Chemiluminescence is the emission of light through a chemical reaction. A significant property of this form of emission is that it produces no heat. This lab will investigate the causes of chemiluminescence and will touch upon some of its specific characteristics.
• Light: Visible light is simply electromagnetic radiation. What makes the radiation visible is its wavelength—that is to say, the range of wavelengths. For light to be visible the wavelength must be between 400nm and 700nm (nm is nanometer or 10-9 meters). The term for any electromagnetic radiation is luminescence. Light can be generated in various forms, some are:
Incandescence: The emission of light due to heat (such as the light bulbs in your house which are essentially just resistors in your home electrical circuit).
Fluorescence and phosphorescence: The emission of light due to radiation energy (like in a TV or fluorescent light bulb).
Laser generation: The concentrated emission of light using stimulated emission.
All of the forms mentioned above work the same way: outside energy excites atoms which then release particles of light called photons. When an atom is excited the electrons go up in energy (and energy levels), when they fall back down to their normal spot, they release energy in the form of light photons. A lightstick uses the same principles, but creates light through a chemical reaction, hence chemiluminescence.
• Chemiluminescence: In nature, an example of chemiluminescence would be the firefly, which very efficiently creates light through a chemical reaction. Through industrial chemistry we have also created a similar form of emission; however, it is still not as efficient as that of a firefly. The most common reaction used in novelty toys like glowsticks is that of Cyalume with hydrogen peroxide. Peroxides give off a lot of energy in chemical reactions, and therefore would be perfect for such a precise and efficient reaction. Cyalume is in fact an oxalate ester (phenyl oxalate ester) which when mixed with hydrogen peroxide forms peroxyacid ester and phenol. The peroxyacid ester decomposes to form more phenol, and an energetic intermediate phase. As it decomposes into two CO2 molecules, it gives up its energy to a waiting dye molecule, which then fluoresces.
The following is a diagram that shows the reaction of the chemicals inclusing the intermediate steps as well as the interations with the dyes:
The equation itself is: cyalume +
H2O2 + dye → trichlorophenol +
2CO2 + dye[♦]
In the equation above the diamond [♦] represents the excited stage during which the chemicals give off light. There are other forms of chemiluminescnce where the excited stage is not the ultimate one, and therefore one must specify where in the chain of occurences light is actually produced.
This lab is very simple to do at home. Though the chemicals are not terribly difficult to buy separately, it is much easier to just buy a glowstick rather than the components that make it up. Glowsticks can be bought either at a local novelty or party store, or online. Just google the term glowstick and you will have multiple options.
Once you have the glowsticks (it should be in tube form, the thicker the better… no necklaces, etc.) the procedures are rather straightforward; however, there are still proper safety guidelines that should be followed. Cyalume can stain or cause harm to skin; therefore, it is important to have a clean and safe workspace and always wear goggles and gloves. Furthermore, this lab also has the dangers of fire and broken glass. We DO NOT take responsibility for any injuries or damages sustained from attempting this lab. Now that we’ve got that out of the way, here’s the lab:
Glowsticks work by mixing Cyalume with hydrogen peroxide to create light. However, to preserve the light during packaging and shipping, the chemicals are not premixed. Therefore, you must snap the cylinder when you want to activate it. The cylinder is full of hydrogen peroxide, and there is a glass vial full of Cyalume. When you snap the cylinder the vial shatters and the chemicals mix. We want to keep the vial intact.
• When you get the glowstick open the top of the tube with a box cutter. Be careful of the hydrogen peroxide and the vial.
• Pour the peroxide into a container and let the vial fall out. Then clean the vial and move it to another container. Then carefully break it and keep the Cyalume in container 2.
You now have the two ingredients for chemiluminescence.
The next step is to mix the chemicals. You will now be able to see them glow, but remember, from this point you only have a few hours of glow; however, through experimentation we found that there are a few things that affects the glow time. The concentration of Cyalume does change the rate of glow but more so the intensity. The main thing that changes this process is how it is attained. With different chemicals people have been able to create momentary burst of intense light through varied mixtures; however, Cyalume has been patented to glow for an extended amount of time in an efficient way. There is one way to easily regulate the lights intensity though, heat!
In keeping with the idea of electron movement with added and reduced energy (heat is energy) it is rather logical that heat would boost the intensity of the glow, and cold would do the inverse. This being said though, one can also logically infer that cold will actually preserve the glow. Try these at home and see what you find, or you can just peek below at our results!
The main work that could be tested on the mixture was the change in luminosity. We put our beaker over gauze and heated it gently, once we saw a few bubbles we stopped. In bird’s eye view photographs there is conclusive evidence that the hypothesis was right. In the image below it is clear that the light is more intense with added energy.
Nonetheless, to demonstrate the point, we found a more visual way to show it. Firstly, the shot from inside the beaker did not seem to visually convey the difference in intensity, and furthermore, a still image would not give you a perspective on time frame and effect. Therefore, we mixed the two chemicals again, put them in a syringe, and soaked a bounty paper towel. The towel held the chemicals brilliantly, and helped with the demonstration. We held up the towel while keeping a flame to it. We made sure that the towel did not catch fire, and the resulting video shows the phenomenon quite well.
Our Experiments & Research
If you have used any of this information or any of these images please go ahead and cite them in your bibliography. For your convenience, this is what the citation would look like in MLA format:
Family, Afrooz. “Science of Glowsticks.” December 24, 2004 Mad Physics. dd mmm. yyyy †
We are glad to share our knowledge with you as long as you cite all of our info, and contact us before you use anything for non-educational purposes (commercial, etc.).
† In the bibliography you must insert the day you visited the site (this is relevant because the site could change at some point), therefore, in the bibliography above replace dd with the day you visited, mmm with the abreviated month, and yyyy with the year (ex: dd mmm. yyyy becomes 23 Dec. 2004).