Femtosecond spectroscopic investigation of the carrier lifetimes in digenite quantum dots and discrimination of the electron and hole dynamics via ultrafast interfacial electron transfer

For the CuxS system there exists several known solid phases such as Cu2S (chalcocite), Cu1.8S (digenite), Cu1.96S (djurleite), and CuS (covellite). All of these phases have been identified as p-type semiconducting materials due to copper vacancies within the lattice, which is responsible for their usefulness as optoelectronic materials. The different CuxS phases show reportedly low band gap energies of greater than or equal to 1.2 eV for the bulk, which makes them potentially ideal for application purposes of photoinduced voltaics or catalysis where activation through visible light is desired. In this study, we report on the femtosecond carrier dynamics of digenite copper sulfide quantum dots. Digenite quantum dots were prepared by a single source precursor type process and the optical transitions and dynamic properties of the photoinduced charge carriers in these novel nanomaterials characterized by femtosecond time-resolved spectroscopy. It is found that the larger quantum dots have longer excited-state lifetimes, which implies a strong surface-induced effect on the relaxation dynamics. In addition, the dynamics of the electron was differentiated from that of the hole by employing the technique of rapid (<100 fs) electron trapping at adsorbed organic electron acceptors such as benzoquinone.