If you noticed that before, you might have seen the small "strips" on the minutes and hours arm on a desktop clock. The effect, Phosphorescence, is emmiting some of the energy absorbed before, and so if you keep the clock in a well lit room and then turn off the light, you'll see these tiny strips glow in the dark!
If this is somehow implemented in a wallpaint, you would be able to see the walls of your room glow at night, and you won't bump into them when walking! (That's true if you prefer turning off all the lights in your house before you sleep )
Radioactivity is a bad choice, you're talking about cancer and mental illness if this were to be real.
So if white phosphorus was somehow "dissolved" or "mixed in" with a paint, the painted surface would glow for a short time after the lights go out. Chemilumicsence wouldnt last for long, as the Phosphorus actually gets oxidized irreversibly.