Energy transfer and 1.8 μm emission in Er3+/Tm3+ co-doped fluorogermanate glasses

The 1.8 μm down-conversion emission properties of Er3+/Tm3+ co-doped fluorogermanate glasses are investigated under 980 nm laser diode (LD) excitation in this paper. The glass properties are systematically evaluated by DSC, XRD, Raman techniques. The spectroscopic properties of Er3+ and Tm3+ including infrared down-conversion (DC) and visible up-conversion (UC) emissions are studied in detail. Meanwhile, the up-conversion emissions at 542 nm, 654 nm of Er3+ are suppressed with a high amount of Tm2O3 added. The Judd-Ofelt parameters and spontaneous transition probability of Tm3+ are illustrated for radiative properties. Besides, the absorption and emission cross sections of Tm3+ in Er3+/Tm3+ co-doped fluorogermanate glasses are provided as potential candidates for mid-infrared applications. The possible energy transfer mechanism is investigated via simplified energy level diagram, and energy transfer efficiency from Er3+ to Tm3+ is as high as 85.9%. In addition, the energy transfer parameters between Er3+ and Tm3+ are analyzed by the phonon sideband theory. The results indicate that the Er3+/Tm3+ co-doped fluorogermanate glasses have potential applications in mid-infrared lasers.