Coumarin 7 functionalized europium-based metal–organic-framework luminescent composites for dual-mode optical thermometry

Abstract

Developing a highly reliable non-contact optical thermometer probe with excellent sensitivity and multi-mode temperature sensing behaviours is always a great challenge. Here, dual-emitting luminescent composites fabricated using a europium-based metal–organic framework (Eu-MOF) and surface-immobilized molecular dye (Coumarin 7) were successfully prepared by a simple solvothermal method, followed by a post-modification strategy. Benefiting from the linear response in fluorescence intensity ratios (FIRs) of Eu³⁺ to Coumarin 7 dye molecules in the temperature range from 10 °C to 90 °C, the composite demonstrated the maximum relative temperature sensitivity (S_r) of 0.50% °C⁻¹ at 90 °C. Moreover, the observed red-shift of Coumarin 7 emission with the temperature readout suggests a dual-mode optical thermal sensing mechanism in the dye-immobilized MOF composite. Their excellent reusability and temperature sensing mechanisms have been also investigated. These results demonstrate the potential of the Coumarin 7 functionalized Eu-MOF composite as a dual-mode optical thermometer for temperature sensing applications.