Enhanced UC red emission in Ce~(3+)/Yb~(3+)/Ho~(3+)tri-doped Na_5Lu_9F_(32) single crystals

摘要

The Na5Lu9F32 single crystals doped with Yb3+/Ho3+ in 1mol%/6mol% and various concentrations of Ce3+ (0, 1.0mol%, 3.0mol%, 6.0mol%) for the up-conversion (UC) luminescence were prepared by an improved Bridgman method. Green and red UC emissions at 545 and 658nm corresponding to the transitions of S-5(2)/(F4I8)-F-5-I-5 and (F5I8)-F-5-I-5 of Ho3+ ions, respectively, were observed under 980nm excitation. The emission color and relative intensity can be effectively adjusted from green to red by varying the Ce3+ concentration from 0 to 6mol%. A nearly pure red UC emission at 658nm can be obtained when Ce3+ content reaches 6mol% and Yb3+/Ho3+ are hold at 1mol%/6mol%. Pump power dependent measure reveals that both UC emissions at 545 and 658nm involve a two-photon process. The cross-relaxation processes of S-5(2)/F-5(4) (Ho3+)+F-2(5/2) (Ce3+)F-5(5) (Ho3+)+F-2(7/2) (Ce3+) and I-5(6) (Ho3+)+F-2(5/2) (Ce3+)I-5(7) (Ho3+)+F-2(7/2) (Ce3+) between Ho3+ and Ce3+ ions are responsible for the quenching of green emission and the enhancement of red emission.