Figure 1

(a) Absorption spectra of PbSe NCs in hexane for different NC sizes (offset for clarity). (b) Peak positions of exciton features in PbSe NCs as well as the energy separation of $1P\mathrm{\text{−}}1S$ as a function of NC radius. (c) TA traces collected with a probe energy tuned to the $1S$ (circles) and $1P$ (squares) peak positions for a 3.5-nm radius PbSe NC sample showing complementary buildup, ${\tau }_B$, and decay, ${\tau }_D$, lifetimes of the $1S$ and $1P$ populations. A pump-probe cross correlation is shown in gray.Reuse & Permissions

Figure 2

(a) Room temperature TA decay traces with indicated $1P$ decay lifetimes, ${\tau }_D$, for PbSe NCs with the indicated $1P$ peak positions (normalized at early time). (b) Energy loss rate as a function of the $1P\mathrm{\text{−}}1S$ separation for CdSe NCs (squares) and PbSe NCs (circles); $1P\mathrm{\text{−}}1S$ separation increases as NC size decreases [see Fig. 1b].Reuse & Permissions

Figure 3

(a) Temperature dependence of intraband relaxation rates for two different sizes of PbSe NCs (squares and circles) and a CdSe NC sample (triangles) (CdSe NC data are scaled for clarity). Rates for PbSe NCs show clear temperature activation, while rates for CdSe NCs remain constant over the studied temperature range. Rates for other studied CdSe NC sizes were also not temperature dependent and are not shown. Best fits of the PbSe NC data to the classical relaxation rate equation described in the text are shown as solid lines. Dashed lines indicate temperature-independent trends. (b) Configuration energy diagram as a function of nuclear coordinate, $Q$, for two electronic states with displaced minima and an energetic barrier to intraband relaxation.Reuse & Permissions