Vacuum-Polarization Screening Corrections to the Low-Lying Energy Levels of Heliumlike Ions

We present results for the two-photon vacuum-polarization screening correction in He-like heavy ions in the range Z=20–100. Values for the ground state as well as for low-lying excited states are given. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of ZnS shell on the Raman spectra from CdSe nanorods

We investigated the influence of an epitaxially grown ZnS shell on the phonon spectra of CdSe nanorods of different sizes. The CdSe related Raman peaks shift with addition of a ZnS shell. The longitudinal optical phonon shifts slightly due to strain and the low‐energy shoulder shifts stronger, which can be explained within a model for surface optical phonons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A finite B-spline basis set for accurate diatomic molecule calculations

A finite basis set particularly adapted for solving the Hartree-Fock equation for diatomic molecules in prolate spheroidal coordinates has been constructed. These basis functions have been devised as products of B-splines times associated Legendre polynomials. Due to the large number of B-splines, the resulting set of eigenfunctions is amply distributed over excited states. This gives the possibility of using these basis sets to calculate sums over excited states, appearing in various orders of perturbation theory. As an illustration, the second-order corrections to the ground-state energy of some atoms and diatomic molecules with closed electron shells have been calculated.     

Photoinduced processes in nanocrystals of cadmium selenide in an external electric field

The dependence of photoinduced processes in cadmium selenide nanocrystals in an external electric field on the energy of the exciting photons is established. A relationship between the photoinduced buildup of photoluminescence and its quenching in an external electric field in quantum sized cadmium selenide nanocrystals is demonstrated. The mechanisms for the quenching of the photoluminescence and for the influence of the exciting photon energy on the photoinduced processes are discussed.     

Exciton fine structure in single CdSe nanorods

We study the optical properties of excitons in one-dimensional (1D) nanostructures at low temperatures. In single CdSe/ZnS core-shell nanorods we observe a fine structure splitting and explain it by exchange interaction. Two peaks are observed with different degrees of linear polarization of DLP<0.85 and DLP>0.95. For small nanorod radii R< or =a(B)/2, an increase in the photoluminescence decay time is found when the temperature increases from 10 to 80 K. The observations are explained by a radius-dependent change in the symmetry of the 1D-exciton ground state which transforms from a dark state into bright states below a critical radius of R(crit) approximately 3.7 nm.     

Lamb shift calculations for high-Z lithium like ions

We present ab initio calculations of the complete gauge invariant set of the self energy and vacuum polarization screening diagrams for the 2p transition in Li like ions. Various contributions to the transition energy are collected. The accuracy of theoretical predictions is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Recombination dynamics of CdTe/CdS core-shell nanocrystals

The recombination dynamics of zinc-blende-type, deep-red emitting CdTe/CdS core-shell nanocrystals is studied over a wide temperature range. Two characteristic decay regimes are found: a temperature-dependent decay component of a few nanoseconds and a long-living temperature-independent component of approximately 315 ns. The average decay time of the exciton states changes from 20 to 5ns when the temperature is increased from 15 to 295 K. At low temperatures, the observed decay behavior is assigned to thermally induced population and decay of the allowed exchange-split exciton states. At temperatures above T>100 K, nonradiative decay channels involving phonons start to contribute to the exciton recombination. The observed broad distribution in decay times, monitored by stretched exponential fitting functions, we explain by variations in the electron-hole overlap caused by a partly incomplete CdTe/CdS core-shell structure and the nearly energy-degenerated bright and dark state superposition.     

Screened self-energy correction to the 2<Emphasis Type="Italic">p</Emphasis><Subscript>3/2</Subscript>-2<Emphasis Type="Italic">s</Emphasis> transition energy in Li-like ions

We present an ab initio calculation of the screened self-energy correction for 1s² 2p_3/2 and 1s² 2s states of Li-like ions with nuclear charge numbers in the range Z = 12?100. The evaluation is carried out to all orders in the nuclear strength parameter Zα. This investigation concludes our calculations of all two-electron QED corrections for the 2p_3/2-2s transition energy in Li-like ions and thus considerably improves theoretical predictions for this transition for high-Z ions.