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 similar to 291 nm (I-1(6)-> H-3(6)), similar to 347 nm (I-1(6)-> F-3(4)), similar to 362 nm (D-1(2)-> H-3(6)), similar to 452 nm (D-1(2)-> F-3(4)), similar to 476 nm ((1)G(4)-> H-3(6)), similar to 642 nm ((1)G(4)-> F-3(4)), and similar to 805 nm (H-3(4)-> H-3(6)) 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. (c) 2007 Elsevier B.V. All rights reserved.