How do excited mercury atoms emit radiation?
When the electrons in the mercury get more energy, they jump up into a higher energy orbital. Once they get there, they “want” to come back down to their original orbital for the atoms to have maximum thermodynamic stability (i.e. least energy arrangement). In the case of mercury, the energy difference between these two orbitals corresponds to that of a photon of X Rays (hence X Ray radiation is emitted from mercury vapor). If you are thinking of radiation other than of the EM spectrum, this happens due to nuclear processes (in the nucleus).
