Temperature-dependent photoluminescence Stokes shift in PbS quantum dots

Following the long dominance of CdSe quantum dots as the paradigm semiconductor nanocrystals for investigating of strong quantum confinement phenomena, attention is paid to the lead chalcogenide quantum dots which possess a level of carrier confinement unachievable in quantum dots of other materials. However, the energy level structure of the lowest 1S–1S exciton in these quantum dots is not defined well. Here, we report on the experimental investigation of absorption and photoluminescence of PbS quantum dots with a mean radius of 2.4 nm and show that the 1S–1S absorption and photoluminescence band maxima obey different temperature dependences. The temperature decrease leads to the increase of the Stokes shift. The results are in qualitative agreement with the assumption that different inherent exciton states within the split 1S–1S exciton state are responsible for the absorption and emission of light by PbS quantum dots.