Persistent luminescence (PersL) in the second near-infrared window (NIR-II, 1000–1700 nm) holds promise for deep-tissue bioimaging and information storage owing to its superior light penetration and minimal background interference. However, current NIR-II PersL materials rely on high-energy ultraviolet/visible light or hazardous X-rays for charging, restricting their practical utility.

In a study published in Materials Today, a research team led by Prof. CHEN Xueyuan and Prof. ZHENG Wei from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a new class of NIR-I (700–1000 nm)-rechargeable multiwavelength NIR-II PersL phosphors.

Researchers engineered (Ln³⁺)-doped CaSnO₃ via Bi²⁺ sensitization, enabling direct charging with tissue-penetrating, low-energy NIR-I photons. Through detailed spectroscopic analysis, they revealed a tunneling-assisted upconversion-like trapping mechanism, and found that the Bi²⁺ ions served as deep electron traps.

Upon NIR-I irradiation, stored electrons tunneled from these deep traps to adjacent shallow traps introduced by Ln³⁺ co-doping, bypassing the conduction band. This phonon-assisted tunneling effectively mimicked an optical upconversion process but operated via a non-radiative charge migration pathway, enabling efficient storage of low-energy NIR-I photons.

By precisely regulating trap depth and distribution through Ln³⁺ doping, researchers achieved intense, multiwavelength NIR-II PersL spanning 1000–1600 nm, with afterglow persistence exceeding five hours after a single NIR-I excitation.

Utilizing this NIR-I rechargeability, researchers demonstrated CaSnO₃:Bi²⁺/Ln³⁺ nanoparticles as reversible NIR-II PersL nanoprobes for subcutaneous optical information encoding and high-contrast deep-tissue imaging in mice. An imaging depth of over 16 mm and a signal-to-background ratio of 19 were achieved. Notably, the PersL can be non-invasively and repeatedly replenished in situ by simple NIR-I illumination, enabling long-term dynamic monitoring.

This study not only advances the mechanistic understanding of PersL but also inspires the design of next-generation smart luminescent materials for interdisciplinary challenges in biomedicine and information technology.