Tm3+-Based Downshifting Nanoprobes with Enhanced Luminescence at 1680 nm for In Vivo Vascular Growth Monitoring

Optical imaging in the 1500-1700 nm region, known as near-infrared IIb (NIR-IIb), shows potential for noninvasive in vivo detection owing to its ultrahigh tissue penetration depth and spatiotemporal resolution. Rare earth-doped nanoparticles have emerged as widely used NIR-IIb probes because of their excellent optical properties. However, their downshifting emissions rarely exhibit sufficient brightness beyond 1600 nm. This study presents tetragonal-phase thulium-doped nanoparticles (Tm