Fig. 2

a UC emission spectra from a single β-NaYF₄:Yb/Er (20/2 mol%) microcrystal doping with 0, 10, and 30 mol% Mn²⁺ ions under the excitation intensity of 1.59 kW cm⁻². b CIE chromaticity coordinates for the UC luminescence of the single β-NaYF₄:Yb/Er (20/2 mol%) microcrystals doping with different amounts of Mn²⁺ ions. c UC emission spectra from a single β-NaYF₄:Yb/Er (20/2 mol%) microcrystal doping with 0, 10, and 30 mol% Mn²⁺ ions under the excitation intensity of 95.52 kW cm⁻²