Figure 9.

a–d) TEM micrographs and size distribution of β‐NaGdF₄:Yb,Er core UCNPs and β‐NaGdF₄:Yb,Er@NaYF₄ core/shell UCNPs with different shell thickness prepared by hot injection method. Reproduced with permission.128 Copyright 2013, American Chemical Society. e–i) TEM images and size distribution of NaYF₄:Yb,Er core NCs and NaYF₄:Yb,Er@NaYF₄ core/shell NCs with different shell thickness via seed‐mediated Ostwald ripening. Reproduced with permission.129 Copyright 2012, American Chemical Society. j–s) TEM images, HRTEM images and their corresponding 3D schematic diagram of NaYF₄:Yb,Er core and those overcoated with 1–4 layers of NaGdF₄ shell, respectively. Reproduced with permission.19 Copyright 2013, Royal Society of Chemistry.