Inorganic X-ray Scintillators Based on a Previously Unnoticed but

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Inorganic X‑ray Scintillators Based on a Previously Unnoticed but Intrinsically Advantageous Metal Center Yaxing Wang,†,‡,∥ Yumin Wang,‡,∥ Xing Dai,‡,∥ Wei Liu,‡ Xuemiao Yin,‡ Long Chen,‡ Fuwan Zhai,‡ Juan Diwu,‡ Chao Zhang,§ Ruhong Zhou,‡ Zhifang Chai,‡ Ning Liu,*,† and Shuao Wang*,‡

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF FLORIDA on 01/31/19. For personal use only.



Key Laboratory of Radiation Physics and Technology, Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, P. R. China ‡ State Key Laboratory of Radiation Medicine and Protection, School for Radiological and Interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, P. R. China § School of Materials Science and Engineering, Anhui University of Science and Technology, Huainan 232001, P. R. China S Supporting Information *

ABSTRACT: Traditional inorganic X-ray scintillators are designed based on several representative metal ions (e.g., Tl+, Pb2+, Bi3+) with highly emissive nature and high atomic number aiming at the outstanding radiation stopping power. The combination of these two features gives rise to a high energy conversion efficiency from X-ray to visible emission, which is a prerequisite for an ideal scintillator and is currently one of the major limits for the further development of this field. Inspired by our recent observation on the intrinsic scintillating phenomenon in the heaviest naturally occurring element uranium, we report here a family of inorganic scintillators through combination of uranyl ions with diverse oxoanion groups (i.e., borate, phosphate, molybdate, germanate, etc.). Na2UO2(MoO4)2·(H2O) (UMO) is selected as a prototype of a uranyl-bearing inorganic scintillator, to show its intrinsic advantages in the X-ray excited luminescence (XEL), strong X-ray attenuation coefficient (XAC), reduced afterglow, and decent radiation stability, as compared with one of the most important commercial inorganic scintillators CsI:Tl.



Tl+ are two predominate candidates for building commercial medical imaging scintillators and are only restricted in the lattices of CsI:Tl and Bi4Ge3O12 (BGO). Ce3+ is highly adaptive in different inorganic oxide lattices (i.e., yttrium aluminum garnet and lutetium oxyorthosilicate).6 The paramount feature of this series of oxide lattices is the high radiation stopping power originating from the chemical compositions with high Zeff, dense structures, and high densities.7 Nevertheless, there are essential driving forces for finding new scintillators with improved radiation stopping power and X-ray to visible emission energy conversion efficiency.2b,5 Uranium is ubiquitous in modern society not only because it is a major resource in nuclear energy but also due to its rich physicochemical properties.8 With a low specific radioactivity, uranium-based functional materials are prosperous in the past decades owing to the versatile redox chemistry, coordination chemistry, and unique electronic structure of uranium. For instance, the unique bonding with enhanced covalency involving 5f orbitals makes U(III) and U(V) unique for constructing molecular magnets with high magnetic aniso-

INTRODUCTION Scintillator materials have been prolifically developed in the past 70 years for detecting ionizing radiations among the nuclear power, high-energy physics, industrial, and security fields, etc.1 Additionally, there is an increased interest in the development of scintillators in medical imaging including X-ray tomography and nuclear medical imaging.2 The desirable features for an ideal scintillator include but are not limited to high light output, fast response time, excellent radiation and hygroscopy hardness, and high energy resolution.3 Besides, scintillators for medical imaging applications require relatively high effective atomic number (Zef f) to endow them with good radiation stopping power, which is beneficial for the control of the received radiation dosage.1b,5 Because X-ray stopping power is proportional to ρZeff 3−4 one of the key criteria for the material design is to improve the density (ρ) and effective atomic number (Zef f).1b Recent development of plastic scintillators particularly benefits from the utilization of highZef f organometallics and nanoparticles as the additives.4 Notably, progress of new scintillators with high radiation stopping power in the past several decades is quite limited. One simple reason for this is that there are very limited amounts of choices for the heavy and highly emissive metal centers as well as the crystal lattice types. For example, Bi3+ and © XXXX American Chemical Society

Received: December 11, 2018

A

DOI: 10.1021/acs.inorgchem.8b03440 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry tropy.9 The U(III)/U(IV) couple exhibits great potentials in the activation of small molecules as well as the electrochemical production of hydrogen from water.10 As the most stable species of uranium under ambient conditions, uranyl(VI) ion (UO22+) adopts the linear dioxo OUO configuration and contains a series of molecular orbitals hybridized between 6d/ 5f orbitals of uranium and 2p orbitals of oxygen (Figure 1a).

effective atomic number (Zeff)), as well as consequent X-ray attenuation coefficient (XAC), suggesting uranium emerges as a distinct metal center to construct a family of uranyl-bearing inorganic scintillators.



EXPERIMENTAL METHODS

Synthesis of Uranyl-Bearing Compounds. Caution! While uranium compounds used in these studies are slightly radioactive, standard precautions were performed for handling radioactive materials. All regents were used as purchased. UMO: UO2(NO3)2· 6H2O (0.1 mmol), Na2MoO4 (0.4 mmol), and 50 (or 100) μL ultrapure water were mixed and added into a PTEF-lined Parr 4749 autoclave with a 10 mL internal volume in a ratio of U:Mo = 1:4. After heating at 200 °C for 72 h and cooling to room temperature at the rate of 7 °C/h, yellow crystals of UMO were obtained. The products were washed with deionized water and then washed with ethanol and dried at room temperature. High-purity phase of UMO was confirmed using powder X-ray diffraction patterns (Figure S1). The UBO, UPO, and UGO are successfully synthesized in different methods. UBO was synthesized in molten boric acid flux. Typically, UO2(NO3)2·6H2O (0.1 mmol), NaNO3 (0.1 mmol), and boric acid (0.6 mmol) were loaded into a 10 mL autoclave, after heating at 200 °C for 24 h and cooling to room temperature at the rate of 5 °C/h; green crystals of UBO were obtained as a pure phase. A pure phase of UPO was synthesized by a hydrothermal method starting with 0.1 mmol of UO2(NO3)2·6H2O, 0.1 mmol of KCl, 0.2 mmol of H3PO3, and 1 mL of H2O. The reaction was heated for 72 h at 190 °C. UGO was obtained by solid state reaction at 1000 °C from Na2CO3 (0.1 mmol), UO2(NO3)2·6H2O (0.1 mmol), and GeO2 (0.3 mmol). UGO was isolated as a minor product in addition with a large amount of impurity of Na2U2O7. Crystallographic Studies. Crystals were mounted on Cryoloops with paratone and optically aligned on a Bruker D8-Venture single crystal X-ray diffractometer equipped with a digital camera. The diffraction data were collected using a Turbo X-ray Source (Mo Kα radiation, λ = 0.71073 Å) adopting the direct-drive rotating anode technique and a CMOS detector at 123 K. The structures were solved by the direct method and refined on F2 by full-matrix least-squares methods using SHELXTL. The refinement result is shown in Table 1. We further determined the unit cell parameters of UBO, UPO, and UGO, which are in agreement with the reported values.14−16 Only the refinement results of UMO are shown in this work. Powder X-ray Diffraction. Powder patterns were collected from 5° to 50°, with a step of 0.02° using a Bruker D8 advance X-ray diffractometer with Cu Kα radiation (λ = 1.54056 Å) equipped with a Lynxeye one-dimensional detector.

Figure 1. (a) Schematic of uranyl valence orbitals (6p and 6s orbitals (uranium) and 2s orbitals (oxygen) are omitted, only orbitals participating in HOMO−LUMO are illustrated); (b) Comparison of the XAC and density values for uranyl-bearing scintillators and typical scintillators with optimized radiation stopping power; (c) Crystal structures of several uranyl-bearing inorganic scintillators. Abb. Na(UO2)B6O10(OH)·2H2O, UBO; K(UO2)(PO4)·4H2O, UPO; Na 2 (UO 2 )(MoO 4 ) 2 ·(H 2 O), UMO; Na 2 (UO 2 )GeO 4 , UGO; Bi4Ge3O12, BGO; Lu2SiO5:Ce, LSO.

This leads to the characteristic luminescence feature originating from the LUMO to HOMO transition, which is widely utilized as the fingerprint information for the identification of the environmental species of uranyl.11 This type of emission is intrinsically bright, compared with the Laporte-forbidden 4f−4f transition based lanthanide emission, and it does not require an additional sensitizer to achieve a highly emissive state. In fact, most inorganic uranyl compounds and natural minerals possess this intrinsic luminescence feature, offering a unique family of luminescent materials with systematically tunable structures and chemical compositions. However, although uranyl luminescence has been historically utilized as toners for glazed ceramic, dinnerware, dentistry, and vaseline glass, currently, functional materials taking the advantage of uranyl luminescence are inherently scarce.12 In our recent work, a significant X-ray excited luminescence (XEL) feature was originally observed in a uranyl-bearing coordination polymer UO2C6H3(COO)2COOH(H2O) (SCU9), which sheds light on the subject of uranium based functional optical materials.12c Uranium based inorganic scintillators should be the next logical research target because one of the manifest drawbacks of SCU-9 is that its density is quite low at 2.85 g/cm3, compared with those of commercial inorganic scintillators.5 Herein, we show that this new scintillating metal cation is highly adaptive in various inorganic lattices. These lattices include but are not limited to uranyl borates, uranyl phosphates, uranyl germinates, and uranyl molybdates. More importantly, uranium displays intrinsic advantages toward those of widely investigated emitters, i.e. diverse crystal lattices, tailored properties (density (ρ) and

Table 1. Crystallographic Data and Structure Refinement for UMO

B

Compound

Na2UO2(MoO4)2·(H2O)

Mass Color and habit Space group a (Å) b (Å) c (Å) Z T (K) λ (Å) ρ (g cm−3) μ (mm−1) R1 wR2 CCDC No.

1303.78 yellow, blocky P212121 8.6005(16) 10.749(2) 11.086(2) 2 296(2) 0.71073 4.225 18.301 0.0169 0.0457 1835201 DOI: 10.1021/acs.inorgchem.8b03440 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Raman Spectroscopy. Raman spectroscopy data were recorded from 600 to 1200 nm using a Craic Technologies microspectrophotometer. IR Spectrum. The powder of pure phase was recorded by Thermo Scientific Nicolet iS50 FT-IR in the range of 400−4000 cm−1. UV−Vis Absorption Spectrum. UV−vis absorption spectrum data were measured from a single crystal of UMO from 200 to 800 nm using a Craic Technologies microspectrophotometer. Afterglow Measurement. The afterglow measurements for SCU-9, UMO, and CsI:Tl are recorded by self-made equipment at Beijing Hamamatsu Photon Techniques INC. For typical data acquisition: the powder sample was placed at the top of the photomultiplier, and then this sample was exposed for about 30 s under a linearly aligned X-ray source. The photon signals were collected at 30 and 100 ms after shutting off the X-ray. Effective Atomic Number (Zeff) Calculation. The Zef f was calculated as the formula

Zeff =

2.94

Table 2. Comparison Results on the Physical Parameters for the Selected Commercial Scintillators and Uranyl-Bearing Scintillators

Compounds Selected commercial scintillators

Uranylbearing scintillators

f1 × (Z1)2.94 + f2 × (Z 2)2.94 + f3 × (Z3)2.94 + ···

Cs2LiYCl6 CsI:Tl BaF2 LSO BGO SCU-9 UBO UPO UMO UGO

Density [g/cm3]a

X-ray attenuation coefficient (XAC) [mm−1]b

Effective atomic number Zef f

3.31 4.51 4.88 7.40 7.13 2.85 3.30 3.64 4.20 5.30

4.65 6.23 6.01 18.69 26.81 9.25 9.34 12.50 16.05 20.70

44.5 54.0 52.7 66.0 75.2 68.3 64.3 69.1 64.3 71.8

a

Data were taken from ref 7. bThe values of XAC are calculated at Xray energy of 25 keV.

where Zi is the fraction of the total number of electrons associated with each element, and f n is the atomic number of each element. X-ray Attenuation Length Calculation. The attenuation length is defined as the depth into the material where the intensity of the Xrays has decreased to about 37% (1/e) of the value at the surface. The calculation formula is x = 1/(μρ), where μ (mass absorption coefficient) is related to material’s photoabsorption and inelastic scattering cross sections, ρ is the density for the material. The data in this work was extracted from ref 9, grazing angle was fixed at 90°, and the photon energy range was from 30 eV to 30 keV. An available calculation is free from the center for X-ray optics at http://henke.lbl. gov/optical_constants/atten2.html.

BaF2, and Cs2LiYCl6. Figure 1c shows the diverse uranyl inorganic compounds with various architectures ranging from the 2D layered structure to porous 3D structure. This is a merit that can be feasible for developing uranyl-bearing inorganic scintillators with tailored properties. Although the layered structure of K(UO2)(PO4)·4H2O (UPO) is distinct from the dense 3D structures of LSO and BGO, the value of Zef f remains to be larger. Furthermore, the choices of diverse oxoanions have a propensity to enrich the properties of the uranyl-bearing inorganic scintillators. For instance, the density (ρ) and X-ray attenuation coefficient (XAC) can be systematically tuned among these compounds, which are the key parameters for the radiation stopping power. Figure 1b shows the comparison results between the uranyl-bearing compounds and the selected commercial scintillators. The XAC and ρ values of the obtained uranyl-bearing inorganic scintillators are significantly larger than those of the reported uranyl-organic crystal with a dramatic increase approaching the record value among all scintillators in general. From the paradigm in Figure 1c, we can propose that an even more dense structure with optimized properties can be synthesized in the near future. Crystal Structure, Luminescence Mechanism, and Scintillation Property of UMO. The intrinsic X-ray scintillation is obseved in the whole family of uranyl-bearing inorganic compounds (Figure S2, Supporting Information). Among these, the new compound Na2(UO2)(MoO4)2·H2O (UMO) is selected as the prototype of the uranyl-inorganic scintillator. The UMO is facilely isolated from the hydrothermal method, and the crystal quality can be elaborately improved by optimizing the reaction conditions. High-quality crystals are synthesized by homogeneous solution crystallization, and centimeter-level crystals can be grown from the normal solution method (Figure S3, Supporting Information). The UMO crystallizes in the orthorhombic system in the P212121 space group. The asymmetric unit of UMO consists of two crystallographically independent Mo sites, one U site, two sodium sites, and one lattice water molecule. The overall structure of UMO can be described as an open threedimensional framework constructed by UO7 pentagonal bipyramids and monomeric MoO4 tetrahedra, with the Na+ ions residing in the channel along the b axis (the third crystal structure in Figure 1c). There are five known examples of sodium-containing uranyl molybdates. Most of them are 2D



RESULTS AND DISCUSSION Versatile Uranyl-Bearing Scintillators and Physical Properties. Figure 1a illustrates the valence orbitals of uranyl, which is well established to interpret the mechanism of its luminescence.13 As mentioned before, this charge transfer luminescence feature originates from radiative relaxation between hybrid 5f/6d and 2p orbitals of uranium and axial oxygen atoms. We collected the UV- and X-ray excited luminescence spectra of the selected uranyl-bearing inorganic compounds, as shown in Figure S2 (Supporting Information). The UV excited spectra of Na(UO2)B6O10(OH)·2H2O (UBO),14 K(UO2)(PO4)·4H2O (UPO),15 Na2(UO2)GeO4 (UGO),16 and Na2(UO2)(MoO4)2·(H2O) (UMO) exhibit the intrinsic green emission with similar peak shapes and positions. In addition, the X-ray excited spectra of UBO and UMO fully duplicate the corresponding UV excited spectra, confirming the nature of self-activated scintillator (Figure S2).3 Besides the optical properties, the primary interaction of X-ray within uranium, i.e. photoabsorption and inelastic scattering cross sections, is significantly larger than that of other emitters in the widely utilized scintillators.12c This endows the uranylbearing compounds with a relatively large Zef f. With respect to the scintillation process, Zef f is vital to the radiation conversion process, where the energy deposits within the scintillators through ionization (photoelectric effect and Compton scattering). In general, the probability of interaction shows an exponential relationship with Zeff.3 Table 2 summaries the values of Zef f for the selected uranyl-bearing scintillators and commercial scintillators. The Zef f value of Na2(UO2)GeO4 (UGO) nearly reaches that of Bi4Ge3O12 (BGO), one of the commercial and critical scintilltors with the highest Zef f value, and is overwhelmingly larger than those of other well-known scintillators constructed by lighter emitters, such as CsI:Tl, C

DOI: 10.1021/acs.inorgchem.8b03440 Inorg. Chem. XXXX, XXX, XXX−XXX

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character qualitatively reveals the luminescence behavior of UMO. In addition, the electronic structure of UMO reveals that the electron distribution of the equatorial ligand species has a significant overlap with U−Oax σ bonding orbitals. Although the underlying scintillation mechanism in UMO is relatively complicated, a plausible mechanism is that the electron distribution of the equatorial ligand species will be ionized by high-energy X-rays, further determining the XEL performance of UMO.20 Figure 3a illustrates that the XEL intensity of UMO increases with the elevation of received X-ray energy density.

layered structures. Besides, molybdates readily form polymerizations between MoO6 and MoO4 units.17 In comparison, the UMO is a relatively dense 3D structure with isolated MoO4 units. The axial uranyl-oxygen bonds of UMO are 1.788(5) and 1.794(5) Å, respectively.17 The equatorial bond lengths of U−O range from 2.277(5) to 2.412(5) Å, and the Mo−O distances of the MoO4 unit range from 1.718(5) to 1.802(5) Å. Typical Raman and infrared frequencies of U−O and Mo−O are clearly observed in Figure S4 and S5 (Supporting Information). An important structural feature of UMO is that all uranium atoms are isolated by MoO42− units in the overall lattice, where all the equatorial oxygen atoms are from MoO42− units. This dense architecture substantially reduces the phonon-assisted relaxation, which is anticipated to enhance the luminescence intensity of uranyl compounds.18 Density functional calculations were performed to intuitively understand the electronic structure of UMO. Figure 2a shows

Figure 3. (a) XEL spectra of UMO under various X-ray tube powers. (b) Intensity integration results on the emission spectra of UMO and BGO. Inset: Scintillation images of UMO and BGO under X-ray radiation (Cu Kα, 40 kV, 40 mA). The images were taken by a camera setup with the same exposure time (5 s), aperture (f 3.5), and ISO value (400).

Fitting of these data in Figure S9 shows good energy-response proportionality, demonstrating the direct conversion of X-ray radiation to detectable photon. Furthermore, we tentatively compared the XEL light yield of UMO with BGO. Figure 3b elucidates the XEL spectra of UMO and BGO exposed under the X-ray radiation with the same tube power. The integrated area of XEL intensity provides a rough estimation on the light yield of UMO and BGO.21 Although the integrated area of the XEL intensity of UMO is 0.57 times as much as that of BGO, the scintillation of UMO is visually more intense than that of BGO, which in fact also better matches the Si photodiodes with a high sensitivity to the green emission (inset of Figure 3b). Radiation-Resistance and Afterglow Measurement for UMO. The scintillators are naturally subject to the ionizing radiation during the practical application. Therefore, radiation resistances on both material integrity and emission intensity are highly desirable. Figure 4 illustrates the stability of the XEL intensity of UMO and the reported SCU-9 compound and commercial scintillator CsI:Tl. The XEL intensity of UMO shows higher radiation hardness than the SCU-9 in the selected dosage range, demonstrating that the radiation damage of the uranyl-bearing inorganic lattice is less sensitive compared to the orgainic−inorgainc hybrid lattice. Moreover, as shown in Figure 4, the radiation hardness of UMO is superior to that of the ionic crystal lattice, such as CsI:Tl. Another intrinsic advantage of UMO is derived from the comparison on the afterglow of UMO, SCU-9, and CsI:Tl, which is associated with the exciton recombination from crystal defects induced by ionizing radiation.22 The ionic crystal lattice of CsI:Tl is known to exhibit significant afterglow signal, which would deteriorate the radiation imaging quality.22

Figure 2. (a) The first Brillouin zone in the reciprocal space (left) and the calculated band structure (right) of UMO; (b) Density of states (DOS) analysis on the UMO. O(ax) represents the contribution from the UO; Oeq represents the contribution from coordinated oxygen (Mo−O−U), O′ represents the contribution from uncoordinated oxygen (Mo−O); (c) The LUMO, HOMO, and HOMO-3 of UMO. HOMO-3 is featured with U−Oax σ bonding character.

the first Brillouin zone in the reciprocal space (left) and the calculated band structure (right) of UMO. The calculated band gap of UMO is about 2.371 eV at the PBE level and 2.965 eV at the LDA+U level, which are in agreement with the experimental value of 2.63 eV (Figures S6 and S7). The density of state (DOS) analyses in Figure 2b indicate that the conduction band edge mainly consists of the U-5f empty orbitals. However, the valence band structure of UMO is more complicated, where the major constituents are the large amounts of O(2p) orbitals including O(eq) (oxygen atoms from Mo−O−U) and O′ (oxygen atoms from Mo−O), and a small amount of U−O ax bonding orbitals. In general, the luminesence of uranyl originates from the electron transfer between the HOMO (U−Oax σ bonding orbital) and LUMO (U-5f empty orbital).12b,19 We further calculated the orbitals of UMO at the gamma point; the U−O σ bonding character was found in a narrow energy range close to the HOMO (0.000 eV), including HOMO−3 (−0.114 eV), HOMO−5 (−0.204 eV), HOMO−7 (−0.257 eV), HOMO−10 (−0.282 eV), and HOMO−13 (−0.388 eV), as shown in Figures 2c and S8. This D

DOI: 10.1021/acs.inorgchem.8b03440 Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry



Article

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Yaxing Wang: 0000-0002-1842-339X Ruhong Zhou: 0000-0001-8624-5591 Shuao Wang: 0000-0002-1526-1102 Author Contributions ∥

Yaxing Wang, Yumin Wang, and Xing Dai contributed equally.

Notes

Figure 4. Comparison of relative XEL intensities of UMO, BGO, SCU-9, and CsI:Tl after exposing with different X-ray doses.

The authors declare no competing financial interest.



ACKNOWLEDGMENTS We are grateful for funding support from the Science Challenge Project (TZ2016004), the National Natural Science Foundation of China (21790374, 21761132019, 21806118, 21825601), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and “The Fundamental Research Funds for the Central Universities” from Sichuan University.

Impressively as shown in Table 3, the afterglow of UMO is down to 0.07% of the original intensity after shutting off the XTable 3. Afterglow Results on the UMO, SCU-9, and CsI:Tl %@30 ms %@100 ms

CsI:Tl

SCU-9

UMO

0.45 0.28

0.16 0.12

0.07 0.06



ray excitation (30 ms cutoff). This is significantly lower than the values of SCU-9 and CsI:Tl, implying that the stability of inorganic crystal lattice based on oxoanion ligand is superior to the hybrid lattices and doped compounds. These initial comparisons give a feasible criterion for further improvement on the uranyl-bearing inorganic scintillators.

(1) (a) Nikl, M.; Yoshikawa, A. Recent R&D Trends in Inorganic Single-Crystal Scintillator Materials for Radiation Detection. Adv. Opt. Mater. 2015, 3, 463−481. (b) Nikl, M. Scintillation detectors for xrays. Meas. Sci. Technol. 2006, 17, R37−R54. (c) Martin, T.; Koch, A.; Nikl, M. Scintillator materials for x-ray detectors and beam monitors. MRS Bull. 2017, 42, 451−457. (2) (a) Eriksson, L.; Melcher, C. L.; Eriksson, M.; Rothfuss, H.; Grazioso, R.; Aykac, M. Design Considerations of Phoswich Detectors for High Resolution Positron Emission Tomography. IEEE Trans. Nucl. Sci. 2009, 56, 182−188. (b) Ronda, C.; Wieczorek, H.; Khanin, V.; Rodnyi, P. Review-Scintillators for Medical Imaging: A Tutorial Overview. ECS J. Solid State Sci. Technol. 2016, 5, R3121. (c) Melcher, C. L. Scintillation crystals for PET. J. Nucl. Med. 2000, 41, 1051− 1055. (3) Knoll, G. F. Radiation Detection and Measurement; John Wiley & Sons: Hoboken, NJ, USA, 2010. (4) Hajagos, T. J.; Liu, C.; Cherepy, N. J.; Pei, Q. High-Z Sensitized Plastic Scintillators: A Review. Adv. Mater. 2018, 30, 1706956. (5) Lecoq, P.; Annenkov, A.; Gektin, A.; Korzhik, M.; Pedrini, C.; Inorganic Scintillators for Detector Systems: Physical Principles and Crystal Engineering; Springer: Heidelberg, GER, 2017. (6) McGregor, D. S. Materials for Gamma-Ray Spectrometers: Inorganic Scintillators. In Annu. Rev. Mater. Res., Vol. 48; Clarke, D. R., Ed.; 2018. (7) Data is available: http://scintillator.lbl.gov/. (8) (a) Liddle, S. T. The Renaissance of Non-Aqueous Uranium Chemistry. Angew. Chem., Int. Ed. 2015, 54, 8604−8641. (b) Chen, W.; Yuan, H. M.; Wang, J. Y.; Liu, Z. Y.; Xu, J. J.; Yang, M.; Chen, J. S. Synthesis, Structure, and Photoelectronic Effects of a Uranium-ZincOrganic Coordination Polymer Containing Infinite Metal Oxide Sheets. J. Am. Chem. Soc. 2003, 125, 9266−9267. (c) Li, P.; Vermeulen, N. A.; Malliakas, C. D.; Gomez-Gualdron, D. A.; Howarth, A. J.; Mehdi, B. L.; Dohnalkova, A.; Browning, N. D.; O’Keeffe, M.; Farha, O. K. Bottom-up construction of a superstructure in a porous uranium-organic crystal. Science 2017, 356, 624− 627. (d) Li, P.; Vermeulen, N. A.; Gong, X.; Malliakas, C. D.; Stoddart, J. F.; Hupp, J. T.; Farha, O. K. Design and Synthesis of a Water-Stable Anionic Uranium-Based Metal-Organic Framework (MOF) with Ultra Large Pores. Angew. Chem., Int. Ed. 2016, 55, 10358−10362.



CONCLUSION The foregoing results demonstrate that the combination of rich coordination chemistry, high effective atomic number, intrinsic luminescence property, and high stability of inorganic uranyl (VI) compounds gives rise to a new family of intrinsic scintillators with potential advantages of high radiation stopping power, symmetrically tunable chemical compositions and crystal lattices, high light yield, insignificant afterglow, and decent radiation hardness. This work not only represents a solid progress on the development of functional materials aiming at depleted uranium disposal but also provides a brand new metal center for building scintillator materials with improved properties.



REFERENCES

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b03440. Experimental methods, details of synthesis, IR, Raman, UV−vis spectra and calculation methods, and crystallographic data (PDF) Accession Codes

CCDC 1835201 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. E

DOI: 10.1021/acs.inorgchem.8b03440 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.8b03440 Inorg. Chem. XXXX, XXX, XXX−XXX