Free-Standing Nanopatterned Films of Silk Sericin and Gellan Gum and the Spectroscopy Studies from Eu ³⁺ -Doped Films

In this study, we investigated the development of flexible and nanopatterned hybrid films composed of silk sericin (SS) and gellan gum (GG) for photonic applications. GG is widely recognized for its ability to form free-standing films with excellent transparency and flexibility, whereas pristine SS films often exhibit limited mechanical and optical performance. By combining SS and GG, we engineered composite films with improved functionality while maintaining high transparency, unlocking new possibilities for diverse applications in biophotonics. Here, soft lithography was employed to fabricate transparent nanostructured SSGG composite films with different geometries. Additionally, we successfully fabricated high-quality, red-emissive optical SSGG composite films by incorporating Eu³⁺ ions at low concentrations. A comprehensive characterization of the composite film's structure was achieved through an integrative approach, combining scanning electron microscopy, atomic force microscopy, vibrational spectroscopy, and thermogravimetric analyses. The interaction between the biopolymer-based films and lanthanide ions was explored, revealing significant modifications in their spectroscopic profile, particularly in the excitation process. We present a possible energy transfer mechanism from biopolymers to the Eu³⁺ ions and discuss the ⁵ <i>D</i> ₀ excited-state lifetime, suggesting coordination within either hydrophilic or hydrophobic environments. Our findings demonstrate that the spectroscopic behavior of the films varies with the preparation method, highlighting the potential for tuning optical properties through material design. These results provide new insights for applications in sensors, smart materials, and optical devices, expanding the scope of biobased photonics.