Effect of Mn2+ concentration in ZnS nanoparticles on photoluminescence andelectron-spin-resonance spectra

Organically capped zinc sulfide nanoparticles doped with different manganes e concentrations were prepared under similar conditions. Only the doping co ncentration was varied. Photoluminescence and electron-spin-resonance (ESR) investigations show some new results. At an optimum concentration of Mn do ping a maximum in the photoluminescence is reached, whereas photoluminescen ce quenching occurs at higher concentrations. ESR investigations show that the spectra arise due to four different contributions of Mn ions, viz., (1) Mn(S-I) in tetrahedral cationic substitution site with T-d symmetry, (2) i solated Mn ions at the surface or interstitial locations (S-II) with octahe dral symmetry (O-h) (3) Mn-Mn dipolar interactions (S-III), and (4) exchang e-coupled Mn clusters (S-IV) in various proportions. Linewidths for all the se (S-I-S-IV) differ from each other. Identification of these components su ggests that S-I may be responsible for the photoluminescence increase, wher eas S-II-S-IV may be responsible for the luminescence quenching in nanopart icles.