Type-I CdSe@CdS@ZnS Heterostructured Nanocrystals with Long Fluorescence Lifetime

Abstract

Conventional single-component quantum dots (QDs) suffer from low recombination rates of photogenerated electrons and holes, which hinders their ability to meet the requirements for LED and laser applications. Therefore, it is urgent to design multicomponent heterojunction nanocrystals with these properties. Herein, we used CdSe quantum dot nanocrystals as a typical model, which were synthesized by means of a colloidal chemistry method at high temperatures. Then, CdS with a wide band gap was used to encapsulate the CdSe QDs, forming a CdSe@CdS core@shell heterojunction. Finally, the CdSe@CdS core@shell was modified through the growth of the ZnS shell to obtain CdSe@CdS@ZnS heterojunction nanocrystal hybrids. The morphologies, phases, structures and performance characteristics of CdSe@CdS@ZnS were evaluated using various analytical techniques, including transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy, fluorescence spectroscopy and time-resolved transient photoluminescence spectroscopy. The results show that the energy band structure is transformed from type II to type I after the ZnS growth. The photoluminescence lifetime increases from 41.4 ns to 88.8 ns and the photoluminescence quantum efficiency reaches 17.05% compared with that of pristine CdSe QDs. This paper provides a fundamental study and a new route for studying light-emitting devices and biological imaging based on multicomponent QDs.

Role of Pyramidal Low-Dimensional Semiconductors in Advancing the Field of Optoelectronics

“…Considering the important role of excitons in optoelectronics, the excitonic behavior related to PSQDs is now considered. Type I heterostructures are composed of two semiconductors with different band gaps in which one material has a higher valence band and lower conduction band than the other [222]. Moreover, type II heterostructures are composed of two semiconductors with medium band gaps (>1.3 eV) where the conduction and valence bands of one mate- Type I heterostructures are composed of two semiconductors with different band gaps in which one material has a higher valence band and lower conduction band than the other [222].…”

“…Type I heterostructures are composed of two semiconductors with different band gaps in which one material has a higher valence band and lower conduction band than the other [222]. Moreover, type II heterostructures are composed of two semiconductors with medium band gaps (>1.3 eV) where the conduction and valence bands of one mate- Type I heterostructures are composed of two semiconductors with different band gaps in which one material has a higher valence band and lower conduction band than the other [222]. Moreover, type II heterostructures are composed of two semiconductors with medium band gaps (>1.3 eV) where the conduction and valence bands of one material are higher than those of the other [223].…”