Optical Temperature‐Sensing Performance of Nd3+:MF2 (M=Ba, Ca, Sr) Crystalline Powders Prepared by Combustion Synthesis

There is a large interest in luminescent materials for application as temperature sensors. In this scenario, we investigate the performance of neodymium‐doped alkaline‐earth fluoride (Nd3+:MF2; M=Ba, Ca, Sr) crystalline powders prepared by combustion synthesis for optical temperature‐sensing applications based on the luminescence intensity ratio (LIR) technique. We observe that the near‐infrared luminescence spectral profile of Nd3+ changes with the temperature in a way that its behavior is suitable for optical thermometry operation within the first biological window. We also observe that the thermometric sensitivities of all studied samples change depending on the spectral integration range used in the LIR analysis. Nd3+:CaF2 presents the largest sensitivity values, with a maximum absolute sensitivity of 6.5×10−3/K at 824 K and a relative sensitivity of 1.71 %/K at human‐body temperature (310 K). The performance of CaF2 for optical thermometry is superior to that of β‐NaYF4, a standard material commonly used for optical bioimaging and temperature sensing, and on par with the most efficient oxide nanostructured materials. The use of thermometry data to help understand structural properties via Judd‐Ofelt intensity standard parameters is also discussed. Optical temperature sensing: Nd3+:CaF2 phosphor shows an excellent performance as an optical temperature sensor for operation within the first biological window. The temperature sensitivity obtained by the luminescence intensity ratio methodology depends on the luminescence intensity integration interval of the spectrum in a two‐channel signal division detection system.