Solution Phase Growth and Ion Exchange in Microassemblies of Lead Chalcogenide Nanoparticles.

We demonstrate the synthesis of micron-sized assemblies of lead chalcogenide nanoparticles with controlled morphology, crystallinity, and composition through a facile room-temperature solution phase reaction. The amine-thiol solvent system enables this synthesis with a unique oriented attachment growth mechanism of nanoparticles occurring on the time scale of the reaction itself, forming single-crystalline microcubes of PbS, PbSe, and PbTe materials. Increasing the rate of reaction by changing reaction parameters further allows disturbing the oriented attachment mechanism, which results in polycrystalline microassemblies with uniform spherical morphologies. Along with polycrystallinity, due to the differences in reactivities of each chalcogen in the solution, a different extent of hollow-core nature is observed in these microparticles. Similar to morphologies, the composition of such microparticles can be altered through very simplistic room-temperature solution phase coprecipitation, as well as ion-exchange reactions. While coprecipitation reactions are successful in synthesizing core-shell microstructures of PbSe-PbTe materials, the use of solution phase ion-exchange reaction allows for the exchange of not only Te with Se but also Ag with Pb inside the core of the PbTe microparticles. Despite exchanging one Pb with two Ag cations, the hollow-core nature of particles aids in the retention of the original uniform microparticle morphology.