Evaluating Inter-Lanthanide Interactions in Co-Doped Zinc Sulfide Nanoparticles for Multiplex Assays

Multiple and distinct lanthanide (Ln)-doped nanoparticles (NPs) can benefit in accessing multiplex assays for photoluminescence-based applications. This study develops Tb–Eu co-doped ZnS nanoparticles (NPs) using different synthetic pathways. These include Zn(Tb)S/Eu, Zn(Eu)S/Tb, Zn(TbEu)S, and ZnS/TbEu NPs, where the lanthanides within parenthesis and after a slash indicate their addition synthetically and postsynthetically, respectively. The differing synthetic protocols affect the dopant concentrations and spatial location in the NPs, which give rise to remarkable differences in interdopant electronic interactions. Both charge trapping- and spectral overlap-mediated interdopant electronic interactions can explain energy transfer from Tb3+ to Eu3+. Control experiments with Tb–Yb, Tb–Sm, and Tb–Tm containing NPs identify the importance of the relative energetics of the Ln2+ ground energy level with respect to the Tb3+ luminescent energy level in controlling the Tb3+–Ln3+ interaction, thus implicating the importance of charge trapping-mediated interdopant electronic interactions. The results discussed provide a solid foundation to identify suitable co-doped NP luminophores.