Near-Infrared-to-Near-Infrared Optical Thermometer BaY₂O₄: Yb³⁺/Nd³⁺Assembled with Photothermal Conversion Performance

Nowadays, the construction of photothermal therapy (PTT) agents integrated with real-time thermometry for cancer treatment in deep tissues has become a research hotspot. Herein, an excellent photothermal conversion material, BaY₂O₄: Yb³⁺/Nd³⁺, assembled with real-time optical thermometry is developed successfully. Ultrasensitive temperature sensing is implemented through the fluorescence intensity ratio of thermally coupled Nd³⁺: ⁴F_j(j = 7/2, 5/2, and 3/2) with a maximal absolute and relative sensitivity of 68.88 and 3.29% K^-1, respectively, which surpass the overwhelming majority of the same type of thermometers. Especially, a thermally enhanced Nd³⁺luminescence with a factor of 180 is detected with irradiation at 980 nm, resulting from the improvement in phonon-assisted energy transfer efficiency. Meanwhile, the photothermal conversion performance of the sample is excellent enough to destroy the pathological tissues, of which the temperature can be raised to 319.3 K after 180 s of near-infrared (NIR) irradiation with an invariable power density of 13.74 mW/mm². Besides, the NIR emission of Nd³⁺can reach a depth of 7 mm in the biological tissues, as determined by an ex vivo experiment. All the results show the potential application of BaY₂O₄: Yb³⁺/Nd³⁺as a deep-tissue PTT agent simultaneously equipped with photothermal conversion and temperature sensing function.