Tuning sub-10 nm single-phase NaMnF3 nanocrystals as ultrasensitive hosts for pure intense fluorescence and excellent T1 magnetic resonance imaging

We report ultrasensitive sub-10 nm NaMnF3 nanocrystals codoped with Yb3+, Er3+/Tm3+ ions, and their intense pure red and near-infrared upconversion emissions in the presence of Mn2+. The nanocrystals showed excellent T-1 contrast in 7 T MRI, implying their potential as single-phase contrast agents for fluorescent deep tissue and MR imaging.