Europium gallium oxide ͑Eu x Ga 1-x ͒ 2 O 3 thin films were deposited on sapphire substrates by pulsed laser deposition with varying Eu content from x = 2.4 to 20 mol %. The optical and physical effects of high europium concentration on these thin films were studied using photoluminescence ͑PL͒ spectroscopy, x-ray diffraction ͑XRD͒, and Rutherford backscattering spectrometry. PL spectra demonstrate that emission due to the 5 D 0 to 7 F J transitions in Eu 3+ grows linearly with Eu content up to 10 mol %. Time-resolved PL indicates decay parameters remain similar for films with up to 10 mol % Eu. At 20 mol %, however, PL intensity decreases substantially and PL decay accelerates, indicative of parasitic energy transfer processes. XRD shows films to be polycrystalline and beta-phase for low Eu compositions. Increasing Eu content beyond 5 mol % does not continue to modify the film structure and thus, changes in PL spectra and decay cannot be attributed to structural changes in the host. These data indicate the optimal doping for optoelectronic devices based on ͑Eu x Ga 1-x ͒ 2 O 3 thin films is between 5 and 10 mol %.

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