Figure 3

Comparison of the up-conversion luminescence spectra of Er³⁺/Yb³⁺ doped Na₅Lu₉F₃₂ single crystals under 980 nm excitation at room temperature; the inset shows the integrated total intensity on Yb³⁺ concentrations in Er³⁺/Yb³⁺ doped Na₅Lu₉F₃₂ single crystals.