Figure 1
From: Upconversion Modulation through Pulsed Laser Excitation for Anti-counterfeiting
Composition and morphology characterization of the as-prepared nanoparticles. (a–c) TEM images of the as-synthesized nanoparticles: (a) NaYF4:Er/Tm (2/0.5%), (b) NaYF4:Er/Tm(2/0.5%)@NaYF4 and (c) NaYF4:Er/Tm(2/0.5%)@NaYF4:Yb (20%); (d–f) The size distribution of the corresponding nanoparticles: (d) NaYF4:Er/Tm (2/0.5%), (e) NaYF4:Er/Tm(2/0.5%)@NaYF4 and (f) NaYF4:Er/Tm(2/0.5%)@NaYF4:Yb (20%); (g) Schematic procedure for the synthesis of hexagonal NaYF4-based core-shell nanoparticles; (h) XRD patterns of the NaYF4:Er/Tm(2/0.5%), NaYF4:Er/Tm(2/0.5%)@NaYF4 and NaYF4:Er/Tm(2/0.5%)@NaYF4:Yb (20%) nanoparticles as indexed in accordance with hexagonal-phase NaYF4 crystal structure (Joint Committee on Powder Diffraction Standards file No. 16-0334).
