The symmetry and electronic structure of the Mn impurity in ZnS nanocrystals have been studied with electron paramagnetic resonance (EPR). Experiments were performed at 9 and 35 GHz on crystals with an average diameter of 35 Å. Changes in the spectra over a period of months indicate a gradual degeneration of the passivating layer that separates individual nanocrystals. These changes allow for the deconvolution of the total EPR spectra into two independent spectra. The first has g=2.003 and ‖A‖=64.5×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$. This spectrum is dominated by Mn-Mn dipolar interactions and is similar to the spectrum of heavily Mn-doped, bulk ZnS. The second spectrum has g=2.001 and ‖A‖=89×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$ with axial-field splittings (D) from 0.05 to 0.10 ${\mathrm{cm}}^{\mathrm{-}1}$. This spectrum is associated with isolated Mn sites near the surface of a nanocrystal. The EPR results are discussed in relation to the previously published optical results.

• Received 10 August 1995

DOI:https://doi.org/10.1103/PhysRevB.52.R14356