Glow In the Dark


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- story by MaterialDistrict

When entering the Materia archive in the dark it never is completely dark. Several yellow, green and blue materials shimmer on the shelves with glow in the dark effects. So what gives these materials this glamorous effects in the dark?

Phosphor is the most known luminescent material, but there are more. Calcium sulfide with strontium sulfide with bismuth as activator, yields blue light with glow times up to 12 hours, red and orange are modifications of the zinc sulfide formula. Red colour can be obtained from strontium sulfide.

Zinc sulfide with about 5 ppm of a copper activator is the most common phosphor for the glow-in-the-dark toys and items. It is also called GS phosphor. The mix of zinc sulfide and cadmium sulfide emit colour depending on their ratio; increasing of the CdS content shifts the output colour towards longer wavelengths; its persistence ranges between 1–10 hours.

Strontium aluminate activated by europium, is a newer material with higher brightness and significantly longer glow persistence; it produces green and aqua hues, where green gives the highest brightness and aqua the longest glow time. It is about 10 times brighter, 10 times longer glowing, and 10 times more expensive than the mix of zinc sulfide and cadmium sulfide.

In most applications, the phosphor is directly added to the plastic used to mold the product, or mixed with a binder for use as paints.

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