Luminescent metal-organic framework material for radiophotovoltaic effect nuclear battery and preparation method thereof

Abstract

The application provides a luminescent metal organic framework material for a radiophotovoltaic effect nuclear battery and a preparation method thereof, the material has a chemical general formula of M-TCPE, wherein M is Zr or Hf, and TCPE is 4,4',4'',4'''-(ethylene-1,1,2,2-tetrayl) tetrakisbenzoic acid. The material is prepared by using a step-by-step pre-assembly-gradient crystallization solvothermal method, M-TCPE is obtained by controlling a pre-assembly temperature of 363 K and a crystallization temperature of 393 K, the material firstly expands the 'anti-heavy atom effect' to the MOF system, and the radiophotoluminescence intensity of Hf-TCPE is increased by 14.6% compared with that of Zr-TCPE. M-TCPE is compounded with PDMS to prepare a flexible fluorescent film, and the flexible fluorescent film is directly attached to a photovoltaic module to form a radiophotovoltaic effect nuclear battery, wherein the maximum output power of the nuclear battery based on Hf-TCPE reaches 1.37 muW, and is increased by 18.1% compared with that of a Zr-based nuclear battery.

Description

Technical Field

[0001] This invention relates to the field of fluorescent materials and radiation-induced photovoltaic nuclear batteries, and particularly to a luminescent metal-organic framework material for radiation-induced photovoltaic nuclear batteries and its preparation method. Background Technology

[0002] A radiation-induced photovoltaic (PV) nuclear battery is a device that converts the decay energy of radioactive isotopes into electrical energy. It boasts advantages such as high energy density, long lifespan, and strong environmental adaptability, making it particularly suitable for scenarios where long-term maintenance is impossible, such as deep space exploration, polar research, and seabed monitoring. A PV battery mainly consists of three parts: a radioactive source, a phosphor layer, and photovoltaic modules. Its working principle is as follows: the radioactive source releases radiation particles (such as...) α particle, β Photovoltaic cells (or X-rays / gamma rays) interact with the phosphor layer to generate radioluminescent photons, which are then absorbed by the photovoltaic module and converted into electrical energy through the photovoltaic effect. In this energy conversion process, the intensity of the radioluminescence generated by the phosphor layer significantly affects the final electrical output performance of the battery. Therefore, the radioluminescence efficiency of the phosphor layer is a key factor determining the battery's output performance. Seeking methods to improve the radioluminescence efficiency, irradiation stability, and sustainable / multi-scenario (corresponding to irradiation stability and flexibility) of the phosphor layer is particularly important.

[0003] Currently, the commonly used phosphor layer materials in radiation-induced photovoltaic (PV) nuclear batteries mainly include ZnS-based phosphors, scintillators, and perovskite nanomaterials. Although these materials have high luminescence properties, they suffer from problems such as weak radiation fluorescence intensity, high energy loss, and poor environmental stability during actual PV energy conversion. Consequently, the energy conversion efficiency of PV nuclear batteries is not high, and the overall electrical output performance is poor during ultra-long-term continuous service.

[0004] In recent years, luminescent metal-organic frameworks (LMOFs) have attracted widespread attention as a new class of fluorescent materials. LMOFs are self-assembled from inorganic metal nodes and organic ligands through strong coordination bonds, exhibiting both structural tunability and high fluorescence quantum yield. In particular, introducing organic ligands with aggregation-induced emission (AIE) properties into MOF frameworks can achieve extremely high fluorescence quantum yields within rigid frameworks, overcoming the defect of fluorescence quenching caused by aggregation in traditional fluorescent molecules at high concentrations or in the solid state. Furthermore, using high atomic number (high Z) metal elements (lead, bismuth, zirconium, hafnium, etc.) as metal nodes can enhance the high efficiency of radiation absorption in MOF materials. Combining these characteristics, high atomic number aggregation-induced emission metal-organic frameworks (Z-AIE type LMOFs) are gradually gaining widespread attention in the fields of radiation detection and energy conversion, demonstrating broad application prospects.

[0005] Meanwhile, related theoretical research has also developed rapidly. Existing studies have shown that introducing non-metallic heavy atoms (such as bromine and iodine) into small organic molecule systems with bond-space conjugated (TBSC) AIE molecular frameworks via covalent bonds can significantly enhance the fluorescence emission intensity of the molecules. This phenomenon is named the "anti-heavy-atom effect," which is distinctly different from the traditional heavy atom effect (i.e., heavy atoms promote intersystem crossing by enhancing spin-orbit coupling, leading to fluorescence quenching). However, this research is currently limited to small organic molecule systems in which non-metallic heavy atoms are replaced by covalent bonds. Whether the "anti-heavy-atom effect" applies to MOF periodic framework systems connected by metal node coordination bonds, and whether high-Z metal nodes in MOFs can also induce fluorescence enhancement, have not yet been reported.

[0006] In summary, existing phosphor layer materials for radiation-induced photovoltaic (PV) nuclear batteries suffer from technical bottlenecks such as low radiative luminescence efficiency, high energy loss, and poor service stability. Furthermore, the applicability of the "anti-heavy atom effect" in MOF systems remains a research gap. Therefore, developing a high Z-AIE-type luminescent metal-organic framework material based on the "anti-heavy atom effect" and its preparation method, and applying it to the phosphor layer of radiation-induced PV nuclear batteries, is of significant scientific importance and practical value for improving the battery's electrical output performance. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a high-atomic-number aggregation-induced emission metal-organic framework (LMOF) based on the "anti-heavy atom effect." TBSC-type AIE molecules are used as organic ligands, and high-atomic-number metals are used as metal nodes. Based on the theory of the "anti-heavy atom effect," two isomorphic luminescent LMOFs are designed. The aggregation-induced emission properties of the ligands and the strong X-ray absorption capability of the high-atomic-number metal nodes synergistically enhance the radioluminescence intensity of the phosphor layer. Simultaneously, the rigid framework structure of the LMOFs enhances the structural stability of the phosphor layer to a certain extent, thereby improving the radioluminescence conversion efficiency and structural stability of the phosphor layer. Ultimately, this enables highly efficient and stable power supply of a radio-induced photovoltaic nuclear battery under special environments such as high dose rates.

[0008] The first aspect of this invention provides a luminescent metal-organic framework material, which is self-assembled from metal nodes and TPE derivative organic ligands via coordination bonds; wherein the metal nodes are one or a combination of two of Zr or Hf, and the TPE derivative organic ligands include 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid, tetra(4-hydroxybiphenyl)ethylene, tetra[4-(4'-carboxyphenyl)phenyl]ethylene, tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene, and tetra(4-methylphenyl)ethylene; preferably, the TPE derivative organic ligand is 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid, abbreviated as H4TCPE; when H4TCPE is used as the organic ligand, the resulting luminescent metal-organic framework material has the general chemical formula M-TCPE, and the crystal structure is as follows. Figure 1 As shown; M represents a metal node, and the crystal structure is as follows: Figure 2 As shown, when M is Zr, the luminescent metal-organic framework material is Zr-TCPE, and when M is Hf, the luminescent metal-organic framework material is Hf-TCPE.

[0009] A second aspect of this invention provides a method for preparing a luminescent metal-organic framework material, comprising: the luminescent metal-organic framework material is prepared by a solvothermal method of stepwise pre-assembly-gradient crystallization, specifically including: Step S1, Metal-Oxide Cluster Pre-assembly: Zirconium salt or hafnium salt is dissolved in a solvent, and a regulator is added before mixing. Pre-assembly is carried out at 353~373K, and the reaction is carried out for 0.5~1.5h. Then, the mixture is cooled to room temperature to obtain a metal-oxygen cluster node precursor solution with a six-core structure. The metal-oxygen cluster node precursor is expressed as M6(μ3-O)4(μ3-OH)4, where M is Zr or Hf. Step S2, Coordination Polymerization Crystallization: The TPE derivative organic ligand from the first aspect is added to the metal-oxygen cluster node precursor solution described in step S1, followed by the addition of deionized water and a regulator to obtain a mixture. The mixture is ultrasonically treated until a clear, light yellow solution is formed, and then transferred to a reaction vessel. The reaction is carried out at 383-403 K for 12-48 h. After the reaction is completed, the mixture is cooled to room temperature and centrifuged to obtain the crystalline product. S3. Post-processing purification: The crystalline product was washed with N,N-dimethylformamide and ethanol, dried at 323~343K for 10~36h, and then ground to obtain luminescent metal-organic framework material powder.

[0010] Further, the zirconium salt in step S1 is at least one of zirconium chloride, nitrate, sulfate, oxalate, alkoxide, and chloride; the hafnium salt is at least one of hafnium chloride, nitrate, sulfate, oxalate, alkoxide, and chloride; preferably, the zirconium salt is zirconium chloride, and the hafnium salt is hafnium chloride. The solvent is at least one selected from N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP); The regulator is at least one of C1-C4 monocarboxylic acids, trifluoroacetic acid, benzoic acid, or inorganic acid; preferably, the regulator is a C1-C4 monocarboxylic acid, wherein the C1-C4 monocarboxylic acids include, but are not limited to, formic acid, acetic acid, propionic acid, and butyric acid. The molar ratio of zirconium salt or hafnium salt: solvent: regulator is 1:(300~800):(30~70); the pre-assembly reaction temperature is 363K and the reaction time is 1h.

[0011] Furthermore, the zirconium salt is ZrCl4; the hafnium salt is HfCl4; the solvent is N,N-dimethylformamide; the regulator is acetic acid; and the molar ratio of zirconium salt or hafnium salt: solvent: regulator is 1:600:50.

[0012] Further, the regulator in step S2 includes, but is not limited to, formic acid, acetic acid, propionic acid, and butyric acid, preferably acetic acid; the molar ratio of the TPE derivative organic ligand to the zirconium salt or hafnium salt in step S1 is 1:(2.5~3.5); the molar ratio of the TPE derivative organic ligand:deionized water:regulator is 1:(50~100):(150~220); the mixture is ultrasonically treated and then reacted in a reactor at a temperature of 393K for 24 hours.

[0013] Furthermore, in step S2, the molar ratio of the TPE derivative organic ligand to the zirconium salt or hafnium salt in step S1 is 1:3; and the molar ratio of the TPE derivative organic ligand: deionized water: regulator is 1:75:185.

[0014] Furthermore, after washing the crystallized product with N,N-dimethylformamide and ethanol in step S3, the crystallized product needs to be dried in a vacuum drying oven at 333K for 24h, and then ground to obtain Zr-TCPE or Hf-TCPE powder.

[0015] A third aspect of this invention provides a flexible composite fluorescent film, wherein the flexible composite fluorescent film is composed of a luminescent metal-organic framework material as described in the first or second aspect and a flexible polymer matrix; the flexible polymer is selected from at least one of polydimethylsiloxane (PDMS), ethylene-vinyl acetate (EVA), polyurethane (PU), and polyvinylidene fluoride (PVDF); preferably, the flexible polymer is polydimethylsiloxane, abbreviated as PDMS; when the luminescent metal-organic framework material is Zr-TCPE, the flexible composite fluorescent film is Zr-TCPE@PDMS, and when the luminescent metal-organic framework material is Hf-TCPE, the flexible composite fluorescent film is Hf-TCPE@PDMS.

[0016] The fourth aspect of this invention provides a method for preparing the flexible composite fluorescent thin film described in the third aspect, the specific steps of which include: S1. Mix the PDMS prepolymer with the curing agent and stir at 313~353K for 4~8h to obtain the PDMS matrix; S2. The prepared luminescent metal-organic framework material powder is mixed and stirred with PDMS matrix for 0.5~1.5h to obtain LMOFs polymer composite slurry; S3. The LMOFs polymer composite slurry is uniformly coated onto the polyimide film substrate by a blade coating method. The blade height, coating temperature and coating speed are controlled to adjust the wet film thickness. Then, it is placed in a vacuum oven at 303~373K for 6~18h to cure and obtain a flexible composite fluorescent film.

[0017] Further, the curing agent in step S1 is a platinum-based siloxane curing agent; the mass ratio of the PDMS prepolymer to the curing agent is (8~12):1, preferably 10:1; after mixing the PDMS prepolymer and the curing agent, the mixture is stirred at 333 K for 6 hours to obtain the PDMS matrix; In step S2, the mass ratio of the luminescent metal-organic framework material powder to the PDMS matrix is ​​(2~6):100; the mixing and stirring time of the powder and the PDMS matrix is ​​1h to obtain LMOFs polymer composite slurry; preferably, the mass ratio of the luminescent metal-organic framework material powder to the PDMS matrix is ​​3:100. In step S3, the coating machine needs to be heated during the LMOFs polymer composite slurry coating process. The heating temperature is controlled at 273~333K, preferably 293K. The coating speed is set to 15~30mm / s, preferably 25mm / s. The blade height, coating temperature and coating speed are controlled to adjust the wet film thickness to 20~120μm, preferably 60μm. After the LMOFs polymer composite slurry is uniformly coated on the polyimide film substrate, it is placed in a 333K vacuum oven for 12h for curing to obtain a flexible composite fluorescent film.

[0018] The fifth aspect of the present invention provides a radiation-induced photovoltaic nuclear battery, the battery comprising a radiation source, a fluorescent layer, and a photovoltaic module; wherein the fluorescent layer is a flexible composite fluorescent film as described in the third or fourth aspect, and the fluorescent layer is directly bonded to the photovoltaic module without air gaps.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) For the first time, the “anti-heavy atom effect” was extended from organic small molecule systems to periodic MOF systems with metal node coordination bonds. In Zr / Hf isomorphic MOFs, it was verified that heavy metal atoms (Hf) can induce fluorescence enhancement (Hf-TCPE increased the radiation fluorescence intensity by 14.6% compared with Zr-TCPE), which overturned the traditional understanding that the heavy atom effect inevitably leads to fluorescence quenching.

[0020] (2) The Hf-TCPE@PDMS composite fluorescent film prepared by the present invention has higher radiation-induced fluorescence conversion efficiency. When applied to a radiation-induced photovoltaic nuclear cell, the maximum output power reaches 1.37 μW, which is 18.1% higher than that of Zr-TCPE@PDMS based cell (1.16 μW). At the same time, the rigid framework structure of LMOFs significantly enhances the radiation resistance stability of the fluorescent layer.

[0021] (3) The present invention adopts the solvothermal method of “stepwise pre-assembly-gradient crystallization”. By independently controlling the pre-assembly temperature (363K) and crystallization temperature (393K) and adding acetic acid regulator stepwise, the target product with high crystallinity and good phase purity can be obtained efficiently. The process has good repeatability and is easy to scale up.

[0022] (4) The fluorescence enhancement method proposed in this invention has universality. It can achieve the modulation of emission wavelength by selecting TBSC-type AIE molecules with different substituent groups, without damaging the properties of the fluorescent material itself. At the same time, the composite fluorescent film is flexible and can be compatible with curved or irregularly shaped photovoltaic modules, thus broadening the application scenarios of the battery.

[0023] (5) The three-layer direct bonding and air gap-free battery structure minimizes optical reflection loss and realizes the integrated design of "radiation absorption-fluorescence emission-photovoltaic conversion", which greatly improves electrical output performance without increasing battery size. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the crystal structure of the general chemical formula M-TCPE.

[0025] Figure 2 This is a schematic diagram of the crystal structure of the metal nodes in M-TCPE.

[0026] Figure 3 This is a flowchart illustrating the fabrication process of luminescent metal-organic framework materials and flexible composite fluorescent thin films.

[0027] Figure 4 PXRD comparison images of Zr-TCPE powder and Hf-TCPE powder.

[0028] Figure 5 The image shows the SEM microstructure of Zr-TCPE.

[0029] Figure 6 The image shows the SEM microstructure of Hf-TCPE.

[0030] Figure 7 This is the radiofluorescence spectrum of the LMOF fluorescent layer.

[0031] Figure 8 This is a structural diagram of a radiation-induced photovoltaic nuclear cell.

[0032] Figure 9 The current-voltage characteristic curves of the radiation-induced photovoltaic nuclear cell with Zr-TCPE and Hf-TCPE phosphor layers are shown. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0034] The main experimental materials used in the embodiments of the present invention are shown in Table 1.

[0035] Table 1 Experimental materials Example 1 Preparation of luminescent metal-organic framework material (Zr-TCPE) and Zr-TCPE@PDMS flexible composite fluorescent film like Figure 3 As shown, this invention employs a stepwise pre-assembly-gradient crystallization solvothermal method to prepare luminescent metal-organic frameworks (LMOFs) materials, and utilizes the prepared LMOF materials to fabricate flexible composite fluorescent films. The process mainly includes four steps: metal-oxygen cluster pre-assembly, coordination polymerization crystallization, post-treatment purification, and flexible composite fluorescent film fabrication. This embodiment details the preparation process of Zr-TCPE powder and the Zr-TCPE@PDMS flexible composite fluorescent film, with the specific steps as follows: ① Metal-oxygen cluster preassembly 100 mg of ZrCl4 (99.99%, AR) was weighed using an electronic balance and dissolved in 20 mL of N,N-dimethylformamide (DMF, 99.5%, AR). 1200 μL of glacial acetic acid (99.99%, AR) was added and the mixture was stirred. The mixture was placed in a 363 K constant temperature drying oven for 1 h to pre-assemble a metal-oxygen cluster node M6(μ3-O)4(μ3-OH)4 precursor with a six-core structure, where M is Zr. The solution was then cooled to room temperature (298 K) to obtain the metal-oxygen cluster node precursor solution.

[0036] ② Coordination polymerization crystallization 100 mg of the TPE derivative organic ligand 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid (H4TCPE, 95%, AR) was added to the obtained metal-oxygen cluster node Zr6(μ3-O)4(μ3-OH)4 precursor solution. Then, 200 μL of deionized water and 1600 μL of acetic acid (glacial acetic acid) were added sequentially, and the mixture was stirred to obtain a mixture. The mixture was sonicated until a clear light yellow solution was formed, and then transferred to a 50 mL polytetrafluoroethylene-lined stainless steel reactor. After sealing, the reactor was placed in a 403 K constant temperature drying oven for 24 h. After the reaction was completed, the mixture was naturally cooled to room temperature, and the white crystalline product was collected by centrifugation.

[0037] ③ Post-processing purification The white crystalline product was washed three times each with N,N-dimethylformamide (DMF) and anhydrous ethanol to thoroughly remove unreacted substances and solvents remaining in the pores of LMOFs. The washed product was then dried in a vacuum drying oven at 333 K for 24 h. After drying, the product was poured into an agate mortar and ground thoroughly into a uniform fine powder to obtain Zr-TCPE powder.

[0038] ④ Preparation of Zr-TCPE@PDMS flexible composite fluorescent film Polydimethylsiloxane (PDMS) prepolymer was mixed with platinum-based siloxane curing agent (SYLGARD 184 curing agent) at a mass ratio of 10:1 and stirred at 333K for 6 hours to obtain the PDMS matrix. In this embodiment, the mass of PDMS and platinum-based siloxane curing agent were 1g and 0.1g, respectively. Zr-TCPE powder and PDMS matrix were mixed and stirred at a mass ratio of 3:100 for 1 hour to obtain LMOFs polymer composite slurry. In this embodiment, the mass ratio of Zr-TCPE powder to PDMS matrix was 30g and 30g, respectively. mg and 1g; the obtained LMOFs polymer composite slurry was uniformly coated onto a clean polyimide film substrate by a blade coating method. During the blade coating process, the blade coating machine needs to be heated. In this embodiment, the blade coating temperature is set between 273~333K, preferably 298K. In addition, improper control of the blade coating speed will lead to uneven coating, and the film thickness and the shape of the entire film will be uneven. In this embodiment, the blade coating speed is controlled between 15~30mm / s, preferably 25mm / s. The wet film thickness is adjusted to 60μm by controlling the blade height, blade coating temperature and blade coating speed. The coated sample is placed in a 333K vacuum oven for 12h to cure, so as to fully remove the air bubbles mixed in the slurry and promote the crosslinking reaction, to obtain a Zr-TCPE@PDMS flexible composite fluorescent film.

[0039] Example 2 Preparation of luminescent metal-organic framework material (Hf-TCPE) and flexible composite fluorescent film (Hf-TCPE@PDMS) This embodiment employs a stepwise pre-assembly-gradient crystallization solvothermal method to prepare Hf-TCPE, and utilizes Hf-TCPE to prepare a flexible Hf-TCPE@PDMS composite fluorescent film. The preparation process is as follows: Figure 3 As shown, the specific steps are as follows: ① Metal-oxygen cluster preassembly Weigh 137 mg of HfCl4 (99.99%, AR) using an electronic balance and dissolve it in 20 mL of N,N-dimethylformamide (DMF, 99.5%, AR). Then add 1200 μL of acetic acid (99.99%, AR) and stir to mix. Place the mixture in a 363 K constant temperature drying oven for 1 h to pre-assemble a metal-oxygen cluster node M6(μ3-O)4(μ3-OH)4 precursor with a six-core structure, where M is Hf. Cool to room temperature (298 K) to obtain the metal-oxygen cluster node precursor solution.

[0040] ② Coordination polymerization crystallization 100 mg of 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid (H4TCPE, 95%, AR) was added to the precursor solution of the metal-oxygen cluster node Hf6(μ3-O)4(μ3-OH)4. Then, 200 μL of deionized water and 1600 μL of acetic acid were added sequentially, and the mixture was stirred to obtain a mixture. The mixture was sonicated until a clear light yellow solution was formed, and then transferred to a 50 mL stainless steel reactor lined with polytetrafluoroethylene. After sealing, the reactor was placed in a constant temperature drying oven at 403 K for 24 h. After the reaction was completed, the mixture was naturally cooled to room temperature, and the white crystalline product was collected by centrifugation.

[0041] ③ Post-processing purification The white crystalline product was washed three times each with N,N-dimethylformamide (DMF) and anhydrous ethanol to thoroughly remove unreacted substances and solvents remaining in the pores of LMOFs. The washed product was then dried in a vacuum drying oven at 333 K for 24 h. After drying, the product was poured into an agate mortar and ground thoroughly into a uniform fine powder to obtain Hf-TCPE powder.

[0042] ④ Preparation of flexible composite fluorescent films Polydimethylsiloxane (PDMS) prepolymer was mixed with platinum-based siloxane curing agent (SYLGARD 184 curing agent) at a mass ratio of 10:1, wherein the mass of PDMS and curing agent were 1g and 0.1g, respectively; the mixture was stirred at 333K for 6h to obtain a PDMS matrix; Hf-TCPE powder and PDMS matrix were mixed and stirred at a mass ratio of 3:100 for 1h to obtain LMOFs polymer composite slurry. In this embodiment, the mass ratio of Hf-TCPE powder to PDMS matrix was 30g and 30g, respectively. mg and 1g; the obtained LMOFs polymer composite slurry was uniformly coated onto a clean polyimide film substrate by a blade coating method. During the blade coating process, the blade coating machine needs to be heated. In this embodiment, the blade coating temperature is set between 273~333K, preferably 298K. In addition, improper control of the blade coating speed will lead to uneven coating, and the film thickness and the shape of the entire film will be uneven. In this embodiment, the blade coating speed is controlled between 15~30mm / s, preferably 25mm / s. The wet film thickness is adjusted to 60μm by controlling the blade height, blade coating temperature and blade coating speed. The coated sample is placed in a 333K vacuum oven for 12h to cure, so as to fully remove the air bubbles mixed in the slurry and promote the crosslinking reaction, to obtain Hf-TCPE@PDMS flexible composite fluorescent film.

[0043] Example 3 Performance Analysis of Luminescent Metal-Organic Framework Materials (Zr-TCPE, Hf-TCPE) To investigate the properties of luminescent metal-organic framework materials, this embodiment performed XRD, SEM, and radiofluorescence analyses on the Zr-TCPE powder prepared in Example 1 and the Hf-TCPE prepared in Example 2. Details are as follows: like Figure 4 The figure shows a comparison of PXRD patterns of Zr-TCPE powder and Hf-TCPE powder. As can be seen from the figure, the PXRD patterns of both Zr-TCPE and Hf-TCPE exhibit diffraction peak positions and relative peak intensity distributions consistent with the simulated curves (calculated based on single-crystal structure data). Both materials show sharp, high-resolution characteristic diffraction peaks at 2θ = 6.5°, 8.5°, 9.5°, 10.5°, 11.5°, and 15.5°, with no obvious impurity peaks or broadening observed, indicating that both materials possess high crystallinity and high phase purity. Furthermore, due to the presence of Zr... 4+ and Hf 4+ Having the same ionic valence state, similar ionic radius, and identical coordination chemistry, MOF frameworks constructed using Zr-TCPE and Hf-TCPE as metal nodes can maintain completely identical topological structures and crystallographic space groups. The high consistency between the PXRD patterns of Zr-TCPE and Hf-TCPE confirms that Zr-TCPE and Hf-TCPE are isomorphic MOF materials; replacing the metal nodes with Hf does not alter the overall framework structure of the materials.

[0044] This result fully demonstrates the successful synthesis of the target product and provides an ideal structural model for subsequent comparative studies of the "anti-heavy atom effect." Under the premise that the organic ligands, crystal structure, porosity, and other variables are completely consistent, by changing only the atomic number of the metal nodes (Zr is converted to Hf), the influence of the heavy atom effect on radioluminescence performance can be examined independently, eliminating the interference of structural differences on performance evaluation. This provides a solid structural evidence basis for verifying the Hf-induced fluorescence enhancement phenomenon.

[0045] like Figure 5 , Figure 6 The figures show the SEM microstructures of Zr-TCPE and Hf-TCPE at the same magnification. As can be seen from the figures, both Zr-TCPE and Hf-TCPE exhibit petal-like or layered stacked nano / micron-sized aggregates. At the same magnification, the particle size distribution, shape characteristics, and surface texture of the two materials are highly similar, with no significant morphological differences due to metal node replacement. Comparison of the PXRD patterns of Zr-TCPE and Hf-TCPE further confirms the conclusions of PXRD from a microscopic morphology perspective, indicating that both are isomorphic MOF materials with the same crystal framework structure.

[0046] comprehensive Figures 4 to 6Analysis revealed that PXRD confirmed Zr-TCPE and Hf-TCPE possess the same crystal structure, high crystallinity, and high phase purity, clarifying an ideal isomorphic comparison system. SEM visually demonstrated the consistent petal-like microstructure of the two materials from a morphological perspective, further verifying their structural isomorphism. These two MOF material systems together provide a structural basis for subsequent research on the "anti-heavy atom effect" in MOF systems, ensuring that the only variable for performance differences is the atomic number of the metal nodes (Zr and Hf), thus reliably attributing the fluorescence enhancement phenomenon to the "anti-heavy atom effect."

[0047] Example 4 Performance testing of composite fluorescent films (Zr-TCPE@PDMS, Hf-TCPE@PDMS) This embodiment tests the radioluminescence properties of the Zr-TCPE@PDMS flexible composite fluorescent film and the Hf-TCPE@PDMS flexible composite fluorescent film prepared in Examples 1 and 2, and compares the radioluminescence intensity of the two films.

[0048] The radioluminescence spectra of flexible composite fluorescent films were measured using an Agilent Cary Eclipse Fluorescence Spectrophotometer. The X-ray excitation source was a miniature X-ray tube (tube voltage set to 35 kV, tube current set to 0.1 mA), with the X-ray emission direction directly facing the surface of the film sample. In this embodiment, the X-ray energy spectrum generated by the X-ray tube has a similar energy range and radiation ionization effect to the X-rays emitted by some radioactive isotopes; therefore, the X-ray tube can be considered as a simulated equivalent source / equivalent test source for the radioactive source. The test conditions were: photomultiplier tube (PMT) voltage of 1000 V, scan rate of 200 nm / min, emission spectral slit width of 1.5 nm, and receiving signal slit width of 5 nm. All tests were performed at room temperature (298 K) and atmospheric pressure. The radioluminescence spectra of each flexible composite fluorescent film under X-ray excitation at an operating voltage of 35 kV and an operating current of 0.1 mA are as follows: Figure 7 As shown.

[0049] from Figure 7As can be seen, the pure PDMS matrix exhibits almost no fluorescence emission signal in the 300-700 nm wavelength range (the curve shows no obvious characteristic peaks, and the coverage area is close to zero), indicating that PDMS, as a flexible matrix, does not possess radioluminescence properties and contributes almost nothing to enhancing the optical signal of the fluorescent layer. After loading the organic ligand H4TCPE, the H4TCPE@PDMS fluorescent layer shows an extremely weak emission peak at approximately 465 nm. This emission peak corresponds to the aggregation-induced emission characteristic emission of the H4TCPE ligand, but the intensity is extremely low, indicating that the absorption and conversion efficiency of the organic ligand for X-rays is limited and cannot be directly used for high-efficiency radioluminescence applications. After introducing metal nodes, the fluorescence performance is significantly improved. The emission peak intensity of the Zr-TCPE@PDMS fluorescent layer prepared in Example 1 is significantly enhanced at 465 nm compared to H4TCPE@PDMS, proving that the introduction of metal-oxygen cluster nodes (Zr-O clusters) effectively improves the material's X-ray absorption capacity and enhances the fluorescence emission of the ligands through an energy transfer mechanism. Furthermore, in Example 2, the Hf-TCPE@PDMS fluorescent layer prepared using Hf with a higher atomic number instead of Zr exhibited the strongest radioluminescence emission under the same testing conditions. Its emission peak intensity was significantly improved compared to Zr-TCPE@PDMS, with an increase of 14.6%.

[0050] Example 5 Composition and performance testing of radiation-induced photovoltaic nuclear batteries This embodiment uses the Zr-TCPE@PDMS and Hf-TCPE@PDMS flexible composite fluorescent films prepared in Examples 1 and 2 to assemble radiation-induced photovoltaic nuclear cells, and tests their electrical output performance. Figure 8 As shown, the battery structure mainly consists of three parts: a radiation source (X-ray device), a fluorescent layer (flexible composite fluorescent film, including M-TCPE luminescent material and PDMS substrate), and a semiconductor photovoltaic module (AlGaInP-based photovoltaic module). The fluorescent layer is directly bonded to the photovoltaic module without air gaps.

[0051] During the test, the tube voltage of the X-ray emitting device was set to 35 kV and the tube current to 0.1 mA. The X-ray emission direction was directly aimed at the phosphor layer, which was in close contact with the surface of the AlGaInP-based photovoltaic module. A dual-channel digital source meter (Keithley 2636A) was used to acquire the current-voltage (IV) characteristic curve of the photovoltaic module. The test was conducted at room temperature (298 K), normal pressure, and in a dark room to avoid interference from ambient light. Figure 9 As shown, the current-voltage characteristic curves of radiation-induced photovoltaic nuclear cells based on Zr-TCPE and Hf-TCPE phosphor layers are presented.

[0052] from Figure 9The current-voltage characteristic curves shown demonstrate that the radiation-induced photovoltaic (PV) cells assembled based on Zr-TCPE@PDMS and Hf-TCPE@PDMS phosphor layers can effectively convert incident X-ray radiation energy into fluorescent photons under X-ray excitation at 35 kV and 0.1 mA, and further output electrical energy through AlGaInP photovoltaic modules. Furthermore, the open-circuit voltages of the two types of cells are similar, both reaching approximately 1.0 V, and the values ​​are very close, indicating that the energy level matching degree and built-in electric field characteristics between the two phosphor layers and the AlGaInP photovoltaic modules are essentially the same.

[0053] Regarding short-circuit current, there is a significant difference between the two types of cells. The short-circuit current of the Hf-TCPE@PDMS-based cell reaches 2.0 μA, while that of the Zr-TCPE@PDMS cell is 1.75 μA, with the former being approximately 14.3% higher than the latter. The magnitude of the short-circuit current directly reflects the ability of the phosphor layer to convert radiant energy into fluorescent photons; that is, the higher the radiofluorescence intensity, the more photons the photovoltaic module can absorb, and the more photogenerated carriers are generated. Combined with the radiofluorescence spectroscopy test results, it can be seen that the fluorescence intensity of Hf-TCPE@PDMS is 14.6% higher than that of Zr-TCPE@PDMS, which is highly consistent with the increase in short-circuit current (14.3%), further verifying from the energy conversion chain perspective that the increase in fluorescence intensity directly translates into a gain in short-circuit current.

[0054] In terms of output power, the maximum output power of the radiation-induced photovoltaic nuclear cell based on the Hf-TCPE@PDMS fluorescent layer is 1.37 μW, which is 18.1% higher than the 1.16 μW of the Zr-TCPE@PDMS fluorescent layer. The increase in output power is slightly higher than the increase in radiation fluorescence intensity of the Hf-based material (14.6%), indicating that factors other than fluorescence intensity also contribute to the additional gain in output power. Output power is determined by open-circuit voltage, short-circuit current, and fill factor. In this embodiment, the open-circuit voltages of the two cells are similar (approximately 1.0 V), while the fill factors differ significantly: the Zr-based cell has a fill factor of 38.8%, while the Hf-based cell reaches as high as 70.0%. Simultaneously, the short-circuit current of the Hf-based cell is also higher than that of the Zr-based cell. The significant increase in fill factor is mainly attributed to the superior photon emission uniformity and lower non-radiative recombination loss of the Hf-based fluorescent layer, resulting in a significantly enhanced collection efficiency of photogenerated carriers. Therefore, the increase in output power of Hf-based cells (18.1%) is higher than the increase in fluorescence intensity (14.6%), mainly due to the combined improvement in fill factor and short-circuit current.

[0055] The fundamental reason for the aforementioned differences in material properties lies in the successful realization of the "anti-heavy atom effect" in MOF systems. Hf (atomic number 72) has a higher atomic number than Zr (atomic number 40), resulting in a larger photoelectric absorption cross-section for X-rays at its metal-oxygen cluster nodes, enabling the generation of more excitons. Simultaneously, within the rigid framework of the TBSC-type AIE ligand H4TCPE, the heavy atom effect of Hf enhances spin-orbit coupling, promoting efficient anti-intersystem crossing of excitons from triplet to singlet states. This bypasses the fluorescence quenching path caused by traditional heavy atoms, thus achieving a complete forward transfer chain that enhances radiation absorption, improves exciton utilization, increases fluorescence quantum yield, and boosts battery output power.

[0056] The above results demonstrate that the Hf-TCPE@PDMS phosphor layer designed based on the "anti-heavy atom effect" significantly improves the short-circuit current and maximum output power while maintaining the open-circuit voltage. Compared with the Zr-based control system, it achieves a power improvement of 18.1%, which fully proves the enhancing effect of high-Z metal nodes (Hf) on the radiation photovoltaic energy conversion performance in the AIE-MOF system and provides experimental basis for the rational design of high-performance radiation photovoltaic nuclear cell phosphor layers.

[0057] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions conceived without inventive effort should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims.

[0058] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A luminescent metal-organic framework material, characterized in that, The luminescent metal-organic framework material is self-assembled from metal nodes and TPE derivative organic ligands via coordination bonds; wherein the metal nodes are one or a combination of two of Zr or Hf, and the TPE derivative organic ligands include 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid, tetra(4-hydroxybiphenyl)ethylene, tetra[4-(4'-carboxyphenyl)phenyl]ethylene, tetra[4-(3,5-dicarboxyphenyl)]tetraphenylethylene, etc. Tetra(4-methylphenyl)ethylene; wherein, when the organic ligand of the TPE derivative is 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid and the metal node is Zr, the luminescent metal-organic framework material is Zr-TCPE; when the organic ligand of the TPE derivative is 4,4',4'',4'''-(ethylene-1,1,2,2-tetramethyl)tetrabenzoic acid and the metal node is Hf, the luminescent metal-organic framework material is Hf-TCPE.

2. A method for preparing a luminescent metal-organic framework material, characterized in that, The material is prepared using a stepwise pre-assembly-gradient crystallization solvothermal method, specifically including the following steps: Step S1, Metal-Oxide Cluster Pre-assembly: Zirconium salt or hafnium salt is dissolved in a solvent, and a regulator is added before mixing. Pre-assembly is carried out at 353~373K, and the reaction is carried out for 0.5~1.5h. Then, the mixture is cooled to room temperature to obtain a metal-oxygen cluster node precursor solution with a six-core structure. The metal-oxygen cluster node precursor is expressed as M6(μ3-O)4(μ3-OH)4, where M is Zr or Hf. Step S2, Coordination Polymerization Crystallization: The TPE derivative organic ligand was added to the metal-oxygen cluster node precursor solution described in step S1, followed by the addition of deionized water and a regulator to obtain a mixture. The mixture was ultrasonically treated and then transferred to a reaction vessel. The reaction was carried out at 383-403 K for 12-48 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged to obtain the crystalline product. S3. Post-processing purification: The crystalline product was washed with N,N-dimethylformamide and ethanol, dried at 323~343K for 10~36h, and then ground to obtain luminescent metal-organic framework material powder.

3. The preparation method according to claim 2, characterized in that, The zirconium salt mentioned in step S1 is at least one of zirconium chloride, nitrate, sulfate, oxalate, alkoxide, and chloride oxide; the hafnium salt is at least one of hafnium chloride, nitrate, sulfate, oxalate, alkoxide, and chloride oxide. The solvent is at least one selected from N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone. The regulator is at least one of C1-C4 monocarboxylic acids, trifluoroacetic acid, benzoic acid, or inorganic acids; wherein, C1-C4 monocarboxylic acids include, but are not limited to, formic acid, acetic acid, propionic acid, and butyric acid; The molar ratio of zirconium salt or hafnium salt: solvent: regulator is 1:(300~800):(30~70).

4. The preparation method according to claim 3, characterized in that, The zirconium salt is a zirconium chloride; the hafnium salt is a hafnium chloride; the solvent is N,N-dimethylformamide; the regulator is acetic acid; and the molar ratio of zirconium salt or hafnium salt: solvent: regulator is 1:600:

50.

5. The preparation method according to claim 2, characterized in that, The regulators mentioned in step S2 include, but are not limited to, formic acid, acetic acid, propionic acid and butyric acid; the molar ratio of the TPE derivative organic ligand to the zirconium salt or hafnium salt in step S1 is 1:(2.5~3.5); the molar ratio of the TPE derivative organic ligand:deionized water:regulator is 1:(50~100):(150~220).

6. The preparation method according to claim 5, characterized in that, The molar ratio of the TPE derivative organic ligand to the zirconium salt or hafnium salt in step S1 is 1:3; the molar ratio of the TPE derivative organic ligand: deionized water: regulator is 1:75:

185.

7. A flexible composite fluorescent film, characterized in that, The flexible composite fluorescent film is composed of the luminescent metal-organic framework material as described in claim 1 or 2 and a flexible polymer matrix; the flexible polymer is selected from at least one of polydimethylsiloxane, ethylene-vinyl acetate, polyurethane, and polyvinylidene fluoride; wherein, when the luminescent metal-organic framework material is Zr-TCPE and the flexible polymer is polydimethylsiloxane, the flexible composite fluorescent film is Zr-TCPE@PDMS; when the luminescent metal-organic framework material is Hf-TCPE and the flexible polymer is polydimethylsiloxane, the flexible composite fluorescent film is Hf-TCPE@PDMS.

8. A method for preparing the flexible composite fluorescent thin film according to claim 7, characterized in that, The specific steps include: S1. Mix the polydimethylsiloxane prepolymer with the curing agent and stir at 313~353K for 4~8h to obtain the polydimethylsiloxane polymer; S2. Mix and stir the luminescent metal-organic framework material powder with polydimethylsiloxane matrix for 0.5~1.5h to obtain LMOFs polymer composite slurry; S3. The LMOFs polymer composite slurry is uniformly coated onto the polyimide film substrate by a blade coating method. The blade height, coating temperature and coating speed are controlled to adjust the wet film thickness. The wet film is then placed in a vacuum oven at 303~373K for 6~18h to cure, thus obtaining a flexible composite fluorescent film.

9. The method for preparing the flexible composite fluorescent thin film according to claim 8, characterized in that, The curing agent is a platinum-based siloxane curing agent; the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (8~12):1; the mass ratio of the luminescent metal-organic framework material powder to the polydimethylsiloxane matrix is ​​(2~6):100; the coating temperature of the coating machine during the LMOFs polymer composite slurry coating process is 273~333K; the coating speed is 15~30mm / s; and the wet film thickness is 20~120μm.

10. A radiation-induced photovoltaic nuclear battery, characterized in that, The battery consists of three parts: a radiation source, a fluorescent layer, and a photovoltaic module; wherein the fluorescent layer adopts the flexible composite fluorescent film as described in any one of claims 7-9, and the fluorescent layer is directly bonded to the photovoltaic module without air gaps.

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