The Band Edge Luminescence of Surface Modified CdSe Nanocrystallites

Abstract

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.

Molybdenum and Tungsten Sulfide Ligands for Versatile Functionalization of All-Inorganic Nanocrystals

“…One possible explanation is the reduction of the effective size of NCs by photo-oxidation. Typically, the Stokes shift is known to be very sensitive to the size of NCs rather than surface passivation, 36,37 where the Stokes shift becomes larger for smaller-sized NCs. Another possibility is the surface charging of NCs during photo-oxidation because the Stokes shift of CdSe NCs with positive and negative charges on their surfaces is predicted to be larger than that of neutral NCs.…”