Multicolor tunability and upconversion enhancement of fluoride nanoparticles by oxygen dopant

Abstract

The ability of manipulating upconversion luminescence of lanthanide-ion doped fluoride upconversion nanoparticles (UCNPs) is particularly important and highly required due to their widely applications in color displays, multiplexing bioassays and multicolor imaging. Here, we developed a strategy for simultaneously tuning color output and enhancing upconversion emission of Yb/Er doped fluoride UCNPs, based on adjusting oxygen doping level. The synthesis of multicolored multifunctional NaGdF4:Yb, Er UCNPs was used as the model host system to demonstrate this protocol. Ammonium nitrate (NH4NO3) was used as oxygen source and added into reaction system at the beginning stage of nucleation and growth process of fluoride UCNPs, which facilitates the formation of enough oxygen atoms and the diffusion of those into fluoride host matrix. The results revealed the multicolour output and upconversion enhancement mainly resulted from the variation of phonon energy and crystal field symmetry of host lattice, respectively. This strategy can be further expanded to other fluorides host matrices. As an example of the application, multicolored UCNPs were used as color converter in light emitting diodes, which can effectively convert near-infrared light into visible ones. It is expected these multicolored UCNPs are promising for applications in multiplexing biodetection, bioimaging (optical and magnetic resonance imaging) and other optical technologies, and the present method for the control of O2- doping may also be used in other functional nanomaterials.