# How do things glow in the dark?

What makes something glow in the dark? The only explanation that I can come up with for what makes things glow in the dark is that there is probably a chemical reaction slowly releasing the light that was previously absorbed. Am I correct?

How does this phenomenon work?

• – Todd Minehardt Aug 26 '15 at 21:07
• Related Why does zinc sulfide glow? – user15489 Aug 26 '15 at 21:07
• – ron Aug 27 '15 at 0:06
• It depends on exactly what you're looking for. The mechanism that powers, say, chemical glowsticks is different from the one that powers children's glow-in-the-dark toys, which is in turn different from the one that powers the glow on old-school watches. – chipbuster Aug 27 '15 at 17:37

When a glow stick breaks, it breaks a thin glass barrier on the inside that allows two different substances to come into contact, mix and react. I am not sure of the exact reaction that occurs, but when chemical bonds are broken they can emit photons (light). In this case, the photons emitted are in the visible spectrum.

The case for glow in the dark stickers is a bit different. All things are absorbing and releasing photons constantly, but in most cases, the photons aren't in the visible spectrum. Glow in the dark things absorb visible light and then release the photons as visible light. This is unlike most other objects which may release them as a lower frequency instead and thus not be visible.

• so is it creating the chemical bonds when they absorb photons and destroying them again when it releases them? – Vince Scalia Aug 27 '15 at 16:38
• In this case, the photons are absorbed by the electrons of the atoms and it excites them into a higher orbit. However, electrons have a certain orbit that they are "most comfortable" and will try to stay there, also called the ground state. Soon after the electron absorbs the photon, it will release it to return to its ground state. Depending on the substance, it will release it at various wavelengths, not necessarily the same wavelength it absorbed it at. Hope this helped :) – Ryan Aug 30 '15 at 21:11
• So the electrons release the light when they return to the valence shells? thanks! – Vince Scalia Aug 31 '15 at 0:51
• exactly so @vincentScalia – Ryan Aug 31 '15 at 0:59
• "in most cases, the photons aren't in the visible spectrum": When you shine light on objects, they do reflect light - that is how we can see their colors. The key to glow in the dark stickers is that they absorb visible light and somehow store that energy, releasing even after the lights are turned off. – Karsten Theis May 20 at 16:02

The spontaneous emission of light by a substance not resulting from heat is luminescence (a type of cold-body radiation). $$\ce{^1}$$

A few types of luminescence are:

• Bioluminescence: Made by living creatures such as fireflies, glow-worms, and many marine creatures.
• Chemoluminescence: made by a chemical reaction. Glow sticks work this way.
• Electroluminescence: made by passing electricity through something like in a light emitting diode (LED).
• Photoluminescence: made by shining light at "luminous" (phosphorescent) paints.
• Röntgenoluminescence: made by shining X-rays at things. (The curious name comes from Wilhelm Röntgen (1845–1923), the discoverer of X-rays.)
• Sonoluminescence: made by passing energetic sound waves through liquids.
• Thermoluminescence: made when photons are emitted from hot materials.
• Riboluminescence: made by rubbing, scratching, or physically deforming crystals.
• Phosphorescence: photoluminescence as a result of triplet-singlet electronic relaxation (typical lifetime: milliseconds to hours)

A chemical absorbs and then re-emits a photon of light, where the energy of the photons matches the available energy states and allowed transitions of the chemical takes place. In phosphorescence, the electron that absorbs the photon undergoes intersystem crossing $$\ce{^2}$$ into a triplet state.

The excited in triplet state returns to the lower energy singlet state. Such transitions, are kinetically unfavored and progress at a slow rate. Most phosphorescent compounds are fast emitters with triplet lifetimes in milliseconds. If triplet lifetimes are minutes or even hours, very slow degradation occurs.$$\ce{^3}$$ $$\ce{^4}$$ In phosphorescent materials, there's a delay between them absorbing energy and giving out light.These substances are so-called "glow-in-the-dark" materials.

To make glow-in-the-dark toys manufacturers mix zinc sulfide or strontium aluminate with plastic giving in glow-in-the-dark toys.$$\ce{^5}$$ $$\ce{^6}$$

Fluorescence

Fluorescent materials produce light instantly, when the excited atoms return to normal, in as little as a hundred thousandth of a second.$$\ce{^4}$$ $$\ce{^7}$$

Chemoluminescence

In the case of chemiluminescence, two chemicals interact which giving energy as a byproduct in the form of light( heatless glow).

When glow sticks are bent, an inner glass tube is broken releasing hydrogen peroxide. Hydrogen peroxide reacts with diphenyl oxalate giving 1,2dioxetanedione, which is unstable. It decomposes to carbon dioxide releasing energy. The energy is absorbed by electrons in dye molecule, that falls down to ground state releasing energy in the form of light.$$\ce{^8}$$ $$\ce{^9}$$

Chemiluminescence can happen naturally as well. In such instances — like fireflies — it is bioluminescence.

Some creatures, such as fireflies and jellyfish, contain chemicals within them that cause them to glow. Some of these creatures glow for protection, camouflage or to attract mates.

Ex 1.Bobtail squid $$\ce{^12}$$ $$\ce{^13}$$

Ex.2 Mycena lampadis ( mushrooms )$$\ce{^14}$$

The principal chemical reaction in bioluminescence involves some light-emitting molecule and an enzyme, generally called the luciferin and the luciferase.$$\ce{^10}$$ $$\ce{^11}$$ $$\ce{^15}$$

Electrochemiluminescence $$\ce{^16}$$is a special form of chemiluminescence in which the light-emitting chemiluminescent reaction is preceded by an electrochemical reaction.$$\ce{^17}$$

References

• just wanted to mention dioxetane should have a bond between the cyclic oxygens. – Blaise May 21 at 9:03
• @ Blaise it is a software error ,will be correted – Chakravarthy Kalyan May 21 at 9:05
• @Melanie Shebel noted.The question is so fabulous and vast that i concentrated on the bioluminescence in vast .My attempt was to bring that beauty that entwines chemistry to living that have developed these millions of years ago.While we try to anslyse it now. Perfection is desired but to bring beauty was my attempt. – Chakravarthy Kalyan May 22 at 9:01
• Understood, but it's very important to give credit to the photo author and not a third party that posted the photo. It's good practice to get as close to the original source as possible. I will edit the answer shortly to give the proper citation. – Melanie Shebel May 23 at 0:17
• @WilliamR.Ebenezer because the gas example is actually incandescence. – A.K. May 23 at 16:42

The glow in the dark phenomena is called luminescence. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. Three of the common mechanisms are:

1. Fluorescence: Light is emitted during the excitation with invisible electromagnetic radiation.
2. Chemoluminescence: A chemical reaction radiates energy in for of electromagnetic radiation (e.g. glow sticks, luziferase reaction,...)
3. Phosphorescence: You can read about the quantum mechanical processes here. There is one interesting thing I want to point out. While the most phosphorescent materials are solid, in this paper, they have reported the synthesis and afterglow of water-soluble ZnS:Cu,Co nanoparticles.

I know Wikipedia is not at all a reference, but there you can find an overview of all types of luminescence.

Reactions emits energy in different forms. Could be heat, light or electrical. If the form emited is light energy form it surely will glow irrespective of the external environmental characteristics in this case dark!