We report a room temperature Fe:ZnSe laser in gain-switched operation and tuning over the 3.9 - 4.8μm spectral range. Mid-IR emission of Fe 2+:ZnSe was studied under three regimes of excitation: ordinary optical (2.92μm) excitation of 5T2 excited state of Fe2+; excitation via 5E level of Cr co-dopant (1.56μm); and excitation via photo-ionization transition of Fe2+ (0.532μm). The energy transfer from Cr2+ (5E level) to Fe 2+ (5T2 level) under 1.56μm wavelength excitation was observed and resulted in simultaneous room temperature emission of Fe:Cr:ZnSe crystal over ultra-broadband spectral range of 2-3 and 3.5-5μm. We also report the observation of mid-IR emission at 3.5-5μm induced by 2+->3+->2+ ionization transitions of the iron ions in Fe:ZnSe. © 2005 Optical Society of America.