A polycrystalline hybrid antimony(III) halide scintillator, its preparation method and application

Abstract

This invention belongs to the field of optoelectronic materials, disclosing a polycrystalline hybrid antimony(III) halide scintillator, its preparation method, and its applications. The chemical formula of the material is A₂SbX₅, where A is a methoxymethyltriphenylphosphonium cation or its derivatives, and X is Cl, Br, or I. All materials are zero-dimensional structures and possess excellent luminescent properties such as high photoluminescence quantum efficiency, large Stokes shift, and broadband emission. The material of this invention is prepared using a simple solution method, and the antimony(III)-based metal avoids the high toxicity of traditional lead halides, making it simple and environmentally friendly. This invention prepares zero-dimensional hybrid antimony halides with the same chemical formula but different crystal structure parameters and photophysical properties. By controlling the arrangement of polycrystalline compounds through crystallization kinetics, the fabrication of X-ray three-dimensional imaging and single-crystal scintillator screens is achieved.

Description

Technical Field

[0001] This invention relates to a polycrystalline hybrid copper (I) halide material, its preparation method and application, belonging to the field of optoelectronic materials. Background Technology

[0002] Three-dimensional X-ray imaging technology can acquire multiple images of a target object from different directions, and then use these images to reconstruct a three-dimensional model of the object. Currently, this technology is widely used in various fields such as medical imaging, remote sensing, food inspection, and national defense. Generally, X-rays can effectively penetrate the target being tested, making them suitable for safety and quality inspection of internal structures. In the biomedical field, doctors can use three-dimensional images to observe the shape and detailed features of lesions from multiple angles, avoiding the limitations of traditional two-dimensional images.

[0003] Scintillators are crucial for realizing three-dimensional X-ray imaging technology, acting as energy converters to transform X-rays into detectable visible light. Commercially available inorganic scintillators suffer from inherent limitations such as high energy consumption during fabrication and poor environmental humidity stability. While organic scintillators can be easily fabricated using low-cost solution methods, they face challenges related to low X-ray absorption coefficients and exciton utilization efficiency. In recent years, low-dimensional organic-inorganic hybrid metal halides have proven to be promising scintillator materials due to their processability, structural tunability, and excellent optoelectronic properties. Among them, hybrid antimony (Sb) halides exhibit superior properties such as low toxicity, environmental stability, and high luminescence quantum efficiency. 3+ Stereochemical activity 5s 2 Lone pairs of electrons promote strong electron-phonon coupling and facilitate the formation of self-trapped excitons, thereby promoting high photoluminescence quantum efficiency and broadband emission. In low-dimensional structures, antimony halides further utilize large Stokes shifts through quantum confinement to reduce energy losses caused by self-absorption.

[0004] Currently, there are two main problems with the application of hybrid antimony halide materials in scintillators. Firstly, the developed hybrid antimony halides mainly rely on extensive replacement of organic ligands, leading to a trial-and-error approach to achieving high photoluminescence quantum efficiency, and increasing preparation costs. Secondly, to achieve X-ray imaging, the scintillator needs to be thoroughly ground and blended with polymers to prepare the scintillator screen. This process results in uneven distribution of the scintillator screen, and optical crosstalk limits imaging performance. Furthermore, the scintillator's scintillation performance is significantly lower than that of pure crystals after being composited with polymers. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a class of polycrystalline hybrid antimony(III) halide scintillators and their preparation method. The material has the general chemical formula A₂SbX₅, where A is a methoxymethyltriphenylphosphonium cation or its derivatives, and X is Cl, Br, or I. The material exhibits excellent optical properties, including high luminescence quantum efficiency, large Stokes shift, and broadband emission. The preparation method is simple, lead-free, and environmentally friendly. The scintillator screen prepared using this material can achieve high-resolution X-ray three-dimensional imaging.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a polycrystalline hybrid antimony(III) halide material, the chemical formula of which is A2SbX5, wherein A is a methoxymethyltriphenylphosphonium cation and its derivative structure, and X is Cl, Br or I; The material has a zero-dimensional structure and exists in at least two different crystal forms.

[0007] Its general structural formula is as follows:

[0008] Wherein, R is selected from one of the following groups:

[0009] B is selected from one of the following groups: .

[0010] Furthermore, the crystal form includes three crystal forms: α, β, and γ.

[0011] The space group of α-A₂SbX₅ is P⁻¹, with unit parameters a = 9.995(2) Å, b = 10.611(2) Å, c = 20.334(4) Å, α = 80.568(5)°, β = 77.568(5)°, γ = 73.727(5)°, Z = 2, and unit volume V = 2011.8(7) Å. 3 ; The space group of β-A₂SbX₅ is P⁻¹, with cell parameters a = 9.850(7) Å, b = 10.594(8) Å, c = 21.548(13) Å, α = 98.68(3)°, β = 94.71(2)°, γ = 105.85(3)°, Z = 2, and cell volume V = 2120(3) Å. 3 ; The space group of γ-A₂SbX₅ is P⁻¹, with cell parameters a = 10.457(2) Å, b = 10.6834(19) Å, c = 22.593(5) Å, α = 90.851(6)°, β = 97.839(5)°, γ = 100.275(5)°, Z = 2, and cell volume V = 2458.3(8) Å. 3 .

[0012] Secondly, the present invention provides a method for preparing a polycrystalline hybrid antimony(III) halide, wherein methoxymethyltriphenylphosphonium halide salt and antimony halide SbX3 are mixed in a molar ratio of 2:1, dissolved in an organic solvent, and the polycrystalline hybrid antimony(III) halide material is obtained by volatilization crystallization.

[0013] Preferably, hybrid antimony(III) halide materials with different crystal forms can be selectively obtained by controlling the type and / or evaporation rate of the organic solvent.

[0014] Preferably, when the organic solvent is dichloromethane, α-A2SbX5 is obtained by rapid evaporation and γ-A2SbX5 is obtained by slow evaporation; when the organic solvent is acetonitrile, β-A2SbX5 is obtained by evaporation crystallization.

[0015] Preferably, the rapid evaporation is the evaporation of the mixture at room temperature; the slow evaporation is the evaporation of the mixture in a sealed, room temperature environment.

[0016] Thirdly, the present invention provides the application of the aforementioned polycrystalline hybrid antimony(III) halide material in the fields of optoelectronic devices or X-ray imaging and detection, OLED devices, solid-state or optoelectronic displays, specifically as follows: Based on the above-mentioned polymorphic hybrid antimony (III) halide materials, which do not emit light under sunlight but exhibit radiative luminescence under ultraviolet and X-ray irradiation and have linear response to X-rays, this material can be prepared into scintillator thin films for use in X-ray detection and three-dimensional imaging.

[0017] Based on the above-mentioned polymorphic hybrid antimony (III) halide materials, they can be fabricated into single-crystal scintillation screens for application in the field of high-resolution X-ray imaging.

[0018] Based on the above-mentioned polymorphic hybrid antimony (III) halide materials, they can be used as light-emitting layers in OLED devices by vacuum evaporation.

[0019] Based on the solid-state luminescence properties of the aforementioned polycrystalline hybrid antimony (III) halide materials, these materials can be ground into powder and used as phosphors in the field of solid-state lighting.

[0020] Based on the above-mentioned polymorphic hybrid antimony (III) halide materials, they can be used as inks in the fields of microelectronic printing and printing.

[0021] Compared with the prior art, the present invention has the following advantages: (1) This invention discloses a polymorphic hybrid antimony (III) halide material and its preparation method. It is synthesized using a simple "solution method", which has low preparation cost and low toxicity and environmental protection characteristics. By changing the crystal structure through polymorphism, the flexibility of the composition and performance control of hybrid metal halide materials is expanded. (2) The polycrystalline hybrid antimony(III) halide materials disclosed in this invention have excellent photophysical properties, exhibiting long-wavelength emission, weak self-absorption and high luminescence quantum efficiency in the solid state. (3) The polycrystalline hybrid antimony (III) halide disclosed in this invention has excellent X-ray response performance, low detection limit and high light yield, and can be prepared into scintillation thin film for application in X-ray detection and three-dimensional imaging. (4) The polymorphic hybrid antimony (III) halide disclosed in this invention can be used to prepare a single-crystal scintillation screen for application in the field of high-resolution X-ray imaging.

[0022] (5) The polymorphic hybrid antimony (III) halide disclosed in this invention can be ground into powder and used as phosphor in the fields of solid-state lighting and optoelectronic display, or it can be prepared into powder and mixed with organic solvent as ink for use in the fields of microelectronic printing and printing. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the general crystal structure formula of the hybrid antimony(III) halide material of the present invention; Figure 2 The normalized solid-state excitation and emission spectra of the hybrid antimony(III) halide materials of this invention are shown. Figure 3 This is a photoluminescence quantum yield diagram of the hybrid antimony(III) halide material of the present invention; Figure 4 The solid-state photoluminescence lifetime decay curve of the hybrid antimony(III) halide material of this invention; Figure 5 The emission spectra of the hybrid antimony (III) halide materials α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5 and γ-(MeOPh3P)2SbCl5 under different doses of X-rays are shown in the present invention. Figure 6X-ray linear response spectra of the hybrid antimony (III) halide materials α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5 and γ-(MeOPh3P)2SbCl5 of the present invention; Figure 7 The radiative luminescence intensity diagrams of the hybrid antimony (III) halide material and the inorganic scintillator BGO of this invention are shown. Figure 8 Three-dimensional image of a conch under X-rays of a scintillator film prepared from the hybrid antimony(III) halide α-(MeOPh3P)2SbCl5 of this invention; Figure 9 High-resolution X-ray image of a single-crystal scintillation screen prepared by the hybrid antimony(III) halide γ-(MeOPh3P)2SbCl5 of the present invention; Figure 10 The emission pattern of the light-emitting layer of the thin-film OLED device prepared by the hybrid antimony(III) halide β-(MeOPh3P)2SbCl5 of the present invention; Figure 11 A schematic diagram of the general crystal structure of (BTP)2SbCl5 prepared as a comparative example; Figure 12 Normalized solid-state excitation and emission spectra of (BTP)2SbCl5 prepared in comparison are shown. Figure 13 Photoluminescence quantum efficiency diagram of (BTP)2SbCl5 prepared in comparison; Figure 14 Emission spectra of (BTP)₂SbCl₅ prepared as a comparative example under different doses of X-rays; Figure 15 The radioluminescence intensity and X-ray linear response spectrum of (BTP)2SbCl5 prepared as a comparative example; Figure 16 A comparison of the light yields of (BTP)2SbCl5 and inorganic scintillator BGO under X-ray irradiation at the same dose rate; Figure 17 X-ray imaging resolution of the scintillator thin film prepared for comparison (BTP)2SbCl5 under X-rays. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0025] A polymorphic hybrid antimony (III) halide material, said material is synthesized by volatilization crystallization of methoxymethyltriphenyl phosphine halide and antimony halide in an organic solvent; this type of material has polymorphic characteristics, having three crystal forms: α, β and γ, and its chemical formula satisfies A2SbX5, where X is at least one of Cl, Br and I.

[0026] Example 1 The synthetic route for polymorphic hybrid antimony(III) halides is as follows:

[0027] Taking A as a methoxymethyltriphenylphosphine cation (MeOPh3P) and X as Cl as an example, the specific preparation processes for the α, β, and γ crystalline compounds are as follows: 1. α-crystal form Weigh out SbCl3 (1 mmol) and methoxymethyltriphenylphosphine chloride (2 mmol) and place them in a 20 mL sample vial. Add 3 mL of dichloromethane organic solvent to dissolve them completely, then rapidly evaporate them. After about 48 h, crystals precipitate out, which is α-(MeOPh3P)2SbCl5.

[0028] 2. γ-crystal form Weigh out SbCl3 (1 mmol) and methoxymethyltriphenylphosphine chloride (2 mmol) and place them in a 20 mL sample vial. Add 3 mL of dichloromethane organic solvent to dissolve them completely, then slowly evaporate them. After about a week, crystals precipitate out, which is γ-(MeOPh3P)2SbCl5.

[0029] 3. β-crystal form Weigh out SbCl3 (1 mmol) and methoxymethyltriphenylphosphine chloride (2 mmol) and place them in a 20 mL sample vial. Add 3 mL of acetonitrile as organic solvent and dissolve completely. Then evaporate and crystallize. After about 48 h, crystals precipitate out, which is β-(MeOPh3P)2SbCl5.

[0030] A schematic diagram of the crystal structure of polymorphic hybrid antimony(III) halides is shown below. Figure 1 As shown, the crystal structure parameters are as follows: Table 1

[0031] Example 2 SC-XRD data were obtained on a Bruker Smart Apex CCD diffractometer at room temperature using ω-2θ scanning with a graphite monochromatic Mo-Kα (λ = 0.71073 Å) radiation source. The structure of (MeOPh3P)2SbCl5 was solved and refined using Olex2 and SHELXS (full matrix least squares over F2) methods, as shown in the figure. Figure 1 As shown.

[0032] The measurements of excitation-emission, luminescence quantum efficiency, and luminescence lifetime decay curves were performed using an Edinburgh FLS-980 spectrophotometer. A 450 W xenon lamp was used for excitation-emission, with an excitation spectrum ranging from 250 nm to 400 nm and an emission spectrum ranging from 400 nm to 800 nm. The test results are as follows: Figure 2 As shown, the emission peaks of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5 and γ-(MeOPh3P)2SbCl5 are located at 612 nm (yellow), 634 nm (orange-yellow) and 664 nm (orange-red), respectively.

[0033] The luminous quantum efficiency was measured using an integrating sphere mode under a 450 W xenon lamp light source. The test results are as follows: Figure 3 As shown, the photoluminescence quantum efficiencies of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5 and γ-(MeOPh3P)2SbCl5 prepared in Example 1 were 98.75%, 66.68% and 27.39%, respectively.

[0034] The luminescence lifetime decay curve was tested using a 375 nm laser, and the test results are as follows: Figure 4 As shown. The luminescence lifetimes of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5 and γ-(MeOPh3P)2SbCl5 prepared in Example 1 were 4.085 μs, 2.478 μs and 3.223 μs, respectively.

[0035] Figure 5 The emission spectra of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5 and γ-(MeOPh3P)2SbCl5 under different doses of X-rays are shown in the figure. As can be seen from the figure, the radiative emission intensity of the disclosed materials increases monotonically with the increase of X-ray dose, and the radiative emission intensity shows a good linear relationship with the X-ray dose.

[0036] Figure 6The relationship between the radiative emission intensity of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5, and γ-(MeOPh3P)2SbCl5 and the X-ray dose rate was investigated, with the detection limit set at a signal-to-noise ratio of 3. The detection limit for α-(MeOPh3P)2SbCl5 was 87.73 nGy / s, for β-(MeOPh3P)2SbCl5 it was 132.03 nGy / s, and for γ-(MeOPh3P)2SbCl5 it was 1488.63 nGy / s, all significantly lower than the detection limit for X-ray medical diagnosis (5.5 µGy / s). (Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide.) Nat. Commun. 2020, 11 , 4329) The light yield comparison diagram of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5, and γ-(MeOPh3P)2SbCl5 with that of the inorganic scintillator BGO under X-ray irradiation at the same dose rate is shown in the figure. Figure 7 As can be seen from the figure, the radiative luminescence intensities of α-(MeOPh3P)2SbCl5, β-(MeOPh3P)2SbCl5, and γ-(MeOPh3P)2SbCl5 under a thickness of 0.1 mm are 1.76, 0.84, and 0.75 times that of the inorganic scintillator BGO, respectively, which can meet the needs of many fields such as space exploration and medical three-dimensional imaging.

[0037] Example 3 Based on the high luminescence quantum efficiency of α-(MeOPh3P)2SbCl5, we attempted to fabricate it into a scintillator thin film for use in X-ray imaging.

[0038] The thin film preparation process was as follows: 2 g of polystyrene-ethylene-butene-styrene (SEBS) polymer was dissolved in 20 mL of toluene and magnetically stirred for 6 hours. 800 mg of α-(MeOPh3P)2SbCl5 sample filtered through a 200-mesh sieve was dispersed in 12 mL of SEBS solution and stirred for 24 hours. The mixture was poured into a mold and then evaporated at room temperature for 12 hours to obtain the scintillator thin film.

[0039] The prepared scintillator thin film does not emit light under sunlight but exhibits high-efficiency emission under ultraviolet and X-ray irradiation. Because different material components have varying X-ray absorption capacities, resulting in different spatial saturations within the scintillator, this can be utilized for optical imaging, such as... Figure 8As shown, the thin film is used to perform planar imaging of the conch from various angles under X-ray irradiation. The multiple planar images are then reconstructed in three dimensions using a filtered back projection algorithm to obtain the X-ray three-dimensional spatial imaging results of the conch. The texture of the conch's cross-section and the internal cavity structure can be clearly observed.

[0040] Example 4 Based on the large cell volume of γ-(MeOPh3P)2SbCl5, it exhibits excellent crystallinity. An attempt has been made to fabricate it into a single-crystal device for advanced optoelectronic applications, such as high-resolution X-ray imaging.

[0041] Preparation of single-crystal scintillation screen: Weigh SbCl3 (1 mmol) and methoxymethyltriphenylphosphine chloride (2 mmol) into a 20 mL sample vial. Add 5 mL of dichloromethane to dissolve completely, then seal the sample vial and store it. Slowly inject 1 mL of ethyl acetate into the vial every week. After two months, a centimeter-scale single-crystal scintillation screen is obtained.

[0042] Based on the excellent light transmittance and radiative emission properties of the single-crystal scintillation screen, it can be used for high-resolution X-ray imaging. For example... Figure 9 As shown, the intricately structured copper mesh can be clearly distinguished under X-ray irradiation.

[0043] Example 5 A large-area luminescent layer of β-(MeOPh3P)2SbCl5 was fabricated using spin coating or drop coating methods, such as... Figure 10 As shown, it emits yellow light under ultraviolet excitation. Therefore, this material can be used as a light-emitting layer in OLED devices.

[0044] Comparative Example Using an organic cation similar in structure to A, benzyltriphenylphosphonium (BTP) was selected as the cation template to supplement the comparative example. The synthetic route of the hybrid antimony(III) halide in the comparative example is as follows:

[0045] SbCl3 (1 mmol) and benzyltriphenylphosphine chloride (2 mmol) were weighed and placed into a 20 mL sample vial. The organic solvent dichloromethane was added and dissolved completely, followed by evaporation and crystallization. Crystals precipitated after approximately 48 h were obtained, which was (BTP)₂SbCl₅. Because the comparative example used a rigid benzyl group to replace the methoxy group in A, thus providing a rigid cationic environment, (BTP)₂SbCl₅ did not produce a polymorphic structure; the crystals prepared in different organic solvents all exhibited the same crystalline phase.

[0046] A schematic diagram of the crystal structure of hybrid antimony(III) halides is shown below. Figure 11 As shown, the crystal structure parameters are as follows: Table 2

[0047] Emission spectrum test results as follows Figure 12 As shown, the emission peak of (BTP)₂SbCl₅ is located at 594 nm (yellow). The luminescence quantum efficiency test results are as follows. Figure 13 As shown, the photoluminescence quantum efficiency of (BTP)2SbCl5 prepared in the comparative example is 99.97%.

[0048] Figure 14 The figure shows the emission spectra of (BTP)2SbCl5 under different doses of X-rays. As can be seen from the figure, the radiative emission intensity of (BTP)2SbCl5 increases monotonically with the increase of X-ray dose, and the radiative emission intensity shows a good linear relationship with the X-ray dose.

[0049] Figure 15 The relationship between the radiative emission intensity of (BTP)₂SbCl₅ and the X-ray dose rate was reflected, and the detection limit was set when the signal-to-noise ratio was equal to 3. The detection limit of (BTP)₂SbCl₅ was 28.680 mGy / s, which indicates that the radiative emission sensitivity of (BTP)₂SbCl₅ is much lower than that of α-(MeOPh₃P)₂SbCl₅.

[0050] A comparison of the light yields of (BTP)₂SbCl₅ and the inorganic scintillator BGO under X-ray irradiation at the same dose rate was obtained. See the results below. Figure 16 As can be seen from the figure, the radiative emission intensity of (BTP)₂SbCl₅ at a thickness of 0.1 mm is only 0.8 times that of the inorganic scintillator BGO. This indicates that the radiative emission capability of (BTP)₂SbCl₅ is weaker than that of α-(MeOPh₃P)₂SbCl₅.

[0051] (BTP)₂SbCl₅ scintillation films were prepared using the same process conditions as the α-(MeOPh₃P)₂SbCl₅ scintillator films in Example 3. The results are as follows: Figure 17 The X-ray imaging resolution of the scintillator thin film prepared based on (BTP)₂SbCl₅ is shown to be 7.1 lp mm. -1 The resolution is lower than that of α-(MeOPh3P)2SbCl5 scintillator films (12 lp mm). -1 ).

[0052] The foregoing has shown and described the basic principles, main features, and application effects of the present invention. However, the above description is only a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other embodiments derived by those skilled in the art without departing from the technical solution of the present invention should be covered within the patent scope of the present invention.

Claims

1. A polycrystalline hybrid antimony(III) halide material, characterized in that, The chemical formula of the material is A2SbX5, wherein A is a methoxymethyltriphenylphosphonium cation and its derivatives, and X is Cl, Br or I; The material has a zero-dimensional structure and exists in at least two different crystal forms.

2. The hybrid antimony(III) halide material according to claim 1, characterized in that, The crystal forms include three types: α, β, and γ.

3. The hybrid antimony(III) halide material according to claim 2, characterized in that, The space group of α-A2SbX5 is P-1, with cell parameters a = 9.995(2) Å, b = 10.611(2) Å, c = 20.334(4) Å, α = 80.568(5)°, β = 77.568(5)°, γ = 73.727(5)°, Z = 2, and cell volume V = 2011.8(7) Å. 3 ; The space group of β-A₂SbX₅ is P⁻¹, with unit parameters a = 9.850(7) Å, b = 10.594(8) Å, c = 21.548(13) Å, α = 98.68(3)°, β = 94.71(2)°, γ = 105.85(3)°, Z = 2, and unit volume V = 2120(3) Å. 3 ; The space group of γ-A₂SbX₅ is P⁻¹, with cell parameters a = 10.457(2) Å, b = 10.6834(19) Å, c = 22.593(5) Å, α = 90.851(6)°, β = 97.839(5)°, γ = 100.275(5)°, Z = 2, and cell volume V = 2458.3(8) Å. 3 .

4. A method for preparing the polycrystalline hybrid antimony(III) halide material according to any one of claims 1-3, characterized in that, Includes the following steps: Methoxymethyltriphenylphosphonium halide and antimony halide SbX3 were mixed in a molar ratio of 2:1, dissolved in an organic solvent, and obtained by volatilization crystallization to obtain the polycrystalline hybrid antimony(III) halide material.

5. The method according to claim 4, characterized in that, By controlling the type and / or evaporation rate of the organic solvent, hybrid antimony(III) halide materials with different crystal forms can be selectively obtained.

6. The method according to claim 5, characterized in that, When the organic solvent is dichloromethane, α-A2SbX5 is obtained by rapid evaporation, and γ-A2SbX5 is obtained by slow evaporation; when the organic solvent is acetonitrile, β-A2SbX5 is obtained by evaporation crystallization.

7. The method according to claim 6, characterized in that, The rapid evaporation refers to evaporating the mixture at room temperature; the slow evaporation refers to evaporating the mixture in a sealed, room temperature environment.

8. The application of a polycrystalline hybrid antimony (III) halide material according to any one of claims 1-3 in the fields of X-ray detection and imaging, optoelectronic devices, solid-state lighting or optoelectronic displays.

9. The application according to claim 8, characterized in that, The X-ray imaging is three-dimensional X-ray imaging.

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