Ligand removal from soluble CdTe nanocrystals evidenced by time-resolved photoluminescence spectroscopy

We present experimental studies on the effect of pyridine treatment on the optical properties of ligand-stabilized colloidal CdTe nanocrystals. We demonstrate, by quasi-stationary and time-resolved photoluminescence (PL) spectroscopy, a drastic reduction in the PL lifetime and a concomitant decrease in the PL yield by more than 90% when dissolving the nanocrystals in pyridine. The pyridine solvent efficiently removes the ligand shell and thus enables a rapid energy transfer from the quantum dot to optically dark surface states or into the solvent. The demonstrated removal of the ligand shell is a key step towards integrating such CdTe nanocrystals in hybrid organic/inorganic nanocomposites, where charges may be efficiently separated at the interface. Due to the small band gap of CdTe, such nanocomposites are likely to yield enhanced conversion efficiencies in photovoltaic devices.