Evidence for a "dark exciton" state of PbS nanocrystals in a silicate glass

Abstract : PbS nanocrystals (diameter of 5–7 nm) were synthesized via sulfur ion implantation in Pb-based glasses and postannealing. They display strong emission at around 1.5 µm due to quantum confinement, and a very large photoluminescence (PL) excitation cross section. The PL intensity and decay rate temperature dependences provide evidence for a large energy splitting (ca. 30 meV) of the emitting exciton ground state fine structure, presumably due to the complex PbS electronic band structure.