Near-Infrared Persistent Luminescence in a Cr3+-Doped Perovskite for Low-Irradiance Imaging

Near-infrared (NIR) persistent luminescence (PersL) materials are attractive multifunctional-material-platforms to real-time-required studies and applications in chemistry and biomedicine. However, the inefficient charging by low-irradiance, noncoherent, and high-tissue-penetration red–NIR light restricts their developments and applications in situ, such as long-term tracking, whole-body, and deep-tissue bioimaging. To address this issue, we develop a novel Cr3+-activated Na0.5Gd0.5TiO3 NIR-PersL material with perovskite structure. It shows over 100 times stronger PersL intensity than those of the best known Cr3+-doped phosphors, including ZnGa2O4, Zn3Ga2GeO8, Zn3Ga2Ge2O10, and LiGa5O8, with low-irradiance (∼2.5 μW·mm–2) and noncoherent red light (laser-free) charging. Based on the structural and spectroscopic studies, we reveal a novel one-photon charging mechanism in the constructed host referred binding energy (HRBE) schemes, which differs from the regular two-photon one of those Cr3+-doped gallates. The host conduction band minimum (CBM) plays a critical factor in the charging efficiency and the charging-required photon numbers. Tissue-penetration verification and in vivo bioimaging demonstrated the potentials of realizing renewed and high signal-to-noise ratio (SNR) in situ imaging with low-irradiance (∼19 μW·mm–2) and noncoherent red–NIR charging. The one-photon charging concept will contribute to the new mechanism to guide the design of the high-tissue-penetration NIR-PersL imaging probes with laser-free and low-irradiance red–NIR excitation.