From the Greek tribein meaning, 'to rub'. Triboluminescence is the creation of light by rubbing or tearing (also called fractoluminescence or mechanoluminescence).

If you go into a dark room with two sugar cubes and let your eyes adjust to the low light level, and then strike them together, you may detect a faint blue glow. The same thing is observed if you take a piece of tape and rip it smartly off the roll. These are manifestations of triboluminescence, the conversion of mechanical energy into light.

If you apply a large amount of energy to a molecule, whether in the form of heat, light, or in this case, mechanical energy, you can drive the electrons into a metastable excited state. When those electrons fall back to a lower energy state (the ground state), they can emit a photon of light, the color of which is determined by how large the change in energy there is. The triboluminescence of sucrose and tape adhesive are both in the ultraviolet and blue regions, making it very dim and barely discernable. More dramatic is the green spark seen when biting on a Wint-o-Green Lifesaver

The green sparkle of Wint-o-Green Lifesavers is partially caused by triboluminescence. Crunching on the candy will cause the sugar to emit blue light. This blue light is then absorbed by methyl salicylate, a component of wintergreen flavoring, which then emits the light in the green. The absorption spectrum of wintergreen overlaps well with the triboluminescence spectrum of sugar. Since most of the emission of wintergreen is in the visible spectrum, it is easier to detect than the direct triboluminescence of sucrose, much of which is in the ultraviolet range.

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