Characterization of Mn2+ Coordination States in ZnS Nanocrystal By EPR Spectroscopy and Related Photoluminescence Properties

Coordination states of Mn²⁺ inside and near the surface of ZnS:Mn nanocrystal (NC) (ca. 1.8 nm in particle radius) coated with poly(acrylic acid) (PAA) were examined by the detailed analysis of electron paramagnetic resonance (EPR). The symmetry of both Mn²⁺ sites inside and near the surface of NC is lower than that of submicron particles (0.125 m in particle radius), because of larger lattice distortion and larger zero field splitting constant. Temperature dependence of line width ( H_pp) of EPR signals from Mn²⁺ inside and near surface sites of ZnS:Mn disappears when the particle radius of ZnS:Mn decreases from 0.125 m to 1.8 nm. These indicate increasing extent of d–d transition and stronger interaction between Mn²⁺ and ZnS as well as between Mn²⁺ and PAA in NC, leading to more effective energy transfer from ZnS and PAA to Mn²⁺. These phenomena explain the high luminescence intensity of ZnS:Mn nanocrystal coated with PAA.