Influence of annealing temperature on structural and optical properties of Lu₂O₃:Eu³⁺, Tb³⁺ transparent films

High-optical quality Lu₂O₃:Eu³⁺ 5 mol%, X Tb³⁺ (X = 0-0.04 mol%) thin films were prepared by the sol-gel process and dip-coating technique. The procedure was as follows: lutetium, europium and terbium nitrates were used as precursors, and ethanol as a solvent. Etylenglycol (EG) was added as a sol stabilizer, and the pH was adjusted by acetic acid. After 10 dipping-cycles, followed by an annealing process (600-900 °C) for 1 h, transparent, smooth and crack-free films (ra = 8-9 nm) were formed. The X-ray diffraction (XRD) results showed crystallized films into the cubic structure at 800°C. The ellipsometry results showed that the thickness of the films varied from 1 to 1.4 μm at 1000 and 600°C, respectively. Finally, the films presented a typical Eu³⁺ red emission at 611 nm (⁵D₀ → ⁷F₂); furthermore, the effect of the Tb³⁺ content showed that the highest emission intensity corresponded to the lower Tb³⁺ content.