Figure 3
From: Morphology evolution and pure red upconversion mechanism of β-NaLuF4 crystals
UC emission spectra (normalized to Er3+ 540 nm emission) of (a) β-NaLuF4:20% Yb/xEr, (b) β-NaLuF4:20% Yb/0.5% Tm/xEr, and (c) β-NaLuF4:20% Yb/1% Tm/xEr (x = 0.5, 2, 5, 10, 20%) under 980 nm excitation. The insets of (a–c) show the corresponding R/G ratio as a function of Er3+ concentration.
