Influence of the shell geometry on the state of charge of CdSe/CdS dot-in-rods nanonocrystals

Summary form only given. Colloidal nanocrystals (Ncs), quantum dots synthesized by means of wet-chemistry, can emit non-classical light at room temperature. In particular, CdSe/CdS dot-in-rods (DRs) with a spherical core and rod like shell have shown linearly polarized single photon emission [1]. A drawback of colloidal nanocrystals as light sources was the phenomenon known as blinking, i.e. photoluminescence fluctuations from ON to OFF periods. It has recently been solved in spherical `giant´ Ncs by growing thicker shells around the core [2]. However this was at the expense of their single photon emission properties. We have recently shown non-blinking behaviour in DRs while keeping single photon emission property by carefully engineering the shell thickness and length [3].Nevertheless these thick shell DRs still display different level of emission characterised by different quantum yields. Figure 1(a) shows a typical photoluminescence timetrace where one cannot discriminate between the different states because of fast switching between them.Here we present time resolved single molecule spectroscopy of isolated DRs, carried out with the aim of extrapolating their emission properties in terms of number of emission states and their typical quantum yields. Using lifetime-intensity correlations without a priori assumptions on the number of states, as in figure 1(b) , we demonstrate that these thick shell DRs are characterized by 3 emission states with typical lifetimes of 60, 25 and 10ns. We attribute these emission states to the exciton, negatively charged exciton and doubly negatively charged exciton [4]. The influence of the length and thickness of the shell, as well as the radius of the core, on the tendency DRs have to get charged is investigated. Finally we will present the impact of the charging of DRs on their single photon emission property. Single photon emission property is assessed by the autocorrelation function of the photoluminescence measured with a H- nbury-Brown and Twiss setup. A comparison between the autocorrelation function and lifetime measurements can reveal if the charging process affects the single photon emission.