Composition Control in Molecular Cluster-Aggregates: A Toolbox for Optical Output Tunability via Energy Transfer Pathways

Composition control is a powerful tool for obtaining high-performance lanthanide (Ln) luminescent materials with adjustable optical outputs. This strategy is well-established for hierarchically structured nanoparticles, but it is rarely applied to molecular compounds due to the limited number of metal centers within a single unit. In this work, we present a series of molecular cluster-aggregates (MCAs) with an icosanuclear core {Ln(2)Eu(2)Tb(16)} (Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb) in which we explore composition control, akin to nanoparticles, to modulate the optical output. More specifically, we target to understand how the presence of a third Ln(III) doping ion would impact the well-known Tb-III -> Eu-III energy transfer and the ratiometric optical thermometry performance based on the Tb-III/Eu-III pair. Photophysical properties at room and at varying temperatures were investigated. Based on experimental data and well-established intrinsic features, such as spin-orbit coupling strength and Ln(III) 4f energy levels ' structure, we discuss the possible luminescent processes present in each MCA and provide insight into qualitative trends that can be rationally correlated throughout the series.

Automated summary

This work presents a study on molecular cluster-aggregates with a 20-metal core, exploring the use of composition control to modulate optical outputs. The impact of a third lanthanide ion on energy transfer and optical thermometry performance is investigated.