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. Pr 3+ 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 Pr 3+, Ho 3+, and Yb 3+ -doped NaGdF 4 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 S r based on the Pr 3+ 1 G 4 → 3 H 5 and Ho 3+ 5 I 6 → 5 I 8 radiative transitions reached 2.4% °C –1 at 40 °C, while the maximal S r obtained using the single-band Pr 3+ emission was 0.8% °C –1 at 10 °C. These findings demonstrate the promise of Pr 3+ -doped nanoparticles as NIR-NIR nanothermometers for thermal sensing applications.