Scientists invent long-lasting, near infrared-emitting material

Nov 20, 2011
Researchers at the University of Georgia 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 only can be seen with a night vision device. Credit: Zhengwei Pan/UGA

Materials that emit visible light after being exposed to sunlight are commonplace and can be found in everything from emergency signage to glow-in-the-dark stickers. But until now, scientists have had little success creating materials that emit light in the near-infrared range, a portion of the spectrum that only can be seen with the aid of night vision devices.

In a paper just published in the early online edition of the journal , however, University of Georgia scientists describe a new material that emits a long-lasting, near-infrared glow after a single minute of exposure to sunlight. Lead author Zhengwei Pan, associate professor of physics and engineering in the Franklin College of Arts and Sciences and the Faculty of Engineering, said the material has the potential to revolutionize medical diagnostics, give the military and a "secret" source of illumination and provide the foundation for highly efficient solar cells.

"When you bring the material anywhere outside of a building, one minute of exposure to light can create a 360-hour release of near-infrared light," Pan said. "It can be activated by indoor fluorescent lighting as well, and it has many possible applications."

The material can be fabricated into that bind to , for example, and doctors could visualize the location of small metastases that otherwise might go undetected. For military and law enforcement use, the material can be fashioned into ceramic discs that serve as a source of illumination that only those wearing can see. Similarly, the material can be turned into a powder and mixed into a paint whose luminescence is only visible to a select few.

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 that emit near-infrared light as a source of illumination. Their phosphorescent material also was mixed into the paint that was used to create the UGA 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. (Imaging parameters are auto, ISO 200, 3-4 seconds of exposure time using a night vision monocular). Credit: Zhengwei Pan/UGA

The starting point for Pan's material is the trivalent chromium ion, a well-known emitter of near-infrared light. When exposed to light, its electrons at ground state quickly move to a higher . As the electrons return to the ground state, energy is released as near-infrared light. The period of light emission is generally short, typically on the order of a few milliseconds. The innovation in Pan's material, which uses matrix of zinc and gallogermanate to host the trivalent chromium ions, is that 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 near-infrared light over period of up to two weeks.

In a process that Pan likens to perfecting a recipe, he and postdoctoral researcher Feng Liu and doctoral student Yi-Ying Lu spent three years developing the material. Initial versions emitted light for minutes, but through modifications to the chemical ingredients and the preparation—just the right amounts of sintering temperature and time—they were able to increase the afterglow from minutes to days and, ultimately, weeks.

"Even now, we don't think we've found the best compound," Pan said. "We will continuously tune the parameters so that we may find a much better one."

The researchers spent an additional year testing the material—indoors and out, as well as on sunny days, cloudy days and rainy days—to prove its versatility. They placed it in freshwater, saltwater and even a corrosive bleach solution for three months and found no decrease in performance.

In addition to exploring biomedical applications, Pan's team aims to use it to collect, store and convert solar energy. "This material has an extraordinary ability to capture and store energy," Pan said, "so this means that it is a good candidate for making significantly more efficient."

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Sean_W
4.2 / 5 (5) Nov 20, 2011
Maybe they could use the ceramic discs as navigation aids for nocturnal cleaning robots.
If they could change the emission wavelength to one that is easilly absorbed by water it could store solar energy to release it as heat during snowstorms to help melt some of the snow and ice from painted road and sidewalks surfaces.
BillFox
4 / 5 (1) Nov 20, 2011
Neat idea with the snow Sean, I can visualize many more applications.
PPihkala
5 / 5 (1) Nov 20, 2011
The cheapest and most abundant near infrared detector: Your digital camera. It can see IR from remote controls, so it probably can see this materials glow also. Some may even own camera phone. Semiconductor photo cells do see also some IR radiation, hence the usability of these devices.
Callippo
1 / 5 (1) Nov 20, 2011
Free PDF study http://www.optics...19-20215

You can buy IR phosphors already from Microtrace http://microtracesolutions.com
Sean_W
1 / 5 (1) Nov 21, 2011
The cheapest and most abundant near infrared detector: Your digital camera. It can see IR from remote controls, so it probably can see this materials glow also. Some may even own camera phone. Semiconductor photo cells do see also some IR radiation, hence the usability of these devices.


I agree that uses which envision giving an advantage to one group over others might not be practical; if a guerilla group can afford guns and ammo they will probably be able to get some IR visual equipment on the cheap. But if the idea is to provide low power illumination in a form that most neighbors won't complain about it would still be useful. Bathing a factory or small military outpost with spot lights all night might annoy lots of people but if it's invisible to the naked eye and not draining power it might be feasible.
antialias_physorg
1 / 5 (1) Nov 21, 2011
Maybe they could use the ceramic discs as navigation aids for nocturnal cleaning robots.

Yes. That was my first thought, too: invisible markings for all kinds of purposes without distracting the eye

- information for navigation systems
- robotics
- replacement of these annoying Datamatrix/QRCode/Barcodes which are being slapped on everything

And the advantage is that it's completely passive. No light source needed (occasional daylight will do)

On the other hand it would be fun to 'hack' these signs. Could be a while before anyone finds out
Isaacsname
not rated yet Nov 21, 2011
How long before somebody gets a tattoo with it ?
Vendicar_Decarian
1 / 5 (1) Nov 21, 2011
"You can buy IR phosphors already from Microtrace" callippo

This isn't a phosphor, and doesn't glow by phosphorescence.

You should try reading the article next time.

socean
not rated yet Nov 25, 2011
What about using the emissions to stimulate something that glows in the visible spectrum? Then the substance becomes a "light battery", charging in the sun and slowly releasing light over time.
socean
not rated yet Nov 25, 2011
What about using the emissions to stimulate something that glows in the visible spectrum? Then the substance becomes a "light battery", charging in the sun and slowly releasing light over time.

If higher energies are needed, re-tune the material to release energy faster. Then make a roll of something coated with it, expose the roll gradually in the sun, and slowly rewind the roll at night.

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