Ligand exchange and stability of CdTe nanoplatelets under mild conditions

CdTe colloidal nanoplatelets (NPLs) are promising two-dimensional quantum emitters, but their optical response remains highly sensitive to surface chemistry and post-synthetic processing. In this work, we examine how precursor stoichiometry and mild ligand-exchange conditions affect the optical stability of CdTe NPLs synthesized at 170°C. By varying the Cd and Te precursor concentrations by ± 50% relative to the standard protocol, we identified a precursor-composition window in which the characteristic excitonic absorption features of ~ 3 ML CdTe NPLs appear rapidly during the early stages of growth. TXRF analysis of purified NPL fractions showed slightly Cd-rich compositions, with Cd/Te ratios ranging from 1.03 to 1.19, consistent with Cd-terminated surfaces stabilized by carboxylate ligands. The optical properties were evaluated by absorption, photoluminescence, and photoluminescence quantum yield measurements, while repeated measurements after storage were used to assess the reliability of the spectral features and the long-term evolution of emission. The main excitonic emission was retained after storage, although an increased long-wavelength contribution indicated partial optical aging of selected samples. We further tested three ligand-exchange strategies commonly used for CdSe-based nanocrystals: carboxylate-to-CdCl₂, carboxylate-to-Zn(DDTC)₂, and carboxylate-to-hexadecanethiol exchange. CdCl₂ and Zn(DDTC)₂ treatments did not produce measurable shifts of the excitonic transitions and led to colloidal destabilization under the applied conditions, whereas hexadecanethiol treatment produced clear surface-related optical changes. These results show that CdTe NPLs can preserve their excitonic optical signature under selected mild post-synthetic conditions, but their surface chemistry is less tolerant to CdSe-derived ligand-exchange protocols than expected.