Evidence of a ZnCr2Se4 Spinel Inclusion at the Core of a Cr-Doped ZnSe Quantum Dot

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• 作者：Weiwei Zheng ; Kedar Singh ; Zhenxing Wang ; Joshua T. Wright ; Johan van Tol ; Naresh S. Dalal ; Robert W. Meulenberg ; Geoffrey F. Strouse
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：March 28, 2012
• 年：2012
• 卷：134
• 期：12
• 页码：5577-5585
• 全文大小：460K
• 年卷期：v.134,no.12(March 28, 2012)
• ISSN：1520-5126

文摘

Herein we report doping of ZnSe by Cr ions leads to formation of small ZnCr₂Se₄ 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 ZnCr₂Se₄ 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鈥揤I 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鈥揥eiss (C鈥揥) temperature of 胃 = 鈭?25 K, and a nearest-neighbor exchange coupling constant of J_NN = 鈭?2.5 K are observed. The formation of stable spinel inclusions in a QD has not been previously reported.