Fluorescence property and dissolution site of Er³⁺ in Ta₂O₅ film prepared by sol-gel method and dip-coating technique

Ta₂O₅–xEr₂O₃ (TE) films were produced by a sol-gel method and a dip-coating technique with heat treatment at 600–1000 °C. Their powders were also prepared from the same sol. The Er³⁺ fluorescence property of the TE films containing various contents of Er³⁺ was measured as a function of the heat-treatment temperature. In crystallized films, the Er³⁺ fluorescence was observed because water-related residues (Ta–OH and H₂O) and carbon-related residues (–CH₃, –CH₂–, –(C ⁼ O)–, and C≡C–H) were removed from the films. It is shown from infrared absorption spectroscopy that Ta–O⁻ and Ta ⁼ O structures dissolve the Er³⁺ ions selectively and play a role in dispersing the Er³⁺. The strongest Er³⁺ fluorescence is observed in the TE film with 2 mol% of Er₂O₃ because of its highest ability to disperse the Er³⁺ ions.