There’s already been a few posts on glow in the dark materials, but I investigated the specific mechanism behind what produces a glow. Specifically, what makes things glow in the dark?
Most glow in the dark items are made with phosphors. A phosphor is any substance that releases visible light in response to radiation. An incoming radiation particle collides with an atom or molecule, exciting an electron. The electron then emits the extra energy as a photon (the most elementary particle of light, a particle with zero mass.) This property of an object, by the way, is known as luminescence, the emission of light not resulting in heat, which itself is a form of cold body radiation.
Radiation probably sounds scary to you, because some types are dangerous, but not all types of radiation will set your spidey senses tingling. Radiation is simply the term for the emission of energy in electromagnetic waves or as subatomic particles. Those particles often cause ionization, as described above. In the case of glow in the dark materials, that ionization is occuring when incoming light excites an electron.
Often the radiation that allows glow in the dark items to glow is the same radiation we’re exposed to on a daily basis – UV rays from the sun. Two materials most often used are Zinc Sulfide and Strontium aluminate.
Zinc Sulfide is a common pigment. When combined with a bit of activator, it is used as a phosphor in many products. Different activators produce different colored glows – silver results in a bright blue, manganese an orange-red, and copper produces the most familiar greenish glow, which, incidentally, is the longest lasting of the three.
Here’s a cool video on how to make your own!
Strontium aluminate is widely considered superior to Zinc Sulfide. It’s a newer development that produces a brighter and longer lasting glow, though it’s slightly more expensive to manufacture. Strontium aluminate glows green or aqua, and the type of glow can be modified by changing its crystal structure. When manufactured to glow brighter, the glow is typically shorter lasting. The relationship is shown in this nifty graph: