In particular, their photo-luminescence (PL) and electroluminescence (EL) properties have led to their widespread development as biological fluorescent tags, 1−3 optical sensors, 4 and tunable lighting/ LEDs. KEYWORDS: colloidal semiconductor, interfacial trap states, lattice mismatch, single-particle fluorescence, fluorescence lifetime C olloidal semiconductor nanocrystals, quantum dots (QDs), have unique optical and optoelectronic properties that, combined with ease of synthesis and processability, have resulted in them becoming one of the most important class of nanomaterials. The combination of reducing blinking while maintaining a small overall QD size and using a Cd-free outer shell of ZnS will be useful in a wide array of applications, particularly for advanced bioimaging. This model highlights a strategy of reducing QD blinking in small QDs by balancing the magnitude of the induced lattice strain, which results in the formation of interfacial trap states between the inner shell and the outer shell, and the confinement potential that determines how accessible the interfacial trap states are. A thorough characterization of the time-resolved fluorescence at the ensemble and single-particle level allowed us to propose a detailed physical model involving both short-lived interfacial trap states and long-lived surface trap states that are coupled. Furthermore, by correlating the fluorescence lifetime components with the fraction of time that a QD spends in the on-state, both with and without applying a threshold, we found evidence for two types of blinking that separately affect the average fluorescence lifetime of a single QD. Here, we show a " Goldilocks " effect to reduce blinking in small (∼7 nm) QDs by carefully controlling the thicknesses of the shells in multishell QDs. One of the main reasons for the limited progress is that the role that interfacial trap states play in blinking in these systems is not very well understood. Blinking suppression with multishell configurations of CdS and ZnS has been reported only for " giant " QDs of 15 nm or more. Ideally, a nontoxic material such as ZnS is preferred to be the outer material in order to reduce environmental and cytotoxic effects. Currently, the most common way to reduce blinking in quantum dots (QDs) is accomplished by using very thick and/or perfectly crystalline CdS shells on CdSe cores.
0 kommentar(er)
