We should give the OP a break here. He is "guilty" of using inappropriate terminology, agreed, but his Physics is not misplaced. He just needs a 'symbol' which means "combined with in some way". I don't know of one
so he should have just used a verbal description.
If you pass a current though Mercury Vapour it will ionise some molecules. When the electrons recombine there will be Photons emitted. The direction of the current to excite this is defined by an external power supply and the ionisation is sustained by the fast electrons that are supplied at the electrodes.
However, although a beam of incident high energy EM (photons) will ionise some of the mercury atoms, the ions will have no preferred direction to go so you can't expect the system to produce an 'electric current' (i.e. to be a generator). The ions will just recombine and emit a range of EM frequencies.
But you could imagine a detector of X Rays, which consisted of a container with mercury vapour in it and a low voltage across it; not high enough to produce ionisation so it would be 'off'. When sufficient flux of X Rays hits the tube, enough ions will be produced for a measurable current to flow. It would strike an arc which could go on for ever unless the supply voltage is removed and the ions would recombine.
A
Geiger Muller tube works in this way but doesn't use Mercury Vapour, which needs to be heated to keep it from condensing. Low pressure Argon gas is commonly used. Also,the design of a GM tube allows very low energy particles through, to ionise the enclosed gas. But it's the same principle.
PS You need some form of 'diode' or one-way device for EM to generate a current in one direction. PV cells and phototransistors do this but not (afaik) ever with mercury.