Morphology and energy transfer in PbS quantum dot arrays formed with supercritical fluid deposition

Lead sulfide (PbS) quantum dots (QDs) were synthesized in our lab with controllable and tunable sizes. Supercritical fluid CO2 (sc-CO2) provides a useful tool to deposit PbS QDs on substrate surfaces with lateral uniformity. Either in the PbS/toluene solution or in the sc-CO2 fabricated film, the absorbance maxima of the PbS QDs do not show an obvious dependence on the PbS QD concentrations. Fluorescence spectra of PbS QDs obtained from the films prepared by the sc-CO2 method indicate energy transfer between PbS QDs with different sizes, the small QDs serving as energy donors and large ones as acceptors. Samples formed with sc-CO2 method measured by photoluminescence (PL) show a red-shift and an enhanced emission intensity with respect to samples formed with solution deposition method (SDM), specifically at cryogenic temperatures.