New Material Emits Near-Infrared Light For Weeks

Researchers have created a material that can absorb one minute of sunlight and release that energy through near-infrared light for 360 hours, or over two weeks. It can also be charged by indoor lighting. The light it releases is invisible to the human eye, but can be seen with the right equipment. More from PhysOrg:

The material can be fabricated into nanoparticles that bind to cancer cells, 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 night vision goggles 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…

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 solar cells significantly more efficient.”

Very cool. It sounds like the kind of thing very clever people will find very clever things to do with. 

This material is phosphorescent, which basically means that it emits light like this: photons of light (ex. from the sun) hit electrons in the material. The electrons absorb that energy (generally one electron can absorb one photon) and as a result orbit farther from their atom’s nucleus, better resisting the positive pull of the protons. Eventually the electrons drop back to a less-energetic state that’s closer to the nucleus, and in the process emit their energy back as a photon. This photon is less energetic than the one they first absorbed, so where the sun’s photon was in the visible light range, the emitted photon is, at least in this case, in the near-infrared range.

If all of this happens in one rapid step then it’s called fluorescence, but if the energized electrons take a detour and take a while to emit a photon, it’s called phosphorescence. This is also what happens in fluorescent lightbulbs: electricity causes mercury in the bulbs to emit ultraviolet light, which is more energetic than visible light. This light is absorbed by fluorescent material in the bulbs, then emitted as visible light. In contrast, incandescent lightbulbs emit light because the filament wire inside is heated to a high temperature, causing it to glow. 

Yes, there are awesome things happening in your lightbulbs. Thanks science! Keep in mind though that mercury is toxic, so remember to take your CFLs to the appropriate recycling center instead of trashing them.

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