Two-step ion-exchange synthetic strategy for obtaining monodisperse NaYF4:Ln3+ nanostructures with multicolor luminescence properties†
Abstract
Monodisperse β-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, or Yb/Tm) nanocrystals with multiform novel morphologies have been synthesized for the first time by a novel two-step ion-exchange route expressed as Y2(OH)5NO3·nH2O (LYH) → Y(OH)xF3−x → β-NaYF4. In step I (LYH → Y(OH)xF3−x), the Y(OH)xF3−x is fabricated using a one-pot method from the starting point of a unit layer at low temperature through a novel style of ion-exchange from LYH based on the special crystal structural similarity between the LYH unit layer and the Y(OH)xF3−x {0001} plane. Of particular interest is that the ion-exchange process in step I can be completed within the initial few minutes, and the unique two-dimensional layered structure of LYH greatly favors the ion-exchange reaction by exfoliating into atomically thick monolayers. Meanwhile, the identical structural framework between Y(OH)xF3−x and β-NaYF4 ensures the in situ ion-exchange reaction in step II. The composition of the intermediate precursor Y(OH)xF3−x can be tuned in a wide range, which gives the synthetic parameters high maneuverability and greatly simplifies the experimental variables. In addition, the luminescence properties showed that the as-prepared β-NaYF4:Ln3+ nanocrystals exhibited strong characteristic multicolor emissions through upconversion and downconversion.