A Sputtering apparatus was equipped with an optical spectrometer by which both the fluorescence from the glow discharge and the luminescence from the growing film could be detected and measured separately. Calcium, magnesium, and lanthanum oxide layers doped with samarium or terbium were used as targets. It was observed that the luminescence appeared when calcium or magnesium oxides were used as host materials, but was absent in the case of lanthanum oxide. The thickness of the layer in which the excitation took place was found to be a few hundred angstroms. The possible reason for the weaker luminescence efficiency of lanthanum oxide in comparison with calcium and magnesium oxides has been discussed.