EPR study of manganese in Cd1-xMnxS quantum dots

Abstract

Cd1-xMnxS quantum dots (QDs) with a diameter d less than or equal to 4.5 nm and manganese concentration from x 0.001 to x 0.15 have been prepared using aqueous Solution precipitation. The EPR measurements have been performed on a 9.5 GHz spectrometer in the temperature range 20-290 K. Two structures are observed in the EPR spectra for all manganese concentrations, a hyperfine structure and a broad EPR line. The hyperfine structure is described by allowed and forbidden hyperfine transitions of the Mn2+ ion central sextet with the hyperfine splitting constant \A\ 9.6 mT and axial-field splitting parameter D ranging from 11.1 to 13.5 mT. The hyperfine structure is attributed to the isolated Mn2+ ions at or near the surface of nanocrystals. The width of the broad resonance and its temperature independence suggest that the wide line originates from noncentral manganese transitions broadened by crystal field effects, as in some disordered materials.