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 p hoto-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. W hile the radiative recombination (approximate to 1 ns) is dominant for larger nanocrystals, we observe a dramatic increase of the non-radiat ive rate below 4 nm as a result of the reduced volume to surface ratio . The combination of ultra-fast and size-selective excitation allows u s to observe a progression of sharp LO-phonon lines signifying the zer o-dimensional character of the nanocrystals and providing information on the strength of the phonon coupling and the homogeneous width of th e quantum-confined ground state.