Photoluminescence properties related to localized states in colloidal PbS quantum dots

We have investigated photoluminescence (PL) properties of PbS quantum dots (QDs) prepared by a colloidal method. The QDs were dispersed into polyvinyl alcohol films in order to investigate the temperature dependence of optical properties. In the visible region, both absorption and PL peaks are clearly observed. The temperature dependence of the absorption energy in QDs is quite different from that in a bulk crystal; the dependence is quantitatively analyzed by considering a thermal-expansion effect on the quantum confinement in QDs. The PL spectra are composed of three PL bands which are classified into two types. Two PL bands among them with the Stokes shifts of 0.25 and 0.47 eV at 10 K are attributed to the defect-related PL bands, and another with the relatively small Stokes shift of 0.17 eV exhibits characteristics of shallow trapped states in the temperature dependence of PL.