Fluorescence spectroscopy studies have shown that, at a single molecule level, fluorophore emission intensity
fluctuates between bright and dark states. These fluctuations, known as blinking, limit the use of fluorophores in
single molecule experiments. Statistical analysis of these intensity fluctuations has demonstrated that the dark
states duration exhibits a universal heavy-tailed power law distribution in organic as well as inorganic
fluorophores. However, the precise reasons underlying the blinking of single fluorophores are still matter of
debate and whether it can be suppressed is not clear. Here we have synthesized CdSe/CdS core/shell quantum
dots (QDs) with thick crystalline shells, which do not blink at low frame rate and established a direct correlation
between shell thickness and blinking occurrences. Single fluorophore blinking and blinking statistics are thus not
as universal as thought so far. We anticipate our results to help better understand the physicochemistry of single
fluorophore emission and rationalize the design of other fluorophores that do not blink. The materials presented
here should readily find interesting applications in biology for single molecule tracking and in photonics as
robust and continuous photon emitter.
Quantum dots are nanometre-sized semiconductor particles exhibiting unique size-dependent electronic
properties. In order to passivate the nanocrystals surface and to protect them from oxidation, we grow a shell
composed of a second semiconductor with a larger bandgap on the core (for example a core / shell CdS / ZnS).
However, the lattice mismatch between the two materials (typically 7% between ZnS and CdS) induces
mechanical stress which can lead to dislocations. To better understand these mechanisms, it is important to be
able to measure the pressure induced on the semiconductor core. We used a nanocrystal doped with manganese
ions Mn<sup>2+</sup>, which provide a phosphorescence signal depending on the local pressure. A few dopant atoms per
nanoparticle were placed at controlled radial positions in a ZnS shell formed layer by layer. The experimental
pressure measurements are in very good agreement with a simple spherically symmetric elastic continuum
model. Using manganese as a pressure gauge could be used to better understand some structural phenomena
observed in these nanocrystals, such as crystalline phases transition, or shell cracking.