Growth and spectroscopic properties investigation of Er:LuYAG and Er/Eu:LuYAG single crystal fibers used in mid-infrared lasers

Er ³⁺ doped laser crystals emitting at ∼3 µm mid-infrared (MIR) waveband have been intensively studied for their essential roles in surgery, military and other fields. In this work, Er: LuYAG and Er/Eu: LuYAG single crystal fibers (SCFs) were successfully grown by micro-pulling-down method for the first time. The as-grown SCFs demonstrated high crystalline quality and excellent transmittance. The distribution of the doping ions was proven to be uniform by XRF and EPMA measurements. The effect of Eu ³⁺ deactivator on the spectroscopic properties was systematically investigated and the spectra parameters were calculated using Judd-Ofelt (J-O) theory. The luminescence decay curves illustrated that the co-doping of Eu ³⁺ reduced the fluorescence lifetime of ⁴I _11/2 upper level and ⁴I _13/2 lower level simultaneously, making the lifetime ratio τ( ⁴I _11/2)/τ( ⁴I _13/2 ) in Er/Eu:LuYAG SCF greater than 1, so that the necessary population inversion can be maintained. It can be speculated that the co-doping of Eu ³⁺ deactivator can effectively suppress the self-terminating bottleneck problem, which is beneficial to realize the ∼3 µm MIR laser output.