On exposure to sunlight, most materials emit visible light and this phenomenon can be seen in emergency signage, stickers that glow in the dark and in many more. However scientists have been unsuccessful in forming materials, which emit light in the near-infrared range, a part of the spectrum only visible with night vision devices.
In the early online publication of the journal “Nature Materials”, University of Georgia scientists have recorded discovery of a novel material that emits a near-infrared long-lasting glow when it is exposed to sunlight for a minute. Zhengwei Pan, a lead author of the journal, stated that the material can serve as a secret illumination source in the law enforcement and military, offer a strong basis for high-efficiency solar cells and also has the potential for transforming diagnostics in the medical field. Pan added that when the material is exposed to light when outside any building, it can produce a 360 h. release of near-infrared light. Pan said that the material can be triggered by fluorescent lighting inside the building as well.
In medical diagnostics, the fabrication of Pan’s material into nanoparticles that attach themselves to cancer cells helps the doctors to detect and locate minute metastases that may otherwise go unidentified. In law enforcement and military, the Pan’s material can be made into ceramic discs that give a secret illumination source, which is visible only through night vision devices. Also, the materials can be made into powder and mixed with paint having less visible luminescence.
The initial stage of Pan’s material is the trivalent chromium ion, which releases energy as near-infrared light on exposure to sunlight. The light emission duration is generally in the range of few milliseconds. The chemical structure of Pan’s material will produce a labyrinth of “traps”, which can absorb excitation energy and preserve it for an extended duration. The material will continuously emit light in the near-infrared range up to two weeks, when the thermal release of the preserved energy to the chromium ions is done.
Source: http://www.uga.edu/