We study the luminescence of surface modified CdSe nanocrystallites. There has been much speculation as to the origin of the band edge emission in these quantum confined structures. Because of their large surface to volume ratios it has been suggested that the emission originates from surface-related states. However, recent theory suggests that the band edge luminescence arises from an optically inactive fine structure state or “dark” exciton. To address this issue we modify the surface of CdSe nanocrystallites with a variety of organic and inorganic ligands. We then monitor the effect changing the surface has on the energetics of the band edge luminescence through photoluminescence and fluorescence line narrowing experiments. Our results are compared with theoretical predictions for the nonresonant and resonant luminescence. We find good agreement between experiment and theory for CdSe nanocrystallites passivated with trioctylphosphine oxide, ZnS, 4-picoline, 4-(trifluoromethyl)thiophenol, and tris(2-ethylhexyl)phosphate. The lack of dependence of our data on surface modification is consistent with a dark exciton description of the band edge luminescence.

We study the band edge luminescence of CdSe nanocrystallites to determine the origin of this emission. Previous studies have attributed the band edge emission to the recombination of photo-generated carriers trapped in localized surface states. Recently a number of “dark exciton” theories have been proposed which explain the luminescence in terms of recombination through internal core states. To address this issue we modify the surface of CdSe nanocrystallites with a number of organic/inorganic ligands and monitor the effect this has on the energetics of the resonant and non-resonant band edge luminescence. Our results for nanocrystallites passivated with trioctylphosphine oxide (TOPO), ZnS, 4-Picoline, 4-(trifluoromethyl)thiophenol, and tris(2-ethylhexyl)phosphate are in agreement with a dark exciton description of the band edge luminescence.