title: Giant excitonic Zeeman splittings in colloidal Co2+ -doped ZnSe quantum dots.
abstract: Colloidal Co(2+):ZnSe diluted magnetic semiconductor quantum dots (DMS-QDs) were prepared by the hot injection method and studied spectroscopically. Ligand-field electronic absorption and magnetic circular dichroism (MCD) spectra confirm homogeneous substitutional speciation of Co(2+) in the ZnSe QDs. Absorption spectra collected at various times throughout the syntheses reveal that dopants are absent from the central cores of the QDs but are incorporated at a constant concentration during nanocrystal growth. The undoped cores are associated with dopant exclusion from the ZnSe critical nuclei. Analysis of low-temperature electronic absorption and MCD spectra revealed excitonic Zeeman splitting energies (DeltaE(Zeeman)) of these Co(2+):ZnSe QDs that were substantially smaller than anticipated from bulk Co(2+):ZnSe data. This reduction in DeltaE(Zeeman) is explained quantitatively by the absence of dopants from the QD cores, where dopant-exciton overlap would be greatest. Since dopant exclusion from nucleation appears to be a general phenomenon for DMS-QDs grown by direct chemical methods, we propose that DeltaE(Zeeman) will always be smaller in colloidal DMS-QDs grown by such methods than in the corresponding bulk materials.
authors.affiliation: Department of Chemistry, Box 351700, University of Washington, Seattle, 98195-1700, USA.
authors.forename: Nick S
authors.initials: NS
authors.lastname: Norberg
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Parks
authors.forename: G Mackay
authors.initials: GM
authors.lastname: Salley
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gamelin