Synthesis, simulation & spectroscopy: physical chemistry of nanocrystals

Abstract

Experiments on nanocrystalline semiconductors form a wide and rapidly expanding field of research. This chapter concentrates on two very different topics within this field. In the first part, pair formation of dopant ions in nanocrystals is discussed. After a general introduction on the influence of pair formation on the luminescence properties, pair formation in nanocrystals is discussed. Due to a difference between the connectivity for sites in the bulk and at the surface, the fraction of dopant pairs depends on the crystallite size. Simulations of the statistical distribution of dopant pair states in a nanocrystal as a function of crystal structure, size and dopant concentration are presented. A closed form approximation for the results of the simulations is derived and the validity is tested. The work presented can be used to estimate dopant pair concentrations in the case of random substitution or a lower limit for the pair concentration if preferential pair formation occurs. The second part of the chapter discusses the luminescence of a single nanocrystalline semiconductor particle. The absence of inhomogeneous broadening and other ensemble averaging effects has provided exciting new insight into the luminescence and quenching mechanisms. The linewidth, blue shift and bleaching of the luminescence of single CdSe/ZnS core/shell nanocrystals are shown and discussed. Finally, potential applications of nanocrystals as luminescent labels in biological systems are presented and a few challenges for future research are discussed.