Boosting NIR-II Luminescence via Ca2+-Formed Band Structure Modulation in Lanthanide-Doped Nanoparticles for Deep-Tissue Bioimaging

Lanthanide-doped nanoparticles with near-infrared-II (NIR-II, 1000-1700 nm) emission hold great promise for deep-tissue bioimaging, yet their luminescence efficiency is often limited by conventional sensitization pathways. Herein, we go beyond this conventional paradigm by introducing a Ca2+-formed band structure modulation in the host lattice to dramatically boost the NIR-II emission of lanthanide-doped nanoparticles. Rational doping of Ca2+ ions restructures the energy levels, enabling the probe to efficiently capture excitation energy and channel it toward NIR-II-emitting lanthanide activators. This Ca2+-induced band structure modulation mechanism not only enhances the absorption cross section but also accelerates energy transfer to the NIR-II-emitting states. As a result, the designed nanoprobes exhibit excellent photostability and a high quantum yield. In vivo bioimaging demonstrates that the resulting nanoprobes enable deep-tissue visualization with an improved signal-to-background ratio. This work establishes a sensitization strategy that goes beyond conventional approaches, positioning lanthanide-based NIR-II probes as promising candidates for advanced biological imaging.