23 September 2020
Lighting up crystalline fireflies
Published online 1 March 2019
Heat stimulates light-emitting reactions in solid crystals, with potential applications in materials research and life sciences.
A childhood fascination with the light emitted by fireflies has led chemist Stefan Schramm to seek new options in chemiluminescence — the generation of light by chemical reactions.
“When I started working in Panče Naumov’s lab at New York University Abu Dhabi, we realized that these reactions had only been studied in solution so far,” says Schramm. In collaboration with the Japan Synchrotron Radiation Research Institute, the researchers worked on making a chemiluminescent solid. After two years of studies they have discovered chemiluminescence in a surprising variety of solid compounds.
Unlike conventional luminescence, driven by absorbed light, the generation of light in these crystals is driven by heat and referred to as thermochemiluminescence. The heating promotes chemical reactions that create energetically excited states, which can later release light in the dark as they settle back into lower energy states.
“I like to call them crystalline fireflies,” says Schramm, evoking the insects that sparked the boyhood fascination which he says drove him towards this research field.
The crystals are made from organic peroxides, in which small rings of carbon, hydrogen and nitrogen atoms carry a peroxide group composed of two bonded oxygen atoms. These high-energy compounds were chosen for investigation because of their previously known chemiluminescence in solution.
Practical applications could soon follow. Schramm suggests possibilities in energy storage, with the crystals able to release energy as light on demand. He also foresees potential in generating light signals that report on the state and progress of chemical reactions in the multi-billion dollar polymer industry.
Schramm, S. et al. Thermochemiluminescent peroxide crystals. Nat. Commun. 10, 997 (2019).