Two-dimensional cuprous perovskite material and preparation method and application thereof

Abstract

The invention relates to the technical field of photoelectric device materials, in particular to a two-dimensional cuprous perovskite material and a preparation method and application thereof. According to the invention, through a new structural engineering strategy, two monovalent Cu < + > are utilized to replace one divalent Pb < 2 + > to construct the novel two-dimensional lead-free perovskite. Dependent structure deformation is excited in the two-dimensional [Cu2Br4] 2-layer to generate a plurality of excited states, and reversible energy transfer related to temperature is presented. According to subsequent experimental results, the two-dimensional cuprous perovskite material has multicolor luminescence adjustability, the photoluminescence quantum yield is close to 100%, and the two-dimensional cuprous perovskite material has ultra-short afterglow life and high-resolution imaging performance, so that the (AMP) 2Cu2Br4 can be well applied to the fields of luminescent materials, scintillators and radiation detection, multi-field application is realized, and the application prospect is wide. Therefore, the technical problem that the industrial application of the existing lead-based halide perovskite material is limited is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic device materials, and particularly relates to a two-dimensional cuprous perovskite material, a preparation method thereof, and an application thereof. Background Art

[0002] Lead-based halide perovskite materials are a class of optoelectronic functional materials with high absorption coefficients, high photoluminescence quantum yields, and tunable radiative emission wavelengths, and can be used in the fields of luminescent materials, scintillators, and radiation detection.

[0003] However, the current lead-based halide perovskite materials exhibit a single color when applied to photochromic luminescent materials and cannot achieve multicolor luminescence. In recent years, two-dimensional organic lead perovskites, as derivatives of typical three-dimensional lead halide perovskites, have become a new generation of luminescent materials. However, the low luminescence efficiency and high toxicity of Pb 2+ ions have further promoted the development of low-dimensional metal halides, which have ultra-high photoluminescence quantum yields, stability, and low toxicity. The anionic metal halide frameworks are separated by bulky organic species, and the electronic interactions between them can be ignored, which enables low-dimensional metal halides to exhibit the respective photophysical properties of photoactive inorganic species. From a structural perspective, the soft lattice of low-dimensional metal halides is prone to structural deformation or reorganization due to phonon vibration in the excited state, which further captures the excited carriers to generate self-trapped excitons. Since the energy levels of self-trapped excitons are usually lower than the initial excited state, the radiative recombination from the self-trapped exciton state always results in low-energy luminescence. According to Kasha's rule, the self-trapped exciton state is usually located at an energy minimum as a result of structural reorganization and is independent of the excitation wavelength. This phenomenon is a fundamental difference between self-trapped exciton emission and other interband electron transition-induced emissions. Therefore, most low-dimensional metal halides tend to exhibit monotonous self-trapped exciton emission of a single color in the entire ultraviolet excitation range, and it is rare to achieve excitation-dependent multicolor luminescence in low-dimensional metal halides.

[0004] The current lead-based halide perovskite materials are also applied to the fields of scintillators and radiation detection. For example, CsPbBr 3 nanocrystals are regarded as candidate materials for the next generation of X-ray scintillators due to their advantages such as high absorption coefficient, high photoluminescence quantum yield, and tunable radiative emission wavelength. However, lead-based halide perovskites have problems such as relatively serious self-absorption effects, poor stability, and lead toxicity, which limit their further practical applications.

[0005] It can be seen that the existing lead-based halide perovskite materials have certain defects in terms of multicolor emission performance and radiative luminescence performance, resulting in the inability of the current lead-based halide perovskite materials to achieve multi-field applications and limiting their further industrial applications. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art, and provides a two-dimensional cuprous perovskite material, a preparation method and an application thereof, and solves the technical problem that the industrial application of the existing lead-based halide perovskite material is limited.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a two-dimensional cuprous perovskite material, the crystal structure of the two-dimensional cuprous perovskite material belongs to two-dimensional perovskite, and the chemical formula of the two-dimensional cuprous perovskite material is (AMP) 2 Cu 2 Br 4 , and the AMP is N-aminomorpholine.

[0008] Optionally, the crystal structure of (AMP) 2 Cu 2 Br 4 is composed of two-dimensional [Cu 2 Br 4 2- layers, and the [Cu 2 Br 4 2- layers are formed by the top-corner sharing connection of [Cu 2 X 6 4- dimers, and the [Cu 2 X 6 4- dimers are formed by the edge-sharing self-condensation of two [CuBr 4 tetrahedrons.

[0009] The present invention provides a preparation method of the above two-dimensional cuprous perovskite material, including the following steps: Mix cuprous bromide powder with hydrobromic acid, add hypophosphorous acid to obtain a mixed solution; mix the mixed solution with N-aminomorpholine, mix evenly, and obtain the two-dimensional cuprous perovskite material by solvothermal method.

[0010] Among them, hydrobromic acid participates in the reaction, and its function is to provide bromide ions, which coordinate with cuprous ions and protonate organic amines at the same time.

[0011] Optionally, the solvent of the solvothermal method is alcohols.

[0012] Optionally, the reaction temperature of the solvothermal method is 70 °C to 90 °C.

[0013] Optionally, the dosage of hypophosphorous acid is 5% to 15% of the molar amount of the reaction substrate of the solvothermal method.

[0014] ​​​​The present invention provides an application of the above-mentioned two-dimensional cuprous perovskite material in the preparation of a photoluminescent material.

[0015] The present invention provides an application of the above-mentioned two-dimensional cuprous perovskite material in the preparation of a thermochromic fluorescent material and a temperature sensor.

[0016] The present invention provides an application of the above-mentioned two-dimensional cuprous perovskite material in the preparation of a radioluminescent material and an X-ray imaging material.

[0017] The beneficial effect of the present invention is that, compared with the prior art, cuprous halide has diverse coordination structures and abundant Cu···Cu bonds, and has multiple electron transfer channels, including charge transfer from metal / halide to ligand, charge transfer from halide to metal, metal-centered transfer, etc. The diverse electron transfer pathways endow cuprous halide perovskite with more opportunities to achieve adjustable and multiple luminescences. The present invention adopts a new structural engineering strategy, that is, using two monovalent Cu + to replace one divalent Pb² + to construct a new type of two-dimensional lead-free perovskite. The degree of excitation-dependent structural deformation in the two-dimensional [Cu 2 Br 4 2- layer generates multiple excited states, presenting temperature-related reversible energy transfer. According to the subsequent experimental results, the two-dimensional cuprous perovskite material in the present invention has multi-color luminescence tunability and a photoluminescence quantum yield close to 100%, has an ultra-short afterglow lifetime and high-resolution imaging performance, thereby indicating that (AMP) 2 Cu 2 Br 4 can be preferably applied to the fields of luminescent materials, scintillators and radiation detection, realizing multi-field applications, and further solving the technical problem that the industrial application of existing lead-based halide perovskite materials is limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the powder X-ray diffraction pattern of (AMP) 2 Cu 2 Br 4 .

[0019] Figure 2 is the schematic crystal structure diagram of (AMP) 2 Cu 2 Br 4 , wherein, (a) is the [CuBr 2 Cu 2 Br 4 tetrahedron and [Cu 4 Br 2 Br 6 ​​4- Dimer structure diagram, (b) is the ball-and-stick model of the [Cu 2 Br 4 2- layer, (c) is the stacking structure of (AMP) 2 Cu 2 Br 4 viewed along the c-axis direction, (d) is the hydrogen bond between the [AMP] + cation and the [Cu 2 Br 4 2- layers.

[0020] Figure 3 is the comparison graph of the powder second harmonic generation signals of (AMP) 2 Cu 2 Br 4 and potassium dihydrogen phosphate at a wavelength of 1064 nm.

[0021] Figure 4 is the phase matching curve of (AMP) 2 Cu 2 Br 4 and potassium dihydrogen phosphate.

[0022] Figure 5 is the photo of the crystal of (AMP) 2 Cu 2 Br 4 under sunlight and ultraviolet light irradiation.

[0023] Figure 6 is the emission spectrum of (AMP) 2 Cu 2 Br 4 at an ultraviolet excitation wavelength of 200 nm - 400 nm.

[0024] Figure 7 is the CIE coordinates of (AMP) 2 Cu 2 Br 4 at different excitation wavelengths.

[0025] Figure 8 is the emission spectrum of (AMP) 2 Cu 2 Br 4 excited by 283 nm, 367 nm and 350 nm.

[0026] Figure 9 is the quantum yield of (AMP) 2 Cu 2 Br 4 under 283 nm excitation. ​​

[0027] Figure 10 is (AMP) 2 Cu 2 Br 4 The quantum yield under 367 nm excitation.

[0028] Figure 11 is (AMP) 2 Cu 2 Br 4 The quantum yield under 350 nm excitation.

[0029] Figure 12 is (AMP) 2 Cu 2 Br 4 The thermogravimetric analysis curve and DSC curve of...

[0030] Figure 13 is (AMP) 2 Cu 2 Br 4 The luminescence pictures of the crystal under 254 nm and 365 nm ultraviolet light irradiation when the temperature increases from 300 K to 400 K.

[0031] Figure 14 is (AMP) 2 Cu 2 Br 4 The emission spectrum of fluorescence intensity varying with temperature in the range of 300 K - 400 K under 283 nm ultraviolet light excitation.

[0032] Figure 15 is (AMP) 2 Cu 2 Br 4 The emission spectrum of fluorescence intensity varying with temperature in the range of 300 K - 400 K under 367 nm ultraviolet light excitation.

[0033] Figure 16 is (AMP) 2 Cu 2 Br 4 The emission spectrum of fluorescence intensity varying with temperature in the range of 300 K - 400 K under 350 nm ultraviolet light excitation.

[0034] Figure 17 Powder diffraction pattern of (AMP)2Cu2Br4 under temperature change in the range of 300 K - 400 K.

[0035] Figure 18 is (AMP) 2 Cu 2 Br 4Powder diffraction patterns of the theoretical and experimental comparison after 20 times of heating and cooling.

[0036] Figure 19 is (AMP) 2 Cu 2 Br 4 Luminescence photos of the @EVA flexible film under bending and stretching under natural light and 254 nm and 365 nm ultraviolet light irradiation.

[0037] Figure 20 is (AMP) 2 Cu 2 Br 4 Luminescence photos of the @EVA flexible film when heated to different temperatures under 365 nm ultraviolet light irradiation.

[0038] Figure 21 Schematic diagram of the thermochromic sensing thermometer with gradient temperature change of (AMP)2Cu2Br4.

[0039] Figure 22 Indicator diagram of the thermochromic sensing thermometer for real-time measurement of local temperature of (AMP)2Cu2Br4.

[0040] Figure 23 is (AMP) 2 Cu 2 Br 4 And the comparison chart of the radioluminescence intensity of LuAG:Ce.

[0041] Figure 24 is (AMP) 2 Cu 2 Br 4 Radiation emission spectra at different dose rates.

[0042] Figure 25 is (AMP) 2 Cu 2 Br 4 X-ray induced afterglow intensity map after X-ray irradiation stops.

[0043] Figure 26 is (AMP) 2 Cu 2 Br 4 Radiation emission intensity under continuous on / off X-ray irradiation.

[0044] Figure 27 Photos of the circuit board and X-ray imaging pictures.

[0045] Figure 28 Crystal structure of Compound 1.

[0046] Figure 29is the fluorescence emission spectrum of compound 1.

[0047] Figure 29 This is the 2D layer structure diagram of compound 2.

[0048] Figure 30 is the powder X-ray diffraction pattern of compound 2.

[0049] Figure 31 The UV absorption spectrum and fluorescence emission spectrum of compound 2. DETAILED DESCRIPTION

[0050] In order to solve the above technical problems, the present invention provides a two-dimensional cuprous perovskite material and a preparation method and application thereof. The technical scheme and embodiments of the present invention are now described in detail in conjunction with the accompanying drawings.

[0051] The present invention is described in detail below through specific examples. The examples are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0052] Reagents and materials: Cuprous bromide (CuBr, MacLean Reagent Company, purity 99%), N-aminomorpholine (AMP, MacLean Reagent Company, purity 99%), hydrobromic acid (HBr, concentration 34%), hypophosphorous acid (H 3 PO 2 , Aladdin Reagent Company, purity 99%), ethanol (EtOH, Aladdin Reagent Company, purity 99%), ethylene-vinyl acetate copolymer (EVA, Aladdin Reagent Company), cyclohexane (McLean Reagent Company, purity 99%). All reagents and solvents were commercially available and used without further purification.

[0053] Example 1 (AMP) 2 Cu 2 Br 4 Synthesis of: 1 mmol of cuprous bromide was dissolved in 1 mL of hydrobromic acid. Then, 0.5 mL of hypophosphorous acid was added to the mixture to prevent oxidation. After that, 4 mL of ethanol solvent was added to the above mixed solution, followed by 1 mmol of N-aminomorpholine. The final mixture was then stirred and heated at 80°C for 5 days. After cooling, it was allowed to evaporate at room temperature for about a week. Then, the blocky colorless crystals were collected, washed with ethanol, and finally dried under vacuum conditions to obtain (AMP) 2 Cu 2 Br 4 .

[0054] (AMP) 2 Cu 2 Br 4 @Preparation of EVA flexible film: Dissolve 2.0 g of ethylene-vinyl acetate copolymer in 5 mL of cyclohexane by stirring at 60 °C for 1 hour to form a transparent solution. Then, add 0.1 g of (AMP) 2 Cu 2 Br 4 powder to the above solution and continue stirring until a homogeneous and viscous fluid is formed. When it can emit light uniformly under ultraviolet light irradiation, stop heating and quickly pour the mixture into a glass mold. After cooling to room temperature in a fume hood, (AMP) 2 Cu 2 Br 4 @EVA flexible film can be obtained.

[0055] Comparative Example 1 Compared with the example, the synthesis method of Comparative Example 1 uses the room temperature evaporation method.

[0056] The molecular formula of Compound 1 prepared in Comparative Example 1 is (N-MPDA)[PbBr 4 , and the crystal system space group is P 2 1 / c , and the unit cell parameters are a = 8.27 Å, b = 8.28 Å, c = 20.06 Å. As Figure 32 shown, based on crystallographic studies, the long-chain N-MPDA spacer can sufficiently separate adjacent inorganic layers along the (001) plane. In addition, N-MPDA does not allow hydrogen bonding between the ammonium group and adjacent perovskites in the (110) structure, thus avoiding close contact between adjacent inorganic layers. Figure 28 shows the photoluminescence emission spectrum measured at an excitation wavelength of 405 nm. As can be seen from Figure 29 , the maximum emission center of Comparative Example 1 is 427 nm. There is no emission signal related to quasi-phase impurities, revealing the phase purity of the single crystal of Comparative Example 1.

[0057] Comparative Example 2 Compared with the example, the synthesis method of Comparative Example 1 uses the room temperature evaporation method.

[0058] The molecular formula of Compound 2 prepared in Comparative Example 2 is (HOOC 4 H 9 NH 3 ) 2 PbBr 4 , and the crystal system space group is Figure 29 The unit cell parameters are a = 8.3390 Å, b = 8.2161 Å, c = 27.5646 Å. As shown in (a) of Pbca , ABA + and BA +Similarly, it is a double-layer cation that separates the inorganic layer, where ABA + is HOOC 4 H 9 NH 3 + , and BA is n -butylamino. Uniquely, different from the van der Waals interaction of the double-layer cation in traditional perovskites, carboxylic acid dimers are constructed in the double-layer organic cation of Compound 2. As Figure 30 shown in (b) therein, the dimer is formed through a pair of O-H···O intermolecular bonds. In this case, the carboxyl group acts as both a donor and an acceptor to generate a dimer in the R 2 2 (8) part, which is a typical characteristic of carboxylic acids. The consistency between the measured X-ray powder diffraction pattern and the X-ray powder diffraction pattern simulated based on the single-crystal structure confirms the purity of the Compound 2 sample, as Figure 30 shown. Compound 2 emits white light under 365 nm excitation. Refer to Figure 31 , the photoluminescence spectrum shows that Compound 2 has a broadband emission in the range of 390 - 700 nm, with a maximum emission peak at 415 nm.

[0059] Structure Characterization Tests: (1) X-ray Diffraction The X-ray single-crystal data of (AMP) α radiation, wavelength Figure 32 = 0.71073 Å, of Cu 2 Cu 2 Br 4 ·2H2O were collected using a Bruker Apex II CCD diffractometer equipped with Mo-K

[0060] (2) Powder X-ray Diffraction Characterization was performed on a Bruker D8 ADVANCE.

[0061] (3) Ultraviolet-Visible Absorption Spectrum The ultraviolet-visible absorption spectrum was collected using a PE Lambda 900 ultraviolet-visible spectrophotometer with BaSO 4 powder as the reflectance reference.

[0062] (4) Differential Scanning Calorimetry Measurement and Thermogravimetric Analysis Measurement Performed on a Rigaku Mettler TG-DTA 8122 simultaneous thermal analyzer, operating at a heating rate of 10 °C / min under a nitrogen atmosphere.

[0063] (5) Second-Harmonic Generation Measurement The second harmonic generation measurement of the powder was carried out using the well-known Kurtz-Perry method. A 1064 nm Nd:YAG laser and a digital oscilloscope connected to a photomultiplier tube module were used to measure (AMP) 2 Cu 2 Br 4 The second harmonic generation intensity of. The (AMP) 2 Cu 2 Br 4 and KH 2 PO 4 samples were sieved into different particle sizes, namely: 26 μm - 48 μm, 48 μm - 75 μm, 75 μm - 100 μm, 100 μm - 150 μm, 150 μm - 180 μm, 180 μm - 250 μm, and 250 μm - 315 μm.

[0064] Luminescence performance test: (1) Photoluminescence characterization The photoluminescence spectrum was obtained using a Hitachi F-7000 fluorescence spectrometer, and the photoluminescence quantum yield was measured by equipping an integrating sphere in a FLS5 fluorescence spectrophotometer.

[0065] (2) Radioluminescence characterization A 1000-type fluorescence spectrometer with an X-ray tube was used to obtain the radioluminescence spectrum. The X-ray source is a silver target X-ray tube, and its parameters are as follows: maximum power: 10 W; maximum voltage: 50 kV; maximum current: 200 λ A; X-ray photon energy: 22 keV. The X-ray response intensity was collected using a Hamamatsu R928 photomultiplier tube. The X-ray dose rate was calibrated by a high-sensitivity X-ray ionization chamber dosimeter, Raycal Corporation model 10×5 - 180.

[0066] Test result analysis (1) Crystal structure analysis High-quality (AMP) 2 Cu 2 Br 4 single crystals were obtained by the solvothermal reaction of N-aminomorpholine and cuprous bromide in a mixed solution of hydrobromic acid, hypophosphorous acid, and ethanol at 80 °C. The crystal structure of (AMP) 2 Cu 2 Br 4 was obtained using an X-ray single crystal diffractometer and a powder X-ray diffractometer. As μ shown, the matching diffraction peaks confirmed the high purity of the sample. The crystal structure belongs to the monoclinic system and has a non-centrosymmetric Figure 1Space group, number 9. Unit cell parameters a = 21.6107(7) Å, b = 6.4902(2) Å, c = 13.0163(4) Å, α = 90 º, β = 107.6750(10) º, Cc = 90 º, Z = 4, unit cell volume V = 1739.46 Å 3 .

[0067] γ is (AMP) 2 Cu 2 Br 4 crystal structure schematic diagram, where (a) is (AMP) 2 Cu 2 Br 4 of [CuBr 4 tetrahedron and [Cu 2 Br 6 4- dimer structure diagram.

[0068] (AMP) 2 Cu 2 Br 4 crystal structure consists of two-dimensional [Cu 2 Br 4 2- layers, and these 2D layers are separated by large [AMP] + cations. As Figure 2 shown in (a), in (AMP) 2 Cu 2 Br 4 structure, each crystallographically independent Cu + ion is coordinated by four Br - anions to form a slightly distorted [CuBr 4 tetrahedron.

[0069] As Figure 2 shown in (b), two [CuBr 4 tetrahedrons further self-condense by sharing edges to form a [Cu 2 X 6 4- dimer, with a weak Cu···Cu bond between them, and the bond length is 2.6121(14) Å. This dimer is a secondary structural unit with four terminal halogen atoms. Subsequently, [Cu 2 X 6 4- dimers are interconnected by sharing vertices, forming long-range ordered [Cu Figure 2 -plane.​​​​2 Br 4 2- Single layer. This [Cu 2 Br 4 2- layer can be regarded as replacing the [PbX 4 2- layer with [Cu 2 X 6 4- dimers in the (100)-oriented [PbX 6 octahedra, representing a new type of two-dimensional halide perovskite layer.

[0070] As bc shown in (c), along the a-axis direction, parallel two-dimensional [Cu 2 Br 4 2- layers are stacked with a displacement of (1 / 2, 1 / 2), which is similar to that of typical Ruddlesden-Popper type two-dimensional perovskites.

[0071] As Figure 2 shown in (d), [AMP] + acts as a space filler between inorganic lamellae and forms a "chelating" effect with bromine atoms through a large number of hydrogen bonds. The protonated ammonium group on the morpholine ring binds tightly to the bromine atoms, making the network structure rigid and causing a large wrinkle in the two-dimensional [Cu 2 Br 4 2- layer. The inorganic [[Cu 2 Br 4 2- layer and the organic [AMP] 2+ quasi-layer are alternately arranged to form a typical two-dimensional hydrogen bond network.

[0072] (2) SHG performance analysis Using commercially available potassium dihydrogen phosphate, abbreviated as KDP, as a standard reference, Kurtz-Perry powder second harmonic generation measurements were carried out under 1064 nm laser irradiation. As Figure 2 shown, in the same particle size range of 45 μm to 425 μm, (AMP) 2 Cu 2 Br 4 showed remarkable second harmonic signals, and the intensity was about 0.8 times that of KDP. Further, a particle size-related second harmonic study was carried out on samples with a controllable particle size range of 26 μm to 315 μm, and the results are as Figure 3 ​​​​​​​As shown, the second harmonic intensity increases monotonically with the increase in particle size, which indicates the phase matching response and demonstrates its potential application in laser technology.

[0073] (3) Photoluminescence property analysis (AMP) 2 Cu 2 Br 4 The bulk crystals of (AMP)2Cu2Br4 exhibit a strong absorption band in the range of 250 nm to 450 nm, which is consistent with the transparent and colorless appearance under daylight. Under ultraviolet light irradiation at 254 nm and 365 nm, (AMP)2Cu2Br4 exhibits strong blue and orange light emissions respectively, indicating the existence of double excited states at different excitation energies. Therefore, bright white light emission is generated under simultaneous excitation by 254 nm and 365 nm ultraviolet light, as Figure 4 shown. The two strongest emission bands at 460 nm and 610 nm appear under ultraviolet light excitation at 283 nm and 367 nm respectively, and the relative intensities of these two emission bands show opposite trends with the excitation wavelength, resulting in a change in the emission color, as Figure 5 shown.

[0074] Based on the photoluminescence emission spectrum, the CIE coordinates gradually change from the blue, white, and orange ranges, presenting excitation-emission adjustable multicolor emission, as Figure 6 shown. Under ultraviolet light excitation at 283 nm, (AMP) 2 Cu 2 Br 4 exhibits a broad blue light emission in the range of 400 nm - 600 nm, with a maximum peak at 460 nm, CIE coordinates of (0.14, 0.16), a full width at half maximum of 68 nm, and a large Stokes shift of 177 nm, as Figure 7 shown. The photoluminescence quantum yield of the blue light emission is as high as 94.84%, exceeding that of most low-dimensional metal perovskites with blue emission, as Figure 8 shown. When the sample is excited by 367 nm ultraviolet light, (AMP) 2 Cu 2 Br 4 shows another broad orange light emission band, with a main wavelength of 610 nm, CIE coordinates of (0.48, 0.43), a full width at half maximum of 142 nm, a Stokes shift of 243 nm, and in addition to the original shoulder peak emission at 460 nm, the photoluminescence quantum yield is 72.08%, as Figure 9 shown.

[0075] As the excitation wavelength increases from 283 nm to 367 nm, the fluctuations in the relative intensities of the two emission bands result in a gradual change in the emission color between the blue and orange regions. In particular, 350 nm ultraviolet light excitation generates dual-band white light emission with perfect CIE coordinates of (0.32, 0.31). It is worth noting that most of the previously reported white light-emitting metal halide materials belong to two-dimensional lead perovskites, and few cuprous halides can achieve this goal. Here, (AMP) 2 Cu 2 Br 4 represents a new white light emitter, opening up a new way for the fabrication of two-dimensional lead-free perovskites as single-component white light-emitting materials. It is worth noting that the photoluminescence quantum yield of the white light emission is close to 86%, higher than that of all white light-emitting two-dimensional lead perovskites, as Figure 10 shown.

[0076] In short, the photoluminescence quantum yields of all emission bands far exceed those of typical two-dimensional lead perovskites, indicating the application advantages of two-dimensional cuprous perovskite materials (AMP) 2 Cu 2 Br 4 in solid-state white light-emitting diodes.

[0077] (4)Thermochromic fluorescence and temperature sensing performance analysis As is well known, based on thermochromic fluorescent materials, the luminescence intensity ratio technique has become one of the mainstream non-contact temperature detection methods. Here, the dual emission bands of (AMP) 2 Cu 2 Br 4 inspire this invention to study the possibility of its thermochromic fluorescence to explore its application in temperature sensing. Due to the enhanced non-radiative transitions caused by thermal vibrations, the intensities of both emission bands decrease monotonically with increasing temperature. To further study the luminescence behavior at high temperatures, thermogravimetric analysis was carried out to test the thermal stability. During the continuous heating from room temperature of 30 °C to about 193 °C, see Figure 11 , according to the thermogravimetric analysis curve, there is no obvious weight loss and structural decomposition behavior, which provides a prerequisite for use at high temperatures.

[0078] During the continuous heating from room temperature to 400 K, (AMP) 2 Cu 2 Br 4 maintains bright blue light emission under 254 nm ultraviolet light irradiation, while the orange light emission excited by 365 nm ultraviolet light gradually turns into white light emission. The evolution photos of the crystal under ultraviolet light are as Figure 12As shown. This vivid thermochromic fluorescence prompted the present invention to further test the photoluminescence emission spectra varying with temperature under different ultraviolet light wavelengths in the temperature range of 300 K to 400 K, in order to Figure 13 ex Taking λ = 283, 350 and 367 nm as examples: As λ and 15 shown, (AMP) 2 Cu 2 Br 4 exhibits stable blue and orange light emissions under ultraviolet light excitations at 283 nm and 367 nm respectively, and the emission intensity decreases monotonically as the temperature increases from 300 K to 400 K. However, under ultraviolet light excitation at 350 nm, the dual emission bands centered at 610 nm and 460 nm show different thermal quenching trends. Specifically, the intensity of the low-energy emission band (610 nm) decreases monotonically with increasing temperature, but the intensity of the high-energy emission band (460 nm) first increases from 300 K to 350 K and then further decreases rapidly until 400 K. Therefore, when (AMP) 2 Cu 2 Br 4 is excited by 350 nm ultraviolet light, the orange light emission band gradually disappears, and a blue-white mixed light emission is presented until 400 K, as Figure 14 shown.

[0079] To clarify the essence of the thermochromic fluorescence, a series of temperature-related structural characterizations were carried out on (AMP) 2 Cu 2 Br 4 Variable-temperature X-ray powder diffraction tests were carried out in the temperature range of 300 K to 400 K. As Figure 16 shown, as the temperature increases, the X-ray powder diffraction pattern of (AMP) 2 Cu 2 Br 4 fits well with the data of the synthesized sample. Even after 20 consecutive cycles of heating and cooling, (AMP) 2 Cu 2 Br 4 still maintains high crystallinity and a stable crystal structure, as Figure 17 shown. The change in luminescence color with temperature and the stability at high temperatures further promoted the present invention to develop its application in high-temperature temperature indication.

[0080] With the change of temperature, the fluorescence intensity ratio at the two emission positions of 460 nm and 610 nm also changes. According to this relationship, the present invention calculated its relative thermal sensitivity to be 56.755% K -1。It has a relative thermal sensitivity superior to the vast majority of previously reported luminescent molecular thermometers based on dual-emission materials, such as metal-organic framework@dye complexes, quantum dots, and dual-rare-earth dopants, indicating its excellent temperature sensing performance.

[0081] Therefore, (AMP) 2 Cu 2 Br 4 becomes an ideal candidate material for constructing a thermochromic fluorescence platform in wearable temperature sensors due to its tunable multicolor luminescence characteristics and high sensing sensitivity with temperature changes. To endow the sensor with good operability and sensing performance, considering that (AMP) 2 Cu 2 Br 4 has high structural and luminescence stability in various organic solvents, the present invention selects transparent ethylene-vinyl acetate copolymer as the optical matrix material to prepare a flexible film. Under ultraviolet light irradiation, the prepared film can still show bright luminescence like a bulk crystal even in the bent and stretched states, indicating its high-performance flexibility and luminescence, as Figure 18 shown. Subsequently, the prepared film was pasted on the outer surface of a beaker filled with oil, and this was used as an example of a reaction kettle, cup, or other container to detect temperature changes, and the results are as Figure 19 shown. As the temperature of the oil increased from 300 K to 400 K, under 365 nm ultraviolet light source irradiation, the orange luminescence of the (AMP) 2 Cu 2 Br 4 film gradually changed to white luminescence. After cooling to 300 K, the white luminescence of the (AMP) 2 Cu 2 Br 4 film returned to its original orange luminescence, having excellent recyclable and repeatable temperature sensing characteristics. In addition, the present invention further assembled a thermochromic sensing thermometer by coating the sample on a 365 nm ultraviolet light-emitting diode (LED) tube. The temperature of the prepared LED tube was adjusted by a hot air blower. At the same time, a traditional thermal expansion thermometer and a thermochromic thermometer were used to measure the real-time temperature. After heating one end of the sensing tube and placing the other end in cold air, due to the temperature gradient existing in the sensing tube, the sensing tube gradually showed different luminescence colors from white (upper part) to orange (bottom part), as Figure 20 shown. Referring to Figure 21 , at different ambient temperatures, the prepared sensing tube showed corresponding luminescence colors, which was consistent with the results of the thermal expansion thermometer. This visible thermochromic thermometer can be used to detect the local temperature of a complex environment, being superior to the traditional thermal expansion thermometer. Generally speaking, these practical studies demonstrated that (AMP) 2 Cu 2 Br4 Potential applications of wearable temperature sensors in real-time contact and non-contact temperature measurements.

[0082] (5) Analysis of radioluminescence properties and X-ray imaging applications High photoluminescence quantum yield, large Stokes shift, and good stability have prompted further research on (AMP) in this work 2 Cu 2 Br 4 for its radioluminescence properties and applications in X-ray imaging. To evaluate the 2 Cu 2 Br 4 attenuation efficiency of X-rays by (AMP), the present invention first calculates the absorption coefficient of (AMP) 2 Cu 2 Br 4 at different X-ray photon energies. Under X-ray excitation with a dose rate of 12.8 Figure 22 Gy ᵢᵣ s - ¹, (AMP) 2 Cu 2 Br 4 shows strong blue radioluminescence, similar to photoluminescence, indicating the same radiative recombination pathway under X-ray and ultraviolet light excitation. It is worth noting that, as μ shown, the radioluminescence intensity of (AMP) 2 Cu 2 Br 4 is 3.7 times that of LuAG:Ce, and the scintillation light yield of LuAG:Ce is 25,000 photon MeV -1 . By comparing the integrated radioluminescence emission spectrum area, the scintillation light yield of (AMP) 2 Cu 2 Br 4 is obtained as 92,400 photon MeV -1 , which is higher than the scintillation light yields of commercially available inorganic scintillators such as 8,000 photon MeV for BGO -1 , 54,000 photon MeV for CsI:Tl -1 , 41,000 photon MeV for CsI:Na -1 , 60,000 photon MeV for GOS -1 , 20,000 photon MeV for CdWO 4 etc. More importantly, (AMP) -1 shows excellent X-ray attenuation performance, which is beneficial for X-ray imaging applications. 2 Cu 2Br 4 has a light yield that exceeds all reported low-dimensional hybrid copper(I) halides, representing the current highest value. To determine the response range of ((AMP) 2 Cu 2 Br 4 to X-ray dose rates, its radioluminescence emission spectra were measured over a wide dose rate range of 5,000 to 50,000 Figure 23 Gy ir s - . As μ shown, the radioluminescence intensity of ((AMP) 2 Cu 2 Br 4 gradually increases with the increase of X-ray dose rate. When the signal-to-noise ratio is 3, the detection limit is 121 n Gy ir s -1 , which is about 45 times lower than the X-ray diagnostic requirement (5.5 Figure 24 Gy ir s -1 ). The good linear relationship between the radioluminescence intensity and the X-ray dose rate under higher dose rate excitation is beneficial for obtaining high contrast in X-ray imaging. By monitoring the change in the radioluminescence emission intensity under X-ray on / off conditions at the highest dose rate of 14.2 μ Gy ir s -1 , the scintillation stability of ((AMP) 2 Cu 2 Br 4 was further evaluated. As μ shown, ((AMP) 2 Cu 2 Br 4 shows a fast scintillation response and the radioluminescence emission intensity recovers to the original intensity after 160 minutes without significant attenuation, indicating its excellent scintillation stability. The highest scintillation light yield, low detection limit, and good radiation resistance demonstrate the potential application of ((AMP) 2 Cu 2 Br 4 in computed tomography imaging.

[0083] To explore the application of ((AMP) 2 Cu 2 Br 4 in X-ray imaging, the present invention first evaluated its afterglow lifetime, which plays a crucial role in the imaging contrast of X-ray scintillators. Generally, a shorter afterglow lifetime is beneficial for high-contrast imaging and reducing residual ghosting. After X-ray cut-off, ((AMP) 2 Cu2 Br 4 The relative radioluminescence emission intensity of Br rapidly drops to about 99% within 0.41 milliseconds, which is shorter than the afterglow lifetimes of most low-dimensional cuprous halide-based scintillators. See Figure 25 . This rapid decay rate indicates its ultra-short afterglow lifetime and high-resolution imaging performance. The spatial resolution of X-ray imaging is calculated by the modulation transfer function. To confirm its potential application in X-ray imaging, (AMP) 2 Cu 2 Br 4 thin films are used as flexible scintillation screens to reflect the intensity differences of X-rays. In this invention, a circuit board is used as the first target object, and there are extremely fine metal wires on the circuit board, which cannot be observed by the naked eye under visible light. However, due to the different X-ray absorption capabilities of the metal wires and the plastic board, these metal wires can be clearly seen under the irradiation of the X-ray source, as shown in Figure 26 Figure 27 . Generally speaking, the ultra-high light yield, spatial resolution, short afterglow lifetime, and ultra-low detection limit of (AMP) 2 Cu 2 Br 4 indicate its excellent scintillation performance and application value in X-ray imaging, non-destructive testing, radiation detection, etc.

[0084] The above description is only the preferred embodiment of the present invention, and the above specific embodiments do not limit the present invention. Within the scope of the technical idea of the present invention, various deformations and modifications can occur. Any retouching, modification, or equivalent replacement made by those of ordinary skill in the art according to the above description shall fall within the scope protected by the present invention.

Claims

1. A two-dimensional cuprous perovskite material, characterized in that: The crystal structure of the two-dimensional cuprous perovskite material belongs to two-dimensional perovskite, the chemical formula of the two-dimensional cuprous perovskite material is (AMP)2Cu2Br4, and the AMP is N-aminomorpholine.

2. The two-dimensional cuprous perovskite material according to claim 1, characterized in that: The crystal structure of (AMP)2Cu2Br4 consists of two-dimensional [Cu2Br4] 2- Layer composition, the [Cu2Br4] 2- Layer is composed of [Cu2X6] 4- The dimers share the same vertices and connect with each other to form [Cu2X6] 4- The dimer is formed by the self-condensation of two [CuBr4] tetrahedra sharing their edges.

3. A method for preparing the two-dimensional cuprous perovskite material according to claim 1 or 2, characterized in that: The steps include: Mixing cuprous bromide powder and hydrobromic acid, adding hypophosphorous acid to obtain a mixed solution; The mixed solution is mixed with N-aminomorpholine, mixed evenly, and a two-dimensional cuprous perovskite material is prepared by a solvothermal method.

4. The method for preparing the two-dimensional cuprous perovskite material according to claim 3, characterized in that: The solvent of the solvothermal method is alcohol.

5. The method for preparing the two-dimensional cuprous perovskite material according to claim 3, characterized in that: The reaction temperature of the solvent thermal method is 70°C to 90°C.

6. The method for preparing the two-dimensional cuprous perovskite material according to claim 3, characterized in that: The amount of the hypophosphorous acid used is 5% to 15% of the molar number of the reaction substrate of the solvothermal method.

7. Use of the two-dimensional cuprous perovskite material according to claim 1 in preparing a photoluminescent material.

8. Use of the two-dimensional cuprous perovskite material according to claim 1 in the preparation of thermochromic fluorescent materials and temperature sensors.

9. Use of the two-dimensional cuprous perovskite material according to claim 1 in the preparation of radiation luminescent materials and X-ray imaging materials.

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