Ultra‐Sensitive Low‐Temperature Upconversion via Interfacial Energy Transfer Toward Visual Cryogenic Nanothermometry

Abstract Nanothermometry with high resolution and sensitivity shows significant potential for both fundamental research and frontier applications. However, achieving real‐time high‐sensitivity temperature sensing in low‐temperature regions at the single nanoparticle level has remained challenging. Here a conceptual strategy is reported to realize the ultra‐sensitive low‐temperature thermoresponsive upconversion by interfacial energy transfer in a core‐shell nanostructure. The nanoscale spatial separation of the sensitizer Yb 3+ and activator Ho 3+ contributes to a remarkable enhancement of the upconversion by suppressing back energy transfer channels in addition to a temporal control of upconversion dynamics. Moreover, the design of non‐thermally coupled upconverting system results in highly sensitive thermochromic upconversion emissions with a contrast red‐to‐green color change and the relative sensitivity is raised up to 15.1% K −1 at 50 K. Furthermore, the sensing limit can be extend above room temperature to 443 K by incorporating another temperature‐responsive Yb 3+ /Tm 3+ layer through a multi‐layer core‐shell architecture design. These findings gain a deep insight into the thermoresponsive upconversion in nanoparticles but also provide a new way for the development of ultrasensitive real‐time visual nanothermometry and other thermoresponsive devices.