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Answer to energy transfer debate could impact areas from photovoltaics to quantum information

In this study, the nanoscale energy transfer system consists of two molecules separated by 6.8 nm at opposite ends of a short, rigid DNA strand, positioned at a controlled distance from a mirror. Image credit: Christian Blum, et al.

nanometers apart plays a key role in many technologies, including photovoltaics, quantum information systems, lighting, and sensors, as well as in biophysics to measure nanometer distances and in photosynthesis. But an open question in this area is what effect, if any, the surrounding photonic environment has on this nanoscale energy transfer. By designing and performing a carefully controlled experiment to answer this question, scientists have settled the debate and found clues to improving the efficiency of many of the technologies that rely on this process. Ads by Google Siemens Electric Vehicle – Quiet, clean and efficient, the mobility of the future. – The scientists, Christian Blum, Niels Zijlstra, Ad Lagendijk, Allard P. Mosk, and Willem L. Vos from the MESA+ Institute for Nanotechnology at the University of Twente in Enschede, The Netherlands (Lagendijk is also with the FOM Institute AMOLF in Amsterdam), along with Martijn Wubs of the Technical University of Denmark in Lyngby and Vinod Subramaniam of the MIRA Institute for Biomedical Engineering and Technical Medicine in Enschede and the MESA+ Institute, have written a paper on the influence of the environment of energy transfer that will be published in an upcoming issue of Physical Review Letters. The specific type of energy transfer the scientists investigated is called Förster resonance energy transfer (FRET), which is the dominant energy transfer mechanism on the nanoscale. In FRET, a quantum of excitation energy is transferred from one optical emitter (the donor) to another (the acceptor) in nanometer proximity. Scientists know that the Förster transfer rate can be controlled by three criteria: the spectral properties of the optical emitters, the distance between the optical emitters, and the relative orientations of the emitters’ dipole moments (a measure corresponding to their electromagnetic properties). But the role of the environment’s photonic properties on Förster transfer has been much less clear. The photonic properties of the environment are characterized by the number of states that can potentially be occupied by a photon, which is referred to as the local density of optical states (LDOS). Scientists know that an environment’s LDOS has a definite impact on some molecular processes; for example, a higher LDOS corresponds to a higher spontaneaous emission rate. Using a more familiar analogy, the researchers explain that the question is similar to asking how our surroundings influence our personal lives in a romantic way. “When you fancy someone, inviting him or her out for dinner is a great idea,” Blum told “The romantic environment may help to fall in love. One may wonder if the romantic environment is the reason for falling in love or if it only helps the affection to show. These matters of the heart are notoriously difficult to disentangle and measure.”



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