has the chemical formula C4HO8Ln, denoted as Ln-MOFs, where the Ln sites are occupied by one, two, or three different rare earth ions. The one, two, or three rare earth ions include sensitizer rare earth ions, activator rare earth ions, and energy-mediated node rare earth ions. The energy-mediated node rare earth ions are used to transfer energy between the sensitizer rare earth ions and the activator rare earth ions to construct an enhanced upconversion luminescence energy transfer pathway.

2. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to claim 1, characterized in that, When the Ln site is occupied by a rare earth ion, it is the sensitizer rare earth ion Yb. 3+ .

3. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to claim 1, characterized in that, When two rare earth ions co-occupy the Ln site, there are two types: sensitizing rare earth ions and activating rare earth ions. The activating rare earth ion is Ho. 3+ Or Eu 3+ .

4. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to claim 1 or 2, characterized in that, When three different rare earth ions co-occupy the Ln site, including sensitizer rare earth ions, activator rare earth ions, and energy-mediated node rare earth ions, the energy-mediated node rare earth ion is Tb. 3+ .

5. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to claim 4, characterized in that, The Ln site is determined by Yb. 3+ 、Tb 3+ and Ho 3+ Jointly occupied, of which Yb 3+ As a sensitizer, Tb 3+ As an energy-mediated node, Ho 3+ As an activator; the upconversion luminescence energy transfer pathway includes Tb 3+ to Ho 3+ Energy transfer to enhance Ho 3+ The upconversion luminescence intensity.

6. The enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to claim 1, characterized in that, The material belongs to an orthorhombic crystal system with space group . Cmca The asymmetric unit of Ln-MOFs contains one rare earth cation Ln. 3+ 3 oxalic acid molecules and 2 formic acid molecules; the Ln 3+ The ion adopts an eight-coordinate geometry, and its coordination environment consists of six carboxyl oxygen atoms provided by three oxalic acid molecules and two oxygen atoms provided by two formic acid molecules; wherein, the oxalic acid ligand is connected to Ln in a bidentate bridging manner through a carboxylic acid group. 3+ The ions extend along the a-axis and c-axis, while the formic acid ligands extend the framework along the b-axis, together forming a three-dimensional framework structure.

7. A method for preparing the enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Weigh a mixture of rare earth salts containing one, two or three different rare earth ions, wherein the one, two or three rare earth ions include sensitizer rare earth ions, activator rare earth ions and energy-mediated node rare earth ions, and add it to the inner liner of a reaction vessel made of polytetrafluoroethylene. (2) Weigh out the oxalic acid ligand and add it to the inner liner of the reactor; (3) In the reactor liner containing rare earth salts and oxalic acid ligands, N,N'-dimethylformamide solvent and deionized water are added sequentially according to the set ratio. The reactor liner is left to stand to allow the contents to mix thoroughly and evenly until the solution is clear and transparent, forming a uniform dispersion. The liner containing the dispersion is sealed according to the correct operating procedure of the reactor and placed in an oven. It is then reacted at 140-170 ℃ for 48-72 hours to allow the DMF solvent to decompose in situ to produce formic acid and rare earth Ln. 3+ Three-dimensional MOFs were formed by self-assembly with deprotonated oxalic acid and formic acid; the product was cooled to room temperature and the resulting bulk crystals were collected by filtration; the bulk crystals were washed with DMF and anhydrous ethanol, respectively; finally, the bulk crystals were placed in a vacuum drying oven and vacuum dried at 70 ~ 80 ℃ for 4 ~ 6 hours to obtain high-purity Ln-MOFs materials.

8. The preparation method according to claim 7, characterized in that, The rare earth salt in step (1) is a rare earth sulfate; 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 three of them.

9. The preparation method according to claim 7, characterized in that, In step (1), the total molar amount of rare earth salt is 0.24 ~ 0.26 mmol, in step (2), the amount of oxalic acid ligand is 0.48 ~ 0.52 mmol, in step (3), the amount of DMF is 5 ~ 8 mL, the amount of deionized water is 2.5 ~ 4 mL, and the volume ratio of DMF to deionized water is 2:

1.

10. The application of the enhanced rare-earth-doped upconversion luminescent metal-organic framework material according to any one of claims 1 to 6 in the fields of optical anti-counterfeiting and secure information storage, characterized in that, The material generates upconversion luminescence under 980 nm near-infrared light excitation, and the upconversion luminescence includes an energy transfer path from energy-mediated node rare earth ions to activator rare earth ions; the material also generates downconversion luminescence under 288 nm ultraviolet light excitation, realizing a downconversion / upconversion dual-mode optical anti-counterfeiting.

Images