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The energies of hydrogenic impurity states with an impurity atom located at the center of a quantum dot and on the axis of a quantum-well wire are studied. These two systems are all assumed to have an infinite confining potential. In the case of the quantum dot, the impurity eigenfunctions are expressed in terms of Whittaker functions and Coulomb scattering functions. The calculated ground-state energy of the impurity approaches the correct limit of three-dimensional hydrogen atom as the radius of the quantum dot becomes very large. In the case of the quantum-well wire, analytical solutions can be obtained if we divide the space into a two-dimensional subspace (perpendicular to the axis of the quantum-well wire) and a one-dimensional subspace (parallel to the axis of the quantum-well wire). The calculated groundstate energy of the quantum-well wire approaches the ground-state energy of the shallow-impurity atom located on the surface as the radius of the wire becomes infinite. Variations of the state energies with the radius of the quantum dot and the quantum-well wire are obtained.

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The spontaneous emission (SE) of quantum dot (QD) excitons into surface plasmons in a cylindrical nanowire is investigated theoretically. Maxwell's equations with appropriate boundary conditions are solved numerically to obtain the dispersion relations of surface plasmons. The SE rate of QD excitons is found to be greatly enhanced at certain values of the exciton bandgap. Application in generation of remote entangled states via superradiance is also pointed out and may be observable with current technology.

We propose to measure the superradiance effect by observing the current through a semiconductor double-dot system. An electron and a hole are injected separately into one of the quantum dots to form an exciton and then recombine radiatively. We find that the stationary current shows oscillatory behavior as one varies the interdot distance. The amplitude of oscillation can be increased by incorporating the system into a microcavity. Furthermore, the current is suppressed if the dot distance is small compared to the wavelength of the emitted photon. This photon trapping phenomenon generates the entangled state and may be used to control the emission of single photons at predetermined times.

Both ensemble and single-molecule measurements were performed to explore the fluorescence properties of Au nanoclusters (NCs). Photoinduced fluorescence enhancement was observed for ensemble NCs in solution, but photobleaching was found at ambient environments. At the single-molecule level, fluorescence blinking and single-step photobleaching were observed. Furthermore, their time-resolved fluorescence shows a single exponential decay with a lifetime of approximately 7 ns and is insensitive to changes in fluorescence intensity. The lifetime distribution is more homogeneous within ensemble Au NCs as compared to CdSe QDs. Therefore, Au NCs have potential applications as nontoxic fluorescent labels for lifetime-based imaging microscopy. However, their low quantum yields and poor photostability are disadvantageous factors, which require further improvement.

Resonant Raman spectroscopy is used to study quantum size effects in CdS films. The lattice softening of the CdS LO-phonon mode in a CdS film with a thickness less than 800 A is observed. As the 0~0 thickness is less than 410 A, the TO-phonon mode is observed at 4880 A excitation wavelength, which is above the band gap of bulk CdS (2.42 eV) at room temperature. These phenomena are attributed to the size quantization effects of the grain size and the low-dimensional thin-film structure. The quantum size effects cause a blueshift of the band gap in the as-deposited CdS thin film. The peak of the TO-phononmode Raman line of the CdS film is observed around 220 cm ', which has a shift of 8 cm ' from the Raman line of the most active TO-phonon mode of bulk CdS. The magnitude of softening energy of the TO-phonon mode is observed to be independent of the film thickness.