Enhanced UC red emission in Ce3+/Yb3+/Ho3+ tri-doped Na5Lu9F32 single crystals

Abstract

The Na5Lu9F32 single crystals doped with Yb3+/Ho3+ in 1 mol%/6 mol% and various concentrations of Ce3+ (0, 1.0 mol%, 3.0 mol%, 6.0 mol%) for the up-conversion (UC) luminescence were prepared by an improved Bridgman method. Green and red UC emissions at 545 and 658 nm corresponding to the transitions of 5S2/5F4 → 5I8 and 5F5 → 5I8 of Ho3+ ions, respectively, were observed under 980 nm excitation. The emission color and relative intensity can be effectively adjusted from green to red by varying the Ce3+ concentration from 0 to 6 mol%. A nearly pure red UC emission at 658 nm can be obtained when Ce3+ content reaches 6 mol% and Yb3+/Ho3+ are hold at 1 mol%/6 mol%. Pump power dependent measure reveals that both UC emissions at 545 and 658 nm involve a two-photon process. The cross-relaxation processes of 5S2/5F4 (Ho3+) + 2F5/2 (Ce3+) → 5F5 (Ho3+) + 2F7/2 (Ce3+) and 5I6 (Ho3+) + 2F5/2 (Ce3+) → 5I7 (Ho3+) + 2F7/2 (Ce3+) between Ho3+ and Ce3+ ions are responsible for the quenching of green emission and the enhancement of red emission.