Description of Chemiluminescence

     Chemiluminescence is the process whereby energy from a chemical reaction is released directly as light without the involvement of heat or flame. Chemiluminescence is not similar to fluorescence (neon signs), phosphorescence (glow in the dark toys), or incandescence (light bulbs), but most similar to bioluminescence. The most common example of this process is the bioluminescence of the firefly!

      The firefly is by far the most efficient example of a bioluminescent system discovered to date. It approaches a theoretical limit by producing 88 photons of light for each 100 molecules of reactant yielding an astonishing 88% efficiency rate! Modern research into chemiluminescence has led to discoveries of dozens of light producing chemical reactions,
but most of them are only about 1% efficient. To give you another example, a light bulb is only about 10% efficient at converting electrical energy to light with the rest of the energy producing heat. It goes to show you that Mother Nature is an efficient user of energy!

     Fireflies use two different chemicals to produce light. The one that produces the light is generically called a "luciferin" and the one that drives or catalyzes the reaction is called a "luciferase." ATP (Adenosine triphosphate) and oxygen are also involved in the reaction. ATP is the chemical that, at the cellular level, provides energy for living things. Because of this, firefly luciferin can be used as a bio-indicator of the presence of energy or life! Bet you didn't know your glow light novelties had so much in common with Mother Nature!

     The main importance of chemiluminescence is in the fact that it is a cold system. Energy in the form of light is produced directly from the chemical reaction without first going through an intermediate stage involving heat. Chemiluminescent glow products never heat up, are not a source of ignition, and are non flammable. This is why modern science wished to copy the firefly! Glow products have an abundance of uses as a cold, portable, light source and are an excellent source of SAFE FUN.

     Chemical glow light products are all very similar. Each product is composed of a flexible outer casing typically made of plastic. Inside the casing is a chemical fluid usually a phenyl oxalate ester and a fluorescent dye. Also inside the casing, floating in this fluid is a thin walled glass ampoule. The glass ampoule typically contains hydrogen peroxide dissolved in phthalic ester. The hydrogen peroxide mix is stored inside the glass ampoule in order to keep it from mixing with the phenyl oxalate ester and starting the light producing chemical reaction. When the glow product is activated by bending it, the thin-walled glass ampoule breaks and its contents mix with the solution outside. Then, the hydrogen peroxide reacts with the phenyl oxalate ester. There have been dozens of reactions discovered to date, and one of them is shown below for a peroxyoxylate system.

     An intermediary is formed during the oxidation reaction that has a high-energy four-member ring. The breakdown of this intermediary transfers energy to the dye molecule, placing the dye molecule into an excited state. The dye molecule fluoresces, as it returns to its ground state, by giving off a photon of light. This is the visible light of the glow product. 

     An interesting point to note is that if the dye molecule can be placed into its excited state through some other means, such as laser excitation, the glow product will produce the same light effect as the dye returns to its ground state and fluoresces!

Classroom Experiment

     The following is a description of an experiment that is suitable for the classroom. It should only be conducted with the close supervision of a qualified teacher.

     By combining a luminescent solution with an oxidizing solution, a bright blue light source is created. To make the luminescent solution, combine:

4 g sodium carbonate
0.2 g luminol
24.0 g sodium bicarbonate
0.5 g ammonium carbonate
0.4 g copper (II) sulfate pentahydrate
1 L distilled water.
Mix to dissolve.

     For the oxidizing solution, dilute 50 mL of 3% hydrogen peroxide to 1 L.

     Mix about 200ml of each of the two solutions in an Erlenmeyer flask or, let the students mix small quantities of each solution at their own desks, and watch for the cool blue glow!

     This experiment uses luminol as the fluorescer, which is a slightly different system than the chemical system used inside a typical glow light product, but the principle is the same. As a side note, luminol is also used in forensic crime scene analysis, whereby it helps identify dried blood by reacting with it and fluorescing!