Experimental observation of exciton splitting and relaxation dynamics from PbS quantum dots in a glass matrix

Multiple optical transitions from PbS quantum dots (QDs) in glass matrix are observed. Energy separations between them amount up to ∼200 meV. Instead of being due to a size distribution of QDs, they are found to be related to a splitting of the lowest exciton levels. Systematic analysis of the relaxation dynamics reveals the lifetimes of the split states ranging from sub-100-ns to ∼μs. Moreover, we observe excited and "intrinsic" states having a sub-100-ps and ∼ns lifetime, respectively. The behavior of the split structure can be modeled by a phonon-assisted relaxation mechanism. This investigation offers a conclusive interpretation for the wide distribution of experimentally observed nonequilibrium carrier lifetimes in PbS QDs.