We present the results of investigations of an emission of a mercury monobromide exciplex in gas-discharge plasma of an atmospheric pressure barrier discharge based on a mixture of mercury dibromide vapor, sulfur hexafluoride, and helium. We optimized the emission power of mercury monobromide exciplexes with respect to the partial pressures of the working mixture. An average emission power of 0.42 W (λmax = 502 nm) is achieved in a cylindrical emission source with a small working volume (0.8 cm3) at a pumping pulse repetition rate of 6 kHz. We determined electron energy distribution functions, transport characteristics, specific discharge power losses for electron processes, electron concentration and temperature, as well as rate constants of elastic and inelastic scattering of electrons by components of the working mixture in relation to the ratio of the field strength to the total concentration of components of the working mixture. We discuss processes that increase the population of the mercury monobromide exciplex. Gas-discharge plasma created in a mixture of mercury dibromide vapor with sulfur hexafluoride and helium can be used as a working medium of an emission source in the blue-green spectral range for the use in scientific research in biotechnology, photonics, and medicine, as well as for creating indicator gas-discharge panels.