Luminescence related processes in semiconductor nanocrystals - The strong confinement regime

This paper summarizes systematic studies on the luminescence from CdSe nanocrystals in the situation of strong zero-dimensional confinement. We discuss the role of surface and defect states, the origin of the photo-darkening and demonstrate by calorimetric adsorption measurements that the internal quantum efficiency is in the range of some 10%. The lifetimes of the intrinsic excitations are strongly size-dependent. While the radiative recombination (approximate to 1 ns) is dominant for larger nanocrystals, we observe a dramatic increase of the non-radiative rate below 4 nm as a result of the reduced volume to surface ratio. The combination of ultra-fast and size-selective excitation allows us to observe a progression of sharp LO-phonon lines signifying the zero-dimensional character of the nanocrystals and providing information on the strength of the phonon coupling and the homogeneous width of the quantum-confined ground state.