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

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.