Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Cryogenic Luminescent Tb/Eu-MOF Thermometer Based on a Fluorine-Modified Tetracarboxylate Ligand Dian Zhao,*,†,‡ Dan Yue,‡ Ling Zhang,‡ Ke Jiang,‡ and Guodong Qian*,‡ †
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Department of Chemistry, Zhejiang Normal University, Jinhua 321004, China ‡ State Key Laboratory of Silicon Materials, Cyrus Tang Center for Sensor Materials and Applications, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
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S Supporting Information *
ABSTRACT: A fluorine-modified tetracarboxylic acid ligand, namely, 2′-fluoro-[1,1′:4′,1′′-terphenyl]-3,3′′,5,5′′-tetracarboxylic acid (H4FTPTC), with suitable triplet energy excited state, was designed and applied to construct the luminescent lanthanide metal−organic frameworks (LnMOFs) for cryogenic temperature sensing. With the lanthanides codoping strategy, we developed a new Tb3+/Eu3+ mixed LnMOF system Tb1−xEuxFTPTC (x = 0.05, 0.1, 0.2), which feature excellent linear responses to temperature with high relative sensitivity in the cryogenic range of 25−125 K. It was found that the relative sensitivity of such mixed LnMOF could readily be tuned by adjusting the incorporation amount of Eu3+ ions in the host framework. In addition, the energy transfer efficiency between the Tb3+ and Eu3+ ions in the framework with different Tb3+/ Eu3+ ratios are also investigated and discussed.
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INTRODUCTION Fast and accurate determination of cryogenic temperature is crucial across a wide range of areas, including basic science, engineering, manufacturing, metallurgy, aerospace, and so on.1−3 With the rapid development of modern technology, many thermal-sensitive materials, such as platinum RTDs,4 special thermistors,5 and silicon diodes,6 have been developed for use as cryogenic temperature sensing and control elements. However, these commonly used sensors have a large size and must be in physical contact with the object being sensed, which is not suitable for remote temperature detection of large-area thermal distributions, fast-moving objects, or at micro-and nanoscales.7,8 In addition, their electrical link modules impede their application in strong magnetic and/or radio frequency fields. Luminescence-based ratiometric techniques7,8 can overcome these drawbacks and provide a very promising alternative for precise temperature measurements due to its self-calibrating, as well as noninvasiveness, observability, high spatial resolution, and sensitivity properties. In the past decade, numerous luminescent materials have been explored to construct the novel ratiometric thermometers. These include semiconducting polymer dots,9 molecular lanthanide coordination compounds,10 Er3+/Yb3+ codoped nanoparticles,11 host−guest composites,12,13 and lanthanide metal−organic frameworks (LnMOFs).7,8,14 LnMOFs, assembled in an orderly manner from lanthanide ions or clusters with organic ligands, are especially useful for engineering the luminescence properties because of the © XXXX American Chemical Society
intrinsic advantages of the porous MOFs and the spectroscopic properties of the lanthanides.15−19 They are versatile multifunctional luminescent materials and have been investigated for a wide range of sensing applications,20−25 especially in temperature measurement. In the multicenter LnMOFs, the luminescence of different lanthanide ions depends strongly on the temperature. Thus, the ratio between the luminescence intensities of two different centers can be employed to realize self-calibrating luminescent thermometers of high accuracy and fast response. With the lanthanides codoping strategy, Qian et al.26 developed the first ratiometric luminescent Tb3+/Eu3+MOF thermometer using the Tb3+/Eu3+ emission ratio as the thermometric parameter, namely, the Eu 0.0069 Tb0.9931 DMBDC (DMBDC = 2,5-dimethoxy-1,4-benzendicarboxylate), which features an operating range of 50−200 K and a maximum relative sensitivity of 1.15% K−1 at 200 K. Since then, based on the same principle, a number of Tb/Eu-MOFs have been realized that deliver good performance in the temperature range of 10−300 K.27−31 Although several excellent Tb/Eu-MOF thermometers for the cryogenic regime have been developed in the past 5 years, it is still a great challenge to fabricate Tb/Eu-MOFs with higher sensitivity. More importantly, effective control and modulation of the energy transfer process in the Tb/Eu-MOF thermometers, Received: June 24, 2018
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DOI: 10.1021/acs.inorgchem.8b01746 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry mainly involving ligand-to-Tb3+, ligand-to-Eu3+, and Tb3+-toEu3+, are critical for the sensing properties. Organic ligands with suitable triplet lowest energy excited state (T1), generally in the range of 22 000−27 000 cm−1, have proved to be capable of sensitizing the Tb3+ and Eu3+ luminescence in the Tb/Eu-MOFs simultaneously.32 Concerning cryogenic thermometers based on the luminescent Tb/EuMOFs, the energy difference between the ligand’s T1 and Tb3+ accepting level should be controlled in a small range in order to ensure that the Tb3+ luminescence is sensitive to cryogenic temperatures, which is a prerequisite for tuning the temperature response of the luminescence intensity ratio between Tb3+ and Eu3+ in the cryogenic region (
