Illustration of resonant electronic Raman scattering and resonant fluorescence. Courtesy of Jingyu Huang, University of Illinois.
“In this work, we point out that resonant electronic Raman scattering and resonant fluorescence may both be useful descriptions of the secondary emission,” Cahill said. “Better understanding of these principles and their limitations can result in improved biological and medical imaging modalities.”
Fluorescence is a process by which light of one color or wavelength is absorbed by a material, e.g., an organic dye or a phosphor, and then emitted as a different color after a brief interval of time. In Raman scattering, the wavelength of light is shifted to a different color in an instantaneous scattering event. Raman scattering is not common in everyday life, but is a critical tool for analytical chemistry.
“Light emission from plasmonic nanostructures at wavelengths shorter than the wavelength of pulsed laser excitation is typically described as the simultaneous absorption of two photons followed by fluorescence, which is used a lot in biological imaging,” said Jingyu Huang, first author of the paper that appears in PNAS.
However, we found that by modeling the emission as Raman scattering from electron-hole pairs can predict how the light emission depends on laser power, pulse duration and wavelength.
“Since we understand more of the mechanism of this kind of light emission, we can help to design the biological and medical imaging experiments better, and at the same time we can also have more insight into the broad background of surface-enhanced Raman scattering, which is also related to this kind of light emission,” Huang said.
In addition to Huang and Cahill, the paper’s authors include Wei Wang, Department of Materials Science and Engineering, and Catherine J. Murphy, Department of Chemistry and the Frederick Seitz Materials Research Laboratory.
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