Scintillator materials containing halide perovskites

Abstract

To provide new scintillator materials of so-called 2D or homologous structures, useful in the fields of the detection of ionizing radiation such as X-rays, gamma rays, and neutrons, the synthesis of which is simple and inexpensive.SOLUTION: There is provided a scintillator material for an ionizing radiation detector comprising a halide perovskite, wherein the perovskite has one of the following formulations: -(A')2(A)n-1[MnX3n+1], or -(A')(A)p-1[MpX3p+1], or -(A')2(A)m[MmX3m+2], or -(A')2(A)q-1[MqX3q+3], wherein n, p, m, and q each contain a positive integer from 1 to 100, A and A' are organic cations, M is a metal chosen from Pb, Bi, Ge or Sn, X is a halogen or a mixture of halogens chosen from Cl, Br, and I, and wherein the perovskite further comprises at least one scintillation activating element N.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the field of scintillators that can be attached to detectors for ionizing radiation such as X-rays and gamma rays, and for ionizing particles. [Background technology]

[0002] Ionizing radiation (including ionizing particles such as protons, neutrons, electrons, muons, alpha particles, ions, X-rays, or gamma radiation) is typically detected using single-crystal scintillators that convert incident radiation into light, which is then converted into an electrical signal using photodetectors such as photomultiplier tubes. A key parameter in the selection of scintillator material is the scintillation efficiency, which corresponds to the number of photons per unit energy of absorbed ionizing radiation. The most common unit used to measure efficiency is the number of photons emitted per incident energy of MeV.

[0003] Amorphous materials have structural defects that trap charge carriers during scattering, such as electrons, holes, and excitons involved in energy transfer in the scintillation mechanism. For this reason, commonly used inorganic scintillators are crystalline, and very often, single crystals. To effectively detect ionizing radiation and increase the probability of collisions between high-energy particles and the scintillator material, they are relatively large in size, i.e., 1 cm². 3 It is preferable that the volume exceeds [a certain value].

[0004] The scintillators used may be single crystals of thallium-doped sodium iodide, thallium or sodium-doped cesium iodide, cerium, or praseodymium-doped lanthanum halides. Lanthanum halide-based crystals have been the subject of research published under U.S. Patent No. 7,067,815, U.S. Patent No. 7,067,816, U.S. Patent Publication No. 2005 / 188914, U.S. Patent Publication No. 2006 / 104880, and U.S. Patent Publication No. 2007 / 241284.

[0005] Recently, in the scientific publication "Scintillation properties of crystals of (C6H5(CH(2)(2)NH3)(2)PbBr4)," IEEE, New York (2009), an organic-inorganic scintillator with a perovskite structure based on lead halides was proposed. The scintillation and luminescence properties measured under a gamma energy of 662 keV were found in a sample with dimensions of 5 × 6 × 1 mm. 3 The study was conducted using single crystals. The efficiency of the scintillation light was measured at a value on the order of 10,000 photons / MeV under low-temperature conditions (liquid nitrogen).

[0006] As detectors, lead halides perovskites have attracted interest in detecting ionizing radiation due to their high stopping power, fault tolerance, high mobility, short lifetime, and tunable bandwidth. Furthermore, they can be obtained by simple single crystal growth using conventional, inexpensive solution methods.

[0007] In the publication “Lead halide perovskites for ionizing radiation detection,” Nature Communications, 10, 12 (2019), the potential photo-yield of these perovskite single crystals can be estimated to be between 120,000 and 270,000 photons / Mev due to the relatively small bandgap width of these materials (which may be less than 2 eV).

[0008] More generally, halogenated perovskites can come in various types and are therefore classified into three-dimensional (or 3D) perovskites, two-dimensional (or 2D) perovskites, and intermediate-dimensional (2D / 3D) perovskites.

[0009] In the classical three-dimensional structure of the general formula ABX3, halogen anions form octahedra linked at their vertices, creating a three-dimensional structure. Elemental cations B, such as lead, reside in the center of the octahedra, while larger cations A, typically organic cations, are located between the octahedra.

[0010] Such materials having a 3D perovskite structure are, for example, compounds with the general formula MAPbX3, where MA is methylammonium, Pb is lead, and X is a halogen such as I, Br, or Cl.

[0011] Alternatively, the material may have a homologous (related) crystalline structure, which is now known as 2D or two-dimensional, characterized by an alternating of n layers of perovskite-type octahedra linked by vertices, separated by layers of organic cations A forming planes that separate the octahedra. More precisely, it is called a 2D structure when n=1 and a homologous or related 2D structure when n>1. This invention relates to such 2D or homologous structures.

[0012] Schematic diagrams of these two possible configurations are described in particular in the publication “Ruddlesden-Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductor” Chem Mater, 2016, or in the publication “X-ray Scintillation in Lead Halide Perovskite Crystals” Scientific Reports, 6, 10 (2016). This latest publication also describes the characteristics of three-dimensional (3D) crystals of MAPbI3 and MAPbBr3 (MA is methylammonium), and the X-ray scintillator of perovskite (EDBE)PbCl4 (EDBE is 2,2'-ethylenedioxy)bis(ethylammonium). This latest publication reports that, due to the large exciton binding energy of the 2D material, the thermal effect is significantly reduced compared to 3D perovskites, and only a limited photo yield of 9,000 photons / MeV is obtained even at room temperature. [Overview of the project]

[0013] The object of the present invention is to provide a novel scintillator material, particularly useful in the field of detecting ionizing radiation such as X-rays, gamma rays, and neutrons, and to provide a novel scintillator material with a so-called 2D or homologous structure that is easy to synthesize and inexpensive.

[0014] More specifically, the present invention relates to a scintillator material for a detector of ionizing radiation, which comprises a halogenated perovskite and preferably consists of a halogenated perovskite. The perovskite corresponds to one of the following formulas: -(A’)2(A) n-1 [M n X 3n+1 , where n is a positive integer in the range from 1 to 100, preferably including positive integers in the range from 1 to 10, and particularly preferably including positive integers in the range from 1 to 4, or -(A’)(A) p-1 [M p X 3p+1 , where p is a positive integer from 1 to 100, preferably including positive integers in the range from 1 to 10, and particularly preferably including positive integers in the range from 1 to 4, or -(A’)2(A) m [M m X 3m+2 , where m is a positive integer from 1 to 100, preferably including positive integers in the range from 1 to 10, and particularly preferably including positive integers in the range from 1 to 4, or -(A’)2(A) q-1 [M q X 3q+3 , where q is a positive integer from 1 to 100, preferably including positive integers in the range from 1 to 10, and particularly preferably including positive integers in the range from 1 to 4, where A and A’ are organic cations, M is a metal preferably selected from Pb, Bi, Ge, and Sn, X is a halogen or a mixture of halogens selected from Cl, Br, and I, and the perovskite further contains at least one scintillation activation element N (different from M).

[0015] According to a preferred embodiment of the present invention, they can clearly be combined with each other as necessary. ― The halogenated perovskite has the formula (A’)2(A) n-1 [M n X 3n+1Corresponding to [], n is more preferably 1 or 2, or equal to 1. - The halide perovskite corresponds to the formula (A’)(A) P-1 [M P X 3p+1 (so-called Dion-Jacobson perovskite), A’ is preferably 3-(aminomethyl)piperidinium (or 3AMP) or 4-(aminomethyl)piperidinium (or 4AMP), and A is preferably methylammonium (MA), and p is more preferably equal to 1 or 2, or even equal to 1. - The halide perovskite corresponds to the formula (A’)2(A) q-1 [M q X 3q+3 , and q is more preferably equal to 1 or 2, or even equal to 1. - The halide perovskite corresponds to the formula (A’)2(A) m [M m X 3m+2 , and m is more preferably equal to 1 or 2, or even equal to 1. - The activating element N is selected from Sb, Bi, Pb, In, and rare earth elements. - The activating element N is selected from Bi, Eu, Sm, Tb, and Yb. - The activating element N is selected from organic molecules that exhibit fluorescence characteristics in the scintillator, particularly 1,4-bis-(5-phenyloxazolyl-2)benzene (POPOP). - The material further includes a neutron absorber selected from isotopes enriched with lithium 6 or boron 10. - The perovskite has the formula (A’)2(A) n-1 [M n X 3n+1 , where n is a positive integer from 1 to 100, preferably including positive integers in the range from 1 to 10, and particularly preferably including positive integers in the range from 1 to 4. - The perovskite has the formula A2[MX4], where M is preferably selected from Pb, Ge, or Sn. - The proportion of the activation element is, on an atomic basis, 1.0×10 -4 <N / M < 0.1, preferably 1.0×10 -3 <N / M < 0.05, and more preferably 1.0×10 -2 <N / M < 1.0×10 -1 and is in such a proportion. - The organic cation A and / or A’ is selected from alkylammonium R-NH3, particularly methylammonium, formamidinium, butylammonium, phenylammonium, phenylethylammonium, 5-aminovaleric acid, benzylammonium, 3-(aminomethyl)piperidinium, or 4-(aminomethyl)piperidinium. - The M element contains Pb, and more preferably is Pb. - The scintillation activation element contains Bi, and more preferably is Bi. - The M element contains Bi, and more preferably is Bi, and the scintillation activation element contains Pb, and more preferably is Pb. - The X element contains Cl, and more preferably is Cl. - The X element is a mixture of at least two halogens selected from Cl, Br, and I. - The material contains two activation elements, one of which has a valence of +I and the other has a valence of +III, particularly an element selected from K, Na, Li, Cs, Rb, Ag, Au, or Cu, and an element selected from Bi, In, Sb, and rare earths, particularly an element selected from Eu, Sm, Tb, and Yb. - The said material is a single crystal.

[0016] The present invention also relates to a scintillator detector for ionizing radiation containing the aforementioned material.

[0017] The scintillator detector particularly includes a photodetector sensitive to wavelengths in the range of 300 nm to 800 nm.

[0018] The scintillator material according to the present invention may be polycrystalline, but is preferably a single crystal.

[0019] The single crystals according to the present invention can be obtained very easily and inexpensively by a single crystal growth process well known to those skilled in the art, known as STL (slow temperature lowering), as described, for example, in the publication cited above, or further in the publication “Modulation of Hybrid Metal Halide Perovskites,” Adv Mater. 2018;30(51). This method is based on the solubility properties of a material precursor (typically a halide of element A) in an aqueous solution. Crystal growth is achieved by cooling, and the solubility of the precursor decreases with temperature.

[0020] According to the present invention, other crystal growth methods are also possible, such as techniques commonly known in English as the "Anti-Solvent Vapor assisted method" or "Inverse Temperature Crystallization." [Modes for carrying out the invention]

[0021] The present invention and its advantages will be better understood by reading the following examples of the present invention and comparative examples. [Examples]

[0022] Example 1 (Invention) In this example, a two-dimensional (or 2D) halogenated perovskite was synthesized. More specifically, the BA2PbCl4 (BA=benzylammonium) type, which further contains bismuth, was synthesized according to the following procedure.

[0023] The crystals were grown in a flask immersed in a constant-temperature oil bath. The initial chemical reagents were 99.999% PbCl2 of Alfa Aesar, benzylammonium chloride (BACI) (>98%) of TCI, and 99.999% Bil3 of Alfa Aesar.

[0024] The compound was weighed to prepare a 10 ml precursor solution of 0.1 MPbCl2. The BACI:PbCl2 ratio was 2:1. The precursor was dissolved in 10 ml of 37% hydrochloric acid (HCl). Next, 3 mol% Bil3 was added. A flask containing 5 ml of the solution was placed in a silicone oil bath heated on a hot plate so that the solution was 100% immersed in oil and stirred overnight at 50°C (Figure 1). The temperature was then raised to 100°C. After a 30-minute stabilization period, the temperature was lowered very slowly (5°C / 30 mins). A 20-minute stabilization period was provided for every 5°C (10 mins) decrease. The temperature was lowered in this manner until it reached room temperature. The crystals were then dried on paper on a hot plate at 50°C. The resulting crystals were in the form of plates 1.5 mm long and 0.2 to 0.3 mm thick.

[0025] Example 2 (Comparison) In this embodiment, the procedure is the same as in Example 1 of the present invention, but bismuth element was not introduced into the crystal composition.

[0026] Example 3 (Comparison) In this example, a three-dimensional (or 3D) halogenated perovskite was synthesized. More specifically, the MAPbCl3 (MA = methylammonium) type was synthesized according to the following procedure.

[0027] The reagents used are 99.999% PbCl2 from Alfa Aesar and 99.999% MACl (methylammonium chloride), also from Alfa Aesar. Prepare a 1 mL precursor solution in 1 M PbCl2. The solvent used is DMF and dimethyl sulfoxide (DMSO) in a 1:1 ratio. Using a micropipette, add 0.5 mL of each reagent to a bottle containing the solvent. Place the bottle in a silicone oil bath heated on a hot plate, immersing the solution in 100% oil and stirring overnight at 50°C. Filter the solution through a 0.45 μm filter and place the stoppered bottle in the oil bath so that the liquid / gas interface corresponds to the oil surface. Increase the temperature to 70°C to induce crystallization. After 1 hour, numerous clear crystals appeared at the bottom of the solution. Three crystals remained in the solution, and the rest were removed. After 6 hours, the three crystals had reached a size of approximately 2 mm in length and 1 mm in thickness.

[0028] Analysis and results: The crystals obtained in Examples 1 to 3 are analyzed using the following technique.

[0029] A.UV spectroscopy The crystal was placed in a vacuum chamber cooled to 14K and subjected to UV excitation using an LED device emitting 365nm radiation. Emission spectra were recorded at 14K and room temperature. The position of the maximum emission peak and the observed emission color are shown in Table 1 below.

[0030] Radioactive emission under BX excitation As mentioned above, scintillation is the ability of a compound to be excited by incident excitation (such as X-rays) and to release energy as photons in the visible range. In fact, the central electrons initially react to high-energy photons (on the order of keV or GeV) to enter an excited state, and after several steps, some electrons can be de-excited in the valence band and emit some visible photons. To confirm the scintillation of the crystals according to Examples 1 to 3 above, they were irradiated using an X-ray generator. The voltage and current were set to 40 keV and 25 mA in each experiment. The samples were placed in a cryostat under vacuum, at a temperature of 14 K and at room temperature.

[0031] The radioactive emission spectrum is recorded using a photodetector placed in the cryostat, and the presence of a scintillation peak (optical peak) is observed.

[0032] The results obtained at 14K and room temperature are shown in Table 1 below.

[0033] C. Pulsed high spectrum A pulse height analyzer was used to measure the scintillation performance of crystals under gamma radiation. Such an instrument records an "impulse height spectrum" by recording electron pulses of different heights from particle and event detectors, digitizing the pulse heights, and recording the number of pulses at each height in a register or channel.

[0034] The scintillation intensity was 662 keV. 137The data was recorded at room temperature in a glove box using a Cs gamma-ray source. A windowless Photonix APD avalanche photodiode (model 630-70-72-510), cooled to 250K at a voltage of 1600V, was used as the photodetector. The output signal was amplified in an ORTEC 672 spectrometer under a shaping time condition of 6 μs. To maximize focusing, the sample was covered with Teflon powder and compressed, except for the cleavage plane for coupling with the photodiode (according to the method described in J.M. de Haas and P. Dorenbos, IEEE Trans.Nucl.Sci. 55, 1086 (2008)). Exposed to a high-energy source, the crystal generates photons that are detected by the photomultiplier tube, regardless of the photon wavelength. The detector used is highly sensitive from UV to IR and can count each photon. In this way, a scintillation histogram is obtained, and the horizontal axis has a value proportional to the amount of emitted light detected by the optical device ( 137 (Measured in Cs using an Advanced Photonix APD 630-70-72-510 detector at a temperature of 270K), the vertical axis represents the number of gamma-photon interaction events with the scintillator. According to this experiment, the more scintillation peaks observed in multiple channels, the greater the number of photons emitted per pulse.

[0035] Furthermore, the presence of such photopeaks makes it possible to determine, in particular, whether the observed scintillation effect can be associated with sufficient energy resolution to distinguish between different isotopes.

[0036] All the results obtained from analyses A to C performed on the crystals of Examples 1 to 3 are summarized in Table 1 below.

[0037] [Table 1]

[0038] The improved scintillation properties of the crystal according to Example 1 of the invention can be seen in the data shown in Table 1. From this, the data representing scintillation under X excitation or y excitation appears to be significantly improved compared to the comparative material.

Claims

1. A scintillation material for a detector of ionizing radiation, comprising a halogenated perovskite, wherein the perovskite has one of the following formulas: - (A') ２ (A) ｎ－１ [M ｎ X ３ｎ＋１ ], n includes positive integers from 1 to 100, or - (A') (A) ｐ－１ [M ｐ X ３ｐ＋１ ], p includes positive integers from 1 to 100, or -(A') ２ (A) ｍ [M ｍ X ３ｍ＋２ [], m includes positive integers from 1 to 100, or - (A') ２ (A) ｑ－１ [M ｑ X ３ｑ＋３ ], q includes positive integers from 1 to 100, A' is 3-(aminomethyl)piperidinium (3AMP) or 4-(aminomethyl)piperidinium (4AMP), A is methylammonium (MA), M is a metal selected from Pb, Bi, Ge, or Sn, and X is a halogen, or a mixture of halogens selected from Cl, Br, and I. The perovskite further comprises at least one scintillation-activating element N different from M, wherein the activating element N is selected from Sb, Bi, Pb, In, and rare earth elements.

2. The material according to claim 1, wherein the activating element N is selected from Bi, Eu, Sm, Tb, and Yb.

3. The material according to claim 1, wherein the perovskite further comprises at least one selected from organic molecules that exhibit fluorescence properties in a scintillator.

4. The material according to any one of claims 1 to 3, further comprising a neutron absorber selected from isotopes enriched with lithium 6 or boron 10.

5. The perovskite is given by formula A ２ [MX] ４ The material according to any one of claims 1 to 4, wherein M is selected from Pb, Ge, or Sn.

6. The proportion of the aforementioned activating element is 1.0 × 10¹⁶ on an atomic basis (mol). －４ The material according to any one of claims 1 to 5, wherein the N / M ratio is on the order of <0.

1.

7. The material according to any one of claims 1 to 6, wherein the element M is Pb.

8. The material according to any one of claims 1 to 7, wherein the scintillation activating element is Bi.

9. The material according to any one of claims 1 to 8, wherein the element M is Bi and the scintillation activating element is Pb.

10. The material according to any one of claims 1 to 9, wherein the element X is Cl.

11. The material according to any one of claims 1 to 9, wherein the element X is a mixture of at least two halogens selected from Cl, Br, and I.

12. The material according to any one of claims 1 to 11, comprising two activating elements, one of which has a valence of +I and the other having a valence of +III, wherein the two activating elements comprise an element selected from K, Na, Li, Cs, Rb, Ag, Au, or Cu, and an element selected from Bi, In, Sb, and rare earth elements.

13. The material according to any one of claims 1 to 12, characterized in that it is a single crystal.

14. A scintillator detector comprising the material according to any one of claims 1 to 13, characterized by including a photodetector that is sensitive to wavelengths in the range of 300 nm to 800 nm.

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