Abstract
The relaxation dynamics of Cu<sub>2</sub>O and Cu<sub>1.8</sub>S quantum dots (QDs) are compared via time-resolved femtosecond pump probe experiments. It is found that Cu<sub>2</sub>O shows extremely long-lived excited states on the microsecond time scale and Cu<sub>1.8</sub>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<sub>2</sub>O 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<sub>1.8</sub>S QDs show efficient PL and the Cu<sub>2</sub>O QDs do not luminescence. In all of the systems, carrier trapping is probably the lifetime limiting process for the conduction band edge depopulation.
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