Radium mixed with copper-doped zinc sulfide produces a paint that will glow in the dark. The radiation from the decaying radium excited electrons in the doped zinc sulfide to a higher energy level. When the electrons returned to the lower energy level, a visible photon was emitted.
Glowing Radium Dial
This is a glowing radium painted dial from the 1950s.
Arma95, Creative Commons License
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