Photoluminescence spectra of highly dispersed alkaline earth oxides provide detailed information on the structure of the surface and on the decay processes of the excited states. Different bands in the excitation as well as in the emission spectra are associated with sets of ions in different coordination on the surface. For Mgo, this is confirmed by compairing the spectra of samples with different surface topographies. In the case of Sr0, the photoluminescence spectra obtained at 300 and 77 K indicate that activated energy transfer occurs from the surface sites in high coordination to those in low coordination, Finally it is shown that, because of its high sensitivity, the emission technique gives evidence of the formation, in extremely low concentration, of 4. 41 -bipypidyl by interaction of pyridine and oxygen on the surface of alkaline earth oxides.