Enhancing Thermal Sensitivity of NIR‐IIb Lanthanide Nanothermometers for In Vivo Luminescence Nanothermometry via Erbium Sublattice‐Mediated Energy Recycling

Abstract Luminescent nanothermometers, particularly with working wavelengths in the NIR‐IIb region (1500–1700 nm), can provide low‐invasive, high‐resolution deep tissue temperature imaging, with great potential for early disease diagnosis and timely therapeutic intervention. However, designing an NIR‐IIb luminescent nanothermometer with high thermal sensitivity in the physiological temperature range remains challenging. Herein, an erbium s ublattice‐ m ediated e nergy r ecycling (SMER) strategy is proposed for nanoparticle microenvironment regulation, significantly enhancing the thermal sensitivity of NIR‐IIb emission. In detail, doping energy trapping centers to regulate the internal lattice environment endows the NIR‐IIb luminescence with temperature responsiveness through cross‐relaxation. Furthermore, by incorporating external medium environmental modulation, the e nvironment q uenching a ssisted d ownshifting (EQAD) process suppresses energy migration (EM) between Er 3+ ions and thereby facilitates energy transfer between Er 3+ and Tm 3+ ions. Within the physiological temperature range, the relative thermal sensitivity (S r ) can reach up to 3% °C −1 (10 °C), which is ≈3 times that of the traditional low erbium‐doped structure, and is the highest value of luminescent nanothermometer currently used for in vivo temperature imaging in the NIR‐IIb region. This study provides deep insight into the downshifting temperature response mechanism within the erbium sublattice structure, offering great potential for advancing deep tissue accurate temperature imaging.