Optical and electron paramagnetic resonance spectroscopy ofCd1−xMnxS quantum dots

Abstract

Cd1−xMnxS quantum dots (QDs) with diameter nm and with manganese concentrations fromx = 0.001 to 0.15 have been prepared using aqueous solution precipitation. Absorption andfluorescence spectra at room temperature have been recorded. No monotonic variation ofthe band gap energy with increasing manganese concentration is observed. The electronparamagnetic resonance (EPR) measurements were performed on a 9.5 GHz spectrometer inthe temperature range 20–290 K. Two structures in the EPR spectra are observed for allthe manganese concentrations: a hyperfine structure and a broad EPR line. Thehyperfine structure is described by allowed and forbidden hyperfine transitions of theMn2+ ion central sextet with hyperfine splitting constant|A| = 9.6 mT and with axial-fieldsplitting parameter D ranging from 11.1 to 13.5 mT. The hyperfine structure is attributed to the isolatedMn2+ ions at or near the surface of the nanocrystals. The width of the broad resonance and itstemperature independence suggest that the wide line originates from the noncentralmanganese transitions broadened by crystal-field effects, as in some disordered materials.