Evidence of a ZnCr 2Se 4 spinel inclusion at the core of a Cr-doped ZnSe quantum dot

Weiwei Zheng, Kedar Singh, Zhenxing Wang, Joshua T. Wright, Johan Van Tol, Naresh S. Dalal, Robert W. Meulenberg, Geoffrey F. Strouse

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Herein we report doping of ZnSe by Cr ions leads to formation of small ZnCr 2Se 4 spinel inclusions within the cubic sphalerite lattice of a 2.8 nm CrZnSe quantum dot (QD). The Cr ion incorporates as a pair of Cr(III) ions occupying edge-sharing tetragonal distorted octahedral sites generated by formation of three Zn ion vacancies in the sphalerite lattice in order to charge compensate the QD. The site is analogous to the formation of a subunit of the ZnCr 2Se 4 spinel phase known to form as inclusions during peritectoid crystal growth in the ternary CrZnSe solid-state compound. The oxidation state and site symmetry of the Cr ion is confirmed by X-ray absorption near edge spectroscopy (XANES), crystal field absorption spectroscopy, and electron paramagnetic resonance (EPR). Incorporation as the Cr(III) oxidation state is consistent with the thermodynamic preference for Cr to occupy an octahedral site within a II-VI semiconductor lattice with a half-filled t 2g d-level. The measured crystal field splitting energy for the CrZnSe QD is 2.08 eV (2.07 eV form XANES), consistent with a spinel inclusion. Further evidence of a spinel inclusion is provided by analysis of the magnetic data, where antiferromagnetic (AFM) exchange, a Curie-Weiss (C-W) temperature of θ = -125 K, and a nearest-neighbor exchange coupling constant of J NN = -12.5 K are observed. The formation of stable spinel inclusions in a QD has not been previously reported.

Original languageEnglish (US)
Pages (from-to)5577-5585
Number of pages9
JournalJournal of the American Chemical Society
Volume134
Issue number12
DOIs
StatePublished - Mar 28 2012
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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