M. D. Sykora

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The performance of photovoltaic and photochemical devices is directly linked to the efficiency with which absorbed photons are converted into electron-hole pairs (excitons). A usual assumption is that one photon produces a single exciton, while the photon energy in the excess of the material's energy gap (the gap that separates the conduction from the(More)
Generation of multiple electron-hole pairs (excitons) by single photons, known as carrier multiplication (CM), has the potential to appreciably improve the performance of solar photovoltaics. In semiconductor nanocrystals, this effect usually has been detected using a distinct dynamical signature of multiexcitons associated with their fast Auger(More)
Effects of air exposure on surface properties, electronic structure, and carrier relaxation dynamics in colloidal PbSe nanocrystals (NCs) were studied using X-ray photoelectron spectroscopy, transmission electron microscopy, and steady-state and time-resolved photoluminescence (PL) spectroscopies. We show that exposure of NC hexane solutions to air under(More)
We show that excitation of solutions of well-passivated PbSe semiconductor nanocrystals (NCs) with ultraviolet (3.1 eV) photons can produce long-lived charge-separated states in which the NC core is left with a nonzero net charge. Since this process is not observed for lower-energy (1.5 eV) excitation, we ascribe it to hot-carrier transfer to some trap site(More)
We study ultrafast photoluminescence (PL) dynamics of Si nanocrystals (NCs). The early-time PL spectra (<1 ns), which show strong dependence on NC size, are attributed to emission involving NC quantized states. The PL spectra recorded for long delays (>10 ns) are almost independent of NC size and are likely due to surface-related recombination. Based on(More)
Photoluminescence blinking--random switching between states of high (ON) and low (OFF) emissivities--is a universal property of molecular emitters found in dyes, polymers, biological molecules and artificial nanostructures such as nanocrystal quantum dots, carbon nanotubes and nanowires. For the past 15 years, colloidal nanocrystals have been used as a(More)
In this communication, we demonstrate a new approach to sensitization of Ru-polypyridine complexes by using semiconductor nanocrystal quantum dots (NQDs). When mixed in solution, the complexes functionalized by carboxylic groups adsorb onto the surface of the NQDs. Excitation of NQDs by 400 nm light leads to fast, 5 ps hole transfer from the photoexcited(More)
Four new helical oligoproline assemblies containing 16, 17, 18, and 19 proline residues and ordered arrays of a Ru(II)-bipyridyl chromophore and a phenothiazine electron-transfer donor have been synthesized in a modular fashion by solid-phase peptide synthesis. These arrays are illustrated and abbreviated as(More)
A molecular assembly based on derivatized polystyrene is described, which mimics both the light-harvesting and energy-conversion steps of photosynthesis. The system is unique in that the two key parts of a photosynthetic system are incorporated in a functional assembly constructed from polypyridine complexes of Ru(II). This system is truly artificial, as(More)
We demonstrate novel methods for the study of multiple exciton generation from a single photon absorption event (carrier multiplication) in semiconductor nanocrystals (or nanocrystal quantum dots) that are complementary to our previously reported transient absorption method. By monitoring the time dependence of photoluminescence (PL) from CdSe nanocrystals(More)