Enhanced carrier multiplication in engineered quasi-type-II quantum dots

Sem informaçãoOne process limiting the performance of solar cells is rapid cooling (thermalization) of hot carriers generated by higher-energy solar photons. In principle, the thermalization losses can be reduced by converting the kinetic energy of energetic carriers into additional electron-hole pairs via carrier multiplication (CM). While being inefficient in bulk semiconductors this process is enhanced in quantum dots, although not sufficiently high to considerably boost the power output of practical devices. Here we demonstrate that thick-shell PbSe/CdSe nanostructures can show almost a fourfold increase in the CM yield over conventional PbSe quantum dots, accompanied by a considerable reduction of the CM threshold. These structures enhance a valence-band CM channel due to effective capture of energetic holes into long-lived shell-localized states. The attainment of the regime of slowed cooling responsible for CM enhancement is indicated by the development of shell-related emission in the visible observed simultaneously with infrared emission from the core.518Sem informaçãoSem informaçãoSem informaçãoC. M. C., L. A. P., K. A. V., I. R., J.M.P. and V. I. K acknowledge support of the Center for Advanced Solar Photophysics (CASP), an Energy Frontier Research Center (EFRC) funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES). N.S.M. is a CASP member supported by LANL Director's Postdoctoral Fellowship. Q. L. and H. L. are CASP affiliates supported by the New Mexico Consortium and Los Alamos National Laboratory

Polarization-Resolved Pump-Probe Method To Determine The Excited-States Of Polymethine Molecules

A pump-probe method based on excited-state transition dipole moment orientations is used to determine the energies of the excited-states of polymethine molecules. The results are compared to the steady-state fluorescence anisotropy technique with good agreement. ©2002 Optical Society of America

Study Of The Dispersion Of Nonlinear Refraction In Insb

We studied the nonlinear refraction due to bound electrons in InSb using femtosecond pulses in the range of 8-13 μm and show that the nonlinear refraction coefficient changes sign at a wavelength around 10 μm. © 2006 Optical Society of America

Spectrum Of Two-Photon Absorption In Insb

The spectrum of two-photon absor ption in undoped InSb is measured by temperature dependent tratismittancc studies using a nanosecond CO2 laser and by pump-probe and Z-scan methods using tunable infrared picosecond and femtosecond sources. © 2006 Optical Society of America

Prospects of Nanoscience with Nanocrystals

International audienceColloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Todays strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, we review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years