EPR Spectra of Mn2+-Doped ZnS Quantum Dots

Powder Mn2+ 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 Mn2+ (0.003-0.008%), showing 10 weak forbidden transitions between the six-line pattern of the MS = -1\2 to MS = 1\2 transition for the six MI values. Spectral simulations have been performed with the Simfonia program with parameters gxx = 2.0064, gyy = 2.0064, gzz = 2.0066, D = 37.4 × 10-4 cm-1, E = 12.5 × 10-4 cm-1, Axx = 63.9 × 10-4 cm-1, Ayy = 64.0 × 10-4 cm-1, and Azz = 64.4 × 10-4 cm-1, suggesting a lower than Td site symmetry for the doped Mn2+ in the cubic ZnS structure. At higher doping concentration (15.9%), a single broad line is observed with isotropic g and A.