Synthesis, structure, and optical properties of SiO₂-Gd ₂O₃:Eu³⁺ nanocomposite thin films

SiO₂-Gd₂O₃:Eu³⁺ nanocomposite thin films were successfully synthesized by a sol-gel method. Precursor solutions were prepared by mixing aqueous rare-earth acetate solutions and ethanolic tetraethylortbosilicate solutions containing trifluoroacetic acid and N,N-dimethylformamide, respectively. The solutions were then spin-coated on silica glass substrates and heat-treated. Two kinds of heat-treatment processes were adopted; one involved heating the coated substrates immediately at temperatures of 700-1000°C, and the other involved preheating them at 300°C, followed by heating at 700-1000°C. In the latter process, denoted a two-step process, SiO₂-GdF₃ composite films formed at 300°C were pyrolytically converted into SiO₂-Gd ₂O₃ nanocomposite films at the higher heating temperatures. This process was effective in enhancing the crystallinity of Gd₂O₃. Observations of the structure and luminescent properties of die films revealed that Eu³⁺ ions were incorporated into cubic-type Gd₂O₃ nanocrystals that were surrounded by the silica matrix. As a result, efficient red emissions at approximately 610 nm were produced from Eu³⁺ in response to a UV light excitation at 256 nm.