Ratiometric Optical Thermometer with High Sensitivity Based on Site-Selective Occupancy of Mn2+ Ions in Li5Zn8Al5Ge9O36 under Controllable Synthesis Atmosphere

A fluorescence intensity ratio (FIR) thermometer based on inorganic luminescence materials is a new-type temperature sensor with potential and significance. However, research based on single transition metal ions dual-emission fluorescence ratio thermometer is very rare. Especially, a FIR thermometer based on Mn2+ ions has never been reported. Here, we successfully control the site-selective occupancy of Mn2+ ions in Li5Zn8Al5Ge9O36 by controlling the synthesis atmosphere conditions. Mn2+ ions form [MnO4] tetrahedrons with a weak crystal field and [MnO6] octahedrons with a strong crystal field corresponding to synthesis atmospheres of N-2 and O-2, respectively. In addition, a novel FIR thermometer Mn2+-doped material Li5Zn8Al5Ge9O36:Mn2+ based on different dependences of Mn2+ ions in different crystal fields on temperature is prepared in 50%N-2+50%O-2 conditions. The thermometer has high sensitivity in the range of 303-383 K including absolute sensitivity (S-a) and relative sensitivity (S-r) (the S-a maximum is 0.476 K-1 at 373 K and the S-r maximum is 8.489% K-1 at 323 K) with low uncertainty (lower 0.1 K). Our researches have added a new and excellent member into optical thermometer materials and provided a valuable reference for exploring a new ratiometric optical thermometer.