From Cd-rich to se-rich--the manipulation of CdSe nanocrystal surface stoichiometry

We report a protocol for manipulating the surface composition of CdSe nanocrystals. By combining the successive ion layer adhesion and reaction (SILAR) method developed by Li et al. J. Am. Chem. Soc. 2003, 125, 12567 with a phosphine-free selenium precursor, the surface stoichiometry of CdSe can be tunably altered from Cd- to Se-rich. By changing the overall surface stoichiometry, we demonstrate ligand binding to specific surface sites. Tertiary phosphines produce a dramatic enhancement in photoluminescence quantum yield of CdSe particles with Se-rich surfaces but have little effect on Cd-rich surfaces. Unpassivated selenium surface sites are also shown to be a cause of the photobrightening behavior of CdSe nanocrystals.