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Article

Electronic Absorption Spectroscopy of Cobalt Ions in Diluted Magnetic Semiconductor Quantum Dots: Demonstration of an Isocrystalline Core/Shell Synthetic Method

Supporting Info

Pavle V. Radovanovic and Daniel R. Gamelin*

Contribution from the Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195-1700

J. Am. Chem. Soc., 2001, 123 (49), pp 12207–12214

DOI: 10.1021/ja0115215

Publication Date (Web): November 16, 2001

Corresponding author. E-mail: Gamelin@chem.washington.edu.

Abstract

This paper reports the application of ligand-field electronic absorption spectroscopy to probe Co²⁺ dopant ions in diluted magnetic semiconductor quantum dots. It is found that standard inverted micelle coprecipitation methods for preparing Co²⁺-doped CdS (Co²⁺:CdS) quantum dots yield dopant ions predominantly bound to the nanocrystal surfaces. These Co²⁺:CdS nanocrystals are unstable with respect to solvation of surface-bound Co²⁺, and time-dependent absorption measurements allow identification of two transient surface-bound intermediates involving solvent−cobalt coordination. Comparison with Co²⁺:ZnS quantum dots prepared by the same methods, which show nearly isotropic dopant distribution, indicates that the large mismatch between the ionic radii of Co²⁺ (0.74 Å) and Cd²⁺ (0.97 Å) is responsible for exclusion of Co²⁺ ions during CdS nanocrystal growth. An isocrystalline core/shell preparative method is developed that allows synthesis of internally doped Co²⁺:CdS quantum dots through encapsulation of surface-bound ions beneath additional layers of CdS.