Glow sticks are a fascinating example of chemiluminescence—a form of light emission that takes place without an external light or heat source. In contrast to other light-emitting processes, such as fluorescence or phosphorescence, chemiluminescence produces light through a direct chemical reaction.

This reaction is also responsible for the glow of many creatures, such as fireflies or deep-sea fish. Their biochemical variant is known as bioluminescence. Such creatures use the glow to communicate, find a partner or attract prey.

The principle of glow sticks is based on a chemical reaction between two liquids that only come into contact when the stick is bent. There is a glass tube inside, which breaks when bent and releases a reaction partner. This liquid mixes with the outer solution and starts the chemical reaction.

The main components of the chemical reaction in glow sticks are typically:

• Hydrogen peroxide as an oxidizing agent.
• Phenyl oxalate ester, which reacts with the hydrogen peroxide.
• A fluorescent dye that determines the final color of the light.

The temperature has a strong influence on the intensity and duration of the glow. If a glow stick is placed in an icebox, for example, the chemical reaction slows down and it glows much longer, but less brightly. In hot water, on the other hand, it glows more intensely but for a shorter time.

Durchführung der Spektroskopie

One of our DIY spectrometers with fiber optic coupling and the following data was used to record the spectra:

• Arrangement: Czerny-Turner
• Focal length: 150 mm
• Slit size: 10 µm
• Grating: 300 lp/mm
• Detector: e9u-LSMD-1304-STD line scan camera with 3648 pixels
• Resolution: 0.17 nm/Pixel
• Light guide: Toslink

The glow sticks were carefully opened to remove the liquids they contained. These were filled into a cuvette for the measurement, in front of which the light guide was then positioned directly.

The recorded spectra show relatively broad emission bands, as is typical for fluorescent organic molecules, in which the fluorescence results from a large number of vibronic transitions. In some cases, two dyes are also contained in a bending light in order to generate the resulting light by additive color mixing.

Conclusion

The investigation of glow sticks with the DIY spectrometer is not only an exciting experiment for demonstrating chemical processes, but also offers the opportunity to learn basic spectroscopic techniques. Glow sticks are an impressive example of how chemical energy can be converted directly into visible light—without any external power source.

With this experiment, students and other interested parties can gain direct access to the fascinating world of chemistry and spectroscopy and discover that science can not only be educational, but also entertaining!

If you would also like to perform the experiment and need help setting up the spectrometer or carrying it out, please contact us. We are happy to help!

Blue bend light

Green bend light

Yellow bend light

Orange bend light

Red bend light

Violet bend light

Mixing glow sticks

Exciting experiments can also be carried out by mixing the liquids of two different glow sticks. This does not always result in a mixed color from a resulting additive color mixture, as might be expected.

In the case of the glow sticks used for this application description, for example, a mixture of the liquid of the yellow glow stick with that of the blue glow stick continued to glow yellow while the blue glow disappeared completely.

There are several possible explanations for this, which could be investigated further:

1. Energy transfer (FRET-like effect):
   When the emission spectrum of the blue component overlaps into the absorption region of the yellow component, non-radiative energy transfer may occur. This means that the blue energy is absorbed by the yellow fluorophore and then re-emitted as yellow light.
2. Internal filter effects:
   A high degree of absorption of the yellow solution in the blue range can cause the blue light to be absorbed “inside” the solution before it reaches the detector. As a result, the blue signal appears greatly attenuated or disappears completely.
3. Chemical interactions:
   When the two systems are mixed, chemical processes can be set in motion that quench the blue illuminant (i. e. suppress its light output). Factors such as pH value, solvent conditions or even competing reaction pathways could play a role here.

It is probably even due to a combination of optical (e. g. energy transfer or internal filter effects) and chemical interactions that result in the blue light source no longer coming into its own in the mixture.