Effect of Oxygen Pressure on the Structure and Luminescence of Europium Doped Gadolinium Oxide Thin Films

Gadolinium oxide has found uses as a dielectric or passivation layer for novel III-V materials and devices, but more recently has been the subject of study as a rare-earth host. It is believed that Gd$_{2}$O$_{3}$ makes a good host for these dopants due to the similarity in ionic radii between the gadolinium ion and the rare-earth dopants. The reported long radiative lifetimes of rare earth dopants in this material make it interesting for optically pumped laser materials. In this study, europium-doped gadolinium oxide (Eu:Gd$_{2}$O$_{3})$ polycrystalline thin films were deposited on sapphire substrates by pulsed laser deposition at 5 and 50 mTorr oxygen pressure. Changes in the crystal structure were observed by x-ray diffraction and photoluminescence. Low-temperature photoluminescence spectra of the $^{5}$D$_{0}-^{7}$F$_{0}$ and $^{7}$F$_{2}$ transitions in the europium ion were recorded with high resolution. Because the $^{5}$D$_{0}-^{7}$F$_{0}$ transition in europium is not subject to fine structure splitting, it provides a useful mechanism for investigation of the local environment. The $^{5}$D$_{0}-^{7}$F$_{2}$ transition is of interest as it results in the most intense emission, making europium doped material useful for red light-emitting phosphors. Radiative lifetimes of the observed transitions are also reported.