Correlation between structural and optical properties of PbS nanocrystals

PbS semiconductor nanocrystals have been synthesized in order to study the modifications of their optical properties in relation to their size. The synthesis has been carried out by using the techniques of colloid chemistry. A fast evolution of the optical absorption spectrum has been noticed following synthesis. immediately after the synthesis reaction, the samples exhibit a structured absorption spectrum with three well-defined excitonic peaks. Within a few minutes, the peaks progressively disappear and a structureless spectrum occurs. A procedure of stabilization of the colloids has been set up in order to allow the study of the structural and optical properties at different stages of their evolution. Fiber-like nanocrystals (2.5 x 25 nm) and platelets have been found in the early stages of the synthesis and nearly cubic nanocrystals (13 nm) are found in later stages of evolution.