A Post-synthetic Modification of II-VI Nanoparticles to Create Tb³⁺ and Eu³⁺ Luminophores

We describe a novel method for creating luminescent lanthanide-containing nanoparticles in which the lanthanide cations are sensitized by the semiconductor nanoparticle's electronic excitation. In contrast to previous strategies, this new approach creates such materials by addition of external salt to a solution of fully formed nanoparticles. We demonstrate this post-synthetic modification for the lanthanide luminescence sensitization of two visible emitting lanthanides (Ln), Tb³⁺ and Eu³⁺ ions, through ZnS nanoparticles in which the cations were added post-synthetically as external Ln(NO₃)₃·xH₂O salt to solutions of ZnS nanoparticles. The post-synthetically treated ZnS nanoparticle systems display Tb³⁺ and Eu³⁺ luminescence intensities that are comparable to those of doped Zn(Ln)S nanoparticles, which we reported previously (J. Phys. Chem. A, 2011, 115, 4031-4041). A comparison with the synthetically doped systems is used to contrast the spatial distribution of the lanthanide ions, bulk versus surface localized. The post-synthetic strategy described in this work is fundamentally different from the synthetic incorporation (doping) approach and offers a rapid and less synthetically demanding protocol for Tb³⁺:ZnS and Eu³⁺:ZnS luminophores, thereby facilitating their use in a broad range of applications.