All elements exhibit characteristic spectral emission lines.
The predominant emission lines of a gas, like Neon, are also very sensitive to and dependent on the temperature of the gas. For gas with temperatures of a few thousand Kelvins, most of the lines are emitted in the visible portion of the spectrum, so only an optical telescope would be able to see such gas. The emission lines from gas with temperatures of approximately 100,000 Kelvins fall in the UV portion of the spectrum, and the emission lines from even hotter gas fall in the X-ray portion of the spectrum. In general, telescopes sensitive to higher energy photons see hotter gas.