Most phosphorescent materials have limited persistence; once the light source is removed, the glow or afterglow quickly fades away. This could happen in minutes, or it may take several hours. A research team at the University of Georgia in Athens, Georgia in the United States has created a new material that can continue to glow for two weeks after the light source has been removed. The research was done by Zhengwei Pan, Yi-Ling and Feng Liu of the Department of Physics and Astronomy, with Zhengwei Pan and Feng Liu also being part of the Faculty of Engineering.
Night Vision Goggles (NVG) Only
Although this material has a much longer persistence than normal, the glow emitted can only be seen with devices such as night vision goggles, so it's unlikely it's going to be used in glow in the dark stickers unless you happen to have NVGs and want decor that can only be seen with them. Night vision devices like NVGs detect light emitted in the infrared range - in the past infrared light was called black light, a term now only used for ultraviolet light - which is mostly thermal in nature. The visual tests carried out on the new material were done using an ITT PVS-14 Generation III night vision monocular.
A Ceramic Material
The material is Zn3Ga2Ge2O10:0.5%Cr3+ or zinc gallogermanate. Zn is zinc, Ga is gallium, Ge is germanium, O is oxygen and the Cr3+ is ionic chromium and the 0.5% is the percentage of the ceramic that is composed of the chromium ions. The ions are used to dope the material; doping being a common method of altering the optical properties of phosphorescent materials.
The light emitted by the zinc gallogermanate was measured to be between the wavelengths of 600-1,000 nanometers or, as mentioned earlier, mostly in the infrared range.
The new material was compared with a known phosphor LumiNova Green which is manufactured by Nemato & Co. Ltd. LumiNova Green is a strontium aluminate phosphor doped with europium and dysprosium - strontium aluminate europium activated phosphors having a much more persistent and brighter afterglow than older materials. The initial intensity of the zinc gallogermanate after the removal of the light source was measured at being 1.7 times more than that of the LumiNova Green, rising to 2.5 times after 10 minutes and to 3.0 times after an hour. The intensity of the zinc gallogermanate after 100 hours was the equivalent of that of the LumiNova Green after 24 hours. The emitted light from the zinc gallogermanate ceramic plate could still be seen (using the NVGs) even after the plate had been kept in darkness for 360 hours (15 days).
The material was shown to quickly charge from a brief exposure to natural light. Being weather resistant, its potential uses include night vision surveillance and solar power. It was also shown to work when underwater. Although the material can be turned into a powder, which could then be incorporated into a paint, doing this decreases the emission time. Even so, a paint made from the zinc gallogermanate powder had an afterglow that lasted over 24 hours after being exposed to natural sunlight for five minutes.