Suppression of the blinking of single QDs by using an N-type semiconductor nanomaterial

Abstract

Single quantum dots (QDs) always exhibit strong blinking in fluorescence intensity when they are on some inert substrates. The blinking activity is attributed to the photoinduced charging of QDs by electron transfer (ET) to trap states in QDs and the surrounding matrix, which has been considered as an undesirable property in many applications. Here, we use N-doped indium tin oxide (ITO) semiconductor nanoparticles to suppress fluorescence blinking activity of single CdSe/ZnS core/shell QDs. The fluorescence characteristics of single QDs in ITO and on SiO2 cover glass are measured by a laser scanning confocal fluorescence microscopy, respectively. It is found that the on-and off-state probability densities of QDs on different substrates both can be fit by a truncated power law. Blinking rates for single QDs on glass and in ITO are also calculated. By contrast, single QDs doped in ITO show that their blinking rate and fluorescence lifetime both decrease. The on-state probability density of single QDs in ITO is approximately two orders of magnitude higher than that of QDs on SiO2 cover glass. It means that single QDs doped in ITO have a longer time to be on-state. Because the Fermi level in QDs is lower than in ITO, when they are in contact, electrons in ITO will transfer to QDs. As a result, the equilibration of their Fermi levels leads to the formation of negatively charged QDs. These electrons fill in the holes of QDs shell and enhance the on-state probability of QDs. Fluorescence decays of single QDs on glass and in ITO are measured by TAC/MCA, and they can be fit by biexponential function. The two lifetime values correspond to the single exciton lifetime and biexciton lifetime of QDs, respectively. It is worth noting that the distribution of the amplitude weighted average lifetime for single QDs in ITO is approximately 41% of that for single QDs on SiO2 cover glass and its full width at half maximum (FWHM) is changed to 50%. For the conduction band potential of QDs is higher than that of ITO, which contributes to photoinduced interfacial electron transfer from QDs to ITO and leads to the increase of nonradiative transition. These indicate that ITO can reduce single exciton and biexciton lifetime of QDs. The study demonstrates that ITO can effectively suppress the blinking activity of QDs.