Visible and ultraviolet upconversion emission in LiNbO3 triply doped with Tm3+, Yb3+, and Nd3+

Visible and ultraviolet upconversion (UC) emission is observed under 800 nm femtosecond laser excitation in LiNbO3 crystals triply doped with Tm3+, Yb3+, and Nd3+ at room temperature. Energy transfer (ET) from Nd3+ to Yb3+ then to Tm3+ is very important in this UC emission process. The overlapping between the emissions of D-1(2) -> F-3(4) and (1)G(4) -> H-3(6), which makes up of blue emission band, is confirmed by transient investigation. From the pump energy dependence investigation, it is known that the dominant populating mechanism for the (1)G(4) state is the two-photon process, and that for D-1(2) is the three-photon process. In our UC emission model, the (1)G(4) state is populated by the ET of F-2(5/2)(Yb3+) + H-3(4)(Tm3+) -> F-2(7/2)(Yb3+) + (1)G(4)(Tm3+), D-1(2) state is populated by the ET of F-3(2) + H-3(4) -> D-1(2) + H-3(6) among Tm3+ ions. For LiNbO3 crystals doped with Tm3+ to the concentration of 0.9 mol %, the measured lifetimes of (1)G(4) and D-1(2) are similar to 80 and 4 mu s. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062152]