SCINTILLATOR MATERIAL COMPRISING A DOPED HALIDE PEROVSKITE

Abstract

A scintillator material for an ionizing radiation detector comprising a halide perovskite, said perovskite having one of the following formulations: (A′).sub.2(A).sub.n-1[M.sub.nX.sub.3n+1] with n a positive integer between 1 and 100, inclusive, or (A′)(A).sub.p-1[M.sub.pX.sub.3p+1] with p a positive integer between 1 and 100, inclusive, or (A′).sub.2(A).sub.m[M.sub.mX.sub.3m+2], with m a positive integer between 1 and 100, inclusive, or (A′).sub.2(A).sub.q-1[M.sub.qX.sub.3q+3], with q a positive integer between 1 and 100, inclusive;
where 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 said perovskite further comprises at least one scintillation activating element N.

Claims

1. A scintillator material for an ionizing radiation detector comprising a halide perovskite, said perovskite having one of the following formulations: (A′).sub.2(A).sub.n-1[M.sub.nX.sub.3n+1] with n a positive integer between 1 and 100, inclusive, or (A′)(A).sub.p-1[M.sub.pX.sub.3p+1] with p a positive integer between 1 and 100, inclusive, or (A′).sub.2(A).sub.m[M.sub.mX.sub.3m+2], with m a positive integer between 1 and 100, inclusive, or (A′).sub.2(A).sub.q-1[M.sub.qX.sub.3q+3], with q a positive integer between 1 and 100, inclusive; where 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, or I, and wherein said perovskite further comprises at least one N scintillation activating element.

2. Material according to the preceding claim, wherein said activating element N is chosen from Sb, Bi, Pb, In and the rare-earth elements.

3. Material according to the preceding claim, wherein said activating element N is chosen from Bi, Eu, Sm, Tb, and Yb.

4. Material according to claim 1, wherein said activating element N is chosen from organic molecules exhibiting fluorescence properties in scintillators, in particular 1,4-bis(5-phenyloxazol-2-yl) benzene (POPOP).

5. Material according to one of the preceding claims, further comprising a neutron absorber chosen from isotopes enriched with lithium-6 or boron-10.

6. Material according to one of the preceding claims, wherein said perovskite has the formulation A.sub.2[MX.sub.4], wherein M is preferably selected from Pb, Ge or Sn.

7. Material according to one of the preceding claims, wherein the proportion of the activating element, on an atomic basis, is of the order of 1.0*10.sup.−4<N/M<0.1.

8. Material according to one of the preceding claims, wherein the organic cation(s) A and/or A′ are chosen from alkyl-ammoniums R—NH.sub.3, in particular methylammonium, formamidinium, butylammonium, phenylammonium, phenylethylammonium, 5-aminovaleric acid, benzylammonium, 3-(aminomethyl)piperidinium, or 4-(aminomethyl)piperidinium.

9. Material according to one of the preceding claims, wherein the element M comprises Pb and preferably is Pb.

10. Material according to one of the preceding claims, wherein the scintillation activating element comprises Bi and preferably is Bi.

11. Material according to one of the preceding claims, wherein the element M comprises Bi and preferably is Bi and wherein the scintillation activating element comprises Pb and preferably is Pb.

12. Material according to one of the preceding claims, wherein the element X comprises Cl and preferably is Cl.

13. Material according to one of claims 1 to 12, wherein the element X is a mixture of at least two halogens chosen from Cl, Br and I.

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

15. Material according to one of the preceding claims, characterized in that it is monocrystalline.

16. Use of a material according to one of the preceding claims for the detection of ionizing radiation.

17. Scintillator detector of ionizing radiation comprising the material of one of claims 1 to 15.

18. Scintillating detector according to the preceding claim, characterized in that it comprises a photodetector sensitive to a wavelength ranging from 300 nm to 800 nm.

Description

EXAMPLE 1 (INVENTION)

[0046] In this example, a two-dimensional (or 2D) halogen-based perovskite was synthesized. More precisely, the form BA.sub.2PbCl.sub.4 (BA=benzylammonium) further comprising bismuth was synthesized by proceeding as follows:

[0047] The crystals were grown in a flask immersed in a thermostatic oil bath. The initial chemical reagents are PbCl.sub.2 from Alfa Aesar 99.999%, benzylammonium chloride (BACl) (>98%) from TCI and BiI.sub.3 99.999% from Alfa Aesar.

[0048] The compounds are weighed to prepare 10 mL of a 0.1 M PbCl.sub.2 precursor solution. The BACl:PbCl.sub.2 ratio was 2:1. The precursors were dissolved in 10 mL of 37% hydrochloric acid (HCl). Then 3% molar BiI.sub.3 was added. The flask containing 5 mL of solution is placed in a silicone oil bath heated by a heating plate so that the solution is 100% immersed in the oil and kept under stirring overnight at 50° C. (FIG. 1). The temperature is then increased to 100° C. After a stabilization time of 30 minutes, the temperature is reduced very slowly (5° C./30 min). Each decrease of 5° C. (10 min) is followed by a 20-min stabilization time. The temperature is reduced in this way until it reaches room temperature. The crystals are then dried with paper at 50° C. on the hot plate. The crystals obtained are in the form of plates with a length of 1.5 mm for a thickness of 0.2 to 0.3 mm.

EXAMPLE 2 (COMPARATIVE)

[0049] In this example, the procedure was the same as that for example 1 according to the invention, but the element bismuth was not introduced into the composition of the crystal.

EXAMPLE 3 (COMPARATIVE)

[0050] In this example, a three-dimensional (or 3D) halogen-based perovskite was synthesized. More precisely, the form MAPbCl.sub.3 (MA=methyl ammonium) was synthesized by proceeding as follows:

[0051] The reagents used are PbCl.sub.2 99.999%, from the company Alfa Aesar and MACI (methyl ammonium chloride) 99.999%, also from Alfa Aesar. A solution of 1 mL precursors of 1 M concentration of PbCl.sub.2 is prepared. The solvent used has a 1:1 ratio of DMF and dimethyl sulfoxide (DMSO). 0.5 mL of each of the reagents is added using a micropipette to a bottle containing the solvent. The bottle is placed in a silicone oil bath heated by a hot plate, the solution being 100% immersed in the oil, and kept stirred overnight at 50° C. The solution is filtered with a 0.45 μm filter, the stoppered bottle is placed in the oil bath so that the liquid/gas interface corresponds to the oil level. The temperature is increased to 70° C. for crystallization to occur. After an hour, a dozen transparent crystals appeared at the bottom of the solution. Three crystals are left in the solution and the others are removed. After 6 more hours the three crystals have reached a size of about 2 mm in length by 1 mm in thickness.

Analysis and Results:

[0052] The crystals obtained according to examples 1 to 3 are analyzed by the following techniques:

[0053] A. UV Spectroscopy

[0054] The crystals were placed in a vacuum chamber cooled to 14 K and subjected to UV excitation by an LED device emitting 365 nm radiation. Emission spectra were recorded at 14 K and at room temperature. The position of the maximum of the emission peak is shown in Table 1 below, as well as the emission color observed.

[0055] B. Radioluminescence Under Excitation X

[0056] As stated earlier, scintillation is the capacity of a compound to become excited under incident excitation (such as X-rays) and return energy as photons in the visible range. Indeed, a central electron first enters an excited state in reaction to a high energy photon (of the order of keV or GeV) and, after several steps, several electrons can become de-excited in the valence band, thus releasing several visible photons.

[0057] In order to verify the scintillation of the crystals according to examples 1 to 3 above, an X-ray generator was used to irradiate them. Voltage and current were set for each experiment at 40 keV and 25 mA. The samples are placed in a cryostat under vacuum, at temperatures of 14 K and at room temperature.

[0058] The radioluminescence spectra are recorded using a photodetector placed in the cryostat and the presence of a scintillation peak (photopeak) is observed. The results obtained at 14 K and at room temperature are shown in Table 1 below.

[0059] C. Pulse Height Spectrum

[0060] A pulse height analyzer was used to measure the scintillation performance of the crystals under gamma radiation. Such an instrument records electronic pulses of different heights from particle and event detectors, digitizes the pulse heights, and records the number of pulses of each height in registers or channels, thus recording an “impulse height spectrum”.

[0061] Scintillation intensity was recorded at room temperature in a glove box using a gamma source of .sup.137Cs at 662 keV. A windowless Photonix APD avalanche photodiode (model 630-70-72-510) under 1600 V voltage and cooled to 250 K was used as the photodetector. The output signal was amplified with shaping time conditions of 6 μs by an ORTEC 672 spectroscopic amplifier. In order to maximize light collection, the samples were covered with Teflon powder and then compressed (according to the technique described in J. T. M. de Haas and P. Dorenbos, IEEE Trans. Nucl. Sci. 55, 1086 (2008)), apart from the cleaved side intended for coupling with the photodiode. Exposed to a high energy source, the crystal produces photons that are detected by a photomultiplier, regardless of the wavelength of the photon. The detector used is sensitive from UV to IR and allows each photon to be counted. In this way, a scintillation histogram is obtained, with values proportional to the quantity of emitted light detected by the optical device (measured with a .sup.137Cs isotopic source with an Advanced Photonix APD 630-70-72-510 detector, said detector being at a temperature of 270 K) on the abscissa, and the numbers of gamma photon interaction events with the scintillator on the ordinate. According to this experiment, the more the scintillation peak is observed with a high number of channels, the higher the number of photons emitted per pulse.

[0062] In addition, the presence of such a photopeak makes it possible notably to determine in particular whether the observed scintillation effect can be associated with a sufficient energy resolution to allow a possible discrimination of the energies of different isotopes.

[0063] All the results obtained for the analyses A to C carried out on the crystals of examples 1 to 3 are collated in Table 1 below.

TABLE-US-00001 TABLE 1 Example 1 (invention) 2 (comparison) 3 (comparison) Matrix (BA).sub.2PbCl.sub.4 (BA).sub.2PbCl.sub.4 (MA)PbCl.sub.3 [Bi] (mol %) 3 — — □.sub.max emission (nm) 540-580 (green) 433 (green-yellow) 400 (UV) UV excitation (14 K) Luminescence under UV yes No emission No emission excitation (T = 298 K) □.sub.Scintillation under X excitation 530-550 nm 539 nm 400 nm (T = 14 K) Scintillation under X excitation Yes Yes (low) No (T = 298 K) Luminescence under □ 400 350 90 (.sup.137Cs at 662 keV) Number of channels (T = 298 K) Presence of a photopeak Yes No No under □ (Cs137) (T = 298 K)

[0064] The improved scintillation properties of the crystal according to example 1 according to the invention are visible in the data shown in Table 1. Data representative of scintillation under X excitation or under □ excitation thus appear significantly improved compared with the comparison materials.