Trivalent Yb/Ho/Ce tri-doped core/shell NaYF4 nanoparticles for tunable upconversion luminescence from green to red

(a) UC emission spectra, (b) R/G ratio, and (c) the digital images of colloidal core NaYF4:Yb3+/Ho3+ nanocrystals doped with 0 mol.%, 4 mol.% and 10 mol.% Ce3+ under 980 nm diode laser of 50 W/cm2 successively