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Preparation and Optoelectronic Property of Core-shell Semiconductor Quantum Dots

Author: HeHongYan
Tutor: FengDongHaiï¼›JiaTianQing
School: East China Normal University
Course: Optics
Keywords: ZnO / ZnS CdTe / CdS Core-shell structure Quantum dots Electro-optical characteristics
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 152
Quote: 1
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Abstract


The core-shell structure of semiconductor quantum dots have unique optical, electrical and catalytic properties, caused academia extensive attention. Wood papers using simple and reasonable synthetic route to prepare a variety of core-shell structure quantum dots and then study its optical characteristics. On the basis of the material composition or morphology characterization, the focus of luminescence and absorption, catalytic activity and ultrafast carrier dynamics. The main work of this paper is summarized as follows: 1. Water bath reflux synthesis of uniform size, better monodisperse ZnO quantum dots and different shell thickness of ZnO / ZnS quantum dots. Means of XPS, TEM, PL crystal form, composition, light-emitting quantum dots were characterized. Light degradation of methyl orange (MO) under ultraviolet light photocatalytic properties of ZnO / ZnS quantum dot. The main conclusions are as follows: (1) XPS, TEM characterization of the composition of the quantum dots, morphology and ZnO, ZnS relative proportion size. ZnO particle size of about 4.8nm, wrapped ZnS shell will further increase the quantum dot size. PL spectra test ZnO quantum dots visible emission peak at 486 nm, wrapped about 2.5nm thickness of ZnS, a bimodal structure are of ZnS defects caused 446nm emission peak as well as the formation of ZnO / ZnS type II core-shell structure resulting from 496nm light-emitting peak. (2) under ultraviolet light, ZnO / ZnS as a catalyst, MO degradation speed, high degradation efficiency. Its catalytic activity than single ZnO or ZnS quantum dots superior. The fundamental reason is that ZnO / ZnS as a type II semiconductor core-shell structure, the light generated electron hole effectively separated in space and reduce the electron-hole recombination probability. 2 synthesized using a water bath reflux method of uniform size, the monodisperse better CdTe quantum dots as well as the different thickness of the shell CdTe / CdS quantum dots. TEM, PL and other means to shape, the light-emitting quantum dots were characterized. Transient differential transmission method based on the pump - probe technology, the use of different shell thickness of the CdTe / CdS quantum dots ultrafast carrier relaxation mechanism. The main conclusions are as follows: (1) a CdTe particle size of approximately 3nm, wrapped CdS shell quantum dot size will further increase. CdTe cores, compared to room temperature for CdTe / CdS quantum dot light emitting peak Location redshift redshift increased with the increase in the thickness of the shell. (2) CdTe and CdTe / CdS quantum dots in the 800nm ??light excitation, the two-photon fluorescence intensity of the fluorescence and excitation light power is approximately quadratic relationship. (3) compared to at CdTe, CdTe / CdS quantum dots carrier having a longer relaxation time, and along with the increase of the thickness of the shell, the relaxation process becomes increasingly slow. Studies have shown that with the introduction of shell and increasing the thickness of the carrier relaxation from surface defects related state relaxation mechanism transition to the carrier spatial separation of the formation of the core / shell interface carrier relaxation.

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