Sensitive and Reliable Fluorescent Thermometer Based on a Red-Emitting Li<sub>2</sub>MgHfO<sub>4</sub>:Mn<sup>4+</sup> Phosphor
Yonghong Qin, Fen Zhong, Yinan Bian, Shruti Hariyani, Yaxin Cao, Jakoah Brgoch, Takatoshi Seto, M.G. Brik, A.M. Srivastava, Xicheng Wang, Yuhua Wang
Abstract
Contactless fluorescent thermometers are rapidly gaining popularity due to their sensitivity and flexibility. However, the development of sensitive and reliable non-rare-earth-containing fluorescent thermometers remains a significant challenge. Here, a new rare-earth-free, red-emitting phosphor, Li2MgHfO4:Mn4+, was developed for temperature sensing. An experimental analysis combined with density functional theory and crystal field calculations reveals that the sensitive temperature-dependent luminescence arises from nonradiative transitions induced by lattice vibration. Li2MgHfO4:Mn4+ also exhibits reliable recovery performance after 100 heating–cooling cycles due to the elimination of surface defects, which is rare but vital for practical application. This study puts forward a new design strategy for fluorescent thermometers and sheds light on the fundamental structure–property relationships that guide sensitive temperature-dependent luminescence. These considerations are crucial for developing next-generation fluorescence-based thermometers.