CDS QUANTUM DOTS IN COLLOIDS AND POLYMER MATRICES - ELECTRONIC-STRUCTURE AND PHOTOCHEMICAL PROPERTIES

We have studied the optical properties and electronic structures of qu antum-confined CdS particles (Q-particles, quantum dots) prepared as C dS colloids in different solvents, CdS particles embedded in polymer m atrices and vacuum evaporated island films of CdS. Due to the quantum- confined effect, the optical spectra of these systems exhibit the expl icit blue shift of fundamental interband absorption and the appearance of well-pronounced exciton peaks at room temperature. The electronic structure of CdS quantum dots was examined by X-ray photoelectron spec troscopy and semi-empirical quantum-chemical calculations were perform ed. Both XRS data and results of calculations reveal the clear differe nce in valence band density of states for CdS Q-particles with respect to bulk CdS. Semiconductor-like electronic structure, especially for d-band, appears for CdS clusters containing more than 100 atoms. We al so compare the relative stability of CdS clusters of different structu re. Additionally, we studied the photochemical properties of CdS Q-par ticles and observed the effect of spectral hole burning in the absorpt ion spectra of CdS colloids in 2-propanol during UV laser irradiation. This phenomenon results probably from selective photo-oxidation of Cd S 0-particles, whose exciton absorption bands are close to irradiation wavelength.