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May 2011

Engineering Exciton Dynamics

Controlling energy transfer at the nanoscale

Maria Luckyanova

Through careful theoretical research, scientists at the Center for Excitonics have harnessed decoherence, which bridges quantum mechanics and classical physics approaches to describing the world.

Through careful theoretical research, scientists at the Center for Excitonics have harnessed decoherence, which bridges quantum mechanics and classical physics approaches to describing the world. This work demonstrates controlled transfer of excitons, tiny mobile concentrations of energy. This breakthrough has far-reaching applications, including artificial photosynthesis, a hot topic in the realm of renewable energy.

Exciton as energy carrier: Excitons in molecules or solids play the essential energy-carrier role. The dynamics of exciton transfer, both within and between molecules, must be controlled to achieve command over artificial photosynthesis, an energy-conversion technology that mimics nature’s evolved method of transforming solar energy into a more usable and storable form. Typically, exciton motion is described by the Förster resonant energy transfer model that describes the process by which an exciton, releasing radiation during collapse, creates another exciton on a neighboring site. On short time scales, however, certain effects, known as coherent quantum effects, not encompassed by FRET can contribute to exciton motion.

Deriving the dynamics of exciton motion: The authors considered these coherent quantum effects with a more detailed theory of exciton dynamics, Redfield theory. Redfield theory shows that engineering decoherence, or the interactions between the exciton and the environment, provides a pathway for controlling exciton motion. Remarkably, the complex dynamics of controlled exciton transfer can be described by an equation that is analogous in form to the better-known and simpler FRET equation.

Moving forward: Applying the findings to a system of three artificial atoms or quantum dots, the scientists have directed the movement of the excitons by tuning properties of the quantum dots and their environment. This work can be used as a framework upon which to build technologies that rely on directed exciton energy transfer.

More Information

Perdomo A, L Vogt, A Najmaie, and A Aspuru-Guzik. 2010. “Engineering directed excitonic energy transfer.” 96 (9), 093114-093116. DOI: 10.1063/1.3323108.

Acknowledgments

This work was funded by the Center for Excitonics, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences.

About the author(s):

  • Maria Luckyanova is in her third year of graduate studies at the Massachusetts Institute of Technology under Professor Gang Chen in the Nanoengineering Lab, a part of the Mechanical Engineering Department. She studies heat transfer through nanostructures using an optical pump and probe technique. She is a member of the Solid State Solar Thermal Energy Conversion EFRC. In her spare time she loves to conduct imaginary symphony orchestras and ride her bike.

Exciting Electrons

Scientists study controlled transfer of tiny energy particles, key to new energy sources

Through careful theoretical research, scientists at the Center for Excitonics have harnessed decoherence, which bridges quantum mechanics and classical physics approaches to describing the world.

Mother Nature turns sunlight and chemicals into energy, and scientists would like to mimic this process to create and store usable energy. Artificial photosynthesis would require controlling the movement of tiny, mobile concentrations of energy. These concentrations, which last a billionth of a second, are called excitons. Scientists showed, in theory, how to control the movement or hopping of excitons. Using a highly detailed approach, they showed that the interactions between the exciton and the environment provide a pathway for controlling the tiny concentration of energy. This theoretical work provides a platform for engineering exciton transfers in solar cells. The research was conducted by the Center for Excitonics, a DOE Energy Frontier Research Center led by the Massachusetts Institute of Technology.

More Information

Perdomo A, L Vogt, A Najmaie, and A Aspuru-Guzik. 2010. “Engineering directed excitonic energy transfer.” 96 (9), 093114-093116. DOI: 10.1063/1.3323108.

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.