Energy transfer in close-packed PbS nanocrystal films

We study the emission properties of close-packed films of PbS nanocrystals that show emission in the infrared. In time resolved photoluminescence measurements, we observe a fast decay time of similar to 400 ps and a slow component between 20 and 80 ns, depending on the temperature, which are attributed to decay from core and surface states, respectively. Photoluminescence excitation and temperature-dependent photoluminescence measurements show that these states are coupled by thermal activation and energy transfer. These transfer processes efficiently replenish the core states with charge carriers from the surface states, increasing the photoluminescence yield.