Non-resonant luminescence enhancement in sol-gel coatings for broadband UV-light conversion on side-emitting optical fibers

Photoluminescence (PL) is a key mechanism for many light conversion applications but often provides only low yield and poor efficiency due to a small interaction cross-section and a relatively narrow range of spectral activity. Here, we present a simple technique to enhance the PL of europium(III) (Eu3+) from sol-gel coatings on the surface of a side-emitting optical fiber. We use small clusters of Ag to boost the emission of Eu3+ by an energy transfer mechanism. The coating???s performance is studied as a function of Ag concentration and annealing time. We report a substantial enhancement in Eu3+ emission under resonant and non-resonant excitation with UV light. However, this enhancement vanishes when the Ag clusters grow into larger nanoparticles with plasmon activity: we demonstrate that silver clusters produce stronger amplification with a broader excitation range than metallic nanoparticles. Moreover, these clusters are easily generated and stabilized in a coating using standard sol-gel techniques, suitable for deposition on the surface of side-emitting fibers. Such fibers can then be employed as line-shaped emitters, for example, for structured illumination purposes.