PbS nanocrystals (diameter of 5–7nm) were synthesized via sulfur ion implantation in Pb-based glasses and postannealing. They display strong emission at around 1.5μm 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. 30meV) of the emitting exciton ground state fine structure, presumably due to the complex PbS electronic band structure.