Abstract
The optical thermometer has shown great promise for use in the fields of aeronautical engineering, environmental monitoring and medical diagnosis. Self-referencing lanthanide thermo-probes distinguish themselves because of their accuracy, calibration, photostability, and temporal dimension of signal. However, the use of conventional lanthanide-doped materials is limited by their poor reproducibility, random distance between energy transfer pairs and interference by energy migration, thereby restricting their utility. Herein, a strategy for synthesizing hetero-dinuclear complexes that comprise chemically similar lanthanides is introduced in which a pair of thermosensitive dinuclear complexes, cycTb-phEu and cycEu-phTb, were synthesized. Their structures were geometrically optimized with an internuclear distance of approximately 10.6Å. The sensitive linear temperature-dependent luminescent intensity ratios of europium and terbium emission over a wide temperature range (50–298K and 10–200K, respectively) and their temporal dimension responses indicate that both dinuclear complexes can act as excellent self-referencing thermometers. The energy transfer from Tb3+ to Eu3+ is thermally activated, with the most important pathway involving the 7F1 Eu3+J-multiplet at room temperature. The energy transfer from the antenna to Eu3+ was simulated, and it was found that the most important ligand contributions to the rate come from transfers to the Eu3+ upper states rather than direct ligand–metal transfer to 5D1 or 5D0. As the first molecular-based thermometer with clear validation of the metal ratio and a fixed distance between the metal pairs, these dinuclear complexes can be used as new materials for temperature sensing and can provide a new platform for understanding the energy transfer between lanthanide ions.
Highlights
Luminescent physical sensors for monitoring temperature have shown great promise for use in the fields of aeronautical engineering, environmental engineering, and industrial processes[1,2,3,4]
A strategy to synthesize hetero-dinuclear complexes that consist of chemically similar lanthanides has been introduced by which cycTb-phEu and cycEu-phTb were produced
The different energy gaps between the ligand triplet state and the acceptor lanthanide ion states, as well as the Tb3+ to Eu3+ energy transfer, result in different luminescence performances for each metal ion, giving an increased temperaturedependent luminescent emission ratio for europium over terbium. Both dinuclear complexes illustrated excellent temperature sensitivity over a wide temperature range, with cycEu-phTb having the best potential as an optical thermometer using an excitation wavelength of 355 nm
Summary
Luminescent physical sensors for monitoring temperature have shown great promise for use in the fields of aeronautical engineering, environmental engineering, and industrial processes[1,2,3,4] They have distinguished advantages over traditional thermometers in terms of a fast response, a high sensitivity, and a tolerance to extreme atmospheres[5,6,7]. Lanthanide luminescent materials have sharp emission bands[11,12] and a large energy shift between the antenna absorption and lanthanide emission[13], which distinguishes them from other luminescent materials, such as organic dyes or quantum dots[14] In addition to these properties, lanthanide luminescence has a long lifetime, allowing time-gated techniques to increase the signal-to-noise ratio[15]. The temperature-dependent quenching and energy transfer between the dopant ions
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