Influence of Surface Modification on the Luminescence of Colloidal ZnO Nanocrystals

The influence of surface modification on the luminescence of colloidal ZnO nanocrystals is described, with particular emphasis given to factors increasing excitonic emission quantum yields. Changes in nanocrystal size, shape, and luminescence intensities have been measured for nanocrystals capped by dodecylamine (DDA) and trioctylphosphine oxide after different growth times. Green trap emission intensities show a direct correlation with surface hydroxide concentrations. Contrary to expectations, there is no direct correlation between excitonic emission quenching and surface hydroxide concentrations. The nearly pure excitonic emission observed after heating in DDA is attributed to the removal of surface defects from the ZnO nanocrystal surfaces and to the relatively high packing density of DDA on the ZnO surfaces. Rapid, nondispersive ripening of ZnO nanocrystals upon heating in DDA is observed and explained using a colloidal growth model.