Supplementary Figure 1: Upconversion mechanism of the Yb,Er/Tm co-doped Ln-UCNPs.
From: Upconversion luminescence imaging of cells and small animals
Under excitation at 980 nm, an electron of Yb3+ is excited from the 2F7/2 to the 2F5/2 level. The energy may be transferred to Er3+/Tm3+ nonradiatively to excite it to the corresponding excited level. For Yb,Er co-doped Ln-UCNPs, the emission bands at 520, 540, and 654 nm may be assigned to 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 transitions of Er3+. For Yb,Tm co-doped Ln-UCNPs, the emission bands at 365, 451, 481, 646 and 800 nm may be assigned to 1D2→3H6, 1D2→3F4, 1G4→3H6, 1G4→3F4, and 3H4→3H6, respectively.
