Small is different:
size related luminescence
Due to the quantum confinement
effects, the II-VI-semiconductor nano-sized particles show intense size-dependent
optical properties and strong visible luminescence. Thus, by changing the nano-crystal
size, one gets fluorophores of different colors. In particular, CdSe nanocrystals
cover most of the visible spectral range from the blue to the red.
A promising route towards tailored nanophase materials is the intelligent exploitation
of non-equilibrium processing techniques, like ion implantation, for synthesis
of buried low-dimensional structures. We have studied CdSe nano-particles synthesized
by ion-implanting constituent atoms in SiO2, thermally grown on Si. The influence
of implantation and post-implantation treatment parameters, with the emphasis
on the less commonly studied influence of (non)stoichiometry, on the nucleation
and growth of compound semiconductor nanocrystals, was investigated by Raman
spectroscopy and small angle scattering of synchrotron radiation at grazing
incidence (GISAXS), yielding the average size and size distributions of QDs,
average inter-particle distance and distance distribution, as well as the fraction
of implanted atoms which were synthesized into CdSe.
These findings were related with PL intensities and the amount of well-crystallized
CdSe QDs.
Stoichiometry emerged as a very important parameter in optimizing PL properties,
since it has a profound influence on the synthesis, size and spatial distribution
of QDs as found by GISAXS.