Eu³⁺-induced clusterization of non-emissive cysteine into bright green assemblies

Clusteroluminescence (CL) offers an effective strategy for generating emission from nonconjugated, heteroatom-rich molecules, yet simple, biocompatible CL systems derived from natural building blocks remain scarce. Here, we report that coordination of Eu³⁺ with intrinsically non-emissive L-cysteine (Cys) induces clusterization and activates intense green emission. Under basic conditions, Eu³⁺ promotes the formation of hierarchical Eu-Cys clusters that exhibit a broad emission centered at ∼525 nm, a large Stokes shift (∼150 nm), excitation-dependent emission, and a 56-fold increase in quantum yield (14%) relative to Eu³⁺ alone. Combined spectroscopic and microscopic analyses reveal that the emission originates from clustered Cys domains rather than Eu-centered excited states, with Eu³⁺ functioning primarily as a structural node that rigidifies heteroatom-rich assemblies and suppresses nonradiative decay. Control experiments with other metal ions and amino acids reveal a pronounced coordination specificity, highlighting the unique cooperative interplay between Eu³⁺'s high coordination propensity and cysteine's thiol-containing ligand topology. This rare-earth-ion-induced clusterization strategy extends CL to single, non-aromatic amino acids into the emissive framework, and providing a general approach for constructing luminescent materials from simple biomolecules.