Morphology Manipulation and Upconversion Luminescence Enhancement of β-NaLuF₄: Er³⁺ Hexagonal Microtubes via Sr²⁺ Doping

Figure 4

SEM images and corresponding HRTEM images and EDS analysis of intermediate products with different reaction time: (a–c) 0.5 h, (d) 2 h, (e) 5 h, and (f) 12 h.

(a)

(b)

(c)

(d)

(e)

(f)