Near‐Infrared Light‐Activated Trap Filling and Luminescent Modulation in Inorganic Photochromics for Penetrable Luminescent Imaging

ABSTRACT Inorganic photochromic materials (IPCs) with luminescent modulation show promising potentials in anti‐counterfeiting and biological imaging. However, existing IPCs can only be effectively activated by high‐energy ultraviolet (UV)/visible (Vis) light or potentially risky x‐ray irradiation, often suffering from severe photobleaching, photodamage, and low penetration. Herein, we present a universal strategy to generate near‐infrared light‐driven trap filling and luminescent modulation behaviors in IPCs, via the energy transfer upconversion (ETU) design. Upon 980 nm irradiation, the synthesized NaNbO 3 :Er 3+ /Yb 3+ displays large luminescent modulation ratio (Δ R t > 80%) and fast response speed to NIR light (10 s, 92%), comparable to or better than those of UV/Vis light irradiation. The designed components exhibit deep‐tissue penetrable luminescent imaging, which is unable to be achieved for existing IPCs. The upconversion‐mediated strategy is quite robust, and can be extended to other systems, by leveraging the ETU process of up‐converting ion pairs (Ln 3+ /Yb 3+ ) to fill the traps and trigger photochromic reaction. Subsequently, the excited state energy of activators is captured by trap centers via a fluorescent resonance energy transfer (FRET), then resulting in luminescent modulation. This work sheds new light on designing NIR light‐driven IPCs, and will contribute substantially to high‐level optical storage and biological applications.