Figure 4
From: Morphology evolution and pure red upconversion mechanism of β-NaLuF4 crystals
Double logarithmic relationship of (a,c) green and (b,d) red UC luminescence intensities versus pump powers in β-NaLuF4:20% Yb/0.5% Tm/xEr and β-NaLuF4:20% Yb/1% Tm/xEr (x = 0.5, 5, 20%) under 980 nm excitation.
