Polymer and biopolymer organic-inorganic composites containing mixed oxides for application in energy up- and down-conversion

Abstract

Organic-inorganic composites are interesting for many commercial applications— the chemical and thermal stability of inorganic oxides combined with the processability and flexibility of organic compounds and polymers provides these composites with attractive mechanical, optical, and thermal properties. In general, the desired properties cannot be found in one single constituent, but adequate association of the components affords composites with complementary properties. In this study, we have synthesized and characterized organic-inorganic composites based on the natural polymers Gellan Gum and Karaya Gum containing luminophores consisting of niobium and gadolinium mixed oxides doped with Eu3+ or Yb3+/Er3+. In this paper luminophores were prepared by a modified non-hydrolytic sol-gel route, and was obtained the organic-inorganic composites by the casting technique. The investigated how the luminophore concentration, 1.0 or 3.0% m/m of gum, affected the luminescent properties of the composites. For all the composites doped with Eu3+, the down-shifting luminescence results revealed an intense emission band at 612 nm, due to the 5D0 → 7F2 transition of Eu3+, as well as an emission band between 300 and 500 nm, attributed to polymer emission, which shifted the chromaticity coordinates toward the blue region. As for the composites doped with Yb3+/Er3+, they displayed bands at 1005 and 1535 nm, ascribed to the 2F5/2 → 2F7/2 and 4I13/2 → 4I15/2 transitions of Yb3+ and Er3+, respectively. The up-conversion luminescence results evidenced emission bands in the visible region, at 520, 550, and 655 nm, assigned to the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 transitions of Er3+, respectively, indicating that two photons were absorbed.