Comparison of the Femtosecond Time-resolved Excited State Dynamics in Copper Oxide and Copper Sulfide Quantum Dots

摘要

The relaxation dynamics of Cu_2O and Cu_(1.8)S quantum dots (QDs) are compared via time-resolved femtosecond pump probe experiments. It is found that Cu_2O shows extremely long-lived excited states on the microsecond time scale and Cu_(1.8)S exhibits much shorter lifetimes in the picosecond time regime. While copper sulfide systems are described in the literature as p-type direct band gap materials, the Cu_2O system is direct band gap, however it has a forbidden lowest-energy state. These differences are expressed in the different lifetimes displayed in the time-resolved femtosecond and nanosecond measurements. Moreover, it is confirmed by photoluminescence spectroscopy that reveals that only the Cu_(1.8)S QDs show efficient PL and the Cu_2O QDs do not luminescence. In all of the systems, carrier trapping is probably the lifetime limiting process for the conduction band edge depopulation.