We report efficient dual-mode up-conversion (UC) and down-shifting (DS) emission in a single Yb3+/Er3+-co-doped -NaYF4 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 -NaYF4. Meanwhile, IEM gives rise to the significant enhancement of UC emission intensity up to 3800 times and strongly enhanced DS emission intensity of Er3+ and Yb3+ by several times in -NaYF4:Yb3+,Er3+ microcrystals. IEM also strongly prolongs the DS emission lifetimes of Er3+ and Yb3+ in visible and near-infrared region. The enhanced UC and DS emission intensities and prolonged lifetimes in -NaYF4:Yb3+,Er3+ are mainly ascribed to the dispersing of localized Yb3+ and Er3+ clusters during IEM.