Enhanced ~3 μm mid-infrared emissions of Ho3+ via Yb3+ sensitization and Pr3+ deactivation in Lu3Al5O12 crystal

Abstract

Ho: LuAG, Yb, Ho: LuAG and Yb, Ho, Pr: LuAG laser crystals with high optical quality were successfully grown by the Czochralski method. Compared with Ho: LuAG and Yb, Ho: LuAG crystals, Yb, Ho, Pr: LuAG crystal not only shows a better absorption characteristic but also exhibits weaker ~2 μm emission, as well as superior mid-infrared (MIR) at ~3 μm emission. The ~3 μm MIR emission intensities of Yb, Ho, Pr: LuAG under excitation of a common 970 nm laser diode (LD) is almost nine times that of the Ho: LuAG crystal and twice as much as that of the Yb, Ho: LuAG crystal. The crystal growth, absorption spectra, J-O parameters, emission spectra, fluorescence lifetimes and the energy transfer mechanism in Yb, Ho, Pr: LuAG crystal were studied in this work. The energy transition efficiency from the lower laser level of Ho3+: 5I7 to Pr3+: 3F2 level is as high as 66.6%, indicating that the Pr3+ ion is an effective deactivation ion for Ho3+ ion in Lu3Al5O12 crystal. All these results show that Yb, Ho, Pr: LuAG crystal may become a promising material for developing solid state lasers at around 3 μm under a conventional 970 nm LD pump.