High-resolution ultrafast scintillator based on exciton space diffusion limitation strategy and preparation method thereof

Abstract

The invention belongs to the technical field of X-ray imaging, and particularly relates to a high-resolution ultrafast scintillator based on an exciton space diffusion limitation strategy and a preparation method of the high-resolution ultrafast scintillator. According to the invention, the dimension of PEA2PbBr4 is reduced from a bulk single crystal to a uniform one-dimensional nanowire by utilizing the space limitation effect of the nano through hole template, so that the space localization of bulk-phase excitons under X-ray excitation is realized. The spatially localized bulk phase excitons significantly shorten the decay time of radioluminescence (shortened from 11.85 ns to 1.87 ns). Meanwhile, benefited from the regularly arranged periodic optical waveguide structure, scintillation photons generated by the PEA2PbBr4 nanowire array can be directionally propagated along the waveguide structure, and the transverse optical propagation and crosstalk effect are reduced, so that high spatial resolution imaging (MTF 0.2 = 57.1 lp / mm) is realized. The strategy provides reference for promoting the application of the organic-inorganic hybrid perovskite material in the field of ultrafast ray imaging.

Description

Technical Field

[0001] This invention belongs to the field of X-ray imaging technology, specifically relating to a high-resolution ultrafast scintillator based on an exciton spatial diffusion confinement strategy and its preparation method. Background Technology

[0002] Scintillator-based X-ray imaging plays an irreplaceable role in high-energy physics experiments, medical radiology (CT, DR), industrial non-destructive testing, security inspection, and geological exploration. With the development and expansion of the X-ray imaging field, ultrafast X-ray imaging, as an emerging and highly promising research direction, has shown vigorous development momentum in recent years. Compared to traditional static X-ray imaging, ultrafast X-ray imaging, with nanosecond or even sub-nanosecond time resolution, can accurately capture transient image information and achieve real-time monitoring of dynamic processes. It has significant value in scenarios such as monitoring the kinetics of lithium dendrite growth in lithium battery anodes, monitoring molten pools in metal additive manufacturing, ultra-high-speed fluid imaging (including internal combustion engine spray fluid dynamics research), and pulsed radiation field imaging. Traditional inorganic scintillators, such as CsI:Tl, NaI:Tl, GOS ceramics, and YAG:Ce, typically have considerable light yield (>25000 photons / MeV) and acceptable decay times (greater than tens or even hundreds of nanoseconds), meeting the performance requirements of most applications. However, when applied to ultrafast X-ray imaging, the decay time of traditional inorganic scintillators is no longer sufficient to meet the requirements of ultrafast decay. This dilemma has driven the research and application of novel scintillators with ultrafast decay time characteristics.

[0003] In recent years, organic-inorganic hybrid perovskite materials have shown application potential in fields such as photodetectors, quantum dot LEDs, and photovoltaic devices due to their high PLQY, good environmental adaptability, and tunable luminescence caused by their natural quantum well structure. Among many organic-inorganic hybrid perovskite materials, PEA2PbBr4 (Phenethyl lead Bromide (C6H5CH2CH2NH3)2PbBr4) is considered a highly promising candidate material for ultrafast radiation and high-energy particle detection due to its moderate band gap, high X-ray absorption coefficient, high hydrogen content, high light yield, and ultrafast decay time. Furthermore, the excellent performance of PEA2PbBr4 has been verified in high-energy X-ray detection, fast neutron detection, ultraviolet-visible light detection, and n / γ discrimination.

[0004] However, PEA2PbBr4 still faces two major bottlenecks when applied to practical ultrafast X-ray imaging: First, the layered structure of PEA2PbBr4 leads to different decay behaviors of surface and bulk excitons. Under high-penetration X-ray excitation, the dominant bulk exciton emission has a slower decay time (>10 ns), which is detrimental to ultrafast X-ray imaging. Second, the growth of PEA2PbBr4 single crystals typically employs slow solvent evaporation at room temperature or cooling crystallization. However, the solubility of PEA2PbBr4 varies drastically with temperature, making uncontrolled polycrystalline growth prone to occur during single crystal growth. This results in the difficulty in obtaining and processing large-size, high-quality PEA2PbBr4 single crystals suitable for imaging. These factors are unfavorable for expanding the application of PEA2PbBr4 in ultrafast X-ray imaging. Therefore, it is necessary to develop a fabrication strategy that can shorten the decay time of PEA2PbBr4 under X-ray excitation and achieve large-area uniform scintillation screens. Summary of the Invention

[0005] To address the problems existing in the prior art, this application provides a high-resolution ultrafast scintillator based on an exciton space diffusion confinement strategy and its preparation method.

[0006] The design concept of the PEA2PbBr4 nanowire (NWs) array scintillation screen (PNSS) with ultrafast decay and high resolution characteristics is as follows: Figure 1 As shown, organic-inorganic perovskite PEA2PbBr4 is considered an ideal candidate material for ultrafast scintillators due to its combination of high luminescence yield (>40000 photons / MeV) and sub-nanosecond decay time (specifically, photoluminescence decay time < 600 ps). Figure 1 (as shown in (a)). However, when used for ultrafast imaging applications with higher energy X-rays / γ-rays, the decay time of PEA2PbBr4 single crystals is significantly prolonged (~16.9 ns). This phenomenon is detrimental to ultrafast X-ray imaging applications. Recent studies by the applicant on the exciton dynamics of PEA2PbBr4 crystals suggest that the density difference between excitons on the PEA2PbBr4 crystal surface and those in the bulk phase may be the reason for the significant increase in decay time under X-rays. During the growth process, the PEA on the surface of the PEA2PbBr4 crystal... + Ion deficiency induced significant compressive strain on the crystal surface. This compressive strain led to differentiated band structures between the surface and bulk phases, as well as self-absorption phenomena (such as...). Figure 1As shown in (b), this also explains the double-peak emission phenomenon in the PL spectrum, while on the other hand, it also causes an increase in surface lattice distortion. The more distorted surface lattice structure creates a localized distribution of surface excitons. Therefore, when using ultraviolet-visible light with shallow penetration depth for excitation, surface excitons tend to be localized on the surface of the PEA2PbBr4 crystal, resulting in a higher exciton density and thus an increased decay time. However, under high-energy rays, the situation is completely different. Figure 1 As shown in (c), since the X-ray penetration depth is sufficient to penetrate the entire crystal, most of the energy is deposited within the PEA2PbBr4 crystal and excites bulk excitons. A small number of excited surface excitons also transfer energy to the bulk excitons through the Förster resonance energy transfer (FRET) process. The diffuse distribution of bulk excitons within the bulk space reduces the exciton density (compared to the case of surface photoexcitation). According to the rate equation for the exciton density over time (Equation. 1), the exciton decay time depends on the exciton density; therefore, the diffuse distribution of bulk excitons leads to a longer decay time. Where N is the exciton density in the system, and t is time. For the effective decay time, γ represents the recombination rate constants of EEA and Auger, etc. Meanwhile, under X-ray excitation, the PEA2PbBr4 bulk single crystal emits bulk exciton-dominated scintillation light in all directions without restriction. During its propagation within the single crystal, this scintillation light continuously undergoes scattering and optical crosstalk, resulting in a decrease in the spatial resolution of scintillation imaging.

[0007] This predicament has prompted researchers to modulate the structure using methods such as doping. However, the core problem of "low bulk exciton density" remains fundamentally unresolved. If, through some form of nanoengineering, the spatial dimension of PEA2PbBr4 is reduced from three dimensions to two or even one dimension, it may be possible to localize the bulk excitons, which originally exhibit long diffusion behavior, resulting in a higher exciton density and ultimately shortening the decay time. Based on this strategy, this invention proposes an innovative approach: directionally growing a one-dimensional PEA2PbBr4 nanowire array within a spatially confined nanoporous template. Utilizing the spatial confinement in two dimensions of real space, the exciton density of the bulk excitons in the PEA2PbBr4 nanowires is enhanced, ultimately leading to a shorter decay time under X-rays. Simultaneously, as... Figure 1 As shown in (d), nanopores are natural optical waveguide structures that can synergistically confine the light emitted by the scintillator within the pore, enabling directional propagation. This reduces optical crosstalk and scattering effects of scintillating light from adjacent pores. Therefore, this strategy theoretically also significantly improves the X-ray imaging resolution of PNSS.

[0008] The present invention provides a method for fabricating high-resolution ultrafast scintillators based on an exciton spatial diffusion confinement strategy. This method employs a negative pressure-assisted two-step solution growth strategy to grow uniform and dense low-dimensional PEA2PbBr4 nanowires (PNSS) in a pixelated nanoporous template. Benefiting from the one-dimensional spatial confinement of bulk exciton diffusion behavior and the resulting increased exciton density, PNSS exhibits faster photoluminescence and radioluminescence decay times compared to PEA2PbBr4 single crystals. Test results show that PNSS exhibits high [percentage missing] at room temperature. 1 / e =1.38 ns, exceeding the ultrafast photoluminescence decay characteristics of PEA2PbBr4 single crystal and 1 / e The PEA2PbBr4 nanowire exhibits an ultrafast radiative decay time of 1.87 ns. Simultaneously, the negative pressure-assisted solution growth method overcomes the defects of traditional solution methods, such as inhomogeneous filling and preferential growth at the pore openings, achieving uniform growth of PEA2PbBr4 nanowires. Leveraging the optical waveguide effect of the nanopore structure, the luminescence of the PEA2PbBr4 nanowires propagates directionally along the pores, reducing lateral light propagation and crosstalk effects, synergistically improving the X-ray imaging resolution of PNSS. X-ray imaging results based on PNSS show that PNSS can perform high-resolution imaging of tiny objects with feature sizes < 20 μm under X-rays, with a spatial resolution of 57.1 lp / mm (when MTF = 0.2). Based on its ultrafast radiative decay time and high imaging resolution and consistency under X-rays, PNSS demonstrates significant application potential in the field of ultrafast X-ray imaging. The radiative decay time control strategy proposed in this invention is also expected to provide potential reference for other scintillator materials.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing a scintillator based on an exciton space diffusion confinement strategy, the method comprising the following steps: (1) Prepare an organic-inorganic hybrid perovskite precursor solution; (2) The organic-inorganic hybrid perovskite precursor solution is dropped onto a pre-cleaned substrate. The nanoporous anodic aluminum oxide template is brought into contact with the droplet. First, one side is brought into contact, and then the other side is lowered to allow the solution to completely penetrate the template and maintain it for a certain period of time. (3) The AAO template to be permeated is subjected to negative pressure assisted pre-permeation together with the substrate. After the vacuum is released, the nanowires are grown under negative pressure heating. After the growth is completed, the temperature is lowered and the substrate is peeled off to obtain the organic-inorganic hybrid perovskite array scintillation screen.

[0010] This invention utilizes a two-step solution growth method assisted by negative pressure (e.g.) Figure 2As shown in (a), three consecutive growth kinetic processes are achieved: capillary wetting, confined nucleation, and directional growth. The core of this process involves first pre-vacuuming to remove air from the nanopores, then breaking the vacuum and using atmospheric pressure as a powerful driving force to "push" the solution into the air-locked channels. Subsequently, a negative pressure heating process is used for growth. This strategy achieves "wetting first, then growth." After growth, PNSS can be successfully peeled off from the substrate, achieving... Figure 2 The self-support shown in (b) also demonstrates that the interface between the PNSS prepared by this strategy and the substrate is less polycrystalline and has no adhesion.

[0011] Furthermore, the organic-inorganic hybrid perovskite is PEA2PbBr4.

[0012] Furthermore, in step (2), the term "holding for a certain period of time" refers to holding for 2-5 minutes.

[0013] Furthermore, in step (3), the pressure of the negative pressure assisted pre-osmosis is -70 kPa, the temperature is 60 ℃, and the time is 5 minutes.

[0014] Furthermore, in step (3), the pressure of the negative pressure heating growth of nanowires is -70 kPa and the temperature is 60 ℃.

[0015] A second aspect of the present invention provides a scintillator based on an exciton space diffusion confinement strategy prepared by the above-described preparation method.

[0016] Furthermore, when the organic-inorganic hybrid perovskite is PEA2PbBr4, the resulting PEA2PbBr4 array scintillation screen achieves a voltage of 59.5 keV. 241 The radiation decay lifetime excited by the Am gamma-ray source is 1.87 ns.

[0017] Furthermore, when the organic-inorganic hybrid perovskite is PEA2PbBr4, the spatial resolution of the obtained PEA2PbBr4 array scintillation screen with an MTF of 0.2 is 57.1 lp / mm.

[0018] A third aspect of the present invention provides an application of the above-mentioned scintillator based on an exciton space diffusion confinement strategy in ultrafast X-ray imaging.

[0019] Compared with the prior art, the beneficial effects of the present invention are: This invention successfully fabricated self-supported PEA2PbBr4 nanowires (PNSS) with uniform filling and optical crosstalk isolation properties. By restricting the spatial diffusion of bulk excitons in the PNSS, the bottleneck of long radiation decay time in PEA2PbBr4 single crystals was overcome, significantly improving the radiation decay time of the PNSS (within...). 241Am gamma-ray excitation =1.87 ns) and X-ray imaging resolution (MTF0.2 = 57.1 lp / mm). Simultaneously, a negative pressure-assisted two-step solution growth method developed based on this strategy overcomes the bottleneck of obtaining high-quality, large-size single crystals of layered organic-inorganic hybrid perovskites and the high processing difficulty, achieving the fabrication of uniform scalable scintillation screens. This invention provides a solution for the development of high spatial resolution fast scintillators in scientific research and application fields such as ultrafast X-ray imaging, and also provides a reference for the fabrication of nanoarrays of other layered organic-inorganic hybrid perovskites. Attached Figure Description

[0020] Figure 1 This invention presents the design concept of a PEA2PbBr4 nanowire PNSS with ultrafast decay and high resolution characteristics. (a) compares the light yield and decay time of PEA2PbBr4 with other scintillator materials; (b) shows a schematic diagram of the exciton radiative recombination process of PEA2PbBr4 single crystal under different excitation sources, where insets (i) and (ii) are schematic diagrams of the lattice structure and band structure differences between the surface and bulk phase of the PEA2PbBr4 single crystal, respectively; (c) shows the imaging mechanism of PEA2PbBr4 single crystal under X-ray excitation, which shows obvious optical crosstalk and resolution degradation; (d) shows the mechanism by which the PEA2PbBr4 nanowire PNSS utilizes the spatial confinement effect of a one-dimensional nanowire array structure to suppress bulk exciton diffusion and achieve a synergistic improvement in decay time and imaging resolution.

[0021] Figure 2 The present invention provides a two-step solution growth method for preparing PNSS with negative pressure assistance, wherein (a) is a flowchart of the preparation of PNSS using the two-step solution growth method with negative pressure assistance; and (b) is a schematic diagram of the prepared self-supporting PNSS.

[0022] Figure 3 The SEM images of the PNSS cross-sections in Example 1 are simulated by controlling the volume of the precursor solution to represent different growth stages.

[0023] Figure 4 Characterization of the PNSS prepared in Example 1 is shown below: (a) is a cross-sectional SEM image of the PNSS and its corresponding EDS mapping of lead (Pb); (b) is an optical photograph of the PNSS, exhibiting good transmittance and uniformity; (c) is a photograph of the PNSS under ultraviolet light excitation; and (d) is a cross-sectional SEM image of the PNSS, showing uniformly filled, directionally grown, dense PEA2PbBr4 nanowires within the vias.

[0024] Figure 5Comparative X-ray diffraction (XRD) patterns of PNSS, PEA2PbBr4 single crystals and blank nanoporous templates prepared in Example 1.

[0025] Figure 6 The strategy and characterization of PNSS prepared by conventional solution filling of nanoporous template in Comparative Example 1 are shown in (a) as a schematic diagram of conventional solution filling of nanoporous template, where (1) and (2) are schematic diagrams of two physical processes that affect the uniformity of PNSS; (b) is a cross-sectional SEM image of PEA-AAO nanowire PNSS prepared by conventional solution filling, and the inset is an optical photograph of the sample under ultraviolet light excitation.

[0026] Figure 7 The steady-state and transient spectra of the PNSS prepared in Example 1 under different excitation sources are shown below. (a) is the steady-state photoluminescence (PL) spectrum of the PNSS at room temperature (300 K) (excitation wavelength 266 nm); (b) is the steady-state radioluminescence (RL) spectrum of the PNSS at room temperature (300 K) (X-ray tube voltage 40 kV); (c) is the transient fluorescence (TRPL) spectrum of the PNSS at room temperature (300 K) (excitation wavelength 213 nm); (d) and (e) are the spectrum at 300 K. 241 Radiation decay curves of PEA2PbBr4 single crystal and PNSS excited by Am gamma rays (59.5 keV), with decay times of respectively. SC =11.85 ns, decay time PNSS =1.87 ns; (f) is a comparison of the decay time of PNSS with that of mainstream ultrafast scintillators.

[0027] Figure 8 The temperature-dependent transient photoluminescence (TRPL) spectrum of the PNSS prepared in Example 1 over a wide temperature range (80-300K).

[0028] Figure 9The following are potential application scenarios of the PNSS prepared in Example 1 in the field of ultrafast X-ray imaging and imaging demonstration under X-ray excitation. Among them, (a) is a schematic diagram of various ultrafast X-ray imaging devices in a synchrotron radiation device, including micro-CT, nano-CT, etc. The expansion of micro-CT and nano-CT in the field of ultrafast imaging has posed new challenges to the time response characteristics of scintillators; (b) is a schematic diagram of the core imaging module in the X-ray high-resolution imaging device: Lens-coupled Imaging Detectors (LIDs); (c) is an imaging structure of PNSS and PEA2PbBr4 single crystal on a laser spot, with PNSS having a periodic optical waveguide structure showing low crosstalk imaging of the spot; (d)-(f) are X-ray images of a copper mesh grid (aperture ≈ 60 μm), USB interface and IC chip based on PNSS; (g) is the X-ray imaging result of a Type-18D resolution card based on PNSS; (h) is the MTF curve of PNSS obtained by the edge method; (i) is a comparison of PNSS with other scintillators in terms of the two key parameters of decay time and imaging resolution. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0031] Example 1: Preparation and characterization of PNSS using a negative pressure-assisted two-step solution growth method The aluminized aluminum oxide (AAO) template (template diameter: 25 mm; pore size: 350 nm; pore spacing: 450 nm; thickness: 50 μm) was manufactured using a negative pressure solution method in a vacuum drying oven. The process includes the following steps: (1) Dissolve 0.7395 g of phenylethyl ammonium bromide (PEABr) and 0.6606 g of lead bromide (PbBr2) in 3 mL of N,N-dimethylformamide at a molar ratio of 2:1 to prepare a transparent and homogeneous PEA2PbBr4 precursor solution. Stir the mixture at room temperature (24 °C) until completely dissolved.

[0032] (2) To simulate cross-sectional SEM images of PNSS at different growth stages, 10 μL, 30 μL, and 60 μL of precursor solutions were dropped onto a glass substrate, which was pre-cleaned ultrasonically in ultrapure water, anhydrous ethanol, and acetone. Then, the AAO template was carefully brought into contact with the droplets, first contacting one side and then gradually lowering it to the other side to allow the solution to slowly and completely penetrate the template. The fully penetrated template was held on the glass substrate for 3 minutes.

[0033] (3) The infiltrated template, along with the glass substrate, was then placed in a vacuum drying oven. A negative pressure-assisted pre-infiltration step was performed by slowly reducing the pressure to -70 kPa and maintaining this state at 60 °C for 5 minutes. Subsequently, the vacuum was released to remove any air locks trapped within the nanochannels using atmospheric pressure. Finally, the vacuum was applied again to -70 kPa to initiate the nanowire growth process at a constant temperature of 60 °C. Ultimately, the resulting sample was removed from the oven, and the substrate was peeled off to obtain PNSS.

[0034] SEM images of PNSS cross-sections at different growth stages were simulated by controlling the precursor solution volume, as shown below. Figure 3 As shown.

[0035] The characterization of the PNSS prepared in this embodiment is as follows: Figure 4 As shown, (a) is a cross-sectional SEM image of PNSS and its corresponding EDS mapping of lead (Pb) element; (b) is an optical photograph of PNSS, showing good transmittance and uniformity; (c) is a luminescence photograph of PNSS under ultraviolet light excitation; (d) is a cross-sectional SEM image of PNSS. Dense, directionally grown PEA2PbBr4 nanowires are uniformly filled within the vias. It can be seen that the obtained PNSS exhibits macroscopically high uniform transmittance characteristics under white light. To characterize the luminescence uniformity of PNSS, ultraviolet light was used to characterize the luminescence consistency. Under ultraviolet light excitation, the luminescence photograph of PNSS shows good uniformity, exhibiting uniform and bright blue luminescence overall, with significantly better luminescence uniformity than PNSS prepared using the atmospheric pressure solution method. Further SEM cross-sectional images and EDS elemental distribution also simultaneously confirmed the successful growth of uniformly distributed PEA2PbBr4 nanowires in PNSS. The XRD spectrum (such as...) Figure 5 The characteristic peaks and narrow half-width at half-maximum (WHM) in the PEA2PbBr4 nanowires (as shown in the figure) that match the single crystal of PEA2PbBr4 further verify the good crystal quality and phase purity of the PEA2PbBr4 nanowires.

[0036] Comparative Example 1: Preparation and Characterization of PNSS Using Conventional Solution-Filled Nanoporous Templates The difference between this comparative example and Example 1 is that the pressure in step (3) is maintained at atmospheric pressure, while the rest remains the same as in Example 1. A schematic diagram of this conventional solution method for filling nanoporous templates is shown below. Figure 6 As shown in (a), in which insets (1) and (2) are schematic diagrams of two physical processes affecting the uniformity of PNSS; cross-sectional SEM images of PEA-AAO nanowire PNSS prepared by conventional solution method are shown in Figure 1. Figure 6 As shown in (b), the inset is an optical photograph of the sample under ultraviolet light excitation. It can be seen that conventional atmospheric pressure solvent evaporation methods easily induce polycrystalline agglomeration at the openings where the nanoporous template contacts the substrate, and are accompanied by uneven filling of the nanoporous template channels (edge ​​enrichment), which is detrimental to imaging applications. We believe these phenomena originate from two potential kinetic processes (as shown in [reference 1], [reference 2], [reference 3], [reference 4], [reference 5], [reference 6], [reference 7], [reference 8], [reference 9], [reference 10], [reference 11], [reference 12], [reference 13], [reference 14], [reference 15], [reference 16], [reference 17], [reference 18], [reference 19], [reference 12 ... Figure 6 (a) The process shown in numbers (1) and (2): (1) Non-uniform filling driven by non-uniform solvent evaporation: During conventional heating, the edges of the nanoporous template are directly exposed to air, and the evaporation rate of DMF solvent is higher than that in the central region. This evaporation gradient induces a negative pressure at the edges, driving the solution to migrate directionally from the center to the edges, resulting in an increase in the concentration of PEA2PbBr4 in the pores at the outer edge of the nanoporous template, causing a macroscopic non-uniform filling phenomenon of "high filling at the outer edge and insufficient filling at the center"; (2) Polycrystalline agglomeration at the via opening: The nucleation energy barrier of the PEA2PbBr4 solution system at the via opening is lower than that inside the channel. This thermodynamic advantage promotes preferential nucleation of the solute in the precursor at the via opening close to the substrate, blocking the solute transport path and inhibiting the internal filling of the via. Cross-sectional SEM images show severe polycrystalline agglomeration at the via opening of the PNSS prepared by conventional solution method. This polycrystalline agglomeration prevents further transport of solute into the via and the continuous growth of PEA2PbBr4 nanowires.

[0037] Besides the two potential kinetic processes mentioned above, there is another factor affecting the growth of PEA2PbBr4 nanowires: Under normal pressure, when the solution begins to wet the pores of the nanoporous template, the air inside the pores is compressed deep within the pores, forming one or more air cushions, creating an airlock effect. The back pressure generated by this locked air resists the capillary force of the solution, preventing it from penetrating deeper, resulting in incomplete filling or only shallow filling.

[0038] Test Example 1: Attenuation Time and Light Yield Test The decay time and light yield of PNSS are crucial for ultrafast imaging applications. To analyze the spectral characteristics and light yield of PNSS and verify the rationality of the strategy of controlling decay time through nanoengineering, this invention systematically characterized the steady-state emission and transient spectra of the PNSS prepared in Example 1 under different excitation sources. First, the PL spectrum of the PNSS was obtained using a reflective optical path test. Under excitation by a 266 nm laser, it emitted bright blue-violet light, with a sharp main emission peak at 415 nm, distinct from the 409 nm main emission peak of the single crystal. This difference may be due to stress relaxation of the PEA2PbBr4 nanowires, which recovers the band gap increase caused by strong surface stress in the PEA2PbBr4 single crystal. The asymmetric PL peak shape revealed by the PL spectrum is also consistent with previous studies. Further variable-power PL spectroscopy also identified the 415 nm main emission peak in the PNSS as originating from exciton emission. It is worth mentioning that, to eliminate the potential influence of substrate luminescence, this invention used the same optical path setting to measure the PL spectrum of a blank template (e.g., ...). Figure 7 (As shown in (a)). The blank template exhibited extremely weak luminescence and significantly different peak positions under the same excitation intensity. This further confirms that the obtained PL spectrum originated from the PEA2PbBr4 nanowires in PNSS. The scintillation yield of PNSS was estimated using X-ray excited radioluminescence (RL) spectra obtained via a reflective optical path. A commercially available YAG:Ce scintillator with a calibrated yield and consistent thickness with PNSS was introduced as a reference. Figure 7 As shown in (b), under X-ray excitation, PNSS exhibits a disappearance of the PL peak at 415 nm and a sharp, stronger main emission peak at 430 nm than YAG:Ce, without any other emission peaks. This RL peak position coincides with the RL emission peak position of single crystals reported in previous studies. This demonstrates that although the nanowires in PNSS have a reduced dimensionality compared to single crystals, the bulk band structure remains largely unchanged, and no defect emission or other radiative recombination channels are introduced. The relative light yield of PNSS is calculated to be 19877 photons / MeV.

[0039] The decay time of PNSS was first characterized by transient fluorescence spectroscopy. Under 213 nm picosecond laser excitation, the room temperature TRPL spectrum (e.g.) Figure 7 (c) shows that PNSS has sub-nanosecond decay characteristics (decay index) =452 ps@418 nm). This value is faster than the photoluminescence decay index (PL) of PEA2PbBr4 single crystal reported in previous studies. This phenomenon is reasonable. Compared to PEA2PbBr4 single crystal, PNSS has a larger surface area and a higher proportion of surface excitons under photoexcitation, which leads to a significant decrease in the PL lifetime of PNSS. Wide temperature range testing (80-300 K) further demonstrates its photoluminescence decay index. Always below 800 ps (e.g.) Figure 8 As shown in the figure, it exhibits good temperature robustness in terms of decay time.

[0040] To further evaluate the decay time characteristics under high-energy ray excitation, our invention employs... 241 Using an Am gamma-ray source (59.5 keV) as the excitation source, and employing an ultrafast single-photon counting system to eliminate detector and system response interference, the radiation decay curves of PNSS and PEA2PbBr4 single crystals were measured. The decay curves of both samples could be well fitted using a single exponential method. Through fitting, the radiation decay lifetime of PNSS was determined to be 1.87 ns (e.g., ...). Figure 7 As shown in (e), the radiation decay lifetime τ = 11.85 ns is significantly faster than that of a single crystal (as shown in (e)). Figure 7 As shown in (d). The significantly shortened radiation decay time compared to single crystals further confirms the rationality of the control strategy proposed in this invention. Lateral comparison shows (e.g.) Figure 7 As shown in (f), PNSS's fast decay performance surpasses that of mainstream fast scintillators such as BaF2, LYSO, and LaBr3:Ce, demonstrating potential application value.

[0041] Test Example 2: Resolution Test The rapid development of ultrafast X-ray imaging technology is driving the emergence of new application scenarios, among which synchrotron radiation-based micro-computed tomography (Micro-CT) is becoming one of the potential core directions (such as...). Figure 9 As shown in (a). This technology can achieve non-destructive three-dimensional reconstruction and two-dimensional transient high-resolution imaging in the natural state of materials. With the increasing demand for in-situ dynamic research (such as transient growth of lithium dendrites, crack propagation, and solidification of molten pools in additive manufacturing), the temporal resolution of traditional Micro-CT has become insufficient, thus spurring the development of Micro-CT technology with dynamic imaging capabilities. The key to achieving high-resolution imaging in Micro-CT lies in the lens-coupled imaging detectors (LIDs) (such as microscope objectives and scintillation screens) composed of microscope objectives and scintillation screens. Figure 9(As shown in (b)). Current mainstream scintillator screens (such as YAG:Ce single-crystal crystals) suffer from low temporal resolution in single-shot two-dimensional transient imaging due to their long decay time, making it difficult to meet the requirements of transient imaging and dynamic observation. In addition, when the spatial resolution requirement increases to the micrometer scale, light scattering and crosstalk generated inside conventional single-crystal scintillators will further reduce the imaging quality. PNSS, with its sub-nanosecond decay time and potential high-resolution imaging capability, holds promise for applications in this area.

[0042] Therefore, to evaluate the imaging resolution, uniformity, and practical feasibility of the PNSS, this invention utilizes an X-ray imaging optical path, employing the PNSS prepared in Example 1 as a scintillation screen to image different objects. First, the effect of the periodic optical waveguide structure in the PNSS on improving imaging resolution is verified. For example... Figure 9 As shown in (c), under the same incident laser beam illumination, the emitted spot on the PNSS exhibits a more localized and shape-reducing morphology than that of the PEA2PbBr4 single crystal. The experimental results clearly demonstrate that, compared to single-crystal scintillators, the PNSS with its periodic optical waveguide structure can better confine the spatial diffusion behavior of excitons, achieve directional propagation of the scintillator beam, and demonstrate higher imaging resolution.

[0043] To closely approximate practical scintillator applications, this invention utilizes a transmission X-ray imaging optical path, demonstrating imaging using PNSS at both high and low magnification coupled optical magnifications. In stark contrast to the inhomogeneous imaging obtained with PEA2PbBr4 single crystal, PNSS exhibits excellent imaging consistency and improved imaging resolution. Figure 9 As shown in (d), X-ray imaging of a copper mesh with a via spacing of 20 μm using PNSS yields clear and sharp absorption-contrast images. This demonstrates PNSS's ability to produce clear images at a feature scale of 20 μm. The imaging results of a USB connector further showcase PNSS's excellent ability to distinguish between materials with different contrast levels. Figure 9 As shown in (e), the plastic casing of the USB connector appears light gray due to its low absorption cross-section, while the internal copper wires appear black due to their high absorption cross-section. Furthermore, PNSS X-ray imaging of IC chips clearly distinguishes the chip pins and internal structures (e.g., Figure 9 As shown in (f), it also demonstrates the excellent imaging uniformity of PNSS.

[0044] To further quantify and confirm the spatial resolution of PNSS, this invention uses PNSS to image Type-18D line-pair cards at a high optical magnification. For example... Figure 9As shown in (g), PNSS can achieve clear imaging of line pairs of 20 lp / mm (ie, 25 μm). Using the edge-cutting method, we obtained the MTF curve of PNSS (as shown in Figure 1). Figure 9 (As shown in (h)). When MTF=0.2, the spatial resolution of PNSS is 57.1 lp / mm, which has good imaging resolution. Figure 9 As shown in (i), PNSS exhibits significant advantages in decay time and imaging resolution compared to various scintillator materials reported in the literature. These data demonstrate that, compared to mainstream ultrafast scintillators, PNSS combines fast decay time and high imaging resolution, making it a highly promising competitor in the field of ultrafast scintillators and likely to find applications in ultrafast X-ray imaging.

[0045] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing a scintillator based on an exciton space diffusion confinement strategy, characterized in that, The preparation method includes the following steps: (1) Prepare an organic-inorganic hybrid perovskite precursor solution; (2) The organic-inorganic hybrid perovskite precursor solution is dropped onto a pre-cleaned substrate. The nanoporous anodic aluminum oxide template is brought into contact with the droplet. First, one side is brought into contact, and then the other side is lowered to allow the solution to completely penetrate the template and maintain it for a certain period of time. (3) The AAO template to be permeated is subjected to negative pressure assisted pre-permeation together with the substrate. After the vacuum is released, the nanowires are grown under negative pressure heating. After the growth is completed, the temperature is lowered and the substrate is peeled off to obtain the organic-inorganic hybrid perovskite array scintillation screen.

2. The method for preparing a scintillator based on an exciton space diffusion confinement strategy according to claim 1, characterized in that, The organic-inorganic hybrid perovskite is PEA2PbBr4.

3. The method for preparing a scintillator based on an exciton space diffusion confinement strategy according to claim 1, characterized in that, In step (2), the term "holding for a certain period of time" refers to holding for 2-5 minutes.

4. The method for preparing a scintillator based on an exciton space diffusion confinement strategy according to claim 1, characterized in that, In step (3), the pressure of the negative pressure assisted pre-osmosis is -70 kPa, the temperature is 60 ℃, and the time is 5 minutes.

5. The method for preparing a scintillator based on an exciton space diffusion confinement strategy according to claim 1, characterized in that, In step (3), the pressure of the negative pressure heating growth of nanowires is -70 kPa and the temperature is 60 ℃.

6. A scintillator based on an exciton space diffusion confinement strategy prepared by the preparation method according to any one of claims 1-5.

7. The scintillator based on the exciton space diffusion confinement strategy according to claim 6, characterized in that, When the organic-inorganic hybrid perovskite is PEA2PbBr4, the resulting PEA2PbBr4 array scintillation screen operates at 59.5 keV. 241 The radiation decay lifetime excited by the Am gamma-ray source is 1.87 ns.

8. The scintillator based on the exciton space diffusion confinement strategy according to claim 6, characterized in that, When the organic-inorganic hybrid perovskite is PEA2PbBr4, the spatial resolution of the obtained PEA2PbBr4 array scintillation screen with MTF=0.2 is 57.1 lp / mm.

9. The application of a scintillator based on an exciton spatial diffusion confinement strategy as described in any one of claims 6-8 in ultrafast X-ray imaging.

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