Thin films of yttrium oxide, Y2O3, were deposited by reactive sputtering and reactive evaporation to determine their suitability as a host for a rare earth doped planar waveguide upconversion laser. The optical properties, structure, and crystalline phase of the films were found to be dependent on the deposition method and process parameters. X-ray diffraction analysis on the "as-deposited" thin films revealed that the films vary from amorphous to highly crystalline with a small broad peak at 29 degrees corresponding to the < 222 > reflections of Y2O3. The samples with the polycrystalline structure had a stoichiometry close to bulk cubic Y2O3. Scanning electron microscopy imaging revealed a regular column structure confirming their crystalline nature. The thin film layers which allowed guiding in both visible and infrared regions had lower refractive indices, higher oxygen content, and a more amorphous structure. Higher oxygen pressures during the deposition lead to a more amorphous layer. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3503621]