Multicolor-tunable emissions of YOF: Ln3+ /Yb3+ (Ln3+ = Ho3+, Er3+, Tm3+) nanophosphors

Color tuning of down-shifting and up-conversion emissions of YOF:Ln(3+)/Yb3+ (Ln(3+) = Er3+, Tm3+) nanophosphors is demonstrated. Nanophosphors were prepared by the modified sol-gel Pechini method and characterized by the X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Samples consist of 20 nm particles crystallized in the rhombohedral crystal structure. Depending on the Ln(3+) / Yb3+ concentration ratio and the type of excitation (UV/VIS or NIR) color of the particles emission varied from the blue to red. Commission Internationale de L'Eclairage chromaticity coordinates of emission colors are given for the range of Ln(3+)/Yb3+ concentration ratios for both down-shifting and up-conversion luminescence. We showed that the emission color of these nanophosphors may be additional tuned by simultaneous excitation with UV-VIS and NIR radiation (in different proportion) which yields unique color labels for the anti-counterfeit and security applications.