Hydrothermal Synthesis of β-NaYF4:Yb, Er Nanocrystals with Upconversion Fluorescence Using Tetraethylene Pentamine as Chelating Ligand

Figure 6

FE-SEM images of NaYF₄:Yb, Er nanocrystals prepared under different reaction times: (a) 2 h; (b) 4 h; (c) 6 h; (d) 8 h; (e) 10 h (RE/TEPA = 1 : 1; water/ethanol = 1 : 1; 16.7 mmol/L).

(a)

(b)

(c)

(d)

(e)