THE BAND-EDGE LUMINESCENCE OF SURFACE-MODIFIED CDSE NANOCRYSTALLITES - PROBING THE LUMINESCING STATE

We study the luminescence of surface modified CdSe nanocrystallites. T here has been much speculation as to the origin of the band edge emiss ion in these quantum confined structures. Because of their large surfa ce 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 structu re state or ''dark'' exciton. To address this issue we modify the surf ace of CdSe nanocrystallites with a variety of organic and inorganic l igands. We then monitor the effect changing the surface has on the ene rgetics of the band edge luminescence through photoluminescence and fl uorescence line narrowing experiments. Our results are compared with t heoretical predictions for the nonresonant and resonant luminescence. We find good agreement between experiment and theory for CdSe nanocrys tallites 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. (C) 1997 Amer ican Institute of Physics.