Separation and phase transition investigation of Yb3+/Er3+ co-doped NaYF4 nanoparticles.

Density gradient ultracentrifuge separation was employed to study the phase transition of Yb(3+)/Er(3+) co-doped NaYF4 from α-phase to β-phase. It was found that the cubic α-phased NaYF4 was rich in Y, exhibited predominantly red luminescence, whilst the newly formed hexagonal β-phased NaYF4 had relatively higher Yb and Er atomic ratios, exhibited green luminescence most strongly.