Oxalic Acid-Assisted Hydrothermal Synthesis and Luminescent of Hexagonal NaYF₄:Ln³⁺ (Ln = Sm, Eu, Yb/Er) Micro/Nanoplates

Figure 4

SEM images of the NaYF₄ products after different time at pH = 6, 200°C: (a)  h; (b)  h; (c)  h; (d)  h.

(a)

(b)

(c)

(d)