Employing Eu,Tb-doped HfO₂ nanocrystals as built-in cryogenic luminescent nanothermometers for commercial coated conductors

This work presents a novel approach for detecting quench or hot spot regimes in coated conductors by depositing luminescent nanocrystals operating as nanothermometers onto the silver protective layer, allowing simultaneous temperature measurements. In this work, we use hafnium oxide (HfO2) nanocrystals doped with Eu3+ and Tb3+ ions, synthesized via a microwave-assisted solvothermal method, which were next spin-coated onto the protective layer of coated conductor tape. HfO2:4.5%Eu3+,0.5%Tb3+ nanocrystals exhibited a relative sensitivity of up to 4.10% K−1 at 40 K. The nanocrystal-derived thin film, with a thickness of 60 ± 10 nm, exhibited good thermometric performance, with a relative sensitivity of 13.51% K−1 at 20 K. It also retained the superconducting properties of the coated conductor.