Exciton thermalization and state broadening contributions to the photoluminescence of colloidal PbSe quantum dot films from 295 to 4.5 K

The temperature-dependent photoluminescence (PL) from thick drop-cast films of similar to 4-5 nm diameter PbSe colloidal quantum dots was investigated in the temperature range of 4.5-295 K. Several samples all exhibit single-peak emission with a simple Arrhenius-type decrease in PL yield as temperature increases. The temperature dependence of the Stokes shift and PL line shape are reproducible and can be quantitatively described over the entire temperature range using a relatively simple, yet accurate thermal model, including state broadening. The Stokes shift is completely described by thermalization of the exciton population and the onset of degeneracy below similar to 100 K. The variation in linewidth is dominated by the same degeneracy effects below similar to 100 K while above similar to 125 K, the variation is controlled by thermal (Lorentzian) dephasing. There is also clear evidence for a substantial and temperature-independent Voigt-type contribution to the state scattering.