Using resonant Raman spectroscopy, the authors report on the alloying effect and localization of electronic states in Zn1−xMgxO (x<0.15) nanostructures with average sizes in the range of 20–150nm. Anomalous intensity enhancement of the second-order longitudinal optical phonon has been observed, which is due to Fröhlich interaction via the localized exciton as the resonant intermediate electronic states. The alloying-induced disorder due to Mg incorporation led to the enhancement of exciton localization as well as the asymmetric broadening of longitudinal optical phonon line shape. The composition in ZnMgO could be determined by the first-order longitudinal optical phonon frequency via a bowinglike quadratic fit. This simple relationship is in perfect match to the modified random-element-isodisplacement model and provides a nondestructive approach to probe the quantitative composition distributions in wurtzite ZnMgO alloy system.
Energy transport in photosynthetic systems can be tremendously efficient. In particular we study exciton transport in the Fenna-Mathews-Olsen (FMO) complex found in green sulphur bacteria. The exciton dynamics and energy transfer efficiency is dependent upon the interaction with the system environment. Based upon realistic, site-dependent, models of the system-bath coupling, we show that this interaction is highly optimised in the case of FMO. Furthermore we identify two transport pathways and note that one is dominated by coherent dynamics and the other by classical energy dissipation. In particular we note a strong correlation between energy transport efficiency and coherence for exciton transfer from bacteriochlorophyll (BChl) 8 to BChl 4. The existence of two clear pathways and the role played by BChl 4 also challenges assumptions around the coupling of the FMO complex to the reaction centre.
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