Exciton storage by Mn2+ in colloidal Mn2+-doped CdSe quantum dots

Colloidal Mn2+-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to tau(exc) = 15 mu s at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by similar to 10(3) and are shown to arise from the creation of excitons by back energy transfer from excited Mn2+ dopant ions. A kinetic model describing thermal equilibrium between Mn2+ IT, and CdSe excitonic excited states reproduces the experimental observations and reveals that, for some quantum dots, excitons can emit with near unity probability despite being similar to 100 meV above the Mn2+ T-4(1) state. The effect of Mn2+ doping on CdSe quantum dot luminescence at high temperatures is thus completely opposite from that at low temperatures described previously.