Emission processes in colloidal PbSe/PbS core-shell quantum dots

The present study describes a thorough investigation of the ground-state exciton emission of PbSe/PbS core-shell colloidal quantum dots (CQDs) with different shell-thickness/core-radius ratio, by recording the photoluminescence (PL) spectra and the corresponding emission decay processes over a temperature range from 1.4 K to 300 K. These spectra were compared with that of the corresponding PbSe core CQDs. All PL spectra showed variation in the emission intensity and peak energy, including two distinct abrupt transitions, upon the increase of the temperature. However, the transitions appeared at different temperatures in the core-shell structures with respect to that of the core. Further on, the PL-decay processes in the core materials showed a single exponent behavior, while the emission of the core-shell CQDs, decayed as a stretched exponent, with an effective lifetime of ∼1 μs, at room temperature, slightly longer than that of the corresponding core.