What makes glow in the dark toys and stickers glow

A.� All glow-in-the-dark products contain phosphors, a substance that radiates visible light after being energized.

�

Q.� What gives phosphors this special property

A.� It's the excitable nature of their atoms. Once energised the electrons in their atoms jump to a higher state, but they can't get rid of this energy and become 'stuck'. The only become unstuck once you stop energising them, by turning off the light, when they can return to their normal state by getting rid of their excess energy, radiating a glowing light as they do so.

�

Q.� How are they charged

A.� Phosphors can be charged in many different ways: with certain types of radiation, electron beams but the average glow in the dark tool is energised by holding it up to a light for a while.

Once energised they can glow for around 10 minutes. However some newer glow in the dark products can emit light for several hours.

�

Usually it is a soft green light, and it is not very bright. You need to be in nearly complete darkness to notice it.

�

Q.� Can any phosphor be used

A.� No, phosphors have particular properties: each requires a particular energy to energise it, produces a particular kind of light and glows for a particular length of time after being energised, known as the phosphors persisitence. Bearing this in mind only certain phosphors are suitable for glow toy and stickers.

�

Q.� And they are

A.� There are a couple of phosphors that can be energised by normal light and have a relatively long afterglow: Zinc Sulphide and Strontium Aluminate. These phosphors are mixed with the plastic before it is moulded into a toy.

�

Strontium Aluminate is the newer substance and the one that can glow for hours.

�

Q.� Are either Zinc Sulphide or Strontium Aluminate used to make the hands of my watch glow too

A.� No, the phosphor has been mixed with a radioactive element and the radioactive emissions energize the phosphor continuously so you don't have to charge your watch.

�

Interested in how something works Click here to post a question to The AnswerBank.

�

by Lisa Cardy