Ionic liquid-assisted synthesis of Yb3+-Tm3+ codoped Y7O6F9 petal shaped microcrystals with enhanced upconversion emission

Abstract Petal-like Yb 3+ -Tm 3+ codoped Y 7 O 6 F 9 microparticles were achieved via ionic liquid-assisted (IL) hydrothermal process. The emission efficiency of Y 7 O 6 F 9 :Yb 3+ /Tm 3+ powders is much stronger than that of Y 2 O 3 :Yb 3+ /Tm 3+ sample. Under excitation at 980 nm with an unfocused laser beam under weak pump density of ∼0.1 W/cm 2 (pump power 10 mW), the UC emission of the sample can been seen clearly. Four emission bands at 477, 540, 647 and 692 nm are observed and correspond to the 1 G 4 state to 3 H 6 state, 1 D 2 state to 3 H 5 state, 1 G 4 sate to 3 F 4 state, and 3 F 3 state to 3 H 6 state transition of Tm 3+ ions. The enhanced UC emission is related to high crystallinity and lower effective phonon energy of oxyfluorides. The ionic liquid (IL) of [BMIM][BF 4 ] is used both as the reaction medium and the source of F − .