Radon, a radioactive inert gas, will, when superheated, begin thermionic emission . Let's put some in a container we can see through (with nothing else to interfere) and heat… it up. Ready? Let's do it..
Electrons most loosely bound to the radon nucleus will move to the next higher available Fermi energy level (meaning the atom will ionize), and then the electrons will fall back to their original energy levels with the emission of a photon. The radon will be glowing - emitting light. The phenomenon will be repeated; more and more atoms of radon will become involved in the process. At first the light will be in the infrared spectrum and we will not be able to see it unaided. At higher heats, electrons are driven to higher and higher energy levels, and when they "fall back" into their orbitals, the will emit shorter and shorter wavelengths (higher and higher frequencies) of light in making the transition. Some reds, oranges, yellows and other colors on up the frequency spectrum will be given off by the glowing gas, but not necessarly all the colors..
Radon is an unstable (radioactive) inert gas. And it has a short half-life. Let's assume that no radioactive decay occurred during our little experiment. We wouldn't want to have to deal with any of the radioactive daughters of radon that might appear and "mess up" our light show..
If the question spoke to the shortening of the half-life of radon by superheating it, that is, if you want to make radon undergo radioactive decay faster by superheating it, set that notion aside. You can't affect its rate of decay by superheating radon. Oddly, almost all isotopes of all elements show a uniform resistance to having their half-lives changed by superheating them. We find little to no evidence of changes in half-lives of radioisotopes in stars, which are massive spheres of plasma that are hot almost beyond imagining. (MORE)