EPR study of ZnS: Mn2+ nanocrystals in Pyrex glasses.

ZnS: Mn2+ nanocrystals embedded in Pyrex glasses were spectrally studied using EPR and photoluminescence techniques. Photoluminescence (PL) and excitation (PLE) spectra revealed that manganese impurities can be classified as two types of luminescent centers, i.e., occupying substitutional sites (Mn2+)sub or interstitial sites (Mn2+)int. Three types of manganese sites of (Mn2+)sub, (Mn2+)int, and Mn clusters were identified by the EPR spectra. An increase of the g1 factor and hyperfine structure (HFS) constant with decreasing sizes of nanocrystals was observed. The increase was attributed to a hybridization of the s-p state of ZnS and the d state of manganese ions enhanced by quantum confinement effects or surface states.