Photoluminescent thin films of europium doped lutetium oxide (Lu 2 O 3: Eu)-an established material for x-ray scintillators-have been grown on glass substrates employing radio-frequency magnetron sputtering deposition technique. Optically transparent, crystalline films were obtained by only controlling the deposition process parameters. Neither any pre-treatment on glass substrate nor any post-deposition treatment on the films was applied. To our knowledge, depositing transparent but crystalline films of Lu 2 O 3: Eu on glass substrates in such a direct way is an achievement that is reported for the first time in the literature. Using separate sputtering targets for the matrix constituent (Lu 2 O 3) and the dopant enabled us to control the doping level of europium atoms in the films. By varying the magnetron power applied to the Eu 2 O 3 target, we produced a series of Lu 2 O 3: Eu thin films with different Eu concentrations. Significant quenching of luminescence by concentration was observed in the films. Detailed chemical and microstructural analyses revealed that europium atoms segregated from the matrix at high concentrations, an important contributor to concentration quenching. Some remarks have been given on finding the europium concentration that will give best scintillator performance.