The effect of oxygen pressure on the structural and photoluminescence properties of pulsed laser deposited (Y-Gd)₃Al₅O₁₂:Ce³⁺ thin films

Thin films of (Y-Gd)₃Al₅O₁₂:Ce³⁺ phosphor were deposited on Si (100) substrate by pulsed laser deposition technique at substrate temperature of 300 °C. The effect of oxygen pressure on the structural and photoluminescence properties of the films have been studied. X-ray diffraction analysis confirmed the formation of Y₃Al₅O₁₂ cubic structure for the films. A slight shift in the diffraction peaks to higher two theta angles was observed from the films when compared to those of the phosphor in powder form. This shift could be attributed to lattice expansion caused by the differences in ionic radius when Y³⁺ is partially substituted by the larger Gd³⁺ ion during laser ablation process. The crystallinity of the films increases as a function of oxygen pressure in the range of 1–20 mTorr then decreases with further increase in pressure to 60 mTorr. Surface morphology of the films were significantly affected by oxygen pressure, with an increased in particle number density for film deposited under 20 mTorr oxygen pressure. Photoluminescence spectra show broad band emission centered at around 545 nm arising from the 5d → 4f electronic transition of Ce³⁺ in the phosphor. The highest PL intensity was obtained from film deposited under 20 mTorr oxygen pressure. Optical measurements show that the films were highly reflective above 500 nm with reflectance up to 94%. Two optical absorption peaks for cerium were observed at around 307 and 467 nm, and found to increase in intensity with oxygen pressure up to 20 mTorr.