Construction of self-sensitized LiErF 4 : 0.5% Tm 3+ @LiYF 4 upconversion nanoprobe for trace water sensing
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ate Key Laboratory of Integrated Optoelectronics, Jilin Key Laboratory of Advanced Gas Sensors, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China 2 Department of Respiratory Medicine, The First Hospital, Jilin University, Changchun 130021, China 3 State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Science, Changchun 130033, China © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 4 April 2020 / Revised: 6 June 2020 / Accepted: 13 June 2020
ABSTRACT LiErF4 was commonly used as a dipolar-coupled antiferromagnet, and was rarely considered as a luminescent material. Herein, we achieved the strong red upconversion emission of LiErF4 simply by an inert shell coating, i.e., LiErF4@LiYF4. Owing to the unique and intrinsic ladder-like energy levels of Er3+ ions, this LiErF4 core–shell nanostructures present red emission (~ 650 nm) under multi-band excitation in the near-infrared (NIR) region (~ 808, ~ 980, and ~ 1,530 nm). A brighter and monochromic red emission can be further obtained via doping 0.5% Tm3+ into the LiErF4 core, i.e., LiErF4: 0.5% Tm3+@LiYF4. The enriched Er3+ ions and strong monochromic red emission natures make LiErF4: 0.5% Tm3+@LiYF4 nanocrystals very sensitive for trace water probing in organic solvents with detection limit of 30 ppm in acetonitrile, 50 ppm in dimethyl sulfoxide (DMSO), and 58 ppm in N, N-dimethylformamide (DMF) under excitation of 808 nm. Due to their superior chemical and physical stability, these nanoprobes exhibit excellent antijamming ability and recyclability, offering them suitable for real-time and long-term water monitoring.
KEYWORDS LiErF4, water detection, upconversion emission, sensor, self-sensitized
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Introduction
Water is the source of life. However, it is considered as an impurity and contaminant in some cases. For example, in organic solvent, the presence of water can lead to catastrophic failures, such as fires and explosions under some circumstances. In petroleum industry, the presence of water may cause a drop in engine’ s performance, resulting in engine damage [1, 2]. Hence, the detection and quantification of trace water is a crucial matter not only in the aforementioned aspects, but also in pharmaceuticals, electronics, and food processing [3]. The primary standard for water detection in sample substances is the highly sensitive Karl Fischer coulometric titration method [4]. However, it has several disadvantages including the use of toxic and expensive chemical reagents, long measuring time, and inability of real-time monitoring [5]. Recently, fluorescence-based optical water sensors appear to be particularly attractive on account of their highly sensitive and selective, easy to fabricate, as well as their capability of remote and in situ monitoring [6–9]. Despite the advance, the majority of the optical water sensors focus on organic luminescent molecules, which suffer from poor reusability a
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