Luminescent Eu(III)/Tb(III)-Based Hybrid Soft Materials: From System Design to Potential Applications

Conspectus Lanthanide ions, especially Eu 3+ and Tb 3+, are renowned for their unique 4f electronic configurations, yielding sharp emission bands, long lifetimes, large Stokes shifts, and high color purity. These intrinsic features, together with multicolor tunability, have made them key emissive centers in the fields of optical sensing, lighting, bioimaging, and anticounterfeiting. Specifically, Eu 3+ emits characteristic red light ( 5 D 0 → 7 F 2 ), while Tb 3+ offers green emission ( 5 D 4 → 7 F 5 ), and their combinations enable color tuning from single colors to multicolor. However, due to the Laporte-forbidden nature of f-f transitions, their luminescence depends heavily on sensitization via the “antenna effect,” where organic ligands (e.g., β-diketones, pyridines, phosphazenes) absorb light and transfer energy to the lanthanide center through intersystem crossing. The resulting photophysical performance is highly dependent on ligand structure and coordination geometry. Traditionally, lanthanide-based luminescent materials have taken the form of rigid coordination complexes, phosphors, and nanomaterials. Although optically efficient, these systems often suffer from poor processability, brittleness, and difficulty in achieving multifunctional integration (e.g., flexibility, dynamic responsiveness). In contrast, emerging lanthanide-based soft materials offer a promising alternative by embedding Eu 3+ /Tb 3+ ions into flexible polymeric or hydrogel matrices. These soft systems not only retain the optical advantages of lanthanide ions but also unlock properties such as mechanical flexibility, self-healing, stretchability, and stimuli-responsiveness. They can also overcome issues of phase separation and efficiency loss through structural integration. Current strategies to incorporate lanthanides include physical doping into polymer or hydrogel matrices, as well as coordination-driven assembly, where lanthanide ions are directly complexed with functional ligands or polymer backbones. The latter approach ensures higher photostability, more homogeneous distribution, and better structural integrity. Representative polymeric matrices include polydimethylsiloxane, polyurethane, and polysulfone, while functional hydrogels often utilize polyacrylamide, gelatin, or nanoclay-enhanced systems. In this Account, we have summarized recent advances in the design, characterization, and application of Eu 3+ /Tb 3+ -based luminescent soft materials. We first outline molecular design principles, such as ligand choice for efficient sensitization, cross-linking strategies, and dynamic bonding motifs, that are crucial to achieving both photophysical performance and mechanical adaptability. We then categorize key material systems, including luminescent coordination polymers, self-healing elastomers, stimuli-responsive hydrogels, and nanocomposite soft materials. Characterization approaches are discussed in tandem with performance metrics such as emission lifetime, toughness, and repair efficiency. Finally, we highlight emerging applications in dynamic anticounterfeiting, smart encryption, wearable optoelectronics, temperature sensing, and luminescence-enhanced solar cells. We hope this Account will inspire continued innovation at the intersection of photophysics and materials mechanics, and guide the rational design of next-generation lanthanide-based soft materials that unify optical excellence with adaptive intelligence for future smart systems.