Persistent Luminescent Nanoparticles with Enhanced Near-Infrared-II Afterglow via Mn²⁺/Ho³⁺ Energy Transfer for High-Resolution Bioimaging

Near-infrared-II (NIR-II) emitting persistent luminescent nanoparticles (PLNPs) hold great potential for in vivo bioimaging due to their advantages of noninvasive excitation, high signal-to-noise ratio (SNR) and deep tissue penetration. However, the afterglow duration of NIR-II PLNPs without ionizing radiation excitation remains relatively short. Here, we designed dual-ion-doped, energy transfer-based, dual-wavelength emitting Zn3Ga2Ge2O10:0.3%Mn2+,0.5%Ho3+ (ZGGO:Mn,Ho) PLNPs through a one-step hydrothermal method. Upon excitation with 254-nm UV light, energy transfer from Mn2+ to Ho3+ significantly enhanced the afterglow intensity in the NIR-II region and extended the afterglow duration from the initial 30 min to 90 min. To improve water solubility, the PLNPs were further modified with polyethylene glycol (PEG) and successfully applied for NIR-II in vivo bioimaging. This energy transfer strategy for enhancing NIR-II afterglow provides a versatile approach for the design of advanced luminescent nanoprobes.