Near‐Infrared Triggered Temperature Self‐Monitoring Photothermal Agents Cs₂NaBiCl₆:Nd³⁺, Yb³⁺@SiO₂@IR780

Abstract Chloride double perovskites have sparked significant interest and opened new avenues for luminescent materials hosts due to their lower phonon energy, flexible compositions, and excellent luminescent property. However, the instability to water has limited its fundamental applications, especially in the biological fields, although its stability has been improved in comparison with lead−based perovskites. Here, nanophosphor Cs₂NaBiCl₆: Nd³⁺, Yb³⁺ (CNBC: Nd³⁺, Yb³⁺) is prepared by a hot‐inject method, and then its stability to water is enhanced by coating a layer of SiO₂ shell. For improving its photothermal conversion ability, organic photothermal agents IR780 is adsorbed on the surface of CNBC: Nd³⁺, Yb³⁺@SiO₂ to form monodispersed temperature self−monitoring photothermal agents CNBC: Nd³⁺, Yb³⁺@SiO₂@IR780, where the temperature sensing property is based on the temperature−dependent lifetimes of Yb³⁺ and the photothermal conversion property comes from the synergistic effect of IR780 and the nonradiative transition of Nd³⁺ during luminescence. The maximum relative sensitivity and photothermal conversion efficiency of CNBC: Nd³⁺, Yb³⁺@SiO₂@IR780 reach 1.44% K⁻¹ at 280 K and 36.8%. Finally, the temperature detection and photothermal antimicrobial ability of CNBC: Nd³⁺, Yb³⁺@SiO₂@IR780 are evaluated through chicken tissue temperature measurement and photothermal ablation effect against Escherichia coli and Staphylococcus aureus (93.3% and 95.1%).