PbSe Core, PbSe/PbS and PbSe/PbSe_xS_1-x Core-Shell Nanocrystal Quantum Dots: Properties and Applications

This chapter details the properties and applications of core-shell nanocrystal quantum dots. It shows the preparation of air-stable PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed-shell nanocrystal quantum dots (NQD). The structural characterization showed a continuous growth of the crystallographic plans without a distinct boundary at the core-shell interface due to a close crystallographic matching. Colloidal PbSe NQDs have currently received special interest due to their unique electronic and optical properties. The bulk PbSe semiconductor has a rocksalt crystal structure and a narrow direct band gap with both valence and conduction band maxima being four-fold degenerate at the L-point of the Brillouin zone. However, the absorption and emission spectra of the core-shell structures were red shifted with respect to the relevant core samples, due to a wavefunction spilling into the low barrier shell. Furthermore, the emission spectra are shifted with respect to their absorption bands, merging from a stokes' shift into anti-stokes' shift behavior, depending on the NQDs and shell thickness and composition.