Optical spectroscopy and laser parameters of Zn2+/Er3+/Yb3+-tridoped LiNbO3 crystal

The Zn/Er/Yb:LiNbO3 and Er/Yb:LiNbO3 crystals were grown by the Czochralski technique. The laser characteristics of 1.54 μm emission were predicted based on the Judd–Ofelt theory, and the intensity parameters Ωt (Ω2=7.23×10−20 cm2, Ω4=3.15×10−20 cm2 and Ω6=1.43×10−20 cm2) were obtained. The stimulated emission cross sections (σem) at 1.54 μm emission in Zn/Er/Yb:LiNbO3 were calculated based on the McCumber theory and the Füchtbauer–Ladenburg theory. The gain cross section spectrum of Zn/Er/Yb:LiNbO3 crystal was also investigated. Under 980 nm excitation, a lenghthening lifetime of 1.54 μm emission and an enhancement of green upconversion emission were observed for Zn/Er/Yb:LiNbO3 crystal. The studies on the power pump dependence and the upconversion mechanism suggested that both green and red upconversion emissions were populated via the three-photon process, and Zn2+ ion tridoping increases the probability of cross relaxation process between the two neighboring Er3+ ions.