Photoluminescence lifetime and absorption spectrum of PbS nanocrystal quantum dots

We determine the photoluminescence (PL) lifetime of octadecylamine capped PbS nanocrystal quantum dots (QDs) with different particle sizes, temperatures, and background materials, by measuring their time-resolved PL spectra and fitting the observation with a double-exponential function. The observed size dependence of absorption-peak shift shows a linear increase with growing particle size. Both the quantum-size confinement and surface-defects induced transitions show impacts on the PL lifetime, where size-dependent lifetime appears as a negative exponential decrease between 2.57-0.71 mu s for 2.35-5.61-nm QDs dispersed in toluene at room temperature. The temperature-dependent lifetime shows an insensitive feature, with peak seen at 3.42 mu s at 200 K and averaging 2.27 +/- 1.15 mu s within the temperature range 7-298 K for 3.6-nm QDs doped in UV-gel. Organic solutions used as background materials have weak effect on the lifetime due to similar dielectric coefficients.