We demonstrate a fourfold increase of the output energy of the gain-switched mid-IR Fe:ZnSe laser. Iron doping of the ZnSe polycrystalline samples was realized using a postgrowth thermal-diffusion method from the metal film. Gain-switched Er:Cr:YSGG (2:8 μm) laser pumped Fe:ZnSe lasing was studied in a Fabry-Perot cavity over a 236-300K temperature range. The maximum output energy reached 4:7 mJ at 4:3 μm and 3:6 mJ at 4:37 μm at 236K and 300K and was limited only by available pump energy. The laser threshold was about 8 mJ and was practically unchanged over the studied temperature range. The laser slope efficiencies, measured with respect to the input pump energy, decreased from 19% to 16% with an increase of temperature from 236 to 300K. The output radiation featured a Gaussian spatial profile with M2 = 2:6. © 2011 Optical Society of America.