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I've noticed that many glow-in-the-dark objects you can purchase in the store are green. Occasionally I would come across something that was orange or blue, but mostly it seems that green is the ubiquitous glow-in-the-dark color.

Does this have anything to do with common wavelengths of light emitted from the relaxing of electrons in some of the more common phosphorescent compounds? Are some phosphorescent compounds just more readily available or "safe" for use in toys?

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    $\begingroup$ Maybe most glow-in-the-dark things are based on the same active molecule? $\endgroup$
    – Ivan Neretin
    Commented May 19, 2019 at 7:24
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    $\begingroup$ Google for glow stick for some of them and zinc sulphate , strontium aluninate for the others. $\endgroup$
    – Alchimista
    Commented May 19, 2019 at 9:58
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    $\begingroup$ There are only a small number of really good, cheap phosphorescent materials for long lasting phosphorescent behaviour. Zinc sulphide is cheap and dominates novelty products, strontium aluminate lasts longer and dominates professional signage. Both are green. Most other colours are achievable with other materials but why use them if you don't need a different colour. So the basic explanation for the preponderance of green is economics not chemistry. $\endgroup$
    – matt_black
    Commented May 25, 2019 at 9:15

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The human eye is most sensitive in green wavelengths. Therefore, if one were to put the same amount of light energy into different wavelengths, the green portion of the spectrum would appear brightest, though it contained no more energy than the rest.

If a phosphor or glow-stick manufacturer is seeking the "greatest bang for the buck", i.e. the most light for the least amount of chemical, green is a good choice.

There is a variety of phosphor colors, such as these listed in Wikipedia:

  • Red: Yttrium oxide-sulfide activated with europium is a red phosphor used for CRT's.

  • Yellow: Zinc cadmium sulfide (Zn,Cd)S:Ag, emits yellow light.

  • Green: Zinc sulfide with copper, ZnS:Cu, emits green light, ~530 nm. It was widely used in CRT oscilloscopes and radar displays because of its long persistence and simple chemistry. It is known as phosphor P31.

  • Blue: Zinc sulfide with few ppm of silver, ZnS:Ag,emits blue light with peaking at 450 nm. It is known as phosphor P22B and, unlike ZnS:Cu, has a very short persistence, so is suitable for slit-photography CRT's.

For a more complete list of phosphors and their colors, see this useful PDF or Phosphor Technology.

Many stores carry a variety of inexpensive chemiluminescent products, such as glow-in-the-dark necklaces and bracelets, in colors ranging from red through violet.

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