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

Organically capped zinc sulfide nanoparticles doped with different manganese concentrations were prepared under similar conditions. Only the doping concentration was varied. Photoluminescence and electron-spin-resonance (ESR) investigations show some new results. At an optimum concentration of Mn doping a maximum in the photoluminescence is reached, whereas photoluminescence 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) isolated Mn ions at the surface or interstitial locations (S-II) with octahedral symmetry (O-h) (3) Mn-Mn dipolar interactions (S-III), and (4) exchange-coupled Mn clusters (S-IV) in various proportions. Linewidths for all these (S-I-S-IV) differ from each other. Identification of these components suggests that S-I may be responsible for the photoluminescence increase, whereas S-II-S-IV may be responsible for the luminescence quenching in nanoparticles.