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Reverse Fluorescence May Enhance Solar Cells

Fluorescence is what gives some pigments an oddly bright, vivid appearance. In fact, fluorescenct pinks, yellows, greens and other colors seem too bright because they really are brighter than they should be. That is, they have molecules that steal light from one color and add it to another. Fluorescent yellow pigment, for example, both reflects yellow light and converts other colors of light hitting it, changing them to yellow as well.

Typically, a fluorescent material converts light to colors lower down the spectrum. High energy blue light, for example, may be converted to lower energy green. Now researchers have developed chemicals that can go the other way, converting lower energy green light to blue.

The advance could lead to improved solar cells by converting unusable light to colors in a cell's useful range.

This isn't the first example of reverse, or up-conversion, fluorescence, but previous experiments only worked with coherent laser light. The new technique converts incoherent light, which is what the sun produces.

One small caveate - it's not very efficient yet. The method converts about 1% of green light to blue. Also, the researchers point out that it will be much more useful to find materials that will convert even lower energy infrared light to something solar cells could handle.

I'm hoping it will eventually lead to an ultra-modern version of those black light posters they used to sell in the mall. Only now, instead of an ultraviolet black light, maybe you could have a special, party-edition space heater to put out infrared light and make your Elvis poster glow.

To learn more about the up-conversion fluorescence experiment, visit APS Focus which covers the paper that appeared in Physical Review Letters on October 6.


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