Fluorescence intermittency of single CdSe/ZnS nanocrystals - local probes for silanol groups on silicon oxide

Fluorescence intermittency, also known as blinking, appears to be a common feature of many different classes of individual emitters. It is characterized by inverse power law distributions for both the ''on'' and ''off'' times. Meanwhile it is generally accepted, that this behaviour is due to trapping and detrapping of charges and correlates with the dielectric properties of the environment surrounding the nanocrystals. To contribute to the current discussion of the physical nature of blinking we investigated the influence of static trap sites in the local surroundings of ZnS coated CdSe nanocrystals spincoated on thermally grown silicon oxide. Therefore we have modified the trap density by changing the amount of silanol groups either by annealing or hydroxylation of the silicon oxide. We found atypical distributions for the ''on'' time statistics which show deviations from the expected power law behaviour only seen at the beginning of the statistics. These deviations depend on the preparation of the silicon oxide and the amount of the silanol groups, allowing a qualitatively correlation between the density of these groups and the blinking of single CdSe/ZnS nanocrystals.