A greenish-blue light emission was observed in sputtered films that were deposited on 773-K substrates from a ZnGa2O4 target. The films prepared were amorphous and had a bilayer structure with a compositional modulation formed by self-assembly. The approximately 2-nm surface layers thick were Zn-rich, and the inner layers Ga-rich, in the 40-nm thick film. As the film thickness increased, the strength of the light emission increased and saturated at approximately 60 nm. The strength of the light-emission intensity revealed a maximum at approximately 200 V for the acceleration voltage. In the case of artificial bilayered ZnO/NiO films, continuous ultrathin surface layers were not easily obtained, and no light emissions were observed.