Evolution of microstructures and optical properties of gadolinium oxide with oxygen flow rate and annealing temperature

In this study, the effects of oxygen flow rate and annealing temperature on Gd ₂ O ₃ structures and optical properties were systematically analyzed. Gd ₂ O ₃ films were deposited on both quartz and ZnS substrates by magnetron sputtering and then annealed under vacuum at 700, 800 and 900 °C. Restructure and phase transformation from cubic to monoclinic occur at different temperatures depending on the oxygen flow rate. The optical band gap, which is more sensitive to the annealing temperature than oxygen flow rate changes from 5.32 to 5.65 eV. The refractive index is approximately 1.75 at 550 nm and is adjustable by the oxygen flow rate. The transmittance of the ZnS substrate with Gd ₂ O ₃ film exceeds 80% and reaches 82% at the 7.5–9.5 μm range. When ZnS is coated on both sides, the transmittance is increased to approximately 90%. Our results indicate that Gd ₂ O ₃ films are promising new candidates for anti-reflective coatings in the infrared region.