Enhancing upconversion luminescence of NaYF4: Yb/Er nanocrystals by Mo3+ doping and their application in bioimaging

Enhancement of upconversion luminescence is imperative for the applications of upconversion nanocrystals (UCNs). In this work, we investigated the upconversion luminescence enhancement of NaYF4:Yb/Er by Mo3+ ion doping. It was found that the upconversion luminescence intensities of the green and red emissions of UCNs co-doped with 10 mol% Mo3+ ions were enhanced by 6 and 8 times, respectively. This enhancement offers a potential increase in the overall detectability of upconversion nanocrystals. HeLa cell imaging using NaYF4:Yb/Er/Mo as luminescent probes showed bright upconversion fluorescence. Moreover, the Mo3+ doping endowed the UCNs with excellent paramagnetic behavior. It is expected that the as-prepared UCNs with a high upconversion luminescence and excellent paramagnetic properties could be promising bi-functional nanoprobes for sensitive multi-modal bioimaging and other optical applications.