CdS quantum dots in colloids and polymer matrices: electronic structure and photochemical properties

Abstract

We have studied the optical properties and electronic structures of quantum-confined CdS particles (Q-particles, quantum dots) prepared as CdS colloids in different solvents, CdS particles embedded in polymer matrices and vacuum evaporated island films of CdS. Due to the quantum-confined effect, the optical spectra of these systems exhibit the explicit 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 photoeletron spectroscopy and semi-empirical quantum-chemical calculations were performed. Both XRS data and results of calculations reveal the clear difference 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 also compare the relative stability of CdS clusters of different structure. Additionally, we studied the photochemical properties of CdS Q-particles and observed the effect of spectral hole burning in the absorption spectra of CdS colloids in 2-propanol during UV laser irradiation. This phenomenon results probably from selective photo-oxidation of CdS Q-particles, whose exciton absorption bands are close to irradiation wavelength.