Dimensionally confined semiconductors

CdSe quantum dots (QDs) have been formed by colloidal routes principally in high boiling point coordinating solvents using highly reactive alkylmetal precursors. Efficient bandedge luminescence has been observed in the orange-red region of the spectrum. The optical properties of QDs synthesised using less reactive precursors is also studied. The exact bandgap of the semiconductor is controlled by the particle size, and in the present work could be varied from 2 to 2.4 eV by varying the particle size from 6-8 nm to 2-3 nm. Two competing colloidal growth processes have been studied by high resolution transmission electron microscopy and optical spectroscopy. We have shown that monodisperse colloids may be obtained provided that a single near-instantaneous initial nucleation event occurs. Electronic and steric surface passivation have been shown to be extremely important with respect to the optical properties of the QDs, A wide-bandgap ZnS coating provides electronic passivation to the CdSe QD species rendering the photoluminescence stable over several months in contrast to the photoluminescence degradation observed with organic ligand passivated QDs. Nanometre scale Au particles have been synthesised capped with organic ligands compatible with the CdSe system. Surface plasmon resonance damping is seen in very small particles (< 3 nm). A controlled heating stage in the presence of trioctylphosphine oxide yields 6-12 nm particles with a strong surface plasmon resonance. Attempts were made to synthesis core-shell type metal-semiconductor nanoparticles principally in the Au-CdSe system. A high temperature synthesis route is shown to provide improved CdSe coating onto the Au particles when compared with the lower temperature routes. However both routes quench bandedge luminescence from the CdSe QDs. (author)Available from British Library Document Supply Centre-DSC:D207373 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo