Nd3+ activated CaF2 NPs as colloidal nanothermometers in the biological window

CaF2 nanoparticles activated with Nd3þ ions have been investigated as potential optical nanothermometers in the biological windows. The variation of the Nd3þ emission around 850 and 1060 nm as a function of the temperature has been measured. A ratiometric approach, based on the relative changes in the intensities of different emission bands of the Nd3þ has been considered to investigate the thermometric properties of the NPs. The evaluated thermal sensitivity is around 0.12% K1, a value that is similar to those found for other water dispersible nanothermometers based on the near-infrared luminescence of the Nd3þ lanthanide ion. The temperature uncertainty is around 1.8 C, small enough to monitor the local temperature during a photothermal treatment