Lanthanide cation-induced tuning of surface capping properties in zinc sulfide nanoparticles: an infrared absorption study

This study reveals the tuning of the vibrational characteristics of the capping ligands in lanthanide [Ln - Sm, Eu, Tb, Dy] cation-incorporated zinc sulfide nanoparticles, Zn(Ln) S, as monitored by Fourier transform infrared (FTIR) spectroscopy. Both stearate and trioctylphosphine oxide (TOPO) were found to act as surface-capping ligands for nanoparticles with multiple coordination environments. The vibrational characteristics of the capping ligands in the undoped ZnS nanoparticles exhibited noticeable differences in absorption as compared to those of the pure zinc stearate and TOPO molecules. Lanthanide cation incorporation tunes the corresponding vibrational characteristics to a significant extent, as compared to that in the undoped ZnS nanoparticles. It has been argued that the observed tuning of the capping ligand IR absorption characteristics is induced by the lanthanide cations that are located near or on the surface of the nanoparticles. The IR spectra suggest a probable change of carboxylate coordination environment in the Zn(Ln) S nanoparticles. The results obtained from the ZnS-based nanoparticles were analyzed based on a semi-quantitative analysis and compared with those from ZnSe and Zn(Tb) Se nanoparticles, in order to evaluate the effect of the constituent anion of the nanoparticles in modulating the IR signature.