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.

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