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ACS Nano. 2018 Jun 26;12(6):5539-5550. doi: 10.1021/acsnano.8b01248. Epub 2018 May 25.

Wave Function Engineering in CdSe/PbS Core/Shell Quantum Dots.

Author information

1
Department of Chemistry and Institute of Materials Science and Engineering , Washington University in St. Louis , One Brookings Drive, CB 1134 , Saint Louis , Missouri 63130 , United States.
2
Department of Chemistry and Cherry L. Emerson Center for Scientific Computation , Emory University , Atlanta , Georgia 30322 , United States.

Abstract

The synthesis of epitaxial CdSe/PbS core/shell quantum dots (QDs) is reported. The PbS shell grows in a rock salt structure on the zinc blende CdSe core, thereby creating a crystal structure mismatch through additive growth. Absorption and photoluminescence (PL) band edge features shift to lower energies with increasing shell thickness, but remain above the CdSe bulk band gap. Nevertheless, the profiles of the absorption spectra vary with shell growth, indicating that the overlap of the electron and hole wave functions is changing significantly. This leads to over an order of magnitude reduction of absorption near the band gap and a large, tunable energy shift, of up to 550 meV, between the onset of strong absorption and the band edge PL. While the bulk valence and conduction bands adopt an inverse type-I alignment, the observed spectroscopic behavior is consistent with a transition between quasi-type-I and quasi-type-II behavior depending on shell thickness. Three effective mass approximation models support this hypothesis and suggest that the large difference in effective masses between the core and shell results in hole localization in the CdSe core and a delocalization of the electron across the entire QD. These results show the tuning of wave functions and transition energies in CdSe/PbS nanoheterostructures with prospects for use in optoelectronic devices for luminescent solar concentration or multiexciton generation.

KEYWORDS:

CdSe/PbS; core/shell; luminescent solar concentrator; multiexciton generation; nanocrystal heterostructure; quantum dots; wave function engineering

PMID:
29787230
DOI:
10.1021/acsnano.8b01248

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