UiO-66(Zr) : Tb³⁺, Eu³⁺/PVDF Composite Films as Dual-Responsive Optical Thermometers for Wide-Range Temperature...

Nanothermometers offer unparalleled capabilities for temperature measurement at the nanoscale, with applications in biological systems, microfluidic devices, and catalysis. Among them, fluorescence-based optical thermometers utilizing Tb³⁺ and Eu³⁺ ions are promising due to their self-referenced ratiometric detection and resistance to environmental fluctuations. However, most lanthanide-based thermometers suffer from reduced sensitivity beyond the cryogenic temperature range, limiting their broader applicability. In this study, we report the synthesis of highly crystalline, Tb³⁺, Eu³⁺ codoped UiO-66(Zr) metal-organic frameworks via a one-pot microemulsion approach. These nanothermometers exhibit thermal sensitivity over a wide operational range, from cryogenic to physiological temperatures and beyond. The robust UiO-66(Zr) framework ensures stability in diverse environments, while the Tb³⁺-Eu³⁺ energy transfer mechanism provides precise, non-blinking, ratiometric detection of temperature. Notably, the relative sensitivity of the nanothermometers increases with temperature, achieving superior performance at 400 K, compared to previously reported lanthanide-terephthalate frameworks. To extend their utility in fluid environments, we fabricated a flexible nanoparticle-PVDF (polyvinylidene fluoride) composite film that retains the thermal sensitivity of the UMET nanothermometers in isopropyl alcohol. Thus, this study establishes a simple, one-pot method to incorporate Ln³⁺ in the UiO-66(Zr) framework for optical thermometry above the cryogenic and room temperature ranges, with potential applications in biological and industrial systems.