Mid-IR emission characteristics of low-phonon erbium-doped ternary chloride-based single crystals

摘要

The mid-infrared fluorescence properties of erbium (Er) doped low-phonon ternary chloride-based crystals (KPb_2Cl_5, Cs_2HfCl_6, CsPbCl_3, CsCdCl_3) have been investigated. All crystals were grown by vertical Bridgman technique. Following optical excitations at 805 nm and 660 nm, all Er~(3+) doped chlorides exhibited infrared emissions at ～2750, ～3500, and ～4500 nm at room temperature. The mid-infrared emission at 4500 nm originating from the ~4I_(9/2)→~4I_(11/2) transition showed long emission lifetime values of ～7.8 ms and ～11.6 ms for Er~(3+) doped Cs_2HfCl_6 and CsCdCl_3 crystals, respectively. In comparison, Er~(3+) doped KPb_2Cl_5 and CsPbCl_3 demonstrated shorter lifetimes of ～3 ms and ～1.8 ms, respectively. The temperature dependence of the ~4I_(9/2) decay times was performed for Er~(3+) doped CsPbCh and CsCdCl_3 crystals. We observed that the fluorescence lifetimes were nearly independent of the temperature, indicating a negligibly small non-radiative decay rate through multiphonon relaxation, as predicted by the energy gap law for low phonon energy hosts. The room temperature stimulated emission cross-sections for the ~4I_(9/2)→~4I_(11/2) transition were determined to be in a range of ～0.14-0.54 × 10~(-20) cm~2 for the studied Er doped chloride crystals.