EPR Spectra of Mn²⁺-Doped ZnS Quantum Dots

Powder Mn 2+ EPR spectra of 5-nm ZnS:Mn quantum dots have been analyzed in detail to account for all the observed fine spectral features. The same spectral features are observed in samples with low doping of Mn 2+ (0.003−0.008%), showing 10 weak forbidden transitions between the six-line pattern of the M S = − 1 / 2 to M S = 1 / 2 transition for the six M I values. Spectral simulations have been performed with the Simfonia program with parameters g xx = 2.0064, g yy = 2.0064, g zz = 2.0066, D = 37.4 × 10 - 4 cm - 1, E = 12.5 × 10 - 4 cm - 1, A xx = 63.9 × 10 - 4 cm - 1, A yy = 64.0 × 10 - 4 cm - 1, and A zz = 64.4 × 10 - 4 cm - 1, suggesting a lower than T d site symmetry for the doped Mn 2+ in the cubic ZnS structure. At higher doping concentration (15.9%), a single broad line is observed with isotropic g and A .