Bright type-II photoluminescence from Mn-doped CdS/ZnSe/ZnS quantum dots with Mn2+ ions as exciton couplers

摘要

Mn2+ ions were introduced as exciton couplers to enhance the quantum yield (QY) of type-II photoluminescence (PL) from CdS/ZnSe/ZnS quantum dots (QDs) with slow hot-exciton cooling and low radiative rate. Transient absorption spectroscopy verifies the faster bleach recovery and faster peak red-shifting at the charge-transfer state. And the transient PL peak of the QDs changes from blue-shifting to red-shifting due to Mn2+ doping. The QY of type-II PL can be enhanced from similar to 35% to similar to 60% by Mn2+ doping. As the energy-transfer-stations of hot excitons during rapid ET (similar to 100 ps), Mn2+ ions transform more excitons from hot to cold for emission. As the couplers of cold excitons during long thermal equilibrium (similar to 100 ns), Mn2+ ions further decrease exciton trapping by strong bidirectional coupling. This work provides a unique way of acquiring high QY of type-II PL, and highlights the general law of PL enhancement in Mn-doped QDs.