Monitoring Ultraviolet Radiation Dosage Based on a Luminescent

Communication Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Monitoring Ultraviolet Radiation Dosage Based on a Luminescent Lanthanide Metal−Organic Framework Xiaoyan Li,†,∥ Yaxing Wang,†,∥ Jian Xie,† Xuemiao Yin,† Mark A. Silver,† Yawen Cai,† Hailong Zhang,† Lanhua Chen,† Guoqing Bian,‡ Juan Diwu,† Zhifang Chai,†,§ and Shuao Wang*,†

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†

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, China ‡ College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China § Laboratory of Nuclear Energy Chemistry and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China S Supporting Information *

could detect radiation in the region from UV to high energy Xand γ-rays because radiation-induced radicals readily quenched the uranyl-based luminescence, resulting in highly sensitive detection capacities.17−19 In this work, we report a luminescent lanthanide metal−organic framework [Tb 7 (OH) 8 (H 2 O) 6 (IDA) 3 (COO) 3 ]·4Cl·2H 2 O (Tb-IDA, IDA = iminodiacetic acid) that can serve as a detection medium for UV radiation. Tuning the color of luminescence is accessible by employing a strategy of doping Tb-IDA with multicolor ions, which results in the synthesis of a ternary series, Gd 99 Tb x Eu y -IDA. One such ternary species, Gd99Tb0.1Eu0.9-IDA, displayed a new radiation-induced change in luminescence color from blue to yellow that spanned across the wider part of the white light region. The outcome of these experiments led to achieving the first lanthanide-based radiation monitor when using a standard CIE chromaticity diagram as a read-in and read-out unit. Tb-IDA was synthesized using a solvothermal method, and the production of a pure phase was confirmed using powder Xray diffraction (PXRD, Figure S1). As shown in Figure 1, TbIDA crystallizes as a 3D structure in the space group P63. The chiral structure is further confirmed by the second harmonic generation (SHG) experiment, as shown in Figure S2. IR and Raman analyses of crystals are shown in Figure S3. The asymmetric unit contains three crystallographically independent Tb centers, one IDA ligand, one formate, six coordinating O atoms (O1, O4, O7, O10, O11, O12), two chloride ions, and two lattice waters (Figure 1a). Bond valence sums (BVS, Table S2) indicate that O1, O7, O11, and O12 should be assigned as μ3-OH because their BVSs range from 1.1 to 1.4. The BVSs of atoms O4 and O10 were determined to be 0.369 and 0.268, respectively, and characterize both of these to be additional coordinating H2O molecules. Tb atoms adopt three different coordination environments in Tb-IDA. Both Tb1 and Tb2 centers display nine-coordinate tricapped trigonal prismatic geometry, while Tb3 resides in eight-coordinate snub disphenoid polyhedra.20,21 The Tb−O bond lengths are all within the range from 2.289 to 2.536 Å (Table S3) and are

ABSTRACT: A luminescent lanthanide metal−organic framework [Tb 7 (OH) 8 (H 2 O) 6 (IDA) 3 (COO) 3 ]·4Cl· 2H2O (Tb-IDA, IDA = iminodiacetic acid) was hydrothermally synthesized and structurally characterized. Monitoring ultraviolet radiation was achieved by correlating the dosage with the luminescence color change in doped Gd99Tb0.1Eu0.9-IDA compound. A linear relationship is developed across a broad range from blue to yellow within a CIE chromaticity diagram.

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he detection and quantification of ultraviolet (UV) radiation is a shared objective among optical-electronic detectors, military applications, chemical synthesis, and other industrial applications.1−3 Besides its scientific and commercial aspects, monitoring UV radiation is of great importance in environmental and medical fields; e.g., excessive exposure to UV radiation often results in harmful effects in organs and tissues.4 Generally, this visually undetectable radiation is observed using indirect approaches, such as through the use of semiconductor materials, including ZnO, SnO2, and leadbased perovskites. These materials are extensively developed on the basis of the photoelectric phenomenon.1,5−7 Although these materials are promising UV detectors, the manufacturing cost, light-to-current conversion efficiency, etc. still hinder their development. In addition, though photochromic materials can directly visualize the radiation received by color change, they can hardly quantify the dosage given that most visible light provides competing contributions to the absorption area.8−10 As an alternative method, a luminescent approach shows attractive advantages over the traditional detectors in terms of fast response and precisely quantifying the radiation dosage.11,12 Metal−organic frameworks (MOFs) are a class of fascinating materials due to their reticular chemistry, rich structural architectures, and modifiable physicochemical properties.13,14 Among them, lanthanide MOFs are prolifically investigated because of their unique f-electron configurations that readily lead to rich luminescent and magnetic properties.15,16 Recently, we demonstrated that two uranyl-based MOFs © XXXX American Chemical Society

Received: May 1, 2018

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DOI: 10.1021/acs.inorgchem.8b01193 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 1. (a) The asymmetric building unit of Tb-IDA. (b) Ball-andstick view of the [Tb7(μ3-OH)8]13+ core. (c) Polyhedral view of [Tb3(μ3-OH)]8+ (far left) and the 2D layers built from [Tb3(μ3OH)]8+ cores when viewed along the c axis (left-of-center). 3D framework achieved by linking [TbO9] tricapped trigonal prisms (right-of-center) to [Tb3(μ3-OH)]8+ cores, as viewed down the a axis (far right). Atom colors: Tb in yellow and blue, O in red, and N in purple. Hydrogen atoms are omitted for clarity.

similar to previously reported distances for trivalent Tb−O compounds.22 Three Tb1 atoms are connected by a μ3-OH to form a trinuclear unit [Tb3(μ3−OH)]8+. Tb3 atoms also form these distinct trimeric species, while Tb2 serves as a node to bridge these [Tb3(μ3-OH)]8+ species, thereby forming a [Tb7(μ3-OH)8]13+ core. The [Tb7(μ3−OH)8]13+ core can be described as a hourglass-like structure (Figure 1b). The 3D structure of Tb-IDA can be divided into two parts, whereby 2D layers comprising alternating [Tb3(μ3−OH)]8+ (Tb1, Tb3, Tb1, etc. Figure 1c) cores are connected by IDA ligands in the [ab] plane, and Tb2 nodes bridge and stabilize these layers against each other to form the 3D extended structure (Figure 1c). When exposed to UV light, the emission intensity of ligand IDA significantly decreased, implying that IDA is particularly sensitive and possibly unstable under this condition. As shown in Figure 2a,b, the electron spin-resonance spectroscopies of fresh and UV-irradiated samples of IDA clearly indicate the formation of radiation-induced radicals and explain the effect that UV light has on the photoluminescence of IDA. This phenomenon suggests that a lanthanide-based radiation dosimeter for UV light is possible by designing a material from a luminescent 4f metal and IDA. However, we cannot observe the radiation response in Tb-IDA because the emission from TbIII is stable, even after prolonged exposure (1 h) to UV radiation (Figure S4). The typical f−f transitions from the excited 5D4 state to the ground 7FJ state (J = 6−3) was observed (Figure 2c and S4). The emission feature of IDA is absent in the compound of Tb-IDA (Figure S4), demonstrating Tb centers are fully sensitized by IDA through the antenna effect.23,24 A lanthanide-based radiation dosimeter should exhibit a change in the emission under radiation conditions, which requires synergistic interactions between IDA and TbIII centers. To achive this goal, a doping strategy was explored in order to tune the luminescence color within the lanthanide compounds. Binary Tb100−xEux-IDA materials were initially studied, and the PXRD patterns (Figure S5) indicate successful structural integration of Eu within this

Figure 2. (a) The solid-state photoluminescence (λExc = 365 nm) before and after UV radiation. (b) ESR spectra of IDA collected before and after UV radiation. (c) Simplified schematic of energy transfer processes in Ln-IDA.

series. The emission spectra of Tb100−xEux-IDA compounds reveal that IDA still serves as a sensitizer in this binary series due to the absence of the emission in the range of 420−550 nm from IDA (Figure S6). The resulting luminescence was found to be tuned from red to green and is in agreement with most lanthanide-based phosphors.25,26 This doping experiment implies that the introduction of dilute 4f-metal ions into the Ln-IDA matrix is sufficient to tune the emission of this material.25,27 A ternary series, Gd99TbxEuy-IDA, was optimally synthesized and found to display clear multicolor emission, including that of the IDA ligand, TbIII, and EuIII (Figure 3a and Figure S7). This property is imperative to developing a potential radiation detection system.

Figure 3. (a) The solid-state emission spectra, (b) CIE chromaticity diagram, and (c) corresponding images of luminescence for Gd99Tb0.1Eu0.9−IDA after being irradiated with different dosages of UV light (λExc = 365 nm). B

DOI: 10.1021/acs.inorgchem.8b01193 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

80 °C for 40 h (Figure S10), which further supports the radical mechanism. In summary, a new luminescent lanthanide-based dosimeter was achieved through precisely controlling the lanthanide species and radiation-sensitive ligands. Furthermore, we have been the first to demonstrate radiation monitoring from the use of a standard CIE chromaticity diagram that serves as a read-in and read-out logical unit. The present work provides a feasible approach to developing luminescent lanthanide-based radiation monitoring materials.

Given that radiation-induced radicals formed in IDA when exposed to UV light, we collected the photoluminescence spectra of Gd99Tb0.1Eu0.9−IDA after fresh samples were exposed to different dosages of UV light as well. Figure 3a clearly illustrates the change in photoluminescence is dependent upon the UV dosage in Gd99Tb0.1Eu0.9−IDA as the intensity remarkably decreases after exposure to only 0.5 mJ of UV light. Evaluation of fresh and UV-irradiated samples by PXRD and FTIR and Raman spectroscopies determined that the phase retains its integrity throughout exposure, even after a high dosage is received (Figure S8a,b,c). Delving deeper into the photoluminescence of Gd99Tb0.1Eu0.9−IDA, the emission intensity from 420 to 520 nm continuously decreases, whereas the luminescence of TbIII and EuIII hardly changes in magnitude. This further supports that the energy transfer from IDA is perturbed solely by the presence of local radicals, and these radicals do not affect the emission from either doped metal. Figure 3b illustrates that the UV dosage is correlated with the color coordinates in the standard CIE chromaticity diagram. The continuous change in the color of emission is discernible and can even be observed with the naked eye, qualifying this material as a unique lanthanide-based dosimeter (Figure 3c). From the viewpoint of developing a read-in and read-out method for UV monitoring, the rich color coordinates in the CIE chromaticity diagram can be used to precisely quantify the dosage of UV light received, as displayed in Table S6. To further investigate the radical species in Gd99Tb0.1Eu0.9IDA, we compared the XPS spectra of the compound before and after exposure to UV radiation. As shown in Figure 4a, the

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01193. Detailed experiment methods, additional structural studies, SHG signal, TG/DSC, emission spectra characterization, BVS calculations, PXRD patterns, FTIR and Raman spectra (PDF) Accession Codes

CCDC 1832371 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.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yaxing Wang: 0000-0002-1842-339X Mark A. Silver: 0000-0002-2285-3616 Shuao Wang: 0000-0002-1526-1102 Author Contributions ∥

These authors contributed equally.

Notes

Figure 4. C 1s XPS core-level spectra of Gd99Tb0.1Eu0.9-IDA (a) before and (b) after 365 nm light irradiation.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21790370, 21790374, 21761132019), the Science Challenge Project (TZ2016004), a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the “Young Thousand Talented Program” in China.

peak belonging to C 1s could be fitted by three subunits located at 284.4 eV, 285.0 eV, and 288.4 eV, which are attributed to the C−C and C−H, C−N, or C−O and OC− O, respectively. After irradiation, the spectrum in Figure 4b reveals the development of a new peak at 285.7 eV and implies the formation of carbon radicals on the IDA ligand by breaking C−H bonds on the α-CH2.28 Meanwhile, other signals at 284.3, 294.9, and 288.4 eV show negligible changes compared to those of unirradiated samples, further supporting the assignment of this new peak. In addition, the absorption spectra of IDA upon irradiation results in an increase in the intensity of absorbance between 275 and 450 nm, which directly affects the intensity of ligand based emission peaks ranging from 420 to 550 nm while the lanthanide based emission is affected (Figure S9).12 This direct observation of the quenched luminescence from the formation of radicals after exposure to UV radiation is responsible for the continuous color change of Gd99Tb0.1Eu0.9-IDA observed in the CIE chromaticity diagram. The recovery of the irradiated sample fluorescence can be achieved by heating the sample at

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DOI: 10.1021/acs.inorgchem.8b01193 Inorg. Chem. XXXX, XXX, XXX−XXX