Figure 4

Decay curves of the Er³⁺/Yb³⁺ co-doped Na₅Lu₉F₃₂ single crystals surveyed at 548 nm under 980 nm excitation, and the inset is the decay times centered at 525, 548 and 668 nm for 1.0% Er³⁺/8% Yb³⁺ co-doped Na₅Lu₉F₃₂ single crystal.