Twinkle Twinkle Little Star

As a kid, my father once bought home a set of glow-in-the-dark stars and planets. It really made me feel happy and wonder about how it is possible. I was too small and really didn’t understand how it all happens, how can something (that’s not powered by matches or electricity) glow even in the dark?

Why Do Glow-in-the-Dark Stickers Glow?

All thanks to chemists (researchers not the medicine shopkeepers ). Glow in the dark plastics and stickers contain phosphorescent chemical. Phosphorescent chemicals absorb light (and become excited, just like I was while looking at those stars) when they are charged using light energy or by placing them in bight light. They then slowly release all the light energy that they absorbed over an extended period of time (hence, the glow in the dark).

In the older days, the only known chemical that used to phosphoresce was zinc sulphide. It used to emit a green glow in the dark. It was the material that was present in my glow-in-the-dark stars. In modern times, newer and varied materials have been discovered that glow and provide various coloured “glows”. Here is a link to a website that sells these varied coloured glow-in-the-dark formulations.

According to many resources, the best and brightest glowing dark pigment is strontium aluminate doped with europium. Strontium aluminate glows significantly brighter and longer compared to zinc sulphide. It is also significantly expensive when compared.

When I was small, everyone used to say that the stars glowed because of Radium and reading more about that made me very interested and inspired by Marie Curie. So, learning that it was zinc sulphide came as a shock to me as I never imagined that zinc can glow. There are certain formulations, however, which use Radium, but they are generally unstable (as Radium is radioactive).