Efficient dual-mode up-conversion and down-shifting emission in β-NaYF4:Yb3+,Er3+ microcrystals via ion exchange

We report efficient dual-mode up-conversion (UC) and down-shifting (DS) emission in a single Yb 3+ /Er 3+ -co-doped β-NaYF 4 microcrystals with controlled morphology and size via a simple Na + ion-exchange modification (IEM) method. IEM well preserves the crystal structure and monodispersed morphology of hydrothermal-synthesized β-NaYF 4 . Meanwhile, IEM gives rise to the significant enhancement of UC emission intensity up to 3800 times and strongly enhanced DS emission intensity of Er 3+ and Yb 3+ by several times in β-NaYF 4 :Yb 3+ ,Er 3+ microcrystals. IEM also strongly prolongs the DS emission lifetimes of Er 3+ and Yb 3+ in visible and near-infrared region. The enhanced UC and DS emission intensities and prolonged lifetimes in β-NaYF 4 :Yb 3+ ,Er 3+ are mainly ascribed to the dispersing of localized Yb 3+ and Er 3+ clusters during IEM.