Effect ofMn2+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) $\mathrm{Mn}{(S}_{I})$ in tetrahedral cationic substitution site with ${T}_{d}$ symmetry, (2) isolated Mn ions at the surface or interstitial locations ${(S}_{\mathrm{II}})$ with octahedral symmetry $({\mathrm{O}}_{h}),$ (3) Mn-Mn dipolar interactions ${(S}_{\mathrm{III}}),$ and (4) exchange-coupled Mn clusters ${(S}_{\mathrm{IV}})$ in various proportions. Linewidths for all these ${(S}_{I}$--${S}_{\mathrm{IV}})$ differ from each other. Identification of these components suggests that ${S}_{I}$ may be responsible for the photoluminescence increase, whereas ${S}_{\mathrm{II}}$--${S}_{\mathrm{IV}}$ may be responsible for the luminescence quenching in nanoparticles.