One-dimensional semiconductor nanostructures combine electron mobility in length direction with the possibility of tailoring the physical properties by confinement effects in radial direction. Here we show that thin CdSe quantum nanowires exhibit low-temperature fluorescence spectra with a specific universal structure of several sharp lines. The structure strongly resembles the pattern of bulk spectra but show a diameter-dependent shift due to confinement effects. Also the fluorescence shows a pronounced complex blinking behavior with very different blinking dynamics of different emission lines in one and the same spectrum. Time- and space-resolved optical spectroscopy are combined with high-resolution transmission electron microscopy of the very same quantum nanowires to establish a detailed structure-property relationship. Extensive numerical simulations strongly suggest that excitonic complexes involving donor and acceptor sites are the origin of the feature-rich spectra.

Semiconductor quantum dots containing two electrons, also called artificial quantum-dot helium atoms, are model structures to investigate the most fundamental many-particle states induced by Coulomb interaction and the Pauli exclusion principle. Here, electronic excitations in quantum-dot helium are investigated by resonant Raman spectroscopy in magnetic fields. We observe transitions from the ground state into the excited singlet state and, in the depolarized Raman configuration which allows spin-flip processes, into the triplet state.

We report on resonant optical spectroscopy of self-assembled InGaAs quantum dots in which the number of electrons can accurately be tuned to N = 0,1,2 by an external gate voltage. Polarization, wave vector, and magnetic field dependent measurements enable us to clearly distinguish between resonant Raman and resonant photoluminescence processes. The Raman spectra for N = 1 and 2 electrons considerably differ from each other. In particular, for N = 2, the quantum-dot He, the spectra exhibit both singlet and triplet transitions reflecting the elementary many-particle interaction. Also the resonant photoluminescence spectra are significantly changed by varying the number of electrons in the QDs. For N = 1 we observe complex spectra possibly induced by strong polaronic effects that are suppressed for N = 2.