This thesis is devoted to quantum dots of ZnO in the size regime 2.5-10 nm.
The focus is directed towards their size dependent properties with special
emphasis on the optical, vibrational and photocatalytic properties. The particles
were synthesized by hydrolysis in alkaline zinc acetate solution.
Analysis and characterisation were performed on both growing particles in
solution as well as on thin particle films. The main characterisation techniques
were UV-vis, florescence, XRD, Raman, electrochemical- and photoelectrochemical
Based on a large set of XRD and UV-vis measurements an empirical relation
between the band gap and the particle size were developed. This enabled
size resolved measurements of the visible fluorescence on growing particles
in solution. We report evidence of mobile trap states responsible for the fluorescence
and discuss a possible surface dependent mechanism for this.
The quantum confinement of the phonon modes were investigated with
Raman spectroscopy and molecular dynamic simulations. We report on a
size depended suppression of the phonon modes and the contribution from
The absolute position of the conduction band edge was determined as a
function of particle size with different photoelectrochemical methods that we
describe in detail. We demonstrate that most of the size dependent shift in
the band gap occurs by a change in the position of the conduction band. We
also show that the parabolic band approximation is valid in a region of
slightly less than 0.1 eV from the conduction band edge, and this even under
an external electric field. An interesting electroabsorption phenomenon
where the absorption locally increases under an applied potential are described
and explained in terms of the quantum confined Stark effect and the
The produced films of the particles show antireflective properties on conducting
glass substrates, which could be interesting from a technological
perspective. The films are demonstrated to show photocatalytic activity with
respect to degradation of organic dyes and for solar water splitting.
T.J Jacobsson production , 2012. , 195 p.