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As we know neon or argon pipes do emit light (whatever range) if they are exposed to an electon current. So does potassium once evaporated in the common street lights.

Question: Does this apply to all gases or at least to homogenous gasess? with homogenous I intend stuff like Cl2 but not CO2. So does any gas emit light, if it is hit by electrons or do some refuse?

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It is not clear what you mean by "electron flow", because you do not specify the electron energy. Is it a beam from an accelerator or a beam "inside" an accelerator, i.e., in an external electric field?

If the atoms/molecules are effectively excited, then there is some radiation due to deactivation of excitations.

If there is no electron flow, but the gas is at the temperature $T$, it may radiate a black body radiation or a less powerful radiation if it is "thin" enough.

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  • $\begingroup$ The energy shall be arbitrary - so as much as you need. Just so that the atoms become excited. So they do all emit light - as you say. $\endgroup$
    – Robetto
    Sep 26, 2016 at 10:57
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Though slightly different, I think you want to look at the Frank-Hertz experiment. If the electrons get enough energy to ionize the gas atoms, then you will have light.

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