Structure and Ultrafast Dynamics of White-Light-Emitting CdSe Nanocrystals

摘要

The recent discovery of white-light emission from ultrasmall CdSe nanocrystals has resulted in a flurry of research to determine the feasibility of this material for solid-state lighting and even biological applications. Traditional nanocrystals, with diameters of >2 nm, exhibit near-monochromatic band-edge photolumines-cence with quantum yields approaching unity for core/shell structures. A broad emission red-shifted from the band-edge emission is also well-known in larger nanocrystals and has been attributed to trap-state emission. However, as the diameter of the nanocrystal is reduced, this deep-trap emission becomes more prevalent and can eventually dominate the nanocrystal emission. El-Sayed and co-workers explored this phenomenon by studying the emission characteristics of small CdSe nanocrystals, including those in the size range of our white-light-emitting nanocrystals. These nanocrystals exhibited a strongly Stokes-shifted band-edge emission feature followed by deep-trap emission that grew with decreasing nanocrystal diameter.