I rolled back the edit because I really am looking for the following:
I am looking for an element or compound that would have a bright green emission when electrically excited and is a gas at between 1 torr and 4 torr. If such a compound could be nontoxic, that would be beneficial.
The pressure range is important.
I'm familiar with the emissions spectra of all the noble gases, but none of them work for me. I want to find such a compound to use in a Geissler tube, which will be excited with about 50kVac at 300 to 500kHz. I am capable of pulling a vacuum down to 0.2 torr, and I normally work between 1 torr and 4 torr.
I know of a Xenon/nitrogen mix that produces the desired color, but it's too fussy for me to achieve, and Xenon is too expensive for this purpose.
Relatedly, I was wondering why the Xenon/nitrogen mixture emits a green light. Neither Xenon or Nitrogen has much green at the appropriate pressure, but somehow the combination, within a narrow range of Nitrogen partial pressure, produces a bright green. What causes this color when the two compounds are mixed together, and how can I predict the color of a given mixture of gases at a given pressure?
I know of the bohr model and balmer series etc, but I don't understand how to apply that to compounds or mixtures of compounds. Is there some other way to predict the spectra produced by mixtures of gases?
It's not easy gettin' green! (Apologies to Kermit)