Glow-in-the-dark devices, which emit visible light after exposure to sunlight, are as commonplace as a wristwatch. But these are not that great when you want to see and not be seen — say you’re a special ops soldier checking the time while tracking an enemy. In that situation, a glow-in-the-night-vision device would be far more effective. Now scientists at the University of Georgia have invented just such a device — a new material that emits a long-lasting infrared glow after a single minute of exposure to light. You can only see the light through night-vision glasses.
Visible-light phosphors have been around since 1996, and nowadays there’s a chemical compound for every color. They’re integrated into traffic signs, security signs, displays and much more, where they emit an afterglow hours after the light shone upon them has gone dark. Now Zhengwei Pan, a physics professor at UGA, has developed the first adaptable, long-lasting near-infrared phosphor, based on the trivalent chromium ion. Its electrons are excited in the presence of light and move to a higher energy state, then fall back to ground state. This energy loss is expressed in a flash of light in the near-infrared realm of the spectrum. But the flash doesn’t last very long, so Pan and colleagues had to trap it.