Saturday, July 4, 2015

ChEmIcAmAzInG - Glowing in the dark

It's so magical...
A night at the disco. Flashing colors all around. A little glowing bracelet around your wrist. The music is so loud you don’t care about everything. But maybe a little question makes its way into your mind…How does this stuff glow? Well, here I am to tell you why.

All the glowing in the dark products contain a chemical structures called phosphors. This name is given to any substance that emits light after being energized in some way. Thousands of chemicals can be classified as phosphors. The great variety of chemicals with this property permits lots of degrees of brightness, color, and length of time they glow after being energized.

A phosphorescent eagle
There are three main types of ways these phosphors can absorb energy and then releasing it: Phosphorescence, Chemiluminescence and Radioluminescence.

Phosphorescent structures, most common for glow in the dark items, are things like the glow in the dark stars many people put on their ceilings, giving a room a magical atmosphere.  These items absorb light radiation and then re-emit the stored light energy over some period of time, at some level of brightness. So the best phosphorescent glow in the dark items are able to store a bit of this light, not all of it, and emit it back out relatively slowly, so it glows longer, because glowing for two microseconds is not so impressing.

To be a little be more specific, this process mostly happens extremely quickly (10 nanoseconds to absorb and emit).  In this special case of phosphorescence, the absorbed light energy transitions to a higher energy state, where it’s trapped. Returning to a lower energy state takes time, and in certain phosphorescent compounds the higher energy state can last minutes or even hours, allowing these compounds to effectively store light energy for a long time. The longer the higher state lifetime, the longer it glows.

Another class of glow in the dark objects is the chemiluminescent variety.  These items glow because of an actual chemical reaction. In this reaction, the interaction between the reagents produces and releases energy. Sometimes this reactions have a fluorescent dye that will convert this energy, usually releasing the light in the UV spectrum, into another form of light that is visible to humans (the visible spectrum). The result is items glowing in different colors.

Have you ever heard of the glow stick? Of course you have. Well, this is the perfect example of a chemiluminescent glowing object. Inside a glow stick there is a sealed glass vial containing some chemical.  This is enclosed inside the plastic glow stick container that contains a different chemical and a fluorescent dye. In order to get it to glow, you have to crack the vial, which releases the chemical it contains. The mixture of the chemicals then reaches the plastic container.   When the chemical reaction starts, it produces energy, then converted by the dye to visible light that is re-emitted….and there you have it! A glow stick in all the colors you want…of course you have to choose the right dye.

So light is not caused by heat in chemiluminescence. But heat does effect it. You can try an experiment to verify this. If you put the glow stick in the freezer, the chemical reaction goes slower and slower and the low temperature produces a dimmer glow that lasts longer.  On the other hand, you can put a glow stick in boiling water and you will see it gets brighter and brighter as the chemical reactions happen faster, but won’t glow for a long time. This phenomenon is common in living creatures and is called Bioluminescence (if you want to learn something about it, go check out this process in Fireflies.)

A tritium energized stick
The radioluminescent objects are the least used of the group. This because the reaction is not very common. In fact, these glowing items work with a mixture of phosphors and a radioactive element. Some radioactive emissions come out of the element and energize the phosphor continuously during the entire life of the element.  Some watches glow using this method. The three most common radioactive materials used here are Radium, which has a half-life of 1600 years. Tritium, which has a half-life of 12 years. Promethium, an artificial element which has a half-life of about 3 years. So the glowing lasts for a long time…a very long time.

Very interesting reactions, don’t you think? I hope you liked it and remember….Never Stop Snooping Around <3


  1. Oh, so that's how it is. I used to buy glow in the dark stickers for the bedroom. I like it when I turn off the light and then my room looks like I'm surrounded by constellations with the glowing stars around me.

    I think this is a wonderful invention.

    1. I used to have the glow-in-the-dark stars stickers for the wall. Every night was magic!! Sure is an outstanding invention :D


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