Rethinking Assumptions: Assessing the Impact of Strong Magnetic Fields on Luminescence Thermometry.

Luminescence (nano)thermometry has exploded in popularity, offering a remote detection way to measure temperature across diverse fields like nanomedicine, microelectronics, catalysis, and plasmonics. A key advantage is its supposed immunity to strong electromagnetic fields, a crucial feature in many environments. However, this assumption lacks comprehensive experimental verification as most of the proposed luminescent thermometers rely on magnetic ions, such as lanthanides. Here, we address this gap by critically examining the thermometric response of the luminescent molecular thermometer [TbEu(bpy)(NO)] (bpy = 2,2'-bipyridine) under high magnetic fields (up to 58 T). Our findings reveal that the conventional intensity-based method for Tb/Eu luminescent thermometers fails even under weak magnetic fields. However, careful data analysis identified specific transitions with minimal magnetic correlation, enabling the thermometer to operate across the entire temperature range up to 20 T, and with larger fields for temperatures exceeding 120 K. This study highlights the strong dependence of thermometric performance on material properties, urging caution, but also offers a path forward for developing robust luminescent thermometers in such environments.