Thermally enhanced near-infrared luminescence in CaSc2O4: Yb3+/Nd3+ nanorods for temperature sensing and photothermal conversion

Abstract

Non-invasive photothermal therapy (PTT) is proposed as a powerful method for cancer treatment, in which a precise temperature monitoring is strongly recommended during the photothermal conversion process to prevent the damage of normal cells. Herein, ultra-sensitive optical thermometry with excellent resolution and outstanding light-to-heat conversion are simultaneously realized in CaSc2O4: Yb3+/Nd3+ nanorods. The temperature sensing of the nanorods is accomplished through fluorescence intensity ratio (FIR) technology based on the thermally coupled levels (TCLs) Nd3+: 4Fj (j = 7/2, 5/2, 3/2), of which the obtained absolute sensitivity is about 6.5 times larger than the optimal value of TCLs-based thermometers reported previously. Meanwhile, an intense thermal enhancement of Nd3+: 4Fj (j = 7/2, 5/2, 3/2) → 4I9/2 transition is found due to the efficiency improvement of phonon-assisted energy transfer process between Yb3+ ions and Nd3+ ions. The penetrability of the near-infrared light emitting by Nd3+ ions is determined by a simple ex vivo experiment, indicating a penetration depth of 8 mm in the biological tissues with negligible effect on FIR values. Beyond that, the nanorods show remarkable photothermal conversion capacity under the excitation of 980 nm wavelength. The properties mentioned above show enormous potentiality of the present nanorods for PTT along with a real-time temperature sensing.