Ligand exchange and stability of CdTe nanoplatelets under mild conditions

<jats:p>CdTe colloidal nanoplatelets (NPLs) are promising two-dimensional quantum emitters, but their surface chemistry has been less studied compared to CdSe NPLs. Understanding and controlling surface properties are critical for their application. In this work, we investigate the conditions under which CdTe NPLs remain stable during post-synthetic ligand exchange in mild organic environments, which is a key step for their further use. During the initial stage of the work, the effect of the stoichiometric ratio of precursors on the optical characteristics and chemical composition of CdTe NPLs obtained at a temperature of 170 °C was analysed. The concentrations of Cd and Te varied within ±50% with respect to our standard version. The results obtained by TXRF demonstrated the formation of compositions with a moderate excess of cadmium (the Cd/Te ratio varied from 1.03 to 1.19). These conclusions are consistent with the concept of Cd-terminated surfaces stabilized by carboxylate ligands. Three standard ligand exchange strategies successfully applied to CdSe nanocrystals (carboxylate → CdCl₂, → Zn(DDTC)₂ and → hexadecanethiol) were tested on CdTe nanocrystals. Contrary to expectations, treatment of CdTe with CdCl₂ or Zn(DDTC)₂ solutions did not result in a measurable shift in exciton transitions and, moreover, caused degradation of the colloidal dispersion. Our studies have identified a range of conditions under which CdTe NPLs retain their integrity during ligand exchange. While some elements of the CdSe-developed protocols can be transferred to CdTe, their applicability is limited by a narrow processing window: beyond a certain treatment time, CdTe nanoplatelets progressively lose optical stability</jats:p>