Mid-IR photoluminescence of Fe2+ and Cr2+ ions in ZnSe crystal under excitation in charge transfer bands

Spectroscopic characterization of Fe: ZnSe(Cr: ZnSe) crystals under visible excitation into the charge transfer bands of Transition Metal ions were studied. The excitation efficiencies of mid-IR photoluminescence between T-5(2)(E-5) and E-5(T-5(2)) states via direct relaxation to the upper laser levels and via metastable upper T-3(1) were investigated. It was demonstrated that the latter route is the dominant process for Cr2+ ions and could provide sufficient pump rate for mid-IR lasing. The pump efficiencies via direct relaxation to the upper laser levels were estimated to be < 2% for both ions under 532 nm excitation wavelength. (C) 2015 Optical Society of America