We investigate the influence of the ambient gas during thermal annealing on the photoluminescence (PL) properties of europium compound thin films on Si substrates. The films were deposited by radio-frequency magnetron sputtering and subsequently annealed in N 2 or O 2 ambient gas by rapid thermal annealing (RTA). The results of X-ray diffraction indicate that the resulting europium compound annealed in N 2 ambient have several silicate phases such as EuSiO 3 and Eu 2 SiO 4 compared to those annealed in O 2 ambient. The spectral results revealed that a broad luminescence associated with Eu 2+ ions, with a maximum intensity at 600 nm and a FWHM of 110 nm, was observed from the thin film annealed at 1000°C in N 2 ambient. However, a series of narrow PL spectra from Eu 3+ ions were observed from the film annealed in O 2 ambient.