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I was wondering whether or not the reason some noble gases, like neon, fluoresce at particular frequencies of the visible spectrum is because of a Stokes effect? I mean, do the neon dimers get stretched out dramatically at a more LUMO state, resonating with high energy electricity due to the high stability of noble gases, and then contract back to a more HOMO state, releasing red light, which has a much lower frequency? Noble gases, like neon, have a high quantum yield, correct?

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  • $\begingroup$ From wikipedia: "The Ne*2 molecule exists in an excited state in an excimer lamp using a microhollow cathode. This emits strongly in the vacuum ultraviolet between 75 and 90 nm with a peak at 83 nm." $\endgroup$
    – Karl
    Jan 28 '20 at 18:08
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    $\begingroup$ Short answer: no. Please look at the spectra in the second figure in this recent answer chemistry.stackexchange.com/a/126980/79678 It is just a matter of excited atoms and ions emitting their characteristic color photons as they relax back to their ground states. In a simple Ne lamp bulb, Ne atoms are excited and ionized by the electric discharge in the bulb. Same in a He-Ne laser. $\endgroup$
    – Ed V
    Jan 28 '20 at 18:36
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Ed has already explained the main ideas. Stokes shift is associated with the concept when you excite a substance with light (or electromagnetic radiation). In neon discharge tubes you are using electrical energy to excite the neon atoms. All the emission you see is from neon atoms. Also recall, that molecular emission has band like structure. Neon light spectrum is nowhere close to this band structure.

enter image description here

Buy a small pocket spectroscope or build your own and see how the spectra look like. The black and white picture has not done justice to the actual extremely beautiful spectrum of Swan bands (observed due to diatomic carbon species).

Swan bands

a more LUMO state, resonating with high energy electricity due to the high stability of noble gases, and then contract back to a more HOMO state, releasing red light, which has a much lower frequency?

This has no scientific meaning, because molecules do not resonate with electricity or electrical energy. I do not know the exact mechanism how electrical energy or even heat is "transformed" into electronic energy, but electrical discharge is quite efficient at exciting atoms or molecules in the gas phase. I am sure it is quite complex, which involves ionization, collisions, recombination etc.

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