Enhanced ultraviolet up-conversion emissions of Tm3+/Yb3+ codoped YF3 nanocrystals

Tm3+/Yb3+ codoped rod-like YF3 nanocrystals were synthesized through a facile hydrothermal method. After annealing in an argon atmosphere, the nanocrystals emitted bright blue and intense ultraviolet (UV) light under a 980-nm continuous wave diode laser excitation. Up-conversion emissions centered at ∼291 nm (1I6 → 3H6), ∼347 nm (1I6 → 3F4), ∼362 nm (1D2 → 3H6), ∼452 nm (1D2 → 3F4), ∼476 nm (1G4 → 3H6), ∼642 nm (1G4 → 3F4), and ∼805 nm (3H4 → 3H6) were recorded using a fluorescence spectrophotometer. Especially, enhanced UV emissions were studied by changing Yb3+/Tm3+ doping concentrations, the annealing temperatures, and the excitation power densities. A possible mechanism, energy transfer–cross relaxation–energy transfer (ET–CR–ET), was proposed based on a simple rate-equation model to elucidate the process of the enhanced UV emissions.