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Title: Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions

Abstract

We have analysed the effect of symmetry breaking on the optical properties of semiconductor nanocrystals due to doping by charged impurities. Using doped CdSe nanocrystals as an example, we show the effects of a Coulomb center on the exciton fine-structure and optical selection rules using symmetry theory and then quantify the effect of symmetry breaking on the exciton fine structure, modelling the charged center using a multipole expansion. The model shows that the presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through mixing and shifting of the hole spin and parity sublevels. This symmetry breaking, particularly for positively charged centers, shortens the radiative lifetime of CdSe nanocrystals even at room temperature, in qualitative agreement with the increase in PL efficiency observed in CdSe nanocrystals doped with positive Ag charge centers [A. Sahu et.al., Nano Lett. 12, 2587, (2012)]. The effect of the charged center on the photoluminescence and the absorption spectra is shown, with and without the presence of compensating charges on the nanocrystal surface. While spectra of individual nanocrystals are expected to shift and broaden with the introduction of a charged center, configuration averaging and inhomogeneous broadening are shown to wash out thesemore » effects. The presence of compensating charges at the NC surface also serves to stabilize the band edge transition energies relative to NCs with no charge centers.« less

Authors:
; ;
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Advanced Solar Photophysics (CASP)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1470556
DOE Contract Number:  
AC52-06NA25396
Resource Type:
Journal Article
Journal Name:
MRS Advances
Additional Journal Information:
Journal Volume: 3; Journal Issue: 14; Related Information: CASP partners with Los Alamos National Laboratory (lead); University of California, Irvine; University of Colorado; Colorado School of Mines; George Mason University; Los Alamos National Laboratory; University of Minnesota; National Renewable Energy Laboratory; Journal ID: ISSN 2059-8521
Publisher:
Materials Research Society (MRS)
Country of Publication:
United States
Language:
English
Subject:
solar (photovoltaic), solar (fuels), solid state lighting, bio-inspired, electrodes - solar, defects, charge transport, materials and chemistry by design, optics, synthesis (novel materials), synthesis (scalable processing)

Citation Formats

Sercel, Peter C., Shabaev, Andrew, and Efros, Alexander L. Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions. United States: N. p., 2018. Web. doi:10.1557/adv.2018.19.
Sercel, Peter C., Shabaev, Andrew, & Efros, Alexander L. Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions. United States. doi:10.1557/adv.2018.19.
Sercel, Peter C., Shabaev, Andrew, and Efros, Alexander L. Mon . "Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions". United States. doi:10.1557/adv.2018.19.
@article{osti_1470556,
title = {Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions},
author = {Sercel, Peter C. and Shabaev, Andrew and Efros, Alexander L.},
abstractNote = {We have analysed the effect of symmetry breaking on the optical properties of semiconductor nanocrystals due to doping by charged impurities. Using doped CdSe nanocrystals as an example, we show the effects of a Coulomb center on the exciton fine-structure and optical selection rules using symmetry theory and then quantify the effect of symmetry breaking on the exciton fine structure, modelling the charged center using a multipole expansion. The model shows that the presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through mixing and shifting of the hole spin and parity sublevels. This symmetry breaking, particularly for positively charged centers, shortens the radiative lifetime of CdSe nanocrystals even at room temperature, in qualitative agreement with the increase in PL efficiency observed in CdSe nanocrystals doped with positive Ag charge centers [A. Sahu et.al., Nano Lett.12, 2587, (2012)]. The effect of the charged center on the photoluminescence and the absorption spectra is shown, with and without the presence of compensating charges on the nanocrystal surface. While spectra of individual nanocrystals are expected to shift and broaden with the introduction of a charged center, configuration averaging and inhomogeneous broadening are shown to wash out these effects. The presence of compensating charges at the NC surface also serves to stabilize the band edge transition energies relative to NCs with no charge centers.},
doi = {10.1557/adv.2018.19},
journal = {MRS Advances},
issn = {2059-8521},
number = 14,
volume = 3,
place = {United States},
year = {2018},
month = {1}
}

Works referenced in this record:

Electronic Impurity Doping in CdSe Nanocrystals
journal, April 2012

  • Sahu, Ayaskanta; Kang, Moon Sung; Kompch, Alexander
  • Nano Letters, Vol. 12, Issue 5
  • DOI: 10.1021/nl300880g

Band-edge exciton in quantum dots of semiconductors with a degenerate valence band: Dark and bright exciton states
journal, August 1996


Photoluminescence Enhancement through Symmetry Breaking Induced by Defects in Nanocrystals
journal, July 2017


Theory of Solutions of Molecules Containing Widely Separated Charges with Special Application to Zwitterions
journal, July 1934

  • Kirkwood, John G.
  • The Journal of Chemical Physics, Vol. 2, Issue 7
  • DOI: 10.1063/1.1749489