High-sensitivity luminescent temperature sensors: MFX:1%Sm 2+ (M = Sr, Ba, X = Cl, Br).

The use of lanthanide luminescence has advanced the field of remote temperature sensing. Luminescence intensity ratio methods relying on emission from two thermally coupled energy levels are popular but suffer from a limited temperature range. Here, we present a versatile luminescent thermometer: Ba(Sr)FBr(Cl):Sm 2+ . The Sm 2+ ion benefits from multiple thermally coupled excited states to extend the temperature range and has strong parity-allowed 4f 6 →4f 5 5d 1 absorption to increase brightness. We conduct a comparative analysis of the temperature sensing performance of Sm 2+ in BaFBr, BaFCl, SrFBr, and SrFCl and address the role of concentration, host, and Boltzmann equilibration. Different thermal coupling schemes, 5 D 1 - 5 D 0 and 4f 5 5d 1 - 5 D 0 , and temperature-dependent lifetimes enable accurate sensing between 350 and 800 kelvin. Differences in 4f 5 5d 1 - 5 D 0 energy gap allows optimization for a temperature range of interest. This type of Sm 2+ -based thermometer holds great potential for temperature monitoring in the wide and relevant range up to 500°C.