The long-wavelength region of the near-infrared-IIb (NIR-IIb, 1,500–1,700 nm) imaging window has become an ideal window for in vivo imaging due to the suppressed photon scattering and near-zero autofluorescence of biological tissues. Therefore, it is necessary to develop fluorescent probes with excellent fluorescence performance and stability for NIR-IIb fluorescence imaging. In this work, zinc-doped silver telluride quantum dots (Zn:Ag₂Te QDs) with bright fluorescence in the NIR-IIb window were synthesized. The introduction of Zn dopants inhibited crystal defects and reduced non-radiative transitions. Therefore, the quantum yield and fluorescence lifetime of Zn:Ag₂Te QDs were significantly improved. In addition, Zn-doping increased the number of ligands on the surface of QDs, thus enhancing the colloidal stability of Zn:Ag₂Te QDs. Moreover, the PEGylated Zn:Ag₂Te QDs with high absolute quantum yield realized noninvasive imaging of cerebral vascular of mouse with high resolution able to distinguish blood capillary, which could be utilized to monitor the brain condition of mice after traumatic brain injury.

Lead sulfide (PbS) quantum dots (QDs) are important near infrared (NIR) luminescent materials with tunable and strong emission covering a broad NIR region. However, their optical properties are quite sensitive to air, water, and high temperature due to the surface oxidation, thus limiting their applications in optoelectronic devices and biological imaging. Herein, a cation-doping strategy is presented to make a series of high-quality Zn-doped PbS QDs with strong emission covering whole second near-infrared window (NIR-II, 1,000-1,700 nm). First-principle calculations confirmed that Zn dopants formed dopant states and decreased the recombination energy gap of host PbS. Notably, the Zn dopants significantly improved the quantum yield, photoluminescence lifetime and thermal stability of PbS QDs. Moreover, the PEGylated Zn-doped PbS QDs emitting in the NIR-IIb window (1,500-1,700 nm) realized the noninvasive imaging of cerebral vascular of mouse with high resolution, being able to distinguish blood capillary. This material not only provides a new tool for deep tissue fluorescence imaging, but is also promising for the development of other NIR related devices.