Long Electron−Hole Separation of ZnO-CdS Core−Shell Quantum Dots

Abstract

The tunability of electronic and optical properties of semiconductor nanocrystal quantum dots (QDs) has been an important subject in nanotechnology. While control of the emission property of QDs in wavelength has been studied extensively, control of the emission lifetime of QDs has not been explored in depth. In this report, ZnO-CdS core–shell QDs were synthesized in a two-step process, in which we initially synthesized ZnO core particles, and then stepwise slow growth of CdS shells followed. The coating of a CdS shell on a ZnO core increased the exciton lifetime more than 100 times that of the core ZnO QD, and the lifetime was further extended as the thickness of shell increased. This long electron–hole recombination lifetime is due to a unique staggered band alignment between the ZnO core and CdS shell, so-called type II band alignment, where the carrier excitation holes and electrons are spatially separated at the core and shell, and the exciton lifetime becomes extremely sensitive to the thickness of the shell. Here, we demonstrated that the emission lifetime becomes controllable with the thickness of the shell in ZnO-CdS core–shell QDs. The longer excitonic lifetime of type II QDs could be beneficial in fluorescence-based sensors, medical imaging, solar cells photovoltaics, and lasers.

A visible light induced photoelectrochemical aptsensor constructed by aligned ZnO@CdTe core shell nanocable arrays/carboxylated g-C3N4 for the detection of Proprotein convertase subtilisin/kexin type 6 gene

“…The type-II interfaces between semiconductors caused spatial separation and increased lifetimes of photogenerated excitons, which decreased internal charge recombination (Xu et al 2009). The type-II band alignment formed when one of the two semiconductors has the energy minimum of both CB and VB .…”

Structure Optimization on the Photoelectric and Photocatalytic Properties of Cu2S and ZnO Complex Films

“…Furthermore, ZnO and Cu 2 S complex films have a good photocatalytic performance. They can completely destruct the undesirable contaminants in both liquid and gaseous phase by using solar or artificial light illumination [12][13]. As we know, the efficiency of photocatalytic reaction is determined by the absorption ability of light and high separation rate of photo-induced electron-hole pair.…”

A Review on the Fabrication of Hierarchical ZnO Nanostructures for Photocatalysis Application

“…Semiconductors, such as CdS, are usually combined with ZnO to form hierarchical heterostructures for visible light photocatalytic degradation due to their narrow band gaps [108,[131][132][133]. For example, nanoscale tree-like CdS/ZnO nanocomposites with a hierarchical architecture showed the ability for selective oxidation of thioanisole and anaerobic reduction of nitro compound 4-nitroaniline under irradiation of artificial solar light [108].…”

“…Especially, Liu et al [90] reported hierarchical flower-like C-doped ZnO superstructures (ZnO flowers) assembled from porous nanosheets, which showed better photocatalytic decomposition of the RhB dye in aqueous solutions than ZnO due to the enhanced light absorption over a wide range of wavelengths. Semiconductors, such as CdS, are usually combined with ZnO to form hierarchical heterostructures for visible light photocatalytic degradation due to their narrow band gaps [108,[131][132][133]. For example, nanoscale tree-like CdS/ZnO nanocomposites with a hierarchical architecture showed the ability for selective oxidation of thioanisole and anaerobic reduction of nitro compound 4-nitroaniline under irradiation of artificial solar light [108].…”