Optical Temperature-Sensing Performance of Nd 3+ :MF 2 (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 (Nd ³⁺ :MF ₂ ; 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 Nd ³⁺ 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. Nd ³⁺ :CaF ₂ 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 CaF ₂ for optical thermometry is superior to that of β-NaYF ₄ , 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.
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