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

Abstract

This work presents a novel approach for detecting quench or hot spot regimes in coated conductors by integrating 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 tapes. HfO 2 :4.5%Eu 3+ ,0.5%Tb 3+ nanocrystals exhibited a relative sensitivity up to 4.80 % 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 9.65 % K -1 at 20 K. It also retained the superconducting properties of the coated conductor.