Praseodymium-Doped Nanoparticles: Candidates for Near-Infrared-II Double- and Single-Band Nanothermometry

Luminescent nanothermometers with high spatial and thermal resolution are desirable for a wide range of temperature-sensing applications. Lanthanide-doped nanoparticles can be excited by and emit light in the near-infrared (NIR) region, rendering them ideal candidates for NIR nanothermometry. Pr3+ has demonstrated thermal sensing ability in the NIR region but only when excited by UV–visible light. Here, we propose a series of NIR-I excited Pr3+, Ho3+, and Yb3+-doped NaGdF4 core/multishell nanoparticles for double- and single-band ratiometric nanothermometry operating in the NIR-II region. Thermal sensing ability was demonstrated in organic and aqueous dispersions as well as for powders. The Sr based on the Pr3+ 1G4 → 3H5 and Ho3+ 5I6 → 5I8 radiative transitions reached 2.4% °C–1 at 40 °C, while the maximal Sr obtained using the single-band Pr3+ emission was 0.8% °C–1 at 10 °C. These findings demonstrate the promise of Pr3+-doped nanoparticles as NIR-NIR nanothermometers for thermal sensing applications.