Adsorption and binding of capping molecules for highly luminescent CdSenanocrystals - DFT simulation studiesElectronic supplementary information (ESI) available: Figure S1. See DOI: 10.1039/c0nr00569j

During CdSenanocrystalgrowth, loss of surface capping molecules occurs leading to a decrease of photoluminescence (PL) quantum yield. In general, aliphatic capping molecules are applied to passivate the surface of CdSenanocrystals to modulate the optical properties of the CdSe. In this work, two kinds of alkylamine ( n -butylamine ( n -BA) and n -hexylamine ( n -HA)) and oleic acid (OA) were used to modify the surfaces of the CdSenanocrystals. From the PL spectra and quantum yield analyses, we observed that the PL emission peak positions of the modified CdSenanocrystals have blue shifted for all three capping molecules. However, the PL quantum yield of the CdSenanocrystals increased after introduction of the alkylamine molecules, but decreased with oleic acid. The detailed mechanism was not clear until now. In this study, a density function theory (DFT) simulation was employed to demonstrate binding energy and charge analyses of CdSe with n -BA, n -HA and OA. By comparing the binding energy of the bare CdSenanocrystals to that of the CdSe with the capping molecules, it was shown that n -BA and n -HA as capping molecules help to increase the charge on Se and decrease it on cadmium of the CdSe. Schematic illustration of PL intensity dependence on charge donation between CdSe and ligands (a) CdSe-HA and (b) CdSe-BA and (c) CdSe-OA