Doping Location-Dependent Energy Transfer Dynamics in Mn-Doped CdS/ZnS Nanocrystals

Dynamics of energy transfer and charge carrier localization in Mn-doped CdS/ZnS core/shell nanocrystals correlated with doping location and concentration are studied <i>via</i> transient absorption measurement of exciton relaxation dynamics. The strong dependence of exciton–Mn energy transfer rate on doping location was directly resolved in the transient bleach recovery and electron intraband absorption data by using layer-by-layer synthesized Mn-doped nanocrystals. With 1.2 nm decrease in doping radius in the ZnS shell, energy transfer rate increases by 6 fold. We identified that hole trapping is the major competing process that inhibits the energy transfer in Mn-doped CdS/ZnS nanocrystals. From the branching ratio of the energy transfer and hole trapping, combined with luminescence quantum yield measurement, we also obtained doping location-dependent radiative relaxation quantum yield of Mn²⁺ ions that is as high as 0.95