Modular Hydrogel‐Based Nano‐Bead Emitters for Bright, Homogeneous Fluorescent Thin Films and 3D Architectures

A modular toolbox based on size‐controlled, mono‐dispersed nanohydrogels (NHGs) functionalized with dye molecules is presented. The resulting nano‐bead emitters (NBEs) are surprisingly very bright and enable the formation of smooth, transparent thin layers that uniformly emit an intense, stable fluorescence, with virtually no constraints on the choice of dye molecules. The NBEs can be deposited or printed onto various substrates, forming high‐emission, stable transparent layers or patterns. The fabrication of 3D sandwich structures with tunable emission properties, including donor‐acceptor pairs, is demonstrated. The homogeneous fluorescence intensity observed over an extended region of the layer originates from the mono‐dispersity and strong negative zeta potential of the precursor nanohydrogels. These NBE layers exhibit remarkable stability, retaining high fluorescence with only moderate degradation even after 12 months. This platform strategy allows for a wide range of fluorescent molecules to be reused to form homogeneous, nanometric‐thin films with a morphology primarily dictated by the size of the nanohydrogels. This unique approach unlocks a broad spectrum of applications in spectroscopy, microscopy, optoelectronic devices, and sensing.