The thermal annealing effects on the optical transparency and luminescent characteristics of the Eu-doped Y₂O₃ thin films have been investigated. The as-deposited Y₂O₃:Eu films exhibited an optical band gap of 5.78 eV with a transparency of 89 % at a wavelength of 550 nm. As the annealing temperature increased from 1000 to 1300 °C, the optical band gap and transparency of the films decreased from 5.77 to 4.91 eV and from 86.8 to 64.5 % at 550 nm, respectively. The crystalline quality of the films was improved with increasing annealing temperature. The annealed Y₂O₃:Eu films emitted a red-color photoluminescence (PL) with the highest emission peak near 612 nm. The PL intensity was increased with increasing annealing temperature to 1200 °C, resulting from the improvement in the crystalline quality of the films. The PL intensity was decreased with further increasing temperature above 1200 °C due to the formation of Y₂SiO₅ phase by the reaction of the film with the quartz substrate.

Keywords: Transparency, Optical band gap, Yttrium oxide, Thermal annealing