SCINTILLATOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63/276,814, filed on November s, 2021 , entitled “SENSITIZATION OF METALORGANIC FRAMEWORKS FOR X-RAY IMAGING SCINTILLATORS,” the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

TECHNICAL FIELD

[0002] Embodiments of the subject matter disclosed herein generally relate to an X-ray scintillator composite material, and more particularly, to an X-ray harvesting system that uses luminescent metal-organic framework (MOF)-fluorescence - chromophore composite films.

DISCUSSION OF THE BACKGROUND

[0003] Highly efficient energy transfer is one of the critical processes central to the functioning of many energy-harvesting systems and can significantly improve the energy utilization efficiency in various light conversion devices, including solar cells and X-ray imaging scintillators. Ionizing radiation, on the other hand, is one of the most critical energy sources relevant to various technological and engineering fields. For instance, very efficient detection or imaging of ionizing radiation is an important topic, owing to its significant scientific and real-life technological implications, ranging from medical radiography, radiation exposure detection, and high-energy physics all the way to astronomical discovery.

[0004] The most-reported X-ray imaging scintillators with good performance always rely on ceramic bulk crystals or perovskite materials, yet the harsh preparation conditions, poor stability, and toxicity of these absorber layers limit their progressive evolution and commercialization. Nevertheless, organic-based scintillators could be an excellent alternative with good processability and stability, but their low imaging resolution and detection limit due to the limited effective atomic number impede their potential X-ray imaging applications [1 to 3].

[0005] A scintillator is a material that exhibits scintillation, i.e. , the property of luminescence, when excited by ionizing radiation. Thus, the scintillator needs to have a material that is excited by the ionizing radiation (X-ray in this case), and the same material or another material needs to be able to transform the electrons and holes formed during the excitation process into light photons, i.e., luminescence. Note that the scintillator does not transform heat into light, as other devices do. Thus, an energy transfer takes place between the place or material where the X-ray radiation is absorbed, and the place or material where the electron-holes pairs are transformed into light.

[0006] An efficient energy transfer between the X-ray absorber centers (the region or material where the X-ray is absorbed) and the luminescence chromophores (the region or material where the light is generated) is a promising approach to preparing high-performance X-ray imaging scintillators. For example, the energy transfer strategy was successfully applied in CsPbBra perovskite nanocrystals to conjugated organic dye nanocomposites (see, for example, International Application No. PCT/IB2022/060479, claiming priority to Provisional Serial No. 63/274,139, filed on November 1 , 2021 , the entire content of which is incorporated by reference herein), eliminating the reabsorption problem in CsPbBra perovskite nanocrystals and highly enhancing the radioluminescence efficiency of the plastic-based scintillator. Another application describes that the energy transfer inside the stacked film of CsPbBra nanosheets with different thicknesses highly enhanced the scintillation performance compared with nanocrystal counterparts. Therefore, exploration of new energy transfer-based materials with good scintillation performance is a promising research direction and urgently needed.

[0007] However, the existing materials used for scintillators do not have a high energy transfer between the various regions discussed above. Thus, there is a need for a new material/system that is capable of a high energy transfer between the X- ray absorber and the luminescence chromophores with a low detection limit.

BRIEF SUMMARY OF THE INVENTION

[0008] According to an embodiment, there is an X-ray imaging film for transforming X-ray radiation into visible light by scintillating. The X-ray imaging film includes a polymer matrix, a metal-organic framework, MOF, and an organic chromophore which is configured to experience thermally activated delayed fluorescence. The MOF and the organic chromophore are encapsulated by the polymer matrix, and an energy transfer efficiency from the MOF to the organic chromophore is larger than 95%.

[0009] According to another embodiment, there is an X-ray imagining system that transforms incoming X-ray radiation into visible light by scintillation, and the system includes an X-ray source configured to generate first X-rays; and an X-ray imagining film configured to receive second X-rays that have passed through a target and to generate a visible image of the target by transforming the second X-rays into the visible light by scintillation. The X-ray imagining film includes a polymer matrix, a metal-organic framework, MOF, and an organic chromophore which is configured to exhibit thermally activated delayed fluorescence. The MOF and the organic chromophore are encapsulated by the polymer matrix, and an energy transfer efficiency from the MOF to the organic chromophore is larger than 95%.

[0010] According to yet another embodiment, there is a method of making an X-ray imaging film and the method includes providing a metal-organic framework, MOF, providing an organic chromophore which is configured to exhibit thermally activated delayed fluorescence, mixing the MOF with the organic chromophore to bond the MOF to the organic chromophore, and encapsulating the MOF and the organic chromophore with a polymer matrix. An energy transfer efficiency from the MOF to the organic chromophore is larger than 95%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1 A is a schematic diagram of a cell unit of a novel combination of a MOF and a thermally activated delayed fluorescence (TADF) chromophore that transform X-ray radiation into visible light, Figure 1 B illustrates the chemical structure of the various parts of the combination, Figure 1 C illustrates the visible light generation mechanism when the combination is illuminated with X-ray radiation, and Figure 1 D illustrates the visible light generation mechanism when the combination is illuminated with UV light ;

[0013] Figure 2 is a flow chart of a method for making the above noted combination of MOF and TADF organic chromophore;

[0014] Figure 3 schematically illustrate the manufacturing steps of the combination of MOF and TADF organic chromophore;

[0015] Figure 4 schematically illustrates the manufacturing of an organic linker used to form the MOF;

[0016] Figure 5 schematically illustrates the manufacturing of the TADF organic chromophore;

[0017] Figure 6 illustrates the spectral overlap between the emission spectra of the MOF and the absorption spectra of the TADF organic chromophore; [0018] Figure 7 illustrates the emission spectra of the combination having different ratios of the MOF and the TADF organic chromophore;

[0019] Figure 8 illustrates the fluorescence up-conversion signal of a given composition of the MOF and the TADF organic chromophore at an early time scale with exponential fittings;

[0020] Figure 9A shows the fs-transient absorption traces of a MOF film and a given combination of the MOF and the TADF organic chromophore at 580 nm while Figure 9B shows the same information for a linker film and a given combination of the linker and the TADF organic chromophore;

[0021 ] Figure 10 illustrates the energy transfer diagram within the combination of the MOF and the TADF organic chromophore;

[0022] Figure 11 illustrates an X-ray scintillating device that uses the combination of the MOF and the TADF organic chromophore; and

[0023] Figure 12A shows the radioluminescence (RL) spectra of the combination of the MOF and the TADF organic chromophore, Figure 12B shows the RL spectra of the combination of the MOF and the TADF organic chromophore and only the TADF organic chromophore, Figure 12C shows the ratios of the emission intensity at various wavelengths for the combination of the MOF and the TADF organic chromophore, and Figure 12D shows the detection limit of the combination.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a specific MOF- fluorescence chromophore composite film. However, the embodiments to be discussed next are not limited to the specific MOF disclosed herein, or to the specific chromophore also discussed herein, but may be applied to other combinations of such materials.

[0025] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0026] According to an embodiment, an efficient and reabsorption-free energy transfer-based nanocomposite scintillator with amplified radioluminescence intensity is introduced. The nanocomposite includes a combination of the MOF and the TADF chromophore. The near-unity energy transfer from the MOF material (in this case, Zr-fcu-BADC-MOF, where “feu” stands for face-centered cubic unit cell, and “BADC” stands for bianthracenedicarboxylic, which is the organic linker of the MOF) to the luminescent center, which is a TADF chromophore (in this case, a carbazole derivative) and the direct harnessing of singlet and triplet excitons upon X-ray radiation of the TADF chromophore enables its highly enhanced radioluminescence. After the incoming X-ray radiation interacts with the metal cluster in the MOF, numerous hot electrons and holes are generated and thermalized to the conduction band minimum and valence band maximum of the MOF. These electron-hole pairs re-combine radiatively, leading to the optical excitation of the linker inside the MOF, which is followed by energy transfer to the TADF chromophores at the interface. On the other hand, the TADF chromophore could be directly excited by the singlet and triplet excitons, since they could harness triplet excitons for light emission through highly efficient spin up-conversion from the non-radiative triplet state to radiative singlet state.

[0027] Time-resolved spectroscopic measurements supported by density functional theory (DFT) calculations indicate unity energy transfer results for the ultra-short distance and the strong spectral overlap between the Zr-fcu-BADC-MOF nanoparticles and the TADF chromophore. Such an ultrashort distance makes the energy transfer from the linker of the Zr-fcu-BADC-MOF to the TADF chromophore much more efficient and makes the direct harnessing of singlet and triplet excitons upon X-ray radiation of the TADF chromophore possible, as evident from the X-ray spectroscopy experiments. Therefore, both radioluminescence enhancement processes endow such composite scintillators with a few hundred micrometers imaging resolution and a low detection limit of 256 nGy/s, 22 times lower than typical X-ray medical imaging doses. These findings provide a powerful design approach and promising new alternative materials to fabricate X-ray imaging scintillators with high sensitivity and stability using an interfacial energy transfer strategy. Details of this novel scintillating material are now discussed with regard to the figures.

[0028] Because good X-ray absorbers need enough high-atomic-number (Z) elements to guarantee their high-incident X-ray absorption, MOFs are among the best candidates beyond perovskite materials. MOFs are robust chemical structures constructed from highly ordered organic linkers and heavy metal clusters with good stability, low toxicity, and an outstanding level of structural and compositional control [4 to 11]. The flexible selection of inorganic building blocks with different atomic numbers could ensure that their ionizing radiation absorption performance is sufficient [12 to 16]. On the other hand, the luminescent center should also harvest both singlet and triplet excitons, since they are generated with a 1 :3 ratio from the recombination of electron-hole pairs after the X-ray excitation. Therefore, TADF chromophores are excellent candidates as luminescent centers due to their minimized singlet-triplet energy gap. This allows them to harness triplet excitons for light emission through highly efficient spin up-conversion from the non-radiative triplet states to radiative singlet states.

[0029] More specifically, Figure 1 A schematically shows a scintillating composite film 100 (called herein simply the “film”) that includes the Zr-fcu-BADC- MOF nanoparticles 110 and the TADF chromophore 130, bonded to each other and embedded into a polymer matrix 160. A Zr-fcu-BADC-MOF nanoparticle 110 includes plural Zr-clusters 112, one of which is illustrated in Figure 1 B, and plural linkers 114 (BADC in this embodiment). The linkers 114 chemically bond to the plural Zr-clusters 112. Figure 1 B shows some atoms 116 of the linker 114 being attached to a Zr-cluster 112 by chemical bonds. The Zr-cluster 112 has a face-centered cubic cell structure, as also shown in Figure 1 B. Figure 1 B also shows the chemical structure of the TADF chromophore 130 with a central aromatic ring 132 chemically bonded to N atoms 134, and some of the N atoms 134 are chemically bonded to other aromatic rings 136 (carbazole derivatives). Returning to Figure 1 A, it also shows that other aromatic rings 136 of the TADF chromophore 130 may directly interact with the Zr cluster 112 and the atoms of the linker 114.

[0030] Figure 1 C schematically illustrates how the incoming X-ray radiation 140 excites the carriers 142 in the singlet S1 and triplet T1 states, both in the MOF 110 and the TADF chromophores 130 components, and the singlet state S1 for the MOF generates light 144 by fluorescence, having a wavelength of about 480 nm. In addition, energy 146 is transferred between the singlet state S1 of the MOF 110 to the singlet state S1 of the TADF chromophores 130, which makes the TADF chromophores to emit light 148 by delayed fluorescence, having a wavelength of about 580 nm. Further, the TADF chromophore 130 itself generates the light 148, due to its own carriers 142 being directly excited by the incoming X-ray radiation 140. The energy transfer 146 is near unity because of the almost perfect alignment of the emission spectrum of D and the absorption spectrum of A, as discussed later with regard to Figure 6. The transferred energy is used by the acceptor A to emit light 148 with a wavelength of 580 nm through scintillation. Note that the emission 148 by the acceptor A results from the triplet excited state T1 undergoing thermally activated reverse intersystem crossing (RISC) 149 to the emissive S1 state, as schematically shown in Figure 1 C. The figure also shows the thermally activated reverse intersystem crossing (rISC) 147. Thus, the combination of the donor D and the acceptor A results in the harnessing of both single S1 and triple T1 states in the acceptor A, which makes this process and film very efficient.

[0031] In addition to this light generation mechanism (fluorescence), the film 100 is also capable of generating light 144/148 due to the energy transfer from the MOF, as illustrated in Figure 1 D, when the MOF is illuminated with UV light 150 instead of the X-ray 140. In this figure, the MOF 110 is directly excited by the ultraviolet-light irradiation 150, which is independent of the X-ray radiation 140. Under the UV irradiation 150, the electrons from the singlet ground state So in the MOF 110 were excited to the singlet excited state Si and then they transfer onto the singlet state Si of the TADF chromophore, as schematically illustrated by the transfer energy arrow 152. Then, the TADF chromophores were excited and emit the visible light 148 through delayed fluorescence, with a wavelength around 580 nm. It is noted that the near unity (equal to or larger than 95%) energy transfer 146/152 from the MOF 110 to the TADF chromophores 130 is achieved due to the ultrashort distance between these components of the film 100 and their strong spectral overlap.

[0032] A method for forming the film 100 is now discussed with regard to Figures 2 to 5. In step 200, the Zr-fcu-BADC-MOF 110 is formed. For example, this step may include a sub-step of mixing bianthracenedicarboxylic acid, i.e. , the linker BADC 114 (15 mg, 33.9 pmol) and zirconium (IV) chloride 112 (23.3 mg, 100 pmol) in N,N-dimethylformamide (3 mL) and water (1 mL) with 2-fluorobenzoic acid (160 mg). The reaction takes place in another sub-step, in a preheated oven at 105 ^e C for 72 h. The yellowish powder is then collected by centrifuge and then washed three times with DMF and three times with methanol to obtain the Zr-fcu-BADC-MOF 110. These steps are also illustrated in Figure 3.

[0033] In one application, the BADC 114 is manufactured as follows. In a flame-dried 100 mL flask, 10,10'-dibromo-9,9'-bianthracene (1 .000 g, 1.952 mmol) is dissolved in anhydrous THF (50 mL) under argon, and the solution is kept at -78 °C for 30 min. An excess of 1 .6 N n-BuLi in hexane (500.2 mg, 4.9 mL, 4 Eq, 7.809 mmol) is added dropwise. During the addition, the initial yellow solution turns darker, and a colorless precipitate is formed. The mixture was stirred at -78 °C for 30-45 min under argon, and then excess CO2 gas was bubbled into the solution by cannula, as shown in Figure 4. The resulting mixture was stirred at -78 °C and then allowed to warm slowly to room temperature overnight. DI H2O (50 mL) was added, and the mixture was concentrated by partial evaporation under reduced pressure, and the residual aqueous phase was acidified with 1 M aqueous HCI to give a cloudy, pale yellow suspension. The solid was then separated by filtration, washed with DI H2O, hexane, AcOEt, and Et20, and finally dried in vacuum oven to generate the [9,9'- bianthracene]-10,10'-dicarboxylic acid (0.69 g, 1 .6 mmol, 80 %).

[0034] Next, in step 202, the TADF chromophores 130 were generated. For this step, 1 3,6-di-tert-butyl-carbazole (7.0 g, 12.00 mmol) 502 were dissolved in 100 ml dry THF, and 1 .0 g anhydrous NaH (57-63% oil dispersion) were then added, as schematically illustrated in Figure 5. After stirring at room temperature for 1 h, 1 .0 g of tetraf luoroterephthalonitrile (5.78 mmol) 504 were added. The mixture was allowed to stir at room temperature for 12 h and quenched with 200 mL H2O. The precipitates were filtered and washed with EtOH and CH2CI2 to generate the TADF chromophores 130 (e.g., a carbazole derivative, C12H9N, and more specifically, for example, (2r,3s,5s,6s)-2,3,5,6-tetrakis(3,6-di-tert-butyl-9H-carbazol -9- yl)terephthalonitrile, having the chemical formula CssHgeNe, as orange solid (4.50 g, 62%)).

[0035] Next, in step 204, the Zr-fcu-BADC-MOF 110 nanoparticles were mixed with the TADF chromophores 130 and sonicated in chloroform for 1 h, and then poly(methyl methacrylate) (PMMA) was added in step 206. Other polymer may be added to embed the Zr-fcu-BADC-MOF 110 nanoparticles and the TADF chromophores 130. Sonication continued for another 2 h during step 208. Then, the mixture was shaken on a shaker for another 3 h to ensure the dispersion of the D-A nanocomposites. The viscous solution was coated in step 210 on a substrate 302, for example, glass plates, and then covered with a beaker to allow the solvent to evaporate slowly to obtain a film with a uniform surface. In one embodiment, the mixture of Zr-fcu-BADC-MOF 110 nanoparticles and the TADF chromophores 130 can be directly coated on the substrate 302, as shown in Figure 3. The obtained film 100 can then be removed in step 212, from the substrate 302, to be used in a scintillation device, as discussed later. Because the Zr-fcu-BADC-MOF 110 nanoparticles donate the energy it is called herein the “donor D” and because the TADF chromophores 130 accept the energy, it is called herein the “acceptor A.” [0036] Upon 400 nm excitation of the film 100, as shown in Figure 6, monotonically increasing the fraction of A 130 in the film 100 completely quenches the emission spectra of D, as shown in Figure 7, which could be attributed to the energy transfer from D to A. Note that An in Figure 7 means that n is the weight percentage [wt %] of the TADF chromophore in the film 100 (which includes the MOF 1 10, the chromophore 130, and the PMMA matrix 160), and D stands for 1 wt % in the film 100. In other words, for D-Ao.4, the film 100 has 1 % D (by weight), 0.4 % A, and the rest is PMMA or other polymer that forms the polymer matrix 160.

[0037] To roughly estimate the surface coverage of the MOF nanoparticle 110 by the TADF molecules 130, the inventors considered the average size of the MOF nanoparticle 110 to be 200 nm when calculating its total surface area. When compared with the total cross-sectional area of the TADF molecules, it was found that the surface coverage was about 100%, and there were also excess molecules distributed near the surface of the MOF particles. Figure 6 shows the spectral overlap 630 between the emission spectrum 610 of D and the absorption spectrum 620 of A, which is highly desired as the D particles are excited by the X-ray radiation and their emitted light beams are then fully absorbed by the A particles, thus achieving the near unity energy conversion previously discussed. In one embodiment, there is an 80% or more overlap 630 between the two spectrum 610 and 620 in the 450 to 550 nm range. Note that in one embodiment, the MOF is selected to absorb X-ray radiation and emit first light waves with a wavelength between 450 and 650 nm and the organic chromophore is selected to absorb second light waves with a wavelength between 400 and 550 nm and to emit visible light with a wavelength between 500 and 700 nm.

[0038] The energy transfer efficiency between the donor D and the acceptor A was first calculated from the quenching of D luminescence intensity, which was more than 90%. However, when the free organic linker 114 of the Zr-fcu-BADC-MOF 1 10 (called herein “L”) replaced the energy donor D, the energy transfer efficiency dropped to around 60% (not shown). These results demonstrate the importance of the highly ordered structure and alignment of the transition dipole moment orientations inside the MOFs that guarantee an efficient energy transfer to the molecular acceptor A. In addition, the simultaneous decrease in the luminescence intensity and excited-state lifetime of D or L and the increase in the luminescence intensity of A provide additional experimental evidence for the energy transfer process.

[0039] Moreover, femtosecond (fs) luminescence up-conversion measurements for the D-Ao.4 nanocomposite film 100 with highest luminescence intensity were performed to deeper investigate the energy transfer efficiency of the D-A system, as illustrated in Figure 8. The decaying and rising components, measured at 480 and 580 nm, respectively, were determined to be around 400 fs. It should be pointed out that the remaining signal at 480 nm could be attributed to the emission decay of the acceptor A due to its overlap with the emission of the donor D in this spectral range. This time constant yielded an energy transfer rate of 10 ¹² s ^-1 and energy transfer efficiency of nearly 100% through the Forster energy transfer model described by equations (1 ) and (2) below. This value agrees well with the complete quenching in the Zr-fcu-BADC-MOF emission upon adding the molecular acceptor in steady-state experiments. The Forster energy transfer model is described by:

1 -FRET ~ ~ (1) ET where T _ET is the energy transfer time constant obtained from the fs-luminescence up- conversion experiments, k _FRET is the energy transfer rate, T _D is the lifetime of D in the absence of A, and s is the energy transfer efficiency.

[0040] The time-resolved photoluminescence results also allowed to estimate the distance between D and A, via equation (3), and the distance was found to be about 5 A. This short D-A distance provides one fundamental prerequisite for a highly efficient energy transfer from the D to A and demonstrates the direct harnessing of singlet and triplet excitons upon X-ray radiation 140 of the TADF chromophore 130. Equation (3) is given by: where R _o is the Forster distance, and r is the distance between D and A.

[0041 ] The highly efficient energy transfer from D 110 to A 130 was also investigated in detail by the fs-transient absorption (fs-TA) pump-probe spectroscopy. Immediately after photo-excitation with fs pulses at 400 nm of the D film, a negative band at 410 nm was observed and assigned to the ground-state bleaching, whereas the positive band from 440 to 700 nm was attributed to photoinduced absorption. For the A film, the ground-state bleaching band overlapped the photoinduced absorption band at around 450 nm, and the negative band from 490 to 700 nm was assigned to the ground-state bleach and stimulated emission because the position encompasses its absorption and emission spectra. After adding A to the film of D to obtain the D-Ao.4 composite 100, a faster decay process in the TA spectra was observed. The quenching in the TA spectra was significantly accelerated, from 35%/2 ps to 60%/2 ps. This new fast decay component was assigned to the energy transfer from D to A. In addition, no spectroscopic signature exists to form the cation or anion radical of the donor and acceptor, excluding the electron transfer possibility in this system under these experimental conditions. [0042] To further clarify the dynamic relaxation mechanism of the D-A nanocomposite film 100 and confirm the role of the interspecies energy transfer, the kinetics traces at 580 nm for the D film and D-Ao.4 nanocomposite film were recorded and fitted, as illustrated in Figures 9A and 9B, respectively. A new fast decay component of about 400 fs was observed after adding A to the D film, which was assigned to the energy transfer from D to A (Figure 3F), which is consistent with the value obtained from the up-conversion measurements. The ultrafast interspecies energy transfer constant was identical to the data obtained from the fs-luminescence up-conversion measurements. Similarly, after replacing the energy donor from D to L, the energy transfer became less efficient. Therefore, no apparent new fast decay component was observed, consistent with the steady-state measurements illustrated in Figure 9B. [0043] The energy transfer within the D-A nanocomposites was further investigated using DFT calculations. The interfacial adsorption model was constructed by placing the A molecules 130 on the side of the exposed carboxyl groups of D 110, as shown in Figure 1 A. The electronic distributions for the valence band maximum (VBM) and conduction band minimum (CBM) of the D slab retained features similar to those in the bulk and exhibited no significant changes after optimizing with A molecules. The optimized interspecies distance d between the centers of D and A molecules (shown in Figure 1A) is estimated to be 10.9 A, consistent with the experimental value. The energy transfer efficiency calculated from equations (2) and (3) using the D-A distance r from the DFT calculation is 99.5%, matching well with the experimental data. In addition, from the calculated projected density of states of the D-A heterojunctions (Figure 4D), the VBM of D is close to the highest occupied molecular orbital (HOMO) of A, whereas the CBM of the D is above the lowest unoccupied molecular orbital (LUMO) of A, leading to a type I alignment character, as illustrated in Figure 10. Such energy alignments of the D-A heterojunctions suggest that efficient energy transfer from the Zr-fcu-BADC- MOF 110 to the TADF chromophore 130 is feasible.

[0044] To explore the influence of such efficient energy transfer efficiency between the D and A particles on a light-harvesting device performance, an X-ray imaging scintillator 1100, as shown in Figure 11 , was fabricated based on the composite film D-A _n 100. The X-ray imaging scintillator 1100 includes the film 100, which is placed at a location so that a human can observe it. The film 100 may be attached to a frame 1110 for support. The frame 1110 may be connected to a support 1111 and actuation mechanism 1113 for supporting the film and also for moving the film along a vertical axis Z as desired by the user. An X-ray source 1112 is placed at a certain distance away from the film 100, so that a target space 1102 is generated. A target 1104 is placed on a target support 1106, between the X-ray source 1112 and the film 110. The X-ray source 1112 may be placed on a corresponding support 1120, which may have an actuation system 1122, for positioning the source vertically and/or horizontally, at a desired distance from the film 100. All the actuation systems may be coordinated by a controller 1130, in a wired or wireless manner. The controller may have an input/output interface so that can receive commands from the user. In one application, the user may control the intensity of the X-ray 1114 emitted by the source 1112 with a controller 1130. A thickness of the film 100 may be between 50 and 500 pm and a size of the film may be about 2x2 cm ² . Note that in this embodiment, the X-ray radiation 1116 that has passed through the target 1104 directly impinges on one surface of the film 100, and the image 1126 of the target is visible to the user on the opposite surface of the film 100. In one application, if the film 100 is formed on a transparent substrate 1128, for example, quartz, the image 1126 of the target is visible through the substrate 1128. In one application, the substrate 1128 may be provided with plural photodetectors 1130 so that the light generated by the composite film 100 is transformed into an electrical signal 1132, and the electrical signal is transmitted to a monitor 1134, which displays the image 1126. Part or all the elements discussed above may be provided in a housing 1101 so that the entire scintillator 1100 is contained. [0045] The radioluminescence (RL) spectra of the D-An nanocomposite films 100 used in the X-ray scintillating device 1 100 follow a trend nearly identical to that of the photoluminescence (PL) spectra, where the RL of the D film progressively decreases upon adding A, as shown in Figure 12A. The RL at the emission maxima of A was highly enhanced by the energy transfer from the Zr-fcu-BADC-MOF, as shown in Figure 12B. From the complete quenching of the Zr-fcu-BADC-MOF RL spectra and the highly enhanced RL of the TADF chromophores, the energy transfer under X-ray excitation is also efficient. The luminescence intensity ratios between 580 and 480 nm, derived from the RL, are two to five times higher than the ratios from the ultraviolet-excited counterparts, as illustrated in Figure 12C. Therefore, the direct harnessing of singlet and triplet excitons for light emission through fluorescence decay channels of the TADF chromophores significantly contributes to enhancing the RL, as 25% of the excited states formed from ion recombination after X-ray radiation are singlet states, whereas the remaining 75% are triplet states. In addition, the D-A nanocomposite film 100 exhibits good photostability; the RL intensity remained at around 98% of the initial value under ionizing radiation with the dose rate of 174 mGy/s for a continuous 4,000 s, comparable to that of commercial plastic scintillators. The X-ray-excited luminescence intensities of the Ao.4 film and D- AO.4 nanocomposite film were linearly correlated with the dose rate of the X-rays. The detection limit highly improved from the Zr-fcu-BADC-MOF film at 15,000 nGy/s and the A film at 1 ,600 nGy/s, to 256 nGy/s for the D-A0.4 nanocomposite film 100, as illustrated in Figure 12D, which is approximately 22 times lower than the standard dosage for X-ray diagnostics (5.5 mGy/s). [0046] Regarding the highly enhanced RL of the D-A nanocomposite films by the near-unity energy transfer from the Zr-fcu-BADC-MOF to the TADF chromophore and the direct harnessing of both singlet and triplet excitons of the TADF chromophores, a D-Ao.4 nanocomposite film 100 was tested within the context of radiography. A complicated steel framework (target 1104 in Figure 11 ) was first placed between the X-ray source 11 12 and the D-Ao.4 nanocomposite film 100 of the imaging device 1100. The significant difference in X-ray absorption for different parts in the steel framework resulted in a spatial intensity contrast displayed on the scintillator screen (not shown). The spatial resolution was calculated as 441 mm by fitting the point spread function of the intensity profile. In addition, the application of this principle of X-ray contrast imaging also enabled inspection of the inner structures of the electronic components. The configuration inside electronic components cannot be observed directly with the naked eye; however, it could be revealed using X-ray imaging with the D-Ao.4 nano-composite film-based scintillator. [0047] Thus, the above embodiments present a novel energy transfer strategy to significantly enhance the RL of X-ray imaging scintillators beyond ceramic and perovskite materials. The embodiments rely on pairing a luminescent MOF 110 (with a high atomic number) with TADF chromophores 130 in a nanocomposite film 100. Note that although Zr-fcu-BADC-MOF was paired with a carbazole derivative 130, other MOF and/or TADF chromophore particles/molecules may be used. The RL from the TADF chromophore is highly enhanced by receiving a nearly 100% energy transfer from the Zr-fcu-BADC-MOF and the direct harnessing of singlet and triplet excitons. Ultrafast time-resolved laser spectroscopy combined with the high-level DFT calculations suggests that the unity energy transfer results from the ultrashort D-A distance and very strong spectral overlap between the donor and the acceptor units. Such an ultrashort distance makes the energy transfer from the linker 114 of the Zr-fcu-BADC-MOF 1 10 to the TADF chromophore 130 much more efficient and makes the direct harnessing of the singlet and triplet excitons of the TADF chromophore possible. The fabricated X-ray imaging scintillator 1100 based on the D-AO.4 nanocomposite film 100 exhibits a few hundred micrometers imaging resolution and a detection limit of 256 nGy/s, which is 22 times lower than the standard dosage for X-ray medical examination, exhibiting great potential for X-ray radiography.

[0048] It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

[0049] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. [0050] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

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