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

CaF2 nanoparticles activated with Nd3+ ions have been investigated as potential optical nanothermometers in the biological windows. The variation of the Nd3+ 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 Nd3+ has been considered to investigate the thermometric properties of the NPs. The evaluated thermal sensitivity is around 0.12% K−1, a value that is similar to those found for other water dispersible nanothermometers based on the near-infrared luminescence of the Nd3+ lanthanide ion. The temperature uncertainty is around 1.8 °C, small enough to monitor the local temperature during a photothermal treatment.