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Quantum wires and dots are unique condensed matter systems where electron and hole localisation can be achieved by lateral confinement down to quasi 0-dimensions. Here we review how these nanostructures are realised and their optical properties, mainly from an experimental point of view. We discuss changes in the energy and momentum relaxation mechanisms as the lateral dimensions are reduced, such as the so-called phonon "bottleneck", using the example of GaAs-GaA1As quantum dots and wires. Examples of strain-relief by deep etching in both, nominally lattice-matched and strained materials are given. The emission of hot luminescence or resonant Raman scattering from dots and wires is shown to be a finger print of exciton localization. Many-body effects are shown to be important in nanostructures such as GaAs-GaAlAs and Si-SiGe dots and wires. The emergence of ultra-thin submonolayer quantum wells has provided further insights into the role of exciton localization in nanostructures and we discuss here the case of submonolayers of InAs embedded in a GaAs matrix.Considerations for devices are discussed along with future trends in the field.

A comparison of the photoluminescence emission from MOCVD overgrown quantum dots (QDs) patterned in MOCVD and MBE grown starting material has been made. Before overgrowth luminescence was obtained from the QDs down to 750Å in diameter fabricated in MBE material whereas after overgrowth only the larger 3000Å QDs luminesce. However when MOCVD material is used the largest dots (3500Å) only luminesce after regrowth. With both types of material the QW emission shifts to higher energies after regrowth.