Photoluminescence properties and energy transfer processes from excitons to Mn~(2+) ions in Mn~(2+)-doped CdS quantum dots prepared by a reverse-micelle method

摘要

We investigated the photoluminescence (PL) properties of Mn~(2+)-doped CdS (CdS: Mn~(2+)) quantum dots (QDs) prepared by a reverse-micelle method. A PL band which originates from the intracation transition, the so-called d-d transition, of tetrahedrally coordinated Mn~(2+) ions, is clearly observed at ～2.1 eV, indicating that Mn~(2+) ions are thoroughly doped inside CdS QDs. By surfacd modification with a Cd(OH)_2 layer, the intensity of the Mn~(2+)-related PL band is increased approximately ten times compared with that without modification, and strong enhancement of the band-edge PL band is observed. The decay profile of the band-edge PL in surface-modified CdS: Mn~(2+) QDs is much faster than that in undoped CdS QDs; this shortened decay time originates from the effective energy transfer process from the excitons of host QDs to Mn~(2+) ions. The PL decay profiles are quantitatively explained on the basis of a three-level model including both the dark-exciton state and the energy transfer process.