Up-conversion emission color tuning in NaLa(MoO4)2: Nd3+/Yb3+/Ho3+ excited at 808Â nm

As alternatives to Yb3+-sensitized up-conversion (UC) materials excited at 980 nm, Nd3+-sensitized UC phosphors irradiated by 808 nm have been used to decrease the absorption of water and alleviate the overheating effect in vivo biological application. Intense red and green UC emissions from 5F5→5I8 and 5F4/5S2→5I8 transitions of Ho3+ appeared in Nd3+/Yb3+/Ho3+ tri-doped NaLa(MoO4)2 through successive energy transfer Nd3+→Yb3+→Ho3+ under 808 nm excitation, in which Yb3+ ions were proven to be the energy transfer bridge between Nd3+ and Ho3+ by lifetime measurement. The variable emission color and intensity ratios of red to green emissions were realized by adjusting the doping concentration of Yb3+, pulse width of the excitation laser and the addition of Ce3+ ion, which depends on the different population pathways to the green and red emitting states of Ho3+. The chromaticity modulation mechanisms of these approaches were proposed, which provides a feasible strategy to tune the UC emission color.