Nanocrystals Bridge Visible, Invisible Spectra

Nanocrystals containing cerium and terbium have been shown to efficiently convert UV and IR to visible light, presenting a possible solution to the bandgap problems in solar panels, among other applications.

Cerium easily absorbs UV light and can either re-emit it or transfer it to terbium, which emits it in the form of visible green light. The nanocrystals were dissolved in transparent solvents with varying refractive indices. While the energy transfer from cerium to terbium was the same in each solvent, lower refractive indices produced a greater amount of green light.

Nanocrystals as a powder, and nanocrystals dissolved in a transparent solvent. Courtesy of Utrecht University.

"This is something that has never been observed before,” said Dr. Andries Meijerink, professor of chemistry at Utrecht University. “This means that the efficiency of the energy transfer between the two luminescent particles is not influenced by the photonic [properties] of the environment. And that is important information for developing all kinds of applications in which invisible UV light or infrared light is converted into visible light."

Those applications include efficient light sources that emit a pleasant light color, solar panels and medicine.

"Solar panels are unable to absorb a substantial part of the sun's infrared light,” said Freddy Rabouw, a doctoral candidate at the school’s Foundation for Fundamental Research on Matter, who also worked on the project. “With the knowledge we have acquired, we can now develop systems that can efficiently convert the infrared part of the sunlight into energy.”

The medical application could be in imaging, Rabouw said. “We are looking for nanoparticles that luminesce with other colors than the body's background signal,” he said. “Such a nanoparticle is then monitored inside the body to see what happens to it.”

The research is published in Nature Communications (doi: 10.1038/ncomms4610).

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