Measurement of Energy Transfer Time in Colloidal Mn-Doped Semiconductor Nanocrystals

摘要

The exciton—dopant energy transfer time in colloidal Mn-doped CdS/ZnS core/shell nanocrystals was investigated via pump—probe transient absorption measurements. The energy transfer time was obtained from the comparative analysis of the dynamics of exciton relaxation in undoped and doped nanocrystal samples with well-defined doping radius and concentration. For this purpose, the transient absorption was measured in the near-IR region probing primarily intraband transition of excitons without signal saturation even at high exciton densities, which is particularly useful for studying the energy transfer in a wide range of exciton densities. With an increasing Mn doping concentration, exciton-dopant energy transfer became faster, effectively competing with both radiative and nonradiative relaxation of exciton. In the spherical Mn-doped CdS/ZnS core/shell nanocrystals studied here, the time scale of energy transfer between a single pair of exciton and Mn~(2+) ion was determined to be ～60 ps.