The application of colloidal quantum dots (CQDs) for the production of low cost photodetectors offers a promising alternative to the expensive epitaxially-grown structures. Technologies based on near-/mid-IR CQDs are not so developed as a full-grown application of visible spectral range CQDs like CdSe. Lead chalcogenide colloidal quantum dots are promising nanomaterials exhibiting an excellent photosensitivity in the near-IR and mid-IR ranges. Bulk materials PbS and PbSe CQDs have band gaps 0.41 and 0.27 eV respectively.

In the past decades a lot of effort was put into the development of the efficient and scalable synthetic methods for the preparation of lead chalcogenide CQDs. It is rather complicated to get broad range of nanocrystals sizes and the narrow size distribution by a single method even for the most developed material namely lead sulfide CQDs.

The procedure for the preparation of smaller PbS nanocrystals by resizing of larger one was developed in our lab by application of oleylamine/oleic acid mixture. Solvents effect and reagent ratio was investigated more in detail. It was found that this transformation is much more general and both lead selenide and telluride nanocrystalls could be resized applying the same reagent. The combination of resizing approach with earlier developed synthetic methods allows to produce the PbS colloidal quantum dots for near IR-applications.

For the further applications of lead chalcogenides CQDs a preparation of photoconductive thin films is necessary. Ligand exchange process in thin films of PbS CQDs was studied by FTIR spectroscopy applying HATR accessory. This innovative approach allows to study the both efficiency and the rate of ligand exchange. Exchange processes were studied for the several ligands (iodide, thiocyanate). Impact of the solvent on the exchange result was analyzed.