Superposition of Quantum Confinement Energy (SQCE) model for estimating shell thickness in core-shell quantum dots: Validation and comparison

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• 作者：Amit D. Saran^a ; Anurag Mehra^a ; Jayesh R. Bellare^a ; ^b ; ^{jb@iitb.ac.in}
• 关键词：Quantum confinement ; Core&ndash ; shell quantum dot ; Microemulsion ; Shell thickness ; CdSe&ndash ; CdS ; CdSe&ndash ; ZnS ; Fluorescence quantum yield
• 刊名：Journal of Colloid and Interface Science
• 出版年：2012
• 期刊代码：125_00219797
• 类别：ch
• 出版时间：15 July, 2012
• 卷：378
• 期：1
• 页码：21-29
• 文件大小：1363 K

摘要

A novel theoretical model based on superposition of core and shell band-gaps, termed as SQCE model, is developed and reported here, which enables one to estimate the shell thickness in a core-shell quantum dot (QD), which is critically important in deciding its optical and electronic properties. We apply the model to two experimental core-shell QD systems, CdSe-CdS and CdSe-ZnS, which we synthesize by microemulsion method. We synthesize and study two series of samples, R and S to study the optical properties. The core size is varied in the R-series (by varying water-to-surfactant ratio, R) whereas the shell thickness is varied in the S-series (by varying the shell-to-core precursor molar ratio, S). The core and core-shell QDs from R-series and S-series are characterized for particle size, shape and crystallographic information. The shell thickness for all core-shell QD samples is estimated by SQCE model, and experimentally measured with TEM and SAXS. A close match is observed between experimental values and model predictions, thus validating the model. Further, the optimum shell thickness (corresponding to maximum quantum yield) values for CdS and ZnS over a 4.26 nm CdSe core have been estimated as 0.585 nm and 0.689 nm, respectively, from the SQCE model. The SQCE model developed in this work is applicable to other core-shell quantum dots also, such as CdTe-CdS, CdTe-CdSe and CdS-ZnS, and will serve as a useful complement to experimental measurement.