Langmuir-Blodgett monolayers of colloidal lead chalcogenide quantum dots: morphology and photoluminescence

Monolayers of PbSe and PbS quantum dots and PbSe/CdSe core/shell quantum dots made by Langmuir-Blodgett deposition are compared, with a focus on the formation, the morphology and the photoluminescence properties of the films. It is shown that PbSe quantum dots suffer from oriented attachment and a complete quenching of their photoluminescence after Langmuir-Blodgett processing. While the oriented attachment can be resolved by growing a CdSe shell around the PbSe core QDs, the photoluminescence of PbSe/CdSe Langmuir-Blodgett monolayers remains largely quenched. In the case of PbS quantum dots, the formation of a close-packed monolayer is more difficult, yet the resulting films show no sign of oriented attachment and their photoluminescence is comparable to that of the original, suspended quantum dots. In spite of their slow oxidation in a matter of weeks, these results mark PbS quantum dots as the preferred material for light-emitting applications in the near IR based on Langmuir-Blodgett monolayers of lead chalcogenide quantum dots.