Optical and surface characterisation of capping ligands in the preparation of InP/ZnS quantum dots

The chemical and physical properties of semiconductor nanocrystals are highly dependent on the surface capping environment. Our synthetic study on InP nanocrystals indicated that the zinc carboxylate salts influence the growth of InP nanocrystals and passivate their surface by removing the surface defects. In this, we study the capping environment of InP nanocrystals by solid-state NMR and IR characterisation. The influence of the concentration of different ligands on the PL wavelength and intensity was exaqmined to investigate the growth and surface passivation mechanisms. The study indicated a weak interaction between the exposed atoms on InP nanocrystal surfaces and the capping molecules, especially zinc carboxylates. The surface passivation prevented the InP nanocrystals from forming dangling bonds and thus reducing surface quenching and leading to improved quantum yields. The presence of zinc carboxylates is also believed to contribute to the slow crystal growth and reduced size distribution of as-prepared InP nanocrystals.