ABSTRACT
Spectral and time-resolved ensem ble and single-particle experiments on colloidal CdSe/ZnS semiconductor nanocrystals (quantum dots, QDs) are presented. Processes decreasing the photoluminescence (PL) lifetime and thus the PL intensity of QDs like ligand depletion, assembly formation with organic dye molecules, photo-oxidation and charge trapping/de-trapping induced blinking of single particles are analysed with special regard to the interrelation between PL intensity, lifetime and spectral fluctuations of the PL. Noticeable similarities o f the respective PL lifetim e-intensity relations (PLIR) independent of the method of surface modification by dyes, ligands or oxygen suggest a common mechanism behind all observed PL quenching effects. The PLIR for single QD intensity fluctuations will be
described analytically to quantify the contribution of strong and weak quenching states. In this way ensemble phenomena accompanied by PL intensity changes are related to averaged, modified single-particle blinking. Finally we discuss charge separation-induced Auger recom bination and electron-phonon coupling as possible physical origins of PL quenching. Analysing spectral diffusion of single QDs, the existence of different charged states is substantiated by proving the occurrence of quantumconfined Stark effect-related spectral shifts of different magnitude.
