Photoluminescence properties and energy transfer processes from excitons to Mn2+ ions in Mn2+-doped CdS quantum dots prepared by a reverse-micelle method

Abstract

We investigated the photoluminescence (PL) properties of Mn2+-doped CdS (CdS:Mn2+) 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 Mn2+ ions, is clearly observed at ∼2.1eV, indicating that Mn2+ ions are thoroughly doped inside CdS QDs. By surface modification with a Cd(OH)2 layer, the intensity of the Mn2+-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:Mn2+ 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 Mn2+ 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.