Fig. 1. XRD diffraction patterns of Na₃ScF₆:Yb/Er nanocrystals synthesized under different reaction temperatures

Fig. 2. Transmission electron microscope (TEM) patterns of Na₃ScF₆:Yb/Er samples obtained at different reaction temperatures
(a): 260 ℃; (b): 280 ℃; (c): 300 ℃

Fig. 3. Transmission electron microscope images of NaScF₄:Yb/Er samples with different soaking times
(a): 0 min; (b): 30 min; (c): 60 min; (d): 90 min

Fig. 4. Under 980 nm excitation at room temperature, (a) up-conversion fluorescence spectra of samples and (b) luminescence photos from Canon camera

Fig. 5. Schematic energy diagram of Yb³⁺, Er³⁺ of UC process under 980 nm excitation