摘要： Visualization of tumor vessels/metastasis and cerebrovascular architecture is vital important for analyzing pathological states of brain diseases and tumor's abnormal blood vessel to improve cancer diagnosis. In vivo fluorescence imaging using second near infrared emission beyond 1500 nm (NIR-IIb) is emerged as a next generation optical imaging method with significant improvement in imaging sensitivity and spatial resolution. Unfortunately, highly biocompatible probe capable of generating NIR-IIb emission with sufficient brightness and uniformed size is still scarce. Here, we have proposed the polyacrylic acid (PAA)-modified NaLnF4:40Gd/20Yb/2Er nanorods (Ln=Y, Yb, Lu, PAA-Ln-NRs) with enhanced downshifting NIR-IIb emission, high quantum yield (QY), relative narrow bandwidth (~160 nm) and high bio-compatibility via Ce3+ doping for high performance NIR-IIb bioimaging. The downshifting emission beyond 1500 nm is improved by 1.75~2.2 times with simultaneously suppressing the upconversion (UC) path in Y, Yb, and Lu hosts via Ce3+ doping. Moreover, compared with the traditionally used Y-based host, the QY of NIR-IIb emission in Lu-based probe in water is improved from 2.2% to 3.6%. The explored bright NIR-IIb emitted PAA-Lu-NRs were used for high sensitivity small tumor (~ 4 mm)/metastatic tiny tumor detection (~ 3 mm), tumor vessel visualization with high spatial resolution (41 μm) and brain vessel imaging. Therefore, our findings open up the opportunity of utilizing lanthanide based NIR-IIb probe with bright 1525 nm emission for in vivo optical-guided tumor vessel/metastasis and non-invasive brain vascular imaging.