The term triboluminescence was coined by Wiedemann in 1888 and it basically means light from friction. The term triboluminescence comes from the Greek word tribein (meaning to rub) and the Latin prefix lumin (meaning light). Triboluminescence is a flash of light produced when a material is subjected to friction, impact or breakage or in plane words can be understood as when the material is crushed, ripped, scratched, or rubbed. Triboluminescence is also known as fractoluminescence, mechanoluminescence and crystalloluminescence.
There is still enigma over the cause of this phenomenon. There are two widely accepted theories:
- The first theory states that the stress that forms in the region at the tip of the crack causes the electrons in the atoms in that location to jump to higher energy states. As the electrons come back to their ground state, they emit visible light.
- The second theory states that the triboluminescence is similar to lightning and caused by an electrical current generated by force applied to the materials. The electrical current travels through the material causing molecules of gas trapped within the crystal to glow. The emission spectrum for sugar indicates that the light comes from the atmospheric nitrogen that fills the gap during fracture.
They are of three main types:
- Elastico-triboluminescence: Luminescence produced during elastic deformation of solids where neither plastic deformation nor fracture is required. Elastico- triboluminescence can be seen in stressed regions of x and y – irradiated alkali halides and ZnS:Mn.
- Plastico-triboluminescence: Luminescence produced during plastic deformation of solids where fracture is not required. Plastico-triboluminescence can be seen in stressed regions of colored alkali halides, II—VI compounds, alkaline-earth oxides, and metals.
- Fracto-triboluminescence: Luminescence produced due to creation of new surfaces during fracture of solids. Fracto -triboluminescence can be seen in uranyl nitrate hexahydrate, impure saccharin, and chlorotriphenyl-methane.
A triboluminescent mineral is a mineral that exhibits this type of behavior. Triboluminescence is present in quartz, sphalerite, fluorite, calcite, muscovite, and many feldspar minerals. Some specimens of common opal produce a bright orange flash.
Triboluminescence finds its use preliminary in civil engineering. Composites can be embedded with triboluminescence materials and can be applied on or used in initial manufacturing of bridges and railway tracks.
The light produced by triboluminescence is very faint because most of the light emitted is in the ultraviolet spectrum (wavelengths < 380nm), and only a small fraction is in the visible spectrum. Research work has to be carried out on how to increase the brightness of the emitted light so that cameras can easily detect and record the light.
See a video evidence of this effect in this YouTube video:
- Frontenot, Ross S., Md Abu S. Shohag, and Okenwa O.I. Okoli. “Chapter 1: Introduction to Triboluminescence.” Triboluminescence Theory, Synthesis, and Application. By David O. Olawale. Springer Verlag, 2016. 1-16
- King, Hobart. “Triboluminescence.” Triboluminesence in Minerals. Web. 18 Jan. 2017
- Crystals and luminescence, Vikram Singh 8R, https://perseengage.files.wordpress.com/2014/11/crystals-and-triboluminescence.pdf
- Olivia Graeve, This University of California, San Diego professor explains the triboluminescence phenomenon and speculates on its underlying causes, TLT Magazine – An STLE Publication, February 2017