Laser Irradiation as a Tool to Control the Resonance Energy Transfer in Bacteriorhodopsin–Quantum Dot Bio-Nano Hybrid Material

 Bacteriorhodopsin (BR) is a natural photosensitive protein which can be considered promising in photovoltaics and optoelectronics because of its ability to produce a pronounced electrochemical response and controllably change its absorption spectrum under light excitation. However, its applicability is limited by its narrow absorption spectrum and low values of the absorption cross sections. Semiconductor quantum dots (QDs), which have high one- and two-photon absorption cross-sections in a UVand NIR spectral regions, respectively, can significantly improve the light sensitivity of BR by means of Förster resonance energy transfer (FRET) from QD to BR. In this work, we demonstrate the possibility to control the efficiency of FRET from QD to BR within electrostatically bound complexes of QD and purple membranes (PM) containing BR. We show that laser irradiation of QDs at different wavelengths leads to distinct changes (rise or decrease) of QD luminescence quantum yield (QY) without changing of QD structure. Such photo-induced changes in the QY of QD lead to a corresponding change in the efficiency of FRET. We have estimated efficiencies of FRET from QD to BR in the PM complexes composed of irradiated and non-irradiated QDs and found the increase in FRET efficiency with irradiated QDs

Optical Properties of Core-Multishell Quantum Dots

During the past decade, colloidal semiconductor nanocrystals or quantum dots (QDs) have become not only a subject of interesting fundamental research, but also a product for real-life applications. Intense activities devoted to enhancement of QDs photoluminescence (PL) quantum yield (QY), starting from early attempts to deposit protective ZnS shells atop CdSe cores, have resulted in novel designs of core-shell QDs with 100% PL QY. In this work we present a detailed analysis of optical properties of core-“multishell” (MS) QDs, whose physical structure is specifically designed to attain maximum localization of excited charge carriers inside luminescent cores, and thereby to achieve 100% PL QY. We have produced samples of core-MS QDs having 3 to 7 shell monolayers, studied the evolution of optical transitions in such QDs during the process of shell deposition, and analyzed the effects of shell thickness on the optical properties of finally obtained QDs. Specifically, studies of PL lifetimes have revealed the possibility of alternative emission mechanism, based on delayed charge carrier transfer from excited outer CdS layer of the multishell into CdSe cores. Keywords: quantum dots, core-shell, multishell, SILA

Exposure of Nuclear Track Emulsion to a Mixed Beam of Relativistic 12^{12}N, 10^{10}C, and 7^7Be Nuclei

A nuclear track emulsion was exposed to a mixed beam of relativistic $^{12}$N, $^{10}$C, and $^7$Be nuclei having a momentum of 2 GeV/$c$ per nucleon. The beam was formed upon charge exchange processes involving $^{12}$C primary nuclei and their fragmentation. An analysis indicates that $^{10}$C nuclei are dominant in the beam and that $^{12}$N nuclei are present in it. The charge topology of relativistic fragments in the coherent dissociation of these nuclei is presented.Comment: ISSN 1063-7788, Pleiades Publishing, Ltd., 201