While visible-light emitters are commonplace, there has been little success in creating materials that emit light in the near-infrared (NIR) — until now. A new material developed at the University of Georgia emits a NIR glow for two weeks after a single minute of exposure to sunlight, or even fluorescent lights. Researchers at the University of Georgia in Athens have developed a new material that emits a long-lasting near-infrared glow after a single minute of exposure to sunlight. By mixing it with paint, they were able to draw an image of the university's logo whose luminescence can be seen only with a night-vision device. (Image: Zhengwei Pan/UGA) The material could be fabricated into nanoparticles that bind to cancer cells, for example, so doctors could visualize small metastases that otherwise might go undetected. For military and law enforcement, the material could be fashioned into ceramic discs that are visible only to those wearing night-vision goggles. It could also provide the foundation for highly efficient solar cells. Zhengwei Pan, associate professor of physics and engineering, and postdoctoral researcher Feng Liu stand in a darkened room, using only their recently invented ceramic discs, which emit near-infrared light, as a source of illumination. Their phosphorescent material also was mixed into the paint that was used to create the University of Georgia logo behind them. There is no other source of illumination in the room; without the aid of a night-vision device, the image would be completely dark. (Image: Zhengwei Pan/UGA) The starting point for the material is the trivalent chromium ion, a well-known emitter of NIR light. When exposed to light, its electrons at ground state quickly move to a higher energy state. As the electrons return to the ground state, energy is released as NIR light. Typically, the period of light emission is on the order of a few milliseconds. The new material uses a matrix of zinc and gallogermanate to host the trivalent chromium ions. Its chemical structure creates a labyrinth of “traps” that capture excitation energy and store it for an extended period. As the stored energy is thermally released back to the chromium ions at room temperature, the compound persistently emits NIR light over a period of up to two weeks. Besides three years developing the material, the researchers spent an additional year testing it — indoors and out, as well as on sunny, cloudy and rainy days — to prove its versatility. They placed it in freshwater and saltwater and even in a corrosive bleach solution for three months and found no decrease in performance. The research was published in Nature Materials. For more information, visit: www.uga.edu