Eu-doped GaN thin films were in situ grown on sapphire substrates by RF plasma-assisted solid-source molecular beam epitaxy technique. Strong red emission at similar to 622 nm from D-5(0)-F-7(2) radiative transitions in Eu3+ ions was observed for all samples. The effects of important growth parameters. such as III/V ratio (Ga flux), Eu cell temperature (Eu flux) and growth temperature, on Eu3+ photoluminescence were studied. X-ray diffraction and secondary ion mass spectroscopy measurements were performed to investigate thin film quality and Eu doping profiles. The strongest Eu3+ luminescence was obtained from GaN:Eu thin films grown under slightly N-rich condition (III/V < 1), while the highest Eu3+ emission efficiency was obtained in thin films grown under Ga-rich condition (III/V >= 1). The optimum Eu doping concentration for Eu3+ luminescence is similar to(0.1-1.0) at% for III/V <= 1 ratio condition. Higher growth temperature ( > 750 degrees C) was also found to enhance Eu3+ luminescence intensity and efficiency. (C) 2009 Elsevier B.V. All rights reserved.