Beta-diketones in the intensification of the luminescence of the silk fibroin films doped rare earth ions

Abstract

Silk fibroin (SF) is a structural protein found in Bombyx mori cocoons and has properties that are potentially applicable in photonics. This biocompatible matrix is an interesting substrate for different ions and molecules. Furthermore, its variable refractive index allows photons to be guided in this material enabling their use as biocompatible and resorbable waveguides, which can be used to provide optical energy for various applications, e.g., therapy or imaging in living tissue. Rare earth ions (RE) play a widely known role in the field of photonics. However, there are few studies involving the production of light in doped SF with RE ions, and the literature results have shown different sensitization of Eu3+ and Tb3+ ions by the SF matrix. This study presented a consistent work on material synthesis, related studies on spectroscopy of RE ions, and the role of beta-diketonate ligand on the energy transfer mechanisms with the emission improvement in the investigated material. As a result, an intensification of emission was observed for Eu3+ doped sample in the presence of 2-thenoyltrifluoroacetone ligand, but similar results were not carried out with acetylacetone ligand insertion. A possible cause was the different access by beta-diketonate to the lanthanide ion in SF matrix due to the ligand–SF interaction. The results presented have characterized the RE–SF interactions and supported the mechanisms of energy transfer improvement for excitation of different RE ions in this matrix being important for future applications in photonics.