Triboluminescence is the phenomena where light is generated when something is rubbed or fractured. The exact mechanism by which triboluminescence works is still under investigation, but the best theories so far propose that the breaking of the structure causes charge separation that release energy upon recombination. This energy is picked up by nearby atoms, in this case europium, and released as light according to their ionization or fluorescence spectra.
Many substances exhibit triboluminescence including sugar and tape. But Europium Tetrakis (Dibenzoylmethide)Triethylammonium is one of the strongest available and its glow can easily be captured by a camera.
It's make by mixing 100mL of Ethanol, 2.93g of dibenzoylmethane, 1.4g of europium nitrate pentahydrate and 1.9mL of triethylamine. The mixture is heated until everything dissolves and then allowed to cool slowly to obtain crystals that are filtered off and washed with ethanol. After thorough drying they are ready for use.