aka...science room
glow stars
The eerie green glow of glow stars is due to phosphorescence. Substances called phosphors absorb energy from light and then slowly release it again over a period of time.
There are many different types of phosphors but zinc sulphide and strontium aluminate are the ones most commonly used for glow-in-the-dark toys and stickers.
Electrons surround the nucleus of an atom in a series of separate energy levels. An electron has to have a particular amount of energy to be in a particular energy level.
When a phosphor absorbs some radiant energy such as visible light or UV rays, the energy makes some of the electrons jump up to a higher energy level. While the electrons are in this higher energy level, the phosphor is storing the energy.
The electrons cannot hold onto their extra energy for ever and eventually fall back down to their original energy levels, releasing the stored energy as visible light. However, it is only when the energy source is removed, eg you turn off your bedroom light, that you can see the light that is being emitted.
This release of visible light can continue for minutes, hours or even days depending on the chemical structure of the phosophor.
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