NIR‐II Afterglow from NIR‐Excitable Nanocomposites for Deep‐Tissue Bioimaging

ABSTRACT Persistent luminescent nanoparticles (PLNPs) have emerged as promising agents for in vivo bioimaging, offering advantages, among them excitation‐free imaging and high signal‐to‐noise ratio (SNR). However, conventional PLNPs are restricted by excitation‐emission wavelengths within the ultraviolet (UV), visible (300–650 nm), and near‐infrared I (NIR‐I, 650–900 nm) regions. This inherent limitation restricts tissue penetration depth, reduces imaging resolution, and poses phototoxicity risks from repeated excitation. Herein, we propose a covalently coupled nanocomposites (PLNPs/UCNPs) consisting of ZnGa 2 O 4 :Ni 2+ PLNPs with NaErF 4 :Yb 3+ ,Mn 2+ upconversion nanoparticles (UCNPs). Following 980 nm laser irradiation, two distinct optical phenomena are observed in this nanocomposite: prolonged NIR‐IIa (1290 nm) persistent luminescence and enhanced NIR‐IIb (1532 nm) down‐conversion luminescence. The NIR‐IIa afterglow is attributed to efficient energy transfer, whereby the red emission (668 nm) of upconverted UCNPs aligns with the 650 nm excitation peak of PLNPs, facilitating efficient Förster resonance energy transfer (FRET), while direct absorption of 980 nm photons by PLNPs further augments the NIR‐IIa afterglow. This design successfully circumvents the limitations imposed by bio‐optical windows. NIR excitation has been demonstrated to be a viable replacement for UV/visible sources for PLNPs, with dual NIR‐II emissions at 1290 and 1532 nm showing considerable promise in terms of their ability to synergistically integrate excitation‐free imaging, deep tissue penetration, and high SNR.