Scintillator material comprising halide perovskite

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 mounted in detectors of ionizing radiation, such as X-rays and gamma rays, and of 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 usually detected using single crystal scintillators that convert the incident radiation into light, which is then converted into an electrical signal using a photodetector such as a photomultiplier tube. An important parameter in the selection of scintillator materials is the scintillation efficiency, which corresponds to the number of photons per unit energy of ionizing radiation absorbed. The most common unit used to measure efficiency is the number of photons emitted per MeV of incident energy.

[0003] Amorphous materials have defects in their structure that cause them to trap charge carriers during scattering, such as electrons, holes, and excitons, which are involved in the energy transfer in the scintillation mechanism. Usually used inorganic scintillators are crystalline for this reason, very often single crystals. To effectively detect ionizing radiation, they are required to have a relatively large size, i.e., 1 cm or larger, in order to increase the collision probability between the high energy particles and the scintillator material. 3 It is preferred that the volume of the sintered body is greater than 1000 μm.

[0004] The scintillators used may in particular be sodium iodide doped with thallium, caesium iodide doped with thallium or sodium, single crystals of lanthanum halides doped with cerium or praseodymium. Crystals based on lanthanum halides have been the subject of works published in particular under US Pat. No. 7,067,815, US Pat. No. 7,067,816, US Patent Application Publication No. 2005 / 188914, US Patent Application Publication No. 2006 / 104880, US Patent Application 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 perovskite structure based on lead halides has been proposed. The scintillation and luminescence properties measured under gamma energy of 662 keV were obtained from a crystal with dimensions 5 × 6 × 1 mm 3 The scintillation light efficiency was measured under cryogenic conditions (liquid nitrogen) at values ​​of the order of 10,000 photons / MeV.

[0006] As detectors, lead halide perovskites are of interest for the detection of ionizing radiation due to their high stopping power, fault tolerance, high mobility, and short lifetime, as well as their tunable bandwidth. Moreover, they can be obtained by simple growth of single crystals by conventional and inexpensive solution techniques.

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

[0008] More generally, there can be many different types of halogen-based perovskites, and therefore a distinction is made between 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 connected at their vertices to form a three-dimensional structure, a cation B of an element such as lead resides in the center of the octahedron, and a larger cation A, typically an organic cation, resides between the octahedra.

[0010] Such materials with a 3D perovskite structure are, for example, compounds of 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) crystal structure, now known as 2D or two-dimensional, i.e. a crystal structure characterized by an alternation of n layers of perovskite-type octahedra connected by their vertices and separated by layers of organic cation A forming planes separating the octahedra. More precisely, when n=1, it is called a 2D structure, and when n>1, it is called a homologous or related 2D structure. The present invention relates to such 2D or homologous structures.

[0012] Schematics of these two possible configurations are notably described in the publication "Ruddlesden-Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductors" 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 characterization of three-dimensional (3D) crystals of MAPbI3 and MAPbBr3 (MA is methylammonium), and of the X-ray scintillator of the perovskite (EDBE) PbCl4 (EDBE is 2,2'-ethylenedioxy) bis(ethylammonium). This latest publication reports that the larger binding energy of the excitons in the 2D material results in a significantly reduced thermal effect compared to the 3D perovskites, and a limited light yield of 9,000 photons / MeV even at room temperature. Summary of the Invention

[0013] The object of the present invention is to provide new scintillator materials, in particular of so-called 2D or homogeneous structure, which are useful in the field of detection of ionizing radiations such as X-rays, gamma rays and neutrons, and which are easy and cheap to synthesize.

[0014] More specifically, the present invention relates to a scintillator material for a detector of ionizing radiation, comprising, and preferably consisting of, a halogenated perovskite, said perovskite corresponding to one of the following formulae: -(A')2(A) n-1 [M n X 3n+1 ], where n is a positive integer ranging from 1 to 100, preferably including a positive integer ranging from 1 to 10, and particularly preferably including a positive integer ranging 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 a positive integer in the range from 1 to 10, and particularly preferably including a positive integer 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 a positive integer in the range from 1 to 10, and particularly preferably including a positive integer 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 a positive integer in the range from 1 to 10, and particularly preferably including a positive integer 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 said perovskite further comprises at least one scintillation activating element N (different from M).

[0015] According to preferred embodiments of the invention, which obviously can be combined with one another as required, The halogenated perovskite has the formula (A')2(A) n-1 [M n X 3n+1], and n is more preferably equal to 1 or 2, or 1. the halogenated perovskite has 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 further preferably equal to 1 or 2, or even equal to 1. the halogenated perovskite has the formula (A')2(A) q-1 [M q X 3q+3 ], with q more preferably equal to 1 or 2, or even equal to 1. the halogenated perovskite has the formula (A')2(A) m [M m X 3m+2 ], with m more preferably equal to 1 or 2, or even equal to 1. said activating element N is selected from Sb, Bi, Pb, In and the rare earth elements; said activating element N is selected from Bi, Eu, Sm, Tb and Yb; said activating element N is chosen from organic molecules exhibiting fluorescent properties in the scintillator, in particular 1,4-bis-(5-phenyloxazolyl-2)benzene (POPOP); the material further comprises a neutron absorber selected from isotopes enriched in lithium-6 or boron-10. the perovskite has the formula (A')2(A) n-1 [M n X 3n+1 ], wherein n is a positive integer from 1 to 100, preferably including a positive integer in the range of 1 to 10, and particularly preferably including a positive integer in the range of 1 to 4. said 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, especially 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, especially an element selected from K, Na, Li, Cs, Rb, Ag, Au, or Cu, and an element selected from Bi, In, Sb, and rare earths, especially 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 especially 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] Single crystals according to the invention can be obtained very simply and cheaply by a single crystal growth process well known to the skilled artisan under the name STL (slow temperature lowering), as described, for example, in the publications 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 solution of a precursor of a material (typically a halide of element A) in an aqueous solution. The growth of the crystals is obtained by cooling, the solubility of the precursor decreasing with temperature.

[0020] According to the invention, other crystal growth methods are of course possible, such as the technique known in commonly used English terms as "Anti-Solvent Vapor assisted method" or "Inverse Temperature Crystallization". DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The invention and its advantages will be better understood on reading the following examples, which are inventive and comparative. EXAMPLES

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

[0023] Crystals were grown in flasks immersed in a thermostatic oil bath. The initial chemical reagents were 99.999% PbCl2 from Alfa Aesar, benzyl ammonium chloride (BACI) from TCI (>98%), and 99.999% Bil3 from Alfa Aesar.

[0024] The compounds were weighed out to prepare 10 ml of a precursor solution of 0.1 M PbCl2. The ratio of BACI:PbCl2 was 2:1. The precursor was dissolved in 10 ml of 37% hydrochloric acid (HCl). Then, 3 mol% of Bil3 was added. A flask with 5 ml of the solution was placed in a silicon oil bath heated by a hot plate so that the solution was 100% immersed in oil and stirred overnight at 50 °C (Figure 1). The temperature was then increased to 100 °C. After a stabilization time of 30 minutes, the temperature was decreased very slowly (5 °C / 30 min). After every decrease of 5 °C (10 min), a stabilization time of 20 minutes was allowed. In this way, the temperature was decreased until room temperature was reached. The crystals were then dried on a hot plate at 50 °C with paper. The obtained crystals are in the form of plates with a length of 1.5 mm and a thickness of 0.2 to 0.3 mm.

[0025] Example 2 (Comparative) In this example, the procedure was similar to that of Example 1 according to the invention, but the element bismuth was not introduced into the composition of the crystal.

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

[0027] The reagents used are PbCl2 99.999% from Alfa Aesar and MACl (methylammonium chloride) 99.999% also from Alfa Aesar. A solution of 1 mL of the precursor with a concentration of 1 M PbCl2 is prepared. The solvent used is DMF and dimethyl sulfoxide (DMSO) in a 1:1 ratio. Using a micropipette, 0.5 mL of each reagent is added to the bottle containing the solvent. The bottle is placed in a silicon oil bath heated by a hot plate, so that the solution is immersed in 100% oil and stirred at 50 °C overnight. The solution is filtered through a 0.45 μm filter and the stoppered bottle is placed in the oil bath so that the liquid / gas interface corresponds to the oil surface. The temperature is raised to 70 °C to allow crystallization. After 1 h, numerous transparent crystals appear at the bottom of the solution. Three crystals remain in the solution and the rest are removed. After 6 h, the three crystals have reached a size of about 2 mm in length and 1 mm in thickness.

[0028] Analysis and Results: The crystals obtained according to Examples 1 to 3 are analyzed by the following techniques.

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

[0030] Radiative emission under BX excitation As mentioned before, scintillation is the ability of a compound to be excited by an incident excitation (such as an X-ray) and to emit energy as photons in the visible range. Indeed, the central electron first enters an excited state in response to a high-energy photon (on the order of keV or GeV) and after several steps some electrons are de-excited in the valence band and can emit several visible photons. To check the scintillation of the crystals according to examples 1 to 3 above, we irradiated them using an X-ray generator. The voltage and current were set to 40 keV and 25 mA for each experiment. The samples are 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 a cryostat, and the presence of scintillation peaks (light peaks) is observed.

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

[0033] C. Pulse Height Spectrum To measure the scintillation performance of crystals under gamma radiation, pulse height analyzers were used. Such instruments record electronic pulses of different heights from particle and event detectors, digitize the pulse heights, and record the number of pulses at each height in a register or channel, thus recording an "impulse height spectrum."

[0034] The scintillation intensity is 662 keV. 137The measurements were made at room temperature in a glove box using a Cs gamma radiation source. A windowless Photonix APD avalanche photodiode (model 630-70-72-510) cooled to 250 K at a voltage of 1600 V was used as the photodetector. The output signal was amplified with a shaping time of 6 μs in an ORTEC 672 spectroscopic amplifier. To maximize light collection, the sample was covered with Teflon powder and compressed (as described in J. T. de Haas and P. Dorenbos, IEEE Trans. Nucl. Sci. 55, 1086 (2008)) except for the cleaved facet for coupling with the photodiode. Exposed to a high energy source, the crystal produces photons that are detected by a photomultiplier tube, regardless of the wavelength of the photons. The detector used is sensitive from UV to IR and can count each photon. In this way, a scintillation histogram is obtained, the horizontal axis having values ​​proportional to the amount of emitted light detected by the optical device ( 137 Cs measured on an Advanced Photonix APD 630-70-72-510 detector at a temperature of 270 K), and the vertical axis has the number of gamma photon interaction events with the scintillator. According to this experiment, the more channels with scintillation peaks observed, the more photons are emitted per pulse.

[0035] Moreover, the presence of such photopeaks makes it possible, inter alia, to determine whether the observed scintillation effects can be associated with sufficient energy resolution that allows the energies of different isotopes to be distinguished.

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

[0037] [Table 1]

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

Claims

1. 1. A scintillation material for a detector of ionizing radiation comprising a halide perovskite, said perovskite having one of the following formulas: -(A') ２ (A) ｎ－１ [M ｎ X ３ｎ＋１ ], n comprises a positive integer from 1 to 100; or -(A')(A) ｐ－１ [M ｐ X ３ｐ＋１ ], p comprises a positive integer from 1 to 100; or -(A') ２ (A) ｍ [M ｍ X ３ｍ＋２ ], m comprises a positive integer from 1 to 100; or -(A') ２ (A) ｑ－１ [M ｑ X ３ｑ＋３ ], q is a positive integer from 1 to 100; A material, wherein A and A' are organic cations, 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, said perovskite further comprising at least one scintillation activating element N.

2. The material of claim 1 , wherein the activating element N is selected from Sb, Bi, Pb, In, and rare earth elements.

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

4. 2. The material according to claim 1, wherein the activating element N is selected from organic molecules exhibiting fluorescent properties in a scintillator, in particular 1,4-bis-(5-phenyloxazolyl-2)benzene (POPOP).

5. 5. The material of claim 1, further comprising a neutron absorber selected from isotopes enriched in Lithium-6 or Boron-10.

6. The perovskite has the formula A ２ [M.X. ４ 6. The material according to claim 1 , wherein M is preferably selected from Pb, Ge or Sn.

7. The ratio of the activating element is 1.0×10 －４ 7. The material according to claim 1 , wherein N / M is of the order of 0.

1.

8. The organic cation A and / or A′ is an alkyl ammonium R—NH ３ 8. The material according to claim 1 , which is selected from ammonium, in particular methylammonium, formamidinium, butylammonium, phenylammonium, phenylethylammonium, 5-aminovaleric acid, benzylammonium, 3-(aminomethyl)piperidinium or 4-(aminomethyl)piperidinium.

9. 9. The material according to any one of claims 1 to 8, wherein said element M comprises Pb, preferably is Pb.

10. 10. The material according to any one of claims 1 to 9, wherein the scintillation activating element comprises Bi, preferably is Bi.

11. 11. The material according to any one of claims 1 to 10, wherein the element M comprises, and is preferably Bi, and the scintillation activating element comprises, and is preferably Pb.

12. 12. The material according to any one of claims 1 to 11, wherein the element X comprises Cl, preferably is Cl.

13. 13. The material of any one of claims 1 to 12, wherein the element X is a mixture of at least two halogens selected from Cl, Br, and I.

14. 14. The material according to claim 1, comprising two activating elements, one of which has a valence +I and the other of which has a valence +III, in particular an element selected from K, Na, Li, Cs, Rb, Ag, Au or Cu, and an element selected from Bi, In, Sb and rare earths, in particular an element selected from Eu, Sm, Tb and Yb.

15. It is characterized by being a single crystal.

15. The material according to any one of claims 1 to 14.

16. 16. Use of a material according to any one of claims 1 to 15 for a detector of ionising radiation.

17. 16. A scintillator detector of ionizing radiation comprising a material according to any one of claims 1 to 15.

18. 20. A scintillator detector as in claim 17 including a photodetector sensitive to wavelengths in the range of 300 nm to 800 nm.

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