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Title: Copper-Doped Inverted Core/Shell Nanocrystals with “Permanent” Optically Active Holes

Abstract

We have developed a new class of colloidal nanocrystals composed of Cu-doped ZnSe cores overcoated with CdSe shells. Via spectroscopic and magneto-optical studies, we conclusively demonstrate that Cu impurities represent paramagnetic +2 species and serve as a source of permanent optically active holes. This implies that the Fermi level is located below the Cu{sup 2+}/Cu{sup 1+} state, that is, in the lower half of the forbidden gap, which is a signature of a p-doped material. It further suggests that the activation of optical emission due to the Cu level requires injection of only an electron without a need for a valence-band hole. This peculiar electron-only emission mechanism is confirmed by experiments in which the titration of the nanocrystals with hole-withdrawing molecules leads to enhancement of Cu-related photoluminescence while simultaneously suppressing the intrinsic, band-edge exciton emission. In addition to containing permanent optically active holes, these newly developed materials show unprecedented emission tunability from near-infrared (1.2 eV) to the blue (3.1 eV) and reduced losses from reabsorption due to a large Stokes shift (up to 0.7 eV). These properties make them very attractive for applications in light-emission and lasing technologies and especially for the realization of novel device concepts such as “zero-threshold”more » optical gain.« less

Authors:
 [1];  [1];  [2];  [3];  [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Chemistry Division
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Chemistry Division and Center for Advanced Solar Photophysics (CASP)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab)
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC); Center for Advanced Solar Photophysics (CASP)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1065772
DOE Contract Number:  
AC52-06NA25396
Resource Type:
Journal Article
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 11; Journal Issue: 11; 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 1530-6984
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; 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

Viswanatha, Ranjani, Brovelli, Sergio, Pandey, Anshu, Crooker, Scott A., and Klimov, Victor I. Copper-Doped Inverted Core/Shell Nanocrystals with “Permanent” Optically Active Holes. United States: N. p., 2011. Web. doi:10.1021/nl202572c.
Viswanatha, Ranjani, Brovelli, Sergio, Pandey, Anshu, Crooker, Scott A., & Klimov, Victor I. Copper-Doped Inverted Core/Shell Nanocrystals with “Permanent” Optically Active Holes. United States. doi:10.1021/nl202572c.
Viswanatha, Ranjani, Brovelli, Sergio, Pandey, Anshu, Crooker, Scott A., and Klimov, Victor I. Fri . "Copper-Doped Inverted Core/Shell Nanocrystals with “Permanent” Optically Active Holes". United States. doi:10.1021/nl202572c.
@article{osti_1065772,
title = {Copper-Doped Inverted Core/Shell Nanocrystals with “Permanent” Optically Active Holes},
author = {Viswanatha, Ranjani and Brovelli, Sergio and Pandey, Anshu and Crooker, Scott A. and Klimov, Victor I.},
abstractNote = {We have developed a new class of colloidal nanocrystals composed of Cu-doped ZnSe cores overcoated with CdSe shells. Via spectroscopic and magneto-optical studies, we conclusively demonstrate that Cu impurities represent paramagnetic +2 species and serve as a source of permanent optically active holes. This implies that the Fermi level is located below the Cu{sup 2+}/Cu{sup 1+} state, that is, in the lower half of the forbidden gap, which is a signature of a p-doped material. It further suggests that the activation of optical emission due to the Cu level requires injection of only an electron without a need for a valence-band hole. This peculiar electron-only emission mechanism is confirmed by experiments in which the titration of the nanocrystals with hole-withdrawing molecules leads to enhancement of Cu-related photoluminescence while simultaneously suppressing the intrinsic, band-edge exciton emission. In addition to containing permanent optically active holes, these newly developed materials show unprecedented emission tunability from near-infrared (1.2 eV) to the blue (3.1 eV) and reduced losses from reabsorption due to a large Stokes shift (up to 0.7 eV). These properties make them very attractive for applications in light-emission and lasing technologies and especially for the realization of novel device concepts such as “zero-threshold” optical gain.},
doi = {10.1021/nl202572c},
journal = {Nano Letters},
issn = {1530-6984},
number = 11,
volume = 11,
place = {United States},
year = {2011},
month = {9}
}